Electronic properties of Fibonacci quasi-periodic heterostructures

We study the electronic states of different GaAs-AlAs Fibonacci quasi-perodic heterostructures grown along the (001) direction. We employ an empirical tight-binding Hamiltonian including spin-orbit coupling together with the surface Green function matching method. We present results for the eighth Fibonacci generation formed from different building blocks. We compare these results with those of the constituent quantum wells and with those of heterostructures containing the same number of GaAs and AlAs slabs after periodic repetition of the building blocks. No Fibonacci spectrum is found in the energy regions near the conduction and valence band edges of GaAs. A selective localization of the local density of states in the GaAs layers is found for many electronic states.     

A high-linearity 100-element diode grid mixer

Grid-mixer arrays can achieve high linearity and dynamic range through quasi-optical power combining. We present a 100-element single-ended diode grid mixer operating at 2.45 GHz. Each element incorporates two diodes in series. We measure an input third-order intercept of 11 W (40.5 dBm), and output third-order intercept of 3.4 W (35.4 dBm), and an associated conversion loss of 5.1 dB. The power-handling capability of the array is 100 times larger than that of a microstrip mixer using a single element. The local oscillator (LO) drive requirement for the entire array is 1.4 W (31.6 dBm). The angular dependence of the array's IF power is also presented and is in agreement with theory     

Interface stability during displacement reactions between Cu<Subscript>2</Subscript>O and Co<Subscript>1−<Emphasis Type="Italic">X</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> alloys at 1223 K

The stability of the reactive interface during the solid-state displacement reaction, Cu₂O+Co_1−X Fe _X =2Cu+(Co_1−X Fe _X )O, is studied as a function of Co-Fe alloy composition at 1223 K. For X≤0.03, the reaction zone has a layered structure, and the cation diffusion in (Co, Fe)O is the rate-limiting step. The interface is unstable in the early stages of the reaction; the instability decreases with time as the oxide thickness increases, and the interface becomes planar at long times. The time required for the attainment of interface planarity increases with the value of X. The reaction kinetics are consistent with the available cation-diffusion data in (Co, Fe)O. For X≥0.045, the product zone is a composite of Cu+(Co, Fe)O, and the rate is limited by the oxygen transport in copper. The transition to interface instability occurs when the oxide can support a cation flux that exceeds the maximum possible oxygen flux in copper. During the reaction, composition gradients develop in (Co, Fe)O because of higher diffusion rates for iron than for cobalt.     

用于千兆以太网基带铜缆接收器均衡的甚高频自适应 连续时间Gm-C 二阶带通滤波器的研究和设计

本文设计了用于千兆以太网基带铜缆接收器均衡的甚高频自适应连续时间Gm-C二阶带通滤波器。基于最陡梯度下降算法，带通滤波器的零点在57－340MHz的频率范围内可以自适应地调节，中心频率为1.278GHz。通过外接电阻伺服环路，滤波器中跨导转换器的跨导值不受工艺偏差和温度变化的影响，采用CSMC－HJ0.6μm CMOS工艺器件模型，用Cadence Spectres仿真器仿真了设计的自适应滤波器电路，仿真结果验证了设计原理和设计的电路。系统的最长学习时间为880个参考时钟周期。     

On the development of a direct method of determining the microcrack resistance curve

This report deals with direct observations of microcrack linkage at the crack tip prior to macroscopic crack initiation. It is shown that this process is directly linked to the inclusion distribution in the material and can be considered in terms of an R curve to describe microcrack development.     

Synthesis, 1H−NMR and Electronic Absorption Spectra,and Halochromic Properties of Bis(2-methyl-1-phenyl-3-isoindolyl)-(het)arylmethane Dyes

Several bis(2-methyl-1-phenyl-3-isoindolyl)-(het)arylmethane perchlorate dye salts have been synthesised, the (het)aryl substituent representing the acceptor systems 2-benzothiazolyl, 1-methyl-2-benzimidazolyl, 4-quinolyl, 4- and 2-pyridyl as well as phenyl.The constitution of these green dye salts was supported by their ¹H-NMR spectra. The variation of the electronic absorption maxima of this dye series was in accord with theoretical considerations based on SCF-CI and PMO calculations. They give rise to the statement that the bathochromic effect of the varied (het)aryl group is essentially due to a LUMO-LUMO interaction with the di-isoindolylmethane cyanine moiety, i.e. a second-order perturbation, enlarging the bathochromic shift caused by the increased twist angles inflicted on the central bonds by the bulkiness of the (het)aryl substituents (a first-order perturbation). The halochromic properties of these dyes are explicable on the same basis.The dissociation constants pK^★ and pK^★_R+ were measured and compared with analogous di-indolyl- (1) and di-indolizinyl-hetaryl-methane dyes (4), showing little difference with regard to the former and the distinct sequence indolizinyl > indolyl > isoindolyl dye series for the latter.     

The contact of elastic regular wavy surfaces

A complete solution in closed form to the elastic contact of a one-dimensional sinusoidal surface with a flat surface was presented by Westergaard in 1939. This paper is concerned with the elastic contact of a two-dimensional sinusoidal surface with a flat. In this case the stress distribution within the elastic solids is three-dimensional. As the load is increased the contact areas change in shape from being circular to square and finally leave a circular region of no contact when the waves are almost squashed flat. The problem is solved in general using a numerical method due to Kalker, but asymptotic solutions in closed form have been found for light loads and also for heavy loads at which contact is almost complete. The variation of the mean separation with load, which determines the volume of the space trapped between the two surfaces, is also found.