32,564 research outputs found
A water level relationship between consecutive gauge stations along Solim\~oes/Amazonas main channel: a wavelet approach
Gauge stations are distributed along the Solim\~oes/Amazonas main channel to
monitor water level changes over time. Those measurements help quantify both
the water movement and its variability from one gauge station to the next
downstream. The objective of this study is to detect changes in the water level
relationship between consecutive gauge stations along the Solim\~oes/Amazonas
main channel, since 1980. To carry out the analyses, data spanning from 1980 to
2010 from three consecutive gauges (Tefe, Manaus and Obidos) were used to
compute standardized daily anomalies. In particular for infra-annual periods it
was possible to detect changes for the water level variability along the
Solim\~oes/Amazonas main channel, by applying the Morlet Wavelet Transformation
(WT) and Wavelet Cross Coherence (WCC) methods. It was possible to quantify the
waves amplitude for the WT infra-annual scaled-period and were quite similar to
the three gauge stations denoting that the water level variability are related
to the same hydrological forcing functions. Changes in the WCC was detected for
the Manaus-Obidos river stretch and this characteristic might be associated
with land cover changes in the floodplains. The next steps of this research,
will be to test this hypotheses by integrating land cover changes into the
floodplain with hydrological modelling simulations throughout the time-series
Phantom Accretion by Black Holes and the Generalized Second Law of Thermodynamics
The accretion of a phantom fluid with non-zero chemical potential by black
holes is discussed with basis on the Generalized Second Law of thermodynamics.
For phantom fluids with positive temperature and negative chemical potential we
demonstrate that the accretion process is possible, and that the condition
guaranteeing the positiveness of the phantom fluid entropy coincides with the
one required by Generalized Second Law. In particular, this result provides a
complementary confirmation that cosmological phantom fluids do not need to have
negative temperatures
Magnetically-controlled impurities in quantum wires with strong Rashba coupling
We investigate the effect of strong spin-orbit interaction on the electronic
transport through non-magnetic impurities in one-dimensional systems. When a
perpendicular magnetic field is applied, the electron spin polarization becomes
momentum-dependent and spin-flip scattering appears, to first order in the
applied field, in addition to the usual potential scattering. We analyze a
situation in which, by tuning the Fermi level and the Rashba coupling, the
magnetic field can suppress the potential scattering. This mechanism should
give rise to a significant negative magnetoresistance in the limit of large
barriers.Comment: 4 pages, 2 figure
Physical boundary state for the quantum tetrahedron
We consider stability under evolution as a criterion to select a physical
boundary state for the spinfoam formalism. As an example, we apply it to the
simplest spinfoam defined by a single quantum tetrahedron and solve the
associated eigenvalue problem at leading order in the large spin limit. We show
that this fixes uniquely the free parameters entering the boundary state.
Remarkably, the state obtained this way gives a correlation between edges which
runs at leading order with the inverse distance between the edges, in agreement
with the linearized continuum theory. Finally, we give an argument why this
correlator represents the propagation of a pure gauge, consistently with the
absence of physical degrees of freedom in 3d general relativity.Comment: 20 pages, 6 figure
Numerical indications on the semiclassical limit of the flipped vertex
We introduce a technique for testing the semiclassical limit of a quantum
gravity vertex amplitude. The technique is based on the propagation of a
semiclassical wave packet. We apply this technique to the newly introduced
"flipped" vertex in loop quantum gravity, in order to test the intertwiner
dependence of the vertex. Under some drastic simplifications, we find very
preliminary, but surprisingly good numerical evidence for the correct classical
limit.Comment: 4 pages, 8 figure
Sinorhizobium Meliloti, A Bacterium Lacking The Autoinducer-2 (AI-2) Synthase, Responds To AI-2 Supplied By Other Bacteria
Many bacterial species respond to the quorum-sensing signal autoinducer-2 (AI-2) by regulating different niche-specific genes. Here, we show that Sinorhizobium meliloti, a plant symbiont lacking the gene for the AI-2 synthase, while not capable of producing AI-2 can nonetheless respond to AI-2 produced by other species. We demonstrate that S. meliloti has a periplasmic binding protein that binds AI-2. The crystal structure of this protein (here named SmlsrB) with its ligand reveals that it binds (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF), the identical AI-2 isomer recognized by LsrB of Salmonella typhimurium. The gene encoding SmlsrB is in an operon with orthologues of the lsr genes required for AI-2 internalization in enteric bacteria. Accordingly, S. meliloti internalizes exogenous AI-2, and mutants in this operon are defective in AI-2 internalization. S. meliloti does not gain a metabolic benefit from internalizing AI-2, suggesting that AI-2 functions as a signal in S. meliloti. Furthermore, S. meliloti can completely eliminate the AI-2 secreted by Erwinia carotovora, a plant pathogen shown to use AI-2 to regulate virulence. Our findings suggest that S. meliloti is capable of \u27eavesdropping\u27 on the AI-2 signalling of other species and interfering with AI-2-regulated behaviours such as virulence
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