Mechanism and calculation of the niche effect in airborne sound transmission

The goal is to interpret and calculate the "niche effect" for the airborne sound transmission through a specimen mounted inside an aperture in the wall between the source and receiving reverberation rooms. The low-frequency sound insulation is known to be worse for the specimen placed at the center than for the specimen mounted at either edge of the aperture. As shown, the aperture with a tested specimen can be simulated at low frequencies as a triple partition where the middle element is the specimen and the role of the edge leaves is played by the air masses entrained at the aperture edges. With a centrally located specimen, such a triple system is symmetric and has two main natural frequencies close together. In this case, the resonant transmission is higher than for the edge arrangement simulated as a double system with one natural frequency. Analogous resonant phenomena are known to reduce the low-frequency transmission loss for symmetric triple windows or solid walls with identical air gaps and lightweight boards on both sides. The theoretical results obtained for the mechanical and acoustical models are in a good agreement with the experimental data.     

Diffractive beam splitter characterization via a power-recycled interferometer

We used the high-precision laser interferometer technique of power recycling to characterize the optical loss of an all-reflective grating beam splitter. This beam splitter was used to set up a Michelson interferometer with a power-recycling resonator with a finesse of 883. Analyzing the results obtained, we determined the beam splitter's total optical loss to be (0.193+/-0.019)%. Low loss all-reflective beam splitters might find application in future high-power laser interferometers for the detection of gravitational waves.     

Wrapping an adhesive sphere with an elastic sheet

We study the adhesion of an elastic sheet on a rigid spherical substrate. Gauss's Theorema Egregium shows that this operation necessarily generates metric distortions (i.e., stretching) as well as bending. As a result, a large variety of contact patterns ranging from simple disks to complex branched shapes are observed as a function of both geometrical and material properties. We describe these different morphologies as a function of two nondimensional parameters comparing, respectively, bending and stretching energies to adhesion. A complete configuration diagram is finally proposed.     

Preconditioning techniques for iterative solvers in the Discrete Sources Method

Different preconditioning techniques for the iterative method MinRes as solver for the Discrete Sources Method (DSM) are presented. This semi-analytical method is used for light scattering computations by particles in the Mie scattering regime. Its numerical schema includes a linear least-squares problem commonly solved using the QR decomposition method. This could be the subject of numerical difficulties and instabilities for very large particles or particles with extreme geometry. In these cases, we showed that iterative methods with preconditioning techniques can provide a satisfying solution.In our previous paper, we studied four different iterative solvers (RGMRES, BiCGStab, BiCGStab(l), and MinRes) considering the performance and the accuracy of a solution. Here, we study several preconditioning techniques for the MinRes method for a variety of oblate and prolate spheroidal particles of different size and geometrical aspect ratio. Using preconditioning techniques we highly accelerated the iterative process especially for particles with a higher aspect ratio.     

Implementation and investigation of iterative solvers in the Discrete Sources Method

The implementation of iterative methods as solvers for the Discrete Sources Method (DSM) is presented. In this method, light scattering computation linear systems with dense and relative small matrices are generated. The linear systems are traditionally solved using the QR-decomposition method. For large particles or particles with extreme geometries even this commonly stable solver can fail. In these cases, we expect that iterative methods can provide a satisfying solution nevertheless.We will present our investigation in two consecutive papers. Here, we study four different iterative solvers (RGMRES, BiCGStab, BiCGStab(l), and MinRes) considering the performance and the accuracy for typical light scattering problems. Using these iterative methods we increased the quality of a solution, especially for oblate spheroids with a higher aspect ratio. Preconditioning technique is considered in the following paper.     

Diffusion in three-dimensional random systems at their percolation thresholds

Extensive Monte Carlo simulations of theant-in-the-labyrinth problem on randomL* L* L simple cubic lattices are performed, forL up to 960 on a CRAY-YMP supercomputer. The exponentk for the rms displacementr witht inrt ^k is found to bek=0.190±0.003. As a second approach, large percolation clusters with chemical shells up to 300 are generated on a simple cubic lattice at criticality. The diffusion equation is then solved by using the exact enumeration technique. The corresponding critical exponentd ^w is found to be 1/d ^w =0.250±0.003.On leave from I. Institut für Theoretische für Physik, Universität Hamburg, D-2000 Hamburg, Federal Republic of Germany.     

Evaluation of semiconducting sensor materials on the basis of catalytic test reaction

Oxidative-reductive properties on the acid-base surfaces of the oxide compositions Sn-Ce-Rh-O and Zr-Mg-Y-O, active as catalysts in the ketonization of secondary alcohols were determined based on the isopropanol conversion selectivity. The kinetics of isopropanol conversion was measured in the oxygen-free atmosphere. Activation energies for both directions of conversion (dehydration to propylene and dehydrogenation to acetone) were calculated. The results were compared with the kinetics over SnO₂ and ZrO₂. Both oxide compositions, Sn-Ce-Rh-O and Zr-Mg-Y-O are oxidative-reductive catalysts containing Lewis acid centers.     

Normal contact stiffness of elastic solids with fractal rough surfaces

Using the boundary element method, we calculate the normal interfacial stiffness and constriction resistance of two elastic bodies with randomly rough surfaces and varying fractal dimensions. The contact stiffness as a function of the applied normal force can be approximated by a power law, with an exponent varying from 0.51 to 0.77 for fractal dimensions varying from 2 to 3.     

Gold-surface binding of molecular switches studied by M?ssbauer spectroscopy

The nonanuclear coordination compound [Mo^IV{(CN)Fe^III(3-methyl-saldptn)}₈]Cl₄ exhibits multiple spin transitions (3-methyl-saldptn = N,N′-bis(3′′-methyl-2′′-hydroxy-benzyliden)-1,7-diamino-4-azaheptane). This spin crossover cluster is bound via a self-assembled monolayer onto a two dimensional array gold surface. M?ssbauer spectroscopy indicates that the thermally and optically induced spin crossover of the compound is maintained. Thereby, the foundation for its potential practical application (e.g. in the field of information storage) was laid.