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排序方式: 共有322条查询结果,搜索用时 265 毫秒
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Tracey M. Clarke Amy M. Ballantyne Jenny Nelson Donal D. C. Bradley James R. Durrant 《Advanced functional materials》2008,18(24):4029-4035
The function of organic solar cells is based upon charge photogeneration at donor/acceptor heterojunctions. In this paper, the origin of the improvement in short circuit current of poly(3‐hexylthiophene)/6,6‐phenyl C61‐butyric acid methyl ester (P3HT/PCBM) solar cells with thermal annealing is examined. Transient absorption spectroscopy is employed to demonstrate that thermal annealing results in an approximate two‐fold increase in the yield of dissociated charges. The enhanced charge generation is correlated with a decrease in P3HT's ionization potential upon thermal annealing. These observations are in excellent quantitative agreement with a model in which efficient dissociation of the bound radical pair into free charges is dependent upon the bound radical state being thermally hot when initially generated, enabling it to overcome its coulombic binding energy. These observations provide strong evidence that the lowest unoccupied molecular orbital (LUMO) level offset of annealed P3HT/PCBM blends may be only just sufficient to drive efficient charge generation in polythiophene‐based solar cells. This has important implications for current strategies to optimize organic photovoltaic device performance based upon the development of smaller optical bandgap polymers. 相似文献
53.
Cover Feature: Nucleoside‐Based Self‐Assembling Drugs for Localized Drug Delivery (ChemMedChem 11/2018) 下载免费PDF全文
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A global comparison of national biodiesel production potentials 总被引:1,自引:0,他引:1
This study presents a consistent, national-level evaluation of potential biodiesel volumes and prices, replicated across 226 countries, territories, and protectorates. Utilizing all commercially exported lipid feedstocks from existing agricultural lands, we compare the upper-limit potential for expanded biodiesel production in terms of absolute biodiesel volumes, profitable potential from biodiesel exports, and potential from expanded vegetable oil production through agricultural yield increases. Country findings are compared across a variety of economic, energy, and environmental metrics. Our results show an upper-limit worldwide volume potential of 51 billion liters from 119 countries; 47 billion of which could be produced profitably at today's import prices. Also significant production gains are possible through increasing agricultural yields: a 12-fold increase over existing potential, primarily hinging on better management of tropical oilseed varietals. 相似文献
57.
The purposes of this study were to describe: (a) the frequency and correlates of behavior problems among a sample of 2- and 3-year-old children from low-income families as seen by their parents and day care teachers, (b) the degree to which parents and teachers agree about the children's behavior problems in their respective contexts, and (c) family characteristics that distinguish toddlers with behavior problems both at home and at day care from the rest of the sample. Parents of 133 toddlers from 10 Chicago day care centers completed measures of child behavior problems, child behavioral intensity, parenting self-efficacy, discipline strategies, and stress. Children's day care teachers also completed a measure of child behavior problems. Parent-reported behavior problems were associated with higher child behavioral intensity, greater parent stress, lower self-efficacy, and discipline strategies characterized by irritability, coercion, and inconsistency. Parent and teacher ratings on child behavior were correlated for boys' behavior problems only. Parents reported more child behavior problems than teachers. Approximately 8% of the children were rated as having behavior problems at home and at day care. Although most of the children are functioning well, many of these parents and toddlers are engaged in highly stressful and coercive relationships. 相似文献
58.
Enhai Zhao John D. Cressler Monir El-Diwany Tracey L. Krakowski Alexei Sadovnikov Dimitar Kocoski 《Solid-state electronics》2006,50(11-12):1748-1755
We present an investigation of the dependence of low-frequency noise on device geometry in advanced npn silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs). The devices examined in this work have fixed emitter width (WE = 0.4 μm), but varying emitter length (0.5 μm LE 20.0 μm), and thus the ratio of the emitter perimeter (PE) to the emitter area (AE) varies widely, making it ideal for examining geometrical effects. The SPICE noise parameter AF extracted from these devices decreases with increasing LE. Furthermore, the low-frequency noise measured on SiGe HBTs with significantly different PE/AE ratios suggests a possibility that the fundamental noise source for the diffusion base current may be located at the emitter periphery. Transistors with different distances between the emitter edge and the shallow trench edge (XEC), and shallow trench edge to deep trench edge (XTC), are also investigated. The SiGe HBTs with a smaller value of XEC have higher low-frequency noise, but no significant difference is found in devices with varying XTC. Explanations of the observed noise behavior are suggested. 相似文献
59.
Effects of simulated digestion in vitro on cell wall polysaccharides from kiwifruit (Actinidia spp.)
Cell wall polysaccharides are resistant to digestion and absorption in the human small intestine and are considered to be delivered to the colon in a chemically unaltered state. In this paper, pulp from green and gold kiwifruit was subjected to in vitro upper-intestinal tract digestion and the chemical and physical changes to cell wall polysaccharides (dietary fibre) were investigated. Yields of insoluble fibre decreased slightly with simulated digestion while soluble fibre yields increased. Constituent sugar and glycosyl linkage analysis of the soluble and insoluble fibre fractions revealed that the chemical composition and structure of the non-starch polysaccharides remained largely unchanged. However, the degree of methylesterification of galacturonic acid residues present in the pectin-rich soluble fibre fractions of both fruit decreased with treatment; size-exclusion chromatography detected changes in the molecular weight profiles of these fractions. These changes may affect the physicochemical properties and fermentability of kiwifruit dietary fibre in the large intestine. 相似文献
60.
The treatment of acid rock drainage (ARD) places extraordinary financial burdens on governments and companies worldwide, and
an improved efficiency in treatment by as little as 1% can save many millions of dollars in rehabilitation. We investigated
a system for treating Fe-rich ARD using a three-stage reactor design. In the first reaction cell, Fe-rich ARD was partially
neutralised using rapid periodic carbonate resuspension with a rotating axial mixer. This was followed by an air-sparged oxidation
chamber and then a second reaction cell, with more carbonate periodically resuspended until a pH of 6.3 was reached, which
was followed by a settlement chamber. This reactor design has a high capacity for neutralisation, with an efficiency of ≈70%
of acidity neutralised by the acid neutralising capacity (g of CaCO3 equivalent) added to the reactor. Axial mixers were tested because of their low-energy requirements and their high reliability.
The intermediate chamber effectively removes Fe by oxidising Fe(II) to Fe(III). Given the amount of acidity neutralised, the
sludge volume produced was low compared to other technologies, providing further potential savings in sludge handling. Waste
carbonate rock proved to be an effective neutralising agent, even though it was about 60% dolomite and 40% magnesite, with
minor calcite, and despite the fact that magnesite has substantially slower dissolution kinetics compared to the more dominant
dolomite. The mixed waste carbonates were capable of raising the pH sufficiently to reduce the heavy metal loadings in Fe-rich
ARD by more than two orders of magnitude. The final settlement stage of the process was shown to be essential for metal precipitation,
for the carry-over of fine carbonates, and CO2 loss. This was associated with a rise in pH, from 6.3 to 7.5. In addition, residual slow-reacting magnesite from the mixed
carbonate remains in the sludge from the first reactor and provides acid buffering capacity within the sludge, which is commonly
lacking in the ARD neutralisation sludge of other systems. 相似文献