6,038 research outputs found
Fermionic Bound States and Pseudoscalar Exchange
We discuss the possibility that fermions bind due to Higgs or pseudoscalar
exchange. It is reasonable to believe on qualitative grounds that this can
occur for fermions with a mass larger than 800-900 GeV. An exchange of a
pseudoscalar boson leads in the non-relativistic limit to an unacceptable
potential which behaves like 1/r^3 at the origin. We show that this singular
behaviour is smeared out when relativistic effects are included
Influence of Four-Wave Mixing and Walk-Off on the Self-Focusing of Coupled Waves
Four-wave mixing and walk-off between two optical beams are! investigated For focusing Kerr media. It is shown that four-wave mixing reinforces the self-focusing of mutually trapped waves by lowering their power threshold for collapse, only when their phase mismatch is small. On the contrary, walk-off inhibits the collapse by detrapping the beams, whose partial centroids experience nonlinear oscillations
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
Demonstration of all-optical beam steering in modulated photonic lattices
We demonstrate experimentally all-optical beam steering in modulated photonic
lattices induced optically by three beam interference in a biased
photorefractive crystal. We identify and characterize the key physical
parameters governing the beam steering, and show that the spatial resolution
can be enhanced by the additional effect of nonlinear beam self-localization.Comment: 3 pages, 3 figure
Including Aortic Valve Morphology in Computational Fluid Dynamics Simulations: Initial Findings and Application to Aortic Coarctation
Computational fluid dynamics (CFD) simulations quantifying thoracic aortic flow patterns have not included disturbances from the aortic valve (AoV). 80% of patients with aortic coarctation (CoA) have a bicuspid aortic valve (BAV) which may cause adverse flow patterns contributing to morbidity. Our objectives were to develop a method to account for the AoV in CFD simulations, and quantify its impact on local hemodynamics. The method developed facilitates segmentation of the AoV, spatiotemporal interpolation of segments, and anatomic positioning of segments at the CFD model inlet. The AoV was included in CFD model examples of a normal (tricuspid AoV) and a post-surgical CoA patient (BAV). Velocity, turbulent kinetic energy (TKE), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) results were compared to equivalent simulations using a plug inlet profile. The plug inlet greatly underestimated TKE for both examples. TAWSS differences extended throughout the thoracic aorta for the CoA BAV, but were limited to the arch for the normal example. OSI differences existed mainly in the ascending aorta for both cases. The impact of AoV can now be included with CFD simulations to identify regions of deleterious hemodynamics thereby advancing simulations of the thoracic aorta one step closer to reality
New features of modulational instability of partially coherent light; importance of the incoherence spectrum
It is shown that the properties of the modulational instability of partially
coherent waves propagating in a nonlinear Kerr medium depend crucially on the
profile of the incoherent field spectrum. Under certain conditions, the
incoherence may even enhance, rather than suppress, the instability. In
particular, it is found that the range of modulationally unstable wave numbers
does not necessarily decrease monotonously with increasing degree of
incoherence and that the modulational instability may still exist even when
long wavelength perturbations are stable.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Helmholtz bright and boundary solitons
We report, for the first time, exact analytical boundary solitons of a generalized cubic-quintic Non-Linear Helmholtz (NLH) equation. These solutions have a linked-plateau topology that is distinct from conventional dark soliton solutions; their amplitude and intensity distributions are spatially delocalized and connect regions of finite and zero wave-field disturbances (suggesting also the classification as 'edge solitons'). Extensive numerical simulations compare the stability properties of recently-reported Helmholtz bright solitons, for this type of polynomial non-linearity, to those of the new boundary solitons. The latter are found to possess a remarkable stability characteristic, exhibiting robustness against perturbations that would otherwise lead to the destabilizing of their bright-soliton counterpart
Modulational instability and nonlocality management in coupled NLS system
The modulational instability of two interacting waves in a nonlocal Kerr-type
medium is considered analytically and numerically. For a generic choice of wave
amplitudes, we give a complete description of stable/unstable regimes for zero
group-velocity mismatch. It is shown that nonlocality suppresses considerably
the growth rate and bandwidth of instability. For nonzero group-velocity
mismatch we perform a geometrical analysis of a nonlocality management which
can provide stability of waves otherwise unstable in a local medium.Comment: 15 pages, 12 figures, to be published in Physica Script
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
SPYGLASS. III. The Fornax-Horologium Association and its Traceback History within the Austral Complex
The study of young associations is essential for building a complete record
of local star formation processes. The Fornax-Horologium association (FH),
including the Fornacis cluster, represents one of the nearest young
stellar populations to the Sun. This association has recently been linked to
the Tuc-Hor, Carina, and Columba associations, building an extensive "Austral
Complex" almost entirely within 150 pc. Using Gaia astrometry and photometry in
addition to new spectroscopic observations, we perform the deepest survey of FH
to date, identifying over 300 candidate members, nearly doubling the known
population. By combining this sample with literature surveys of the other
constituent populations, we produce a contiguous stellar population covering
the entire Austral Complex, allowing the definitions of sub-populations to be
re-assessed along with connections to external populations. This analysis
recovers new definitions for FH, Tuc-Hor, Columba, and Carina, while also
revealing a connection between the Austral complex and the Sco-Cen-affiliated
Platais 8 cluster. This suggests that the Austral complex may be just a small
component of a much larger and more diverse star formation event. Computing
ages and tracing stellar populations back to formation reveals two distinct
nodes of cospatial and continuous formation in the Austral Complex, one
containing Tuc-Hor, and the other containing FH, Carina, and Columba. This
mirrors recent work showing similar structure elsewhere, suggesting that these
nodes, which only emerge through the use of traceback, may represent the
clearest discrete unit of local star formation, and a key building block needed
to reconstruct larger star-forming events.Comment: Accepted to ApJ; 29 pages, 10 figures, 5 tables in two-column
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