1,765 research outputs found
Kinetic description of avalanching systems
Avalanching systems are treated analytically using the renormalization group
(in the self-organized-criticality regime) or mean-field approximation,
respectively. The latter describes the state in terms of the mean number of
active and passive sites, without addressing the inhomogeneity in their
distribution. This paper goes one step further by proposing a kinetic
description of avalanching systems making use of the distribution function for
clusters of active sites. We illustrate application of the kinetic formalism to
a model proposed for the description of the avalanching processes in the
reconnecting current sheet of the Earth magnetosphere.Comment: 9 page
Seven years of marine environmental changes monitoring at coastal OOCS stations (Catalan Sea, NW Mediterranean)
Since March 2009 up to the present (more than 7 years now), the
Operational Observatory of the Catalan Sea (OOCS; http://www2.ceab.csic.es/
oceans/) remains a witness of persistent marine environmental changes. The OOCS
has two fixed observation stations at the head of the Blanes Canyon (200 m depth,
41.66°N; 2.91°E) and at the Blanes bay (20 m depth, 41.67°N; 2.80°E) in the Catalan
Sea, NW Mediterranean. At the canyon station, a multi-parametric buoy presently
installed delivers high frequency (by 30 min) and multi-parametric oceanographic
(i.e. salinity, temperature, chlorophyll, turbidity, as well as light intensity in the
PAR range for the upper 50 m depth) and atmospheric (air temperature, relative
humidity, wind speed and direction and PAR) data. Subsurface photos and videos
by an IP high resolution fisheye camera attached to the buoy are also delivered
at 4-hour basis. Data and multimedia are transmitted in near real time for public
access, via combined GSM/GPRS and 3G connections. At both stations, CTD profiles
and water samples (collected for nutrients and picoplankton analyses) are carried
out on board a research vessel at fortnightly basis. Numerical simulations along
with the time series of in-situ observations show inter-annual seasonality anomalies
possibly linked to global environmental changes. The lower-atmosphere and
upper-sea environmental time series data collected prove the occurrence of shifting
patterns of heat and matter fluxes impacting pelagic and benthic organisms.Peer Reviewe
Distributed Generation and Resilience in Power Grids
We study the effects of the allocation of distributed generation on the
resilience of power grids. We find that an unconstrained allocation and growth
of the distributed generation can drive a power grid beyond its design
parameters. In order to overcome such a problem, we propose a topological
algorithm derived from the field of Complex Networks to allocate distributed
generation sources in an existing power grid.Comment: proceedings of Critis 2012 http://critis12.hig.no
Continuous Time Random Walks in periodic systems: fluid limit and fractional differential equations on the circle
In this article, the continuous time random walk on the circle is studied. We
derive the corresponding generalized master equation and discuss the effects of
topology, especially important when Levy flights are allowed. Then, we work out
the fluid limit equation, formulated in terms of the periodic version of the
fractional Riemann-Liouville operators, for which we provide explicit
expressions. Finally, we compute the propagator in some simple cases. The
analysis presented herein should be relevant when investigating anomalous
transport phenomena in systems with periodic dimensions.Comment: 14 pages, 1 figure. References added. Published versio
A sandpile model with tokamak-like enhanced confinement phenomenology
Confinement phenomenology characteristic of magnetically confined plasmas
emerges naturally from a simple sandpile algorithm when the parameter
controlling redistribution scalelength is varied. Close analogues are found for
enhanced confinement, edge pedestals, and edge localised modes (ELMs), and for
the qualitative correlations between them. These results suggest that tokamak
observations of avalanching transport are deeply linked to the existence of
enhanced confinement and ELMs.Comment: Manuscript is revtex (latex) 1 file, 7 postscript figures Revised
version is final version accepted for publication in PRL Revisions are mino
Fractional generalization of Fick's law: a microscopic approach
In the study of transport in inhomogeneous systems it is common to construct
transport equations invoking the inhomogeneous Fick law. The validity of this
approach requires that at least two ingredients be present in the system.
First, finite characteristic length and time scales associated to the dominant
transport process must exist. Secondly, the transport mechanism must satisfy a
microscopic symmetry: global reversibility. Global reversibility is often
satisfied in nature. However, many complex systems exhibit a lack of finite
characteristic scales. In this Letter we show how to construct a generalization
of the inhomogeneous Fick law that does not require the existence of
characteristic scales while still satisfying global reversibility.Comment: 4 pages. Published versio
Impacto del consejo médico para dejar de fumar durante la gestación
ObjetivoEl consumo de tabaco entre las mujeres ha aumentado en España en los últimos años, especialmente entre los grupos en edad reproductiva. El objetivo del estudio es evaluar el impacto del consejo médico integrado en la atención prenatal sobre el consumo de tabaco durante el embarazo y en el posparto.DiseñoEstudio de intervención cuasiexperimental.EmplazamientoHospital del Mar de Barcelona.PacientesEl grupo control estaba constituido por 219 pacientes que acudieron para atención al parto al hospital del Mar en 1996, el grupo de intervención, por 169 pacientes atendidas durante el embarazo en el mismo hospital en 1997.IntervencionesLas pacientes del grupo control habían recibido atención habitual. Las gestantes del grupo de intervención recibieron de forma sistemática un consejo estructurado para dejar de fumar, reforzado por un folleto elaborado con esta finalidad.Mediciones y resultadosLos grupos de intervención y control no presentaban diferencias estadísticamente significativas en las variables sociodemográficas ni en el consumo de tabaco. En ambos grupos se determinó la evolución del hábito tabáquico durante el embarazo a lo largo de las visitas prenatales, y a los 6 meses posparto, a través de una entrevista telefónica. De las gestantes del grupo control, 44 (20,1%) habían dejado de fumar antes de la primera visita prenatal y 11 (5%) lo hicieron durante el embarazo. En el grupo de intervención 26 (17,7%) habían dejado de fumar espontáneamente y 16 (10,9%) dejaron de fumar durante el embarazo. De las que dejaron de fumar completamente durante el embarazo, se mantenían abstinentes a los 6 meses el 36,4% de las mujeres del grupo de control y el 64,3% en el grupo de intervención (p = 0,002).ConclusionesEl consejo para dejar de fumar en la visita prenatal produce un aumento discreto en la proporción de abandonos, y una disminución significativa de las recaídas en el posparto.ObjectiveWomen´s tobacco consumption has increased in Spain in recent years, especially among women of reproductive age. This study aims to evaluate the impact of medical counselling integrated into pre-natal care on tobacco consumption during pregnancy and the period after delivery.DesignQuasi-experimental intervention study.SettingHospital del Mar, Barcelona.Patients219 patients who attended the Hospital del Mar for delivery during 1996 (control group) and 169 patients seen during their pregnancies at the same hospital in 1997 (intervention group).InterventionsThe control group patients had received normal care. The pregnant women in the intervention group received systematic structured counselling on giving up smoking, backed up by a special brochure composed for this purpose.Measurements and resultsThe intervention and control groups showed no statistically significant differences either in their social or demographic variables or in their tobacco consumption. In both groups the evolution of their smoking during pregnancy was determined during their pre-natal visits and six months after delivery through a telephone interview. 44 of the women in the control group (20.1%) gave up smoking before their first pre-natal visit, and 11 (5%) gave up during pregnancy. In the intervention group 26 (17.7%) had given up spontaneously and 16 (10.9%) gave up during pregnancy. Of those who gave up completely during pregnancy, 36.4% of women in the control group and 64.3% in the intervention group remained abstinent at six months (P=.002).ConclusionsCounselling at pre-natal checkups to give up smoking lightly increases the number of women who give up and reduces significantly the number of post-delivery backsliders
- …