Earticle

본 논문에서는 머신러닝 기반의 악성코드 분류에 있어 오버피팅 문제를 비롯하여 실제로 실행되지 않는 코드가 APK에 포함되는 문제 등을 해결하기 위해 모든 API들의 연관성을 통해 그룹화하며, 제어 흐름 분석을 통해 실제로 실행되는 코드에 대한 분석을 수행하는 툴을 개발하였다. 툴은 약 1,500라인으로 이루어진 자바 기반의 소프트웨어로, 전체 API에 대한 빈도 분석을 수행하거나 생성된 제어 흐름 그래프를 바탕으로 빈도 분석을 수행한다. 툴을 이용하여 모든 버전에서의 총 39032개의 메서드에 대해 4972개의 그룹으로 축소할 수 있으며, 클래스를 포함한 결과로는 총 12123개의 그룹으로 축소할 수 있다. 결과 분석을 위해서 본 논문에서는 총 7개의 패밀리에서 7,000개의 APK를 랜덤으로 수집하였으며, 수집된 APK를 이용하여 feature를 축소하는 기법을 검증하였다. 또한, 추출된 데이터에서 빈도가 20% 이상으로 나타난 API만을 선별하여 feature를 더욱 축소하여 최종적으로 263개의 feature로 축소하였다.

While several machine learning technique has been implemented for Android malware categorization, there is still difficulty in analyzing due to overfitting problem and including of un-executable code, etc. In this paper, we introduce our implemented tool to address these problems. Tool is consists of approximately 1,500 lines of Java code, and perform Flow analysis on set of APIs, or on control flow graph. Our tool groups all the API by its relationship and only perform analysis on actually executing code. Using our tool, we grouped 39032 APIs into 4972 groups, and 12123 groups with result of including class names. We collected 7,000 APKs from 7 families and evaluated our feature reduction technique, and we also reduced features again with selecting APIs that have frequency more than 20%. We finally reduced features to 263-numbers of feature for our collected APKs.

Numerical study on a lifting system developed for shallow sea test is performed by a CFD model. In this study, the flow behaviors in a lifting pump and flexible hoses is simulated by using FLUENT, a commercial CFD model. Two cases for calculation the pump cavitation behavior are selected according to the hose length and the depth of lifting pump. From the numerical results, it is found that the vortex flow is observed in the first-stage stator and the calculated NPSH meets the minimum required by a lifting pump based on the shallow sea environments.

We carried out numerical studies to investigate the single- and two-phase flow characteristics in the single- and multi-channels. We used the finite volume method to solve the mass and momentum conservation equations. The volume of fluid model is used to predict the two-phase flow in the channel. We obtained the distribution of velocity fields, pressure drop and air volume fraction for different water mass flow rates. We also calculated the distribution of mass flow rates in the multi-channels to understand how the flow is distributed in the channels. The calculated results for the single- and two-phase flow are partly compared with the present experimental data both qualitatively and quantitatively, showing relatively good agreement between them. The numerical scheme used in this study predicts well the characteristics of single-and two-phase flow in a multi-channel.

A conservative finite-volume numerical method for unstructured grids with the cell-centered method has been developed for computing flow and heat transfer by combining the attractive features of the existing pressure-based procedures with the advances made in unstructured grid techniques. This method uses an integral form of governing equations for arbitrary convex polyhedra. Care is taken in the discretization and solution procedure to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. For both convective and diffusive fluxes the forms superior to both accuracy and stability are particularly adopted and formulated through a systematic study on the existing approximation ones. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are computed by using a linear reconstruction based on the divergence theorem. Momentum interpolation is used to prevent the pressure checkerboarding and a segregated solution strategy is adopted to minimize the storage requirements with the pressure-velocity coupling by the SIMPLE algorithm. An algebraic solver using iterative preconditioned conjugate gradient method is used for the solution of linearized equations. The flow analysis code (PowerCFD) developed by the present method is evaluated for its application to several 2-D structured-mesh benchmark problems using a variety of unstructured quadrilateral and triangular meshes. The present flow analysis code by using unstructured grids with the cell-centered method clearly demonstrate the same accuracy and robustness as that for a typical structured mesh.

A computational investigation of blood flow in a coronary artery grafted by artificial bypass was performed to determine such geometric parameters as the curvature of radius, approach length, and angle of end-to-side anastomosis. Transient flow features in the host artery were computed using FVM and SIMPLE algorithms. We compared flow distributions and wall shear stresses in two simple models, planar and non-planar, and confirmed that the non-planar bypass model was more conducive to suppressing intimal hyperplasia. Our non-planar model with $60^{\circ}$ of anastomosis and a 1.0 diameter approach length and radius of curvature predicts a relatively small, spatially-extended high-OSI (>0.01) zone, as well as an increased average wall shear stress on this zone.

근해역 채광시험을 위해 제작된 양광펌프의 성능을 검증하고 곡관을 포함하는 유연관내 고-액 혼합물의 유동특성을 파악하기 위한 고-액 2상류 유동실험을 수행하였다. 총 양정 55 m의 양광펌프는 원심펌프로서 펌프의 상하단에는 유연관이 연결된다. 실험에 사용된 유연관은 해양채광에 적합하도록 직경 100 mm, 단위길이 10 m로 제작되었다. 실험결과 20%의 고체체적점유율까지 양광실험에 무리가 없는 것으로 확인하였으며 기존에 개발된 전산모델의 예측이 실험결과와 유사함을 확인하였다.Introduction

The flow characteristics of solid-liquid two-phase mixtures in a flexible hose are investigated using the experiments. Also the performance of the lifting pump for the offshore mining test are estimated. This centrifugal pump with the total head of 55 m is for lifting the minerals on the seabed. The inlet of this pump is connected to the flexible hose, which is attached to the miner collector. The flexible hose is specially manufactured for the use in mining test with 100 mm in diameter. The results show the performance of the lifting pump is good for the offshore test.

Rubber is used in many industrial products, such as hoses, rubber belts, and oil seals. In particular, more than 200 rubber parts are used in automobiles. The design technology of these parts is largely dependent on field experience, which leads to lengthy and expensive developing procedures. However, with the help of recent developments in nonlinear computer analysis, new rubber products can be developed at low cost. In this study, rubber injection molding design variables, such as location and number of gates, were optimized using computer-aided engineering with the cross-WLF equation to produce CLIP rubber products made from ethylene propylene diene monomer(EPDM). The validity of the proposed design was evaluated by comparison with actual forming results.

A nodeless variables finite element method for analysis of two-dimensional, steady-state viscous incompressible flow is presented. The finite element equations are derived from the governing Navier-Stokes differential equations and a corresponding computer program is developed. The proposed method is evaluated by solving the examples of the lubricant flow in journal bearing and the flow in the lid-driven cavity. An adaptive meshing technique is incorporated to improve the solution accuracy and, at the same time, to reduce the analysis computational time. The efficiency of the combined adaptive meshing technique and the nodeless variables finite element method is illustrated by using the example of the flow past two fences in a channel.

A potentiometric biosensor employing a CO3-2 ion-selective electrode(ISE) and malic enzyme immobilization in al flow injection analysis (FIA) system was constructed. Analytical parameters were optimized for L-malate determination . The CO3-2 -ISE-FIA system was composed of a pump, an injector, a malic enzyme (EC1.1.1.40) reactor, a CO3-2 ion-selective electrode, a pH/mV meter and a recorder. Cofactor NADP was also injected with substrate for theenzyme reaction into the system. Optimized analytical parameters for L-malate determination in the CO3-2 ISE-FIA system were as follows ; flow rate, 14.5ml/hr ; sample injection volume, 100ul; enzyme loading in the reactor, 20 units ; length of the enzyme reactor , 7 cm ; tubing length form the enzyme reactor to the detector as a geometric factor in FIA, 15 cm . The response time for measuring the entire L-malate concentration range (10-2 ~10-5 mol/L ; 4 injections )was <15minutes . In this CO3-2 -ISE-FIA system, the potential differences due to th eformation of CO3-2 by the reaction of malic enzyme on L-malate were correlated to L-malate concentration in the range of 10-2 ~10-5mol/L ; the detection limit was 10-5 mol/L. This potentionmetric CO3-2 ISE--FIA system was found to be useful for L-malate measurement.

Ion-selective eleltrodes(ISEs) are simple electrodechemical devices for the direct measurement of ions in the samples. A novel potentiometric biosensor for the determination of L-Malate or D-isocitrate has been developed by using CO2-3 -ISE-FIA system was composed of a pump, an injector, a malic enzyme or isocitric dehydrogenase enzyme reactor, a CO2-3 -ISE, a pH/mV meter, and an integrater. The various factors, such as buffer capacity types of plstericizer and polymer, were optimized for the CO2-3 selectivity. In this novel CO2-3 --ISE-FIA system, the potential difference due to the amount of CO2-3 produced from each enzyme reaction was proportional to the amount of L-malate or D-isocitrate.

Chemical mechanical polishing (CMP) is a very precise planarization technique where a wafer is polished by a slurry-coated pad. A slurry is dropped on the rotating pad surface and is supplied between the wafer and the pad. This research aims at reducing the slurry consumption and removing waste particles quickly from the wafer. To study the roles of grooves, slurry flows were simulated using the volume of fluid method (two-phase model for air and slurry) for pads with no grooves, and for pads with circular grooves.

A second moment turbulence closure using the elliptic-blending equation is introduced to analyze the turbulence and heat transfer in a square sectioned U-bend duct flow. The turbulent heat flux model based on the elliptic concept satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. Also, the traditional GGDH heat flux model is compared with the present elliptic concept-based heat flux model. The turbulent heat flux models are closely linked to the elliptic-blending second moment closure which is used for the prediction of Reynolds stresses. The predicted results show their reasonable agreement with experimental data for a square sectioned U-bend duct flow field adopted in the present study.

This work presents the three-dimensional analysis of flow and heat transfer performed for a wire-wrapped fuel assembly of liquid metal reactor using Reynolds-averaged Wavier-Stokes analysis in conjunction with 557 model as a turbulence closure. The whole fuel assembly has been analyzed for one period of the wire-spacer using periodic boundary conditions at inlet and outlet of the calculation domain. Three different assemblies, two 7-pin wire-spacer fuel assemblies and one bare rod bundle, apart from the pressure drop calculations for a 19-pin case, have been analyzed. Individual as well as a comparative analysis of the flow field and heat transfer have been discussed. Also, discussed is the position of hot spots observed in the wire-spacer fuel assembly. The flow field in the subchannels of a bare rod bundle and a wire-spacer fuel assembly is found to be different. A directional temperature gradient is found to exist in the subchannels of a wire-spacer fuel assembly Local Nusselt number in the subchannels of wire-spacer fuel assemblies is found to vary according to the wire-wrap position while in case of bare rod bundle, it's found to be constant.

The characteristic of a supersonic inlet system with three-dimensional bump which is substituted for the diverter or conventional ramp-type compression systems has been studied numerically. A comprehensive numerical analysis has been performed to understand the three-dimensional flow field including shock/boundary layer interaction and growth of turbulent boundary layer that might occur around a three-dimensional bump in a supersonic inlet. The current numerical simulations showed the supersonic bump-type inlet which is modified from a conventional ramp-type inlet to control shock/boundary layer interaction effectively and evolved to maximize inlet performance.

The linear instability of reacting shear flow is analyzed with special emphasis on the effects of the heat release and variable transport properties. Both analytic profiles and laminar solutions of the boundary-layer equations are used as base flows. The growth rates of the instabilities are sensitive to the laminar profiles, differing by more than a factor of 2 according to which profile is used. Thus, it is important to base the analysis on accurate laminar profiles. Accounting for variable transport properties also changes the mean profiles considerably, and so including them in the computation of the laminar profiles is equally important. At larger heat release, two modes that are stronger in the outer part of the shear layer have the highest growth rates; they also have shorter wavelengths than the center mode.

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with the k- ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge- Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two- dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper, a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency of oscillation. Also the average temperature of vapor plugs decreased.