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

Short-Term Managerial Contracts Facilitate Cartels

This paper shows how a series of commonly observed short-term CEO employment contracts improves cartel stability compared to a long-term contract. When a manager’s short-term appointment is renewed if and only if the firm hits a certain profit target, then (a) defection from collusion results in superior firm performance and thus reduces the chance of being fired immediately, while (b) future punishment results in inferior firm performance, thereby increasing the chance of being fired in the future. The introduction of this reemployment tradeoff intertwines with the usual monetary tradeoff and weakly improves cartel stability. Studying the impact of fixed versus variable salary components, I find that fixed components facilitate collusion with a short-term contract, while not affecting cartel stability with a long-term contract. I extend the model to argue how short-term renewable contracts are a source of cyclical collusive pricing. Finally, interpreting the results in the light of firm financing shows how debt-financed firms can form more stable cartels than equity-financed firms

Anchor loads in taut moorings: The impact of inverse catenary shakedown

Taut mooring systems have become prospective alternatives for the station keeping of offshore floating facilities in deep water. The associated embedded anchors cause a part of the mooring line to be buried in the seabed − the inverse catenary − which introduces a requirement to predict the load and uplift angle at the padeye, where the chain is connected to the anchor. The padeye load and angle depend on the shape and tension profile of the inverse catenary, which must be assessed in the mooring system design. The dynamic interaction between the embedded chain and the soil in the inverse catenary is not usually considered in this analysis. Instead, the inverse catenary is assessed statically, albeit potentially using cyclically-degraded soil strength parameters. The present study employs the lumped mass method to simulate the dynamic response of mooring lines under different imposed oscillations at the fairlead, where the chain is connected to the floating facility. A new chain-soil interaction model, which includes hysteresis effects associated with irrecoverable relative chain-soil displacement is calibrated by experimental results. Simulations of cyclic vessel motion are then performed, and the resulting chain-seabed interaction is observed. During constant-amplitude vessel motion cycles, the load angle at the padeye significantly decreases due to progressive ratcheting or ‘shakedown’ of the inverse catenary from the initial static profile towards a straighter profile. This effect is due to the hysteretic soil response and creates a less onerous loading condition for the anchor which may be beneficial, but is conventionally overlooked in design. At the end of the present study, an elastic bound method is proposed to estimate the profile of the inverse catenary after shakedown. A parametric study illustrates the performance of this simple method for predicting the steady state condition

Performance of a shallow skirted foundation for TLP mooring in carbonate silt

This paper presents centrifuge test results of the response of a shallow skirted foundation in a normally consolidated fine-grained carbonate silt. The foundation is subjected to monotonic and cyclic loading relevant to mooring of a deep water Tension Leg Platform (TLP). The loading sequences represented a range of mean and cyclic load regimes allowing for the systematic analysis of foundation response rather than a single design case.A theoretical framework to account for the loss of embedment during mobilization including dragdown of the adjacent soil is proposed, as well as consideration of gapping and cyclic strength.</p

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