552 research outputs found
On the visibility of electron-electron interaction effects in field emission spectra
One of the most convenient methods to obtain information about the energy
distribution function of electrons in conducting materials is the measurement
of the energy resolved current in field emission (FE) experiments.
Its high energy tail (above the Fermi edge) contains invaluable
information about the nature of the electron--electron interactions inside the
emitter. Thus far, has been calculated to second order in the
tunnelling probability, and it turns out to be divergent toward the Fermi edge
for a wide variety of emitters. The extraction of the correlation properties
from real experiments can potentially be obscured by the eventually more
divergent contributions of higher orders as well as by thermal smearing around
. We present an analysis of both factors and make predictions for the
energy window where only the second order tunnelling events dominate the
behaviour of . We apply our results to the FE from Luttinger
liquids and single-wall carbon nanotubes.Comment: 7 pages, 3 figures, to appear in Solid State Communication
First-principles study of nucleation, growth, and interface structure of Fe/GaAs
We use density-functional theory to describe the initial stages of Fe film
growth on GaAs(001), focusing on the interplay between chemistry and magnetism
at the interface. Four features appear to be generic: (1) At submonolayer
coverages, a strong chemical interaction between Fe and substrate atoms leads
to substitutional adsorption and intermixing. (2) For films of several
monolayers and more, atomically abrupt interfaces are energetically favored.
(3) For Fe films over a range of thicknesses, both Ga- and As-adlayers
dramatically reduce the formation energies of the films, suggesting a
surfactant-like action. (4) During the first few monolayers of growth, Ga or As
atoms are likely to be liberated from the interface and diffuse to the Fe film
surface. Magnetism plays an important auxiliary role for these processes, even
in the dilute limit of atomic adsorption. Most of the films exhibit
ferromagnetic order even at half-monolayer coverage, while certain
adlayer-capped films show a slight preference for antiferromagnetic order.Comment: 11 two-column pages, 12 figures, to appear in Phys. Rev.
Public knowledge and credibility perceptions of the FDA as a tobacco regulator
efforts that increase the public's understanding of the FDA's role as a tobacco regulator may positively impact views of the agency's credibility. This may in turn improve public reception to the FDA's messages and regulations. Implications This study is the first to show nationally representative estimates of both knowledge and credibility of the FDA as a tobacco regulator. Our research shows further that knowledge of the FDA's tobacco regulatory roles is likely to be an important factor related to perceived credibility of the FDA. Increasing the public's knowledge of the FDA's roles may enhance the agency's credibility, which can improve public reception to messages and regulations.Introduction Since the U.S. Food and Drug Administration (FDA) was granted regulatory authority over tobacco products in 2009, few studies have examined perceived credibility of the FDA in this role. The current study assessed knowledge and credibility of the FDA as a regulator of tobacco products. Methods In a nationally representative survey of U.S. adults (N = 4758), we assessed knowledge that the FDA regulates the manufacture, distribution, and marketing of cigarettes, and credibility of the FDA as a tobacco regulator. We examined demographic differences in knowledge and credibility, and associations of knowledge and trust in government with credibility perceptions. Results Less than half of respondents reported knowing the FDA regulates how cigarettes are sold (46.8%) and advertised (49.7%), and only 36.0% knew the FDA regulates how cigarettes are made, with few demographic differences. Respondents reported that the FDA was moderately credible in regulating tobacco. Knowledge of the FDA as a tobacco regulator and trust in government were the strongest predictors of credibility. Being of younger age, being White (compared to African American), and being male were associated with higher credibility ratings of the FDA. Conclusions Much of the public still does not know that the FDA regulates tobacco products, and credibility perceptions are moderate. Greater knowledge of the FDA's regulatory role was associated with higher credibilit
The Sunrise Mission
The first science flight of the balloon-borne \Sunrise telescope took place
in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset Island in northern
Canada. We describe the scientific aims and mission concept of the project and
give an overview and a description of the various hardware components: the 1-m
main telescope with its postfocus science instruments (the UV filter imager
SuFI and the imaging vector magnetograph IMaX) and support instruments (image
stabilizing and light distribution system ISLiD and correlating wavefront
sensor CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry systems,
and the general electronics architecture. We also explain the optimization of
the structural and thermal design of the complete payload. The preparations for
the science flight are described, including AIV and ground calibration of the
instruments. The course of events during the science flight is outlined, up to
the recovery activities. Finally, the in-flight performance of the
instrumentation is briefly summarized.Comment: 35 pages, 17 figure
Self-Consistent Quasi-Particle RPA for the Description of Superfluid Fermi Systems
Self-Consistent Quasi-Particle RPA (SCQRPA) is for the first time applied to
a more level pairing case. Various filling situations and values for the
coupling constant are considered. Very encouraging results in comparison with
the exact solution of the model are obtained. The nature of the low lying mode
in SCQRPA is identified. The strong reduction of the number fluctuation in
SCQRPA vs BCS is pointed out. The transition from superfluidity to the normal
fluid case is carefully investigated.Comment: 23 pages, 18 figures and 1 table, submitted to Phys. Rev.
Macromolecular theory of solvation and structure in mixtures of colloids and polymers
The structural and thermodynamic properties of mixtures of colloidal spheres
and non-adsorbing polymer chains are studied within a novel general
two-component macromolecular liquid state approach applicable for all size
asymmetry ratios. The dilute limits, when one of the components is at infinite
dilution but the other concentrated, are presented and compared to field theory
and models which replace polymer coils with spheres. Whereas the derived
analytical results compare well, qualitatively and quantitatively, with
mean-field scaling laws where available, important differences from ``effective
sphere'' approaches are found for large polymer sizes or semi-dilute
concentrations.Comment: 23 pages, 10 figure
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
- âŠ