3,793 research outputs found
Interacting Brownian motions in infinite dimensions with logarithmic interaction potentials
We investigate the construction of diffusions consisting of infinitely
numerous Brownian particles moving in and interacting via
logarithmic functions (two-dimensional Coulomb potentials). These potentials
are very strong and act over a long range in nature. The associated equilibrium
states are no longer Gibbs measures. We present general results for the
construction of such diffusions and, as applications thereof, construct two
typical interacting Brownian motions with logarithmic interaction potentials,
namely the Dyson model in infinite dimensions and Ginibre interacting Brownian
motions. The former is a particle system in , while the latter is
in . Both models are translation and rotation invariant in space,
and as such, are prototypes of dimensions , respectively. The
equilibrium states of the former diffusion model are determinantal or Pfaffian
random point fields with sine kernels. They appear in the thermodynamical
limits of the spectrum of the ensembles of Gaussian random matrices such as
GOE, GUE and GSE. The equilibrium states of the latter diffusion model are the
thermodynamical limits of the spectrum of the ensemble of complex non-Hermitian
Gaussian random matrices known as the Ginibre ensemble.Comment: Published in at http://dx.doi.org/10.1214/11-AOP736 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Potential of mean force and the charge reversal of rodlike polyions
A simple model is presented to calculate the potential of mean force between
a polyion and a multivalent counterion inside a polyelectrolite solution. We
find that under certain conditions the electrostatic interactions can lead to a
strong attraction between the polyions and the multivalent counterions,
favoring formation of overcharged polyion-counterion complexes. It is found
that small concentrations of salt enhance the overcharging, while an excessive
amount of salt hinders the charge reversal. The kinetic limitations to
overcharging are also examined.Comment: To be published in the special issue of Molecular Physics in honor of
Prof. Ben Wido
The management of acute parathyroid crisis secondary to parathyroid carcinoma: a case report
<p>Abstract</p> <p>Introduction</p> <p>Hypercalcaemic hyperparathyroid crisis is a rare but life-threatening complication of primary hyperparathyroidism. Parathyroid carcinoma is a rare malignancy with an incidence of 0.5% to 4% of all reported cases of primary hyperparathyroidism.</p> <p>Case presentation</p> <p>We report the case of a 60-year-old Caucasian man with hypercalcaemic hyperparathyroid crisis associated with parathyroid carcinoma. He presented with a classic hypercalcaemic syndrome and his serum calcium and parathyroid hormone levels were at 4.65 mmol/L and 1743 ng/L, respectively. He initially presented with a two-week history of weakness and lethargy and a one-week history of vomiting, polyuria and polydipsia. An emergency left thyroid lobectomy and left lower parathyroidectomy were performed. There was a prompt decrease in his parathyroid hormone level immediately after surgery. Histology revealed that our patient had a 4-cm parathyroid carcinoma.</p> <p>Conclusion</p> <p>In patients with parathyroid carcinoma, the optimal surgical treatment is <it>en bloc </it>resection with ipsilateral thyroid lobectomy and removal of any enlarged or abnormal lymph nodes. Surgery is the only curative treatment. In our patient, prompt surgical intervention proved successful. At six months the patient is well with no evidence of disease recurrence. This case highlights the importance of considering a hyperparathyroid storm in the context of a parathyroid carcinoma. Parathyroid carcinoma is a rare entity and our knowledge is mainly derived from case reports and retrospective studies. This case report increases awareness of this serious and life-threatening complication. This report also illustrates how prompt and appropriate management provides the best outcome for the patient.</p
The antisaccade task as an index of sustained goal activation in working memory: modulation by nicotine
The antisaccade task provides a laboratory analogue of situations in which execution of the correct behavioural response requires the suppression of a more prepotent or habitual response. Errors (failures to inhibit a reflexive prosaccade towards a sudden onset target) are significantly increased in patients with damage to the dorsolateral prefrontal cortex and patients with schizophrenia. Recent models of antisaccade performance suggest that errors are more likely to occur when the intention to initiate an antisaccade is insufficiently activated within working memory. Nicotine has been shown to enhance specific working memory processes in healthy adults. MATERIALS AND METHODS: We explored the effect of nicotine on antisaccade performance in a large sample (N = 44) of young adult smokers. Minimally abstinent participants attended two test sessions and were asked to smoke one of their own cigarettes between baseline and retest during one session only. RESULTS AND CONCLUSION: Nicotine reduced antisaccade errors and correct antisaccade latencies if delivered before optimum performance levels are achieved, suggesting that nicotine supports the activation of intentions in working memory during task performance. The implications of this research for current theoretical accounts of antisaccade performance, and for interpreting the increased rate of antisaccade errors found in some psychiatric patient groups are discussed
The Underestimation Of Egocentric Distance: Evidence From Frontal Matching Tasks
There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues
Generalized Ricci Curvature Bounds for Three Dimensional Contact Subriemannian manifolds
Measure contraction property is one of the possible generalizations of Ricci
curvature bound to more general metric measure spaces. In this paper, we
discover sufficient conditions for a three dimensional contact subriemannian
manifold to satisfy this property.Comment: 49 page
Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream
Streams draining peatlands export large quantities of carbon in different chemical forms and
are an important part of the carbon cycle. Radiocarbon (14C) analysis/dating provides unique
information on the source and rate that carbon is cycled through ecosystems, as has recently
been demonstrated at the air-water interface through analysis of carbon dioxide (CO2) lost
from peatland streams by evasion (degassing). Peatland streams also have the potential to
release large amounts of methane (CH4) and, though 14C analysis of CH4 emitted by ebullition
(bubbling) has been previously reported, diffusive emissions have not. We describe methods
that enable the 14C analysis of CH4 evaded from peatland streams. Using these methods, we
investigated the 14C age and stable carbon isotope composition of both CH4 and CO2 evaded
from a small peatland stream draining a temperate raised mire. Methane was aged between
1617-1987 years BP, and was much older than CO2 which had an age range of 303-521 years
BP. Isotope mass balance modelling of the results indicated that the CO2 and CH4 evaded
from the stream were derived from different source areas, with most evaded CO2 originating
from younger layers located nearer the peat surface compared to CH4. The study demonstrates
the insight that can be gained into peatland carbon cycling from a methodological
development which enables dual isotope (14C and 13C) analysis of both CH4 and CO2 collected
at the same time and in the same way
Sublittoral soft bottom communities and diversity of Mejillones Bay in northern Chile (Humboldt Current upwelling system)
The macrozoobenthos of Mejillones Bay (23°S; Humboldt Current) was quantitatively investigated over a 7-year period from austral summer 1995/1996 to winter 2002. About 78 van Veen grab samples taken at six stations (5, 10, 20 m depth) provided the basis for the analysis of the distribution of 60 species and 28 families of benthic invertebrates, as well as of their abundance and biomass. Mean abundance (2,119 individuals m-2) was in the same order compared to a previous investigation; mean biomass (966 g formalin wet mass m-2), however, exceeded prior estimations mainly due to the dominance of the bivalve Aulacomya ater. About 43% of the taxa inhabited the complete depth range. Mean taxonomic Shannon diversity (H', Log e) was 1.54 ± 0.58 with a maximum at 20 m (1.95 ± 0.33); evenness increased with depth. The fauna was numerically dominated by carnivorous gastropods, polychaetes and crustaceans (48%). About 15% of the species were suspensivorous, 13% sedimentivorous, 11% detritivorous, 7% omnivorous and 6% herbivorous. Cluster analyses showed a significant difference between the shallow and the deeper stations. Gammarid amphipods and the polychaete family Nephtyidae characterized the 5-mzone, the molluscs Aulacomya ater, Mitrella unifasciata and gammarids the intermediate zone, while the gastropod Nassarius gayi and the polychaete family Nereidae were most prominent at the deeper stations. The communities of the three depth zones did not appear to be limited by hypoxia during non-El Niño conditions. Therefore, no typical change in community structure occurred during El Niño 1997–1998, in contrast to what was observed for deeper faunal assemblages and hypoxic bays elsewhere in the coastal Humboldt Current system
Bilateral Assessment of Functional Tasks for Robot-assisted Therapy Applications
This article presents a novel evaluation system along with methods to evaluate bilateral coordination of arm function on activities of daily living tasks before and after robot-assisted therapy. An affordable bilateral assessment system (BiAS) consisting of two mini-passive measuring units modeled as three degree of freedom robots is described. The process for evaluating functional tasks using the BiAS is presented and we demonstrate its ability to measure wrist kinematic trajectories. Three metrics, phase difference, movement overlap, and task completion time, are used to evaluate the BiAS system on a bilateral symmetric (bi-drink) and a bilateral asymmetric (bi-pour) functional task. Wrist position and velocity trajectories are evaluated using these metrics to provide insight into temporal and spatial bilateral deficits after stroke. The BiAS system quantified movements of the wrists during functional tasks and detected differences in impaired and unimpaired arm movements. Case studies showed that stroke patients compared to healthy subjects move slower and are less likely to use their arm simultaneously even when the functional task requires simultaneous movement. After robot-assisted therapy, interlimb coordination spatial deficits moved toward normal coordination on functional tasks
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