Non-equilibrium dynamics in the dual-wavelength operation of Vertical external-cavity surface-emitting lasers

Microscopic many-body theory coupled to Maxwell's equation is used to investigate dual-wavelength operation in vertical external-cavity surface-emitting lasers. The intrinsically dynamic nature of coexisting emission wavelengths in semiconductor lasers is associated with characteristic non-equilibrium carrier dynamics which causes significant deformations of the quasi-equilibrium gain and carrier inversion. Extended numerical simulations are employed to efficiently investigate the parameter space to identify the regime for two-wavelength operation. Using a frequency selective intracavity etalon, two families of modes are stabilized with dynamical interchange of the strongest emission peaks. For this operation mode, anti-correlated intensity noise is observed in agreement with the experiment. A method using effective frequency selective filtering is suggested for stabilization genuine dual-wavelength output.Comment: 15 pages, 7 figure

Mode-locking in vertical external-cavity surface-emitting lasers with type-II quantum-well configurations

A microscopic study of mode-locked pulse generation is presented for vertical external-cavity surface-emitting lasers utilizing type-II quantum well configurations. The coupled Maxwell semiconductor Bloch equations are solved numerically where the type-II carrier replenishment is modeled via suitably chosen reservoirs. Conditions for stable mode-locked pulses are identified allowing for pulses in the \unit[100]{fs} range. Design strategies for type-II configurations are proposed that avoid potentially unstable pulse dynamics.Comment: Main paper with supplementary material

'Going green'?: The limitations of behaviour change programmes as a policy response to escalating resource consumption

This paper contributes to a growing body of literature highlighting the limitations of behaviour change and the emergence of a social practice approach to reframe responses to escalating resource consumption. Drawing insights from interviews with Australian households and workshops with behaviour change practitioners, we demonstrate how the 'Going Green' discourse, which focuses on targeting individuals to participate in 'easy' sustainability actions, overlooks the majority of consumption implicated in everyday practices. This leaves unchallenged the complex ways in which our lives are becoming more resource intensive. We argue for an ontological framing of social change underpinned by theories of social practice. Rather than considering policies, regulations and infrastructures involving urban form, housing, transport and infrastructure provision as 'external factors' separate from behaviour, practice theories accord them integral status in the constitution of social order and change. This represents a more challenging agenda for practitioners and governments in shifting and transforming everyday life

Transitioning to low carbon communities - from behaviour change to systemic change: Lessons from Australia

Transitioning to low carbon communities requires an understanding of community practices and resultant emissions, as well as the technologies, infrastructures and institutions associated with and accessed by communities. Moreover, it requires an understanding of the connections between these integrated system components, its dynamics, a defined transition and potential 'levers' involved in 'transitioning'. This paper accepts the notion that 'levers' include programmes designed to achieve practice or behaviour change in households which result in less carbon intensive lifestyles, and focuses on the factors that shape human behaviour and influence householder energy consumption. Research to date by the authors and others indicates that a comprehensive socio-technical framework that considers both individual psychological factors as well as the systems, standards and norms under which individuals operate is fundamental to the development of successful strategies to shift towards low carbon communities. A database has been compiled of over one hundred local programmes aimed at realising carbon neutral communities across Australia largely through approaches to behaviour change. This paper presents the findings of an analysis of these programmes, particularly with regard to the extent to which they take account of a socio-technical framework or understanding of domestic consumption behaviours and whether they are aware of or aim to influence changing standards and expectations around consumption practices within the home. While a number of exemplary community-based programmes adopt an integrated approach to addressing both technical and behavioural dimensions in the shift to low carbon communities, it was found that most fail to take sufficient account of the systems, standards and norms shaping consumption. Conclusions include directions for policy and programme design based on the study findings

Using decision analysis to evaluate candidate OMPs for the South African west coast rock lobster fishery

Simulation models frequently are used to provide information to assist in decision-making in natural resource management. The sheer volume of information to process can be overwhelming, however, and there is a danger that some management objectives are not adequately considered, because of the difficulties of making decisions when there are multiple, conflicting objectives. Formal decision-analysis methods have been used in conservation biology to choose among simulation model results. This paper suggests that they can also be used in South African fisheries management, where simulation models are used extensively in developing operational management procedures

Analogue Gravity and ultrashort laser pulse filamentation

Ultrashort laser pulse filaments in dispersive nonlinear Kerr media induce a moving refractive index perturbation which modifies the space-time geometry as seen by co-propagating light rays. We study the analogue geometry induced by the filament and show that one of the most evident features of filamentation, namely conical emission, may be precisely reconstructed from the geodesics. We highlight the existence of favorable conditions for the study of analogue black hole kinematics and Hawking type radiation.Comment: 4 pages, revised versio

The great Australian nightmare? The problem of escalating housing aspirations and expectations and adaptation to climate change

The dominant trend in Australian cities towards large, detached, energy intensive dwellings in poorly serviced, low-density, urban fringe locations, leaves governments, households and communities more vulnerable to the impacts of climate change and does little to aid mitigation. Given the multiple and competing objectives of the stakeholders involved, reducing domestic energy consumption is more complex than attempting to change what Shove (2010) refers to as the ABC ('attitudes, behaviours and choices') of individual householders. What is needed is a better understanding of the dynamic and integrated processes resulting in escalating expectations and aspirations for Australian housing. Along this vein, we suggest the 'great Australian dream' is actually becoming a great Australian nightmare. In our critique we investigate what is meant by a 'normal' home and how aspirations and expectations for housing have changed over time. Drawing on theories of social practice we look at what goes on inside homes to explore how everyday practices and the design of houses are mutually constitutive. In our analysis we find that seemingly common-place aspirations for housing are the result of changing practices, such as cooking, eating and entertaining, which are resulting in escalating trajectories of consumption. We conclude by suggesting how policy attention could be refocused on transforming the relationship between house design and everyday practice to address climate change

On the generation and the nonlinear dynamics of X-waves of the Schroedinger equation

The generation of finite energy packets of X-waves is analysed in normally dispersive cubic media by using an X-wave expansion. The 3D nonlinear Schroedinger model is reduced to a 1D equation with anomalous dispersion. Pulse splitting and beam replenishment as observed in experiments with water and Kerr media are explained in terms of a higher order breathing soliton. The results presented also hold in periodic media and Bose-condensed gases.Comment: 18 pages, 6 figures, corrected version to be published in Physical Review

Origin of the approximate universality of distributions in equilibrium correlated systems

We propose an interpretation of previous experimental and numerical experiments, showing that for a large class of systems, distributions of global quantities are similar to a distribution originally obtained for the magnetization in the 2D-XY model . This approach, developed for the Ising model, is based on previous numerical observations. We obtain an effective action using a perturbative method, which successfully describes the order parameter fluctuations near the phase transition. This leads to a direct link between the D-dimensional Ising model and the XY model in the same dimension, which appears to be a generic feature of many equilibrium critical systems and which is at the heart of the above observations.Comment: To appear in Europhysics Letter