7,840 research outputs found
Fullerene-based molecular nanobridges: A first-principles study
Building upon traditional quantum chemistry calculations, we have implemented
an {\em ab-initio} method to study the electrical transport in nanocontacts. We
illustrate our technique calculating the conductance of C molecules
connected in various ways to Al electrodes characterized at the atomic level.
Central to a correct estimate of the electrical current is a precise knowledge
of the local charge transfer between molecule and metal which, in turn,
guarantees the correct positioning of the Fermi level with respect to the
molecular orbitals. Contrary to our expectations, ballistic transport seems to
occur in this system.Comment: 4 pages in two-column forma
Pulmonary thromboembolism and alveolar hemorrhage as initial manifestations of systemic lupus erythematosus
Systemic lupus erythematosus (SLE) is an autoimmune disease that affects multiple organs. SLE can affect the lung, the pulmonary vasculature, and the pleura. A 38-year-old female with limb pain and ecchymosis who later developed pulmonary thromboembolism and alveolar hemorrhage is presented here. Clinical, imaging, laboratory, and histopathological evidence is presented. The patient met the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR) criteria for SLE. Furthermore, the patient had a Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score of 35; thus, indicating severe disease. This case is an example of concomitant venous and arterial lung complications in an SLE patient
The kinematics of the quadrupolar nebula M1-75 and the identification of its central star
The link between the shaping of bipolar planetary nebulae and their central
stars is still poorly understood. The kinematics and shaping of the multipolar
nebula M 1-75 are hereby investigated, and the location and nature of its
central star are briefly discussed. Fabry-Perot data from GHaFAS on the WHT
sampling the Doppler shift of the [N II] 658.3 nm line are used to study the
dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model.
Multi-wavelength images and spectra from the WFC and IDS on the INT, and from
ACAM on the WHT, allowed us to constrain the parameters of the central star.
The two pairs of lobes, angularly separated by ~22 degrees, were ejected
simultaneously approx. ~3500-5000 years ago, at the adopted distance range from
3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point
symmetry. The shaping of the nebula could be explained by wind interaction in a
system consisting of a post-AGB star surrounded by a disc warped by radiative
instabilities. This requires the system to be a close binary or a single star
which engulfed a planet as it died. On the other hand, we present broad- and
narrow-band images and a low S/N optical spectrum of the highly-reddened,
previously unnoticed star which is likely the nebular progenitor. Its estimated
V-I colour allows us to derive a rough estimate of the parameters and nature of
the central star.Comment: 8 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Importance of Grazing Management in Improving Water Use Efficiency of Tropical Forage Grasses
The growing number of extreme weather events has created the need to identify tropical forage grasses with greater water use efficiency (WUE) to cope with water-limited conditions. WUE can be defined as the ratio of forage biomass produced per unit of water used. However, WUE is a dynamic ratio that changes according to environmental gradients (e.g., water or nutrient availability) or ontogenetic drift (e.g., changes in root to shoot biomass allocation across phenological stages). Furthermore, genetic improvement leading to greater WUE is likely to result in smaller plants that produce less than the required forage biomass to sustain good animal performance. Bearing that in mind, other alternatives for improving WUE must be taken into consideration. Grazing management is one among such alternatives. Results from a greenhouse experiment conducted with a number of forage grasses (Cenchrus ciliaris, Chloris gayana, Megathyrsus maximus, Urochloa spp.) at the Alliance of Bioversity-CIAT showed that different grazing intensities lead to various WUEs. Improved WUE values in grasses can be achieved through grazing management if it moderates the process of evapotranspiration by 1) reducing leaf area per plant; and 2) maintaining soil cover from pasture growth and productivity. Our results suggest that WUE in pastures planted with tropical forage grasses can be enhanced through moderate rotational grazing
Angular-Distribution Of Fluorescence From Photoionization-Produced He+ (N=2)
We report the first measurement of the angular distribution of the 304-Ă
He + ( n = 2 ) radiation following photoionization. This distribution reflects the alignment of the ion, which is related to the fraction Ο = Ï ( 2 p , k d ) [ Ï ( 2 p , k s ) + Ï ( 2 p , k d ) ] of d component in the electron wave. The experimental angular distributions correspond to alignments of -0.62 ± 0.03 and -0.62 ± 0.02 at photon energies of 65.5 and 66.5 eV, respectively. These translate into ratios Ο = 0.25 ± 0.04 and 0.25 ± 0.03 , in good agreement with close-coupling calculations
An Electrochemical Study of Frustrated Lewis Pairs: A Metal-free Route to Hydrogen Oxidation
[Image: see text] Frustrated Lewis pairs have found many applications in the heterolytic activation of H(2) and subsequent hydrogenation of small molecules through delivery of the resulting proton and hydride equivalents. Herein, we describe how H(2) can be preactivated using classical frustrated Lewis pair chemistry and combined with in situ nonaqueous electrochemical oxidation of the resulting borohydride. Our approach allows hydrogen to be cleanly converted into two protons and two electrons in situ, and reduces the potential (the required energetic driving force) for nonaqueous H(2) oxidation by 610 mV (117.7 kJ mol(â1)). This significant energy reduction opens routes to the development of nonaqueous hydrogen energy technology
The second flight of the SUNRISE balloon-borne solar observatory: overview of instrument updates, the flight, the data and first results
The SUNRISE balloon-borne solar observatory, consisting of a 1~m aperture
telescope that provided a stabilized image to a UV filter imager and an imaging
vector polarimeter, carried out its second science flight in June 2013. It
provided observations of parts of active regions at high spatial resolution,
including the first high-resolution images in the Mg~{\sc ii}~k line. The
obtained data are of very high quality, with the best UV images reaching the
diffraction limit of the telescope at 3000~\AA\ after Multi-Frame Blind
Deconvolution reconstruction accounting for phase-diversity information. Here a
brief update is given of the instruments and the data reduction techniques,
which includes an inversion of the polarimetric data. Mainly those aspects that
evolved compared with the first flight are described. A tabular overview of the
observations is given. In addition, an example time series of a part of the
emerging active region NOAA AR~11768 observed relatively close to disk centre
is described and discussed in some detail. The observations cover the pores in
the trailing polarity of the active region, as well as the polarity inversion
line where flux emergence was ongoing and a small flare-like brightening
occurred in the course of the time series. The pores are found to contain
magnetic field strengths ranging up to 2500~G and, while large pores are
clearly darker and cooler than the quiet Sun in all layers of the photosphere,
the temperature and brightness of small pores approach or even exceed those of
the quiet Sun in the upper photosphere.Comment: Accepted for publication in The Astrophysical Journa
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