On the Nonlinear Thermal Evolution of Solar Corona Structures     

C.A. Mendoza-Briceño 《Astrophysics and Space Science》1997,256(1-2):387-392

The thermal evolution of structures is investigated for different values of the size of structure. A simplified cooling function and a constant heating mechanism are assumed. Analytical criteria for thermal instability are obtained. It is found that the response of the thermal structure not only depends on the amplitude of the disturbances, but also on whether the disturbance increases or decreases the initial steady temperature. Additionally, the evolution of the structure is examined numerically by using a time-dependent code under the assumption that the inertia terms are small. In particular, the analytical criteria obtained for thermal instability are verified.  相似文献   

Relationships Between Saline Ground Water Soil, and Leaf Tissue Composition of the Phreatophyte Mezquite     

F. L. García-Carreño  E. Troyo-Diéguez  J. L. Ochoa 《Ground water》1992,30(5):676-682

  相似文献   

Erratum: Fluorescent H₂ in the reflection nebula NGC 2023 – I. Recent observations     

M. S. K. McCartney  P. W. J. L. Brand  M. G. Burton  A. Chrysostomou 《Monthly notices of the Royal Astronomical Society》2001,321(4):784-784

  相似文献   

Two 100-Mpc-scale structures in the three-dimensional distribution of radio galaxies and their implications     

Kate Brand  Steve Rawlings  Gary J. Hill  Mark Lacy  Ewan Mitchell  Joe Tufts 《Monthly notices of the Royal Astronomical Society》2003,344(1):283-306

  相似文献   

On the self-consistency of evolutionary synthesis models     

Miguel Cerviño 《Astrophysics and Space Science》2003,284(2):897-900

Evolutionary synthesis models have been used to study the physical properties of unresolved populations in a wide range of scenarios. Unfortunately, their self-consistency is difficult to test and there are some theoretical open questions without an answer: (1) The change of the homology relations assumed in the computation of isochrones due to the effect of stellar winds (or rotation) and the discontinuities in the stellar evolution are not considered. (2) There is no consensus about how the isochrones must be integrated. (3) The discreteness of the stellar populations (that produce an intrinsic statistical dispersion) usually are not taken into account, and model results are interpreted in a deterministic way instead of a statistical one. The objective of this contribution is to present some inconsistencies in the computation and some cautions in the application of the results of such codes. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Microwave and hard X-Ray observations of a solar flare with a time resolution better than 100 ms     

P. Kaufmann  F. M. Strauss  J. E. R. Costa  B. R. Dennis  A. Kiplinger  K. J. Frost  L. E. Orwig 《Solar physics》1983,84(1-2):311-319

Simultaneous microwave and X-ray observations are presented for a solar flare detected on May 8, 1980 starting at 19:37 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28–490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms, respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive peaks in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240 ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5 s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model.  相似文献   

Geochemistry of late stage medium to high-K calc-alkaline and shoshonitic dykes in the Ulukişla Basin (Central Anatolia, Turkey): Petrogenesis and tectonic setting     

M. A. Kurt  M. Alpaslan  M. C. Göncüoǧlu  A. Temel 《Geochemistry International》2008,46(11):1145-1163

  相似文献   

The pathway of mercury in contaminated waters determined by association with organic carbon (Tagus Estuary,Portugal)     

João Canário  Carlos ValeMarta Nogueira 《Applied Geochemistry》2008

Reactive dissolved Hg (Hg_R), non-reactive dissolved Hg (Hg_NR), particulate Hg (Hg_P), dissolved organic C (DOC), particulate organic C (POC), salinity and other interpretative parameters were determined in water samples collected in the North Channel and in adjacent areas of the Tagus estuary (Portugal). Higher concentrations of both dissolved and particulate Hg in the North Channel indicate a pollution source and raise the possibility of Hg escaping to adjacent areas by tidal action. This transport was confirmed by the increase of Hg_R with salinity and Hg_NR with DOC, along a longitudinal axis paralleling the North Channel. Apparently, Hg leaving this channel is progressively complexed by inorganic and organic ligands. Near the mouth of the estuary, values decreased reflecting dilution with seawater. Moreover the Hg_P:POC ratio also increased seaward, suggesting mixing with Hg enriched particles that escaped the North Channel, or incorporation of dissolved Hg species in river-derived particles. These results suggest that the pathway of anthropogenic Hg in contaminated waters may be identified by their enrichment in organic matter, both in the dissolved and particulate fraction.  相似文献   

First U–Pb SHRIMP age of the Hauterivian stage, Neuquén Basin, Argentina     

M. Beatriz Aguirre-Urreta  Pablo J. Pazos  Darío G. Lazo  C. Mark Fanning  Vanesa D. Litvak   《Journal of South American Earth Sciences》2008,26(1):91-99

A high-resolution ion-microprobe (SHRIMP) U–Pb zircon age from a tuff layer intercalated in the ammonoid bearing sedimentary succession of the Neuquén Basin in Argentina provides a robust geochronologic date to add to the absolute ages and to improve the relative chronology of the Early Cretaceous Hauterivian stage. The tuff layer appears interbedded between shales of the upper member (Agua de la Mula) of the Agrio Formation within the Spitidiscus riccardii ammonoid zone (base of the Late Hauterivian) yielding a date of 132.5 ± 1.3 Ma. This date confirms and supports an accurate correlation between the ammonoid biostratigraphy of the Neuquén Basin with the Western Mediterranean Province of the Tethys during the Early Cretaceous and matches with the most recently published time scale. It also casts doubts on the validity of K–Ar ages on glauconite-grains recently reported from the Lower Cretaceous of the Vocontian Basin of France.  相似文献   

Response of antioxidant systems to copper in the gills of the clam Ruditapes decussatus     

Florence Geret  Angela Serafim  Luisa Barreira  Maria Joo Bebianno 《Marine environmental research》2002,54(3-5)

Copper (Cu) is an essential element for biological systems, however, when present in excess, is toxic. Metallothioneins can play an important role in Cu homeostasis and detoxification. Moreover, Cu can catalyse the production of toxic hydroxyl radicals that cause lipid peroxidation but defence systems in the cells can limit the oxidative damage. The present study was performed to investigate the effect of three Cu concentrations (0.5, 2.5 and 25 μg l⁻¹) on the response of antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathion peroxidase and total glutathion peroxidase), total proteins, metallothioneins (MT), malondialdehyde (MDA) concentrations in the gills of the clam, Ruditapes decussatus. The activity of antioxidant enzymes and total proteins, MT and MDA concentrations were measured in the gills of the clams after 1, 3, 7, 14, 21 and 28 days of Cu exposure. Results indicate that Cu only induces an imbalance in the oxygen metabolism during the first week of Cu exposure due to a decrease in mitochondrial SOD and CAT, selenium-dependent and total glutathion peroxidase activities. Cu also causes lipid peroxidation, measured by the MDA formation, that was Cu dependent. In the gills of clams exposed to 25 μg Cu/l, the excess of Cu triggers the induction of MT synthesis after 3 days of exposure.  相似文献