490 research outputs found
Scattering of Long Folded Strings and Mixed Correlators in the Two-Matrix Model
We study the interactions of Maldacena's long folded strings in
two-dimensional string theory. We find the amplitude for a state containing two
long folded strings to come and go back to infinity. We calculate this
amplitude both in the worldsheet theory and in the dual matrix model, the
Matrix Quantum Mechanics. The matrix model description allows to evaluate the
amplitudes involving any number of long strings, which are given by the mixed
trace correlators in an effective two-matrix model.Comment: 39 pages, 6 figure
On the Yang-Lee and Langer singularities in the O(n) loop model
We use the method of `coupling to 2d QG' to study the analytic properties of
the universal specific free energy of the O(n) loop model in complex magnetic
field. We compute the specific free energy on a dynamical lattice using the
correspondence with a matrix model. The free energy has a pair of Yang-Lee
edges on the high-temperature sheet and a Langer type branch cut on the
low-temperature sheet. Our result confirms a conjecture by A. and Al.
Zamolodchikov about the decay rate of the metastable vacuum in presence of
Liouville gravity and gives strong evidence about the existence of a weakly
metastable state and a Langer branch cut in the O(n) loop model on a flat
lattice. Our results are compatible with the Fonseca-Zamolodchikov conjecture
that the Yang-Lee edge appears as the nearest singularity under the Langer cut.Comment: 38 pages, 16 figure
Loop Equations for + and - Loops in c = 1/2 Non-Critical String Theory
New loop equations for all genera in non-critical string
theory are constructed. Our loop equations include two types of loops, loops
with all Ising spins up (+ loops) and those with all spins down ( loops).
The loop equations generate an algebra which is a certain extension of
algebra and are equivalent to the constraints derived before in the
matrix-model formulation of 2d gravity. Application of these loop equations to
construction of Hamiltonian for string field theory is
considered.Comment: 21 pages, LaTex file, no figure
Empirical likelihood estimation of the spatial quantile regression
The spatial quantile regression model is a useful and flexible model for analysis of empirical problems with spatial dimension. This paper introduces an alternative estimator for this model. The properties of the proposed estimator are discussed in a comparative perspective with regard to the other available estimators. Simulation evidence on the small sample properties of the proposed estimator is provided. The proposed estimator is feasible and preferable when the model contains multiple spatial weighting matrices. Furthermore, a version of the proposed estimator based on the exponentially tilted empirical likelihood could be beneficial if model misspecification is suspect
Unstable fingering patterns of Hele-Shaw flows as a dispersionless limit of the KdV hierarchy
We show that unstable fingering patterns of two dimensional flows of viscous
fluids with open boundary are described by a dispersionless limit of the KdV
hierarchy. In this framework, the fingering instability is linked to a known
instability leading to regularized shock solutions for nonlinear waves, in
dispersive media. The integrable structure of the flow suggests a dispersive
regularization of the finite-time singularities.Comment: Published versio
Analytic Continuation of Liouville Theory
Correlation functions in Liouville theory are meromorphic functions of the
Liouville momenta, as is shown explicitly by the DOZZ formula for the
three-point function on the sphere. In a certain physical region, where a real
classical solution exists, the semiclassical limit of the DOZZ formula is known
to agree with what one would expect from the action of the classical solution.
In this paper, we ask what happens outside of this physical region. Perhaps
surprisingly we find that, while in some range of the Liouville momenta the
semiclassical limit is associated to complex saddle points, in general
Liouville's equations do not have enough complex-valued solutions to account
for the semiclassical behavior. For a full picture, we either must include
"solutions" of Liouville's equations in which the Liouville field is
multivalued (as well as being complex-valued), or else we can reformulate
Liouville theory as a Chern-Simons theory in three dimensions, in which the
requisite solutions exist in a more conventional sense. We also study the case
of "timelike" Liouville theory, where we show that a proposal of Al. B.
Zamolodchikov for the exact three-point function on the sphere can be computed
by the original Liouville path integral evaluated on a new integration cycle.Comment: 86 pages plus appendices, 9 figures, minor typos fixed, references
added, more discussion of the literature adde
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
TG/DTG-DSC and high temperature in-situ XRD analysis of natural thaumasite
This paper investigated thermal properties of natural thaumasite, such as phase composition and reaction mechanism of thermal decomposition using simultaneous TG/DTG-DSC in Ar and Air medium up to 1673 K, coupled with masspectrometer for analysis of evolving gases, and in-situ powder X-ray diffraction measurements. The transitional solid phases, grown with increasing of temperature at thaumasite thermal decomposition, are calcium hydrogen carbonate (Ca(HCO3)2) and hydrogen sulphate (Ca(HSO4)2), calcite, anhydrite, calcium silicates (wolastonite and larnite), calcium silico-carbonate (spurrite), and calcium silico-sulphate (ternesite). The thermal decomposition in both gaseous media includes the stages of dehydration, dehydroxylation, dacarbonation and desulphuration with obtaining a solid residue of varying degrees of crystallinity. The main solid phase, grown at the highest temperatures, is larnite.
Based on the obtained results it was proposed the scheme of chemical reactions, which presents the reaction mechanism of thaumasite thermal decomposition. The defined scheme has both fundamental importance by adding new details of reference data, and practical application for thaumasite identification in chemical archaeology, and in the chemistry of cement and cement-based materials
The ABCDEF's of Matrix Models for Supersymmetric Chern-Simons Theories
We consider N = 3 supersymmetric Chern-Simons gauge theories with product
unitary and orthosymplectic groups and bifundamental and fundamental fields. We
study the partition functions on an S^3 by using the Kapustin-Willett-Yaakov
matrix model. The saddlepoint equations in a large N limit lead to a constraint
that the long range forces between the eigenvalues must cancel; the resulting
quiver theories are of affine Dynkin type. We introduce a folding/unfolding
trick which lets us, at the level of the large N matrix model, (i) map quivers
with orthosymplectic groups to those with unitary groups, and (ii) obtain
non-simply laced quivers from the corresponding simply laced quivers using a
Z_2 outer automorphism. The brane configurations of the quivers are described
in string theory and the folding/unfolding is interpreted as the
addition/subtraction of orientifold and orbifold planes. We also relate the
U(N) quiver theories to the affine ADE quiver matrix models with a
Stieltjes-Wigert type potential, and derive the generalized Seiberg duality in
2 + 1 dimensions from Seiberg duality in 3 + 1 dimensions.Comment: 30 pages, 5 figure
Isotopic and spin selectivity of H_2 adsorbed in bundles of carbon nanotubes
Due to its large surface area and strongly attractive potential, a bundle of
carbon nanotubes is an ideal substrate material for gas storage. In addition,
adsorption in nanotubes can be exploited in order to separate the components of
a mixture. In this paper, we investigate the preferential adsorption of D_2
versus H_2(isotope selectivity) and of ortho versus para(spin selectivity)
molecules confined in the one-dimensional grooves and interstitial channels of
carbon nanotube bundles. We perform selectivity calculations in the low
coverage regime, neglecting interactions between adsorbate molecules. We find
substantial spin selectivity for a range of temperatures up to 100 K, and even
greater isotope selectivity for an extended range of temperatures,up to 300 K.
This isotope selectivity is consistent with recent experimental data, which
exhibit a large difference between the isosteric heats of D_2 and H_2 adsorbed
in these bundles.Comment: Paper submitted to Phys.Rev. B; 17 pages, 2 tables, 6 figure
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