1,411 research outputs found
Overlapping Coalition Formation for Efficient Data Fusion in Multi-Sensor Networks
This paper develops new algorithms for coalition formation within multi-sensor networks tasked with performing wide-area surveillance. Specifically, we cast this application as an instance of coalition formation, with overlapping coalitions. We show that within this application area sub-additive coalition valuations are typical, and we thus use this structural property of the problem to we derive two novel algorithms (an approximate greedy one that operates in polynomial time and has a calculated bound to the optimum, and an optimal branch-and-bound one) to find the optimal coalition structure in this instance. We empirically evaluate the performance of these algorithms within a generic model of a multi-sensor network performing wide area surveillance. These results show that the polynomial algorithm typically generated solutions much closer the optimal than the theoretical bound, and prove the effectiveness of our pruning procedure
Input-output relations at dispersing and absorbing planar multilayers for the quantized electromagnetic field containing evanescent components
By using the Green-function concept of quantization of the electromagnetic
field in dispersing and absorbing media, the quantized field in the presence of
a dispersing and absorbing dielectric multilayer plate is studied.
Three-dimensional input-output relations are derived for both amplitude
operators in the -space and the field operators in the coordinate
space. The conditions are discussed, under which the input-output relations can
be expressed in terms of bosonic operators. The theory applies to both
(effectively) free fields and fields, created by active atomic sources inside
and/or outside the plate, including also evanescent-field components.Comment: 14 pages, 1 figur
Nodal Spin Density Wave and band topology of the FeAs based materials
The recently discovered FeAs-based materials exhibit a Spin Density
Wave (SDW) in the undoped state, which gives way to superconductivity upon
doping. Here we show that due to an interesting topological feature of the band
structure, the SDW state cannot acquire a full gap. This is demonstrated within
the SDW mean-field theory of both a simplified two band model and a more
realistic 5-band model. The positions of the nodes are different in the two
models and can be used to detected the validity of each model.Comment: rewritten for clarit
Checkerboard charge density wave and pseudogap in high- cuprates
We consider the scenario where a 4-lattice constant, rotationally symmetric
charge density wave (CDW) is present in the underdoped cuprates. We prove a
theorem that puts strong constraint on the possible form factor of such a CDW.
We demonstrate, within mean-field theory, that a particular form factor within
the allowed class describes the angle-resolved photoemission and scan tunneling
spectroscopy well. We conjecture that the ``large pseudogap'' in cuprates is
the consequence of this type of charge density wave.Comment: We add a new section II on the symmetry property of the checkerboard
CD
Resonant dipole-dipole interaction in the presence of dispersing and absorbing surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, equations of motion and an effective Hamiltonian for treating both the
resonant dipole-dipole interaction between two-level atoms and the resonant
atom-field interaction are derived, which can suitably be used for studying the
influence of arbitrary dispersing and absorbing material surroundings on these
interactions. The theory is applied to the study of the transient behavior of
two atoms that initially share a single excitation, with special emphasis on
the role of the two competing processes of virtual and real photon exchange in
the energy transfer between the atoms. In particular, it is shown that for weak
atom-field interaction there is a time window, where the energy transfer
follows a rate regime of the type obtained by ordinary second-order
perturbation theory. Finally, the resonant dipole-dipole interaction is shown
to give rise to a doublet spectrum of the emitted light for weak atom-field
interaction and a triplet spectrum for strong atom-field interaction.Comment: 15 pages, 1 figure, RevTE
Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor
The concept of stimulated emission of bosons has played an important role in
modern science and technology, and constitutes the working principle for
lasers. In a stimulated emission process, an incoming photon enhances the
probability that an excited atomic state will transition to a lower energy
state and generate a second photon of the same energy. It is expected, but not
experimentally shown, that stimulated emission contributes significantly to the
zero resistance current in a superconductor by enhancing the probability that
scattered Cooper pairs will return to the macroscopically occupied condensate
instead of entering any other state. Here, we use time- and angle-resolved
photoemission spectroscopy to study the initial rise of the non-equilibrium
quasiparticle population in a BiSrCaCuO cuprate
superconductor induced by an ultrashort laser pulse. Our finding reveals
significantly slower buildup of quasiparticles in the superconducting state
than in the normal state. The slower buildup only occurs when the pump pulse is
too weak to deplete the superconducting condensate, and for cuts inside the
Fermi arc region. We propose this is a manifestation of stimulated
recombination of broken Cooper pairs, and signals an important momentum space
dichotomy in the formation of Cooper pairs inside and outside the Fermi arc
region.Comment: 16 pages, 4 figure
Resonant Energy Exchange between Atoms in Dispersing and Absorbing Surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, a master equation describing both the resonant dipole-dipole interaction
(RDDI) and the resonant atom-field interaction (RAFI) in the presence of
dispersing and absorbing macroscopic bodies is derived, with the relevant
couplings being expressed in terms of the surroundings-assisted Green tensor.
It is shown that under certain conditions the RDDI can be regarded as being
governed by an effective Hamiltonian. The theory, which applies to both weak
and strong atom-field coupling, is used to study the resonant energy exchange
between two (two-level) atoms sharing initially a single excitation. In
particular, it is shown that in the regime of weak atom-field coupling there is
a time window, where the energy transfer follows a transfer-rate law of the
type obtained by ordinary second-order perturbation theory. Finally, the
spectrum of the light emitted during the energy transfer is studied and the
line splittings are discussed.Comment: 9 pages, 5 figs, Proceedings of ICQO'2002, Raubichi, to appear in
Optics and Spectroscop
Atomic entanglement near a realistic microsphere
We study a scheme for entangling two-level atoms located close to the surface
of a dielectric microsphere. The effect is based on medium-assisted spontaneous
decay, rigorously taking into account dispersive and absorptive properties of
the microsphere. We show that even in the weak-coupling regime, where the
Markov approximation applies, entanglement up to 0.35 ebits between two atoms
can be created. However, larger entanglement and violation of Bell's inequality
can only be achieved in the strong-coupling regime.Comment: 16 pages, 4 figures, Late
From disease incubation to disease receipt:Representing epidemics and race in pre- and post-second world war American cinema (1931–1939 and 1950–1962)
This article analyses continuities and changes in how disease has been instrumentalised in cinema as a way of conceptualizing race—comparing five films depicting epidemics produced before the Second World War and five after. In the 1930s films, non-white populations often passively accept assistance in dealing with epidemic disease—a paternalistic white savior narrative—but not always with “gratitude”, and sometimes direct resistance. Here, epidemics take root in physical sites of economic “underdevelopment”, perpetuated further by perceived “premodern” cultural practices demarcated down the lines of race or ethnicity, and intersect with other gendered and socio-economic categories. After the war, while some cinematic tropes such as the “white knight” continue, other narratives emerge including a shift in emphasis away from the Othered environment as the nexus of disease (the disease’s “incubation”), and towards greater alarm about the appearance of disease within recipient, frequently white, communities
Fusion at Detection Level for Frontal Object Perception
International audienceIntelligent vehicle perception involves the correct detection and tracking of moving objects. Taking into account all the possible information at early levels of the perception task can improve the final model of the environment. In this paper, we present an evidential fusion framework to represent and combine evidence from multiple lists of sensor detections. Our fusion framework considers the position, shape and appearance information to represent, associate and combine sensor detections. Although our approach takes place at detection level, we propose a general architecture to include it as a part of a whole perception solution. Several experiments were conducted using real data from a vehicle demonstrator equipped with three main sensors: lidar, radar and camera. The obtained results show improvements regarding the reduction of false detections and mis-classifications of moving objects
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