On the causes of the observed magnetic field imbalance in solar active regions     

I. V. Oreshina  B. V. Somov 《Astronomy Letters》2006,32(11):787-793

Based on a topological magnetic field model for active region (AR) 8086 observed on September 15–21, 1997, we calculate the evolution of the magnetic flux imbalance during its disk passage. We have established possible causes of the observed imbalance. Using model ARs produced by perfectly balanced magnetic field sources as examples, we show that even in this case, the observed imbalance can reach a significant value, depending on the AR size and location. The peculiar properties of the magnetic field imbalance in ARs predicted by the topological model must be taken into account when present-day magnetographic observations of the Sun are interpreted.  相似文献   

Swimming with…Devonian fish     

Lance B. Morrissey  Philippe Janvier  Simon J. Braddy  John P. Bennett  Susan B. Marriott  Peter R. Tarrant 《Geology Today》2006,22(2):66-67

Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle.  相似文献   

Observation of, and temporal variations in, solar p-mode multiplet frequency asymmetries at  ℓ= 2      

W. J. Chaplin  Y. Elsworth  G. R. Isaak  B. A. Miller  R. New  S. Thiery  P. Boumier  A. H. Gabriel 《Monthly notices of the Royal Astronomical Society》2003,343(1):343-352

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Collisionless Slowing Down of Nova and Supernova Shells in Magnetized Interstellar Medium     

D. A. Osipyan  H. B. Nersisyan  H. H. Matevosyan 《Astrophysics》2003,46(4):434-444

The collisionless interaction of an expanding plasma cloud with a magnetized background plasma is examined in the framework of a 3D kinetic-hydrodynamic model. The slowing down of a hydrogen cloud is studied for high Alfven-Mach numbers and magneto-laminar interaction parameters. A particle-in-cell method is used to study the dynamics of the magnetic field, plasma cloud, background plasma, and collisionless shock wave generated by the intense particle flux. A numerical simulation is consistent with the nonstationary interactions between the plasma shells formed during nova and supernova explosions and the interstellar plasma medium.  相似文献   

Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers     

E. García  L. De Haro  C. O'Sullivan  G. Cahill  J. A. López Fernández  F. Tercero  B. Galocha  J. L. Besada 《Experimental Astronomy》2003,15(3):173-193

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the “Centro Astronómico de Yebes” is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Hard X-ray light curves of high-mass X-ray binaries     

S. Laycock  M. J. Coe  C. A. Wilson  B. A. Harmon  M. Finger 《Monthly notices of the Royal Astronomical Society》2003,338(1):211-218

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Reply: on the importance of scale in biochronological analysis: a reply to Cuenca‐Bescós     

M. Hernndez Fernndez  B. Azanza  M. A. lvarez Sierra 《第四纪科学杂志》2006,21(4):415-416

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Design of 2-M to 6-M Liquid Mirror Containers     

Robert Content 《Experimental Astronomy》2003,15(3):123-145

A new design is proposed for large (up to 6-m) liquid mirror containers. The design uses Kevlar, foam and aluminum, as in previous designs, but with a different configuration that makes the container lighter, stronger and more rigid. The results of finite element analysis are presented, consisting in the deformations due to temperature changes and to weight, and in the security factor for each material when maximum constraints are applied. Tilt rigidity is also analyzed. They show that the composite material construction technique gives a good performance up to 6 m diameters. The figures and tables contained in this paper can be used as recipes to build containers having diameters between 2 and 6 m. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Intercomparison of the seasonal cycle of tropical surface stress in 17 AMIP atmospheric general circulation models     

N. H. Saji  B. N. Goswami 《Climate Dynamics》1997,13(7-8):561-585

 The mean state of the tropical atmosphere is important as the nature of the coupling between the ocean and the atmosphere depends nonlinearly on the basic state of the coupled system. The simulation of the annual cycle of the tropical surface wind stress by 17 atmospheric general circulation models (AGCMs) is examined and intercompared. The models considered were part of the Atmospheric Model Intercomparison Project (AMIP) and were integrated with observed sea surface temperature (SST) for the decade 1979–1988. Several measures have been devised to intercompare the performance of the 17 models on global tropical as well as regional scales. Within the limits of observational uncertainties, the models under examination simulate realistic tropical area-averaged zonal and meridional annual mean stresses. This is a noteworthy improvement over older generation low resolution models which were noted for their simulation of surface stresses considerably weaker than the observations. The models also simulate realistic magnitudes of the spatial distribution of the annual mean surface stress field and are seen to reproduce realistically its observed spatial pattern. Similar features are observed in the simulations of the annual variance field. The models perform well over almost all the tropical regions apart from a few. Of these, the simulations over Somali are interesting. Over this region, the models are seen to underestimate the annual mean zonal and meridional stresses. There is also wide variance between the different models in simulating these quantities. Large model-to-model variations were also seen in the simulations of the annual mean meridional stress field over equatorial Indian Ocean, south central Pacific, north east Pacific and equatorial eastern Pacific oceans. It is shown that the systematic errors in simulating the surface winds are related to the systematic errors in simulating the Inter-Tropical Convergence Zone (ITCZ) in its location and intensity. Weaker than observed annual mean southwesterlies simulated by most models over Somali is due to weaker than observed southwesterlies during the Northern Hemisphere summer. This is related to the weaker than observed land precipitation simulated by most models during the Northern Hemisphere summer. The diversity in simulation of the surface wind over Somali and equatorial Indian ocean is related to the diversity of AGCMs in simulating the precipitation zones in these regions. Received: 2 August 1996 / Accepted: 7 February 1997  相似文献   

Radon variations in a Hungarian village     

E. Tóth  F. Deak  C. S. Gyurkócza  Z. S. Kasztovszky  R. Kuczi  G. Marx  B. Nagy  S. Oberstedt  L. Sajó-Bohus  C. S. Sükösd  G. Toth  N. Vajda 《Environmental Geology》1997,31(1-2):123-127

 A steady radon exhalation is assumed in most publications. In a village of North-East Hungary, however, high radon concentrations have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of geochemical phenomena. Received: 20 November 1995 · Accepted: 18 June 1996  相似文献