884 research outputs found
Time-dependent toroidal compactification proposals and the Bianchi type I model: classical and quantum solutions
In this work we construct an effective four-dimensional model by
compactifying a ten-dimensional theory of gravity coupled with a real scalar
dilaton field on a time-dependent torus. This approach is applied to
anisotropic cosmological Bianchi type I model for which we study the classical
coupling of the anisotropic scale factors with the two real scalar moduli
produced by the compactification process. Under this approach, we present an
isotropization mechanism for the Bianchi I cosmological model through the
analysis of the ratio between the anisotropic parameters and the volume of the
Universe which in general keeps constant or runs into zero for late times. We
also find that the presence of extra dimensions in this model can accelerate
the isotropization process depending on the momenta moduli values. Finally, we
present some solutions to the corresponding Wheeler-DeWitt (WDW) equation in
the context of Standard Quantum Cosmology.Comment: LaTeX source, 16 pages, Modified title and additional references.
Advances in High Energy Physics, 201
Freed-Witten anomaly in general flux compactification
Turning on a NS-NS three-form flux in a compact space drives some D-branes to
be either Freed-Witten anomalous or unstable to decay into fluxes by the
appearance of instantonic branes. By applying T-duality on a toroidal
compactification, the NS-flux is transformed into metric fluxes. We propose a
T-dual version of the Atiyah-Hirzebruch Spectral Sequence upon which we
describe the Freed-Witten anomaly and the brane-flux transition driven by NS
and metric fluxes in a twisted torus. The required conditions to cancel the
anomaly and the appearance of new instantonic branes are also described. In
addition, we give an example in which all D6-branes wrapping Freed-Witten
anomaly-free three-cycles in the twisted torus T^6/Z(2)XZ(2) are nevertheless
unstable to be transformed into fluxes. Evenmore we find a topological
transformation between RR, NS-NS and metric fluxes driven by a chain of
instantonic branes.Comment: v3: Shortened version. Examples added. Main results unchange
High-dimensional quantum cryptography with twisted light
Quantum key distributions (QKD) systems often rely on polarization of light
for encoding, thus limiting the amount of information that can be sent per
photon and placing tight bounds on the error that such a system can tolerate.
Here we describe a proof-of-principle experiment that indicates the feasibility
of high-dimensional QKD based on the transverse structure of the light field,
allowing for the transfer of more than 1 bit per photon. Our implementation
uses the orbital angular momentum (OAM) of photons and the corresponding
mutually unbiased basis of angular position (ANG). Our experiment uses a
digital micro-mirror device for the rapid generation of OAM and ANG modes at 4
kHz, and a mode sorter capable of sorting single photons based on their OAM and
ANG content with a separation efficiency of 93\%. Through the use of a
7-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel
capacity of 2.05 bits per sifted photon. Our experiment shows that, in addition
to having an increased information capacity, QKD systems based on spatial-mode
encoding will be more tolerant to errors and thus more robust against
eavesdropping attacks
Microplastics in the Antarctic marine system: An emerging area of research
It was thought that the Southern Ocean was relatively free of microplastic contamination; however, recent studies and citizen science projects in the Southern Ocean have reported microplastics in deep-sea sediments and surface waters. Here we reviewed available information on microplastics (including macroplastics as a source of microplastics) in the Southern Ocean. We estimated primary microplastic concentrations from personal care products and laundry, and identified potential sources and routes of transmission into the region. Estimates showed the levels of microplastic pollution released into the region from ships and scientific research stations were likely to be negligible at the scale of the Southern Ocean, but may be significant on a local scale. This was demonstrated by the detection of the first microplastics in shallow benthic sediments close to a number of research stations on King George Island. Furthermore, our predictions of primary microplastic concentrations from local sources were five orders of magnitude lower than levels reported in published sampling surveys (assuming an even dispersal at the ocean surface). Sea surface transfer from lower latitudes may contribute, at an as yet unknown level, to Southern Ocean plastic concentrations. Acknowledging the lack of data describing microplastic origins, concentrations, distribution and impacts in the Southern Ocean, we highlight the urgent need for research, and call for routine, standardised monitoring in the Antarctic marine system
Mosquito-Host Interactions during and after an Outbreak of Equine Viral Encephalitis in Eastern Panama
Mosquito blood meals provide information about the feeding habits and host preference of potential arthropod-borne disease vectors. Although mosquito-borne diseases are ubiquitous in the Neotropics, few studies in this region have assessed patterns of mosquito-host interactions, especially during actual disease outbreaks. Based on collections made during and after an outbreak of equine viral encephalitis, we identified the source of 338 blood meals from 10 species of mosquitoes from Aruza Abajo, a location in Darien province in eastern Panama. A PCR based method targeting three distinct mitochondrial targets and subsequent DNA sequencing was used in an effort to delineate vector-host relationships. At Aruza Abajo, large domesticated mammals dominated the assemblage of mosquito blood meals while wild bird and mammal species represented only a small portion of the blood meal pool. Most mosquito species fed on a variety of hosts; foraging index analysis indicates that eight of nine mosquito species utilize hosts at similar proportions while a stochastic model suggests dietary overlap among species was greater than would be expected by chance. The results from our nullmodel analysis of mosquito diet overlap are consistent with the hypothesis that in landscapes where large domestic animals dominate the local biomass, many mosquito species show little host specificity, and feed upon hosts in proportion to their biomass, which may have implications for the role of livestocking patterns in vector-borne disease ecology.Mosquito blood meals provide information about the feeding habits and host preference of potential arthropod-borne disease vectors. Although mosquito-borne diseases are ubiquitous in the Neotropics, few studies in this region have assessed patterns of mosquito-host interactions, especially during actual disease outbreaks. Based on collections made during and after an outbreak of equine viral encephalitis, we identified the source of 338 blood meals from 10 species of mosquitoes from Aruza Abajo, a location in Darien province in eastern Panama. A PCR based method targeting three distinct mitochondrial targets and subsequent DNA sequencing was used in an effort to delineate vector-host relationships. At Aruza Abajo, large domesticated mammals dominated the assemblage of mosquito blood meals while wild bird and mammal species represented only a small portion of the blood meal pool. Most mosquito species fed on a variety of hosts; foraging index analysis indicates that eight of nine mosquito species utilize hosts at similar proportions while a stochastic model suggests dietary overlap among species was greater than would be expected by chance. The results from our nullmodel analysis of mosquito diet overlap are consistent with the hypothesis that in landscapes where large domestic animals dominate the local biomass, many mosquito species show little host specificity, and feed upon hosts in proportion to their biomass, which may have implications for the role of livestocking patterns in vector-borne disease ecology
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