Spectral analysis of young gamma-ray pulsars with Fermi

The Large Area Telescope (LAT) is the main instrument on board the Fermi Gamma-ray Space Telescope, launched on June 11, 2008. Thanks to its large effective area, good resolution and excellent sensitivity, Fermi has opened a new era for gamma-ray astronomy, in particular it has identified many new gamma-ray pulsars, that will help to study in detail the emission mechanism of these sources. We present a study on the spectrum emission and common features of J0007+7303, J0205+6449, J1833-1034 and J1124-5916 that, together with the Crab, are among the youngest pulsars in the galaxy, with an estimated age  yr.     

Use of pixelated detectors for the identification of defects and charge collection effects in mercuric iodide (HgI2) single crystal material

Physical structure of pixelated detectors provides a unique tool to evaluate the effects of different types of defects in the semiconductor material that is used to fabricate the detectors. The spectroscopic performance measured for individual pixels or groups of pixels can be used to correlate point defects or fields of inhomogeneities within the material with the charge collected from photoelectric events. A block of single crystal mercuric iodide of approximately 18×18 mm² area and between 6 and 10 mm thick is prepared. The homogeneity of this material is then investigated with light in the transparent region for HgI₂ using an optical microscope. Several types of defects can be identified in this way by the scattering of light, for example, single large inclusions or voids and areas of haziness consisting of fields of small inclusions. Standard procedures are used to fabricate from this block a pixelated detector with a 121-pixel anode structure. The performance of each pixel is measured, and differences in charge collection are correlated with the optical data. Measurement data are presented, and possible mechanisms of the interactions between the defects and the charge carriers are discussed.     

A High Energy Resolution Gamma-Ray TES Microcalorimeter with Fast Response Time

We report on the development of the fast response gamma-ray TES microcalorimeter composed of a bulk Sn absorber coupled to a Ti/Au TES. In order to realize a TES microcalorimeter with a large absorber and a fast response time, besides taking saturation and linearity into account, study of the effect of thermal diffusion in the absorber on energy resolution is essential. Therefore, we performed 3 dimensional simulations using SPICE to calculate the effect of thermal diffusion in the absorber on energy resolution. By fabricating a device with the optimized heat capacity of the absorber and the thermal conductance between the absorber and the TES based on the simulation result, we have demonstrated an energy resolution of 38.4±0.9 eV at 60 keV with a time constant of 0.5 ms.      

Rejecting incomplete charge-collection events in CdZnTe and other semiconductor detectors

In an ideal single-carrier-type gamma ray detector, the amplitudes of the signals and the carrier drift times are correlated variables. However, if the charges produced by an incident photon are not fully collected, as is the case in CdZnTe detectors containing crystal defects, the above correlation does not hold. This permits the application of an event recognition algorithm to identify these incomplete charge collection (ICC) events, caused by the “bad” regions inside a detector, so that they can be removed from pulse height spectra. The ICC events primarily contribute to the Compton continuum and the low-energy tail of the photopeak. Thus, rejecting such events should not affect significantly the photopeak efficiency, but should improve the spectral response, e.g., the peak-to-Compton ratio, for a detector fabricated from material with relaxed crystal quality requirements. Such crystals are those currently available from vendors. The use of stronger ICC correlation-function rejection criteria can improve the energy resolution of these lower-quality crystals, but at the price of a loss in photoefficiency.     

An optimised method for material identification using a photon counting detector

X-ray photon counting detectors have become a competitive alternative to energy integrating systems in certain domains. However, processing methods currently used in radiography for investigating the composition of an object are an extension of dual energy methods and have started to show their limits with an increasing number of counting windows (bins). Thus, in a context of material recognition for homeland security, this study aims to introduce a new data processing method suitable for any type of detector, in integrating or counting mode, regardless of the number of bins. Additionally, a criterion to quantify the influence of the number of counting windows as well as the influence of their threshold position has been developed.The optimisation process is conducted in simulation by considering ideal detectors, and the results, for detectors with m=2, 3, 4 and 5 counting windows, are compared to those obtained with an analytical criterion developed in the literature and adapted to our study context. Both methods give identical results. In the final part, the performances of a spectrometric detector (energy windows width of 1 keV) and of optimised systems with m=2, 3, 4 and 5 bins are analysed for homogeneous plastic identification. The results show an increase in performance with increase in bin number until the performance level of the spectrometric detector is reached.Moreover, a discussion on the optimisation robustness as a function of material thickness to be identified is presented. The spectrometric detector, which does not require any optimisation of the bins thresholds, appears then to be a candidate of choice for material recognition when using X-ray photon counting detectors.     

SIMULATE Program: a gamma ray spectroscopy tool

A software package which simulates the virtual creation of gamma ray spectra emitted from a combination of radioactive sources, as seen by a semiconductor or scintillation detector, is presented . It partially utilizes Monte Carlo techniques based on the physics of gamma ray spectroscopy. In addition, certain algorithms are used to compensate for the premature termination of the fate of the detected photons of any particular energy.     

An adaptive algorithm for nonlinear system identification

There are several methods — fixed, adaptive, recursive — for the identification of linear and bilinear systems from input-output measurements that are noisy. However, literature is rather scarce as far as such techniques are concerned for the identification of nonlinear systems. The objective of this paper, therefore, is to suggest an iterative technique for the identification of nonlinear system parameters from measurements that are noisy. This technique requires the transformation of a nonlinear system in the state variable form into an input-output autoregressive moving average exogenous (armax) model. The pseudo linear regression algorithm, which has been extensively used for the identification of linear systems, can then be used to identify the nonlinear system parameters. Using this technique simulation studies were carried out which, indeed, confirm the efficacy of the method.     

Commonly applied smoothing of IR spectra showed unappropriate for the identification of plant leaf samples

The use of infrared spectroscopy has spread from single compound research to the investigation of complex biological samples. In infrared spectroscopy, spectral pre-treatment techniques have been assumed to be equally applicable and effective in the analysis of biological samples with complex chemical composition and structure. In this research, the most commonly used pre-treatment techniques were investigated based on the identification of species from whole leaf samples of pharmaceutically important Epilobium and Hypericum genera. Two spectral collection modes were used; whole leaf transmission and KBr-tablet transmission mode. The results of this study do not support the current standard in pre-treatment methods. After the frequency decomposition of a spectral signal by Fourier transform and wavelet decomposition, it was revealed that the important information of whole plant leaf as an example of biological samples was contained in the spectral details. Therefore, smoothing techniques were not appropriate because high frequency information is lost. A vast majority of published work used a Savitzky-Golay smoothing method on infrared spectra of complex biological samples. This method was shown to be less effective. In contrast, taking the derivative of the spectra showed significantly better results; with this pre-treatment method, the overlapping bands become more evident.     

输入信息不完备下预报-校正类识别法探讨

输入信息测试不完备是结构动力测试中常遇到的问题,本文在回顾这方面文献的基础上,重点对预报-校正迭代算法进行了研究,针对该算法提出的第一类迭代过程,分别从部分输入未知和全部输入未知两方面进行讨论,从理论分析和数值算例说明了该迭代算法存在的不足,证明了学者们长期以来对该算法提出的疑问.     

Theoretical study of isotope effect in La-doped Y-123

The recent oxygen isotope effect measurement made in the system YBa_2-x La _x Cu₃O₇ (0x0.5) is analyzed using the two-carrier model which describes a superconducting system as a mass anisotropic system consisting of charge carriers with two different masses as a result of lattice defects or oxygen deficiency. The extent to which Ba, Cu, and O atoms participate in the phonon-mediated Cooper pairing interaction is elucidated. The relationship between the theoretically deduced mass anisotropic factor andT _c agrees closely with the experimental results of Uemuraet al. [28]. Furthermore, the superconducting energy gap toT _c ratio is found to be close to 3.5. Excellent agreement is also achieved between the theoretically calculated oxygen isotopic constant and the experimental results of Bornemann and Morris [12].     

聚合物沉积物对注入剖面测井的影响

由于聚合物水溶液粘度大 ,流动剖面拉长 ,不利于同位素示踪剂载体的均匀扩散。在井底出现絮状物、果冻状松散沉淀物和颗粒状沉淀物分别组成的 3个沉积段。井筒沉积物使电磁流量计的测量值偏高或计数不规则。在测量注聚剖面时 ,宜采用多参数测量 ,运用综合解释技术消除沉积物给注聚剖面测井带来负面的影响。     

An ontology-based hybrid methodology for image synthesis and identification with convex objects

ABSTRACT

One of the core challenges in developing a computer system for machine learning is to make the system learn efficiently and effectively like a real human by grasping the domain knowledge exemplified by human experts. In this challenge, we have introduced a hybrid image synthesis model that can simulate one of the human’s learning capabilities in the vision field – the ability to synthesize images of convex objects by identifying solid geometries and textures of specific objects using few photographs. We have incorporated an ontology-based, domain knowledge on solid geometries into our model to synthesize large number of training images with only a minimum number of input images. Our initial experiments have shown that our model has convincing improvements by demonstrating a substantially better FAR/FRR/EER results when it is compared with a smaller set of non-synthetic images.     

2.5维C/SiC复合材料弹性参数不确定性识别方法研究

提出了一种2.5维C/SiC编织复合材料弹性参数不确定性识别方法。采用刚度平均法获得复合材料等效弹性参数理论预测值。选取对结构动态特性影响较大的3个弹性参数E11,E22和G12作为待识别参数;在确定性识别结果基础上,采用拉丁超立方体采样构造随机试验样本,开展不确定性参数识别方法仿真研究。仿真结果表明,针对考虑弹性参数不确定性的2.5维C/SiC复合材料,采用所提出的方法能够准确识别材料弹性参数的均值与标准差,建立反映实际结构动态特性统计意义的精确动力学模型。     

Investigation of Ni/4H-SiC diodes as radiation detectors with low doped n-type 4H-SiC epilayers

The development of SiC minimum ionising particle (MIP) detectors imposes severe constrains in the electronic quality and the thickness of the material due to the relatively high value of the energy required to produce an electron–hole pair in this material by MIP against the value for Si. In this work, particle detectors were made using semiconductor epitaxial undoped n-type 4H-SiC as the detection medium. The thickness of the epilayer is on the order of 40 μm and the detectors are realised by the formation of a nickel silicide on the silicon surface of the epitaxial layer (Schottky contact) and of the ohmic contact on the back side of 4H-SiC substrate. The low doping concentration (6×10¹³ cm⁻³) of the epilayer allows the detector to be totally depleted at relatively low reverse voltages (100 V). We present experimental data on the charge collection properties by using 5.486 MeV -particles impinging on the Schottky contact. A 100% charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the -particle extrapolated range in SiC. The diffusion contribution of the minority change carriers to CCE is pointed out. By comparing measured CCE values to the outcomes of drift–diffusion simulation, values are inferred for the hole lifetime within the neutral region of the charge carrier generation layer.     

An inverse approach for pressure load identification

An inverse approach for the identification of pressure loading on a structure has been proposed and developed. In this approach, surface measurements of structural response (e.g. strain, displacement and velocity field measurements, such as can be measured with 3D digital image correlation) are utilized as input data and are combined with numerical simulations to identify the pressure load on a structure. The inverse approach has been verified by numerical benchmarks involving pressure identification under quasi-static as well as dynamic impulse loading conditions, and also been validated by an experiment involving a quasi-static pressure load. The results indicate that the proposed inverse method can identify not only the magnitude of the quasi-static pressure but also the impulsive pressure loading history. The developed inverse approach offers an opportunity to apply inverse analysis techniques to identify interactive pressure loads (such as those resulting from a blast wave) on structures in explosive events.     

Problem identification in maintenance modelling: a case study

This paper is concerned with a problem identification and problem focus process in maintenance modelling. It endeavours to describe the process of moving from vague problem understanding towards more specific problem formulation and problem focus in the pursuit of practical decision making. This process was conducted using several analytical tools that complemented each other such as regression analyses, snapshot modelling and delay time modelling. As in many case studies related to maintenance modelling, this study also makes use of the experience of experts. It can be seen from the paper that subjective data estimates can prove to be a useful input for modelling. The analysis shows how simple modelling of maintenance problems can provide useful insights and better understanding of the problem in hand.     

一种不需要次级通道建模的有源噪声控制算法

对有源噪声控制的研究,绝大部分都是建立在次级通道已知的基础上,或者通过在线或离线辨识来建模次级通道,通过分析滤波-XLMS（FXLMS）算法收敛的几何特性实现有源噪声的无模型控制。子带技术是将信号通过不同频带的滤波器,把信号分解到不同频带的子带中,对各子带信号分别进行相应的处理,并减少处理时间。将两者相结合,运用子带技术,采用过采样无延迟子带结构消除单频噪声、窄带噪声以及宽带噪声,降噪效果明显。相比传统的XLMS滤波算法,该算法降低了运算量,且实现结构简单。     

Monte Carlo study of a 3D Compton imaging device with GEANT4

In this paper we investigate, with a detailed Monte Carlo simulation based on Geant4, the novel approach of Lenti (2008) [1] to 3D imaging with photon scattering. A monochromatic and well collimated gamma beam is used to illuminate the object to be imaged and the photons Compton scattered are detected by means of a surrounding germanium strip detector. The impact position and the energy of the photons are measured with high precision and the scattering position along the beam axis is calculated. We study as an application of this technique the case of brain imaging but the results can be applied as well to situations where a lighter object, with localized variations of density, is embedded in a denser container. We report here the attainable sensitivity in the detection of density variations as a function of the beam energy, the depth inside the object and size and density of the inclusions. Using a 600 keV gamma beam, for an inclusion with a density increase of 30% with respect to the surrounding tissue and thickness along the beam of 5 mm, we obtain at midbrain position a resolution of about 2 mm and a contrast of 12%. In addition the simulation indicates that for the same gamma beam energy a complete brain scan would result in an effective dose of about 1 mSv.     

System identification of bridges with nonlinear foundations

Abstract

In the present study, the nonparametric method of system identification proposed by Masri et al. has been used to treat simulated earthquake response data of a bridge with nonlinear foundations. It is found that the method is promising for estimation of functions which represent the dynamic characteristics of bridges and provides a sound basis for study of the safety assessment of a bridge by using earthquake response data of the bridge.