Characterizing Planetary Orbits and the Trajectories of Light

Exact analytic expressions for planetary orbits and light trajectories in the Schwarzschild geometry are presented. A new parameter space is used to characterize all possible planetary orbits. Different regions in this parameter space can be associated with different characteristics of the orbits. The boundaries for these regions are clearly defined. Observational data can be directly associated with points in the regions. A possible extension of these considerations with an additional parameter for the case of Kerr geometry is briefly discussed.Comment: 49 pages total with 11 tables and 10 figure

Streaking strong-field double ionization

Double ionization in intense laser fields can comprise electron correlations which manifest in the nonindependent emission of two electrons from an atom or molecule. However, experimental methods that directly access the electron emission times have been scarce. Here we explore the application of an all-optical streaking technique to strong-field double ionization, both theoretically and experimentally. We show that both sequential and nonsequential double-ionization processes lead to streaking delays that are distinct from each other and single ionization. Moreover, coincidence detection of ions and electrons provides access to the emission time difference, which is encoded in the two-electron momentum distributions. The experimental data agree very well with simulations of sequential double ionization. We further test and discuss the application of this method to nonsequential double ionization, which is strongly affected by the presence of the streaking field

A Modeling Study of Eulerian and Lagrangian Aspects of Shelf Circulation off Duck, North Carolina

The effects of wind-forced upwelling and downwelling on the continental shelf off Duck, North Carolina, are studied through experiments with a two-dimensional numerical primitive equation model. Moored and shipboard measurements obtained during August–November 1994 as part of the Coastal Ocean Processes (CoOP) Inner Shelf Study (ISS) are used for model–data comparisons. The model is initialized with realistic stratification and forced with observed wind and heat flux data. Both strongly stratified and weakly stratified conditions, found during August and October, respectively, are studied. August is characterized by fluctuating alongshelf wind direction, and October is dominated by downwelling-favorable winds. The across-shelf momentum balance is primarily geostrophic on the continental shelf. The alongshelf momentum balance is mainly between the Coriolis force and vertical diffusion with additional contributions from the local acceleration and nonlinear advection terms. The model solutions are utilized to acquire detailed information on the time- and space-dependent variability of the across-shelf circulation and transport and to investigate the dependence of this circulation on the seasonal change in stratification. When the stratification breaks down, as in October, the across-shelf transport is reduced significantly in comparison with the theoretical Ekman transport for large wind stress values. The paths of individual model water parcels are traced using two methods: calculation of Lagrangian trajectories and time evolution of three Lagrangian label fields. The August period produces complex Lagrangian dynamics because of the switching between upwelling and downwelling winds. The October period illustrates a mean downwelling response that advects parcels across and along the shelf and vertically

Subfemtosecond steering of hydrocarbon deprotonation through superposition of vibrational modes

Subfemtosecond control of the breaking and making of chemical bonds in polyatomic molecules is poised to open new pathways for the laser-driven synthesis of chemical products. The break-up of the C-H bond in hydrocarbons is an ubiquitous process during laser-induced dissociation. While the yield of the deprotonation of hydrocarbons has been successfully manipulated in recent studies, full control of the reaction would also require a directional control (that is, which C-H bond is broken). Here, we demonstrate steering of deprotonation from symmetric acetylene molecules on subfemtosecond timescales before the break-up of the molecular dication. On the basis of quantum mechanical calculations, the experimental results are interpreted in terms of a novel subfemtosecond control mechanism involving non-resonant excitation and superposition of vibrational degrees of freedom. This mechanism permits control over the directionality of chemical reactions via vibrational excitation on timescales defined by the subcycle evolution of the laser waveform

Transverse Momentum Distributions for Heavy Quark Pairs

We study the transverse momentum distribution for a $pair$ of heavy quarks produced in hadron-hadron interactions. Predictions for the large transverse momentum region are based on exact order $\alpha_s^3$ QCD perturbation theory. For the small transverse momentum region, we use techniques for all orders resummation of leading logarithmic contributions associated with initial state soft gluon radiation. The combination provides the transverse momentum distribution of heavy quark pairs for all transverse momenta. Explicit results are presented for $b\bar b$ pair production at the Fermilab Tevatron collider and for $c\bar c$ pair production at fixed target energies.Comment: LaTeX (27 pages text, 8 figures not included, but available on request

The LatMix summer campaign : submesoscale stirring in the upper ocean

Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 96 (2015): 1257–1279, doi:10.1175/BAMS-D-14-00015.1.Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s–1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.The bulk of this work was funded under the Scalable Lateral Mixing and Coherent Turbulence Departmental Research Initiative and the Physical Oceanography Program. The dye experiments were supported jointly by the Office of Naval Research and the National Science Foundation Physical Oceanography Program (Grants OCE-0751653 and OCE-0751734).2016-02-0

The LatMix Summer Campaign: Submesoscale Stirring in the Upper Ocean

Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m² s⁻¹ as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.A Google Earth interactive map of shipboard, autonomous, and airborne surveys during the summer 2011 LatMix experiment is available online as supplemental material ( http://dx.doi.org/10.1175/BAMS-D-14-00015.2). To explore these maps, you need Google Earth viewer installed on your computer. The software is free and could be downloaded online (from https://www.google.com /earth/). A user guide is available online as well (at http:// earth.google.com/userguide/).This is the publisher’s final pdf. The published article is copyrighted by the American Meteorological Society and can be found at: https://www2.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams

Lagrangian characteristics of continental shelf flows forced by periodic wind stress

International audienceThe coastal ocean may experience periods of fluctuating along-shelf wind direction, causing shifts between upwelling and downwelling conditions with responses that are not symmetric. We seek to understand these asymmetries and their implications on the Eulerian and Lagrangian flows. We use a two-dimensional (variations across-shelf and with depth; uniformity along-shelf) primitive equation numerical model to study shelf flows in the presence of periodic, zero-mean wind stress forcing. The model bathymetry and initial stratification is typical of the broad, shallow shelf off Duck, NC during summer. After an initial transient adjustment, the response of the Eulerian fields is nearly periodic. Despite the symmetric wind stress forcing, there exist both mean Eulerian and Lagrangian flows. The mean Lagrangian displacement of parcels on the shelf depends both on their initial location and on the initial phase of the forcing. Eulerian mean velocities, in contrast, have almost no dependence on initial phase. In an experiment with sinusoidal wind stress forcing of maximum amplitude 0.1Nm and period of 6 days, the mean Lagrangian across-shelf displacements are largest in the surface and bottom boundary layers. Parcels that originate near the coast in the top 15m experience complicated across-shelf and vertical motion that does not display a clear pattern. Offshore of this region in the top 10m a rotating cell feature exists with offshore displacement near the surface and onshore displacement below. A mapping technique is used to help identify the qualitative characteristics of the Lagrangian motion and to clarify the long time nature of the parcel displacements. The complexity of the Lagrangian motion in a region near the coast and the existence of a clear boundary separating this region from a more regular surface cell feature offshore are quantified by a calculation from the map of the largest Lyapunov exponent