779 research outputs found
The Relation between Solar Eruption Topologies and Observed Flare Features I: Flare Ribbons
In this paper we present a topological magnetic field investigation of seven
two-ribbon flares in sigmoidal active regions observed with Hinode, STEREO, and
SDO. We first derive the 3D coronal magnetic field structure of all regions
using marginally unstable 3D coronal magnetic field models created with the
flux rope insertion method. The unstable models have been shown to be a good
model of the flaring magnetic field configurations. Regions are selected based
on their pre-flare configurations along with the appearance and observational
coverage of flare ribbons, and the model is constrained using pre-flare
features observed in extreme ultraviolet and X-ray passbands. We perform a
topology analysis of the models by computing the squashing factor, Q, in order
to determine the locations of prominent quasi-separatrix layers (QSLs). QSLs
from these maps are compared to flare ribbons at their full extents. We show
that in all cases the straight segments of the two J-shaped ribbons are matched
very well by the flux-rope-related QSLs, and the matches to the hooked segments
are less consistent but still good for most cases. In addition, we show that
these QSLs overlay ridges in the electric current density maps. This study is
the largest sample of regions with QSLs derived from 3D coronal magnetic field
models, and it shows that the magnetofrictional modeling technique that we
employ gives a very good representation of flaring regions, with the power to
predict flare ribbon locations in the event of a flare following the time of
the model
Similarities and Differences In Adolescence-Onset Versus Adulthood-Onset Sexual Abuse Incidents
A sample of males who had first committed sexual offences against children in either adolescence (n= 230; M= 14.0 years, SD= 1.5) or adulthood (n= 280; M= 34.4 years, SD= 11.7) were compared on measures relating to the circumstances of their first known sexual abuse incident. Considerable diversity in the circumstances of these first incidents was observed for both groups. However, adulthood-onset sexual abuse most often occurred following a long-standing familial relationship with a female victim, and in a home setting. The first incident for adolescence-onset offenders also tended to occur in the context of a long-term relationship and against a female child in a home setting, but more commonly against a nonfamilial victim. Adulthood-onset offenders abused older children, were more likely to engage in penetrative sexual behaviors, and went on to abuse over a longer duration than adolescence-onset offenders. Adolescence-onset offences were more likely to be witnessed by a third party. Findings and their implications for prevention are considered from a situational crime prevention perspective. © 2015 Elsevier Ltd
Predicting multiple victim versus single victim sexual abuse: an examination of distal factors and proximal factors associated with the first abuse incident
Official and confidential self-report data on 83 convicted adult male sexual abusers were analysed to examine whether sexual offending progression can be better predicted from distal antecedents, or from proximal antecedents and outcomes associated with the first sexual abuse incident. Fifty-six offenders who sexually abused more than one victim (multiple victim offenders; MVOs) were compared to 27 offenders who sexually abused a single victim only (single victim offenders; SVOs). MVOs were younger at the time of their first sexual abuse incident, and were more likely to first abuse male and non-familial children. With the exception of sexual attraction to male children, no differences were found between the two groups on distal antecedents. Proximal antecedents and outcomes associated with the first sexual abuse incident were significantly related to multiple victim offending. Logistic regression analysis identified the presence of sexual difficulties in the month prior to the first abuse incident, and sexual excitement immediately preceding the first incident, as significant unique predictors. Implications for risk assessment and risk management are discussed, and future research directions proposed
RF-MEMS switch actuation pulse optimization using Taguchi's method
Copyright @ 2011 Springer-VerlagReliability and longevity comprise two of the most important concerns when designing micro-electro-mechanical-systems (MEMS) switches. Forcing the switch to perform close to its operating limits underlies a trade-off between response bandwidth and fatigue life due to the impact force of the cantilever touching its corresponding contact point. This paper presents for first time an actuation pulse optimization technique based on Taguchi’s optimization method to optimize the shape of the actuation pulse of an ohmic RF-MEMS switch in order to achieve better control and switching conditions. Simulation results show significant reduction in impact velocity (which results in less than 5 times impact force than nominal step pulse conditions) and settling time maintaining good switching speed for the pull down phase and almost elimination of the high bouncing phenomena during the release phase of the switch
An Interface Region Imaging Spectrograph first view on Solar Spicules
Solar spicules have eluded modelers and observers for decades. Since the
discovery of the more energetic type II, spicules have become a heated topic
but their contribution to the energy balance of the low solar atmosphere
remains unknown. Here we give a first glimpse of what quiet Sun spicules look
like when observed with NASA's recently launched Interface Region Imaging
Spectrograph (IRIS). Using IRIS spectra and filtergrams that sample the
chromosphere and transition region we compare the properties and evolution of
spicules as observed in a coordinated campaign with Hinode and the Atmospheric
Imaging Assembly. Our IRIS observations allow us to follow the thermal
evolution of type II spicules and finally confirm that the fading of Ca II H
spicules appears to be caused by rapid heating to higher temperatures. The IRIS
spicules do not fade but continue evolving, reaching higher and falling back
down after 500-800 s. Ca II H type II spicules are thus the initial stages of
violent and hotter events that mostly remain invisible in Ca II H filtergrams.
These events have very different properties from type I spicules, which show
lower velocities and no fading from chromospheric passbands. The IRIS spectra
of spicules show the same signature as their proposed disk counterparts,
reinforcing earlier work. Spectroheliograms from spectral rasters also confirm
that quiet Sun spicules originate in bushes from the magnetic network. Our
results suggest that type II spicules are indeed the site of vigorous heating
(to at least transition region temperatures) along extensive parts of the
upward moving spicular plasma.Comment: 6 pages, 4 figures, accepted for publication in ApJ Letters. For
associated movies, see http://folk.uio.no/tiago/iris_spic
Detection of supersonic downflows and associated heating events in the transition region above sunspots
IRIS data allow us to study the solar transition region (TR) with an
unprecedented spatial resolution of 0.33 arcsec. On 2013 August 30, we observed
bursts of high Doppler shifts suggesting strong supersonic downflows of up to
200 km/s and weaker, slightly slower upflows in the spectral lines Mg II h and
k, C II 1336 \AA, Si IV 1394 \AA, and 1403 \AA, that are correlated with
brightenings in the slitjaw images (SJIs). The bursty behavior lasts throughout
the 2 hr observation, with average burst durations of about 20 s. The locations
of these short-lived events appear to be the umbral and penumbral footpoints of
EUV loops. Fast apparent downflows are observed along these loops in the SJIs
and in AIA, suggesting that the loops are thermally unstable. We interpret the
observations as cool material falling from coronal heights, and especially
coronal rain produced along the thermally unstable loops, which leads to an
increase of intensity at the loop footpoints, probably indicating an increase
of density and temperature in the TR. The rain speeds are on the higher end of
previously reported speeds for this phenomenon, and possibly higher than the
free-fall velocity along the loops. On other observing days, similar bright
dots are sometimes aligned into ribbons, resembling small flare ribbons. These
observations provide a first insight into small-scale heating events in
sunspots in the TR.Comment: accepted by ApJ
High-resolution Observations of the Shock Wave Behavior for Sunspot Oscillations with the Interface Region Imaging Spectrograph
We present the first results of sunspot oscillations from observations by the
Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is
identified in both the slit-jaw images and the spectra of several emission
lines formed in the transition region and chromosphere. We first apply a single
Gaussian fit to the profiles of the Mgii 2796.35 {\AA}, Cii 1335.71 {\AA}, and
Si iv 1393.76 {\AA} lines in the sunspot. The intensity change is about 30%.
The Doppler shift oscillation reveals a sawtooth pattern with an amplitude of
about 10 km/s in Si iv. In the umbra the Si iv oscillation lags those of Cii
and Mgii by about 3 and 12 s, respectively. The line width suddenly increases
as the Doppler shift changes from redshift to blueshift. However, we
demonstrate that this increase is caused by the superposition of two emission
components. We then perform detailed analysis of the line profiles at a few
selected locations on the slit. The temporal evolution of the line core is
dominated by the following behavior: a rapid excursion to the blue side,
accompanied by an intensity increase, followed by a linear decrease of the
velocity to the red side. The maximum intensity slightly lags the maximum
blueshift in Si iv, whereas the intensity enhancement slightly precedes the
maximum blueshift in Mgii. We find a positive correlation between the maximum
velocity and deceleration, a result that is consistent with numerical
simulations of upward propagating magnetoacoustic shock waves.Comment: 5 figures, in ApJ. Correction of time lags (correct values are 3 and
12s) made on June 17 201
Homologous Helical Jets: Observations by IRIS, SDO and Hinode and Magnetic Modeling with Data-Driven Simulations
We report on observations of recurrent jets by instruments onboard the
Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory (SDO)
and Hinode spacecrafts. Over a 4-hour period on July 21st 2013, recurrent
coronal jets were observed to emanate from NOAA Active Region 11793. FUV
spectra probing plasma at transition region temperatures show evidence of
oppositely directed flows with components reaching Doppler velocities of +/-
100 km/s. Raster Doppler maps using a Si IV transition region line show all
four jets to have helical motion of the same sense. Simultaneous observations
of the region by SDO and Hinode show that the jets emanate from a source region
comprising a pore embedded in the interior of a supergranule. The parasitic
pore has opposite polarity flux compared to the surrounding network field. This
leads to a spine-fan magnetic topology in the coronal field that is amenable to
jet formation. Time-dependent data-driven simulations are used to investigate
the underlying drivers for the jets. These numerical experiments show that the
emergence of current-carrying magnetic field in the vicinity of the pore
supplies the magnetic twist needed for recurrent helical jet formation.Comment: 15 pages, 10 figures, accepted by Ap
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