8,858 research outputs found
Mixed rectilinear sources localization under unknown mutual coupling
In this paper, a novel rectilinearity-based localization method for mixed near-field (NF) and far-field (FF) sources is proposed under unknown mutual coupling. The multiple parameters including direction of arrival (DOA), range and mutual coupling coefficient (MCC) are decoupled, thus only three one-dimensional (1-D) spectral searches are required to estimate the parameters of mixed rectilinear signals successively. Furthermore, the closed-form deterministic Cramer–Rao bound (CRB) of the concerned problem is also derived. Simulation results are provided to demonstrate the effectiveness of the proposed method for the classification and localization of mixed rectilinear sources
Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions
Future wireless systems are envisioned to create an endogenously
holography-capable, intelligent, and programmable radio propagation
environment, that will offer unprecedented capabilities for high spectral and
energy efficiency, low latency, and massive connectivity. A potential and
promising technology for supporting the expected extreme requirements of the
sixth-generation (6G) communication systems is the concept of the holographic
multiple-input multiple-output (HMIMO), which will actualize holographic radios
with reasonable power consumption and fabrication cost. The HMIMO is
facilitated by ultra-thin, extremely large, and nearly continuous surfaces that
incorporate reconfigurable and sub-wavelength-spaced antennas and/or
metamaterials. Such surfaces comprising dense electromagnetic (EM) excited
elements are capable of recording and manipulating impinging fields with utmost
flexibility and precision, as well as with reduced cost and power consumption,
thereby shaping arbitrary-intended EM waves with high energy efficiency. The
powerful EM processing capability of HMIMO opens up the possibility of wireless
communications of holographic imaging level, paving the way for signal
processing techniques realized in the EM-domain, possibly in conjunction with
their digital-domain counterparts. However, in spite of the significant
potential, the studies on HMIMO communications are still at an initial stage,
its fundamental limits remain to be unveiled, and a certain number of critical
technical challenges need to be addressed. In this survey, we present a
comprehensive overview of the latest advances in the HMIMO communications
paradigm, with a special focus on their physical aspects, their theoretical
foundations, as well as the enabling technologies for HMIMO systems. We also
compare the HMIMO with existing multi-antenna technologies, especially the
massive MIMO, present various...Comment: double column, 58 page
Topological-phase effects and path-dependent interference in microwave structures with magnetic-dipolar-mode ferrite particles
Different ways exist in optics to realize photons carrying nonzero orbital
angular momentum. Such photons with rotating wave fronts are called twisted
photons. In microwaves, twisted fields can be produced based on small ferrite
particles with magnetic-dipolar-mode (MDM) oscillations. Recent studies showed
strong localization of the electric and magnetic energies of microwave fields
by MDM ferrite disks. For electromagnetic waves irradiating MDM disks, these
small ferrite samples appear as singular subwavelength regions with time and
space symmetry breakings. The fields scattered by a MDM disk are characterized
by topologically distinctive power-flow vortices and helicity structures. In
this paper we analyze twisted states of microwave fields scattered by MDM
ferrite disks. We show that in a structure of the fields scattered by MDM
particles, one can clearly distinguish rotating topological-phase dislocations.
Specific long-distance topological properties of the fields are exhibited
clearly in the effects of path-dependent interference with two coupled MDM
particles. Such double-twisted scattering is characterized by topologically
originated split-resonance states. Our studies of topological-phase effects and
path-dependent interference in microwave structures with MDM ferrite particles
are based on numerical analysis and recently developed analytical models. We
present preliminary experimental results aimed to support basic statements of
our studies.Comment: Submitted to Phys. Rev.
Persistent Challenges of Quantum Chromodynamics
Unlike some models whose relevance to Nature is still a big question mark,
Quantum Chromodynamics will stay with us forever. Quantum Chromodynamics (QCD),
born in 1973, is a very rich theory supposed to describe the widest range of
strong interaction phenomena: from nuclear physics to Regge behavior at large
E, from color confinement to quark-gluon matter at high densities/temperatures
(neutron stars); the vast horizons of the hadronic world: chiral dynamics,
glueballs, exotics, light and heavy quarkonia and mixtures thereof, exclusive
and inclusive phenomena, interplay between strong forces and weak interactions,
etc. Efforts aimed at solving the underlying theory, QCD, continue. In a
remarkable entanglement, theoretical constructions of the 1970s and 1990s
combine with today's ideas based on holographic description and strong-weak
coupling duality, to provide new insights and a deeper understanding.Comment: Julius Edgar Lilienfeld Prize Lecture at the April Meeting of APS,
Dallas, TX, April 22-25, 2006; v.2: reference added; v.3: reference adde
Localization, Mapping and SLAM in Marine and Underwater Environments
The use of robots in marine and underwater applications is growing rapidly. These applications share the common requirement of modeling the environment and estimating the robots’ pose. Although there are several mapping, SLAM, target detection and localization methods, marine and underwater environments have several challenging characteristics, such as poor visibility, water currents, communication issues, sonar inaccuracies or unstructured environments, that have to be considered. The purpose of this Special Issue is to present the current research trends in the topics of underwater localization, mapping, SLAM, and target detection and localization. To this end, we have collected seven articles from leading researchers in the field, and present the different approaches and methods currently being investigated to improve the performance of underwater robots
Journeys from quantum optics to quantum technology
Sir Peter Knight is a pioneer in quantum optics which has now grown to an important branch of modern physics to study the foundations and applications of quantum physics. He is leading an effort to develop new technologies from quantum mechanics. In this collection of essays, we recall the time we were working with him as a postdoc or a PhD student and look at how the time with him has influenced our research
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