175 research outputs found
Quasimonoenergetic electron beams produced by colliding cross-polarized laser pulses in underdense plasmas
The interaction of two laser pulses in an underdense plasma has proven to be
able to inject electrons in plasma waves, thus providing a stable and tunable
source of electrons. Whereas previous works focused on the "beatwave" injection
scheme in which two lasers with the same polarization collide in a plasma, this
present letter studies the effect of polarization and more specifically the
interaction of two colliding cross-polarized laser pulses. It is shown both
theoretically and experimentally that electrons can also be pre-accelerated and
injected by the stochastic heating occurring at the collision of two
cross-polarized lasers and thus, a new regime of optical injection is
demonstrated. It is found that injection with cross-polarized lasers occurs at
higher laser intensities.Comment: 4 pages, 4 figure
Modeling terahertz emissions from energetic electrons and ions in foil targets irradiated by ultraintense femtosecond laser pulses
Terahertz (THz) emissions from fast electron and ion currents driven in
relativistic, femtosecond laser-foil interactions are examined theoretically.
We first consider the radiation from the energetic electrons exiting the
backside of the target. Our kinetic model takes account of the coherent
transition radiation due to these electrons crossing the plasma-vacuum
interface as well as of the synchrotron radiation due to their deflection and
deceleration in the sheath field they set up in vacuum. After showing that both
mechanisms tend to largely compensate each other when all the electrons are
pulled back into the target, we investigate the scaling of the net radiation
with the sheath field strength. We then demonstrate the sensitivity of this
radiation to a percent-level fraction of escaping electrons. We also study the
influence of the target thickness and laser focusing. The same sheath field
that confines most of the fast electrons around the target rapidly sets into
motion the surface ions. We describe the THz emission from these accelerated
ions and their accompanying hot electrons by means of a plasma expansion model
that allows for finite foil size and multidimensional effects. Again, we
explore the dependencies of this radiation mechanism on the laser-target
parameters. Under conditions typical of current ultrashort laser-solid
experiments, we find that the THz radiation from the expanding plasma is much
less energetic -- by one to three orders of magnitude -- than that due to the
early-time motion of the fast electrons
Angular momentum evolution in laser-plasma accelerators
The transverse properties of an electron beam are characterized by two
quantities, the emittance which indicates the electron beam extend in the phase
space and the angular momentum which allows for non-planar electron
trajectories. Whereas the emittance of electron beams produced in laser- plasma
accelerator has been measured in several experiments, their angular momentum
has been scarcely studied. It was demonstrated that electrons in laser-plasma
accelerator carry some angular momentum, but its origin was not established.
Here we identify one source of angular momentum growth and we present
experimental results showing that the angular momentum content evolves during
the acceleration
Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime
Electron self-injection and acceleration until dephasing in the blowout
regime is studied for a set of initial conditions typical of recent experiments
with 100 terawatt-class lasers. Two different approaches to computationally
efficient, fully explicit, three-dimensional particle-in-cell modelling are
examined. First, the Cartesian code VORPAL using a perfect-dispersion
electromagnetic solver precisely describes the laser pulse and bubble dynamics,
taking advantage of coarser resolution in the propagation direction, with a
proportionally larger time step. Using third-order splines for macroparticles
helps suppress the sampling noise while keeping the usage of computational
resources modest. The second way to reduce the simulation load is using
reduced-geometry codes. In our case, the quasi-cylindrical code CALDER-CIRC
uses decomposition of fields and currents into a set of poloidal modes, while
the macroparticles move in the Cartesian 3D space. Cylindrical symmetry of the
interaction allows using just two modes, reducing the computational load to
roughly that of a planar Cartesian simulation while preserving the 3D nature of
the interaction. This significant economy of resources allows using fine
resolution in the direction of propagation and a small time step, making
numerical dispersion vanishingly small, together with a large number of
particles per cell, enabling good particle statistics. Quantitative agreement
of the two simulations indicates that they are free of numerical artefacts.
Both approaches thus retrieve physically correct evolution of the plasma
bubble, recovering the intrinsic connection of electron self-injection to the
nonlinear optical evolution of the driver
Observation of beam loading in a laser-plasma accelerator
Beam loading is the phenomenon which limits the charge and the beam quality
in plasma based accelerators. An experimental study conducted with a
laser-plasma accelerator is presented. Beam loading manifests itself through
the decrease of the beam energy, the reduction of dark current and the increase
of the energy spread for large beam charge. 3D PIC simulations are compared to
the experimental results and confirm the effects of beam loading. It is found
that, in our experimental conditions, the trapped electron beams generate
decelerating fields on the order of 1 GV/m/pC and that beam loading effects are
optimized for trapped charges of about 20 pC.Comment: 10 pages,4 figure
Application des recommandations dans la prise en charge du cancer de l’endomètre en pratique clinique. Étude rétrospective bretonne
National audienceObjective - To assess the use of French Cancer Institute recommendations for the diagnosis and treatment of endometrial cancer. Methods - Retrospective observational study involving 137Â patients with endometrial cancer between 2011 and 2013. Results - Both MRI and pathological assessment with correct report as recommended were used for 66.4% of patients with endometrial cancer. For patients with correct preoperative assessment, 44.9% of patients were uncorrectly classified and upgraded on final pathological analysis of hysterectomy concerning lymph node involvement risk. These patients did not have confident surgical assessment, according this risk. Conclusion - To improve relevance of preoperative assessment in endometrial cancer, radiological and pathological expertise is required. However, even performed optimally, preoperative assessment does not allow correct risk stratification of lymph node involvement in endometrial cancer. This ineffective stratification leads to propose sentinel lymph node biopsy with hysterectomy in case of preoperative low risk endometrial cancer assessment
Les immunothérapies spécifiques dans le traitement des cancers
The offer of anti-cancer drugs has recently been disrupted by the introduction of checkpoint inhibitors on the market. Currently, one anti-CTLA-4, two anti-PD-1 and two anti-PD-L1 are authorized in the European Union, in seven different types of cancer. The clinical development of these therapies is still in full swing: in July 2017, more than 1 500 clinical trials were evaluating anti-PD-1, anti-PD-L1 and anti-CTLA-4 drugs in about twenty different locations and this number continues to increase. In the short term in France, other immunotherapies, the CAR-T cells, will complete this therapeutic arsenal. These immunotherapies appear as a real revolution in the treatment of some cancers. Nevertheless, many issues are associated with these therapies, particularly regarding the identification of good responders, the proper use of these drugs including the management of therapeutic strategies and safety profile, as well as the organization of care. In addition, the expenses associated with ipilimumab, nivolumab and pembrolizumab are substantial and almost tripled in one year, going from 120Â million euros in 2015 to more than 340Â million euros in 2016. This raises the question of the ability of the current healthcare system to maintain equitable access to innovation and best treatments for all patients. For all these reasons, the French National Cancer Institute decided to dedicate its thematic annual report on these innovative immunotherapies, targeting in particular checkpoint inhibitors and CAR-T cells, in order to produce an inventory of current data and an analysis regarding the different issues associated with these therapies
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Linking institutional context to the community and career embeddedness of skilled migrants: The role of destination- and origin-country identifications
Supplementary Information is available online at: https://link-springer-com.ezproxytest.brunel.ac.uk/article/10.1057/s41267-024-00683-w#Sec140 .Migration is one of the most pressing global issues of our time. However, relatively little is known about the factors and mechanisms that govern the post-migration experiences of skilled migrants. We adopt an acculturation- and social identity-based approach to examine how differences between institutional characteristics in the destination and origin country, as well as migrants’ experiences with formal and informal institutions shape their identification with the destination and origin country and contribute to their community and career embeddedness. Our study of 1709 highly skilled migrants from 48 origin countries in 12 destination countries reveals that the institutional environment migrants encounter provides both sources of opportunity (potential for human development and value-congruent societal practices) and sources of disadvantage (experienced ethnocentrism and downgrading). These contrasting dynamics affect migrants’ destination-country identification, their origin-country identification and, ultimately, their embeddedness in the destination country. Our results have important implications for multinational enterprises and policy makers that can contribute to enhancing skilled migrants’ community and career embeddedness. For example, these actors may nurture a work environment and provide supportive policies that buffer against the institutional sources of disadvantage we identified in this study, while helping migrants to leverage the opportunities available in the destination country.Open access funding provided by Vienna University of Economics and Business (WU).. Sebastian Reiche gratefully acknowledges the support from the Ministerio de Ciencia e Innovación, grant ECO2015-68272-P funded by MCIN/AEI/https://doi-org.ezproxytest.brunel.ac.uk/10.13039/501100011033, and by “ERDF A way of making Europe”, by the European Union. Mila Lazarova acknowledges the support of the Canada Research Chairs Program. Lena Zander would like to gratefully acknowledge Jan Wallanders och Tom Hedelius stiftelse and Tore Browaldhs stiftelse, Sweden, for financially supporting her research project (P17-0117) and the workshop organized at Sigtuna Folkhögskola for the research team in June, 2022. Eric Davoine gratefully acknowledges the NCCR LIVES for their financial support
Loss of paraplegin drives spasticity rather than ataxia in a cohort of 241 patients with SPG7
Objective : We took advantage of a large multinational recruitment to delineate genotype-phenotype correlations in a large, trans-European multicenter cohort of patients with spastic paraplegia gene 7 (SPG7).
Methods : We analyzed clinical and genetic data from 241 patients with SPG7, integrating neurologic follow-up data. One case was examined neuropathologically.
Results : Patients with SPG7 had a mean age of 35.5 +/- 14.3 years (n = 233) at onset and presented with spasticity (n = 89), ataxia (n = 74), or both (n = 45). At the first visit, patients with a longer disease duration (> 20 years, n = 62) showed more cerebellar dysarthria (p < 0.05), deep sensory loss (p < 0.01), muscle wasting (p < 0.01), ophthalmoplegia (p < 0.05), and sphincter dysfunction (p < 0.05) than those with a shorter duration (< 10 years, n = 93). Progression, measured by Scale for the Assessment and Rating of Ataxia evaluations, showed a mean annual increase of 1.0 +/- 1.4 points in a subgroup of 30 patients. Patients homozygous for loss of function (LOF) variants (n = 65) presented significantly more often with pyramidal signs (p < 0.05), diminished visual acuity due to optic atrophy (p < 0.0001), and deep sensory loss (p < 0.0001) than those with at least 1 missense variant (n = 176). Patients with at least 1 Ala510Val variant (58%) were older (age 37.6 +/- 13.7 vs 32.8 +/- 14.6 years, p < 0.05) and showed ataxia at onset (p < 0.05). Neuropathologic examination revealed reduction of the pyramidal tract in the medulla oblongata and moderate loss of Purkinje cells and substantia nigra neurons.
Conclusions : This is the largest SPG7 cohort study to date and shows a spasticity-predominant phenotype of LOF variants and more frequent cerebellar ataxia and later onset in patients carrying at least 1 Ala510Val variant
The LUNEX5 project
http://accelconf.web.cern.ch/AccelConf/FEL2012/papers/froa03.pdfInternational audienceLUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. The project consists of a Free Electron Laser (FEL) line enabling the most advanced seeding configurations: High order Harmonic in Gas (HHG) seeding and Echo Enable Harmonic Generation (EEHG) with in-vacuum (potentially cryogenic) undulators of 15 and 30 mm period. Two accelerator types feed this FEL line : a 400 MeV Conventional Linear Accelerator (CLA) using superconducting cavities compatible with a future upgrade towards high repetition rate, for the investigations of the advanced FEL schemes; and a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA), to be qualified in view of FEL application, in the single spike or seeded regime. Two pilot user experiments for timeresolved studies of isolated species and solid state matter dynamics will take benefit of LUNEX5 FEL radiation and provide feedback of the performance of the different schemes under real user conditions
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