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461.
Explosive welding technique is widely used in many industries. This technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding methods. Interlayer plays an important role to improve the welding quality and control energy loss during the collision process. In this paper, the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium interlayer. Microstructure details of welded composite plate were observed through optical and scanning electron microscope. Interlayer-base plate interface morphology showed a wavy structure with solid melted regions inside the vortices. Moreover, the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of Cu–Ti, i.e. CuTi, Cu2Ti, CuTi2, Cu4Ti, etc. To study the mechanical properties of composite plates, mechanical tests were conducted, including the tensile test, bending test, shear test and Vickers hardness test. Numerical simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method, Euler and Arbitrary Lagrangian-Eulerian method. The multi-physics process of explosive welding, including detonation, jetting and interface morphology, was observed with simulation. Moreover, simulated plastic strain, temperature and pressure profiles were analysed to understand the welding conditions. Simulated results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent plates. At the collision point, both alloys behave like fluids, resulting in the formation of a wavy morphology with vortices, which is in good agreement with the experimental results. 相似文献
462.
We present two frameworks for designing random search methods for discrete simulation optimization. One of our frameworks is very broad (in that it includes many random search methods), whereas the other one considers a special class of random search methods called point‐based methods, that move iteratively between points within the feasible region. Our frameworks involve averaging, in that all decisions that require estimates of the objective function values at various feasible solutions are based on the averages of all observations collected at these solutions so far. Also, the methods are adaptive in that they can use information gathered in previous iterations to decide how simulation effort is expended in the current iteration. We show that the methods within our frameworks are almost surely globally convergent under mild conditions. Thus, the generality of our frameworks and associated convergence guarantees makes the frameworks useful to algorithm developers wishing to design efficient and rigorous procedures for simulation optimization. We also present two variants of the simulated annealing (SA) algorithm and provide their convergence analysis as example application of our point‐based framework. Finally, we provide numerical results that demonstrate the empirical effectiveness of averaging and adaptivity in the context of SA. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012 相似文献
463.
This paper addresses a two‐machine open shop scheduling problem, in which the machines are not continuously available for processing. The processing of an operation affected by a non‐availability interval can be interrupted and resumed later. The objective is to minimize the makespan. We present two polynomial‐time approximation schemes, one of which handles the problem with one non‐availability interval on each machine and the other for the problem with several non‐availability intervals on one of the machines. Problems with a more general structure of the non‐availability intervals are not approximable in polynomial time within a constant factor, unless . © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006 相似文献
464.
Gregory A. Daddis 《战略研究杂志》2013,36(3):357-384
This article examines the relationship between the White House and the US Military Assistance Command, Vietnam (MACV) during President Richard M. Nixon's administration. It argues that dysfunctional civil-military relations between 1969 and 1972 undermined the implementation of a sound military strategy during the United States' withdrawal from South Vietnam as Nixon attempted to achieve ‘peace with honor’ during the Vietnam War's final campaigns. By 1972, the relationship between the White House and MACV headquarters had reached the nadir of civil-military relations during the Southeast Asian conflict and had served to undercut the United States' ability to effectively disengage from a long and bitterly contested war. 相似文献
465.
Ross A. Kennedy 《战略研究杂志》2013,36(7):1058-1070
The books under review here, by Robert F. Hannigan, John A. Thompson, Trygve Throntveit, and Adam Tooze, offer an interpretation of Wilsonian internationalism and what happened to it in the 1920s. For Tooze and Hannigan, Wilsonianism was primarily a project to attain American predominance in the world. For Throntveit, Wilsonian internationalism constituted a pragmatic yet radical effort to end competitive power politics. Thompson disagrees with these arguments and asserts that the key to understanding US policy lay in how US leaders conceptualized American power. Thompson’s interpretation is especially compelling in explaining why the United States failed to engage itself more assertively in international affairs in the 1920s – a failure Tooze suggests undermined the viability of the postwar international system. 相似文献
466.
467.
Nicholas A Lambert 《战略研究杂志》2013,36(2):272-297
The Fisher naval revolution of 1904–10 represented a deliberate attempt to achieve defense transformation to bolster Britain's pretensions to global naval supremacy. The vision called for smaller, more capable forces to do the work of larger, more expensive conventional formations. It consisted of three main elements. First, the replacement of the traditional station fleet system for protecting overseas interests by rapid deployment forces comprised of battlecruisers that could be ‘maneuvered’ by wireless to combat specific enemy threats. Second, at home, instead of a sea control strategy based upon a superior battle-fleet, a sea denial strategy based on flotilla defense commanded and controlled from London via wireless. The third element of the Fisher revolution depended upon ‘plunging’, or shaping and directing technological change through a special relationship with armaments firms. A sophisticated information-communications network was integral to the revolution. 相似文献
468.
James A. Nathan 《Small Wars & Insurgencies》2013,24(2):243-253
Robert S. McNamara [and Brian Van De Mark,] In Retrospect: The Tragedy and Lessons of Vietnam, NewYork:NewYork Times Books, Random House, 1995. Pp.xviii + 414. $27.50. ISBN 08129–2523–8. 相似文献
469.
A recent article, ‘Rage Against the Machines’, does a disservice to the debate over what explains counterinsurgency (COIN) success. While it establishes a negative correlation between the diffusion of military mechanization in the state system and COIN success, its theoretical argument does not hold up under close scrutiny and its micro-case comparison of two units in Iraq during 2003–2004 ignores obvious counter-examples and factors that influence COIN success, such as leadership. A deeper inquiry would have revealed that there is much more to COIN success than simply not having access to vehicles. 相似文献
470.
David A. Patten 《Small Wars & Insurgencies》2013,24(5):879-906
Taking insurgency sponsorship as an instrument states have available for achieving foreign policy objectives, I consider how state-sponsors could best manipulate their support to maximize control of the proxy group. Building on research that models the state-sponsor–insurgent relationship using a principal–agent framework, I identify two key vulnerabilities to which the state-sponsor is exposed: adverse selection and agency slack. As an original contribution to the literature on state-sponsorship of insurgency, I articulate reasons why certain forms of support would be most conducive to overcoming these problems and illustrate how South Africa and Iran used those kinds of support to influence the behavior of their proxies, RENAMO and Hezbollah. Additionally, I consider how this principal–agent analysis of insurgency sponsorship also could apply when the principal is an international terrorist organization such as al Qaeda. Finally, I address the relevance of these ideas to two contemporary conflicts taking place in Syria and the Congo. 相似文献