Optimal Axes of Siberian Snakes for Polarized Proton Acceleration

Accelerating polarized proton beams and storing them for many turns can lead to a loss of polarization when accelerating through energies where a spin rotation frequency is in resonance with orbit oscillation frequencies. First-order resonance effects can be avoided by installing Siberian Snakes in the ring, devices which rotate the spin by 180 degrees around the snake axis while not changing the beam's orbit significantly. For large rings, several Siberian Snakes are required. Here a criterion will be derived that allows to find an optimal choice of the snake axes. Rings with super-period four are analyzed in detail, and the HERA proton ring is used as an example for approximate four-fold symmetry. The proposed arrangement of Siberian Snakes matches their effects so that all spin-orbit coupling integrals vanish at all energies and therefore there is no first-order spin-orbit coupling at all for this choice, which I call snakes matching. It will be shown that in general at least eight Siberian Snakes are needed and that there are exactly four possibilities to arrange their axes. When the betatron phase advance between snakes is chosen suitably, four Siberian Snakes can be sufficient. To show that favorable choice of snakes have been found, polarized protons are tracked for part of HERA-p's acceleration cycle which shows that polarization is preserved best for the here proposed arrangement of Siberian Snakes.Comment: 14 pages, 16 figure

Research and development of high-performance light-weight fuel cell electrodes final report, nov. 1, 1963 - oct. 31, 1964

High performance light weight fuel cell electrode developmen

Phase structure and monopoles in U(1) gauge theory

We investigate the phase structure of pure compact U(1) lattice gauge theory in 4 dimensions with the Wilson action supplemented by a monopole term. To overcome the suppression of transitions between the phases in the simulations we make the monopole coupling a dynamical variable. We determine the phase diagram and find that the strength of the first order transition decreases with increasing weight of the monopole term, the transition thus ultimately getting of second order. After outlining the appropriate topological characterization of networks of currents lines, we present an analysis of the occurring monopole currents which shows that the phases are related to topological properties.Comment: 22 pages (latex), 14 figures (available upon request), BU-HEP 94-

Bubble Shape Oscillations and the Onset of Sonoluminescence

An air bubble trapped in water by an oscillating acoustic field undergoes either radial or nonspherical pulsations depending on the strength of the forcing pressure. Two different instability mechanisms (the Rayleigh--Taylor instability and parametric instability) cause deviations from sphericity. Distinguishing these mechanisms allows explanation of many features of recent experiments on sonoluminescence, and suggests methods for finding sonoluminescence in different parameter regimes.Comment: Phys. Rev. Lett., in pres

The Crystal Structure of Ethyl p-Azoxybenzoate

The low-temperature form (solid I) of the smectogenic compound ethyl p-azoxybenzoate (C18H18N2Os) is stable below 90 °C. The triclinic unit cell of space group P] and dimensions a = 7.56 + 0.02, b-- 18 35 + 0.07, c= 6.28 + 0.01 A, ¢¢= 94.38 ° + 0.30 °, ,8= 97.21 _+ 0.31 °, and y = 83.97 ° + 0.25 ° contains two molecules and has a calculated density of 1.325 g.cm-3. The observed density is 1.315 + 0.013 g.cm-3. Integrated intensities were measured at room temperature by a 20--~ scan on a four-circle diffractometer equipped with a post-diffraction monochromator and scintillation detector. The crystal structure was refined by full-matrix least-squares methods with 1460 independent reflections to a final R index of 0 093. The molecules are nearly planar (the normals to the planes of the two benzene rings diverge by only 0-5 °) and are packed in a parallel array, as contrasted with the imbricated structure which has been observed for several nematogenic crystalline solids. The carbonyl and nitroso oxygen atoms are all in the cis conformation, resulting in a large dipole component in the plane of the molecule and perpendicular to its long axis. It is speculated that this feature of the molecular structure may be characteristic of smectogenic compounds

Comment on Mie Scattering from a Sonoluminescing Bubble with High Spatial and Temporal Resolution [Physical Review E 61, 5253 (2000)]

A key parameter underlying the existence of sonoluminescence (SL)is the time relative to SL at which acoustic energy is radiated from the collapsed bubble. Light scattering is one route to this quantity. We disagree with the statement of Gompf and Pecha that -highly compressed water causes the minimum in scattered light to occur 700ps before SL- and that this effect leads to an overestimate of the bubble wall velocity. We discuss potential artifacts in their experimental arrangement and correct their description of previous experiments on Mie scattering.Comment: 10 pages, 2 figure

Simulation of Micro-Electronic FlowFET Systems

A microelectronic fluidic system has been investigated by modeling and 3D simulation of fluid flow controlled by an applied gate voltage. The simulations have helped to characterize a novel FlowFET (a fluidic Field Effect Transistor) device under fault-free conditions. The FlowFET operates by applying a voltage field from a gate electrode in the insulated side wall of a microchannel to modulate the ␣-potential at the shear plane [1]. The change in ␣-potential can be used to control both the magnitude and direction of the electroosmotic flow in the microchannel

The Crystal Structure of p-Azoxyanisole

The stable crystalline form ofp-azoxyanisole is assigned to space group P21/a (C~h) with four molecules in the unit cell having parameters a= 15-776, b= 8.112, e= 11-018 A and b\u27= 114 57 °. The crystal structure was refined by full-matrix least-squares to a final R value of 0.091 using 2507 reflections measured with a manually operated single-crystal diffractometer. The molecules are arranged in the unit cell with their long axes approximately perpendicular to the (100) plane. The angle between the normals to the two benzene rings is 22.6 °, and the -N=N- bond conformation departs from the planar trans position by approximately 4 2 °