• 한국멀티미디어학회논문지
• /
• 제10권9호
• /
• pp.1197-1208
• /
• 2007

오늘날 대부분의 스마트카드는 자바카드 플랫폼을 채택한 자바카트가 표준안으로 자리매김 하고 있다. 자바카드 기술은 이식성, 플랫폼 독립성, 높은 보안성 기능을 스마트카드에 제공한다. 그러나 자바카드는 일반 스마트카드에 비해 자바 언어 상의 특성으로 인해 실행속도 저하의 단점을 갖고 있다. 실행속도에 영향을 끼치는 요소는 자바 카드가 데이터를 저장하는 방식과 자바카드 설치기가 애플릿을 설치하는 방식 때문이다. 본 논문에서는 자바카드 프로그램의 적재와 실행의 속도를 개선시키기 위한 방안으로 자바카드에서 EEPROM에 데이터에 대한 저장, 갱신, 삭제하는 과정들을 처리 속도가 빠른 RAM을 이용하여 자바카드의 속도를 개선할 수 있다. 이를 위해 자바카드에서 RAM을 활용한 방법으로 자바카드 환경에 맞는 선반입 LRU-OBL 버퍼 캐쉬 기법을 제시한다. 자바카드에서 생성되는 모든 데이터들을 데이터 특성에 따라 버퍼 캐쉬에서 관리함으로써 EEPROM에 대한 기록 횟수를 최대한 줄여 자바카드의 프로그램 적재 및 실행속도를 향상시킨다.

• Tribology and Lubricants
• /
• 제2권1호
• /
• pp.61-68
• /
• 1986

Effects of the ram-pressure on the THD-performance of pivoted pad thrust bearings are investigated experimentally. A sector-shaped tilting pad thrust bearing and a rotating disk are used. Temperature distribution on the disk surface as well as on the pad surface, distribution of the pressure generated within the fluid film, and the film thickness are measured continuously in the circumferential direction after thermal equilibrium is established. The ram-pressure is proportional to the mean pressure of oil film and to the rotational speed of the disk and affects the maximum pressure and the pressure distribution. The temperature rise on the mating surface of the disc and the pad, contacting with the oil film, is proportional to to the bearing load and the disk speed. The ram-pressure and the temperature rise on the disk surface are dominant factors that affect the THD-performance of pivoted pad thrust bearings.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
• /
• pp.162-166
• /
• 2003

In combined forward-backward extrusion with controlled forward speed by a counter punch, accurate parts with forward rod can be formed. As an extension of this method, reverse extrusion is proposed, in which the extruded forward rod is pushed back while the main punch is kept at the final position after the forward-backward extrusion process. The experiment is carried out using lead as a model material. With the reverse extrusion method, longer forward rods can be formed without under-filling defect than that by combined extrusion with controlling extrusion speed.

• 한국연소학회지
• /
• 제5권1호
• /
• pp.31-41
• /
• 2000

A numerical study was conducted to investigate the combustion phenomena of regular start and unstart processes based on ISL#s RAMAC 30 experiments with different diluent amounts in a ram accelerator. The initial projectile launching speed was 1800m/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with $5CO_2\;or\;4CO_2$. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1800m/s, as was found in the experiments using a steel-covered projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the regular start and unstart processes found in the experiments with an aluminum-covered projectile. The numerical results matched almost exactly to the experimental results. As a result, it was found that the regular start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년 영문 학술대회
• /
• pp.519-524
• /
• 2008

A numerical study is conducted to investigate propulsion performance enhancement based on S225 experiment case of ISL(French-German Research Institute of Saint-Louis)'s superdetonative ram accelerator. For govern equation, multi-species Navier-Stokes equation coupled with Baldwin-Lomax turbulence modeling is used. Govern equation is discretized by Roe's FDS and integrated by LU-SGS time integration. Detailed chemical reaction about $H_2/O_2/CO_2$ for high pressure is considered. $2H_2+O_2+2.5CO_2$ mixture was used for propellant gas. For the same over-driven factor, the launching speed of computation was faster than one of S225. Another configuration and condition of S225 was applied. A flame structure is very different from S225. For strong mixture case, it shows ignition by viscous effect. Acceleration and speed increment is higher than S225 computation and experiment. By using more strong mixture, propulsion performance was enhanced.

• International Journal of Contents
• /
• 제5권4호
• /
• pp.75-80
• /
• 2009

Recently high-speed memory array based on RAM, which is a type of solid-state drive (SSD), has been introduced to handle the input/output (I/O) bottleneck. But there are only a few performance studies on RAM based SSD storage with regard to diverse workloads. In this paper, we focus on the file system for RAM based memory array based NGS (Next Generation Storage) system which is running on Linux operating system. Then we perform benchmark tests on practical file systems including Ext3, ReiserFS, XFS. The result shows XFS significantly outperforms other file systems in tests that represent the storage and data requests typically made by enterprise applications in many aspects. The experiment is used to design the dedicated file system for NGS system. The results presented here can help enterprises improve their performance significantly.

• 한국통신학회논문지
• /
• 제35권6B호
• /
• pp.948-953
• /
• 2010

본 논문에서는 슈퍼스칼라 구조를 가진 시스템의 명령어 캐시에서 효율적으로 소프트오류를 검출할 수 있는 기법을 제안한다. 명령어 캐시로 주로 사용되는 고속 정적 RAM(Random Access Memory)에 적용할 수 있으며 1D 패리티와 인터리빙을 통해 기존 기법들과 비교하여 더 적은 메모리 오버헤드로 연집오류를 검출할 수 있다. 정적 RAM에서는 소프트오류의 발생만을 확인하고 검출된 소프트오류의 정정은 명령어 캐시의 캐시 미스와 같이 처리하여 하위 메모리로부터 명령어들을 다시 인출하는 방식이다. 이를 통해 명령어 캐시의 성능에 영향을 주지 않으면서 연집오류를 검출하고 정정할 수 있으며 최대 4$\times$4의 윈도우 내에서 발생된 연집오류를 검출 할 수 있다. 제안된 방식을 이용하면 256비트 $\times$ 256비트 크기의 메모리에서 기존의 4-way 인터리빙 기법에서 검출에 필요한 패리티 크기의 25%만으로도 동일한 4비트의 연집오류를 검출 할 수 있다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1993년도 하계학술대회 논문집 B
• /
• pp.1206-1208
• /
• 1993

This paper is to study and realize a measuring device for complex dielectric constants. The device is consisted in order of interface unit, external RAM, programmable counter, D/A converter, measuring circuit, Sample & Hold circuit, A/D converter and related control circuits. Various excitation waves are digitalized and sent to the 4096 static RAM by personal computer. These data saved in the RAM are converted to analog excitation waves through D/A converter. The frequency of excitation wave is depend on the read-out speed of the RAM according to clock pulses. Such generated waves are applied to dielectrics under test and their responses are sampled and converted to digital data through A/D converter. The computer takes the digital data and calculates finally the complex dielectric constants. The frequencies for Measurement ranges from 0.04 Hz to 10 kHz.

• 대한조선학회논문집
• /
• 제34권4호
• /
• pp.42-52
• /
• 1997

수중램제트(underwater ram-jet)는 램흡입부(ram intake), 혼합실(mixing chamber) 및 노즐(nozzle)로 구성되어 있으며, 램흡입부로 유입된 작동유체는 압력이 증가되며 이 증압된 작동유체에 혼합실로부터 고압공기를 분사하여 기 액이상류를 형성하여 노즐을 통과하면서 대기압까지 팽창을 하여 작동유체를 고속으로 가속시켜 노즐출구로부터 추력을 얻는 방식으로 차세대 초고속 선박추진장치이다. 본 연구에서는 80노트를 낼 수 있는 선내관통형(buried type vessel) 램제트의 최적 노즐형상데이터를 이용하여 제반변수(벽마찰계수, 가스속도, 기포반경, 대기온도, 질량유량비, 디퓨저면적비, 작동유체의 속도구배)의 변화가 추진특성에 미치는 영향을 파악하였다.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
• /
• pp.123-132
• /
• 2002

A numerical study was conducted to investigate the combustion phenomena of normal start and unstart processes based on ISL's RAMAC 30 experiments with different diluent amounts and fill pressures in a ram accelerator. The initial projectile launching speed was 1.8 km/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with 5 $CO_2$ or 4 $CO_2$. Experiments with same condition except for projectile surface material demonstrated that ignition was successful with an aluminum projectile, but no combustion was observed in case of a steel projectile. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1.8 km/s, as was found in the experiments using a steel projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the normal start and unstart processes found in the experiments with an aluminum projectile. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations coupled with a Baldwin-Lomax turbulence model and detailed chemistry reaction equations of $H_2/O_2/CO_2$ suitable for high-pressure gaseous combustion were considered. The governing equations were discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit, time accurate integration method. The numerical results matched almost exactly to the experimental results. As a result, it was found that the normal start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.