9,622 research outputs found
Computer Analysis of Architecture Using Automatic Image Understanding
In the past few years, computer vision and pattern recognition systems have
been becoming increasingly more powerful, expanding the range of automatic
tasks enabled by machine vision. Here we show that computer analysis of
building images can perform quantitative analysis of architecture, and quantify
similarities between city architectural styles in a quantitative fashion.
Images of buildings from 18 cities and three countries were acquired using
Google StreetView, and were used to train a machine vision system to
automatically identify the location of the imaged building based on the image
visual content. Experimental results show that the automatic computer analysis
can automatically identify the geographical location of the StreetView image.
More importantly, the algorithm was able to group the cities and countries and
provide a phylogeny of the similarities between architectural styles as
captured by StreetView images. These results demonstrate that computer vision
and pattern recognition algorithms can perform the complex cognitive task of
analyzing images of buildings, and can be used to measure and quantify visual
similarities and differences between different styles of architectures. This
experiment provides a new paradigm for studying architecture, based on a
quantitative approach that can enhance the traditional manual observation and
analysis. The source code used for the analysis is open and publicly available
Synthetic gauge potential and effective magnetic field in a Raman medium undergoing molecular modulation
We theoretically demonstrate non-trivial topological effects for a probe
field in a Raman medium undergoing molecular modulation processes. The medium
is driven by two non-collinear pump beams. We show that the angle between the
pumps is related to an effective gauge potential and an effective magnetic
field for the probe field in the synthetic space consisting of a synthetic
frequency dimension and a spatial dimension. As a result of such effective
magnetic field, the probe field can exhibit topologically-protected one-way
edge state in the synthetic space, as well as Landau levels which manifests as
suppression of both diffraction and sideband generation. Our work identifies a
previously unexplored route towards creating topological photonics effects, and
highlights an important connection between topological photonics and nonlinear
optics
A model explaining neutrino masses and the DAMPE cosmic ray electron excess
We propose a flavored neutrino mass and dark matter~(DM) model
to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature
an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only
the first two lepton generations of the Standard Model are charged under the
new gauge symmetry. A vector-like fermion , which is our DM
candidate, annihilates into and via the new gauge boson
exchange and accounts for the DAMPE excess. We have found that the data
favors a mass around 1.5~TeV and a mass around 2.6~TeV, which can
potentially be probed by the next generation lepton colliders and DM direct
detection experiments.Comment: 7 pages, 3 figures. V2: version accepted by Physics Letters
The Correspondence between Convergence Peaks from Weak Lensing and Massive Dark Matter Haloes
The convergence peaks, constructed from galaxy shape measurement in weak
lensing, is a powerful probe of cosmology as the peaks can be connected with
the underlined dark matter haloes. However the capability of convergence peak
statistic is affected by the noise in galaxy shape measurement, signal to noise
ratio as well as the contribution from the projected mass distribution from the
large-scale structures along the line of sight (LOS). In this paper we use the
ray-tracing simulation on a curved sky to investigate the correspondence
between the convergence peak and the dark matter haloes at the LOS. We find
that, in case of no noise and for source galaxies at , more than
peaks with (signal to noise ratio) are related to
more than one massive haloes with mass larger than .
Those massive haloes contribute to high peaks ()
with the remaining contributions are from the large-scale structures. On the
other hand, the peaks distribution is skewed by the noise in galaxy shape
measurement, especially for lower SNR peaks. In the noisy field where the shape
noise is modelled as a Gaussian distribution, about high peaks
() are true peaks and the fraction decreases to for
lower peaks (). Furthermore, we find that high peaks
() are dominated by very massive haloes larger than .Comment: 13 pages, 11 figures, 4 tables, accepted for publication in MNRAS.
Our mock galaxy catalog is available upon request by email to the author
([email protected]
EUCLIA - Exploring the UV/optical continuum lag in active galactic nuclei. I. a model without light echoing
The tight inter-band correlation and the lag-wavelength relation among
UV/optical continua of active galactic nuclei have been firmly established.
They are usually understood within the widespread reprocessing scenario,
however, the implied inter-band lags are generally too small. Furthermore, it
is challenged by new evidences, such as the X-ray reprocessing yields too much
high frequency UV/optical variations as well as it fails to reproduce the
observed timescale-dependent color variations among {\it Swift} lightcurves of
NGC 5548. In a different manner, we demonstrate that an upgraded inhomogeneous
accretion disk model, whose local {\it independent} temperature fluctuations
are subject to a speculated {\it common} large-scale temperature fluctuation,
can intrinsically generate the tight inter-band correlation and lag across
UV/optical, and be in nice agreement with several observational properties of
NGC 5548, including the timescale-dependent color variation. The emergent lag
is a result of the {\it differential regression capability} of local
temperature fluctuations when responding to the large-scale fluctuation. An
average speed of propagations as large as of the speed of light
may be required by this common fluctuation. Several potential physical
mechanisms for such propagations are discussed. Our interesting
phenomenological scenario may shed new light on comprehending the UV/optical
continuum variations of active galactic nuclei.Comment: 18 pages, 8 figures. ApJ accepted. Further comments are very welcome
Transverse Mode Revival of a Light-Compensated Quantum Memory
A long-lived quantum memory was developed based on light-compensated cold
Rb atoms in a dipole trap. The lifetime of the quantum memory was
improved by 40 folds, from 0.67 ms to 28 ms with the help of a compensation
laser beam. Oscillations of the memory efficiency due to the transverse mode
breathing of the singly-excited spin wave have been clearly observed and
clarified with a Monte-Carlo simulation procedure. With detailed analysis of
the decoherence processes of the spin wave in cold atomic ensembles, this
experiment provides a benchmark for the further development of high-quality
quantum memories.Comment: 4 pages, 4 figure
Central engine afterglow of Gamma-ray Bursts
Before 2004, nearly all GRB afterglow data could be understood in the context
of the external shocks model. This situation has changed in the past two years,
when it became clear that some afterglow components should be attributed to the
activity of the central engine; i.e., the {\it central engine afterglow}. We
review here the afterglow emission that is directly related to the GRB central
engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in
pre-{\it Swift} era, has become generally accepted now.Comment: 4 pages including 1 figure. Presented at the conference "Astrophysics
of Compact Objects" (July 1-7, 2007; Huangshan, China
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