16,848 research outputs found
Integrating Human Rights into the Extractive Industries: How Investment Contracts Can Achieve Protection
Models of magnetized neutron star atmospheres: thin atmospheres and partially ionized hydrogen atmospheres with vacuum polarization
Observed X-ray spectra of some isolated magnetized neutron stars display
absorption features, sometimes interpreted as ion cyclotron lines. Modeling the
observed spectra is necessary to check this hypothesis and to evaluate neutron
star parameters.We develop a computer code for modeling magnetized neutron star
atmospheres in a wide range of magnetic fields (10^{12} - 10^{15} G) and
effective temperatures (3 \times 10^5 - 10^7 K). Using this code, we study the
possibilities to explain the soft X-ray spectra of isolated neutron stars by
different atmosphere models. The atmosphere is assumed to consist either of
fully ionized electron-ion plasmas or of partially ionized hydrogen. Vacuum
resonance and partial mode conversion are taken into account. Any inclination
of the magnetic field relative to the stellar surface is allowed. We use modern
opacities of fully or partially ionized plasmas in strong magnetic fields and
solve the coupled radiative transfer equations for the normal electromagnetic
modes in the plasma. Spectra of outgoing radiation are calculated for various
atmosphere models: fully ionized semi-infinite atmosphere, thin atmosphere,
partially ionized hydrogen atmosphere, or novel "sandwich" atmosphere (thin
atmosphere with a hydrogen layer above a helium layer. Possibilities of
applications of these results are discussed. In particular, the outgoing
spectrum using the "sandwich" model is constructed. Thin partially ionized
hydrogen atmospheres with vacuum polarization are shown to be able to improve
the fit to the observed spectrum of the nearby isolated neutron star RBS 1223
(RX J1308.8+2127).Comment: Accepted for publications in Astronomy and Astrophysics, 9 pages, 12
figure
Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754
RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and
considerable observational resources have been devoted to it. However, current
models are unable to satisfactorily explain the data. We show that our latest
models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a
condensed surface can fit the entire spectrum, from X-rays to optical, of RX
J1856.5-3754, within the uncertainties. In our simplest model, the best-fit
parameters are an interstellar column density N_H \approx 1x10^20 cm^-2 and an
emitting area with R^infty \approx 17 km (assuming a distance to RX
J1856.5-3754 of 140 pc), temperature T^infty \approx 4.3x10^5 K, gravitational
redshift z_g \sim 0.22, atmospheric hydrogen column y_H \approx 1 g cm^-2, and
magnetic field B \approx (3-4)x10^12 G; the values for the temperature and
magnetic field indicate an effective average over the surface. We also
calculate a more realistic model, which accounts for magnetic field and
temperature variations over the neutron star surface as well as general
relativistic effects, to determine pulsations; we find there exist viewing
geometries that produce pulsations near the currently observed limits. The
origin of the thin atmospheres required to fit the data is an important
question, and we briefly discuss mechanisms for producing these atmospheres.
Our model thus represents the most self-consistent picture to date for
explaining all the observations of RX J1856.5-3754.Comment: 11 pages, 8 figures; MNRAS, accepte
Distribution and contamination status of heavy metals in estuarine sediments near Cua Ong Harbour, Ha Long Bay, Vietnam
The distribution, controlling geochemical factors and contamination status of heavy metals in estuarine sediments near Cua Ong Habor, Ha Long Bay (Vietnam) were investigated. 36 surface sediment samples were collected and analyzed for major elements (Al, Ca, Fe, K, Mg, S), heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn), organic matter, loss on ignition (LOI), grain size composition and pH. Spatial distribution patterns of heavy metals as well as their controlling factors were elucidated based on geochemical mapping and statistical methods such as the Pearson ProductMoment linear correlation and Factor Analysis. The results illustrated that the distribution patterns of As, Cd, Cr, Cu, Ni, Pb and Zn are mainly controlled by organic matter and clay minerals and determined by the distribution of the finegrained fraction (F < 63 µm) in the sediments. In contrast, Fe and Mn compounds seem to exert some control on the distribution of Co. Carbonates partly control the distribution of Mn, but are not important with respect to the other studied heavy metals. The contamination status by heavy metals was assessed based on comparison with Canadian, Wisconsin- United States and Flemish numerical Sediment Quality Guidelines, and calculation of Geo-accumulation Index (Igeo) and Enrichment Factor (EF). The results indicated that natural processes such as weathering and erosion of bedrock are the main supply sources of heavy metals in sediments near Cua Ong Harbor. Among the studied heavy metals, only As is of concern whereas Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn seem to reflect their background concentrations in sediments of Ha Long Bay
Branes from a non-Abelian (2,0) tensor multiplet with 3-algebra
In this paper, we study the equations of motion for non-Abelian N=(2,0)
tensor multiplets in six dimensions, which were recently proposed by Lambert
and Papageorgakis. Some equations are regarded as constraint equations. We
employ a loop extension of the Lorentzian three-algebra (3-algebra) and examine
the equations of motion around various solutions of the constraint equations.
The resultant equations take forms that allow Lagrangian descriptions. We find
various (5+d)-dimensional Lagrangians and investigate the relation between them
from the viewpoint of M-theory duality.Comment: 44+1 pages, reference added, typos corrected, and several discussions
added; v3, reference added, many typos corrected, the language improved; v4,
some typos and references corrected, final version to appear in J. Phys.
Asymmetrical structure of ionization and kinematics in the Seyfert galaxy NGC 5033
We present integral field spectroscopy of NGC 5033, a low luminosity Seyfert
galaxy. The observations were made with INTEGRAL, a fiber based system
operating at the WHT. The intensity map of the H emission line
represents a spiral or ring-like pattern of HII regions. On the contrary, the
[OIII] intensity map morphology is markedly anisotropic. The strong
morphological differences imply that the [OIII] emitters represent highly
ionized gas illuminated by the central source. The [OIII] map morphology is
compatible with a biconical structure of ionization induced by strong
extinction in the galaxy disc that also obscures half of the spheroidal stellar
bulge. We identify the spectrum corresponding to the Seyfert 1 nucleus from the
presence of H broad emission lines. This spectrum is located in a region
where strong extinction is expected but exhibits the bluest spectral energy
distribution. The Seyfert 1 nucleus seems to be offcenter with respect to the
stellar rotation center. This result has been also found in other Seyfert
galaxies and interpreted in terms of a past merger. The offcentering could
indicate the presence of nonsymmetric departures in the gravitational potential
which could be fueling the active nucleus. The kinematics of the [OIII]
emitters show important deviations at a kpc scale with respect to the stellar
velocity field and show features related to the asymmetrical morphology of the
high ionization region.Comment: 9 pages, accepted for publication in Astronomy and Astrophysics.
Figures 1 and 7 are attached as .gif file
Exploring the phase space of multiple states in highly turbulent Taylor-Couette flow
We investigate the existence of multiple turbulent states in highly turbulent
Taylor-Couette flow in the range of to ,
by measuring the global torques and the local velocities while probing the
phase space spanned by the rotation rates of the inner and outer cylinder. The
multiple states are found to be very robust and are expected to persist beyond
. The rotation ratio is the parameter that most strongly
controls the transitions between the flow states; the transitional values only
weakly depend on the Taylor number. However, complex paths in the phase space
are necessary to unlock the full region of multiple states. Lastly, by mapping
the flow structures for various rotation ratios in a Taylor-Couette setup with
an equal radius ratio but a larger aspect ratio than before, multiple states
were again observed. Here, they are characterized by even richer roll structure
phenomena, including, for the first time observed in highly turbulent TC flow,
an antisymmetrical roll state.Comment: 9 pages, 7 figure
Radiative properties of highly magnetized isolated neutron star surfaces and approximate treatment of absorption features in their spectra
In the X-ray spectra of most X-ray dim isolated neutron stars (XDINSs)
absorption features with equivalent widths (EWs) of 50 -- 200 eV are observed.
We theoretically investigate different models to explain absorption features
and compare their properties with the observations. We consider various
theoretical models for the magnetized neutron star surface: naked condensed
iron surfaces and partially ionized hydrogen model atmospheres, including
semi-infinite and thin atmospheres above a condensed surface. The properties of
the absorption features (especially equivalent widths) and the angular
distributions of the emergent radiation are described for all models. A code
for computing light curves and integral emergent spectra of magnetized neutron
stars is developed. We assume a dipole surface magnetic field distribution with
a possible toroidal component and corresponding temperature distribution. A
model with two uniform hot spots at the magnetic poles can also be employed.
Light curves and spectra of highly magnetized neutron stars with parameters
typical for XDINSs are computed using different surface temperature
distributions and various local surface models. Spectra of magnetized model
atmospheres are approximated by diluted blackbody spectra with one or two
Gaussian lines having parameters, which allow us to describe the model
absorption features. To explain the prominent absorption features in the soft
X-ray spectra of XDINSs a thin atmosphere above the condensed surface can be
invoked, whereas a strong toroidal magnetic field component on the XDINS
surfaces can be excluded.Comment: 54 pages, 17 figures, accepted for publication in A&
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Artificial intelligence approaches to predicting and detecting cognitive decline in older adults: A conceptual review.
Preserving cognition and mental capacity is critical to aging with autonomy. Early detection of pathological cognitive decline facilitates the greatest impact of restorative or preventative treatments. Artificial Intelligence (AI) in healthcare is the use of computational algorithms that mimic human cognitive functions to analyze complex medical data. AI technologies like machine learning (ML) support the integration of biological, psychological, and social factors when approaching diagnosis, prognosis, and treatment of disease. This paper serves to acquaint clinicians and other stakeholders with the use, benefits, and limitations of AI for predicting, diagnosing, and classifying mild and major neurocognitive impairments, by providing a conceptual overview of this topic with emphasis on the features explored and AI techniques employed. We present studies that fell into six categories of features used for these purposes: (1) sociodemographics; (2) clinical and psychometric assessments; (3) neuroimaging and neurophysiology; (4) electronic health records and claims; (5) novel assessments (e.g., sensors for digital data); and (6) genomics/other omics. For each category we provide examples of AI approaches, including supervised and unsupervised ML, deep learning, and natural language processing. AI technology, still nascent in healthcare, has great potential to transform the way we diagnose and treat patients with neurocognitive disorders
A Unified Approach for Multi-Scale Synchronous Correlation Search in Big Time Series -- Full Version
The wide deployment of IoT sensors has enabled the collection of very big
time series across different domains, from which advanced analytics can be
performed to find unknown relationships, most importantly the correlations
between them. However, current approaches for correlation search on time series
are limited to only a single temporal scale and simple types of relations, and
cannot handle noise effectively. This paper presents the integrated SYnchronous
COrrelation Search (iSYCOS) framework to find multi-scale correlations in big
time series. Specifically, iSYCOS integrates top-down and bottom-up approaches
into a single auto-configured framework capable of efficiently extracting
complex window-based correlations from big time series using mutual information
(MI). Moreover, iSYCOS includes a novel MI-based theory to identify noise in
the data, and is used to perform pruning to improve iSYCOS performance.
Besides, we design a distributed version of iSYCOS that can scale out in a
Spark cluster to handle big time series. Our extensive experimental evaluation
on synthetic and real-world datasets shows that iSYCOS can auto-configure on a
given dataset to find complex multi-scale correlations. The pruning and
optimisations can improve iSYCOS performance up to an order of magnitude, and
the distributed iSYCOS can scale out linearly on a computing cluster.Comment: 18 page
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