1,228 research outputs found
Regional and Climatic Controls on Seasonal Dust Deposition in the Southwestern US
Vertical dust deposition rates (dust flux) are a complex response to the interaction of seasonal precipitation, wind, changes in plant cover and land use, dust source type, and local vs. distant dust emission in the southwestern U.S. Seasonal dust flux in the Mojave-southern Great Basin (MSGB) deserts, measured from 1999 to 2008, is similar in summer-fall and winter-spring, and antecedent precipitation tends to suppress dust flux in winter-spring. In contrast, dust flux in the eastern Colorado Plateau (ECP) region is much larger in summer-fall than in winter-spring, and twice as large as in the MSGB. ECP dust is related to wind speed, and in the winter-spring to antecedent moisture. Higher summer dust flux in the ECP is likely due to gustier winds and runoff during monsoonal storms when temperature is also higher. Source types in the MSGB and land use in the ECP have important effects on seasonal dust flux. In the MSGB, wet playas produce salt-rich dust during wetter seasons, whereas antecedent and current moisture suppress dust emission from alluvial and dry-playa sources during winter-spring. In the ECP under drought conditions, dust flux at a grazed-and-plowed site increased greatly, and also increased at three annualized, previously grazed sites. Dust fluxes remained relatively consistent at ungrazed and currently grazed sites that have maintained perennial vegetation cover. Under predicted scenarios of future climate change, these results suggest that an increase in summer storms may increase dust flux in both areas, but resultant effects will depend on source type, land use, and vegetation cover
Zusammenlegung von Arbeitslosen- und Sozialhilfe: Zwei Gesetzentwürfe
Die Bundesregierung hat Mitte August den lange angekündigten Hartz IV–Gesetzentwurf, der die Zusammenlegung von Arbeitslosen- und Sozialhilfe für Erwerbsfähige regelt, vorgelegt. Bereits Anfang Juli hatte die Hessische Landesregierung mit dem Existenzgrundlagengesetz (EGG) einen eigenen Gesetzentwurf zu diesem Teil der Arbeitsmarktreformen vorgestellt. Wie sind diese beiden Gesetzentwürfe im Hinblick auf die Zielsetzung einer erfolgreichen Reduzierung der Langzeitarbeitslosigkeit in Deutschland zu bewerten? --
Interplay of charge-transfer and Mott-Hubbard physics approached by an efficient combination of self-interaction correction and dynamical mean-field theory
Late transition-metal oxides with small charge-transfer energy raise
issues for state-of-the-art correlated electronic structure schemes such as the
combination of density functional theory (DFT) with dynamical mean-field theory
(DMFT). The accentuated role of the oxygen valence orbitals in these compounds
asks for an enhanced description of ligand-based correlations. Utilizing the
rocksalt-like NiO as an example, we present an advancement of charge
self-consistent DFT+DMFT by including self-interaction correction (SIC) applied
to oxygen. This introduces explicit onsite O correlations as well as an
improved treatment of intersite correlations. Due to the efficient SIC
incorporation in a pseudopotential form, the DFT+sicDMFT framework is an
advanced but still versatile method to address the interplay of charge-transfer
and Mott-Hubbard physics. We revisit the spectral features of stoichiometric
NiO and reveal the qualitative sufficiency of local DMFT self-energies in
describing spectral peak structures usually associated with explicit nonlocal
processes. For LiNiO, prominent in-gap states are verified by the
present theoretical study.Comment: 8 pages, 6 figure
Next-to-Leading Order QCD Corrections for the B⁰B⁰ Mixing with an Extended Higgs Sector
We present a calculation of the B0B0 mixing including next-to-leading order (NLO) QCD corrections within the Two-Higgs Doublet Model (2HDM). The QCD corrections at NLO are contained in the factor denoted by η2 which modifies the result obtained at the lowest order of perturbation theory. In the Standard Model case, we confirm the results for η2 obtained by Buras, Jamin and Weisz [Nucl. Phys, B 347 (1990) 491]. The factor η2 is gauge and renormalization prescription invariant and it does not depend on the infrared behaviour of the theory, which constitutes an important test of the calculations. The NLO calculations within the 2HDM enhance the LO result up to 18%, which affects the correlation between MH and Vtd
A composite reference section for terminal Proterozoic strata of southern Namibia
Integrated sequence stratigraphic and chemostratigraphic data yield a framework for correlations of stratigraphic units in the terminal Proterozoic to Cambrian Witvlei and Nama Groups of Namibia. Coupled with precise U-Pb zircon age constraints, these correlations make it possible to construct a composite reference section for use in calibrating terminal Proterozoic chronostratigraphy. The Namibian reference section starts with two distinct glacial horizons and extends up to within 1 million years of the Proterozoic-Cambrian boundary. The two glacial horizons may represent each of two distinct Varanger-age glaciations better known from the North Atlantic region. From the higher of the two glacial horizons up, the composite stratigraphy preserves one of the thickest and most complete available records of carbon-isotope variability in post-Varanger terminal Proterozoic seawater. Four carbon-isotope chemostratigraphic intervals are recognized: (1) a postglacial negative δ^(13)C excursion (Npg interval); (2) a rising interval (Pr interval) of increasing positive delta 13 C values; (3) a falling interval (Pf interval) characterized by decreasing positive δ^(13)C and culminating in near zero or negative values; and (4) an interval of moderately positive, relatively invariant δ^(13)C values (I interval) that extends up to the unconformity that contains the Proterozoic-Cambrian boundary. Each of these chemostratigraphic intervals can be recognized in widely separated correlative sections around the world. By comparing sediment accumulation rate in the radiometrically calibrated Namibian stratigraphy with sediment accumulation rates in correlative sections in Arctic Canada and Oman, a maximum age of 564 Ma is estimated for the end of the younger Varanger glaciation, 25 m.y. younger than previous estimates
Lead-free, luminescent perovskite nanocrystals obtained through ambient condition synthesis
Heterovalent substitution of toxic lead is an increasingly popular design
strategy to obtain environmentally sustainable variants of the exciting
material class of halide perovskites. Perovskite nanocrystals (NCs) obtained
through solution-based methods exhibit exceedingly high optical quality.
Unfortunately, most of these synthesis routes still require reaction under
inert gas and at very high temperatures. Herein we present a novel synthesis
routine for lead-free double perovskite NCs. We combine hot injection and
ligand-assisted reprecipitation (LARP) methods to achieve a low-temperature and
ambient atmosphere-based synthesis for manganese-doped Cs_{2}NaBiCl_{6} NCs. Mn
incorporation is critical for the otherwise non-emissive material, with a 9:1
Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and
quantum yield (QY). Higher temperatures slightly increased the material's
performance, yet NCs synthesized at room temperature were still emissive,
highlighting the versatility of the synthetic approach. Furthermore, the NCs
show excellent long-term stability in ambient conditions, facilitating
additional investigations and energy-related applications
Spin-Peierls instability of the U(1) Dirac spin liquid
Quantum spin liquids are tantalizing phases of frustrated quantum magnets. A
complicating factor in their realization and observation in materials is the
ubiquitous presence of other degrees of freedom, in particular lattice
distortion modes (phonons). These provide additional routes for relieving
magnetic frustration, thereby possibly destabilizing spin-liquid ground states.
In this work, we focus on triangular-lattice Heisenberg antiferromagnets, where
recent numerical evidence suggests the presence of an extended U(1) Dirac spin
liquid phase which is described by compact quantum electrodynamics in 2+1
dimensions (QED), featuring gapless spinons and monopoles as gauge
excitations. Its low energy theory is believed to flow to a strongly-coupled
fixed point with conformal symmetries. Using complementary perturbation theory
and scaling arguments, we show that a symmetry-allowed coupling between
(classical) finite-wavevector lattice distortions and monopole operators of the
U(1) Dirac spin liquid generally induces a spin-Peierls instability towards a
(confining) 12-site valence-bond solid state. We support our theoretical
analysis with state-of-the-art density matrix renormalization group
simulations. Away from the limit of static distortions, we demonstrate that the
phonon energy gap establishes a parameter regime where the spin liquid is
expected to be stable.Comment: 23 pages, 10 figure
Myc Regulates Embryonic Vascular Permeability and Remodeling
Previous work has shown that c-Myc is required for adequate vasculogenesis and angiogenesis. To further investigate the contribution of Myc to these processes, we conditionally expressed c-Myc in embryonic endothelial cells using a tetracycline-regulated system. Endothelial Myc overexpression resulted in severe defects in the embryonic vascular system. Myc-expressing embryos undergo widespread edema formation and multiple hemorrhagic lesions. They die between embryonic days 14.5 and 17.5. The changes in vascular permeability are not caused by deficiencies in vascular basement membrane composition or pericyte coverage. However, the overall turnover of endothelial cells is elevated as is revealed by increased levels of both proliferation and apoptosis. Whole-mount immunohistochemical analysis revealed alterations in the architecture of capillary networks. The dermal vasculature of Myc-expressing embryos is characterized by a reduction in vessel branching, which occurs despite upregulation of the proangiogenic factors vascular endothelial growth factor-A and angiopoietin-2. Thus, the net outcome of an excess of vascular endothelial growth factor-A and angiopoietin-2 in the face of an elevated cellular turnover appears to be a defect in vascular integrity. (Circ Res. 2009;104:1151-1159.
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