DIRAC EQUATION FOR A COULOMB SCALAR, VECTOR AND TENSOR INTERACTION

There is now motivating experimental evidence for relativistic symmetries in nuclei and hadrons, namely pseudospin and spin symmetry limits of the Dirac equation besides the old theoretical backgrounds. The most fundamental ingredients in such studies are definitely the wave functions and energy eigenvalues. Here, having in mind the importance of the Coulomb term as well as the degeneracy-removing role of tensor interaction, we obtain the exact solutions to the problem for Coulomb scalar, vector and tensor terms in both spin and pseudospin symmetry limits. We see that, contrary to many other common cumbersome techniques, the problem is simply solved via the methodology of supersymmetric quantum mechanics.

High Power THz Generation from Sub-ps Bunches of Relativistic Electrons

ABSTRACTWe describe a > 100 Watt broadband THz source that takes advantage of the relativistic enhancement of the radiation from accelerating electrons according to the formula assigned the name of Sir Joseph Larmor[1, 2]. This is in contrast to the typical 1 milliwatt sources available in a laboratory. Specifically, for relativistic electrons the emission is enhanced by the fourth power of the increase in mass. Thus for 100 MeV electrons, for which the mass increases by a factor of ∼ 200, the enhancement is > 109. The experiments use a new generation of light source called an energy recovery linac (ERL) [3], in which bunches of electrons circulate once, but in which their energy is recovered. In such a machine the electron bunches can be very much shorter than those, say, in storage rings or synchrotrons.The Jefferson Lab facility operates in new limits of emission from relativistic particles involving both multiparticle coherence and near-field emission in which the velocity (Coulomb) term in the classical electrodynamical theory becomes as important as the acceleration term (synchrotron radiation).The sub-picosecond pulses of light offer unique capabilities in 2 specific areas, namely time-resolved dynamics, and imaging. High resolution THz spectroscopy has recently revealed sharp vibrational modes for many materials including malignant tissue, proteins, DNA, pharmaceuticals and explosive materials. Energetically the THz range embraces superconducting bandgaps, and regions of intense interest in the understanding of systems in which correlated motions of electrons are important, such as colossal magneto-resistive and high-Tc materials. The very high power levels of the new source will allow non-linear effects to be observed as well as the creation of novel states of materials, including electric-field driven localization[4]. We will give examples of existing work in these areas and present opportunities afforded by the new source.

EXACT SOLUTION OF THE DIRAC EQUATION FOR A SINGULAR CENTRAL POWER POTENTIAL

We compute an exact solution of the Dirac equation for a certain power law potential that consists of two parts: a scalar and a vector, where the latter contains a Coulomb term. We obtain energies that turn out to depend only on the strength of the Coulomb part of the potential, but not on the remaining power law part. We show that our ansatz also yields a bound state solution for the lowest excited state. This work is an extension of Franklins result.7

Zur Kristallchemie des ersten Blei-Zink-Silicium-Telluroxids: PbZn4SiTeO10 / On the Crystal Chemistry of the First Lead Zinc Silicon Tellurium Oxyde PbZn4SiTeO10

Single crystals of the new lead zinc silicon tellurium oxide PbZn4SiTeO10 have been prepared by solid state reaction in air. The compound is colourless and crystallizes in orthorhombic symmetry, space group D162h Pnma, with the cell parameters: a = 6.542 (5), b = 15.624(4), c = 8.280(4) Å, Z = 4. The structure has been determined from a single crystal X-ray study and refined to the conventional values R = 0.032 and wR(F2) = 0.050. Zn2+ and Si4+ show tetrahedral and Te6+ octahedral coordination by O2-.The crystal structure is dominated by a 3∞ [Zn4O10]12- framework with isolated TeO66+ and SiO44+ polyhedra. Pb2+ ions are incorporated in the network. The centres of negative charge of the lone pairs of Pb2+ are estimated by calculations of the Coulomb term of the lattice energy

Study of Water and Dimethylformamide Interaction by Computer Simulation

Monte Carlo simulations of water-dimethylformamide (DMF) mixtures were performed in the isothermal and isobaric ensemble at 298.15 K and 1 atm. The intermolecular interaction energy was calculated using the classical 6-12 Lennard-Jones pairwise potential plus a Coulomb term. The TIP4P model was used for simulating water molecules, and a six-site model previously optimised by us was used to represent DMF. The potential energy for the water-DMF interaction was obtained via standard geometric combining rules using the original potential parameters for the pure liquids. The radial distribution functions calculated for water-DMF mixtures show well characterised hydrogen bonds between the oxygen site of DMF and hydrogen of water. A structureless correlation curve was observed for the interaction between the hydrogen site of the carbonyl group and the oxygen site of water. Hydration effects on the stabilisation of the DMF molecule in aqueous solution have been investigated using statistical perturbation theory. The results show that energetic changes involved in the hydration process are not strong enough to stabilise another configuration of DMF than the planar one.