A warped m= 2 water maser disc in V778 Cyg?     

Natalia Babkovskaia  Juri Poutanen  Anita M. S. Richards  Ryszard Szczerba 《Monthly notices of the Royal Astronomical Society》2006,370(4):1921-1927

The silicate carbon star V778 Cyg is a source of 22-GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated     -like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly warped   m = 2  disc observed edge-on. Water masers and silicate dust emission (detected by the Infrared Astronomical Satellite and Infrared Space Observatory ) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas–dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of  1.7 ± 0.1 M_⊙  , the disc radius of  40 ± 3  au and the distance between companions of ∼80 au. Using a dust–gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc.  相似文献   

Pelagic fish abundance in relation to regional environmental variation in the Gulf of Finland, northern Baltic Sea     

Peltonen  Heikki; Luoto  Miska; Paakkonen  Jari-Pekka; Karjalainen  Miina; Tuomaala  Antti; Ponni  Jukka; Viitasalo  Markku 《ICES Journal of Marine Science》2007,64(3):487-495

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Modelling and inversion of electromagnetic data using an approximate plate model     

Markku Pirttijärvi  Risto Pietilä  Aimo Hattula  Sven-Erik Hjelt 《Geophysical Prospecting》2002,50(5):425-440

This paper presents a computational method for the interpretation of electromagnetic (EM) profile data in the frequency domain using a thin plate model within a two-layer earth. The modelling method is based on an integral equation formulation, where the conductor is represented by a lattice structure composed of two-dimensional surface elements. Several approximations are used to simplify the theoretical basis and to decrease the computation time. The simple parametric model allows efficient use of optimization methods. We employ a linearized inversion scheme based on singular value decomposition and adaptive damping. The new forward computation method and the parameter optimization are combined in the computer program, emplates . The modelling examples demonstrate that the approximate method is capable of describing the characteristic behaviour of the EM response of a thin plate-like conductor in conductive surroundings. The efficacy of the inversion is demonstrated using both synthetic and field data. An optional depth compensation method is used to improve the interpreted values of the depth of burial. The results show that the method is cost effective and suitable for interactive interpretation of EM data.  相似文献   

Model studies on the effect of nitric acid vapour on cirrus cloud activation     

Jukka Hienola  Markku Kulmala  Ari Laaksonen 《Atmospheric Research》2003,65(3-4):235-250

The effect of elevated nitric acid concentrations on cloud particle number concentrations and sizes of mixed phase cirrus cloud (containing both supercooled liquid and frozen ice particles) is studied using a detailed multicomponent condensation model. Our model calculations suggest that high nitric acid volume mixing ratios (VMRs), corresponding to upper tropospheric measurements, can increase the ice crystal number concentrations substantially especially in the case of freezing of non-activated solution droplets (as opposed to freezing of supercooled cloud droplets). This is due to increased droplet sizes caused by nitric acid absorption and the resulting uptake of water.  相似文献   

Determinants and constraints of integrating natural acacias into mechanised rain-fed agricultural schemes Sennar State,Sudan     

Mustafa Kamil Mahmoud Fahmi  Elamin Sanjak Mohamed  Markku Kanninen  Olavi Luukkanen  Fobissie Blese Kalame  Abdalla Mirghani Eltayeb 《GeoJournal》2015,80(4):555-567

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Micrometeorological Observations of a Microburst in Southern Finland     

Leena Järvi  Ari-Juhani Punkka  David M. Schultz  Tuukka Petäjä  Harri Hohti  Janne Rinne  Toivo Pohja  Markku Kulmala  Pertti Hari  Timo Vesala 《Boundary-Layer Meteorology》2007,125(2):343-359

On the afternoon of 3 July 2004 in Hyytiälä (Juupajoki, Finland), convective cells produced a strong downburst causing forest damage. The SMEAR II field station, situated near the damage site, enabled a unique micrometeorological analysis of a microburst with differences above and inside the canopy. At the time of the event, a squall line associated with a cold front was crossing Hyytiälä with a reflectivity maximum in the middle of the squall line. A bow echo, rear-inflow notch, and probable mesovortex were observed in radar data. The bow echo moved west-north-west, and its apex travelled just north of Hyytiälä. The turbulence data were analysed at two locations above the forest canopy and at one location at sub-canopy. At 1412 EET (Eastern European Time, UTC+2), the horizontal and vertical wind speed increased and the wind veered, reflecting the arrival of a gust front. At the same time, the carbon dioxide concentration increased due to turbulent mixing, the temperature decreased due to cold air flow from aloft and aerosol particle concentration decreased due to rain scavenging. An increase in the number concentration of ultra-fine particles (< 10 nm) was detected, supporting the new particle formation either from cloud outflow or due to rain. Five minutes after the gust front (1417 EET), strong horizontal and downward vertical wind speed gusts occurred with maxima of 22 and 15 m s^?1, respectively, reflecting the microburst. The turbulence spectra before, during and after the event were consistent with traditional turbulence spectral theory.  相似文献   

On the Honkasalo term in tidal corrections to gravimetric observations     

Markku Heikkinen 《Journal of Geodesy》1979,53(3):239-245

The Honkasalo term is discussed and the author arrives at the conclusion that its application to gravimetric observations is harmful and should be avoided.  相似文献   

Industrial minerals and rocks, aggregates and natural stones in the Nordic countries     

Kurt Johansson Rune B. Larsen Markku J. Lehtinen Lars Persson Mika Raeisaenen Stig A. Schack Pedersen Paer Weihed Nils-Gunnar Wik 《《幕》》2008,31(1):133-139

The Nordic countries, including Greenland, have a long tradition in mining. The industrial minerals sector is expanding in most Nordic countries and extensive development has taken place during the last few years. The main commodities mined are carbonate rocks, quartz, feldspar, apatite, olivine and talc.
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies.  相似文献   

Preface     

Markku Kulmala  Guest Editor 《Tellus. Series B, Chemical and physical meteorology》2007,59(3):337-337

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Physics of accretion in the millisecond pulsar XTE J1751 − 305     

Marek Gierli&#;ski  Juri Poutanen † 《Monthly notices of the Royal Astronomical Society》2005,359(4):1261-1276

We have undertaken an extensive study of X-ray data from the accreting millisecond pulsar XTE J1751 − 305 observed by RXTE and XMM–Newton during its 2002 outburst. In all aspects this source is similar to the prototypical millisecond pulsar SAX J1808.4 − 3658, except for the higher peak luminosity of 13 per cent of Eddington, and the optical depth of the hard X-ray source, which is larger by a factor ∼2. Its broad-band X-ray spectrum can be modelled by three components. We interpret the two soft components as thermal emission from a colder  ( kT ∼ 0.6 keV)  accretion disc and a hotter (∼1 keV) spot on the neutron star surface. We interpret the hard component as thermal Comptonization in plasma of temperature ∼40 keV and optical depth ∼1.5 in a slab geometry. The plasma is heated by the accretion shock as the material collimated by the magnetic field impacts on to the surface. The seed photons for Comptonization are provided by the hotspot, not by the disc. The Compton reflection is weak and the disc is probably truncated into an optically thin flow above the magnetospheric radius. Rotation of the emission region with the star creates an almost sinusoidal pulse profile with an rms amplitude of 3.3 per cent. The energy-dependent soft phase lags can be modelled by two pulsating components shifted in phase, which is naturally explained by a different character of emission of the optically thick spot and optically thin shock combined with the action of the Doppler boosting. The observed variability amplitude constrains the hotspot to lie within 3°–4° of the rotational pole. We estimate the inner radius of the optically thick accreting disc to be about 40 km. In that case, the absence of emission from the antipodal spot, which can be blocked by the accretion disc, gives the inclination of the system as ≳70°.  相似文献