Browsing by Issue Date, starting with "2002-04-05"

Now showing 1 - 20 of 74758

Applying lightweight directory access protocol service on session certification authority
(2002-04-05)
Yeh, YS
;
Lai, WS
;
Cheng, CJ
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
Lightweight Directory Access Protocol (LDAP) service is a new technology being applied on the Internet. On large-scale network systems using Transmission control protocol (TCP)/Internet protocol (IP), there is no standard suggested for single directory-certainly without one to be routinely used on the scale of intranets. LDAP service has many great features, such as providing quick and advanced search, quick response and hierarchy view of data. It also can be utilized to many different applications. Certification Authority (CA) is a trusted system, and it plays an important role just like a notary bridging between end-entities and helps end-entities to establish a secure environment. If someone wants to trade or communicate with others, he or she needs the certificate issued by the CA to help him or her get the trust from others. When a number of end-entities need this service, the load of CA may become huge. Using distributed CAs may sound Eke a good idea, but it costs too much. In this paper, we have designed a Session CA using a directory system to share its load without the necessity to maintain the Certificate Revocation List (CRL) because the lifetime of the attribute certificate is very short. With these great features of LDAP service mentioned above, it becomes desirable that we can apply them to design a new CA system. By using LDAP service, we can reduce the load of certification significantly between CA and endentity. In addition, this new technology can reduce the maintenance work of administration and improve the efficiency of our new proposed CA. Furthermore, combining with Role-Based Access Control (RBAC) and attribute certificate, the security of our system is greatly improved. (C) 2001 Elsevier Science B.V. All rights reserved.
An efficient traffic control scheme for TCP over ATM GFR services
(2002-04-05)
Chan, CT
;
Wang, PC
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
In ATM networks, the guaranteed frame rate (GFR) service category has been defined to support user applications which are neither able to specify the range of traffic parameter values, nor able to comply with the behavior rules. It provides a packet-level rate guarantee with a given maximum packet size. The service specifies that the excessive traffic from a user should share the available resource fairly. In this paper, we investigate TCP/IP packet transmission over ATM by using a selective packet-discard strategy with tracking of the available buffer space and a packet push-out buffering scheme to accommodate the GFR service. The simulation results show that our proposed method fulfills the requirements of GFR service as well as improves the TCP throughput under the common FIFO scheduling. A feasible implementation approach is also addressed. (C) 2001 Elsevier Science B.V. All rights reserved.
A necessary condition for a graph to be the visibility graph of a simple polygon
(2002-04-06)
Chen, CY
;
應用數學系
;
Department of Applied Mathematics
Two vertices of a simple polygon P are visible if the line segment joining them does not intersect the exterior of P. The visibilitly graph of P is a graph G obtained by representing each vertex of P by a vertex of G and two vertices of G are joined by an edge if and only if their corresponding vertices in P are visible. A graph G is a visibility graph if there exists a simple polygon P such that G is isomorphic to the visibility graph of P. No characterization of visibility graphs is available. Coullard and Lubiw derived a necessary condition for a graph to be the visibility graph of a simple polygon. They proved that any 3-connected component of a visibility graph has a 3-clique ordering starting from any triangle. However, Coullard and Lubiw insisted on the non-standard definition of visibility (the line segment joining two visible vertices may not go through intermediate vertices) and they said they do not know if their result will hold under the standard definition of visibility. The purpose of this paper is to prove that Coullard and Lubiw's result still holds under the standard definition of visibility. (C) 2002 Elsevier Science B.V. All rights reserved.
Metalorganic chemical vapor deposition of tungsten carbonitride films by bis(tertbutylimido)bis(diethylamido)tungsten.
(2002-04-07)
Chuang, SH
;
Chiu, HT
;
Chou, YH
;
Chang, YH
;
Chen, SF
Syntheses of molybdenum nitrido complexes from (NH4)(2)Mo2O7.
(2002-04-07)
Yeng, MY
;
Chiu, HT
;
Chuang, SH
;
Lo, CP
;
Peng, SM
Synthesis and liquid crystalline behavior of photoreactive side-chain liquid-crystalline polyoxetanes containing cinnamoyl biphenyl mesogen.
(2002-04-07)
Fan, GY
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
SiCl3CCl3 as a novel precursor for chemical vapor deposition of amorphous carbon films.
(2002-04-07)
Chiu, HT
;
Chang, YH
;
Wang, LS
;
Peng, CW
;
Lee, CY
Metallo-organic chemical vapor deposition of tantalum carbide and tantalum nitride thin films from (BuCH)-Bu-t=Ta(CH2 Bu-t)(3) and (BuN)-Bu-t=Ta(CH2 Bu-t)(3).
(2002-04-07)
Chiu, HT
;
Chang, YH
;
Chang, PJ
;
Wu, JB
;
Peng, SM
Extrusion of three-layer composite hexagonal clad rods
(2002-04-10)
Wu, CW
;
Hsu, RQ
;
機械工程學系
;
Department of Mechanical Engineering
Composite clad rods consisting of three different materials are applied extensively as conductors, electrodes and chemical devices. Commercial applications involving low temperature niobium-tin alloy (Nb3Sn) superconductor rods, which have a pure niobium (Nb) core, a copper-tin (Cu-Sn) alloy outer sleeve and a Nb3Sn diffusion layer in between, stipulate these conductors as, electrodes that are intended for processing as rods of various shapes. During the extrusion process, non-homogeneous deformation tends to occur because the billet consists of materials with different mechanical properties. In this study, the authors present a numerical simulation model based on the upper-bound theorem to analyze three-layer composite clad rods with a hexagonal cross-section under extrusion. A velocity field is also generated with the assistance of a product's cross-section profile functions. The velocity component in the extrusion axis is expressed as a convex distribution. Analytical results indicate that various process variables such as the semi-die angle, reduction of area, friction condition of the die and combinations of the three constituent materials, prominently influence the extrusion process. Moreover, the extrusion pressure, product dimension-change and the probability of sound extrusion are related closely to the process variables. (C) 2002 Elsevier Science B.V. All rights reserved.
Phase-shifterless beam-steering micro-slotline antenna
(2002-04-11)
Chen, CC
;
Tzuang, CKC
;
電信工程研究所
;
Institute of Communications Engineering
Implementation of a broadband duct ANC system using adaptive spatially feedforward structure
(2002-04-11)
Bai, MR
;
Zeung, P
;
機械工程學系
;
Department of Mechanical Engineering
An adaptive spatially feedforward algorithm is proposed for broadband attenuation of noise in ducts. Acoustic feedback generally exists in this active noise control structure. Munjal and Eriksson (1988 Journal of Acoustical Society of America 84, 1086-1093) derived an ideal controller for the spatially feedforward structure. The ideal controller can be partitioned into two parts. The first part represents a repetitive controller that can be implemented by an infinite impulse response (IIR) filter, whereas the second part represents the dynamics of transducer that can be implemented by a finite impulse response (FIR) filter. In the paper, the IIR filter is merged with the original plant. The FIR filter is adaptively updated by the least-mean-square (LMS) algorithm to accommodate perturbations and uncertainties in the system. The proposed algorithm is implemented via a floating point digital signal processor and compared with other commonly used algorithms such as the Filtered-X LMS algorithm, the feedback neutralization algorithm, and the Filtered-U LMS algorithm. Experimental results show that the system has attained 15-7 dB maximal attenuation in the frequency band 200-600 Hz. (C) 2002 Elsevier Science Ltd.
A method to characterize the dielectric and interfacial properties of metal-insulator-semiconductor structures by microwave measurement
(2002-04-15)
Lue, HT
;
Tseng, TY
;
Huang, GW
;
電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
We have developed a method to investigate the dielectric and interfacial properties of gate dielectric thin films by microwave measurement. Ba0.5Sr0.5TiO3 (BST) thin films were deposited on 10 Omega cm (normal) and 10 k Omega cm [high-resistivity, (HR)] silicon substrates at the same time by rf magnetron sputtering. For the BST/HR-silicon, coplanar waveguides (CPW) were fabricated and measured at microwave frequencies with thru-reflect-line calibration while capacitance (C-V) measurements were carried out for BST/normal silicon. From the phase change of CPW transmission line and the maximum capacitance in C-V measurement, the dielectric constants of both the BST thin film and interface layer can be determined. Furthermore, the behaviors of insertion loss versus bias voltage were investigated. The results indicate that our method can provide useful information to study the dielectric and interfacial properties of metal-insulator-semiconductor structures. (C) 2002 American Institute of Physics.
虎頭
(2002-04-20)
管管
An analysis of the combined effects of organic toxicants
(2002-04-22)
Chen, CY
;
Lu, CL
;
環境工程研究所
;
Institute of Environmental Engineering
This paper presents a basic database for the joint actions of 44 binary mixtures of various organic toxicants on Escherichia coli. The multiple toxicity behaviors observed from the E. coli organisms were analyzed and compared with previous works based on the Microtox tests, The two kinds of tests produced quite different responses, in terms of the joint action mode and the sum of toxic units, to various organic mixtures. However, detailed analyses with the considerations of the chemical's mechanisms of toxicity and the slope of toxicant's dose-response curve have revealed several general criteria for the prediction of combined effects of organic toxicants. First, for both reactive and non-reactive toxicants, either additive or less than additive (antagonistic) joint actions will be observed for chemicals of the same mechanism of toxicity. Second, the mixture of reactive toxicants with different mechanisms is the only category of organic mixtures associated with frequent observations of synergism. Third, greater-than-additive (synergistic) effects are inherently associated with toxicants having flat dose-response curves. Less than additive effects are, however, mainly related to a chemical's display steep close-response curves. Model analyses indicate that the observed synergistic effects are due to response addition or response multiplication joint actions. Hence, most of the synergistic joint actions are non-interactive in nature and are governed by the dose-response relationships of individual toxicants. (C) 2002 Elsevier Science B.V. All rights reserved.
Miscibility, melting, and crystallization of poly(trimethylene terephthalate)/poly(ether imide) blends
(2002-04-25)
Huang, JM
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Miscibility, melting, and crystallization behaviors of solution-blended poly trimethylene terephthalate) (PTT)/poly(ether imide) (PEI) blends ha,e been investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and polarized light microscopy (PLM). These blends show a single and composition-dependent glass transition temperatures over the entire composition range, implying that these blends are fully miscible in the amorphous region. The enthalpy of the middle endotherm melting of the primary crystallization decreases with increasing PEI content in the blend. Recrystallization of PTT during heating scan in DSC is either retarded or fully inhibited by the presence of PEI. In nonisothermal crystallization, the depression of crystallization temperature of PTT also depends on the blend composition and cooling rate; the presence of PEI decreases the PTT segments migrating to the crystallite-melt interface, The effects of temperature and PEI content on the spherulite growth rate of PTT were evaluated by PLM. The spherulite growth rate decreases with the, increase of the PEI content, implying that it is a thermodynamically dominant process. Both thermodynamic and kinetic factors cause total inhibition of PTT crystallization at higher PEI content in the blend. (C) 2002 John Wiley Sons, Inc.
Time requirement for rapid-mixing in coagulation
(2002-04-25)
Kan, CC
;
Huang, CP
;
Pan, JRS
;
環境工程研究所
;
Institute of Environmental Engineering
Mechanisms of coagulation have been widely investigated by many researchers. Little is understood about the critical role of rapid-mixing in water treatment. In this study, a photometric dispersion analyzer (PDA) was employed to monitor clay coagulation by alum and polymeric aluminum chloride (PACl). The effect of rapid-mixing time on particle removal was studied. A standard jar test was performed to determine the degree of destabilization of particles. Maximum ratio outputs of PDA measurements were inversely related to residual turbidities. Adequate rapid-mixing times evaluated from both PDA and mixing tests were close to each other. Studies of coagulation mechanisms at various rapid-mixing times indicated that mixing time had significant impact on charge neutralization and sweep coagulation. The difference in residual turbidity can be attributed to the characteristics of microflocs. The rise in residual turbidity in sweep coagulation suggested the breakage of microflocs. (C) 2002 Elsevier Science B.V. All rights reserved.
Bi3.25La0.75Ti3O12 thin films on ultrathin Al2O3 buffered Si for ferroelectric memory application
(2002-04-29)
Chen, SY
;
Sun, CL
;
Chen, SB
;
Chin, A
;
材料科學與工程學系
We have investigated the physical and electrical properties of Bi3.25La0.75Ti3O12 (BLT) thin films on Pt/Ti/SiO2/Si and on Al2O3(6 nm)/Si, which are used for one-transistor-one-capacitor and one-transistor ferroelectric memory, respectively. The BLT thin films on both substrates show good capacitance-voltage characteristics and the same threshold voltage shift of 1.6 V at applied +/-10 V bias. However, the leakage current of BLT on Al2O3/Si at -100 kV/cm is two orders of magnitude lower than that on Pt. The comparable memory characteristics and much reduced leakage current of BLT on Al2O3/Si are the strong advantages as compared with BLT on Pt because it is directly related to switching energy and device scaling down. (C) 2002 American Institute of Physics.
Parallel distance transforms on a linear array architecture
(2002-04-30)
Chia, TL
;
Wang, KB
;
Chen, Z
;
Lou, DC
;
資訊科學與工程研究所
Distance transformation (DT) has been widely used for image matching and shape analysis. In this paper, a parallel algorithm for computing distance transformation is presented. First, it is shown that the algorithm has an execution time of 6N - 4 cycles, for an N x N image using a parallel architecture that requires [N/2] parallel processors. By doing so, the real time requirement is fulfilled and its execution time is independent of the image contents. In addition, a partition method is developed to process an image when the parallel architecture has a fixed number of processing elements (PEs); say two or more. The total execution time for an N x N image by employing a fixed number of PEs is 2[N-2/M + 2(M - 1)], when M is the fixed number of PEs. (C) 2002 Elsevier Science B.V. All rights reserved.
Consistent quantization of noncommutative D-brane in non-constant B field background
(2002-04-30)
Lee, JC
;
電子物理學系
;
Department of Electrophysics
We perform the consistent quantization of open string D-brane in non-constant NS-NS closed string B field background by directly imposing the worldsheet conformal symmetry. In addition to the previous noncommutative D-brane coordinates quantization with constant noncommutative paxameter theta, we obtain a set of constraints on the B field which can be interpreted as a quantum consistent deformation of a curved noncommutative D-brane.
Optimum design for a thermally stable multifinger power transistor
(2002-05-01)
Liao, CH
;
Lee, CP
;
Wang, NL
;
Lin, B
;
電子工程學系及電子研究所
The thermal stability of multifinger bipolar transistors has been analyzed theoretically. Coupled equations are solved to study the onset of instability and its dependence on the distributions of ballasting resistors. Analytical expressions were derived for the emitter ballasting distribution for optimum stable operation. Compared to conventional methods with uniform ballasting, the optimized design can significantly increase the stable operating current of the transistor. An absolutely stable operating condition is also derived. At this condition, the device never becomes unstable.