Inverse Scattering Transform for the Camassa-Holm equation

An Inverse Scattering Method is developed for the Camassa-Holm equation. As an illustration of our approach the solutions corresponding to the reflectionless potentials are explicitly constructed in terms of the scattering data. The main difference with respect to the standard Inverse Scattering Transform lies in the fact that we have a weighted spectral problem. We therefore have to develop different asymptotic expansions.Comment: 17 pages, LaTe

The history of phytolith research in Australasian archaeology and palaeoecology

Although phytolith research has come of age in archaeology and palaeoecology internationally, it has remained relatively marginalised from mainstream practice in Australasia. The region’s initial isolation from international scientific communities and uniqueness of its vegetation communities, has led to an exclusive set of challenges and interruptions in phytolith research. Examining a history of Australasian phytolith research presents the opportunity to recognise developments that have made phytoliths a powerful tool in reconstructing past environments and human uses of plants. Phytolith research arrived early in Australia (1903), after a convoluted journey from Germany (1835–1895) and Europe (1895–1943), but phytoliths were initially misidentified as sponge spicules (1931–1959). Formal understanding of phytoliths and their applications began in Australasia during the late 1950s, continuing throughout the 1960s and 1970s (1959–1980). After a brief hiatus, the modern period of phytolith analyses in Australasian archaeological and palaeoenvironmental research began in the 1980s (1984–1992), focusing on investigating the deep past. Advancements continued into the 1990s and early 2000s. Wallis and Hart declared in 2003 that Australian phytolith research had finally come of age, but more a fitting description would be that it had peaked. Since then phytolith research in Australasia slowed down considerably (2005-present). Local phytolith reference collections for Australasian flora, critical for identifying ancient phytoliths, are essentially no longer produced

RELACIÓN ENTRE EL RENDIMIENTO ACADÉMICO DE LOS INGRESANTES Y EL ABANDONO DE LOS ESTUDIOS UNIVERSITARIOS: COMPARACIÓN ENTRE CARRERAS DE INGENIERÍA Y ECONOMICAS

La preocupación por orientar adecuadamente los recursos que se afectan a los programas de apoyo a los estudiantes de primer año de las carreras, nos llevó a trabajar intentando generar un modelo que sea capaz de determinar, anticipadamente, que estudiantes se encontrarían en situación de abandonar sus estudios. En una primera aplicación del modelo, se analizó la correlación entre el rendimiento académico y el abandono para diez cohortes de ingresantes, de las dos carreras de Ingeniería que ofrece la Universidad Nacional de Luján, observándose una significativa correlación entre el rendimiento académico del estudiante en el primer cuatrimestre y el abandono de los estudios durante el segundo, tercero y cuarto cuatrimestre. En este trabajo, presentamos los resultados que se alcanzaron al aplicar el mismo modelo a las diez cohortes, equivalentes, de estudiantes de las dos carreras del campo de las Ciencias Económicas que se ofrecen en la misma Institución: Licenciatura en Administración y Licenciatura en Comercio Internacional. Las principales conclusiones a las que arribamos es que el modelo se valida positivamente al cambiar el origen disciplinar de las carreras en las que se aplica. Por otra parte, existe mayor correlación entre el rendimiento académico en el primer cuatrimestre y el momento en que se abandonan los estudios para los estudiantes de carreras de Ciencias Económicas que la observada en los de Ingeniería. Se repite el fenómeno observado para las carreras de Ingeniería, de disminuir la correlación entre el rendimiento académico y el abandono para la cohorte 2002. También se detecta una diferencia significativa respecto de la moda para la cantidad de asignaturas aprobadas durante el primer cuatrimestre para las cuatro carreras

Alluvial fan records from southeast Arabia reveal multiple windows for human dispersal

The dispersal of human populations out of Africa into Arabia was most likely linked to episodes of climatic amelioration, when increased monsoon rainfall led to the activation of drainage systems, improved freshwater availability, and the development of regional vegetation. Here we present the first dated terrestrial record from southeast Arabia that provides evidence for increased rainfall and the expansion of vegetation during both glacial and interglacial periods. Findings from extensive alluvial fan deposits indicate that drainage system activation occurred during Marine Isotope Stage (MIS) 6 (ca. 160–150 ka), MIS 5 (ca. 130–75 ka), and during early MIS 3 (ca. 55 ka). The development of active freshwater systems during these periods corresponds with monsoon intensity increases during insolation maxima, suggesting that humid periods in Arabia were not confined to eccentricity-paced deglaciations, and providing paleoenvironmental support for multiple windows of opportunity for dispersal out of Africa during the late Pleistocene

An early MIS 3 pluvial phase in Southeast Arabia: climatic and archaeological implications

Climatic changes in Arabia are of critical importance to our understanding of both monsoon variability and the dispersal of anatomically modern humans (AMH) out of Africa. The timing of dispersal is associated with the occurrence of pluvial periods during Marine Isotope Stage (MIS) 5 (ca. 130–74 ka), after which arid conditions between ca. 74 and 10.5 ka are thought to have restricted further migration and range expansion within the Arabian interior. Whilst a number of records indicate that this phase of aridity was punctuated by an increase in monsoon strength during MIS 3, uncertainties regarding the precision of terrestrial records and suitability of marine archives as records of precipitation, mean that the occurrence of this pluvial remains debated. Here we present evidence from a series of relict lake deposits within southeastern Arabia, which formed at the onset of MIS 3 (ca. 61–58 ka). At this time, the incursion of monsoon rainfall into the Arabian interior activated a network of channels associated with an alluvial fan system along the western flanks of the Hajar Mountains, leading to lake formation. Multiproxy evidence indicates that precipitation increases intermittently recharged fluvial systems within the region, leading to lake expansion in distal fan zones. Conversely, decreased precipitation led to reduced channel flow, lake contraction and a shift to saline conditions. These findings are in contrast to the many other palaeoclimatic records from Arabia, which suggest that during MIS 3, the latitudinal position of the monsoon was substantially further south and did not penetrate the peninsula. Additionally, the occurrence of increased rainfall at this time challenges the notion that the climate of Arabia following MIS 5 was too harsh to permit the further range expansion of indigenous communities

Developing a framework of Quaternary dune accumulation in the northern Rub' al-Khali, Arabia

Located at the crossroads between Africa and Eurasia, Arabia occupies a pivotal position for human migration and dispersal during the Late Pleistocene. Deducing the timing of humid and arid phases is critical to understanding when the Rub' al-Khali desert acted as a barrier to human movement and settlement. Recent geological mapping in the northern part of the Rub' al-Khali has enabled the Quaternary history of the region to be put into a regional stratigraphical framework. In addition to the active dunes, two significant palaeodune sequences have been identified. Dating of key sections has enabled a chronology of dune accretion and stabilisation to be determined. In addition, previously published optically stimulated luminescence (OSL) dates have been put in their proper stratigraphical context, from which a record of Late Pleistocene dune activity can be constructed. The results indicate the record of dune activity in the northern Rub' al-Khali is preservation limited and is synchronous with humid events driven by the incursion of the Indian Ocean monsoon

Experimental investigation of the effect of high pressure nozzle geometry on spray characteristics

Phase Doppler Anemometry (PDA) measurements [1] are applied to low length to diameter ratio (L/D) multi-hole nozzles operating with at high fuel pressure (20 MPa) that are implemented in the new Euro6 generation of Gasoline Direct Injection engines. For these multi-jets spray, the authors intend to demonstrate; the importance of the spray shape, the effect of hole design and the reorganisation dynamic of the drop size distribution by turbulent mixing. To do so, we report significant experimental effort along with careful data reduction, exercised to understand the spray behaviour, in particular separating the sources of experimental uncertainty from the flow physics. A practical methodology is adopted as a compromise between measurement effort, error removal, and the need to understand underlying physical processes within the spray plume. The present work focuses mostly on the drop size and velocity profiles (two-component) perpendicular to the plume direction

Multiple phases of human occupation in Southeast Arabia between 210,000 and 120,000 years ago

Changing climatic conditions are thought to be a major control of human presence in Arabia during the Paleolithic. Whilst the Pleistocene archaeological record shows that periods of increased monsoon rainfall attracted human occupation and led to increased population densities, the impact of arid conditions on human populations in Arabia remains largely speculative. Here, we present data from Jebel Faya in Southeast (SE) Arabia, which document four periods of human occupation between c. 210,000 and 120,000 years ago. The Jebel Faya record indicates that human occupation of SE Arabia was more regular and not exclusively linked to major humid periods. Our data show that brief phases of increased rainfall additionally enabled human settlement in the Faya region. These results imply that the mosaic environments in SE Arabia have likely formed a population refugia at the end of the Middle and the beginning of the Late Pleistocene.