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排序方式: 共有162条查询结果,搜索用时 20 毫秒
1.
The tone sense multiaccess with partial collision detection (TSMA/PCD) protocol is particularly suitable for a packet satellite system serving an area with a dense population of earth stations. By incorporating a narrowband ground radio channel for broadcasting busy ones, the earth stations are able to avoid packet collisions by sensing for the absence of busy tones before transmitting packets. Partial collision detection capability can also be achieved. Single-tone TSMA/PCD gives 97% of the carrier-sense multiaccess with collision detection (CSMA/CD) throughput when N =10 tones are used, while for multitone and slot-by-slot announcement TSMA/PCD protocols only N =8 and N =2, respectively, are sufficient to drive the system to the CSMA/CD performance 相似文献
2.
As technology evolves, it is now feasible to implement sophisticated adaptive routing schemes on networks which support different kinds of services with heterogeneous bandwidth characteristics. Adaptive routing can increase the network throughput by routing calls to less congested paths. It can also be used to bypass transmission facility failures. In this paper, we analyze and compare two adaptive routing schemes. The first is called theMaximum mean time to blocking (MTB) routing which is based on themean time to blocking measure of a link. This measure captures the traffic rates, bandwidth characteristic and link capacity information and reflects more accurately the congestion status of different paths. The second is theM
2 routing, which is a modification of the least loaded routing (LLR). Aggregation of link status information can significantly reduce signalling traffic. We show in this paper that with properly designed aggregation, the aggregatedM
2 and MTB routings can have performance that approach that of the non-aggregated schemes. The use of complete sharing and restricted access policies together with trunk reservation control in multirate loss networks are also studied. 相似文献
3.
Tae-Sung Jung Do-Chan Choi Sung-Hee Cho Myong-Jae Kim Seung-Keun Lee Byung-Soon Choi Jin-Sun Yum San-Hong Kim Dong-Gi Lee Jong-Chang Son Myung-Sik Yong Heung-Kwun Oh Sung-Bu Jun Woung-Moo Lee Haq E. Kang-Deog Suh Ali S.B. Hyung-Kyu Lim 《Solid-State Circuits, IEEE Journal of》1997,32(11):1748-1757
A 3.3-V 16-Mb nonvolatile memory having operation virtually identical to DRAM with package pin compatibility has been developed. Read and write operations are fully DRAM compatible except for a longer RAS precharge time after write. Fast random access time of 63 ns with the NAND flash memory cell is achieved by using a hierarchical row decoder scheme and a unique folded bit-line architecture which also allows bit-by-bit program verify and inhibit operation. Fast page mode with a column address access time of 21 ns is achieved by sensing and latching 4 k cells simultaneously. To allow byte alterability, nonvolatile restore operation with self-contained erase is developed. Self-contained erase is word-line based, and increased cell disturb due to the word-line based erase is relaxed by adding a boosted bit-line scheme to a conventional self-boosting technique. The device is fabricated in a 0.5-μm triple-well, p-substrate CMOS process using two-metal and three-poly interconnect layers. A resulting die size is 86.6 mm2, and the effective cell size including the overhead of string select transistors is 2.0 μm2 相似文献
4.
Suk Choo Chung Chang Duck Kong Young Ha Yum 《Journal of Mechanical Science and Technology》1987,1(2):133-139
The dynamic characteristics of the Korean Yi-dynasty bell type structure, including the acoustic effects, are analyzed both theoretically and experimentally. The numerical solutions of natural frequencies and mode shape for membrane and flexural behavior are obtained by using the NASTRAN program for the finite element method with plate shell elements of triangular and quadrilateral types. Test bells, A and B types similar to the Kap-Sa bell in Kong-Ju chosen among typical Korean Yi-dynasty bells, are manufactured on different scales to the original bell. To consider the effects of the variation of the structural dimension on the dynamic response, these bells are analyzed with respect to the variation of the thickness of the wall and the bottom rim and the asymmetric Dang-Jwas. The impact method with the Fast Fourier Transform Analyzer is adopted to experimentally assess the dynamic response. Results are in good agreement with the numerical solutions. 相似文献
5.
Ji Hoon Yang Min Hyung Yum Eun Jung Kim Myeung Hoi Kwon Cheol Woong Yang Ha-Jin Song Yong-Wan Jin 《Carbon》2006,44(11):2219-2223
Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C2H2, NH3, and N2 gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules. 相似文献
6.
Solar Cells: Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells (Small 34/2017)
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7.
Montesinos CA Tse ZT Chan YJ Elhawary H Rea M Hamed A Young I Lamperth M 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2012,226(1):49-54
The static magnetic field of a magnetic resonance imaging scanner can be distorted by the presence of materials, perturbing the spatial encoding process in magnetic resonance imaging and often resulting in image artifacts. The relationship between the image artifact size and magnetic susceptibility of the material specimen is of interest to engineers for the design of devices that are to be compatible with the imaging volume of the scanner. In this study, a finite-element method was used to simulate the distorted magnetic field of samples with different susceptibilities. With the knowledge of the external- and self- magnetic field interactions, a Lorentz correction was applied to compute the magnetic field deviation. The simulated results were then validated by the corresponding experimental magnetic resonance images. 相似文献
8.
Sang-Nyung Kim Cheol-Hong Kim Bum-Su Youn Hag-Ki Yum 《Journal of Mechanical Science and Technology》2007,21(4):654-663
Nuclear power plant components suffer pipe shedding, cracking, thermal fatigue, bending and supporting bracket breakage during
their life span. Notably, the horizontal inlet nozzle of steam generator is prone to thermal stratification frequently due
to its operational characteristics. As a result, PWRs in many countries including the U.S.A. suffered a lot of pipe cracks
and leakages around the late 1970s, as the thermal stress inflicted by thermal stratification formed in the horizontal inlet
nozzle of steam generator during transition (auxiliary feedwater injection) was not reflected on power plant design.
Therefore, we classified the nuclear power plants in Korea into KSNP and Westinghouse-type(W) power plants (Kori # 1,2,3,4, Yeonggwang # 1,2 and Uljin # 1,2) and conducted an experiment on thermal stratification and
thermal cycling in relation to the volume of auxiliary feedwater injected into the horizontal inlet nozzle of steam generator
and hot water flowing back from steam generator. As a result, it was found out that KSNP was hardly prone to thermal stratification
while thermal stratification occurred in the horizontal inlet nozzle of steam generator in Westinghouse-tvpe(W) power plants, necessitating a solution to address such a phenomenon.•• 相似文献
9.
10.
Giuseppe Calogero Jun-Ho Yum Alessandro Sinopoli Gaetano Di Marco Michael Grätzel Mohammad Khaja Nazeeruddin 《Solar Energy》2012,86(5):1563-1575
We present the photoelectrochemical properties of dye-sensitized solar cells using natural pigments containing betalains and anthocyanins as sensitizers. The dyes extracted from grape, mulberry, blackberry, red Sicilian orange, Sicilian prickly pear, eggplant and radicchio have shown a monochromatic incident photon to current efficiency (IPCE) ranging from 40% to 69%. Short circuit photocurrent densities (Jsc) up to 8.8 mA/cm2, and open circuit voltage (Voc) ranging from 316 to 419 mV, were obtained from these natural dyes under 100 mW/cm2 (AM 1.5) simulated sunlight. The best solar conversion efficiency of 2.06% was achieved with Sicilian prickly pear fruits extract. The influence of pH and co-absorbers on natural sensitizers, were investigated and discussed. 相似文献