Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs (original) (raw)
Related papers
Ultrafast x-ray science at the Advanced Light Source
2000
Our scientific understanding of the static or time-averaged structure of condensed matter on the atomic scale has been dramatically advanced by direct structural measurements using x-ray techniques and modern synchrotron sources. Of course the structure of condensed matter is not static, and to understanding the behavior of condensed matter at the most fundamental level requires structural measurements on the time scale on which atoms move. The evolution of condensed-matter structure, via the making and breaking of chemical bonds and the rearrangement of atoms, occurs on the fundamental time scale of a vibrational period, ;100 fs. Atomic motion and structural dynamics on this time scale ultimately determine the course of phase transitions in solids, the kinetic pathways of chemical reactions, and even the efficiency and function of biological processes. The integration of x-ray measurement techniques, a high-brightness femtosecond x-ray source, femtosecond lasers, and stroboscopic pump-probe techniques will provide the unique capability to address fundamental scientific questions in solidstate physics, chemistry, AMO physics, and biology involving structural dynamics. In this paper, we review recent work in ultrafast x-ray science at the ALS including time-resolved diffraction measurements and efforts to develop dedicated beamlines for femtosecond x-ray experiments.
Ultrafast X-ray sources and applications
Comptes Rendus de l'Académie des Sciences - Series IV - Physics, 2000
The recent development of ultrafast X-ray sources makes conceivable the analysis of subpicosecond transient structures. This paper describes these new techniques and reports the first experiments dedicated to the analysis of atomic motions on this time-scale. © 2000 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS
A broadband laser plasma x-ray source for application in ultrafast chemical structure dynamics
A plasma source free from characteristic emission lines is described, based on laser irradiation of a water jet in a helium atmosphere. Various key aspects of the laser interaction are presented along with practical characterization of the observed isotropic ϳ4-10 keV x-ray emissions, measurements of which indicate subpicosecond duration. Observations are consistent with a vacuum heating plasma mechanism at the helium-water interface and indicate strong potential for in-house ultrafast chemical structure dynamics application when coupled to contemporary detector developments.
Physics of Fluids B: Plasma Physics, 1993
Time-resolved spectroscopy (with a 2 psec temporal resolution) of plasmas produced by the interaction between solid targets and a high contrast subpicosecond table top terawatt (T3) laser at lOI W/cm', is used to study the basic processes which control the x-ray pulse duration. Short x-ray pulses have been obtained by spectral selection or by plasma gradient scalelength control. Time-dependent calculations of the atomic physics [Whys. Fluids B 4, 2007, 19921 coupled to a Fokker-Planck code [Phys. Rev. Lett. 53, 1461, 19841 indicate that it is essential to take into account the non-Maxwellian character of the electron distribution for a quantitative analysis of the experimental results.
Ultrafast time-resolved X-ray diffraction
International Quantum Electronics Conference, 2005.
Femtosecond laser-generated plasmas emit ultrashort X-ray pulses in the multi-keV range, which allow the extension of X-ray spectroscopy into the ultrafast time-domain. We report here on the generation of such short X-ray pulses and their application for time-resolved diffraction as a means to directly study ultrafast structural dynamics in laser-excited solids.
X-ray synchrotron studies of ultrafast crystalline dynamics
Journal of Synchrotron Radiation, 2005
Ultrafast X-ray experiments at synchrotron sources hold tremendous promise for measuring the atomistic dynamics of materials under a wide variety of transient conditions. In particular, the marriage of synchrotron radiation and ultrafast laser technology is opening up a new frontier of materials research. Structural changes initiated by femtosecond laser pulses can be tracked in real time using time-resolved X-ray diffraction on picosecond time scales or shorter.
2007
Time-resolved x-ray absorption fine structure (XAFS) spectroscopy with picosecond temporal resolution is a new method to observe electronic and geometric structures of short-lived reaction intermediates. It combines an intense femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light Source (SLS). We present key experiments on charge transfer reactions as well as spin-crossover processes in coordination chemistry compounds next to solvation dynamics studies of photogenerated atomic radicals.