A comprehensive study of the long pulse Nd:YAG laser drilling of multi-layer carbon fibre composites

The results of an extensive experimental study of the free running Nd:YAG laser drilling of a multi-layer carbon fibre composite, where adjacent layers have differently orientated fibres, are reported. For holes drilled with the laser operating in fixed-Q mode at 1064 nm, parallel sections of blind holes illustrating discontinuities in the hole size along a given section direction will be shown to occur at the interface between adjacent layers. An explanation for this effect is proposed. Detailed single pulse drilling characteristics will be presented illustrating the exit hole diameter as a function of pulse energy and material thickness. These characteristics illustrate a ‘stable' drilling regime in which the exit hole diameters are least sensitive to changes in pulse energy or material thickness and a less ‘stable' regime in which they are more strongly dependent on these parameters. Drilling characteristics will be given for two different beam qualities, illustrating the greater drilling depth and reduced hole size achievable with an improved beam quality. Finally holes drilled through a 2 mm thick sample of material with multiple pulses are considered. Size distribution curves for entrance and exit holes will be presented. The total energy required (number of pulses × pulse energy) to drill through 2 mm thick material will be reported as a function of pulse energy in stationary air and argon atmospheres and in a partial vacuum, illustrating a threshold energy which is dependent upon the drilling atmosphere. The threshold energies will be discussed with reference to plasma formation and the reactivity of the drilling atmosphere.     

Search for rare and forbidden decays D+ --> h+/- e+/- e+

Using 0.8 x 10(6) D+ D- pairs collected with the CLEO-c detector at the psi(3770) resonance, we have searched for flavor-changing neutral current and lepton-number-violating decays of D+ mesons to final states with dielectrons. We find no indication of either, obtaining 90% confidence level upper limits of B(D+ --> pi+ e+ e-) < 7.4 x 10(-6), B(D+ --> pi- e+ d+) < 3.6 x 10(-6), B(D+ --> K+ e+ e-) < 6.2 x 10(-6), and B(D+ --> K- e+ e+) < 4.5 x 10(-6).     

MiniMax: What has been learned thus far

Summary A small experiment, ?MiniMax?, has been set up in the C0 intersection region of the Fermilab Tevatron to seek evidence for disoriented chiral condensates and to study other forward physics phenomena. The experiment consists of a proportional wire chamber telescope accompanied by scintillation (trigger) counters, a lead converter, and followed by an electromagnetic calorimeter. The solid angle accepted is a cone centered at pseudorapidity (η) of 4.1 and of radius (in η-ϕ space) of about 0.6. Over 2.5 million events thus far have demonstrated the successful operation of the apparatus, however to date the analysis has not progressed sufficiently to permit any conclusions concerning disoriented chiral condensates. presented byL. W. Jones Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Polarized emission from a rhenium metal-ligand complex

We report the first observation of polarized emission from a rhenium-phenanthroline complex, Re(CO)₃(phen)Cl. Highly luminescent rhenium complexes are known, with quantum yields near 0.5 and lifetimes in excess of 10 s. The detection of polarized emission suggests the use of rhenium complexes as probes of the hydrodynamics of large macromolecular complexes and for use in fluorescence polarization immunoassays with gated detection.     

Raman spectrographic system for quantitative analysis of isotopic hydrogen mixtures for muon catalysis experiments

We show that Raman spectral lines from H₂, D₂, T₂, HD, HT and DT are readily resolved, permitting an effective means to analyze isotopic hydrogen mixtures used in muon-catalyzed fusion experiments. We propose a Raman spectrographic system to allow for real-time analysis of targets involving all three isotopes of hydrogen.