179 research outputs found
Description of surface transport in the region of the Belizean Barrier Reef based on observations and alternative high-resolution models
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Ocean Modelling 106 (2016): 74–89, doi:10.1016/j.ocemod.2016.09.010.The gains from implementing high-resolution versus less costly low-resolution models to
describe coastal circulation are not always clear, often lacking statistical evaluation. Here
we construct a hierarchy of ocean-atmosphere models operating at multiple scales within
a 1×1° domain of the Belizean Barrier Reef (BBR). The various components of the
atmosphere-ocean models are evaluated with in situ observations of surface drifters, wind
and sea surface temperature. First, we compare the dispersion and velocity of 55 surface
drifters released in the field in summer 2013 to the dispersion and velocity of simulated
drifters under alternative model configurations. Increasing the resolution of the ocean
model (from 1/12° to 1/100°, from 1 day to 1 h) and atmosphere model forcing (from
1/2° to 1/100°, from 6 h to 1 h), and incorporating tidal forcing incrementally reduces
discrepancy between simulated and observed velocities and dispersion. Next, in trying to
understand why the high-resolution models improve prediction, we find that resolving
both the diurnal sea-breeze and semi-diurnal tides is key to improving the Lagrangian
statistics and transport predictions along the BBR. Notably, the model with the highest
ocean-atmosphere resolution and with tidal forcing generates a higher number of looping
trajectories and sub-mesoscale coherent structures that are otherwise unresolved. Finally,
simulations conducted with this model from June to August of 2013 show an
intensification of the velocity fields throughout the summer and reveal a mesoscale
anticyclonic circulation around Glovers Reef, and sub-mesoscale cyclonic eddies formed
in the vicinity of Columbus Island. This study provides a general framework to assess the
best surface transport prediction from alternative ocean-atmosphere models using metrics
derived from high frequency drifters’ data and meteorological stations.This research is supported by the National Science Foundation award NSF-OCE
1260424
Fixel-Based Analysis of Visual Pathway White Matter in Primary Open-Angle Glaucoma
Purpose: White matter (WM) degeneration of the visual pathways in primary open-angle glaucoma (POAG) is well documented, but its exact pathophysiology remains unclear. To date, glaucomatous WM degeneration has been exclusively studied using diffusion tensor imaging (DTI) only. However, DTI measures lack direct biological interpretation, and the approach itself suffers from multiple technical limitations. Fixel-based analysis (FBA) is a novel framework for studying WM degeneration, overcoming DTI's technical limitations and providing biologically meaningful metrics. FBA measures fiber density (FD), representing early microstructural changes, and fiber-bundle cross section (FC), representing late macrostructural changes. In this study, we use FBA to study glaucomatous degeneration of the pregeniculate optic tracts (OTs) and postgeniculate optic radiation (ORs) in POAG. Methods: This was a cross-sectional case-control study with 12 POAG patients and 16 controls. Multi-shell diffusion-weighted images were acquired. FBA was used to produce a population template, and probabilistic tractography was used to track the OTs and ORs in template space. Finally, FD and FC of the tracts of interest were compared between the two groups. Results: Compared with the controls, the OTs of the patients exhibited a significant (familywise error corrected P < 0.05) decrease in FD and FC, whereas their ORs exhibited a significant decrease in FD but not in FC. Conclusions: FBA provides sensitive measures to assess WM changes in glaucoma. Our findings suggest that the OTs of glaucoma patients exhibit signs of more advanced WM degeneration compared with the ORs. This potentially implicates anterograde trans-synaptic propagation as the primary cause of glaucomatous spread along the visual pathways
A new epigean false scorpion: Roncus sumadijae n. sp. (Neobisiidae, Pseudoscorpiones) from the Balkan Peninsula (Western Serbia)
A new endemic epigean species from the village of Adžina Livada, nr. Kragujevac, Mts. Gledićke Planine, western Serbia, is erected, described and thoroughly illustrated. Its main morphometric characters and important diagnostic features are analyzed and compared to the two closest congeners, Roncus ivanjicae B. Ćurčić, and R. golijae B. Ćurčić from western Serbia, respectively
Chiral symmetry breaking of magnetic vortices by sample roughness
Finite-element micromagnetic simulations are employed to study the chiral
symmetry breaking of magnetic vortices, caused by the surface roughness of
thin-film magnetic structures. An asymmetry between vortices with different
core polarizations has been experimentally observed for square-shaped
platelets. E.g., the threshold fields for vortex core switching were found to
differ for core up and down. This asymmetry was however not expected for these
symmetrically-shaped structures, where both core polarizations should behave
symmetrically. Three-dimensional finite element simulations are employed to
show that a small surface roughness can break the symmetry between vortex cores
pointing up and down. A relatively small sample roughness is found sufficient
to reproduce the experimentally observed asymmetries. It arises from the lack
of mirror-symmetry of the rough thin-film structures, which causes vortices
with different handedness to exhibit asymmetric dynamics
Magnetic Vortex Core Reversal by Excitation of Spin Waves
Micron-sized magnetic platelets in the flux closed vortex state are
characterized by an in-plane curling magnetization and a nanometer-sized
perpendicularly magnetized vortex core. Having the simplest non-trivial
configuration, these objects are of general interest to micromagnetics and may
offer new routes for spintronics applications. Essential progress in the
understanding of nonlinear vortex dynamics was achieved when low-field core
toggling by excitation of the gyrotropic eigenmode at sub-GHz frequencies was
established. At frequencies more than an order of magnitude higher vortex state
structures possess spin wave eigenmodes arising from the magneto-static
interaction. Here we demonstrate experimentally that the unidirectional vortex
core reversal process also occurs when such azimuthal modes are excited. These
results are confirmed by micromagnetic simulations which clearly show the
selection rules for this novel reversal mechanism. Our analysis reveals that
for spin wave excitation the concept of a critical velocity as the switching
condition has to be modified.Comment: Minor corrections and polishing of previous versio
Lateral and Medial Ventral Occipitotemporal Regions Interact During the Recognition of Images Revealed from Noise
Several studies suggest different functional roles for the medial and the lateral sections of the ventral visual cortex in object recognition. Texture and surface information is processed in medial sections, while shape information is processed in lateral sections. This begs the question whether and how these functionally specialized sections interact with each other and with early visual cortex to facilitate object recognition. In the current research, we set out to answer this question. In an fMRI study, 13 subjects viewed and recognized images of objects and animals that were gradually revealed from noise while their brains were being scanned. We applied dynamic causal modeling (DCM) a method to characterize network interactions to determine the modulatory effect of object recognition on a network comprising the primary visual cortex (V1), the lingual gyrus (LG) in medial ventral cortex and the lateral occipital cortex (LO). We found that object recognition modulated the bilateral connectivity between LG and LO. Moreover, the feed-forward connectivity from Vito LG and LO was modulated, while there was no evidence for feedback from these regions to V1 during object recognition. In particular, the interaction between medial and lateral areas supports a framework in which visual recognition of objects is achieved by networked regions that integrate information on image statistics, scene content and shape rather than by a single categorically specialized region within the ventral visual cortex
Sensitivity of storm surge predictions to atmospheric forcing during Hurricane Isaac
Storm surge and overland flooding can be predicted with computational models at high levels of resolution. To improve efficiency in forecasting applications, surge models often use atmospheric forcing from parametric vortex models, which represent the surface pressures and wind fields with a few storm parameters. The future of storm surge prediction could involve real-time coupling of surge and full-physics atmospheric models; thus, their accuracies must be understood in a real hurricane scenario. The authors compare predictions from a parametric vortex model (using forecast tracks from the National Hurricane Center) and a full-physics coupled atmosphere-wave-ocean model during Hurricane Isaac (2012). The predictions are then applied within a tightly coupled, wave and surge modeling system describing the northern Gulf of Mexico and the floodplains of southwest Louisiana. It is shown that, in a hindcast scenario, a parametric vortex model can outperform a data-assimilated wind product, and given reasonable forecast advisories, a parametric vortex model gives reasonable surge forecasts. However, forecasts using a full-physics coupled model outperformed the forecast advisories and improved surge forecasts. Both approaches are valuable for forecasting the coastal impacts associated with tropical cyclones
Degradation of linuron in soil by two fungi
Two fungal strains were applied to soil polluted with herbicide in order to
determine their degradation potential. Three experimental setups were used.
In the first setup, the soil in pots was contaminated by linuron in final
concentration of 1 ppm. Suspensions of Phanerocheate chrysosporium and
Trichoderma asperellum were applied separately or in combination. Tomato
plantlets were transplanted and chlorophyll content in their leaves was
determined at two time points during plant growth. In the second setup in
pots, the final concentration of linuron was lower, 0.45 ppm. In the third
setup 0.1 ppm of linuron was applied in the field plot. Plantlets of lettuce
were transplanted and chlorophyll content was measured as indicator of plant
stress. The content of linuron in soil was determined by HPLC. The applied
fungal strains significantly reduced toxic effect of 0.45 ppm linuron on
plants, which was not the case for 1 ppm linuron. Both fungi, applied
separately or in combination, were effective in decreasing the linuron
content in the soil. However, in field conditions the combination of both
fungi was the most effective. [Projekat Ministarstva nauke Republike Srbije,
br. III43010
Insight and emotion regulation in schizophrenia:A brain activation and functional connectivity study
Background: Insight is impaired in the majority of schizophrenia patients. The exact neural correlates of impaired insight remain unclear. We assume that the ability to regulate emotions contributes to having good clinical insight, as patients should be able to regulate their emotional state in such a way that they can adapt adequately in order to cope with impaired functioning and negative stigma associated with a diagnosis of schizophrenia. Numerous studies have shown emotional dysregulation in schizophrenia. We investigated the association between insight and brain activation and connectivity during emotion regulation. Methods: Brain activation during emotion regulation was measured with functional MRI in 30 individuals with schizophrenia. Two emotion regulation strategies were examined: cognitive reappraisal and expressive suppression. Clinical insight was measured with the Schedule for the Assessment of Insight - Expanded, and cognitive insight was measured with the Beck Cognitive Insight Scale. Whole brain random effects multiple regression analyses were conducted to assess the relation between brain activation during emotion regulation and insight. Generalized psychophysiological interaction (gPPI) was used to investigate the relation between task related connectivity and insight. Results: No significant associations were found between insight and neural correlates of cognitive reappraisal. For clinical insight and suppression, significant positive associations were found between symptom relabeling and activation in the left striatum, thalamus and insula, right insula and caudate, right pre-and postcentral gyrus, left superior occipital gyrus and cuneus and right middle and superior occipital gyrus and cuneus. Furthermore, reduced clinical insight was associated with more connectivity between midline medial frontal gyrus and right middle occipital gyrus. For cognitive insight and suppression, significant positive associations were found between self-reflectiveness and activation in pre-and postcentral gyrus and left middle cingulate gyrus. Conclusions: Our results suggest an association between the capacity to relabel symptoms and activation of brain systems involved in cognitive-emotional control and visual processing of negative stimuli. Furthermore, poorer self-reflectiveness may be associated with brain systems subserving control and execution
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