SIMLA: Simulating laser-particle interactions via classical and quantum electrodynamics

We present the Fortran code SIMLA, which is designed for the study of charged particle dynamics in laser and other background fields. This can be done classically via the Landau-Lifshitz equation, or alternatively, via the simulation of photon emission events determined by strong-field quantum-electrodynamics amplitudes and implemented using Monte-Carlo type routines. Multiple laser fields can be included in the simulation and the propagation direction, beam shape (plane wave, focussed paraxial, constant crossed, or constant magnetic), and time envelope of each can be independently specified.Comment: Submitted to Comp. Phys. Comm. The associated computer program and corresponding manual will be made available on the CPC librar

Transverse spreading of electrons in high-intensity laser fields

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 Letter

Generative Governance: An Exploration

In this paper, we will talk about various tools/modes and how they specifically apply to non-profit governance. These modes will bring into focus new ways organizations can creatively and collectively transform and propel themselves into a future of growth and sustainability.https://digital.sandiego.edu/npi-bpl-governance/1006/thumbnail.jp

BPS Amplitudes, Helicity Supertraces and Membranes in M-Theory

We study BPS dominated loop amplitudes in M-theory on T^2. For this purpose we generalize the concept of helicity supertraces to nine spacetime dimensions. These traces distinguish between various massive supermultiplets and appear as coefficients in their one-loop contributions to n-graviton scattering amplitudes. This can be used to show that only ultrashort BPS multiplets contribute to the R^4 term in the effective action, which was first computed by Green, Gutperle and Vanhove. There are two inequivalent ultrashort BPS multiplets which describe the Kaluza-Klein states and the wrapped membranes that cover the torus a number of times. From the perspective of the type-II strings they correspond to momentum and winding states and D0 or D1 branes.Comment: 15 page

Short Distance Contributions to Graviton-Graviton Scattering: Matrix Theory versus Supergravity

We study graviton scattering in the presence of higher dimensional operators - particularly, R^4 - arising from loop effects. We find that the results do not correspond to any known terms in the effective action of Matrix Theory, thus lending support to the idea that the finite N Matrix Theory has no simple relation to supergravity with large compactification radii.Comment: 13 pages, LaTeX file with 3 Postscript figures. Uses epsf.tex and fps.sty macros. Revisions of v2: some comments in the end of section 3 have been remove

Spin Dependence of D0-brane Interactions

The long-range, spin-dependent forces between D0-branes are related to long-range fundamental string interactions using duality. These interactions can then be computed by taking the long distance non-relativistic expansion of string four-point amplitudes. The results are in accord with the general constraints of Matrix Theory.Comment: 6 pages, latex, no figures, talk presented at STRINGS97, substantial revisions in results and conclusion

Mutation independently affects reproductive traits and dauer larvae development in mutation accumulation lines of Caenorhabditis elegans

Developmental decisions are important in organismal fitness. For the nematode Caenorhabditis elegans, which is naturally found in the ephemeral food patches formed by rotting plant material, correctly committing to dauer or non-dauer larval development is key to genotype survival. To investigate the link between reproductive traits, which will determine how populations grow, and dauer larvae formation, we have analysed these traits in mutation accumulation lines of C. elegans. We find that reproductive traits of individual worms-the total number of progeny and the timing of progeny production-are highly correlated with the population size observed in growing populations. In contrast, we find no relationship between reproduction traits and the number of dauer larvae observed in growing populations. We also do not observe a mutational bias in dauer larvae formation. These results indicate that the control of dauer larvae formation is distinct from the control of reproduction and that differences in dauer larvae formation can evolve rapidly

Qualität definieren. Fünf unterschiedliche Ansätze

Die Autoren untersuchen den Begriff der "Qualität" im Kontext von Bildung. "Zu diesem Zweck werden Denkweisen über Qualität analysiert und in ihrer Bedeutung für den Bildungsbereich herausgearbeitet. Das Verhältnis dieser Denkweisen untereinander wird erörtert, und schließlich werden ihre philosophischen und politischen Grundlagen verdeutlicht.... Die internationale Diskussion wird in systematischer Weise aufgearbeitet; die Möglichkeiten und Grenzen der Übertragung von Qualitäts(sicherungs) konzepten aus dem privatwirtschaftlichen Produktions- und Dienstleistungsbereich werden klar herausgearbeitet." (DIPF/Orig.

Lattice QCD calculation of hadronic light-by-light scattering

We perform a lattice QCD calculation of the hadronic light-by-light scattering amplitude in a broad kinematical range. At forward kinematics, the results are compared to a phenomenological analysis based on dispersive sum rules for light-by-light scattering. The size of the pion pole contribution is investigated for momenta of typical hadronic size. The presented numerical methods can be used to compute the hadronic light-by-light contribution to the anomalous magnetic moment of the muon. Our calculations are carried out in two-flavor QCD with the pion mass in the range of 270 to 450MeV, and contain so far only the diagrams with fully connected quark lines.Comment: 5 pages, 5 figure

S and U-duality Constraints on IIB S-matrices

S and U-duality dictate that graviton scattering amplitudes in IIB superstring theory be automorphic functions on the appropriate fundamental domain which describe the inequivalent vacua of (compactified) theories. A constrained functional form of graviton scattering is proposed using Eisenstein series and their generalizations compatible with: a) two-loop supergravity, b) genus one superstring theory, c) the perturbative coupling dependence of the superstring, and d) with the unitarity structure of the massless modes. The form has a perturbative truncation in the genus expansion at a given order in the derivative expansion. Comparisons between graviton scattering S-matrices and effective actions for the first quantized superstring are made at the quantum level. Possible extended finiteness properties of maximally extended quantum supergravity theories in different dimensions is implied by the perturbative truncation of the functional form of graviton scattering in IIB superstring theory.Comment: 36 pages, 5 figures, LaTeX, (minor) eq. corr., to appear in NP