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排序方式: 共有6791条查询结果,搜索用时 15 毫秒
991.
Li Liu Cheuk‐Lam Ho Wai‐Yeung Wong Kai‐Yin Cheung Man‐Kin Fung Wai‐Ting Lam Aleksandra B. Djurii Wai‐Kin Chan 《Advanced functional materials》2008,18(18):2824-2833
A series of solution‐processable and strongly visible‐light absorbing polyplatinynes containing oligothienyl–fluorene ring hybrids were synthesized and characterized. These rigid‐rod organometallic materials are soluble in polar organic solvents and show intense absorptions in the visible spectral region, rendering them excellent candidates for bulk heterojunction polymer solar cells. The photovoltaic behavior depends significantly on the number of thienyl rings along the polymer chain, and some of these polymer solar cells show high power conversion efficiencies (PCEs) of up to 2.9% and a peak external quantum efficiency to 83% under AM1.5 simulated solar illumination. The effect of oligothienyl chain length on improving the polymer solar cell efficiency and on their optical and charge transport properties is elucidated in detail. At the same blend ratio of 1:5, the light‐harvesting capability and PCE increase markedly with increasing number of thienyl rings. The power dependencies of the solar cell parameters (including the short‐circuit current density, open‐circuit voltage, fill‐factor, and PCE) were also examined. The present work opens up an attractive avenue to developing conjugated metallopolymers with broad and strong solar energy absorptions and tunable solar cell efficiency and supports the potential of metalated conjugated polymers for efficient power generation. 相似文献
992.
Yangyang Sun Lingbo Zhu Hongjin Jiang Jiongxin Lu Wei Wang C.P. Wong 《Journal of Electronic Materials》2008,37(11):1691-1697
Carbon nanotube (CNT) arrays/films were transferred onto copper substrates via eutectic tin/lead (SnPb) solder pastes. The
morphologies, thermal stabilities, adhesion to substrates, and electrical properties of the as-transferred CNT arrays were
studied. The CNT arrays generated negligible expansion or contraction below 250°C. The adhesion of CNT arrays to the substrate
was significantly improved by the transfer process. An ohmic contact was formed between the transferred CNT arrays and the
Sn-Pb solder. Four-probe electrical measurements yielded the resistance of the as-transferred CNT films under the electrode
to be around 0.0056 Ω, from which the resistivity of each individual CNT tube was calculated to be 2.44 × 10−4 Ω cm. 相似文献
993.
C.K. Wong J.H.L. Pang J.W. Tew B.K. Lok H.J. Lu F.L. Ng Y.F. Sun 《Microelectronics Reliability》2008,48(4):611-621
This paper examines various aspects of SAC (Sn–3.8Ag–0.7Cu wt.%) solder and UBM interactions which may impact interconnection reliability as it scales down. With different solder joint sizes, the dissolution rate of UBM and IMC growth kinetics will be different. Solder bumps on 250, 80 and 40 μm diameter UBM pads were investigated. The effect of solder volume/pad metallization area (V/A) ratio on IMC growth and Ni dissolution was investigated during reflow soldering and solid state isothermal aging. Higher V/A ratio produced thinner and more fragmented IMC morphology in SAC solder/Ni UBM reflow soldering interfacial reaction. Lower V/A ratio produced better defined IMC layer at the Ni UBM interface. When the ratio of V/A is constant, the IMC morphology and growth trend was found to be similar. After 250 h of isothermal aging, the IMC growth rate of the different bump sizes leveled off. No degradation in shear strength was observed in these solder bump after 500 h of isothermal aging. 相似文献
994.
Collaborative decoding is an approach that can achieve diversity and combining gain by exchanging decoding information among a cluster of physically separated receivers. On AWGN channels, the least-reliable-bits (LRB) exchange scheme can achieve performance close to equal-gain combining (EGC) of all received symbols from all receivers, while reducing the amount of information that must be exchanged. In this paper, we analyze the error performance of collaborative decoding with the LRB exchange scheme when nonrecursive convolutional codes are used. The analysis is based on the observation that the extrinsic information generated in the collaborative decoding of these convolutional codes can be approximated by Gaussian random variables. A density-evolution model based on a single maximum a posteriori decoder is used to obtain the statistical characteristics of the extrinsic information. With the statistical knowledge of the extrinsic information, we develop an approximate upper bound for the error performance of the collaborative decoding process. Numerical results show that our analysis gives very good predictions of the bit error rate for collaborative decoding with LRB exchange. At high signal-to-noise ratios collaborative decoding with properly chosen parameters can achieve the same error performance as EGC of all received symbols from all receiving nodes. 相似文献
995.
P Yan X Zhou M Shah S T C Wong 《IEEE transactions on information technology in biomedicine》2008,12(1):109-117
High-throughput genome-wide RNA interference (RNAi) screening is emerging as an essential tool to assist biologists in understanding complex cellular processes. The large number of images produced in each study make manual analysis intractable; hence, automatic cellular image analysis becomes an urgent need, where segmentation is the first and one of the most important steps. In this paper, a fully automatic method for segmentation of cells from genome-wide RNAi screening images is proposed. Nuclei are first extracted from the DNA channel by using a modified watershed algorithm. Cells are then extracted by modeling the interaction between them as well as combining both gradient and region information in the Actin and Rac channels. A new energy functional is formulated based on a novel interaction model for segmenting tightly clustered cells with significant intensity variance and specific phenotypes. The energy functional is minimized by using a multiphase level set method, which leads to a highly effective cell segmentation method. Promising experimental results demonstrate that automatic segmentation of high-throughput genome-wide multichannel screening can be achieved by using the proposed method, which may also be extended to other multichannel image segmentation problems. 相似文献
996.
Inspired by the principle of holography we present a concept for making simple transmission screens that can focus an incident wave into a sub-wavelength spot in the near field. The screen is made out of closely spaced, unequal slits cut on a metallic sheet. Fullwave simulations are presented for an example screen that focuses an incident plane wave down to a spot having a peak-to-null beamwidth equal to lambda/10 . 相似文献
997.
998.
Andrew P Breksa III Marlene B Hidalgo Rosalind Y Wong 《Journal of the science of food and agriculture》2008,88(12):2194-2200
BACKGROUND: We completed a study over a 200‐day period examining the stability of limonin glucoside formulated into three beverage matrices. RESULTS: Beverages containing limonin glucoside were found to contain limonin (0.13–20.10 mg L?1) during their initial testing; however, these concentrations were directly attributable to the presence of contaminating limonin in the particular lot of limonin glucoside used to prepare the beverage and did not increase over the test period. Likewise, limonin glucoside concentrations did not vary significantly, with the exception of the beverage matrix that included vitamin B2. Exposure of the vitamin B2‐containing beverages to light resulted in a rapid reduction in the limonin glucoside content. Liquid chromatographic–mass spectrometric and nuclear magnetic resonance results from the analyses of pre‐ and post‐light exposed beverages suggest photooxidation of the furan moiety as the likely degradation pathway. CONCLUSION: Results from this study indicate that limonin glucoside is resistant to degradation into limonin, the stability of limonin glucoside formulated into beverages exceeds six months and that limonin glucoside should not be formulated into beverages containing vitamin B2 unless the beverages are protected from light. Published in 2008 by John Wiley & Sons, Ltd. 相似文献
999.
In this paper, a wide variety of high dielectric constant (k) composite materials which have been developed and evaluated for embedded capacitor application are reviewed. Current research efforts toward achieving high dielectric performance including highk and low dielectric loss for polymer composites are presented. New insights into the effect of unique properties of the nanoparticle filler, filler modification and the dispersion between filler and polymer matrix on the dielectric properties of the nanocomposites are discussed in details. 相似文献
1000.
Qing Xu Yan Wang Feng Chen Wing-Han Wong Zi-Bo Zhang De-Long Zhang 《Journal of the American Ceramic Society》2019,102(11):6407-6413
Fluorescence and absorption spectra at 530 nm (2H11/2→4I15/2), 560 nm (4S3/2→4I15/2), 660 nm (4F9/2→4I15/2), 980 nm (4I11/2→4I15/2), 1530 nm (4I13/2→4I15/2), and 2710 nm (4I11/2→4I13/2) of Er3+ in Gd3Ga5O12 single-crystal codoped with Pr3+ have been measured. Judd-Ofelt analysis yields the intensity parameters Ω2 = (0.68 ± 0.03) × 10−20 cm2, Ω4 = (0.60 ± 0.07) × 10−20 cm2, and Ω6 = (0.90 ± 0.17) × 10−20 cm2. A comparison with previously reported values of Er3+-only doping case shows that Pr3+-codoping causes slight change of both Ω2 and Ω4, while onefold increase of Ω6. From calculated radiative rates and measured fluorescence spectra, Er3+ emission cross-section spectra were calibrated at first. Then, the absorption cross-section spectra were calculated using McCumber relation. In parallel, the absorption cross-section spectra were also obtained from the measured absorption spectrum, and compared with those obtained from the McCumber relation. The comparison shows that both methods give consistent result of absorption cross-section spectrum. Further comparison with Er3+-only doping case shows that Pr3+-codoping causes considerable change of Er3+ cross-section value. In spectrally mixing regions of Er3+ and Pr3+, Pr3+ emission affects little the determination of Er3+ emission cross-section as Pr3+ fluorescence is much weaker than Er3+ fluorescence due to low Pr3+ concentration. 相似文献