Optimal perturbation for two-dimensional vortex systems: route to non-axisymmetric state

We investigate perturbations that maximize the gain of disturbance energy in a two-dimensional isolated vortex and a counter-rotating vortex pair. The optimization is carried out using the method of Lagrange multipliers. For low initial energy of the perturbation ( ), the nonlinear optimal perturbation/gain is found to be the same as the linear optimal perturbation/gain. Beyond a certain threshold , the optimal perturbation/gain obtained from linear and nonlinear computations are different. There exists a range of for which the nonlinear optimal gain is higher than the linear optimal gain. For an isolated vortex, the higher value of nonlinear optimal gain is attributed to interaction among different azimuthal components, which is otherwise absent in a linearized system. Spiral dislocations are found in the nonlinear optimal perturbation at the radial location where the most dominant wavenumber changes. Long-time nonlinear evolution of linear and nonlinear optimal perturbations is studied. The evolution shows that, after the initial increment of perturbation energy, the vortex attains a quasi-steady state where the mean perturbation energy decreases on a slow time scale. The quasi-steady vortex state is non-axisymmetric and its shape depends on the initial perturbation. It is observed that the lifetime of a quasi-steady vortex state obtained using the nonlinear optimal perturbation is longer than that obtained using the linear optimal perturbation. For a counter-rotating vortex pair, the mechanism that maximizes the energy gain is found to be similar to that of the isolated vortex. Within the linear framework, the optimal perturbation for a vortex pair can be either symmetric or antisymmetric, whereas the structure of the nonlinear optimal perturbation, beyond the threshold, is always asymmetric. No quasi-steady state for a counter-rotating vortex pair is observed

Significance of Animal's Postmortem Examination

<p>An ante-mortem examination can quickly discover several disorders that are not readily obvious. Therefore, detecting and diagnosing disease is a fundamental cause for postmortem examinations. This is done not only to guarantee that the meat is safe for consumers to ingest, but also to implement preventive measures to manage disease at the farm level itself. We consider three main points-</p&gt

Uprising African swine fever: Prevention and control

<p>Recently, African swine fever (ASF) has extended from sub-Saharan Africa to the Trans-Caucasus region, Eastern Europe, and portions of the Russian Federation. There are notable parallels between the disease and the African context in this new epidemiological scenario, but there are also notable distinctions, such as the significant role of wild boar. Gaining further insight into this novel scenario will facilitate enhanced management and stop the spread of illness. This page compares these various circumstances and provides up-to-date information on the immunological response to infection, the pathophysiology of ASF virus strains, and the potential for vaccine development. There is a discussion of knowledge gaps and future control chances. </p&gt

Novel approach for tension testing micro tubes

Due to the miniaturization of products, new or modified processes are required to create small components. With the development of these new processes, it is also important to establish methods to evaluate the mechanical properties of the materials used in these components. These properties are necessary for accurately creating representative predictive models and simulations. At the same time, this evaluation can be challenging as sampling specimens become smaller the securing and handling of these smaller specimens becomes very difficult. Recently, researchers made studies to develop and model the micro tube hydroforming (MTHF) process. In many of these studies, the mechanical properties used were either traditional book values or were values obtained directly from the manufacturers. The question then becomes, how do the manufacturers determine their provided mechanical properties? The research in this study focuses on the development and testing of a new process to determine the mechanical properties of stainless steel micro tubes. Specifically, a set of clamps for securing a micro tube in a standard tension-testing machine were developed. A method for localizing the stress within the middle of a specimen was developed and the findings are presented in this paper

Actual and predicted prevalence of alcohol consumption during pregnancy in Latin America and the Caribbean: systematic literature review and meta-analysis

ABSTRACT Objective To estimate the prevalence of alcohol consumption during pregnancy among the general population of Latin America and the Caribbean, by country, in 2012. Methods Three steps were taken: a comprehensive, systematic literature search; meta-analyses, assuming a random-effects model for countries with published studies; and regression modelling (data prediction) for countries with either no published studies or too few to obtain an estimate. Results Based on 24 existing studies, the pooled prevalence of alcohol consumption during pregnancy among the general population was estimated for Brazil (15.2%; 95% confidence interval [95%CI]: 10.4%–20.8%) and Mexico (1.2%; 95%CI: 0.0%–2.7%). The prevalence of alcohol consumption during pregnancy among the general population was predicted for 31 countries and ranged from 4.8% (95%CI: 4.2%–5.4%) in Cuba to 23.3% (95%CI: 20.1%–26.5%) in Grenada. Conclusions Greater prevention efforts and measures are needed in the countries of Latin America and the Caribbean to prevent pregnant women from consuming alcohol during pregnancy and decrease the rates of Fetal Alcohol Spectrum Disorder. Additional high quality studies on the prevalence of alcohol consumption during pregnancy in Latin America and the Caribbean are also needed