A density functional perspective for one-particle systems

Density functional theory is discussed in the context of one-particle systems. We show that the ground state density $\rho_0(x)$ and energy $E_0$ are simply related to a family of external potential energy functions with ground state wave functions $\psi_n(x) \propto \rho_0(x)^n$ and energies $E_n=2nE_0$ for certain integer values of $n$.Comment: 7 pages, ReVTeX4, submitted to Am. J. Phy

Vibration modes of an orbiting radio telescope

Vibration mode shape and frequencies of orbiting radio telescop

The flutter of towed rigid decelerators

Flutter of towed rigid decelerators, and relationships between geometric and aerodynamic parameters defining unconditional stability boundar

Photoionization, Numerical Resolution, and Galaxy Formation

Using cosmological simulations that incorporate gas dynamics and gravitational forces, we investigate the influence of photoionization by a UV radiation background on the formation of galaxies. In our highest resolution simulations, we find that photoionization has essentially no effect on the baryonic mass function of galaxies at $z=2$, down to our resolution limit of 5e9 M_\sun. We do, however, find a strong interplay between the mass resolution of a simulation and the microphysics included in the computation of heating and cooling rates. At low resolution, a photoionizing background can appear to suppress the formation of even relatively massive galaxies. However, when the same initial conditions are evolved with a factor of eight better mass resolution, this effect disappears. Our results demonstrate the need for care in interpreting the results of cosmological simulations that incorporate hydrodynamics and radiation physics. For example, we conclude that a simulation with limited resolution may yield more realistic results if it ignores some relevant physical processes, such as photoionization. At higher resolution, the simulated population of massive galaxies is insensitive to the treatment of photoionization and star formation, but it does depend significantly on the amplitude of the initial density fluctuations. By $z=2$, an $\Omega=1$ cold dark matter model normalized to produce the observed masses of present-day clusters has already formed galaxies with baryon masses exceeding 1e11 M_\sun.Comment: 25 pages, w/ embedded figures. Submitted to ApJ. Also available at http://www-astronomy.mps.ohio-state.edu/~dhw/Docs/preprints.htm

Documenting Food Safety Claims and Their Influence on Product Prices

In response to increasing customer attention to food attributes, agribusinesses are employing novel product differentiation strategies. As an example, we investigate the use of food safety claims on new packaged food products from the food manufacturers’ perspective. First, using two product innovation databases, we investigate claim use on labels in seven English-speaking countries over the period from 1980 to 2008. Then, based on manufacturer recommended selling prices and using U.S. data (from 2002 to 2008), we apply parametric and nonparametric hedonic methods to identify supply-side (agribusiness) valuations of chemical and microbiological claims in two food categories. We identify a significant 5 cent premium per ounce for a “preservative free†claim in spoonable yogurts. We do not find a statistically significant impact for “E. coli free†messages on meat and poultry products but find a significant price premium (19.3 cents and 25.7 cents per ounce in the two models) for “antibiotic free†claims in this category.food safety claims, parametric and nonparametric hedonic models, price premium, Marketing,

Simulating Cosmic Structure Formation

We describe cosmological simulation techniques and their application to studies of cosmic structure formation, with particular attention to recent hydrodynamic simulations of structure in the high redshift universe. Collisionless N-body simulations with Gaussian initial conditions produce a pattern of sheets, filaments, tunnels, and voids that resembles the observed large scale galaxy distribution. Simulations that incorporate gas dynamics and dissipation form dense clumps of cold gas with sizes and masses similar to the luminous parts of galaxies. Models based on inflation and cold dark matter predict a healthy population of high redshift galaxies, including systems with star formation rates of 20 M_{\sun}/year at z=6. At z~3, most of the baryons in these models reside in the low density intergalactic medium, which produces fluctuating Lyman-alpha absorption in the spectra of background quasars. The physical description of this ``Lyman-alpha forest'' is particularly simple if the absorption spectrum is viewed as a 1-dimensional map of a continuous medium instead of a collection of lines. The combination of superb observational data and robust numerical predictions makes the Lyman-alpha forest a promising tool for testing cosmological models.Comment: Latex w/ paspconf.sty, 25 pages, 8 ps figs. To appear in Origins, eds. J. M. Shull, C. E. Woodward, & H. Thronson (ASP Conference Series