845 research outputs found
Numerical Study on Impulse Ventilation for Smoke Control in an Underground Car Park
AbstractThis study examines smoke control capacity of impulse ventilation system (IVS) in an underground car park. An analysis is made in relation to important parameters including jet fan number, jet fan velocity, extract rate and system robustness on fire position. The comparison with ductwork system is also performed to determine the different effect of smoke control between two systems. Fire Dynamic Simulator version 5.30 is applied to simulate 10 scenarios in a 80 m long, 40 m wide and 3.2 m height domain witha fire source simulating a car fire with an peak heat release rate of 4 MW. Results show that impulse ventilation system not noly prohibit fire smoke spreading but also maintain a good visibility providing clear access for fighters. However it may cause temperature rise on the downwind zone of fire source with a maximum value between 80-100 and fire plume e tilt. Smoke control capacity of impulse ventilation system is sensitive to jet fan numbers. Too high jet fan velocity may cause severe smoke recirculation. Increment in extract rate is conductive to relay jet flows. An impulse ventilation system can effectively control smoke movement and induce smoke to extract points under two typical different fire locations, which is of great practical importance. Impulse ventilation system seems superior to ductwork system in maintaining high visibility
Effect of gluon-exchange pair-currents on the ratio G(E(P))/G(M(P))
The effect of one-gluon-exchange (OGE) pair-currents on the ratio for the proton is investigated within a nonrelativistic
constituent quark model (CQM) starting from nucleon wave
functions, but with relativistic corrections. We found that the OGE
pair-currents are important to reproduce well the ratio .
With the assumption that the OGE pair-currents are the driving mechanism for
the violation of the scaling law we give a prediction for the ratio of the neutron.Comment: 5 pages, 4 figure
The fermion dynamical symmetry model for the even--even and even--odd nuclei in the Xe--Ba region
The even--even and even--odd nuclei Xe-Xe and
Ba-Ba are shown to have a well-realized fermion dynamical symmetry. Their low-lying energy levels can be
described by a unified analytical expression with two (three) adjustable
parameters for even--odd (even--even) nuclei that is derived from the fermion
dynamical symmetry model. Analytical expressions are given for wavefunctions
and for transition rates that agree well with data. The distinction
between the FDSM and IBM limits is discussed. The experimentally
observed suppression of the the energy levels with increasing quantum
number can be explained as a perturbation of the pairing interaction on
the symmetry, which leads to an Pairing effect for nuclei.Comment: submitted to Phys. Rev. C, LaTeX, 31 pages, 8 figures with postscript
files available on request at [email protected]
The liquid-vapor interface of an ionic fluid
We investigate the liquid-vapor interface of the restricted primitive model
(RPM) for an ionic fluid using a density-functional approximation based on
correlation functions of the homogeneous fluid as obtained from the
mean-spherical approximation (MSA). In the limit of a homogeneous fluid our
approach yields the well-known MSA (energy) equation of state. The ionic
interfacial density profiles, which for the RPM are identical for both species,
have a shape similar to those of simple atomic fluids in that the decay towards
the bulk values is more rapid on the vapor side than on the liquid side. This
is the opposite asymmetry of the decay to that found in earlier calculations
for the RPM based on a square-gradient theory. The width of the interface is,
for a wide range of temperatures, approximately four times the second moment
correlation length of the liquid phase. We discuss the magnitude and
temperature dependence of the surface tension, and argue that for temperatures
near the triple point the ratio of the dimensionless surface tension and
critical temperature is much smaller for the RPM than for simple atomic fluids.Comment: 6 postscript figures, submitted to Phys. Rev.
Mott Transition in Degenerate Hubbard Models: Application to Doped Fullerenes
The Mott-Hubbard transition is studied for a Hubbard model with orbital
degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments,
we conjecture that the Mott-Hubbard transition takes place for U/W \propto
\sqrt{N}, where U is the Coulomb interaction and W is the band width. This is
supported by exact diagonalization and Monte-Carlo calculations. Realistic
parameters for the doped fullerenes lead to the conclusion that stoichiometric
A_3 C_60 (A=K, Rb) are near the Mott-Hubbard transition, in a correlated
metallic state.Comment: 4 pages, revtex, 1 eps figure included, to be published in Phys.Rev.B
Rapid Com
Revisiting vertical structure of neutrino-dominated accretion disks: Bernoulli parameter, neutrino trapping and other distributions
We revisit the vertical structure of neutrino dominated accretion flows
(NDAFs) in spherical coordinates with a new boundary condition based on the
mechanical equilibrium. The solutions show that NDAF is significantly thick.
The Bernoulli parameter and neutrino trapping are determined by the mass
accretion rate and the viscosity parameter. According to the distribution of
the Bernoulli parameter, the possible outflow may appear in the outer region of
the disk. The neutrino trapping can essentially affect the neutrino radiation
luminosity. The vertical structure of NDAF is like a "sandwich", and the
multilayer accretion may account for the flares in gamma-ray bursts.Comment: 7 pages, 2 figures, Accepted for publication in Astrophysics & Space
Scienc
Mutations in multidomain protein MEGF8 identify a Carpenter syndrome subtype associated with defective lateralization
Carpenter syndrome is an autosomal-recessive multiple-congenital-malformation disorder characterized by multisuture craniosynostosis and polysyndactyly of the hands and feet; many other clinical features occur, and the most frequent include obesity, umbilical hernia, cryptorchidism, and congenital heart disease. Mutations of RAB23, encoding a small GTPase that regulates vesicular transport, are present in the majority of cases. Here, we describe a disorder caused by mutations in multiple epidermal-growth-factor-like-domains 8 (MEGF8), which exhibits substantial clinical overlap with Carpenter syndrome but is frequently associated with abnormal left-right patterning. We describe five affected individuals with similar dysmorphic facies, and three of them had either complete situs inversus, dextrocardia, or transposition of the great arteries; similar cardiac abnormalities were previously identified in a mouse mutant for the orthologous Megf8. The mutant alleles comprise one nonsense, three missense, and two splice-site mutations; we demonstrate in zebrafish that, in contrast to the wild-type protein, the proteins containing all three missense alterations provide only weak rescue of an early gastrulation phenotype induced by Megf8 knockdown. We conclude that mutations in MEGF8 cause a Carpenter syndrome subtype frequently associated with defective left-right patterning, probably through perturbation of signaling by hedgehog and nodal family members. We did not observe any subject with biallelic loss-of function mutations, suggesting that some residual MEGF8 function might be necessary for survival and might influence the phenotypes observed
Magnetic properties of exactly solvable doubly decorated Ising-Heisenberg planar models
Applying the decoration-iteration procedure, we introduce a class of exactly
solvable doubly decorated planar models consisting both of the Ising- and
Heisenberg-type atoms. Exact solutions for the ground state, phase diagrams and
basic physical quantities are derived and discussed. The detailed analysis of
the relevant quantities suggests the existence of an interesting quantum
antiferromagnetic phase in the system.Comment: 9 pages, 9 figures, submitted to Physical Review
The spectral gap for some spin chains with discrete symmetry breaking
We prove that for any finite set of generalized valence bond solid (GVBS)
states of a quantum spin chain there exists a translation invariant
finite-range Hamiltonian for which this set is the set of ground states. This
result implies that there are GVBS models with arbitrary broken discrete
symmetries that are described as combinations of lattice translations, lattice
reflections, and local unitary or anti-unitary transformations. We also show
that all GVBS models that satisfy some natural conditions have a spectral gap.
The existence of a spectral gap is obtained by applying a simple and quite
general strategy for proving lower bounds on the spectral gap of the generator
of a classical or quantum spin dynamics. This general scheme is interesting in
its own right and therefore, although the basic idea is not new, we present it
in a system-independent setting. The results are illustrated with an number of
examples.Comment: 48 pages, Plain TeX, BN26/Oct/9
Quantum computing with mixed states
We discuss a model for quantum computing with initially mixed states.
Although such a computer is known to be less powerful than a quantum computer
operating with pure (entangled) states, it may efficiently solve some problems
for which no efficient classical algorithms are known. We suggest a new
implementation of quantum computation with initially mixed states in which an
algorithm realization is achieved by means of optimal basis independent
transformations of qubits.Comment: 2 figures, 52 reference
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