409 research outputs found
Betatron emission as a diagnostic for injection and acceleration mechanisms in laser-plasma accelerators
Betatron x-ray emission in laser-plasma accelerators is a promising compact
source that may be an alternative to conventional x-ray sources, based on large
scale machines. In addition to its potential as a source, precise measurements
of betatron emission can reveal crucial information about relativistic
laser-plasma interaction. We show that the emission length and the position of
the x-ray emission can be obtained by placing an aperture mask close to the
source, and by measuring the beam profile of the betatron x-ray radiation far
from the aperture mask. The position of the x-ray emission gives information on
plasma wave breaking and hence on the laser non-linear propagation. Moreover,
the measurement of the longitudinal extension helps one to determine whether
the acceleration is limited by pump depletion or dephasing effects. In the case
of multiple injections, it is used to retrieve unambiguously the position in
the plasma of each injection. This technique is also used to study how, in a
capillary discharge, the variations of the delay between the discharge and the
laser pulse affect the interaction. The study reveals that, for a delay
appropriate for laser guiding, the x-ray emission only occurs in the second
half of the capillary: no electrons are injected and accelerated in the first
half.Comment: 8 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1104.245
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
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
The dynamics of the non-heme iron in bacterial reaction centers from Rhodobacter sphaeroides
AbstractWe investigate the dynamical properties of the non-heme iron (NHFe) in His-tagged photosynthetic bacterial reaction centers (RCs) isolated from Rhodobacter (Rb.) sphaeroides. Mössbauer spectroscopy and nuclear inelastic scattering of synchrotron radiation (NIS) were applied to monitor the arrangement and flexibility of the NHFe binding site. In His-tagged RCs, NHFe was stabilized only in a high spin ferrous state. Its hyperfine parameters (IS=1.06±0.01mm/s and QS=2.12±0.01mm/s), and Debye temperature (θD0~167K) are comparable to those detected for the high spin state of NHFe in non-His-tagged RCs. For the first time, pure vibrational modes characteristic of NHFe in a high spin ferrous state are revealed. The vibrational density of states (DOS) shows some maxima between 22 and 33meV, 33 and 42meV, and 53 and 60meV and a very sharp one at 44.5meV. In addition, we observe a large contribution of vibrational modes at low energies. This iron atom is directly connected to the protein matrix via all its ligands, and it is therefore extremely sensitive to the collective motions of the RC protein core. A comparison of the DOS spectra of His-tagged and non-His-tagged RCs from Rb. sphaeroides shows that in the latter case the spectrum was overlapped by the vibrations of the heme iron of residual cytochrome c2, and a low spin state of NHFe in addition to its high spin one. This enabled us to pin-point vibrations characteristic for the low spin state of NHFe
TRACE ELEMENT BIOACCUMULATION IN THE EDIBLE MILK SNAIL (OTALA LACTEA) AND CABRILLA (OTALA PUNCTATA) IN MARRAKECH, MOROCCO
editorial reviewedMorocco is the first land snail exporter in the world and the majority of snail production consists of individuals collected from nature. These gastropods are known to accumulate high levels of trace metals in their tissues hence the main objective of this study. We aimed firstly to investigate the bioaccumulation efficiency of Pb, Cd, Zn, Cu and Ca in Otala spp. snails, the most commonly widespread and the most consumed species in the Marrakech region, and then evaluate the potential risk on human health. Soil, foot, viscera and shell of adult snails were picked from six sampling stations in Al Haouz plain and analysed by ICP-MS. Results showed that the investigated snails accumulated all the examined elements with significant variations among the different tissues. The Principal Component and Bioaccumulation Factor analyses demonstrated that Otala spp. are macroconcentrators for Cd and microconcentrators for Pb. Furthermore, their shell accumulated more Ca, foot accumulated more Cu and viscera accumulated more Zn, Cd and Pb. In addition, the detected concentrations of toxic metals (Pb and Cd) were higher than the maximum admissible limits according to the European regulation except for Pb in the reference station. In conclusion, Otala spp. snails in our region can be used as bioindicators of trace element bioavailability and their consumption must be limited to avoid any possible intoxications
Long-term follow up of the FL2000 study comparing CHVP-interferon to CHVP-interferon plus rituximab in follicular lymphoma
Supervised learning for the automated transcription of spacer classification from spoligotype films
<p>Abstract</p> <p>Background</p> <p>Molecular genotyping of bacteria has revolutionized the study of tuberculosis epidemiology, yet these established laboratory techniques typically require subjective and laborious interpretation by trained professionals. In the context of a Tuberculosis Case Contact study in The Gambia we used a reverse hybridization laboratory assay called spoligotype analysis. To facilitate processing of spoligotype images we have developed tools and algorithms to automate the classification and transcription of these data directly to a database while allowing for manual editing.</p> <p>Results</p> <p>Features extracted from each of the 1849 spots on a spoligo film were classified using two supervised learning algorithms. A graphical user interface allows manual editing of the classification, before export to a database. The application was tested on ten films of differing quality and the results of the best classifier were compared to expert manual classification, giving a median correct classification rate of 98.1% (inter quartile range: 97.1% to 99.2%), with an automated processing time of less than 1 minute per film.</p> <p>Conclusion</p> <p>The software implementation offers considerable time savings over manual processing whilst allowing expert editing of the automated classification. The automatic upload of the classification to a database reduces the chances of transcription errors.</p
A proposal for multi-tens of GW fully coherent femtosecond soft X-ray lasers
X-ray free-electron lasers1,2 delivering up to 131013 coherent photons in femtosecond pulses are bringing about a revolution in X-ray science3?5. However, some plasma-based soft X-ray lasers6 are attractive because they spontaneously emit an even higher number of photons (131015), but these are emitted in incoherent and long (hundreds of picoseconds) pulses7 as a consequence of the amplification of stochastic incoherent self-emission. Previous experimental attempts to seed such amplifiers with coherent femtosecond soft X-rays resulted in as yet unexplained weak amplification of the seed and strong amplification of incoherent spontaneous emission8. Using a time-dependent Maxwell?Bloch model describing the amplification of both coherent and incoherent soft X-rays in plasma, we explain the observed inefficiency and propose a new amplification scheme based on the seeding of stretched high harmonics using a transposition of chirped pulse amplification to soft X-rays. This scheme is able to deliver 531014 fully coherent soft X-ray photons in 200 fs pulses and with a peak power of 20 GW
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