Browsing by Author "Kao, HC"

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Decoupling of degenerate positive-norm states in Witten's string field theory
(2003-04-15)
Kao, HC
;
Lee, JC
;
電子物理學系
;
Department of Electrophysics
We show that the degenerate positive-norm physical propagating fields of the open bosonic string can be gauged to the higher rank fields at the same mass level. As a result, their scattering amplitudes can be determined from those of the higher spin fields. This phenomenon arises from the existence of two types of zero-norm states with the same Young representations as those of the degenerate positive-norm states in the old covariant first quantized (OCFQ) spectrum. This is demonstrated by using the lowest order gauge transformation of Witten's string field theory (WSFT) up to the fourth massive level (spin-five), and is found to be consistent with conformal field theory calculation based on the first quantized generalized sigma-model approach. In particular, on-shell conditions of zero-norm states in the OCFQ stringy gauge transformation are found to correspond, in a one-to-one manner, to the background ghost fields in off-shell gauge transformation of WSFT. The implication of decoupling of scalar modes on Sen's conjectures is also briefly discussed.
Effects of inert diluent segment and hydrogen bonding in poly(styrene-co-methacrylamide) copolymers
(2003)
Kao, HC
;
Kuo, SW
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A series of random poly(styrene-co-methacrylacmide) (PS-co-PMAAM) copolymers were prepared by free radical polymerization of styrene and methacrylamide monomers. The PS and PMAAM units of the copolymer do not have any specific interaction based on the Kwei equation and the infrared spectroscopy result, indicating that the styrene plays strictly as an inert diluent segment on the PMAAM main chain. This result offers an opportunity to enhance the miscibility and specific interaction between the amide group of PMAAM and the functional group of second polymer by reducing the strong self-association of the PMAAM.
Syntheses and characterizations of in situ blended metallocence polyethylene/clay nanocomposites
(2003-12-01)
Kuo, SW
;
Huang, WJ
;
Huang, SB
;
Kao, HC
;
Chang, FC
In this paper, we report the preparation of in situ blends of metallocence polyethylene (mPE) with montmorillonite (clay). The polymerization activity of polyethylene decreases upon increasing the amount of the clay feed. The mPE nanocomposites still possess their original melting and crystallization temperatures, but the melting and crystallization enthalpies decrease upon increasing the clay content. In addition, the polymer interaction parameter between mPE and exfoliated clay sheets was calculated to be -0.204 based on a modified Kim-Bae equilibrium melting depression equation. All of the isothermal crystallization kinetics data fit well to the Avrami crystallization equation. We found that increasing the clay content results in a faster rate of crystallization, but pure mPE still crystallizes the fastest. Using a small amount of pretreated clay results in a more homogeneous and finer dispersion of the clay in the polymer matrix, as determined by wide-angle X-ray diffraction and transmission electron microscopy analyses. Both the values of T-1rho(H) in the solid-state NMR spectra of the fast and slow components show increment upon increasing the clay content, which indicates that either the mobile phase tends to increase its rigidity in the clay-containing system. (C) 2003 Elsevier Ltd. All rights reserved.
Systematic low-temperature expansion in the Ginzburg-Landau model
(2000-05-01)
Kao, HC
;
Rosenstein, B
;
Lee, JC
;
電子物理學系
;
Department of Electrophysics
Consistent perturbation theory for thermodynamical quantities in strongly type-II superconductors in a magnetic field at low temperatures is developed. It is complementary to the existing expansion valid at high temperatures. Magnetization and specific heat are calculated to two-loop order and compare well with existing Monte Carlo simulations, other theories, and experiments.
Thermal behavior and specific interaction in high glass transition temperature PMMA copolymer
(2003-10-01)
Kuo, SW
;
Kao, HC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A series of high glass transition temperature copolymers based on poly(methyl methacrylate) (PMMA) were prepared by free radical copolymerization of methacrylamide and methyl methacrylate monomers in dioxane solvent. The thermal properties and hydrogen-bonding interactions of these poly(methacrylamide-co-methyl methacrylate) (PMAAM-co-PMMA) copolymers with various compositions were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and solid-state nuclear magnetic resonance (NMR) spectroscopy. A large positive deviation in the behavior of T-g, based on the Kwei equation from DSC analyses, indicates that strong hydrogen bonding exists between these two monomer segments. The FTIR and solid-state NMR spectroscopic analyses give positive evidence for the hydrogen-bonding interaction between the carbonyl group of PMMA and the amide group of PMAAM (e.g. by displaying significant changes in chemical shifts). Furthermore, the proton spin-lattice relaxation time in the rotating frame (T-1rho(H)) has one single value over the entire range of compositions of copolymers, and gives a value shorter than the average predicted. The proton relaxation behavior indicates the rigid nature of the copolymer. (C) 2003 Published by Elsevier Ltd.
Thermal properties, specific interactions, and surface energies of PMMA terpolymers having high glass transition temperatures and low moisture absorptions
(2005-03-10)
Chen, JK
;
Kuo, SW
;
Kao, HC
;
Chang, FC
;
應用化學系
We have prepared a series of poly(methyl methacrylate) (PMMA)-based terpolymers that have high glass transition temperatures and low moisture absorptions by the free radical copolymerization of methyl methacrylate, methacrylamide, and styrene in dioxane. We have investigated the effects of the styrene content on the glass transition temperatures, hydrogen bonding interactions, surface energies, moisture absorption, and molecular weights of these poly(methyl methacrylate-co-methacryl ami de-co-styrene) (Poly(MMA-co-MAAM-co-S)) terpolymers by differential scanning calorimetry, Fourier transform infrared and X-ray photoelectron spectroscopies, contact angle measurements, and gel permeation chromatography. The results indicate that the glass transition temperatures, hydrogen bonding strengths, surface energies, molecular weights, and the moisture absorption decreased upon increasing the PS content in most of the terpolymer systems. In addition, the moisture absorptions of some selected terpolymers decreased even through they possess higher values of T, than pure PMMA. These selected terpolymers have the potential to replace pure PMMA in optical device applications. (c) 2005 Elsevier Ltd. All rights reserved.