Fulltext search in archive

The results of raw whey rheological behavior investigation - particularly viscosity, dependence on temperature, time, and share rate, are presented. The whey samples have been examined under temperature ranging from 17 to 90 °C and under share rate ranging from 0.34 to 68 s^-1. The measurements have been performed using rotary digital viscometer (concentric cylinders geometry). The material was found to be temperature dependent (non-linearly), time dependent and shear thinning. Received data have been successfully characterized by several mathematical models (power, exponential, and polynomial) in MATLAB® software with satisfying correlations between experimental and computed results. Following correlations have been achieved: temperature dependence with r² = 0.993 using polynomial model, time dependence with r² = 0.985 using power model, and shear thinning behavior r² = 0.998 using power model. The results are quite useful for practical design of technological equipment such as pumps and piping.

The rheological behaviour of egg yolk after different storage periods and temperatures was investigated using rotational viscometer. The eggs were stored for 1, 2, 3, 4 and 8 weeks at constant temperatures: 4 °C, 8 °C, 12 °C and 16 °C. The apparent viscosity was measured as a function of shear rate. For given shearing rate, the viscosity was measured in dependence on shearing time. The decrease of viscosity with storage time is attributed to the balance of different osmotic pressure from yolk and albumen of fresh egg. The yolk (with higher dry matter then albumen) absorbs water from albumen through vitelline membrane. It was found that yolk samples exhibited shear-thinning and thixotropic behaviour. The shear-thinning behaviour was fitted well into simple models. The resting of sample at room temperature caused increase of viscosity. This effect is explained by drying off of testing yolk, the regeneration of yolk structures and changing chemical composition during resting. The time-dependant viscosity decreased rapidly with time and at lower share rates reached an equilibrium stage. The time-dependant viscosity was also found to decrease with storage time. The value of pH was changed (increased) during storing. No clear dependence between pH value and viscosity was confirmed.

This present study is focused on the modeling of the most important potato pest i.e Colorado potato beetle (Leptinotarsa decemlineata, Say 1824) development in relation to the climate conditions over the area of the Czech Republic. The aim was to develop a model allowing the assessment of the CPB possible spread under the climate change. For the estimation of the CPB occurrence in expected climate conditions we used a dynamic model CLIMEX that enables to determine the suitability of a given location climate for the pests survival and infestation capability based on known pests requirements to the climate conditions. Following the validation and calibration of the model outputs, the meteorological data were altered according to three Global Circulation Models (ECHAM4, HadCM3, NCAR-PCM) that were driven by two SRES emission scenarios (A2, B1) with two assumed levels of climate system sensitivity for period 2025 and 2050. Model output, for current and expected climate conditions, were visualized by GIS using a digital landscape model. Under all climate change scenarios we noted a widening of CPB distribution area and change in the infestation pressure of the pest.

In this work phenological phases of three species - ramson (Allium ursinum L.), hawthorn (Crataegus oxyacantha L.) and oak tree (Quercus robur L.) were evaluated on two research plots Lednice and Lanžhot during 1961-2007. Both plots represent protected flood-plain forests with no forestry management. The aim of this work is to assess which meteorological parameters influence the most duration of phenophases, to analyse shifts of phenophase timing during the period 1961 to 2007 and to compare phenological and temperature trends in this period. The meteorological and phenological data processed by software AnClim and FenoClim. Results showed that maximum and mean temperature influenced the duration of phenophases most significantly. The higher temperatures caused shortening of phenophases and vice versa. Per 1°C temperature increas the given phenophase its length will decrease by 2.3 days in case of oak tree, by 0.8 days in the case of hawthorn and by 1.3 days in the case of ramson. The onset of phenophases has advanced by 9 to 10 days during the period of 47 years.

A method for the characterising of the behaviour of the beef meat at compressive loading was investigated. Both compressive and relaxation tests have been used. Results of the relaxation tests have shown that the boiled beef can be described in terms of the Maxwell model of the strain behaviour. Parameters of this model are dependent on the values of the loading force. The description of the observed behaviour of the beef under compressive loading thus needs some other model. It is shown that the obtained results on the compressive loading of the beef can be explained in the framework of the hyperelastic - viscous body.

Two methods for estimating daily global solar radiation (R_G) based on the daily temperature extremes and precipitation sum are compared in the study. All parameters necessary for application of both methods were derived either from literature or from climatic characteristics easily available at the given meteorological stations excluding need for measured R_G data. The performance of both methods was assessed with a help of meteorological database including 4 stations in the Czech Republic (data were provided by the Czech Hydrometeorological Institute) and 6 in Austria (data provided by the Austrian Weather Service) containing in total 41 640 observational day. For each day in the database observed daily sum of R_G, daily maximum and minimum temperatures and precipitation sum were available. Coefficient of determination, slope of regression line forced through origin, mean bias error (MBE) and root mean square error (RMSE) were used as performance indicators. The first method proposed by Winslow et al. (2001) - Eq. (1) is capable to explain 86% of daily R_G variability, with systematic error represented by MBE equaling to 0.19 MJ.m^-2.day^-1 and random error indicated by RMSE reaching up to 3.09. The second method published by Thornton and Running (1999)-Eq. (2) was found to be in almost all parameters inferior to the Eq. (1) and thus the Eq. (1) is recommended to be used in the Central European region (up to 600 m above the sea level). This method might be recommended for stations where neither measured R_G or sunshine duration hours exist. However, one should take into consideration that relative MBE and RMSE are in some months higher than 10% and 30% respectively, which may compromise results of subsequent calculations made with use of estimated solar radiation data and alter the order of the method suitability.

The paper presents the software procedure (using MAPLE 11) intended for considerable reduction of digital image data set to more easily treatable extent. The example with image of peach stone is presented. Peach stone, displayed on the digital photo, was represented as a polygon described by the coordinates of the pixels creating its perimeter. The photos taken in high resolution (and corresponding data sets) contain coordinates of thousands of pixels - polygon's vertexes. Presented approach substitutes this polygon by the new one, where smaller number of vertexes is used. The task is solved by use of adapted least squares method. The presented algorithm enables reduction of number of vertexes to 10 % of its original extent with acceptable accuracy +/- one pixel (distance between initial and final polygon). The procedure can be used for processing of similar types of 2D images and acceleration of following computations.

The problem of the identification of the elastic properties of eggshell, i.e. the evaluation of the Young's modulus and Poisson's ratio is solved. The eggshell is considered as a rotational shell. The experiments on the egg compression under quasistatic loading have been conducted. During these experiments a strain on the eggshell surface has been recorded. By the mutual comparison between experimental and theoretical values of strains the influence of the elastic constants has been demonstrated.

The results of the previous studies have suggested that the estimated R_G values are loaded with an error, which might compromise the precision of the subsequent crop model applications. Therefore a detailed analysis of the error propagation was made using two crop models i.e. CERES-Barley and CERES-Wheat. Database of meteorological data originating from 8 stations in Austria and Czech Republic was used in order to carry out the analysis. It has been found that even application of the method based on sunshine duration that yield the lowest bias in R_G estimates significantly influences number of key crop model outputs. It has been also noted that in 5-6 seasons out of 100 cases the deviation greater than ±10 % is to be expected whilst the occurrence of ±25% could not be also ruled out. The precision of the yield estimates and other crop model outputs is lower then expected but still acceptable for most application with mean bias error in range of 2.0-4.1% when estimates based on the diurnal temperature range and cloud cover are used. In this case yield deviations over ±10% occurred in about 20% cases (depending on the crop) whilst the probability of significant yield departure (±25%) doubled of that found for the previous method. The methods based on the diurnal temperature range and daily precipitation sum showed an increase of the systematic bias of yield of winter wheat and considerably higher number of seasons with yield departures over ±25%. Utilisation of the methods based on the diurnal temperature range only for the purposes of seasonal yield forecasting or climate change impact assessment is questionable as the probability of significant yield departure is very high (as well as the systematic error). These findings should act as an incentive to the further research aimed at development of more precise and widely applicable methods of estimating daily R_G based more on the underlying physical principles and/or remote sensing approach. Overall decrease of the existing uncertainties in the R_G estimates would clearly result into increase of the reliability of subsequent applications that use R_G as input variable.

The rheological properties of four different ketchups were determined. The viscosity, shear rate and shear stress were measured by use of Anton Paar DV-3 P Digital Viscometer and received data can be successfully characterized by several models, primarily by Hershel - Bulkley model. The ketchup was found to be a typical time-dependent thixotropic fluid. Shear stress and viscosity decrease with time of shear. Decrease during first 300 s is more significant than later decrease. The influence of spindle speed, shear rate potentially, on a sample viscosity was observed. The viscosity was rapidly changing during low speeds. The data were compared with Carreau model. Many other dependeces (low and high shear rates, difference between mixed and rested material etc.) were observed and modelled with satisfying results. Dependence of shear stress on shear rate under two temperatures was also examined. The tendency of increasing shear stress with increasing shear rate is evident. The samples were examined under temperature 22 °C and temperature 7 °C.

The influence of the eggshell shape on the stress distribution under internal pressure is studied. A mathematical description of the hen's eggshell is proposed. The analytical expressions for the membrane solution are presented. Obtained results are used for the evaluation of a set of domestic hen's eggs. 28 eggs were analysed in this study. The weight of eggs ranged from 49.55 g to 61.08 g, the egg shape ranged from 72.82 % to 84.94 %, the average eggshell thickness ranged from 0.343 to 0.433 mm. The eggshell strength is given namely by the maximum values both of meridian and circumferential forces. The dependence of the meridian force maximum on the egg shape index has some tendency to increase with egg shape index. The outlined linear dependence is very weak, the coefficient of correlation is about 0.45.

The increase in the infestation pressure of various pathogens will be one the most important factors limiting the crop production under the future climate conditions. Weather driven NegFry model has been used for estimating future Phytophthora infestans occurrence at four experimental potato stations of the State Institute for Agriculture Supervision and Testing. Both the infestation dates of Phytophthora infestans occurrence and the shape of the critical number curve were analyzed using observed weather data as well as datasets constructed according to four climate change scenarios that were based on two global circulation models. The results show the shift of the infestation pressure to the beginning of the year and describe increasing trend of critical number reaching to detecting of the first Phytophthora infestans occurrence for 2025 and 2050. Scenarios created according to HadCM and SRES - A2 seem to be more suitable for disease development.