23,901 research outputs found
Interlaminar stresses in composite laminates: A perturbation analysis
A general method of solution for an elastic balanced symmetric composite laminate subject to a uniaxial extension was developed based upon a perturbation analysis of a limiting free body containing an interfacial plane. The solution satisfies more physical requirements and boundary conditions than previous investigations, and predicts smooth continuous interlaminar stresses with no instabilities. It determines the finite maximum intensity for the interlaminar normal stress in all laminates, provides mathematical evidences for the singular stresses in angle-ply laminates, suggests the need for the experimental determination of an important problem parameter, and introduces a viable means for solving related problems of practical interest
A limiting analysis for edge effects in angle-ply laminates
A zeroth order solution for edge effects in angle ply composite laminates using perturbation techniques and a limiting free body approach was developed. The general method of solution for laminates is developed and then applied to the special case of a graphite/epoxy laminate. Interlaminar stress distributions are obtained as a function of the laminate thickness to width ratio h/b and compared to existing numerical results. The solution predicts stable, continuous stress distributions, determines finite maximum tensile interlaminar normal stress for two laminates, and provides mathematical evidence for singular interlaminar shear stresses
Theoretical description of a DNA-linked nanoparticle self-assembly
Nanoparticles tethered with DNA strands are promising building blocks for
bottom-up nanotechnology, and a theoretical understanding is important for
future development. Here we build on approaches developed in polymer physics to
provide theoretical descriptions for the equilibrium clustering and dynamics,
as well as the self-assembly kinetics of DNA-linked nanoparticles. Striking
agreement is observed between the theory and molecular modeling of DNA tethered
nanoparticles.Comment: Accepted for publication in Physical Review Letter
Baryon resonances and hadronic interactions in a finite volume
In a finite volume, resonances and multi-hadron states are identified by
discrete energy levels. When comparing the results of lattice QCD calculations
to scattering experiments, it is important to have a way of associating the
energy spectrum of the finite-volume lattice with the asymptotic behaviour of
the S-matrix. A new technique for comparing energy eigenvalues with scattering
phase shifts is introduced, which involves the construction of an exactly
solvable matrix Hamiltonian model. The model framework is applied to the case
of decay, but is easily generalized to include
multi-channel scattering. Extracting resonance parameters involves matching the
energy spectrum of the model to that of a lattice QCD calculation. The
resulting fit parameters are then used to generate phase shifts. Using a sample
set of pseudodata, it is found that the extraction of the resonance position is
stable with respect to volume for a variety of regularization schemes, and
compares favorably with the well-known Luescher method. The model-dependence of
the result is briefly investigated.Comment: 7 pages, 3 figures. Talk presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), June 24-29, 2012, Cairns,
Australi
Dragging a polymer chain into a nanotube and subsequent release
We present a scaling theory and Monte Carlo (MC) simulation results for a
flexible polymer chain slowly dragged by one end into a nanotube. We also
describe the situation when the completely confined chain is released and
gradually leaves the tube. MC simulations were performed for a self-avoiding
lattice model with a biased chain growth algorithm, the pruned-enriched
Rosenbluth method. The nanotube is a long channel opened at one end and its
diameter is much smaller than the size of the polymer coil in solution. We
analyze the following characteristics as functions of the chain end position
inside the tube: the free energy of confinement, the average end-to-end
distance, the average number of imprisoned monomers, and the average stretching
of the confined part of the chain for various values of and for the number
of monomers in the chain, . We show that when the chain end is dragged by a
certain critical distance into the tube, the polymer undergoes a
first-order phase transition whereby the remaining free tail is abruptly sucked
into the tube. This is accompanied by jumps in the average size, the number of
imprisoned segments, and in the average stretching parameter. The critical
distance scales as . The transition takes place when
approximately 3/4 of the chain units are dragged into the tube. The theory
presented is based on constructing the Landau free energy as a function of an
order parameter that provides a complete description of equilibrium and
metastable states. We argue that if the trapped chain is released with all
monomers allowed to fluctuate, the reverse process in which the chain leaves
the confinement occurs smoothly without any jumps. Finally, we apply the theory
to estimate the lifetime of confined DNA in metastable states in nanotubes.Comment: 13pages, 14figure
Constraints on Deflation from the Equation of State of Dark Energy
In cyclic cosmology based on phantom dark energy the requirement that our
universe satisfy a CBE-condition ({\it Comes Back Empty}) imposes a lower bound
on the number of causal patches which separate just prior to
turnaround. This bound depends on the dark energy equation of state with . More accurate measurement of will
constrain . The critical density in the model has a lower
bound or
when the smallest bound state has size m, or m,
respectively.Comment: 23 pages, 3 figures, typos fixe
Simulations of grafted polymers in a good solvent
We present improved simulations of three-dimensional self avoiding walks with
one end attached to an impenetrable surface on the simple cubic lattice. This
surface can either be a-thermal, having thus only an entropic effect, or
attractive. In the latter case we concentrate on the adsorption transition, We
find clear evidence for the cross-over exponent to be smaller than 1/2, in
contrast to all previous simulations but in agreement with a re-summed field
theoretic -expansion. Since we use the pruned-enriched Rosenbluth
method (PERM) which allows very precise estimates of the partition sum itself,
we also obtain improved estimates for all entropic critical exponents.Comment: 5 pages with 9 figures included; minor change
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