16,889 research outputs found
Giant Electron-hole Charging Energy Asymmetry in Ultra-short Carbon Nanotubes
Making full usage of bipolar transport in single-wall carbon nanotube (SWCNT)
transistors could permit the development of two-in-one quantum devices with
ultra-short channels. We report on clean 10 to 100 nm long suspended
SWCNT transistors which display a large electron-hole transport asymmetry. The
devices consist of naked SWCNT channels contacted with sections of
SWCNT-under-annealed-gold. The annealed gold acts as an n-doping top gate which
creates nm-sharp barriers at the junctions between the contacts and naked
channel. These tunnel barriers define a single quantum dot (QD) whose charging
energies to add an electron or a hole are vastly different ( charging
energy asymmetry). We parameterize the transport asymmetry by the ratio
of the hole and electron charging energies . We show that this
asymmetry is maximized for short channels and small band gap SWCNTs. In a small
band gap SWCNT device, we demonstrate the fabrication of a two-in-one quantum
device acting as a QD for holes, and a much longer quantum bus for electrons.
In a 14 nm long channel, reaches up to 2.6 for a device with a
band gap of 270 meV. This strong transport asymmetry survives even at
room temperature
Monomial integrals on the classical groups
This paper presents a powerfull method to integrate general monomials on the
classical groups with respect to their invariant (Haar) measure. The method has
first been applied to the orthogonal group in [J. Math. Phys. 43, 3342 (2002)],
and is here used to obtain similar integration formulas for the unitary and the
unitary symplectic group. The integration formulas turn out to be of similar
form. They are all recursive, where the recursion parameter is the number of
column (row) vectors from which the elements in the monomial are taken. This is
an important difference to other integration methods. The integration formulas
are easily implemented in a computer algebra environment, which allows to
obtain analytical expressions very efficiently. Those expressions contain the
matrix dimension as a free parameter.Comment: 16 page
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Suicide and self-harm in Britain: researching risk and resilience using UK surveys
Aim The main aim of this study was to raise awareness of surveys that could be used to inform self-harm and suicide prevention work. We asked:
What UK survey datasets are available for research?
What aspects of people’s lives are associated with self-harm and attempted suicide?
How do statistical findings resonate with people’s lived experience? What implications do they see?
Findings Survey analyses revealed that risk factors for self-harm are wide ranging and include:
Mental health
Physical health and health behaviours
Social relationships
Stressful events
Employment and financial circumstances
Identity and demographics
Many different factors are independently associated with self-harm. There is a dose relationship, with more exposure to a factor linked with increased risk. Risks are cumulative that is, exposure to multiple factors is associated with greater risk.
Through facilitated consultation, men with lived experience, bereaved family members, and practitioners identified recommendations for responding to suicidal distress in men. These related to the following three main areas:
1. Recognising need: who is ‘ill enough’?
Permission - men said that they often did not know they were entitled to help
Ask - people who outwardly appear to be functioning may not be
Persistence - ask and offer help more than once.
2. Facilitating access: right words, time and place
What is available - support is needed with ongoing stress as well as for crises
Find the words - men wanted examples of how to ask for help
Allow time - employers expect recovery to be swift, some men felt rushed to come off medications or were discharged from services they still needed.
3. Adjusting delivery: equal engagement
Power - some were uncomfortable with service dynamics, preferring peer support
Every service contact counts - negative contacts had particular impact
Safe spaces - may be different for men and women.
Methods
There were three strands of work:
Secondary analysis of nine survey series, spanning more than twenty years
Linkage of 144,000 survey participants to information on whether they were alive in 2013 and whether they had taken their own life
Facilitated consultation, through depth interviews with people with lived experience
Peculiarities in the Spectrum of the Adjoint Scalar Kinetic Operator in Yang-Mills Theory
We study the spectrum of low-lying eigenmodes of the kinetic operator for
scalar particles, in the color adjoint representation of Yang-Mills theory. The
kinetic operator is the covariant Laplacian, plus a constant which serves to
renormalize mass. In the pure gauge theory, our data indicates that the
interval between the lowest eigenvalue and the mobility edge tends to infinity
in the continuum limit. On these grounds, it is suggested that the perturbative
expression for the scalar propagator may be misleading even at distance scales
that are small compared to the confinement scale. We also measure the density
of low-lying eigenmodes, and find a possible connection to multi-critical
matrix models of order m=1.Comment: 9 pages, 14 figure
Inverse Compton Emission from Galactic Supernova Remnants: Effect of the Interstellar Radiation Field
The evidence for particle acceleration in supernova shells comes from
electrons whose synchrotron emission is observed in radio and X-rays. Recent
observations by the HESS instrument reveal that supernova remnants also emit
TeV gamma-rays; long awaited experimental evidence that supernova remnants can
accelerate cosmic rays up to the ``knee'' energies. Still, uncertainty exists
whether these gamma-rays are produced by electrons via inverse Compton
scattering or by protons via neutral pion decay. The multi-wavelength spectra
of supernova remnants can be fitted with both mechanisms, although a preference
is often given to neutral pion decay due to the spectral shape at very high
energies. A recent study of the interstellar radiation field indicates that its
energy density, especially in the inner Galaxy, is higher than previously
thought. In this paper we evaluate the effect of the interstellar radiation
field on the inverse Compton emission of electrons accelerated in a supernova
remnant located at different distances from the Galactic Centre. We show that
contribution of optical and infra-red photons to the inverse Compton emission
may exceed the contribution of cosmic microwave background and in some cases
broaden the resulted gamma-ray spectrum. Additionally, we show that if a
supernova remnant is located close to the Galactic Centre its gamma-ray
spectrum will exhibit a ``universal'' cutoff at very high energies due to the
Klein-Nishina effect and not due to the cut-off of the electron spectrum. As an
example, we apply our calculations to the supernova remnants RX J1713.7-3946
and G0.9+0.1 recently observed by HESS.Comment: 4 pages, 4 figures. Uses emulateapj.cls. Accepted by ApJ
The Cauchy convergence of T and P-approximant templates for test-mass Kerr binary systems
In this work we examine the Cauchy convergence of both post-Newtonian
(T-approximant) and re-summed post-Newtonian (P-approximant) templates for the
case of a test-mass orbiting a Kerr black hole along a circular equatorial
orbit. The Cauchy criterion demands that the inner product between the and
order approximation approaches unity, as we increase the order of
approximation. In previous works, it has been shown that we achieve greater
fitting factors and better parameter estimation using the P-approximant
templates for both Schwarzschild and Kerr black holes. In this work, we show
that the P-approximant templates also display a faster Cauchy convergence
making them a superior template to the standard post-Newtonian templates.Comment: 5 pages, Replaced with shortened published versio
Discrete quantum gravity in the framework of Regge calculus formalism
An approach to the discrete quantum gravity based on the Regge calculus is
discussed which was developed in a number of our papers. Regge calculus is
general relativity for the subclass of general Riemannian manifolds called
piecewise flat ones. Regge calculus deals with the discrete set of variables,
triangulation lengths, and contains continuous general relativity as a
particular limiting case when the lengths tend to zero. In our approach the
quantum length expectations are nonzero and of the order of Plank scale
. This means the discrete spacetime structure on these scales.Comment: LaTeX, 16 pages, to appear in JET
Comparison of 20nm silver nanoparticles synthesized with and without a gold core: Structure, dissolution in cell culture media, and biological impact on macrophages
Widespread use of silver nanoparticles raises questions of environmental and biological impact. Many synthesis approaches are used to produce pure silver and silver-shell gold-core particles optimized for specific applications. Since both nanoparticles and silver dissolved from the particles may impact the biological response, it is important to understand the physicochemical characteristics along with the biological impact of nanoparticles produced by different processes. The authors have examined the structure, dissolution, and impact of particle exposure to macrophage cells of two 20 nm silver particles synthesized in different ways, which have different internal structures. The structures were examined by electron microscopy and dissolution measured in Rosewell Park Memorial Institute media with 10% fetal bovine serum. Cytotoxicity and oxidative stress were used to measure biological impact on RAW 264.7 macrophage cells. The particles were polycrystalline, but 20 nm particles grown on gold seed particles had smaller crystallite size with many high-energy grain boundaries and defects, and an apparent higher solubility than 20 nm pure silver particles. Greater oxidative stress and cytotoxicity were observed for 20 nm particles containing the Au core than for 20 nm pure silver particles. A simple dissolution model described the time variation of particle size and dissolved silver for particle loadings larger than 9 μg/ml for the 24-h period characteristic of many in-vitro studies
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