222 research outputs found
Investigating the Dynamics and Density Evolution of Returning Plasma Blobs from the 2011 June 7 Eruption
This work examines infalling matter following an enormous Coronal Mass
Ejection (CME) on 2011 June 7. The material formed discrete concentrations, or
blobs, in the corona and fell back to the surface, appearing as dark clouds
against the bright corona. In this work we examined the density and dynamic
evolution of these blobs in order to formally assess the intriguing morphology
displayed throughout their descent. The blobs were studied in five wavelengths
(94, 131, 171, 193 and 211 \AA) using the Solar Dynamics Observatory
Atmospheric Imaging Assembly (SDO/AIA), comparing background emission to
attenuated emission as a function of wavelength to calculate column densities
across the descent of four separate blobs. We found the material to have a
column density of hydrogen of approximately 2 10 cm,
which is comparable with typical pre-eruption filament column densities.
Repeated splitting of the returning material is seen in a manner consistent
with the Rayleigh-Taylor instability. Furthermore, the observed distribution of
density and its evolution are also a signature of this instability. By
approximating the three-dimensional geometry (with data from STEREO-A),
volumetric densities were found to be approximately 2 10 g
cm, and this, along with observed dominant length-scales of the
instability, was used to infer a magnetic field of the order 1 G associated
with the descending blobs.Comment: 9 pages, 13 figures, accepted for publication in Ap
Eruption of a Kink-Unstable Filament in Active Region NOAA 10696
We present rapid-cadence Transition Region And Coronal Explorer (TRACE)
observations which show evidence of a filament eruption from active region NOAA
10696, accompanied by an X2.5 flare, on 2004 November 10. The eruptive
filament, which manifests as a fast coronal mass ejection some minutes later,
rises as a kinking structure with an apparently exponential growth of height
within TRACE's field of view. We compare the characteristics of this filament
eruption with MHD numerical simulations of a kink-unstable magnetic flux rope,
finding excellent qualitative agreement. We suggest that, while tether
weakening by breakout-like quadrupolar reconnection may be the release
mechanism for the previously confined flux rope, the driver of the expansion is
most likely the MHD helical kink instability.Comment: Accepted by ApJ Letters. 4 figures (Fig. 3 in two parts). For MPEG
files associated with Figure 1, see:
http://www.mssl.ucl.ac.uk/~drw/papers/kink/ktrace.mpg
http://www.mssl.ucl.ac.uk/~drw/papers/kink/kmdi.mpg
http://www.mssl.ucl.ac.uk/~drw/papers/kink/ksimu.mp
Adversarial Hamiltonian learning of quantum dots in a minimal Kitaev chain
Determining Hamiltonian parameters from noisy experimental measurements is a
key task for the control of experimental quantum systems. An experimental
platform that recently emerged, and where knowledge of Hamiltonian parameters
is crucial to fine-tune the system, is that of quantum dot-based Kitaev chains.
In this work, we demonstrate an adversarial machine learning algorithm to
determine the parameters of a quantum dot-based Kitaev chain. We train a
convolutional conditional generative adversarial neural network (Conv-cGAN)
with simulated differential conductance data and use the model to predict the
parameters at which Majorana bound states are predicted to appear. In
particular, the Conv-cGAN model facilitates a rapid, numerically efficient
exploration of the phase diagram describing the transition between elastic
co-tunneling and crossed Andreev reflection regimes. We verify the theoretical
predictions of the model by applying it to experimentally measured conductance
obtained from a minimal Kitaev chain consisting of two spin-polarized quantum
dots coupled by a superconductor-semiconductor hybrid. Our model accurately
predicts, with an average success probability of \%, whether the
measurement was taken in the elastic co-tunneling or crossed Andreev
reflection-dominated regime. Our work constitutes a stepping stone towards
fast, reliable parameter prediction for tuning quantum-dot systems into
distinct Hamiltonian regimes. Ultimately, our results yield a strategy to
support Kitaev chain tuning that is scalable to longer chains
Detection of Stellar-like Abundance Anomalies in the Slow Solar Wind
The elemental composition of the Sun's hot atmosphere, the corona, shows a distinctive pattern that is different from the underlying surface or photosphere. Elements that are easy to ionize in the chromosphere are enhanced in abundance in the corona compared to their photospheric values. A similar pattern of behavior is often observed in the slow-speed (<500 km s−1) solar wind and in solar-like stellar coronae, while a reversed effect is seen in M dwarfs. Studies of the inverse effect have been hampered in the past because only unresolved (point-source) spectroscopic data were available for these stellar targets. Here we report the discovery of several inverse events observed in situ in the slow solar wind using particle-counting techniques. These very rare events all occur during periods of high solar activity that mimic conditions more widespread on M dwarfs. The detections allow a new way of connecting the slow wind to its solar source and are broadly consistent with theoretical models of abundance variations due to chromospheric fast-mode waves with amplitudes of 8–10 km s−1, sufficient to accelerate the solar wind. The results imply that M-dwarf winds are dominated by plasma depleted in easily ionized elements and lend credence to previous spectroscopic measurements
Absolute-Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib and 13 Type Ic
supernovae (collectively known as stripped-envelope supernovae) are studied by
collecting data on the apparent magnitude, distance, and interstellar
extinction of each event. Weighted and unweighted mean absolute magnitudes of
the combined sample as well as various subsets of the sample are reported. The
limited sample size and the considerable uncertainties, especially those
associated with extinction in the host galaxies, prevent firm conclusions
regarding differences between the absolute magnitudes of supernovae of Type Ib
and Ic, and regarding the existence of separate groups of overluminous and
normal-luminosity stripped-envelope supernovae. The spectroscopic
characteristics of the events of the sample are considered. Three of the four
overluminous events are known to have had unusual spectra. Most but not all of
the normal luminosity events had typical spectra. Light curves of
stripped-envelope supernovae are collected and compared. Because SN 1994I in
M51 was very well observed it often is regarded as the prototypical Type Ic
supernova, but it has the fastest light curve in the sample. Light curves are
modeled by means of a simple analytical technique that, combined with a
constraint on E/M from spectroscopy, yields internally consistent values of
ejected mass, kinetic energy, and nickel mass.Comment: 39 pages, 14 figures, 7 tables; Accepted to A
Understanding the Relationship between Solar Coronal Abundances and F10.7 cm Radio Emission
Sun-as-a-star coronal plasma composition, derived from full-Sun spectra, and the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r = 0.88) during solar cycle 24. However, this correlation becomes nonlinear during increased solar magnetic activity. Here we use cotemporal, high spatial resolution, multiwavelength images of the Sun to investigate the underlying causes of the nonlinearity between coronal composition (FIP bias) and F10.7 solar index correlation. Using the Karl G. Jansky Very Large Array, Hinode/EIS (EUV Imaging Spectrometer), and the Solar Dynamics Observatory, we observed a small active region, AR 12759, throughout the solar atmosphere from the photosphere to the corona. The results of this study show that the magnetic field strength (flux density) in active regions plays an important role in the variability of coronal abundances, and it is likely the main contributing factor to this nonlinearity during increased solar activity. Coronal abundances above cool sunspots are lower than in dispersed magnetic plage regions. Strong magnetic concentrations are associated with stronger F10.7 cm gyroresonance emission. Considering that as the solar cycle moves from minimum to maximum, the sizes of sunspots and their field strength increase with the gyroresonance component, the distinctly different tendencies of radio emission and coronal abundances in the vicinity of sunspots is the likely cause of saturation of Sun-as-a-star coronal abundances during solar maximum, while the F10.7 index remains well correlated with the sunspot number and other magnetic field proxies
Pro-Apoptotic Apoptosis Protease–Activating Factor 1 (Apaf-1) Has a Cytoplasmic Localization Distinct from Bcl-2 or Bcl-XL
How Bcl-2 and its pro-survival relatives prevent activation of the caspases that mediate apoptosis is unknown, but they appear to act through the caspase activator apoptosis protease–activating factor 1 (Apaf-1). According to the apoptosome model, the Bcl-2–like proteins preclude Apaf-1 activity by sequestering the protein. To explore Apaf-1 function and to test this model, we generated monoclonal antibodies to Apaf-1 and used them to determine its localization within diverse cells by subcellular fractionation and confocal laser scanning microscopy. Whereas Bcl-2 and Bcl-xL were prominent on organelle membranes, endogenous Apaf-1 was cytosolic and did not colocalize with them, even when these pro-survival proteins were overexpressed or after apoptosis was induced. Immunogold electron microscopy confirmed that Apaf-1 was dispersed in the cytoplasm and not on mitochondria or other organelles. After the death stimuli, Bcl-2 and Bcl-xL precluded the release of the Apaf-1 cofactor cytochrome c from mitochondria and the formation of larger Apaf-1 complexes, which are steps that presage apoptosis. However, neither Bcl-2 nor Bcl-xL could prevent the in vitro activation of Apaf-1 induced by the addition of exogenous cytochrome c. Hence, rather than sequestering Apaf-1 as proposed by the apoptosome model, Bcl-2–like proteins probably regulate Apaf-1 indirectly by controlling upstream events critical for its activation
Understanding the Relationship between Solar Coronal Abundances and F10.7 cm Radio Emission
Sun-as-a-star coronal plasma composition, derived from full-Sun spectra, and
the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r =
0.88) during solar cycle 24. However, this correlation becomes nonlinear during
increased solar magnetic activity. Here, we use co-temporal, high spatial
resolution, multi-wavelength images of the Sun to investigate the underlying
causes of the non-linearity between coronal composition (FIP bias) and F10.7
solar index correlation. Using the Karl G. Jansky Very Large Array (JVLA),
Hinode/EIS (EUV Imaging Spectrometer), and the Solar Dynamic Observatory (SDO),
we observed a small active region, AR 12759, throughout the solar atmosphere
from the photosphere to the corona. Results of this study show that the
magnetic field strength (flux density) in active regions plays an important
role in the variability of coronal abundances, and it is likely the main
contributing factor to this non-linearity during increased solar activity.
Coronal abundances above cool sunspots are lower than in dispersed magnetic
plage regions. Strong magnetic concentrations are associated with stronger
F10.7 cm gyroresonance emission. Considering that as the solar cycle moves from
minimum to maximum, the size of sunspots and their field strength increase with
gyroresonance component, the distinctly different tendencies of radio emission
and coronal abundances in the vicinity of sunspots is the likely cause of
saturation of Sun-as-a-star coronal abundances during solar maximum, while the
F10.7 index remains well correlated with the sunspot number and other magnetic
field proxies.Comment: 15 pages, 5 figures, 2 tables, accepted for publication in The
Astrophysical Journa
Effects of ethical leadership on emotional exhaustion in high moral intensity situations
© 2015 Elsevier Inc. Emotional exhaustion is a threat to standard operations, particularly in organizations in which physical safety is at risk. High moral intensity is inherent in such organizations due to the magnitude of consequences associated with ethical/unethical conduct. The authors proposed a psychological process in which ethical leadership affects emotional exhaustion directly and indirectly through team cohesion. As military operational contexts typically are (or frequently have the potential to become) high moral intensity situations, the authors tested their model among 338 military personnel deployed in combat zones. They found that: (1) team cohesion partially mediated the relationship between ethical leadership and emotional exhaustion, and (2) this psychological process of direct and indirect effects of ethical leadership did not hold among individuals approaching the low end of conscientiousness
- …