13,165 research outputs found
Box-ball system: soliton and tree decomposition of excursions
We review combinatorial properties of solitons of the Box-Ball system
introduced by Takahashi and Satsuma in 1990. Starting with several definitions
of the system, we describe ways to identify solitons and review a proof of the
conservation of the solitons under the dynamics. Ferrari, Nguyen, Rolla and
Wang 2018 proposed a soliton decomposition of a configuration into a family of
vectors, one for each soliton size. Based on this decompositions, the authors
have proposed a family of measures on the set of excursions which induces
invariant distributions for the Box-Ball System. In this paper, we propose a
new soliton decomposition which is equivalent to a branch decomposition of the
tree associated to the excursion, see Le Gall 2005. A ball configuration
distributed as independent Bernoulli variables of parameter is in
correspondence with a simple random walk with negative drift and
infinitely many excursions over the local minima. In this case the authors have
proven that the soliton decomposition of the walk consists on independent
double-infinite vectors of iid geometric random variables. We show that this
property is shared by the branch decomposition of the excursion trees of the
random walk and discuss a corresponding construction of a Geometric branching
process with independent but not identically distributed Geometric random
variables.Comment: 47 pages, 33 figures. This is the revised version after addressing
referee reports. This version will be published in the special volume of the
XIII Simposio de Probabilidad y Procesos Estoc\'asticos, UNAM Mexico, by
Birkhause
Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
We present 2D MHD simulations of the radiatively driven outflow from a
rotating hot star with a dipole magnetic field aligned with the star's rotation
axis. We focus primarily on a model with moderately rapid rotation (half the
critical value), and also a large magnetic confinement parameter, . The magnetic field
channels and torques the wind outflow into an equatorial, rigidly rotating disk
extending from near the Kepler corotation radius outwards. Even with
fine-tuning at lower magnetic confinement, none of the MHD models produce a
stable Keplerian disk. Instead, material below the Kepler radius falls back on
to the stellar surface, while the strong centrifugal force on material beyond
the corotation escape radius stretches the magnetic loops outwards, leading to
episodic breakout of mass when the field reconnects. The associated dissipation
of magnetic energy heats material to temperatures of nearly K, high
enough to emit hard (several keV) X-rays. Such \emph{centrifugal mass ejection}
represents a novel mechanism for driving magnetic reconnection, and seems a
very promising basis for modeling X-ray flares recently observed in rotating
magnetic Bp stars like Ori E.Comment: 5 pages, 3 figures, accepted by ApJ
Phase transition in a log-normal Markov functional model
We derive the exact solution of a one-dimensional Markov functional model
with log-normally distributed interest rates in discrete time. The model is
shown to have two distinct limiting states, corresponding to small and
asymptotically large volatilities, respectively. These volatility regimes are
separated by a phase transition at some critical value of the volatility. We
investigate the conditions under which this phase transition occurs, and show
that it is related to the position of the zeros of an appropriately defined
generating function in the complex plane, in analogy with the Lee-Yang theory
of the phase transitions in condensed matter physics.Comment: 9 pages, 5 figures. v2: Added asymptotic expressions for the
convexity-adjusted Libors in the small and large volatility limits. v3: Added
one reference. Final version to appear in Journal of Mathematical Physic
A Landslide Climate Indicator from Machine Learning
In order to create a Landslide Hazard Index, we accessed rain, snow, and a dozen other variables from the National Climate Assessment Land Data Assimilation System. These predictors were converted to probabilities of landslide occurrence with XGBoost, a major machine-learning tool. The model was fitted with thousands of historical landslides from the Pacific Northwest Landslide Inventory (PNLI)
The Effect of Porosity on X-ray Emission Line Profiles from Hot-Star Winds
We investigate the degree to which the nearly symmetric form of X-ray
emission lines seen in Chandra spectra of early-type supergiant stars could be
explained by a possibly porous nature of their spatially structured stellar
winds. Such porosity could effectively reduce the bound-free absorption of
X-rays emitted by embedded wind shocks, and thus allow a more similar
transmission of red- vs. blue-shifted emission from the back vs. front
hemispheres. For a medium consisting of clumps of size l and volume filling
factor f, in which the `porosity length' h=l/f increases with local radius as h
= h' r, we find that a substantial reduction in wind absorption requires a
quite large porosity scale factor h' > 1, implying large porosity lengths h >
r. The associated wind structure must thus have either a relatively large scale
l~ r, or a small volume filling factor f ~ l/r << 1, or some combination of
these. The relatively small-scale, moderate compressions generated by intrinsic
instabilities in line-driving seem unlikely to give such large porosity
lengths, leaving again the prospect of instead having to invoke a substantial
(ca. factor 5) downward revision in assumed mass-loss rates.Comment: 6 pages in apj-emulate; 3 figures; submitted to Ap
Effects of Inventory Bias on Landslide Susceptibility Calculations
Many landslide inventories are known to be biased, especially inventories for large regions such as Oregon's SLIDO or NASA's Global Landslide Catalog. These biases must affect the results of empirically derived susceptibility models to some degree. We evaluated the strength of the susceptibility model distortion from postulated biases by truncating an unbiased inventory. We generated a synthetic inventory from an existing landslide susceptibility map of Oregon, then removed landslides from this inventory to simulate the effects of reporting biases likely to affect inventories in this region, namely population and infrastructure effects. Logistic regression models were fitted to the modified inventories. Then the process of biasing a susceptibility model was repeated with SLIDO data. We evaluated each susceptibility model with qualitative and quantitative methods. Results suggest that the effects of landslide inventory bias on empirical models should not be ignored, even if those models are, in some cases, useful. We suggest fitting models in well-documented areas and extrapolating across the study region as a possible approach to modeling landslide susceptibility with heavily biased inventories
The male of the species: a profile of men in nursing
Aim: To establish a profile of men in nursing in Western Australia and explore the perception of men in nursing from the perspective of male and female nurses.
Background: A project team, including some of the current authors, produced a YouTube video and DVD about men in nursing which led to further inquiry on this topic.
Design: The study employed a non-experimental, comparative, descriptive research design focused on a quantitative methodology, using an online survey in early 2014.
Method: A convenience sample incorporated registered and enrolled nurses and midwives in Western Australia.
Findings: The range of data included demographic information and the respondents’ perceptions of men in nursing were collected. Findings indicated that the main reasons for choosing a career in nursing or midwifery were similar for both genders. Common mis-perceptions of men in nursing included: most male nurses are gay; men are not suited to nursing and men are less caring and compassionate than women. Suggestions to promote nursing to men included: nurses are highly skilled professionals; there is the potential to make a difference for patients; nursing offers stable employment, professional diversity and opportunities for team work. There is a diminished awareness of opportunities for men in nursing and negative stereotypes related to men in nursing persist.
Conclusion: The study produced recommendations which included: using the right message to target the recruitment for men and promoting a more realistic understanding of the profile and perception of men in nursing
Test of Guttmann and Enting's conjecture in the eight-vertex model
We investigate the analyticity property of the partially resummed series
expansion(PRSE) of the partition function for the eight-vertex model.
Developing a graphical technique, we have obtained a first few terms of the
PRSE and found that these terms have a pole only at one point in the complex
plane of the coupling constant. This result supports the conjecture proposed by
Guttmann and Enting concerning the ``solvability'' in statistical mechanical
lattice models.Comment: 15 pages, 3 figures, RevTe
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Targeting RyR Activity Boosts Antisense Exon 44 and 45 Skipping in Human DMD Skeletal or Cardiac Muscle Culture Models.
Systemic delivery of antisense oligonucleotides (AO) for DMD exon skipping has proven effective for reframing DMD mRNA, rescuing dystrophin expression, and slowing disease progression in animal models. In humans with Duchenne muscular dystrophy treated with AOs, low levels of dystrophin have been induced, and modest slowing of disease progression has been observed, highlighting the need for improved efficiency of human skipping drugs. Here, we demonstrate that dantrolene and Rycals S107 and ARM210 potentiate AO-mediated exon skipping of exon 44 or exon 45 in patient-derived myotube cultures with appropriate mutations. Further, dantrolene is shown to boost AO-mediated exon skipping in patient-derived, induced cardiomyocyte cultures. Our findings further validate the ryanodine receptors (RyR) as the likely target responsible for exon skip boosting and demonstrate potential applicability beyond exon 51 skipping. These data provide preclinical support of dantrolene trial as an adjuvant to AO-mediated exon-skipping therapy in humans and identify a novel Rycal, ARM210, for development as a potential exon-skipping booster. Further, they highlight the value of mutation-specific DMD culture models for basic discovery, preclinical drug screening and translation of personalized genetic medicines
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