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Pulse chirping effect on controlling the transverse cavity oscillations in nonlinear bubble regime

Chinese Physics B 2017年第2期26卷 313-319页

作者： H Vosoughian z riazi H Afarideh G Sarri Laser and Optic Institute Nuclear Science and Technology Research Institute Tehran Iran physics and Accelerator School Nuclear Science and Technology Research Institute Tehran Iran Department of Energy Engineering and Physics Amirkabir University of Technology P. O. Box 15875-4413 Tehran Iran School of Mathematics and Physics The Queen's University of Belfast BT7 INN Belfast United Kingdom

The propagation of an intense laser pulse in an under-dense plasma induces a plasma wake that is suitable for the acceleration of electrons to relativistic energies. For an ultra-intense laser pulse which has a longitudinal size shorter than the plasma wavelength, λp, instead of a periodic plasma wave, a cavity free from cold plasma electrons, called a bubble, is formed behind the laser pulse. An intense charge separation electric field inside the moving bubble can capture the electrons at the base of the bubble and accelerate them with a narrow energy spread. In the nonlinear bubble regime, due to localized depletion at the front of the pulse during its propagation through the plasma, the phase shift between carrier waves and pulse envelope plays an important role in plasma response. The carrier–envelope phase（CEP） breaks down the symmetric transverse ponderomotive force of the laser pulse that makes the bubble structure unstable. Our studies using a series of two-dimensional（2D） particle-in-cell（PIC） simulations show that the frequency-chirped laser pulses are more effective in controlling the pulse depletion rate and consequently the effect of the CEP in the bubble regime. The results indicate that the utilization of a positively chirped laser pulse leads to an increase in rate of erosion of the leading edge of the pulse that rapidly results in the formation of a steep intensity gradient at the front of the pulse. A more unstable bubble structure, the self-injections in different positions, and high dark current are the results of using a positively chirped laser pulse. For a negatively chirped laser pulse, the pulse depletion process is compensated during the propagation of the pulse in plasma in such a way that results in a more stable bubble shape and therefore, a localized electron bunch is produced during the acceleration process. As a result, by the proper choice of chirping, one can tune the number of self-injected electrons, the size of accelerated bunch

关键词： bubble regime plasma wake field positively chirped laser pulse

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Investigation of Seismotectonics and Seismicity in South of Caspian Sea

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地学前缘 2009年第S1期16卷 52-53页

作者： z.S.riazi-Rad Chaloos Branch Islami Azad University

In this study region,those fault-lines with northwestern -southeastern trend are the oldest structures of the region,whose formation is believed to date back to orogeny phase of *** the mentioned trend the northwestern southwestern trends also had outcrop in the studied region and recent seismic data indicate that in the studied region the active presence of North Firouzabad transpressional fault-line causes formation of fault scarps and very deep valleys

关键词： seismotectonics seismicity Caspian Sea risk

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Exploring the impact of COVID-19 on the movement behaviors of children and youth:A scoping review of evidence after the first year

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Journal of Sport and Health Science 2021年第6期10卷 675-689页

作者： Derek C.Paterson Katelynn Ramage Sarah A.Moore Negin riazi Mark S.Tremblay Guy Faulkner School of Kinesiology Faculty of EducationUniversity of British ColumbiaVancouverBritish Columbia V6T 1Z4Canada School of Health and Human Performance Dalhousie UniversityHalifaxNova Scotia B3H 4R2Canada Children’s Hospital of Eastern Ontario Research Institute OttawaOntario K1H 5B2Canada Department of Pediatrics University of OttawaOttawaOntario K1N 6N5Canada

Purpose:The objective of this scoping review was to summarize systematically the available literature investigating the relationships between the coronavirus disease 2019(COVID-19)pandemic and movement behaviors(physical activity,sedentary behavior,and sleep)of school-aged children(aged 511 years)and youth(aged 1217 years)in the first year of the COVID-19 ***:Searches for published literature were conducted across 6 databases on 2 separate search dates(November 25,2020,and January 27,2021).Results were screened and extracted by 2 reviewers(DCP and KR)independently,using *** numeric analysis and content analysis were undertaken to present thematically the findings of included studies according to the associated impact on each movement ***:A total of 1486 records were extracted from database searches;of those,150 met inclusion criteria and were included for *** 150 articles,110 were empirical studies examining physical activity(n=77),sedentary behavior/screen time(n=58),and sleep(n=55).Results consistently reported declines in physical-activity time,increases in screen time and total sedentary behavior,shifts to later bed and wake times,and increases in sleep *** reported impacts on movement behaviors were greater for youth than for ***:The COVID-19 pandemic is related to changes in the quantity and nature of physical activity,sedentary behavior,and sleep among children and *** is an urgent need for policy makers,practitioners,and researchers to develop solutions for attenuating adverse changes in physical activity and screen time among children and youth.

关键词： Pandemic Physical activity Screen time Sedentary Sleep

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