238 research outputs found
Some remarks on D-branes and defects in Liouville and Toda field theories
In this paper we analyze the Cardy-Lewellen equation in general diagonal
model. We show that in these models it takes simple form due to some general
properties of conformal field theories, like pentagon equations and OPE
associativity. This implies, that the Cardy-Lewellen equation has simple form
also in non-rational diagonal models. We specialize our finding to the
Liouville and Toda field theories. In particular we prove, that conjectured
recently defects in Toda field theory indeed satisfy the cluster equation. We
also derive the Cardy-Lewellen equation in all Toda field theories and
prove that the forms of boundary states found recently in Toda field
theory hold in all theories as well.Comment: 30 pages, some comments, explanations and references adde
On the crossing relation in the presence of defects
The OPE of local operators in the presence of defect lines is considered both
in the rational CFT and the Virasoro (Liouville) theory. The duality
transformation of the 4-point function with inserted defect operators is
explicitly computed. The two channels of the correlator reproduce the
expectation values of the Wilson and 't Hooft operators, recently discussed in
Liouville theory in relation to the AGT conjecture.Comment: TEX file with harvmac; v3: JHEP versio
Coexistence of Long-Range Magnetic Order and Superconductivity from Campbell Penetration Depth Measurements
Application of a tunnel-diode resonator (TDR) technique for studies of the
vortex response in magnetic superconductors is described. Operating at very
small excitation fields and sufficiently high frequency, TDR was used to probe
small-amplitude linear AC response in several types of single crystals where
long-range magnetic order coexists with bulk superconductivity. Full local -
moment ferromagnetism destroys superconductivity and can coexist with it only
in a narrow temperature range ( K). In contrast, weak ferromagnetic
as well as antiferromagnetic orders can coexist with bulk superconductivity and
may even lead to enhancements of vortex pinning. By analyzing the Campbell
penetration depth we find sharp increase of the true critical current in the
vicinity of the magnetic phase transitions. We conclude that critical magnetic
fluctuations are responsible for this enhancement
Upper bounds on the low-frequency stochastic gravitational wave background from pulsar timing observations: current limits and future prospects
Using a statistically rigorous analysis method, we place limits on the
existence of an isotropic stochastic gravitational wave background using pulsar
timing observations. We consider backgrounds whose characteristic strain
spectra may be described as a power-law dependence with frequency. Such
backgrounds include an astrophysical background produced by coalescing
supermassive black-hole binary systems and cosmological backgrounds due to
relic gravitational waves and cosmic strings. Using the best available data, we
obtain an upper limit on the energy density per unit logarithmic frequency
interval of \Omega^{\rm SMBH}_g(1/8yr) h^2 <= 1.9 x 10^{-8} for an
astrophysical background which is five times more stringent than the earlier
Kaspi et al. (1994) limit of 1.1 x 10^{-7}. We also provide limits on a
background due to relic gravitational waves and cosmic strings of \Omega^{\rm
relic}_g(1/8yr) h^2 <= 2.0 x 10^{-8} and \Omega^{\rm cs}_g(1/8yr) h^2 <= 1.9 x
10^{-8} respectively. All of the quoted upper limits correspond to a 0.1% false
alarm rate together with a 95% detection rate. We discuss the physical
implications of these results and highlight the future possibilities of the
Parkes Pulsar Timing Array project. We find that our current results can 1)
constrain the merger rate of supermassive binary black hole systems at high red
shift, 2) rule out some relationships between the black hole mass and the
galactic halo mass, 3) constrain the rate of expansion in the inflationary era
and 4) provide an upper bound on the dimensionless tension of a cosmic string
background.Comment: Accepted by Ap
Status Update of the Parkes Pulsar Timing Array
The Parkes Pulsar Timing Array project aims to make a direct detection of a
gravitational-wave background through timing of millisecond pulsars. In this
article, the main requirements for that endeavour are described and recent and
ongoing progress is outlined. We demonstrate that the timing properties of
millisecond pulsars are adequate and that technological progress is timely to
expect a successful detection of gravitational waves within a decade, or
alternatively to rule out all current predictions for gravitational wave
backgrounds formed by supermassive black-hole mergers.Comment: 10 pages, 3 figures, Amaldi 8 conference proceedings, accepted by
Classical & Quantum Gravit
Development of a pulsar-based timescale
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA)
project we develop the first pulsar-based timescale that has a precision
comparable to the uncertainties in international atomic timescales. Our
ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the
free atomic timescale Echelle Atomique Libre (EAL). The EPS can be used to
detect fluctuations in atomic timescales and therefore can lead to a new
realisation of Terrestrial Time, TT(PPTA11). We successfully follow features
known to affect the frequency of the International Atomic Timescale (TAI) and
we find marginally significant differences between TT(PPTA11) and TT(BIPM11).
We discuss the various phenomena that lead to a correlated signal in the pulsar
timing residuals and therefore limit the stability of the pulsar timescale.Comment: Accepted for publication in MNRA
Microscopic Selection of Fluid Fingering Pattern
We study the issue of the selection of viscous fingering patterns in the
limit of small surface tension. Through detailed simulations of anisotropic
fingering, we demonstrate conclusively that no selection independent of the
small-scale cutoff (macroscopic selection) occurs in this system. Rather, the
small-scale cutoff completely controls the pattern, even on short time scales,
in accord with the theory of microscopic solvability. We demonstrate that
ordered patterns are dynamically selected only for not too small surface
tensions. For extremely small surface tensions, the system exhibits chaotic
behavior and no regular pattern is realized.Comment: 6 pages, 5 figure
The Mean Pulse Profile of PSR J0737-3039A
General relativity predicts that the spin axes of the pulsars in the
double-pulsar system (PSR J0737-3039A/B) will precess rapidly, in general
leading to a change in the observed pulse profiles. We have observed this
system over a one-year interval using the Parkes 64-m radio telescope at three
frequencies: 680, 1390 and 3030 MHz. These data, combined with the short survey
observation made two years earlier, show no evidence for significant changes in
the pulse profile of PSR J0737-3039A, the 22-ms pulsar. The limit on variations
of the profile 10% width is about 0.5 deg per year. These results imply an
angle delta between the pulsar spin axis and the orbit normal of <~ 60 deg,
consistent with recent evolutionary studies of the system. Although a wide
range of system parameters remain consistent with the data, the model proposed
by Jenet & Ransom (2004) can be ruled out. A non-zero ellipticity for the
radiation beam gives slightly but not significantly improved fits to the data,
so that a circular beam describes the data equally well within the
uncertainties.Comment: 7 pages, 4 figures, accepted by ApJ Letter
The international pulsar timing array project: using pulsars as a gravitational wave detector
The International Pulsar Timing Array project combines observations of
pulsars from both Northern and Southern hemisphere observatories with the main
aim of detecting ultra-low frequency (~10^-9 to 10^-8 Hz) gravitational waves.
Here we introduce the project, review the methods used to search for
gravitational waves emitted from coalescing supermassive binary black-hole
systems in the centres of merging galaxies and discuss the status of the
project.Comment: accepted by Classical and Quantum Gravity. Review talk for the
Amaldi8 conference serie
Detection of serum MMP-7 and MMP-9 in cholangiocarcinoma patients: evaluation of diagnostic accuracy
<p>Abstract</p> <p>Background</p> <p>Cholangiocarcinoma is an aggressive tumor with a tendency for local invasion and distant metastases. Timely diagnosis is very important because surgical resection (R0) remains the only hope for a cure. However, at present, there is no available tumor marker that can differentiate cholangiocarcinoma from benign bile duct disease. Previous studies have demonstrated that matrix metalloproteinase (MMP)-7 and MMP-9 are frequently expressed in cholangiocarcinoma specimens.</p> <p>Methods</p> <p>This study was designed to determine whether the serum levels of MMP-7 and MMP-9 can discriminate cholangiocarcinoma patients from benign biliary tract disease patients in comparison to carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9). We measured the level of CEA, CA19-9, MMP-7 and MMP-9 in the serum of 44 cholangiocarcinoma and 36 benign biliary tract diseases patients.</p> <p>Results</p> <p>Among the serum levels of CEA, CA19-9, MMP-7 and MMP-9, only the serum MMP-7 level was significantly higher in the patients with cholangiocarcinoma (8.9 ± 3.43 ng/ml) compared to benign biliary tract disease patients (5.9 ± 3.03 ng/ml) (<it>p </it>< 0.001). An receiver operating characteristic (ROC) curve analysis revealed that the detection of the serum MMP-7 level is reasonably accurate in differentiating cholangiocarcinoma from benign biliary tract disease patients (area under curve = 0.73; 95% CI = 0.614–0.848). While the areas under the curve of the ROC curves for CEA, CA19-9 and MMP-9 were 0.63 (95% CI = 0.501–0.760), 0.63 (95% CI = 0.491–0.761) and 0.59 (95% CI = 0.455–0.722), respectively.</p> <p>Conclusion</p> <p>Serum MMP-7 appears to be a valuable diagnostic marker in the discrimination of cholangiocarcinoma from benign biliary tract disease. Further prospective studies for serum MMP-7 measurement should be carried out to further investigate the potential of this molecule as a biomarker of cholangiocarcinoma.</p
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