印度分布式发电的发展现状

全球约18亿多人口存在电力供应不足状况,这些人大多数居住在发展中国家的偏远地区。尽管许多发展中国家正在努力实施农村电力方案,但据观察,财政困难仍然是执行的首要瓶颈问题。政府正在努力扩大农村地区的电网,但同时也面临着如无法回收成本、缺乏切实可行的价格机制等一系列问题。     

Identifying FMRI model violations with lagrange multiplier tests

The standard modeling framework in functional magnetic resonance imaging (fMRI) is predicated on assumptions of linearity, time invariance and stationarity. These assumptions are rarely checked because doing so requires specialized software, although failure to do so can lead to bias and mistaken inference. Identifying model violations is an essential but largely neglected step in standard fMRI data analysis. Using Lagrange multiplier testing methods we have developed simple and efficient procedures for detecting model violations such as nonlinearity, nonstationarity and validity of the common double gamma specification for hemodynamic response. These procedures are computationally cheap and can easily be added to a conventional analysis. The test statistic is calculated at each voxel and displayed as a spatial anomaly map which shows regions where a model is violated. The methodology is illustrated with a large number of real data examples.     

美国政府标准话音编码器的比较

本文把美国政府新的标准4800bps码激励线性预测(CELP)编码器跟2400bps线性预测(LPC—10e)以及16000bps连续可变斜率增量调制△M(CVSD)的联邦标准话音编码器作了一番比较。比较包括:话音质量、安静/噪声环境下/信道中的清晰度、说话人识别、摸拟和数字实现要求、转接(tandem)编码和编码时延。业已表明,在话音质量方面,4800bps的CELP要比LPC—10e和CVSD有很大改善。虽然CELP要比CVSD或LPC—10e要求大得多的计算量,但用一个新一代的单片数字信号处理器就能实现CELP编码器。不同计算量的CELP的实现方法之间提供了互操作性(interoperability),而它的强抗扰性能可允许说话人千差万别、背景噪声环境可有多种多样,也能容忍各种不同的摸拟损伤(即幅频响应不平坦的送话器和非平坦信道)、多次转接和误码。这些特点使得CELP对于许多话音应用来说都很理想。     

Comparison of entropy and complexity measures for the assessment of depth of sedation

Entropy and complexity of the electroencephalogram (EEG) have recently been proposed as measures of depth of anesthesia and sedation. Using surrogate data of predefined spectrum and probability distribution we show that the various algorithms used for the calculation of entropy and complexity actually measure different properties of the signal. The tested methods, Shannon entropy (ShEn), spectral entropy, approximate entropy (ApEn), Lempel-Ziv complexity (LZC), and Higuchi fractal dimension (HFD) are then applied to the EEG signal recorded during sedation in the intensive care unit (ICU). It is shown that the applied measures behave in a different manner when compared to clinical depth of sedation score--the Ramsay score. ShEn tends to increase while the other tested measures decrease with deepening sedation. ApEn, LZC, and HFD are highly sensitive to the presence of high-frequency components in the EEG signal.     

Optical and morphological properties of InGaAs/AlGaAs self-assembled quantum dot nanostructures for 980 nm room temperature emission

This work deals with the study of optical and morphological properties of InGaAs/AlGaAs quantum dot(QD) structures grown by molecular beam epitaxy(MBE) . Photoluminescence(PL) emission energies,activation energies of PL quenching and QD sizes are studied as functions of the Al content in the AlyGa1-yAs confining layers(CL) . We show that the PL emission energy of In(Ga) As/AlyGa1-yAs QD structures increases with increasing y and that the sizes of InAs/AlyGa1-yAs QDs decrease with increasing y. By the comparison of the experimental results with those of an effective-mass model developed to calculate the QD fundamental transition energies,we show that the blueshift of emission energy has to be ascribed not only to the increase in barrier discontinuities that confine the carriers into QDs but even to effects related to changes of the QD morphology dependent on CL composition. Moreover,we show that the Al content in the barriers determines also the activation energy of thermal quenching of PL,which depends on the thermal escape of carriers from QD levels. These studies resulted in the preparation of structures with efficient light-emission in the 980 nm spectral window of interest for lightwave communications.     

一种区别等温淬火球铁中各种相的简单方法

即使对于经验丰富的检验者来说,在黑白衬度下辨别等温淬火球铁的各种相也是困难的。在等温淬火球铁的基体上,奥氏体、未溶铁素体和共晶碳化物都是白色,这些相难以相互区别。有一种简单的方法解决这一问题。采用这种方法,可使各种相呈现不同的颜色。方法如下: 将等温淬火试样按通常的方法制样,抛光后用2—4％的硝酸酒精溶液浸蚀。浸蚀的目的是使相界分明,而不是为了着色。浸蚀     

Pinhole SPECT imaging: compact projection/backprojection operator for efficient algebraic reconstruction

We describe the efficient algebraic reconstruction (EAR) method, which applies to cone-beam tomographic reconstruction problems with a circular symmetry. Three independant steps/stages are presented, which use two symmetries and a factorization of the point spread functions (PSFs), each reducing computing times and eventually storage in memory or hard drive. In the case of pinhole single photon emission computed tomography (SPECT), we show how the EAR method can incorporate most of the physical and geometrical effects which change the PSF compared to the Dirac function assumed in analytical methods, thus showing improvements on reconstructed images. We also compare results obtained by the EAR method with a cubic grid implementation of an algebraic method and modeling of the PSF and we show that there is no significant loss of quality, despite the use of a noncubic grid for voxels in the EAR method. Data from a phantom, reconstructed with the EAR method, demonstrate 1.08-mm spatial tomographic resolution despite the use of a 1.5-mm pinhole SPECT device and several applications in rat and mouse imaging are shown. Finally, we discuss the conditions of application of the method when symmetries are broken, by considering the different parameters of the calibration and nonsymmetric physical effects such as attenuation.     

Segmentation of trabeculated structures using an anisotropic Markov random field: application to the study of the optic nerve head in glaucoma

The study of the architecture of the optic nerve head (ONH) may provide valuable information about the development and progression of glaucoma. To this end, we have generated three-dimensional datasets from monkey eyes under controlled intraocular pressure (IOP). Segmentation of the connective tissues in this area is crucial to obtain an accurate measurement of geometrical parameters and to build mechanical models. However, this segmentation is made difficult by the complicated geometry and the artifacts introduced in the dataset building process. We present a novel segmentation algorithm, based on expectation-maximization, which incorporates an anisotropic Markov random field (MRF) to introduce prior knowledge about the geometry of the structure. The structure tensor is used to characterize the predominant structure direction and the spatial coherence at each point. The algorithm, which has been validated on an artificial validation dataset that mimics our ONH datasets, shows significant improvement over an isotropic MRF. Results on the real datasets demonstrate the ability of the new algorithm to obtain accurate, spatially consistent segmentations of this structure.     

A safe transmission line for MRI

Magnetic resonance imaging (MRI) has been established as a reliable and safe imaging method for the human body. However, electric conductors, such as cables situated near or in the human body, should be avoided because induced currents in the cables can cause hazardous heating in the surrounding tissue. In this paper, a new principle for the design of a transmission line is introduced and demonstrated, which is capable of avoiding dangerous heating of cables. The principle is based on transformers placed along the line, splitting the long line into several short not resonant and thus safe sections. A transformer design is introduced along with the theoretical aspects for both the avoidance of the undesired induced currents and the reduction of signal attenuation. Furthermore, the design fulfills the geometrical requirements of the side lumen of a standard catheter. Matching networks, whose elements are determined by power matching, are used to reduce signal attenuation by the transformers. A prototype was built to validate both theory and the simulations. As demonstrated in this work, it is possible to build safe transmission lines for MRI, making applications such as active catheter tracking possible. We expect that even new applications, such as safe intravascular imaging will be possible in a safe manner in the future.