Showing papers by "National Tsing Hua University published in 1998"

Precambrian Sponges with Cellular Structures

Abstract: Sponge remains have been identified in the Early Vendian Doushantuo phosphate deposit in central Guizhou (South China), which has an age of approximately 580 million years ago. Their skeletons consist of siliceous, monaxonal spicules. All are referred to as the Porifera, class Demospongiae. Preserved soft tissues include the epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel. Among thousands of metazoan embryos is a parenchymella-type of sponge larvae having a shoe-shaped morphology and dense peripheral flagella. The presence of possible amphiblastula larva suggests that the calcareous sponges may have an extended history in the Late Precambrian. The fauna indicates that animals lived 40 to 50 million years before the Cambrian Explosion.

Noticing in second language acquisition: a critical review

Abstract: This article examines the Noticing Hypothesis – the claim that second language learners must consciously notice the grammatical form of their input in order to acquire grammar. I argue, first, that the foundations of the hypothesis in cognitive psychology are weak; research in this area does not support it, or even provide a clear interpretation for it. The problem of interpreting the hypothesis is much more acute in the area of language acquisition. Partly because the hypothesis is not based on any coherent theory of language, it is very difficult to determine exactly what it means in this context,or to draw testable predictions from it.In the absence of specific predictions, research on form-focused instruction and feedback provide indirect tests, the results of which create additional problems for the hypothesis. The various problems can be eliminated or greatly reduced if the Noticing Hypothesis is reformulated as a claim that noticing is necessary for the acquisition of metalinguistic knowledge but n...

Carry-select adder using single ripple-carry adder

Abstract: Instead of using dual carry-ripple adders, a carry select adder scheme using an add-one circuit to replace one carry-ripple adder requires 29.2% fewer transistors with a speed penalty of 5.9% for bit length n=64. If speed is crucial for this 64 bit adder, then two of the original carry-select adder blocks can be substituted by the proposed scheme with a 6.3% area saving and the same speed.

The emergence of the unmarked in second language phonology

Abstract: This paper discusses the simplification of forms ending in obstruents by native speakers of Mandarin, in particular two effects that are not obviously motivated by either the native- or the target-language grammars: a tendency to devoice final voiced obstruents and a tendency to maximize the number of bisyllabic forms in the output. These patterns are accounted for within Optimality Theory, which describes a grammar as a set of universal, ranked constraints. It is argued that the devoicing and bisyllabicity effects result from universal markedness constraints that are present in all grammars but that are masked in the learner's native-language grammar by the effects of higher ranking constraints.

Ring Strain Energies from ab Initio Calculations

Abstract: A new approach employing ab initio calculations is suggested for evaluating the strain energy of ring molecules as well as for estimating the relative contribution of different sources of strain to the ring strain energy. The approach developed is calibrated by reproducing experimentally determined strain energies of mono- and bicyclohydrocarbons, cyclic ethers, and amines. It is then used to predict ring strain energies of cyclic phosphoesters, hydrogen fluoride cyclic clusters, and magnesium dialdehyde cyclic chelates. The usefulness of the method is demonstrated in disclosing the role of ring strain in the enhanced reactivity of a five-membered cyclic phosphate relative to its acyclic analogue and six-membered ring counterpart.

Electric current effects upon the Sn\Cu and Sn\Ni interfacial reactions

Abstract: Electromigration-induced failures in integrated circuits have been intensively studied recently; however, electromigration effects upon interfacial reactions have not been addressed. These electromigration effects in the Sn/Cu and Sn/Ni systems were investigated in this study by analyzing their reaction couples annealed at 200°C with and without the passage of electric current. The intermetallics formed were e-(Cu3Sn) and η-(Cu6Sn5) phases in the Sn/Cu couples and Ni3Sn4 phase in the Sn/Ni couples. The same intermetallics were formed in the two types of couples with and without the passage of electric current. The thickness of the reaction layers was about the same in the two types of couples of the Sn/Cu system. In the Sn/Ni system, the growth of the intermetallic compound was enhanced when the flow direction of electrons and that of diffusion of Sn were the same. But the effect became inhibiting if the directions of these two were opposite. Theoretical calculation indicated that in the Sn/Ni system, the electromigration effect was significant and was 28% of the chemical potential effect for the Sn element flux when the Ni3Sn4 layer was 10 µm thick. For the Sn and Cu fluxes in the Sn/Cu reaction couples, similar calculations showed that the electromigration effects were only 2 and 4% of the chemical potential effects, respectively. These calculated results were in good agreement with the experimental observations that in the Sn/Cu system the electric current effects were insignificant upon the interfacial reactions.

Syntheses and Structures of Organically Templated Iron Phosphates

Abstract: Iron phosphates are of interest because of rich crystal chemistry and practical applications. New crystalline iron phosphates have been prepared in aqueous or predominantly nonaqueous solvents under mild hydrothermal conditions using organic amines as structure-directing agents. The effects of pH, solvent, and temperature on the reaction products are discussed. FePOs have been prepared with 1-D chain, 2-D layered, and 3-D open framework structures. An FePO containing a chiral amine is also synthesized. This review will summarize some of the results of the work in the area of organically templated iron phosphates.

On deterministic traffic regulation and service guarantees: a systematic approach by filtering

Abstract: We develop a filtering theory for deterministic traffic regulation and service guarantees under the (min, +)-algebra. We show that traffic regulators that generate f-upper constrained outputs can be implemented optimally by a linear time-invariant filter with the impulse response f/sub */ under the (min, +)-algebra, where f/sub */ is the subadditive closure defined in the paper. Analogous to the classical filtering theory, there is an associate calculus, including feedback, concatenation, "filter bank summation", and performance bounds. The calculus is also applicable to the concept of service curves that can be used for deriving deterministic service guarantees. Our filtering approach not only yields easier proofs for more general results than those in the literature, but also allows us to design traffic regulators via systematic methods such as concatenation, filter bank summation, linear system realization, and FIR-IIR realization. We illustrate the use of the theory by considering a window flow control problem and a service curve allocation problem.

Ultrahigh Gain Gyrotron Traveling Wave Amplifier

Abstract: Mode competition in the gyrotron traveling wave amplifier is shown to be intricately connected to the interplay between the absolute/convective instabilities, circuit losses, and reflective feedback. Physical origins of spurious oscillations are analyzed and characterized. Fundamental understanding of these processes leads to a device concept which provides zero-drive stability at ultrahigh gain. The scheme was verified in a proof-of-principle experiment in the $\mathrm{Ka}$ band, producing 93 kW saturated peak power at $26.5%$ efficiency, 70 dB gain, and a 3 dB bandwidth of 3 GHz.

A polynomial time approximation scheme for minimum routing cost spanning trees

Abstract: Given an undirected graph with nonnegative costs on the edges, the routing cost of any of its spanning trees is the sum over all pairs of vertices of the cost of the path between the pair in the tree. Finding a spanning tree of minimum routing cost is NP-hard, even when the costs obey the triangle inequality. We show that the general case is in fact reducible to the metric case and present a polynomial-time approximation scheme valid for both versions of the problem. In particular, we show how to build a spanning tree of an n-vertex weighted graph with routing cost at most (1 +) of the minimum in time O(n O( 1 ) ). Besides the obvious connection to network design, trees with small routing cost also nd application in the construction of good multiple sequence alignments in computational biology. The communication cost spanning tree problem is a generalization of the minimum routing cost tree problem where the routing costs of dierent pairs are weighted by dierent requirement amounts. We observe that a randomized O(logn log logn)-approximation for this problem follows directly from a recent result of Bartal, where n is the number of nodes in a metric graph. This also yields the same approximation for the generalized sum-of-pairs alignment problem in computational biology.

Urinary levels of inorganic and organic arsenic metabolites among residents in an arseniasis-hyperendemic area in Taiwan.

Abstract: In order to elucidate whether urinary levels of inorganic and organic arsenic metabolites are associated with previous exposure to high-arsenic artesian well water, a total of 302 residents of age 30 yr or older were recruited from three arseniasis-hyperendemic villages in Taiwan. Most study subjects had stopped consuming high-arsenic artesian well water for more than 20 yr. The mean total arsenic (Ast) determined by inductively coupled plasma mass spectrometer (ICPMS) was 267.05 +/- 20.95 microg/L, and the mean level of inorganic arsenic and its metabolites (Asi) was 86.08 +/- 3.43 microg/L. In the multivariate analysis, urinary dimethylarsinic acid (DMA) levels were significantly inversely associated with age, with women exhibiting significantly lower urinary amounts of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), organic arsenic (Aso), and Ast compared to men. After adjustment for age and sex, previous cumulative arsenic exposure through consumption of artesian well water was significantly associated with elevated urinary levels of MMA and DMA, but not As(III) + As(V), Aso and Ast. In the multivariate analysis, the percentage of Aso in Ast was significantly higher in men than women, but this was not significantly associated with age. The percentage of As(III) + As(V) in Asi increased significantly with age, while the reverse was noted with DMA in Asi. Women had a significantly higher DMA percentage but lower As(III) + As(V) and MMA percentages in Asi than men. After adjustment for age and sex, the percentages of As(III) + As(V) in Asi were significantly inversely associated with previous arsenic exposure through consumption of artesian well water. Data suggested that women seem to possess a more efficient arsenic methylation capability than men, and aging diminishes this methylation capability; furthermore, the higher the cumulative arsenic exposure, the greater is the body burden of inorganic arsenic, mainly in the form of MMA and DMA.

Thermal and corrosion behavior of P2O5-Na2O-CuO glasses

Abstract: Lead free sodium-copper-phosphate glasses in the range (mol%) 30-80P2O5, 0-70Na2O and 0-70CuO were investigated. The glass formation region is P2O5≥40, CuO≤50 and Na2O≤60 mol%. Glasses with a glass transition temperature (Tg) below 420°C, a thermal expansion coefficient from 258 × 10−7 to 99 × 10−7/°C and a dissolution rate in 30°C deionized water at the order of 10−7 g/cm2 min can be prepared. Substitution of CuO for Na2O increases Tg, the softening temperature (Td), hardness and chemical durability and decreases the thermal expansion coefficient. The structure of 50P2O5-(50 - x)Na2O-xCuO glass was examined by XPS and FTIR spectroscopies, which reveal the formation of POCu bonds in these glasses. The formation of POCu bonds, which replace PωO− ⋯ Na+ bonds while keeping the same fraction of POP bonds, increases the crosslink density in the glass network and, therefore, enhances the chemical durability and increases Tg, Td and the hardness of the glasses.

Robust tracking enhancement of robot systems including motor dynamics: a fuzzy-based dynamic game approach

Abstract: A robust tracking control design of robot systems including motor dynamics with parameter perturbation and external disturbance is proposed in this study via adaptive fuzzy cancellation technique. A minimax controller equipped with a fuzzy-based scheme is used to enhance the tracking performance in spite of system uncertainties and external disturbance. The design procedure is divided into three steps. At first, a linear nominal robotic control design is obtained via model reference tracking with desired eigenvalue assignment. Next, a fuzzy logic system is constructed and then tuned to eliminate the nonlinear uncertainties as possibly as it can to enhance the tracking robustness. Finally, a minimax control scheme is specified to optimally attenuate the worst-case effect of both the residue due to fuzzy cancellation and external disturbance to achieve a minimax tracking performance. In addition, an adaptive fuzzy-based dynamic game theory is introduced to solve the minimax tracking problem. The proposed method is appropriate for the robust tracking design of robotic systems with large parameter perturbation and external disturbance. A simulation example of a two-link robotic manipulator driven by DC motors is also given to demonstrate the effectiveness of proposed design method's tracking performance.

A study on the effects of vibrations on the surface finish using a surface topography simulation model for turning

Abstract: In this paper, a surface topography simulation model is established to simulate the surface finish profile generated after a turning operation. The surface topography simulation model incorporates the effects of the relative motion between the cutting tool and the workpiece with the effects of tool geometry to simulate the resultant surface geometry. It is experimentally shown that the surface topography simulation model can properly simulate the surface profile generated by turning operations. The surface topography simulation model is used to study the effects of vibrations on the surface finish profile. It is found that the vibration frequency ratio is a more important vibration parameter than the vibration frequency on the characterization of the surface finish profile. The vibration frequency ratio is the ratio between the vibration frequency and the spindle rotational speed.

Formation of Segregation Morphology in Crystalline/Amorphous Polymer Blends: Molecular Weight Effect

Abstract: In a melt-miscible crystalline/amorphous polymer blend, crystallization is accompanied with the segregation of amorphous diluent. Depending on the distance of segregation, various types of segregation morphology, including interlamellar, interfibrillar, and interspherulitic, may be created. In this study, we systematically investigated the effects of molecular weight (MW) of both crystalline and amorphous component on the formation of segregation morphology in polycaprolactone (PCL)/poly(vinyl chloride) (PVC) blends. Optical microscopy and small-angle X-ray scattering (SAXS) revealed that the extent of interfibrillar morphology increased with decreasing MW of PCL (MPCL). However, in the blends containing oligomeric PCL, interfibrillar segregation also involved the exclusion of uncrystallizable PCL short chains. The volume fraction of PVC expelled into the interfibrillar regions was calculated from SAXS linear crystallinity and bulk crystallinity. The results indicated that the transport of PVC into interf...

Statistical change detection with moments under time-varying illumination

Abstract: In this paper, an illumination-independent statistical change detection method is proposed. The proposed method consists of two parts. First, based on our defined circular shift moments, structural changes can be distinguished from those due to time-varying illumination in the noise-free case. Moreover, the amount of computation is less than that of the shading model method. Second, in the light of the characteristics of the defined moments, a statistical decision rule is also proposed to cope with the effects of noise. The change detection problem can be treated as one of hypothesis testing. Critical values can be chosen according to the desired level of significance. Experimental results indicate that the proposed method detects changes accurately in the time-varying illumination case.

Efficient repeating pattern finding in music databases

Abstract: In this paper, we propose an approach for the extraction of the repeating patterns in music objects A repeating pattern is a sequence of notes which appears more than once in a music object It is one of the most important music features which can be used for both content-based retrieval of music data and music data analysis We propose a data structure called correlative matrix and its associated algorithms for extracting all repeating patterns in a music object Experiments are also performed and the results are analyzed to show the efficiency and the effectiveness of our approach

Antiviral Activities of Methylated Nordihydroguaiaretic Acids. 1. Synthesis, Structure Identification, and Inhibition of Tat-Regulated HIV Transactivation

Abstract: Nordihydroguaiaretic acid (NDGA, meso-1) possesses four phenolic hydroxyl groups. Treatment of NDGA with 0.50-4.1 equiv of dimethyl sulfate and 3.0-6.0 equiv of potassium carbonate in acetone at 56 degrees C gave nine methylated products. Eight of those mono-, di-, tri-, and tetra-O-methylated NDGAs were isolated in pure form, and their structures were identified unambiguously by spectroscopic methods. A preparative amount of tetramethyl NDGA M4N (10) was obtained in 99% yield from NDGA by use of 4.1 equiv of dimethyl sulfate for the methylation. Among the eight different methylated NDGAs (2-6 and 8-10), tetra-O-methyl-NDGA (10) showed the strongest anti-HIV activity (IC50 11 microM). Chemically synthesized 3'-O-methyl-NDGA ((+/-)-2) showed identical anti-HIV activity (IC50 25 microM) to the lignan isolated from Creosote Bush. Lignans with methylated catecholic hydroxyl groups can be produced in large quantities with low cost. At drug concentrations below 30 microM tetramethyl NDGA (10) was a stronger anti-HIV agent than mono- and dimethylated NDGAs.

A parallel decoding scheme for turbo codes

Abstract: The recursive computations in the MAP-based decoding of turbo codes usually introduce a significant amount of decoding delay. In this paper, we present a method for reducing the decoding delay by means of segmenting a block into several sub-blocks, which are partially overlapped. The proposed sub-block segmentation scheme allows for the parallel decoding of each component code by using several sub-block decoders. The number of steps for the recursive computations in each sub-block decoder is reduced to O(N/W), where W is the number of segmented sub-blocks. The decoding delay is approximately one-Wth that of a conventional MAP-based turbo-coding system. The cost paid is a slight degradation in bit error rate performance and a reasonable increase in hardware complexity.

Systolic array implementation of Euclid's algorithm for inversion and division in GF(2/sup m/)

Abstract: This paper presents two new systolic arrays to realize Euclid's algorithm for computing inverses and divisions in finite fields GF(2/sup m/) with the standard basis representation. One of these two schemes is parallel-in parallel-out, and the other is serial-in serial-out. The former employs O(m/sup 2/) area complexity to provide the maximum throughput in the sense of producing one result every clock cycle, while the latter achieves a throughput of one result per m clock cycles using O(m log,m) area complexity. Both of the proposed architectures are highly regular and, thus, well suited to VLSI implementation. As compared to existing related systolic architectures with the same throughput performance, the proposed parallel-in parallel-out scheme reduces the hardware complexity (and, thus, the area-time product) by a factor of O(m) and the proposed serial-in serial-out scheme by a factor of O(m/log/sub 2/m).

Thermo-Raman studies on anatase and rutile

Abstract: One application of Raman spectroscopy is in the identification of the structure and the monitoring of the transformation of a sample in a thermal process. In this work, Raman spectra were taken continuously from xerogel TiO2 in a thermal process with heating, sintering and cooling. The variations in the Raman spectra indicated the transformation of xerogel first to amorphous TiO2, then to anatase and finally to rutile. The intensities of the characteristic Raman bands of anatase and rutile were studied by thermo-Raman spectroscopy as a function of temperature, and they were found to vary considerably. The intensities for both anatase and rutile became weak at high temperatures and recovered during the cooling period. © 1998 John Wiley & Sons, Ltd.

A structure-specified H/sup /spl infin// optimal control design for practical applications: a genetic approach

Abstract: A robust H/sup /spl infin// optimal design problem under a structure-specified controller is investigated for systems with parameter variations and disturbance uncertainties. A simple and facile design algorithm is proposed to solve the structure-specified H/sup /spl infin// optimization problem via genetic searching approach from suboptimal perspective. The proposed design method is very suitable for practical control systems. Therefore, the gap between the theoretical H/sup /spl infin// control and practical engineering designs can be filled up. Two examples involving a single input-single output (SISO) phase-locked-loop motor speed system with a lead/lag type controller and an MIMO supermaneuverable F18/HARV fighter aircraft system with a PID-type controller are given to illustrate the design procedure and exhibit the performance of the proposed method.