Strategies to reduce microbial risk and improve quality of fresh and processed strawberries: A review

Strawberries are one of the most important fruits in the Mediterranean diet and have been widely investigatedfor their nutritional and nutraceutical properties. Concern about the safety of fresh and processed strawberrieshas increased in recent years due to the emergence of several outbreaks of foodborne pathogens linked to theirconsumption. The use of chlorine as a disinfectant has been identified as a concern due to public health issuesand limited efficacy at removing contamination, and preventing cross-contamination. This has led to the de-velopment of novel alternatives to chlorine disinfection and thermal treatments, which include, among others,the use of organic acids, high pressure processing, intense pulsed light, or pulsed electricfields. These tech-nologies do not generally affect the nutritional and organoleptic properties of the product and some of these havebeen reported to stimulate the production of valuable compounds in strawberries and to improve their overallquality.This work forms part of the FRESAFE Research Project (Mitigation Strategies to Reduce the Microbial Risks and Improve the Quality and Safety of Frozen and Ready-to-Eat Strawberries), funded by the Spanish Ministry of Economy, Industry and Competitiveness (AGL2016-78086-R). This work was also supported by the CERCA Programme of Generalitat de Catalunya. T. Lafarga is in receipt of Juan de la Cierva contract awarded by the Spanish Ministry of Economy, Industry, and Competitiveness (FJCI-2016-29541). I. Aguiló-Aguayo thanks the Spanish Ministry of Economy, Industry and Competitiveness and the European Social Fund for the Postdoctoral Senior Grant Ramon y Cajal (RYC-2016-19949)

Numerical Simulation of the Thermodependant Viscohyperelastic Behavior of Polyethylene Terephthalate Near the Glass Transition Temperature: Prediction of the Self-Heating During Biaxial Tension Test

The poly ethylene terephthalate near the glass transition temperature highlights a strongly non linear elastic and viscous behaviour when biaxially stretched at high strain rates representative of the injection stretch blow moulding process. A non linear visco-hyperelastic model, where characteristics are coupled to the temperature, has already been identified from equi-biaxial tension experimental results. The weak form of the mechanical part of the model is presented and implemented into a finite element code developed in the Matlab environment and validated by comparing numerical simulation of equibiaxial testing with the analytical solution in the isothermal case. Considering the thermal aspects, an experimental study, where PETsheets are heated using infrared (IR for short) lamps is also presented. The modeling of the IR radiation of the sheet helps to identify the thermal properties of the PET. The thermal model is then implemented in the finite element code, coupled to the 2D viscoelasticmodel. A discussion ismade to justify the accuracy of the assumption made on homogeneity of the temperature field through the thickness. The simulation of the 2D plane stress equibiaxial test shows the important influence of the thermal aspects and the coupled thermo-mechanical software is used to quantify the selfheating phenomenon in the case of the biaxial elongations of PET sheets at high strain rates. POLYM. ENG. SCI., 53:2683–2695, 2013. ª2013 Society of Plastics Engineer

Study of solidification of continuously cast steel round billets using numerical modelling

The paper is dedicated to the verification of solidification of continuously cast round steel billets using numerical modelling based on the finite element method. The aim of numerical modelling is to optimize the production of continuously cast steel billets of round format. The paper describes the pre-processing, processing and post-processing phases of numerical modelling. Also, the problems with determination of the thermodynamic properties of materials and the heat transfer between the individual parts of the casting system, including the definition of the heat losses along the casting strand in the primary and secondary cooling, were discussed. The first results of numerical simulation show the so-called thermal steady state of continuous casting. The temperature field, the metallurgical length and the thickness of the shell at the end of the mould were predicted. The further research will be concentrated on the prediction the risk of the cracks and the porosity based on the different boundary conditions.Web of Science62122622

Numerical Modelling of Heat Phenomena Induced by Heat Radiation

Disertační práce se zabývá problematikou optimalizace ohřevu kovových skořepinových forem pomocí soustavy infrazářičů. Práce se soustředí na diferenciální evoluční algoritmy, které využívá pro tuto optimalizaci. Na konkrétním příkladu je ukázáno, že klasický diferenciální evoluční algoritmus obecně zaručuje jen konvergenci k lokálnímu minimu ohodnocující funkce. Proto byla navržena vhodná modifikace tohoto algoritmu. Pro modifikovaný algoritmus je dokázána asymptotická konvergence ke globálnímu minimu ohodnocující funkce dle pravděpodobnosti. Dále jsou odvozena tvrzení popisující využití náhodných jedinců v procesu konvergence v případě stagnace modifikovaného algoritmu. Výsledek numerické optimalizace umístění zářičů nad formou je následně použit pro modelování nestacionárního teplotního pole v tělese formy v průběhu jejího ohřevu.Z praktického hlediska disertační práce přináší teoreticky podloženou a kvantifikovatelnou metodu polohování infrazářičů nad kovovou skořepinovou formou. Spolu s modelováním teplotního pole přináší praktický a účinný příspěvek k technologii výroby plastové imitace kůže (Slush Moulding Technology). Naproti tomu modifikovaný diferenciální evoluční algoritmus je univerzální a účinná optimalizační technika, která může být testována a použita v celé řadě optimalizačních úloh. Předložená teoretická tvrzení a závěry týkající se modifikovaného diferenciálního evolučního algoritmu mají obecnou platnost a jsou použitelná v celé řadě oborů i mimo oblast modelování teplotních jevů.The doctoral thesis deals with an optimization technique that can be used to find optimized positioning of infrared heaters over a shell metal mould. The thesis is focused on differential evolution algorithms that are used for this optimization. It is shown by means of a specific example that the classic differential evolution algorithm in general guarantees only convergence to a local minimum of the cost function. Therefore, a modification of the classic differential evolution algorithm is designed. For the modified algorithm asymptotic convergence in probability to the global minimum of the cost function is proved. Several statement are presented describing utilization of random individuals in the convergence process when stagnation of the modified algorithm takes place. The result of the numerical optimization of the infrared heaters positioning over the mould is subsequently used for modelling of the non-stationary temperature field in the mould in the course of its heating.From the practical point of view, the presented thesis brings a theoretically based and quantifiable method for infrared heaters positioning over the shell metal mould. Together with the temperature field modelling it brings a feasible contribution to the Slush Moulding Technology. On the other hand, the modified differential evolution algorithm is a universal and efficient optimization tool. It can be tested and utilized in a wide range of optimization tasks with very good prospects. The presented theoretical statements and conclusions concerning the modified differential evolution algorithm have general validity and go far beyond the area of heat phenomena modelling

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Numerical modelling of cold crucible induction melting (CCIM) process and fabrication of high value added components of titanium and its alloys

This dissertation concerns the development of a numerical modelling of cold crucible induction melting (CCIM) and the fabrication of high value added components of titanium and its alloys. Titanium and its alloys have emerged as a very attractive metal for numerous applications: medical prostheses, aerospace industry, automotive industry, power generation, sport equipment, and marine engineering. The reason lie in their attractive properties, such as excellent biocompatibility, high specific strength, excellent corrosion resistance, excellent high temperature creep resistance, and good fracture toughness. However, the application of titanium is often limited by its relatively high cost. This high cost of titanium makes casting very attractive route. However, is it difficult to cast these alloys by conventional casting techniques because of the titanium reactivity at high temperatures, which reacts with the crucible and mould components. The CCIM process is currently the most effective means of melting these alloys. The CCIM is an innovative process to melt high melting point reactive materials such as titanium alloys. The melting and casting of the material is performed in vacuum or in a protective atmosphere in order to prevent any contamination of the charge. Moreover, a water cooled segmented crucible is used instead of a ceramic crucible to avoid any kind of reaction among the charge and the crucible. The magnetic field generated by an external coil penetrates through the slits of the crucible and generates induced currents in the charge, which are responsible of melting it due to Joule heating. The drawbacks of this process are the poor efficiency due to great percentage of heat that is removed by the cooling system and the small superheat of the melt, which can cause solidification problems. In this dissertation, we have selected the CCIM process to melt and cast titanium alloys. The aim of this dissertation consists on increasing the scientific knowledge about the CCIM process by means of both a numerical and an experimental approach. The main part of the dissertation focuses on the development of a numerical modelling of CCIM to optimize of the main parameters of the process. The task of optimizing melt superheat faces the challenge of finding optimal combination of crucible height to diameter ratio, number of inductor turns, crucible design, current strength, and frequency. Variation of any of the after mentioned factors influences the shape of melt meniscus and, as a result, flow pattern and energy balance. The second part deals with the set-up of an installation of CCIM and the fabrications of titanium components. As a result of the present work some goals have been achieved, being the most important: a) Development of numerical modelling of CCIM, b) setting up of a CCIM installation, and c) casting of titanium parts.Tesi honek “Cold crucible induction melting (CCIM)” prozesuaren simulazio numerikoaren gainean eta prozesu honen bidez titaniozko balio erantsi altuko osagaiak ekoizteko modua tratatzen du. Titanioak eta bere aleazioek interes handia sortu dute aplikazio industrial askotan: mediku protesiak, aeronautika, automozioa, energia generazioa, kirol ekipamendua eta itsas ingeniaritza. Arrazoia bere ezaugarri erakargarrietan errotzen da: biokonpatibilitate bikaina, erresistentzia espezifiko altua, korrosioaren aurkako erresistentzia ezin hobea, tenperatura alturako isurpenaren aurkako erresistentzia paregabea eta hausturaren aurkako erresistentzia. Hala ere, bere kostu altuak bere aplikazioak murrizten ditu. Galdaketa-prozesuek kostu txikiagoko produktuetara daramate. Hala ere, zaila da aleazio hauek galdaketa prozesu konbentzionalekin urtzea, tenperatura handitan erreaktibotasun handia daukate eta. CCIM prozesua aleazio hauek galdatzeko prozesu eraginkorren arten dago gaur egun. CCIM prozesua material erreaktiboak urtzeko prozesu berritzailea da. Bai urtze bai galdaketa hutsean edo atmosfera babesle baten egiten da materialaren erreakzioa saihesteko. Gainera, ohiko zeramikozko arragoen ordez segmentudun kobrezko arragoa erabiltzen da. Kanpoko harilak sortutako kanpo magnetikoa arragoaren arteketatik barneratzen da eta indukziozko korronteak sortzen ditu kargan, karga bera urtuz Joule beroketagatik. Prozesu honen arazoak efizientzia eskasa (hozte sistemak xurgatzen duen beroagatik) eta solidotzearazoak eragin ditzakeen gainberotze txikia dira. Tesi honetan, CCIM prozesua aukeratu dugu titaniozko aleazioak galdaketa prozesuaren bidez fabrikatzeko. Tesi honen helburua CCIM prozesuaren gaineko ezaguera zientifikoa handitzean datza bai ikuspegi teorikoa bai ikuspegi esperimentala erabiliz. Tesiko alderdi nagusia prozesuaren parametro nagusiak optimizatzeko CCIM prozesuaren zenbakizko modelizazioaren garapenaran gainean tratatzen du. Gainberotze tenperatura optimizatzeko zeregina arragoaren altura diametro ratioa, harilaren espira kopurua, arragoaren diseinua, korrontea eta frekuentziaren balio optimoa aurkitzean datza. Aipatutako faktoreen edozein aldaketek meniskoaren egoeran eragiten du, eta ondorioz, jariakinaren patroian eta energi balantzean. Tesiaren bigarren atalak CCIM instalazio bat abiarazteaz eta titaniozko osagaiak fabrikatzeaz dihardu. Lan honen emaitz garrantzitsuenak hurrengokoak dira: a) CCIM prozesuaren modelo numerikoaren garapena. b) CCIM prozesuaren instalazio baten abiaraztea. c) Titaniozko piezen galdaketa.Esta tesis trata sobre el desarrollo de un modelo numérico del “cold crucible induction melting (CCIM)” y la fabricación de componentes de alto valor añadido de titanio y sus aleaciones mediante este proceso. El titanio y sus aleaciones se han convertido en un metal muy atractivo para numerosas aplicaciones: prótesis médicas, industria aeroespacial, industria de automoción, generación de energía, deporte e ingeniería marina. La razón radica en sus propiedades atractivas, tales como excelente biocompatibilidad, alta resistencia específica, excelente resistencia a la corrosión, excelente resistencia a la fluencia a alta temperatura y buena resistencia a la fractura. Sin embargo, la aplicación de titanio es a menudo limitada por su coste relativamente alto. Los procesos de fundición conducen a productos de menores costes. Sin embargo, es difícil fundir estas aleaciones por técnicas de moldeo convencionales, debido a la reactividad de titanio a altas temperaturas, que reacciona con el crisol y molde. El proceso CCIM es actualmente el medio más eficaz de fusión de estas aleaciones. El CCIM es un proceso innovador en la que la fusión y colada del material se realiza bajo vacío o dentro de una atmósfera protectora y donde se utiliza un crisol refrigerado segmentado de cobre en vez de los habituales crisoles cerámicos para evitar cualquier tipo de reacción entre la carga y el crisol. El campo magnético generado por una bobina externa penetra a través de las ranuras del crisol y genera corrientes inducidas en la carga, las cuales son las responsables de la fusión debido al calentamiento Joule. Los inconvenientes de este proceso son la baja eficiencia debido al gran porcentaje de calor que se elimina por el sistema de refrigeración y el pequeño sobrecalentamiento del metal fundido, que puede causar problemas de solidificación. En esta tesis, hemos seleccionado el proceso CCIM para fundir y colar las aleaciones de titanio. El objetivo de esta tesis consiste en aumentar el conocimiento científico sobre el proceso CCIM tanto de un modo numérico como un modo experimental. La parte principal de la tesis se centra en el desarrollo de un modelo numérico de CCIM para optimizar de los principales parámetros del proceso. La tarea de optimizar sobrecalentamiento se enfrenta al reto de encontrar la combinación óptima de la altura del crisol a diámetro, número de espiras del inductor, diseño del crisol, intensidad de corriente y frecuencia. La variación de cualquiera de los factores mencionados influye en la forma del menisco del metal líquido y, como resultado, el patrón del fluido y el balance de energía. La segunda parte trata de la puesta en marcha de una instalación de CCIM y la fabricación de componentes de alto valor añadido de titanio. Como resultado de este trabajo se han logrado algunos objetivos, siendo los más importantes: a) Desarrollo de modelos numéricos del CCIM. b) Puesta a punto de una instalación CCIM. c) Fundición de piezas de titanio

An Experimental Investigation to Facilitate an Improvement in the Design of an Electromagnetic Continuous Casting Mould

An electromagnetic continuous casting mould designed is proposed with a non-uniform slit distribution structure. This design has aimed to reduce the number of slits so that the mould’s strength is enhanced, whilst maintaining a similar metallurgy effect. In this paper, the metallurgy effect for the designed mould is investigated through the magnetic field distribution along the casting direction, the uniformity feature in the vicinity of the meniscus region, the temperature variation of the molten alloy pool and the mould wall. The results show that the designed mould achieved a similar effect as compared to the original mould; however, the configuration is simplified. This research highlights the topic of mould structure optimization, which would enable the Electromagnetic continuous casting (EMCC) technique to be utilized with greater ease by industry