1,900 research outputs found
Synchrotron and Compton Components and their Variability in BL Lac Objects
BL Lacertae objects are extreme extragalactic sources characterized by the
emission of strong and rapidly variable nonthermal radiation over the entire
electromagnetic spectrum. Synchrotron emission followed by inverse Compton
scattering in a relativistic beaming scenario is generally thought to be the
mechanism powering these objects. ...Comment: 4 pages, TeX plus 3 figures. Proceedings of the conference "X-ray
Astronomy 1999", September 6-10,1999, Bologn
The Space Object Ontology
Achieving space domain awareness requires the
identification, characterization, and tracking of space objects.
Storing and leveraging associated space object data for purposes
such as hostile threat assessment, object identification, and
collision prediction and avoidance present further challenges.
Space objects are characterized according to a variety of
parameters including their identifiers, design specifications,
components, subsystems, capabilities, vulnerabilities, origins,
missions, orbital elements, patterns of life, processes, operational
statuses, and associated persons, organizations, or nations. The
Space Object Ontology provides a consensus-based realist
framework for formulating such characterizations in a
computable fashion. Space object data are aligned with classes
and relations in the Space Object Ontology and stored in a
dynamically updated Resource Description Framework triple
store, which can be queried to support space domain awareness
and the needs of spacecraft operators. This paper presents the
core of the Space Object Ontology, discusses its advantages over
other approaches to space object classification, and demonstrates
its ability to combine diverse sets of data from multiple sources
within an expandable framework. Finally, we show how the
ontology provides benefits for enhancing and maintaining longterm
space domain awareness
Life cycle assessment of shale gas in the UK
The remarkable US growth of shale gas and the associated decrease in the US natural gas prices has catalysed an increasing interest of shale gas resource exploration in other areas of the world. Commercial drilling operations have not yet commenced, but exploration is taking place in some European countries, including the UK. Major environmental concerns, regarding the amount and the handling method of the emissions associated with hydraulic fracturing, the disposal of waste water and the low well productivity, have pushed some countries to ban exploration and trials. We contextualized the shale gas extraction to the UK condition where the estimate of recoverable gas has made the debate on shale gas highly interesting. We used the methodology of Life Cycle Assessment (LCA) and estimated the environmental burden of shale gas production, processing and distribution at low pressure to the consumer. In this paper we have reported the detailed hot spot analysis of the impact of shale gas on the watersheds
The Swift X-ray Telescope Cluster Survey II. X-ray spectral analysis
(Abridged) We present a spectral analysis of a new, flux-limited sample of 72
X-ray selected clusters of galaxies identified with the X-ray Telescope (XRT)
on board the Swift satellite down to a flux limit of ~10-14 erg/s/cm2 (SWXCS,
Tundo et al. 2012). We carry out a detailed X-ray spectral analysis with the
twofold aim of measuring redshifts and characterizing the properties of the
Intra-Cluster Medium (ICM). Optical counterparts and spectroscopic or
photometric redshifts are obtained with a cross-correlation with NED.
Additional photometric redshifts are computed with a dedicated follow-up
program with the TNG and a cross-correlation with the SDSS. We also detect the
iron emission lines in 35% of the sample, and hence obtain a robust measure of
the X-ray redshift zX. We use zX whenever the optical redshift is not
available. Finally, for all the sources with measured redshift,
background-subtracted spectra are fitted with a mekal model. We perform
extensive spectral simulations to derive an empirical formula to account for
fitting bias. The bias-corrected values are then used to investigate the
scaling properties of the X-ray observables. Overall, we are able to
characterize the ICM of 46 sources. The sample is mostly constituted by
clusters with temperatures between 3 and 10 keV, plus 14 low-mass clusters and
groups with temperatures below 3 keV. The redshift distribution peaks around
z~0.25 and extends up to z~1, with 60% of the sample at 0.1<z<0.4. We derive
the Luminosity-Temperature relation for these 46 sources, finding good
agreement with previous studies. The quality of the SWXCS sample is comparable
to other samples available in the literature and obtained with much larger
X-ray telescopes. Our results have interesting implications for the design of
future X-ray survey telescopes, characterised by good-quality PSF over the
entire field of view and low background.Comment: 27 pages, 15 figures; minor typos corrected. To be published in A&A,
Volume 567, July 2014. Websites of the SWXCS project:
http://www.arcetri.astro.it/SWXCS/ and http://swxcs.ustc.edu.cn
Myeloid derived suppressor cells in multiple myeloma: Preclinical research and translational opportunities
Immunosuppressive cells have been reported to play an important role in tumor progression mainly because of their capability to promote immuneescape, angiogenesis and metastasis. Among them, myeloid derived suppressor cells (MDSCs) have been recently identified as immature myeloid cells, induced by tumor-associated inflammation, able to impair both innate and adaptive immunity. While murine MDSCs are usually identified by the expression of CD11b and Gr-1, human MDSCs represent a more heterogeneous population characterized by the expression of CD33 and CD11b, low or no HLA-DR and variable CD14 and CD15. In particular, the last two may alternatively identify monocyte-like or granulocyte-like MDSC subsets with different immunosuppressive properties. Recently, a substantial increase of MDSCs has been found in peripheral blood and bone marrow (BM) of multiple myeloma (MM) patients with a role in disease progression and/or drug resistance. Preclinical models recapitulating the complexity of the MM-related BM microenvironment (BMM) are major tools for the study of the interactions between MM cells and cells of the BMM (including MDSCs) and for the development of new agents targeting MM-associated immune suppressive cells. This review will focus on current strategies for human MDSCs generation and investigation of their immunosuppressive function in vitro and in vivo, taking into account the relevant relationship occurring within the MM-BMM. We will then provide trends in MDSC-associated research and suggest potential application for the treatment of MM
Wide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state
The blazar 1ES 1959+650 was observed twice by BeppoSAX in September 2001
simultaneously with optical observations. We report here the X-ray data
together with the optical, R_C magnitude, light curve since August 1995. The
BeppoSAX observations were triggered by an active X-ray status of the source.
The X-ray spectra are brighter than the previously published X-ray
observations, although the source was in an even higher state a few months
later, as monitored by the ASM onboard RossiXTE, when it was also detected to
flare in the TeV band. Our X-ray spectra are well represented by a continuosly
curved model up to 45 keV and are interpreted as synchrotron emission, with the
peak moving to higher energies. This is also confirmed by the slope of the
X-ray spectrum which is harder than in previous observations. Based on our
optical and X-ray data, the synchrotron peak turns out to be in the range
0.1-0.7 keV. We compare our data with non simultaneous radio to TeV data and
model the spectral energy distribution with a homogeneous, one-zone synchrotron
inverse Compton model. We derive physical parameters that are typical of low
power High Energy peaked Blazar, characterised by a relatively large beaming
factor, low luminosity and absence of external seed photons.Comment: 12 pages, 6 figures, accepted by A&
Models for the Type Ic Hypernova SN 2003lw associated with GRB 031203
The Gamma-Ray Burst 031203 at a redshift z=0.1055 revealed a highly reddened
Type Ic Supernova, SN 2003lw, in its afterglow light. This is the third well
established case of a link between a long-duration GRB and a type Ic SN. The SN
light curve is obtained subtracting the galaxy contribution and is modelled
together with two spectra at near-maximum epochs. A red VLT grism 150I spectrum
of the SN near peak is used to extend the spectral coverage, and in particular
to constrain the uncertain reddening, the most likely value for which is
E_{G+H}(B-V) about 1.07 +/- 0.05. Accounting for reddening, SN 2003lw is about
0.3 mag brighter than the prototypical GRB-SN 1998bw. Light curve models yield
a 56Ni mass of about 0.55 solar mass. The optimal explosion model is somewhat
more massive (ejecta mass about 13 solar mass) and energetic (kinetic energy
about 6 times 10^52 erg) than the model for SN 1998bw, implying a massive
progenitor (40 - 50 solar mass). The mass at high velocity is not very large
(1.4 solar mass above 30000 km/s, but only 0.1 solar mass above 60000 km/s),
but is sufficient to cause the observed broad lines. The similarity of SNe
2003lw and 1998bw and the weakness of their related GRBs, GRB031203 and
GRB980425, suggest that both GRBs may be normal events viewed slightly off-axis
or a weaker but possibly more frequent type of GRB.Comment: 19 pages, 8 figures, accepted for publication in Ap
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