890 research outputs found

    Correlation between microstructure and magnetotransport in organic semiconductor spin valve structures

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    We have studied magnetotransport in organic-inorganic hybrid multilayer junctions. In these devices, the organic semiconductor (OSC) Alq3_3 (tris(8-hydroxyquinoline) aluminum) formed a spacer layer between ferromagnetic (FM) Co and Fe layers. The thickness of the Alq3_3 layer was in the range of 50-150 nm. Positive magnetoresistance (MR) was observed at 4.2 K in a current perpendicular to plane geometry, and these effects persisted up to room temperature. The devices' microstructure was studied by X-ray reflectometry, Auger electron spectroscopy and polarized neutron reflectometry (PNR). The films show well-defined layers with modest average chemical roughness (3-5 nm) at the interface between the Alq3_3 and the surrounding FM layers. Reflectometry shows that larger MR effects are associated with smaller FM/Alq3_3 interface width (both chemical and magnetic) and a magnetically dead layer at the Alq3_3/Fe interface. The PNR data also show that the Co layer, which was deposited on top of the Alq3_3, adopts a multi-domain magnetic structure at low field and a perfect anti-parallel state is not obtained. The origins of the observed MR are discussed and attributed to spin coherent transport. A lower bound for the spin diffusion length in Alq3_3 was estimated as 43±543 \pm 5 nm at 80 K. However, the subtle correlations between microstructure and magnetotransport indicate the importance of interfacial effects in these systems.Comment: 21 pages, 11 figures and 2 table

    Effects of carrier mobility and morphology in organic semiconductor spin valves

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    We studied spin transport in four organic semiconductors (OSCs) with different electronic properties. Magnetoresistance (MR) effects were observed up to room temperature in junctions based on an electron-carrying OSC, tris(8-hyroxyquinoline) aluminum (Alq3) and a hole-carrying OSC, copper phthalocyanine (CuPc). The MR shows similar temperature dependence for these two OSCs. We also investigated junctions based on two high lateral mobility electron-carrying OSCs, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N,N'-bis(4-trifluoromethylbenzyl)-1,4,5,8-naphthalenetetracarboxylic diimide (CF3-NTCDI). However, these junctions showed much weaker spin transport effects. Morphological studies suggest that these high mobility OSC films have much rougher surfaces than either Alq3 or CuPc, therefore the degradation of spin transport may originate from enhanced scattering due to the rougher FM/OSC interfaces. Our study shows that FM/OSC interfaces play an important role for spin transport in organic devices and need further exploration

    A chronic disease outreach program for Aboriginal communities

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    Background. Our objective is to describe a program to improve awareness and management of hypertension, renal disease, and diabetes in 3 remote Australian Aboriginal communities. Methods. The program espouses that regular integrated checks for chronic disease and their risk factors are essential elements of regular adult health care. Programs should be run by local health workers, following algorithms for testing and treatment, with backup, usually from a distance, from nurse coordinators. Constant evaluation is essential to develop community health profiles and adapt program structure. Results. Participation ranged from 65% to 100% of adults. Forty-one percent of women and 72% of men were current smokers. Body weight varied markedly by community. Although excessive in all, rates of chronic diseases also differed markedly among communities. Rates increased with age, but the greatest numbers of people with morbidities were middle age and young adults. Multiple morbidities were common by middle age. Hypertension and renal disease were early features, whereas diabetes was a variable and later manifestation of this integrated chronic disease syndrome. Adherence to testing and treatment protocols improved markedly over time. Substantial numbers of new diagnoses were made. Blood pressure improved in people in whom antihypertensive agents were started or increased. Components of a systematic activity plan became more clearly defined with time. Treatment of people in the community with the greatest disease burden posed a large additional workload. Lack of health workers and absenteeism were major impediments to productivity. Conclusion. We cannot generalize about body habitus, and chronic disease rates among Aboriginal adults. Pilot data are needed to plan resources based on the chronic disease burden in each community. Systematic screening is useful in identifying high-risk individuals, most at an early treatable stage. Community-based health profiles provide critical information for the development of rational health policy and needs-based health services

    Effects of syntactic cueing therapy on picture naming and connected speech in acquired aphasia

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    Language therapy for word-finding difficulties in aphasia usually involves picture naming of single words with the support of cues. Most studies have addressed nouns in isolation, even though in connected speech nouns are more frequently produced with determiners. We hypothesised that improved word finding in connected speech would be most likely if intervention treated nouns in usual syntactic contexts. Six speakers with aphasia underwent language therapy using a software program developed for the purpose, which provided lexical and syntactic (determiner) cues. Exposure to determiners with nouns would potentially lead to improved picture naming of both treated and untreated nouns, and increased production of determiner plus noun combinations in connected speech. After intervention, picture naming of treated words improved for five of the six speakers, but naming of untreated words was unchanged. The number of determiner plus noun combinations in connected speech increased for four speakers. These findings attest to the close relationship between frequently co-occurring content and function words, and indicate that intervention for word-finding deficits can profitably proceed beyond single word naming, to retrieval in appropriate syntactic contexts. We also examined the relationship between effects of therapy, and amount and intensity of therapy. We found no relationship between immediate effects and amount or intensity of therapy. However, those participants whose naming maintained at follow-up completed the therapy regime in fewer sessions, of relatively longer duration. We explore the relationship between therapy regime and outcomes, and propose future considerations for research

    The Reach of the Fermilab Tevatron and CERN LHC for Gaugino Mediated SUSY Breaking Models

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    In supersymmetric models with gaugino mediated SUSY breaking (inoMSB), it is assumed that SUSY breaking on a hidden brane is communicated to the visible brane via gauge superfields which propagate in the bulk. This leads to GUT models where the common gaugino mass m1/2m_{1/2} is the only soft SUSY breaking term to receive contributions at tree level. To obtain a viable phenomenology, it is assumed that the gaugino mass is induced at some scale McM_c beyond the GUT scale, and that additional renormalization group running takes place between McM_c and MGUTM_{GUT} as in a SUSY GUT. We assume an SU(5) SUSY GUT above the GUT scale, and compute the SUSY particle spectrum expected in models with inoMSB. We use the Monte Carlo program ISAJET to simulate signals within the inoMSB model, and compute the SUSY reach including cuts and triggers approriate to Fermilab Tevatron and CERN LHC experiments. We find no reach for SUSY by the Tevatron collider in the trilepton channel. %either with or without %identified tau leptons. At the CERN LHC, values of m1/2=1000m_{1/2}=1000 (1160) GeV can be probed with 10 (100) fb1^{-1} of integrated luminosity, corresponding to a reach in terms of mtgm_{\tg} of 2150 (2500) GeV. The inoMSB model and mSUGRA can likely only be differentiated at a linear e+ee^+e^- collider with sufficient energy to produce sleptons and charginos.Comment: 17 page revtex file with 9 PS figure

    Viable Supersymmetric Models with an Inverted Scalar Mass Hierarchy at the GUT Scale

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    Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation matter scalars, and sub-TeV third generation and Higgs scalars) have been proposed to ameliorate phenomenological problems arising from flavor changing neutral currents (FCNCs) and CP violating processes, while satisfying conditions of naturalness. Models with an IMH already in place at the GUT scale have been shown to be constrained in that for many model parameter choices, the top squark squared mass is driven to negative values. We delineate regions of parameter space where viable models with a GUT scale IMH can be generated. We find that larger values of GUT scale first and second generation scalar masses act to suppress third generation scalars, leading to acceptable solutions if GUT scale gaugino masses are large enough. We show examples of viable models and comment on their characteristic features. For example, in these models the gluino mass is bounded from below, and effectively decouples, whilst third generation scalars remain at sub-TeV levels. While possibly fulfilling criteria of naturalness, these models present challenges for detection at future pp and e^+e^- collider experiments.Comment: 16 page REVTEX file with 6 PS figure

    International Stem Cell Collaboration: How Disparate Policies between the United States and the United Kingdom Impact Research

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    As the scientific community globalizes, it is increasingly important to understand the effects of international collaboration on the quality and quantity of research produced. While it is generally assumed that international collaboration enhances the quality of research, this phenomenon is not well examined. Stem cell research is unique in that it is both politically charged and a research area that often generates international collaborations, making it an ideal case through which to examine international collaborations. Furthermore, with promising medical applications, the research area is dynamic and responsive to a globalizing science environment. Thus, studying international collaborations in stem cell research elucidates the role of existing international networks in promoting quality research, as well as the effects that disparate national policies might have on research. This study examined the impact of collaboration on publication significance in the United States and the United Kingdom, world leaders in stem cell research with disparate policies. We reviewed publications by US and UK authors from 2008, along with their citation rates and the political factors that may have contributed to the number of international collaborations. The data demonstrated that international collaborations significantly increased an article's impact for UK and US investigators. While this applied to UK authors whether they were corresponding or secondary, this effect was most significant for US authors who were corresponding authors. While the UK exhibited a higher proportion of international publications than the US, this difference was consistent with overall trends in international scientific collaboration. The findings suggested that national stem cell policy differences and regulatory mechanisms driving international stem cell research in the US and UK did not affect the frequency of international collaborations, or even the countries with which the US and UK most often collaborated. Geographical and traditional collaborative relationships were the predominate considerations in establishing international collaborations

    Functional Polymorphisms in IL13 Are Protective against High Schistosoma mansoni Infection Intensity in a Brazilian Population

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    IL-13 is a signature cytokine of the helper T cell type 2 (TH2) pathway which underlies host defense to helminthic infection and activates production of IgE in both parasitized populations and in urban settings after allergen exposure.Two functional polymorphisms in IL13, rs1800925 (or c.1-1111C>T) and rs20541 (or R130Q) were previously found to be associated with Schistosoma hematobium infection intensity. They have not been thoroughly explored in S. mansoni-endemic populations, however, and were selected along with 5 tagging SNPs for genotyping in 812 individuals in 318 nuclear families from a schistosomiasis-endemic area of Conde, Bahia, in Brazil. Regression models using GEE to account for family membership and family-based quantitative transmission disequilibrium tests (QTDT) were used to evaluate associations with total serum IgE (tIgE) levels and S. mansoni fecal egg counts adjusted for non-genetic covariates. We identified a protective effect for the T allele at rs20541 (P = 0.005) against high S. mansoni egg counts, corroborated by QTDT (P = 0.014). Our findings also suggested evidence for protective effects for the T allele at rs1800925 and A allele at rs2066960 after GEE analysis only (P = 0.050, 0.0002).The two functional variants in IL13 are protective against high S. mansoni egg counts. These markers showed no evidence of association with tIgE levels, unlike tIgE levels previously studied in non-parasitized or atopic study populations
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