On creeping flow over a cylinder rotating in presence of translating plane boundary

Summary The paper deals with the problem, consisting in determination of plane, steady, creeping flow in the infinite domain bounded by a straight line and a cricle. The flow is generated by movements of these boundaries with respect to an assumed system of coordinates. The straight line may translate along itself, and the circle may rotate around its centre.Mathematically, this problem reduces to solution of the biharmonic equation with conditions for fluid velocity posed on the two lines bounding the domain. Conditions for uniqueness, of velocity, pressure and of the stress tensor have to be also taken into account.The method of solution applied in the paper consists of two steps.In the first on, a function is derived, which maps conformally the domain of solution onto an annulus. The function turns out to be the bilinear one.In the second step, the differential problem just mentioned is transformed to the annual domain, and its solution is sought in form of the two Goursat functions, each one being represented by the Laurent series supplied by some additional logarithmic terms. A system of linear equations for unknown coefficients of these functions follows from the boundary conditions.All coefficients of the Goursat functions-except seven-vanish, so that the functions represent in fact an exact solution in theannular domain. This is true also in theoriginal, infinite domain, because the mapping function, is exact, too.The paper contains four streamline patterns, corresponding to four characteristic sets of boundary conditions.     

An acoustic pyrometer system for tomographic thermal imaging inpower plant boilers

The paper presents an acoustic pyrometry method for the reconstruction of temperature maps inside power plant boilers. It is based on measuring times-of-flight of acoustic waves along a number of straight paths in a cross-section of the boiler; via an integral relationship, these times depend on the temperature of the gaseous medium along the paths. On this basis, 2D temperature maps can be reconstructed using suitable inversion techniques. The structure of a particular system for the measurement of the times-of-flight is described, and two classes of reconstruction algorithms are presented. The algorithms proposed have been applied to both simulated and experimental data measured in power plants of the Italian National Electricity Board (ENEL). The results obtained appear fairly satisfactory, considering the small data sets that it was possible to acquire in the tested boilers     

An integral method to analyze the glass-crystal transformation kinetics by differential scanning calorimetry under non-isothermal regime. Application to the crystallization of the Ge0.08Sb0.15Se0.77 chalcogenide glass

In this article, a theoretical procedure has been developed for the kinetic study of the glass-crystal transformations under continuous heating regime in materials involving formation and growth of nuclei, obtaining the corresponding parameters: kinetic exponent, activation energy, and pre-exponential frequency. It is an integral procedure, which is based on a transformation rate independent of the thermal history of the material and assumes that the quoted rate depends only on the transformed fraction, x, across the f(x) function, and temperature, considering that these variables are independent ones. Therefore, the transformation rate is expressed as the product of two separable functions of absolute temperature and the transformed fraction. The quoted f(x) function corresponds to a theoretical method that we have developed and recently published, whose details are given in the Sect. “Basic theory” of this study. The above-mentioned integral procedure considers the same pair of temperatures for the different heating rates and obtains a constant value for temperature integral and, therefore, a plot of a function of the transformed fraction versus the reciprocal of the heating rate leads to a straight line with an intercept of zero, if the value of kinetic exponent is correctly chosen. The process may be repeated for other pairs of temperatures and, consequently, other straight lines will be obtained. By using different values of kinetic exponent for each of the quoted lines, it is taken the best correlation coefficient to choose the quoted exponent more suitable. On the other hand, by using the first mean value theorem to approach the temperature integral, one obtains a relationship between a function of the temperature and other function of the transformed fraction. The logarithmic form of the quoted relationship leads to a straight line, whose slope and intercept allow the obtaining of the activation energy and of the pre-exponential frequency. In addition, this study applies the quoted procedure to the analysis of the crystallization kinetics of the Ge_0.08Sb_0.15Se_0.77 glassy alloy resulting in ranges of variation both of the kinetic exponent, n, with the temperature and of the activation energy, E, with the crystallized fraction, which contain the values of n and E, obtained according to the already quoted theoretical method, that we have developed and recently published. This fact shows the reliability of the theoretical procedure described in this article to analyze the glass-crystal transformation kinetics of glassy alloy.     

Deformation mechanism maps for ceramics

Deformation mechanism maps may be constructed for either a constant grain size or a constant temperature. A simple method is described for constructing maps at constant temperature, and maps are presented for two representative oxides, a carbide, and three alkali halides. A method is also described for superimposing a set of similar deformation mechanism maps.     

Application of Koistinen and Marburger’s athermal equation for volume fraction of martensite to diffusional transformations obtained on continuous cooling 0·13%C high strength low alloy steel

Abstract

Koistinen and Marburger’s (KM) equation for the variation of volume fraction of athermal martensite y with temperature Tbelow the M _s has been applied to continuous cooling diffusional data. The data consisted of dilatometer curves obtained on continuous cooling of a 0·13%C high strength low alloy steel. The KM equation takes the form, ln(1 - y) = α(M _s - T ). Plots of -ln (1 - y) against temperature for what are thought to be grain boundary ferrite, intragranular ferrite, proeutectoid ferrite, and pearlite give a series of straight lines of increasing slope α. Intersections of these lines give the temperature of transformation points in good agreement with those on the dilatometry curves. Values of α obtained for each transformation are compared with those previously obtained for martensite in plain carbon and alloy steels and ferrite in Fe–9%Ni.     

Kritische substrattemperaturen: I. Messverfahren zur festlegung der kritischen substrattemperaturen und bestimmung der kritischen geraden bei CdSe,Cd und Se

This paper discusses possible methods of measuring substrate temperature and assessing the dependence of the critical substrate temperature on the density of the incident molecule beam. The so-called “critical straight line” was determined from temperature gradients on the substrate. The results are compared with those obtained from earlier measurements carried out using the extrapolation method¹ and from measurements reported by Salimova et al. and by Ginthers.By comparing the critical straight lines, developed by the various authors using different measuring methods, for CdSe, Cd and Se over the density range of the incident beam from 10¹² to 10¹⁷ molecules cm^?2 s^?1, the effect of the glass used and of its composition on the position of the critical straight line is examined. The effect of mechanical and chemical cleaning on the values of the critical temperatures for substrate glasses including microscope slides has also been assessed.     

Homogenization of very rough interfaces separating two piezoelectric solids

The main aim of this paper is to derive homogenized equations in explicit form of the linear piezoelectricity in two-dimensional domains separated by an interface which highly oscillates between two parallel straight lines. First, the basic equations of the linear theory of piezoelectricity are written down in matrix form. Then, following the techniques presented recently by these authors, the explicit homogenized equation and the associate continuity condition, for generally anisotropic piezoelectric materials, are derived. They are then written down in component form for some specific cases. Since the obtained equations are totally explicit, they are significant in practical applications.     

“Oscillating” Riemann invariants of the hyperbolic systems of partial differential equations

The phenomenon of wavenumber oscillations in a wave packet representing an RF pulse propagating in a dispersive medium was studied by numerical methods. An explanation is suggested in the context of nonlinear geometrical optics (NGO), where the wavenumber is a Riemann invariant that remains constant on characteristics of the corresponding equations. The wavenumber oscillations arise in the region of intersection of the characteristics of the equations. It is demonstrated that the intersection of characteristics is due to the approximation neglecting the interaction between narrow-band wave packets constituting the pulse. With the packet interaction ignored, the characteristics are straight lines. If the interaction is allowed for, the characteristics do not intersect and may significantly differ in shape from straight lines. Consequently, an external observer moving at a constant velocity crosses the same characteristic many times, thus perceiving the wave-number as an oscillating function.     

Research on the Dx Split Method Based on an Algorithm to Draw a Line

The problem is that the real line that shows on the computer monitor is not accurate.So we research the algorithms in which drawing a straight line with the Dx split method.In this paper,it is proved that the lines of display pixel lines are not smooth,and they are composed of many splicings of short straight lines.It plays an important scientific role to elucidate the homogenization mechanism of controlling and regulation that insert point back to a straight line.It lays a foundation of showing a straight ...     

Effects of Environmental Temperature and Compression Energy on Polymorphic Transformation During Tabletting

The effects of temperature on the polymorphic transformation and the compression of chlorpropamlde forms A and C during tabletting were investigated by X-ray diffractometry. The X-ray diffraction profiles of the sample powders deagglomerated after compression were recorded to calculate the degree of polymorphic transformation. A single punch eccentric tabletting machine equipped with two load cells (upper and lower punches) and with a noncontact displacement transducer was used to measure the compression stress, energy and distance between punches. A heater and a liquid nitrogen pool were mounted on the die of the tabletting machine, and the die temperature was controlled with a thermocontroller. Two types of compression methods, multi-tabletting at room temperature and single tabletting at 0-45°C, were used in the present study. In the first method, the stable form A or metastable form C was loaded in to the die and the sample was compressed with a compression stress of 196 MPa. Compression was repeated from 1 to 30 times. The results for forms A and C suggested that both forms were mutually transformed, and that the content of forms A and C reached equilibrium above 100 J/g of compression energy after more than 10-times compression. After 30-times compression, the content of A, C, and the noncrystalline solid form were almost constant at about 45%, 25% and 30%, respectively. The compression energy was estimated to be 500-600 J/g. In the second method, single tabletting at 0° and 45°C, the amount of form C transformed from form A at 45°C was about two times larger than that at 0°C at the same compression energy. The amount of form A transformed from form C at 45°C was almost the same as that transformed at 0°C. This suggests that the mechanochemical stability of form A was affected by compression temperature, while that of form C was independent of temperature. The crushing strength (CS) of from A tablet was about two times higher than that of form C even at the same porosity. The relationships between log (CS) of form A tablets compressed at 0 or 45°C and porosity showed straight lines with the same slope, but the slope for form C tablets compressed at 45°C was smaller than that for those compression at 0°C. From these results it appears that the transformation mechanism of forms A and C during compression was as follows: Form A or C was converted to a noncrystalline solid by mechanical energy, and then the solid was transformed into form A or C. The transformation of every form was affected by the environmental temperature.     

Effects of Environmental Temperature and Compression Energy on Polymorphic Transformation During Tabletting

Abstract

The effects of temperature on the polymorphic transformation and the compression of chlorpropamlde forms A and C during tabletting were investigated by X-ray diffractometry. The X-ray diffraction profiles of the sample powders deagglomerated after compression were recorded to calculate the degree of polymorphic transformation. A single punch eccentric tabletting machine equipped with two load cells (upper and lower punches) and with a noncontact displacement transducer was used to measure the compression stress, energy and distance between punches. A heater and a liquid nitrogen pool were mounted on the die of the tabletting machine, and the die temperature was controlled with a thermocontroller. Two types of compression methods, multi-tabletting at room temperature and single tabletting at 0–45°C, were used in the present study. In the first method, the stable form A or metastable form C was loaded in to the die and the sample was compressed with a compression stress of 196 MPa. Compression was repeated from 1 to 30 times. The results for forms A and C suggested that both forms were mutually transformed, and that the content of forms A and C reached equilibrium above 100 J/g of compression energy after more than 10-times compression. After 30-times compression, the content of A, C, and the noncrystalline solid form were almost constant at about 45%, 25% and 30%, respectively. The compression energy was estimated to be 500–600 J/g. In the second method, single tabletting at 0° and 45°C, the amount of form C transformed from form A at 45°C was about two times larger than that at 0°C at the same compression energy. The amount of form A transformed from form C at 45°C was almost the same as that transformed at 0°C. This suggests that the mechanochemical stability of form A was affected by compression temperature, while that of form C was independent of temperature. The crushing strength (CS) of from A tablet was about two times higher than that of form C even at the same porosity. The relationships between log (CS) of form A tablets compressed at 0 or 45°C and porosity showed straight lines with the same slope, but the slope for form C tablets compressed at 45°C was smaller than that for those compression at 0°C. From these results it appears that the transformation mechanism of forms A and C during compression was as follows: Form A or C was converted to a noncrystalline solid by mechanical energy, and then the solid was transformed into form A or C. The transformation of every form was affected by the environmental temperature.     

Exact and approximate analytic solutions of the nonlinear convective fin problem with temperature-dependent thermal conductivity

This article shows that the well-known nonlinear boundary value problem of the differential equation for temperature distribution of convective straight fins with temperature-dependent thermal conductivity is exactly solvable in an implicit form. Furthermore, an exact solution in an explicit form is derived. Also, an accurate analytic solution (series solution) is obtained by a new variation of the Adomian decomposition method.     

The morphology of axial and branched nanowire heterostructures

We present an extensive investigation of the epitaxial growth of Au-assisted axial heterostructure nanowires composed of group IV and III-V materials and derive a model to explain the overall morphology of such wires. By analogy with 2D epitaxial growth, this model relates the wire morphology (i.e., whether it is kinked or straight) to the relationship of the interface energies between the two materials and the particle. This model suggests that, for any pair of materials, it should be easier to form a straight wire with one interface direction than the other, and we demonstrate this for the material combinations presented here. However, such factors as kinetics and the use of surfactants may permit the growth of straight double heterostructure nanowires. Finally, we demonstrate that branched nanowire heterostructures, also known as nanotrees, can be successfully explained by the same model.     

Detection of linear features in synthetic-aperture radar images by use of the localized Radon transform and prior information

A new linear-features detection method is proposed for extracting straight edges and lines in synthetic-aperture radar images. This method is based on the localized Radon transform, which produces geometrical integrals along straight lines. In the transformed domain, linear features have a specific signature: They appear as strongly contrasted structures, which are easier to extract with the conventional ratio edge detector. The proposed method is dedicated to applications such as geographical map updating for which prior information (approximate length and orientation of features) is available. Experimental results show the method's robustness with respect to poor radiometric contrast and hidden parts and its complementarity to conventional pixel-by-pixel approaches.     

基于超声回波能量峰值点拟合的气体超声波流量计信号处理方法

针对气体超声波流量计信号处理中难以找到稳定特征点的问题,从回波信号能量的角度出发,研究了回波信号能量的变化规律。回波能量信号轮廓的上升段中间部分比较稳定且中间部分包络线斜率相对较大,近似一条直线。因此,提出一种基于回波能量峰值点拟合的信号处理方法,即连接回波能量信号上升段相邻的峰值点并求得各连线的斜率,选取斜率较大的4条连线作为特征直线,将这4条特征直线对应的右端点作为特征峰值点,并拟合成一条直线,以该直线与x轴的交点作为特征点,从而计算出超声波的传播时间。在基于FPGA和DSP的双核心系统上实时实现该信号处理方法,并在国家认可的检测机构进行标定实验,结果表明:基于回波能量峰值点拟合信号处理方法的双声道气体超声波流量计系统达到1级精度,可测流量范围为30~1200m³/h。     

Anwendung Flüssiger Kristalle in der Materialprüfung

Application of Liquid Crystals for Materials Testing. Cholesteric liquid crystals are recently known to be suitable for temperature measurement which can be done by observation of colour variation created by the layers of the cholesteric liquid crystals. The main advantages of liquid crystals over conventional temperature measurement are their low thermal capacity and the possibility of showing large temperature maps. By the cinematographic method the variation of temperature maps as a function of time can be recorded. Until now those informations were received only by relativly costly equipment i. e. infrared cameras.     

Thermo-electro-elastic fields accompanying plastic deformation

The thermo-electro-elastic coupled fields excited by an arbitrary dynamic dislocation ensemble in a piezoelectric medium are studied in a general statement on the basis of the developed 5D formalism. The found general relations are specified for the case when coupled fields are produced by a single straight dislocation moving at a constant speed v. The limiting behavior of derived expressions is analyzed at v → 0. In particular, the static electro-elastic field of a straight dislocation in a piezoelectric is expressed in a compact form similar to the known Barnett-Swanger formula describing dislocation distortions in a purely elastic medium. It is shown that the thermal component of dislocation fields may be essential only for fast dislocations with the speed v of order of the sound velocity. The temperature distribution around the moving dislocation is also analytically studied in details for the case of non-piezoelectric elastic materials. It is shown that metals and ionic crystals manifest a qualitative difference in described thermal effects. The results of the developed theory are compared with the existing experimental data. It is shown that there is a quantitative agreement between them.     

Using deformation mechanism maps to depict flow processes in superplastic ultrafine-grained materials

Deformation mechanism maps are a very useful tool for displaying deformation mechanisms as a function of the three fundamental parameters of high temperature flow: the applied stress, the testing temperature and the grain size of the material. These maps are used extensively in the field of high temperature creep but there has been very little use with ultrafine-grained (UFG) metals. This article reviews the principles of deformation mechanism maps, presents examples of maps for some representative metals processed by equal-channel angular pressing or high-pressure torsion and then describes a simple procedure for constructing maps for UFG materials.     

A historical view of imaging systems and technology

When approached from a historical viewpoint the development of many important imaging systems throughout history often share common ground. Extremely important was the development of the idea of mathematical projection which provides methods for making an image that conformally represents the object. The prime example is the discovery of the stereographic projection by Hipparchus of Nicaea in the second century BC. The stereographic projection provided the basis for the astrolabe, an astronomical device that acted both as an instrument of observation and as an analog computer. The stereographic projection and similar ones also provided the basis for the world maps of the ancients which utilized a grid of longitude and latitude. When the ancient Greek books were rediscovered in the Renaissance, the maps provided the impetus for the age of exploration. The Mercator projection of the sixteenth century was obtained as a logarithmic transformation of the stereographic projection. The Mercator projection provided sea captains with maps that had a rectangular grid of latitude and longitude and also had the property that straight lines represented courses of constant compass directions. The development of the telescope and microscope in the early seventeenth century provided means to obtain images that could not be seen by the unaided eye. Galileo's discovery of the moons of Jupiter led to Roemer's determination in 1676 that light travels at a finite velocity. Unknowingly, Roemer also discovered the relativistic Doppler effect, which in the present century helped to establish our concept of the expanding universe. The relativistic Doppler factor mathematically is none other than the expression for the stereographic projection of Hipparchus. The development of high energy physics in this century has led to images of the microworld of subatomic particles. In this environment Einstein's equation E = mc² finds verification. This equation is a result of the theory of special relativity. The basic mathematics of special relativity is contained in the Lorentz transform. Again we can return to Hipparchus, because the Lorentz transform follows from a sequential application of the stereographic projection.