Partially incoherent optical vortices in self-focusing nonlinear media

We observe stable propagation of spatially localized single- and double-charge optical vortices in a self-focusing nonlinear medium. The vortices are created by self-trapping of partially incoherent light carrying a phase dislocation, and they are stabilized when the spatial incoherence of light exceeds a certain threshold. We confirm the vortex stabilization effect by numerical simulations and also show that the similar mechanism of stabilization applies to higher-order vortices.     

Induced spatiotemporal modulation instability in a noninstantaneous self-defocusing medium

We demonstrate theoretically and experimentally that induced spatiotemporal modulation instability can exist in a self-defocusing medium if the nonlinearity is noninstantaneous. We predict the growth rate as a function of the spatial and temporal frequencies of the modulation and the response time of the nonlinearity and confirm it by our experiments.     

Chemisorption and decomposition of nitric oxide on ruthenium

Nitric oxide, strongly chemisorbed on ruthenium, is desorbed almost completely as oxygen and nitrogen. Oxygen, nitrogen, and nitric oxide were observed singly on ruthenium with field emission microscopy. Thermal desorption spectroscopy from Ru(101̄0) showed that molecular nitrogen is only physisorbed but nitrogen from NO decomposition is strongly chemisorbed. Nitrogen from NO shows three binding states, the most strongly bound being present to only a small extent. NO shows three and two binding states when adsorbed at 120 K and 295 K respectively. Work function measurements gave Δφ = 1.3 eV for a monolayer of NO. NO is dissociatively adsorbed above 250 K but a lower temperature limit was not established. The decomposition of NO on $\text{Ru}\text{(10}\text{1}\text{0)}$ under high vacuum conditions is catalytic in that no oxides of ruthenium were observed to form in the process.     

Routes to chaos in the Maxwell-Bloch equations

We consider the single-mode Maxwell-Bloch equations describing a Doppler-broadening ring laser. For different parameter ranges this system undergoes period-doubling, intermittency, and two-frequency routes to chaos as a single parameter (e.g., detuning) is varied, as has been observed in recent experiments with He-Ne and He-Xe lasers.     

Relationships between the J-integral and the crack opening displacement for stationary and extending cracks

Relationships between the J-integral and the crack opening displacement δ_t are obtained by exploiting the dominance of the Hutchinson-Rice-Rosengren singularity in the crack-tip region. The coefficient d_n that relates J to δ_t, is dependent on the material deformation properties and is independent of crack configuration under small-scale yielding conditions. For low hardening materials, d_n appears to be configuration dependent in the fully yielded state. Similarly, the slope of the J-resistance curve is relatable to an operationally defined crack opening angle if J-controlled crack growth conditions are met. These relationships are corroborated by finite element results for the complete regime of elastic-plastic deformation and experimental data for A533B steels, HY-80 steels and several other ductile metals.     

Author index for volume 81

Certain types of integral inequalities which were established by LaSalle, Gollwitzer, Langenhop, Bondge, and Pachpatte are reviewed and unified. The bounds provided by these inequalities can be used in the study of the theory of partial differential and integral equations.