Browsing by Issue Date, starting with "1996-08-29"

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Blends of poly(ethylene terephthalate) with co[poly(ethylene terephthalate-p-oxybenzoate)] .3. Crystallization behavior observed by polarized light microscopy
(1996-08-29)
Ou, CF
;
Lin, CC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Poly(ethylene terephthalate) (PET) has been melt-mixed at 293 degrees C with two types of co[poly(ethylene terephthalate-p-oxybenzoate)] (POB-PET) copolyester, designated as P28 and P82, at the level of 10 wt %. The different p-acetoxybenzoic acid/PET mole ratios are 20/80 in P28 and 80/20 in P82. The blends were heated to 305 degrees C and then cooled to 25 degrees C at rate of 10 degrees C/min. The crystalline morphology of these blends in the range from 25 degrees C to 305 degrees C is monitored by polarized light microscopy. Morphologic observations revealed a quicker appearance of crystalline in the blends upon the addition of 10 wt % copolyester as a nucleating agent. It is found that P28, which contains fewer POB units, is much more advantageous to the nucleation process than P82, which contains more POB units. According to the optical photomicrographs, sufficient uniformity of distribution of copolyester domains in the PET matrix is reached after 8 min blending. (C) 1996 John Wiley & Sons, Inc.
Blends of poly(ethylene terephthalate) with co[poly(ethylene terephthalate-p-oxybenzoate)] .3. Crystallization behavior observed by polarized light microscopy
(1996-08-29)
Ou, CF
;
Lin, CC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Poly(ethylene terephthalate) (PET) has been melt-mixed at 293 degrees C with two types of co[poly(ethylene terephthalate-p-oxybenzoate)] (POB-PET) copolyester, designated as P28 and P82, at the level of 10 wt %. The different p-acetoxybenzoic acid/PET mole ratios are 20/80 in P28 and 80/20 in P82. The blends were heated to 305 degrees C and then cooled to 25 degrees C at rate of 10 degrees C/min. The crystalline morphology of these blends in the range from 25 degrees C to 305 degrees C is monitored by polarized light microscopy. Morphologic observations revealed a quicker appearance of crystalline in the blends upon the addition of 10 wt % copolyester as a nucleating agent. It is found that P28, which contains fewer POB units, is much more advantageous to the nucleation process than P82, which contains more POB units. According to the optical photomicrographs, sufficient uniformity of distribution of copolyester domains in the PET matrix is reached after 8 min blending. (C) 1996 John Wiley & Sons, Inc.
Blends of poly(ethylene terephthalate) with co[poly(ethylene terephthalate-p-oxybenzoate)] .4. Interchange reactions and their effects on the thermal and crystallization behaviors
(1996-08-29)
Ou, CF
;
Lin, CC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Poly(ethylene terephthalate) (PET) was blended with a co[poly(ethylene terephthalate-p-oxybenzoate)] (POB-PET) copolyester which is a liquid crystalline polymer consisting of p-oxybenzoate and ethylene terephthalate units in a 40/60 mol ratio (P46). The level of P46 liquid crystalline polymer varies from 10 to 50 wt %. All the blends were prepared by melt-mixing in a Brabender Plasticorder at 275 degrees C for different times. The thermal and crystallization behaviors of blends depend on the blending time and the composition of blends, viz., the content of the p-oxybenzoate (POB) moiety incorporated into the blends. The interchange reactions detected by proton NMR analysis occur during the processing at a greater level if the blending time increases. These interchange reactions hinder the crystallization processes of PET and result in a decrease of the melting point, the heat of fusion, crystallization temperature, and the heat of crystallization of the original PET. The effects of the interchange reaction on thermal and crystallization behaviors of the blends may be attributed to the insertion of the rigid POB units into the soft PET chain. (C) 1996 John Wiley & Sons, Inc.
Effect of magnesium on mechanical properties of Al2O3/Al-Zn-Mg-Cu metal matrix composites formed by squeeze casting
(1996-08-30)
Hsieh, JH
;
Chao, CG
;
交大名義發表
;
材料科學與工程學系
;
National Chiao Tung University
Al2O3/Al-Zn-Mg-Cu composites containing 2.0 similar to 3.0 wt.% Mg in the matrix alloy have been fabricated by squeeze casting. Light microscopy, scanning electron microscopy and image analysis were used to examine and analyze the details of microstructure and the fracture surface. Tensile tests were utilized to evaluate the mechanical properties. The aging behavior of the composites was studied by using differential scanning calorimetry technique and microhardness tests. The microhardness and ultimate tensile strength (UTS) of the composites increase with increasing Mg content. The maximum microhardness and UTS of the composites occur at 120 degrees C aging for 24 h.
A Laplace transform solution for tracer tests in a radially convergent flow field with upstream dispersion
(1996-09-01)
Chen, JS
;
Liu, CW
;
Chen, CS
;
Yeh, HD
;
環境工程研究所
When tracers are introduced into an injection borehole, noticeable concentration gradients at the injection well may cause a backward spreading of the initial plume during radially convergent tracer tests. Based on this concept a non-rigorous mathematical model is developed to estimate the effect of backward spreading. The injection well with an instantaneous slug input is treated as a mathematical source and the initial plume at the injection well is allowed to move upstream. The model assumes that advection and longitudinal dispersion are the transport mechanisms in a radially converging how field. The Laplace transform solution for solute concentration in an infinite porous medium is obtained using the method of Green's function. Breakthrough curves are computed by numerically inverting the Laplace transform solution. As compared with the solution of Moench, it is concluded that the presence of backward movement of initial plume yields a decrease of peak concentration and spreading out of breakthrough curve tails. This effect is significant for small Peclet numbers and can be neglected for large Peclet numbers. A field tracer test is carried out to demonstrate the applicability of the model. The experimental data are fitted with the type curves of this study, and those of Moench's study, to determine dispersivity and aquifer porosity. The results show that dispersivity values estimated by matching the two type curves are different. Because it neglects backward dispersion, Moench's solution overestimates the dispersivity and effective aquifer porosity.
The electroluminescence and photoluminescence characteristics of films of poly(phenylene vinylene)/gel-glass interpenetrating networks
(1996-09-01)
Chang, WP
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of poly(phenylene vinylene) (PPV)/gel-glass composites were prepared from mixtures of PPV precursor and silicon alkoxide methanol solution by employing a sol-gel process. The PPV/gel-glass composite, which is an interpenetrating network (IPN) structure, is used as the emissive layer in a polymeric light-emitting diode (LED). The addition of a small quantity of titanium ethoxide catalysed the reaction of gel-glass formation, making the PPV/gel-glass formation successful without phase separation and the luminescence of the composite film tunable. The luminescence characteristics of these PPV/gel-glass composites are dependent on the raw-material composition of silicon alkoxide and the molar ratio of PPV to gel-glass. From the ultra-violet/visible absorption spectrum, the conjugated length of these PPV/gel-glass composites can be seen to be shorter than that of pure PPV. The resultant PPV/gel-glasses emit light over a wide range from yellow-green (550 nm) to blue (484 nm) in the photoluminescence spectrum. Electroluminescent devices made from PPV/gel-glass 4 composites in the molar ratios of 1/1.17 and 1/2.33 shows a maximum emission peak at 515 and 510 nm, respectively. These PPV/gel-glass 4 LEDs showed a higher relative electroluminescence efficiency and a longer lifetime than pure PPV. The improvement in the device stability is related to the reduction of the thermal vibration of PPV chains during operation and the hindrance of carrier mobility in the IPN structure. Copyright (C) 1996 Elsevier Science Ltd.
Fabrication and analyses of negative-birefringent thin film compensator with characteristic matrix
(1996-09-01)
Yoo, JC
;
Shieh, HPD
;
光電工程研究所
;
Institute of EO Enginerring
We fabricated a multilayer negative-birefringent film as a phase compensator to minimize light leakage from twisted nematic liquid crystal displays in oblique incidence. The multilayer film stack is composed of alternating thin layers of silicon dioxide and titanium dioxide, which is magnetron sputtered on the glass substrates. The experiment agrees with the characteristic matrix calculation. Since each layer is not ''thin'' enough compared with visible spectra, the multilayer thin stack induces interference phenomena, and consequently reduces the transmittance. In order to eliminate the interference, we optimized the multilayer thin film to achieve high transmittance in the region of visible spectra.
Microstructure and crystal phases of praseodymium oxides in zinc oxide varistor ceramics
(1996-09-01)
Lee, YS
;
Liao, KS
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Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effect of sintering temperature on the microstructure and crystal phases of the intergranular praseodymium oxides in ZnO varistor ceramics was investigated using transmission electron microscopy and high-resolution electron microscopy. The ZnO grains were three-dimensionally separated from the intergranular praseodymium oxides. On the basis of microdiffraction analyses of the intergranular layer, the phase transformation from fcc-Pr6O11 into hcp-Pr2O3 was found when the sintering temperature increased from 1300 degrees to 1350 degrees C. The defect reaction equation and the decrease of donor concentration with increasing sintering temperature can verify the certainty of phase transition during the liquid-phase sintering observed by transmission elecron microscopy. Additionally, on the basis of the small variations of the breakdown voltage per grain boundary, the number of active grain boundaries is not a dominant factor for the donor concentration dependence on the sintering temperature.
A novel cladding structure for semiconductor quantum-well lasers with small beam divergence and low threshold current
(1996-09-01)
Yen, ST
;
Lee, CP
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University
A novel cladding structure is proposed and analyzed for semiconductor quantum-well lasers ttl achieve a small vertical-beam divergence and a low threshold current density simultaneously, This cladding structure is designed to guide a wide optical mode but with a high peak intensity in quantum wells. The wide expansion of the optical mode results in a small beam divergence. In addition, the high optical intensity in quantum wells causes a low threshold current density, This novel cladding structure is optimized. The result shows that this type of cladding structures can achieve a beam divergence as small as 14.6 degrees while the threshold current density remains small.
Delayed precise invalidation - A software cache coherence scheme
(1996-09-01)
Hwang, TS
;
Lu, NP
;
Chung, CP
;
交大名義發表
;
資訊工程學系
Software cache coherence schemes are very desirable in the design of scalable multiprocessors and massively parallel processors. The authors propose a software cache coherence scheme named 'delayed precise invalidation' (DPI). DPI is based on compiler-time markings of references and a hardware local invalidation of stale data in parallel and selectively. With a small amount of additional hardware and a small set of cache management instructions, this scheme provides more cacheability and allows invalidation of partial elements in an array, overcoming some inefficiencies and deficiencies of previous software cache coherence schemes.
AC permeability of the flux-line liquid in the anisotropic high-T-c superconducting crystals
(1996-09-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
AC properties of the flux-line liquid in the anisotropic high-temperature superconducting crystals in a parallel field are theoretically investigated. The ac responses in the simple flux-flow regime are analyzed from associated effective ac-magnetic permeability calculated on the hydrodynamic theory basis. The responses are studied as functions of anisotropic ratio and sample dimensions. The results illustrate the influence of the platelet crystal's size on permeability in the anisotropic superconductors while in the isotropic superconductors, the relationship of responses between a square rod and cylinder is found. It indicates that the permeability of a cylinder can be essentially replaced by that of a square rod and vice versa. The geometric effect on response is also elucidated in the isotropic superconductors.
A novel structure for three-dimensional silicon magnetic transducers to improve the sensitivity symmetry
(1996-09-01)
Lin, HY
;
Lei, TF
;
Jeng, JJ
;
Pan, CL
;
Chang, CY
A three-dimensional silicon magnetic transducer with symmetric sensitivities in the x-, y- and z-directions and small cross sensitivity has been demonstrated. Devices are based on a design of a vertical Hall structure using the surrounding trench and symmetric design to suppress the cross sensitivity. The fabrication process is simple and can be used as a part of a standard integrated circuit process. The results show that almost equal sensitivities in all three components of magnetic field can be obtained by coating Ni/Co thin films on the backside of the substrates. The cross sensitivity is only 1.3% of the sensitivity.
Capacitor-couple ESD protection circuit for deep-submicron low-voltage CMOS ASIC
(1996-09-01)
Ker, MD
;
Wu, CY
;
Cheng, T
;
Chang, HH
;
電子工程學系及電子研究所
Capacitor-couple technique used to lower snapback-trigger voltage and to ensure uniform ESD current distribution in deep-submicron CMOS on-chip ESD protection circuit is proposed, The coupling capacitor is realized by a poly layer right under the wire-bonding metal pad without increasing extra layout area to the pad. A timing-original design model has been derived to calculate the capacitor-couple efficiency of this proposed ESD protection circuit, Using this capacitor-couple ESD protection circuit, the thinner gate oxide of CMOS devices in deep-submicron low-voltage CMOS ASIC can be effectively protected.
A novel structure for three-dimensional silicon magnetic transducers to improve the sensitivity symmetry
(1996-09-01)
Lin, HY
;
Lei, TF
;
Jeng, JJ
;
Pan, CL
;
Chang, CY
A three-dimensional silicon magnetic transducer with symmetric sensitivities in the x-, y- and z-directions and small cross sensitivity has been demonstrated. Devices are based on a design of a vertical Hall structure using the surrounding trench and symmetric design to suppress the cross sensitivity. The fabrication process is simple and can be used as a part of a standard integrated circuit process. The results show that almost equal sensitivities in all three components of magnetic field can be obtained by coating Ni/Co thin films on the backside of the substrates. The cross sensitivity is only 1.3% of the sensitivity.
Toxicity of organic mixtures containing cyanogenic toxicants
(1996-09-01)
Chen, CY
;
Huang, CF
;
環境工程研究所
;
Institute of Environmental Engineering
In this study we evaluated the joint actions of cyanogenic toxicants with other organic chemicals using Microtox(R) tests. Experimental results indicated that greater than additive effect seldom occurred when these chemicals were mixed with nonreactive toxicants. However, the likelihood of synergistic effects exceeded 30% when reacting with a reactive chemical. Among the cyanogenic toxicants investigated in this study, malononitrile, lactonitrile, and alpha-hydroxy-isobutyronitrile have an approx. 50% likelihood of acting via synergism mode with other reactive toxicants. On the other hand, the joint actions related to acetonitrile and allyl cyanide are either additive or less than additive. Moreover, the likelihood of encountering synergistic effects markedly increases if the slopes of the dose-response curves for the two chemicals tested are small. Therefore, slope and certain characteristics of a chemical structure can apparently be used as indices to assess the potential hazard for a specific organic mixture. Furthermore, the complex joint action exerts a certain deterministic influence over the joint action mode of cyanogenic toxicants. This type of joint action, which quite frequently leads to an obvious antagonistic or even detoxification phenomena, could have some useful toxicological and pharmacological applications. Lastly, estimating the mixture toxicity on the basis of the concentration addition model is not always appropriate considering the high percentage of cases in this study showing synergism.
Application of Aspergillus oryzae and Rhizopus oryzae for Cu(II) removal
(1996-09-01)
Huang, CP
;
Huang, CP
;
環境工程研究所
;
Institute of Environmental Engineering
Biosorption of copper(II) by the untreated and acid-treated fungal biomass has been studied in both batch and column modes. Two species, Aspergillus oryzae and Rhizopus oryzae, were used in this study. A. oryzae mycelia (undergoing acid-washing) exhibit a clear advantage in Cu(II) removal, compared with other adsorbents. The acid-washing process can strongly enhance the adsorption capacity for A. oryzae mycelia. However, acid-washing does not alter the metal adsorption capacity of R. oryzae mycelia. The result indicates that acid-washing is not only a pretreatment step but also a regeneration step in the heavy metal removal process. These dual purposes, therefore, give the acid-washing biomass an indication of successful prospect. Cultivating A. oryzae in pellet form is an effective means of mycelium immobilization. The method established in this study provides the high-yield, uniformly-sized particles (2-3 mm in diameter), which are effective in solid-liquid separation. This pellet column can completely remove metals before breakpoint. After the breakpoint, a significant amount of Cu(II) removal over a long period has been observed. This is thought to be the result of intracellular uptake. Copyright (C) 1996 Elsevier Science Ltd
Performance evaluation of a high-value scheduling policy for real-time main memory databases
(1996-09-01)
Tseng, SM
;
Chin, YH
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
With the decrease in hardware prices, storing databases in main memory has become feasible for meeting the high-performance requirements of real-time applications. In this paper, an efficient scheduling policy is proposed for scheduling transactions with values in real- time main memory databases, where the value of a transaction means its worthiness to a real-time application of it is completed before the deadline. Through detailed performance evaluation, the proposed policy is shown to outperform the existing policies in both minimizing the number of missed transactions and maximizing the obtained values under various system environments. A cost formula for evaluating the optimal memory size to store partial databases such as to maximize the net profits is developed from the economic standpoint. Some suggestions are given for scheduling value-based transactions in real-time main memory databases.
Method for determining the fast axis and phase retardation of a wave plate
(1996-09-01)
Chiu, MH
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Chen, CD
;
Su, DC
;
光電工程研究所
;
Institute of EO Enginerring
Based on the heterodyne interferometric technique and the discrimination technique of using two light beams with different wavelengths, a novel method for identifying the fast axis of a wave plate and evaluating its phase retardation is presented. Some of the merits of the method, such as, a simple optical setup, high stability, better resolution, and easier operation, are presented, and the validity of the method is demonstrated. (C) 1996 Optical Society of America.
Grain-boundary surface states of (Ba, Pb)TiO3 positive temperature coefficient ceramics doped with different additives and its influence on electrical properties
(1996-09-01)
Chen, LF
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical properties of positive temperature coefficient of resistance (PTCR) ceramics of composition (Ba, Pb, La)TiO3 prepared from commercial BaTiO3 powders doped with different additives were studied. It was proposed here that different additives might have generated the corresponding number of possible surface states, such as, the segregation behavior of Mn ions (3d transition metal ions), oxygen adsorption reaction resulting from BN addition, the action of Ca replacing the Ti sites (Ca''(Ti)), and the natural intrinsic defects (V''(Ba), V''(Pb)). In general, some experimental derivations were also offered that majority of the surface states, which possessed their individual surface energy level, possibly coexisted onto the grain surface. Utilizing the concept of the coexistence of different types of surface states in the energy band, a satisfactory point-to-point agreement was obtained between the measured result and calculated values for the resistivity curve. Our experimental results were analyzed based on the terms of the Heywang-Jonker model and have shown that the assumption of a Hewang barrier was a reasonable approach for our set of samples; however, the distribution and types of grain-boundary acceptor states classification were required.
Structural analysis model for mat foundations
(1996-09-01)
Liou, GS
;
Lai, SC
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
A simplified structural analysis model for mat foundations with grid floor beams as stiffeners is presented here. In the model, the Winkler type of subgrade reaction spring is assumed for the whole area under the mar foundation, and the yield-line theory of slab is used to lump the Winkler springs under slabs to the corresponding locations under the adjacent floor beams of the slabs. Therefore, each floor beam is now supported by springs with a segmentally linearly varied spring constant. The total analysis model for the mat foundation is then simplified to be a grid beam system on an elastic foundation with a segmentally linearly varied spring constant, and is subjected to loadings from the columns of the building structure. Some numerical comparisons with the results by a sophisticated finite-element model are made in order to demonstrate the effectiveness and efficiency of the presented analysis model.