Diurnal thermal cycling effects on microwave signatures of thin seaice

To investigate effects of diurnal thermal cycles on C-band polarimetric backscatter and millimeter-wave emission from sea ice, the authors carried out a winter experiment at the outdoor geophysical research facility (GRF) in the cold regions research and engineering laboratory (CRREL), the ice sheet grew from open sea water to a thickness of 10 cm in 2.5 days, during which they took polarimetric backscatter data with a C-band scatterometer, interlaced with brightness temperature measurements at 90 GHz in conjunction with meteorological and sea ice characterizations. The initial ice growth in the late morning was slow due to high insolation. As the air temperature dropped during the night, the growth rate increased significantly. Air temperature changed drastically from about -12 to -36°C between day and night, the diurnal thermal cycle repeated itself the next day and the growth rate varied in the same manner. Ice temperature profiles clearly show the diurnal response in the ice sheet with a lag of 2.5 h behind the time of the maximum short-wave incident solar radiation. The diurnal cycles are also evident in the millimeter-wave brightness temperature data, measured sea ice backscatter revealed substantial diurnal variations up to 6 dB with repeatable cycles in synchronization with the temperature cycles and the brightness temperature modulations, the diurnal cycles in backscatter indicate that the dominant scattering mechanism related to thermodynamic processes in sea ice is reversible, a diurnal backscatter model based on sea ice electrodynamics and thermodynamics explains the observed diurnal signature. This work shows that diurnal effects are important for inversion algorithms to retrieve sea ice geophysical parameters from remote sensing data acquired with a satellite synthetic aperture radar (SAR) or scatterometer on Sun-synchronous orbits     

Enhanced resonant tunneling real-space transfer in δ-dopedGaAs/InGaAs gated dual-channel transistors grown by MOCVD

We report the observation of pronounced N-shaped negative differential resistance (NDR) and negative transconductance at high drain and gate fields in δ-doped GaAs/InGaAs gated dual-channel transistors (DCTs) by tunneling real-space transfer (TRST). By virtue of varying the sheet density of the δ-doping layer as well as the thickness of the GaAs barrier, pronounced multiple-state NDR characteristics were obtained accompanying the gate current characteristic at room temperature. A peak-to-valley current ratio (PVR) of 15 was obtained which, to our knowledge, is the highest among the reported TRST devices at room temperature. The proposed devices possess potential advantages of ease of growth and fabrication     

High-Responsivity Photodetector in Standard SiGe BiCMOS Technology

For high-speed optoelectronic applications such as fiber-optic data communication systems, photodetectors (PDs) with high responsivity in Si-related processes are required. In this letter, a result of the effort along this line is reported. A novel device named phototransistor PD (PTPD) was realized in a commercial 0.35-mum SiGe BiCMOS technology. The device combines a surface PD (SPD) and a conventional SiGe heterojunction PT (HPT). It was shown that the SPD enhanced light absorption and the PTPD showed significant performance improvement over HPT. Responsivities of 5.2 A/W for an 850-nm light and 9.5 A/W for a 670-nm light were achieved in the PTPD, with floating base and SPD terminals.     

Memetic Algorithms for Optimizing Adaptive Linear Array Patterns by Phase-Position Perturbation

In this paper, based on the phase-position perturbation method, an innovative optimal adaptive antenna technique is proposed, where the deduced radiation pattern formulas available for searching optimal solutions are used to search the optimal weighting vector. The optimal radiation pattern designs of adaptive antenna are studied by the phase-position perturbation method. Memetic algorithms are used to search the optimal weighting vector of the phase-position perturbations for the array factor. The design for an optimal radiation pattern of an adaptive antenna can not only adjustably suppress the interferers by placing nulls at the directions of the interfering sources, but at the same time provide a maximum main lobe in the direction of the desired signal, i.e., to maximize the signal-to-interference ratio. To achieve this goal, a new convergent method, referred to as the two-way convergent method for memetic algorithms, is proposed. The memetic algorithm combines a genetic algorithm and local search heuristics to solve combinatorial optimization problems. The memetic algorithm is a kind of improved type of the traditional genetic algorithm. By using a local search procedure, it can avoid the shortcomings of the traditional genetic algorithm, whose termination criteria are set up by using the trial and error method. This proposed method is also able to solve the multipath problem, which exists at the same time in this communication system. The optimal radiation pattern concept can be implemented in practical wireless communication systems. Simulation results are also given in this paper.     

A 4-MB on-chip L2 cache for a 90-nm 1.6-GHz 64-bit microprocessor

A 4-MB L2 data cache was implemented for a 64-bit 1.6-GHz SPARC(r) RISC microprocessor. Static sense amplifiers were used in the SRAM arrays and for global data repeaters, resulting in robust and flexible timing operation. Elimination of the global clock grid over the SRAM array saves power, enabled by combining the clock information with array select signals. Redundancy was implemented flexibly, with shift circuits outside the main data array for area efficiency. The chip integrates 315 million transistors and uses an 8-metal-layer 90-nm CMOS process.     

Electrostatic linear actuator with a long stroke rolling spring guide

In contrast with diverse design concepts of actuators, we have developed an electrostatic linear actuator integrated with a long stroke rolling spring guide. The rolling spring guide realizes guiding function through rolling movements of two parallel preloaded belt-shaped springs. The electrostatic actuating force is generated by applying electrical fields to the structure of spring guide. Besides the driving voltage, the geometric size and the preloaded span of the spring guide are the main influential parameters of electrostatic actuating force and actuating displacement. With adequate adjustment of the preloaded span, this electrostatic actuator can generate not only a large actuating displacement in /spl mu/m range, but also a fine positioning displacement in /spl mu/m range. The finite element analysis (FEA) and the geometric analysis are applied to analyze spring stress and to derive the shape equation of the spring guide. Furthermore, a theoretical model for our electrostatic actuating principle is deduced on the basis of the shape equation. In addition to the theoretical analyses, the performance of the electrostatic actuator is experimentally tested and studied.     

光纤通信中声子损耗对受激布里渊散射的影响

对光纤通信系统中的受激布里渊散射（SBS）以及声子损耗对SBS的影响进行了研究.理论上,通过数值计算得出增大声子损耗能够提高布里渊阈值的结论;实验上,测量了不同长度的光纤在不同输入光功率下的反向Stokes光及输出光,观察了光纤中加入声子阻塞器对SBS阈值的影响,并测量了阻塞器位于光纤中不同位置时的SBS.研究结果表明,在光纤线路中加入声子阻塞器可以提高SBS阈值,而且在光纤的不同位置的阻塞器对SBS影响有所不同,在被测的60 km光纤上起点30 km处插入阻塞器时的布里渊阈值最高.     

Performance evaluation of random power capture on mobile communications

Power assignment schemes are man‐made methods to enhance the capture effect of radio communications. In a previous study, Wen and Yang investigated the combined capture effect of the fixed power assignment scheme, Rayleigh fading, and near–far effect on the performance of packet radios. The performance analysis was limited to an infinite population environment. This assumption is reasonable for a conventional packet radio system with a vast service area. However, for a cellular mobile system, a finite population model should be used. In this paper, we analyse the combined natural and man‐made capture effect on the performance of a cellular system with finite population in each cell. A random power assignment scheme is adopted to produce the man‐made capture. The system throughput and delay are carried out by a Markov model. Some numerical calculations are used to demonstrate the degree of performance improvement. Copyright © 2001 John Wiley & Sons, Ltd.     

Comprehensive study on a novel bidirectional tunnelingprogram/erase NOR-type (BiNOR) 3-D flash memory cell

In this paper a recently proposed bidirectional tunneling program/erase (P/E) NOR-type (BiNOR) flash memory is extensively investigated. With the designated localized p-well structure, uniform Fowler-Nordheim (FN) tunneling is first fulfilled for both program and erase operations in NOR-type array architecture to facilitate low power applications. The BiNOR flash memory guarantees excellent tunnel oxide reliability and is provided with fast random access capability. Furthermore, a three-dimensional (3D) current path in addition to the conventional two-dimensional (2D) conduction is proven to improve the read performance. The BiNOR flash memory is thus promising for low-power, high-speed, and high-reliability nonvolatile memory applications