491 research outputs found
Conifold geometries, topological strings and multi-matrix models
We study open B-model representing D-branes on 2-cycles of local Calabi--Yau
geometries. To this end we work out a reduction technique linking D-branes
partition functions and multi-matrix models in the case of conifold geometries
so that the matrix potential is related to the complex moduli of the conifold.
We study the geometric engineering of the multi-matrix models and focus on
two-matrix models with bilinear couplings. We show how to solve this models in
an exact way, without resorting to the customary saddle point/large N
approximation. The method consists of solving the quantum equations of motion
and using the flow equations of the underlying integrable hierarchy to derive
explicit expressions for correlators. Finally we show how to incorporate in
this formalism the description of several group of D-branes wrapped around
different cycles.Comment: 35 pages, 5.3 and 6 revise
Integrability in SFT and new representation of KP tau-function
We are investigating the properties of vacuum and boundary states in the CFT
of free bosons under the conformal transformation. We show that transformed
vacuum (boundary state) is given in terms of tau-functions of dispersionless KP
(Toda) hierarchies. Applications of this approach to string field theory is
considered. We recognize in Neumann coefficients the matrix of second
derivatives of tau-function of dispersionless KP and identify surface states
with the conformally transformed vacuum of free field theory.Comment: 25 pp, LaTeX, reference added in the Section 3.
An Exact Prediction of N=4 SUSYM Theory for String Theory
We propose that the expectation value of a circular BPS-Wilson loop in N=4
SUSYM can be calculated exactly, to all orders in a 1/N expansion and to all
orders in g^2 N. Using the AdS/CFT duality, this result yields a prediction of
the value of the string amplitude with a circular boundary to all orders in
alpha' and to all orders in g_s. We then compare this result with string
theory. We find that the gauge theory calculation, for large g^2 N and to all
orders in the 1/N^2 expansion does agree with the leading string theory
calculation, to all orders in g_s and to lowest order in alpha'. We also find a
relation between the expectation value of any closed smooth Wilson loop and the
loop related to it by an inversion that takes a point along the loop to
infinity, and compare this result, again successfully, with string theory.Comment: LaTeX, 22 pages, 3 figures. Argument corrected and two new sections
adde
Surface modification of polymeric materials by cold atmosphericplasma jet
In this work we report the surface modification of different engineering polymers, such as, polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP) by an atmospheric pressure plasma jet (APPJ). It was operated with Ar gas using 10 kV, 37 kHz, sine wave as an excitation source. The aim of this study is to determine the optimal treatment conditions and also to compare the polymer surface modification induced by plasma jet with the one obtained by another atmospheric pressure plasma source the dielectric barrier discharge (DBD). The samples were exposed to the plasma jet effluent using a scanning procedure, which allowed achieving a uniform surface modification. The wettability assessments of all polymers reveal that the treatment leads to reduction of more than 40 degrees in the water contact angle (WCA). Changes in surface composition and chemical bonding were analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-Transformed Infrared spectroscopy (FTIR) that both detected incorporation of oxygen-related functional groups. Surface morphology of polymer samples was investigated by Atomic Force Microscopy (AFM) and an increase of polymer roughness after the APPJ treatment was found. The plasma-treated polymers exhibited hydrophobic recovery expressed in reduction of the O-content of the surface upon rinsing with water. This process was caused by the dissolution of low molecular weight oxidized materials (LMWOMs) formed on the surface as a result of the plasma exposure. (C) 2014 Elsevier B.V. All rights reserved
O- and H- induced surface core level shifts on Ru(0001): Prevalence of the additivity rule
In previous work on adsorbate-induced surface core level shifts (SCLSs), the
effects caused by O atom adsorption on Rh(111) and Ru(0001) were found to be
additive: the measured shifts for first layer Ru atoms depended linearly on the
number of directly coordinated O atoms. Density-functional theory calculations
quantitatively reproduced this effect, allowed separation of initial and final
state contributions, and provided an explanation in terms of a roughly constant
charge transfer per O atom. We have now conducted similar measurements and
calculations for three well-defined adsorbate and coadsorbate layers containing
O and H atoms: (1 x 1)-H, (2 x 2)-(O+H), and (2 x 2)-(O+3H) on Ru(0001). As H
is stabilized in fcc sites in the prior two structures and in hcp sites in the
latter, this enables us to not only study coverage and coadsorption effects on
the adsorbate-induced SCLSs, but also the sensitivity to similar adsorption
sites. Remarkably good agreement is obtained between experiment and
calculations for the energies and geometries of the layers, as well as for all
aspects of the SCLS values. The additivity of the next-neighbor
adsorbate-induced SCLSs is found to prevail even for the coadsorbate
structures. While this confirms the suggested use of SCLSs as fingerprints of
the adsorbate configuration, their sensitivity is further demonstrated by the
slightly different shifts unambiguously determined for H adsorption in either
fcc or hcp hollow sites.Comment: 9 pages including 4 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Growth of fat slits and dispersionless KP hierarchy
A "fat slit" is a compact domain in the upper half plane bounded by a curve
with endpoints on the real axis and a segment of the real axis between them. We
consider conformal maps of the upper half plane to the exterior of a fat slit
parameterized by harmonic moments of the latter and show that they obey an
infinite set of Lax equations for the dispersionless KP hierarchy. Deformation
of a fat slit under changing a particular harmonic moment can be treated as a
growth process similar to the Laplacian growth of domains in the whole plane.
This construction extends the well known link between solutions to the
dispersionless KP hierarchy and conformal maps of slit domains in the upper
half plane and provides a new, large family of solutions.Comment: 26 pages, 6 figures, typos correcte
Continuum Annulus Amplitude from the Two-Matrix Model
An explicit expression for continuum annulus amplitudes having boundary
lengths and is obtained from the two-matrix model for the
case of the unitary series; . In the limit of vanishing
cosmological constant, we find an integral representation of these amplitudes
which is reproduced, for the cases of the and the , by a continuum approach consisting of quantum mechanics of loops
and a matter system integrated over the modular parameter of the annulus. We
comment on a possible relation to the unconventional branch of the Liouville
gravity.Comment: 9 pages, OU-HET 190, revised version. A part of the conclusions has
been corrected. A new result on integral representation of the annulus
amplitudes has been adde
Towards a first-principles theory of surface thermodynamics and kinetics
Understanding of the complex behavior of particles at surfaces requires
detailed knowledge of both macroscopic and microscopic processes that take
place; also certain processes depend critically on temperature and gas
pressure. To link these processes we combine state-of-the-art microscopic, and
macroscopic phenomenological, theories. We apply our theory to the O/Ru(0001)
system and calculate thermal desorption spectra, heat of adsorption, and the
surface phase diagram. The agreement with experiment provides validity for our
approach which thus identifies the way for a predictive simulation of surface
thermodynamics and kinetics.Comment: 4 pages including 3 figures. Related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
- …