Combination of large nanostructures and complex band structure for high performance thermoelectric lead telluride

The complexity of the valence band structure in p-type PbTe has been shown to enable a significant enhancement of the average thermoelectric figure of merit (zT) when heavily doped with Na. It has also been shown that when PbTe is nanostructured with large nanometer sized Ag_2Te precipitates there is an enhancement of zT due to phonon scattering at the interfaces. The enhancement in zT resulting from these two mechanisms is of similar magnitude but, in principle, decoupled from one another. This work experimentally demonstrates a successful combination of the complexity in the valence band structure with the addition of nanostructuring to create a high performance thermoelectric material. These effects lead to a high zT over a wide temperature range with peak zT > 1.5 at T > 650 K in Na-doped PbTe/Ag_2Te. This high average zT produces 30% higher efficiency (300–750 K) than pure Na-doped PbTe because of the nanostructures, while the complex valence band structure leads to twice the efficiency as the related n-type La-doped PbTe/Ag_2Te without such band structure complexity

Production of exotic isotopes in complete fusion reactions with radioactive beams

The isotopic dependence of the complete fusion (capture) cross section is analyzed in the reactions $^{130,132,134,136,138,140,142,144,146,148,150}$Xe+$^{48}$Ca with stable and radioactive beams. It is shown for the first time that the very neutron-rich nuclei $^{186-191}$W can be reached with relatively large cross sections by complete fusion reactions with radioactive ion beams at incident energies near the Coulomb barrier. A comparison between the complete fusion and fragmentation reactions for the production of neutron-rich W and neutron-deficient Rn isotopes is performed.Comment: 13 pages, 6 figures, accepted in PR

Optimal entanglement criterion for mixed quantum states

We develop a strong and computationally simple entanglement criterion. The criterion is based on an elementary positive map Phi which operates on state spaces with even dimension N >= 4. It is shown that Phi detects many entangled states with positive partial transposition (PPT) and that it leads to a class of optimal entanglement witnesses. This implies that there are no other witnesses which can detect more entangled PPT states. The map Phi yields a systematic method for the explicit construction of high-dimensional manifolds of bound entangled states.Comment: 4 pages, no figures, replaced by published version (minor changes), Journal-reference adde

Analytic solution of the Boltzmann equation in an expanding system

For a massless gas with constant cross section in a homogeneous, isotropically expanding spacetime we reformulate the relativistic Boltzmann equation as a set of non-linear coupled moment equations. For a particular initial condition this set can be solved exactly, yielding the first analytical solution of the Boltzmann equation for an expanding system. The non-equilibrium behavior of this relativistic gas can be mapped onto that of a homogeneous, static non-relativistic gas of Maxwell molecules.Comment: 5 pages, 1 figure; minor changes, accepted for publication in Phys. Rev. Let

Sample processor for chemical analysis

An apparatus is provided which can process numerous samples that must be chemically analyzed by the application of fluids such as liquid reagents, solvents and purge gases, as well as the application of dumps for receiving the applied fluid after they pass across the sample, in a manner that permits numerous samples to be processed in a relatively short time and with minimal manpower. The processor includes a rotor which can hold numerous cartridges containing inert or adsorbent material for holding samples, and a pair of stators on opposite sides of the rotor. The stators form stations spaced along the path of the cartridges which lie in the rotor, and each station can include an aperture in one stator through which a fluid can be applied to a cartridge resting at that station, and an aperture in the other stator which can receive the fluid which has passed through the cartridge. The stators are sealed to the ends of the cartridges lying on the rotor, to thereby isolate the stations from one another

Quantifying non-Markovianity of continuous-variable Gaussian dynamical maps

We introduce a non-Markovianity measure for continuous-variable open quantum systems based on the idea put forward in H.-P. Breuer, that is, by quantifying the flow of information from the environment back to the open system. Instead of the trace distance we use here the fidelity to assess distinguishability of quantum states. We employ our measure to evaluate non-Markovianity of two paradigmatic Gaussian channels: the purely damping channel and the quantum Brownian motion channel with Ohmic environment. We consider different classes of Gaussian states and look for pairs of states maximizing the backflow of information. For coherent states we find simple analytical solutions, whereas for squeezed states we provide both exact numerical and approximate analytical solutions in the weak coupling limit

Parametric Feedback Resonance in Chaotic Systems

If one changes the control parameter of a chaotic system proportionally to the distance between an arbitrary point on the strange attractor and the actual trajectory, the lifetime τ of the most stable unstable periodic orbit in the vicinity of this point starts to diverge with a power law. The volume in parameter space where τ becomes infinite is finite and from its nonfractal boundaries one can determine directly the local Liapunov exponents. The experimental applicability of the method is demonstrated for two coupled diode resonators