Associated Charmonium Production in p-pbar Annihilation

In this paper we summarize our recent results for low energy associated charmonium production cross sections, using 1) crossing symmetry, and 2) an explicit hadronic model. These predictions are of relevance to the planned charmonium and charmonium hybrid production experiment PANDA at GSI.Comment: 5 pages, 5 figures. Contribution to the Second Meeting of the APS Topical Group on Hadron Physics GHP2006. (Nashville, TN, 22-24 Oct. 2006

Fluid flow and heat transfer around mechanical seals.

Mechanical seals are used extensively on rotary applications where the sealed fluid is under pressure. They may rightly be considered to be generally reliable and trouble free, many giving lives of over 3 years. However, a significant number, particularly on arduous and often critical duties, exhibit apparently random mid-life failure characteristics which cannot be easily explained. Of these "random" failures, the largest proportion appear to be attributable to overheating due to loss of the vital interface fluid film. The mechanism of interface film loss depends on a large number of interrelated variables and a substantial amount of work has been carried out over many years to attempt to alleviate the problem. Little work however has been reported on the nature of the fluid flow around the seal; this is determined by seal chamber geometry and affects the removal of potentially deleterious heat, vapour or gases, and solids. At present, many seals are required to run in "stuffing boxes" - cavities designed for soft packing rather than mechanical seals. The aim of this project has been to study the flow behaviour in these stuffing boxes and a number of novel chamber designs. The techniques involved using transparent housings and direct measurements of convective heat transfer coefficients. Significant improvements over existing designs were achieved using a housing flared at 45° away from the seal and this design forms the basis of recommendations for improved seal systems. This design was tested under simulated field conditions described in a Design Study and Case Study and found to be successful. The recommendations are backed up by a mathematical model of turbulence viscosity which seeks to explain some of the complex structured flows observed. A corollary to the thesis explains how the results of this work will form a major input to improved international standards

BB Intermeson Potentials in the Quark Model

In this paper we derive quark model results for scattering amplitudes and equivalent low energy potentials for heavy meson pairs, in which each meson contains a heavy quark. This "BB" system is an attractive theoretical laboratory for the study of the nuclear force between color singlets; the hadronic system is relatively simple, and there are lattice gauge theory (LGT) results for V_BB(r) which may be compared to phenomenological models. We find that the quark model potential (after lattice smearing) has qualitative similarities to the LGT potential in the two B*B* channels in which direct comparison is possible, although there is evidence of a difference in length scales. The quark model prediction of equal magnitude but opposite sign for I=0 and I=1 potentials also appears similar to LGT results at intermediate r. There may however be a discrepancy between the LGT and quark model I=1 BB potentials. A numerical study of the two-meson Schrodinger equations in the (bqbar)(bqbar) and (cqbar)(cqbar) sectors with the quark model potentials finds a single "molecule", in the I=0 BB* sector. Binding in other channels might occur if the quark model forces are augmented by pion exchange.Comment: 30 pages, 5 figures, revtex and epsfig. Submitted to Phys. Rev.

Sunjammer

No abstract available

Early career professionals: the mission of a task force

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133554/1/jth13363_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133554/2/jth13363.pd

Activation mechanisms in sodium-doped Silicon MOSFETs

We have studied the temperature dependence of the conductivity of a silicon MOSFET containing sodium ions in the oxide above 20 K. We find the impurity band resulting from the presence of charges at the silicon-oxide interface is split into a lower and an upper band. We have observed activation of electrons from the upper band to the conduction band edge as well as from the lower to the upper band. A possible explanation implying the presence of Hubbard bands is given.Comment: published in J. Phys. : Condens. Matte

Stability of atomic clocks based on entangled atoms

We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of $N$ atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as $N^{1/6}$ compared to the atomic shot noise level.Comment: 4 pages, 2 figures, revtex

Spin Gap in Two-Dimensional Heisenberg Model for CaV4_4O9_9

We investigate the mechanism of spin gap formation in a two-dimensional model relevant to Mott insulators such as CaV$_4$O$_9$. From the perturbation expansion and quantum Monte Carlo calculations, the origin of the spin gap is ascribed to the four-site plaquette singlet in contrast to the dimer gap established in the generalized dimerized Heisenberg model.Comment: 8 pages, 6 figures available upon request (Revtex