Oxidative Stress and Mitochondrial Dysfunction in Down's Syndrome: Relevance to Aging and Dementia

Genome-wide gene deregulation and oxidative stress appear to be critical factors determining the high variability of phenotypes in Down's syndrome (DS). Even though individuals with trisomy 21 exhibit a higher survival rate compared to other aneuploidies, most of them die in utero or early during postnatal life. While the survivors are currently predicted to live past 60 years, they suffer higher incidence of age-related conditions including Alzheimer's disease (AD). This paper is centered on the mechanisms by which mitochondrial factors and oxidative stress may orchestrate an adaptive response directed to maintain basic cellular functions and survival in DS. In this context, the timing of therapeutic interventions should be carefully considered for the successful treatment of chronic disorders in the DS population

Measurement of Multiphase Flow Characteristics Via Image Analysis Techniques: The Fluidization Case Study

In this chapter, an overview on some imaging-based experimental techniques for the analysis of complex multiphase systems is reported. In particular, some techniques aimed at the study of fluidization dynamics will be analyzed and discussed, as developed by our research grou

Lagrangian Simulation of Bubbling Dynamics in a Lab-Scale 2D Fluidized Bed

The present work focuses on the development of a novel computational code able to predict with a reasonable level of accuracy the bubble behavior in gas fluidized beds with minimum computational demands. The code simulates the bubble chaotic rise motion and coalescence along bed height via simple lagrangian tracking of bubbles. An original empirical model for the assessment of bubble-bubble interactions is developed. The code is used to simulate a lab-scale unit in bubbling and slugging mode. On this basis, fast simulations are performed to successfully predict bubble population and fluxes within the bed. The main aim of this code is to be embedded within CAPE codes for the process simulation. The model adopted by the code is also well suited for multi-scale modeling approach since physical parameters can be obtained from both experimental data or CFD simulation. Preliminary results of the simulations, in terms of distributions for bubble size and number as well as local hold up values, are compared with relevant experimental data

Free surface oxygen transfer in large aspect ratio unbaffled bio-reactors, with or without draft-tube

It is widely accepted that animal cell damage in aerated bioreactors is mainly related to the bursting of bubbles at the air-liquid interface. A viable alternative to sparged bioreactors may be represented by uncovered unbaffled stirred tanks, which have been recently found to be able to provide sufficient mass transfer through the deep free surface vortex which takes place under agitation conditions. As a matter of fact, if the vortex is not allowed to reach impeller blades, no bubble formation and subsequent bursting at the free-surface, along with relevant cells damage, occurs.In this work oxygen transfer performance of large aspect ratio unbaffled stirred bioreactors, either equipped or not with an internal draft tube, is presented, in view of their use as biochemical reactors especially suited for shear sensitive cell cultivation

Gas-Fluidization Characteristics of Binary Mixtures of Particles in 2D Geometry

The bubbling behaviour of fluidized beds has been thoroughly investigated in the last decades by means of several techniques, e.g. X-ray, Inductance, Resistance and Impedance based techniques, PIV. In recent years, Digital Image Analysis Techniques have shown their potential for accurate and cost effectively measurements. Most of the work related to bubble behaviour analysis deals with Single-sized particles, while almost all industrial equipment operates with multi-sized particles. Although considerable work has been done in the past with focus on the analysis of the mixing-segregation behaviour and predictions of fluid dynamics regime transitions, a lack of knowledge still exists in the analysis of bubbles properties measurements for the case of polydispersed systems. In this work, digital image analysis has been adopted to accurately measure fundamental global parameters such as bubble hold up and bed expansion as well as average bubble hold-up distribution maps or bubble size distributions in bubbling fluidized beds of binary mixtures of particles. The experiments have been carried out at steady state conditions with binary mixtures of corundum particles, at various inlet gas velocities. This preliminary study has been performed with the aim to collect valuable data for future development of predictive models and validation of CFD codes

Mass transfer and hydrodynamic characteristics of a Long Draft Tube Self-ingesting Reactor (LDTSR) for gas-liquid-solid operations

Gas-liquid stirred vessels are widely employed to carry out chemical reactions involving a gas reagent and a liquid phase. The usual way for introducing the gas stream into the liquid phase is through suitable distributors placed below the impeller. An interesting alternative is that of using “self ingesting” vessels where the headspace gas phase is injected and dispersed into the vessel through suitable surface vortices. In this work the performance of a Long Draft Tube Self-ingesting Reactor dealing with gas-liquid-solid systems, is investigated. Preliminary experimental results on the effectiveness of this contactor for particle suspension and gas-liquid mass transfer performance in presence of solid particles are presented. It is found that the presence of low particle fractions causes a significant increase in the minimum speed required for vortex ingestion of the gas. Impeller pumping capacity and gas-liquid mass transfer coefficient are found to be affected by the presence of solid particles, though to a lesser extent than with other self-ingesting devices

Local gas-liquid hold-up and interfacial area via light sheet and image analysis

Particle Image Velocimetry techniques coupled with advanced Image Processing tools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas-liquid contactors. In this work, an effective experimental technique for measuring local gas hold-up and interfacial area, as well as bubble size distribution, is discussed. The technique, hereafter referred to as Laser Induced Fluorescence with Shadow Analysis for Bubble Sizing (LIF-SABS) is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available within PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and an optical filter is placed in front of the camera optics, in order to allow only fluoresced light to reach the camera CCD. In this way bubbles intercepted by the laser sheet are clearly identified thanks to the neat shade resulting in the images. This allows excluding from subsequent analysis all bubbles visible in the images but not actually intercepted by the laser sheet, so resulting in better spatial resolution and data reliability. When trying to analyze image information the problem arises that bubble sizes are generally underestimated, due to the fact that the laser sheet randomly cuts bubbles over non-diametrical planes, leading to an apparent bubble size distribution even in the ideal case of single sized bubbles. Clearly in the case of bubbles with a size distribution the experimental information obtained is affected by the superposition of effects. A statistical correction for estimating local gas hold-up and specific interfacial area from relevant apparent data as obtained by laser sheet illumination and image analysis is discussed and applied to preliminary experimental data obtained in a gas-liquid stirred vessel

A NOVEL TECHNIQUE FOR MEASURING LOCAL BUBBLE SIZE DISTRIBUTION

A novel experimental technique for measuring the local gas hold-up and the statistical distribution of local bubble size, is proposed. The technique is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available in PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and a band-pass optical filter is placed in front of the camera optics, in order to allow only fluoresced light to reach the camera CCD. In this way bubbles intercepted by the laser sheet are clearly identified thanks to the neat shade resulting in the images. This allows excluding from subsequent analysis all bubbles visible in the images but not actually intercepted by the laser sheet, so resulting in better spatial resolution and data reliability. Preliminary data obtained in a stirred gas-liquid dispersion confirm the technique viability and reliability

Measurement techniques and modelling of multiphase systems.

Multiphase systems are often encountered in process industry. Widely diffused applications and operations involve the contact between different phases (gas-solid, gasliquid, solid liquid, etc.) for different purposes, such as chemical reactions of physical operations (heat transfer, mass transfer). Multiphase flows are therefore one of the most frequent applied fields in chemical engineering. The present thesis is aimed at the development of experimental techniques for the investigation of multiphase flow in general, with particular focus on the analysis of gas-solid and gas-liquid systems. Notably, the development of image analysis techniques is the central thread of the present contribution, and it will be shown that the knowledge so far accumulated allowed to obtain considerable results in both fields investigated. The approach to multiphase systems here adopted is based on the development of novel reliable experimental techniques for the assessment of multiphase system properties and subsequent collection of new experimental information through application of the original techniques here developed. The techniques are mainly based on image analysis, they are non-intrusive, capable of securing several properties simultaneously and cost effective. In particular, the expertise in digital image processing was applied to the investigation of two different classes of multiphase systems, i.e. gas-liquid dispersions and dense gas-solid systems (fluidized beds). With reference to gas liquid dispersions, an effective experimental technique for measuring local gas hold-up and interfacial area, as well as bubble size distribution, was developed and subsequently exploited for collecting experimental information. The technique, named Laser Induced Fluorescence with Shadow Analysis for Bubble Sizing (LIF-SABS) is based on laser sheet illumination of the gas-liquid dispersion and synchronized image acquisition, i.e. on equipment typically available within PIV set-ups. With reference to fluidized beds, a digital image analysis technique was developed vi to study the fluidization dynamics of a lab-scale two-dimensional bubbling bed. Several significant bubble properties were simultaneously measured, ranging from overall bed properties to bubble size and bubble velocity distributions. Moreover, since a lack of knowledge exists on the bubbling dynamics of mixed powders, a large experimental campaign was set up to investigate the fluidization behavior of such powder mixtures. In the field of fluidized bed modeling, a novel linear stability criterion for the state of homogeneous fluidization regime was developed, based on a new mathematical model for gas-fluidized beds. A fully predictive criterion for the stability of homogeneous fluidization state was proposed and validated with literature data

Communicating Criterion-Related Validity Using Expectancy Charts: A New Approach

Often, personnel selection practitioners present the results of their criterion-related validity studies to their senior leaders and other stakeholders when trying to either implement a new test or validate an existing test. It is sometimes challenging to present complex, statistical results to non-statistical audiences in a way that enables intuitive decision making. Therefore, practitioners often turn to expectancy charts to depict criterion-related validity. There are two main approaches for constructing expectancy charts (i.e., use of Taylor-Russell tables or splitting a raw dataset), both of which have considerable limitations. We propose a new approach for creating expectancy charts based on the bivariate-normal distribution. The new method overcomes the limitations inherent in the other two methods and offers a statistically sound and user-friendly approach for constructing expectancy charts