Self-Similarity Properties of the Kerch Peninsula Stream Network and Their Comparison with the Results of Structural and Geomorphological Analysis

Izvestiya, Atmospheric and Oceanic Physics - The results of the fractal analysis of a drainage network reconstructed using a digital elevation model and the structural and geomorphological analysis...     

Super-Fast Line-Profile Variability in the Spectra of OBA-Stars: B1-Star <Emphasis Type="Italic">ρ</Emphasis> Leo

This study continues our investigation of the super-fast variability of line profiles in the spectra of early-type stars. We have investigated the line-profile variability in spectra of OBA-stars with the SCORPIO multi-mode focal reducer mounted at the 6-m SAO RAS telescope. Regular short-period variations of the H and He lines in the spectra of the B1I star ρ Leo were detected with periods ranging from 2 to 90 minutes, as well as irregular line-profile variations on time intervals less than 1 minute. A possible origin of rapid spectral variations is discussed.     

Estimates of abundance of the short-baseline (1-3 meters) slopes for different Venusian terrains using terrestrial analogues

The interplanetary mission, Venera-D, which is currently being planned, includes a lander. For a successful landing, it is necessary to estimate the frequency distributions of slopes of the Venusian surface at baselines that are comparable with the horizontal dimensions of lander (1–3 m). The available data on the topographic variations on Venus preclude estimates of the frequency of the short-wavelength slopes. In our study, we applied high-resolution digital terrain models (DTM) for specific areas in Iceland to estimate the slopes on Venus. The Iceland DTMs have 0.5 m spatial and 0.1 m vertical resolution. From the set of these DTMs, we have selected those that morphologically resemble typical landscapes on Venus such as tessera, shield, regional, lobate, and smooth plains. The mode of the frequency distribution of slopes on the model tessera terrain is within a 30°–40° range and a fraction of the surface has slopes <7°, which is considered as the upper safety limit. This is the primary interest. The frequency distribution of slopes on the model tessera is not changed significantly as the baseline is changed from 1 m to 3 m. The terrestrial surfaces that model shield and regional plains on Venus have a prominent slope distribution mode between 8°–20° and the fraction of the surfaces with slopes <7° is less than 30% on both 1 m and 3 m baselines. A narrow, left-shifted histogram characterizes the model smooth plains surfaces. The fraction of surfaces with slopes <7° is about 65–75% for the shorter baseline (1 m). At the longer baseline, the fraction of the shallow-sloped surfaces is increased and fraction of the steep slopes is decreased significantly. The fraction of surfaces with slopes <7° for the 3-m baseline is about 75–88% for the terrains that model both lobate and smooth plains.     

The use of slump structures as palaeoslope orientation estimators

The two main methods of estimating palaeoslope direction from slump structure orientation data are reviewed. The mean axis method takes the downslope direction as the perpendicular to the mean slump fold axis. The separation are method estimates the downslope direction by the bisector of a planar separation angle between groups of slump folds with opposite downplunge asymmetry. The advantages and disadvantages of each method are considered in detail, by reference first to idealized slump fold distributions and then to a compilation of sixty natural slump fold axis distributions, mostly from published data. Among the advantages of the mean axis method are the ease of deriving confidence limits for estimates and its applicability where fold asymmetry data are unavailable. The main advantage of the separation are method is its validity for strongly skewed fold axis samples. The statistical robustness of the mean axis method, however, due to its reliance on average properties of data, makes it more generally reliable than the separation arc method which depends on extreme properties of data. A procedure for determining palaeoslope directions is suggested which reflects the respective strengths of the two methods.     

The volatile component of quaternary ignimbrite magmas from the North Island,New Zealand

Ignimbrites from the central North Island consist mainly of glass or its devitrified product (70–95%); their phenocryst mineralogy is varied and includes plag., hyp., ti-mag., ilm., aug., hblende, biot., san., qtz, ol., with accessory apatite, zircon and pyrrhotite. The Fe-Mg minerals can be used to divide the ignimbrites into four groups with hyp.+aug. reflecting high quench temperatures and biot.+hblende +hyp.+aug., low quench temperatures. Oxygen fugacities lie above the QMF buffer curve and even in ignimbrites with low crystal contents the solid phases apparently buffered fO₂. Some ignimbrites contain the assemblage actinolite, gedrite, magnetite and hematite, reflecting post-eruption oxidation. The mineralogy also allows estimation of using pyrrhotite and thence , . The assemblage biotite-sanidine can be used to estimate and thence . Water fugacity is calculated in a variety of ways using both biotite and hornblende as well as the combining reaction . It is high and approaches P _total in most ignimbrites (~4kb) but is lower in unwelded pumice breccias. Comparison of temperature estimates using mineral geothermometers for the various phenocryst phases suggests that the ignimbrite magmas showed temperature differences of 60–100 °C and pressure differences of several kilobars. Individual magma chambers therefore, would have extended over several kilometres vertically. The chemical potential of water may have been constant through the magma.     

Organochlorine residues,eggshell thickness,and nest success in barn owls from the Chesapeake Bay

Eggs of barn owls (Tyto alba) were collected from 18 nests in offshore duck blinds on the Maryland side of the lower Potomac River estuary in 1972 and 1973 and analyzed for organochlorine residues. DDE was found in 100% of the clutches, PCBs in 89%, and dieldrin in 78%. Eggshell thickness was inversely correlated with concentrations of DDE, DDD, and dieldrin residues. Six of the 18 clutches had mean DDE residues above 5 ppm, and eggshell thickness in these six clutches was significantly less (P<0.001) than in the other 12 clutches. The owls produced 1.7 young per active nest in 1973. This rate is slightly below the reproductive rate needed to maintain a stable population. An estimated 15% of the population carried concentrations of organochlorine residues that may have been detrimental to their reproduction. Passerine birds, taken extensively as food by a small proportion of the population, are believed to have been the source of elevated concentrations of organochlorines in these barn owls.