25,479 research outputs found
Use of NASTRAN as a teaching aid
Recent experiences with incorporating NASTRAN as a teaching tool in undergraduate courses was found pedagogically sound. Students with no previous computerized structures background are able to readily grasp the program's logic and begin solving realistic problems rapidly. The educational benefit is significantly enhanced by NASTRAN's plotting feature. However, the cost of operating the level 12 version makes the program difficult to justify
A Green's function approach to the natural vibration of thin spherical shell segments - A numerical method Final report
Green function approach to natural vibration of thin spherical shell segment
Structural analysis of light aircraft using NASTRAN
An application of NASTRAN to the structural analysis of light aircraft was conducted to determine the cost effectiveness. A model of the Baby Ace D model homebuilt aircraft was used. The NASTRAN model of the aircraft consists of 193 grid points connected by 352 structural members. All members are either rod or beam elements, including bending of unsymmetrical cross sections and torsion of noncircular cross sections. The aerodynamic loads applied to the aircraft were in accordance with FAA regulations governing the utility category aircraft
Energy absorption by "sparse" systems: beyond linear response theory
The analysis of the response to driving in the case of weakly chaotic or
weakly interacting systems should go beyond linear response theory. Due to the
"sparsity" of the perturbation matrix, a resistor network picture of
transitions between energy levels is essential. The Kubo formula is modified,
replacing the "algebraic" average over the squared matrix elements by a
"resistor network" average. Consequently the response becomes semi-linear
rather than linear. Some novel results have been obtained in the context of two
prototype problems: the heating rate of particles in Billiards with vibrating
walls; and the Ohmic Joule conductance of mesoscopic rings driven by
electromotive force. Respectively, the obtained results are contrasted with the
"Wall formula" and the "Drude formula".Comment: 8 pages, 7 figures, short pedagogical review. Proceedings of FQMT
conference (Prague, 2011). Ref correcte
Quantum response of weakly chaotic systems
Chaotic systems, that have a small Lyapunov exponent, do not obey the common
random matrix theory predictions within a wide "weak quantum chaos" regime.
This leads to a novel prediction for the rate of heating for cold atoms in
optical billiards with vibrating walls. The Hamiltonian matrix of the driven
system does not look like one from a Gaussian ensemble, but rather it is very
sparse. This sparsity can be characterized by parameters and that
reflect the percentage of large elements, and their connectivity respectively.
For we use a resistor network calculation that has direct relation to the
semi-linear response characteristics of the system.Comment: 7 pages, 5 figures, expanded improved versio
Invaded cluster algorithm for equilibrium critical points
A new cluster algorithm based on invasion percolation is described. The
algorithm samples the critical point of a spin system without a priori
knowledge of the critical temperature and provides an efficient way to
determine the critical temperature and other observables in the critical
region. The method is illustrated for the two- and three-dimensional Ising
models. The algorithm equilibrates spin configurations much faster than the
closely related Swendsen-Wang algorithm.Comment: 13 pages RevTex and 4 Postscript figures. Submitted to Phys. Rev.
Lett. Replacement corrects problem in printing figure
The tidal stripping of satellites
We present an improved analytic calculation for the tidal radius of
satellites and test our results against N-body simulations.
The tidal radius in general depends upon four factors: the potential of the
host galaxy, the potential of the satellite, the orbit of the satellite and
{\it the orbit of the star within the satellite}. We demonstrate that this last
point is critical and suggest using {\it three tidal radii} to cover the range
of orbits of stars within the satellite. In this way we show explicitly that
prograde star orbits will be more easily stripped than radial orbits; while
radial orbits are more easily stripped than retrograde ones. This result has
previously been established by several authors numerically, but can now be
understood analytically. For point mass, power-law (which includes the
isothermal sphere), and a restricted class of split power law potentials our
solution is fully analytic. For more general potentials, we provide an equation
which may be rapidly solved numerically. Over short times (\simlt 1-2 Gyrs
satellite orbit), we find excellent agreement between our analytic and
numerical models. Over longer times, star orbits within the satellite are
transformed by the tidal field of the host galaxy. In a Hubble time, this
causes a convergence of the three limiting tidal radii towards the prograde
stripping radius. Beyond the prograde stripping radius, the velocity dispersion
will be tangentially anisotropic.Comment: 10 pages, 5 figures. Final version accepted for publication in MNRAS.
Some new fully analytic tidal radii have been added for power law density
profiles (including the isothermal sphere) and some split power law
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