Condensed concepts

Max Weber is one of the founders of sociology. This post is about two separate and interesting things I recently learned about him. A while ago I discussed Different phases of growth and change in human organisations , based on a classic article from Harvard Business Review. [Which had no references or data!] My friend Charles Ringma recently brought to my attention somewhat related ideas from Max Weber. According to Wikipedia Weber distinguished three  ideal types  of political leadership (alternatively referred to as three types of domination, legitimisation or authority): [52] [111] charismatic domination  ( familial  and  religious ), traditional domination  ( patriarchs ,  patrimonialism ,  feudalism ) and legal domination  (modern law and state,  bureaucracy ). [112] In his view, every historical relation between rulers and ruled contained such elements and they can be analysed on the basis of  this tripartite distinction . [113]  He notes that the instability o

Most of my posts on spin-crossover materials have been concerned with organometallic compounds. However, this phenomena can also occur in inorganic materials. Furthermore, it may be particularly relevant in geophysics. A  previous post discussed how strong electron correlations may play a role in geomagnetism and DMFT calculations have given some insight. A nice short overview and introduction is Electronic spin transition of iron in the Earth's deep mantle  Jung‐Fu Lin Steven D. Jacobsen Renata M. Wentzcovitch [It contains the figure below] The main material o f interest is  magnesiowüstite, an alloy of magnesium and iron oxide, ( Mg 1 − x Fe x )O Experimental studies and DFT calculations suggest that as the pressure increases the iron ions undergo a transition from high spin to low spin. The basic physics is that the pressure reduces the Fe-O bond lengths which increases the crystal field splitting. In geophysics, the pressure increases as one goes further underg

Alternative title: An exciting alternative career for Ph.Ds in condensed matter theory! There is a fascinating long article in The New York Times Magazine How Data (and Some Breathtaking Soccer) Brought Liverpool to the Cusp of Glory  The club is finishing a phenomenal season — thanks in part to an unrivaled reliance on analytics. This is in the tradition of Moneyball. Most of the data analytics team at Liverpool have physics Ph.Ds. It is led by Ian Graham who completed a Ph.D. on polymer theory at Cambridge. On the one hand, I loved the article because my son and I are big Liverpool fans. We watch all the games, some in the middle of the night. On the other hand, I was a bit surprised that I liked the article since I am a strong critic of the use of metrics in most contexts , especially in the evaluation of scientists and institutions. However, I came to realise that, in many ways, what Liverpool is doing is not the blind use of metrics but rather using data as just one facto

Every year in Australia there is a week of science outreach events in pubs, Pint of Science . I am giving a  talk  tomorrow night,  Emergence: from physics to sociology. Here are the slides. In the past, when explaining emergence I have liked to use the example of geometry.  However, one can argue that a limitation of that case is there are not necessary many interacting components to the system. Hence, I think the example of language,  discussed by Michael Polanyi is better.

In any crystal the elementary excitations of the lattice are phonons. The dispersion relation for these quasi-particles relates their energy and momentum. This dispersion relation determines thermodynamic properties such as the temperature dependence of the specific heat and plays a significant role in electron-phonon scattering and superconductivity in elemental superconductors. A nice introduction is in chapter 13 of Marder's excellent text . [The first two figures below are taken from there]. The dispersion relation is usually determined in at least one of three different ways. 1. The classical mechanics of balls and harmonic springs, representing atoms and chemical bonds, respectively. One introduces empirical parameters for the strengths of the bonds (spring constants). 2. First-principles electronic structure calculations, often based on density functional theory (DFT). This actually just determines the spring constants in the classical model. 3. Inelastic neutron sca

I have written a first draft of a chapter introducing phase diagrams and phase transitions to a layperson. I welcome any comments and suggestions. Feel free to try it out on your aunt or uncle!

Today we just take it for granted that crystals are composed of periodic arrays of interacting atoms. However, that was only established definitively one hundred years ago. I have been brushing up on phonons with Marder's nice textbook, Condensed Matter Physics . There are two historical perspectives that I found particularly fascinating. Both involve Max Born . In a solid the elastic constants completely define the speeds of sound (and the associated linear dispersion relationship). In a solid of cubic symmetry, there are only three independent elastic constants, C_11, C_44, and C_12. Cauchy and Saint Venant showed that if all the atoms in a crystal interact through pair-wise central forces then C_44=C_12. However, in a wide range of elemental crystals, one finds that C_12 is 1-3 times larger than C_44. This discrepancy caused significant debate in the 19th century but was resolved in 1914 by Born who showed that angular forces between atoms could explain the violation of th

Today I am giving a seminar for the School of Political Science and International Studies at UQ. Here are the slides.