ESTIMATING RHEOLOGICAL PROPERTIES OF YOGURT USING DIFFERENT VERSIONS OF THE FREUNDLICH MODEL AND DESIGN MATRICES

The rheological properties described by the consistency coefficient and flow behavior index can be estimated from the relationship between shear stress and shear strain rate following a Freundlich model. An additional rheological property of concern to food scientists studying yogurt is yield stress. They extend the Freundlich model to include a three-parameter model called the Herschel-Bulkley model. In addition, the Herschel-Bulkley model is often linearized by taking logarithms of both sides. An additional complication is the viscometer limits the range of shear strain rates. The objectives of this study are to compare parameter estimates from the three models and to investigate the effects of different designs on the models

USING NONLINEAR FIXED AND MIXED MODELS TO STUDY ACCLIMATION TO HEAT STRESS IN CATTLE

Researchers studying acclimation of cattle to heat stress want to know if exposure to heat stress in controlled chambers will help cattle adjust to climatic conditions in the field. The four parameter nonlinear PET model is used to study the relationship between core body temperature and ambient temperature. This model works well when cattle are challenged by heat stress but the model is less useful for thermoneutral conditions. Both proc Nlin and Nlmixed are used to compare and contrast the field parameters between the controlled and the potentially acclimated group. Simulation studies were used to compare the effectiveness of proc Nlin versus proc Nlmixed. The results are helpful, not only for researchers who study acclimation, but also for those who study sensitivity, tolerance and robustness of cattle during heat stress

USING TIME SERIES TO STUDY DYNAMICS OF SWEAT RATES OF HOLSTEIN COWS EXPOSED TO INITIAL AND PROLONGED SOLAR HEAT STRESS

Sweating is a very important way for cows to cope with heat stress. We are interested in the ability of Holstein cows to sustain high sweat or evaporation rates when exposed to solar radiation. There were two solar heat stress treatments: onset and prolonged. The onset data provided an opportunity to examine the impact of sudden exposure to a solar thermal load. The prolonged data allowed us to examine the impact of exposure to solar heat stress for an expended period (5 hr). Two questions of interest were: Do cows sweat at a constant or cyclic rate? Is there a difference in the dynamics of the two treatments: onset and prolonged solar heat stress? The data were examined for stationarity. In the time domain, we fit ARIMA models and estimated the parameters. In the frequency domain, we used nonparametric spectral estimation to identify cyclic patterns in the sweat rates. The usefulness of each technique for analyzing the dynamics of sweat rates is discussed

A COMPARISON OF ANALYTIC AND BAYESIAN APPROACHES FOR CHARACTERIZING THERMAL HYSTERESIS IN CATTLE USING ALGEBRAIC AND GEOMETRIC DISTANCES

A high ambient temperature poses a serious threat to cattle. Above a certain threshold, an animal’s body temperature (Tb) appears to be driven by the hot cyclic air temperature (Ta) and hysteresis occurs. Elliptical hysteresis describes the output of a process in response to a simple harmonic input, and the trajectory forms a closed loop. The hysteresis loop shows a rotated elliptical pattern which depends on the lag between Tb and Ta. The objectives of this study are 1) to characterize hysteresis using bootstrapped ellipse specific nonlinear least squares 2) to reformulate models using the Bayesian method, and 3) to assess the contribution of the Bayesian approach by comparing the risks using two metrics: algebraic and geometric. Comparisons and illustrations are made using simulations over three levels of signal strength. For each method; bootstrap and Bayes, both algebraic and geometric distances are compared based on the root mean square distance (RMSE) from fitting the hysteresis loop. Data from a heat stressed steer in a field experiment was analyzed to illustrate and compare the results from each method

Longer fixation duration while viewing face images

The spatio-temporal properties of saccadic eye movements can be influenced by the cognitive demand and the characteristics of the observed scene. Probably due to its crucial role in social communication, it is argued that face perception may involve different cognitive processes compared with non-face object or scene perception. In this study, we investigated whether and how face and natural scene images can influence the patterns of visuomotor activity. We recorded monkeys’ saccadic eye movements as they freely viewed monkey face and natural scene images. The face and natural scene images attracted similar number of fixations, but viewing of faces was accompanied by longer fixations compared with natural scenes. These longer fixations were dependent on the context of facial features. The duration of fixations directed at facial contours decreased when the face images were scrambled, and increased at the later stage of normal face viewing. The results suggest that face and natural scene images can generate different patterns of visuomotor activity. The extra fixation duration on faces may be correlated with the detailed analysis of facial features

Exponential Distribution of Locomotion Activity in Cell Cultures

In vitro velocities of several cell types have been measured using computer controlled video microscopy, which allowed to record the cells' trajectories over several days. On the basis of our large data sets we show that the locomotion activity displays a universal exponential distribution. Thus, motion resulting from complex cellular processes can be well described by an unexpected, but very simple distribution function. A simple phenomenological model based on the interaction of various cellular processes and finite ATP production rate is proposed to explain these experimental results.Comment: 4 pages, 3 figure

Simulating carbon capture by enhanced weathering with global croplands: an overview of key processes highlighting areas of future model development

Enhanced weathering (EW) aims to amplify a natural sink for CO2 by incorporating powdered silicate rock with high reactive surface area into agricultural soils. The goal is to achieve rapid dissolution of minerals and release of alkalinity with accompanying dissolution of CO2 into soils and drainage waters. EW could counteract phosphorus limitation and greenhouse gas (GHG) emissions in tropical soils, and soil acidification, a common agricultural problem studied with numerical process models over several decades. Here, we review the processes leading to soil acidification in croplands and how the soil weathering CO2 sink is represented in models. Mathematical models capturing the dominant processes and human interventions governing cropland soil chemistry and GHG emissions neglect weathering, while most weathering models neglect agricultural processes. We discuss current approaches to modelling EW and highlight several classes of model having the potential to simulate EW in croplands. Finally, we argue for further integration of process knowledge in mathematical models to capture feedbacks affecting both longer-term CO2 consumption and crop growth and yields

Simultaneous free-volume modeling of the self-diffusion coefficient and dynamic viscosity at high pressure

International audienceA free-volume model of the dynamic viscosity and the self-diffusion coefficients was discussed. The temperature-pressure variations of the dynamic viscosity and the self-diffusion coefficients of small molecules were predicted. The compounds, carbon tetrachloride, cyclohexane, benzene, chlorotrifluoromethane, tetramethylsilane and methylcyclohexane were used for the investigation. The relation between microstructure, free volume and different complex thermophysical properties were emphasized by the model

Inverse chemical modeling and radiocarbon dating of palaeogroundwaters: The Tertiairy Ledo-paniselian aquifer in Flanders, Belgium.

Groundwater samples from the Ledo-Paniselian aquifer have been interpreted for chemical reaction patterns