227 research outputs found
Veterinary Examination and Restraint Caged Birds
Today\u27s growing interest in companion and aviary birds presents a challenge to the practitioner to implement rational veterinary care. A complete and cautious physical examination aided by proper restraint is necessary in the diagnosis of cage bird diseases. Clinical examination can be difficult due to the nature of the birds and their small size
On the cusp of cusps: a universal model for extreme scattering events in the ISM
The scattering structures in the ISM responsible for so-called ``extreme
scattering events" (ESEs), observed in quasars and pulsars, remain enigmatic.
Current models struggle to explain the high-frequency light curves of ESEs, and
a recent analysis of a double lensing event in PSR\,B0834+06 reveals features
of ESEs that may also be challenging to accommodate via existing models. We
propose that these features arise naturally when the lens has a cusp-like
profile, described by the elementary cusp catastrophe. This is an
extension of previous work describing pulsar scintillation as arising from
fold catastrophes in thin, corrugated plasma sheets along the line of
sight. We call this framework of describing the lens potentials via elementary
catastrophes ``doubly catastrophic lensing", as catastrophes (e.g. folds and
cusps) have long been used to describe universal features in the light curves
of lensing events that generically manifest, regardless of the precise details
of the lens. Here, we argue that the lenses themselves may be described by
these same elementary structures. If correct, the doubly catastrophic lensing
framework would provide a unified description of scintillation and ESEs, where
the lenses responsible for these scattering phenomena are universal and can be
fully described by a small number of unfolding parameters. This could enable
their application as giant cosmic lenses for precision measurements of coherent
sources, including FRBs and pulsars.Comment: 10 pages, 10 figure
Crossing singularities in the saddle point approximation
We describe a new phenomenon in the study of the real-time path integral,
where complex classical paths hit singularities of the potential and need to be
analytically continued beyond the space for which they solve the boundary value
problem. We show that the behavior is universal and central to the problem of
quantum tunneling. These analytically continued complex classical paths enrich
the study of real-time Feynman path integrals
Complex classical paths in quantum reflections and tunneling
The real-time propagator of the symmetric Rosen-Morse, also known as the
symmetric modified P\"oschl-Teller, barrier is expressed in the
Picard-Lefschetz path integral formalism using real and complex classical
paths. We explain how the interference pattern in the real-time propagator and
energy propagator is organized by caustics and Stoke's phenomena, and list the
relevant real and complex classical paths as a function of the initial and
final position. We discover the occurrence of singularity crossings, where the
analytic continuation of the complex classical path no longer satisfies the
boundary value problem and needs to be analytically continued. Moreover, we
demonstrate how these singularity crossings play a central role in the
real-time description of quantum tunneling
Refractive lensing of scintillating FRBs by sub-parsec cloudlets in the multi-phase CGM
We consider the refractive lensing effects of ionized cool () gas cloudlets in the circumgalactic medium (CGM) of galaxies.
In particular, we discuss the combined effects of lensing from these cloudlets
and scintillation from plasma screens in the Milky Way interstellar medium
(ISM). We show that, if the CGM comprises a mist of sub-parsec cloudlets with
column densities of order (as predicted by McCourt et
al. (2018)), then FRBs whose sightlines pass within a virial radius of a CGM
halo will generically be lensed into tens of refractive images with a scattering timescale. These images will be resolved by
scintillating screens in the Milky Way ISM, and therefore are expected to
suppress scintillation. From this, we argue that positive detections of FRB
scintillation can constrain the properties of these cool-gas cloudlets, with
current scintillation observation disfavouring the cloudlet model. We propose
that sheet-like geometries for the cool gas in the CGM can reconcile quasar
absorption measurements (from which we infer the presence of the cool gas with
structure on sub-parsec scales) and the unexpected lack of lensing signals from
this gas thus far observed
Scintillated microlensing: measuring cosmic distances with fast radio bursts
We propose a novel means of directly measuring cosmological distances using
scintillated microlensing of fast radio bursts (FRBs). In standard strong
lensing measurements of cosmic expansion, the main source of systematic
uncertainty lies in modeling the mass profile of galactic halos. Using
extra-galactic stellar microlensing to measure the Hubble constant avoids this
systematic uncertainty as the lens potential of microlenses depends only on a
single parameter: the mass of the lens. FRBs, which may achieve nanosecond
precision on lensing time delays, are well-suited to precision measurements of
stellar microlensing, for which the time delays are on the order of
milliseconds. However, typical angular separations between the microlensed
images on the order of microarcseconds make the individual images impossible to
spatially resolve with ground-based telescopes. We propose leveraging
scintillation in the ISM to resolve the microlensed images, effectively turning
the ISM into an astrophysical-scale interferometer. Using this technique, we
estimate a 6\% uncertainty on from a single observed scintillated
microlensing event, with a sub-percent uncertainty on achievable with
only 30 such events. With an optical depth for stellar microlensing of
, this may be achievable in the near future with upcoming FRB
telescopes
Intra-Articular Hip Corticosteroid Injection as a Predictor for THA Outcomes: A Retrospective Study
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