3,086 research outputs found
Reconstructing propagation networks with natural diversity and identifying hidden sources
Our ability to uncover complex network structure and dynamics from data is
fundamental to understanding and controlling collective dynamics in complex
systems. Despite recent progress in this area, reconstructing networks with
stochastic dynamical processes from limited time series remains to be an
outstanding problem. Here we develop a framework based on compressed sensing to
reconstruct complex networks on which stochastic spreading dynamics take place.
We apply the methodology to a large number of model and real networks, finding
that a full reconstruction of inhomogeneous interactions can be achieved from
small amounts of polarized (binary) data, a virtue of compressed sensing.
Further, we demonstrate that a hidden source that triggers the spreading
process but is externally inaccessible can be ascertained and located with high
confidence in the absence of direct routes of propagation from it. Our approach
thus establishes a paradigm for tracing and controlling epidemic invasion and
information diffusion in complex networked systems.Comment: 20 pages and 5 figures. For Supplementary information, please see
http://www.nature.com/ncomms/2014/140711/ncomms5323/full/ncomms5323.html#
Discovery of six high-redshift quasars with the Lijiang 2.4m telescope and the Multiple Mirror Telescope
Quasars with redshifts greater than 4 are rare, and can be used to probe the
structure and evolution of the early universe. Here we report the discovery of
six new quasars with -band magnitudes brighter than 19.5 and redshifts
between 2.4 and 4.6 from the YFOSC spectroscopy of the Lijiang 2.4m telescope
in February, 2012. These quasars are in the list of quasar candidates
selected by using our proposed criterion and the photometric redshift
estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine
candidates were observed by YFOSC, and five among six new quasars were
identified as quasars. One of the other three objects was identified as
a star and the other two were unidentified due to the lower signal-to-noise
ratio of their spectra. This is the first time that quasars have been
discovered using a telescope in China. Thanks to the Chinese Telescope Access
Program (TAP), the redshift of 4.6 for one of these quasars was confirmed by
the Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum and
emission line properties of these six quasars, as well as their central black
hole masses and Eddington ratios, were obtained.Comment: 7 pages, 2 figures, published in Research in Astronomy and
Astrophysics (RAA) as a lette
Accurate and Fast Compressed Video Captioning
Existing video captioning approaches typically require to first sample video
frames from a decoded video and then conduct a subsequent process (e.g.,
feature extraction and/or captioning model learning). In this pipeline, manual
frame sampling may ignore key information in videos and thus degrade
performance. Additionally, redundant information in the sampled frames may
result in low efficiency in the inference of video captioning. Addressing this,
we study video captioning from a different perspective in compressed domain,
which brings multi-fold advantages over the existing pipeline: 1) Compared to
raw images from the decoded video, the compressed video, consisting of
I-frames, motion vectors and residuals, is highly distinguishable, which allows
us to leverage the entire video for learning without manual sampling through a
specialized model design; 2) The captioning model is more efficient in
inference as smaller and less redundant information is processed. We propose a
simple yet effective end-to-end transformer in the compressed domain for video
captioning that enables learning from the compressed video for captioning. We
show that even with a simple design, our method can achieve state-of-the-art
performance on different benchmarks while running almost 2x faster than
existing approaches. Code is available at https://github.com/acherstyx/CoCap
Nematic topological superconducting phase in Nb-doped Bi2Se3
A nematic topological superconductor has an order parameter symmetry, which
spontaneously breaks the crystalline symmetry in its superconducting state.
This state can be observed, for example, by thermodynamic or upper critical
field experiments in which a magnetic field is rotated with respect to the
crystalline axes. The corresponding physical quantity then directly reflects
the symmetry of the order parameter. We present a study on the superconducting
upper critical field of the Nb-doped topological insulator NbxBi2Se3 for
various magnetic field orientations parallel and perpendicular to the basal
plane of the Bi2Se3 layers. The data were obtained by two complementary
experimental techniques, magnetoresistance and DC magnetization, on three
different single crystalline samples of the same batch. Both methods and all
samples show with perfect agreement that the in-plane upper critical fields
clearly demonstrate a two-fold symmetry that breaks the three-fold crystal
symmetry. The two-fold symmetry is also found in the absolute value of the
magnetization of the initial zero-field-cooled branch of the hysteresis loop
and in the value of the thermodynamic contribution above the irreversibility
field, but also in the irreversible properties such as the value of the
characteristic irreversibility field and in the width of the hysteresis loop.
This provides strong experimental evidence that Nb-doped Bi2Se3 is a nematic
topological superconductor similar to the Cu- and Sr-doped Bi2Se3
Virus-like particle secretion and genotype-dependent immunogenicity of dengue virus serotype 2 DNA vaccine
Dengue virus (DENV), composed of four distinct serotypes, is the most important and rapidly emerging arthropod-borne pathogen and imposes substantial economic and public health burdens. We constructed candidate vaccines containing the DNA of five of the genotypes of dengue virus serotype 2 (DENV-2) and evaluated the immunogenicity, the neutralizing (Nt) activity of the elicited antibodies, and the protective efficacy elicited in mice immunized with the vaccine candidates. We observed a significant correlation between the level of in vitro virus-like particle secretion, the elicited antibody response, and the protective efficacy of the vaccines containing the DNA of the different DENV genotypes in immunized mice. However, higher total IgG antibody levels did not always translate into higher Nt antibodies against homologous and heterologous viruses. We also found that, in contrast to previous reports, more than 50% of total IgG targeted ectodomain III (EDIII) of the E protein, and a substantial fraction of this population was interdomain highly neutralizing flavivirus subgroup-cross-reactive antibodies, such as monoclonal antibody 1B7-5. In addition, the lack of a critical epitope(s) in the Sylvatic genotype virus recognized by interdomain antibodies could be the major cause of the poor protection of mice vaccinated with the Asian 1 genotype vaccine (pVD2-Asian 1) from lethal challenge with virus of the Sylvatic genotype. In conclusion, although the pVD2-Asian 1 vaccine was immunogenic, elicited sufficient titers of Nt antibodies against all DENV-2 genotypes, and provided 100% protection against challenge with virus of the homologous Asian 1 genotype and virus of the heterologous Cosmopolitan genotype, it is critical to monitor the potential emergence of Sylvatic genotype viruses, since vaccine candidates under development may not protect vaccinated humans from these viruses
Masked Spatio-Temporal Structure Prediction for Self-supervised Learning on Point Cloud Videos
Recently, the community has made tremendous progress in developing effective
methods for point cloud video understanding that learn from massive amounts of
labeled data. However, annotating point cloud videos is usually notoriously
expensive. Moreover, training via one or only a few traditional tasks (e.g.,
classification) may be insufficient to learn subtle details of the
spatio-temporal structure existing in point cloud videos. In this paper, we
propose a Masked Spatio-Temporal Structure Prediction (MaST-Pre) method to
capture the structure of point cloud videos without human annotations. MaST-Pre
is based on spatio-temporal point-tube masking and consists of two
self-supervised learning tasks. First, by reconstructing masked point tubes,
our method is able to capture the appearance information of point cloud videos.
Second, to learn motion, we propose a temporal cardinality difference
prediction task that estimates the change in the number of points within a
point tube. In this way, MaST-Pre is forced to model the spatial and temporal
structure in point cloud videos. Extensive experiments on MSRAction-3D,
NTU-RGBD, NvGesture, and SHREC'17 demonstrate the effectiveness of the proposed
method.Comment: Accepted by ICCV 202
GRB 120422A: A Low-luminosity Gamma-ray Burst Driven by Central Engine
GRB 120422A is a low-luminosity Gamma-ray burst (GRB) associated with a
bright supernova, which distinguishes itself by its relatively short T90 ~ 5 s
and an energetic X-ray tail. We analyze the Swift BAT and XRT data and discuss
the physical implications. We show that the early steep decline in the X-ray
light curve can be interpreted as the curvature tail of a late emission episode
around 58-86 s, with a curved instantaneous spectrum at the end of the emission
episode. Together with the main activity in the first ~ 20 s and the weak
emission from 40 s to 60 s, the prompt emission is variable, which points
towards a central engine origin, in contrast to the shock breakout origin as
invoked to interpret some other nearby low-luminosity supernova GRBs. The
curvature effect interpretation and interpreting the early shallow decay as the
coasting external forward shock emission in a wind medium both give a
constraint on the bulk Lorentz factor \Gamma to be around several. Comparing
the properties of GRB 120422A and other supernova GRBs, we found that the main
criterion to distinguish engine-driven GRBs from the shock breakout GRBs is the
time-averaged luminosity, with a separation line of about ~ 10^48 erg s^-1.Comment: ApJ accepted version; 6 pages, 1 table, 5 figures; minor changes;
references update
Exploring dark matter spike distribution around the Galactic centre with stellar orbits
Precise measurements of the stellar orbits around Sagittarius A* have
established the existence of a supermassive black hole (SMBH) at the Galactic
centre (GC). Due to the interplay between the SMBH and dark matter (DM), the DM
density profile in the innermost region of the Galaxy, which is crucial for the
DM indirect detection, is still an open question. Among the most popular models
in the literature, the theoretical spike profile proposed by Gondolo and Silk
(1999; GS hereafter) is well adopted. In this work, we investigate the DM spike
profile using updated data from the Keck and VLT telescopes considering that
the presence of such an extended mass component may affect the orbits of the
S-stars in the Galactic center. We examine the radius and slope of the
generalized NFW spike profile, analyze the Einasto spike, and discuss the
influence of DM annihilation on the results. Our findings indicate that an
initial slope of for the generalized NFW spike profile is
ruled out at a 95% confidence level. Additionally, the spike radius larger than 21.5 pc is rejected at 95% probability for the Einasto spike
with , which also contradicts the GS spike model. The constraints
with the VLT/GRAVITY upper limits are also projected. Although the GS NFW spike
is well constrained by the Keck and VLT observation of S2, an NFW spike with a
weak annihilation cusp may still be viable, as long as the DM annihilation
cross section satisfies \left \gtrsim 7.7\times
10^{-27}~{\rm cm^3\,s^{-1}} (m_{\rm DM}/100~{\rm GeV}) at 95% level.Comment: 12 pages, 10 figures and 1 table. Accepted for publication in MNRA
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