Pore-scale analysis of the minimum liquid film thickness around elongated bubbles in confined gas-liquid flows

© 2017 Elsevier Ltd The fluid mechanics of elongated bubbles in confined gas-liquid flows in micro-geometries is important in pore-scale flow processes for enhanced oil recovery and mobilization of colloids in unsaturated soil. The efficiency of such processes is traditionally related to the thickness of the liquid film trapped between the elongated bubble and the pore's wall, which is assumed constant. However, the surface of long bubbles presents undulations in the vicinity of the rear meniscus, which may significantly decrease the local thickness of the liquid film, thus impacting the process of interest. This study presents a systematic analysis of these undulations and the minimum film thickness induced in the range Ca=0.001-0.5 and Re=0.1-2000. Pore-scale Computational Fluid Dynamics (CFD) simulations are performed with a self-improved version of the opensource solver ESI OpenFOAM which is based on a Volume of Fluid method to track the gas-liquid interface. A lubrication model based on the extension of the classical axisymmetric Bretherton theory is utilized to better understand the CFD results. The profiles of the rear meniscus of the bubble obtained with the lubrication model agree fairly well with those extracted from the CFD simulations. This study shows that the Weber number of the flow, We=CaRe, is the parameter that best describes the dynamics of the interfacial waves. When We 0.1, a larger number of wave crests becomes evident on the surface of the rear meniscus of the bubble. The liquid film thickness at the crests of the undulations thins considerably as the Reynolds number is increased, down to less than 60% of the value measured in the flat film region. This may significantly influence important environmental processes, such as the detachment and mobilization of micron-sized pollutants and pathogenic micro-organisms adhering at the pore's wall in unsaturated soil

Buckling of orthotropic webs in process machinery

Many webs in web process machinery exhibit out-of-plane deformations, defined as troughs, in free web spans between rollers. In other cases when the troughs become severe the out-of-plane web deformations will begin to transcend rollers. Any out-of-plane web deformations that transcend rollers are defined as wrinkles. Troughs and wrinkles in webs are often undesirable as they can interfere with web processes such as coating, they can result in web breaks and thereby decreased productivity, or these deformations may become permanent and result in quality loss.Many plastic film, paper, tissue and nonwoven webs are highly anisotropic either by design or just as a result of the process by which the web is made. The first objective of this paper is to show how anisotropic web properties affect the buckling and wrinkling tendencies of these webs. Previously algorithms have been developed that show how roller misalignment can induce troughs and wrinkles. The second objective of this paper is to demonstrate how web orthotrophy can affect the allowable roller misalignment in a web span and the web tension required to sustain a wrinkle upon a roller.Mechanical and Aerospace Engineerin

Analysis of trough formation and lateral steering of a web due to a tapered downstream roller

Cylindrical rollers are never perfectly cylindrical. A common defect of a cylindrical roller is radial taper. A roller with a radial taper will induce a lateral shear force into the web. This shear force will cause a steering effect as well as a cross machine direction compressive stress which can lead to the formation of troughs and wrinkles in a web. This publication addresses these topics and presents a model to help determine the specification for taper in "cylindrical" rollers. An analytical model is presented, experiments were performed, and the data was compared to predictions from the proposed model.Mechanical and Aerospace Engineerin

Predicting web wrinkles on rollers

There are two levels of web instability in web lines. The first level of web instability is called web troughs. Web troughs are due to the instability of webs that occur in free web spans. Web troughs have been shown to be predictable using traditional buckling theory. Closed form expressions have been developed and verified in the lab that predict when web troughs will result from roller misalignment and roller taper. Web troughs can be a nuisance in web processes where the web must be planar. The troughs themselves may not damage the web but can be responsible for reductions in web quality after processing that can result in lost profit.The next level of instability is called web wrinkles. Web wrinkles are due to the instability of webs that are transiting rollers. When webs transit rollers they assume the shape of a sector of a cylindrical shell. A cylindrical shell of web is much more stable than the web in free spans. Compressive stresses which are two to three orders of magnitude larger than those required to induce web troughs are necessary to buckle the cylindrical shell. This paper will demonstrate that web wrinkles are a post buckling phenomena that result from web troughs. The source of the high compressive stresses needed to buckle the web into wrinkles on rollers will be shown. We will show how web wrinkles can be predicted and we will show experimental verification for the cases where a misaligned or tapered rollers were the source of the troughs and wrinkles. Web wrinkles can damage the web as a result of inelastic deformation, fold-overs, and in the worst case may cause full separation or failure of the web. When web wrinkles can be predicted, they can also be prevented.Mechanical and Aerospace Engineerin

Potential contribution of HIV during first-line tuberculosis treatment to subsequent rifampicin-monoresistant tuberculosis and acquired tuberculosis drug resistance in South Africa: a retrospective molecular epidemiology study

Background: South Africa has a high burden of rifampicin-resistant tuberculosis (including multidrug-resistant [MDR] tuberculosis), with increasing rifampicin-monoresistant (RMR) tuberculosis over time. Resistance acquisition during first-line tuberculosis treatment could be a key contributor to this burden, and HIV might increase the risk of acquiring rifampicin resistance. We assessed whether HIV during previous treatment was associated with RMR tuberculosis and resistance acquisition among a retrospective cohort of patients with MDR or rifampicin-resistant tuberculosis. Methods: In this retrospective cohort study, we included all patients routinely diagnosed with MDR or rifampicin-resistant tuberculosis in Khayelitsha, Cape Town, South Africa, between Jan 1, 2008, and Dec 31, 2017. Patient-level data were obtained from a prospective database, complemented by data on previous tuberculosis treatment and HIV from a provincial health data exchange. Stored MDR or rifampicin-resistant tuberculosis isolates from patients underwent whole-genome sequencing (WGS). WGS data were used to infer resistance acquisition versus transmission, by identifying genomically unique isolates (single nucleotide polymorphism threshold of five). Logistic regression analyses were used to assess factors associated with RMR tuberculosis and genomic uniqueness. Findings: The cohort included 2041 patients diagnosed with MDR or rifampicin-resistant tuberculosis between Jan 1, 2008, and Dec 31, 2017; of those, 463 (22.7%) with RMR tuberculosis and 1354 (66.3%) with previous tuberculosis treatment. In previously treated patients, HIV positivity during previous tuberculosis treatment versus HIV negativity (adjusted odds ratio [OR] 2.07, 95% CI 1.35-3.18), and three or more previous tuberculosis treatment episodes versus one (1.96, 1.21-3.17) were associated with RMR tuberculosis. WGS data showing MDR or rifampicin-resistant tuberculosis were available for 1169 patients; 360 (30.8%) isolates were identified as unique. In previously treated patients, RMR tuberculosis versus MDR tuberculosis (adjusted OR 4.96, 3.40-7.23), HIV positivity during previous tuberculosis treatment (1.71, 1.03-2.84), and diagnosis in 2013-17 (1.42, 1.02-1.99) versus 2008-12, were associated with uniqueness. In previously treated patients with RMR tuberculosis, HIV positivity during previous treatment (adjusted OR 5.13, 1.61-16.32) was associated with uniqueness as was female sex (2.50 [1.18-5.26]). Interpretation: These data suggest that HIV contributes to rifampicin-resistance acquisition during first-line tuberculosis treatment and that this might be driving increasing RMR tuberculosis over time. Large-scale prospective cohort studies are required to further quantify this risk. Funding: Swiss National Science Foundation, South African National Research Foundation, and Wellcome Trust

Design principles for riboswitch function

Scientific and technological advances that enable the tuning of integrated regulatory components to match network and system requirements are critical to reliably control the function of biological systems. RNA provides a promising building block for the construction of tunable regulatory components based on its rich regulatory capacity and our current understanding of the sequence–function relationship. One prominent example of RNA-based regulatory components is riboswitches, genetic elements that mediate ligand control of gene expression through diverse regulatory mechanisms. While characterization of natural and synthetic riboswitches has revealed that riboswitch function can be modulated through sequence alteration, no quantitative frameworks exist to investigate or guide riboswitch tuning. Here, we combined mathematical modeling and experimental approaches to investigate the relationship between riboswitch function and performance. Model results demonstrated that the competition between reversible and irreversible rate constants dictates performance for different regulatory mechanisms. We also found that practical system restrictions, such as an upper limit on ligand concentration, can significantly alter the requirements for riboswitch performance, necessitating alternative tuning strategies. Previous experimental data for natural and synthetic riboswitches as well as experiments conducted in this work support model predictions. From our results, we developed a set of general design principles for synthetic riboswitches. Our results also provide a foundation from which to investigate how natural riboswitches are tuned to meet systems-level regulatory demands

Beneficial Fitness Effects Are Not Exponential for Two Viruses

The distribution of fitness effects for beneficial mutations is of paramount importance in determining the outcome of adaptation. It is generally assumed that fitness effects of beneficial mutations follow an exponential distribution, for example, in theoretical treatments of quantitative genetics, clonal interference, experimental evolution, and the adaptation of DNA sequences. This assumption has been justified by the statistical theory of extreme values, because the fitnesses conferred by beneficial mutations should represent samples from the extreme right tail of the fitness distribution. Yet in extreme value theory, there are three different limiting forms for right tails of distributions, and the exponential describes only those of distributions in the Gumbel domain of attraction. Using beneficial mutations from two viruses, we show for the first time that the Gumbel domain can be rejected in favor of a distribution with a right-truncated tail, thus providing evidence for an upper bound on fitness effects. Our data also violate the common assumption that small-effect beneficial mutations greatly outnumber those of large effect, as they are consistent with a uniform distribution of beneficial effects

Interleukin 7 from Maternal Milk Crosses the Intestinal Barrier and Modulates T- Cell Development in Offspring

Background Breastfeeding protects against illnesses and death in hazardous environments, an effect partly mediated by improved immune function. One hypothesis suggests that factors within milk supplement the inadequate immune response of the offspring, but this has not been able to account for a series of observations showing that factors within maternally derived milk may supplement the development of the immune system through a direct effect on the primary lymphoid organs. In a previous human study we reported evidence suggesting a link between IL-7 in breast milk and the thymic output of infants. Here we report evidence in mice of direct action of maternally-derived IL-7 on T cell development in the offspring. Methods and Findings  We have used recombinant IL-7 labelled with a fluorescent dye to trace the movement in live mice of IL-7 from the stomach across the gut and into the lymphoid tissues. To validate the functional ability of maternally derived IL- 7 we cross fostered IL-7 knock-out mice onto normal wild type mothers. Subsets of thymocytes and populations of peripheral T cells were significantly higher than those found in knock-out mice receiving milk from IL-7 knock-out mothers. Conclusions/Significance Our study provides direct evidence that interleukin 7, a factor which is critical in the development of T lymphocytes, when maternally derived can transfer across the intestine of the offspring, increase T cell production in the thymus and support the survival of T cells in the peripheral secondary lymphoid tissue

Modular construction of mammalian gene circuits using TALE transcriptional repressors

An important goal of synthetic biology is the rational design and predictable implementation of synthetic gene circuits using standardized and interchangeable parts. However, engineering of complex circuits in mammalian cells is currently limited by the availability of well-characterized and orthogonal transcriptional repressors. Here, we introduce a library of 26 reversible transcription activator–like effector repressors (TALERs) that bind newly designed hybrid promoters and exert transcriptional repression through steric hindrance of key transcriptional initiation elements. We demonstrate that using the input-output transfer curves of our TALERs enables accurate prediction of the behavior of modularly assembled TALER cascade and switch circuits. We also show that TALER switches using feedback regulation exhibit improved accuracy for microRNA-based HeLa cancer cell classification versus HEK293 cells. Our TALER library is a valuable toolkit for modular engineering of synthetic circuits, enabling programmable manipulation of mammalian cells and helping elucidate design principles of coupled transcriptional and microRNA-mediated post-transcriptional regulation.National Institutes of Health (U.S.) (Grant 5R01CA155320-04)National Institutes of Health (U.S.) (Grant P50GM098792)National Institutes of Health (U.S.) (Grant 1R01CA173712-01