NEC

About: NEC is a company organization based out in Tokyo, Japan. It is known for research contribution in the topics: Signal & Layer (electronics). The organization has 33269 authors who have published 57670 publications receiving 835952 citations. The organization is also known as: NEC Corporation & NEC Electronics Corporation.

Data link control protocols for wireless ATM access channels

Abstract: Describes data link control procedures for wireless ATM access channels based on a dynamic TDMA/TDD frame-work. The system provides integrated ATM services including available bit-rate (ABR) data and constant/variable bit-rate (CBR/VBR) voice or video through the addition of wireless-specific medium access control (MAC) and data link control (DLC) protocol layers between the physical and ATM network layers. The purpose of the DLC protocol layer is to insulate the ATM network layer from wireless channel impairments by selective retransmission of erroneous or lost cells before they are released to the ATM layer. The DLC methods described exploit the on-demand ABR burst transmission capability of the dynamic TDMA channel to retransmit unacknowledged cells in available slots not allocated to service data. Specific error recovery procedures are outlined for both (asynchronous) ABR and (isochronous) CBR services. For ABR, the DLC operation follows a group ACK/NACK based selective reject (SREJ) procedure on a burst-burst basis, without time limits for completion. For CBR, the retransmission procedure is constrained to complete within a specified time interval, so that isochronous delivery of cells to the ATM layer can be maintained. The proposed protocols have been validated using a software emulator which incorporates a choice of radio channel models, dynamic TDMA/TDD MAC, and ABR or CBR DLC. Numerical results show that the data link control protocols under consideration can significantly improve wireless ATM service quality over impaired radio channels for both packer data ABR and stream type CBR virtual circuits.

TWINE: A Lightweight Block Cipher for Multiple Platforms ⋆

Abstract: This paper presents a 64-bit lightweight block cipher TWINE supporting 80 and 128- bit keys. TWINE realizes quite small hardware implementation similar to the previous lightweight block cipher proposals, yet enables efficient software implementations on various platforms, from micro-controller to high-end CPU. This characteristic is obtained by the use of generalized Feistel structure combined with an improved block shuffle, introduced at FSE 2010. Keywords: lightweight block cipher, generalized Feistel structure, block shuffle

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.

In silico discovery of small-molecule Ras inhibitors that display antitumor activity by blocking the Ras-effector interaction.

Abstract: Mutational activation of the Ras oncogene products (H-Ras, K-Ras, and N-Ras) is frequently observed in human cancers, making them promising anticancer drug targets. Nonetheless, no effective strategy has been available for the development of Ras inhibitors, partly owing to the absence of well-defined surface pockets suitable for drug binding. Only recently, such pockets have been found in the crystal structures of a unique conformation of Ras⋅GTP. Here we report the successful development of small-molecule Ras inhibitors by an in silico screen targeting a pocket found in the crystal structure of M-Ras⋅GTP carrying an H-Ras–type substitution P40D. The selected compound Kobe0065 and its analog Kobe2602 exhibit inhibitory activity toward H-Ras⋅GTP-c-Raf-1 binding both in vivo and in vitro. They effectively inhibit both anchorage-dependent and -independent growth and induce apoptosis of H-rasG12V–transformed NIH 3T3 cells, which is accompanied by down-regulation of downstream molecules such as MEK/ERK, Akt, and RalA as well as an upstream molecule, Son of sevenless. Moreover, they exhibit antitumor activity on a xenograft of human colon carcinoma SW480 cells carrying the K-rasG12V gene by oral administration. The NMR structure of a complex of the compound with H-Ras⋅GTPT35S, exclusively adopting the unique conformation, confirms its insertion into one of the surface pockets and provides a molecular basis for binding inhibition toward multiple Ras⋅GTP-interacting molecules. This study proves the effectiveness of our strategy for structure-based drug design to target Ras⋅GTP, and the resulting Kobe0065-family compounds may serve as a scaffold for the development of Ras inhibitors with higher potency and specificity.

Effects of impurity doping in lead zirconate-titanate ceramics

Abstract: Impurity doping effects on the properties of lead zirconate-titanate ceramics have been investigated from the internal bias field viewpoint. The internal bias field is strengthened by doping with single or multiple acceptors, but is weakened by single or multiple donors. Equimolar mixed acceptor and donor dopants have no influence on the internal bias field. These facts suggest that the internal bias field is caused by complexes of acceptor atoms and oxygen vacancies. The internal bias field gives rise to effects on the domain wall motions. It prohibits the poling process, increases the mechanical quality factor and accelerates the aging change in the frequency constant. The mechanical quality factor and the aging change are proportional to the internal bias field. However, when the internal bias field reorients itself parallel to the spontaneous polarization in a short time after poling, the aging change becomes small, even for a specimen having a strong internal bias field.