Ultrasonic techniques for nondestructive testing of standing trees

The aim of this study is to assess wood quality of standing trees with ultrasonic velocity methods. The ultrasonic techniques currently used are: scattering based techniques that use travel time and other wave parameters for measuring the elastic constants of wood, and ultrasonic tomographic imaging techniques which seek to provide a high resolution picture of the defect. Scattering based techniques were firstly used as nondestructive techniques with increment cores of 5 mm diameter. On these specimens measurements with bulk waves--longitudinal and shear were used to detect the influence of sylvicultural treatment (pruning) on wood quality and also to detect defects (slope of grain, wavy figures). High resolution imaging techniques were developed for imaging abnormalities induced by biological attacks of fungi or insects in standing trees. In this case, ultrasonic tomography refers to cross-sectional imaging of trees from data collected by illuminating the tree from different directions. Ultrasonic images were reconstructed from the time of flight. The images were reconstructed from 120 measurements in situ and through the bark with direct transmission technique, using 1 MHz transducers. The resolution is 5 cm.     

Modeling of the Martian environment for radiation analysis

A model for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (GCR) has been developed. Solar modulated primary particles rescaled for conditions at Mars are transported through the Martian atmosphere down to the surface, with altitude and backscattering patterns taken into account. The altitude to compute the atmospheric thickness profile has been determined by using a model for the topography based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. The Mars surface composition has been modeled based on averages over the measurements obtained from orbiting spacecraft and at various landing sites, taking into account the possible volatile inventory (e.g. CO₂ and H₂O ices) along with its time variations throughout the Martian year. The Mars Radiation Environment Model has been made available worldwide through the Space Ionizing Radiation Effects and Shielding Tools (SIREST) website, a project of NASA Langley Research Center. This site has been developed to provide the scientific and engineering communities with an interactive site containing a variety of environmental models, shield evaluation codes, and radiation response models to allow a thorough assessment of ionizing radiation risk for current and future space missions.     

Degradation of historical paper: nondestructive analysis by the NMR-MOUSE

The NMR-MOUSE is a mobile sensor for single-sided NMR inspection of organic materials which takes advantage of the principles of magnetic resonance and inside-out-NMR. Historical books dating from the 17th century were measured at different points by positioning the NMR-MOUSE on the paper. Different degrees of paper degradation can be discriminated from the regularized inverse Laplace transform of the envelope of the acquired echo signals. For the first time the degradation of historical paper was characterized entirely nondestructively by NMR. As a contribution to current preservation efforts, NMR shows great promise for future use in damage assessment of historical documents.     

Fear and its implications for stock markets

The value of stocks, indices and other assets, are examples of stochastic processes with unpredictable dynamics. In this paper, we discuss asymmetries in short term price movements that can not be associated with a long term positive trend. These empirical asymmetries predict that stock index drops are more common on a relatively short time scale than the corresponding raises. We present several empirical examples of such asymmetries. Furthermore, a simple model featuring occasional short periods of synchronized dropping prices for all stocks constituting the index is introduced with the aim of explaining these facts. The collective negative price movements are imagined triggered by external factors in our society, as well as internal to the economy, that create fear of the future among investors. This is parameterized by a “fear factor” defining the frequency of synchronized events. It is demonstrated that such a simple fear factor model can reproduce several empirical facts concerning index asymmetries. It is also pointed out that in its simplest form, the model has certain shortcomings.     

Mössbauer spectroscopy of iron meteorite Dronino and products of its corrosion

The results of the first study of iron meteorite Dronino and products of its corrosion by Mössbauer spectroscopy are presented. Mössbauer parameters for iron phase, sulfide inclusions, products of terrestrial corrosion and iron oxides in concretion are determined and analyzed.     

无损光谱技术在彩绘陶质文物分析中的应用进展

彩绘陶质文物拥有丰富的信息内涵,对于研究我国古代历史文化、经济商贸、科学技术发展起到极其重要的作用。但由于彩绘陶质文物的珍贵性和不可破坏性,普通分析技术难以满足其测试要求,近年来无损光谱技术被引入文物分析检测领域并逐渐得到应用。本工作从彩绘颜料分析、陶胎分析以及器物信息提取等三个方面阐述了激光拉曼显微光谱、激光诱导击穿光谱、能量色散X射线荧光光谱等无损光谱技术应用的现状、方法原理、特点及局限性,并对无损光谱技术在彩绘陶质文物分析中的应用进行了展望。     

Spectroscopic techniques for the forensic analysis of textile fibers

A review has been conducted on the application of the spectroscopic techniques to the comparative study and identification of different textile fibers. Microspectrophotometry in the ultraviolet-visible range and Raman spectroscopy are the main techniques investigated with this aim in the forensic field. UV-Vis MSP is the first recommended technique, which is principally used to study the color of the fibers. A more complete approximation focused on determining the specific color of the fibers providing adding Raman spectroscopy to the analytical scheme. Sometimes, it also provided information about the polymeric nature of the fibers. Regarding FTIR spectroscopy, it is the recommended tool to determine the fiber nature. Raman and FTIR spectroscopy are complementary techniques and a frequent recommendation is a combination of both techniques, in order to get a comprehensive analysis of textile fibers. On the other hand, new and more informative analytical techniques are emerging to the analysis of textile fibers as traces related with criminal contacts, such as infrared chemical imaging spectroscopy and X-ray fluorescence spectroscopy.     

Special techniques for the Auger analysis of microelectronic devices

Microelectronic devices are becoming more complex and device features are getting smaller as the level of integration continues to increase. Although scanning Auger microscopy has been applied extensively to the analysis of microelectronic devices with a great deal of success, the analysis of current and future devices is presenting new challenges. The major limitations are (1) features of interest in microelectronic circuits are often comparable in size to the beam diameter of commercial Auger microprobes, and (2) the electron beam tends to drift about on the specimen surface because of mechanical instability and differential thermal expansion of the apparatus. In this paper, we present two different techniques developed to overcome these limitations. In the specimen modulation technique, the modulating signal is applied to the electrically isolatable regions of a device instead of to the electron energy analyzer. This method of modulation permits the detection of only the Auger electrons that are emitted from the modulated region. Spurious contributions from adjacent areas inadvertently illuminated by the analyzing beam are suppressed. In the position modulation technique, the analyzing beam is scanned repetitively across the feature to be analyzed and the Auger signal is synchronously detected at the scan frequency. The resulting Auger signal magnitude is shown to be unaffected by beam drift. This method of signal detection eliminates the error and uncertainty caused by beam instability during long-term depth profiling, but is applicable only to specimens with certain geometries.     

Computational techniques for the analysis and design of dielectric-loaded plasmonic circuitry

The finite element and the beam propagation method, two widely used methods in photonics, are utilized for the analysis of plasmonic components based on the dielectric-loaded plasmonic waveguide. Two components are chosen as examples and are subsequently numerically investigated by employing the aforementioned methods, in order to demonstrate their applicability in plasmonics. Specifically, a microring resonator add-drop filter and a Mach–Zehnder interferometric switch are analyzed by means of the finite element and the beam propagation method, respectively. The formulation adopted is clearly presented in both cases and the case-dependent implementation details are thoroughly discussed.     

A review on sonic crystal,its applications and numerical analysis techniques

This paper presents a review study on sonic crystal, their development and present status. The paper also focuses on some of the applications of sonic crystal and numerical methods to study these crystals. Sonic crystals are periodic arrangement of scatterers, whose interaction with acoustic waves leads to the formation of band gap. Band gap are regions of frequencies where the sound propagation is significantly restricted from the sonic crystal. This property is used in many applications such as sound barrier, frequency filter, acoustic imaging etc. The paper presents a review of all these applications. Further the paper presents some of the numerical methods used to calculate the band gap formation in sonic crystal.     

Model for Formation of Dunes at the North Martian Pole

The Mars Global Surveyor Mars Orbiter Camera （MOC） took images of a series of strange horseshoe-shaped dunes at the North Martian pole in 2004. These dunes would be formed due to the strong Martian winds whose pattern is different from that on the Earth. We study the cause of the formation of these dunes and make a model for them. In this model, wind speed near the north Martian pole can be evaluated based on the shape of the dunes. We also estimate the surpassing speed of dunes of different sizes.     

A site determination for Mu* and its implications

A chain of arguments is made which draws on the experimental results ofSR, muon-pion-decay channeling, and³He channeling in deuterium-implanted silicon and which leads to a plausible site for the anomalous muonium atom Mu^* in the group-IV semiconductors. I propose that Mu^* in silicon occupies the deuterium position approximately 1.6 Å from a Si atom in a [111] anti-bonding direction and that analogous sites are occupied in Ge and diamond. Some possible implications of this site assignment are discussed.     

Rapid nondestructive analysis of threading dislocations in wurtzite materials using the scanning electron microscope

We describe the use of electron channeling contrast imaging in the scanning electron microscope to rapidly and reliably image and identify threading dislocations (TDs) in materials with the wurtzite crystal structure. In electron channeling contrast imaging, vertical TDs are revealed as spots with black-white contrast. We have developed a simple geometric procedure which exploits the differences observed in the direction of this black-white contrast for screw, edge, and mixed dislocations for two electron channeling contrast images acquired from two symmetrically equivalent crystal planes whose g vectors are at 120° to each other. Our approach allows unambiguous identification of all TDs without the need to compare results with dynamical simulations of channeling contrast.     

An embedding for general relativity and its implications for new physics

We show that any solution of the 4D Einstein equations of general relativity in vacuum with a cosmological constant may be embedded in a solution of the 5D Ricci-flat equations with an effective 4D cosmological “constant” Λ that is a specific function of the extra coordinate. For unified theories of the forces in higher dimensions, this has major physical implications. Authors Bahram Mashhoon and Paul Wesson belong to The S.T.M. Consortium, http://astro.uwaterloo.ca/~wesson.     

Variability of the terrestrial window and its physical implications

Summary We show that the frequencies of atmospheric molecular thermal vibrations significantly influence the spectral positioning of the terrestrial window. The bandpass filtering process of this window is confined to the region starting from theE-region and extending to an altitude not exceeding about 600 km. This indicates that a significant part of the infrared radiation emanating from lower altitudes is absorbed directly into the ionosphere. Implicitly, the infrared radiation field as viewed downward from the top of the ozonosphere is continuously ?mapped? into the ionosphere in terms of temperature and hence ionization variations. This mapping may be a vital cause of ionospheric irregularities. Factors that influence the transmission coefficient of the terrestrial window are mentioned and discussed. In particular, it is shown that if the terrestrial thermal radiation shifts in response to a temperature change in accordance with Wien's displacement law, the terrestrial window cannot correspondingly shift and continue aligning itself approximately with the peak of the spectrum unless different atmospheric molecules dominate the vibrational process. However, whether different molecules dominate the vibrational process or not, a change in atmospheric temperature makes the transmission coefficient of the window change in the same sense. Consequently, the much reported role played by the window in moderating the temperature of the Earth-Atmosphere system is apparently carried out even when the latter temperature changes provided that the accompanying adjustments do not put the spectral location of the window completely off the terrestrial radiation spectrum. Finally it is shown that if certain substances are introduced in sufficient quantities into the troposphere (in gaseous or aerosol forms), the bandpass filtering process of the terrestrial window may consequently operate in the latter and hence cause regional or global warming.     

Proposal for underwater structural analysis using the techniques of ESPI and digital holography

The purpose of this article is to study the application of the holographic interferometry techniques in the structural analysis of submarine environment. These techniques are widely used today, with applications in many areas. Nevertheless, its application in submarine environments presents some challenges. The application of two techniques, electronic speckle pattern interferometry (ESPI) and digital holography, comparison of advantages and disadvantages of each of them is presented. A brief study is done on the influence of water properties and the optical effects due to suspended particles as well as possible solutions to minimize these problems.     

一种无损测量多层半导体材料厚度的新方法

通过研究GaAs半导体材料厚度对量子效率的影响入手,提出一种利用分光光度计直接测量多层半导体厚度的新方法.根据光学干涉原理,将分光光度计测量出的反射率波谷值代入编写的JAVA程序进行计算,从而可直接得出多层半导体材料厚度,使用该方法得到的半导体层厚度误差＜9%,满足测试精度要求.此方法可用于半导体外延片材料分析、工艺提高以及批量无损测量.     

Architecture of columnar nacre, and implications for its formation mechanism

We analyze the structure of Haliotis rufescens nacre, or mother-of-pearl, using synchrotron spectromicroscopy and x-ray absorption near-edge structure spectroscopy. We observe imaging contrast between adjacent individual nacre tablets, arising because different tablets have different crystal orientations with respect to the radiation's polarization vector. Comparing previous data and our new data with models for columnar nacre growth, we find the data are most consistent with a model in which nacre tablets are nucleated by randomly distributed sites in the organic matrix layers.