High gain millimetric negative resistance low noise amplifiers

The limited gain available from GaAs FETs and HEMTs at millimetric frequencies can be overcome by using the devices in a negative resistance amplifier configuration. The advantage of the solid-state negative resistance amplifier over the transmission amplifier is that the gain available is not limited by the active device used. It has been shown that, over a narrow bandwidth, significantly higher gain can be obtained from a negative resistance amplifier, when compared to a transmission amplifier using the same device, while maintaining the same overall noise performance. This has been demonstrated experimentally using a 0.25 mu m HEMT device.<>     

Cyclic Wiener filtering: theory and method

Conventional time and space filtering of stationary random signals, which amounts to forming linear combinations of time translates and space translates, exploits the temporal and spatial coherence of the signals. By including frequency translates as well, the spectral coherence that is characteristic of cyclostationary signals can also be exploited. Some of the theoretical concepts underlying this generalized type of filtering, called frequency-shift (FRESH) filtering, are developed. The theory of optimum FRESH filtering, which is a generalization of Wiener filtering called cyclic Wiener filtering, is summarized, and the theory is illustrated with specific examples of separating temporally and spectrally overlapping communications signals, including AM, BPSK, and QPSK. The structures and performances of optimum FRESH filters are presented, and adaptive adjustment of the weights in these structures is discussed. Also, specific results on the number of digital QAM signals that can be separated, as a function of excess bandwidth, are obtained     

Value‐centric framework and pareto optimality for design and acquisition of communication satellites

Investments in space systems are substantial, indivisible, and irreversible, characteristics of high‐risk investments. Traditional approaches to system design, acquisition, and risk mitigation are derived from a cost‐centric mindset, and as such they incorporate little information about the value of the spacecraft to its stakeholders. These traditional approaches are appropriate in stable environments. However, the current technical and economic conditions are distinctly uncertain and rapidly changing. Consequently, these traditional approaches have to be revisited and adapted to the current context. We propose that in uncertain environments, decision‐making with respect to design and acquisition choices should be value‐based. We develop a value‐centric framework, analytical tools, and an illustrative numerical example for communication satellites. Our two proposed metrics for decision‐making are the system's expected value and value uncertainty. Expected value is calculated as the expected NPV of the satellite. The cash inflow is calculated as a function of the satellite loading, its transponder pricing, and market demand. The cash outflows are the various costs for owning and operating the satellite. Value uncertainty emerges due to uncertainties in the various cash flow streams, in particular because of market conditions. We propagate market uncertainty through Monte Carlo simulation, and translate it into value uncertainty for the satellite. The end result is a portfolio of Pareto‐optimal satellite design alternatives. By using value and value uncertainty as decision metrics in the down‐selection process, decision‐makers draw on more information about the system in its environment, and in making value‐based design and acquisition choices, they ultimately make more informed and better choices. Copyright © 2009 John Wiley & Sons, Ltd.     

Disruption of seven hypothetical aryl alcohol dehydrogenase genes from Saccharomyces cerevisiae and construction of a multiple knock-out strain

By in silicio analysis, we have discovered that there are seven open reading frames (ORFs) in Saccharomyces cerevisiae whose protein products show a high degree of amino acid sequence similarity to the aryl alcohol dehydrogenase (AAD) of the lignin-degrading fungus Phanerochaete chrysosporium. Yeast cultures grown to stationary phase display a significant aryl alcohol dehydrogenase activity by degrading aromatic aldehydes to the corresponding alcohols. To study the biochemical and the biological role of each of the AAD genes, a series of mutant strains carrying deletion of one or more of the AAD-coding sequences was constructed by PCR-mediated gene replacement, using the readily selectable marker kanMX. The correct targeting of the PCR-generated disruption cassette into the genomic locus was verified by analytical PCR and by pulse-field gel electrophoresis (PFGE) followed by Southern blot analysis. Double, triple and quadruple mutant strains were obtained by classical genetic methods, while the construction of the quintuple, sextuple and septuple mutants was achieved by using the marker URA3 from Kluyveromyces lactis, HIS3 from Schizosaccharomyces pombe and TRP1 from S. cerevisiae. None of the knock-out strains revealed any mutant phenotype when tested for the degradation of aromatic aldehydes using both spectrophotometry and high performance liquid chromatography (HPLC). Specific tests for changes in the ergosterol and phospholipids profiles did not reveal any mutant phenotype and mating and sporulation efficiencies were not affected in the septuple deletant. Compared to the wild-type strain, the septuple deletant showed an increased resistance to the anisaldehyde, but there is a possibility that the nutritional markers used for gene replacement are causing this effect.     

Aspects of the design of low noise, negative resistance, reflectionmode transistor amplifiers

The authors consider the use of microwave transistors in the negative resistance reflection mode and present the conditions for optimum noise performance. Possible advantages include the possibility of higher gain in the millimeter-wave region, which can be achieved by absorbing the parasitic common lead inductance into the feedback circuit designed to generate the negative resistance, and the existence of a failsafe mode of operation, in that the failure of the active device or its power supply is likely to lead a low return loss, resulting in a small insertion loss through the amplifiers, which may permit continued, although degraded, system operation. The latter potential advantage has proved to be of interest to radar system designers     

低价、高效、微波产品用的TPA覆铜版

随着信息产业的飞速发展,高频信号设备,如高速计算机、移动电话、卫星通信等,都已从兆赫频段扩展到千兆赫,这就意味着对它们所用的微波电路基板提出了更高的要求.长期以来,高频微波基板几乎没有越出使用聚四氟乙烯的老传统,但是,它有若干缺点玻璃化温度低,故刚性差;加工复杂,故成本高;金属化孔镀层与孔壁的结合力弱,故可靠性不高. 多年来,美国GIL科技公司一直在研制替代聚四氟乙烯的材料,经过姐妹公司的合作,终于研制成功了TPA板材,这种材料克服了上述缺点,从而获得了美国专利.本文介绍了TPA层压板的电气特性、机械特性和热效应,给出了许多宝贵数据.     

Accelerated Growth and Early Breeding of Holstein Heifers

Twenty-four Holstein heifers were fed grain and alfalfa hay ad libitum for accelerated growth from 91 kg body weight until verification of pregnancy (Treatment A). Grain then was deleted until near time of freshening. They were bred at second estrus if they weighed at least 305 kg. An additional 24 heifers were fed a conventional roughage ration to allow a growth rate corresponding to the Beltsville growth standard and were bred when 15 to 16 mo of age (Treatment S). Observations were of growth rate, reproductive and productive performance, and length of herd life under normal culling.The A heifers gained 38% faster to 364 kg body weight (1.1 versus .8 kg/day). Average weights and ages were first estrus 275 kg, 8.3 mo (A), 288 kg, 10.2 mo (S); first breeding 319 kg, 9.6 mo (A), 392 kg, 16.8 mo (S); and first calving 560 kg, 19.7 mo (A), 26.9 mo (S). Differences in body dimensions at given weights were negligible. Treatment effects on dystocia were inconclusive. Lactation number, numbers of animals milked 100+ days, and average milk yields (kg) were: 1st lactation 24, 4436 (A), 22, 5415 (S); 2nd–22, 5295 (A), 18, 5903 (S); 3rd–12, 6278 (A), 10, 6407 (S); 4th–6, 7181 (A), 5, 5269 (S). Mean accumulative milk yields per animal to 36 mo of age were 7173 (A) and 4853 kg (S). Accelerated growth and early breeding did not affect herd life.     

A novel digital predistorter technique using an adaptive neuro-fuzzy inference system

This letter presents a novel digital predistorter technique using an adaptive neuro-fuzzy inference system (ANFIS). The proposed approach employs real-time input and output signals of a nonlinear power amplifier as inputs to the ANFIS, so as to approximate the inverse functions of the power amplifier. The antecedent and consequent parameters of the FIS constructed by the ANFIS are tuned using backpropagation and least squares algorithms. Simulation shows that this novel technique has improved the linearity of a WCDMA signal by a further 4 dBc compared to a conventional look-up table (secant) approach. Moreover, this proposed technique is capable of adapting to instantaneous variation in the power amplifier response through time, which is a topic often omitted by researchers in this area.     

Image reconstruction based on human and monkey cone mosaics

The image reconstruction capacity of the actual foveal cone sampling mosaics of an adult monkey and human is investigated through computer simulations. A retinocortical mapping model in which positions are known and disorder is compensated (DC) has been implemented using classical Whittaker-Kotelnikov-Shannon (WKS) reconstruction theory and a two-dimensional hexagonal tessellation technique that maps the cone lattice onto a perfectly hexagonal grid. The DC model has been compared with a retinocortical mapping model in which cone positions are also known but position disorder is uncompensated (DU) in the reconstruction process. A control model has also been implemented using WKS reconstruction based on sampled data obtained with simulated perfectly hexagonal lattices whose Nyquist limits are equivalent to those of the human and monkey lattices. Quantitative comparisons of these models are based on the RMS error per pixel between the original and reconstructed images. Results of these simulations demonstrate a pronounced superiority of the DC over the DU model. The results of these simulations, which use “biologically correct” sampling lattices, document a potential image reconstruction advantage when foveal cone positions are known.     

The formation and interpretation of defect images from crystalline materials in a scanning transmission electron microscope.

The technique of scanning transmission electron microscopy (STEM) has been employed usefully in studies of amorphous materials, and the theory of image formation and interpretation in this case has been well developed. Less attention has been given to the practical and theoretical problems associated with the use of STEM for the examination of crystalline materials. In this case the contrast mechanisms are dominated by Bragg diffraction and so they are quite different from those occurring in amorphous substances. In this paper practical techniques for the observation and interpretation of contrast from defects in crystalline materials are discussed. It is shown that whilst images of defects are obtained readily under all typical STEM operating conditions, the form of the image and the information it contains varies with the angle subtended at the specimen by the detector. If this angle is too large significant image modifications relative to the "conventional" transmission electron microscope case may occur and the resolution of the image may degrade. If this angle is too small, then signal to noise considerations make an interpretation of the image difficult. In this paper we indicate how the detector angle may be chosen correctly, and also present techniques for setting up a STEM instrument for imaging a crystalline material containing lattice defects.