Hi you guys, Lindsay here. Welcome back to my channel Inside the Hymn. You guys saw the Butterick Fall Pattern First Impression Review that I did a few days ago and now we've got simplicity and then following this one will be McCalls. They are rolling these things out really quickly so I'm trying to keep up so that you guys can see the patterns and maybe more importantly see what I think of the patterns. So without further ado let's get started. I'm already on the new patterns page. If you're curious you access that by going to patterns and then simplicity and then new patterns. So let's see what they've got for I guess this is they don't really title it like they do for the McCalls brand but I'm guessing fall early fall late summer something like that. Okay first up we've got this little top with some very interesting sleeve actually some very interesting sleeve details. Let's get this open big so we can see look how cool this one is. Hold on their site is a little hard to get used to navigating. Okay look how fun that is that's really cool. Okay let's get a closer look. I guess we've got a split sleeve with a bow and a ruffle and then a full sleeve with a ruffle this version which is a tie-up sleeve with a bell like an open bell sleeve and then this must be her version you just can't see the ruffle really well. Here are our line drawings doleman sleeve this is really cute and am I alone in thinking that this is fun and different but still very wearable. I'm really digging this a lot here are the girls together cute I love this I love this a lot that's definitely going on my list I just think it's so fun and different but still very flattering and wearable I don't think you'll look like too weird but you'll definitely look you know fashionable and trendy love this one simplicity 8694 is going on the list for sure. Okay next we have a kimono she's got um what is that oh oh okay so it's got like a um I don't know what do you guys want to call that like a extra panel and then this one that buttons in the center with a gathered sleeve this is a cropped one I guess with a waistband and then here's the one she's wearing which I guess is the same as a it just has contrast fabric I'm not big into kimonos to be honest guys like I probably should be because they are so wearable here in the fall and winter like I would be able to wear them a lot um but I just don't find them to be super flattering I guess I don't know maybe they're just too retro for me I'm getting a very big like rock and roll 70s vibe maybe it's her styling too with like the multiple multiple necklaces and the washed jeans um but I don't know I wish again as I always say with simplicity patterns I wish they showed people in some of at least one other view I mean throw me a bone here um or they would have made up one of these that isn't the most obvious like I can pretty much tell what that's going to look like on a body but I don't know what these two look like these could be cool maybe I'll have to wait and see when you guys make them or other people make them what I think um okay next up is a okay so they've been doing a lot of like reworking the vintage patterns and this is one of them this is a calf tan one of the jiffy easy cut easy sew which means that I mean these are the pattern pieces it's literally rectangles a little next cut out and then you can shorten them or lengthen them so pretty straightforward here but are you supposed to wear this out or is it a cover up or what I don't know I don't understand captain's very very well I'm assuming you know it's like a house coat all right then we've got a it looks like a vintage like a reworked vintage dress here with a like high collar or high neckline and a little peter pan collar some interesting gathering for the bust you know bit and glare like usual you also have these pockets I guess or yeah you can do the pockets look at those pattern pieces that's kind of cool again this I'm not a vintage girl either but I imagine if you are this one could be likeable to you where's it from I wonder oh look at the cute back there's like a bow in the back but they aren't really showing that oh they didn't do the bow oh they did but not as dramatic look at those back waist darts I'm telling you I don't like vintage aesthetic because the fit to me isn't very modern like how wide she is up here but they did some really great tailoring back in the day I wish they would bring some of that back I mean all of this shaping like you would think she had darts or in a waist seam but it she doesn't it's literally one whole piece but this shaping is all accomplished because of these darts please bring the darts back okay um oh interesting little shirt dress here okay look how cute this is I love this it's like a regular shirt dress and then it's got this wrap around asymmetrical panel thing that's kind of cool right what do we think of that little sleeve detail here this one's got tie sleeves without the crossover panel and this one's just got regular cuffed sleeves I think this is super cute again it's like a twist on the traditional which if that's their vibe for this collection I am feeling it I am all about it let's see obviously you know that the stripe plays really well with this you know panel um but it could be really great and just a solid shirting too do we get any back photos oh there's one no seams but it does have a yoke so at least that's a step in the right direction look at the line drawings again there's our backs and you guys it's really truly not difficult to add fisheye darts to the back to give yourself a little bit of waist cinching for me it's so important because up here I am like a 14 and on the hip I'm like a 20 22 so you can't really grade between those sizes and whenever you do inevitably the waist is like very very baggy so when I add fisheye darts it allows me to be a little bit more relaxed in the sizing of the waist but still achieve an hourglass shape to the dress I think that the tie does help with that because you can kind of cinch in a little bit let's see you can see it better here so she is getting a little bit of waist definition on the side so that's just why I harp about dart shaping on shift dresses okay mrs knit again with an asymmetrical hem um we've got a very defined waistband this ruching as I've said before is extremely flattering it covers all of your you know if you have a belly or you know issues with your midriff this hides it all which is great I love this little like it's like a flutter sleeve but it's a not as dramatic flutter sleeve which is nice here are our line drawing so we've got yeah asymmetrical hem regular hem long dolman sleeve a flutter dolman sleeve two neck options so lots of variation in between all of these um and then on our backs pretty much all the same except for the skirt and the waistband cute little knit dress I didn't buy a ton of knits when I was in New York because I just don't find myself loving making knit dresses for some reason um I mean I do like the ones that I have made I don't know I don't know why maybe there aren't enough really great knit dress patterns so maybe I should give this one a go all right now we've got another shiftish looking dress that's gonna be cute it's definitely fun is that a good description it's fun okay so this one's giving me like you know prairie vibes with the applique but if you left that off I don't know bubble sleeve maybe not this one's super cute very peasant dress which is okay I'm down for peasant dresses you know 70s vibes same with this one but it has a button placket and again we only get the one like we only get her dressed up in one I kind of like the proportions of it I like the um pier waist like the higher seam it's not sitting at her natural waist it's higher I like the shorter length and the long sleeve and the high neckline like these proportions to me are ringing very cute and sweet which is very much my aesthetic I really love sweet darling I just don't know about all this applique rickrack and trimmings and that's that's not necessarily my jam but so princess seams that's great and in the back I don't know if you noticed there was some darts here so also great shaping um and then I think the skirt is just gathered yeah we can't see the bottom yeah the trims a little much but I think that it could be you found some I don't know you could really work with this and make it maybe cuter than what they did but I don't hate it it actually kind of works together I just wouldn't it's not in my mind like to put pink trim and green rickrack and gold but you could you could definitely hit up the trim section of your fabric store or trim store and and do something really cute with this I think and these like little pin tucks or I don't know what are those called are really cute and different I like this I like the shape of it I like the idea of it eight six eight nine going on the list I think where are we okay here's a Mimi G let's see what she's up to you hmm I know that there are a lot of Mimi G fans out there but this I'm not sure about maybe it's the fabric application I do appreciate she made two different views amen for that this looks really cute in the drawing she's got bust arts and then a center back seam that's it and then a pleated skirt or ruffle or pleated band or a gather or sorry I can't even talk this is a circle skirt this is not pleated or gathered it's like a circle skirt added out to the hem and then we've got a cuffed hem here or this sleeve or this bell I think my mind is just kind of like all over the place after seeing these pictures yeah I'm just not like digging the fabrics I mean that's a really big stiff bow right by your face you know I'm saying I don't know Mimi I don't know I can't tell if I like it I like the drawings okay fabric choice I guess is just pretty critical here yeah okay now we've got a sew chic mrs dress I don't know the sew chic brand oh is that like a a partnership sew chic do they make other patterns yeah sew chic pattern company for simplicity again vintage vibes here very you know 50s with the sweetheart neckline and a shoulder panel here little puppy sleeve the bias trims a good detail and then this little band and let's look at some of the oh look at all these seam lines very cute and then these huge back darts and shoulder darts again they just really paid attention to that stuff back in the day I wish we could take some of it and apply it maybe not all of it but at least some of it yeah she's got a great fitting bodice I mean she looks great it fits spectacularly as it should okay good job sew chic all right now we've got a vintage blouse and dickie okay um that's a very pronounced specific collar dolman sleeve we've got some bust darts and here is our dickie are they gonna excuse me are they gonna show how that is like warm oh here we go so this is what a dickie does it goes under your sweater but it's not actually like an entire button down it just looks like it is so you make this and this and then you wear this underneath sometimes they attach to each other um like a little buttons or snaps or something I don't know if this does or not but I don't know like I'm all four vintage patterns like being remade but is this modern enough I mean I think that I don't know I guess it depends there are some people who love the quintessential vintage and like to look like they've been picked up from another decade and placed in current times but for me if I'm going to do vintage it has to look it still has to look like something you could get in the stores today and I'm not sure that that's that but I can see some people really being able to pull it off so I'm not knocking it I'm just saying it's not for me okay now we've got a one shoulder top oh this is kind of cool all right I can't say I love the like pronounced cost but that's easy enough to change it's like a like you took a min shirt and you put it on sideways where the collar is over here okay clear this one with the bow of course oh and I like the sleeves that are on this too I would look how cool this button version is but of course they don't show us any of that um here are the backs there's literally not a single dart on this guys so it is pretty much a sack here they do have some pictures of her with it untucked so kind of so let me get rid of this so kind of tunic-y like a tunic yeah um it doesn't look terrible I guess the shirting fabric really favors this just kind of like a line without any um without any shaping um because it does just kind of naturally float away from the body which can be flattering um and here she is with a little french tuck this could be cute I could see I could see people pulling this one off and looking really really cute I want to see these these are so much different than these I wish they would make more than one I volunteer simplicity if you want to give me the patterns ahead of time I'll make a version for you okay now we've got just sleeves a set of sleeves that I assume you can attach to any simplicity pattern with a set in sleeve I don't know about that you can't really do that today they vary but okay well let's look at them I don't know this is a really weird pattern cover with all these random arms but there they are if you need some sleep ready this one is really sweet I do like that a lot this one's not terrible these other ones I don't know it could be fun to just get like a basic like shift dress or even fit and flare and like just do a bunch of different sleeves these pictures are cracking me up okay girls cool oh here this is probably easier to tell what's going on well there you go if you need some sleeves you can get simplicity eight six nine five okay now we are looking at some oversized blazers oversized blazers are very trendy this one is adorable I would wear that in a heartbeat maybe not with light wash jeans but it's really cute this just looks like you got it at Goodwill from the 80s but this application is very modern with the printed bodice even like the floral printed bodice so what are the differences here okay we have one with a notched collar one without a notched collar and these two are the same ones in a print and ones in a solid okay they did make two versions so I'm happy about that yeah this is too cool love this yeah she looks like she just rated her husband's closet but this girl looks awesome so fabric application is key I don't know that I would do it in a traditional suiting um but I do love the modern take on it for sure okay now we've got some pull on pants very athleisure is that pretty sure I guess athleisure is still very very on so we've got the racing stripes we've got a wide leg a more tapered leg without racing stripes and then tapered leg with racing stripes right wow look at all those lines I can't barely tell what's going on okay there you go let's see her strutting her style are they gonna show us this jacket because I'm kind of feeling that jacket there you go it's like sweatpants but it all depends on fabric application you could make this out of like black suiting fabric and do like satin black racing stripes or even white or cream satin racing stripes and have like some really sharp looking drawstring pants okay now we've got a skirt not vintage surprisingly I was getting a vintage vibe from it maybe because of the length I don't really do pencil skirts personally because I've never really found one that I really love this little mini version that was really cute and I also love this little asymmetrical hem here but this long length like this I just I don't think it would look flattering on my pear shape but we've got I'm assuming there's another dart underneath this little panel here with the covered buttons different hems and in the back we've got two darts I prefer four darts in the back for a pencil skirt that's again because I'm going from like probably in the waist like a 16 to a 22 so I need more shaping but I did a tutorial gosh a couple years ago about full seat adjustments for skirts so if you're wanting to make a pencil skirt like this or like I guess it's like a slight a line go check that out and you can see how to get them to fit you really well on the back side okay next cute why do I feel like I've seen this one maybe they headed on instagram or something so this is a pattern hacking pattern um let's see what the options are to shorten the sleeve and add a ruffle to shorten the length and add a ruffle and to add a drawstring and some different pockets so those are pretty decent pattern hacks I think um the last time I did a simplicity first impression of the pattern hacking brand it was like the hacks were too basic it was like obviously I can shorten a dress you know obviously I can make a knee-length dress a maxi dress you know that doesn't take I don't need your help with that I can figure that out on my own but these are actually pretty different so that's good so your base pattern is like they're obviously going for like a military look here with the patch and all of these patch pockets but you can get some pretty different looks here adding the ruffle certainly feminizes it um so yeah you can get some good stuff going here she is so pretty okay um let's see it looks like we have an outfit we all think of the base pattern it's all right I guess again with the oversized you can see how much it's falling off her shoulders that's supposed to be yeah I guess so it's a little bit of a drop shoulder um so yeah it could be cute I don't know that it necessarily has to be like military you can definitely leave these things off um these two I guess and you have like a basic like utility jacket but I you know me I love a ruffle so anytime you add a ruffle to anything I'm like oh that could be cute okay we've got some pattern hacking pants let's see the base pattern's really cute so you can make them like I guess calf length or ankle length obviously you can turn them into a track pant how is that oh with buttons up the side maybe that's hard to tell from the drawings a cropped pant with cutouts okay interesting and then a cropped pant with a frayed hem yeah this is button ups button up the side okay well they did get these to fit her really well the base pattern so that says something although she's like a size zero so cute as a gene I just what fabric would you make something like this out of something that doesn't fray like velvet um and like these button up ones what would you use there like some kind of athletic fabric I don't know again I wish they well I guess they want to make the base pattern here but they could have shown us some others at least at least a drawing like a with fabric applied to the drawing you know having a hard time visualizing that one so okay now we've got a Mimi G knit jacket pants and leggings cute this is adorable okay so yeah we've got like a zip up kind of a bomber jacket but not totally it does have the knit waistband and the knit cuffs but this is all really cute I wonder how hard it is to get that all that and then leggings with similar stripes and a little zip detail here cute and then they're supposed to oh the MC hammer pants are back did she not make those these look like the leggings to me John I want to see what these look like maybe she would put them on her blog interesting two-part sleeve yeah you could probably use out some scraps for these pieces if you have like a bunch of french terry or sweatshirt fleece or whatever you can use up a bunch of scraps for these pieces they're not that big oh she did color block of sleeve too oh it's three where's the side oh interesting but the back is all one I don't know if you can tell that or not interesting that's cute it would take some thought but that's really cute I want to see the baggy crotch one okay now we've got a knit leggings tops and belt all right okay weekend wear maybe this one's cute this is just kind of basic but oh it's separate and then leggings I can't tell is D is this D and F combined or does this sewn in to D like is D really just E and F together I don't know that could go a bunch of different ways I can't totally tell if that is going to be fussy or comfortable but here she is oh she's one out on her skateboard in this outfit okay good to know good to know here she is this seems low to me I wish this were up here on really long sleeves is that supposed to be like that yeah what do y'all think I'm not sure about that one all right next up for anything oh which is their athleisure line okay let's see we've got a pullover these are our like henley or half zip pullovers with a bunch of different variations we've got a little pocket here there's some kind of something going on here this one has a pocket on the sleeve and little inset ins this one has a kangaroo pocket and this one has zip here maybe they did do a is that a placket still I can't remember zipper shield zipper shield which is nice that's a good detail so yeah kangaroo pocket inset thing here sleeve pocket little thumb holes which people like if they're like riding a bike or something this one has like princess seams they all have two part sleeves um drawstring and then this has um that little pocket up top what is this is that like you put little water bottles in there like this is um elasticized at the top and it's like two pockets in the back yeah I guess so I guess it's what you put back there I don't know does anybody out there have ready to wear with that on it what goes in there what is it just like a purse like you didn't just put like your keys in your wallet and anything you want just right there and these are not zips these are just like inseam princess seam pockets I'm not really feeling this uh fabric very shiny this one I'm sure that this is one of the ones they've gotten at joanne this looks really cute yeah the zipper shield is a nice detail this is cute I'm sure when it's cooler out I'll start looking for stuff like this um to wear to the gym um now we've got one for men which I'm not going to cover because I don't sew for men but if you're looking to make something for your guy here's some little workout clothes for him and then doll clothes the mommy and me little girls clothes bags um it looks like Madeline has a new panty set you can check out let's see cosplay little kids oh wait what happened here lots of cosplay okay lots of cosplay lots of little mermaid oh and for your doll too cute um well this is a fun slave over and then these are all from the last definitely from the last um so if you want to see my first impression on any of these go to the last um oh no these are new look that's what happened okay we switched over to new look I was like I know these look familiar so these are the new new look patterns I did do a first impression review on them so if you want to see those I will provide a link from right here where you can go check it out but other than that I feel like we did okay with simplicity this time around I really am digging their um early fall late summer collection I really I was liking it a lot more in the beginning and then kind of like tapered off toward the end but some of these like this top and this dress um possibly this one will definitely end up in my pattern stash I really like this one too let me know what you thought in the comments which one was your favorite which one will you definitely be buying and until next time I will see you guys very soon bye


Okay. Thank you. Thanks to the organizers. Thank you to Cesar for the invitation. I will present this paper, which is done with Alexander Cano, Cesar Mantilla, Laura Prada, Meardo Restrepo, Cesar and Laura are in the floor, so if you have questions, you can do it to them. And then this is, this paper is about the trade of between liquidity and insurance. And what we do is that we apply lab in the field experiment to Colombian rural workers. So the main objective of the paper is to understand this trade off in the context of this population. And what we do is to propose this experiment, which they basically have to choose between receiving a payment in cash or in a voucher. So I will explain that in a moment. Given the limit of time that I have around eight minutes, I will skip all the slides related to regressions, outputs, and I will basically present the intuition part of the paper. So regarding the motivation, you know, Colombia is the OECD country with the highest self-employment rate, which half of the employment, roughly speaking, is an informal employment. And this somehow resembles the, you know, the dual labor market structure in which there is a primary labor market, say formal labor market, which basically pays higher salaries and higher returns to education. And then there is another sector, say the informal one, which is characterized by the absence of non-wage benefits. There are no, there is no job security, or at least it's scarce, stability and safety nets are, say, scarcer. On the other hand, rural workers are more exposed to jobs and somehow they are, the labor markets that they face are more informal, you know. And the numbers in the Colombian context say that in the rural markets the self-employment rate is as high as 80 percent, which is a lot. On the other hand, these people have access to limited constrained financial services, which are usually used to cover basic needs. And there is also evidence showing that the effects of shocks on health and education are more persistent. So taking everything together is hard to formalize rural workers and that's why it's important to understand well this tradeoff. So why formalizing rural labor, rural labor, sorry, it's hard. Well, they both, users and providers may have distorted perception of non-wage benefits. You know, universal health coverage may cause more and more loss of issues also people that live in rural areas are subject to higher transportation or transaction costs. And on the other hand, they are exposed to all the risks, different from risk related to health and most important, risk related to production, right. So production in the rural areas is riskier. And probably the risk is more important, more salient than health risks. On top of that, it's harder to enforce any agreement that we can think of or we can somehow implement to a low change. You know, Colombia is also characterized and that's part of the name of this conference by this strong inequality and that inequality is even stronger in the rural areas, when you compare workers with land tenants that the inequality is very, very large. And then you will think of the system that we have right now in Colombia, the system makes the or would make the land tenants to pay and the question then is how can we convince these land tenants to pay for the social security of their workers, right. Even if there is a change in the law such that they have to pay then how you can monitor these contracts between the land tenants and the workers. So in principle, any contract with a stronger element associated to the social security for the workers is harder to implement in the rural area. Then what this means is that we need rural labor contracts that on one hand are attracted to workers, on the other hand that they are not blocked by the tenants and besides that, that they go beyond health and pension coverage. This paper is related with point one. So in dealing with this general question on how to make more formal labor markets in the rural context, we started by analyzing what happened to workers. So what is our lab in the field experiment about? The question there is about how a voucher payment is attractive to workers in exchange for better insurance and somehow we are inspired by the European voucher system where schemes are subsidized domestic services. You know what there is known as the black market. They have this voucher system to make these domestic employees be somehow contribute to the social security system. So what we do is that we in the lab, we make subjects to perform labor activity, somehow give the idea to the people that they are going to be paid by their work. So what we do is that they have to separate beans from white and dark beans. And then basically they have to choose between either be paid by cash, which is 30,000 Colombian pesos, probably speaking a daily minimum wage. And they have to receive the comparison with different vouchers that increase or decrease in their value, the expected value from 25 to 34,000 Colombian pesos. And then there is an income shock, which is our measure of risk in which they have a chance to lose 20,000 pesos. And then this happens when they receive the cash. But if they, okay, perfect. And if they receive the voucher, then that happens with 10% of probabilities, okay. We did this with rural workers in the department of Quindio, which is in the middle of the coffee region in Colombia. So what they receive is this kind of table. As I said before, we randomized whether they started by facing, you know, from the lowest voucher to the highest voucher or the other way around. But basically they have to choose, right, whether to receive the payment in cash or voucher. This is the relationship in terms of expected values of the voucher and cash. So we start with some of the vouchers that have an expected value smaller than the cash and then others that pay more. We also randomized whether the show-up fee is paying cash or voucher, okay. And we do this just to test whether there is a transaction cost effect that makes people to not take the voucher instead of the cash. Okay, so these are some photos. We implemented this in all the municipalities in Quindio. This is, sorry, this is the order of the events within the lab. They first, of course, they have to sign on informal consent. They first make the decisions in all the comparison between the cash and all the vouchers. Then they have to separate the beans. And then we draw one of the decisions to pay. And depending on the decision, they receive a voucher or the cash. And then we implemented the final questionnaire. And probably this is the most important message from this experiment, which is that the show-up fee, I told you they either receive cash or voucher and there are no differences there. So at least for these people, this dimension of transaction cost is not important. Maybe because they are already in the urban part of the municipality. So they somehow already sunk the cost to arrive to the market. And then here, what I show you is the different decisions related to whether they receive the voucher in ascending way or a descending way. So in the horizontal axis, I have the different schemes of the voucher, and this is the cumulative probabilities. And we find that there is a difference between receiving the vouchers in a descending or an ascending way. And I think this gives also an important point related to policy implementation regarding this topic. Most important, we also did the same experiment to students in Armenia, in Kindio. And we find that in both groups, when they are exposed to the voucher, the rule of work is take the vouchers from 32% to 56%. This is the number for the more generous voucher. And for the students, these numbers are smaller. They are saying that the students are somehow value more the liquidity. But also this says how hard is to implement social security by vouchers. Because even if this payment, which is the largest one, the only half of people takes that. Even if in expected value, they receive more, they don't take the voucher as often as we thought. So just I think I already mentioned this. So just to sum up, we introduce a very simple insurance scheme. This scheme seems to be insufficient in the sense that they are not voluntarily prone to take this voucher. Only with this more generous voucher, half of people is willing to take it. The sending order is important because this means that probably if we think in a policy in this direction, we can implement first a policy, a very generous policy. And then with time, we can make it less generous. And I think this is the main message. Thank you. Thank you.


So, let us now look at something called a multi-component diffusion equation diffusion coefficient right, what we did originally was to get fixed law for applied to a binary mixture where we notice that you have something called a binary diffusion coefficient that is a diffusion coefficient that is valid for a pair of species and then we now switched into a multi-component mixture where we wanted to look at how the diffusion happens in a situation where we have lots of species and now we came up with a monstrous equation the other day which under some conditions might begin to look like fixed law let us say for example again for a binary mixture but what we noticed was even in the presence of multiple species the role of the binary diffusion coefficient was still there that is to say we were still looking at mixing happening between a pair of species at a time right. So if you now had like three species ABC then we were looking at a DAB, DBC and the DCA okay so we are now three diffusion binary diffusion coefficients for each pair of species that is involved there but many times when you are looking at let us say 10s or 100s of species then we now have to worry about binary diffusion coefficients of each of the species which with each other species right. So that becomes little bit more complicated and it is not quite amenable to further simplification for example when we now did the multi-component diffusion equation we could reduce it to fixed law for the case of a binary mixture okay by making lots of simplifications in trying to justify disregarding the three other terms and to look for only the first term that contributes to this and then we could see okay fixed laws is retrieved but the question is if you had a truly multi-component mixture could be even think about a something like a fixed law something as simple as a fixed law right and for this the binary diffusion coefficient is going to be a bit painful to deal with because we are now saying that you have to have a DAB times gradient YA DA DBC times gradient YB and so on and these binary diffusion coefficients are not going to be the same right. So therefore many times it is worthwhile to think about what is called as a multi-component diffusion coefficient this is not the reality okay the binary diffusion coefficients are the reality whereas we will now think about a multi-component diffusion coefficient artificially used artificially used to relate to relate diffusion velocities as a function of linear combination of concentration gradients. So the way we want to do this is so commonly approximate as let us say yi vi vector is equal to minus di gradient yi i equals 1 to n course or we should also be able to say xi vi vector is equal to di gradient xi right we have seen this before for a binary mixture like for example if I now multiplied both sides by row the mixed density then I get rho i vi vector is equal to minus rho di gradient yi previously we have done this only for a binary mixture so if you were to apply this to a species a then we would have a DAB so that has two subscripts to denote that this D is valid for a pair of species a and b but now we are looking at a multi-component mixture that means we have more than two species but we are having only one subscript that is to say we now want to tag the diffusion coefficient only to one species much like how it is CP or maybe thermal conductivity or any of those quantities would be that does not make sense honestly because as we said if some species has to mix into another species you need to have other species involved in this process right so DAB made sense because it was actually for a pair of species that way but di how can you have a diffusion coefficient that depends only on one species the answer in this situation is as I said it is a bit artificial but it is not too artificial okay because what we could now think about is how is this species how is one particular species in a mixture mixing relative to let us say a species that abundantly present in the mixture let us now begin to think about how each of the species in the mixture is going to mix with a one species that is the most abundant in the mixture right so typically in combustion applications we are now looking at like fuel air mixtures right in air you have a lot of nitrogen that is pretty much sitting there and that is like an abundant species around so if it is now possible for us to think about how each of the species like the fuel or the intermediates the products the oxidizer air the oxygen that is and so on mix with nitrogen okay and that is just present like a reservoir and it did not matter to nitrogen or the abundant species how well it mixed with the individual species it is not going to get affected because it is available in abundance right when that is the case then it is possible for us to still think about the diffusion happening were for a power of species as opposed to a tagging it to only one particular species but we achieve the goal of thinking about only one species you simply do not worry about the abundance species right so so the way to be typically do this is this is this is valid this is valid when one species is in large concentration large concentration and others are in trace now typically trace is a word that is used for something that is very very small okay so it is sort of like an exaggeration that we are trying to do here in saying that when we are now having most species that are present in nominal quantities not negligible not in abundance we cannot really say trace but you get the idea that this is strictly speaking valid when one of them is in large concentrations other in trace but we will not go ahead and say well we will identify an abandoned species the other ones are not going to be in trace but we will still go with this idea right okay. So then what happens generally if we use then we then use di is now considered identical to what is called as din okay that is the that is as if you are now looking at a binary diffusion coefficient of each of the species relative to the abandoned species okay and this you can now say is generally written as 1-xi divided by sigma j equals 1 to n and j unequal to i xj divided by dij so that means we are actually using the dij information for all the species okay in the in the mixture in evaluating the what we call now as the multi-component diffusion coefficient okay strictly speaking this the derivation can be possible only if you make an assumption that all the species are having equal velocities whereas we would ignore that if we have to apply this situation where there is not the case and that is in general not the case alright. So that there is an assumption that goes with it which we normally while it in addition there is also one more caveat that we have to use which is use this for n-1 species okay and obtain the dn okay as follows the point we could the point the reason why we cannot use this for all the n species is if you were to use something like this and therefore get something like this and then plug it in your species conservation equations and add strictly speaking we cannot set the summation of all these diffusion fluxes due diffusion mass fluxes to 0 okay so it is sort of like it sort of violates mass conservation. Therefore strictly speaking if you are going to use this kind of a multi-component diffusion coefficient and correspondingly your relationship between the diffusion velocity for the species and its concentration gradient can be expressed as simply like a fixed law okay that is what we are trying to do we are trying to get this form for relating your vi's to gradient yi's or vi stars I should say to gradient xi's right. So if you have to do this then do not do not do this for all the n species okay the n species has to be obtained from adopting sigma yi vi vector is equal to 0 i equals 1 to n and sigma i equals 1 to n yi equal to 1 okay. Use these two things your dn as sigma j unequal to n dj gradient yj divided by sigma j unequal to n gradient yj but many times again just as we ignore the assumption that is involved here in saying that the velocities of all the species is or equal we also many times ignore this that we just say let us not worry about the nth multi-component diffusion coefficient being obtained this way provided all the n-1 diffusion coefficients are obtained this way okay you see that these are actually the multi-component diffusion coefficients they are obtained so this is ignored many times okay let us now move on what we have done so far in trying to look at conservation equations in general for a reacting flow system of truly multi-component mixture is to derive the species conservation equation okay. We did this for a binary mixture we now expanded it for a multi-component mixture then we notice that we need to have a closure for capital VI vector for which we wrote the multi-component diffusion equation and then looked at what are all the situations by which you could simplify this and we have got to this point okay and when you also noticed that as you now add up the species conservation equation all the species conservation equations you will now get your overall continuity equation for the mixture as if it was a non-reacting single species case right we have not shown this in these lectures for the multi-component species conservation equation but that I would like to leave it as an exercise for you to go back look at the multi-component species conservation equation equations and then add them up to show that even for a truly multi-component system you should get the overall continuity equation to be like a single species non-reacting situation alright so that means we have in our kitty the species conservation equation and the overall continuity equation these are two things that we have okay and of course we also have the multi-component diffusion equation so far we could now count the number of unknowns in our minds density for example density of the mixture is one of the unknowns the corresponding equation that you can think about is like the overall continuity equation right and then you have a mixture velocity the mass average to mixture velocity that is showing up in the overall continuity equation that is an unknown for which typically we resolved the momentum equation for the mixture right which is what we would now go ahead and do and then we have the mass fraction is an unknown yi for i equals 1 to n for which we now have species conservation equations 1 to n and species conservation equations which in turn shows up capital VI for which we have the multi-component diffusion equation okay or its simplifications or many derivatives which ultimately leads something like a fixed law but if you do not want to do the simplifications you want to deal with the multi-component equation in all its complexity then keep in mind that you have a xi showing up there we need an equation for grad xi rather than for yi which is your unknown in your in your list therefore you need to now use n equations that relate xi and yi okay so as and when you now come across unknowns you have to start thinking about corresponding equations to solve okay so in this list so far of course wi contains temperature for which we will have to resort to the energy balance okay and then we will find that the momentum equation involves pressure for which we also have to look for the equation of state so that will completely close the system of equations so in what we have looked for so far we have not listed the mixture momentum mixture energy and mixture equation of state these these three are yet to be done so let us now do that so momentum equation I am just going to write it out I am not going to do anything to derive this and I am going to adopt the tensor index notation to do this in tensor index notation rho times vj dou vj by dou x sorry dou vi by dou xj plus dou vi over dou t is equal to minus dou p over dou xi and xj delta ij plus dou by dou xj of mu dou vi over dou xj plus dou vj divided by dou xi minus 2 by 3 mu dou vk over dou xk delta ij close the brackets there plus vi where vi is equal to rho times sigma k equals 1 to n yk fki I am going to say a lot of things now just say now I am going to write it out okay first in terms of index notation if you now have one subscript that means we are looking at a vector okay so for example we now say bi that is a vector it is i goes from 1 to 3 1 1 2 3 it will take index values 1 2 3 for 3 components in a three dimensional space okay we can probably go a little bit backwards bi is actually rho times sigma k equals 1 to n yk fki all right and then of course rho does not depend on the summation it could be taken in and if you now were to think about rho yk as rho k rho k fki fki obviously is a vector but k means that depends on species right so whenever we seen a f corresponding a small f corresponding to a species before we did not do we did this not too far back we probably did it like last class or yeah that is true this is nothing but the body force per unit mass okay so in this case it is going to be like the ith component of the kth species body force okay so ith component of the body force per unit mass of the species k here so it is sort of like acceleration we went through this sometime back times its density it is going to mean that this is actually done per unit volume okay this is a volumetric equation this equation is now valid at a particular point on a per unit volume basis that is the reason why we are multiplying by density because this is actually per unit mass times density gives you per unit volume all right so fki is basically body force per unit wall unit mass and therefore we now want to do this to plug it into this equation so bi then is like the net body force on the mixture all right this keeps in mind that the body force could be different for different species okay and this is because you are looking at like an electric field or magnetic field that could be acting on different species differently and so on okay then I want to also point out that we have a summation over repeated indices in place okay so if you now have like a vj and vj and xj then we have to sum over the repeated index the remaining index will be I which is the prevalent index in the entire equation so this is for the ith component of the vector equation as in this case for example you now see just that the summation is in place over here as well where ?ij is the Kronecker delta and Kronecker delta stands for a value of 1 when i is equal to j and 0 when i is not equal to j therefore this basically will give you a gradient p so what we use to write in vector equation vector notation is grad p needs to go through a complicated route over here and this is first of all assuming that we are looking at a Newtonian fluid for the mixture all right and or rather we should say Stokesian fluid okay because it also has in place the Stokes hypothesis about the relationship between the linear viscosity and the bulk viscosity and here ?vk over ?xk again has a repeated index summation over it so that actually indicates a divergence of velocity all right so the divergence indicates a dilatation and the – 2 by 3 mu is a coefficient that comes out because of the bulk viscosity so that is acting on the dilatation of the fluid and of course for an incompressible fluid ?vk over ?xk will be equal to 0 the divergence is 0 that is actually coming from the overall continuity equation if you sum up your overall continuity equation and recognize that the mixture is incompressible then the density does not change with time and your and the divergence of velocity will be equal to 0 so you should be able to get this right so in all these things we now are having to reckon with two more new things that have that we have not seen before the first one is pressure okay and the second one is mu everything else is supposed to be counted as either an unknown or given unknowns that we have already counted the row in the overall continuity equation and vi or vj whatever it is in the overall continuity equation again yk is an unknown that is counted in these species conservation equation fk I is supposed to be given to us okay on how individual species is being acted upon by body forces per unit mass of them therefore the thing that we do not know here is P that is an that is reckoned as an unknown okay whereas mu is a parameter in the problem it is reckoned as a fluid property the question is we now have a mixture of fluids okay what mu do we take all right so keep that in mind we have a little problem here okay keep that in mind and we will proceed in fact we are now continuing to our search for more equations because the species conservation equation had a wi on the right hand side which had a temperature in the Rhenius term okay so we want to now close for temperature and for this we want to now look for the energy equation so of course we now also have a pressure and we will now have to close for that with the equation of state we will do that next but the next thing that you are going to do right now is the energy equation the energy equation just like the momentum equation is also written for the mixture that means we are not worried about energy of this of a particular species and so on the only thing that we do that is species specific is the mass conservation for a particular species okay but rest of the things we do for the mixture as a whole so if the energy equation is also applied to the mixture now there are several ways in which you could write the energy equation so one of the maybe the mother of all equations would be to write out an equation for the stagnation enthalpy because the stagnation enthalpy will take into account the kinetic energy involved in the motion of the of the mixture and it will also involve the pressure work because we would now say H is equal to E plus P by rho okay where E is the internal energy and P by rho is the pressure and density you now look at a change in enthalpy it also takes into account not only the internal energy change but also the pressure work term and that is for the H the enthalpy alone okay if you are now looking at H not which is H plus V squared over 2 then it also takes into account kinetic energy changes so the mother of all equations probably should be to write in terms of the stagnation enthalpy now what I would like to point out here is that is overdoing things a little bit the reason is if you were to write your energy equation in terms of the stagnation enthalpy keep it with you and then you take a dot product of your momentum equation with velocity vector which is of course we are now looking at the mixture velocity that is the mass averaged mixed velocity of the mixture you take a dot product of this is a vector equation okay so you now take a dot product of this equation with velocity you now get this in dimensions of energy okay and that would be what is called as the mechanical energy equation that means this equation then will only deal with the mechanical energy there is a reason why in many Phc qualifying exams people may ask you something that you learnt in your undergraduate fluid mechanics is the Bernoulli's equation a statement of energy conservation or is it a statement of momentum conservation the answer is both right you could conserve momentum or you could conserve mechanical energy it is a matter of just taking a dot product of the momentum equation to get a mechanical energy right so in other words if you are conserving momentum it is amounting to conserving mechanical energy what it does not do is to conserve the thermal energy okay so if you now obtained your mechanical energy and subtracted that from the energy equation written in terms of the stagnation enthalpy then you get an energy equation that takes into account only the thermal energy conservation okay that is what we would do we would just write out the equation for the thermal energy conservation we will not worry about the stagnation enthalpy at all right. So here we are rho dh over dt equals minus gradient q vector plus q dot plus rho sigma capital k equals 1 to n yk fk vector dot vk vector plus phi plus dp over dt now I told you any time you now look at an equation that keeps going on and on okay do not worry about it you start looking at it term by term okay and then start making sense out of this capital d over dt capital d over capital dt refers to the substantial derivative or material derivative or total derivative right which in turn would be like dou by dou t plus v dot del that is operator that we have to replace for this to look at the this is this is essentially the inertial term in general which can now be looked at in an Eulerian frame of reference as a unsteady term and a convective term together right. Now if you were to if you were to derive this for yourself you would understand that you got the divergence because this was actually a surface term in a arbitrary control volume this is the way we actually got our species conservation equation derivation okay we had a surface mass flux across the control surface okay and then we applied the Gauss's divergence theorem to get a divergence so whenever you have a divergence you had immediately think that this is actually coming from like a surface or from the sides okay and we will expand on this q dot is actually the what do you think is q dot let us let us just tease ourselves a little bit for a minute what do you think is q dot sorry energy supplied by what external source damn you knew the answer what else could have been what are we looking for here what are we looking for why are we here huh put into the reactor did you say put you put into the why would I put into the reactor I am a combustion person right I want to get out something right I put in fuel and I want to get heat so how many of you think that this q dot is actually the heat that is coming out of the reactions like half hands up why or is the heat from the reactions hidden in the here anywhere this is the test of a combustion scientist or a student they should say right where is the heat released from chemical reactions present in this we should probably ask this question at the end of explaining all the terms but I cannot wait I mean that is what I am really looking for forget about everything else in fact I will forget about lots of those right so some of these are basically written once and then we will say we will forget about this but we cannot forget the heat released from chemical reactions because that is how that is our essence right where is it in this is it the q dot right the q dot is essentially an external energy release rate term so this is a is the heat released due to chemical reactions contained within your system or is it or is it to be externally put in right so you now take like a reactor or a combustor or whatever it is and then you now put in your air and you put in your fuel okay and do we have to put in heat no right where was the heat contained that is now released the H where is the where is it in the H standard what the standard heats of formation of what the products of this on the reactants right so this this H is the mixture enthalpy mixture specific enthalpy okay so what is going to happen here is H is the mixture specific the reason why we are multiplying by rho specific means per unit mass okay specific enthalpy and that is given by equal to sigma k capital K equals 1 to n yk hk where yk is the mass fraction still unknown okay in the system of equations but hk is the specific enthalpy of species k okay by the way notice that we have shifted from a and b or i and j and all those things for species to a capital K because if we now did this with the tensor index notation we had i's and j's competing with us okay so we now use capital K for species from now on yeah so hk is the specific enthalpy of species k that still does not show you the heat due to the chemical reactions because you now further have to identify that hk is equal to ? hf not k plus integral t ref to t cpk dt small cpk dt there are two things that I would like to point out in this this is what is contributing to your heat release this is not the full heat release of course this is only the standard heat of formation of the kth species if you now plug this in here you now go on to get a summation yk ? hfk that is like saying I want to add up all the heats of formation of all the species that are involved in this mixture weighted by their mass fraction okay and keep in mind it is a products that are going to have very high negative heats of formation the reactants are not going to have that high negative heats of formation they could have like small negative heats of formation or 0 or close to 0 or small positive or positive or more positive heats of formation all that stuff that algebraic sum is like the net heat that we are going to get by thinking about a hypothetical process by which we broke down the reactants into reference elements by putting in some heat and then got the reference elements to form the products right and then get lot more heat than what we put in right that is what is the heat release from the chemical reactions is hidden in there okay the other thing is we were actually writing this equation searching for temperature as an unknown and look at where it is that is in the sensible enthalpy term on the top of this integral that is the unknown right so okay let us look at a few other terms let us look at grad sorry divergence Q or what would skew first of all so I told you it is coming from the surface so this is heat flux okay so this is heat flux this is an energy rate equation okay so this is actually per unit time whatever we are writing here is actually per unit time things are happening as they happening you are looking at what is happening per instead per unit time right and this is like heat flux that means what is happening per unit time per square meter per unit area right so what is this heat flux this is now going to be like equal to minus k grad T plus rho sigma capital K equals 1 to N HK YK capital VK vector plus or ut sigma I equals 1 to N sigma J equals 1 to N XJ DT comma I divided by W capital W I DIJ times capital VI vector minus capital VJ vector plus QR vector clearly heat flux is a vector okay which is now going at an arbitrary direction say arbitrary it is going at a direction not exactly normal to a surface it is having like a N N N vector unit vector unit normal vector that we have to take a component with respect to and that is how you would get the Gauss's divergence theorem applied over there and then there are about 1 2 3 4 yeah 4 terms there okay how do you get 4 terms the first term minus k gradient T what is it that is a heat conduction the heat conduction is actually coming from this from the sides at from a particular point because you have a temperature gradient with respect to this point and the adjacent point right so if you if you had a harder region on the side you are now going to have heat into this point if you are going to have a cooler region on this side you are going to have heat away from this point right so that is the familiar Fourier law of heat conduction so effectively we are assuming that we are looking at a Fourier fluid that means a fluid that the heat conducting fluid that satisfies Fourier law all right but the fluid is actually a mixture of lots of species okay so what is this k it is a conductivity of the mixture right so similar to this mu being viscosity of the mixture so we need to have an idea of how to deduce the conductivity of the mixture and the viscosity of the mixture for a mixture whose composition is yet to be solved for okay so actually we do not know this and this is changing from point to point and time to time okay in this mixture because the composition is changing as we go from fuel air over here to lots of stuff and then finally some products and so on okay so I am not going to tell you how the mu and k depend on the species concentration instantaneously I am going to put this out in a website with that that the that this video will go with it has to go to kinetic theory okay so we now we cannot do this in the continuum framework we will write out equations that that give you this later on what is this term can we carefully look at this okay rho is out you can take this in then make it make this rho rho yk as rho k hk all right capital vk as a matter of fact so long as we had yk hk sigma you would get back your H okay but then you had a capital vk that prevents you from summing over only yk hk right yk is weighting the summation sorry vk is weighting the summation what is capital vk that is the diffusion velocity of species k right how did we get this term the answer is you see when we were looking at this we had a dou by dou t plus v dot del H the v there is the mixture average the is a mass average velocity of the mixture okay and then keep in mind that H is sigma yk hk the mass average velocity of the mixture is not species dependent it is now a mixture property so you could have pulled it out of a summation and kept your sigma yk hk as H that is how you got your H okay but in reality how is the enthalpy flowing into your point and getting out of that point this looks like it is convection right in convection of enthalpy but this is like convection of enthalpy of the mixture okay but in reality whenever any matter moves it carries with it mass momentum and energy that is the reason why we are able to do mass conservation momentum conservation and energy conservation here we now have a bunch of species each of which is carrying some mass for which we did a species conservation equation at any particular point okay and then we had a mixture momentum conservation all right but if you now thinking about the energy or the enthalpy that the species carries with it okay now it carries with it enthalpy at its velocity but what we have accounted for is like a overall enthalpy that the mixture carries at the mixture velocity that is what this accounts for then there is a deficit there is still enthalpy carried by individual species at its diffusion velocity with respect to a mixed affixed coordinate system right in reality it is carrying its enthalpy at its velocity but then now we have to taken like a mixture average mass average velocity of the mixture okay and then that does not depend on species anymore so we should now be able to add up a contribution of all the species put together in terms of enthalpy to see how the enthalpy of the mixture gets convicted right but then there was one more contribution that we forgot there is like a diffusion velocity with which the enthalpy is still going all right that is coming up if you now have a mixed affixed coordinate system that is what this is so you now have a vk times hk okay so that is actually the enthalpy of the mixture that is due to diffusion okay so you have to keep that in mind and then this is pretty interesting this is what you would call as the due for effect okay where this is the opposite of the sordid effect that we saw the other day okay where there what we saw was if you now had a temperature gradient it gave rise to a contribution to a concentration gradient here if you now have diffusion velocities okay which in turn are supposed to be functions of concentration gradients it gives rise to a heat flux okay so why you had a temperature gradient giving rise to a concentration gradient is called sordid effect where you have a concentration gradient giving rise to a heat flux is is called the due for effect okay and you can clearly see that you have a dt, i divided by dij showing up here as well all right so that is what is called as the due for effect and finally qr is a radiation heat flux so what we have had so far here is only the conductive heat flux therefore you also have to add a radiation heat flux the radiation heat flux will have to be model based on Stefan's law and if you are look at an enclosure or something of that sort you have to have these shape factors coming in and so on absorptivities and emissivities and all those things that is something that you want to do separately but at the moment you just had to plug in a keep in mind that it is going to depend on temperature okay so it has a t to the 4 expression and that could be an unknown because temperature is an unknown okay so you could plug in an expression for that if you want we will stop here for now and then pick it up from here next week we still have few more terms to go we want to know what this is what this is and so on okay the energy equation takes some amount of energy.


Hi, my name is Steve Altschuler. I'm running for Longmont City Council in the at-large position I'd like to tell you why I'm running for City Council. First of all, I'm a constitutionalist I believe in the First and Second Amendments. I'm also a free market capitalist I've had my own business for over 35 years. I know what it is to have to manufacturer products, sell a product, install a product, stand behind the product Nobody on City Council right now has any of that experience They have their own pet projects where they want to take the money from people that are working hard To give to other people and in my opinion, that's not what our government is supposed to be doing Our government should be protecting us with fire and police and maintaining roads It is not the government's responsibility to be in the housing market There are other companies that can do that Right now our Longmont City Council wants to spend 12 million dollars of taxpayer money to tear down the YMCA I think that's ridiculous By the way, I also don't think that the City Council should have ever owned a recreation center a Recreation center even though I enjoy going there. That's for the free market people can come in buy the property build the building Government doesn't need that what you have to realize is if there are a thousand government jobs and 2000 public service jobs Everybody needs to be taxed 50% to play to pay for the salaries for the government workers You need to have less government workers and more private sector workers One of the ways that the Longmont City Council is not helping The citizens of Longmont is for instance with property taxes right now. We're about to have a 40% tax increase Longmont City Council has done nothing to help lower that amount Because if they get 10% of the property tax bill or 20% I don't know the full number They just got a 40% increase. So they're looking out for their own coffers. If you look at real estate City councils all across Boulder County have arranged for builders to have low-income housing But if they don't want low-income housing, they can give money to the city in lieu of low-income housing That's called extortion, but that money goes into their city coffers that they get to use on pet projects I would like to see the City Council manage the city and not Corrupt the city to go for all of their pet projects Again, my name is Steve Altjuler. I'm running for Longmont City Council and I look forward to hearing from you. Thank you