Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Gamma-ray bursts (GRB's), short and intense pulses of low-energy $\ensuremath{\gamma}$ rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last decade, several space missions---BATSE (Burst and Transient Source Experiment) on the Compton Gamma-Ray Observatory, BeppoSAX and now HETE II (High-Energy Transient Explorer)---together with ground-based optical, infrared, and radio observatories have revolutionized our understanding of GRB's, showing that they are cosmological, that they are accompanied by long-lasting afterglows, and that they are associated with core-collapse supernovae. At the same time a theoretical understanding has emerged in the form of the fireball internal-external shocks model. According to this model GRB's are produced when the kinetic energy of an ultrarelativistic flow is dissipated in internal collisions. The afterglow arises when the flow is slowed down by shocks with the surrounding circumburst matter. This model has had numerous successful predictions, like the predictions of the afterglow itself, of jet breaks in the afterglow light curve, and of the optical flash that accompanies the GRB's. This review focuses on the current theoretical understanding of the physical processes believed to take place in GRB's.

/pdf/the-physics-of-gamma-ray-bursts-2v7vwfzv9l.pdf

The physics of gamma-ray bursts

Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV m-1 (refs 1–3) These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators4,5 as compact next-generation sources of energetic electrons and radiation To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread1,2,3, which limits potential applications Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 109 electrons above 80 MeV) Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance The results open the way for compact and tunable high-brightness sources of electrons and radiation

https://escholarship.org/content/qt9c55r46s/qt9c55r46s.pdf?t=lnras5

High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding

Submitted for the DPP06 Meeting of The American Physical Society Generating Multi-GeV Electron Bunches Using Laser Wakefield Acceleration in the Blowout Regime WARREN B. MORI, WEI LU, MICHAIL TZOUFRAS, FRANK TSUNG, CHAN. JOSHI, UCLA, JORGE VIEIRA, RICARDO FONSECA, LUIS SILVA, IST, UCLA TEAM, IST TEAM — The extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than in current accelerators has been well documented. We show here that 100TW to 2000TW class lasers can excite large amplitude wakefields and be stably self-guided in very underdense plasmas to produce 1 to 10 GeV mono-energetic, self-injected electron beams with nCs of charge. For such powers the plasma wakes can be excited by the nearly complete blowout, i.e., expulsion, of plasma electrons by the radiation pressure of a short pulse laser. The proposed regime is distinct from the “bubble regime” in that it advocates using lower densities and wider spot sizes while keeping the intensity relatively constant in order to increase the output electron beam energy and keep the efficiency high. Our theoretical results are verified by three-dimensional particle-in-cell simulations.

/pdf/generating-multi-gev-electron-bunches-using-laser-wakefield-1jnnzb2xfu.pdf

Generating Multi-GeV Electron Bunches Using Laser Wakefield Acceleration in the Blowout Regime

A new method of controllable injection to generate high quality electron bunches in the nonlinear blowout regime driven by electron beams is proposed and demonstrated using particle-in-cell simulations. Injection is facilitated by decreasing the wake phase velocity through varying the spot size of the drive beam and can be tuned through the Courant-Snyder (CS) parameters. Two regimes are examined. In the first, the spot size is focused according to the vacuum CS beta function, while in the second, it is focused by the plasma ion column. The effects of the driver intensity and vacuum CS parameters on the wake velocity and injected beam parameters are examined via theory and simulations. For plasma densities of $\ensuremath{\sim}1{0}^{19}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$, particle-in-cell simulations demonstrate that peak normalized brightnesses $\ensuremath{\gtrsim}1{0}^{20}\text{ }\text{ }\mathrm{A}/{\mathrm{m}}^{2}/{\mathrm{rad}}^{2}$ can be obtained with projected energy spreads of $\ensuremath{\lesssim}1%$ within the middle section of the injected beam, and with normalized slice emittances as low as $\ensuremath{\sim}10\text{ }\text{ }\mathrm{nm}$.

https://link.aps.org/pdf/10.1103/PhysRevAccelBeams.23.021304

Generating high quality ultrarelativistic electron beams using an evolving electron beam driver

Boosted Frame PIC Simulations of LWFA: Towards the Energy Frontier

Studies of particle wake potentials in plasmas

A systematic investigation of the longitudinal fields excited in a plasma by a short, dense beam of positrons is carried out using two-dimensional, cylindrical geometry, particle-in-cell code simulations. In particular, we examine the behavior of the accelerating and decelerating fields of the wakefield as a function of beam charge, radius, length, and plasma density. The parameters are chosen to be consistent with those employed in current and future experiments designed to elucidate the physics of positron beam‐plasma interactions.

/pdf/parametric-exploration-of-intense-positron-beam-plasma-267fic0pgu.pdf

Warren Mori

Papers

Generating Multi-GeV Electron Bunches Using Laser Wakefield Acceleration in the Blowout Regime

Generating high quality ultrarelativistic electron beams using an evolving electron beam driver

Boosted Frame PIC Simulations of LWFA: Towards the Energy Frontier

Studies of particle wake potentials in plasmas

Parametric exploration of intense positron beam–plasma interactions