571 research outputs found
Enhancing real-time human detection based on histograms of oriented gradients
In this paper we propose a human detection framework based on an enhanced version of Histogram of Oriented Gradients (HOG) features. These feature descriptors are computed with the help of a precalculated histogram of square-blocks. This novel method outperforms the integral of oriented histograms allowing the calculation of a single feature four times faster. Using Adaboost for HOG feature selection and Support Vector Machine as weak classifier, we build up a real-time human classifier with an excellent detection rate.Peer Reviewe
Are the renormalized band widths in TTF-TCNQ of structural or electronic origin? - An angular dependent NEXAFS study
We have performed angle-dependent near-edge x-ray absorption fine structure
measurements in the Auger electron yield mode on the correlated
quasi-one-dimensional organic conductor TTF-TCNQ in order to determine the
orientation of the molecules in the topmost surface layer. We find that the
tilt angles of the molecules with respect to the one-dimensional axis are
essentially the same as in the bulk. Thus we can rule out surface relaxation as
the origin of the renormalized band widths which were inferred from the
analysis of photoemission data within the one-dimensional Hubbard model.
Thereby recent theoretical results are corroborated which invoke long-range
Coulomb repulsion as alternative explanation to understand the spectral
dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.Comment: 6 pages, 5 figure
Time resolved X ray absorption spectroscopy of infrared laser induced temperature jumps in liquid water
A time resolved X ray absorption study of the structural dynamics of liquid water on a picosecond timescale is presented. We apply femtosecond midinfrared pulses to resonantly excite the intramolecular O H stretching band of liquid water and monitor the transient response in the oxygen K edge absorption spectrum with picosecond X ray pulses. In this way, structural changes in the hydrogen bond network of liquid water upon an ultrafast temperature jump of approximately 20 K are investigated. The changes of the X ray absorption as induced by such a temperature jump are about 3.2 . This demonstrates that our method serves as a sensitive probe of transient structural changes in liquid water and that combined infrared laser synchrotron experiments with substantially shorter X ray pulses, such as generated with a femtosecond slicing scheme, are possibl
General-Sum Multi-Agent Continuous Inverse Optimal Control
IEEE Modelling possible future outcomes of robot-human interactions is of importance in the intelligent vehicle and mobile robotics domains. Knowing the reward function that explains the observed behaviour of a human agent is advantageous for modelling the behaviour with Markov Decision Processes (MDPs). However, learning the rewards that determine the observed actions from data is complicated by interactions. We present a novel inverse reinforcement learning(IRL) algorithm that can infer the reward function in multi-agent interactive scenarios. In particular, the agents may act boundedly rational (i.e., sub-optimal), a characteristic that is typical for human decision making. Additionally, every agent optimizes its own reward function which makes it possible to address non-cooperative setups. In contrast to other methods, the algorithm does not rely on reinforcement learning during inference of the parameters of the reward function. We demonstrate that our proposed method accurately infers the ground truth reward function in two-agent interactive experiments
Simple proof of gauge invariance for the S-matrix element of strong-field photoionization
The relationship between the length gauge (LG) and the velocity gauge (VG)
exact forms of the photoionization probability amplitude is considered. Our
motivation for this paper comes from applications of the Keldysh-Faisal-Reiss
(KFR) theory, which describes atoms (or ions) in a strong laser field (in the
nonrelativistic approach, in the dipole approximation). On the faith of a
certain widely-accepted assumption, we present a simple proof that the
well-known LG form of the exact photoionization (or photodetachment)
probability amplitude is indeed the gauge-invariant result. In contrast, to
obtain the VG form of this probability amplitude, one has to either (i) neglect
the well-known Goeppert-Mayer exponential factor (which assures gauge
invariance) during all the time evolution of the ionized electron or (ii) put
some conditions on the vector potential of the laser field.Comment: The paper was initially submitted (in a previous version) on 16
October 2006 to J. Phys. A and rejected. This is the extended version (with 2
figures), which is identical to the paper published online on 12 December
2007 in Physica Script
Logarithmic two-loop corrections to the Lamb shift in hydrogen
Higher order logarithmic corrections to the
hydrogen Lamb shift are calculated. The results obtained show the two-loop
contribution has a very peculiar behavior, and significantly alter the
theoretical predictions for low lying S-states.Comment: 14 pages, including 2 figures, submitted to Phys. Rev. A, updated
with minor change
Decay versus survival of a localized state subjected to harmonic forcing: exact results
We investigate the survival probability of a localized 1-d quantum particle
subjected to a time dependent potential of the form with
or . The particle is
initially in a bound state produced by the binding potential . We
prove that this probability goes to zero as for almost all values
of , , and . The decay is initially exponential followed by a
law if is not close to resonances and is small; otherwise
the exponential disappears and Fermi's golden rule fails. For exceptional sets
of parameters and the survival probability never decays to zero,
corresponding to the Floquet operator having a bound state. We show similar
behavior even in the absence of a binding potential: permitting a free particle
to be trapped by harmonically oscillating delta function potential
Time evolution of non-Hermitian Hamiltonian systems
We provide time-evolution operators, gauge transformations and a perturbative
treatment for non-Hermitian Hamiltonian systems, which are explicitly
time-dependent. We determine various new equivalence pairs for Hermitian and
non-Hermitian Hamiltonians, which are therefore pseudo-Hermitian and in
addition in some cases also invariant under PT-symmetry. In particular, for the
harmonic oscillator perturbed by a cubic non-Hermitian term, we evaluate
explicitly various transition amplitudes, for the situation when these systems
are exposed to a monochromatic linearly polarized electric field.Comment: 25 pages Latex, 1 eps figure, references adde
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