Showing papers by "NEC published in 1999"

Scalable routing strategies for ad hoc wireless networks

Abstract: We consider a large population of mobile stations that are interconnected by a multihop wireless network. The applications of this wireless infrastructure range from ad hoc networking (e.g., collaborative, distributed computing) to disaster recovery (e.g., fire, flood, earthquake), law enforcement (e.g., crowd control, search-and-rescue), and military (automated battlefield). Key characteristics of this system are the large number of users, their mobility, and the need to operate without the support of a fixed (wired or wireless) infrastructure. The last feature sets this system apart from existing cellular systems and in fact makes its design much more challenging. In this environment, we investigate routing strategies that scale well to large populations and can handle mobility. In addition, we address the need to support multimedia communications, with low latency requirements for interactive traffic and quality-of-service (QoS) support for real-time streams (voice/video). In the wireless routing area, several schemes have already been proposed and implemented (e.g., hierarchical routing, on-demand routing, etc.). We introduce two new schemes-fisheye state routing (FSR) and hierarchical state routing (HSR)-which offer some competitive advantages over the existing schemes. We compare the performance of existing and proposed schemes via simulation.

Self-collimating phenomena in photonic crystals

Abstract: We found that self-determining collimated light is generated in a photonic crystal fabricated on silicon. The divergence of the collimated beam is insensitive to that of the incident beam and much smaller than the divergence that would be generated in conventional Gaussian optics. The incident-angle dependence of the self-collimated light propagation including lens-like divergent propagation was interpreted in terms of the highly modulated dispersion surfaces with inflection points, where the curvature changes from downward to upward corresponding to respectively a concave/convex-lens case. This demonstration is an important step towards controlling beam profile in photonic crystal integrated light circuits and towards developing “photonic crystalline optics.”

A robust adaptive beamformer for microphone arrays with a blocking matrix using constrained adaptive filters

Abstract: This paper proposes a new robust adaptive beamformer applicable to microphone arrays. The proposed beamformer is a generalized sidelobe canceller (GSC) with a new adaptive blocking matrix using coefficient-constrained adaptive filters (CCAFs) and a multiple-input canceller with norm-constrained adaptive filters (NCAFs). The CCAFs minimize leakage of the target-signal into the interference path of the GSC. Each coefficient of the CCAFs is constrained to avoid mistracking. The input signal to all the CCAFs is the output of a fixed beamformer. In the multiple-input canceller, the NCAFs prevent undesirable target-signal cancellation when the target-signal minimization at the blocking matrix is incomplete. The proposed beamformer is shown to be robust to target-direction errors as large as 200 with almost no degradation in interference-reduction performance, and it can be implemented with several microphones. The maximum allowable target-direction error can be specified by the user. Simulated anechoic experiments demonstrate that the proposed beamformer cancels interference by over 30 dB. Simulation with real acoustic data captured in a room with 0.3-s reverberation time shows that the noise is suppressed by 19 dB. In subjective evaluation, the proposed beamformer obtains 3.8 on a five-point mean opinion score scale, which is 1.0 point higher than the conventional robust beamformer.

System for personalizing, organizing and managing web information

Abstract: The present invention provides a hypermedia database for managing bookmarks, which allows a user to organize hypertext documents for querying, navigating, sharing and viewing. In addition, the hypermedia database also provides access control to the information in the database. The hypermedia database of the present invention parses meta-data from bookmarked documents and indexes and classifies the documents. The present invention supports advanced query and navigation of a collection of bookmarks, especially providing various personalized bookmark services. In one embodiment, the present invention utilizes a proxy server to observe a user's access patterns to provide useful personalized services, such as automated URL bookmarking, document refresh, and bookmark expiration. In addition, a user may also specify various preference in bookmark management, e.g., ranking schemes (i.e. by referral, access frequency, or popularity) and navigation tree fan-out. A subscription service which retrieves new or updated documents of user-specified interests is also provided.

An O-tree representation of non-slicing floorplan and its applications

Abstract: We present an ordered tree, O-tree, structure to represent non-slicing floorplans. The O-tree uses only n(2+[Ig n]) bits for a floorplan of n rectangular blocks. We define an admissible placement as a compacted placement in both x and y direction. For each admissible placement, we can find an O-tree representation. We show that the number of possible O-tree combinations is O(n! 2/sup 2n-2//n/sup 1.5/). This is very concise compared to a sequence pair representation which has O((n!)2) combinations. The approximate ratio of sequence pair and O-tree combinations is O(n/sup 2/(n/4e)/sup n/). The complexity of the O-tree is even smaller than a binary tree structure for slicing floorplan which has O(n! 2/sup 5n-3//n/sup 1.5/) combinations. Given an O-tree, it takes only linear time to construct the placement and its constraint graph. We have developed a deterministic floorplanning algorithm utilizing the structure of O-tree. Empirical results on MCNC benchmarks show promising performance with average 16% improvement in wire length, and 1% less in dead space over previous CPU-intensive cluster refinement method.

First-principles study of edge states of H-terminated graphitic ribbons

Abstract: The existence of the edge states of single-layered H-terminated graphitic ribbons predicted by Nakada et al. [Phys. Rev. B 54, 17 954 (1996)] has been confirmed by first-principles calculations within the framework of the local-density approximation and the pseudopotentials. The edge states in cases of stacked ribbons have also been examined, and it has been found that the existence of the edge states is dependent on the stacking manner. This phenomenon can be understood from the electronic structures of $\mathrm{AA}$- and $\mathrm{AB}$-stacked bulk graphite.

Heterostructures of Single-Walled Carbon Nanotubes and Carbide Nanorods

Abstract: A method based on a controlled solid-solid reaction was used to fabricate heterostructures between single-walled carbon nanotubes (SWCNTs) and nanorods or particles of silicon carbide and transition metal carbides. Characterization by high-resolution transmission electron microscopy and electron diffraction indicates that the heterostructures have well-defined crystalline interfaces. The SWCNT/carbide interface, with a nanometer-scale area defined by the cross section of a SWCNT bundle or of a single nanotube, represents the smallest heterojunction that can be achieved using carbon nanotubes, and it can be expected to play an important role in the future fabrication of hybrid nanodevices.

Unintrusive customization techniques for Web advertising

Abstract: Most online advertisement systems in place today use the concept of consumer targeting: each user is identified and, according to his or her system setup, browsing habits and available off-line information, categorized in order to customize the advertisements for highest user responsiveness. This constant monitoring of a user's online habits, together with the trend to centralize this data and link it with other databases, continuously nurtures fears about the growing lack of privacy in a networked society. In this paper, we propose a novel technique of adapting online advertisement to a user's short term interests in a non-intrusive way. As a proof-of-concept we implemented a dynamic advertisement selection system able to deliver customized advertisements to users of an online search service or Web directory. No user-specific data elements are collected or stored at any time. Initial experiments indicate that the system is able to improve the average click-through rate substantially compared to random selection methods.

Photonic crystals for micro lightwave circuits using wavelength-dependent angular beam steering

Abstract: Light-beam steering that is extremely wavelength dependent has been demonstrated by using photonic crystals fabricated on Si. The scanning span reached 50° with only a 1% shift of incident wavelength at around 1 μm. The resulting angular dispersion is two orders of magnitude larger than that achieved with conventional prisms or gratings. The application of such superprism phenomena promises to enable the fabrication of integrated micro lightwave circuits that will allow more efficient use of wavelength resources when used in wavelength multiplexers/demultiplexers or dispersion compensators by enabling lower loss and broader bandwidth.

Superprism phenomena in photonic crystals: toward microscale lightwave circuits

Abstract: The superprism phenomenon, the dispersion of light 500 times stronger than the dispersion in conventional prisms, was demonstrated at optical wavelengths in photonic crystals (PC's) fabricated on Si. Drastic light-beam steering in the PC's was achieved by slightly changing the incident wavelength or angle. The scanning span reached 50/spl deg/ with only a 1% shift of incident wavelength, and reached 140/spl deg/ with only a 14/spl deg/ shift of the incident angle at wavelengths around 1 /spl mu/m. The propagation direction was quantitatively interpreted in terms of highly anisotropic dispersion surfaces derived by photonic band calculation. The physics behind this demonstration will open a novel field called photonic crystalline optics. The application of these phenomena promises to enable the fabrication of integrated microscale lightwave circuits (/spl mu/LC's) on Si with large scale integrated (LSI)-compatible lithography techniques. Such /spl mu/LC's will allow more efficient use of wavelength resources when used in wavelength multiplexers/demultiplexers or dispersion compensators by enabling lower loss and broader bandwidth.

Robust digital watermarking

Abstract: A watermarking procedure that is applicable to images, audio, video and multimedia data to be watermarked divides the data to be watermarked into a set of n×n blocks, such as the 8×8 blocks of MPEG. The same watermark signal can be distributed throughout the set of blocks in a large variety of ways. This allows the insertion algorithm to be changed without affecting the decoders. The decoding procedure first sums together the DCT coefficients of N sets of 8×8 blocks to form a set of N summed 8×8 blocks and then extracts the watermark from the summed block. Since the sum of the DCT blocks is equal to the DCT of the sum of the intensity blocks, efficient decoding can occur in both the spatial and frequency domains. The symmetric nature of the decoding process allows geometric distortions to be handled in the spatial domain and other signal distortions to be handled in the frequency domain. Moreover, insertion of a watermark signal into image data and the subsequent extraction of the watermark from watermarked image data which has been subject to distortion between the times of insertion and extraction involves the insertion of multiple watermarks designed to survive predefined distortions of the image data, such as panscan or letterbox mode transformations. Alternatively, a registration pattern in the image data, after the image data containing the registration pattern is subject to an unknown distortion, is used to compensate for distortion of the watermarked image data.

Device for recording video signals and device for displaying electronic program guide

Abstract: A video recorder for recording content signals including audio and video signals, comprises a module for receiving program information signals designating a program identifier, starting and ending time of a program, a first storage device (103), a first recording module for continuously recording the content signals at least one channel in the first storage device, and a module for deleting the content signals of the oldest program recorded in the first storage device in reference with the program information signals.

Image display device with element driving device for matrix drive of multiple active elements

Abstract: An image display device has multiple active elements arranged therein, such as an organic EL (Electro-Luminescence) element to matrix-drives these active elements. In the image display device, when a switching element is turned on with a control signal applied to a control electrode, a control current on a signal electrode is converted to a control voltage by a second transistor, held in a holding capacitor, and applied to a gate electrode of a first transistor. Thus, the signal electrode is applied with the control current, not with a control voltage, for controlling the operation of the active element. A drive voltage to be applied to a power supply electrode is converted to a drive current and supplied to the active element.

Permeability and electromagnetic-interference characteristics of Fe–Si–Al alloy flakes–polymer composite

Abstract: A magnetic sheet made of Fe–Si–Al flakes was found to have excellent permeability and electromagnetic-interferences characteristics in a quasimicrowave band. The flakes prepared by attrition were embedded in a polymer with their planes lying parallel to the sheet plane. This sheet exhibits a peculiar dual dispersion in permeability. The Curie temperature of the flakes increases with increasing specific surface area of the flakes. This suggests the composition of the flakes changes to excess Fe by oxidation of Si and Al. This deviation from the Sendust composition brings an increase of a magnetoelastic effect and the dual frequency dispersion seems to be associated with stress caused by attrition. On the basis of these results, flakes with more desirable permeability characteristics were produced from raw powder with less Fe content. Consequently, we could fabricate a magnetic composite that possesses superior noise suppressing effect in a quasi-microwave band.

System and method for providing customized advertising on the World Wide Web

Abstract: A system and method for customized advertisement selection and delivery on the World Wide Web (WWW) upon the Internet. The advertising system has a database server which stores advertisements and their campaign information, and an advertisement server which generates electronic advertisements available to a client system. In the system, a customization process which customized the electronic advertisements to be delivered to each client system is performed. A user connects to a web site and is presented with an editorial page or a list of search results. The system inserts a customized advertisement into the page that matches the page content or search topic. No identifiable data is collected during the interaction with the user. Advertisers can specify display constraints for each advertisement. The system will adapt all unrestricted parameters in order to maximize the user's click-through probability.

The impact of bias temperature instability for direct-tunneling ultra-thin gate oxide on MOSFET scaling

Abstract: This paper presents a new reliability scaling scenario for CMOS devices with direct-tunneling ultra-thin gate oxide. Device degradation due to bias-temperature instability (BTI) was studied. First, the stress voltage dependence of BTI results indicate that the direct-tunneling electron and/or hole transport does not play a major role in the degradation mechanism. Secondly, it was found that the threshold voltage change caused by BTI for the PMOSFET limits the device lifetime, which is shorter than that defined by hot-carrier induced degradation for the NMOSFET. It originates from the difference of supply voltage dependence between BTI and hot-carrier degradation.

QOS protection system

Abstract: A QOS protection system can switch a current system and a reserved system depending upon degradation of quality through monitoring of arriving condition of packet to perform transmission with guarantee of QOS. The QOS protection system in a redundant system includes detection means for monitoring the packet flow and detecting at least the quality of degradation of the packet flow and switching means for performing switching between the current system and the reserved system when the detection means detects degradation of quality.

Density-functional approach to electron dynamics: Stable simulation under a self-consistent field

Abstract: We propose efficient and stable numerical methods for simulating the electron dynamics within the time-dependent density-functional theory and the nonlocal pseudopotential. In this scheme, time evolution of the wave function is followed by self-consistently solving the time-dependent Kohn-Sham equation using the higher-order Suzuki-Trotter type split-operator method. To eliminate the numerical instability problem and increase the time step for the integration, we introduce the railway curve scheme to interpolate the self-consistent potential and the cutoff schemes to smooth the kinetic energy operator and the charge density. Applying these techniques to the electron dynamics of an Al cluster and the electron-ion dynamics of an excited K cluster, we found that they significantly improve the stability and efficiency. This opens the possibility of performing subpicosecond-long simulations of the transient dynamics of electrons and ions for a number of materials.

IP network access for portable devices

Abstract: A guest station on a foreign network is provided IP access by the foreign (i.e., hosting) network without changes to the guest station, including settings for IP address, next-hop-router (gateway), and netmask. An access router automatically detects guests and their home-IP-address and assigns a local care-of address to every guest. For outgoing traffic, the router replaces the guest's original/home IP address with the care-of address, and the reverse is performed for incoming traffic. IP traffic may thus be initiated, and responses received at the temporary current location without having to change its IP address.

GaN crystal film, a group III element nitride semiconductor wafer and a manufacturing process therefor

Abstract: A GaN crystal film having a mask patterned in a stripe for forming multiple growing areas on a sapphire substrate and coalesced GaN crystals covering the mask dividing the areas, grown from the neighboring growing areas, comprising defects where multiple dislocations along with the stripe are substantially aligned with the normal line of the substrate, in the crystal areas over the mask, and dislocations propagating in substantially parallel with the substrate surface while, in the vicinity of the areas where the crystals are coalesced over the mask, propagating substantially in the normal line of the substrate surface, and a manufacturing process therefor. According to this invention, there can be provided a GaN crystal film in which strain, defects and dislocations are reduced and which tends not to generate cracks.

Bias temperature instability in scaled p/sup +/ polysilicon gate p-MOSFET's

Abstract: The bias temperature instability in surface-channel p/sup +/ polysilicon gate p-MOSFETs was evaluated. It was found that a large negative threshold voltage shift (/spl Delta/V/sub th,BT/) is induced by negative bias temperature (BT) stress in short-channel p/sup +/ polysilicon gate p-MOSFETs. This Vth shift, which depends on the gate length of p-MOSFETs, is a new degradation mode. In this degradation, the negative /spl Delta/V/sub th,BT/ increases significantly with a reduction in the gate length. It was shown that this is because of the local degradation of the gate oxide near the gate edge. This degradation is caused by the electrochemical reaction between holes and oxide defects and it is enhanced by boron penetration through the gate oxide from p/sup +/-gate. For the bias temperature instability in p/sup +/-gate p-MOSFETs, sufficient care should be taken in scaled dual-gate CMOS devices.

Elastic Response of Carbon Nanotube Bundles to Visible Light

Abstract: Distinct macroscopic movements of the filaments consisted of single-wall carbon nanotube bundles were observed under visible light illumination. The movements, sensitive to the intensity of the light, were attributed to the elastic deformations of the bundles of nanotubes. Light-induced electrical currents in the carbon nanotube filaments aligned between two metal electrodes were also observed. The mechanism for the observed phenomena is discussed by considering the physical interlinks of the optical, thermal, electrical, and elastic effects of nanotube bundles.

Experimental evaluation of impact ionization coefficients in GaN

Abstract: The impact ionization coefficient of electrons (/spl alpha//sub n/) in GaN is determined as a function of the electric field strength from gate-current analysis in the prebreakdown regime of AlGaN/GaN heterojunction field effect transistors (HJFETs). The experimentally obtained /spl alpha//sub n/, where the assumed effective length of the high electric field is precisely defined since its upper bound is closely limited due to the small gate-drain separation, agrees with that extrapolated from Monte Carlo simulation. It is experimentally confirmed that the breakdown field of GaN is higher than that of GaAs by a factor of about eight.

Distributed agent software system and method having enhanced process mobility and communication in a computer network

Abstract: A distributed software system and method are provided for use with a plurality of potentially heterogeneous computer machines connected as a network. The system may comprise at least one agent comprising a protection domain, wherein the protection domain of the at least one agent resides on at least two of the plurality of computer machines. A plurality of objects is contained within the protection domain of the at least one agent, a first object residing on a first of the at least two computer machines and a second object residing on a second of the at least two computer machines. The objects are selectively movable among the at least two computer machines by a programmer of the system. The first object on the first computer machine may access the second object on the second computer machine in a location-transparent or network-transparent manner; that is, without knowledge of the physical address of the second object on the second computer machine and regardless of the selective movement of either the first object or the second object among the first and second computer machines. The agent is mobile and may migrate, in whole or in part, to any other machine or machines in the network. Each distributed agent may be distributed among one, several or many of the machines of the network. Migration of agents, even during process execution, is straightforward and maintains consistency across the network. Specifically, other agents may continue to access a particular agent after it has migrated without any prior notification to the agents themselves.

Mechanism of the Effect of NiCo, Ni and Co Catalysts on the Yield of Single-Wall Carbon Nanotubes Formed by Pulsed Nd:YAG Laser Ablation

Abstract: We revealed that the yield of SWNTs formed by Nd:YAG laser ablation depends on the target composition with yields following the order CxNiyCoy > CxNiy ≫ CxCoz. The SWNT bundles in the web formed when using the CxNiyCoy target (web-CxNiyCoy) is thicker and longer than those in the web-CxNiy. The diameters of the SWNTs in the web-CxNiyCoy were larger and more uniform than those of the SWNTs in the web-CxNiy. The NiCo particles in the web-CxNiyCoy and the Ni particles in the web-CxNiy were nanometer sized and were embedded in the amorphous carbon flakes that were dispersed throughout the weblike deposits. Filmlike deposits were formed when using the CxCoz targets, and nanometer-sized Co particles in these deposits were localized within sub-millimeter-sized areas. Examination of the target surfaces revealed that Ni emits from the CxNiy target more efficiently than NiCo from the CxNiyCoy target or Co from the CxCoz target during the laser ablation. On the basis of these results, we provide an explanation of ho...

Simulation vector generation from HDL descriptions for observability-enhanced statement coverage

Abstract: Validation of RTL circuits remains the primary bottleneck in improving design turnaround time, and simulation remains the primary methodology for validation. Simulation-based validation has suffered from a disconnect between the metrics used to measure the error coverage of a set of simulation vectors, and the vector generation process. This disconnect has resulted in the simulation of virtually endless streams of vectors which achieve enhanced error coverage only infrequently. Another drawback has been that most error coverage metrics proposed have either been too simplistic or too inefficient to compute. Recently, an effective observability-based statement coverage metric was proposed along with a fast companion procedure for evaluating it. The contribution of our work is the development of a vector generation procedure targeting the observability-based statement coverage metric. Our method uses repeated coverage computation to minimize the number of vectors generated. For vector generation, we propose a novel technique to set up constraints based on the chosen coverage metric. Once the system of interacting arithmetic and Boolean constraints has been set up, it can be solved using hybrid linear programming and Boolean satisfiability methods. We present heuristics to control the size of the constraint system that needs to be solved. We present experimental results which show the viability of automatically generating vectors using our approach for industrial RTL circuits. We envision our system being used during the design process, as well as during post-design debugging.

“Bucky Shuttle” Memory Device: Synthetic Approach and Molecular Dynamics Simulations

Abstract: Thermal treatment is reported to convert finely dispersed diamond powder to multiwall carbon nanocapsules containing fullerenes such as ${\mathrm{C}}_{60}$. We investigate the internal dynamics of a related model system, consisting of a $\mathrm{K}@{\mathrm{C}}_{60}^{+}$ endohedral complex enclosed in a ${\mathrm{C}}_{480}$ nanocapsule. We show this to be a tunable two-level system, where transitions between the two states can be induced by applying an electric field between the ${\mathrm{C}}_{480}$ end caps, and discuss its potential application as a nonvolatile memory element.

AMORE: A World Wide Web image retrieval engine

Abstract: Search engines are useful because they allow the user to find information of interest from the World Wide Web. However, most of the popular search engines today are textuals they do not allow the user to find images from the Web. This paper describes AMORE, a Web search engine that allows the user to retrieve images from the Web by specifying relevant keywords or a similar image. Text and image search can also be combined. Moreover, we have developed a Query Result Visualization Environment that allows the organization of the results if many images are retrieved. In this paper we present AMORE’s user interface and explain the technique for retrieving images visually similar to a user specified image. The method of automatically assigning relevant keywords to the images is then explained. Finally, the architecture of the system as well as some interesting observations of our experiences with AMORE are discussed.