A comparison of the finite difference and finite element methods for heat transfer calculations

The finite difference method and finite element method for heat transfer calculations are compared by describing their bases and their application to some common heat transfer problems. In general it is noted that neither method is clearly superior, and in many instances, the choice is quite arbitrary and depends more upon the codes available and upon the personal preference of the analyst than upon any well defined advantages of one method. Classes of problems for which one method or the other is better suited are defined

The Use of Finite Element Methodology in Designing Ultrasonic Tests and the Detection of Weak Bond Planes

The ideal ultrasonic test should define unambiguously the size and location of defects, require a minimum of signal processing (i.e., operator intuition and decision) and use a minimum number of transducers. To do this it is necessary to choose the appropriate transducers and transducer locations; unfortunately this may require a time consuming series of iterative pre-test s using samples with manufactured defects which are presumed to behave similarly to real defects. The question arises as to whether numerical simulations may not provide a faster and more efficient way to design these tests. Accordingly a series of numerical tests were designed to: a) demonstrate the validity of numerical simulation; b) define the range of problems which can be treated numerically; c) describe the protocol for determining the optimal transducer position; d) determine the type of signal processing which would provide the maximum information

Experimental study of acoustic displays of flight parameters in a simulated aerospace vehicle

Evaluating acoustic displays of target location in target detection and of flight parameters in simulated aerospace vehicle

Interactive computation of radiation view factors

The development of a pair of computer programs to calculate the radiation exchange view factors is described. The surface generation program is based upon current graphics capabilities and includes special provisions which are unique to the radiation problem. The calculational program uses a combination of contour and double area integration to permit consideration of radiation with obstruction surfaces. Examples of the surface generation and the calculation are given

Respective influences of pair breaking and phase fluctuations in disordered high Tc superconductors

Electron irradiation has been used to introduce point defects in a controlled way in the CuO2 planes of underdoped and optimally doped YBCO. This technique allows us to perform very accurate measurements of Tc and of the residual resistivity in a wide range of defect contents xd down to Tc=0. The Tc decrease does not follow the variation expected from pair breaking theories. The evolutions of Tc and of the transition width with xd emphasize the importance of phase fluctuations, at least for the highly damaged regime. These results open new questions about the evolution of the defect induced Tc depression over the phase diagram of the cupratesComment: 5 pages, 4 figure

The Use of Temperature Pulses to Detect Debonding of Honeycomb Sandwich Panels

The objectives of this study were twofold: (1) Develop a combined finite difference thermal evaluation scheme and a rapid structural deformation assessment technique for a circular facesheet delamination in a honeycomb sandwich panel subject to incident thermal irradiation. (2) Use the method of 1) to evaluate the effectiveness of a thermal delamination inspection tool

Simple theory of extremely overdoped HTS

We demonstrate the existence of a simple physical picture of superconductivity for extremely overdoped CuO2 planes. It possesses all characteristic features of HTS, such as a high superconducting transition temperature, the $d_{x^2 - y^2}$ symmetry of order parameter, and the coexistence of a single electron Fermi surface and a pseudogap in the normal state. Values of pseudogap are calculated for different doping levels. An orbital paramagnetism of preformed pairs is predicted.Comment: 7 pages, 1 figur

Colossal Magnetoresistance in the Mn2+ Oxypnictides NdMnAsO1-xFx

Colossal magnetoresistance (CMR) is a rare phenomenon in which the electronic resistivity of a material can be decreased by orders of magnitude upon application of a magnetic field. Such an effect could be the basis of the next generation of magnetic memory devices. Here we report CMR in the antiferromagnetic oxypnictide NdMnAsO1-xFx as a result of competition between an antiferromagnetic insulating phase with strong electron correlations and a paramagnetic semiconductor upon application of a magnetic field. The discovery of CMR in antiferromagnetic Mn2+ oxypnictide materials could open up an array of materials for further investigation and optimisation for technological applications

Phase separation and pairing in coupled chains and planes

A generalization of the $t-J$ model in a system of two coupled chains or planes is studied by numerical diagonalization of small clusters. In particular, the effect of density fluctuations between these one- or two-dimensional coupled layerson intralayer phase separation and pairing is analyzed. The most robust signals of superconductivity are found at quarter filling for couplings just before the fully interlayer phase separated regime. The possibility of an enhancement of the intralayer superconducting pairing correlations by the interlayer couplings is investigated.Comment: 13 pages + 3 figures, available upon request, LATEX, preprint ORNL/CCIP/93/1

Measurement of the Hyperfine Structure and Isotope Shifts of the 3s23p2 3P2 to 3s3p3 3Do3 Transition in Silicon

The hyperfine structure and isotope shifts of the 3s23p2 3P2 to 3s3p3 3Do3 transition in silicon have been measured. The transition at 221.7 nm was studied by laser induced fluorescence in an atomic Si beam. For 29Si, the hyperfine A constant for the 3s23p2 3P2 level was determined to be -160.1+-1.3 MHz (1 sigma error), and the A constant for the 3s3p3 3Do3 level is -532.9+-0.6 MHz. This is the first time that these constants were measured. The isotope shifts (relative to the abundant isotope 28Si) of the transition were determined to be 1753.3+-1.1 MHz for 29Si and 3359.9+-0.6 MHz for 30Si. This is an improvement by about two orders of magnitude over a previous measurement. From these results we are able to predict the hyperfine structure and isotope shift of the radioactive 31Si atom, which is of interest in building a scalable quantum computer