Dynamics of nonlinear cross-equatorial flow in the deep ocean

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1996The transformation of potential vorticity within and stability of nonlinear deep western boundary currents in an idealized tropical ocean are studied using a shallowwater model. Observational evidence indicates that the potential vorticity of fluid parcels in deep western boundary currents must change sign as they cross the equator, but this evidence is otherwise unable to clarify the process. A series of numerical experiments investigate this transformation in a rectangular basin straddling the equator. A mass source located in the northwestern corner feeds fluid into the domain where it is constrained to cross the equator to reach a distributed mass sink. Dissipation is included as momentum diffusion. The Reynolds number, defined as the ratio of the mass source per unit depth to the viscosity, determines the nature of the flow, and a critical value, Rec, divides its possible behavior into two regimes. For Re < Rec, the flow is laminar and well described by linear theory. For Re just above the critical value, the flow is time-dependent, with cyclonic eddies forming in the western boundary current near the equator. For still larger Reynolds number, eddies of both signs emerge and form a complicated, interacting network that extends into the basin several deformation radii from the western boundary, as well as north and south of the equator. The eddy field is established as the mechanism for potential vorticity transformation in nonlinear cross-equatorial flow. The analysis of vorticity fluxes follows from the flux-conservative form of the absolute vorticity equation. It is shown that the zonally integrated meridional flux of vorticity across the equator using no slip boundary conditions is virtually zero even in the strongly nonlinear limit suggesting that the eddies are extremely efficient vorticity transfer agents. A decomposition of the vorticity fluxes into components due to mean advection, eddy transport, and friction, reveals the growth with Reynolds number of a turbulent boundary layer that exchanges vorticity between the inertial portion of the boundary current and a frictional sub-layer where modification is straightforward. A linear stability analysis of the shallow-water system in the tropical ocean examines the initial formation of the eddy field. The formulation assumes that the basic state is purely meridional and on a local f-plane. Realistic western boundary current profiles undergo a horizontal shear instability that is partially stabilized by viscosity. Calculations at several latitudes indicate that the instability is enhanced in the tropics where the internal deformation radius is a maximum. The linear stability analysis predicts a length scale of the disturbance, a location for its origin, and a critical Reynolds number that agree well with numerical results.Financial support for this research was provided by NSF grant number OCE- 9115915 and ONR ASSERT grant number N00014-94-1-0844

Helicity operators for mesons in flight on the lattice

Motivated by the desire to construct meson-meson operators of definite relative momentum in order to study resonances in lattice QCD, we present a set of single-meson interpolating fields at non-zero momentum that respect the reduced symmetry of a cubic lattice in a finite cubic volume. These operators follow from the subduction of operators of definite helicity into irreducible representations of the appropriate little groups. We show their effectiveness in explicit computations where we find that the spectrum of states interpolated by these operators is close to diagonal in helicity, admitting a description in terms of single-meson states of identified J^{PC}. The variationally determined optimal superpositions of the operators for each state give rapid relaxation in Euclidean time to that state, ideal for the construction of meson-meson operators and for the evaluation of matrix elements at finite momentum.Comment: 25 pages, 14 figures; v2: minor changes to reflect journal versio

NDL: A Domain-Specific Language for Device Drivers

Device drivers are difficult to write and error-prone. They are usually written in C, a fairly low-level language with minimal type safety and little support for device semantics. As a result, they have become a major source of instability in operating system code. This paper presents NDL, a language for device drivers. NDL provides high-level abstractions of device resources and constructs tailored to describing common device driver operations. We show that NDL allows for the coding of a semantically correct driver with a code size reduction of more than 50% and a minimal impact on performance

A linear diffusivity model of near-surface, cross-shore particle dispersion from a numerical simulation of central California’s coastal ocean

A simple diffusion model of cross-shore mixing employing an inhomogeneous diffusivity is applied to near-surface particle dispersion within a high-resolution numerical model of the central California coastal ocean. The theoretical model employs a linear diffusivity, Ky = νy, where y is the cross-shore coordinate and ν a constant, as traditionally assumed for wall-layer flows. A realistic implementation of the Regional Ocean Modeling System (ROMS) is used to generate hundreds of thousands of three-dimensional, passive particle trajectories. Particles were released daily along the inner shelf for one model year, 2002, tracked for 16 days and treated statistically as an instantaneous point-source release. Application of the theoretical model to the observed moments of particle position yielded estimates for the offshore slope of the diffusivity, ν ∼ 3 – 4 cm s–1. Using this value, the cross-shore particle density was well described over the outer continental shelf and slope by an analytical solution to the theoretical model. Unlike wall turbulence, the implied mixing length was not equal to the distance from the coast, but was found to be equal to the local first mode internal Rossby radius of deformation. The successful theoretical model has many potential applications, such as quantifying the amount of offshore larval loss from the shelf and/or carbon loss from the coastal upwelling zone

Caught in the act: Implications for the increasing abundance of mafic enclaves during the eruption of the Soufriere Hills Volcano, Montserrat

An exceptional opportunity to sample several large blocks sourced from the same region of the growing Soufrière Hills lava dome has documented a significant increase in the presence of mafic enclaves in the host andesite during the course of a long-lived eruptive episode with several phases. In 1997 (Phase I) mafic inclusions comprised ~1 volume percent of erupted material; in 2007 (Phase III) deposits their volumetric abundance increased to 5–7 percent. A broader range of geochemically distinctive types occurs amongst the 2007 enclaves. Crystal-poor enclaves generally have the least evolved (basaltic) compositions; porphyritic enclaves represent compositions intermediate between basaltic and andesitic compositions. The absence of porphyritic enclaves prior to Phase III magmatism at Soufrière Hills Volcano suggests that a mixing event occurred during the course of the current eruptive episode, providing direct evidence consistent with geophysical observations that the system is continuously re-invigorated from depth

Intercollegiate Cross Country Competition: Effects of Warm-up and Racing on Salivary Levels of Cortisol and Testosterone

International Journal of Exercise Science 7(4) : 318-328, 2014. Team intercollegiate athletic competition is associated with an increase in salivary cortisol (C) and testosterone (T) in men and women. The present study was designed to determine the hormonal effects of warm-up and racing in cross country runners – a sport that has both individual and team components. Members of the Emory University men’s and women’s varsity cross country teams gave saliva samples before warm-up, after warm-up, and immediately after the finish of each of two intercollegiate invitational meets held one year apart in the same setting (2010, N = 10 men, 15 women; 2011, N = 15 men, 20 women ). For some racers warm-up was associated with a significant decrease in C (2010 men p = .04; 2011 women, p = .004). With the exception of the 2011 men, warm-up was associated with an increase in T (2010 men, P = .012; 2010 women, p = .006; 2011 women, p = .056). For men and women in both years, racing was related to a substantial increase in both C and T (C: 2010 and 2011 men, p = .001; 2010 women, p = .011; 2011 women, p \u3c .001) (T: 2010 and 2011 men and women, p \u3c .001). Finish time was not related to levels of C or T. Increased hormone levels may result from the psychological effects of competition, physical exertion, or some combination of the two. Competition-related increases in C and T presumably benefit performance in cross country racing and other sports, but the exact character of these benefits remains to be determined

Exotic and excited-state radiative transitions in charmonium from lattice QCD

We compute, for the first time using lattice QCD methods, radiative transition rates involving excited charmonium states, states of high spin and exotics. Utilizing a large basis of interpolating fields we are able to project out various excited state contributions to three-point correlators computed on quenched anisotropic lattices. In the first lattice QCD calculation of the exotic 1-+ eta_c1 radiative decay, we find a large partial width Gamma(eta_c1 -> J/psi gamma) ~ 100 keV. We find clear signals for electric dipole and magnetic quadrupole transition form factors in chi_c2 -> J/psi gamma, calculated for the first time in this framework, and study transitions involving excited psi and chi_c1,2 states. We calculate hindered magnetic dipole transition widths without the sensitivity to assumptions made in model studies and find statistically significant signals, including a non-exotic vector hybrid candidate Y_hyb? -> eta_c gamma. As well as comparison to experimental data, we discuss in some detail the phenomenology suggested by our results and the extent to which it mirrors that of quark potential models and make suggestions for the interpretation of our results involving exotic quantum numbered states

Dispersion and connectivity estimates along the U.S. west coast from a realistic numerical model

Near-surface particle dispersion, larval dispersal and connectivity along the U.S west coast were explored using a realistic numerical model of the California Current System. Seasonal model velocities were qualitatively and quantitatively evaluated using Global Drifter Program data. The model displayed a clear seasonal cycle of eddy energy near the coast with energy maxima southwest of major headlands. Eddy speeds were correlated with drifter-based estimates during summer and fall when compared spatially. Over six million passive, Lagrangian particles were released in the upper 20 m of the water column within 10 km of the California and Oregon coasts and tracked for 7 years. The effect of subgridscale vertical turbulence was parameterized with a random walk model. Resulting trajectories yielded climatological maps of particle dispersion. Particle densities varied with release region, release season and time-since-release. Dispersal distances and coastal connectivity varied with season of release, release location, release depth and pelagic larval duration (PLD). Connectivity was clearly influenced by major geographic features such as the Gulf of the Farallones and Cape Mendocino. Given a moderate (30–60 day) PLD, mean dispersal distances varied from ∼10–230 km, with standard deviations of ∼130–220 km. For release locations from Palos Verdes to Point Sur, the primary direction of dispersal was northward for a moderate PLD, regardless of season. For long PLDs (120–180 day), mean dispersal distances were larger (∼40–440 km), with standard deviations of ∼330–540 km. In winter given a long PLD, dispersal was primarily southward for release locations north of Point Arena. Increasing release depths to 40–60 m altered mean dispersal distances by 50–250 km polewards, but had little effect on standard deviations. Point Conception did not act as a barrier to dispersal for source regions in the Southern California Bight

The stability of an NPZ model subject to realistic levels of vertical mixing

The linear stability of a vertically-distributed, Nutrient-Phytoplankton-Zooplankton (NPZ) ocean ecosystem model is analyzed to understand how vertical mixing influences biological dynamics. In the absence of vertical diffusion, the model generally exhibits both stable fixed point and limit cycle behavior, depending on the depth and choice of parameters. Diffusion couples the dynamics of nearby levels and can induce stable profiles as well as oscillatory dynamical trajectories that become vertically phase-locked for large mixing levels. Calculations of the Lyapunov exponent reveal that vertical diffusion can drive this model into a chaotic state, though this occurs only for levels of diffusion well below those found in nature. The dynamics of the model, assuming macrozooplankton are the dominant grazers in the ecosystem, are compared to those in which microzooplankton dominate, with a faster grazing rate and poor assimilation efficiency. While the coupled physical-macrozooplanton system has a stable profile, the coupled microzooplankton profile remains unstable, even at large mixing levels. Fluctuations occur on time scales varying between a few days and a few months, depending on the parameters and magnitude of diffusion

Electron beam profile imaging in the presence of coherent optical radiation effects

High-brightness electron beams with low energy spread at existing and future x-ray free-electron lasers are affected by various collective beam self-interactions and microbunching instabilities. The corresponding coherent optical radiation effects, e.g., coherent optical transition radiation, render electron beam profile imaging impossible and become a serious issue for all kinds of electron beam diagnostics using imaging screens. Furthermore, coherent optical radiation effects can also be related to intrinsically ultrashort electron bunches or the existence of ultrashort spikes inside the electron bunches. In this paper, we discuss methods to suppress coherent optical radiation effects both by electron beam profile imaging in dispersive beamlines and by using scintillation imaging screens in combination with separation techniques. The suppression of coherent optical emission in dispersive beamlines is shown by analytical calculations, numerical simulations, and measurements. Transverse and longitudinal electron beam profile measurements in the presence of coherent optical radiation effects in non-dispersive beamlines are demonstrated by applying a temporal separation technique.Comment: 12 pages, 11 figures, submitted to Phys. Rev. ST Accel. Beam