8,290 research outputs found
Emittance growth in linear induction accelerators
The Dual-Axis Radiographic Hydrotest (DARHT) facility uses bremsstrahlung
radiation source spots produced by the focused electron beams from two linear
induction accelerators (LIAs) to radiograph large hydrodynamic experiments
driven by high explosives. Radiographic resolution is determined by the size of
the source spot, and beam emittance is the ultimate limitation to spot size. On
the DARHT Axis-II LIA we measure an emittance higher than predicted by
theoretical simulations, and even though this axis produces sub-millimeter
source spots, we are exploring ways to improve the emittance. Some of the
possible causes for the discrepancy have been investigated using
particle-in-cell (PIC) codes, although most of these are discounted based on
beam measurements. The most likely source of emittance growth is a mismatch of
the beam to the magnetic transport, which can cause beam halo.Comment: 20th Int. Conf. on High-Power Particle Beams, Washington, DC, May,
201
Nematode communities, plant nutrient economy and life-cycle characteristics jointly determine plant monoculture performance over 12 years
A Hybrid Monte Carlo Method for Surface Growth Simulations
We introduce an algorithm for treating growth on surfaces which combines
important features of continuum methods (such as the level-set method) and
Kinetic Monte Carlo (KMC) simulations. We treat the motion of adatoms in
continuum theory, but attach them to islands one atom at a time. The technique
is borrowed from the Dielectric Breakdown Model. Our method allows us to give a
realistic account of fluctuations in island shape, which is lacking in
deterministic continuum treatments and which is an important physical effect.
Our method should be most important for problems close to equilibrium where KMC
becomes impractically slow.Comment: 4 pages, 5 figure
Moonlighting function of Phytochelatin synthase1 in extracellular defense against fungal pathogens
Band structure of SnTe studied by Photoemission Spectroscopy
We present an angle-resolved photoemission spectroscopy study of the
electronic structure of SnTe, and compare the experimental results to ab initio
band structure calculations as well as a simplified tight-binding model of the
p-bands. Our study reveals the conjectured complex Fermi surface structure near
the L-points showing topological changes in the bands from disconnected
pockets, to open tubes, and then to cuboids as the binding energy increases,
resolving lingering issues about the electronic structure. The chemical
potential at the crystal surface is found to be 0.5eV below the gap,
corresponding to a carrier density of p =1.14x10^{21} cm^{-3} or 7.2x10^{-2}
holes per unit cell. At a temperature below the cubic-rhombohedral structural
transition a small shift in spectral energy of the valance band is found, in
agreement with model predictions.Comment: 4 figure
Hyperon-nucleon scattering and hyperon masses in the nuclear medium
We analyze low-energy hyperon-nucleon scattering using an effective field
theory in next-to-leading order. By fitting experimental cross sections for
laboratory hyperon momenta below 200 MeV/c and using information from the
hypertriton we determine twelve contact-interaction coefficients. Based on
these we discuss the low-density expansion of hyperon mass shifts in the
nuclear medium.Comment: 10 pages, 2 figure
Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies
Superluminous supernovae (SLSNe) are very bright explosions that were only
discovered recently and that show a preference for occurring in faint dwarf
galaxies. Understanding why stellar evolution yields different types of stellar
explosions in these environments is fundamental in order to both uncover the
elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In
this paper, we present the first results of our project to study SUperluminous
Supernova Host galaxIES, focusing on the sample for which we have obtained
spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (~50% in
our sample) occur in a class of galaxies that is known as Extreme Emission Line
Galaxies (EELGs). The probability of this happening by chance is negligible and
we therefore conclude that the extreme environmental conditions and the SLSN
phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more
massive, more metal-rich galaxies with softer radiation fields. Therefore, if
SLSNe-II constitute a uniform class, their progenitor systems are likely
different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average,
not found in as extreme environments as H-poor SLSNe. We propose that H-poor
SLSNe result from the very first stars exploding in a starburst, even earlier
than GRBs. This might indicate a bottom-light initial mass function in these
systems. SLSNe present a novel method of selecting candidate EELGs independent
of their luminosity.Comment: Published version, matches proofs. Accepted 2015 February 13. 23
pages, 8 figures, 4 tables. Minor changes with respect to previous versio
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