2,906 research outputs found
Modelling Fast-Alfv\'en Mode Conversion Using SPARC
We successfully utilise the SPARC code to model fast-Alfv\'en mode conversion
in the region via 3-D MHD numerical simulations of helioseismic
waves within constant inclined magnetic field configurations. This was achieved
only after empirically modifying the background density and gravitational
stratifications in the upper layers of our computational box, as opposed to
imposing a traditional Lorentz Force limiter, to ensure a manageable timestep.
We found that the latter approach inhibits the fast-Alfv\'en mode conversion
process by severely damping the magnetic flux above the surface.Comment: Proceedings of GONG 2012 / LWS/SDO-5 / SOHO 27 (Eclipse on the Coral
Sea: Cycle 24 Ascending) Conference, November 12 -16, 2012, Palm Cove,
Australi
Directional Time-Distance Probing of Model Sunspot Atmospheres
A crucial feature not widely accounted for in local helioseismology is that
surface magnetic regions actually open a window from the interior into the
solar atmosphere, and that the seismic waves leak through this window, reflect
high in the atmosphere, and then re-enter the interior to rejoin the seismic
wave field normally confined there. In a series of recent numerical studies
using translation invariant atmospheres, we utilised a "directional
time-distance helioseismology" measurement scheme to study the implications of
the returning fast and Alfv\'en waves higher up in the solar atmosphere on the
seismology at the photosphere (Cally & Moradi 2013; Moradi & Cally 2014). In
this study, we extend our directional time-distance analysis to more realistic
sunspot-like atmospheres to better understand the direct effects of the
magnetic field on helioseismic travel-time measurements in sunspots. In line
with our previous findings, we uncover a distinct frequency-dependant
directional behaviour in the travel-time measurements, consistent with the
signatures of MHD mode conversion. We found this to be the case regardless of
the sunspot field strength or depth of its Wilson depression. We also isolated
and analysed the direct contribution from purely thermal perturbations to the
measured travel times, finding that waves propagating in the umbra are much
more sensitive to the underlying thermal effects of the sunspot.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journa
The Effect of Acupressure at GB-21 and SP-6 Acupoints on Anxiety Level and Maternal-Fetal Attachment in Primiparous Women: a Randomized Controlled Clinical Trial
Background: Delivery is one of the most stressful events in women’s life. Excessive anxiety, in turn, increases delivery and pregnancy complications. Mother’s positive experience of delivery leads to more effective maternal-fetal attachment in the first few hours of birth.
Objectives: The present study aimed to compare the effects of acupressure at two different acupoints on anxiety level and maternal-fetal attachment in primiparous women.
Materials and Methods: In this study, 150 primiparous women were allocated to acupressure at GB-21 acupoint, acupressure at SP-6 acupoint, and control group. The women in their active phase of delivery were enrolled in the study and pressure was applied to the acupoints for 20 minutes. Mother’s anxiety level was assessed using Spielberger’s questionnaire before and one hour after the intervention. In addition, maternal-fetal attachment behaviors were evaluated using Avant’s questionnaire during the first breastfeeding. Then the data were introduced to the SPSS (v. 13) and were analyzed using t test and one way ANOVA.
Results: The results revealed no significant difference among the three groups regarding the anxiety level before the intervention (P > 0.05). One hour after the intervention, this measure was significantly lower in the intervention groups in comparison to the control group (P 0.05). Moreover, maternal-fetal attachment was higher in the intervention groups in comparison with the control group (P < 0.001).
Conclusions: Acupressure at both acupoints reduced anxiety level and increased maternal-fetal attachment. This method can be easily used in the delivery room
Helioseismic analysis of the solar flare-induced sunquake of 2005 January 15
We report the discovery of one of the most powerful sunquakes detected to
date, produced by an X1.2-class solar flare in active region 10720 on 2005
January 15. We used helioseismic holography to image the source of seismic
waves emitted into the solar interior from the site of the flare. Acoustic
egression power maps at 3 and 6 mHz with a 2 mHz bandpass reveal a compact
acoustic source strongly correlated with impulsive hard X-ray and
visible-continuum emission along the penumbral neutral line separating the two
major opposing umbrae in the -configuration sunspot that predominates
AR10720. The acoustic emission signatures were directly aligned with both hard
X-ray and visible continuum emission that emanated during the flare. The
visible continuum emission is estimated at J,
approximately 500 times the seismic emission of J. The
flare of 2005 January 15 exhibits the same close spatial alignment between the
sources of the seismic emission and impulsive visible continuum emission as
previous flares, reinforcing the hypothesis that the acoustic emission may be
driven by heating of the low photosphere. However, it is a major exception in
that there was no signature to indicate the inclusion of protons in the
particle beams thought to supply the energy radiated by the flare. The
continued strong coincidence between the sources of seismic emission and
impulsive visible continuum emission in the case of a proton-deficient
white-light flare lends substantial support to the ``back -- warming''
hypothesis, that the low photosphere is significantly heated by intense Balmer
and Paschen continuum-edge radiation from the overlying chromosphere in
white-light flares.Comment: 12 pages, 7 figures, published in MNRA
A theory of non-local linear drift wave transport
Transport events in turbulent tokamak plasmas often exhibit non-local or
non-diffusive action at a distance features that so far have eluded a
conclusive theoretical description. In this paper a theory of non-local
transport is investigated through a Fokker-Planck equation with fractional
velocity derivatives. A dispersion relation for density gradient driven linear
drift modes is derived including the effects of the fractional velocity
derivative in the Fokker-Planck equation. It is found that a small deviation (a
few percent) from the Maxwellian distribution function alters the dispersion
relation such that the growth rates are substantially increased and thereby may
cause enhanced levels of transport.Comment: 22 pages, 2 figures. Manuscript submitted to Physics of Plasma
Implementation and Evaluation of a Cooperative Vehicle-to-Pedestrian Safety Application
While the development of Vehicle-to-Vehicle (V2V) safety applications based
on Dedicated Short-Range Communications (DSRC) has been extensively undergoing
standardization for more than a decade, such applications are extremely missing
for Vulnerable Road Users (VRUs). Nonexistence of collaborative systems between
VRUs and vehicles was the main reason for this lack of attention. Recent
developments in Wi-Fi Direct and DSRC-enabled smartphones are changing this
perspective. Leveraging the existing V2V platforms, we propose a new framework
using a DSRC-enabled smartphone to extend safety benefits to VRUs. The
interoperability of applications between vehicles and portable DSRC enabled
devices is achieved through the SAE J2735 Personal Safety Message (PSM).
However, considering the fact that VRU movement dynamics, response times, and
crash scenarios are fundamentally different from vehicles, a specific framework
should be designed for VRU safety applications to study their performance. In
this article, we first propose an end-to-end Vehicle-to-Pedestrian (V2P)
framework to provide situational awareness and hazard detection based on the
most common and injury-prone crash scenarios. The details of our VRU safety
module, including target classification and collision detection algorithms, are
explained next. Furthermore, we propose and evaluate a mitigating solution for
congestion and power consumption issues in such systems. Finally, the whole
system is implemented and analyzed for realistic crash scenarios
Charged particle dynamics in the presence of non-Gaussian L\'evy electrostatic fluctuations
Full orbit dynamics of charged particles in a -dimensional helical
magnetic field in the presence of -stable L\'evy electrostatic
fluctuations and linear friction modeling collisional Coulomb drag is studied
via Monte Carlo numerical simulations. The L\'evy fluctuations are introduced
to model the effect of non-local transport due to fractional diffusion in
velocity space resulting from intermittent electrostatic turbulence. The
probability distribution functions of energy, particle displacements, and
Larmor radii are computed and showed to exhibit a transition from exponential
decay, in the case of Gaussian fluctuations, to power law decay in the case of
L\'evy fluctuations. The absolute value of the power law decay exponents are
linearly proportional to the L\'evy index . The observed anomalous
non-Gaussian statistics of the particles' Larmor radii (resulting from outlier
transport events) indicate that, when electrostatic turbulent fluctuations
exhibit non-Gaussian L\'evy statistics, gyro-averaging and guiding centre
approximations might face limitations and full particle orbit effects should be
taken into account.Comment: 5 pages, 5 figures. Accepted as a letter in Physics of Plasma
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