605 research outputs found
Almost everywhere uniqueness of blow-up limits for the lower dimensional obstacle problem
We answer a question left open in [4] and [3], by proving that the blow-up of minimizers u of the lower dimensional obstacle problem is unique at generic point of the free boundary
A high Eddington-ratio, true Seyfert 2 galaxy candidate: implications for broad-line-region models
A bright, soft X-ray source was detected on 2010 July 14 during an
XMM--Newton slew at a position consistent with the galaxy GSN 069 (z=0.018).
Previous ROSAT observations failed to detect the source and imply that GSN 069
is now >240 times brighter than it was in 1994 in the soft X-ray band. We
report here results from a ~1 yr monitoring with Swift and XMM-Newton, as well
as from optical spectroscopy. GSN 069 is an unabsorbed, ultra-soft source in
X-rays, with no flux detected above ~1 keV. The soft X-rays exhibit significant
variability down to timescales of hundreds of seconds. The UV-to-X-ray spectrum
of GSN 069 is consistent with a pure accretion disc model which implies an
Eddington ratio of ~0.5 and a black hole mass of ~ 1.2 million solar masses. A
new optical spectrum, obtained ~3.5 months after the XMM-Newton slew detection,
is consistent with earlier spectra and lacks any broad line component,
classifying the source as a Seyfert 2 galaxy. The lack of cold X-ray absorption
and the short timescale variability in the soft X-rays rule out a standard
Seyfert 2 interpretation of the X-ray data. We discuss our results within the
framework of two possible scenarios for the broad-line-region (BLR) in AGN,
namely the two-phase model (cold BLR clouds in pressure equilibrium with a
hotter medium), and models in which the BLR is part of an outflow, or
disc-wind. Finally, we point out that GSN 069 may be a member of a population
of super-soft AGN whose SED is completely dominated by accretion disc emission,
as it is the case in some black hole X-ray binary transients during their
outburst evolution. The disc emission for a typical AGN with larger black hole
mass than GSN 069 does not enters the soft X-ray band, so that GSN 069-like
objects would likely be missed by current X-ray surveys, or mis-classified as
Compton-thick candidates. (ABRIDGED)Comment: Accepted for publication in MNRA
Towards the Use of Neuromusculoskeletal Modeling in Clinical Practice:A Feasibility Study in Parkinson Disease Patients
Continuous flow analysis method for determination of soluble iron and aluminium in ice cores
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Shaping and Dilating the Fitness Landscape for Parameter Estimation in Stochastic Biochemical Models
The parameter estimation (PE) of biochemical reactions is one of the most challenging tasks in systems biology given the pivotal role of these kinetic constants in driving the behavior of biochemical systems. PE is a non-convex, multi-modal, and non-separable optimization problem with an unknown fitness landscape; moreover, the quantities of the biochemical species appearing in the system can be low, making biological noise a non-negligible phenomenon and mandating the use of stochastic simulation. Finally, the values of the kinetic parameters typically follow a log-uniform distribution; thus, the optimal solutions are situated in the lowest orders of magnitude of the search space. In this work, we further elaborate on a novel approach to address the PE problem based on a combination of adaptive swarm intelligence and dilation functions (DFs). DFs require prior knowledge of the characteristics of the fitness landscape; therefore, we leverage an alternative solution to evolve optimal DFs. On top of this approach, we introduce surrogate Fourier modeling to simplify the PE, by producing a smoother version of the fitness landscape that excludes the high frequency components of the fitness function. Our results show that the PE exploiting evolved DFs has a performance comparable with that of the PE run with a custom DF. Moreover, surrogate Fourier modeling allows for improving the convergence speed. Finally, we discuss some open problems related to the scalability of our methodology
A year-round measurement of water-soluble trace and rare earth elements in arctic aerosol: Possible inorganic tracers of specific events
This study presents the year-round variability of the water-soluble fraction of trace elements (wsTE) and rare earth elements (wsREE) among size segregated airborne particulate matter samples collected at Ny-Å lesund in the Svalbard Archipelago from 26 February 2018 to 26 February 2019. Six different aerosol dimensional fractions were collected using a multi-stage Andersen impactor to better understand local and global circulation with the aim of disentangling the source of inorganic tracers from specific natural or anthropogenic sources. The wsTE and wsREE content, especially in the finest fractions in remote areas, is primarily related to long-range transport and it gives valuable information on (1) the global circulation, (2) the natural sources and (3) the contribution of human activities to aerosol composition. A Factor Analysis was applied to the dataset, including levoglucosan and methanesulfonic acid (MSA), to assess the possibility of using certain inorganic tracers as indicators of specific transport events or circulation regimes. We also investigate back-trajectories to determine potential source areas
Realfast: Real-Time, Commensal Fast Transient Surveys with the Very Large Array
Radio interferometers have the ability to precisely localize and better
characterize the properties of sources. This ability is having a powerful
impact on the study of fast radio transients, where a few milliseconds of data
is enough to pinpoint a source at cosmological distances. However, recording
interferometric data at millisecond cadence produces a terabyte-per-hour data
stream that strains networks, computing systems, and archives. This challenge
mirrors that of other domains of science, where the science scope is limited by
the computational architecture as much as the physical processes at play. Here,
we present a solution to this problem in the context of radio transients:
realfast, a commensal, fast transient search system at the Jansky Very Large
Array. Realfast uses a novel architecture to distribute fast-sampled
interferometric data to a 32-node, 64-GPU cluster for real-time imaging and
transient detection. By detecting transients in situ, we can trigger the
recording of data for those rare, brief instants when the event occurs and
reduce the recorded data volume by a factor of 1000. This makes it possible to
commensally search a data stream that would otherwise be impossible to record.
This system will search for millisecond transients in more than 1000 hours of
data per year, potentially localizing several Fast Radio Bursts, pulsars, and
other sources of impulsive radio emission. We describe the science scope for
realfast, the system design, expected outcomes, and ways real-time analysis can
help in other fields of astrophysics.Comment: Accepted to ApJS Special Issue on Data; 11 pages, 4 figure
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