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排序方式: 共有750条查询结果,搜索用时 31 毫秒
681.
Yahua Li Jackson S.D. Yucheng Zhao Simon Fleming 《Lightwave Technology, Journal of》2005,23(5):1907-1912
This paper presents an experimental study on the dynamics of Raman fiber lasers that use highly GeO/sub 2/-doped fibers as an active medium and a dual-wavelength (1060 and 1090 nm) Nd/sup 3+/-doped fiber laser as a pump source. The 1090-nm pump wavelength is located within the SiO/sub 2/ Raman gain spectrum relating to the 1060-nm pump wavelength, and competition is observed between Raman amplification of the 1090-nm emission with the 1060-nm emission used as the pump source and Raman lasing, which is independent of the 1090-nm amplification and which is also uses the 1060-nm emission as the pump source. Several pump configurations have been demonstrated to generate specific Stokes emissions generated through Raman lasing or amplification. Changing the gain-to-loss ratio by introducing intracavity loss of Raman emissions or increasing the Raman fiber length within each configuration can force either Raman amplification or lasing to dominate. The maximum slope efficiency as a function of the launched pump power was /spl sim/55% with a total output power of 1.6 W produced. A red shift of both the pump and the Stokes wavelengths is experimentally observed when the launched diode pump power is scaled up. 相似文献
682.
In digital communication systems, variable-length Walsh codes, also called orthogonal variable spreading factor codes, are used to support simultaneous variable-rate data transmission. This paper describes algorithms for dynamic variable- length Walsh code assignment. Optimal assignment criterion is derived and an efficient data structure for maintaining variable- length Walsh codes is introduced. The benefits of code reallocation are also studied. Performance is evaluated via simulation. 相似文献
683.
OECC is a world-class international optoelectronics and communications conference, convened annually in the Asia Pacific region. This year it was held jointly with the Australian domestic conference, ACOFT, which is in its 33rd year and one of the world?s longest running optical fiber conferences. These conferences were collocated, but held as separate events, with the 21st Congress of the International Commission for Optics (ICO). They were held 7 to 10 July 2008 at Australia?s leading conference venue, the Sydney Convention & Exhibition Centre at Darling Harbour. 相似文献
684.
Mobile WiMAX systems: performance and evolution 总被引:1,自引:0,他引:1
Fan Wang Ghosh A. Sankaran C. Fleming P. Hsieh F. Benes S. 《Communications Magazine, IEEE》2008,46(10):41-49
Mobile WiMAX was successfully adopted by ITU as one of the IMT-2000 technologies in November 2007. Since then mobile WiMAX (a.k.a. IP-OFDMA) has officially become a major global cellular wireless standard along with 3GPP UMTS/HSPA and 3GPP2 CDMA/ EVDO. Mobile WiMAX is an OFDM-based technology available for deployment today, and new WIMAX devices come to market at much reduced cost than that of current 3G solutions. Currently over 260 service providers are deploying fixed, portable and mobile WiMAX networks in 110 countries. This article provides an overview of the mobile WiMAX system and its performance under various configurations, channel conditions, and types of data traffic. Furthermore, the article provides an overview of mobile WiMAX evolution. 相似文献
685.
G.S. Hwang E. Fleming B. Carne S. Sharratt Y. Nam P. Dussinger Y.S. Ju M. Kaviany 《International Journal of Heat and Mass Transfer》2011,54(11-12):2334-2340
We design and test a low thermal/hydraulic resistance, multi-artery heat-pipe spreader vapor chamber. Liquid (water) is supplied to a highly concentrated heat-source region through a monolayer evaporator wick and a set of lateral converging arteries, fabricated from sintered, spherical copper particles. The monolayer wick allows for a minimum evaporator resistance of 0.055 K/(W/cm2), which is related to a critical transition where the receding meniscus approaches the particle neck. Similar behavior is also observed in a monolayer-wick evaporator, partially submerged in liquid bath. After this minimum, local dryout occurs and increases the resistance. However, a continuous liquid supply through the lateral arteries does not allow for total dryout in the test limit of 580 W/cm2. These thermal/hydraulic behaviors are predicted using the local thermal equilibrium and nonequilibrium models. 相似文献
686.
D. J. Curran T. J. Fleming G. Kawachi C. Ohtsuki M. R. Towler 《Journal of materials science. Materials in medicine》2009,20(11):2235-2241
Hydrothermal treatment is traditionally employed to improve the sinterability of powder compacts by reducing porosity and
increasing apparent density. The effect of hydrothermal treatment on green powder compacts has been assessed in order to better
understand how treatment may affect the sinterability of the bodies. Laboratory synthesised nano sized hydroxyapatite (HA)
and a commercial zirconia (ZrO2) powder have been ball milled together to create composite mixtures containing 0–5 wt% ZrO2 loadings. Disc shaped bodies have been formed using uniaxial and subsequent isostatic pressure. The resultant coherent samples
were subjected to hydrothermal treatment at either 120 or 250°C for 10 h in order to assess the effect of this processing
technique on the physical, mechanical and microstructural properties of the green composites. ZrO2 loadings up to 3 wt% increased apparent density from 90 to 92%, whereas increased loading to 5 wt% increased flexural strength,
from 6 to 9 MPa. Increasing the hydrothermal treatment temperature increased open porosity, from ~44 to ~48% and reduced biaxial
flexural strengths of the treated bodies compared to those of their room temperature isostatically pressed counterparts (~10
to ~6 MPa). 相似文献
687.
688.
Seonghyuk Ko Jan Pekarovic Paul D. Fleming Pnina Ari-Gur 《Materials Science and Engineering: B》2010,166(2):127-131
Nanosized titanium dioxide (TiO2) photocatalytic papers were successfully prepared using a natural zeolite microparticle retention aid in papermaking. Applying a factorial experimental design, natural zeolite has been demonstrated to be the most significant and interactive factor for increasing the TiO2 retention rate in paper stock. The photocatalysis of as-prepared sheets was evaluated with toluene as one of the representative volatile organic compounds (VOCs). Under UV irradiation, it was shown to be effective in removing gaseous toluene by photodecomposition, assisted by adsorption. It was revealed that natural zeolite plays an important role in both increasing retention rate of TiO2 nanoparticles and enhancing photocatalytic efficiency of the paper. The photocatalytic paper can be potentially applied for environmental purification. 相似文献
689.
Christine F. Baes Bayode O. Makanjuola Filippo Miglior Gabriele Marras Jeremy T. Howard Allison Fleming Christian Maltecca 《Journal of dairy science》2019,102(3):2807-2817
Inbreeding depression is a growing concern in livestock because it can detrimentally affect animal fitness, health, and production levels. Genomic information can be used to more effectively capture variance in Mendelian sampling, thereby enabling more accurate estimation of inbreeding, but further progress is still required. The calculation of inbreeding for herd management purposes is largely still done using pedigree information only, although inbreeding coefficients calculated in this manner have been shown to be less accurate than genomic inbreeding measures. Continuous stretches of homozygous genotypes, so called runs of homozygosity, have been shown to provide a better estimate of autozygosity at the genomic level than conventional measures based on inbreeding coefficients calculated through conventional pedigree information or even genomic relationship matrices. For improved and targeted management of genomic inbreeding at the population level, the development of methods that incorporate genomic information in mate selection programs may provide a more precise tool for reducing the detrimental effects of inbreeding in dairy herds. Additionally, a better understanding of the genomic architecture of inbreeding and incorporating that knowledge into breeding programs could significantly refine current practices. Opportunities to maintain high levels of genetic progress in traits of interest while managing homozygosity and sustaining acceptable levels of heterozygosity in highly selected dairy populations exist and should be examined more closely for continued sustainability of both the dairy cattle population as well as the dairy industry. The inclusion of precise genomic measures of inbreeding, such as runs of homozygosity, inbreeding, and mating programs, may provide a path forward. In this symposium review article, we describe traditional measures of inbreeding and the recent developments made toward more precise measures of homozygosity using genomic information. The effects of homozygosity resulting from inbreeding on phenotypes, the identification and mapping of detrimental homozygosity haplotypes, management of inbreeding with genomic data, and areas in need of further research are discussed. 相似文献
690.
Shalat SL Solo-Gabriele HM Fleming LE Buckley BT Black K Jimenez M Shibata T Durbin M Graygo J Stephan W Van De Bogart G 《The Science of the total environment》2006,367(1):80-88
Arsenic from chromated copper arsenate (CCA)-treated wood, widely used in playgrounds and other outdoor equipment, can persist as surface residues on wood. This raises concerns about possible health risks associated with children playing on CCA-treated playgrounds. In a Pilot Study, 11 children (13-71 months) in homes with and without CCA-treated playgrounds were evaluated with post-exposure hand rinses and urine for total arsenic. Samples of wood, soil, and mulch, as well as synthetic wipes, were sampled for total arsenic. In non-CCA-treated playgrounds vs. CCA-treated playgrounds, respectively, wood arsenic was <2.0 mg/kg vs. mean arsenic 2370 mg/kg (range 1440-3270 mg/kg); soil arsenic was <3.0 mg/kg vs. mean arsenic of 19 mg/kg (range 4.0-42 mg/kg); mulch arsenic at one non-CCA-treated playground was 0.4 mg/kg vs. two CCA-treated playgrounds of 0.6 and 69 mg/kg. The arsenic removed using a synthetic wipe at non-CCA-treated playgrounds was <0.5 microg, while mean arsenic from CCA-treated wood was 117 microg (range 1.0-313). The arsenic mass from hand rinses for children who played at non-CCA-treated playgrounds was <0.2 microg, while mean arsenic mass was 0.6 microg (range <0.2-1.9) at CCA-treated playgrounds. Mean urinary total arsenic levels were 13.6 pg/ml (range 7.2-23.1 pg/ml) for all children evaluated, but there was no association between access to CCA-playgrounds and urinary arsenic levels. Arsenic speciation was not performed. This preliminary Pilot Study of CCA-treated wood playgrounds observed dislodgeable arsenic on 11 children's hands after brief periods of play exposure. Future efforts should increase the number of children and the play exposure periods, and incorporate speciation in order to discriminate between various sources of arsenic. 相似文献