Desert vegetation and timing of solar radiation

Timing and amount of solar radiation were examined as factors influencing the distribution of seven perennial plants on a small mountain located in the Chihuahuan Desert. Average direct beam solar radiation fluxes at differing times throughout the day and year were estimated with computer calculations. Principal components analysis was used to reduce the number of solar radiation parameters and include the maximum available information with a manageable number of variables. The remaining solar radiation parameters were compared to plant distributions using redundancy analysis and generalized additive models. Unimodal, bimodal, and monotonic responses were all found depending upon the species and solar radiation parameter. Niche separation at this location depends upon the timing as well as the amount of solar radiation.     

Changes in temperature and precipitation extremes in the CMIP5 ensemble

Twenty-year temperature and precipitation extremes and their projected future changes are evaluated in an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), updating a similar study based on the CMIP3 ensemble. The projected changes are documented for three radiative forcing scenarios. The performance of the CMIP5 models in simulating 20-year temperature and precipitation extremes is comparable to that of the CMIP3 ensemble. The models simulate late 20th century warm extremes reasonably well, compared to estimates from reanalyses. The model discrepancies in simulating cold extremes are generally larger than those for warm extremes. Simulated late 20th century precipitation extremes are plausible in the extratropics but uncertainty in extreme precipitation in the tropics and subtropics remains very large, both in the models and the observationally-constrained datasets. Consistent with CMIP3 results, CMIP5 cold extremes generally warm faster than warm extremes, mainly in regions where snow and sea-ice retreat with global warming. There are tropical and subtropical regions where warming rates of warm extremes exceed those of cold extremes. Relative changes in the intensity of precipitation extremes generally exceed relative changes in annual mean precipitation. The corresponding waiting times for late 20th century extreme precipitation events are reduced almost everywhere, except for a few subtropical regions. The CMIP5 planetary sensitivity in extreme precipitation is about 6 %/°C, with generally lower values over extratropical land.     

Photometrische Kalibrierung von Schmidtspiegelaufnahmen durch ein bildteilendes Hilfsprisma

Plates of the Tautenburg Schmidt can be calibrated with the aid of a beam-splitting prisma only if Schraffierkassette plates are used. The effects of image structure, scintillation and intermittence on in-focus images are different for the main component and the prismatic companion. Therefore, such plates cannot be used to set up a photometric scale.     

The Fine Structure of the Spiral-arms

An explanation for filaments inclined to the galactic plane observed in the next-inner spiral-arm is sought in terms of self-consistent z-oscillations. These filaments or „shingles”︁ are observed to be ˜ 1.4 kpc long, 70 pc thick and inclined to the plane by ˜ 12°. In a collisionless axi-symmetric stellar system we simplify the BOLTZMANN and POISSON equations by assuming a constant density normal to the galactic plane up to z ≈︂ 200 pc and by assuming a constant radial component of the spatial coordinates. The condition for selfconsistency in the linear approximation results in shingles 1.3 kpc long, inclined to the plane by 17°. The length of the shingles is independent of the radial distance R from the centre and the inclination depends inversely on R as is observed.     

Radio spectra of some markarian galaxies

Radio spectra of 16 Markarian galaxies are studied between 2.7 and 15.5 GHz. The Seyfert-type galaxies have power-law spectra with an average spectral index of -0.82, except for MRK 348, which is an active galaxy with a complex spectrum. The galaxies with featureless optical spectra have rather flat radio spectra, similar to BL Lac-type objects.     

Geology and activity around volcanoes on Io from the analysis of NIMS spectral images

The last two successful flybys of Io by Galileo in 2001 (orbits I31, I32) allowed the Near Infrared Mapping Spectrometer to enrich its collection of IR spectral image cubes of the satellite. These data cover hemispheric portions of Io, several volcanic centers as well as their surroundings with a spatial resolution ranging from 2 to 93 km pixel⁻¹. They map thermal emission from the hot-spots and the distribution of solid SO₂ in the 1.0-4.7 μm spectral range. We obtain maps of SO₂ abundance and granularity from the NIMS data using the method of Douté et al. (2002, Icarus 158, 460-482). The maps are correlated to distinguish four different physical units that indicate zones of SO₂ condensation, metamorphism and sublimation. We relate these information with visible images from Galileo's Solid State Imaging System and with detailed mapping of the thermal emission produced by Io's surface. Our principal goal is to understand the mechanisms controlling how lava, pyroclastics and gas are emitted by different types of volcanoes and how these products evolve. The 800 km diameter white ring of fallout created by a violent “Pillanian” eruption during summer of 2001 is at least partly composed of solid SO₂ and has enriched preexisting regional deposits. Orange materials have been recently or are currently emplaced 240 km south from the main eruption site, possibly as sulfur flows. A similar event may have taken place in the past at Ababinili Patera (12.5° N, 142° W). Carefull study of SO₂ maps covering the Emakong region also suggests that sulfur forms the bright channel-fed flow emerging from the south eastern side of the caldera. Within the main caldera of Tvashtar Catena completely cooled patches of crust exist. Elsewhere, the caldera is still cooling from previous episodes of flooding. We confirm that Amirani emits constantly large amount of SO₂ gas by interaction of fresh lava with the volatiles of the underlying plains. Nevertheless SO₂ frost is not the major component of the bright white ring seen in the SSI images. Over the whole Gish Bar region, SO₂ frost seems barely stable and is constantly regenerated. The stability increases along gray filamentary structures which could be faults filled with materials having peculiar thermal properties. Northwest of Gish Bar Patera, a localized bright deposit shows an unusual spectral signature potentially indicative of H₂O molecules forming ice crystals or being trapped in a nonidentified matrix. The Chaac region may present a thickened old crust reducing the geothermal flux to levels lower than 0.5 W m⁻² and thus creating a cold trap for SO₂. Looking at the abundance and degree of metamorphose of SO₂, we establish the relative age of different flows and ejecta for the Sobo Fluctus. Finally the assumption that the white patches in visible images indicate SO₂ rich deposits is once again challenged. In the Camaxtli region we identify a topographically controlled compact white deposit showing only moderate SO₂ abundance. In contrast, we detect two spots of quite pure SO₂ ice on the gray flanks of Emakong. Furthermore, the close association of fumarolic SO₂ and red S₂ already noted for several volcanic centers is observed at Tupan.     

Seismic Ground Motion Expected for the Eastern District of Naples

The seismic ground motion of a test area in the eastern district of Naples is computed with a hybrid technique based on the mode summation and the finite difference methods. This technique allows us the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, we consider the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, which is located about 90 km from the epicenter.The detailed geological setting is reconstructed from a large number of drillings. The sub-soil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow neapolitan tuff), representing the neapolitan bedrock. The detailed information available on mechanical properties of the sub-soil and its geometry warrants the application of the sophisticated hybrid technique.As expected, the sedimentary cover causes an increase of the signal's amplitudes and duration. If thin peat layers are present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such layers, that tend to seismically decouple the upper from the lower part of the structure.For SH-waves, the influence of the variations of the S-wave velocities on the spectral amplification is studied, by considering locally measured velocities and values determined from near-by down-hole measurements. The comparison between the computed spectral amplifications confirms the key role of an accurate determination of the seismic velocities of the different layers.The comparison performed between a realistic 2-D seismic response and a standard 1-D response, based on the vertical propagation of waves in a plane layered structure, shows considerable difference, from which it is evident that serious caution must be taken in the modelling of expected ground motion at a specific site.     

Geotechnical assessment of the bearing capacity of coal mine floors

Summary This investigation concerns 3 longwall faces having variable strata and mining conditions, but supported by 202 tonnes hydraulic 6-leg chocks. Bearing capacity tests along the faces were conducted to evaluate the factors influencing floor deformation and failure. The effect of size, shape and perimeter of the base plates, thickness of the floor layer, time and moisture on the ultimate bearing capacity of the floor was measured and discussed. Application of this work is the prediction of stability and support performance of face ends, as well as the design of support systems and ground control on production faces.     

Climatic response of thick leaf spruce (Picea crassifolia) tree-ring width at different elevations over Qilian Mountains, northwestern China

Tree-ring cores of thick leaf spruce (Picea crassifolia) taken from four sites at different elevations, in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies using standard dendrochronological methods. Results indicate that with increasing altitude the chronologies’ year-to-year variations decreased. Hence, the sensitivity of the tree-ring chronologies to climate decreases with altitude. Further analysis showed that the significant limiting factor on tree growth is spring precipitation. Measurements of stomata density and leaf dry weight suggest the species’ ecological adaptation strategy changes with elevation. At high elevation the metabolic rate of thick leaf spruce decreases, thus showing the effect of the climate.     

Chemical denudation rates in Kärkevagge, Swedish Lapland

This study examines the spatial and temporal variability of chemical denudation rates in Kärkevagge, northern Sweden. The chemical flux rates within the valley are strongly influenced by the local geology. Chemical denudation rates determined for the study period are more than double those previously reported in the literature for this valley. Rates of greater than 46t km⁻² a⁻¹ were measured at the valley mouth over the course of the melt season. This difference is likely due to differences in measurement technique compared to that used by past researchers. This rate is also much higher than for other arctic and alpine watersheds. Chemical denudation in Kärkevagge is comparable to larger temperate rivers. The rapid chemical denudation in Kärkevagge is likely due to sulfide weathering creating acid solutions.