Search

We show that for collisions of electrons with a high-intensity laser, discrete photon emissions introduce a transverse beam spread which is distinct from that due to classical (or beam shape) effects. Via numerical simulations, we show that this quantum induced transverse momentum gain of the electron is manifest in collisions with a realistic laser pulse of intensity within reach of current technology, and we propose it as a measurable signature of strong-field quantum electrodynamics., Comment: 5 pages, 3 figures. Accepted for publication in Physical Review Letters

We demonstrate that charged particles in a sufficiently intense standing wave are compressed toward, and oscillate synchronously at, the maxima of the electric field. This unusual trapping behaviour, which we call 'anomalous radiative trapping' (ART), opens up new possibilities for the generation of radiation and particle beams, both of which are high-energy, directed and collimated. ART also provides a mechanism for particle control in high-intensity QED experiments., Comment: 5 pages, 5 pdf figures. Version 2: extended discussion of particle trajectories, references added

We study nonperturbative pair production in intense, focused laser fields called e-dipole pulses. We address the conditions required, such as the quality of the vacuum, for reaching high intensities without initiating beam-depleting cascades, the number of pairs which can be created, and experimental detection of the created pairs. We find that e-dipole pulses offer an optimal method of investigating nonperturbative QED., Comment: 5 pages, 2 pdf figures. Version 2: extended discussion of cascades, references updated. To appear in PRL

We discuss radiation reaction effects on charges propagating in ultra-intense laser fields. Our analysis is based on an analytic solution of the Landau-Lifshitz equation. We suggest to measure radiation reaction in terms of a symmetry breaking parameter associated with the violation of null translation invariance in the direction opposite to the laser beam. As the Landau-Lifshitz equation is nonlinear the energy transfer within the pulse is rather sensitive to initial conditions. This is elucidated by comparing colliding and fixed target modes in electron laser collisions., Comment: 8 pages, 6 figures

We develop a numerical formulation to calculate the classical motion of charges in strong electromagnetic fields, such as those occurring in high-intensity laser beams. By reformulating the dynamics in terms of SL(2,C) matrices representing the Lorentz group, our formulation maintains explicit covariance, in particular the mass-shell condition. Considering an electromagnetic plane wave field where the analytic solution is known as a test case, we demonstrate the effectiveness of the method for solving both the Lorentz force and the Landau-Lifshitz equations. The latter, a second order reduction of the Lorentz-Abraham-Dirac equation, describes radiation reaction without the usual pathologies., Comment: 21 pages, 6 figures

We investigate existence and linear stability of coupled vortex solitons supported by cascaded four-wave mixing in a Raman active medium excited away from the resonance. We present a detailed analysis for the two- and three-component vortex solitons and demonstrate the formation of stable and unstable vortex solitons, and associated spatio-temporal helical beams, under the conditions of the simultaneous frequency and vortex comb generation., Comment: 8 pages, 10 figures, to be published in Phys. Rev. A

This brief article uses a question and answer format to review basic information about medical management of children with attention deficit disorders (ADD). Questions address: characteristics of ADD; how parents and teachers can tell if a child might have ADD; types of services and programs which help these children and their families; medications prescribed for ADD children; how psychostimulants appear to help ADD children; common side effects of psychostimulant medications; the use of tricyclic antidepressants in treating ADD; side effects of tricyclic antidepressant medications; ADD children who do not respond well to medication; dispensing of medications at school to an ADD child; monitoring of effectiveness of medications and other treatments; the role of the ADD child's teacher; and refutations of common myths associated with ADD medications. (DB)

Little has been written about the practical considerations for reforming schools from the inside. This booklet explores how people responsible for schools can develop better relationships, new forms of colleagueship, and new ways of working together more productively. Three aphorisms describe the phenomenon of faculty-led school improvement: (1) taking a trip without a roadmap; (2) rebuilding the airplane while in flight; and (3) rediscovering the "if it's not local, it's not real" adage. To restructure education effectively, educators must foster the dynamics of group functioning and build an environment in which research-proven teaching methodologies promoting positive student interaction can flourish. Cooperation and collaboration are often hampered when groups of teachers and students are asked to work together without using group building activities, which incorporate heterogeneous grouping, positive interdependence, group reward, and individual accountability. Four chapters discuss specific group builders to enhance positive interactions between administrators and teachers, among teachers, and among both younger and older students. The last chapter discusses approaches to assessing the outcomes of the interactive process. Numerous sources for group-building activities are included, along with a selected bibliography of 35 references. (MLH)