7,608 research outputs found
Nonmetallic impurities improve mechanical properties of vapor-deposited tungsten
Mechanical properties of vapor deposited tungsten are improved by selective incorporation of various nonmetallic impurities. Addition of trace quantities of carbon, nitrogen, or oxygen can significantly increase both low and high temperature yield strength without greatly affecting ductile-to-brittle transition temperature
Effects of additions of nonmetallics on the properties of vapor-deposited tungsten
Nonmetallic additive effects on properties of vapor deposited tungste
Gravitational infall in the hard wall model
An infalling shell in the hard wall model provides a simple holographic model
for energy injection in a confining gauge theory. Depending on its parameters,
a scalar shell either collapses into a large black brane, or scatters between
the hard wall and the anti-de Sitter boundary. In the scattering regime, we
find numerical solutions that keep oscillating for as long as we have followed
their evolution, and we provide an analytic argument that shows that a black
brane can never be formed. This provides examples of states in infinite-volume
field theory that never thermalize. We find that the field theory expectation
value of a scalar operator keeps oscillating, with an amplitude that undergoes
modulation.Comment: 7 pages, 4 figure
Convergence of all-order many-body methods: coupled-cluster study for Li
We present and analyze results of the relativistic coupled-cluster
calculation of energies, hyperfine constants, and dipole matrix elements for
the , , and states of Li atom. The calculations are
complete through the fourth order of many-body perturbation theory for energies
and through the fifth order for matrix elements and subsume certain chains of
diagrams in all orders. A nearly complete many-body calculation allows us to
draw conclusions on the convergence pattern of the coupled-cluster method. Our
analysis suggests that the high-order many-body contributions to energies and
matrix elements scale proportionally and provides a quantitative ground for
semi-empirical fits of {\em ab inito} matrix elements to experimental energies.Comment: 4 pages, 3 figure
Fermionization of two-component few-fermion systems in a one-dimensional harmonic trap
The nature of strongly interacting Fermi gases and magnetism is one of the
most important and studied topics in condensed-matter physics. Still, there are
many open questions. A central issue is under what circumstances strong
short-range repulsive interactions are enough to drive magnetic correlations.
Recent progress in the field of cold atomic gases allows to address this
question in very clean systems where both particle numbers, interactions and
dimensionality can be tuned. Here we study fermionic few-body systems in a one
dimensional harmonic trap using a new rapidly converging effective-interaction
technique, plus a novel analytical approach. This allows us to calculate the
properties of a single spin-down atom interacting with a number of spin-up
particles, a case of much recent experimental interest. Our findings indicate
that, in the strongly interacting limit, spin-up and spin-down particles want
to separate in the trap, which we interpret as a microscopic precursor of
one-dimensional ferromagnetism in imbalanced systems. Our predictions are
directly addressable in current experiments on ultracold atomic few-body
systems.Comment: 12 pages, 6 figures, published version including two appendices on
our new numerical and analytical approac
Vapor Deposited Tungsten for Application as a Thermionic Emitter Material
Purity and resistance to grain growth of vapor deposited tungsten tubing for use as thermionic emitte
Effect of dopant atoms on local superexchange in cuprate superconductors: a perturbative treatment
Recent scanning tunneling spectroscopy experiments have provided evidence
that dopant impurities in high- Tc superconductors can strongly modify the
electronic structure of the CuO2 planes nearby, and possibly influence the
pairing. To investigate this connection, we calculate the local magnetic
superexchange J between Cu ions in the presence of dopants within the framework
of the three-band Hubbard model, up to fifth-order in perturbation theory. We
demonstrate that the sign of the change in J depends on the relative
dopant-induced spatial variation of the atomic levels in the CuO2 plane,
contrary to results obtained within the one-band Hubbard model. We discuss some
realistic cases and their relevance for theories of the pairing mechanism in
the cupratesComment: 5 pages, 4 figures, revised versio
An interpolatory ansatz captures the physics of one-dimensional confined Fermi systems
Interacting one-dimensional quantum systems play a pivotal role in physics.
Exact solutions can be obtained for the homogeneous case using the Bethe ansatz
and bosonisation techniques. However, these approaches are not applicable when
external confinement is present. Recent theoretical advances beyond the Bethe
ansatz and bosonisation allow us to predict the behaviour of one-dimensional
confined systems with strong short-range interactions, and new experiments with
cold atomic Fermi gases have already confirmed these theories. Here we
demonstrate that a simple linear combination of the strongly interacting
solution with the well-known solution in the limit of vanishing interactions
provides a simple and accurate description of the system for all values of the
interaction strength. This indicates that one can indeed capture the physics of
confined one-dimensional systems by knowledge of the limits using wave
functions that are much easier to handle than the output of typical numerical
approaches. We demonstrate our scheme for experimentally relevant systems with
up to six particles. Moreover, we show that our method works also in the case
of mixed systems of particles with different masses. This is an important
feature because these systems are known to be non-integrable and thus not
solvable by the Bethe ansatz technique.Comment: 22 pages including methods and supplementary materials, 11 figures,
title slightly change
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