83 research outputs found
Application and reliability of techniques for landslide site investigation, monitoring and early warning – outcomes from a questionnaire study
The presented questionnaire study summarizes an evaluation of approaches,
techniques and parameters of slope-instability investigation and monitoring
of their occurrence, reliability and the applicability of the monitoring
techniques for early warning. The study is based on information collected
from 86 monitored landslides in 14 European and Asian countries. Based on
the responses, lidar ALS (airborne laser scanners), geophysical logging, aerial photographs,
resistivity surveying, GB InSAR (ground-based synthetic aperture radar
interferometer) and the refraction seismic were considered
the most reliable methods for investigation of structure and character of
landslides. Especially lidar ALS and geophysical logging were ranked high
despite their application at relatively few landslides. Precipitation
amount, pore-water pressure and displacement monitored by wire
extensometers, dGPS and total stations, followed by air temperature and
EM-emissions monitoring and displacement monitored by the TM 71 crack gauge
were considered the most promising parameters for early warning
M31 Globular Cluster X-ray Sources: XMM-Newton and Chandra results
(Abridged) We present the results of M31 globular cluster (GC) X-ray source
survey, based on the data of XMM-Newton and Chandra observations covering ~6100
sq.arcmin of M31. We detected 43 X-ray sources coincident with globular cluster
candidates from optical surveys. The estimated isotropic X-ray luminosities of
GC sources lie between ~10e35 and ~10e39 erg/s in the 0.3 - 10 keV energy band.
The spectral properties and variability of M31 GC X-ray sources are consistent
with that derived for the LMXBs in the bulges of M31 and Milky Way. We found
that ~80% of the M31 GC sources with multiple flux measurements available show
significant variability on a time scales from days to years. The X-ray
luminosity function of GC sources is found to be significantly different from
that of the point sources in the bulge and disk of M31 and that of the Galactic
GC X-ray sources. GC sources make dominant contribution to the bright source
counts in the areas of M31 covered by the survey: ~40% of the total number of
sources with luminosities above 10e37 ergs/s reside in GCs with fraction of GC
sources rising to 67-90% for the luminosities above 10e38 ergs/s. The
contribution of the GC sources to the total number of bright sources found in
M31 is much higher than in the Milky Way galaxy, but surprisingly close to that
of the early-type galaxies. The brightest M31 GC sources tend to reside at
large galactocentric distances outside the central bulge. We found that
globular clusters hosting bright X-ray sources are optically brighter and more
metal rich than the rest of M31 globular clusters. The brightest sources with
luminosities above ~10e38 ergs/s show tendency to reside in more metal poor
clusters.Comment: 17 pages including 7 tables, 17 figures, uses emulateapj style.
Submitted to ApJ, a version with full resolution images is available at
http://hea.iki.rssi.ru/~tsp/papers/m31_gcs_astro_ph.ps.g
A Synoptic X-ray Study of M31 with the Chandra-HRC
We have obtained 17 epochs of Chandra High Resolution Camera (HRC) snapshot
images, each covering most of the M31 disk. The data cover a total baseline of
2.5 years and contain a mean effective exposure of 17 ks. We have measured the
mean fluxes and long-term lightcurves for 166 objects detected in these data.
At least 25% of the sources show significant variability. The cumulative
luminosity function (CLF) of the disk sources is well-fit by a power-law with a
slope comparable to those observed in typical elliptical galaxies. The CLF of
the bulge is a broken power law similar to measurements made by previous
surveys. We note several sources in the southwestern disk with L_X > 10^{37}
erg/s . We cross-correlate all of our sources with published optical and radio
catalogs, as well as new optical data, finding counterpart candidates for 55
sources. In addition, 17 sources are likely X-ray transients. We analyze
follow-up HST WFPC2 data of two X-ray transients, finding F336W (U-band
equivalent) counterparts. In both cases, the counterparts are variable. In one
case, the optical counterpart is transient with F336W = 22.3 +/- 0.1 mag. The
X-ray and optical properties of this object are consistent with a ~10 solar
mass black hole X-ray nova with an orbital period of ~20 days. In the other
case, the optical counterpart varies between F336W = 20.82 +/- 0.06 mag and
F336W = 21.11 +/- 0.02 mag. Ground-based and HST observations show this object
is bright (V = 18.8 +/- 0.1) and slightly extended. Finally, the frequency of
bright X-ray transients in the M31 bulge suggests that the ratio of neutron
star to black hole primaries in low-mass X-ray binaries (NS/BH) is ~1.Comment: 68 pages (27 text), 8 tables, 16 figures, 1 appendix, accepted by
ApJ; accepted version contains reorganized text, new tables and figures, and
updated result
The Nature of Ultra-Luminous Compact X-Ray Sources in Nearby Spiral Galaxies
Studies were made of ASCA spectra of seven ultra-luminous compact X-ray
sources (ULXs) in nearby spiral galaxies; M33 X-8 (Takano et al. 1994), M81 X-6
(Fabbiano 1988b; Kohmura et al. 1994; Uno 1997), IC 342 Source 1 (Okada et al.
1998), Dwingeloo 1 X-1 (Reynolds et al. 1997), NGC 1313 Source B (Fabbiano &
Trinchieri 1987; Petre et al. 1994), and two sources in NGC 4565 (Mizuno et al.
1999). With the 0.5--10 keV luminosities in the range 10^{39-40} ergs/s, they
are thought to represent a class of enigmatic X-ray sources often found in
spiral galaxies. For some of them, the ASCA data are newly processed, or the
published spectra are reanalyzed. For others, the published results are quoted.
The ASCA spectra of all these seven sources have been described successfully
with so called multi-color disk blackbody (MCD) emission arising from
optically-thick standard accretion disks around black holes. Except the case of
M33 X-8, the spectra do not exhibit hard tails. For the source luminosities not
to exceed the Eddington limits, the black holes are inferred to have rather
high masses, up to ~100 solar masses. However, the observed innermost disk
temperatures of these objects, Tin = 1.1--1.8 keV, are too high to be
compatible with the required high black-hole masses, as long as the standard
accretion disks around Schwarzschild black holes are assumed. Similarly high
disk temperatures are also observed from two Galactic transients with
superluminal motions, GRO 1655-40 and GRS 1915+105. The issue of unusually high
disk temperature may be explained by the black hole rotation, which makes the
disk get closer to the black hole, and hence hotter.Comment: submitted to ApJ, December 199
Reverse Engineering Gene Networks with ANN: Variability in Network Inference Algorithms
Motivation :Reconstructing the topology of a gene regulatory network is one
of the key tasks in systems biology. Despite of the wide variety of proposed
methods, very little work has been dedicated to the assessment of their
stability properties. Here we present a methodical comparison of the
performance of a novel method (RegnANN) for gene network inference based on
multilayer perceptrons with three reference algorithms (ARACNE, CLR, KELLER),
focussing our analysis on the prediction variability induced by both the
network intrinsic structure and the available data.
Results: The extensive evaluation on both synthetic data and a selection of
gene modules of "Escherichia coli" indicates that all the algorithms suffer of
instability and variability issues with regards to the reconstruction of the
topology of the network. This instability makes objectively very hard the task
of establishing which method performs best. Nevertheless, RegnANN shows MCC
scores that compare very favorably with all the other inference methods tested.
Availability: The software for the RegnANN inference algorithm is distributed
under GPL3 and it is available at the corresponding author home page
(http://mpba.fbk.eu/grimaldi/regnann-supmat
A ROSAT HRI survey of bright nearby galaxies
We use the extensive public archive of ROSAT High Resolution Imager (HRI)
observations to carry out a statistical investigation of the X-ray properties
of nearby galaxies. Specifically we focus on the sample of 486 bright (B_T <
12.5) northern galaxies studied by Ho, Filippenko and Sargent (HFS) in the
context of their exploration of the optical spectroscopic properties of nearby
galactic nuclei. Over 20% of HFS galaxies are encompassed in ROSAT HRI fields
of reasonable (> 10ks) exposure. The X-ray sources detected within the optical
extent of each galaxy are categorised as either nuclear or non-nuclear
depending on whether the source is positioned within or outside of a 25
arcsecond radius circle centred on the optical nucleus. A nuclear X-ray source
is detected in over 70% of the galaxies harbouring either a Seyfert or LINER
nucleus compared to a detection rate of only ~40% in less active systems. The
correlation of the H alpha luminosity with nuclear X-ray luminosity previously
observed in QSOs and bright Seyfert 1 galaxies appears to extend down into the
regime of ultra-low luminosity (L(x)~10^38 - 10^40 erg/s) active galactic
nuclei (AGN). The inferred accretion rates for this sample of low-luminosity
AGN are significantly sub-Eddington. In total 142 non-nuclear sources were
detected. In combination with published data for M31 this leads to a luminosity
distribution (normalised to an optical blue luminosity of L(B) = 10^10
L(solar)) for the discrete X-ray source population in spiral galaxies of the
form dN/dL38 = 1.0 +/- 0.2 L38^-1.8, where L38 is the X-ray luminosity in units
of 10^38 erg/s. The implied L(x)/L(B) ratio is ~1.1 x 10^39 erg/s/(10^10
L(solar)). The nature of the substantial number of ``super-luminous''
non-nuclear objects detected in the survey is discussed.Comment: 20 pages, 7 figures, accepted for publication in MNRAS. Also
available from http://www.star.le.ac.uk/~tro/papers/xhfs.p
Guidelines for the selection of appropriate remote sensing technologies for landslide detection, monitoring and rapid mapping: the experience of the SafeLand European Project
SBMLsqueezer: A CellDesigner plug-in to generate kinetic rate equations for biochemical networks
<p>Abstract</p> <p>Background</p> <p>The development of complex biochemical models has been facilitated through the standardization of machine-readable representations like SBML (Systems Biology Markup Language). This effort is accompanied by the ongoing development of the human-readable diagrammatic representation SBGN (Systems Biology Graphical Notation). The graphical SBML editor CellDesigner allows direct translation of SBGN into SBML, and vice versa. For the assignment of kinetic rate laws, however, this process is not straightforward, as it often requires manual assembly and specific knowledge of kinetic equations.</p> <p>Results</p> <p>SBMLsqueezer facilitates exactly this modeling step via automated equation generation, overcoming the highly error-prone and cumbersome process of manually assigning kinetic equations. For each reaction the kinetic equation is derived from the stoichiometry, the participating species (e.g., proteins, mRNA or simple molecules) as well as the regulatory relations (activation, inhibition or other modulations) of the SBGN diagram. Such information allows distinctions between, for example, translation, phosphorylation or state transitions. The types of kinetics considered are numerous, for instance generalized mass-action, Hill, convenience and several Michaelis-Menten-based kinetics, each including activation and inhibition. These kinetics allow SBMLsqueezer to cover metabolic, gene regulatory, signal transduction and mixed networks. Whenever multiple kinetics are applicable to one reaction, parameter settings allow for user-defined specifications. After invoking SBMLsqueezer, the kinetic formulas are generated and assigned to the model, which can then be simulated in CellDesigner or with external ODE solvers. Furthermore, the equations can be exported to SBML, LaTeX or plain text format.</p> <p>Conclusion</p> <p>SBMLsqueezer considers the annotation of all participating reactants, products and regulators when generating rate laws for reactions. Thus, for each reaction, only applicable kinetic formulas are considered. This modeling scheme creates kinetics in accordance with the diagrammatic representation. In contrast most previously published tools have relied on the stoichiometry and generic modulators of a reaction, thus ignoring and potentially conflicting with the information expressed through the process diagram. Additional material and the source code can be found at the project homepage (URL found in the Availability and requirements section).</p
The Hard X-ray Luminosity of OB Star Populations: Implications for the Contribution of Star Formation to the Cosmic X-ray Background
We present an empirical analysis of the integrated X-ray luminosity arising
from populations of OB stars. In particular, we utilize results from the
All-Sky Monitor on RXTE, along with archival data from previous missions, to
assess the mean integrated output of X-rays in the 2-10 keV band from accreting
early-type binaries within 3 kpc of the Sun. Using a recent OB star census of
the Solar neighborhood, we then calculate the specific X-ray luminosity per O
star from accretion-powered systems. We also assess the contribution to the
total X-ray luminosity of an OB population from associated T Tauri stars,
stellar winds, and supernovae. We repeat this exercise for the major Local
Group galaxies, concluding that the total X-ray luminosity per O star spans a
broad range from 2 to 20e34 erg/s. Contrary to previous results, we do not find
a consistent trend with metallicity; in fact, the specific luminosities for M31
and the SMC are equal, despite having metallicities which differ by an order of
magnitude. In light of these results, we assess the fraction of the observed
2-10 keV emission from starburst galaxies that arises directly from their OB
star populations, concluding that, while binaries can explain most of the hard
X-ray emission in many local starbursts, a significant additional component or
components must be present in some systems. A discussion of the nature of this
additional emission, along with its implications for the contribution of
starbursts to the cosmic X-ray background, concludes our report.Comment: aastex, 30 pages including 2 tables and 1 figure. To appear in Ap
Comparative Microbial Modules Resource: Generation and Visualization of Multi-species Biclusters
The increasing abundance of large-scale, high-throughput datasets for many closely related organisms provides opportunities for comparative analysis via the simultaneous biclustering of datasets from multiple species. These analyses require a reformulation of how to organize multi-species datasets and visualize comparative genomics data analyses results. Recently, we developed a method, multi-species cMonkey, which integrates heterogeneous high-throughput datatypes from multiple species to identify conserved regulatory modules. Here we present an integrated data visualization system, built upon the Gaggle, enabling exploration of our method's results (available at http://meatwad.bio.nyu.edu/cmmr.html). The system can also be used to explore other comparative genomics datasets and outputs from other data analysis procedures – results from other multiple-species clustering programs or from independent clustering of different single-species datasets. We provide an example use of our system for two bacteria, Escherichia coli and Salmonella Typhimurium. We illustrate the use of our system by exploring conserved biclusters involved in nitrogen metabolism, uncovering a putative function for yjjI, a currently uncharacterized gene that we predict to be involved in nitrogen assimilation
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