Interfacial charge transfer in nanoscale polymer transistors

Interfacial charge transfer plays an essential role in establishing the relative alignment of the metal Fermi level and the energy bands of organic semiconductors. While the details remain elusive in many systems, this charge transfer has been inferred in a number of photoemission experiments. We present electronic transport measurements in very short channel ($L < 100$ nm) transistors made from poly(3-hexylthiophene) (P3HT). As channel length is reduced, the evolution of the contact resistance and the zero-gate-voltage conductance are consistent with such charge transfer. Short channel conduction in devices with Pt contacts is greatly enhanced compared to analogous devices with Au contacts, consistent with charge transfer expectations. Alternating current scanning tunneling microscopy (ACSTM) provides further evidence that holes are transferred from Pt into P3HT, while much less charge transfer takes place at the Au/P3HT interface.Comment: 19 preprint pages, 6 figure

Variable Stars in Local Group Galaxies. IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II

We present a search and analysis of variable stars in the recently discovered Crater~II dwarf galaxy. Based on $B$, $V$, $I$ data collected with the Isaac Newton Telescope (FoV$\sim$0.44 square degrees) we detected 37 variable stars, of which 34 are bone-fide RR Lyrae stars of Crater~II (28 RRab, 4 RRc, 2 RRd). We applied the metal-independent ($V$, $B-V$) Period--Wesenheit relation and derived a true distance modulus ($\mu$ = 20.30$\pm$0.08 mag ($\sigma$=0.16 mag). Individual metallicities for RR Lyrae stars were derived by inversion of the predicted $I$-band Period-Luminosity relation. We find a mean metallicity of [Fe/H]=-1.64 and a standard deviation of $\sigma_{[Fe/H]}$ =0.21 dex, compatible with either negligible or vanishing intrinsic metallicity dispersion. The analysis of the Colour-Magnitude Diagram reveals a stark paucity of blue horizontal branch stars, at odds with other Galactic dwarfs, and globular clusters with similar metal abundances.Comment: 14 pages, 8 figures, accepted for publications on MNRAS. Time series photometry is available in the manuscript source ta

Temporal networks of face-to-face human interactions

The ever increasing adoption of mobile technologies and ubiquitous services allows to sense human behavior at unprecedented levels of details and scale. Wearable sensors are opening up a new window on human mobility and proximity at the finest resolution of face-to-face proximity. As a consequence, empirical data describing social and behavioral networks are acquiring a longitudinal dimension that brings forth new challenges for analysis and modeling. Here we review recent work on the representation and analysis of temporal networks of face-to-face human proximity, based on large-scale datasets collected in the context of the SocioPatterns collaboration. We show that the raw behavioral data can be studied at various levels of coarse-graining, which turn out to be complementary to one another, with each level exposing different features of the underlying system. We briefly review a generative model of temporal contact networks that reproduces some statistical observables. Then, we shift our focus from surface statistical features to dynamical processes on empirical temporal networks. We discuss how simple dynamical processes can be used as probes to expose important features of the interaction patterns, such as burstiness and causal constraints. We show that simulating dynamical processes on empirical temporal networks can unveil differences between datasets that would otherwise look statistically similar. Moreover, we argue that, due to the temporal heterogeneity of human dynamics, in order to investigate the temporal properties of spreading processes it may be necessary to abandon the notion of wall-clock time in favour of an intrinsic notion of time for each individual node, defined in terms of its activity level. We conclude highlighting several open research questions raised by the nature of the data at hand.Comment: Chapter of the book "Temporal Networks", Springer, 2013. Series: Understanding Complex Systems. Holme, Petter; Saram\"aki, Jari (Eds.

The Host Galaxies of Gamma-Ray Bursts I: ISM Properties of Ten Nearby Long-Duration GRB Hosts

We present the first observations from a large-scale survey of nearby (z < 1) long-duration gamma-ray burst (LGRB) host galaxies, which consist of eight rest-frame optical spectra obtained at Keck and Magellan. Along with two host galaxy observations from the literature, we use optical emission line diagnostics to determine metallicities, ionization parameters, young stellar population ages, and star formation rates. We compare the LGRB host environments to a variety of local and intermediate-redshift galaxy populations, as well as the newest grid of stellar population synthesis and photoionization models generated with the Starburst99/Mappings codes. With these comparisons we investigate whether the GRB host galaxies are consistent with the properties of the general galaxy population, and therefore whether they may be used as reliable tracers of star formation. We find that LGRB host galaxies generally have low-metallicity ISM environments out to z ~ 1. The ISM properties of our GRB hosts, including metallicity, ionization parameter, and young stellar population age, are significantly different from the general galaxy population, host galaxies of nearby broad-lined Type Ic supernovae, and nearby metal-poor galaxies.Comment: 29 pages, 19 figures, 5 tables, accepted for publication in A

Down-regulation of adhesion molecules and other inflammatory biomarkers after moderate wine consumption in healthy women: a randomized trial

Background: Moderate alcohol consumption is cardioprotective. The mechanism for this beneficial effect might be reduced inflammatory responses, as suggested by prospective studies and small clinical trials in men. No studies have evaluated the antiinflammatory effects of wine in women. Objective: We investigated whether low-dose intake of white and red wines has differential effects on inflammatory markers in women. Design: In a crossover study, we randomly assigned 35 healthy women to two 4-wk periods of 20 g ethanol/d as white or red wine, preceded by two 4-wk washout periods. Before and after interventions, we measured serum lipids, circulating inflammatory biomarkers, cellular adhesion molecules (CAMs), and adhesion of monocytes to stimulated endothelial cells. Results: HDL cholesterol increased, and the serum concentrations of high-sensitivity C-reactive protein, intercellular adhesion molecule-1, CD40L, and interleukin-6 decreased after either wine (P< 0.01, all). Vascular CAM-1 and E-selectin decreased (P <0.01) only after red wine. CAM expression by mononuclear cells was blunted after either wine, with a greater suppressant effect of red wine. Enhanced adhesion of monocytes to stimulated endothelial cells was reduced by 51% (95% CI:-57%,-45%) after white wine and by 89% (95% CI: -96%, -82%) after red wine (P <0.01 for between-wine differences). Conclusions: Moderate wine consumption is associated with beneficial effects on various inflammatory pathways related to endothelial activation in women. Probably because of its higher polyphenol content, red wine shows superior antiinflammatory effects than does white wine. Reducing low-grade inflammation and endothelial activation may be another potential mechanism by which alcoholic beverages exert their cardioprotective effect

A Green's function approach to transmission of massless Dirac fermions in graphene through an array of random scatterers

We consider the transmission of massless Dirac fermions through an array of short range scatterers which are modeled as randomly positioned $\delta$- function like potentials along the x-axis. We particularly discuss the interplay between disorder-induced localization that is the hallmark of a non-relativistic system and two important properties of such massless Dirac fermions, namely, complete transmission at normal incidence and periodic dependence of transmission coefficient on the strength of the barrier that leads to a periodic resonant transmission. This leads to two different types of conductance behavior as a function of the system size at the resonant and the off-resonance strengths of the delta function potential. We explain this behavior of the conductance in terms of the transmission through a pair of such barriers using a Green's function based approach. The method helps to understand such disordered transport in terms of well known optical phenomena such as Fabry Perot resonances.Comment: 22 double spaced single column pages. 15 .eps figure

Rebuild the Academy: Supporting academic mothers during COVID-19 and beyond

The issues facing academic mothers have been discussed for decades. Coronavirus Disease 2019 (COVID-19) is further exposing these inequalities as womxn scientists who are parenting while also engaging in a combination of academic related duties are falling behind. These inequities can be solved by investing strategically in solutions. Here we describe strategies that would ensure a more equitable academy for working mothers now and in the future. While the data are clear that mothers are being disproportionately impacted by COVID-19, many groups could benefit from these strategies. Rather than rebuilding what we once knew, let us be the architects of a new world

Elevational Gradients in Bird Diversity in the Eastern Himalaya: An Evaluation of Distribution Patterns and Their Underlying Mechanisms

BACKGROUND: Understanding diversity patterns and the mechanisms underlying those patterns along elevational gradients is critically important for conservation efforts in montane ecosystems, especially those that are biodiversity hotspots. Despite recent advances, consensus on the underlying causes, or even the relative influence of a suite of factors on elevational diversity patterns has remained elusive. METHODS AND PRINCIPAL FINDINGS: We examined patterns of species richness, density and range size distribution of birds, and the suite of biotic and abiotic factors (primary productivity, habitat variables, climatic factors and geometric constraints) that governs diversity along a 4500-m elevational gradient in the Eastern Himalayan region, a biodiversity hotspot within the world's tallest mountains. We used point count methods for sampling birds and quadrats for estimating vegetation at 22 sites along the elevational gradient. We found that species richness increased to approximately 2000 m, then declined. We found no evidence that geometric constraints influenced this pattern, whereas actual evapotranspiration (a surrogate for primary productivity) and various habitat variables (plant species richness, shrub density and basal area of trees) accounted for most of the variation in bird species richness. We also observed that ranges of most bird species were narrow along the elevation gradient. We find little evidence to support Rapoport's rule for the birds of Sikkim region of the Himalaya. CONCLUSIONS AND SIGNIFICANCE: This study in the Eastern Himalaya indicates that species richness of birds is highest at intermediate elevations along one of the most extensive elevational gradients ever examined. Additionally, primary productivity and factors associated with habitat accounted for most of the variation in avian species richness. The diversity peak at intermediate elevations and the narrow elevational ranges of most species suggest important conservation implications: not only should mid-elevation areas be conserved, but the entire gradient requires equal conservation attention

Dark Matter Search Results from the PICO-2L C3F8 Bubble Chamber

New data are reported from the operation of a 2 liter C3F8 bubble chamber in the SNOLAB underground laboratory, with a total exposure of 211.5 kg days at four different energy thresholds below 10 keV. These data show that C3F8 provides excellent electron-recoil and alpha rejection capabilities at very low thresholds. The chamber exhibits an electron-recoil sensitivity of 98.2%. These data also include the first observation of a dependence of acoustic signal on alpha energy. Twelve single nuclear recoil event candidates were observed during the run. The candidate events exhibit timing characteristics that are not consistent with the hypothesis of a uniform time distribution, and no evidence for a dark matter signal is claimed. These data provide the most sensitive direct detection constraints on WIMP-proton spin-dependent scattering to date, with significant sensitivity at low WIMP masses for spin-independent WIMP-nucleon scattering.The PICO Collaboration would like to thank SNOLAB and its staff for providing an exceptional underground laboratory space and invaluable technical support. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under award DE-SC-0012161. Fermi National Accelerator Laboratory is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359. Part of the research described in this paper was conducted under the Ultra Sensitive Nuclear Measurements Initiative at Pacific Northwest National Laboratory, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy. We acknowledge the National Science Foundation for their support including Grants No. PHY-1242637, No. PHY-0919526, and No. PHY-1205987. We acknowledge the support of the National Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation (CFI). We also acknowledge support from the Kavli Institute for Cosmological Physics at the University of Chicago. We acknowledge the financial support of the Spanish Ministerio de Economia y Competitividad, Consolider MultiDark CSD2009-00064 Grant. We acknowledge support from the Department of Atomic Energy (DAE), Government of India, under the Center for AstroParticle Physics II project (CAPP-II) at Saha Insititute of Nuclear Physics (SINP), Kolkata. We acknowledge the Czech Ministry of Education, Youth and Sports, Grant No. LM2011027. We acknowledge technical assistance from Fermilab's Computing, Particle Physics, and Accelerator Divisions, and from A. 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