On density effects and large structure in turbulent mixing layers

Plane turbulent mixing between two streams of different gases (especially nitrogen and helium) was studied in a novel apparatus. Spark shadow pictures showed that, for all ratios of densities in the two streams, the mixing layer is dominated by large coherent structures. High-speed movies showed that these convect at nearly constant speed, and increase their size and spacing discontinuously by amalgamation with neighbouring ones. The pictures and measurements of density fluctuations suggest that turbulent mixing and entrainment is a process of entanglement on the scale of the large structures; some statistical properties of the latter are used to obtain an estimate of entrainment rates. Large changes of the density ratio across the mixing layer were found to have a relatively small effect on the spreading angle; it is concluded that the strong effects, which are observed when one stream is supersonic, are due to compressibility effects, not density effects, as has been generally supposed

Studies of mercury in water, sediment, and fish in Mississippi: Concentrations, speciation, cycling, and isotopic composition

The goal of this project is to better understand the biogeochemical cycle of mercury (Hg) in Mississippi to aid those managing the resources and developing related policy. To that end, Hg levels were determined in a total of 202 fish from Enid, Sardis and Grenada Lakes; Enid and Grenada have fish consumption advisories due to Hg. In addition, total-Hg and methylmercury (MeHg) levels were determined in the inflow and outflows from Enid and Sardis Lakes and in bottom sediment and suspended solids in Enid Lake. Potential sources of Hg to Enid Lake were investigated, including precipitation and runoff from urban, agricultural, and wetland/forest areas, which flow into the Yocona River. A range of water quality parameters were measured to determine the primary factors controlling the distribution and transport of Hg species in the watershed. Concentrations in the fish generally increased with fish size (age) and trophic position. The suggested consumption limit for bass and crappie, commonly targeted by fishers, are \u3c5 meals per month for adults and \u3c12 meals per year for children. Wetland areas were determined to be hotspots for MeHg in the watershed with relatively high concentrations in water and fish, but runoff from agricultural areas likely provides the largest input of Hg to Enid Lake by transport of particle-bound-Hg. Wet deposition accounts for an estimated 33 kg and 15 kg of Hg deposited annually via rainfall to the Little Tallahatchie (Sardis) and Yocona River (Enid) watersheds, respectively. Mercury fluxes for Enid Lake based on concentrations in the inflow and outflow, and water-flow measurements are reported by season and during a storm event. The feasibility of using remote sensing (satellite imagery) to model the distribution of total suspended solids and Hg following a rainstorm event will be shown. Finally, results from the first study of total-Hg, MeHg, and Hg isotopic composition in sediment from a cold seep from the northern Gulf of Mexico is discussed. Hg levels in the sediment from the cold seep were similar to background sites, and cold seeps are likely not significant sources of MeHg to Gulf waters

Knowledge Summary 27: Death reviews: maternal, perinatal and child

Many maternal, perinatal and child deaths are preventable and progress towards Millennium Development Goals 4&5, to reduce child mortality and improve maternal health, has been insufficient in many parts of the world. Well-implemented death reviews provide opportunities to examine the circumstances surrounding a woman’s or child’s death, and improve the delivery of health services to prevent such deaths in the future. Several types of review processes exist to evaluate deaths in diverse settings, given different data availability and levels of service delivery. Both consistent surveillance and effective response are needed to ensure that maternal, perinatal and child deaths are identified and reviewed, so that recommendations can be made, and action can be taken to prevent further deaths

Active Control of Transition Using the Lorentz Force

A new concept and technique has been developed to directly control boundary-layer transition and turbulence. Near-wall vertical motions are directly suppressed through the application of Lorentz force. Current (j) and magnetic (b) fields are applied parallel to the boundary and normal to each other to produce a Lorentz force (j x B) normal to the boundary. This approach is called magnetic turbulence control (MTC). Experiments have been performed on flat-plate transitional and turbulent boundary layers in water seeded with a weak electrolyte

Large Structure Dynamics and Entrainment in the Mixing Layer at High Reynolds Number

Observations were made on a turbulent mixing layer in a water channel at Reynolds numbers up to 3 x 10^6 . Flow visualization with dyes revealed (once more) large coherent structures and showed their role in the entrainment process; observations of the reaction of a base and an acid indicator injected on the two sides of the layer, respectively, gave some indication of where molecular mixing occurs. Autocorrelations of streamwise velocity fluctuations, using an LDV, revealed a fundamental periodicity associated with the large structures. The surprisingly long correlation times suggest time scales much longer than had been supposed; it is argued that the mixing layer dynamics at any point is coupled to the large structure further downstream, and some possible consequences about the effects of initial conditions and,. of the influence of apparatus geometry are discussed

Book reviews

Teaching/Communication/Extension/Profession,

Stable and Unstable Accretion Flows with Angular Momentum near a Point Mass

The properties of axisymmetric accretion flows of cold adiabatic gas with zero total energy in the vicinity of a Newtonian point mass are characterized by a single dimensionless parameter, the thickness of incoming flow. In the limit of thin accretion flows with vanishing thickness, we show that the governing equations become self-similar, involving no free parameters. We study numerically thin accretion flows with finite thickness as well as those with vanishing thickness. Mass elements of the incoming flow enter the computational regime as thin rings. In the case with finite thickness, after a transient period of initial adjustment, an almost steady-state accretion shock with a small oscillation amplitude forms, confirming the previous work by Molteni, Lanzafame, \& Chakrabarti (1994). The gas in the region of vorticity between the funnel wall and the accretion shock follows closed streamlines, forming a torus. This torus, in turn, behaves as an effective barrier to the incoming flow and supports the accretion shock which reflects the incoming gas away from the equatorial plane. The postshock flow, which is further accelerated by the pressure gradient behind the shock, goes through a second shock which then reflects the flow away from the symmetry axis to form a conical outgoing wind. As the thickness of the inflowing layer decreases (or if the ratio of the half thickness to the distance to the funnel wall along the equatorial plan is smaller than $\sim0.1$), the flow becomes unstable. In the case with vanishing thickness, the accretion shock formed to stop the incoming flow behind the funnel wall oscillates quasi-periodically with an amplitude comparable to the thickness. The structure between the funnel wall and the accretion shock is destroyed as the shock moves inwards toward the central mass and re-generatedComment: ApJ accepted, 23 pages, uuencoded, compressed postscript file, 11 figures available upon request from [email protected]

The eVALuate study: two parallel randomised trials, one comparing laparoscopic with abdominal hysterectomy, the other comparing laparoscopic with vaginal hysterectomy

OBJECTIVE: To compare the effects of laparoscopic hysterectomy and abdominal hysterectomy in the abdominal trial, and laparoscopic hysterectomy and vaginal hysterectomy in the vaginal trial. DESIGN: Two parallel, multicentre, randomised trials. Setting 28 UK centres and two South African centres. Participants 1380 women were recruited; 1346 had surgery; 937 were followed up at one year. PRIMARY OUTCOME: outcome Rate of major complications. RESULTS: In the abdominal trial laparoscopic hysterectomy was associated with a higher rate of major complications than abdominal hysterectomy (11.1% v 6.2%, P = 0.02; difference 4.9%, 95% confidence interval 0.9% to 9.1%) and the number needed to treat to harm was 20. Laparoscopic hysterectomy also took longer to perform (84 minutes v 50 minutes) but was less painful (visual analogue scale 3.51 v 3.88, P = 0.01) and resulted in a shorter stay in hospital after the operation (3 days v 4 days). Six weeks after the operation, laparoscopic hysterectomy was associated with less pain and better quality of life than abdominal hysterectomy (SF-12, body image scale, and sexual activity questionnaires). In the vaginal trial we found no evidence of a difference in major complication rates between laparoscopic hysterectomy and vaginal hysterectomy (9.8% v 9.5%, P = 0.92; difference 0.3%, − 5.2% to 5.8%), and the number needed to treat to harm was 333.We found no evidence of other differences between laparoscopic hysterectomy and vaginal hysterectomy except that laparoscopic hysterectomy took longer to perform (72 minutes v 39 minutes) and was associated with a higher rate of detecting unexpected pathology (16.4% v 4.8%, P = < 0.01). However, this trial was underpowered. CONCLUSIONS: Laparoscopic hysterectomy was associated with a significantly higher rate of major complications than abdominal hysterectomy. It also took longer to perform but was associated with less pain, quicker recovery, and better short term quality of life. The trial comparing vaginal hysterectomy with laparoscopic hysterectomy was underpowered and is inconclusive on the rate of major complications; however, vaginal hysterectomy took less time

Alfalfa Varieties

Alfalfa (Medicago sativa) is the highest yielding, highest quality legume forage crop raised in Kentucky. This crop forms the basis of Kentucky\u27s cash hay enterprise and is an important component in dairy, horse, beef and sheep diets. In 1990, 320,000 acres of alfalfa were produced in Kentucky, averaging 3.4 tons of dry matter yield per acre. At $75 per ton, the value of this alfalfa to Kentucky farmers would be$81.6 million. This report will provide current yield data on alfalfa varieties currently in the Kentucky Alfalfa Variety Trials. Also, guidelines on selecting alfalfa varieties will be discussed