7,459 research outputs found
Transient electrophoretic current in a nonpolar solvent
The transient electric current of surfactants dissolved in a nonpolar solvent
is investigated both experimentally and theoretically in the parallel-plate
geometry. Due to a low concentration of free charges the cell can be completely
polarized by an external voltage of several volts. In this state, all the
charged micelles are compacted against the electrodes. After the voltage is set
to zero the reverse current features a sharp discharge spike and a broad peak.
This shape and its variation with the compacting voltage are reproduced in a
one-dimensional drift-diffusion model. The model reveals the broad peak is
formed by a competition between an increasing number of charges drifting back
to the middle of the cell and a decreasing electric field that drives the
motion. After complete polarization is achieved, the shape of the peak stops
evolving with further increase of the compacting voltage. The spike-peak
separation time grows logarithmically with the charge content in the bulk. The
time peak is a useful measure of the micelle mobility. Time integration of the
peak yields the total charge in the system. By measuring its variation with
temperature, the activation energy of bulk charge generation has been found to
be 0.126 eV.Comment: 7 pages, 5 figure
On the Riemann Tensor in Double Field Theory
Double field theory provides T-duality covariant generalized tensors that are
natural extensions of the scalar and Ricci curvatures of Riemannian geometry.
We search for a similar extension of the Riemann curvature tensor by developing
a geometry based on the generalized metric and the dilaton. We find a duality
covariant Riemann tensor whose contractions give the Ricci and scalar
curvatures, but that is not fully determined in terms of the physical fields.
This suggests that \alpha' corrections to the effective action require \alpha'
corrections to T-duality transformations and/or generalized diffeomorphisms.
Further evidence to this effect is found by an additional computation that
shows that there is no T-duality invariant four-derivative object built from
the generalized metric and the dilaton that reduces to the square of the
Riemann tensor.Comment: 36 pages, v2: minor changes, ref. added, v3: appendix on frame
formalism added, version to appear in JHE
Massive Type II in Double Field Theory
We provide an extension of the recently constructed double field theory
formulation of the low-energy limits of type II strings, in which the RR fields
can depend simultaneously on the 10-dimensional space-time coordinates and
linearly on the dual winding coordinates. For the special case that only the RR
one-form of type IIA carries such a dependence, we obtain the massive
deformation of type IIA supergravity due to Romans. For T-dual configurations
we obtain a `massive' but non-covariant formulation of type IIB, in which the
10-dimensional diffeomorphism symmetry is deformed by the mass parameter.Comment: 21 page
How dsDNA breathing enhances its flexibility and instability on short length scales
We study the unexpected high flexibility of short dsDNA which recently has
been reported by a number of experiments. Via the Langevin dynamics simulation
of our Breathing DNA model, first we observe the formation of bubbles within
the duplex and also forks at the ends, with the size distributions independent
of the contour length. We find that these local denaturations at a
physiological temperature, despite their rare and transient presence, can lower
the persistence length drastically for a short DNA segment in agreement with
experiment
Ramond-Ramond Cohomology and O(D,D) T-duality
In the name of supersymmetric double field theory, superstring effective
actions can be reformulated into simple forms. They feature a pair of vielbeins
corresponding to the same spacetime metric, and hence enjoy double local
Lorentz symmetries. In a manifestly covariant manner --with regard to O(D,D)
T-duality, diffeomorphism, B-field gauge symmetry and the pair of local Lorentz
symmetries-- we incorporate R-R potentials into double field theory. We take
them as a single object which is in a bi-fundamental spinorial representation
of the double Lorentz groups. We identify cohomological structure relevant to
the field strength. A priori, the R-R sector as well as all the fermions are
O(D,D) singlet. Yet, gauge fixing the two vielbeins equal to each other
modifies the O(D,D) transformation rule to call for a compensating local
Lorentz rotation, such that the R-R potential may turn into an O(D,D) spinor
and T-duality can flip the chirality exchanging type IIA and IIB
supergravities.Comment: 1+37 pages, no figure; Structure reorganized, References added, To
appear in JHEP. cf. Gong Show of Strings 2012
(http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/Talks/Thursday/Gongshow/Lee.pdf
Particle number fluctuations in nuclear collisions within excluded volume hadron gas model
The multiplicity fluctuations are studied in the van der Waals excluded
volume hadron-resonance gas model. The calculations are done in the grand
canonical ensemble within the Boltzmann statistics approximation. The scaled
variances for positive, negative and all charged hadrons are calculated along
the chemical freeze-out line of nucleus-nucleus collisions at different
collision energies. The multiplicity fluctuations are found to be suppressed in
the van der Waals gas. The numerical calculations are presented for two values
of hard-core hadron radius, fm and 0.5 fm, as well as for the upper
limit of the excluded volume suppression effects.Comment: 19 pages, 4 figure
The local symmetries of M-theory and their formulation in generalised geometry
In the doubled field theory approach to string theory, the T-duality group is
promoted to a manifest symmetry at the expense of replacing ordinary Riemannian
geometry with generalised geometry on a doubled space. The local symmetries are
then given by a generalised Lie derivative and its associated algebra. This
paper constructs an analogous structure for M-theory. A crucial by-product of
this is the derivation of the physical section condition for M-theory
formulated in an extended space.Comment: 20 pages, v2: Author Name corrected, v3: typos correcte
International Stock Market Efficiency: A Non-Bayesian Time-Varying Model Approach
This paper develops a non-Bayesian methodology to analyze the time-varying
structure of international linkages and market efficiency in G7 countries. We
consider a non-Bayesian time-varying vector autoregressive (TV-VAR) model, and
apply it to estimate the joint degree of market efficiency in the sense of Fama
(1970, 1991). Our empirical results provide a new perspective that the
international linkages and market efficiency change over time and that their
behaviors correspond well to historical events of the international financial
system.Comment: 21 pages, 2 tables, 6 figure
A Double Sigma Model for Double Field Theory
We define a sigma model with doubled target space and calculate its
background field equations. These coincide with generalised metric equation of
motion of double field theory, thus the double field theory is the effective
field theory for the sigma model.Comment: 26 pages, v1: 37 pages, v2: references added, v3: updated to match
published version - background and detail of calculations substantially
condensed, motivation expanded, refs added, results unchange
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