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NHK Laboratories Note
 2005
NHK Laboratories Note No.496
Comparison of Measured Rain Attenuation in the 12-GHz Band with Prediction
Fumiaki MINEMATSU,Yoichi SUZUKI,Masashi KAMEI,Kazuyoshi SHOGEN

IEICE Transactions on Communications, vol.E88-B, no.6, 2005, pp.2419-2426
Abstract
The rain attenuation in the 12-GHz band and one-minute-rain rate were measured in Tokyo over a four-year period (2000-2003). The statistical characteristics of this data are presented. The one-minute-rain rates at 0.01% of time percentage of year in Tokyo and Osaka are compared to other past and recent values. The comparison of measured rain attenuation in the 12-GHz band in Tokyo and Osaka with prediction by ITU-R methods is conducted. The root-mean-square prediction error of rain attenuation for the prediction by ITU-R Rec.P.618 is evaluated. Convective rain cell effects can be seen in the scatter diagram of one-minute-rain rate and rain attenuation. However, it is found that the effect is not properly accounted for by the slant path length adjustment factor of P.618-8. A reliable rain attenuation prediction requires some revisions of the slant path length adjustment factor with taking local weather characteristics into account for the P.618-8.
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NHK Laboratories Note No.495
Separation of Sound Sources Propagated in the Same Direction
Akio ANDO, Masakazu IWAKI, Kazuho ONO, Koichi KUROZUMI

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol.E88-A, no.7, 2005, pp.1665-1672
Abstract
This paper describes a method for separating a target sound from other noise arriving in a single direction when the target cannot, therefore, be separated by directivity control. Microphones are arranged in a line toward the sources to form null sensitivity points at given distances from the microphones. The null points exclude non-target sound sources on the basis of weighting coefficients for microphone outputs determined by blind source separation. The separation problem is thereby simplified to instantaneous separation by adjustment of the time-delays for microphone outputs. The system uses a direct (i.e. non-iterative) algorithm for blind separation based on second-order statistics, assuming that all sources are non-stationary signals. Simulations show that the 2-microphone system can separate a target sound with separability of more than 40 dB for the 2-source problem, and 25 dB for the 3-source problem when the other sources are adjacent.
Copyright The Institute of Electronics, Information and Communication Engineers.
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NHK Laboratories Note No.494
Organic Light-Emitting Diodes Using Multifunctional Phosphorescent Dendrimers with Iridium-Complex Core and Charge-Transporting Dendrons
Toshimitsu TSUZUKI, Nobuhiko SHIRASAWA1, Toshiyasu SUZUKI1 and Shizuo TOKITO
(Materials Science)

*1: Institute for Molecular Science,
Abstract
We report a novel class of light-emitting materials for use in organic light-emitting diodes (OLEDs): multifunctional phosphorescent dendrimers that have a phosphorescent core and dendrons based on charge-transporting building blocks. We synthesized first-generation and second-generation dendrimers consisting of a fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] core and hole-transporting phenylcarbazole-based dendrons. Smooth amorphous films of these dendrimers were formed by spin-coating them from solutions. The OLEDs using the dendrimer exhibited bright green or yellowish-green emission from the Ir(ppy)3 core. The OLEDs using the film containing a mixture of the dendrimer and an electron-transporting material exhibited higher efficiency than those using the neat dendrimer film. The external quantum efficiency of OLEDs using the film containing a mixture of the first-generation dendrimer and an electron-transporting material was as high as 7.6%.[DOI : 10.1143/JJAP.44.4151]
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JJAP : http://www.ipap.jp/jjap/index.htm
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NHK Laboratories Note No.493
Photoconductive Properties of Organic Films Based on Porphine Complex Evaluated with Image Pickup Tubes
Satoshi AIHARA, Kazunori MIYAKAWA, Yuji OHKAWA, Tomoki MATSUBARA, Tamotsu TAKAHATA, Shiro SUZUKI, Misao KUBOTA, Kenkichi TANIOKA, Norihiko KAMATA1 and Daiyo TERUNUMA1
(Advanced Broadcasting Devices)

*1:Department of Functional Materials Science, Saitama University,
Abstract
We have fabricated two types of organic photoconductive films; a layered structure of tetra(4-methoxyphenyl) porphine cobalt complex (Co-TPP) and bathocuproine (BCP) (target A), and another of Co-TPP, tris-8-hydroxyquinoline aluminum (Alq3) and BCP (target B). The photoconductive properties of each film have been measured using image pickup tubes. The dark current was drastically reduced in target B compared with that in target A at the same applied electric field. The external quantum efficiency reached 20% in target B, which is twenty times higher than that in target A. Image pickup of a test chart from target B at standard TV operation was also demonstrated. High resolution and excellent tone sufficient for television use has been obtained. [DOI : 10.1143/JJAP.44.3743]
labnote493.pdf
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JJAP : http://www.ipap.jp/jjap/index.htm
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NHK Laboratories Note No.492
Organic Thin-Film Transistors with High Electron Mobility Based on Perfluoropentacene
Youji INOUE, Youichi SAKAMOTO1, Toshiyasu SUZUKI1, Masafumi KOBAYASHI2, Yuan GAO2 and Shizuo TOKITO
(Materials Science)

*1:Institute for Molecular Science,
*2:Kanto Denka Kogyo Co., Ltd.,
Abstract
We report on n-channel organic thin-film transistors (OTFTs) based on the novel n-type organic semiconductor, perfluoropentacene. The transistor exhibits excellent electrical characteristics, with a high electron mobility of 0.22 cm2/(V s) and a good current on/off ratio of 105. The electron mobility is comparable to the hole mobility of a pentacene OTFT. By combining the n-type perfluoropentacene and the p-type pentacene, we have fabricated ambipolar OTFTs and complementary inverter circuits. The OTFTs with heterostructures of the p- and n-type organic semiconductors can operate as an ambipolar device with high electron and hole mobilities of 0.042 and 0.041 cm2/(V s). The complementary inverter using an n-channel perfluoropentacene OTFT and a p-channel pentacene OTFT exhibits excellent transfer characteristics with a voltage gain of 45. A complementary inverter using the ambipolar OTFTs is also demonstrated. [DOI : 10.1143/JJAP.44.3663]
labnote492.pdf
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NHK Laboratories Note No.491
Phosphorescent-sensitized Triplet-triplet Annihilation in Tris (8-hydroxyquinoline) Aluminum
Isao TANAKA and Shizuo TOKITO
(Materials Science)
Journal of Applied Physics?AVol.97, No.11, 113532, [4p.](2005)
Abstract
We characterized the photoluminescence properties of an amorphous triss8-hydroxyquinolined aluminum (Alq3) thin film heavily doped with fac triss2-phenylpyridined iridium [Irsppyd3] at 8 K. Not only green fluorescence but also red phosphorescence from Alq3 was clearly observed, where Ir(ppy)3 plays the important role as a phosphorescent sensitizer for Alq3. The triplet energy of Alq3 was estimated to be 2.03 eV from the highest energy peak of the phosphorescence spectrum. The fluorescence intensity was proportional to the excitation power. On the other hand, the deviation from the linearity of the phosphorescence intensity to the excitation power was observed above, 0.01 W/cm2. This nonlinear phosphorescence behavior is well explained by the simple triplet-triplet annihilation theory. It was demonstrated that the efficient triplet energy transfer from Ir(ppy)3 enables us to observe triplet-triplet annihilation in Alq3. © 2005 American Institute of Physics. [ DOI: 10.1063/1.1925764 ]

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NHK Laboratories Note No.490
A4-sized Flexible Ferroelectric Liquid-crystal Displays with Micro Color Filters
Hiroto Sato, Hideo Fujikake, Takeshi Murashige, Hiroshi Kikuchi, Taiichiro Kurita and Fumio Sato
(Materials Science)
Journal of the Society for Information Display, Vol.13, Issue6, pp.461-468 (2005)
Abstract
We demonstrated an A4-paper-sized flexible ferroelectric liquid-crystal (FLC) color displays fabricated by using a new plastic-substrate-based process which was developed for large-sized devices. Finely patterned color filters and ITO electrodes were formed on a plastic substrate by a transfer method to avoid surface roughness and thermal distortion of the substrate, which induce disordering of the FLC molecular alignment. The thickness of an FLC/monomer solution sandwiched by two plastic-film substrates was well controlled over a large area by using flexographic printing and lamination techniques. Molecular-aligned polymer walls and fibers were formed in the FLC by a twostep photopolymerization-induced phase-separation method using UV-light irradiation. A fabricated A4-sized flexible-sheet display for color-segment driving was able to exhibit color images even when it was bent.
labnote490.pdf
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