Two types of differential rotation of the solar corona     

Olga G. Badalyan 《New Astronomy》2010,15(1):135-143

The differential rotation of the solar corona has been analyzed using as the input data the brightness of the coronal green line Fe xiv 530.3 nm for more than five activity cycles. It is found that the character of rotation of the solar corona changes during the activity cycle. Approximately at the middle of the descending branch the differential rotation is weakly pronounced, while the greatest differential gradient is observed at the ascending branch and, occasionally, at the maximum of the cycle. An explanation of this difference has been suggested. The total rotation rate of the corona can be represented as a superposition of two rotation modes (components) – the fast and slow ones. The synodic period of the fast mode near the equator is about 27 days, increasing slightly with latitude. The synodic period of the slow mode exceeds 30 days. The changing relative fraction of these two modes results in variation of the latitude dependence of the observed rotation rate during the activity cycle. The characteristics of two principal types of differential rotation of the solar corona have been determined. The first type consists of the fast mode alone and is established approximately at the middle of the descending branch of the cycle. The second type is the sum of both modes with the fast mode dominating at low latitudes and the slow mode at high latitudes. The results obtained can be used for in-depth study of interaction of the velocity field and dynamo mechanism in the Sun and stars.  相似文献   

Satellite-based peatland mapping: Potential of the MODIS sensor     

Dirk Pflugmacher  Olga N. Krankina  Warren B. Cohen 《Global and Planetary Change》2007,56(3-4):248

Peatlands play a major role in the global carbon cycle but are largely overlooked in current large-scale vegetation mapping efforts. In this study, we investigated the potential of the Moderate Resolution Imaging Spectroradiometer (MODIS) to capture the extent and distribution of peatlands in the St. Petersburg region of Russia by analyzing the relationships between peatland cover fractions derived from reference maps and  1-km resolution MODIS Nadir BRDF-Adjusted Reflectance (NBAR) data from year 2002.First, we characterized and mapped 50 peatlands from forest inventory and peat deposit inventory data. The peatlands represent three major nutritional types (oligotrophic, mesotrophic, eutrophic) and different sizes (0.6–7800 ha). In addition, parts of 6 peatlands were mined for peat and these were mapped separately. The reference maps provided information on peatland cover for 1105 MODIS pixels. We performed regression analysis on 50% of the pixels and reserved the remainder for model validation. Canonical correlation analysis on the MODIS reflectance bands and the peatland cover fractions produced a multi-spectral peatland cover index (PCI), which served as the predictor in a reduced major axis (RMA) regression model. The results suggest a high potential for mapping peatlands with MODIS. The RMA regression models explained much of the variance in the PCI (r² = 0.74 for mined and r² = 0.81 for unmined peatlands). Model validation showed high correlation between observed versus predicted peatland cover (mined: r = 0.87; unmined: r = 0.92). We used the models to derive peatland cover estimates for the St. Petersburg region and compared the results to current MODIS land cover maps.  相似文献   

Do young martian ray craters have ages consistent with the crater count system?     

William K. Hartmann  Cathy Quantin  Olga Popova 《Icarus》2010,208(2):621-21

McEwen et al. (McEwen, A.S., Preblich, B.S., Turtle, E.P., Artemieva, N.A., Golombek, M.P., Hurst, M., Kirk, R.L., Burr, D.M., Christensen, P. [2005]. Icarus 176, 351-381) developed a useful test for the internal consistency of crater-count chronometry systems. They argued that certain multi-kilometer, fresh-looking martian craters with prominent rays should be the youngest or near-youngest craters in their size range. The “McEwen et al. test” is that the ages determined from crater densities of the smallest superimposed craters (typically diameter D ∼ 5-20 m) should thus be comparable to the expected formation intervals of the host primary. McEwen et al. concluded from MOC data that crater chronometry failed this test by factors of 700-2000. We apply HiRISE and other imagery to eight different young craters in order to re-evaluate their arguments. We use existing crater chronology systems as well as the reported observed production rate of 16 m craters (Malin, M.C., Edgett, K., Posiolova, L., McColley, S., Noe Dobrea, E. [2006]. Science 314, 1573-1557; Hartmann, W.K., Quantin, C., Mangold, N. [2007]. Icarus 186, 11-23; Kreslavsky [2007]. Seventh International Conference on Mars, 3325). Every case passes the McEwen et al. test. We conclude that the huge inconsistencies suggested by McEwen et al. are spurious. Many of these craters show evidence of impact into ice-rich material, and appear to have ice-flow features and sublimation pits on their floors. As production rate data improve, decameter-scale craters will provide a valuable way of dating these young martian geological formations and the processes that modify them.  相似文献   

Electronic state of Fe2+ in (Mg,Fe)(Si,Al)O3 perovskite and (Mg,Fe)SiO3 majorite at pressures up to 81 GPa and temperatures up to 800 K     

Olga V. Narygina  I. Yu. Kantor  C. A. McCammon  L. S. Dubrovinsky 《Physics and Chemistry of Minerals》2010,37(6):407-415

Despite a large number of studies of iron spin state in silicate perovskite at high pressure and high temperature, there is still disagreement regarding the type and P–T conditions of the transition, and whether Fe²⁺ or Fe³⁺ or both iron cations are involved. Recently, our group published results of a Mössbauer spectroscopy study of the iron behaviour in (Mg,Fe)(Si,Al)O₃ perovskite at pressures up to 110 GPa (McCammon et al. 2008), where we suggested stabilization of the intermediate spin state for 8- to 12-fold coordinated ferrous iron (^[8–12]Fe²⁺) in silicate perovskite above 30 GPa. In order to explore the behaviour in related systems, we performed a comparative Mössbauer spectroscopic study of silicate perovskite (Fe_0.12Mg_0.88SiO₃) and majorite (with two compositions—Fe_0.18Mg_0.82SiO₃ and Fe_0.11Mg_0.88SiO₃) at pressures up to 81 GPa in the temperature range 296–800 K, which was mainly motivated by the fact that the oxygen environment of ferrous iron in majorite is quite similar to that in silicate perovskite. The ^[8–12]Fe²⁺ component, dominating the Mössbauer spectra of majorites, shows high quadrupole splitting (QS) values, about 3.6 mm s^?1, in the entire studied P–T region (pressures to 58 GPa and 296–800 K). Decrease of the QS of this component with temperature at constant pressure can be described by the Huggins model with the energy splitting between low-energy e _g levels of ^[8–12]Fe²⁺ equal to 1,500 (50) cm^?1 for Fe_0.18Mg_0.82SiO₃ and to 1,680 (70) cm^?1 for Fe_0.11Mg_0.88SiO₃. In contrast, for the silicate perovskite dominating Mössbauer component associated with ^[8–12]Fe²⁺ suggests the gradual change of the electronic properties. Namely, an additional spectral component with central shift close to that for high-spin ^[8–12]Fe²⁺ and QS about 3.7 mm s^?1 appeared at ~35 (2) GPa, and the amount of the component increases with both pressure and temperature. The temperature dependence of QS of the component cannot be described in the framework of the Huggins model. Observed differences in the high-pressure high-temperature behaviour of ^[8–12]Fe²⁺ in the silicate perovskite and majorite phases provide additional arguments in favour of the gradual high-spin—intermediate-spin crossover in lower mantle perovskite, previously reported by McCammon et al. (2008) and Lin et al. (2008).  相似文献   

Hydrothermal alterations of modern organic sediments at the Ashadze-1 hydrothermal field,Mid-Atlantic Ridge, 13° N     

I. F. Gablina  E. A. Popova  T. A. Sadchikova  T. A. Khusid  N. S. Os’kina  V. E. Bel’tenev  V. V. Shilov 《Doklady Earth Sciences》2010,433(2):998-1002

For the first time detailed investigations of hydrothermal alterations on microbiota of ore-bearing sediments of the Ashadze-1 field (13° N, Mid-Atlantic Ridge) were carried out and local mineral-geochemical zoning was established. For the first time for the region, enriching of Mg sediments related with hydrothermal activity was revealed. It was concluded that hydrotherms affecting sediments are characterized with a high Mg content.  相似文献   

Vulnerability of simple reinforced concrete buildings to damage by rockfalls   总被引：3，自引：3，他引：0  

Olga Mavrouli  Jordi Corominas 《Landslides》2010,7(2):169-180

A procedure is presented for investigating the response of reinforced concrete buildings to rockfall impact. The method considers a single rock hit on the basement columns, and it includes four steps: (a) calculation of the probability of a rock impact on a member of the load-bearing system, taking into account the block size and the design of the structure; (b) evaluation of the response of one or more structural elements to the hit based on element capacity; (c) in the case of structural element failure, assessment of the robustness of the whole structural system, calculating the potential for progressive collapse; and (d) calculation of a damage index (DI), which is the ratio of structural elements that fail to the total number of structural elements. The proposed method is applied to a reinforced concrete building for a range of rockfall paths and intensities. The analysis has been carried out for a 2-m-diameter block and velocities < 3.5 m/s. The possible damage range is found to be highly variable, with DI values ranging from 0.01 to 1 depending on the impact location and block velocity.  相似文献   

Oxygen isotope fractionation between apatite-bound carbonate and water determined from controlled experiments with synthetic apatites precipitated at 10-37 °C     

Christophe Lécuyer  Vincent Balter  François Fourel  Romain Amiot  Olga Otero  Gérard Panczer  Rossana Martini 《Geochimica et cosmochimica acta》2010,74(7):2072-584

The oxygen isotope fractionation between the structural carbonate of inorganically precipitated hydroxyapatite (HAP) and water was determined in the range 10-37 °C. Values of 1000 ln α() are linearly correlated with inverse temperature (K) according to the following equation: 1000 ln α() = 25.19 (±0.53)·T⁻¹ − 56.47 (±1.81) (R² = 0.998). This fractionation equation has a slightly steeper slope than those already established between calcite and water ( [O’Neil et al., 1969] and [Kim and O’Neil, 1997]) even though measured fractionations are of comparable amplitude in the temperature range of these experimental studies. It is consequently observed that the oxygen isotope fractionation between apatite carbonate and phosphate increases from about 7.5‰ up to 9.1‰ with decreasing temperature from 37 °C to 10 °C. A compilation of δ¹⁸O values of both phosphate and carbonate from modern mammal teeth and bones confirms that both variables are linearly correlated, despite a significant scattering up to 3.5‰, with a slope close to 1 and an intercept corresponding to a 1000 ln α() value of 8.1‰. This apparent fractionation factor is slightly higher or close to the fractionation factor expected to be in the range 7-8‰ at the body temperature of mammals.  相似文献   

Configurations of dynamo waves in a two-layer medium and the 11-year solar cycle     

E. P. Popova 《Astronomy Letters》2011,37(3):210-217

The behavior of dynamo waves in a two-layer medium is investigated in terms of the Parker dynamo model. The solar cycle duration is shown to depend on the ratio of turbulent diffusivities in the layers. Meridional circulation has been incorporated into the Parker system. An increase in the intensity of meridional flows is shown to decelerate the propagation of dynamo waves. The minimum of solar magnetic activity can occur not only in the case of intense meridional circulation in both layers but also when a difference in physical characteristics arises between the layers and the meridional flows are moderate.  相似文献   

An intercomparison of model-simulated in extreme rainfall and temperature events during the last half of the twentieth century. Part 1: mean values and variability     

Matilde Rusticucci  José Marengo  Olga Penalba  Madeleine Renom 《Climatic change》2010,98(3-4):493-508

In this study we examine the performance of eight of the IPCC AR4 global coupled climate models used in the WCRP CMIP3 Multimodel Dataset, as well as their ensemble mean, in simulating annual indices of extreme temperature and precipitation climate events in South America. In this first part we focus on comparing observed and modeled mean values and interannual variability. Two extreme temperature indices based on minimum temperature (warm nights and frost days) and three indices of extreme precipitation (R95t, R10 and consecutive dry days), obtained both from meteorological stations during 1961–2000 and model outputs, were compared. The number of warm nights are better represented by models than the FD. The interannual variability pattern is also in good agreement with the observed values. For precipitation, the index that is best represented by the models is the R95t, which relates the extreme precipitation to local climate. The maximum of dryness observed over the central Argentinian Andes or the extensive dry season of the Amazon region could not be represented by any model.  相似文献   

Landslides triggered by the 1949 Khait earthquake, Tajikistan, and associated loss of life   总被引：3，自引：0，他引：3  

Stephen G. Evans  Nicholas J. Roberts  Anatoli Ischuk  Keith B. Delaney  Galina S. Morozova  Olga Tutubalina 《Engineering Geology》2009,109(3-4):195-212

Earthquake-triggered landslides are a major geological hazard in Central Asia. In July 1949, the M7.4 Khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the Tien Shan Mountains, central Tajikistan. These landslides involved widespread rock-slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region. In the Yasman valley hundreds of loess landslides coalesced to form a massive loess flow (est. vol. 245 Mm³) that travelled up to 20 km on a slope of only 2°. In an adjacent valley, the Khait landslide involved transformation of an earthquake-triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement. It travelled 7.41 km over a vertical distance of 1421 m with an estimated average velocity of ~30 m/s. We estimate its volume as 75 Mm³, an order of magnitude less that previously published estimates. The Khait landslide was simulated using DAN. The number of casualties due to earthquake-triggered landslides in the epicentral region was considerable. Approximately 4000 people were killed in the Yasman valley loess flow as 20 villages (kishlaks) were overwhelmed. In the Khait landslide alone we estimate ca. 800 people lost their lives when the villages of Khait and Khisorak were overrun by rapidly moving debris. Our data indicates that a total of approximately 7200 people were killed by earthquake-triggered landslides in the epicentral region of the Khait earthquake and that, in terms of loss of life, the 1949 Yasman valley loess flow was one of the most destructive landslides in recent history.  相似文献