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. 相似文献
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
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
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
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
Solutions of portfolio optimization problems are often influenced by errors or misspecifications due to approximation, estimation
and incomplete information. Selected methods for analysis of results obtained by solving stochastic programs are presented
and their scope illustrated on generic examples – the Markowitz model, a multiperiod bond portfolio management problem and
a general strategic investment problem. The approaches are based on asymptotic and robust statistics, on the moment problem
and on results of parametric optimization. 相似文献
If one has to determine multiple residues of modern pesticides and/or other groups of (semi)polar and/or thermally unstable contaminants with a wide range of physico-chemical properties within a single analytical run, it can be complicated to obtain low limits of quantitation (LOQ), good precision as well as relevant trueness of results for all the target analytes. Matrix components, which are unavoidably present in analyzed samples (even after the thorough clean-up step), may be responsible for miscellaneous adverse affects impairing different stages of the GC and/or LC determinative step. In this review, the nature of various types of matrix effects are discussed together with suggestions for prevention, reduction and/or compensation of their occurrence when determining troublesome analytes in foods and other complex biotic matrices. 相似文献
The presented paper contains a suggestion and an analysis of a two-level preconditioner appropriate for unstructured meshes. The convergence analysis is done for H1-equivalent forms in the two-dimensional case; ways for generalization are discussed, too. The efficiency is demonstrated by numerical experiments. 相似文献
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
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.