Decay of bcc-structure and of bond-orientational order in a fluid

The decay of an initially prepared bcc structure and the bond-orientational order (anisotropy of the first coordination shell) are studied in a non-equilibrium molecular dynamics simulation for a fluid of 1024 particles interacting with a repulsive r^-12 potential. Data are presented for pair-correlation functions and order parameters associated with an angle dependence described by cubic harmonics of the ranks 4, 6 and 8. These cubic pair-correlation functions and cubic order parameters are defined by the expansion of the pair-correlation function and of the bond orientational distribution function with respect to Cartesian tensors. The relaxation of the local anisotropy shows a pretransformational slowing down for densities approaching the freezing point.     

Zur Theorie des Abbaus von Kettenmolekülen

Zusammenfassung In der Arbeit wird eine Methode zur praktischen Anwendung der mathematischen Ergebnisse der statistischen Theorie des Abbaus vonKettenmolekülen angegeben. Ausgehend von dem Ansatz und der L?sung von R. Simha (16) wird für die Berechnung der in der mathematischen L?sung auftretenden zahlreichen Konstanten ein Schema aufgestellt. Ferner wird der Spezialfall behandelt, da der Abbau nicht bis zum Monomeren verl?uft. Au\erdem wird eine N?herungsl?sung für jene F?lle angegeben, in denen die exakte L?sung infolge des gro\en Rechenaufwandes nicht anwendbar ist. Abschlie\end wird kurz das umgekehrte Problem, die Berechnung der Abbauwahrscheinlichkeiten aus experimentell bestimmten Abbaukurven, behandelt.     

Monitoring of fluid motion in a micromixer by dynamic NMR microscopy

The velocity distribution of liquid flowing in a commercial micromixer has been determined directly by using pulsed-field gradient NMR. Velocity maps with a spatial resolution of 29 microm x 43 microm were obtained by combining standard imaging gradient units with a homebuilt rectangular surface coil matching the mixer geometry. The technique provides access to mixers and reactors of arbitrary shape regardless of optical transparency. Local heterogeneities in the signal intensity and the velocity pattern were found and serve to investigate the quality and functionality of a micromixer, revealing clogging and inhomogeneous flow distributions.     

Disorder-induced freezing of dynamical spin fluctuations in underdoped cuprate superconductors

We study the dynamical spin susceptibility of a correlated d-wave superconductor (dSC) in the presence of nonmagnetic disorder, using an unrestricted Hartree-Fock approach. This model provides a concrete realization of the notion that disorder slows down spin fluctuations, which eventually "freeze out." The evolution of disorder-induced spectral weight transfer agrees qualitatively with experimental observations on underdoped cuprate superconductors. For sufficiently large disorder concentrations, static spin density wave (SDW) order is created when droplets of magnetism nucleated by impurities overlap. We also study the disordered stripe state coexisting with a dSC and compare its magnetic fluctuation spectrum to that of the disorder-generated SDW phase.     

Small-molecule vacuum processed melamine-C60, organic field-effect transistors

The transfer of benchtop knowledge into large scale industrial production processes represents a challenge in the field of organic electronics. Large scale industrial production of organic electronics is envisioned as roll to roll (R2R) processing which nowadays comprises usually solution-based large area printing steps. The search for a fast and reliable fabrication process able to accommodate the deposition of both insulator and semiconductor layers in a single step is still under way. Here we report on the fabrication of organic field effect transistors comprising only evaporable small molecules. Moreover, both the gate dielectric (melamine) and the semiconductor (C₆₀) are deposited in successive steps without breaking the vacuum in the evaporation chamber. The material characteristics of evaporated melamine thin films as well as their dielectric properties are investigated, suggesting the applicability of vacuum processed melamine for gate dielectric layer in OFETs. The transistor fabrication and its transfer and output characteristics are presented along with observations that lead to the fabrication of stable and virtually hysteresis-free transistors. The extremely low price of precursor materials and the ease of fabrication recommend the evaporation processes as alternative methods for a large scale, R2R production of organic field effect transistors.     

Multiple and sign‐changing solutions for the multivalued p ‐Laplacian equation

We consider a class of elliptic inclusions under Dirichlet boundary conditions involving multifunctions of Clarke's generalized gradient. Under conditions given in terms of the first eigenvalue as well as the Fu?ik spectrum of the p ‐Laplacian we prove the existence of a positive, a negative and a sign‐changing solution. Our approach is based on variational methods for nonsmooth functionals (nonsmooth critical point theory, second deformation lemma), and comparison principles for multivalued elliptic problems. In particular, the existence of extremal constant‐sign solutions plays a key role in the proof of sign‐changing solutions (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On approximation methods for the solution of one dimensional singular integral equations

In the present paper we give a survey on some new result obtained in the last few years in the theory of approximation methods for one dimensional singular equations (among others to the methods of collocation and of mechanical quadratures). Conditions for convergence and stability of these methods in the spaces L ^p (1<p<∞) and H ^α (=Lip_α)(0<α<1) are formulated and their rate of convergence is determined. simultaneously here for the first time the necessitgy of the conditions for the convergence of the methods mentioned above is investigated. In the first section a general and uniform methods for the treatment of projection methods for linear operator equations in Banach spaces in presented. The Core of this methods with unbounded projectors which is closely connected with a far-reaching generalization of the stability concept of S.G. Mikhlin.