Teaching Makes Grad Students Smarter

One of the best pieces of career advice I received as an undergrad was that if i wanted to go to grad school I should work as a TA for the freshman and sophomore level physics classes.  As a TA for those classes I learned how to do all of the basics of mechanics, thermodynamics, electromagnetism, and even a bit of quantum mechanics in my sleep.  I can still solve elastic collision problems on autopilot.  And it turns out that one of the big tricks to doing well on the physics GRE (aside from just being really smart) is to be able to do freshman and sophomore level physics very rapidly.  I credit most of my "decent but not terribly impressive" physics GRE score to those shifts in the tutoring labs on the 3rd floor of the Eyring Science Center.

But you don't have to take my tales of benefits of teaching as the only evidence for the link between teaching and success.  A paper in Nature (see the review by the Chronicle of Higher Ed) purports to have objectively created a measurement of the quality of a grad student in the physical sciences as a researcher and then tracked that quality for groups of grad students that worked as TA's versus others that simply worked as researchers.  To measure research quality they had 95 grad students write research proposals twice - once early in their grad careers and again several years later. The proposals where then graded by a review panel similar to those used by the NIH and NSF. Interestingly, they found that the two abilities most improved by teaching were generating testable hypothesis and valid research designs.

The authors limit their speculation as to why those two qualities are improved by teaching experience, but my guess is that teaching emphasizes understanding how fundamental concepts (e.g., conservation laws in physics) are used over and over again in progressively more advanced ways.

Cosmology Can Possibly Solve the Neutrino Hierarchy Problem.

There are three neutrino species in the standard model, hereafter refereed to as 1, 2, and 3, that we know have mass from atmospheric and solar neutrino oscillation experiments. Furthermore, data from these experiments put constraints on the mass-splittings between these three neutrinos.  From atmospheric experiments we know the mass differences between 2 and 3 is |M²₂₃| ~ 1.4x10^-3 eV² and from the solar neutrino experiments we know the mass splitting between 1 and 2 is M²₁₂ ~ 7.9x10^-5 eV².

So here is the problem: We know that the neutrinos have mass and we know what their mass splittings are but we don't know their hierarchy or in other words the order of their masses as shown in the figure to the right. For example, it could be that neutrino 3 is the most massive of the three... but it can also be the case that it is the least massive.  This is what I mean by the neutrino hierarchy problem I used in the title.

Cosmology To The Rescue!

Fortunately, there are cosmological measurements that can be made that may solve this issue in the future. In this post I will discuss a wonderful paper that pioneered these details was written by Jimenez et al.  The solution goes like this:

1.  CMB and large scale structure experiments give us a bound on the sum of the neutrino masses denoted as Σ = m₁+m₂+m₃.  The current bound is that  Σ  is between 0.05eV and 0.3eV.

2. After Σ is better constrained in the future, the mass splitting Δ = m₃ - m₁, importantly with sign!, can be be measured from the matter power spectrum of large scale structure for the given Σ.  The plot above shows how the matter power spectrum, P(k), is altered by the different values of Δ.  Once Δ is known with confidence, including sign, the problem is solved.



3. The plot above shows forecasts for how well we will be able to tell the difference between the normal inverted hierarchy given future experiments. (Normal being where m₃ is larger and invereted when it is smaller.)

4.  Furthermore, cosmolgy should be able to shed light on whether neutrinos are Dirac or Majorana particles. (If Majorana they are their own anti-particle and if Dirac they are not.) The below flow chart shows how this works.  First, double beta-decay experiments may be able to determine directly if neutrinos are their own anti-particle.  But if future experiments fail to see a signal, cosmology may help answer if this is because the signal is just too weak or whether it is because neutrinos really are Dirac. As you can see, if Σ is just right and if the hierarchy is inverted or degenerate, cosmology will be able to demonstrate neutrinos are in fact Dirac.

So in conclusion: It appears cosmology may be able to provide a wealth of insight into neutrino physics in the coming years.  Through cosmology we may solve the neutrino hierarchy problem and even possibly say whether or not neutrinos are Dirac.

Jimenez, R., Kitching, T., Peña-Garay, C., & Verde, L. (2010). Can we measure the neutrino mass hierarchy in the sky? Journal of Cosmology and Astroparticle Physics, 2010 (05), 35-35 DOI: 10.1088/1475-7516/2010/05/035

"Rational" Referees May Hurt The Peer Review Process.

Those of us who work in academic fields hope that the peer review process in some sense works.  Thurner and Hanel recently studied the effects of one particular entity that may hurt the process: the rational referee.  Here, rational referes to someone who largely accepts or rejects a paper by factoring in how the acceptance or rejection of the paper will impact himself/herself. (To me this is not the best definition of rational which is why I have put it in quotes "" in the title.  However, I am reporting their work so I will stick to their definition.)

From the authors:

A fundamental problem of the peer review process is that it introduces conflicting interests or moral hazard problems in a variety of situations. By accepting high quality work and thus promoting it, the referee risks to draw the attention to these ideas and possibly away from her own. A post-doc looking for his next position is maybe not happy to accept a good paper of his peer who competes for the same position. A big-shot in a particular field might fear to risk his ’guru status’ by accepting challenging and maybe better ideas than his own, etc. In other words, referees who optimize their overall ’utility’ (status, papers, fame, position, ...) might find that accepting good scientific work of others is in direct conflict with their own utility maximization. In the following we call utility optimizing referees rational.

Though one might argue that it is obvious that self interests would hurts peer review, we would like to be able to put some numbers behind the idea so as to "quantify" how bad the problem might be.

To test the effects of a rational referee, the authors ran several simulations where papers are refereed by 3 types of referees described below.  The scientific quality of the papers follow a Gaussian distribution, ie each paper "is assigned an 'IQ' index... drawn from a normal distribution" with mean=100 and standard deviation = 10.  In addition to being a referee, each person in the simulation is also an author of a paper himself/herself but never referees their own paper.  Here are the types of referees considered:

• The correct referee: This person is competent to judge the quality of the work, and only accepts the best scientific papers given.  (Using an algorithm described in the above paper.)
• The stupid referee: This is someone who is not competent to properly judge the work and so the acceptance or rejection is random. (Who hasn't run across this? :) )
• The rational referee: This is someone who compares the quality of the paper they are refereeing to the quality of their own work and accepts or rejects accordingly.

At this point it should be pointed out that if the average paper accepted has a score of 100, then the peer review process does no better than flipping a coin.  With that said, here are some plots:

The above plots show the results of average paper quality versus the fraction of rational referees.  The three separate colored curves are for different fractions of "stupid" referees.  For example, the blue curve has 10% of the referees being stupid.

The plot above here shows what happens after t publication rounds.  Fig. a is when all referees are correct. As you can see the average paper IQ is ~120.  Fig. b shows a histogram of the IQ of the papers accepted compared to the gaussian distribution they were drawn from.  Fig. c is the same as Fig. a except now 10% of the referees are rational and Fig. d is the same as Fig. b with the same caveat.  If only 10% of referees are rational, the paper quality diminishes significantly.

Conclusions:

The authors conclude thus:

The presence of relatively small fractions of ’rational’ and/or ’random’ referees (deviating from correct behavior) considerably reduces the average quality of published or sponsored science as a whole... systemic level. Our message is clear: if it can not be guar- anteed that the fraction of ’rational’ and ’random’ referees is confined to a very small number, the peer review system will not perform much better than by accepting papers by throwing (an unbiased!) coin.

 And as we all know, referees that factor in their own self interest or are incompetent to judge the works they are assigned exist.  As may be inferred from above, if these two groups aren't kept in check, the process may become no more reliable than flipping a coin.

Stefan Thurner, & Rudolf Hanel (2010). Peer-review in a world with rational scientists: Toward selection of the average E-Print arXiv: 1008.4324v1

Do Scientists Sometimes Publish Just To Be Cited?

Speaking of the Hořava gravity excitement, Luboš Motlhad this to say about four months after Hořava's initial publication:

Fifty papers have been written about the Hořava-Lifshitz gravity (NYU about it). Aside from the first author - Petr Hořava - and the most recent group of authors, everyone in this list seems to have gotten carried away...

They knew that someone would refer to them, whatever they write, so they often (incorrectly) connected the new bandwagon to their older work and/or offered solutions that would only be interesting if the theory actually worked...

So Motl seems to be implying that, outside of a few important papers like the one from Hořava, some scientists published papers largely to catch a bandwagon wave that was sure to bring lots of citations, even if the work was not high quality.

I'm not going to speculate whether or not this is true.  However, it raises an interesting question: Do scientists sometimes publish papers because it is a good opportunity to generate citations, even if the quality of the paper is not that great?

I guess even scientists are human.  That said, I'm not sure it is the ethical thing to do.

A quick shot of my galaxy simulation

[Updated]

I mentioned previously that I have been working on a galaxy simulation with a star forming region in the center. Things have been progressing, I think I can go to running 3D simulations sometime in the next two months. I will share more information when I have it, but I just wanted to share a cool picture that I made from my simulation.This is a density map of the r and z directions (x and y, on this image) of a galaxy, or a slice in the x-z plane at y=0 if you prefer. So top and bottom of the image correspond to above and below the galaxy. We are looking at the galactic disk edge on.

There are a few cool things about this image that made me excited, mostly the long filaments coming out of the galaxy. I was excited about this because that is almost exactly what we see in real galaxies, and is exactly what we are trying to find through simulations. The one problem I had here is I messed up with a certain parameter which made the galaxy not be in hydro-static equilibrium to start out, which means it kind of collapsed in on itself. That explains why the disk is so narrow and so dense.

[Update]
I failed to mention that this image was rendered in ParaView. I also have a few movies that I made relating to this simulation (again rendered in ParaView). A movie showing density can be found here (Note: It is large, 27 MB). Another showing speed (magnitude of velocity) can be found here (also large, 33 MB).

What I have been doing this summer

So I started out this summer by being a TA which went well (I haven't received any death threats from my students). The rest of my summer has been focused on research, specifically learning how to model things on the computer. As of right now I have two co-advisors, one who focuses on the computation aspect of our project, and the other on the observation aspect. I am supposed to be the one that translates between the two and keeps them both up to speed on what the other is doing. In the process I learn both computation and observation (and maybe some instrumentation). So far I am learning a lot and the project I am working on seems fun.

We are focusing on two galaxies to get a good idea of what is happening in their cores in order to understand AGN and galactic blowout. What is galactic blowout? That can best be explained with a picture. This picture was taken using Hubble Space Telescope by my advisor Gerald Cecil a while back. It is an image of central region of NGC 3079.You can see the expanding bubble of gas in the middle. It is this expanding bubble that we are interested in. Notability the curvature of the filaments the source of the bubble and the circumstances that made it form. My job is to figure out a way to model this as realistically as possible.

For that I have been learning how to use a hydrodynamics code called Athena. There were other codes I could have used (like VH-1 for example) but my other advisor Fabian Heitsch recommended Athena for this type of project. So I downloaded Athena and went to work figuring out how to use it. I would say that it is a very well written code (of the little that I have used it) and that it is very intuitive and easy to learn (it's written in C). Right now I have been making up some toy models to get a good sense of how it works and what I can do with it. Recently (this week) I have been working on getting the data out and into an interesting format (one that I can show people and wow them with). On that note I have a short video for you guys.

What I have here is an extremely simple (emphasis on extremely, and simple) model of the disk of a galaxy (a constant density disk with exponential fall off to halo densities, not very realistic but for now it works). I have insterted a "starburst" in the center with an over-pressure region (luminosity/supernova) along with some wind (i.e. kinetic energy, matter outflow). The computation is only doing 2D, and is small enough that I am running it on my laptop.

Here the x-y plane represents the computaion grid (250 grid points in the x, 500 in the y). The z axis is density. I took the output from Athena and fed it into MATLAB and turned it into a movie that I am posting here. I hope you enjoy. When I have real stuff (with good physical interpretation) I will post about that.

The Research Doldrums

Back when nautical vessels were 100% wind powered, there was a saying that what sailors feared more than storms were calms - times when the wind simply refused to blow, leaving the ship effectively stranded. Near the equator there is a region called the doldrums where strong solar heating of the earth's surface creates strong vertical motions that tend to stifle horizontal winds, leaving ships stuck.

Anyone who has been in basic science research for a while can tell you that research is a little like sailing in a wooden sailboat on the wide oceans. Sometimes you discover the New World, sometimes you get raided by pirates, and sometimes you get stuck in the doldrums, baking under a hot sun, waiting for the winds to pick up and get you moving again. And although modern researchers have more options than becalmed 17th century sailors, sometimes it doesn't seem that way.

I am currently stuck in the doldrums. I am trying to improve our models of the sun by improving the way we model physics at small-scales. This falls under the long-standing problem of how to model turbulence, which has an annoying tendency to take large scale motions, break those motions into increasingly smaller scale motions, and finally dissipate the kinetic energy in small scale motions via viscosity. It's a hard problem and I'm not trying to solve it so much as use what little insight others have gained to improve our models of the sun.

I have two so-called turbulence models that should do this, but when I implement them into our code sadness ensues. One of these models seems to upset the fundamental balances of how energy is transported outwards in the solar convection zone and defies all my attempts to understand why it does so. The other appears to be extremely computationally expensive making it more work than it is worth. I have been working on these two problems for several months now, but every time I make a little progress and I feel a slight breeze and begin to think the wind might be picking up, it dies down again. And so I remain stranded on my little boat of research, praying for some wind.

Ironically, the sun remains in the doldrums as well with almost no magnetic activity. Perhaps it can't get its small-scale turbulence models to work either.

To Observe or To Compute?

At CU we have two parts to our comprehensive exam. Comps 1 is a test which I have previously vented about at length here, here, and here. Comps 2 is a "publication-quality research project presented orally" along with a bit of on-the-spot grilling by your professors. This is designed to be done by the start of your third year, which means I am currently in the process of selecting a project. I have narrowed things down to two good options:

1. I could continue to work on dynamo models of the sun and sun-like stars by implementing and testing improved small-scale turbulence models. In a nut-shell, our code cannot hope to resolve all of the turbulent scales of motion on the sun, so instead we resolve the largest scales and then parametrize the effects of the smaller scales as enhanced diffusion of momentum, heat, and magnetic field. Currently, we use a simple, effective, and essentially unphysical parametrization. I have played with some improved methods, so one possibility is for me to do my Comps 2 on a serious study of ways to improve our "turbulent closure model".
2. I could go off the beaten path a little bit and do some work on actual observations of the sun. The interior of the sun can be "imaged" by measuring how acoustic waves propagate through the sun in basically the same ways that geologists use earthquakes to probe the Earth's interior. This is known as helioseismology. My project would be to characterize the uncertainty caused by one source of helioseismic error.
   

I could probably make a greater impact by sticking with #1 and in the long run I would prefer to stick with computational work, but Comps 2 would also be a good chance for me to get some experience with actual observations. And I hear that actual experience with observations is a good thing when it comes to getting a post-doc. So the question is to observe or to compute for Comps 2? I'd love to hear your thoughts.

Saturating the Departmental Specialization Instability

This started off as a comment on Bill's post "Departmental Specialization" but just got too darn long for a comment.

I agree that there seems to be an instability, if you will, that would lead departments to specialize. The more success a department has in a certain field, the easier it will be to get funding, high-quality grad students/faculty, and good facilities in that field. I think what saturates this instability in most departments is that the popularity and funding levels for the various sub-fields wax and wane on time scales of ~10 years while faculty hires operate on time scales of ~30 years. This means that while one field, say cosmology, might be really hot right now, if you devote all of your faculty hires and facilities to cosmology for the next few years then in 10 years you may be unable to adapt to whatever new sub-field has become hot because you have a faculty full of cosmologists.

I saw first-hand an example of this at an university that we shall refer to as High Tc U. In the mid- to late-1980's, high temperature superconductors were a really hot area of research. Funding was plentiful and breakthroughs were coming at an amazing rate. High Tc U. jumped onto the superconductor band-wagon and hired quite a few experimentalists and theorists in the field. For a while, High Tc U. was swimming in grants and publishing papers like political parties publish annoying mailers. It was a Mecca for superconductivity research and superconductivity research was where everybody wanted to be.

Fast forward to a few years ago when I got to know the department. High Tc U. is still a Mecca for superconductivity research, but now the funding is hard to come by and the breakthroughs are few and far between. Because of the slew of hires in one sub-field, some of the other sub-fields suffered and the department wasn't able to keep pace in some other areas. To be honest, High Tc U. is only now, 20 years later, regaining the balance it had before the superconductor revolution. The only way to regain that balance was to wait for 20 years for retirements and growth in the department to bring in a critical mass of new people in areas like nuclear, condensed matter, and AMO that can compliment and collaborate with the superconductivity people while focusing on their sub-fields that are better funded and more popular today.

My theory is that while there are some departments like UIUC's physics department that can continue to thrive with one dominant sub-field, there are others that try to become "the superconductor department" or "the supernova department", hire a bunch of faculty for ~30 years in that one area, and then watch as the field cools off after 5-10 years. By having a broad department, you can react to whatever new fields show promise quickly and weather the ~10 year fluctuations in funding levels for various fields.

Departmental Identity

The Astrophysical and Planetary Sciences (APS) Department at the University of Colorado is an interesting creature that I've been meaning to post on for some time now. As the name suggests, our department has a somewhat divided nature. We have people who would call themselves physicists that work on things like plasmas, fluid dynamics, and general relativity. We have people who consider themselves astronomers that do everything from solar observations to observational/numerical cosmology. We have people who associate mostly with geologists that study everything from the surfaces of Mars and Io to the composition of asteroids and comets. The APS department really defies identification with a single academic discipline. We are something like an astronomy department that accreted pieces of what are traditionally physics and geology departments.

This, of course, is a mixed blessing. When we talk about classes, there are invariably disputes between the astronomers, physicists, and geologists over what needs to be included in the "core" courses. Physicist want to see the grad students take courses with the physics department like E&M, quantum mechanics, and statistical mechanics. Astronomers want to take some of that, but also include classes on radiative transfer and data analysis. Meanwhile, the geologists in our midst feel that topics like fluid dynamics, geochemistry, and planetary surfaces are indispensable. And so we go around and around this topic every time somebody brings it up and invariably some group feels disenfranchised. Currently in the APS department, the physicists and astronomers have metaphorically ganged up on the geologists and so I take classes on quantum mechanics and radiative transfer, but not planetary surfaces.

On the other hand, when I visited the University of Illinois, I found the opposite case (Bill, be sure to correct me if I'm wrong). Illinois has a lot of good research areas, but there is no question that condensed matter is king in that department. While this solves the lack of identity problem we have at CU, it does have it's own weaknesses as well. As an incoming grad student, I wasn't positive what I wanted to do my research on. At CU, I could have gone in literally a couple dozen different directions. While Illinois has other research options beyond condensed matter, the breadth of options certainly isn't anywhere near what it is in Colorado.

My obviously biased opinion is that departments shouldn't be too intent on defining themselves as "the condensed matter department" or "the cosmology department". Although there are issues with being a broad department, I think the hassle pays dividends as various sub-fields wax and wane in popularity. However, I am interested to hear your thoughts. Is your department broad or focused and is that a good thing?

Summer Time and the Living's Easy

Here at CU, it's been academic summer for nearly 6 weeks now and for me that means that for the past 6 weeks I have been doing just one thing: research. That's right - no homework assignments, no lectures to attend, no grad student meetings, just pure research. Oh how I love the summer.

Don't misunderstand me - classes, homework, and grad student meetings have their place and are very important, but they do serve to clutter up my schedule. For example, here's the contents of my Google Calendar (which is the only thing that keeps me sane and where I need to be during the school year) for April 7:

08:00 - 08:30 Register for Classes
09:00 - 10:50 Survey Kyle's Students*
11:00 - 11:50 Astrophysical and Space Plasmas (Lecture)
12:00 - 12:50 Collunchium (Lunch with Colloquium Speaker)
13:00 - 13:50 Observations and Statistics (Lecture)
14:30 - 15:50 Meet with Don*
16:00 - 16:50 Colloquium

On top of that, I also had to squeeze in a couple hours for research and a couple more for homework, not including the items marked with an asterisk which were already homework. All in all, it added up to a hectic day where I had to stop what I was doing and switch to something else about every hour.

Now compare that to my schedule for today:

08:00 - 18:00: Research

You see, the days are just a long (in some cases a bit longer) in terms of hours worked, but instead of running around and working on a half dozen totally different things, I get to focus on a single objective. Today, for example, I am monitoring a couple of simulations that test a new sub-grid scale model for our code, running a simulation to explore a particularly interesting dynamo case where the simulated star just can't seem to find a stable configuration, and analyzing data from that simulation to explore why it can't find its happy place. In other words, all of my efforts are focused on improving our understand of how stars generate their magnetic fields.

So, what are you doing this summer? With any luck, you're blissfully doing research as well, but there are other worthwhile pursuits. I hope your summers are as enjoyable and relaxing as mine.

Presentation and NSF Prizes

First as an administrative thing:

Since Steve has no longer been notifying people of the papers we will use in our theory talks I decided to post them here since I know many people who go to these meetings check out the blog.(They are also allowed to contribute. int hint. :)) The papers I will draw from for my next lecture are these:

http://arxiv.org/pdf/astro-ph/0401547
http://arxiv.org/pdf/hep-th/0410270

Also, I thought this was interesting- The National Academy of Sciences is petitioning the NSF to grants prises of several million dollars to scientists who tackle big problems.

Delusions of Grandeur

Well, after seeing all of Joe's posts I figure that it should me my turn too. So in response to the last post by Joe...
Don't worry I'll figure out your Theory of Everything (TOE) dreams. That's what I am here for! You just keeping looking at your Cosmology business and I'll take care of the rest. Yes, yes you might say that I am having delusions of grandeur but I figure that you need to start somewhere, right? Unfortunately, I still don't understand anything but the first few pages of Polchinski so I have a long way to go. It is really amazing to me how much there is to learn. I wish I had more time and less homework so that I could do some new physics (and for that matter, Mathematics too).
I think I better stop there otherwise I might start complaining, and most everyone who knows me has heard my rant about just wanting to do research! Hopefully this summer I can find myself a very cushy String Theory research internship. That will set me straight. So I will sign off and start looking for those internships!