Energy spectra in turbulent bubbly flows

We conduct experiments in a turbulent bubbly flow to study the nature of the transition between the classical $-$5/3 energy spectrum scaling for a single-phase turbulent flow and the $-$3 scaling for a swarm of bubbles rising in a quiescent liquid and of bubble-dominated turbulence. The bubblance parameter, which measures the ratio of the bubble-induced kinetic energy to the kinetic energy induced by the turbulent liquid fluctuations before bubble injection, is often used to characterise the bubbly flow. We vary the bubblance parameter from $b = \infty$ (pseudo-turbulence) to $b = 0$ (single-phase flow) over 2-3 orders of magnitude ($0.01 - 5$) to study its effect on the turbulent energy spectrum and liquid velocity fluctuations. The probability density functions (PDFs) of the liquid velocity fluctuations show deviations from the Gaussian profile for $b > 0$, i.e. when bubbles are present in the system. The PDFs are asymmetric with higher probability in the positive tails. The energy spectra are found to follow the $-$3 scaling at length scales smaller than the size of the bubbles for bubbly flows. This $-$3 spectrum scaling holds not only in the well-established case of pseudo-turbulence, but surprisingly in all cases where bubbles are present in the system ($b > 0$). Therefore, it is a generic feature of turbulent bubbly flows, and the bubblance parameter is probably not a suitable parameter to characterise the energy spectrum in bubbly turbulent flows. The physical reason is that the energy input by the bubbles passes over only to higher wave numbers, and the energy production due to the bubbles can be directly balanced by the viscous dissipation in the bubble wakes as suggested by Lance $\&$ Bataille (1991). In addition, we provide an alternative explanation by balancing the energy production of the bubbles with viscous dissipation in the Fourier space.Comment: J. Fluid Mech. (in press

Three-dimensional Lagrangian Voronoi analysis for clustering of particles and bubbles in turbulence

Three-dimensional Voronoi analysis is used to quantify the clustering of inertial particles in homogeneous isotropic turbulence using data from numerics and experiments. We study the clustering behavior at different density ratios and particle response times (i.e. Stokes numbers St). The Probability Density Functions (PDFs) of the Voronoi cell volumes of light and heavy particles show a different behavior from that of randomly distributed particles -i.e. fluid tracers-implying that clustering is present. The standard deviation of the PDF normalized by that of randomly distributed particles is used to quantify the clustering. Light particles show maximum clustering for St around 1-2. The results are consistent with previous investigations employing other approaches to quantify the clustering. We also present the joint PDFs of enstrophy and Voronoi volumes and their Lagrangian autocorrelations. The small Voronoi volumes of light particles correspond to regions of higher enstrophy than those of heavy particles, indicating that light particles cluster in higher vorticity regions. The Lagrangian temporal autocorrelation function of Voronoi volumes shows that the clustering of light particles lasts much longer than that of heavy or neutrally buoyant particles. Due to inertial effects, the Lagrangian autocorrelation time-scale of clustered light particles is even longer than that of the enstrophy of the flow itself.Comment: J. Fluid Mech. 201

An easy to control all-metal in-line-series ohmic RF MEMS switch

Copyright @ 2010 Springer-VerlagThe analysis, design and simulation of a novel easy to control all-metal in-line-series ohmic RF MEMS switch is presented, for applications where the operating frequency ranges from DC to 4 GHz. The proposed switch, due to its unique shape and size, assures high isolation and great linearity fulfilling the necessary requirements as concerns loss, power handling and power consumption. Simplicity has been set as the key success factor implying robustness and high fabrication yield. On the other hand, the specially designed cantilever-shape (hammerhead) allows distributed actuation force ensuring high controllability as well as reliability making the presented RF MEMS switch one of its kind

Seedling Production Systems for Smallholder Forestry Development: Local Practices versus National Policies in the Philippines

The tree seedling nursery sector in the Philippines is influenced by a number of national level policies affecting the number and type of species produced. Policies favour high-volume production of a limited range of mostly exotic species, and research indicates that seedlings are often of low physical and genetic quality. Local knowledge on best species for sites is not being communicated to people planting. A project funded by the Australian Centre for International Agricultural Research is investigating measures to improve the performance and effectiveness of the forestry seedling production system in Leyte and Mindanao in the Philippines. Seedlings are produced by government agencies, in community forestry projects and by individual private operators; the main customers are smallholder tree farmers. Communities and private individuals quickly set up nurseries when there is a demand for seedlings, but these nurseries tend to be ephemeral and lack financial sustainability. While large nurseries offer opportunities for economies of scale, small nurseries operate on a low cost basis, and are more widely distributed, and their seedlings are more accessible to smallholders, who lack transport facilities. Small private nurseries, while having limited access to new technology, often produce seedlings of quality similar to government and community nurseries. However, they require assistance in access to high-quality germplasm and training in improved seed production technology, to play a greater role in expansion of plantation forestry. This paper reports survey findings on seedling production systems, and examines the link between national level policies and local level practices

Infection and risk perception of sars-cov-2 among airport workers: A mixed methods study

This is a mixed-methods research study carried out on a cohort of airport workers during the SARS-CoV-2 pandemic. We used quantitative and qualitative methods to describe the infection and risk perception of SARS-CoV-2 in a cohort of workers at the International Airport El Dorado/Luis Carlos Galán Sarmiento in Bogotá, Colombia. An incidence of SARS-CoV-2 infection of 7.9% was found in the workers. A high perception of risk was associated with activities such as using public transport. Risk perception is strongly influenced by practices related to work conditions and environments. These findings could help us understand the pandemic’s dynamics and the conceptions of the risk of transmission to promote policies on health and safety in this group of workers

Optimizing the random search of a finite-lived target by a L\'evy flight

In many random search processes of interest in chemistry, biology or during rescue operations, an entity must find a specific target site before the latter becomes inactive, no longer available for reaction or lost. We present exact results on a minimal model system, a one-dimensional searcher performing a discrete time random walk or L\'evy flight. In contrast with the case of a permanent target, the capture probability and the conditional mean first passage time can be optimized. The optimal L\'evy index takes a non-trivial value, even in the long lifetime limit, and exhibits an abrupt transition as the initial distance to the target is varied. Depending on the target lifetime, this transition is discontinuous or continuous, separated by a non-conventional tricritical point. These results pave the way to the optimization of search processes under time constraints.Comment: Supplementary material can be found at the end of the main documen

RUNX1 and breast cancer

News on: Runx1 stabilizes the mammary epithelial cell phenotype and prevents epithelial to mesenchymal transition, by Hong et al. Oncotarget. 2017; 8:17610-27. doi: 10.18632/oncotarget.15381

Effect of PDGF-BB on Human Retinal Pericytes

Background – The majority of ocular conditions seen in patients with diabetic retinopathy are a result of damage to the retinal vasculature, which leads to microaneurysms, hemorrhage, and eventually neovascularization. The first step in the pathogenesis of these conditions is derived from the loss of Human Retinal Pericytes (HRPs), or cells which are essential to the preservation of the integrity of the retinal vasculature, and PDGF-BB is the primary promotor of growth and recruitment for HRPs. Aim - Patients with NPDR produce lower levels of PDGF-BB than in normal conditions, which could contribute to the loss of pericytes early in diabetic retinopathy. The purpose of this study is to evaluate the effect of PDGF-BB on HRPs in vitro to determine whether or not the longevity of the HRPs can be preserved with the intent of contributing to development of therapeutic interventions for patients with diabetic retinopathy. This is the first PDGF-BB study on its effect on the viability and longevity of HRPs. Methods – Three groups of HRPs were treated with three different concentrations of PDGF-BB which correlate to concentrations found in patients with PDR, NPDR, and normal conditions. These three concentrations were also compared with a negative control group which was not treated. After 24 and 48 hours the viable cells were counted by triptan blue measurements. The results were reported by evaluating viable cells at 24 and 48 hours, growth of each group between these time periods, and significant growth differences between groups at each time period. Each group was grown in triplicates and an average from these triplicates was used during analysis. Results – Of the results found, three were clinically significant. Pertaining to viability, the NPDR group was the only one with a significant result at 24 hours. Growth difference analysis was significant for the PDR group at the 24-hour period. Growth difference between all groups was significant at the 24 hours mark but not at 48. Conclusion – Of the results obtained, significant results were only seen at the 24 hours period which is thought to be a result of the well space not being large enough to accommodate growth beyond the 24-hour time frame. The finding of a statistically significant difference at 24 hours but not 48 hours further suggests this as the complication as well. That being said, significant growth difference was seen with the PDR group, which was treated with high levels of PDGF-BB. This finding is consistent with the hypothesis that PDGF-BB levels encourage the growth of HRP cells. Discussion - Previous clinical trials on PDGF-BB inhibitors showed that they did not help patients with diabetic retinopathy due to the inherent deficiency of HRPs found in these patients. We anticipate results from this study will support an opposing approach by supplementing PDGF-BB, rather than blocking leading to innovative clinical outcomes

Vivienda adecuada para grupos vulnerables en San Pedro Itzicán, Poncitlán, Jalisco

El siguiente documento presenta el Proyecto de Aplicación Profesional llamado Vivienda Adecuada para Grupos Vulnerables que tiene como finalidad generar acciones de mejoramiento y propuestas de vivienda para los habitantes de San Pedro Itzicán en el municipio de Poncitlán, para lograr disminuir el número de viviendas en Jalisco que se encuentran en condiciones poco habitables. Las propuestas del proyecto están enfocadas en mecanismos óptimos de gestión, financiamiento y realizar prototipos de casa habitación en base a diagnósticos previos para atender problemáticas, pero que se adecúen a las necesidades específicas de cada familia y su estilo de vida, a la vez que se implementan sistemas constructivos simples para su propia ejecución. La metodología se basa en identificar las problemáticas constantes entre las viviendas desempeñando el papel de un asesor técnico. Se invita a generar una comunidad participativa donde se acerca al representante de la familia y se le realizan ciertas preguntas, previo a una reunión con autoridades, censo y difusión sobre el apoyo que se les brinda y el compromiso de ambas partes. Durante el periodo de primavera se realizaron portafolios de 21 beneficiarios interesados de diferentes barrios, mientras que en el periodo de otoño se realizaron los expedientes de 12 beneficiarios. Dichos expedientes contienen información como documentación, cartas compromiso, carta de solicitud, fichas de diagnóstico, planos con preexistencias y propuestas, planos arquitectónicos y planos estructurales. Para ello, se realizaron visitas de campo para obtener información y llegar a un acuerdo sobre los resultados, principalmente para que los prototipos de las casas cumplieran con las características estructurales y de habitabilidad que se espera de la vivienda adecuada, las cuales se dividen en etapas para los beneficiarios puedan realizarlas de manera progresiva. Como parte de los productos, se realizó una exploración geotécnica del suelo, propuestas sobre cimentación, cálculo estructural de losas, planos arquitectónicos y estructurales, sistema de captación de agua (SCALL), propuestas de ventanearía y puertas, así como tres tipos de presupuestos los cuales contenían de manera independiente y conjunta: materiales, mano de obra, y materiales con mano de obra, para considerar los distintos escenarios en los que las familias beneficiarias podrían participar en los programas sociales existentes.ITESO, A.C