662 research outputs found
Ventricular diastolic filling characteristics in stage-24 chick embryos after extra-embryonic venous obstruction
Alteration of extra-embryonic venous blood flow in stage-17 chick embryos
results in well-defined cardiovascular malformations. We hypothesize that
the decreased dorsal aortic blood volume flow observed after venous
obstruction results in altered ventricular diastolic function in stage-24
chick embryos. A microclip was placed at the right lateral vitelline vein
in a stage-17 (52-64 h of incubation) chick embryo. At stage 24 (4.5 days
of incubation), we measured simultaneously dorsal aortic and
atrioventricular blood flow velocities with a 20-MHz pulsed-Doppler
velocity meter. The fraction of passive and active filling was integrated
and multiplied by dorsal aortic blood flow to obtain the relative passive
and active ventricular filling volumes. Data were summarized as means +/-
S.E.M. and analyzed by t-test. At similar cycle lengths ranging from 557
ms to 635 ms (P>0.60), dorsal aortic blood flow and stroke volume measured
in the dorsal aorta were similar in stage-24 clipped and normal embryos.
Passive filling volume (0.07+/-0.01 mm(3)) was decreased, and active
filling volume (0.40+/-0.02 mm(3)) was increased in the clipped embryo
when compared with the normal embryo (0.15+/-0.01 mm(3), 0.30+/-0.01
mm(3), respectively) (P<0.003). In the clipped embryos, the passive/active
ratio was decreased compared with that in normal embryos (P<0.001).
Ventricular filling components changed after partially obstructing the
extra-embryonic venous circulation. These results suggest that material
properties of the embryonic ventricle are modified after temporarily
reduced hemodynamic load
Fermi liquid interactions and the superfluid density in d-wave superconductors
We construct a phenomenological superfluid Fermi liquid theory for a
two-dimensional d-wave superconductor on a square lattice, and study the effect
of quasiparticle interactions on the superfluid density. Using simple models
for the dispersion and the Landau interaction function, we illustrate the
deviation of these results from those for the isotropic superfluid. This allows
us to reconcile the value and doping dependence of the superfluid density slope
at low temperature obtained from penetration depth measurements, with
photoemission data on nodal quasiparticles.Comment: 5 latex pages, 1 eps-figure. submitted to PR
Variational Monte Carlo study of the ground state properties and vacancy formation energy of solid para-H2 using a shadow wave function
A Shadow Wave Function (SWF) is employed along with Variational Monte Carlo
techniques to describe the ground state properties of solid molecular
para-hydrogen. The study has been extended to densities below the equilibrium
value, to obtain a parameterization of the SWF useful for the description of
inhomogeneous phases. We also present an estimate of the vacancy formation
energy as a function of the density, and discuss the importance of relaxation
effects near the vacant site
High Speed Solution of Spacecraft Trajectory Problems Using Taylor Series Integration
Taylor series integration is implemented in a spacecraft trajectory analysis code-the Spacecraft N-body Analysis Program (SNAP) - and compared with the code s existing eighth-order Runge-Kutta Fehlberg time integration scheme. Nine trajectory problems, including near Earth, lunar, Mars and Europa missions, are analyzed. Head-to-head comparison at five different error tolerances shows that, on average, Taylor series is faster than Runge-Kutta Fehlberg by a factor of 15.8. Results further show that Taylor series has superior convergence properties. Taylor series integration proves that it can provide rapid, highly accurate solutions to spacecraft trajectory problems
Phase fluctuations, dissipation and superfluid stiffness in d-wave superconductors
We study the effect of dissipation on quantum phase fluctuations in d-wave
superconductors. Dissipation, arising from a nonzero low frequency optical
conductivity which has been measured in experiments below , has two
effects: (1) a reduction of zero point phase fluctuations, and (2) a reduction
of the temperature at which one crosses over to classical thermal fluctuations.
For parameter values relevant to the cuprates, we show that the crossover
temperature is still too large for classical phase fluctuations to play a
significant role at low temperature. Quasiparticles are thus crucial in
determining the linear temperature dependence of the in-plane superfluid
stiffness. Thermal phase fluctuations become important at higher temperatures
and play a role near .Comment: Presentation improved, new references added (10 latex pages, 3 eps
figures). submitted to PR
The Fueling and Evolution of AGN: Internal and External Triggers
In this chapter, I review the fueling and evolution of active galactic nuclei
(AGN) under the influence of internal and external triggers, namely intrinsic
properties of host galaxies (morphological or Hubble type, color, presence of
bars and other non-axisymmetric features, etc) and external factors such as
environment and interactions. The most daunting challenge in fueling AGN is
arguably the angular momentum problem as even matter located at a radius of a
few hundred pc must lose more than 99.99 % of its specific angular momentum
before it is fit for consumption by a BH. I review mass accretion rates,
angular momentum requirements, the effectiveness of different fueling
mechanisms, and the growth and mass density of black BHs at different epochs. I
discuss connections between the nuclear and larger-scale properties of AGN,
both locally and at intermediate redshifts, outlining some recent results from
the GEMS and GOODS HST surveys.Comment: Invited Review Chapter to appear in LNP Volume on "AGN Physics on All
Scales", Chapter 6, in press. 40 pages, 12 figures. Typo in Eq 5 correcte
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
Production of Pairs Accompanied by Nuclear Dissociation in Ultra-Peripheral Heavy Ion Collision
We present the first data on pair production accompanied by nuclear
breakup in ultra-peripheral gold-gold collisions at a center of mass energy of
200 GeV per nucleon pair. The nuclear breakup requirement selects events at
small impact parameters, where higher-order corrections to the pair production
cross section should be enhanced. We compare the pair kinematic distributions
with two calculations: one based on the equivalent photon approximation, and
the other using lowest-order quantum electrodynamics (QED); the latter includes
the photon virtuality. The cross section, pair mass, rapidity and angular
distributions are in good agreement with both calculations. The pair transverse
momentum, , spectrum agrees with the QED calculation, but not with the
equivalent photon approach. We set limits on higher-order contributions to the
cross section. The and spectra are similar, with no evidence
for interference effects due to higher-order diagrams.Comment: 6 pages with 3 figures Slightly modified version that will appear in
Phys. Rev.
Fabrication of fillable microparticles and other complex 3D microstructures
Three-dimensional (3D) microstructures created by microfabrication and additive manufacturing have demonstrated value across a number of fields, ranging from biomedicine to microelectronics. However, the techniques used to create these devices each have their own characteristic set of advantages and limitations with regards to resolution, material compatibility, and geometrical constraints that determine the types of microstructures that can be formed. We describe a microfabrication method, termed StampEd Assembly of polymer Layers (SEAL), and create injectable pulsatile drug-delivery microparticles, pH sensors, and 3D microfluidic devices that we could not produce using traditional 3D printing. SEAL allows us to generate microstructures with complex geometry at high resolution, produce fully enclosed internal cavities containing a solid or liquid, and use potentially any thermoplastic material without processing additives
Functional Characterization of N297A, A Murine Surrogate for low-Fc Binding Anti-Human CD3 Antibodies
Several low- or non-FcR binding anti-human CD3 monoclonal antibodies have been under investigation for the treatment of autoimmune diseases. To model the mechanism of action of these anti-human CD3 mAbs in the murine system, an Fc-modified anti-mouse CD3 antibody (N297A) was generated. N297A exhibited similar biological effects as Fc-modified anti-human CD3 antibodies including rapid, reversible reduction in peripheral leukocyte numbers, differential modulation of activated versus resting T cells, and reduced levels of induced cytokine release compared to the non-Fc-modified parent antibody. In an in vivo model of colitis induced by adoptive transfer of IL–10-deficient cells, administration of N297A significantly reduced body weight loss. As N297A shared many functional characteristics of non-FcR binding anti-human CD3 mAbs both in vitro and in vivo, it provides a means to model the mechanisms of action of Fc-modified anti-human CD3 antibodies in mouse
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