318 research outputs found
A theorem on topologically massive gravity
We show that for three dimensional space-times admitting a hypersurface
orthogonal Killing vector field Deser, Jackiw and Templeton's vacuum field
equations of topologically massive gravity allow only the trivial flat
space-time solution. Thus spin is necessary to support topological mass.Comment: published in Classical and Quantum Gravity 13 (1996) L2
G\"odel Type Metrics in Three Dimensions
We show that the G{\" o}del type Metrics in three dimensions with arbitrary
two dimensional background space satisfy the Einstein-perfect fluid field
equations. There exists only one first order partial differential equation
satisfied by the components of fluid's velocity vector field. We then show that
the same metrics solve the field equations of the topologically massive gravity
where the two dimensional background geometry is a space of constant negative
Gaussian curvature. We discuss the possibility that the G{\" o}del Type Metrics
to solve the Ricci and Cotton flow equations. When the vector field
is a Killing vector field we finally show that the stationary G{\" o}del Type
Metrics solve the field equations of the most possible gravitational field
equations where the interaction lagrangian is an arbitrary function of the
electromagnetic field and the curvature tensors.Comment: 17 page
Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption
Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mg HUFA g(-1)) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r = 0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r = 0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r = 0.74) and chrysophytes (r = 0.70). Accordingly, the EPA + DHA content of perch muscle decreased with increasing total phosphorus (r(2) = 0.80) and dissolved organic carbon concentration (r(2) = 0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers. (C) 2016 The Authors. Published by Elsevier Ltd.Peer reviewe
Topologically massive gravito-electrodynamics: exact solutions
We construct two classes of exact solutions to the field equations of
topologically massive electrodynamics coupled to topologically massive gravity
in 2 + 1 dimensions. The self-dual stationary solutions of the first class are
horizonless, asymptotic to the extreme BTZ black-hole metric, and regular for a
suitable parameter domain. The diagonal solutions of the second class, which
exist if the two Chern-Simons coupling constants exactly balance, include
anisotropic cosmologies and static solutions with a pointlike horizon.Comment: 15 pages, LaTeX, no figure
Mass and angular momentum of asymptotically AdS or flat solutions in the topologically massive gravity
We study the conserved charges of supersymmetric solutions in the
topologically massive gravity theory for both asymptotically flat and constant
curvature geometries.Comment: REVTEX4, 8 pages, no figures, added 2 references and a few clarifying
remark
Spinor formulation of topologically massive gravity
In the framework of real 2-component spinors in three dimensional space-time
we present a description of topologically massive gravity (TMG) in terms of
differential forms with triad scalar coefficients. This is essentially a real
version of the Newman-Penrose formalism in general relativity. A triad
formulation of TMG was considered earlier by Hall, Morgan and Perjes, however,
due to an unfortunate choice of signature some of the spinors underlying the
Hall-Morgan-Perjes formalism are real, while others are pure imaginary. We
obtain the basic geometrical identities as well as the TMG field equations
including a cosmological constant for the appropriate signature. As an
application of this formalism we discuss the Bianchi Type exact
solutions of TMG and point out that they are parallelizable manifolds. We also
consider various re-identifications of these homogeneous spaces that result in
black hole solutions of TMG.Comment: An expanded version of paper published in Classical and Quantum
Gravity 12 (1995) 291
Finding the region of pseudo-periodic tandem repeats in biological sequences
SUMMARY: The genomes of many species are dominated by short sequences repeated consecutively. It is estimated that over 10% of the human genome consists of tandemly repeated sequences. Finding repeated regions in long sequences is important in sequence analysis. We develop a software, LocRepeat, that finds regions of pseudo-periodic repeats in a long sequence. We use the definition of Li et al. [1] for the pseudo-periodic partition of a region and extend the algorithm that can select the repeated region from a given long sequence and give the pseudo-periodic partition of the region. AVAILABILITY: LocRepeat is available a
Origin and control of spin currents in a magnetic triplet Josephson junction
We study the appearance of a Josephson spin current in a model triplet
superconductor junction with a magnetically-active tunnelling barrier. We find
three distinct mechanisms for producing a spin current, and we provide a
detailed discussion of the symmetry properties and the physical origins of
each. By combining these three basic mechanisms, we find that it is possible to
exercise fine control over the spin currents. In particular, we show that
unlike the charge current, the spin currents on either side of the barrier need
not be identical.Comment: 5 pages, 4 figures, RevTe
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