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Experimental studies and phase field modeling of microstructure evolution during solidification with electromagnetic stirring

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中国有色金属学会会刊：英文版 2010年第S3期20卷 774-780页

作者： p.GERALD TENNYSON p.KUMAR H.LAKSHMI G.pHANIKUMAR p.DUTTA Department of Metallurgical and Materials Engineering Indian Institute of Technology National Facility for Semisolid Forming Department of Mechanical EngineeringIndian Institute of Science

Thixocasting requires manufacturing of billets with non-dendritic *** alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic *** heat treatment was used to produce a transition from rosette to globular *** current and the duration of stirring were explored as control *** induction heating of the billet during stirring was quantified using experimentally determined thermal *** effect of processing parameters on the dendrite fragmentation was *** computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process.A non-isothermal alloy solidification model was used for *** morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined *** scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system *** results were interpreted in the light of existing theories of microstructure refinement and globularisation.

关键词： electromagnetic stirring non-dendritic phase field modeling microstructure

Cryogenic and conventional milling of AZ91 magnesium alloy

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Journal of Magnesium and Alloys 2024年第6期12卷 2503-2519页

作者： Vikas Marakini Srinivasa pai p Gururaj Bolar Bhaskara p Achar Department of Mechanical Engineering Nitte(Deemed to be University)NMAM Institute of Technology(NMAMIT)Nitte 574110India Department of Mechanical and Industrial Engineering Manipal Institute of TechnologyManipal Academy of Higher EducationManipal 576104India

Use of magnesium is the need of the hour due to its low density as well as its high strength-to-weight and stiffness-to-weight ratio *** study focuses on the effectiveness of liquid nitrogen(LN_(2))assisted cryogenic machining on the surface integrity(SI)characteristics of AZ91 magnesium *** milling using uncoated carbide inserts have been performed under liquid nitrogen(LN_(2))assisted cryogenic condition and compared with conventional(dry)*** are performed using machining parameters in terms of cutting speeds of 325,475,625 m/min,feed rates of 0.05,0.1,0.15 mm/teeth and depth of cuts of 0.5,1,1.5 mm *** significant surface integrity characteristics such as surface roughness,microhardness,microstructure,and residual stresses have been *** of SI characteristics with respect to milling parameters have been identified using statistical technique such as ANOVA and signal-to-noise(S/N)ratio ***,the multi criteria decision making(MCDM)techniques such as additive ratio assessment method(ARAS)and complex proportional assessment(COpRAS)have been utilized to identify the optimal conditions for milling AZ91 magnesium alloy under both dry and cryogenic *** of LN_(2)during machining,resulted in reduction in machining temperature by upto 29%with a temperature drop from 251.2℃under dry condition to 178.5℃in cryogenic *** showed the advantage of performing cryogenic milling in improving the surface integrity to a significant *** machining considerably minimized the roughness by upto 28%and maximised the microhardness by upto 23%,when compared to dry *** speed has caused significant impact on surface roughness(95.33%-dry,92.92%-cryogenic)and surface microhardness(80.33%-dry,82.15%-cryogenic).Due to the reduction in machining temperature,cryogenic condition resulted in compressive residual stresses(maximumσ║=-113 Mpa)on the alloy *** indicate no

关键词： Magnesium alloy Cryogenic machining Roughness Microhardness Microstructure Residual stress Multi criteria decision making

Restructuring of plasmonic nanoparticle aggregates with arbitrary particle size distribution in pulsed laser fields

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Chinese physics B 2016年第11期25卷 563-570页

作者： A E Ershov A p Gavrilyuk S V Karpov S p polyutov Institute of Computational Modeling Russian Academy of SciencesKrasnoyarsk 660036Russia L.V.Kirensky Institute of physics of the Russian Academy of Sciences Krasnoyarsk 660036Russia Siberian Federal University Krasnoyarsk 660028Russia Siberian State Aerospace University Krasnoyarsk 660037Russia

We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles（resonant domains） in large colloidal nanoparticle aggregates having different interparticle gaps and particle size *** processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle *** describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action,we introduce the factor of spectral *** on calculation of changes in thermodynamic,mechanical,and optical characteristics of the domains,the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps,an average particle size,and the degree of *** in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of *** obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.

关键词： resonant arbitrary pulsed dipole manifestation alterations extinction remaining aggregate colloidal

Atomic-scale simulations of material behaviors and tribology properties for BCC metal film

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Chinese physics B 2016年第1期25卷 412-418页

作者： H D Aristizabal p A parra p Lopez E Restrepo-parra pCM Computational Applications Universidad Nacional de Colombia-Sede ManizalesA.A.127ManizalesColombi Universidad Cató1ica de Manizales A.A.357ManizalesColombia

This work has two main purposes：（i） introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and （ii） providing a better understanding of instrumented indentation measurements, presenting an example of nanoindentation and scratch test simulations. To reach these purposes, three-dimensional molecular dynamics （MD） simulations of nanoindentation and scratch test technique were carried out for generic thin films that present BCC crystalline structures. Structures were oriented in the plane （100） and placed on FCC diamond substrates. A pair wise potential was employed to simulate the interaction between atoms of each layer and a repulsive radial potential was used to represent a spherical tip indenting the sample. Mechanical properties of this generic material were obtained by varying the indentation depth and dissociation energy. The load-unload curves and coefficient of friction were found for each test; on the other hand, dissociation energy was varied showing a better mechanical response for films that present grater dissociation energy. Structural change evolution was observed presenting vacancies and slips as the depth was varied.

关键词： molecular dynamics pair wise potential repulsive radial potential dissociation energy

Internal valves in populations of Meridion circulare from the A’er Mountain region of northeastern China:Implications for taxonomy and systematics

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Journal of Systematics and Evolution 2011年第5期49卷 486-494页

作者： J.p.KOCIOLEK Department of Ecology and Evolutionary Biology University of Colorado Museum of Natural History University of Colorado

A population of Meridion circulare ***(Greville) *** from Inner Mongolia was found to produce Innenschalen or internal *** of this population with light and scanning electron microscopy showed morphological differentiation between vegetative and spore *** valves typically bear costae and one rimoportula at the *** lack costae and have two rimoportulae,one at the headpole and the other at the *** is plasticity in the production of valve morphologies,and a variety of vegetative valve and spore combinations are *** population of *** *** has initial valves of over 90 μm in length,and all of the initial cells encountered are acostate and bear two *** observations suggest that either spores are the product of sexual reproduction,or that initial valves may be produced parthenogenetically in *** as products of the sexual process have not been reported in diatoms previously,and parthenogenesis in Meridion was reported previously but discounted in other published *** plasticity of valve morphologies expressed in *** ***,between vegetative valves and spores(and back) across a short temporal period suggests that diatoms can alter their cell wall structure dramatically and quickly in response to external variables.

关键词： Bacillariophyceae diatom Innenschalen internal valves Meridion systematics.

OpTIMAL pRICING OF A pERSONALIZED pRODUCT

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Journal of Systems Science and Systems Engineering 2008年第1期17卷 30-35页

作者： Suresh p.SETHI School of Management The University of Texas at Dallas 800 W.Campbell Rd.RichardsonTX 75080

This paper deals with optimal pricing of a personalized product such as a personal portrait or photo. A new model of the pricing structure inspired by two real-life cases is introduced to the literature and solved to obtain optimal photo sitting fees and the final product price. A sensitivity analysis with respect to the problem parameters is performed.

关键词： personalized product pricing salvage loss

Feature-Based Aggregation and Deep Reinforcement Learning:A Survey and Some New Implementations

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IEEE/CAA Journal of Automatica Sinica 2019年第1期6卷 1-31页

作者： Dimitri p.Bertsekas the Department of Electrical Engineering and Computer Science and the Laboratory for Information and Decision SystemsMassachusetts Institute of Technology

In this paper we discuss policy iteration methods for approximate solution of a finite-state discounted Markov decision problem, with a focus on feature-based aggregation methods and their connection with deep reinforcement learning schemes. We introduce features of the states of the original problem, and we formulate a smaller "aggregate" Markov decision problem, whose states relate to the features. We discuss properties and possible implementations of this type of aggregation, including a new approach to approximate policy iteration. In this approach the policy improvement operation combines feature-based aggregation with feature construction using deep neural networks or other calculations. We argue that the cost function of a policy may be approximated much more accurately by the nonlinear function of the features provided by aggregation, than by the linear function of the features provided by neural networkbased reinforcement learning, thereby potentially leading to more effective policy improvement.

关键词： Reinforcement learning dynamic programming Markovian decision problems aggregation feature-based architectures policy iteration deep neural networks rollout algorithms

The role of the Mg_(17)Al_(12)-phase in the high-pressure die-cast magnesium-aluminum alloy system

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Journal of Magnesium and Alloys 2023年第11期11卷 4235-4246页

作者： J.p.Weiler Meridian Lightweight Technologies Canada

The Mg_(17)Al_(12)β-phase is highly influential to the performance of magnesium-aluminum high-pressure die-casting alloys. Numerous studies have investigated the effect of this phase on the room temperature and elevated-temperature mechanical properties as well as the corrosion,flammability, thermal conductivity and castability performance. This work summarizes the results of these works, as well as the studies that describe control of the Mg_(17)Al_(12)-phase through alloying additions that modify the microstructure and resulting alloy performance. The results of this work can be used as a basis for the development of alloying additions that enable modifications to the performance of high-pressure die-cast magnesium-aluminum-based alloys.

关键词： Magnesium alloys HpDC Alloy development properties

Surface plasmon oscillations in a semi-bounded semiconductor plasma

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plasma Science and Technology 2018年第2期20卷 76-81页

作者： M SHAHMANSOURI A p MISRA Department of physics Faculty of ScienceArak University Department of Mathematics Siksha BhavanaVisva-Bharati University

We study the dispersion properties of surface plasmon（Sp） oscillations in a semi-bounded semiconductor plasma with the effects of the Coulomb exchange（CE） force associated with the spin polarization of electrons and holes as well as the effects of the Fermi degenerate pressure and the quantum Bohm *** from a quantum hydrodynamic model coupled to the poisson equation,we derive the general dispersion relation for surface plasma *** results in this context are *** dispersion properties of the surface waves are analyzed in some particular cases of interest and the relative influence of the quantum forces on these waves are also studied for a nano-sized Ga As semiconductor *** is found that the CE effects significantly modify the behaviors of the Sp *** present results are applicable to understand the propagation characteristics of surface waves in solid density plasmas.

关键词： surface plasmon oscillations semiconductor plasma semi-bounded plasma