Thermal behavior of selected Czech marble samples

The definition as well as prediction of rock thermal behavior seems to be a quite difficult problem significantly effected by rock composition and structure. Temperature increase causes various changes of rock material (such as decomposition, oxidation, phase and polymorphic transformation, etc.). These changes are connected to thermal expansion with following appearance of tensions and cracks in minerals and rock structure. After consequential temperature decrease, developed tensions and cracks still influence the process. This study presents the application of thermogravimetric analysis, differential thermal analysis and thermomechanical analysis in characterization of selected marble thermal behavior. The texture and morphological orientation of calcite grains for marble samples was determined by optical microscopy. FTIR spectroscopy application along with X-ray diffraction (XRD) extended data about mineralogical composition. According to optical microscopy, the calcite grains show marked morphological anisotropy in one direction for some samples. Therefore, the thermal expansion had to be measured in three different (perpendicular to each other) directions. It is evident, that the effect of temperature on the final marble properties depends not only on mineralogical composition, but also on structure, texture and morphological orientation of grains. All these facts significantly influence the interpretation of differences in various marble thermal behavior.     

Preparation and characterization of porous cordierite for potential use in cellular ceramics

Cordierite porous ceramics Z, X, and K were prepared using three mixtures of clay minerals: Z from kaolinite, talc, and aluminum hydroxide, X from kaolinite, talc, vermiculite, and aluminum hydroxide, and K from kaolinite, talc, and magnesium oxide. Ceramics were different in porosity, specific surface area, cordierite polymorphs, and secondary crystalline phases. Vermiculite influenced textural architecture of calcined cordierite ceramics X and predestinated crystallization of the high-temperature hexagonal α-cordierite with secondary minerals enstatite, spinel and corundum. Ceramics Z contained low-temperature orthorhombic β-cordierite, enstatite, and corundum, K was diphase of β-cordierite and forsterite. Total pore area (TPA) and specific surface area (SSA) of X, in spite of the higher porosity and the pore size distribution in the range of 300–1000 nm, were smaller in comparison with TPA and SSA of Z. Ceramics K retained high porosity, two maxima at 300–1000 nm and 50–200 nm in the pores size distribution, and the highest TPA and SSA compared to those observed in ceramics Z and X. Presented at the 8th Conference on Solid State Chemistry, 6-11 July 2008, Bratislava, Slovak Republic.     

Inhomogeneity effects on the crack driving force in elastic and elastic-plastic materials

This article evaluates the effect of material inhomogeneities on the crack-tip driving force in general inhomogeneous bodies and reports results for bimaterial composites. The theoretical model, based on Eshelby material forces, makes no assumptions about the distribution of the inhomogeneities or the constitutive properties of the materials. Inhomogeneities are modeled by making the stored energy have an explicit dependence on the reference coordinates. Then the material inhomogeneity effect on the crack-tip driving force is quantified by the term C_inh, which is the integral of the gradient of the stored energy in the direction of crack growth. The model is demonstrated by two model problems: (i) bimaterial elastic composite using asymptotic solutions and (ii) graded elastic and elastic-plastic compact tension specimen using numerical methods for stress analysis.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Equation of state of copolymer melts: The poly(vinyl acetate)–polyethylene pair

The pressure—volume—temperature properties of a series of copolymers ranging in content from 18 to 40 wt % of vinyl acetate, and up to a maximum pressure of 1800 kg/cm² are studied. The results for the melt state can be satisfactorily fitted by the scaled equation of state, developed previously and applied to single-component systems and to mixtures. The dependence of the scaling parameters for the copolymers on composition deviates from that expected for a mixture, where volumes at elevated pressures can be predicted without further recourse to experiment. These differences are discussed in terms of the sequential structure of the copolymer chain and its series of interfaces between the two species.     

Thermal expansivity of particulate composites: Interlayer versus molecular model

We continue the comparison of the results of an interlayer model, based on the theory of elastic continua, and a molecular model, derived from a theory of mixtures, previously presented in terms of bulk moduli K. We now derive expressions for the dependence of the thermal expansivity _c on the volume fraction _f of the filler, at low and elevated values of _f . Correspondencies between the characteristic parameters, viz. adhesion and repulsion ratios on the one hand, and interlayer content and thermal properties of matrix, filler, and layer, on the other, are examined. Since in the molecular theory both andK are derived from an equation of state, the identical set of parameters determines both functions and suggests correlations between them.     

A 2D-Planar Dielectrophoretic Model with Electro-Thermally Induced Fluid Motion and the Stability of Trapping Zones

Dielectrophoresis (DEP) is an electrokinetics-based phenomenon that involves the motion of a particle due to the interaction between an applied nonuniform electric field and an induced dipole moment. This technique is very effective in particle manipulation and separation. Earlier studies on control-amenable models to describe the motion of a neutrally buoyant, neutrally charged particle in a chamber with a parallel electrode array have restricted the motion of the particle to one dimension. Here, incorporating the electro-thermal fluid motion as well, we present a 2D-planar DEP model and study the effect of electro-thermal fluid motion on particle trapping.     

Graphical Representations of Speed: Obstacles Preservice K‐8 Teachers Experience

This study examines the difficulties college students experience when creating and interpreting graphs in which speed is one of the variables. Nineteen students, all preservice elementary or middle school teachers, completed an upper‐level course exploring algebraic concepts. Although all of these preservice teachers had previously completed several mathematics courses, including calculus, they demonstrated widespread misconceptions about the variable speed. This study identifies four cognitive obstacles held by the students, provides excerpts of their graphical constructions and verbal interpretations, and discusses potential causes for the confusion. In particular, misconceptions arose when students interpreted the behavior and nature of speed within a graphical context, as well as in situations where they were required to construct a graph involving speed as a variable. The study concludes by offering implications for the teaching and learning of speed and its interpretation within a graphical setting.     

Application of material forces to fracture of inhomogeneous materials: illustrative examples

The material forces concept has become an elegant tool in continuum mechanics for the calculation of the thermodynamic driving force of a defect. Based on this concept, we have recently shown that inhomogeneities essentially shield or anti-shield crack tips from applied far-field stresses. The goal of this paper is to illustrate this by considering the model example of a crack in a CT-type specimen that contains a bimaterial interface. The crack driving force is calculated as the sum of the far-field driving force and the crack-tip shielding or anti-shielding. Several cases of inhomogeneity in either thermal or elastic properties are considered. Rather simple hand calculations are provided in addition to numerical results to illustrate the advantages of using the material forces concept.     

Concerning free volume quantities and the glass temperature

Free volume quantities proposed earlier by Boyer and Simha in connection with the glass transition are reformulated by taking into account the temperature dependence of the thermal expansivities α _l and α_g for the liquid and the glass, respectively. This necessitates an extrapolation of the liquid to temperatures below Tg which is performed by means of the reduced volume-temperature function established and given a theoretical foundation previously. For the glass, low temperature experimental data, encompassing all relaxations occuring below T_g, are required.

Two polymer series are examined in detail, namely, poly(methacrylates) and poly(vinyl) alkyl ethers, where α_g has been measured between at least 30°K and T_g. Results for poly(methylacrylate) and poly(styrene) are also given. The systematic decrease in the product (αl - αg) · T|_T=Tg with increasing length of the side chain noted previously is considerably reduced but not eliminated when the appropriately corrected expression is substituted instead. However, the free volume fraction related to the quantity αlT|_T=Tg remains more nearly invariant in the polymers analyzed.

An alternative treatment is discussed which considers an occupied volume expanding below T_g by a mechanism of thermal vibrations solely. Experimental and theoretical means of obtaining this quantity arc suggested.