1,213 research outputs found
Accelerometers can measure total and activity-specific energy expenditures in free-ranging marine mammals only if linked to time-activity budgets
Peer reviewedPostprin
Maximum Running Speed of Captive Bar-Headed Geese Is Unaffected by Severe Hypoxia
While bar-headed geese are renowned for migration at high altitude over the Himalayas, previous work on captive birds suggested that these geese are unable to maintain rates of oxygen consumption while running in severely hypoxic conditions. To investigate this paradox, we re-examined the running performance and heart rates of bar-headed geese and barnacle geese (a low altitude species) during exercise in hypoxia. Bar-headed geese (n = 7) were able to run at maximum speeds (determined in normoxia) for 15 minutes in severe hypoxia (7% O2; simulating the hypoxia at 8500 m) with mean heart rates of 466ñ8 beats minĂąïżœïżœ1. Barnacle geese (n = 10), on the other hand, were unable to complete similar trials in severe hypoxia and their mean heart rate (316 beats.minĂąïżœïżœ1) was significantly lower than bar-headed geese. In bar-headed geese, partial pressures of oxygen and carbon dioxide in both arterial and mixed venous blood were significantly lower during hypoxia than normoxia, both at rest and while running. However, measurements of blood lactate in bar-headed geese suggested that anaerobic metabolism was not a major energy source during running in hypoxia. We combined these data with values taken from the literature to estimate (i) oxygen supply, using the Fick equation and (ii) oxygen demand using aerodynamic theory for bar-headed geese flying aerobically, and under their own power, at altitude. This analysis predicts that the maximum altitude at which geese can transport enough oxygen to fly without environmental assistance ranges from 6,800 m to 8,900 m altitude, depending on the parameters used in the model but that such flights should be rare
Accurate evaluation of the interstitial KKR-Green function
It is shown that the Brillouin zone integral for the interstitial KKR-Green
function can be evaluated accurately by taking proper care of the free-electron
singularities in the integrand. The proposed method combines two recently
developed methods, a supermatrix method and a subtraction method. This
combination appears to provide a major improvement compared with an earlier
proposal based on the subtraction method only. By this the barrier preventing
the study of important interstitial-like defects, such as an electromigrating
atom halfway along its jump path, can be considered as being razed.Comment: 23 pages, RevTe
Non-linear regression models for Approximate Bayesian Computation
Approximate Bayesian inference on the basis of summary statistics is
well-suited to complex problems for which the likelihood is either
mathematically or computationally intractable. However the methods that use
rejection suffer from the curse of dimensionality when the number of summary
statistics is increased. Here we propose a machine-learning approach to the
estimation of the posterior density by introducing two innovations. The new
method fits a nonlinear conditional heteroscedastic regression of the parameter
on the summary statistics, and then adaptively improves estimation using
importance sampling. The new algorithm is compared to the state-of-the-art
approximate Bayesian methods, and achieves considerable reduction of the
computational burden in two examples of inference in statistical genetics and
in a queueing model.Comment: 4 figures; version 3 minor changes; to appear in Statistics and
Computin
and couplings in QCD
We calculate the and couplings using QCD sum rules on the
light-cone. In this approach, the large-distance dynamics is incorporated in a
set of pion wave functions. We take into account two-particle and
three-particle wave functions of twist 2, 3 and 4. The resulting values of the
coupling constants are and .
From this we predict the partial width \Gamma (D^{*+} \ra D^0 \pi^+ )=32 \pm
5~ keV . We also discuss the soft-pion limit of the sum rules which is
equivalent to the external axial field approach employed in earlier
calculations. Furthermore, using and the pole
dominance model for the B \ra \pi and D\ra \pi semileptonic form factors
is compared with the direct calculation of these form factors in the same
framework of light-cone sum rules.Comment: 27 pages (LATEX) +3 figures enclosed as .uu file MPI-PhT/94-62 ,
CEBAF-TH-94-22, LMU 15/9
Sporting embodiment: sports studies and the (continuing) promise of phenomenology
Whilst in recent years sports studies have addressed the calls âto bring the body back inâ to theorisations of sport and physical activity, the âpromise of phenomenologyâ remains largely under-realised with regard to sporting embodiment. Relatively few accounts are grounded in the âfleshâ of the lived sporting body, and phenomenology offers a powerful framework for such analysis. A wide-ranging, multi-stranded, and interpretatively contested perspective, phenomenology in general has been taken up and utilised in very different ways within different disciplinary fields. The purpose of this article is to consider some selected phenomenological threads, key qualities of the phenomenological method, and the potential for existentialist phenomenology in particular to contribute fresh perspectives to the sociological study of embodiment in sport and exercise. It offers one way to convey the âessencesâ, corporeal immediacy and textured sensuosity of the lived sporting body. The use of Interpretative Phenomenological Analysis (IPA) is also critically addressed.
Key words: phenomenology; existentialist phenomenology; interpretative phenomenological analysis (IPA); sporting embodiment; the lived-body; Merleau-Pont
Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5
We describe our theoretical formalism and computational scheme for making
ab-initio calculations of the dynamic paramagnetic spin susceptibilities of
metals and alloys at finite temperatures. Its basis is Time-Dependent Density
Functional Theory within an electronic multiple scattering, imaginary time
Green function formalism. Results receive a natural interpretation in terms of
overdamped oscillator systems making them suitable for incorporation into spin
fluctuation theories. For illustration we apply our method to the nearly
ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5.
We compare and contrast the spin dynamics of these two metals and in each case
identify those fluctuations with relaxation times much longer than typical
electronic `hopping times'Comment: 21 pages, 9 figures. To appear in Physical Review B (July 2000
Hyperbaric oxygen preconditioning ameliorates blood-brain barrier damage induced by hypoxia through modulation of tight junction proteins in an in vitro model
Aim To explore the effects of hyperbaric oxygen preconditioning
(HBOP) on the permeability of blood-brain barrier
(BBB) and expression of tight junction proteins under hypoxic
conditions in vitro.
Methods A BBB in vitro model was constructed using the
hCMEC/D3 cell line and used when its trans-endothelial
electrical resistance (TEER) reached 80-120 Ω · cm2 (tested
by Millicell-Electrical Resistance System). The cells were
randomly divided into the control group cultured under
normal conditions, the group cultured under hypoxic conditions
(2%O2) for 24 h (hypoxia group), and the group
first subjected to HBOP for 2 h and then to hypoxia (HBOP
group). Occludin and ZO-1 expression were analyzed by
immunofluorescence assay.
Results Normal hCMEC/D3 was spindle-shaped and
tightly integrated. TEER was significantly reduced in the
hypoxia (P = 0.001) and HBOP group (P = 0.014) compared
to control group, with a greater decrease in the hypoxia
group. Occludin membranous expression was significantly
decreased in the hypoxia group (P = 0.001) compared to
the control group, but there was no change in the HBOP
group. ZO-1 membranous expression was significantly decreased
(P = 0.002) and cytoplasmic expression was significantly
increased (P = 0.001) in the hypoxia group compared
to the control group, although overall expression
levels did not change. In the HBOP group, there was no
significant change in ZO-1 expression compared to the
control group.
Conclusion Hyperbaric oxygen preconditioning protected
the integrity of BBB in an in vitro model through modulation
of occludin and ZO-1 expression under hypoxic conditions
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