73,062 research outputs found
Computer program for structural analysis of layered orthotropic ring-stiffened shells of revolution (SALORS): Linear stress analysis option
Program handles segmented, laminar, orthotropic shells with discrete rings. Meridional variations are handled in material properties, temperatures, and wall thickness. Allows for linear variations of temperature through each layer of shell wall
Break-up of shells under explosion and impact
A theoretical and experimental study of the fragmentation of closed thin
shells made of a disordered brittle material is presented. Experiments were
performed on brown and white hen egg-shells under two different loading
conditions: fragmentation due to an impact with a hard wall and explosion by a
combustion mixture giving rise to power law fragment size distributions. For
the theoretical investigations a three-dimensional discrete element model of
shells is constructed. Molecular dynamics simulations of the two loading cases
resulted in power law fragment mass distributions in satisfactory agreement
with experiments. Based on large scale simulations we give evidence that power
law distributions arise due to an underlying phase transition which proved to
be abrupt and continuous for explosion and impact, respectively. Our results
demonstrate that the fragmentation of closed shells defines a universality
class different from that of two- and three-dimensional bulk systems.Comment: 11 pages, 14 figures in eps forma
Relativistic shells: Dynamics, horizons, and shell crossing
We consider the dynamics of timelike spherical thin matter shells in vacuum.
A general formalism for thin shells matching two arbitrary spherical spacetimes
is derived, and subsequently specialized to the vacuum case. We first examine
the relative motion of two dust shells by focusing on the dynamics of the
exterior shell, whereby the problem is reduced to that of a single shell with
different active Schwarzschild masses on each side. We then examine the
dynamics of shells with non-vanishing tangential pressure , and show that
there are no stable--stationary, or otherwise--solutions for configurations
with a strictly linear barotropic equation of state, , where
is the proper surface energy density and . For {\em
arbitrary} equations of state, we show that, provided the weak energy condition
holds, the strong energy condition is necessary and sufficient for stability.
We examine in detail the formation of trapped surfaces, and show explicitly
that a thin boundary layer causes the apparent horizon to evolve
discontinuously. Finally, we derive an analytical (necessary and sufficient)
condition for neighboring shells to cross, and compare the discrete shell model
with the well-known continuous Lema\^{\i}tre-Tolman-Bondi dust case.Comment: 25 pages, revtex4, 4 eps figs; published in Phys. Rev.
Stability of generally stiffened anisotropic noncircular cylinders
Continuous filament grid-stiffened structure is a stiffening concept that combines structural efficiency and damage tolerance. However, finite element design of such structures against buckling is expensive due to the complexities of the structure. An analytical model of such a structure is developed using a penalty method (artificial springs) with a first order shear deformation theory (FSDT). The buckling analysis under combined loadings is done using energy method with a penalty/Rayleigh-Ritz technique. The penalty/Rayleigh-Ritz approach is computationally less demanding when compared to the finite element solution and mesh generation. Apart from the published research works on buckling of stiffened plates and shells by finite element and finite strips, research works on buckling of stiffened plates and shells utilize three different approaches; smeared, column, and discrete approaches. The discrete approach considers the discrete effects of the stiffeners in the buckling behavior by modeling stiffeners as line of bending (EI) and torsion (GJ) stiffnesses on panel skin. Some local deformations are lost when stiffeners are modeled as (EI) and (GJ) stiffeners. This approach becomes difficult in the case of plate stiffened in more than two directions. Most of the work done using the discrete approach involved the Classical Plate Theory (CLPT) rather than the FSDT. We report on our formulation of a discrete approach coupled with a penalty formulation and FSDT
Non-Fermi liquids from holography
We report on a potentially new class of non-Fermi liquids in
(2+1)-dimensions. They are identified via the response functions of composite
fermionic operators in a class of strongly interacting quantum field theories
at finite density, computed using the AdS/CFT correspondence. We find strong
evidence of Fermi surfaces: gapless fermionic excitations at discrete shells in
momentum space. The spectral weight exhibits novel phenomena, including
particle-hole asymmetry, discrete scale invariance, and scaling behavior
consistent with that of a critical Fermi surface postulated by Senthil.Comment: 10 pages, 16 figures. v2: added references, corrected figures, some
minor changes. v3: figure 5 replace
Quantum transport through single and multilayer icosahedral fullerenes
We use a tight-binding Hamiltonian and Green functions methods to calculate
the quantum transmission through single-wall fullerenes and bilayered and
trilayered onions of icosahedral symmetry attached to metallic leads. The
electronic structure of the onion-like fullerenes takes into account the
curvature and finite size of the fullerenes layers as well as the strength of
the intershell interactions depending on to the number of interacting atom
pairs belonging to adjacent shells. Misalignment of the symmetry axes of the
concentric icosahedral shells produces breaking of the level degeneracies of
the individual shells, giving rise some narrow quasi-continuum bands instead of
the localized discrete peaks of the individual fullerenes. As a result, the
transmission function for non symmetrical onions are rapidly varying functions
of the Fermi energy. Furthermore, we found that most of the features of the
transmission through the onions are due to the electronic structure of the
outer shell with additional Fano-like antiresonances arising from coupling with
or between the inner shells.Comment: 16 pages, 5 figur
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