Comparison of carbon and opal export rates between summer and spring bloom periods in the region of the Antarctic Polar Front, SE Atlantic.

Although primary production in the Antarctic Circumpolar Current is not above the world average and carbon burial rates are low, 70% of the world's opal burial occurs in this zone and it has been suggested that blooms of large diatoms are responsible for this extraordinary situation. Here we compare export fluxes during bloom and steady-state situations near the Antarctic Polar Front in the SE Atlantic.In a previous expedition during the austral spring, we observed the development of a bloom that led to the sudden export of particles (Rutgers van der Loeff et al., 1997). Here we report the results of a second expedition to the same area in summer (Dec-Jan), 3 years later. 234Th was monitored in the surface water and in Rosette casts down to a water depth of 500m as tracer of export production in an intensive sampling program within a box of 275 x 375 km.The distribution of particulate and dissolved 234Th was remarkably constant over time and location. Total (dissolved + particulate) 234Th activities were depleted relative to its parent 238U at the surface (234Th/238U activity ratio approximately 83%), reaching equilibrium at a depth of around 190m. This constant depletion corresponds to a 234Th export rate of 1115 dpm m-2 d-1, 35% of the value observed during the spring bloom

A report on visits of fake clients, pretending to be in need of emergency contraception, to health facilities in Bulawayo, Zimbabwe

To identify bottlenecks in the delivery of comprehensive reproductive health care in Bulawayo, Zimbabwe's second city, a study was performed utilising volunteers pretending to be in need of emergency contraception. A total of 55 private, Zimbabwe National Family Planning Council, municipal and government health facilities were visited. These consultations resulted in 9 (16%) correct, 1 possiblycorrect and 15 wrong prescriptions for the morning-after pill (MAP); no treatment was prescribed in 30 instances. Public sector health personnel were very judgemental in their attitude toward sexually active teenagers. Although the Essential Drug List of Zimbabwe is quite clear about the MAP, many health providers are not aware of this, and others do not even have/use this book

Measurements of the instantaneous velocity difference and local velocity with a fiber-optic coupler

New optical arrangements with two single-mode input fibers and a fiber-optic coupler are devised to measure the instantaneous velocity difference and local velocity. The fibers and the coupler are polarization-preserving to guarantee a high signal-to-noise ratio. When the two input fibers are used to collect the scattered light with the same momentum transfer vector but from two spatially separated regions in a flow, the obtained signals interfere when combined via the fiber-optic coupler. The resultant light received by a photomultiplier tube contains a cross-beat frequency proportional to the velocity difference between the two measuring points. If the two input fibers are used to collect the scattered light from a common scattering region but with two different momentum transfer vectors, the resultant light then contains a self-beat frequency proportional to the local velocity at the measuring point. The experiment shows that both the cross-beat and self-beat signals are large and the standard laser Doppler signal processor can be used to measure the velocity difference and local velocity in real time. The new technique will have various applications in the general area of fluid dynamics.Comment: Patent number: 67437 for associated information on the hardware, see http://karman.phyast.pitt.edu/horvath

Loose packings of frictional spheres

We have produced loose packings of cohesionless, frictional spheres by sequential deposition of highly-spherical, monodisperse particles through a fluid. By varying the properties of the fluid and the particles, we have identified the Stokes number (St) - rather than the buoyancy of the particles in the fluid - as the parameter controlling the approach to the loose packing limit. The loose packing limit is attained at a threshold value of St at which the kinetic energy of a particle impinging on the packing is fully dissipated by the fluid. Thus, for cohesionless particles, the dynamics of the deposition process, rather than the stability of the static packing, defines the random loose packing limit. We have made direct measurements of the interparticle friction in the fluid, and present an experimental measurement of the loose packing volume fraction, \phi_{RLP}, as a function of the friction coefficient \mu_s.Comment: 6 pages, 5 figure

Hysteresis at low Reynolds number: the onset of 2D vortex shedding

Hysteresis has been observed in a study of the transition between laminar flow and vortex shedding in a quasi-two dimensional system. The system is a vertical, rapidly flowing soap film which is penetrated by a rod oriented perpendicular to the film plane. Our experiments show that the transition from laminar flow to a periodic K\'arm\'an vortex street can be hysteretic, i.e. vortices can survive at velocities lower than the velocity needed to generate them.Comment: RevTeX file 4 pages + 5 (encapsulated postscript) figures. to appear in Phys.Rev.E, Rapid Communicatio

Vorticity statistics in the two-dimensional enstrophy cascade

We report the first extensive experimental observation of the two-dimensional enstrophy cascade, along with the determination of the high order vorticity statistics. The energy spectra we obtain are remarkably close to the Kraichnan Batchelor expectation. The distributions of the vorticity increments, in the inertial range, deviate only little from gaussianity and the corresponding structure functions exponents are indistinguishable from zero. It is thus shown that there is no sizeable small scale intermittency in the enstrophy cascade, in agreement with recent theoretical analyses.Comment: 5 pages, 7 Figure