Monday, February 29, 2016

You really should take a vacation

Today is the first day of classes for the beginning of the academic year. I am back to a regular teaching load. Last year, I posted about the most discouraging thing about the first week of semester.

In preparation for a busy semester, I took last week off work (my last two posts were automated) and visited my son who has just moved to Canberra (ironically where I grew up) and spent time with my wife backpacking in one of my favourite places, Kosciusko National Park. Some photos are below. This reminded me of the importance of vacations and down time, of the therapeutic value of the nature drug, and of turning off your email occasionally. 

Blue lake

A view of the Rams Head Range from the upper reaches of the Thredbo river above Dead Horse Gap.

A brumby (wild horse) near Cascades Hut.

Wednesday, February 24, 2016

What are the best interdisciplinary courses for undergraduate science majors?

Previously I posted about how science has changed [it is much more interdisciplinary and computational] and undergraduate science education really needs to catch up. I endorsed a great course on Physical models of living systems that Phil Nelson teaches and has just published a text for. [He kindly sent me a complimentary copy recently.].

In the recent UQ review of the B.Sc. there was some discussion of whether there should be more interdisciplinary courses offered and even whether one or two might be compulsory.
That got me thinking about what the best courses would be.

Energy and the Environment
David  MacKay at Cambridge has a book Sustainable energy: without the hot air

Advanced instrumentation and precision measurement
NMR, x-ray crystallography, laser spectroscopy, mass spectrometry, microscopy, ...
This should not just introduce these methods as "black boxes" but also describe the underlying science and let students have hands on experience.

Chemical biophysics or Biophysical chemistry
Either of Phil Nelson's two texts are idea models. On the other hand, they involve purely classical physics. One needs to also look at some quantum mechanics that relates to spectroscopy.

Computational biomolecular simulation and materials science
Again hands on experience is essential. But, a "black box" mentality must be avoided.

Materials science and engineering
There is a classic text by Callister, but a colleague tells me it is to much from the perspective of a metallurgist.

Here I think it needs to be continually emphasised that there is no point offering such courses if they are not rigorous and coherent. They need to be "owned" by just a few faculty. Courses will multiple guest lecturers from multiple departments quickly degenerate into a "dogs breakfast" and political nightmares. A single text is highly desirable.

What do you think?
What courses would you suggest?
What are suitable texts?

Friday, February 19, 2016

We need to tighten eligibility criteria and enforce them

There are several trends this post addresses:
  • declining success rates on grant applications due to decreasing funding and increasing numbers of applicants
  • desires to provide more opportunities for young people, women, and minorities
  • the desire of administrators to be seen to be providing more opportunities
  • the increasingly large amount of time required to prepare grant applications
  • the large amount of time and money spent processing, assessing and ranking grant applications
So who should be allowed to apply for a specific grant or fellowship program?
How rigorously will eligibility requirements be enforced? 
Will there be allowance for "special cases"?

First, it is important to acknowledge that any grant or fellowship program has certain eligibility criteria: type of institution, career stage, gender, nationality, number of grants already held, ...

A few things I have been recently been involved in that I thought were good.

Expressions of Interest.
Prior to a full application, potential applicants sent a copy of their CV and a paragraph or two about their specific proposed application. A committee screened these and then discourages or forbids some of the applicants from applying. The promising ones may get constructive feedback about the direction their application could take.

Rigid enforcement of eligibility criteria.
Given the opportunity it is amazing to see the reasons that people can come up with as to why they are "special" and "entitled" to apply. It ranges from personal situations (illness, career interruptions,...), family situations (e.g. childcare, the career choices of their spouse) to scientific claims (U of Mediocrity really is the best place in the world for my research, ..., I am just on the verge of big breakthrough, ..., my equipment broke,...).
Some would say we were "heartless" in throwing out almost all these claims.
Dealing with these claims, particularly when administrators write ambiguous eligibility criteria and allow for "compelling" special reasons, wastes a lot of time and can create ill filling.

Reducing the number of people who can apply by more exclusive eligibility criteria.
Significantly reducing the applicant pool for one program, by only allowing those with permanent positions to apply. The argument was that the university should only be investing scarce resources in people who they had made a long term commitment to.
Some cried this is "not fair". Maybe it isn't. But at least it reduced the number of applications to a "manageable" level. And there are other programs that people with permanent positions cannot apply for.

The political obstacles to making changes like the above can be considerable. It relates to the challenge of setting priorities. A concrete example is the controversy back in 2009 when the UK funding body, EPSRC, tried to ban "serial unsuccessful" applicants.

To me any program that has a less than 20 per cent success rate needs to be tightened up. Unfortunately, that is most programs!

Wednesday, February 17, 2016

Linear magnetoresistance in Dirac semi-metals turns out to be boring

An enduring theme on this blog is that one should always consider "boring" explanations for "surprising" experimental results before invoking the exotica beloved and promoted by luxury journals. An example was the extremely large magnetoresistance materials.

In most metals the magnetoresistance [change in electrical resistance with external magnetic field B] depends quadratically on the B.
The past few years there have been a plethora of papers about linear magnetoresistance in topological insulators, iron pnictide superconductors, and Dirac semi-metals. I wrote a post which discusses the issue and also links to an earlier post that considers different theoretical explanations.
Many of these papers, particularly those in the baby Natures, want to link the linear magnetoresistance to the Dirac cone and possibly the Berry geometric phase associated with it.

However, there are some critical and constructive papers. For example,
Magnetotransport of proton-irradiated BaFe2As2 and BaFe1.985Co0.015As2 single crystals 
D. A. Moseley, K. A. Yates, N. Peng, D. Mandrus, A. S. Sefat, W. R. Branford, and L. F. Cohen
By using proton-beam irradiation to change the defect scattering density, we find that the dependence of the magnitude of the linear magnetoresistance on scattering quite clearly contravenes this prediction [of Abrikosov's quantum model].
There is a nice paper that gives a rather mundane explanation for the experiments.
Linear magnetoresistance in metals: Guiding center diffusion in a smooth random potential
Justin C. W. Song, Gil Refael, and Patrick A. Lee
We predict that guiding center (GC) diffusion yields a linear and nonsaturating (transverse) magnetoresistance in 3D metals. Our theory is semiclassical and applies in the regime where the transport time is much greater than the cyclotron period and for weak disorder potentials which are slowly varying on a length scale much greater than the cyclotron radius. Under these conditions, orbits with small momenta along magnetic field B are squeezed and dominate the transverse conductivity. When disorder potentials are stronger than the Debye frequency, linear magnetoresistance is predicted to survive up to room temperature and beyond. We argue that magnetoresistance from GC diffusion explains the recently observed giant linear magnetoresistance in 3D Dirac materials.
In their calculations the Berry phase plays no role.

Monday, February 15, 2016

A career transition from theoretical physics to public policy

Robert Socolow has an interesting career history. He started out in elementary particle theory, with a Ph.D at Harvard, a postdoc at Berkeley and was an Assistant Professor at Yale. He then made a transition to environmental and energy policy, joining the faculty in Mechanical and Aerospace Engineering at Princeton in 1971. There is an interesting letter he wrote to Steve Fels in 1969 that describes his transition in research interests.

Two years ago Socolow gave a Homage to Frank von Hippel, a physicist who made a similar transition, focusing on nuclear policy and arms control. It is worth reading. Here are some comments Socolow made about physics.
Physics is a special way of knowing, within science. Physics stresses simplification – incredibly useful when other fields place a much lower value on simplification. The physics approach shines a light on other sciences, provides accessibility for outsiders (the intelligent layman).  
Although our cohort stopped working at the frontier of physics, arguably we didn’t leave physics but rather we enlarged the scope of physics. APS has remained our institutional home. A whole cohort of us moved from frontier physics into fields that did not exist beforehand -- fields that did not construct entry points until a long time afterwards. In the 1970s our cohort had a role in creating APS institutions like the Panel on Public Affairs (POPA), the Forum on Physics and Society, and the APS Fellows Program. Frank and I were two of the first six APS Fellows whose route to Fellow was via the Forum on Physics and Society. 
Less than a week ago I was at Harvard for a reunion of all those who received Ph.D.’s in Physics from Harvard, as well as faculty from all periods and current graduate students. There were two morning panels on alternative careers for physicists, featuring alumni now doing different things. Sadly, in my view, nearly all of the panelists had moved from physics to finance. I invited myself onto one panel, and Dan Kammen was on the other one. We reminded the audience that critically important problems were out there which physicists could contribute to. Our message seemed not especially welcome.
I do think physicists have a lot to contribute. Socolow and von Hippel are great role models. However, I also think we have to be careful about "physics hubris", most commonly manifested in two related directions. The first is being naive about how complex problems are. Second, being arrogant and thinking that we are smarter than others who have already spent a lot of time working on these problems. Previously, I wrote about How (not) to break into a new field.

Thursday, February 11, 2016

Meeting to brainstorm strategies to efficiently reduce productivity

Last week The Economist had a good article about how in organisations today there is so little time to  think and do "deep work". Instead people are too busy going to meetings!
The article is stimulated by a Harvard Business Review cover article on "collaborative overload" and a new book, “Deep Work: Rules for Focused Success in a Distracted World” by Cal Newport.

Minor point. I think the article title, "The collaboration curse: The fashion for making employees collaborate has gone too far" is a misnomer (at least in terms of the way academics think about collaboration). I don't think most meetings are actually about collaboration, but rather discussing, deciding on, communicating, and implementing policies.
But, I do think the pressure to collaborate, particularly across research groups, disciplines, departments, and institutions has gone too far. But, that is not the biggest problem...

Here are a few relevant quotes from the article.
interruptions, even short ones, increase the total time required to complete a task by a significant amount. A succession of studies have shown that multitasking reduces the quality of work as well as dragging it out.

whereas managers may notice the benefits of collaboration, they fail to measure its costs. ...
estimate that knowledge workers spend 70-85% of their time attending meetings (virtual or face-to-face), dealing with e-mail, talking on the phone or otherwise dealing with an avalanche of requests for input or advice. Many employees are spending so much time interacting that they have to do much of their work when they get home at night.
The biggest problem with collaboration is that it makes what Mr Newport calls “deep work” difficult, if not impossible. Deep work is the killer app of the knowledge economy: it is only by concentrating intensely that you can master a difficult discipline or solve a demanding problem. Many of the most productive knowledge workers go out of their way to avoid meetings and unplug electronic distractions. Peter Drucker, a management thinker, argued that you can do real work or go to meetings but you cannot do both. Jonathan Franzen, an author, unplugs from the internet when he is writing. Donald Knuth, a computer scientist, refuses to use e-mail on the ground that his job is to be “on the bottom of things” rather than “on top of things”. Richard Feynman, a legendary physicist, extolled the virtues of “active irresponsibility” when it came to taking part in academic meetings. 
Why have organisations been so naive about collaboration? One reason is that collaboration is much easier to measure than “deep work ... 
A second reason is that managers often feel obliged to be seen to manage: left to their own devices they automatically fill everybody’s days with meetings and memos rather than letting them get on with their work. 
Helping people to collaborate is a wonderful thing. Giving them the time to think is even better.
So what should we do?
Maybe do slow science , perhaps focus more on multiple alternative hypotheses.

Wednesday, February 10, 2016

Is this the ultimate compliment for your paper?

For someone to put the main points to a popular song!

Yesterday I heard an interesting talk "Truths we must tell ourselves if we are to manage climate change" at UQ by Robert Socolow [aged 80!].

He is well known for a paper, Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies

The paper considers Seven ways to reduce carbon emissions. Glenn Wolkenfeld has written corresponding lyrics to the tune of the classic Paul Simon song, 50 ways to leave your lover!

Socolow has an interesting career history, having started out in theoretical physics, working on elementary particles. I will write more about that career transition later.

Tuesday, February 9, 2016

Wave-function based electronic structure methods are "scientifically legitimate"

Peter Fulde [who turns 80 in 2 months!] has a nice informative 2 page Commentary Wavefunction-based electronic structure calculations for solids.

For electronic structure calculation there are two distinct alternative methods (formulations): those based on Density Functional Theory (DFT) and wave function based approaches.

Fulde directly addresses an "objection" to the latter raised by Walter Kohn in his Nobel Prize Lecture. He suggested that for more than one thousand electrons a many-body wave function is not "scientifically legitimate" because it suffers from the the "exponential wall" problem.
(i) It cannot be calculated with sufficient accuracy.
(ii) It cannot be represented numerically sufficiently well that it can be stored and later retrieved.

Fulde states

The exponential wall problem is avoided when we characterize the many-electron wavefunction not by a vector ψ(r1σ1, ... , rNσN) in Hilbert space but instead by a vector |Ω) in operator space, with the cumulant metric given by equation (3). The operator S in |Ω) = |1 + S) is a cumulant scattering operator.

The point we wish to emphasize is that a numerical representation of the results for the different contributions to |S) poses no problem. 

Although he does not spell it out (I think) the cumulants here are in quantum chemistry related to "coupled cluster" methods and in solid state physics a very simple example is a Gutzwiller projection. These kind of connections between chemistry and physics techniques are nicely brought out in Fulde's classic book, which I highly recommend. It is where I first learnt about such connections.

I thank Mohammad Sherafati for bringing the article to my attention.

Monday, February 8, 2016

The case for quantum materials

Nature Physics has an editorial The Rise of Quantum Materials.
In a refreshing change for the Nature Publishing Group, it is devoid of hype.
The editorial nicely gives the scientific background to the sociological observation:

 As it has become clear that the study of emergent properties is no longer restricted to strongly correlated electron systems, a new, broader description has become necessary. And the term that seems to be gaining currency on departmental websites and research programmes is quantum materials. 

[Indeed, I just got a grant with a title "The bad metallic state in quantum materials"]

My only minor comment is that the editorial does not quite explain why "quantum" is appropriate nomenclature.
I would say that is because on some level they have macroscopic properties [e.g. quantised magnetic flux in superconducting vortices and quantised Hall resistance] that are quantum mechanical in sense that they involve Planck's constant. This is the point I try to bring out in my colloquium on emergent quantum matter.

Friday, February 5, 2016

Introducing scientific dignitaries and charlatans

I find it interesting to listen to the introductions that different seminar speakers get. Sometimes the introduction tells you more about the host than the speaker.

Introductions I don't like may include:

"Sarah has published lots of Nature and Science papers."

Mention of the h-index or number of citations.

Mention of amounts of grant money.

"John has done important work in quantum biology".

"The speaker needs no introduction (so I won't give one)".
I have heard this many times but I did not really know the speaker.

A live dialogue between the host and speaker about the details. e.g., "When did you get your Ph.D with me? So how long have you been at Sydney now?"

"When I Googled him this is what I found out ...."

Recitation from an old university web page. For a few years I sometimes got introduced as someone who does research on the "electrical conductivity of DNA". I finally discovered that this was because if you Googled me the first hit was an old university web page that listed this. I worked on this for a few months before I discovered all the experiments were duds. I eventually got the old page removed and have not had this introduction since.

Glowing accounts of how great the speaker is, when he is a charlatan or mediocre. This either reflects hypocrisy or poor judgement on the part of the host.

Introductions I do like include:

A very brief career history.

A very brief statement of what scientific contribution the speaker is best known for.

Any personal connection between the host and the speaker. e.g. "We were postdocs together at Rice University".

Thursday, February 4, 2016

We should not give up on falsifiability

No, we should redouble our efforts!

Over past few years some scientists, particularly string theorists, have suggested that we should give up on the idea of falsifiability as a criterion for deciding whether or not to accept or reject a specific scientific theory. (A good theory is one that one can perform a specific experiment, whose outcome may lead to the rejection of the theory).
For example, in 2014 in answer to the question, "What scientific idea is due for retirement?" Sean Carroll's answer was Falsifiability. He uses this to justify string theory and the multiverse.

First, I think several important points need to be conceded and acknowledged.

1. There are subtle philosophical issues associated with falsifiability. Popper did not have the last word!

2. In practise, rarely will a theory get rejected just because there is experimental data that is inconsistent with it. Sometimes the data will get rejected. Other times the theory will get modified.

3. In practise, rarely do many scientists actually focus on falsifiability. For example, theorists generally don't write papers or give talks suggesting specific experiments that could be used to falsify their favourite theory or latest calculation.

I would argue that 3. happens partly because it is actually extremely difficult to come up with specific do-able experiments that will give definitive results that can clearly falsify a theory, particularly in condensed matter or theoretical chemistry. As I have said before, good science is hard work. 

But, the solution is not to give up on falsifiability. To me this is throwing the baby out with the bath water. It is a bit like discussions of foreign aid for poverty alleviation. Currently, some programs waste money and others actually cause more harm than good. But, the solution is not to give up but focus on supporting programs that actually do make a positive difference.

I think Einstein's General Relativity does provide a nice example of falsifiability, contrary to what Sean Carroll claims. This is because besides Einstein's theory there are many alternative theories: Newton, Brans-Dicke, Cartan, ...
We are celebrating the centenary of GR and not some alternative theory because they have largely been ruled out by experiment ....

I think that science would be better off if we all worked a little harder and thought a little more critically about how integrate falsifiability more into science.

What do you think?

Tuesday, February 2, 2016

Mrs. Pauling was right about two things

For Christmas (two years ago) my sister-in-law gave me a copy of
Ava Helen Pauling: Partner, Activist, Visionary by Mina Carson, a historian at Oregon State University, which is home to the Linus Pauling archives. I read it then but it has taken me a while to get around to writing this post.

Aside: There are many personal dimensions to this gift choice. My sister-in-law and her family live in Corvallis, and their younger daughter attends Linus Pauling Middle School. Of course, they knew about my great admiration of Pauling. But also, the author has been in a book club with my sister-in-law.

I enjoyed reading the book and it gave me a different perspective on Pauling's life. Although, some of the more intimate details in the book I would rather not have known about...

The author nicely highlights how Ava Helen was really the driving force behind Linus' political activism, which ultimately led to his second Nobel Prize (in Peace) for the Partial Nuclear Test Ban Treaty. It is interesting to wonder whether today she would have shared the prize with him.

But, here I want to focus on two things that really struck me from the book.

In the 1950s Mrs. Pauling advocated two positions that we (or at least most people) just take for granted today. Yet at the time, the Paulings were persecuted for their advocacy of these views, particularly by powerful political, governmental, and commercial interests.

1. Above ground nuclear testing and the associated radiation exposure is bad for peoples health.

2. Faculty at public universities should be allowed to hold and advocate any political views they choose.

The context of the second was the Loyalty Oath Controversy that ripped apart UC Berkeley from 1949-1951.

Monday, February 1, 2016

Novel spin-orbit coupling in the absence of local inversion symmetry

Normally we associate spin-orbit coupling with degenerate atomic orbitals (or energy bands) associated with d- or f-orbitals. However, in solid state physics a quite distinct type of spin-orbit coupling can occur and has attracted a lot of interest over the past decade.

In a seminal 2005 paper [which took 12 months for PRL to publish!] Kane and Mele proposed that in graphene a spin quantum Hall effect could occur due to spin-orbit coupling. Moreover, this paper proposed that this state was a topological insulator, starting a whole industry. I want to just focus on the spin-orbit coupling term in the Hamiltonian that is the first step in their argument.

This term arises because there are two carbon atoms per primitive unit cell in the crystal lattice. [A and B sub lattice]. It does not have local inversion symmetry.

How large is Delta_so ?
Kane and Mele estimated, based on a crude argument, that is was about 1.2 Kelvin. But, then they gave a renormalisation group argument, claiming that electron-electron interactions would increase the value to something like 7.5 K.
However, much more sophisticated analysis, such as this one, showed that Delta_so arose from subtle pi-sigma orbital mixing and was orders of magnitude smaller! Hence, the chance of seeing a quantum spin Hall effect in graphene are extremely unlikely.

Aside. This illustrates you can be wrong about something but still stimulate a whole new field. But, in fairness, everything is correct about the paper, except the parameter estimate for graphene. This is quite different to people who publish papers that are just plain wrong, but still stimulate positive outcomes.

What about other systems?
A nice example is monolayer MoS2, as discussed here.

A full three-dimensional crystal of MoS2 has inversion symmetry. However, a monolayer does not.
If you take a Mo atom as an inversion centre, a S atom is mapped onto an empty location.
Delta_so is estimated to be about 500 K.
It is orders of magnitude larger than graphene because the bare-spin orbit coupling is much larger due to the heavy Mo atoms.

A similar spin-orbit coupling has been proposed to occur in a quasi-one-dimensional metal, Li0.9Mo6O17.