Effect of phonon scattering from neutral and charged impurity centers on the lattice heat conductivity of PbTe:(Tl, Na)

Experimental data on the effect of thallium and sodium impurities on the lattice heat conductivity of PbTe at room temperature are reported. Because the lattice of lead chalcogenides is strongly polarized near charged impurities, the effect of impurities on the lattice heat conductivity depends substantially on their charge state. This property of the material has been used to determine the charge state of the thallium impurity in PbTe. The results obtained argue for a model of quasi-local thallium-impurity states which assumes low electron-correlation energy at an impurity center. Fiz. Tverd. Tela (St. Petersburg) 40, 1206–1208 (July 1998)     

Laser spectroscopy of the 1s HFS of H-like ions at a bunched beam in the storage ring ESR

The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in ²⁰⁷Pb⁸¹⁺. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics from an ion beam at relativistic velocities. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of density in electron-cyclotron-resonance plasma

A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data     

Adiabatic passage Hartmann-Hahn cross polarization in NMR under magic angle sample spinning

We have recently demonstrated that polarization transfer using an adiabatic passage through the Hartmann-Hahn condition (APHH-CP) by a variation of the radio-frequency amplitude can substantially improve the transfer efficiency over Hartmann-Hahn cross polarization. Here we show that APHH-CP can be combined with fast magic angle sample spinning (MAS). The heteronuclear dipolar order, established in the course of the transfer, can indeed be created and preserved.     

Transformation of malonic acid adsorbed on a clay-mineral by gamma irradiation

The effect of clay on the radiolysis of malonic acid solutions was studied. The results showed an enhanced of decarboxylation rather than condensation reactions.     

Experimental study of acoustic probing of electrical space charge in solid insulators

Experimental results are presented on acoustic probing of electric fields in solid insulators. An experimental apparatus and methods are described for acoustic measurements of the bulk space charge density and electric field strength in solid insulators. The sensitivity and spatial resolution of the acoustic probe technique are determined.Institute of Introscopy Research, Polytechnical University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 62–67, September, 1993.     

Efficient Collocation Schemes for Singular Boundary Value Problems

We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point.