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61.
Przemysław Rybiński Grażyna Janowska Ludomir Ślusarski 《Journal of Thermal Analysis and Calorimetry》2010,101(2):665-670
The article presents the results of testing thermal properties and combustibility of butadieneacrylonitrile
rubber with 18% contents of bounded acrylonitrile, NBR 18. Two types of silica, Zeosil 175C and Ultrasil VN-3, with different
specific surfaces were used as filler.
Zeosil 175C and Ultrasil VN-3 were modified via cryogenic dezaggregation method. The activity of
unmodified and cryogenic modified silica toward butadiene-acrylonitrile rubber were investigated.
The sulphur and peroxide vulcanizates contained 20, 30, 40, and 50 phr. of the filler were studied.
The article discusses also the test results of thermal stability and flammability of NBR 18 containing
silica prepared "in situ" from alkoxysilane precursor.
The test results were obtained with the use of derivatograph, measurements of flammability by the
method of oxygen index, and in air.
The effect of the silica modification on the SEM and AFM was also examined.
The method of cryogenic modification enables to achieve increase of mineral fillers activity towards
elastomer and reduction in the flammability of NBR 18 vulcanizates.
It has been found that the modification of the vulcanizates of NBR 18 with tetraethoxysilane that
makes it possible to form silica "in situ" reduces the flammability of cross-linked rubbers. 相似文献
62.
Ludomir Newelski 《Transactions of the American Mathematical Society》2002,354(3):925-943
We propose a model-theoretic framework for investigating profinite structures. We prove that in many cases small profinite structures interpret infinite groups. This corresponds to results of Hrushovski and Peterzil on interpreting groups in locally modular stable and o-minimal structures.
63.
Joanna Faber Krzysztof Brodzik Anna Gołda-Kopek Damian Łomankiewicz Jan Nowak Antoni Świątek 《Chemical Papers》2015,69(6):799-809
The investigation of air pollution is a highly important field of research. Air quality in a vehicle’s interior has attracted growing attention since people spend much of their time in vehicles and those frequently travelling in new cars are exposed to harmful compounds. The main air pollutants inside new vehicles are volatile organic compounds (VOCs), present as a result of interior materials’ de-gassing. Among the sampling methods used in indoor air quality research, active sampling for VOCs collection is one method that has been extensively described and applied. The present study sought to implement passive sampling with Radiello® samplers to collect air samples directly in the car factory. The results from passive sampling were compared with results derived from active sampling using Carbograph 1TD and silicagel coated with 2,4-dinitrophenylhydrazine cartridges, based on previously validated methods. The identification and quantification of organic compounds was performed using gas chromatography with flame ionisation coupled with a mass spectrometer after thermal desorption. Aldehydes were determined by means of high-performance liquid chromatography. In the present study, the results obtained with the use of active and passive methods of air sampling were compared, correlations between the two sampling methods were designated and the repeatability of passive sampling was detailed. 相似文献
64.
Wlodzimierz Ogryczak Michał Przyłuski Tomasz Śliwiński 《Mathematical Methods of Operations Research》2017,86(3):625-653
In problems of portfolio selection the reward-risk ratio criterion is optimized to search for a risky portfolio offering the maximum increase of the mean return, compared to the risk-free investment opportunities. In the classical model, following Markowitz, the risk is measured by the variance thus representing the Sharpe ratio optimization and leading to the quadratic optimization problems. Several polyhedral risk measures, being linear programming (LP) computable in the case of discrete random variables represented by their realizations under specified scenarios, have been introduced and applied in portfolio optimization. The reward-risk ratio optimization with polyhedral risk measures can be transformed into LP formulations. The LP models typically contain the number of constraints proportional to the number of scenarios while the number of variables (matrix columns) proportional to the total of the number of scenarios and the number of instruments. Real-life financial decisions are usually based on more advanced simulation models employed for scenario generation where one may get several thousands scenarios. This may lead to the LP models with huge number of variables and constraints thus decreasing their computational efficiency and making them hardly solvable by general LP tools. We show that the computational efficiency can be then dramatically improved by alternative models based on the inverse ratio minimization and taking advantages of the LP duality. In the introduced models the number of structural constraints (matrix rows) is proportional to the number of instruments thus not affecting seriously the simplex method efficiency by the number of scenarios and therefore guaranteeing easy solvability. 相似文献
65.
We construct examples of Gromov hyperbolic
Coxeter groups of arbitrarily large dimension.
We also extend Vinbergs theorem to show that if a Gromov
hyperbolic Coxeter group is a virtual Poincaré duality group
of dimension n,
then n 61.Coxeter groups acting on their associated complexes have been extremely
useful source of examples and insight into nonpositively curved spaces
over last several years. Negatively curved (or Gromov hyperbolic)
Coxeter groups were much more elusive. In particular their existence in
high dimensions was in doubt.In 1987 Gabor Moussong [M] conjectured that there is a universal bound on
the virtual cohomological dimension of any Gromov hyperbolic Coxeter group.
This question was also raised by Misha Gromov [G] (who thought that perhaps
any construction of high dimensional negatively curved spaces requires
nontrivial number theory in the guise of arithmetic groups in an essential
way), and by Mladen Bestvina [B2].In the present paper we show that high dimensional Gromov hyperbolic Coxeter
groups do exist, and we construct them by geometric or group theoretic but
not arithmetic means. 相似文献
66.
Let p ∈ {1, ∞}. We show that any continuous linear operator T from A1 (a) to Ap (b) is tame, i.e., there exists a positive integer c such that sup x||Tx||k/|x|ck ∞ for every k ∈ N. Next we prove that a similar result holds for operators from A∞(a) to Ap(b) if and only if the set Mb,a of all finite limit points of the double sequence (bi /aj ) i,j∈N is bounded. Finally we show that the range of every tame operator from A∞(a) to A∞(b) has a Schauder basis. 相似文献
67.
To characterize an activity of silica toward elastomers usually the parameters of the filler structure and a possibility of its interactions with macromolecules of a matrix are taken into consideration [1,2,3]. As a rule, low molecular weight substances of different polarity are dissolved in a rubber mix (e.g. accelerators, activators, crosslinking substances, etc). They undergo adsorption on the surface of active fillers what exerts an effect on a structure of a network formed and influences mechanical properties of vulcanizates at the same time. 相似文献