28,477 research outputs found
Statistical aspects of carbon fiber risk assessment modeling
The probabilistic and statistical aspects of the carbon fiber risk assessment modeling of fire accidents involving commercial aircraft are examined. Three major sources of uncertainty in the modeling effort are identified. These are: (1) imprecise knowledge in establishing the model; (2) parameter estimation; and (3)Monte Carlo sampling error. All three sources of uncertainty are treated and statistical procedures are utilized and/or developed to control them wherever possible
Break-up fragment topology in statistical multifragmentation models
Break-up fragmentation patterns together with kinetic and configurational
energy fluctuations are investigated in the framework of a microcanonical model
with fragment degrees of freedom over a broad excitation energy range. As far
as fragment partitioning is approximately preserved, energy fluctuations are
found to be rather insensitive to both the way in which the freeze-out volume
is constrained and the trajectory followed by the system in the excitation
energy - freeze-out volume space. Due to hard-core repulsion, the freeze-out
volume is found to be populated un-uniformly, its highly depleted core giving
the source a bubble-like structure. The most probable localization of the
largest fragments in the freeze-out volume may be inferred experimentally from
their kinematic properties, largely dictated by Coulomb repulsion
More on Phase Structure of Nonlocal 2D Generalized Yang-Mills Theories (nlgYM's)
We study the phase structure of nonlocal two dimensional generalized Yang -
Mills theories (nlgYM) and it is shown that all order of model
of these theories has phase transition only on compact manifold with (on
sphere), and the order of phase transition is 3. Also it is shown that the
model of nlgYM has third order phase
transition on any compact manifold with ,
and has no phase transition on sphere.Comment: 11 pages, no figure
The String Calculation of QCD Wilson Loops on Arbitrary Surfaces
Compact string expressions are found for non-intersecting Wilson loops in
SU(N) Yang-Mills theory on any surface (orientable or nonorientable) as a
weighted sum over covers of the surface. All terms from the coupled chiral
sectors of the 1/N expansion of the Wilson loop expectation values are
included.Comment: 10 pages, LaTeX, no figure
The stability of the spectator, Dirac, and Salpeter equations for mesons
Mesons are made of quark-antiquark pairs held together by the strong force.
The one channel spectator, Dirac, and Salpeter equations can each be used to
model this pairing. We look at cases where the relativistic kernel of these
equations corresponds to a time-like vector exchange, a scalar exchange, or a
linear combination of the two. Since the model used in this paper describes
mesons which cannot decay physically, the equations must describe stable
states. We find that this requirement is not always satisfied, and give a
complete discussion of the conditions under which the various equations give
unphysical, unstable solutions
Continuous phase transitions with a convex dip in the microcanonical entropy
The appearance of a convex dip in the microcanonical entropy of finite
systems usually signals a first order transition. However, a convex dip also
shows up in some systems with a continuous transition as for example in the
Baxter-Wu model and in the four-state Potts model in two dimensions. We
demonstrate that the appearance of a convex dip in those cases can be traced
back to a finite-size effect. The properties of the dip are markedly different
from those associated with a first order transition and can be understood
within a microcanonical finite-size scaling theory for continuous phase
transitions. Results obtained from numerical simulations corroborate the
predictions of the scaling theory.Comment: 8 pages, 7 figures, to appear in Phys. Rev.
Calculating the Rest Tension for a Polymer of String Bits
We explore the application of approximation schemes from many body physics,
including the Hartree-Fock method and random phase approximation (RPA), to the
problem of analyzing the low energy excitations of a polymer chain made up of
bosonic string bits. We accordingly obtain an expression for the rest tension
of the bosonic relativistic string in terms of the parameters
characterizing the microscopic string bit dynamics. We first derive an exact
connection between the string tension and a certain correlation function of the
many-body string bit system. This connection is made for an arbitrary
interaction potential between string bits and relies on an exact dipole sum
rule. We then review an earlier calculation by Goldstone of the low energy
excitations of a polymer chain using RPA. We assess the accuracy of the RPA by
calculating the first order corrections. For this purpose we specialize to the
unique scale invariant potential, namely an attractive delta function potential
in two (transverse) dimensions. We find that the corrections are large, and
discuss a method for summing the large terms. The corrections to this improved
RPA are roughly 15\%.Comment: 44 pages, phyzzx, psfig required, Univ. of Florida preprint,
UFIFT-HEP-94
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