Browsing by Author "Wu, TC"

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A linguistic approach to a Chinese query model
(2001-01-01)
Liang, T
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Wu, TC
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資訊工程學系
;
Department of Computer Science
As network and input technologies have improved rapidly, researches in information retrieval have become more important than ever. An user-friendly and efficient query interface will certainly facilitate utilization of an information retrieval system. In this paper, a linguistic approach to Chinese query models is proposed and investigated. It includes Chinese linguistic variables, quantifiers and combination queries. Meanwhile, an improved computation method is proposed to handle general conjunctive queries, and it is proved to be better than traditional fuzzy computation in terms of a higher level of retrieval satisfaction. Experimental results also verify that the proposed quantifiers do not only simplify a multi-criteria request. bur also yield a higher level of retrieval satisfaction than do Boolean queries.
Anisotropic pinning effect on a Nb thin film with triangular arrays of pinning sites
(2004-06-01)
Wu, TC
;
Kang, PC
;
Horng, L
;
Wu, JC
;
Yang, TJ
A superconducting Nb thin film with triangular arrays of pinning sites has been fabricated to investigate the commensurate vortex lattices. Vortex-vortex interactions in this pattern film make the observed anisotropy in the pinning properties. Periodic minima appear in the magnetoresistance curves at equal field intervals that can be associated with matching effect. The transport properties at near critical temperatures show anisotropic pinning properties related to the configuration of pinning centers. The critical current is depressed when the driving force is applied along the short diagonal in the rhombic unit cell of pinning array. It implies that the pinning potential along the short diagonal creates a moving channel of vortices in triangular arrays of defects. The pinned and interstitial vortices can be movable in an incommensurate vortex row and a straight unhindered one-dimensional path. (C) 2004 American Institute of Physics.
Broadcasting secrets in communication networks
(1998-03-01)
Chang, CC
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Wu, TC
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Yeh, YS
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資訊科學與工程研究所
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Institute of Computer Science and Engineering
One property of a broadcast channel is that a single message broadcasted from an originator may be received simultaneously by several recipients in communication links. Based on the Chinese remainder theorem (CRT), we propose a new secure broadcasting scheme to distribute different secrets in one single broadcasting transaction such that each of the secrets is dedicated to different authorized recipients. On receiving the ciphertext broadcasted by the originator, only authorized recipients can obtain and authenticate their dedicated secrets individually, while no secret is revealed to unauthorized recipients. In a single broadcasting transaction, each authorized recipient cannot know who are the other intended recipients for this transaction. Furthermore, the processes for decryption and authentication of the dedicated secret are performed through simple arithmetic computation, i.e., modular operations, hence it is suitable for the applications that the recipient has less computing power. We also show that the proposed scheme can withstand the attack on replaying a previously intercepted broadcasting message.
ID-based structured multisignature schemes
(2001)
Lin, CY
;
Wu, TC
;
Hwang, JJ
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資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
The signing structure of a multisignature scheme specifies the signing order for all signers when signing messages, and any multisignature not obeying the specified signing order will be verified as invalid. In accordance with the different responsibilities of the participant signers, the signing structure of a multisignature scheme could be further classified as the following three types: serial, parallel and mixed, where the mixed structure is regarded as the mix of the serial and the parallel, Based on the well-known ID-based public key system, we will propose three ID-based structured multisignature schemes and each scheme respectively realizes the serial, parallel and mixed signing structures. In the proposed schemes, the length of a multisignature is fixed and the verification of a multisignature is efficient, regardless of the number of signers involved, Besides, any invalid partial multisignature can be effectively identified during the generation of the multisignature.
New identity-based society oriented signature schemes from pairings on elliptic curves
(2005-01-05)
Lin, CY
;
Wu, TC
;
Zhang, FG
;
Hwang, JJ
;
資訊管理與財務金融系註：原資管所+財金所
In this paper, we will propose two identity-based society oriented signature schemes that allow a group of co-signers to collaboratively generate a single signature for a message. The first proposed scheme is designated with known signers and the second scheme is with anonymous signers. Both schemes make use of pairings on elliptic curves in construction and thus have the merits of simplicity in design and efficiency in performance. In the proposed scheme with anonymous signers, a signer may participate in several different signing groups and may join or leave a signing group dynamically in a secure and efficient manner. (C) 2003 Elsevier Inc. All rights reserved.
Pinning effects induced by periodic arrays of structural corrugations in Nb thin films
(2003-05-01)
Horng, L
;
Wu, JC
;
Kang, PC
;
Lin, PH
;
Wu, TC
Artificial vortex pinning arrays have been fabricated by electron-beam lithography in conjunction with reactive ion etching in Nb superconducting thin films in order to investigate flux pinning. Based on the structural corrugation in the Nb thin film, the square lattice of defects that act as pinning centers was created. A strong periodic pinning effect, as the vortex lattice matches the array of defects, can be observed in the evolution of resistivity and critical current with the applied magnetic fields in the mixed state of the Nb film, thus, revealing a synchronized pinning effect due to structural corrugation. This result is in agreement with the resistivity-temperature curves at matching fields and half-integer matching fields in which a crossover occurs for temperatures exceeding a certain threshold value. The phenomenon is related to the presence of the pinning structure at matching fields.
Remarks on using RSA with low exponent in a public network
(2002-03-01)
He, WH
;
Wu, TC
;
Lin, CY
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
The authors give a counterexample to show that the RSA-based cryptosystem with low exponent proposed by Lee and Chang (Computer Communications 21 (1998)) is vulnerable to the low exponent attack with respect to their suggested lower boundary for the size of the public encryption key. That is, an eavesdropper can recover the plaintext from the ciphertext without knowing the secret decryption key, even though the size of the secret decryption key is large enough. The authors also suggest a new lower boundary for the size of the public encryption key for the Lee-Chang cryptosystem to enforce secrecy.
Temperature dependence of vortex configuration by honeycomb hole arrays in a superconducting Nb film
(2005-05-15)
Wu, TC
;
Wang, JC
;
Horng, L
;
Wu, JC
;
Yang, TJ
A honeycomb array of submicrometer holes in a Nb superconducting thin film has been fabricated to investigate the flux pinning effect. It is found that the minima positions reveal two regimes characterized by the matching fields and the fractional ones. It is believed that the complex behavior may come from more than one vortex being captured per pinning site. Furthermore, the temperature dependence of the saturation number of vortices per pinning site together with vortex-vortex interaction gives the complex vortex configurations. (c) 2005 American Institute of Physics.
The ac effect of vortex pinning in the arrays of defect sites on Nb films
(2006-04-15)
Wu, TC
;
Horng, L
;
Wu, JC
;
Hsiao, CW
;
Kolacek, J
Niobium thin films with spacing-graded array of submicrometer-scaled holes had been fabricated using electron beam lithography through a lift-off technique. The magnetoresistance measurements and current-voltage characteristics were carried out with the external magnetic field applied perpendicular to the film plane, in which commensurable effects were observed in both experiments. The magnetoresistance with positive/negative directions of dc current revealed identical curves except the dips at matching fields separated. Two distinct current-voltage curves, which resulted from the positive and negative applied current directions, respectively, were discerned when the external magnetic field was fixed at the matching field, which is believed to be due to asymmetry pinning potential in the spacing-graded array of holes. In addition, ac current-voltage curve measured at matching field showed a ratchet bump along with another extra peak associated with incommensurable effect. (C) 2006 American Institute of Physics.
Vortex dynamics in Nb thin films with triangular potential
(2005-06-01)
Wu, TC
;
Kang, PC
;
Wu, JC
;
Horng, L
;
Yang, TJ
Triangular artificial antidot arrays in Nb superconducting thin films have been fabricated to investigate the flux pinning effect when the magnetic field is applied perpendicular to the film. The spacing of the defect is around 545 nm and the diameter of the defect is around 300 nm. Arrays of triangular lattice show anisotropic properties of pinning effect induced by the anisotropic structure. The vortex-vortex interaction force is stronger when the vortices move along the short axis in the rhombic unit cell and cause an overall higher normalized critical current.
Vortex dynamics in spacing-graded array of defects on a niobium film
(2006-05-15)
Wu, TC
;
Horng, L
;
Wu, JC
;
Hsiao, CW
;
Kolacek, J
We have investigated the vortex dynamics in the niobium films having a spacing-graded array of pinning sites. The samples were fabricated by using electron beam lithography through a lift-off technique. The pinning sites of 200 nm in diameter were arranged with a constant hole-defect separation in x-axis direction and graded separation in y-axis direction from 392 nm to 408 nm. The magneto-resistance measurements and current-voltage characteristics were explored with the external magnetic field applied perpendicular to the film plane. Dc current-voltage measured at matching field revealed two distinct curves resulted from the positive and negative applied current directions, respectively. This is believed to be due to an asymmetry pinning potential formed in the spacing-graded array of holes, giving rise to asymmetry Lorentz forces. De voltage drop measured with respect to the ac current applied along the x-axis of the sample showed two separated maxima, which can be explained using the dynamics of pinned vortex lattice and interstitial vortices in the asymmetry pinning landscape. (c) 2006 Elsevier B.V. All rights reserved.