1,660 research outputs found
A First-Quantized Formalism for Cosmological Particle Production
We show that the amount of particle production in an arbitrary cosmological
background can be determined using only the late-time positive-frequency modes.
We don't refer to modes at early times, so there is no need for a Bogolubov
transformation. We also show that particle production can be extracted from the
Feynman propagator in an auxiliary spacetime. This provides a first-quantized
formalism for computing particle production which, unlike conventional
Bogolubov transformations, may be amenable to a string-theoretic
generalization.Comment: 18 pages, LaTeX; v2: significantly revised for clarity; conclusions
unchange
Quaternion Octonion Reformulation of Quantum Chromodynamics
We have made an attempt to develop the quaternionic formulation of Yang -
Mill's field equations and octonion reformulation of quantum chromo dynamics
(QCD). Starting with the Lagrangian density, we have discussed the field
equations of SU(2) and SU(3) gauge fields for both cases of global and local
gauge symmetries. It has been shown that the three quaternion units explain the
structure of Yang- Mill's field while the seven octonion units provide the
consistent structure of SU(3)_{C} gauge symmetry of quantum chromo dynamics
Characteristics of pebble- and cobble-sized clasts along the Curiosity rover traverse from Bradbury Landing to Rocknest
We have assessed the characteristics of clasts along Curiosity's traverse to shed light on the processes important in the genesis, modification, and transportation of surface materials. Pebble- to cobble-sized clasts at Bradbury Landing, and subsequentl
Climacteric fruit ripening: Ethylene-dependent and independent regulation of ripening pathways in melon fruit
Cantaloupe melons have a typical climacteric behaviour with ethylene playing a major role in the regulation of the ripening process and
affecting the ripening rate. Crossing of Cantaloupe Charentais melon with a non-climacteric melon indicated that the climacteric character is
genetically dominant and conferred by two duplicated loci only. However, other experiments made by crossing two non-climacteric melons
have generated climacteric fruit, indicating that different and complex genetic regulation exists for the climacteric character. Suppression of
ethylene production by antisense ACC oxidase RNA in Charentais melon has shown that, while many ripening pathways were regulated by
ethylene (synthesis of aroma volatiles, respiratory climacteric and degreening of the rind), some were ethylene-independent (initiation of
climacteric, sugar accumulation, loss of acidity and coloration of the pulp). Softening of the flesh comprised both ethylene-dependent and
independent components that were correlated with differential regulation of cell wall degrading genes. These results indicate that climacteric
(ethylene-dependent) and non-climacteric (ethylene-independent) regulation coexist during climacteric fruit ripening. In addition, ethylenesuppressed
melons allowed demonstrating that the various ethylene-dependent events exhibited differential sensitivity to ethylene and that
ethylene was promoting sensitivity to chilling injury. Throughout this review, the data generated with melon are compared with those
obtained with tomato and other fruit
Octonion Quantum Chromodynamics
Starting with the usual definitions of octonions, an attempt has been made to
establish the relations between octonion basis elements and Gell-Mann \lambda
matrices of SU(3)symmetry on comparing the multiplication tables for Gell-Mann
\lambda matrices of SU(3)symmetry and octonion basis elements. Consequently,
the quantum chromo dynamics (QCD) has been reformulated and it is shown that
the theory of strong interactions could be explained better in terms of
non-associative octonion algebra. Further, the octonion automorphism group
SU(3) has been suitably handled with split basis of octonion algebra showing
that the SU(3)_{C}gauge theory of colored quarks carries two real gauge fields
which are responsible for the existence of two gauge potentials respectively
associated with electric charge and magnetic monopole and supports well the
idea that the colored quarks are dyons
Quaternion-Octonion Unitary Symmetries and Analogous Casimir Operators
An attempt has been made to investigate the global SU(2) and SU(3) unitary
flavor symmetries systematically in terms of quaternion and octonion
respectively. It is shown that these symmetries are suitably handled with
quaternions and octonions in order to obtain their generators, commutation
rules and symmetry properties. Accordingly, Casimir operators for SU(2)and
SU(3) flavor symmetries are also constructed for the proper testing of these
symmetries in terms of quaternions and octonions
Atmospheric Chemistry of tert-butylamine and AMP
The atmospheric chemistry of (CH3)3CNH2 (tert-butylamine, tBA) and (CH3)2(CH2OH)CNH2 (2-amino-2-methyl-1-propanol, AMP) has been studied by quantum chemistry methods and in photo-oxidation experiments in the EUPHORE chamber in Valencia (Spain). Aerosol formation and composition has been quantified. Yields of nitramines and other products in the photo-oxidations have been determined and complete photo-oxidation schemes including branching between the major reaction routes have been obtained. Published by Elsevier Ltd
Electric current circuits in astrophysics
Cosmic magnetic structures have in common that they are anchored
in a dynamo, that an external driver converts kinetic energy into internal
magnetic energy, that this magnetic energy is transported as Poynting fl ux across the magnetically dominated structure, and that the magnetic energy
is released in the form of particle acceleration, heating, bulk motion,
MHD waves, and radiation. The investigation of the electric current system is
particularly illuminating as to the course of events and the physics involved.
We demonstrate this for the radio pulsar wind, the solar flare, and terrestrial
magnetic storms
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
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