22,527 research outputs found
Pfaff systems theory and the unifications of gravitation and electromagnetism
We show in the framework of Pfaff systems theory, the functional dependences of the general analytic solutions of a suitable system of involutive differential equations describing the differences between the analytic solutions of the conformal and "Poincar\'e" Lie equations. Then we ascribe to the infinitesimal variations of the parametrizing functionals some physical meanings as the electromagnetic and gravitation potentials. We also deduce their corresponding fields of interactions together with the differential equations they must satisfy. Then we discuss on various possible physical interpretations
Macroscopic detection of the strong stochasticity threshold in Fermi-Pasta-Ulam chains of oscillators
The largest Lyapunov exponent of a system composed by a heavy impurity
embedded in a chain of anharmonic nearest-neighbor Fermi-Pasta-Ulam oscillators
is numerically computed for various values of the impurity mass . A
crossover between weak and strong chaos is obtained at the same value
of the energy density (energy per degree of freedom)
for all the considered values of the impurity mass . The threshold \epsi
lon_{_T} coincides with the value of the energy density at which a
change of scaling of the relaxation time of the momentum autocorrelation
function of the impurity ocurrs and that was obtained in a previous work ~[M.
Romero-Bastida and E. Braun, Phys. Rev. E {\bf65}, 036228 (2002)]. The complete
Lyapunov spectrum does not depend significantly on the impurity mass . These
results suggest that the impurity does not contribute significantly to the
dynamical instability (chaos) of the chain and can be considered as a probe for
the dynamics of the system to which the impurity is coupled. Finally, it is
shown that the Kolmogorov-Sinai entropy of the chain has a crossover from weak
to strong chaos at the same value of the energy density that the crossover
value of largest Lyapunov exponent. Implications of this result
are discussed.Comment: 6 pages, 5 figures, revtex4 styl
Three-dimensional calculation of shuttle charging in polar orbit
The charged particles environment in polar orbit can be of sufficient intensity to cause spacecraft charging. In order to gain a quantitative understanding of such effects, the Air Force is developing POLAR, a computer code which simulates in three dimensions the electrical interaction of large space vehicles with the polar ionospheric plasma. It models the physical processes of wake generation, ambient ion collection, precipitating auroral electron fluxes, and surface interactions, including secondary electron generation and backscattering, which lead to vehicle charging. These processes may be followed dynamically on a subsecond timescale so that the rapid passage through intense auroral arcs can be simulated. POLAR models the ambient plasma as isotropic Maxwellian electrons and ions (0+, H+), and allows for simultaneous precipitation of power-law, energetic Maxwellian, and accelerated Gaussian distributions of electrons. Magnetic field effects will be modeled in POLAR but are currently ignored
Polar orbit electrostatic charging of objects in shuttle wake
A survey of DMSP data has uncovered several cases where precipitating auroral electron fluxes are both sufficiently intense and energetic to charge spacecraft materials such as teflon to very large potentials in the absence of ambient ion currents. Analytical bounds are provided which show that these measured environments can cause surface potentials in excess of several hundred volts to develop on objects in the orbiter wake for particular vehicle orientations
Heat sterilizable and impact resistant Ni-Cd battery development Quarterly report, 1 Apr. - 30 Jun. 1969
Electrochemistry, battery engineering, and impact tests of heat sterilizable nickel cadmium cell
On optical forces in spherical whispering gallery mode resonators
In this paper we discuss the force exerted by the field of an optical cavity
on a polarizable dipole. We show that the modification of the cavity modes due
to interaction with the dipole significantly alters the properties of the
force. In particular, all components of the force are found to be
non-conservative, and cannot, therefore, be derived from a potential energy. We
also suggest a simple generalization of the standard formulas for the optical
force on the dipole, which reproduces the results of calculations based on the
Maxwell stress tensor.Comment: To pe published in Optics Express Focus Issue: "Collective phenomena
in photonic, plasmonic and hybrid structures
A systematic review of factors associated with side-effect expectations from medical interventions
Background: Fear of side-effects can result in non-adherence to medical interventions, such as medication and chemotherapy. Side-effect expectations have been identified as strong
predictors of later perception of side-effects. However, research investigating predictors of side-effect expectations is disparate.
Objective: To identify factors associated with side-effect expectations.
Search strategy: We systematically searched Embase, Ovid MEDLINE, Global Health, PsycARTICLES, PsycINFO, Web of Science and Scopus.
Inclusion criteria: Studies were included if they investigated associations between any predictive factor and expectations of side-effects from any medical intervention.
Data extraction and synthesis: We extracted information about participant characteristics, medication, rates of side-effects expected, and predictors of side-effect expectations. Data
were narratively synthesised.
Main results: We identified sixty-four citations, reporting on seventy-two studies. Predictors fell into five categories: personal characteristics; clinical characteristics; psychological traits and state; presentation format of information; and information sources used. Using verbal risk descriptors (e.g. ‘common’) compared to numerical descriptors (e.g. percentages), having
lower quality of life or wellbeing, and currently experiencing symptoms were associated with increased side-effect expectations.
Discussion and conclusions: Decreasing unrealistic side-effect expectations may lead to decreased experience of side-effects and increased adherence to medical interventions.
Widespread communications about medical interventions should describe the incidence of side-effects numerically. Evidence suggests that clinicians should take particular care with patients with lower quality of life, who are currently experiencing symptoms and who have previously experienced symptoms from treatment. Further research should investigate
different clinical populations and aim to quantify the impact of the media and social media on side-effect expectations
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