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1.
通过有限元方法分析不同加工路线和条件对Al-4.5Cu-2Mg合金微观形变行为的影响。合金采用4种不同的加工技术和条件制备,分别为有或无细化剂的常规重力铸造、流变铸造和SIMA工艺。以合金的光学显微结构作为代表性体积元(RVEs),采用两种不同的边界条件模拟合金在单轴载荷作用下的变形行为,最后将模拟的应力-应变行为与实验结果进行比较。结果表明,微观结构形态对应力和应变分布及承载能力具有显著影响,共晶相比α(Al)相能承受更高的载荷,具有较薄且均匀分布的共晶网络结构的球状α(Al)相能提供更好的应力和应变分布。因此,SIMA加工合金比其他技术加工合金拥有更好的应力和应变分布。最后,将该合金的模拟屈服强度与实验进行验证,结果具有较好的一致性。  相似文献   
2.
Asymmetric patchy Ag/Cu Janus nanoparticles (NPs) were synthesized via a “seed-mediated” approach. This is the first report of synthesis of nanometer sized metal-based Janus NPs without using complicated methods. Selective adsorption of the surfactant onto the seed NPs leads to the formation of Janus type structure. Subsequently the reduction potential of Ag+/Ag0 and Cu2+/Cu0 systems directs the formation of the “patch”. The patchy Janus NPs show significant antifungal activity towards a potent rice pathogen thus offering the prospect of future application in crop protection.  相似文献   
3.
The present exercise is an attempt to generalize a probability model referring to the waiting time distribution for conception in a mixed group of fecund females with two varying levels of fecundity, based on a census sample truncated at time T =t from the date of resumption of fecundity following an earlier conception (Biswas, 1975, Sankhya, Series B, 37, Part III). The generalization is made in two aspects, viz. instead of fixed conception rates, time-dependent rates decreasing with the age of the woman have been used. Additionally, unlike the model of Biswas (1975) consisting of two different fecund groups, three different levels of fecundity have been taken into consideration in this paper. Estimates of the proportion of fecund females over time, viz. πi(t) (i = 1, 2, 3) are attempted by the method of maximum likelihood on the basis of a census sample truncated at time T = t under the generalized set up.  相似文献   
4.
New algorithms are presented for power-system complex node voltage estimation, based on statistical linearization of power-flow equations and a least-squares criterion. To illustrate the algorithms a 7-bus power network is simulated on a computer and a comparison is made with estimates obtained through the conventional Taylor series approach.  相似文献   
5.
P BISWAS  R NARASIMHAN 《Sadhana》2012,37(1):149-169
In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip fields in a FCC single crystal are studied. Finite element simulations are performed within a mode I, plane strain modified boundary layer framework by prescribing the two term (K − T) elastic crack tip field as remote boundary conditions. The material is assumed to obey a rate-dependent crystal plasticity theory. The orientation of the single crystal is chosen so that the crack surface coincides with the crystallographic (010) plane and the crack front lies along [10[`1]][10\overline 1] direction. Solutions corresponding to different stress intensity rates [(K)\dot]\dot{{K}}, T-stress values and strain rate exponents m are obtained. The results show that the stress levels ahead of the crack tip increase with [(K)\dot]\dot{{K}} which is accompanied by gradual shrinking of the plastic zone size. However, the nature of the shear band patterns around the crack tip is not affected by the loading rate. Further, it is found that while positive T-stress enhances the opening and hydrostatic stress levels ahead of crack tip, they are considerably reduced with imposition of negative T-stress. Also, negative T-stress promotes formation of shear bands in the forward sector ahead of the crack tip and suppresses them behind the tip.  相似文献   
6.
The paper deals with the problem of rigorous modelling of flexible spacecraft and their stabilization. The attitude dynamics of the satellite bus and the equations for vibration of a flexible beam attached to it are derived. The complete system dynamics are given by a coupled set of ordinary and partial differential equations. The effects of controls applied on the. bus and/or on the flexible beam are investigated. It is shown that stabilization of the flexible spacecraft can be achieved by use of simple feedback controls.  相似文献   
7.
8.
The paper is motivated towards developing a generalized probability model describing the longevity of a system exposed to paired risks R1 and R2 which are dependent. The bivariate exponential model of Freund (1961) with failure times X and Y under risks R1 and R2 with a time-independent hazard rate set-up has been generalized by incorporating an additional age factor, t, as a variable. The hazard rates due to R1 and R2 have been changed from a to α(t) = αtα?1, and from β to β(f) = βtβ?1 where α,β > 0 which are Weibull hazard functions for α,β > 1. Further conditions are imposed such that α is changed to α' when R2 is off and β is changed to β' when R1 is off. The trivariate distribution of Freund so generalized has again been doubly truncated in the range a  t  b, for a, b > 0; and the conditional distribution of X and Y given t has been used to study the role of the component's age in the context of the system's survival under paired dependent risks in the finite age range.  相似文献   
9.
‘Georgia-Jet’ sweet potatoes were grown at CO2 concentrations of 354, 431, 506, and 659 ppm for 90 days. Elevated CO2 concentrations decreased protein, total carotenoids and insoluble dietary fiber. An increase in dry matter and a reddish-orange color was observed at 506 and 659 ppm CO2 concentrations. Sensory evaluation scores for flavor and moistness indicated that sweet potatoes grown under high CO2 concentrations were acceptable and not different from the control.  相似文献   
10.
The literature is replete with models that examine various aspects of cellular manufacturing (CM), such as optimisation of cell layouts. However, many firms may realise zero to marginal returns from CM. Given this uncertainty, the manager should first determine the value of CM to the firm before deploying it. Although traditional valuation models employing discounted cash flow analysis allow for uncertainty, they treat future investments as fixed when computing the investment’s present value. The real options (RO) logic of valuation allows the manager to exercise the option to invest in or abandon a project based on expected outcomes. Future investments are thus options. This paper presents an RO model for CM migration that addresses whether a firm should migrate to CM; and it prescribes the sequence of cell deployment, which has not been addressed in the literature. Our model is also much more transparent and accessible to practitioners, with an accompanying software tool for prospective users. Finally, we use simulation extensively to discover the drivers of the optimal cell deployment sequence. Our results show that there is a complex interplay between net present value, speed of cellularisation, inter-cell learning and volatility in terms of their influence on the cell sequence.  相似文献   
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