44,473 research outputs found
Chain Reconnections observed in Sympathetic Eruptions
The nature of various plausible causal links between sympathetic events is
still a controversial issue. In this work, we present multi-wavelength
observations of sympathetic eruptions, associated flares and coronal mass
ejections (CMEs) occurring on 2013 November 17 in two close-by active regions.
Two filaments i.e., F1 and F2 are observed in between the active regions.
Successive magnetic reconnections, caused by different reasons (flux
cancellation, shear and expansion) have been identified during the whole event.
The first reconnection occurred during the first eruption via flux cancellation
between the sheared arcades overlying filament F2, creating a flux rope and
leading to the first double ribbon solar flare. During this phase we observed
the eruption of overlaying arcades and coronal loops, which leads to the first
CME. The second reconnection is believed to occur between the expanding flux
rope of F2 and the overlying arcades of the filament F1. We suggest that this
reconnection destabilized the equilibrium of filament F1, which further
facilitated its eruption. The third stage of reconnection occurred in the wake
of the erupting filament F1 between the legs of overlying arcades. This may
create a flux rope and the second double ribbon flare and a second CME. The
fourth reconnection was between the expanding arcades of the erupting filament
F1 and the nearby ambient field, which produced the bi-directional plasma flows
towards both upward and downward. Observations and a nonlinear force-free field
extrapolation confirm the possibility of reconnection and the causal link
between the magnetic systems.Comment: 37 pages, 17 figures, Accepted for publication in Ap
Development of a Geant4 Solid for Stereo Mini-jet Cells in a Cylindrical Drift Chamber
Stereo mini-jet cells will be indispensable components of a future
linear collider central tracker such as JLC-CDC. There is, however, no official
Geant4 solid available at present to describe such geometrical objects, which
had been a major obstacle for us to develop a full Geant4-based simulator with
stereo cells built in. We have thus extended Geant4 to include a new solid
({\tt TwistedTubs}), which consists of three kinds of surfaces: two end planes,
inner and outer hyperboloidal surfaces, and two so-called twisted surfaces that
make slant and twisted -boundaries. Design philosophy and its realization
in the Geant4 framework are described together with algorithmic details. We
have implemented stereo cells with the new solid, and tested them using
geantinos and Pythia events ( at ).
The performance was found reasonable: the stereo cells consumed only 25% more
CPU time than ordinary axial cells.Comment: 24 pages, 15 figures, to be published in Computer Physics
Communication
Use of stereo camera systems for assessment of rockfish abundance in untrawlable areas and for recording pollock behavior during midwater trawls
We describe the application of two types of stereo camera
systems in fisheries research, including the design, calibration, analysis techniques, and precision of the data
obtained with these systems. The first is a stereo video system deployed by using a quick-responding winch with a
live feed to provide species- and size- composition data adequate to produce acoustically based biomass estimates
of rockfish. This system was tested on the eastern Bering Sea slope where rockfish were measured. Rockfish sizes were similar to those sampled with a bottom trawl and the relative error in multiple measurements of the same rockfish in multiple still-frame images was small. Measurement errors of up to 5.5% were found on a calibration target of known size. The second system consisted of a pair of still-image digital cameras mounted
inside a midwater trawl. Processing of the stereo images allowed fish length, fish orientation in relation to the camera platform, and relative distance of the fish to the trawl netting to be determined. The video system was useful for surveying fish in Alaska, but it could also be used
broadly in other situations where it is difficult to obtain species-composition or size-composition information.
Likewise, the still-image system could be used for fisheries research to obtain data on size, position, and
orientation of fish
A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes
Air fluorescence measurements of cosmic ray energy must be corrected for
attenuation of the atmosphere. In this paper we show that the air-showers
themselves can yield a measurement of the aerosol attenuation in terms of
optical depth, time-averaged over extended periods. Although the technique
lacks statistical power to make the critical hourly measurements that only
specialized active instruments can achieve, we note the technique does not
depend on absolute calibration of the detector hardware, and requires no
additional equipment beyond the fluorescence detectors that observe the air
showers. This paper describes the technique, and presents results based on
analysis of 1258 air-showers observed in stereo by the High Resolution Fly's
Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics
Journa
Effects of Coronal Density and Magnetic Field Distributions on a Global Solar EUV Wave
We investigate a global extreme-ultraviolet (EUV) wave associated with a
coronal mass ejection (CME)-driven shock on 2017 September 10. The EUV wave is
transmitted by north- and south-polar coronal holes (CHs), which is observed by
the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations
Observatory A (STEREO-A) from opposite sides of the Sun. We obtain key findings
on how the EUV wave interacts with multiple coronal structures, and on its
connection with the CME-driven shock: (1) the transmitted EUV wave is still
connected with the shock that is incurvated to the Sun, after the shock has
reached the opposite side of the eruption; (2) the south CH transmitted EUV
wave is accelerated inside an on-disk, low-density region with closed magnetic
fields, which implies that an EUV wave can be accelerated in both open and
closed magnetic field regions; (3) part of the primary EUV wavefront turns
around a bright point (BP) with a bipolar magnetic structure when it approaches
a dim, low-density filament channel near the BP; (4) the primary EUV wave is
diffused and apparently halted near the boundaries of remote active regions
(ARs) that are far from the eruption, and no obvious AR related secondary waves
are detected; (5) the EUV wave extends to an unprecedented scale of ~360{\deg}
in latitudes, which is attributed to the polar CH transmission. These results
provide insights into the effects of coronal density and magnetic field
distributions on the evolution of an EUV wave, and into the connection between
the EUV wave and the associated CME-driven shock.Comment: 16 pages, 8 figures, and 3 animations available at
http://doi.org/10.13140/RG.2.2.12408.29442 ,
http://doi.org/10.13140/RG.2.2.25830.06723 , and
http://doi.org/10.13140/RG.2.2.19119.18088 ; published in Ap
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