• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.320-326
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• 1999

In rapidly solidified $Al_{92-x}Nd_8$(Cu,Ag)x ($0{\leq}X{\leq}10at%$) alloys, amorphous single phases were obtained in the ranges of $Oat%{\leq}X{\leq}4at%$ for Al-Nd-Cu system and $Oat%{\leq}X{\leq}6at%$ for Al-Nd-Ag system, respectively. Mesoscopic structures consisted of amorphous and crystalline phases were formed above solute ranges. It was founded that the mesoscopic structures were also formed near 1st exothermic peak on DSC curve by aging in amorphous single phase alloys. For example, amorphous $Al_{92-x}Nd_8$(Cu,Ag)x (X=2.4at%) alloys containing nanoscale Al particles and compounds, i.e., mesoscopic structure, exhibited higher tensile fracture strength(${\sigma}_f$) than those of amorphous single phase alloys with the same composition. The ${\sigma}_f$ showed a maximum value in the $V_f$ ranges of 10~15%. The reason is presumed that the nanoscale precipitates which have higher mechanical strength compared with the amorphous phase with the same composition act as an effective resistance to shear deformation of the amorphous matrix.

• Interaction and multiscale mechanics
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• v.3 no.1
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• pp.23-37
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• 2010

Concrete is a heterogeneous material consisting of coarse aggregate, mortar matrix and interfacial zones at the meso level. Though studies have been done to interpret the fracture process in concrete using meso level models, not much work has been done for simulating the macroscopic behaviour of reinforced concrete structures using the meso level models. This paper presents a procedure for the mesoscopic analysis of reinforced concrete beams using a modified micro truss model. The micro truss model is derived based on the framework method and uses the lattice meshes for representing the coarse aggregate (CA), mortar matrix, interfacial zones and reinforcement bars. A simple procedure for generating a random aggregate structure is developed using the constitutive model at meso level. The study reveals the potential of the mesoscopic numerical simulation using a modified micro truss model to predict the nonlinear response of reinforced concrete structures. The modified micro truss model correctly predicts the load-deflection behaviour, crack pattern and ultimate load of reinforced concrete beams failing under different failure modes.

• Polymer(Korea)
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• v.30 no.6
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• pp.453-463
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• 2006

Molecular simulation is an exceptionally useful method for predicting self-assembled structures in various macromolecular systems, enlightening the origins of many interesting molecular events such as protein folding, polymer micellization, and ordering of molten block copolymer. The length scales of those events ranges widely from sub-nanometer scale to micron-scale or to even larger, which is the main obstacle to simulate all the events in an ab initio principle. In order to detour this major obstacle in the molecular simulation approach, a molecular model can be rebuilt by sacrificing some unimportant molecular details, based on two different perspectives with respect to the resolution of model. These two perspectives are generally referred to as 'atomistic' and 'mesoscopit'. This paper reviews various simulation methods for macromolecular self-assembly in both atomistic and mesoscopic perspectives.

• Structural Engineering and Mechanics
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• v.19 no.5
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• pp.519-533
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• 2005

The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

• Computers and Concrete
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• v.13 no.2
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• pp.187-207
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• 2014

This paper mainly discusses the influence of the aggregate properties including grading, shape, content and distribution on the chloride diffusion coefficient, as well as the initiation time of steel corrosion from a probabilistic point of view. Towards this goal, a simulation method of random aggregate structure (RAS) based on elliptical particles and a procedure of finite element analysis (FEA) at meso-scale are firstly developed to perform the analysis. Next, the chloride diffusion coefficient ratio between concrete and cement paste $D_{app}/D_{cp}$ is chosen as the index to represent the effect of aggregates on the chloride diffusion process. Identification of the random distribution of this index demonstrates that it can be viewed as actually having a normal distribution. After that, the effect of aggregates on $D_{app}/D_{cp}$ is comprehensively studied, showing that the appropriate properties of aggregates should be decided by both of the average and the deviation of $D_{app}/D_{cp}$. Finally, a case study is conducted to demonstrate the application of this mesoscopic method in predicting the initiation time of steel corrosion in reinforced concrete (RC) structures. The mesoscopic probabilistic method developed in this paper can not only provide more reliable evidences on the proper grading and shape of aggregates, but also play an important role in the probability-based design method.

• Journal of the Korean Vacuum Society
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• v.2 no.4
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• pp.433-438
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• 1993

전자의 파동성에 기인하는 여러 가지 양자간섭 현상을 연구하기 위하여, 금속의 미세고리구조을 제작하였다. 전자의 양자간섭과 가간섭 역충돌 효과에 의한 자기저항의 진동형상이 관측되었으며, 자기저항의 비주기 섭동 현상과 비국재현상도 관찰되어 중시적 전기 전도도의 일반식에 의하여 설명되었다. 또한 AlGaAs/GaAs 의 이차원 전자가스총을 이용한 고리구조도 제작되어, 양자 효과와 탄동적 수송의 영역에서 자기저항이 측정되었다.

• Computers and Concrete
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• v.15 no.4
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• pp.485-501
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• 2015

Cooling by the flow of water through an embedded cooling pipe has become a common and effective artificial thermal control measure for massive concrete structures. However, an extreme thermal gradient induces significant thermal stress, resulting in thermal cracking. Using a mesoscopic finite-element (FE) mesh, three-phase composites of concrete namely aggregate, mortar matrix and interfacial transition zone (ITZ) are modeled. An equivalent probabilistic model is presented for failure study of concrete by assuming that the material properties conform to the Weibull distribution law. Meanwhile, the correlation coefficient introduced by the statistical method is incorporated into the Weibull distribution formula. Subsequently, a series of numerical analyses are used for investigating the influence of the correlation coefficient on tensile strength and the failure process of concrete based on the equivalent probabilistic model. Finally, as an engineering application, damage and failure behavior of concrete cracks induced by a water-cooling pipe are analyzed in-depth by the presented model. Results show that the random distribution of concrete mechanical parameters and the temperature gradient near water-cooling pipe have a significant influence on the pattern and failure progress of temperature-induced micro-cracking in concrete.

• Structural Engineering and Mechanics
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• v.30 no.1
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• pp.99-117
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• 2008

This paper presents a comprehensive approach to the evaluation of macroscopic material parameters for natural stone and quarry masonry. To that end, a reliable non-linear material model on a meso-scale is developed to cover the random arrangement of stone blocks and quasi-brittle behaviour of both basic components, as well as the impaired cohesion and tensile strength on the interface between the blocks and mortar joints. The paper thus interrelates the following three problems: (i) definition of a suitable periodic unit cell (PUC) representing a particular masonry structure; (ii) derivation of material parameters of individual constituents either experimentally or running a mixed numerical-experimental problem; (iii) assessment of the macroscopic material parameters including the tensile and compressive strengths and fracture energy.

• ETRI Journal
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• v.18 no.4
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• pp.301-313
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• 1997

We have found that in the ballistic electron transport in a ring structure, the junction-backscattering contribution is critical for all the major features of the Aharonov-Bohm-type interference patterns. In particular, by considering the backscattering effect, we present new and clear interpretation about the physical origin of the secondary minima in the electrostatic Aharonov-Bohm effect and that of the h/2e oscillations when both the electric and magnetic potentials are present. We have devised a convenient scheme of expanding the conductance by the junction backscattering amplitude, which enables us to determine most important electron paths among infinitely many paths and to gain insight about their contributions to the interference patterns. Based on the scheme, we have identified various interesting interference phenomena in the ballistic ring structure and found that the backscattering effect plays a critical role in all of them.

• Rapid Communication in Photoscience
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• v.4 no.2
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• pp.29-30
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• 2015

Since the first report on long-term durable perovskite solar cell in 2012, a surge of interest in perovskite solar cell has been received due to its superb photovoltaic performance exceeding 20%. $MAPbI_3$ ($MA=CH_3NH_3$) perovskite film is able to be prepared simply by solution processesof either sequential two-step or single step procedure. Since $MAPbI_3$ shows balanced charge transport property with micrometer scale charge diffusion length, it can be applied to any kind of junction structures. Mostly studied structure is mesoscopic structure employing mesoporous oxide layer in perovskite film. Photovoltaic performance is primarilyin fluenced by the quality of perovskite film but interfaces are equally important. In this mini review, emergence and evolution of perovskite solar cell are described.