Showing papers by "National Tsing Hua University published in 1994"

Estimating population size via sample coverage for closed capture-recapture models.

Abstract: A nonparametric estimation technique is proposed which uses the concept of sample coverage in order to estimate the size of a closed population for capture-recapture models where time, behavior, or heterogeneity may affect the capture probabilities. The technique also provides a unified approach to catch-effort models that allows for heterogeneity among removal probabilities. Real data examples are given for illustration. A simulation study investigates the behavior of the proposed procedure.

Medium access control of wireless LANs for mobile computing

Abstract: To provide high-speed seamless services for mobile computing, an effective medium access control capable of dealing with mobility issues in multicell wireless local area networks is needed. The physical layers discussed include direct sequence spread spectrum (DS-SS), frequency hopped spread spectrum (FH-SS), and diffuse infrared. Both spread spectrum transmissions are in the 2.4 to 2.4835 GHz ISM band, according to FCC part 15.247. >

Plasmons and optical properties of carbon nanotubes

Abstract: The optical properties of carbon nanotubes are studied within the gradient approximation. The calculated dielectric function exhibits many divergent structures, due to the divergencies in its density of states. As a result, the electron-energy-loss spectrum has many peak structures, including a prominent one at \ensuremath{\sim}6 eV, which is identified as the collective excitations of the \ensuremath{\pi}-band electrons. This plasmon is found to be insensitive to both radius and chiral angle, due to the unique one-dimensional band structure of carbon nanotubes. The result is consistent with the experimental measurements. The reflectance also exhibits many interesting features, including a weak but sharp plasmon edge at \ensuremath{\sim}6 eV.

The L3 silicon microvertex detector

Abstract: The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout.

A nonlinear H∞ control design in robotic systems under parameter perturbation and external disturbance

Abstract: A state feedback H∞optimal disturbance attenuation for the model reference control of rigid robotic systems is studied. The disturbances affecting the system dynamics come from the residue of the applied torques due to perturbations of the system parameters and external noise. The design objective is that the disturbance attentuation level must be less than or equal to a desired positive value γ. By combining the nonlinear minimax control technique with the work of Johansson (1990) we are able to present an explicit global solution to this nonlinear time-varying H∞ -control problem. In particular, it turns out that if y, the desired attenuation level, is greater than the magnitude of the weighting matrix on control inputs, then a state feedback law achieving the desired performance can be explicitly constructed. Hence, it is advantageous to consider our approach for H∞ tracking control of other physical systems, Finally, extensive simulations are made for tracking control of a two-link robotic manipulator...

A new motion compensation method for image sequence coding using hierarchical grid interpolation

Abstract: Presents a new motion estimation method for low bit-rate image sequence coding that uses a hierarchical decomposition of the current image frame to describe scene motion in terms of displacement and deformation of variable-sized rectangular regions. Because the conventional blockmatching motion compensation method (BMA) can only cope with the problem of translational movement of the scene, some researchers have proposed deformable-block-based motion compensation such as control grid interpolation (CGI) and the triangle-based method (TBM). CGI begins with a spatial displacement for a small number of points in an image, termed control points. TBM partitions the image frame into triangular patches with equal size that are deformable during the motion compensation. These methods do not consider using the different motion characteristics and the shape properties of the moving objects, but instead apply the same motion estimation algorithm to every part of the scene which may be stationary or moving. The present authors propose a new motion compensation method called hierarchical grid interpolation (HGI) which segments a frame into various quadrangles with different sizes (described by quadtree segmentation) according to the motion activity. In the experiments, the authors compare HGI with the conventional BMA and TBM. HGI requires less computation, produces less prediction error, and requires lower transmission bit-rate. It also achieves a subjective image quality that is better than the conventional motion compensation coder. >

An improved hysteresis current controller for reducing switching frequency

Abstract: In this paper, an improved invertor hysteresis current controller is proposed. It coordinates the switching of the three-phase switches in the d-q phase plane. In addition to the current error, information of the current error derivative is further employed so that one can take more advantage of adding the zero voltage vector for reducing the switching frequency. A simple hardware implementation of the improved hysteresis current controller is also proposed such that merits of the conventional hysteresis current controller can still be kept. Theoretical basis and some simulation and experimental results are presented to demonstrate the validity of the improved hysteresis current controller. >

A self-organizing fuzzy sliding-mode controller design for a class of nonlinear servo systems

Abstract: A self-organizing fuzzy controller to augment a sliding-mode control (SOFSMC) scheme for a class of nonlinear systems is proposed. The motivation behind this scheme is to combine the best features of self-organizing fuzzy control and sliding-mode control to achieve rapid and accurate tracking control of a class of nonlinear systems. The chatter encountered by most sliding-mode control schemes is greatly alleviated without sacrificing invariant properties. A stability analysis is presented; the design guidelines and the class of applicable systems are clearly identified. To verify the scheme, the authors performed experiments on its implementation in a magnetic levitation system. The results show that both alleviation of chatter and robust performance are achieved; the advantages of the scheme are indicated in comparison with the conventional sliding-mode design. >

Differential cross sections for plasmon excitations and reflected electron-energy-loss spectra.

Abstract: Electron differential inverse mean free paths for volume-plasmon excitations and differential probabilities for surface-plasmon excitations have been calculated using dielectric response theory. A model dielectric function which satisfied sum rules and agreed with optical data was established for these calculations. In surface-plasmon calculations, we considered electron-impact emissions of the reflected electron-energy-loss spectroscopy. Formulations were made for obliquely incident electrons with the recoil effect and without the small-scattering-angle assumption. For volume-plasmon excitations, we evaluated corrections due to the exchange and ${\mathit{Z}}_{1}^{3}$ effects. Comparison between calculated results and experimental data extracted from reflected electron-energy-loss spectra showed good agreement. Calculated differential cross sections have been used to solve the transport equation for the angular and energy flux spectra of reflected electrons. Contributions to the spectra from single and plural plasmon excitations were analyzed. It was found that calculated spectra were in good agreement with measured data.

Heat Transfer Measurement and Analysis for Sintered Porous Channels

Abstract: This paper presents the results of heat transfer measurement and analysis for two 5×5×1 cm porous channels. The channels were made of sintered bronze beads with two different mean diameters, d p =0.72 and 1.59 mm. The local wall temperature distribution, inlet and outlet pressure and temperatures, and heat transfer coefficients were measured for heat flux of 0.8, 1.6, 2.4, and 3.2 W/cm 2 with air velocity ranging from 0.16 to 5 m/s and inlet air pressure of 1∼3 atm

Active oxygen species are involved in the induction of micronuclei by arsenite in XRS-5 cells.

Abstract: The human carcinogen, arsenic, is genotoxic to mammalian cells in vitro. The mechanism is largely unknown, although the involvement of free radicals has been suggested. Since the X-ray sensitive Chinese hamster ovary cell line, XRS-5, is also sensitive to several free-radical generating agents, including H2O2, we have used this cell line to test whether the genotoxic effect of arsenite is mediated via the generation of active-oxygen species. The results indicate that the XRS-5 cells are more sensitive to arsenite in terms of cell-killing and micronucleus induction compared to the parental CHO-K1 cells. The level of arsenic uptake and release, the levels of elementary components for arsenic detoxification, glutathione and glutathione S-transferase activities in these two cell lines are very similar. The XRS-5 cells, however, were shown to have 6-fold lower catalase activity in comparison to CHO-K1 cells. Moreover, catalase could effectively reduce the frequency of arsenite-induced micronuclei. These results indicate that the low catalase activity may be an important reason why XRS-5 cells are more sensitive to the toxic effects of arsenite, and arsenite probably induces micronuclei via the overproduction of H2O2. The XRS-5 cells had a higher background level of micronuclei, and were also more sensitive to gamma-rays in terms of induction of micronuclei. Catalase, however, did not reduce the background level or the frequency of gamma-ray-induced micronuclei. Therefore, the lower catalase activity seems to bear little relation to the high background level of micronuclei and the hypersensitivity to gamma-rays in micronucleus induction in XRS-5 cells.

A fuzzy controller improving a linear model following controller for motor drives

Abstract: Since the dynamic response trajectory of a traditional fuzzy controller can not be quantitatively controlled, a fuzzy model following controller is proposed in this paper. In the proposed controller, an output feedback linear model following controller (LMFC) is first designed according to the roughly estimated plant model to let its response follow the output generated by a reference model. Then a model following error driven control signal is synthesized such that good model following characteristics can be preserved at various operating conditions. The proposed controller is applied to the speed control of an induction motor drive. Dynamic signal analysis of the model following behavior is made and the procedure for constructing the control algorithms is described in detail. The performance of the drive and the effectiveness of the proposed controller are demonstrated by some simulated and experimental results. >

Magnetoreception in Honeybees

Abstract: Magnetoreception by honeybees ( Apis mellifera ) is demonstrated by such activities as comb building and homing orientation, which are affected by the geomagnetic field. In other magnetoreceptive species, iron oxide crystals in the form of magnetite have been shown to be necessary for primary detection of magnetic fields. Here it is shown that trophocytes, which are apparently the only iron granule—containing cells in honeybees, contain super-paramagnetic magnetite. These cells are innervated by the nervous system, which suggests that trophocytes might be primarily responsible for magnetoreception. Electron microscopy also shows cytoskeletal attachments to the iron granule membrane.

Floating gate or flash EPROM transistor array having contactless source and drain diffusions

Abstract: Novel contactless FLASH EPROM cell and array designs, and methods for fabricating the same is based on a unique drain-source-drain configuration, in which a single source diffusion is shared by two columns of transistors. An elongated first drain diffusion region, an elongated source diffusion region, and an elongated second drain diffusion region, are formed in a semi-conductor substrate along essentially parallel lines. Field oxide regions are grown on opposite sides of the first and second drain diffusion regions. Floating gates and control gate wordlines are formed orthogonal to the drain-source-drain structure to establish two columns of storage cells having a shared source region. The shared source region is coupled through a bottom block select transistor to a virtual ground terminal. Each drain diffusion region is coupled through a top block select transistor to global bitline. The cell structure uses two metal global bitlines which extend essentially parallel to the drain, source and drain diffusion regions, and a virtual ground conductor which couples a plurality of columns of transistors to a virtual ground terminal through a horizontal conductor, such as a buried diffusion line.

Ethanol‐induced crack healing in poly(methyl methacrylate)

Abstract: The crack healing induced by ethanol in poly(methyl methacrylate) (PMMA) has been studied at temperatures of 40–60°C. Crack healing occurs because the effective glass transition temperature of PMMA is reduced to below the test temperature by ethanol plasticization. It is found that crack closure rate is constant at a given temperature. The fracture strength of healed PMMA is lower than that of the original samples. By comparing the fracture stress with the morphology of the crack edge on the PMMA surface, we found that a high degree of swelling is responsible for the incomplete recovery of mechanical strength. The fractography of the completely healed sample shows a very different fracture morphology from that of virgin PMMA. The transport of ethanol in PMMA also is studied. At lower temperatures, transport is described by ideal Case II behavior. As the temperature increases, the kinetics shift from ideal Case II to anomalous behavior. The first stage of crack healing is controlled by Case I transport. © 1994 John Wiley & Sons, Inc.

Superconductivity near phase separation in models of correlated electrons

Abstract: Numerical and analytical studies of several models of correlated electrons are discussed Based on exact diagonalization and variational Monte Carlo techniques, we have found indications that the two-dimensional t-J model superconducts near phase separation in the regime of quarter-filling density, in agreement with previous results reported by Dagotto and Riera [Phys Rev Lett 70, 682 (1993)] At this density the dominant channel is ${\mathit{d}}_{\mathit{x}}^{2}$-${\mathit{y}}^{2}$, but a transiton to s-wave superconductivity is observed decreasing the electronic density In addition, the one-band t-U-V model has also been studied using a mean-field approximation An interesting region of ${\mathit{d}}_{\mathit{x}}^{2}$-${\mathit{y}}^{2}$ superconductivity near phase separation is observed in the phase diagram, and its implications for recent self-consistent studies of d-wave condensates in the context of the high-${\mathit{T}}_{\mathit{c}}$ cuprates are briefly discussed Finally, the two-band Hubbard model on a chain is also analyzed Superconducting correlations near phase separation exist in this model, as it occurs in the t-J model Based on these nontrivial examples it is conjectured that electronic models tend to have superconducting phases in the vicinity of phase separation, and this regime of parameter space should be explored first when a new model for superconductivity is proposed Reciprocally, if it is established that a model does not phase separate, even in an extended parameter space, then we believe that its chances of presenting a superconducting phase are considerably reduced

Constant-returns endogenous growth with pollution control

Abstract: Pollution control with positive externality from the government is incorporated in an endogenous growth model with “AK” production function The result indicate that if consumption and abatement expenditure grows at a constant rate, pollution stock will have smaller growth rate The growth rate of consumption in a command economy will in general be greater than in a competitive economy A greater intertemporal elasticity of substitution will result in a lower growth rate only if the household's preference parameter against pollution is sufficiently small The development strategy of pursuing higher growth rate accompanied by more pollution in the early stage of economic development is economically justifiable The utility in a wealthier economy is always higher in all stages of development than in a poorer economy, as is the pollution stock, although it may converge in the steady state

Collision-avoidance by fuzzy-logic control for automated guided vehicle navigation

Abstract: A fuzzy approach to collision avoidance for automated guided vehicle (AGV) navigation is proposed. Static obstacles with no a priori position information as well as moving obstacles with unknown trajectories are considered in this study. Intuitive and subjective human ideas of collision avoidance are modeled into fuzzy rules. Fuzzy logic is applied in the inference procedure for AGV navigation, such that the AGV is guided from the starting point toward the target without colliding with obstacles. Furthermore, the proposed method can also be used for the navigation of multiple AGVs, where each AGV must avoid other AGVs as well as obstacles in the environment. Simulation results are presented to show the feasibility of the proposed fuzzy approach. © 1994 John Wiley & Sons, Inc.

Minimax robust deconvolution filters under stochastic parametric and noise uncertainties

Abstract: The author consider the design of robust deconvolution filters for linear discrete time systems with stochastic parameter and noise uncertainties. It is assumed that some large but bounded uncertainties exist in the driving and measurement noise covariances as well as the second-order statistics of stochastic parameters and initial conditions. Three kinds of minimax sensitivity criteria are used to develop the techniques to the synthesis of minimax deconvolution filters under uncertain linear stochastic systems. Their approach is based on saddle-point theory and the sensitivity analysis of Kalman filters. The design algorithms give the recursive realization of the minimax deconvolution filters for the time-varying uncertain systems under fairly general conditions. For the time-invariant uncertain case the existence and solutions of steady-state deconvolution filters are further developed. Finally, the utility of the minimax design approaches and the properties of the resulting minimax deconvolution filters are illustrated by a numerical example. >

Control of transcription and mRNA turnover as mechanisms of metabolic repression of α‐amylase gene expression

Abstract: Summary Carbon metabolites suppress the expression of α-amylase genes in germinating seeds and in suspension-cultured cells of rice. We have used suspension cell culture as a model system to study the mechanisms of metabolic regulation of α-amylase gene expression in rice. Both transcription rate and mRNA stability increased as cells were starved of sucrose; the transcription rate of α-amylase genes in cells starved of sucrose for 24 h was seven times greater than in cells provided with sucrose. The half-life of α-amylase mRNA was less than 1 h in cells provided with sucrose, but increased to 12 h in cells starved of this sugar. A protein synthesis inhibitor, cycloheximide (CHX), induced massive accumulation of a-amylase mRNA in cells provided with sucrose. The longer half-life of mRNA induced by sucrose starvation and the massive accumulation of mRNA caused by CHX were specific to the α-amylase genes, since actin genes were not similarly affected. Our findings suggest that both transcriptional and post-transcriptional control mechanisms are important in the metabolic regulation of α-amylase gene expression and de novo synthesized proteins are involved in these mechanisms. The expression of α-amylase and actin genes is regulated in an opposite manner by sugars, which also suggests the operation of a differential regulatory mechanism under different growth conditions.

A robust speed controller for induction motor drives

Abstract: A speed controller considering the effects of parameter variations and external disturbance for indirect field-oriented induction motor drives is proposed in this paper. First a microprocessor-based indirect field-oriented induction motor drive is implemented and its dynamic model at nominal case is estimated. Based on the estimated model, an integral plus proportional (IP) controller is quantitatively designed to match the prescribed speed tracking specifications. Then a dead-time compensator and a simple robust controller are designed and augmented to reduce the effects of parameter variations and external disturbances. The desired speed tracking control performance of the drive can be preserved under wide operating range, and good speed load regulating performance can also be obtained. Theoretic basis and implementation of the proposed controller are detailedly described. Some simulated and experimental results are provided to demonstrate the effectiveness of the proposed controller. >

Buckling of Elliptically Delaminated Composite Plates

Abstract: The buckling of laminated plates with elliptic delamination under compressive loading was studied experimentally and analytically. In the experiment, a tensiletest machine was used to determine the load-displacement behavior of the delaminated plates under uniaxial loading and the buckling strength was extracted therefrom. In analysis, a nonlinear finite element program based on the updated Lagrangian formulation was developed to analyze the response of the laminated plates. The formulation includes large displacements and large rotations. The plates were divided into finite elements and the degenerated shell elements were used. The Newton-Raphson method was used to solve the resulting equation for the nonlinear system and a displacement-controlled scheme was used in the solution procedure near the buckling load. This process was repeated until a desired accuracy was achieved. The buckling behavior of mixed and global types of the delaminated composite plates were examined. Four parameters, including the ...

Reachability testing: an approach to testing concurrent software

Abstract: Concurrent programs are more difficult to test than sequential programs because of nondeterministic behavior. An execution of a concurrent program nondeterministically exercises a sequence of synchronization events, called a synchronization sequence (or SYN-sequence). Nondeterministic testing of a concurrent program P is to execute P with a given input many times in order to exercise distinct SYN-sequences and produce different results. We present a new testing approach, called reachability testing. If P with input X contains a finite number of SYN-sequences, reachability testing of P with input X can execute all possible SYN-sequences of P with input X. We show how to perform reachability testing of concurrent programs using read and write operations. Also, we present results of empirical studies comparing reachability and nondeterministic testing. Our results indicate that reachability testing has advantages over nondeterministic testing. >

Speech recognition using weighted HMM and subspace projection approaches

Abstract: A weighted hidden Markov model (HMM) algorithm and a subspace projection algorithm are proposed to address the discrimination and robustness issues for HMM-based speech recognition. A robust two-stage classifier is also proposed to incorporate these two approaches to further improve the performance. The weighted HMM enhances its discrimination power by first jointly considering the state likelihoods of different word models, then assigning a weight to the likelihood of each state, according to its contribution in discriminating words. The robustness of this model is then improved by increasing the likelihood difference between the top and the second candidates. The subspace projection approach discards unreliable observations on the basis of maximizing the divergence between different word pairs. To improve robustness, the mean of each cluster is then adjusted to obtain maximum separation different clusters. The performance was evaluated with a highly confusable vocabulary consisting of the nine English E-set words. The test was conducted in a multispeaker (100 talkers), isolated-word mode. The 61.7% word accuracy for the original HMM-based system was improved to 74.9% and 76.6%, respectively, by using the weighted HMM and the subspace projection methods. By incorporating the weighted HMM in the first stage and the subspace projection in the second stage, the two-stage classifier achieved a word accuracy of 79.4%. >