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871.
The interfacial tension between the molten metal and the surrounding plasma environment affects the circulation of molten
metal in the weld pool, heat transfer, and the eventual structure and properties of the weld metal. Since the effect of plasma
on the interfacial tension of molten metals is not known, interfacial tension values between low pressure argon plasma and
pure copper and iron were measured. The variables studied were temperature and the intensity of plasma emission. 相似文献
872.
Comments that a critical element in the final report of the American Psychological Association (APA) Task Force on the Victims of Crime and Violence may be lost simply because of the enormity and complexity of the issues involved. The real nature of the victim's emotional experience is often not directly addressed by researchers or service providers in the mental health community. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
873.
A 1.3 ?m laser in a compact disc package is coupled to single-mode fibre using two graded-index lenses in a nearly confocal scheme. An increase in the alignment tolerance at the lens-lens interface by a factor of six suggests the design for a potentially very low-cost connectorised laser package. The coupling efficiency of approx. 6% (?12 dB) is shown to be adequate for local loop applications. 相似文献
874.
875.
P. S. Theocaris 《Acta Mechanica》1991,89(1-4):93-121
Summary Cellular solids and brittle foams are increasingly finding application in constructions mainly as core materials for loaded sandwich structures where the loading of the structure generates multiaxial stress states on them. It has been established that the principal mechanism of deformation is based on the cell-wall bending and closed-cell as well as open-cell foams present similar stiffnesses. Therefore simple relations are found for their tensile, compressive and shear strengths and their elastic properties.It has been established in this paper that the modes of failure of such materials can be satisfactorily described by the elliptic paraboloid failure criterion for the general orthotropic body. Then, as soon as the yield or failure stresses in simple tension and compression are measured along the three principal stress directions of the material the failure locus is unequivocally defined and all the properties of the material under any complicated load can be accurately established. However, since these materials fail in the compression-compression-compression octant of the principal stress space by elastic buckling, the EPFS-criterion is cut-off by an ellipsoid surface, with intercepts along the principal axes the respective compressive failure stresses.The criterion thus established yields satisfactory results. It has been tested among others in a reticulated vitreous carbon foam as well as in an aluminium foam. The experimental results for these foams existing in the literature are fitting better with this universal criterion than any other considered, thus indicating the validity of the elliptic paraboloid failure criterion also for this type of materials. 相似文献
876.
Pull-out experiments have been carried out on single production fibres under carefully controlled conditions. Four parameters were determined. The interfacial yield stresses, of about 9–14 MPa, were very much smaller than the shear strengths of the bulk polymers in the case of an epoxy, whether post-cured or not, and a non-post-cured polyester. Values for the work of fracture of the interface varied from 140 to 300 Jm?2, and again were less than those of the polymer. Interface failure sometimes took place in the epoxy rather than at the fibre surface, whereas with the polyester it always took place at the fibre surface. After interface failure, pull-out was governed by friction, with maximum shear stresses of 7–10 MPa for polyester, and 21–34 MPa for epoxy, the higher values being obtained for the post-cured resins. Average frictional shear stresses were sometimes less than a half of the maximum shear stress, indicating that the fibre Poisson's shrinkage was playing an important role in the pull-out process. A silicone release agent reduced the frictional shear stresses to 2·5 MPa, with both resins. 相似文献
877.
D. Knig S. Carvajal-Gonzalez A. M. Downs J. Vassy P. Rigaut 《Journal of microscopy》1991,161(3):405-433
Within the concept of point processes, a review is presented of quantities which can be used in studies of three-dimensional (3-D) aggregates of particles. Suitable characteristics and estimators are given for both unmarked and marked point processes. To demonstrate the feasibility of such quantitative approaches, an application in histology, dealing with 3-D arrangements of cell nuclei in rat liver, is described. Using a confocal scanning light microscope, 3-D images are recorded and image analysis used to obtain the coordinates of the centroid, together with the volume and DNA content, of each cell nucleus. Examples of results are given, using both unmarked and marked point processes. In the latter case, cell type, nuclear volume and ploidy group are suitable marks. 相似文献
878.
879.
Heat shock induces thermotolerance and inhibition of lysis in a lysogenic strain of Lactococcus lactis. 总被引:1,自引:0,他引:1
P Boutibonnes B Gillot Y Auffray B Thammavongs 《International journal of food microbiology》1991,14(1):1-9
In this preliminary work, the heat shock response of lactic acid bacteria was investigated and characterized. Log-phase Lactococcus lactis cells pre-incubated at 40 degrees C before heat challenge at 52 degrees C for 30 min demonstrated increased thermotolerance as compared with cells pre-incubated at 30 degrees C. The response persisted for at least 60 min. Additionally, we demonstrated that: (i) the physiological expression of the heat shock response is temperature dependent; (ii) ethanol 4.0% (v/v) caused, to a lesser extent, a response similar to the heat shock; and (iii) hydrogen peroxide failed to induce a detectable response. Furthermore, we suggest that the induction of the heat shock response increases the resistance of a lysogenic strain of L. lactis, treated by mitomycin C (1.25 micrograms/ml), to lysis by the bacteriophage. 相似文献
880.
Equalization with oversampling in multiuser CDMA systems 总被引:2,自引:0,他引:2
Some of the major challenges in the design of new-generation wireless mobile systems are the suppression of multiuser interference (MUI) and inter-symbol interference (ISI) within a single user created by the multipath propagation. Both of these problems were addressed successfully in a recent design of A Mutually Orthogonal Usercode-Receiver (AMOUR) for asynchronous or quasisynchronous code division multiple access (CDMA) systems. AMOUR converts a multiuser CDMA system into parallel single-user systems regardless of the multipath and guarantees ISI mitigation, irrespective of the channel locations. However, the noise amplification at the receiver can be significant in some multipath channels. In this paper, we propose to oversample the received signal as a way of improving the performance of AMOUR systems. We design Fractionally Spaced AMOUR (FSAMOUR) receivers with integral and rational amounts of oversampling and compare their performance with the conventional method. An important point that is often overlooked in the design of zero-forcing channel equalizers is that sometimes, they are not unique. This becomes especially significant in multiuser applications where, as we will show, the nonuniqueness is practically guaranteed. We exploit this flexibility in the design of AMOUR and FSAMOUR receivers and achieve noticeable improvements in performance. 相似文献