Hexagonal spiral growth in the absence of a substrate

Experiments on the formation of spiraling hexagons (350 - 1000 nm in width) from a solution of nanoparticles are presented. Transmission electron microscopy images of the reaction products of chemically synthesized cadmium nanocrystals indicate that the birth of the hexagons proceeds without assistance from static screw or edge dislocatons, that is, they spiral without constraints provided by an underlying substrate. Instead, the apparent growth mechanism relies on what we believe is a dynamical dislocation identified as a dense aggregate of small nanocrystals that straddles the spiraling hexagon at the crystal surface. This nanocrystal bundle, which we term the "feeder", also appears to release nanocrystals into the spiral during the growth process.Comment: 4 pages, 5 figure

Gravity-Yang-Mills-Higgs unification by enlarging the gauge group

We revisit an old idea that gravity can be unified with Yang-Mills theory by enlarging the gauge group of gravity formulated as gauge theory. Our starting point is an action that describes a generally covariant gauge theory for a group G. The Minkowski background breaks the gauge group by selecting in it a preferred gravitational SU(2) subgroup. We expand the action around this background and find the spectrum of linearized theory to consist of the usual gravitons plus Yang-Mills fields charged under the centralizer of the SU(2) in G. In addition, there is a set of Higgs fields that are charged both under the gravitational and Yang-Mills subgroups. These fields are generically massive and interact with both gravity and Yang-Mills sector in the standard way. The arising interaction of the Yang-Mills sector with gravity is also standard. Parameters such as the Yang-Mills coupling constant and Higgs mass arise from the potential function defining the theory. Both are realistic in the sense explained in the paper.Comment: 61 pages, no figures (v2) some typos correcte

Azimuthal Correlation in Lepton-Hadron Scattering via Charged Weak-Current Processes

We consider the azimuthal correlation of the final-state particles in charged weak-current processes. This correlation provides a test of perturbative quantum chromodynamics. The azimuthal asymmetry is large in the semi-inclusive processes in which we identify a final-state hadron, say, a charged pion compared to that in the inclusive processes in which we do not identify final-state particles and use only the calorimetric information. In semi-inclusive processes the azimuthal asymmetry is more conspicuous when the incident lepton is an antineutrino or a positron than when the incident lepton is a neutrino or an electron. We analyze all the possible charged weak-current processes and study the quantitative aspects of each process. We also compare this result to the ep scattering with a photon exchange.Comment: 25 pages, 2 Postscript figures, uses RevTeX, fixes.st

Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields

The drift and diffusion of a cloud of ions in a fluid are distorted by an inhomogeneous electric field. If the electric field carries the center of the distribution in a straight line and the field configuration is suitably symmetric, the distortion can be calculated analytically. We examine the specific examples of fields with cylindrical and spherical symmetry in detail assuming the ion distributions to be of a generally Gaussian form. The effects of differing diffusion coefficients in the transverse and longitudinal directions are included

Relativistic Effects in S-Wave Quarkonium Decay

The decay widths of S-wave quarkonia (\etc,\etb\to \gg{~~and~~} \J,\U\to\ee) are calculated on the basis of a quasipotential approach. The nontrivial dependence on relative quark motion of decay amplitude is taken into consideration via quarkonium wave function. It is shown that relativistic corrections may be large (10-50 %) and comparable with QCD corrections.Comment: 10 pages, no figure

Neutral atomic carbon in the globules of the Helix

We report detection of the 609u line of neutral atomic carbon in globules of the Helix nebula. The measurements were made towards the position of peak CO emission. At the same position, we obtained high-quality CO(2-1) and 13CO(2-1) spectra and a 135" x 135" map in CO(2-1). The velocity distribution of CI shows six narrow (1 -> 2 km/sec) components which are associated with individual globules traced in CO. The CI column densities are 0.5 -> 1.2 x 10^16/cm^2. CI is found to be a factor of ~6 more abundant than CO. Our estimate for the mass of the neutral envelope is an order of magnitude larger than previous estimates. The large abundance of CI in the Helix can be understood as a result of the gradual photoionisation of the molecular envelope by the central star's radiation field.Comment: 5 pages, Latex, AAS macros, 3 EPS figures, to appear in Astrophysical Journal Letter

Enhancing the heavy Higgs signal with jet-jet profile cuts

The jet-jet profile, or detailed manner, in which transverse energy and mass are distributed around the jet-jet system resulting from the hadronic decay of a $Z$ boson in the process Higgs$\to ZZ$ at a proton-proton collider energy of 40\tev is carefully examined. Two observables are defined that can be used to help distinguish the $\ell^+\ell^-$-jet-jet signal from Higgs decay from the ``ordinary'' QCD background arising from the large transverse momentum production of single $Z$ bosons plus the associated jets. By making cuts on these observables, signal to background enhancement factors greater than $100$ can be obtained.Comment: 16 pages, Univ. Florida IFT-93-

Dynamics of Phase Transitions: The 3D 3-state Potts model

In studies of the QCD deconfining phase transition or cross-over by means of heavy ion experiments, one ought to be concerned about non-equilibrium effects due to heating and cooling of the system. In this paper we extend our previous study of Glauber dynamics of 2D Potts models to the 3D 3-state Potts model, which serves as an effective model for some QCD properties. We investigate the linear theory of spinodal decomposition in some detail. It describes the early time evolution of the 3D model under a quench from the disordered into the ordered phase well, but fails in 2D. Further, the quench leads to competing vacuum domains, which are difficult to equilibrate, even in the presence of a small external magnetic field. From our hysteresis study we find, as before, a dynamics dominated by spinodal decomposition. There is evidence that some effects survive in the case of a cross-over. But the infinite volume extrapolation is difficult to control, even with lattices as large as $120^3$.Comment: 12 pages; added references, corrected typo

Magnetocaloric Studies of the Peak Effect in Nb

We report a magnetocaloric study of the peak effect and Bragg glass transition in a Nb single crystal. The thermomagnetic effects due to vortex flow into and out of the sample are measured. The magnetocaloric signature of the peak effect anomaly is identified. It is found that the peak effect disappears in magnetocaloric measurements at fields significantly higher than those reported in previous ac-susceptometry measurements. Investigation of the superconducting to normal transition reveals that the disappearance of the bulk peak effect is related to inhomogeneity broadening of the superconducting transition. The emerging picture also explains the concurrent disappearance of the peak effect and surface superconductivity, which was reported previously in the sample under investigation. Based on our findings we discuss the possibilities of multicriticality associated with the disappearance of the peak effect.Comment: 30 pages, 10 figure