title: Sodder children disappearance

text: With the end of official efforts to resolve the case, the Sodder family did not give up hope. They had flyers printed up with pictures of the children, offering a $5,000 reward (soon doubled) for information that would have settled the case for even one of them. In 1952, they put up a billboard at the site of the house (and another along U.S. Route 60 near Ansted) with the same information. It would in time become a landmark for traffic through Fayetteville on U.S. Route 19 (today State Route 16).


title: Sodder children disappearance

text: The family's efforts soon brought another reported sighting of the children after the fire. Ida Crutchfield, a woman who ran a Charleston hotel, claimed to have seen the children approximately a week afterwards. "I do not remember the exact date", she said in a statement. The children had come in, around midnight, with two men and two women, all of whom appeared to her to be "of Italian extraction". When she attempted to speak with the children, "[o]ne of the men looked at me in a hostile manner; he turned around and began talking rapidly in Italian. Immediately, the whole party stopped talking to me". She recalled that they left the hotel early the next morning. Investigators today do not, however, consider her story credible, as she had only first seen photos of the children two years after the fire, five years before she came forward.


title: Sodder children disappearance

text: George followed up leads in person, traveling to the areas from where tips had come. A woman from St. Louis, Missouri, claimed Martha was being held in a convent there. A bar patron in Texas claimed to have overheard two other people making incriminating statements about a fire that happened on Christmas Eve in West Virginia some years before. None of those proved significant. When George heard later that a relative of Jennie's in Florida had children that looked similar to his, the relative had to prove the children were his own before George was satisfied.


title: Sodder children disappearance

text: In 1967, George went to the Houston area to investigate another tip. A woman there had written to the family, saying that Louis had revealed his true identity to her one night after having too much to drink. She believed that he and Maurice were both living in Texas somewhere. However, George and his son-in-law, Grover Paxton, were unable to speak with her. Police there were able to help them find the two men she had indicated, but they denied being the missing sons. Paxton said years later that doubts about that denial lingered in George's mind for the rest of his life.


title: Sodder children disappearance

text: Another letter that they received that year brought the Sodders what they believed was the most credible evidence that at least Louis was still alive. One day Jennie found in the mail a letter addressed to her, postmarked in Central City, Kentucky, with no return address. Inside was a picture of a young man of around 30 with features strongly resembling Louis's, who would have been in his 30s if he had survived. On the back was written:


title: Sodder children disappearance

text: The family hired another private detective to go to Central City and look into the missive, but he never reported back to the Sodders and they were unable to locate him afterwards. The picture nonetheless gave them hope. They added it to the billboard (leaving Central City out of it and any other published information out of fear that Louis might come to harm) and put an enlargement of it over their fireplace.


title: Sodder children disappearance

text: George admitted to the "Charleston Gazette-Mail" late the next year that the lack of information had been "like hitting a rock wall—we can't go any further". He nevertheless vowed to continue. "Time is running out for us", he admitted in another interview around that time. "But we only want to know. If they did die in the fire, we want to be convinced. Otherwise, we want to know what happened to them".


title: Sodder children disappearance

text: George Sodder died in 1969. Jennie and her surviving children—except John, who never talked about the night of the fire except to say that the family should accept what happened and move on with their lives—continued to seek answers to their questions about the missing children's fate. After George's death, Jennie stayed in the family home, putting up fencing around it and adding additional rooms. For the rest of her life she wore black in mourning and tended the garden at the site of the former house. After her death in 1989, the family finally took the weathered, worn billboard down.


title: Sodder children disappearance

text: The surviving Sodder children, joined by their own children, continued to publicize the case and investigate leads. They, along with older Fayetteville residents, have theorized that the Sicilian Mafia was trying to extort money from George and the children may have been taken by someone who knew about the planned arson and said they would be safe if they left the house. They were possibly taken back to Italy. If the children had survived all those years and were aware that their parents and siblings had survived too, the family believes, they may have avoided contact in order to keep them from harm.


title: Sodder children disappearance

text: Sylvia Sodder Paxton, the youngest of the surviving Sodder siblings, died in 2021. She was in the house on the night of the fire, which she said was her earliest memory. "I was the last one of the kids to leave home", she recalled to the "Gazette-Mail" in 2013. She and her father often stayed up late, talking about what might have happened. "I experienced their grief for a long time". She believed that her siblings survived that night, and assisted with efforts to find them and publicize the case. Her daughter said in 2006: "She promised my grandparents she wouldn't let the story die, that she would do everything she could".


title: Sodder children disappearance

text: In the 21st century, the family's efforts have come to include online forums like websleuths.com in addition to media coverage. The increase in the latter has led some who have examined the case to believe that the children did, in fact, die in 1945. George Bragg, a local author who wrote about the case in his 2012 book "West Virginia's Unsolved Murders", believes that John was telling the truth in his original account, when he said he tried to physically awaken his siblings before fleeing the house. He allows that that conclusion may still not be correct: "Logic tells you they probably did burn up in the fire, but you can't always go by logic."


title: Sodder children disappearance

text: Stacy Horn, who did a segment on the case for National Public Radio around its 60th anniversary in 2005, also believes the children's death in the fire is the most plausible solution. In a contemporaneous post on her blog with material she had to cut from her story for time, she noted that the fire had continued to smolder all night after the house collapsed and that two hours was not enough time to search the ash thoroughly. Even if it had been, the firefighters may not have known what to look for. "However", she said, "there is enough genuine weirdness about this whole thing ... that if someday it is learned that the children did not die in the fire I won't be shocked".


title: Sodder children disappearance

text: In 2022, the History Channel aired an episode of its series "History's Greatest Mysteries" that detailed the events of the case.


title: Maxwell–Boltzmann distribution

text: In physics (in particular in statistical mechanics), the Maxwell–Boltzmann distribution, or Maxwell(ian) distribution, is a particular probability distribution named after James Clerk Maxwell and Ludwig Boltzmann.


title: Maxwell–Boltzmann distribution

text: It was first defined and used for describing particle speeds in idealized gases, where the particles move freely inside a stationary container without interacting with one another, except for very brief collisions in which they exchange energy and momentum with each other or with their thermal environment. The term "particle" in this context refers to gaseous particles only (atoms or molecules), and the system of particles is assumed to have reached thermodynamic equilibrium. The energies of such particles follow what is known as Maxwell–Boltzmann statistics, and the statistical distribution of speeds is derived by equating particle energies with kinetic energy.


title: Maxwell–Boltzmann distribution

text: Mathematically, the Maxwell–Boltzmann distribution is the chi distribution with three degrees of freedom (the components of the velocity vector in Euclidean space), with a scale parameter measuring speeds in units proportional to the square root of formula_8 (the ratio of temperature and particle mass).


title: Maxwell–Boltzmann distribution

text: The Maxwell–Boltzmann distribution is a result of the kinetic theory of gases, which provides a simplified explanation of many fundamental gaseous properties, including pressure and diffusion. The Maxwell–Boltzmann distribution applies fundamentally to particle velocities in three dimensions, but turns out to depend only on the speed (the magnitude of the velocity) of the particles. A particle speed probability distribution indicates which speeds are more likely: a randomly chosen particle will have a speed selected randomly from the distribution, and is more likely to be within one range of speeds than another. The kinetic theory of gases applies to the classical ideal gas, which is an idealization of real gases. In real gases, there are various effects (e.g., van der Waals interactions, vortical flow, relativistic speed limits, and quantum exchange interactions) that can make their speed distribution different from the Maxwell–Boltzmann form. However, rarefied gases at ordinary temperatures behave very nearly like an ideal gas and the Maxwell speed distribution is an excellent approximation for such gases. This is also true for ideal plasmas, which are ionized gases of sufficiently low density.


title: Maxwell–Boltzmann distribution

text: The distribution was first derived by Maxwell in 1860 on heuristic grounds. Boltzmann later, in the 1870s, carried out significant investigations into the physical origins of this distribution. The distribution can be derived on the ground that it maximizes the entropy of the system. A list of derivations are:


title: Maxwell–Boltzmann distribution

text: For a system containing a large number of identical non-interacting, non-relativistic classical particles in themodynamic equilibrium, the fraction of the particles within an infinitesimal element of the three-dimensional velocity space formula_10, centered on a velocity vector of magnitude formula_11, is given by


title: Maxwell–Boltzmann distribution

text: where formula_13 is the particle mass, formula_14 is the Boltzmann constant, and formula_15 is thermodynamic temperature.


title: Maxwell–Boltzmann distribution

text: formula_16 is a probability distribution function, properly normalized so that formula_17 over all velocities is unity.


title: Maxwell–Boltzmann distribution

text: One can write the element of velocity space as formula_18, for velocities in a standard Cartesian coordinate system, or as formula_19 in a standard spherical coordinate system, where formula_20 is an element of solid angle.


title: Maxwell–Boltzmann distribution

text: The Maxwellian distribution function for particles moving in only one direction, if this direction is formula_21, is


title: Maxwell–Boltzmann distribution

text: which can be obtained by integrating the three-dimensional form given above over formula_23 and formula_24.


title: Maxwell–Boltzmann distribution

text: Recognizing the symmetry of formula_16, one can integrate over solid angle and write a probability distribution of speeds as the function


title: Maxwell–Boltzmann distribution

text: This probability density function gives the probability, per unit speed, of finding the particle with a speed near formula_11. This equation is simply the Maxwell–Boltzmann distribution (given in the infobox) with distribution parameter formula_28.


title: Maxwell–Boltzmann distribution

text: The Maxwell–Boltzmann distribution is equivalent to the chi distribution with three degrees of freedom and scale parameter formula_28.


title: Maxwell–Boltzmann distribution

text: With the Darwin–Fowler method of mean values, the Maxwell–Boltzmann distribution is obtained as an exact result.


title: Maxwell–Boltzmann distribution

text: This distribution is used for describing systems in equilibrium. However, most systems do not start out in their equilibrium state. The evolution of a system towards its equilibrium state is governed by the Boltzmann equation. The equation predicts that for short range interactions, the equilibrium velocity distribution will follow a Maxwell–Boltzmann distribution. To the right is a molecular dynamics (MD) simulation in which 900 hard sphere particles are constrained to move in a rectangle. They interact via perfectly elastic collisions. The system is initialized out of equilibrium, but the velocity distribution (in blue) quickly converges to the 2D Maxwell–Boltzmann distribution (in orange).


title: Maxwell–Boltzmann distribution

text: The mean speed formula_35, most probable speed (mode) , and root-mean-square speed formula_36 can be obtained from properties of the Maxwell distribution.


title: Maxwell–Boltzmann distribution

text: This works well for nearly ideal, monatomic gases like helium, but also for molecular gases like diatomic oxygen. This is because despite the larger heat capacity (larger internal energy at the same temperature) due to their larger number of degrees of freedom, their translational kinetic energy (and thus their speed) is unchanged.


title: Maxwell–Boltzmann distribution

text: where formula_50 is the adiabatic index, is the number of degrees of freedom of the individual gas molecule. For the example above, diatomic nitrogen (approximating air) at , formula_51 and


title: Maxwell–Boltzmann distribution

text: the true value for air can be approximated by using the average molar weight of air (), yielding at (corrections for variable humidity are of the order of 0.1% to 0.6%).


title: Maxwell–Boltzmann distribution

text: The original derivation in 1860 by James Clerk Maxwell was an argument based on molecular collisions of the Kinetic theory of gases as well as certain symmetries in the speed distribution function; Maxwell also gave an early argument that these molecular collisions entail a tendency towards equilibrium. After Maxwell, Ludwig Boltzmann in 1872 also derived the distribution on mechanical grounds and argued that gases should over time tend toward this distribution, due to collisions (see H-theorem). He later (1877) derived the distribution again under the framework of statistical thermodynamics. The derivations in this section are along the lines of Boltzmann's 1877 derivation, starting with result known as Maxwell–Boltzmann statistics (from statistical thermodynamics). Maxwell–Boltzmann statistics gives the average number of particles found in a given single-particle microstate. Under certain assumptions, the logarithm of the fraction of particles in a given microstate is proportional to the ratio of the energy of that state to the temperature of the system:


title: Maxwell–Boltzmann distribution

text: The assumptions of this equation are that the particles do not interact, and that they are classical; this means that each particle's state can be considered independently from the other particles' states. Additionally, the particles are assumed to be in thermal equilibrium.


title: Maxwell–Boltzmann distribution

text: The denominator in Equation () is a normalizing factor so that the ratios formula_58 add up to unity — in other words it is a kind of partition function (for the single-particle system, not the usual partition function of the entire system).


title: Maxwell–Boltzmann distribution

text: Because velocity and speed are related to energy, Equation () can be used to derive relationships between temperature and the speeds of gas particles. All that is needed is to discover the density of microstates in energy, which is determined by dividing up momentum space into equal sized regions.


title: Maxwell–Boltzmann distribution

text: where "Z" is the partition function, corresponding to the denominator in Equation (). Here "m" is the molecular mass of the gas, "T" is the thermodynamic temperature and "k" is the Boltzmann constant. This distribution of formula_58 is proportional to the probability density function "f" for finding a molecule with these values of momentum components, so:


title: Maxwell–Boltzmann distribution

text: The normalizing constant can be determined by recognizing that the probability of a molecule having "some" momentum must be 1.


title: Maxwell–Boltzmann distribution

text: The distribution is seen to be the product of three independent normally distributed variables formula_61, formula_62, and formula_63, with variance formula_64. Additionally, it can be seen that the magnitude of momentum will be distributed as a Maxwell–Boltzmann distribution, with formula_65. The Maxwell–Boltzmann distribution for the momentum (or equally for the velocities) can be obtained more fundamentally using the H-theorem at equilibrium within the Kinetic theory of gases framework.


title: Maxwell–Boltzmann distribution

text: where formula_66 is the infinitesimal phase-space volume of momenta corresponding to the energy interval formula_67.


title: Maxwell–Boltzmann distribution

text: Making use of the spherical symmetry of the energy-momentum dispersion relation formula_68, this can be expressed in terms of formula_67 as


title: Maxwell–Boltzmann distribution

text: Since the energy is proportional to the sum of the squares of the three normally distributed momentum components, this energy distribution can be written equivalently as a gamma distribution, using a shape parameter, formula_72 and a scale parameter, formula_73.


title: Maxwell–Boltzmann distribution

text: Using the equipartition theorem, given that the energy is evenly distributed among all three degrees of freedom in equilibrium, we can also split formula_74 into a set of chi-squared distributions, where the energy per degree of freedom, formula_75, is distributed as a chi-squared distribution with one degree of freedom,


title: Maxwell–Boltzmann distribution

text: At equilibrium, this distribution will hold true for any number of degrees of freedom. For example, if the particles are rigid mass dipoles of fixed dipole moment, they will have three translational degrees of freedom and two additional rotational degrees of freedom. The energy in each degree of freedom will be described according to the above chi-squared distribution with one degree of freedom, and the total energy will be distributed according to a chi-squared distribution with five degrees of freedom. This has implications in the theory of the specific heat of a gas.


title: Maxwell–Boltzmann distribution

text: Recognizing that the velocity probability density "f" is proportional to the momentum probability density function by


title: Maxwell–Boltzmann distribution

text: which is the Maxwell–Boltzmann velocity distribution. The probability of finding a particle with velocity in the infinitesimal element about velocity is


title: Maxwell–Boltzmann distribution

text: Like the momentum, this distribution is seen to be the product of three independent normally distributed variables formula_79, formula_23, and formula_24, but with variance formula_82.


title: Maxwell–Boltzmann distribution

text: Each component of the velocity vector has a normal distribution with mean formula_85 and standard deviation formula_86, so the vector has a 3-dimensional normal distribution, a particular kind of multivariate normal distribution, with mean formula_87 and covariance formula_88, where formula_89 is the formula_90 identity matrix.


title: Maxwell–Boltzmann distribution

text: The Maxwell–Boltzmann distribution for the speed follows immediately from the distribution of the velocity vector, above. Note that the speed is


title: Maxwell–Boltzmann distribution

text: where formula_93 and formula_94 are the spherical coordinate angles of the velocity vector. Integration of the probability density function of the velocity over the solid angles formula_20 yields an additional factor of formula_96.


title: Maxwell–Boltzmann distribution

text: The speed distribution with substitution of the speed for the sum of the squares of the vector components:


title: Maxwell–Boltzmann distribution

text: where formula_100 is the Gamma function. This result can be used to calculate the moments of speed distribution function:


title: Cavitation

text: Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery. These shock waves are strong when they are very close to the imploded bubble, but rapidly weaken as they propagate away from the implosion.


title: Cavitation

text: Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion. This results in surface fatigue of the metal causing a type of wear also called "cavitation". The most common examples of this kind of wear are to pump impellers, and bends where a sudden change in the direction of liquid occurs. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation and non-inertial cavitation.


title: Cavitation

text: The process in which a void or bubble in a liquid rapidly collapses, producing a shock wave, is called inertial cavitation. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants. In artificial objects, it can occur in control valves, pumps, propellers and impellers.


title: Cavitation

text: Non-inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers, etc.


title: Cavitation

text: Since the shock waves formed by collapse of the voids are strong enough to cause significant damage to parts, cavitation is typically an undesirable phenomenon in machinery (although desirable if intentionally used, for example, to sterilize contaminated surgical instruments, break down pollutants in water purification systems, emulsify tissue for cataract surgery or kidney stone lithotripsy, or homogenize fluids). It is very often specifically prevented in the design of machines such as turbines or propellers, and eliminating cavitation is a major field in the study of fluid dynamics. However, it is sometimes useful and does not cause damage when the bubbles collapse away from machinery, such as in supercavitation.


title: Cavitation

text: Inertial cavitation was first observed in the late 19th century, considering the collapse of a spherical void within a liquid. When a volume of liquid is subjected to a sufficiently low pressure, it may rupture and form a cavity. This phenomenon is coined "cavitation inception" and may occur behind the blade of a rapidly rotating propeller or on any surface vibrating in the liquid with sufficient amplitude and acceleration. A fast-flowing river can cause cavitation on rock surfaces, particularly when there is a drop-off, such as on a waterfall.


title: Cavitation

text: Other ways of generating cavitation voids involve the local deposition of energy, such as an intense focused laser pulse (optic cavitation) or with an electrical discharge through a spark. Vapor gases evaporate into the cavity from the surrounding medium; thus, the cavity is not a vacuum at all, but rather a low-pressure vapor (gas) bubble. Once the conditions which caused the bubble to form are no longer present, such as when the bubble moves downstream, the surrounding liquid begins to implode due its higher pressure, building up inertia as it moves inward. As the bubble finally collapses, the inward inertia of the surrounding liquid causes a sharp increase of pressure and temperature of the vapor within. The bubble eventually collapses to a minute fraction of its original size, at which point the gas within dissipates into the surrounding liquid via a rather violent mechanism which releases a significant amount of energy in the form of an acoustic shock wave and as visible light. At the point of total collapse, the temperature of the vapor within the bubble may be several thousand kelvin, and the pressure several hundred atmospheres.


title: Cavitation

text: Inertial cavitation can also occur in the presence of an acoustic field. Microscopic gas bubbles that are generally present in a liquid will be forced to oscillate due to an applied acoustic field. If the acoustic intensity is sufficiently high, the bubbles will first grow in size and then rapidly collapse. Hence, inertial cavitation can occur even if the rarefaction in the liquid is insufficient for a Rayleigh-like void to occur. High-power ultrasonics usually utilize the inertial cavitation of microscopic vacuum bubbles for treatment of surfaces, liquids, and slurries.


title: Cavitation

text: The physical process of cavitation inception is similar to boiling. The major difference between the two is the thermodynamic paths that precede the formation of the vapor. Boiling occurs when the local temperature of the liquid reaches the saturation temperature, and further heat is supplied to allow the liquid to sufficiently phase change into a gas. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid at a certain temperature.


title: Cavitation

text: In order for cavitation inception to occur, the cavitation "bubbles" generally need a surface on which they can nucleate. This surface can be provided by the sides of a container, by impurities in the liquid, or by small undissolved microbubbles within the liquid. It is generally accepted that hydrophobic surfaces stabilize small bubbles. These pre-existing bubbles start to grow unbounded when they are exposed to a pressure below the threshold pressure, termed Blake's threshold. The presence of an incompressible core inside a cavitation nucleus substantially lowers the cavitation threshold below the Blake threshold.


title: Cavitation

text: The vapor pressure here differs from the meteorological definition of vapor pressure, which describes the partial pressure of water in the atmosphere at some value less than 100% saturation. Vapor pressure as relating to cavitation refers to the vapor pressure in equilibrium conditions and can therefore be more accurately defined as the equilibrium (or saturated) vapor pressure.


title: Cavitation

text: Non-inertial cavitation is the process in which small bubbles in a liquid are forced to oscillate in the presence of an acoustic field, when the intensity of the acoustic field is insufficient to cause total bubble collapse. This form of cavitation causes significantly less erosion than inertial cavitation, and is often used for the cleaning of delicate materials, such as silicon wafers.


title: Cavitation

text: Hydrodynamic cavitation is the process of vaporisation, bubble generation and bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in local pressure. Cavitation will only occur if the local pressure declines to some point below the saturated vapor pressure of the liquid and subsequent recovery above the vapor pressure. If the recovery pressure is not above the vapor pressure then flashing is said to have occurred. In pipe systems, cavitation typically occurs either as the result of an increase in the kinetic energy (through an area constriction) or an increase in the pipe elevation.


title: Cavitation

text: Hydrodynamic cavitation can be produced by passing a liquid through a constricted channel at a specific flow velocity or by mechanical rotation of an object through a liquid. In the case of the constricted channel and based on the specific (or unique) geometry of the system, the combination of pressure and kinetic energy can create the hydrodynamic cavitation cavern downstream of the local constriction generating high energy cavitation bubbles.


title: Cavitation

text: Based on the thermodynamic phase change diagram, an increase in temperature could initiate a known phase change mechanism known as boiling. However, a decrease in static pressure could also help one pass the multi-phase diagram and initiate another phase change mechanism known as cavitation. On the other hand, a local increase in flow velocity could lead to a static pressure drop to the critical point at which cavitation could be initiated (based on Bernoulli's principle). The critical pressure point is vapor saturated pressure. In a closed fluidic system where no flow leakage is detected, a decrease in cross-sectional area would lead to velocity increment and hence static pressure drop. This is the working principle of many hydrodynamic cavitation based reactors for different applications such as water treatment, energy harvesting, heat transfer enhancement, food processing, etc.


title: Cavitation

text: There are different flow patterns detected as a cavitation flow progresses: inception, developed flow, supercavitation, and choked flow. Inception is the first moment that the second phase (gas phase) appears in the system. This is the weakest cavitating flow captured in a system corresponding to the highest cavitation number. When the cavities grow and becomes larger in size in the orifice or venturi structures, developed flow is recorded. The most intense cavitating flow is known as supercavitation where theoretically all the nozzle area of an orifice is filled with gas bubbles. This flow regime corresponds to the lowest cavitation number in a system. After supercavitation, the system is not capable of passing more flow. Hence, velocity does not change while the upstream pressure increase. This would lead to an increase in cavitation number which shows that choked flow occurred.


title: Cavitation

text: The process of bubble generation, and the subsequent growth and collapse of the cavitation bubbles, results in very high energy densities and in very high local temperatures and local pressures at the surface of the bubbles for a very short time. The overall liquid medium environment, therefore, remains at ambient conditions. When uncontrolled, cavitation is damaging; by controlling the flow of the cavitation, however, the power can be harnessed and non-destructive. Controlled cavitation can be used to enhance chemical reactions or propagate certain unexpected reactions because free radicals are generated in the process due to disassociation of vapors trapped in the cavitating bubbles.


title: Cavitation

text: Orifices and venturi are reported to be widely used for generating cavitation. A venturi has an inherent advantage over an orifice because of its smooth converging and diverging sections, such that it can generate a higher flow velocity at the throat for a given pressure drop across it. On the other hand, an orifice has an advantage that it can accommodate a greater number of holes (larger perimeter of holes) in a given cross sectional area of the pipe.


title: Cavitation

text: The cavitation phenomenon can be controlled to enhance the performance of high-speed marine vessels and projectiles, as well as in material processing technologies, in medicine, etc. Controlling the cavitating flows in liquids can be achieved only by advancing the mathematical foundation of the cavitation processes. These processes are manifested in different ways, the most common ones and promising for control being bubble cavitation and supercavitation. The first exact classical solution should perhaps be credited to the well-known solution by Hermann von Helmholtz in 1868. The earliest distinguished studies of academic type on the theory of a cavitating flow with free boundaries and supercavitation were published in the book "Jets, wakes and cavities" followed by "Theory of jets of ideal fluid". Widely used in these books was the well-developed theory of conformal mappings of functions of a complex variable, allowing one to derive a large number of exact solutions of plane problems. Another venue combining the existing exact solutions with approximated and heuristic models was explored in the work "Hydrodynamics of Flows with Free Boundaries" that refined the applied calculation techniques based on the principle of cavity expansion independence, theory of pulsations and stability of elongated axisymmetric cavities, etc. and in "Dimensionality and similarity methods in the problems of the hydromechanics of vessels".


title: Cavitation

text: A natural continuation of these studies was recently presented in "The Hydrodynamics of Cavitating Flows" – an encyclopedic work encompassing all the best advances in this domain for the last three decades, and blending the classical methods of mathematical research with the modern capabilities of computer technologies. These include elaboration of nonlinear numerical methods of solving 3D cavitation problems, refinement of the known plane linear theories, development of asymptotic theories of axisymmetric and nearly axisymmetric flows, etc. As compared to the classical approaches, the new trend is characterized by expansion of the theory into the 3D flows. It also reflects a certain correlation with current works of an applied character on the hydrodynamics of supercavitating bodies.


title: Cavitation

text: Hydrodynamic cavitation can also improve some industrial processes. For instance, cavitated corn slurry shows higher yields in ethanol production compared to uncavitated corn slurry in dry milling facilities.


title: Cavitation

text: This is also used in the mineralization of bio-refractory compounds which otherwise would need extremely high temperature and pressure conditions since free radicals are generated in the process due to the dissociation of vapors trapped in the cavitating bubbles, which results in either the intensification of the chemical reaction or may even result in the propagation of certain reactions not possible under otherwise ambient conditions.


title: Cavitation

text: In industry, cavitation is often used to homogenize, or mix and break down, suspended particles in a colloidal liquid compound such as paint mixtures or milk. Many industrial mixing machines are based upon this design principle. It is usually achieved through impeller design or by forcing the mixture through an annular opening that has a narrow entrance orifice with a much larger exit orifice. In the latter case, the drastic decrease in pressure as the liquid accelerates into a larger volume induces cavitation. This method can be controlled with hydraulic devices that control inlet orifice size, allowing for dynamic adjustment during the process, or modification for different substances. The surface of this type of mixing valve, against which surface the cavitation bubbles are driven causing their implosion, undergoes tremendous mechanical and thermal localized stress; they are therefore often constructed of extremely strong and hard materials such as stainless steel, Stellite, or even polycrystalline diamond (PCD).


title: Cavitation

text: Cavitating water purification devices have also been designed, in which the extreme conditions of cavitation can break down pollutants and organic molecules. Spectral analysis of light emitted in sonochemical reactions reveal chemical and plasma-based mechanisms of energy transfer. The light emitted from cavitation bubbles is termed sonoluminescence.


title: Cavitation

text: Hydrophobic chemicals are attracted underwater by cavitation as the pressure difference between the bubbles and the liquid water forces them to join. This effect may assist in protein folding.


title: Cavitation

text: Cavitation plays an important role for the destruction of kidney stones in shock wave lithotripsy. Currently, tests are being conducted as to whether cavitation can be used to transfer large molecules into biological cells (sonoporation). Nitrogen cavitation is a method used in research to lyse cell membranes while leaving organelles intact.


title: Cavitation

text: Cavitation plays a key role in non-thermal, non-invasive fractionation of tissue for treatment of a variety of diseases and can be used to open the blood-brain barrier to increase uptake of neurological drugs in the brain.


title: Cavitation

text: In wounds caused by high velocity impacts (like for example bullet wounds) there are also effects due to cavitation. The exact wounding mechanisms are not completely understood yet as there is temporary cavitation, and permanent cavitation together with crushing, tearing and stretching. Also the high variance in density within the body makes it hard to determine its effects.


title: Cavitation

text: It has been suggested that the sound of "cracking" knuckles derives from the collapse of cavitation in the synovial fluid within the joint.


title: Cavitation

text: In industrial cleaning applications, cavitation has sufficient power to overcome the particle-to-substrate adhesion forces, loosening contaminants. The threshold pressure required to initiate cavitation is a strong function of the pulse width and the power input. This method works by generating acoustic cavitation in the cleaning fluid, picking up and carrying contaminant particles away in the hope that they do not reattach to the material being cleaned (which is a possibility when the object is immersed, for example in an ultrasonic cleaning bath). The same physical forces that remove contaminants also have the potential to damage the target being cleaned.


title: Cavitation

text: Cavitation has been applied to egg pasteurization. A hole-filled rotor produces cavitation bubbles, heating the liquid from within. Equipment surfaces stay cooler than the passing liquid, so eggs don't harden as they did on the hot surfaces of older equipment. The intensity of cavitation can be adjusted, making it possible to tune the process for minimum protein damage.


title: Cavitation

text: Cavitation has been applied to vegetable oil degumming and refining since 2011 and is considered a proven and standard technology in this application. The implementation of hydrodynamic cavitation in the degumming and refining process allows for a significant reduction in process aid, such as chemicals, water and bleaching clay, use.


title: Cavitation

text: Cavitation has been applied to Biodiesel production since 2011 and is considered a proven and standard technology in this application. The implementation of hydrodynamic cavitation in the transesterification process allows for a significant reduction in catalyst use, quality improvement and production capacity increase.


title: Cavitation

text: Cavitation is, in many cases, an undesirable occurrence. In devices such as propellers and pumps, cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency. Noise caused by cavitation can be particularly undesirable in naval vessels where such noise may render them more easily detectable by passive sonar. Cavitation has also become a concern in the renewable energy sector as it may occur on the blade surface of tidal stream turbines.


title: Cavitation

text: When the cavitation bubbles collapse, they force energetic liquid into very small volumes, thereby creating spots of high temperature and emitting shock waves, the latter of which are a source of noise. The noise created by cavitation is a particular problem for military submarines, as it increases the chances of being detected by passive sonar.


title: Cavitation

text: Although the collapse of a small cavity is a relatively low-energy event, highly localized collapses can erode metals, such as steel, over time. The pitting caused by the collapse of cavities produces great wear on components and can dramatically shorten a propeller's or pump's lifetime.


title: Cavitation

text: After a surface is initially affected by cavitation, it tends to erode at an accelerating pace. The cavitation pits increase the turbulence of the fluid flow and create crevices that act as nucleation sites for additional cavitation bubbles. The pits also increase the components' surface area and leave behind residual stresses. This makes the surface more prone to stress corrosion.


title: Cavitation

text: Major places where cavitation occurs are in pumps, on propellers, or at restrictions in a flowing liquid.


title: Cavitation

text: As an impeller's (in a pump) or propeller's (as in the case of a ship or submarine) blades move through a fluid, low-pressure areas are formed as the fluid accelerates around and moves past the blades. The faster the blade moves, the lower the pressure can become around it. As it reaches vapor pressure, the fluid vaporizes and forms small bubbles of gas. This is cavitation. When the bubbles collapse later, they typically cause very strong local shock waves in the fluid, which may be audible and may even damage the blades.


title: Cavitation

text: Suction cavitation occurs when the pump suction is under a low-pressure/high-vacuum condition where the liquid turns into a vapor at the eye of the pump impeller. This vapor is carried over to the discharge side of the pump, where it no longer sees vacuum and is compressed back into a liquid by the discharge pressure. This imploding action occurs violently and attacks the face of the impeller. An impeller that has been operating under a suction cavitation condition can have large chunks of material removed from its face or very small bits of material removed, causing the impeller to look spongelike. Both cases will cause premature failure of the pump, often due to bearing failure. Suction cavitation is often identified by a sound like gravel or marbles in the pump casing.


title: Cavitation

text: Common causes of suction cavitation can include clogged filters, pipe blockage on the suction side, poor piping design, pump running too far right on the pump curve, or conditions not meeting NPSH (net positive suction head) requirements.


title: Cavitation

text: In automotive applications, a clogged filter in a hydraulic system (power steering, power brakes) can cause suction cavitation making a noise that rises and falls in synch with engine RPM. It is fairly often a high pitched whine, like set of nylon gears not quite meshing correctly.


title: Cavitation

text: Discharge cavitation occurs when the pump discharge pressure is extremely high, normally occurring in a pump that is running at less than 10% of its best efficiency point. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to flow out the discharge. As the liquid flows around the impeller, it must pass through the small clearance between the impeller and the pump housing at extremely high flow velocity. This flow velocity causes a vacuum to develop at the housing wall (similar to what occurs in a venturi), which turns the liquid into a vapor. A pump that has been operating under these conditions shows premature wear of the impeller vane tips and the pump housing. In addition, due to the high pressure conditions, premature failure of the pump's mechanical seal and bearings can be expected. Under extreme conditions, this can break the impeller shaft.


title: Cavitation

text: Discharge cavitation in joint fluid is thought to cause the popping sound produced by bone joint cracking, for example by deliberately cracking one's knuckles.


title: Cavitation

text: Since all pumps require well-developed inlet flow to meet their potential, a pump may not perform or be as reliable as expected due to a faulty suction piping layout such as a close-coupled elbow on the inlet flange. When poorly developed flow enters the pump impeller, it strikes the vanes and is unable to follow the impeller passage. The liquid then separates from the vanes causing mechanical problems due to cavitation, vibration and performance problems due to turbulence and poor filling of the impeller. This results in premature seal, bearing and impeller failure, high maintenance costs, high power consumption, and less-than-specified head and/or flow.


title: Cavitation

text: To have a well-developed flow pattern, pump manufacturer's manuals recommend about (10 diameters?) of straight pipe run upstream of the pump inlet flange. Unfortunately, piping designers and plant personnel must contend with space and equipment layout constraints and usually cannot comply with this recommendation. Instead, it is common to use an elbow close-coupled to the pump suction which creates a poorly developed flow pattern at the pump suction.


title: Cavitation

text: With a double-suction pump tied to a close-coupled elbow, flow distribution to the impeller is poor and causes reliability and performance shortfalls. The elbow divides the flow unevenly with more channeled to the outside of the elbow. Consequently, one side of the double-suction impeller receives more flow at a higher flow velocity and pressure while the starved side receives a highly turbulent and potentially damaging flow. This degrades overall pump performance (delivered head, flow and power consumption) and causes axial imbalance which shortens seal, bearing and impeller life.


title: Cavitation

text: Cavitation can occur in control valves. If the actual pressure drop across the valve as defined by the upstream and downstream pressures in the system is greater than the sizing calculations allow, pressure drop flashing or cavitation may occur. The change from a liquid state to a vapor state results from the increase in flow velocity at or just downstream of the greatest flow restriction which is normally the valve port. To maintain a steady flow of liquid through a valve the flow velocity must be greatest at the vena contracta or the point where the cross sectional area is the smallest. This increase in flow velocity is accompanied by a substantial decrease in the fluid pressure which is partially recovered downstream as the area increases and flow velocity decreases. This pressure recovery is never completely to the level of the upstream pressure. If the pressure at the vena contracta drops below the vapor pressure of the fluid bubbles will form in the flow stream. If the pressure recovers after the valve to a pressure that is once again above the vapor pressure, then the vapor bubbles will collapse and cavitation will occur.


title: Cavitation

text: When water flows over a dam spillway, the irregularities on the spillway surface will cause small areas of flow separation in a high-speed flow, and, in these regions, the pressure will be lowered. If the flow velocities are high enough the pressure may fall to below the local vapor pressure of the water and vapor bubbles will form. When these are carried downstream into a high pressure region the bubbles collapse giving rise to high pressures and possible cavitation damage.


title: Cavitation

text: Experimental investigations show that the damage on concrete chute and tunnel spillways can start at clear water flow velocities of between , and, up to flow velocities of , it may be possible to protect the surface by streamlining the boundaries, improving the surface finishes or using resistant materials.


title: Cavitation

text: When some air is present in the water the resulting mixture is compressible and this damps the high pressure caused by the bubble collapses. If the flow velocities near the spillway invert are sufficiently high, aerators (or aeration devices) must be introduced to prevent cavitation. Although these have been installed for some years, the mechanisms of air entrainment at the aerators and the slow movement of the air away from the spillway surface are still challenging.


title: Cavitation

text: The spillway aeration device design is based upon a small deflection of the spillway bed (or sidewall) such as a ramp and offset to deflect the high flow velocity flow away from the spillway surface. In the cavity formed below the nappe, a local subpressure beneath the nappe is produced by which air is sucked into the flow. The complete design includes the deflection device (ramp, offset) and the air supply system.


title: Cavitation

text: Some larger diesel engines suffer from cavitation due to high compression and undersized cylinder walls. Vibrations of the cylinder wall induce alternating low and high pressure in the coolant against the cylinder wall. The result is pitting of the cylinder wall, which will eventually let cooling fluid leak into the cylinder and combustion gases to leak into the coolant.


title: Cavitation

text: It is possible to prevent this from happening with the use of chemical additives in the cooling fluid that form a protective layer on the cylinder wall. This layer will be exposed to the same cavitation, but rebuilds itself. Additionally a regulated overpressure in the cooling system (regulated and maintained by the coolant filler cap spring pressure) prevents the forming of cavitation.


title: Cavitation

text: From about the 1980s, new designs of smaller gasoline engines also displayed cavitation phenomena. One answer to the need for smaller and lighter engines was a smaller coolant volume and a correspondingly higher coolant flow velocity. This gave rise to rapid changes in flow velocity and therefore rapid changes of static pressure in areas of high heat transfer. Where resulting vapor bubbles collapsed against a surface, they had the effect of first disrupting protective oxide layers (of cast aluminium materials) and then repeatedly damaging the newly formed surface, preventing the action of some types of corrosion inhibitor (such as silicate based inhibitors). A final problem was the effect that increased material temperature had on the relative electrochemical reactivity of the base metal and its alloying constituents. The result was deep pits that could form and penetrate the engine head in a matter of hours when the engine was running at high load and high speed. These effects could largely be avoided by the use of organic corrosion inhibitors or (preferably) by designing the engine head in such a way as to avoid certain cavitation inducing conditions.


title: Cavitation

text: Some hypotheses relating to diamond formation posit a possible role for cavitation—namely cavitation in the kimberlite pipes providing the extreme pressure needed to change pure carbon into the rare allotrope that is diamond. The loudest three sounds ever recorded, during the 1883 eruption of Krakatoa, are now understood as the bursts of three huge cavitation bubbles, each larger than the last, formed in the volcano's throat. Rising magma, filled with dissolved gasses and under immense pressure, encountered a different magma that compressed easily, allowing bubbles to grow and combine.


title: Cavitation

text: Cavitation can occur in the xylem of vascular plants. The sap vaporizes locally so that either the vessel elements or tracheids are filled with water vapor. Plants are able to repair cavitated xylem in a number of ways. For plants less than 50 cm tall, root pressure can be sufficient to redissolve the vapor. Larger plants direct solutes into the xylem via "ray cells", or in tracheids, via osmosis through bordered pits. Solutes attract water, the pressure rises and vapor can redissolve. In some trees, the sound of the cavitation is audible, particularly in summer, when the rate of evapotranspiration is highest. Some deciduous trees have to shed leaves in the autumn partly because cavitation increases as temperatures decrease.


title: Cavitation

text: Cavitation plays a role in the spore dispersal mechanisms of certain plants. In ferns, for example, the fern sporangium acts as a catapult that launches spores into the air. The charging phase of the catapult is driven by water evaporation from the annulus cells, which triggers a pressure decrease. When the negative pressure reaches approximately 9MPa, cavitation occurs. This rapid event triggers spore dispersal due to the elastic energy released by the annulus structure. The initial spore acceleration is extremely large – up to 10 times the gravitational acceleration.


title: Cavitation

text: Just as cavitation bubbles form on a fast-spinning boat propeller, they may also form on the tails and fins of aquatic animals. This primarily occurs near the surface of the ocean, where the ambient water pressure is low.


title: Cavitation

text: Cavitation may limit the maximum swimming speed of powerful swimming animals like dolphins and tuna. Dolphins may have to restrict their speed because collapsing cavitation bubbles on their tail are painful. Tuna have bony fins without nerve endings and do not feel pain from cavitation. They are slowed down when cavitation bubbles create a vapor film around their fins. Lesions have been found on tuna that are consistent with cavitation damage.


title: Cavitation

text: Some sea animals have found ways to use cavitation to their advantage when hunting prey. The pistol shrimp snaps a specialized claw to create cavitation, which can kill small fish. The mantis shrimp (of the "smasher" variety) uses cavitation as well in order to stun, smash open, or kill the shellfish that it feasts upon.


title: Cavitation

text: Thresher sharks use 'tail slaps' to debilitate their small fish prey and cavitation bubbles have been seen rising from the apex of the tail arc.


title: Cavitation

text: In the last half-decade, coastal erosion in the form of inertial cavitation has been generally accepted. Bubbles in an incoming wave are forced into cracks in the cliff being eroded. Varying pressure decompresses some vapor pockets which subsequently implode. The resulting pressure peaks can blast apart fractions of the rock.


title: Cavitation

text: As early as 1754, the Swiss mathematician Leonhard Euler (1707–1783) speculated about the possibility of cavitation. In 1859, the English mathematician William Henry Besant (1828–1917) published a solution to the problem of the dynamics of the collapse of a spherical cavity in a fluid, which had been presented by the Anglo-Irish mathematician George Stokes (1819–1903) as one of the Cambridge [University] Senate-house problems and riders for the year 1847. In 1894, Irish fluid dynamicist Osborne Reynolds (1842–1912) studied the formation and collapse of vapor bubbles in boiling liquids and in constricted tubes.


title: Cavitation

text: The term "cavitation" first appeared in 1895 in a paper by John Isaac Thornycroft (1843–1928) and Sydney Walker Barnaby (1855–1925) — son of Sir Nathaniel Barnaby (1829 – 1915), who had been Chief Constructor of the Royal Navy — to whom it had been suggested by the British engineer Robert Edmund Froude (1846–1924), third son of the English hydrodynamicist William Froude (1810–1879). Early experimental studies of cavitation were conducted in 1894-5 by Thornycroft and Barnaby and by the Anglo-Irish engineer Charles Algernon Parsons (1854-1931), who constructed a stroboscopic apparatus to study the phenomenon. Thornycroft and Barnaby were the first researchers to observe cavitation on the back sides of propeller blades.


title: Cavitation

text: In 1917, the British physicist Lord Rayleigh (1842–1919) extended Besant's work, publishing a mathematical model of cavitation in an incompressible fluid (ignoring surface tension and viscosity), in which he also determined the pressure in the fluid. The mathematical models of cavitation which were developed by British engineer Stanley Smith Cook (1875–1952) and by Lord Rayleigh revealed that collapsing bubbles of vapor could generate very high pressures, which were capable of causing the damage that had been observed on ships' propellers. Experimental evidence of cavitation causing such high pressures was initially collected in 1952 by Mark Harrison (a fluid dynamicist and acoustician at the U.S. Navy's David Taylor Model Basin at Carderock, Maryland, USA) who used acoustic methods and in 1956 by Wernfried Güth (a physicist and acoustician of Göttigen University, Germany) who used optical Schlieren photography.


title: Cavitation

text: In 1944, Soviet scientists Mark Iosifovich Kornfeld (1908–1993) and L. Suvorov of the Leningrad Physico-Technical Institute (now: the Ioffe Physical-Technical Institute of the Russian Academy of Sciences, St. Petersburg, Russia) proposed that during cavitation, bubbles in the vicinity of a solid surface do not collapse symmetrically; instead, a dimple forms on the bubble at a point opposite the solid surface and this dimple evolves into a jet of liquid. This jet of liquid damages the solid surface. This hypothesis was supported in 1951 by theoretical studies by Maurice Rattray, Jr., a doctoral student at the California Institute of Technology. Kornfeld and Suvorov's hypothesis was confirmed experimentally in 1961 by Charles F. Naudé and Albert T. Ellis, fluid dynamicists at the California Institute of Technology.


title: Cavitation

text: A series of experimental investigations of the propagation of strong shock wave (SW) in a liquid with gas bubbles, which made it possible to establish the basic laws governing the process, the mechanism for the transformation of the energy of the SW, attenuation of the SW, and the formation of the structure, and experiments on the analysis of the attenuation of waves in bubble screens with different acoustic properties were begun by pioneer works of Soviet scientist prof.V.F. Minin at the Institute of Hydrodynamics (Novosibirsk, Russia) in 1957–1960, who examined also the first convenient model of a screen - a sequence of alternating flat one-dimensional liquid and gas layers. In an experimental investigations of the dynamics of the form of pulsating gaseous cavities and interaction of SW with bubble clouds in 1957–1960 V.F. Minin discovered that under the action of SW a bubble collapses asymmetrically with the formation of a cumulative jet, which forms in the process of collapse and causes fragmentation of the bubble.


title: Economy of Poland

text: The economy of Poland is an industrialized, mixed economy with a developed market that serves as the sixth-largest in the European Union by nominal GDP and fifth-largest by GDP (PPP). Poland boasts extensive public services characteristic of most developed economies. Since 1988, Poland has pursued a policy of economic liberalization but it retained an advanced public welfare system. This includes universal free public healthcare and education (including tertiary), extensive provisions of free public childcare and parental leave provisions. The country is considered by many to be a successful post-communist state. It is classified as a high-income economy by the World Bank, ranking 23th worldwide in terms of GDP (PPP), 22nd in terms of GDP (nominal), and 23th in the 2018 Economic Complexity Index.


title: Economy of Poland

text: The largest component of its economy is the service sector (62.3.%), followed by industry (34.2%) and agriculture (3.5%). With the economic reform of 1989, the Polish external debt increased from $42.2 billion in 1989 to $365.2 billion in 2014. Poland shipped US$224.6 billion worth of goods around the globe in 2017, while exports increased to US$221.4 billion. The country's top export goods include machinery, electronic equipment, vehicles, furniture, and plastics.Its economy was the only one in the EU to avoid a recession through the 2007–08 economic downturn.


title: Economy of Poland

text: As of 2019, the Polish economy had been growing steadily for 28 years, a record high in the EU. This record was only surpassed by Australia in the world economy. GDP per capita at purchasing power parity has grown on average by 6% p.a. over the last 20 years, the highest in Central Europe. The country increased its GDP seven-fold since 1990.


title: Economy of Poland

text: Poland has seen the largest increase in GDP per capita (more than 100%) both among the former Eastern Bloc countries, and compared to the EU-15 (around 45%). It has had uninterrupted economic growth since 1992, even after the financial crisis of 2007–2008.


title: Economy of Poland

text: The Polish state steadfastly pursued a policy of economic liberalization throughout the 1990s, with positive results for economic growth but negative results for some sectors of the population. The privatization of small and medium state-owned companies and a liberal law on establishing new firms has encouraged the development of the private business sector, which has been the main drive for Poland's economic growth. The agricultural sector remained handicapped by structural problems, surplus labor, inefficient small farms, and a lack of investment. Restructuring and privatization of "sensitive sectors" (e.g. coal), has also been slow, but the foreign investments in energy and steel have begun to turn the tide. Also, reforms in health care, education, the pension system, and state administration have resulted in larger than expected fiscal pressures. Improving this account deficit and tightening monetary policy, with a focus on inflation, are priorities for the Polish government. Further progress in public finance depends mainly on the reduction of public sector employment, and an overhaul of the tax code to incorporate farmers, who currently pay significantly lower taxes than other people with similar income levels.


title: Economy of Poland

text: Since the global recession of 2009, Poland's GDP continued to grow. In 2009, at the high point of the crisis, the GDP for the European Union as a whole dropped by 4.5% while Polish GDP increased by 1.6%. As of November 2013, the size of the EU's economy remains below the pre-crisis level, while Poland's economy increased by a cumulative 16%. The major reasons for its success appear to be a large internal market (in terms of population it is sixth in the EU) and a business-friendly political climate. The economic reforms implemented after the fall of socialism in the 1990s have also played a role; between 1989 and 2007 Poland's economy grew by 177%, faster than other countries in Eastern and Central Europe, while at the same time millions were left without work.


title: Economy of Poland

text: However, the economic fluctuations of the business cycle did affect Poland's unemployment rate, which by early 2013 reached almost 11%. This level was still below European average and has begun falling subsequently. As of October 2017, Poland's unemployment rate stood at 4.6% according to Eurostat.


title: Economy of Poland

text: In the period from 1989 to 2018, Poland's GDP increased by 826.96% and it was the best result in Europe. In the same period, Ireland's GDP grew by 789.43%, Slovakia's by 783.83% and the Czech Republic by 549.47%. In 1990, the Polish national income amounted to USD 65.978 billion, and by 2017 it had increased to USD 524.5 billion. Achieving these results was possible thanks to the privatization of state-owned enterprises, the development of private entrepreneurship, but also the rapid increase in work efficiency and openness to foreign direct investments. In 2018, the Polish economy grew by 5.1% compared to 4.8% in 2017. Economic growth in the fourth quarter of 2018 in Poland amounted to 4.9% on an annual basis and compared to the third quarter, where GDP increased by 5.1%, it was slightly lower. During this period, investments increased by 6.7%, private consumption also increased by 4.3%, and domestic demand increased by 4.8%. The PMI index in January 2019 was 48.2 points. and was higher than in December 2018 when it amounted to 47.6 points.


title: Economy of Poland

text: Since 2015, under the Law and Justice (PiS) government, Poland has seen a growing wave of economic nationalism, with state-owned PZU in 2015 agreeing to buy a 25.3-percent stake in Alior Bank; PZU, together with the Polish Development Fund, buying a 32.8% stake in Bank Pekao by UniCredit in 2017; state-owned PKN Orlen merging with its fellow state-run utility Energa in 2020; and further plans to take over smaller rival Lotos. The minister also suggested Poland should have greater control over the economy.


title: Economy of Poland

text: The following table shows the main economic indicators in 1980–2021 (with IMF staff estimates in 2022–2027). Inflation under 5% is in green.


title: Economy of Poland

text: Unemployment in Poland became a major problem after the fall of socialism, although the economy previously had high levels of hidden unemployment. The unemployment rate then fell to 10% by the late 1990s and then increased again in the first few years of the 21st century, reaching a peak of 20% in 2002. It has since decreased, although unevenly. Since 2008 the unemployment rate in Poland has consistently been below European average.


title: Economy of Poland

text: With the collapse of the rouble-based COMECON trade bloc in 1991, Poland reoriented its trade. As early as 1996, 70% of its trade was with EU members. Neighboring Germany is Poland's main trading partner today. Poland joined the European Union in May 2004. Before that, it fostered regional integration and trade through the Central European Free Trade Agreement (CEFTA), which included Hungary, the Czech Republic, Slovakia and Slovenia.


title: Economy of Poland

text: Poland is a founding member of the World Trade Organization. As a member of the European Union, it applies the common external tariff to goods from other countries including the United States. Poland's major imports are capital goods needed for industrial retooling and for manufacturing inputs. The country's exports also include machinery but are highly diversified. The most successful exports are furniture, foods, motor boats, light planes, hardwood products, casual clothing, shoes and cosmetics. Germany is by far the biggest importer of Poland's exports as of 2013. In the agricultural sector, the biggest money-makers abroad include smoked and fresh fish, fine chocolate, and dairy products, meats and specialty breads, with the exchange rate conducive to export growth. Food exports amounted to 62 billion złoty in 2011, increasing by 17% from 2010. Most Polish exports to the U.S. receive tariff benefits under the Generalized System of Preferences (GSP) program. Poland ranks in the top 20 in the world both in terms of exports and imports, recording a clear trade surplus.


title: Economy of Poland

text: Poland is less dependent on external trade than most other Central and Eastern European countries, but its volume of trade with Europe is still substantial. In 2011 the volume of trade (exports plus imports) with the Euro area as share of GDP was 40%, a doubling from the mid 1990s. 30% of Poland's exports are to Germany and another 30% to the rest of Europe. There has been substantial increase in Poland's exports to Russia. However, in August 2014, exports of fruits and vegetables to Russia fell dramatically following its politically motivated ban by Moscow.


title: Economy of Poland

text: Foreign direct investment (FDI) was at 40% of GDP in 2010, a doubling over the level in 2000. Most FDI into Poland comes from France, Germany and the Netherlands. Polish firms in turn have foreign investments primarily in Italy and Luxembourg. Most of the internal FDI is in manufacturing, which makes it susceptible to economic fluctuations in the source countries.


title: Economy of Poland

text: The UAE has become Poland's largest trading partner in the Arab world, said Roman Chalaczkiewicz, Polish Ambassador to the UAE, speaking to Gulf News.


title: Economy of Poland

text: The government offers investors various forms of state aid, such as CIT tax at the level of 19% and investment incentives in 14 Special Economic Zones (among others: income tax exemption, real estate tax exemption, competitive land prices), several industrial and technology parks, the possibility to benefit from the EU structural funds, brownfield and greenfield locations. According to the National Bank of Poland (NBP), the level of FDI inflow into Poland in 2006 amounted to €13.9 billion.


title: Economy of Poland

text: According to an Ernst & Young report, Poland ranks 7th in the world in terms of investment attractiveness. However, Ernst & Young's 2010 European attractiveness survey reported that Poland saw a 52% decrease in FDI job creation and a 42% decrease in number of FDI projects since 2008. According to the OECD (www.oecd.org) report, in 2004 Poles were one of the hardest-working nations in Europe. 2010 the World Economic Forum ranked Poland near the bottom of OECD countries in terms of the clarity, efficiency and neutrality of the legal framework used by firms to settle disputes.


title: Economy of Poland

text: Before World War II, Poland's industrial base was concentrated in the coal, textile, chemical, machinery, iron, and steel sectors. Today it extends to fertilizers, petrochemicals, machine tools, electrical machinery, electronics, car manufacture and shipbuilding.


title: Economy of Poland

text: Poland's industrial base suffered greatly during World War II, and many resources were directed toward reconstruction. The socialist economic system imposed in the late 1940s created large and unwieldy economic structures<ref name="Poland 11/07"></ref> operated under a tight central command. In part because of this systemic rigidity, the economy performed poorly even in comparison with other economies in Central Europe.


title: Economy of Poland

text: In 1990, the Tadeusz Mazowiecki government began a comprehensive reform programme to replace the centralised command economy with a market-oriented system. While the results overall have been impressive, many large state-owned industrial enterprises, particularly the rail, mining, steel, and defence sectors, have remained resistant to change and the downsizing required to survive in a market-based economy.


title: Economy of Poland

text: The non-prescription medicines market, which accounts for about one-third of the total market value, was worth PLN 7.5bn in 2008. This value includes drugs and non-drugs such as dietary supplements, cosmetics, dressings, dental materials, diagnostic tests and medical devices. The prescription medicines market was worth PLN 15.8bn.


title: Economy of Poland

text: In 2019, the country was the 3rd largest world producer of rhenium; 5th largest producer of silver in the world; the 12th largest producer of copper; the world's 14th largest producer of sulfur; in addition to being the world's 14th largest producer of salt.


title: Economy of Poland

text: Agriculture employs 8.2% of the workforce but contributes 3.8% to the gross domestic product (GDP), reflecting relatively low productivity. Unlike the industrial sector, Poland's agricultural sector remained largely in private hands during the decades of real socialist [sic] rule. Most of the former state farms are now leased to farmer tenants. Lack of credit is hampering efforts to sell former state farmland. Currently, Poland's 2 million private farms occupy 90% of all farmland and account for roughly the same percentage of total agricultural production. Farms are small—8 hectares on average—and often fragmented. Farms with an area exceeding 15 ha accounted for 9% of the total number of farms but cover 45% of total agricultural area. Over half of all farm households in Poland produce only for their own needs with little, if any, commercial sales.


title: Economy of Poland

text: Poland is a net exporter of processed fruit and vegetables, meat, and dairy products. Processors often rely on imports to supplement domestic supplies of wheat, feed grains, vegetable oil, and protein meals, which are generally insufficient to meet domestic demand. However, Poland is the leading EU producer of potatoes and rye and is one of the world's largest producers of sugar beets and triticale. Poland also is a significant producer of rapeseed, grains, hogs, and cattle. Poland is the sixth-largest producer and exporter of apples in the entire world.


title: Economy of Poland

text: Poland, especially after joining the European Union in 2004, became a place frequently visited by tourists. Most tourist attractions in Poland are connected with natural environment, historic sites and cultural events. They draw millions of tourists every year from all around the world. According to Tourist Institute's data, Poland was visited by 15.7 million tourists in 2006, and by 15 million tourists in 2007, out of the total number of 66.2 million foreign visitors. In 2016 the number of arrivals to Poland amounted to 80.5 million. 17.5 million of this number are arrivals considered for tourism purposes (with at least one night's stay), making it the 16th most visited country in the world. The most popular cities are Kraków, Warsaw, Gdańsk, Wrocław, Łódź, Poznań, Szczecin, Lublin, Toruń, Sopot, Zakopane and the Wieliczka Salt Mine. The best recreational destinations include Poland's Masurian Lake District, Baltic Sea coast, Tatra Mountains (the highest mountain range of Carpathians), Sudetes and Białowieża Forest. Poland's main tourist offers consist of sightseeing within cities and out-of-town historical monuments, business trips, qualified tourism, agrotourism, mountain hiking (trekking) and climbing among others.


title: Economy of Poland

text: While transforming the country to a market-oriented economy during 1992–97, the government privatized some banks, recapitalized the rest and introduced legal reforms that made the sector competitive. These reforms, and the health and relative stability of the sector, attracted a number of strategic foreign investors. At the beginning of 2009, Poland's banking sector had 51 domestic banks, a network of 578 cooperative banks and 18 branches of foreign-owned banks. In addition, foreign investors had controlling stakes in nearly 40 commercial banks, which made up 68% of the banking capital. Banks in Poland reacted to the financial crisis of 2009 by restraining lending, raising interest rates, and strengthening balance sheets. Subsequently, the sector started lending again, with an increase of more than 4% expected in 2011.


title: Economy of Poland

text: The segment of the private equity market that finances early-stage high-risk companies, with the potential for fast growth, 130 active firms in Poland (as of March 2019). Between 2009 and 2019, these entities have invested locally in over 750 companies, an average of 9 companies per portfolio. Since 2016, new legal institutions have been established for entities implementing investments in enterprises in the seed or startup phase. In 2018, venture capital funds invested in Polish startups (0.033% of GDP). As of March 2019, total assets managed by VC companies operating in Poland are estimated at . The total value of investments of the Polish VC market is worth .


title: Economy of Poland

text: Poland is served by an extensive network of railways. In most cities, the main railway station is located near a city centre and is well connected to the local transportation system. The infrastructure is operated by Polish State Railways, part of state-run PKP Group. The rail network is very dense in western and northern Poland, while the eastern part of the country is less developed. The capital city, Warsaw, has the country's only rapid transit system: the Warsaw Metro.


title: Economy of Poland

text: The most important airport in Poland is Warsaw 'Frederic Chopin' International Airport. Warsaw's airport is the main international hub for LOT Polish Airlines. In addition to Warsaw Chopin, Wrocław, Gdańsk, Katowice, Kraków and Poznań all have international airports. In preparation for the Euro 2012 football championships jointly hosted by Poland and Ukraine, a number of airports around the country were renovated and redeveloped. This included the building of new terminals with an increased number of jetways and stands at both Copernicus Airport in Wrocław and Lech Wałęsa Airport in Gdańsk.


title: Economy of Poland

text: Poland has 412,264 km (256,170 mi) of public roads overall. Polish public roads are grouped into categories related to administrative division, which include National roads, Voivodeship roads, Powiat roads and Gmina roads. Motorways and expressways are part of the national road network. As of 10 January 2020, there are 4000 km of motorways and expressways in use.


title: Economy of Poland

text: Selection of major Polish companies including from the list of 500 largest companies in Poland compiled by magazine "Polityka":


title: Economy of Poland

text: Poland has a very good location for transporting locally made components or products to the rest of Europe. For example, when moving production from China, the new factory in Poland can move their goods in 24 hours to most populated parts of Europe, and in 48 hours to all Europe.


title: Economy of Poland

text: Poland, measured by the purchasing power parity index, is the sixth economy in the European Union and eighth in Europe, slightly ahead of the Netherlands.


title: Economy of Poland

text: Poland also recorded GDP growth during the 2008–09 financial crisis. More than half of Poles who are economically active have a job (56%).


title: Economy of Poland

text: Although the Polish economy is catching up with the countries of Western Europe, this process is progressing slowly. So far, taking into account the level of social development, Poland has managed to overtake Portugal. There is a great deal of variation between regions. Masovian voivodeship is on a similar level to the richest regions of Spain and most regions of France (82% of the EU average). However, it should be remembered that the GDP of this voivodeship is mainly generated by Warsaw. Lower Silesian voivodeship with a GDP of $16,000 is on par with Portugal and the regions of Spain and Greece. Subsequent voivodeships reached about 50% of the EU average, and the poorest voivodships of the eastern wall have GDP per capita comparable to Romania and Bulgaria.


title: Economy of Poland

text: Polish capital has several large concerns in this region of Europe, i.e. PKN Orlen, which has its stations in Germany and Lithuania, Polsat, which also invests in Lithuania, the ITI Group. Poland has a highly developed road network, most of the A1, A2, A4 highways and expressways, including S6 and S7, are fully completed. The next ones are to be ready by 2023. Their construction by private companies is financed in part by the European Union. In the coming years, Poland is to receive approximately EUR 4.5 billion for the modernization of railways.


title: Economy of Poland

text: Poland is one of the key immigration destination in the EU having attracted more non-EU immigrants than any other EU country for a few consecutive years.


title: Masters of the Universe

text: Masters of the Universe (sometimes referred to as the He-Man or She-Ra series) is a sword and planet-themed media franchise created by Mattel. The main premise revolves around the conflict between He-Man (the alter ego of Prince Adam) and Skeletor on the planet Eternia, with a vast lineup of supporting characters in a hybrid setting of medieval sword and sorcery, and sci-fi technology. A follow-up series, "" revolves around He-Man's sister She-Ra and her rebellion against on the planet Etheria. Since its initial launch, the franchise has spawned a variety of products, including multiple lines of action figures, six animated television series, several comic series, video games, books and magazines, a daily newspaper comic strip, and two feature films (one animated, one live action).


title: Masters of the Universe

text: He-Man and the accompanying Masters of the Universe franchise would make their debut in 1981 with Mattel's release of the original "Masters of the Universe" 5.5-inch action-figure toy line. Masters of the Universe, often abbreviated as MOTU, would begin its mythos through the minicomics that accompanied the toys throughout the 1980s. These initial mini comics were soon followed by several children's books and issues of DC Comics. However, the Masters of the Universe franchise would become best known through Filmation's groundbreaking "He-Man and the Masters of the Universe" animated series. Debuting in the fall of 1983, the Filmation series ran 130 episodes over two seasons until November 1985.


title: Masters of the Universe

text: Since its inception, Masters of the Universe has usually placed its focus on the two primary characters, the blond muscular He-Man, "the most powerful man in the Universe," and his nemesis, the evil skull-faced, blue-skinned sorcerer Skeletor and their many moral-themed encounters on the planet Eternia. Set in a hybrid world of sword and sorcery and technological sci-fi, He-Man battles with Skeletor to prevent him from conquering Eternia and discovering the secrets of Castle Grayskull—a mysterious ancient fortress with a skull-shaped facade, containing great power and magic. As with many toy franchises that have been transferred to several different media, there are a number of story differences between the various versions of Masters of the Universe. In most continuities from the Filmation series onward, He-Man is the secret identity of Prince Adam, the son of King Randor and Queen Marlena, the ruling royal family of Eternia. Adam becomes He-Man by holding aloft his magic Power Sword and uttering the words "By the power of Grayskull…" and serves as the protector of good on Eternia. He is first given this ability by the Sorceress of Castle Grayskull, a powerful magic user and mystic guardian of the castle, who in many depictions is able to transform herself into the falcon Zoar. Upon Adam's transformation into He-Man, his cowardly green pet tiger Cringer becomes the mighty Battle Cat, a giant armored beast that He-Man often rides into battle.


title: Masters of the Universe

text: He-Man's most prominent allies include Man-At-Arms, a wise loyal veteran soldier and inventor; and his adopted daughter Teela, a spirited and skillful female warrior, often portrayed as captain of the Eternian Royal Guard and a potential love interest of He-Man/Prince Adam. The childlike Trollan magician Orko also often features as one of He-Man's closest allies; as does Stratos, a flying bird-man from the kingdom of Avion; Ram-Man, a stout dimwitted warrior with springlike legs and a large helmet that encloses his head and upper torso; and Man-E-Faces, an actor with face-changing abilities.


title: Masters of the Universe

text: Skeletor is originally described as an evil being from another dimension and in some later MOTU lore as a disfigured and vengeful relative of the royal family, known as Keldor. From his lair on Snake Mountain, Skeletor would assemble his "Evil Warriors" to assist in his various schemes to conquer Eternia. These core minions usually include Beast Man, an orange-furred, apelike master of beasts; Mer-Man, an aquatic fishlike ocean warlord; Evil-Lyn, a powerful sorceress and one of Skeletor's most feared and competent associates; Trap Jaw, an iron-jawed criminal with a mechanical arm that can be fitted by a various assortment of weapons; and Tri-Klops, a mercenary swordsman with a rotating three-eyed visor.


title: Masters of the Universe

text: The series overall would feature a wide and ever-expanding cast of heroic and villainous characters added to the toy line, the Filmation cartoon, and other media; with the franchise far outshining prior expectations, continuing to grow through 1983 and 1984. The release of the animated cartoon movie "" in the spring of 1985 introduced He-Man's twin sister She-Ra (with her secret alter ego Princess Adora) and the arch-villain Hordak (leader of the Evil Horde and the former master of Skeletor) on the planet . Stemming from the animated movie, Filmation went on to produce 93 episodes of the series "", which ran until the end of 1987, along with the "." Other main characters of the She-Ra series would include Swift Wind, winged unicorn and alter ego of She-Ra's trusty steed Spirit; , mystical living beam of light and mentor to She-Ra; and her allies Glimmer, magically inclined onetime leader of the rebellion; Bow, skilled archer and the main male protagonist of the series; , Bow's owllike, rainbow-eared companion; Madame Razz, absent-minded witch with her sarcastic sentient ; and Queen Angella, Glimmer's mother and angel-winged queen of the Bright Moon; along with Hordak's spell-casting witch ; shape-shifting spy ; bumbling bug-eyed henchman Mantenna; Force Squad captain Catra; evil scientist Modulok; beastly warrior Grizzlor; energy-draining ; and thuggish henchwoman .


title: Masters of the Universe

text: Various children's books, magazines, comics, read-along records/cassette tapes, and other merchandise were also released worldwide around this time, with much of the content based primarily on the Filmation He-Man and She-Ra series. The live-action film "Masters of the Universe" was released in 1987 by Cannon Films, starring Dolph Lundgren and Frank Langella. The later 1980s mini comics, Marvel comics series, and UK magazine comics continued the adventures of He-Man and She-Ra past the end of the two Filmation series. However, popularity had waned by the end of 1987 and a planned continuation of the original toy line under the heading of "The Powers of Grayskull" (set in ancient Eternia, featuring the villain King Hiss and He-Man's ancestor He-Ro) was started, but eventually scrapped.


title: Masters of the Universe

text: He-Man would be brought back in 1989 in an entirely new and space-based cartoon series and toy line known as "The New Adventures of He-Man." Only He-Man and Skeletor would return as major characters to join the battle between Galactic Guardians and Space Mutants on the planet Primus. Jetlag Productions would go on to produce 65 episodes of the New Adventures cartoon, with a few mini comics and adventure magazines also created for this new series. Ultimately, though, the series would not be as successful and the entire franchise would go on a hiatus for more than a decade.


title: Masters of the Universe

text: After some success with a "Commemorative Series" rerelease of the classic action figures in 2000, Mattel relaunched the toy line with all-new action figures, playsets, and vehicles, sculpted by Four Horsemen Studios in 2002. As part of the relaunch, a modern updated animated series was also created by Mike Young Productions, lasting for 39 episodes; featuring He-Man and his ensemble of heroic warriors, now called the "Masters of the Universe," battling Skeletor's minions and, later, King Hiss, the ancient and evil lord of the Snake Men. Characters such as Mekaneck, heroic warrior with a mechanical extending neck; Buzz-Off, heroic beelike flying Andreenid warrior; Clawful, large villainous crab-like henchman; Whiplash, evil reptilian Caligar with a deadly tail; Stinkor, foul-smelling mutated Paleezean; and many others would gain more prominent backstories during this series. Several volumes of comic books were also produced to go along with the series by Image Comics and MVCreations. Although popular with longtime fans and collectors (with mini-statue figures being released by NECA until 2007), the new series failed to catch on with a larger audience and was canceled in 2004.


title: Masters of the Universe

text: From 2008 to 2020, a new assortment of Masters of the Universe action figures has been released under the banner of "Masters of the Universe Classics." Primarily geared toward the collector's market, the series made up an entirely new story in "Classics bios" and used various elements from previous Masters of the Universe lore, many times changing those elements to suit the new story, with characters from all previous incarnations (and also featured a continuation of the original mini comics line). DC Comics would soon follow suit and relaunch a new grittier, contemporary version of the Masters of the Universe franchise, releasing various new comic book series from 2012 until 2020; featuring crossovers with the DC Comics Universe, ThunderCats, and a new origin for She-Ra, culminating in Hordak's conquest of Eternia.


title: Masters of the Universe

text: In 2020, Mattel released a new line of 5.5" scale action figures, vehicles and playsets under the Masters of the Universe Origins line.


title: Masters of the Universe

text: Netflix and DreamWorks released an animated series entitled "She-Ra and the Princesses of Power" in 2018, which released five seasons until 2020. This was followed in 2021 by , a new Netflix animated series produced by Kevin Smith.


title: Masters of the Universe

text: Mattel began development of He-Man and the Masters of the Universe in the late 1970s with "Conan the Barbarian"–inspired concepts from Roger Sweet, Mark Taylor, Donald F. Glut, and several other contributors. The catalyst for the creation of He-Man began in 1976, when Mattel's CEO Ray Wagner declined a request to produce a toy line of action figures based on the characters from the George Lucas film "Star Wars", with the film's toy rights being acquired by Kenner instead. Upon the commercial success of the film trilogy and all related merchandise during the next few years, Mattel attempted to launch several unsuccessful toy lines, none of which captured the public's imagination or made a significant dent in the toy market.


title: Masters of the Universe

text: In the race to design the next hit action figure, Roger Sweet, a lead designer working for Mattel's Preliminary Design Department throughout much of the 1970s and 1980s, according to his book "Mastering the Universe: He-Man and the Rise and Fall of a Billion-Dollar Idea", was the first to conceptualize the idea of He-Man. However, this is not officially acknowledged by Mattel, and authorship of the He-Man character has been subject to debate. According to various former Mattel designers, Roger Sweet drew inspiration for the designs of his first He-Man prototypes from fantasy drawings of Mattel packaging designer Mark Taylor, which included a drawing of a He-Man-like character called Torak.


title: Masters of the Universe

text: Roger Sweet presented the He-Man concept to Ray Wagner at the Mattel Product Conference, in the form of three large three-dimensional plaster prototype models, which Sweet dubbed the "He-Man Trio." These prototypes were molded from extensively modified Big Jim action figures (Battle Cat would also be adapted from a tiger in the Big Jim toy line). The He-Man Trio models were an axe-wielding barbarian, a tank-headed soldier, and a spaceman with a Boba Fett–like helmet. Out of the three concepts, the barbarian version of He-Man was chosen to be the basis of the toy line (this original trio-prototype idea was released around 30 years later as the figure Vykron, and the barbarian concept on its own as Vikor, in the "Masters of the Universe Classics" line).


title: Masters of the Universe

text: "The only way I was going to have a chance to sell this [to Wagner] was to make three 3D models—big ones. I glued a Big Jim figure [from another Mattel toy line] into a battle action pose and I added a lot of clay to his body. I then had plaster casts made. These three prototypes, which I presented in late 1980, brought He-Man into existence. I simply explained that this was a powerful figure that could be taken anywhere and dropped into any context because he had a generic name: He-Man!"


title: Masters of the Universe

text: Originally set under the working title "Lords of Power," the name "Masters of the Universe" came into being when it was suggested that the former name of the toy line was too religious in nature. The roster of characters would soon expand past the main hero, He-Man, and Mark Taylor would draw inspiration for the series main villain, Skeletor, from his 1971 sketch entitled The King of Styx, along with early renderings of his characters Demo-Man and D-Man. Taylor would create preliminary designs for several other original characters as well, with additional ideas or direction from Mark Ellis and Paul Cleveland, among others, but the premise behind the toy line had not yet been fully established. The backstory of He-Man was first conceptualized for special mini-comic books that Mattel marketing director Mark Ellis promised distributors would accompany the toys. Mattel had DC Comics mock up a comic book, with the earliest storybooks written by Donald F. Glut. With major distributor Toys "R" Us concerned that "five-year-olds don't read", Mark Ellis then first proposed the idea of an animated TV special. This would eventually lead to a meeting with Filmation head Lou Scheimer and the creation of the "He-Man and the Masters of the Universe" animated series.


title: Masters of the Universe

text: Earlier in 1980, the rights-holders of Conan the Barbarian had been negotiating the character's toy rights with Mattel and they entered into an agreement the following year regarding characters from the 1982 Conan movie. However, with Mattel introducing the Masters of the Universe toy line in 1982, the rights-holders sued Mattel claiming the character was an infringement on the character of Conan. Mattel eventually won the lawsuit and after legal agreements were dissolved, it was stated that the toy line was never intended for the Conan film. However, some Conan influence can be seen, as Roger Sweet has claimed to have drawn some inspiration from the paintings of Frank Frazetta, a fantasy artist with many works depicting Conan the Barbarian, when creating He-Man.


title: Masters of the Universe

text: The "Masters of the Universe" toy line was created by Mattel in 1981, and first released to stores in 1982 as 5½-inch action figures (as opposed to the 3¾-inch size used by Kenner's Star Wars and Hasbro's lines). The two main characters, He-Man ("the most powerful man in the universe") and his arch-enemy Skeletor ("evil lord of destruction") were the first released in action figure form, along with other core characters of the series: Man-At-Arms ("heroic master of weapons"), Beast Man ("Skeletor's savage henchman"), and Battle Cat ("He-Man's fighting tiger").


title: Masters of the Universe

text: Later on that year, the first wave of action figures in 1982 would also include Teela ("heroic warrior goddess"), Mer-Man ("evil ocean warlord"), Stratos ("heroic winged warrior"), and Zodac ("the cosmic enforcer"). The Teela action figure was originally proposed as representing both the Sorceress character (when wearing the figure's "snake armor") and the Teela character (when without the "snake armor"), as Mattel believed there would not be enough demand for two female action figures in the initial wave. Alongside the first wave of figures were the Battle Ram ("mobile launcher") and Wind Raider ("assault lander") vehicles and the playset Castle Grayskull ("fortress of power and mystery"). These first figures as well as Castle Grayskull were primarily designed by Mark Taylor, although the final production sculpt of the original He-Man action figure was completed by Tony Guerrero and the first vehicles were designed by Ted Mayer.


title: Masters of the Universe

text: Brief descriptions of the characters would appear on the packaging and box art (with illustrations by Errol McCarthy, Rudy Obrero, William Garland, William George, and others). However, the lore of "Masters of the Universe" would be first fully explored through the mini-comics that accompanied the action figures throughout the duration of the line (with 49 distinct comics being issued from 1981 until 1987). The original four mini comics, "He-Man and the Power Sword", "The King of Castle Grayskull", "Battle in the Clouds", and "The Vengeance of Skeletor" were made by Mattel in 1981 and written by Donald F. Glut, with artwork by Alfredo Alcala. He-Man is introduced in the first mini comic, "He-man and the Power Sword", as a wandering barbarian, leaving behind his jungle tribe on Eternia. The world of Eternia is initially depicted as dealing with the aftermath of a great war that has devastated once-powerful civilizations, leaving behind their fantastical machinery and weapons. The events of the war have also opened a rift between dimensions, which has allowed the evil warlord Skeletor to travel into Eternia. This inaugural incarnation of Skeletor sets his sights on obtaining both halves of the Power Sword (originally split in two in these early stories), in order to gain entry into the ancient Castle Grayskull (depicted, in these early comics, as being inhabited by the ghostly "Spirit of Castle Grayskull"). The main premise being that whomever attains control of Castle Grayskull will gain the power to become Master of the Universe. To combat Skeletor, He-Man is given special powers, armor, and weapons by the Sorceress (she has green skin in her debut appearance and is wearing the "snake armor" that came with the original Teela action figure, instead of adorning her more familiar birdlike attire, as seen in the Filmation series). He-Man (not yet with the dual identity of Prince Adam) is supported in these initial stories by his heroic allies: Battle Cat (without the dual form of Cringer), Man-At-Arms, Teela, and Stratos, the winged warrior (who erroneously came fighting on the side of Skeletor in the initial mini-comic). Skeletor, in turn, enlists the help of the brutish apelike Beast Man and fishlike Mer-Man to battle He-Man or his heroic warriors.