1,186 research outputs found
Towards solving generic cosmological singularity problem
The big bounce transition of the quantum FRW model in the setting of loop
quantum cosmology is presented. We determine the physical self-adjoint
Hamiltonian generating the dynamics. It is used to define, via the Stone
theorem, an evolution operator. We examine properties of expectation values of
physical observables in the process of the quantum big bounce transition. The
dispersion of observables are studied in the context of the Heisenberg
uncertainty principle. We suggest that the real nature of the bounce may become
known only after we quantize the Belinskii-Khalatnikov-Lifshitz scenario, which
concerns the generic cosmological singularity.Comment: 4 pages, no figures; talk presented at the Multiverse and Fundamental
Cosmology Conference, 10-14 September, 2012, Szczecin, Poland; to be
published in the AIP Conference Proceedings Serie
Probing the cosmological singularity with a particle
We examine the transition of a particle across the singularity of the
compactified Milne (CM) space. Quantization of the phase space of a particle
and testing the quantum stability of its dynamics are consistent to one
another. One type of transition of a quantum particle is described by a quantum
state that is continuous at the singularity. It indicates the existence of a
deterministic link between the propagation of a particle before and after
crossing the singularity. Regularization of the CM space leads to the dynamics
similar to the dynamics in the de Sitter space. The CM space is a promising
model to describe the cosmological singularity deserving further investigation
by making use of strings and membranes.Comment: 19 pages, 7 figures, revtex4, added references, version accepted for
publication in Class. Quantum Gra
Combinatorial Channel Signature Modulation for Wireless ad-hoc Networks
In this paper we introduce a novel modulation and multiplexing method which
facilitates highly efficient and simultaneous communication between multiple
terminals in wireless ad-hoc networks. We term this method Combinatorial
Channel Signature Modulation (CCSM). The CCSM method is particularly efficient
in situations where communicating nodes operate in highly time dispersive
environments. This is all achieved with a minimal MAC layer overhead, since all
users are allowed to transmit and receive at the same time/frequency (full
simultaneous duplex). The CCSM method has its roots in sparse modelling and the
receiver is based on compressive sampling techniques. Towards this end, we
develop a new low complexity algorithm termed Group Subspace Pursuit. Our
analysis suggests that CCSM at least doubles the throughput when compared to
the state-of-the art.Comment: 6 pages, 7 figures, to appear in IEEE International Conference on
Communications ICC 201
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