16,736 research outputs found
Environment-dependent prey capture in the Atlantic mudskipper (Periophthalmus barbarus)
Few vertebrates capture prey in both the aquatic and the terrestrial environment due to the conflicting biophysical demands of feeding in water versus air. The Atlantic mudskipper (Periophthalmus barbarus) is known to be proficient at feeding in the terrestrial environment and feeds predominately in this environment. Given the considerable forward flow of water observed during the mouth-opening phase to assist with feeding on land, the mudskipper must alter the function of its feeding system to feed successfully in water. Here, we quantify the aquatic prey-capture kinematics of the mudskipper and compare this with the previously described pattern of terrestrial feeding. Prior to feeding in the aquatic environment, the gill slits open, allowing water to be expelled through the gill slits. The opposite happens in terrestrial feeding during which the gill slits remain closed at this point. In water, the expansive movements of the head are larger, amounting to a larger volume increase and are initiated slightly later than in the terrestrial environment. This implies the generation of strong suction flows when feeding in water. Consequently, the kinematic patterns of the hydrodynamic tongue during terrestrial feeding and aquatic suction feeding are similar, except for the amplitude of the volume increase and the active closing of the gill slits early during the terrestrial feeding strike. The mudskipper thus exhibits the capacity to change the kinematics of its feeding apparatus to enable successful prey capture in two disparate environments
NiO Exchange Bias Layers Grown by Direct Ion Beam Sputtering of a Nickel Oxide Target
A new process for fabricating NiO exchange bias layers has been developed.
The process involves the direct ion beam sputtering (IBS) of a NiO target. The
process is simpler than other deposition techniques for producing NiO buffer
layers, and facilitates the deposition of an entire spin-valve layered
structure using IBS without breaking vacuum. The layer thickness and
temperature dependence of the exchange field for NiO/NiFe films produced using
IBS are presented and are similar to those reported for similar films deposited
using reactive magnetron sputtering. The magnetic properties of highly textured
exchange couples deposited on single crystal substrates are compared to those
of simultaneously deposited polycrystalline films, and both show comparable
exchange fields. These results are compared to current theories describing the
exchange coupling at the NiO/NiFe interface.Comment: 9 pages, Latex 2.09, 3 postscript figures. You can also this
manuscript at http://www.wsrcc.com/alison/fixed-nio/manuscript.html To be
published in _IEEE Trans. Magn._, Nov. 199
Upper limit to in scalar-tensor gravity theories
In a previous paper (Serna & Alimi 1996), we have pointed out the existence
of some particular scalar-tensor gravity theories able to relax the
nucleosynthesis constraint on the cosmic baryonic density. In this paper, we
present an exhaustive study of primordial nucleosynthesis in the framework of
such theories taking into account the currently adopted observational
constraints. We show that a wide class of them allows for a baryonic density
very close to that needed for the universe closure. This class of theories
converges soon enough towards General Relativity and, hence, is compatible with
all solar-system and binary pulsar gravitational tests. In other words, we show
that primordial nucleosynthesis does not always impose a very stringent bound
on the baryon contribution to the density parameter.Comment: uuencoded tar-file containing 16 pages, latex with 5 figures,
accepted for publication in Astrophysical Journal (Part 1
Cross-section and polarization of neutrino-produced 's made simple
Practical formulae are derived for the cross-section and polarization of the
lepton produced in deep-inelastic neutrino-nucleon scattering in the
frame of the simple quark-parton model.Comment: 10 pages, no figure
A sequential regularization method for time-dependent incompressible Navier--Stokes equations
The objective of the paper is to present a method, called sequential regularization method (SRM), for the nonstationary incompressible Navier-Stokes equations from the viewpoint of regularization of differential-algebraic equations (DAEs) , and to provide a way to apply a DAE method to partial differential-algebraic equations (PDAEs). The SRM is a functional iterative procedure. It is proved that its convergence rate is O(ffl m ), where m is the number of the SRM iterations and ffl is the regularization parameter. The discretization and implementation issues of the method are considered. In particular, a simple explicit difference scheme is analyzed and its stability is proved under the usual step size condition of explicit schemes. It appears that the SRM formulation is new in the Navier-Stokes context. Unlike other regularizations or pseudo-compressibility methods in the Navier-Stokes context, the regularization parameter ffl in the SRM need not be very small, and the regularized..
Magnetic relaxation of a system of superparamagnetic particles weakly coupled by dipole-dipole interactions
The effect of long range dipole-dipole interactions on the thermal
fluctuations of the magnetization of an assembly of single-domain ferromagnetic
particles is considered. If orientational correlations between the particles
are neglected, the evolution of the magnetization orientations may be described
by a nonlinear Fokker-Planck equation (FPE) reducing to the usual linear one in
the limit of infinite dilution [W.F. Brown Jr, Phys. Rev. 130, 1677 (1963)].
The thermally activated relaxation time scale of the assembly is estimated,
leading to a simple modification of the axially symmetric asymptotes for the
superparamagnetic relaxation time.Comment: 31 pages, 3 figures, regular articl
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