There were no role models, there was no discussion.  I get there the first day and they call me to the office and the principal tells me, he says, in order for you to go here, you have to look like the rest of the young men. How about, how do you do that? I've always felt like a woman, I never felt like a guy or a man, and I started living as a woman when I was still in my teens and in the beginning I didn't know how or what I was going to do, I just knew it had to be so. In the streets with my friends, hanging on the corner with them drinking and messing with the girls, something that I was doing just to fit in, then at night I would get dressed, go in and get dressed, about 12, one o'clock at night, go in and change clothes and go out in the streets because I knew what was going on out in the streets after one, two o'clock in the morning.  She dismissed me, the guy who was about five years old in the program, and she brought me into the living room and said, it's an accident, and she asked me the question, is that the way it is? And I said, yes mama, that's the way it is.  Who makes this choice and what does it cost them? The answers to these questions can be seen in the lives of gay African American men living in Philadelphia today. Men who exhibit a wide range of personal styles, but who are united by their race and their sexual preference. This is the story of a part of the African American community that after years of silence and persecution is stepping out of the shadows to help save themselves and their community from destruction. I think that black gays need to do more personal integration of their race and their sexuality with the other components of their life more so than the white community. And for that reason, there probably needs to be a special bonding among black gays because it's simply more difficult for us to be gay because we are black, because we come from a community that doesn't want to deal with this issue at all except in very specific, stereotyped ways. The family lies at the heart of African American culture. From the family grows the individual, the church, the community.  Ashley, to tell the truth, I haven't talked to my family about it, only for two reasons. I don't believe in true confessions. I think for me it's important to tell people things that they are equipped to deal with. I want someone to know who's going to be supportive of me. I don't want to go through that combative thing where I have to fight with them about who I am. Also, at the same time, I don't think that my sister needs to justify why she might marry a man or why she's a heterosexual. So for me to try to give an explanation of who I am, I think sort of betrays really who I am. My mother didn't want to accept me at first. And when she found out, she wasn't sure, she didn't want to believe it. Then she asked me, why? I don't know. It's just something that I feel. We went through a thing, a serious thing about my being gay. And I think it's easier for them to think of me simply as their son who is doing various professional and civic activities and think of me as a person that they are very proud of for those reasons, rather than thinking of me as a gay person who was doing the things that I do professionally or in the community. At the time, I didn't understand it. I don't think, at first I thought it was that the fact that she just hated it. But as we've got, Avaz got an older and I talked to my mother, she says it was just, she knew how other people felt and she didn't want me to be hurt by what other people say and how they acted towards me. Being the only son and being the only boy, being the oldest, that was a bit much. I knew how she was going to react once I told them. It was just hard coming out and telling them because the guy was supposed to be the one to keep the family growing. You're supposed to get the mother, the grandchild. When Gary really told me that he was gay, I felt relieved because I knew inside he didn't want me to know and I thought he would hurt himself if I would find out or when he did tell him I said, well at least one thing, I can accept that, at least you're not out here killing anybody or hurting anybody and I will always love you for what you are, no matter what you are, and we can really talk now and work things out and he cried and said, mommy, I just didn't want you to know. From the beginning I mean I was against it, I mean I strongly felt that this wasn't it. And when I came to realize that this is what Whitney wanted and this is what she felt comfortable with, I mean let's put it this way, it grew on me, it grew on me and I feel that she handled it so why couldn't I handle it?  It was exciting because I never imagined that guys who were gay actually got together and talked and lived and breathed and did all the things that they did. We curled out here and we didn't dress in women's clothes though, but we curled out here and put on makeup on occasions, you know and went out and flaunched it. There was a defiance in that time in my teenage years. Being gay in Philadelphia was, I thought it was very exciting, it was very exciting. We had more places to go, although I wasn't of age to go, but I'd sneak in or bought some like age cards to get in. To me the most terrific change has been, it's not a feminine deity, it's just I'm a gay man. It's the assertion of saying I like another man with my mustache, with my beard, with my airing in my ear and he can have his mustache, his beard, his airing in his ear and we like each other. Historically, the gay scene in Philadelphia divided along racial lines.  Few black faces could be seen in the gay pride demonstrations of that time.    One of Unity's founders, James Roberts, read a statement of the organization's purpose.  This organization will undertake concrete action and social change within the gay and lesbian community and among peoples of color. This organization would unite men of color, whether they're gay identified, bisexual or simply men who love other men. There would be three purposes for the existence of this organization. The primary purpose would be to encourage positive self-esteem among gay men of color in this general area, the city of Philadelphia and the surrounding counties. The organization would also protest the racism in the white, middle-class, male-dominated gay and lesbian community. And it would deal with the homophobia and heterosexism that exist among people of color. The barriers, the discrimination, the prejudice that confronted black gay men in Philadelphia began within the African American community itself.  Religious taboos, which will be very strong in the black family. And then the taboo of the black society in general, where being exclusively homosexual is frowned upon because you need to increase your numbers in order to increase your status as a minority and improve your status. There's a lot that comes into play when you start dealing with this great black community who wants to walk around and worry about taking an ass-kicking every day. I was called names. I was bottled and stoned and bricked and all those biblical things. Naturally, the other kids at some point in time, they'll be lost, made, slurs, thrown. And invariably would end up with somebody getting punched out, because we weren't taking that sort of stuff. We had a group of fellas that were going around actually, how can I say it, taking money from you, running you off the street, they actually had girls boarded up in their houses afraid to come out.  I think it was particularly difficult in the first two or three years that I was practicing law because I was in a very large corporate law firm in Philadelphia where homosexuality was something that simply did not exist as a topic to be discussed except as a topic to be ridiculed. You learn to be quiet except in those instances where you think you can actually accomplish something. And learning when to be proactive and say, wait a minute, why did you do that is difficult. And I think it comes with maturity. You don't want to fly off the handle of the senior partner who has just made a joke about gay bashing or about some fairy when he's making points with the other people around him. You will make no points with him or with other people necessarily by calling him the task for that.  And there's a lot, a lot of pain, there's a lot, a lot of suffering that comes along with that term. Being a double minority is hard enough living in this country being black.  Homosexuality is just, it's not cheap this year. And it's just something that everybody's not ready for. Something that everybody's not ready to accept. This is something that's a given when you accept this lifestyle. You know there are obstacles, you know there are landmines, you know there are eggshells and you learn how to walk on the eggshells, you learn how to walk around the landmines and you just kind of like deal with society because society at this point is not ready to deal with us.  The more that I ignored it, the worse my life got. The more I pushed it away, it came back with double and triple force. It's like one of my graduate professors used to say, the energies we repress do not go away because we repress them. Homophobia can contribute to the continuation of unsafe sexual practices. For a man who does not love himself may not care enough to protect himself and his partners from infection with AIDS.  Over half the Philadelphians who have died from AIDS as of 1989 have been black. Most of these have been gay or bisexual men.  I lost several friends to AIDS and I think a lot of people still don't know the devastation of it. They're still carefree, unconcerned. I don't think they really know until they've lost someone really close and I have. I've talked to people where a member of their family has died and they're not allowed to come to the funeral.   They don't know where to go. The community was devastated because so many families were being robbed with the death of a youth. The church was, they didn't express the devastation but they were certainly concerned because I know that one particular instance we lost the minister, we lost several prominent people. And suddenly people began to take notice that this really is a horrible killer. They came in, doctors came in, about seven or eight of them came in. I knew them, you know. And she finally broke down and told me. She told me I did have a choice. Rather I could tell my mother, my family if I chose to. So I told my mom. And like Gary and I are very close. We do a lot together. And my daughter, she helps out a lot too. She's not ashamed, you know, or afraid. But her husband, my daughter's husband, he did, she just had a baby.  And she explained to him that you can't catch it like that.  Y'all don't have it. I guess he won't have it either. The Black gay community has begun to respond, to defend itself against AIDS, to help rebuild itself image by taking responsibility for its own survival. When you're addressing an issue that affects you as an individual and your lifestyle, then you have to take issue on that not only here in the street, but in the political arena as well. So I think the educational process is not only for our health and our jevity, but how it affects us in the political arena as well. Exactly. So we have to make those numbers to make that difference. So you can talk about what you feel about and what's a part of your lifestyle, not only here on the street corner, but in the rooms that differences can be made. I think we have to start looking at that.  You do anything that you want to do.  We have that right. Right. African American gay men are raising families, helping to provide stable, supportive homes for children from communities wracked by drugs and poverty. You're giving something to a person that really needed it at that time and they still need it with what's going on the world. So you have so many children that people just don't care about at all.   African American gay men are fighting to save lives by providing AIDS educational outreach to the community wherever it is needed. Black people are dying from very high numbers and it doesn't seem that the education is specific enough for us. We still think that a lot of people still think that it's a white gay disease, which it's not. That's why I emphasize that Black people are dying because we haven't gotten information. We still have a difficult time accepting the fact that AIDS is running rampant in our community. They don't really care about people dying or my friends dying. It doesn't seem like that I'm working fast enough or harder than that. It's important for me to work with Black gay people in my community. I mean that's really important. So this is where I belong in terms of working with people.  I should say that's my calling for lack of a better word.  Everyone in this room had lost friends and lovers to AIDS. Some were PWAs themselves. If these men were to survive as individuals, they had to organize as a community for no one in power cares about Black gay men. The federal government will not save them. The city government will not save them. The medical profession will not save them. There is simply too much prejudice, too little money. To claim their freedom, Black gay men must bear the responsibility for saving themselves. They had to organize to demand the services they needed to survive. They had to organize to build their future through actions based on love and care. It's togetherness. It's something we all should have. Being able to share things, do things with. Instead of, I've got, what can we do for me? It's what can we do for each other? Togetherness is what we mean, more of that. Between crack and AIDS, our community is being decimated. And if we don't do something now, while we still can, while we still have people who know how to do something about what's going on, we're going to be in trouble because we're losing people from all levels. Every time we lose one individual, we're damaged, we're hurt. So we need to work on it right now. We really need to get going. We really need to get moving with this thing. We're the ones who have held families together. And we're not some segment over here. We're the brothers, we're the sisters, we're the aunts, we're the uncles, we're the teachers, the preachers, all of that. We're part of a war and a roof for the black community. And unless we're dealt with constructively, the community cannot survive.


So, Wing Chun, if you talk about passively, this is the stance, so it's opposite of intercepting his fist. What Wing Chun does, the strategy is to block and attack at the same time, okay? So if he's attacking, I'm blocking and attacking at the same time, or if it's straight, right? I want to block and attack at the same time, okay? Which is pretty fast. Pretty fast kind of compared to other martial arts, because other martial arts will be to attack, when you block and then punch, right? Or it will be to block and then punch, right? So most martial arts will be two beats. In Wing Chun, we condense that into one beat, right? One beat, right? One beat, block and attack at the same time. So that's where Wing Chun is very useful, because it's that much faster. Now, that is the strategy of Wing Chun, is to be able to do those things simultaneously.


Good afternoon everybody. I will come back to the post lunch session of the first day. Before breaking for lunch, we had derived the heat diffusion equation and one of the things which we wanted to emphasize again was what is this heat diffusion equation? What are we trying to find out? Essentially, our aim in any energy equation is to get the heat transfer rate. And heat transfer is directly related as we saw in the first lecture, heat transfer is directly related to the driving temperature difference. So, our aim through in any of these issues actually whether it is conduction or convection or even radiation for that matter, we are trying to get the temperature distribution. It means how does temperature vary in the given problem in the given domain of interest. So, whether if it is a conduction problem, how does temperature vary with respect to that space variable which is x, y or z. And if we are able to get a solution to an equation which gives me the final answer in the form t is a function of x, y, z, then I can calculate q by using Fourier's law by getting the differentiation of the temperature distribution. I can calculate heat flux etcetera in all possible direction. So, the bottom line or the main main objective which we are interested in when we derive the heat diffusion equation is to obtain the temperature distribution or the temperature field as we call it. So, we our aim is to not get q directly, our aim is to get t as a function of x, y, z or time. So, this is the time. So, if you are able to get this distribution that means I want t as a function of x, y, z and t which means my differential equation should not be in terms of q which is the dependent variable. What are my independent variables x, y, z, t a combination of these or all of these, these are the independent variables. By independent variables I mean if I have a differential equation d y by d x is equal to 2 hypothetically, x is called as the independent variable, y is called as the dependent variable. This is the dependent variable, this is the independent variable that means what I control and what is dependent on what I control. So, x, y, z and t are the independent variables here and temperature is the dependent variable. So, I want therefore, a differential equation not in terms of q, but actually in terms of t that is the aim. In fact, you start off with this box with this rectangular parallelepiped etcetera where you write everything in terms of q x, q y, q z so on and so forth. This was what you did and when we did that we did not stop with the final form of the equation as d q x by d x plus d q y by d y plus d q z by d z plus volumetric generation term is equal to rho v c p d t by d d time. We did not stop with this form. In fact, I will just go back to the document see here. We came up with this form and right here 2.16 this equation this was not the differential form that we stopped with. This is also ok, but this relates temperature on one side and heat transfer rates on the other side. I do not want heat transfer rate, I want the temperature distribution. Therefore, we substitute q in terms of the temperatures by using Fourier's law and substitute for the heat transfer rates here and then once I finish this mathematics, I come up with what I call as a complete general. This is the most general form of the heat diffusion equation in the Cartesian coordinates. Most general y because when we derive this, we did not make any assumptions on the property k. We took temperature to be a function of space x, y, z and time only we made a statement that the volumetric heat generation rate is uniform. That means it is not that the volumetric heat generation rate is more in one part and less in other part. It is not more here and less here. We said q dot is a constant for the given control volume. So, volumetric heat generation rate is constant. Apart from that, we said that rho C p of course are constant. Beyond that, we did not make any assumption. Therefore, this is the most general form of the heat diffusion equation. This I think all undergraduate institutions teach this. It is one of the favorite questions for teachers to ask, students to derive this etcetera, but when we are deriving it more often than not, we derive it just as a routine exercise without understanding why what is done. For example, this one Taylor series which Professor Prabhu went over that Taylor series expansion is a logical obvious step, but people, students most of the time just what we say memorize this step without understanding what this is and how this is come. This is not come from thin air. This is just a mathematical function f of x plus h is equal to f of x plus d f by d x times h so on and so forth. One of the first things that we study when we do calculus definition of limits, this comes from there. So, this is the most general form of the equation and from this solution of this equation, we can get temperature distribution as a function of x, y, z and time as I mentioned. So, you would get, I would get when I solve this differential equation, I would get t as a function of x, y, z and time. So, I would get t in general as x, y, z and t and if I want this to be a two dimensional conduction, then I would have to eliminate these two. If I want it to be one dimensional, it can just be function of x, y, z etcetera. It need not be a function of t at least for the first part of this conduction course, we would have temperature or a steady state distribution that we are going to talk about. Now, various simplifications, well what kind of an equation is this? This is a second order, why do I know it is second order? Because it is d square t by dx square form.  So, it is quite a complicated equation in terms of its appearance actually and almost all of us will say I cannot solve this. So, we can solve this numerically, but to obtain analytical solutions to obtain solutions using paper and pen, it is very difficult to do using this equation therefore, we go in for certain simplifications or approximations. So, in fact that is why I said in the morning we need to list down the assumptions that we make when we solve a problem. Are we taking 2 d? Are we taking 1 d? Actually probably in real life the problem might be a two dimensional problem, but if we feel that one dimensional solution is to get an idea of what is the range of this temperature, may be it is off by a factor of 0.2 or something, but that is ok. I will at least get an idea of the range of operating temperatures then may be one dimensional conduction analysis is also ok. So, looking at the problem, looking at the situation, looking at the accuracy needed we can go in for 1 d, 2 d or 3 d or transient mode of solution. So, first approximation or assumption is when k is constant this comes out, k comes out of all the differential sign I get q dot by k here and rho C p by k was defined as 1 over alpha. If I say the steady state problem temperature does not change with respect to time. What do I mean by steady state? If I if I measure the temperature now and measure it say after 15 minutes after 2 hours, tomorrow day after tomorrow whatever it is things do not change with respect to time. That means it is invariant with respect to time right hand side drops off I am left with only left hand side terms right hand side goes to 0 automatically that is the case this is my general form with where we are dealing with steady state 3 dimensional conduction with variable thermal conductivity. Why is it variable? Because k is inside the bracket it is not taken out therefore it is a variable thermal conductivity q dot with uniform volumetric heat generation. So, equation 2.20 represents 3 d steady conduction problem conduction equation with uniform volumetric heat generation and variable thermal conductivity. Now in this I put q dot equal to 0 this goes off I put 1 d in x direction this term that is d by d by and d by d z go off ultimately I am left with d by d x of k d t by d x equal to 0 1 dimensional steady state 1 dimensional x steady state no volumetric heat generation this partial derivatives therefore become regular derivatives because we are talking of 1 d problem and if k is a constant k comes out you can divide through by k I get a very very nice equation that is d square t by d x square equal to 0.  So, this is the basic general 3 d unsteady equation with uniform volumetric heat generation and variable thermal conductivity. So, this is the most general equation now I said let us get 1 d form for this. So, if I say steady state. So, when we list the assumptions in a problem we will put steady state 1 this implies d by d t of everything is equal to 0. So, I will cancel this and put this reason as number 1 assumption 1 cancels it this no volumetric heat generation implies q dot equal to 0. So, this goes to 0 this is approximation 2 assumption 3 is 1 dimensional in x implies what d by d x. d y of everything is 0 and d by d z of everything is 0. So, this and this go off because of assumption or approximation number 3 and I will therefore get the differential equation as d by d x of k d t by d x equal to 0. Now, fourth assumption was k is a constant this implies d square t by d x square equal to 0. So, k is a constant this gives me a very easy to solve. Simple what kind of an equation is this second order equation partial or ordinary ordinary differential equations. So, this is second order ODE constant coefficient basically there is one in front of it right hand side is 0 it is a very easy equation for which I know the analytical solution. I know the analytical solution means I can derive this very easily. So, second order equation means I need two boundary conditions. So, at x is equal to x 1 I should specify t at x is equal to x 2 I should specify another t. So, two boundary conditions that means when I integrate this equation when I integrate this equation I will get let us do it first step will give me d t by d x is equal to c 1 second integration will give me t of x is equal to c 1 x plus c 2. So, in order to get c 1 and c 2 I will apply this boundary conditions x is equal to x 1 I will get t 1. So, I will get t 1 is equal to c 1 x 1 plus c 2 t 2 equal to c 2 x 2 plus c 2 you subtract one from the other you can eliminate c 1 you can eliminate c 2 get c 1 so on and so forth it is not a big deal. So, all of us know how to solve this equation. Now, let us just go and do this here it is already done for us I will come back to this problem in a minute. This governing equation we said was second order ordinary differential equation and this one has k inside we have taken k out in this equation. So, 2.220 a is almost identical to the one we wrote on the white board except that the k has been pulled out. What are the possible boundary conditions? I said we need two boundary conditions here and the possible boundary and initial conditions initial conditions are important when we are dealing with a transient or time varying problem means what? If I have temperature as a function of time that means I have where I am saying temperature varies with respect to time then it is only logical that I give a temperature initial temperature. For example, if a metal is coming out from a casting or something it has to be cooled so it is coming out at say 800 degree centigrade that has to be given it cannot come out at 500 and expect the same behavior as you would expect one hour later if it came at 800 degree centigrade. So, we always have to given initial condition in case of a transient problem. So, that is why we say boundary and initial conditions what are the boundary conditions? What are the forms of boundary conditions we can have? One I already told you guys this is this one. So, I have a prescribed temperature at two different boundaries x is equal to x 1, t is equal to t 1, x is equal to x 2, t equal to t 2. What are the other forms? So, let us just go to that because heat conduction equation is second order in the spatial coordinates two boundary conditions must be expressed for each coordinate to describe the system. Suppose I had a two second order differential equation this one I had shown was p square t by dx square. Suppose I had governing equation for example like this I had a plate this is a hypothetical thing, but in 2D conduction we always give this kind of problem this is the coordinate axis t 1, t 1, t 0, t 0. So, obviously this is a two dimensional problem 2D heat conduction problem we know logically that if these two are at higher temperature let us say t naught greater than t 1. So, heat is coming from here and here higher temperature heat flow is going to be like this. So, I have to have d square t by dx square plus d square t by dy square equal to 0 with k is equal to constant. So, this is a second order PDE in x and y. So, for this equation I need four boundary conditions y I need two boundary conditions in x is equal to x 1 x is equal to x 2 y is equal to y 1 y equal to y 2 this y 1 y 2 may be 0 etcetera that I do not care, but definitely let us say if this is a plate of length l and height h I can specify four boundary conditions very easily. So, at this is the x axis at for a y axis we say x is equal to 0. So, x is equal to 0 t equal to t naught y equal to 0 t equal to t naught we got two boundary conditions let us write it down. x is equal to l on this phase x is equal to l t is equal to t 1 y is equal to h t is equal to t 1 y is equal to h represents this phase distance h from here. So, I have four boundary conditions which have been specified for this problem. So, all these boundary conditions incidentally have been constant temperature prescribed boundary conditions, but in real life we can have need not be constant temperature it can be constant heat flux it can be insulated it can be free convection or force convection boundary conditions by that what I mean let us say let us take the same rectangle and I say this one is t naught this is insulated what do you mean by insulated no heat is flowing through the surface. So, instead of t naught I specify this as an insulated boundary condition which means I mean which means I say q is equal to 0 through the surface. So, that gives me an insulated boundary condition. So, we are going to see how to mathematically represent these conditions the commonly listed conditions are given here in this table the first one is the first one is prescribed constant temperature at x is equal to 0 and at all times t temperature is fixed at t s this one prescribed surface temperature prescribed or constant heat flux by constant heat flux condition I mean that let me just go back here constant heat flux condition heat flux condition by that I mean q double prime is equal to constant what does that mean how do I relate temperature and heat flux how do I relate temperature and heat flux temperature and heat flux are related by Fourier's law. So, if q double prime is constant I can basically say what let us just go back here minus k d t by d x at the wall is constant what is that q double prime is what minus k d t by d x by Fourier's law how did we get that q is equal to minus k a d t by d x I have divided by a I got this one. So, this is a constant. So, why have I converted this heat flux boundary condition to a temperature boundary condition because my differential equation was d square t by d x square form we have to remember that the dependent variable is not q, but t. So, though I have a constant heat flux boundary condition let us say solar radiation I have a flat panel this is the collector I think many of you are familiar with solar radiation business. So, I have radiation is incident at the rate of g watt per meter square this is a constant heat flux boundary conditions g is specified and this remains constant at the surface. So, if I put the coordinates like this at x is equal to 0 q is q double prime is equal to g that is not useful for me to solve this equation because it has independent dependent variable as t what do I do therefore is to write this in terms of d t by d x at x is equal to 0 at the wall at x is equal to 0 q double prime is fixed. Therefore, I can relate temperature or its derivative to a heat flux. So, with this in mind again why am I emphasizing this is that you can have heat flux boundary condition, but we have to be able to convert it to a temperature function. Now, if the surface is insulated that means there is no heat transfer to the through the surface insulated or adiabatic what is adiabatic thermodynamics tells me adiabatic means something where there is no heat transfer. So, in adiabatic or insulated surface implies q double prime of s equal to 0 very nice why is it very nice because this tells me d t by d x d t by d x is equal to 0. So, very powerful equation I have this q double prime is minus k d t by d x at x is equal to 0 I have this equation I am just setting the left hand side q double prime to 0 k you can divide through by k I will get d t by d x at the wall is equal to 0 what is this d t by d x at the wall temperature gradient at the wall is equal to 0. Remember fluid mechanics we had d u by d y d u by d y was related directly to the shear stress here also d t by d x we are calling we can call that y basically gradient gradient of temperature with respect to the coordinate direction that is directly related to the heat transfer rate we will see that later. So, d t by d x equal to 0 is a very very useful boundary condition not anywhere it is at the wall this is for insulated boundary condition. And it essentially tells me that at the surface and just before that there is no temperature gradient last of the this is called boundary condition of the first kind this is called the boundary condition of the second kind this is a special case of 2 2 is constant wall heat flux case finite heat flux. And when the finite value is turned to 0 you get this one d t by d x is equal to 0 and you can see very nicely it is shown these are all taken representations from various text books only they also reproduce them this represents the slope d t by the blue line here represents the slope d t by d x essentially is a slope of the temperature distribution where is it is not at some internal location it is at the wall location. So, d t by d x at x is equal to 0 is nothing but q double prime s divided by k with a negative sign the slope is related to the heat flux directly. And when the slope is equal to 0 it means that look at the curve here it is asymptotically it is basically the blue line is at tangent to the temperature distribution. Last boundary condition is again a specific form of this heat flux if this heat flux essentially is because of convection I can relate the left hand side minus k d t by d x that is x is equal to 0 to the convective heat transfer coefficient that is h times t infinity minus t of 0 comma t what is it looks complicated it is nothing it says conventionally of course, this arrows here show that there is a flow of a fluid with temperature t infinity and it is giving you a heat transfer coefficient h associated with it. Now, in conduction heat transfer when we are doing conduction now this h is given to us a priory that means it is already known we do not have to compute this. So, 25 watt per meter square Kelvin these are all known quantities once we go to convective heat transfer this same conduction problem where we are we were given flow over as a reactor fuel rod was cooled with a convective heat transfer coefficient of 100 watt per meter square Kelvin. The same problem you can have where h has to be calculated and by an appropriate correlation you will get h and then we solve the problem for now in conduction this is specified h t infinity is specified and we are looking at heat flow from left to right why because temperature is decreasing in the positive x direction. So, h times t infinity that means this fluid temperature has to be larger than the surface temperature here. So, t infinity minus t of 0 comma t why is this 0 because it represents x is equal to 0 and t is for at all times this boundary surface temperature. So, convective heat transfer coefficient times t infinity minus the surface temperature at all times that is equal to minus k d t by x equal to at x equal to 0. So, these are given special names first condition is called boundary condition of the first kind which is called Dirichlet's condition. Second condition where constant heat flux is specified it is called as the Neumann condition, but these are all information that is given to you special case of the constant heat flux is adiabatic or perfectly insulated case and convective heat transfer condition is the most general and obviously as you can see it is a slightly more involved boundary condition why is it involved we will just see convective heat transfer condition is minus k d t by d x at x is equal to 0 is equal to h times t infinity minus t at 0 comma t both these represent surface temperature at the wall x is equal to 0 this is the solid here this is the fluid here. So, I have temperature at this wall which is to go here the gradient of the temperature at the wall actually I do not know that I have to calculate that. So, as you see here this quantity and this quantity is related both these are directly related when the right hand side was 0 it was very easy I could write d t by d x equal to 0 I can relate this temperature at this location to a temperature at another point slightly away from it by d t by d x equal to 0, but here I cannot do that very easily because this derivative also has this unknown temperature in it. So, it is a slightly bit more involved boundary condition nevertheless it is very useful it is used most of the time in fact we will write recast this at x is equal to 0 is equal to minus h over k t infinity minus t at x is equal to 0 comma time. So, this will be recast like this and you can apply it to the solution of the equation. Now, we go back to the problem that we the problem that we had left the this problem we had intentionally left out because I did not talk about the boundary conditions then. So, this is a temperature distribution across a wall of one across a wall which is one meter thick at a certain instant of time. It is actually most of these problems you know are very very straight forward and it turns out that these are exercises in understanding English. So, if we are careful in interpreting each and every word I think all of us will get full marks in any course problem is we are unable to interpret things correctly. So, temperature distribution across a wall what is given a one meter thick wall is given here shown in blue here at a certain instant of time. So, at some instant of time it is given as t of x is equal to a plus v x plus c x square now a question will rise. So, at another instant of time is it different yes the answer is yes because what has been done is at a given time when these conditions were there this is the expression or this is the curve fit to the temperature distribution that has been obtained and given to us a plus v x plus c x square where a is 800 b is minus 350 and c is minus 60 and temperature is in degree centigrade x is in meters. So, it is a polynomial curve fit which has been given at a given instant of time notice that this one does not have a time dependency why because time dependency has already been observed when I say that temperature distribution at a given instant of time when I say at a given instant of time t equal to 15 seconds after start of the process t is equal to 500 seconds after start of the process. So, I have specified a time and then given you this distribution whereas, if I say the general temperature distribution of for this surface with respect to time is then this equation is not valid there has to be a time factor in the general expression. I hope I am clear in this I am sure there will be some questions related to this problem keep it waiting we will take it later. So, somebody has done a curve fit for this problem where t of x has been given to us a uniform heat generation of 1000 watt per meter cube is present very nice. So, e dot g is given to us in the wall area 10 meter square. So, this is some furnace wall or something whatever it is there is a wall whose area into the plane of the board into the plane of the paper is 10 meter square. The properties of this material are k is equal to 40 watt per meter Kelvin constant density there is a row missing here. So, 1600 kg per meter cube and c p is 4 kilo joule per kilogram Kelvin the figure c p units are incorrect 4 kilo joule per kilogram Kelvin. So, there is a kg missing in the figure what are we supposed to find determine the rate of heat transfer entering the wall at x is equal to 0 and leaving the wall at x is equal to 1 meter. What is this they say please find rate of heat transfer that means wattage what is the watts for heat coming in at this boundary and what is going out at this boundary. We will come back to this question second one the rate of change of energy storage in the wall the third is time rate of temperature change at x is equal to 0.25 somewhere here and x is equal to 0.5. So, very interesting problem actually. So, what is asked first have you understood what is given to us. I reemphasize we have been given a temperature distribution which appears steady state that means it is at a given instant of time very nice. But we are asked to find rate of heat transfer entering the wall at x is equal to 0 and leaving the wall at x is equal to L will these be different. On first thoughts that means can I just look at the problem and just want to blindly solve it the answer would be yes these both are equal because we are talking of steady state at that instant of time. But we have to remember there is this E generation term which is sitting here that means some heat is coming in some more is generated. So, it has to be this what is going out has to be different it obviously is not going to be the same as what is coming in. So, if you are able to understand and approach the problem we will not mean for surprises when we get mathematically that these two numbers are different. So, if you are fixing in our mind that these two have to be same then we are going to look for mistakes that we have not made and try to make these two equal. So, with this background let us see assumptions 1D conduction in x direction yes we are not concerned with 2D homogeneous medium with constant properties uniform volumetric heat generation constant properties means k rho C p everything has been taken as constant uniform heat generation that means this q dot which is given is uniform everywhere. And this temperature distribution is coefficients are all known to us. So, first part is very straight forward rate of heat transfer entering the wall and leaving the wall. So, entering means what coming from left to right this way I have a temperature distribution for the solid. So, Fourier's law gives me the heat transfer rate q dot sorry q is equal to minus k A d t by d x. So, if I have t as a function of x which I have here d t by d x if I calculate I should just apply the formula and get q let us see what we have done. So, d t by d x has been evaluated first so I will just do it here in a minute. Temperature distribution temperature distribution is A plus B x plus C x square d t by d x why do I write a partial derivative here? So, remember though the temperature distribution looks to be a steady state distribution we when we wrote the when we read the problem we said at a given instant of time has been given that means at another time the functional form is not going to be this. So, therefore t is essentially actually it is a function of x and t actually it is this, but when we fix this t becomes only a function of when we fix a value of t when this is given t becomes only a function of x. So, it appears as a steady state solution, but actually it is a transient solution at a given instant of time. So, derivative will give me B plus 2 C x. So, heat transfer rate at x is equal to 0 is minus k A d t by d x at x is equal to 0 I have k I have A I have d t by d x when I substitute d t by d x at x is equal to 0 I will get B plus 2 C times 0.  So, Q at x is equal to 0 is minus k times A times coefficient B same expression I can use for x is equal to L Q is equal to minus k A. So, B plus 2 C L so, beyond this there is nothing to write I have this equation minus B k A put in the numbers 140 kilo watt is coming in from the left hand side outgoing is 188 kilo is expected coming in is 140 outgoing is 188 why is it so? It is obviously going to be larger because 140 has come in some 100 watts has been generated per unit volume I do not know that is 100 let me look at the number it is 1000 watt per meter cube there is an error in the figure this is watt per meter cube here 1000 watt per meter cube has been generated and that is going to some of it is going to go out therefore, I am going to have a Q out which is larger than Q in. Now, this itself will tell me that we are going to have a temperature change with respect to time because 1000 watt per meter cube is generated and 140 came in 188 is going out. So, there has to be some kind of storage so, we are going to have a temperature change. So, that is what is calculated in part 2 calculate the rate of change of energy storage in the wall right hand side of the energy balance E dot in minus E dot out plus E dot generated equal to E dot stored. So, we are asked to find rate of energy storage or change in energy of the wall. So, E dot stored therefore, is this E dot in I have calculated 140 E dot out is 188 E dot generated Q dot is watt per meter cube times the volume associated with this geometry area is 10 meter squared times 1 which is 10 times 1 10 meter cube is the volume. So, 1000 times 10 meter cube is here that is what is multiplied here. So, E stored comes out to be minus 38 kilo watt very interesting because see energy coming in 140 energy going out 188. We said there is a heat generation and is it contributing to a rise in temperature or a drop in temperature that is clear when you look at this term. So, just by looking at these 240 and 188 we will not be able to say whether there is a rise in temperature or a drop in temperature that will become clear only when I put in this balance equation. So, it comes out that E dot stored is negative which means rho V C p d t by d t is negative all the terms except d t by d t are positive. So, d t by d t comes out to be negative it means temperature is going to drop with respect to time. So, last part yes we got an answer for that temperature drops with respect to time we are asked to find time rate of change 2 changes are here time rate of change of the temperature at any point in the medium may be determined by the governing equation this one just 1 d transient equation has been recast what is it rho C p by k d t by d t equal to d square t by d x square plus q dot that is the governing equation I have I want d t by d t. So, everything else comes to the right hand side and therefore, I can write d d square t by d x square I will write it in a form which is convenient to me second derivative of the temperature I have temperature distribution given to us already first derivative was calculated first derivative was calculated here B plus 2 c x second derivative will come out to be B derivative of B is 0. So, I will have 2 c is the second derivative this is going to be used directly there 2 c. So, d square t by d x square will come out to be 2 c substitute that here q dot is known 1000 watt per meter cube put in all the numbers we get d t by d t is minus 5.94 times 10 to the minus 4 degree centigrade with respect to per unit time or per second means there is a drop of about 0.006 degree centigrade per second it does not seem much, but if you are going to have this process go on for an extended period of time say per hour that means you are having 3600 seconds then this could start becoming a significant quantity. And what this problem also tells me that merely looking at these 2 numbers I cannot get an idea of whether it is heating or cooling I have to look at this complete form of energy balance minus sign here e dot stored indicates that temperature is going to drop and mathematically if I made a mess here and I got positive 5.94 we should wake up and say whether this is what is correct because this involves energy balance and this there is some mistakes we have to go back and look at these things. So, double multiple ways of checking the same thing conceptually Fourier's law can always be used to compute and it is evident that temperature at every point of the wall is decreasing with respect to time. So, I can take couple of questions if there are I see 3 questions here let us quickly go to Amal Jyoti Kerala, yeah please go ahead. So, my question is that sir in the derivation of the heat conduction equation. So, we have taken the amount of energy which is stored as rho Cp dot t by dot t one term is the final which is on the right hand side rho Cp dot t by dot t d x d by d z. So, in that term it is given as the it is the internal energy which is stored in the material. Now, internal energy is defined as it is m Cp d t sorry m Cv d t. So, why do you take as Cp instead of Cv? Suppose you are having a material gas which is a stationary gas condenser we can take it as Cv you know rather to take it as Cp over. See rho is m rho times v is clear rho times d x d y d z that is m. Now, if you are conduction if you are talking of inner solid Cp Cv is all the same if you are talking of a gas then Cp and Cv will be different, but Cp and Cv we are saying is energy change with respect to temperature. If you are talking of gas where you are dealing with conduction and there is no you know what you say precisely only conduction then we have essentially to if you are dealing with internal energy it has to be Cv. If there is no flow Cp and Cv will still become the same thermodynamics if you see what is H? H is Cp times t u is Cv times t, but what is H and u related? H is equal to u plus Pv and that Pv essentially has come because of the flow aspect of the fluid. So, if I am not going to have a fluid if you have a flow you can actually take Cp Cv all coming out to be the same. So, Cp Cv let us not get into the integrities of it it is the change of energy with respect to time. The moment I have a flow then I cannot use Cv I have to use H plus therefore, in fact we do not use this form of the equation at all we will have to go to the complete derivation of the actual equation for conduction. Conduction if you are talking it is next question and I take a start in fraction. Hyderabad. Hello sir this general equation, can I make use of it for a molten metal? Molten metal means there will be flow right. Yes, yes sir. Hello actually to answer your question for molten metal I cannot take directly you see why because in a molten metal that is what standard Stefan problem is told for a Stefan problem you have both the molten metal that is the you have both solid and liquid as the interface is moving see if you have both solid and liquid you have half of the portion solid and half of the portion liquid. See let us just take standard Stefan problem which is called let us say this is my plane wall this is a container in which the conduction is taking place only in this direction. And this is let us say I have applied either constant wall temperature or constant heat flux boundary condition earlier it was solid. Now after certain time it just melts that is this complete thing has become now liquid and this is solid. Now to answer your question within liquid there is conduction and convection because there is natural convection but within solid yes I can apply Fourier's law of conduction within liquid yes I can apply Fourier's law of conduction but in addition to conduction there is natural convection. So, it is very hard to answer your question directly there is no one way of answering it. So, it depends how we are handling or which type of problem we are solving. So, we cannot to put it very simplistically we cannot use it directly because there is convection. For the entire volume. For entire volume it is not possible to use Fourier's law of conduction or the heat diffusion equation. How about heat transfer between this molten material and the solid material. They are also there also you can only apply the boundary condition but you cannot apply the heat diffusion equation. For liquid zone for liquid zone how can I apply heat diffusion equation because natural convection is taking place. See in the liquid zone I think it is not possible for us to apply heat diffusion equation only for the solid zone only for the solid zone we can apply the heat diffusion equation but not for the liquid zone why because there is natural convection there are fluid velocities which are involved. So, we cannot apply heat diffusion equation for liquid but we can definitely apply for solid but the solid is moving I mean the solid portion is decreasing. But as long as we know which is the solid portion I can always apply the heat diffusion equation. At the interface I can only apply the boundary condition not the heat diffusion equation. So, we will have minus k d t by d x on the left hand side should be equal to minus k d t by d x on the right hand side whatever be the appropriate values of the thermal So, precisely what is called as Stefan problem it is a moving boundary problem ok. Thank you. Yeah, VIT Pune please. Hello, my question is there will be problem 3.1 which we have solved. In the third parameter that is we in that in that in that we calculate that is time rate of change of temperature but in this equation while calculating daba 2 by daba 2 t by daba x square we have a x that is and which is which is basically for the I mean the steady state temperature dispatcher how can we use this particular temperature distribution for calculating the unsteady state equation. The question is that in this problem which we just solved problem 2.1 part 3 this question is though we are saying it is a steady state distribution I am I am just phrasing what you have told it is though it is a steady state temperature distribution how am I using the unsteady form of the governing equation the slide which which has part 3 how can I use dT by dT equal to ok. The answer to that is actually that again I have told you this part this problem it is a local steady state that means dT dT by dT is going to represent a change in temperature with respect to time. Now at this instant of time I have this particular temperature distribution that is all I am getting by this A plus B x plus C x square at another instant of time because of this kind of energy transfer which has happened and e dot stored which has become minus 38 kilowatt I am going to have a different temperature distribution. For example, if I want to draw some kind of arbitrary temperature distribution this need not be representative of this problem. Let us say I have some some wall like this and at a given instant of time T equal to T 1 I have this kind of a temperature profile all I am saying this this has been given to us T of x is equal to A plus B x plus C x square this is given at this time. Now what we are saying is this is a steady state distribution at T equal to T 1. Now dT by dT is contributing to the shift or to the change in the temperature distribution or the temperature profile because of the fact that the problem is unsteady because we have e dot stored is equal to minus 38 kilowatt what is this going to contribute this is going to contribute to a net drop in the temperature. So, how is that drop in the temperature manifested that drop in the temperature is going to get I cannot have a same curve which is going to say that it represents a new temperature distribution at a new time no it has to shift and probably it will shift something like this or I do not know how what is the nature, but there will be a shift for time T equal to T 2 where new constants will have to be evaluated it may not even have the same form A plus B x plus C x square, but this thing is these two are related these two curves are related by energy diffusion equation definitely because that is the unsteadyness associated with dT by dT rho C p dT by dT equal to d square T by d x square plus q dot by k and here also there is a k. So, time T equal to T 1 and time T equal to T 2 I am relating when I am going to say what is the rate of decrease of temperature with respect to time because that is what T 2 minus T 1 divided by delta T I am bringing in time here. So, I have to use the unsteady nature of the governing equation that is why I have to use this form.


I think it's actually the first time I'm talking through a microphone, so. Oh, that's fine. Yeah, this talk is basically about sharing the story of our team when we were trying to apply GitOps principles to maintaining a large number of environments. And yeah, I think there's a few important points here due to know that at the beginning. I don't want to sell you anything, right? It's just about showing basically the way we are working because we've been heading out to Google to kind of find like other kind of publicly accepted ways to approach this multiple environment problem. And we didn't find anything, so we come up kind of with our own way. Yeah, and I want to share this. Maybe we also missed something which is completely obvious. So maybe we're doing it entirely wrong. In this case, I'm also happy to hear your concerns afterwards in the Q&A. But yeah, let's get into it. So the agenda of this talk today, first I want to give you a bit of context, like who are we, who's, who's Rosh, and what are we doing? And then I'll be going into these technical details here about how we use GitOps. And there will also be a demo and I don't know if we have time for Q&A at the end, but I try to finish on time. So first of all, yeah, my name is Alex. I'm actually from Zurich in Switzerland. It's nice to be here. I'm super excited to be talking here and glad you're joining me. By the way, like, Zurich is this picture there on the bottom left, so I can highly recommend it in case you're going to Europe to visit. It's an awesome place. But yeah, currently I'm working as a technical lead at the Edge infrastructure team in Rosh. And actually for this one, who here has heard of Rosh already? Because I think it's the, oh wow, that's actually more than I was expecting. So for those of you who don't know, right? Rosh is a healthcare company. They're doing, or we're doing like a lot of stuff, like medication, right? Cancer therapies is one big division. The other thing is diagnostics. So in case you have heard of COVID, like all these PCR tests, or many of the PCR tests which are being run in the labs, they are being run on Rosh and analyzers. And what is such a chemical company? What are they doing in the world of software, right? And the point is that we all know software is becoming more and more important everywhere. Also in healthcare, the digital healthcare is a big thing which is coming. This is one use case which exists, or will exist in the future, which is like this more and more personalized medicine. So you can imagine if you want to kind of, yeah, customize your medication for every patient, you can't do this with like teams of senior scientists, right? There are not enough senior scientists available on this planet. So you need to do a lot of automation there. And basically I'm working in a team, like an internal platform team in Rosh where we're trying to make this happen. So we are basically building a platform which makes it easy for Rosh to deploy applications into laboratories, into hospitals, into pharmacies, doctor's offices. And we're doing this basically by deploying a large number of Kubernetes clusters around the world.  All right. So with this, let's talk about how we use GitOps. And the way we use GitOps is basically the way everybody uses GitOps. So we have a Kubernetes cluster here on the right. We have a Git repository on the left. And in the middle in our case we use flux and customize to synchronize these two things, right? Now the interesting part comes here. We not have one Kubernetes cluster, but we have many of them as I mentioned. And like the important part here is all these Kubernetes clusters in our case, they are not like handcrafted different environments for different teams, right? All these Kubernetes clusters we're talking potentially about thousands of them at some point. They should look more or less identical. So they should have the same stack deployed of like Prometheus, Grafana, whatever you want to deploy there. And so mostly the same, although there might be like small customizations, like you can imagine if these clusters are running in different locations to different hospitals, you might want to give them a name, for example, right? So that this name is visible on the Grafana page. And the question we kind of run into is like how do we do GitOps in this case, right? And the answer we came up with in the beginning was this one. And so we just had a single Git repository and we all connected all these Kubernetes clusters to the same Git repository using flux. And I mean, this obviously is kind of nice because it helps us to keep all these clusters in sync. But over time we realized that we are running into some issues here. And the first one was these customizations, right? So how do we, like if all these clusters are seeing the same files, how do we like display different name in one of the Grafana instances? The next one is also like these were planned customizations, right? So we knew in advance that we want to display different names in all these Grafana instances. But like the reward is also messy, right? So we need to be able to deploy some hotfixes. And yeah, how do we do this in this case, right? How can we deploy a hotfix to a specific cluster without affecting all the other ones at the same time? And kind of in the same direction goes the question of can we roll out? Like how can we, I don't know, for example, update from ETHIS to a newer version but not deploy this change on all the clusters at the same time. Then the next one, or the next issue we were running into was separating access permissions. So yeah, I mean with like modern Git host or tools, right? Like GitLab and so on, it's kind of easy to separate right access permissions. But in our case, like these clusters are really separated, like spread around the world. Different people are responsible for it. Like how can we separate, for example, read access permissions on these repositories? That's kind of hard to do in Git. And last but not least, another problem we had was geographical co-location. So connectivity is not always a given as much as we would like to have this. So we needed to somehow host these Git repositories also close to the actual clusters which are using them.  But in the end, we decided to go a completely different route, which is to create, yeah, a separate Git repository basically for every cluster. So that we have a one-to-one mapping for these clusters and Git repositories. And the nice thing is that basically we inverted this list here on the left, right? So we solved all the problems we had before. But now the new issue is popping up, like how do we now keep all these clusters in sync? And not only like how do we keep these repositories in sync, but also how do we initialize them? I mean, we don't want like a person sitting there like writing these these files to have a gig repository kind of manually, right? Now the solution we came up with was hopefully like fairly obvious when looking at this is to use a template. And the nice thing about this approach is that here on the right side, you basically still have your standard GitOps approach, right? You can still use all the tools you know and love, like Argo, Flux, or Terraform, whatsoever. And the new party on the left, we actually internally started calling it Magops for MetaGitOps, obviously. And the question which was kind of popping up here, like what tools exist to help us, yeah, help us with this process, right? Is there anything out there we could use? We tried a few things, but in the end, we decided that like none of these existing solutions was fully working for our use case. And this is why we set out to first create like a new tool. We started using internally, which is called FoxOps. And this FoxOps tool, which I will demo afterwards, is basically helping exactly with this, right? This helps initializing all these repositories. And the nice part is it also helps to keep all the repositories in sync by allowing you to make updates in the template and then rolling out these updates to the actual, we call them incarnations without actually destroying any hotfixes that were made. Like if we change something in the template and we have some hotfix active in a particular cluster, we can still roll out these updates to this particular repository as long as the change is not directly in the same location. In which case we would get a conflict. Now the way FoxOps works is basically like every web application works. So there's an API with a database behind the scenes. And there's also like a very basic UI at the moment. Like all of this is very basic at the stage. But the idea is this API is basically, yeah, it takes templates from Git. So templates are also just Git repositories. You make versions by creating Git tags. And using the API, you can say, hey, please create me another incarnation of this templates at this location. Or please roll out this update at this location. And the SQL database is there because FoxOps itself keeps a bit of a state to keep an inventory of all the incarnations that has been creating. So we can use this FoxOps UI in our case as like the single point of like seeing, okay, we have all these like Git repositories they are all at this and this template version. Yeah, so it helps us to keep an overview basically what we did in the past. Although, I mean, just for you to know, right, in our case, we mostly use the API directly, especially for creating. So we automated everything into end. So we use only the API, but the UI is always there for some kind of manual intervention if needed. Yeah, I'm not going into detail of this slide. By the way, we open source FoxOps. It's also a fairly new topic for us. And it's super, super alpha at this stage. So please don't use it. But like here you can see like just maybe afterwards if you want to check the slides, like how it compares to the existing tools like cookie cutter and copier, which you might have heard. The important part is I think that the biggest difference is that cookie cutter and copier, these are command line tools which you can run on your laptop. Whereas FoxOps is kind of this like this hosted service which you could host somewhere and then you get this overview of like who created which incarnation. And I think I'm done with my slides already. Going to the demo. Just want to say that the disclaimer again, so FoxOps at this stage is somehow a POC which made it into production as usual. So please don't use it or please use it, but only do so if you have some time to also contribute to it because you will very quickly run into like missing features or bugs which will not make this a pleasant experience at this stage. All right, so let's see the demo. So what I want to show you in this demo is basically a use case similar to the one I was explaining before, right? So let's imagine we're a software as a service company, we are hosting our product for our customers but for some reason our product is not perfectly multi-tenant capable. So we need to, yeah, for every customer we need to create a separate instance, maybe spin up some separate cloud re-resources for this particular customer. And basically what you can see here is I just prepared a small GitLab group. We basically like this infrastructure thing is like all our different customer accounts here. So these are the repositories in which we want to commit our GitOps infrastructure as code for every customer. And then here we have a template folder at the moment there's only one template. And this is the template we're going to use to fill all these incarnations. So I'm going to show you the template first and then afterwards I will show you the FoxOps UI and I think we will just be going to like two use cases. The first one would be like let's onboard a new customer. So spin up like new infrastructure for them. The second one let's update an existing customer to like a newer version of the template. So looking at this template here, just how it looks like, I mean it's basically how a template always looks like. There is a metadata file in this case it's called fengine.yaml. In this metadata file you basically can define like variables that you can use in this template. So in this case this template only takes a single variable which is the customer name and it's getting a type of string, right? And then here in this template sub-folder these are the files which are then actually committed afterwards by FoxOps to the incarnation. So in this case we want to commit some Terraform folder here. Actually we're a very cheap software service company. The only thing we do at the moment for our customers is creating them a password. And also a username and you can see already here this is now actually like the FoxOps templating syntax. So here we're using this template variable. We have just been defining before. And by the way FoxOps internally is using so FoxOps is written in Python it's using the JINJA to template engine so you can do all the fancy templating stuff you want like loops, if statements, variables, transformations, whatever. Okay so, oh and the last thing which I can maybe show you here is that templates are a version, right? So we just use git tags in this case. At the moment we're having a version 0.1 and there's also a version 0.2. The only difference in version 0.2 is I updated a Terraform provider. I updated a random Terraform provider from one version to another. All right now let's go to the very basic FoxOps UI. So this is the overview page of FoxOps there. There are not more pages at the moment. But what you see here are basically these two incarnations I have been creating already before. So let me quickly change back here just to you for you to see this again. This was our structure, right? And these were our different customer accounts. So far we have two or three of these accounts and let's say now we want to create another account for a customer who just bought our product. And unfortunately we don't have any auto completion here or selection whatsoever. But basically here on this create incarnation page we are saying okay this is the target repository we want to initialize the template and this would be in this case infrastructure account C. Then FoxOps does support creating these incarnations and subdirectories but in this case we will just do it in the root star directory. And here we specify where the template is coming from and I hope I remembered the correct part here. I think it's demo slash templates, infra templates, yeah. And let's also initialize them with version 0.1. Down here we give the variables, right? So in this case the customer name, he would be like in this case customer C.  So I'm not cheating here. So clicking on create and this should hopefully not take more than, it actually worked crazy. Always scared of these demos. Yeah, the files appeared. So here you can see like we have the Terraform files and if we check this output.tf from before we can see that FoxOps rendered this value or less this value into this particular file. Yeah, second use case would be let's update one of our existing customers. Like this is our pilot customer, right? He always wants to get the new versions first. Like all we have to do here is I clicked on incarnation. I typed in like please use now this version 0.2 template version, making an update. And let's see. So what you would see and now this button here became active which is like taking you to the latest merge request which was created by FoxOps. So for all the other ones I just initialized the repository without doing any merge request. This is now the first time we're doing an update here. So if I click on this button I get to this merge request. It actually was merged already automatically. There's a feature in FoxOps to to auto merge. These updates I use this. But what you will see here in the changes basically is that yeah, this was the update I was doing and then the templates repository. So basically updating the Terraform provider from 3.4.0 to 3.4.3 including the log file. And yeah, I think that's it for the demo already. Let me see. Oh, I have one more slide. I mean where could something like this be useful? I mean besides this like GitOps use case which I was showing you here. Like another use case we're looking into is for microservice repositories.  You might want to share pipeline configuration. You might want to share built tooling, directory structure whatsoever. So having a tool like FoxOps. In this case you could also use like one of the other tools like copier especially. But to keep all these repositories in sync it's certainly a nice way of doing it. And I think that's all.


Hi, my name is Michael Murray, I'm Senior Visiting Scholar in Philosophy at Franklin and Marshall College in Lancaster, Pennsylvania in the U.S., and I'm here today to talk to you about science and religion, the relationship between the two, and looking at some contemporary challenges that have been raised to religion from the domain of science. To begin I want to talk a bit about the history of the relationship between science and religion, and we'll begin with a story that's often been told about Galileo and the Catholic Church. So in 1615 Galileo was reeling from the first round of public condemnations that had been made of his views about astronomy. According to his view, the sun stands at the center of the solar system and the earth revolves around it and also moves on its axis. And as you might know, this was a view that was not widely held by the Catholic Church or for that matter by the Protestant reformers of the time. According to them, as they understood the scriptures, it's the earth that stands at the center of the cosmos. And everything revolves around it. Galileo was convinced that the empirical evidence showed otherwise and he aimed to convince other people of that through his writings. But Galileo also regarded himself as a devout Christian, and as a result he was keen to find a way to reconcile his religious commitments with his newfound scientific discoveries. His way of doing that was to conclude that the Bible just did not teach what the Church authorities claimed. In fact, his view was that the Bible didn't aim to teach scientific truths at all. In fact, Galileo said in words that are often quoted, although not at the length that I'll quote them here, the following. Galileo wrote, Since the Holy Ghost did not intend to teach us whether heaven moves or stands still, whether its shape is spherical or like a discus or extended in a plane, nor whether the earth is located at its center or off to one side, then so much less was it intended to settle for us any other conclusion of the same kind. I would say here something that was heard from an ecclesiastic of the most eminent degree that the intention of the Holy Ghost is to teach us how one goes to heaven and not how the heavens go. The connection between science and religion is not just one of historical curiosity, as we might suppose if we focus just on the Galileo story, but one of substantial contemporary importance. Battles between science and religion are probably most well known and most evident in the U.S., where that battle continues to be fought primarily between Christians of a conservative variety and scientists. But it's also true that these debates are going on broadly across the globe. They're being carried on both in public and privately in China, Russia, Israel, and in numerous Middle Eastern countries as well, where similar issues arise at the interface between Islam and science. So in order to know how to think about the connection between science and religion, we first need to know exactly what science is. We have to define our terms here clearly, because there are different ways of understanding it and depending on how we understand it, we'll understand the relationship between science and religion differently. So we'll begin with a very minimalist definition of science, which is something like this. It's a collective judgment of professional scholars who aim to explain the workings of the natural world through empirically testable theories. Now notice here I'm defining science not as a practice or as a discipline, since practices and disciplines won't have significant points of conflict with religion. Instead, we're defining science as a set of claims, claims made by a certain sort of scholar who's engaging in a certain kind of work, those kind of work that scientists normally engage in. In thought of this way, there are three different ways of thinking about the relationship between religion and science, three ways in which you might think that they intersect. On one, we would say that science and religion conflict in principle. On a second view, we might say that science and religion cannot conflict in principle. And on the third view, the view that I'm going to defend, we could say that science and religion may or may not conflict, whether they do depends on what those religious claims are and what scientists affirm. So let's take a look at these three views in turn. So on the first view, science and religion are in principle in conflict. So why would someone hold that view? Well according to this view, the claims of religion and the claims of science are locked in conflict in such a way that only one or the other can survive. This is sometimes called the warfare model of the relationship between science and religion, a phrase that's been used since the late 19th century taking its cue from a famous book that was published in the late 19th century. And this view was especially popular during that period and in the early 20th century as well, though there are many defenders of it today. One of those defenders is the famous Harvard scientist, E.O. Wilson. He wrote a book a few years ago with the title, Consilience. And Wilson puts it this way, acceptance of the supernatural conveyed a great advantage throughout prehistory when the brain was evolving. Thus it's in sharp contrast to biology, which was developed as a product of the modern age and is not underwritten by genetic algorithms. The uncomfortable truth is that the two beliefs are not factually compatible, says Wilson. As a result he continues, those who hunger for both intellectual and religious truth will never acquire both in full measure. So what should we think about this view of in principle conflict, the view that we find expressed in Wilson's writings? Well, first of all, there's something here on this view where the very definition of science and religion causes the conflict. But what are the definitions that are in play here? So some who defend this sort of model do so because they're adopting really quite contentious definitions of science and religion. For example, some claim that religion consists of beliefs that are drawn from purported divine revelations. And that these beliefs are held entirely on the basis of authority. So you believe those claims that come from revelation because you believe the authority of the purported revealer of those truths. Science, on the other hand, according to this view, consists of beliefs that are justified by sense experience and by the scientific method. So you might wonder just given that characterization of the relation between religion and science, does it actually follow that they're in principle and conflict? And the answer is no, because it could be, given that characterization, that the same truth is revealed in whatever revealed text you take as authoritative might also be the claim that's being affirmed by scientists. So what do we have to add in order to draw the conclusion that science and religion are in principle and conflict on this point of view? Well, what we have to add is something that's really quite controversial. The principle conflict arises only when we add to this characterization of science that the only justifiable beliefs about the natural world are those that arise from sense experience and the scientific method. And when we add to the characterization of religion, that the only justifiable beliefs about the natural world are those that are held on the basis of religious authority. The problem is those definitions don't seem to be very plausible, especially in the case of religion, holding up the only justifiable beliefs about the natural world are those that are held on the basis of religious authority. There are very few people who would affirm that that's a reasonable understanding of religion. So on this view as a result to accept the teachings of the Bible or the Koran about the natural world is to be anti-scientific because it's not held on the basis of the scientific method and to accept the deliverances of experience and the scientific method would be anti-religious because on this view the only justification for holding these views about the natural world is that they're revealed by a religious text. So if you were to hold this sort of view then you really have to choose. It's science or religion. One can win only at the expense of the other. Some actually defend this model because they think it's a straightforward reading of the history of the relationship between science and religion. So you might take the Galileo affair as one example of this or even previously it's it's oftentimes claimed although this is not actually the case that that Christian figures for example held that the earth is flat and science later proves that that's wrong or religion says that the earth doesn't move and science later proves that in fact it does orbit the Sun and rotates on his axis or religious religion says that the universe is less than 10,000 years old and then science proves it's 14 billion years old or religion claims that human beings are directly created by God and then science shows instead that human beings are descended from earlier primates and so on. So you might think on this reading of the history science and religion are locked in this kind of conflict because religious believers are committed to the idea that they're supposed to draw these claims about the natural world from revelation but in fact when the science comes along it shows them that these views are wrong and so the two stand in this perpetual state of conflict. But as I mentioned earlier it's not really clear that this is a reasonable way to characterize the relationship between science and religion. This is not a characterization which we should accept. Even if scientists were to accept that the only way to justify scientific beliefs is through sense experience and the application of the scientific method it's worth noting that nothing from the domain of science justifies the scientist in that claim. That is the claim that science alone provides us with justified beliefs about the natural world. That itself's an epistemological claim, a philosophical and normative claim, and not something that we could justify by appealing to sense experience in the scientific method. So there's something self-refuting about that way of trying to understand science. Second is that it grossly mischaracterizes the relationship between science and religion. So it's simply not true that the only way in which conflicts, apparent conflicts between religious claims or claims from purported revelation and science, that the only way to resolve those conflicts is for religion to concede the point. And you can see this by looking at certain historical examples. So for example in the early 20th century the reigning cosmological model was something that's known now as the steady state model. And on the steady state model the universe is eternal and not expanding. It's simply a static universe that doesn't change in any significant way other than movements of the parts. And many religious believers, especially those within the monotheistic tradition, struggled with the steady state theory because they believed that their religious revelation taught that in fact the universe had an origin and time. And so Christians, Muslims and Jews who were confronting the steady state theory really wrestled with how to reconcile their religious beliefs with the science. And many of them concluded that they couldn't. That either this had showed that religious belief was false or that something was wrong with the science. And of course what happened in the mid 20th century was that science in fact did change and came to the conclusion that in fact the universe had an origin, an origin, and something we now describe as the Big Bang. Now of course scientists didn't reverse course on this point, didn't change their beliefs because they were appealing to religious revelation. But it simply shows that the relationship between these two are more complicated than this simplified historical narrative would lead us to believe.