Nearsightedness of Electronic Matter

In an earlier paper, W. Kohn had qualitatively introduced the concept of "nearsightedness" of electrons in many-atom systems. It can be viewed as underlying such important ideas as Pauling's "chemical bond," "transferability" and Yang's computational principle of "divide and conquer." It describes the fact that, for fixed chemical potential, local electronic properties, like the density $n(r)$, depend significantly on the effective external potential only at nearby points. Changes of that potential, {\it no matter how large}, beyond a distance $\textsf{R}$ have {\it limited} effects on local electronic properties, which rapidly tend to zero as function of $\textsf{R}$. In the present paper, the concept is first sharpened for representative models of uncharged fermions moving in external potentials, followed by a discussion of the effects of electron-electron interactions and of perturbing external charges.Comment: final for

Darwin's Other Books: “Red” and “Transmutation” Notebooks, “Sketch,” “Essay,” and Natural Selection

Study of Darwin's unpublished works, freely available on-line through the American Natural History Museum, reveals the origins of his thoughts on evolution

Judd on Phenomena

Donald Judd’s 1964 essay 'Specific Objects' probably remains his most well-known. In it, he described new artworks characterized by, among other features, 'a quality as a whole' instead of conventional 'part-by-part structure,' the 'use of three dimensions' and 'real space' as opposed to depiction, 'new materials [that] aren’t obviously art,' and the unadorned appearance and 'obdurate identity' of materials as they are. Judd held that the 'shape, image, color and surface' of these objects were more 'specific,' that is to say, 'more intense, clear and powerful,' than in previous art. While these positions demonstrate Judd’s subjective preferences as an artist and art critic, they also convey some of the wider debates driving American avant-garde practices in the 1960s, such as the supposed 'insufficiencies of painting and sculpture' as mediums. Art historians tend to find such breadth appealing of course - sweeping statements bring retrospective order to what was actually haphazard and unruly. But Judd knew that you lose much in eliminating complexity for the sake of clarity. He emphasized this point in his earlier essay 'Local History' so as to qualify the more general of his own arguments. 'The history of art and art’s condition at any time are pretty messy,' he declared. 'They should stay that way.

The Fool

Poetry by Jared Kohn

Rising Wage Dispersion, After All ! The German Wage Structure at the Turn of the Century

Using register data from the IAB employment sample, this paper studies the wage structure in the German labor market throughout the years 1992{2001. Wage dispersion has generally been rising. The increase was more pronounced in East Germany and occurred predominantly in the lower part of the wage distribution for women and in the upper part for men. Censored quantile wage regressions reveal diverse age and skill patterns. Applying Machado/Mata (2005)-type decompositions I conclude that differences in the composition of the work force only had a small impact on the observed wage differentials between East and West Germany, but changes in the characteristics captured better parts of the observed wage changes over time. --Wage inequality,censored quantile regression,Machado/Mata decomposition,IABS,East Germany,West Germany

Particle Efficient Importance Sampling

The efficient importance sampling (EIS) method is a general principle for the numerical evaluation of high-dimensional integrals that uses the sequential structure of target integrands to build variance minimising importance samplers. Despite a number of successful applications in high dimensions, it is well known that importance sampling strategies are subject to an exponential growth in variance as the dimension of the integration increases. We solve this problem by recognising that the EIS framework has an offline sequential Monte Carlo interpretation. The particle EIS method is based on non-standard resampling weights that take into account the look-ahead construction of the importance sampler. We apply the method for a range of univariate and bivariate stochastic volatility specifications. We also develop a new application of the EIS approach to state space models with Student's t state innovations. Our results show that the particle EIS method strongly outperforms both the standard EIS method and particle filters for likelihood evaluation in high dimensions. Moreover, the ratio between the variances of the particle EIS and particle filter methods remains stable as the time series dimension increases. We illustrate the efficiency of the method for Bayesian inference using the particle marginal Metropolis-Hastings and importance sampling squared algorithms