Stability of Covariant Relativistic Quantum Theory

In this paper we study the relativistic quantum-mechanical interpretation of the solution of the inhomogeneous Euclidean Bethe-Salpeter equation. Our goal is to determine conditions on the input to the Euclidean Bethe-Salpeter equation so the solution can be used to construct a model Hilbert space and a dynamical unitary representation of the Poincaré group. We prove three theorems that relate the stability of this construction to properties of the kernel and driving term of the Bethe-Salpeter equation. The most interesting result is that the positivity of the Hilbert space norm in the non-interacting theory is not stable with respect to Euclidean covariant perturbations defined by Bethe-Salpeter kernels. The long-term goal of this work is to understand which model Euclidean Green functions preserve the underlying relativistic quantum theory of the original field theory. Understanding the constraints imposed on the Green functions by the existence of an underlying relativistic quantum theory is an important consideration for formulating field-theory motivated relativistic quantum models.This work supported in part by the U.S. Department of Energy, under contract DE-FG02-86ER40286     

Electronic properties of epitaxial 6H silicon carbide

The electrical conductivity and Hall coefficient were measured in the temperature range from 78 to 900 K for n-type epitaxially grown 6H silicon carbide. A many-valley model of the conduction band was used in the analysis of electron concentration as a function of temperature. From this analysis, the density of states mass to the free electron mass ratio per ellipsoid was calculated to be 0.45. It was estimated that the constant energy surface of the conduction band consists of three ellipsoids. The ionization energy of the shallowest nitrogen donor was found to be 105 meV, when the valley-orbit interaction was taken into account. The electron scattering mechanisms in the epitaxial layers were analyzed and it was shown that the dominant mechanism limiting electron mobility at high temperatures is inter-valley scattering and at low temperatures (200 K), impurity and space charge scattering. A value of $\text{360}\text{cm}{}^2\text{V}$ sec was calculated for the maximum room temperature Hall mobility expected for electrons in pure 6H SiC. The effect of epitaxial growth temperature on room temperature Hall mobility was also investigated.     

Pigments from fusarium moniliforme sheldon : Structure and 13C nuclear magnetic resonance assignments of an azaanthraquinone and three naphthoquinones

Physico-chemical techniques established the novel structure of 8-O-methylbostrycoidin, the main pigment from Fusarium moniliforme as 6,8-dimethoxy-5-hydroxy-3-methyl-2-azaanthraquinone. The structures of three biogenetically related naphthoquinones were elucidated by comparison of spectroscopic data.     

Pionization in pp interactions at 12 and 24 GeV/c

Inclusive π⁻ and π⁺ distributions in the region of small longitudinal c.m. momenta, from pp interactions at 12 and 24 GeV/c, are presented and compared with CERN-ISR data. Interesting scaling and factorization properties are found. The extent to which the observed behavior can be interpreted as evidence for pionization is discussed.     

Fabrication of asymmetric molecular junctions by the oriented assembly of dithiocarbamate rectifiers

The oriented assembly of molecules on metals is a requirement for rectification in planar metal-molecule-metal junctions. Here, we demonstrate how the difference in adsorption kinetics between dithiocarbamate and thioacetate anchor groups can be utilized to form oriented assemblies of asymmetric molecules that are bound to Au through the dithiocarbamate moiety. The free thioactate group is then used as a ligand to bind Au nanoparticles and to form the desired metal-molecule-metal junction. Besides allowing an asymmetric coupling to the electrodes, the molecules exhibit an asymmetric molecular backbone where the length of the alkyl chains separating the electrodes from a central, para-substituted phenyl ring differs by two methylene units. Throughout the junction fabrication, the layers were characterized by photoelectron spectroscopy, infrared spectroscopy, and scanning tunneling microscopy. Large area junctions using a conducting polymer interlayer between a mercury-drop electrode and the self-assembled monolayer prove the relationship between electrical data and molecular structure.     

Analysis of the sequential fission observed in collisions of100Mo +100Mo and120Sn +120Sn around 20 A·MeV

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactions¹⁰⁰Mo +¹⁰⁰Mo at 18.7, 23.7 A·MeV and¹²⁰Sn +¹²⁰Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step — mass asymmetry, relative velocity, in-plane and out-of-plane angles — have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay.