Two new analytic approximations of the Chandrasekhar's H function for isotropic scattering     

Dragomir M. Davidovi?  Jovan Vukani? 《Icarus》2008,194(1):389-397

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High-Speed BVRI Photometry of SS Cyg at Quiescence and at Outburst     

Diana Kjurkchieva  Dragomir Marchev  Waldemar Ogloza 《Astrophysics and Space Science》1998,262(1):53-74

BVRI photometry of SS Cyg from the end of 1996 and the beginning of 1997 is presented. The star underwent an eruption around December 11. The amplitude of which was slightly bigger than those of observed earlier eruptions. We saw some indication of the future outburst in the decreasing of brightness in all colours by about 0.4 mag during the last two weeks before the event. The emission of the system moved strongly to the shorter wavelengths at outburst. Our multicolour data confirm the existence of a light variability with the orbital (spectroscopic) period at quiescence. Moreover we found for the first time that this variability exists also at outburst but its amplitude is 3–5 times smaller. Whereas the amplitudes of the orbital variability at quiescence decrease to the longer wavelengths, they increase at outburst to the longer wavelengths. The orbital folded curve at quiescence has two-wave shape and was fitted well by the different visibility of two diametrical opposite hot spots (210000 K) with angular size 10⁰ on the magnetic poles of the white dwarf. An analogy between the two basic states of the U Gem-star SS Cyg, the polar AM Her and Z Cam-star RX And was found.  相似文献   

Multistage alkaline permanganate degradation of a type II kerogen     

Dragomir Vitorovi&#x;  Mirjana Djordjevi&#x;  Andr Ambls  Jean C. Jacquesy 《Organic Geochemistry》1984,5(4):259-265

The products of a 27-step alkaline permanganate degradation of a type II kerogen from a sample of Toarcian shale, Paris Basin, have been studied. The high yield of oxidation products consisted of 1.86% neutrals and bases, 24.48% ether-soluble acids, and 45.95% precipitated, ether-insoluble acids, based on weight of original kerogen. The ether-soluble acids and the soluble products of further permanganate degradation of precipitated acids were found to consist mostly of saturated unbranched C₆–C₂₂ α,ω-dicarboxylic and C₉–C₂₅ monocarboxylic acids. Significant amounts of aromatic monocarboxylic, dicarboxylic and tricarboxylic acids were also found. Alkane tri- and tetracarboxylic acids were obtained in small concentration.  相似文献   

Multicolour Photometry of RX and During 1994/95     

Diana Kjurkchieva  Dragomir Marchev  Waldemar Ogloza 《Astrophysics and Space Science》1997,250(2):261-269

The cataclysmic star RX And was observed in the states standstill and quiescence. They differed not only in the light level but in the type of variations around this level. The standstill observed by us turned out quite near to the maximum light and its duration was unusually long. The energy distribution of RX And at the standstill seemed similar to the spectrum of an accretion disk. Two variabilities with periods 3 h 43 min and 1 h 26 min were found at the standstill but only the second of them was present at quiescence too. The star did not show light variability with the spectroscopic period. We tried to interpret some of the results by the supposition that the Z Cam-stars are an intermediate subtype of the cataclysmic stars evolving from UX UMa-subtype to U Gem-subtype and that probably RX And presents a pattern of Z Cam-star that is very near to the U Gem-subtype.  相似文献   

Multicolour Photometry of AM Her During 1994–96     

Diana Kjurkchieva  Dragomir Marchev  Marek Drozdz 《Astrophysics and Space Science》1998,262(4):453-476

Multicolour photometry of the polar AM Her was obtained during 3 observational seasons (1994/95/96). The star was in its high state for most of the observations. It was in its low state in '96 April. It was established that these two states differ not only in the average light level but in the larger amplitudes of variations at low state than at high state. Moreover the energy distributions of the two states differ in the stronger dependence of the flux on ν at high state than at low state. The Fourier analysis of the photometric data shows variability with the spectroscopic (orbital) period. The amplitudes of this variability in all colours are about two times bigger at low state than at high state. An attempt to explain the photometric behaviour of AM Her by a model of dominant emission of two hot spots at the magnetic poles of the white dwarf was made and the spot parameters were determined. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Consequences of anthropogenic activity for two remote alpine lakes in NW Slovenia as tracked by sediment geochemistry     

Gregor Muri  Branko Čermelj  Radojko Jaćimović  Dragomir Skaberne  Andrej Šmuc  Martina Burnik Šturm  Janja Turšič  Polona Vreča 《Journal of Paleolimnology》2013,50(4):457-470

Several geological and geochemical parameters were determined in the sediments of the 5th (5 J) and 6th (6 J) Triglav Lakes, Julian Alps (NW Slovenia), in order to study the impact of natural catchment characteristics and anthropogenic activity. Fish were introduced into both lakes in 1991 and a mountain hut lies on the shore of 5 J. Sedimentary grain size (GS) was distinctly coarser in 5 J than 6 J, with arithmetic means ranging between 46 and 60 and 23–36 μm, respectively. In contrast, the mineralogical composition of the two sediments was similar. Calcite predominated strongly, comprising more than 77 % of total minerals, while dolomite and quartz were rare. Organic carbon (OC) and total nitrogen (TN) concentrations were highest in surficial sediments, with levels of 14.4 and 1.8 %, and 19.3 and 2.4 % observed in 5 J and 6 J, respectively. C/N ratios (atomic) were lowest in the same surface sediments, with the two lakes characterized by similar values (9.6 vs. 9.4, respectively), suggesting a predominance of autochthonous organic matter (OM) in both lakes. Contemporary δ¹³C values were lower in 5 J (?21.0 ‰) than 6 J (?18.5 ‰) sediments. Considerable changes in these four parameters were observed in recently deposited material, reflecting a shift in the trophic status of both lakes that was likely induced by the introduction of fish. In addition, the smaller and shallower 6 J seemed to respond to changes faster than the larger and deeper 5 J, indicating the higher sensitivity of the former. δ¹⁵N values in surface sediments of 5 J and 6 J were ?2.9 and ?4.4 ‰, respectively, with levels increasing gradually with depth to approximately +1.0 ‰ in deeper sediments. The observed changes could most likely be attributed to the atmospheric deposition of reactive nitrogen. The mountain hut has seemingly not had a significant enough impact on the lakes to be recorded in their sediments.  相似文献   

Testing fractal coefficients sensitivity on real and simulated earthquake data     

Dragomir Gospodinov  Alexander Marinov  Elisaveta Marekova 《Acta Geophysica》2012,60(3):794-808

We examined the behavior of different fractal dimensions when applied to study features of earthquake spatial distribution on different types of data. We first examined simulated spatial fields of points of different clustering level, following the so called Soneira-Peebles model. The model was chosen because it displays some similarity to the real clustering structure of earthquakes occurring on hierarchically ordered faults. The analysis of the capacity, clustering and correlation dimensions revealed that their behavior did not completely correlate with the clustering level of the simulated data sets. We also studied temporal variations of the fractal coefficients, characterizing the spatial distribution of the 1999 İzmit-Düzce aftershock sequence. The calculated coefficient values demonstrated analogous behavior like for the simulated data. They exposed different variability in time, but for all of them a systematic fluctuation was observed before the occurrence of the Düzce earthquake. Our analysis revealed that although fractal coefficients could be applied to measure earthquake clustering, they should be used with caution, trying to figure out the best coefficient for a certain data set.  相似文献   

An investigation of the significance of local site effects in Plovdiv, Bulgaria     

Aleksandre Kandilarov  Kuvvet Atakan  Jens Havskov  Dragomir Gospodinov 《Bulletin of Earthquake Engineering》2009,7(1):181-198

Plovdiv is the second largest city in the Republic of Bulgaria. A large part of the city is located on Holocene alluvial sediments and the oldest neighborhoods are situated on syenitic rock outcrops. We believe that local site effects may be an important contributor to the destruction caused by earthquakes. The primary objective of this study was to estimate quantitatively the local site effects in the central area of Plovdiv in terms of fundamental site frequency and amplification factor. Another important objective was to see how these correlate with the geological structures underlying the city. Measurements of the seismic noise at more than two hundred regularly placed points were made in the central area of the city. The H/V spectra were then calculated and analyzed to determine the spatial distribution of the fundamental site frequency and the amplification factor. The results exhibit very good correlation with the local geology. They were also compared with an intensity map from the strong 1928 Plovdiv earthquake. The comparison clearly demonstrates that the local site effects were the main factor in the destruction of buildings—the zones where the most damage was observed are also the zones where we have low fundamental site frequencies and high amplifications. Similarly the areas with high fundamental site frequencies and low amplification factors cover the neighborhoods where less damage has been observed. This study may form a basis for a more comprehensive and systematic microzonation study in Plovdiv.  相似文献   

Response of phenological events to climate warming in the southern and south-eastern regions of Romania     

Georgeta?Bandoc  Remus?Pr?v?lieEmail author  Cristian?Patriche  Elena?Dragomir  Maria?Tomescu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):1113-1129

The analysis of phenological changes in vegetation is essential for the assessment of the response and adaptation of ecosystems/agro-ecosystems to climate change. This study analyses spatial and temporal changes in phenological events (phenophases) and in the climatic growing season in southern and south-eastern Romania, based on mean monthly temperature values recorded between 1961 and 2010 at 24 weather stations, spread out uniformly in the study area. By using the histophenogram method for extracting the mean phenophases length (eight in total, i.e. growing season onset, budding–leafing, flowering, fruiting, maturing, dissemination, start of leaf loss and end of leaf loss) and that of the overall growing season, this paper aims to analyse current phenological changes (in three periods, 1991–2000, 2001–2010 and 1991–2010) in relation to 1961–1990, which is the reference interval in various global climatic studies. Following the analysis of the theoretical phenology length, based on the temperature thresholds (between 5 and 25 °C) that differentiate biological cycles of vegetation, results showed an overall increase in phenological activity (especially in the past decade, 2001–2010), except for two phenophases (fruiting and dissemination), for which largely dominant length decreases were identified. Quantitatively, increases (and null changes, in a few cases) in phenological length generally range between 0–5 days/0–10% (e.g. in the budding–leafing phenophase) and 11–15 days/10.1–20% (maturing), considering the absolute changes or percentages in the three periods, compared to the reference interval 1961–1990. For the most part, the current decrease in the fruiting and dissemination phenophases falls in the interval ?1 to ?5 days/?10.1 to ?20%, compared to the reference period. At the same time, it was noticed that the entire growing season has been expanding, especially in the past decade, when numerous increase instances of up to 15 days were recorded, corresponding to a dominant interval of 0–10% from the period 1961–1990. The results can be particularly useful for adapting the different types of crops to future climate changes, considering that the study area has a high agro-ecological importance.  相似文献   

On the applicability of the RETAS model for forecasting aftershock probability in underground mines (Kiirunavaara Mine,Sweden)     

Gospodinov  Dragomir  Dineva  Savka  Dahnér-Lindkvist  Christina 《Journal of Seismology》2022,26(5):1023-1037

Aftershock series of even comparatively small seismic events can pose a risk to the mining operation or the personnel in deep underground mines as the main shocks and some of the aftershocks can cause damage in the rock mass. Stochastic modeling was applied in this study for the analysis of the temporal evolution of aftershock occurrence probability during a M1.85 aftershock sequence in Kiirunavaara Mine, Sweden. The Restricted Epidemic-Type Aftershock Sequence (RETAS) model was chosen for estimation of the aftershock occurrence probability. This model considers all events with magnitude above the magnitude of completeness M₀ and has the advantage of including the Modified Omori Formula (MOF) model and Epidemic-Type Aftershock Sequence (ETAS) model as its end versions, considering also all intermediate models. The model was applied sequentially to data samples covering cumulative periods of time, starting from the first 2 h after the main event and increasing them by 2 h until the period covered the entire 72-h sequence. For each sample, the best-fit RETAS version was identified and the probability of a M?≥?0.5 aftershock for every next 2 h was determined through Monte Carlo simulation. The feasibility of the resulting probability evolution for suspension and re-starting of the mining operations was discussed together with possible prospects for future development of the methodology.

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