5,912 research outputs found
Young people and ICT 2002: findings from a survey conducted in Autumn 2002
This report describes a survey that explored the attitudes and experiences of young people aged 5-18 and their parents, in relation to the use of information and communications technology (ICT) at home and at schoo
Fractional Quantum Hall Physics in Jaynes-Cummings-Hubbard Lattices
Jaynes-Cummings-Hubbard arrays provide unique opportunities for quantum
emulation as they exhibit convenient state preparation and measurement, and
in-situ tuning of parameters. We show how to realise strongly correlated states
of light in Jaynes-Cummings-Hubbard arrays under the introduction of an
effective magnetic field. The effective field is realised by dynamic tuning of
the cavity resonances. We demonstrate the existence of Fractional Quantum Hall
states by com- puting topological invariants, phase transitions between
topologically distinct states, and Laughlin wavefunction overlap.Comment: 5 pages, 3 figure
Reply Comment: Comparison of Approaches to Classical Signature Change
We contrast the two approaches to ``classical" signature change used by
Hayward with the one used by us (Hellaby and Dray). There is (as yet) no
rigorous derivation of appropriate distributional field equations. Hayward's
distributional approach is based on a postulated modified form of the field
equations. We make an alternative postulate. We point out an important
difference between two possible philosophies of signature change --- ours is
strictly classical, while Hayward's Lagrangian approach adopts what amounts to
an imaginary proper ``time" on one side of the signature change, as is
explicitly done in quantum cosmology. We also explain why we chose to use the
Darmois-Israel type junction conditions, rather than the Lichnerowicz type
junction conditions favoured by Hayward. We show that the difference in results
is entirely explained by the difference in philosophy (imaginary versus real
Euclidean ``time"), and not by the difference in approach to junction
conditions (Lichnerowicz with specific coordinates versus Darmois with general
coordinates).Comment: 10 pages, latex, no figures. Replying to - "Comment on `Failure of
Standard Conservation Laws at a Classical Change of Signature'", S.A.
Hayward, Phys. Rev. D52, 7331-7332 (1995) (gr-qc/9606045
Supersolid phases of light in extended Jaynes-Cummings-Hubbard systems
Jaynes-Cummings-Hubbard lattices provide unique properties for the study of
correlated phases as they exhibit convenient state preparation and measurement,
as well as "in situ" tuning of parameters. We show how to realize charge
density and supersolid phases in Jaynes-Cummings-Hubbard lattices in the
presence of long-range interactions. The long-range interactions are realized
by the consideration of Rydberg states in coupled atom-cavity systems and the
introduction of additional capacitive couplings in quantum-electrodynamics
circuits. We demonstrate the emergence of supersolid and checkerboard solid
phases, for calculations which take into account nearest neighbour couplings,
through a mean-field decoupling.Comment: 9 pages with 6 figures, accepted for publication in Physical Review
Black holes, cosmological singularities and change of signature
There exists a widespread belief that signature type change could be used to
avoid spacetime singularities. We show that signature change cannot be utilised
to this end unless the Einstein equation is abandoned at the suface of
signature type change. We also discuss how to solve the initial value problem
and show to which extent smooth and discontinuous signature changing solutions
are equivalent.Comment: 14pages, Latex, no figur
Quantum gravity in the very early universe
General relativity describes the gravitational field geometrically and in a
self-interacting way because it couples to all forms of energy, including its
own. Both features make finding a quantum theory difficult, yet it is important
in the high-energy regime of the very early universe. This review article
introduces some of the results for the quantum nature of space-time which
indicate that there is a discrete, atomic picture not just for matter but also
for space and time. At high energy scales, such deviations from the continuum
affect the propagation of matter, the expansion of the universe, and perhaps
even the form of symmetries such as Lorentz or CP transformations. All these
effects may leave traces detectable by sensitive measurements, as pointed out
here by examples.Comment: 10 pages, plenary talk at "6th International Conference on Physics
and Astrophysics of Quark Gluon Plasma" (ICPAQGP 2010), Goa, Indi
Comparative genomics of Salmonella enterica serovars Derby and Mbandaka, two prevalent serovars associated with different livestock species in the UK
Background
Despite the frequent isolation of Salmonella enterica sub. enterica serovars Derby and Mbandaka from livestock in the UK and USA little is known about the biological processes maintaining their prevalence. Statistics for Salmonella isolations from livestock production in the UK show that S. Derby is most commonly associated with pigs and turkeys and S. Mbandaka with cattle and chickens. Here we compare the first sequenced genomes of S. Derby and S. Mbandaka as a basis for further analysis of the potential host adaptations that contribute to their distinct host species distributions.
Results
Comparative functional genomics using the RAST annotation system showed that predominantly mechanisms that relate to metabolite utilisation, in vivo and ex vivo persistence and pathogenesis distinguish S. Derby from S. Mbandaka. Alignment of the genome nucleotide sequences of S. Derby D1 and D2 and S. Mbandaka M1 and M2 with Salmonella pathogenicity islands (SPI) identified unique complements of genes associated with host adaptation. We also describe a new genomic island with a putative role in pathogenesis, SPI-23. SPI-23 is present in several S. enterica serovars, including S. Agona, S. Dublin and S. Gallinarum, it is absent in its entirety from S. Mbandaka.
Conclusions
We discovered a new 37 Kb genomic island, SPI-23, in the chromosome sequence of S. Derby, encoding 42 ORFS, ten of which are putative TTSS effector proteins. We infer from full-genome synonymous SNP analysis that these two serovars diverged, between 182kya and 625kya coinciding with the divergence of domestic pigs. The differences between the genomes of these serovars suggest they have been exposed to different stresses including, phage, transposons and prolonged externalisation. The two serovars possess distinct complements of metabolic genes; many of which cluster into pathways for catabolism of carbon sources
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