Bert Verlinden

A Three-Dimensional Multiscale Model for Gas Exchange in Fruit

Respiration of bulky plant organs such as roots, tubers, stems, seeds, and fruit depends very much on oxygen (O2) availability and often follows a Michaelis-Menten-like response. A multiscale model is presented to calculate gas exchange in plants using the microscale geometry of the tissue, or vice versa, local concentrations in the cells from macroscopic gas concentration profiles. This approach provides a computationally feasible and accurate analysis of cell metabolism in any plant organ during hypoxia and anoxia. The predicted O2 and carbon dioxide (CO2) partial pressure profiles compared very well with experimental data, thereby validating the multiscale model. The important microscale geometrical features are the shape, size, and three-dimensional connectivity of cells and air spaces. It was demonstrated that the gas-exchange properties of the cell wall and cell membrane have little effect on the cellular gas exchange of apple (Malus × domestica) parenchyma tissue. The analysis clearly confirmed that cells are an additional route for CO2 transport, while for O2 the intercellular spaces are the main diffusion route. The simulation results also showed that the local gas concentration gradients were steeper in the cells than in the surrounding air spaces. Therefore, to analyze the cellular metabolism under hypoxic and anoxic conditions, the microscale model is required to calculate the correct intracellular concentrations. Understanding the O2 response of plants and plant organs thus not only requires knowledge of external conditions, dimensions, gas-exchange properties of the tissues, and cellular respiration kinetics but also of microstructure.

Effect of biological variability on the robustness of NIR models for soluble solids content of apples

A statistical analysis was performed on a large spectral data set to analyse the effect of orchard, season and cultivar. Season and cultivar were responsible for a major amount of the spectral variability, whereas the influence of the orchard was low and only appeared for certain cultivars during specific seasons. The robustness of the calibration models for soluble solids content with respect to the three factors was tested based on external validations. It was found that the accuracy of the models increased considerably when including more variability in the calibration set. Further, overfitting of the calibration model was avoided. On the other hand, adding more data to the calibration set increased the chance of adding atypical data, which resulted in reduced model accuracy. It is, therefore, important to construct the calibration data set in such a way that it is representative for future measurements. When the effect of a certain factor is known a priori, e.g. cultivar, it is recommended to use specific calibration models.

Resistance to sensitization and intergranular corrosion through extreme randomization of grain boundaries

Abstract Two grades of austenitic stainless steel, type 304 and 316L, were cold rolled to different reductions by unidirectional and by cross rolling. Subsequent solutionizing of the cold rolled samples produced noticeable textural differences in type 304, but insignificant differences in type 316L. Both the solutionized materials had however the same trend in grain boundary character distribution (GBCD): an increasing fraction of random boundaries with an increasing pre-solutionizing reduction percentage. The degree of sensitization (DOS) was measured by the double loop electrochemical potentiokinetic reactivation (DL-EPR) test in both the alloys. The susceptibility to intergranular corrosion was assessed by the standard weight loss technique (practice B, A262 ASTM) in type 304 alloy. These increased with increase in random boundary concentration, but then dropped significantly beyond a ‘critical’ concentration—a pattern observed in both the grades. Such a pattern may be explained from a balance between nucleation rate of Cr-carbides and grain boundary Cr-flux, though postulating an exact model is premature at this stage. The present study, however, demonstrates a clear possibility of remarkable improvement in DOS and IGC through extreme grain boundary randomization.

Comparison of the effects of silicon and aluminium on the tensile behaviour of multiphase TRIP-assisted steels

Ghent University,Laboratory for Iron and Steelmaking, Technologiepark 9, B-9052 Ghent, Belgium(Received July 12, 2000)(Accepted in revised form November 21, 2000)Keywords: TRIP-steels; Microstructure; Phase transformations; Mechanical propertiesIntroductionMultiphase TRIP-assisted steels are a new generation of low alloy high strength steels that exhibitexceptional formability [1]. The remarkable strength to ductility balance results from the occurrenceduring testing of the Transformation Induced Plasticity (TRIP) phenomenon [2], which involves thestrain-induced transformation of austenite to martensite. The presence of austenite in the initialmicrostructure appears to be critical to the achievement of the desired properties. The retention ofaustenite is usually obtained by the combined effect of an appropriate chemistry and a typicalheat-treatment. In this respect, it is known that silicon and aluminium may both retard the kinetics ofcarbide formation and thus favour the austenite stabilisation by a bainitic holding stage [3]. Despite thisqualitative knowledge, very little literature can be found that rigorously compares the effect of siliconand aluminium on the austenite retention, on the extent of the TRIP effect, and on the resulting tensilebehaviour, all other chemical constituents have been kept constant [4]. The objective of this paper is toquantitatively assess the influence of aluminium and silicon contents, in view of the development ofmultiphase TRIP-assisted steels.Materials and Experimental ProcedureThe chemical compositions of the steels studied in this work are given in Table 1. Specific care wastaken to keep the same carbon content for each alloy. The slabs were initially hot and cold-rolled tothicknesses between 0.8mm and 1.0mm, following classical processing routes.The desired multiphase microstructure was obtained as displayed in Figure 1. The cold-rolledmaterial was first annealed for 4 minutes in the (a1g) region at a temperature 25°C above its Ac1temperature. It was then rapidly cooled and held at an intermediate temperature (i.e. between 375°C and450°C), where bainite formation takes place and contributes to the stabilisation of the austenite. Theheat-treatment was eventually interrupted by quenching the samples to room temperature. After the

Influence of annealing conditions on the mechanical and microstructural behavior of electroplated Cu-TSV

In this paper, the effect of annealing condition on the microstructural and mechanical behavior of copper through-silicon via (Cu-TSV) is studied. The hardness of Cu-TSV scaled with the Hall–Petch relation, with the average hardness values of 1.9 GPa, 2.2 GPa and 2.3–2.8 GPa, respectively for the annealed, room temperature (RT) aged and the as-deposited samples. The increase in hardness toward the top of the as-deposited sample is related to the decrease in grain size. The annealed and the as-deposited samples showed a constant elastic modulus (E-modulus) value across the length of Cu-TSV of 140 GPa and 125 GPa respectively, while the RT aged sample showed a degradation in E-modulus from the bottom of the TSV (140 GPa) to the top (110 GPa). These differences in E-modulus values and trends under the different test conditions were found to be unrelated with the crystallographic texture of the samples, but could be related to the presence of residual stresses. No correlation is found between the hardness and E-modulus data. This is attributed to the coupling and competitive effects of grain size and residual stresses, with the grain size effect having a dominant influence on hardness, while the presence of residual stresses dominated the E-modulus result.

Genotype effects on internal gas gradients in apple fruit

A permeation-diffusion-reaction model was applied to study gas exchange of apple fruit (Kanzi, Jonagold, and Braeburn) as effected by morphology and respiratory metabolism. The gas exchange properties and respiration parameters of the fruit organ tissues were measured. The actual internal tissue geometry of the fruit was reconstructed from digital fruit images and the model was solved over this geometry using the finite element method. The model was validated based on measurements of internal gas concentrations and the gas flux of the fruit to its environment. Both measurements and an in silico study revealed that gradients of metabolic gases exist in apple fruit, depending on diffusion properties and respiration of the different cultivars. Macroscale simulation confirmed that Jonagold has large potential for controlled atmosphere (CA) storage while low diffusion properties of cortex tissue in Braeburn indicated a risk of storage disorder development. Kanzi had less O(2) anoxia at CA storage compared with Braeburn.

A continuum model for metabolic gas exchange in pear fruit.

Exchange of O2 and CO2 of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O2 and increased CO2 levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres.

Logistic regression analysis of factors influencing core breakdown in 'Conference' pears

Core breakdown of ‘Conference’ pears (Pyrus communis L.) is characterised by softening and browning of tissue near the core and is associated with the development of cavities. The disorder causes large economic losses of ‘Conference’ pears in Belgium, stored under controlled atmospheres. Factors that influence development of the disorder, CO2 and O2 concentration, the size and weight of the pear, the picking date and the storage temperature, were investigated. Multiple logistic regression was used to establish prediction and classification models for both internal browning and cavity development. Over-mature fruit was more susceptible to core breakdown during storage. It was also found that pears with a large weight had a higher probability of developing brownheart. R 2 values from 0.7 to 0.92 were obtained between the predicted and measured percentages of brownheart and cavities. The models classified up to 86% of the pears correctly. In a final analysis, the time sequence of the symptoms occurring during core breakdown disorder development was modelled with a generalized logits model.

A respiration–diffusion model for ‘Conference’ pears I: model development and validation

Abstract A respiration–diffusion model based on Ficks second law of diffusion and Michaelis–Menten kinetics, including non-competitive CO2 inhibition, was developed to predict the internal O2 and CO2 concentrations in ‘Conference’ pears. The ‘respiration-free’ diffusion and ‘diffusion-free’ respiration parameters, determined in previous independent experiments, were incorporated in the respiration–diffusion model. The system of coupled non-linear partial differential equations was solved numerically for a three-dimensional pear geometry, by means of the finite element method. When Michaelis–Menten kinetics are used to describe a process like gas exchange of fruits, which involves both gas diffusion and respiration, the Michaelis–Menten parameters were assigned a higher value than those obtained when respiration was first uncoupled from the diffusion process and then described by means of Michaelis–Menten kinetics. The maximal O2 consumption and fermentative CO2 production were diffusion-independent, but the Michaelis–Menten constants measured on cell protoplasts were considerably smaller when compared with the corresponding apparent Michaelis–Menten constants determined from respiration measurements on intact pears. The model was successfully validated for its prediction of the total pear gas exchange and the gas concentration under the skin, and is suited to simulating three-dimensional internal O2 and CO2 dioxide profiles in pears as a function of the storage atmosphere.

The starch gelatinization in potatoes during cooking in relation to the modelling of texture kinetics

Abstract A dynamic model for texture changes during cooking treatments of potato samples was developed. The model includes the kinetics of the gelatinization process and was compared with a simpler model lacking this feature. Model parameters were derived from texture measurements on potato samples. The experimental results and simulations show that the gelatinization process contributes only to a limited extent to the texture.