Wake collapse in a stratified fluid.

A two-dimensional model is used to obtain quantitative data on characteristics of turbulently mixed wakes of bodies submerged in stratified fluids (more dense below than above). The time between turbulent mixing and maximum expansion of the wake before vertical collapse starts is 0.44 T, where T is the local Väisälä-Brunt period. Time after mixing for maximum rate of horizontal spreading is about 2.0 T. The average Väisälä-Brunt period for the oceans and atmosphere is discussed. It is predicted that the wake collapse phenomenon is not unusual in these environments. The characteristic time for the most active phase of vertical wake collapse should be between a few minutes to several tens of minutes. Qualitative observations of aircraft vapor trails tend to confirm that the phenomenon does occur at full scale.

Wake collapse in stratified fluid: experimental exploration of scaling characteristics.

Passage of a submerged self-propelled body or other mixing device produces a region of more or less homogeneous fluid, in a fluid having a stable vertical density gradient (stratified), which initially expands vertically and then falls back (collapses). Maximum expansion Z(2) at time t(2) after the start of mixing are dependent variables related to the diameter Z(1) of propeller or mixer and to the Väisälä-Brunt period T by T/t(2) = 2.5 and Z(2)t(2)/Z(1)T = 1.3. These scaling relations are first-order approximations.

Convergence and strain waves caused by a submerged turbulent disturbance in stratified fluids.

Short bursts of submerged turbulent mixing in stratified water (every-where denser below than above) is shown to cause waves of surface convergence, divergence, and strain. Quantitative data are given for four experiments.

Successful establishment of third-line antiretroviral therapy in Malawi: lessons learned.

SETTING: Malawi has an extensive national antiretroviral treatment (ART) program, and although less than 2% of all patients receive second-line ART, there are increasingly more patients failing on these regimens. OBJECTIVE: To establish a virtual ART committee using limited available local facilities and expertise to recommend third-line regimens based on genotype resistance of samples sent abroad. DESIGN: A secretariat and a laboratory sample hub were established. The committee started work after locally organizing training courses. Decisions about ART regimens were mainly based on a relatively simple, previously described algorithm, which allowed decisions to be taken without extensive expert knowledge. RESULTS: Of the 25 applications assessed, 23 samples were sent for resistance testing from June 2017 to April 2018. Major protease inhibitor (PI) resistance was detected in 65% of the samples. PI resistance was found even in patients exposed to PIs for short periods. In particular, patients who received co-administration of PIs and rifampicin frequently showed resistance mutations. CONCLUSION: Third-line ART using genotypic resistance testing and algorithm-based treatment regimens are feasible in low-resource settings. Our model can serve as a base for similar programs initiating programmatic third-line ART in other African countries.

An autonomous lab on a chip for space flight calibration of gravity-induced transcellular calcium polarization in single-cell fern spores.

This report describes the development of lab-on-a-chip device designed to measure changes in cellular ion gradients that are induced by changes in gravitational (g) forces. The bioCD presented here detects differential calcium ion concentrations outside of individual cells. The device includes sufficient replicates for statistical analysis of the gradients around multiple single cells and around control wells that are empty or include dead cells. In the data presented, the degree of the cellular response correlates with the magnitude of the g-force applied via rotation of the bioCD. The experiments recorded the longest continuous observation of a cellular response to hypergravity made to date, and they demonstrate the potential utility of this device for assaying the threshold of cells' g-force responses in spaceflight conditions.