Although several laser-plasma-based methods have been proposed for generating energetic electrons, positrons and γ-photons, manipulation of their microstructures is still challenging, and their ...angular momentum control has not yet been achieved. Here, we present and numerically demonstrate an all-optical scheme to generate bright GeV γ-photon and positron beams with controllable angular momentum by use of two counter-propagating circularly-polarized lasers in a near-critical-density plasma. The plasma acts as a 'switching medium', where the trapped electrons first obtain angular momentum from the drive laser pulse and then transfer it to the γ-photons via nonlinear Compton scattering. Further through the multiphoton Breit-Wheeler process, dense energetic positron beams are efficiently generated, whose angular momentum can be well controlled by laser-plasma interactions. This opens up a promising and feasible way to produce ultra-bright GeV γ-photons and positron beams with desirable angular momentum for a wide range of scientific research and applications.
Abstract
Astrophysical jets are ubiquitous in the universe and often associated with compact objects, and their interactions with the ambient medium not only dissipate their own energy but also ...provide ideal circumstances for particle acceleration. By means of theoretical analysis and particle-in-cell simulations, here we study the ion acoustic shock wave (IASW) formation and consequent ion acceleration when electron–positron (
e
−
e
+
) jets are injected into ambient electron–ion plasmas. It is found that the Buneman instability can be excited first, which induces the formation of an ion acoustic wave (IAW). As the amplitude of the IAW increases, its waveform is steepened and subsequently an IASW is formed. Some ions in the ambient plasmas will be reflected when they encounter the IASW, and thus can be accelerated to form an energetic ion beam. For an initial
e
−
e
+
jet with the Lorentz factor
γ
0
= 100 and the ion–electron mass ratio
m
i
/
m
e
= 1836, the ions can be accelerated up to 580 MeV. This study deepens our understanding of the fireball model of gamma-ray bursts, the shock model of pulsar wind nebulae, the origin of cosmic rays, and other related astrophysical processes.
Ultrashort intense optical pulses in the mid-infrared (mid-IR) region are very important for broad applications ranging from super-resolution spectroscopy to attosecond X-ray pulse generation and ...particle acceleration. However, currently, it is still difficult to produce few-cycle mid-IR pulses of relativistic intensities using standard optical techniques. Here, we propose and numerically demonstrate a novel scheme to produce these mid-IR pulses based on laser-driven plasma optical modulation. In this scheme, a plasma wake is first excited by an intense drive laser pulse in an underdense plasma, and a signal laser pulse initially at the same wavelength (1 micron) as that of the drive laser is subsequently injected into the plasma wake. The signal pulse is converted to a relativistic multi-millijoule near-single-cycle mid-IR pulse with a central wavelength of ~5 microns via frequency-downshifting, where the energy conversion efficiency is as high as approximately 30% when the drive and signal laser pulses are both at a few tens of millijoules at the beginning. Our scheme can be realized with terawatt-class kHz laser systems, which may bring new opportunities in high-field physics and ultrafast science.
Optical modulators can have high modulation speed and broad bandwidth, while being compact. However, these optical modulators usually work for low-intensity light beams. Here we present an ultrafast, ...plasma-based optical modulator, which can directly modulate high-power lasers with intensity up to 10(16) W cm(-2) to produce an extremely broad spectrum with a fractional bandwidth over 100%, extending to the mid-infrared regime in the low-frequency side. This concept relies on two co-propagating laser pulses in a sub-millimetre-scale underdense plasma, where a drive laser pulse first excites an electron plasma wave in its wake while a following carrier laser pulse is modulated by the plasma wave. The laser and plasma parameters suitable for the modulator to work are based on numerical simulations.
Relativistic positron sources with high spin polarization have important applications in nuclear and particle physics and many frontier fields. However, it is challenging to produce dense polarized ...positrons. Here we present a simple and effective method to achieve such a positron source by directly impinging a relativistic high-density electron beam on the surface of a solid target. During the interaction, a strong return current of plasma electrons is induced and subsequently asymmetric quasistatic magnetic fields as high as megatesla are generated along the target surface. This gives rise to strong radiative spin flips and multiphoton processes, thus leading to efficient generation of copious polarized positrons. With three-dimensional particle-in-cell simulations, we demonstrate the production of a dense highly polarized multi-GeV positron beam with an average spin polarization above 40% and nC-scale charge per shot. This offers a novel route for the studies of laserless strong-field quantum electrodynamics physics and for the development of high-energy polarized positron sources.Relativistic positron sources with high spin polarization have important applications in nuclear and particle physics and many frontier fields. However, it is challenging to produce dense polarized positrons. Here we present a simple and effective method to achieve such a positron source by directly impinging a relativistic high-density electron beam on the surface of a solid target. During the interaction, a strong return current of plasma electrons is induced and subsequently asymmetric quasistatic magnetic fields as high as megatesla are generated along the target surface. This gives rise to strong radiative spin flips and multiphoton processes, thus leading to efficient generation of copious polarized positrons. With three-dimensional particle-in-cell simulations, we demonstrate the production of a dense highly polarized multi-GeV positron beam with an average spin polarization above 40% and nC-scale charge per shot. This offers a novel route for the studies of laserless strong-field quantum electrodynamics physics and for the development of high-energy polarized positron sources.
Idiopathic granulomatous mastitis (IGM) is a rare and benign inflammatory breast disease with ambiguous aetiology. Contrastingly, lactational mastitis (LM) is commonly diagnosed in breastfeeding ...women. To investigate IGM aetiology, we profiled the microbial flora of pus and skin in patients with IGM and LM. A total of 26 patients with IGM and 6 patients with LM were included in the study. The 16S rRNA sequencing libraries were constructed from 16S rRNA gene amplified from total DNA extracted from pus and skin swabs in patients with IGM and LM controls. Constructed libraries were multiplexed and paired-end sequenced on HiSeq4000. Metagenomic analysis was conducted using modified microbiome abundance analysis suite customised R-resource for paired pus and skin samples. Microbiome multivariable association analyses were performed using linear models. A total of 21 IGM and 3 LM paired pus and skin samples underwent metagenomic analysis. Bray−Curtis ecological dissimilarity distance showed dissimilarity across four sample types (IGM pus, IGM skin, LM pus, and LM skin; PERMANOVA, p < 0.001). No characteristic dominant genus was observed across the IGM samples. The IGM pus samples were more diverse than corresponding IGM skin samples (Shannon and Simpson index; Wilcoxon paired signed-rank tests, p = 0.022 and p = 0.07). Corynebacterium kroppenstedtii, reportedly associated with IGM in the literature, was higher in IGM pus samples than paired skin samples (Wilcoxon, p = 0.022). Three other species and nineteen genera were statistically significant in paired IGM pus−skin comparison after antibiotic treatment adjustment and multiple comparisons correction. Microbial profiles are unique between patients with IGM and LM. Inter-patient variability and polymicrobial IGM pus samples cannot implicate specific genus or species as an infectious cause for IGM.
Los casos de COVID-19 siguen aumentando rápidamente en muchos países a pesar de la vacunación. La mejor forma de combatirlo es la protección personal. En este estudio desarrollamos un juego serio de ...la web (WSG-COVID-19.SP) para promover las estrategias de aprendizaje para protegerse contra el COVID-19. También probamos la validez y usabilidad del sistema. WSG-COVID-19.SP fue desarrollado de acuerdo a la teoría situada de aprendizaje y retroalimentación diagnóstica. Contiene seis historias con 17 objetivos de aprendizaje. Se usa un enfoque de resolución de problemas para promover el uso de mascarillas, lavado de manos y distanciamiento social. Se usó el análisis de portafolio para identificar los problemas y el proceso de aprendizaje. El índice global de validez de contenido de la escala (S-CVI) fue utilizado para evaluar su eficacia. La usabilidad fue probada mediante una encuesta de web de 71 estudiantes de una universidad para evaluar su aceptación tecnológica y la capacidad del juego para promover la protección personal. El S-CVI era 0,81. La usabilidad y aceptabilidad no correspondían con la especialización del usuario (ya sea que esté relacionada con la tecnología de la información) ni con el género. Un 84,5% de los usuarios quería continuar la práctica porque estaban motivados por los resultados diagnósticos. WSG-COVID-19.SP exhibe un contenido válido y una alta satisfacción del usuario. The number of new COVID-19 cases continues to rise rapidly in many countries despite vaccination. The best way to counter the spread of COVID-19 is self-protection. This study documents the development of a web-based serious game (WSG-COVID-19.SP) to promote effective learning strategies for self-protection against COVID-19 and to test the game's content validity and usability. WSG-COVID-19.SP was developed using situated learning theory and diagnostic feedback mechanism. The game includes six situation storylines with 17 learning objectives. It uses a problem-solving approach to foster practices such as wearing masks, washing hands, and social distancing. Portfolio analysis was used to diagnose learning problems and report on the learning process. An overall summary index--the scale-level content validity index (S-CVI)--was used to evaluate content validity. Usability was tested through a website survey from 71 students from one university to gauge their technological acceptance and the game's capability to promote future self-protection behaviors. The S-CVI was 0.81. Usability and acceptability were neither related to the users' college major (whether it is information technology-related) nor to gender. Among the respondents, 84.5% agreed to continue with the self-protection practice as they were motivated by the real-time diagnostic function. The WSG-COVID-19.SP game system has adequate content validity and a high user satisfaction rating. PALABRAS CLAVE | KEYWORDS COVID-19, juegos serios, usabilidad, escenario interactivo, aprendizaje basado en la situación, protección personal. COVID-19, serious game, usability, interactive scenario, situated-based learning, self-protection.
PDF
