369 research outputs found
Drift-Kinetic Modeling of Particle Acceleration and Transport in Solar Flares
Based on the drift-kinetic theory, we develop a model for particle
acceleration and transport in solar flares. The model describes the evolution
of the particle distribution function by means of a numerical simulation of the
drift-kinetic Vlasov equation, which allows us to directly compare simulation
results with observations within an actual parameter range of the solar corona.
Using this model, we investigate the time evolution of the electron
distribution in a flaring region. The simulation identifies two dominant
mechanisms of electron acceleration. One is the betatron acceleration at the
top of closed loops, which enhances the electron velocity perpendicular to the
magnetic field line. The other is the inertia drift acceleration in open
magnetic field lines, which produces antisunward electrons. The resulting
velocity space distribution significantly deviates from an isotropic
distribution. The former acceleration can be a generation mechanism of
electrons that radiate loop-top nonthermal emissions, and the latter be of
escaping electrons from the Sun that should be observed by in-situ measurements
in interplanetary space and resulting radio bursts through plasma
instabilities.Comment: 32 Pages, 11 figures, accepted by Ap
Hyperlink Management System and ID Converter System: enabling maintenance-free hyperlinks among major biological databases
Hyperlink Management System (HMS) is a system for automatically updating and maintaining hyperlinks among major public databases in the field of life science. We daily create corresponding tables of data IDs of major databases for human genes and proteins, and provide a CGI-program that returns correct and up-to-date URLs for showing data of various databases that correspond to user-specified IDs. The HMS can deal with various IDs: accession numbers of International Nucleotide Sequence Databases, HUGO Gene Symbols and IDs of UniProt, PDB, H-InvDB and others, and it can return URLs of various databases: H-InvDB, HUGO Gene Nomenclature Committee Database, NCBI Entrez Gene, UniProt, PDB and others. For example, 23 297 pages of Locus view of H-InvDB are reachable by using HUGO Gene Symbols through the HMS. Not only the CGI-program, the HMS provides a Web page for finding and opening URLs of these databases. Although hyperlinking is an effective way of relating biological data among different databases, updating hyperlinks has been a laborious work. The HMS fully automates the job, enabling maintenance-free hyperlinks. We also developed the ID Converter System (ICS) for simply converting data IDs by using corresponding tables in the HMS. The HMS and ICS are freely available at http://biodb.jp/
Flare Ribbons Observed with G-band and FeI 6302A Filters of the Solar Optical Telescope on Board Hinode
The Solar Optical Telescope (SOT) on board Hinode satellite observed an X3.4
class flare on 2006 December 13. Typical two-ribbon structure was observed, not
only in the chromospheric CaII H line but also in G-band and FeI 6302A line.
The high-resolution, seeing-free images achieved by SOT revealed, for the first
time, the sub-arcsec fine structures of the "white light" flare. The G-band
flare ribbons on sunspot umbrae showed a sharp leading edge followed by a
diffuse inside, as well as previously known core-halo structure. The underlying
structures such as umbral dots, penumbral filaments and granules were visible
in the flare ribbons. Assuming that the sharp leading edge was directly heated
by particle beam and the diffuse parts were heated by radiative back-warming,
we estimate the depth of the diffuse flare emission using the intensity profile
of the flare ribbon. We found that the depth of the diffuse emission is about
100 km or less from the height of the source of radiative back-warming. The
flare ribbons were also visible in the Stokes-V images of FeI 6302A, as a
transient polarity reversal. This is probably related to "magnetic transient"
reported in the literature. The intensity increase in Stokes-I images indicates
that the FeI 6302A line was significantly deformed by the flare, which may
cause such a magnetic transient.Comment: 14 pages, 7 figures, PASJ in pres
Internet Image Viewer (iiV)
<p>Abstract</p> <p>Background</p> <p>Visualizing 3-dimensional (3-D) datasets is an important part of modern neuroimaging research. Many tools address this problem; however, they often fail to address specific needs and flexibility, such as the ability to work with different data formats, to control how and what data are displayed, to interact with values, and to undo mistakes.</p> <p>Results</p> <p>iiV, an interactive software program for displaying 3-D brain images, is described. This tool was programmed to solve basic problems in 3-D data visualization. It is written in Java so it is extensible, is platform independent, and can display images within web pages.</p> <p>iiV displays 3-D images as 2-dimensional (2-D) slices with each slice being an independent object with independent features such as location, zoom, colors, labels, etc. Feature manipulation becomes easier by having a full set of editing capabilities including the following: undo or redo changes; drag, copy, delete and paste objects; and save objects with their features to a file for future editing. It can read multiple standard positron emission tomography (PET) and magnetic resonance imaging (MRI) file formats like ECAT, ECAT7, ANALYZE, NIfTI-1 and DICOM. We present sample applications to illustrate some of the features and capabilities.</p> <p>Conclusion</p> <p>iiV is an image display tool with many useful features. It is highly extensible, platform independent, and web-compatible. This report summarizes its features and applications, while illustrating iiV's usefulness to the biomedical imaging community.</p
Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
We study the non-thermal emissions in a solar flare occurring on 2003 May 29
by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This
flare shows several typical behaviors of the HXR and microwave emissions: time
delay of microwave peaks relative to HXR peaks, loop-top microwave and
footpoint HXR sources, and a harder electron energy distribution inferred from
the microwave spectrum than from the HXR spectrum. In addition, we found that
the time profile of the spectral index of the higher-energy (\gsim 100 keV)
HXRs is similar to that of the microwaves, and is delayed from that of the
lower-energy (\lsim 100 keV) HXRs. We interpret these observations in terms
of an electron transport model called {\TPP}. We numerically solved the
spatially-homogeneous {\FP} equation to determine electron evolution in energy
and pitch-angle space. By comparing the behaviors of the HXR and microwave
emissions predicted by the model with the observations, we discuss the
pitch-angle distribution of the electrons injected into the flare site. We
found that the observed spectral variations can qualitatively be explained if
the injected electrons have a pitch-angle distribution concentrated
perpendicular to the magnetic field lines rather than isotropic distribution.Comment: 32 pages, 12 figures, accepted for publication in The Astronomical
Journa
A Systematic Examination of Particle Motion in a Collapsing Magnetic Trap Model for Solar Flares
Context. It has been suggested that collapsing magnetic traps may contribute
to accelerating particles to high energies during solar flares.
Aims. We present a detailed investigation of the energization processes of
particles in collapsing magnetic traps, using a specific model. We also compare
for the first time the energization processes in a symmetric and an asymmetric
trap model.
Methods. Particle orbits are calculated using guiding centre theory. We
systematically investigate the dependence of the energization process on
initial position, initial energy and initial pitch angle.
Results. We find that in our symmetric trap model particles can gain up to
about 50 times their initial energy, but that for most initial conditions the
energy gain is more moderate. Particles with an initial position in the weak
field region of the collapsing trap and with pitch angles around 90 degrees
achieve the highest energy gain, with betatron acceleration of the
perpendicular energy the dominant energization mechanism. For particles with
smaller initial pitch angle, but still outside the loss cone, we find the
possibility of a significant increase in parallel energy. This increase in
parallel energy can be attributed to the curvature term in the parallel
equation of motion and the associated energy gain happens in the center of the
trap where the field line curvature has its maximum. We find qualitatively
similar results for the asymmetric trap model, but with smaller energy gains
and a larger number of particles escaping from the trap.Comment: 11 pages, 13 figures. To be published in Astronomy and Astrophysic
Magnetic Reconnection in Non-Equilibrium Ionization Plasma
We have studied the effect of time-dependent ionization and recombination
processes on magnetic reconnection in the solar corona. Petschek-type steady
reconnection, in which model the magnetic energy is mainly converted at the
slow-mode shocks, was assumed. We carried out the time-dependent ionization
calculation in the magnetic reconnection structure. We only calculated the
transient ionization of iron; the other species were assumed to be in
ionization equilibrium. The intensity of line emissions at specific wavelengths
were also calculated for comparison with {\it Hinode} or other observations in
future. What we found is as follows: (1) iron is mostly in non-equilibrium
ionization in the reconnection region, (2) the intensity of line emission
estimated by the time-dependent ionization calculation is significantly
different from that with the ionization equilibrium assumption, (3) the effect
of time-dependent ionization is sensitive to the electron density in the case
that the electron density is less than cm, (4) the effect of
thermal conduction lessens the time-dependent ionization effect, (5) the effect
of radiative cooling is negligibly small even if we take into account
time-dependent ionization.Comment: accepted for publication in The Astrophysical Journa
Human Rehearsal Processes and the Frontal Lobes: PET Evidence
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71395/1/j.1749-6632.1995.tb38134.x.pd
Frequency comb transferred by surface plasmon resonance
Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a sub-wavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 x 10(-19) in absolute position, 2.92 x 10(-19) in stability and 1Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits.open
- …