5,582 research outputs found
Cellular Blood Flow
The fluid dynamics video that is presented here outlines recent advances in
the simulation of multiphase cellular blood flow through the direct numerical
simulations of deformable red blood cells (RBCs) demonstrated through several
numerical experiments. Videos show particle deformation, shear stress on the
particle surface, and the formation of particle clusters in both
Hagen-Poiseuille and shear flow.Comment: 2 pages, one hyperlink to 2 video
Existence and Uniqueness of Solutions in Nonassociated Mohr-coulomb Elastoplasticity:<strong/>
In 1902 Jacques Hadamard [1] formulated three conditions that mathematical models of physical phenomena should satisfy, namely that: (a) A solution exists (b) The solution is unique (c) The solution depends continuously on the problem data Problems involving models that satisfy all of these conditions are termed well-posed. Otherwise, if one or more conditions are violated, the problem is said to be ill-posed. The meaning of condition (a) is quite clear. Conditions (b) and (c) are often intimately linked and can for many practical purposes be coalesced into a single condition. In finite element analysis “non-unique ” solutions are often generated by altering the problem data slightly, for example through introduction of random imperfections. It is relatively well known (though not always appreciated to its full extent) that standard elastoplastic constitutive models may violate conditions (b) and (c) if the flow rule is not associated. Indeed, since the pioneering work of Rice [2], the ensuing ill
Absolute dimensions of eclipsing binaries. XXVIII. BK Pegasi and other F-type binaries: Prospects for calibration of convective core overshoot
We present a detailed study of the F-type detached eclipsing binary BK Peg,
based on new photometric and spectroscopic observations. The two components,
which have evolved to the upper half of the main-sequence band, are quite
different with masses and radii of (1.414 +/- 0.007 Msun, 1.988 +/- 0.008 Rsun)
and (1.257 +/- 0.005 Msun, 1.474 +/- 0.017 Rsun), respectively. The 5.49 day
period orbit of BK Peg is slightly eccentric (e = 0.053). The measured
rotational velocities are 16.6 +/- 0.2 (primary) and 13.4 +/- 0.2 (secondary)
km/s. For the secondary component this corresponds to (pseudo)synchronous
rotation, whereas the primary component seems to rotate at a slightly lower
rate. We derive an iron abundance of [Fe/H] =-0.12 +/- 0.07 and similar
abundances for Si, Ca, Sc, Ti, Cr and Ni. Yonsei-Yale and Victoria-Regina
evolutionary models for the observed metal abundance reproduce BK Peg at ages
of 2.75 and 2.50 Gyr, respectively, but tend to predict a lower age for the
more massive primary component than for the secondary. We find the same age
trend for three other upper main-sequence systems in a sample of well studied
eclipsing binaries with components in the 1.15-1.70 Msun range, where
convective core overshoot is gradually ramped up in the models. We also find
that the Yonsei-Yale models systematically predict higher ages than the
Victoria-Regina models. The sample includes BW Aqr, and as a supplement we have
determined a [Fe/H] abundance of -0.07 +/- 0.11 for this late F-type binary. We
propose to use BK Peg, BW Aqr, and other well-studied 1.15-1.70 Msun eclipsing
binaries to fine-tune convective core overshoot, diffusion, and possibly other
ingredients of modern theoretical evolutionary models.Comment: Accepted for publication in Astronomy and Astrophysic
Changes in intracellular ion activities induced by adrenaline in human and rat skeletal muscle
To study the stimulating effect of adrenaline (ADR) on active Na+/K+ transport we used double-barrelled ion-sensitive micro-electrodes to measure the activities of extracellular K+ (aKe) and intracellular Na+ (aNai) in isolated preparations of rat soleus muscle, normal human intercostal muscle and one case of hyperkalemic periodic paralysis (h.p.p.). In these preparations bath-application of ADR (10−6 M) resulted in a membrane hyperpolarization and transient decreasesaKe andaNai which could be blocked by ouabain (3×10−4 M). In the h.p.p. muslce a continuous rise ofaNai induced by elevation ofaKe to 5.2 mM could be stopped by ADR. In addition, the intracellular K+ activity (aKi), the free intracellular Ca2+ concentration (pCai) and intracellular pH (pHi) were monitored in rat soleus muscle. During ADRaKi increased, pHi remained constant and intracellular Ca2+ apparently decreased. In conclusion, our data show that ADR primarily stimulates the Na+/K+ pump in mammalian skeletal muscle. This stimulating action is not impaired in the h.p.p. muscle
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