Sunspot nests     

M. J. M Castenmiller  C. Zwaan  E. B. J. Van Der Zalm 《Solar physics》1986,105(2):237-255

For the period August 1959–December 1964 the Greenwich Photoheliographic Results were searched for sunspot nests. Such a nest is a sequence of sunspot groups that appear within a small area on the solar surface and that last for several months. The search procedure is described and data for 41 probable sunspot nests are given. At least three quarters of these nests appear to be real, and not chance clusters.The nests are the same type of activity sequences as the Fleckenherde discovered by Becker (1955) and the complexes of activity pointed out by Gaizauskas et al. (1983). The complexes of activity as defined by Bumba and Howard (1965) are different patterns, however; the relation between complexes and the nests is shown.Some properties of the nests are: (i) many nests appear as double structures; (ii) single nests and components of double nests are quite compact: the effective areas are comparable to those of medium-large sunspot groups; (iii) each nest rotates at its own steady rate about the Sun; (iv) the intrinsic scatter in the rotation rates is much larger than the trend in the differential rotation; (v) displacements in latitude are less than a few meters per second; (vi) many nests live for 6 to 15 Carrington rotation periods, the minimum lifetime is not yet determined; (vii) the fraction of the sunspot groups that are members of nests is large (at least 30%).  相似文献   

The emergence of magnetic flux   总被引：1，自引：0，他引：1  

Cornelis Zwaan 《Solar physics》1985,100(1-2):397-414

This paper first summarizes the morphology and dynamics of emerging flux regions and arch filament systems and then discusses detailed observations of a particular active region with emerging magnetic flux.The central part of the growing active region shows abnormal granulation and a weak magnetic field that, locally, is transverse. In the border zone, strong downward flows occur in the chromopshere and photosphere (small features with strong magnetic fields (faculae, pores) are formed here.) Near the leading and following edge, sunspots are formed by the coalescence of such small magnetic elements.The observational data are interpreted by means of a heuristic model of an emergent magnetic loop-shaped bundle consisting of many flux tubes. In this model we incorporate the theory of convective collapse and the buoyancy of flux tubes. The observed complexity in the structure and dynamics, including strong transverse fields and velocity shear, is attributed to the emergence of several flux regions within the active region at different orientations.  相似文献   

Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review     

Geert Cornelis  C. Anette Johnson  Tom Van Gerven  Carlo Vandecasteele 《Applied Geochemistry》2008

An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.  相似文献   

Editorial     

Cornelis De Jager  Zdeněk Švestka 《Solar physics》1978,56(1):3-4

  相似文献   

A parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment   总被引：1，自引：0，他引：1  

Wim M. Cornelis  Donald Gabriels  Roger Hartmann 《Geomorphology》2004,59(1-4):43

A new parameterisation for the threshold shear velocity to initiate deflation of dry and wet particles is presented. It is based on the balance of moments acting on particles at the instant of particle motion. The model hence includes a term for the aerodynamic forces, including the drag force, the lift force and the aerodynamic-moment force, and a term for the interparticle forces. The effect of gravitation is incorporated in both terms. Rather than using an implicit function for the effect of the aerodynamic forces as reported earlier in literature, a constant aerodynamic coefficient was introduced. From consideration of the van der Waals force between two particles, it was further shown that the effect of the interparticle cohesion force between two dry particles on the deflation threshold should be inversely proportional to the particle diameter squared. The interparticle force was further extended to include wet bonding forces. The latter were considered as the sum of capillary forces and adhesive forces. A model that expresses the capillary force as a function of particle diameter squared and the inverse of capillary potential was deduced from consideration of the well-known model of Fisher and the Young–Laplace equation. The adhesive force was assumed to be equal to tensile strength, and a function which is proportional to particle diameter squared and the inverse of the potential due to adhesive forces was derived. By combining the capillary-force model and the adhesive force model, the interparticle force due to wet bonding was simplified and written as a function of particle diameter squared and the inverse of matric potential. The latter was loglinearly related to the gravimetric moisture content, a relationship that is valid in the low-moisture content range that is important in the light of deflation of sediment by wind. By introducing a correction to force the relationship to converge to zero moisture content at oven dryness, the matric potential–moisture content relationship contained only one unknown model parameter, viz. moisture content at −1.5 MPa. Working out the model led to a rather simple parameterisation containing only three coefficients. Two parameters were incorporated in the term that applies to dry sediment and were determined by using experimental data as reported by Iversen and White [Sedimentology 29 (1982) 111]. The third parameter for the wet-sediment part of the model was determined from wind-tunnel experiments on prewetted sand and sandy loam aggregates. The model was validated using data from wind-tunnel experiments on the same but dry sediment, and on data obtained from simulations with the model of Chepil [Soil Sci. Soc. Am. Proc. 20 (1956) 288]. The experiments showed that soil aggregates should be treated as individual particles with a density equal to their bulk density. Furthermore, it was shown that the surface had to dry to a moisture content of about 75% of the moisture content at −1.5 MPa before deflation became sustained. The threshold shear velocities simulated with our model were found to be in good agreement with own observations and with simulations using Chepil's model.  相似文献   

Fluvial response to rapid high‐amplitude lake‐level changes during the Late Weichselian and early Holocene,Ain River valley,Jura, France     

Cornelis Kasse 《Boreas: An International Journal of Quaternary Research》2014,43(2):403-421

In the present paper the effects of rapid, high‐amplitude base‐level changes during the last glacial‐interglacial transition were studied for the Ain River in eastern France. During the Würm glacial maximum (MIS 2) rapid aggradation by deep‐water Gilbert‐type deltas and shallow‐water fan deltas occurred at the margins of a 20 to 50 m deep proglacial lake. A temporal high‐amplitude lake‐level fall of 60 m resulted in gravel deposition by forced‐regressive deltas, followed by rapid lake‐level rise and fine‐grained glaciolacustrine deposition. During the final deglaciation, a rapid base‐level fall of 40 m resulted in a complex fluvial response. Knickpoint formation and headward incision of the highstand deltas and concomitant deposition of gravel sheets by forced‐regressive deltas and braided systems occurred in several depocentres on the former glacial lake floor. Preservation of highstand and falling‐stage deposits and terrace formation in the incised valley depended on vertical incision and lateral channel migration. Terraces are well developed in the former lake‐floor depressions, whereas vertical incision was dominant in the higher lake‐floor areas. The Ain terrace staircase was likely formed by autogenic processes during a single allogenic base‐level fall. This case study possibly offers an analogue for the preservation of interglacial highstand coastal deltas during sea‐level fall at warm‐to‐cold climate transitions, although the rates of base‐level fall are different.  相似文献   

A numerical scheme for calculating stresses and strain rates in glaciers     

Cornelis J. van der Veen 《Mathematical Geology》1989,21(3):363-377

The stress and strain-rate fields in a glacier or other type of rock with known rheological properties can be calculated by using a numerical solution technique. Calculations are based on force-balance equations and the constitutive relation for polar ice, and do not involve any mathematical approximations. The geometry is prescribed. Basal velocities also are prescribed, either by specifying their values or by relying on a sliding relation. All other quantities are determined numerically.  相似文献   

Geochemical studies in the drainage basin of the Rio Vouga,Portugal. IV. Impact of land use on the hydrogeochemistry of natural waters in the Vouzela region   总被引：1，自引：0，他引：1  

Rob N. J. Comans  Cornelis H. Van Der Weijden  Simon P. Vriend 《Environmental Geology》1987,9(2):119-128

A hydrogeochemical study of the impact of land use on the composition of natural waters in the Vouzela region in northern Portugal was carried out during the summer of 1983. Water samples were collected from spring and major streams in the area and analyzed for major constituents and some trace elements. Analysis of variance and subsequent pairwise contrast tests demonstrated that waters from agricultural areas are significantly enriched in constiluents such as Na, K, Ca, Mg, Sr, Cl, SO₄, and NO₃. High concentrations of these ions in agricultural areas are the result of both the application of fertilizers and enhanced evaporation by the intensive irrigation of agricultural lands. Constitutents such as H₄SiO₄, HCO₃, F, and probably Li, which are typically related to mineral weathering, were not affected by land use. In waters from forested areas the concentration of most constituents was about 20% higher than in waters from uncultivated areas with mainly a grass cover. This reflects the difference in the evapotranspiration of these two vegetation types. The chemistry of the Rio Zela clearly reflects differences in land use in the Rio Zela valley.  相似文献   

Sources of the Slowly-Varying Component of Solar Microwave Emission and their Relationship with their Host Active Regions     

K.F. Tapping  C. Zwaan 《Solar physics》2001,199(2):317-344

Daily surveys of the solar disc made at 2.8 cm wavelength over the period 1–13 November 1981, complemented by magnetograms and H filtergrams, are used to examine the relationship between sources of the slowly varying component of solar radio emission and properties of their host regions. Two classes of source are noted: diffuse and compact. Sources are designated compact when smaller than 40. The diffuse sources may be explained in terms of free–free thermal emission from trapped plasma in loops overlying the active region. The great majority of compact sources can be accounted for in terms of gyroresonance from thermal electrons in the strong magnetic fields overlying sunspots. A small minority are less amenable to this explanation. They are associated with magnetic complexity and dynamism, lie close to magnetic polarity reversals, and could be non-thermal. Microwave sources are an evolutionary feature common to all but the smallest active regions.  相似文献   

Lunar materials: Their mineralogy,petrology and chemistry     

Cornelis Klein Jr. 《Earth》1972

The manned Apollo 11, 12, 14 and 15 and the automated Luna 16 lunar missions have provided us with lunar rock and regolith (soil) samples from a number of geologically distinct sites. The mare regions were sampled by Apollo 11, 12 and Luna 16, whereas Apollo 14 landed on a terrain with more relief, the Fra Mauro Formation which represents an ejecta blanket from the Imbrian Basin, and Apollo 15 touched down near the lunar highlands. The samples collected consist of a mixture, mainly of basalt, breccia and regolith (soil-particulate matter, generally < 1 cm in size). The basalts show considerable variation in texture, mineralogy and chemistry and probably represent fragments from various parts of relatively thin and extensive lava flows in the maria. The breccias represent regolith material which was indurated to varying degrees by impact events. The regolith is a product of the breakdown, again by impact, of coherent rock masses of basalt and breccia.  相似文献