11,059 research outputs found
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Shock wave boundary layer interaction studied by high-speed schlieren
Shock wave boundary layer interactions at compression ramps have been examined by high-speed schlieren. A total of six ramps with angles ranging from 20 deg to 30 deg, the ramp angle effect on the SWBLI is thus studied. The present high-speed schlieren with a frame rate of 20 kHz generates a large ensemble of 9000 images, which secures the convergence of the statistics of the schlieren intensity. The rms of the schlieren intensity is of great interest, as it enables visualisation of the flow features that are not observable in the raw schlieren images, such as the corner separation/low momentum region, the spot of strong flow unsteadiness right after the shock wave and the location of the peak fluctuation over the ramp. Through the present systematic experimental investigation of SWBLI, the highspeed schlieren is demonstrated to be of great capability for SWBLI study
Automatic Concept Discovery from Parallel Text and Visual Corpora
Humans connect language and vision to perceive the world. How to build a
similar connection for computers? One possible way is via visual concepts,
which are text terms that relate to visually discriminative entities. We
propose an automatic visual concept discovery algorithm using parallel text and
visual corpora; it filters text terms based on the visual discriminative power
of the associated images, and groups them into concepts using visual and
semantic similarities. We illustrate the applications of the discovered
concepts using bidirectional image and sentence retrieval task and image
tagging task, and show that the discovered concepts not only outperform several
large sets of manually selected concepts significantly, but also achieves the
state-of-the-art performance in the retrieval task.Comment: To appear in ICCV 201
Multiplicity one theorems: the Archimedean case
Let be one of the classical Lie groups \GL_{n+1}(\R), \GL_{n+1}(\C),
\oU(p,q+1), \oO(p,q+1), \oO_{n+1}(\C), \SO(p,q+1), \SO_{n+1}(\C), and
let be respectively the subgroup \GL_{n}(\R), \GL_{n}(\C), \oU(p,q),
\oO(p,q), \oO_n(\C), \SO(p,q), \SO_n(\C), embedded in in the
standard way. We show that every irreducible Casselman-Wallach representation
of occurs with multiplicity at most one in every irreducible
Casselman-Wallach representation of . Similar results are proved for the
Jacobi groups \GL_{n}(\R)\ltimes \oH_{2n+1}(\R), \GL_{n}(\C)\ltimes
\oH_{2n+1}(\C), \oU(p,q)\ltimes \oH_{2p+2q+1}(\R), \Sp_{2n}(\R)\ltimes
\oH_{2n+1}(\R), \Sp_{2n}(\C)\ltimes \oH_{2n+1}(\C), with their respective
subgroups \GL_{n}(\R), \GL_{n}(\C), \oU(p,q), \Sp_{2n}(\R),
\Sp_{2n}(\C).Comment: To appear in Annals of Mathematic
The Accretion Wind Model of the Fermi Bubbles (II): Radiation
In a previous work, we have shown that the formation of the Fermi bubbles can
be due to the interaction between winds launched from the hot accretion flow in
Sgr A* and the interstellar medium (ISM). In that work, we focus only on the
morphology. In this paper we continue our study by calculating the gamma-ray
radiation. Some cosmic ray protons (CRp) and electrons must be contained in the
winds, which are likely formed by physical processes such as magnetic
reconnection. We have performed MHD simulations to study the spatial
distribution of CRp, considering the advection and diffusion of CRp in the
presence of magnetic field. We find that a permeated zone is formed just
outside of the contact discontinuity between winds and ISM, where the
collisions between CRp and thermal nuclei mainly occur. The decay of neutral
pions generated in the collisions, combined with the inverse Compton scattering
of background soft photons by the secondary leptons generated in the collisions
and primary CR electrons can well explain the observed gamma-ray spectral
energy distribution. Other features such as the uniform surface brightness
along the latitude and the boundary width of the bubbles are also explained.
The advantage of this accretion wind model is that the adopted wind properties
come from the detailed small scale MHD numerical simulation of accretion flows
and the value of mass accretion rate has independent observational evidences.
The success of the model suggests that we may seriously consider the
possibility that cavities and bubbles observed in other contexts such as galaxy
clusters may be formed by winds rather than jets.Comment: 13 pages,6 figures, accepted for publication in Ap
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Pharmaceutical and personal care products-induced stress symptoms and detoxification mechanisms in cucumber plants.
Contamination of agricultural soils by pharmaceutical and personal care products (PPCPs) resulting from the application of treated wastewater, biosolids and animal wastes constitutes a potential environmental risk in many countries. To date a handful of studies have considered the phytotoxicity of individual PPCPs in crop plants, however, little is known about the effect of PPCPs as mixtures at environmentally relevant levels. This study investigated the uptake and transport, physiological responses and detoxification of a mixture of 17 PPCPs in cucumber seedlings. All PPCPs were detected at higher concentrations in roots compared to leaves, with root activity inhibited in a dose-dependent manner. At 5-50 μg/L, the mature leaves exhibited burnt edges as well as a reduction in photosynthesis pigments. Reactive oxygen species (ROS) production and lipid peroxidation increased with increasing PPCP concentrations; and their contents were greater in roots than in leaves for all PPCP treatments. Enzymes involved in various functions, including oxidative stress (superoxide dismutase and ascorbate peroxidase) and xenobiotic metabolism (peroxidase and glutathione S-transferase), were elevated to different levels depending on the PPCP concentration. Glutathione content gradually increased in leaves, while a maxima occurred at 0.5 μg L-1 PPCPs in roots, followed by a decrease thereafter. This study illustrated the complexity of phytotoxicity after exposure to PPCP mixtures, and provided insights into the molecular mechanisms likely responsible for the detoxification of PPCPs in higher plants
Modulated Unit-Norm Tight Frames for Compressed Sensing
In this paper, we propose a compressed sensing (CS) framework that consists
of three parts: a unit-norm tight frame (UTF), a random diagonal matrix and a
column-wise orthonormal matrix. We prove that this structure satisfies the
restricted isometry property (RIP) with high probability if the number of
measurements for -sparse signals of length
and if the column-wise orthonormal matrix is bounded. Some existing structured
sensing models can be studied under this framework, which then gives tighter
bounds on the required number of measurements to satisfy the RIP. More
importantly, we propose several structured sensing models by appealing to this
unified framework, such as a general sensing model with arbitrary/determinisic
subsamplers, a fast and efficient block compressed sensing scheme, and
structured sensing matrices with deterministic phase modulations, all of which
can lead to improvements on practical applications. In particular, one of the
constructions is applied to simplify the transceiver design of CS-based channel
estimation for orthogonal frequency division multiplexing (OFDM) systems.Comment: submitted to IEEE Transactions on Signal Processin
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