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41.
Although there is now a considerable volume of high-strain (<105 cycles) fatigue data for uniaxial tension-compression and simple-bending conditions, relatively little information is available regarding the effects of stress and strain biaxiality. A method which has been used to study the effects of biaxiality on longlife fatigue strength is to subject thin-walled tubes to repeated internal pressure and an end load which is in phase with, and a linear function of, the pressure. The object of the present research was to use this method to study the influence of stress biaxiality on the high-strain fatigue behavior of a high strength, aluminum-4% copper alloy at room temperature. From a continuum-mechanics point of view, this material is completely elastic after the first few load cycles. Cylinder results for hoop to axial stress ratios of 2:1, 1:1, 1:2 and 2: ?1 suggest that fatigue failure of this material in the life range 103 to 105 cycles is primarily dependent on the maximum range of tensile stress. This conclusion and a study of fracture surfaces led to the use of linear-elastic fracture mechanics to interpret the fatigue and brittle fracture behavior of these cylinders. 相似文献
42.
N.T. Crosby 《Trends in analytical chemistry : TRAC》1982,1(11):IV-V
Food legislation is enacted throughout the world, both to protect the health of the consumer and to prevent fraud. The food analyst plays a major part in the enforcement of such legislation, particularly as modern analytical techniques now enable trace constituents at ng/g levels to be detected. 相似文献
43.
De Souza EJ Gao L McCarthy TJ Arzt E Crosby AJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(4):1391-1396
We conduct experimental investigations of macroscopic capillary forces between two flat rigid substrates characterized by their advancing and receding contact angles with water. Our results exhibit excellent agreement with theoretical predictions obtained by the numerical solution of the capillary equation. On the basis of this comparison, we use the measurements of the capillary force to investigate the phenomenon of contact angle hysteresis. We present examples of force measurements for surfaces that display low, moderate, and high contact angle hysteresis and compare results for a larger variety of substrates. Finally, we show that for the case of water, the role of viscosity is insignificant within the range of force and velocity measured in the present work. 相似文献
44.
De Souza EJ Brinkmann M Mohrdieck C Crosby A Arzt E 《Langmuir : the ACS journal of surfaces and colloids》2008,24(18):10161-10168
Motivated by experimental results, we present numerical and analytical calculations of the capillary force exerted by a capillary bridge spanning the gap between two parallel flat plates of asymmetric wettability. Depending on whether the sum of the two contact angles is smaller or larger than 180 degrees, the capillary force is either attractive or repulsive at small separations D between the plates. In either cases the magnitude of the force diverges as D approaches zero. The leading order of this divergence is captured by an analytical expression deduced from the geometry of the meniscus of a flat capillary bridge. The results for substrates with different wettability reveal an interesting behavior: with the sum of the contact angles fixed, the magnitude of the capillary force and the rupture separation decreases as the asymmetry in contact angles is increased. In addition, we present the rupture separation, i.e., the maximal extension of a capillary bridge, as a function of the contact angles. Our results provide an extensive picture of surface wettability effects on capillary adhesion. 相似文献
45.
A series of prochiral 3-hydroxyglutaronitrile derivatives 1–5 has been enzymically hydrolysed to the corresponding nitrile-carboxylic acids 1b–5b with enantiomeric excesses ranging from 22–84%. In all cases the products were of the (S)-configuration. 相似文献
46.
Triply coupled high performance liquid chromatography using diode array detection and positive ion electrospray mass spectrometry of 2- and 3-hydroxypyridine is presented. Considerations of the physical method for coupling the two detectors, the influence of pH on retention times, the cone voltage of the mass spectrometer and the linear concentration ranges are described. Data from both detectors are aligned and interpolated. The analyte mass spectra are reduced to 20 significant masses. Principal components plots on the raw, normalised and standardised data, derivatives to determine composition 1 regions, deconvolution and procrustes analysis to compare data from both detectors are discussed. Common trends in both mass spectral and diode array chromatograms are interpreted. This paper represents a new approach to common processing of chromatographic data from two detectors. 相似文献
47.
Mulliken's model for the intensity of charge-transfer absorption bands in donor/acceptor complexes is extended to transition-metal compounds. Attention is focused on the analysis of systems containing a central metal ion and symmetrically equivalent π-acceptor ligands. The theory is illustrated for a one-donor/two-acceptor complex in D2d point symmetry. Results are stated for symmetries of commonly occurring transition-metal compounds that display well-documented metal-to-ligand charge-transfer transitions. 相似文献
48.
A Three-dimensional Model of the Human Immunodeficiency Virus Type 1 Integration Complex 总被引:3,自引:0,他引:3
Summary While the general features of HIV-1 integrase function are understood, there is still uncertainty about the composition of
the integration complex and how integrase interacts with viral and host DNA. We propose an improved model of the integration
complex based on current experimental evidence including a comparison with the homologous Tn5 transposase containing bound
DNA and an analysis of DNA binding sites using Goodford’s GRID. Our model comprises a pair of integrase dimers, two strands
of DNA to represent the viral DNA ends and a strand of bent DNA representing the host chromosome. In our model, the terminal
four base pairs of each of the viral DNA strands interact with the integrase dimer providing the active site, while bases
one turn away interact with a flexible loop (residues 186–194) on the second integrase dimer. We propose that residues E152,
Q148 and K156 are involved in the specific recognition of the conserved CA dinucleotide and that the active site mobile loop
(residues 140–149) stabilises the integration complex by acting as a barrier to separate the two viral DNA ends. In addition,
the residues responsible for DNA binding in our model show a high level of amino acid conservation. 相似文献
49.
Neil K. Gibbs Mary Norval Nicola J. Traynor Markus Wolf Brian E. Johnson John Crosby 《Photochemistry and photobiology》1993,57(3):584-590
Urocanic acid (UCA) is a major UV chromophore in the upper layers of the skin where it is found predominantly as the trans isomer. UV irradiation induces photoisomerisation of trans-UCA to cis-UCA which has been shown to mimic some of the immunosuppressive properties of UV exposure. We examined the wavelength dependence for trans-UCA to cis-UCA photoisomerisation in vitro and in mouse skin in vivo over the spectral range270–340 nm. The resulting action spectra were very similar with maximal effectiveness at300–315 nm and equal activity at 270 nm and325–330 nm, demonstrating that UVA-II radiation (320–340nm) is efficient at UCA photoisomerisation. These action spectra differed markedly from the trans-UCA absorption spectrum in vitro and also the reported action spectrum for UV suppression of contact hypersensitivity in mice. These findings suggest that the relationship between cis-UCA formation in skin and UV-induced immunosuppression may be complex. 相似文献
50.
Cooper SM Cox RJ Crosby J Crump MP Hothersall J Laosripaiboon W Simpson TJ Thomas CM 《Chemical communications (Cambridge, England)》2005,(9):1179-1181
Mutation of the mupW gene in the mupirocin biosynthetic gene cluster in Pseudomonas fluorescens results in efficient production of a novel pseudomonic acid metabolite, mupirocin W, which lacks the characteristic tetrahydropyran ring, and reveals the role of the mupW gene in pseudomonic acid biosynthesis. 相似文献