1,969 research outputs found
The timing of meals
In most individuals, food intake occurs as discrete bouts or meals, and little attention has been paid to the factors that normally determine when meals will occur when food is freely available. On the basis of experiments using rats, the authors suggest that when there are no constraints on obtaining food and few competing activities, 3 levels of interacting controls normally dictate when meals will start. The first is the genetically determined circadian activity pattern on which nocturnal animals tend to initiate most meals in the dark. The second is the regularly occurring changing of the light cycle: These changes provide temporal anchors. The third relates to the size of the preceding meal, such that larger meals cause a longer delay until the onset of the next meal. Superimposed on these 3 are factors related to learning, convenience, and opportunity
Rebuttal of comments by Griffiths, Lader and Greenblatt to Review by Woods and Winger
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46348/1/213_2005_Article_BF02245828.pd
Gravitational Collapse and Fragmentation in Molecular Clouds with Adaptive Mesh Refinement
We describe a powerful methodology for numerical solution of 3-D
self-gravitational hydrodynamics problems with extremely high resolution. Our
method utilizes the technique of local adaptive mesh refinement (AMR),
employing multiple grids at multiple levels of resolution. These grids are
automatically and dynamically added and removed as necessary to maintain
adequate resolution. This technology allows for the solution of problems in a
manner that is both more efficient and more versatile than other fixed and
variable resolution methods. The application of AMR to simulate the collapse
and fragmentation of a molecular cloud, a key step in star formation, is
discussed. Such simulations involve many orders of magnitude of variation in
length scale as fragments form. In this paper we briefly describe the
methodology and present an illustrative application for nonisothermal cloud
collapse. We describe the numerical Jeans condition, a criterion for stability
of self-gravitational hydrodynamics problems. We show the first well-resolved
nonisothermal evolutionary sequence beginning with a perturbed dense molecular
cloud core that leads to the formation of a binary system consisting of
protostellar cores surrounded by distinct protostellar disks. The scale of the
disks, of order 100 AU, is consistent with observations of gaseous disks
surrounding single T-Tauri stars and debris disks surrounding systems such as
Pictoris.Comment: 10 pages, 6 figures (color postscript). To appear in the proceedings
of Numerical Astrophysics 1998, Tokyo, March 10-13, 199
Solving the subset-sum problem with a light-based device
We propose a special computational device which uses light rays for solving
the subset-sum problem. The device has a graph-like representation and the
light is traversing it by following the routes given by the connections between
nodes. The nodes are connected by arcs in a special way which lets us to
generate all possible subsets of the given set. To each arc we assign either a
number from the given set or a predefined constant. When the light is passing
through an arc it is delayed by the amount of time indicated by the number
placed in that arc. At the destination node we will check if there is a ray
whose total delay is equal to the target value of the subset sum problem (plus
some constants).Comment: 14 pages, 6 figures, Natural Computing, 200
Static stretching of the hamstring muscle for injury prevention in football codes: a systematic review
Purpose: Hamstring injuries are common among football players. There is still disagreement regarding prevention. The aim of this review is to determine whether static stretching reduces hamstring injuries in football codes.
Methods: A systematic literature search was conducted on the online databases PubMed, PEDro, Cochrane, Web of Science, Bisp and Clinical Trial register. Study results were presented descriptively and the quality of the studies assessed were based on Cochrane’s ‘risk of bias’ tool.
Results: The review identified 35 studies, including four analysis studies. These studies show deficiencies in the quality of study designs.
Conclusion: The study protocols are varied in terms of the length of intervention and follow-up. No RCT studies are available, however, RCT studies should be conducted in the near future
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Convective transport of formaldehyde to the upper troposphere and lower stratosphere and associated scavenging in thunderstorms over the central United States during the 2012DC3 study
Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2
The linear dispersion relation in graphene[1,2] gives rise to a surprising
prediction: the resistivity due to isotropic scatterers (e.g. white-noise
disorder[3] or phonons[4-8]) is independent of carrier density n. Here we show
that acoustic phonon scattering[4-6] is indeed independent of n, and places an
intrinsic limit on the resistivity in graphene of only 30 Ohm at room
temperature (RT). At a technologically-relevant carrier density of 10^12 cm^-2,
the mean free path for electron-acoustic phonon scattering is >2 microns, and
the intrinsic mobility limit is 2x10^5 cm^2/Vs, exceeding the highest known
inorganic semiconductor (InSb, ~7.7x10^4 cm^2/Vs[9]) and semiconducting carbon
nanotubes (~1x10^5 cm^2/Vs[10]). We also show that extrinsic scattering by
surface phonons of the SiO2 substrate[11,12] adds a strong temperature
dependent resistivity above ~200 K[8], limiting the RT mobility to ~4x10^4
cm^2/Vs, pointing out the importance of substrate choice for graphene
devices[13].Comment: 16 pages, 3 figure
Preconditioning of mesenchymal stromal cells with low-intensity ultrasound: influence on chondrogenesis and directed SOX9 signaling pathways
Background: Continuous low-intensity ultrasound (cLIUS) facilitates the chondrogenic differentiation of human mesenchymal stromal cells (MSCs) in the absence of exogenously added transforming growth factor-beta (TGFβ) by upregulating the expression of transcription factor SOX9, a master regulator of chondrogenesis. The present study evaluated the molecular events associated with the signaling pathways impacting SOX9 gene and protein expression under cLIUS.
Methods: Human bone marrow-derived MSCs were exposed to cLIUS stimulation at 14 kPa (5 MHz, 2.5 Vpp) for 5 min. The gene and protein expression of SOX9 was evaluated. The specificity of SOX9 upregulation under cLIUS was determined by treating the MSCs with small molecule inhibitors of select signaling molecules, followed by cLIUS treatment. Signaling events regulating SOX9 expression under cLIUS were analyzed by gene expression, immunofluorescence staining, and western blotting.
Results: cLIUS upregulated the gene expression of SOX9 and enhanced the nuclear localization of SOX9 protein when compared to non-cLIUS-stimulated control. cLIUS was noted to enhance the phosphorylation of the signaling molecule ERK1/2. Inhibition of MEK/ERK1/2 by PD98059 resulted in the effective abrogation of cLIUS-induced SOX9 expression, indicating that cLIUS-induced SOX9 upregulation was dependent on the phosphorylation of ERK1/2. Inhibition of integrin and TRPV4, the upstream cell-surface effectors of ERK1/2, did not inhibit the phosphorylation of ERK1/2 and therefore did not abrogate cLIUS-induced SOX9 expression, thereby suggesting the involvement of other mechanoreceptors. Consequently, the effect of cLIUS on the actin cytoskeleton, a mechanosensitive receptor regulating SOX9, was evaluated. Diffused and disrupted actin fibers observed in MSCs under cLIUS closely resembled actin disruption by treatment with cytoskeletal drug Y27632, which is known to increase the gene expression of SOX9. The upregulation of SOX9 under cLIUS was, therefore, related to cLIUS-induced actin reorganization. SOX9 upregulation induced by actin reorganization was also found to be dependent on the phosphorylation of ERK1/2.
Conclusions: Collectively, preconditioning of MSCs by cLIUS resulted in the nuclear localization of SOX9, phosphorylation of ERK1/2 and disruption of actin filaments, and the expression of SOX9 was dependent on the phosphorylation of ERK1/2 under cLIUS
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