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排序方式: 共有620条查询结果,搜索用时 46 毫秒
61.
62.
Scott Grandison Jean-Marc Vanden-Broeck Demetrios T. Papageorgiou Touvia Miloh Boaz Spivak 《Journal of Engineering Mathematics》2008,62(2):133-148
The formation of nonlinear axisymmetric waves on inviscid irrotational liquid jets in the presence of radial electric fields
is considered. Gravity is neglected but surface tension is considered. Electrohydrodynamic waves of arbitrary amplitude and
wavelength are computed using finite-difference methods. Particular attention is paid to nonlinear traveling waves. In the
first class of problems, an electric field generated by placing the liquid jet inside a hollow cylindrical electrode held
at constant voltage, its axis coinciding with that of the jet, is studied. The jet is assumed to be a perfect conductor whose
free surface is stressed by the electric field acting in the hydrodynamically passive annulus. In the second class of problems,
the annular gas is a perfect conductor that transmits a constant voltage onto the liquid/gas surface. The liquid axisymmetrically
wets a constant-radius cylindrical rod electrode placed coaxially with respect to the hollow outer electrode, and held at
a different constant voltage. The fluid dynamics and electrostatics need to be addressed simultaneously in the inner region.
Axisymmetric interfacial waves influenced by surface tension and electrical stresses are computed in both cases. The computations
are capable of following highly nonlinear solutions and predict, for certain parameter values, the onset of interface pinching
accompanied with the formation of toroidal bubbles. For given wave amplitudes, the results suggest that, for the former case,
the electric field delays bubble formation and reduces wave steepness, while for the latter case the electric field promotes
bubble formation, all other parameters being equal. 相似文献
63.
Simulating testing conditions leading to evaluate the intergranular stress corrosion cracking sensitivity of structural alloys is crucial to estimate the lifetime of in-service components. Former studies have pointed out that a simple modification of the design of slow strain rate tensile specimens was particularly convenient for evaluating the susceptibility to intergranular stress corrosion cracking of nickel-base alloys. The aim of the present work is to characterize and model the mechanical behaviour of such specimens. Validation of proposed modelling relies mainly on tensile tests carried on specimens equipped with strain gages. One of the striking results is that, for a given displacement rate of the heads of the specimen, a much slower strain rate can be obtained locally in comparison with the strain rate of an equivalent smooth specimen. 相似文献
64.
Morphology development during the synthesis at room temperature of an interpenetrating polyurethane/poly(methyl methacrylate) network was investigated by small-angle X-ray scattering in relation with their relative kinetics of formation, determined by Fourier transform infra red spectroscopy. When the time lag between the onset of the two reactions is short, macroscopic phase separation occurs as the polyurethane network is incompletely formed. However, when the time lag increases, the poly(methyl methacrylate) forms into a more continuous network which limits the growth of phase separation to a close environment. 相似文献
65.
Size effects on the DC characteristics and low frequency noise of double polysilicon NPN bipolar transistors 总被引:1,自引:0,他引:1
Nicolas Valdaperez Jean-Marc Routoure Daniel Bloyet Rgis Carin Serge Bardy 《Microelectronics Reliability》2005,45(7-8):1167-1173
DC and low frequency noise measurements have been carried out for double polysilicon NPN bipolar transistors. Our experiments have highlighted unexpected geometrical dependencies for the base saturation current density and low frequency noise. A model, taking into account a variation of the interfacial oxide thickness at the periphery of the emitter has been proposed and it has been successfully applied to the experimental results. 相似文献
66.
Bacterial-based additives for the production of artificial snow: What are the risks to human health?
Arnaud Lagriffoul Rafik Absi Jean-Marc Berjeaud Edmond E. Creppy Jean-Pierre Gadonna Cindy E. Morris 《The Science of the total environment》2010,408(7):1659-1666
For around two decades, artificial snow has been used by numerous winter sports resorts to ensure good snow cover at low altitude areas or more generally, to lengthen the skiing season. Biological additives derived from certain bacteria are regularly used to make artificial snow. However, the use of these additives has raised doubts concerning the potential impact on human health and the environment. In this context, the French health authorities have requested the French Agency for Environmental and Occupational Health Safety (Afsset) to assess the health risks resulting from the use of such additives. The health risk assessment was based on a review of the scientific literature, supplemented by professional consultations and expertise. Biological or chemical hazards from additives derived from the ice nucleation active bacterium Pseudomonas syringae were characterised. Potential health hazards to humans were considered in terms of infectious, toxic and allergenic capacities with respect to human populations liable to be exposed and the means of possible exposure. Taking into account these data, a qualitative risk assessment was carried out, according to four exposure scenarios, involving the different populations exposed, and the conditions and routes of exposure. It was concluded that certain health risks can exist for specific categories of professional workers (mainly snowmakers during additive mixing and dilution tank cleaning steps, with risks estimated to be negligible to low if workers comply with safety precautions). P. syringae does not present any pathogenic capacity to humans and that the level of its endotoxins found in artificial snow do not represent a danger beyond that of exposure to P. syringae endotoxins naturally present in snow. However, the risk of possible allergy in some particularly sensitive individuals cannot be excluded. Another important conclusion of this study concerns use of poor microbiological water quality to make artificial snow. 相似文献
67.
Noureddine Azzam Julien Chaves-Jacob Salim Boukebbab Jean-Marc Linares 《The International Journal of Advanced Manufacturing Technology》2014,72(5-8):1073-1083
This study proposes a method to adapt the geometry of the toolpath to a specified target. In the case study presented, the geometrical target is to remove a constant thickness on the rough workpiece. This case is normally present in the polishing of the femoral component of knee prostheses. In fact, an operator carries out these operations manually. The aim of this study is to contribute to the automation of prosthesis production, notably, in the preparation of surface polishing. The proposed method can deform and adapt a toolpath to ensure the required geometry of the machined surface. The proposed toolpath deformation method is composed of three steps: alignment, toolpath deformation, and toolpath smoothing. Alignment between the measured surface of the roughcast prostheses and the nominal toolpath is carried out by an Iterative Closest Point (ICP) algorithm. The principle of this algorithm is to find the optimal rigid transformation to readjust the toolpath on the measured surface. Subsequently, the toolpath is deformed to remove the constant thickness of the roughcast prostheses. Next, to increase the machined quality, a smoothing stage is carried out on the obtained toolpath. Experimental tests on industrial prostheses geometry are conducted to validate the effectiveness of this method. 相似文献
68.
The yeast Candida deformans CBS 2071 produces an extracellular lipase which was shown to catalyse the production of various esters by the esterification of free fatty acids, even in the presence of a large molar excess of water. To clone the gene encoding this extracellular lipase, Saccharomyces cerevisiae was transformed with C. deformans genomic libraries and screened for lipolytic activity on a medium containing rapeseed oil emulsion and rhodamine B. Three members of a lipase gene family (CdLIP1, CdLIP2 and CdLIP3) were cloned and characterized. Each deduced lipase sequence has a Gly-His-Ser-Leu-Gly-(Gly/Ala)-Ala conserved motif, eight cysteine residues and encodes an N-terminal signal sequence. MALDI-TOF mass spectrometry analysis of a proteolytic digest of the lipase produced was used to obtain experimental evidence that the CdLIP1 gene encoded the extracellular lipase. Recombinant expression studies confirmed that the cloned genes encoded functional lipases. The three lipases are very similar to lipases from the related species Yarrowia lipolytica. Significant homologies were also found with several yeast and fungal lipases. As C. deformans CBS 2071 was previously considered to be synonymous with Y. lipolytica, the strains were compared for the extent of nucleotide divergence in the variable regions (D1/D2) at the 5'-end of the large-subunit (26S) ribosomal DNA (rDNA) gene. This rDNA region has diverged sufficiently to suggest that C. deformans is a separate species. The nucleotide sequences of the CdLIP1, CdLIP2 and CdLIP3 genes will appear in the EMBL nucleotide sequence database under Accession Nos AJ428393, AJ428394 and AJ428395, respectively. 相似文献
69.
70.
Marlin Magallanes-Perdomo Sylvain Meille Jean-Marc Chenal Elodie Pacard Jérôme Chevalier 《Journal of the European Ceramic Society》2012,32(11):2765-2775
A discussion of the effects of Bioglass® powder crystallisation on the in vitro bioactivity in simulated body fluid (SBF) is presented.Starting from Bioglass® powder, different glass–ceramics were obtained by thermal treatments between 580 °C and 800 °C, with variable crystallisation content (from 10 to 92 wt%). All samples (glass and glass–ceramics) showed apatite formation at their surface when immersed in SBF. In case of the glass and the samples with lowest crystallinity, the first step of apatite formation involved a homogenous dissolution followed by an amorphous calcium phosphate (CaP) layer precipitation. For the samples with a high crystallisation content, heterogeneous dissolution occurred. For the first time, the Stevels number of the amorphous phase is used to explain the possible dissolution of the crystalline phase present in materials with a similar chemical composition of the Bioglass®. All samples presented at 21 days of immersion in SBF B-type hydroxycarbonate apatite crystals. 相似文献