定时截尾缺失数据下指数分布的统计推断

试验数据缺失是产品寿命试验中经常遇到的情况，处理起来比较复杂。当寿命分布为指数分布时，给出了定时截尾寿命试验数据缺失场合下样本分布参数的点估计及区间估计的一种近似方法。通过大量的Monte-Cado数值模拟试验，在缺失数据数目不太大时，参数估计的精度还是令人满意的。并从理论上证明可利用枢轴量赢的分布对参数m作区间估计。     

Numerical conformal mapping of multiply connected regions onto the second, third and fourth categories of Koebe?s canonical slit domains

This paper presents a boundary integral method for approximating the conformal mappings from any bounded or unbounded multiply connected region G onto the second, third and fourth categories of Koebe?s canonical slit domains. The method can be also used for calculating the conformal mappings of simply and doubly connected regions. The method is an extension of the author?s method for the first category of Koebe?s canonical slit domains (see [M.M.S. Nasser, Numerical conformal mapping via a boundary integral equation with the generalized Neumann kernel, SIAM J. Sci. Comput. 31 (2009) 1695-1715]). Three numerical examples are presented to illustrate the performance of the proposed method.     

Photoluminescence of Ge nanostructures grown by gas source molecular beam epitaxy on silicon (1 1 8) surface

In this paper, we present a photoluminescence (PL) study of Si/Ge/SiGe/Si structures grown by gas source molecular beam epitaxy on an (1 1 8) undulated surface with various Ge coverage. Nucleation and growth of Ge films is obtained by the Stranski–Krastanov mechanism. The influence of the substrate orientation on the changeover 2D–3D growth mode is investigated. Furthermore, we show the use of growing an SiGe wetting layer to control the uniformity of the Ge island size. The PL signal related to the Ge islands is found to be highly dependent of the power excitation and is observed up to room temperature.     

Photo-transformations of 6-chloro-3-propargyloxy-2-aryl-4-oxo-4H-1-benzopyran: 1,4-hydrogen abstraction in propargylethers

1,4-Biradicals generated in the Norrish type-II reactions of 3-propargyloxy-2-arylchromones lead to cyclic products involving the 2-aryl group. The formation and distribution of products varied with the nature of 2-aryl group.     

Experimental observation of lattice distortions due to a flux line lattice in niobium

A polarized neutron scattering investigation of the flux line lattice in the type-II superconductor niobium is reported. A modulation of the nuclear lattice has been detected, and the magnitude of the first Fourier component of the lattice distortion established relative to the magnitude of the magnetic scattering. This constitutes the first experimental observation of lattice distortions due to the presence of magnetic flux lines within the bulk of a type-II superconductor. Using a simple microscopic model the lattice distortion in niobium is estimated. A new mechanism is suggested for the coupling of the flux line lattice to the crystallographic lattice. The experimental technique opens up the possibility of investigating the microscopic mechanism of flux line - nuclear lattice interactions, in particular the pinning of flux lines within the bulk of a type-II superconductor. Received: 8 August 1997 / Accepted: 16 October 1997     

Type-II InAs/GaSb superlattices for very long wavelength infrared detectors

Type-II superlattices (SLs) can be designed for semiconductor band gaps as large as 400 meV down to semimetallic. This flexibility in design makes them an excellent candidate for infrared photodiodes with cut-off wavelengths beyond 15 μm. There are relatively few options for high-performance infrared detectors to cover wavelengths longer than 15 μm, especially for operating temperatures above 15 K. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection in the very long wavelength infrared (VLWIR) range (λ>15 μm). There is a variety of possible designs for these SLs which will produce the same narrow band gap by adjusting individual layer thicknesses, or indium content, in the InGaSb layer. Several of these different design options have been grown and characterized. These designs often require monolayer control per layer over hundreds of repeats in the SL. Photoresponse spectra for type-II SLs are compared to show how the design choices not only change the band gap but also the band structure, as reflected in features observed in the spectra. Theoretical modeling results are used to interpret the photoresponse spectra. SLs with cut-off wavelengths ranging from 15 to 25 μm are covered.     

Ordered State and Superfluidity of Quasi-Two-Dimensional Excitons in Type-II Quantum Wells

One of the best ways to obtain unambiguous experimental evidence for the superfluidity of excitons is to observe phenomena that are directly related to the phase of the condensed excitons. As an advantageous candidate for this purpose, we propose a quasi-two-dimensional exciton system in type-II quantum wells (QWs). We consider the condensed excitons in the type-II QW irradiated by a weak laser light and show that under the control of an external current J ex , the system takes the ordered state with (without) net superflow of excitons at T = 0 K when J ex is larger (smaller) than a certain critical value. Introducing probable mechanisms of phase transitions, we calculate the transition temperatures and construct the phase diagram.     

Quantum-Statistics Behavior of the Exciton-Biexciton System In GaAs/AlAs Type-II Superlattices

We have investigated the quantum-statistics behavior of the exciton-biexciton system from the photoluminescence properties in (GaAs) m /(AlAs) m type-II superlattices with m = 12 and 13 monolayers, where the lowest-energy type-II exciton consists of the n = 1 X electron of AlAs and n = 1 o heavy hole of GaAs. The long exciton lifetime of the order of w s due to the indirect transition nature enables us to obtain precisely the density relation between the exciton and biexciton from the line-shape analysis of time-resolved photoluminescence spectra. In a relatively low exciton-density region, the biexciton density obeys a well-known square law. At an exciton density around 1 2 10 10 cm m 2 , the biexciton density suddenly increases with a threshold-like nature. This behavior, which is realized at a bath temperature up to 8 K under an excitation power of the order of 100 mW/cm 2 , results from the characteristics of Bose-Einstein statistics of the exciton-biexciton system.     

Activity Coefficients of Electrolytes from Liquid Membrane Cells. XII. Magnesium,Lanthanum, and Tris(ethylenediamine)cobalt(III) Salts of the 1,5-Naphthalenedisulfonate Anion at 298.15 K

Activity coefficients of the highly charged electrolytes Mgds, La₂ds₃, and [Co(en)₃]₂ds₃ (en = ethylenediamine, ds²⁻=1,5-naphthalenedisulfonate anion), were determined at 298.15 K using liquid-membrane cells. These salts are found not to display large negative deviations from the Debye-Hückel limiting slope in the dilute regions, which characterize the corresponding sulfate salts. Theoretical calculations based on the primitive model (charged hard spheres in an unstructured dielectric medium) reproduce the behavior of these salts correctly up to concentrations of 0.01 mol⋅kg⁻¹ or more (0.1 mol⋅kg⁻¹ for Mgds), although ds²⁻, far from resembling a charged sphere, is a planar ion with charges distant from one another. The Pitzer model parameter values are reported for the activity and osmotic coefficients.     

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??In this paper, we estimate parameters of gamma life distribution and normal life distribution by EM algorithm based on Type-II hybrid censored data. The covariance matrices are derived as well. Some numerical examples are also presented for illustration.