Z -> b\bar{b} Versus Dynamical Electroweak Symmetry Breaking involving the Top Quark

In models of dynamical electroweak symmetry breaking which sensitively involve the third generation, such as top quark condensation, the effects of the new dynamics can show up experimentally in Z->b\bar{b}. We compare the sensitivity of Z->b\bar{b} and top quark production at the Tevatron to models of the new physics. Z->b\bar{b} is a relatively more sensitive probe to new strongly coupled U(1) gauge bosons, while it is generally less sensitive a probe to new physics involving color octet gauge bosons as is top quark production itself. Nonetheless, to accomodate a significant excess in Z->b\bar{b} requires choosing model parameters that may be ruled out within run I(b) at the Tevatron.Comment: LaTex file, 19 pages + 2 Figs., Fermilab-Pub-94/231-

Adaptive control of CO2_2 bending vibration: deciphering field-system dynamics

We combined adaptive closed-loop optimization, phase-shaping with a restricted search space and imaging to control dynamics and decipher the optimal pulse. The approach was applied to controlling the amplitude of CO$_2$ bending vibration during strong-field Coulomb explosion. The search space was constrained by expressing the spectral phase as a Taylor series, which generated pulses with characteristics commensurate with the natural physical features of this problem. Optimal pulses were obtained that enhanced bending by up to 56% relative to what is observed with comparably intense, transform limited pulses. We show that (1) this judicious choice of a reduced parameter set made unwrapping the dynamics more transparent and (2) the enhancement is consistent with field-induced structural changes to a bent excited state of CO$_2^{2+}$, which theoretical simulations have identified as the state from which the explosion originates.Comment: 4 pages, 3 figures, 1 table, added reference

Adhesive for aluminum withstands cryogenic temperatures

Polyurethane adhesive mixed to various proportions with milled glass fibers match the thermal characteristics of 2014-T6 aluminum at cryogenic temperatures

Absolute Efficiency Measurements of NE-213 ORGANIC Phosphors for Detecting 14.4 and 2.6 Mev Neutrons

Efficiency measurements of organic phosphor scintillator for detecting 14.4 and 2.6 MeV neutron

Co-rich cobalt platinum nanowire arrays: effects of annealing

The effects of annealing on the crystal structure and magnetic properties of Co-rich cobalt platinum nanowire arrays embedded in anodic aluminium oxide membranes have been investigated. For this purpose, a rapid thermal annealing to temperatures of 300 °C to 800 °C has been used. Transmission electron microscopy and scanning electron microscopy show that the nanowires have a mean diameter of 14 nm and an estimated wire density of 7.8×1010 cm-2. From x-ray diffraction patterns, we find that the nanowires are hcp and possess a preferred texture in which the c axis of the grains tends to lie along the major axis of the wire. Vibrating sample magnetometry measurements indicate that the easy axis is along the nanowire axis direction. Hysteresis loops, saturation magnetization, squareness ratio (Mr/Ms), and coercivity (perpendicular and parallel to the nanowire axis) have all been investigated as a function of the annealing temperature (TA). Coercivity parallel to the wire axis first increases with TA, attains a maximum at 600 °C (which is 150% of the as-deposited sample), and then decreases. By contrast there is relatively little change in the coercivity measured perpendicular to the wires. The saturation magnetization for the as-deposited sample is 1360 emu/cc and remains almost constant for annealing temperatures up to 500 °C: for TA>500 °C it decreases significantly. The maximum (Mr/Ms) ratio attained in this study is 0.99, the highest value reported thus far for cobalt platinum alloy nanowires. The data suggest that these materials are potential candidates for high-density magnetic recording media

Fluids confined in wedges and by edges: Virial series for the line-thermodynamic properties of hard spheres

This work is devoted to analyze the relation between the thermodynamic properties of a confined fluid and the shape of its confining vessel. Recently, new insights in this topic were found through the study of cluster integrals for inhomogeneous fluids that revealed the dependence on the vessel shape of the low density behavior of the system. Here, the statistical mechanics and thermodynamics of fluids confined in wedges or by edges is revisited, focusing on their cluster integrals. In particular, the well known hard sphere fluid, which was not studied in this framework so far, is analyzed under confinement and its thermodynamic properties are analytically studied up to order two in the density. Furthermore, the analysis is extended to the confinement produced by a corrugated wall. These results rely on the obtained analytic expression for the second cluster integral of the confined hard sphere system as a function of the opening dihedral angle 0 < β < 2π. It enables a unified approach to both wedges and edges.Fil: Urrutia, Ignacio. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Origin of rebounds with a restitution coefficient larger than unity in nanocluster collisions

We numerically investigate the mechanism of super rebounds for head-on collisions between nanoclusters in which the restitution coefficient is larger than unity. It is confirmed that the temperature and the entropy of the nanocluters decrease after the super rebounds by our molecular dynamics simulations. It is also found that the initial metastable structure plays a key role for the emergence of the super rebounds.Comment: 8 pages, 10 figures, to be published in Phys. Rev.

Two hard spheres in a pore: Exact Statistical Mechanics for different shaped cavities

The Partition function of two Hard Spheres in a Hard Wall Pore is studied appealing to a graph representation. The exact evaluation of the canonical partition function, and the one-body distribution function, in three different shaped pores are achieved. The analyzed simple geometries are the cuboidal, cylindrical and ellipsoidal cavities. Results have been compared with two previously studied geometries, the spherical pore and the spherical pore with a hard core. The search of common features in the analytic structure of the partition functions in terms of their length parameters and their volumes, surface area, edges length and curvatures is addressed too. A general framework for the exact thermodynamic analysis of systems with few and many particles in terms of a set of thermodynamic measures is discussed. We found that an exact thermodynamic description is feasible based in the adoption of an adequate set of measures and the search of the free energy dependence on the adopted measure set. A relation similar to the Laplace equation for the fluid-vapor interface is obtained which express the equilibrium between magnitudes that in extended systems are intensive variables. This exact description is applied to study the thermodynamic behavior of the two Hard Spheres in a Hard Wall Pore for the analyzed different geometries. We obtain analytically the external work, the pressure on the wall, the pressure in the homogeneous zone, the wall-fluid surface tension, the line tension and other similar properties

Chiral Hierarchies, Compositeness and the Renormalization Group

A wide class of models involve the fine--tuning of significant hierarchies between a strong--coupling ``compositeness'' scale, and a low energy dynamical symmetry breaking scale. We examine the issue of whether such hierarchies are generally endangered by Coleman--Weinberg instabilities. A careful study using perturbative two--loop renormalization group methods finds that consistent large hierarchies are not generally disallowed.Comment: 22 pp + 5 figs (uuencoded and submitted separately), SSCL-Preprint-490; FERMI-PUB-93/035-