Preliminary observations of coronal magnetic fields before and after solar proton events     

Jesusa Valdez  Martin D. Altschuler 《Solar physics》1970,15(2):446-452

Maps of the coronal magnetic field before and after several proton flares were examined. There are indications that large scale changes occur in both the photospheric and coronal magnetic field as a consequence of large proton flares.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Über Interferenzfarben im polarisierten Licht an Substanzen mit Dispersion der Doppelbrechung (Brewster-Herschel-Farben)     

S. Rösch 《Mineralogy and Petrology》1962,8(1):36-48

Ohne ZusammenfassungMit 4 TextabbildungenHerrn Prof.K. H. Scheumann zum 80. Geburtstag gewidmet.  相似文献   

Model Atmospheres of AGB Stars: Dynamics, Molecules and Dust     

Susanne Höfner  Uffe G. Jφrgensen  Rita Loidl 《Astrophysics and Space Science》1997,255(1-2):281-287

The atmospheres and circumstellar envelopes of AGB stars are characterized by complex physical phenomena like shock waves caused by stellar pulsation or formation of molecules and dust which often lead to a heavy mass loss and have a strong influence on IR properties as observed by ISO. To allow a physical interpretation of various observations we have constructed improved dynamical model atmospheres of long-period variables. In this contribution we mainly investigate the dependence of the atmospheric structure and its variability on stellar pulsation, molecular opacities and time-dependent dust formation. IR spectra resulting from our models are discussed in detail by Loidl et al. (1997b) and compared to ISO-SWS spectra obtained by Hron et al. (1997). This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Bibliographia Cretacea 12     

Jürgen Schöbel 《Cretaceous Research》1983,4(3):281-313

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Rb-Sr and Sm-Nd ages and isotopic geochemistry of Archaean granodioritic gneisses from Eastern Finland     

Hervé Martin  Catherine Chauvel  Bor-Ming Jahn  Philippe Vidal 《Precambrian Research》1983,20(1):79-91

Twenty granodioritic rocks and one amphibolitic enclave of the “basement” of the Suomussalmi-Kuhmo Archaean (2.65 Ga) greenstone belts (central-eastern Finland), have been chosen together with one greenstone sample for Rb-Sr and Sm-Nd geochronological and isotopic studies.The granitoïd rocks are subdivided into three groups: two generations of grey gneisses and a post-belt augen gneiss. The Rb-Sr ages of the first and second generation of grey gneisses are 2.86 ± 0.09 and 2.62 ± 0.07 Ga, respectively. These results are corroborated by Sm-Nd data. The post-belt augen gneiss gives an age of 2.51 ± 0.11 Ga. The results show that the two generations of grey gneisses, the greenstone belts and the post-greenstone augen gneiss, were developed over a period > 350 Ma. The two generations of grey gneisses show identical I_Sr values (0.7023 ± 8 and 0.7024 ± 6) which contrast with that of the augen gneiss (0.7049 ± 8). The low I_Sr and the near-chondritic ?_T^CHUR values indicate that the grey gneisses cannot derived from much older continental materials. Trace element studies suggest that these grey gneisses have had a multi-stage development. The augen gneiss with a moderately high I_Sr is likely to be derived from a granodiorite originated by partial melting of older sialic crust. The more probable parent rock seems to be the first generation grey gneisses. The I_Sr and average Rb/Sr values preclude the greenstone belt and the second generation of grey gneisses as the protolith.  相似文献   

Stochastic Hill's equations for the study of errant rocket burns in orbit     

Martin Ostoja-Starzewski  James M. Longuski 《Celestial Mechanics and Dynamical Astronomy》1992,54(4):295-303

The problem of errant rocket burns in low Earth orbit is of growing interest, especially in the area of safety analysis of nuclear powered spacecraft. The development of stochastic Hill's equations provides a rigorous mathematical tool for the study of such errant rocket maneuvers. These equations are analyzed within the context of a theory of linear dynamical systems driven by a random white noise. It is established that the trajectories of an errant rocket are realizations of a Gauss-Markov process, whose mean vector is given by the solution of a deterministic rocket problem. The time-dependent covariance matrix of the process is derived in an explicit form.  相似文献   

NEW APPROACH TO ESTIMATING SOLAR RADIATION FROM SATELLITE IMAGERY*   总被引：1，自引：1，他引：0  

Gary L. Powell  Anthony J. Brazel  Martin J. Pasqualetti 《The Professional geographer》1984,36(2):227-233

A significantly less expensive but comparatively accurate means of estimating solar radiation from satellite imagery is demonstrated. Opaque cloud cover is visually extracted from nondigitized, photographic forms of GOES satellite imagery and solar radiation is estimated using this information as input into a relatively simple solar model. Daily root mean square, mean absolute and mean bias errors were 13.2, 8.6 and 1.1 percent, respectively. Maps of the spatial distribution of solar radiation for Arizona are included.  相似文献   

Is the Universe flat?     

Martin J. Rees 《Journal of Astrophysics and Astronomy》1984,5(4):331-348

The evidence for unseen mass (which is briefly reviewed) suggests that the cosmological density parameter Ω is at least 0.1–0.2. An Einstein-de-Sitter ‘flat’ universe with Ω = 1 — which is appealing for theoretical reasons — can only be reconciled with the data if the galaxies are more ‘clumped’ than the overall mass distribution, and are poor tracers of the unseen mass even on scales of several Mpc. Possible forms for the unseen mass are discussed; and feedback processes are outlined whereby galaxy formation can be suppressed in underdense regions.  相似文献   

Atmospheric response to soil-frost and snow in Alaska in March   总被引：2，自引：0，他引：2  

N. Mölders  J. E. Walsh 《Theoretical and Applied Climatology》2004,77(1-2):77-105

Summary A hydro-thermodynamic soil-vegetation model including soil freezing/thawing (soil-frost) and snow-metamorphism has been integrated into the PennState/NCAR Mesoscale Meteorological Model MM5 in a two-way coupled mode. A hierarchy of simulations with and without the soil-frost module, each combined with and without the snow module, shows the influence of snow-cover and soil-frost on weather in Alaska. Herein the landscape is featured as it is typically by mesoscale models.Theoretical considerations suggest that organic soil types should be considered in mesoscale modeling because of their different thermal and hydrological behavior as compared to mineral soils. The Ludwig-Soret and Dufour effects are small, but increase appreciably during freezing/thawing and snow-melt.The snow and soil-frost processes have a demonstrable impact on the surface thermal and hydrological regimes and on the near-surface atmospheric conditions even on the short (synoptic) timescales. The presence of snow-cover results in a highly stable stratification. In cloud-free areas, the enhanced loss of radiant energy and cooling of the air over snow-cover lead to a positive feedback to relatively colder, drier conditions. In cloudy areas, a positive feedback to warmer, moister conditions develops over snow-cover. As the changes in atmospheric humidity and temperature caused by snow-cover propagate into the pressure field, sea level pressure is lower by more than 1hPa in the simulations with snow-cover. Although the effect of soil-frost alone is an order of magnitude smaller, the soil-frost snow system leads to an increase of the pressure difference to 1.2hPa. The changes in the pressure field alter wind speed and direction slightly.Soil-frost results in soil temperature differences of 2–5K in the upper soil layers, while snow results in differences of 3–10K. Soil-frost has a notably greater impact in cloud-free than cloudy areas. When a snow-cover is present, frozen soil enhances the insulating effect of a snow-cover in cloudy areas, but reduces it in cloud-free areas. In cloudy areas, soil-frost without snow-cover leads to cooler, drier atmospheric conditions relative to no frost. In cloudy areas, soil-frost under a snow-cover reduces the water supply to the atmosphere as compared to snow-covered conditions without soil-frost. The combined effects of soil-frost and snow increase precipitation locally by as much as 12.2mm/ 48h. If mesoscale modeling does not consider the soil-frost snow system, predicted water vapor fluxes will be too high in cloud-free areas, and too low in cloudy areas.  相似文献   

Refined relationship between the position of the fundamental OH stretching and the first overtones for clays     

S.?PetitEmail author  A.?Decarreau  F.?Martin  R.?Buchet 《Physics and Chemistry of Minerals》2004,31(9):585-592

The aim of this paper is to determine a relationship between the wavenumbers of the first OH-stretching overtones (W_2OH) and the wavenumbers of the OH-stretching fundamentals (W_OH) to help to interpret the near-infrared (NIR) spectra. The first overtone (2OH) bands appear at wavenumbers less than twice those of the fundamental bands (OH), due to the anharmonic character of vibrations, X = W_2OH/2 - W_OH, with X being the anharmonicity constant. Talc samples with various crystal chemistries are used to solve the equation and the experimental data are well fitted with X = –85.6 cm^–1. As far as the authors are aware, it is the first time that the anharmonicity constant for the OH-stretching vibrations is determined for phyllosilicates. The anharmonicity constant remains almost unchanged for several types of clay samples. Therefore the relation, established from talc samples because their absorption bands are narrow and their wavenumber range of OH vibrations is wide, can be used for any other clay minerals.  相似文献