Showing papers by "NEC published in 2000"

Focused Crawling Using Context Graphs

Abstract: Maintaining currency of search engine indices by exhaustive crawling is rapidly becoming impossible due to the increasing size and dynamic content of the web. Focused crawlers aim to search only the subset of the web related to a specific category, and offer a potential solution to the currency problem. The major problem in focused crawling is performing appropriate credit assignment to different documents along a crawl path, such that short-term gains are not pursued at the expense of less-obvious crawl paths that ultimately yield larger sets of valuable pages. To address this problem we present a focused crawling algorithm that builds a model for the context within which topically relevant pages occur on the web. This context model can capture typical link hierarchies within which valuable pages occur, as well as model content on documents that frequently cooccur with relevant pages. Our algorithm further leverages the existing capability of large search engines to provide partial reverse crawling capabilities. Our algorithm shows significant performance improvements in crawling efficiency over standard focused crawling.

Efficient receipt-free voting based on homomorphic encryption

Abstract: Voting schemes that provide receipt-freeness prevent voters from proving their cast vote, and hence thwart vote-buying and coercion. We analyze the security of the multi-authority voting protocol of Benaloh and Tuinstra and demonstrate that this protocol is not receiptfree, opposed to what was claimed in the paper and was believed before. Furthermore, we propose the first practicable receipt-free voting scheme. Its only physical assumption is the existence of secret one-way communication channels from the authorities to the voters, and due to the public verifiability of the tally, voters only join a single stage of the protocol, realizing the "vote-and-go" concept. The protocol combines the advantages of the receipt-free protocol of Sako and Kilian and of the very efficient protocol of Cramer, Gennaro, and Schoenmakers, with help of designated-verifier proofs of Jakobsson, Sako, and Impagliazzo. Compared to the receipt-free protocol of Sako and Kilian for security parameter l (the number of repetitions in the non-interactive cut-andchoose proofs), the protocol described in this paper realizes an improvement of the total bit complexity by a factor l.

One-dimensional metallofullerene crystal generated inside single-walled carbon nanotubes.

Abstract: Electron microscope imaging for gadolinium metallofullerenes encapsulating in single-wall carbon nanotubes [(Gd@C82)n@SWNTs] identifies the single Gd atom encaged in each. The intermolecular distance between Gd@C82 is extremely regular, regarding the chains of Gd@C82 as novel one-dimensional crystals. Chemical state analysis of Gd atoms suggests evidence for charge transfer from Gd to either a fullerene cage or a nanotube. The slopes of the temperature dependence of electric resistance for the mat-like films of (Gd@C82)n@SWNTs and (C60)n@SWNTs are much steeper than that for empty SWNTs, suggesting the electron scattering due to the electrostatic potential from inside fullerenes playing an important role.

SEMINT: a tool for identifying attribute correspondences in heterogeneous databases using neural networks

Abstract: One step in interoperating among heterogeneous databases is semantic integration: Identifying relationships between attributes or classes in diAerent database schemas. SEMantic INTegrator (SEMINT) is a tool based on neural networks to assist in identifying attribute correspondences in heterogeneous databases. SEMINT supports access to a variety of database systems and utilizes both schema information and data contents to produce rules for matching corresponding attributes automatically. This paper provides theoretical background and implementation details of SEMINT. Experimental results from large and complex real databases are presented. We discuss the eAectiveness of SEMINT and our experiences with attribute correspondence identification in various environments. ” 2000 Elsevier Science B.V. All rights reserved.

The smallest carbon nanotube.

Abstract: We report here the discovery of the smallest possible carbon nanotube. This has a diameter of 4 A, which is the narrowest attainable that can still remain energetically stable, as predicted by theory. These nanotubes are confined inside multiwalled carbon nanotubes and their diameter corresponds to that of a C20 dodecahedron with a single carbon atom at each of its twenty apices. Unlike larger carbon nanotubes, which, depending on their diameter and helicity, can be either metallic or semiconducting, these smallest nanotubes are always metallic.

Crystal structure and ferroelectric properties of A Bi 2 Ta 2 O 9 ( A = Ca , Sr, and Ba)

Abstract: Crystal structures and ferroelectric properties of a series of Bi-layered compounds, ${\mathrm{CaBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9},$ ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9},$ and ${\mathrm{BaBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9},$ were investigated. The structures of ${\mathrm{CaBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ and ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ are orthorhombic, while that of ${\mathrm{BaBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ is pseudotetragonal on the macroscopic scale but consists of microdomains with orthorhombic distortion. The ferroelectric Curie temperature of ${\mathrm{CaBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ was over 600 \ifmmode^\circ\else\textdegree\fi{}C, and that of ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ was over 300 \ifmmode^\circ\else\textdegree\fi{}C. ${\mathrm{BaBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9},$ in contrast, showed relaxor-type ferroelectric behavior; that is, in the plot of temperature dependence of dielectric constant, a broad peak appeared around 60 \ifmmode^\circ\else\textdegree\fi{}C. As the size of the A-site cation decreases from ${\mathrm{Ba}}^{2+}$ to ${\mathrm{Ca}}^{2+},$ the lattice mismatch between ${\mathrm{TaO}}_{2}$ and $A\mathrm{O}$ planes in the perovskite-type unit of $A{\mathrm{Ta}}_{2}{\mathrm{O}}_{7}$ increases and the structural distortion becomes more pronounced. This distortion leads to the higher Curie temperature and the larger spontaneous ferroelectric polarization.

Context in Web Search.

Abstract: Web search engines generally treat search requests in isolation. The results for a given query are identical, independent of the user, or the context in which the user made the request. Nextgeneration search engines will make increasing use of context information, either by using explicit or implicit context information from users, or by implementing additional functionality within restricted contexts. Greater use of context in web search may help increase competition and diver-

Element-Selective Single Atom Imaging

Abstract: Electron energy-loss spectroscopy (EELS) is widely used to identify elemental compositions of materials studied by microscopy. We demonstrate that the sensitivity and spatial resolution of EELS can be extended to the single-atom limit. A chemical map for gadolinium (Gd) clearly reveals the distribution of Gd atoms inside a single chain of metallofullerene molecules (Gd@C82) generated within a single-wall carbon nanotube. This characterization technique thus provides the "eyes" to see and identify individual atoms in nanostructures. It is likely to find broad application in nanoscale science and technology research.

MDL-based context-dependent subword modeling for speech recognition

Abstract: Context-dependent phone units, such as triphones, have recently come to be used to model subword units in speech recognition systems that are based on the use of hidden Markov models(HMMs).While most such systems employ clustering of the HMM parameters(e.g., subword clustering and state clustering)to control the HMM size, so as to avoid poor recognition accuracy due to a lack of training data, none of them provide any effective criteria for determining the optimal number of clusters.This paper proposes a method in which state clustering is accomplished by way of phonetic decision trees and in which the minimum description length(MDL)criterion is used to optimize the number of clusters.Large-vocabulary Japanese-language recognition experiments show that this method achieves higher accuracy than the maximum-likelihood approach.

Lightwave propagation through a 120° sharply bent single-line-defect photonic crystal waveguide

Abstract: We have demonstrated 1.55 μm wavelength lightwave propagation through a 120° sharply bent waveguide formed in a triangular-lattice two-dimensional photonic crystal (2D PC). Such propagation has not previously been experimentally confirmed. The photonic crystal was fabricated in a silicon-on-insulator (SOI) wafer with the top silicon layer of the wafer used as a core layer. A 877-μm-long single-line-defect waveguide was formed in the PC with a sharp 120° bend near the middle of the waveguide. A tapered-hemispherical-end fiber was coupled to the input end of the waveguide for the light input, and the output from the other end of the waveguide was directly observed by scanning its near-field profile with another tapered-hemispherical-end fiber.

Supporting web query expansion efficiently using multi-granularity indexing and query processing

Abstract: A method and apparatus for efficient query expansion using reduced size indices and for progressive query processing. Queries are expanded conceptually, using semantically similar and syntactically related words to those specified by the user in the query to reduce the chances of missing relevant documents. The notion of a multi-granularity information and processing structure is used to support efficient query expansion, which involves an indexing phase, a query processing and a ranking phase. In the indexing phase, semantically similar words are grouped into a concept which results in a substantial index size reduction due to the coarser granularity of semantic concepts. During query processing, the words in a query are mapped into their corresponding semantic concepts and syntactic extensions, resulting in a logical expansion of the original query. Additionally, the processing overhead is avoided. The initial query words can then be used to rank the documents in the answer set on the basis of exact, semantic and syntactic matches and also to perform progressive query processing.

Mechanical stress effect of etch-stop nitride and its impact on deep submicron transistor design

Abstract: This paper, focusing on the effect of a plasma-enhanced CVD (PECVD) nitride contact-etch-stop layer, reports that process-induced mechanical stress affects the performance of short-channel CMOSFETs. We argue that the internal stress in the nitride layer changes transconductance (G/sub m/), thereby degrading NMOSFET performance by up to 8% and improving PMOSFET performance up to 7%. These performance changes are caused by changes of the electron and hole mobilities, so a precise transistor model considering this mobility change is necessary for deep-submicron transistor design.

Social Choice Theory and Recommender Systems: Analysis of the Axiomatic Foundations of Collaborative Filtering

Abstract: The growth of Internet commerce has stimulated the use of collaborative filtering (CF) algorithms as recommender systems. Such systems leverage knowledge about the behavior of multiple users to recommend items of interest to individual users. CF methods have been harnessed to make recommendations about such items as web pages, movies, books, and toys. Researchers have proposed several variations of the technology. We take the perspective of CF as a methodology for combining preferences. The preferences predicted for the end user is some function of all of the known preferences for everyone in a database. Social Choice theorists, concerned with the properties of voting methods, have been investigating preference aggregation for decades. At the heart of this body of work is Arrow's result demonstrating the impossibility of combining preferences in a way that satisfies several desirable and innocuous-looking properties. We show that researchers working on CF algorithms often make similar assumptions. We elucidate these assumptions and extend results from Social Choice theory to CF methods. We show that only very restrictive CF functions are consistent with desirable aggregation properties. Finally, we discuss practical implications of these results.

Compressibility and Polygonization of Single-Walled Carbon Nanotubes under Hydrostatic Pressure

Abstract: Single-walled carbon nanotubes show linear elasticity under hydrostatic pressure up to 1.5 GPa at room temperature. The volume compressibility, measured by in situ synchrotron x-ray diffraction, has been determined to be $0.024\mathrm{GPa}{}^{\ensuremath{-}1}$. Theoretical calculations suggest that single-walled carbon nanotubes are polygonized when they form bundles of hexagonal close-packed structure and the intertubular gap is smaller than the equilibrium spacing of graphite (002) $(d\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.35\phantom{\rule{0ex}{0ex}}\AA{})$. It has also been determined that the deformation of the trigonal nanotube lattice under hydrostatic pressure is reversible up to 4 GPa, beyond which the nanotube lattice is destroyed.

System and method for intelligent caching and refresh of dynamically generated and static web content

Abstract: A system for updating Web pages stored in cache based on modifications to data stored in a database is disclosed. The system for updating stored Web pages may be part of a larger system having a database management system for storing data used to generate Web pages. The database management system is capable of identifying modified data stored in the database. The system for updating stored Web pages is comprised of one or more servers programmed for maintaining associations between the stored Web pages and the stored data, and receiving the identity of modified data from the memory management system. In addition, the servers are capable of determining, from the identified modified data and the maintained associations, which stored Web pages are associated with the identified modified data. Furthermore, the servers are capable of communicating an update command to the cache that contains the stored Web pages associated with the identified modified data, for the purpose of updating the stored Web pages.

Graphitic ribbons without hydrogen-termination: Electronic structures and stabilities

Abstract: The graphitic ribbons with H termination have been the subject of recent studies, but we investigated the ribbons without H termination using tight-binding and first-principles calculations. The ribbons with armchair edge were found to have phonon frequencies near 2000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ which has been solely ascribed to the one-dimensional carbon allotrope, carbyne. Comparative studies of the formation energies suggest that ribbons will grow more easily in the direction perpendicular to the zigzag edge, consistent with a recent experiment.

Video summarization using singular value decomposition

Abstract: The authors propose a novel technique for video summarization based on singular value decomposition (SVD). For the input video sequence, we create a feature-frame matrix A, and perform the SVD on it. From this SVD, we are able, to not only derive the refined feature space to better cluster visually similar frames, but also define a metric to measure the amount of visual content contained in each frame cluster using its degree of visual changes. Then, in the refined feature space, we find the most static frame cluster, define it as the content unit, and use the context value computed from it as the threshold to cluster the rest of the frames. Based on this clustering result, either the optimal set of keyframes, or a summarized motion video with the user specified time length can be generated to support different user requirements for video browsing and content overview. Our approach ensures that the summarized video representation contains little redundancy, and gives equal attention to the same amount of contents.

Low chirp observed in directly modulated quantum dot lasers

Abstract: We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as a reference. Low chirp was obtained not only in the ground state lasing but in the second level lasing of quantum dots as well.

On-line unsupervised outlier detection using finite mixtures with discounting learning algorithms

Abstract: Outlier detection is a fundamental issue in data mining, specifically in fraud detection, network intrusion detection, network monitoring, etc. SmartSifter is an outlier detection engine addressing this problem from the viewpoint of statistical learning theory. This paper provides a theoretical basis for SmartSifter and empirically demonstrates its effectiveness. SmartSifter detects outliers in an on-line process through the on-line unsupervised learning of a probabilistic model (using a finite mixture model) of the information source. Each time a datum is input SmartSifter employs an on-line discounting learning algorithm to learn the probabilistic model. A score is given to the datum based on the learned model with a high score indicating a high possibility of being a statistical outlier. The novel features of SmartSifter are: (1) it is adaptive to non-stationary sources of data; (2) a score has a clear statistical/information-theoretic meaning; (3) it is computationally inexpensive; and (4) it can handle both categorical and continuous variables. An experimental application to network intrusion detection shows that SmartSifter was able to identify data with high scores that corresponded to attacks, with low computational costs. Further experimental application has identified a number of meaningful rare cases in actual health insurance pathology data from Australia's Health Insurance Commission.

Maximally entangled mixed states under nonlocal unitary operations in two qubits

Abstract: We propose mixed states in two qubits that have a property that the amount of entanglement of these states cannot be increased by any unitary transformation. The property is proven when the rank of the states is less than 4, and confirmed numerically in the other general cases. The corresponding entanglement of formation specified by its eigenvalues gives an upper bound of that for density matrices with the same eigenvalues. Further, as a simple application of the upper bound of the entanglement of formation, we analyze the entanglement of formation of the state generated by a decohered controlled-NOT gate in the spin-boson model.

Packet scheduling device

Abstract: In the packet scheduling device, the output class selection part is made to conduct the selective output of priority class, based on the weight count value calculated from a weight value corresponding to minimum guarantee bandwidth for each priority class and the amount of packet accumulated in each queue. The output class selection part operates so that if the weight count value is “0” or more, then the packet length of variable-length packet data to be output is subtracted from the current weight count value to give a renewed weight count value. On the other hand, if the weight count value is less than “0”, until reaching a predetermined repeat count (Cmax−1), the weight value of each priority class is added to the weight count value of all priority classes, and, when reaching the repeat count (Cmax−1), the weight value is added to the weight count value of all priority classes or replaced by half the weight value. Thereby, the weight count value is made to be more than “0”, and the values thus renewed are subject to the rule of round robin so as to select the priority class.

Focused search engine and method

Abstract: A focused search engine and method are directed to crawling vast search spaces comprising markup language documents, for example. Both topic distillation and site distillation methodologies are incorporated into an integrated topic-focused search strategy. Categorization of search results may be initiated by the search engine itself; alternatively, topic categories of interest may be specified in conjunction with the original request for information.

Method of setting up AD HOC local area network, method of communicating using said network, and terminal for use with said network

Abstract: An ad hoc LAN is set up in an environment in which there simultaneously exist a backbone-connected LAN connected by a high-speed backbone network and an ad hoc LAN not connected to the backbone network, wherein the ad hoc LAN is capable of communicating simultaneously with both LANs. An ad hoc LAN is defined as one multicast group used within the backbone network and backbone-connected LAN. This makes it possible for a terminal, which is connected to the ad hoc LAN and backbone-connected LAN simultaneously so that it may communicate with both LANs, to participate in the ad hoc LAN in the same manner as it would participate in a multicast group of a conventional backbone-connected LAN. As a result, the terminal construction is simplified and the terminal can be connected to an ad hoc LAN and backbone-connected LAN simultaneously.

Temperature dependence of the Raman spectra of single-wall carbon nanotubes

Abstract: Raman spectra of single-wall carbon nanotubes (SWCNTs) were measured at different temperatures by varying the incident laser power. The elevated temperature of the SWCNTs and multiwall carbon nanotubes (MWCNTs) is confirmed to be due to the presence of impurities, defects, and disorder. The temperature coefficient of the frequency of the C–C stretching mode E2g (GM) and that of the radial breathing mode in the SWCNT were determined to be ∼−0.038 and ∼−0.013 cm−1/K, respectively. It is found that the temperature coefficient of the GM in the SWCNT is larger than that of the MWCNT, highly oriented pyrolytic graphite, and the graphite. This is attributed to the structural characteristic of the SWCNT—a single tubular carbon sheet with smaller diameter.

Organic el display device having an improved image quality

Abstract: A drive unit for driving a corresponding one of organic EL elements of an active matrix EL display device includes a blanking switch for blanking the video signal stored in a storage capacitor in each frame period before the start of the next frame period. A drive transistor drives a corresponding EL element based on the correct current supplied for this If the video signal is a current signal, a transistor operating as a current-voltage converter is provided

NBTI enhancement by nitrogen incorporation into ultrathin gate oxide for 0.10-/spl mu/m gate CMOS generation

Abstract: We investigated the degradation of device reliability due to Negative Bias Temperature Instability (NBTI) of PMOSFET with ultrathin gate oxide. It was experimentally demonstrated that the chemical reactions at the gate oxide/substrate interface and/or diffusion of hydrogen related species are the major cause of the NBTI. We also found that nitridation of gate oxide enhances NBTI. In order to suppress the NBTI, the density of hydrogen terminated silicon bond at the interface needs to be minimized. Thus, the concentration of nitrogen in thin gate oxide has to be optimized in terms of the reliability reduction due to NBTI.

System and method for efficient content delivery using redirection pages received from the content provider original site and the mirror sites

Abstract: A content delivery system is disclosed. The content delivery system includes a content provider original site configured for communicating with end users over at least one communication network. The content delivery system also includes a memory accessible by the content provider original site for identifying which content has been stored in a mirror site. In response to an end user request for particular content, the content provider original site is capable of accessing the memory, determining if the requested content is stored in a mirror site, and communicating a page to the requesting end user containing a meta-tag for redirecting the requesting end user to load the requested content from the mirror site.

An Auction Protocol Which Hides Bids of Losers

Abstract: Many auction protocols using practical cryptographic means have successfully achieved capability of hiding the bids of each entity, but not the values of bids themselves. In this paper we describe an auction protocol which hides the bids of non-winners even from the bid-opening centers, and still makes it possible to publicly verify the validity of the winning bid, i.e. that it was the highest bid submitted. The first approach to such a protocol was made by Kikuchi et al in [KHT98]. However, several deficiencies have been pointed out regarding their protocol; for example, it is not well suited for handling tie bids.