Protons colliding with crystalline ice: proton reflection and collision induced water desorption at low incidence energies

We present results of classical trajectory (CT) calculations on the sticking of protons to the basal plane (0001) face of crystalline ice, for normal incidence at a surface temperature (Ts) of 80 K. The calculations were performed for moderately low incidence energies (Ei) ranging from 0.05 to 4.0 eV. Surprisingly, significant reflection is predicted at low values of Ei (< or = 0.2 eV) due to repulsive electrostatic interactions between the incident proton and the surface water molecules with one of their H-atoms pointing upward toward the gas phase. The sticking probability increases with Ei and converges to unity for Ei > or = 0.8 eV. In the case of sticking, the proton is trapped in the ice forming a Zundel complex (H5O2+), with an average binding energy of 9.9 eV with a standard deviation of 0.5 eV, independent of the value of Ei. In nearly all sticking trajectories, the proton is implanted into the ice surface, with a penetration depth that increases with Ei. The strong interaction with the neighboring water molecules leads to a local rupture of the hydrogen bonding network, resulting in collision induced desorption of water (puffing), a process that occurs with significant probability even at the lowest Ei considered. The probability of water desorption increases with Ei. In nearly all trajectories in which water desorption occurs, a single three-coordinated water molecule is desorbed from the topmost monolayer.     

Self-to-other ratios measured in an opera chorus in performance

Four volunteer members of the chorus of Opera Australia, representing four different voice categories, wore binaural pairs of wireless microphones during a penultimate dress rehearsal on the Opera Theater stage of the Sydney Opera House. From the recordings, data were obtained on sound levels and on the self-to-other ratios (SORs). The sound levels were comparable to those found in loud music in chamber choir performance. The average SOR ranged from +10 to +15 dB. Compared to chamber choirs in other types of room, the SOR values were high. On a separate occasion, the stage support parameters ST1 (early reflections) and ST2 (late reflections) were measured over the whole stage area. ST1 was about -16 dB, which is typical for opera stages, and -20 dB for ST2, which is unusually low. It is concluded that the SOR in the opera chorus depends mostly on choir formation, which is highly variable, and that an opera chorus artist generally can hear his or her own voice very well, but little of the others and of the orchestra. This was confirmed by informal listening to the recordings.     

Search for Higgs bosons decaying into bb and produced in association with a vector boson in pp collisions at square root of s = 1.8 TeV

We present a new search for H0V production, where H0 is a scalar Higgs boson decaying into bb with branching ratio beta, and V is a Z0 boson decaying into e+e-, mu+mu-, or nunu. This search is then combined with previous searches for H0V where V is a W+/- boson or a hadronically decaying Z0. The data sample consists of 106 +/- 4 pb(-1) of pp collisions at square root of s = 1.8 TeV accumulated by the Collider Detector at Fermilab. Observing no evidence of a signal, we set 95% Bayesian credibility level upper limits on sigma(pp --> H0V) x beta. For H0 masses of 90, 110, and 130 GeV/c2, the limits are 7.8, 7.2, and 6.6 pb, respectively.     

Liquid crystal polymers from swallow-tailed mesogens

Swallow-tailed compounds containing an acetylenic unit have been synthesized. Only those compounds with a three ring structure exhibited liquid-crystalline phases. The platinum catalysed addition of these monomers to compounds containing Si-H groups was used to synthesize polymeric materials. Only those polymers with the tetramethyldisiloxane unit showed mesophases. The synthesis, characterization, and phase behaviour are described.     

The Transient Behaviour of a Cyclic Queue

This paper studies a cyclic queueing problem arising in civil engineering earthmoving projects. There are m excavators and n trucks which queue to be loaded by the excavators. The problem is therefore equivalent to a machine interference problem with m operators and n machines. The size of the haul fleet must be optimized, so as to minimize the cost per unit volume of earth moved. Graphs which show regions of optimal n in the parameter space are presented for the steady-state D/D/1, M/D/1 and E _k /M/1 models. The effect of operating the M/M/m system in short work shifts, so that the initial conditions and transient behaviour are important, is then analysed and quantified as a correction to the optimal number of trucks in the haul fleet from the steady-state solution.     

On the influence of coloration on the intrinsic luminescence in NaCl

The dependence of quenching of the π and σ intrinsic luminescence in pure and doped NaCl crystals has been studied as a function of irradiation time near LNT. Three stages in the luminescence quenching have been found. The first stage is very dependent on impurities concentration and is inhibited for high concentration.     

First results from the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg d of Ge net exposure after cuts for recoil energies between 10 and 100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross section for all WIMP masses above 15 GeV/c2, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10(-43) cm2 at a WIMP mass of 60 GeV/c2.     

INAA of Aerosol Samples in Mexico City

Total solid particles (TSP), respirable particles (RP) PM10 and 17 metallic pollutants were measured in dwellings in the Metropolitan Zone of Mexico Valley (MZMV) by gravimetry and instrumental neutron activation analysis (INAA). Monitoring was performed in Northeast, Center, Southeast and Southwest Zones in the winter and spring seasons. In general, the average concentration of contaminants (derived from industrial activities) that we have determined have increased with time. TSP and RP PM10 are often above the US and Mexican norms.