343 research outputs found
Comments on Paper Prepared by C. T. Warwick on the Subject of My Ideas of an Ideal District Organization as It Relates to Maintenance, Equipment, Traffic and Safety.
Parallax of PSR J1744-1134 and the Local Interstellar Medium
We present the annual trigonometric parallax of PSR J1744-1134 derived from
an analysis of pulse times of arrival. The measured parallax, pi = 2.8+/-0.3
mas ranks among the most precisely determined distances to any pulsar. The
parallax distance of 357+/-39 pc is over twice that derived from the dispersion
measure using the Taylor & Cordes model for the Galactic electron distribution.
The mean electron density in the path to the pulsar, n_e = (0.0088 +/- 0.0009)
cm^{-3}, is the lowest for any disk pulsar. We have compared the n_e for PSR
J1744-1134 with those for another 11 nearby pulsars with independent distance
estimates. We conclude that there is a striking asymmetry in the distribution
of electrons in the local interstellar medium. The electron column densities
for pulsars in the third Galactic quadrant are found to be systematically
higher than for those in the first. The former correlate with the position of
the well known local HI cavity in quadrant three. The excess electrons within
the cavity may be in the form of HII clouds marking a region of interaction
between the local hot bubble and a nearby superbubble.Comment: revised version accepted for publication in ApJ Letters; reanalysis
of uncertainty in parallax measure and changes to fig
Diffusion as mixing mechanism in granular materials
We present several numerical results on granular mixtures. In particular, we
examine the efficiency of diffusion as a mixing mechanism in these systems. The
collisions are inelastic and to compensate the energy loss, we thermalize the
grains by adding a random force. Starting with a segregated system, we show
that uniform agitation (heating) leads to a uniform mixture of grains of
different sizes. We define a characteristic mixing time, , and
study theoretically and numerically its dependence on other parameters like the
density. We examine a model for bidisperse systems for which we can calculate
some physical quantities. We also examine the effect of a temperature gradient
and demonstrate the appearance of an expected segregation.Comment: 15 eps figures, include
New procedures for testing whether stock price processes are martingales
We propose procedures for testing whether stock price processes are
martingales based on limit order type betting strategies. We first show that
the null hypothesis of martingale property of a stock price process can be
tested based on the capital process of a betting strategy. In particular with
high frequency Markov type strategies we find that martingale null hypotheses
are rejected for many stock price processes
Casimir Scaling from Center Vortices: Towards an Understanding of the Adjoint String Tension
We argue that the approximate ``Casimir scaling'' of the string tensions of
higher-representation Wilson loops is an effect due to the finite thickness of
center vortex configurations. It is shown, in the context of a simple model of
the Z(2) vortex core, how vortex condensation in Yang-Mills theory can account
for both Casimir scaling in intermediate size loops, and color-screening in
larger loops. An implication of our model is that the deviations from exact
Casimir scaling, which tend to grow with loop size, become much more pronounced
as the dimensionality of the group representation increases.Comment: 13 pages, including 3 eps figures, Latex2e. Two references adde
The intellectual influence of economic journals: quality versus quantity
The evaluation of scientific output has a key role in the allocation of
research funds and academic positions. Decisions are often based on quality indicators
for academic journals, and over the years, a handful of scoring methods have
been proposed for this purpose. Discussing the most prominent methods (de facto
standards) we show that they do not distinguish quality from quantity at article level.
The systematic bias we find is analytically tractable and implies that the methods are
manipulable. We introduce modified methods that correct for this bias, and use them
to provide rankings of economic journals. Our methodology is transparent; our results
are replicable
Planeamiento territorial sostenible: un reto para el futuro de nuestras sociedades; criterios aplicados
In a large part of the 17 sustainable development objectives set as goals for humanity by the UN, sustainability can be glimpsed. As a result of the dominant socio-productive model, the only way to head towards more sustainable territories that allow achieving and maintaining the well-being of the world's population is to bear in mind the need to properly plan territorial development. This work reflects on this need and takes a step forward in the definition of the main criteria to achieve territorial sustainability at regional and local scales
A protocol paper for the MOTION Study—A longitudinal study in a cohort aged 60 years and older to obtain mechanistic knowledge of the role of the gut microbiome during normal healthy ageing in order to develop strategies that will improve lifelong health and wellbeing
Background: Advances in medicine and public health mean that people are living longer; however, a significant proportion of that increased lifespan is spent in a prolonged state of declining health and wellbeing which places increasing pressure on medical, health and social services. There is a social and economic need to develop strategies to prevent or delay age-related disease and maintain lifelong health. Several studies have suggested links between the gut microbiome and age-related disease, which if confirmed would present a modifiable target for intervention development. The MOTION study aims to determine whether and how changes in the gut microbiome are associated with physical and mental capacity. A comprehensive longitudinal multiparameter study such as this has not been previously undertaken. Methods: MOTION is a longitudinal prospective cohort study with a focus on gut health and cognitive function. 360 healthy individuals aged 60 years and older, living in East Anglia, UK will be recruited to the study, stratified into one of three risk groups (cohorts) for developing dementia based on their cognitive function. Participants will attend study appointments every six months over four years, providing stool and blood samples and a health questionnaire. Participants will also undergo physical measurements and cognitive tests at alternating appointments, and undergo Optical Coherence Tomography scans at 3 timepoints. Two subgroups of participants in the study will provide colonic tissue biopsies (n = ≥30 from each cohort), and brain imaging (n = 30) at two timepoints. Discussion: This study will provide new insights into the gut-(microbiota)-brain axis and the relationship between age-associated changes in gut microbe populations and cognitive health. Such insights could help develop new microbe-based strategies to improve lifelong health and wellbeing
Preheat Effects on Microballoon Laser-Fusion Implosions
Nonequilibrium hydroburn simulations of early laser-driven compression experiments indicate that low energy photons from the vicinity of the ablation surface are preheating the microballoon-pushers, thereby severely limiting the compressions achieved (similar degradation may result from 1 to 4 percent energy deposition by superthermal electrons). This implies an 8- to 27-fold increase in the energy requirements for breakeven, unless radiative preheat can be drastically reduced by, say, the use of composite ablator-pushers. (auth
Human resources for maternal health: multi-purpose or specialists?
A crucial question in the aim to attain MDG5 is whether it can be achieved faster with the scaling up of multi-purpose health workers operating in the community or with the scaling up of professional skilled birth attendants working in health facilities. Most advisers concerned with maternal mortality reduction concur to promote births in facilities with professional attendants as the ultimate strategy. The evidence, however, is scarce on what it takes to progress in this path, and on the 'interim solutions' for situations where the majority of women still deliver at home. These questions are particularly relevant as we have reached the twentieth anniversary of the safe motherhood initiative without much progress made
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