Water-vapor adsorption on calcium-boroaluminosilicate glass fibers

The water-vapor adsorption isotherms of E-glass fibers were measured as a function of their aging in humid and aqueous environments, and of the amount of B₂O₃ in the glass composition. The specific surface area for adsorption was determined, independently, using inert gas adsorption, while X-ray photoelectron spectroscopy (XPS) was used to characterize the surface composition. In contrast to silica, where submonolayer coverage is observed in the low pressure range of the isotherm, these multicomponent glasses adsorbed the equivalent of 1 to 3 layers of water. The shape of the isotherms revealed that multilayer adsorption of water occurs on the fiber surfaces before the formation of a complete monolayer, i.e., water adsorption on these glass fibers was non-uniform, in general. It was found that the aging of these fibers in humid or aqueous environments greatly enhanced their capacity to adsorb water at low pressure, but the B₂O₃ content of the fibers had little effect.     

Measurement of deeply virtual compton scattering beam-spin asymmetries

The beam-spin asymmetries in the hard exclusive electroproduction of photons on the proton (e p-->epgamma) were measured over a wide kinematic range and with high statistical accuracy. These asymmetries result from the interference of the Bethe-Heitler process and of deeply virtual Compton scattering. Over the whole kinematic range (x(B) from 0.11 to 0.58, Q2 from 1 to 4.8 GeV2, -t from 0.09 to 1.8 GeV2), the azimuthal dependence of the asymmetries is compatible with expectations from leading-twist dominance, A approximately a sinphi/(1+c cosphi). This extensive set of data can thus be used to constrain significantly the generalized parton distributions of the nucleon in the valence quark sector.     

A self-driven laser oscillator for directly producing bandwidth-limited pulses of about 1 nsec

We report a self-driven Nd:YAG oscillator system that directly produces bandwidth-limited output pulses with durations from < 0.5 to #62; 2.5 nsec. We obtain the pulses by independently adjusting the temporal content of an initially gated noise pulse, the frequency dependent feedback properties of the optical cavity, and the system gain.     

Experimental study of exclusive 2H(e,e'p)n reaction mechanisms at high Q2

The reaction 2H(e,e'p)n has been studied with full kinematic coverage for photon virtuality 1.75NN transition is the primary contribution at higher momenta.     

Classroom demonstrations of acoustic beamforming

A tabletop apparatus permitting demonstrations and hands-on student exercises in the acoustic beamforming of linear arrays is described. The apparatus can be used to demonstrate how interference effects from two or more linearly arranged sources produce patterns of maxima and minima as described by theory. A transmitting array is attached to the top of a rotating table and a receiving transducer provides voltages to a signal processor. Students measure the angular speed of the rotating table and the voltages produced by the receiving transducer as a function of time. These data can be analyzed in a spreadsheet program and compared to theory. The angles at which signal maxima occur correspond well to theory and useful teaching discussions result from comparisons of signal maxima magnitudes. The spreadsheet analysis can also provide the students a graphical demonstration of l'H?pital's rule.     

Measurement of the neutron F2 structure function via spectator tagging with CLAS

We report on the first measurement of the F(2) structure function of the neutron from the semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ?100 MeV/c and their angles to ?100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F(2)(n) data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65相似文献