Sensitive observations of radio recombination lines in Orion and W51: the data and detection of systematic recombination line blueshifts proportional to impact broadening

Sensitive spectral observations made in two frequency bands near 6.0 and 17.6 GHz are described for Orion and W51. Using frequency switching we were able to achieve a dynamic range in excess of 10,000 without fitting sinusoidal or polynomial baselines. This enabled us to detect lines as weak as T _A ∼1 mK in these strong continuum sources. Hydrogen recombination lines with Δn as high as 25 have been detected in Orion. In the Orion data, where the lines are stronger, we have also detected a systematic shift in the line center frequencies proportional to linewidth that cannot be explained by normal optical depth effects.     

A RESPONSE OF A RANDOMLY LAYERED EARTH TO AN ELECTRIC POINT OR DIPOLE SOURCE*

A point source or a dipole source of electric current, placed on a randomly layered semi-infinite medium, produces an inhomogeneous random potential field on the surface. The variance of the random potential, normalized with reference to the normal field (that is, a field due to a point source or a dipole source on a homogeneous medium), falls off inversely as the distance from the source. The conductivity of the layers is assumed to vary randomly about a mean value (unity) such that the variations can be represented by a zero mean homogeneous random function. Further the variations are assumed to be small compared to the mean so that the first order perturbation is adequate. The analysis shows that the dipole field is more sensitive than the single pole field to the conductivity variations.     

Carbon-Oxidizing and Sulfate-Reducing Bacteria in Mozhaisk Reservoir Soils

The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied.     

Impact of Earth radiation pressure on GPS position estimates

GPS satellite orbits available from the International GNSS Service (IGS) show a consistent radial bias of up to several cm and a particular pattern in the Satellite Laser Ranging (SLR) residuals, which are suggested to be related to radiation pressure mismodeling. In addition, orbit-related frequencies were identified in geodetic time series such as apparent geocenter motion and station displacements derived from GPS tracking data. A potential solution to these discrepancies is the inclusion of Earth radiation pressure (visible and infrared) modeling in the orbit determination process. This is currently not yet considered by all analysis centers contributing to the IGS final orbits. The acceleration, accounting for Earth radiation and satellite models, is introduced in this paper in the computation of a global GPS network (around 200 IGS sites) adopting the analysis strategies from the Center for Orbit Determination in Europe (CODE). Two solutions covering 9 years (2000–2008) with and without Earth radiation pressure were computed and form the basis for this study. In previous studies, it has been shown that Earth radiation pressure has a non-negligible effect on the GPS orbits, mainly in the radial component. In this paper, the effect on the along-track and cross-track components is studied in more detail. Also in this paper, it is shown that Earth radiation pressure leads to a change in the estimates of GPS ground station positions, which is systematic over large regions of the Earth. This observed “deformation” of the Earth is towards North–South and with large scale patterns that repeat six times per GPS draconitic year (350 days), reaching a magnitude of up to 1 mm. The impact of Earth radiation pressure on the geocenter and length of day estimates was also investigated, but the effect is found to be less significant as compared to the orbits and position estimates.     

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: V. Palynological evidence for deforestation and increased erosion

Pollen spectra from seven short cores taken from deltaic sites in the central and northern parts of Lake Tanganyika provide information about vegetation changes around the lake during the last 5000 years. Pollen analysis was undertaken to understand the history and timing of catchment deforestation and its causal linkage to excess sedimentation and ecosystem change in Lake Tanganyika. The spectra are dominated by grass pollen at all levels in every core. Grass pollen percentage values range between 40 and 80%. Low values of arboreal pollen taxa (1–20%) were documented from most cores except core LT-98-2M. Core LT-98-2M represents the longest duration vegetation record of this study (close to 5000 years BP), and records the onset of increasingly arid conditions in the Late Holocene, especially after 500 A.D., with the probable replacement of forest by open grassland in the Mahale Mountains region. The pollen/spore content for other cores showed a consistent trend of a decrease in grass pollen and an increase in pteridophyte and forest indicator pollen taxa during the last few centuries, contemporaneous with other indications of increased watershed disturbance from forest clearing (especially isotopes and lake faunal change). The timing or strength of this trend is not tied to specific levels of watershed disturbance. However, increasing fern spore abundance does occur progressively later towards the south, where modern human population densities are lower. Although increasing fern spore abundance is consistent with a land-clearing hypothesis, the rising arboreal pollen percentages are seemingly counterintuitive. One possible explanation is that increasing arboreal pollen proportions reflects the recycling of abundant pollen of this type from rapidly eroding soils. Another likely explanation for this finding is that land clearing involved the replacement of miombo woodland, with its mixture of trees producing little pollen and understory grasses producing large amounts of pollen, by the present day cassava, banana, and legume agricultural systems, all of which are poor pollen producers. This shift in catchment vegetation would increase the relative contribution of Afromontane pollen transported long distances from the surrounding highland regions. This hypothesis is consistent with both the lack of correlation of palynological history with specific watershed deforestation attributes, as well as the broader historical record of human habitation in the Lake Tanganyika region. This study also highlights the need for both modern pollen transect data from the region and comparative cores from low elevation swamps or ponds (wetlands) in the region with smaller catchment areas.     

Landslide triggering scenarios in homogeneous geological contexts: The area surrounding Acri (Calabria, Italy)

The paper describes a methodology to detect landslide triggering scenarios in geological homogeneous areas and for some specific landslide categories. In these scenarios, the rainfall–landslide relationship as well as the pluviometric load conditions influencing slope instability have to be investigated.The methodology is applied to an area located in northern Calabria (Italy) and affected by widespread and different slope instability phenomena. Outcropped, fractured, and deeply weathered crystalline rock masses, determining geologic homogeneous conditions, are present. In the same area, suitable and homogeneous climatic features have also been found.According to the methodology adopted, the hydrologic analysis of rainfall time-series is initially carried out notwithstanding historical data concerning landslide mobilization, but using simple models to determine critical pluviometric scenarios for the three landslide categories: shallow, medium-deep, and deep. Landslide-triggering scenarios individualized according to this procedure are less significant as compared to the landslide mobilization detected in the study area by means of historical research and ascribed to the three landslide categories according to geomorphologic analysis.Subsequently, the possible landslide triggering scenarios are outlined by carefully investigating the hydrologic analysis limited to the periods identified according to the historical data.In the study area and approximately for all the areas characterized by the outcrop of fractured and deeply weathered crystalline rocks, significant triggering scenarios can be outlined. In particular, shallow landslide triggers could be activated by rainfall events with intensities exceeding 90 mm/day and/or with amounts exceeding 160 mm. As for medium-deep and deep landslides, triggering mechanisms are more complicated; and effective rainfall contribution must be taken into account compared to groundwater storage. Moreover, a more complex link between deep landslides and precipitation is confirmed.The results obtained to date highlight the potential of this methodology, which enables us to define and progressively improve the knowledge framework by means of a work sequence integrating different disciplinary tools and results.     

E (B-V) determination from an UV-visual two-colour diagram: O and B stars in the catalogue of stellar ultraviolet fluxes

We present here, for the O and B type stars in the Catalogue of Stellar Ultraviolet Fluxes, an approach which does not require a precise knowledge of spectral type and luminosity class for derivingE(B-V) colour excesses. The method is based on the use of an UV-visual two-colour diagram; galactic variations in the interstellar extinction law are analyzed and fully taken into account. Our results have been compared with those derived by using the differences between observed and intrinsic colours for stars with known spectral classification. The very good agreement in a large number of cases (94 per cent) demonstrates that our approach permits the derivation of reliable colour excess values for early type stars even if only a rough spectral classification is available.     

The solubility of quartz in aqueous sodium chloride solution at 350°C and 180 to 500 bars

The solubility of quartz in 2, 3, and 4 molal NaCl was measured at 350°C and pressures ranging from 180 to 500 bars. The molal solubility in each of the salt solutions is greater than that in pure water throughout the measured pressure range, with the ratio of solubility in NaCl solution to solubility in pure water decreasing as pressure is increased. The measured solubilities are significantly higher than solubilities calculated using a simple model in which the water activity in NaCl solutions decreases either in proportion to decreasing vapor pressure of the solution as salinity is increased or in proportion to decreasing mole fraction of water in the solvent.