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101.
Late-type stars with chromospheric and coronal activities exceeding those of the Sun and other stars with well-defined cycles are considered. These rotate more rapidly than stars with well established cycles; for single stars, this appears to be due to their younger ages. The spots on such stars cover several per cent of the total area, which is an order of magnitude higher than for the Sun at its activity maximum. Our wavelet analysis of the chromospheric-emission variability, which has been observed since 1965 in the framework of the HK project, indicates that the period of the axial rotation of some of these starts varies from year to year. This is most pronounced in two “Good” stars according to the classification of Baliunas et al., HD 149661 and HD 115404, and also in a star with a more complex variability, HD 101501. No similar effect is exhibited by the “Excellent” cyclic-activity stars. Such variations in the period can be observed during epochs of appreciable rotational modulations of the chromospheric-emission fluxes, most likely, immediately after the maximum of a long-period wave (cycle?). This seems to provide evidence for the existence of huge activity complexes in the chromospheres of these stars, whose longitudes remain virtually constant over several years; they drift from fairly high latitudes to the equator at speeds close to the value typical of sunspots. The observed period variations are most likely due to differential rotation of the same sign that is known for the Sun. Our results provide independent confirmation of similar conclusions obtained by us previously using zonal models for highly spotted stars. Other activity features of a selected star group and the implications of the results for the theory of stellar and solar dynamos are discussed. 相似文献
102.
103.
A Bianchi type I string cosmological model in the presence of a magnetic flux is investigated. A few plausible assumptions regarding the parametrization of the cosmic string and magneto-fluid are introduced and some exact analytical solutions are presented. 相似文献
104.
The evaluation of the vulnerability of the karst aquifer and the source in the Coteţul Dobreştilor system was performed on
the basis of geological, hydrogeological and pedological data. The methods proposed in the Final Report of COST Action 620
were used. The available field data resulted in assessing the parameters P, I and in characterizing the saturated aquifer karstic network parameter (K). The soil cover over the carbonate deposits is generally shallow and easily bypassed by the superficial flow, the protection
of the karstic aquifer and the source thus being minimal. 相似文献
105.
We present evidence for a thick (∼100 km) sequence of cogenetic rocks which make up the root of the Sierra Nevada batholith
of California. The Sierran magmatism produced tonalitic and granodioritic magmas which reside in the Sierra Nevada upper-
to mid-crust, as well as deep eclogite facies crust/upper mantle mafic–ultramafic cumulates. Samples of the mafic–ultramafic
sequence are preserved as xenoliths in Miocene volcanic rocks which erupted through the central part of the batholith. We
have performed Rb-Sr and Sm-Nd mineral geochronologic analyses on seven fresh, cumulate textured, olivine-free mafic–ultramafic
xenoliths with large grainsize, one garnet peridotite, and one high pressure metasedimentary rock. The garnet peridotite,
which equilibrated at ∼130 km beneath the batholith, yields a Miocene (10 Ma) Nd age, indicating that in this sample, the
Nd isotopes were maintained in equilibrium up to the time of entrainment. All other samples equilibrated between ∼35 and 100
km beneath the batholith and yield Sm-Nd mineral ages between 80 and 120 Ma, broadly coincident with the previously established
period of most voluminous batholithic magmatism in the Sierra Nevada. The Rb-Sr ages are generally consistent with the Sm-Nd
ages, but are more scattered. The 87Sr/86Sr and 143Nd/144Nd intercepts of the igneous-textured xenoliths are similar to the ratios published for rocks outcroping in the central Sierra
Nevada. We interpret the mafic/ultramafic xenoliths to be magmatically related to the upper- and mid-crustal granitoids as
cumulates and/or restites. This more complete view of the vertical dimension in a batholith indicates that there is a large
mass of mafic–ultramafic rocks at depth which complement the granitic batholiths, as predicted by mass balance calculations
and experimental studies. The Sierran magmatism was a large scale process responsible for segregating a column of ∼30 km thick
granitoids from at least ∼70 km of mainly olivine free mafic–ultramafic residues/cumulates. These rocks have resided under
the batholith as granulite and eclogite facies rocks for at least 70 million years. The presence of this thick mafic–ultramafic
keel also calls into question the existence of a “flat” (i.e., shallowly subducted) slab at Central California latitudes during
Late Cretaceous–Early Cenozoic, in contrast to the southernmost Sierra Nevada and Mojave regions.
Received: 27 December 1997 / Accepted: 11 June 1998 相似文献
106.
Olivier Féménias Tudor Berza Mihai Tatu Hervé Diot Daniel Demaiffe 《International Journal of Earth Sciences》2008,97(3):479-496
The Motru Dyke Swarm intrudes the Precambrian Danubian basement of the Southern Carpathians (Romania). It is a marker of a
sub-volcanic event that occurred during the early Palaeozoic (Cambrian to Ordovician). The geographical distribution of dykes
on a ∼2,000 km2 area is heterogeneous; several areas of high dyke density have been the subject of a detailed petrological and geochemical
study. Taken altogether, the 150 samples define a single complete magmatic series, from basaltic andesite to rhyolite. Whole-rock
major element variations show a medium- to high-K, calc-alkaline magmatic suite. The compositional variations and the general
decrease of trace element contents (both compatible and incompatible, including REEs) from basaltic andesite to rhyolite are
consistent with 1) the fractionation of the observed phenocryst assemblages, Ca-amphibole (Ti-pargasite to magnesiohornblende)
followed by intermediate plagioclase, clinopyroxene and accessory biotite and quartz and 2) the absence of lower and/or upper
crustal contamination. Trace elements diagrams display typical arc patterns (LILE, Pb and LREE enrichment and relative depletion
in Nb-Ta, Zr-Hf and Ti). The Th/U, Nb/Ta and Zr/Hf ratios are constant and close to the mantle values throughout the whole
series, which argues that the parental magma was generated from a single and homogeneous enriched lithospheric mantle source.
The field regional evidence implies that melting occurred during a late- to post-orogenic period of lithospheric extension,
and thus took place quite lately after the cessation of Pan-African subduction. 相似文献
107.
The authors present synthetically the great variety of the forms of relief in Romania, which create a real natural attraction, satisfying any side of tourist demand. The most significant poles of Romanian tourism, represented by the Carpathians, the unique Danube Delta, the Black Sea offer great possibilities for winter sports, hiking, climbing, water sports, fishing and hunting, sun bathing and medical treatment, owing to the immense balneary potentialities of the country.In the development of Romanian tourism an important part has had and is still having the scientific research activity achieved in the Tourism Department of a specialized institute of researches. The studies worked out in this field are divided into several categories, dealing with subjects of conjuncture and prognosis, economic efficiency, revaluation of territory, improvement of activity in various resorts, launching of new produces, sociology investigations, new iteneraries etc.The authors also present a selective bibliography. 相似文献
108.
Jasim?Al-KhalidiEmail author Mihai?Dima Sabina?Stefan 《Theoretical and Applied Climatology》2018,133(1-2):179-190
The impact of large-scale modes on Iraq climate is investigated here based on winter and spring fields of temperature and precipitation. The temperature data (1971–2010) was recorded at 8 stations whereas the precipitation fields (1981–2010) were recorded at 18 locations. Empirical orthogonal function analyses were performed in order to characterize the spatial variability of the Iraq climatological parameters. The relationships between the global sea surface temperature, sea level pressure, and geopotential height fields with the dominant modes of Iraq temperature and precipitation were also investigated. Correlation and regression maps emphasize links between Iraq climate and large-scale modes, like the Atlantic Multidecadal Oscillation and the El Niño Southern Oscillation phenomenon. 相似文献
109.
Climate Dynamics - Variations of the global sea level pressure (SLP) field reflect atmospheric and oceanic influences and have a profound influence on temperature, precipitation and the global... 相似文献
110.
A new argyrodite occurrence has been discovered in the Ro?ia Montan? ore deposit located in the South Apuseni Mountains, Romania. Argyrodite is associated with common base metal sulfides and sulfosalts (galena, sphalerite, chalcopyrite, tetrahedrite ± alabandite, pyrite, and marcasite), tellurides (hessite, altaite, sylvanite) and rare electrum grains in the Ag-rich Cârnicel vein hosted by an extracraterial phreatomagmatic breccia within the Cârnic massif. SEM and EPMA analyses revealed that this argyrodite is Te-rich and a mean Ag8.04Ge0.9Te2.07S3.77 formula was calculated. This phase could be the germaniferous equivalent of the previously-described Te-rich canfieldite. To cite this article: L. Bailly et al., C. R. Geoscience 337 (2005). 相似文献