Solution-Processed n-Type Organic Field-Effect Transistors With High on /off Current Ratios Based on Fullerene Derivatives

Solution-processed n-type organic field-effect transistors (OFETs) based on the fullerene derivative {6}-1-(3-(2- thienylethoxycarbonyl)-propyl)-{5}-l-phenyl-[5,6]-C61 (TEPP) and phenyl-C61-butyric acid methyl ester (PCBM) in a multiring source/drain structure are reported. Devices with TEPP show high electron mobility up to 7.8 x 10^-2 cm²/Vs in the saturation regime for bottom-contact OFETs with Au S/D electrodes with a solution-processed fullerene derivative. The ON/OFF ratios reported in this letter, which are in the range of 10⁵ -10⁶, are among the highest values reported for such devices. This mobility is always higher compared to PCBM devices prepared in identical conditions. The mobility of TEPP and PCBM increased with increasing temperatures in the range of 100-300 K with activation energy of 78 and 113 meV, respectively, which suggests that the thermally activated hopping of electrons is dominant in TEPP.     

Effect of alloying and heat treatment on the structure and tribological properties of nitrogen-bearing stainless austenitic steels under abrasive and adhesive wear

The effect of nitrogen, silicon, and aging modes on the structure, resistance to abrasive and adhesive wear, friction factor, and mechanical properties of nitrogen-bearing (0.27–0.83% N) chromium-manganese austenitic steels is studied. It is shown that it is possible to ensure a favorable combination of mechanical and tribological properties in such steels by choosing the appropriate chemical composition and aging mode. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 9–18, May, 2007.     

Thermal simulation for geometric optimization of metallizedpolypropylene film capacitors

In this paper, the authors use an analytical model to calculate the losses in the metallized polypropylene film capacitors. The model is validated experimentally for capacitors having the same capacitance but different geometry. For each group of capacitors, a temperature distribution in the roll is assumed with the aim of optimizing its thermal performance. It appears that the heating of a long capacitor is higher than that of an equivalent flat capacitor subjected to the same electric stresses     

A New Algorithm for the Elimination of Common Subexpressions in Hardware Implementation of Digital Filters by Using Genetic Programming

A new algorithm based on Genetic Programming (GP) for the problem of optimization of Multiple constant Multiplication (MCM) by Common Subexpression Elimination(CSE) is developed. This method is used for hardware optimization for DSP systems. A solution based on Genetic Programming is shown in this paper. The performance of the technique is demonstrated in one- and multi-dimensional digital filters with constant coefficients.     

Performance of space-time codes for a large number of antennas

We study the asymptotic behavior of space-time codes when the number of transmit and receive antennas grows to infinity. Specifically, we determine the behavior of pairwise error probabilities with maximum-likelihood (ML) decoding and with three types of receiver interfaces: the ML interface, the linear zero-forcing (ZF) interface, and the linear minimum-mean-square-error (MMSE) interface. Two situations are studied: when the number of receiving antennas grows to infinity while the number of transmitting antennas is finite, and when both numbers grow to infinity but their ratio remains constant. We show that with ML or linear interfaces the asymptotic performance of space-time codes is determined by the Euclidean distances between codewords. Moreover, with the two linear interfaces examined here the number r of receive antennas must be much larger than the number t of transmit antennas to avoid a sizeable loss of performance; on the other hand, when r ≫ t, the performance of these linear interfaces comes close to that of ML. The dependence of error probabilities on Euclidean distance is valid for intermediate signal-to-noise ratios (SNRs) even when the number of antennas is small. Simulations validate our theoretical findings, and show how asymptotic results may be substantially valid even in a nonasymptotic regime: thus, even for few antennas, off-the-shelf codes may outperform space-time codes designed ad hoc     

Strength of Metals at High Strain Rates

Results of metal testing in impact tension–compression and indentation are analyzed. As the analysis of these data demonstrates, the strength of metals increases greatly with strain rates and at moderate indentation rates. At high indentation rates, a decrease in the specific energy (per unit volume of a displaced material) necessary for the formation of a conical cavity was observed. The account of the effects of viscosity, temperature increase upon plastic deformation and its localization can be used to explain the above phenomena.     

Response mechanism of SiC-based MOS field-effect gas sensors

SiC-based field-effect gas sensors with catalytic platinum electrodes (Pt-MOSiC) have been subjected to a series of gas response measurements. Structural analysis of the Pt electrodes revealed that the gas sensitivity and the selectivity of Pt-MOSiC gas sensors depend on two major parameters: the porosity and the catalytic activity of the Pt electrodes. Pt-MOSiC gas sensors with thick, dense Pt electrodes only exhibit hydrogen sensitivity, whereas Pt-MOSiCs with thin porous gates exhibit a broad range of gas sensitivities similar to resistive metal-oxide gas sensors. A model is put forward that explains the nonhydrogen gas response of Pt-MOSiC devices and of conventional polycrystalline metal-oxide materials on a common basis.     

Vapor phase synthesis of ZnO structures

We observed zinc oxide structures formed in an oxygen-containing atmosphere as a result of oxidation of the surface of zinc droplets. The gas-phase oxidation leads to the formation of hollow ZnO whiskers on the metal surface, which grow due to the transport of zinc vapor through their channels. It was found that high partial pressures of zinc and atomic oxygen give rise to fractal structures, which appear in a cascade process involving the sequential formation of zinc oxide vapor, ZnO clusters, and cluster aggregates as a result of the cluster-cluster interaction. A deposit of ZnO synthesized on the cathode surface exhibits a columnar structure.