458 research outputs found
Risk Factors for Hospital Malpractice Exposure: Implications for Managers and Insurers
The possibility of identifying certain variables that might serve as predictors of above- or below-average medical malpractice claims experience was explored. Results showed that it is possible to identify significant risk factors
Generalizing the autonomous Kepler Ermakov system in a Riemannian space
We generalize the two dimensional autonomous Hamiltonian Kepler Ermakov
dynamical system to three dimensions using the sl(2,R) invariance of Noether
symmetries and determine all three dimensional autonomous Hamiltonian Kepler
Ermakov dynamical systems which are Liouville integrable via Noether
symmetries. Subsequently we generalize the autonomous Kepler Ermakov system in
a Riemannian space which admits a gradient homothetic vector by the
requirements (a) that it admits a first integral (the Riemannian Ermakov
invariant) and (b) it has sl(2,R) invariance. We consider both the
non-Hamiltonian and the Hamiltonian systems. In each case we compute the
Riemannian Ermakov invariant and the equations defining the dynamical system.
We apply the results in General Relativity and determine the autonomous
Hamiltonian Riemannian Kepler Ermakov system in the spatially flat Friedman
Robertson Walker spacetime. We consider a locally rotational symmetric (LRS)
spacetime of class A and discuss two cosmological models. The first
cosmological model consists of a scalar field with exponential potential and a
perfect fluid with a stiff equation of state. The second cosmological model is
the f(R) modified gravity model of {\Lambda}_{bc}CDM. It is shown that in both
applications the gravitational field equations reduce to those of the
generalized autonomous Riemannian Kepler Ermakov dynamical system which is
Liouville integrable via Noether integrals.Comment: Reference [25] update, 21 page
Nonstationary excitations in Bose-Einstein condensates under the action of periodically varying scattering length with time dependent frequencies
We investigate nonstationary excitations in 3D-Bose-Einstein condensates in a
spherically symmetric trap potential under the modulation of scattering length
with slowly varying frequencies (adiabatic modulation). By numerically solving
the Gross-Pitaevskii equation we observe a step-wise increase in the amplitude
of oscillation due to successive phase locking between driving frequency and
nonlinear frequency. Such a nonstationary excitation has been shown to exist by
an analytic approach using variational procedure and perturbation theory in the
action-angle variables. By using a canonical perturbation theory, we have
identified the successive resonance excitations whenever the driven frequency
matches the nonlinear frequency or its subharmonics.Comment: 17 pages, 6 figures (to be published in Physica D
Symmetry, singularities and integrability in complex dynamics III: approximate symmetries and invariants
The different natures of approximate symmetries and their corresponding first
integrals/invariants are delineated in the contexts of both Lie symmetries of
ordinary differential equations and Noether symmetries of the Action Integral.
Particular note is taken of the effect of taking higher orders of the
perturbation parameter. Approximate symmetries of approximate first
integrals/invariants and the problems of calculating them using the Lie method
are considered
2H and 27Al Solid-State NMR Study of the Local Environments in Al-Doped 2-Line Ferrihydrite, Goethite, and Lepidocrocite.
Although substitution of aluminum into iron oxides and oxyhydroxides has been extensively studied, it is difficult to obtain accurate incorporation levels. Assessing the distribution of dopants within these materials has proven especially challenging because bulk analytical techniques cannot typically determine whether dopants are substituted directly into the bulk iron oxide or oxyhydroxide phase or if they form separate, minor phase impurities. These differences have important implications for the chemistry of these iron-containing materials, which are ubiquitous in the environment. In this work, 27Al and 2H NMR experiments are performed on series of Al-substituted goethite, lepidocrocite, and 2-line ferrihydrite in order to develop an NMR method to track Al substitution. The extent of Al substitution into the structural frameworks of each compound is quantified by comparing quantitative 27Al MAS NMR results with those from elemental analysis. Magnetic measurements are performed for the goethite series to compare with NMR measurements. Static 27Al spin-echo mapping experiments are used to probe the local environments around the Al substituents, providing clear evidence that they are incorporated into the bulk iron phases. Predictions of the 2H and 27Al NMR hyperfine contact shifts in Al-doped goethite and lepidocrocite, obtained from a combined first-principles and empirical magnetic scaling approach, give further insight into the distribution of the dopants within these phases.J.K., A.J.I., D.M. and N.P. were supported by an NSF grant collaborative research grant in chemistry CHE0714183. An allocation of time upon the NANO computer cluster at the Center for Functional Nanomaterials, Brookhaven National Laboratory, U.S.A., which is supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886 is also acknowledged. D.S.M. and C.P.G. thank the EPSRC and the EU-ERC for support.This is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acs.chemmater.5b0085
Lie symmetries for two-dimensional charged particle motion
We find the Lie point symmetries for non-relativistic two-dimensional charged
particle motion. These symmetries comprise a quasi-invariance transformation, a
time-dependent rotation, a time-dependent spatial translation and a dilation.
The associated electromagnetic fields satisfy a system of first-order linear
partial differential equations. This system is solved exactly, yielding four
classes of electromagnetic fields compatible with Lie point symmetries
Frequencies and Damping rates of a 2D Deformed Trapped Bose gas above the Critical Temperature
We derive the equation of motion for the velocity fluctuations of a 2D
deformed trapped Bose gas above the critical temperature in the hydrodynamical
regime. From this equation, we calculate the eigenfrequencies for a few
low-lying excitation modes. Using the method of averages, we derive a
dispersion relation in a deformed trap that interpolates between the
collisionless and hydrodynamic regimes. We make use of this dispersion relation
to calculate the frequencies and the damping rates for monopole and quadrupole
mode in both the regimes. We also discuss the time evolution of the wave packet
width of a Bose gas in a time dependent as well as time independent trap.Comment: 13 pages, latex fil
Backlund transformations for many-body systems related to KdV
We present Backlund transformations (BTs) with parameter for certain
classical integrable n-body systems, namely the many-body generalised
Henon-Heiles, Garnier and Neumann systems. Our construction makes use of the
fact that all these systems may be obtained as particular reductions
(stationary or restricted flows) of the KdV hierarchy; alternatively they may
be considered as examples of the reduced sl(2) Gaudin magnet. The BTs provide
exact time-discretizations of the original (continuous) systems, preserving the
Lax matrix and hence all integrals of motion, and satisfy the spectrality
property with respect to the Backlund parameter.Comment: LaTeX2e, 8 page
Cosmic Dynamics of Bose-Einstein Condensates
A dynamical correspondence is established between positively curved,
isotropic, perfect fluid cosmologies and quasi-two-dimensional, harmonically
trapped Bose-Einstein condensates by mapping the equations of motion for both
systems onto the one-dimensional Ermakov system. Parameters that characterize
the physical properties of the condensate wavepacket, such as its width,
momentum and energy, may be identified with the scale factor, Hubble expansion
parameter and energy density of the universe, respectively. Different forms of
cosmic matter correspond to different choices for the time-dependent trapping
frequency of the condensate. The trapping frequency that mimics a
radiation-dominated universe is determined.Comment: 12 pages, no figures. Extended discussion. In Press, Classical and
Quantum Gravit
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