1,791 research outputs found
Density-Dependent Synthetic Gauge Fields Using Periodically Modulated Interactions
We show that density-dependent synthetic gauge fields may be engineered by
combining periodically modu- lated interactions and Raman-assisted hopping in
spin-dependent optical lattices. These fields lead to a density- dependent
shift of the momentum distribution, may induce superfluid-to-Mott insulator
transitions, and strongly modify correlations in the superfluid regime. We show
that the interplay between the created gauge field and the broken sublattice
symmetry results, as well, in an intriguing behavior at vanishing interactions,
characterized by the appearance of a fractional Mott insulator.Comment: 5 pages, 5 figure
Black Holes in the Presence of Cosmological Constant and Large N Brane World
Analytic form has been obtained for four-dimensional black holes with a
minimal Hawking temperature in a theory with cosmological constant, dilaton and
gauge fields. In general dimensions, black hole solutions are shown to exist
and their asymptotic behaviors are obtained. In theories of ten dimension, N
coincident D3-branes as the boundary of an space are constructed by
embedding black D3-branes, with a five-dimensional compactified space of
negligible size if N is large, which provide natural realizations of the
Randall-Sundrum scenario. For this background, the cosmological
constant is a higher order perturbation and its effect on the spectra of
standard model fields on the branes can be calculated.Comment: 12 pages, no figure
Comment on "Coherent Ratchets in Driven Bose-Einstein Condensates"
C. E. Creffield and F. Sols (Phys. Rev. Lett. 103, 200601 (2009)) recently
reported finite, directed time-averaged ratchet current, for a noninteracting
quantum particle in a periodic potential even when time-reversal symmetry
holds. As we explain in this Comment, this result is incorrect, that is,
time-reversal symmetry implies a vanishing current.Comment: revised versio
Dynamics of matter-wave solitons in a ratchet potential
We study the dynamics of bright solitons formed in a Bose-Einstein condensate
with attractive atomic interactions perturbed by a weak bichromatic optical
lattice potential. The lattice depth is a biperiodic function of time with a
zero mean, which realises a flashing ratchet for matter-wave solitons. The
average velocity of a soliton and the directed soliton current induced by the
ratchet depend on the number of atoms in the soliton. We employ this feature to
study collisions between ratchet-driven solitons and find that soliton
transport can be induced through their interactions. In the regime when
matter-wave solitons are narrow compared to the lattice period the ratchet
dynamics is well described by the effective Hamiltonian theory.Comment: 4 pages, 5 figure
Social contact structures and time use patterns in the Manicaland Province of Zimbabwe.
BACKGROUND: Patterns of person-to-person contacts relevant for infectious diseases transmission are still poorly quantified in Sub-Saharan Africa (SSA), where socio-demographic structures and behavioral attitudes are expected to be different from those of more developed countries. METHODS AND FINDINGS: We conducted a diary-based survey on daily contacts and time-use of individuals of different ages in one rural and one peri-urban site of Manicaland, Zimbabwe. A total of 2,490 diaries were collected and used to derive age-structured contact matrices, to analyze time spent by individuals in different settings, and to identify the key determinants of individuals' mixing patterns. Overall 10.8 contacts per person/day were reported, with a significant difference between the peri-urban and the rural site (11.6 versus 10.2). A strong age-assortativeness characterized contacts of school-aged children, whereas the high proportion of extended families and the young population age-structure led to a significant intergenerational mixing at older ages. Individuals spent on average 67% of daytime at home, 2% at work, and 9% at school. Active participation in school and work resulted the key drivers of the number of contacts and, similarly, household size, class size, and time spent at work influenced the number of home, school, and work contacts, respectively. We found that the heterogeneous nature of home contacts is critical for an epidemic transmission chain. In particular, our results suggest that, during the initial phase of an epidemic, about 50% of infections are expected to occur among individuals younger than 12 years and less than 20% among individuals older than 35 years. CONCLUSIONS: With the current work, we have gathered data and information on the ways through which individuals in SSA interact, and on the factors that mostly facilitate this interaction. Monitoring these processes is critical to realistically predict the effects of interventions on infectious diseases dynamics
Rotating Solution of Einstein-Maxwell Dilaton Gravity with Unusual Asymptotics
We study electrically charged, dilaton black holes, which possess
infinitesimal angular momentum in the presence of one or two Liouville type
potentials. These solutions are neither asymptotically flat nor (anti)-de
Sitter. Some properties of the solutions are discussed.Comment: 11 pages, Accepted (Int. J. Theor. Phys.
Energy and seismic retrofit of historic timber-framed houses in Portugal: Building predictive models in future scenarios
This research addresses the comparison of building performance before and after implementing energy and seismic retrofitting techniques within simulation models, under the current climate condition vs. predicted environment conditions (2030-2100). It aims to identify a set of feasible interventions within distinct indoor building conditions (number of inhabitants and occupancy schedule) in three design scenarios. To this end, we adopt parametric modelling tools (Rhinoceros, Grasshopper, EnergyPlus) combined with a multicriteria decision analysis (M-MACBETH, Measuring Attractiveness through a Categorical-Based Evaluation Technique). This model is tested in an historic house, a multi-storey overhanging timber-framed house in Lisbon parish, which is representative of valuable traditional construction systems in high seismic hazard zone in the Mediterranean basin. Future studies can address other building simulations evaluated against architectural, structural, environmental, and economic-related parameters. The influence of weighting on the interventions against different criteria can be addressed also considering the uncertainty about the impact of each group of intervention in sensitivity and robustness analyses.info:eu-repo/semantics/publishedVersio
Charged Dilaton Black Holes with a Cosmological Constant
The properties of static spherically symmetric black holes, which are either
electrically or magnetically charged, and which are coupled to the dilaton in
the presence of a cosmological constant, are considered. It is shown that such
solutions do not exist if the cosmological constant is positive (in arbitrary
spacetime dimension >= 4). However, asymptotically anti-de Sitter black hole
solutions with a single horizon do exist if the cosmological constant is
negative. These solutions are studied numerically in four dimensions and the
thermodynamic properties of the solutions are derived. The extreme solutions
are found to have zero entropy and infinite temperature for all non-zero values
of the dilaton coupling constant.Comment: 12 pages, epsf, phyzzx, 4 in-text figures incl. (minor typos fixed, 1
reference added
Charged Nariai Black Holes With a Dilaton
The Reissner-Nordstrom-de Sitter black holes of standard Einstein-Maxwell
theory with a cosmological constant have no analogue in dilatonic theories with
a Liouville potential. The only exception are the solutions of maximal mass,
the Charged Nariai solutions. We show that the structure of the solution space
of the Dilatonic Charged Nariai black holes is quite different from the
non-dilatonic case. Its dimensionality depends on the exponential coupling
constants of the dilaton. We discuss the possibility of pair creating such
black holes on a suitable background. We find conditions for the existence of
Charged Nariai solutions in theories with general dilaton potentials, and
consider specifically a massive dilaton.Comment: 20 pages, LaTeX, 4 figures, submitted to Phys. Rev.
Do naked singularities generically occur in generalized theories of gravity?
A new mechanism for causing naked singularities is found in an effective
superstring theory. We investigate the gravitational collapse in a spherically
symmetric Einstein-Maxwell-dilaton system in the presence of a pure
cosmological constant "potential", where the system has no static black hole
solution. We show that once gravitational collapse occurs in the system, naked
singularities necessarily appear in the sense that the field equations break
down in the domain of outer communications. This suggests that in generalized
theories of gravity, the non-minimally coupled fields generically cause naked
singularities in the process of gravitational collapse if the system has no
static or stationary black hole solution.Comment: 4 pages including 2 eps figures, to be published in Physical Review
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