Showing papers by "National Tsing Hua University published in 1988"
TL;DR: In this article, the authors examined the interpretation of gain and bandwidth from the dispersion relation for the gyrotron traveling wave tube (gyro-TWT) and the cyclotron auto-resonance maser (CARM) amplifiers.
Abstract: Issues concerning the interpretation of gain and bandwidth from the dispersion relation are examined for the gyrotron traveling wave tube (gyro-TWT) and the cyclotron auto-resonance maser (CARM) amplifiers. A general method for the determination of the critical current for oscillation is illustrated. Despite the broad bandwidth predicted for the CARM amplifier by the commonly employed dispersion relation, it is seen in particle simulation that single-particle interaction. Rather than collective amplification, prevails over much of the band. Reasons for the discrepancy are analyzed. >
196 citations
TL;DR: A case of lexical tone recognition for Mandarin speech is discussed using a combination of vector quantization and hidden Markov modelling techniques to convert the observation sequence into a symbol sequence for Hidden Markov modeling.
Abstract: A case of lexical tone recognition for Mandarin speech is discussed using a combination of vector quantization and hidden Markov modelling techniques. The observation sequence was a sequence of vectorized parameters consisting of a logarithmic pitch interval and its first derivative. The vector quantization was applied to convert the observation sequence into a symbol sequence for Hidden Markov modeling. The speech database was provided by seven male and seven female college students, with each pronouncing 72 isolated monosyllabic utterances. A probabilistic model for each of the four tones was generated. A series of tonal recognition tests were then conducted to evaluate the effects of pitch reference base, codebook size, and tonal model topology. Future consideration of Mandarin speech recognition is also discussed. >
191 citations
TL;DR: Fluid-to-solid mass transfer coefficients were determined by measuring extraction rates of β-naphthol in supercritical carbon dioxide in a packed-bed as discussed by the authors, where β naphthols were extracted from supercritical CO 2.
129 citations
TL;DR: In this paper, the sinterability of hydroxylapatite-zirconia composite powder compacts depends strongly on differential shrinkage between the powder components of the composite.
Abstract: Sintering of hydroxylapatite-zirconia (doped with 3 mol% Y2O3) composite powder compacts was studied. Hydroxylapatite powder was prepared from Ca(OH)2 and H3PO4, and zirconia powder was prepared from ZrOCl2 · 8H2O and YCl3. The sinterability of hydroxylapatite-zirconia composite powder compacts depends strongly on differential shrinkage between the powder components of the composite. Smaller differential shrinkage results in better sinterability. By increasing the calcination temperature of zirconia powder and/or decreasing that of hydroxylapatite powder improves the sinterability of the composite powder compacts. The phase distribution and total amounts of crystal phases depend on the sintered density of compacts. Hydroxylapatite and cubic zirconia are the major phases of compacts with high sintered densities, whereas α- and β-tricalcium phosphate and CaZrO3 are the major phases of compacts with low sintered densities.
125 citations
TL;DR: In this paper, a method including the effects of fiber length and orientation distribution to predict elastic moduli of short fiber reinforced thermplastics (FRTP) is presented, where the fiber length distribution in FRTP has an asymmetric character with a tail at the long fiber end.
Abstract: A method including the effects of fiber length and orientation distribution to predict elastic moduli of short fiber reinforced thermplastics (FRTP) is presented. The fiber length distribution in FRTP has an asymmetric character with a tail at the long fiber end. Statistical distribution functions such as Weibull or log-normal can be used to represent this kind of distribution. Orientation distribution of fibers in FRTP can be characterized by a single parameter exponential function, . A large λ indicates a highly oriented material whereas small λ represents a quasi-isotropic material. As fiber length and orientation distribution functions have been characterized, the elastic moduli of FRTP can be predicted. First, the mean elastic moduli of unidirectional plies are predicted through the fiber length distribution. Then the stacking sequence of laminate is assumed to be as the fiber orientation distribution of FRTP, and the overall elastic moduli of FRTP are estimated based on the laminate-plate method.
124 citations
TL;DR: In this article, the stabilization of time-delay systems containing saturating actuators is considered and two kinds of feedback stabilizing laws are treated: state feedback and sampled-state feedback.
Abstract: The problem of the stabilization of time-delay systems containing saturating actuators is considered. Two kinds of feedback stabilizing laws are treated: state feedback and sampled-state feedback. Several sufficient conditions are derived to guarantee the stability of the saturating time-delay system under control. Each of these results, expressed by a scalar inequality, permits us to assess the transient behaviour of the controlled system. The results presented enable a practical consideration of the unavoidable saturation of the actuators and give an insight into the stabilization analysis of saturating time-delay systems.
113 citations
TL;DR: A modified version of the fast parallel thinning algorithm proposed by Zhang and Suen is presented, which preserves the original merits such as the contour noise immunity and good effect in thinning crossing lines; and overcomes the original demerits.
110 citations
TL;DR: In this paper, a wet-chemical approach is applied to derive fine powders with compositions 11 mol% CeO/sub 2/-ZrO/Sub 2/, 1 mol% YO/ sub 1.5/-10 mol% CZO/CZRO/CSO/SSO/BSO/SCO/SOCO.
Abstract: A wet-chemical approach is applied to derive fine powders with compositions 11 mol% CeO/sub 2/-ZrO/sub 2/, 1 mol% YO/sub 1.5/- 10 mol% CeO/sub 2/-ZrO/sub 2/, 12 mol% CeO/sub 2/-ZrO/sub 2/, and 2 mol% YO/sub 1.5/-10 mol% CeO/sub 2/-ZrO/sub 2/ by the coprecipitation method. The characteristics of the as-derived powders are evaluated through thermal analysis and electron microscopy. The sintering behavior of the calcined powders is carried out at 1400/sup 0/ and 1500/sup 0/C for 1 to 10 h. Sintered density higher than 98% of theoretical is achieved for sintering at 1400/sup 0/C for several hours. The as-sintered density dependence on the sintering condition is related to the extent of tetragonal-to-monoclinic phase transformation as well as the associated microcracks. Partial substitution by Y/sub 2/O/sub 3/ in CeO/sub 2/-ZrO/sub 2/ results in reduced grain size and tends to stabilize the tetragonal structure. Y/sub 2/O/sub 3/ is more effective than CeO/sub 2/ with respect to the grain size refinement and tetragonal stability. In addition, Y/sub 2/O/sub 3/ substitution in CeO/sub 2/-ZrO/sub 2/ increases the hardness, while it decreases the fracture toughness.
104 citations
TL;DR: The data indicate that copper adversely affects the primary charge separation at the PSII reaction centre, and it is suggested that the inhibition is due to creation of a lesion close to the reaction center, leading to increased dissipation of incoming excitation energy to heat.
Abstract: The room temperature fluorescence induction of chloroplasts was utilized as a probe to locate the site of inhibition on PSII by copper. It was found that, while the initial fluorescence yield was hardly affected, the variable fluorescence yield was lowered without significant change in its kinetics. Addition of DCMU, or abolishing oxygen evolution capability by Tris treatment, did not alter this basic inhibition pattern. Copper was also found to lower the fluorescence yield of chloroplasts treated with linolenic acid which inhibited the secondary electron transport on both oxidizing and reducing sides of PSII. The data indicate that copper adversely affects the primary charge separation at the PSII reaction center. We suggest that the inhibition is due to creation of a lesion close to the reaction center, leading to increased dissipation of incoming excitation energy to heat.
80 citations
TL;DR: The phase development sequence of Ba2Ti9O20 during heating was found to be in the following order: BaTi5O11 > BaTi4O9 > Ba2 Ti9O 20 as mentioned in this paper.
Abstract: The phase development sequence based on a composition equivalent to Ba2Ti9O20 during heating is found to be in the following order: BaTi5O11 > BaTi4O9 > Ba2Ti9O20. The lowest rate of formation of Ba2Ti9O20 is caused by its high surface energy and interface energy, which result in a low nucleation rate. The existence of BaTi5O11 in calcined powder helps to form Ba2Ti9O20 in sintered compacts. The effect of BaTi5O11 on Ba2Ti9O20 formation can be explained by their similar oxygen packing and by reduced volume change during transformation. The amount of BaTi5O11 formed during heating depends greatly on the compositional homogeneity of powders. The addition of SnO2 aids the formation of Ba2Ti9O20 by reduced strain energy at transformation and reduced surface energy.
73 citations
TL;DR: In this article, the effect of aging on abrasion rate of an Al-50wt%Zn-23wt%Mg75wt% SiC composite was investigated and compared with that for Al- 50wt% Zn- 23wt% Mg alloy aging at temperatures of 120, 160 and 200 °C.
TL;DR: In this article, the authors studied the kinetics of partial oxidation of methanol to produce hydrogen in a continuous-flow reactor and derived the rate equation using the Langmuir-Hinshelwood-Hougen-Watson formulation.
TL;DR: In this article, a co-precipitation method has been employed to prepare CeO2-ZrO2 ceramics, which is expected to yield highly sinterable material at lower sintering temperatures.
Abstract: The co-precipitation method has been employed to prepare CeO2-ZrO2 ceramics. The application of a wet chemical method is expected to yield highly sinterable material at lower sintering temperatures. The characteristics of the synthesized powders are evaluated with respect to the particle size distribution, calcination step, and the degree of agglomeration. The sintering behaviour of the prepared powder is studied at various temperatures to obtain different phase distributions and grain sizes. The amount of the monoclinic phase in the as-sintered specimen is decreased with increasing CeO2 contents in CeO2-ZrO2. 13.7 mol% CeO2 is sufficient to achieve a tetragonal phase in the CeO2-ZrO2 system. In addition, Y2O3 and MgO dopants in CeO2-ZrO3 reduce the grain size and result in a fully tetragonal phase for the 10 mol% CeO2 matrix.
TL;DR: It was found that the ratio of oxygen diffusivity in gels to that in water decreased with incubation time, from 32% to a constant level of 20% when the late period of exponential growth phase was reached.
TL;DR: In this article, a modified ejector-absorber absorption refrigeration cycle is presented and analyzed for an R-22/DME-TEG system with a 0·5 heat-exchanger effectiveness and a 0.85 nozzle efficiency.
TL;DR: An approach for realizing the N-point discrete Fourier transform (DFT) of an input sequence is presented and is combined with H.T. King's (1981) approach to construct a two-dimensional array for computing the two- dimensional DFT.
Abstract: An approach for realizing the N-point discrete Fourier transform (DFT) of an input sequence is presented. It is then combined with H.T. King's (1981) approach to construct a two-dimensional array for computing the two-dimensional DFT. This mixed model takes stream input and produces stream output. In addition, no extra I/O time delay is required before performing the row (column) transform of the two-dimensional DFT. >
TL;DR: The blood compatibility of SBS-g-HEMA as measured by the Lee-White clotting test was better than that of S BS and polystyrene and was quite similar to that of PHEMA.
Abstract: Solvent-cast films of styrene-butadiene-styrene triblock copolymer (SBS) were synthesized and a poly(2-hydroxyethyl methacrylate) (PHEMA) layer was grafted onto these films using Co 60 gamma-ray irradiation. The IR absorption spectrum of the graft copolymer was taken and its surface morphology studied by a scanning electron microscope. The degree of grafting and the mechanical properties of SBS, SBS-g-HEMA, and PHEMA were measured. In order to study its biocompatibility, contact angle and blood clotting time experiments were performed. The degree of grafting was related to the soaking time, film thickness and total irradiation dosage. However, it levelled off at 7% when the total dosage reached 1 Mrad. It was found that the mechanical properties of SBS-g-HEMA were the same as those of SBS and were superior to those of PHEMA. The blood compatibility of SBS-g-HEMA as measured by the Lee-White clotting test was better than that of SBS and polystyrene and was quite similar to that of PHEMA.
TL;DR: In this article, the roles of barium and niobium on the dielectric properties of TiO2 ceramics are explained after the migration mechanism and the influence of Barium and Niobium have been analyzed.
Abstract: Ultrahigh relative dielectric constants with stable frequency and temperature dependence as well as relatively low loss tangent are found in barium and niobium doped TiO2 ceramics with a silver electrode. The roles of barium and niobium on the dielectric properties of the ceramics are explained after the migration mechanism and the influence of barium and niobium have been analysed. Both silver electrodes made from silver paste and evaporated aluminium electrodes are employed in the study, their effects are also discussed. The migration mechanism proposed is electron hopping among oxygen vacancies. Dissolving barium into TiO2 ceramics creates an additional oxygen vacancy which results in an increase in conductivity and relaxation frequency of the loss tangent. In contrast, niobium tends to reduce the concentration of oxygen vacancies and causes the opposite effect. The effects of barium and niobium on the concentration of the oxygen vacancy are supported by results of densification and microstructural investigations.
TL;DR: In this article, the properties of polyurethane films cast from solutions and emulsions are studied using infra-red spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, wide-angle X-ray diffraction and tensile elongation testing.
TL;DR: Analytical results indicate that hair arsenic of the patients is significantly higher than that of the controls, but still below the critical value of 1 μg/g, and the patients showed significantly lower concentrations of Se and Zn in the urine and blood than the normal controls.
Abstract: Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Extensive epidemiological study implicates that high arsenic content in artesian well water is the responsible causal factor of the disease. In the present study the concentrations of arsenic, selenium, and zinc in the body fluids and hair of patients with Blackfoot disease, in comparison to age- and sex-matched normal controls, are investigated. Two analytical techniques that include atomic absorption spectrometry and neutron activation analysis were used for the analysis of urine, serum, hair, and whole blood. The analytical results indicate that hair arsenic of the patients is significantly higher than that of the controls, but still below the critical value of 1 microgram/g. In addition, the patients showed significantly lower concentrations of Se and Zn in the urine and blood than the normal controls. The possible connection of these elements with the etiology of the disease is discussed.
TL;DR: By means of the reaction of atomic H or D (produced either in a microwave discharge or on a W filament) with either NO2 or O3 or atomic O, they have prepared and trapped OH and OD radicals in solid Ar at 12 K, characterized by their infrared absorption lines at 354820 and 261610 m−1, respectively as discussed by the authors.
TL;DR: It is shown that the partial bus networks with K classes are useful in applications requiring high performance and degree of fault tolerance with moderate cost, and a type of multiple bus network with partial bus-memory connection is proposed.
Abstract: The authors study the performance of multiprocessor systems employing multiple buses as the interconnection networks under a nonuniform requesting model, called the hierarchical requesting model. The effective memory bandwidth is chosen as the performance measure. The networks investigated include multiple bus networks with full bus-memory connection, multiple bus networks with single bus-memory connection, and multiple bus networks with partial bus-memory connection. The authors also propose a type of multiple bus network with partial bus-memory connection, called partial bus networks with K classes. The N costs and fault-tolerant capabilities of the multiple bus networks are also evaluated and compared to one another. It is shown that the partial bus networks with K classes are useful in applications requiring high performance and degree of fault tolerance with moderate cost. >
TL;DR: In this article, the kinetics of hydrogen-induced slow crack growth (SCG) under constant load was studied in two stainless steel alloys containing mixtures of bcc and fcc phases, and the results confirmed that a higher rate of supply and accumulation of hydrogen in the region ahead of the crack tip allows a higher cracking velocity.
Abstract: The kinetics of hydrogen-induced slow crack growth (SCG) under constant load was studied in two stainless steel alloys containing mixtures of bcc and fcc phases. FERRALIUM 255, a duplex stainless steel, consisting of ∼50 pct austenite in a ferrite matrix, was tested in hydrogen gas at 0 to 100 °C with the loading axis both perpendicular and parallel to the rolling direction. In addition, specimens of AISI 301 were deformed in air in different ways to produce various amounts of bcc phase in an austenite matrix prior to testing in H2 gas at room temperature. The kinetics of subcritical slow crack growth (SCG) in these alloys was compared with that for austenitic and for ferritic stainless steels. The SCG rates were rationalized in terms of differences in hydrogen permeation in the two phases. The results confirm that a higher rate of supply and accumulation of hydrogen in the region ahead of the crack tip allows a higher cracking velocity.
TL;DR: An OPF (optimal power flow) program based on the Newton methodology has been implemented, as the first step in the development of a VAr (reactivevolt-ampere) planning program for the Taiwan Power Company as mentioned in this paper.
Abstract: An OPF (optimal power flow) program based on the Newton methodology has been implemented, as the first step in the development of a VAr (reactive-volt-ampere) planning program for the Taiwan Power Company. The strength of the Newton method was demonstrated by extensive system tests. Of particular importance is the demonstration that binding inequality constraints could be selected and enforced reliably and efficiently. Different levels of functional capabilities regarding infeasible solutions have been identified; and test results showed that they could be satisfied effectively. Detailed test results on the selection and enforcement of binding inequality constraints are presented in an effort to clarify some uncertainties that have persisted in this key aspect of the Newton-OPF methodology. >
TL;DR: A parallel algorithm for corner finding on the skeletons of digital curves is described, instead of computing the abrupt change of slopes with the chain code sequence, the degree of bending via an extended 3 × 3 mask is considered in corner finding.
TL;DR: In this article, the relationship between cobalt thin films and (001) GaAs has been studied by transmission electron microscopy, energy-dispersive analysis of x-rays in a scanning-TEM, Auger electron spectroscopy and x-ray photoelectron spectrograph.
Abstract: Interfacial reactions between cobalt thin films and (001) GaAs have been studied by transmission electron microscopy, energy-dispersive analysis of x-rays in a scanningTEM, Auger electron spectroscopy and x-ray photoelectron spectroscopy. The completely reacted layer was found to be “β-Ga203/(CoGa, CoAs)/GaAs.” The formation of a surface layer ofβ-Ga2O3 and the use of encapsulated samples minimized As loss from the reacted layer. Both CoGa and CoAs were found to grow epitaxially on (001) GaAs. The orientation relationships between CoGa and GaAs were determined to be [001] CoGa//[001] GaAs and (220) CoGa//(220) GaAs. The Burgers vectors of interfacial dislocations were identified as 1/2 〈101〉 and 1/2 〈011〉 which are inclined to the (001) GaAs surface. Almost all of the CoGa films were found to be epitaxially related to the surface. No interfacial dislocations were observed in most of the epitaxial CoAs films which are considered to be pseudomorphic with respect to GaAs. The orientation relationships between CoAs and GaAs were determined to be [101] CoAs//[011] GaAs and (020) CoAs//(220) GaAs. Two-step annealing was found to be effective in promoting epitaxial growth.
TL;DR: In this paper, electron microscopic analysis has been used to investigate the interfacial phenomena in a high-temperature alloy system, where an oxidation-induced transformation was observed between theγ matrix and the oxide scale.
Abstract: Electron microscopic analysis has been used to investigate the interfacial phenomena in a high-temperature alloy system. During high-temperature oxidation of Fe-8.9Al-3Cr-31 Mn-0.87C alloy at 800 and 1000° C, an oxidation-induced transformation a layer was observed between theγ matrix and the oxide scale. The morphology of the oxidized sample was studied by scanning electron microscopy, and the elemental redistribution of the constituents was evaluated using an electron microprobe. The concentration of elements was detected with the ZAF-corrected quantitative program. It is believed that the formation of theα layer was caused by the selective oxidation of manganese during the oxidation process. The thickness of theα layer increased with both oxidation time and temperature, the temperature having the greater influence on this transformed layer. In addition, the interfacial concentrations at theγ/α andα/oxide boundaries were employed to investigate the selective oxidation of manganese.
TL;DR: In this article, the authors describe the computer-aided engineering analysis of a linearly tapered coat-hanger die and develop the design formula for a die to deliver uniform flow.
Abstract: We describe the computer-aided engineering analysis of a linearly tapered coat-hanger die in this paper. The general governing equation for flow distribution inside the die was derived first. On the basis of this equation, we have developed the design formula for a die to deliver uniform flow. In addition, we have also examined the variations of lateral flow uniformities and residence time distributions of polymeric liquids under several different design and operating conditions: (1) using manifolds with non-circular cross-sections, (2) adjusting production widths, (3) delivering fluids with different viscosities, and (4) enlarging manifolds for practical production considerations.
TL;DR: In this article, a model reference adaptive speed controller for a current-fed induction motor drive is proposed, which uses a proportional-integral (PI) adaptation to satisfy the hyperstability condition for load and machine parameter changes of the drive.
Abstract: A model reference adaptive speed controller for a current-fed induction motor drive is proposed. The controller uses a proportional-integral (PI) adaptation to satisfy the hyperstability condition for load and machine parameter changes of the drive. Only the available information on the states and output of the reference model as well as the plant output are required. No explicit parameter identification is needed. The controller can be designed simply by using a reduced reference model without particularly degrading the performance, so it is easy to implement practically. The hardware implementation is detailed, and some experimental results are given to demonstrate its effectiveness. >
TL;DR: In this paper, a commercial CuO ZnO catalyst was used for cyclohexanol de-hydrogenation in a fixed-bed micro-reactor, and the results showed that the catalyst maintained constant activity at low oxygen: cyclhexanol mol ratios and its stability was dependent on the reaction temperature.