Near-infrared (NIR) spectra of Centaurs and Kuiper belt objects

We present here an extensive survey of near-infrared (NIR) spectra of Kuiper belt objects (KBOs) and Centaurs taken with the Keck I Telescope. We find that most spectra in our sample are well characterized by a combination of water ice and a featureless continuum. A comparative analysis reveals that the NIR spectral properties have little correlation to the visible colors or albedo, with the exception of the fragment KBOs produced from the giant impact on 2003 EL61. The results suggest that the surface composition of KBOs is heterogeneous, though the exposure of water ice may be controlled by geophysical processes. The Centaurs also display diverse spectral properties, but the source of the variability remains unclear. The results for both the KBOs and the Centaurs point to inherent heterogeneity in either the processes acting on these objects or materials from which they formed

Comment on "Phonon Spectrum and Dynamical Stability of a Dilute Quantum Degenerate Bose-Fermi Mixture

We show that the conclusions of a recent PRL by Pu et al is incorrect.Comment: late

Draco -- A Failure of the Tidal Model

We test whether the structural properties of the nearby dwarf spheroidal (dSph) galaxy Draco, a well-studied Milky Way companion, can be reconciled with the suggestion that dSphs are unbound tidal remnants with a large depth extent along the line of sight. In order to apply the observational test of this hypothesis suggested by Klessen & Zhao, we use public photometric data from the Sloan Digital Sky Survey (SDSS) to explore the width of Draco's blue horizontal branch over a range of areas covering 0.06 square degrees to 6.25 square degrees centered on Draco. The SDSS database is the only currently existing database with sufficient depth and area coverage to permit a stringent test of the tidal models. We show that blue horizontal branch stars extend beyond the previously inferred limiting radii of Draco, consistent with the observed absence of a truncated stellar surface density profile of this dSph. We calculate new models for a galaxy without dark matter, using Draco's morphological properties as constraints. The resulting models are unable to reproduce the narrow observed horizontal branch width of Draco, which stays roughly constant regardless of the field of view. We conclude that Draco cannot be the remnant of a tidally disrupted satellite, but is probably strongly dark-matter dominated. (ABSTRACT ABBREVIATED)Comment: 26 pages, 9 figures included, accepted for publication in ApJ, high-resolution version available at http://www.aip.de./~ralf/Publications/p22.abstract.htm

On the r-matrix structure of the hyperbolic BC(n) Sutherland model

Working in a symplectic reduction framework, we construct a dynamical r-matrix for the classical hyperbolic BC(n) Sutherland model with three independent coupling constants. We also examine the Lax representation of the dynamics and its equivalence with the Hamiltonian equation of motion.Comment: 20 page

Distributed lag models for hydrological data

The distributed lag model (DLM), used most prominently in air pollution studies, finds application wherever the effect of a covariate is delayed and distributed through time. We explore the use of modified formulations of DLMs to provide flexible varying-coeficient models with smoothness constraints, applicable in any setting in which lagged covariates are regressed on a time-dependent response. The models are applied to simulated flow and rainfall data and to flow data from a Scottish mountain river, with particular emphasis on approximating the relationship between environmental covariates and flow regimes in order to detect the influence of unobserved processes. It was found that under certain rainfall conditions some of the variability in the influence of rainfall on flow arises through a complex interaction between antecedent ground wetness and the time-delay in rainfall. The models are able to identify subtle changes in rainfall response, particularly in the location of peak influence in the lag structure and offer a computationally attractive approach for fitting DLMs

Drastic Reduction of Shot Noise in Semiconductor Superlattices

We have found experimentally that the shot noise of the tunneling current $I$ through an undoped semiconductor superlattice is reduced with respect to the Poissonian noise value $2eI$, and that the noise approaches 1/3 of that value in superlattices whose quantum wells are strongly coupled. On the other hand, when the coupling is weak or when a strong electric field is applied to the superlattice the noise becomes Poissonian. Although our results are qualitatively consistent with existing theories for one-dimensional mulitple barriers, the theories cannot account for the dependence of the noise on superlattice parameters that we have observed.Comment: 4 Pages, 3Figure