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871.
Resampling methods are often invoked in risk modelling when the stability of estimators of model parameters has to be assessed. The accuracy of variance estimates is crucial since the operational
risk management affects strategies, decisions and policies. However, auxiliary variables and the complexity of the sampling
design are seldom taken into proper account in variance estimation. In this paper bootstrap algorithms for finite population
sampling are proposed in presence of an auxiliary variable and of complex samples. Results from a simulation study exploring
the empirical performance of some bootstrap algorithms are presented.
相似文献
872.
873.
In this paper we consider a complete connected noncompact Riemannian manifold M with bounded geometry and spectral gap. We prove that the Hardy type spaces X k (M), introduced in a previous paper of the authors, have an atomic characterization. An atom in X k (M) is an atom in the Hardy space H 1(M) introduced by Carbonaro, Mauceri, and Meda, satisfying an ??infinite dimensional?? cancellation condition. As an application, we prove that the Riesz transforms of even order $\nabla^{2k} \mathcal{L}^{-k}$ map X k (M) into L 1(T 2k M). 相似文献
874.
N. Morales Mendoza S. Goyanes C. Chiliotte V. Bekeris G. Rubiolo R. Candal 《Physica B: Condensed Matter》2012,407(16):3203-3205
Magnetic binary nanofillers containing multiwall carbon nanotubes (MWCNT) and hercynite were synthesized by Chemical Vapor Deposition (CVD) on Fe/AlOOH prepared by the sol–gel method. The catalyst precursor was fired at 450 °C, ground and sifted through different meshes. Two powders were obtained with different particle sizes: sample A (50–75 μm) and sample B (smaller than 50 μm). These powders are composed of iron oxide particles widely dispersed in the non-crystalline matrix of aluminum oxide and they are not ferromagnetic. After reduction process the powders are composed of α-Fe nanoparticles inside hercynite matrix. These nanofillers are composed of hercynite containing α-Fe nanoparticles and MWCNT. The binary magnetic nanofillers were slightly ferromagnetic. The saturation magnetization of the nanofillers depended on the powder particle size. The nanofiller obtained from powder particles in the range 50–75 μm showed a saturation magnetization 36% higher than the one formed from powder particles smaller than 50 μm. The phenomenon is explained in terms of changes in the magnetic environment of the particles as consequence of the presence of MWCNT. 相似文献
875.
The electronic properties of surfaces and buried interfaces can vary considerably in comparison to the bulk. In turn, analyzing bulk properties, without including those of the surface, is understandably challenging. Hard X-ray photoelectron spectroscopy (HAXPES) allows the well known ability of photoemission to interrogate the electronic structure of material systems with bulk volume sensitivity. This is achieved by tuning the kinetic energy range of the analyzed photoelectrons in the multi-keV regime. This unique ability to probe truly bulk properties strongly compliments normal photoemission, which generally probes surface electronic structure that is different than the bulk selected examples of HAXPES and possible implications towards the study of complex oxide-based interfaces and highly correlated systems are discussed. 相似文献
876.
An Nd:YVO4 amplifier consisting of two modules end pumped at 808?nm at 30?W total absorbed power has been designed for efficient, diffraction-limited amplification of ultrafast pulses from low-power seeders. We investigated amplification with a 50?mW, 7?ps Nd:YVO4 oscillator, a 2?mW, 15?ps Yb fiber laser, and a 30?mW, 300?fs Nd:glass laser. Output power as high as 9.5?W with 8?ps pulses was achieved with the 250?MHz vanadate seeder, whereas the 20?MHz fiber laser was amplified to 6?W. The femtosecond seeder allowed extracting Fourier-limited 4?ps pulses at 7?W output power. To our knowledge, these are the shortest pulses from any Nd:YVO4 laser device with at least 7?W output power. This suggests a novel approach to exploit the gain bandwidth of vanadate amplifiers with high output power levels. Such amplifier technology promises to offer an interesting alternative to high-power thin disk oscillators at few picoseconds duration, as well as to regenerative amplifiers with low-repetition-rate fiber seeders. 相似文献
877.
Almoro PF Waller L Agour M Falldorf C Pedrini G Osten W Hanson SG 《Optics letters》2012,37(11):2088-2090
A technique for enhanced deterministic phase retrieval using a partially developed speckle field (PDSF) and a spatial light modulator (SLM) is demonstrated experimentally. A smooth test wavefront impinges on a phase diffuser, forming a PDSF that is directed to a 4f setup. Two defocused speckle intensity measurements are recorded at the output plane corresponding to axially-propagated representations of the PDSF in the input plane. The speckle intensity measurements are then used in a conventional transport of intensity equation (TIE) to reconstruct directly the test wavefront. The PDSF in our technique increases the dynamic range of the axial intensity derivative for smooth phase objects, resulting in a more robust solution to the TIE. The SLM setup enables a fast and accurate recording of speckle intensity. Experimental results are in good agreement with those obtained using the iterative phase retrieval and digital holographic methods of wavefront reconstruction. 相似文献
878.
本文讨论壁面湍流发展的相干结构的观点.在简要的历史文献综述后,我们回顾一些基本观点,
并且介绍相干结构的思想.基于大量主要是由实验所得的结果,本文通过广泛运用的事件检
测技术,探讨湍流边界层内部和外部区域发生的现象.我们从边界层内部区域发生的现象、
边界层外部大尺度运动的发展和涡结构动力学的角度来描述流动的现象.在文章的
第2部分,介绍从背景流动中推演出湍流相干结构的各种方法以及在各种方法框架下所得到的结果,
讨论速度梯度张量不变量、压力的Hessian矩阵分析和本征正交分解等方法.每一个过程
都有``相干结构'的特定的定义,满足恰当的数学构架,并可以对湍流数据做相干结构动力
学分析.这一工作可能会对当前流体动力学家在湍流研究中用到的最新理论和技术的传播有
所贡献. 相似文献
879.
880.