39,170 research outputs found
Towards Analyzing Semantic Robustness of Deep Neural Networks
Despite the impressive performance of Deep Neural Networks (DNNs) on various
vision tasks, they still exhibit erroneous high sensitivity toward semantic
primitives (e.g. object pose). We propose a theoretically grounded analysis for
DNN robustness in the semantic space. We qualitatively analyze different DNNs'
semantic robustness by visualizing the DNN global behavior as semantic maps and
observe interesting behavior of some DNNs. Since generating these semantic maps
does not scale well with the dimensionality of the semantic space, we develop a
bottom-up approach to detect robust regions of DNNs. To achieve this, we
formalize the problem of finding robust semantic regions of the network as
optimizing integral bounds and we develop expressions for update directions of
the region bounds. We use our developed formulations to quantitatively evaluate
the semantic robustness of different popular network architectures. We show
through extensive experimentation that several networks, while trained on the
same dataset and enjoying comparable accuracy, do not necessarily perform
similarly in semantic robustness. For example, InceptionV3 is more accurate
despite being less semantically robust than ResNet50. We hope that this tool
will serve as a milestone towards understanding the semantic robustness of
DNNs.Comment: Presented at European conference on computer vision (ECCV 2020)
Workshop on Adversarial Robustness in the Real World (
https://eccv20-adv-workshop.github.io/ ) [best paper award]. The code is
available at https://github.com/ajhamdi/semantic-robustnes
The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines
The galaxy 3C\,316 is the brightest in the radio band among the
optically-selected candidates exhibiting double-peaked narrow optical emission
lines. Observations with the Very Large Array (VLA), Multi-Element Remotely
Linked Interferometer Network (e-MERLIN), and the European VLBI Network (EVN)
at 5\,GHz have been used to study the radio structure of the source in order to
determine the nature of the nuclear components and to determine the presence of
radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent
east-west emission structure with a total extent of about 3 kpc. The EVN image
shows seven discrete compact knots on an S-shaped line. However, none of these
knots could be unambiguously identified as an AGN core. The observations
suggest that the majority of the radio structure belongs to a powerful radio
AGN, whose physical size and radio spectrum classify it as a compact
steep-spectrum source. Given the complex radio structure with radio blobs and
knots, the possibility of a kpc-separation dual AGN cannot be excluded if the
secondary is either a naked core or radio quiet.Comment: 12 pages, 3 figures, 2 tables. Accepted for publication in the MNRA
Four dual AGN candidates observed with the VLBA
According to hierarchical structure formation models, merging galaxies are
expected to be seen in different stages of their coalescence. However,
currently there are no straightforward observational methods neither to select
nor to confirm a large number of dual active galactic nuclei (AGN) candidates.
Most attempts involve the better understanding of double-peaked narrow emission
line sources, to distinguish the objects where the emission lines originate
from narrow-line kinematics or jet-driven outflows from those which might
harbour dual AGN. We observed four such candidate sources with the Very Long
Baseline Array (VLBA) at 1.5 GHz with 10 milli-arcsecond angular
resolution where spectral profiles of AGN optical emission suggested the
existence of dual AGN. In SDSS J210449.13-000919.1 and SDSS J23044.82-093345.3,
the radio structures are aligned with the optical emission features, thus the
double-peaked emission lines might be the results of jet-driven outflows. In
the third detected source SDSS J115523.74+150756.9, the radio structure is less
extended and oriented nearly perpendicular to the position angle derived from
optical spectroscopy. The fourth source remained undetected with the VLBA but
it has been imaged with the Very Large Array at arcsec resolution a few months
before our observations, suggesting the existence of extended radio structure.
In none of the four sources did we detect two radio-emitting cores, a
convincing signature of duality.Comment: 35 pages, 3 figures, 2 tables, accepted for publication in Ap
Resolving the pulsations of subdwarf B stars: HS 0039+4302, HS 0444+0458, and an examination of the group properties of resolved pulsators
We continue our program of single-site observations of pulsating subdwarf B
(sdB) stars and present the results of extensive time series photometry of HS
0039+4302 and HS 0444+0458. Both were observed at MDM Observatory during the
fall of 2005. We extend the number of known frequencies for HS 0039+4302 from 4
to 14 and discover one additional frequency for HS 0444+0458, bringing the
total to three. We perform standard tests to search for multiplet structure,
measure amplitude variations, and examine the frequency density to constrain
the mode degree .
Including the two stars in this paper, 23 pulsating sdB stars have received
follow-up observations designed to decipher their pulsation spectra. It is
worth an examination of what has been detected. We compare and contrast the
frequency content in terms of richness and range and the amplitudes with
regards to variability and diversity. We use this information to examine
observational correlations with the proposed pulsation mechanism as
well as alternative theories.Comment: 32 pages, 18 figures, 7 tables. Accepted for publication in MNRA
The relationship between seasonal changes in anti-oxidative system and freezing tolerance in the leaves of evergreen woody plants of Sabina
AbstractAlthough the relationships between reactive oxygen species (ROS) and membrane damage, between anti-oxidative enzyme activity and chilling tolerance, and between antioxidant concentration and chilling tolerance are well documented, the mechanisms responsible for survival of evergreen woody Sabina plants to survive temperatures below −30 °C are not well understood. In this study, seasonal changes in the activities of the anti-oxidative enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX), as well as levels of ascorbic acid (ASA), glutathione (GSH), proline (Pro), carotenoids (Car) and lipid peroxidation were examined in the leaves of Sabina przewalskii Kom. and Sabina chinensis (Lin.) Ant. Leaves were sampled at monthly intervals from the summer of 2004 to spring of 2005. Anti-oxidative enzyme activities and antioxidant contents were affected by declining temperatures in the autumn (September to October) and winter (November to January) and increasing temperatures in the spring (February to April). Activities of POD, CAT and APX, as well as contents of ASA, GSH, Car and Pro increased with the decrease in temperature. The highest values were found in the winter. In contrast, the leaf content of thiobarbituric acid-reactive substances (TBARS) increased markedly in the autumn and remained relatively constant during the following winter. In the autumn, presumably in anticipation of acclimation during the winter, leaf freezing tolerance was closely correlated with the activities of anti-oxidative enzymes and contents of antioxidants, indicating that anti-oxidative systems in the leaves played an important role in limiting the production of free radicals to protect membrane integrity. Freezing tolerance in evergreen woody plants of Sabina is correlated with an increased capacity to scavenge or detoxify ROS by the anti-oxidative system. ROS accumulated as part of the cold acclimation response may induce anti-oxidative defence systems for the acquisition of freezing tolerance in the leaves. The results also suggested that a better capacity for anti-oxidative defences in S. przewalskii might account for its greater capacity for freezing tolerance than S. chinensis
VLBI observation of the newly discovered z=5.18 quasar SDSS J0131-0321
Few high-redshift, radio-loud quasars are known to date. The extremely
luminous, radio-bright quasar, SDSS J013127.34-032100.1 was recently discovered
at a redshift of . We observed the source with high resolution very
long baseline interferometry (VLBI) at 1.7 GHz with the European VLBI Network
(EVN) and found a single compact radio component. We estimated a lower limit to
the brightness temperature of the detected radio component, T_B~10^{11} K.
Additionaly, when compared to archival radio data, the source showed
significant flux density variation. These two findings are indicative of the
blazar nature of the source.Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter
Parsec-scale jet properties of the gamma-ray quasar 3C 286
The quasar 3C~286 is one of two compact steep spectrum sources detected by
the {\it Fermi}/LAT. Here, we investigate the radio properties of the
parsec(pc)-scale jet and its (possible) association with the -ray
emission in 3C~286. The Very Long Baseline Interferometry (VLBI) images at
various frequencies reveal a one-sided core--jet structure extending to the
southwest at a projected distance of 1 kpc. The component at the jet base
showing an inverted spectrum is identified as the core, with a mean brightness
temperature of ~K. The jet bends at about 600 pc (in
projection) away from the core, from a position angle of to
. Based on the available VLBI data, we inferred the proper motion
speed of the inner jet as mas yr (), corresponding to a jet speed of about at an inclination
angle of between the jet and the line of sight of the observer. The
brightness temperature, jet speed and Lorentz factor are much lower than those
of -ray-emitting blazars, implying that the pc-scale jet in 3C~286 is
mildly relativistic. Unlike blazars in which -ray emission is in
general thought to originate from the beamed innermost jet, the location and
mechanism of -ray emission in 3C~286 may be different as indicated by
the current radio data. Multi-band spectrum fitting may offer a complementary
diagnostic clue of the -ray production mechanism in this source.Comment: 9 pages, 4 figures, accept for publication in MNRA
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