Synthesemethoden für keramische Materialien. Hochtechnologiewerkstoffe

The new developments in the field of gas phase synthesis, synthesis from the condensed phases and solid‐state synthesis allowing for the fabrication of new ceramic materials for diverse technical applications have been reviewed. The Flame Spray Pyrolysis, aqueous and non‐aqueous sol‐gel techniques, hydro‐ and solvothermal methods, polymer pyrolysis route and high pressure techniques have been considered as synthesis methods with great technical potential.     

Structural characterization,thermal investigation,and liquid crystalline behavior of 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene

Using the Williamson method, a new dye 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene (CODA) with liquid crystalline properties was synthesized. The structure and the thermal behavior of CODA were investigated by means of nuclear magnetic resonance, X-ray diffraction, differential scanning calorimetry, and light polarized optical microscopy techniques. The thermophysical processes were monitored by heating–cooling cycles, but the formation of liquid crystal phases were exhibited only for small values of the cooling rates. For the first heating–cooling cycle, the melting and the solidification processes, thus the characteristic temperatures, are shifted to higher values when compared to the following cycles.     

Evaluation of force fields for molecular simulation of polyhedral oligomeric silsesquioxanes

Polyhedral oligomeric silsesquioxanes (POSS) are nanometer-size molecules suitable for the production of organic-inorganic nanocomposite materials. These organic-inorganic nano-building blocks show promise for enabling the production of polymeric materials of exceptional mechanical properties as well as novel composite materials. While the experimental studies of these materials have rapidly evolved in the past decade, their theoretical investigation is still in its infancy. Toward the validation of force fields for the molecular simulation of POSS-containing systems, we present the charge-transfer reactive (CTR) force field for the molecular simulation of polyhedral oligomeric silsesquioxane (POSS) molecules and compare the ability of this, and several force fields taken from the literature, to predict the thermophysical properties of POSS-containing systems. The literature force fields compared include the universal force field (UFF) and the COMPASS and Hybrid-COMPASS force fields. Predictions from molecular dynamics simulations of the structural parameters (unit cell vectors), melting temperature, and FT-IR spectra of crystals of POSS monomers are presented. The POSS monomers investigated are octahydride, octamethyl, and octapropyl POSS. Predicted quantities are compared to experimental results where available and provide molecular-level physical insight into several aspects of the behavior of POSS molecules. While all the force fields tested perform reasonably well, our results indicate that the Hybrid-COMPASS and CTR force fields predict structural properties that are in good agreement with experimental data.     

Functional expansions for finding traveling wave solutions

The paper proposes a generalized analytic approach which allows to find traveling wave solutions for some nonlinear PDEs. The solutions are expressed as functional expansions of the known solutions of an auxiliary equation. The proposed formalism integrates classical approaches as tanh method or $G^{\prime }/G$ method, but it open the possibility of generating more complex solutions. A general class of second order PDEs is analyzed from the perspective of this formalism, and clear rules related to the balancing procedure are formulated. The KdV equation is used as a toy model to prove how the results obtained before through the $G^{\prime }/G$ approach can be recovered and extended, in an unified and very natural way.     

Uniqueness properties of solutions of Schrödinger equations

Under suitable assumptions on the potentials V and a, we prove that if u∈C([0,1],H¹) is a solution of the linear Schrödinger equation

     

Total oxidation of benzene using Cu-Cr mixed oxide as catalyst

Benzene total oxidation on a Cu-Cr supported catalyst was investigated using the work function method. Above 300°C, the majority of the oxygen species on the surface was O²⁻ in the absence or in the presence of hydrocarbon.     

Interaction of faults under slip‐dependent friction. Non‐linear eigenvalue analysis

We analyse the evolution of a system of finite faults by considering the non‐linear eigenvalue problems associated to static and dynamic solutions on unbounded domains. We restrict our investigation to the first eigenvalue (Rayleigh quotient). We point out its physical significance through a stability analysis and we give an efficient numerical algorithm able to compute it together with the corresponding eigenfunction. We consider the anti‐plane shearing on a system of finite faults under a slip‐dependent friction in a linear elastic domain, not necessarily bounded. The static problem is formulated in terms of local minima of the energy functional. We introduce the non‐linear (static) eigenvalue problem and we prove the existence of a first eigenvalue/eigenfunction characterizing the isolated local minima. For the dynamic problem, we discuss the existence of solutions with an exponential growth, to deduce a (dynamic) non‐linear eigenvalue problem. We prove the existence of a first dynamic eigenvalue and we analyse its behaviour with respect to the friction parameter. We deduce a mixed finite element discretization of the non‐linear spectral problem and we give a numerical algorithm to approach the first eigenvalue/eigenfunction. Finally we give some numerical results which include convergence tests, on a single fault and a two‐faults system, and a comparison between the non‐linear spectral results and the time evolution results. Copyright © 2004 John Wiley & Sons, Ltd.     

Heat Capacities and Thermal Properties of a Homogeneous Ethylene-1-octene Copolymer by Adiabatic Calorimetry

Specific heat capacities of a homogeneous ethylene-1-octene copolymer were measured by adiabatic calorimetry in the temperature range from 5 to 400 K (stepwise heating at averaged rates of approximately 1 to 34 K h^–1, after cooling at rates in the range from 8 K h^–1 to 4 K min^–1). The glass transition takes place from roughly 205 to225 K and is centred around approximately 215 K. At the latter temperature, also the temperature drifts during the stabilisation periods are at maximum. Clearly, with devitrification above 215 K also melting sets in. Using two sets of reference data (one for branched and linear polyethylenes, BPE, and the other for strictly linear polyethylene, LPE)for completely crystalline and for completely amorphous material, the crystallinity of the polymer was calculated as a function of temperature, within the two-phase model. In heating, the crystallinity decreased from 0.254 to zero in the temperature range from 220 to 360 K, confirming earlier DSC heat capacity measurements. During the stabilisation periods, below325 K, negative drifts were observed, related to endothermic effects caused by melting. However, in the temperature range from 325 K up to the end melting temperature, 360 K, positive drifts were measured, reflecting exothermic effects. These are attributed to recrystallisation phenomena. The occurrence and amount of recrystallisation depend on the thermal history of the sample: slower cooling and a longer time spent at a temperature of annealing clearly diminish recrystallisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of Gas Entry Point on Plasma Chemistry,Ion Energy and Deposited Alumina Thin Films in Filtered Cathodic Arc

The effect of gas entry point on the plasma chemistry, ion energy distributions and resulting alumina thin film growth have been investigated for a d.c. cathodic arc with an aluminum cathode operated in an oxygen/argon atmosphere. Ions of aluminum, oxygen and argon, as well as ions originating from the residual gas are investigated, and measurements for gas entry at both the cathode and close to the substrate are compared. The latter was shown to result in higher ion flux, lower levels of ionised residual gas, and lower ion energies, as compared to gas inlet at the cathode. These plasma conditions that apply when gas entry at the substrate is used result in a higher film deposition rate, less residual gas incorporation, and more stoichiometric alumina films. The results show that the choice of gas entry point is a crucial parameter in thin film growth using reactive PVD processes such as reactive cathodic arc deposition.     

Generalized Time-Varying Riccati Theory: A Popov Operator Based Approach

We derive in this paper necessary and sufficient conditions for the existence of the stabilizing solution to the differential Riccati equation, with indefinite sign quadratic term. The key object of the present approach is the Popov operator, associated with a controlled exponentially dichotomic evolution and a quadratic cost. Special attention is paid to the classical positivity theory and a time-varying version of the celebrated Kalman-Yakubovich- Popov Lemma is given under relaxed assumptions.