Twelfth Paper: "Near-field radiative heat transfer in many-body systems"

My twelfth paper has been published! It is in volume 93, issue 2 of Reviews of Modern Physics, and an older preprint of it is available too for those who don't have access to academic journals (it is identical in content and only differs in formatting). Unlike my previous blog posts about published papers that I have written, this one will not strictly use the thousand most common words in English. This is because unlike my previous papers, which put forth novel ideas advancing the field of nanophotonics, this is a review paper that gives a broad historical scientific overview of the subject, namely, the flow of heat through light (i.e. electromagnetic (EM) fields) between objects that are typically separated by less than 1 micron (approximately 1% of the width of a typical human hair). It goes over work that other scientists have done theoretically and experimentally in this subject, and this paper in particular is divided into two main sections.

The first section, to which my PhD advisor & I made most of our contributions, is about the flow of heat via EM fields between just 2 objects. Relevant issues include choices of materials (mainly metals/conductors versus insulators), choices of shapes for objects, advances in experimental measurement techniques, advances in computational simulation techniques, and derivations of upper limits to the flow of heat via EM fields between 2 objects (mostly referring to my previous 2 papers that were the subject of the following linked blog post).

The second section, which constitutes the bulk of the paper, is about the flow of heat via EM fields among more than 2 objects. Relevant issues include changes in temperature over time in objects that are very small compared to their separations, the fact that the heat flow among more than 2 objects involves very complicated interactions among them, the fact that material properties could depend on temperature so there could be many possible sets of object temperatures where heat flows but temperatures don't change, heat flow via EM fields over distances longer than 1 micron, applications of heat flow via EM fields to microscopy techniques, heat flow via EM fields in materials that can be attracted to permanent magnets, and applications of heat flow via EM fields to engineer new devices.

Eighth, Ninth, Tenth, and Eleventh Papers

My eighth, ninth, tenth, and eleventh papers have been published! These require subscriptions to read, so here are alternate links to older preprints for the eighth, ninth, tenth, and eleventh papers, respectively (which have most of the same content, with some minor changes to explanations, citations, and figures relative to the published versions). As with my previous papers, in the interest of explaining these ideas in a way that is easy to understand, I am using the ten hundred most used words in English (except for the two lines that came before this one), as put together from the XKCD Simple Writer. I will use numbers sometimes without completely writing them out, use words for certain names of things without explaining further, and explain less used words when they come up. Keep reading to see what comes next. While these papers aren't as closely related to each other as the previous three, there are enough relations that I'm putting them together in a single post. These papers need a lot more math (note: "math" isn't one of the ten hundred words) than the papers before, and because they need a lot of thinking to get, I actually won't say as much about them.

On another note, this is a milestone for me because these are the last papers from my PhD in which I was a leading author. I still have one more review paper left to be published, but as that has been submitted to the journal and as I'm not the leading author, I don't really need to worry about that at this point. (Of course, once that is published, I will write a blog post summarizing it, though as it is a review paper, that summary will probably be quite short.) Thus, I am truly done with the work from my PhD, and can fully shift my mindset away from physics toward thinking about problems in transportation policy, as I will do in my postdoctoral research at UC Davis.

Fifth, Sixth, and Seventh Papers

My fifth, sixth, and seventh papers have been published! These require subscriptions to read, so here are alternate links to older preprints for the fifth, sixth, and seventh papers, respectively (which have most of the same content, with some minor changes to explanations, citations, and figures relative to the published versions). As with my previous papers, in the interest of explaining these ideas in a way that is easy to understand, I am using the ten hundred most used words in English (except for the two lines that came before this one), as put together from the XKCD Simple Writer. I will use numbers sometimes without completely writing them out, use words for certain names of things without explaining further, and explain less used words when they come up. Keep reading to see what comes next. I'm putting these three papers together in a single post because they form a trilogy of sorts, all having to do with finding the biggest number for how much heat, through light, can go from one body to another when they are really close together, or can go from one body into outer space. These papers need a lot more math (note: "math" isn't one of the ten hundred words) than the papers before, and because they need a lot of thinking to get, I actually won't say as much about them.

The fifth paper is called "T Operator Bounds on Angle-Integrated Absorption and Thermal Radiation for Arbitrary Objects", and is in volume 123, issue 5 of Physical Review Letters. This is the one that has to do with how much heat, through light, can go from one body to outer space. People knew before that the number for how much heat really big bodies can put through light into outer space grows like the surface area of the body, but for really small bodies it grows like the space of the whole body (volume), and they were not sure how these two things join in between. This paper lets people figure out what the most heat is that can go from a body through light into outer space no matter what the largest shape the body can sit in, and shows how to join the things that people knew before for middle-size bodies of different shapes. (Another press release from my department can be found here.)

The sixth paper is called "Fundamental limits to radiative heat transfer: Theory", and is in volume 101, issue 3 of Physical Review B, while the seventh paper is called "Fundamental Limits to Radiative Heat Transfer: The Limited Role of Nanostructuring in the Near-Field", and is in volume 124, issue 1 of Physical Review Letters. Those two papers go together, so I'll write about them together. The sixth paper is about the math behind figuring out the biggest number for heat, through light, to go between two bodies. The seventh paper shows that heat, through light, going between two big flat bodies that are close together can be pretty close to the biggest number possible, so making the shapes of the bodies less simple than just flat surfaces is of no use.

Fourth Paper: "Impact of nuclear vibrations on van der Waals and Casimir interactions at zero and finite temperature"

My fourth paper has been published! It is in volume 5, issue 11 of Science Advances, which is an open-access journal, so anyone can read it. As with my previous papers, in the interest of explaining these ideas in a way that is easy to understand, I am using the ten hundred most used words in English (except for the two lines that came before this one), as put together from the XKCD Simple Writer. I will use numbers sometimes without completely writing them out, use words for certain names of things without explaining further, and explain less used words when they come up. Keep reading to see what comes next.

In papers that came before this one, I looked at how to do a better job of figuring out the van der Waals (vdW) forces, which are the forces that let geckos (small animals with hard skin over which your finger can slip easily) stick to anything no matter what it is made of, between molecules, which are the little things that make up most of the stuff we see and are in turn made of smaller things called atoms; I also looked at how to do a better job of figuring out how heat (through light) goes between different molecules, especially when they are near larger bodies, and that needed me to do a better job of considering how molecules can make changes on each other through light, and that means that I need to better consider how the full atoms within molecules move toward and away from each other in a way that repeats itself. In this paper, I used the new way from the paper that came before of considering how molecules can make changes on each other through light to show what happens with vdW forces between molecules and larger bodies, especially when they aren't as cold as possible but are as hot as a room you might go into each day. It turns out that for small or long thin molecules made of carbon atoms, our work can do a pretty good job of showing how being as hot as a room can make vdW forces look very different. For some kinds of large thin sheets of atoms, like boron nitride in which every other atom is boron or nitrogen, our work still does a pretty good job because the electrons, which are the parts of the atoms that are the smallest, lightest, and move around the most, are still pretty close to the centers of the atoms. On the other hand, for other kinds of large thin sheets of atoms, like graphene in which every atom is carbon, our work has some more problems, because electrons in graphene can move around a lot more than our work might make you think, and the ways in which those electrons change how the rest of the atoms move around when they are as hot as a room (instead of as cold as possible) makes vdW forces harder to figure out than our work can say. This means we still need to do more work to better figure out how vdW forces look for those kinds of sheets.

My Time in Luxembourg and at the META19 Conference in Lisbon

This is an update from my recent travel to Luxembourg and Lisbon. I had the privilege of traveling to Luxembourg to deliver an invited talk to my collaborator's group; we have published 2 papers together, are about to have a third published (for which I'll write a post once the publication is official), and are working on a fourth. It was productive to meet with my collaborators to hash out the details of our fourth paper together, and I think I did reasonably well delivering my talk, for which the first part was about the work with my collaborators modeling fluctuational electromagnetic phenomena at the interface between small objects that have to be treated at the atomic scale and large objects that can be treated as continuous, and the second part was about my more recent work purely within my group putting upper bounds on thermal radiation and heat transfer. Additionally, I appreciated the interesting conversations I had after my talk with various members of that group.

I also got to go to the META19 Conference in Lisbon, which is centered around research in nanophotonics and metamaterials; there, I presented an invited talk about the aforementioned work on upper bounds to heat transfer, which my advisor graciously let me do in his place. It was great to meet people that I knew associated with my advisor but hadn't seen in a few years, and we got to discuss each other's work in great depth; I got to also meet a few other people for the first time, and had some good conversations with them about our respective projects too. That said, while I think the delivery of my presentation there was good, I did feel like I could have done a better job of preparing my presentation in a way that better fit the context: my presentation may have been too theoretical, so for an audience of engineers who care more about using metamaterials and nanophotonic architectures to make new devices, I could have been clearer about broad physical insights and done a better job connecting the findings in my work to ideas of interest to such researchers. Additionally, I could have probably done a better job networking, though my reticence was in part due to uncertainty on my part regarding my future plans.

I also had a day in each city to explore, but there were issues in each case. For one, neither Luxembourg nor Lisbon are especially tourist-oriented cities compared to places like London, Paris, Madrid, Barcelona, or Berlin, as far as I've heard: both cities have a lot of nice restaurants and cafes as well as many nice viewpoints and other areas to simply hang out and relax, but there aren't so many specific attractions, as Luxembourg is known more for housing EU governmental offices as well as international finance companies, while Lisbon seems to generally not have invested in tourism as much. I did hear in each place that the surrounding countrysides are beautiful, so perhaps that is where more tourism happens and where more interesting things can be seen. (Also, it didn't help that I was in Lisbon on a Monday, when many things are closed.) For another, both cities are not especially good for people like me in power wheelchairs who want to travel independently; people who are able-bodied, in manual wheelchairs, or have disabilities that require them to be assisted by partners or personal care attendants full-time may be better served. In Luxembourg, I didn't feel like I missed too much because it's a fairly small city anyway, and the public transit buses were accessible (though there were some issues even there). In Lisbon, I felt like I missed more because it is a bigger city, yet its Metro rapid transit train system, which is supposedly accessible, actually has large gaps between the train floors and platforms, and most of the buildings have large steps to enter. I do hope to visit Europe again, but when I do, I hope to make sure it will be a city/area that is more friendly to people in power wheelchairs.

My Time at the 2019 APS March Meeting

This is a quick update from my trip to the 2019 APS March Meeting in Boston, Massachusetts at the beginning of March. I felt like my time overall was somewhat mixed, though positive on balance. On the negative side, my talk was lumped into a totally unrelated session on a Thursday afternoon, in which the talks weren't of interest to me and were generally not so well-delivered, the audience consisted almost entirely of the speakers who left after their own talks (and that included me after I saw what was happening, though I was grateful that some of my friends came for my talk), and the first talk which was supposed to be a 36 minute-long invited talk was canceled in the absence of the speaker, leading to a break during that time. Additionally, my advisor and I were busy preparing a paper unrelated to the work I would be presenting, and I've also been taking my time to figure out what I want to do after graduation, so I didn't prepare a schedule of talks to attend as well as I had in the previous two years. That said, on the positive side, I paced myself properly in attending talks, and I did appreciate having conversations with people from my department as well as people I knew in college about our work as well as future plans. I also had a lot of fun hanging out with friends from college as well as graduate school, and though I could have done a better job networking, I did try to reach out as much as I could. Finally, I had a great time skipping the last day of the conference and visiting MIT instead, where I got to catch up with professors from the physics department as well as other people whom I knew well in college (and met some people for the first time too); I felt like that was a far more useful & productive move. Next year, I hope to be able to present in a session more relevant to my current research interests, and to do a better job of tailoring my networking and session attendance to my future interests (which I hope will have solidified by then).

Third Paper: "Phonon-Polariton Mediated Thermal Radiation and Heat Transfer among Molecules and Macroscopic Bodies: Nonlocal Electromagnetic Response at Mesoscopic Scales"

My third paper has been published! It is in volume 121, issue 4 of Physical Review Letters, and an older preprint of it is available too for those who don't have access to academic journals (it has all of the same figures and ideas, though it is missing a few sentences of further explanation as well as a couple of new citations that were inserted for the final publication). As with my previous papers, in the interest of explaining these ideas in a way that is easy to understand, I am using the ten hundred most used words in English (except for the two lines that came before this one), as put together from the XKCD Simple Writer. I will use numbers sometimes without completely writing them out, use words for certain names of things without explaining further, and explain less used words when they come up. Keep reading to see what comes next.

In the paper that came before this one, I looked at how to do a better job of figuring out the van der Waals (vdW) forces, which are the forces that let geckos (small animals with hard skin over which your finger can slip easily) stick to anything no matter what it is made of, between molecules, which are the little things that make up most of the stuff we see and are in turn made of smaller things called atoms. I tried to figure out how these forces look at distances where the fact that molecules are made of atoms is important, but if those molecules are near much larger bodies, the fact that the larger bodies are made of atoms and molecules should be less important; it turns out that at those distances, how fast light goes matters a lot, and using ways to figure out these forces exactly instead of using easier ways to figure out those forces makes a big change in what those forces are. That paper was able to show how to bring together all of these different ideas from considering large and small bodies in a single way where none of those ideas can be ignored. That would be important when considering new kinds of molecules like graphene, which is made of a lot of carbon atoms in a thin sheet, or really long molecules like DNA or those found in foods, when those molecules are near larger bodies that we make.

This paper looks at the same sorts of molecules, but not at vdW forces anymore. Instead, in this paper, I look at how heat (through light) goes between different molecules, especially when they are near larger bodies. For that, I need to do a better job of considering how molecules can make changes on each other through light, and that means that I need to better consider how the full atoms within molecules move toward and away from each other in a way that repeats itself. By doing that, I can now show how heat through light goes between different molecules, whether they are close together or far away from each other. When people considered heat going through light between larger bodies, they found that the heat would keep growing as the bodies came closer together, and that growing wouldn't stop; from knowing how things work every day, we know that once bodies come close enough, they touch each other, and the growing stops at some point. In this paper, I've shown that when molecules come close together, the heat grows for a while, but if they come close enough, that growing does stop, so I've been able to show what distance we can say two molecules touch each other, so that heat going between molecules happens through them touching instead of through light. This is really important for things like graphene, which are used as part of things used for making power from the sun by getting its light and heat, and also for making new things that can become part of computers made of really small things like molecules that work because of heat going between different parts.

My Time at the 2018 APS March Meeting

This is a quick update from my trip to the 2018 APS March Meeting in Los Angeles, California at the beginning of March. I felt like I learned many lessons from my trip to the 2017 APS March Meeting and was able to apply them here. Chief among them, I realized that a large part of this conference is networking, whether that involves the formation of new relationships or the maintenance of old ones, so I got to enjoy myself more in meeting with old friends and collaborators and making some new connections as well; that also meant that I focused more on going to talks of immediate relevance to my research interests as well as my friends' talks to show them support, and I didn't worry about trying to fill each day by attending talks and sessions like I did last year. I was able to present my work this time too: I presented a model for vibrational contributions to radiative heat transfer and van der Waals interactions among molecules, along with interesting results in specific systems. This was in a session that included people from both the microscopic van der Waals and macroscopic Casimir communities, and while I was the only one who discussed heat transfer per se, I did get to see a nice mixture of the two communities, and some interesting discussions did come out of that. Overall, I had a great time, but I do think that as I progress further in my graduate research career, it may be good to not only continue to attend the APS March Meeting in the future but look into more specialized conferences too.

Halfway through Fourth Year

I realized that I hadn't written anything broadly about my progress through the PhD program in a while, so I should do that now. I'm halfway through the fourth year of the program, and this year has allowed me to take on more responsibilities compared to last academic year.

For one, I'm now doing more projects than I was last year. In particular, last year, my main focus was on fleshing out a way to combine atomistic and continuum treatments of electrodynamic response in order to understand van der Waals interactions among molecules and larger bodies (which was the subject of my second paper). I did a bit of work on the side extending this to situations where the molecules may deform, and while that work still hasn't been published yet, it was not particularly difficult to understand what was going on there given the broader picture of mesoscopic van der Waals interactions. In any case, I was able to basically focus on one major project whose path and end goal seemed fairly well-defined, and as a result, I was able to take things a bit easier. By contrast, right now I'm working on two parallel projects incorporating vibrational effects into this description of molecular response and seeing how that affects the van der Waals interactions as well as heat transfer between molecules. This required quite a bit more formulation and writing & testing code on my part, and featured significantly more uncertainty in the results, because while the basic formulation of van der Waals interactions between molecules and macroscopic bodies for my previous project could be relatively easily extrapolated from our collaborators' description of interactions among molecules alone (and the resulting physical interactions were relatively more predictable), I wasn't really sure what to expect with respect to the modification of these interactions due to vibrations, nor what to expect for heat transfer or thermal emission at all; this is because as far as I can tell, other people haven't really considered molecular vibrations in such a context in an ab-initio manner thus far. Thus, I've felt like in terms of research, I have a lot more work and more uncertainty on my plate now than I did a year ago.

For another, I was a TA for the first time last semester and am a TA again this semester. This semester is turning out to be particularly interesting in that regard, because while last semester I was a TA for a graduate-level quantum mechanics class where I could basically count on students knowing what they were doing and not needing me to hold their hands at every obstacle, this semester I am a TA for a freshman-level linear algebra class that is being taught as an engineering class for the first time; not only am I assisting with a class for which the curriculum is being developed afresh, but this class has a diverse group of freshman who are from less-resourced schools and may have less formal math and science background than some of their peers here, so beyond ensuring that I be an effective pedagog for freshmen, I now have to make sure that I can connect with these students by making myself feel inclusive rather than forbidding.

Most broadly, I now have to think more seriously about what I want to do after I graduate, as that point comes nearer. The big question is whether I want to stay in academia or not, given both the locations where I may find interesting opportunities and the nature of such opportunities. For a while, I thought that I would more likely want to leave academia given the tough odds of finding a tenured faculty position in a place that I would like to be, so I at least thought of doing an internship this coming summer outside of academia. While I still haven't ruled out the latter idea, I have come to realize that I enjoy academic research enough to consider continuing it for at least a few years after graduation, and I've also realized that it isn't necessarily a good choice to try to divine my career many years in the future based on my assessment of my current research progress, as that future becomes less certain the farther away it is. Given that, I also feel like a summer internship could disrupt the pace of my current research, so I would want to engage in it if I could be reasonably sure that it would actually help with my current research. However, if I forswear a summer internship to focus on my current research, then I have to really make sure that I fully investigate my options following graduation; for example, I have a few ideas on research topics to pursue following graduation, but I have no idea how feasible they are because they're in an adjacent field with which I have essentially no experience, so I need to get to know people in that field and make those connections to facilitate my next move. I'm going to the 2018 APS March Meeting next week, so with the uncertainty about my research projects & directions in the short- & long-terms along with the need to more seriously network with researchers in the field, this upcoming conference does feel like it has higher stakes for me than the one I went to last year, when I wasn't as worried about such things.

Such seems to be the course of research in a PhD. I'm glad that I've been able to take up these responsibilities and become a more well-rounded researcher & educator, and the uncertainty of research is gratifying to the extent that I get to investigate different ideas with the chance to fail and improve further in the hopes that I will ultimately hit upon something successful. However, the flip side of that uncertainty is stress when I realize that I have to deliver in some way, whether that means making a good impression & networking effectively at a conference or seriously considering upcoming career moves (where I again would have to make a good impression upon whoever may be evaluating me for a job). Ultimately, my hope is that I can continue to work hard & stay focused on what I need to do without letting that stress and uncertainty cloud my decision-making in the hope that my hard work will pay off, in the same way that in my second year, when I was stressed about my slow research progress relative to some of my peers, I simply pressed on and was eventually rewarded (through the fruit of my labor) with a publication at the beginning of my third year; even if that payoff doesn't come in the way that I expect, my hope is also that by that point, I will have cast a wide enough net that other options will be available to me too.

Second Paper: "Unifying Microscopic and Continuum Treatments of van der Waals and Casimir Interactions"

My second paper has been published! It is in volume 118, issue 26 of Physical Review Letters, and an older preprint of it is available too for those who don't have access to academic journals (it has all of the same figures and ideas, though it is missing a few sentences of further explanation as well as a couple of new citations that were inserted for the final publication). As with my first paper, in the interest of explaining these ideas in a way that is easy to understand, I am using the ten hundred most used words in English (except for the two lines that came before this one), as put together from the XKCD Simple Writer. I will use numbers sometimes without completely writing them out, use words for certain names of things without explaining further, and explain less used words when they come up. Keep reading to see what comes next.

My Time at the 2017 APS March Meeting

This is just a quick update from my graduate studies. In the middle of March, I was able to attend the 2017 APS March Meeting in New Orleans, Louisiana; this is the first conference that I have attended in any capacity. I had a ton of fun being able to travel there and meet with old friends, collaborators whom I had not yet met in person, and other people that I didn't know but who have been working on similar things to me; it was great being able to discuss interesting potential project ideas with them. Going to many talks was also cool, giving me a good sense of the state of my field and the sort of work that other people are doing, though in many respects, I honestly feel like I learned more just from talking with people at length in more informal settings. Finally, the highlight for me was getting to present my own work and seeing the interest that many people took in it: I was presenting a semiclassical electromagnetics approach to van der Waals interactions between molecules and larger bodies in a session dominated by density functional and atomistic long-range many-body approaches to van der Waals interactions solely in [large] molecular systems, so I was truly gratified to see that members of the audience saw value and significance in what I've been doing, especially given how different my talk was from those that came before and after it in that session. Overall, I had an amazing time, and I hope to be able to attend other conferences, both similar to this as well as more specific to my research, during my remaining time in graduate school.

First Paper: "Nonadditivity of van der Waals forces on liquid surfaces"

My first paper has been published! It is in volume 94, issue 3 of Physical Review E, and an older preprint of it is available too for those who don't have access to academic journals (it has all of the same figures and ideas, though it is missing a few sentences of further explanation as well as a couple of new citations that were inserted for the final publication). In the interest of explaining these ideas in a way that is easy to understand, I am using the ten hundred most used words in English (except for the two lines that came before this one), as put together from the XKCD Simple Writer and the Wiktionary list of the 1000 most used words. I will use numbers sometimes without completely writing them out, use words for certain names of things without explaining further, and explain less used words when they come up. Keep reading to see what comes next.