New developments in PAC and PAD

Recent developments in both methods, Perturbed Angular Correlation (PAC) and Perturbed Angular Distribution (PAD) concern improvements in the instrumentation for various applications and sophistications in detail rather than methodology. These will be illustrated by examples from PAC and PAD studies which investigate local structural properties of semiconductors and metallic surfaces, and local magnetic contributions in ferromagnetic metals, nonmagnetic materials, and high-temperature superconductors and related oxides.     

Bounded rational driver models

This paper introduces a car following model where the driving scheme takes into account the deficiencies of human decision making in a general way. Additionally, it improves certain shortcomings of most of the models currently in use: it is stochastic but has a continuous acceleration. This is achieved at the cost of formulating the model in terms of the time derivative of the acceleration, making it non-Newtonian. However, the recipe for construction of bounded rational driver models proposed in this paper seems to be very general and can be applied to most, if not all of the traditional car-following models. Received 18 November 2002 / Received in final form 6 February 2003 Published online 1st April 2003 RID="a" ID="a"e-mail: ialub@fpl.gpi.ru RID="b" ID="b"e-mail: peter.wagner@dlr.de RID="c" ID="c"e-mail: reinhard.mahnke@physik.uni-rostock.de     

Introduction to PAC/PAD

Both methods, Perturbed Angular Correlation (PAC) utilizing radioactive probes and Perturbed Angular Distribution (PAD) following nuclear reactions measure hyperfine interaction parameters and allow to study magnetism on a rather local scale. While both techniques are based on the same theory the underlying concepts are quite different. Examples on local moments, influence of the nearest-neighbor to the magnetic field in ferromagnets, Knight shifts in nonmagnetic materials, and magnetism in high-temperature superconductors and related oxides illustrate the recent developments within the methods and the improvements in their sensitivity and resolution.     

Outflow Probability for Drift–Diffusion Dynamics

The proposed explanations are provided for the one–dimensional diffusion process with constant drift by using forward Fokker–Planck technique. We present the exact calculations and numerical evaluation to get the outflow probability in a finite interval, i.e. first passage time probability density distribution taking into account reflecting boundary on left hand side and absorbing border on right hand side. This quantity is calculated from balance equation which follows from conservation of probability. At first, the initial-boundary-value problem is solved analytically in terms of eigenfunction expansion which relates to Sturm–Liouville analysis. The results are obtained for all possible values of drift (positive, zero, negative). As application we get the cumulative breakdown probability which is used in theory of traffic flow. PACS numbers: 02.60.Lj, 02.50.–r, 02.50.Fz, 02.50.Ga     

Dependency of injection seeding and spectral purity of a single resonant KTP optical parametric oscillator on the phase matching condition

For spectroscopic and remote sensing applications injection seeded optical parametric oscillators (OPOs) are well established. In this paper we study the dependencies of signal resonant injection seeding of an OPO on its resonator length, phase matching angle and pump power in detail. The quality of the seeding process is assessed by stabilising the seed laser on a molecular absorption line of water vapour and using a water vapour absorption cell as a narrow bandwidth filter for the injection seeded radiation. A reduction of the acceptance of injection seeding is observed with increasing pump power. For small phase mismatch injection seeding with a spectral purity of 99.7% was observed at 13-fold OPO threshold. A signal pulse energy of 38 mJ with 50% pump depletion was achieved with a beam parameter M² of about 6. PACS 42.65.Yj; 42.79.Nv; 42.79.Qx     

Coordination complexes of the dimethyl-thio-phosphonium cation and ligand exchange

The quantitative exchange of a 4-(dimethylamino)pyridine ligand on the dimethyl-thio-phosphonium cation by Me3P demonstrates the coordinative nature of the N-P and P-P bond and diversifies a fundamentally important new direction in the coordination chemistry of phosphorus as an acceptor.     

Ultrashort light pulses generated from modulation instability: background removal and soliton content

Modulation instability can be used to convert a continuous light wave into a train of pulses on a constant background. It is a longstanding discussion whether these pulses can be converted into solitons. We clarify the situation by using a more general mathematical context, invoking the Akhmediev breather, Peregrine soliton and Kuznetsov-Ma soliton solutions of the wave equation, and suggest the use of a Mach–Zehnder interferometer to remove the background. Expressions for the pulse widths and peak powers thus obtained are presented, and their soliton content is determined. It turns out that more than 95 % of each pulse’s energy can be converted to a soliton.