32,991 research outputs found
Investigation of a hopping transporter concept for lunar exploration
Performance and dynamic characteristics determined for hopping transporter for lunar exploratio
Spacecraft control/flexible structures interaction study
An initial study to begin development of a flight experiment to measure spacecraft control/flexible structure interactions was completed. The approach consisted of developing the equations of motion for a vehicle possessing a flexible solar array, then linearizing about some nominal motion of the craft. A set of solutions is assumed for array deflection using a continuous normal mode method and important parameters are identified. Interrelationships between these parameters, measurement techniques, and input requirements are discussed which assure minimization of special vehicle maneuvers and optimization of data to be obtained during the normal flight sequence. Limited consideration is given to flight data retrieval and processing techniques as correlated with the requirements imposed by the measurement system. Results indicate that inflight measurement of the bending and torsional mode shapes and respective frequencies, and damping ratios, is necessary. Other parameters may be measured from design data
Revised Huang-Yang multipolar pseudopotential
A number of authors have recently pointed out inconsistencies of results
obtained with the Huang-Yang multipolar pseudo-potential for low-energy
scattering [K. Huang and K. C. Yang, Phys. Rev. A, v 105, 767 (1957); later
revised in K. Huang, ``Statistical Mechanics'', (Wiley, New York, 1963)]. The
conceptual validity of their original derivation has been questioned. Here I
show that these inconsistencies are rather due to an {\em algebraic} mistake
made by Huang and Yang. With the corrected error, I present the revised version
of the multipolar pseudo-potential
Repulsive Casimir Pistons
Casimir pistons are models in which finite Casimir forces can be calculated
without any suspect renormalizations. It has been suggested that such forces
are always attractive. We present three scenarios in which that is not true.
Two of these depend on mixing two types of boundary conditions. The other,
however, is a simple type of quantum graph in which the sign of the force
depends upon the number of edges.Comment: 4 pages, 2 figures; RevTeX. Minor additions and correction
Relations among Supersymmetric Lattice Gauge Theories via Orbifolding
We show how to derive Catterall's supersymmetric lattice gauge theories
directly from the general principle of orbifolding followed by a variant of the
usual deconstruction. These theories are forced to be complexified due to a
clash between charge assignments under U(1)-symmetries and lattice assignments
in terms of scalar, vector and tensor components for the fermions. Other
prescriptions for how to discretize the theory follow automatically by
orbifolding and deconstruction. We find that Catterall's complexified model for
the two-dimensional N=(2,2) theory has two independent preserved
supersymmetries. We comment on consistent truncations to lattice theories
without this complexification and with the correct continuum limit. The
construction of lattice theories this way is general, and can be used to derive
new supersymmetric lattice theories through the orbifolding procedure. As an
example, we apply the prescription to topologically twisted four-dimensional
N=2 supersymmetric Yang-Mills theory. We show that a consistent truncation is
closely related to the lattice formulation previously given by Sugino.Comment: 20 pages, LaTeX2e, no figur
Periodic orbit effects on conductance peak heights in a chaotic quantum dot
We study the effects of short-time classical dynamics on the distribution of
Coulomb blockade peak heights in a chaotic quantum dot. The location of one or
both leads relative to the short unstable orbits, as well as relative to the
symmetry lines, can have large effects on the moments and on the head and tail
of the conductance distribution. We study these effects analytically as a
function of the stability exponent of the orbits involved, and also numerically
using the stadium billiard as a model. The predicted behavior is robust,
depending only on the short-time behavior of the many-body quantum system, and
consequently insensitive to moderate-sized perturbations.Comment: 14 pages, including 6 figure
The dynamics of laser droplet generation
We propose an experimental setup allowing for the characterization of laser
droplet generation in terms of the underlying dynamics, primarily showing that
the latter is deterministically chaotic by means of nonlinear time series
analysis methods. In particular, we use a laser pulse to melt the end of a
properly fed vertically placed metal wire. Due to the interplay of surface
tension, gravity force and light-metal interaction, undulating pendant droplets
are formed at the molten end, which eventually completely detach from the wire
as a consequence of their increasing mass. We capture the dynamics of this
process by employing a high-speed infrared camera, thereby indirectly measuring
the temperature of the wire end and the pendant droplets. The time series is
subsequently generated as the mean value over the pixel intensity of every
infrared snapshot. Finally, we employ methods of nonlinear time series analysis
to reconstruct the phase space from the observed variable and test it against
determinism and stationarity. After establishing that the observed laser
droplet generation is a deterministic and dynamically stationary process, we
calculate the spectra of Lyapunov exponents. We obtain a positive largest
Lyapunov exponent and a negative divergence, i.e., sum of all the exponents,
thus indicating that the observed dynamics is deterministically chaotic with an
attractor as solution in the phase space. In addition to characterizing the
dynamics of laser droplet generation, we outline industrial applications of the
process and point out the significance of our findings for future attempts at
mathematical modeling.Comment: 7 two-column pages, 8 figures; accepted for publication in Chaos
[supplementary material available at
http://www.matjazperc.com/chaos/laser.html
The Attractor and the Quantum States
The dissipative dynamics anticipated in the proof of 't Hooft's existence
theorem -- "For any quantum system there exists at least one deterministic
model that reproduces all its dynamics after prequantization" -- is constructed
here explicitly. We propose a generalization of Liouville's classical phase
space equation, incorporating dissipation and diffusion, and demonstrate that
it describes the emergence of quantum states and their dynamics in the
Schroedinger picture. Asymptotically, there is a stable ground state and two
decoupled sets of degrees of freedom, which transform into each other under the
energy-parity symmetry of Kaplan and Sundrum. They recover the familiar Hilbert
space and its dual. Expectations of observables are shown to agree with the
Born rule, which is not imposed a priori. This attractor mechanism is
applicable in the presence of interactions, to few-body or field theories in
particular.Comment: 14 pages; based on invited talk at 4th Workshop ad memoriam of Carlo
Novero "Advances in Foundations of Quantum Mechanics and Quantum Information
with Atoms and Photons", Torino, May 2008; submitted to Int J Qu Inf
unreinforced masonry buildings
A recent earthquake of M=4.9 occurred on 29 October 2007 in C, ameli, Denizli, which is located in a seismically active region at southwest Anatolia, Turkey. It has caused extensive damages at unreinforced masonry buildings like many other cases observed in Turkey during other previous earthquakes. Most of the damaged structures were non-engineered, seismically deficient, unreinforced masonry buildings. This paper presents a site survey of these damaged buildings. In addition to typical masonry damages, some infrequent, event-specific damages were also observed. Reasons for the relatively wide spread damages considering the magnitude of the event are discussed in the paper
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