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71.
The effect of alkyl substituents in 2-alkylbutadienes on their hydromagnesiation with alkylmagnesium halides was studied. 相似文献
72.
Jitka Eysseltova 《Monatshefte für Chemie / Chemical Monthly》2005,45(6):1567-1572
Solubility isotherms in LiNO3 – LiX – H2O (X = Cl, Br, I) systems at 298.15 K were measured for the first time with special regard to the retrograde solubility of lithium nitrate trihydrate. The compositions of solutions used as media in absorption refrigerators and heat pumps were compared with the results and subsequently discussed. 相似文献
73.
Effect of thermal decomposition processes on the thermal properties of carbon fiber reinforced cement composites in high-temperature range 总被引:1,自引:0,他引:1
R. Černý Jitka Němečková Pavla Rovnaníková P. Bayer 《Journal of Thermal Analysis and Calorimetry》2007,90(2):475-488
Thermal conductivity, specific heat capacity, thermal diffusivity and linear thermal expansion coefficient of two types of
carbon fiber reinforced cement composites are measured in the temperature range up to 800°C. Thermal conductivity and thermal
diffusivity are also determined for the specimens exposed to thermal load up to 800°C before the measurement. Differential
thermal analysis (DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis
(XRD) are utilized for the assessment of thermal decomposition processes taking place in the high temperature range under
consideration.
The high temperature thermal properties of the studied materials are found to be positively affected by the application of
the high alumina cement and in the case of the Portland cement based composite also by using the autoclaving procedure in
the production process. Also, the randomly distributed carbon fibers that can reduce the damage of the pore structure by the
thermal decomposition processes are identified as a positive factor in this respect. A comparison of thermal conductivity
vs. temperature curves obtained for the specimens pre-heated to different temperatures is found to be a useful tool in the identification
of major dynamic effects in the specimens due to the thermal decomposition reactions. The results are in a good agreement
with the DTA, MIP, SEM and XRD analyses. The character of the thermal conductivity measurements that in fact includes the
effects of convection and radiation into the thermal conductivity coefficient can be beneficial for a simple assessment of
the influence of the fire on a dividing structure. 相似文献
74.
Roman ?ermák Martin Obadal Petr Poní?il Martina Polášková Karel Stoklasa Jitka He?ková 《European Polymer Journal》2006,42(9):2185-2191
Resuming our comprehensive study, present Part II directs attention towards the effects of mould temperature and holding pressure on the tensile properties of neat and β-nucleated isotactic polypropylenes. A commercial-grade of isotactic polypropylene was modified with a β-specific nucleator. From both the original material (α-iPP) and the β-nucleated material (β-iPP), tensile test specimens were injection-moulded. Stress-strain measurements performed at room temperature revealed a positive influence of higher mould temperatures but negligible effect of holding pressure on the elastic modulus of injection-moulded specimens. It was suggested that at optimum processing conditions the elastic modulus of both α- and β-iPP may be comparable. The softening effect of β-form manifested itself in systematically lower yield stress values of β-iPP as compared to α-iPP. The yield strain of both α- and β-iPP decreased with the increase of mould temperature and the decrease of holding pressure. Prolonged solidification times at higher mould temperatures negatively influenced the strain at break of the specimens; the values of β-iPP exceeded by several folds those of α-iPP. The stress at break of β-iPP decreased correspondingly to strain at break. On the contrary, the increase of strain at break in α-iPP was followed by a decrease of stress at break. 相似文献
75.
Klejdus B Lojková L Lapcík O Koblovská R Moravcová J Kubán V 《Journal of separation science》2005,28(12):1334-1346
An efficient method of modifier addition for supercritical fluid extraction (SFE) of polar isoflavones was developed and yielded extraordinarily high recoveries. To find the optimal extraction conditions, a temperature and pressure optimization and modifier impact study was performed in naturally contaminated and spiked samples. Ultra-fast high-performance liquid chromatography/mass spectrometry (HPLC/MS) was used for the determination of isoflavones on an Atlantis dC18 high-speed reversed phase chromatographic column (20 x 2.1 mm, 3 microm particle size). A newly elaborated supercritical fluid extraction (SFE) procedure allowed more accurate (< 5%) and precise (< 4-7%) determination of isoflavones in biological materials. The HPLC/MS method significantly reduced analysis time with simultaneous improvement of sensitivity and detection limits. The on-column limits of detection LOD (S/N = 3) for isoflavone glycosides (daidzin, genistin, glycitin, ononin, and sissotrin) were 1.3-3.6 fmol and 0.2-1.0 fmol for aglycones (daidzein, glycitein, genistein, formononetin, and biochanin A), respectively. 相似文献
76.
77.
A new device has been developed for the trapping of volatile pollutants in trapping solvents. The device allows solvent recirculation and cryogenic trapping of evaporated volatiles to minimize the stripping effect and any losses of volatile analytes. Due to solvent recirculation, the trapping solvent column height remains constant during the extraction without any need for replenishment. Also mass transfer conditions are favorable due to the flattened shape of bubbles of CO2 and the longer extraction time. The bubbles have higher interfacial area and they have to pass a three times longer distance in the solvent column. The device produces more concentrated extracts, reduces solvent consumption, and reduces or eliminates its evaporation to the environment. The cryotrapping part reduces losses of volatile analytes and the stripping effect. It also enables single-phase extraction into much smaller solvent volumes. Due to constant and favorable extraction conditions, the precision of the method was also greatly improved (RSDs decreased from 2.2 to 0.8%). As proved by a set of rapid spiked-sample extractions of highly volatile compounds at very high flow rates, the relative standard deviation of the experiments performed in the new device is 3.5 times lower. 相似文献
78.
R.I. Dzhelyadin S.V. Golovkin A.S. Konstantinov V.F. Konstantinov V.P. Kubarovski L.G. Landsberg V.A. Mukhin V.F. Obraztsov T.I. Petrunina Yu.D. Prokoshkin V.A. Viktorov A.M. Zaitsev 《Physics letters. [Part B]》1981,102(4):296-298
Sixty events of the rare eletromagnetic decay ω→π0μ+μ? have been detected. The branching ratio for this decay been obtained to be BR(ω→π0μ+μ?) = (9.6 ± 2.3) × 10?5. The effective mass spectrum for muon pairs has been measured and the electromagnetic transition form-factor for the vertex ωπ0, Fω(mμμ2;mπ20) = (1 ? mμμ2/Λ2)?1, has been determined, Λ = (0.65 ± 0.03) GeV/c2. The results are compared with the vector-meson dominance model. 相似文献
79.
Jitka Havrnkov Zuzana Limpouchov Karel Prochzka 《Macromolecular theory and simulations》2005,14(9):560-568
Summary: A new computational algorithm for dynamic lattice Monte Carlo simulations of the associative behavior of heteroarm copolymers in selective solvents was developed and optimized for efficient and relatively fast simulation studies. The algorithm is based on the Siepmann and Frenkel variant of the bias self‐avoiding walk procedure. Simultaneously, a new criterion for recognition of an associate was proposed. The first results on the micellization of heteroarm star copolymers are presented.
80.
Scenarios for Multistage Stochastic Programs 总被引:9,自引:0,他引:9
A major issue in any application of multistage stochastic programming is the representation of the underlying random data process. We discuss the case when enough data paths can be generated according to an accepted parametric or nonparametric stochastic model. No assumptions on convexity with respect to the random parameters are required. We emphasize the notion of representative scenarios (or a representative scenario tree) relative to the problem being modeled. 相似文献