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991.
Kejian Li Gabriel Spartacus Jiling Dong Pengjun Cao Keesam Shin 《Materials and Manufacturing Processes》2017,32(16):1851-1855
Ultrasonic shot peening (USP) is an efficient way to improve the mechanical behavior of 301 stainless steel by inducing severe plastic deformation on its surface. However, this surface treatment induces complex microstructural evolutions, such as grain refinement and phase transformation. Therefore, a better understanding of those evolution mechanisms is critical to optimize the USP treatment. In this work, we rely on various electron microscope observations to compare a specimen before and after a 5-min shot peening treatment. We found an affected layer of ~450?µm with a significant increase in hardness on the top surface by a factor of 2.7 times. Inside this layer, we noticed a nanoscale grain layer of ~130?µm, the most strengthened layer, containing nanoscale grain of α′, with few γ and a large amount of low angle grain boundaries on the topmost. Afterward, we observed coarse grains with deformation twins, which seem to be a preferential site for martensite nucleation, especially at their intersection, and a high density of dislocation. We also conducted experiments to determine a possible scenario for the microstructural evolution, based on those observations. 相似文献
992.
Yann Jansen Roland E. Logé Pierre-Yves Manach Gabriel Carbuccia Marc Milesi 《International Journal of Material Forming》2017,10(5):707-716
Experimental and numerical cup drawing process has been investigated on 0.65 mm zinc sheets. The cup exhibits anisotropic earrings due to the material microstructure. The material formability is studied through elliptical bulge tests in the rolling, diagonal and transverse direction. High anisotropy of the formability is observed. The numerical simulation of cup drawing is then made and demonstrates the correct fitting with experimental results. A stress formability criterion developed by Jansen et al. [14] is then implemented into a finite element method software and applied to predict the material rupture observed for some process conditions. The risk zone of the cup is subjected to some strain path changes according to the simulation whereas the strain value does not explain the rupture according to the experimental formability measured by the bulge tests. It has been shown that the rupture is due to some critical stresses, which are reached in the risk zone of the cup. The use of the stress criterion and its non-dependence on the strain path change allows the fracture prediction. Finally, the numerical fracture propagation by the “kill element method”, as briefly discussed by Bouchard et al. [4], is used and shows a good similarity with the experience. 相似文献
993.
Assessment of methods for computing the closest point projection,penetration, and gap functions in contact searching problems
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Ján Kopačka Dušan Gabriel Jiří Plešek Miran Ulbin 《International journal for numerical methods in engineering》2016,105(11):803-833
In computational contact mechanics problems, local searching requires calculation of the closest point projection of a contactor point onto a given target segment. It is generally supposed that the contact boundary is locally described by a convex region. However, because this assumption is not valid for a general curved segment of a three‐dimensional quadratic serendipity element, an iterative numerical procedure may not converge to the nearest local minimum. To this end, several unconstrained optimization methods are tested: the Newton–Raphson method, the least square projection, the sphere and torus approximation method, the steepest descent method, the Broyden method, the Broyden–Fletcher–Goldfarb–Shanno method, and the simplex method. The effectiveness and robustness of these methods are tested by means of a proposed benchmark problem. It is concluded that the Newton–Raphson method in conjunction with the simplex method significantly increases the robustness of the local contact search procedure of pure penalty contact methods, whereas the torus approximation method can be recommended for contact searching algorithms, which employ the Lagrange method or the augmented Lagrangian method. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
994.
Michelle Gabriel 《Housing Studies》2008,23(4):527-540
In an editorial entitled ‘Living Room’ for the journal Urban Geography (Vol. 25, 2004) Susan Smith made reference to the ‘tired state of housing studies’. Smith argued that the ‘post-social turn’ in sociology and cultural geography has largely gone unnoticed by housing researchers and because of this, the radical implications of its epistemology have yet to be explicitly addressed. This post-social turn, elsewhere referred to as Science and Technology Studies, Actor Network theory, feminist technoscience and post-humanism, calls on researchers to decentre the human as the nucleus of social life and in turn recognize the significance of non-human actors (e.g. animals, technology and material artefacts) within social analysis. While in recent years housing scholars have begun to embrace post-structuralist accounts of social life, including discursive and constructionist theories, there has only been limited engagement with post-social assumptions and concepts. In view of this gap, this paper reviews recent developments in post-social theory with a specific focus on the implications of this approach for housing studies. 相似文献
995.
Estimates of costs and the corresponding benefits of particle filtration have been derived for a standard office building. Reduction in occupants’ exposure to particles during their workday is anticipated to reduce their morbidity and mortality. Filtration may also reduce the costs associated with building and HVAC cleaning. Conversely, losses of occupant productivity due to sensory offending pollutants emitted from used ventilation filters can lead to significant economic losses. The results of the present analysis are strongly dependent on several key input parameters; consequently, the sensitivity of the results to these parameters was evaluated as part of this study. The study also acknowledges that the benefits-to-costs ratio depends on the perspective of the stakeholder: the employer renting the building is impacted by occupant performance and building energy costs; the building owner is impacted by maintenance of the building and its HVAC system; society is impacted by the employees’ health and welfare. Regardless of perspective, particle filtration is anticipated to lead to annual savings significantly exceeding the running costs for filtration. However, economic losses resulting from even a small decrease in productivity caused by sensory pollutants emitted from used ventilation filters have the potential to substantially exceed the annual economic benefits of filtration. Further studies are required to determine if meaningful benefits can be obtained from more frequent filter replacement or application of different filtration techniques that limit the emission of offending pollutants into the ventilation air. 相似文献
996.
Abd El-Shafey I. Ahmed John N. Hay Michael E. Bushell John N. Wardell Gabriel Cavalli 《Reactive and Functional Polymers》2008,68(10):1448-1458
Novel N-halamine biocidal polymers were prepared by co-polymerizing a heterocyclic ring-based monomer with tolylene-2,6-diisocyanate and toluene-2,4-diisocyanate. The resulting polyurethanes were halogenated; chlorinated, brominated or iodinated. The rate of bacterial killing by the halogenated derivatives was determined both with and without halogen quenching and one of them was evaluated for use in water filters. The effect of these polymers on bacterial growth-rates was also determined. 相似文献
997.
Gaertner H Lebeau O Borlat I Cerini F Dufour B Kuenzi G Melotti A Fish RJ Offord R Springael JY Parmentier M Hartley O 《Protein engineering, design & selection : PEDS》2008,21(2):65-72
The HIV coreceptor CCR5 is a validated target for both the prevention and therapy of HIV infection. PSC-RANTES, an N-terminally modified analogue of one of the natural chemokine ligands of CCR5 (RANTES/CCL5), is a potent inhibitor of HIV entry into target cells. Here, we set out to engineer the anti-HIV activity of PSC-RANTES into another natural CCR5 ligand (MIP-1beta/CCL4), by grafting into it the key N-terminal pharmacophore region from PSC-RANTES. We were able to identify MIP-1beta/CCL4 analogues that retain the receptor binding profile of MIP-1beta/CCL4, but acquire the very high anti-HIV potency and characteristic inhibitory mechanism of PSC-RANTES. Unexpectedly, we discovered that in addition to N-terminal structures from PSC-RANTES, the side chain of Lys33 is also necessary for full anti-HIV potency. 相似文献
998.
Gabriel Cendejas Felipe Arreguín Csar Flores Ivn Villalobos Eugenio Flores Flavio Vzquez 《Catalysis Today》2008,130(2-4):486-491
A series of potassium alcoholates was obtained from the reaction between KOH and ethylene glycol, resorcinol, 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol, 4,4′-sulfonyldiphenol. These salts were employed to initiate the anionic ring opening polymerization of propylene oxide (PO). The molecular weight distribution of the propylene oxide oligomers prepared by this method and the initiator structure were correlated. These oligomers were characterized through Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) spectroscopies and size exclusion chromatography (SEC). It was found that the molecular weight and polydispersity of the synthesized poly(propylene oxide) (PPO) is highly dependant on the initiator structure and solubility in the reactive medium. The oligomers obtained using di-potassium resorcinolate exhibited a molecular weight distribution more polydisperse than that of PO oligomers synthesized by means of di-potassium ethylene glycolate. In the case of the PO polymerizations started by the potassium salts of 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol and 4,4′-sulfonyldiphenol, the oligomer chains showed very broad molecular weight distributions. In general, lower solubility and augmentation of the polymer polydispersity were observed when the number of aromatic rings in the initiator structure increased. The experimental results were contrasted with those obtained from quantum chemical semiempirical calculations at AM1 level. The peculiar behavior exhibited by the initiators with an aromatic structure could be explained in terms of different reactivities of the initiation sites. The theoretical studies revealed that the ring in the aromatic initiators promotes an unsymmetrical growing when the PPO chains are formed. In contrast, the identical reactivity of both initiation sites in the ethylene glycolate produces a symmetrical growing during the PO polymerization. 相似文献
999.
Alessandro Cresti Norbert Nemec Blanca Biel Gabriel Niebler François Triozon Gianaurelio Cuniberti Stephan Roche 《Nano Research》2008,1(5):361-394
Two-dimensional graphene, carbon nanotubes, and graphene nanoribbons represent a novel class of low dimensional materials
that could serve as building blocks for future carbon-based nanoelectronics. Although these systems share a similar underlying
electronic structure, whose exact details depend on confinement effects, crucial differences emerge when disorder comes into
play. In this review, we consider the transport properties of these materials, with particular emphasis on the case of graphene
nanoribbons. After summarizing the electronic and transport properties of defect-free systems, we focus on the effects of
a model disorder potential (Anderson-type), and illustrate how transport properties are sensitive to the underlying symmetry.
We provide analytical expressions for the elastic mean free path of carbon nanotubes and graphene nanoribbons, and discuss
the onset of weak and strong localization regimes, which are genuinely dependent on the transport dimensionality. We also
consider the effects of edge disorder and roughness for graphene nanoribbons in relation to their armchair or zigzag orientation.
This article is published with open access at Springerlink.com 相似文献
1000.
Gabarda S Cristóbal G 《Journal of the Optical Society of America. A, Optics, image science, and vision》2008,25(9):2309-2319
We present a computational algorithm for isotrigon texture discrimination. The aim of this method consists in discriminating isotrigon textures against a binary random background. The extension of the method to the problem of multitexture discrimination is considered as well. The method relies on the fact that the information content of time or space-frequency representations of signals, including images, can be readily analyzed by means of generalized entropy measures. In such a scenario, the Rényi entropy appears as an effective tool, given that Rényi measures can be used to provide information about a local neighborhood within an image. Localization is essential for comparing images on a pixel-by-pixel basis. Discrimination is performed through a local Rényi entropy measurement applied on a spatially oriented 1-D pseudo-Wigner distribution (PWD) of the test image. The PWD is normalized so that it may be interpreted as a probability distribution. Prior to the calculation of the texture's PWD, a preprocessing filtering step replaces the original texture with its localized spatially oriented Allan variances. The anisotropic structure of the textures, as revealed by the Allan variances, turns out to be crucial later to attain a high discrimination by the extraction of Rényi entropy measures. The method has been empirically evaluated with a family of isotrigon textures embedded in a binary random background. The extension to the case of multiple isotrigon mosaics has also been considered. Discrimination results are compared with other existing methods. 相似文献