374 research outputs found
The Effect of a Reduction in Phosphate Application on Soil Phosphate Pools
Excessive use of manure and fertilisers in western Europe has led to high phosphorus (P) contents in many agricultural soils leading to environmental P losses by overland flow, subsurface drainage and leaching to groundwater. To stop phosphate build up in the soil and leaching to surface and ground waters, the Dutch government is gradually reducing allowable phosphate application on grassland from 130 kg/ha per year in 2005 to 90 kg/ha per year in 2015. This will lead to a reduction of the phosphate surplus from 40 in 2005 to 0 kg/ha per year. To investigate the impact of reductions in application rates on soil phosphate, leaching and grass production, a field experiment was started in 1997 on four dairy farms on two sandy soils, a peat and a clay soil
Multipartite Entanglement and Frustration
Some features of the global entanglement of a composed quantum system can be
quantified in terms of the purity of a balanced bipartition, made up of half of
its subsystems. For the given bipartition, purity can always be minimized by
taking a suitable (pure) state. When many bipartitions are considered, the
requirement that purity be minimal for all bipartitions can engender conflicts
and frustration arises. This unearths an interesting link between frustration
and multipartite entanglement, defined as the average purity over all
(balanced) bipartitions.Comment: 15 pages, 7 figure
The ART-XC telescope on board the SRG observatory
ART-XC (Astronomical Roentgen Telescope - X-ray Concentrator) is the hard
X-ray instrument with grazing incidence imaging optics on board the
Spektr-Roentgen-Gamma (SRG) observatory. The SRG observatory is the flagship
astrophysical mission of the Russian Federal Space Program, which was
successively launched into orbit around the second Lagrangian point (L2) of the
Earth-Sun system with a Proton rocket from the Baikonur cosmodrome on 13 July
2019. The ART-XC telescope will provide the first ever true imaging all-sky
survey performed with grazing incidence optics in the 4-30 keV energy band and
will obtain the deepest and sharpest map of the sky in the energy range of 4-12
keV. Observations performed during the early calibration and performance
verification phase as well as during the on-going all-sky survey that started
on 12 Dec. 2019 have demonstrated that the in-flight characteristics of the
ART-XC telescope are very close to expectations based on the results of ground
calibrations. Upon completion of its 4-year all-sky survey, ART-XC is expected
to detect ~5000 sources (~3000 active galactic nuclei, including heavily
obscured ones, several hundred clusters of galaxies, ~1000 cataclysmic
variables and other Galactic sources), and to provide a high-quality map of the
Galactic background emission in the 4-12 keV energy band. ART-XC is also well
suited for discovering transient X-ray sources. In this paper, we describe the
telescope, results of its ground calibrations, major aspects of the mission,
the in-flight performance of ART-XC and first scientific results.Comment: 19 pages, 30 figures, accepted for publication in Astronomy and
Astrophysic
DFTB+, a software package for efficient approximate density functional theory based atomistic simulations
DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods. Based on the DFTB framework, it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green's functions, and many more. DFTB+ can be used as a user-friendly standalone application in addition to being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives
Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
We report on \ixpe observations of the Be-transient X-ray pulsar LS V +44
17/RX J0440.9+4431 at two luminosity levels during the giant outburst in
January--February 2023. Considering the observed spectral variability and
changes in the pulse profiles, the source was likely caught in super- and
sub-critical states with significantly different emission region geometry,
associated with the presence of accretion columns and hot spots, respectively.
We focus here on the pulse-phase resolved polarimetric analysis and find that
the observed dependencies of the polarization degree and polarization angle
(PA) on pulse phase are indeed drastically different for the two observations.
The observed differences, if interpreted within the framework of the rotating
vector model (RVM), imply dramatic variations of the spin axis inclination and
the position angle and the magnetic colatitude by tens of degrees within just a
few days separating the observations. We suggest that the apparent changes in
the observed PA phase dependence are predominantly related to the presence of a
polarized unpulsed component in addition to the polarized radiation associated
with the pulsar itself. We show that the observed PA phase dependence in both
observations can then be explained with a single set of RVM parameters defining
the pulsar's geometry. We also suggest that the additional polarized component
is likely produced by scattering of the pulsar radiation off the equatorial
disk wind.Comment: 9 pages, 5 figures, submitted to A&
Worldwide variations in artificial skyglow
Open access journalDespite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program.MILIEU (FU Berlin)Federal Ministry of Education and Research, GermanyEU COST Action ES1204 (Loss of the Night Network)European Research Council (ERC) under the EU's Seventh Framework Program (FP7/2007-2013)panish Network for Light Pollution StudiesNational Aeronautics and Space Administration (Goddard Space Flight Center)Ohio State UniversityUniversity of IowaThe Adam Mickiewicz Universit
Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16
We report on the first observation of a radio-quiet Active Galactic Nucleus
(AGN) using polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source
was pointed with the Imaging X-ray Polarimetry Explorer (IXPE) starting on May
14, 2022 for a net observing time of 486 ks, simultaneously with XMM-Newton (58
ks) and NuSTAR (83 ks). A polarization degree smaller than (at the
99% c.l.) is derived in the 2-8 keV energy range, where emission is dominated
by the primary component ascribed to the hot corona. The broad-band spectrum,
inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is
well reproduced by a power law with photon index and a
high-energy cutoff keV. A comparison with Monte Carlo
simulations shows that a lamp-post and a conical geometry of the corona are
consistent with the observed upper limit, a slab geometry is allowed only if
the inclination angle of the system is less than 50.Comment: 7 pages, 3 figures, 1 table. Submitted to MNRAS Letter
Complex variations in X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January- February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on the pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. We then show that the observed PA phase dependence in both observations can be explained with a single set of RVM parameters defining the pulsar s geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind
Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
We report spectro-polarimetric results of an observational campaign of the
bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by
IXPE, NICER and INTEGRAL. Consistently with previous results, the broad-band
spectrum is characterized by a lower-energy component, attributed to the
accretion disc with 1 keV, plus unsaturated
Comptonization in thermal plasma with temperature keV and
optical depth , assuming a slab geometry. We measure the
polarization degree in the 2-8 keV band per cent and
polarization angle , consistent with the
previous X-ray polarimetric measurements by OSO-8 as well as with the direction
of the radio jet which was earlier observed from the source. While polarization
of the disc spectral component is poorly constrained with the IXPE data, the
Comptonized emission has a polarization degree per cent and a
polarization angle aligned with the radio jet. Our results strongly favour a
spreading layer at the neutron star surface as the main source of the
polarization signal. However, we cannot exclude a significant contribution from
reflection off the accretion disc, as indicated by the presence of the iron
fluorescence line.Comment: 10 pages, 7 figures, accepted for publication in MNRA
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