Civil rights and the American Negro; a documentary history,

Mode of access: Internet

Ranking de recursos y dieta óptima en desiertos nordpatagónicos

La jerarquización de recursos constituye uno de los procedimientos más empleados para evaluar la subsistencia de los cazadores-recolectores en el pasado. Para el Centro Occidente Argentino (COA) esta jerarquización se fundaba en el tamaño corporal de las presas. Aquí incorporamos datos sobre los costos de manejo, generando el primer ordenamiento de recursos para la región que contempla los elementos requeridos por los modelos de optimización (Kcal/tiempo post-encuentro). Luego del guanaco (Lama guanicoe) —presa de mayor rendimiento— este ranking situó en segundo y tercer lugar a los huevos de Rheidae y los armadillos (Dasypodidae), respectivamente, resaltando la importancia de presas tradicionalmente consideradas de bajo rendimiento. Siguiendo la teoría de aprovisionamiento óptimo, elaboramos el modelo de amplitud de dieta (MAD) para los desiertos más representativos de Nordpatagonia: el de Monte y el patagónico. En este último, la mayor disponibilidad de guanacos tornó menos ventajosa la incorporación de nuevos ítems a la dieta. Para el Monte, la dieta óptima se amplió, incluyendo recursos menores como ciertos peces (i.e., Percichthys trucha). En definitiva, el MAD permitió reinterpretar tendencias temporales en la subsistencia humana, sosteniendo una ampliación en el espectro de recursos explotados hacia el Holoceno tardío en el COA. En general, las expectativas del MAD son confirmadas con el registro zooarqueológico regional.Prey ranking of animal resources is critical to the evaluation of decision-making of past foragers. Previous work in Central Western Argentina (CWA) has used a ranking of resources on the basis of size and weight alone. Here we present the first CWA resource ranking that incorporates handling costs. Our ranking puts the guanaco (Lama guanicoe) in first place, followed by Rheidae eggs and armadillos (Dasypodidae), and highlights the importance of certain resources commonly assumed to be lowranking. Following the optimal foraging theory, we develop the diet-breath model (DBM) for two of the most representative environments of North Patagonia: the Monte and Patagonian deserts. The higher encounter rates with the first-ranked prey, guanaco, in the Patagonia desert, discourages the incorporation of lower-ranking resources into the diet. In contrast, lower guanaco encounter rates in the Monte desert favors a wider optimal diet model, including the incorporation of fish (i.e., Percichthys trucha). The DBM was used to (re)interpret temporal trends in human subsistence and to support the idea of an expansion of the diet during the Late Holocene in CWA. In general terms, the DBM expectations are confirmed with the regional zooarchaeological record.Fil: Corbat, Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Gil, Adolfo Fabian. Universidad Tecnologica Nacional. Facultad Reg.san Rafael. Instituto de Evolucion, Ecologia Historica y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto de Evolucion, Ecologia Historica y Ambiente.; ArgentinaFil: Bettinger, Robert. University of California; Estados UnidosFil: Neme, Gustavo Adolfo. Universidad Tecnologica Nacional. Facultad Reg.san Rafael. Instituto de Evolucion, Ecologia Historica y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto de Evolucion, Ecologia Historica y Ambiente.; ArgentinaFil: Zangrando, Atilio Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin

Chirped pulse amplification in an extreme-ultraviolet free-electron laser

International audienceChirped pulse amplification in optical lasers is a revolutionary technique, which allows the generation of extremely powerful femtosecond pulses in the infrared and visible spectral ranges. Such pulses are nowadays an indispensable tool for a myriad of applications, both in fundamental and applied research. In recent years, a strong need emerged for light sources producing ultra-short and intense laser-like X-ray pulses, to be used for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences. This demand was satisfied by the advent of short-wavelength free-electron lasers. However, for any given free-electron laser setup, a limit presently exists in the generation of ultra-short pulses carrying substantial energy. Here we present the experimental implementation of chirped pulse amplification on a seeded free-electron laser in the extreme-ultraviolet, paving the way to the generation of fully coherent sub-femtosecond gigawatt pulses in the water window (2.3-4.4 nm)

Pulse Duration of Seeded Free-Electron Lasers

The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL) pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial experimental parameter that needs to be characterized. We measured the pulse shape of an extremeultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods, one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities. The measurements were carried out at the seeded FEL facility FERMI. The FEL temporal pulse characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they were compared to the predictions of a theoretical model. The measurements allowed a direct observation of the pulse lengthening and splitting at saturation, in agreement with the proposed theory

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Photoinduced isomerization reactions lie at the heart of many chemical processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics occurring on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free-electron laser to trace the ultrafast ring opening of gas-phase thiophenone molecules following ultraviolet photoexcitation. When combined with ab initio electronic structure and molecular dynamics calculations of the excited- and ground-state molecules, the results provide insights into both the electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state are shown to be driven by ballistic S–C bond extension and to be complete within 350 fs. Theory and experiment also enable visualization of the rich ground-state dynamics that involve the formation of, and interconversion between, ring-opened isomers and the cyclic structure, as well as fragmentation over much longer timescales