The effect of hydrodynamic conditions on the detection of aqueous solutions of toluene by means of an inverted graded-index fiber

This paper deals with the effect of hydrodynamic conditions on the detection of toluene dissolved in water by means of fibers with a truncated parabolic inverted-graded index (IGI) profile. The detection is based on refractive-index changes of a detection layer of polydimethylsiloxane (PDMS) applied on the fiber which are induced by penetration of toluene into the layer. The dependence of the response of the sensing fiber placed in a flow cell on the flow velocity of the detected aqueous solution of toluene has been investigated. The sensing fiber was successively exposed to flows of distilled water and aqueous solutions of toluene. The fiber responses were measured for three chosen concentrations of the toluene solutions and for five flow velocities of the solutions. From these results the dependence of the relative decrease of the output signal on the flow velocity was determined. It has been found that the magnitude of output signal changes is approximately proportional to the solution concentration and the rate of the signal changes in the tested concentration range depends approximately linearly on the solution flow velocity.     

Macerals in bituminous coals and the coking process: Part 1: Effect of basic coal properties on the process of thermal degradation

Bituminous coals produced in the Ostrava—Karviná coal basin show considerable variation in their maceral composition and rank. In order to explain the significance of the petrographic composition, structure and chemical parameters in coal degradation processes, a large number of coal samples was investigated. From the relationships obtained, the behaviour of macerals during these processes is discussed. It is found that isometamorphic vitrinites are characterized by a distinctive behaviour affected to a first approximation by the atomic ratios C/H and C/O. Inertinite, despite its occasional significantly higher volatile matter, does not yield an appreciable amount of fused material.     

Control Lyapunov functions for adaptive nonlinear stabilization

For the problem of stabilization of nonlinear systems linear in unknown constant parameters, we introduce the concept of an adaptive control Lyapunov function (aclf) and use Sontag's constructive proof of Artstein's theorem to design an adaptive controller. In this framework the problem of adaptive stabilization of a nonlinear system is reduced to the problem of nonadaptive stabilization of a modified system. To illustrate the construction of aclf's we give an adaptive backstepping lemma which recovers our earlier design.     

New aspects in cationization of lignocellulose materials. VII. Modification of spruce wood meal with quarternary ammonium groups

Trimethylammonium-2-hydroxypropyl (TMAHP) derivatives of spruce wood meal (SWM) and holocellulose of this specia were prepared by the reaction of wood meal with 3-chlor-2-hydroxy-propyltrimethylammoniumchloride (CHMAC) in alkaline medium. The TMAHP samples were fractionated and yields and exchange capacity (Q) of individual fractions were compared with beech and aspen fractions obtained under the same conditions. As it is evident from ¹³C-NMR spectroscopy and GPC analysis the water soluble fraction from TMAHP–SWM consists only of lignin–saccharide degradation products. The NaOH extracts of TMAHP–SWM and TMAHP–holocellulose as well as the water-soluble fraction from TMAHP–holocellulose are polymeric materials. From TMAHP–SWM only 3.1% of alkali-soluble material could be extracted, while from TMAHP–holocellulose 15.7% of water-soluble and 7.9% of alkali-soluble materials were obtained.     

Grain-size dependence of fracture stress in anisotropic brittle solids

The stress concentrations that occur at grain boundaries due to thermal expansion anisotropy and elastic stress concentration are discussed, and the stress intensity factor that results from these stresses is estimated. The procedure for the stress intensity factor calculation is based on the model in which a spherical crystal (grain) is forced into a cavity of equal size possessing annular or radial cracks emanating from the boundary. The stress intensity factor equation thus obtained is extended to include the effect of elastic stress concentration due to the presence of a cavity, and is subsequently used to predict the grain-size dependence of strength in anisotropic brittle ceramics. In assessing the degradation of strength with increasing grain size in non-cubic ceramics, it is shown that, in addition to grain size, the effect of pre-existing crack size must also be considered. Cubic ceramics, on the other hand, are known to exhibit no thermal expansion anisotropy and, based on the present model, their strength is predicted to be governed by the pre-existing flaw size, rather than the grain size.     

Nonterminal unsaturated silane coupling agents for mineral-filled ethylene–propylene rubber

This paper describes the results of an experimental investigation concerning the effect of reactive organofunctional unsaturated silanes on mechanical properties of mineral-filled ethylene–propylene elastomers. The tested group of the unsaturated silanes was prepared by hydrosilylation syntheses. The experimental silanes, 2,6-octadienyltriethoxysilane, cis-2-butenyltriethoxysilane, 2-(3-cyclohexenylethyl)triethoxysilane, and 2-(3-cyclohexenylethyl)methyldiethoxysilane, led to a considerable improvement in mechanical and electrical properties of mineral-filled vulcanizates based on peroxide-cured ethylene–propylene elastomers. From the tested silanes, the 3-cyclohexenylethylsilanes impart an improvement comparable with the action of vinyltris(2-methoxyethoxy)silane, presently used as a standard coupling agent in mineral-filled peroxide-cured elastomers.     

Particle-size dependence of thermoelastic stress intensity factor in two-phase materials

The stress intensity factor is estimated for an annular crack originating from the particle-matrix interface in residual stress fields associated with a spherical particle of lower thermal expansion than that of the matrix. It is shown that the stress intensity factor is a function of particle size and pre-existing crack length. Spontaneous matrix cracking will occur when the particle size exceeds a critical value,R _c. Close agreement between the calculated and experimental values forR _c is obtained. The analysis is applicable to all particulate composites where there is volume increase of a particle induced either by phase transformation or thermal expansion mismatch.     

Reactive polymers,XXXVII. An investigation of the internal structure of polymeric sorbents based on poly(2,3-epoxypropyl methacrylate-co-ethylene dimethacrylate)

The internal structure of polymeric sorbents based on 2,3-epoxypropyl methacrylateethylene dimethacrylate was investigated by means of mercury porosimetry and by employing the sorption method. The results were confronted with characteristic chromatographic data and helped to elucidate the relationships existing between the internal structure of copolymers and their chromatographic properties.