836 research outputs found
Quadratic solitons as nonlocal solitons
We show that quadratic solitons are equivalent to solitons of a nonlocal Kerr
medium. This provides new physical insight into the properties of quadratic
solitons, often believed to be equivalent to solitons of an effective saturable
Kerr medium. The nonlocal analogy also allows for novel analytical solutions
and the prediction of novel bound states of quadratic solitons.Comment: 4 pages, 3 figure
Collapse arrest and soliton stabilization in nonlocal nonlinear media
We investigate the properties of localized waves in systems governed by
nonlocal nonlinear Schrodinger type equations. We prove rigorously by bounding
the Hamiltonian that nonlocality of the nonlinearity prevents collapse in,
e.g., Bose-Einstein condensates and optical Kerr media in all physical
dimensions. The nonlocal nonlinear response must be symmetric, but can be of
completely arbitrary shape. We use variational techniques to find the soliton
solutions and illustrate the stabilizing effect of nonlocality.Comment: 4 pages with 3 figure
Temperature compensated, humidity insensitive, high-T<sub>g</sub> TOPAS FBGs for accelerometers and microphones
Spherical collapse of dark energy with an arbitrary sound speed
We consider a generic type of dark energy fluid, characterised by a constant
equation of state parameter w and sound speed c_s, and investigate the impact
of dark energy clustering on cosmic structure formation using the spherical
collapse model. Along the way, we also discuss in detail the evolution of dark
energy perturbations in the linear regime. We find that the introduction of a
finite sound speed into the picture necessarily induces a scale-dependence in
the dark energy clustering, which in turn affects the dynamics of the spherical
collapse in a scale-dependent way. As with other, more conventional fluids, we
can define a Jeans scale for the dark energy clustering, and hence a Jeans mass
M_J for the dark matter which feels the effect of dark energy clustering via
gravitational interactions. For bound objects (halos) with masses M >> M_J, the
effect of dark energy clustering is maximal. For those with M << M_J, the dark
energy component is effectively homogeneous, and its role in the formation of
these structures is reduced to its effects on the Hubble expansion rate. To
compute quantitatively the virial density and the linearly extrapolated
threshold density, we use a quasi-linear approach which is expected to be valid
up to around the Jeans mass. We find an interesting dependence of these
quantities on the halo mass M, given some w and c_s. The dependence is the
strongest for masses lying in the vicinity of M ~ M_J. Observing this
M-dependence will be a tell-tale sign that dark energy is dynamic, and a great
leap towards pinning down its clustering properties.Comment: 25 pages, 6 figures, matches version published in JCA
Molecular Dynamics Simulation of Spinodal Decomposition in Three-Dimensional Binary Fluids
Using large-scale molecular dynamics simulations of a two-component
Lennard-Jones model in three dimensions, we show that the late-time dynamics of
spinodal decomposition in concentrated binary fluids reaches a viscous scaling
regime with a growth exponent , in agreement with experiments and a
theoretical analysis for viscous growth.Comment: 4 pages, 3 figure
Dynamic and volumetric variables reliably predict fluid responsiveness in a porcine model with pleural effusion
Background: The ability of stroke volume variation (SVV), pulse pressure variation (PPV) and global end-diastolic volume (GEDV) for prediction of fluid responsiveness in presence of pleural effusion is unknown. The aim of the present study was to challenge the ability of SVV, PPV and GEDV to predict fluid responsiveness in a porcine model with pleural effusions.
Methods: Pigs were studied at baseline and after fluid loading with 8 ml kg−1 6% hydroxyethyl starch. After withdrawal of 8 ml kg−1 blood and induction of pleural effusion up to 50 ml kg−1 on either side, measurements at baseline and after fluid loading were repeated. Cardiac output, stroke volume, central venous pressure (CVP) and pulmonary occlusion pressure (PAOP) were obtained by pulmonary thermodilution, whereas GEDV was determined by transpulmonary thermodilution. SVV and PPV were monitored continuously by pulse contour analysis.
Results: Pleural effusion was associated with significant changes in lung compliance, peak airway pressure and stroke volume in both responders and non-responders. At baseline, SVV, PPV and GEDV reliably predicted fluid responsiveness (area under the curve 0.85 (p<0.001), 0.88 (p<0.001), 0.77 (p = 0.007). After induction of pleural effusion the ability of SVV, PPV and GEDV to predict fluid responsiveness was well preserved and also PAOP was predictive. Threshold values for SVV and PPV increased in presence of pleural effusion.
Conclusions: In this porcine model, bilateral pleural effusion did not affect the ability of SVV, PPV and GEDV to predict fluid responsiveness
Nature Park Amager:Examining the transition from urban wasteland to a rewilded ecotourism destination
Parametric localized modes in quadratic nonlinear photonic structures
We analyze two-color spatially localized modes formed by parametrically
coupled fundamental and second-harmonic fields excited at quadratic (or chi-2)
nonlinear interfaces embedded into a linear layered structure --- a
quasi-one-dimensional quadratic nonlinear photonic crystal. For a periodic
lattice of nonlinear interfaces, we derive an effective discrete model for the
amplitudes of the fundamental and second-harmonic waves at the interfaces (the
so-called discrete chi-2 equations), and find, numerically and analytically,
the spatially localized solutions --- discrete gap solitons. For a single
nonlinear interface in a linear superlattice, we study the properties of
two-color localized modes, and describe both similarities and differences with
quadratic solitons in homogeneous media.Comment: 9 pages, 8 figure
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