36 research outputs found
A Structure for Quasars
This paper proposes a simple, empirically derived, unifying structure for the
inner regions of quasars. This structure is constructed to explain the broad
absorption line (BAL) regions, the narrow `associated' ultraviolet and X-ray
warm absorbers (NALs); and is also found to explain the broad emission line
regions (BELR), and several scattering features, including a substantial
fraction of the broad X-ray Iron-K emission line, and the bi-conical extended
narrow emission line region (ENLR) structures seen on large kiloparsec scales
in Seyfert images. Small extensions of the model to allow luminosity dependent
changes in the structure may explain the UV and X-ray Baldwin effects and the
greater prevalence of obscuration in low luminosity AGN.Comment: 35 pages, including 8 color figures (figures 4abc are big).
Astrophysical Journal, in press. Expanded version of conference paper
astro-ph/000516
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
The Cr(VI) Stability in Contaminated Coastal Groundwater: Salinity as a Driving Force
Chromium concentrations in seawater are less than 0.5 μg/L, but the Cr(VI) in contaminated coastal groundwater affected by Cr-bearing rocks/ores and/or human activities, coupled with the intrusion of seawater may reach values of hundreds of μg/L. A potential explanation for the stability of the harmful Cr(VI) in contaminated coastal aquifers is still unexplored. The present study is an overview of new and literature data on the composition of coastal groundwater and seawater, aiming to provide potential relationships between Cr(VI) with major components in seawater and explain the elevated Cr(VI) concentrations. It is known that the oxidation of Cr(III) to Cr(VI) and the subsequent back-reduction of Cr(VI) processes, during the transport of the mobilized Cr(VI) in various aquifers, facilitate the natural attenuation process of Cr(VI). Moreover, the presented positive trend between B and Cr(VI) and negative trend between δ53Cr values and B concentration may suggest that seawater components significantly inhibit the Cr(VI) reduction into Cr(III), and provide insights on the role of the borate, [B(OH)4]− ions, a potential buffer, on the stability of Cr(VI) in coastal groundwater. Therefore, efforts are needed toward the prevention and/or minimization of the contamination by Cr(VI) of in coastal aquifers, which are influenced by the intrusion of seawater and are threatened by changes in sea level, due to climate change. The knowledge of the contamination sources, hotspots and monitoring of water salinization processes (geochemical mapping) for every coastal country may contribute to the optimization of agricultural management strategies
The Cr(VI) Stability in Contaminated Coastal Groundwater: Salinity as a Driving Force
Chromium concentrations in seawater are less than 0.5 mu g/L, but the
Cr(VI) in contaminated coastal groundwater affected by Cr-bearing
rocks/ores and/or human activities, coupled with the intrusion of
seawater may reach values of hundreds of mu g/L. A potential explanation
for the stability of the harmful Cr(VI) in contaminated coastal aquifers
is still unexplored. The present study is an overview of new and
literature data on the composition of coastal groundwater and seawater,
aiming to provide potential relationships between Cr(VI) with major
components in seawater and explain the elevated Cr(VI) concentrations.
It is known that the oxidation of Cr(III) to Cr(VI) and the subsequent
back-reduction of Cr(VI) processes, during the transport of the
mobilized Cr(VI) in various aquifers, facilitate the natural attenuation
process of Cr(VI). Moreover, the presented positive trend between B and
Cr(VI) and negative trend between delta Cr-53 values and B concentration
may suggest that seawater components significantly inhibit the Cr(VI)
reduction into Cr(III), and provide insights on the role of the borate,
[B(OH)(4)](-) ions, a potential buffer, on the stability of Cr(VI) in
coastal groundwater. Therefore, efforts are needed toward the prevention
and/or minimization of the contamination by Cr(VI) of in coastal
aquifers, which are influenced by the intrusion of seawater and are
threatened by changes in sea level, due to climate change. The knowledge
of the contamination sources, hotspots and monitoring of water
salinization processes (geochemical mapping) for every coastal country
may contribute to the optimization of agricultural management
strategies
Distribution of Selenium in the Soil–Plant–Groundwater System: Factors Controlling Its Bio-Accumulation
Selenium (Se) is an essential micronutrient for humans and animals, but both Se excess and deficiency can cause various health risks. Since Greece is among the European countries where people have very low Se-serum, the present study is focused on the Se distribution in cultivated and non-cultivated plants and relative soil coming from the Neogene basins of Greece (Assopos-Thiva and Attica), aiming to define potential Se-source/es and factors controlling Se bio-accumulation and enrichment in food. The dry weight Se values are relatively low (0.1–0.9 mg/kg) with the highest Se contents in garlic, beet and lettuce from the Assopos basin, where the translocation percentage [(mplant/msoil) × 100] for Se, P and S is much higher compared to non-cultivated Attica basin. There is a diversity between the Se source in soil and coastal groundwater which is used for irrigation in the cultivated Assopos–Thiva basin. The soil pH and oxidizing conditions (Eh) are considered the main driving force to make Se available for plant uptake. Potential sources for Se in Greece are Fe-Cu-Zn-sulphide ores and peat deposits in northern Greece, with a Se content ranging from decades to hundreds of mg/kg. Application of the leaching testing protocol is necessary to select the most appropriate proportion of additives to improve the Se deficiencies in agricultural soil
Cultural applications for mobile devices: issues and requirements for authoring tools and development platforms
This paper explores requirements that authoring tools and development platforms should satisfy for the development of cultural applications tailored for deployment on Personal Digital Assistants (PDAs) and mobile phones. To effectively determine such requirements the paper reviews the use of mobile technologies in the context of cultural organizations and tourism and examines three "real world" case studies that focus on the use of PDAs and mobile phones for providing cultural and tourist information, keeping the visitors' interest and attention, as well as promoting various cultural organizations and tourist facilities. This approach allows the extraction of a set of PDA and mobile phone application requirements, the implementation of which is based on the apparatus offered by authoring tools and development platforms. The paper reviews and evaluates the design and development facilities provided by state-of-the-art multimedia application development tools for PDAs and mobile phones: Macromedia Flash Lite, Navipocket, Java 2 Micro Edition and Microsoft .Net platform for the Mobile Web. The paper concludes with a set of recommendations related to the way authoring tools and development platforms should be exploited in order to gratify application and designer needs for developing cultural and tourist applications