Stochastic Transition between Turbulent Branch and Thermodynamic Branch of an Inhomogeneous Plasma

Transition phenomena between thermodynamic branch and turbulent branch in submarginal turbulent plasma are analyzed with statistical theory. Time-development of turbulent fluctuation is obtained by numerical simulations of Langevin equation which contains submarginal characteristics. Probability density functions and transition rates between two states are analyzed. Transition from turbulent branch to thermodynamic branch occurs in almost entire region between subcritical bifurcation point and linear stability boundary.Comment: 10 pages, 8 figures, to be published in J. Phys. Soc. Jp

Long-Period Transport Changes in the Eastern North Atlantic and Their Simulation by Propagating Waves

An analysis is presented of geostrophic volume transport across a zonal line along 28-degrees-N in the eastern Atlantic. The data are from an array of five moorings with 200-km spacing carrying temperature sensors and one current meter each for 1 or 2 years. Transport changes in the main thermocline relative to a fixed depth level are obtained by the use of temperature-salinity relationships. The transport variability is simulated by two propagating waves with first-order baroclinic mode structure. Solutions exist with annual and semi-annual periods and zonal wavelengths of 100-200 km and 300 km, respectively. Assuming quasi-geostrophic dynamics and using results on the Reynolds stress, the dominating waves of annual and semi-annual period are found to propagate to the southwest, with 45-degrees-60-degrees and 25-degrees to the south off the westward direction, respectively. Wave solutions with a 90-day period and a zonal wavelength of about 300 km are interpreted as an effect of barotropic waves arising due to horizontal temperature inhomogeneity. The propagation is about +/-25-degrees off the westward direction. In general, good approximations are obtained with the propagating wave simulations in the western and central part of the array, while large differences occur between observation and simulation close to the Canary archipelago. Possible causes for these differences are discussed

Barotropic and Baroclinic Tidal Currents in the Eastern Basins of the North Atlantic

Data from a large-scale moored array in the Iberian and Canary basins are used to determine the energies of barotropic and baroclinic M2 and S2 tides. An analysis of time-varying dynamical modes is performed. The results for barotropic modes confirm the global surface tide model results of Schwiderski (1980) for this region. The barotropic modes dominate in the deep basins, but increased baroclinic contributions are usually found over rough topography. At three locations near the continental slope in the southern Canary Basin the baroclinic modes dominate the barotropic mode. Results from an array of three moorings at the northern part of the Cape Verde Rise show an inverse behavior of barotropic and baroclinic energies, such that the baroclinic energy is steadily enhanced while the barotropic energy is reduced towards the continental margin. The increase in baroclinic energy is consistent with a generation of internal tides close to the shelf by surface tidal forcing over topography. Further evidence for this process is provided by the 2-week periodicity of the first-order baroclinic mode at the slope, corresponding to the spring-neap cycle of the barotropic tide

Toward Regional Characterizations of the Oceanic Internal Wavefield

Many major oceanographic internal wave observational programs of the last 4 decades are reanalyzed in order to characterize variability of the deep ocean internal wavefield. The observations are discussed in the context of the universal spectral model proposed by Garrett and Munk. The Garrett and Munk model is a good description of wintertime conditions at Site-D on the continental rise north of the Gulf Stream. Elsewhere and at other times, significant deviations in terms of amplitude, separability of the 2-D vertical wavenumber - frequency spectrum, and departure from the model's functional form are noted. Subtle geographic patterns are apparent in deviations from the high frequency and high vertical wavenumber power laws of the Garrett and Munk spectrum. Moreover, such deviations tend to co-vary: whiter frequency spectra are partnered with redder vertical wavenumber spectra. Attempts are made to interpret the variability in terms of the interplay between generation, propagation and nonlinearity using a statistical radiative balance equation. This process frames major questions for future research with the insight that such integrative studies could constrain both observationally and theoretically based interpretations

Observations and models of inertial waves 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 February, 1980The structure of the inertial peak in deep ocean kinetic energy spectra is studied here. Records were obtained from Polymode arrays deployed in the Western North Atlantic Ocean (40°W to 70°W, 15°N to 42°N). The results are interpreted both in terms of local sources and of turning point effects on internal waves generated at lower latitudes. In most of the data, there is a prominent inertial peak slightly above f; however, the peak height above the background continuum varies with depth and geographical environment. Three classes of environment and their corresponding spectra emerge from peak height variations: class 1 is the 1500 m level near the Mid-Atlantic Ridge, with the greatest peak height of 18 db; class 2 includes (a) the upper ocean (depth less than 2000 m), (b) the deep ocean (depth greater than 2000 m) over rough topography, and (c) the deep ocean underneath the Gulf Stream, with intermediate peak height of 11.5 db; class 3 is the deep ocean over smooth topography, with the lowest peak height of 7.5 db. Near f, the horizontal coherence scale is 0(60 km) at depths from 200 m to 600 m, and the vertical coherence scale is O(200 m) just below the main thermocline. A one turning point model is developed to describe inertial waves at mid-latitudes, based on the assumption that inertial waves are randomly generated at lower latitudes (global generation) where their frequency-wavenumber spectrum is given by the model of Garrett and Munk (1972 a, 1975). Using the globally valid wave functions obtained by Munk and Phillips (1968), various frequency spectra near f are calculated numerically. The model yields a prominent inertial peak of 7 db in the horizontal velocity spectrum but no peaks in the temperature spectrum. The model is latitudinally dependent: the frequency shift and bandwidth of the inertial peak decrease with latitude; energy level near f is minimum at about 30° and higher at low and high latitudes. The observations of class 3 can be well-described by the model; a low zonal wavenumber cutoff is required to produce the observed frequency shift of the inertial peak. The differences between the global generation model and the observations of class 1 and class 2 are interpreted as the effects of local sources. A locally forced model is developed based on the latitudinal modal decomposition of a localized source function. Asymptotic eigensolutions of the Laplace's tidal equation are therefore derived and used as a set of expansion functions. The forcing is through a vertical velocity field specified at the top or bottom boundaries of the ocean. For white noise forcing, the horizontal velocity spectrum of the response has an inertial peak which diminishes in the far-field. With the forcing located at either the surface or the bottom, several properties of the class 2 observations can be described qualitatively by a combination of the global and local models. The reflection of inertial waves from a turbulent benthic boundary layer is studied by a slab model of given depth. Frictional effects are confined to the boundary layer and modelled by a quadratic drag law. For given incident waves, reflection coefficients are found to be greater than 0.9 for the long waves which contain most of the energy. This result suggests that energy-containing inertial waves can propagate over great distance as is required by the validity of the model of global generation.This work was supported by the National Science Foundation through grant OCE 76-80210 and its continuation OEE 78-19833

Progress in prevention of mother-to-child transmission of HIV infection in Ukraine: results from a birth cohort study

<p>Abstract</p> <p>Background</p> <p>Ukraine was the epicentre of the HIV epidemic in Eastern Europe, which has the most rapidly accelerating HIV epidemic world-wide today; national HIV prevalence is currently estimated at 1.6%. Our objective was to evaluate the uptake and effectiveness of interventions for prevention of mother-to-child transmission (PMTCT) over an eight year period within operational settings in Ukraine, within the context of an ongoing birth cohort study.</p> <p>Methods</p> <p>The European Collaborative Study (ECS) is an ongoing birth cohort study in which HIV-infected pregnant women identified before or during pregnancy or at delivery were enrolled and their infants prospectively followed. Three centres in Ukraine started enrolling in 2000, with a further three joining in September 2006.</p> <p>Results</p> <p>Of the 3356 women enrolled, 21% (689) reported current or past injecting drug use (IDU). Most women were diagnosed antenatally and of those, the proportion diagnosed in the first/second trimester increased from 47% in 2000/01 (83/178) to 73% (776/1060) in 2006/07 (p < 0.001); intrapartum diagnosis was associated with IDU (Adjusted odds ratio 4.38; 95%CI 3.19–6.02). The percentage of women not receiving any antiretroviral prophylaxis declined from 18% (36/205) in 2001 to 7% in 2007 (61/843) (p < 0.001). Use of sdNVP alone substantially declined after 2003, with a concomitant increase in zidovudine prophylaxis. Median antenatal zidovudine prophylaxis duration increased from 24 to 72 days between 2000 and 2007. Elective caesarean section (CS) rates were relatively stable over time and 34% overall. Mother-to-child transmission (MTCT) rates decreased from 15.2% in 2001 (95%CI 10.2–21.4) to 7.0% in 2006 (95%CI 2.6–14.6). In adjusted analysis, MTCT risk was reduced by 43% with elective CS versus vaginal delivery and by 75% with zidovudine versus no prophylaxis.</p> <p>Conclusion</p> <p>There have been substantial improvements in use of PMTCT interventions in Ukraine, including earlier diagnosis of HIV-infected pregnant women and increasing coverage with antiretroviral prophylaxis and the initial MTCT rate has more than halved. Future research should focus on hard-to-reach populations such as IDU and on missed opportunities for further reducing the MTCT rate.</p