1,301 research outputs found
Top-down Attention Recurrent VLAD Encoding for Action Recognition in Videos
Most recent approaches for action recognition from video leverage deep
architectures to encode the video clip into a fixed length representation
vector that is then used for classification. For this to be successful, the
network must be capable of suppressing irrelevant scene background and extract
the representation from the most discriminative part of the video. Our
contribution builds on the observation that spatio-temporal patterns
characterizing actions in videos are highly correlated with objects and their
location in the video. We propose Top-down Attention Action VLAD (TA-VLAD), a
deep recurrent architecture with built-in spatial attention that performs
temporally aggregated VLAD encoding for action recognition from videos. We
adopt a top-down approach of attention, by using class specific activation maps
obtained from a deep CNN pre-trained for image classification, to weight
appearance features before encoding them into a fixed-length video descriptor
using Gated Recurrent Units. Our method achieves state of the art recognition
accuracy on HMDB51 and UCF101 benchmarks.Comment: Accepted to the 17th International Conference of the Italian
Association for Artificial Intelligenc
Neurocognitive consequences of iatrogenicphthalate exposure during critical illness in children: a study of a development and validation cohort
Dynamics of zz spin correlations in the square-lattice spin-1/2 isotropic XY model
Using the Jordan-Wigner fermionization in two dimensions we obtain the zz
wave vector- and frequency-dependent structure factor for the spin-1/2
isotropic XY model on a spatially anisotropic square lattice. We use the
obtained results to discuss a role of the interchain interaction for the
dynamic properties of quasi-one-dimensional systems.Comment: 9 pages, latex, 3 figure
On the stability of hole crystals in layered cuprates
Recent STM measurements have revealed the existence of periodic charge
modulations at the surface of certain cuprate superconductors. Here we show
that the observed patterns are compatible with the formation of a
three-dimensional crystal of doped holes, with space correlations extending
between different Cu-O layers. This puts severe constraints on the dynamical
stability of the crystallised hole structure, resulting in a close relationship
between the periodicity of the electronic modulation and the interlayer
distance.Comment: completed reference list, fig. 3 corrected; accepted for publication
in Eur. Phys. J. B, Rapid Note
Flow and Noise Control in High Speed and High Reynolds Number Jets Using Plasma Actuators
The idea of manipulating flow to change its characteristics is over a century old. Manipulating instabilities of a jet to increase its mixing and to reduce its radiated noise started in the 1970s. While the effort has been successful in low-speed and low Reynolds number jets, available actuators capabilities in terms of their amplitude, bandwidth, and phasing have fallen short in control of high-speed and high Reynolds number jets of practical interest. Localized arc filament plasma actuators have recently been developed and extensively used at Gas Dynamics and Turbulence Laboratory (GDTL) for control of highspeed and high Reynolds number jets. While the technique has been quite successful and is very promising, all the work up to this point had been carried out using small high subsonic and low supersonic jets from a 2.54 cm diameter nozzle exit with a Reynolds number of about a million. The preliminary work reported in this paper is a first attempt to evaluate the scalability of the technique. The power supply/plasma generator was designed and built in-house at GDTL to operate 8 actuators simultaneously over a large frequency range (0 to 200 kHz) with independent control over phase and duty cycle of each actuator. This allowed forcing the small jet at GDTL with azimuthal modes m = 0, 1, 2, 3, plus or minus 1, plus or minus 2, and plus or minus 4 over a large range of frequencies. This power supply was taken to and used, with minor modifications, at the NASA Nozzle Acoustic Test Rig (NATR). At NATR, 32 actuators were distributed around the 7.5 in. nozzle (a linear increase with nozzle exit diameter would require 60 actuators). With this arrangement only 8 actuators could operate simultaneously, thus limiting the forcing of the jet at NATR to only three azimuthal modes m = plus or minus 1, 4, and 8. Very preliminary results at NATR indicate that the trends observed in the larger NASA facility in terms of the effects of actuation frequency and azimuthal modes are similar in both small GDTL and larger NASA jets. However, the actuation authority seems to fall short in the larger jet at higher Mach numbers, resulting in decreased amplitude response compared to the small jet, which is attributed at this point to the lack of sufficient number of actuators. The preliminary results seem also to suggest that amplitude of actuation tones is similar in both the small and larger jets
Magnetization Measurements of Antiferromagnetic Domains in Sr\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e
The Cu3O4 layer in Sr2Cu3O4Cl2 is a variant of the square CuO2 lattice of the high-temperature superconductors, in which the center of every second plaquette contains an extra Cu2+ ion. Whereas the ordering of the spins in the ground-state and the spin-wave excitations of this frustrated spin system are both well understood, we find peculiar behavior resulting from antiferromagnetic domain walls. Pseudodipolar coupling between the two sets of Cu2+ ions results in a ferromagnetic moment, the direction of which reflects the direction of the antiferromagnetic staggered moment, allowing us to probe the antiferromagnetic domain structure. After an excursion to the high fields (\u3e1 T), as the field is lowered, we observe the growth of domains with ferromagnetic moment perpendicular to the field. This gives rise to a finite domain wall susceptibility at small fields, which diverges near 100 K, indicating a phase transition. We also find that the shape of the sample influences the domain-wall behavior
Effect of the additional second neighbor hopping on the charge dynamics in the t-J model
The effect of the additional second neighbor hopping t' on the charge
dynamics of the t-J model in the underdoped regime is studied within the
fermion-spin theory. The conductivity spectrum of the t-t'-J model shows the
low-energy peak and unusual midinfrared band, while the resistivity exhibits a
nearly temperature linear dependence with deviation at low temperature in the
underdoped regime. Although the qualitative feature of the charge dynamics in
the t-t'-J model is the same as in the case of the t-J model, the additional
second neighbor hopping t' leads to a clear shift of the position of the
midinfrared band to the higher energies in the conductivity spectrum, and
suppress the range of the deviation from the temperature linear dependence in
the resistivity.Comment: 12 pages, five figures are included, accepted for publication in
Phys. Lett. A (2002
Direct Observation of the Quantum Energy Gap in S = 1/2 Tetragonal Cuprate Antiferromagnets
Using an electron spin resonance spectrometer covering a wide range of
frequency and magnetic field, we have measured the low energy excitations of
the S=1/2 tetragonal antiferromagnets, Sr_{2}CuO_{2}Cl_{2} and
Sr_{2}Cu_{3}O_{4}Cl_{2}. Our observation of in-plane energy gaps of order 0.1
meV at zero external magnetic field are consistent with a spin wave
calculation, which includes several kinds of quantum fluctuations that remove
frustration. Results agree with other experiments and with exchange anisotropy
parameters determined from a five band Hubbard model.Comment: 4 pages, 3 figure
Asymmetry of the electron spectrum in hole-doped and electron-doped cuprates
Within the t-t'-J model, the asymmetry of the electron spectrum and
quasiparticle dispersion in hole-doped and electron-doped cuprates is
discussed. It is shown that the quasiparticle dispersions of both hole-doped
and electron-doped cuprates exhibit the flat band around the (\pi,0) point
below the Fermi energy. The lowest energy states are located at the
(\pi/2,\pi/2) point for the hole doping, while they appear at the (\pi,0) point
in the electron-doped case due to the electron-hole asymmetry. Our results also
show that the unusual behavior of the electron spectrum and quasiparticle
dispersion is intriguingly related to the strong coupling between the electron
quasiparticles and collective magnetic excitations.Comment: 8 pages, 3 figures, typo corrected, added detailed calculations and
updated figure 3 and references, accepted for publication in Phys. Lett.
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