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1.
Hyungson Ki Jyoti Mazumder Pravansu S. Mohanty 《Metallurgical and Materials Transactions A》2002,33(6):1817-1830
A three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor
(L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free
surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling, and multiple reflections, are considered and applied
to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes
equation and energy equation. Both thermocapillary force and recoil pressure, which are the major driving forces for the melt
flow, are incorporated in the formulation. For melting and solidification processes at the solid/liquid (S/L) interface, the
mixture continuum model has been employed. The article consists of two parts. This article (Part I) presents the model formulation
and discusses the effects of evaporation, free surface evolution, and multiple reflections on a steady molten pool to demonstrate
the relevance of these interfacial phenomena. The results of the full keyhole simulation and the experimental verification
will be provided in the companion article (Part II). 相似文献
2.
Measurements in the CROCUS reactor at EPFL, Lausanne, are reported for the critical water level and the inverse reactor period for several different sets of delayed supercritical conditions. The experimental configurations were also calculated by four different calculation methods. For each of the supercritical configurations, the absolute reactivity value has been determined in two different ways, viz.: (i) through direct comparison of the multiplication factor obtained employing a given calculation method with the corresponding value for the critical case (calculated reactivity: ρcalc); (ii) by application of the inhour equation using the kinetic parameters obtained for the critical configuration and the measured inverse reactor period (measured reactivity: ρmeas). The calculated multiplication factors for the reference critical configuration, as well as ρcalc for the supercritical cases, are found to be in good agreement. However, the values of ρmeas produced by two of the applied calculation methods differ appreciably from the corresponding ρcalc values, clearly indicating deficiencies in the kinetic parameters obtained from these methods. 相似文献
3.
Jyoti Parikh 《Energy》1985,10(7):793-804
Since many of the factors related to rural energy systems are gradually being quantified, there is a need to construct a model that integrates a number of these factors simultaneously in a consistent framework. Therefore, a general linear programming model is developed to capture energy and agricultural interactions existing in the rural areas of developing countries. Energy used for agriculture includes fertilizers, irrigation, and mechanization. Several technological choices of each of the above are considered and so are several crop commodities, several types of livestock, and farmers of different income groups along with their assets, i.e. land holdings, livestock, etc. The by-products of agriculture, i.e. biomass, such as crop residues, animal dung, wood, etc., can be used to generate energy. On the demand side the use of them for feed, fuel, and fertilizer must be considered. Thus, the household sector (which is the largest user of noncommercial energy), as well as the rural industries sector, is intimately related to the agriculture sector. Twelve different energy sources and several conversion technologies, such as biogas, charcoal kilns, alcohol distilleries, etc., are considered. The model is applicable to low-income, biomass-scarce developing countries. However, different types of countries will require different approximations, and their needs for detailing some aspects or other may vary. The model is suitable for policy purposes because it considers several income groups separately and considers how different changes affect each of them. 相似文献
4.
5.
Many of the targeted applications for powder-metallurgy materials, particularly in the automotive industry, undergo cyclic
loading. It is, therefore, essential to examine the fatigue mechanisms in these materials. The mechanisms of fatigue-crack
initiation and propagation in ferrous powder-metallurgy components have been investigated. The fatigue mechanisms are controlled
primarily by the inherent porosity present in these materials. Since most, if not all, fatigue cracks initiate and propagate
at the specimen surface, surface replication was used to determine the role of surface porosity in relation to fatigue behavior.
Surface replication provides detailed information on both initiation sites and on the propagation path of fatigue cracks.
The effect of microstructural features such as pore size and pore shape, as well as the heterogeneous microstructure on crack
deflection, was examined and is discussed. Fracture surfaces were examined to elucidate a mechanistic understanding of fatigue
processes in these materials. 相似文献
6.
A review is provided of the use of analytical models and two dimensional (2D) and three dimensional (3D) microstructure based
FEM models to accurately predict the properties of particle reinforced composite materials. It is shown that analytical models
do not account for the microstructural factors that influence the mechanical behavior of the material. 2D models do capture
the anisotropy in deformation behavior induced by anisotropy in particle orientation. The experimentally-observed dependence
of Young's modulus and tensile strength is confirmed by the 2D microstructure-based numerical model. However, because of the
2D stress state, a realistic comparison to actual experimental values is not possible. A serial sectioning process can be
used to reproduce and visualize the 3D microstructure of particle reinforced metal matrix composites. The 3D microstructure-based
FEM accurately represents the alignment, aspect ratio, and distribution of the particles. Comparison with single particle
and multiparticle models of simple shape (spherical and ellipsoidal) shows that the 3D microstructure-based approach is more
accurate in simulating and understanding material behavior. 相似文献
7.
Effect of Li+ ions on structure,properties, and actuation of cellulose electro‐active paper actuator
We have reported an electro‐active paper actuator from regenerated cellulose. After dissolving cellulose fibers with a solution of lithium chloride in N,N‐dimethylacetamide, cellulose was regenerated by combining distillation of cellulose solution along with washing with the mixture of deionized water, isopropyl alcohol, and running water. However, the effect of Li+ ions on structure, properties, and the actuation behavior of the actuator was not studied. This article describes the changes in these parameters when the Li+ ions are removed by subjecting it to different running water exposure time. The structure and properties of cellulose electro‐active paper and its actuation behavior were studied. As Li+ ions content reduced from 4354.17 to 10.26 ppm by increasing the exposure time of running water, crystallinity, Young's modulus, and bending displacement decreased. Details about the investigation have been explained. This elimination of ions is important to increase the piezoelectric effect in EAPap by decreasing the ion migration effect. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
8.
RK Dhiman AK Seth S Jain YK Chawla JB Dilawari 《Canadian Metallurgical Quarterly》1998,43(6):1311-1316
Results of eight multicenter, randomized, placebo-controlled, double-blind, parallel-group studies were pooled to assess the efficacy of the angiotensin II-receptor blocker irbesartan over the dose range of 1 to 900 mg. A total of 2955 adults with a seated diastolic blood pressure of 95 to 110 mm Hg were randomized to treatment with oral irbesartan once daily or placebo for 6 to 8 weeks. Office blood pressure was measured at trough (24+/-3 hours after the last dose) and peak (3+/-1 hours after the last dose) by mercury sphygmomanometry. Demographic characteristics (mean blood pressure; 151/101 mm Hg; mean age, 54 years; 63% male; and 82% white) were similar across all dose groups. After the groups were pooled, antihypertensive efficacy was assessed by therapeutic response (trough seated diastolic blood pressure <90 mm Hg or a reduction from baseline of > or = 10 mm Hg) and by modeling of the maximum reductions in trough and peak seated diastolic and systolic blood pressure. Antihypertensive effects increased with increasing doses and reached a plateau at > or = 300 mg. Irbesartan 150 mg provided placebo-subtracted reductions in trough seated systolic and diastolic blood pressure of approximately 8 and approximately 5 mm Hg, respectively, with 56% of patients displaying a favorable response. In conclusion, irbesartan provides clinically significant blood pressure lowering, with a clear relationship between (log) dose and antihypertensive effect. 相似文献
9.
Quantification of response time in poly(vinyl alcohol)–metal complex thermochromic polymeric systems
Thermochromic poly(vinyl alcohol) (PVA)‐based material was synthesized and an extensive study of its thermochromic behavior with respect to response time was carried out. It was observed that it is possible to manipulate the response time by keeping control over chemical and physical parameters. The response time, which is the most important property of a smart material, has in this case been found to be very much influenced by rate of heat transfer into the material. Different compositions of the thermochromic material and their corresponding response time with respect to rate of heat transfer were studied and correlated. First, a theoretical equation was derived and later on it was experimentally verified to quantify the response time in PVA–metal complex‐based thermochromic systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4832–4834, 2006 相似文献
10.