Showing papers by "National Cheng Kung University published in 1991"

Memoryless stabilization of uncertain dynamic delay systems: Riccati equation approach

Abstract: The authors present a procedure for obtaining the memoryless linear state feedback control of uncertain dynamic delay systems. The uncertainties are time varying and within a given compact set. This method is an extension of the Riccati equation approach proposed by I.R. Petersen and C.V. Hollot (1986). The extension is straightforward. Also the uncertainties do not need to satisfy the matching conditions. >

Surface Curvature Effect on Slot-Air-Jet Impingement Cooling Flow and Heat Transfer Process

Abstract: Experiments are performed to study 'surface curvature effects on the impingement cooling flow and the heat transfer processes over a concave and a convex surface. A single air jet issuing from different size slots continuously impinges normally on the concave side or the convexside of a heated semicylindrical surface. An electrical resistance wire is used to generate smoke, which allows us to visualize the impinging flow structure. The local heat transfer Nusselt number along the surfaces is measured. For impingement on a convex surface, three-dimensional counterrotating vortices on the stagnation point are initiated, which result in the enhancement of the heat transfer process. For impingement on a concave surface, the heat transfer Nusselt number increases with increasing surface curvature, which suggests the initiation of Taylor-Gortler vortices along the surface. In the experiment, the Reynolds number ranges from 6000 to 350,000, the slot-to-plate spacing from 2 to 16, and the diameter-to-slot-width ratio D/b from 8 to 45.7. Correlations of both the stagnation point and the average Nusselt number over the curved surface, which account for the surface curvature effect, are presented. 1 Introduction Impingement cooling has been widely used to cool a heat transfer component exposed to a high temperature or a high heat flux environment. The impingement cooling jet has the advantage that it is readily moved to the location of interest and removes a large amount of heat. It has been widely used in such industrial systems as high-temperature gas turbines, paper drying, glass manufacturing, and high-density electronic equipment. The impinging jet used in these systems is air. Over the past 30 years, impingement cooling heat transfer has been extensively studied. Good review articles are available (Martin, 1977; Becko, 1976). The impinging flow structure (Donaldson and Snedeker, 1971a, 1971b), the local heat transfer, and the correlations of average Nusselt number in terms of relevant parameters have been well studied (Gardon and Cobonpue, 1963; Gardon and Akfirat, 1966; Korger and Krizek, 1965; Zumbrunnen et al., 1989). However, the impingement cooling studied in the past was on a flat plate. The situation of impingement cooling over a curved surface may frequently be encountered. However, the studies of impingement cooling on a curved surface are rela­tively few. Chupp et al. (1969) studied the impingement cooling heat transfer for an array of round jets impinging on a concave surface. The geometric configuration studied is very similar to the case for cooling of the leading edge of a gas turbine airfoil. They measure the local Nusselt number and correlate the av­erage Nusselt number in terms of the Reynolds number, the nozzle-to-plate spacing, and some nondimensional parameters of geometry. However, the local heat transfer obtained is ac­tually an average over a relatively large space. A similar ge­ometry is also studied by Metzger et al. (1969,1972) and Hrycak (1978, 1981). Tabakoff and Clevenger (1972) study three dif­ferent configurations of impinging jets on a concave surface: the single slot jet, the one-dimensional row of round jets, and the two-dimensional array of jets. Both the local and the av­erage Nusselt number are determined. However, the local heat transfer Nusselt number obtained is again an average over a relatively large space. A few correlations of average Nusselt numbers for slot jet impingement cooling over a concave or a

Charmless nonleptonic rare decays of B mesons.

Abstract: Branching ratios of nonleptonic exclusive two-body decays of $B$ mesons without final-state charm particles are studied in detail. The technique used for evaluating the nonleptonic decay amplitudes is elucidated. The dominant charmless decay channels are ${B}_{u}^{+}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\eta}}^{\ensuremath{'}}, {\ensuremath{\pi}}^{+}{\ensuremath{\eta}}^{\ensuremath{'}}, {\ensuremath{\rho}}^{+}{\ensuremath{\pi}}^{0}, {\ensuremath{\rho}}^{+}\ensuremath{\eta}, {\ensuremath{\rho}}^{+}{\ensuremath{\eta}}^{\ensuremath{'}}, {\ensuremath{\rho}}^{+}\ensuremath{\omega}$, ${B}_{d}^{0}\ensuremath{\rightarrow}{K}^{0}{\ensuremath{\eta}}^{\ensuremath{'}}, \ensuremath{\eta}{\ensuremath{\eta}}^{\ensuremath{'}}, {\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\eta}}^{\ensuremath{'}}, {K}^{*+}{\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\rho}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}, {K}^{*+}{\ensuremath{\rho}}^{\ensuremath{-}}, {\ensuremath{\rho}}^{+}{\ensuremath{\rho}}^{\ensuremath{-}}$, which should be interesting for experimental observation. The implications of the quark-diagram scheme are also discussed.

Automatic clutter-canceler for microwave life-detection systems

Abstract: A microprocessor-controlled automatic clutter-cancellation subsystem, consisting of a programmable microwave attenuator and a programmable microwave phase-shifter controlled by a microprocessor-based control unit, has been developed for a microwave life-detection system (L-band 2 GHz or X-band 10 GHz). This system can remotely sense breathing and heartbeat movements of living subjects. This automatic clutter-cancellation subsystem improves manual clutter-cancellation in microwave systems. A series of experiments have been conducted to demonstrate the applicability of this microwave life-detection system for rescue purposes. The 2-GHz system performs well for remotely detecting human breathing and heartbeat signals through a pile of rubble of up to about three feet thick. >

A heuristic search approach to feeder switching operations for overload, faults, unbalanced flow and maintenance

Abstract: The general feeder switching problem is essentially combinatorial, i.e. suitable for analysis by heuristic search methods. An explicit search method is developed to identify feasible switching options under the constraint of a radial structure. Feeder overload, transformer overload, phase current over-unbalance, service restoration after faults, and maintenance are considered. The number of switching operations for resolution of these problems is an important factor for practical use. An explicit search structure is proposed. Based on this search structure heuristic rules and evaluation functions are exploited to quickly find a solution with relatively few switching operations and even balancing of system load. The method is efficient and reliable. A distribution system of the Taiwan Power Company is used to test the results. >

Optimal force distribution in multiple-chain robotic systems

Abstract: The force-distribution problem in multiple-chain robotic systems is to solve for the setpoints of the chain contact forces and input joint torques for a particular system task. It is usually underspecified, and an optimal solution may be obtained. The generality of the compact-dual linear programming (LP) method that can accept a variety of linear objective functions for different applications over a wide range of multiple-chain systems (multilegged vehicles, dexterous hands, and multiple manipulators) is demonstrated; and the solutions for several common problems of force distribution including slippage avoidance, minimum effort, load balance, and temporal continuity are proposed. This is illustrated by solving the force-distribution problem of a grasping system being developed called Digits. Efficiency considerations and elimination of redundant constraints are also discussed. With four fingers grasping an object, considering a conservative friction coefficient (for safety margins on friction constraints) and using a combined objective function for achieving the goals of minimum effort, load balance, and temporal continuity, the CPU time on a VAX-11/785 computer is less than 45 ms (using a linear programming package in the IMSL library). Therefore, it is believed that rather general use of the compact-dual LP method may be made to define a suitable objective function for a particular application and to solve the corresponding force-distribution problem in real time. >

Effects of 30-h sleep loss on cardiorespiratory functions at rest and in exercise.

Abstract: The effects of 30-h sleep deprivation on cardiorespiratory function either at rest or in exercise were studied in 15 young healthy male volunteers. All subjects performed 1-min incremental exercise tests on a bicycle ergometer until exhaustion and endurance exercise tests at 3/4 of their maximal work rates. Arterialized venous blood samples were withdrawn at rest and during exercise tests to investigate the influence of sleep loss on blood gases. In addition, resting plasma catecholamine levels were also measured in ten subjects. The results showed that 1) resting heart rate, plasma catecholamine levels, and blood pH were decreased while minute ventilation (VI) and CO2 production (VCO2) were increased after 30 h of sleep loss (P less than 0.05), and 2) the maximal exercise performance was reduced by sleeplessness, as indicated by the decreases in the maximal heart rate, peak VI, peak VCO2, peak O2 consumption, and time to exhaustion (P less than 0.05). However, no significant changes in exercise endurance, arterialized venous pH, and PCO2 were found in exercise after sleep deprivation either. We therefore conclude that 30-h sleep loss alters cardiorespiratory function at rest and the ability to perform maximal exercise but not exercise endurance.

A hierarchical neural network model based on a C/V segmentation algorithm for isolated Mandarin speech recognition

Abstract: A novel algorithm simultaneously performing consonant/vowel (C/V) segmentation and pitch detection is proposed. Based on this algorithm, a consonant enhancement method and a hierarchical neural network scheme are explored for Mandarin speech recognition. As a result, an improvement of 12% in consonant recognition rate is obtained and the number of recognition candidates is reduced from 1300 to 63. A series of experiments over all Mandarin syllables (about 1300) is demonstrated in the speaker-dependent mode. Comparisons with the decoder timer waveform algorithm are evaluated to show that the performance is satisfactory. An overall recognition rate of 90.14% is obtained. >

Efficient formulation of the force-distribution equations for simple closed-chain robotic mechanisms

Abstract: Force distribution is the inverse dynamics problem for multiple-chain systems in which the motion is completely specified and the internal forces/torques to effect this motion are to be determined. A computationally efficient formulation for the force-distribution problem is presented. This formulation is applicable to a number of simple closed-chain robotic mechanisms, including dexterous hands, multiple manipulators, and multilegged vehicles. Modeling of chain contacts is relatively general so that hard point contact, soft finger contact or rigid contact with an irregularly-shaped object or with uneven terrain may be handled. The dynamic effects of the chains and physical limits on their actuators are efficiently included in the formulation through the use of the inverse dynamics and Jacobian relationships for each chain. Based on this efficient formulation, a variety of methods may then be developed to solve the force-distribution problem. >

Analysis of subsidence due to a point sink in an anisotropic porous elastic half space

Abstract: Analytical solutions of the long-term consolidation deformation and excess pore water pressure due to fluid withdrawal from a saturated anisotropic porous elastic half space are presented. In the analysis, both the permeability and the elastic properties are considered cross-anisotropic. Cases of pervious and impervious half-space boundary are studied. The consolidation settlements as effected by the anisotropy and boundary conditions for pore water are illustrated and discussed.

Control of separated flow by a two-dimensional oscillating fence

Abstract: Control of separated flow behind a backward-facing step using a two-dimensional oscillating fence installed upstream has been investigated in this work. Parameters of the flow considered included the reduced frequency of the oscillating fence, the distance from the oscillating to the backward-facing step, the ratio of the maximum height of the oscillating fence to the step height, and the Reynolds number. It was found that with the experimental parameters properly selected the time-mean reattachment length of the separation region could be reduced over 40%, compared to the case without the presence of an oscillating fence. The evolution of unsteady flow behind a backward-facing step was further studied in detail by a phase-averaging measurement technique. The results obtained indicate that suppression of the separated flow behind the step is mainly due to the downwash motion induced by the vortical structure released upstream from the oscillating fence, when it convects over the step.

Alopecia syphilitica, a simulator of alopecia areata: histopathology and differential diagnosis.

Abstract: Alopecia syphilitica (AS) may be "moth-eaten" or diffuse, clinically, and be confused with alopecia areata (AA) or other alopecias. The English language literature contains scant information regarding the histopathology of AS, and the resemblance between AS and AA has not been given adequate recognition. We report the histopathological findings of AS from nine patients with secondary syphilis and acute hair loss. The alopecia was moth-eaten in four patients and diffuse, but slightly moth-eaten, in five. Microscopically, the dermoepidermal interface was not involved. The numbers of hair follicles were diminished, with increased numbers of catagens and telogens. Lymphocytic infiltration was present around the hair bulbs and fibrous tracts in eight cases. Plasma cells were present in four biopsies. Other less common findings included lymphocytes in the isthmus, parabulbal lymphoid aggregates, and granulomatous infiltrate in the upper dermis. The findings, save for the follicular changes, resembled those of macular/maculopapular syphilides outside the scalp. With the follicular changes, the overall patterns resembled AA closely. The modified Steiner stain did not reveal spirochetes in any of our cases and failed to differentiate between AS and AA. Comparing the AS cases to 13 cases of AA, we found only a few differentiating features. The presence of peribulbal eosinophils strongly suggests AA. Without peribulbal eosinophils, the presence of plasma cells, abundant lymphocytes in the isthmus, or parabulbal lymphoid aggregates suggests AS.

Cryptosystem for group oriented cryptography

Abstract: A practical non-interactive scheme is proposed to simultaneously solve several open problems in group oriented cryptography. The sender of the information is allowed to determine the encryption/decryption keys as well as the information destination without any coordination with the receiving group. The encrypted message is broadcasted to the receiving group and the receivers may authenticate themselves for legitimacy of the information directly from the ciphertext. The security of the scheme can be shown to be equivalent to the difficulty of solving the discrete logarithm problem.

Kinetics, mechanism, and time course analysis of lipase‐catalyzed hydrolysis of high concentration olive oil in AOT–isooctane reversed micelles

Abstract: Candida rugosa lipase has been used to investigate the hydrolysis of high concentration olive oil in the AOT–isooctane reversed micellar system at Wo = 10, pH 7.1, and 37°C. Results from this work show the hydrolytic reaction obeys Michaelis–Menten kinetics up to the initial substrate concentration of 1.37M, with turnover number kcat and Michaelis constant KM of 67.1 μmol/min mg enzyme and 0.717M, respectively. A competitive inhibition by the main product, oleic acid, has been found with a dissociation constant KI for the complex EP* of 0.089M. The rate equation was further analyzed in the time course reaction and was found in agreement with the experimental results for lower substrate concentrations, up to 0.341M. Large deviation occurred at high substrate concentrations, which may be due to the effects of large consumption of water on kinetics, on the formation of glycerol, and on the deactivation of lipase in the hydrolysis reaction as well.

Kinetics of enzymatic hydrolysis of olive oil in biphasic organic-aqueous systems

Abstract: A theoretical model for the lipase-catalyzed hydrolysis of high-concentration olive in biphasic isooctane-aqueous systems has been proposed and confirmed by experiments. The enzymatic reaction of the Michaelis-Menten type that occurred at the interface between organic and aqueous phases was assumed in deriving the rate equations, from which the maximum reaction rate could be obtained by carefully adjusting the volume ratio between the two phases to the optimal value. Equilibrium conversions higher than 98% for 0.1 g/L olive oil in isooctane were attained for systems with volume ratios up to one. Fractions of lipase and lipase-substrate complex adsorbed at the interface increased and seemed to approach to asymptotic values as the rotation speed of impeller increased. Activity of the lipase showed no apparent change between 26 and 37 degrees C, but decrease rapidly with temperature above 43 degrees C. The methodology presented in this work might be used to find kinetic parameters for reactor design and scaleup.

Dynamic modeling of the mold filling process in an injection molding machine

Abstract: This paper presents the development of a nonlinear mathematical model for the study of the mold filling process in an injection molding machine. The model is formulated by the Reynolds transport theorem which is applied to describe the polymer flow dynamics. The mold filling process can be approximated by the transient phenomenon of the non-Newtonian fluids flowing through a closed conduit. The comparison between the experimental results and the theoretical simulation indicate that the nonlinear model is a reasonable representation of the mold filling dynamics when the acrylonitrile-butadiene-styrene (ABS) is injected into a disk shape mold. The actuation system dynamics of an injection molding machine are also investigated. The results indicate that the nonlinear model can also adequately predict the transient behavior of the actuation system.

Impact interactions between two vibration systems under random excitation

Abstract: The exact stationary solutions of the random response of two special vibration systems with impact interactions are formulated in this paper. Between the two systems, the Hertz contact law is used to model the contact process during vibration. A clearance is also introduced. The excitation is assumed to be a stationary white Gaussian process with zero mean and acting on the two systems independently. By assuming the ratio of the excitation and damping parameter of each system to be the same, the exact solutions can be found through solving the time-independent Fokker-Planck equation. The effects of contact stiffness, clearance and the system properties on the response are discussed probabilistically. From this study, it is found that, under some cases, the contact phenomena still play an important role on the response even when the clearance is larger than three times the root mean square response of the corresponding linear systems.

Effects of bond coat preoxidation on the properties of ZrO2-8wt.% Y2O3/Ni-22Cr-10Al-1Y thermal-barrier coatings

Abstract: Plasma-sprayed thermal barrier coatings (TBCs) consist of an intermediate MCrAlY bond coat to protect the substrate superalloy from oxidation/hot corrosion and a thermal insulating zirconia-based ceramic top coat. This system is developed for advanced turbine-engine, hot-section components. In this study the as-sprayed Ni-22Cr-10Al-1Y bond coat was subjected to preoxidation treatment at 1000° C for 1, 50, 100, and 200 hr, also at 1100°C, 1200°C and 1300°C for 1 hr to form an oxide scale before subsequent deposition of a ZrO2-8wt.% Y2O3 top coat. The oxidation kinetics were measured, and the phase constitution and morphology of pregrown oxides on the Ni-22Cr-1Y bond coat were analyzed by x-ray diffractometer and SEM/EDS to elucidate the improvement and degradation mechanisms of the new system. The results of the experiments in this study showed that the tentative ZrO2-8wt.% Y2O3 TBC specimens with preoxidized Ni-22Cr-10Al-1Y bond coat, when properly processed, exhibited lower oxidation rates and generally longer lifetime compared with traditional TBC specimens.