1,958 research outputs found
Deforming tachyon kinks and tachyon potentials
In this paper we investigate deformation of tachyon potentials and tachyon
kink solutions. We consider the deformation of a DBI type action with gauge and
tachyon fields living on D1-brane and D3-brane world-volume. We deform tachyon
potentials to get other consistent tachyon potentials by using properly a
deformation function depending on the gauge field components. Resolutions of
singular tachyon kinks via deformation and applications of deformed tachyon
potentials to scalar cosmology scenario are discussed.Comment: To appear in JHEP, 19 pages, 5 eps figures, minor changes and one
reference adde
Weakly bound atomic trimers in ultracold traps
The experimental three-atom recombination coefficients of the atomic states
Na, Rb and Rb,
together with the corresponding two-body scattering lengths, allow predictions
of the trimer bound state energies for such systems in a trap. The
recombination parameter is given as a function of the weakly bound trimer
energies, which are in the interval for large
positive scattering lengths, . The contribution of a deep-bound state to our
prediction, in the case of Rb, for a particular trap, is
shown to be relatively small.Comment: 5 pages, 1 figur
The ^4He trimer as an Efimov system
We review the results obtained in the last four decades which demonstrate the
Efimov nature of the He three-atomic system.Comment: Review article for a special issue of the Few-Body Systems journal
devoted to Efimov physic
Decision Problems for Nash Equilibria in Stochastic Games
We analyse the computational complexity of finding Nash equilibria in
stochastic multiplayer games with -regular objectives. While the
existence of an equilibrium whose payoff falls into a certain interval may be
undecidable, we single out several decidable restrictions of the problem.
First, restricting the search space to stationary, or pure stationary,
equilibria results in problems that are typically contained in PSPACE and NP,
respectively. Second, we show that the existence of an equilibrium with a
binary payoff (i.e. an equilibrium where each player either wins or loses with
probability 1) is decidable. We also establish that the existence of a Nash
equilibrium with a certain binary payoff entails the existence of an
equilibrium with the same payoff in pure, finite-state strategies.Comment: 22 pages, revised versio
Transition Constraints for Temporal Attributes
Representing temporal data in conceptual data models and ontologies is required by various application domains. For it to be useful for modellers to represent the information precisely and reason over it, it is essential to have a language that is expressive enough to capture the required operational semantics of the time-varying information. Temporal modelling languages have little support for temporal attributes, if at all, yet attributes are a standard element in the widely used conceptual modelling languages such as EER and UML. This hiatus prevents one to utilise a complete temporal conceptual data model and keep track of evolving values of data and its interaction with temporal classes. A rich axiomatisation of fully temporised attributes is possible with a minor extension to the already very expressive description logic language DLRUS. We formalise the notion of transition of attributes, and their interaction with transition of classes. The transition specified for attributes are extension, evolution, and arbitrary quantitative extension
Geometrical Tachyon Kinks and NS5 Branes
We further investigate the 5 ring background using the tachyon map.
Mapping the radion fields to the rolling tachyon helps to explain the motion of
a probe -brane in this background. It turns out that the radion field
becomes tachyonic when the brane is confined to one dimensional motion inside
the ring. We find explicit solutions for the geometrical tachyon field that
describe stable kink solutions which are similar to those of the open string
tachyon. Interestingly in the case of the geometric tachyon, the dynamics is
controlled by a cosine potential. In addition, we couple a constant electric
field to the probe-brane, but find that the only stable kink solutions occur
when there is zero electric field or a critical field value. We also
investigate the behaviour of Non-BPS branes in this background, and find that
the end state of any probe brane is that of tachyonic matter 'trapped' around
the interior of the ring. We conclude by considering compactification of the
ring solution in one of the transverse directions.Comment: Latex, 24 pages, 1 eps fig; clarifying comments added to Section 2;
typos correcte
Microscopic theory of atom-molecule oscillations in a Bose-Einstein condensate
In a recent experiment at JILA [E.A. Donley et al., Nature (London) 417, 529
(2002)] an initially pure condensate of Rb-85 atoms was exposed to a specially
designed time dependent magnetic field pulse in the vicinity of a Feshbach
resonance. The production of new components of the gas as well as their
oscillatory behavior have been reported. We apply a microscopic theory of the
gas to identify these components and determine their physical properties. Our
time dependent studies allow us to explain the observed dynamic evolution of
all fractions, and to identify the physical relevance of the pulse shape. Based
on ab initio predictions, our theory strongly supports the view that the
experiments have produced a molecular condensate.Comment: 18 pages, 20 figure
Fluid-membrane tethers: minimal surfaces and elastic boundary layers
Thin cylindrical tethers are common lipid bilayer membrane structures,
arising in situations ranging from micromanipulation experiments on artificial
vesicles to the dynamic structure of the Golgi apparatus. We study the shape
and formation of a tether in terms of the classical soap-film problem, which is
applied to the case of a membrane disk under tension subject to a point force.
A tether forms from the elastic boundary layer near the point of application of
the force, for sufficiently large displacement. Analytic results for various
aspects of the membrane shape are given.Comment: 12 page
Special Geometry of Euclidean Supersymmetry III: the local r-map, instantons and black holes
We define and study projective special para-Kahler manifolds and show that
they appear as target manifolds when reducing five-dimensional vector
multiplets coupled to supergravity with respect to time. The dimensional
reductions with respect to time and space are carried out in a uniform way
using an epsilon-complex notation. We explain the relation of our formalism to
other formalisms of special geometry used in the literature. In the second part
of the paper we investigate instanton solutions and their dimensional lifting
to black holes. We show that the instanton action, which can be defined after
dualising axions into tensor fields, agrees with the ADM mass of the
corresponding black hole. The relation between actions via Wick rotation, Hodge
dualisation and analytic continuation of axions is discussed.Comment: 72 pages, 2 figure
Green manure in coffee systems in the region of Zona da Mata, Minas Gerais: characteristics and kinetics of carbon and nitrogen mineralization.
The use of green manure may contribute to reduce soil erosion and increase the soil organic matter content and N availability in coffee plantations in the Zona da Mata, State of Minas Gerais, in Southeastern Brazil. The potential of four legumes (A. pintoi, C. mucunoides, S. aterrimum and S. guianensis)to produce above-ground
biomass, accumulate nutrients and mineralize N was studied in two coffee plantations of subsistence farmers under different climate conditions. The biomass production of C. mucunoides was influenced by the shade of the coffee plantation.C. mucunoides tended to mineralize more N than the other legumes due to the low polyphenol content and polyphenol/N ratio. In the first year, the crop establishment of A. pintoi in the area took longer than of the other legumes, resulting in lower biomass production and N2 fixation. In the long term, cellulose was the main
factor controlling N mineralization. The biochemical characteristics, nutrient accumulation and biomass production of the legumes were greatly influenced by
the altitude and position of the area relative to the sun
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