Transient Temperature Near a Void in a Material Heated by a Moving Laser Beam

Thermal methods in nondestructive testing utilize the fact that the thermal properties of a defect differ from those of the host material so that temperature distortions result when the material is heated. If the temperature distortions are measured (e.g., by an infrared camera), the data can be analyzed.to possibly locate and/or size the defect. Heating materials having defects has been accomplished in the past by using heat sources such as halogen lamps, hot air, or pulsed lasers

Photothermal Length Measurement of Vickers Cracks in SI3N4

Ceramic materials are gaining ever increasing popularity in different high—technology applications, especially in those where high temperatures are used. However, the mechanical strength of ceramics has thus far set limitations on their utilizing. The critical size of cracks in ceramic material depends on the force applied, but in typical applications it is less than 100 µm. This small size in addition to the fact that critical cracks are often closed makes the use of conventional NDT methods in crack detection very difficult or even impossible. More nuisance comes from the porosity of the material which takes methods needing immersing in liquids out of consideration

Response of Laser-Induced Thermal Lens Effect at Solid Surface

Recently Kuo et al. [1,2] and Satio et al.[3] presented the surface-thermal lens (STL) technique, this novel photothermal deformation technique has attracted great attention because it is a highly sensitive, noncontact and nondestructive measurement[4–6]. In this technique, a modulated pump beam is focused on the sample surface to produce the surface deformation and a cw probe beam is incident at the deformation region. Differing from the conventional photothermal deformation techniques, the spot size of the probe beam at the sample surface is much larger than the pump beam one. Then the probe beam reflected from the surface produces a diffraction pattern at the detection plane. More recently, STL technique has been successfully applied to study the temperature dependence of the thermal conductivity of semiconductor materials[5], weak absorption of optical thin films[6] and characterization of the solid materials[7,8]. However, the mechanism of STL phenomena has not been completely understood. Most theoretical models took no account of the influence of the air-thermal lens (ATL), although some experiment showed that the air significantly affected the detected diffraction pattern[2]. In addition, it is necessary to characterize frequency responses of signals because the response is used to determine the thermal property of the solid materials[5]

Deep Thermoacoustic Imaging Using Scanning Electron Acoustic Microscopy

There has developed over the past few years some controversy [1] over the meaning and use of terms such as “thermal wave imaging” vs. “thermoacoustic imaging” or “Thermal Wave Microscopy” as opposed to “Scanning Electron Acostic Microscopy” (SEAM). The issue in question is the extent of the role played by acoustics directly on the imaging. In the present work, SEAM studies of a prepared test standard are presented which show that macroscopic elastic properties can play an important role in imaging. The SEAM technique uses Coordinate Modulation (CM) of the electron beam [2] rather than the more commonly used intensity modulation via beam blanking. Defects as deep as 26 thermal diffusion lengths in stainless steel have been clearly imaged with this technique. This work strongly supports the Jackson -Amer thermal bending model [3] for low frequency (up to approximately 100kHz in small specimens) acoustic detection in the solid as compared to the theory of Opsal and Rosencwaig [4] which does not incorporate total specimen response to the thermal source. This problem has more recently been theoretically investigated by Favro [5,6], who has developed a more general theory encompasing both the Opsal-Rosencwaig short wavelength limit and the Jackson-Amer long wavelength limit. Favro’s theory also accounts for features in the image shown

Optimisation of NMR dynamic models I. Minimisation algorithms and their performance within the model-free and Brownian rotational diffusion spaces

The key to obtaining the model-free description of the dynamics of a macromolecule is the optimisation of the model-free and Brownian rotational diffusion parameters using the collected R1, R2 and steady-state NOE relaxation data. The problem of optimising the chi-squared value is often assumed to be trivial, however, the long chain of dependencies required for its calculation complicates the model-free chi-squared space. Convolutions are induced by the Lorentzian form of the spectral density functions, the linear recombinations of certain spectral density values to obtain the relaxation rates, the calculation of the NOE using the ratio of two of these rates, and finally the quadratic form of the chi-squared equation itself. Two major topological features of the model-free space complicate optimisation. The first is a long, shallow valley which commences at infinite correlation times and gradually approaches the minimum. The most severe convolution occurs for motions on two timescales in which the minimum is often located at the end of a long, deep, curved tunnel or multidimensional valley through the space. A large number of optimisation algorithms will be investigated and their performance compared to determine which techniques are suitable for use in model-free analysis. Local optimisation algorithms will be shown to be sufficient for minimisation not only within the model-free space but also for the minimisation of the Brownian rotational diffusion tensor. In addition the performance of the programs Modelfree and Dasha are investigated. A number of model-free optimisation failures were identified: the inability to slide along the limits, the singular matrix failure of the Levenberg–Marquardt minimisation algorithm, the low precision of both programs, and a bug in Modelfree. Significantly, the singular matrix failure of the Levenberg–Marquardt algorithm occurs when internal correlation times are undefined and is greatly amplified in model-free analysis by both the grid search and constraint algorithms. The program relax (http://www.nmr-relax.com) is also presented as a new software package designed for the analysis of macromolecular dynamics through the use of NMR relaxation data and which alleviates all of the problems inherent within model-free analysis

Precise Thermal NDE for Quantifying Structural Damage

We have developed precise thermal NDE as a wide-area inspection tool to quantify structural damage within airframes and bridge decks. We used infrared cameras and image processing to produce precise temperature, thermal inertia, and cooling-rate maps of flash-heated aircraft skins. These maps allowed us to distinguish major structural defects from minor flaws which do not warrant costly repairs. We quantified aircraft skin corrosion defects with metal losses as low as 5% with 3% overall uncertainty [1–6]. We proved the feasibility of precise thermal NDE to inspect naturally-heated asphalt-concrete bridge decks. To this end, we quantified structural damage within asphalt-concrete slabs by locating the sites, and determining the relative volumes, of concrete displacements from 2-inch deep and 4-inch deep synthetic delaminations in asphalt-concrete slabs [4–8]

Exact models for anisotropic relativistic stars

We present a class of exact solutions of the Einstein gravitational field equations describing spherically symmetric and static anisotropic stellar type configurations. The solution is represented in a closed integral form. The energy density and both radial and tangential pressure are finite and positive inside the anisotropic star. The energy density, radial pressure, pressure-density ratio and the adiabatic speed of sound are monotonically decreasing functions. Several stellar models with the anisotropy coefficient proportional to r2 are discussed, the values of the basic physical parameters of the star (radius, mass and red shift) and bound on anisotropy parameter is obtained.link_to_subscribed_fulltex

From Nylonkong to Haiwankong: an imagination

The recent developments have shown the advantages of the thermographic technique for the detection of corrosion and disbonds in aircraft structures[l–3]. These have typically involved the application of heat with an infrared source and imaging the induced temperature change with an infrared imager. This offers a rapid method for detecting corrosion and quantifying its extent in single layer structures. In these application, the heating and imaging components of the system remain stationary during the measurement cycle. Two disadvantages of this technique are the expense of the infrared imager and the large power requirement for the infrared heater

A Tentative Analysis of the Modernized Functions of International Metropolises

綜觀工業化國家的國際性城市，都具有全球性或大區域性的現代化城市功能，其總體特征，該城市所在地區的工業經歷與城市職能經歷過一個相當長的城市化、現代化過程，并與世界經濟一體化日益接軌，并走向現代化、國際化的趨勢。國際性城市具有許多復雜的現代化城市特征，也具有很強的城市輻射功能，但其最核心的作用就是城市的現代化功能。本文就城市現代化功能的作用、強度與現代化設施系統以及完善市場經濟體系等作一些探索，期望在學術討論的池塘中引出一些漪漣或浪花。The international metropolises of the industrialized countries , observed comprehensively, they all have the global or large regional modernized urban functions. Their general features, the industry economy of the region where these cities locate and their urban functions have gone through rather a long process of urbanization and modernization. and have gone into the international integrated economy gradually and been developing toward the trend of modernization, informationalization and internationalization. The international metropolises have many complex modernized urban features and powerful radiating functions, but the core is the modernized function. This thesis studies a series of elements of international metropolis. such as modernized function, main function, aviation function, market economical system function. industries intensification, modernized transportation system, cultural function and so of'. Here we try to analyze the primary problems of international metropolis, show the essential character of some important international metropolises in the world. In addition, we are glad to discuss these problems with experts who are interested in them to inspire the spray of academic problems