Dehydration kinetics by non-isothermal techniques

The kinetics of thermal degradation of some cementitious calcium aluminates, sulfoaluminates, sulfoferrites and carboaluminates were studied. Activation energies, obtained by Morris and Rogers and Kissinger techniques, were found to be in good agreement with each other.

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Zusammenfassung Die thermische Zersetzungskinetik einiger im Zement befindlicher Kalziumaluminate, Sulfoaluminate, Sulfoferrite und Karboaluminate wurde untersucht. Die nach den Methoden von Morris und Rogers, sowie Kissinger erhaltenen Aktivierungsenergien stimmten gut überein.

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Résumé On a étudié la cinétique de la décomposition thermique de plusieurs constituants du ciment tels les aluminates, sulfoaluminates, sulfoferrites et carboaluminates de calcium. Les énergies d'activation obtenues en appliquant la méthode de Morris et Rogers ainsi que celle de Kissinger sont concordantes.

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Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

Dissociative electron attachment to CO2

The 4.4 eV dissociative electron attachment peak in CO₂ was reinvestigated paying particular attention to (i) its structure associated with vibrational excitation and to (ii) the temperature dependence of the onset. For this purpose we have used two specially designed crossed beams machines, one having a trochoidal electron analyzer (TEM) and one with a hemispherical electron analyzer (HEM) for the production of the highly monochromatized electron beams (with FWHM’s down to 5 and 50 meV, respectively). The present results confirm the earlier findings in (i) interpreting the dominant structures of the 4.4 eV peak as being due to vibrationally excited states of CO in the reaction CO₂+e → O⁻+CO and (ii) assigning the much weaker and narrower structures to the intermediate CO ₂ ⁻ . In the temperature range between 300 and 245 K almost no temperature dependence of the onset can be seen in the present study. In comparison to NO and CO where the onset is vertical the CO₂ threshold behavior is less steep indicating that in the CO₂ case a different type of transition must be responsible for the onset of the O⁻ production. Besides DA to CO₂ we have for comparison and calibration purposes investigated also DA to CO and NO. Dedicated to Prof. Jan Janča on the occasion of his 60th birthday. Work was carried out within the Association EURATOM-OEAW and partially supported by the FWF, OENB, and BMWV, Wien, Austria.     

Experimental investigations and modelling studies of ozone producing corona discharges

The ozone generation by negative corona discharge in coaxial cylindrical system of electrodes have been studied experimentally in Ar+O₂ and N₂+O₂ mixtures. Both in argon and nitrogen mixtures with oxygen the monotonous decrease in ozone concentration [O₃] was observed at decreasing oxygen content in mixtures and the constant input energy density η. The rate coefficients for the ozone generation and ozone decomposition were obtained by fitting experimentally measured data [O₃]=f(η) with Vasiljev-Eremin formula. The calculated rate coefficient for ozone generation in N₂+O₂ mixtures at low content of oxygen (below 20%) was found considerably higher than that in Ar+O₂ mixtures. Increase in the rate coefficients for ozone generation and decomposition was observed with decreasing content of oxygen in both mixtures. The experimental results are in qualitative agreement with the simple model incorporating five main chemical processes in mechanism of ozone generation. The research was partially supported by Slovak Grant Agency under project 1/765920 The UK EPSRC (Grant GM/98944) and NATO Joint Project PST CLG 976544.     

Interactive effects of age and gender on levels of toxic and potentially toxic metals in children hair in different urban environments

Children growth and development may be affected by metal exposure. The objective of the present study was to investigate the interactive effects of age and gender on children hair toxic metal levels in urban environment of two Russian cities. A total of 2021 children living in Moscow and Novosibirsk aged 1–18 years old were examined. Hair Al, As, Cd, Hg, Ni, Pb and Sn levels were assessed using inductively-coupled plasma mass-spectrometry in dynamic reaction cell mode. Children from Novosibirsk were characterised by higher hair Al (37%), As (385%), Cd (127%), Hg (11%), Ni (23%), Pb (72%) and Sn (25%) in comparison to Moscow values. In the general cohort, boys had higher Al (13%), As (51%), Cd (65%), Pb (63%) and Sn (18%) levels, whereas hair Ni was higher in girls (17%). Further analysis demonstrated age-specific gender differences. In particular, only hair Ni and Cd levels were higher in male toddlers and pre-schoolers from Novosibirsk as compared to females. No gender difference was detected in Moscow. Maximal gender differences in hair metal levels were detected in adolescents for both locations. International Union of Pure and Applied Chemistry (IUPAC) reference values for all groups were also calculated. The overall reference limits for the studied children population were Al (1.335–3.340 µg/g), As (0.021–0.384 µg/g), Cd (0.000–1.389 µg/g), Hg (0.024–0.722 µg/g), Ni (0.076–0.701 µg/g), Pb (0.050–1.490 µg/g) and Sn (0.070–1.026 µg/g). Two-way ANOVA demonstrated significant effects of age, gender and age*gender interaction on hair metals in both cities. At the same time, the age-specific changes in hair metal content were more expressed in children from Novosibirsk, being exposed to higher metal pollution. The obtained data demonstrate that age, gender as well as the particular rate of pollution in each location should be taken into account during interpretation of hair test results.     

高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

Sarracenia alata (Alph.Wood) Alph.Wood Microcuttings as a Source of Volatiles Potentially Responsible for Insects’ Respond

Rare carnivorous plants representing the genus Sarracenia are perceived as very interesting to scientists involved in various fields of botany, ethnobotany, entomology, phytochemistry and others. Such high interest is caused mainly by the unique capacity of Sarracenia spp. to attract insects. Therefore, an attempt to develop a protocol for micropropagation of the Sarracenia alata (Alph.Wood) Alph.Wood, commonly named yellow trumpets, and to identify the specific chemical composition of volatile compounds of this plant in vitro and ex vivo was undertaken. Thus, the chemical volatile compounds excreted by the studied plant to attract insects were recognized with the application of the headspace solid-phase microextraction (HS-SPME) coupled with the GC-MS technique. As the major volatile compounds (Z)-3-hexen-1-ol (16.48% ± 0.31), (E)-3-hexen-1-ol acetate (19.99% ± 0.01) and β-caryophyllene (11.30% ± 0.27) were identified. Further, both the chemical assumed to be responsible for attracting insects, i.e., pyridine (3.10% ± 0.07), and whole plants were used in in vivo bioassays with two insect species, namely Drosophila hydei and Acyrthosiphon pisum. The obtained results bring a new perspective on the possibilities of cultivating rare carnivorous plants in vitro since they are regarded as a valuable source of bioactive volatile compounds, as including ones with repellent or attractant activity.     

Dissociative electron attachment to CF2Cl2

Using a recently constructed high resolution crossed electron/molecular beam apparatus consisting of a hemispherical electron monochromator and a quadrupole mass spectrometer we have measured the relative production cross sections for CI^– and F^– via electron attachment to CF₂Cl₂. The relative Cl^– cross section is placed on an absolute scale by reference to an absolute rate coefficient using a calibration method involving integration of the measured anion signal. The most efficient Cl^– production process is at about zero energy and its magnitude is resolution limited. The present high resolution value of 6 × 10^–16 cm² compares well with an earlier value reported by Chen and Chantry. A second peak is detected at around 0.8 eV in accordance with some of the earlier beam and swarm measurements. The observed production of F^– has an appearance energy of 1.9 eV and the energy of maximum cross section is 3.36 eV, the latter value comparing well with several previous studies.