5,344 research outputs found

    Global 3D Simulations of Disc Accretion onto the classical T Tauri Star BP Tauri

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    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

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    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

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    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

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    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

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    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

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    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

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    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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