Manipulation and removal of defects in spontaneous optical patterns

Defects play an important role in a number of fields dealing with ordered structures. They are often described in terms of their topology, mutual interaction and their statistical characteristics. We demonstrate theoretically and experimentally the possibility of an active manipulation and removal of defects. We focus on the spontaneous formation of two-dimensional spatial structures in a nonlinear optical system, a liquid crystal light valve under single optical feedback. With increasing distance from threshold, the spontaneously formed hexagonal pattern becomes disordered and contains several defects. A scheme based on Fourier filtering allows us to remove defects and to restore spatial order. Starting without control, the controlled area is progressively expanded, such that defects are swept out of the active area.Comment: 4 pages, 4 figure

Spatial correlations in hexagons generated via a Kerr nonlinearity

We consider the hexagonal pattern forming in the cross-section of an optical beam produced by a Kerr cavity, and we study the quantum correlations characterizing this structure. By using arguments related to the symmetry broken by the pattern formation, we identify a complete scenario of six-mode entanglement. Five independent phase quadratures combinations, connecting the hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of a non-linear quantum calculation technique, quantum correlations among the mode photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure

Geotechnical design and construction aspects of a pipeline-escarpment crossing

This paper describes geotechnical design and construction aspects of a large diameter pipeline which traverses a steep and tall escarpment in deep water on its route to shore from a hydrocarbon field offshore of Australia. Key geotechnical challenges of this crossing, which are discussed in this paper include (i) pipeline route selection, (ii) calcareous seabed conditions, (iii) deep-water earthworks necessary to profile the escarpment, (iv) overall stability assessment, and (v) evaluation of necessary pipe-soil interaction parameters in relation to pipeline performance when subject to imposed metocean and product-slugging loads. These data were also used to determine appropriate construction methods, earthworks profiling and to assess pipeline fatigue life at the crossing. Insights from escarpment profiling and pipeline installation are also presented.</p