77 research outputs found
Reflective Ghost Imaging through Turbulence
Recent work has indicated that ghost imaging may have applications in
standoff sensing. However, most theoretical work has addressed
transmission-based ghost imaging. To be a viable remote-sensing system, the
ghost imager needs to image rough-surfaced targets in reflection through long,
turbulent optical paths. We develop, within a Gaussian-state framework,
expressions for the spatial resolution, image contrast, and signal-to-noise
ratio of such a system. We consider rough-surfaced targets that create fully
developed speckle in their returns, and Kolmogorov-spectrum turbulence that is
uniformly distributed along all propagation paths. We address both classical
and nonclassical optical sources, as well as a computational ghost imager.Comment: 13 pages, 3 figure
A dynamical time operator in Dirac's relativistic quantum mechanics
A self-adjoint dynamical time operator is introduced in Dirac's relativistic
formulation of quantum mechanics and shown to satisfy a commutation relation
with the Hamiltonian analogous to that of the position and momentum operators.
The ensuing time-energy uncertainty relation involves the uncertainty in the
instant of time when the wave packet passes a particular spatial position and
the energy uncertainty associated with the wave packet at the same time, as
envisaged originally by Bohr. The instantaneous rate of change of the position
expectation value with respect to the simultaneous expectation value of the
dynamical time operator is shown to be the phase velocity, in agreement with de
Broglie's hypothesis of a particle associated wave whose phase velocity is
larger than c. Thus, these two elements of the original basis and
interpretation of quantum mechanics are integrated into its formal mathematical
structure. Pauli's objection is shown to be resolved or circumvented. Possible
relevance to current developments in interference in time, in Zitterbewegung
like effects in spintronics, grapheme and superconducting systems and in
cosmology is noted
Conveyor belt clock synchronization
A protocol for synchronizing distant clocks is proposed that does not rely on
the arrival times of the signals which are exchanged, and an optical
implementation based on coherent-state pulses is described. This protocol is
not limited by any dispersion that may be present in the propagation medium
through which the light signals are exchanged. Possible improvements deriving
from the use of quantum-mechanical effects are also addressed.Comment: 8 pages, 7 figure
Codivergence of Mycoviruses with Their Hosts
BACKGROUND: The associations between pathogens and their hosts are complex and can result from any combination of evolutionary events such as codivergence, switching, and duplication of the pathogen. Mycoviruses are RNA viruses which infect fungi and for which natural vectors are so far unknown. Thus, lateral transfer might be improbable and codivergence their dominant mode of evolution. Accordingly, mycoviruses are a suitable target for statistical tests of virus-host codivergence, but inference of mycovirus phylogenies might be difficult because of low sequence similarity even within families. METHODOLOGY: We analyzed here the evolutionary dynamics of all mycovirus families by comparing virus and host phylogenies. Additionally, we assessed the sensitivity of the co-phylogenetic tests to the settings for inferring virus trees from their genome sequences and approximate, taxonomy-based host trees. CONCLUSIONS: While sequence alignment filtering modes affected branch support, the overall results of the co-phylogenetic tests were significantly influenced only by the number of viruses sampled per family. The trees of the two largest families, Partitiviridae and Totiviridae, were significantly more similar to those of their hosts than expected by chance, and most individual host-virus links had a significant positive impact on the global fit, indicating that codivergence is the dominant mode of virus diversification. However, in this regard mycoviruses did not differ from closely related viruses sampled from non-fungus hosts. The remaining virus families were either dominated by other evolutionary modes or lacked an apparent overall pattern. As this negative result might be caused by insufficient taxon sampling, the most parsimonious hypothesis still is that host-parasite evolution is basically the same in all mycovirus families. This is the first study of mycovirus-host codivergence, and the results shed light not only on how mycovirus biology affects their co-phylogenetic relationships, but also on their presumable host range itself
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