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41.
The geochemical behavior of U, Th series nuclides in surface marine sediments collected fromthe Red Sea coastal environment of Sudan was examined using daughter/parent and nonisotopic activity ratios. Pronounced anomalous behavior of several series of nuclides has been observed, particularly at shallower depths. On the average, the 234U/238U ratio is fairly constant and close to 1.13, suggesting scavenging of 234U from the overlying water column. In shallow-water sediments collected from the biologically productive area of the fringing reef and from the tidal-flat of Sanganeb atoll, compared to harbor and deep-sea sediments, 238U was found in large excess relative to 232Th. The 228Th/232Th disequilibrium indicates rapid sedimentation at shallower sites, which agrees well with data reported in the literature for similar environments. Depletion was observed of precursor thorium isotopes (230Th, 232Th) with respect to their mobile daughter isotopes of radium (226Ra, 228Ra). On the other hand, there is surface enrichment of 228Th and 210Po with respect to their progenitors 228Ra and 226Ra, as demonstrated by the 228Th : 228Ra and 210Po : 226Ra activity ratio, which is greater than unity in all the sediments analyzed. The 210Po/226Ra ratio is fairly constant (average 3.2). 相似文献
42.
导言 对于项目经理而言,项目成功是一个非常重要的问题.John Wateridge先生在其出版的一本著作(1995)[1]中谈到(我在其他地方也阐述过Turner,1999[2],Turner,2000[3]),有一个最为重要的因素决定着项目的成功.如果你不这样做,注定会走向失败;如果按照要求做,成功机会便会大大增加(尽管一些其他不利因素也可能会导致失败). 相似文献
43.
The rate of filtration and the water content of cake are influenced by the existence of a dense skin in a highly compressible
cake. The phenomenon of the dense skin has been rarely studied, and its existence has not been verified experimentally. In
this study, the porosity variation in a very compressible cake is measured by using a new experimental apparatus, and with
this the existence of dense skin has been established experimentally. ‘Unified theory on solid-liquid separation’, a recently
developed theory, is utilized for calculating the porosity variation in a very compressible cake. 相似文献
44.
MN Janakiraman KD Watenpaugh PK Tomich KT Chong SR Turner RA Tommasi S Thaisrivongs JW Strohbach 《Canadian Metallurgical Quarterly》1998,8(10):1237-1242
Potent, non-peptidic, dihydropyrone sulfonamide HIV protease inhibitors have been previously described. Crystallographic analysis of dihydropyrone sulfonamide inhibitor/HIV protease complexes suggested incorporation of a second, C2 symmetry-related sulfonamide group. Selected bis-sulfonamide dihydropyrone analogues display high HIV protease inhibitory activity. 相似文献
45.
S Dawson D Bennett SD Carter M Bennett J Meanger PC Turner MJ Carter I Milton RM Gaskell 《Canadian Metallurgical Quarterly》1994,56(2):133-143
Twelve specific pathogen-free cats were infected either by intra-articular inoculation or by contact exposure to one of two strains of feline calicivirus (FCV), either F65, a field strain originating from an outbreak of lameness in a group of cats, or a vaccine strain. Following either route of exposure, both strains induced signs typical of FCV infection including oral and nasal ulceration, conjunctivitis and ocular discharge. These signs were of equal severity for both virus strains, but overall, following either route of infection, F65 induced more severe disease than the vaccine strain, with marked pyrexia, lethargy and lameness. Vaccine virus only induced a relatively mild lameness following intra-articular inoculation. Gross pathological and histopathological lesions were seen in some of the joints, but again changes were more severe in the F65-exposed cats. Virus was isolated from both normal and affected joints from both groups of F65-exposed cats, and from a joint from each cat inoculated intra-articularly with vaccine virus. Mild transient lameness was also seen in one of two control cats inoculated intra-articularly, but no pathological changes were seen or virus isolated from joints. A cDNA probe used in RNA dot blot hybridisation experiments was found to be specific and more sensitive than virus isolation in detecting FCV in selected tissues. This may be useful in future studies on the pathogenesis of FCV disease and in studies on viral persistence in FCV carriers. 相似文献
46.
47.
The use of a surface developer, pyrocatechol, to process transmission electron microscope negatives has been shown to have significant advantages over the conventional D-19 process. The process described here is tolerant of a large margin of error in the electron exposure and produces a negative that not only retains details both in the highlight as well as the faint regions, but also preserves local contrast. These characteristics are particularly useful in convergent beam electron diffraction applications where one encounters a wide contrast range. Improved acuteness and an enhanced signal to noise ratio due to the prolonged exposures associated with this process have also been observed. 相似文献
48.
The compression creep behavior was monitored at constant temperature and/or relative humidity for two slabstock foams with different hard-segment content. The tests were performed by applying a constant load (free falling weight) and then monitoring the strain as a function of time over a 3-h time period. A near linear relationship is obtained for linear strain versus log time after a short induction period for both foams and at most conditions studied (except at temperatures near and above 125°C). The slope of this relationship or the initial creep rate is dependent on the initial strain level, espcially in the range of 10–60% deformation. This dependence is believed to be related to the cellular structs buckling within this range of strain. At deformations greater than 60% and less than 10%, the solid portion of the foam is thought to control the compressive creep behavior in contrast to the cellular texture. Increasing relative humidity does cause a greater amount of creep to occur and is believed to be a result of water acting as a plasticizer. For low humidities increasing the temperature from 30 to 85°C, a decrease in the rate of creep is observed at a 65% initial deformation. At 125°C, an increase in the creep rate is seen and is believed to be related to chemical as well as additional structural changes taking place in the solid portion of the foams. The creep rate is higher for the higher hard-segment foam (34 wt %) than that of the lower (21 wt %) at all of the conditions studied and for the same initial deformation level. This difference is principally attributed to the greater amount of hydrogen bonds available for disruption in the higher hard-segment foam. © 1994 John Wiley & Sons, Inc. 相似文献
49.
50.
F. H. Sam Froes 《Powder Metallurgy and Metal Ceramics》2007,46(5-6):303-310
The approaches to production of titanium powder injection molded parts are reviewed. Historically, oxygen levels have been
too high for structural use (particularly with the Ti-6Al-4V alloy). However, recent advances in starting powders, binders
and sintering facilities now allow oxygen levels in the Ti-6Al-4V alloy to be controlled to about 0.2 wt.% oxygen. This should
result in significant expansion of the titanium PIM market place into aerospace, automobiles, surgical instruments, dentistry,
communication devices (such as computers and cell phones), knives and guns.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 118–125, 2007. 相似文献