459 research outputs found
Relating the generating functionals in field/antifield formulation through finite field dependent BRST transformation
We study the field/antifield formulation of pure Yang Mills theory in the
framework of finite field dependent BRST transformation. We show that the
generating functionals corresponding to different solutions of quantum master
equation are connected through the finite field dependent BRST transformations.
We establish this result with the help of several explicit examples.Comment: Revtex4, 18 pages, No figs, Accepted in Eur. Phys. J
Nafion-stabilized Pt Nanoparticles and the Effect of Pt Distribution on the Electrochemical Reduction of Oxygen
Nafion stabilized Pt sols was prepared by using methanol to reduce the precursor H2PtCl6. No other ingredient was used in the preparation and Pt nanoparticles of 2 -3 nm size were obtained. Platinum nanoparticles were found to form aggregates. The aggregate size and the stability of Pt sols could be changed by solvent treatment. This suggests that SO3¯ functional groups of Nafion stabilized Pt nanoparticles and that the aggregates formed due to the formation of ionic clusters of Nafion. The electrochemical reduction of oxygen was examined with carbon supported Nafion-Pt catalysts of different aggregate size. At low overpotential, the kinetic rate was not changed by the aggregate size. At high overpotential region where mass-transfer limitation phenomenon was observed, the reaction rate increased with decreasing aggregate size. It indicates that smaller aggregates, i.e., the more even Pt distribution, are less subjected to mass-transfer limitation and could consequently provide better electrode performance
BV formulation of higher form gauge theories in a superspace
We discuss the extended BRST and anti-BRST symmetry (including shift
symmetry) in the Batalin-Vilkovisky (BV) formulation for two and three form
gauge theories. Further we develop the superspace formulation for the BV
actions for these theories. We show that the extended BRST invariant BV action
for these theories can be written manifestly covariant manner in a superspace
with one Grassmann coordinate. On the hand a superspace with two Grassmann
coordinates are required for a manifestly covariant formulation of the extended
BRST and extended anti-BRST invariant BV actions for higher form gauge
theories.Comment: 30 pages, No figure, version to appear in EPJ
Field dependent nilpotent symmetry for gauge theories
We construct the field dependent mixed BRST (combination of BRST and
anti-BRST) transformations for pure gauge theories. These are shown to be an
exact nilpotent symmetry of both the effective action as well as the generating
functional for certain choices of the field dependent parameters. We show that
the Jacobian contributions for path integral measure in the definition of
generating functional arising from BRST and anti-BRST part compensate each
other. The field dependent mixed BRST transformations are also considered in
field/antifield formulation to show that the solutions of quantum master
equation remain invariant under these. Our results are supported by several
explicit examples.Comment: 25 pages, No figures, Revte
Diffusion of particles moving with constant speed
The propagation of light in a scattering medium is described as the motion of
a special kind of a Brownian particle on which the fluctuating forces act only
perpendicular to its velocity. This enforces strictly and dynamically the
constraint of constant speed of the photon in the medium. A Fokker-Planck
equation is derived for the probability distribution in the phase space
assuming the transverse fluctuating force to be a white noise. Analytic
expressions for the moments of the displacement along with an
approximate expression for the marginal probability distribution function
are obtained. Exact numerical solutions for the phase space
probability distribution for various geometries are presented. The results show
that the velocity distribution randomizes in a time of about eight times the
mean free time () only after which the diffusion approximation becomes
valid. This factor of eight is a well known experimental fact. A persistence
exponent of is calculated for this process in two dimensions
by studying the survival probability of the particle in a semi-infinite medium.
The case of a stochastic amplifying medium is also discussed.Comment: 9 pages, 9 figures(Submitted to Phys. Rev. E
Application of genomicsassisted breeding for generation of climate resilient crops: progress and prospects
CCAFS Climat
Grain Surface Models and Data for Astrochemistry
AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions
Late Cretaceous Vicariance in Gondwanan Amphibians
Overseas dispersals are often invoked when Southern Hemisphere terrestrial and freshwater organism phylogenies do not fit the sequence or timing of Gondwana fragmentation. We used dispersal-vicariance analyses and molecular timetrees to show that two species-rich frog groups, Microhylidae and Natatanura, display congruent patterns of spatial and temporal diversification among Gondwanan plates in the Late Cretaceous, long after the presumed major tectonic break-up events. Because amphibians are notoriously salt-intolerant, these analogies are best explained by simultaneous vicariance, rather than by oceanic dispersal. Hence our results imply Late Cretaceous connections between most adjacent Gondwanan landmasses, an essential concept for biogeographic and palaeomap reconstructions
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