1,215 research outputs found
Recommended from our members
Modelling and optimisation of design of non-conventional instrument transformers
In this paper, we have proposed, modelled and optimised several designs of non-conventional instrument transformer (NCIT) for high voltage overhead transmission lines (400kV). We have discussed several parameters and investigated how they influence the sensitivity of our NCIT, consisting of magnetic shape memory (MSM) element, magnetic circuit and an LVDT (linear variable differential transformer). One of the most used conductors in these lines, 528-Al1/69-ST1A ACSR conductor (old code MOOSE), was modelled together with the MSM element and the magnetic circuit in ANSYS APDL. Based on the obtained results we have given suggestions on how NCIT could be designed taking into account a choice of the most appropriate material for this application. The way how the model was developed was presented as well as calculations of errors in the model in ANSYS APDL for electromagnetic problems
Bohmian mechanics in relativistic quantum mechanics, quantum field theory and string theory
I present a short overview of my recent achievements on the Bohmian
interpretation of relativistic quantum mechanics, quantum field theory and
string theory. This includes the relativistic-covariant Bohmian equations for
particle trajectories, the problem of particle creation and destruction, the
Bohmian interpretation of fermionic fields and the intrinsically Bohmian
quantization of fields and strings based on the De Donder-Weyl covariant
canonical formalism.Comment: 6 pages, talk given at Third International Workshop DICE2006,
Piombino, Italy, September 11-15, 200
-brane type I superstring background fields in terms of type IIB ones by canonical method and T-duality approach
We consider type IIB superstring theory with embedded -brane and choose
boundary conditions which preserve half of the initial supersymmetry. In the
canonical approach that we use, boundary conditions are treated as canonical
constraints. The effective theory, obtained from the initial one on the
solution of boundary conditions, has the form of the type I superstring theory
with embedded -brane. We obtain the expressions for -brane background
fields of type I theory in terms of the -brane background fields of type
IIB theory. We show that beside known even fields, they contain
squares of odd ones, where is world-sheet parity
transformation, . We relate result of this paper and
the results of [1] using T-dualities along four directions orthogonal to
-brane
Type I background fields in terms of type IIB ones
We choose such boundary conditions for open IIB superstring theory which
preserve N=1 SUSY. The explicite solution of the boundary conditions yields
effective theory which is symmetric under world-sheet parity transformation
. We recognize effective theory as closed type I
superstring theory. Its background fields,beside known even fields of
the initial IIB theory, contain improvements quadratic in odd ones.Comment: 4 revtex pages, no figure
Gauge symmetries decrease the number of Dp-brane dimensions
It is known that the presence of antisymmetric background field
leads to noncommutativity of Dp-brane manifold. Addition of the linear dilaton
field in the form , causes the appearance of the
commutative Dp-brane coordinate . In the present article we show
that for some particular choices of the background fields, and $\tilde a^2\equiv [ (G-4BG^{-1}B)^{-1}\
]^{\mu\nu}a_\mu a_\nu=0$, the local gauge symmetries appear in the theory. They
turn some Neuman boundary conditions into the Dirichlet ones, and consequently
decrease the number of the Dp-brane dimensions.Comment: We improve Sec.4. and Conclusion and we added the Appendix in order
to clarify result
Strings, T-duality breaking, and nonlocality without the shortest distance
T-duality of string theory suggests nonlocality manifested as the shortest
possible distance. As an alternative, we suggest a nonlocal formulation of
string theory that breaks T-duality at the fundamental level and does not
require the shortest possible distance. Instead, the string has an objective
shape in spacetime at all length scales, but different parts of the string
interact in a nonlocal Bohmian manner.Comment: 7 pages, revised, to appear in Eur. Phys. J.
s-wave Cooper pair insulators and theory of correlated superconductors
The pseudogap state of cuprate high-temperature superconductors has been
often viewed as either a yet unknown competing order or a precursor state to
superconductivity. While awaiting the resolution of the pseudogap problem in
cuprates, we demonstrate that local pairing fluctuations, vortex liquid
dynamics and other precursor phenomena can emerge quite generally whenever
fermionic excitations remain gapped across the superconducting transition,
regardless of the gap origin. Our choice of a tractable model is a lattice band
insulator with short-range attractive interactions between fermions in the
s-wave channel. An effective crossover between Bardeen-Cooper-Schrieffer (BCS)
and Bose-Einstein condensate (BEC) regimes can be identified in any band
insulator above two dimensions, while in two dimensions only the BEC regime
exists. The superconducting transition is "unconventional" (non-pair-breaking)
in the BEC regime, identified by either the bosonic mean-field or XY
universality class. The insulator adjacent to the superconductor in the BEC
regime is a bosonic Mott insulator of Cooper pairs, which may be susceptible to
charge density wave ordering. We construct a function of the many-body
excitation spectrum whose non-analytic changes define a sharp distinction
between band and Mott insulators. The corresponding "second order transition"
can be observed out of equilibrium by driving a Cooper pair laser in the Mott
insulator. We explicitly show that the gap for charged bosonic excitations lies
below the threshold for Cooper pair breakup in any BEC regime, despite quantum
fluctuations. Our discussion ends with a view of possible consequences for
cuprates, where antinodal pair dynamics has certain features in common with our
simple s-wave picture.Comment: 18 pages, 4 figures, published versio
Boson-fermion unification, superstrings, and Bohmian mechanics
Bosonic and fermionic particle currents can be introduced in a more unified
way, with the cost of introducing a preferred spacetime foliation. Such a
unified treatment of bosons and fermions naturally emerges from an analogous
superstring current, showing that the preferred spacetime foliation appears
only at the level of effective field theory, not at the fundamental superstring
level. The existence of the preferred spacetime foliation allows an objective
definition of particles associated with quantum field theory in curved
spacetime. Such an objective definition of particles makes the Bohmian
interpretation of particle quantum mechanics more appealing. The superstring
current allows a consistent Bohmian interpretation of superstrings themselves,
including a Bohmian description of string creation and destruction in terms of
string splitting. The Bohmian equations of motion and the corresponding
probabilistic predictions are fully relativistic covariant and do not depend on
the preferred foliation.Comment: 30 pages, 1 figure, revised, to appear in Found. Phy
Quantum Transparency of Anderson Insulator Junctions: Statistics of Transmission Eigenvalues, Shot Noise, and Proximity Conductance
We investigate quantum transport through strongly disordered barriers, made
of a material with exceptionally high resistivity that behaves as an Anderson
insulator or a ``bad metal'' in the bulk, by analyzing the distribution of
Landauer transmission eigenvalues for a junction where such barrier is attached
to two clean metallic leads. We find that scaling of the transmission
eigenvalue distribution with the junction thickness (starting from the single
interface limit) always predicts a non-zero probability to find high
transmission channels even in relatively thick barriers. Using this
distribution, we compute the zero frequency shot noise power (as well as its
sample-to-sample fluctuations) and demonstrate how it provides a single number
characterization of non-trivial transmission properties of different types of
disordered barriers. The appearance of open conducting channels, whose
transmission eigenvalue is close to one, and corresponding violent mesoscopic
fluctuations of transport quantities explain at least some of the peculiar
zero-bias anomalies in the Anderson-insulator/superconductor junctions observed
in recent experiments [Phys. Rev. B {\bf 61}, 13037 (2000)]. Our findings are
also relevant for the understanding of the role of defects that can undermine
quality of thin tunnel barriers made of conventional band-insulators.Comment: 9 pages, 8 color EPS figures; one additional figure on mesoscopic
fluctuations of Fano facto
- …