135 research outputs found
Hamiltonian Electric/Magnetic Duality and Lorentz Invariance
In (3+1) Hamiltonian form, the conditions for the electric/magnetic
invariance of generic self-interacting gauge vector actions and the definition
of the duality generator are obvious. Instead, (3+1) actions are not
intrinsically Lorentz invariant. Imposing the Dirac-Schwinger stress tensor
commutator requirement to enforce the latter yields a differential constraint
on the Hamiltonian which translates into the usual Lagrangian form of the
duality invariance condition obeyed by Maxwell and Born-Infeld theories. We
also discuss covariance properties of some analogous scalar models.Comment: 7 pages, LaTeX, no figure
Shock-Free Wave Propagation in Gauge Theories
We present the shock-free wave propagation requirements for massless fields.
First, we briefly argue how the "completely exceptional" approach, originally
developed to study the characteristics of hyperbolic systems in 1+1 dimensions,
can be generalized to higher dimensions and used to describe propagation
without emerging shocks, with characteristic flow remaining parallel along the
waves. We then study the resulting requirements for scalar, vector,
vector-scalar and gravity models and characterize physically acceptable actions
in each case.Comment: 30 pages, LaTeX, no figure
Supersymmetric Strings and Waves in D=3, N=2 Matter Coupled Gauged Supergravities
We construct new 1/2 supersymmetric solutions in D=3, N=2, matter coupled,
U(1) gauged supergravities and study some of their properties. In the most
general case they represent a string superposed with gravitational and
Chern-Simons electromagnetic waves. The waves are attached to the string and
the solution satisfies an electromagnetic self-duality relation. When the sigma
model is non-compact it interpolates between an asymptotically Kaigorodov space
and a naked singularity. For the compact sigma model there is a regular horizon
with the Kaigorodov geometry and asymptotically it is either Minkowskian or a
pp-wave. When the sigma manifold is flat our solutions describe either AdS_3 or
Kaigorodov space or a pp-wave in AdS_3.Comment: 19 pages, 1 figure, v2:a reference added, minor improvement
Godel-Type Metrics in Various Dimensions
Godel-type metrics are introduced and used in producing charged dust
solutions in various dimensions. The key ingredient is a (D-1)-dimensional
Riemannian geometry which is then employed in constructing solutions to the
Einstein-Maxwell field equations with a dust distribution in D dimensions. The
only essential field equation in the procedure turns out to be the source-free
Maxwell's equation in the relevant background. Similarly the geodesics of this
type of metric are described by the Lorentz force equation for a charged
particle in the lower dimensional geometry. It is explicitly shown with several
examples that Godel-type metrics can be used in obtaining exact solutions to
various supergravity theories and in constructing spacetimes that contain both
closed timelike and closed null curves and that contain neither of these. Among
the solutions that can be established using non-flat backgrounds, such as the
Tangherlini metrics in (D-1)-dimensions, there exists a class which can be
interpreted as describing black-hole-type objects in a Godel-like universe.Comment: REVTeX4, 19 pp., no figures, improved and shortened version, note the
slight change in the title [accepted for publication in Classical and Quantum
Gravity
Lienard-Wiechert Potentials in Even Dimensions
The motion of point charged particles is considered in an even dimensional Minkowski space-time. The potential functions corresponding to the massless scalar and the Maxwell fields are derived algorithmically. It is shown that in all even dimensions particles lose energy due to acceleration
Heterotrophic ammonium removal by a novel hatchery isolate Acinetobacter calcoaceticus STB1
Cataloged from PDF version of article.A novel bacterial strain, STB1, was isolated from a commercial sea bass hatchery and found to display high heterotrophic ammonium removal characteristics at different concentrations of ammonium (NH4+-N). The species identity of STB1 was determined via 16S rRNA gene sequence analysis to be Acinetobacter calcoaceticus. We evaluated ammonium removal characteristics of STB1 at varying ammonium concentrations, and observed that STB1 can almost completely remove ammonium at low (50 mg l -1), and medium (100 mg l -1) concentrations within 72 h, while 45% ammonium removal was observed at a higher concentration (210 mg l -1) during the same period. Trace amount of the metabolized ammonium was converted to nitrite or nitrate and 22.16% of total nitrogen was incorporated into cell biomass, while 4.34% of total nitrogen was initially incorporated into cell biomass and subsequently released to the supernatant fraction in the 100 mg l -1 sample. Most of the remaining conversion products are expected to be gaseous denitrification products. Toxicological studies with Artemia salina (brine shrimp) nauplii revealed that STB1 strain is non-toxic to Artemia larvae, which suggests that STB1 can be safely and efficiently utilized in water quality enrichment in aquatic ecosystems. © 2012 Elsevier Ltd
Efficient ammonium removal from aquatic environments by Acinetobacter calcoaceticus STB1 immobilized on an electrospun cellulose acetate nanofibrous web
Cataloged from PDF version of article.A novel biocomposite material was developed by immobilizing an ammonia-oxidizing bacterial strain, Acinetobacter calcoaceticus STB1, on an electrospun porous cellulose acetate (CA) nanofibrous web. Ammonium removal characteristics of the STB1 immobilized CA nanofibrous web were determined at varying initial ammonium concentrations, and removal rates of 100%, 98.5% and 72% were observed within 48 h for 50 mg L-1, 100 mg L-1 and 200 mg L-1 samples, respectively. Most of the ammonia is inferred to be converted into nitrogen or is accumulated as bacterial biomass, as only trace amounts of ammonium were converted into nitrite or nitrate. Reusability test results indicate that, at an initial ammonium concentration of 100 mg L-1, bacteria-immobilized CA nanofibrous webs can be reused for at least 5 cycles. SEM images of the STB1/CA nanofibrous web after five cycles of reuse and rigorous washing demonstrate that bacterial biofilms strongly adhere to nanofiber surfaces
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