• Title/Summary/Keyword: Small stack

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An Implementation of Single Stack Multi-threading for Small Embedded Systems

  • Kim, Yong-Seok
    • Journal of the Korea Society of Computer and Information
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    • v.21 no.4
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    • pp.1-8
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    • 2016
  • In small embedded systems including IoT devices, memory size is very small and it is important to reduce memory amount for execution of application programs. For multi-threaded applications, stack may consume a large amount of memory because each thread has its own stack of sufficiently large size for worst case. This paper presents an implementation of single stack multi-threading, called SSThread (Single Stack Thread), by sharing a stack for all threads to reduce stack memory size. By using SSThread, multi-threaded applications can be programmed based on normal C language environment and there is no requirement of transporting multi-threading operating systems. It consists of several library functions and various C macro definitions. Even though some functional restrictions in comparison to operating systems supporting complete multi-thread functionalities, it is very useful for small embedded systems with tiny memory size and it is simple to setup programming environment for multi-thread applications.

Operation of A Small MCFC Stack Using New Designed Circular Separator (새로운 원반형 구조의 분리판을 사용한 소형 용융탄산염 스택의 운전)

  • Han, Jonghee;Roh, Gil-Tae;Yoon, Sung Pill;Nam, Suk Woo;LIm, Tae Hoon;Hong, Seong Ahn
    • Transactions of the Korean hydrogen and new energy society
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    • v.14 no.3
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    • pp.229-235
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    • 2003
  • A 50W class MCFC stack was operated in order to test a new design of the circular shaped separator. in the new design, the anode gas was supplied into the stack and was exhausted out of the stack after the anode reaction. The exhausted gas was reacted with the cathode gas supplied with excess oxygen in the vessel in which the stack was placed. Then the reacted gas flowed into the cathode side of the stack and was exhausted through the outlet located in the center of the stack. The average voltage of the single cells in the stack was 0.835V under the current density of $150mA/cm^2$, initially, and the degradation rate of the stack voltage was 1.7%/1,000h. High stack voltage with good stability of the present stack was due to the small temperature gradient in the stack. The small temperature gradient as well as the easiness of temperature control was the result of the new configuration of the separator which utilized the heat of the combustion reaction between anode outlet gas and the cathode inlet gas for heating the stack.

Effect of stack configuration on the performance of 10W PEMFC stack (10W급 고분자 전해질 연료전지 스택의 구조적 차이에 다른 운전 특성 비교)

  • Yim, Sung-Dae;Kim, Byung-Ju;Sohn, Young-Jun;Yoon, Young-Gi;Yang, Tae-Hyun;Kim, Chang-Soo;Kim, Young-Chai
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.06a
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    • pp.286-286
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    • 2009
  • A small PEM fuel cell has two different stack configurations such as active and passive stacks. The active stack has a distintion of high power density although it makes system complex by using alr blower and related BOPs resulting in large system volume. On the contrary, passive stack has an advantage of compact system because it doesn't need air supplying devices although it reveals relatively low stack power density. In this study we fabricated two 10W PEMFC stacks with different stack configurations, active and passive stacks, and tested their performance and stability. The active stack consists of 13cells with an active area of $5cm^2$. The passive stack has 12cells with an active area of $16cm^2$. When we compared the stack performance of those stacks, the active stack showed higher power density compared to the passive stack, particularly at high voltage regions. However, at low voltage and high current regions, the passive stack performance was comparable to the active stack. The stack stability was largely dependent on the fuel humidity, particularly for active stack. At low humidity conditions, the active stack performance was decreased continuously and the cell voltage distribution was not uniform showing seriously low cell voltage at center cells mainly due to the cell drying. The passive stack showed relatively stable behavior at low humidity and the stack performance was largely dependent on the atmospheric conditions.

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Development of the Control Algorithm for the Small PEM Fuel Cell Stack (소형 PEM 연료전지 스택의 제어 알고리즘 개발)

  • Kim, Tae-Hoon;Choi, Woo-Jin
    • The Transactions of the Korean Institute of Power Electronics
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    • v.15 no.2
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    • pp.134-141
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    • 2010
  • Small PEM (Proton Exchange Membrane) fuel cell systems do not require humidification and have great commercialization possibilities. However, methods for controlling small PEM fuel cell stacks have not been clearly established. In this paper, a control method for small PEM fuel cell systems using a dual closed loop with a static feedforward structure is defined and realized using a DSP (Digital Signal Processor). The fundamental elements that need to be controlled in fuel cell systems include the supply of air and hydrogen, water management inside the stack, and heat management of the stack. For small PEM fuel cell stacks operated without a separate humidifier, fans are essential for air supply, heat management, and water management of the stack. A purge valve discharges surplus water from the stack. The proposed method controls the fan using double control loops to quicken transient response of the fan thereby improving the supply rate of air. Feedback control to compensate for the voltage change in fuel cell stack improves the response characteristics in fuel cell to load variations. The feasibility of proposed method was proved by the experiments with a 60W small PEM fuel cell system and operation of a notebook computer using this system.

Design and implementation of TCP/IP protocol stack for small real-time kernels (소형 실시간 커널을 위한 TCP/IP 프로토콜 설계및 구현)

  • 윤재식;김재양;정선태
    • 제어로봇시스템학회:학술대회논문집
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    • 1997.10a
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    • pp.414-417
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    • 1997
  • Many small-sized real-time kernels do not provide memory management and device drivers, not to mention file management. In this paper, we propose a design and implementation of TCP/IP protocol stack for such small real-time kernels based on [6] where we studied issues to be considered for porting the functionalities of TCP/IP for such small real-time kernels.

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Control of Small PEM Fuel Cell Stack by a Microprocessor (마이크로프로세서를 이용한 소형 PEM 연료전지 스택의 제어)

  • Kim, Tae-Hoon;Choi, Woo-Jin
    • The Transactions of the Korean Institute of Power Electronics
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    • v.13 no.6
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    • pp.469-475
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    • 2008
  • In this paper, control of small PEM(Proton Exchange Membrane) fuel cell stack by a microprocessor is introduced. The water management of fuel cell stack inside, a key technique in fuel cell control, can be achieved by adjusting the required air flow for fuel and cooling, and by purging the excessive water from the stack. It is very important to precisely control the BOS(Balance of Stack) since the stable operation of the fuel cell system mainly depends on it. In this study the fuel efficiency of the system is improved by the control of the system based on the measured air flow and purge cycle during the optimal operation and its effectiveness is proved by the experiments. The operating stability of the system is improved by the developed controller using a microprocessor and it is expected to be widely used for the control of small PEM fuel cell stack.

Numerical Simulation on Self-heating for Interlayer Tunneling Spectroscopy in $Bi_2Sr_2CaCu_2O_{8+x}$

  • Park, Jae-Hyun;Lee, Hu-Jong
    • Progress in Superconductivity
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    • v.9 no.1
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    • pp.18-22
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    • 2007
  • For interlayer tunneling spectroscopy using a small stack of $Bi_2Sr_2CaCu_2O_{8+x}$ (Bi-2212) intrinsic junctions in a high-bias range, large self-heating takes place due to the poor thermal conductivity of Bi-2212. In this study, we numerically estimate the self-heating around a Bi-2212 sample stack for I-V or dI/dV-V measurements. Our results show that the temperature discrepancy between the Bi-2212 sample stack and top Au electrodes due to bias-induced self-heating is small enough along the c-axis direction of Bi-2212. On the other hand, the lateral temperature discrepancy between the sample stack and the Bi-2212 on-chip thermometer stack can be as large as ${\sim}20\;K$ for the highest bias required to observe the pseudogap hump structure. We thus suggest a new in-situ ac thermometry, employing the Au current-bias electrode itself deposited on top of the sample stack as the resistive thermometer layer, which is supposed to allow safe temperature measurements for the interlayer tunneling spectroscopy.

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Development of a Lightweight 200W Direct Methanol Fuel Cell Stack for UAV Applications and Study of its Operating Characteristics (II) (무인항공기용 200W 급 직접메탄올연료전지 경량화 스택 제작 및 작동 특성 연구 (II))

  • Kang, Kyung-Mun;Park, Sung-Hyun;Gwak, Geon-Hui;Ji, Hyun-Jin;Ju, Hyun-Chul
    • Transactions of the Korean hydrogen and new energy society
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    • v.23 no.3
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    • pp.243-249
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    • 2012
  • A lightweight 200W direct methanol fuel cell (DMFC) stack is designed and fabricated to power a small scale Unmanned Aerial Vehicle (UAV). The DMFC stack consists of 33-cells in which membrane-electrode assemblies (MEAs) having an active area of 88 $cm^2$ are sandwiched with lightweight composite bipolar plates. The total stack weight is around 3.485 kg and stack performance is tested under various methanol feed concentrations. The DMFC stack delivers a maximum power of 248 W at 13.2 V and $71.3^{\circ}C$ under methanol feed concentration of 1.2 M. In addition, the voltage of individual cell in the 33-cell stack is measured at various current levels to ensure the stability of DMFC stack operations. The cell voltage distribution data exhibit the maximum cell voltage deviation of 28 mV at 15 A and hence the uniformity of cell voltages is acceptable. These results clearly demonstrate that DMFC technology becomes a potential candidate for small-scale UAV applications.

Enhancement of Internal Network Security in Small Networks Using UTM and ELK Stack (UTM과 ELK Stack을 활용한 소규모 네트워크의 내부망 보안 강화방안)

  • Song Ha Min;DongHwi Lee
    • Convergence Security Journal
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    • v.24 no.1
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    • pp.3-9
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    • 2024
  • Currently, cyberattacks and security threats are constantly evolving, and organizations need quick and efficient security response methods. This paper proposes ways to strengthen internal network security by utilizing Unified Threat Management (UTM) equipment to improve network security and effectively manage and analyze the log data of the internal network collected through these equipment using Elastic Stack (Elasticsearch, Logstash, Kibana, hereinafter referred to as ELK Stack).

Performance Analysis of Shared Stack Management for Sensor Operating Systems (센서 운영 체제를 위한 공유 스택 기법의 성능 분석)

  • Gu, Bon-Cheol;Heo, Jun-Young;Hong, Ji-Man;Cho, Yoo-Kun
    • Journal of KIISE:Computer Systems and Theory
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    • v.35 no.1
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    • pp.53-59
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    • 2008
  • In spite of increasing complexity of wireless sensor network applications, most of the sensor node platforms still have severe resource constraints. Especially a small amount of memory and absence of a memory management unit (MMU) cause many problems in managing application thread stacks. Hence, a shared-stack was proposed, which allows several threads to share one single stack for minimizing the amount of memory wasted by fixed-size stacks. In this paper, we present the memory usage models for thread stacks by deriving the overflow probability of the fixed-size stack and the shared-stack and also show that the shared-stack is more reliable than the fixed-size stack.