• 대한핵의학회지
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• 제26권1호
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• pp.8-13
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• 1992

Low doses of ionizing radiation from external or internal sources cause heterogeneous distribution of energy deposition events in the exposed biological system. With the cell being the individual element of the tissue system, the fraction of cells hit, the dose received by the hit, and the biological response of the cell to the dose received eventually determine the effect in tissue. The hit cell may experience detriment, such as change in its DNA leading to a malignant transformation, or it may derive benefit in terms of an adaptive response such as a temporary improvement of DNA repair or temporary prevention of effects from intracellular radicals through enhanced radical detoxification. These responses are protective also to toxic substances that are generated during normal metabolism. Within a multicellular system, the probability of detriment must be weighed against the probability of benefit through adaptive responses with protection against various toxic agents including those produced by normal metabolism. Because irradiation can principally induce both, detriment and adaptive responses, one type of affected cells may not be simply summed up at the expense of cells with other types of effects, in assessing risk to tissue. An inventory of various types of effects in the blood forming system of mammals, even with large ranges of uncertainty, uncovers the possibility of benefit to the system from exposure to low doses of low LET radiation. This experimental approach may complement epidemiological data on individuals exposed to low doses of ionizing radiation and may lead to a more rational appraisal of risk.

• Current Photovoltaic Research
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• 제3권2호
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• pp.61-64
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• 2015

In solar industry, numerous researchers reported about cold spray method among various electrode formation technic, but there are no known a bonding mechanism of metal powder. In this study, a cross-section of copper electrode formed by cold spray method was observed and heterogeneous phase between silicon substrate and copper electrode was analyzed using morphology observation technic. SEM and TEM analysis were performed to analyze a crystallinity and distribution shape of heterogeneous copper phase. Molecular dynamics simulation was performed to calculate glass transition temperature of copper metal. In the result, amorphous copper phase was observed near interface between silicon substrate and metal electrode. The results of the molecular dynamics simulation show that an amorphous copper phase could be formed at a temperature below the melting point of copper because cold spraying resulted in a lower glass transition temperature.

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.345-358
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• 2018

Heterogeneous structure and, particularly, low resistance to tension stresses leads to different mechanical properties of the concrete in different loading situations. To solve this problem, the tension zone of concrete elements is reinforced. Development of the cracks, however, becomes even more complicated in the presence of bar reinforcement. Direct tension test is the common layout for analyzing mechanical properties of reinforced concrete. This study investigates scatter of the test results related with arrangement of bar reinforcement. It employs results of six elements with square $60{\times}60mm$ cross-section reinforced with one or four 5 mm bars. Differently to the common research practice (limited to the average deformation response), this study presents recordings of numerous strain gauges, which allows to monitor/assess evolution of the deformations during the test. A simple procedure for variation assessment of elasticity modulus of the concrete is proposed. The variation analysis reveals different deformation behavior of the concrete in the prisms with different distribution of the reinforcement bars. Application of finite element approach to carefully collected experimental data has revealed the effects, which were neglected during the test results interpretation stage.

• International Journal of Concrete Structures and Materials
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• 제19권1E호
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• pp.11-16
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• 2007

Recently, probabilistic neural network (PNN) has been proposed to predict the compressive strength of concrete for the known effect of improvement on PNN by the iteration method. However, an empirical method has been incorporated in the PNN technique to specify its smoothing parameter, which causes significant uncertainty in predicting the compressive strength of concrete. In this study, a modified probabilistic neural network (MPNN) approach is hence proposed. The global probability density function (PDF) of variables is reflected by summing the heterogeneous local PDFs which are automatically determined by the individual standard deviation of each variable. The proposed MPNN is applied to predict the compressive strength of concrete using actual test data from a concrete company. The estimated results of MPNN are compared with those of the conventional PNN. MPNN showed better results than the conventional PNN in predicting the compressive strength of concrete and provided promising results for the probabilistic approach to predict the concrete strength by using the individual standard deviation of a variable.

• Computers and Concrete
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• 제7권5호
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• pp.469-482
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• 2010

This paper investigates the concrete permeability through a numerical and statistical approach. Concrete is considered as a random heterogeneous composite of three phases: aggregates, interfacial transition zones (ITZ) and matrix. The paper begins with some classical bound and estimate theories applied to concrete permeability and the influence of ITZ on these bound and estimate values is discussed. Numerical samples for permeability analysis are established through random aggregate structure (RAS) scheme, each numerical sample containing randomly distributed aggregates coated with ITZ and dispersed in a homogeneous matrix. The volumetric fraction of aggregates is fixed and the size distribution of aggregates observes Fuller's curve. Then finite element method is used to solve the steady permeation problem on 2D numerical samples and the overall permeability is deduced from flux-pressure relation. The impact of ITZ on overall permeability is analyzed in terms of ITZ width and contrast ratio between ITZ and matrix permeabilities. Hereafter, 3680 samples are generated for 23 sample sizes and 4 contrast ratios, and statistical analysis is performed on the permeability dispersion in terms of sample size and ITZ characteristics. By sample theory, the size of representative volume element (RVE) for permeability is then quantified considering sample realization number and expected error. Concluding remarks are provided for the impact of ITZ on concrete permeability and its statistical characteristics.

• 한국정보통신학회논문지
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• 제9권5호
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• pp.1142-1148
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• 2005

본 논문에서는 클라이언트들의 작업부하를 분산하기 위한 측정 알고리즘을 제안하였다. 이 알고리즘은 작업들이 재배치되는 것을 허용할 때, 송신자가 수신자에게 요청한 처리량만큼 적절하게 전송하여야 한다. 이 양은 송신자와 수신자의 협상 과정에서 동적으로 결정된다. 전송하여야 할 작업량을 결정할 때 전송 노드는 수신하는 다른 노드들의 처리 속도를 포함하여 송신 노드와 수신 노드의 현재 부하상태, 재배치하기에 적절한 작업의 처리 요구량 등의 요소들을 고려하여야 한다. 이러한 분석에 근거하여 이기종 분산 웹서버 시스템에 적합한 새로운 알고리즘을 제안하고, 기존 알고리즘과의 성능을 비교하였다. 시뮬레이션을 통하여 본 논문에서 제안한 알고리즘이 CPU 이용율과 응답시간에서 성능의 개선을 보였다.

• The Journal of Asian Finance, Economics and Business
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• 제5권4호
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• pp.73-83
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• 2018

The purpose of this paper is to examine the relationship between regional financial development and corporate investment efficiency as well as the relationship between firm-level characteristics and corporate investment efficiency. Using a large sample of A-listed companies in China from CSMAR database between 2003 and 2016, this paper explores corporate investment efficiency and its influencing factors in emerging market on the basis of heterogeneous stochastic frontier model. The results show that: (1) the average investment efficiency of Chinese listed companies is 74.5%, and the investment efficiency of large enterprises, state-owned enterprises and enterprises with relatively high financial development level is significantly higher; (2) compared with average corporate investment efficiency in the year 2003, the investment efficiency of different types of enterprises in 2016 is significantly higher, and the gap is gradually widening; (3) enterprise heterogeneity namely firm size, nature of property right, and institutional environment reflected by the level of regional financial development indirectly affects corporate investment efficiency by influencing the financing constraints and uncertainty. The findings suggest that to improve corporate investment efficiency in emerging market, financial market should be accelerated, regional balance should be restored and the differences among regions, industries and differences between public and private sectors should be eliminated.

• 정보처리학회논문지C
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• 제12C권2호
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• pp.217-222
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• 2005

IEEE 802.11기반 무선 랜은 가정과 사무실 환경에서 무선 연결 서비스를 제공하는 대표적인 기술이다. 최근 들어 HDTV나 화상회의 또는 VoIP와 같은 실시간 멀티미디어 서비스들에 대한 요구가 증가함에 따라 이를 뒷받침하기 위한 QoS (Quality of Service) 지원 메커니즘인 IEEE 802.11e가 제안되었다. 본 논문에서는 IEEE 802.11e 기술이 확산되면서 발생할 수 있는 IEEE 802.11e와 IEEE 802.11b 기술의 혼재 상황에서의 불공평 문제에 대하여 다룬다.

• 산업경영시스템학회지
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• 제8권11호
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• pp.57-68
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• 1985

Theories of capital have historically been amongst the most fertile sources of economic controversy. Many aspects of the modern debate, if not the techniques employed in its exposition, would have been as familiar to Marx, Ricardo, Bohm-Bawerk or Wicksell as to any present-day Cambridge economist. That conotroversies should arise in the course of theorizing cm the concept of capital and the function of profit is not surprising: that these debates have been so vigorous and virluent cannot be divorced from the general ideological and specific implications associated with the theories. In the context of a textbook on the theories of economic growth, the central question associated with capital that must he faced is whether the existence in the real world of heterogeneous capital goods inevitably invalidate; the conclusions of simple theories of "parables" which incorporate no more than a conception of a single, malleable, capital good. All the Cambridge writers have, to a greater or lesser extent, been concerned to deny that any unit can be found in which heterogeneous capital goods can be aggregated so as to simultaneously satisfy the pair of neoclassical requirements described above. Some of them have been more prepared than others to countenance such a possibility or, for practical purposes, to use some concept of aggregate capital in their models, but they are all deeply suspicious of attempts to use aggregate production function, incorporating aggregate "capital", so as to explain the flow of output, relative factor prices and the distribution of income.tribution of income.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2968-2976
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• 2021

This paper introduces a method to reconstruct the three-dimensional (3D) microstructure of two-phase materials, e.g., porous materials such as highly irradiated nuclear fuel, from two-dimensional (2D) sections via a multi-objective optimization genetic algorithm. The optimization is based on the comparison between the reference and reconstructed 2D sections on specific target properties, i.e., 2D pore number, and mean value and standard deviation of the pore-size distribution. This represents a multi-objective fitness function subject to weaker hypotheses compared to state-of-the-art methods based on n-points correlations, allowing for a broader range of application. The effectiveness of the proposed method is demonstrated on synthetic data and compared with state-of-the-art methods adopting a fitness based on 2D correlations. The method here developed can be used as a cost-effective tool to reconstruct the pore structure in highly irradiated materials using 2D experimental data.