Vies moyennes de niveaux de 53Mn excités par la réaction 50Cr (α, pγ)53Mn

Les propriétés électromagnétiques du noyau 53Mn sont étudiées à l'aide de la réaction 50Cr(α, pγ)53Mn à Eα = 14,5 MeV. Les rayonnements γ sont détectés en coïncidence avec les groupes de protons observés à l'aide d'un détecteur annulaire placé à 180° dans l'axe du faisceau. Des rapports d'embranchement de transitions γ sont donnés. La méthode d'atténuation de l'effet Doppler a été utilisée pour déduire les vies moyennes : niveau de 3,42 MeV, τ = 1,0 +0,6-0,4 ps ; niveau de 3,44 MeV, τ = 0,13 +0,05-0,04ps ; niveau de 4,15 MeV, τ = 0,07 ± 0,02 ps. Pour les niveaux à Ex < 3 MeV nos valeurs de τ sont en accord avec des résultats obtenus ailleurs. Pour le niveau de 3,44 MeV nous déduisons Jπ = 15/2- sans ambiguïté. Certaines probabilités de transitions B(M1) et B(E2) sont déterminées et comparées aux prédictions des modèles récents

Description of an ancient social bee trapped in amber using diagnostic radioentomology

The application of non-invasive imaging technologies using X-radiation (diagnostic radioentomology, ‘DR') is demonstrated for the study of amber-entombed social bees. Here, we examine the external and internal morphology of an Early Miocene (Burdigalian) stingless bee (Apinae: Meliponini) from the Dominican Republic using non-destructive X-ray microtomography analysis. The study permits the accurate reconstruction of features otherwise obscured or impossible to visualize without destroying the sample and allows diagnosis of the specimen as a new species, Proplebeia adbita Greco and Enge

Sub-6-fs blue pulses generated by quasi-phase-matching second-harmonic generation pulse compression

Abstract. : We demonstrate a novel scalable and engineerable approach for the frequency-doubling of ultrashort pulses. Our technique is based on quasi-phase-matching and simultaneously provides tailored dispersion and nonlinear frequency conversion of few-cycle optical pulses. The method makes use of the spatial localization of the conversion process and the group velocity mismatch in a chirped grating structure. The total group delay of the nonlinear device can be designed to generate nearly arbitrarily chirped second-harmonic pulses from positively or negatively chirped input pulses. In particular, compressed second-harmonic pulses can be obtained. A brief summary of the underlying theory is presented, followed by a detailed discussion of our experimental results. We experimentally demonstrate quasi-phase-matching pulse compression in the sub-10-fs regime by generating few-cycle pulses in the blue to near-ultraviolet spectral range. Using this new frequency conversion technique, we generate sub-6-fs pulses centered at 405nm by second-harmonic generation from a 8.6fs Ti:sapphire laser pulse. The generated spectrum spans a bandwidth of 220THz. To our knowledge, these are the shortest pulses ever obtained by second-harmonic generatio

Spectral signature of short attosecond pulse trains

We report experimental measurements of high-order harmonic spectra generated in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800nm laser field and a fraction (less than 10%) of its second harmonic. Additional spectral peaks are observed between the harmonic peaks, which are due to interferences between multiple pulses in the train. The position of these peaks varies with the CEO and their number is directly related to the number of pulses in the train. An analytical model, as well as numerical simulations, support our interpretation

Description of an ancient social bee trapped in amber using diagnostic radioentomology

The application of non-invasive imaging technologies using X-radiation (diagnostic radioentomology, ‘DR’) is demonstrated for the study of amber-entombed social bees. Here, we examine the external and internal morphology of an Early Miocene (Burdigalian) stingless bee (Apinae: Meliponini) from the Dominican Republic using non-destructive X-ray microtomography analysis. The study permits the accurate reconstruction of features otherwise obscured or impossible to visualize without destroying the sample and allows diagnosis of the specimen as a new species, Proplebeia adbita Greco and Engel

THE 18O + 12C FUSION-EVAPORATION REACTION

No abstract availabl

Fascitis necrotizante, cuando el tiempo vale oro

La Fascitis Necrotizante es una infección de partes blandas que puede provocar una rápida destrucción del tejido afectado con necrosis y sepsis grave, potencialmente mortal. Los factores predisponentes son diabetes, neoplasias, alcoholismo, enfermedad hepática y renal crónica, entre otras. Es una urgencia médica que requiere un tratamiento quirúrgico precoz, y terapia antibiótica endovenosa de amplio espectro con el fin de disminuir la tasa de mortalidad. Presentamos el caso de un paciente con antecedente de linfoma T hepático que presentó fascitis necrotizante en el miembro inferior izquierdo secundario a Bacillus Cereus

A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions

We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10−1 mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer