370 research outputs found
Reasons to withhold intra-arterial thrombolysis in clinical practice
Background: In selected stroke centers intra-arterial thrombolysis (IAT) is used for the treatment of acute stroke patients presenting within 6hours of symptom onset. However, data about eligibility of acute stroke patients for IAT in clinical practice are very scarce. Methods: We collected prospectively data on indications advising for or against IAT of 230 consecutive stroke patients in a tertiary stroke center. Results: 76 patients (33.0%) presented within 3hours, 69 (30%) between 3 and 6hours of symptom onset and 85 (37%) later than 6hours. Arteriography was performed in 71 patients (31%) and IAT in 46 (20%). In 11 patients no or only peripheral branch occlusions were seen on arteriography and therefore IAT was not performed. In 9 patients the ICA was occluded and barred IAT and in five anatomical or technical difficulties made IAT impossible. 72 patients presenting within 6hours did not undergo arteriography and thrombolysis, mostly because of mild (n=44) or rapidly improving neurological deficits (n=13). Other reasons to withhold IAT were CT and/or clinical findings suggesting lacunar stroke due to small vessel occlusion (n=7), limiting comorbidty (n=7) and baseline international normalized ratio>1.7 (n=1). Conclusions: A third of the patients underwent diagnostic arteriography and one fifth received IAT. The most important reasons to withhold thrombolysis were presentation beyond the 6hours time window and mild or rapidly improving symptom
Nonlinear Stability in the Generalised Photogravitational Restricted Three Body Problem with Poynting-Robertson Drag
The Nonlinear stability of triangular equilibrium points has been discussed
in the generalised photogravitational restricted three body problem with
Poynting-Robertson drag. The problem is generalised in the sense that smaller
primary is supposed to be an oblate spheroid. The bigger primary is considered
as radiating. We have performed first and second order normalization of the
Hamiltonian of the problem. We have applied KAM theorem to examine the
condition of non-linear stability. We have found three critical mass ratios.
Finally we conclude that triangular points are stable in the nonlinear sense
except three critical mass ratios at which KAM theorem fails.Comment: Including Poynting-Robertson Drag the triangular equilibrium points
are stable in the nonlinear sense except three critical mass ratios at which
KAM theorem fail
Coupled-mode equations and gap solitons in a two-dimensional nonlinear elliptic problem with a separable periodic potential
We address a two-dimensional nonlinear elliptic problem with a
finite-amplitude periodic potential. For a class of separable symmetric
potentials, we study the bifurcation of the first band gap in the spectrum of
the linear Schr\"{o}dinger operator and the relevant coupled-mode equations to
describe this bifurcation. The coupled-mode equations are derived by the
rigorous analysis based on the Fourier--Bloch decomposition and the Implicit
Function Theorem in the space of bounded continuous functions vanishing at
infinity. Persistence of reversible localized solutions, called gap solitons,
beyond the coupled-mode equations is proved under a non-degeneracy assumption
on the kernel of the linearization operator. Various branches of reversible
localized solutions are classified numerically in the framework of the
coupled-mode equations and convergence of the approximation error is verified.
Error estimates on the time-dependent solutions of the Gross--Pitaevskii
equation and the coupled-mode equations are obtained for a finite-time
interval.Comment: 32 pages, 16 figure
Singularities of bi-Hamiltonian systems
We study the relationship between singularities of bi-Hamiltonian systems and
algebraic properties of compatible Poisson brackets. As the main tool, we
introduce the notion of linearization of a Poisson pencil. From the algebraic
viewpoint, a linearized Poisson pencil can be understood as a Lie algebra with
a fixed 2-cocycle. In terms of such linearizations, we give a criterion for
non-degeneracy of singular points of bi-Hamiltonian systems and describe their
types
Systematic study of the effect of short range correlations on the form factors and densities of s-p and s-d shell nuclei
Analytical expressions of the one- and two-body terms in the cluster
expansion of the charge form factors and densities of the s-p and s-d shell
nuclei with N=Z are derived. They depend on the harmonic oscillator parameter b
and the parameter which originates from the Jastrow correlation
function. These expressions are used for the systematic study of the effect of
short range correlations on the form factors and densities and of the mass
dependence of the parameters b and . These parameters have been
determined by fit to the experimental charge form factors. The inclusion of the
correlations reproduces the experimental charge form factors at the high
momentum transfers (). It is found that while the parameter
is almost constant for the closed shell nuclei, He, O and
Ca, its values are larger (less correlated systems) for the open shell
nuclei, indicating a shell effect in the closed shell nuclei.Comment: Latex, 21 pages, 6 figures, 1 tabl
Equation of state for Universe from similarity symmetries
In this paper we proposed to use the group of analysis of symmetries of the
dynamical system to describe the evolution of the Universe. This methods is
used in searching for the unknown equation of state. It is shown that group of
symmetries enforce the form of the equation of state for noninteracting scaling
multifluids. We showed that symmetries give rise the equation of state in the
form and energy density
, which
is commonly used in cosmology. The FRW model filled with scaling fluid (called
homological) is confronted with the observations of distant type Ia supernovae.
We found the class of model parameters admissible by the statistical analysis
of SNIa data. We showed that the model with scaling fluid fits well to
supernovae data. We found that and (), which can correspond to (hyper) phantom fluid, and to a
high density universe. However if we assume prior that
then the favoured model is close to concordance
CDM model. Our results predict that in the considered model with
scaling fluids distant type Ia supernovae should be brighter than in
CDM model, while intermediate distant SNIa should be fainter than in
CDM model. We also investigate whether the model with scaling fluid is
actually preferred by data over CDM model. As a result we find from
the Akaike model selection criterion prefers the model with noninteracting
scaling fluid.Comment: accepted for publication versio
Dark Matter, Light Stops and Electroweak Baryogenesis
We examine the neutralino relic density in the presence of a light top
squark, such as the one required for the realization of the electroweak
baryogenesis mechanism, within the minimal supersymmetric standard model. We
show that there are three clearly distinguishable regions of parameter space,
where the relic density is consistent with WMAP and other cosmological data.
These regions are characterized by annihilation cross sections mediated by
either light Higgs bosons, Z bosons, or by the co-annihilation with the
lightest stop. Tevatron collider experiments can test the presence of the light
stop in most of the parameter space. In the co-annihilation region, however,
the mass difference between the light stop and the lightest neutralino varies
between 15 and 30 GeV, presenting an interesting challenge for stop searches at
hadron colliders. We present the prospects for direct detection of dark matter,
which provides a complementary way of testing this scenario. We also derive the
required structure of the high energy soft supersymmetry breaking mass
parameters where the neutralino is a dark matter candidate and the stop
spectrum is consistent with electroweak baryogenesis and the present bounds on
the lightest Higgs mass.Comment: 24 pages, 8 figures; version published in Phys.Rev.
Variational and Geometric Structures of Discrete Dirac Mechanics
In this paper, we develop the theoretical foundations of discrete Dirac
mechanics, that is, discrete mechanics of degenerate Lagrangian/Hamiltonian
systems with constraints. We first construct discrete analogues of Tulczyjew's
triple and induced Dirac structures by considering the geometry of symplectic
maps and their associated generating functions. We demonstrate that this
framework provides a means of deriving discrete Lagrange-Dirac and nonholonomic
Hamiltonian systems. In particular, this yields nonholonomic Lagrangian and
Hamiltonian integrators. We also introduce discrete
Lagrange-d'Alembert-Pontryagin and Hamilton-d'Alembert variational principles,
which provide an alternative derivation of the same set of integration
algorithms. The paper provides a unified treatment of discrete Lagrangian and
Hamiltonian mechanics in the more general setting of discrete Dirac mechanics,
as well as a generalization of symplectic and Poisson integrators to the
broader category of Dirac integrators.Comment: 26 pages; published online in Foundations of Computational
Mathematics (2011
Channel Coupling in Reactions
The sensitivity of momentum distributions, recoil polarization observables,
and response functions for nucleon knockout by polarized electrons to channel
coupling in final-state interactions is investigated using a model in which
both the distorting and the coupling potentials are constructed by folding
density-dependent effective interactions with nuclear transition densities.
Calculations for O are presented for 200 and 433 MeV ejectile energies,
corresponding to proposed experiments at MAMI and TJNAF, and for C at 70
and 270 MeV, corresponding to experiments at NIKHEF and MIT-Bates. The relative
importance of charge exchange decreases as the ejectile energy increases, but
remains significant for 200 MeV. Both proton and neutron knockout cross
sections for large recoil momenta, MeV/c, are substantially
affected by inelastic couplings even at 433 MeV. Significant effects on the
cross section for neutron knockout are also predicted at smaller recoil
momenta, especially for low energies. Polarization transfer for proton knockout
is insensitive to channel coupling, even for fairly low ejectile energies, but
polarization transfer for neutron knockout retains nonnegligible sensitivity to
channel coupling for energies up to about 200 MeV. The present results suggest
that possible medium modifications of neutron and proton electromagnetic form
factors for can be studied using recoil
polarization with relatively little sensitivity due to final state
interactions.Comment: Substantially revised version accepted by Phys. Rev. C; shortened to
49 pages including 21 figure
Coupling dynamics of a geared multibody system supported by Elastohydrodynamic lubricated cylindrical joints
A comprehensive computational methodology to study the coupling dynamics of a geared multibody system supported by ElastoHydroDynamic (EHD) lubricated cylindrical joints is proposed throughout this work. The geared multibody system is described by using the Absolute-Coordinate-Based (ACB) method that combines the Natural Coordinate Formulation (NCF) describing rigid bodies and the Absolute Nodal Coordinate Formulation (ANCF) characterizing the flexible bodies. Based on the finite-short bearing approach, the EHD lubrication condition for the cylindrical joints supporting the geared system is considered here. The lubrication forces developed at the cylindrical joints are obtained by solving the Reynolds’ equation via the finite difference method. For the evaluation of the normal contact forces of gear pair along the Line Of Action (LOA), the time-varying mesh stiffness, mesh damping and Static Transmission Error (STE) are utilized. The time-varying mesh stiffness is calculated by using the Chaari’s methodology. The forces of sliding friction along the Off-Line-Of-Action (OLOA) are computed by using the Coulomb friction models with a time-varying coefficient of friction under the EHD lubrication condition of gear teeth. Finally, two numerical examples of application are presented to demonstrate and validate the proposed methodology.National Natural Science Foundations of China under Grant
11290151, 11221202 and 11002022, Beijing Higher
Education Young Elite Teacher Project under Grant YETP1201
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