Optical and Electronic Investigation of Hydrogen-Bonded Organic Semiconductor Quinacridone

The viability of solar power is currently limited by the expense and processing limitations of existing inorganic technology. Organic semiconductors offer the possibility of scalable, economically appealing solar cell technologies. Quinacridone is a promising material which has recently been shown to have electronic properties comparable to the fully π-conjugated, but structurally similar pentacene, while remaining chemically stable in air. In order to better understand the potential of quinacridone as a candidate material for viable, next generation solar cells we have fabricated a number of thin-film samples and device structures and characterized them by a suite of optical and electronic tests. Absorbance and temperature-dependent photoluminescence studies were used as a probe to investigate the electronic states of vapor deposited quinacridone thin films, finding exciton binding energies consistent with excitonic states delocalized across several molecules. Impedance spectroscopy measurements were used to measure the temperature-dependent photoconductivity of Gold : Quinacridone : Gold MSM structures, finding that quinacridone is almost an order of magnitude more conductive under laser illumination. Diode structures of ITO:PEDOT:Quinacridone:Al were fabricated to measure the IV characteristics under light and dark conditions, as well as the transient photocurrent and photovoltage. These studies confirmed that the light current generation of the diodes was not limited by charge transfer state lifetimes, as charge extraction occurs on a much faster time scale. However, we found that the low mobility of our quinacridone thin films, caused by their low crystalline order, decreased the probability of exciton dissociation, limiting the production of usable power

The concept of community and the character of networks

Many case studies have examined Community Networks and we have at hand a good many rich and well grounded accounts of local experiences and outcomes as they have been observed in local circumstances. This sort of detailed, highly contextualized empirical work is essential to an understanding of contingent phenomena such as the performance of a Community Network. What we also need though, are theoretical approaches that are abstract enough to interpret the character and performance of differently situated Community Networks. The concept of community, the character of networks, and the implications of marrying the two, need to be teased out. To this end, I suggest that Community Networks be understood analytically as amodern hybrids that derive their ontological characteristics from a conflation of binaries. From this analytic perspective the Community Network is seen to be a sociotechnical assemblage that hybridizes the social and the technical, and not a set of technologies brought to bear on the social. The innovative feature of this particular form of sociotechnical assemblage, from an analytic point of view, is that it brings together community and network as both ontological concepts and as empirically observable phenomenon. The characterization of the assemblage as a community but also as a network is thus critiqued, and the differences between these two abstractions are explored, and it is further argued that the contrary ontology of the assemblage manifest structures that are at once heterarchic, and hierarchic

06061 Abstracts Collection -- Theory of Evolutionary Algorithms

From 05.02.06 to 10.02.06, the Dagstuhl Seminar 06061 ``Theory of Evolutionary Algorithms\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Wafer-Scale Nanopatterning and Translation into High-Performance Piezoelectric Nanowires

The development of a facile method for fabricating one-dimensional, precisely positioned nanostructures over large areas offers exciting opportunities in fundamental research and innovative applications. Large-scale nanofabrication methods have been restricted in accessibility due to their complexity and cost. Likewise, bottom-up synthesis of nanowires has been limited in methods to assemble these structures at precisely defined locations. Nanomaterials such as PbZr_xTi_(1−x)O_3 (PZT) nanowires (NWs)—which may be useful for nonvolatile memory storage (FeRAM), nanoactuation, and nanoscale power generation—are difficult to synthesize without suffering from polycrystallinity or poor stoichiometric control. Here, we report a novel fabrication method which requires only low-resolution photolithography and electrochemical etching to generate ultrasmooth NWs over wafer scales. These nanostructures are subsequently used as patterning templates to generate PZT nanowires with the highest reported piezoelectric performance (d_(eff) ~ 145 pm/V). The combined large-scale nanopatterning with hierarchical assembly of functional nanomaterials could yield breakthroughs in areas ranging from nanodevice arrays to nanodevice powering

Separation of suspended particles in microfluidic systems by directional-locking in periodic fields

We investigate the transport and separation of overdamped particles under the action of a uniform external force in a two-dimensional periodic energy landscape. Exact results are obtained for the deterministic transport in a square lattice of parabolic, repulsive centers that correspond to a piecewise-continuous linear-force model. The trajectories are periodic and commensurate with the obstacle lattice and exhibit phase-locking behavior in that the particle moves at the same average migration angle for a range of orientation of the external force. The migration angle as a function of the orientation of the external force has a Devil's staircase structure. The first transition in the migration angle was analyzed in terms of a Poincare map, showing that it corresponds to a tangent bifurcation. Numerical results show that the limiting behavior for impenetrable obstacles is equivalent to the high Peclet number limit in the case of transport of particles in a periodic pattern of solid obstacles. Finally, we show how separation occurs in these systems depending on the properties of the particles

Antibody-Based Ticagrelor Reversal Agent in Healthy Volunteers.

BACKGROUND: Ticagrelor is an oral P2Y12 inhibitor that is used with aspirin to reduce the risk of ischemic events among patients with acute coronary syndromes or previous myocardial infarction. Spontaneous major bleeding and bleeding associated with urgent invasive procedures are concerns with ticagrelor, as with other antiplatelet drugs. The antiplatelet effects of ticagrelor cannot be reversed with platelet transfusion. A rapid-acting reversal agent would be useful. METHODS: In this randomized, double-blind, placebo-controlled, phase 1 trial, we evaluated intravenous PB2452, a monoclonal antibody fragment that binds ticagrelor with high affinity, as a ticagrelor reversal agent. We assessed platelet function in healthy volunteers before and after 48 hours of ticagrelor pretreatment and again after the administration of PB2452 or placebo. Platelet function was assessed with the use of light transmission aggregometry, a point-of-care P2Y12 platelet-reactivity test, and a vasodilator-stimulated phosphoprotein assay. RESULTS: Of the 64 volunteers who underwent randomization, 48 were assigned to receive PB2452 and 16 to receive placebo. After 48 hours of ticagrelor pretreatment, platelet aggregation was suppressed by approximately 80%. PB2452 administered as an initial intravenous bolus followed by a prolonged infusion (8, 12, or 16 hours) was associated with a significantly greater increase in platelet function than placebo, as measured by multiple assays. Ticagrelor reversal occurred within 5 minutes after the initiation of PB2452 and was sustained for more than 20 hours (P\u3c0.001 after Bonferroni adjustment across all time points for all assays). There was no evidence of a rebound in platelet activity after drug cessation. Adverse events related to the trial drug were limited mainly to issues involving the infusion site. CONCLUSIONS: In healthy volunteers, the administration of PB2452, a specific reversal agent for ticagrelor, provided immediate and sustained reversal of the antiplatelet effects of ticagrelor, as measured by multiple assays. (Funded by PhaseBio Pharmaceuticals; ClinicalTrials.gov number, NCT03492385.)

A national level assessment of metal contamination in bats

Abstract Many populations of bat species across the globe are declining, with chemical contamination one of many potential stressors implicated in these demographic changes. Metals still contaminate a wide range of habitats, but the risks to bats remain poorly understood. This study is the first to present a national scale assessment of toxic metal (Cd, Pb) and essential trace metal (Cu, Zn) concentrations in bats. Metal concentrations in tissues (kidneys, liver, stomach -stomach content, bones and fur) were measured in 193 Pipistrellus sp. in England and Wales using ICP-MS, and compared to critical toxic concentrations for small mammals. The concentrations of metals determined in bat tissues were generally lower than those reported elsewhere. Strong positive associations were found between concentrations in tissues for a given metal (liver and kidneys for Cd, Cu and Pb; stomach and fur and fur and bones for Pb), suggesting recent as well as long term exposure to these contaminants. In addition, positive correlations between concentrations of different metals in the same tissues (Cd and Zn, Cu and Zn, Cd and Pb, Pb and Zn) suggest a co-exposure of metals to bats. Approximately 21% of the bats sampled contained residues of at least one metal at concentrations high enough to elicit toxic effects (associated with kidney damage), or to be above the upper level measured in other mammal species. Pb was found to pose the greatest risk (with 7–11% of the bats containing concentrations of toxicological concern), followed by Cu (4–9%), Zn (0.5–5.2%) and Cd (0%). Our data suggest that leaching of metals into our storage matrix, formaldehyde, may have occurred, especially for Cu. The overall findings suggest that metal contamination is an environmental stressor affecting bat populations, and that further research is needed into the direct links between metal contamination and bat population declines worldwide

Fur : A non-invasive approach to monitor metal exposure in bats

This paper presents a novel assessment of the use of fur as a non-invasive proxy to biomonitor metal contamination in insectivorous bats. Concentrations of metals (cadmium, copper, lead and zinc) were measured using ICP-MS in tissues (kidneys, liver, stomach and stomach content, bones and fur) obtained from 193 Pipistrellus pipistrellus/pygmaeus bats. The bats were collected across a gradient of metal pollution in England and Wales. The utility of small samples of fur as an indicator of metal exposure from the environment was demonstrated with strong relationships obtained between the concentrations of non-essential metals in fur with concentrations in stomach content, kidneys, liver and bones. Stronger relationships were observed for non-essential metals than for essential metals. Fur analyses might therefore be a useful non-invasive proxy for understanding recent, as well as long term and chronic, metal exposure of live animals. The use of fur may provide valuable information on the level of endogenous metal exposure and contamination of bat populations and communities