43,553 research outputs found
Hamming Compressed Sensing
Compressed sensing (CS) and 1-bit CS cannot directly recover quantized
signals and require time consuming recovery. In this paper, we introduce
\textit{Hamming compressed sensing} (HCS) that directly recovers a k-bit
quantized signal of dimensional from its 1-bit measurements via invoking
times of Kullback-Leibler divergence based nearest neighbor search.
Compared with CS and 1-bit CS, HCS allows the signal to be dense, takes
considerably less (linear) recovery time and requires substantially less
measurements (). Moreover, HCS recovery can accelerate the
subsequent 1-bit CS dequantizer. We study a quantized recovery error bound of
HCS for general signals and "HCS+dequantizer" recovery error bound for sparse
signals. Extensive numerical simulations verify the appealing accuracy,
robustness, efficiency and consistency of HCS.Comment: 33 pages, 8 figure
Inhibition of Connexin43 hemichannels impairs spatial short-term memory without affecting spatial working memory
Astrocytes are active players in higher brain function as they can release gliotransmitters, which are essential for synaptic plasticity. Various mechanisms have been proposed for gliotransmission, including vesicular mechanisms as well as non-vesicular ones, for example by passive diffusion via connexin hemichannels (HCs). We here investigated whether interfering with connexin43 (Cx43) HCs influenced hippocampal spatial memory. We made use of the peptide Gap19 that blocks HCs but not gap junction channels and is specific for Cx43. To this end, we microinfused transactivator of transcription linked Gap19 (TAT-Gap19) into the brain ventricle of male NMRI mice and assessed spatial memory in a Y maze. We found that the in vivo blockade of Cx43 HCs did not affect the locomotor activity or spatial working memory in a spontaneous alternation Y maze task. Cx43 blockade did however significantly impair the spatial short-term memory in a delayed spontaneous alternation Y maze task. These results indicate that Cx43 HCs play a role in spatial short-term memory
Cosmic ray short burst observed with the Global Muon Detector Network (GMDN) on June 22, 2015
We analyze the short cosmic ray intensity increase ("cosmic ray burst": CRB)
on June 22, 2015 utilizing a global network of muon detectors and derive the
global anisotropy of cosmic ray intensity and the density (i.e. the
omnidirectional intensity) with 10-minute time resolution. We find that the CRB
was caused by a local density maximum and an enhanced anisotropy of cosmic rays
both of which appeared in association with Earth's crossing of the heliospheric
current sheet (HCS). This enhanced anisotropy was normal to the HCS and
consistent with a diamagnetic drift arising from the spatial gradient of cosmic
ray density, which indicates that cosmic rays were drifting along the HCS from
the north of Earth. We also find a significant anisotropy along the HCS,
lasting a few hours after the HCS crossing, indicating that cosmic rays
penetrated into the inner heliosphere along the HCS. Based on the latest
geomagnetic field model, we quantitatively evaluate the reduction of the
geomagnetic cut-off rigidity and the variation of the asymptotic viewing
direction of cosmic rays due to a major geomagnetic storm which occurred during
the CRB and conclude that the CRB is not caused by the geomagnetic storm, but
by a rapid change in the cosmic ray anisotropy and density outside the
magnetosphere.Comment: accepted for the publication in the Astrophysical Journa
Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry
We present the first identification in interstellar space of the thioformyl
radical (HCS) and its metastable isomer HSC. These species were detected toward
the molecular cloud L483 thanks to observations carried out with the IRAM 30m
telescope in the 3 mm band. We derive beam-averaged column densities of 7e12
cm-2 for HCS and 1.8e11 cm-2 for HSC, which translate to fractional abundances
relative to H2 of 2e-10 and 6e-12, respectively. Although the amount of sulfur
locked by these radicals is low, their detection allows to put interesting
constraints on the chemistry of sulfur in dark clouds. Interestingly, the
H2CS/HCS abundance ratio is found to be quite low, around 1, in contrast with
the oxygen analogue case, in which the H2CO/HCO abundance ratio is around 10 in
dark clouds. Moreover, the radical HCS is found to be more abundant than its
oxygen analogue, HCO. The metastable species HOC, the oxygen analogue of HSC,
has not been yet observed in space. These observational constraints are
confronted with the outcome of a recent model of the chemistry of sulfur in
dark clouds. The model underestimates the fractional abundance of HCS by at
least one order of magnitude, overestimates the H2CS/HCS abundance ratio, and
does not provide an abundance prediction for the metastable isomer HSC. These
observations should prompt a revision of the chemistry of sulfur in
interstellar clouds.Comment: Accepted for publication in A&A Letter
Topological B-Model on Weighted Projective Spaces and Self-Dual Models in Four Dimensions
It was recently shown by Witten on the basis of several examples that the
topological B-model whose target space is a Calabi-Yau (CY) supermanifold is
equivalent to holomorphic Chern-Simons (hCS) theory on the same supermanifold.
Moreover, for the supertwistor space CP^{3|4} as target space, it has been
demonstrated that hCS theory on CP^{3|4} is equivalent to self-dual N=4 super
Yang-Mills (SYM) theory in four dimensions. We consider as target spaces for
the B-model the weighted projective spaces WCP^{3|2}(1,1,1,1|p,q) with two
fermionic coordinates of weight p and q, respectively - which are CY
supermanifolds for p+q=4 - and discuss hCS theory on them. By using twistor
techniques, we obtain certain field theories in four dimensions which are
equivalent to hCS theory. These theories turn out to be self-dual truncations
of N=4 SYM theory or of its twisted (topological) version.Comment: 12 pages; v2: minor clarification, 3 references added, published
versio
How major depressive disorder affects the ability to decode multimodal dynamic emotional stimuli
Most studies investigating the processing of emotions in depressed patients reported impairments in the decoding of negative emotions. However, these studies adopted static stimuli (mostly stereotypical facial expressions corresponding to basic emotions) which do not reflect the way people experience emotions in everyday life. For this reason, this work proposes to investigate the decoding of emotional expressions in patients affected by Recurrent Major Depressive Disorder (RMDDs) using dynamic audio/video stimuli. RMDDs’ performance is compared with the performance of patients with Adjustment Disorder with Depressed Mood (ADs) and healthy (HCs) subjects. The experiments involve 27 RMDDs (16 with acute depression - RMDD-A, and 11 in a compensation phase - RMDD-C), 16 ADs and 16 HCs. The ability to decode emotional expressions is assessed through an emotion recognition task based on short audio (without video), video (without audio) and audio/video clips. The results show that AD patients are significantly less accurate than HCs in decoding fear, anger, happiness, surprise and sadness. RMDD-As with acute depression are significantly less accurate than HCs in decoding happiness, sadness and surprise. Finally, no significant differences were found between HCs and RMDD-Cs in a compensation phase. The different communication channels and the types of emotion play a significant role in limiting the decoding accuracy
Modeling the Sun's open magnetic flux and the heliospheric current sheet
By coupling a solar surface flux transport model with an extrapolation of the
heliospheric field, we simulate the evolution of the Sun's open magnetic flux
and the heliospheric current sheet (HCS) based on observational data of sunspot
groups since 1976. The results are consistent with measurements of the
interplanetary magnetic field near Earth and with the tilt angle of the HCS as
derived from extrapolation of the observed solar surface field. This opens the
possibility for an improved reconstruction of the Sun's open flux and the HCS
into the past on the basis of empirical sunspot data.Comment: 16 pages, 5 figures, Accepted for publication in Ap
On Supertwistors, the Penrose-Ward Transform and N=4 super Yang-Mills Theory
It was recently shown by Witten that B-type open topological string theory
with the supertwistor space CP^{3|4} as a target space is equivalent to
holomorphic Chern-Simons (hCS) theory on the same space. This hCS theory in
turn is equivalent to self-dual N=4 super Yang-Mills (SYM) theory in four
dimensions. We review the supertwistor description of self-dual and
anti-self-dual N-extended SYM theory as the integrability of super Yang-Mills
fields on complex (2|N)-dimensional superplanes and demonstrate the equivalence
of this description to Witten's formulation. The equivalence of the field
equations of hCS theory on an open subset of CP^{3|N} to the field equations of
self-dual N-extended SYM theory in four dimensions is made explicit.
Furthermore, we extend the picture to the full N=4 SYM theory and, by using the
known supertwistor description of this case, we show that the corresponding
constraint equations are (gauge) equivalent to the field equations of hCS
theory on a quadric in CP^{3|3}xCP^{3|3}.Comment: 48 pages; version to appear in ATM
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