Selecting creep models using Bayesian methods

The development of creep prediction models has been a field of extensive research and many different models have already been proposed. This paper presents an evaluation method of the prediction quality of creep models for specific experimental data. Within the scope of this paper, the model according to Bockhold and the model according to Heidolf are examined. First, the parameters of the models are identified with respect to existing experimental data. This is done using a sampling based approach of Bayesian updating developed by Ba?ant and Chern. In extension to the method by Ba?ant and Chern, the uncertainty coming from inaccurate measurement data is taken into account in the definition of the likelihood function within the updating algorithm. The more inaccurate the measurements are, the more uncertain the estimated model parameters and model prognoses become. The identification is performed for different short- and long-term creep tests. The intension is not to validate these models intensively, but to evaluate their prognoses for the individually tested creep behavior. The results show that the identifiability of the models?? parameters is different for both models and consequently the models prognoses differ in their uncertainties. Second, the models are evaluated using two different strategies: the stochastic model selection according to MacKay, Beck and Yuen based on the Ockham factor, and a comparison of the uncertainties taking into account parameter and model uncertainties. The results of the evaluation of the creep models differ for various experimental tests. Model Heidolf is more flexible and gives a better fit to the data, however, it fails to predict reliable long-term creep deformations using only short-term measurements compared to model Bockhold. Comparing the evaluation methods, the analysis of uncertainties of the creep prognosis proofs to be more stable than the evaluation using the stochastic model selection.     

Erratum to: Evaluation of the Particle Bonding for Aluminum Sample Produced by Spark Plasma Sintering

Journal of Materials Engineering and Performance -     

Evaluation of the Particle Bonding for Aluminum Sample Produced by Spark Plasma Sintering

Journal of Materials Engineering and Performance - Spark plasma sintering (SPS) is a powder metallurgy process that sinters powder materials within a short time by simultaneous application...     

<Emphasis Type="Italic">N</Emphasis>-Acylated Bacteriohopanehexol-Mannosamides from the Thermophilic Bacterium <Emphasis Type="Italic">Alicyclobacillus acidoterrestris</Emphasis>

Identification of molecular species of various N-acylated bacteriohopanehexol-mannosamides from the thermophilic bacterium Alicyclobacillus acidoterrestris by semipreparative HPLC and by RP-HPLC with ESI is described. We used triple-quadrupole type mass spectrometer, ¹H and ¹³C NMR for analyzing this complex lipid. CD spectra of two compounds (model compound—7-deoxy-d-glycero-d-allo-heptitol obtained by stereospecific synthesis, and an isolated derivative of hopane) were also measured and the absolute configuration of both compounds was determined. On the basis of all the above methods, we identified the full structure of a new class of bacteriohopanes, represented by various N-acylated bacteriohopanehexol-mannosamides.     

Arsenic in atmospheric deposition at the Czech-Polish border: two sampling campaigns 20 years apart

Arsenic (As) occurs in atmospheric deposition both in soluble and insoluble forms, mainly bound to fine aerosol particles (less than 2.5 microm). Interception deposition (i.e. fog, dew and ice accretion) represents a specific type of atmospheric deposition, which has been much more contaminated with As than bulk deposition. This study compares the As amount and its binding forms in bulk and interception deposition in the winters of 1984-1986 and 2003-2005 in the Orlické hory mountains (Adlergebirge) near the Czech-Polish border; sampled and analysed by the same methodology. The As concentrations in ice accretions decreased 16 times over the twenty year period (from 50 microg L(-1) to 3 microg L(-1)), while the pH values increased by 0.8 units. As concentrations in snow decreased from 15 microg L(-1) in 1984-1986 to <2 microg L(-1) in 2003-2005. This decline mirrored the considerable decrease in industrial emissions in Central Europe. Higher acidity of interception deposition (about 1 pH unit) in comparison with the bulk deposition was observed in both sampling periods. The quantity of bulk deposition (snowfall) also influenced the As concentration in interception deposition. Dry periods resulted in higher As-amounts in interception deposition due to limited washing of atmospheric aerosol particles by wet deposition. The As concentration and stability in atmospheric deposition are important for the study of subsequent As-migration and/or accumulation in soil -- groundwater -- surface water.     

Engineered Glycosidases for the Synthesis of Analogs of Human Milk Oligosaccharides

Enzymatic synthesis is an elegant biocompatible approach to complex compounds such as human milk oligosaccharides (HMOs). These compounds are vital for healthy neonatal development with a positive impact on the immune system. Although HMOs may be prepared by glycosyltransferases, this pathway is often complicated by the high price of sugar nucleotides, stringent substrate specificity, and low enzyme stability. Engineered glycosidases (EC 3.2.1) represent a good synthetic alternative, especially if variations in the substrate structure are desired. Site-directed mutagenesis can improve the synthetic process with higher yields and/or increased reaction selectivity. So far, the synthesis of human milk oligosaccharides by glycosidases has mostly been limited to analytical reactions with mass spectrometry detection. The present work reveals the potential of a library of engineered glycosidases in the preparative synthesis of three tetrasaccharides derived from lacto-N-tetraose (Galβ4GlcNAcβ3Galβ4Glc), employing sequential cascade reactions catalyzed by β3-N-acetylhexosaminidase BbhI from Bifidobacterium bifidum, β4-galactosidase BgaD-B from Bacillus circulans, β4-N-acetylgalactosaminidase from Talaromyces flavus, and β3-galactosynthase BgaC from B. circulans. The reaction products were isolated and structurally characterized. This work expands the insight into the multi-step catalysis by glycosidases and shows the path to modified derivatives of complex carbohydrates that cannot be prepared by standard glycosyltransferase methods.     

Performance of Sulfate-reducing Passive Bioreactors for the Removal of Cd and Zn from Mine Drainage in a Cold Climate

Mine Water and the Environment - Passive treatment is a promising, green technology that is increasingly being used for mine drainage treatment. However, several challenges remain concerning its...     

A New and Fast HPLC Method for Determination of Rutin, Troxerutin, Diosmin and Hesperidin in Food Supplements Using Fused-Core Column Technology

A new and fast high-performance liquid chromatography (HPLC) method using fused-core column for separation of rutin, troxerutin, diosmin, and hesperidin has been developed and used for determination of these flavonoids in food supplements. Efficient separation of flavonoids and internal standard methylparaben was achieved on the fused-core column Ascentis Express RP-Amide (100?×?3.0 mm), particle size 2.7 μm, with mobile phase acetonitrile/water solution of acetic acid pH?3 (30:70, v/v) at a flow rate of 1.0 mL?min^?1 and at temperature 50 °C. The detection wavelengths were set at 283 nm for hesperidin and at 255 nm for rutin, troxerutin, diosmin, and internal standard methylparaben. Under the optimal chromatographic conditions, good linearity with correlation coefficients in the range (r?=?0.9991–0.9998; n?=?7) for all flavonoids was achieved. Commercial samples of food supplements were extracted with 100 % dimethyl sulfoxide using ultrasound bath for 10 min and then diluted to methanol. A 5-μL sample volume of the filtered solution was directly injected into the HPLC system. Accuracy of the method defined as a mean recovery of flavonoids from food supplement matrix was in the range 96.2–104.4 % for all flavonoids. The intraday method precision was satisfactory, and relative standard deviations of sample analysis including preparation and determination of different food supplements were in the range 0.5–3.5 % for all flavonoids. The developed method has shown high sample throughput during sample preparation process, modern separation approach, and short time (5 min) of analysis.