Instability of the magnetization reversal front in superconductors with a nonlinear anisotropic current-voltage characteristic

The instability of a magnetic flux flow in a system of vortices and antivortices in superconductors with a power (exponent m) anisotropic current-voltage characteristic was studied theoretically. It was shown that instability arose even at a comparatively weak anisotropy of the current-carrying properties of a superconductor if m?1. The dispersion equation determining the dependence of the increment of instability growth on the wave number was derived and analyzed.     

The electronic structure of the azabenzenes an ab initio MO-SCF-LCAO study

Ab initio MO-SCF-LCAO calculations have been carried out for benzene and the azabenzenes pyridine, pyridazine, pyrimidine, pyrazine, s-triazine and s-tetrazine, and the results are presented.The general structure of the molecular orbitals is discussed and a classification scheme referring to an ideal case of cylindrical symmetry is described. Orbital energies, empirically corrected for reorganization and correlation, have been used to make assignments for the photoelectron spectra. A number of molecular properties have been computed and are discussed in relation to available experimental information.The electrostatic potential around each molecule is presented in the form of contour maps. Each nitrogen lone pair gives rise to a region of negative potential. The depths of these minima give some information about the relation between electronic structure and basicity. The potential in regions of high π-electron density is negative only in benzene and pyridine. This fact can be correlated with the increasing resistance against direct electrophilic substitution for the azabenzenes as compared to benzene itself.The calculations have been performed using contracted Gaussian functions as a basis. Four s- and two p-type atomic orbitals were used for carbon and nitrogen, whereas for hydrogen two s- and one pσ-type functions were used.     

Anisotropic origin of the bending instability of the flux-antiflux interface in type-II superconductors

The physical nature of the macroturbulence in vortex matter in YBCO superconductors is investigated by means of a magneto-optic study of the instability in a single crystal prepared especially for this purpose. The instability develops near those sample edges where the oppositely directed flow of vortices and antivortices, guided by twin boundaries, is characterized by the discontinuity of the tangential component of the hydrodynamic velocity. This fact indicates that the macroturbulence is analogous to the instability of fluid flow at a surface of a tangential velocity discontinuity in classical hydrodynamics and is related to the anisotropic flux motion in the superconductor.     

Non-local,frequency and relaxation time dependent effects in the dispersion of Alfvén waves in bismuth

A non-local calculation of the dispersion of Alfvén waves in bismuth is presented for the configuration $\text{q}\text{∥}\text{C}{}_3\text{,}\text{B}\text{∥}\text{C}{}_2\text{,}\text{E}{}_{\mathrm{RF}}\text{∥}\text{C}{}_{\mathrm{I}}$. and B? parallel to the sample surface. The numerical results show that the non-local effects are of decisive importance in the analysis of experimental data, the local theory being applicable only at very high magnetic fields and comparatively low microwave frequencies. The dispersion is, in addition, very sensitive to the value of the relaxation times for the charge carriers. Excellent agreement with experiments performed at 45 and 300 GHz is obtained.     

Modeling of micromachined silicon–polymer 2-2 composite matching layers for 15 MHz ultrasound transducers

Silicon–polymer composites fabricated by micromachining technology offer attractive properties for use as matching layers in high frequency ultrasound transducers. Understanding of the acoustic behavior of such composites is essential for using them as one of the layers in a multilayered transducer structure. This paper presents analytical and finite element models of the acoustic properties of silicon–polymer composites in 2-2 connectivity. Analytical calculations based on partial wave solutions are applied to identify the resonance modes and estimate effective acoustic material properties. Finite Element Method (FEM) simulations were used to investigate the interaction between the composite and the surrounding load medium, either a fluid or a solid, with emphasis on the acoustic impedance of the composite. Composites with lateral periods of 20, 40 and 80 μm were fabricated and used as acoustic matching layers for air-backed transducers operating at 15 MHz. These composites were characterized acoustically, and the results were compared with analytical calculations. The analytical model shows that at low to medium silicon volume fraction, the first lateral resonance in the silicon–polymer 2-2 composite is defined by the composite period, and this lateral resonant frequency is at least 1.2 times higher than that of a piezo-composite with the same polymer filler. FEM simulations showed that the effective acoustic impedance of the silicon–polymer composite varies with frequency, and that it also depends on the load material, especially whether this is a fluid or a solid. The estimated longitudinal sound velocities of the 20 and 40 μm period composites match the results from analytical calculations within 2.7% and 2.6%, respectively. The effective acoustic impedances of the 20 and 40 μm period composites were found to be 10% and 26% lower than the values from the analytical calculations. This difference is explained by the shear stiffness in the solid, which tends to even out the surface displacements of the composites.     

Development and validation of an LC‐MS/MS method for quantification of Δ9‐tetrahydrocannabinolic acid A (THCA‐A), THC,CBN and CBD in hair

For analysis of hair samples derived from a pilot study (‘in vivo’ contamination of hair by sidestream marijuana smoke), an LC‐MS/MS method was developed and validated for the simultaneous quantification of Δ9‐tetrahydrocannabinolic acid A (THCA‐A), Δ9‐tetrahydrocannabinol (THC), cannabinol (CBN) and cannabidiol (CBD). Hair samples were extracted in methanol for 4 h under occasional shaking at room temperature, after adding THC‐D₃, CBN‐D₃, CBD‐D₃ and THCA‐A‐D₃ as an in‐house synthesized internal standard. The analytes were separated by gradient elution on a Luna C18 column using 0.1% HCOOH and ACN + 0.1% HCOOH. Data acquisition was performed on a QTrap 4000 in electrospray ionization‐multi reaction monitoring mode. Validation was carried out according to the guidelines of the German Society of Toxicological and Forensic Chemistry (GTFCh). Limit of detection and lower limit of quantification were 2.5 pg/mg for THCA‐A and 20 pg/mg for THC, CBN and CBD. A linear calibration model was applicable for all analytes over a range of 2.5 pg/mg or 20 pg/mg to 1000 pg/mg, using a weighting factor 1/x. Selectivity was shown for 12 blank hair samples from different sources. Accuracy and precision data were within the required limits for all analytes (bias between ?0.2% and 6.4%, RSD between 3.7% and 11.5%). The dried hair extracts were stable over a time period of one to five days in the dark at room temperature. Processed sample stability (maximum decrease of analyte peak area below 25%) was considerably enhanced by adding 0.25% lecithin (w/v) in ACN + 0.1% HCOOH for reconstitution. Extraction efficiency for CBD was generally very low using methanol extraction. Hence, for effective extraction of CBD alkaline hydrolysis is recommended. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantum mechanics of successive measurements with arbitrary meter coupling

We study successive measurements of two observables using von Neumann's measurement model. The two-pointer correlation for arbitrary coupling strength allows retrieving the initial system state. We recover Lüders rule, the Wigner formula and the Kirkwood-Dirac distribution in the appropriate limits of the coupling strength.     

Characterization of the Intensity Distribution in a Single Laser Spot Applied to the Annealing of Ion-Implanted Silicon

By means of the annealing events of ion-implanted p-type silicon in liquid phase epitaxy (implantation dose 2.5 × 10¹⁶ As⁺/cm²) the degree of homogeneity of a bent quartz rod diffuser for single pulses of a Q-switched Nd-glass laser (λ = 1.06 μm) is investigated using SEM-EBIC, TEM and RBS. Starting from discrete distributions of EBIC signal heights in the annealing spot the specific distribution of recrystallized monocrystalline and polycrystalline regions as well as the transition between them are proved by TEM diffraction contrast studies. The perfect recrystallization for a locally optimum laser energy density as well as the rectangular shape of the carrier concentration profile are proved by RBS measurements. At different positions of the measuring point within the annealing area RBS, too, renders it possible to point out local inhomogeneities of the energy density distribution in the case of low-quality beam diffusers.