A hybrid technique for analyzing wire antennas in the presence of a plane interface

A hybrid technique which combines the method of moments (MM) with ray methods is employed to analyze the radiation of wires in the presence of a plane interface. In this technique, which is an extension of that proposed for combining the MM with the uniform geometrical theory of diffraction (GTD), a piecewise sinusoid (PWS) Galerkin method formulation is used. In this paper the basic assumption is made that a PWS dipole can be replaced by three sources of transverse, spherical waves, so that their fields can be treated separately by standard ray methods. Via this procedure the MM matrix can be easily augmented to account for the wire-interface interactions. Calculations of the field both radiated in the antenna half-space and transmitted through a plane interface are found in very good agreement with those performed by using the rigorous Sommerfeld integral representation. These results show that this technique provides an accuracy which is widely acceptable in most engineering applications, even when the wire is placed very close to the interface. This approach, which employs ray methods to calculate reflected and transmitted field contributions, appears promising to treat the case of curved interfaces.     

Graphical techniques for analyzing failure data with the percentileresidual-life function

Graphical data-analysis techniques for studying the empirical behavior of the hazard (failure) rate, based on a relationship between the maximum and minimum of the α-percentile residual life function to the minimum and maximum, respectively, of the hazard rate, are presented. Knowledge of these critical points is useful in controlling the system percentile life through burn-in. The graphical techniques are illustrated with a previously published data-set consisting of the empirical hazard rate of aircraft-engine components     

A model for analyzing handoff algorithms [cellular radio]

A model for analyzing the performance of handoff algorithms based on signal strength measurements made by mobile stations in a lognormal fading environment is presented. This model enables one to evaluate the effect of averaging the hysteresis on the handoff process. Handoffs are related to level crossings of the difference between the received signal strengths from two base stations. The algorithm performance is derived by modeling the level crossings as Poisson processes with time-varying rate functions. The model is seen to yield results that agree with simulations over the range of algorithm parameters of practical interest. These results can be used to determine the averaging interval and hysteresis level that achieve the optimum tradeoff between the number of unnecessary handoffs and the delay in handing off     

A socio-technical model for deploying expert systems. I. Thegeneral theory

This paper is addressed to an audience of managers and senior analysts involved with planning and controlling the knowledge engineering life cycle. A general framework for understanding the sociotechnical implications of expert systems is provided. It is argued that expert systems comprise two distinct but entwined subsystems. There is a technical component that concerns the task domain and the knowledge engineering process. There is a social dimension of how users and managers relate to the system and how the system fits with the organization. The authors believe that understanding the associations between these factors is essential in evaluating the efficiency and effectiveness of expert systems     

Optimization of signal sets for partial-response channels. I.Numerical techniques

Given a linear, time-invariant, discrete-time channel, the problem of constructing N input signals of finite length K that maximize minimum l₂ distance between pairs of outputs is considered. Two constraints on the input signals are considered: a power constraint on each of the N inputs (hard constraint) and an average power constraint over the entire set of inputs (soft constraint). The hard constraint, problem is equivalent to packing N points in an ellipsoid in min(K,N-1) dimensions to maximize the minimum Euclidean distance between pairs of points. Gradient-based numerical algorithms and a constructive technique based on dense lattices are used to find locally optimal solutions to the preceding signal design problems. Two numerical examples are shown for which the average spectrum of an optimized signal set resembles the water pouring spectrum that achieves Shannon capacity, assuming additive white Gaussian noise     

A new model for the post-stress interface trap generation inhot-carrier stressed p-MOSFETs

A new insight into the post-stress interface trap (N_it) generation in hot-electron stressed p-MOSFETs is presented. N_it generation is suppressed for positive oxide field but enhanced for negative oxide field. This observation provides strong support for a two-carrier model, involving the recombination between trapped electrons and inversion holes. While post-stress interface instability has generally been associated with hole trapping and hydrogen transport, our results clearly show the importance of electron traps on the long term stability of the Si-SiO₂ interface, and that the two-carrier model provides a consistent explanation for post-stress N_it generation in p-MOSFETs stressed under hot-electron injection     

Theory of polarization spreading techniques. I

Presents an analysis of a series of techniques grouped under the denomination “polarization spreading”, the intent of which is that of making the performance of a coherent optical receiver insensitive to the polarization transformations occurring along the optical fiber, without resorting to polarization compensation or control. The principle on which Polarization spreading operates is that of spreading the signal power over different states of polarization, so that heterodyning of at least half of the optical incident bit energy is always ensured. The main results obtained concern a condition that guarantees the maximum heterodyned signal energy, some classes of spreading waveforms satisfying the above condition, the derivation of the structure and the performance of optimum receivers in Gaussian noise. The results encompass most of the binary optical coherent modulation schemes proposed and experimented, such as ASK, FSK and DPSK     

Spindt阴极电容模型

本文用数值方法，计算了Ｓｐｉｎｄｔ阴极的电容，给出了—族曲线，与实验结果比较接近，对真空微电子微波三极管的设计有一定意义。     

A model for the static properties of DH lasers

The various subproblems for DH lasers such as field distribution, carrier profile, and temperature distribution are investigated. Solutions to these problems are obtained either analytically or by precise numerical methods. By combining the subproblems, a detailed model for the static properties is obtained. The model is applicable as well below as above threshold and properties of interest in the application of DH lasers such as threshold current, field distribution at a given current, and light current characteristics can be found. Nonlinear characteristics are found even for ideal symmetrical lasers. These "kinks" are associated with higher order modes and appear at relatively high values of the optical power.     

Prediction/cancellation techniques for fading broadcastingchannels. I. PSK signals

An approach for reducing the effects of multiplicative noise, such as fading, on the performance of mobile broadcasting transmission systems is introduced. The proposed method is based on a noise prediction/cancellation technique and is applied to phase-shift keyed (PSK) signals. By exploiting the statistical characteristics of the multipath fading signal and its strong correlation properties, a novel sequential receiver structure is derived that uses a detection algorithm which identifies the most probable transmitted sequence in the maximum-likelihood detection sense. The algorithm has been obtained for both Rayleigh and Rician fading channels. The proposed detection technique has been evaluated for various QPSK schemes operated in channels corrupted by a combination of additive white Gaussian noise (AWGN) and fading. The computer simulation results obtained show that by using a relatively simple receiver with a prediction algorithm of second order, considerable error floor reductions are achieved by the proposed receivers. As a direct result of these error floor reductions substantial bit error rate (BER) improvements of more than three orders of magnitude over conventionally detected schemes are obtained     

Pt/PZT铁电薄膜结晶性能与界面结构研究

锆钛酸铅[Pb(ZrxTi1-x)O3,PZT]薄膜具有优异的铁电性能,其中以(111)取向的PZT薄膜铁电性能更优异。目前对影响PZT薄膜取向生长的因素还未完全研究清楚,而PZT薄膜制备中,薄膜的择优取向生长控制是薄膜制备工艺的难点。采用TEM观察界面微观结构,利用高斯软件在TPSS/def2-TZVP水平下计算优化出PbxPt团簇分子的结构,发现界面层上形成的这类分子属于量子点范畴,结构上与PZT薄膜(111)晶面取向相似。提出高温退火生成的大量PbxPt团簇分子是(111)晶面取向生长的"诱导剂",控制界面层这种物质的生成和扩散可以控制PZT薄膜(111)取向生长。     

A theoretical model for analyzing the dynamic behavior of a misaligned rotor with active magnetic bearings

The dynamic response of a misaligned rotor, mounted in two identical active magnetic bearings (AMBs) was numerically investigated in this work. Three simplified models of current biased radial active magnetic bearings were presented, where four, six and eight electromagnets were powered by the bias current i₀ and respective control current. The magnetic forces acting on the rotor, the coil currents and the displacement of the rotor were obtained through an electromagnetic theory. The AMBs’ dynamics support parameters were modelled by linearised direct cross axes stiffness and damping coefficients. These are strongly dependent on the air gap between the stator and the shaft. A spatial model of a misaligned rotor with two degrees of freedom was presented. The motion equations were established for the rotor bearing system and simulated with Newmark method. Simulations results were carried out to survey the dynamic behavior of spatial misaligned rotor mounted in AMBs. The angular misalignment was such that the 2× and 4× running speed components are predominant. Their magnitudes varied with the number of magnets in the bearing and with the air gap between the stator and the shaft.     

P-N结中的一个新电容模型——光生电荷的常分布电容(英文)

This paper initially suggests a new capacitance model, i.e., the constant distribution capacitance of photogenerated charge (C.D.C.P.C.). The capacitance originating from the distribution of photogenerated charge in a junction region does not connect with alternative electric signals applied on the junction. It essentially distinguishes from the depletion and diffusion differential capacitances as previously known. Since the photo-generated charge, Q, and the photogenerated voltage, V, are connected by the equation, Q-CV, where C is just the C.D.C.P.C. the importance of this new capacitance model is self-evident. In the paper, the expressions of C.D.C.P.C. under the condition of approximately abrupt and graded junctions are deduced respectively at low forward bias. As the examination of the validity of the C.D.C.P.C. model, the deduced results are applied to the contactless test method of the device leakage and a good agreement between the theoretic calculation and experimental results is obtained, which enables the quantitative determination of the device leakage by the high frequency photoconductor decay method to be possible,     

I.I.R. digital filter design using constrained optimisation techniques

A new design method for all-pole infinite impulse response (i.i.r.) digital filters is introduced. The method involves minimising the area between the ideal lowpass filter response in the passhand and the actual passband response, subject to a quadratic constraint which ensures filter realisability. A unique solution is obtained to the minimisation which relates the filter weights to the eigenvector of a Toeplitz matrix. The filters are seen to have a small ripple in the passhand and a sharp cutoff in the stopband.     

A dynamic-threshold SOI device with a J-FET embedded sourcestructure and a merged body-bias-control transistor. I. A J-FET embeddedsource structure properties

The floating-body effects in SOI CMOSFETs are fully suppressed by embedding a J-FET source structure immediately beneath the source/drain junction. The drain of the J-FET consists of a Schottky barrier diode; the holes generated in the body can easily be ejected into the source through the forward-biasing of this diode. The source-drain breakdown voltage and drain-induced barrier-lowering characteristics of this device are the same as those of a bulk device. With this structure, the body potential syncrhronously couples to the gate bias in the dynamic mode without potential hysteresis when the body-to-source resistance is properly designed. The inverter-chain delay time should be 45% of that of a bulk device operating at 1 V without an excess load     

A physical-based equivalent circuit model for an organic/electrolyte interface

The aim of this work is to develop an equivalent circuit model for the metal-organic semiconductor-electrolyte structures that are typically used as transducers in biosensor devices. In particular, a perylene derivative material is implemented in the active layer of a gold-semiconductor-electrolyte stack. Our approach is extending the standard range of the bias voltages applied for devices that operate in water. This particular characterisation protocol allows to distinguish and investigate the different mechanisms that occur at the different layers and interfaces: adsorption of ions in the semiconductor; accumulation and charge exchange of carriers at the semiconductor/electrolyte interface; percolation of the ionic species through the organic semiconductor; ion diffusion across the electrolyte; ion adsorption and charge exchange at the platinum interface. We highlight the presence of ion percolation through the organic semiconductor layer, which is described in the equivalent circuit model by means of a de Levie impedance. The presence of percolation has been demonstrated by environmental scanning electron microscopy and profilometry analysis. Although percolation is much more evident at high negative bias values, it is still present even at low bias conditions. The very good agreement between the model and the experimental data makes the model a valid tool for studying the transducing mechanisms between organic films and the physiological environment.     

An optimal control model for analyzing human postural balance

The question posed in this study is whether optimal control and state estimation can explain selection of control strategies used by humans, in response to small perturbations to stable upright balance. To answer this question, a human sensorimotor control model, compatible with previous work by others, was assembled. This model incorporates linearized equations and full-state feedback with provision for state estimation. A form of gain-scheduling is employed to account for nonlinearities caused by control and biomechanical constraints. By decoupling the mechanics and transforming the controls into the space of experimentally observed strategies, the model is made amenable to the study of a number of possible control objectives. The objectives studied include cost functions on the state deviations, so as to control the center of mass, provide a stable platform for the head, or maintain upright stance, along with a cost function on control effort. Also studied was the effect of time delay on the stability of controls produced using various control strategies. An objective function weighting excursion of the center of mass and deviations from the upright stable position, while taking advantage of fast modes of the system, as dictated by inertial parameters and musculoskeletal geometry, produces a control that reasonably matches experimental data. Given estimates of sensor performance, the model is also suited for prediction of uncertainty in the response.<>     

Noniterative techniques for GPR imaging through a nonplanar air-ground interface

It is often advantageous to acquire pulse-echo ground-penetrating radar (GPR) measurements from antennas that are offset from the air-ground interface by a nonnegligible distance, either because the ground's surface is rough, or because measurements must be collected remotely. This paper describes the effects of incorrectly estimating the location of the air-ground interface on GPR images created with the plane-to-plane backpropagation (PPB) method. To compensate for a nonplanar air-ground interface, the wideband time-domain synthetic aperture method is reviewed and reformulated, using Snell's law of refraction, to account for measurements taken some distance above an undulating interface. A modification of the PPB algorithm that accounts for a nonplanar interface is also formulated, and examples of imaging with both methods are given to validate, the algorithms' performance for surface variations that are relatively smooth with respect to the radar waveform wavelengths. Additionally, a method for inferring the surface topography from the radar returns is described. Finally, the modified PPB is demonstrated by imaging buried targets sensed in field-acquired data.     

Internet服务故障的影响分析模型

通过分析通用Internet服务体系结构,提取出Internet服务中主要的被管对象类以及分析被管对象类之间的相互关联关系,提出了一个Internet服务故障影响分析模型,此模型涵盖了高层服务与实现支撑该服务的IT基础设施之间的关系。实验结果表明,基于该模型能够有效地分析Internet服务故障对该服务的影响。     

Modal, ray, and beam techniques for analyzing the EM scattering byopen-ended waveguide cavities

The problem of high-frequency electromagnetic scattering by open-ended waveguide cavities with an interior termination is analyzed via three different approaches. When cavities can be adequately modeled by joining together piecewise separable waveguide sections, a hybrid combination of asymptotic high-frequency and modal techniques is employed. In the case of more arbitrarily shaped waveguide cavities for which modes cannot even be defined in the conventional sense, the geometrical optics ray approach proves to be highly useful. However, at sufficiently high frequencies, both of these approaches tend to become inefficient; hence, a paraxial Gaussian beam technique, which retains much of the simplicity of the ray approximation but is potentially more efficient, is investigated. Typical numerical results based on the different approaches are discussed