Interaction of laser radiation with the material during production powders and fibers

Воздействие лазерного излучения на твердое тело приводит к изменению температурного поля обрабатываемого вещества. Характер нагрева, определяющийся скоростями изменения температуры, температурных градиентов, оказывается различным в зависимости от свойств обрабатываемого материала и условий обработки. Основными физическими параметрами процесса лазерной обработки твердых тел являются удельная мощность поглощенного лазерного потока 104–109 Вт/см2 и время взаимодействия металла с лучом 10–5–10–8 с. При взаимодействии подобных импульсов излучения с поверхностью происходит мгновенное взрывоподобное плавление части материала и перевод окружающего поверхность вещества в плазменное состояние. Последующее расширение плазмы сопровождается возникновением ударной волны с пиковым давлением 1–10 ГПа, которая действует на материал, и имеет место диспергирование металла. Решена математическая задача нагрева и плавления цилиндрической пластины нормально падающим на ее поверхность световым потоком лазерного излучения, описываемая системой уравнений теплопроводности в трех сечениях нагреваемой пластины, которые характеризуются временным фактором воздействия лазерного излучения на вещество: 1) 0 ≤ t ≤ tm; 2) t > tm; 3) tm tm; 3) tm < t ≤ th (here tm, th is the time moment corresponding to the beginning of the formation of the liquid phase and the end of the melting of the plate, respectively). The calculated dependences of changes in the surface temperature of metal alloys X18N10T, X15N60 during the action of a laser radiation pulse with a duration of τ=5 ms are presented. The presence of a phase transition associated with metal melting (an inflection in the curves) leads to a temporary decrease in the rate of temperature growth. The distribution of temperature fields causes a significant heterogeneity in the distribution of temperature over the thickness of materials, which reaches 2000 °C or more depending on the thickness of the metal and the conditions of exposure. The temperature curves of the surface heating repeat the shape of the pulse, and the temperature of the rest of the metal has a nonlinear tendency to increase with the output to the asymptote. It is established that the process of explosive metal sputtering requires heating the volume of the material above the melting point at a thickness of 300–350 microns and an impact energy of 7–8 J. Reducing the level of energy impact to 5–6 J and increasing the thickness of the workpiece more than 500 microns does not provide the distribution of temperature fields required for the implementation of the spraying process

The Spin-2 Equation on Minkowski Background

The linearised general conformal field equations in their first and second order form are used to study the behaviour of the spin-2 zero-rest-mass equation on Minkowski background in the vicinity of space-like infinity.Comment: Contribution to the Proceedings of the Spanish Relativity Meeting ERE 2012, 4 page

Journal Staff

A time-dependent coordinate transformation of a constant coeffcient hyperbolic equation which results in a variable coeffcient problem is considered. By using the energy method, we derive well-posed boundary conditions for the continuous problem. It is shown that the number of boundary conditions depend on the coordinate transformation. By using Summation-by-Parts (SBP) operators for the space discretization and weak boundary conditions, an energy stable finite dieffrence scheme is obtained. We also show how to construct a time-dependent penalty formulation that automatically imposes the right number of boundary conditions. Numerical calculations corroborate the stability and accuracy of the approximations

On the nonlinear relationship between wall shear stress topology and multi-directionality in coronary atherosclerosis

Background and Objective: In this paper we investigate twelve multi-directional/topological wall shear stress (WSS) derived metrics and their relationships with the formation of coronary plaques in both computational fluid dynamics (CFD) and dynamic fluid-structure interaction (FSI) frameworks. While low WSS is one of the most established biomechanical markers associated with coronary atherosclerosis progression, alone it is limited. Multi-directional and topological WSS derived metrics have been shown to be important in atherosclerosis related mechanotransduction and near-wall transport processes. However, the relationships between these twelve WSS metrics and the influence of both FSI simulations and coronary dynamics is understudied. Methods: We first investigate the relationships between these twelve WSS derived metrics, stenosis percentage and lesion length through a parametric, transient CFD study. Secondly, we extend the parametric study to FSI, both with and without the addition of coronary dynamics, and assess their correlations. Finally, we present the case of a patient who underwent invasive coronary angiography and optical coherence tomography imaging at two time points 18 months apart. Associations between each of the twelve WSS derived metrics in CFD, static FSI and dynamic FSI simulations were assessed against areas of positive/negative vessel remodelling, and changes in plaque morphology. Results: 22–32% stenosis was the threshold beyond which adverse multi-directional/topological WSS results. Each metric produced a different relationship with changing stenoses and lesion length. Transient haemodynamics was impacted by coronary dynamics, with the topological shear variation index suppressed by up to 94%. These changes appear more critical at smaller stenosis levels, suggesting coronary dynamics could play a role in the earlier stages of atherosclerosis development. In the patient case, both dynamics and FSI vs CFD changes altered associations with measured changes in plaque morphology. An appendix of the linear fits between the various FSI- and CFD-based simulations is provided to assist in scaling CFD-based results to resemble the compliant walled characteristics of FSI more accurately. Conclusions: These results highlight the potential for coronary dynamics to alter multidirectional/topological WSS metrics which could impact associations with changes in coronary atherosclerosis over time. These results warrant further investigation in a wider range of morphological settings and longitudinal cohort studies in the future.Harry J. Carpenter, Mergen H. Ghayesha, Anthony C. Zander, Peter J. Psalti

Creating a multi-center rare disease consortium - the Consortium of Eosinophilic Gastrointestinal Disease Researchers (CEGIR).

 Eosinophilic gastrointestinal disorders (EGIDs) affect various segments of the gastrointestinal tract. Since these disorders are rare, collaboration is essential to enroll subjects in clinical studies and study the broader population. The Rare Diseases Clinical Research Network (RDCRN), a program of the National Center for Advancing Translational Sciences (NCATS), funded the Consortium of Eosinophilic Gastrointestinal Disease Researchers (CEGIR) in 2014 to advance the field of EGIDs. CEGIR facilitates collaboration among various centers, subspecialties, patients, professional organizations and patient-advocacy groups and includes 14 clinical sites. It has successfully initiated two large multi-center clinical studies looking to refine EGID diagnoses and management. Several pilot studies are underway that focus on various aspects of EGIDs including novel therapeutic interventions, diagnostic and monitoring methods, and the role of the microbiome in pathogenesis. CEGIR currently nurtures five physician-scholars through a career training development program and has published more than 40 manuscripts since its inception. This review focuses on CEGIR's operating model and progress and how it facilitates a framework for exchange of ideas and stimulates research and innovation. This consortium provides a model for progress on other potential clinical areas