A Study of the Propagation of Optical Spectra Using a Wavelength Independent Formulation of Diffraction Theory and Coherence Theory

Abstract

Basic relations in diffraction theory and coherence theory are rederived in spatial coordinates in units of a wavelength for each monochromatic component of the field. It is found that each component behaves identically in these coordinates independent of wavelength. This theory makes it clear that there is an intrinsic spectral shift that always occurs for any deterministic field as it propagates from a region near its sources into the far field. This theory also leads to a set of special conditions under which a partially coherent field has the same spectrum over a plane near its sources and also at every point in its far field. These conditions are believed to be satisfied by the fields radiated by natural thermal sources. Equations are given describing the relationships between the spectra of the source, the field near the source, and the radiation field under a wide range of conditions.     

On the random differential quadrature (RDQ) method: consistency analysis and application in elasticity problems

Differential Quadrature (DQ) is an efficient derivative approximation technique but it requires a regular domain with uniformly arranged nodes. This restricts its application for a regular domain only discretized by the field nodes in a fixed pattern. In the presented random differential quadrature (RDQ) method however this restriction of the DQ method is removed and its applicability is extended for a regular domain discretized by randomly distributed field nodes and for an irregular domain discretized by uniform or randomly distributed field nodes. The consistency analysis of the locally applied DQ method is carried out, based on it approaches are suggested to obtain the fast convergence of function value by the RDQ method. The convergence studies are carried out by solving 1D, 2D and elasticity problems and it is concluded that the RDQ method can effectively handle regular as well as irregular domains discretized by random or uniformly distributed field nodes.     

具有压电元件的功能梯度弹性薄板的振动特性

考虑一功能梯度薄板,其上下表面嵌有压电执行元件。根据逆压电效应,将电场强度转换成作用于板上的等效电载荷。假设梯度材料的物性参数为板厚度方向坐标的幂函数,应用达朗贝尔原理,导出了具有压电元件的功能梯度弹性薄板的动力学方程。采用变量分离与Navier解,得到四边简支功能梯度板的固有特性与电场强度间的关系。并进一步通过数值例子讨论了电场强度、材料的梯度指数等对板固有特性的影响。研究结果表明,调整作用于执行元件上的电场强度可以实现对板的振动特性的控制,而材料的梯度化可影响板的固有频率,在设计中应予以考虑。     

稳恒强磁场技术的发展及其在材料科学中的应用

综述了稳恒强磁场发生技术的发展及其在材料科学中的应用，超导强磁体经济实用，成为强磁场材料科学研究的首选设备，强磁场能够显著改变材料的相变过程，组织取向和流体流动状况，利用强磁场的这些作用有可能形成多种材料制备过程的强场控制理论和控制技术。     

Titanium: The implant material of today

The use of metals for the replacement of structural components of the human body has been with us for some considerable time. The metals originally used were stainless steels which have gradually been replaced by cobalt-chromium alloys. Although titanium has been used since the late forties, it is only relatively recently that it has gained widespread interest. Titanium and its alloys are being used more and more in preference to the cobalt-chromium alloys and has broadened the field of applications. The features which make titanium such an interesting material are its excellent corrosion resistance in the biological environment, combined with an exception degree of biocompatibility which it shares with only a handful of other materials. In this review the background to the clinical use of titanium is discussed with particular attention to the biological aspects of the material. While there are now many clinical uses for titanium and its alloys their main areas of application are in the field of dentistry and orthopaedics and these are described in some detail.     

Choice of input fields in stochastic finite elements

The problem of the arbitrary choice of variables for random field modelling in structural mechanics or in soil mechanics is treated. For example, it is relevant to ask the question of whether it is best to choose a stiffness field along a beam element or to choose its reciprocal field, the flexibility field, as the input to the stochastic finite element model. To answer this question the focus should be on the error of the output of the mechanical model rather than on the input field itself when discretizing the field through replacing it by a field defined in terms of a finite number of random variables. Several reported discretization methods define these random variables as integrals of the product of the field and some suitable weight functions. In particular, the weight functions can be Dirac delta functions whereby the random variables become the field values at a finite set of given points. The replacement field is often defined as the linear regression of the original field on the considered vector of the weighted integrals of the field. For example, this holds for discretizations obtained by truncation of the Karhunen–Loéve expansion of the field, but only approximately so for truncations of expansions given in terms of any other complete orthogonal function basis. Solely discretizations based on the linear regression method are considered herein. The solution to the problem of best choice of the vector of weight functions is not universal but depends on the mechanical problem under consideration as well as on the choice of the input field. Obviously it makes a difference whether it is the stiffness field or its reciprocal field that is chosen to be represented by a vector of weighted averages of the field. As a test example a lognormal stiffness field along the axis of a linear-elastic Bernoulli–Euler column is considered. Then the exact one-to-one conversion from the stiffness field to the flexibility field is directly obtained. From the form of two functionals that have similarity to the potential energy functional and the complementary energy functional, respectively, both derived from the differential equation of the column displacement and the relevant boundary conditions, it can be expected that the discretization of the flexibility field is preferable over the discretization of the stiffness field. Direct mechanical considerations support this expectation.     

A compact stripline transducer for measuring a pulsed electromagnetic field

A stripline transducer for measuring a pulsed electromagnetic field is proposed, the shape of which enables its electrical length to be increased considerably while keeping its actual dimensions small. An expression is obtained for the potential-difference distribution along the stripline transducer when it is excited by a pulsed electromagnetic field of step-shaped form. The theoretical results obtained are confirmed by experiment.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 45–46, April, 1994.     

Analysis of three-dimensional transient seepage into ditch drains from a ponded field

An analytical solution in the form of infinite series is developed for predicting time-dependent three-dimensional seepage into ditch drains from a flat, homogeneous and anisotropic ponded field of finite size, the field being assumed to be surrounded on all its vertical faces by ditch drains with unequal water level heights in them. It is also assumed that the field is being underlain by a horizontal impervious barrier at a finite distance from the surface of the soil and that all the ditches are being dug all the way up to this barrier. The solution can account for a variable ponding distribution at the surface of the field. The correctness of the proposed solution for a few simplified situations is tested by comparing predictions obtained from it with the corresponding values attained from the analytical and experimental works of others. Further, a numerical check on it is also performed using the Processing MODFLOW environment. It is noticed that considerable improvement on the uniformity of the distribution of the flow lines in a three-dimensional ponded drainage space can be achieved by suitably altering the ponding distribution at the surface of the soil. As the developed three-dimensional ditch drainage model is pretty general in nature and includes most of the common variables of a ditch drainage system, it is hoped that the drainage designs based on it for reclaiming salt-affected and water-logged soils would prove to be more efficient and cost-effective as compared with designs based on solutions developed by making use of more restrictive assumptions. Also, as the developed model can handle three-dimensional flow situations, it is expected to provide reliable and realistic drainage solutions to real field situations than models being developed utilizing the two-dimensional flow assumption. This is because the existing two-dimensional solutions to the problem are actually valid not for a field of finite size but for an infinite one only.     

Calibration of circular loop antennas

The calibration of a measuring loop antenna means assigning an antenna factor K for each frequency in the entire measurement band. Such a loop antenna factor can be found either by calculating the impedances of the loop, or by using a well-defined standard magnetic field of a transmitting antenna. For both methods, it is necessary to obtain an accurate relation between the magnetic field and the geometrical dimensions of the loops. Generally, a manufactured loop has a complex geometric shape with complex electrical behavior so that its impedances cannot be accurately determined. The standard magnetic field method must then be used for traceability of the calibration. The necessary expressions, taking into account the dimensions of the loops with finite conductor radii including the current distribution along the loop, are given. Greene's equations are accurately calculated with mathematics software on a personal computer for the near-zone as standard average magnetic field. With the procedure presented here, the calibration is reduced to an accurate measurement of attenuation     

Theoretical description of fiber Bragg reflectors prepared by Fresnel diffraction images

The theory of Fresnel diffraction images is applied to Bragg-grating formation in a germanium-doped silica fiber. Fresnel diffraction images arise from the near-field diffraction at a periodic mask. The diffraction images are calculated as a function of the propagation distance for several mask configurations. The average of the diffraction-image intensities is calculated for a single longitudinal repetitive interval, and it is shown that the period of the resulting average intensity field is twice that of the original mask period. In some cases the periodic mask can be predicted for a desired average intensity field by calculation of the magnitude of its Fourier coefficients.     

Non-equilibrium Dynamics of Interacting Tunneling States in Glasses

After the temporary application of a strong electric bias field to a glass sample at temperatures in the milli-Kelvin range its dielectric constant is increased and then decays slowly back to its equilibrium value. We studied these dielectric non-equilibrium properties of the polyester glass Mylar and the borosilicate glass BK7 as a function of bias field and temperature. We find that the decay to equilibrium depends on the duration of the applied bias field substantially only if the sample has been biased for several thousand seconds or longer. The decay curves after shorter bias field applications are influenced rather by the rate by which the field has been changed. Following the ”dipole gap” theory¹ we assume that the observed excess dielectric response originates in the non-equilibrium dynamics of tunneling states (TSs) that are strongly coupled. Our analysis of the data within the framework of strongly coupled pairs of TSs indicates three competing equilibrium destroying processes, leading to the observed dynamics. Obviously the energy relaxation rate of TSs depends on the bias field since it changes the energy splitting of TSs by coupling to their dipole moments. In addition, a quick enough field sweep can drive TSs non-adiabatically between their energy eigen-states yielding sweep rate dependent decay times. The third process results in decay times independent of temperature and the bias field sweep rate and duration. We propose a picture where the field lifts the tunneling particle in potential wells beyond its original double well as the cause of the third contribution. The decay towards equilibrium is by quantum mechanical tunneling. Moreover, our observations indicate that below a material dependent temperature the relaxation of TSs is caused primarily by interactions between them. PACS numbers: 61.43.Fs, 05.70.Ln, 66.35.+a, 77.22.-d     

Performance and applications of the UVscope instrument

UVscope is a portable multi-pixels photon detector developed at IASF-Pa to support experimental activities in the high-energy astrophysics and cosmic rays field. The instrument, working in single photon counting mode, is designed to directly measure light flux in the wavelengths range 300-650 nm. Thanks to its features and operational flexibility, the instrument can be used in a wide field of applications where the knowledge of the environmental luminosity is required, as in the characterization of sites for ground-based Cherenkov and fluorescence telescopes, and for cross-calibration of their cameras.The present version of UVscope is based on a Multi Anode Photo Multiplier Tube and it is completed by a motorized mount and a filter wheel which allow to make low-light measurements, at programmed pointing directions and at different filter wavelengths. In this paper, the instrument is firstly presented in all its components; then the procedures adopted for its absolute and relative calibration are detailed. The performance of UVscope is evaluated and, finally, current and planned scientific applications are described.     

振动驱动的电磁－永磁复合驱动建模

对一种新的电磁-永磁复合激励永磁体偏转驱动的机理进行振动应用理论分析和实验验证研究。对于这种电磁－永磁复合激励方式,提出一种基于面磁荷计算电磁扭矩的数值方法,建立电磁扭矩随电流和永磁体偏摆角度变化的数学模型,并将理论建模进行对比试验研究,验证所提出理论分析方法的正确性和基于永磁体偏摆驱动在振动驱动领域应用的可行性。     

The critical velocities of a load moving on a floating ice plate that is subjected to in-plane forces

The critical velocities of moving loads over floating ice plates were determined by several authors. In all of these analyses it was assumed that the in-plane force field in the ice cover is zero. However, due to constrained thermal strains, in-plane forces do occur in the field. The purpose of the present paper is to determine its effect upon the critical velocities of the moving loads. It is shown that a uniform compression force field reduces the critical velocity whereas a tension force field has the opposite effect. Graphs are presented to show these findings.     

Optimization of cryostabilized superconducting generator windings cooled by the thermosiphon method

The problem of optimum parameter choice for the superconducting field winding when using the thermosophon cooling method has been discussed.As an optimum criterion, the magnetic flow within the superconducting field winding at a given outer radius of rim cylinder is chosen. The restrictions it imposes on the superconducting field winding cryostabilization and mechanical strength of its supporting elements are taken into consideration. The parameters to be optimized are: the inner and outer radii of the superconducting field winding, superconducting field winding current, ratio of the superconductor area to the matrix area in the multifilamentary composite conductor, cooling channel dimensions, and dimensions of the superconducting field winding supporting elements. The optimum magnetic flows for the stabilized and non-stabilized windings and for windings made of normal metal are compared.     

Scattering by simple and nonsimple shapes by the combined method of ray tracing and diffraction: application to circular cylinders

The combined method of ray tracing and diffraction (CMRD) is an efficient and accurate technique for computing the scattered field in focal regions of optical systems. Here we extend the CMRD concept so it can be used to compute fields scattered by objects of simple as well as nonsimple shapes. To that end we replace the scattering object by an equivalent, planar phase object; use ray tracing to determine its location, aperture area, amplitude distribution, and phase distribution; and use standard Kirchhoff diffraction theory to compute the field scattered by the equivalent phase object. To illustrate the practical use of the CMRD we apply it to a two-dimensional problem in which a plane or cylindrical wave is normally incident upon a circular cylinder. For this application we determine the range of validity of the CMRD by comparing its results for the scattered field with those obtained by use of an exact eigenfunction expansion.     

Aberrations of diffracted wave fields. I. Optical imaging

The concept of aberrations of diffracted waves is revisited by using the Rayleigh-Sommerfeld theory of diffraction, and it is pointed out that these aberrations are in a class by themselves; they are only deceptively similar to the aberrations of a rotationally symmetric imaging system. Although an exact Fourier-transform expression can be written for the diffracted wave field, its numerical calculation is cumbersome because of the dependence of the aberrations of the diffracted wave on the observation point. This is true regardless of whether the diffracted wave field is observed on a plane or a hemisphere. It is shown that the Fresnel and Fraunhofer approximations, which neglect these aberrations and thereby simplify the calculations, are valid in imaging applications.     

Method of determining the magnetic field of a recording head by using tapes of various coating thicknesses

In magnetic recording, the field configuration of the writing head is of major importance, but it is difficult to measure its actual strength. This paper describes a method of determining both the field geometry of a head and the field strength by using tapes of various coating thicknesses. By differentiating the magnetic flux with respect to the thickness, remanence curves are obtained. These curves may be compared to the remanence which was measured statically. This way, the oersteds of the head field can be determined in a much closer vicinity to the head gap than by previously described methods.     

An in vitro and in vivo investigation of the biological behavior of a ferrimagnetic cement for highly focalized thermotherapy

The cancer treatment by local hyperthermia, using a high frequency electromagnetic field is an extensively studied subject. For this propose it was developed a ferrimagnetic cement (FC) to be injected directly into the tumor. In this study it was determined the FC injectability, its capability to generate heat when placed within a magnetic field and its interaction with a modified simulated body fluid using SEM/EDS and XRD. The FC biological response was assessed by the intramuscular implantation in rats and histological analysis of the surrounding tissues. The results suggest that FC can be injected directly into the tumor, its temperature can be increased when exposed to a magnetic field and the surface of the immersed samples quickly becomes coated with precipitate denoting its ionic change with the surrounding medium. The histological analysis revealed a transient local inflammatory reaction, similar to the control material, only slightly more abundant during the first weeks, with a gradual decrease over the implantation time. Based on these results, we concluded that FC might be useful for highly focalized thermotherapy, with a good potential for clinical use.