Positivity and matrix semigroups

We study various aspects of how certain positivity assumptions on complex matrix semigroups affect their structure. Our main result is that every irreducible group of complex matrices with nonnegative diagonal entries is simultaneously similar to a group of weighted permutations. We also consider the corresponding question for semigroups and discuss the effect of the assumption that a fixed linear functional has nonnegative values when restricted to a given semigroup.     

Electron microscopy studies of potassium sodium niobate ceramics.

Using electron microscopy, K0.5Na0.5NbO3 (KNN) ceramics sintered at 1030 degrees C for 8 h and 1100 degrees C for 2 and 24 h was studied. The scanning electron microscopy and X-ray spectrometry revealed that the materials consisted of a matrix phase in which the (Na+K)/Nb ratio corresponded closely to the nominal composition and a small amount of Nb-rich secondary phase. A bimodal microstructure of cube-shaped grains was revealed in the fracture and thermally-etched surfaces of the KNN. In the ceramics sintered at 1100 degrees C, the larger grains (up to 30 mum across), contained angular trapped pores. The transmission electron microscopy analysis revealed that the crystal planes of the grains bordering the intragranular pore faces were of the {100} family with respect to the simple perovskite cell. Ferroelectric domains were observed in the grains of this material.     

Die Nusseltsche Zahl für laminare Strömung im zylindrischen Rohr mit konstanter Wandtemperatur

Summary The Nusselt modulus for laminar flow through a pipe with constant temperature of the walls has been determined as a function of the Peclet modulus. This function is represented by a diagram.     

Simulation Support to EPR-based Dentin Characterization

Treatment of dental caries as one of the most economically relevant human disease can rely only on the understanding of the caries progress through dentin. As it can be seen from the frequency of tooth decay among different animals, its existence and progress strongly depend on the mineral part arrangement, especially on the orientation of the hydroxyapatite (HA) crystals, which resist the mechanical and chemical stress very anisotropically. It is therefore not surprising that different attempts have been made to unravel the mystery of dentin growth and HA crystals arrangement. By dentin irradiation with gamma-rays, very stable CO₃ ^? radicals are generated within HA crystals which due to the anisotropic magnetic coupling enable detection of their orientational distribution via angular-dependent electron paramagnetic resonance spectroscopy. The latter can be significantly enhanced if the whole angular dependence can be fitted simultaneously within certain dentin structural models. As shown in this work, even subtle information like the orientation of the tubules relative to the pulp or the orientation of HA crystals relative to the tubules can be extracted. The sensitivity to different sample geometry is discussed to provide the best possible characterization.     

Joint characteristic functions construction via copulas

When modelling dependent risks it is important to be able to generate joint distributions with given marginals. One of the ways which may be useful in connection with using the Fast Fourier Transform is to construct joint characteristic functions from marginal characteristic functions. In this paper a class of n-dimensional continuous copulas is presented which in turn lead to a simple construction of joint characteristic functions with given marginal characteristic functions. Bounds on various measures of correlation are also given.     

Editorial

The credit crisis is a complex societal problem in which many phenomena and actors are involved. If one wants to analyze the causes of this problem, try to stabilize the situation and prevent new fall backs, a multi-disciplinary approach is prescribed. A careful analysis based on the scientific methodology of societal complexity is needed in order to find how the credit crisis happened and how new crises can be prevented. Theories of multiple disciplines must be used by a multi disciplinary team to analyze the situation and to find sustainable options. This process can be accomplished by following the Compram Methodology of DeTombe. The Compram Methodology provides a framework for policy making which includes many methods and tools. The Compram Methodology is specialized to handle complex interdisciplinary world-wide problems and to offer a step-by-step approach of analyzing the problem, finding and implementing sustainable interventions and evaluating the effects. The Compram Methodology offers a bird’s-eye view on the complexity of the problem and gives directions to policy makers to build their decisions on using a multi-disciplinary, multi-actor approach. In this article the credit crisis is discussed in relation with the Compram Methodology. Aspects of the credit crisis are described with an emphasis on the role of the actors. Based on the Compram Methodology directions can be provided for handling the credit crisis and avoiding future similar problems.     

Measurements of cavitation bubble dynamics based on a beam-deflection probe

We present an optodynamic measurement of a laser-induced cavitation bubble and its oscillations based on a scanning technique using a laser beam-deflection probe. The deflection of the beam was detected with a fast quadrant photodiode which was built into the optical probe. The applied experimental setup enabled us to carry out one- or two-dimensional scanning of the cavitation bubble, automatic control of the experiment, data acquisition and data processing. Shadow photography was used as a comparative method during the experiments.     

Analysis of the Thermal Stability of Very Thin Surface Layers of Corrosion Inhibitors by Time-of-Flight Secondary Ion Mass Spectrometry

The powerful nature of the secondary ion mass spectrometry (SIMS) technique was explored in order to analyse very thin surface layers that were self-assembled on steel material from acidic solution. These surface layers are adsorbed corrosion inhibitors. The SIMS technique proved useful to characterise the molecular structure and homogeneity of thin surface layers in the nanometre range of specific analytes on the metallic substrate. Using SIMS, the thermal stability of these layers was further investigated and the desorption energy at a certain temperature was determined, where special attention was devoted to the method’s static limit. In order to compare, and for certain cases emphasise, the benefits gained by using SIMS in such surface analysis compared with the X-ray photoelectron spectroscopy (XPS) method, the same samples were also analysed by means of the latter. XPS is usually considered to be the most powerful analytical tool in surface analysis studies, but, as shown herein, it has certain limitations compared to SIMS. Finally, the surface topography was investigated by employing atomic force microscopy (AFM) in order to carry out a comprehensive surface analysis.

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Graphical Abstract ?

     

Viscosity and electrophoretic mobility of cesium fullerenehexamalonate in aqueous solutions--comparing experiments and theories on nanometer-sized spherical polyelectrolyte

The viscosity of aqueous solutions of cesium fullerenehexamalonate T h -C 66(COOCs) 12, a rigid spherical nanometer-sized polyvalent salt, was measured by the Ubbelohde-type viscometer. The measurements were performed without added salt at 25 degrees C in the concentration range between 7 and 320 g/dm (3). THe concentration dependence of the obtained reduced viscosity was compared with the theoretical prediction, taking into account contributions stemming from the intrinsic viscosity, hydrodynamic perturbations of the hypothetically bare fullerenehexamalonate macroion, the primary electroviscous effect, and the secondary electroviscous effect. Using the geometric radius of the bare macroion from the previous measurements of the estimated effective charge of the macroion and from the small-angle X-ray scattering data of the estimated thickness of the compact shell of counterions electrostatically bound to the macroion, a good agreement between theory and the experiment was obtained in the range of the lowest and of the highest concentrations. Electrostatic interactions are identified as the main cause of the increased reduced viscosity at the lowest measured concentrations. At the highest concentrations, electrostatic interactions are effectively screened, and the influence of binary hydrodynamic interactions and perturbations of the hypothetical bare macroion prevails over electrostatic contributions to the increased viscosity. The electrophoretic mobility of the fullerenehexamalonate ion in aqueous salt-free medium was computed with the same value for the radius of the fullerenehexamalonate macroion as that used in the calculation of viscosity. The numerical solution of Ohshima's equation agreed well with the experimental values.