282 research outputs found
Feasibility of transit photometry of nearby debris discs
Dust in debris discs is constantly replenished by collisions between larger
objects. In this paper, we investigate a method to detect these collisions. We
generate models based on recent results on the Fomalhaut debris disc, where we
simulate a background star transiting behind the disc, due to the proper motion
of Fomalhaut. By simulating the expanding dust clouds caused by the collisions
in the debris disc, we investigate whether it is possible to observe changes in
the brightness of the background star. We conclude that in the case of the
Fomalhaut debris disc, changes in the optical depth can be observed, with
values of the optical depth ranging from for the densest dust
clouds to for the most diffuse clouds with respect to the background
optical depth of .Comment: 19 pages, 15 figures, accepted for publication in MNRA
Dust absorption and scattering in the silicon K-edge
The composition and properties of interstellar silicate dust are not well
understood. In X-rays, interstellar dust can be studied in detail by making use
of the fine structure features in the Si K-edge. The features in the Si K-edge
offer a range of possibilities to study silicon-bearing dust, such as
investigating the crystallinity, abundance, and the chemical composition along
a given line of sight. We present newly acquired laboratory measurements of the
silicon K-edge of several silicate-compounds that complement our measurements
from our earlier pilot study. The resulting dust extinction profiles serve as
templates for the interstellar extinction that we observe. The extinction
profiles were used to model the interstellar dust in the dense environments of
the Galaxy. The laboratory measurements, taken at the Soleil synchrotron
facility in Paris, were adapted for astrophysical data analysis and implemented
in the SPEX spectral fitting program. The models were used to fit the spectra
of nine low-mass X-ray binaries located in the Galactic center neighborhood in
order to determine the dust properties along those lines of sight. Most lines
of sight can be fit well by amorphous olivine. We also established upper limits
on the amount of crystalline material that the modeling allows. We obtained
values of the total silicon abundance, silicon dust abundance, and depletion
along each of the sightlines. We find a possible gradient of
dex/kpc for the total silicon abundance versus the Galactocentric distance. We
do not find a relation between the depletion and the extinction along the line
of sight.Comment: 18 pages, 16 figures. Accepted for publication in Astronomy and
Astrophysic
Investigating the interstellar dust through the Fe K-edge
The chemical and physical properties of interstellar dust in the densest
regions of the Galaxy are still not well understood. X-rays provide a powerful
probe since they can penetrate gas and dust over a wide range of column
densities (up to ). The interaction (scattering and
absorption) with the medium imprints spectral signatures that reflect the
individual atoms which constitute the gas, molecule, or solid. In this work we
investigate the ability of high resolution X-ray spectroscopy to probe the
properties of cosmic grains containing iron. Although iron is heavily depleted
into interstellar dust, the nature of the Fe-bearing grains is still largely
uncertain. In our analysis we use iron K-edge synchrotron data of minerals
likely present in the ISM dust taken at the European Synchrotron Radiation
Facility. We explore the prospects of determining the chemical composition and
the size of astrophysical dust in the Galactic centre and in molecular clouds
with future X-ray missions. The energy resolution and the effective area of the
present X-ray telescopes are not sufficient to detect and study the Fe K-edge,
even for bright X-ray sources. From the analysis of the extinction cross
sections of our dust models implemented in the spectral fitting program SPEX,
the Fe K-edge is promising for investigating both the chemistry and the size
distribution of the interstellar dust. We find that the chemical composition
regulates the X-ray absorption fine structures in the post edge region, whereas
the scattering feature in the pre-edge is sensitive to the mean grain size.
Finally, we note that the Fe K-edge is insensitive to other dust properties,
such as the porosity and the geometry of the dust.Comment: 11 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Trapping of drops by wetting defects
Controlling the motion of drops on solid surfaces is crucial in many natural phenomena and technological processes including the collection and removal of rain drops, cleaning technology and heat exchangers. Topographic and chemical heterogeneities on solid surfaces give rise to pinning forces that can capture and steer drops in desired directions. Here we determine general physical conditions required for capturing sliding drops on an inclined plane that is equipped with electrically tunable wetting defects. By mapping the drop dynamics on the one-dimensional motion of a point mass, we demonstrate that the trapping process is controlled by two dimensionless parameters, the trapping strength measured in units of the driving force and the ratio between a viscous and an inertial time scale. Complementary experiments involving superhydrophobic surfaces with wetting defects demonstrate the general applicability of the concept. Moreover, we show that electrically tunable defects can be used to guide sliding drops along actively switchable tracks—with potential applications in microfluidic
X-ray extinction from interstellar dust: Prospects of observing carbon, sulfur and other trace elements
We present a study on the prospects of observing carbon, sulfur, and other
lower abundance elements (namely Al, Ca, Ti and Ni) present in the interstellar
medium using future X-ray instruments. We focus in particular on the detection
and characterization of interstellar dust along the lines of sight. We compare
the simulated data with different sets of dust aggregates, either obtained from
past literature or measured by us using the SOLEIL-LUCIA synchrotron beamline.
Extinction by interstellar grains induces modulations of a given photolelectric
edge, which can be in principle traced back to the chemistry of the absorbing
grains. We simulated data of instruments with characteristics of resolution and
sensitivity of the current Athena, XRISM and Arcus concepts. In the relatively
near future, the depletion and abundances of the elements under study will be
determined with confidence. In the case of carbon and sulfur, the
characterization of the chemistry of the absorbing dust will be also
determined, depending on the dominant compound. For aluminum and calcium,
despite the large depletion in the interstellar medium and the prominent dust
absorption, in many cases the edge feature may not be changing significantly
with the change of chemistry in the Al or Ca bearing compounds. The
exinction signature of large grains may be detected and modeled, allowing a
test on different grain size distributions for these elements. The low cosmic
abundance of Ti and Ni will not allow us a detailed study of the edge features.Comment: 12 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysic
Interstellar oxygen along the line of sight of Cygnus X-2
Interstellar dust permeates our Galaxy and plays an important role in many
physical processes in the diffuse and dense regions of the interstellar medium.
High-resolution X-ray spectroscopy, coupled with modelling based on laboratory
dust measurements, provides a unique probe to investigate the interstellar dust
properties along our line of sight towards Galactic X-ray sources. Here, we
focus on the oxygen content of the interstellar medium through its absorption
features in the X-ray spectra. To model the dust features, we perform a
laboratory experiment using the electron microscope facility located at the
University of Cadiz in Spain, where we acquire new laboratory data in the
oxygen K-edge. We study 18 dust samples of silicates and oxides with different
chemical compositions. The laboratory measurements are adopted for our
astronomical data analysis. We carry out a case study on the X-ray spectrum of
the bright low-mass X-ray binary Cygnus X-2, observed by XMM-Newton. We
determine different temperature phases of the ISM, and parameterize oxygen in
both gas (neutral and ionised) and dust form. We find Solar abundances of
oxygen along the line of sight towards the source. Due to both the relatively
low depletion of oxygen into dust form and the shape of the oxygen cross
section profiles, it is challenging to determine the precise chemistry of
interstellar dust. However, silicates provide an acceptable fit. Finally, we
discuss the systematic discrepancies in the atomic (gaseous phase) data of the
oxygen edge spectral region using different X-ray atomic databases, and also
consider future prospects for studying the ISM with the Arcus concept mission.Comment: Accepted for publication in A&A, 15 pages, 11 figure
Magnesium and silicon in interstellar dust: an X-ray overview
The dense Galactic environment is a large reservoir of interstellar dust.
Therefore, this region represents a perfect laboratory to study the properties
of the cosmic dust grains. X-rays are the most direct way to detect the
interaction of light with dust present in these dense environments. The
interaction between the radiation and the interstellar matter imprints specific
absorption features in the X-ray spectrum. We study them with the aim of
defining the chemical composition, the crystallinity and structure of the dust
grains which populate the inner regions of the Galaxy. We investigate the
magnesium and the silicon K-edges detected in the Chandra/HETG spectra of eight
bright X-ray binaries, distributed in the neighbourhood of the Galactic centre.
We model the two spectral features using accurate extinction cross sections of
silicates, that we have measured at the synchrotron facility Soleil, France.
Near the Galactic centre magnesium and silicon show abundances similar to the
solar ones and they are highly depleted from the gas phase
( and ). We find that amorphous
olivine with a composition of is the most representative
compound along all lines of sight according to our fits. The contribution of
Mg-rich silicates and quartz is low (less than ). On average we observe a
percentage of crystalline dust equal to . For the extragalactic source
LMC X-1, we find a preference for forsterite, a magnesium-rich olivine. Along
this line of sight we also observe an underabundance of silicon .Comment: 16 pages, 7 figures, recommended for publication in Astronomy and
Astrophysic
Urinary EpCAM in urothelial bladder cancer patients: characterisation and evaluation of biomarker potential
Background:
Epithelial cell adhesion molecule is overexpressed in bladder tumours and released from bladder cancer cells in vitro. We test the hypotheses that urinary EpCAM could act as a biomarker for primary bladder cancer detection and risk stratification.
Methods:
Epithelial cell adhesion molecule was measured by ELISA in urine from 607 patients with primary bladder tumours and in urine from 53 non-cancer controls. Mann–Whitney tests and ROC analyses were used to determine statistical significance and discrimination between non-cancer controls and different stages and grades of disease. Multivariable modelling and Kaplan–Meier analyses were used to determine prognostic significance. The structure of urinary EpCAM was investigated by western blotting and mass spectrometry.
Results:
Urinary EpCAM levels increase with stage and grade of bladder cancer. Alongside grade and stage, elevated urinary EpCAM is an independent indicator of poor prognosis with a hazard ratio of 1.76 for bladder cancer-specific mortality. The soluble form of EpCAM in urine is the extracellular domain generated by cleavage between ala243 and gly244. Further studies are required to define the influence of other urinary tract malignancies and benign urological conditions on urinary EpCAM.
Conclusion:
The extracellular domain of EpCAM is shed into urine by bladder tumours. Urinary EpCAM is a strong indicator of bladder cancer-specific survival, and may be useful within a multi-marker panel for disease detection or as a stand-alone marker to prioritise the investigation and treatment of patients. The mechanisms and effects of EpCAM cleavage in bladder cancer are worthy of further investigation, and may identify novel therapeutic targets
The polyAT, intronic IVS11-6 and Lys939Gln XPC polymorphisms are not associated with transitional cell carcinoma of the bladder
Chemical carcinogens from cigarette smoking and occupational exposure are risk factors for bladder transitional cell carcinoma (TCC). The Xeroderma Pigmentosum Group C (XPC) gene is essential for repair of bulky adducts from carcinogens. The Xeroderma Pigmentosum Group C gene polymorphisms may alter DNA repair capacity (DRC), thus giving rise to genetic predisposition to bladder cancer. Recent studies have demonstrated linkage disequilibrium between three polymorphisms in the XPC gene (polyAT, IVS11-6 and Lys939Gln) and these have been shown to influence the DRC, as well as to be associated with bladder cancer risk. We analysed all three XPC polymorphisms in 547 bladder TCC patients and 579 cancer-free controls to investigate the association between these polymorphisms and bladder cancer susceptibility, and we also attempted to assess gene–environmental interactions. We confirmed strong linkage disequilibrium among the polymorphisms (Lewontin's D′>0.99). Using logistic regression adjusting for smoking, occupational and family history, neither the heterozygote nor the homozygote variants of these polymorphisms were associated with increased bladder cancer risk (adjusted odds ratio [95% confidence interval] for heterozygote 0.82 [0.63–1.07], 0.82 [0.63–1.08] and 0.83 [0.63–1.08] for PolyAT, IVS11-6 and Lys939Gln, respectively and homozygote variant, 0.98 [0.68–1.42], 0.99 [0.69–1.43] and 1.01 [0.70–1.46]). Moreover, we did not find any significant interaction between these XPC polymorphisms and environmental exposure to cigarette smoking and occupational carcinogens
The X-ray side of the absorption by interstellar dust in the Milky Way
X-ray spectroscopy of interstellar dust (ID), seen in absorption against spectra of bright background sources, is a powerful tool to investigate and provide novel information on the chemistry of dust grains. For example, sharp and deep absorption features of Mg, Si, O and Fe, which are the building blocks of silicates, fall in the X-ray band. Therefore X-ray spectroscopy can also successfully study the nature of the iron inclusion in dust. The shift and the structure of a given absorption feature is indeed different for different absorbing dust grains. High-quality data have already revealed that Mg-rich silicates are favored with respect to the Fe-rich population and that Fe is most likely in metallic form. The modeling of spectra of present and future X-ray facilities will take now advantage of our new laboratory measurements, from several species, of the absorption features which are key for a complete understanding of the ID chemistry
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