Interaction-induced localization of anomalously-diffracting nonlinear waves

We study experimentally the interactions between normal solitons and tilted beams in glass waveguide arrays. We find that as a tilted beam, traversing away from a normally propagating soliton, coincides with the self-defocusing regime of the array, it can be refocused and routed back into any of the intermediate sites due to the interaction, as a function of the initial phase difference. Numerically, distinct parameter regimes exhibiting this behavior of the interaction are identified.Comment: Physical Review Letters, in pres

Wave instabilities in the presence of non vanishing background in nonlinear Schrodinger systems

We investigate wave collapse ruled by the generalized nonlinear Schroedinger (NLS) equation in 1+1 dimensions, for localized excitations with non-zero background, establishing through virial identities a new criterion for blow-up. When collapse is arrested, a semiclassical approach allows us to show that the system can favor the formation of dispersive shock waves. The general findings are illustrated with a model of interest to both classical and quantum physics (cubic-quintic NLS equation), demonstrating a radically novel scenario of instability, where solitons identify a marginal condition between blow-up and occurrence of shock waves, triggered by arbitrarily small mass perturbations of different sign

HAIL DAMAGE TO WHITE PINE AND OTHER TREES

A hailstorm which occurred in an accessible forested area on June 25, 1954, was studied for its immediate and subsequent effects upon trees growing in the area. Considerable mortality of branch extremities and severe stem and branch lesions occurred initially on these trees. Height and diameter measurements taken in 1955 and again in 1959 revealed a slight reduction in growth of white pine trees in the hail zone when compared to the growth of non-affected trees. Several fungi which were encountered in stems and branches of various tree species apparently gained entrance to the trees via the primary hail lesions. With healing of the wounds, it was noted that little or no further development took place in underlying stained pockets of wood. In addition, many of these discolored pockets buried beneath healed lesions were found to be sterile. There appeared to be few, if any, permanent effects on trees originally wounded during a violent hailstorm. </jats:p

THE EFFECT OF ARTIFICIAL DEFOLIATION OF VARIOUS AGES OF LEAVES UPON WHITE PINE GROWTH

Foliage injuries produced by disease-causing organisms or adverse environmental influences may be confined to leaves of a specific age occurring among the "perennial" foliage of coniferous trees. Inadequate information exists concerning the effectiveness of leaves of different ages in promoting the growth of forest trees. An experiment was conducted to assess the effects of artificial removal of foliage of different ages from white pine trees upon height and diameter growth, subsequent axial development and foliage vigor. Although the observations show that all three ages of foliage are utilized in the growth of white pine, it is indicated that during the growing season the one-year-old foliage may be more important than the two-year-old foliage or foliage produced during the current year. </jats:p

LOCOMOTIVE SMOKE DAMAGE TO JACK PINE

Soot-laden smoke emanating from a railroad roundhouse suppressed the growth of jack pine trees (Pinus banksiana Lamb.) located in the immediate vicinity. A close correlation was found to exist between the annual wood increment of these trees and the numbers of steam engines serviced in the roundhouse each year. </jats:p

SULPHUR DIOXIDE INJURY TO TREES IN THE VICINITY OF PETROLEUM REFINERIES

Damaging concentrations of atmospheric sulphur dioxide have, under favorable environmental conditions, caused severe injury to susceptible trees growing in the vicinity of petroleum refineries located at Clarkson, Ontario and East St. Paul, Manitoba. The damage is described and the factors contributing to recent injury are discussed. Recommendations for correlating tree damage with sulphur dioxide emanations from refineries and for preventing recurrent damages are made. </jats:p