Microwave Parametric Frequency Dividers With Conversion Gain

A novel active parametric frequency divider configuration using coupled microstrip transmission lines and two balanced pseudomorphic HEMTs (pHEMTs) is presented. The analysis of the divide-by-2 circuit presented applies the principles of subharmonic generation using a nonlinear reactance to an active semiconductor device such as a pHEMT. A 2-1-GHz active analog frequency divider is designed and fabricated, with measurements showing a 20% bandwidth, 13.5-dB conversion gain, and harmonic rejection levels of more than 22 dBc. A maximum conversion gain of 18 dB is also achieved. These higher conversion efficiencies and the ability to cascade dividers allow for higher order division ratios to be achieved with the same topology.     

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.     

Electron hydration energy: Nonempirical estimate

Based on the results of quantum chemical calculations, the energies of vertical (photoionization) electron removal from superficial and bulk water layers are estimated as 2.9 and 4.4 eV respectively. For the first time, a nonempirical estimate of the electron hydration energy is obtained, 2.6 eV, which characterizes the electron state both at the superficial and bulk hydration. To find these value, molecular cluster systems modeling the Bjerrum defects of the hydrogen-bond network of water localizing the additional electron were calculated. Typical ways of the reorganization of defects upon the electron removal are identified. Conditions under which the relaxation of defects is reversible upon the re-addition of the charge are determined. The pre-existence of defects is shown not to be an indispensable condition of the effective localization of excess electrons by water. Small distortions, as well as breakage, of the continuity of the hydrogen-bond network are sufficient. Original Russian Text ? Yu.V. Novakovskaya, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 139–151.     

Homogeneous and Heterogeneous Crystallization in Nanometer-Sized Regions of the Copper Halide Phase in Photochromic Glasses

The halide phase in copper halide photochromic glasses is studied by the small-angle X-ray scattering (SAXS) technique. The dependences of the volume and composition of the halide phase on the temperature of primary heat treatment are determined. The temperature of the formation of a vacuum pore upon cooling from the temperature of primary heat treatment and the temperature of pore disappearance upon heating are investigated as functions of the size of the halide phase regions. The influence of the size of the halide phase regions and the temperature of secondary heat treatment on the crystallization temperature of the halide phase is elucidated. It is shown that the previously observed increase in the crystallization temperature of the halide phase with an increase in the size of the phase regions is associated with the change-over from homogeneous to heterogeneous crystallization. In turn, the mechanism of crystallization depends on the region where the vacuum pore is formed. In the case when the effective radii of drops are less than 130–140 Å, the vacuum pore is formed in the bulk of a liquid drop and the homogeneous crystallization occurs. The nuclei of heterogeneous crystallization arise when the formation of the vacuum pore is accompanied by the destruction of the vitreous matrix. This takes place when the radii of liquid drops are larger than 165–170 Å. The nuclei of heterogeneous crystallization disappear upon heat treatment of glasses at temperatures above 600°C. As a result, upon cooling from these temperatures, the homogeneous crystallization is observed in all cases and the crystallization temperature does not depend on the size of the halide phase regions.     

Measurement of the Metal Surface Acidity/Electronegativity of Pt(110)

In previous work, it has been found that a hydrogen-covered Pt(110) surface is acidic, but quantification of the acidity has not yet been done. In this paper a spectroscopic method is developed to measure the acidity of a metal surface for the first time. The technique involves measuring the intensity of the N–H stretch from the C₅H₄XNH⁺ that forms when hydrogen coadsorbs with pyridine, 2-fluoropyridine and 3-fluoropyridine. The Bethe approximation is then used to estimate the metal surface acidity/electronegativity (MSAEL). The proton affinity/MSAEL of Pt(110) has been determined to be 907 ± 4 kJ/mol at high coverage. This is the first time the MSAEL has been measured on a metal surface. Implications for fuel cell catalysis are discussed.     

All-optical phase-independent logic elements based on phase shiftinduced by coherent soliton collisions

We demonstrate, for the first time to our knowledge, that a fast coherent collision between two Kerr spatial solitons can give rise to a significant phase shift for both interacting beams. The maximal collision-induced phase shift ≈π rad takes place when the amplitudes of the solitons are equal (η₁=η₂) and the length of the interaction zone is comparable with a soliton phase period. Depending on the ratio η₂/η₁, and the collision angle between the solitons, the magnitude of the phase shift can be varied within a reasonable range, for example from 180° to 40°. The analysis of the effect performed by the finite-difference beam-propagation method has shown that it is insensitive to the initial phase difference between the incident beams (δ_i), even in the case when η ₁≠η₂. It has been demonstrated that the phenomenon can be used for all-optical three-soliton logic elements, which are capable of providing more than 3-dB signal amplification and possess bi -independent output characteristics     

Surface Hardening of Steels and Alloys Using a Corona Discharge

Metal Science and Heat Treatment -     

A New Generation of Steels for Metallic Structures

Metal Science and Heat Treatment -     

Designing Inorganic Substances and Materials with Specified Properties

The fundamental approaches to creation inorganic substances and materials are discused on the basis of electron structure of substances, formation of hierarchic structure and macroscopic properties of materials under various external effects that are realized in different production processes. The problems in designing materials and materials science as a whole are considered.     

Tensile,creep, and low-cycle fatigue behavior of a cast γ-TiAl-based alloy for gas turbine applications

The influence of chemical composition on the microstructure of the γ-titanium aluminide alloy Ti-48Al-2W-0.5Si (at. pct) and the accompanying tensile, low-cycle fatigue, and creep properties has been evaluated. The study showed that small variations in chemical composition and casting procedures resulted in considerable variations in the microstructure, yielding vastly different mechanical properties. Low contents of aluminum and tungsten led to a coarse-grained lamellar (γ/α ₂) microstructure with high creep resistance. A composition close to the nominal one produced a duplex (γ+γ/α ₂) structure with favorable strength, ductility, and low-cycle fatigue properties. By controlling the solidification and cooling rates at casting, a pseudoduplex (PS-DP) microstructure with a unique combination of high strength and high fatigue and creep resistance can be obtained. These unique properties can be explained by the diffuse boundaries between the relatively small γ grains and the neighboring lamellar colonies, combined with semicoherent interfaces between the γ and α ₂ phases. At tensile and low-cycle fatigue loading, these boundaries act like high-angle boundaries, producing a virtually fine-grained material promoting strength, whereas at creep loading, grain-boundary sliding is hindered in the semicoherent interfaces leading to high creep resistance.