Switching the Conductance of a Molecular Junction using a Proton Transfer Reaction

A novel mechanism for switching a molecular junction based on a proton transfer reaction triggered by an external electrostatic field is proposed. As a specific example to demonstrate the feasibility of the mechanism, the tautomers [2,5-(4-hydroxypyridine)] and {2,5-[4(1H)-pyridone]} are considered. Employing a combination of first-principles electronic structure calculations and Landauer transport theory, we show that both tautomers exhibit very different conductance properties and realize the "on" and "off" states of a molecular switch. Moreover, we provide a proof of principle that both forms can be reversibly converted into each other using an external electrostatic field.Comment: 14 pages, 5 figure

Servidor de datos y página web para el aprendizaje de SIG en la ingeniería forestal

Los Sistemas de Información geográfica (SIG) son una herramienta de trabajo habitual en el ámbito de la ingeniería forestal, tanto en la faceta de redacción de proyectos, como en la investigación sobre el medio ambiente y el territorio. Cada vez hay más información cartográfica disponible desde servidores de diferentes instituciones, por lo que consideramos que es muy útil contar con una herramienta de organización de la información. En el trabajo que se presenta, se pretende proporcionar a los estudiantes e investigadores en materia forestal un portal que contenga información actualizada y ordenada sobre los recursos existentes compatibles con los SIG. Por tanto constituiráuna herramienta de apoyo que facilitarála fase de documentación, búsqueda de datos compatibles y aprendizaje de las herramientas que sirven de base para el desarrollo de cualquier trabajo técnico o de investigación relacionado con el medio ambiente y el territorio que se apoye en los SIG

Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in very-high-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as sub-sets) and smaller-scale simulations dedicated to individual aspects were carried out and are on-going. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the on-going new round of MC simulations.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at arXiv:1307.223

Mutation analysis of the LCE3B/LCE3C genes in Psoriasis

<p>Abstract</p> <p>Background</p> <p>An association between a common deletion comprising the late cornified envelope LCE3B and LCE3C genes (LCE3C_LCE3B-del) and Psoriasis (Ps) has been reported. The expression of these LCE genes was induced after skin barrier disruption and was also strong in psoriatic lesions. The damage to the skin barrier could trigger an epidermal response that includes the expression of genes involved in the formation of skin barrier.</p> <p>Methods</p> <p>We determined the LCE3C_LCE3B-del genotype in 405 Ps patients and 400 healthy controls from a Northern Spain region (Asturias). These patients and controls were also genotyped for the rs4112788 single nucleotide polymorphism, in strong linkage disequilibrium with the LCE3C_B cluster. The LCE3B and LCE3C gene variant was determined in the patients through SSCA, DHPLC, and direct sequencing.</p> <p>Results</p> <p>Allele and genotype frequencies did not differ between patients and controls for the rs4112788 and LCE3C_LCE3B-del polymorphisms. However, del/del homozygotes were significantly higher among patients with chronic plaque type Ps who did not develop arthritis (p = 0.03; OR = 1.4; 95%CI = 1.03-1.92). The analysis of the coding sequence of LCE3B and LCE3C in the patients who had at least one copy of this showed that only one patient has a no previously reported LCE3B variant (R68C).</p> <p>Conclusion</p> <p>Our work suggested that homozygosity for a common LCE3C_LCE3B deletion contributes to the risk of developing chronic plaque type Ps without psoriatic arthritis. Our work confirmed previous reports that described an association of this marker with only skin manifestations, and supported the concept of different genetic risk factors contributing to skin and joint disease.</p

Detection of very high energy gamma-ray emission from the gravitationally-lensed blazar QSO B0218+357 with the MAGIC telescopes

Context. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components, spatially indistinguishable by gamma-ray instruments, but separated by a 10-12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. Aims. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma- ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1. Methods. MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data, obtained by Fermi-LAT and MAGIC, are used to set constraints on the extragalactic background light. Results. Very high energy gamma-ray emission was detected from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray sources detected to date. The observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broad band emission can be modeled in the framework of a two zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.Comment: 11 pages, 6 figures, accepted for publication in A&

Limits to dark matter annihilation cross-section from a combined analysis of MAGIC and Fermi-LAT observations of dwarf satellite galaxies

We present the first joint analysis of gamma-ray data from the MAGIC Cherenkov telescopes and the Fermi Large Area Telescope (LAT) to search for gamma-ray signals from dark matter annihilation in dwarf satellite galaxies. We combine 158 hours of Segue 1 observations with MAGIC with 6-year observations of 15 dwarf satellite galaxies by the Fermi-LAT. We obtain limits on the annihilation cross-section for dark matter particle masses between 10 GeV and 100 TeV - the widest mass range ever explored by a single gamma-ray analysis. These limits improve on previously published Fermi-LAT and MAGIC results by up to a factor of two at certain masses. Our new inclusive analysis approach is completely generic and can be used to perform a global, sensitivity-optimized dark matter search by combining data from present and future gamma-ray and neutrino detectors.Comment: 19 pages, 3 figures. V2: Few typos corrected and references added. Matches published version JCAP 02 (2016) 03

Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3

Context. Recently, the high-energy (HE, 0.1-100 GeV) $\gamma$-ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic $\gamma$-ray binary. Aims. This work aims at the detection of very-high-energy (VHE, >100 GeV) $\gamma$-ray emission and the search for modulation of the VHE signal with the orbital period of the binary system. Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission. Energy spectra are obtained for the orbit-averaged data set, and for the orbital phase bin around the VHE maximum. Results. VHE $\gamma$-ray emission is detected with a statistical significance of 6.4 $\sigma$. The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the $1-10$ TeV energy range is $(1.4 \pm 0.2) \times 10^{35}$ erg/s. A luminosity of $(5 \pm 1) \times 10^{35}$ erg/s is reached during 20% of the orbit. HE and VHE $\gamma$-ray emissions are anti-correlated. LMC P3 is the most luminous $\gamma$-ray binary known so far.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&

A search for spectral hysteresis and energy-dependent time lags from X-ray and TeV gamma-ray observations of Mrk 421

Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three "target-of-opportunity" (ToO) observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering X-ray and optical/ultraviolet bands) and VERITAS (covering TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-LAT) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e.g. the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at $\gtrsim 4\times 10^{-4}$ Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies.Comment: 45 pages, 15 figure

The sub-TeV transient Gamma-Ray sky: challenges and opportunities

The detection of gravitational waves and neutrinos from astrophysical sources with gamma-ray counterparts officially started the era of Multi-Messenger Astronomy. Their transient and extreme nature implies that monitoring the VHE sky is fundamental to investigate the non-electromagnetic signals. However, the limited effective area of space-borne instruments prevents observations above a few hundred GeV, while the small field of view and low duty cycle of IACTs make them unsuited for extensive monitoring activities and prompt response to transients. Extensive Air Shower arrays (EAS) can provide a large field of view, a wide effective area and a very high duty cycle. Their main difficulty is the distinction between gamma-ray and cosmic-ray initiated air showers, especially below the TeV range. Here we present some case studies stressing the importance that a new EAS array in the Southern Hemisphere will be able to survey the sky from below 100 GeV up to several TeV. In the energy domain between 100 and 400 GeV we expect the strongest electromagnetic signatures of the acceleration of ultra-relativistic particles in sources like SNRs, blazar jets and gamma-ray bursts, as recently proved by IACT observations. This spectral window is also crucial to understand the Universe opacity to high energy radiation, thus providing constraints on the cosmological parameters. We will discuss the implications of VHE radiation on the mechanisms at work and we will focus on the advantages resulting from the ability to monitor the energy window lying between the domain of space-borne detectors and ground-based facilities