共查询到20条相似文献,搜索用时 0 毫秒
1.
Han SI Marseille O Gehlen C Blümich B 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,152(1):87-94
Pipe flow of blood in tubes of 1 and 7 mm inner diameter, respectively, was investigated employing two-dimensional NMR velocity imaging and PFG propagator measurements at different Reynolds numbers between 10 and 3500. The results are compared to flow of a water/glycerol mixture of matching viscosity under identical conditions. The transition from laminar to turbulent flow is observed by both a flattening of the velocity profile and a change of the propagator shape. For blood flow this transition is found to be shifted toward higher Reynolds numbers as compared to the transition of the water/glycerol mixture. This observation is in agreement with predictions from hydraulic measurements and is a consequence of the non-Newtonian flow characteristics of blood as a suspension of erythrocytes and plasma. Likewise, a deviation from the laminar flow condition is observed for blood at low Reynolds numbers between 10 and 100. This phenomenon is unknown for Newtonian liquids and is explained by the onset of a geometrical arrangement of the erythrocytes, the so-called rouleaux effect. 相似文献
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O. P. Kuznetsova D. A. Khalilov I. I. Aliev B. V. Yastrebov A. M. Vasserman E. V. Prut 《Russian Journal of Physical Chemistry B, Focus on Physics》2009,3(6):1004-1007
Spin probe EPR spectroscopy was used to study the local dynamics of vulcanizates of an ethylenepropylene-diene elastomer and
rubber powders prepared from them. It was revealed that the preparation of rubber powders is accompanied by the formation
of a polymer network with an essentially nonuniform local structure. 相似文献
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The technology of target preparation for direct and indirect laser irradiation is developed to study the shock compressibility of materials on the Sokol-2 and Iskra-5 laser facilities. Copper and aluminum films with a density close to that of the bulk materials are prepared by ion-beam deposition. The difference in the densities of the film and bulk materials is 0.8–1.7%, and the accuracy of density measurement is 0.4–1.5%. Processes for the preparation of porous materials (aluminum, copper, nickel, gold, etc.) are also devised. Porous cop-per samples of thickness 10–50 μm, pore size 0.1–5.0 μm, mean density 0.065–0.4 g/cm3, and porosity 20–140 are obtained. The preparation of freely suspended film targets 0.1–0.2 μm thick that are irradiated by picosecondlaser shots on the Progress-P and élas-PS facilities is described. 相似文献
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I-Hsiang Tseng Stephanie S. Watson Li-Piin Sung 《Journal of nanoparticle research》2011,13(5):2195-2204
Metal oxide nanoparticles are small but easily form agglomerates in suspension, depending on the strength of particle–particle
and particle–media interactions. To understand the agglomeration behavior of nanoparticles in media and relate to it to product
performance testing, measurement methods are desired to characterize highly scattering metal oxide nanoparticle suspensions
without dilution. In this article, we describe the advantages of using photocorrelation spectroscopy (PCS) in a backscattering
detection configuration to carry out a realistic agglomerate size measurement in multiple scattering media found in most metal
oxide nanoparticle suspensions. The dynamic behavior of nano-titanium dioxide (TiO2) particles in buffer solutions of different chemical composition and pH values was investigated as a sample system using
PCS. The resulting autocorrelation functions (AFs) at different time intervals, particle concentrations, and pH values were
measured at several detection angles. The AF exhibits a multi-mode relaxation time feature and the calculated hydrodynamic
diameters strongly depended on media composition and detection angle. This result indicates that the size and dispersion of
nano-TiO2 agglomerates are significantly affected by solution media. A measurement protocol for determining size and dispersion of
metal oxide particles in media is proposed and related to a performance test found in industry. 相似文献
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J. -L. Zinszner P. Forquin G. Rossiquet 《The European physical journal. Special topics》2012,206(1):107-115
To characterize the penetration resistance of a ceramic target during impact, it is necessary to take into consideration the mechanical behaviour of the fragmented ceramic. In the present work, a series of numerical simulations have been performed to design an experimental configuration named the “normal impact test”. The aim of this configuration is to generate a strong fragmentation of the ceramic tile and to prevent any ejection of debris in order to analyse the fragmentation properties of the impacted ceramic. An anisotropic damage model has been used to perform these computations. The Weibull parameters that constitute input data of this model have been identified from four-point flexural tests performed on the so-called Hexoloy® silicon carbide. Finally, the numerical predictions are compared to the failure pattern of the fragmented ceramic. 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2019,(1)
<正>In the field of geology, it is necessary to get the information about the rock geological time, which includes absolute geologic age and relative geologic age [1]. Tracing the evolutionary history of the earth is one of the research tasks of earth science. Time, space, material and motivation are the basic elements for studying geological processes and environmental evolution, and time is the basis for studying 相似文献
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Jing Zhu XinYang Miao Kun Zhao HongLei Zhan Qiong Zhou WenZheng Yue 《中国科学:物理学 力学 天文学(英文版)》2018,61(5):054221
正In the petroleum industry,the exploitation of oil and gas is necessarily achieved by perforation,and a considerable number of research studies have been conducted with the objective of improving the recovery rates of oil and gas[1,2].New perforation methods are urgently needed to accelerate the development of energy resources.Drilling rock by laser is a non-contact process that can be used to drill holes in a 相似文献
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The wettability of a powder is important, especially in chemical and pharmaceutical technologies when considering the manufacturing process and the properties of the final product. However, contact angle methods for powders are problematic. The common measurement techniques are the sessile drop method and the liquid penetration method. In this work the determination of contact angles of powders by liquid penetration is considered. In particular, we investigated the influence of the sample preparation and sampling device on the wetting process. A bulk with constant properties during the measurement must be guaranteed. We postulate a packing procedure to obtain reproducible measurements by ensuring constant powder properties. 相似文献
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傅里叶变换红外光谱法对珍珠粉和贝壳粉的研究 总被引:1,自引:0,他引:1
通过FTIR比较研究了淡水养殖珍珠的珍珠粉和贝壳粉样品原样、角壳蛋白以及250、400℃和750℃热处理2h后红外光谱的差异。结果表明,珍珠粉和贝壳粉的主要成分均为文石型碳酸钙,并含有少量有机质和水分。2种粉末角壳蛋白红外吸收峰型基本相似,仅在2113.3cm-1处存在差异。250℃加热后,两者成分结构基本没有变化;400℃加热后2种粉末有机物完全分解,珍珠粉文石碳酸钙的晶型部分转变为方解石型,而贝壳粉碳酸钙已完全转化为方解石型;750℃加热后两者的碳酸钙晶形均已完全转化为方解石型,且有大量碳酸钙分解为氧化钙。 相似文献
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After listening to a sound that is presented repeatedly, subjects report hearing different transforms of the original sound. The frequency of reported transforms is a sensitive index of some speech disorders as well as cognitive flexibility in aging. In this paper, we propose and investigate quantitative measures that characterize the dynamics of this phenomenon, known as the verbal transformation effect. In particular, we show that the distribution of the dwell time, the time spent perceiving a string of a given phonemic form before switching to another form, obeys a power law for normal subjects with an exponent valued between 1 and 2. This result suggests that within this paradigm there is no characteristic time scale for the perceptual process. Additionally, we analyze the correlation properties of the transforms. We suggest that the complexity measures and techniques introduced here might be useful diagnostic tools for a number of speech and cognitive disorders. (c) 1995 American Institute of Physics. 相似文献
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Characterizing the structure of small-world networks 总被引:1,自引:0,他引:1
We give exact relations for small-world networks (SWN's) which are independent of the "degree distribution," i.e., the distribution of nearest-neighbor connections. For the original SWN model, we illustrate how these exact relations can be used to obtain approximations for the corresponding basic probability distribution. In the limit of large system sizes and small disorder, we use numerical studies to obtain a functional fit for this distribution. Finally, we obtain the scaling properties for the mean-square displacement of a random walker, which are determined by the scaling behavior of the underlying SWN. 相似文献
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For the design of silos and similar equipment for storage, handling and processing of particulate materials, a thorough understanding of the mechanical behaviour of powders is of great importance. Whereas strength properties of powders have been investigated by many workers, the elastic behaviour at small deformations has been much less in focus. In that respect, a simple preliminary theory of uniaxial elasticity has been derived for particles, based on a simple system of spherical and monosized particles of a homogenous and elastically isotropic material. The equation σ = Ep?el2 gives the relationship between stress, elastic modulus and elastic deformation for the unloading of a given powder at a specific consolidation stress/ compression level. Comparisons with experimental results of real powders in a uniaxial tester show surprisingly good agreement in many cases. The equation seems to describe the elasticity of powders fairly well, although it is only a preliminary derivation based on simple considerations. 相似文献
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Thorsten Feldmann Christoph Promberger Stefan Recksiegel 《The European Physical Journal C - Particles and Fields》2012,72(2):1867
We show that the dimension of the geometric shape formed by the phenomenologically valid points inside a multi-dimensional
parameter space can be used to characterize different new physics models and to define a quantitative measure for the distribution
of the points. We explain a simple algorithm to determine the box-counting dimension from a given set of parameter points,
and illustrate our method with examples from different models that have recently been studied with respect to precision flavor
observables. 相似文献
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Patrick Susini Stephen McAdams Suzanne Winsberg Ivan Perry Sandrine Vieillard Xavier Rodet 《Applied Acoustics》2004,65(8):763-790
The aim of the psychoacoustic study presented here was to characterize listeners' preferences for a set of sounds produced by different brands and models of indoor air-conditioning units. In addition, some synthetic sounds, created by interpolation between recorded sound samples, were integrated into the set. The multidimensional perceptual space and the corresponding physical space representative of the sound set were determined with multidimensional scaling (MDS). Then the preferences for different classes of listeners were related to the physical space. The best spatial model yielded by the MDS had three common dimensions and specificities. The three dimensions are correlated with the ratio of the noisy part of the spectrum to the harmonic part (NHR), with the spectral center of gravity (SC) and with loudness (N). Two classes of listeners can be distinguished in terms of preference. For one, preference varied primarily with loudness, whereas for the other it varied more with SC and NHR. However, for one class the preference grew with the parameter NHR, while it decreased for the other class. The results replicate under different laboratory conditions and indicate the usefulness of this sound quality assessment approach for characterizing appliance noises. 相似文献