Shape vs. volume: Invariant shape descriptors for 3D region of interest characterization in MRI

We propose a new approach for quantifying regions of interest (ROIs) in medical image data. Rotationally invariant shape descriptors (ISDs) were applied to 3D brain regions extracted from MRI scans of 5 Parkinson's patients and 10 control subjects. We concentrated on the thalamus and the caudate nucleus since prior studies have suggested they are affected in Parkinson's disease (PD). In the caudate, both the ISD and volumetric analyses found significant differences between control and PD subjects. The ISD analysis however revealed additional differences between the left and right caudate nuclei in both control and PD subjects. In the thalamus, the volumetric analysis showed significant differences between PD and control subjects, while ISD analysis found significant differences between the left and right thalami in control subjects but not in PD patients, implying disease-induced shape changes. These results suggest that employing ISDs for ROI characterization both complements and extends traditional volumetric analyses. © 2006 IEEE.

Comparison of acoustic velocity perturbation measurements using PIV vs. two-microphone technique

Understanding combustion instabilities requires accurate measurements of the acoustic velocity perturbation into injectors. This is often accomplished via the use of the two microphone technique, as this only requires two pressure transducers. However, measurements of the actual velocities emerging from the injectors are not often taken, leaving questions regarding the assumptions about the acoustic velocity. A comparison of velocity measured at downstream of the injector with that of two-microphone technique can show the accuracy and limitations of two-microphone technique. In this paper, velocity measurements are taken using both particle image velocimetry (PIV) and the two-microphone technique in a high pressure facility designed for aeroengine injector measurements. The flow is excited using an area modulation device installed on the choked end of the combustion chamber, with PIV measurements enabled by optical access downstream of the injector through a quartz tube and windows. Acoustic velocity perturbations at the injector are determined by considering the Fourier transformed pressure fluctuations for two microphones installed at a known distance upstream of the injector. PIV measurements are realized by seeding the air flow with micrometric water particles under 2.5 bar pressure at ambient temperature. Phase locked velocity fields are realized by synchronizing the acquisition of PIV images with the revolution of the acoustic modulator using the pressure signal measured at the face of injector. The mean velocity fluctuation is calculated as the difference between maximum and minimum velocities, normalized by the mean velocity of the unforced case. Those values are compared with the peak-to-peak velocity fluctuation amplitude calculated by the two-microphone technique. Although the ranges of velocity fluctuations for both techniques are similar, the variation of fluctuation with forcing frequencies diverges significantly with frequency. The differences can be attributed to several limitations associated with of both techniques, such as the quality of the signal, the signal/noise ratio, the accuracy of PIV measurements and the assumption of isentropic flow of the particle velocity from the plenum through the injector. We conclude that two-microphone methods can be used as a reference value for the velocity fluctuation in low order applications such as flame transfer functions, but not for drawing conclusions regarding the absolute velocity fluctuations in the injector. Copyright © 2013 by ASME.

Room temperature mobility above 2100 cm2/Vs in Al0.3Ga0.7N/AIN/GaN heterostructures grown on sapphire substrates by MOCVD

Al0.3Ga0.7N/AlN/GaN HEMT structures with significantly high mobility have been grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. At room temperature (RT) a Hall mobility of 2104 cm(2)/Vs and a two-dimensional electron gas (2DEG) density of 1.1x10(13) cm(-2) are achieved, corresponding to a sheet resistance of 277.8 Omega/sq. The elimination of V-shaped defects were observed on Al0.3Ga0.7N/AlN/GaN HEMT structures and correlated with the increase of 2DEG mobility. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim.

基于ISO9000和CMMs的需求开发和需求管理平台框架的研究

文章通过分析国内外当前软件需求开发和需求管理中的主要技术和存在的主要问题,并在研究ISO9000和SW-CMM、SA-CMM在软件需求开发和需求管理要求的基础上,结合现代软件工程的需求实现技术,提出了基于ISO9000和CMMs的需求开发和管理平台框架,用于指导国内软件组织软件需求开发和需求管理的实践工作。

SCADA系统中交流采样器设计

介绍了SCADA系统中交流采样器的功能，提出了基于DSP技术和CAN总线的系统构架，详细阐述了系统的硬件和软件设计方法，探讨了一种基于消息的嵌入式系统程序设计思想，最后给出了设计结论。

Polyimide structure-property relationships - I. Polyimide properties vs dianhydride configuration

X-ray crystal structures of 2,2',3,3'-and 3,3',4,4'-biphenyltetracarboxylic dianhydride (2,2',3,3'- and 3,3',4,4'-BPDA) were determined. The dianhydride isomers have different symmetry caused by difference in two anhydride group positions and the dihedral angles between the two phenyl rings are 62.9 degrees for 2,2',3,3',-BPDA and 0 degrees for 3,3',4,4'-BPDA respectively. The polyimides from 2,2',3,3'-BPDA exhibit enhanced solubility, higher thermal stability, and higher glass transition temperature (T-g) compared with those from 3,3',4,4'-BPDA.