340 research outputs found
Extended Source Effects in Astrometric Gravitational Microlensing
Extended source size effects have been detected in photometric monitoring of
gravitational microlensing events. We study similar effects in the centroid
motion of an extended source lensed by a point mass. We show that the centroid
motion of a source with uniform surface brightness can be obtained
analytically. For a source with circularly symmetric limb-darkening profile,
the centroid motion can be expressed as a one-dimensional integral, which can
be evaluated numerically. We found that when the impact parameter is comparable
to the source radius, the centroid motion is significantly modified by the
finite source size. In particular, when the impact parameter is smaller than
the source radius, the trajectories become clover-leaf like. Such astrometric
motions can be detected using space interferometers such as the Space
Interferometry Mission. Such measurements offer exciting possibilities of
determining stellar parameters such as stellar radius to excellent accuracy.Comment: 10 pages, 2 figures, submitted to MNRA
Gravitational Lenses With More Than Four Images: I. Classification of Caustics
We study the problem of gravitational lensing by an isothermal elliptical
density galaxy in the presence of a tidal perturbation. When the perturbation
is fairly strong and oriented near the galaxy's minor axis, the lens can
produce image configurations with six or even eight highly magnified images
lying approximately on a circle. We classify the caustic structures in the
model and identify the range of models that can produce such lenses. Sextuple
and octuple lenses are likely to be rare because they require special lens
configurations, but a full calculation of the likelihood will have to include
both the existence of lenses with multiple lens galaxies and the strong
magnification bias that affects sextuple and octuple lenses. At optical
wavelengths these lenses would probably appear as partial or complete Einstein
rings, but at radio wavelengths the individual images could probably be
resolved.Comment: 30 pages, including 12 postscript figures; accepted for publication
in Ap
Analytic Time Delays and H_0 Estimates for Gravitational Lenses
We study gravitational lens time delays for a general family of lensing
potentials, which includes the popular singular isothermal elliptical potential
and singular isothermal elliptical density distribution but allows general
angular structure. Using a novel approach, we show that the time delay can be
cast in a very simple form, depending only on the observed image positions.
Including an external shear changes the time delay proportional to the shear
strength, and varying the radial profile of the potential changes the time
delay approximately linearly. These analytic results can be used to obtain
simple estimates of the time delay and the Hubble constant in observed
gravitational lenses. The naive estimates for four of five time delay lenses
show surprising agreement with each other and with local measurements of H_0;
the complicated Q 0957+561 system is the only outlier. The agreement suggests
that it is reasonable to use simple isothermal lens models to infer H_0,
although it is still important to check this conclusion by examining detailed
models and by measuring more lensing time delays.Comment: 16 pages with 2 embedded figures; submitted to Ap
Using Quadruple Lenses to probe the Structure of the Lensing Galaxy
We show here that quadruple lenses can be useful laboratories to probe
whether the potential of the lensing galaxy is purely elliptical or whether an
additional distortion is present in the deflector plane. For this test we only
have to know the relative image positions of the quadruple lens system and the
(relative) center of light position of the lensing galaxy. Furthermore we
introduce new methods which easily allow us to determine the location (rotation
angle relative to the image positions) of the major axis of the lensing galaxy.
In due course we can determine the parity of the four images as well. We apply
these methods to the 8 currently known quadruple lenses and find that in the
case of MG 0414+0534, CLASS 1608+656 and HST 12531-2914 it is impossible to
accommodate the relative image positions and the galaxy position with any
elliptical potential whereas the other five cases can be described very well
with a simple elliptical potential. This method will have important impacts for
-fits and the reconstruction of galaxy models for quadruple lenses.Comment: 10 pages, 2 Postscript figures, uses AASTeX v4.0 macro
Lensing by a singular isothermal sphere and a black hole
Most galaxies host central supermassive black holes. As two galaxies merge,
the black holes also merge. The final single black hole may suffer a kick due
to asymmetric gravitational radiation and may not be at the centre of the
galaxy; off-centre black holes may also be produced by other means such as
sustained acceleration due to asymmetric jet power. We model the main galaxy as
a singular isothermal sphere and the black hole as an off-centre point lens,
and study the critical curves and caustics using complex notation. We identify
the critical parameters that govern the transitions in the topology of critical
curves, caustics and pseudo-caustics, and find the number of images can be two,
three, four and five. We show examples of image configurations, including cases
where three highly de-magnified images are found close to the centre. The
perturbation on the image magnification due to the black hole scales linearly
with its mass in the off-centre case, and quadratically when the black hole is
at the centre. Such images are difficult to observe unless high-contrast and
high-resolution imaging facilities (e.g., the Square Kilometer Array in the
radio) become available.Comment: 10 pages, 10 figures, MNRAS, in pres
A Common Variant of PNPLA3 (p.I148M) Is Not Associated with Alcoholic Chronic Pancreatitis
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110441.pdf (publisher's version ) (Open Access)BACKGROUND: Chronic pancreatitis (CP) is an inflammatory disease that in some patients leads to exocrine and endocrine dysfunction. In industrialized countries the most common aetiology is chronic alcohol abuse. Descriptions of associated genetic alterations in alcoholic CP are rare. However, a common PNPLA3 variant (p.I148M) is associated with the development of alcoholic liver cirrhosis (ALC). Since, alcoholic CP and ALC share the same aetiology PNPLA3 variant (p.I148M) possibly influences the development of alcoholic CP. METHODS: Using melting curve analysis we genotyped the variant in 1510 patients with pancreatitis or liver disease (961 German and Dutch alcoholic CP patients, 414 German patients with idiopathic or hereditary CP, and 135 patients with ALC). In addition, we included in total 2781 healthy controls in the study. RESULTS: The previously published overrepresentation of GG-genotype was replicated in our cohort of ALC (p-value <0.0001, OR 2.3, 95% CI 1.6-3.3). Distributions of genotype and allele frequencies of the p.I148M variant were comparable in patients with alcoholic CP, idiopathic and hereditary CP and in healthy controls. CONCLUSIONS: The absence of an association of PNPLA3 p.I148M with alcoholic CP seems not to point to a common pathway in the development of alcoholic CP and alcoholic liver cirrhosis
Genetic Analyses of Heme Oxygenase 1 (HMOX1) in Different Forms of Pancreatitis
Contains fulltext :
107993.pdf (publisher's version ) (Open Access)BACKGROUND: Heme oxygenase 1 (HMOX1) is the rate limiting enzyme in heme degradation and a key regulator of inflammatory processes. In animal models the course of pancreatitis was ameliorated by up-regulation of HMOX1 expression. Additionally, carbon monoxide released during heme breakdown inhibited proliferation of pancreatic stellate cells and might thereby prevent the development of chronic pancreatitis (CP). Transcription of HMOX1 in humans is influenced by a GT-repeat located in the promoter. As such, HMOX1 variants might be of importance in the pathogenesis of pancreatitis. METHODS: The GT-repeat and SNP rs2071746 were investigated with fluorescence labelled primers and by melting curve analysis in 285 patients with acute pancreatitis, 208 patients with alcoholic CP, 207 patients with idiopathic/hereditary CP, 147 patients with alcoholic liver cirrhosis, and in 289 controls, respectively. GT-repeat analysis was extended to a total of 446 alcoholic CP patients. In addition, we performed DNA sequencing in 145 patients with alcoholic CP, 138 patients with idiopathic/hereditary CP, 147 patients with alcoholic liver cirrhosis, and 151 controls. Exon 3 screening was extended to additional patients and controls. RESULTS: S- and L-alleles of the GT-repeat, genotypes and alleles of SNP rs2071746 and non-synonymous variants detected by sequencing were found with similar frequencies in all groups. CONCLUSIONS: Although functional data implicate a potential influence of HMOX1 variants on the pathogenesis of pancreatitis, we did not find any association. As rare non-synonymous HMOX1 variants were found in patients and controls, it is rather unlikely that they will have functional consequences essential for pancreatitis development
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DNA methylation-based classification of central nervous system tumours.
Accurate pathological diagnosis is crucial for optimal management of patients with cancer. For the approximately 100 known tumour types of the central nervous system, standardization of the diagnostic process has been shown to be particularly challenging-with substantial inter-observer variability in the histopathological diagnosis of many tumour types. Here we present a comprehensive approach for the DNA methylation-based classification of central nervous system tumours across all entities and age groups, and demonstrate its application in a routine diagnostic setting. We show that the availability of this method may have a substantial impact on diagnostic precision compared to standard methods, resulting in a change of diagnosis in up to 12% of prospective cases. For broader accessibility, we have designed a free online classifier tool, the use of which does not require any additional onsite data processing. Our results provide a blueprint for the generation of machine-learning-based tumour classifiers across other cancer entities, with the potential to fundamentally transform tumour pathology
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