Understanding Local and Macroscopic Electron Mobilities in the Fullerene Network of Conjugated Polymer‐based Solar Cells: Time‐Resolved Microwave Conductivity and Theory

The efficiency of bulk heterojunction (BHJ) organic photovoltaics is sensitive to the morphology of the fullerene network that transports electrons through the device. This sensitivity makes it difficult to distinguish the contrasting roles of local electron mobility (how easily electrons can transfer between neighboring fullerene molecules) and macroscopic electron mobility (how well‐connected is the fullerene network on device length scales) in solar cell performance. In this work, a combination of density functional theory (DFT) calculations, flash‐photolysis time‐resolved microwave conductivity (TRMC) experiments, and space‐charge‐limit current (SCLC) mobility estimates are used to examine the roles of local and macroscopic electron mobility in conjugated polymer/fullerene BHJ photovoltaics. The local mobility of different pentaaryl fullerene derivatives (so‐called ‘shuttlecock’ molecules) is similar, so that differences in solar cell efficiency and SCLC mobilities result directly from the different propensities of these molecules to self‐assemble on macroscopic length scales. These experiments and calculations also demonstrate that the local mobility of phenyl‐C₆₀ butyl methyl ester (PCBM) is an order of magnitude higher than that of other fullerene derivatives, explaining why PCBM has been the acceptor of choice for conjugated polymer BHJ devices even though it does not form an optimal macroscopic network. The DFT calculations indicate that PCBM's superior local mobility comes from the near‐spherical nature of its molecular orbitals, which allow strong electronic coupling between adjacent molecules. In combination, DFT and TRMC techniques provide a tool for screening new fullerene derivatives for good local mobility when designing new molecules that can improve on the macroscopic electron mobility offered by PCBM.     

Optical and electrical properties and phonon drag effect in low temperature TEP measurements of AgSbSe2 thin films

Polycrystalline thin films of silver antimony selenide have been deposited using a reactive evaporation technique onto an ultrasonically cleaned glass substrate at a vacuum of 10-5 torr. The preparative parameters, like substrate temperature and incident fluxes, have been properly controlled in order to get stoichiometric, good quality and reproducible thin film samples. The samples are characterized by XRD, SEM, AFM and a UV-vis-NIR spectrophotometer. The prepared sample is found to be polycrystalline in nature. From the XRD pattern, the average particle size and lattice constant are calculated. The dislocation density, strain and number of crystallites per unit area are evaluated using the average particle size. The dependence of the electrical conductivity on the temperature has also been studied and the prepared AgSbSe2 samples are semiconducting in nature. The AgSbSe2 thin films exhibited an indirect allowed optical transition with a band gap of 0.64 eV. The compound exhibits promising thermoelectric properties, a large Seebeck coefficient of 30 mV/K at 48 K due to strong phonon electron interaction. It shows a strong temperature dependence on thermoelectric properties, including the inversion of a dominant carrier type from p to n over a low temperature range 9-300 K, which is explained on the basis of a phonon drag effect.     

Influence of Texture on Taste: Insights Gained During Studies of Hardness, Juiciness, and Sweetness of Apple Fruit

Apple flesh can be considered as a living structure within which juice and tastants are encapsulated in individual cells. The breakdown of this structure and release of juice varies between hard and soft apples. We hypothesized that the texture of the fruit and the way it releases juice during chewing would therefore influence the perception of sweetness. Time‐intensity (TI) techniques were used by a trained panel to study the temporal changes in the intensity of “juiciness” and “sweetness” during consumption of apples that varied in mechanical hardness (measured by puncture test). All apple samples had a similar water content, but the pattern of juice release was markedly different. Juice was released into the mouth in a pattern of increasing and then deceasing intensity. The maximum intensity (Imax), duration of the stimulus (DUR), and area under the TI curve (AUC) were significantly higher for hard compared with soft apples. The impact of juice release on perception of sweetness was examined using apples in which the Imax and AUC for juiciness of soft apples were half the value of those for firm apples. There was no consistent difference in Imax, DUR, or AUC for sweet taste in these 2 sets of apples. We concluded that sufficient juice was released from soft and less juicy apples to ensure that sweetness perception was maximized. These results are discussed in relation to earlier studies that demonstrated that texture (thickening agents) suppresses flavor perception in solutions and juices.     

Using Public Housing to Achieve Self-Sufficiency: Can We Predict Success?

In the United States since the mid-1980s, self-sufficiency programs have sought to transform public housing developments from permanent housing into way stations for low-income people. This article presents exploratory research on the predictors of success in these programs. Statistical analysis of longitudinal survey data from participants in an early public housing self-sufficiency program points to lack of previous welfare experience and the presence of prior vocational training as being predictors of program success. In-depth interviews suggest that having a high-school education is important for success, and any additional education prior to participating in a self-sufficiency program is helpful. Interviews also indicate that successful program graduates alienate themselves from social groups that discourage self-sufficiency.     

In‐depth characterization of granular starch‐graft‐polyester compositions as obtained by in situ polymerization of lactones from the starch surface

The synthesis of poly(ε‐caprolactone) (PCL)‐grafted granular starch was carried out either in bulk (without solvent) or in toluene suspension by a two‐step procedure. First step relied upon the activation of the hydroxyl groups available at the starch surface by alkylaluminum derivatives like AlEt₃ and removal of non‐surface‐grafted organo‐aluminum active species. The latter species were made free in solution by reaction with the remaining water molecules still contaminating the polymerization medium despite intensive drying of the starch granules. In the second step, ε‐caprolactone was polymerized via a coordination‐insertion ring‐opening polymerization as initiated by the surface‐grafted aluminum alkoxide species. The present contribution aims at investigating various parameters such as nature of the alkyl aluminum activator and monomer (δ‐valerolactone was studied as well), temperature, concentration, and addition of a solvent (polymerization in toluene suspension), reaction time, and also the experimental procedure used to recover the polyester chains and measure the grafting efficiency. It turns out that, under the studied conditions, dialkylaluminum alkoxides surface‐grafted onto the starch granules were more likely generated and promote a fast polymerization reaction with the formation of grafted PCL chains with a molecular weight that can be as high as 225 000 (M_n value) for polymerization carried out in toluene suspension. Copyright © 2004 Society of Chemical Industry     

Public policy and biofuels: The way forward?

The use of biofuels has been given much attention by governments around the world, especially in increasingly energy-hungry OECD nations. Proponents have argued that they offer various advantages over hydrocarbon-based fuels, especially with respect to reducing dependence on OPEC-controlled oil, minimizing greenhouse gas (GHG) emissions, and ensuring financial and lifestyle continuity to farmers and agriculturally dependent communities. This paper adds to the continuing technical debate by addressing the issue from a holistic public policy perspective. In particular, it looks at the proposed benefits of biofuels, yet also addresses the implications of increased demand on the global and regional environment, in addition to the economic welfare of developing nations. Furthermore, it posits that short-term reliance on biofuels vis-à-vis other alternative energy sources may potentially inhibit the development and maturation of longer-term technologies that have greater potential to correct the harmful effects of fossil-fuel dependence. In light of this, the manifold policy instruments currently employed or proposed by governments in developed nations to promote biofuels emerge as questionable.     

Lexical acquisition in elementary science classes.

The purpose of this study was to further researchers' understanding of lexical acquisition in the beginning primary schoolchild by investigating word learning in small-group elementary science classes. Two experiments were conducted to examine the role of semantic scaffolding (e.g., use of synonymous terms) and physical scaffolding (e.g., pointing to referents) in children's acquisition of novel property terms. Children's lexical knowledge was assessed using multiple tasks (naming, comprehension, and definitional). Children struggled to acquire meanings of adjectives without semantic or physical scaffolding (Experiment 1), but they were successful in acquiring extensive lexical knowledge when offered semantic scaffolding (Experiment 2). Experiment 2 also shows that semantic scaffolding used in combination with physical scaffolding helped children acquire novel adjectives and that children who correctly named pictures of adjectives had acquired definitions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of Consultancy skills for future IT professionals via group working

Organisations face an increasingly competitive and uncertain global environment, after recent experience of unparalleled technological advances and political shifts. Increased dependence on Information Technology (IT) will require appropriate human resource strategies, to develop individuals who will be capable of operating successfully within new organisational structures, with reduced management layers and a requirement for teamworking. This paper presents a university-industry based partnership, revolving around a final year Group Consultancy project, in which undergraduate students work with an external client on a live problem. The project involves the use ofaction research methodology, where academic ideas are applied in the ‘real’ world of business. This is described in the context of group projects, which examine thelegacy system problems faced by three multi-national organisations. Revans, the unsung hero of Action Learning, who showed me that the best learning happens in real life with real problems and real people, and not in classrooms with know-all teachersCharles Handy The Age of Unreason, p45     

Two-year-olds' search strategies and visual tracking in a hidden displacement task.

Children younger than 3 years have difficulty with search tasks that involve hidden displacement. Partial visual information was provided about a ball's path as it moved toward a hiding place. Children (2.0 and 2.5 years old) saw a ball rolling down a ramp placed behind a transparent screen with 4 opaque doors. A wall, placed on the ramp and directly behind 1 of the doors, protruded above the screen and stopped the ball. Children were asked to find the ball. The transparency of the screen permitted visual tracking of the ball between the doors, but its final resting place was obscured. Both age groups were equally proficient at tracking the ball as it rolled behind the screen, but the 2.5-year-olds were more likely to reach to the correct door. Looking behavior was related to errors in the younger group in that tracking that stopped short or continued past the correct door was associated with incorrect choices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)