Irina Severin

Bioprocess Modeling and Control

The bioprocess advancement is determined by the living cells capabilities and characteristics, the bioreactor performance as well as by the cultivation media composition and the main parameters evolution. The high metabolic network complexity inside the cells often determine very sophisticated, non-linear growth and product formation kinetics, with further consequences on the bioprocess behavior, but at the same time on the product quality and yield.

Phenomena associated to aging of silica optical fibers

Four commercial single mode silica fibers were subjected to aging testing in hot water at different temperatures and durations. Static fatigue testing have showed an oscillating behaviour of fiber failure strength versus the aging duration, that may be explained through the structural relaxation phenomenon at the glass-polymer coating interface. For several aging durations, fibers appeared more resistant under static stress than the non-aged ones. The fiber strength measured dynamically, using a two point bending test, slightly decreased in the same aging conditions. Dynamic fatigue testing of as-aged fibers under permanent stress revealed an overall decrease of failure stress and a change of Weibull distribution towards a bi-modal dispersion. As-aged fibers presented a permanent curvature following aging treatment and drying.

Reliability Evolution of Optical Fibre Subjected to Chemical Environment

The increased optical fiber development for a variety of physical and chemical measurements using smart structures and sensors leads to investigate the mechanical and chemical reliability of standard commercial acrylate polymer coated fibers. A comparison of mean failure strength of as-aged fibres to the water influence for similar exposure duration has revealed the highest sensitivity to dimethyl sulfoxide reagent (DMSO). SEM investigation revealed different damage levels in function of the aging conditions.

Progress in reliability of silica optical fibres

Silica optical fibres that were developed for telecommunication networks extend their use for sensors and smart structures. Their reliability and expected lifetime has appeared as a major concern. Series of experiments were implemented in order to assess fibre behaviour in different environmental conditions, including chemical corrosion and mechanical stress. Optical fibres were aged in water under controlled stress overlapping microwave energy for different durations. Fibre samples were wound on different diameter mandrels applying consequently a non-uniform tensile, respectively compression stress in function of the fibres section. Different experimental combinations were implemented in order to separate aging factor effects. Then, these aged / stretched fibres were dynamic tensile tested at different strain rates and results were statistically treated using Weibull theory. In certain cases and testing conditions, comparison with as received fibres has revealed strength increase with a generally mono-modal defect distribution on the fibre surface. Base on previous and current results, the structural relaxation phenomenon at the silica cladding - polymer coating interface might be evidenced.

Semiautomatic High Frequency Ultrasonic Testing System for Welded Plastic Pipes

The present paper proves the feasibility of a semi-automatic control system of high frequency ultrasound for welded plastic pipes, by ultrasonic methods. The paper presents the main existing types of plastic materials, the technological joining possibilities, the problems that may occur in welding and control and the reasoning of the chosen examination method. The theoretical size of the reference ultrasonic parameters for the propagation of ultrasounds through the flawless juncture. The samples were welded using electro fusion (EF) under different working conditions. The samples were assessed circumferentially, every 10 degrees, on different working frequencies. A semi-automatic control system was designed and developed. For the optimal working frequency, a set of 10 measurements was done, in similar working conditions, on the automatic control stand, in order to test the systems’ capability and the results’ repeatability. The measured values were compared with the limits considered to be admissible using Shewhart statistic control charts.

Tensile Characterizations of Optical Fiber Embedded in Epoxy Glass Composite

Photosensitive single mode optical fibers have been embedded in composite sample in order to be used in optical sensors which monitor the health of civil engineering structure.A simple composite with epoxy vinyl ester matrix reinforced with E-glass unidirectional fibers was implemented using two embedded optical fibers. Interfacial adhesion stress was determined using pull-out test and stress values are correlated to fracture mechanisms based on SEM observations.

The Influence of Leadership in Implementing Management Systems

Abstract This paper presents a new perspective of the implementation of Management Systems within organizations in order to increase the success rate. The objective is to analyse how the leadership could influence positively or negatively the implementation, according to the leadership approach chosen. It offers a method to analyse the maturity of the leadership for any organization, based on existing leadership models, completing these models with specificities of a Management System. The Maturity Grid is extended to key elements of the Organizational Leadership: Strategic Planning, Process and Performance. The results expected are to change the current understanding of leadership during a Management System implementation(leadership seen as a principle) to an active leadership, implemented at organizational level. It propose an alternative of the classic management approach, to a Performance Management approach, that integrates naturally the leadership in all processes and methods

Optical Fiber Embedded in Epoxy Glass Unidirectional Fiber Composite System

We aimed to embed silica optical fibers in composites (epoxy vinyl ester matrix reinforced with E-glass unidirectional fibers in mass fraction of 60%) in order to further monitor the robustness of civil engineering structures (such as bridges). A simple system was implemented using two different silica optical fibers (F1—double coating of 172 μm diameter and F2—single coating of 101.8 μm diameter respectively). The optical fibers were dynamically tensile tested and Weibull plots were traced. Interfacial adhesion stress was determined using pull-out test and stress values were correlated to fracture mechanisms based on SEM observations. In the case of the optical fiber (OF) (F1)/resin system and OF (F1)/composite system, poor adhesion was reported that may be correlated to interface fracture at silica core level. Relevant applicable results were determined for OF (F2)/composite system.

Intelligent Techniques for Fed-Batch Bioprocess Control

Bioprocesses are appreciated as difficult to control because their dynamic behavior is highly nonlinear and time varying, in particular, when they are operating in fed batch mode. For this kind of bioprocess where the mathematical model contains many structured and unstructured uncertainties, we try to combine different intelligent techniques based on natural syllogisms of these techniques. In order to obtain a high bioprocess productivity it is essential to accord the benefits of the classical control strategy (i.e. the analytical determination of the optimum) with the subjective bioprocess characterization (due to the human expert) in order to diminish the on line information scarcity. The research objective of this study was to develop an appropriate control method for a new complex bioprocess and to implement it on a laboratory plant. Hence, an intelligent control structure has been designed in order to produce biomass and to maximize the specific growth rate.

Aging and strength improvement of silica optical fibers

The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers, a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a long fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending insensitivity. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new method for increasing fiber strength. Submitted to a mechanical stretching, fibers were plunged into hot water and aged for several days. Then, the fibers were removed from the water and various weights were suspended on the fiber ends. Just before the fiber rupture, the fibers were unloaded and subjected to dynamic tensile tests at different velocities. Result analysis proved that the aging in hot water increased the fiber strength. The Weibulls diagram study shows a bimodal dispersion of defects on the fiber surface and the important role of polymer coating.