71,280 research outputs found
Plasma-based Control of Supersonic Nozzle Flow
The flow structure obtained when Localized Arc Filament Plasma Actuators
(LAFPA) are employed to control the flow issuing from a perfectly expanded Mach
1.3 nozzle is elucidated by visualizing coherent structures obtained from
Implicit Large-Eddy Simulations. The computations reproduce recent experimental
observations at the Ohio State University to influence the acoustic and mixing
properties of the jet. Eight actuators were placed on a collar around the
periphery of the nozzle exit and selectively excited to generate various modes,
including first and second mixed (m = +/- 1 and m = +/- 2) and axisymmetric (m
= 0). In this fluid dynamics video
http://ecommons.library.cornell.edu/bitstream/1813/13723/2/Alljoinedtotalwithmodetextlong2-Datta%20MPEG-1.m1v,
http://ecommons.library.cornell.edu/bitstream/1813/13723/3/Alljoinedtotalwithmodetextlong2-Datta%20MPEG-2.m2v},
unsteady and phase-averaged quantities are displayed to aid understanding of
the vortex dynamics associated with the m = +/- 1 and m = 0 modes excited at
the preferred column-mode frequency (Strouhal number 0.3). The unsteady flow in
both contains a broad spectrum of coherent features. For m = +/- 1, the
phase-averaged flow reveals the generation of successive distorted elliptic
vortex rings with axes in the flapping plane, but alternating on either side of
the jet axis. This generates a chain of structures where each interacts with
its predecessor on one side and its successor on the other. Through self and
mutual interaction, the leading segment of each loop is pinched and passes
through the previous ring before rapidly breaking up, and the mean jet flow
takes on an elliptic shape. The m = 0 mode exhibits relatively stable roll-up
events, with vortex ribs in the braid regions connecting successive large
coherent structures.Comment: 3 pages. Video submission to Gallery of Fluid Motion, American
Physical Society, Division of Fluid Dynamics, 62nd Annual Meeting, November
22-24, 2009, Minneapolis, MN. Replacement deletes TeX commands to correct web
link
On a Centrality Maximization Game
The Bonacich centrality is a well-known measure of the relative importance of
nodes in a network. This notion is, for example, at the core of Google's
PageRank algorithm. In this paper we study a network formation game where each
player corresponds to a node in the network to be formed and can decide how to
rewire his m out-links aiming at maximizing his own Bonacich centrality, which
is his utility function. We study the Nash equilibria (NE) and the best
response dynamics of this game and we provide a complete classification of the
set of NE when m=1 and a fairly complete classification of the NE when m=2. Our
analysis shows that the centrality maximization performed by each node tends to
create undirected and disconnected or loosely connected networks, namely
2-cliques for m=1 and rings or a special "Butterfly"-shaped graph when m=2. Our
results build on locality property of the best response function in such game
that we formalize and prove in the paper.Comment: 10 pages, 11 figure
Conformational Dynamics of Supramolecular Protein Assemblies in the EMDB
The Electron Microscopy Data Bank (EMDB) is a rapidly growing repository for
the dissemination of structural data from single-particle reconstructions of
supramolecular protein assemblies including motors, chaperones, cytoskeletal
assemblies, and viral capsids. While the static structure of these assemblies
provides essential insight into their biological function, their conformational
dynamics and mechanics provide additional important information regarding the
mechanism of their biological function. Here, we present an unsupervised
computational framework to analyze and store for public access the
conformational dynamics of supramolecular protein assemblies deposited in the
EMDB. Conformational dynamics are analyzed using normal mode analysis in the
finite element framework, which is used to compute equilibrium thermal
fluctuations, cross-correlations in molecular motions, and strain energy
distributions for 452 of the 681 entries stored in the EMDB at present. Results
for the viral capsid of hepatitis B, ribosome-bound termination factor RF2, and
GroEL are presented in detail and validated with all-atom based models. The
conformational dynamics of protein assemblies in the EMDB may be useful in the
interpretation of their biological function, as well as in the classification
and refinement of EM-based structures.Comment: Associated online data bank available at:
http://lcbb.mit.edu/~em-nmdb
Corrections for a constant radial magnetic field in the g-2 and electric-dipole-moment experiments with muons in storage rings
We calculate the corrections for constant radial magnetic field in muon g--2
and electric-dipole-moment experiments in storage rings. While the correction
is negligible for the current generation of g--2 experiments, it affects the
upcoming muon electric-dipole-moment experiment at Fermilab.Comment: 8 page
Chaos, Metastability and Ergodicity in Bose-Hubbard Superfluid Circuits
The hallmark of superfluidity is the appearance of metastable flow-states
that carry a persistent circulating current. Considering Bose-Hubbard
superfluid rings, we clarify the role of "quantum chaos" in this context. We
show that the standard Landau and Bogoliubov superfluidity criteria fail for
such low-dimensional circuits. We also discuss the feasibility for a coherent
operation of a SQUID-like setup. Finally, we address the manifestation of the
strong many-body dynamical localization effect.Comment: 8 pages, 5 figs, review several results that concern Bose-Hubbard
superfluid circuit
Yard-Sale exchange on networks: Wealth sharing and wealth appropriation
Yard-Sale (YS) is a stochastic multiplicative wealth-exchange model with two
phases: a stable one where wealth is shared, and an unstable one where wealth
condenses onto one agent. YS is here studied numerically on 1d rings, 2d square
lattices, and random graphs with variable average coordination, comparing its
properties with those in mean field (MF). Equilibrium properties in the stable
phase are almost unaffected by the introduction of a network. Measurement of
decorrelation times in the stable phase allow us to determine the critical
interface with very good precision, and it turns out to be the same, for all
networks analyzed, as the one that can be analytically derived in MF. In the
unstable phase, on the other hand, dynamical as well as asymptotic properties
are strongly network-dependent. Wealth no longer condenses on a single agent,
as in MF, but onto an extensive set of agents, the properties of which depend
on the network. Connections with previous studies of coalescence of immobile
reactants are discussed, and their analytic predictions are successfully
compared with our numerical results.Comment: 10 pages, 7 figures. Submitted to JSTA
STS-26 solid rocket booster post flight structural assessment
A post flight assessment of the Space Shuttle's Solid Rocket Boosters was conducted at the John F. Kennedy Space Center in Florida after the launch of STS-26. The two boosters were inspected for structural damage and the results of this inspection are presented. Overall, the boosters were in good condition. However, there was some minor damage attributed to splash down. Some of this damage is a recurring problem. Explanations of these problems are provided
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