2,111 research outputs found
Comparison between Eulerian diagnostics and finite-size Lyapunov exponents computed from altimetry in the Algerian basin
Transport and mixing properties of surface currents can be detected from
altimetric data by both Eulerian and Lagrangian diagnostics. In contrast with
Eulerian diagnostics, Lagrangian tools like the local Lyapunov exponents have
the advantage of exploiting both spatial and temporal variability of the
velocity field and are in principle able to unveil subgrid filaments generated
by chaotic stirring. However, one may wonder whether this theoretical advantage
is of practical interest in real-data, mesoscale and submesoscale analysis,
because of the uncertainties and resolution of altimetric products, and the
non-passive nature of biogeochemical tracers. Here we compare the ability of
standard Eulerian diagnostics and the finite-size Lyapunov exponent in
detecting instantaneaous and climatological transport and mixing properties. By
comparing with sea-surface temperature patterns, we find that the two
diagnostics provide similar results for slowly evolving eddies like the first
Alboran gyre. However, the Lyapunov exponent is also able to predict the
(sub-)mesoscale filamentary process occuring along the Algerian current and
above the Balearic Abyssal Plain. Such filaments are also observed, with some
mismatch, in sea-surface temperature patterns. Climatologies of Lyapunov
exponents do not show any compact relation with other Eulerian diagnostics,
unveiling a different structure even at the basin scale. We conclude that
filamentation dynamics can be detected by reprocessing available altimetric
data with Lagrangian tools, giving insight into (sub-)mesoscale stirring
processes relevant to tracer observations and complementing traditional
Eulerian diagnostics
Lagrangian transport in a microtidal coastal area: the Bay of Palma, island of Mallorca, Spain
Coastal transport in the Bay of Palma, a small region in the island of
Mallorca, Spain, is characterized in terms of Lagrangian descriptors. The data
sets used for this study are the output for two months (one in autumn and one
in summer) of a high resolution numerical model, ROMS, forced atmospherically
and with a spatial resolution of 300 m. The two months were selected because
its different wind regime, which is the main driver of the sea dynamics in this
area. Finite-size Lyapunov Exponents (FSLEs) were used to locate
semi-persistent Lagrangian coherent structures (LCS) and to understand the
different flow regimes in the Bay. The different wind directions and regularity
in the two months have a clear impact on the surface Bay dynamics, whereas only
topographic features appear clearly in the bottom structures. The fluid
interchange between the Bay and the open ocean was tudied by computing particle
trajectories and Residence Times (RT) maps. The escape rate of particles out of
the Bay is qualitatively different, with a 32 more of escape rate of
particles to the ocean in October than in July, owing to the different
geometric characteristics of the flow. We show that LCSs separate regions with
different transport properties by displaying spatial distributions of residence
times on synoptic Lagrangian maps together with the location of the LCSs.
Correlations between the time-dependent behavior of FSLE and RT are also
investigated, showing a negative dependence when the stirring characterized by
FSLE values moves particles in the direction of escape
The reduction of plankton biomass induced by mesoscale stirring: a modeling study in the Benguela upwelling
Recent studies, both based on remote sensed data and coupled models, showed a
reduction of biological productivity due to vigorous horizontal stirring in
upwelling areas. In order to better understand this phenomenon, we consider a
system of oceanic flow from the Benguela area coupled with a simple
biogeochemical model of Nutrient-Phyto-Zooplankton (NPZ) type. For the flow
three different surface velocity fields are considered: one derived from
satellite altimetry data, and the other two from a regional numerical model at
two different spatial resolutions. We compute horizontal particle dispersion in
terms of Lyapunov Exponents, and analyzed their correlations with phytoplankton
concentrations. Our modelling approach confirms that in the south Benguela
there is a reduction of biological activity when stirring is increased.
Two-dimensional offshore advection and latitudinal difference in Primary
Production, also mediated by the flow, seem to be the dominant processes
involved. We estimate that mesoscale processes are responsible for 30 to 50% of
the offshore fluxes of biological tracers. In the northern area, other factors
not taken into account in our simulation are influencing the ecosystem. We
suggest explanations for these results in the context of studies performed in
other eastern boundary upwelling areas
Burridge-Knopoff Models as Elastic Excitable Media
We construct a model of an excitable medium with elastic rather than the
usual diffusive coupling. We explore the dynamics of elastic excitable media,
which we find to be dominated by low dimensional structures, including global
oscillations, period-doubled pacemakers, and propagating fronts. We suggest
that examples of elastic excitable media are to be found in such diverse
physical systems as Burridge-Knopoff models of frictional sliding, electronic
transmission lines, and active optical waveguides
Inhomogeneities and caustics in the sedimentation of noninertial particles in incompressible flows
In an incompressible flow, fluid density remains invariant along fluid
element trajectories. This implies that the spatial distribution of
non-interacting noninertial particles in such flows cannot develop density
inhomogeneities beyond those that are already introduced in the initial
condition. However, in certain practical situations, density is measured or
accumulated on (hyper-) surfaces of dimensionality lower than the full
dimensionality of the flow in which the particles move. An example is the
observation of particle distributions sedimented on the floor of the ocean. In
such cases, even if the initial distribution of noninertial particles is
uniform within a finite support in an incompressible flow, advection in the
flow will give rise to inhomogeneities in the observed density. In this paper
we analytically derive, in the framework of an initially homogeneous particle
sheet sedimenting towards a bottom surface, the relationship between the
geometry of the flow and the emerging distribution. From a physical point of
view, we identify the two processes that generate inhomogeneities to be the
stretching within the sheet, and the projection of the deformed sheet onto the
target surface. We point out that an extreme form of inhomogeneity, caustics,
can develop for sheets. We exemplify our geometrical results with simulations
of particle advection in a simple kinematic flow, study the dependence on
various parameters involved, and illustrate that the basic mechanisms work
similarly if the initial (homogeneous) distribution occupies a more general
region of finite extension rather than a sheet.Comment: 56 pages, 17 figure
Hydrodynamic provinces and oceanic connectivity from a transport network help designing marine reserves
Oceanic dispersal and connectivity have been identified as crucial factors
for structuring marine populations and designing Marine Protected Areas (MPAs).
Focusing on larval dispersal by ocean currents, we propose an approach coupling
Lagrangian transport and new tools from Network Theory to characterize marine
connectivity in the Mediterranean basin. Larvae of different pelagic durations
and seasons are modeled as passive tracers advected in a simulated oceanic
surface flow from which a network of connected areas is constructed.
Hydrodynamical provinces extracted from this network are delimited by frontiers
which match multi-scale oceanographic features. By examining the repeated
occurrence of such boundaries, we identify the spatial scales and geographic
structures that would control larval dispersal across the entire seascape.
Based on these hydrodynamical units, we study novel connectivity metrics for
existing reserves. Our results are discussed in the context of ocean
biogeography and MPAs design, having ecological and managerial implications
Classical analogies for the force acting on an impurity in a Bose-Einstein condensate
We study the hydrodynamic forces acting on a small impurity moving in a
two-dimensional Bose-Einstein condensate at non-zero temperature. The
condensate is modelled by the damped-Gross Pitaevskii (dGPE) equation and the
impurity by a Gaussian repulsive potential coupled to the condensate. For weak
coupling, we obtain analytical expressions for the forces acting on the
impurity, and compare them with those computed through direct numerical
simulations of the dGPE and with the corresponding expressions for classical
forces. For non-steady flows, there is a time-dependent force dominated by
inertial effects and which has a correspondence in the Maxey-Riley theory for
particles in classical fluids. In the steady-state regime, the force is
dominated by a self-induced drag. Unlike at zero temperature, where the drag
force vanishes below a critical velocity, at low temperatures the impurity
experiences a net drag even at small velocities, as a consequence of the energy
dissipation through interactions of the condensate with the thermal cloud. This
dissipative force due to thermal drag is similar to the classical Stokes' drag.
There is still a critical velocity above which steady-state drag is dominated
by acoustic excitations and behaves non-monotonically with impurity's speed.Comment: 21 pages, 4 figures. Supplementary movies available at:
https://cloud.ifisc.uib-csic.es/nextcloud/index.php/s/AFzw6JxNW77DT6
Climaterio y sexualidad
Objective: To study the impact that climacterium causes in the sexual life of the women resident in Mérida and to identify what sexual changes take place.Methodology: A descriptive and retrospective study was prepared with 102 menopausal women, aged from 45 to 59. Results: The measurements more affected before menopause were sexual desire, vaginal lubrication and sexual satisfaction. 65.6% of those polled women showed alteration in their sexual function after menopause. 33% of women stated that they do not have any difficulty in their sexuality while 22.5% tagged dissatisfaction with body changes as the cause of their difficulties.Conclusion: Mainly menopause has had a negative impact on the sexuality of the women studied. Nursing professionals should be aware and deal with this issue from the scope of their competences.Objetivo: Estudiar el impacto que produce el climaterio en la vida sexual de las mujeres que residen en Mérida e identificar los cambios sexuales que tienen lugar. Metodología: Se ha elaborado un estudio de carácter descriptivo y retrospectivo con 102 mujeres con menopausia natural y una edad comprendida entre los 45 y los 59 años.Resultados: Las dimensiones más afectadas tras la menopausia han sido: deseo sexual, lubricación vaginal y satisfacción sexual. Un 65.6% de las mujeres encuestadas presenta alteración de su función sexual después de la menopausia. El 33% de mujeres afirma no tener ninguna dificultad en su función sexual, mientras que el 22.5% señalan como principal motivo de sus dificultades la insatisfacción con los cambios corporales. Conclusión: Mayoritariamente la menopausia ha generado un impacto negativo en la sexualidad de las mujeres que han participado en el estudio. El profesional de enfermería debería tomar conciencia y abordar este problema desde el ámbito de sus competencias
Diversity and noise effects in a model of homeostatic regulation of the sleep-wake cycle
Recent advances in sleep neurobiology have allowed development of
physiologically based mathematical models of sleep regulation that account for
the neuronal dynamics responsible for the regulation of sleep-wake cycles and
allow detailed examination of the underlying mechanisms. Neuronal systems in
general, and those involved in sleep regulation in particular, are noisy and
heterogeneous by their nature. It has been shown in various systems that
certain levels of noise and diversity can significantly improve signal
encoding. However, these phenomena, especially the effects of diversity, are
rarely considered in the models of sleep regulation. The present paper is
focused on a neuron-based physiologically motivated model of sleep-wake cycles
that proposes a novel mechanism of the homeostatic regulation of sleep based on
the dynamics of a wake-promoting neuropeptide orexin. Here this model is
generalized by the introduction of intrinsic diversity and noise in the
orexin-producing neurons in order to study the effect of their presence on the
sleep-wake cycle. A quantitative measure of the quality of a sleep-wake cycle
is introduced and used to systematically study the generalized model for
different levels of noise and diversity. The model is shown to exhibit a clear
diversity-induced resonance: that is, the best wake-sleep cycle turns out to
correspond to an intermediate level of diversity at the synapses of the
orexin-producing neurons. On the other hand only a mild evidence of stochastic
resonance is found when the level of noise is varied. These results show that
disorder, especially in the form of quenched diversity, can be a key-element
for an efficient or optimal functioning of the homeostatic regulation of the
sleep-wake cycle. Furthermore, this study provides an example of constructive
role of diversity in a neuronal system that can be extended beyond the system
studied here.Comment: 18 pages, 12 figures, 1 tabl
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