Browsing by Author "Li, YC"

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Effect of prolonged HAART on oral colonization with Candida and candidiasis
(2006-01-20)
Yang, YL
;
Lo, HJ
;
Hung, CC
;
Li, YC
;
生物科技學系
Background: Progressive cell-mediated immunodeficiency with decrease of CD4+ lymphocyte count to less than or equal to 200 cells/mm(3) is a major risk factor for colonization with Candida species and development of candidiasis. Oropharyngeal candidiasis may occur in up to 90% of human immunodeficiency virus (HIV)-infected patients during the course of the disease. This study is to determine the effect of prolonged highly active antiretroviral therapy (HAART) on oropharyngeal colonization with Candida species and oral candidiasis. Methods: A prospective, longitudinal follow-up study in HIV-infected patients receiving HAART. Results: The mean CD4+ count increased from 232.5 to 316 cells/mm(3) and the proportion of patients whose CD4+ count less than 200 cells/mm(3) decreased from 50.0% to 28.9% (p = 0.0003) in patients receiving HAART for at least 2 years. The prevalence of oral candidiasis decreased from 10.6% to 2.1% (p = 0.004). The decrease in Candida colonization was less impressive, falling from 57.8% to 46.5% (p = 0.06). Of the 142 patients enrolled in at least two surveys, 48 (33.8%) remained colonized with Candida and 42 (29.6%) remained negative. In the remaining 52 patients, 34 switched from culture positive to negative, and an increase in CD4+ lymphocytes was noted in 91.2% of them. Among the 18 patients who switched from culture negative to positive, 61.1% also demonstrated an increase in CD4+ lymphocyte count (p = 0.01). Conclusion: These findings indicate that HAART is highly effective in decreasing oral candidiasis in association with a rise in CD4+ lymphocyte counts, but only marginally effective in eliminating Candida from the oropharynx.
Electron inelastic interactions with overlayer systems
(1999-06-15)
Kwei, CM
;
Chiou, SY
;
Li, YC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An overlayer system composed of a thin film on the top of a semi-infinite substrate was studied in this work for electron inelastic interactions. Analytical expressions for the depth-dependent inelastic differential and integral inverse mean free paths were derived for both incident and escaping electrons. The interface (film-substrate) effect and the surface (vacuum-film) effect were analyzed by comparing the results of an overlayer system and a semi-infinite system. It was found that the interface effect extended to several angstroms on both sides of the interface for a 500 eV electron incident into or escaping from the vacuum-SiO2-Si and the vacuum-Au-Ni systems. An application of the spatial-varying inelastic differential inverse mean free paths was made by Monte Carlo simulations of the electron elastic backscattering from an overlayer system. Good agreement was found between results calculated presently and data measured experimentally on the elastic reflection coefficient. (C) 1999 American Institute of Physics. [S0021-8979(99)00712-4].
Electron inelastic mean free paths and surface excitation parameters for GaAs
(2004-11-15)
Kwei, CM
;
Li, YC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Surface excitation parameters and inelastic mean free paths of electrons are of importance in the analyses of surface sensitive electron spectroscopies. When probe electrons are near the surface of a solid or the interface of an overlayer system, electron inelastic mean free paths become depth-dependent. These mean free paths and surface excitation parameters were calculated for electrons crossing the surface of GaAs. Calculations were performed for both incident and outgoing electrons by the use of a dielectric response theory. Applications were made to estimate the elastic backscattering intensity of electrons at different emission angles using the Monte Carlo simulations. Good agreement was found between calculated results and experimental data on the ratio of the elastic reflection coefficient for a GaAs sample relative to a Ni reference. Such a ratio was used to determine the effective electron inelastic mean free paths in GaAs by employing the surface excitation parameter obtained from Monte Carlo simulations. (C) 2004 Elsevier B.V. All rights reserved.
Energy losses of charged particles moving parallel to the surface of an overlayer system
(2003-06-01)
Kwei, CM
;
Hwang, SJ
;
Li, YC
;
Tung, CJ
;
電子工程學系及電子研究所
An energetic charged particle moving parallel to the surface of an overlayer system was studied. This system was composed of a thin film on the top of a semi-infinite substrate. Based on the dielectric response theory, the induced potentia I was formulated by solving the Poisson. equation and matching the boundary conditions. The stopping force was built-up using the energy-momentum conservation relations and the extended. Drude dielectric functions with spatial dispersion. Surface (vacuum-film) and interface (film-substrate) excitations were included in the formulations of the interaction between charged particles and the overlayer system. Results of the wake potential were presented for protons moving parallel to a vacuum-copper-silicon system. Dependences of the induced potential and the stopping force on film thickness, distance of the proton from surface, and proton velocity were investigated. (C) 2003 American Institute of Physics.
Energy spectra of electrons quasi-elastically backscattered from solid surfaces
(2004-05-07)
Kwei, CM
;
Li, YC
;
Tung, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The energy distribution of electrons quasi -elastically backscattered from solids has been investigated. Monte Carlo, (MC) simulations were performed for the study of the recoil energy shift and the broadening of this distribution for backscattered electrons from Si and Au. In these simulations, electron interaction cross sections were obtained from calculations based on the dielectric response theory for inelastic interactions, including volume and surface excitations, and elastic interactions. The depth-dependent electron inelastic mean free path for volume excitations and the probability of surface excitations were calculated using the dielectric functions derived from optical data. The relativistic partial-wave expansion method was applied to calculate the elastic scattering cross section for a potential of the atom in the solid. The Rutherford-type recoil energy was included in the MC simulations by either considering or neglecting the thermal effect of atomic vibrations. Such an effect was applied using the single scattering model. The intensity of electrons quasi -elastically backscattered from Si and Au was simulated for incident electrons of an energy distribution. The adjustment for the spectrometer energy resolution was allowed. An analytic expression for the intensity of backscattered electrons by a single scattering was derived explicitly. A, comparison of simulated results with experimental data was made and discussed.
Influence of the direction of motion on the inelastic interaction between electrons and solid surfaces
(2005-09-01)
Li, YC
;
Tu, YH
;
Kwei, CM
;
Tung, CJ
;
電子工程學系及電子研究所
Theoretical derivations of the inelastic differential inverse mean free path (DIMFP) and inelastic mean free path (IMFP) for electrons crossing solid surfaces were made for different crossing angles and electron distances relative to the crossing point at the surface. Individual contributions from volume and surface excitations were separated and analyzed for electrons traveling inside and outside the solid. Extended Drude dielectric functions were employed to calculate the DIMFP and inverse IMFP for electrons incident into and escaping from Cu. It was found that the DIMFP and inverse IMFP for electrons moving inside the solid were approximately independent of crossing angle and position of electrons due to the compensation of volume and surface excitations. For electrons moving deep inside the solid, the DIMFP and inverse IMFP reduced to the values for electrons moving in an infinite solid. As electrons traveling in the vacuum, the DIMFP and inverse IMFP became greater for glancing incident and escaping angles since surface excitations were more probable. The surface excitation parameter (SEP) for electrons traveling in vacuum showed an angular dependence. The SEP of escaping electrons was found larger than that of incident electrons due to the attractive force exerted by the induced surface charges. The calculated SEP was found to follow a simple expression. (c) 2005 Elsevier B.V. All rights reserved.
Melt processing of polypropylene/clay nanocomposites modified with maleated polypropylene compatibilizers
(2004)
Wang, Y
;
Chen, FB
;
Li, YC
;
Wu, KC
;
應用化學系
Maleic arthydride-grafted polypropylene (PPgMA) and organically modified clay composites were prepared in a plasticorder. PPgMAs, including PB3150, PB3200, PB3000, and E43, with a wide range of MA content and molecular weight were used. The structure was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM). PPgMA compatibilizers gave rise to similar degree of dispersion beyond the weight ratio of 3 to 1 with the exception of E43, which had the highest MA content and the lowest molecular weight. It was found that thermal instability and high melt index were responsible for ineffective modification by E43. Furthermore, PPgMA with low melting point and high melt index was compounded at low equilibrium temperature in order to maintain a certain level of torque. We then modified polypropylene/organoclay nanocomposites with different levels of PPgMA compatibilizers on a twin-screw extruder. The PP/E43/clay system, as shown through XRD patterns and TEM observation, yielded the poorest clay dispersion among the compatibilizers under investigation. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by dynamical mechanical analysis and thermogravimetric analysis, respectively. Though PPgMA with lower molecular weight and higher MA content could lead to good clay dispersion in PP/clay composites, it caused the deterioration in both mechanical and thermal properties of PP/PPgMA/clay composites. (C) 2003 Elsevier Ltd. All fights reserved.