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Search Results: 1 - 10 of 361649 matches for " S. Y. Chong "
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Numerical Modeling of Mass Transfer for Solvent-Carbon Dioxide System at Supercritical (Miscible) Conditions
G.H. Chong,S.Y. Spotar,R. Yunus
Journal of Applied Sciences , 2009,
Abstract: A numerical procedure of mathematical model for mass transfer between a droplet of organic solvent and a compressed antisolvent is presented for conditions such that the two phases are fully miscible. The model is applicable to the supercritical antisolvent (SAS) method of particle formation. In this process, solute particles precipitate from an organic solution when sprayed into a compressed antisolvent continuum. Effects of operating temperature and pressure on droplet behavior were examined. The CO2 critical locus and the conditions for which the densities of solvent and carbon dioxide are equal are identified. Calculations were performed using Peng-Robinson equation of state. The model equations were put into the form that allowed the application of the Matlab standard solver pdepe. Calculations with toluene, ethanol, acetone (solvents) and carbon dioxide (antisolvent) demonstrated that droplets swell upon interdiffusion when the solvent is denser than the antisolvent and shrink when the antisolvent is denser. Diffusion modeling results might be used for data interpretation or experiments planning of the more complex real SAS process.
Shock Response Spectra Reconstruction of Pointwise Explosive-Induced Pyroshock Based on Signal Processing of Laser Shocks
S. Y. Chong,J. R. Lee,C. W. Kong
Shock and Vibration , 2014, DOI: 10.1155/2014/695836
Abstract: Pyroshock has been an issue of great concern for aerospace and defense industrial applications. When pyroshock devices are detonated, they can easily cause failures in electronic, optical, relay, and magnetic components generally in mid- and far-fields which is not avoidable at the design level. Thus, many numerical and experimental pyroshock simulations have been widely studied to predict explosive-induced pyroshock effect quantitatively, especially the shock response spectrum (SRS). In this study, a laser shock-based pyroshock reconstruction method is proposed to simulate a pointwise explosive-induced pyroshock signal. The signal processing algorithm for the laser shock-based pyroshock reconstruction is developed in a LabVIEW platform and consists of subbands decomposition, SRS matching in decomposed bands, and wave synthesizing. Then, two experimental setups are configured to obtain pyroshock signals and laser shock signals at four points in an aluminum plate. The reconstructed pyroshock signals synthesized according to the signal processing of the laser shocks demonstrate high similarity to the real pyroshock signals, where the similarity is evaluated by the mean acceleration difference between the SRS curves. The optimized settings of the subband decomposition were obtained and can be in the future used in a pyroshock simulator based on laser shock for pyroshock simulation at any arbitrary point. 1. Introduction Pyrotechnic shock or pyroshock has been an issue of great concern for aerospace and defense industrial applications. Pyroshock is the transient oscillatory response of a structure to loading (high frequency and high magnitude stress waves) induced by the detonation of pyrotechnic devices using pointwise or linear explosives [1], incorporated into or attached to the structure. As a result, its high frequency energy can easily cause failures in electronic, optical, relay, and magnetic components, especially in aerospace applications during the separation of structural subsystems, the deployment of appendages, and the activation or deactivation of subsystems [2]. Various pyroshock simulation methods, which are generally classified as experimental and numerical simulations, have been studied to predict pyroshock effects quantitatively on the intended pyroshock environments. These pyroshock environments can be classified as near-, mid-, and far-field environments [1, 3]. Then, a shock response spectrum (SRS) is used as a tool to analyze and quantify a pyroshock. The SRS is a graphical representation of maximum response regarding a single
SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk
S. Deguchi,J. Nakashima,Y. Zhang,S. S. N. Chong,K. Koike,S. Kwok
Physics , 2010, DOI: 10.1093/pasj/62.2.391
Abstract: We present the result of radio observations of red supergiants in the star cluster, Stephenson's #2, and candidates for red supergiants in the star clusters, Mercer et al. (2005)'s #4, #8, and #13, in the SiO and H$_2$O maser lines.The Stephenson's #2 cluster and nearby aggregation at the South-West contain more than 15 red supergiants. We detected one at the center of Stephenson's #2 and three in the south-west aggregation in the SiO maser line, and three of these 4 were also detected in the H2O maser line. The average radial velocity of the 4 detected objects is 96 km s^{-1}, giving a kinematic distance of 5.5 kpc, which locates this cluster near the base of the Scutum-Crux spiral arm. We also detected 6 SiO emitting objects associated with the other star clusters. In addition, mapping observations in the CO J=1--0 line toward these clusters revealed that an appreciable amount of molecular gas still remains around Stephenson's #2 cluster in contrast to the prototypical red-supergiant cluster, Bica et al.'s #122. It indicates that a time scale of gas expulsion differs considerably in individual clusters.
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.
Enhancement of Gain in L-Band Bismuth-Based Erbium-Doped Fibre Amplifier Using an Un-pumped EDF and Midway Isolator
W Y Chong,S W Harun,H Ahmad,
W.Y.Chong
,S.W.Harun,H.Ahmad

中国物理快报 , 2004,
Abstract: A hybrid L-band erbium-doped fibre amplifier (EDFA) with enhanced gain characteristic is demonstrated without a significant noise figure penalty. It uses a backward C-band amplified stimulated emission from both the ends of a bismuth-based EDFA system to pump an unpumped erbium-doped fibre (EDF) for gain enhancing. The maximum gain enhancement of 4.0dB is obtained at wavelength 1604nm with EDF length of 20m. The gain spectrum is reasonably flat in this amplifier compared with the amplifier without an EDF. The gain varies from 27.4dB to 30.2dB at wavelength region 1564--1608nm with incorporation of 20m EDF. Noise figure also varies from 6.0 to 7.7dB at this wavelength region.
Novel organic-inorganic layered oxide with spin ladder structure
B. Ingham,J. L. Tallon,S. V. Chong,R. -S. Liu,L. -Y. Jang
Physics , 2005,
Abstract: Structural analysis of a layered manganese tungstate diaminoalkane hybrid series suggests that this compound forms a spin-5/2 spin-ladder structure. We use X-ray diffraction, electron microscopy and x-ray absorption spectroscopy results to infer the structure. DC magnetization of the manganese compound and a possible copper analogue appear to show that the manganese system behaves like 1-dimensional antiferromagnetic Heisenberg chains (i.e. $J_{\parallel} \gg J_{\perp})$ while the copper system is fitted well by a $S = {1/2}$ spin ladder model, giving the parameters $g = 1.920 \pm 0.008$, $J_{\parallel}/k_B = -0.3 \pm 1.4$K; $J_{\perp}/k_B = 213.6 \pm 1.1$K. The ability to tune adjacent inorganic layers of the hybrid materials by altering the length of the organic `spacer' molecules gives enormous promise for the use of these materials, especially when doped, to provide a greater understanding of spin ladder systems.
Pectin Extraction and Characterization from Red Dragon Fruit (Hylocereus polyrhizus): A Preliminary Study
K.K. Woo,Y.Y. Chong,S.K. Li Hiong,P.Y. Tang
Journal of Biological Sciences , 2010,
Abstract: The present study was focused on the potential of red dragon fruit (Hylocereus polyrhizus) peel to be a source of pectin. The peel of red dragon fruit was collected from the local beverages factory and oven dried before pectin extraction. Dried fruit peels were first blended with distilled water and further acidified with different volume of citric acid to pH 3.0, 3.5 and 4.0, respectively. The acidified samples were then treated at 75°C in different time interval (30, 60 and 120 min) to extract pectin from the fruit peel. Highest yield with a total of 14.86% was obtained in 60 min extraction, pH 3.5. Characterization of the extracted pectin in terms of glucose content and degree of esterification was conducted. Highest glucose content was observed in sample extracted for 60 min, pH 4.0, whilst sample with the highest degree of esterification (DE) was obtained from treatment at pH 4.0, 120 min.
Work Stress of Teachers from Primary and Secondary Schools in Hong Kong
Alan H.S. Chan,K. Chen,Elaine Y.L. Chong
Lecture Notes in Engineering and Computer Science , 2010,
Abstract:
Unconventional modes in lasers with spatially varying gain and loss
Li Ge,Y. D. Chong,S. Rotter,H. E. Türeci,A. D. Stone
Physics , 2011, DOI: 10.1103/PhysRevA.84.023820
Abstract: We discuss a class of lasing modes created by a spatially inhomogeneous gain profile. These lasing modes are "extra modes", in addition to, and very different from, conventional lasing modes, which arise from the passive cavity resonances. These new modes do not have high intensity across the entire gain region, but instead are localized at the gain boundary and throughout the gain-free region. They are surface modes, originating from the transmission resonances of the gain-free region. Using an S-matrix description we connect these surface modes to the lasing modes in PT-symmetric (balanced gain-loss) cavities.
Berry's phase and the anomalous velocity of Bloch wavepackets
Y. D. Chong
Physics , 2009, DOI: 10.1103/PhysRevB.81.052303
Abstract: The semiclassical equations of motion for a Bloch electron include an anomalous velocity term analogous to a $k$-space "Lorentz force", with the Berry connection playing the role of a vector potential. By examining the adiabatic evolution of Bloch states in a monotonically-increasing vector potential, I show that the anomalous velocity can be explained as the difference in the Berry's phase acquired by adjacent Bloch states within a wavepacket.
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