Origin of the Sinai-Negev erg, Egypt and Israel: mineralogical and geochemical evidence for the importance of the Nile and sea level history

The Sinai-Negev erg occupies an area of 13,000 km2 in the deserts of Egypt and Israel. Aeolian sand of this erg has been proposed to be derived from the Nile Delta, but empirical data supporting this view are lacking. An alternative source sediment is sand from the large Wadi El Arish drainage system in central and northern Sinai. Mineralogy of the Negev and Sinai dunes shows that they are high in quartz, with much smaller amounts of K-feldspar and plagioclase. Both Nile Delta sands and Sinai wadi sands, upstream of the dunes, also have high amounts of quartz relative to K-feldspar and plagioclase. However, Sinai wadi sands have abundant calcite, whereas Nile Delta sands have little or no calcite. Overall, the mineralogical data suggest that the dunes are derived dominantly from the Nile Delta, with Sinai wadi sands being a minor contributor. Geochemical data that proxy for both the light mineral fraction (SiO2/10-Al2O3 + Na2O + K2O-CaO) and heavy mineral fraction (Fe2O3-MgO-TiO2) also indicate a dominant Nile Delta source for the dunes. Thus, we report here the first empirical evidence that the Sinai-Negev dunes are derived dominantly from the Nile Delta. Linkage of the Sinai-Negev erg to the Nile Delta as a source is consistent with the distribution of OSL ages of Negev dunes in recent studies. Stratigraphic studies show that during the Last Glacial period, when dune incursions in the Sinai-Negev erg began, what is now the Nile Delta area was characterized by a broad, sandy, minimally vegetated plain, with seasonally dry anastomosing channels. Such conditions were ideal for providing a ready source of sand for aeolian transport under what were probably much stronger glacial-age winds. With the post-glacial rise in sea level, the Nile River began to aggrade. Post-glacial sedimentation has been dominated by fine-grained silts and clays. Thus, sea level, along with favorable climatic conditions, emerges as a major influence on the timing of dune activity in the Sinai-Negev erg, through its control on the supply of sand from the Nile Delta. The mineralogy of the Sinai-Negev dunes is also consistent with a proposed hypothesis that these sediments are an important source of loess in Israel

Fine dust emissions from active sands at coastal Oceano Dunes, California

Sand dunes and other active sands generally have a low content of fine grains and, therefore, are not considered to be major dust sources in current climate models. However, recent remote sensing studies have indicated that a surprisingly large fraction of dust storms are generated from regions covered by sand dunes, leading these studies to propose that sand dunes might be globally relevant sources of dust. To help understand dust emissions from sand dunes and other active sands, we present in situ field measurements of dust emission under natural saltation from a coastal sand sheet at Oceano Dunes in California. We find that saltation drives dust emissions from this setting that are on the low end of the range in emissions produced by non-sandy soils for similar wind speed. Laboratory analyses of sand samples suggest that these emissions are produced by aeolian abrasion of feldspars and removal of clay-mineral coatings on sand grain surfaces. We further find that this emitted dust is substantially finer than dust emitted from non-sandy soils, which could enhance its downwind impacts on human health, the hydrological cycle, and climate.</p

Comparison of Helicobacter Pylori Genotypes Obtained from the Oropharynx and Stomach of the Same Individuals -A Pilot Study

R e c e i ve d M a rc h 3 , 2 0 12 ; A c c e p t e d Ju n e 2 5 , 2 0 1 2 . Key words: Helicobacter pylori -Real-time PCR -Genotyping -OropharynxStomach -Comparison Abstract: Helicobacter pylori has been recently detected in the oral cavity and oropharynx. However, the role it plays in oral and oropharyngeal pathogenesis remains unclear. The virulence of H. pylori strains can be distinguished according to the virulence factors genes carried. Our research has been focused on realtime PCR analysis of cagA and vacA genes of H. pylori strains in tonsils and tonsillar squamous cell cancer and their comparison with H. pylori strains obtained fro

Erratum: The solar orbiter radio and plasma waves (RPW) instrument (Astronomy and Astrophysics (2020) 642 (A12) DOI: 10.1051/0004-6361/201936214)

The erratum concerns Fig. 9 entitled "Antenna radio-electrical properties" for which some of the parameters are not correct. The new figure with new parameters is provided in Fig. 1 of this corrigendum. Fig. 1. Corrected Antenna radio-electrical properties. (Figure Presented)

Role of calcium cycling versus restitution in the mechanism of repolarization alternans

T-wave alternans, a powerful marker of arrhythmic events, results from alternation in action potential duration (APD). The underlying cellular mechanism of APD alternans is unknown but has been attributed to either intracellular calcium (Ca2+) cycling or membrane ionic currents, manifested by a steep slope of cellular APD restitution. To address these mechanisms, high-resolution optical mapping techniques were used to measure action potentials and Ca2+ transients simultaneously from hundreds of epicardial sites in the guinea pig model of pacing-induced T-wave alternans (n=7). The pacing rates (ie, alternans threshold) at which T-wave (369+/-11 bpm), APD (369+/-21 bpm), and Ca2+ (371+/-29 bpm) alternans first appeared were comparable. Importantly, the site of origin of APD alternans and Ca2+ alternans consistently occurred together near the base of the left ventricle, not where APD restitution was steepest. In addition, APD and Ca2+ alternans were remarkably similar both spatially and temporally during discordant alternans. In conclusion, the mechanism underlying T-wave alternans in the intact heart is more closely associated with intracellular Ca2+ cycling rather than APD restitution

Criterios Clínicos para el Manejo de las Complicaciones del Tejido Blando Periimplantar

Fil: Seni, SL. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I; Argentina.Fil: Mollo, LN. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I; Argentina.Fil: Katra, R. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I; Argentina.Fil: Bugatto, AL. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I; Argentina.Fil: Puia, SA. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I; Argentina.Las complicaciones del tejido blando periimplantar condicionan la apariencia estética y el pronóstico clínico de los implantes y son, en la actualidad, cada vez más diagnosticadas. Los defectos gingivales aso-ciados a implantes dentales incluyen recesiones, fe-nestraciones o dehiscencias en la superficie mucosa vestibular, inflamación gingival, ausencia de encía insertada/queratinizada, falta de volumen y presen-cia de concavidades gingivales que generan sombras y oscuridad en la mucosa. La detección de éstas en forma temprana permite establecer un plan de tra-tamiento en busca de soluciones eficaces. Mediante la presentación de una serie de casos, abordaremos distintos procedimientos para aumento de los tejidos blandos periimplantarios y la corrección de defectos. La ganancia de encía queratinizada ha demostrado tener un impacto positivo en la estabilidad a largo pla-zo de todos los tejidos implantarios

Análisis de Factores Etiológicos : desencadenantes de alveolitis

Fil: Markiewicz, J. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Ortodoncia; Argentina.Fil: Bugatto, A. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Ortodoncia; Argentina.Fil: Mollo, L. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Ortodoncia; Argentina.Fil: Katra, R. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Ortodoncia; Argentina.Fil: Seni, S. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Ortodoncia; Argentina.Fil: Puia, S. Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Ortodoncia; Argentina.La alveolitis dental se caracteriza por la aparición de dolor agudo que rodea al alvéolo postextracción, que aumenta de intensidad entre el primer y tercer día posterior a la cirugía, seguido por una pérdida parcial o total de coágulo, con o sin halitosis. Si bien su etiología se considera multifactorial, es muy controversial la responsabilidad que tienen los factores de riesgo en su desarrollo

Estudio del Miedo en Pacientes Frente a la Extracción del Tercer Molar

Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I. Buenos Aires, Argentina.Universidad de Buenos Aires. Facultad de Psicología. Maestría en Psicología Educacional. Buenos Aires, Argentina.Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I. Buenos Aires, Argentina.Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I. Buenos Aires, Argentina.Universidad de Buenos Aires. Facultad de Odontología. Cátedra de Cirugía y Traumatología Bucomaxilofacial I. Buenos Aires, Argentina

Numerical Study of Shear Stress Distribution Over Sand Ripples Under Terrestrial and Martian Conditions

Flat sand beds subjected to wind stress are unstable, and the wind action results in two types of aeolian sand ripples: normal ripples and megaripples. The distinction between the two types is based on two characteristics: i) the normal ripple pattern usually has a wavelength of up to 30 cm, while the megaripple wavelength is on the order of meters; and ii) unimodal distributions of sand grain size lead to normal ripples, while bimodal distributions result in megaripples. On Mars, the distinction between the two types is more difficult to ascertain because the length scales of normal ripples and megaripples can overlap, and often, there is no detailed information regarding their grain size distribution. Unlike normal ripples, megaripples show transverse instability, whose mechanism remains elusive, resulting in a much larger sinuosity of the crestline than normal ripples. In this study, we investigate the megaripples’ transverse instability by using field measurements, wind tunnel experiments and numerical simulations of a three-dimensional ripple model. We show that (a) coarse grains accumulate at megaripple crests, with a corresponding reduction of the lateral sand transport along the crest, and (b) the transverse instability of megaripples is generated by a positive feedback between the height of the crest and the accumulation of coarse grains, with more grains accumulating on the higher portions of the crest. The outcomes of this positive feedback are that the thickness of the coarse grain armoring layer along the crest is not uniform and that it correlates with the crest height. In turn, these height differences drive the transverse instability such that higher portions of the ripple migrate more slowly than the lower sections, creating a wavy crestline. An analysis of Martian ripple images shows variations in the sinuosity index, suggesting that this characteristic can be useful in distinguishing between normal ripples and megaripples on Mars