5,231 research outputs found
Aharonov-Bohm Problem for Spin-One
The basic AB problem is to determine how an unshielded tube of magnetic flux
affects arbitrarily long-wavelength charged particles impinging on it.
For spin-1 at almost all the particles do not penetrate the tube, so the
interaction essentially is periodic in (AB effect). Below-threshold
bound states move freely only along the tube axis, and consequent induced
vacuum currents supplement rather than screen . For a pure magnetic
interaction the tube must be broader than the particle Compton wavelength,
i.e., only the nonrelativistic spin-1 AB problem exists.Comment: 15 pages, Late
A New Kinematic Distance Estimator to the LMC
The distance to the Large Magellanic Cloud (LMC) can be directly determined
by measuring three of its properties, its radial-velocity field, its mean
proper motion, and the position angle \phi_ph of its photometric line of nodes.
Statistical errors of 2% are feasible based on proper motions obtained with any
of several proposed astrometry satellites, the first possibility being the
Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic
error is likely to be in the determination of \phi_ph. I suggest two
independent methods to measure \phi_ph, one based on counts of clump giants and
the other on photometry of clump giants. I briefly discuss a variety of methods
to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page
The planets around NN Serpentis : still there
We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the William Herschel Telescope and New Technology Telescope, the RISE camera on the Liverpool Telescope and HAWK-I on the Very Large Telescope to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25 yr. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36 s that has set in since 2010 compared to the previous 8 yr of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9 ± 0.5 and 15.3 ± 0.3 yr, and masses of 2.3 ± 0.5 and 7.3 ± 0.3 MJ. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07 s relative to the best-fitting model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems
InP/Ga0.47In0.53As monolithic, two-junction, three-terminal tandem solar cells
The work presented has focussed on increasing the efficiency of InP-based solar cells through the development of a high-performance InP/Ga(0.47)In(0.53)As two-junction, three-terminal monolithic tandem cell. Such a tandem is particularly suited to space applications where a radiation-hard top cell (i.e., InP) is required. Furthermore, the InP/Ga(0.47)In(0.53)As materials system is lattice matched and offers a top cell/bottom cell bandgap differential (0.60 eV at 300 K) suitable for high tandem cell efficiencies under AMO illumination. A three-terminal configuration was chosen since it allows for independent power collection from each subcell in the monolithic stack, thus minimizing the adverse impact of radiation damage on the overall tandem efficiency. Realistic computer modeling calculations predict an efficiency boost of 7 to 11 percent from the Ga(0.47)In(0.53)As bottom cell under AMO illumination (25 C) for concentration ratios in the 1 to 1000 range. Thus, practical AMO efficiencies of 25 to 32 percent appear possible with the InP/Ga(0.47)In(0.53)As tandem cell. Prototype n/p/n InP/Ga(0.47)In(0.53)As monolithic tandem cells were fabricated and tested successfully. Using an aperture to define the illuminated areas, efficiency measurements performed on a non-optimized device under standard global illumination conditions (25 C) with no antireflection coating (ARC) give 12.2 percent for the InP top cell and 3.2 percent for the Ga(0.47)In(0.53)As bottom cell, yielding an overall tandem efficiency of 15.4 percent. With an ARC, the tandem efficiency could reach approximately 22 percent global and approximately 20 percent AMO. Additional details regarding the performance of individual InP and Ga(0.47)In(0.53)As component cells, fabrication and operation of complete tandem cells and methods for improving the tandem cell performance, are also discussed
2008 LC18: a potentially unstable Neptune Trojan
The recent discovery of the first Neptune Trojan at the planet's trailing
(L5) Lagrange point, 2008 LC18, offers an opportunity to confirm the formation
mechanism of a member of this important tracer population for the Solar
system's dynamical history. We tested the stability of 2008 LC18's orbit
through a detailed dynamical study, using test particles spread across the
orbital uncertainties in a, e, i and {\Omega}. This showed that the wide
uncertainties of the published orbit span regions of both extreme dynamical
instability, with lifetimes 1 Gyr
lifetimes). The stability of 2008 LC18's clones is greatly dependent on their
semi-major axis and only weakly correlated with their eccentricity. Test
particles on orbits with an initial semi-major axis less than 29.91 AU have
dynamical half-lives shorter than 100 Myr; in contrast, particles with an
initial semi-major axis greater than 29.91 AU exhibit such strong dynamical
stability that almost all are retained over the 1 Gyr of our simulations. More
observations of this object are necessary to improve the orbit. If 2008 LC18 is
in the unstable region, then our simulations imply that it is either a
temporary Trojan capture, or a representative of a slowly decaying Trojan
population (like its sibling the L4 Neptunian Trojan 2001 QR322), and that it
may not be primordial. Alternatively, if the orbit falls into the larger,
stable region, then 2008 LC18 is a primordial member of the highly stable and
highly inclined component of the Neptune Trojan population, joining 2005 TN53
and 2007 VL305. We attempted to recover 2008 LC18 using the 2.3m telescope at
Siding Spring Observatory to provide this astrometry, but were unsuccessful due
to the high stellar density of its current sky location near the galactic
centre. The recovery of this object will require a telescope in the 8m class.Comment: 11 pages, 3 figures, 1 table, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Distribution of equilibrium free energies in a thermodynamic system with broken ergodicity
At low temperatures the configurational phase space of a macroscopic complex
system (e.g., a spin-glass) of interacting particles may split
into an exponential number of
ergodic sub-spaces (thermodynamic states). Previous theoretical studies assumed
that the equilibrium collective behavior of such a system is determined by its
ground thermodynamic states of the minimal free-energy density, and that the
equilibrium free energies follow the distribution of exponential decay. Here we
show that these assumptions are not necessarily valid. For some complex
systems, the equilibrium free-energy values may follow a Gaussian distribution
within an intermediate temperature range, and consequently their equilibrium
properties are contributed by {\em excited} thermodynamic states. This work
will help improving our understanding of the equilibrium statistical mechanics
of spin-glasses and other complex systems.Comment: 7 pages, 2 figure
Pulmonary Alveolar Proteinosis- A Case Report
ABSTRACT
Background: Pulmonary Alveolar Proteinosis (PAP) is a rare pulmonary disorder caused by a congregation of excessive lipoproteinaceous material in the alveolar spaces due to impaired surfactant metabolism. The congregation of the protein in the alveolar space leads to difficulty in breathing, impaired pulmonary immunity, and susceptibility to both opportunistic and acquired pulmonary infections. Although Pulmonary Alveolar Proteinosis is rare, there are potential treatments. Whole-lung lavage is the most widely accepted therapy and course of treatment. An additional form of therapy, GM-CSF stimulating therapy, uses recombinant deoxyribonucleic acid (DNA) technology to increase white cell production.
Purpose: The purpose of this case report is to follow a patient through whole-lung lavage therapy to determine outcome and clinical improvement.
Case Description: This case report follows a 55-year-old female patient diagnosed with secondary, idiopathic Pulmonary Alveolar Proteinosis through eight normal saline whole-lung lavages. The patient’s treatment was led by a pulmonologist with previous Pulmonary Alveolar Proteinosis experience.
Outcome: By the end of the first four lavages, the patient showed clinical improvement, but during a two-month break from therapy, symptoms returned. Following the break, the patient underwent four additional lung lavage sessions and experienced similar relief as in previous courses of treatment.
Discussion: The patient did complete an additional eight lavages to wash out excess lipoproteinaceous material to provide a longer period of symptom relief. The additional form of therapy, GM-CSF, is not a therapy option for this patient as the disease was idiopathic in nature. The last available treatment option for this patient is a lung transplant
On-Line Learning with Restricted Training Sets: An Exactly Solvable Case
We solve the dynamics of on-line Hebbian learning in large perceptrons
exactly, for the regime where the size of the training set scales linearly with
the number of inputs. We consider both noiseless and noisy teachers. Our
calculation cannot be extended to non-Hebbian rules, but the solution provides
a convenient and welcome benchmark with which to test more general and advanced
theories for solving the dynamics of learning with restricted training sets.Comment: 19 pages, eps figures included, uses epsfig macr
Finite size scaling in neural networks
We demonstrate that the fraction of pattern sets that can be stored in
single- and hidden-layer perceptrons exhibits finite size scaling. This feature
allows to estimate the critical storage capacity \alpha_c from simulations of
relatively small systems. We illustrate this approach by determining \alpha_c,
together with the finite size scaling exponent \nu, for storing Gaussian
patterns in committee and parity machines with binary couplings and up to K=5
hidden units.Comment: 4 pages, RevTex, 5 figures, uses multicol.sty and psfig.st
Winds of Planet Hosting Stars
The field of exoplanetary science is one of the most rapidly growing areas of
astrophysical research. As more planets are discovered around other stars, new
techniques have been developed that have allowed astronomers to begin to
characterise them. Two of the most important factors in understanding the
evolution of these planets, and potentially determining whether they are
habitable, are the behaviour of the winds of the host star and the way in which
they interact with the planet. The purpose of this project is to reconstruct
the magnetic fields of planet hosting stars from spectropolarimetric
observations, and to use these magnetic field maps to inform simulations of the
stellar winds in those systems using the Block Adaptive Tree Solar-wind Roe
Upwind Scheme (BATS-R-US) code. The BATS-R-US code was originally written to
investigate the behaviour of the Solar wind, and so has been altered to be used
in the context of other stellar systems. These simulations will give
information about the velocity, pressure and density of the wind outward from
the host star. They will also allow us to determine what influence the winds
will have on the space weather environment of the planet. This paper presents
the preliminary results of these simulations for the star Bo\"otis,
using a newly reconstructed magnetic field map based on previously published
observations. These simulations show interesting structures in the wind
velocity around the star, consistent with the complex topology of its magnetic
field.Comment: 8 pages, 2 figures, accepted for publication in the peer-reviewed
proceedings of the 14th Australian Space Research Conference, held at the
University of South Australia, 29th September - 1st October 201
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