Good morning friends. I am Pura and today we will discuss the following question. The scalar product of the vector i cap plus j cap plus k cap with a unit vector along the sum of vectors 2 i cap plus 4 j cap minus 5 k cap and lambda i cap plus 2 j cap plus 3 k cap is equal to 1. Find the value of lambda. Let us begin with the solution now. Let vector a is equal to 2 i cap plus 4 j cap minus 5 k cap and vector b is equal to lambda i cap plus 2 j cap plus 3 k cap. Now we have to find the sum of vector a and vector b. So we have vector a plus vector b is equal to vector a is equal to 2 i cap plus 4 j cap minus 5 k cap plus vector b is equal to lambda i cap plus 2 j cap plus 3 k cap. This is equal to 2 plus lambda i cap plus 4 plus 2 gives 6 j cap minus 5 plus 3 gives minus 2 k cap. Now the unit vector along vector a plus vector b is n cap and it is given by n cap is equal to vector a plus vector b upon mod of vector a plus vector b. This is equal to now vector a plus vector b is equal to 2 plus lambda i cap plus 6 j cap minus 2 k cap upon mod of 2 plus lambda i cap plus 6 j cap minus 2 k cap. This is equal to 2 plus lambda i cap plus 6 j cap minus 2 k cap upon under root of 2 plus lambda whole square plus 6 square plus minus 2 whole square and this is for the equal to 2 plus lambda i cap plus 6 j cap minus 2 k cap upon under root of 2 plus lambda whole square plus 36 plus 4. And this is equal to 2 plus lambda i cap plus 6 j cap minus 2 k cap upon under root of 2 plus lambda whole square plus 36 plus 4 is equal to 40. So we get n cap is equal to this. Now we are given that the scalar product of i cap plus j cap plus k cap with n cap is equal to 1 that is we are given that 2 plus lambda i cap plus 6 j cap minus 2 k cap upon under root of 2 plus lambda whole square plus 40 dot i cap plus j cap plus k cap is equal to 1. Now this implies 2 plus lambda into 1 gives 2 plus lambda 6 into 1 gives 6. So we get plus 6 and minus 2 into 1 gives minus 2 upon under root of 2 plus lambda whole square plus 40 is equal to 1. This implies now in the numerator we get lambda plus 6 is equal to now we multiply 1 with under root of 2 plus lambda whole square plus 40. So we get under root of 2 plus lambda whole square plus 40. Squaring both the sides we get lambda plus 6 whole square is equal to 2 plus lambda whole square plus 40. This implies now lambda plus 6 whole square is equal to lambda square plus 12 lambda plus 36 and this is equal to now 2 plus lambda whole square is equal to 4 plus 4 lambda plus lambda square plus 40. Canceling lambda square on both the sides we get this implies 12 lambda minus 4 lambda is equal to 4 plus 40 is equal to 44 minus 36 and this implies 8 lambda is equal to 8 and this further implies lambda is equal to 1. Hence we write our answer as lambda is equal to 1. Hope you have understood the solution. Bye and take care.


Are we getting remakes of Pokemon Gold and Silver or really Heart Gold and Soul Silver to be specific since technically those games were brought back one time already. We have something interesting to discuss in regards to that and what Nintendo might be doing and why. Or really the Pokemon company? I don't know. It's hard to tell them apart when it comes to the actual mainline Pokemon games. That being said, before I get into that, we have a couple giveaways going on right now. It's for an Xbox Series X, a PlayStation 5, or a Nintendo Switch. It is our 50,000 subscriber celebration. Thank you so much for getting us to that milestone. To enter, go down to the description and we also have an October giveaway that is going on as well for two copies of Pikmin 3 Deluxe. Again, you want to win one of those copies? Go down into the description and good freaking luck. Oh, and by the way, let's give this video to a thousand likes. If you don't like this video, I will kick your dog. Alright, let's get into this. In Japan, Nintendo has filed some new trademarks. The trademarks published today, but they were actually filed at the very beginning of the month. Trademarks usually take a while to go through. They were filed on September 7th. So what it is, is Nintendo has filed for trademarks for Soul Silver and Heart Gold. Some of their trademarks for prior Pokemon games are currently expired. Nintendo doesn't renew them very often, unless they're planning to repackage and resell. So what's interesting about refiling this trademark is it covers 50 products and services, including merchandise and stuff like that, but also includes video game programs. So what's interesting about that is the potential that the Pokemon Company and Nintendo are actually working on, well, a Soul Silver slash Heart Gold remake of sorts. Now, this would not be super surprising, obviously Pokemon Sword and Shield is one of the most popular Pokemon games ever made, like in the history of the franchise. And let's go Pikachu, let's go Eevee, did an easy 10, 11 million in sales. And having another Let's Go game go to the Silver and Gold, which is Gen 2, would not be all that surprising. It almost feels like a natural progression.  But I mean, they sold decently well, over 10 million copies. There's not a reason to think they couldn't revisit that again. And next year might be a great year for that because they went with a new generation in Sword and Shield. They went with DLC this year. They could go Let's Go with the Soul Silver and Heart Gold games next year. And then the year after could be another new gem, whatever follows up Pokemon Sword and Shield. So I think this is extremely interesting to know because without a Pokemon game this year, clearly there's going to be a Pokemon game next year. They kind of broke the streak this year. They had had a new Pokemon game come out every year for like eight straight years. They broke the streak this year with DLC, but you know they're developing something behind the scenes. They're not just making DLC, right? They have another game in the works to come likely next year. So this would make a ton of sense. So you think about it logically.  You think about the success of Let's Go Pikachu and Let's Go Eevee. You think about the success of obviously Sword and Shield. There's going to be more Pokemon games coming to Switch. I predict at least three more Pokemon games coming to Switch before this Switch moves onto the next gen Switch. And even then the Pokemon company likes to hold on the old platforms so you could see a fourth. This year having a Pokemon game is obviously ideal for Nintendo. Yes, it's the 35th anniversary of Zelda. Yes, it's the 35th anniversary of Metroid. And yes, I think we're going to get Breath of the Wild 2. But here's the thing. I think we're going to get Breath of the Wild 2 early in the year. Like first six months, sometime before E3. And I think the Pokemon game is going to be the holiday game. That's just my general thoughts on this. Because Pokemon games can launch at any time, by the way. They've launched Pokemon games outside of the holiday. But I feel like having Breath of the Wild 2 come out early in the year is something that really favors Nintendo's momentum. Because that game, just like the first one, is an evergreen title. Almost more evergreen than Pokemon is at this point. So I do think that Pokemon would benefit more from a holiday push. Whereas Breath of the Wild is going to crush it no matter what. Like yeah, Pokemon is going to sell big numbers at any point. But it will sell even bigger numbers during the holiday. I think, you know, with what we're seeing with Breath of the Wild still in the top 10 every single week, every single month. That clearly they can just release that game at any time and people are going to keep buying it. So I do think that Breath of the Wild 2 should come out early in the year. Then have this Pokemon game come out later. Now as for, am I excited for these games? Well, I have not played Sword and Shield. I know. It's almost blasphemy to say that. Because I did tell people. I mean, a lot of you new folks might not know this.  Because I hadn't played a Pokemon game in like 15 years. I just, I fell, you know, I was a big person during Gen 1. I enjoyed gold and silver. And then I kind of fell off with the franchise. I felt like they made things more complicated than they needed to be. And I realized for a casual player, you can ignore a lot of these complexities. But I liked playing competitively against others without having to worry about all of the massive complications. So I just, I ended up kind of falling out of love with the series. But I've always respected the Pokemon franchise. And I've wanted to get back into it. But just every time I've dipped my toes, I ended up not really liking what I was playing. Now Sword and Shield is a game that I do plan to play. You know, I don't know what opinions I'm going to have on it. Or maybe I should wait. I don't know. You guys let me know. Some people think it's a game I should skip. It's not a good one to try to get back into the franchise with. But I did play Let's Go Pikachu and Let's Go Eevee. Obviously, I played those games because Gen 1 is my favorite generation of Pokemon. So, you know, we're talking red, blue, green in some territories, and obviously yellow. Yellow is my favorite of the bunch.  So, and this one seemed to follow more after that one. Just because you're going to have Pokemon following you. And I think that I really enjoyed Let's Go Pikachu and Let's Go Eevee. I know some people think, oh, easy cash grab. Didn't like the motion controls. I really enjoyed it. I thought it was fantastic. Pokemon in the overworld was just mind blowing to me. And I realized that, you know, this continued in the Sword and Shield. So, it's not considered a new feature anymore. But I still really enjoyed that Pokemon in the overworld thing. I didn't mind the motion controls. I didn't mind that it didn't add in updated mechanics. I know some people were upset with the game because other, you know, quote-unquote remakes added in updated mechanics from more current games. They didn't. They kept this really strict to just how it was back in the day. This is how it's going to be now. And that's what I loved about it because they didn't mess with what I loved. So, that's just me though, of course. So, I played that. And I would probably buy this because I did enjoy Gold and Silver. And yes, I did play Heart Gold and Soul Silver. And wasn't necessarily a fan of the new mechanics they added back in. But you know what? With this trademark, if they're going to do it, they're clearly going to follow after Heart Gold and Soul Silver. And probably have some of those newer mechanics in it. If it's a let's go type of game. It doesn't mean it will be a let's go type of game. It could be more like a sword and shield type of game. You know, we don't know that the let's go style is going to continue. Especially when you see the success of Sword and Shield, it could definitely go more in that direction because obviously it sold almost twice the amount of games. But we'll have to wait and see on that. Obviously, we also have to wait and see how the DLC, the final DLC performs, which the Frozen Tundra, I believe it should be coming soon. That DLC should be coming soon. It's supposed to be here before the end of the year. Maybe it's not coming until November or December, but it'll be here. I don't know. You guys are going to have to let me know what you think about all this down in the comments below. Do you think them renewing this trademark, when they don't always renew Pokemon trademarks, means something?  Obviously, time will tell. You guys, let me know what you think about this down in the comments below. I am Nathaniel Roblejant from Nintendo Prime. Sure to answer those giveaways. And I'll catch you in the next one.


Okay, so we've calculated all of those values, those annual values, of these various quantities that we've selected here. Now we're going to extract them, and they are now available to plot. You can see the period is 1958 to 2012, and the quantities we have are the atmospheric water vapor, we have ocean surface temperature, ocean ice cover, we've got the planetary albedo, we've got surface air temperature, we've got sea surface temperature. And we can start plotting these and seeing what they look like. Let's start out with the surface air temperature. So this is the global average surface air temperature for the model, and it should be plotting that up for us shortly. There it is. So we can expand that window a little bit. We can change the scale here. So let's go from 9, 8.5 to 23 on the vertical scale just to get a finer vertical scale on this. So the red curve shows us how land, average global land temperatures are changing over time in the model. The blue curve shows us how the open ocean temperatures are changing the model. The open ocean is going to be warmer, as you can see, by several degrees than land. It's the part of the ocean surface that isn't frozen, and the ocean in general warms up more than the land and is warmer than land on average because it doesn't go to as high latitudes, in particular in the southern hemisphere. So ocean temperatures are going to be warmer than land temperatures. The open ocean, the blue curve is warmer than the full ocean, which includes ice-covered regions of the ocean. It's the green curve. And the black is the global average temperature. It's the average of all the regions, whether they're open ocean, ice-covered ocean, or land. That's what the black curve represents. Let's zoom in on that curve. So we can see we started out in 1958 with a global average temperature of about 13.8 degrees Celsius, roughly what the global average temperature is prior to the increase in CO2 that's taken place since then. And we've warmed up by 2010 or 2012 to a temperature that's close to 17.8 degrees. So we've gone from about 13.8 to about 17.8. We've warmed up by about 4 degrees Celsius in response to that instantaneous CO2 doubling that took place in 1958. So you can see how long it's taking the global temperature to equilibrate to that increase in CO2. Many decades, although we can see that we are asymptotically approaching a new equilibrium value. If we were to extend this several decades into the future, as it turns out, we would probably see a net warming of 4.5 degrees Celsius relative to that initial temperature of 13.8 degrees Celsius. And that is consistent with the fact that this particular model, the GISS climate model, the NASA Goddard Institute for Space Studies climate model from the 1980s, has a relatively high climate sensitivity of about 4.5 degrees Celsius, equilibrium climate sensitivity for CO2 doubling. And that's consistent with the transient result that we're seeing here as the temperature is approaching. It's equilibrium response to that instantaneous CO2 doubling. But we can look at many other quantities in this model in addition to surface temperatures. And so that's what we'll do next.


Welcome back to this course of nano structured materials, synthesis, properties, self assembly and applications. We are now in the module 3 and we are trying to understand the concept of self assembly and the applications that self assemble nano structures can be used for. And in self assembly we have finished two lectures on self assembly and now today we will have the third lecture on self assembly and this is the lecture 9 of module 3. So, self assembly can be done at interfaces as shown in this figure here. If you have an interface between two different mediums, so two different media means say you have liquid and solid. So, between the liquid and the solid you have an interface. So, can you self assemble that means can you arrange nano particles or nano structures at this interface. So, this interface if you bring around nano particles can you arrange them in a particular fashion like this or in any other fashion may be in a square pattern or in a triangular pattern. So, that would be assembly at interfaces. Now, based on the how the interface is formed what are the two different phases one of the type of interface you can have is the liquid air interface. That means you have one liquid on top you have air. So, where the air is meeting the liquid you have the air liquid interface. You can have self assembled structures made of nano particles at this interface. Then you can have two different liquids and the interface between two different liquids this is possible when the two liquids coexist with each other. That means they do not dissolve in each other and it an example is like water and oil. So, water and oil do not mix. So, when you have a layer of water and a layer of oil you will have an interface and at that liquid-liquid interface you can have assembly of particles. So, oil generally you can have many types of oil in the laboratory you are used to chemicals like toluene, benzene, hexane. These are non-polar solvents and these are like oil which do not dissolve in water. So, they are non-polar water is polar and between the non-polar liquid and a polar liquid there will be an interface. So, that will give rise to this liquid-liquid interface. Then you can have a liquid in contact with the solid and that will give you a liquid-solid interface. So, that can be very easy if you have say a silica surface and on top you have a drop of water then it will create a interface between the liquid and solid. Now, there are some of the main techniques which are used today to make these kind of nano structures or the assembly at the interfaces can be due by the well-known Langmuir-Bloget technique. We will discuss this in detail. Then you can have sedimentation or evaporation induced self-assembly. Then you can have adsorption of nano particles on a surface. So, there are different types of techniques one can use to make ordered assemblies of nano particles at interfaces. So, first let us discuss the liquid air interface. So, by the name you can understand that you have a liquid on top of which you have air. So, you have an assembly on the surface of the liquid there is a contact between molecules of air and the molecules of the liquid. Now, at that interface how to make assembled nano structures? The technique that commonly people use to make nano structures at the liquid air interface is using the Langmuir-Bloget technique. And it is more or less it is called programmed self-assembly. You utilize the solvent or the liquid in most cases is water in the LB technique or the Langmuir-Bloget technique. So, you are basically looking at the water air interface and there the hydrophobic and hydrophilic properties of the molecules are very important for this kind of technique. So, hydrophobic and hydrophilic for example, you have water. So, you will have hydrophilic interactions and if you have a surface which is for example, you can have a silica surface which is hydrophilic and you can change the hydrophilic silica surface by using a silane say alkyl silane and you can make it hydrophobic. So, you these interactions between hydrophobic surfaces with hydrophilic or hydrophobic molecules is important for making nano structures using the LB technique. The surface tension of water plays a crucial role in this technique since water is the key liquid being used in Langmuir-Bloget technique and hence the surface tension of water will be very important. So, let us understand what is this LB film or the Langmuir-Bloget film. So, it contains one or more monolayers of the material. So, a film made at the liquid air interface of some nanoparticles on the liquid which is water on the water surface that is basically a Langmuir-Bloget film and this process as we have discussed has is made at the air water interface. So, this is the photograph of a LB trough. So, this is called an LB trough it is made normally of Teflon and you have water inside on top of which you want to make the film and on either side of this trough you see these kind of Teflon rods square rods. So, they create a pressure on the film. So, they are called barriers and so this one moves inwards and this one also moves inwards creates a pressure on the surface of the fluid here and the fluid here is water and if there are molecules on top of water you can dip a substrate on the inside the liquid and pull it out and the molecules on top of this water will make a film on the substrate which can be dipped from the top. So, this can be controlled through a computer the rate at which the barriers move the rate at which you dip the substrate etcetera can be controlled. So, this is basically the LB trough it is called and the process which occurs is that you are moving this barrier which are there one and two barriers. So, they are here on two extremes and you are pulling this barrier inside from both directions and the water has got these molecules on top of it. So, when you are creating a pressure and you are dipping the substrate from the top or pulling it out here the arrow is showing that you are pulling out the substrate. So, the substrate is here which was dipped in the liquid and is being pulled out. So, when you do that then the molecules on the liquid on the top of the liquid the molecules on top of the liquid come on top of the substrate. So, typically if you have a substrate which is hydrophilic then the hydrophilic part of this molecule will be adhered towards the substrate or adhered on the substrate. So, depending on what kind of film you want whether you want the hydrophobic part sticking out or the hydrophilic part sticking out you have to take the surface of the substrate accordingly. So, this is the basic process you are pushing from both sides the barriers which are at these two extremes and creating a pressure on the film of water and the film of water has got these molecules on top of them which will get coated on to the substrate and that will form the mono layer. So, one layer of the molecules are now coated on the substrate when you take out the substrate. So, this is again showing you now different types of molecular assembly which you can achieve using the LB technique. So, here in the first case you see there is water and you have your substrate and you are pulling out the substrate. The substrate is chosen such that you want the film to be on a particular substrate and you choose the substrate accordingly. So, you put in pressure from either side. So, the two barriers are moving in and one mono layer is forming at the water and air interface. So, on top you have air below you have water and you are having a mono layer or an assembly of molecules at the air water interface. Now, instead of pulling it out you can pull it in. So, this is an LB deposition on a hydrophilic surface. Now, you can do LB deposition on a hydrophilic surface for the second layer. So, this is first layer is formed now you want to make the second layer. So, after the first layer is formed. So, the substrate has come up now you push it back. So, this is showing when you push it back then on top of the first layer a second layer will start forming and you see the two hydrophobic parts are close to each other. So, when you push in the substrate the second layer of molecules on top of the water layer will form the second layer and ultimately you will get a substrate which has got two layers. So, it is a bi layer on top of the substrate. On a hydrophobic surface if you do the same thing which you did here, here you pulled out the substrate it was a hydrophilic surface. When you have a hydrophobic surface you push in the substrate and you have an LB film with details on top of the hydrophobic surface. So, depends on what kind of substrate you have whether hydrophilic or hydrophobic then the first mono layer either you have to pull out the substrate or push in the substrate depending on what kind of substrate you have whether it is hydrophilic or hydrophobic. Now, you can have multiple layers and there are different classifications of these LB films. For example, this is showing a three layered LB film and it is called the Z type because all the molecules are pointing in the same direction. So, you have one layer with the head group pointing in towards the surface of the substrate then the second layer is again pointing towards the surface of the substrate the third layer is also pointing in this direction. This is the opposite type where the tails are close to the substrate and this is on a hydrophobic surface and this is an X type on a hydrophobic surface. So, if you have alternate that is one pointing in this way the second pointing that way the third one again in the reverse direction then that is called a Y type of a molecular assembly or a Y type of LB film. So, you have different types of LB films and this is precisely the process by which you make the Langmuir Blodgett films on substrates. So, what are the interactions when you are making the film? So, this is the trough which we discussed. So, this trough contains water and also it contains the molecules which are spread out on the surface of water and you want to make an LB film using these molecules on a substrate. Now, the two barriers are shown here this is one barrier and this is another barrier and you have to push the two barriers close to each other as when you are dipping the substrate to make the film. Now you can have different types of molecular arrangements when you are making the film. So, as you are bringing the barriers are at a distance. So, the average area per molecule is very large when the two barriers are far off. So, when the two barriers are very far off then the number of molecules per unit area is less. So, the number of molecules per unit area is very less when the two barriers are very far apart and the surface pressure the surface pressure when the barriers are very far apart is very less. When you are bringing the two barriers closer the number of molecules per the average area per molecule you can say is becoming lesser and lesser as you are bringing the barriers close to each other. So, then the surface pressure rises. So, the surface pressure rises and as you bring it further down it again rises and this whole plot of the change in surface pressure with decreasing distance of the barrier layers or you can say decreasing distance this decreasing average area available to one molecule. If you lower that the surface area the surface pressure is increasing and there are certain stages as you can see the slope of the curve changes at this point and then again changes at this point and then there is a further change here. So, this region till you come to the first point is called the gaseous two dimensional phase when the molecules on the surface of water are totally disordered that is called the gaseous two dimensional phase. When the area available to the molecule decreases the molecules start getting arranged in a particular fashion and that is the expanded two dimensional phase or it is called the liquid like phase liquid like two dimensional phase. On further closing down the gap between the two barriers you are forcing the molecules to arrange in a definite pattern and that is called the solid like two dimensional phase or the condensed two dimensional phase. If you bring the barriers further close the pressure will increase drastically and at a particular point the film which was very well structured like a solid like regular pattern will collapse and you will have breakdown of the film Langmuir Blodgett film. So, you have different sections of this plot the gaseous two dimensional phase the liquid like 2D phase the condensed 2D phase and then the collapsed film at very high surface pressure that is when the barrier distance the distance between the two barriers is very low. This is can be shown on top of the surface it will appear like this when it is very well ordered. So, the films will look like this where the blue balls are basically the hydrophilic or the polar head groups and these are the carbon chains or the hydrophobic tail which are pointing outside the aqueous layer. Now, the same plot which we called a Langmuir Blodgett isotherm where you plot the surface pressure with the area available to each molecule on the surface. So, this in a simplified form for lecithin which is a molecule like this it has a head group which is this tri alkyl ammonium head group and then this hydrophobic chains. So, you have the 2D gaseous phase. So, if you have lecithin molecules on water and you are applying barrier pressure that means bringing the barriers close together then you first go from the 2D gaseous phase to 2D liquid like phase. Then the 2D condensed phase and then at this point you see the there is a breakdown the pressure no more increases because the ordered 2D phase has collapsed and the Langmuir Blodgett film has broken down. So, this is an example of an L B isotherm. These are experimental data. So, these are T M images of L B films and you can see these are mixed octadecyl amine. Octadecyl amine will have large this chains octadecyl chains this 18 carbon chains and you have gold nanoparticle they form monolayers at various surface pressures. So, you can see that you have low pressure 17.5 milli Newtons per meter applied here and the film is not continuous. As you are increasing the pressure the film is becoming more homogenous more continuous and at 25 nanometers it appears to be exactly homogenous. Again if you overshoot this pressure in this particular case say you go to 30 milli Newtons per meter you start the breakdown of the film and now you see these holes within the film. So, after 25 milli Newton per meter you have basically reached the collapsed form stage of as shown in the L B isotherm. So, in this L B isotherm at a particular pressure for lecithin this is like 200 centimeter square where the pressure is something like 40 may be 40 or 42 milli Newtons per meter and if you are around that then the lecithin film breaks down. In this particular case of octadecyl amine gold nanoparticle monolayers the pressure at which the film breaks down is around 25 to 26 milli Newton per meter and at in this is another picture of L B films. So, you can see very nice assembly of silica spheres made by L B method and you can see a very compact self assembly of nanoparticles. So, at different barrier distances. So, if you look at the barrier again let me show you the picture this is the real L B trough the barriers are here at the two extremes and when you are bringing them together the pressure will increase and this is shown more schematically the barriers when they move towards each other lower the area available to the molecules on the surface and then the molecules start organizing or assembling into regular patterns. Of course, once it forms a complete film if you put extra pressure that means if you bring the barriers closer to each other then the film will disrupt and. So, that is the example that we did of octadecyl amine with gold nanoparticle monolayers and this was silica spheres making an L B film and forming an assembly of nanoparticles. Now that was air water interface that is liquid and air interface. So, that was one kind of interface how to make self assembled structures at the air liquid interface. We can also have liquid-liquid interface. So, two liquids and then how we can adsorb nanoparticles at that interface to form assembly of nanoparticles. So, in this case the free energy of the system reduces the reduction in the total free energy system is important for the adsorption. So, whenever adsorption occurs at this interface it should lower the free energy of the system. So, let us consider an oil water interface and this delta E is the surface energy reduction which will contribute to the lowering of the free energy. So, this surface energy reduction is given by these terms where these gammas are basically the surface tension of the oil water interface, the particle water and the particle oil. So, you have different gammas depending on the material you have which oil you have and which nanoparticle you are using. You will have different numbers for these and you can calculate for a particle of size of radius A what would be the reduction in the surface energy based on this equation and that will give rise to a reduction in the free energy which will lead to the adsorption of the nanoparticles at the liquid-liquid interface. So, for an example this equation if you take these numbers for example, you take the surface tension between the oil and water to be 35.7 milli Newton per meter. And similarly, you take the particle what the oil interface to have a surface tension of 15 milli Newton per meter and the particle water to have 40 milli Newton per meter. Then that change or the reduction in the surface energy is about minus 5 k T. So, this k B here is the Boltzmann constant and so it is about minus 5 k T if the diameter of this particle here A is of course, radius. So, if the radius is 1.4 nanometer that is for 2.8 nanometer diameter particles this value comes to around minus 5 k B T. And it is to be noted that E here the reduction in energy delta E is directly proportional to the square of the radius. So, the energy gain is smaller and the assembly is less stable for smaller nanoparticles because it depends on the square of the radius. So, and it is negative. So, if it is the particle size is very small then the monolayer that you get the L V film you get the self assembled layer which you get on the liquid-liquid interface is much less stable than for particles which have a larger radii and that is given by this equation. So, this is an example of self assembly of colloidal nanoparticles at a fluid-fluid or liquid-liquid interface. So, the two liquids here are toluene and water toluene is a organic solvent it is non-polar water is polar and they do not they are not miscible. And so when two liquids which are immiscible meet they make an interface and what happens if you add some cadmium selenide nanoparticles this cadmium selenide nanoparticles will form an assembly at the toluene water interface. So, if you see these circles so more clear here if you see these circles you can see that green emission is coming from the 525 nanometer emission from the cadmium selenide nanoparticles which are at the interface of the toluene and water. So, the water is outside and toluene is inside and at the interface the cadmium selenide nanoparticles will arrange themselves. So, if you excite them with this 488 nanometer laser then you can see a green emission which comes at 525 nanometer is green emission is coming from only this interface area. If you take a depth profiling that means this is looking at the same droplet, but in the z direction. So, you are going down in the z direction you see that when you are going at inside the particle. So, it is at the top surface you see something then you this is the particle is becoming larger because you are now at the center of the particle. So, the cross section is larger again you are going down further the cross section becomes smaller and smaller and when you go into the center of the particle there is no emission because the emission is all at the periphery. And so that suggests that tells you that the cadmium selenide has not gone inside the liquid particle, but it is at the interface. So, this is a confirmation by confocal fluorescence imaging using studying it studying the fluorescence coming out from different depths of the same particle of the same interface and that tells you the self assembly has taken place at the interface. Now, you can come to the example of a solid liquid interface. So, we looked at liquid air interface we looked at liquid liquid interface and then now we want to look at liquid solid interface. So, in liquid solid interface you can prepare an assembly of particles by the evaporation mediated method. So, here the key step or the most important step is how you evaporate the solvent on top of the solid liquid interface and what is left behind on the solid substrate. So, this process can however be assisted by electrostatic interactions van der Waal forces and dipolar interactions. And it is very important because this methodology of making assembly on solids is very useful going by the liquid solid interface root by because you can make large area structures. So, you can take a large solid surface and you can slowly evaporate the liquid and create a self assembly of nano particles on the surface of the solid and you can use them for applications. And examples of semiconductors metal magnetic nano particles have all been demonstrated in the recent past using evaporation mediated method on the liquid solid interface. So, this is an example of a liquid solid interface it is a classic paper on a published in nature in 2006 where people have used evaporation mediated method to form patterns. So, you see these are patterns of colloidal particles lead selenide on silver nanoparticles.


So, up until about a month ago, I was working as a postdoc at Drexel University. Unfortunately, I'm looking for a job right now. I was doing cool stuff like this at my job, tracking cells, that was all cool, but I wasn't always at Ivory Tower Academic. In fact, I spent the 90s working for a major television home shopping station. And while I was there, I was programming primarily in a language called COBOL. So anyone here use COBOL? A few people, maybe, not so many. So, I mean, we all have our ideas about COBOL. This is kind of what I thought I was getting into when I started programming COBOL, but it turns out, like, you can't really kill COBOL. So, if you go to the Micro Focus COBOL website, you'll find all these amazing statistics. They didn't have the exclamation points, but I added them because I think they really intended them to be there. And you can make a lot of money programming in COBOL as well. So, in fact, I've given a talk about some good things that I think programmers can learn from COBOL, but today I wanted to talk about some of the bad things about COBOL. I could take the easy way out and just say, like, it does tend to, COBOL programs do tend to be written to model the doodly appendages and so on, but that's that very interesting. So, I thought I would talk about an interesting bug I found. So, I was at QDC for about 10 years. This is towards the end of my tenure there that I found this bug. And of course, this isn't the exact program, but it's illustrating what the program was. And I thought I had seen everything I could see in COBOL. It's not a very complicated language, but this, I thought, was pretty interesting. So, even if you haven't seen COBOL before, it's pretty straightforward, I think. So, we've got some data declarations and we've got some business logic. So, business logic is pretty simple. If they're shipping by Federal Express, they should get the shipping date should be the next day, otherwise it should be two weeks from now. You know, this is 20 years ago. And then we have some other things. If the customer type is an employee or they're paying with a QVC credit card, then they get free shipping, otherwise everyone pays $4.99, okay? So, then at the bottom, we have these display things. That's how you print out values in COBOL. So, the expecting shipping date should be, well, it's not shipping from Federal Express, it's US mail, that's what US means. And so, it should be two weeks out. In fact, that's what it prints out. So, for the shipping charge, the customer type is an employee and so we think that the price should be zero, right? They should get free shipping. However, that's not what happened. In this case, the shipping was $4.99. Like, what the heck is going on here? Everything looks fine. And obviously, this is a serious production problem because the employees aren't getting the free shipping, right? So, we gotta look into this and see what's going on. So, one thing I didn't have at my disposal now that I have now, then that I have now is syntax highlighting editors. So, if you put that into a syntax highlight editor, like VI, it highlights that period there. Oh, so what's going on with that period? Who knows? So, there's some interesting, so there's actually two things going on with that period, but we have to go into some history to explain what's happening with that. So, this is Grace Hopper, of course. She's one of the creators of Cobalt. She's got this interesting quote that I found online. I'll read this out. Humans are allergic to change. They love to say, we've always done it this way. I try to fight that. That's why I have a clock on my wall that runs counterclockwise, right? Which is kind of a crazy thing when you think about the reputation that Cobalt has now. There's all this entrenched code sitting for 60 years in banks and things that people don't wanna get rid of, right? But for its time, Cobalt was a pretty radical language. It's created in 1959, so it's almost 60 years old, and it had two important design goals that are related to this bug. One was that it's got an English language syntax that we saw, right? It doesn't look like math. Like Fortran, other languages of time, looked a lot like math. This looks like English, right? And also, it's supposed to be business computing. So, reports and money. In fact, if you've used a computer to make a presentation, you're kind of, you know, yeah, in some way have Grace Hopper in her vision of computer programming to be things other than, like, misaltredectories and physics experiments, right? So, let's talk about this English language syntax and what's going on with that period. So, most languages, modern languages, have a kind of recursive syntax. So this is a bit of the syntax from C. And the thing I wanna point out is that we have statement up at the top, and statement can be a number of different things, including a selection statement, and the selection statement can have other statements inside of it. It can go in cursively, on and on and on. And this is so common that we kind of don't even think about it with languages nowadays. But COBOL does not work that way. COBOL has a hierarchical structure, in a particular, so we have program and divisions which we saw when I kind of brushed over and paragraphs and then sentences and statements. So, a statement is more or less what we're used to thinking of except that they can't be recursively defined. And a sentence is a group of state, one or more statements, terminating with a period. Okay? So some of you are starting to think about where I'm going with this. Okay, so I should also say, and part of the reason I was confused by this bug is that we had two different systems, COBOL systems and QVC. The one that I mostly worked on did if statements this way, where every time you had it, if you had to close it with an end if. So it's a little, so this is pretty familiar if you used to other languages. So it turned out I discovered actually just this week that this if end if was a relatively new thing that was added to COBOL only in like the mid 80s. So our other system did not support this. So they always had to use these periods. So without that, it gets very complicated to deal with like deskted if statements. So they had this thing called next sentence, which would break out of if statements. So to make sure that the if went with the, that else went with the first if and not the second if. And so this period is problematic for a number of reasons. One is that like they're very hard to see. They're only like for terminals at the time probably would only be a single pixel. And you know, if you've ever have tried to move code around in like Python where white space is important, it's even more of an issue with the period because it can break up control structures. Okay, so that's one thing this period is problematic. Secondly, this is what hard drive, this is what a five megabyte hard drive looked like in like the time that COBOL came out. So hard disk space was far too valuable to waste on computer programs. So programs were stored on things like this. This is a punch card. They've been used for everything from looms to the election and things like that. So how did these work? So there were a number of ways that data could be encoded but for a program, what would happen is that one card would represent one line of your program. There's 80 columns. So there's 80 characters that you could have in your program. All right. So then if you have, so that was one line. This is what an entire program would look like, right? So imagine what would happen if you dropped this, right?  So what people would do is you'd reserve some of the columns at the beginning for a sequence number so that if you drop them, you could put them through a sorter and a mechanical sorter will put them back the way they should be, right? And then, okay, so what happens? You wanna have like subroutines and things. You can't repeat those numbers. So you'd reserve some other space at the end for some sort of a program ID and you could sort on that as well. And so here is a card for, this is from Fortran, but you can see here, this is the statement number five columns and there's eight columns at the end for an identification number.  The scheme that COBOL used was even more complicated. But they had like different areas, area A and area B. And so in fact, we didn't use this either. We had, we always compiled in my system with a free flag. So it was free format. We didn't have to worry about any of this. But if you were in these constraints, you really only get 61 characters on every line for your actual code. Anything after that is just totally ignored. It's like a comment or white space. So this is what people coded in back then. You can see that this has those different divisions there. That doesn't even have anything after column 72. So anyway, you can kind of guess what the bug was at this point. So I lied a little bit. This is what the program really looked like. And this is kind of syntactic white space here. And so that period was in column 73, so it was ignored. So this, right, so it wasn't there. So this is really what the code looked like. So it was kind of over there. In fact, I knew some programmers who would tape a string, like a piece of thread between column 72 and column 73, so that wouldn't happen. What's next? Right, so my fix was to just move it over one line, and that's what fixed the program. So that's how I punch card ate my program. So thank you. Thank you.


But why do men cut back on communication after the chase phase? Well, there's two primary reasons. One is he's pulling back because he's just not that into you and we'll get into that in a moment. Or the second reason is he feels secure in the relationship and he doesn't need constant communication.