5,575 research outputs found
Energization of charged test particles in magnetohydrodynamic fields: waves vs turbulence picture
Direct numerical simulations of 3D compressible MHD turbulence were performed
in order to study the relation between waves modes and coherent structures and
the consequent energization of test particles. Moreover, the question of which
is the main mechanism of this particle energization is rigorously discussed. In
particular, using the same initial conditions, we analyzed the non-linear and
linear evolution of a turbulent state along with the case of randomized phases.
Then, the behavior of the linear and non-linear simulations were compared
through the study of time evolution of particle kinetic energy and preferential
concentration. Also, spatio temporal spectra were used to identify the presence
of wave modes and quantify the fraction of energy around the MHD modes in
linear and non-linear simulations. Finally, the variation of the correlation
time of the external forcing is studied in detail along with the effect on the
particle energization (and clustering) and the presence of wave modes. More
specifically, particle energization tends to decrease when the fraction of
linear energy increase, supporting the idea that energization by structures is
the dominant mechanism for particle energization instead of resonating with
wave modes as suggested by Fermi energization theory
Type 2 diabetes and reduced exercise tolerance: A review of the literature through an integrated physiology approach
The association between type 2 diabetes mellitus (T2DM) and heart failure (HF) is well established. Early in the course of the diabetic disease, some degree of impaired exercise capacity (a powerful marker of health status with prognostic value) can be frequently highlighted in otherwise asymptomatic T2DM subjects. However, the literature is quite heterogeneous, and the underlying pathophysiologic mechanisms are far from clear. Imaging-cardiopulmonary exercise testing (CPET) is a non-invasive, provocative test providing a multi-variable assessment of pulmonary, cardiovascular, muscular, and cellular oxidative systems during exercise, capable of offering unique integrated pathophysiological information. With this review we aimed at defying the cardiorespiratory alterations revealed through imaging-CPET that appear specific of T2DM subjects without overt cardiovascular or pulmonary disease. In synthesis, there is compelling evidence indicating a reduction of peak workload, peak oxygen assumption, oxygen pulse, as well as ventilatory efficiency. On the contrary, evidence remains inconclusive about reduced peripheral oxygen extraction, impaired heart rate adjustment, and lower anaerobic threshold, compared to non-diabetic subjects. Based on the multiparametric evaluation provided by imaging-CPET, a dissection and a hierarchy of the underlying mechanisms can be obtained. Here we propose four possible integrated pathophysiological mechanisms, namely myocardiogenic, myogenic, vasculogenic and neurogenic. While each hypothesis alone can potentially explain the majority of the CPET alterations observed, seemingly different combinations exist in any given subject. Finally, a discussion on the effects -and on the physiological mechanisms-of physical activity and exercise training on oxygen uptake in T2DM subjects is also offered. The understanding of the early alterations in the cardiopulmonary response that are specific of T2DM would allow the early identification of those at a higher risk of developing HF and possibly help to understand the pathophysiological link between T2DM and HF
High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers
In recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated
Optical Quality Resorbable Calcium-Phosphate Glasses for Biophotonic Applications
Recently developed calcium-phosphate glass formulations are proposed in this chapter as a new class of materials for biomedical optics and photonics. The glasses have been designed and carefully prepared in our laboratory to be dissolvable in biological fluids while being optically transparent, mechanically reliable both in dry and humid environments, and suitable for both preform extrusion and fiber drawing. Optical fibers have been drawn from these glasses using our custom-made induction heated drawing tower and showed attenuation loss values from one to two orders of magnitude lower than the counterpart polymeric-based bioresorbable devices reported in literature. In addition, the optical fibers have been implanted in living rats for several weeks and no clinical signs of any adverse effect have been found. Results on the inscription and characterization of different types of fiber Bragg grating-based optical filters will be also shown, together with the demonstration of the suitability of the above-mentioned bioresorbable optical fibers for time-domain diffuse optical spectroscopy
Toward the fabrication of extruded microstructured bioresorbable phosphate glass optical fibers
The steps toward the fabrication of directly extruded microstructured fiber preforms made of a bioresorbable phosphate glass are herein presented, analyzing the features of the process from the glass synthesis to the manufacturing of the fiber. The realization of these fibers leverages on three main pillars: an optically transparent bioresorbable glass, its extrusion into a preform, and the fiber drawing. The glass has been designed and carefully prepared in our laboratory to be dissolvable in a biological fluid while being optically transparent and suitable for both preform extrusion and fiber drawing. To support the production of an optimized die for the preform extrusion, a simplified laminar flow model simulation has been employed. This model is intended as a tool for a fast and reliable way to catch the complex behavior of glass flow during each extrusion and can be regarded as an effective design guide for the dies to fulfill the specific needs for preform fabrication. After die optimization, extrusion of a capillary was realized, and a stacking of extruded tubes was drawn to produce a microstructured optical fiber made of bioresorbable phosphate glass
Computed Tomography of the Coronary Arteries
MSCT Coronary Angiography is a fast developing non-invasive diagnostic technique that can detect a coronary stenosis. The detection of a coronary stenosis is hampered by limited image quality and by motion artefacts and extensive calcifications. However, MSCT-coronary angiography is highly reliable to rule out coronary stenosis. The role of MSCT-coronary angiography in the diagnostic work-up of coronary artery disease needs further research
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