Projections of Agricultural and Fish and Wildlife Water Demand in the Ouachita River Basin: A Linear Programming Approach

The availability of an abundant water supply has been a major resource of the Ouachita River Basin. In recent years, water requirements for a number of uses have increased, raising the concern that future water shortages could occur in the basin. The purpose of the study reported here was to estimate future water demand for irrigation, commercial fisheries, and fish and wildlife uses

Polychromatic guide star: feasibility study

International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS

Polychromatic guide star: feasibility study

International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS

Curie temperatures of titanomagnetite in ignimbrites: Effects of emplacement temperatures, cooling rates, exsolution, and cation ordering

Pumices, ashes, and tuffs from Mt. St. Helens and from Novarupta contain two principal forms of titanomagnetite: homogeneous grains with Curie temperatures in the range 350–500°C and oxyexsolved grains with similar bulk composition, containing ilmenite lamellae and having Curie temperatures above 500°C. Thermomagnetic analyses and isothermal annealing experiments in combination with stratigraphic settings and thermal models show that emplacement temperatures and cooling history may have affected the relative proportions of homogeneous and exsolved grains and have clearly had a strong influence on the Curie temperature of the homogeneous phase. The exsolved grains are most common where emplacement temperatures exceeded 600°C, and in laboratory experiments, heating to over 600°C in air causes the homogeneous titanomagnetites to oxyexsolve rapidly. Where emplacement temperatures were lower, Curie temperatures of the homogeneous grains are systematically related to overburden thickness and cooling timescales, and thermomagnetic curves are generally irreversible, with lower Curie temperatures measured during cooling, but little or no change is observed in room temperature susceptibility. We interpret this irreversible behavior as reflecting variations in the degree of cation ordering in the titanomagnetites, although we cannot conclusively rule out an alternative interpretation involving fine-scale subsolvus unmixing. Shortrange ordering within the octahedral sites may play a key role in the observed phenomena. Changes in the Curie temperature have important implications for the acquisition, stabilization, and retention of natural remanence and may in some cases enable quantification of the emplacement temperatures or cooling rates of volcanic units containing homogeneous titanomagnetites

Population Structure of Humpback Whales from Their Breeding Grounds in the South Atlantic and Indian Oceans

Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region

A revised chronostratigraphic framework for the Aptian of the Essaouira-Agadir Basin, a candidate type section for the NW African Atlantic Margin

International audienceThe Essaouira-Agadir Basin (EAB) of Morocco contains the most extensive exposure of Aptian to Lower Albian strata onshore the NW African Atlantic Margin. This paper documents the first high-resolution, multi-disciplinary stratigraphic approach for the Aptian to Lower Albian on the NW African Atlantic Margin.Previous biostratigraphic work almost exclusively relied on long-distance correlation of ammonoids to the Mediterranean-Caucasian Realm. Recent biostratigraphic work has questioned some of the previous interpretations, highlighting significant faunal endemism and complications with correlation to other key Aptian sections.This study focuses on 5 key sections: Tiskatine, Id Amran, Assaka, and DSDP 416/370. Distribution of ammonoids, foraminifera, and calcareous nannofossils are reported from a bed-by-bed collection made at Tiskatine.The analysis of foraminiferal and calcareous nannofossil assemblages enable correlation to standard zonation schemes; but also highlights the urgent need of revision and future work on the integration of these schemes across disciplines. The study, further, includes d13Ccarb, d13Corg, and total organic carbon (TOC) data that is compared to reference material from the Vocontian Basin.The combined litho-, bio-, chemo-, and sequence stratigraphic analysis establishes a robust chronostratigraphic framework for regional and super-regional correlations and a type section is proposed for the Aptian of NW Africa at Tiskatine

A new sedimentary and biostratigraphic framework for the Callovian-Oxfordian transition on the Atlantic margin of Morocco

A major global marine transgression occurred during the Callovian to Early Kimmeridgian, which was interrupted locally by a hiatus during the Late Callovian to Early Oxfordian. The transgression may have been a major driver for extensive coral buildup development in the Oxfordian. The depositional hiatus may be related to a combination of eustasy, local tectonic activity and hinterland movements, highlighting the potential influence of tectonism on sedimentary evolution in sedimentary basins. Whilst a regional Late Callovian-Early Oxfordian hiatus has been recorded extensively in the Tethys realm, this study has improved the biostratigraphic and sedimentary record from Morocco, and for the first time documents the Late Callovian-Early Oxfordian depositional hiatus in the Atlantic realm. Detailed sedimentary facies analysis of Callovian to Oxfordian carbonates and siliciclastics (Ouanamane Formation) demonstrates a major transgression from continental and coastal sediments, through oolitic mid-inner ramp deposits, brachiopod-rich middle ramp deposits, and ultimately to outer ramp marls, sharply overlain by Middle Oxfordian coral buildups across the basin. Repeated hard- and firmgrounds and bioturbated bed tops highlight transgressive surfaces traceable basinwide, which suggests low sedimentation rates in the upper Ouanamane Formation. Localized siliciclastic input is evidence for episodes of erosion in the same interval. Collection of new fossil specimens (ammonites, brachiopods, echinoderms, foraminifera) and revision of existing fossil material suggest this interval corresponds to a hiatus or condensed section in the Callovian-Oxfordian transition. The uppermost part of the Ouanamane Formation is of early Middle Oxfordian age and is directly overlain by Middle Oxfordian coral buildups. Onset of buildup construction is considered synchronous based on the new biostratigraphic data. Observations in Moroco compare with the sedimentary evolution around the Tethys, and in particular with the Arabian Plate. The Callovian-Oxfordian depositional hiatus corresponds to eustatic sea level changes, which were possibly driven my global cooling, and was likely overprinted by local tectonics