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We used atomic force microscopy (AFM) and scanning surfacepoten- tial microscopy (SSPM) to invest-igate the effect of extended defects (0.5 $\sim$ 3 $\mu$m) on the charge distribution in a GaN epilayer grown by on (0001) sapphire by using metalorganic chemical-vapor deposition. The surface at an extended defect present in the undoped GaN film was observed to be negatively charged and to have a showing higher potential at the defect region than at the defect-free region. The SSPM results showed that defect was negatively charged and that its potential was propor-tional to the size of the defect. 원자간력 현미경(AFM: Atomic Force Microscope)과 주사전위 현미경(SSPM: Scanning Surface Potential Micro-scope)을 이용해 금속유기-화학증기증착방법(MOCVD)으로 성장한 GaN 박막에서 확장된 결함(Extended defect)이 전하분포에 미치는 영향을 연구하였다. GaN 내에 존재하는 확장된 결함은 음전하로 대전되어 있으며, 결함이 없는 영역에 비해 상대적으로 그 중앙과 주변에서 더 높은 전위를 가짐이 관측되었다. SSPM 결과로부터 결함의 크기와 대전되는 음전하의 양(또는 전위)이 서로 비례함을 확인할 수 있었다.
Recently, computer modelling is increasingly used as a design tool, which requires more detailed data for heat transfer coefficients in various regions of the induction motor. But there are little information about those of rotor fan and endring because of difficulty in measuring signals in rotating bodies. In the present studies, the temperature signals were precisely measured with self-developed telemetry system, which had multi-channels and high rotational speed. After some losses were compensated, the heat transfer coefficients of the rotor endring and fan surfaces were measured. Minimum heat transfer region was existed with endcap plate distance and maximum heat transfer was found at some rotor fan width. It was also studied that how the guide plate and endcap inside rib effected on the rotor heat transfer. The higher heat transfer were obtained with decreasing guide plate distance, increasing the number and height of endcap inside rib. The correlation equations of the results were obtained and compared with others. Above results of the heat transfer coefficients can be used as basic data for cooling design of the various kind of motors.
At design stage of new motor or when taking remedial action of old motor, a lot of information can be obtained from thermal parameters analysis. This study focused on the temperature rise of TEFC induction motor with respect to various thermal parameters. Frame heat transfer had the most important effect on coil temperature rise. But those of air gap and rotor fan had no effect. This fact shows fan action is more important than fin action in the case of rotor fan. Coil temperature can be more decreased by cooling near the heat sources than any other parts from the results of thermal conductivity and loss tests. Variation of cooling air flow rate and motor volume effects on coil temperature were also tested. These tests suggest that improvement of cooling fan performance is important in reducing the coil temperature rise. Thermal equivalent program was verified by comparison of some experimental results.
Mobile IP는 네트웍 계층에서 이동성을 제공하지만, Triangle routing이라는 단점을 지니고 있다. 본 논문에서는 DNS의 UPDATE 기능을 이용해 Home Agent와 DNS 간의 연동을 통해 Triangle routing 문제를 개선하는 D-MIP를 제안한다. D-MIP는 Mobile IP 기반에서 동작하면서 Correspondent Node 쪽에 어떠한 수정도요구하지 않으며, 현실적으로 구현하기 쉬운 인증 체계를 갖는다.
Redundancy elimination or deduplication over network packets requires significant computing resources to find basic units of repeated contents, called chunks, by checking every byte in every packet. In this paper, we present the first constant-time chunking algorithm that divides every packet into a predefined number of chunks, irrespective of the packet size. In addition, we present the best implementation practice for packet-level deduplication by selecting an optimal combination of chunking, fingerprinting, and hash table algorithms. Through experiments with real traffic, we confirm that the throughput is improved by three times, compared with even the state-of-the-art scheme.
The end winding is an important part in induction motor for thermal analysis. But there is little information on the heat transfer coefficient of that surfaces because of geometrical complexity. So our experimental object is to know the heat transfer coefficient of end winding and find the optimum design parameter of rotor fan. Carbon coated papers were used for a uniform heat generating surfaces which were easy to fabricate. The experiments of some parameters were performed as varying rotation speed of rotor fan. We obtained the local and average Nusselt number of the end winding surfaces by correcting radiation and conduction losses errors. The results showed that the average Nusselt number increased with rotor fan blade number and width but decreased with end winding length. However, the increasing limits existed in the case of rotor fan width and blade number. So optimum design value were obtained for rotor fan width and blade numbers.
We studied the temperature distribution and heat transfer characteristics of TEFC induction motor with thermal network program for more efficient design and better cooling performance of it. We knew the characteristics and the windage loss of outer cooling fan from fan test experiments. Frame axial and peripheral heat transfer coefficients and endwinding heat transfer coefficient were measured by various model experiments and then, compared with other experimental results. Frame was the main heat transfer surface, load-side and fan-side surface were not thermally symmetric from the heat flux distribution analysis. Steady and unsteady temperature distributions were measured by real motor experiments. From the results, we knew that rotor surface temperature was higher than coil temperature and the hottest spot in the coil was loadside endwinding outside surface. We compared the simulation results with those of real motor test and the two results showed a good agreement.