Elasticity of stiff polymer networks

We study the elasticity of a two-dimensional random network of rigid rods ("Mikado model"). The essential features incorporated into the model are the anisotropic elasticity of the rods and the random geometry of the network. We show that there are three distinct scaling regimes, characterized by two distinct length scales on the elastic backbone. In addition to a critical rigidity percolation region and a homogeneously elastic regime we find a novel intermediate scaling regime, where the elasticity is dominated by bending deformations.     

The Electron Relaxation to Stationary States in Collision Dominated Plasmas in Molecular Gases

The temporal collision dominated relaxation of electrons to new stationary states, starting from initial stationary states and due to jump-like changes of the electric field, was studied in the plasmas of the molecular gases N₂ and CO. Numerical solving of the time dependent Boltzmann equation for the electrons yields the temporal evolution of their energy distribution function and of resulting macroscopic quantities. The varying relaxation due to different values of the field strength in the final stationary state has been investigated considering the molecules of the plasma only as vibrationally non-excited and, in another case, including the additional impact of collisions with vibrationally excited molecules. The results obtained are discussed and, in particular, the relaxation times found for the transitions to the new stationary states are analysed on the basis of the energy transfer effectiveness by the collision processes. An approximative microphysical basis for the understanding of the main features of the relaxation in such complex molecular gas plasmas could be obtained.     

Ultrasound in organic electrosynthesis

Mechanical effects induced by ultrasonication can be very helpful for the activation of electrochemical reactions. The continuous cleaning of the electrodes by ultrasound irradiation of the electrochemical cell or the enhancement of mass transfer at the electrodes are examples of such activation. Finally, ultrasonication can play an important part for the orientation of reactions whose selectivities are very sensitive to stirring. Two very different examples have been chosen to illustrate these phenomena: the indirect electrooxidation of di-ketone-L-sorbose into the corresponding ketogulonic acid and the direct electroreduction of acetophenone into pinacol.     

A combined transient and steady state approach for robust lifetime spectroscopy with micrometer resolution

We present the combination of two complementary micro‐photoluminescence spectroscopic techniques operating in transient and steady state condition, respectively. Introducing the time domain into the well‐established micro‐photoluminescence mapping approach operating under steady state conditions demonstrates a distinct improvement of the robustness and reliability in the determination of charge carrier lifetime measured with micrometer spatial resolution. Lifetimes from 50 ns to above ms are accessible. We elaborate a calibration procedure and apply the combined all‐photoluminescence setup to high‐performance multicrystalline silicon. A lifetime image obtained from the established photoluminescence imaging technique is reconstructed from the microscopic map by considering lateral diffusion and optical blurring, revealing a more detrimental influence of small angle grain boundaries as well as a higher lifetime within grains as may be deduced from the standard imaging technique. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

2D CP/MASC Isotropic Chemical Shift Correlation Established byH Spin Diffusion

A new 2D solid-state CP/MAS¹³C NMR exchange experiment for through-space isotropic chemical shift correlation is proposed and demonstrated. Through-space correlation is established via a second cross polarization from¹³C to¹H and subsequent¹H spin diffusion. A third cross polarization results in the final¹³C–¹³C isotropic chemical shift correlation. The¹H spin diffusion time is a variable parameter allowing different mean square magnetization displacements to be probed. Experimental results on mixtures of differently¹³C-labeled alanine and polyethylene indicate that this site-selective 2D technique can be used to characterize domain sizes and proximities over a wide range of length scales (1–200 nm) in solids such as polymers or biological materials.     

Characterisation of the acoustic cavitation cloud by two laser techniques

An experimental investigation of the size and volumetric concentration of acoustic cavitation bubbles is presented. The cavitation bubble cloud is generated at 20 kHz by an immersed horn in a rectangular glass vessel containing bi-distilled water. Two laser techniques, laser diffraction and phase Doppler interferometry, are implemented and compared. These two techniques are based on different measuring principles. The laser diffraction technique analyses the light pattern scattered by the bubbles along a line-of-sight of the experimental vessel (spatial average). The phase Doppler technique is based on the analysis of the light scattered from single bubbles passing through a set of interference fringes formed by the intersection of two laser beams: bubble size and velocity distributions are extracted from a great number of single-bubble events (local and temporal average) but only size distributions are discussed here. Difficulties arising in the application of the laser diffraction technique are discussed: in particular, the fact that the acoustic wave disturbs the light scattering patterns even when there are no cavitation bubbles along the measurement volume. As a consequence, a procedure has been developed to correct the raw data in order to get a significant bubble size distribution. After this data treatment has been applied the results from the two measurement techniques show good agreement. Under the emitter surface, the Sauter mean diameter D(3, 2) is approximately 10 microm by phase Doppler measurement and 7.5 microm by laser diffraction measurement at 179 W. Note that the mean measured diameter is much smaller than the resonance diameter predicted by the linear theory (about 280 microm). The influence of the acoustic power is investigated. Axial and radial profiles of mean bubble diameters and void fraction are also presented.     

Sonolysis of levodopa and paracetamol in aqueous solutions

Pharmaceutical products are often present in wastewater treatment effluents, rivers, lakes and, more rarely, in groundwater. The advanced oxidation methods, like ultrasound, find a promising future in the area of wastewater treatment. The aim of this paper is to evaluate the influence of several parameters of the ultrasound process on the degradation of paracetamol, a widely used non-steroidal anti-inflammatory recalcitrant drug found in water and levodopa, the most frequently prescribed drug for the treatment of Parkinson disease. Experiments were carried out at 574, 860 and 1134 kHz of ultrasonic frequency with horn-type sonicator and actual power values of 9, 17, 22 and 32 W at 20 °C. Initial concentrations of 25, 50, 100 and 150 mg L^?1 of both products were used. Treatment efficiency was assessed following changes in pharmaceuticals concentration and chemical oxygen demand.The sonochemical degradation of both products follows a pseudo-first-order reaction kinetics. Complete removal of pharmaceuticals was achieved in some cases but some dissolved organic carbon remains in solution showing that long lived intermediates were recalcitrant to ultrasound irradiation. Pollutants conversion and COD removal were found to decrease with increasing the initial solute concentration and decreasing power. The best results were obtained with 574 kHz frequency. Investigations using 1-butanol as radical scavenger and H₂O₂ as promoter revealed that pollutants degradation proceeds principally through radical reactions, although some differences were observed between both molecules. Addition of H₂O₂ had a positive effect on degradation rate, but the optimum concentration of hydrogen peroxide depends on the pollutant.     

Metallic state in cubic FeGe beyond its quantum phase transition

We report on results of electrical resistivity and structural investigations on the cubic modification of FeGe under high pressure. The long-wavelength helical order (T(C) = 280 K) is suppressed at a critical pressure p(c) approximately 19 GPa. An anomaly at T(X)(p) and strong deviations from a Fermi-liquid behavior in a wide pressure range above p(c) suggest that the suppression of T(C) disagrees with the standard notion of a quantum critical phase transition. The metallic ground state persisting at high pressure can be described by band-structure calculations if zero-point motion is included. The shortest FeGe interatomic distance display discontinuous changes in the pressure dependence close to the T(C)(p) phase line.