Supercontinuum generation by nanosecond dual-wavelength pumping in microstructured optical fibers.

We study experimentally the spectral evolution of supercontinua in two different microstructured fibers that are pumped with nanosecond pulses from dual-wavelength sources of either 1064/532 nm or 946/473 nm output. The experimental findings are compared with simulations based on numerically solving the nonlinear Schrödinger equation. The role of cascaded cross-phase modulation processes and the group-delay properties of the fiber are emphasized and demonstrated to determine the extent of the broadening of the continua to the visible wavelengths.

Periodically poled BaMgF(4) for ultraviolet frequency generation.

Ferroelectric domain inversion has been demonstrated in BaMgF(4) . Transparency has been measured to <140nm, and no change in transmission was measured under 157-nm irradiation for >1.1x10(9) shots at 2mJ/cm(2) per pulse. First-order quasi-phase-matched generation of 157 nm is predicted by use of grating periods as long as 1.5mum. This material should permit shorter-wavelength chi((2)) frequency-mixing processes than with any other crystalline material.

Pressure effects on the proximal heme pocket in myoglobin probed by Raman and near-infrared absorption spectroscopy.

The influence of high pressure on the heme protein conformation of myoglobin in different ligation states is studied using Raman spectroscopy over the temperature range from 30 to 295 K. Photostationary experiments monitoring the oxidation state marker bands demonstrate the change of rebinding rate with pressure. While frequency changes of vibrational modes associated with rigid bonds of the porphyrin ring are <1 cm(-1), we investigate a significant shift of the iron-histidine mode to higher frequency with increasing pressure (approximately 3 cm(-1) for deltaP = 190 MPa in Mb). The observed frequency shift is interpreted structurally as a conformational change affecting the tilt angle between the heme plane and the proximal histidine and the out-of-plane iron position. Independent evidence for iron motion comes from measurements of the redshift of band III in the near-infrared with pressure. This suggests that at high pressure the proximal heme pocket and the protein are altered toward the bound state conformation, which contributes to the rate increase for CO binding. Raman spectra of Mb and photodissociated MbCO measured at low temperature and variable pressure further support changes in protein conformation and are consistent with glasslike properties of myoglobin below 160 K.

Dinucleotide repeats in the human surfactant protein-B gene and respiratory-distress syndrome.

Pulmonary surfactant, a lipoprotein complex, is essential for normal lung function, and deficiency of surfactant can result in respiratory-distress syndrome (RDS) in the prematurely born infant. Some studies have pointed towards a genetic contribution to the aetiology of RDS. Because the surfactant protein B (SP-B) is important for optimal surfactant function and because it is involved in the pathogenesis of pulmonary disease, we investigated the genetic variability of the SP-B gene in individuals with and without RDS. We identified a 2.5 kb BamHI polymorphism and studied its location, nature and frequency. We localized this polymorphism in the first half of intron 4 and found that it is derived by gain or loss in the number of copies of a motif that consists of two elements, a 20 bp conserved sequence and a variable number of CA dinucleotides. Variability in the number of motifs resulting from either deletion (in 55.3% of the cases with the variation) or insertion (44.7%) of motifs was observed in genomic DNAs from unrelated individuals. Analysis of 219 genomic DNAs from infants with (n = 82) and without (n = 137) RDS showed that this insertion/deletion appears with significantly higher frequency in the RDS population (29.3 as against 16.8%, P < 0.05).