Measurement of the electric quadrupole moment of the 4d2D5/2 level in 88Sr+

The quadrupole moment of the 4d (2)D(5/2) level in 88Sr+ has been measured to be 2.6(3)ea(2)(0), where a(0) is the Bohr radius and e the elementary charge. A single laser-cooled strontium ion was confined in an end cap trap with a variable dc quadrupole potential, and measurements were made on the 5s (2)S(1/2)-4d (2)D(5/2) transition at 674 nm using a femtosecond optical frequency comb. This work shows that measurements of the unperturbed 88Sr+ transition frequency with sub-Hz uncertainty are possible and is important in understanding the reproducibility of ion trap optical frequency standards.     

Modelling of the transition from conductive to convective burning in porous energetic materials

This paper is concerned with a theoretical interpretation of an abrupt shift from the slow conductive to fast convective burning observed in the combustion of gas-permeable explosives under gradual elevation of the ambient pressure. The paper is a revision of our recent communication on the problem, and is based on the amended heat equation, which meets the requirement of the conservation of energy lacking in the previous model. It appears, however, that both formulations lead (in appropriately chosen units) to a largely similar picture of the transition. The transition is triggered by a localised autoignition in the extended resistance-induced preheat zone formed ahead of the advancing deflagration, provided the pressure difference between hot gas products and gases deep inside the pores of the unburned solid exceed a certain critical level. For moderately high activation energies the critical overpressures are comparable to those observed experimentally. In line with observations, the critical overpressure increases with diminishing permeability. The amended formulation implies the possibility of overpressure-driven gasification waves occurring even in the absence of chemical heat release.     

The Quiver of an Algebra Associated to the Mantaci-Reutenauer Descent Algebra and the Homology of Regular Semigroups

We develop the homology theory of the algebra of a regular semigroup, which is a particularly nice case of a quasi-hereditary algebra in good characteristic. Directedness is characterized for these algebras, generalizing the case of semisimple algebras studied by Munn and Ponizovksy. We then apply homological methods to compute (modulo group theory) the quiver of a right regular band of groups, generalizing Saliola’s results for a right regular band. Right regular bands of groups come up in the representation theory of wreath products with symmetric groups in much the same way that right regular bands appear in the representation theory of finite Coxeter groups via the Solomon-Tits algebra of its Coxeter complex. In particular, we compute the quiver of Hsiao’s algebra, which is related to the Mantaci-Reutenauer descent algebra.     

Threshold and suprathreshold temporal integration effects in the crossed and uncrossed human acoustic stapedius reflex

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold TI measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%-4%, p greater than 0.05) but were significantly larger in the crossed condition at higher criterion levels (5%-6%, p less than 0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.     

Influence of distributed solid-phase reactions on deflagrations in confined porous propellants

Combustion processes in energetic materials are often modeled by a surface gasification reaction followed by a distributed gaseous flame. However, under confinement, deflagrations in porous or granular propellants are generally accompanied by an increasing pressure difference, or overpressure, between the burned-gas region and the unburned reactants deep within the pores of the material. As the overpressure and/or the solid-phase reaction rate become sufficiently large, the gaseous and solid reaction zones tend to merge into a single multiphase reaction region. Furthermore, in certain parameter regimes, the gas flame penetrates into the porous solid, resulting in subsurface gaseous combustion. When the activation energies of the gaseous and solid-phase reactions are of the same order of magnitude and/or the overpressure becomes significant, gasification reactions may also become active within the solid, thus eliminating a distinct propellant surface and forming a distributed multiphase reaction layer. A large activation-energy analysis of this scenario is presented to study the effects of distributed solid reactions on the deflagration structure and the burning-rate response. The burning-rate eigenvalue is obtained from a numerical solution of the reaction-zone problem, and the results are calculated for various overpressures as well as different gas-to-solid activation-energy and thermal conductivity ratios. It is observed that increasing overpressure results in a more spatially distributed solid-phase reaction and a rapidly increasing flame-propagation speed.     

On hadronic production of the ηc and other cc̄ bound states

We discuss various mechanisms for inclusive production of cc? bound states in hadron-hadron interactions. We conclude that for η_c, η′_c alone, among the bound states, the cross section for production is mainly due to the annihilation of two constituent gluons in a color singlet state. We give detailed results for η_c production cross sections.     

Inverse semigroups and varieties of finite semigroups

In this paper we shall present a new construction of the free inverse monoid on a set X. Contrary to the previous constructions of [9, 11], our construction is symmetric and originates from classical ideas of language theory. The ingredients of this construction are the free group on X and the relation that associates to a word w of the free monoid on X, the set of all pairs (u, v) such that uv = w. It follows at once from our construction that the free inverse monoid on X can be naturally embedded into the Schützenberger product of two free groups of basis X. We shall also give some connections with the theory of expansions as developed by Rhodes and Birget [2, 3].     

Quark loops,vector dominance and photon total cross sections

We calculate the contribution of quark loops including one-gluon exchange to photon total cross sections. We add to this contribution vector-dominance terms corresponding to discrete resonances. The loop contributions represent the contribution of the high-mass continuum. The results of this approach agree to within the experimental error with measurements from 2 GeV up to 200 GeV.