Thermal conductivity of doped PbTe-based solid solutions with off-center impurities

The coefficients of thermopower and electrical and thermal conductivity in the PbTe_0.8Se_0.1 S _0.1 solid solution with electron concentration (4.6–54) × 10¹⁸ cm^?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb_1?x Sn_xTe_1?x Se_x alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L₀ numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L₀ = 0.75 is obtained for a lightly doped sample at ～130 K.     

Experimental evidence of a relationship between monomer plasma residence time and carboxyl group retention in acrylic acid plasma polymers

Decreasing carboxyl retention in deposits from the glow region of an acrylic acid plasma was measured by X-ray photoelectron spectroscopy and chemical derivatisation as the collection distance from the monomer vapour inlet was increased. Volatilisation of plasma polymerised acrylic acid was detected after trifluoroethanol derivatisation; this is correlated with evaporation of low molecular weight components observed previously.     

Allocentric Versus Egocentric Spatial Memory After Unilateral Temporal Lobectomy in Humans.

Thirty patients who had undergone either a right or left unilateral temporal lobectomy (14 RTL; 16 LTL) and 16 control participants were tested on a computerized human analogue of the Morris Water Maze. The procedure was designed to compare allocentric and egocentric spatial memory. In the allocentric condition, participants searched for a target location on the screen, guided by object cues. Between trials, participants had to walk around the screen, which disrupted egocentric memory representation. In the egocentric condition, participants remained in the same position, but the object cues were shifted between searches to prevent them from using allocentric memory. Only the RTL group was impaired on the allocentric condition, and neither the LTL nor RTL group was impaired on additional tests of spatial working memory or spatial manipulation. The results support the notion that the right anterior temporal lobe stores long-term allocentric spatial memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analytical multipoint moment matching reduction of distributed thermal networks

In this paper, the multipoint moment matching method for model order reduction of discretized linear thermal networks is extended to distributed linear thermal networks. As a result, from the analytical canonical forms of distributed linear thermal networks, reduced thermal networks are derived analytically. This direct construction of the reduced network, from the exact analytical solutions, avoids the inevitable inaccuracies inherent in conventional surface and volume meshing. It allows nearly exact reduced thermal network construction by domain decomposition for arbitrarily complicated structures.     

Time-resolved spectroscopy of infrared active vibrations in 2,5-dioctyloxy poly(phenylene vinylene) films

We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×10¹³ photons/cm² per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation.     

Application of novel extractants for actinide(III)/ lanthanide(III) separation in hollow-fibre modules

Separation tests using hollow-fibre modules were performed for the difficult selective extraction of trivalent actinides over fission lanthanides from acidic media. This article shows that with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine as the extractant, up to 94% americium could be extracted from 1.0 kmol/m³ HNO₃, with minimal lanthanide co-extraction. Using a synergistic mixture of bis(chlorophenyl)dithiophosphinic acid and tri-n-octyl phosphine oxide, tests were performed on extraction, lanthanide scrubbing and stripping. In the extraction test, up to 99.99% americium could be extracted from 0.5 kmol/m³ HNO₃, with approximately one third of the lanthanides being co-extracted. Mass transfer calculations using a consistent set of input data showed good agreement with the experiments.     

Design principles underlying circadian clocks.

A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both the flexibility of clock networks and the relationships between various desirable properties such as robust entrainment, temperature compensation, and stability to environmental variations and parameter fluctuations. We use this to argue that the complexity provides the flexibility necessary to simultaneously attain multiple key properties of circadian clocks. As part of our analysis we show how to quantify the key evolutionary aims using infinitesimal response curves, a tool that we believe will be of general utility in the analysis of regulatory networks. Our results suggest that regulatory and signalling networks might be much less flexible and of lower dimension than their apparent complexity would suggest.     

Adaptive antenna system design for multi-element combining with transient interrupted channels

This paper presents an analysis and design procedure for a buoyant cable array antenna used for satellite communications. The towed multi-element array is susceptible to washovers and fluctuations due to the ocean wave interaction with the floating hose where the elements are housed. A model of system performance for coherent multi-element combining is presented based on the dropouts and fades of the individual elements. The array design, including the number and spacing of elements, is shown to be highly dependent on the individual element exposure characteristics and the degree of correlation of the fades between channels. The joint statistics of the array are analyzed using a binary conditional element exposure model and a first-order Markov interelement correlation model. Using this analysis, a family of array designs meeting the communications requirements is produced.     

LiNbO3 optical waveguides formed in a new proton source

Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r₃₃=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided