163 research outputs found
Single shot phase contrast imaging using laser-produced Betatron x-ray beams
Development of x-ray phase contrast imaging applications with a laboratory
scale source have been limited by the long exposure time needed to obtain one
image. We demonstrate, using the Betatron x-ray radiation produced when
electrons are accelerated and wiggled in the laser-wakefield cavity, that a
high quality phase contrast image of a complex object (here, a bee), located in
air, can be obtained with a single laser shot. The Betatron x-ray source used
in this proof of principle experiment has a source diameter of 1.7 microns and
produces a synchrotron spectrum with critical energy E_c=12.3 +- 2.5 keV and
10^9 photons per shot in the whole spectrum.Comment: 3 pages, 3 figure
Quasi-monoenergetic electron beams production in a sharp density transition
International audienceUsing a laser plasma accelerator, experiments with a 80 TW and 30 fs laser pulse demonstrated quasi-monoenergetic electron spectra with maximum energy over 0.4 GeV. This is achieved using a supersonic He gas jet and a sharp density ramp generated by a high intensity laser crossing pre-pulse focused 3 ns before the main laser pulse. By adjusting this crossing pre-pulse position inside the gas jet, among the laser shots with electron injection more than 40% can produce quasi-monoenergetic spectra. This could become a relatively straight forward technique to control laser wakefield electron beams parameters
Demonstration of the synchrotron-type spectrum of laser-produced Betatron radiation
Betatron X-ray radiation in laser-plasma accelerators is produced when
electrons are accelerated and wiggled in the laser-wakefield cavity. This
femtosecond source, producing intense X-ray beams in the multi kiloelectronvolt
range has been observed at different interaction regime using high power laser
from 10 to 100 TW. However, none of the spectral measurement performed were at
sufficient resolution, bandwidth and signal to noise ratio to precisely
determine the shape of spectra with a single laser shot in order to avoid shot
to shot fluctuations. In this letter, the Betatron radiation produced using a
80 TW laser is characterized by using a single photon counting method. We
measure in single shot spectra from 8 to 21 keV with a resolution better than
350 eV. The results obtained are in excellent agreement with theoretical
predictions and demonstrate the synchrotron type nature of this radiation
mechanism. The critical energy is found to be Ec = 5.6 \pm 1 keV for our
experimental conditions. In addition, the features of the source at this energy
range open novel perspectives for applications in time-resolved X-ray science.Comment: 5 pages, 4 figure
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Tracking ultrafast solid-state dynamics using high harmonic spectroscopy
WWe establish time-resolved high harmonic generation (tr-HHG) as a powerful spectroscopy method for tracking photoinduced dynamics in strongly correlated materials through a detailed investigation of the insulator-to-metal phase transitions in vanadium dioxide. We benchmark the technique by comparing our measurements to established momentum-resolved ultrafast electron diffraction, and theoretical density functional calculations. Tr-HHG allows distinguishing of individual dynamic channels, including a transition to a thermodynamically hidden phase. In addition, the HHG yield is shown to be modulated at a frequency characteristic of a coherent phonon of the equilibrium monoclinic phase over a wide range of excitation fluences. These results demonstrate that tr-HHG is capable of tracking complex dynamics in solids through its sensitivity to the band structure
Developmental malformation of the corpus callosum: a review of typical callosal development and examples of developmental disorders with callosal involvement
This review provides an overview of the involvement of the corpus callosum (CC) in a variety of developmental disorders that are currently defined exclusively by genetics, developmental insult, and/or behavior. I begin with a general review of CC development, connectivity, and function, followed by discussion of the research methods typically utilized to study the callosum. The bulk of the review concentrates on specific developmental disorders, beginning with agenesis of the corpus callosum (AgCC)—the only condition diagnosed exclusively by callosal anatomy. This is followed by a review of several genetic disorders that commonly result in social impairments and/or psychopathology similar to AgCC (neurofibromatosis-1, Turner syndrome, 22q11.2 deletion syndrome, Williams yndrome, and fragile X) and two forms of prenatal injury (premature birth, fetal alcohol syndrome) known to impact callosal development. Finally, I examine callosal involvement in several common developmental disorders defined exclusively by behavioral patterns (developmental language delay, dyslexia, attention-deficit hyperactive disorder, autism spectrum disorders, and Tourette syndrome)
Anterior and posterior commissures in agenesis of the corpus callosum: alternative pathways for attention processes?
Developmental absence (agenesis) of the corpus callosum (AgCC) is a congenital brain malformation resulting from disruption of corpus callosum formation, a structure that is crucial for the transfer and integration of information, including attention processes, across the brain. This study aimed to investigate previously proposed candidates for alternative inter-hemispheric pathways in AgCC by examining (1) white matter volume and microstructure of the anterior and posterior commissures in children with AgCC compared to typically developing controls (TDC), and (2) in children with AgCC, examine the associations of white matter volume and microstructure of the anterior and posterior commissures and any remaining corpus callosum with attention processes. Participants were 21 children with AgCC (13 complete, 8 partial) recruited from The Royal Children's Hospital, Melbourne, and 30 TDC aged 8–17 years. T1-and diffusion-weighted MR sequences were used to calculate volume and microstructural parameters. Neuropsychological testing assessed attention processes. We found the anterior commissure was significantly larger in volume in children with AgCC than TDC (p = .027), with reduced mean FA (p = .001) associated with increased mean RD (p < .001). In children with AgCC, we found microstructural properties of the anterior commissure associated with attentional processes, specifically, mean FA of the anterior commissure was associated with better divided attention (p = .03), and the association between alerting attention and mean AD and RD was found to be moderated by age (p = .027, p = .008) and the degree of corpus callosum agenesis (p = .025, p = .016). Furthermore, in partial AgCC, larger posterior commissure volume was associated with better orienting attention (p = .035). In conclusion, we provide evidence that the volume and microstructure of the anterior commissure are altered in children with AgCC, and this neuroplastic response might have an influence on attention processes
Fatty Acid Composition and Thermal Properties of Lipid From Milk and Butter From Lactating Holstein Cows Fed a Supplemental Lipid Either High or Low In Palmitic Acid
Abstract of paper presented at the 2006 Joint Annual Meeting of the American Dairy Science Association & the American Society of Animal Science
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