Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam

The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration (μ 500 MeV) with an intense laser pulse (a0>10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy >30 MeV

General features of experiments on the dynamics of laser-driven electron–positron beams

The experimental study of the dynamics of neutral electron–positron beams is an emerging area of research, enabled by the recent results on the generation of this exotic state of matter in the laboratory. Electron–positron beams and plasmas are believed to play a major role in the dynamics of extreme astrophysical objects such as supermassive black holes and pulsars. For instance, they are believed to be the main constituents of a large number of astrophysical jets, and they have been proposed to significantly contribute to the emission of gamma-ray bursts and their afterglow. However, despite extensive numerical modelling and indirect astrophysical observations, a detailed experimental characterisation of the dynamics of these objects is still at its infancy. Here, we will report on some of the general features of experiments studying the dynamics of electron–positron beams in a fully laser-driven setup

Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (>= 1 T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of epsilon(B) approximate to 10(-3) is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets

Experimental signatures of the quantum nature of radiation reaction in the field of an ultraintense laser

The motion of an electron in an external field of arbitrary intensity is one of the most fundamental outstanding problems in electrodynamics. Remarkably, there is no unanimously accepted theoretical solution for high intensities and little or no experimental data to date. The basic challenge is the inclusion of the self-interaction of the electron with the fields emitted by the electron itself -- the so-called radiation reaction (RR). As is well known, solutions exist for specific parameter ranges. At low field-strength, where RR is negligible, the equation of motion is the well-known Lorentz equation. At higher field-strength in the classical limit the Landau-Lifshitz equation is the accepted solution. For the strongest fields a full quantum description is required and this is currently the subject of active research. We report on the first experimental evidence of strong radiation reaction during the interaction of a relativistic electron beam with an intense laser field

A spectrometer for ultrashort gamma-ray pulses with photon energies greater than 10 MeV

We present a design for a pixelated scintillator based gamma-ray spectrometer for non-linear inverse Compton scattering experiments. By colliding a laser wakefield accelerated electron beam with a tightly focused, intense laser pulse, gamma-ray photons up to 100 MeV energies and with few femtosecond duration may be produced. To measure the energy spectrum and angular distribution, a 33 × 47 array of cesium-iodide crystals was oriented such that the 47 crystal length axis was parallel to the gamma-ray beam and the 33 crystal length axis was oriented in the vertical direction. Using an iterative deconvolution method similar to the YOGI code, modeling of the scintillator response using GEANT4 and fitting to a quantum Monte Carlo calculated photon spectrum, we are able to extract the gamma ray spectra generated by the inverse Compton interaction

Feline low-grade alimentary lymphoma: an emerging entity and a potential animal model for human disease

Background: Low-grade alimentary lymphoma (LGAL) is characterised by the infiltration of neoplastic T-lymphocytes, typically in the small intestine. The incidence of LGAL has increased over the last ten years and it is now the most frequent digestive neoplasia in cats and comprises 60 to 75% of gastrointestinal lymphoma cases. Given that LGAL shares common clinical, paraclinical and ultrasonographic features with inflammatory bowel diseases, establishing a diagnosis is challenging. A review was designed to summarise current knowledge of the pathogenesis, diagnosis, prognosis and treatment of feline LGAL. Electronic searches of PubMed and Science Direct were carried out without date or language restrictions. Results: A total of 176 peer-reviewed documents were identified and most of which were published in the last twenty years. 130 studies were found from the veterinary literature and 46 from the human medicine literature. Heterogeneity of study designs and outcome measures made meta-analysis inappropriate. The pathophysiology of feline LGAL still needs to be elucidated, not least the putative roles of infectious agents, environmental factors as well as genetic events. The most common therapeutic strategy is combination treatment with prednisolone and chlorambucil, and prolonged remission can often be achieved. Developments in immunohistochemical analysis and clonality testing have improved the confidence of clinicians in obtaining a correct diagnosis between LGAL and IBD. The condition shares similarities with some diseases in humans, especially human indolent T-cell lymphoproliferative disorder of the gastrointestinal tract. Conclusions: The pathophysiology of feline LGAL still needs to be elucidated and prospective studies as well as standardisation of therapeutic strategies are needed. A combination of conventional histopathology and immunohistochemistry remains the current gold-standard test, but clinicians should be cautious about reclassifying cats previously diagnosed with IBD to lymphoma on the basis of clonality testing. Importantly, feline LGAL could be considered to be a potential animal model for indolent digestive T-cell lymphoproliferative disorder, a rare condition in human medicine

Inégalité de revenu et état de santé : une relation ambiguë

Au cours de ces dernières années, de nombreux chercheurs issus de divers domaines des sciences sociales ont posé l'existence d'une relation entre inégalité de revenu et état de santé, l’ont examiné dans des études empiriques et ont commencé à proposer des applications de politiques. Cependant, de nombreuses ambiguïtés persistent et, par conséquent, personne ne sait comment cette relation fonctionne réellement. Dans ce cadre, ce bref article se propose d'enquêter sur ce qui est connu à ce jour sur la relation entre inégalité de revenu et état de santé et offre des suggestions quant à la façon de produire davantage de santé.inégalité de revenu, santé

Impact of COVID-19 pandemic on the health-related quality of life of frontline workers: the case of seven low-income Eastern African countries

Abstract Purpose This study aimed to explore the potential impact of the COVID-19 pandemic on the health-related quality of life (HRQoL) of humanitarian and healthcare workers and its related factors in seven Eastern African countries (EAC). Methods A sample of frontline workers filled out an online cross-sectional survey questionnaire comprising socio-demographic, degree of symptoms of depression, anxiety, insomnia, and distress, alcohol and tobacco consumption, health-related quality of life (HRQoL) using Short Form 6-Dimension version 2 (SF-6Dv2) and Clinical Outcomes in Routine Evaluation 6-Dimension (CORE-6D), and fear of COVID-19 (FCV-19S) questionnaires. Multivariate regressions were conducted to identify independent factors associated with HRQoL. Results Of total 721 study participants, mean (standard deviation) scores for SF-6Dv2 and CORE-6D were 0.87 (0.18) and 0.81 (0.14), respectively. Participants with an education level below a university degree, having chronic diseases, been tested positive to COVID-19, with traumatic memories, depression, insomnia, distress, and stress were found to have lower HRQoL likelihood in terms of SF-6Dv2 scores during the COVID-19 pandemic. Similarly, participants with chronic diseases, exposure to COVID-19 patients, depression, insomnia, distress, stress, tested positive with COVID-19, and high level of fear of COVID-19, had lower HRQoL likelihood in terms of CORE-6D scores. Participants who were married had higher HRQoL likelihoods in terms of SF-6Dv2 scores. Conclusion Some personal and mental health characteristics, and COVID-19 related factors, were predictors of lower HRQoL of frontline workers in EAC. These findings should be meaningful while designing sustainable interventions and guidelines aiming to improve the HRQoL of frontline workers during a pandemic situation