624 research outputs found
On perturbations of the isometric semigroup of shifts on the semiaxis
We study perturbations of the semigroup of shifts
on with the property that belongs to a certain Schatten-von Neumann class \gS_p with .
We show that, for the unitary component in the Wold-Kolmogorov decomposition of
the cogenerator of the semigroup , {\it any singular}
spectral type may be achieved by \gS_1 perturbations. We provide an explicit
construction for a perturbation with a given spectral type based on the theory
of model spaces of the Hardy space . Also we show that we may obtain {\it
any} prescribed spectral type for the unitary component of the perturbed
semigroup by a perturbation from the class \gS_p with
Equilibration between edge states in the fractional quantum Hall effect regime at high imbalances
We experimentally study equilibration between edge states, co-propagating at
the edge of the fractional quantum Hall liquid, at high initial imbalances. We
find an anomalous increase of the conductance between the fractional edge
states at the filling factor in comparison with the expected one for
the model of independent edge states. We conclude that the model of independent
fractional edge states is not suitable to describe the experimental situation
at .Comment: 4 page
Evidence for the Luttigger liquid density of states in transport across the incompressible stripe at fractional filling factors
We experimentally investigate transport across the incompressible stripe at
the sample edge in the fractional quantum Hall effect regime at bulk filling
factors and . We obtain the dependence of the equilibration
length, that is a phenomenological characteristics of the transport, on the
voltage imbalance and the temperature, at high voltage imbalances. These
dependencies are found to be of the power-law form, which is a strong evidence
for the Luttigger liquid density of states.Comment: 4 pages, to appear in EP
Spin susceptibility and polarization field in a dilute two-dimensional electron system in (111) silicon
We find that the polarization field, B_chi, obtained by scaling the
weak-parallel-field magnetoresistance at different electron densities in a
dilute two-dimensional electron system in (111) silicon, corresponds to the
spin susceptibility that grows strongly at low densities. The polarization
field, B_sat, determined by resistance saturation, turns out to deviate to
lower values than B_chi with increasing electron density, which can be
explained by filling of the upper electron subbands in the fully spin-polarized
regime
Strongly enhanced effective mass in dilute two-dimensional electron systems: System-independent origin
We measure the effective mass in a dilute two-dimensional electron system in
(111)-silicon by analyzing temperature dependence of the Shubnikov-de Haas
oscillations in the low-temperature limit. A strong enhancement of the
effective mass with decreasing electron density is observed. The mass
renormalization as a function of the interaction parameter r_s is in good
agreement with that reported for (100)-silicon, which shows that the relative
mass enhancement is system- and disorder-independent being determined by
electron-electron interactions only.Comment: As publishe
N=2 Liouville Theory with Boundary
We study N=2 Liouville theory with arbitrary central charge in the presence
of boundaries. After reviewing the theory on the sphere and deriving some
important structure constants, we investigate the boundary states of the theory
from two approaches, one using the modular transformation property of annulus
amplitudes and the other using the bootstrap of disc two-point functions
containing degenerate bulk operators. The boundary interactions describing the
boundary states are also proposed, based on which the precise correspondence
between boundary states and boundary interactions is obtained. The open string
spectrum between D-branes is studied from the modular bootstrap approach and
also from the reflection relation of boundary operators, providing a
consistency check for the proposal.Comment: 1+48 pages, no figure. typos corrected and references added. the
version to appear in JHE
Supersymmetry enhancement by monopole operators
We describe a method which allows one to study hidden symmetries in a large
class of strongly coupled supersymmetric gauge theories in three dimensions. We
apply this method to the ABJM theory and to the infrared limit of N=4 SQCD with
adjoint and fundamental matter. We show that the U(N) ABJM model with
Chern-Simons level k=1 or k=2 has hidden N=8 supersymmetry. Hidden
supersymmetry is also shown to occur in N=4 d=3 SQCD with one fundamental and
one adjoint hypermultiplet. The latter theory, as well as the U(N) ABJM theory
at k=1, are shown to have a decoupled free sector. This provides evidence that
both models are dual to the infrared limit of N=8 U(N) super-Yang-Mills theory.Comment: 29 pages, late
Biomass burning and pollution aerosol over North America: Organic components and their influence on spectral optical properties and humidification response
Thermal analysis of aerosol size distributions provided size resolved volatility up to temperatures of 400°C during extensive flights over North America (NA) for the INTEX/ICARTT experiment in summer 2004. Biomass burning and pollution plumes identified from trace gas measurements were evaluated for their aerosol physiochemical and optical signatures. Measurements of soluble ionic mass and refractory black carbon (BC) mass, inferred from light absorption, were combined with volatility to identify organic carbon at 400°C (VolatileOC) and the residual or refractory organic carbon, RefractoryOC. This approach characterized distinct constituent mass fractions present in biomass burning and pollution plumes every 5â10 min. Biomass burning, pollution and dust aerosol could be stratified by their combined spectral scattering and absorption properties. The ânonplumeâ regional aerosol exhibited properties dominated by pollution characteristics near the surface and biomass burning aloft. VolatileOC included most water-soluble organic carbon. RefractoryOC dominated enhanced shortwave absorption in plumes from Alaskan and Canadian forest fires. The mass absorption efficiency of this RefractoryOC was about 0.63 m2 gâ1 at 470 nm and 0.09 m2 gâ1 at 530 nm. Concurrent measurements of the humidity dependence of scattering, Îł, revealed the OC component to be only weakly hygroscopic resulting in a general decrease in Îł with increasing OC mass fractions. Under ambient humidity conditions, the systematic relations between physiochemical properties and Îł lead to a well-constrained dependency on the absorption per unit dry mass for these plume types that may be used to challenge remotely sensed and modeled optical properties
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