21,188 research outputs found
The oxidation and sublimation of graphite in simulated re-entry environments
Graphite oxidation and sublimation in simulated reentry environment
Public Release of 2dF data from the Fornax Cluster Spectroscopic Survey
Thanks to the 2dF spectrograph on the Anglo-Australian Telescope, we have
recently completed the first stage of a complete spectroscopic survey more than
one order of magnitude larger than any previous study, measuring 7000 spectra
in a 6 sq.deg. area as part of our study of the Fornax Cluster. In this article
we describe the public release of 3600 spectra from our first field. We hope
that this public release will encourage colleagues making surveys for rare
objects to choose these fields, as much of the follow-up spectroscopy that
might be required is available from our data.Comment: To appear in the AAO Newsletter. Data online at
http://astro.ph.unimelb.edu.au/data
Controlled exchange interaction for quantum logic operations with spin qubits in coupled quantum dots
A two-electron system confined in two coupled semiconductor quantum dots is
investigated as a candidate for performing quantum logic operations on spin
qubits. We study different processes of swapping the electron spins by
controlled switching on/off the exchange interaction. The resulting spin swap
corresponds to an elementary operation in quantum information processing. We
perform a direct time evolution simulations of the time-dependent Schroedinger
equation. Our results show that -- in order to obtain the full interchange of
spins -- the exchange interaction should change smoothly in time. The presence
of jumps and spikes in the corresponding time characteristics leads to a
considerable increase of the spin swap time. We propose several mechanisms to
modify the exchange interaction by changing the confinement potential profile
and discuss their advantages and disadvantages
Local correlation functional for electrons in two dimensions
We derive a local approximation for the correlation energy in two-dimensional
electronic systems. In the derivation we follow the scheme originally developed
by Colle and Salvetti for three dimensions, and consider a Gaussian
approximation for the pair density. Then, we introduce an ad-hoc modification
which better accounts for both the long-range correlation, and the
kinetic-energy contribution to the correlation energy. The resulting functional
is local, and depends parametrically on the number of electrons in the system.
We apply this functional to the homogeneous electron gas and to a set of
two-dimensional quantum dots covering a wide range of electron densities and
thus various amounts of correlation. In all test cases we find an excellent
agreement between our results and the exact correlation energies. Our
correlation functional has a form that is simple and straightforward to
implement, but broadly outperforms the commonly used local-density
approximation
Trispectrum versus Bispectrum in Single-Field Inflation
In the standard slow-roll inflationary cosmology, quantum fluctuations in a
single field, the inflaton, generate approximately Gaussian primordial density
perturbations. At present, the bispectrum and trispectrum of the density
perturbations have not been observed and the probability distribution for these
perturbations is consistent with Gaussianity. However, Planck satellite data
will bring a new level of precision to bear on this issue, and it is possible
that evidence for non-Gaussian effects in the primordial distribution will be
discovered. One possibility is that a trispectrum will be observed without
evidence for a non-zero bispectrum. It is not difficult for this to occur in
inflationary models where quantum fluctuations in a field other than the
inflaton contribute to the density perturbations. A natural question to ask is
whether such an observation would rule out the standard scenarios. We explore
this issue and find that it is possible to construct single-field models in
which inflaton-generated primordial density perturbations have an observable
trispectrum, but a bispectrum that is too small to be observed by the Planck
satellite. However, an awkward fine tuning seems to be unavoidable.Comment: 15 pages, 3 figures; journal versio
Developing guidelines for the human-wildlife interactions in conservation translocations
Workshop:
Conservation translocation is a widely used management intervention to restore locally extinct or augment severely depleted species. Human dimension issues that influence the achievement of these aims are encountered at five different stages of the project life cycle: 1) Planning, 2) Initiation, 3) Implementation, 4) Ending, and 5) Post-exit stage. Overlooking such dimension may jeopardise the success of the project. Understanding and addressing human-wildlife interaction issues improve community involvement, peers’ acceptance and the support from various interest groups.
In this workshop we propose to discuss participants’ experiences in human dimensions related to each of the 5 stages of a project’s life cycle.  Discussions aims to expand on findings from the IUCN/SSC CTSG HWIWG 2022 Guidelines to Facilitate Human-Wildlife Interactions in Conservation Translocations, to identify best practice and key issues for each stage to inform planning and promote wildlife conservation, collaboration amongst groups and coexistence
Localization problem of the quasiperiodic system with the spin orbit interaction
We study one dimensional quasiperiodic system obtained from the tight-binding
model on the square lattice in a uniform magnetic field with the spin orbit
interaction. The phase diagram with respect to the Harper coupling and the
Rashba coupling are proposed from a number of numerical studies including a
multifractal analysis. There are four phases, I, II, III, and IV in this order
from weak to strong Harper coupling. In the weak coupling phase I all the wave
functions are extended, in the intermediate coupling phases II and III mobility
edges exist, and accordingly both localized and extended wave functions exist,
and in the strong Harper coupling phase IV all the wave functions are
localized. Phase I and Phase IV are related by the duality, and phases II and
III are related by the duality, as well. A localized wave function is related
to an extended wave function by the duality, and vice versa. The boundary
between phases II and III is the self-dual line on which all the wave functions
are critical. In the present model the duality does not lead to pure spectra in
contrast to the case of Harper equation.Comment: 10 pages, 11 figure
Spin Hall Drag
We predict a new effect in electronic bilayers: the {\it Spin Hall Drag}. The
effect consists in the generation of spin accumulation across one layer by an
electric current along the other layer. It arises from the combined action of
spin-orbit and Coulomb interactions. Our theoretical analysis, based on the
Boltzmann equation formalism, identifies two main contributions to the spin
Hall drag resistivity: the side-jump contribution, which dominates at low
temperature, going as , and the skew-scattering contribution, which is
proportional to . The induced spin accumulation is large enough to be
detected in optical rotation experiments.Comment: 5 pages, 2 figure
On the jets, kinks, and spheromaks formed by a planar magnetized coaxial gun
Measurements of the various plasma configurations produced by a planar
magnetized coaxial gun provide insight into the magnetic topology evolution
resulting from magnetic helicity injection. Important features of the
experiments are a very simple coaxial gun design so that all observed
geometrical complexity is due to the intrinsic physical dynamics rather than
the source shape and use of a fast multiple-frame digital camera which provides
direct imaging of topologically complex shapes and dynamics. Three key
experimental findings were obtained: (1) formation of an axial collimated jet
[Hsu and Bellan, Mon. Not. R. Astron. Soc. 334, 257 (2002)] that is consistent
with a magnetohydrodynamic description of astrophysical jets, (2)
identification of the kink instability when this jet satisfies the
Kruskal-Shafranov limit, and (3) the nonlinear properties of the kink
instability providing a conversion of toroidal to poloidal flux as required for
spheromak formation by a coaxial magnetized source [Hsu and Bellan, Phys. Rev.
Lett. 90, 215002 (2003)]. A new interpretation is proposed for how the n=1
central column instability provides flux amplification during spheromak
formation and sustainment, and it is shown that jet collimation can occur
within one rotation of the background poloidal field.Comment: Physics of Plasmas (accepted
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