4,118 research outputs found
Time-resolved refractive index and absorption mapping of light-plasma filaments in water
By means of a quantitative shadowgraphic method, we performed a space-time
characterization of the refractive index variation and transient absorption
induced by a light-plasma filament generated by a 100 fs laser pulse in water.
The formation and evolution of the plasma channel in the proximity of the
nonlinear focus were observed with a 23 fs time resolution.Comment: 3 pages, 3 picture
Tunneling mediated by conical waves in a 1D lattice
The nonlinear propagation of 3D wave-packets in a 1D Bragg-induced band-gap
system, shows that tranverse effects (free space diffraction) affect the
interplay of periodicity and nonlinearity, leading to the spontaneous formation
of fast and slow conical localized waves. Such excitation corresponds to
enhanced nonlinear transmission (tunneling) in the gap, with peculiar features
which differ on the two edges of the band-gap, as dictated by the full
dispersion relationship of the localized waves.Comment: 5 pages, 6 figure
Bird assemblages in a Malagasy forest-agricultural frontier : Effects of habitat structure and forest cover
Peer reviewe
Extreme Events in Resonant Radiation from Three-dimensional Light Bullets
We report measurements that show extreme events in the statistics of resonant
radiation emitted from spatiotemporal light bullets. We trace the origin of
these extreme events back to instabilities leading to steep gradients in the
temporal profile of the intense light bullet that occur during the initial
collapse dynamics. Numerical simulations reproduce the extreme valued
statistics of the resonant radiation which are found to be intrinsically linked
to the simultaneous occurrence of both temporal and spatial self-focusing
dynamics. Small fluctuations in both the input energy and in the spatial phase
curvature explain the observed extreme behaviour.Comment: 5 pages, 5 figures, submitte
Response of Pinus sylvestris L. to recent climatic events in the French Mediterranean region
International audienceExceptional climatic events from 2003 to 2005 (scorching heat and drought) affected the whole of the vegetation in the French Mediterranean region and in particular Scott pines (Pinus sylvestris L.), one of the most important forest tree species in this area. To understand its response to these extreme conditions, we investigated its radial growth, branch length growth, architectural development and reproduction for the period 19952005, and linked these variables to climatic parameters. We used four plots situated in southeastern France and presenting different levels of site quality and potential forest productivity. The results show that: (1) the climatic episode 20032005 was highly detrimental to the growth (bole and branches), crown development, and cone production but favoured the production of male flowers; (2)these variables depend on climatic factors of both the current and previous years; (3) the 2003 scorching heat impact was strong but was mainly apparent from 2004; it was part of a 6-year-long unfavourable cycle beginning in 2000, characterized by high minimum and maximum temperatures and very dry springs;(4) in spite of a significant effect of site quality, the Scots pine's response to extreme climatic conditions was homogeneous in the French Mediterranean area; and (5) the stress induced by poor site conditions generally resulted in the same consequences for tree growth, architecture, and reproduction as in unfavourable climatic conditions.Des événements climatiques exceptionnels de 2003 à 2005 (canicule et sécheresse) ont affecté la végétation dans la région de la Méditerranée française et en particulier le pin sylvestre (Pinus sylvestris L.), une des principales essences forestières de cette région. Pour comprendre sa réponse à ces conditions extrêmes, nous avons examiné sa croissance radiale, la croissance en longueur des branches, le développement architectural et la reproduction pendant la période 1995-2005 et avons relié ces variables avec les paramètres climatiques. Nous avons utilisé quatre placettes situées dans le sud-est de la France et présentant des niveaux différents de qualité stationnelle et de productivité forestière potentielle. Les résultats montrent que : (1) l'épisode climatique 2003-2005 était fortement néfaste à la croissance (tronc et branches), au développement du houppier et à la production de cônes, mais a favorisé la production de fleurs mâles; (2) ces variables dépendent des facteurs climatiques des années en cours et précédente; (3) l'impact de canicule 2003 était fort, mais était principalement apparent de 2004; il faisait partie d'un cycle défavorable de 6 ans commençant en 2000, caractérisé par des hautes températures minimales et maximales et des printemps très secs; (4) malgré un effet significatif de la qualité stationnelle, la réponse du pin sylvestre aux conditions climatiques extrêmes était homogène dans la zone méditerranéenne française; Et (5) le stress provoqué par de mauvaises conditions stationnelles avait généralement les mêmes conséquences pour la croissance , l'architecture et la reproduction du pin sylvestre que des conditions climatiques défavorables
A NASTRAN model of a large flexible swing-wing bomber. Volume 5: NASTRAN model development-fairing structure
The NASTRAN model plan for the fairing structure was expanded in detail to generate the NASTRAN model of this substructure. The grid point coordinates, element definitions, material properties, and sizing data for each element were specified. The fairing model was thoroughly checked out for continuity, connectivity, and constraints. The substructure was processed for structural influence coefficients (SIC) point loadings to determine the deflection characteristics of the fairing model. Finally, a demonstration and validation processing of this substructure was accomplished using the NASTRAN finite element program. The bulk data deck, stiffness matrices, and SIC output data were delivered
The Incidence of Medicare
The Medicare program transfers more than $200 billion annually from taxpayers to beneficiaries. This paper considers the incidence of such transfers. First, we examine the net tax payments and program expenditures for individuals in different lifetime income groups. We find Medicare has led to net transfers from the poor to the wealthy, as a result of relatively regressive financing mechanisms and the higher expenditures and longer survival times of wealthier beneficiaries. Even with recent financing reforms, net transfers to the wealthy are likely to continue for at least several more decades. Second, we consider the insurance value of Medicare in providing a missing market for health insurance. With plausible parameter values, our simulations suggest that low-income elderly benefitted more than the dollar flows would suggest. Including this insurance value implies that, on net, there is faint redistribution from the highest income deciles to the lowest income deciles. We also consider the likely distributional impact of several proposed reforms in Medicare financing and benefits.
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