Electronic thermal conductivity at high temperatures: Violation of the Wiedemann-Franz law in narrow band metals

We study the electronic part of the thermal conductivity kappa of metals. We present two methods for calculating kappa, a quantum Monte-Carlo (QMC) method and a method where the phonons but not the electrons are treated semiclassically (SC). We compare the two methods for a model of alkali-doped C60, A3C60, and show that they agree well. We then mainly use the SC method, which is simpler and easier to interpret. We perform SC calculations for Nb for large temperatures T and find that kappa increases with T as kappa(T)=a+bT, where a and b are constants, consistent with a saturation of the mean free path, l, and in good agreement with experiment. In contrast, we find that for A3C60, kappa(T) decreases with T for very large T. We discuss the reason for this qualitatively in the limit of large T. We give a quantum-mechanical explanation of the saturation of l for Nb and derive the Wiedemann-Franz law in the limit of T much smaller than W, where W is the band width. In contrast, due to the small W of A3C60, the assumption T much smaller than W can be violated. We show that this leads to kappa(T) \sim T^{-3/2} for very large T and a strong violation of the Wiedemann-Franz law.Comment: 8 pages, 4 figure

Lawn clipping management

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Radial Temperature Profiles of X-Ray--Emitting Gas Within Clusters of Galaxies

Previous analyses of ASCA data of clusters of galaxies have found conflicting results regarding the slope of the temperature profile of the hot X-ray gas within clusters, mainly because of the large, energy-dependent point spread function (PSF) of the ASCA mirrors. We present a summary of all ASCA-determined cluster temperature profiles found in the literature, and find a discrepancy in the radial temperature trend of clusters based on which PSF-correction routine is used. This uncertainty in the cluster temperature profile in turn can lead to large uncertainties in the amount of dark matter in clusters. In this study, we have used ROSAT PSPC data to obtain independent relative temperature profiles for 26 clusters, most of which have had their temperature profiles determined by ASCA. Our aim is not to measure the actual temperature values of the clusters, but to use X-ray color profiles to search for a hardening or softening of the spectra with radius for comparison to ASCA-derived profiles. The radial color profiles indicate that outside of the cooling flow region, the temperature profiles of clusters are in general constant. Within 35% of the virial radius, we find a temperature drop of 20% at 10 keV and 12% at 5 keV can be ruled out at the 99% confidence level. A subsample of non-cooling flow clusters shows that the condition of isothermality applies at very small radii too, although cooling gas complicates this determination in the cooling flow subsample. The colors predicted from the temperature profiles of a series of hydrodynamical cluster simulations match the data very well, although they cannot be used to discriminate among different cosmologies. An additional result is that the color profiles show evidence for a central peak in metallicity in low temperature clusters.Comment: 39 pages, 15 embedded Postscript figures, uses aaspp4.sty, accepted for publication in Astrophysical Journa

Mass Models and Sunyaev-Zeldovich Effect Predictions for a Flux Limited Sample of 22 Nearby X-Ray Clusters

We define a 90% complete, volume-limited sample of 31 z<0.1 x-ray clusters and present a systematic analysis of public ROSAT PSPC data on 22 of these objects. Our efforts are undertaken in support of the Penn/OVRO SZE survey, and to this end we present predictions for the inverse Compton optical depth towards all 22 of these clusters. We have performed detailed Monte Carlo simulations to understand the effects of the cluster profile uncertainties on the SZE predictions given the OVRO 5.5-meter telescope beam and switching patterns; we find that the profile uncertainties are one of the least significant components of our error budget for SZE-based distance measurements. We also present baryonic masses and baryon mass fractions derived under the assumption of hydrostatic equilibrium for these 22 clusters. The mean baryonic mass fraction within R_500 \sim 500 h^-1 kpc is (7.02 \pm 0.28) x 10^-2 h^-3/2, or (19.8 \pm 0.8) x 10^-2 for h=0.5. We confirm the Allen et al. (1993) claim of an excess absorbing column density towards Abell 478, but do not find similar anomalies in the other 21 clusters in our sample. We also find some evidence for an excess of soft counts in the ROSAT PSPC data. A measurement of H_o using these models and OVRO SZE determinations will be presented in a second paper.Comment: 51 pages, 6 figures included in text. Added comparison of different cosmologies; accepted for publication in Ap

Magneto-optical spectra of closely spaced magnetite nanoparticles

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe 3O4 smagnetited nanoparticles s8-nm diameterd and polysmethylmethacrylated . Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for sdilute compositesd to 540 nm concentrated . We present a theory based on the discrete-dipole approximation which accounts for optical coupling between magnetite particles. Qualitative correlations between theoretical calculations and experimental data suggest that the shifts in spectral peak position depend on both interparticle distance and geometrical configuratio

Analytical modeling of large-angle CMBR anisotropies from textures

We propose an analytic method for predicting the large angle CMBR temperature fluctuations induced by model textures. The model makes use of only a small number of phenomenological parameters which ought to be measured from simple simulations. We derive semi-analytically the $C^l$-spectrum for $2\leq l\leq 30$ together with its associated non-Gaussian cosmic variance error bars. A slightly tilted spectrum with an extra suppression at low $l$ is found, and we investigate the dependence of the tilt on the parameters of the model. We also produce a prediction for the two point correlation function. We find a high level of cosmic confusion between texture scenarios and standard inflationary theories in any of these quantities. However, we discover that a distinctive non-Gaussian signal ought to be expected at low $l$, reflecting the prominent effect of the last texture in these multipoles

Dipole Interactions and Electrical Polarity in Nanosystems -- the Clausius-Mossotti and Related Models

Point polarizable molecules at fixed spatial positions have solvable electrostatic properties in classical approximation, the most familiar being the Clausius-Mossotti (CM) formula. This paper generalizes the model and imagines various applications to nanosystems. The behavior is worked out for a sequence of octahedral fragments of simple cubic crystals, and the crossover to the bulk CM law is found. Some relations to fixed moment systems are discussed and exploited. The one-dimensional dipole stack is introduced as an important model system. The energy of interaction of parallel stacks is worked out, and clarifies the diverse behavior found in different crystal structures. It also suggests patterns of self-organization which polar molecules in solution might adopt. A sum rule on the stack interaction is found and tested. Stability of polarized states under thermal fluctuations is discussed, using the one-dimensional domain wall as an example. Possible structures for polar hard ellipsoids are considered. An idea is formulated for enhancing polarity of nanosystems by intentionally adding metallic coatings.Comment: 18 pages (includes 6 embedded figures and 3 tables). New references, and other small improvements. Scheduled for publication by J. Chem. Phys., Jan. 200