Theory of two-photon measurement of laser output

Two-photon fluorescence and second-harmonic generation experiments have been used recently to study the picosecond structure of laser signals. A general theory of these measurements is presented in this work, which includes a detailed analysis of the possible responses of the measurement to a mode-locked laser that produces pulses and to a free-running laser that produces a noise-like output. Shapes Of the expected response patterns are calculated; second-order statistics that describe statistical departures from the expected patterns are also determined. Results are given for an arbitrary number of laser modes and general mode spectrum, in computationally useful forms for small and large mode number. Illustrative examples for large mode number are worked out for Gaussian and uniform mode profile curves; in addition, exact results are obtained for the uniform case of any (odd) number of modes. Sample response patterns for the case of a free-running laser are calculated by Monte-Carlo technique for Gaussian and uniform mode spectra. Results that reduce to special cases treated in various prior works are pointed out and new findings are discussed.     

Loss-Minimizing Control of PMSM With the Use of Polynomial Approximations

Normally, lookup-table-based methods are being utilized for loss-minimizing control of permanent magnet synchronous motors (PMSMs). But numerous repetitive experiments are required to make a lookup table, and the program size becomes bulky. In this paper, analytic methods for finding the loss-minimizing solution are studied. Since the solution lies either in the interior or on the voltage limit boundary, two different cases are dealt with separately. In both cases, fourth-order polynomials are derived. To obtain approximate solutions, methods of order reduction and linear approximation are utilized. The accuracies are good enough for practical use. These approximate solutions are fused into a proposed loss-minimizing algorithm and implemented in an inverter digital signal processor. Experiments were done with a real PMSM developed for a sport utility fuel cell electric vehicle. The analytically derived minima were justified by experimental evidences, and the dynamic performances over a wide range of speed were shown to be satisfactory.     

Extraction of essential interactions through multiple observations of human demonstrations

This paper describes a new approach on how to teach a robot everyday manipulation tasks under the "Learning from Observation" framework. In this approach, human demonstrations, which are made up of mutual interactions between a grasped object and an environmental object, are observed and a reusable manipulation task model is automatically generated. Most of the similar approaches so far assume that a demonstration can be well understood from a single demonstration. However, a single demonstration contains ambiguity, in that interactions which are essential to complete a task cannot be discerned without prior task dependent knowledge, which should be obtained from observation. To address these issues, a technique to integrate multiple observations of demonstrations is proposed. The demonstrations differ, but are virtually the same task. The shared interactions among all the demonstrations are considered to be essential and a task model is generated from their symbolic representations. Then, the relative trajectories corresponding to each essential interaction are generalized by calculating their mean and variance, and they are also stored in the task model, which is used to reproduce skilled behavior. This approach is examined by using a human-form robot, which successfully imitates human demonstrations of everyday tasks.     

Analysis of Variance of Traffic Usage Data

Procedures are developed and illustrated by application to real usage data of analysis of variance techniques for measuring components of variance in the data due to trend and arbitrary random variability in usage of equipment in a group as a whole. The usage data are obtained by periodic scanning of the equipment group at fixed intervals. Procedures for fitting the Polya distribution to the data are presented. Fitted Polya distributions are used to estimate the effects of trend on blocking. The procedures are extended to measuring and estimating the effects on blocking of day-to-day traffic variation and are illustrated by application to real usage data. A procedure is presented for adjusting estimates of variance for autocorrelation due to the usage measurement procedure and call holding times. The adjustment procedure is based on incomplete research and is, therefore, tentative. The effects of using a variance-stabilizing transformation of the data are shown. Other areas of application of the theory and procedures are discussed.     

Behavior of Hilbert networks under perturbations of their elements

We study the behavior of a Hilbert network (i.e., a finite or countably infinite network whose variables are in a Hilbert space and in which the associated total energy is finite) whose elements are affected by perturbations. More specifically, we will give estimates for a change of the current distribution caused by (a) perturbations of the elements of the nominal network when the voltage sources are fixed, and (b) a change of voltage sources in a network whose elements are perturbed. The conditions given in our theorems imply insensitivity and robust stability of the nominal network. The applications of the results are illustrated by an example of an infinite network.This research was supported by the NSF Grant #DMS-9102910.     

共蒸发三步法制备CIGS薄膜的性质

采用PID温度控制器控制共蒸发设备中蒸发源及衬底加热的温度,以三步法工艺制备CIGS(Cu(In,Ga)Se2)薄膜,通过恒功率加热衬底测试温度的变化,可实现在线组分监测,得到CIGS薄膜的组成重现性很好.CIGS薄膜的表面光洁,粗糙度多数小于10nm.但是组成相同的CIGS薄膜,其结晶择优取向可能不同,主要有(112)和(220)/(204)两种;其结晶形貌也有很大的不同,晶粒粗大且成柱状的薄膜电池效率高,虽然从Cu/(In Ga)＜1的组成可以认为CIGS薄膜为贫Cu结构,但Hall测试多数CIGS薄膜呈p型,少数呈n型.     

Derivation and application of a class of generalized boundaryconditions [electromagnetic scattering]

Boundary conditions involving higher order derivatives are presented for simulating surfaces whose reflection coefficients are known analytically, numerically, or experimentally. Procedures for determining the coefficients of the derivatives are discussed, along with the effect of displacing the surface where the boundary conditions are applied. Provided the coefficients satisfy a duality relation, equivalent forms of the boundary conditions involving tangential field components are deduced, and these provide the natural extension to nonplanar surfaces. As an illustration, a metal-backed uniform dielectric layer is simulated. It is shown that fourth-order conditions are capable of providing an accurate simulation for layers at least a quarter of a wavelength in thickness     

A comparison of deconvolution techniques for the ultrasonicnondestructive evaluation of materials

Several major deconvolution techniques commonly used for seismic applications are studied and adapted for ultrasonic NDE (nondestructive evaluation) applications. Comparisons of the relative merits of these techniques are presented based on a complete set of simulations on some real ultrasonic pulse echoes. Methods that rely largely on a reflection seismic model, such as one-at-a-time L(1) spike extraction and MVD (minimum variance deconvolution), are not suitable for the NDE applications discussed here because they are limited by their underlying model. L(2) and Wiener filtering, on the other hand, do not assume such a model and are, therefore, more flexible and suitable for these applications. The L(2) solutions, however, are often noisy due to numerical ill conditions. This problem is partially solved in Wiener filtering, simply by adding a constant desensitizing factor q. The computational complexities of these Wiener filtering-based techniques are relatively moderate and are, therefore, more suitable for potential real-time implementations.     

Electromagnetic field of a rectangular patch of uniform and lineardistributions of current

Closed-form expressions for a class of indefinite double integrals are presented. Using these formulas, exact analytical expressions for the magnetic vector potential and the electric and magnetic fields of a rectangular patch of uniform and linear distributions of electric current in an unbounded homogeneous medium are derived. The field expressions obtained are valid everywhere, in particular in the source region. Computed results verifying the correctness and accuracy of these expressions are presented     

小孔径螺旋型光电导天线的太赫兹辐射特性研究

研究了小孔径螺旋型光电导天线的太赫兹辐射特性.利用太赫兹时域光谱技术测量了螺旋型光导天线辐射的太赫兹波谱,得到了其时域发射光谱.通过快速傅里叶变换得到相应的频域光谱,同时对两种不同孔径螺旋天线的太赫兹辐射特性进行了比较.实验结果表明,太赫兹信号强度会随偏置电压的增大而增强;在偏置电压和泵浦光功率相同的情况下,较小孔径的...     

激光空泡脉动特性的实验和理论研究

采用自行研制的基于光偏转原理的高灵敏度光纤传感器研究了激光在水中铝靶表面产生的等离子体空泡及其脉动特性。通过实验获得了激光等离子体空泡在靶表面两次膨胀收缩的全过程；判定了空泡在两次脉动中对应的最大和最小泡半径。进而结合空泡溃灭理论，推算了激光空泡在各次脉动周期中含气量的变化。实验结果表明，激光空泡的含气量越小，空泡收缩越剧烈，气泡所能收缩的最小泡半径越小，其相应溃灭周期也越短。     

Adaptive control of libration angle of a satellite

Analytical conditions and practical methods of their realization are proposed for solving a problem of tracking a command signal for nonlinear disturbed system. Nonlinear plants, which linear part has unknown parameters and nonlinear part and disturbance are bounded and unknown, are considered. The paper illustrates a possibility of applications of proposed algorithms to control libration angle of satellite.     

Analysis of limit energy characteristics of planar demultiplexers

The energy gain and number of channels of a planar demultiplexer operating in a modern wave-length-division-multiplexing fiber-optic communication line are analyzed. The study involves the Fourier analysis and overlap integrals for complex fields. Reversible and irreversible demultiplexers are considered. The optimal parameters of the devices are determined. These parameters ensure the maximum gain and number of channels. Advantages and disadvantages of the devices are discussed, and desirable values of their parameters are recommended.     

Electromagnetic and optical behavior of two classes of dielectric lenses

Two families of spherically symmetric dielectric lenses are considered. Their optical properties are studied, and the radial eigenfunctions describing the electromagnetic field inside the lenses are found in terms of hypergeometric functions. Among the members of these two families are the Luneburg lens, the Maxwell fisheye, the isotropic lens of Eaton, and a lens that behaves like a metal reflector.     

Estimation of the sampled impulse-response of a channel

The paper describes various techniques for estimating the sampled impulse-response of a noisy linear channel. The estimators are suitable for use with maximum-likelihood detection processes such as the Viterbi-algorithm detector, in applications where a digital data signal is transmitted over a channel introducing severe intersymbol interference and where the receiver may or may not have some prior knowledge of the channel. Results of computer simulation tests are presented, showing, for each estimator, the magnitude of the error in the channel estimate over the reception of a typical data signal. Both time-invariant and time-varying channels are used in the tests and the performances of the estimators are compared for the different cases where the receiver initially has some or no knowledge of the channel and where the detected data symbols are all correct or contain some errors. It is shown that, even under quite unfavourable conditions, a surprisingly good estimate of the channel can be obtained by means of a relatively simple estimator.     

On a conjecture of Helleseth regarding pairs of binary m-sequences

Binary m-sequences are maximal-length sequences generated by shift registers of length m, that are employed in navigation, radar, and spread-spectrum communication. It is well known that given a pair of distinct m-sequences, the crosscorrelation function must take on at least three values. This correspondence addresses a conjecture made by Helleseth in 1976, that if m is a power of 2, then there are no pairs of binary m-sequences with a 3-valued crosscorrelation function. This conjecture is proved under the assumption that the three correlation values are symmetric about -1     

Calculation of Capacitance Coefficients for a System of Irregular Finite Conductors on a Dielectric Sheet

The capacitance coefficients for a system of irregular finite conductors on a dielectric sheet are considered. There are two parts to the Green's function-integral equation approach considered herein: the first deals with a derivation of Green's functions for a desired mathematical model; the second solves the integral equation by a discretization procedure in which a solution for a large number of unknowns is required-a significant limitation. This approach, however, allows treatment of rather complex finite geometric configurations that are useful in the design of modern thin-film circuits. An integral representation of the Green's functions for the desired mathematical model is presented in which ground planes are assumed at finite distances from the dielectric sheet. However, in this paper, final results are obtained only for the case in which ground planes are at infinity. Numerical results are presented for some typical multiconductor systems. For the case of a two-dimensional parallel strip problem, the result of the present analysis compares well with that available in the literature.     

Reliability of quantum-mechanical communication systems

We are concerned with the detection of a set ofMmessages that are transmitted over a channel disturbed by chaotic thermal noise when quantum effects in the communication systems are taken into account. Our attention is restricted to the special case in which the density operators specifying the state of the received field are commutative. In particular, the performance of two special communication systems is evaluated. For a system in which orthogonal signals with known amplitudes and random phases are transmitted over an additive white Gaussian channel, the structure of an optimum receiver is found. Expressions for the system reliability function and channel capacity are derived. For a system in which orthogonal signals are transmitted over a Rayleigh fading channel, the optimum performance is obtained. The optimum degree of diversity for an equal-strength diversity system is found numerically as a function of the average thermal-noise energy and information rate.     

Uniqueness of the generators of brain evoked potential maps

This study considers the uniqueness of neuronal generators of human brain evoked potentials measured on the scalp using the physical and mathematical properties of the volume conductor model. The results are applicable to a realistic, nonhomogeneous head shape where the potential map is known on a continuous set of points on the scalp. It is shown that sources which occupy “zero volume” in space such as point dipoles or sources distributed on an open surface or a line are uniquely defined by the potential maps. Finite volume nonoverlapping sources are also uniquely defined by their potential map. However, there are infinitely many different but overlapping sources which can create the same map. Several examples of such sources are provided. It is shown that there is a unique, minimum volume source which can be defined in this case. Results suggest that if a reconstruction of the sources starts from a continuous scalp map (obtained by interpolation of the data between electrode sites), one can obtain unique results concerning the source parameters that are not available in a search for a source whose potential map fits only at a discrete set of points