Electronic Structure and Thermoelectric Properties of Si-Based Clathrate Compounds

Thermoelectric properties of Au-substituted Si-based clathrates, Ba₈AuGa₁₃Si₃₂ and Ba₆A₂AuGa _x Si_45−x (A = Sr, Eu, x = 13, 14), were experimentally and theoretically investigated. The polycrystalline samples of the Au-substituted Si-based clathrates were prepared by using the spark plasma sintering technique. The electronic structure of Ba₆A₂AuGa₁₃Si₃₂ was theoretically calculated by ab initio calculations, and the thermoelectric properties of Ba₆A₂AuGa _x Si_45−x were estimated through the calculated electronic structure. The effective mass of Ba₆A₂AuGa _x Si_45−x was experimentally estimated to be greater than that of Ba₈AuGa₁₃Si₃₂. Experimentally observed electronic properties agree with the calculations for Ba₆A₂AuGa _x Si_45−x . The maximum ZT value of Ba₆Sr₂AuGa₁₄Ge₃₁ is about 0.5 at 850 K. The calculated thermoelectric properties agree very well with the experimental results in the range from room temperature to 900 K.     

Crystallographic, Thermoelectric, and Mechanical Properties of Polycrystalline Ba8Al x Si46−x Clathrates

The Al content dependence of crystallographic, thermoelectric, and mechanical properties is reported for polycrystalline Ba₈Al _x Si_46?x (nominal x = 15 to 17) clathrates prepared by combining arc melting and spark plasma sintering methods. The elastic constants and the coefficient of thermal expansion (CTE), which are also important properties for designing thermoelectric devices, are presented. Powder x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy (EDX) indicate that the type I clathrate is the major phase of the samples but impurity phases (mainly BaAl₂Si₂, Si, and Al) are included in the samples with high Al contents. The actual Al content x determined by EDX ranges from approximately 14 to 15. The absolute value of the Seebeck coefficient increases and the electrical conductivity decreases as the Al content increases. The changes in Seebeck coefficient and electrical conductivity are explained in terms of the dependence of the carrier concentration on the Al content. The elastic constants and the CTE of the samples depend weakly on the Al content. Some of the properties are compared with reported data of single crystals of Ba₈Al₁₆Ge₃₀, Ba₈Ga₁₆Ge₃₀, Sr₈Ga₁₆Ge₃₀, silicon, and germanium as standard references. The effective mass, Hall carrier mobility, and lattice thermal conductivity, which govern the transport properties, are determined to be ~ 2.4m ₀, ~ 7 cm² V^?1 s^?1, and ~ 1.3 W m^?1 K^?1, respectively, for actual Al content x of about 14.77. The thermoelectric figure of merit ZT is estimated to be about 0.35 at 900 K for actual Al content x of about 14.77.     

Architecture and Performance Comparison of High-speed Switch Networks

This paper evaluates and analyzes performance of the growable switch, bypass queue switch, and tandem banyan switch in ATM networks.     

Test of Inseparability Criteria for Squeezed Number States of the Radiation Field

We investigate the efficiency of inseparability criteria in detecting the entanglement properties of two-mode non-Gaussian states of the electromagnetic field. We focus our study on the relevant class of two-mode squeezed number states. These states combine the entangling capability of two-mode squeezers with the non-Gaussian character (nonclassicality) of number states. They allow for some exact analytical treatments, and include as a particular case the two-mode Gaussian squeezed vacuum. We show that the generalized PPT criterion recently proposed by Shchukin and Vogel, based on higher order statistical moments, is very efficient in detecting the entanglement for this class of non-Gaussian states.     

First-Principles Study of Semiconducting Clathrate Ba<Subscript>8</Subscript>Al<Subscript>16</Subscript>Ge<Subscript>30</Subscript>

We calculated electronic structures of Ba₈Al₁₆Ge₃₀ in some Al-Ge framework configurations without nearest-neighbor Al-Al bonds by using a first-principles method. The calculated band structures are similar in outline but different in detail. We also calculated thermoelectric properties by using the electronic structures to analyze the experimental results on a sintered Ba₈Al₁₆Ge₃₀ sample. The calculated properties nearly agree with the experimental results; however, the calculated temperature dependences of electrical conductivity are slightly different from one another, because of differences in electronic structure. In this paper, we discuss the temperature dependence from the viewpoints of nonparabolic band effects.     

Clinical usefulness of helical-scanning CT for the evaluation of arteriosclerotic carotid lesions

We examined arteriosclerotic carotid lesions in 76 patients using helical scanning CT (HES-CT), and evaluated the clinical usefulness of this method. A high speed slip-ring X-ray CT system was used. Scanning of the neck was performed for a 30 second period following intravenous bolus injection of non-ionic contrast medium, while couch top movement was 2.0 mm/sec. Multiplannar reconstruction images (MPR-image) and 3-dimensional surface images (3D-image) were reconstructed from the continuous raw data. MPR-images offered axial, coronal and sagittal images in which the lesion could be seen from any direction, and 3D-images that could be freely rotated were obtained by using a track ball and monitor. Eighteen cases were also evaluated by conventional angiography. Excellent HES-CT images were obtained in 73 cases, showing occlusion in 13, stenosis in 34, plaques without calcification in 15 and plaques with calcification in 74 vessels. A good correlation was obtained between HES-CT and angiogram in most cases, and in 6 cases, HES-CT was superior in the detection of stenosis, because it enabled us to observe the lesion from various directions. These results suggested that HES-CT was a minimally invasive, useful diagnostic method for the evaluation of arteriosclerotic carotid disease.