4,581 research outputs found
Dynamic screening of a localized hole during photoemission from a metal cluster
Recent advances in attosecond spectroscopy techniques have fueled the
interest in the theoretical description of electronic processes taking place in
the subfemtosecond time scale. Here we study the coupled dynamic screening of a
localized hole and a photoelectron emitted from a metal cluster using a
semi-classical model. Electron density dynamics in the cluster is calculated
with Time-Dependent Density Functional Theory and the motion of the
photoemitted electron is described classically. We show that the dynamic
screening of the hole by the cluster electrons affects the motion of the
photoemitted electron. At the very beginning of its trajectory, the
photoemitted electron interacts with the cluster electrons that pile up to
screen the hole. Within our model, this gives rise to a significant reduction
of the energy lost by the photoelectron. Thus, this is a velocity dependent
effect that should be accounted for when calculating the average losses
suffered by photoemitted electrons in metals.Comment: 15 pages, 5 figure
Rotation of the nucleus, gas kinematics and emission pattern of comet 8P/Tuttle : preliminary results from optical imaging of the CN coma
Transient and asymmetric dust structures in the TeV-bright nova RS Oph revealed by spectropolarimetry
A long-standing question related to nova eruptions is how these eruptions can
lead to the formation of dust despite the ostensibly inhospitable environment
for dust within the hot, irradiated ejecta. Novae in systems such as the
symbiotic binary RS Oph offers a articularly clear view of some nova shocks and
any associated dust production. Here we use spectropolarimetric monitoring of
the RS Oph starting two days after its eruption in 2021 Aug. to show that: dust
was present in the RS Oph system as early as two days into the 2021 eruption;
the spatial distribution of this early dust was asymmetric, with components
both aligned with and perpendicular to the orbital plane of the binary; between
two and nine days after the start of the eruption, this early dust was
gradually destroyed; and dust was again created, aligned roughly with the
orbital plane of the binary, more than 80 days after the start of the outburst,
most likely as a result of shocks that arose as the ejecta interacted with
circumbinary material concentrated in the orbital plane. Modelling of X-rays
and very-high energy GeV and TeV emission from RS Oph days to months into the
2021 eruption suggests that collisions between the ejecta and the circumbinary
material may have led to shock formation in two regions: the polar -
perpendicular to the orbital plane where collimated outflows have been observed
after prior eruptions, and a circumbinary torus in the orbital plane. The
observations described here indicate that dust formed in approximately the same
two regions, supporting the connection between shocks and dust in novae and
revealing a very early onset of asymmetry. The spectropolarimetric signatures
of RS Oph in the first week into the 2021 outburst indicate: polarized flux
across the H{\alpha} emission line and position angle orientation relative to
the radio axis are similar to the spectropolarimetric signatures of AGNs.Comment: 9 pages, 10 figures, 1 table, resubmitted to the Astronomy &
Astrophysics after the first reviewer's repor
Nanoparticles as a possible moderator for an ultracold neutron source
Ultracold and very cold neutrons (UCN and VCN) interact strongly with
nanoparticles due to the similarity of their wavelengths and nanoparticles
sizes. We analyze the hypothesis that this interaction can provide efficient
cooling of neutrons by ultracold nanoparticles at certain experimental
conditions, thus increasing the density of UCN by many orders of magnitude. The
present analytical and numerical description of the problem is limited to the
model of independent nanoparticles at zero temperature. Constraints of
application of this model are discussed
Could One Find Petroleum Using Neutrino Oscillations in Matter?
In neutrino physics, it is now widely believed that neutrino oscillations are
influenced by the presence of matter, modifying the energy spectrum produced by
a neutrino beam traversing the Earth. Here, we will discuss the reverse
problem, i.e. what could be learned about the Earth's interior from a single
neutrino baseline energy spectrum, especially about the Earth's mantle. We will
use a statistical analysis with a low-energy neutrino beam under very
optimistic assumptions. At the end, we will note that it is hard to find
petroleum with such a method, though it is not too far away from technical
feasibility.Comment: 6 pages, 4 figures, EPL LaTeX. Final version to be published in
Europhys. Let
Radiography of the Earth's Core and Mantle with Atmospheric Neutrinos
A measurement of the absorption of neutrinos with energies in excess of 10
TeV when traversing the Earth is capable of revealing its density distribution.
Unfortunately, the existence of beams with sufficient luminosity for the task
has been ruled out by the AMANDA South Pole neutrino telescope. In this letter
we point out that, with the advent of second-generation kilometer-scale
neutrino detectors, the idea of studying the internal structure of the Earth
may be revived using atmospheric neutrinos instead.Comment: 4 pages, LaTeX file using RevTEX4, 2 figures and 1 table included.
Matches published versio
-cofiniteness of 2-cyclic permutation orbifold models
In this article, we consider permutation orbifold models of -cofinite
vertex operator algebras of CFT type. We show the -cofiniteness of the
2-cyclic permutation orbifold model for an arbitrary
-cofinite simple vertex operator algebra of CFT type. We also give a
proof of the -cofiniteness of a -orbifold model of the
lattice vertex operator algebra associated with a rank one positive
definite even lattice by using our result and the -cofiniteness of
.Comment: 25 pages, no figure, some typo are correcte
Exponential bounds for the probability deviations of sums of random fields
Non-asymptotic exponential upper bounds for the deviation probability for a sum of independent random fields are obtained under Bernstein's condition and assumptions formulated in terms of Kolmogorov's metric entropy. These estimations are constructive in the sense that all the constants involved are given explicitly. In the case of moderately large deviations, the upper bounds have optimal log-asymptotices. The exponential estimations are extended to the local and global continuity modulus for sums of independent samples of a random field
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