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排序方式: 共有318条查询结果,搜索用时 31 毫秒
1.
The behaviour of Hastelloy C22 steel (N06022 UNS) in solutions at pH 3 and different temperatures, for radioactive water reprocessing plants was studied. The corrosion potential was found to increase with temperature. In the neighbourhood of the active-passive potentials, Hastelloy steel was corroded by means of a transient form. In addition, the potentials of the active and transpassive peaks shifted towards more negative values with increasing temperature. The transpassive peak increased with temperature and its potential shifted towards smaller values. The temperature increase led to a reduction of the passive region and a higher current in the passivity. As shown by current instabilities during the backward scan and a higher current than those in the forward transpassivity scan, all of the oxide layer could not be destroyed at the breakdown transpassive potentials. From electrochemical impedance spectroscopy (EIS), apparently the thickness of the passive oxide decreased with temperature in the prepassive region. In passivity, the EIS showed an enhancement of corrosion for higher potentials or temperatures. At the passivity-transpassivity limit potentials, an inductive loop may be the result of adsorption. It was found that the diameter of the capacitive semi-circle and the inductive loop decreased when the temperature increased, indicating an enhancement of corrosion and a decrease in adsorption. The number of active sites and oxidation rate were determined at different potentials. 相似文献
2.
In nuclear installations, tritiated water is generally produced in the process of detritiation of air circulating in the glove boxes. The goal of this work concerns enrichment of this tritiated water at low concentration by electrolysis. The choice of this electrolyzer was dictated by the passivity of selected materials to the radiolysis in low-level tritiated water and the selectivity of the method avoiding further elimination of tritiated water and moisture before release in environment. According to the results, it is feasible to treat non-negligible volume of low-level tritiated water using a cathodic palladium membrane coated on an ionic solid polymer membrane. Presence of a palladium black deposit on the palladium membrane improves effectiveness. Enrichment in tritiated water depends on the isotopic separation factor, thereby the current and the permeability values. 相似文献
3.
Observations about the evolution of damage to limestone during freeze/thaw cycles using ultrasonic methods (involving wave velocity and attenuation) help understand the physical mechanisms which give rise to damage under frost action. The ultrasonic methods commonly applied rely on theoretical models of frost propagation in porous media and are based on thermodynamic considerations and on capillarity theory. Under the necessary conditions of rock damage formation,i.e. high degrees of saturation and negative temperatures, the geometry of the porous network constitutes the dominant factor which determines the nature of the resulting damages. This parameter controls the degree of saturation of materials both in structural work and under natural conditions. The degree of saturation is among the major factors which aggravate frost degradation of limestone at temperatures below 0°C. Data supplied by the recordings of ultrasonic wave attenuation in limestone during freeze/thaw cycles help characterise and identify the different types of damage. 相似文献
4.
Jean‐David Génevaux Eric Galin Adrien Peytavie Eric Guérin Cyril Briquet François Grosbellet Bedrich Benes 《Computer Graphics Forum》2015,34(6):198-210
We introduce a compact hierarchical procedural model that combines feature‐based primitives to describe complex terrains with varying level of detail. Our model is inspired by skeletal implicit surfaces and defines the terrain elevation function by using a construction tree. Leaves represent terrain features and they are generic parametrized skeletal primitives, such as mountains, ridges, valleys, rivers, lakes or roads. Inner nodes combine the leaves and subtrees by carving, blending or warping operators. The elevation of the terrain at a given point is evaluated by traversing the tree and by combining the contributions of the primitives. The definition of the tree leaves and operators guarantees that the resulting elevation function is Lipschitz, which speeds up the sphere tracing used to render the terrain. Our model is compact and allows for the creation of large terrains with a high level o detail using a reduced set of primitives. We show the creation of different kinds of landscapes and demonstrate that our model allows to efficiently control the shape and distribution of landform features. 相似文献
5.
We generalize Kedlaya and Umans’ modular composition algorithm to the multivariate case. As a main application, we give fast algorithms for many operations involving triangular sets (over a finite field), such as modular multiplication, inversion, or change of order. For the first time, we are able to exhibit running times for these operations that are almost linear, without any overhead exponential in the number of variables. As a further application, we show that, from the complexity viewpoint, Charlap, Coley, and Robbins’ approach to elliptic curve point counting can be competitive with the better known approach due to Elkies. 相似文献
6.
Elena Lopez Adrien Leygue Emmanuelle Abisset-Chavanne Sebastien Comas-Cardona Christophe Aufrere Christophe Binetruy Francisco Chinesta 《International Journal of Material Forming》2017,10(3):317-328
The fundamental macroscopic material property needed to quantify the flow in a fibrous medium viewed as a porous medium is the permeability. Composite processing models require the permeability as input data to predict flow patterns and pressure fields. As permeability reflects both the magnitude and anisotropy of the fluid/fiber resistance, efficient numerical techniques are needed to solve linear and nonlinear homogenization problems online during the flow simulation. In a previous work the expressions of macroscopic permeability were derived in a double-scale porosity medium for both Newtonian and rheo-thinning resins. In the linear case only a microscopic calculation on a representative volume is required, implying as many microscopic calculations as representative microscopic volumes exist in the whole fibrous structure. In the non-linear case, and even when the porous microstructure can be described by a unique representative volume, microscopic calculation must be carried out many times because the microscale resin viscosity depends on the macroscopic velocity, which in turn depends on the permeability that results from a microscopic calculation. Thus, a nonlinear multi-scale problem results. In this paper an original and efficient offline-online procedure is proposed for the efficient solution of nonlinear flow problems in porous media. 相似文献
7.
Diego Canales Adrien Leygue Francisco Chinesta David González Elías Cueto Eric Feulvarch Jean‐Michel Bergheau Antonio Huerta 《International journal for numerical methods in engineering》2016,108(9):971-989
This paper proposes a generalized finite element method based on the use of parametric solutions as enrichment functions. These parametric solutions are precomputed off‐line and stored in memory in the form of a computational vademecum so that they can be used on‐line with negligible cost. This renders a more efficient computational method than traditional finite element methods at performing simulations of processes. One key issue of the proposed method is the efficient computation of the parametric enrichments. These are computed and efficiently stored in memory by employing proper generalized decompositions. Although the presented method can be broadly applied, it is particularly well suited in manufacturing processes involving localized physics that depend on many parameters, such as welding. After introducing the vademecum‐generalized finite element method formulation, we present some numerical examples related to the simulation of thermal models encountered in welding processes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
Joris Vaillant Abderrahmane Kheddar Hervé Audren François Keith Stanislas Brossette Adrien Escande Karim Bouyarmane Kenji Kaneko Mitsuharu Morisawa Pierre Gergondet Eiichi Yoshida Suuji Kajita Fumio Kanehiro 《Autonomous Robots》2016,40(3):561-580
We describe the research and the integration methods we developed to make the HRP-2 humanoid robot climb vertical industrial-norm ladders. We use our multi-contact planner and multi-objective closed-loop control formulated as a QP (quadratic program). First, a set of contacts to climb the ladder is planned off-line (automatically or by the user). These contacts are provided as an input for a finite state machine. The latter builds supplementary tasks that account for geometric uncertainties and specific grasps procedures to be added to the QP controller. The latter provides instant desired states in terms of joint accelerations and contact forces to be tracked by the embedded low-level motor controllers. Our trials revealed that hardware changes are necessary, and parts of software must be made more robust. Yet, we confirmed that HRP-2 has the kinematic and power capabilities to climb real industrial ladders, such as those found in nuclear power plants and large scale manufacturing factories (e.g. aircraft, shipyard) and construction sites. 相似文献
9.
We consider a Riemann surface X defined by a polynomial f(x,y) of degree d, whose coefficients are chosen randomly. Hence, we can suppose that X is smooth, that the discriminant δ(x) of f has d(d−1) simple roots, Δ, and that δ(0)≠0, i.e. the corresponding fiber has d distinct points {y1,…,yd}. When we lift a loop 0∈γ⊂C−Δ by a continuation method, we get d paths in X connecting {y1,…,yd}, hence defining a permutation of that set. This is called monodromy.Here we present experimentations in Maple to get statistics on the distribution of transpositions corresponding to loops around each point of Δ. Multiplying families of “neighbor” transpositions, we construct permutations and the subgroups of the symmetric group they generate. This allows us to establish and study experimentally two conjectures on the distribution of these transpositions and on transitivity of the generated subgroups.Assuming that these two conjectures are true, we develop tools allowing fast probabilistic algorithms for absolute multivariate polynomial factorization, under the hypothesis that the factors behave like random polynomials whose coefficients follow uniform distributions. 相似文献
10.
We have designed a new symbolic-numeric strategy for computing efficiently and accurately floating point Puiseux series defined by a bivariate polynomial over an algebraic number field. In essence, computations modulo a well-chosen prime number p are used to obtain the exact information needed to guide floating point computations. In this paper, we detail the symbolic part of our algorithm. First of all, we study modular reduction of Puiseux series and give a good reduction criterion for ensuring that the information required by the numerical part is preserved. To establish our results, we introduce a simple modification of classical Newton polygons, that we call “generic Newton polygons”, which turns out to be very convenient. Finally, we estimate the size of good primes obtained with deterministic and probabilistic strategies. Some of these results were announced without proof at ISSAC’08. 相似文献