Recent Aeolian Origin of Surficial Gypsum Crusts in Southern Tunisia: Geomorphological,Archaeological and Remote Sensing Evidence

Recent quarring of the surficial gypsum crusts adjacent to Djebel Sidi Bou Hellas has revealed sections typically showing a discontinuous surface gravel cover underlain by more than 7 m of microcrystalline gypsum. The location, elongate shape, form in cross-section and chemistry of this deposit suggests an aeolian origin, whereby aeolian sands have been trapped against a glacis d'erosion terrace, and subsequently consolidated by meteoric waters. One gypsum quarry revealed a midden and the remains of a Roman dwelling now buried within the crust. A radiocarbon date of organic matter in the midden and a Roman coin found within it suggest an age of AD324–345 for the deposit. This is the first firm date for a surficial gypsum crust in southern Tunisia and the age is surprisingly young. Previous studies have speculated on phases of crust development between the Villefranchian and early Holocene but none since. Remote sensing and field evidence show that gypsiferous sands are currently deflated from the dry parts of the mudflats of Chott Fedjaj. They are subsequently transported in a southwesterly trajectory and trapped against glacis on the southern margins of Chott Fedjaj, forming contemporary analogues of the Roman deposit. Sands that are not trapped form dune fields and sandflats where gypsum crusts appear to be forming today. If the source area of gypsum sands has remained constant since Roman times, then the predominant wind direction has moved 45° to the southwest since then. The other possible source of aeolian gypsum for the Roman deposit, the vast mudflats of Chott Djerid, involves an even greater change in predominant wind direction. © 1997 John Wiley & Sons, Ltd.     

On the hydrodynamics of bobbing cones

The paper describes an experimental investigation into the hydrodynamics of a right circular cone undergoing transient forced vertical oscillations in otherwise still water. Attention is given to the vertical fluid force and the relative vertical motion between the cone and its intersection with the adjacent free water surface. Comparisons are made between linear theory and experimental results extracted from paired response time histories obtained with input displacements of opposite sign. Comparisons are also made with the predictions obtained from fully non-linear numerical models. A slowly varying setup is observed in the measured relative vertical motion and a new second order term is identified in order to formulate a theoretical explanation.     

Solar Magnetograms at 12 μm Using the Celeste Spectrograph

We present the first solar vector magnetogram constructed from measurements of infra-red Mg I 12.32-μm line spectra. Observations were made at the McMath-Pierce Telescope using the Celeste spectrometer/polarimeter. Zeeman-split Stokes line spectra were fitted with Seares profiles to obtain the magnetic field parameters. Maps of absolute field strength, line-of-sight angle, and azimuth are presented. Analysis shows that the variation in field strength within a spatial resolution element, 2 arcseconds, is greatest in the sunspot penumbra and that this is most likely caused by vertical field strength gradients, rather than horizontal image smearing. Widths of the Zeeman-split σ components, assuming a formation layer thickness of 200 km, indicate that vertical field strength gradients can be as large as 6.5 G/km in a penumbra.     

Iowa catalog of solar X-ray flux (2–12 Å)

The absolute X-ray flux from the whole disc of the sun in the wave length range 2 to 12 Å has been observed for a prolonged period by University of Iowa equipment on the earth-orbiting satellite Explorer 33 and the moon-orbiting satellite Explorer 35, both of the Goddard Space Flight Center of the National Aeronautics and Space Administration. The observations are continuing at the date of writing (July 1969). A comprehensive catalog of the flux F (2–12 Å) is being produced. The observational technique and the scheme of reducing data are described herein. Sample tabulations and plots are given. A catalog of tabular and graphical data with a time resolution of either 81.8 or 163.6 sec has been completed for the following periods: From Explorer 33: 2 July 1966 to 27 July 1967 From Explorer 35: 26 July 1967 to 18 September 1968 These blocks of data have been delivered to the National Space Science Data Center National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771, U.S.A. and made available through that agency to interested workers in solar and ionospheric physics. Further blocks of data will be made available as they are completed. An abridged summary of principal flares is published in the monthly Solar-Geophysical Data of the U.S. Department of Commerce, Environmental Science Services Administration.     

New cataclysmic variable 1RXS J073346.0+261933 in Gemini

In the course of our search for the optical identifications of ROSAT X-ray sources, we have found a highly variable object with a very unusual behavior on long time scales, rare color indices, and a high X-ray-to-optical flux ratio. We present the archival light curve from the Catalina Sky Survey, optical spectroscopy from RTT150, and time-resolved photometry from the Astrotel-Caucasus telescope. The object appears to be a magnetic cataclysmic variable (a polar) with an orbital period P = 3.20 h.     

REGIONAL DEVELOPMENT: MORE THAN EVER,THE BUSINESS OF AMERICA

Community-produced spaces such as community gardens are attracting widespread scholarly interest for the potential of not only food production, but also for social, environmental, and educational benefits. Yet community gardens have also been scrutinized as sites of governmentality that produce neoliberal subjects. In this article, six case studies are analyzed as representative of three ways to organize and manage gardens—grassroots, externally-organized, and active nonprofit management. I use performativity theory to examine how definitions and enactments of community can be used to include, exclude, or bridge difference. The analysis highlights some of the specific moments in garden organizing and management that influence participation or resistance to community-oriented urban food production.     

CHANNEL MIGRATION AND REGENERATION OF BALD CYPRESS IN WESTERN TENNESSEE

Bald cypress (Taxodium distichum) regeneration was examined in the bottomland forest of the lower Hatchie River in western Tennessee. Bald cypress is found mostly in abandoned meanders. Its absence along the active channel indicates that colonization begins after the meander cuts off, creating an oxbow lake. Analysis of the size, the age, and the spatial structure of the stands indicates that the individuals first establish along the margins of the lake, and then colonize the interior as the lake fills in and new surfaces are exposed. Bald cypress will dominate abandoned meanders for several centuries. However, it will not regenerate in stands with a well-developed forest canopy. Bald cypress is eventually replaced by shade tolerant species and, therefore, only rarely occurs on older surfaces. Channel migration and the subsequent creation of oxbows will maintain bald cypress as a major component of bottomland forests. However, many of the major streams in the lower Mississippi River alluvial valley have been channelized. Maintenance of a straightened channel will exclude the creation of oxbows. Therefore, a primary regeneration opportunity for bald cypress disappears in many areas. [Key words: channel migration, exact probabilities, floodplain forest, oxbow lakes, Taxodium distichum, Tennessee.]     

Black gold to green gold: regional energy policy and the rehabilitation of coal in response to climate change

Energy production has come under increasing scrutiny as concerns about energy security and climate change have risen. In the UK changes in government structure and privatisation of the electricity industry have led to the emergence of multi-level governance. This means that decisions on how to reduce carbon dioxide emissions from the electricity-generating sector should no longer be solely a national policy decision. Previous studies have sought to explore how renewable energy may develop under multi-level governance, but this paper pays attention to a traditional fossil fuel source, coal, which is still an important means of electricity generation. Coal is the most abundant fossil fuel and advocates argue that carbon capture and storage techniques could make coal 'clean', paving the way for a long-term, secure and low emission way to produce energy. This study focuses on the Yorkshire and Humber Region, which has had a long association with coal mining and looks at the implications of this as the region seeks to develop a climate change action plan and an energy strategy within the new regional governance structures. The paper argues that the regional networks developed to address climate change are influenced by existing social power structures and alliances. The region as a territorial structure becomes a useful device in promoting national priorities.     

The cloud imaging and particle size experiment on the Aeronomy of Ice in the mesosphere mission: Instrument concept,design, calibration,and on-orbit performance

The Cloud Imaging and Particle Size Experiment (CIPS) is one of three instruments aboard the Aeronomy of Ice in the Mesosphere spacecraft. CIPS provides panoramic ultraviolet images of the atmosphere over a wide range of scattering angles in order to determine the presence of polar mesospheric clouds, measure their spatial morphology, and constrain the parameters of cloud particle size distribution. The AIM science objectives motivate the CIPS measurement approach and drive the instrument requirements and design, leading to a configuration of four wide-angle cameras arrayed in a ‘+’ arrangement that covers a 120° (along orbit track)×80° (across orbit track) field of view. CIPS began routine operations on May 24, 4 weeks after AIM was launched. It measures scattered radiances from PMCs near 83 km altitude to derive cloud morphology and particle size information by recording multiple exposures of individual clouds to derive PMC scattering phase functions and detect nadir horizontal spatial scales to approximately 3 km. This paper describes the instrument design, its prelaunch characterization and calibration, and flight operations. Flight observations and calibration activities confirm performance inferred during ground test, verifying that CIPS exceeds its measurement requirements and goals. These results are illustrated with example flight images that demonstrate the instrument measurement performance.     

Modeling of the 10-μm natural laser emission from the mesospheres of Mars and Venus

Nonthermal emission which occurs in the cores of the 9.4- and 10.4-μm CO₂ bands on Mars has been recently identified as a natural atmospheric laser. The emission is believed to be excited by absorption of near-ir solar flux, followed by collisional transfer to the 00°1 state of CO₂. A numerical model based on this mechanism is developed which includes the solar pumping contributed by ～2 × 10⁴ near-ir CO₂ lines. The non-Local Thermodynamic Equilibrium (NLTE) radiative transfer problem is solved to obtain the 00°1 vibrational state population. This model successfully reproduces the existing center-to-limb observations, although higher spatial resolution observations are needed for a definitive test. The model also predicts total fluxes which are close to the observed values. The strength of the emission is predicted to be closely related to the instantaneous near-ir solar heating rate. Calculation of the CO₂ level populations in this model supports the identification of this emission as a natural atmospheric laser. Both Mars and Venus are predicted to exhibit level inversions; at large zenith distances several percent of the emergent intensity will be due to stimulated emission. While the stimulated emission present in these lines is not large enough to be of importance to mesospheric radiative equilibrium, it has other interesting consequences. The construction of large-volume radiation-pumped lasers, which utilize CO₂ planetary mesospheres as a gain medium, is theoretically possible.