Phonon scattering mechanisms in suspended nanostructures from 4 to 40 K

We have developed specially designed semiconductor devices for the measurement of thermal conductance in suspended nanostructures. By means of a novel subtractive comparison, we are able to deduce the phonon thermal conductance of individual nanoscale beams of different geometry and dopant profiles. The separate roles of important phonon scattering mechanisms are analyzed and a quantitative estimation of their respective scattering rates is obtained using the Callaway model. Diffuse surface scattering proves to be particularly important in the temperature range from 4 to 40 K. The rates of other scattering mechanisms, arising from phonon-phonon, phonon-electron, and phonon-point defect interactions, also appear to be significantly higher in nanostructures than in bulk samples

Determination of |V_us| from hadronic tau decays

The recent update of the strange spectral function and the moments of the invariant mass distribution by the OPAL collaboration from hadronic tau decay data are employed to determine |V_us| as well as m_s. Our result, |V_us|=0.2208\pm0.0034, is competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. Furthermore, the error associated to our determination of |V_us| can be reduced in the future since it is dominated by the experimental uncertainty that will be eventually much improved by the B-factories hadronic tau data. Another improvement that can be performed is the simultaneous fit of both |V_us| and m_s to a set of moments of the hadronic tau decays invariant mass distribution, which will provide even a more accurate determination of both parameters.Comment: 6 pages. Invited talk given by E.G. at the XXXXth Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, 5-12 Mar 200

Electron transport through quantum wires and point contacts

We have studied quantum wires using the Green's function technique and the density-functional theory, calculating the electronic structure and the conductance. All the numerics are implemented using the finite-element method with a high-order polynomial basis. For short wires, i.e. quantum point contacts, the zero-bias conductance shows, as a function of the gate voltage and at a finite temperature, a plateau at around 0.7G_0. (G_0 = 2e^2/h is the quantum conductance). The behavior, which is caused in our mean-field model by spontaneous spin polarization in the constriction, is reminiscent of the so-called 0.7-anomaly observed in experiments. In our model the temperature and the wire length affect the conductance-gate voltage curves in the same way as in the measured data.Comment: 8 page

Economic Considerations Relating to the Sale of Municipal Utilities

Today approximately 3,500 electric utility systems in the United States are owned by investors, cities, and consumers, such as rural electric cooperatives. About 2,000 of these electric systems are municipal (city-owned) and serve 13.5% of the consumers in the United States, while the investor owned utilities total around 480 and serve 79.0% of the customers. The remaining 1,000 systems are rural cooperatives which serve 7.5% of the consumers. This publication concerns a study of the 2,000 electric systems that are municipally owned. They constitute more than half of the electric systems in the United States but serve only 13.5% of the consumers, thus most of them are smaller than the investor owned systems

Stochastic heating of a molecular nanomagnet

We study the excitation dynamics of a single molecular nanomagnet by static and pulsed magnetic fields. Based on a stability analysis of the classical magnetization dynamics we identify analytically the fields parameters for which the energy is stochastically pumped into the system in which case the magnetization undergoes diffusively and irreversibly a large angle deflection. An approximate analytical expression for the diffusion constant in terms of the fields parameters is given and assessed by full numerical calculations.Comment: 5 pages, 4 figures, to appear in Phys. Rev.

Spin dependent electron transport through a magnetic resonant tunneling diode

Electron transport properties in nanostructures can be modeled, for example, by using the semiclassical Wigner formalism or the quantum mechanical Green's functions formalism. We compare the performance and the results of these methods in the case of magnetic resonant-tunneling diodes. We have implemented the two methods within the self-consistent spin-density-functional theory. Our numerical implementation of the Wigner formalism is based on the finite-difference scheme whereas for the Green's function formalism the finite-element method is used. As a specific application, we consider the device studied by Slobodskyy et all. [Phys. Rev. Lett. 90, 246601 (2003)] and analyze their experimental results. The Wigner and Green's functions formalisms give similar electron densities and potentials but, surprisingly, the former method requires much more computer resources in order to obtain numerically accurate results for currents. Both of the formalisms can successfully be used to model magnetic resonant tunneling diode structures.Comment: 13 pages and 12 figure

Small quantum networks operating as quantum thermodynamic machines

We show that a 3-qubit system as studied for quantum information purposes can alternatively be used as a thermodynamic machine when driven in finite time and interfaced between two split baths. The spins are arranged in a chain where the working spin in the middle exercises Carnot cycles the area of which defines the exchanged work. The cycle orientation (sign of the exchanged work) flips as the difference of bath temperatures goes through a critical value.Comment: RevTeX, 4 pages, 7 figures. Replaced by version accepted for publication in EP

How Employment Discrimination Plaintiffs Fare in Federal Court

This article presents the full range of information that the Administrative Office’s data convey on federal employment discrimination litigation. From that information, the authors tell three stories about (1) bringing these claims, (2) their outcome in the district court, and (3) the effect of appeal. Each of these stories is a sad one for employment discrimination plaintiffs: relatively often, the numerous plaintiffs must pursue their claims all the way through trial, which is usually a jury trial; at both pretrial and trial these plaintiffs lose disproportionately often, in all the various types of employment discrimination cases; and employment discrimination litigants appeal more often than other litigants, with the defendants doing far better on those appeals than the plaintiffs

How Employment Discrimination Plaintiffs Fare in Federal Court

This article presents the full range of information that the Administrative Office’s data convey on federal employment discrimination litigation. From that information, the authors tell three stories about (1) bringing these claims, (2) their outcome in the district court, and (3) the effect of appeal. Each of these stories is a sad one for employment discrimination plaintiffs: relatively often, the numerous plaintiffs must pursue their claims all the way through trial, which is usually a jury trial; at both pretrial and trial these plaintiffs lose disproportionately often, in all the various types of employment discrimination cases; and employment discrimination litigants appeal more often than other litigants, with the defendants doing far better on those appeals than the plaintiffs