999 research outputs found
Applications catalog of pyrotechnically actuated devices/systems
A compilation of basic information on pyrotechnically actuated devices/systems used in NASA aerospace and aeronautic applications was formatted into a catalog. The intent is to provide (1) a quick reference digest of the types of operational pyro mechanisms and (2) a source of contacts for further details. Data on these items was furnished by the NASA Centers that developed and/or utilized such devices to perform specific functions on spacecraft, launch vehicles, aircraft, and ground support equipment. Information entries include an item title, user center name, commercial contractor/vendor, identifying part number(s), a basic figure, briefly described purpose and operation, previous usage, and operational limits/requirements
Electrophoresis of a rod macroion under polyelectrolyte salt: Is mobility reversed for DNA?
By molecular dynamics simulation, we study the charge inversion phenomenon of
a rod macroion in the presence of polyelectrolyte counterions. We simulate
electrophoresis of the macroion under an applied electric field. When both
counterions and coions are polyelectrolytes, charge inversion occurs if the
line charge density of the counterions is larger than that of the coions. For
the macroion of surface charge density equal to that of the DNA, the reversed
mobility is realized either with adsorption of the multivalent counterion
polyelectrolyte or the combination of electrostatics and other mechanisms
including the short-range attraction potential or the mechanical twining of
polyelectrolyte around the rod axis.Comment: 8 pages, 5 figures, Applied Statistical Physics of Molecular
Engineering (Mexico, 2003). Journal of Physics: Condensed Matters, in press
(2004). Journal of Physics: Condensed Matters, in press (2004
Quarantine generated phase transition in epidemic spreading
We study the critical effect of quarantine on the propagation of epidemics on
an adaptive network of social contacts. For this purpose, we analyze the
susceptible-infected-recovered (SIR) model in the presence of quarantine, where
susceptible individuals protect themselves by disconnecting their links to
infected neighbors with probability w, and reconnecting them to other
susceptible individuals chosen at random. Starting from a single infected
individual, we show by an analytical approach and simulations that there is a
phase transition at a critical rewiring (quarantine) threshold w_c separating a
phase (w<w_c) where the disease reaches a large fraction of the population,
from a phase (w >= w_c) where the disease does not spread out. We find that in
our model the topology of the network strongly affects the size of the
propagation, and that w_c increases with the mean degree and heterogeneity of
the network. We also find that w_c is reduced if we perform a preferential
rewiring, in which the rewiring probability is proportional to the degree of
infected nodes.Comment: 13 pages, 6 figure
Optical Metrics and Projective Equivalence
Trajectories of light rays in a static spacetime are described by
unparametrised geodesics of the Riemannian optical metric associated with the
Lorentzian spacetime metric. We investigate the uniqueness of this structure
and demonstrate that two different observers, moving relative to one another,
who both see the universe as static may determine the geometry of the light
rays differently. More specifically, we classify Lorentzian metrics admitting
more than one hyper--surface orthogonal time--like Killing vector and analyze
the projective equivalence of the resulting optical metrics. These metrics are
shown to be projectively equivalent up to diffeomorphism if the static Killing
vectors generate a group , but not projectively equivalent in
general. We also consider the cosmological --metrics in Einstein--Maxwell
theory and demonstrate that optical metrics corresponding to different values
of the cosmological constant are projectively equivalent.Comment: 18 pages, two figures, final version, to appear in Physical Review
Three-dimensional magnetic flux rope structure formed by multiple sequential X-line reconnection at the magnetopause
On 14 June 2007, four Time History of Events and Macroscale Interactions during Substorms spacecraft observed a flux transfer event (FTE) on the dayside magnetopause, which has been previously proved to be generated by multiple, sequential X-line reconnection (MSXR) in a 2-D context. This paper reports a further study of the MSXR event to show the 3-D viewpoint based on additional measurements. The 3-D structure of the FTE flux rope across the magnetospheric boundary is obtained on the basis of multipoint measurements taken on both sides of the magnetopause. The flux rope's azimuthally extended section is found to lie approximately on the magnetopause surface and parallel to the X-line direction; while the axis of the magnetospheric branch is essentially along the local unperturbed magnetospheric field lines. In the central region of the flux rope, as distinct from the traditional viewpoint, we find from the electron distributions that two types of magnetic field topology coexist: opened magnetic field lines connecting the magnetosphere and the magnetosheath and closed field lines connecting the Southern and Northern hemispheres. We confirm, therefore, for the first time, the characteristic feature of the 3-D reconnected magnetic flux rope, formed through MSXR, through a determination of the field topology and the plasma distributions within the flux rope. Knowledge of the complex geometry of FTE flux ropes will improve our understanding of solar wind-magnetosphere interaction.Astronomy & AstrophysicsSCI(E)5ARTICLE51904-191111
The kernel of the edth operators on higher-genus spacelike two-surfaces
The dimension of the kernels of the edth and edth-prime operators on closed,
orientable spacelike 2-surfaces with arbitrary genus is calculated, and some of
its mathematical and physical consequences are discussed.Comment: 12 page
Entanglement of Three-Qubit Geometry
Geometric quantum mechanics aims to express the physical properties of quantum systems in terms of geometrical features preferentially selected in the space of pure states. Geometric characterisations are given here for systems of one, two, and three spin- particles, drawing attention to the classification of quantum states into entanglement types
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