11 research outputs found
Non-modal stability analysis of magneto-hydrodynamic flow in a single pipe
No full textA complete understanding of the stability of fluid flows under varying magnetic field profiles is imperative for achieving control of plasma and operating fluids in the blankets of future fusion reactors. In this context, the primary objective of this study is to investigate the influence of varying magnetic profiles on the flow regime of a generic fluid, which is representative of both thermonuclear plasma and conductive fluids within a nuclear fusion reactor. To this aim in this work non-modal stability theory is adopted to perform stability analysis of a magneto-hydrodynamic (MHD) flow in an infinite circular pipe in order to study the effects of the magnetic field on the fluid dynamics of the pipe flow. In particular, the effects on the general stability of two magnetic field profiles are compared with the reference case of a pipe Poiseuille flow without magnetic field. Firstly, the classic modal stability technique is employed to study asymptotical stability. Then, non-modal stability analysis is applied to magneto-hydrodynamic pipe flow to study the system's response for a finite time immediately after a perturbation. Fourier–Chebyshev Petrov–Galerkin spectral method is used to compute the eigenvalues and pseudospectra of the weak formulation associated with the linearised system. Investigations on the dependence of spectra and transient growths on the specific magnetic profiles are conducted for different values of perturbation wave numbers. The obtained results show that in general the magnetic field has an effect of stabilization on the system, which depends on the specific magnetic profile considered. In addition, the non-modal stability analysis reveals that the inclusion of the magnetic field mitigates the effects of perturbations also in the short term, a phenomenon that cannot be seen using only modal stability analysis
Fenomeni di interazione ed erosione nei materiali a diretto contatto con il plasma nei reattori a fusione a confinamento magnetico
No full textIl soggetto della tesi è lo studio dei fenomeni di interazione del plasma con i materiali a diretto contatto con esso, chiamati anche Plasma Facing Components. In particolare viene analizzata l'erosione prodotta sulla prima parete (first Wall) e sul divertore provocata da eventi di instabilità del plasma, i Vertical Displacement Events (VDEs) e gli Edge Localized Modes
Monte Carlo and Molecular Dynamics Simulations of Plasma-Material Interactions
No full textThe design of a suitable interface between plasma heated at millions of kelvin and the environment is one of the most critical areas within nuclear fusion research. The surface of interface components should sustain the energy delivered by plasma as electromagnetic radiation and transported through charge carriers such as ions and electrons.
The ratio between available plasma energy and heated surface increases with device dimension, so that for ITER and future fusion reactors the energy density striking the tokamak walls will be order of magnitude higher compared to what happens in current facilities.
Several plasma material interaction phenomena are relevant for PFCs design. The high energy heavy particles striking the chamber walls produce sputtering. The magnetic confinement suffer from frequent plasma instabilities, which result in a fast release of plasma energy on Plasma Facing Components. The ensuing thermal and mechanical actions produce material damage, erosion, thermal ablation and melting. Components lifetime is strongly limited by such extreme phenomena and require careful design and material selection to avoid unwanted maintenance stops and replacements.
The main aim of this research activity is to evaluate the PFMs erosion due to thermal ablation, to understand how material properties are affected by plasma interactions and how correctly select PFMs, without relying simply on empiric correlations with limited validity.
The main part of the performed work consist in the development of Molecular Dynamics and Monte Carlo Simulation aimed to evaluate the thermal properties of PFMs and to investigate how high energy electrons produced within the plasma carry energy towards tokamak chamber walls.
The analysis of Plasma Material Interactions has been historically carried out by putting together experimental activity and empiric relationships accounting for complex physical effects in an approximate fashion. The current research activity wants to investigate such phenomena starting from the underlying physical basic principles and through a comparison with experimental data with minimum employ of empiric relationship
Feasibility of a Stop Smoking Program for Healthcare Workers in an Italian Hospital: Econometric Analysis in a Total Worker Health® Approach
No full textBackground: Over 20% of healthcare workers (HCWs) are active smokers. Smoking is a targeted issue for workplace health promotion (WHP) programs. Objective: Our study aims to evaluate the effectiveness of the Stop Smoking Promotion (SSP) intervention, a 6-hour training course for HCWs, which took place from May 2018 to July 2019. Methods: We compared HCWs who successfully quit smoking (n = 15) to those who did not (n = 25) in terms of Sickness Absence Days (SADs). Moreover, we conducted an econometric analysis by calculating the return on investment and implementing a break-even analysis. Findings: Among the 40 enrolled workers, a success rate of 37.5% was observed after a span of over two years from the SSP intervention (with nurses and physicians showed the best success rate). Overall, participants showed a noticeable absenteeism reduction after the SSP intervention, with a reduction rate of 85.0% in a one-year period. The estimated ROI for the hospital was 1.90, and the break-even point was 7.85. In other words, the organization nearly doubled its profit from the investment, and the success of at least eight participants balanced costs and profits. Conclusion: Our pilot study confirms that WHP programs are simple and cost-saving tools which may help improve control over the smoking pandemic in healthcare settings
THEORETICAL AND COMPUTER MODELS OF 3-DIMENSIONAL GRAIN BOUNDARY MIGRATION WITH MOBILE PARTICLES
No full textIn this work, the migration of a three-dimensional (3D) spherical crystal in the presence of mobile particles using a Monte Carlo algorithm was studied. Different concentrations of particles (f) and different particle mobility (Mp) were used. It was found that the grain size reaches a critical radius (Rc) which depends exclusively on f. This dependence can be written as: Rc∝fThe presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
BUBBLE GRAIN GROWTH IN ICE: EXPERIMENTS AND SIMULATION
No full textHailstones in the clouds develop under various environmental conditions (temperature, humidity, wind, etc.), which impact the size and texture of the ice composing the hail. The stratified structures within a hailstone provide direct insight into the stages it underwent during its growth. In each region, the grains grow with numerous bubbles both inside them and along the grain boundaries (GBs). As hail takes shape, its grain size gradually increases while within the storm cloud and this growth continues even after it falls to the ground. Grain growth is a thermally activated process that modifies the structure of hail, influenced by the presence of bubbles and atmospheric contaminants accumulated within the cloud.
This study examines the evolution of grain size in a cylindrical hailstone containing bubbles, employing theoretical equations and a Monte Carlo-based (MC) growth model. The computational results contribute to a better understanding of the interaction between GBs and pre-existing bubbles, thereby elucidating the grain size evolution in hailstone containing bubbles near the melting point. Additionally, the study assesses the significance of bubbles in retaining information about a storm within hailstones.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Does Surgical Approach Influence Complication Rate of Hip Hemiarthroplasty for Femoral Neck Fractures? A Literature Review and Meta-Analysis
No full textBackground: Femoral neck fractures are an epidemiologically significant issue with major effects on patients and health care systems, as they account for a large percentage of bone injuries in the elderly. Hip hemiarthroplasty is a common surgical procedure in the treatment of displaced femoral neck fractures. Several surgical approaches may be used to access the hip joint in case of femoral neck fractures, each with its own benefits and potential drawbacks, but none of them has consistently been found to be superior to the others. This article aims to systematically review and compare the different approaches in terms of the complication rate at the last follow-up. Methods: an in-depth search on PubMed/Scopus/Web of Science databases and a cross-referencing search was carried out concerning the articles comparing different approaches in hemiarthroplasty and reporting detailed data. Results: A total of 97,576 hips were included: 1030 treated with a direct anterior approach, 4131 with an anterolateral approach, 59,110 with a direct lateral approach, and 33,007 with a posterolateral approach. Comparing the different approaches, significant differences were found in both the overall complication rate and the rate of revision surgery performed (p < 0.05). In particular, the posterolateral approach showed a significantly higher complication rate than the lateral approach (8.4% vs. 3.2%, p < 0.001). Furthermore, the dislocation rate in the posterolateral group was significantly higher than in the other three groups considered (p < 0.026). However, the posterolateral group showed less blood loss than the anterolateral group (p < 0.001), a lower intraoperative fractures rate than the direct anterior group (p < 0.035), and shorter mean operative time than the direct lateral group (p < 0.018). Conclusions: The posterolateral approach showed a higher complication rate than direct lateral approach and a higher prosthetic dislocation rate than the other three types of surgical approaches. On the other hand, patients treated with posterolateral approach showed better outcomes in other parameters considered, such as mean operative time, mean blood loss and intraoperative fractures rate. The knowledge of the limitations of each approach and the most common associated complications can lead to choosing a surgical technique based on the patient’s individual risk
Predicting needlestick and sharps injuries in nursing students: Development of the SNNIP scale
No full textAim To develop an instrument to investigate knowledge and predictive factors of needlestick and sharps injuries (NSIs) in nursing students during clinical placements. Design Instrument development and cross-sectional study for psychometric testing. Methods A self-administered instrument including demographic data, injury epidemiology and predictive factors of NSIs was developed between October 2018-January 2019. Content validity was assessed by a panel of experts. The instrument's factor structure and discriminant validity were explored using principal components analysis. The STROBE guidelines were followed. Results Evidence of content validity was found (S-CVI 0.75; I-CVI 0.50-1.00). A three-factor structure was shown by exploratory factor analysis. Of the 238 participants, 39% had been injured at least once, of which 67.3% in the second year. Higher perceptions of "personal exposure" (4.06,SD3.78) were reported by third-year students. Higher scores for "perceived benefits" of preventive behaviours (13.6,SD1.46) were reported by second-year students
Clinical study and Health Technology Assessment (HTA) of a Robot-Assisted Gait Training on children with neurological disorders: A quasi-experimental study
No full textBackground: Even if clinical evidence on effectiveness is still lacking, innovative technological solutions like robotic gait training technologies are gaining increasing attention in pediatric neuromotor rehabilitation.
Aim: This study aims to provide clinical-technological analysis for pediatric rehabilitation centers, build a rationale for driving future ideal rehabilitative pathways, and identify the most relevant criteria to evaluate robotic rehabilitation of the gait.
Design: Pre-post test design.
Setting: The robotic device comprises a bilaterally driven gait orthosis, computer-controlled guidance, and a non-immersive virtual reality system. Robotic-assisted locomotor treadmill therapy (RAGT) training was customized regarding training onset, duration, and specific gait parameters.
Population: We assessed 47 patients (mean age: 9.6 years, SD: 3.8 years; 23 females) with several neurologic diseases subjected to RAGT and patient-centered therapy (i.e., traditional therapy).
Methods: Inpatients were assessed in motor control, gait, cognition, and autonomies. The clinical investigation was integrated with a Health Technology Assessment (HTA) study, to investigate the introduction and impact of RAGT compared to patient-centered rehabilitation techniques and identify the most relevant criteria to assess the use of robotic rehabilitation technologies.
Results: The Patient-centered vs. Hybrid (RAGT+patient-centered) group showed a statistically significant difference between pre-treatment and post-treatment in Gross Motor Function Classification System (GMFM) total mean score (p=0.02). A significant increase in the distance walked in 6 minutes was found in the comparison between pre and post-treatment evaluation in the hybrid group: average pre-post 126 vs. 156 meters (t(13) = 2.78: p<0.01).
Conclusions: The HTA process provided the weights of each evaluation element described in the decision tree. Safety is considered the most important domain, followed by Ethical Aspects and Clinical Effectiveness, which reached about the same weight as the technical characteristics. Less importance was given to organizational aspects and costs
