Modelling the kinetics of thermal inactivation of apple polyphenoloxidase

The enzymatic browning of fruits and vegetables caused by mechanical injury during postharvest storage or processing is initiated by the catalytic action of polyphenoloxidase (PPO). A bleaching treatment prior to processing is still considered mostly effective in inhibiting the catalytic activity of PPO, and thus controlling undesirable enzymatic browning. In this work, different mathematical routines were assessed in terms of their adequacy to describe the thermal inactivation of PPO from Golden apples over a range of temperatures from 62.5 to 72.5 ºC. The classical approach to kinetic modelling of the decay activity of apple PPO, commonly reported to follow a first-order model, employs a two-step procedure, in which the model parameters are individually obtained, by each temperature studied, using non-linear or linear regressions. Thereafter, the estimated parameters are further used to calculate their temperature dependence. Alternatively, a one-step method provides a regression fit to all experimental data sets, with the temperature dependence equation being directly built in the kinetic model. This fitting technique thus, (a) avoids the estimation of intermediate parameters and, (b) substantially increases the degrees of freedom and hence the precision of parameters’ estimates. Within this issue was further explored the logarithmic transformation of the mathematical equations used on the adequacy of the model to describe experimental data. In all cases non-weighted least-squares regression procedures were used. Both the examination and criticism of the current modelling strategies were done by assessing statistical data obtained, such as the confidence intervals of the estimates, correlation coefficients, sum of squares, and residuals normality

The impact of concentrated pig production in Flanders : a spatial analysis

Historically concentrated livestock production and, consequently, manure production and management in Belgium have resulted in severe environmental impacts. One major impact, nitrate leaching from soil to surface water, is being tackled through the European Nitrates Directive by imposing strict fertilization standards. However, another significant impact of manure management is the emission of greenhouse gasses (GHG - CO2, CH4, NH3 and N2O) into the air, thereby contributing to global warming. Calls have been made to reduce the high manure pressure and related environmental effects in Belgium by relocating and more evenly spreading livestock production. This paper explores the spatial spreading of CO2-equivalent emissions from livestock production in Belgium and attempt to answer the following question: ‘Can spatial reallocation of livestock production in Belgium reduce the impact of GHG emissions?’. This question is translated into several research objectives: 1) conduct an economic (cost minimization) and environmental (GHG minimization) optimization for 3 manure management scenarios, 2) determine the main differences between both approaches, and 3) determine the marginal spatial impact on CO2 emissions of a decrease in manure pressure (i.e., increased spreading of pig production). To conduct the analysis, a model was developed that builds on the spatial mathematical programming multi-agent manure allocation model developed by Van der Straeten et al. (2010). Three options for manure management are inserted: transport of raw manure from nutrient excess to nutrient deficit areas, biological treatment of manure (manure processing) and manure separation. The model optimizes, at municipal level, either the cost-efficiency, either the environmental effect of the manure market in Belgium based on Belgian fertilization standards. While cost-efficiency is calculated based on transport distances and cost of manure separation and processing, GHG emissions, and hence, carbon footprint, are determined based on a life cycle analysis type calculation. The results of the model simulations show that, while the economic optimum is reached by maximizing the transport of raw manure until fertilization standards are fulfilled and subsequently separating and processing the excess manure, the environmental optimum, from a carbon footprint point of view, is reached by separating all manure as this option has the lowest CO2 emissions, mainly due to the limited manure storage time. Moreover, the analyses indicate that rearrangement of the spatial spreading of livestock production in Belgium will not substantially decrease CO2 emissions. As manure storage is the main contributor to the carbon footprint, solutions should rather lie in changing these storage systems

A heuristic mathematical model for the dynamics of sensory conflict and motion sickness

By consideration of the information processing task faced by the central nervous system in estimating body spatial orientation and in controlling active body movement using an internal model referenced control strategy, a mathematical model for sensory conflict generation is developed. The model postulates a major dynamic functional role for sensory conflict signals in movement control, as well as in sensory-motor adaptation. It accounts for the role of active movement in creating motion sickness symptoms in some experimental circumstance, and in alleviating them in others. The relationship between motion sickness produced by sensory rearrangement and that resulting from external motion disturbances is explicitly defined. A nonlinear conflict averaging model is proposed which describes dynamic aspects of experimentally observed subjective discomfort sensation, and suggests resulting behaviours. The model admits several possibilities for adaptive mechanisms which do not involve internal model updating. Further systematic efforts to experimentally refine and validate the model are indicated

A heuristic mathematical model for the dynamics of sensory conflict and motion sickness

The etiology of motion sickness is now usually explained in terms of a qualitatively formulated sensory conflict hypothesis. By consideration of the information processing task faced by the central nervous system in estimating body spatial orientation and in controlling active body movement using an internal model referenced control strategy, a mathematical model for sensory conflict generation is developed. The model postulates a major dynamic functional role for sensory conflict signals in movement control, as well as in sensory motor adaptation. It accounts for the role of active movement in creating motion sickness symptoms in some experimental circumstances, and in alleviating them in others. The relationship between motion sickness produced by sensory rearrangement and that resulting from external motion disturbances is explicitly defined. A nonlinear conflict averaging model describes dynamic aspects of experimentally observed subjective discomfort sensation, and suggests resulting behavior

Linear response strength functions with iterative Arnoldi diagonalization

We report on an implementation of a new method to calculate RPA strength functions with iterative non-hermitian Arnoldi diagonalization method, which does not explicitly calculate and store the RPA matrix. We discuss the treatment of spurious modes, numerical stability, and how the method scales as the used model space is enlarged. We perform the particle-hole RPA benchmark calculations for double magic nucleus 132Sn and compare the resulting electromagnetic strength functions against those obtained within the standard RPA.Comment: 9 RevTeX pages, 11 figures, submitted to Physical Review

Dam Rain and Cumulative Gain

We consider a financial contract that delivers a single cash flow given by the terminal value of a cumulative gains process. The problem of modelling and pricing such an asset and associated derivatives is important, for example, in the determination of optimal insurance claims reserve policies, and in the pricing of reinsurance contracts. In the insurance setting, the aggregate claims play the role of the cumulative gains, and the terminal cash flow represents the totality of the claims payable for the given accounting period. A similar example arises when we consider the accumulation of losses in a credit portfolio, and value a contract that pays an amount equal to the totality of the losses over a given time interval. An explicit expression for the value process is obtained. The price of an Arrow-Debreu security on the cumulative gains process is determined, and is used to obtain a closed-form expression for the price of a European-style option on the value of the asset. The results obtained make use of various remarkable properties of the gamma bridge process, and are applicable to a wide variety of financial products based on cumulative gains processes such as aggregate claims, credit portfolio losses, defined-benefit pension schemes, emissions, and rainfall.Comment: 25 Pages, 1 Figur

Experimental study and model for healthy and pathological synovial fluid

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In the present work a comparative rheological study of healthy and pathological synovial fluid (SF)is presented. The SF samples were obtained from healthy dogs or dogs with rupture of cranial cruciate ligament. The rheological measurements were carried out at 25 oC and 38 oC, i.e. at room temperature and at the regular temperature of the dog’s body. A stainless steel rotating disk of 20 mm diameter was used on the rheometer AR-G2 and the gap between the plate and the disk was up to 125 μm. It was found that for the healthy SF, the viscosity was reduced by three orders of magnitude (from 40 Pa·s to 0.04 Pa·s) as γ(dot) was increased from 10-3 up to 800 s-1. For the pathological cases and for the same range of shear rates the viscosity values were between 1 Pa·s and 10-2 Pa·s. An established rheological model, i.e. the Carreau model, was used to describe the flow curves with successful results. Finally, the viscoelastic behavior was recorded by oscillatory and creep measurements and the obtained results indicate that the retardation time increases in consecutive measurements and also that the Cox-Merz rule is applicable in SF rheology