So why should you come and take civil and environmental engineering? Well, let me introduce you to a couple of Latin terms. The first term, schiere, you'll recognize as being the basis for the word science, means to know in Latin. And the second word, ingenere, basis for the word engineering, means to create. So have you ever been in a math class or a science class and you're looking at something and studying it very carefully and you're wondering, well, how do I go about applying this? What am I going to be able to do with this piece of information beyond the questions that are being asked in my science class?   You like to build something. You've made something out of Legos or some sort of toy or you've built something in a shop. And as you're creating it, it behaves in a way that's a little strange or you're not exactly certain why it works, but you know it works. Well, what we want to do in a class as engineers is learn how to put together, combine what you know with how you create. And so you can create in a fashion that actually predicts and controls the future, controls the behavior of whatever it is you create. What I try to do in my class is give you that first moment where you create something for the first time but you've made a relatively complex prediction about what that something is going to do.  Now this course is civil and environmental engineering. Civil engineering basically referring to people, a citizen. An environmental engineering and viral means in a circle everything around us as people, as citizens. So in civil environmental engineering we're going to split the class into two parts and talk, first of all, about things that we need as people. Basically buildings, we'll talk a lot about structures and how we determine whether a structure is going to stand up or whether it's going to fall down and how we analyze that. We can build it, we can test it, we can guess. But guessing is not going to be good enough if you want to build something that's going to stand up for many years and also use a realistic amount of materials. Now on the other side of things, the environment around us there are many things that affect the environment around us water, air, things like that. Well we're interested in looking how those behave and how we interact with them, how we change them and how they change us. And again we need to learn some of the details about those things in order to make good predictions and ultimately to build things that fit our purposes. So would you like to be an engineer? Well it takes about 10,000 hours to become an expert at something or so they say. We're not going to become complete experts but why don't you start with the first 200 hours in my class and let's see where we go.


So, far in module 5, we looked at the electronic properties of materials and in module 6, we are going to take a look at the optoelectronic properties of material. Materials which combine both the optical property as well as the electronic property together, we call this as optoelectronic properties because most of the gadgets that we use in today's life, we coupled both the optical property of a material and the corresponding electronic property of a material to harvest either informations or to harvest displays. So, generally these are termed as optoelectronics and in the next few lectures, I would be concentrating on some of the materials which really stand out in today's technology which will underline the need for why we need new materials and also I will try to explain in the next few lectures, why organic molecules plays a important role in optoelectronic devices. Today if you are handling any of the gadgets like iPod or cell phone or pump computers, all the displays are more or less governed by small molecules either they are metal organic complexes or much more easier version could be the organic molecules. So, as we looked at the genie inside a lattice which brings in magnetism and electronic properties together, I have coined this term the genie in organic molecules. There is a great potential in every organic molecule especially when you consider optoelectronic properties and we need to understand what these governing properties are, what are the issues that are involved in controlling optoelectronic properties. So, when we think of organic molecules for optoelectronic applications, we can by and large call that area as organic photonics. In other words, photonic applications that are actually initiated by using organic molecules to stand out clearly, there are two important applications which underline the importance of organic molecules. One is called organic LEDs and the other upcoming area is photovoltaics or solar cells. In this year, January 2010, there was an article or in a conclave, they decided that the technology for 2010 will be the year of LED displays and true to this decision made by those in the display technology, several versions of organic displays have come into picture in this year and needless to say that this technology is going to affect the landscape of photonic applications displays in a very big way in the next five years and because this year is a year of LED displays, I personally thought that we should lay more emphasis on organic displays compared to even inorganic displays. For those who are wondering why we talk about organic displays because all the gadgets that you use currently show some sort of LED response and they are all based on inorganic materials and mainly those are governed by gallium nitride. Inorganic materials based on gallium nitride are the ones which are used in photonic display materials. So, therefore, I would like to emphasis more on the use of organic. This cartoon tells that the more we go for different gadgets, the more we are interested in full color display. Nobody is settled with a black and white or a monochrome display. Those days have gone, we are looking not only for multicolor display, but we are looking for high resolution display. So, what is this which governs a full color display? Full color displays are basically initiated by the use of organic materials in today's technology and whatever color that you are seeing is nothing but manifestation of organic materials that are coated on the screen. Whether you call it a computer display, monitor or TV monitor or anything, these are all coated with choice organic materials. This is the recent display made by Sony and as you see here, this is a Sony market which is actually bringing out a new generation OLED TV. This is high density TV. It looks like a computer monitor, but this is actually a TV and the whole display whatever you see here, the display here, this is all projected from an organic LED screen. So, the display that is responsible or the light that is coming out of this display unit is mainly organic molecules. It is not based on gallium nitrite, but it is based on organic molecules. So, this is almost a most recent invasion and you would also see in the market 3D OLED displays are being advertised by Samsung. So, all the new generation displays have bigger screens. Display screens can vary from 29 inch to 41 inch display screens mostly governed by organics. The cartoons here shows another generation of displays that are coming. These are called flexible substrates, flexible substrates where you can use it in variety of application even in car windshield and so on. You can actually have some displays coming and mainly this is coming from organic electronics. Only with organics, you can make such flexible displays. With inorganic phosphorus or inorganic photo luminescent material, it is impossible to make such flexible ones. Here is a situation where you can display on a flexible screen. This is with the paper substrate. This is with the polymer substrate. Usually it is a PET based substrate, but here this is a paper substrate on which displays can be initiated and this is actually brought up by Siemens and here is another display may not be of a very high quality, but essentially tells you that you have another flexible substrate which can be used in your pen. This is a pen holder where you can actually pull out a screen and then you can scroll it back.  So, these are flexible substrates on which organic molecules are used for displays and here is another classical example of what the organic displays can do. This is the new generation Kodak cameras that are coming, digital cameras and the beauty is the display what you get here is now made of OLED display material and you can also see here this is also a OLED material reason why we need OLED material because you have the same sharpness and it almost consumes one tenth of the power that gallium nitride based LED will consume. Therefore, you have a longer battery life and you get better resolution and also you can make wider screen or large area display. Therefore, you can do this at a very economically viable way you can generate bigger display. So, this is catching up and in few years from now all the displays in our electronic gadgets that we handle will all be organic and this is example of digital frame. Now, this is coming into picture you have so many photos that you store in your cameras and you do not know when to see it you can actually take your hard drive from the camera and you can put it in this digital frame at home it will keep on displaying all thousands of photos that you are copying. So, this may be a good entertainment to keep the visitors occupied when they are sitting in the living room waiting for you and here is another OLED display from a foreign company which shows a full color display mainly tuned from organic LEDs and of course needless to say you also have the mobile which is made of OLED and there are other applications where you can look for OLED this is a table lamp made of OLED lighting and the important advantage is this gives you cool light more brightness, but it is still cooler it does not irritate your eyes and also the efficiency of this organic lamps are very high that you can even operate with 3 volt battery you do not you do not need even a AC supply you can just do it wherever you want you get the same brightness and lot of lighting applications are also affected these days using organic LEDs. Then the whole question comes where is my organic material in this device devices and how does the organic material work or what is the mechanism by which this organic material throws light. So, that is a good question to ask so the question we will try to answer in the next few slides how does a organic device works. This is a simple example of a diode if you have a diode and if you connect it to a battery then the electrons go from the anode material yeah so the electron flows from the anode material and the sorry the holes go from the anode material and the electron flows from the cathode and you can see here at this interface you have both the holes and electrons combining and photons come out during this excitonic recombination when the photons come out at this interlayer yeah so in this animation you would see a electron and a hole recombining. So, at this interface if you can put an organic layer then the photon can actually excite the organic material and the desired light can be harvested. So, this is typically the view diagram of a basic OLED structure where you have a cathode on the top and you have an anode at the bottom anode is preferably a ITO indium tin oxide which is coated in glass therefore, it is a transparent anode it is a transparent anode cathode can be opaque cathode typically can be aluminum or calcium and between this there are crucial layers, but the layer of importance to us is the organic layer which we call this as emissive layer EML and you can sandwich this organic layer with the electron transport layer because the electrons has to flow from here towards the emissive layer and holes have to flow from here towards the emissive layer. So, you have to control the traffic or control the mobility of the organic of the electron as well as the holes and you should make sure that the combination of electron and hole both occurs at the emissive layer. So, when there is a combination of electron hole pair which forms an exciton that exciton will give away photon which will excite in turn your organic material. So, there are lot of crucial issues that are involved in this it is not a simple five layer structure which forms a OLED because the number of electrons that keeps coming here and the number of holes that are going towards the emissive layer both needs to be controlled not only that the speed with which these electrons come here and the speed with which the holes come at the emissive layer which we call it as mobility. Mobility of the carriers also matter, so a proper recombination has to occur in this layer if this is not effective then the combination can happen here or the combination can happen in this region and thereby giving some other light which is not of a desired nature. So, there are several issues involved in selecting the electron transport and the hole transport layer and the issues related to emissive layer and also the homo-lumo gap of cathode homo-lumo gap of ITO all these are crucial ingredients in designing a organic LED. So, this is a basic structure we will come to the issues later now if I am going to put organic materials here incidentally these are also organic materials which are polymeric in nature. So, if I am going to put organic materials here now what are all the issues that will decide the basic performance of a LED which we can see now there are different ways that I can harvest light from this organic LED structure the different combinations for a full color display I would like to touch basic light basic colors are red blue and green and combination of red blue and green gives white light and mix of these two colors gives you yellow mix of these two colors gives you magenta and then cyan. So, combination of RGB gives you white light therefore, you essentially get a full spectrum display when you have material which can give red light material which can give blue material which can give green light. So, if you are looking for a full color display of this nature then there are three approaches one is take a red and try to get red color as you see in this case and green for green blue for blue which means you are going to use three materials to get all three colors. And another one is to go for blue to red blue to green and blue to blue down conversion where blue is of a high energy emission therefore, you can put proper filters here and try to get from blue a down conversion to red blue down conversion to green blue down conversion to blue. So, this is another way you can actually get your RGB colors this is another way to get RGB color the other approach which is of interest to us is take a white light emitting molecule and put filter here filter to get only red color and filter to get only green filter to get only blue color. So, you are essentially having only one molecule and you are getting three different colors. So, this way you can actually minimize on your device fabrication protocol instead of having three materials or instead of going for down conversion you use one material which gives full color spectrum, but use proper filter to get only the desired light. So, this way also you can get RGB there are different approaches this is another approach which is popular in the market where people try to use blue and get all the colors very few white light emitting molecules are there white light emitting molecules can be used for full color display as well as for white light emission for OLED lamps or for lighting applications therefore, making white light emitting molecules has dual advantage one is you can down convert it for desired lights another thing you can use this white light molecules for even organic white light emitting lamps. So, for this reason there is special emphasis on white light emitting molecules and companies are investing a lot of money specially for white light emission. Here is another protocol I have already told you so I may not run through this, but there are different ways of making a device, but need based you can actually get different displays. If you preferentially activate one of the pixel then you would get white or you would get green or you would get blue or you get red all from the same architecture and in such cases you need to have stackings of this order where you can get different pixels. This is the example that I quoted in the previous slide this is another example which I emphasis from the previous slide on white LED and this is the stacked OLED which gives you this set of performance. So, you have transparent contact for all the devices that you have, but this stack OLEDs essentially will give you the preferred light as and when you try to ask for it. One of the thing that we need to understand is how do I know what sort of molecule it is and how do I categorize different organic molecules and what is the number that I should resort to. This is based on CIE diagram because it has been accepted to represent the color of your molecule based on CIE coordinates and CIE coordinates is actually based on a two dimensional graphical plot which tells you the numbers. So, if you have a number marked here then the x and y component of that will give you an idea that it is a blue light emitting molecule. If you mark something here then you are talking about your y coordinate and x coordinate which gives you typically a pure green one. We are actually concerned about white and if you look at it white light emitting molecule the magic number for that comes somewhere here and it is usually 0.33, 0.33 so if you are x and y of your CIE coordinates is 0.33, 0.33 you are talking about a proper mix of blue green and red together they give you a white light whose coordinates are mentioned as 0.33, 0.33 either way if it is not matching to 0.33 then one of the colors will dominate. So, this is the way you usually categorize what sort of molecule you have so that such a molecule if you give the CIE coordinates will immediately be used for a specific application. Where did it all start? We need to actually give credit for Tang and Vanslik who actually brought the AL Q3 into focus and this is typically a AL Q3 complex which is actually in the animation and if you make a device such as glass, ITO, diamond and AL Q3 capped with the cathode then you can see that a OLED performance occurs where with increasing voltage you see the current and the light intensity exponentially going. This was the first demonstration as early as 1987 and I should also record this as a historical fact because 1986 and 1987 has been a path breaking years for most of the discoveries as far as electronic and optoelectronic applications are concerned. As I discussed with you in module 5, I have told you how the lanthanum manganite was discovered to show colossal magneto resistance that was in 1986 one paper came and then 1986 also this high temperature superconductivity came into picture where this wonder molecule was discovered, yttrium barium copper oxide that was also in 1986 and again you see here 1989 the first report on organic LED was published. Therefore, these are really crucial and formative years where many path breaking device application oriented discoveries were made in solid state materials. Therefore, this is a golden era in one sense to say solid state chemistry came into much of focus because in solid state whether it is organic molecule or a inorganic solid both started showing interesting properties. So, I will go one step further to highlight to you what exactly is happening in these compounds, why light is coming at all?  So, this photon can be used for activating any or promoting any molecule or exciting any molecule. So, what really happens between a hole and the electron when hole and electron combines they actually form a hole electron pair which further leads to singlet exciton as I shared with you in while discussing organic spin valves. I told you the percentage of singlet excitons according to spin statistics is 25 percent and triplet exciton is 75 percent with this 25 percent comes all the light that you are harvesting from organic molecule because triplet exciton is a slow process spin forbidden, but it goes through a radiation less deactivation, but it is possible one to harvest this triplet exciton convert it into singlet excitons and you can try to increase on the efficiency of your excitonic emission governed by singlets. So, once you get a singlet exciton it can again go through a thermal deactivation which can be useless does not really merit any attention or it can actually go through a emission process and this emission can actually go through another two effects one is the external emission and that is what is exactly coming out as displace, but the internal reflection law is something that we need to put up with that is why most of the displace you see a heating effect coming and that is all because of the light that that goes as a internal loss. So, there are many ways that this internal loss is being minimized in this new generation display materials, but we are concerned now only about the external emission. So, this is the pathway by which you get light once you let hole and electron combined. So, this is the mechanistic process for a electro luminescent device. Now, what are all the organic molecules which really govern such a show or what really controls the organic displace we can define that or we can broadly divided between two set of compounds one those which are polymeric in nature P P V for example is a classic example and even now in commercial devices P P V is used we will come to this later, but the other wonder molecule is the molecular material and this is a typical example of aluminum Q 3 and this is called as 8 hydroxy quinolinato aluminum 3 complex popularly abbreviated as L Q 3 and this L Q 3 this is the quinoline moiety and there are 3 such quinoline moieties which actually coordinate to aluminum center here and you have the coordination actually happening from nitrogen this is a nitrogen atom and this is oxygen atom 3 oxygens actually satisfy the valency of your aluminum. Therefore, this is a electrically neutral molecule L Q 3 and this L Q 3 is a wonder molecule because it was used by Kodak for the first time in device applications. So, this is actually nicknamed as Kodak molecule because this molecule is also covered by IPR by Kodak company therefore, it is a proprietary molecule and no one can infringe in using aluminum Q 3 for making devices without the permission from Kodak company. So, if you think of any organic molecule the first thing that should strike your mind is L Q 3. In fact, the Kodak company has brought out the digital display in the cameras which is actually made of L Q 3 and some other hybrid molecules. So, this is the most popular or billion dollar molecule. So, to say which is actually controlling the optoelectronic applications as of now, but there are several such molecules which are being generated. We are going to see in next few lectures a special study on this L Q 3 or several other molecules which really govern the organic displays. So, having said that I have been talking to you more about L Q 3 which is lying in this place in the device application, but there are several other organic molecules which also top up to the complexity or simplicity of this device. As I told you, you have a HDL that is whole transport material and you also have a electron transport material. So, these are the whole injecting layers which are mostly polymeric in nature. As you see here, they are all polymeric in nature and it is very easy to grow such polymeric films by thermal evaporation. So, you can make a thin layer here. To get a good support, you can also use intermediate layers like this which is mostly P dot PSS. We can come to that later and there are other whole transporting materials which are NPB, TPD. This can also be used other than this whole injecting layers and we also have electron injecting layer which is happening here. These are the whole injecting layers. These are the whole transport layers. The electron injecting layers are mainly coming from molecules like lithium fluoride which are insulators. Therefore, they help electrons to accumulate at the cathode LIF interface and then they proceed together. So, instead of having a random electron transport across the interface, they act like a barrier, but these barriers are of very thin dimension. So, that all the electrons that are flowing, they get collected at the interface and then they flow together. As you would see the water gushing out of the opening, floodgates from a dam, all the electrons get accumulated and they flow into the electron transport layer. These are the popular electron transport layers. One can think of Al Q 3. It is both emissive layer. It is also good electron transporting layer. BCP is another layer. PBD is another layer. As you would see here, mostly in this combination, you can either use a purely organic molecule, small molecule or you can use a metal organic complex. Whereas, in the whole transport materials is predominantly small molecules or polymers which are used. So, just to give you an idea, what it takes to make organic light emitting molecule? You have several combinations that are in picture, but the grandeur of organic LED is based on the emissive layer. So, that has to be tuned properly so that you get all the necessary display information that you can get. So, that is crucial. Now, having discussed something about what these molecules are and how it basically works, I will spend little time on how to fabricate an organic device compared to the multi layers that we discussed in the previous module on electronic materials. Organic device making efforts are rather easier comparatively, but there is a stringent protocol that is followed because it has to be moisture free, although it can be handled at very low vacuum conditions. In the spin electronic application or spin tronic devices, I emphasize that you need absolutely a very high vacuum, but in organic device applications, you do not need very high vacuum, but a moderate vacuum of the order of 10 power minus 5 tau that is enough. So, in the next few slides, I will discuss with you about what it takes to make an organic device. So, how to fabricate an organic device? This is a simple belger setup which can be used for making these devices and this is a vacuum chamber and in this vacuum chamber you have source boards which are kept here and you can heat the source boards. So, you can keep your organic molecules here and thermally you can evaporate this. This is a shutter which is kept there for a slow stream of these molecules to come up and once there is a proper flux of this organic molecules coming, then you can open the shutter and you can try to deposit in the substrate which probably you may be able to see here. There is a substrate here and there is also a thickness monitor unit which is a quartz balance which is kept there which can measure the thickness of the layer that is coming in terms of angstrom. How much angstrom of the organic layer is formed per minute? So, you can essentially control from say 10 to 20 nanometer or if you want to make a 70 nanometer thick film or a 100 nanometer thick film, it is possible for you to control the thickness using a quartz monitor that is called thickness monitor that is kept within the chamber so that you can effortlessly work on the thickness of the layer that you are depositing. So, all it takes is to apply vacuum and then once the required vacuum is reached then you can flush it with some gas say argon and then at optimum pressure you can try to heat this sources and there is a steady flux of this organic molecule which is going and it will get deposited in a substrate. In a typical experiment you can actually make 5 to 6 devices at one time. So, you can actually play with many devices if you can go for such a protocol. This is typically the way the chamber looks this is a device fabrication chamber. So, it may be alarming but this is the way it is done it involves all the other electronics in it. So, just to give you a flare because it is not as easy as you see here the machine actually looks bit more rugged as you see in this case. This is the deposition chamber in which you make the device. Now, once you do the device your first idea or your temptation would be to look at the electro luminescence. But before you do the electro luminescence you also should know what set of color your molecule is emitting. So, that you will know what is the shift in the color when you put it in a in a EL device because this machine gives you photo luminescence spectra that is your PL emission of your organic molecule will be C. But when you actually develop a solid state material then the electro luminescent EL emission need not be the same as your PL emission it can be different. At the same time if you can retain the same PL emission characteristics in EL emission then you have made a real good device. In any case you will get an idea about what the actual photo luminescent property of your material is and how you transcend to make another material with a device configuration. So, this will help you in interpreting the photo physical properties of your material. So, PL instrument is actually used for getting PL emission and this is a IV measurement unit which is just unit involving multimeter and your current source this will help you to get current versus voltage curve. So, if you are making a organic LED your electro luminescent device typically will have some feature like this where up to a particular voltage there will be no current and at this threshold voltage then you will see current flowing that means your electro luminescent device is going to produce light. Light will start appearing as after you have applied a threshold voltage. So, this information you can get out of this IV measurement curve and also this Minolta CS100 can give you not only an idea about the current density it will also tell you the luminescent density. As you increase the voltage the brightness or the glow of your electro luminescent device will start increasing with increasing voltage. So, Minolta will give you the coordinates of your light output and typically the graph will look like this we will look at it later. So, having said that I just want to concentrate now on few examples and show you how organic molecules can be used to fine tune color or to understand what is responsible for this color displays. So, I am going to take some examples in the next few slides I will tell you what is this white light emission and with few examples as to how to harvest white light because white light lighting is becoming popular and I will also tell you white light can be engineered not just from the organic molecule, but from the EL device. The device the way you make can also be manipulated to give you white light not necessary the white light has to come from the molecule. So, the EL device has lot of features in it which controls the light output. So, first example confirmation dependent white light emission what is this confirmation dependent I am going to show you a molecule which is actually called Di Benzoth thiozolyl ethylene. There is a ethylene molecule which is actually integrating two Benz thiozolyl molecules therefore, it is called cis DBE for convenience I will use this abbreviation cis DBE this is nothing but Benz thiozolyl because thiozolyl molecule is there nitrogen sulphur is there and this is your benzene ring. So, this is Benz thiozolyl ethylene. So, two Benz thiozolyl units are there which is integrated to a ethylene double bond in this case this is a cis configuration therefore, you call it a cis DBE in this case this is trans configuration. So, you call this as trans DBE and it is easy to make both cis and trans if you start with Malic acid and fumaric acid. So, if you start with two different starting materials you can end up with two geometrical isomers one is cis DBE one is trans DBE. So, essentially they are same stereochemically they are different. Now, if you look at the dihedral angle then the angle is 40 degree which means it is a bent molecule in this case it is a 177 degree across the double bond. So, if you look at this compound it is nearly planar whereas, in this case it is a bent molecule. So, same molecule but with different conformers what this has to do and how it affects the EL emission.  What you would immediately see is this is a more featured emission in the case of cis DBE compared to trans DBE although the broadening is there for both the molecules you see there is a substantial broadening for the cis DBE kind of compared to trans DBE. So, if you actually look at the full width at half maxima. So, you are talking about the full width at half maxima somewhere here. So, if you look at the full width at half maxima it is more than 150 nanometers it is more than 150 nanometers which means it covers part of the blue area if blue light if it covers part of green and it also covers part of the red light emitting area. So, if you have all 3 components are coming then there is a broad emission which amounts to white light typically a white light emitting molecule should have full width at half maxima which is 150 nanometers. So, if it is a 150 nanometer broad emission that means you have all 3 components in place and if they are of nearly equal intensity then you can clearly talk about a pure white light. So, what is the question under discussion for us now you say cis DBE is giving white light and trans DBE is not giving white light, but both are same molecules just geometrically they are different. So, you can try to understand what really it takes and this is the photo luminescent decay patterns of the stereo isomers as you would see for cis DBE it is very very different compared to trans DBE this can be fitted to a double exponential model where both have nearly the same tau 2 values which is 0.7 nanoseconds which comes somewhere here the linearity, but you have the tau 1 values which are different where cis DBE has a much faster decay component compared to trans DBE. You can actually try to translate I will go to the next slide try to translate this dynamic photo luminescent spectra of this geometrical isomers what you do you shine light you just pump in light and then you excite the molecule allow that to decay for the first few nanoseconds and keep on capturing the light that is coming out at different nanoseconds. So, you can essentially plot for different nanoseconds emission and you can also do that for cis DBE as you could see here cis DBE in the first 2 nanoseconds the emission is here and as you let it through to decay with different nanoseconds you can see that the peak is shifting towards red whereas, if you look at trans DBE in the same time scale the peak maxima is still the same. So, in one case the peak maxima keeps on going to a red shifted emission in another case it is still the same. So, that means there are different singlet states I will come to this issue bit more later in the slides to come the singlet states that are responsible for this fluorescence is different or in other words there are different singlet states that are responsible for PL emission as far as cis DBE is concerned whereas, for trans DBE that seems to be only one singlet which is responsible for emission. So, as a result when you let it decay only that particular chromophory group or that singlet state is responsible for color emission. So, this much we can understand from the dynamic photo luminescence spectra therefore, if you do a semi empirical calculation and try to look at what really is happening in the case of trans DBE you would see that the HOMO that is the highest occupied molecular orbital the electron density mapping shows that the charge resonance is confined only to the Benz thaisaline ring in the lowest unoccupied molecular orbital the electron is actually the charges transferred across the ring through the ethylene double bond in the excited state. If you look at the this slide is for cis DBE and this is the situation for the HOMO and this is the situation for the lumo and if you go to higher levels for example, lumo plus one you can see that the charge resonance is not only happening between these two rings but also there is a space charge resonance that is happening space charge resonance that is happening where there is a where there is a criss-talk between two rings across the rings not through the bond. So, you have both through bond effect and through space effect both are contributing to the charge resonance. So, this is the situation for HOMO minus one now let us see what really happens to trans DBE molecule in trans DBE you can see that in the HOMO the electron is delocalized and there is no significant change in the case of lumo it is nearly remaining the same. So, based on this one can conclude that in the case of cis DBE you have several singlet states which are responsible this HOMO plus one can contribute your lumo can contribute to the emission whereas, in the case of trans DBE the charge resonance seems to happen only via one singlet state. As a result you can say that the several singlet states that are involved in the cis DBE is responsible for the wide broad emission. So, wide light emission in cis DBE is actually coming from several singlet states whereas, it is because of one singlet state which is responsible predominantly for emission in trans. You can try to use this cis DBE with poly fluorine substrate or matrix you can mix it and make a device of this sort aluminum cis DBE p dot p s s and i t o if you make this at 8 volt you can see the threshold is somewhere here and at 8 volt you can see a nice device performance which is also showing a wide light. If you look at this here it is showing a wide light at approximately 8 volts, but from device point of view 8 volt is not something which is interesting you need to go much lower, but this is a proof of concept to say that wide light can be produced with simple molecules like cis DBE if we can put it with the p o 4 matrix. So, this just to show you that small molecules can be used for engineering wide light. I am also going to give you another example. In this case it is not small molecule, but it is a zinc complex of a benz thaisol and again I can show you that it is not only to do with the organic molecule, but even the interface in a electro luminescence device which can be responsible for wide light and this is the structure of a zinc benz thaisol molecule which actually shows a dimeric nature. So, we popularly mention this as a dimer like this and such a dimer can throw some light and the as you see here the electron mapping of the homo lumo shows that the electron density is always localize in one of the organic moieties. And if you look at the photo luminescent characteristics of this complex you can see here this is the P L emission of your B Z T which is benz thaisol and once it is coordinated to zinc it is blue shifted and there is a shift in the P L nevertheless the nature or the characteristics of your P L remains nearly the same which means it is dominated by ligand. Therefore, it is ligand to metal charge transfer which is happening in Z B Z T and this is typically the curve.  This is the electro luminescent pattern of your LED device which has zinc benz thaisol here and typically the thickness of this benz thaisol layer is of the order of 80 nanometers and at 80 nanometers despite you vary the current density you still see a broad emission characteristics. So, if you look at the full width at half maxima you can see it is more than this is somewhere around 30 and then this is around. So, more than 250 nanometer 200 nanometer broadening is there when you use a zinc B Z T in this device configuration. So, where does it come from because I already told you in the previous slide that the P L emission is only of this fashion whereas in EL it is actually going through that. So, how can we evaluate that if you deconvolute this EL spectra you can see several components that are responsible for this light and one of the way you can understand this is by varying the current density and with all the current density values if the EL emission is going to be same then you call that mechanism as xyplex. So, the white light in this case is not actually coming from zinc benz thaisol, but zinc benz thaisol can actually form a xyplex pair with your whole transport layer and that xyplex pair will be responsible to give a white light like this. In the next lecture I will cover those issues, but I can just sum up for today that what is this xyplex that is forming. So, I T O actually electron hole goes from here to T P D and electron hole comes from here to the interface region that is your Z N B Z T and electron comes from aluminum to this layer and there is a xyplex pair that is forming here which is a coulombic pair which is responsible for such a white light emission. The mechanism of which we will discuss at a later stage however I should also tell you if I am going to change the Z B Z T from 800 angstrom to 600 angstrom immediately you see that this broad emission is disappearing and the EL is resembling something of the P L of your Z N B Z T. Therefore, the interface effects are dominant in electro luminescent devices therefore one has to have a caution exercise over the thickness of the organic layers that you are making. If you go for thick layers then the interface dominates over the photo luminescent property of the organic molecule. So, this is a classic example to show how the thickness can alter your electro luminescent property. So, to conclude I just want to show you the pixel that is coming out of this Z N B Z T based LED which clearly shows that you have a white light emission which is having a coordinates of 0.33 0.33. So, two examples I have given to you one is a small molecule one is a molecular complex and both can give you broad emission, but the emission that comes from this particular example will lower the quantum efficiency while the emission that comes from C S D B will contribute more to the quantum efficiency the issues can be discussed at a later stage. So, I will conclude by showing that there is a great excitement in display devices and we are predominantly concentrating on white light emission examples of this white light emission. I showed you two examples of a simple organic molecule which can help you fine tune the color and also I told you how by controlling thickness of this organic layers one can get white light or modify the light. So, I stop here for now.


This week, we're getting electronically specific because it's a great time to see what the best deals are for home theater shoppers and gifters this season. Robert Herron, nobody is better to talk about this than you. You always bring the knowledge. So where do we begin on the gift guide? I want to buy somebody a TV. Where do I start? Let's start with the very best in eye candy for 2023. And that really has become the OLED displays that are available right now, the organic light emitting diodes. These TVs deliver that perfect black, that incredible contrast that makes color pop, beautiful viewing angles. And there really is nothing better out there. Companies like LG, Samsung and Sony make the very best models. If the budget permits, and you just want to go right to the head of the line in terms of what it is, what is the best thing I could buy right now? That's the short story for that. Now if you want to save a little bit of money, are you talking about there's like what what is the average price of those? It depends on the screen size. Say for a typical 55 inch screen, you're talking about $1,500, maybe a little bit cheaper when it really gets down to the Black Friday pricing on up to a solid five figures if you want to go all the way up to say the 90 plus inch screen sizes, which are now available, which is kind of crazy. That is something to keep in mind. Let's bring it back down to earth then. They are beautiful screens though. In terms of eye candy, that's where you go. Oh, do I have to do I have to not send you the 90 inch screen, Tom? That's what it was going to be. You're going to buy it. I'm not going to turn it down. Yeah, you might have to turn it down a wall or two. Now for good value at good prices, LCD is still the the workhorse of the TV industry. And I was helping a friend shop for a sub $500 55 inch TV recently. We came across a wonderful LG that was available at local at our local Costco. They are 8000. This is a turned out to be a fantastically reviewed unit for currently at about $350, which is a wonderful price for that kind of a 4k screen at that at that price point, it fit their budget and their needs perfectly. However, if you had a little bit more money to spend something closer to that $500 budget or maybe just slightly above high sense and TCL are the ones I love the most high sense in terms of their UAK that's literally their flagship. That is competitive with even the very best LCDs out there today. They also have a step down version to use six, which is almost as good. And it will still provide that bright punchy picture. And likewise with TCL, they have the QM eight, which is just fantastic. I have previewed this at CES last January. It is an amazingly bright and detailed display with wicked contrast. I mean, just very, very good. And then they also have a step down version called the Q seven that provides good value in terms of picture performance and screen size options again up to up to 90 plus inches. If you really need something super sized. Now with Google TV operating system on these listings here, which is interesting to say they are a Roku more often. That is that is a choice. Granted, generally speaking, the more expensive TVs usually have better processors built into them. And they will provide a better app experience overall. I think Google TV is an okay app experience. I think Samsung's you version of their ties and operating system for their TVs is an okay option. I think LG does a pretty good job with their web OS option for that built in app experience as well. And we'll get into some additional streaming options here in a second. But one thing I wanted to mention is with all of these flat panel TVs is that the need for a good audio experience period. Soundbars are the simple way to do it beyond they're very popular and they're very easy to do. And a couple companies that are really worth mentioning are the the ones I love the most. And number one, I would put up there is Sonos in particular. I have done work for Sonos in the past, and I have given them lots of critical feedback on their products. That is just one of the easiest to use setups I've I've enjoyed. I love the sound quality. It's it's not exactly the cheapest option out there. But what you pay for you, I think you really get a good value in terms of just audio performance, room correction features, if you're an iOS user, and other features like that, that just I love the products in general. However, if you want to save a little money, and you just need something to help your current TV sound better period, Roku of all people makes a wonderful streaming bar, their Streambar Pro products, good prices, good performance for what it is, and it integrates their streaming products, which are fantastic. And it's available even very, very affordable pricing. That's also a Streambar, or I should say a soundbar product, I would even be comfortable using outdoors just for temporary use or semi permanent anyway. Now if the budget is really kind of like, okay, I want the absolute best, what is the craziest thing I could buy right now, that's going to drive a large room. Check out Nakamichi and what they're doing with the Nakamichi Dragon. This is a custom made system. They make a few of these every month, and they are well reviewed. Everyone seems to love them who gets their ears on them. It's kind of the ultimate high end. If you were going to spend something similar with Sonos, you'd be buying a pretty big kit. Nakamichi is kind of doing that all in one with that particular product. And it's just three bucks is a lot, but it's not, you know, it's not sky high really. No, and incorporates wireless quote unquote products. Generally, you have to plug these into a wall somewhere, but you don't need to connect them with individual wires for transmitting the sound to each speaker, which is really nice. Now, likewise, I was talking about streaming products. There are really only two that I recommend and one would be Roku and their streaming products. The Roku Express 4k plus is my low cost recommendation. They have an express version, just regular that isn't the 4k plus. I do not recommend that one. The 4k plus adds an actual power button and a volume control, which the regular and granted cheaper express version doesn't. And if you're trying to just have that all in one experience where it's like, Hey, I don't want to use two remotes at the same time. Stick with that 4k plus. That's a great way to do an inexpensive upgrade on a TV you may already have. And you just want to make sure that it's going to provide a good streaming experience with any service currently available. Now, likewise, if you are an Apple user iOS user, and that is your product, the Apple TV 4k 4k plus in particular is or I think it's just the 4k. That is the one to get. If you already are in the Apple ecosystem, stick with that product. And it is something that you will just learn. It will integrate seamlessly with everything you use. It provides terrific performance. It is built like a tank. It will last for years. And it's it's right up there with any of the very best streaming products currently. And they're not huge anymore either. They're they're getting to be hockey puck size. They're not as small as the Roku Express, of course, but you know, they're totally. Yeah. Yeah, they hide pretty well on a small console or even behind TV itself. I've been purchasing a bunch of these products recently. I helped a relative basically ditch cable television service. Their bill was over 300 bucks a month for cable and internet service. And they were paying for hardware they no longer even had. And there's a tip if I could just give one is take a look at your bills. If you if you're a long time cable or satellite subscriber, you'd be surprised at what they've been billing you for over the years. And they will never tell you it's like, Oh, by the way, you don't need this anymore, or here's a better option for less money. They'll never do that. And that's just something to keep in mind when you do that. Also, for any of the TVs I just mentioned, they're all internet enabled.  But for ease of use, have it connect to the TV or have it connect to your internet service automatically and do all those upgrades and firmware updates automatically. And that will make it so that every time you turn it on, the apps are ready to go. The TV is less buggy than it may have been when it first shipped. And I think for any product out there, even things like your streaming products, they provide regular updates as well. And it's good just to keep that kind of stuff updated. And finally, when you're shopping through the holiday season with either Black Friday coming up or any throughout the rest of the year, just realize that this is a good time to take a look at what the cheapest prices will be and realize those prices will come around again before soon, if you can't buy right now. And services like Amazon necessarily do not have the lowest prices that you're going to find. And do check other sources. It doesn't even matter what the product category is. I was shopping for Chromebooks recently and I realized that Best Buy had much better pricing for some of the devices I was looking for than Amazon or anyone else. And the same could be said for something like Walmart. Amazon isn't the be all and all. They're convenient as can be, no doubt. But look around when you're going to make the decision on what to buy. And then your sources like Costco, too, or your subscription or membership clubs, those things are wonderful for a reason in their own way. And they provide either. It sounds like it makes a lot of sense to figure out the model you want, then do a little price comparison rather than just see what one place like Amazon is going to offer you as their Black Friday deal. I agree 100 percent. And I'm always looking for like, what's my favorite TV of the year? What will be the lowest price on that? And when? And if right now through the holiday season isn't really going to do it for you, I'm thinking TV specific. Think about when, say, like the Super Bowl rolls rolls around in February, I guarantee you there'll be another big sale and it will match very closely with the current price is. Don't ever feel like you're you have to do it now. There's not going to be another opportunity again at this price point. It will always come around again. Don't don't fall for the panic. Yeah. Yeah. Yeah. Take your time and get what you want and and save some money. Don't pay full price.


We put all information together in a systematic way and I think it will be the most easiest and efficient way for foreigners to understand what is needed. Ukraine is now protecting the freedom and democracy and freedom has its own price. It's really important to understand that Ukraine is part of Europe and we are protecting European values and European democracy.


Did we have any? A great presentation.  Now, I know you were talking about research, but I wanted to ask, the research was over what period of time with regards to the health and to your blood health and whatnot. Because I would assume. Are you asking for me personally or the studies that I've seen out there? Or studies you've seen. And the reason I'm asking is you could be taking a lot of fat. And you might not see the blockage to your arteries or whatever over a short amount of time. But what happens over long run? Has there been any research? I'll admit, there's not that many studies out there in scientific published research. And I'm caveatting that pretty closely. For intermittent fasting, the studies that we see are far more on things like calic restriction. But what we indicate is, and this is why I said that IFOC is it doesn't really matter what you're eating. From that perspective, as long as you're doing that intermittent fasting and the calic restriction, I can say I've tracked my own data a number of years. And this is now getting away from the intermittent fasting component and the diet and nutrition component of it. And looking at it, doing things like a low carb paleo, particularly when you're combining that plus lifting heavy stuff, what you see is your HDL numbers skyrocket, your triglycerides end up plummeting. And it seems to have pretty positive impacts, like things like, so I track what's called a high sensitivity C reactive protein. It's a measure of inflammation. Mine last time I checked was too low to be measured. That's with the crazy diet and stuff that I end up eating. There's an infographic on bulletproofexec.com that talks about butter research like that. But the best research of all is the human race. Our brains are built out of fat. We evolve to eat fat.    And that's how it works. So the idea that somehow we're supposed to not do that and he was giving himself heart disease isn't borne out because people who eat more fat tend to be higher performer. They reproduce better. And the whole ancestral health movement shows us that eating more fat makes you healthier, not unhealthy, as long as it's naturally occurring healthy fat, not this canola synthetic junk. It's really fascinating if you're asking that question to dig into the history of why we believe fat is bad for us. And this is a really modern view. We've only had this since about the 1930s, 1940s. You had Ancel Keys. And basically with that, we started getting this whole fat phobia. Before that, it was well known that, hey, in case you wanted to put on a lot of fat, you'd feed the same thing we've fed cattle. You'd give them a lot of grains, a lot of carbohydrates. But if you wanted to lose weight, there's tons of basically meat diets. At that time, where you ate meat, you lost fat, you gained muscle mass. And there's some couple good books about it. Gary Chobbs has a book, Good Calories, Bad Calories. It's literally like a tumet information. It's one of the few books in my life I've ever taken notes on. If you're fascinated between the biochemistry and the history of it, he's a former writer for science, goes into great detail. He has another book that's a little bit more accessible to the masses about the history entitled Why We Get Fat and What to Do About It. And again, ping me, I've got a whole bunch of links. You can find me on Twitter. I'm Jolly on Twitter. My website's A Jolly Life, and I don't publish quite enough things on there. Do we have time for more questions or? Oh, we gotta wrap it up. Okay, wrapping it up, again, I'd like to give some thanks to my Dave Asprey, bulletproof executive. Dave's got pretty much all the same information, same sort of things that I think about. Josh Whedon, again, the Whedon Protocol. Patrick Friedman, he spoke at the Personalized Life Extension Conference. Also, Martin Birkin, Leen Gaines. He's popularized intermittent fasting, particularly among the bodybuilders that more than anyone else. And also the IF Life is pretty good. And I think John Bacardi just published a really good PDF on this, but I haven't had time to read it. So go check out those resources or again, ping me if you've got any questions and I'll be around for the rest of the day. What's your website? Ajollylife.com. A, A. The letter A, Jolly, J-O-L-L-Y, life, L-I-F-E, dot com. Cause you know, life's a lot better when you're having fun.


cutaneous circulation has many special features. First of all remember that unlike any other circulation the amount of cutaneous circulation is not determined by its metabolic requirements. In fact the metabolic requirement of the skin is quite less and if solely based on metabolic requirement its circulation will be very very less. However the amount of cutaneous circulation is governed by the requirement of thermo regulation depending on that whether heat has to be conserved or heat has to be lost. So in case of hot environment where heat has to be lost from the body in that case cutaneous circulation can increase to as much as 150 ml per 100 gram per minute and in case where vasoconstriction occurs that means in cold it can be very low to as low as 1 ml per 100 gram tissue per minute. So this concept on thermo regulation I have dealt in the video on temperature regulation that you can have a look. But here apart from this we will deal with certain special characteristics of cutaneous circulation. So first comes the presence of arteriovenous amastomosses. So this diagram here shows that this is the presence of arteriole and these are the venules and these are running deep in the dermis and you see this connection runs in the superficial dermis as well and then at the level of the epidermis what we are seeing that there is a capillary loop arising. So there is arterios then there is a formation of the capillaries then veins which are taking away the blood back to these venous plexus. Now two things to note here one you see that the blood is flowing in parallel and opposite direction. So like suppose this is the incoming blood right and this is the taking away of blood in the venules. So this is parallel and opposite flow of blood and this is what is known as counter current flow. We will talk about it a little bit later. But here you see that there is presence of arteriovenous anastomosses that is direct connections between the arterioles and the veins and these arteriovenous anastomosses are present in apical regions in the body that is they are present in palms, soles, then the fingertips right and toes also, then ears, nose and some other face areas like lips. So presence of these AV anastomosses is important for thermoregulation. You see what happens suppose there is cold. So in cold there will be vasoconstriction and these AV anastomosses are supplied by a sympathetic vasoconstrictor fibers very important sympathetic vasoconstrictor fibers and when there is a activation of this sympathetic system it causes vasoconstriction of these anastomosses. So blood will be shunted from the arterios to the veins directly. It will not go via these AV loops so this AV anastomosses is basically closing this channel and there will be decrease in blood supply to the superficial surface that is the epidermis. So due to vasoconstriction there is decreased blood supply to the surface of the skin. So what? So if there is decreased blood supply there will be decrease in the heat loss from the blood vessels to the environment right. So that is very important the function of the arteriovenous anastomosses and that is also the reason that in these areas you see when there is cold what happens your hands and feet fingertips your nose tip they are cold right they are much closer to the environmental temperature why? Because the blood supply to these areas decreased and the heat is not coming to the surface so these areas are much closer to the environmental temperature. On the other hand when it is warm it is hot what happens that there is loss of this activation of the sympathetic system it leads to vasodilation and hence the blood flow occurs to the skin surface. So that is the importance of these arteriovenous anastomosses. So remember they are very important for thermoregulation and they are supplied by sympathetic vasoconstrictor fibres and unlike the other arterioles of the body they do not respond to metabolites no response to the metabolites please remember this because you know that locally what happens in other tissue beds and even in other regions of the skin where there are only arterios and not arteriovenous anastomosses the arterios respond to the accumulation of the metabolites as well so that whatever is the local metabolism in the skin the arterios will be responsive to that as well but these av anastomosses solely respond to sympathetic supply plus also to the local temperature local skin temperature whether it is hot so both to heat and cold they respond but not to the metabolites. Coming to the next important concept that is the presence of countercurrent flow in circulation. Now we will take one example suppose the environment is cold then what will happen that warm blood whatever warm blood is reaching to the skin even though there is vasoconstriction some blood flow will happen to the skin isn't it so once that warm blood reaches to the skin there will be heat loss from the skin to the environment right but due to this countercurrent flow what happens that heat moves from the arterial side to the venous side and hence whatever blood reaches to the skin that will become less warm understanding this is going to become less warm because already the heat transfer has occurred from the arterial side to the venous side and hence this warm blood is going back to the core areas otherwise what will happen there will be more heat loss and cold blood will go into the core regions of the body but because of this heat movement two things happen one warm blood reaches to the core regions second there is less loss of heat from the surface because here the blood is less warm and you know that energy loss depends on the energy gradient right so here because less warm so the heat gradient is less so less heat will be lost from the skin to the environment what will happen in case of hot environment hot environment opposite will happen so let us try to understand it in opposite manner what will happen in hot environment let me just delete it so in case of hot weather warm blood is coming right and here much much more warmer blood will reach to the skin surface so again the heat gain will be less because the heat loss and heat gain depend on the temperature gradient so if here it is much more warm so heat gain from the environment will be less since the temperature gradient is less between the environment and the blood so that is how counter current flow helps in heat conservation in cold environment and less heat gain in hot environment moving on to some local reactions of the skin out of which first one is white reaction what is white reaction see when the skin is stroked firmly by an object what happens that there appears a white line so if I stroke firmly there will appear a white line you can try it on yourself and why this white line occurs because once that stroking occurs there occurs due to this stroking constriction of the pre capillary sphincters okay pre capillary sphincters that is before the capillary there are certain sphincters they constrict because of the mechanical effect of the stroking and this prevents the entry of blood into the capillaries and whatever blood is there it drains out so the region which has been stroked becomes white so this is white reaction and why does it occur it occurs because of the constriction of the pre capillary sphincters next local reaction which we will see in a skin is triple response and what is this triple response triple response consists of three responses as its name suggests that is there is redness then there is flare flare means flaring of the redness increase in the redness in the area surrounding and there is formation of the wheel that is a local swelling so what happens when the skin is struck more firmly than that which is happening in the white reaction when it is struck more firmly we see this triple response and what is happening that redness occurs due to local capillary dilation here what we saw in white reaction there is constriction of these sphincters in red reaction these capillaries which are there they dilate and that is just by the mechanical effect of the injury right so when there is local dilation there will be increase in the blood flow and this blood flow will be seen as redness then flare flare is that suppose this is the area which is injured spreading redness to the surrounding area is flare and why this happens this happens because behind the capillaries there will be arterioles right so these arterioles also dilate and when these arterioles also dilate then whatever are the capillaries which are supplied by these arterioles they will also dilate so the surrounding area will also become red so redness first one due to capillary dilation flare due to arterial dilation okay and wheel wheel why it occurs that occurs due to increase in the capillary permeability increase in the capillary permeability and what happens when there is increase in the capillary permeability the water will flow out of the capillaries into the surrounding tissues that there will be extravacation of the fluid and this is going to lead to local swelling so this triple response we see in a skin and the cause is basically redness occurs due to capillary dilation due to local mechanical effect and flare and wheel occur because of arterial dilation and increase capillary permeability respectively but this response involves nerves and very interesting phenomena is seen here which is not seen anywhere that is the only example of orthodromic conduction so we will see what is this so what is happening that there is a phenomena known as axon reflex axon reflex and this is responsible for flare and wheel so suppose here this is showing the skin and this is the site of injury now the nerves there are stimulated and what happens that these nerves will carry the signal to the spinal cord that is the orthodromic conduction right but via one branch there is conduction back to the skin and this is anti-dromic conduction axon reflex is the only example in the body of anti-dromic conduction and these nerve fibers actually release two substances one is substance P and second is CGRP okay and these both of them are responsible for arterial dilation so they are responsible for flare and the wheel that is increase in the capillary permeability is caused by substance P substance P is responsible for increasing capillary permeability and hence responsible for local swelling of the skin so that was about triple response coming to the next part that is the nerve supply as I told you that there is very interesting nerve supply one is sympathetic vasoconstrictor which is supplying the arterioles everywhere and also the AV anastomosis right which I told you how it is important in causing shunting of blood during cold and the other one is sympathetic cholinergic and sympathetic cholinergic actually supplies the skin near the sweat glands right and when these sympathetic cholinergic fibers are activated there is release of acetylcholine and what happens you do this there is actually conversion of quinineogen to brady quinine see basically this sympathetic cholinergic causes secretion of the sweat right and sweat contains an enzyme which is responsible for conversion of quinineogen to brady quinine and brady quinine is a vasodilator that is how in case of hot environment both there is activation of sweat secretion and also there is local vasodilation in the skin so this is one example of sympathetic cholinergic supply in the body which basically supply the sweat glands now with this we have dealt with the major characteristics of the cutaneous circulation but I will answer some why questions here that one why we have blushing in case of embarrassment why our skin becomes redder when we are embarrassed and there is blanching in case of fear or anxiety see skin in the head neck and shoulder region it is supplied by sympathetic vasoconstrictor fibers which are directly under the central control so basically in case of embarrassment the emotional reaction which occurs in amygdala from there there is inhibition of the sympathetic activity and this inhibition of the sympathetic activity will lead to vasodilation and then hence it will lead to blushing on the other hand sympathetic activation occurs in case of fear anxiety so again amygdala reaction it leads to activation of the sympathetic activity and it leads to vasoconstriction and this blanching occurs in the head neck and shoulder region so that is first second is that why in case of cold the skin appears red rudiness occurs in cold see we are telling that in cold there will be vasoconstriction then why there is reddish appearance of the skin in case of cold that is because the muscles in the blood vessels respond locally directly to the temperature so initially when there is cold there is this spasm of the muscles so that leads to the vasoconstriction correct but as the temperature decreases more and more towards the colder side this muscles stop responding and hence there is loss of the muscle spasm thus leading to vasodilation understanding so it is this local vasodilation because the muscles have a stop responding because of too much cold that we see local redness of the skin in case of too much cold third is we may see an alternating phenomena of vasoconstriction and vasodilation because cold will lead to local vasoconstriction local arterial or constriction will occur right so that is going to lead to vasoconstriction this in turn is going to lead to ischemia okay decrease in blood supply to the skin and hence there will be accumulation of the metabolites okay accumulation of metabolites will again act on the arterioles and that will lead to vasodilation because these arterioles will dilate and there will be increase in the blood supply to the skin so in severe cold we may get alternating periods of constriction and dilation and here we are talking about the normal and here we are talking about the normal arterioles not the avianastomosis arterioles understanding because they are I said that they do not respond to the metabolites so this phenomena of local vasoconstriction and vasodilation is known as louis hunting phenomena louis hunting phenomena and when pathological it leads to renaught phenomena what is that that local vasoconstriction will be so much that ischemia will occur and ultimately it will lead to sinuses because more of oxygen will be extracted from the hemoglobin leading to accumulation of deoxygenated hemoglobin and there will be sinuses then accumulation of metabolites vasodilation and this in turn will lead to redness and this phenomena is known as renaught phenomena so two terms you remember louis hunting phenomena and renaught phenomena and finally there is a question asked in the exams also it is asked that why patient of shock should not be warmed beyond the point which can cause a rise in body temperature so warming of a patient of shock has to be limited why because if the person is warmed too much there will be arterial dilation isn't it so body temperature has risen that will lead to arterial dilation for the heat loss to occur so now the body wants to regulate the temperature so for the heat loss there will be arterial dilation however this arterial dilation will lead to decrease in the peripheral resistance okay decrease in peripheral resistance and this decrease peripheral resistance will lead to decrease in blood pressure so we are treating the person for shock and we want the blood pressure to be maintained but because of the rise in the body temperature for the heat loss to occur there will be arterial dilation but that is in turn going to decrease the peripheral resistance remember that the skin is a very important site for peripheral resistance because there are two types of arterioles one is avianastomosis is there which is also important resistance vessels and then there is a normal arterioles also and both contribute to peripheral resistance and both will dilate thus causing decrease in the peripheral resistance and that is also one reason that why it is so much difficult to exercise in hot environment because in hot environment both of these will dilate and there will be decrease in the peripheral resistance and for exercise we want blood pressure to be higher so blood pressure cannot be maintained if the person is exercising in hot environment due to the fall in the peripheral resistance and the person may collapse when exercising in hot environment so that was all about the special characteristics of the cutaneous circulation thanks for watching the video if you liked it do press the like button share the video with others and don't forget to subscribe to the channel physiology open thank you


What I'm saying if you would give me a few days in this beautiful place You think you slick man you trying your best to throw salt All you got to do is subscribe to my channel man. Stop acting like T-World is another planet It's not bro. It's my YouTube channel. If you want to be a part of it, just subscribe Dr. Phil. Stop. You got to let me know. I think you need to have yourself checked out You need to put your finger down so you don't have to step outside and run me my face Yeah, okay, you already know I'm not playing with you I think if you would give me a chance to go to this place You petty bro You petty bro like that's why you sipping that water like that bro.