Showing papers by "National Tsing Hua University published in 2002"
TL;DR: In this article, the formation of planetesimals via the gravitational instability of solids that have settled to the midplane of a circumstellar disk was investigated, and it was shown that the mixing becomes ineffective when the surface density ratio of soloids to gas exceeds a critical value.
Abstract: We investigate the formation of planetesimals via the gravitational instability of solids that have settled to the midplane of a circumstellar disk. Vertical shear between the gas and a subdisk of solids induces turbulent mixing that inhibits gravitational instability. Working in the limit of small, well-coupled particles, we find that the mixing becomes ineffective when the surface density ratio of solids to gas exceeds a critical value. Solids in excess of this precipitation limit can undergo midplane gravitational instability and form planetesimals. However, this saturation effect typically requires increasing the local ratio of solid to gaseous surface density by factors of 2-10 times cosmic abundances, depending on the exact properties of the gas disk. We discuss existing astrophysical mechanisms for augmenting the ratio of solids to gas in protoplanetary disks by such factors and investigate a particular process that depends on the radial variations of orbital drift speeds induced by gas drag. This mechanism can concentrate millimeter-sized chondrules to the supercritical surface density in ≤ few × 106 yr, a suggestive timescale for the disappearance of dusty disks around T Tauri stars. We discuss the relevance of our results to some outstanding puzzles in planet formation theory—the size of the observed solar system and the rapid type I migration of Earth-mass bodies.
509 citations
TL;DR: The results of the study demonstrated that the genipin-crosslinked chitosan microspheres have a superior biocompatibility and a slower degradation rate than the glutaraldehyde-cross linked chitOSanmicrospheres, which may be a suitable polymeric carrier for long-acting injectable drug delivery.
507 citations
TL;DR: Simulation studies show that this estimator compares well with maximum likelihood estimators (i.e., empirical Bayes estimators from the Bayesian viewpoint) for which an iterative numerical procedure is needed and may be infeasible.
Abstract: Consider a stochastic abundance model in which the species arrive in the sample according to independent Poisson processes, where the abundance parameters of the processes follow a gamma distribution. We propose a new estimator of the number of species for this model. The estimator takes the form of the number of duplicated species (i.e., species represented by two or more individuals) divided by an estimated duplication fraction. The duplication fraction is estimated from all frequencies including singleton information. The new estimator is closely related to the sample coverage estimator presented by Chao and Lee (1992, Journal of the American Statistical Association 87, 210-217). We illustrate the procedure using the Malayan butterfly data discussed by Fisher, Corbet, and Williams (1943, Journal of Animal Ecology 12, 42-58) and a 1989 Christmas Bird Count dataset collected in Florida, U.S.A. Simulation studies show that this estimator compares well with maximum likelihood estimators (i.e., empirical Bayes estimators from the Bayesian viewpoint) for which an iterative numerical procedure is needed and may be infeasible.
455 citations
TL;DR: The main objective of this sequel is to solve the out-of-sequence problem that occurs in the load balanced Birkhoff-von Neumann switch with one-stage buffering by adding a load-balancing buffer in front of the first stage and a resequencing-and-output buffer after the second stage.
328 citations
TL;DR: The cytotoxic examination suggested that the chitosan–alginate beads cross-linked by genipin had a good cellular compatibility and swelling ratios decreased as the pH or concentration of alginate in the gelling solution was decreased.
304 citations
Patent•
28 Mar 2002TL;DR: A self-aligned, nonvolatile memory structure based upon phase change materials, including chalcogenides, can be made with a very small area on an integrated circuit as mentioned in this paper.
Abstract: A self-aligned, nonvolatile memory structure based upon phase change materials, including chalcogenides, can be made with a very small area on an integrated circuit The manufacturing process results in self-aligned memory cells requiring only two array-related masks defining the bit lines and word lines Memory cells are defined at intersections of bit lines and word lines, and have dimensions that are defined by the widths of the bit lines and word lines in a self-aligned process The memory cells comprise structures including a selection device, a heating/barrier plate layer and a phase change memory element, vertically arranged at the intersections of the bit lines and word lines
281 citations
TL;DR: In this article, the combined effects of foam porosity (e=0.7, 0.8, and 0.95) and flow Reynolds number (1900≤Re≤7800) were examined.
Abstract: Convective heat transfer and friction drag in a duct inserted with aluminum foams have been studied experimentally. The combined effects of foam porosity (e=0.7, 0.8, and 0.95) and flow Reynolds number (1900≤Re≤7800) are examined. Frictional drags for flow across the aluminum foam are measured by pressure taps, while interstitial heat transfer coefficients in the aluminum foam are determined using a transient single-blow technique with a thermal non-equilibrium two-equation model. Solid material temperature distribution is further measured for double check of the heat transfer results. To understand the frictional drag mechanisms, smoke-wire flow visualization is conducted in the aluminum-foam ducts. Results show that both the friction factor and the volumetric heat transfer coefficient increase with decreasing the foam porosity at a fixed Reynolds number. In addition, the aluminum foam of e=0.8 has the best thermal performance under the same pumping power constraint among the three aluminum foams investigated. Finally, empirical correlations for pore Nusselt number are developed in terms of pore Reynolds number under various foam porosities
278 citations
TL;DR: In this paper, a two-dimensional transient heat transfer model for different methods of heat dissipation is used to simulate the temperature distribution in lithium-ion batteries, and it is found that forced convection cooling can mitigate temperature rise in the battery.
271 citations
TL;DR: An efficient recognition of K+ by 15-crown-5 functionalized gold nanoparticles in aqueous matrix containing physiologically important cations, such as Li+, Cs+, NH4+, Mg2+, Ca2+, and excess amount of Na+.
Abstract: Reported here is an efficient recognition of K+ by 15-crown-5 functionalized gold nanoparticles in aqueous matrix containing physiologically important cations, such as Li+, Cs+, NH4+, Mg2+, Ca2+, and excess amount of Na+. Upon exposure to K+, the colloidal solution changes from red to blue, in response to surface plasmon absorption of dispersed and aggregated nanoparticles. The concentration ranges of K+ detected in this study are 0.099−0.48 mM and 7.6 μM−0.14 mM, when concentrations of colloidal gold are 54.9 and 7.1 nM, respectively. Recognition of K+ and formation of the aggregates are proposed via a sandwich complex of 2:1 between 15-crown-5 moiety and K+. Also discussed is the possibility of a preorganized structure of 15-crown-5 at the water−organic interface for the efficient complexation with K+.
259 citations
TL;DR: In this article, a three-electrode impedance study was conducted to investigate the relationship between PVDF/HFP-based electrolytes and lithium metal and it was found that the interfacial impedance of a Li-C half-cell consists of the impedances of two interfaces and is therefore often mistakenly used in the interpretation of the behaviour of a single carbon electrode.
248 citations
TL;DR: In this paper, a new experimental method using grazing-incidence X-ray diffraction is presented with its principles based upon the conventional sin c method, and the proposed method utilizes an asymmetrical diffraction geometry for which the Xray beam is incident at a grazing angle g to the sample surface.
07 Nov 2002
TL;DR: A variant of priority queuing model is proposed to approximate burst loss probability and the results show that the model provides an accurate estimation and evaluation of the performance of deflection routing in Arpanet-2 topology indicates thatdeflection routing evidently brings significant blocking performance gain.
Abstract: This paper concerns itself with the performance of deflection routing in optical burst-switched networks based on just-enough-time (JET) signaling. Generally speaking, buffer requirement is not vital for JET-based optical burst switching (OBS). However, if deflection routing is enabled, optical buffers are necessary to solve the insufficient offset time problem. A variant of priority queuing model is proposed to approximate burst loss probability and the results show that the model provides an accurate estimation. We also evaluate the performance of deflection routing in Arpanet-2 topology. Simulation results indicate that deflection routing evidently brings significant blocking performance gain, especially with fewer wavelengths and under lighter load. In addition, we notice that excessive deflection will cause longer end-to-end delay and reduce the blocking performance. Therefore, it is necessary to control the maximum allowed deflection occurrences of a burst.
TL;DR: The results obtained in this study show that there still exist a variety of organochlorine pesticide residues in the sediments from the near shore of central Taiwan.
TL;DR: The results obtained in this study showed that there still exist a variety of OCP residues in the river sediments in Taiwan, depicting that the sediments have contaminated for a long time.
TL;DR: In this paper, the authors used X-ray diffraction (XRD) to determine the preferred orientations of TiN films with different film thickness and found that the dominant preferred orientation of the TiN coatings for the deposition conditions was (111), especially for the films thicker than 1 μm.
Abstract: Titanium nitride (TiN) film was deposited on 304 stainless steel using a hollow cathode discharge ion-plating (HCD-IP) technique. Film thickness and N/Ti ratio were controlled. The depth profile of the composition was determined by secondary ion spectroscopy (SIMS). The results showed that the compositions of the films were uniform for the films deposited at the same deposition conditions. The purpose of this study is to investigate the variation of structure and mechanical properties of the TiN films with different film thickness. The preferred orientations of TiN films were determined using X-ray diffraction (XRD). The dominant preferred orientation of the TiN coatings for the deposition conditions was (111), especially for the films thicker than 1 μm. The residual stress of the TiN films was also measured by XRD using sin2 Ψ method. The residual stress was ranging from −5.93 to −2.70 GPa, varying with film thickness. Hardness of the films was measured by nanoindentation. The hardness values were ranging from 14.9 to 33.6 GPa, increasing with the film thickness. The ultimate interfacial shear stress between TiN/304SS was determined by in-situ strip tension of the TiN-coated specimens in a scanning electron microscope (SEM) chamber. The limiting thickness for the effective measurement of interfacial shear strength by the in-situ strip tension method is close to 0.5 μm. N/Ti ratios of the thin films were all at 0.8 measured using both X-ray photoelectron spectrometer (XPS) and Rutherford backscattering spectrometer (RBS). The packing factors of TiN films, calculated from the results of RBS, were 0.62–0.99, increasing with film thickness and leveling off at a thickness above 1.2 μm.
TL;DR: The inter- and intramolecular Diels-Alder reactions of in situ generated masked o-benzoquinones produced cycloadducts in excellent selectivities and the efficacy of the methodology is demonstrated by several examples of the total synthesis of natural products.
Abstract: An account of the synthetic utility of masked o-benzoquinones is provided. The inter- and intramolecular Diels-Alder reactions of in situ generated masked o-benzoquinones produced cycloadducts in excellent selectivities. New synthetic methodologies have been developed for the synthesis of highly substituted ring systems including bicyclo[2.2.2]octenones, oxatricycles, triquinanes, polysubstituted cyclohexanes, and bicyclo[4.2.2]decenones with complete stereocontrol from easily accessible 2-methoxyphenols via the Diels-Alder reaction of masked o-benzoquinones. Other reactions of adducts derived from masked o-benzoquinones are also described. The efficacy of our methodology is demonstrated by several examples of the total synthesis of natural products.
TL;DR: The pattern in noncoding regions, because they are less affected by natural selection than are coding regions, can reflect better the history of human evolution and can serve as a baseline for understanding the maintenance of SNPs in human populations.
Abstract: The worldwide pattern of single nucleotide polymorphism (SNP) variation is of great interest to human geneticists, population geneticists, and evolutionists, but remains incompletely understood. We studied the pattern in noncoding regions, because they are less affected by natural selection than are coding regions. Thus, it can reflect better the history of human evolution and can serve as a baseline for understanding the maintenance of SNPs in human populations. We sequenced 50 noncoding DNA segments each approximately 500 bp long in 10 Africans, 10 Europeans, and 10 Asians. An analysis of the data suggests that the sampling scheme is adequate for our purpose. The average nucleotide diversity (pi) for the 50 segments is only 0.061% +/- 0.010% among Asians and 0.064% +/- 0.011% among Europeans but almost twice as high (0.115% +/- 0.016%) among Africans. The African diversity estimate is even higher than that between Africans and Eurasians (0.096% +/- 0.012%). From available data for noncoding autosomal regions (total length = 47,038 bp) and X-linked regions (47,421 bp), we estimated the pi-values for autosomal regions to be 0.105, 0.070, 0.069, and 0.097% for Africans, Asians, Europeans, and between Africans and Eurasians, and the corresponding values for X-linked regions to be 0.088, 0.042, 0.053, and 0.082%. Thus, Africans differ from one another slightly more than from Eurasians, and the genetic diversity in Eurasians is largely a subset of that in Africans, supporting the out of Africa model of human evolution. Clearly, one must specify the geographic origins of the individuals sampled when studying pi or SNP density.
TL;DR: Cross-beam scattering experiments and quantum calculations on the H + HD → H2 + D reaction find that the motion of the system along the reaction coordinate slows down as it approaches the top of the reaction barrier, thereby allowing vibrations perpendicular to the reaction coordinates and forward scattering.
Abstract: Quantum dynamical processes near the energy barrier that separates reactants from products influence the detailed mechanism by which elementary chemical reactions occur. In fact, these processes can change the product scattering behaviour from that expected from simple collision considerations, as seen in the two classical reactions F + H(2) --> HF + H and H + H(2) --> H(2) + H and their isotopic variants. In the case of the F + HD reaction, the role of a quantized trapped Feshbach resonance state had been directly determined, confirming previous conclusions that Feshbach resonances cause state-specific forward scattering of product molecules. Forward scattering has also been observed in the H + D(2) --> HD + D reaction and attributed to a time-delayed mechanism. But despite extensive experimental and theoretical investigations, the details of the mechanism remain unclear. Here we present crossed-beam scattering experiments and quantum calculations on the H + HD --> H(2) + D reaction. We find that the motion of the system along the reaction coordinate slows down as it approaches the top of the reaction barrier, thereby allowing vibrations perpendicular to the reaction coordinate and forward scattering. The reaction thus proceeds, as previously suggested, through a well-defined 'quantized bottleneck state' different from the trapped Feshbach resonance states observed before.
TL;DR: The results indicated that the genipin-fixed acellular tissue provided a better microenvironment for tissue regeneration than its glutaraldehyde-fixed counterpart, due to its low cytotoxicity, and suggested that it might be used as a tissue-engineering matrix in the clinical applications.
TL;DR: In this paper, an eutectic melting point for [emim][PF 6 ]+water is found at 314 K with about 5.5 W% of water.
TL;DR: The results suggest the use of thermosensitive polymer solutions or hydrogels is potential in controlled release antiglaucoma ophthalmic drugs.
TL;DR: The proposed scheme has shown its robustness on low output voltage distortion, excellent voltage regulation, and it is insensitive to load variation, even under nonlinear loads.
Abstract: This paper presents a novel discrete-time sliding-mode control algorithm for an uninterruptible power supply (UPS) inverter design. The approach offers a dual-loop design, in which a current predictor utilizes the tracking error of output voltage to estimate the desired inductor current, while a current controller is adopted to regulate the inductor current and, thus, produces a control command to the pulsewidth modulation inverter. An explicit condition for stable controller design is derived. The efficacy of this scheme is validated via a successful implementation on a digital-signal-processor-based UPS inverter. The proposed scheme has shown its robustness on low output voltage distortion, excellent voltage regulation, and it is insensitive to load variation, even under nonlinear loads. Experimental studies were performed to further validate the effectiveness of this scheme.
TL;DR: In this article, organic-inorganic hybrids were prepared using diglycidyl ether of bisphenol A (DGEBA) type epoxy and tetraethoxysilane via the sol-gel process.
TL;DR: The new observations reported in this paper indicate the existence of a diverse and already differentiated cnidarian fauna, long before the Cambrian evolutionary event.
TL;DR: In this paper, the isothermal section of the ternary Sn-Cu-Ni system at 240°C was proposed on the basis of experimental results of this study and related information on phase equilibrium available in the literature.
Abstract: Ternary Sn-Cu-Ni alloys were prepared and annealed at 240°C. The annealed alloys were metallographically examined and the equilibrium phases formed were identified on the basis of compositional determinations and x-ray diffraction (XRD) analysis. The isothermal section of the ternary Sn-Cu-Ni system at 240°C was proposed on the basis of experimental results of this study and related information on phase equilibrium available in the literature. The binary compounds, Cu6Sn5, Ni3Sn2, and Ni3Sn4, have very extensive ternary solubility. Continuous solid solutions form between Cu and Ni as well as between Cu3Sn and Ni3Sn. In addition to the isothermal section, the liquidus projection of the Sn-Cu-Ni system was determined based on results from the existing literature. Interfacial reactions between Sn-Cu alloys and Ni substrate and the primary solidification phases of various Sn-Cu-Ni alloys were also examined in this study.
TL;DR: In this article, photo-definable material with patternable characteristics served as the bonding layer between the silicon wafers, and the results indicated that SU-8 is the best material with a bonding strength of up to 213 kg cm−2 (20.6 MPa).
Abstract: In this paper we present a silicon wafer bonding technique for 3D microstructures using MEMS process technology. Photo-definable material with patternable characteristics served as the bonding layer between the silicon wafers. A bonding process was developed and several types of photo-definable material were tested for bonding strength and pattern spatial resolution. The results indicated that SU-8 is the best material with a bonding strength of up to 213 kg cm−2 (20.6 MPa), and a spatial resolution of 10 μm, at a layer thickness of up to 100 μm. The low-temperature bonding technique that is presented is particularly suitable for microstructure and microelectronics integration involved in MEMS packaging.
TL;DR: The results showed that MAWT was negatively correlated with %VO2max, RHR and RVO2(p<0.01), which suggests that long-hour shifts (>10 h) should assign a lower work intensity than for an 8-h workday.
Abstract: For safe job design, it is necessary to know the maximum acceptable work time (MAWT) for a given workload. The aim was to establish the relationship between MAWT and physical workload. Cycling test...
TL;DR: In this paper, the structure of the molecular film, determined separately via low-energy electron diffraction, includes a c(23 × √3) stripe phase and c(3 × 2√ 3) saturated phases.
Abstract: The chemisorption of 1-decanethiol on the Au(111) single crystal has been studied with synchrotron-based, high-resolution photoemission spectroscopy with molecular film prepared from both gas-phase dosing and solution immersion to vary surface coverage over a wider range. The structure of the molecular film, determined separately via low-energy electron diffraction, includes a c(23 × √3) stripe phase and c(3 × 2√3) saturated phases. Careful curve fitting of the S 2p2/3 core level reveals that there is only one sulfur species at a binding energy of 162.1 eV in the film and the spectrum of the S 2p core level does not vary with the surface coverage and existence temperature of the decanethiolate. This finding is inconsistent with the sulfur-pairing model proposed based on X-ray scattering and standing wave studies. Up to two C 1s core levels at 284.0 and 285.0 eV can be observed, depending on the surface coverage. Angle-resolved X-ray photoelectron spectroscopy measurements are utilized to provide a direct ...
TL;DR: This work constructs a Bayesian network on the basis of expert knowledge and historical data for fault diagnosis on a distribution feeder in Taiwan and the experimental results validate the practical viability of the proposed approach.
Abstract: The Bayesian network is a probabilistic graphical model in which a problem is structured as a set of variables (parameters) and probabilistic relationships among them. The Bayesian network has been effectively used to incorporate expert knowledge and historical data for revising the prior belief in the light of new evidence in many fields. However, little research has been done to apply the Bayesian network for fault location in power delivery systems. We construct a Bayesian network on the basis of expert knowledge and historical data for fault diagnosis on a distribution feeder in Taiwan. The experimental results validate the practical viability of the proposed approach.