2,706 research outputs found
The Steady-State Transport of Oxygen through Hemoglobin Solutions
The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated
Diffusivity Measurements of Human Methemoglobin
Experimental measurements of the diffusion coefficient of human methemoglobin were made at 25°C with a modified Stokes diaphragm diffusion cell. A Millipore filter was used in place of the ordinary fritted disc to facilitate rapid achievement of steady state in the diaphragm. Methemoglobin concentrations varied from approximately 5 g/100 ml to 30 g/100 ml. The diffusion coefficient in this range decreased from 7.5 x 10^(-7) cm^2/sec to 1.6 x 10^(-7) cm^2/sec
Cohomology for infinitesimal unipotent algebraic and quantum groups
In this paper we study the structure of cohomology spaces for the Frobenius
kernels of unipotent and parabolic algebraic group schemes and of their quantum
analogs. Given a simple algebraic group , a parabolic subgroup , and
its unipotent radical , we determine the ring structure of the cohomology
ring . We also obtain new results on computing
as an -module where is a
simple -module with high weight in the closure of the bottom
-alcove. Finally, we provide generalizations of all our results to the
quantum situation.Comment: 18 pages. Some proofs streamlined over previous version. Additional
details added to some proofs in Section
On the ill/well-posedness and nonlinear instability of the magneto-geostrophic equations
We consider an active scalar equation that is motivated by a model for
magneto-geostrophic dynamics and the geodynamo. We prove that the non-diffusive
equation is ill-posed in the sense of Hadamard in Sobolev spaces. In contrast,
the critically diffusive equation is well-posed. In this case we give an
example of a steady state that is nonlinearly unstable, and hence produces a
dynamo effect in the sense of an exponentially growing magnetic field.Comment: We have modified the definition of Lipschitz well-posedness, in order
to allow for a possible loss in regularity of the solution ma
Emergence of fractal behavior in condensation-driven aggregation
We investigate a model in which an ensemble of chemically identical Brownian
particles are continuously growing by condensation and at the same time undergo
irreversible aggregation whenever two particles come into contact upon
collision. We solved the model exactly by using scaling theory for the case
whereby a particle, say of size , grows by an amount over the
time it takes to collide with another particle of any size. It is shown that
the particle size spectra of such system exhibit transition to dynamic scaling
accompanied by the emergence of fractal of
dimension . One of the remarkable feature of this
model is that it is governed by a non-trivial conservation law, namely, the
moment of is time invariant regardless of the choice of the
initial conditions. The reason why it remains conserved is explained by using a
simple dimensional analysis. We show that the scaling exponents and
are locked with the fractal dimension via a generalized scaling relation
.Comment: 8 pages, 6 figures, to appear in Phys. Rev.
Condensation phase transitions of symmetric conserved-mass aggregation model on complex networks
We investigate condensation phase transitions of symmetric conserved-mass
aggregation (SCA) model on random networks (RNs) and scale-free networks (SFNs)
with degree distribution . In SCA model, masses diffuse
with unite rate, and unit mass chips off from mass with rate . The
dynamics conserves total mass density . In the steady state, on RNs and
SFNs with for , we numerically show that SCA
model undergoes the same type condensation transitions as those on regular
lattices. However the critical line depends on network
structures. On SFNs with , the fluid phase of exponential mass
distribution completely disappears and no phase transitions occurs. Instead,
the condensation with exponentially decaying background mass distribution
always takes place for any non-zero density. For the existence of the condensed
phase for at the zero density limit, we investigate one
lamb-lion problem on RNs and SFNs. We numerically show that a lamb survives
indefinitely with finite survival probability on RNs and SFNs with ,
and dies out exponentially on SFNs with . The finite life time
of a lamb on SFNs with ensures the existence of the
condensation at the zero density limit on SFNs with at which
direct numerical simulations are practically impossible. At ,
we numerically confirm that complete condensation takes place for any on RNs. Together with the recent study on SFNs, the complete condensation
always occurs on both RNs and SFNs in zero range process with constant hopping
rate.Comment: 6 pages, 6 figure
Generic effective source for scalar self-force calculations
A leading approach to the modelling of extreme mass ratio inspirals involves
the treatment of the smaller mass as a point particle and the computation of a
regularized self-force acting on that particle. In turn, this computation
requires knowledge of the regularized retarded field generated by the particle.
A direct calculation of this regularized field may be achieved by replacing the
point particle with an effective source and solving directly a wave equation
for the regularized field. This has the advantage that all quantities are
finite and require no further regularization. In this work, we present a method
for computing an effective source which is finite and continuous everywhere,
and which is valid for a scalar point particle in arbitrary geodesic motion in
an arbitrary background spacetime. We explain in detail various technical and
practical considerations that underlie its use in several numerical self-force
calculations. We consider as examples the cases of a particle in a circular
orbit about Schwarzschild and Kerr black holes, and also the case of a particle
following a generic time-like geodesic about a highly spinning Kerr black hole.
We provide numerical C code for computing an effective source for various
orbital configurations about Schwarzschild and Kerr black holes.Comment: 24 pages, 7 figures, final published versio
Zeta functions of quantum graphs
In this article we construct zeta functions of quantum graphs using a contour
integral technique based on the argument principle. We start by considering the
special case of the star graph with Neumann matching conditions at the center
of the star. We then extend the technique to allow any matching conditions at
the center for which the Laplace operator is self-adjoint and finally obtain an
expression for the zeta function of any graph with general vertex matching
conditions. In the process it is convenient to work with new forms for the
secular equation of a quantum graph that extend the well known secular equation
of the Neumann star graph. In the second half of the article we apply the zeta
function to obtain new results for the spectral determinant, vacuum energy and
heat kernel coefficients of quantum graphs. These have all been topics of
current research in their own right and in each case this unified approach
significantly expands results in the literature.Comment: 32 pages, typos corrected, references adde
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