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Search Results: 1 - 10 of 336473 matches for " K. P. Cheng "
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Good Agricultural Practice (GAP) -Does It Ensure a Perfect Supply of Medicinal Herbs for Research and Drug Development?
P C Leung,K F Cheng
International Journal of Applied Research in Natural Products , 2008,
Abstract: Summary: While users of herbal formulae have been disappointed with the lack of uniformity with the quality of herbs provided by the herb suppliers of different standings, they do not have better means of supply. The tradition of identifying special geographic regions, as being specific for the best supply of certain herbal items is no longer reliable since the large demand for large quantities of quality supply could not be satisfied by limited plantations in those regions. A comprehensive recommendation of agricultural practice: from seedling, planting, fertilizing, harvesting, storage to distribution, can be offered as a compromise. There is good prospect of an excellent supply of quality herbal products with uniformity, if Good Agricultural Practice (GAP) could be practiced and enforced. Although the need for GAP is urgent, and Japan, China and World Health Organization, have one after the other, written up their recommendation, to put GAP into real practice would need special efforts and takes time. GAP in China is particularly difficult, not only because the herbal items involved are of great numbers but because the current practice of growing medicinal herbs, their marketing and distribution, have been counterproductive to the introduction of the new system of GAP. At this stage, GAP will not be able to satisfy the extensive need for quality and uniformity. Short of the knowledge of the exact, accurate nature of the active components within a herb, there will be no perfect guarantee on the quality supply. Henceforth, even when GAP becomes a mature practice, what is required for quality control, viz, different levels of authentication, from chemical finger printing to molecular, DNA identification, will remain necessary as cross-checking mechanisms to make sure that uniformity in scientific experiments and drug development could be maintained
Thermal X-Ray Pulses Resulting From Pulsar Glitches
Anisia P. S. Tang,K. S. Cheng
Physics , 2000, DOI: 10.1086/319427
Abstract: The non-spherically symmetric transport equations and exact thermal evolution model are used to calculate the transient thermal response to pulsars. The three possible ways of energy release originated from glitches, namely the `shell', `ring' and `spot' cases are compared. The X-ray light curves resulting from the thermal response to the glitches are calculated. Only the `spot' case and the `ring' case are considered because the `shell' case does not produce significant modulative X-rays. The magnetic field ($\vec B$) effect, the relativistic light bending effect and the rotational effect on the photons being emitted in a finite region are considered. Various sets of parameters result in different evolution patterns of light curves. We find that this modulated thermal X-ray radiation resulting from glitches may provide some useful constraints on glitch models.
Gamma-ray properties of globular clusters and the "fundamental planes"
P. Tam,A. Kong,C. Y. Hui,K. S. Cheng
Physics , 2011,
Abstract: We report on the discovery of gamma-ray emission from several globular clusters (GCs), including Terzan 5, the second known gamma-ray GCs. By now, more than a dozen GCs are known to emit gamma-rays of energies above 100 MeV, thus enabling us to carry out the first detailed correlation study with several cluster properties. We found strong correlations between the observed gamma-ray luminosities and four cluster parameters: stellar encounter rate, metallicity [Fe/H], and energy densities of the soft photons at the cluster locations. These "fundamental planes" of gamma-ray GCs put an intimate relation of the observed gamma-rays to the underlying millisecond pulsar population and have important implications on the origin of the gamma-ray emission of GCs.
High-Energy Emission of the First Millisecond Pulsar
C. -Y. Ng,J. Takata,G. C. K. Leung,K. S. Cheng,P. Philippopoulos
Physics , 2014, DOI: 10.1088/0004-637X/787/2/167
Abstract: We report on X-ray and gamma-ray observations of the millisecond pulsar B1937+21 taken with the Chandra X-ray Observatory, XMM-Newton, and the Fermi Large Area Telescope. The pulsar X-ray emission shows a purely non-thermal spectrum with a hard photon index of 0.9+/-0.1, and is nearly 100% pulsed. We found no evidence of varying pulse profile with energy as previously claimed. We also analyzed 5.5 yr of Fermi survey data and obtained much improved constraints on the pulsar's timing and spectral properties in gamma-rays. The pulsed spectrum is adequately fitted by a simple power-law with a photon index of 2.38+/-0.07. Both the gamma-ray and X-ray pulse profiles show similar two-peak structure and generally align with the radio peaks. We found that the aligned profiles and the hard spectrum in X-rays seem to be common properties among millisecond pulsars with high magnetic fields at the light cylinder. We discuss a possible physical scenario that could give rise to these features.
High-energy emissions from the gamma-ray binary LS 5039
J. Takata,Gene C. K. Leung,P. H. T. Tam,A. K. H. Kong,C. Y. Hui,K. S. Cheng
Physics , 2014, DOI: 10.1088/0004-637X/790/1/18
Abstract: We study mechanisms of multi-wavelength emissions (X-ray, GeV and TeV gamma-rays) from the gamma-ray binary LS~5039. This paper is composed of two parts. In the first part, we report on results of observational analysis using four year data of \fermi\ Large Area Telescope. Due to the improvement of instrumental response function and increase of the statistics, the observational uncertainties of the spectrum in $\sim$100-300 MeV bands and $>10$GeV bands are significantly improved. The present data analysis suggests that the 0.1-100GeV emissions from LS~5039 contain three different components; (i) the first component contributes to $<$1GeV emissions around superior conjunction, (ii) the second component dominates in 1-10GeV energy bands and (iii) the third component is compatible to lower energy tail of the TeV emissions. In the second part, we develop an emission model to explain the properties of the phase-resolved emissions in multi-wavelength observations. Assuming that LS~5039 includes a pulsar, we argue that both emissions from magnetospheric outer gap and inverse-Compton scattering process of cold-relativistic pulsar wind contribute to the observed GeV emissions. We assume that the pulsar is wrapped by two kinds of termination shock; Shock-I due to the interaction between the pulsar wind and the stellar wind and Shock-II due to the effect of the orbital motion. We propose that the X-rays are produced by the synchrotron radiation at Shock-I region and the TeV gamma-rays are produced by the inverse-Compton scattering process at Shock-II region.
Comprehensive characterization of indoor airborne bacterial profile

P L Chan,P H F Yu,Y W Cheng,C Y Chan,P K Wong,

环境科学学报(英文版) , 2009,
Abstract: This is the first detailed characterization of the airborne bacterial profiles in indoor environments. Two restaurants were selected for this study. Fifteen genera of bacteria were isolated from each restaurant and identified by three different bacterial identification systems including MIDI, Biolog and Riboprinter . The dominant bacteria of both restaurants were Gram-positive bacteria in which Micrococcus and Bacillus species were the most abundant. Most bacteria identified were representative species of skin and respiratory tract of human, and soil. Although the bacterial levels in these two restaurants were below the limit of the Hong Kong Indoor Air Quality Objective (HKIAQO) Level 1 standard (i.e., < 500 cfu/m3), the majority of these bacteria were opportunistic pathogens. These results suggested that the identity of airborne bacteria should also be included in the IAQ to ensure there is a safety guideline for the public.
Temperature and Safety Profiles of Needle-Warming Techniques in Acupuncture and Moxibustion
X. Y. Gao,C. Y. Chong,S. P. Zhang,K. W. E. Cheng,B. Zhu
Evidence-Based Complementary and Alternative Medicine , 2012, DOI: 10.1155/2012/168393
Abstract: The needle-warming technique combines acupuncture and moxibustion, and it is commonly practised in China to relieve pain conditions. However, burning of moxa has many disadvantages. This study examined the temperature and safety profiles of such technique. First, skin temperature changes during needle-warming were examined in anesthetized animals to determine the safe distance for needle-warming moxibustion in human subjects. Then, the practical distance for needle-warming in human subjects were verified. Finally, the temperature profiles of the needle during needle-warming moxibustion were examined using an infrared camera. Our results show that during needle-warming moxibustion there is little heat being conducted into deep tissue via the shaft of the needle, and that the effective heating time to the acupoint is rather short compared to the period of moxibustion. These findings suggest that the needle-warming technique is an inefficient way of acupoint thermal stimulation and should be modified and improved using new technologies.
Determinants of antigenicity and specificity in immune response for protein sequences
Yulong Wang, Wenjun Wu, Nicolas N Negre, Kevin P White, Cheng Li, Parantu K Shah
BMC Bioinformatics , 2011, DOI: 10.1186/1471-2105-12-251
Abstract: Our analysis using protein properties suggested that sequence composition combined with evolutionary information and predicted secondary structure, as well as solvent accessibility is sufficient to predict successful peptide epitopes. The antigenicity and the specificity in immune response were also found to depend on the epitope length. We trained the B-Cell Epitope Oracle (BEOracle), a support vector machine (SVM) classifier, for the identification of continuous B-Cell epitopes with these protein properties as learning features. The BEOracle achieved an F1-measure of 81.37% on a large validation set. The BEOracle classifier outperformed the classical methods based on propensity and sophisticated methods like BCPred and Bepipred for B-Cell epitope prediction. The BEOracle classifier also identified peptides for the ChIP-grade antibodies from the modENCODE/ENCODE projects with 96.88% accuracy. High BEOracle score for peptides showed some correlation with the antibody intensity on Immunofluorescence studies done on fly embryos. Finally, a second SVM classifier, the B-Cell Region Oracle (BROracle) was trained with the BEOracle scores as features to predict the performance of antibodies generated with large protein regions with high accuracy. The BROracle classifier achieved accuracies of 75.26-63.88% on a validation set with immunofluorescence, immunohistochemistry, protein arrays and western blot results from Protein Atlas database.Together our results suggest that antigenicity is a local property of the protein sequences and that protein sequence properties of composition, secondary structure, solvent accessibility and evolutionary conservation are the determinants of antigenicity and specificity in immune response. Moreover, specificity in immune response could also be accurately predicted for large protein regions without the knowledge of the protein tertiary structure or the presence of discontinuous epitopes. The dataset prepared in this work and the classifier
Development of Computer Controlled FES System with Improved Circuit Design
K.W.E. Cheng,C.Y. Tang,C.P. Tsui
Journal of Applied Sciences , 2006,
Abstract: An advanced computer controlled system for FES is developed that is aimed to give successful control to the electrical stimulation of muscle which is the time-varying nonlinear system. The performance of control systems is designed to be robust and can adapt to change in system gains. A DSP is programmed with Simulink for the study. In the circuit side, the new design of FES circuit is proposed that is connected together with the computer system. The circuit can give sufficient voltage without magnetic transformer that can also reduce significantly the circuit size and weight.
Flavor symmetry breaking and scaling for improved staggered actions in quenched QCD
M. Cheng,N. H. Christ,C. Jung,F. Karsch,R. D. Mawhinney,P. Petreczky,K. Petrov
Physics , 2006, DOI: 10.1140/epjc/s10052-007-0336-1
Abstract: We present a study of the flavor symmetry breaking in the pion spectrum for various improved staggered fermion actions. To study the effects of link fattening and tadpole improvement, we use three different variants of the p4 action - p4fat3, p4fat7, and p4fat7tad. These are compared to Asqtad and also to naive staggered. To study the pattern of symmetry breaking, we measure all 15 meson masses in the 4-flavor staggered theory. The measurements are done on a quenched gauge background, generated using a one-loop improved Symanzik action with $\beta=10/g^2 = 7.40, 7.75,$ and 8.00, corresponding to lattice spacings of approximately a = .31 fm., .21 fm., and .14 fm. We also study how the lattice scale set by the $\rho$ mass on each of these ensembles compares to one set by the static quark potential.
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