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排序方式: 共有581条查询结果,搜索用时 31 毫秒
571.
Jaroslav Sedl
ek Duan Galusek Peter van
rek Ralf Riedel Alan Atkinson Xin Wang 《Journal of the European Ceramic Society》2008,28(15):2983-2993
The response of Al2O3, Al2O3–SiC–(C) and Al2O3–C nanocomposites to grinding was investigated in terms of changes of quality of ground surfaces and of the weight losses with time. The study used monolithic polycrystalline aluminas as references, and alumina-based composites with nanosized SiC and C inclusions and with alumina matrix grain size varying from submicrometer to approximately 4 μm. The studied materials can be roughly divided into two groups. Materials with submicrometer alumina matrix grains (Group 1) wear predominantly by plastic deformation and grooving. Coarse-grained materials (Group 2) wear by mixed wear mechanism involving crack initiation and interlinking accompanied by grain pull-out, plastic deformation and grooving. The wear rate of composites increases with increasing volume fraction of SiC. The Group 2 materials wear much faster then those with submicron microstructure. In all cases (with one exception) the wear resistance of composites was higher than that of pure aluminas of comparable grain sizes used as reference materials. 相似文献
572.
Ivana?PoustkováEmail author Jaroslav?Dobiá? Ingrid?Steiner Jan?Poustka Michal?Vold?ich 《European Food Research and Technology》2004,219(5):534-539
Varnishes used for the inner coatings of food cans are often based on epoxy resins or vinylic organosols. The epoxy resins can be produced from bisphenol A (BPA) and bisphenol F (BPF), and these also contain bisphenol A diglycidyl ether (BADGE) or bisphenol F diglycidyl ether (BFDGE) as stabilising components. These compounds may break down during storage and also by the influence of food simulants. The stability of BADGE and BFDGE were studied using reverse-phase gradient high-performance liquid chromatography (RP-HPLC) with ultraviolet detection (UV). Three experimental conditions for spiked simulants were compared: (1) the storage at 25 °C (C1), (2) the storage at 40 °C (C2) and (3) the storage at 25 °C after 15 min heating at 120 °C (C3). Distilled water, 3% acetic acid and 10% ethanol were used as food simulants. It was observed that BADGE is more stabile than BFDGE. The loss of BADGE and BFDGE were minimal in 10% ethanol (39 and 46% at 25 °C, 60 and 69% at 40 °C, respectively) and highest in 3% acetic acid (60 and 63% at 25 °C, 76 and 82% at 40 °C, respectively). At experiment (C3), the hardest conditions, significant degradation was not shown in comparison with conditions (C1) and (C2), contrariwise BADGE and BFDGE in 10% ethanol were minimal degradated at conditions (C3) from all these experiments (loss of 5 and 8%, respectively). 相似文献
573.
Zalán Z Hudáček J Tóth-Markus M Husová E Solichová K Hegyi F Plocková M Chumchalová J Halász A 《Journal of the science of food and agriculture》2011,91(4):672-679
BACKGROUND: In the tubers of Jerusalem artichoke (Helianthus tuberosus L.) the main carbohydrate is the well‐known prebiotic inulin, which is a good growth substrate for gut microorganisms. Jerusalem artichoke tuber is traditionally consumed boiled or pickled rather than in fermented form. Lactic acid bacteria are traditionally used in the production of fermented foods; nevertheless their behavior and metabolite production are considerably influenced by the substrate. The purpose of this study was to investigate the growth and production of the most important sensorically and antimicrobially active metabolites of different Lactobacillus strains on Jerusalem artichoke juice. RESULTS: All investigated strains grew well (in the range 109 cfu mL?1) in the media. The organic acids (lactic acid, 110–337 mmol L?1; acetic acid, 0–180 mmol L?1; and succinic acid, 0–79 mmol L?1), hydrogen peroxide (0.25–1.77 mg L?1), mannitol (0.06–3.24 g L?1), acetoin and diacetyl production of strains varies not only according to the species but also from strain to strain, which will be demonstrated and discussed in the paper. CONCLUSION: Our results showed that lactobacilli can be used for the fermentation of Jerusalem artichoke, which in this form could be used, alone or mixed with other raw food material, as a new synbiotic functional food. Copyright © 2011 Society of Chemical Industry 相似文献
574.
Electronically controlled oscillator with linear frequency adjusting for four‐phase or differential quadrature output signal generation
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Roman Sotner Norbert Herencsar Jan Jerabek Jaroslav Koton Tomas Dostal Kamil Vrba 《International Journal of Circuit Theory and Applications》2014,42(12):1264-1289
This paper introduces novel four‐phase oscillator employing two Dual‐Output Controlled Gain Current Follower Buffered Amplifiers (DO‐CG‐CFBAs), single Current Amplifier, three resistors, and two grounded capacitors suitable for differential quadrature signal production (floating outputs). To control the frequency of oscillation (FO) and condition of oscillation (CO), only the current gain adjustment of active elements is used. The circuit was designed by well‐known state variable approach. The oscillator employs three active elements for linear control of FO and to adjust CO and provides low‐impedance voltage outputs. Furthermore, two straightforward ways of automatic amplitude gain control were used and compared. Active elements with very good performance are implemented to fulfill required features. Suitable CMOS implementation of introduced DO‐CG‐CFBA was shown. Important characteristics of the designed oscillator were verified experimentally and by PSpice simulations to confirm theoretical and expected presumptions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
575.
Andrea Rossnerova Katerina Honkova Irena Chvojkova Daniela Pelclova Vladimir Zdimal Jaroslav A. Hubacek Lucie Lischkova Stepanka Vlckova Jakub Ondracek Stepanka Dvorackova Jan Topinka Pavel Rossner Jr. 《International journal of molecular sciences》2021,22(15)
A DNA methylation pattern represents an original plan of the function settings of individual cells and tissues. The basic strategies of its development and changes during the human lifetime are known, but the details related to its modification over the years on an individual basis have not yet been studied. Moreover, current evidence shows that environmental exposure could generate changes in DNA methylation settings and, subsequently, the function of genes. In this study, we analyzed the effect of chronic exposure to nanoparticles (NP) in occupationally exposed workers repeatedly sampled in four consecutive years (2016–2019). A detailed methylation pattern analysis of 14 persons (10 exposed and 4 controls) was performed on an individual basis. A microarray-based approach using chips, allowing the assessment of more than 850 K CpG loci, was used. Individual DNA methylation patterns were compared by principal component analysis (PCA). The results show the shift in DNA methylation patterns in individual years in all the exposed and control subjects. The overall range of differences varied between the years in individual persons. The differences between the first and last year of examination (a three-year time period) seem to be consistently greater in the NP-exposed subjects in comparison with the controls. The selected 14 most differently methylated cg loci were relatively stable in the chronically exposed subjects. In summary, the specific type of long-term exposure can contribute to the fixing of relevant epigenetic changes related to a specific environment as, e.g., NP inhalation. 相似文献
576.
Even rka Jaroslav Kol
ek Andriy Synytsya Kateina Hrukov Jaroslav Maixner Jií ttina 《Starch - St?rke》2012,64(6):481-488
A‐ and B‐wheat starch (in native or acetylated form) and potato starch (slightly acetylated) were subjected to benzylation with benzylchloride in various reaction conditions and at various reaction times (40–100°C, 1–90 h). Modified and original starches were characterized by elemental analysis and spectroscopic methods (FT‐IR and 1H NMR). The semicrystalline or amorphous character was indicated by X‐ray powder (XRD) patterns. Rheological properties of benzyl starch of DS ∼ 1 were measured by small amplitude oscillation shear rheology (SAOS) using the rheometer Haake Rheostress RS 80. The results indicated predominantly elastic behavior because the storage modulus was higher than the loss modulus over the whole frequency range; it corresponded to a true gel. The storage and loss moduli increased with increasing frequency while the tangent of phase did not change and was approximately δ = 40°. 相似文献
577.
578.
The nonionogenic pyrene-based tenside, poly(ethylene glycol) pyrenebutanoate, was prepared and applied in capillary isoelectric focusing with fluorometric detection. This dye was used here as a buffer additive in capillary isoelectric focusing for a dynamic modification of the sample of proteins and microorganisms. The values of the isoelectric points of the labeled bioanalytes were calculated with use of the fluorescent pI markers and were found comparable with pI of the native compounds. The mixed cultures of proteins and microorganisms, Escherichia coli CCM 3954, Staphylococcus epidermidis CCM 4418, Proteus vulgaris, Enterococcus faecalis CCM 4224, and Stenotrophomonas maltophilia, the strains of the yeast cells, Candida albicans CCM 8180, Candida krusei, Candida parapsilosis, Candida glabrata, Candida tropicalis, and Saccharomyces cerevisiae were reproducibly focused and separated by the suggested technique. Using UV excitation for the on-column fluorometric detection, the minimum detectable amount was down to 10 cells injected on the separation capillary. 相似文献
579.
Work rolls in hot rolling mills are thermally and mechanically loaded; both of these loading aspects are difficult to measure. Laboratory tests can be used for the specification of the thermal load in the cooling area; however a thermal load in a roll gap is still difficult to measure. The paper describes an experimental technique developed for monitoring the work roll surface temperature by sensors embedded in the work roll. Continuous hot rolling pilot line trials were performed for different process conditions. One parameter, for example, roll cooling, rolling velocity, reduction, or skin cooling, can easily be changed during the trials, and the effect on the thermal cycle of the work roll can be directly measured. These thermal measurements give very detailed information about the temperature field. An inverse heat‐conduction model has been developed to compute the surface boundary condition from the measured temperatures. The heat flux and heat transfer coefficient distribution along the roll circumference can be obtained afterwards. The results for different rolling velocities and reductions (up to 50%) are shown. 相似文献
580.
José Marcial Maria Rita Cicconi Carolyn I. Pearce Jaroslav Kloužek James J. Neeway Richard Pokorný Miroslava Vernerová John S. McCloy Emily T. Nienhuis Rolf Sjöblom Jamie L. Weaver Russell J. Hand Pavel Hrma Daniel R. Neuville Albert A. Kruger 《Journal of the American Ceramic Society》2023,106(3):1716-1731
There is wide industrial interest in developing robust models of long-term (>100 years) glass durability. Archeological glass analogs, glasses of similar composition, and alteration conditions to those being tested for durability can be used to evaluate and inform such models. Two such analog glasses from a 1500-year-old vitrified hillfort near Uppsala, Sweden have previously been identified as potential analogs for low concentration Fe-bearing aluminosilicate nuclear waste glasses. However, open questions remain regarding the melting environment from which these historic glasses were formed and the effect of these conditions on their chemical durability. A key factor to answering the previous melting and durability questions is the redox state of Fe in the starting and final materials. Past work has shown that the melting conditions of a glass-forming melt may influence the redox ratio value (Fe+3/∑Fe), a measure of a glass's redox state, and both melting conditions and the redox ratio may influence the glass alteration behavior. Synthetic analogs of the hillfort glasses have been produced using either fully oxidized or reduced Fe precursors to address this question. In this study, the melting behavior, glass transition temperature, oxidation state, network structure, and chemical durability of these synthesized glass analogs is presented. Resulting data suggests that the degree of network connectivity as impacted by the oxidation state of iron impacted the behavior of the glass-forming melt but in this case does not affect the chemical durability of the final glass. Glasses with a lower degree of melt connectivity were found to have a lower viscosity, resulting in a lower glass transition temperature and softening temperature, as well as in a lower temperature of foam onset and temperature of foam maximum. This lower degree of network connectivity most likely played a more significant role in accelerating the conversion of batch chemicals into glass than the presence of water vapor in the furnace's atmosphere. Future work will focus on using the results from this work with outcomes from other aspects of this project to evaluate long-term glass alteration models. 相似文献