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International audience; Pearl millet is among the top three-cereal production in one of the most climate vulnerable regions, sub-Saharan Africa. Its Sahelian origin makes it adapted to grow in poor sandy soils under low soil water regimes. Pearl millet is thus considered today as one of the most interesting crops to face the global warming. Flowering time, a trait highly correlated with latitude, is one of the key traits that could be modulated to face future global changes. West African pearl millet landraces, can be grouped into early- (EF) and late-flowering (LF) varieties, each flowering group playing a specific role in the functioning and resilience of Sahelian smallholders. The aim of this study was thus to detect genes linked to flowering but also linked to relevant traits within each flowering group. We thus investigated genomic and phenotypic diversity in 109 pearl millet landrace accessions, i.e., 66 early-flowering and 43 late-flowering, grown in the groundnut basin, the first area of rainfed agriculture in Senegal dominated by dry cereals (millet, maize, and sorghum) and legumes (groundnuts, cowpeas). We were able to confirm the role of PhyC gene in pearl millet flowering and identify several other genes that appear to be as much as important, such as FSR12 and HAC1 . HAC1 and two other genes appear to be part of QTLs previously identified and deserve further investigation. At the same time, we were able to highlight a several genes and variants that could contribute to the improvement of pearl millet yield, especially since their impact was demonstrated across flowering cycles.

Cultivated diversity is considered an insurance against major climatic variability. However, since the 1980s, several studies have shown that climate variability and agricultural changes may already have locally eroded crop genetic diversity. We studied pearl millet diversity in Senegal through a comparison of pearl millet landraces collected 40 years apart. We found that more than 20% of villages visited in 1976 had stopped growing pearl millet. Despite this, its overall genetic diversity has been maintained but differentiation between early- and late-flowering accessions has been reduced. We also found stronger crop-to-wild gene flow than wild-to-crop gene flow and that wild-to-crop gene flow was weaker in 2016 than in 1976. In conclusion, our results highlight genetic homogenization in Senegal. This homogenization within cultivated pearl millet and between wild and cultivated forms is a key factor in genetic erosion and it is often overlooked. Improved assessment and conservation strategies are needed to promote and conserve both wild and cultivated pearl millet diversity.

The paper presents a synthesis of the approach recently developed to constrain the nature and the age of recent element mobility in weathering profiles. The approach relies on a comparison of variations of trace elements and U-series disequilibria in weathering profiles. It is exemplified in the case of old lateritic profiles from the Kaya toposequence, Burkina Faso. Trace elements and 238 U 234 U 230 Th disequilibria have been analysed in whole rock samples from two pits located in very contrasted topographical positions. Trace element data show that the whole toposequence is marked by an intense chemical remobilization, including uranium, from the cap to the lower part of the profiles. 238 U 234 U 230 Th disequilibrium data outline that all the levels of the profiles are affected by recent UTh fractionations, and that each level of the toposequence is marked by U gains and losses. The chronological approach developed in this paper leads to an age of about 400 kyr for the dismantling of the iron cap, and ages ranging from 0 to 400 kyr for U accumulation in the pink clay horizon of the profiles. The depth repartition of U accumulation in the profile implies that the remobilisation processes in this toposequence varied through time, on time constants similar to those of climatic variations. To cite this article: F. Chabaux et al., C. R. Geoscience 335 (2003).

The potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960’s (e.g., Rosholt et al. 1966; Hansen and Stout 1968). This interest results from the dual property of the nuclides of the U and Th radioactive series (1) to be fractionated during water-rock interactions and (2) to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters. Therefore, the study of radioactive disequilibria in surface environments should help to bring information about the nature, the intensity but also the time-scale of the water-rock interactions produced during weathering and related chemical transfers. These different properties have justified many of the studies on U-Th series in weathering profiles and river waters. Rosholt (1982), Scott (1982) and Osmond and Ivanovich (1992) gave a synthesis of the studies of U-series in weathering and surface hydrology up to the 1980’s and the 1990’s respectively. Here, we present the main directions taken in these domains over the last decade. They were partly stimulated by the analytical developments made in the measurement of the medium half-life nuclides of 238U series (i.e., 234U-230Th-226Ra) in the mid-1980’s, namely, the use of thermal ionisation mass spectrometry (TIMS) (e.g., Chen et al. 1986; Edwards et al. 1987; Cohen et al. 1991; Chabaux 1993;Chabaux et al. 1994) and more recently the use of MC ICP-MS (Turner et al. 2001; Robinson et al. 2002) for U and Th isotope analysis. Details of these developments are given in this volume (Goldstein and Stirling 2003). Compared to the radioactive counting methods previously used, the new techniques permit (1) a reduction by one order of magnitude or more of the size of the sample required for …

Geochemical and mineralogical investigations, including measurements of major and trace elements, Sr isotope ratios, and 238U-234U-230Th activity ratios, were made on an old African laterite to reconstruct its formation steps and assess recent chemical mobilization. The present data support a scenario of discontinuous formation for the laterite, with different bedrock weathering conditions during the formation of each unit, rather than a scenario of continuous formation. Absolute accumulation of Fe, U, and lanthanides in the uppermost ferruginous unit suggests an autochthonous origin of this iron cap by leaching of an older overlying profile. Present chemical distributions of lanthanides, as well as of Rb, K, Ba, and Sr, within the profile cannot be linked to the mineralogical distribution of both relictual primary and authigenic secondary phases. Complementary lanthanide patterns indicate that these elements were primarily accumulated in the uppermost ferruginous unit before further remobilization and accumulation in the underlying horizons. These redistribution processes may be related to the chemical instability of the ferruginous cap. The 238U-234U-230Th disequilibria indicate that recent U mobilization occurs in the whole profile and that, as for lanthanides, there is a vertical redistribution of U from the uppermost ferruginous unit to the underlying horizons. Moreover, these data show that both U losses and gains exist at each level of the profile. A simple modeling of this double U mobilization process is proposed to interpret the 238U-234U-230Th data. Differences in the mobilization and fractionation intensities of the U input and removal processes can account for the two evolution trends, which distinguish the ferruginous unit from the underlying ones. Furthermore, on the basis of this modeling, the profile appears to be in a transient state because of recent changes in the U mobilization conditions, which could correspond to major Pleistocene climatic variations.

Soil isotopic dating is important for understanding mass transfers related to rock weathering. Here we evaluate a method including TIMS analyses of (234U/238U) activity ratios on

The geochemical development of laterites, a very common superficial formation in the tropics, is still a matter of debate. To determine the main steps of their formation, and to interpret lateral geochemical variations often observed within laterites, we studied the Kaya ferricrete in northern Burkina Faso by analysing two profiles in contrasting topographic positions. We determined the mineralogy and the composition in major and trace elements of whole rocks and of < 0.2 mu m granulometric fractions. The nature and proportion of relictual primary minerals and of secondary clays and Fe-oxyhydroxides control the distribution of major and soluble trace elements. The distribution patterns of Fe, transition metals, lanthanides, U and Th in the two profiles require (i) an initial accumulation in the top ferruginous horizon during its formation and (ii) a secondary redistribution downwards in the underlying horizons. Lanthanides, Ni and Co were remobilized to a much greater extent than Cu and Sc, whereas Fe, V, Cr and Th accumulated in the ferruginous horizon. The uphill better drained profile showed more intense redistribution than the downhill profile. Uranium in particular is poorly redistributed in the downhill profile, whereas it was redistributed like the lanthanides in the uphill profile. Remobilizations are also more intensely recorded in the fine fractions than in the whole rocks. These results allow us to propose a scenario for the formation of the Kaya laterite that accounts for both vertical and lateral chemical distributions. They also highlight the potential of multimethod geochemical studies to uncover the sequence of evolution of weathering profiles.

La datation isotopique des sols est importante pour comprendre les transferts de matière liés à l'altération. Nous présentons ici une méthode incluant l'analyse par TIMS des déséquilibres (234U/238U) de fractions inférieures à 0,2 micromètres d'une latérite du Cameroun. Les variations avec la profondeur du rapport d'activité (234U/238U) font apparaître des déséquilibres importants à la base des unités pédologiques et un retour progressif vers l'équilibre au-dessus. Ces résultats suggèrent que les fractionnements de l'uranium ont lieu à la base des unités et que les fractions analysées évoluent probablement en système clos au sein de chaque unité. L'utilisation chronométrique de ces résultats donnerait un âge global de 1,5 Ma pour le développement de cette latérite. (Résumé d'auteur)

Plaque removal is an important part of good oral hygiene. Many short-term studies have compared the effectiveness of an electric toothbrush in plaque removal to that of a conventional, manual toothbrush. Previous studies proved the electric toothbrush to be more effective on a short-term basis; however, little is known about its long-term effects. In a study that examined 32 patients over a 12-month period, the authors found electric toothbrushing to be more effective in plaque removal. The study measured the differences in abrasion, gingival recession, gingival bleeding, and plaque scores. The study also concluded that no significant gingival abrasion was caused by electric toothbrushing.

Isotopic dating of laterites remains problematic and controversial. Comparison of the available data shows contradictory ages. The Rb-Sr, K-Ar and 4~ chronometers provide ages of several tens of millions years ([1], [2], [3]), while (234U/238U) disequilibria ([4], [5]) and l~ analyses ([6]) lead to recent ages. In fact, the different chronometers were not applied strictly to the same soil fractions (whole rock, clay fraction, pure mineral phase), which could partly explain the contradictory results. Actually, any analysed fraction may consist of inherited, altered and weathering mineral phases. This study was thought to analyse the same soil fractions with two different chronometers, the Rb-Sr and the (234U/238U) disequilibria methods. They were applied on < 0.2 gm fraction from the Goyoum laterite (Cameroon) consisting of three petrologic units: a saprolite at the base, a intermediate nodular zone, and a soft topsoil. The < 0.2 gm fraction was extracted from two profiles, it contains essentially kaolinite and Feoxyhydroxides. The Rb and Sr concentrations and the Sr and U isotope ratios were determined by thermoionisation mass spectrometry. The data reveal complex and wide variations of the 87Sr/86Sr and 87Rb/86Sr ratios with depth, with different patterns in each profile. No isochron line can be drawn in an 878r/86Sr v s S7Rb/s6sr diagram. The data scatters in the mixing and in the isochron diagrams suggest a Sr isotopic heterogeneity which could represent either an initial Sr isotopic variability of the analysed fractions, or a secondary process disturbing a previously homogeneous system. The (234U/238U) activity ratio varies from 0.85 to 1.20 in each profile (see Fig. 1). No correlation appears with the 87Sr/86Sr ratio. The variations of the (234U/238U) activity ratio with depth are similar in both profiles. An important disequilibrium is visible at the base of the saprolite with a (234U/238U) ratio significantly below unity. Above, the values tend progressively towards equilibrium. A second important (234U/23Su) disequilibrium occurs at the base of the nodular zone with values below and above unity. Like in the saprolite, the values tend towards equilibrium in the nodular zone. A third similar sequence could possibly exist in the topsoil. The fact that the (234U/238U) variations are similar in both studied profiles inclines us to believe that these variations are characteristic of the whole lateritic profile. The lateritic formation would then contain two horizons of U fractionation with progressive return to secular equilibrium above them. The lower horizon at the base of the saprolite, shows an enrichment of 23Su which could result from leaching of the bedrock initially in secular equilibrium, inducing preferential loss of 234U and crystallisation of residual minerals depleted in 234U. The progressive trend to secular equilibrium suggests no further fractionation in the saprolite The intermediate horizon at the base of the nodular zone could record perturbation of the kaolinite + Feoxyhydroxides mixture that could be either a recrystallisation of the pre-existing minerals or an addition of one or several new mineral phases. The fact that (234U/238U) activity ratios are again below unity suggest another episode of mineral leaching with formation of 234U-enriched fluids. However, migration of these fluids over only short distances could explain crystallisation of minerals enriched in 234U. Return to the secular equilibrium of the mineral fractions suggests a confinement of the process in the transition zone. For each fractionation front, a migration rate of 6 to 8 m/Ma may be calculated. The occurrence of (234U/238U) disequilibria in the Goyoum laterite emphasises that this laterite is presently affected by geochemical fractionations. The location of the fractionation zones at the lower parts of the petrographical units, allows to consider that the fractionation of U mirrors the pedological history of the laterite. It may also be considered that the

The continued high percentages of skilled personnel in the United States (U.S.) Armed Forces that are currently leaving the service has becomes, not merely a personnel problem for the military, but for the U.S. as well. Much controversy surrounds the social and economic foundations with which the political and military establishment must deal. This thesis presents a methodology for analyzing the possible utilization of selective parolees from various institutions into the U.S. Armed Forces. The proposal in this thesis, it is believed, could drastically reduce current manpower shortfalls in the military institutions. The jobless parolee is a drain on the tax-structure both local and national. An employed parolee would stop this drain by producing taxable income. Finally, the severe problem of a revolving door-type-recidivism which has defied solutions could possibly be partially solved b this approach, The author admits that this approach is unusual, yet, it is possibly a valid assertion that unusual problems require creative and sometimes unusual solutions. http://archive.org/details/thefeasibilitynd1094517591 Captain, United States Marine Corps Approved for public release; distribution is unlimited.