Gas transport in surface grafted polypropylene films with poly(acrylic acid) chains

This work describes the grafting reaction of poly(acrylic acid) (PA) onto the surface of polypropylene (PP) films carried out with ultraviolet radiation, using benzophenone as photoinitiator and water as solvent. By increasing the reaction time, graft percentages of 3.5, 6.5, 12.9, 19.8, 29.4, and 36.0% were obtained. Micrographs of the modified films show that grafting exclusively occurs on the PP films surface. The values of the permeability coefficient of oxygen, nitrogen, carbon dioxide, carbon monoxide, argon, methane, ethane, ethylene, and propane across the grafted films undergo a sharp drop. The interpretation of the permeation results suggest that radicals created in the tertiary carbons of the grafted chains by effect of UV light or by chain transfer reactions may highly crosslink the PA grafted layer. A rigid layer involving both strong hydrogen bonding and chains crosslinking is formed at grafting percentages of 3.5% that strongly hinders gas permeation across that layer. Destruction of hydrogen bonding by partially replacing protons of acrylic acid residues by sodium/silver cations increases the permeability of the surface grafted films. Finally, the films permselectivity is hardly affected by the grafted layer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2421–2431, 2007     

Interpreting OPERA results on superluminal neutrino

OPERA has claimed the discovery of superluminal propagation of neutrinos. We analyze the consistency of this claim with previous tests of special relativity. We find that reconciling the OPERA measurement with information from SN1987a and from neutrino oscillations requires stringent conditions. The superluminal limit velocity of neutrinos must be nearly flavor independent, must decrease steeply in the low-energy domain, and its energy dependence must depart from a simple power law. We construct illustrative models that satisfy these conditions, by introducing Lorentz violation in a sector with light sterile neutrinos. We point out that, quite generically, electroweak quantum corrections transfer the information of superluminal neutrino properties into Lorentz violations in the electron and muon sector, in apparent conflict with experimental data.     

A hollow cathode for high-resolution optogalvanic spectroscopy: Application to uranium

Summary We report the design criteria and performance characteristics of a hollow-cathode tube developed especially for high-resolution Doppler-free laser spectroscopy. It is simple to construct and is easily demountable. Narrow homogeneous line widths of refractory and highly reactive-element transitions have been observed by applying intermodulated detection scheme. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Heterodyne of optically pumped fir molecular lasers and direct frequency measurement of new lines

Direct frequency measurements of optically pumped far infrared (fir) molecular lasers are reported, also for new lines. This heterodyne technique is versatile and simple. By controlling some parameters of resonator and pump source, possible causes of error are evidenced in the precise frequency determination. The implications for molecular spectroscopy are also discussed.     

A new efficient far-infrared optically pumped laser gas: CH3 18OH

The¹²CH₃ ¹⁸OH molecule has been investigated for new far-infrared laser lines by optically pumping it with a cw waveguide CO₂ laser. The larger tunability (318 MHz) with respect to a conventional CO₂ laser permits the pumping of many¹²CH₃ ¹⁸OH lines. As a consequence 100 new laser lines have been discovered, ranging from 34.6 m to 653.2 m in wavelength. The infrared spectrum of¹²CH₃ ¹⁸OH has been observed and all the fundamental vibration energies measured.