Synthesis of multivariable,basically non-interacting systems with significant plant uncertainty

This paper presents a synthesis technique for basically non-interacting, time-invariant, linear, minimum-phase, multi-variable feedback control systems with significant plant uncertainty. The technique permits precise design to specifications in the frequency domain, of the form k_i¹(ω)?|τ_ii(jω)|?k_i²(ω), |τ_ij(jω)|?k_ij(ω), i/n=j, to be satisfied over the range of plant parameter uncertainty, where T = [τ_αβ] is the matrix of transfer functions of the closed-loop system, and the k's are a priori specified. The specifications are achieved with loop transmission elements of minimum ‘bandwidth’.A computerized iteration scheme is developed. At each iteration the problem is one of designing separate, single input-output systems with parameter uncertainty. An exact synthesis technique exists for this problem. Two detailed examples are given: one, a rotating d.c. to a.c. converter, in which parameter uncertainty is by a factor of 10 (1000%) and the second with parameter uncertainty factors up to 100.     

Properties and convergence of a posteriori probabilities in classification problems

This report investigates the behavior of the a posteriori probabilities for classification problems in which the observations are not identically distributed. Some basic properties of the a posteriori probabilities are presented; then, it is shown that for each class the a posteriori probability converges a.s. to a random variable. Conditions are given for a.s. convergence of the a posteriori probability to 1 for the true class (and to 0 for all other classes).The results are illustrated for the case of two classes and binary observations, and finally a numerical example is presented.     

Laser operation with two orthogonally polarized transverse modes

Laser resonator configurations, which enable laser operation with two orthogonally polarized transverse modes, are presented. The intensity distributions of these two modes can be chosen to be complementary, so the gain medium can be exploited more efficiently than with a single mode, leading to improved output power. Moreover, the two modes can be combined and efficiently transformed into a single high-quality beam. Basic principles and experimental results with Nd:YAG lasers are presented.     

Crack-like processes governing the onset of frictional slip

We perform real-time measurements of the net contact area between two blocks of like material at the onset of frictional slip. We show that the process of interface detachment, which immediately precedes the inception of frictional sliding, is governed by three different types of detachment fronts. These crack-like detachment fronts differ by both their propagation velocities and by the amount of net contact surface reduction caused by their passage. The most rapid fronts propagate at intersonic velocities but generate a negligible reduction in contact area across the interface. Sub-Rayleigh fronts are crack-like modes which propagate at velocities up to the Rayleigh wave speed, V _R, and give rise to an approximate 10% reduction in net contact area. The most efficient contact area reduction (~20%) is precipitated by the passage of ‘slow detachment fronts’. These fronts propagate at ‘anomalously’ slow velocities, which are over an order of magnitude lower than V _R yet orders of magnitude higher than other characteristic velocity scales such as either slip or loading velocities. Slow fronts are generated, in conjunction with intersonic fronts, by the sudden arrest of sub-Rayleigh fronts. No overall sliding of the interface occurs until either of the slower two fronts traverses the entire interface, and motion at the leading edge of the interface is initiated. Slip at the trailing edge of the interface accompanies the motion of both the slow and sub-Rayleigh fronts. We might expect these modes to be important in both fault nucleation and earthquake dynamics.     

Atmospheric modulation transfer function in the infrared

In high-resolution ultranarrow field-of-view thermal imagers, image quality over relatively long path lengths is typically limited by atmospheric degradation, especially atmospheric blur. We report our results and analyses of infrared images from two sites, Fort A. P. Hill and Aberdeen Proving Ground. The images are influenced by the various atmospheric phenomena: scattering, absorption, and turbulence. A series of experiments with high-resolution equipment in both the 3-5- and 8-13-microm regions at the two locations indicate that, as in the visible, image quality is limited much more by atmosphere than by the instrumentation for ranges even of the order of only a few kilometers. For paths close to the ground, turbulence is more dominant, whereas for paths involving higher average elevation, aerosol modulation transfer function (MTF) is dominant. As wavelength increases, turbulence MTF also increases, thus permitting aerosol MTF to become more dominant. A critical role in aerosol MTF in the thermal infrared is attributed to absorption, which noticeably decreases atmospheric transmission much more than in the visible, thereby reducing high-spatial-frequency aerosol MTF. These measurements indicate that atmospheric MTF should be a basic component in imaging system design and analysis even in the infrared, especially as higher-resolution hardware becomes available.     

Testing juntas

We show that a boolean valued function over n variables, where each variable ranges in an arbitrary probability space, can be tested for the property of depending on only J of them using a number of queries that depends only polynomially on J and the approximation parameter ε. We present several tests that require a number of queries that is polynomial in J and linear in ε⁻¹. We show a non-adaptive test that has one-sided error, an adaptive version of it that requires fewer queries, and a non-adaptive two-sided version of the test that requires the least number of queries. We also show a two-sided non-adaptive test that applies to functions over n boolean variables, and has a more compact analysis.We then provide a lower bound of on the number of queries required for the non-adaptive testing of the above property; a lower bound of for adaptive algorithms naturally follows from this. In establishing this lower bound we also prove a result about random walks on the group Z^q₂ that may be interesting in its own right. We show that for some , the distributions of the random walk at times t and t+2 are close to each other, independently of the step distribution of the walk.We also discuss related questions. In particular, when given in advance a known J-junta function , we show how to test a function for the property of being identical to up to a permutation of the variables, in a number of queries that is polynomial in J and ε⁻¹.     

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Charge distribution in magnesium aluminate spinel (MAS) results in the formation of a space‐charge region that plays a critical role in assigning functional properties. Significant theoretical advances explaining this phenomenon have been accomplished, even though quantitative experimental support from nano‐scale granular MAS is only indirect. In this work, the electrostatic potential distribution in nano‐scale grains of nonstoichiometric MAS (MgO·0.95Al₂O₃ and MgO·1.07Al₂O₃) was measured by off‐axis electron holography (OAEH) and compared to the distribution of cations and defects in this material as measured by electron energy‐loss spectroscopy (EELS). In this manner, we studied the roles of composition, grain size, and applied electric field (EF) on the formation of a space‐charge region. We quantitatively demonstrated that regardless of grain size, the vicinity of MgO·0.95Al₂O₃ grain boundaries presented an excess of Mg⁺² cations, whereas the vicinity of MgO·1.07Al₂O₃ grain boundaries included an excess of Al⁺³ cations. The degree of structural disorder (ie, the inversion parameter, i) indicated that as‐synthesized MAS were significantly disordered (i between 0.37 and 0.41), with values decreasing toward equilibrium ordering values following annealing (i between 0.27 and 0.31). The application of an external ~150 V/cm EF during annealing further enhanced lattice ordering (i between 0.16 and 0.19). Such variations in the distribution of cations and defects should determine the space‐charged potential (SCP). However, using these measurements to calculate the SCP was not possible due to the wide range of values reported for formation energies of defects (0.82‐8.78 eV). Consequently, we correlated local ionic ordering with electrostatic potential in nonstoichiometric MAS. The magnitudes of the SCP in both MgO·0.95Al₂O₃ and MgO·1.07Al₂O₃ decreased following annealing from ?3.4 ± 0.3 V and 2.0 ± 0.2 V to ?2.0 ± 0.2 V and 1.6 ± 0.1 V, respectively.     

First Principles Investigation of Cold Curves of Metals

The rapid development of better high pressure experimental techniques combined with efficient and accurate density functional calculations of the structural properties of materials provide a new avenue to promote the study of materials at high pressures, which is currently based mostly on simple phenomenological modelling. The progress of experimental results into higher-pressure regimes represents a challenge to the phenomenological approaches, which can be addressed by carefully considered ab initio calculations. We present cold curves of several elements, calculated using different approximations of DFT and compare them with available experimental data. The comparison shows good agreement both in simple single phase and complex multi-phase cases. It suggests that DFT may be used to extrapolate high pressure behaviour of materials beyond the currently possible pressure range, with a robust estimate of the accuracy of the extrapolation based on various DFT implementations.     

MSA-Lab：模型驱动的微服务集成设计平台

从单体系统迁移到微服务系统是当前业界对遗留系统实施再工程化的主流选项之一,基于单体遗留系统的微服务体系架构重构则是实现该迁移的关键步骤.目前学界多集中在微服务识别方法的研究上;业界虽有许多面向微服务架构的遗留系统重构的实践,但缺乏系统性的方法及高效鲁棒的工具.鉴于此,在微服务识别与模型驱动开发方法前期研究的基础上,研发一种模型驱动的、可用于单体遗留系统微服务化重构的集成设计平台MSA-Lab.它通过分析单体遗留系统运行日志中的方法调用序列,对其中的类和数据表进行类型识别和聚类以构造抽象微服务,同时生成包括微服务图和微服务序列图在内的系统架构设计模型.它包括用于微服务自动识别与设计模型自动生成的核心部件MSA-Generator,以及用于微服务静态结构模型与动态行为模型可视化展现、交互式建模、模型语法约束检验的核心部件MSA-Modeller.在MSA-Lab平台上,通过对4个开源项目实施有效性、鲁棒性、功能转换完备性等实验以及对3个同类型工具实施性能对比实验,结果表明:所提平台拥有很好的有效性、鲁棒性及实现面向日志的功能转换完备性,且性能更加优越.     

PCP Characterizations of NP: Toward a Polynomially-Small Error-Probability

This paper strengthens the low-error PCP characterization of NP, coming closer to the upper limit of the BGLR conjecture. Consider the task of verifying a written proof for the membership of a given input in an NP language. In this paper, this is achieved by making a constant number of accesses to the proof, obtaining error probability that is exponentially small in the total number of bits that are read.