Finding Transition Pathways on Manifolds

We consider noise-induced transition paths in randomly perturbed dynami- cal systems on a smooth manifold. The classical Freidlin-Wentzell large devia- tion theory in Euclidean spaces is generalized and new forms of action functionals are derived in the spaces of functions and the space of curves to accommodate the intrinsic constraints associated with the manifold. Numerical meth- ods are proposed to compute the minimum action paths for the systems with constraints. The examples of conformational transition paths for a single and double rod molecules arising in polymer science are numerically investigated

Precision shooting: Sampling long transition pathways

The kinetics of collective rearrangements in solution, such as protein folding and nanocrystal phase transitions, often involve free energy barriers that are both long and rough. Applying methods of transition path sampling to harvest simulated trajectories that exemplify such processes is typically made difficult by a very low acceptance rate for newly generated trajectories. We address this problem by introducing a new generation algorithm based on the linear short-time behavior of small disturbances in phase space. Using this ``precision shooting'' technique, arbitrarily small disturbances can be propagated in time, and any desired acceptance ratio of shooting moves can be obtained. We demonstrate the method for a simple but computationally problematic isomerization process in a dense liquid of soft spheres. We also discuss its applicability to barrier crossing events involving metastable intermediate states.Comment: 9 pages, 12 figures, submitted to J. Chem. Phy

Creep dynamics of elastic manifolds via exact transition pathways

We study the steady state of driven elastic strings in disordered media below the depinning threshold. In the low-temperature limit, for a fixed sample, the steady state is dominated by a single configuration, which we determine exactly from the transition pathways between metastable states. We obtain the dynamical phase diagram in this limit. At variance with a thermodynamic phase transition, the depinning transition is not associated with a divergent length scale of the steady state below threshold, but only of the transient dynamics. We discuss the distribution of barrier heights, and check the validity of the dynamic phase diagram at small but finite temperatures using Langevin simulations. The phase diagram continues to hold for broken statistical tilt symmetry. We point out the relevance of our results for experiments of creep motion in elastic interfaces.Comment: 14 pages, 18 figure

Distributing Power: A transition to a civic energy future

There is growing interest, from a range of stakeholders, in the potential of distributed low-carbon electricity generation in delivering a low-carbon energy system. Yet there are still significant gaps in understanding, particularly regarding the feasibility of scaling up distributed generation from technological, governance, regulation, policy, and financial perspectives. The aim of this report is to address these gaps within the context of the Thousand Flowers pathway

Alternative education and transition pathways for early school-leavers

This study examined the tangible and intangible 12 month outcomes achieved by disadvantaged young people participating in an alternative learning program in regional Australia. It combined desk research, qualitative interviews and psychosocial measures to assess the program’s effectiveness. The report shares these findings along-with nine key enabling factors contributing to the program’s evidenced success. Learnings warrant consideration from policy-makers and others involved in the design and/or delivery of re-engagement programs for early school leavers.&nbsp

Spontaneous-emission suppression via multiphoton quantum interference

The spontaneous emission is investigated for an effective atomic two-level system in an intense coherent field with frequency lower than the vacuum-induced decay width. As this additional low-frequency field is assumed to be intense, multiphoton processes may be induced, which can be seen as alternative transition pathways in addition to the simple spontaneous decay. The interplay of the various interfering transition pathways influences the decay dynamics of the two-level system and may be used to slow down the spontaneous decay considerably. We derive from first principles an expression for the Hamiltonian including up to three-photon processes. This Hamiltonian is then applied to a quantum mechanical simulation of the decay dynamics of the two-level system. Finally, we discuss numerical results of this simulation based on a rubidium atom and show that the spontaneous emission in this system may be suppressed substantially.Comment: 18 pages, 7 figures, latest version with minor change

Zero Emission Vessels transition pathways

The reports seeks to understand the milestones and enablers over the required timeframe to create the necessary conditions for the evolution of different pathways towards decarbonisation. It considers how cost, operating profile and policy measures could influence this and identifies milestones over time with regards to the safety, technical, social, economic and environmental aspects of the potential zero-emission vessels (ZEVs) and the associated supply of the zero-carbon fuel options