5,535 research outputs found
Shock Theory of a Bubbly Liquid in a Deformable Tube
Shock propagation through a bubbly liquid filled in a deformable cylindrical tube is considered. Quasi-one-dimensional
bubbly flow equations that include fluid-structure interaction are formulated, and the steady shock
relations are derived. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water
mixture in a polycarbonate tube, and stress waves in the tube material are measured. The experimental data indicate
that the linear theory cannot properly predict the propagation speeds of shock waves in mixture-filled tubes; the shock
theory is found to more accurately estimate the measured wave speeds
Shock propagation through a bubbly liquid in a deformable tube
Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one-dimensional mixture-averaged flow equations that include fluid–structure interaction are formulated. The steady shock relations are derived and the nonlinear effect due to the gas-phase compressibility is examined. Experiments
are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material and pressure
on the tube wall are measured. The experimental data indicate that the linear theory is incapable of properly predicting the propagation speeds of finite-amplitude waves
in a mixture-filled tube; the shock theory is found to more accurately estimate the measured wave speeds
Supersolid state in fermionic optical lattice systems
We study ultracold fermionic atoms trapped in an optical lattice with
harmonic confinement by combining the real-space dynamical mean-field theory
with a two-site impurity solver. By calculating the local particle density and
the pair potential in the systems with different clusters, we discuss the
stability of a supersolid state, where an s-wave superfluid coexists with a
density-wave state of checkerboard pattern. It is clarified that a confining
potential plays an essential role in stabilizing the supersolid state. The
phase diagrams are obtained for several effective particle densities.Comment: 7 pages, 5 figures, Phys. Rev. A in pres
Dendritic cells are critical accessory cells for thymus-dependent antibody responses in mouse and in man
We report that dendritic cells (DC) are necessary and potent accessory cells for anti-sheep erythrocyte responses in both mouse and man. In mice, a small number of DC (0.3-1% of the culture) restores the response of B/T-lymphocyte mixtures to that observed in unfractionated spleen. An even lower dose (0.03-0.1% DC) is needed if the T cells have been primed to antigen. Responses are both antigen and T cell dependent. Selective depletion of DC from unfractionated spleen with the monoclonal antibody 33D1 and complement ablates the antibody response. In contrast to DC, purified spleen macrophages are weak or inactive stimulators. However, when mixed with DC, macrophages can increase the yield of antibody-secreting cells about 2-fold. In man, small number (0.3-1%) of blood DC stimulate antibody formation in vitro. Purified human monocytes do not stimulate but in low doses (1% of the culture) inhibit the antibody response. Likewise, selective removal of human monocytes with antibody and complement enhances or accelerates the development of antibody-secreting cells. We conclude that DC are required for the development of T-dependent antibody responses by mouse and human lymphocytes in vitro
The effect of gas drag on the growth of protoplanets -- Analytical expressions for the accretion of small bodies in laminar disks
Planetary bodies form by accretion of smaller bodies. It has been suggested
that a very efficient way to grow protoplanets is by accreting particles of
size <<km (e.g., chondrules, boulders, or fragments of larger bodies) as they
can be kept dynamically cold. We investigate the effects of gas drag on the
impact radii and the accretion rates of these particles. As simplifying
assumptions we restrict our analysis to 2D settings, a gas drag law linear in
velocity, and a laminar disk characterized by a smooth (global) pressure
gradient that causes particles to drift in radially. These approximations,
however, enable us to cover an arbitrary large parameter space. The framework
of the circularly restricted three body problem is used to numerically
integrate particle trajectories and to derive their impact parameters. Three
accretion modes can be distinguished: hyperbolic encounters, where the 2-body
gravitational focusing enhances the impact parameter; three-body encounters,
where gas drag enhances the capture probability; and settling encounters, where
particles settle towards the protoplanet. An analysis of the observed behavior
is presented; and we provide a recipe to analytically calculate the impact
radius, which confirms the numerical findings. We apply our results to the
sweepup of fragments by a protoplanet at a distance of 5 AU. Accretion of
debris on small protoplanets (<50 km) is found to be slow, because the
fragments are distributed over a rather thick layer. However, the newly found
settling mechanism, which is characterized by much larger impact radii, becomes
relevant for protoplanets of ~10^3 km in size and provides a much faster
channel for growth.Comment: accepted for publication in Astronomy & Astrophysic
Induced local spin-singlet amplitude and pseudogap in high cuprates
In this paper we show that local spin-singlet amplitude with d-wave symmetry,
, can be induced by short-range spin correlations even
in the absence of pairing interactions. Fluctuation theory is formulated to
make connection between pseudogap temperature $T^{*}$, pseudogap size
$\Delta_{pg}$ and . In the present scenario for the
pseudogap, the normal state pseudogap is caused by the induced local
spin-singlet amplitude due to short-range spin correlations, which compete in
the low energy sector with superconducting correlations to make go to
zero near half-filling. Calculated falls from a high value onto the
line and closely follows mean-field N\'{e}el temperature .
The calculated is in good agreement with experimental results. We
propose an experiment in which the present scenario can be critically tested.Comment: 5 pages, 3 figure
Heat Capacity and Magnetic Phase Diagram of the Low-Dimensional Antiferromagnet YBaCuO
A study by specific heat of a polycrystalline sample of the low-dimensional
magnetic system YBaCuO is presented. Magnetic fields up to 14 T are
applied and permit to extract the (,) phase diagram. Below
T, the N\'eel temperature, associated with a
three-dimensional antiferromagnetic long-range ordering, is constant and equals
K. Above , increases linearly with and a
field-induced increase of the entropy at is related to the presence of an
isosbestic point at K, where all the specific heat curves cross.
A comparison is made between YBaCuO and the quasi-two-dimensional
magnetic systems BaNiVO, SrCuOCl, and
PrCuO, for which very similar phase diagrams have been reported. An
effective field-induced magnetic anisotropy is proposed to explain these phase
diagrams.Comment: 14 pages, 7 figure
Planetesimal-driven planet migration in the presence of a gas disk
We report here on an extension of a previous study by Kirsh et al. (2009) of
planetesimal-driven migration using our N-body code SyMBA (Duncan et al.,
1998). The previous work focused on the case of a single planet of mass Mem,
immersed in a planetesimal disk with a power-law surface density distribution
and Rayleigh distributed eccentricities and inclinations. Typically 10^4-10^5
equal-mass planetesimals were used, where the gravitational force (and the
back-reaction) on each planetesimal by the Sun and planetwere included, while
planetesimal-planetesimal interactions were neglected. The runs reported on
here incorporate the dynamical effects of a gas disk, where the Adachi et al.
(1976) prescription of aerodynamic gas drag is implemented for all bodies. In
some cases the Papaloizou and Larwood (2000) prescription of Type-I migration
for the planet are implemented, as well as a mass distribution. In the gas-free
cases, rapid planet migration was observed - at a rate independent of the
planet's mass - provided the planet's mass was not large compared to the mass
in planetesimals capable of entering its Hill sphere. In such cases, both
inward and outward migrations can be self-sustaining, but there is a strong
propensity for inward migration. When a gas disk is present, aerodynamic drag
can substantially modify the dynamics of scattered planetesimals. For
sufficiently large or small mono-dispersed planetesimals, the planet typically
migrates inward. However, for a range of plausible planetesimal sizes (i.e.
0.5-5.0 km at 5.0 AU in a minimum mass Hayashi disk) outward migration is
usually triggered, often accompanied by substantial planetary mass accretion.
The origins of this behaviour are explained in terms of a toy model. The
effects of including a size distribution and torques associated with Type-I
migration are also discussed.Comment: 37 pages, 17 figures, Accepted for publication in Icaru
Superconductivity in the Three-Fold Charge-Ordered Metal of the Triangular-Lattice Extended Hubbard Model
The quarter-filling extended Hubbard model on the triangular lattice is
studied to explore pairing instability in the three-fold charge-ordered (CO)
metal. We derive a second-order strong-coupling effective Hamiltonian of doped
carriers into the three-fold CO insulator at electron density of , and
then study the - and -wave superconductivities down to by
using the BCS mean-field approximation. It is found that the triplet -wave
pairing is more stable than the -wave one. We also point out that this
coexisting state of the charge ordering and superconductivity is possible to
have critical temperature .Comment: 4 pages, 7 figure
Calculation of the average Green's function of electrons in a stochastic medium via higher-dimensional bosonization
The disorder averaged single-particle Green's function of electrons subject
to a time-dependent random potential with long-range spatial correlations is
calculated by means of bosonization in arbitrary dimensions. For static
disorder our method is equivalent with conventional perturbation theory based
on the lowest order Born approximation. For dynamic disorder, however, we
obtain a new non-perturbative expression for the average Green's function.
Bosonization also provides a solid microscopic basis for the description of the
quantum dynamics of an interacting many-body system via an effective stochastic
model with Gaussian probability distribution.Comment: RevTex, no figure
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