29,107 research outputs found
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
Eigenstate Structure in Graphs and Disordered Lattices
We study wave function structure for quantum graphs in the chaotic and
disordered regime, using measures such as the wave function intensity
distribution and the inverse participation ratio. The result is much less
ergodicity than expected from random matrix theory, even though the spectral
statistics are in agreement with random matrix predictions. Instead, analytical
calculations based on short-time semiclassical behavior correctly describe the
eigenstate structure.Comment: 4 pages, including 2 figure
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
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
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
Nonperturbative Matching for Field Theories with Heavy Fermions
We examine a paradox, suggested by Banks and Dabholkar, concerning
nonperturbative effects in an effective field theory which is obtained by
integrating out a generation of heavy fermions, where the heavy fermion masses
arise from Yukawa couplings. They argue that light fermions in the effective
theory appear to decay via instanton processes, whereas their decay is
forbidden in the full theory. We resolve this paradox by showing that such
processes in fact do not occur in the effective theory, due to matching
corrections which cause the relevant light field configurations to have
infinite action.Comment: 10 pages, no figures, uses harvmac, Harvard University Preprint
HUTP-93/A03
A major advance in powder metallurgy
Ultramet has developed a process which promises to significantly increase the mechanical properties of powder metallurgy (PM) parts. Current PM technology uses mixed powders of various constituents prior to compaction. The homogeneity and flaw distribution in PM parts depends on the uniformity of mixing and the maintenance of uniformity during compaction. Conventional PM fabrication processes typically result in non-uniform distribution of the matrix, flaw generation due to particle-particle contact when one of the constituents is a brittle material, and grain growth caused by high temperature, long duration compaction processes. Additionally, a significant amount of matrix material is usually necessary to fill voids and create 100 percent dense parts. In Ultramet's process, each individual particle is coated with the matrix material, and compaction is performed by solid state processing. In this program, Ultramet coated 12-micron tungsten particles with approximately 5 wt percent nickel/iron. After compaction, flexure strengths were measured 50 percent higher than those achieved in conventional liquid phase sintered parts (10 wt percent Ni/Fe). Further results and other material combinations are discussed
Representations of the Multicast Network Problem
We approach the problem of linear network coding for multicast networks from
different perspectives. We introduce the notion of the coding points of a
network, which are edges of the network where messages combine and coding
occurs. We give an integer linear program that leads to choices of paths
through the network that minimize the number of coding points. We introduce the
code graph of a network, a simplified directed graph that maintains the
information essential to understanding the coding properties of the network.
One of the main problems in network coding is to understand when the capacity
of a multicast network is achieved with linear network coding over a finite
field of size q. We explain how this problem can be interpreted in terms of
rational points on certain algebraic varieties.Comment: 24 pages, 19 figure
Supersymmetry breaking in a warped slice with Majorana-type masses
We study the five-dimensional (5D) supergravity compactified on an orbifold
S^1/Z_2, where the U(1)_R symmetry is gauged by the graviphoton with Z_2-even
coupling. In contrast to the case of gauging with Z_2-odd coupling, this class
of models has Majorana-type masses and allows the Scherk-Schwarz (SS) twist
even in the warped spacetime. Starting from the off-shell formulation, we show
that the supersymmetry is always broken in an orbifold slice of AdS_5,
irrespective of the value of the SS twist parameter. We analyze the spectra of
gaugino and gravitino in such background, and find the SS twist can provide
sizable effects on them in the small warping region.Comment: 1+20 pages, 6 figure
A heavy Higgs boson from flavor and electroweak symmetry breaking unification
We present a unified picture of flavor and electroweak symmetry breaking
based on a nonlinear sigma model spontaneously broken at the TeV scale. Flavor
and Higgs bosons arise as pseudo-Goldstone modes. Explicit collective symmetry
breaking yields stable vacuum expectation values and masses protected at one
loop by the little-Higgs mechanism. The coupling to the fermions generates
well-definite mass textures--according to a U(1) global flavor symmetry--that
correctly reproduce the mass hierarchies and mixings of quarks and leptons. The
model is more constrained than usual little-Higgs models because of bounds on
weak and flavor physics. The main experimental signatures testable at the LHC
are a rather large mass m_{h^0} = 317\pm 80 GeV for the (lightest) Higgs boson
and a characteristic spectrum of new bosons and fermions at the TeV scale.Comment: 5 page
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