Were rivers flowing across the Sahara during the last interglacial? Implications for human migration through Africa.

Human migration north through Africa is contentious. This paper uses a novel palaeohydrological and hydraulic modelling approach to test the hypothesis that under wetter climates c.100,000 years ago major river systems ran north across the Sahara to the Mediterranean, creating viable migration routes. We confirm that three of these now buried palaeo river systems could have been active at the key time of human migration across the Sahara. Unexpectedly, it is the most western of these three rivers, the Irharhar river, that represents the most likely route for human migration. The Irharhar river flows directly south to north, uniquely linking the mountain areas experiencing monsoon climates at these times to temperate Mediterranean environments where food and resources would have been abundant. The findings have major implications for our understanding of how humans migrated north through Africa, for the first time providing a quantitative perspective on the probabilities that these routes were viable for human habitation at these times

Dataset associated with "Temporal Variations of NDVI and LAI and Interactions with Hydroclimatic Variables in a Large and Agro-Ecologically Diverse Region"

It contains the dataset used to produce Figure 2 in the manuscript and to estimate relationships of hydroclimatic variables with vegetation indices. Each variable is a monthly regional average (for combined Sacramento and San Joaquin river basins, California) and spans from October 2002 to September 2015. These regional averages have been estimated using different datasets which are cited in the manuscript. Description of dataset is as follows: 1. Dataset 1: Regional averages of monthly hydroclimatic and vegetation anomalies 2. Dataset 2: Mean and standard deviations of monthly hydroclimatic and vegetation anomalies 3. Dataset 3: Prewhitened time series of monthly hydroclimatic and vegetation anomalies 4. Dataset 4: Prewhitened-detrended time series monthly hydroclimatic and vegetation anomalies 5. Dataset 5: Annual time series of regional hydroclimatic and vegetation anomalies See supplementary information provided with the manuscript for more information.Satellite based vegetation indices are increasingly used to characterize seasonal and interannual variations in vegetation as well as vegetation’s response to hydroclimatic variability. However, differences in the behavior of vegetation indices are not well understood over large spatial extents (e.g., 0.5° or larger). We hypothesize that normalized difference vegetation index (NDVI) and leaf area index (LAI) can exhibit different behaviors due to different relationships with hydroclimatic variables. To test this hypothesis, observations of monthly precipitation, discharge, temperature, vapor pressure deficit, evapotranspiration, and total water storage anomalies (TWSA) are processed for the combined Sacramento and San Joaquin river basins in California for 13 water years (October 2002-September 2015). Estimates of NDVI and LAI are obtained for the same period from MODerate resolution Imaging Spectroradiometer (MODIS). The seasonal cycle of NDVI peaks 2-3 months earlier than LAI. The seasonal variation in NDVI follows the seasonality of TWSA (i.e. water availability) whereas the seasonal cycle of LAI follows the seasonality in mean temperature and vapor pressure deficit (i.e. atmospheric water demand). Cross-correlation analyses of NDVI and LAI with the hydroclimatic variables show that LAI is more strongly correlated with most of the hydroclimatic variables considered.This work was supported by a grant provided by Bureau of Educational and Cultural Affairs, US Department of State under the umbrella of foreign Fulbright scholarship program

Hyper-resolution mapping of regional storm surge and tide flooding: comparison of static and dynamic models

Storm tide (combination of storm surge and the astronomical tide) flooding is a natural hazard with significant global social and economic consequences. For this reason, government agencies and stakeholders need storm tide flood maps to determine population and infrastructure at risk to present and future levels of inundation. Computer models of varying complexity are able to produce regional-scale storm tide flood maps and current model types are either static or dynamic in their implementation. Static models of storm tide utilize storm tide heights to inundate locations hydrologically connected to the coast, whilst dynamic models simulate physical processes that cause flooding. Static models have been used in regional-scale storm tide flood impact assessments, but model limitations and coarse spatial resolutions contribute to uncertain impact estimates. Dynamic models are better at estimating flooding and impact but are computationally expensive. In this study we have developed a dynamic reduced-complexity model of storm tide flooding that is computationally efficient and is applied at hyper-resolutions (<100 m cell size) over regional scales. We test the performance of this dynamic reduced-complexity model and a separate static model at three test sites where storm tide observational data are available. Additionally, we perform a flood impact assessment at each site using the dynamic reduced-complexity and static model outputs. Our results show that static models can overestimate observed flood areas up to 204 % and estimate more than twice the number of people, infrastructure, and agricultural land affected by flooding. Overall we find that that a reduced-complexity dynamic model of storm tide provides more conservative estimates of coastal flooding and impact

Corporate Social Responsibility from a sustainable development perspective and its influence in the business competitiveness of San Martin

La Responsabilidad Social Empresarial (RSE) ha adquirido un relevante protagonismo en los últimos años como signo del compromiso de la empresa con sus distintos grupos de interés, la empresa socialmente responsable debe ser consciente que su accionar puede ocasionar impactos a cualquier individuo o grupo de interés. A nivel científico se ha demostrado que la RSE influye de forma positiva sobre los resultados financieros de las empresas de gran nivel, pero no se ha estudiado su impacto sobre la competitividad, una variable que tiene gran interés para los directivos de empresas por su repercusión a nivel estratégico e integral y su consiguiente implicación en el desarrollo de cualquier sector empresarial más aún si esta se trata de una Mipyme. Por otro lado, a pesar del importante peso relativo que en la economía tienen las Mipymes, y su tratamiento diferenciado a la hora de diseñar políticas estratégicas, son pocos los estudios que apliquen la RSE en las Mipymes. Este trabajo examina cómo contribuye a la competitividad de las Mipymes la adopción de prácticas de RSE bajo el enfoque de desarrollo sostenible, utilizando para ello un estudio realizado a 130 empresas de tamaño, micro, pequeño y mediano, ubicadas en la Región San Martin, Perú. Aplicando para eso escalas de medición, para evaluar las acciones de RSE y la Competitividad Empresarial consideradas como tales en su dimensión correspondiente. Los resultados demuestran que más allá de la teoría, de maquillaje empresarial o de moda fugaz, las acciones de RSE, desde la óptica de los gestores de las empresas tienen una influencia significativa en la competitividad de las Mipymes manufactureras de la Región San Martin.Corporate Social Responsibility (CSR) has acquired an important role in recent years as a sign of commitment to the company and its various interest groups, the socially responsible company should be aware that their actions can cause impacts to any individual or interest group. Scientifically it has been shown that CSR has a positive influence on the financial results of the high level companies, but has not been studied its impact on competitiveness, a variable that is of great interest to business managers for their impact on strategic and comprehensive level and subsequent involvement in the development of any business sector even more so if this is a Mipyme. On the other hand, despite the important relative weight in the economy they have Mipymes, and differential treatment when designing strategic policies, few studies applying CSR in Mipymes. This work examines how it contributes to the competitiveness of Mipymes adopting CSR practices under the sustainable development approach, using a study of 130 micro, small and medium companies, located in the San Martin Region, Peru. By applying for this measurement scales to assess the actions of CSR and Business Competitiveness considered in the corresponding dimension. The results show that beyond theory, business makeup or fleeting fashion, CSR activities have a significant influence on the competitiveness of manufacturing Mipymes in the San Martin region

Direct transition from a disordered to a multiferroic phase on a triangular lattice

Competing interactions and geometric frustration provide favourable conditions for exotic states of matter. Such competition often causes multiple phase transitions as a function of temperature and can lead to magnetic structures that break inversion symmetry, thereby inducing ferroelectricity [1-4]. Although this phenomenon is understood phenomenologically [3-4], it is of great interest to have a conceptually simpler system in which ferroelectricity appears coincident with a single magnetic phase transition. Here we report the first such direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic in the triangular lattice antiferromagnet RbFe(MoO4)2 (RFMO). A magnetic field extinguishes the electric polarization when the symmetry of the magnetic order changes and ferroelectricity is only observed when the magnetic structure has chirality and breaks inversion symmetry. Multiferroic behaviour in RFMO provides a theoretically tractable example of ferroelectricity from competing spin interactions. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that the chiral magnetic order of the triangular lattice antiferromagnet gives rise to a pseudoelectric field, whose temperature dependence agrees with that observed experimentally.Comment: 16 pages pdf including 3 figure

Spectroscopic binaries in the Solar Twin Planet Search program: from substellar-mass to M dwarf companions

Previous studies on the rotation of Sun-like stars revealed that the rotational rates of young stars converge towards a well-defined evolution that follows a power-law decay. It seems, however, that some binary stars do not obey this relation, often by displaying enhanced rotational rates and activity. In the Solar Twin Planet Search program we observed several solar twin binaries, and found a multiplicity fraction of $42\% \pm 6\%$ in the whole sample; moreover, at least three of these binaries (HIP 19911, HIP 67620 and HIP 103983) clearly exhibit the aforementioned anomalies. We investigated the configuration of the binaries in the program, and discovered new companions for HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which the latter is orbited by a $0.06$ M$_\odot$ brown dwarf in a 1-month long orbit. We report the orbital parameters of the systems with well-sampled orbits and, in addition, the lower limits of parameters for the companions that only display a curvature in their radial velocities. For the linear trend binaries, we report an estimate of the masses of their companions when their observed separation is available, and a minimum mass otherwise. We conclude that solar twin binaries with low-mass stellar companions at moderate orbital periods do not display signs of a distinct rotational evolution when compared to single stars. We confirm that the three peculiar stars are double-lined binaries, and that their companions are polluting their spectra, which explains the observed anomalies.Comment: 13 pages, 7 figures, accepted for publication in MNRA