652 research outputs found
Can inhomogeneties accelerate the cosmic volume expansion?
If expanding and contracting regions coexist in the universe, the speed of
the cosmic volume expansion can be accelerated. We construct simple
inhomogeneous dust-filled universe models in which the speed of the cosmic
volume expansion is accelerated for finite periods. These models are
constructed by removing spherical domains from the Einstein-de Sitter universe
and filling each domain with a Lemaitre-Tolman-Bondi dust sphere possessing the
same gravitational mass as the removed region. This represents an exact
solution of the Einstein equations. We find that acceleration of the cosmic
volume expansion is realized in some cases when the size of the contracting
region is comparable to the horizon radius of the Einstein-de Sitter universe
though this model is very different from the universe observed today. This
result implies that non-linear general relativistic effects of inhomogeneities
are very important to realize the acceleration of the cosmic volume expansion.Comment: 12 pages,5 figures. version published in Progress of Theoretical
Physic
Flavor, CP and Metaplectic Modular Symmetries in Type IIB Chiral Flux Vacua
We examine symmetries of chiral four-dimensional vacua of Type IIB flux
compactifications with vanishing superpotential . We find that the supersymmetric MSSM-like and Pati-Salam vacua possess enhanced discrete
symmetries in the effective action below the mass scale of stabilized complex
structure moduli and dilaton. Furthermore, a generation number of
quarks/leptons is small on these vacua where the flavor, CP and metaplectic
modular symmetries are described in the framework of eclectic flavor symmetry.Comment: 30 pages, 5 figure
Environmentally relevant stressors alter memory formation in the pond snail Lymnaea
Stress alters adaptive behaviours such as learning and memory. Stressors can either enhance or diminish learning, memory formation and/or memory recall. We focus attention here on how environmentally relevant stressors alter learning, memory and forgetting in the pond snail, Lymnaea stagnalis. Operant conditioning of aerial respiration causes associative learning that may lead to long-term memory (LTM) formation. However, individual ecologically relevant stressors, combinations of stressors, and bio-active substances can alter whether or not learning occurs or memory forms. While the behavioural memory phenotype may be similar as a result of exposure to different stressors, how each stressor alters memory formation may occur differently. In addition, when a combination of stressors are presented it is difficult to predict ahead of time what the outcome will be regarding memory formation. Thus, how combinations of stressors act is an emergent property of how the snail perceives the stressors.</jats:p
A possible role of the ATP-sensitive potassium ion channel in determining the duration of spike-bursts in mouse pancreatic β-cells
AbstractThe pancreatic β-cell displays an electrical activity consisting of spike bursts and silent phases at glucose concentrations of about 10 mM. The mechanism of initial depolarization induced by glucose is well defined. However, the mechanism inducing the silent phase has not been fully elucidated. In the present study, the possibility of involvement of ATP-sensitive K+ channels in repolarization was examined using the patch-clamp technique in the cell-attached recording configuration. Ouabain (0.1 mM), an inhibitor of Na+/K+-ATPase, caused a complete suppression of ATP-sensitive K+ channel activity followed by typical biphasic current deflections, which were due to action potentials. The channel activity was also inhibited by removal of K+ from a perifusion solution. Furthermore, the activity of ATP-sensitive K+ channels was markedly inhibited either by replacement of external NaCl with LiCl or by addition of amiloride (0.2 mM), a blocker of Na+/H+ antiport. Addition of L-type Ca2+ channel blockers such as Nifedipine or Mn2+ induced the complete suppression of K+ channel activity. These findings strongly suggest that a fall in ATP consumption results in sustained depolarization, and that the repolarizations interposed between spike-bursts under normal ionic conditions are due to the periodical fall of ATP concentration brought about by periodical acceleration of ATP consumption at Na+/K+-pumps. It is concluded that the elevation of intracellular Na+ concentration as a consequence of accelerated Na+/Ca2+-countertransport during the period of spike-burst enhances ATP consumption, leading to a fall in ATP concentration which is responsible for termination of spike-burst and initiation of repolarization
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Participation in Sports Organizations and the Prevention of Functional Disability in Older Japanese: The AGES Cohort Study
Background: We sought to examine prospectively the difference in the association between incident functional disability and exercise with or without sports organization participation. Methods: The study was based on the Aichi Gerontological Evaluation Study (AGES) Cohort Study data. In October 2003, self-reported questionnaires were mailed to 29,374 non-disabled Japanese individuals aged 65 years or older. Of these, 13,310 individuals were introduced to the Study, and they were followed for 4 years. Analysis was carried out on 11,581 subjects who provided all necessary information for the analysis. Results: Analysis was carried out on incident functional disability by 4 groups of different combinations of performance of exercise and participation in a sports organization Active Participant (AP), Exercise Alone (EA), Passive Participant (PP) and Sedentary (S). Compared to the AP group, the EA group had a hazard ratio (HR) of 1.29 (1.02–1.64) for incident functional disability. No significant difference was seen with the PP group, with an HR of 1.16 (0.76–1.77). When a measure of social networks was added to the covariates, the HR of the EA group dropped to 1.27 (1.00–1.61), and significant differences disappeared. In contrast, it showed hardly any change when social support was added. Conclusion: The results suggested that, even with a regular exercise habit, incident functional disability may be better prevented when a person participates in a sports organization than when he/she does not. In addition, participation in a sports organization correlates positively with social networks, which may lead to a small decrease in incident functional disability
Sedimentary membrane lipids recycled by deep-sea benthic archaea
http://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt06-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt06-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt06-22/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt08-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/chikyu/902/
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