412 research outputs found
Growth control of GaAs nanowires using pulsed laser deposition with arsenic over pressure
Using pulsed laser ablation with arsenic over pressure, the growth conditions
for GaAs nanowires have been systematically investigated and optimized. Arsenic
over pressure with As molecules was introduced to the system by thermal
decomposition of polycrystalline GaAs to control the stoichiometry and shape of
the nanowires during growth. GaAs nanowires exhibit a variety of geometries
under varying arsenic over pressure, which can be understood by different
growth processes via vapor-liquid-solid mechanism. Single-crystal GaAs
nanowires with uniform diameter, lengths over 20 m, and thin surface oxide
layer were obtained and can potentially be used for further electronic
characterization
Efficient single-photon emission from electrically driven InP quantum dots epitaxially grown on Si(001)
The heteroepitaxy of III-V semiconductors on silicon is a promising approach
for making silicon a photonic platform for on-chip optical interconnects and
quantum optical applications. Monolithic integration of both material systems
is a long-time challenge, since different material properties lead to high
defect densities in the epitaxial layers. In recent years, nanostructures
however have shown to be suitable for successfully realising light emitters on
silicon, taking advantage of their geometry. Facet edges and sidewalls can
minimise or eliminate the formation of dislocations, and due to the reduced
contact area, nanostructures are little affected by dislocation networks. Here
we demonstrate the potential of indium phosphide quantum dots as efficient
light emitters on CMOS-compatible silicon substrates, with luminescence
characteristics comparable to mature devices realised on III-V substrates. For
the first time, electrically driven single-photon emission on silicon is
presented, meeting the wavelength range of silicon avalanche photo diodes'
highest detection efficiency
Moduli backreaction and supersymmetry breaking in string-inspired inflation models
We emphasize the importance of effects from heavy fields on supergravity
models of inflation. We study, in particular, the backreaction of stabilizer
fields and geometric moduli in the presence of supersymmetry breaking. Many
effects do not decouple even if those fields are much heavier than the inflaton
field. We apply our results to successful models of Starobinsky-like inflation
and natural inflation. In most scenarios producing a plateau potential it
proves difficult to retain the flatness of the potential after backreactions
are taken into account. Some of them are incompatible with non-perturbative
moduli stabilization. In natural inflation there exist a number of models which
are not constrained by backreactions at all. In those cases the correction
terms from heavy fields have the same inflaton-dependence as the uncorrected
potential, so that inflation may be possible even for very large gravitino
masses.Comment: 29 pages, 1 figure, comments added, subsection 2.3 added, published
versio
Zoonotic Diseases Report 2014
De Staat van zoönosen geeft jaarlijks een overzicht van infectieziekten die overgaan van dier op mens, de zogenoemde zoönosen. Het gaat om de mate waarin meldingsplichtige zoönosen voorkomen en de ontwikkelingen daarvan op de lange termijn. Hierbij betreft het zowel het aantal ziektegevallen bij mensen als het voorkomen van deze ziekteverwekkers bij dieren. Ook worden elk jaar opmerkelijke voorvallen uitgelicht en wordt een thema behandeld. Voor de meeste zoönosen zijn in 2014 geen uitgesproken veranderingen waargenomen. Wel is het aantal mensen met leptospirose (waarvan de bekendste vorm de ziekte van Weil is) aanmerkelijk hoger dan het vorige jaar, van gemiddeld 30 gevallen in de afgelopen jaren naar 97 in 2014. Ook steeg het aantal Hantavirusinfecties (van gemiddeld 13 in de voorgaande jaren naar 36 in 2014). UItgelicht Een opmerkelijke gebeurtenis in 2014 is dat twee patiënten in een ziekenhuis zijn opgenomen met een ernstige longontsteking na een infectie met Chlamydia caviae. Beide patiënten bleken thuis cavia's te houden die een luchtweginfectie hadden doorgemaakt. Verder was er sinds 2003 weer een uitbraak van vogelgriep bij pluimveebedrijven veroorzaakt door een hoogpathogeen virus. Hierbij zijn vier van de vijf besmette bedrijven onafhankelijk van elkaar besmet geraakt. Het virus was vermoedelijk afkomstig van trekkende watervogels. Het is onbekend of dit virustype overdraagbaar is op de mens; wereldwijd zijn daar geen gevallen van bekend. Vogels Het thema van dit jaar is 'Onze gevleugelde vrienden' en gaat over zoönosen die via vogels kunnen worden overgebracht, zoals de papegaaienziekte. Hierbij wordt onder andere beschreven op welke vliegroutes van trekvogels gezamenlijke broed- en voederplaatsen liggen waar ze elkaar kunnen treffen en zoönoseverwekkers aan elkaar zouden kunnen overdragen.The Zoonotic Diseases Report provides an annual overview of infectious diseases transmitted from animals to humans, so-called zoonotic diseases or zoonoses. It focuses on the degree to which notifiable zoonoses occur and how they develop over the long term. Specifically, this concerns both the number of human cases and the occurrence of these pathogens in animals. Noteworthy incidents of zoonoses are also highlighted each year and a particular theme is discussed. For most zoonoses, no pronounced changes were observed in 2014. Nonetheless, the number of people with leptospirosis (of which the most well-known form is Weil's disease) was considerably higher than in the previous year, rising from an average of 30 cases in recent years to 97 cases in 2014. The number of Hantavirus infections also rose (from an average of 13 cases in the previous years to 36 cases in 2014). A closer look A notable event in 2014 is the admission of two patients to hospital with serious lung infections after being infected with Chlamydia caviae. Both patients kept guinea pigs at home that suffered from respiratory infections. There was also the first outbreak of highly pathogenic avian influenza since 2003 affecting five poultry farms. Four of the five farms became contaminated independently of each other. It is thought that the virus was transmitted from waterfowls. It is not known whether the particular virus strain can be transmitted to humans; worldwide no cases of such transmission have been reported. Birds This year's theme is 'Our winged friends'. It focuses on zoonoses that can be transmitted by birds, such as psittacosis (parrot fever). The migratory routes that coincide with shared breeding and feeding locations where migratory birds can come into contact with one another and thereby possibly transmit zoonotic pathogens to each other are also described.NVW
Systematics of M-theory spinorial geometry
We reduce the classification of all supersymmetric backgrounds in eleven
dimensions to the evaluation of the supercovariant derivative and of an
integrability condition, which contains the field equations, on six types of
spinors. We determine the expression of the supercovariant derivative on all
six types of spinors and give in each case the field equations that do not
arise as the integrability conditions of Killing spinor equations. The Killing
spinor equations of a background become a linear system for the fluxes,
geometry and spacetime derivatives of the functions that determine the spinors.
The solution of the linear system expresses the fluxes in terms of the geometry
and specifies the restrictions on the geometry of spacetime for all
supersymmetric backgrounds. We also show that the minimum number of field
equations that is needed for a supersymmetric configuration to be a solution of
eleven-dimensional supergravity can be found by solving a linear system. The
linear systems of the Killing spinor equations and their integrability
conditions are given in both a timelike and a null spinor basis. We illustrate
the construction with examples.Comment: 46 pages. v2: systematics of a null spinor basis is included in
section
Pharmacological inhibition of TBK1/IKKε blunts immunopathology in a murine model of SARS-CoV-2 infection
TANK-binding kinase 1 (TBK1) is a key signalling component in the pro-duction of type-I interferons, which have essential antiviral activities,including against SARS-CoV-2. TBK1, and its homologue IκB kinase-ε (IKKε), can also induce pro-inflammatory responses that contribute to pathogen clearance. While initially protective, sustained engagement of type-I interferons is associated with damaging hyper-inflammation found in severe COVID-19 patients. The contribution of TBK1/IKKε signalling to these responses is unknown. Here we find that the small molecule idronoxil inhibits TBK1/IKKε signalling through destabilisation of TBK1/IKKε protein complexes. Treatment with idronoxil, or the small molecule inhibitor MRT67307, suppresses TBK1/IKKε signalling and attenuates cellular and molecular lung inflammation in SARS-CoV-2-challenged mice. Our findings additionally demonstrate that engagement of STING is not the major driver of these inflammatory responses and establish a critical role for TBK1/IKKε signalling in SARS-CoV-2 hyper inflammation
Eating Disorder Intervention, Prevention, and Treatment: Recommendations for School Counselors
Permission to include this article granted by the American School Counselor AssociationSchool counselors are in daily contact with the highest risk group for developing eating disorders-children and adolescents. School counselors are in a position to identify at-risk individuals, implement effective
school-based prevention programs, make appropriate referrals, and provide support for recovering individuals. An overview of a theory of recovery for eating disorders
reinforces the importance of early intervention.Ye
Universal de Sitter solutions at tree-level
Type IIA string theory compactified on SU(3)-structure manifolds with
orientifolds allows for classical de Sitter solutions in four dimensions. In
this paper we investigate these solutions from a ten-dimensional point of view.
In particular, we demonstrate that there exists an attractive class of de
Sitter solutions, whose geometry, fluxes and source terms can be entirely
written in terms of the universal forms that are defined on all SU(3)-structure
manifolds. These are the forms J and Omega, defining the SU(3)-structure
itself, and the torsion classes. The existence of such universal de Sitter
solutions is governed by easy-to-verify conditions on the SU(3)-structure,
rendering the problem of finding dS solutions purely geometrical. We point out
that the known (unstable) solution coming from the compactification on SU(2)x
SU(2) is of this kind.Comment: 20 pages, 3 figures, v2: added reference
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