(HP)Ge Measurement of spectra for diagnostic X-ray beams

The X-ray spectra applied in diagnostic radiology to the energy range between 50 and 125 kVp, were experimentally determined using a high-purity germanium detector, (HP)Ge, coupled to a multichannel analyser. A simple stripping procedure was implemented, according to that described by Seelentag and Panzer, to correct the pulse height distribution and then to determine the photon spectra. The measurements were performed for those conditions where the X-ray beam is transmitted through Pb filters 0.2-0.7 mm thick. It was necessary to estimate the effective dose in the same way that it is done for radiology diagnosis room shielding projects. The spectra were also determined to the X-ray qualities recommended by the IEC for primary diagnostic X-ray and for X-ray beams attenuated by aluminium filters 2.5-42.5 mm thick. The spectra obtained were compared with data derived from the literature presenting good agreement.     

Flux flow noise power spectra in the presence of local pinning interactions

We derive expressions for the dc flux flow voltage and for the flux flow noise power spectrum in type II superconductors using a model in which flux bundles travel a distance1 less than the sample widthL before being stopped for finite times by local pinning interactions. The frequency dependence of the power spectrum is shown to be identical to our earlier derivation, where we assumed that pinning and release of flux bundles occurred in zero times, an assumption we now show to be incorrect. This frequency dependence has been shown to lead to good agreement for experimentally measured transit times, which have repeatedly been shown to be too short when obtained from models of uninter-rupted flux transit across the sample width. The concept of a pinned fraction arises naturally in our model, and occurs because of two factors; first, in certain regions the Lorentz force is not sufficient to overcome pinning, and second, in regions where flux flow occurs, fluxoids will be held up for brief periods because of interaction with local pinning centers. The expressions for the noise power at zero frequency and the dc voltage are modified by factors that depend on averages of1.Research supported by U.S. ERDA Grant No. E(11–1) 2890.     

Advanced TTT composite materials for aeronautical purposes: Compression after impact (CAI) behaviour

The purpose of this paper is to examine the behaviour of the dry stitched composites when they are subjected to low velocity impact loads. Such composites have been laminated in combination with the Resin Film Infusion (RFI) technique.The experimental results exposed in this document are obtained from the Compression before Impact (CBI) and Compression after Impact (CAI) test efforts.The CAI behavioural determination of such composites is very important in terms of residual strength status after impact because in this case their use in primary aeronautical structures has also to satisfy the stringent Certification Requirements for Airworthiness.Traditional stitching methodologies, using Kevlar 29 threads as a 3-directional reinforcement, are compared to other advanced techniques such as the “tufting” and z-pins insertion.Following the optimization of the needle pass and the pitching line, normalized compression tests have been performed on a number of specimens which have been obtained through the utilization of different fabrication techniques in both before and after impact conditions. This has been done so as to evaluate the strength decay due to the impact damage. The subjec tests¹ were performed at the Alenia Aeronautica laboratories and in accordance with the AECMA ST Std prEN 6038 standards. Finally a review and a discussion of the experimental results conclude the paper.     

Measurement device for noise factor of microchannel plate

A new method for noise power factor determination of microchannel plates (MCPs) is described in this paper. The new measuring condition and specific measuring instrument are reported. The system consists of a vacuum chamber, an electron gun, a high-voltage supply, an imaging luminance meter, control units, a signal processing circuit, an A/D converter, a D/A converter, a communication unit, an industrial computer, and measurement software. This measuring method fills a void in measuring technology for the noise factor of MCPs, and it can make a scientific assessment of MCP noise characteristics and provide theoretical direction and technology support for the research and development of high-performance low light level (LLL) devices.     

Measurement of static and vibration-induced phase noise in UHF thin-film resonator (TFR) filters

Measurements of the static phase noise and vibration sensitivity of thin-film resonator (TFR) filters operating at 640 and 2110 MHz have been made. They show that the short-term frequency instability of the filters is small compared with that induced in the oscillator signal by the sustaining stage amplifier PM (phase modulation) noise. In-oscillator measurement of filter performance under vibration indicates that fractional frequency vibration sensitivities (δf ₀/f₀) are on the order of several parts in 10^-9/g. Because the percentage bandwidth and order (number of poles) of the filters was fairly constant, so was the product of the center frequency and group delay. Thus, the fractional frequency vibration sensitivity of the filters can be expressed alternatively as carrier signal phase sensitivity to vibration. The τ-ω₀ product for the filters that were tested was on the order of 300 rad, so that the equivalent phase sensitivity to vibration was approximately 1 grad/g     

The geometric mean of power (amplitude) spectra has a much smallerbias than the classical arithmetic (RMS) averaging

The statistical properties of the geometric mean of power (amplitude) spectra resulting from a discrete Fourier transform (DFT) are compared with those of arithmetic (RMS) averaging. The statistical properties are verified by means of frequency-domain and time-domain simulations. It is shown that the asymptotic bias of the geometric mean is a function of the fourth-order moments of the measurement noise     

V型双缸柴油机噪声源识别试验研究

以某V型双缸柴油机为研究对象,结合单缸熄火法与近场声压扫描法对该柴油机噪声源进行识别试验研究。首先,在不同工况下采用单缸熄火法分离出燃烧噪声和机械噪声,量化内部激励噪声源对整机噪声的贡献度,识别在工况下燃烧噪声和机械噪声的辐射频谱特性;然后,利用近场声压扫描快速定位工况下主要辐射表面的主要辐射部件,识别燃烧噪声和机械噪声的主要传递路径;最后,根据识别结果进行隔声降噪试验验证。该识别方法可为明确柴油机降噪方向与降噪具体目标提供参考。     

A new compact circuit-level model of semiconductor lasers: investigation of relative intensity noise and frequency noise spectra

We introduce a new compact noise equivalent circuit model of semiconductor lasers (SLs) from the rate equation including Langevin noise sources. The noise sources are described in terms of the spectral properties of the relative intensity noise (RIN) and frequency/phase noise (FN). Unlike the previous noise equivalent circuit models, which are based on two different DC and small-signal circuit models, using only a single circuit model, the static and dynamic responses and also the noise characteristics of SLs, can be investigated. We examine the validity of the presented noise circuit model by comparing the simulated results with the analytical and numerical results available in the literatures.     

一种降低D类功率放大器开关噪声的设计

传统D类功率放大器因特有的开关噪声对水下电子设备的信号接收、通信控制和信号传输等电信号产生很大的干扰,限制了D类功率放大器在水下电子设备中的广泛应用针对这一现象,首先阐明了Σ-Δ调制的D类功率放大器降低开关噪声的原理,然后对传统调制方式和Σ-Δ调制方式的D类功率放大器进行原理分析,并在Simulink软件中进行仿真对比。仿真结果表明,传统D类功率放大器在开关频率处的开关噪声能量高,Σ-Δ调制的D类功率放大器的开关噪声能量分散在一定的带宽内,并且开关噪声能量峰值低于传统D类功率放大器。     

基于雷达图特征提取和近红外光谱技术的葛根粉鉴别方法研究

基于雷达图表示原理,对葛根粉的近红外光谱进行了鉴别研究。首先,利用近红外光谱技术获得了中药葛根粉在12000cm~(-1)~4000cm~(-1)范围内的近红外漫反射光谱作为指纹图谱,然后采用多层雷达图对指纹图谱逐步进行特征提取,最后用优选图特征进行分类研究。该方法在保证数据整体性的前提下,有很好的直观可视性,最小识别误差率达1.04%。研究结果表明该方法既是一种可行的葛根粉鉴别新方法,同时又可作为可视化中药指纹图谱模式分析新方法 。     

功率超声换能器电声效率及辐射声功率的测量

在高频电功率计方法的基础上,本文提出了一种能够直接测量大功率压电超声换能器在实用状态下的辐射超声功率以及电声效率的新方法。与传统的高频电功率计法相比,本方法避免了介电以及机械损耗功率的测试,简化了测试步骤。     

Prediction of collision-induced dissociation spectra of common N-glycopeptides for glycoform identification

Confident identification of the glycan moieties in glycopeptides by collision-induced dissociation (CID) requires accurate prediction of the CID spectrum of the glycopeptides. In this Article, the kinetic model for the prediction of peptide CID spectra is extended to predict the CID spectra of N-glycopeptides. The model was trained with 1831 ion-trap CID spectra of N-glycopeptides and is able to predict ion-trap CID spectra with excellent accuracy in ion intensities for N-glycopeptides up to 8000 u in mass. A total of 524 common glycoforms including complex N-glycans with 2-4 antennas, plus high-mannose type and hybrid type, can be predicted.     

InsPecT: identification of posttranslationally modified peptides from tandem mass spectra

Reliable identification of posttranslational modifications is key to understanding various cellular regulatory processes. We describe a tool, InsPecT, to identify posttranslational modifications using tandem mass spectrometry data. InsPecT constructs database filters that proved to be very successful in genomics searches. Given an MS/MS spectrum S and a database D, a database filter selects a small fraction of database D that is guaranteed (with high probability) to contain a peptide that produced S. InsPecT uses peptide sequence tags as efficient filters that reduce the size of the database by a few orders of magnitude while retaining the correct peptide with very high probability. In addition to filtering, InsPecT also uses novel algorithms for scoring and validating in the presence of modifications, without explicit enumeration of all variants. InsPecT identifies modified peptides with better or equivalent accuracy than other database search tools while being 2 orders of magnitude faster than SEQUEST, and substantially faster than X!TANDEM on complex mixtures. The tool was used to identify a number of novel modifications in different data sets, including many phosphopeptides in data provided by Alliance for Cellular Signaling that were missed by other tools.     

B2 功率超声振动系统的电声效率测量

本用导纳圆图法和谐振导计算法，分别对用于超声清洗和塑料焊接的两个振动系统的电声效率进行了测量，结果表明在小信号和功率输出下，其电声效率基本相等，测量误差不超过±１５％。为通过电声效率和电功率测量，确定功率超声振动系统的输出声功率提供了可能途径。     

圆柱绕流近壁面处气动噪声源识别研究

对物体高速行驶下的气动噪声现象的认识和描述一直以来都是气动声学领域探索的基本问题和难点问题,尤其对物体近壁面处声源的产生及其声辐射缺乏有效的描述手段。该研究以圆柱绕流为研究对象,结合数值仿真手段,基于涡声方程的声源项描述圆柱绕流近壁面处的声源特性,建立声源识别方法。研究表明,该方法描述的声源存在不该有声源的位置出现声源的现象。研究进一步基于质点振速的矢量波动方程,将不能辐射噪声的源分离,较为准确地识别出了圆柱绕流气动噪声源的大小和位置。该研究在探索识别圆柱绕流气动噪声源方法的同时,也为准确识别气动噪声源特征提供了有效的方法。     

Method of power recycling in CoAxial Mach-Zehnder interferometers for low noise measurements

We present the first experimental study of a new type of power recycling microwave interferometer designed for low noise measurements. This system enhances sensitivity to phase fluctuations in a device under test, independent of input power levels. The single sideband thermal white phase noise floor of the system has been lowered by 8 dB (reaching −185 dBc/Hz at 1 kHz offset frequency) at relatively low power levels (13 dBm).