Pyrene–benzothiadiazole-based copolymers for application in photovoltaic devices

The preparation and characterisation of four narrow band gap pyrene-benzothiadiazole based alternating copolymers is presented. An investigation of the impact of attaching different solubilising groups to the pyrene repeat units on the optical, electrochemical and thermal properties of the resulting materials was undertaken along with studies on the aggregation of polymer chains in the solid state. Unsurprisingly, polymers which had the smaller 2-ethylhexyl chains attached to the pyrene units (PPEH-DTBT and PPEH-DTffBT) displayed lower molecular weights relative to polymers with larger 2-hexyldecyl substituents (PPHD-DTBT and PPHD-DTffBT). Despite this, the 2-ethylhexyl substituted polymers displayed narrower optical band gaps relative to their analogous 2-hexyldecyl substituted polymers. Of all polymers synthesised, PPEH-DTBT displayed the lowest optical band gap (1.76 eV) in the series. All polymers display degradation temperatures in excess of 300°C. Polymers with smaller alkyl chains on the pyrene units display shallower HOMO levels which could be due to increased intramolecular charge transfer between the donor and acceptor units. Preliminary investigations on bulk heterojunction solar cells with a device structure ITO/PEDOT:PSS/Polymer:PC70BM/Ca/Al were undertaken. Polymer/PC70BM blend ratios of 1/3 were used in these studies and have indicated that PPEH-DTBT displayed the highest efficiency with a PCE of 1.86 %

Emergent global oscillations in heterogeneous excitable media: The example of pancreatic beta cells

Using the standard van der Pol-FitzHugh-Nagumo excitable medium model I demonstrate a novel generic mechanism, diversity, that provokes the emergence of global oscillations from individually quiescent elements in heterogeneous excitable media. This mechanism may be operating in the mammalian pancreas, where excitable beta cells, quiescent when isolated, are found to oscillate when coupled despite the absence of a pacemaker region.Comment: See home page http://lec.ugr.es/~julya

Progress Report on E356

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

The Gamow-Teller Strength Function for 37-Cl → 37-Ar

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Reducing conflict-related employee strain: The benefits of an internal locus of control and a problem-solving conflict management strategy

Workplace conflict is a potent stressor, but most previous research has focused on its effect on productivity and performance rather than on individual well-being. This paper examines the moderating roles of an individual's internal locus of control and a problem-solving conflict management strategy. In the cross-sectional study, among 774 health care workers in the Netherlands, employees' internal locus of control did moderate the relationship between experienced conflict at work and psychological strain, which was measured using a 13-item Dutch adaptation of the Occupational Stress Indicator. In addition, this moderation was mediated by the active conflict management strategy of problem solving; people with a more internal locus of control use a problem-solving conflict management strategy more often and, as a result, experience less psychological strain in cases of workplace conflict. Implications for conflict theory, for future research, and for practice are discussed

Understanding Scientific Practices: The Role of Robustness Notions

This article explores the role of `robustness-notions¿ in an account of the engineering sciences. The engineering sciences aim at technological production of, and intervention with phenomena relevant to the (dis-)functioning of materials and technological devices, by means of scientific understanding thereof. It is proposed that different kinds of robustness-notions enable and guide scientific research: (1) Robustness is as a metaphysical belief that we have about the physical world ¿ i.e., we believe that the world is robust in the sense that the same physical conditions will always produce the same effects. (2) `Same conditions ¿ same effects¿ functions as a regulative principle that enables and guides scientific research because it points to, and justifies methodological notions. (3) Repetition, variance and multiple-determination function as methodological criteria for scientific methods that justify the acceptance of epistemological and ontological results. (4) Reproducibility and stability function as ontological criteria for the acceptance of phenomena described by A¿B. (5) Reliability functions as an epistemological criterion for the acceptance of epistemological results, in particular law¿like knowledge of a conditional form: ¿A¿B, provided Cdevice, and unless other known and/or unknown causally relevant conditions.¿ The crucial question is how different kinds of robustness¿notions are related and how they play their part in the production and acceptance of scientific results. Focus is on production and acceptance of physical phenomena and the rule-like knowledge thereof. Based on an analysis of how philosoophy of science tradtionally justified scientific knowledge, I propose a general schema that specifies how inferences to the claim that a scientific result has a certain epistem ological property (such as truth) are justified by scientific methods that meet specific methodological criteria. It is proposed that `same conditions ¿ same effects¿ as a regulative criterion justifies `repetition, variation and ultiple¿determination¿ as methodological criteria for the production and acceptance of (ontological and epistemological) scientific result

Fractal floc size, settling velocity and implications for water clarity in partially mixed-estuaries: the role of small, organic-rich particles

Observations and analysis presented here suggest that properties of suspended particulate matter (SPM) in the water column of partially mixed estuaries, including floc size and settling velocity, are strongly related to the relative concentrations of inorganic versus organic matter in suspension. In regions with high inorganic SPM concentrations, addition of organic matter tends to increase the median size and settling velocity of flocs, removing both organic and inorganic SPM from the water column and enhancing water clarity relative to that in the absence of organics. In contrast, in regions with lower inorganic SPM concentration, suspended organic matter appears to decrease the median size and settling velocity of flocs, which keeps SPM in suspension and reduces water clarity relative to that seen in the absence of organics. Smaller particle sizes also have larger surface area to volume ratios, increasing light scattering and further degrading light penetration. The ecological and water quality ramifications with regards to light penetration and water clarity are significant. Specific sections of moderate energy, partially-mixed estuaries tend to have enhanced fractions of inorganic versus organic matter in suspension in response to positive feedbacks driven by settling velocity and estuarine residual transport. In the upper water column, higher percent organic matter, smaller floc size, smaller settling velocity, and lower SPM concentration are favored. Conversely, in the lower water column, higher percent inorganic matter, larger floc size, larger settling velocity, and higher SPM concentration are favored. Interaction with two-layer transport patterns then promotes estuarine trapping of inorganic matter relative to organic matter. Estuarine residual transport further segregates organic and inorganic matter along the length of partially mixed estuaries, causing smaller, organicrich, slowly settling flocs to make up a larger fraction of SPM in the lower estuary. In contrast, flocs in the upper estuary tend to be larger, dominantly inorganic, and have larger settling velocities. In response to estuarine eutrophication (i.e., an increase in the rate of supply of organic matter), floc size and settling velocity are likely to evolve differently in distinct sections of partially mixed estuaries and differently in more turbid versus less turbid systems. In areas of relatively high inorganic sediment concentration, such as the upper estuary, organic matter and sediment will combine into larger, rapidly settling flocs, and more inorganic matter is likely to settle to the bed than in the absence of eutrophication. This may locally result in a net improvement in water clarity in the upper water column relative to less eutrophic conditions. When eutrophication occurs in the lower estuary, however, lower concentrations of inorganic sediment combined with increased organic matter will favor smaller, more slowly settling flocs. The net result will be more SPM in suspension and decreased water clarity. Because of these feedback mechanisms, it is also possible that partially mixed estuaries with relatively high inorganic SPM concentrations will see net improvement of upper water column clarity in response to eutrophication, while estuaries with low inorganic SPM concentrations will see marked degradation of water clarity. This study synthesizes observations collected by the authors in three large, partially mixed estuaries located along the mid-Atlantic coast of the United States, specifically the Chesapeake Bay, the Potomac River, and the York River. Floc size distributions were determined via in situ laser diffraction and floc imaging, while organic and inorganic SPM concentrations were quantified by filtration of co-located water samples. Beam attenuation measured water clarity, and bulk floc density was estimated by dividing mass concentration by volume concentration. Floc settling velocity was estimated via a modified Stokes Law as a function of floc size and density. Size-specific floc settling velocity and bulk density were also estimated by settling camera image analysis where possible

Scoped types and aspects for real-time Java

Abstract. Real-time systems are notoriously difficult to design and implement, and, as many real-time problems are safety-critical, their solutions must be reliable as well as efficient and correct. While higher-level programming models (such as the Real-Time Specification for Java) permit real-time programmers to use language features that most programmers take for granted (objects, type checking, dynamic dispatch, and memory safety) the compromises required for real-time execution, especially concerning memory allocation, can create as many problems as they solve. This paper presents Scoped Types and Aspects for Real-Time Systems (STARS) a novel programming model for real-time systems. Scoped Types give programmers a clear model of their programs ’ memory use, and, being statically checkable, prevent the run-time memory errors that bedevil models such as RTSJ. Our Aspects build on Scoped Types guarantees so that Real-Time concerns can be completely separated from applications ’ base code. Adopting the integrated Scoped Types and Aspects approach can significantly improve both the quality and performance of a real-time Java systems, resulting in simpler systems that are reliable, efficient, and correct.