Crop planning optimization model: the validation and verification processes

Each optimization problem in the area of natural resources claims for a specific validation and verification (V&V) procedures which, for overwhelming majority of the models, have not been developed so far. In this paper we develop V&V procedures for the crop planning optimization models in agriculture when the randomness of harvests is considered and complex crop rotation restrictions must hold. We list the criteria for developing V&V processes in this particular case, discuss the restrictions given by the data availability and suggest the V&V procedures. To show its relevance, they are applied to recently constructed stochastic programming model aiming to serve as a decision support tool for crop plan optimization in South Moravian farm. We find that the model is verified and valid and if applied in practice—it thus offers a plausible alternative to standard decision making routine on farms which often leads to breaking the crop rotation rules.     

Study of the Ternary Systems M (II)(NO3)2–LiNO3–H2O ( M (II)?5?Mg, Ca, Sr, Ba) at 25°C

 The isothermal solubility diagrams of four aqueous systems containing lithium nitrate and nitrates of group IIA metals – magnesium, calcium, strontium, and barium – were studied at 25°C. No double salt formation was observed. The results were compared with similar nitrate and chloride systems. Some trends in the shape of the phase diagrams were observed. Hydration analysis was applied to the solubility branches, rendering information about ionic processes in saturated solutions. Further, the ratio of activity coefficients of the saturating solid phase in ternary and binary solutions (γ/γ₀) was obtained.     

Finite volume schemes for multi-dimensional hyperbolic systems based on the use of bicharacteristics

In this paper we present recent results for the bicharacteristic based finite volume schemes, the so-called finite volume evolution Galerkin (FVEG) schemes. These methods were proposed to solve multi-dimensional hyperbolic conservation laws. They combine the usually conflicting design objectives of using the conservation form and following the characteristics, or bicharacteristics. This is realized by combining the finite volume formulation with approximate evolution operators, which use bicharacteristics of the multi-dimensional hyperbolic system. In this way all of the infinitely many directions of wave propagation are taken into account. The main goal of this paper is to present a self-contained overview on the recent results. We study the L ¹-stability of the finite volume schemes obtained by various approximations of the flux integrals. Several numerical experiments presented in the last section confirm robustness and correct multi-dimensional behaviour of the FVEG methods. This research has been supported under the VW-Stiftung grant I 76 859, by the grant No 201/03 0570 of the Grant Agency of the Czech Republic, by the Deutsche Forschungsgemeinschaft grant GK 431 and partially by the European network HYKE, funded by the EC as contract HPRN-CT-2002-00282.     

Scenario-based stochastic programs: Resistance with respect to sample

A contamination technique is presented as a numerically tractable tool to post-optimization and analysis of robustness of the optimal value of scenario-based stochastic programs and of the expected value problems. Detailed applications of the method concern the two-stage stochastic linear programs with random recourse and the corresponding robust optimization problems.This work was supported by the Grant Agency of the Czech Republic under Grant No. 402/93/0631.     

Use of aluminum containers in the determination of oxygen in organic substances by elemental microanalysis

The possibility of using cheap aluminum containers in oxygen elemental microanalysis of organic substances was studied. The absolute values of oxygen retention displayed by aluminum containers, as compared with silver ones, for CH(N)O(S)(Br) substances are shown. The magnitude of retention due an aluminum container is reproducible under given conditions. The precision and accuracy of the results of oxygen determination in CH(N)O compounds pyrolyzed in aluminum containers at 980 °C do not differ from the precision and accuracy of the results obtained with the use of silver containers.     

Evaluation of two-dimensional gas chromatography-time-of-flight mass spectrometry for the determination of multiple pesticide residues in fruit

In recent years, comprehensive two-dimensional gas chromatography (GC x GC) has attained increasing attention for its outstanding separation potential and capability to solve demanding analytical tasks. Trace level analysis of pesticides residues in complex food matrices represents such a demanding task. For some commodities, such as baby food, the requirements on method detection limits are very strict and the unambiguous confirmation of the pesticide presence based on mass spectrometric detection is required. In this work, GC x GC coupled to time-of-flight mass spectrometry (TOF MS) has been evaluated for the determination of pesticides residues in fruit samples. Twenty modern pesticides with a broad range of physico-chemical properties were analysed in apple and peach samples. It has been demonstrated that the application of comprehensive two-dimensional gas chromatography brings distinct advantages such as enhanced separation of target pesticides from matrix co-extracts as well as their improved detectability. The limits of detection of the pesticides comprised in the study (determined at S/N = 5) ranged from 0.2 to 30 pg, injected with the exception of the last eluted deltamethrin, for which 100 pg could be detected. When compared to one-dimentional GC-TOF MS analysis under essentially the same conditions the detectability enhancement was 1.5-50-fold. Full mass spectral information by time-of-flight mass spectrometry and the deconvolution capability of the dedicated software allowed for reliable identification of most pesticides at levels below 0.01 mg/kg (< 10 pg injected) in fruit. Performance characteristics of the GC x GC-TOF MS method, such as linearity of calibration curves, repeatability of (summed) peak areas, as well as repeatability of first and second dimension retention times, were shown to fully satisfy the requirements for trace level analysis of the pesticide residues in food.     

Investigation of phenolic acids in yacon (Smallanthus sonchifolius) leaves and tubers

Thin-layer chromatographic (TLC) screening of crude extracts of dried leaves and tubers of yacon (Smallanthus sonchifolius, Asteraceae) and products of acid hydrolysis of tubers on the silica gel HPTLC plates using the developing solvents ethyl acetate-formic acid-water (85:10:15, v/v/v) and n-hexane-ethyl acetate-formic acid (20:19:1, v/v/v) proved the presence of chlorogenic, caffeic and ferulic acid. These phenolic acids were isolated from the crude extract of yacon leaves by preparative TLC, and identified after elution by HPLC/MS, as well as by direct injection of the crude extract into the HPLC/MS system. Acid hydrolysis of tubers released the increased amount of phenolic acids (e.g. caffeic acid and ferulic acid), flavonoid quercetin and an unidentified flavonoid, which was detected by TLC analysis. Ferulic acid, isomers of dicaffeoylquinic acid and still an unidentified derivative of chlorogenic acid (Mr = 562) as constituents of yacon leaves and ferulic acid as constituent of yacon tubers are reported here for the first time. These acids gave significant contribution to the radical scavenging activity detected directly on the TLC plate sprayed with 1,1-diphenyl-2-picrylhydrazyl (DPPH).     

Characterization of dextrans by size-exclusion chromatography on unmodified silica gel columns, with light-scattering detection, and capillary electrophoresis with laser-induced fluorescence detection

Unmodified silica gel size-exclusion columns were used in an on-line combination with light-scattering detection for a size characterization of dextrans. The influence of electrostatic interactions on analyte retention was briefly investigated. Size-exclusion chromatography was also used for evaluation of the fluorescence labeling procedure for dextrans with 8-aminonaphthalene-1,3,6-trisulfonic acid. The derivatives obtained through this procedure were used for electrophoretic measurements with laser-induced fluorescence detection. A comparison between the size-exclusion data and capillary electrophoresis indicates that the effectiveness of fluorescent labeling decreases with molecular mass of the dextran analytes.     

Solubility in the Systems MCl (M = Na, K)–1,4-Dioxane–Water at 25 ^C

Phase equilibria in the ternary systems, sodium chloride–dioxane–water and potassium chloride–dioxane–water, have been studied at 25 ^C and a section method for the determination of the immiscibility boundary has been tested. The phase diagrams exhibit the difference between the two systems. In the sodium chloride system an area of two liquid phases occurs, whereas with potassium chloride only a smooth solubility curve exists.Dedicated to Prof. Jaroslav Podlaha, an extraordinary chemist and great human being, on the occasion of his 70th birthday.