Perception of global image contrast is predicted by the same spatial integration model of gain control as detection and discrimination

How are the image statistics of global image contrast computed? We answered this by using a contrast-matching task for checkerboard configurations of ‘battenberg’ micro-patterns where the contrasts and spatial spreads of interdigitated pairs of micro-patterns were adjusted independently. Test stimuli were 20 × 20 arrays with various sized cluster widths, matched to standard patterns of uniform contrast. When one of the test patterns contained a pattern with much higher contrast than the other, that determined global pattern contrast, as in a max() operation. Crucially, however, the full matching functions had a curious intermediate region where low contrast additions for one pattern to intermediate contrasts of the other caused a paradoxical reduction in perceived global contrast. None of the following models predicted this: RMS, energy, linear sum, max, Legge and Foley. However, a gain control model incorporating wide-field integration and suppression of nonlinear contrast responses predicted the results with no free parameters. This model was derived from experiments on summation of contrast at threshold, and masking and summation effects in dipper functions. Those experiments were also inconsistent with the failed models above. Thus, we conclude that our contrast gain control model (Meese & Summers, 2007) describes a fundamental operation in human contrast vision.

Strongly localized moving discrete dissipative breather-solitons in Kerr nonlinear media supported by intrinsic gain

We investigate the mobility of nonlinear localized modes in a generalized discrete Ginzburg-Landau-type model, describing a one-dimensional waveguide array in an active Kerr medium with intrinsic, saturable gain and damping. It is shown that exponentially localized, traveling discrete dissipative breather-solitons may exist as stable attractors supported only by intrinsic properties of the medium, i.e., in the absence of any external field or symmetry-breaking perturbations. Through an interplay by the gain and damping effects, the moving soliton may overcome the Peierls-Nabarro barrier, present in the corresponding conservative system, by self-induced time-periodic oscillations of its power (norm) and energy (Hamiltonian), yielding exponential decays to zero with different rates in the forward and backward directions. In certain parameter windows, bistability appears between fast modes with small oscillations and slower, large-oscillation modes. The velocities and the oscillation periods are typically related by lattice commensurability and exhibit period-doubling bifurcations to chaotically "walking" modes under parameter variations. If the model is augmented by intersite Kerr nonlinearity, thereby reducing the Peierls-Nabarro barrier of the conservative system, the existence regime for moving solitons increases considerably, and a richer scenario appears including Hopf bifurcations to incommensurately moving solutions and phase-locking intervals. Stable moving breathers also survive in the presence of weak disorder. © 2014 American Physical Society.

Gain bandwidth optimisation and enhancement in ultra-long Raman fibre laser based amplifiers

We show experimentally a 57nm gain bandwidth for an ultra-long Raman fiber laser based amplification technique using only a single pump wavelength. The enhanced gain bandwidth and gain flatness is investigated for single and multi-cavity designs. ©2010 IEEE.

Frontline employees’ innovative service behavior as key to customer loyalty:insights into FLEs’ resource gain spiral

Many service firms require frontline service employees (FLEs) to follow routines and standardized operating procedures during the service encounter, to deliver consistently high service standards. However, to create superior, pleasurable experiences for customers, featuring both helpful services and novel approaches to meeting their needs, firms in various sectors also have begun to encourage FLEs to engage in more innovative service behaviors. This study therefore investigates a new and complementary route to customer loyalty, beyond the conventional service-profit chain, that moves through FLEs' innovative service behavior. Drawing on conservation of resources (COR) theory, this study introduces a resource gain spiral at the service encounter, which runs from FLEs' emotional job engagement to innovative service behavior, and then leads to customer delight and finally customer loyalty. In accordance with COR theory, the proposed model also includes factors that might hinder (customer aggression, underemployment) or foster (colleague support, supervisor support) FLEs' resource gain spiral. A multilevel analysis of a large-scale, dyadic data set that contains responses from both FLEs and customers in multiple industries strongly supports the proposed resource gain spiral as a complementary route to customer loyalty. The positive emotional job engagement-innovative service behavior relationship is undermined by customer aggression and underemployment, as hypothesized. Surprisingly though, and contrary to the hypotheses, colleague and supervisor support do not seem to foster FLEs' resource gain spiral. Instead, colleague support weakens the engagement-innovative service behavior relationship, and supervisor support does not affect it. These results indicate that if FLEs can solicit resources from other sources, they may not need to invest as many of their individual resources. In particular, colleague support even appears to serve as a substitute for FLEs' individual resource investments in the resource gain spiral.

Modulating membership grades to gain consensus for fuzzy set uncertainty values in a clinical decision support system

This paper deals with a very important issue in any knowledge engineering discipline: the accurate representation and modelling of real life data and its processing by human experts. The work is applied to the GRiST Mental Health Risk Screening Tool for assessing risks associated with mental-health problems. The complexity of risk data and the wide variations in clinicians' expert opinions make it difficult to elicit representations of uncertainty that are an accurate and meaningful consensus. It requires integrating each expert's estimation of a continuous distribution of uncertainty across a range of values. This paper describes an algorithm that generates a consensual distribution at the same time as measuring the consistency of inputs. Hence it provides a measure of the confidence in the particular data item's risk contribution at the input stage and can help give an indication of the quality of subsequent risk predictions. © 2010 IEEE.

Dark soliton generation from semiconductor optical amplifier gain medium in ring fiber configuration

We have investigated the mode-lock operation from a semiconductor optical amplifier (SOA) gain chip in the ring fibre configuration. At lower pump currents, the laser generates dark soliton pulses both at the fundamental repetition rate of 39 MHz and supports up to the 6th harmonic order corresponding to 234-MHz repetition rate with an output power of ∼2.1 mW. At higher pump currents, the laser can be switched between the bright, dark and concurrent bright and dark soliton generation regimes.