Showing papers by "National Tsing Hua University published in 1990"

Inertial effects of a Dirac particle.

Abstract: Stationary laboratories on Earth accelerate and rotate relative to the local inertial frames. Any experiment precise enough would detect and/or need to take into account the effects due to acceleration and rotation. We derive these inertial effects for a Dirac particle in a straightforward and unified way within the framework of special relativity. The effects found include the Bonse-Wroblewski phase shift due to acceleration, the Sagnac-type effect, the rotation-spin effect, and the redshift of the kinetic energy.

Photocatalytic oxidation of phenol in the presence of hydrogen peroxide and titanium dioxide powders

Abstract: The effect of hydrogen peroxide on the photocatalytic oxidation of phenol on illuminated TiO 2 has been investigated The experimental results indicate that transition metal ions, such as Fe 3+ and Cu 2+ , affect the photocatalytic oxidation of phenol In the absence of added H 2 O 2 the ferric ions induce the occurrence of the photo-Fenton-type reaction so that the phenol removal of an initial 1000 mg 1 −1 solution is enhanced from 23 to 33% within 8 h However, the cupric ions show a negative effect In the presence of added H 2 O 2 , both the ferric and the cupric ions enhance the phenol oxidation rate drastically A 1000 mg 1 −1 phenol solution can be completely decomposed within 1 h and the total organic carbon removal reaches 80% A reaction mechanism which involves the generation of hydroxyl radicals is proposed

The influence of aluminium content to the stacking fault energy in Fe-Mn-Al-C alloy system

Abstract: Four Fe-30Mn-0.9C-XAl alloys are employed to investigate the influence of aluminium content to the stacking fault energy in Fe-Mn-Al-C alloy system. The range of aluminium content is zero to 8.47 wt%. Based on the thermodynamic model, the stacking fault energy can be obtained through calculation. Increasing the aluminium content will make the stacking fault energy of Fe-30Mn-0.9C based alloys increase at 300 K.

On the stability bounds of singularly perturbed systems

Abstract: The stability bound problem of linear time-invariant singularly perturbed systems is considered. A set of new stability conditions based on the frequency-domain representation is derived. The stability criteria can be easily verified by computing certain singular values within finite frequency intervals. Illustrative examples show that the proposed criteria actually induce a less conservative epsilon bound than the existing criteria, and for certain cases an infinite epsilon bound may be obtained. >

Methanol-Induced crack healing in poly(methyl methacrylate)†

Abstract: Crack healing in poly(methyl methacrylate) (PMMA) by methanol treatment at 40°C–60°C has been investigated. It is found that the methanol treatment reduces the glass transition temperature in PMMA. Crack healing only occurs at an operating temperature higher than the effective glass transition temperature. There are two distinctive stages for crack healing based on the recovery of mechanical strength. The first stage corresponds to the progressive healing due to wetting, which has a constant crack closure rate at a given temperature. Immediately following the first stage, the second stage corresponding to diffusion enhances the quality of healing behavior. The surface morphologies obtained during healing and after fracture tests confirm these two stages. By comparing the fracture stress with the fractography, the fracture surface for stage I of crack healing is coplanar to the original crack surface. On the other hand, the original crack surface is destroyed in stage II of crack healing. It occurs in the region incorporating the original healed surface and appears to be like the Virgin fracture surface. It is also found that the tensile fracture stress of PMMA treated by methanol can recover to that of the virgin material. In addition, it is interesting to find that after sustained methanol treatment, the “snake bone” phenomenon on the fracture surface emerges.

Investigation of two plane paralleltiinven ilated jets

Abstract: Measurements of mean velocity components, mean flow direction, turbulent intensities and Reynolds shear stress were made with a split film probe of hot wire anemometer to investigate the flow field generated by two identical jets of air issuing from plane parallel nozzles in a common end wall and mixing with the ambient room air. Due to the sensitivity of the split film probe to the flow direction, the reverse flow in the converging region was detected by the split film probe and observed by flow visualization. The mean velocity approaches self-preservation in both the converging and the combined regions, while the turbulent intensities and Reynolds shear stress approach self-preservation in the combined region only. The trajectory of the maximum velocity is almost unchanged by variance of nozzle spacing in the converging region. The distance of the merging point from the nozzle exit increases linearly with nozzle spacing. The spread of the converging jet increases more rapidly than that of the combined jet.

Influence of stoichiometry on the microstructure and positive temperature coefficient of resistivity of semiconducting barium titanate ceramics

Abstract: The influence of stoichiometry, i.e., Ba/Ti ratio, on the microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of BaTiO3 was investigated. Fine-grain microstructures are obtained for Ba-rich, stoichiometric, low-temperature-sintered, Ti-rich materials. The room-temperature resistivities (ρRT) of the fine-grain Ti-rich samples are large (>108Ω·cm). Excess Ba2+ ions can decrease the ρRT, by more than 2 orders of magnitude, because of the compensation of barium vacancies near the grain-boundary regions. Rapid cooling after sintering can also decrease ρRT (⋍100×) and is ascribed to the suppression of reoxidation. Large-grain microstructures and low ρRT, on the other hand, are generally observed for Ti-rich and Al2O3-SiO2-TiO2-added samples after sintering at a temperature higher than the corresponding eutectic point.

Voronoi diagrams of moving points in the plane

Abstract: In this paper, we consider the dynamic Voronoi diagram problem. In this problem, a given set of planar points are moving and our objective is to find the Voronoi diagram of these moving points at any time t. A preprocessing algorithm and a query processing algorithm are presented in this paper. Assume that the points are in k-motion, and it takes O(k) time to find the roots of a polynomial with degree O(k). The preprocessing algorithm uses \(O(k^2 n^3 logn\cdot2^{O(\alpha (n)^{5k + 1} )} )\) time to process moving functions of given points, and uses \(O(k^2 n^3 \cdot2^{O(\alpha (n)^{5k + 1} )} )\) space to store the preprocessing result where α(n) is the functional inverse of Ackermann's function. The query processing algorithm is designed to report the Voronoi diagram of these points for a query time t. It takes O(n) time which is optimal.

Easily testable iterative logic arrays

Abstract: Iterative logic arrays (ILAs) are studied with respect to two testing problems. First, a variety of conditions is presented. Meeting these conditions guarantees an upper bound on the size of the test set for the ILA under consideration. Second, techniques for designing optimally testable ILAs are presented. The arrays treated are, in some cases, more general than those that have been reported by other researchers: they include multidimensional and inhomogeneous arrays. Octagonally connected arrays and bilateral arrays are also discussed. The results indicate that the characteristics of the individual cell functions (e.g. whether they are bijective) are a good guide to the test complexity of the overall array. Matrix multiplication, as an example, is shown to have several different optimally testable implementations. The results are useful for combinational and pipelined arrays and for certain systolic arrays. >

Designing efficient parallel algorithms on mech-connected computers with multiple broadcasting

Abstract: Semigroup and prefix computations on two-dimensional mesh-connected computers with multiple broadcasting (2-MCCMBs) are studied. Previously, only square 2-MCCMBs with N processing elements were considered for semigroup computations of N data items, and O(N/sup 1/6/) time was required. It is found that square machines are not the best form for semigroup computations, and an O(N/sup 1/8/)-time algorithm is derived on an N/sup 5/8/*N/sup 3/8/ rectangular 2-MCCMB. This time complexity can be further reduced to O(N/sup 1/9/) if fewer processing elements are used. Parallel algorithms for prefix computations with the same time complexities are derived. >

Ordering Behavior of Lead Magnesium Niobate Ceramics with A‐Site Substitution

Abstract: The ordering behavior of lanthanum-modified lead magnesium niobate ceramics was investigated over a wide range of lanthanum content (from 0 to 50 at.%). The ordering of magnesium and niobium ions in the B site was examined by X-ray diffraction, and the superlattice reflection was associated with the A(B′1/2B″1/2)O3-type partial ordering structure. Moreover, the ordering degree increased pronouncedly with respect to lanthanum content of the sample and almost reached unity at [La] = 50 at.%. Finally, a comparison of the ordering behavior was performed among several lead magnesium niobate (PMN) samples with different A-site substitutional ions. The mechanism used to enhance the ordering of PMN by A-site substitution is then described by the effect of high valence.

Experimental and Computational Study of Turbulent Flows in a Channel With Two Pairs of Turbulence Promoters in Tandem

Abstract: Measurements and computations are presented of mean velocity and turbulence intensity for an arrangement of two pairs of turbulence promoters mounted in tandem in developing channel flow. The Reynolds number (ReD) and the pitch ratio (PR) were varied in the range of 1.2 x 10E4 to 1.2 x 10E5 and 1 to 100, respectively. The three pitch ratios 5, 10, 15 were found to provide three characteristic flows which are a useful test of the computational models. The effects of PR on the reattachment lengths and the pressure loss as well as the influence of ReD on the reattachment length were documented in detail. It was found that PR=10 was preferable to PR=5 and PR=15 from the standpoint of heat transfer enhancement.

Manganese(II) induces cell division and increases in superoxide dismutase and catalase activities in an aging deinococcal culture.

Abstract: Addition of Mn(II) at 2.5 microM or higher to stationary-phase cultures of Deinococcus radiodurans IR was found to trigger at least three rounds of cell division. This Mn(II)-induced cell division (Mn-CD) did not occur when the culture was in the exponential or death phase. The Mn-CD effect produced daughter cells proportionally reduced in size, pigmentation, and radioresistance but proportionally increased in activity and amount of the oxygen toxicity defense enzymes superoxide dismutase and catalase. In addition, the concentration of an Mn-CD-induced protein was found to remain high throughout the entire Mn-CD phase. It was also found that an untreated culture exhibited a growth curve characterized by a very rapid exponential-stationary transition and that cells which had just reached the early stationary phase were synchronous. Our results suggest the presence of an Mn(II)-sensitive mechanism for controlling cell division. The Mn-CD effect appears to be specific to the cation Mn(II) and the radioresistant bacteria, deinococci.

Adaptive chattering alleviation of variable structure systems control

Abstract: A new adaptive chattering alleviation algorithm for variable structure systems (VSS) control is proposed. The adaptive control algorithm consists of two phases. In phase one, the authors try to minimise the time required to reach the switching surface. In phase two, they alleviate the chattering about the switching surfaces in the sliding mode. The automatic switching between these two phases is based on a recursive prediction procedure performed at each step. The automatic adjustment of the controllers is called an adaptive VSS control algorithm. The algorithm can be applied to uncertain linear and nonlinear systems. The resulting trajectories of a nonlinear robotic experiment indicate almost no chattering at all. Moreover, this clear-cut benefit is not obtained at the expense of any added time required to reach the steady state.

Multi-year multi-case optimal VAR planning

Abstract: An integrated methodology for long-term VAr planning is presented that results in determining the timing (year), the location, and the amount of VAr compensation. The system security and investment and operating economics are taken into account. The proposed methodology is an integration of the Newton-OPF with the generalized Benders decomposition (GBD). The total problem is decomposed into two levels: master and slave. The master level deals with the investment decision of installing discretized new VAr devices. The slave level deals with operating the existing controllers, in conjunction with the new devices solved in the master level, to maintain system feasibility and to reduce MW losses. The overall solution methodology contains numerous extensions to the basic theory. Tests performed on actual Taiwan power system data have been encouraging. Sample results are presented. >

A failure analysis of water jet drilling in composite laminates

Abstract: Delamination is a major concern in the manufacturing processes of composite materials. It reduces not only the structural integrity of the laminate but also the long-term reliability of the assembly. Water jet drilling, in spite of its advantages of no tool wear and thermal damage, often creates delamination composite laminate at bottom. The current paper presents an analytical approach to study the delamination during drilling by water jet piercing. The analysis uses fracture mechanics with plate theory to describe the mechanism of delamination. This model predicts an optimal water jet pressure for no delamination as a function of hole depth and material parameters (opening-mode delamination fracture toughness and modulus of elasticity). Good agreement is achieved with data obtained from water jet drilling of graphite epoxy laminate. The predicted optimal water jet pressure can be applied in a control scheme for maximizing the productivity of water jet drilling of composite laminates.

A wide-band millimeter-wave gyrotron traveling-wave amplifier experiment

Abstract: A saturated instantaneous bandwidth (FWHM) of at least 10% in a Ka-band gyrotron traveling-wave tube (gyro-TWT) with uniform interaction waveguide and magnetic field was obtained. A relatively low alpha ( identical to nu /sub perpendicular to // nu /sub ///) beam has resulted in stable saturated operation and broad bandwidth. This, together with the overall performance of the tube (18.4-kW maximum power at 18.6% efficiency and 18-dB gain), strongly reinforces the possibility of developing a new generation of millimeter traveling-wave amplifiers based on the gyro-TWT. >

Reaction Sequence and Effects of Calcination and Sintering on Microwave Properties of (Ba,Sr)O‐Sm2O3‐TiO2 Ceramics

Abstract: The reaction sequence of 0.15(Ba0.95Sr0.05)O· 0.15Sm2O3· 0.7TiO2 ceramics during heating as well as the effects of calcination and sintering on microwave properties were investigated. Quantitative microscopic analysis was performed to obtain the volume fraction of the phases. It was found that the amount of second phase, especially TiO2 (rutile), greatly affected the temperature coefficient of resonant frequency of the ceramics. The higher the amount of TiO2 phase, the more positive or the less negative the temperature coefficient of resonant frequency. The temperature coefficient of BaO · Sm2O3· 5TiO2 was calculated using the logarithmic mixing rule to be −30 ppm/°C. The volume fractions of the phases varied with conditions of calcination and sintering. Therefore, by varying calcination and/or sintering temperature, the temperature coefficient of resonant frequency could be adjusted to nearly zero.

A strongly implicit solver for two-dimensional elliptic differential equations

Abstract: A strongly implicit solver is proposed in the present investigation for solving a large set of algebraic equations that arise from a discretization of an elliptic differential equation. Based on the guessed θNW and θSE values (solutions at the northwest and the southeast corners of a computational cell), the nine-diagonal coefficient matrix is factored in terms of a lower and an upper triangular matrix with only seven nonzero diagonals. The solution procedure then is iterated with a successive overrelaxation (SOR) factor until the solution converges within a prescribed tolerance. In the present solver, there is no need to evaluate the residual for the guessed solution. The CPU time thus is reduced a great amount for a single iteration. In addition, the storage is only one-half as large as that required by the SIP solver because the original matrix is no longer needed after it is factored. The convergence rate of the SIP solver is very sensitive to the cancellation parameter a. The present solver needs no ...

Kinetics of the reaction OH + NH3 in the range 273-433 K.

Abstract: The kinetics of the reaction OH + NH{sub 3} have been studied by means of the flash photolysis/laser-induced fluorescence technique. The rate of this reaction was investigated in the range 273-433 K under more extensive conditions (68 < P/Torr < 504, 0.29 < (NH{sub 3})/10{sup 15} molecules cm{sup {minus}3} < 36.1) than previously. The results from experiments with the Xe lamp and with the KrF laser for photolysis agree well within the experimental uncertainties, indicating the absence of interference due to excess NH{sub 2} laser for photolysis agree well within the experimental uncertainties, indicating the absence of interference due to excess NH{sub 2} which was produced by photolysis with the Xe lamp. A fit of rate coefficients to the Arrhenius equation yields k = (3.29 {plus minus} 1.02) {times} 10{sup {minus}12} exp({minus}(922 {plus minus} 100)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, with k = (1.47 {plus minus} 0.07) {times} 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} at 297 K; the uncertainties represent one standard error.

Formation and growth morphology of oxidation-induced ferrite layer in Fe-Mn-Al-Cr-C alloys

Abstract: Three austenitic Fe-31 Mn-9Al-xCr-0.87C alloys (x=0, 3 and 6) have been oxidized in dry air at 800 to 1100 ° C. An oxidation-induced ferrite layer is observed between the oxide layer and the austenite matrix. The ferrite layer is formed due to the selective oxidation of manganese. Qualitative and quantitative electron microscopic techniques are employed to investigate the morphological development and elemental redistribution in the alloy system. The mechanism of the formation and growth of the ferrite layer and the diffusion path of the carbon due to austenitic decomposition are explored.

Equilibrium phase relations in the Bi-Ca-Sr-Cu-O system at 850 and 900 °C

Abstract: The phase relations of equilibrium compounds in the pseudoternary system Bi{sub 2}O{sub 3}-(Ca,Sr)O-CuO at 850 and 900 {degree}C were studied The ratio of Ca:Sr was fixed at 1:2 Starting materials of Bi{sub 2}O{sub 3}, CaCO{sub 3}, SrCo{sub 3} and CuO with various ratios were mixed, pressed into pellets, and heated at or above and then brought back to 850 or 900 {degree}C for different durations to ensure that equilibrium had been reached The products were cooled in air or quenched in liquid nitrogen and then identified by x-ray powder diffraction At 850 {degree}C, only the superconducting phase, Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub {ital x}}(2122), was observed inside the triangle The other stable phases were all positioned on the boundary lines, and included CuO{center dot}3/5MO, CuO{center dot}MO, CuO{center dot}2MO, 11/2Bi{sub 2}O{sub 3}{center dot}09MO, Bi{sub 2}O{sub 3}{center dot}4MO, Bi{sub 2}O{sub 3}{center dot}9MO, and a solid solution, Bi{sub 2}O{sub 3}{center dot}xMO, where 016 {le} x {le} 082 and MO represents 1/3(CaO{center dot}2SrO) At 900 {degree}C, the above boundary line phases remained stable but the 2122 phase was not observed The tie lines among the stable phases in the two isotherms were established

Superconductivity with Tc(zero) above 105 K in Tl-containing septenary oxides with Y1Ba2Cu3Oy-like structure

Abstract: A family of high- T c superconductors with T c(zero) above 105 K is described. The compounds are seven-element blends with the general formula Tl 0.5 Pb 0.5 Ca 0.8 A 0.2 Sr 2 Cu 2 O x ( A = Y ), and rare-earth elements La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb). The results represent one of the first cases where chemical substitution has significantly raised T c in a known compound. The septenary compounds are tetragonal in structure with almost identical lattice parameters to those of now-famous Y 1 Ba 2 Cu 3 O y structure. The samples were highly reproducible, stable and remarkably homogeneous both in composition and structure. The preparative conditions were found to be much less stringent than those of other copper-based high- T c superconductors.

Y-Ba-Cu-O superconducting films grown on (100) magnesia and sapphire substrates by a melt growth method without crucible

Abstract: Superconducting Y-Ba-Cu-O films were successfully prepared by a melt growth method without crucible on (100) MgO and sapphire substrates using a Ba2Cu7O10 flux It was found that without a Y2BaCuO5 (211) buffer layer, film formation is not feasible due to a wetting problem The 211 layer reacts with the melt and is partly converted to the YBa2Cu3Ox (123) film The 123 film thickness is 1/2 to 2/3 that of the former 211 layer, whose quality in turn dominates the surface structure of the 123 film The degree of preferred (00L) orientation is greater than 99% for the films on the 211 buffered (100) MgO, and 80% for those on the (100) sapphire 2 to 3 mu m superconducting films with Tc-onset>80 K and Tc-zero>60 K were reproducibly obtainable on (100) MgO

Hydrothermal processings to produce magnetic particulates

Abstract: alpha -Fe/sub 2/O/sub 3/, gamma -Fe/sub 2/O/sub 3/, and alpha -FeOOH powders were used as starting materials to prepare barium hexaferrite hydrothermally. Since strontium hexaferrite and lanthanum-doped calcium hexaferrite have coercivities similar to that of barium ferrite, the hydrothermal synthesis of strontium hexaferrite and lanthanum-doped calcium hexaferrite were also explored. The reaction products obtained with the various starting materials are described. Electron micrographs showed that alpha -Fe/sub 2/O/sub 3/, gamma -Fe/sub 2/O/sub 3/, or alpha -FeOOH dissolved in the solution first, and then barium hexaferrite nucleated and grew from the solution. >