12,787 research outputs found
An analytical model of prominence dynamics
Solar prominences are magnetic structures incarcerating cool and dense gas in
an otherwise hot solar corona. Prominences can be categorized as quiescent and
active. Their origin and the presence of cool gas (~K) within the hot
(~K) solar corona remains poorly understood. The structure and dynamics
of solar prominences was investigated in a large number of observational and
theoretical (both analytical and numerical) studies. In this paper, an analytic
model of quiescent solar prominence is developed and used to demonstrate that
the prominence velocity increases exponentially, which means that some gas
falls downward towards the solar surface, and that Alfven waves are naturally
present in the solar prominences. These theoretical predictions are consistent
with the current observational data of solar quiescent prominences.Comment: Update Final Journal Print Version along with other Metadat
A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from Radio Pulses
Multipath propagation in the interstellar medium distorts radio pulses, an
effect predominant for distant pulsars observed at low frequencies. Typically,
broadened pulses are analyzed to determine the amount of propagation-induced
pulse broadening, but with little interest in determining the undistorted pulse
shapes. In this paper we develop and apply a method that recovers both the
intrinsic pulse shape and the pulse broadening function that describes the
scattering of an impulse. The method resembles the CLEAN algorithm used in
synthesis imaging applications, although we search for the best pulse
broadening function, and perform a true deconvolution to recover intrinsic
pulse structre. As figures of merit to optimize the deconvolution, we use the
positivity and symmetry of the deconvolved result along with the mean square
residual and the number of points below a given threshold. Our method makes no
prior assumptions about the intrinsic pulse shape and can be used for a range
of scattering functions for the interstellar medium. It can therefore be
applied to a wider variety of measured pulse shapes and degrees of scattering
than the previous approaches. We apply the technique to both simulated data and
data from Arecibo observations.Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
Transverse instability of the antiproton beam in the Recycler Ring
The brightness of the antiproton beam in Fermilab's 8 GeV Recycler ring is
limited by a transverse instability. This instability has occurred during the
extraction process to the Tevatron for large stacks of antiprotons even with
dampers in operation. This paper describes observed features of the
instability, introduces the threshold phase density to characterize the beam
stability, and finds the results to be in agreement with a resistive wall
instability model. Effective exclusion of the longitudinal tails from Landau
damping by decreasing the depth of the RF potential well is observed to lower
the threshold density by up to a factor of two.Comment: 3 pp. Particle Accelerator, 24th Conference (PAC'11) 2011. 28 Mar - 1
Apr 2011. New York, US
Plate on Plate Technique of Minimally Invasive Percutaneous Plate Osteosynthesis in Distal Tibial Fractures, an Easy and Inexpensive Method of Fracture Fixation
Background: Plate on plate technique can lessen operative time and patient morbidity.
Objectives: This study aimed to evaluate the outcomes of minimally invasive percutaneous plate osteosynthesis (MIPPO) using plate on plate technique of locking plate fixation for closed fractures of distal tibia in a prospective study.
Patients and Methods: Twenty-five patients with distal tibial fractures were treated by MIPPO using locking plate by plate on plate technique. Preoperative variables including age of patient, mode of trauma, type of fracture and soft tissue status were recorded for each patient. Perioperative variables included surgical time and radiation exposure. Postoperative variables included wound status, time to union, return to activity and the American orthopaedic foot and ankle score (AOFAS).
Results: All the fractures had united at one year. The average time to union was 16.8 weeks. There were two cases of superficial infection and two cases of deep infection, which required removal of hardware after the fracture was united. The average AO foot and ankle score was 83.6 in our study population.
Conclusions: MIPPO using locking plate by plate on plate technique was a safe, effective, inexpensive and easily reproducible method for the treatment of distal tibial fractures in properly selected patients, which minimized operative time and soft tissue morbidity
A Review of âMusic and Movementâ Therapies for Children with Autism: Embodied Interventions for Multisystem Development
The rising incidence of Autism Spectrum Disorders (ASDs) has led to a surge in the number of children needing autism interventions. This paper is a call to clinicians to diversify autism interventions and to promote the use of embodied music-based approaches to facilitate multisystem development. Approximately 12% of all autism interventions and 45% of all alternative treatment strategies in schools involve music-based activities. Musical training impacts various forms of development including communication, social-emotional, and motor development in children with ASDs and other developmental disorders as well as typically developing children. In this review, we will highlight the multisystem impairments of ASDs, explain why music and movement therapies are a powerful clinical tool, as well as describe mechanisms and offer evidence in support of music therapies for children with ASDs. We will support our claims by reviewing results from brain imaging studies reporting on music therapy effects in children with autism. We will also discuss the critical elements and the different types of music therapy approaches commonly used in pediatric neurological populations including autism. We provide strong arguments for the use of music and movement interventions as a multisystem treatment tool for children with ASDs. Finally, we also make recommendations for assessment and treatment of children with ASDs, and provide directions for future research
Monolithic InP-Based Grating Spectrometer for Wavelength-Division Multiplexed Systems at 1.5 ÎŒm
A monolithic InP-based grating spectrometer for use in wavelength-division multiplexed systems at 1.5 ÎŒm is reported.
The spectrometer uses a single etched reflective focusing diffraction grating and resolves >50 channels at 1 nm spacing with a ~0.3nm channel width and at least 19dB channel isolation. Operation is essentially of the state of the input polarisation
Relativistic spin precession in the binary PSR J11416545
PSR J11416545 is a precessing binary pulsar that has the rare potential to
reveal the two-dimensional structure of a non-recycled pulsar emission cone. It
has undergone of relativistic spin precession in the
years since its discovery. In this paper, we present a detailed Bayesian
analysis of the precessional evolution of the width of the total intensity
profile, to understand the changes to the line-of-sight impact angle ()
of the pulsar using four different physically motivated prior distribution
models. Although we cannot statistically differentiate between the models with
confidence, the temporal evolution of the linear and circular polarisations
strongly argue that our line-of-sight crossed the magnetic pole around MJD
54000 and that only two models remain viable. For both these models, it appears
likely that the pulsar will precess out of our line-of-sight in the next
years, assuming a simple beam geometry. Marginalising over suggests
that the pulsar is a near-orthogonal rotator and provides the first
polarization-independent estimate of the scale factor () that
relates the pulsar beam opening angle () to its rotational period ()
as : we find it to be at 1.4
GHz with 99\% confidence. If all pulsars emit from opposite poles of a dipolar
magnetic field with comparable brightness, we might expect to see evidence of
an interpulse arising in PSR J11416545, unless the emission is patchy.Comment: Accepted for publication in Astrophysical Journal Letter
RFI Identification and Mitigation Using Simultaneous Dual Station Observations
RFI mitigation is a critically important issue in radio astronomy using
existing instruments as well as in the development of next-generation radio
telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA
involve multiple stations with spacings of up to a few thousands of kilometers
and thus can exploit the drastically different RFI environments at different
stations. As demonstrator observations and analysis for SKA-like instruments,
and to develop RFI mitigation schemes that will be useful in the near term, we
recently conducted simultaneous observations with Arecibo Observatory and the
Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and
using the mostly uncorrelated RFI between the two sites to excise RFI from
several generic kinds of measurements such as giant pulses from Crab-like
pulsars and weak HI emission from galaxies in bands heavily contaminated by
RFI. This paper presents observations, analysis, and RFI identification and
excision procedures that are effective for both time series and spectroscopy
applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for
publication in Radio Scienc
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