5,362 research outputs found
Global 3D Simulations of Disc Accretion onto the classical T Tauri Star BP Tauri
The magnetic field of the classical T Tauri star BP Tau can be approximated
as a superposition of dipole and octupole moments with respective strengths of
the polar magnetic fields of 1.2 kG and 1.6 kG (Donati et al. 2008). We adopt
the measured properties of BP Tau and model the disc accretion onto the star.
We observed in simulations that the disc is disrupted by the dipole component
and matter flows towards the star in two funnel streams which form two
accretion spots below the dipole magnetic poles. The octupolar component
becomes dynamically important very close to the star and it redirects the
matter flow to higher latitudes. The spots are meridionally elongated and are
located at higher latitudes, compared with the pure dipole case, where
crescent-shaped, latitudinally elongated spots form at lower latitudes. The
position and shape of the spots are in good agreement with observations. The
disk-magnetosphere interaction leads to the inflation of the field lines and to
the formation of magnetic towers above and below the disk. The magnetic field
of BP Tau is close to the potential only near the star, inside the
magnetospheric surface, where magnetic stress dominates over the matter stress.
A series of simulation runs were performed for different accretion rates. They
show that an accretion rate is lower than obtained in many observations, unless
the disc is truncated close to the star. The torque acting on the star is about
an order of magnitude lower than that which is required for the rotational
equilibrium. We suggest that a star could lose most of its angular momentum at
earlier stages of its evolution.Comment: 11 pages, 13 figures, submitted to MNRA
Issues of sustainable food production in Latvia
The article presents main results of the first in Latvia study addressing the issues of the development of Latvia’s sustainable food
production. For detailed research two main themes for Latvia’s agri-food sector’s sustainability were chosen: 1) the issues related to
further development of the organic farming and processing; where the special attention has been paid to organic milk processing; and
obtaining of organic pigmeat and beef in different Latvia’s regions; 2) quality and environment management systems enforcement -
mandatory and voluntary and the trends of implementation of the international management standards (ISO 9001, ISO 22000;
HACCP DS 3027:2002; ISO 14001). The publications, legal documents and databases of Latvia’s governmental and nongovernmental
institutions were used as materials and the qualitative and quantitative research methods were applied for this empirical
research. The assessment of present situation and the proposals for further development has been given
Global 3D Simulations of Disc Accretion onto the classical T Tauri Star V2129 Oph
The magnetic field of the classical T Tauri star V2129 Oph can be modeled
approximately by superposing slightly tilted dipole and octupole moments, with
polar magnetic field strengths of 0.35kG and 1.2kG respectively (Donati et al.
2007). Here we construct a numerical model of V2129 Oph incorporating this
result and simulate accretion onto the star. Simulations show that the disk is
truncated by the dipole component and matter flows towards the star in two
funnel streams. Closer to the star, the flow is redirected by the octupolar
component, with some of the matter flowing towards the high-latitude poles, and
the rest into the octupolar belts. The shape and position of the spots differ
from those in a pure dipole case, where crescent-shaped spots are observed at
the intermediate latitudes. Simulations show that if the disk is truncated at
the distance of 6.2 R_* which is comparable with the co-rotation radius, 6.8
R_*, then the high-latitude polar spots dominate, but the accretion rate
obtained from the simulations is about an order of magnitude lower than the
observed one. The accretion rate matches the observed one if the disk is
disrupted much closer to the star, at 3.4 R_*. However, the octupolar belt
spots strongly dominate. Better match has been obtained in experiments with a
dipole field twice as strong. The torque on the star from the
disk-magnetosphere interaction is small, and the time-scale of spin evolution,
2 x10^7-10^9 years is longer than the 2x10^6 years age of V2129 Oph. The
external magnetic flux of the star is strongly influenced by the disk: the
field lines connecting the disk and the star inflate and form magnetic towers
above and below the disk. The potential (vacuum) approximation is still valid
inside the Alfv\'en (magnetospheric) surface where the magnetic stress
dominates over the matter stress.Comment: 15 pages, 15 figures, after major revision, added 3 figures, 2
tables. Accepted to MNRA
The Moving Hotspots model for kHz QPOs in accreting neutron stars
3D MHD simulation of accretion onto neutron stars have shown in the last few
years that the footprint (hotspot) of the accretion flow changes with time. Two
different kinds of accretion, namely the funnel flow and the equatorial
accretion produced by instabilities at the inner disk, produce different kinds
of motion of the hotspot. The funnel flow produces hotspots that move around
the magnetic pole, while instabilities produce other hotspots that appear
randomly and move along the equator or slightly above. The angular velocities
of the two hotspots are different, the equatorial one being higher and both
close to the Keplerian velocity in the inner region. Modeling of the
lightcurves of these hotspots with Monte Carlo simulations show that the
signatures produced in power specra by them, if observed, are QPOs plus low
frequency components. Their frequencies, general behavior and features describe
correctly most of the properties of kHz QPOs, if we assume the funnel flow
hotspots as the origin of the lower kHz QPO and instabilities as the origin of
the upper kHz QPO.Comment: 4 pages, 2 figures, to appear in the Proceedings of the ASTRONS 2010
conferenc
Spectral variability of classical T Tauri stars accreting in an unstable regime
Classical T Tauri stars (CTTSs) are variable in different time-scales. One
type of variability is possibly connected with the accretion of matter through
the Rayleigh-Taylor instability that occurs at the interface between an
accretion disc and a stellar magnetosphere. In this regime, matter accretes in
several temporarily formed accretion streams or `tongues' which appear in
random locations, and produce stochastic photometric and line variability. We
use the results of global three-dimensional magnetohydrodynamic simulations of
matter flows in both stable and unstable accretion regimes to calculate
time-dependent hydrogen line profiles and study their variability behaviours.
In the stable regime, some hydrogen lines (e.g. H-beta, H-gamma, H-delta,
Pa-beta and Br-gamma) show a redshifted absorption component only during a
fraction of a stellar rotation period, and its occurrence is periodic. However,
in the unstable regime, the redshifted absorption component is present rather
persistently during a whole stellar rotation cycle, and its strength varies
non-periodically. In the stable regime, an ordered accretion funnel stream
passes across the line of sight to an observer only once per stellar rotation
period while in the unstable regime, several accreting streams/tongues, which
are formed randomly, pass across the line of sight to an observer. The latter
results in the quasi-stationarity appearance of the redshifted absorption
despite the strongly unstable nature of the accretion. In the unstable regime,
multiple hot spots form on the surface of the star, producing the stochastic
light curve with several peaks per rotation period. This study suggests a CTTS
that exhibits a stochastic light curve and a stochastic line variability, with
a rather persistent redshifted absorption component, may be accreting in the
unstable accretion regime.Comment: 20 pages, 11 figures, 1 table, accepted for publication in MNRA
Changes in the vector of industrial policy and possibilities for the innovative development of the industrial regions
In the present paper, reasons for the increased interest in industrial policy in both developed and developing countries are explained. The systematisation of the results of the development of Russian industry from 1989 to 2014 showed a lack of systematic selection of its priorities, preventing the formation of a strategic vector of industrial policy. The target diversity of the industrial policy is established at the different economic development stages of the country. In the context of economic sanctions against Russia, it is shown that the emergence of a new industrial policy vector is connected to the need for import substitution and concomitant changes in the development model of the domestic economy. The dynamics and characteristics of the industrial development area are shown by the example of a highly developed region like the Central Urals. The total level of organisational innovation activity continues to be low and composes only 12%, although in the manufacturing sector this index is higher than the regional economy index by four absolute percentage points. The industrial policy of the Central Urals is analysed and innovation drivers of the industrial sector of the regional economy are established. The possibilities of the defence, civil engineering, mining, chemical/pharmaceutical and forestry complexes of the Sverdlovsk Region to implement its import substitution policy are explained. The most significant investment projects that will reduce the import dependence of the regional economy are presented. The possibilities of the research sector and created innovation infrastructure of the region in solving this problem are shown. It is necessary to develop the regional laws on the elaboration of industrial policy according to the basic regulations of the Federal Law “On Industrial Policy in the Russian Federation.”This article has been prepared with the support of the Russian Humanitarian Science Foundation Grant 14-02-00331 «Innovative and technological development of the region: assessment, forecasting and ways of achievement.
Development of a Methodology for the Economic Assessment of Managerial Decisions as a Factor of Increased Economic Security
The article notes that the emergence of such a phenomenon as the interdependence of security and development, the so-called security-development nexus, becomes a determinant during the development of strategic documents at all hierarchical levels. It gives relevance to the search for methodological solutions that would on a strategic level take into account any potential threats to economic security, and on a tactical level provide for pragmatic actions that are not in conflict with the strategic development vector of business entities. The authors identify the instability factors that pose a real threat to economic security. They substantiate the expediency of forming a new model of the national economy development with a focal point on new industrialization. The article factors in the most important trends in the development of the global economy that determine the strategic vector of enhancing the economic security in Russia. It is ascertained that in the conditions of new industrialization, the intellectual core of the high-tech economy sector is formed by convergent technologies (NBICS technologies). The authors offer a methodological approach to the economic assessment of managerial decisions in the context of uncertainty. They also identify methodological principles that must be taken into account in developing a modern methodology for the economic assessment of business decisions. The principles include forming a preferred reality, or the so-called “vision of the future,” the priority of network solutions as the basis for the formation of new markets; mass customization and individualization of demands, principal changes in the profile of competences that ensure competitiveness on the labor market, use of the ideology of inclusive development and impact investment that creates common values. The proposed methodology is based on the optimum combination of traditional methods used for the economic assessment of managerial decisions with the method of real options and reflexive assessments with regard to entropy as a measure of uncertainty. The proposed methodological approach has been tested in respect of the Ural mining and metallurgical complex.The article has been prepared with the support of the grant from the Russian Foundation for Basic Research № 16–06–00403 "Modelling the Motivational Potentials of the Multi-subject Industrial Policy in the Context of New Industrialization"
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