7,081 research outputs found
Direct Imaging by SDO AIA of Quasi-periodic Fast Propagating Waves of ~2000 km/s in the Low Solar Corona
Quasi-periodic, propagating fast mode magnetosonic waves in the corona were
difficult to observe in the past due to relatively low instrument cadences. We
report here evidence of such waves directly imaged in EUV by the new SDO AIA
instrument. In the 2010 August 1 C3.2 flare/CME event, we find arc-shaped wave
trains of 1-5% intensity variations (lifetime ~200 s) that emanate near the
flare kernel and propagate outward up to ~400 Mm along a funnel of coronal
loops. Sinusoidal fits to a typical wave train indicate a phase velocity of
2200 +/- 130 km/s. Similar waves propagating in opposite directions are
observed in closed loops between two flare ribbons. In the k- diagram
of the Fourier wave power, we find a bright ridge that represents the
dispersion relation and can be well fitted with a straight line passing through
the origin. This k- ridge shows a broad frequency distribution with
indicative power at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz
(period 181 s) temporally coincides with quasi-periodic pulsations of the
flare, suggesting a common origin. The instantaneous wave energy flux of
estimated at the coronal base is comparable
to the steady-state heating requirement of active region loops.Comment: Accepted by Astrophysical Journal Letters, 5 figures, 6 pages. Press
Release at the AAS Solar Physics Division 2011 Meeting, Las Cruces, New
Mexico, June 15, see movies at
http://www.lmsal.com/press/apjl2011_magnetosoni
In the light of time
The concept of time is examined using the second law of thermodynamics that was recently formulated as an equation of motion. According to the statistical notion of increasing entropy, flows of energy diminish differences between energy densities that form space. The flow of energy is identified with the flow of time. The non-Euclidean energy landscape, i.e. the curved space–time, is in evolution when energy is flowing down along gradients and levelling the density differences. The flows along the steepest descents, i.e. geodesics are obtained from the principle of least action for mechanics, electrodynamics and quantum mechanics. The arrow of time, associated with the expansion of the Universe, identifies with grand dispersal of energy when high-energy densities transform by various mechanisms to lower densities in energy and eventually to ever-diluting electromagnetic radiation. Likewise, time in a quantum system takes an increment forwards in the detection-associated dissipative transformation when the stationary-state system begins to evolve pictured as the wave function collapse. The energy dispersal is understood to underlie causality so that an energy gradient is a cause and the resulting energy flow is an effect. The account on causality by the concepts of physics does not imply determinism; on the contrary, evolution of space–time as a causal chain of events is non-deterministic
A New Algorithm for the Detection of Inter-cluster Galaxy Filaments using Galaxy Orientation Alignments
We present a new algorithm to detect inter-cluster galaxy filaments based
upon the assumption that the orientations of constituent galaxies along such
filaments are non-isotropic. We apply the algorithm to the 2dF Galaxy Redshift
Survey catalogue and find that it readily detects many straight filaments
between close cluster pairs. At large inter-cluster separations (>15 Mpc), we
find that the detection efficiency falls quickly, as it also does with more
complex filament morphologies. We explore the underlying assumptions and
suggest that it is only in the case of close cluster pairs that we can expect
galaxy orientations to be significantly correlated with filament direction.Comment: 7 pages, 5 figures, accepted for publication in MNRA
Principal Component Analysis as a Tool for Characterizing Black Hole Images and Variability
We explore the use of principal component analysis (PCA) to characterize
high-fidelity simulations and interferometric observations of the millimeter
emission that originates near the horizons of accreting black holes. We show
mathematically that the Fourier transforms of eigenimages derived from PCA
applied to an ensemble of images in the spatial-domain are identical to the
eigenvectors of PCA applied to the ensemble of the Fourier transforms of the
images, which suggests that this approach may be applied to modeling the sparse
interferometric Fourier-visibilities produced by an array such as the Event
Horizon Telescope (EHT). We also show that the simulations in the spatial
domain themselves can be compactly represented with a PCA-derived basis of
eigenimages allowing for detailed comparisons between variable observations and
time-dependent models, as well as for detection of outliers or rare events
within a time series of images. Furthermore, we demonstrate that the spectrum
of PCA eigenvalues is a diagnostic of the power spectrum of the structure and,
hence, of the underlying physical processes in the simulated and observed
images.Comment: 16 pages, 17 figures, submitted to Ap
A stable quasi-periodic 4.18 d oscillation and mysterious occultations in the 2011 MOST light curve of TWHya
We present an analysis of the 2011 photometric observations of TW Hya by the
MOST satellite; this is the fourth continuous series of this type. The
large-scale light variations are dominated by a strong, quasi-periodic 4.18 d
oscillation with superimposed, apparently chaotic flaring activity; the former
is most likely produced by stellar rotation with one large hot spot created by
a stable accretion funnel in the stable regime of accretion while the latter
may be produced by small hot spots, created at moderate latitudes by unstable
accretion tongues. A new, previously unnoticed feature is a series of
semi-periodic, well defined brightness dips of unknown nature of which 19 were
observed during 43 days of our nearly-continuous observations. Re-analysis of
the 2009 MOST light curve revealed the presence of 3 similar dips. On the basis
of recent theoretical results, we tentatively conclude that the dips may
represent occultations of the small hot spots created by unstable accretion
tongues by hypothetical optically thick clumps.Comment: Printed in MNRA
Biologically inspired composite image sensor for deep field target tracking
The use of nonuniform image sensors in mobile based computer vision applications can be an effective solution when computational burden is problematic. Nonuniform image sensors are still in their infancy and as such have not been fully investigated for their unique qualities nor have they been extensively applied in practice. In this dissertation a system has been developed that can perform vision tasks in both the far field and the near field. In order to accomplish this, a new and novel image sensor system has been developed. Inspired by the biological aspects of the visual systems found in both falcons and primates, a composite multi-camera sensor was constructed. The sensor provides for expandable visual range, excellent depth of field, and produces a single compact output image based on the log-polar retinal-cortical mapping that occurs in primates. This mapping provides for scale and rotational tolerant processing which, in turn, supports the mitigation of perspective distortion found in strict Cartesian based sensor systems. Furthermore, the scale-tolerant representation of objects moving on trajectories parallel to the sensor\u27s optical axis allows for fast acquisition and tracking of objects moving at high rates of speed. In order to investigate how effective this combination would be for object detection and tracking at both near and far field, the system was tuned for the application of vehicle detection and tracking from a moving platform. Finally, it was shown that the capturing of license plate information in an autonomous fashion could easily be accomplished from the extraction of information contained in the mapped log-polar representation space.
The novel composite log-polar deep-field image sensor opens new horizons for computer vision. This current work demonstrates features that can benefit applications beyond the high-speed vehicle tracking for drivers assistance and license plate capture. Some of the future applications envisioned include obstacle detection for high-speed trains, computer assisted aircraft landing, and computer assisted spacecraft docking
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Cryo-EM Studies of TMEM16F Calcium-Activated Ion Channel Suggest Features Important for Lipid Scrambling.
As a Ca2+-activated lipid scramblase and ion channel that mediates Ca2+ influx, TMEM16F relies on both functions to facilitate extracellular vesicle generation, blood coagulation, and bone formation. How a bona fide ion channel scrambles lipids remains elusive. Our structural analyses revealed the coexistence of an intact channel pore and PIP2-dependent protein conformation changes leading to membrane distortion. Correlated to the extent of membrane distortion, many tightly bound lipids are slanted. Structure-based mutagenesis studies further reveal that neutralization of some lipid-binding residues or those near membrane distortion specifically alters the onset of lipid scrambling, but not Ca2+ influx, thus identifying features outside of channel pore that are important for lipid scrambling. Together, our studies demonstrate that membrane distortion does not require open hydrophilic grooves facing the membrane interior and provide further evidence to suggest separate pathways for lipid scrambling and ion permeation
Reference shape effects on Fourier transform holography
Soft-x-ray holography which utilizes an optics mask fabricated in direct contact with the sample, is a widely applied x-ray microscopy method, in particular, for investigating magnetic samples. The optics mask splits the x-ray beam into a reference wave and a wave to illuminate the sample. The reconstruction quality in such a Fourier-transform holography experiment depends primarily on the characteristics of the reference wave, typically emerging from a small, high-aspect-ratio pinhole in the mask. In this paper, we study two commonly used reference geometries and investigate how their 3D structure affects the reconstruction within an x-ray Fourier holography experiment. Insight into these effects is obtained by imaging the exit waves from reference pinholes via high-resolution coherent diffraction imaging combined with three-dimensional multislice simulations of the x-ray propagation through the reference pinhole. The results were used to simulate Fourier-transform holography experiments to determine the spatial resolution and precise location of the reconstruction plane for different reference geometries. Based on our findings, we discuss the properties of the reference pinholes with view on application in soft-x-ray holography experiments
Observational Study Of the Quasi-Periodic Fast Propagating Magnetosonic Waves and the Associated Flare on 2011 May 30
On 2011 May 30, quasi-periodic fast propagating (QFP) magnetosonic waves
accompanied by a C2.8 flare were directly imaged by the Atomospheric Imaging
Assembly instrument on board the Solar Dynamics Observatory. The QFP waves
successively emanated from the flare kernel, they propagated along a cluster of
open coronal loops with a phase speed of 834 km/s during the flare's rising
phase, and the multiple arc-shaped wave trains can be fitted with a series of
concentric circles. We generate the k-omega diagram of the Fourier power and
find a straight ridge that represents the dispersion relation of the waves.
Along the ridge, we find a lot of prominent nodes which represent the available
frequencies of the QFP waves. On the other hand, the frequencies of the flare
are also obtained by analyzing the flare light curves using the wavelet
technique. The results indicate that almost all the main frequencies of the
flare are consistent with those of the QFP waves. This suggests that the flare
and the QFP waves were possibly excited by a common physical origin. On the
other hand, a few low frequencies revealed by the k-omega diagram can not be
found in the accompanying flare. We propose that these low frequencies were
possibly due to the leakage of the pressure-driven p-mode oscillations from the
photosphere into the low corona, which should be a noticeable mechanism for
driving the QFP waves observed in the corona.Comment: Published in Ap
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