Large eddy simulation and laboratory experiments on the decay of grid wakes in strongly stratified flows

A detailed analysis of the flow structure resulting from the combination of turbulence and internal waves is carried out and visualized by means of the Schlieren method on waves in a strongly stratified fluid at the Laboratory of the IPM in Moscow. The joint appearance of the more regular internal wave oscillations and the small-scale turbulence that is confined vertically to the Ozmidov length scale favours the use of a simple geometrical analysis to investigate their time-space span and evolution. This provides useful information on the collapse of internal wave breaking processes in the ocean and the atmosphere. The measurements were performed under a variety of linear stratifications and different grid forcing scales, combining the grid wake and velocity shear. A numerical simulation using LES on the passage of a single bar in a linearly stratified fluid medium has been compared with the experiments identifying the different influences of the environmental agents on the actual effective vertical diffusion of the wakes. The equation of state, which connects the density and salinity, is assumed to be linear, with the coefficient of the salt contraction being included into the definition of salinity or heat. The characteristic internal waves as well as the entire beam width are related to the diameter of the bar, the Richardson number and the peak-to-peak value of oscillations. The ultimate frequency of the infinitesimal periodic internal waves is limited by the maximum buoyancy frequency relating the decrease in the vertical scale with the anisotropy of the velocity turbulent r.m.s. velocity.Peer ReviewedPreprin

Dynamic relational contracts under complete information

This paper considers a long-term relationship between two agents who both undertake an action or investment that produces a joint benefit. Agents have an opportunity to expropriate some of the joint benefit for their own use. Agents have quasi-linear preferences. Two cases are considered: where agents are risk averse but where limited liability constraints do not bind, and where agents are risk neutral and subject to limited liability constraints. We ask how to structure the investments and division of the surplus over time to avoid expropriation. In the risk-averse case, the dynamics of actions and surplus may or may not be monotonic depending on whether or not a first-best allocation can be sustained. Agents may underinvest but never overinvest. If the first-best allocation is not sustainable, there is a trade-off between risk sharing and surplus maximization; surplus may not be at its constrained maximum even in the long run and the “amnesia” property of pure risk-sharing models fails to hold. In contrast, in the risk-neutral case there may be an initial phase in which one agent overinvests and the other underinvests. Both actions and surplus converge monotonically to a stationary state, where surplus is maximized subject to the self-enforcing constraints

Effects of boron foliar sprays on tomato cultivation

Boron deficiency is very harmful in tomato (Solanum lycopersicum L.) cultivation. Boron foliar sprays can be used as a mean of preventing plant stunting, that results in low growth, poor onset of flowers and fruits, fruit physiological disorders, and hence, low tomato productivity. Boron sources and polyol like surfactants can affect foliar sprays' effectiveness. This work had the objective of evaluating foliar sprays of boric acid, borax and B-ethanolamine, with or without, polyol surfactant. The experiment was carried out in a 3×2+2 factorial arranged in randomized blocks with four replications. Plants of tomato cultivar 'Tangerine' F1 were fed with complete nutrient solution containing 5 μmol L-1 of B. These plants were sprayed with the three sources of boron, with or without a polyol like surfactant at 14 days intervals until the production cycle was complete. The additional treatments were: a positive control (C+), in which the plants received 20 μmol L-1 B, and a negative control (C-), in which the plants received 5 μmol L-1 B via nutrient solution, both without supply of B via foliar sprays. We evaluated plant height, root volume, number of flowers and fruits; dry matter production; nutrient contents and accumulation, in four phenological stages, and fresh and dry matter of fruits at the harvest. The data obtained were subjected to analysis of variance and the treatments compared by mean test. Leaf sprays improved the tomato growth and production compared to the (C-) treatment, but the adequate B supply by roots (C+) was the most efficient method for nutrition of tomato plants with boron. Among the boron sources, B-ethanolamine and boric acid were those which promoted the best results in tomato production, compared to the foliar application of borax. The use of the polyol like surfactant did not result in significant improvements on growth and production of the tomato plantsAuthors gratefully acknowledge the financial support by Spanish Ministry of Economy and Competitiveness project: AGL2013-44474-R and the Brazilian government agencies CAPES and CNP

Biological recognition and cellular trafficking of targeted RNA-lipid nanoparticles

Biopharmaceutic

STAT6 variants associate with relapse of fosinophilic esophagitis in patients receiving long-term proton pump inhibitor therapy

Background & Aims: Based on histologic features, variants in STAT6 are associated with a poor initial response to proton pump inhibitor (PPI) therapy in pediatric patients with eosinophilic esophagitis (EoE). We investigated whether these genetic variants are associated with a poor long-term response in children with EoE who initially responded to PPI therapy. Methods: We performed a prospective longitudinal cohort study of children ages 2 to 16 years who met the diagnostic criteria for EoE (≥15 eosinophils/high-power field [eos/hpf]), responded to 8 weeks of treatment with 2 mg/kg/d PPI (<15 eos/hpf), and whose dose then was reduced to 1 mg/kg/d PPI (maintenance therapy) for 1 year, at which point biopsy specimens were collected by endoscopy. Genomic DNA was isolated from formalin-fixed paraffin-embedded biopsy tissue and was genotyped for variants of STAT6. Remission of inflammation was assessed at eos/hpf thresholds of <15 and ≤5. Results: Among 73 patients who received 1 mg/kg/d PPI maintenance therapy for 1 year, 13 patients (18%) had 6 to 14 eos/hpf, 36 patients (49%) had 5 or fewer eos/hpf, and 24 patients (33%) relapsed to EoE (≥15 eos/hpf). Carriage of any of 3 STAT6 variants in linkage disequilibrium (r2 ≥0.8; rs324011, rs167769, or rs12368672) was associated with a 2.3- to 2.8-fold increase in the odds of EoE relapse, and with a 2.8- to 4.1-fold increase in the odds of having 6 to 14 eos/hpf. For rs324011, the odds ratio [95% CI] for relapse was 2.77 [1.11, 6.92]; P = .029, and the odds ratio [95% CI] for having 6 to 14 eos/hpf was 3.06 [1.27, 7.36]; P = .012. Conclusions: Pediatric EoE patients who initially respond to PPI therapy and carry STAT6 variants rs324011, rs167769, or rs12368672 are at increased risk of relapse after 1 year of PPI maintenance therapy

Pass/Fail, A-F, or 0-100? Optimal Grading of Eager Students

This paper analyzes optimal grading in a world that focuses on top grades. Students choose an effort level, their performance is graded, and their grade correlates with their future income. Ex-ante, the policy maker chooses the optimal coarseness of the grading scale to maximize student welfare. When choosing their effort, students overweight outstanding - or salient - grades. I show that this behavior leads to excessive effort levels when grading is fully informative, and that coarse grading can be used to counterbalance incentives. Thus, salience can help explain why grading ranges from Pass/Fail scales (tenure decisions) via A-F-scales (school) to fully disclosing scores (e.g. SAT)