Reducing Lattice Thermal Conductivity of the Thermoelectric Compound AgSbTe2 (P4/mmm) by Lanthanum Substitution: Computational and Experimental Approaches

In this study we performed lattice dynamics first-principles calculations for the promising thermoelectric (TE) compound AgSbTe₂, and estimated the stability of its three polymorphs over a wide temperature range from 0 to 600 K. We calculated the vibrational density of states of the AgSbTe₂ (P4/mmm) phase. The results suggested that formation of substitutional defects at Ag-sublattice sites impedes lattice vibrations, thereby reducing lattice thermal conductivity. We focused on calculations based on the Debye approximation for the compound La_0.125Ag_0.875SbTe₂, and predicted reduction of the average sound velocity from 1684 to 1563 m s^?1 as a result of La doping. This is manifested as a ca. 14% reduction in thermal conductivity. To confirm the results from computation we produced two Ag–Sb–Te-based alloys, a ternary alloy without La addition and a quaternary alloy containing La. We measured the thermal conductivity of both alloys by use of the laser flash analysis method, and, as a result of La alloying, observed a reduction in thermal conductivity from 0.92 to 0.71 W m^?1 K^?1 at 573 K, as calculated from first principles.     

Flexible polypyrrole/ClO4 films formed in aqueous solutions

The preparation of high quality polypyrrole film in aqueous solutions is described. The new polypyrrole films were produced in a phthalate buffer solution (pH 4) with perchlorate as the electrolyte. Very smooth and remarkably flexible free-standing films were grown electrochemically. The conductivity of the polypyrrole film exhibits an inverse dependency on the film thickness. The mechanical properties of these films, such as tensile strength and the modulus of elasticity, are better than the reported properties for polypyrrole/tosylate films prepared in organic solutions. In comparison with the polypyrrole films prepared in phosphate buffer solution, the stability of the polypyrrole films prepared in phthalate buffer are improved considerably. The morphology and composition of the conducting film is described and a mechanism for their formation is proposed.     

Age-specific variation in aneuploidy incidence among biochemical screening programs

A human cytomegalovirus mutant that was isolated for resistance (10-fold) to the antisense oligonucleotide fomivirsen (ISIS 2922) exhibited cross-resistance to a modified derivative of fomivirsen with an identical base sequence but little or no resistance to an oligonucleotide with an unrelated sequence. No changes in the mutant's DNA corresponding to the fomivirsen target sequence were found.     

A cohesin domain from Clostridium thermocellum: the crystal structure provides new insights into cellulosome assembly

The most common major comorbid disorders associated with eating disorders include substance use disorders, personality disorders, mood disorders, anxiety disorders, and obesity. To test conceptual models of the relationship between the eating disorders and these comorbid disorders, complex research paradigms are needed, including epidemiological studies, behavior-genetic studies, and longitudinal research designs. Comorbidity may be a significant factor to consider as approaches to the treatment of eating disorders continue to evolve.     

A direct field-oriented controller for induction motor drives usingtapped stator windings

The implementation of a direct method of field orientation that requires little knowledge of machine parameters and uses only readily measurable quantities is discussed. The system uses tapped stator windings to measure the air-gap flux. The signals from the tapped windings are also used in a flux-regulation loop. A speed controller is implemented using the ripples created in the tapped windings by the motion of the rotor slots through the flux for speed information     

Physical and Medium Access Control criteria for the optimal Medium Access Control protocol data unit size in Automatic Repeat Request‐enabled connections in IEEE 802.16e/ WiMAX systems

In this paper, we address an aspect of the mutual influence between the physical (PHY) layer budding blocks (forward error correction (FEC) blocks) and the medium access control (MAC) level allocations in the uplink and downlink of IEEE 802.16e/WiMAX systems. In these systems, it is possible to transmit MAC level frames, denoted MAC protocol data units (PDUs), such that a PDU contains an integral number of fixed size data blocks. We compute the optimal size of a PDU according to two criteria, one related to the PHY layer and one related to the MAC layer. In relation to the PHY layer, the criterion maximizes the average number of data bits that are transmitted in a PHY slot. In relation to the MAC layer, the criterion maximizes the goodput of the PDU. The goodput depends on the success probability of the PDU, which in turn depends on the FEC blocks over which the PDU is allocated. We then compare the maximal PDU goodputs in different sizes of the FEC blocks and the data blocks. The main outcome is that the PDU goodput is sensitive in those cases in which data blocks are very large. We also give guidelines on how to choose the best modulation/coding scheme to use in a scenario where the signal‐to‐noise ratio can change significantly during transmissions, to maximize the PDU goodput. Finally, we compare between the two criteria. Copyright © 2013 John Wiley & Sons, Ltd.