Ethane aerosol phase evolution in Titan's atmosphere

Strong experimental evidence is presented that the northern polar cloud observed in Titan's atmosphere by the Cassini orbiter (VIMS) was indeed composed of ethane aerosol as proposed by Griffith et al. [2006. Science 313, 1620-1622]. We report on the condensation and phase behavior of ethane aerosol under atmospheric conditions of Titan (145 hPa, 40 km altitude, 70-90 K, 10-30 ppm ethane in nitrogen). The results were obtained in an in-situ collisional cooling experiment combined with Fourier-transform infrared (FTIR) spectroscopy. Apart from the liquid phase, three crystalline phases (solid I, solid II, metastable) and the transitions into each other have been observed in the ethane aerosol. The phases were found to have a significant effect on the particles' IR spectra, their growth dynamics and the final size of the aerosols which varies between 0.5 and 4 μm (compared to 1-3 μm observed on Titan). This has strong implications on the ethane vapor pressure, precipitation and optical aerosol detection.     

7. Ancient Fossil Record and Early Evolution (ca. 3.8 to 0.5 Ga)

Once life appeared, it evolved and diversified. From primitive living entities, an evolutionary path of unknown duration, likely paralleled by the extinction of unsuccessful attempts, led to a last common ancestor that was endowed with the basic properties of all cells. From it, cellular organisms derived in a relative order, chronology and manner that are not yet completely settled. Early life evolution was accompanied by metabolic diversification, i.e. by the development of carbon and energy metabolic pathways that differed from the first, not yet clearly identified, metabolic strategies used. When did the different evolutionary transitions take place? The answer is difficult, since hot controversies have been raised in recent years concerning the reliability of the oldest life traces, regardless of their morphological, isotopic or organic nature, and there are also many competing hypotheses for the evolution of the eukaryotic cell. As a result, there is a need to delimit hypotheses from solid facts and to apply a critical analysis of contrasting data. Hopefully, methodological improvement and the increase of data, including fossil signatures and genomic information, will help reconstructing a better picture of life evolution in early times as well as to, perhaps, date some of the major evolutionary transitions. There are already some certitudes. Modern eukaryotes evolved after bacteria, since their mitochondria derived from ancient bacterial endosymbionts. Once prokaryotes and unicellular eukaryotes had colonized terrestrial ecosystems for millions of years, the first pluricellular animals appeared and radiated, thus inaugurating the Cambrian. The following sections constitute a collection of independent articles providing a general overview of these aspects.     

Software for producing trichromatic images in astronomy

We present a software package for combining three monochromatic images of an astronomical object into a trichromatic color image. We first discuss the meaning of true colors in astronomical images. We then describe the different steps of our method, choosing the relevant dynamic intensity range in each filter, inventorying the different colors, optimizing the color map, modifying the balance of colors, and enhancing contrasts at low intensity levels. While the first steps are automatic, the last two are interactive.     

The hydrogen ortho-to-para ratio in the stratospheres of the giant planets

Observations of the H₂ S(0) and S(1) quadrupole lines in the four giant planets by the short-wavelength spectrometer of the Infrared Space Observatory are analyzed. These lines probe pressure levels located between 10 and 1 mbar and allow us to determine the stratospheric hydrogen para fraction for the first time. In Jupiter and Saturn, the stratospheric para fraction is close to its tropopause value. In the stratosphere of these planets as well as in Neptune’s, the para fraction presents a significant departure from thermodynamic equilibrium. This situation results from a lagged conversion between the ortho and the para states as molecular hydrogen is transported upward under the influence of turbulent eddy diffusion. In contrast, the uranian stratosphere lies close to thermodynamic equilibrium. The magnitude of the departure from thermodynamic equilibrium appears to be anti-correlated with the amount of stratospheric aerosols. To validate this assumption, we estimate the hydrogen equilibration time with a one-dimensional diffusion model for different conversion processes in the gas phase or on aerosols. The comparison between our results and the tropospheric estimates from Conrath et al. (1998, Icarus,135, 501-517) shows that paramagnetic conversion on aerosols matches the estimated tropospheric and stratospheric relaxation times in the four giant planets. In contrast, paramagnetic conversion in the gas phase can only explain the relaxation times measured in Jupiter and Saturn atmospheres. This situation provides quantitative evidence for an equilibration mechanism dominated by conversion on aerosols.     

Hydrological and geotechnical investigations of mass movements in an equatorial city (Yaoundé, Cameroon)

In the present study, mass movements (landslide and mudslide) bound to a gully located at Mendong, a suburb of Yaoundé in Cameroon were examined using hydrological, geotechnical and geomorphological observations. The data indicate that water is an important causative factor of mass movements in the area studied. In fact, the water flow (waste water and runoff) provokes the saturation of materials at the slope foot. These materials lose their mechanical qualities and some deep ruptures generate landslide. During the rainy season, when the cumulative rainfall is more than 200 mm, these landslides are accompanied by mudslides that generate disturbances on the infrastructure situated around the gully and farther downstream. The economic and environmental damages resulting from the Mendong mass movements are considerable, such as degradation of the topography, losses in farm land, transportation and downstream sedimentation in a pond situated at the slope foot, loss of life and damage to the economy. All this calls for a multidisciplinary and integrated approach to hazard assessment and risk mitigation, which included data collection and interpretation, growing public and authority awareness, and preventing or reducing runoff and waste water flows by proper management and drainage.     

Drag and bulk aerodynamic coefficients over shallow water

From direct measurements of the vertical turbulent fluxes of momentum, heat, and water vapor over shallow water, the drag and bulk aerodynamic coefficients are computed and compared with those obtained via the profile technique. The results show thatC _D =C _T =C _E =1.2×10^?3, with variability among their mean values being ? 20 %. All measurements were taken at 8 m above the water surface at Lake Hefner, Oklahoma. The measurement platform was a rectangular tower located within the lake and approximately 1 km from the nearest shore. The depth of the lake at the tower was 8 m.     

Resolving the Geometry of Hydraulic Fractures from Tilt Measurements

This paper discusses the resolution of geometrical characteristics of pressurized fractures from tiltmeter data. The quasi-static deformation and tilt field induced by such fractures can be modeled by superposition of displacement discontinuity (DD) singularities. Despite the relatively common use of such measurements to infer fracture characteristics, there is a widespread misunderstanding of what can be accurately determined, depending on the relative distance between the tiltmeter array and the fracture. We investigate in detail the resolution of the dimensions and orientation of hydraulic fractures or faults from tilt measurements. In particular, we formally prove that at a distance larger than about twice the characteristic length of the fracture, elastostatic measurements such as those measured by tiltmeters are not able to resolve independently all the dimensions of the fracture, although the fracture volume can be robustly inverted from the data. The resolution of fracture orientation is also discussed using an analysis based on a spatial Fourier Transform of the tilt field. The relative angle between the plane where the measurements are located and the fracture plane plays a major role in the accuracy of this estimation. In an illustrative field example, where the measurements are located in the far-field of the fracture deformation field, we show how a single DD singularity can be used to model tiltmeter data and efficiently obtain the fracture orientation and volume.     

Design charts for a deep circular tunnel under non-uniform loading

Summary This paper describes design charts which can be used to quickly predict the size and shape of the failed rock regions caused by the excavation of a deep tunnel, and the induced closure for cases of non-uniformin-situ stress fields. Through a simple graphical construction, the design charts can also be used to evaluate the performance of a support system.Previously of J. F. T. Agapito and Associates, U.S.A.