1,105 research outputs found
3D Radio and X-Ray Modeling and Data Analysis Software: Revealing Flare Complexity
We have undertaken a major enhancement of our IDL-based simulation tools
developed earlier for modeling microwave and X-ray emission. The object-based
architecture provides an interactive graphical user interface that allows the
user to import photospheric magnetic field maps and perform magnetic field
extrapolations to almost instantly generate 3D magnetic field models, to
investigate the magnetic topology of these models by interactively creating
magnetic field lines and associated magnetic flux tubes, to populate the flux
tubes with user-defined nonuniform thermal plasma and anisotropic, nonuniform,
nonthermal electron distributions; to investigate the spatial and spectral
properties of radio and X-ray emission calculated from the model, and to
compare the model-derived images and spectra with observational data. The
application integrates shared-object libraries containing fast gyrosynchrotron
emission codes developed in FORTRAN and C++, soft and hard X-ray codes
developed in IDL, a FORTRAN-based potential-field extrapolation routine and an
IDL-based linear force free field extrapolation routine. The interactive
interface allows users to add any user-defined radiation code that adheres to
our interface standards, as well as user-defined magnetic field extrapolation
routines. Here we use this tool to analyze a simple single-loop flare and use
the model to constrain the 3D structure of the magnetic flaring loop and 3D
spatial distribution of the fast electrons inside this loop. We iteratively
compute multi-frequency microwave and multi-energy X-ray images from realistic
magnetic fluxtubes obtained from an extrapolation of a magnetogram taken prior
to the flare, and compare them with imaging data obtained by SDO, NoRH, and
RHESSI instruments. We use this event to illustrate use of the tool for general
interpretation of solar flares to address disparate problems in solar physics.Comment: 12 pages, 11 figures, ApJ accepte
Development of tests for measurement of primary perceptual-motor performance
Tests for measuring primary perceptual-motor performance for assessing space environment effects on human performanc
Movement Kinematics and their Relationship with Performance in Target Acquisition Task Using a Mouse
Movement kinematics has been shown useful for characterizing the process of aiming movement in target acquisition tasks. There are multiple kinematic measures reported in the literature, but their relationship to eventual performance is not well documented. To determine the relationship between various kinematic measures and movement performance, data were collected from participants aged 21 to 90 years with a wide range of psychomotor ability. When computed across age groups, time to peak velocity (TPV), time to peak acceleration (TPA), and time from peak velocity until the end of movement (TPVEND) were found to correlate with movement performance. However, the relationships diminished when the correlations were computed within age groups (except for TPVEND). More interestingly, despite the extensive report, certain kinematic measures such as peak velocity were found to be uncorrelated with performance. Thus, when performance is the focus, improvement should be made to reduce TPV, TPA, and TPVEND.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Spatial Evidence for Transition Radiation in a Solar Radio Burst
Microturbulence, i.e. enhanced fluctuations of plasma density, electric and
magnetic fields, is of great interest in astrophysical plasmas, but occurs on
spatial scales far too small to resolve by remote sensing, e.g., at ~ 1-100 cm
in the solar corona. This paper reports spatially resolved observations that
offer strong support for the presence in solar flares of a suspected radio
emission mechanism, resonant transition radiation, which is tightly coupled to
the level of microturbulence and provides direct diagnostics of the existence
and level of fluctuations on decimeter spatial scales. Although the level of
the microturbulence derived from the radio data is not particularly high,
/n^2 ~ 10^{-5}$, it is large enough to affect the charged particle
diffusion and give rise to effective stochastic acceleration. This finding has
exceptionally broad astrophysical implications since modern sophisticated
numerical models predict generation of much stronger turbulence in relativistic
objects, e.g., in gamma-ray burst sources.Comment: 13 pages, 4 figures, ApJL accepte
Instrumental oscillations in RHESSI count rates during solar flares
Aims: We seek to illustrate the analysis problems posed by RHESSI spacecraft
motion by studying persistent instrumental oscillations found in the
lightcurves measured by RHESSI's X-ray detectors in the 6-12 keV and 12-25 keV
energy range during the decay phase of the flares of 2004 November 4 and 6.
Methods: The various motions of the RHESSI spacecraft which may contribute to
the manifestation of oscillations are studied. The response of each detector in
turn is also investigated. Results: We find that on 2004 November 6 the
observed oscillations correspond to the nutation period of the RHESSI
instrument. These oscillations are also of greatest amplitude for detector 5,
while in the lightcurves of many other detectors the oscillations are small or
undetectable. We also find that the variation in detector pointing is much
larger during this flare than the counterexample of 2004 November 4.
Conclusions: Sufficiently large nutation motions of the RHESSI spacecraft lead
to clearly observable oscillations in count rates, posing a significant hazard
for data analysis. This issue is particularly problematic for detector 5 due to
its design characteristics. Dynamic correction of the RHESSI counts, accounting
for the livetime, data gaps, and the transmission of the bi-grid collimator of
each detector, is required to overcome this issue. These corrections should be
applied to all future oscillation studies.Comment: 8 pages, 10 figure
Surface plasmon in 2D Anderson insulator with interactions
We study the effect of interactions on the zero-temperature a.c. conductivity
of 2D Anderson insulator at low frequencies. We show that the enhancement of
the real part of conductivity due to the Coulomb correlations in the occupation
numbers of localized states results in the change of the sign of imaginary part
within a certain frequency range. As a result, the propagation of a surface
plasmon in a localized system becomes possible. We analize the dispersion law
of the plasmon for the two cases: unscreened Coulomb interactions and the
interactions screened by a gate electrode spaced by some distance from the
electron plane.Comment: latex 22 pages + 2 uuencoded figure
Radio Spectral Evolution of an X-ray Poor Impulsive Solar Flare: Implications for Plasma Heating and Electron Acceleration
We present radio and X-ray observations of an impulsive solar flare that was
moderately intense in microwaves, yet showed very meager EUV and X-ray
emission. The flare occurred on 2001 Oct 24 and was well-observed at radio
wavelengths by the Nobeyama Radioheliograph (NoRH), the Nobeyama Radio
Polarimeters (NoRP), and by the Owens Valley Solar Array (OVSA). It was also
observed in EUV and X-ray wavelength bands by the TRACE, GOES, and Yohkoh
satellites. We find that the impulsive onset of the radio emission is
progressively delayed with increasing frequency relative to the onset of hard
X-ray emission. In contrast, the time of flux density maximum is progressively
delayed with decreasing frequency. The decay phase is independent of radio
frequency. The simple source morphology and the excellent spectral coverage at
radio wavelengths allowed us to employ a nonlinear chi-squared minimization
scheme to fit the time series of radio spectra to a source model that accounts
for the observed radio emission in terms of gyrosynchrotron radiation from
MeV-energy electrons in a relatively dense thermal plasma. We discuss plasma
heating and electron acceleration in view of the parametric trends implied by
the model fitting. We suggest that stochastic acceleration likely plays a role
in accelerating the radio-emitting electrons.Comment: 22 pages, 10 figure
Study of flare energy release using events with numerous type III-like bursts in microwaves
The analysis of narrowband drifting of type III-like structures in radio
bursts dynamic spectra allows to obtain unique information about primary energy
release mechanisms in solar flares. The SSRT spatially resolved images and a
high spectral and temporal resolution allow direct determination not only the
positions of its sources but also the exciter velocities along the flare loop.
Practically, such measurements are possible during some special time intervals
when the SSRT (about 5.7 GHz) is observing the flare region in two high-order
fringes; thus, two 1D scans are recorded simultaneously at two frequency bands.
The analysis of type III-like bursts recorded during the flare 14 Apr 2002 is
presented. Using-muliwavelength radio observations recorded by SSRT, SBRS,
NoRP, RSTN we study an event with series of several tens of drifting microwave
pulses with drift rates in the range from -7 to 13 GHz/s. The sources of the
fast-drifting bursts were located near the top of the flare loop in a volume of
a few Mm in size. The slow drift of the exciters along the flare loop suggests
a high pitch-anisotropy of the emitting electrons.Comment: 16 pages, 6 figures, Solar Physics, in press, 201
Brownian motion with dry friction: Fokker-Planck approach
We solve a Langevin equation, first studied by de Gennes, in which there is a
solid-solid or dry friction force acting on a Brownian particle in addition to
the viscous friction usually considered in the study of Brownian motion. We
obtain both the time-dependent propagator of this equation and the velocity
correlation function by solving the associated time-dependent Fokker-Planck
equation. Exact results are found for the case where only dry friction acts on
the particle. For the case where both dry and viscous friction forces are
present, series representations of the propagator and correlation function are
obtained in terms of parabolic cylinder functions. Similar series
representations are also obtained for the case where an external constant force
is added to the Langevin equation.Comment: 18 pages, 13 figures (in color
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