Understanding liquid-jet atomization cascades via vortex dynamics

Temporal instabilities of a planar liquid jet are studied using direct numerical simulation (DNS) of the incompressible Navier-Stokes equations with level-set (LS) and volume-of-fluid (VoF) surface tracking methods. $\lambda_2$ contours are used to relate the vortex dynamics to the surface dynamics at different stages of the jet breakup, namely, lobe formation, lobe perforation, ligament formation, stretching, and tearing. Three distinct breakup mechanisms are identified in the primary breakup, which are well categorized on the parameter space of gas Weber number ($We_g$) versus liquid Reynolds number ($Re_l$). These mechanisms are analyzed here from a vortex dynamics perspective. Vortex dynamics explains the hairpin formation, and the interaction between the hairpins and the Kelvin-Helmholtz (KH) roller explains the perforation of the lobes, which is attributed to the streamwise overlapping of two oppositely-oriented hairpin vortices on top and bottom of the lobe. The formation of corrugations on the lobe front edge at high $Re_l$ is also related to the location and structure of the hairpins with respect to the KH vortex. The lobe perforation and corrugation formation are inhibited at low $Re_l$ and low $We_g$ due to the high surface tension and viscous forces, which damp the small scale corrugations and resist hole formation. Streamwise vorticity generation - resulting in three-dimensional instabilities - is mainly caused by vortex stretching and baroclinic torque at high and low density ratios, respectively. Generation of streamwise vortices and their interaction with spanwise vortices produce the liquid structures seen at various flow conditions. Understanding the liquid sheet breakup and the related vortex dynamics are crucial for controlling the droplet size distribution in primary atomization.Comment: Submitted for publication in Journal of Fluid Mechanics. 56 pages; 52 figure

Length-scale cascade and spread rate of atomizing planar liquid jets

The primary breakup of a planar liquid jet is explored via direct numerical simulation (DNS) of the incompressible Navier-Stokes equation with level-set and volume-of-fluid interface capturing methods. PDFs of the local radius of curvature and the local cross-flow displacement of the liquid-gas interface are evaluated over wide ranges of the Reynolds number ($Re$), Weber number ($We$), density ratio and viscosity ratio. The temporal cascade of liquid-structure length scales and the spread rate of the liquid jet during primary atomization are analyzed. The formation rate of different surface structures, e.g. lobes, ligaments and droplets, are compared for different flow conditions and are explained in terms of the vortex dynamics in each atomization domain that we identified recently. With increasing $We$, the average radius of curvature of the surface decreases, the number of small droplets increases, and the cascade and the surface area growth occur at faster rates. The spray angle is mainly affected by $Re$ and density ratio, and is larger at higher $We$, at higher density ratios, and also at lower $Re$. The change in the spray spread rate versus $Re$ is attributed to the angle of ligaments stretching from the jet core, which increases as $Re$ decreases. Gas viscosity has negligible effect on both the droplet-size distribution and the spray angle. Increasing the wavelength-to-sheet-thickness ratio, however, increases the spray angle and the structure cascade rate, while decreasing the droplet size. The smallest length scale is determined more by surface tension and liquid inertia than by the liquid viscosity, while gas inertia and liquid surface tension are the key parameters in determining the spray angle.Comment: Submitted for publication to International Journal of Multiphase Flow. 37 pages; 33 figure

Dynamics of a spatially developing liquid jet with slower coaxial gas flow

A three-dimensional round liquid jet within a low-speed coaxial gas flow is numerically simulated and explained via vortex dynamics ($\lambda_2$ method). The instabilities on the liquid-gas interface reflect well the vortex interactions around the interface. Certain key features are identified for the first time. Two types of surface deformations are distinguished, which are separated by a large indentation on the jet stem: First, those near the jet start-up cap are encapsulated inside the recirculation zone behind the cap. These deformations are directly related to the dynamics of the growing cap and well explained by the vortices generated there. Second, deformations occurring farther upstream of the cap are mainly driven by the Kelvin-Helmholtz (KH) instability at the interface. Three-dimensional deformations occur in the vortex structures first, and the initially axisymmetric KH vortices deform and lead to several liquid lobes, which stretch first as thinning sheets and then either continue stretching directly into elongated ligaments - at lower relative velocity - or perforate to create liquid bridges and holes - at higher relative velocity. The different scenarios depend on Weber and Reynolds numbers based on the relative gas-liquid velocity as was found in the temporal studies. The deformations in the upstream region are well portrayed in a frame moving with the convective velocity of the liquid jet. The usefulness of the temporal analyses are now established.Comment: Presented at ICLASS 2018 conference; 8 pages; 19 Figure

Iron-deficiency anemia among children in southwest Iran

Background. Iron deficiency is a major health problem worldwide and especially in developing countries. Irondeficiency anemia has adverse effects on the development of children. Objective. The purpose of this study was to determine the prevalence of iron-deficiency anemia in children under 5 years of age in southwest Iran. The study also sought to investigate the association between socioeconomic,demographic, cultural, and nutritional factors and iron-deficiency anemia in the selected area. Methods. A randomized, cross-sectional study was performed of children 6 to 59 months of age living in urban and rural areas of Ahwaz District in Khuzestan Province. At eight randomly selected health centers, the children\u2019s height (or length) and weight were measured, and information on length and weight at birth was obtained from growth charts. Blood samples were taken from 337 randomly selected children. Results. The results showed that 43.9% of the children had anemia and 29.1% iron-deficiency anemia. The highest prevalence of iron-deficiency anemia was in the 12- to 24-month age group. In the urban areas, infants 6 to 11 months of age had the highest prevalence of irondeficiency anemia. Conclusions. The high prevalence of iron-deficiency anemia among children in southwest Iran indicates a major nutrition and health problem

Effects of Iranian economic reforms on equity in social and healthcare financing: A segmented regression analysis

Objectives: One of the main objectives of the Targeted Subsidies Law (TSL) in Iran was to improve equity in healthcare financing. This study aimed at measuring the effects of the TSL, which was implemented in Iran in 2010, on equity in healthcare financing. Methods: Segmented regression analysis was applied to assess the effects of TSL implementation on the Gini and Kakwani indices of outcome variables in Iranian households. Data for the years 1977-2014 were retrieved from formal databases. Changes in the levels and trends of the outcome variables before and after TSL implementation were assessed using Stata version 13. Results: In the 33 years before the implementation of the TSL, the Gini index decreased from 0.401 to 0.381. The Gini index and its intercept significantly decreased to 0.362 (p<0.001) 5 years after the implementation of the TSL. There was no statistically significant change in the gross domestic product or inflation rate after TSL implementation. The Kakwani index significantly increased from -0.020 to 0.007 (p<0.001) before the implementation of the TSL, while we observed no statistically significant change (p=0.81) in the Kakwani index after TSL implementation. Conclusions: The TSL reform, which was introduced as part of an economic development plan in Iran in 2010, led to a significant reduction in households� income inequality. However, the TSL did not significantly affect equity in healthcare financing. Hence, while measuring the long-term impact of TSL is paramount, healthcare decision-makers need to consider the efficacy of the TSL in order to develop plans for achieving the desired equity in healthcare financing. Copyright © 2018 The Korean Society for Preventive Medicine

The trend of national and subnational burden of maternal conditions in Iran from 1990 to 2013: The study protocol

Background: It is widely accepted that maternal mortality is a proxy for maternal health status. Maternal deaths only represent the top of the iceberg; morbidity due to maternal causes apart from maternal mortality, poses a huge burden on women's families. There is an excessive need to widen the research on maternal morbidity. Here, we explain the framework of our study on maternal conditions and their burden in Iran as a part of the National and Sub-national Burden of Diseases (NASBOD) study. Methods: A systematic search will be carried out for both published and unpublished data on maternal mortality and morbidity reported between 1985 and 2013. Data collected through systematic review and those obtained from national and sub-national surveys will be extracted in a data set. Two statistical models will be applied: Bayesian Autoregressive Multi-level models and Spatio-Temporal Regression models. Models will be used to overcome the problem of data gaps across provinces, years and age groups. Discussion: In order to control and manage maternal conditions and to make more efficient and cost-effective policies, there is an excessive need for data on the burden of such diseases. There are a few sub-national analyses of the burden of disease. In the current study, burden of maternal conditions will be assessed at national and sub-national levels in Iran between 1990 and 2013. The results of this study are undoubtedly required to provide comprehensive information at the national and provincial levels to administer interventions more effectively, since the priority based policies need regional assessments and comparisons

IL-35 Is a Novel Responsive Anti-inflammatory Cytokine — A New System of Categorizing Anti-inflammatory Cytokines

It remains unknown whether newly identified anti-inflammatory/immunosuppressive cytokine interleukin-35 (IL-35) is different from other anti-inflammatory cytokines such as IL-10 and transforming growth factor (TGF)-β in terms of inhibition of inflammation initiation and suppression of full-blown inflammation. Using experimental database mining and statistical analysis methods we developed, we examined the tissue expression profiles and regulatory mechanisms of IL-35 in comparison to other anti-inflammatory cytokines. Our results suggest that in contrast to TGF-β, IL-35 is not constitutively expressed in human tissues but it is inducible in response to inflammatory stimuli. We also provide structural evidence that AU-rich element (ARE) binding proteins and microRNAs target IL-35 subunit transcripts, by which IL-35 may achieve non-constitutive expression status. Furthermore, we propose a new system to categorize anti-inflammatory cytokines into two groups: (1) the house-keeping cytokines, such as TGF-β, inhibit the initiation of inflammation whereas (2) the responsive cytokines including IL-35 suppress inflammation in full-blown stage. Our in-depth analyses of molecular events that regulate the production of IL-35 as well as the new categorization system of anti-inflammatory cytokines are important for the design of new strategies of immune therapies