4,960 research outputs found
VISJET & VISFLOOD: Software for environment hydraulic modeling & visualization
We present two general interactive PC-based modeling and visualization software systems developed for
the study of two types of environmental water flows: buoyant jet mixing and urban drainage problems.
VISJET (http://www.aoe-water.hku.hk/visjet) is arguably the most robust software with advanced
graphics for the prediction of mixing and transport of effluent discharges into a stratified crossflow. The
prediction engine is a Lagrangian model for buoyant jets with three-dimensional trajectories, and is based
on extensive basic experiments and turbulence model calculations. It can be used in outfall design and
environmental impact assessment, and as an educational or training tool. VISFLOOD
(http://www.aoe-water.hku.hk/visflood) is based on the numerical solution of the Saint-Venant equations,
and caters for the simulation of unsteady flood propagation in urban drainage systems. Both software
systems are fully interactive with data interrogation; the 3D visualization is fully integrated with the
model engine, and enables the user to appreciate the context of the problem in a most effective way. Both
models have been well-validated against laboratory and field data, and have been applied to many actual
engineering projects. This software product is an outcome of a grant by the Hong Kong Innovation and
Technology Fund (ITF).published_or_final_versio
Size effect on magnetism of Fe thin films in Fe/Ir superlattices
In ferromagnetic thin films, the Curie temperature variation with the
thickness is always considered as continuous when the thickness is varied from
to atomic planes. We show that it is not the case for Fe in Fe/Ir
superlattices. For an integer number of atomic planes, a unique magnetic
transition is observed by susceptibility measurements, whereas two magnetic
transitions are observed for fractional numbers of planes. This behavior is
attributed to successive transitions of areas with and atomic planes,
for which the 's are not the same. Indeed, the magnetic correlation length
is presumably shorter than the average size of the terraces. Monte carlo
simulations are performed to support this explanation.Comment: LaTeX file with Revtex, 5 pages, 5 eps figures, to appear in Phys.
Rev. Let
Dielectric catastrophe at the magnetic field induced insulator to metal transition in Pr1-xCaxMnO3 (x=0.30, 0.37) crystals
The dielectric permittivity and resistivity have been measured simultaneously
as a function of magnetic field in Pr1-xCaxMnO3 crystals with different doping.
A huge increase of dielectric permittivity was detected near percolation
threshold. The dielectric and conductive properties are found to be mutually
correlated throughout insulator to metal transition evidencing the dielectric
catastrophe phenomenon. Data are analyzed in a framework of Maxwell-Garnett
theory and the Mott-Hubbard theory attributed to the role of strong Coulomb
interactions.Comment: 5 pages, 5 figure
On the low temperature properties and specific anisotropy of pure anisotropically paired superconductors
Dependences of low temperature behavior and anisotropy of various physical
quantities for pure unconventional superconductors upon a particular form of
momentum direction dependence for the superconducting order parameter (within
the framework of the same symmetry type of superconducting pairing) are
considered. A special attention is drawn to the possibility of different
multiplicities of the nodes of the order parameter under their fixed positions
on the Fermi surface, which are governed by symmetry. The problem of an
unambiguous identification of a type of superconducting pairing on the basis of
corresponding experimental results is discussed. Quasiparticle density of
states at low energy for both homogeneous and mixed states, the low temperature
dependences of the specific heat, penetration depth and thermal conductivity,
the I-V curves of SS and NS tunnel junctions at low voltages are examined. A
specific anisotropy of the boundary conditions for unconventional
superconducting order parameter near for the case of specular reflection
from the boundary is also investigated.Comment: 20 page
Role of Fibronectin in the Adhesion of Acinetobacter baumannii to Host Cells
Adhesion to host cells is an initial and important step in Acinetobacter baumannii pathogenesis. However, there is relatively little information on the mechanisms by which A. baumannii binds to and interacts with host cells. Adherence to extracellular matrix proteins, such as fibronectin, affords pathogens with a mechanism to invade epithelial cells. Here, we found that A. baumannii adheres more avidly to immobilized fibronectin than to control protein. Free fibronectin used as a competitor resulted in dose-dependent decreased binding of A. baumannii to fibronectin. Three outer membrane preparations (OMPs) were identified as fibronectin binding proteins (FBPs): OMPA, TonB-dependent copper receptor, and 34 kDa OMP. Moreover, we demonstrated that fibronectin inhibition and neutralization by specific antibody prevented significantly the adhesion of A. baumannii to human lung epithelial cells (A549 cells). Similarly, A. baumannii OMPA neutralization by specific antibody decreased significantly the adhesion of A. baumannii to A549 cells. These data indicate that FBPs are key adhesins that mediate binding of A. baumannii to human lung epithelial cells through interaction with fibronectin on the surface of these host cells
Quantifying trading behavior in financial markets using Google Trends
Crises in financial markets affect humans worldwide. Detailed market data on trading decisions reflect some of the complex human behavior that has led to these crises. We suggest that massive new data sources resulting from human interaction with the Internet may offer a new perspective on the behavior of market participants in periods of large market movements. By analyzing changes in Google query volumes for search terms related to finance, we find patterns that may be interpreted as “early warning signs” of stock market moves. Our results illustrate the potential that combining extensive behavioral data sets offers for a better understanding of collective human behavior
Electrodynamics of a Clean Vortex Lattice
We report on a microscopic evaluation of electrodynamic response for the
vortex lattice state of a model s-wave superconductor. Our calculation accounts
self-consistently for both quasiparticle and order parameter response and
establishes the collective nature of linear response in the clean limit. We
discuss the effects of homogeneous and inhomogeneous pinning on the optical
conductivity and the penetration depth, and comment on the relationship between
macroscopic and local penetration depths. We find unexpected relationships
between pinning arrangements and conductivity due to the strongly non-local
response.Comment: 4 pages, 2 figure
Critical Exponents of the Fully Frustrated 2-D Xy Model
We present a detailed study of the critical properties of the 2-D XY model
with maximal frustration in a square lattice. We use extensive Monte Carlo
simulations to study the thermodynamics of the spin and chiral degrees of
freedom, concentrating on their correlation functions. The gauge invariant
spin-spin correlation functions are calculated close to the critical point for
lattice sizes up to ; the chiral correlation functions are
studied on lattices up to . We find that the critical exponents of
the spin phase transition are , and , which are to be
compared with the unfrustrated XY model exponents and . We
also find that the critical exponents of the chiral transition are
, , , and
, which are different from the expected 2-D Ising
critical exponents. The spin-phase transition occurs at which
is about 7\% above the estimated chiral critical temperature . However, because of the size of the statistical errors, it is
difficult to decide with certainty whether the transitions occur at the same or
at slightly different temperatures. Finally, the jump in the helicity modulus
in the fully frustrated system is found to be about 23\% below the unfrustrated
universal value. The most important consequence of these results is that the
fully frustrated XY model appears to be in a novel universality class. Recent
successful comparisons of some of these results with experimental data are also
briefly discussed. (TO APPEAR IN PRB)Comment: 47 pages (PHYZZX
Dopamine Regulation of Amygdala Inhibitory Circuits for Expression of Learned Fear.
GABAergic signaling in the amygdala controls learned fear, and its dysfunction potentially contributes to posttraumatic stress disorder (PTSD). We find that sub-threshold fear conditioning leads to dopamine receptor D4-dependent long-term depression (LTD) of glutamatergic excitatory synapses by increasing inhibitory inputs onto neurons of the dorsal intercalated cell mass (ITC) in the amygdala. Pharmacological, genetic, and optogenetic manipulations of the amygdala regions centered on the dorsal ITC reveal that this LTD limits less salient experiences from forming persistent memories. In further support of the idea that LTD has preventive and discriminative roles, we find that LTD at the dorsal ITC is impaired in mice exhibiting PTSD-like behaviors. These findings reveal a novel role of inhibitory circuits in the amygdala, which serves to dampen and restrict the level of fear expression. This mechanism is interfered with by stimuli that give rise to PTSD and may also be recruited for fear-related psychiatric diseases.1110Ysciescopu
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