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Search Results: 1 - 10 of 565230 matches for " C. M. Hui "
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VERITAS observations of M87 from 2007 to present
C. M. Hui,for the VERITAS collaboration
Physics , 2009,
Abstract: M87 is a nearby radio galaxy and because of its misaligned jet, it is possible to correlate detailed spatially-resolved emission regions in the radio, optical to X-ray waveband with unresolved but contemporaneous flux measurements in the TeV regime. Hence, M87 provides a unique opportunity to reveal the emission mechanisms responsible for high energy gamma-ray emission from active galactic nuclei. Observations with VERITAS since 2007 have resulted in 90 hours of data while 2008 observations were part of a concerted effort involving the three major atmospheric Cherenkov observatories: H.E.S.S., MAGIC and VERITAS. As a result of the TeV campaign, a high flux state of M87 was detected in February 2008 showing multiple flares with rapid variability. We will present the comprehensive results from VERITAS observations since 2007 and also show preliminary results from the 2009 campaign.
Second Harmonic Generation for a Dilute Suspension of Coated Particles
P. M. Hui,C. Xu,D. Stroud
Physics , 2003, DOI: 10.1103/PhysRevB.69.014203
Abstract: We derive an expression for the effective second-harmonic coefficient of a dilute suspension of coated spherical particles. It is assumed that the coating material, but not the core or the host, has a nonlinear susceptibility for second-harmonic generation (SHG). The resulting compact expression shows the various factors affecting the effective SHG coefficient. The effective SHG per unit volume of nonlinear coating material is found to be greatly enhanced at certain frequencies, corresponding to the surface plasmon resonance of the coated particles. Similar expression is also derived for a dilute suspension of coated discs. For coating materials with third-harmonic (THG) coefficient, results for the effective THG coefficients are given for the cases of coated particles and coated discs.
Dimensional Crossover in the Effective Second Harmonic Generation of Films of Random Dielectrics
P. M. Hui,C. Xu,D. Stroud
Physics , 2003, DOI: 10.1103/PhysRevB.69.014202
Abstract: The effective nonlinear response of films of random composites consisting of a binary composite with nonlinear particles randomly embedded in a linear host is theoretically and numerically studied. A theoretical expression for the effective second harmonic generation susceptibility, incorporating the thickness of the film, is obtained by combining a modified effective-medium approximation with the general expression for the effective second harmonic generation susceptibility in a composite. The validity of the thoretical results is tested against results obtained by numerical simulations on random resistor networks. Numerical results are found to be well described by our theory. The result implies that the effective-medium approximation provides a convenient way for the estimation of the nonlinear response in films of random dielectrics.
HAWC Observation of Supernova Remnants and Pulsar Wind Nebulae
C. M. Hui,H. Zhou,for the HAWC Collaboration
Physics , 2015,
Abstract: The majority of Galactic TeV gamma-ray sources are pulsar wind nebulae (PWNe) and supernova remnants (SNRs), and the most common association for unidentified sources is PWN. Many of these sources were discovered in TeV by imaging air Cherenkov telescopes using overlapping pointed observations over sections of the Galactic plane. The HAWC observatory is a survey type instrument in the Northern hemisphere with an energy range of 100 GeV to 100 TeV. Preliminary analysis of data recorded with the partially completed HAWC array taken since 2013 shows extended detections that are coincident with known TeV SNRs and PWNe. The full array became operational in early 2015 and has been steadily surveying the Northern sky since. I will discuss detections in HAWC data taken since 2013 associated with PWNe and SNRs.
Differential games of partial information forward-backward doubly stochastic differential equations and applications
Eddie C. M. Hui,Hua Xiao
Mathematics , 2011,
Abstract: This paper is concerned with a new type of differential game problems of forwardbackward stochastic systems. There are three distinguishing features: Firstly, our game systems are forward-backward doubly stochastic differential equations, which is a class of more general game systems than other forward-backward stochastic game systems without doubly stochastic terms; Secondly, forward equations are directly related to backward equations at initial time, not terminal time; Thirdly, the admissible control is required to be adapted to a sub-information of the full information generated by the underlying Brownian motions. We give a necessary and a sufficient conditions for both an equilibrium point of nonzero-sum games and a saddle point of zero-sum games. Finally, we work out an example of linear-quadratic nonzero-sum differential games to illustrate the theoretical applications. Applying some stochastic filtering techniques, we obtain the explicit expression of the equilibrium point.
Secure Chained Threshold Proxy Signature without and with Supervision  [PDF]
Zoe L. JIANG, S. M. YIU, Y. DONG, L. C. K. HUI, S. H. Y. WONG
Journal of Software Engineering and Applications (JSEA) , 2009, DOI: 10.4236/jsea.2009.24034
Abstract: Threshold Proxy Signature (TPS) scheme facilitates a manager to delegate his signing capability to a group of n2 sub-ordinates without revealing his own private key, such that a subgroup of at least t2 ≤ n2 subordinates is required to generate a proxy signature. In reality, the situation can be more complicated. First of all, the subgroup may further delegate their proxy signing capabilities to another group of n3 subordinates such that at least another subgroup of at least t3 ≤ n3 subordinates are of the proxy signing capabilities (in the form of a chain). t2 can be unequal to t3 depending on the concrete requirement. This is a group-to-group delegation problem. In addition, a supervising agent (SA) may be introduced in the above chain to supervise the subordinates, such that proxy signing can only be successfully executed with SA’s agreement. This is a delegation with supervision problem in the threshold delegation chain described above. These two extensions of delegation problems are not solved yet. This paper designs two provably secure cryptographic schemes Chained Threshold Proxy Signature (CTPS) scheme and Chained Threshold Proxy Signature with Supervision (CTPSwS) scheme to solve these two delegation problems.
Connective Tissue Energy Loss Comparison between Joints with and without Hypermobility  [PDF]
Stephen A. Tatarkov, Angela C. Tesny, Brittany M. Lauck, Louis A. DiBerardino III, Hui Shen
Journal of Biomedical Science and Engineering (JBiSE) , 2017, DOI: 10.4236/jbise.2017.105B003
Abstract:
Joint hypermobility syndrome is a condition in which a joint can move effortlessly beyond the normal limit of motion expected for that joint. This syndrome is affected by some factors including gender and tends to be inherited. It may cause some symptoms such as pain in an individual’s synovial joints. The objective of the current study was to compare the energy loss of connective tissues between joints with and without hypermobility. A differential equation model, namely the Kelvin-Voigt model, was used for the energy loss analysis. The results show the difference in energy loss for the tissues attached to joints with and without joint hypermobility. As the stiffness of the connective tissue decreases, the energy loss increases. Muscle activity about the ankle was measured via electromyography during simple functional tasks, and the recorded data were used to correlate with the theoretical analysis of the energy loss. The result would shed light on the pathology analysis of the symptoms such as the cause of pain.
Early Electrophysiological Basis of Experience-Associated Holistic Processing of Chinese Characters
Hui Chen, Cindy M. Bukach, Alan C.-N. Wong
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0061221
Abstract: Recent studies have found holistic processing to be a marker of expertise for perception of words in alphabetic (e.g., English) and non-alphabetic (e.g., Chinese) writing systems, consistent with what has been found for faces and other objects of face-like expertise. It is unknown, however, whether holistic processing of words occurs in an early, perceptual stage as it does for faces. We examined how early holistic processing of Chinese characters emerges by recording the event-related potentials (ERPs) in an adaptation paradigm. Participants judged if the top parts of two sequentially presented characters were the same or different while ignoring the bottom part. An early potential (P1) at the posterior channels was smaller when the attended top parts were the same compared with when they are different, indicating an adaptation effect. Critically, for trials with identical top parts, P1 was larger when the irrelevant bottom parts were different, indicating a release of adaptation. This effect was present only when the two character parts were aligned but not misaligned, and only for characters but not for pseudocharacters. The finding of early sensitivity to all parts of a Chinese character suggests that Chinese characters are represented holistically at a perceptual level.
Cellular automata models of traffic flow along a highway containing a junction
Simon C. Benjamin,Neil F. Johnson,P. M. Hui
Physics , 1996, DOI: 10.1088/0305-4470/29/12/018
Abstract: We examine various realistic generalizations of the basic cellular automaton model describing traffic flow along a highway. In particular, we introduce a {\em slow-to-start} rule which simulates a possible delay before a car pulls away from being stationary. Having discussed the case of a bare highway, we then consider the presence of a junction. We study the effects of acceleration, disorderness, and slow-to-start behavior on the queue length at the entrance to the highway. Interestingly, the junction's efficiency is {\it improved} by introducing disorderness along the highway, and by imposing a speed limit.
Sagittarius B2 Main: A Cluster of Ultra-Compact HII Regions and Massive Protostellar Cores
Jun-Hui Zhao,M. C. H. Wright
Physics , 2011, DOI: 10.1088/0004-637X/742/1/50
Abstract: The ionized core in the Sgr B2 Main star-forming region was imaged using the Submillimeter Array archival data observed for the H26$\alpha$ line and continuum emission at 0.86 millimeter with an angular resolution 0.3\arcsec. Eight hyper-compact H26$\alpha$ emission sources were detected with a typical size in the range of 1.6--20$\times10^2$ AU and electron density of 0.3--3$\times10^7$ cm$^{-3}$, corresponding to the emission measure 0.4--8.4$\times10^{10}$ cm$^{-6}$ pc. The H26$\alpha$ line fluxes from the eight hyper-compact HII sources imply that the ionization for each of the sources must be powered by a Lyman continuum flux from an O star or a cluster of B stars. The most luminous H26$\alpha$ source among the eight detected requires an O6 star that appears to be embedded in the ultra-compact HII region F3. In addition, $\sim$ 23 compact continuum emission sources were also detected within the central 5\arcsec$\times$3\arcsec\,($\sim0.2$ pc) region. In the assumption of a power-law distribution for the dust temperature, with the observed brightness temperature of the dust emission we determined the physical properties of the submillimeter emission sources showing that the molecular densities are in the range of 1--10$\times10^8$ cm$^{-3}$, surface densities between 13 to 150 $g$ cm$^{-2}$, and total gas masses in the range from 5 to $\gtrsim$ 200 $M_\odot$ which are 1 or 2 orders of magnitude greater than the corresponding values of the Bonnor-Ebert mass. With a mean free-fall time scale of 2$\times10^3$ y, each of the massive protostellar cores are undergoing gravitational collapse to form new massive stars in the Sgr B2 Main core.
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