474 research outputs found
Tailored Raman-resonant four-wave-mixing processes
Nonlinear optical processes are strongly dominated by phase relationships among electromagnetic fields involved. In this paper, we theoretically and experimentally show that in a Raman-resonant four-wave-mixing process, the first anti-Stokes and Stokes generations can be tailored in a variety of ways by manipulating the phase relationships among the relevant electromagnetic fields
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
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
New Computer-Aided Diagnosis of Dementia Using Positron Emission Tomography: Brain Regional Sensitivity-Mapping Method
Purpose: We devised a new computer-aided diagnosis method to segregate dementia using one estimated index (Total Z
score) derived from the Brodmann area (BA) sensitivity map on the stereotaxic brain atlas. The purpose of this study is to
investigate its accuracy to differentiate patients with Alzheimer’s disease (AD) or mild cognitive impairment (MCI) from
normal adults (NL).
Methods: We studied 101 adults (NL: 40, AD: 37, MCI: 24) who underwent 18FDG positron emission tomography (PET)
measurement. We divided NL and AD groups into two categories: a training group with (Category A) and a test group
without (Category B) clinical information. In Category A, we estimated sensitivity by comparing the standard uptake value
per BA (SUVR) between NL and AD groups. Then, we calculated a summated index (Total Z score) by utilizing the sensitivitydistribution
maps and each BA z-score to segregate AD patterns. To confirm the validity of this method, we examined the
accuracy in Category B. Finally, we applied this method to MCI patients.
Results: In Category A, we found that the sensitivity and specificity of differentiation between NL and AD were all 100%. In
Category B, those were 100% and 95%, respectively. Furthermore, we found this method attained 88% to differentiate ADconverters
from non-converters in MCI group.
Conclusions: The present automated computer-aided evaluation method based on a single estimated index provided good
accuracy for differential diagnosis of AD and MCI. This good differentiation power suggests its usefulness not only for
dementia diagnosis but also in a longitudinal study.浜松医科大学学位論文 医博第695号(平成27年3月16日
Benefits of Artificially Generated Gravity Gradients for Interferometric Gravitational-Wave Detectors
We present an approach to experimentally evaluate gravity gradient noise, a
potentially limiting noise source in advanced interferometric gravitational
wave (GW) detectors. In addition, the method can be used to provide sub-percent
calibration in phase and amplitude of modern interferometric GW detectors.
Knowledge of calibration to such certainties shall enhance the scientific
output of the instruments in case of an eventual detection of GWs. The method
relies on a rotating symmetrical two-body mass, a Dynamic gravity Field
Generator (DFG). The placement of the DFG in the proximity of one of the
interferometer's suspended test masses generates a change in the local
gravitational field detectable with current interferometric GW detectors.Comment: 16 pages, 4 figure
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
Optical technology for arbitrarily manipulating amplitudes and phases of coaxially propagating highly discrete spectra
The development of new optical technology plays a key role in the essential evolution of optical science. In this article, we experimentally demonstrate an optical technology that enables the arbitrary manipulation of amplitudes and phases of highly discrete spectra. This optical technology is simple and practically useful: we may only place a few fundamental optical elements on an optical axis and control their thicknesses precisely. As a typical application, we show generation of a train of ultrashort pulses in the time domain, with a pulse duration close to 1 fs and a repetition rate exceeding 100 THz
Statistics of low-energy levels of a one-dimensional weakly localized Frenkel exciton: A numerical study
Numerical study of the one-dimensional Frenkel Hamiltonian with on-site
randomness is carried out. We focus on the statistics of the energy levels near
the lower exciton band edge, i. e. those determining optical response. We found
that the distribution of the energy spacing between the states that are well
localized at the same segment is characterized by non-zero mean, i.e. these
states undergo repulsion. This repulsion results in a local discrete energy
structure of a localized Frenkel exciton. On the contrary, the energy spacing
distribution for weakly overlapping local ground states (the states with no
nodes within their localization segments) that are localized at different
segments has zero mean and shows almost no repulsion. The typical width of the
latter distribution is of the same order as the typical spacing in the local
discrete energy structure, so that this local structure is hidden; it does not
reveal itself neither in the density of states nor in the linear absorption
spectra. However, this structure affects the two-exciton transitions involving
the states of the same segment and can be observed by the pump-probe
spectroscopy. We analyze also the disorder degree scaling of the first and
second momenta of the distributions.Comment: 10 pages, 6 figure
Arterial/venous plasma nicotine concentrations following nicotine nasal spray
Background and objectives : Arterial (A) and venous (V) plasma nicotine and cotinine concentrations were measured after nasal nicotine spray in tobacco smokers of both genders. The hypothesis for this research was that a greater A/V difference in plasma nicotine would be present in males than females because males have greater skeletal muscle mass to bind nicotine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42031/1/228-55-9-639_90550639.pd
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