OK, atantio'n... OK, we're starting. The real earth has seasons. This is actually the top of the atmosphere incoming solar radiation as a function of obliquity. So, latitude here. Top of the atmosphere insulation for varying obliquities. Earth is not on here. Earth is 23 or something. I'm not very good with the real world sometimes. It's 23. So, of course, zero obliquity is this line here. As you increase the obliquity, it's rather interesting. Perhaps it's easier to understand this one more. This is the incoming solar radiation at solstice when the sun is overhead at the latitude of obliquity. So, if there's no obliquity, of course, you still get the same plot, most incoming solar radiation at the equator as you increase the obliquity. You get more and more incoming solar radiation coming in at higher and higher latitudes. When the obliquity is 90 degrees, then, of course, the sun is overhead at the pole and the pole gets very warm. And you get a reverse temperature gradient. You don't need much obliquity in order. So, here, the obliquity is 30 degrees. When the obliquity is 30 degrees, which is not much more than today's obliquity, then, in summer, you have more incoming solar radiation at the pole than you do at the equator, even though the pole is further from 30 than the equator is from 30. But the length of the day is much longer. So, you have to take that into account. And then perhaps a little bit more surprising is that when the obliquity is actually above 54 degrees, it turns out, then, on the annual mean, you get more incoming solar radiation at the pole than you do at the equator. So, if you've got... So, even with our... I mean, the obliquity is about 23.5 or something like that. And it has varied slightly over the millennia, not so much, but a few degrees here and there. And the variations in the obliquity are thought to give rise to the ice ages. That's the famous theory of Milutyn Milankovic. It's interesting. It's still a little bit of an unsolved problem. Most people think they've solved the problem as to how the actual variations in obliquity rise to the ice ages. But they seem to do so. Mars has had very large variations in obliquity over the past few billions of years. It's about 30 degrees now, I think. A bit less. It may have been as large as 60 in the past because Mars is closer to Jupiter. And it's the other planets that should give rise to variations in obliquity. But nonetheless, even with our current obliquity of 23, we get finished long seasons. So the basic upshot of that is that we get... The highly cell is not centred. The equator, if this arises in the summer hemisphere, is a rising motion, essentially the ICCZ. And you get a much stronger winter cell and a weaker summer cell. And there's a corresponding theory for that. Again, there are many theories for this. The theory most related to the held-how theory for the seasonal case is that Linzen and Howe was a student actually at MIT in the late 70s. Did a lot of this. And of course it becomes... I don't know whether Simone will talk about this or not, but part of it is that this, of course, is not a steady state. The seasons are going back and forth. Essentially, the back and forth of the winter cell in the summer cell are the monsoons, in a sense. We shouldn't separate them too much. But the monsoons tend to be concentrated in various regions like India, Southeast Asia, a weak monsoon in Arizona, even because of the influence of continents. But we probably shouldn't think of the continents as causing the monsoon any more than we think of the convection as causing the hadler cell. But nonetheless, if we didn't have the continents, the monsoons would not be like they are today. But I won't talk about that at all. Good. OK, so I'll lead in to the main events. So, and Helen, sorry, Linsen and Hal, did this various... It's more or less the same kind of theory, except now the air is rising off the equator. And they go through the mathematics and they get the same kind of... This is the temperature in... Well, let me have a look. This is the angular momentum conserving temperature here on the equilibrium temperature. So, it's... I would say this, getting into the off equatorial hadler cell, you're getting into sort of coen research as to... And people disagree about the very similitude of the Linsen and Hal theory. I would say that the coen's opinions of the Linsen and Hal theory is quantitatively wrong, partly because it doesn't take into account the unsteadiness, the fact that the seasons are shifting back and forth. It assumes that we're always in a quasi-steady circulation. But the winter hadler cell is more or less angular momentum conserving. So, you get this much stronger winter cell here and a weaker summer cell here. And, well, at least the experiments, some of the experiments which we've done in our group with Ruth Geane, who'll talk about it next week, tend to show that the winter cell is a little bit more angular momentum conserving and follows the theory of Linsen and Hal, which is a variation of the Hal and Hal theory. But the summer cell, which is this guy, really doesn't behave in any shape or form like an angular momentum conserving cell. It's really, this cell is really, if you will, driven by the effects of biotinicalities as high latitudes. I'm going back and forth over the seasons. So, as the seasons progress, I should really have a movie of this, shouldn't I, if I was adept as Brian is. As the seasons progress, this would shrink and become the summer cell. The summer cell would become the winter cell and the regime would change from being angular momentum conserving to more of an edit-driven cell. And that's the progression of the seasons. Here are some numerical simulations just to show kind of thing. This is with a dry model. Simulations by Alex Patterson, who's in our group in Exeter. This is a three-dimensional model, full model. This is the stream function, the temperature. Uh-oh, I think I have, this is the problem with talking too long. I did something, some batteries. Let's see if these work. Obliquity is zero. This is the stream function and temperature. This is the annual mean. At the high, obliquity, 60 degrees, you're actually seeing warmer poles than you are than at the equator. So it's kind of interesting. But bizarrely enough, surprising enough perhaps, you're still seeing on the annual mean a similar structure with hadler cells close to the equator and ferrule cells on either side. Is that forcing and then you're taking the annual mean? No, no, no. Seasonal forcing. So this is a dry model with a, but a seasonal varying forcing following astronomy. What is this? This is the actual simulation. This is the actual circulation at solstice. So this is the winter hemisphere. This is the summer hemisphere. 30 degrees obliquity, 60 degrees obliquity, very warm at the pole. More or less dominated by a single hadler cell when you get to high obliquity. Hardly any. There's now the ferrule cell, nor is there a summer hadler cell. Just one single hadler cell. Interestingly enough though, the hadler cell does not, still, I'm quite understood this, as to why the hadler cell is not really centered more. It's not centered anywhere close to where it is hottest. It's still concentrated fairly at low latitudes. These are actually zonal isometric runs now. We take the, we get rid of all three dimensional effects and just have a zonal isometric planet, sort of as in the original conception of Hadley. And how and held, I guess if you want to make a contribution to the Hadler cell theory you should change your name to begin with an H. You know Hadley, how. So if there are any H's in the audience, you know what your career should be. This is 60 degrees obliquity. So that suggests a strong inter hemispheric. Yes, strong inter hemispheric Hadler cell indeed. Yes, rising in the summer hemisphere, sinking in the winter hemisphere. But it's still, I mean this is, it's interesting that this is a three dimensional simulation. So this is the zonal isometric simulation at high obliquity. It's not all that much difference because you're not getting middle latitude eddys which give rise to the main differences because you're not getting bioclinic instability. Why don't you go to 90? Oh, we have that, I'm just not showing it here. Sorry. Yeah, we've done it at 92, I just don't have those figures. Sorry. No. The answer is no to all your questions. Well, it would be Linsen and How really in that. Actually, it doesn't work terribly well. We've done some comparisons which is part of the reason for doing it dry between this and Linsen and How and Linsen and How doesn't work terribly well. I don't know. I'd have to... The thermal, well... No, there's no necessary contradiction there because you can imagine rising here, moving that way, and then you will get easterlies because the angular moment... Oh, I think you shouldn't think about the annual mean is the answer to that. Yeah, but Health and Who? Health and Who is an annual mean theory, yes. But when you have high obliquity... Are you conserving any questions? And yes, there's going to be easterly wins. I'm not even going to... going down the annual mean path for high obliquity is... I think you're thinking about it the wrong way. I think you need to think about it separately for the seasons and average them. Yes. Actually, I haven't done that experiment, but it's a good experiment to do. They don't look the same. Yeah, I can imagine. Yeah, I imagine they don't look the same. Yeah. Yeah, okay. Yeah, yeah, I don't... Well, Health and... Yeah, Health and How breaks down, yes. Indeed. It's not going to work. And I think... I'm in agreement with... I would have... Pardon? Yeah. Even with a dry model, I think they'd be different. We may have done that. If we haven't done it, we should do it. It's a good... It's a little bit hard to do it with a dry model. We're not set up for that here. But I'll mark it down. Thank you. Just another little problem with Health and How, by the way, is that the zonal wind is discontinuous in the Health-How theory. It increases, and then it... to the edge of the heartless cell, and then it drops discontinuously until you get the... the radiated equilibrium wind. The... It's interesting if... the Health-How theory, or the angular momentum conserving theory, perhaps seems to actually do better when you slow down the rotation. So this is actually the plots of a fast rotating earth, a fast rotating planet, slower and still slower.  So the prediction of the theory is that the... heartless cell extends much longer, much further, and it's actually quite flat. The temperature gradient is quite flat at low rotation rates, so you don't get baroclinic instability. The planet isn't rotating fast enough to give you baroclinic instability. So that if you actually perform simulations at low rotation rates, this is earth, this is earth with... a tenth of the rotation, this is... I shouldn't say earth. A planet with one tenth of the rotation, this is one hundredth of the rotation, which is approaching Venus. What we're actually plotting is the angular momentum, M, normalised by omega A squared, subtracted by one. So essentially, where it is all white, it's conserving angular momentum. And the three plots, well, look at the top plot really and the bottom plot. This is courtesy of Greg Collier, also at Exeter. The zonally symmetric model is actually conserving angular momentum, and it's all the way to the edge of the heartless cell or nearly conserving angular momentum all the way to the heartless cell. So the heartless cell is pushed almost all the way to the pole here. And there's the overturning circulation. So it is obeying the predictions of the theory qualitatively. The heartless cell is extending further and further. Another phenomenon which then appears in the three-dimensional model is you get super rotation. Super rotation meaning that you get a strong jet at the equator at high altitudes. So here, the air is going around much faster than the planet's surface. In fact, that also happens in Venus. In Venus, you've got winds well over 100 metres per second at high altitudes at the equator. The planet is rotating incredibly slowly. It's a sidereal day, the rotation rate is one-two-hundredth of the Earth. So one can almost wonder on Venus how the winds even know that the planet is rotating. It's going so slowly. But if you take this, it's interesting, again I haven't shown it, but if you take omega A to be, the rotation rate to be one-thousandth of the Earth, it finally collapses. The winds finally collapse. And the heartless cell gets pushed off kind of all the way to the pole and the winds entirely collapse. Maybe I've got a plot here. Oh yeah. The winds still haven't quite collapsed of the rotation, but they're almost there. Anyway, it's kind of interesting to think that these angular momentum conserving theories and going back to Schneider and Venus only has a three degree of liquidity. So it has no seasons to speak of and it's rotating very slowly. It's kind of interesting to think that these angular momentum conserving type arguments probably apply better to Venus than to Earth. So there we go. And here's the overturning circulation. Oh, and here's Venus. Here's the meridional winds on Venus. So say look at this, the left hand picture, meridional wind is zero more or less at the equator. The positive in the northern hemisphere to about 60 degrees and about 60 degrees also in the southern hemisphere. So we've got a heartless cell pushing out on Venus to about 60 degrees where it stops. If you apply the theory in our simulations, it actually, we would expect it actually to go even further forwards than 60 degrees. But it doesn't. The real Venus stops at about 60. And here's another set of observations of the meridional wind. Here going to about 45 or 50 degrees. OK. That's the end of the heartless cell. More or less. I want to talk a little bit about tropical dynamics. Or keep on talking about tropical dynamics. It's rather funny actually thinking about the heartless cell because somehow heartless cellers, there's another branch of tropical dynamics when you go to the tropics, what you think about, if you actually go there, you're not thinking, oh, this is a heartless cell. You know, where is it?  You're sweating like crazy, but it's not evaporating so you're getting hotter so you sweat more. And then you think of the trade winds and so on. So you don't think of the heartless cell. So the whole branch of tropical dynamics, which isn't to do with the heartless cell. OK. Yes, a complete change. I'm going to think about radiation for a minute. I just want to explain why we have a tropopause. And the main thing I want you to get, there are two things I want you to take home at the end of this lecture as to why we have a tropopause, and they're both what it is not caused by. It is not caused by ozone. We have ozone absorbing heat in the sodosphere, so you might think or be told that temperature starts to increase in the sodosphere and it's falling in the troposphere and where it turns around to increase because of ozone. That's the tropopause. No. Ozone certainly affects the tropopause. It doesn't cause it. The other thing which you might hear, you don't really hear it often, so these are kind of straw men, is that convection goes up and where the convection stops, that's the tropopause. Well, it sort of is, but why does the convection stop there? It's because the tropopause is there. It's not. So all of these things have to be consistent, but there's no particular reason why the tropopause should be at 10 km. In fact, we'll look at Venus again towards the end. The tropopause on Venus is at 60 km high. Venus is quite similar in some ways, apart from the rotation to Earth, but okay, so just radiation, just a little bit about radiation. Imagine we've got some incoming solar radiation here, outgoing solar radiation out here, and some of it will be absorbed in here. Radiation is an incredibly complicated subject, but it's fairly well understood, but I'm going to make some fairly... Mainly I'm going to imagine that radiation is not a big spectrum. It's a single band or two bands. We have solar radiation, we have infrared radiation, and that's it. Some comes in, some goes out, some is absorbed, and some is emitted, and the amount that's emitted is proportional to the magnitude of the fourth. How much is absorbed is called the optical depth, and that's tau, so you can imagine without too much difficulty. The I by the tau, which is the change in the radiation, is minus, minus B. So this first term here tells you that it's absorbed, depending upon the optical depth, tau and this B, which I will take to be sigma t to the fourth, and that's a grey assumption. It tells you how much is emitted. So this is a basic equation of radiative transfer, and a lot, but not all, of the radiative forcing on Earth can be understood by taking the atmosphere to be grey. But people actually know about radiation are actually rather reluctant to make the grey approximation. One reason is that you can actually do these equations almost line back, well, band by band with lots of, with a separate equation for each frequency, and then you sum them all up at the end, and different frequencies have different levels of absorption. And that is important for quantitative measurements. But for now, we won't worry about that. So we, furthermore, will just assume that radiation is going up and down, assume that all the solar radiation is absorbed at the surface, and that's not too bad of an approximation. So we get an equation for the downwards radiation, imaginatively called D, and the upwards radiation imaginatively called U. So these are these two equations. These are this equation, but for the downwards radiation and the upwards radiation, there's actually a different sign involved because tau, which is the optical depth, we take to be zero at the top of the atmosphere, and whatever it is at the bottom of the atmosphere, it's about five. It tells you how much radiation gets absorbed as you pass through. So the downwards radiation is going to larger values of tau. The upwards radiation is going to smaller values of tau. You end up with a different sign. Now, tau is a function of the radiation concentration of the atmospheric composition. The main greenhouse gas in the atmosphere is, what's the main greenhouse gas in the atmosphere? Water vapor. Yeah, not carbon dioxide. Water vapor. Carbon dioxide is number two. And therefore, it's a function of height. If we know what the atmospheric composition is, we can imagine that tau is some function of height. And more or less, it again, just for our purposes, we will assume that tau falls more or less exponentially with height e to the minus z over h. And h is the scale height of the absorber. And because it is water vapor, this scale height is about two kilometers. If we didn't have water vapor in the atmosphere, it would just be the scale height of the atmosphere itself, which would be about eight kilometers. But in fact, I don't know if it's about two kilometers. So if we know what tau is, this is a function of z, which we're going to specify here. And we're going to specify, then tau becomes a vertical coordinate. And then the most basic thing you can ask is, what is the radiative equilibrium temperature? Let's say it's a function of height. We're going to say tau is the minus z. And if there is the radiative equilibrium temperature, there is no net convergence of radiation in a given level. Because if there's a convergence of radiation, it would mean that the atmosphere is heating. But we said it's an equilibrium, so there can't be. So in equilibrium, d by d z of u minus d, which is the convergence of radiation, again assigned because one is going up and one is going down, is zero. So therefore d by d tau of u minus d must be equal to zero. So that's a condition for radiative equilibrium of a column. And I'm assuming no solar radiation is absorbed, which would be a kind of a detail at the level of this argument. These equations are called Schwarzschild equations, by the way. Some people call them. I always have trouble with this. Shouldn't even bother, should I? Schwarzschild is an astrophysicist. We also did work on black holes.  OK, so we want to just solve these equations with d by d tau of u minus d equals zero. And we can actually do that. It's not too difficult. This is the solution. Tells us what the up. Wood radiation is the downwards radiation and b, which is b now is not the buoyancy, b is sigma t to the fourth. These are the solutions. A little bit of algebra under the algebra. And what is u of l t? U of l t is the upwards radiation at the top of the atmosphere. The outgoing infrared radiation at the top of the atmosphere. That must now, and we know what that is. Because the outgoing infrared radiation at the top of the atmosphere is equal to the incoming solar radiation. Because the planet is in equilibrium. So we'll take that as our boundary condition. Because these are ODEs, the first order ODEs, so they need a single boundary condition. And then, since we've got this tau equals tau naught e to the minus z, we know that gives us, in fact, this solution for the temperature. So we can calculate analytically what the temperature profile is as a function of height in a column. Yes, that's right. That's right. There's no, indeed, there is no, do I have an l here? Yes, I have an l. That's right. Okay, l here. Subscript l. Thank you. It is long wave. There's no solar absorption. Indeed. Yes, I secretly introduce an l. And that gives us the temperature as a function of height knowing what this outgoing long wave radiation is at the top. Because I'm just going to take that as a boundary condition. Because it's an equilibrium calculation. And I get this and what does it look like? It looks like this. Well, these are various curves depending on what the optical depth is. I'm very, the optical depth here for a given outgoing radiation. So the outgoing long wave radiation at the top is, then determines what the temperature is at the top of the atmosphere. It's at the top of the atmosphere. Oops, a little typo here. Forget this t equals. Finish my talk here. At the top of the atmosphere, tau is zero. So b, which is sigma t to the fourth, is the outgoing long wave radiation divided by two. So if we're specifying what the outgoing long wave radiation is, it's equivalent to specifying what the temperature is at the top of the atmosphere in this radiative equilibrium case. And you can see that what it does is it increases rapidly. This is for increasing values of tau. For increasing values of tau, it just gets warmer and warmer. And that's why, of course, we have a greenhouse effect. If tau was zero, no greenhouse gases, temperature would be 220 here. A larger tau, tau is 360 here. In reality, tau is about three, I guess. Of course, it varies in reality. As water comes and goes in a particular column, it varies a lot. It is just the same curve with different values of the outgoing long wave radiation. So I'm specifying the outgoing long wave radiation, and that's equivalent to specifying really what the solar constant is. Because the incoming radiation equals the outgoing radiation. One thing about global warming, which we can forget if it's easy to forget, is that after we put CO2 in the atmosphere, the outgoing long wave radiation is going to be the same. Still got a balanced incoming solar radiation. So unless clouds have changed, unless there's more clouds, unless the albedo has changed, we've still got exactly the same outgoing long wave radiation as we have now. OK, so this is the radiative equilibrium temperature increasing like crazy at the bottom of the atmosphere. It's really warm at the bottom of the atmosphere. What is that going to give you? It's going to give you convection, right? So that's why we have... That's ultimately, again, why we will have convection. And we'll have more convection where it's hot. And so we tend to get more convection in the tropics. And what's going to happen? Convection is going to give you a lapse rate which is specified by either a dry adiabatic lapse rate or a moist adiabatic lapse rate, depending on whether the moisture is present or not. But it's going to... What it's going to do is this. It's going to reduce the temperature gradients here. And so you're going to get convection until this temperature reaches the radiative equilibrium temperature and then you are no longer unstable. And this break here is the tropopause. So we haven't mentioned ozone. Ozone just causes this temperature to go up again up here. It causes this to go up again there. It doesn't really influence... And much of the absorption of ozone is high up in the stratosphere. So in fact the... Do I have it? My U.S. standard atmosphere has gone. It was right at the back. But the U.S. standard atmosphere has got a fairly isothermal stratosphere until you get up to the upper stratosphere. This is for the tropics, right? What about the extra? The extra tropics, in fact, the same argument applies. Why is the extra tropics in that most... That's a deeper question than that's a rather deep question. I'm not going to answer right now because I'm not sure I know the answer. This same argument applies. Because all I'm... Certainly in the absence of anything... In the absence of any other motion the middle attitudes would still be unstable. If there were no other circulation the middle attitudes would still be unstable. So you'd still have convection. If you didn't have a large-scale circulation you would just be in one of these regimes here. Like this green curve would still be unstable. But in fact, the middle attitudes are less convectively unstable than the tropics because the large-scale motion baroclinic instability is also actually moving heat upwards. So what actually happens in the middle attitudes is that you just get a difference that this lapse rate here is not so much driven by convection but it's driven by baroclinic instability, the large-scale edges, which are shifting heat up. So then we can actually calculate what this height is. You have one curve for the radiative equilibrium. I have one curve for the radiative equilibrium and then I'm going to imagine that it adjusts. Let's say because of convection and convection is specifying a lapse rate. So what specifies the point at the surface? That is the key question, Franco. That is the key question. But let's not do that. Let's assume no matter what this scale height here, H, is going to be of order a couple of kilometres because if temperature falls off, of course it's going to affect things quantitatively. But the amount of water vapor falls off with temperature. So we'll assume that we know that. Then Franco asked the question, what determines this intercept? That puzzled me for a long time and I should give credit here to my colleague, Pablo Zorita-Goto, and we confused each other for about six months before we figured it out, sort of. This is the radiative equilibrium temperature. For my first assumption, let's just assume then we have this red line, which we don't have any red chalk, but let's assume that it starts from here and we specify the lapse rate and then it will go up to there. And then that would be the height of the tropopause. That is what I've actually done in this first calculation. Take the surface temperature equal to the radiative equilibrium temperature. So if I know what this lapse rate is and I know what this temperature is, I go up to here and that gives me this value of the tropopause here. But that's too high. That's too high of a value because, in fact, it starts down like this. Yeah, actually you don't. That was our first thought, but you don't because it's something a little bit like an equilibrium constraint. Let's suppose we make another guess and we take it here and we go up to here. Now, what we've done, we've said, if we do this, we've guessed this fairly arbitrarily and go up to here, we'll get the outgoing radiation correct. The outgoing radiation u would be sigma t to the fourth. But then let's do the radiative calculation backwards and go down from the top with this temperature profile and solve the radiative transfer equations going from the top down. That would give us what the upwards radiation is as a function of height. It will give us some value here, knowing what the temperature is there and the temperature profile is there. It will give us something u at the bottom equals something, something. I don't know what that is yet, but a function of how high this is. This something we know has to equal sigma t ground to the fourth because that's the radiation which is being emitted by the ground. But it won't be if I choose this height arbitrarily. I have to choose it in a special way so that the upwards radiation at the bottom of the atmosphere is equal to sigma tg to the fourth because that's essentially the way of getting the entire atmosphere into equilibrium. So what you actually have to do is do an iterative calculation.  You see if that upwards radiation is sigma tg to the fourth if it isn't to adjust. The atmosphere does that itself. There's many clever iterative algorithms built into nature. So it gets it. This is what we did with Pablo. We can calculate what this height is doing it analytically. It's a rather complicated calculation and it gives you that. Now, that gives you about the various constants in here. I should stop for a break, I guess. Gamma is the lapse rate. Tt is the temperature of the chopper poles which we know is that temperature up there. Tau is the temperature of the surface. Ha is the scale height. So I guess in as a parameter and we get this formula. And just two other quick things. When we are one other quick thing, if we have global warming the outgoing longwave radiation stays the same after we've got to equilibrium because incoming solar is outgoing in for bed. But we know it warms because that's the greenhouse effect. So it goes from... That's our original chopper poles temperature profile. It warms to give us this red line because of global warming. The temperature of the chopper poles has to stay the same. The temperature of the chopper poles has to increase with global warming. I'm sorry, the height, thank you. The height of the chopper poles has to increase and it's one of the most robust predictions aside from the fact that temperature will increase. The height of the chopper poles has to increase. And I'll just skip that. The lapse rate also causes things to change because the most adiabatic lapse rate changes. So if you know about that the fact that the lapse rate changes makes things actually go up a little bit more. If you don't know about the most adiabatic lapse rate, don't worry about that. Just think of this. So you can predict that the height of the chopper poles putting the numbers in goes up about 300 metres for each degree rise in temperature which is actually kind of significant. And this, by the way, my own is C-Mip. I took away all my C-Mip slides after John's talk. Except for this one. This is the little dot. Well, this is the height of the chopper poles in a whole bunch of C-Mip models as a function of latitude. And this is metres per decade. So, you know, they're all varying but on average the C-Mip models are increasing in heights by about 70 metres per decade. And which is kind of not insignificant especially if you're an airline and you want to fly in the stratosphere to get above the weather, you're going to have to fly higher. OK, so let's stop and have a... But let's not have half an hour otherwise we'll never finish. Let's come back in 20 minutes or something. Or less if you can.


Since my arrival in Australia almost 21 years ago, I've seen Australia make quite a bit of effort when I first got here on gender equity and we sort of stalled for the last 10 years. But we need to think about our ways to improve gender equity within our disciplines and within academia. And so I think Athena Swan of all the programs I've seen around the world is the program that seems to be having the biggest effect. It's really getting universities and research organizations to think about the problems and measure them, come up with ways to fix those problems and then act upon those problems and then re-measure and see how we've done. And so from my perspective it's the thing that I think has the best chance of making meaningful change in our sector. I see technology and science that underpins that technology as being really the big game changer for Australia in the future. If we do it well, we're going to remain a prosperous nation. If we do it poorly, then we're going to be less prosperous. We have a lot of talent across Australia and science and technology needs some of the brightest minds that Australia has to offer. All the evidence is that that's half in men, half in women. And when systematically we look at a university and we see that only 20% of our senior professors, for example, are women, you know you're throwing away a lot of valuable talent. That valuable talent is stuff we simply cannot afford to lose. From my perspective at ANU my hope is to by engaging more effectively with women I'm going to actually have an advantage over people around the world and an advantage here in Australia of attracting the best talent and that's what universities are all about. It's about attracting great talent and resourcing it to do great things. And if I have the advantage of getting an extra segment of the population, women, that's going to be great for my institution. I guess I've spent most of my life working with men and women, more men than women. My own Nobel Prize winning team had no women in it all. It reflected the generation of astronomers that I grew up with. I had a very strong mother who I guess taught me how valuable female contributions can be and that I don't want to see those contributions excluded. So to me it's just sort of almost a human rights aspect. It's something I feel very strongly that if we're going to have I guess a society I want to live in when that is equal I guess I need to help make the change. And so to me it's an actual absolutely fundamental part of living in a society that I want to be part of. One of the I think common misconceptions about dealing with gender equity is that it's a female problem. In my field which is 70% male the lack of women in it is a problem for the whole discipline. So it's a problem that men as well as women need to embrace. And so within the Athena Swan program and for example male champions of change and other great initiatives we have in Australia you know the role that men are going to be playing and trying to fix the problem is not to be understated. So I'm hoping to be joined by male and females in the Athena Swan program as it rolls out here in Australia.


The film you are about to see tells the story of the United States Army parachute-rigged. This soldier is one of the most important factors in the security of the United States. For in the final analysis, the ability of our country to respond in a matter of hours to deliver troops and supplies to any trouble spot in the world depends on his skilled hands and alert mind. The greatest demonstration of confidence has been made by thousands and thousands of paratroopers the moment they made their very first jump. This is the making of the rigor, the man in the red cap. The lives of these men may well depend on you. That is, if you're a U.S. Army parachute-rigged. As a parachute-rigger, you often jump with the men whose parachutes you have packed. As they land safely, you feel a deep pride. You know that the way you rig the heavy equipment is a major factor in deciding whether or not it will be delivered safely. Yes, your job demands a lot of know-how, attention to detail, and just plain sweat. But most of all, it requires training. As you think about it, memory takes you back to where it all began, to the start of your basic airborne training at Fort Benning, Georgia. Although you aren't aware of it at the time, volunteering for airborne training is a necessary preliminary to becoming a U.S. Army parachute-rigger.  Then suddenly you discover inner physical resources you never knew you had. When you feel as if you can do a mile and four minutes, you're ready to start jump training. First, you get the feel of it by dropping from the 34-foot mock tower. Next, you jump with seven buddies as a group. Then you go higher to the 250-foot free tower. Finally, you move up to 1,250 feet and qualify as a paratrooper. At the graduation ceremony, you receive your wings and find that you are assigned to an airborne division. Your division needs parachute-riggers. Unknown to you, a personnel officer pulls the records of a few highly-rated paratroopers and gives them to the company commander of the air equipment support company. The company commander interviews you, then decides that you have the prerequisites of a parachute-rigger. He offers you the opportunity to attend the three-month parachute-riggers course. This training will qualify you for an airdrop supply company, air equipment repair and depot company, or the airborne division air equipment support company. He emphasizes that only the division's top paratroopers are eligible to become parachute-riggers. On your arrival at the parachute-rigger school, the director of the airborne department greets the new students. His words confirm the first impression that a parachute-rigger's duties are many and varied. Four weeks will be spent in learning to pack parachutes, four weeks in learning to maintain parachutes, and four weeks in learning airdrop methods. There is a wide variety in your fellow students. Some of you come from other branches of the service. The director makes it clear that it will be a difficult three months. The work will be hard, but the dividends will be rewarding. He wishes the men good luck. The packing phase of the course begins in the pack shed with emphasis on fundamentals. You learn that before a parachute can be packed, it must be properly laid out with all tangles removed. Your instructor deliberately tangles your first chute as an example of how it might arrive from the drop zone. It's in such bad shape that it looks like the only way to straighten it out will be with a pair of scissors.  First thing to look for is a key tangle. Find it and part of the puzzle is solved. As you follow his instructions, you wonder if you'll ever become as skillful as he is. Finally, after hours of practice and concentration, you realize you have acquired the knack. Once the proper layout of the parachute is mastered, you are shown how to fold the canopy. Each individual gore must be inspected and folded in correct sequence. It looks easy enough. Then you try. By now you've been taught that as soon as the canopy is folded and back on the table, you must make sure that there is no fabric in the channel. When you're satisfied that it's okay, you raise your hand for a check by the instructor. In his opinion, a three-year-old child could have done better.  Finally, after more attempts than you'd care to admit, the instructor conceives that the canopy is perfectly folded. To your surprise, you find yourself feeling a little proud. The next operation in the packing phase proves a lot easier. It consists of stowing the canopy and closing the deployment bag. As soon as the instructor okays it, your bag is ready for the stowing of suspension lines. As with most phases of training, stowing of suspension lines is something the entire class practices together. You remember the trouble you had learning to fold the canopy and are determined that this time the instructor will give you an AOK on the first attempt. He doesn't like it. Again, you find practice makes perfect. When seasoned with equal parts of skill and knowledge, this time you're confident you'll pass inspection. As the days and weeks go by, you find you are learning more difficult subjects with greater speed. In fact, the entire class experiences an accelerated learning process. Now comes the first big event in your rigor training, the first moment of truth.  You find yourself taking a very personal interest in the job, since it's you who will make the jump. As you fly toward the drop zone with the parachute you pack, you reach one inescapable conclusion. If it doesn't open, you fail the course in more ways than one. Well, this is where you find out.  It is a feeling that can be shared only by those who have succeeded at something few other men have attempted. Here in the maintenance shed, here in the maintenance shed, you will be given instruction in maintaining and repairing the parachute you have learned to pack. Keeping a shoot in good condition is also vital to a jumpers safety. First you get a thorough course in operating sewing machines. So thorough that you want to apply for a pass, so you can go home and tell your mother what she's been doing wrong. Once the general art of operating sewing machines has been mastered, you learn how to use light duty machines to patch or replace sections in a canopy. Another conventional machine, the heavy duty, is used to repair harnesses and other webbing. You are also taught how to operate such specialized sewing machines as a zigzag machine, used to sew the suspension lines to the canopy. A hook-eye attaching machine for attaching hooks to parachute pack trays. A bar-tacking machine for reinforcing the ripcord pocket.  Sometimes a darning machine may not be available, so you're taught how to do the job by hand. Other hand repairs taught include replacing grommets and inspecting and assembling harness quick release assemblies. Again and again it is emphasized that no matter what type of repair you make, you must always inspect the parachute thoroughly. A special shadow box table is provided for inspection of the canopy. This table with its lights underneath allows you to spot any defect in the fabric. All defects must be noted on an inspection tag. An identical inspection is made after the defects have been repaired. This final inspection will also serve as a double check to ensure that when the paratrooper jumps, his parachute will be in perfect condition. In the airdrop hanger you will be taught how to pack cargo parachutes and rig loads. First instruction is in the packing of the G11A parachute whose canopy is 100 feet in diameter. Because of the size of the canopy, a large fan is used to help fold the gourds. Since three men are needed for the job, teamwork is important in packing it. The parachute is capable of supporting 3,500 pounds and may be used in clusters up to eight. You discover that stowing the G11A canopy into the deployment bag is an operation of much greater magnitude than with the main troop parachute. Your instructor watches every move closely, ready to stop you if you make the slightest mistake. Stowing the suspension lines isn't exactly a one-man job either. Later you find that the same general packing procedures apply to the G12D parachute which supports 2,200 pounds. Its canopy is 64 feet in diameter. You have learned to pack all the personnel and cargo parachutes in common use by the army and are now ready to learn how to rig supplies for airdrops. As with parachutes, where you started on the smallest, you are first taught to rig the two smallest loads. One of these, the A7A sling container, is capable of holding 500 pounds. The other small load, the A21, is a sling and cover container, also capable of holding 500 pounds. Both containers are used principally in drops from army aircraft. After being taught to load them on dummy aircraft in the hangar, you go out to the airfield to work on the real thing. Simultaneous instruction is given on different procedures and different aircraft. While some students are taught wing load methods, others learn door load procedures. Later, at the drop zone, you see how these loads are dropped. Non-fragile items such as blankets or clothing are rigged without parachutes and dropped free fall. Other items such as rations and gasoline are rigged with honeycomb cushioning material and a small stabilizing parachute for high velocity drops. Each student is also given a chance to be a kicker, that is you fly with the aircraft and eject a small load, such as this container with a standard parachute for a low velocity drop. Back to the airdrop rigging area and one of the most important phases of the course, rigging heavy equipment for airdrop. You are taught that a definite routine is followed in rigging all heavy equipment, beginning with preparation. To prepare this vehicle, you take such preparatory measures as installing protective covers and securing removable parts. Learn that the parachute rigger normally uses the modular type of platform for a load of this sort. This platform comes in four-foot sections and can be assembled into different sizes, eight feet to 24 feet. To prepare the platform, the tie-down clevises must be installed. After the item and the platform are prepared, the second step in the rigging routine is padding. This is done with a material called honeycomb. You are taught to take logs of honeycomb and expand them into sheets. This honeycomb padding will absorb the landing shock when the G pits the ground. Lowering this load onto the pads requires teamwork. It weighs almost two tons and it wouldn't do to drop it. The next step in the rigging routine, how to install the specific lashings that hold the item to the platform. The next step in rigging heavy equipment is attachment of parachutes. For this vehicle, one G11A parachute is used. The rigging is more than routine. A qualified parachute rigger must be able to determine which type and number of parachutes to use for each specific item. He must also decide what size and shape padding and number of lashings the item requires. And he must judge which platform will best meet a given situation. As the training continues, you realize that the same general rigging principles apply to all heavy loads. However, specific methods apply to each individual item and these must be thoroughly mastered. The assembly line method is the system a rigger will most often use when he returns to his unit. The assembly line may be as long as 200 feet and have seven stations, one for each step in the rigging. In actual operation, you as a rigger will be in charge of one of these stations, supervising personnel of the unit to whom the equipment belongs. Just as in a Detroit assembly line, preparation for the item to be rigged is all important. The honeycomb is prepared at station two. The vehicle to be rigged in this instance a jeep is prepared at this station. Wind shields are secured and other components checked. Then it is positioned on the honeycomb. At the same time, another vehicle is having lashings installed at station four. Then at the fifth station, cargo parachutes are stowed on the load. Here the release assembly and other components are prepared and placed on the vehicle. At the last station, the vehicle is given a complete inspection by a qualified parachute rigger. At the end of the line, completely rigged vehicles are placed aboard a transporter for movement to the airfield. The next day you're at the airfield ready for another crucial test. To see that the heavy equipment you have rigged will sustain the impact of an actual drop. Both the rigger and the loadmaster are experts in their respective fields and because of this, a feeling of mutual respect is enjoyed by both. The rigger's technical knowledge must be relied upon by the loadmaster for the airdrop portion of the joint inspection. This inspection is vitally important and it is thorough down to the last detail. The US Air Force 25K loader is designed for quick and efficient loading of heavy items. After the vehicle is loaded and secured, there's a second inspection to make sure that everything is still A-OK. The extraction system is checked out carefully and you're examined carefully too. For you're going to jump after the equipment you've rigged. From your seat in the aircraft, you see the extraction parachute as it inflates, pulling out the heavy drop load. You see the parachutes you packed inflate, lowering the equipment to the drop zone. The aircraft circles and you make your first tailgate jump. As you descend, you realize that with this jump you are making a great stride toward a new phase in your military career. This is the climax of your parachute rigger's training. Now you are no longer a student to your instructor. Except for the final graduation ceremonies, you are a qualified parachute rigger. Their own emotions can best be described by the way you feel when the instructor lets you try on his rigger's cap for size. It is a proud symbol of the skills, knowledge, and sense of responsibility you have gained during your three months at the Parachute Rigger School. These intangibles are most accurately summed up perhaps by words from the rigger's pledge, words that have become almost a part of you. I will keep constantly in mind that until men grow wings, their parachutes must be dependable. I will never pass over any defect, nor neglect any repair, no matter how small. I will stand ready to jump with any parachute which I have certified as properly inspected and packed. I will remember always that the other man's life is as dear to him as mine is to me. I will be sure, always. Most of all, you will never forget this, that the United States Army Paratrooper has placed in the hands of the U.S. Army Parachute Rigger his most valued possession, his life.


So tonight's videos are on section 10.3. This first video we're just going to review what we talked about yesterday with arc length and arc measure. So remember from yesterday that arc measure represents the same angle as the central angle of the arc. So when we are asked to find the measure of arc AB, here's arc AB and that measure has to be equal to its central angle, which is this angle of 100 degrees. So the first thing we're going to write in here is 100 degrees. Now by the way, on your note sheet you need to copy this picture down. Do arc AB so that there's a 100 degree angle here and you can see that the radius is 5 inches. Okay so let's move to arc length. Now remember that arc length is actually the distance if you were to start at A and walk around the circle so that you end up at point B, that is the arc length. So in order to find that we use the formula, remember the measure of arc AB over 360 degrees times the circumference of the circle. So we've already got the measure of arc AB is 100, so 100 over 360. And now we need to find the circumference of our circle. So remember that circumference is equal to pi times diameter and if the radius of this circle is 5, the diameter of this circle would be 10. And so the circumference of this circle is 10 pi. So I'm going to enter that here, 10 pi over 1 and now I'm going to do some reducing. So 100 over 360, the zeros cancel if you divide both by 10, so we have 10 over 36 and if we think about what goes into both 10 and 36, we come up with 2 goes into 10 5 times and 2 goes into 36 18 times and we're going to multiply that by 10 pi. And so we end up with 50 pi over 18. So 50 pi over 18, we can actually reduce a little bit further. So we know that 2 also goes into both 50 and 18, so we're going to reduce this to 25 pi over 9. So we would say that this has an arc length of 25 pi over 9.


The power to convertor there are lot of questions as to V dc is reverse biasing this diode. Now, do not come jump to those conclusions. So, I will explain to you why what the I will explain to you the advantages that we can get by connecting tertiary winding to this source. You do not have to connect this tertiary winding to the source. You can connect it to a separate winding something similar to the fly back, but then you need to have a third winding. I will repeat you need to have a third winding and current should flow in that third winding when you open the switch s for the magnetizing current to flow. For the magnetizing current to flow we have to provide a path in the third winding second winding it is not possible here. One made to have a fly back connection something similar have a separate capacitor that capacitor gets charged or you can connect it directly to V dc. Now, what are the advantages of connecting to V dc? You just see here if I connect this diode if I connect this tertiary winding to the supply V dc what is the voltage rating of the what is the voltage rating of of this winding and what is the current rating of this winding by the what is the current rating this coil has to carry it has to carry only the magnetizing current the peak value corresponds to the corresponding value that was flowing in the primary just prior to opening the switch and multiplied by the turns ratio turns ratio that current was flowing in i n 1 now it has to flow through n 3. What is the when the when this diode is on what is the voltage that is being applied to this winding when I when I when the diode is on voltage applied to this winding is V dc. So, if I assume that l 3 is the self inductance of this coil voltage applied is V dc having n 3 number of turns what is the duration what is the maximum value of d that I can have I can determine and what should be the conductor size and the insulation that I need to wind this transformer we will discuss in detail here is the equivalent analysis I will quickly I will go through i 1 is equal to i 2 prime plus i m i m is the magnetizing current V is applied to l m l m is the magnetizing inductance of the transformer i m increases linearly with time V induced in n 2 supplies current to the load what it means is voltage induced in the secondary will supply the current to the load that forward bias is d 2 and whatever the voltage induced here is V dc into the turns ratio the equivalent circuit in the tertiary is V dc what is the voltage rating of d 3 see here voltage applied to the primary is with the n 1 turns is V dc with the dot as positive. So, this terminal is positive voltage induced in this coil is V dc into the turns ratio now turns ratio is n 3 and n 1. So, positive of the battery is connected to the negative of the voltage source a induced voltage source something it is here positive of the battery is connected to the negative of the voltage induced or negative of the voltage source which is induced in the winding V dc and that is and this voltage d 3 has to this voltage d 3 has to voltage rating I mean the d 3 I can determine from supply voltage and the turns ratio. So, comes up to be this one current rating I know the equivalent peak current of the magnetizing peak value of the magnetizing current when i 1 is 0 i 2 is equal to 0 i m and i l should be continuous i l can flow through d f now voltage across d 2 is voltage induced in n 2 itself what is the voltage across d 2 here voltage across d 2 is voltage induced in n 2 see this when diode d f is conducting this point gets connected here. So, voltage induced in d 2 is the voltage rating of sorry voltage induced in n 2 is the voltage rating of d 2, but then what is the voltage induced in d 2 when 1 is see there are 2 values you just find out here when primary switch 1 is called switch 1 switch s is closed it is V dc. Similarly, when diode d 3 is conducting voltage applied to this coil is V dc voltage applied to this coil is V dc having n 3 turns what will be the voltage induced in what will be the voltage induced in n 2 now voltage applied to n 3 is V dc what will be the voltage induced in n 2 that voltage d 2 has to block when the switch s is closed d 2 gets forward biased when s is open when d 3 starts conducting d 2 gets reverse biased and the voltage that it has to block is voltage induced in n 2 that is proportional to V dc turns ratio between n 3 and n 2 turns ratio between n 3 and n 2. Similarly, I can determine the voltage rating of the switch as well because voltage applied to n 3 is V dc there will be voltage induced in n 1 in addition there is V dc as well the total voltage the s has to block the sum of these 2 voltages procedure is the same. So, voltage across s is V dc plus n 1 plus n 3 voltage across in n 2 is V dc into n 2 into n 3 that is the voltage rating the d 2 itself what is the value of n 3. So, increase in flux V dc d t into n 1 V dc d 2 into n 1 is the flux n 1 d phi by d t is equal to V dc these are increase in flux. Now, how does the flux decrease it is because of the current that is flowing in n 3 same voltage V dc divided by n 3 into some time. Now, let us see how much is that now if I equate increase in flux should be equal to decrease in flux for the steady state t a is given by n 3 by n 1 into d t n 3 by n 1 into d t if both of them have see for the core flux to become 0 for the 4 core flux become to 0 t a should be less than 1 minus d into t. Now, we will see why the core flux has to become 0 for the core flux to become 0 core flux has to become 0 d flux has to become 0 before closing the switch for the next time. So, t a should be less than 1 minus d into t t a should be less than 1 minus d into t. So, that is a condition that I am applying here. So, d must be limited to d max such that n 3 by n 1 d max t should be equal to 1 minus d into t. So, max d max is half d max is half if n 3 is equal to n 1 if n 3 is equal to n 1 d max is equal to 1. So, number of turns is the same now. So, may be and n 3 cross sectional area of the conductor that is used in the tertiary coil is very small compared to the primary and secondary why secondary has to carry the equivalent load current primary has to carry magnetizing current as well as the load equivalent load current whereas, the tertiary should carry or will carry only the magnetizing current. So, I need to have a very thin conductor number of turns in the primary and tertiary I am keeping it same. So, that my winding of the transformer or during fabrication it becomes easier one thick conductor one thin conductor I will take them together and I will wind it it becomes easier number of turns is the same. So, it becomes easy. So, it is not only the design we need to worry about the fabrication the effort that is required to fabricate the transformer as well. So, that is the one of the reasons of connecting this tertiary across the supply. Now, if I choose n 3 is equal to n 1 and if d max is greater than 0.5 what happens see I have chosen n 3 is equal to n 1 and d is greater than 0.5 what will happen for the first time I will close the switch d max is greater than 0.5 controller decided the switch is on for a longer time. So, the flux see this equation here d phi is given by v d t into d v d c into d t into n v d c into n v d c into d t into n 1 this is the rate of the flux. So, it has started from 0 I am neglecting the residual flux the slope here is what is the equation says slope here is v d c divided by n 1 this is see d phi by d t is v d c divided by n 1. So, v d c divided by n 1 this is d into t. Now, n 1 and n 3 have the same number of turns voltage applied to the coil is also the same n 3 is connected across v d c n 1 is also connected across v d c. So, d phi is minus d phi by d t is v d c divided by n 1. Now, d into t d into d into d into d into d into d is greater than 0.5. So, what will happen when I close the switch flux falls, but then slope of the line is the same it is again v d c divided by n 3 that is equal to n 1 this slope is the same, but then switch is on for a longer time this is for a shorter time definitely flux will not become 0 flux will not become 0 at t there is some finite flux at the end of the first cycle. In the second cycle again I will close what will happen now same condition slope is the same v d c divided by n 1 the switch is on for a longer time this is d into t for the second cycle it has reached a much higher value after sometime I will open the switch again it is v d c divided by n 3 or n 1. So, end the flux in the core at the end of the second cycle is I will repeat the value of the flux at the end of the second cycle is much higher than the flux the value of the flux at the end of the first cycle because this period is smaller than this period slope is the same slope is the same this period is much higher than this. So, definitely it will not become 0 again in the second cycle I will increase now this value is higher than the previous and the value of flux at the end of 2 t is higher than the value of flux at t in the third cycle what will happen it will go further. So, what may happen of flux sorry transformer will saturate and once the core saturates you know there is no d phi by d t current is limited by only current is limited by its internal resistance. Now, in order to have high q you are used leads wire or whatever which has a very small resistance and current will be too high may damage your source you may damage your switch or a transformer may damage everything. So, if I connect the tertiary winding to the coil sorry if I connect the tertiary winding to the source and if n 1 is equal to n 3 d cannot be greater than 0.5 d cannot be greater than 0.5 n 1 is equal to n 3 my fabrication becomes designing and fabrication if I become relatively simpler. So, this what it is given the equivalent circuits here this is negative d phi by d t this is the equivalent circuit when I close the switch current in l m increase at the magnetizing current when I open the switch it was through source here if n 1 is equal to n 3 it is the same voltage itself. So, increase in current should be equal to decrease in current l m is the same source value is the same. So, duration should be the same if one is if off period is smaller than the on period flux will saturate sorry core will saturate if on period is less than the off period flux in the core becomes 0 no problem flux core transformer will not saturate core will saturate. Therefore, d is less than 5 discontinuous flux operation it is something like this slopes are the same because number of turns is the same voltage is also the same these are the various voltage wave forms primary current wave form through the tertiary this is the current through d 2 current through d 2 current through l f is this this current is almost like a current source I will say almost constant current I am trying to maintain increase or decreases increase or decreases. So, d 2 current peak current rating is the peak current that is flowing through l f these are the various this is about forward converter there are various issues as well these are some special cases see here I have not connected to the supply tertiary winding could be a fly back the capacitor I do not know whether to explain this or not I will just anyway I will explain. Suppose, what if I do not have a tertiary winding see if I do not have a tertiary winding and if there is d 2 here then the circuit cannot work because there is no path for the magnetizing current assume that there is no d 2 assume there is no d 2 I will just explain to you circuit here there is no d 2. Now, you see current enters the dot current leaves the dot no problem this is the path when I open the switch current enter the dot. So, the magnetizing current should enter the dot can it enter the in the secondary yes no problem. So, the secondary whatever the current that is flowing magnetizing current can flow through this path. So, now d f has to carry in addition to l f sorry in addition to whatever the current inductor in addition to inductor current it has to carry the magnetizing current as well will this work my gut feeling is it may not work why see what happens here when I close this when I open the switch the equivalent circuit is something like this equivalent circuit is something like this. It is actually what is the voltage equation here for this coil what is the voltage applied is 0 I am applying a 0 voltage here voltage. So, will the flux decay it entirely depends on the winding resistance entirely depends on the winding resistance if the winding resistance is very small flux will not decay flux will not decay something similar to inductor current flowing like this. In the sense if the resistance is very small current will remain approximately constant if the current remains approximately constant flux in the core also will remain approximately constant. So, when I had open the switch sorry when I had close the switch flux increases when I open the switch magnetizing current trying to tries to flow through this path yes there is a path in the very first cycle. Since the winding resistance is very small your current may not decay the equation is l d a by d t plus r into i is equal to 0 if r is very small. So, l d a by d t is equal to 0 in other words i remains constant i is constant is not it l d a by d t is equal to 0 l cannot be 0. So, d a by d t is 0. So, the I am I will remain constant. So, magnetizing current will not decay in the second cycle it the flux will start from a finite value and therefore, the core may saturate. So, you require three windings there is no way about, but then there are modifications may be as we go along if time permits we will see otherwise I will encourage you to go through the literature both again even in forward converter as well as fly back converter. If I see the B H low operation in the first quadrant only operation in the quadrant only now how do I increase in other words I am using a transformer I am using a core, but I am not using the other half of the B H curve can I improve the utilization the core. So, use bidirectional core excitation that is something similar to AC current excitation current becomes negative. So, B H loop is transverse in the negative direction as well can I use it yes let us see in other words I may have to use a two forward converters may be this converter is known as the push pull converter push pull converter why both converters deliver power to the load in each half cycle both of them are pushing power to the load both halfs name should have been push push converter, but then it is known as a push pull converter. I do not think I can start this push pull converter look something like this as the power rating increases one has to go from forward to push pull forward converter is suitable till say 500 to 700 watts or so the reasons are same as what we give for fly back the forward as the power rating increases definitely I need to increase the I have to use the magnetics I have to improve the utilization of the magnetics.   In a fly back converter when the air gap is introduced in the transformer to reduce saturation how can it fall output voltage equation? Yeah I agree I understand your question. If there is an air gap see whatever the expression that we have derived first of all there are lot of approximation that we have made then it is ok see V R deriving an expression what is the voltage equation how did you derive the transfer of equation by equating volt second per turn volt second per turn. So what is the voltage applied to the primary? I said V dc but it is wrong it is not V dc see there are one is what are the errors that are introduced one is this coil has its own resistance R this device has its own voltage drop. So therefore actually it is V dc minus i into R minus V switch is the voltage applied to the coil if the winding resistance is very small if V s is very small compared to this then yes I can neglect otherwise you have to take the device drop especially if I am using a very low solar voltage panel then I have to switch now one volt may be comparable with your 12 volt solar panel then I have to take this into account this drops this drops. So that has to be taken care while designing the number of turns is suitable values of N 1 and N 2 take now it is not definitely not V dc we are not applying V dc to the coil voltage actual voltage is resistance drop minus the saturation for example, see you know AC what is the voltage induced in this what is the voltage here definitely not V 1 N 1 into N 2 definitely not V 1 into it is V 1 by V 2 is equal to N 1 by N 2 no this is not equal it is true for an ideal transformer it is true for an ideal transformer actually it is E 1 is to E 2 is equal to N 1 by N 2 E 1 is E 2 is equal to N 1 by N 2 not V 1 by V 2 is equal to N 1 by N 2 I need to the winding resistance leakage everything here in addition there is a switch drop as well and that may be comparable with or comparable to the solar panel itself. So, 1 volt or 2 volts you may not be able to neglect. So, take care while choosing the suitable turns ratio it is not V 1 by V 2 is equal to N 1 by N 2 please. Sir, in a discontinuous conduction mode the current is always going to be in 0 level. So, for operating in a converter in a discontinuous mode it reduce our efficiency. So, how can we. Which converter are you talking about? Sir, what the forward converter? Now, what do you mean by conduction and discontinuous conduction? Sir, continuous. No, no, what exactly. Sir, because if we operate our. No, please see there are I am not talking about load current being discontinuous the flux in the core is discontinuous please it is not the load current see if I take a just an ordinary buck discontinuous conduction means the inductor current see there is a difference see ordinary buck converter when I am saying discontinuous conduction it is this inductor current becoming discontinuous becoming 0 prior to just prior to closing the switch it is something like this I L for a buck converter when in fly back and forward or using a transformer or in isolated DC to DC converter in isolated DC to DC they come fly back forward and push pull discontinuous means flux in the core flux in the core flux in the core see if you see the current waveforms this is the inductor current is almost a current source almost a current source, but the flux has become 0 see here flux has become 0 much before closing the switch for the second time. So, this is discontinuous conduction please do not mix up two issues in the sense in non isolated converters discontinuous conduction implies inductor current in isolated DC to DC converter discontinuous implies flux in the core this current is approximately current source, but then flux in the core has become 0 here and therefore, the discontinuous conduction. So, another question so in that case what is our condition of the load current so whether we are supplying by a discontinuous mode to a load. So, what is the load current condition whether it is continuous or discontinuous where have you connected the load you tell me you are connecting the load across the capacitor is not it this voltage is constant we are regulating this voltage at a constant value. If the circuit is complete current will flow there is nothing like discontinuous load current you can have discontinuity in load current only if there is an open circuit because v naught is regulated at a particular value it is it is supposed to remain constant v naught is supposed to remain constant. So, if the circuit is complete current has to flow so load current will remain constant as long as load resistance remains constant that has nothing to do with discontinuity in flux or whatever please. So, do not try to make seen drives for that matter when you said discontinuous conduction current in the armature is 0 in non isolated power supplies discontinuous implies inductor current becomes 0 not the load current you are connecting the load across the capacitor and that voltage is supposed to remain constant if there is if the circuit is complete current has to flow discontinuity in current can happen only when there is an open circuit is that ok. Paramati go ahead with your question. My question is what is the frequency range of fly back converter when we are using ferrite core transformer? Frequency depends on the power ratings or power and voltage ratings I cannot give any unique answer it all depends on the power rating see there are two types of switching one is the hard switching and a soft switching if you are doing a very hard switching in order to reduce the size you may try to increase the switching frequency your losses will increase you may not be able to go for a higher value it all depends on the power rating the way you switch the way you switch are you doing a soft switching or a hard switching what do you mean by hard switching soft switching I will tell you sometime later towards the end of may be next lecture it all see there is no unique answer to your question it depends on the amount of power the device has to handle the voltage and current rating now please see there is a question from Schupper regarding load current one parameter we have to consider that boundary between two modes what will be decided the value of inductor hello sir why forward converter can be designed for a higher rating compared to fly back converter you try to understand the operation of fly back and forward what are you doing in fly back you are storing the magnetizing energy you know you are storing energy in the magnetizing inductance and transferring it to the output stage what are you doing in forward you are simultaneously drawing the current primary and secondary both of them are carrying current simultaneously so you have to design the transformer accordingly cross sectional area of the conductor that cross sectional area of the conductor that is used to wind the primary coil is much thicker than the one that is used in fly back fly back it has to carry only the magnetizing current whereas in forward the primary current the primary coil has to carry magnetizing current as well as the equivalent secondary current you are using a thicker conductor see the difference in operation itself what is the effect of leakage used in fly back converter what do you mean by what do you mean by what is the effect of leakage you have to take care of the energy associated with the leakage inductance I showed you the circuit configuration in the last class I will show you the equivalent circuit transformer equivalent circuit see here this is the leakage magnetizing this is the fly back when I close the switch yes this is the path when I open the switch there is a path for the magnetizing current there is no path for the energy that is stored in a leakage inductance so if you do not have any path definitely there will be a voltage spike appearing across this switch might damage of course there are ways either you put a snubber across the switch you put a snubber across the switch or you modify the circuit itself the circuit modification I had shown in the last class please refer to yesterday's lecture note it is there is one power circuit configuration I have why again I have to draw when I close both the switches yes this is the path when I open the switch whatever the current that is flowing the magnetizing inductance it will try to flow through this path sorry do not see it so this is the path when you close s 1 and s 2 this is the direction of current this direction current has to be maintained is there a path yes there is a path that current now can flow through bold lines I will draw this is to take care of leakage energy associated with leakage inductance there are other way circuits also


I'm pleased to introduce Carl Youngblood who will address us next. Carl has been an avid technology enthusiast since early childhood and has been earning a living as a software engineer since 1997. He was a Mormon missionary for two years in Brazil where his newfound aptitude for language led him to eventually get a degree in Portuguese from Brigham Young University and later a master's in computer science from the University of Washington. Carl's struggle to apply his faith meaningfully in today's rapidly changing world led him to co-found the Mormon Transhumanist Association in 2006. Carl is passionate about science, technology, religion, philosophy and the performing arts. And he is vice president director and co-founder of the MTA. Did I hit buttons here? So they just gave away all my slides. Sorry about that. Hopefully you guys didn't, you weren't really paying any attention, right? Just a second here. It's great to be with you. By the way, we actually do productive pro-social beneficial humanitarian things with the money you give us. I just wanted to clarify that. Please send your... So far it's a very low amount between... It's negative, right? Yeah, actually it's negative. Anyway, transhumanists are often characterized as technological cheerleaders, naively proclaiming that advances in science and technology will in and of themselves eventually and inevitably cure all human ills. There is certainly some justification for this stereotype, but the same insights that have led many in this movement to make surprising positive predictions about the future have also caused many of them to explore potential challenges and existential risks, more thoroughly and creatively than others. Religious transhumanists in particular have the opportunity to make some urgent and vital contributions, which is the subject of my talk today. Using the term disruption when talking about technology has become a cliche among Silicon Valley entrepreneurs, but it is particularly apt when we're talking not about those who are building the new technologies, but those who are left behind, those who are disrupted. The term was first used in the context of technological innovation by a claimed business management expert and happens to be Mormon as well, Clayton Christensen. He used it to refer to the type of technological innovation that takes incumbents by surprise and leaves them unable to adapt to new market conditions. So there's a number of alarming disruptions that are currently taking place much more quickly than many people realize or are prepared for. In general, we're moving away from the centralized technologies of the 20th century towards decentralized, headless replacements. Mass media is giving way to internet-based news, streaming entertainment and aggregation services. Newspapers, mainstream media outlets and cable channels are rapidly losing market share. Increased consumer choice also means that citizens are less likely than ever to participate in a shared civic culture or narrative, which increases political polarization and gridlock. Viral sharing, filter bubbles and click-based ad revenues are incentivizing the spread of disinformation, so-called fake news to the point where it is influencing politics and threatening national security. And internet giants have a short-term profit interest in allowing it to spread, unfortunately. They're starting to work on it, though. I got something from Facebook saying they take this seriously. So we'll see what happens. Centralized energy and utility grids are beginning to be replaced by rooftop solar and battery storage. Power companies that planned their growth based on revenue projections from selling generated electricity are being relegated more and more to grid management, where there are far tighter profit margins and much less room for expansion. The exponential cheapening of solar technology took them by surprise. Blockchain technology has enabled individuals to anonymously transfer any amount of monetary value across national borders without reliance on any central authority. If you want to know how that even works, I'd be happy to discuss it with you. I'm really fascinated by this. It has also been rapidly adopted by the financial industry. We were surprised by that. I thought there would be resistance, but they quickly jumped on the bandwagon. And the second generation of this technology is now getting started. Smart contracts will make it possible to create unstoppable companies operating outside of all legal jurisdictions funded directly by anonymous stakeholders on the blockchain. They will also enable more transparent and secure governance in both public and private spheres. Eventually we may even see more traditional functions of government such as health care, police and military protection, fire protection, whatever, managed and arbitrated through these kinds of anonymous exchanges. Blockchain technologies have also been instrumental in the emergence of a truly decentralized internet that is no longer reliant on central authorities for name resolution. So you think the internet's decentralized, but it's really not. There are still authorities in charge of who gets what domain names and they're controlled by governments. Also, authorities in charge of blocking access to servers that are located in physical countries. But with this new technology that really, after the NSA announcement, a lot of hackers really got PO'd with the NSA and other people. And they are now building a blockchain-based decentralized internet that will be truly unstoppable. So the only way it'll be impossible for countries to control internet access without disconnecting their citizens entirely, which would completely handicap them in today's economy. So we'll probably see another land grab for domain names as well when that happens as people jump on these totally decentralized services. There's recently been a lot of debate about so-called sharing economy and the industries that it's disrupting. Uber and Airbnb are the most well-known examples of this trend and they're having a significant impact on the transportation and hospitality sectors. Uber claims that its current system is only the beginning. Eventually it intends to get rid of drivers altogether and is heavily researching autonomous driving technologies, along with Google, Tesla and other car manufacturers. And although these technologies are expected to become available to consumers within the next decade, a more immediate disruption is already taking place in the trucking industry. Full driverless navigation is still difficult in urban areas where a high level of intelligence is required for safe navigation. But driving on interstate highways is a solved problem. And trucking companies are already making autonomous shipments. This happened a few months ago with Budweiser. This is especially alarming when you consider that truck driver is currently the most commonly reported profession on tax returns in the United States, employing over 3.5 million people. Within the next five years, most of these truck drivers will be out of a job. Think about that. Reports of a strong economic recovery mask a more serious underlying problem. A growing number of low skilled laborers have ceased to look for work altogether and therefore they're not even counted in the commonly used unemployment rate. Most people report unemployment at like 5%, 6%, 7%. It's really probably more like 15 to 20%. The economists recently reported on research conducted by Ann Case and Angus Deaton for the Brookings Institute. They said, quote, the authors suspect more amorphous long term forces are at work. The fundamental cause is still a familiar tale of economic malaise. Trade and technological progress have snuffed out opportunities for the low skilled, especially in manufacturing, but social changes are also in play. As economic life has become less secure, low skilled white men have tended towards unstable cohabiting relationships rather than marriages. They have abandoned traditional communal religion in favor of churches that emphasize personal identity and they have become more likely to stop working or looking for work entirely. The breakdown of family, community and clear structures of life in favor of individual choice has liberated many but left others who fail, blaming themselves and feeling helpless and desperate. In his recent book Men Without Work, demographer Nicholas Eberstadt provides compelling evidence of the problems emerging from these macroeconomic trends. He explains, here then is the underlying contradiction of economic life in America's second gilded age. A period of what might at best be described as indifferent economic growth has somehow produced markedly more wealth for its wealth holders and markedly less work for its workers. This paradox may help explain a number of otherwise perplexing features of our time, such as the steep drop in popular satisfaction with the direction of the country, the increasing attraction of extremist voices in electoral politics, and why overwhelming majorities continue to tell public opinion pollsters year after year that our ever richer America is still stuck in a recession. Though I don't have time to delve further into these details, this brief survey of recent technological trends and the larger effects they're having on society helps to demonstrate how profoundly our world is changing in good and bad ways. The challenges caused by these rapid accelerating changes are more than just logistical and their solutions will require more than just scientific research. When we crafted the Mormon transhumanist affirmation, we deliberately placed a qualifier on our claim about the importance of science and technology in realizing human exaltation. We believe that these are critical and are among the means ordained of God for this purpose, but other ingredients are also necessary, including compassionate outreach and prophetic vision. Long-held narratives such as those about rugged individualism, self-reliance, and national pride may need to be reframed in light of our world's increasingly connected economy and environment. Many traditional religious narratives are failing to resonate with and inspire people as they used to and are being rejected in favor of more virulent forms of fundamentalism and extremism. Trumbling social structures are failing to sustain and support displaced workers at their time of greatest need. Evolving narratives and the changing needs of every era have fueled a constant demand for profits. That's P-R-O-P-H-E-T-S. And the accelerating pace of change in this, the dispensation of the fullness of times, has made the need for prophetic inspiration even more urgent. In the words of Emerson, the need was never greater for new revelation than now. The Mormon tradition offers many remarkable insights on prophecy and prophets, much of which I believe has been neglected and misunderstood as prophecy has become institutionalized. Most Mormons today think of prophethood and presidency in the church as synonymous and habitually refer to the president of the church as the prophet. At their local and general conferences, Mormons ritualistically affirm the top leaders of the church as prophets, seers, and revelators, for the most part confining their use of these terms to the church's highest leadership. But the early Mormon conception of prophet differed in significant ways and can still be found underneath this institutional veneer. Joseph Smith's view of prophecy and revelation was radically egalitarian, a source of inspiration that rained down on men, women, and children. Indeed, Joseph's spiritual journey began with faith in the premise that anyone who lacked wisdom could seek inspiration. When asked if he was a prophet, he replied, Yes, and so is everyone else who has the testimony of Jesus, for it is the spirit of prophecy. Joseph based his views on the biblical exhortations of Paul, who taught that people should be eager to prophesy. In fact, in the KJV it says they should covet to prophesy. And Moses, who when told that others were prophesying in the camp, explained, Are you jealous for my sake? Would that all the Lord's people were prophets, and that the Lord would put his spirit upon them? The Book of Mormon echoes this egalitarian view of prophecy. Nephi remarked that there were many prophets in the Jerusalem of his days, and Enos later wrote that there were exceedingly many prophets among them. The book also teaches that the Lord shall speak to all nations of the earth, and they shall write it. And tells the story of two prophets, Abinadiah and Samuel, who had no ecclesiastical authority at all. In fact, who condemned those who were in authority? It could be said that the Book of Mormon teaches that prophecy is a common privilege and even a duty shared by all conscientious souls of every religious persuasion throughout the world. And what are the characteristics of a prophet? Prophets discern the signs of the times. They are keenly aware of the zeitgeist. They perceive a pressing need or injustice, and they articulate a call to action that resonates with and mobilizes people. They start social movements. Contrary to popular opinion, prophets rarely predict the future. Rather than being foretellers, they are foretellers, presenting visions of what the future could be in a way that compels people to realize them. The most potent form of prophecy is self-fulfilling. Much in contrast with modern LDS portrayals of Jesus and other prophets as meek and gentle souls who never swore and never raised their voices and who were unceasingly loyal to religious authority, prophets are iconoclasts, ridiculing fraudulent piety and corrupt traditions seeming even to betray their own religion and culture as they do so. Imagine the establishment's reaction to Isaiah when he proclaimed, Your new moons and your appointed festivals my soul hates. They have become a burden to me. I am weary of burying them. When you stretch out your hands, I will hide my eyes from you. Even though you make many prayers, I will not listen. Abraham J. Heschel in his classic work on this topic, The Prophets, explains, The striking surprise is that prophets of Israel were tolerated at all by their people. To the Patriots they seemed pernicious. To the pious multitude blasphemous. To the men in authority seditious. What gave them the strength to demythologize precious certainties, to attack what was holy, to hurl blasphemies at priest and king, to stand up against all in the name of God? The prophets must have been shattered by some cataclysmic experience in order to be able to shatter others. Prophets have a seemingly disproportionate sense of indignation over the injustice in the world. Jesus of Nazareth, for example, was never more angry than when he criticized the Pharisees for their religious arrogance and their oppression of the poor, calling them a generation of vipers. Heschel explains further, The prophets' preoccupation with justice and righteousness has its roots in a powerful awareness of injustice. That justice is a good thing, a fine goal, even a supreme ideal is commonly accepted. What is lacking is a sense of the monstrosity of injustice. Moralists of all ages have been eloquent in singing the praises of virtue. The distinction of the prophets was in their remorseless unveiling of injustice and oppression, in their comprehension of social, political, and religious evils. They were not concerned with the definition, but with the predicament of justice, with the fact that those called upon to apply it defied it. Prophets warn of potential calamities if their voice is not heeded, but their power consists in turning people from their destructive course, rather than in seeing their warnings fulfilled, which brings them no pleasure, setting aside a few rather unprophetic slip-ups on the part of Jonah. Heschel elaborates, The words of the prophet are stern, sour, stinging, but behind his austerity is love and compassion for humanity. Ezekiel sets forth what all other prophets imply. Have I any pleasure in the death of the wicked, says the Lord God, and not rather than he should turn from his way and life? Indeed, every prediction of disaster is in itself an exhortation to repentance. The prophet is sent not only to upbraid, but also to strengthen the weak hands and make firm the feeble knees. Almost every prophet brings consolation, promise, and the hope of reconciliation, along with censure and castigation. He begins with a message of doom. He concludes with a message of hope." While many ancient and modern accounts describe or imagine gods as being indifferent to the plight of humans and concerned with far weightier matters, the prophetic conception of God is one of deep attention to the seemingly trivial details of human actions. Says Heschel, To the prophet no subject is as worthy of consideration as the human plight. In the prophet's message, nothing that has bearing upon good and evil is small or trite in the eyes of God. What the prophets proclaim is God's intimate relatedness to us. It is this fact that puts all of life in a divine perspective in which human rights become, as it were, divine prerogatives. Humanity stands under God's concern." This image of a deeply connected and compassionate God is echoed in the Book of Moses account of the vision of Enoch. And it came to pass that the God of heaven looked upon the residue of the people and he wept. And Enoch bore record of it, saying, How is it that the heavens weep and shed forth their tears as the rain upon the mountains? And Enoch said unto the Lord, How is it thou canst weep, seeing thou art holy and from all eternity to all eternity? The Lord said unto Enoch, Behold, these thy brethren, they are the workmanship of mine own hands.  Wherefore should not the heavens weep? Seeing these shall suffer. These characteristics of keen attention to human interests and to the specific challenges of our time, compassion for the less fortunate, abhorrence of their oppression, and courage to stand up against injustice are the hallmarks of prophecy and should be the aspirations of every true Mormon. Heschel admonishes us. These characteristics of keen attention, sorry, here we are. If intense regard and concern for humanity is the mark of a moral act, then inspiration of the prophets in which God's regard and concern for humanity are disclosed and in which the prophet is entrusted with a mission to help the people must be viewed as an eminently moral act. The moral aspect sets the prophetic act from intellectual, artistic and mystical experiences. The vigorous compassion and creativity of a true spirit of prophecy is what will be required for humanity's successful transition through the turbulent labor pains of our transhuman era. My confident hope is that as secular and religious institutions falter and buckle under the stress of accelerating change, they will in their desperation become more and more willing to try the remedies prescribed to them by those of us who take up the prophetic mantle and articulate compelling visions of the future. There will always be a need for prophecy. Our mastery of present problems is never sufficient to handle them with ease. Ingenuity and inspiration are indispensable. Art always goes before science. May we answer this call and make diligent use of both of these. Thank you.