INFLUENCE OF A LEVELNESS DEFECT IN A THRUST BEARING ON THE DYNAMIC BEHAVIOUR OF AN ELASTIC SHAFT

This paper examines the non-linear dynamic behaviour of a flexible shaft. The shaft is mounted on two journal bearings and the axial load is supported by a defective hydrodynamic thrust bearing at one end. The defect is a levelness defect of the rotor. The thrust bearing behaviour must be considered to be non-linear because of the effects of the defect. The shaft is modelled with typical beam finite elements including effects such as the gyroscopic effects. A modal technique is used to reduce the number of degrees of freedom. Results show that the thrust bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non-linear analysis.     

Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

An empirical characterization of the quality of DTI data and the efficacy of dyadic sorting

Metrics calculated from images acquired using the diffusion tensor imaging (DTI) technique possess a systematic bias that depends on signal-to-noise ratio (SNR). Dyadic sorting provides a simple method for remediating some of this bias within a region(s) of interest (ROI). Although this bias and its removal using dyadic sorting have been studied previously within a theoretical framework, one can employ precise geometric knowledge of microstructures to perform an empirical comparison between expected DTI results and those measured with a scanner. In this project, the biasing effect of low SNR (approximately 1-10) on DTI eigenvalues was measured directly using water-filled capillary structures of two different sizes, and the magnitude of the corrective effect of dyadically sorting eigenvector-eigenvalue pairs was characterized. Multiple DTI series were acquired for determining DTI metrics at eight unique SNR values, using T(R) to vary signal intensity via T(1) contrast. Differences between the second and third eigenvalues, which should be equal for prolate geometry, ranged from approximately 23% to 45% and from 19% to 41% for large and small inner diameter capillaries after sorting eigenvalues by magnitude, and ranged from approximately 1% to 18% and from 1% to 4% after dyadic sorting. A high-resolution DTI series was used to observe the effect of ROI size on dyadic sorting. For restriction of diffusion on the scale of the small capillary at SNR approximately 18, an ROI with > or =50 pixels is adequate to determine fractional anisotropy to 99% accuracy, while larger ROI are required to resolve the two smaller eigenvalues to the same accuracy ( approximately 330-390 pixels). At low values of SNR, the iteration of dyadic sorting is suggested to achieve good accuracy. A method for the incorporation of empirical measurements into a bias-correction map, which would be useful for characterizing uncertainty and for reducing systematic bias in DTI data, is introduced.     

基于相关性的中红外温度与发射率分离算法

温度和发射率是耦合在一起的.在精确获得大气参数的情况下,由传感器的辐射测量反演地表的温度与发射率,仍然是一个病态问题,必须采取一定的策略进行温度与发射率的分离.因此,温度与发射率的分离是红外遥感的核心问题.文章在分析无太阳直射光影响时大气下行辐射和含有大气残留的地表发射率之间关系的基础上,提出了一个针对野外测量中红外高光谱数据的温度与发射率分离算法.该算法利用大气下行辐射和含有大气残留的地表发射率之间的相关性作为判据来优化地表温度,进而获得地表发射率.基于模拟的中红外高光谱数据,对算法的精度进行评价.结果表明,该算法能够获得较高的地表温度和发射率反演精度;具有较广的适用范围,对测量过程中大气下行辐射变化不敏感;同时算法具有一定的抗噪性.     

Use of capillaries in the construction of an MRI phantom for the assessment of diffusion tensor imaging: demonstration of performance

Although diffusion tensor imaging (DTI) shows great potential for the diagnosis of a variety of pathologies, no consensus for an appropriate assessment standard of DTI exists. This study examined the feasibility of using water-filled arrays of glass capillaries to construct a DTI phantom suitable for making repeated and reproducible measurements required in a quality assessment program. Three phantoms were constructed using arrays of capillaries with three inner diameters (23, 48, and 82 μm). Data were acquired using DTI protocols; the fractional anisotropy (FA), mean apparent diffusion coefficient (ADC) and principal eigenvectors of the diffusion tensors were calculated. This study demonstrated four results: (1) echo-planar images show that susceptibility within the capillary arrays does not lead to substantial differences in precessional frequency in regions containing the arrays and neither do the regions show noticeable image distortion; (2) principal eigenvectors of the diffusion tensors agree to within <10.3° of the array orientations; (3) mean FA values (0.18–0.50) and ADC values (1.40–1.93×10−³ mm²/s) within specified regions of interest are in general agreement with simulations after a simple noise correction; and (4) these array performance characteristics are observable using a typical clinical DTI protocol.     

Disappearance of shell effects and persistence of an even-odd staggering in the fragment production in nuclear reactions at relativistic energies

The isotopic distributions of fragments produced in the spallation of uranium are strongly influenced by the fission of the excited prefragments, highly fissile nuclei. The competition between fission and evaporation around the doubly-magic nucleus Pb is discussed. The light fragments from Fe beam are produced with a strong enhancement of even-even nuclei compared to the odd-odd in the region of nuclei with equal number of neutrons and protons, N ～ Z. This staggering in the production of light fragments is not observed in the production of heavy fragments, and is in contradiction with the basis of the statistical model of deexcitation of a hot nucleus. Pairing interaction as a function of the excitation energy and as a function of the isospin of the nucleus are questioned.     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.     

PHOTODYNAMIC INHIBITION OF ESCHERICHIA COLI DNA POLYMERASE I BY 8-METHOXYPSORALEN PLUS NEAR ULTRAVIOLET IRRADIATION

Abstract— Morphological abnormality due to the UV irradiation of sperm and its modification by photoreactivation (PR) were studied in the sea urchin, Hemicentrotus pukherrimus. When sperm was UV-irradiated and allowed to fertilize unirradiated eggs, the effect of the UV was manifested as an abnormal morphology of embryos in the gastrula or later stages. The UV-induced morphological abnormality was prevented by photoreactivation when the fertilized eggs were illuminated with visible light. In the experiments on a stage-dependent change of PR effectiveness, it was found that an illumination sufficed to effect a nearly complete PR when applied up to the onset of the first DNA synthetic phase, while the PR effectiveness declined thereafter. Illumination after the completion of DNA synthesis had little effect for PR.     

多约束水平运输问题的时间费用均衡

基于为顾客提供最佳服务的现代营销理念,剖析了从一定产地到一定销地所发生的运输问题,构建了时间用均衡的目标模式及多目标约束水平MC^2运输问题的数学模型,本文在建立一系列定义,定理的基础上,提出了认明时间费用均衡解空间的优化决策方法,并结合示例展现了这一方法在解决客观实际问题中的有效性。     

Comparison of α CH and CF activation in alkyl transition metal complexes: a DFT and CASSCF study

DFT (B3PW91) and CASSCF calculations have been carried out to study the relative α migratory abilities of H and F in alkyl transition metal complexes. It is shown that the activation energy is considerably lower to migrate H than F, whereas the energies of reaction are similar for the two reactions. A study of the electron configurations and the orbitals describing these configurations shows that the high activation energy for F is due to a 4-electron repulsion between an F lone pair and the occupied Ru=C π orbital.