4,780 research outputs found
The Populations of Comet-Like Bodies in the Solar system
A new classification scheme is introduced for comet-like bodies in the Solar
system. It covers the traditional comets as well as the Centaurs and
Edgeworth-Kuiper belt objects. At low inclinations, close encounters with
planets often result in near-constant perihelion or aphelion distances, or in
perihelion-aphelion interchanges, so the minor bodies can be labelled according
to the planets predominantly controlling them at perihelion and aphelion. For
example, a JN object has a perihelion under the control of Jupiter and aphelion
under the control of Neptune, and so on. This provides 20 dynamically distinct
categories of outer Solar system objects in the Jovian and trans-Jovian
regions. The Tisserand parameter with respect to the planet controlling
perihelion is also often roughly constant under orbital evolution. So, each
category can be further sub-divided according to the Tisserand parameter. The
dynamical evolution of comets, however, is dominated not by the planets nearest
at perihelion or aphelion, but by the more massive Jupiter. The comets are
separated into four categories -- Encke-type, short-period, intermediate and
long-period -- according to aphelion distance. The Tisserand parameter
categories now roughly correspond to the well-known Jupiter-family comets,
transition-types and Halley-types. In this way, the nomenclature for the
Centaurs and Edgeworth-Kuiper belt objects is based on, and consistent with,
that for comets.Comment: MNRAS, in press, 11 pages, 6 figures (1 available as postscript, 5 as
gif). Higher resolution figures available at
http://www-thphys.physics.ox.ac.uk/users/WynEvans/preprints.pd
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
Dynamics of Learning with Restricted Training Sets I: General Theory
We study the dynamics of supervised learning in layered neural networks, in
the regime where the size of the training set is proportional to the number
of inputs. Here the local fields are no longer described by Gaussian
probability distributions and the learning dynamics is of a spin-glass nature,
with the composition of the training set playing the role of quenched disorder.
We show how dynamical replica theory can be used to predict the evolution of
macroscopic observables, including the two relevant performance measures
(training error and generalization error), incorporating the old formalism
developed for complete training sets in the limit as a
special case. For simplicity we restrict ourselves in this paper to
single-layer networks and realizable tasks.Comment: 39 pages, LaTe
The WARPS survey - IV: The X-ray luminosity-temperature relation of high redshift galaxy clusters
We present a measurement of the cluster X-ray luminosity-temperature relation
out to high redshift (z~0.8). Combined ROSAT PSPC spectra of 91 galaxy clusters
detected in the Wide Angle ROSAT Pointed Survey (WARPS) are simultaneously fit
in redshift and luminosity bins. The resulting temperature and luminosity
measurements of these bins, which occupy a region of the high redshift L-T
relation not previously sampled, are compared to existing measurements at low
redshift in order to constrain the evolution of the L-T relation. We find a
best fit to low redshift (z1 keV, to be L proportional
to T^(3.15\pm0.06). Our data are consistent with no evolution in the
normalisation of the L-T relation up to z~0.8. Combining our results with ASCA
measurements taken from the literature, we find eta=0.19\pm0.38 (for Omega_0=1,
with 1 sigma errors) where L_Bol is proportional to (1 + z)^eta T^3.15, or
eta=0.60\pm0.38 for Omega_0=0.3. This lack of evolution is considered in terms
of the entropy-driven evolution of clusters. Further implications for
cosmological constraints are also discussed.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Towards an integrated pipeline for the in-silico prediction of plant microRNAs and their precursors
MicroRNAs (miRNAs) are endogenous, small (~ 20 nt), single-stranded, non-coding RNAs that result from the processing of transcribed precursor hairpin structures. They are increasingly recognized as playing crucial roles as post-transcriptional antisense regulators of gene expression through regulation of mRNA stability or translational efficiency.
The detection of homologs of known miRNAs through comparative genomic approaches has proved relatively tractable. However, the ab-initio prediction of potentially lineage-specific miRNA precursors through computational methods poses several additional difficulties, not least the fact that not all thermodynamically plausible transcribed hairpins are processed to yield mature miRNAs.
We have developed a Support Vector Machine that considers up to 78 features associated with the primary and secondary structures and thermodynamic characteristics of candidate hairpin structures. Our SVM is highly specific in the discrimination of true miRNA precursors from “spurious” hairpins with levels of false positive predictions that are low relative to comparable methods. We also show how our SVM functions as part of an in-silico pipeline for the prediction of novel miRNA precursors in plant genomes
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
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