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Particle shape consideration in numerical simulation of assemblies of irregularly shaped particles

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Particuology 2011年第4期9卷 387-397页

作者： Saba Abedi ali asghar mirghasemi School of Civil Engineering College of Engineering University of Tehran

The mechanical behavior of granular materials depends much on the shape of the constituent particles. Therefore appropriate modeling of particle, or grain, shape is quite important. This study employed the method of direct modeling of grain shape （Matsushima ＆ Saomto, 2002）, in which, the real shape of a grain is modeled by combining arbitrary number of overlapping circular elements which are connected to each other in a rigid way. Then, accordingly, a discrete-element program is used to simulate the assembly of grains. In order to measure the effects of grain shape on mechanical properties of assembly of grains, three types of grains-high angular grains, medium angular grains and round grains are considered where several biaxial tests are conducted on assemblies with different grain types, The results show that the angularity of grains greatly affects the behavior of granular soil.

关键词： Discrete element method Granular soil Angularity Confining pressure

Numerical and experimental direct shear tests for coarse-grained soils

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Particuology 2009年第1期7卷 83-91页

作者： Ahad Bagherzadeh-Khalkhali ali asghar mirghasemi School of Civil Engineering College of EngineeringUniversity of TehranTehranIran

The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method （DEM）. Experimental tests on such soil specimens were based on using the techniques designated as ＂parallel＂ and ＂scalping＂ to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.

关键词： Discrete element method Direct shear test Micromechanics Coarse-grained soil Shear strength

Micromechanics of breakage in sharp-edge particles using combined DEM and FEM

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Particuology 2008年第5期6卷 347-361页

作者： Ahad Bagherzadeh-Khalkhali ali asghar mirghasemi Soheil Mohammadi School of Civil Engineering University College of EngineeringUniversity of Tehran

By combining DEM （Discrete Element Method） and FEM （Finite Element Method）, a model is established to simulate the breakage of twodimensional sharp-edge particles, in which the simulated particles are assumed to have no cracks. Particles can, however, crush during different stages of the numerical analysis, if stress-based breakage criteria are fulfilled inside the particles. With this model, it is possible to study the influence of particle breakage on macro- and micro-mechanical behavior of simulated angular materials. Two series of tests, with and without breakable particles, are simulated under different confining pressures based on conditions of biaxial tests. The results, presented in terms of micromechanical behavior for different confining pressures, are compared with macroparameters. The influence of particle breakage on microstructure of sharp-edge materials is discussed and the related confining pressure effects are investigated. Breakage of particles in rockfill materials are shown to reduce the anisotropy coefficients of the samples and therefore their strength and dilation behaviors.

关键词： DEM FEM Particle breakage Rockfill Micromechanics Anisotropy Confining pressure

Resolving the Routine Presence of Kyanite, Andalusite and Sillimanite across a Region using Foliation Intersection/Inflection Axes Preserved in Porphyroblasts, Petrographic Observations and Thermobarometry

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Acta Geologica Sinica(English Edition) 2012年第5期86卷 1241-1250页

作者： asghar ali School of Earth and Environmental Science James Cook University Townsville Queensland 4811 Australia Department of Geology University of Peshawar Peshawar Khyber Pakhtunkhwa 25120 Pakistan

Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al2 SiO5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al2SiO5 triple point. All three Al2SiO5 polymorphs grew in the Chl, Bt, Ms, Grt, St, Pl and Crd bearing Ordovician Clayhole Schist in Balcooma, northeastern Australia separately along a looped P-T-t-D path that swaps from clockwise to anticlockwise in the tectono-metamorphic history of the region. Kyanite grew during crustal thickening in an Early Silurian Orogenic event followed by decompression/heating, andalusite and fibrolitic sillimanite growth during Early Devonian exhumation.

关键词： Al2SiO5 triple point microtextures foliation intersection/inflection axes Barrovian sequence episodic porphyroblast growth

Energy Efficiency in ARQ-Based Multi-Hop Systems and the Tradeoff with Throughput

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China Communications 2023年第6期20卷 60-71页

作者： ali asghar Haghighi Electrical and Computer Engineering Group Golpayegan College of EngineeringIsfahan University of TechnologyGolpayegan 87717-67498Iran

The minimum energy per bit(EPB)as the energy efficiency(EE)metric in an automatic retransmission request(ARQ)based multi-hop system is analyzed under power and throughput *** ARQ protocols including type-I(ARQ-I)and repetition redundancy(ARQ-RR)are considered and expressions for the optimal power allocation(PA)are *** the obtained optimal powers,the EE-throughput tradeoff(EETT)is analyzed and the EETT closed-form expressions for both ARQ protocols and in arbitrary average channel gain values are *** is shown that how different throughput requirements,especially the high levels,affect the EE ***,asymptotic analysis is made in the feasible high throughput values and lower and upper EETT bounds are derived for ARQ-I *** evaluate the EE a distributed PA scenario,as a benchmark,is presented and the energy savinggain obtained from the optimal PA in comparison with the distributed PA for ARQ-I and ARQ-RR protocols is discussed in different throughput values and node locations.

关键词： ARQ cooperative relaying energy efficiency green communication multi-hop systems routing algorithms throughput analysis

Rare Earth Elements Geochemistry of Sheikh-Marut Laterite Deposit,NW Mahabad,West-Azarbaidjan Province,Iran

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Acta Geologica Sinica(English Edition) 2013年第1期87卷 176-185页

作者： ali ABEDINI ali asghar CALAGARI Geology Department Faculty of SciencesUrmia University Geology Department Faculty of Natural SciencesUniversity of Tabriz

Laterite deposit at Sheikh-Marut （NW occurred within middle-upper Permian carbonate Mahabad, West-Azarbaidjan province, Iran） rocks. It consists of seven stratiform and/or discontinuous lenticular layers extending over 4.2 km in length and having thicknesses ranging from 3 to 14 m. Mineralogical data show that the ores contain kaolinite and hematite as major and boehmite, diaspore, halloysite, amesite, anatase, and muscovite-illite as minor mineral phases. The computed Ce anomaly values in the ores range from 0.05 to 20.84. Conservative index （e.g., Eu/Eu＊） suggests that this deposit is a product of alteration and weathering of basaltic rocks. Rhythmic increment of EREE values of the ores with approaching to the carbonate bedrocks shows an in-situ occurrence of lateritization processes. Mass change calculations of elements indicate that two competing processes namely leaching and fixation were the major regulating factors in concentration variation of REEs （La-Lu） in this deposit. The obtained results show that pH increase of weathering solutions by carbonate bedrocks, existence of organic matters, and the degree of comlexation with organic ligands played remarkable role in distribution of REEs during lateritization. Further geochemical considerations revealed that secondary phosphates, Mn-oxides and -hydroxides, diaspore, and anatase were the potential hosts for REEs in this deposit.

关键词： laterite geochemistry REEs Sheikh-Marut deposit Mahabad Iran

Survey on Video Security:Examining Threats,Challenges,and Future Trends

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Computers, Materials & Continua 2024年第9期80卷 3591-3635页

作者： ali asghar Amna Shifa Mamoona Naveed asghar Department of Artificial Intelligence Faculty of ComputingThe Islamia University of BahawalpurBahawalpur63100Pakistan School of Computer Science College of Science and EngineeringUniversity of GalwayGalwayH91 TK33Ireland

Videos represent the most prevailing form of digital media for communication,information dissemination,and ***,theirwidespread use has increased the risks of unauthorised access andmanipulation,posing significant *** response,various protection approaches have been developed to secure,authenticate,and ensure the integrity of digital *** study provides a comprehensive survey of the challenges associated with maintaining the confidentiality,integrity,and availability of video content,and examining how it can be *** then investigates current developments in the field of video security by exploring two critical research ***,it examine the techniques used by adversaries to compromise video data and evaluate their *** these attack methodologies is crucial for developing effective defense ***,it explores the various security approaches that can be employed to protect video data,enhancing its transparency,integrity,and *** compares the effectiveness of these approaches across different use cases,including surveillance,video on demand(VoD),and medical videos related to disease ***,it identifies potential research opportunities to enhance video data protection in response to the evolving threat *** this investigation,this study aims to contribute to the ongoing efforts in securing video data,providing insights that are vital for researchers,practitioners,and policymakers dedicated to enhancing the safety and reliability of video content in our digital world.

关键词： Attacks threats security services video manipulation video security

Thermophoresis and concentration effects in a fourth grade peristaltic flow with convective walls

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Journal of Central South University 2017年第7期24卷 1654-1662页

作者： ali Aamir asghar S Awais M Department of Mathematics COMSATS Institute of Information TechnologyAttock 43600Pakistan Department of Mathematics COMSATS Institute of Information TechnologyIslamabad 44000Pakistan Department of Mathematics King Abdulaziz UniversityJeddah 21432Saudi Arabia

In this investigation,we have studied the peristaltic fluid flow in an asymmetric channel with convective *** grade fluid model has been utilized in view of the fact that the results of all other differential type models can be deduced as the special *** effects of heat and mass transfer are *** thermophoresis effects occur in the energy *** heat and mass boundary conditions have been given special *** wave length and low Reynolds number approximations are utilized for the *** analytic solutions for the velocity,temperature and concentration profiles are calculated using perturbation technique and elaborated in the form of graphical observations for various physical quantities.

关键词： fourth grade fluid convective boundary conditions pumping and trapping peristalsis

Slip effects on streamline topologies and their bifurcations for peristaltic flows of a viscous fluid

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Chinese Physics B 2014年第6期23卷 341-352页

作者： Z.asghar N.ali Department of Mathematics and Statistics International Islamic University

We discuss the effects of the surface slip on streamline patterns and their bifurcations for the peristaltic transport of a Newtonian fluid. The flow is in a two-dimensional symmetric channel or an axisymmetric tube. An exact expression for the stream function is obtained in the wave frame under the assumptions of long wavelength and low Reynolds number for both cases. For the discussion of the particle path in the wave frame, a system of nonlinear autonomous differential equations is established and the methods of dynamical systems are used to discuss the local bifurcations and their topological changes. Moreover, all types of bifurcations and their topological changes are discussed graphically. Finally, the global bifurcation diagram is used to summarize the bifurcations.

关键词： viscous fluid slip condition streamline topologies bifurcation