DC and RF performance of GaAs MESFET fabricated on silicon substrate using epitaxial lift-off technique

GaAs MESFETs have been fabricated on a silicon substrate using a molecular beam epitaxy grown film detached from its growth substrate and attached on a silicon substrate covered with a dielectric. The device processing is done on the silicon substrate. The MESFETs exhibit I/sub DSS/=130 mA/mm, g/sub m/=135 mS/mm and for 1.3 mu m gate length unity current gain cut-off frequency f/sub T/ of 12 GHz. Excellent device isolation with subpicoampere leakage currents is obtained.<>     

Modelling the electro-osmotically enhanced pressure dewatering of activated sludge

The mechanical dewatering of biological materials, such as activated sludge, is troublesome due to their high compressibility. The dewatering can be improved drastically by the use of electro-osmosis, a technique in which a direct current electric field is applied to the filter cake, inducing an electro-kinetic displacement of the liquid phase. In this article, a model is presented which describes this process for a one-dimensional, one-sided filter press. The model starts from two existing models, each describing a part of the process [Iwata, M., Igami, H., Murase, T., 1991. Analysis of electroosmotic dewatering. Journal of Chemical Engineering of Japan 24(1), 45-50; Sørensen, P.B., Moldrup, P., Hansem, J.A., 1996. Filtration and expression of compressible cakes. Chemical Engineering Science 51(6), 967-979]. A robust solution scheme for the basic flux and continuity equations is used to describe filtration and expression. Regarding the electro-osmosis, an adapted form of the Darcy equation, expressing electro-osmotic induced flow as well as pressure induced flow, is integrated into the former solution scheme. This permits the simulation of the overall process using a single model. Validation of the model revealed that the experimental piston height during dewatering can be described accurately provided that temperature effects are taken into account.     

Praseodymium and copper cation-exchange capacities of neutral-detergent fibres relative to composition and fermentation kinetics

The cation-exchange capacity (CEC) of 12 neutral-detergent fibres (NDF) was measured using the elements praseodymium (Pr III) and copper (Cu II) at pH 3.5. CEC was positively correlated with lignin and nitrogen content as well as the lignin: acid-detergent fibre ratio of the NDF. CEC was also measured using Pr at pH 7.0. Increasing the pH of exchange from 3.5 to 7.0 significantly increased the CEC. Lignin had a higher correlation with CEC at pH 7.0. The relationship between CEC and the fermentation rates of NDF was non-significant. However, lag, i.e. the period of time before the initiation of fermentation, tended to decrease with increasing CEC. NDF influences the rumen ecosystem by buffering rumen pH, exchanging cations to influence osmotic pressure, and providing substrate and microenvironments for anaerobic microorganisms. Consequently, CEC needs to be measured at conditions which simulate the rumen. It is recommended that the Pr method should be used to measure CEC as it is a simple, yet robust technique that can be buffered to simulate conditions of the entire gastrointestinal tract ranging in pH from 2.0 to 7.0.     

Influence of the pressure profile inside a dense membrane on the rate of permeation

Lee¹ showed that molecular transport in all isothermal membrane processes, based on dense layers, can be described with one single general equation, including only measurable conditions from outside of the membrane. Following arguments given by Paul² for homogeneous rubber membranes, Lee assumed the pressure everywhere inside the membrane to be equal to the feed side pressure. In this paper the question is stated whether this assumption always holds for very thin and/or nonhomogeneous membranes like asymmetric membranes made of semicrystalline polymers. A study based on less stringent assumptions of the pressure profile inside the membrane is performed. The results show that in most cases this pressure profile does not play a major role in the permeation process.     

Nonlinearized approach to profile inversion

A method for reconstructing the index of refraction of a bounded inhomogeneous object of known geometric configuration from measured far-field scattering data is presented. This work is an extension of recent results on the direct scattering problem wherein the governing domain integral equation was solved iteratively by a successive relaxation technique. The relaxation parameters were chosen to minimize the residual error at each step. Convergence of this process was established for indices of refraction much larger than required for convergence of the Born approximation. For the inverse problem, the same technique is applied, except is this case both the index of refraction and the field are unknown. Iterative solutions for both unknowns are postulated with two relaxation parameters at each step. They are determined by simultaneously minimizing the residual errors in satisfying the domain integral equation and matching the measured data. This procedure retains the nonlinear relation between the two unknowns. Numerical results are presented for the dielectric slab. The algorithm is shown to be effective in cases where the iterative solution of the direct problem is rapidly convergent and outperforms the Born-based approaches.     

Analytical Approach to Grid Operation With Phase Shifting Transformers

Analytical expressions are derived to gain insight in the operating principles of phase shifting transformers (PSTs) in a highly meshed grid. To this extent, the dc load flow algorithm is adapted to account for such devices. This leads to a linear expression for the relation between PST settings and the active power flow in the lines. Based on these equations, the total transfer capacity (TTC) can be described mathematically, which allows for optimization. Furthermore, the linear least squares method is used to distribute a cross-border transport evenly over the interconnectors.     

Optimization of transmitter and receiver filters for digitalcommunication systems using mean field annealing

A technique for finding transmitter and receiver filters for a wide class of digital communication systems which minimize the bit-error rate (BER) is presented. The technique uses Monte Carlo simulation to estimate the BER and mean field annealing (MFA) to optimize the pulse shapes. Modeling of the link can be as complex as simulation will allow, while MFA is resistant to the statistical variation in the BER estimate from the simulation. Initially, the MFA technique was applied to a binary symmetric channel in a nonsimulation environment, and an approximate analysis of the behavior of MFA for this problem was performed. In a more complex example, MFA was coupled with Monte Carlo simulation techniques to find near-optimal transmit and receive filters for a satellite communications link, taking 6 CPU hours on a DECstation 3100. The BER of the link was found to be as much as three orders of magnitude lower when using the MFA-constructed optimal filters than when using filters from other comparison results. For this example, the pulse shapes obtained using MFA exhibit a low BER even as the parameter controlling the nonlinearity of the satellite-link model is varied over a wide range, thus showing the solution is robust     

Copper contamination of high purity germanium (HP-Ge) through Li-diffusion

It will be shown in this paper that the Li diffusion in HP-Ge, used for γ-ray detectors, always introduces extra Cu. This Cu has a negative influence on the detector resolution. It originates from the Li suspension used. We suggest that the actual diffusion temperature should be kept below 300°C.     

In vitro dissolution of two oral controlled release preparations of diclofenac sodium.

The development of controlled release formulations has brought about the need for appropriate quality control methods such as in vitro dissolution testing. Such tests are principally designed to obtain correlation with the in vivo performance of the formulation (1,2,3). If an in vitro test can be defined offering a good correlation the test may serve for routine quality control or may be useful in screening new drug formulations.     

设计和仿真无线局域网设备天线

对带有开关电路的2.4 GHz极化分集印刷天线进行电磁场及电磁场与电路协同仿真 通过采用极化分集技术,可以用低成本PCB基片制造具有良好接收机性能的无线局域网设备(WLAN)天线.本文将描述如何使用最新的三维电磁场(EM)仿真工具来设计和仿真一对2.4GHz正交极化的印刷偶极子天线,同时预测表面电流和相关的远场辐射图.