504 research outputs found
Random Walks on a Fluctuating Lattice: A Renormalization Group Approach Applied in One Dimension
We study the problem of a random walk on a lattice in which bonds connecting
nearest neighbor sites open and close randomly in time, a situation often
encountered in fluctuating media. We present a simple renormalization group
technique to solve for the effective diffusive behavior at long times. For
one-dimensional lattices we obtain better quantitative agreement with
simulation data than earlier effective medium results. Our technique works in
principle in any dimension, although the amount of computation required rises
with dimensionality of the lattice.Comment: PostScript file including 2 figures, total 15 pages, 8 other figures
obtainable by mail from D.L. Stei
Observation of anomalous decoherence effect in a quantum bath at room temperature
Decoherence of quantum objects is critical to modern quantum sciences and
technologies. It is generally believed that stronger noises cause faster
decoherence. Strikingly, recent theoretical research discovers the opposite
case for spins in quantum baths. Here we report experimental observation of the
anomalous decoherence effect for the electron spin-1 of a nitrogen-vacancy
centre in high-purity diamond at room temperature. We demonstrate that under
dynamical decoupling, the double-transition can have longer coherence time than
the single-transition, even though the former couples to the nuclear spin bath
as twice strongly as the latter does. The excellent agreement between the
experimental and the theoretical results confirms the controllability of the
weakly coupled nuclear spins in the bath, which is useful in quantum
information processing and quantum metrology.Comment: 22 pages, related paper at http://arxiv.org/abs/1102.557
Dynamic and volumetric variables reliably predict fluid responsiveness in a porcine model with pleural effusion
Background: The ability of stroke volume variation (SVV), pulse pressure variation (PPV) and global end-diastolic volume (GEDV) for prediction of fluid responsiveness in presence of pleural effusion is unknown. The aim of the present study was to challenge the ability of SVV, PPV and GEDV to predict fluid responsiveness in a porcine model with pleural effusions.
Methods: Pigs were studied at baseline and after fluid loading with 8 ml kg−1 6% hydroxyethyl starch. After withdrawal of 8 ml kg−1 blood and induction of pleural effusion up to 50 ml kg−1 on either side, measurements at baseline and after fluid loading were repeated. Cardiac output, stroke volume, central venous pressure (CVP) and pulmonary occlusion pressure (PAOP) were obtained by pulmonary thermodilution, whereas GEDV was determined by transpulmonary thermodilution. SVV and PPV were monitored continuously by pulse contour analysis.
Results: Pleural effusion was associated with significant changes in lung compliance, peak airway pressure and stroke volume in both responders and non-responders. At baseline, SVV, PPV and GEDV reliably predicted fluid responsiveness (area under the curve 0.85 (p<0.001), 0.88 (p<0.001), 0.77 (p = 0.007). After induction of pleural effusion the ability of SVV, PPV and GEDV to predict fluid responsiveness was well preserved and also PAOP was predictive. Threshold values for SVV and PPV increased in presence of pleural effusion.
Conclusions: In this porcine model, bilateral pleural effusion did not affect the ability of SVV, PPV and GEDV to predict fluid responsiveness
Emotional stress as a trigger of myasthenic crisis and concomitant takotsubo cardiomyopathy: a case report
<p>Abstract</p> <p>Introduction</p> <p>Myasthenia gravis is a neuromuscular junction post-synaptic autoimmune disorder. Myasthenic crisis is characterized by respiratory failure requiring mechanical ventilation. Takotsubo cardiomyopathy is a rare clinical syndrome defined as a profound but reversible left ventricular dysfunction in the absence of coronary artery disease.</p> <p>Case presentation</p> <p>We report a unique case of a 60-year-old Hispanic woman with myasthenia gravis who developed takotsubo cardiomyopathy and concomitant myasthenic crisis that appear to have been triggered by a stressful life event. On admission, she presented with severe mid-sternal chest pain and shortness of breath shortly after a personally significant stressful life event. A pertinent neurological examination showed bilateral facial weakness and right ptosis. The left ventriculogram showed apical ballooning with hyperdynamic proximal segments with sparing of the apex. Her troponin I level was elevated, while cardiac catheterization revealed no significant coronary artery disease. The findings were consistent with takotsubo cardiomyopathy. Shortly after cardiac catheterization, she developed bilateral ophthalmoparesis and significant bulbar and respiratory muscle weakness. Forced vital capacity values were persistently less than 1 L. The patient developed respiratory failure and required endotracheal intubation. After plasmapheresis and corticosteroid treatment, her clinical course improved with successful extubation. A normal left ventricle chamber size and a normal ejection fraction were noted by an echocardiogram repeated 10 months later.</p> <p>Conclusion</p> <p>This is the first reported case of the simultaneous triggering of both takotsubo cardiomyopathy and myasthenic crisis by the physiologic consequences of a state of severe emotional stress. We hypothesize that the mechanism underlying the rare association of takotsubo cardiomyopathy with myasthenic crisis involves excessive endogenous glucocorticoid release, a high-catecholamine state, or a combination of both. We advocate careful cardiac monitoring of myasthenia gravis patients during acute emotional or physical stress, as there is potential risk of developing takotsubo cardiomyopathy.</p
A first estimate of triply heavy baryon masses from the pNRQCD perturbative static potential
Within pNRQCD we compute the masses of spin-averaged triply heavy baryons
using the now-available NNLO pNRQCD potentials and three-body variational
approach. We focus in particular on the role of the purely three-body
interaction in perturbation theory. This we find to be reasonably small and of
the order 25 MeV Our prediction for the Omega_ccc baryon mass is 4900(250) in
keeping with other approaches. We propose to search for this hitherto
unobserved state at B factories by examining the end point of the recoil
spectrum against triple charm.Comment: 18 figures, 21 page
Sixty Years of Modern Human Origins in the American Anthropological Association
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65197/1/aa.2003.105.1.89.pd
Using Land-Based Surveys to Assess Sea Duck Abundance and Behavior in Nearshore Waters of Southern New England, USA
Nearshore waters provide very important habitat for sea ducks (Tribe Mergini) during migration and winter, but gathering information on sea duck use of shallow nearshore waters is challenging because traditional aerial and boat-based surveys are expensive, are usually conducted infrequently, and are often not feasible near the coast. The objective of this study was to use land-based surveys to characterize spatiotemporal variation in the abundance and behavior (e.g., foraging, flying) of Common Eider (Somateria mollissima) and scoters (Melanitta spp.) in nearshore waters of southern New England. Surveys (60–120 min per survey, n = 1,044 surveys) were conducted throughout the day from February 2009 to July 2010 to assess diurnal and seasonal variation in sea duck behavior and spatial distribution at nine sites in southern Rhode Island. The density of sea ducks resting or foraging on the water exhibited little diurnal variation, whereas flight activity dramatically increased nearer to sunrise. Sea duck densities and passage rates (individuals/km2/hr) peaked during migration periods from October through November and February through April, although there were important seasonal differences between sites. For example, the highest densities of Common Eider during fall were in a protected estuary, whereas abundance of scoters during fall was greater at a coastal headland. The relative activity of Common Eider on the water and in flight was similar among sites, whereas scoters exhibited highly variable activity among sites, particularly during winter and spring. The spatiotemporal patterns in abundance and behavior of sea ducks in nearshore waters that we detected using land-based surveys provides essential, complementary information to that available from other types of waterfowl and seabird surveys in southern New England
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A panel of induced pluripotent stem cells from chimpanzees: A resource for comparative functional genomics
Comparative genomics studies in primates are restricted due to our limited access to samples. In order to gain better insight into the genetic processes that underlie variation in complex phenotypes in primates, we must have access to faithful model systems for a wide range of cell types. To facilitate this, we generated a panel of 7 fully characterized chimpanzee induced pluripotent stem cell (iPSC) lines derived from healthy donors. To demonstrate the utility of comparative iPSC panels, we collected RNA-sequencing and DNA methylation data from the chimpanzee iPSCs and the corresponding fibroblast lines, as well as from 7 human iPSCs and their source lines, which encompass multiple populations and cell types. We observe much less withinspecies variation in iPSCs than in somatic cells, indicating the reprogramming process erases many inter-individual differences. The low within-species regulatory variation in iPSCs allowed us to identify many novel inter-species regulatory differences of small magnitude
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