Investigations on methane hydrate formation,dissociation,and viscosity in gas-water-sand system

Understanding the kinetics and viscosity of hydrate slurry in gas-water-sand system is of great significance for the high-efficiency and high-safety development of natural gas hydrates.The effect of micronsized sands with various concentrations and particle sizes on the hydrate formation,dissociation,and viscosity in gas-water-sand system are investigated in this work.The experimental results show that the hydrate induction time in the sandy system is slightly prolonged compared to the pure gas-water system,and the inhibition effect first strengthens and then weakens as the sand concentration increases from0 wt%to 5 wt%.Besides,the difference of hydrate formation amount in various cases is not obvious.The concentration and particle size of sand have little effect on the kinetics of hydrate formation.Both promoting and inhibiting effects on hydrate formation have been found in the sandy multiphase fluid.For the viscosity characteristics,there are three variations of hydrate slurry viscosity during the formation process:Steep drop type,S-type and Fluctuation type.Moreover,appropriate sand size is helpful to reduce the randomness of slurry viscosity change.Meanwhile,even at the same hydrate volume fraction,the slurry viscosity in the formation process is significantly higher than that in dissociation process,which needs further research.This work provides further insights of hydrate formation,dissociation,and viscosity in gas-water-sand system,which is of great significance for safe and economic development of natural gas hydrates.

Effectiveness of azithromycin mass drug administration on trachoma:a systematic review

Backgrounds:Azithromycin mass drug administration(MDA)is a key part of the strategy for controlling trachoma.This systematic review aimed to comprehensively summarize the present studies of azithromycin MDA on trachoma;provide an overview of the impact of azithromycin MDA on trachoma in different districts;and explore the possible methods to enhance the effectiveness of azithromycin MDA in hyperendemic districts.Methods:PubMed,Embase,the Cochrane Central Register of Controlled Trials,Web of Science,and ClinicalTrials.gov were searched up to February 2021 with no language restriction.Studies reporting the effect of azithromycin MDA on trachoma were included.Mathematical modeling studies,animal studies,case reports,and reviews were excluded.The trachomatous inflammation-follicular(TF)<5.0%was used to judge the effect of azithromycin MDA on eliminating trachoma as a public health problem.Two researchers independently conducted the selection process and risk of bias assessment.Results:A total of 1543 studies were screened,of which 67 studies including 13 cluster-randomized controlled trials and 54 non-randomized studies were included.The effect of azithromycin MDA on trachoma was closely related to the baseline prevalence in districts.For the districts with baseline prevalence between 5.0%and 9.9%,a single round of MDA achieved a TF<5.0%.For the districts with baseline between 10.0%and 29.9%,annual MDA for 3 to 5 years reduced TF<5.0%.However,for the districts with high level of baseline prevalence(TF>30.0%),especially with baseline TF>50.0%,annual MDA was unable to achieve the TF<5.0%even after 5 to 7 years of treatment.Quarterly MDA is more effective in controlling trachoma in these hyperendemic districts.Conclusions:Azithromycin MDA for controlling trachoma depends on the baseline prevalence.The recommendation by the World Health Organization that annual MDA for 3 to 5 years in the districts with TF baseline>10.0%is not appropriate for all eligible districts.