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Search Results: 1 - 10 of 270380 matches for " K. -H. Ho "
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Thermal Effect and Frequency Response Analyses on Heterojunction Bipolar Power Transistor
K. F. Yarn,K. H. Ho
Active and Passive Electronic Components , 2001, DOI: 10.1155/2001/78036
Abstract: Heterojunction bipolar transistors (HBT) based on Npn AlGaAs/GaAs material system have attracted considerable attention for microwave power and digital applications due to their high speed and high current capabilities. In this paper, a numerical model based on the Npn AlGaAs/GaAs HBT structure for the carrier transport is presented. Three figures of merit on device operation, current gain, cut-off frequency and maximum oscillation frequency are calculated. Besides, thermal instability plays an important role on power HBT resulted from the low thermal conductivity in GaAs. The generated heat will increase the junction temperature and cause self-destruction. Therefore, the thermal runaway study of the junction temperature, current–voltage (IV) characteristics and frequency response using an analytical thermal model is described.
Practical Entanglement Distillation Scheme Using Recurrence Method And Quantum Low Density Parity Check Codes
H. F. Chau,K. H. Ho
Physics , 2009,
Abstract: Many entanglement distillation schemes use either universal random hashing or breeding as their final step to obtain almost perfect shared EPR pairs. In spite of a high yield, the hardness of decoding a random linear code makes the use of random hashing and breeding infeasible in practice. In this pilot study, we analyze the performance of the recurrence method, a well-known entanglement distillation scheme, with its final random hashing or breeding procedure being replaced by various efficiently decodable quantum codes. Among all the replacements investigated, the one using a certain adaptive quantum low density parity check (QLDPC) code is found to give the highest yield for Werner states over a wide range of noise level --- the yield for using this QLDPC code is higher than the first runner up by more than 25\% over a wide parameter range. In this respect, the effectiveness of using QLDPC codes in practical entanglement distillation is illustrated.
Purifying GHZ States Using Degenerate Quantum Codes
K. H. Ho,H. F. Chau
Physics , 2008,
Abstract: Degenerate quantum codes are codes that do not reveal the complete error syndrome. Their ability to conceal the complete error syndrome makes them powerful resources in certain quantum information processing tasks. In particular, the most error-tolerant way to purify depolarized Bell states using one-way communication known to date involves degenerate quantum codes. Here we study three closely related purification schemes for depolarized GHZ states shared among $m \geq 3$ players by means of degenerate quantum codes and one-way classical communications. We find that our schemes tolerate more noise than all other one-way schemes known to date, further demonstrating the effectiveness of degenerate quantum codes in quantum information processing.
An Adaptive Entanglement Distillation Scheme Using Quantum Low Density Parity Check Codes
K. H. Ho,H. F. Chau
Physics , 2008,
Abstract: Quantum low density parity check (QLDPC) codes are useful primitives for quantum information processing because they can be encoded and decoded efficiently. Besides, the error correcting capability of a few QLDPC codes exceeds the quantum Gilbert-Varshamov bound. Here, we report a numerical performance analysis of an adaptive entanglement distillation scheme using QLDPC codes. In particular, we find that the expected yield of our adaptive distillation scheme to combat depolarization errors exceed that of Leung and Shor whenever the error probability is less than about 0.07 or greater than about 0.28. This finding illustrates the effectiveness of using QLDPC codes in entanglement distillation.
Study of the Wealth Inequality in the Minority Game
K. H. Ho,F. K. Chow,H. F. Chau
Physics , 2004, DOI: 10.1103/PhysRevE.70.066110
Abstract: To demonstrate the usefulness of physical approaches for the study of realistic economic systems, we investigate the inequality of players' wealth in one of the most extensively studied econophysical models, namely, the minority game (MG). We gauge the wealth inequality of players in the MG by a well-known measure in economics known as the modified Gini index. From our numerical results, we conclude that the wealth inequality in the MG is very severe near the point of maximum cooperation among players, where the diversity of the strategy space is approximately equal to the number of strategies at play. In other words, the optimal cooperation between players comes hand in hand with severe wealth inequality. We also show that our numerical results in the asymmetric phase of the MG can be reproduced semi-analytically using a replica method.
Minority Game With Peer Pressure
H. F. Chau,F. K. Chow,K. H. Ho
Physics , 2003, DOI: 10.1016/j.physa.2003.10.009
Abstract: To study the interplay between global market choice and local peer pressure, we construct a minority-game-like econophysical model. In this so-called networked minority game model, every selfish player uses both the historical minority choice of the population and the historical choice of one's neighbors in an unbiased manner to make decision. Results of numerical simulation show that the level of cooperation in the networked minority game differs remarkably from the original minority game as well as the prediction of the crowd-anticrowd theory. We argue that the deviation from the crowd-anticrowd theory is due to the negligence of the effect of a four point correlation function in the effective Hamiltonian of the system.
Central Neurocytoma and Epidermoid Tumor Occurring as Collision Tumors: A Rare Association  [PDF]
Peter Y. M. Woo, Ho Hung Cheung, Calvin H. K. Mak, Siu Ki Chan, Kar Ming Leung, Kwong Yau Chan
Open Journal of Modern Neurosurgery (OJMN) , 2014, DOI: 10.4236/ojmn.2014.41007
Abstract: Different brain tumors of distinct histology can co-exist in the setting of phakomatoses or as a complication of radiotherapy. In the absence of these predisposing factors, this phenomenon is uncommon. When the lesions are in close proximity they are described as collision tumors and are extremely rare. A 58-year-old woman presented with persistent headache and cognitive decline for three months. Magnetic resonance imaging revealed a tumor arising from the atrium of the left lateral ventricle with heterogeneous contrast enhancement. This intraventricular lesion was adjacent to another extensive infiltrating tumor of the basal cisterns. Operative findings revealed a vascular ventricular tumor and gross total resection was achieved. An adjacent avascular basal cistern tumor with a pearly white sheen was encountered and partial excision was performed. The histopathological diagnosis was central neurocytoma and epidermoid tumor. There is only one documented description of a central neurocytoma co-existing with a tumor of different pathology. To our knowledge, this is the first reported collision tumor case involving central neurocytoma. Since the incidence of both lesions co-existing juxtaposed is extremely low, a chronic oncogenetic inflammatory process stimulated by the epidermoid tumor to the subventricular region is suggested. Other mechanisms for tumor collision are discussed and we suggest a classification system for this rare association to reflect their pathogenesis.
Thermoplastic Polyurethane Elastomer Nanocomposites: Morphology, Thermophysical, and Flammability Properties
Wai K. Ho,Joseph H. Koo,Ofodike A. Ezekoye
Journal of Nanomaterials , 2010, DOI: 10.1155/2010/583234
Abstract: Novel materials based on nanotechnology creating nontraditional ablators are rapidly changing the technology base for thermal protection systems. Formulations with the addition of nanoclays and carbon nanofibers in a neat thermoplastic polyurethane elastomer (TPU) were melt-compounded using twin-screw extrusion. The TPU nanocomposites (TPUNs) are proposed to replace Kevlar-filled ethylene-propylene-diene-monomer rubber, the current state-of-the-art solid rocket motor internal insulation. Scanning electron microscopy analysis was conducted to study the char characteristics of the TPUNs at elevated temperatures. Specimens were examined to analyze the morphological microstructure during the pyrolysis reaction and in fully charred states. Thermophysical properties of density, specific heat capacity, thermal diffusivity, and thermal conductivity of the different TPUN compositions were determined. To identify dual usage of these novel materials, cone calorimetry was employed to study the flammability properties of these TPUNs.
Radiative neutrino mass generation and dark energy
K. Bamba,C. Q. Geng,S. H. Ho
Physics , 2008, DOI: 10.1088/1475-7516/2008/09/001
Abstract: We study the models with radiative neutrino mass generation and explore the relation between the neutrino masses and dark energy. In these models, the pseudo-Nambu-Goldston bosons (pNGBs) arise at two-loop level via the Majorana neutrino masses. In particular, we demonstrate that the potential energy of the pNGB can be the dark energy potential and the observed value of the equation of state (EoS) parameter of the universe, $i.e.$, $w\simeq -1$, can be realized.
Large-scale magnetic fields from inflation due to Chern-Simons-like effective interaction
K. Bamba,C. Q. Geng,S. H. Ho
Physics , 2008, DOI: 10.1088/1475-7516/2008/11/013
Abstract: We discuss the generation of large-scale magnetic fields due to the breaking of the conformal invariance in the electromagnetic field through the $CPT$-even dimension-six Chern-Simons-like effective interaction with a fermion current in inflationary cosmology. It is shown that the magnetic fields on 1Mpc scale with the field strength of $\sim 10^{-9}$G at the present time can be generated even for the scale of the effective interaction being the Planck scale.
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