168,925 research outputs found
Fast human activity recognition based on structure and motion
This is the post-print version of the final paper published in Pattern Recognition Letters. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2011 Elsevier B.V.We present a method for the recognition of human activities. The proposed approach is based on the construction of a set of templates for each activity as well as on the measurement of the motion in each activity. Templates are designed so that they capture the structural and motion information that is most discriminative among activities. The direct motion measurements capture the amount of translational motion in each activity. The two features are fused at the recognition stage. Recognition is achieved in two steps by calculating the similarity between the templates and motion features of the test and reference activities. The proposed methodology is experimentally assessed and is shown to yield excellent performance.European Commissio
Turbulence control by developing a spiral wave with a periodic signal injection in the complex Ginzburg-Landau equation
Turbulence control in the two-dimensional complex Ginzburg-Landau equation is
investigated. A new approach is proposed for the control purpose. In the
presence of a small spiral wave seed initiation, a fully developed turbulence
can be completely annihilated by injecting a single periodic signal to a small
fixed space area around the spiral wave tip. The control is achieved in a
parameter region where the spiral wave of the uncontrolled system is absolutely
unstable. The robustness, convenience and high control efficiency of this
method is emphasized, and the mechanism underlying these practical advantages
are intuitively understood.Comment: 12 pages, figures can be found in the following journa
Observation of a single atom in a magneto-optical trap
Fluorescence from Cs atoms in a magneto-optical trap is detected under conditions of very low atomic density. Discrete steps are observed in the fluorescent signal versus time and are associated with the arrival and departure of individual trapped atoms. Histograms of the frequency of occurrence of a given level of fluorescence exhibit a series of uniformly spaced peaks that are attributed to the presence of N = 0, 1, 2 atoms in the trap
Oriented gap opening in the magnetically ordered state of Iron-pnicitides: an impact of intrinsic unit cell doubling on the square lattice by atoms
We show that the complicated band reconstruction near Fermi surfaces in the
magnetically ordered state of iron-pnictides observed by angle-resolved
photoemission spectroscopies (ARPES) can be understood in a meanfield level if
the \emph{intrinsic unit cell doubling} due to As atoms is properly considered
as shown in the recently constructed S microscopic effective model. The
(0,) or (,0) col-linear antiferromagnetic (C-AFM) order does not open
gaps between two points at Fermi surfaces linked by the ordered wave vector but
forces a band reconstruction involving four points in unfolded Brillouin zone
(BZ) and gives rise to small pockets or hot spots. The S symmetry naturally
chooses a staggered orbital order over a ferro-orbital order to coexist with
the C-AFM order. These results strongly suggest that the kinematics based on
the S symmetry captures the essential low energy physics of iron-based
superconductors.Comment: 5 figures, 5 page
Evidence for horizon-scale power from CMB polarization
The CMB temperature power spectrum offers ambiguous evidence for the
existence of horizon-scale power in the primordial power spectrum due to
uncertainties in spatial curvature and the physics of cosmic acceleration as
well as the observed low quadrupole. Current polarization data from WMAP
provide evidence for horizon-scale power that is robust to these uncertainties.
Polarization on the largest scales arises mainly from scattering at z<6 when
the universe is fully ionized, making the evidence robust to ionization history
variations at higher redshifts as well. A cutoff in the power spectrum is
limited to C=k_C/10^{-4} Mpc^{-1}<5.2 (95% CL) by polarization, only slightly
weaker than joint temperature and polarization constraints in flat LCDM
(C<4.2). Planck should improve the polarization limit to C<3.6 for any model of
the acceleration epoch and ionization history as well as provide tests for
foreground and systematic contamination.Comment: 4 pages, 2 figures; submitted to Phys. Rev. D (Rapid Communications).
Code for modified reionization in CAMB and CosmoMC available at
http://background.uchicago.edu/camb_rpc
Cognitive Radio from Hell: Flipping Attack on Direct-Sequence Spread Spectrum
In this paper, we introduce a strong adversarial attack, referred to as the
flipping attack, on Direct-Sequence Spread Spectrum (DSSS) systems. In this
attack, the attacker, which is appropriately positioned between the transmitter
and the receiver, instantaneously flips the transmitted symbols in the air at
50% rate, thereby driving the channel capacity to zero. Unlike the traditional
jamming attack, this attack, when perfectly executed, cannot be detected at the
receiver using signal-to-noise-ratio measurements. However, this attack
necessitates the attacker to perfectly know the realizations of all the
channels in the model. We first introduce the consequences of the flipping
attack on narrowband frequency-flat channels, and subsequently discuss its
feasibility in wideband frequency-selective channels. From the legitimate
users' perspective, we present a method to detect this attack and also propose
heuristics to improve the error-performance under the attack. We emphasize that
future cyber-physical systems that employ DSSS should design transceivers to
detect the proposed flipping attack, and then apply appropriate
countermeasures
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