Prof Gerd Schröder-Turk - Amorphous ‘signature’ states packing and tessellation models - 2024-05-16

Abstract - The concept of random close packed or maximally random jammed configurations in particles is well established: Granular particles, particularly frictionless spheres, do not manage to attain the crystalline close packed configurations but ‘get stuck’ in this amorphous state. This effect is due to a geometric frustration that the locally densest configuration cannot expand into the globally densest crystalline configuration. 

In this talk, we will look at a broader range of packing or tessellation models and discuss amorphous states similar to what the random close packed is for the packing problem. We will look at tessellations and packing problems defined by optimization with respect to certain properties, such as interface area in the Kelvin problem, packing density in the Kepler problem, or cell centrality as in the Quantizer problem. 

In all known cases, the optimal solutions are crystalline configurations with long range order. Amorphous disordered structures are generally considered to be intermittent metastable states that prevent the system from attaining the optimal ordered structures. To date, no optimization problem has been identified where the groundstate  is a disordered configuration. While we do not find a disordered groundstate, we here show that the use Lloyd’s algorithm as a fast quench generates a very stable universal disordered state in the three-dimensional Quantizer problem, despite the existence of lower-energy crystalline configurations.

We will discuss these states in terms of the degree of density uniformity of the packings and ask the question whether these pertinent disordered states can be used as a signature of the model that defines the tessellation. 

Biography - Prof Gerd Schröder-Turk hold a PhD degree from the Australian National University, for his thesis “Skeletons in the Labyrinth”. 

He has held academic appointments in theoretical physics and applied maths departments at the Australian National University, the Friedrich-Alexander University Erlangen-Nuremberg and Murdoch University. 

He is a Fellow of the American Physical Society and the recipient of the 2014 Emmy-Noether-Prize, the 2019 Camurus Lipid Research Foundation Fellowship award and the 2023 Allan Schoen Award. He is currently a Professor at Murdoch University and an Honorary Associate Professor at the Australian National University. Aside from his teaching and research roles, he takes a keen interest in higher education policy and university governance, and has held roles as Senate member of Murdoch University and in the National Executive of the Australian Institute of Physics. 

A/Prof Anthony Stickland - Solid-liquid Separation of Compressible Suspensions - 2023-10-09 

Abstract: Suspensions of fine and cohesive particles demonstrate pressure dependent rate and extent during solid-liquid separation. This is usually termed ‘compressible’ behaviour. Such suspensions are common across minerals processing, water treatment, and food processing, to name but a few. Unfortunately, traditional theories of sedimentation and filtration assume incompressible behaviour. In contrast, compressional rheology, developed in 1987, is a theoretical framework for compressible suspensions that explicitly incorporates pressure dependent effects. Since 1987, researchers at The University of Melbourne have developed a suite of sedimentation, centrifugation and filtration techniques for extracting locally varying compressibility and permeability. These properties are used in process models of thickeners, filters, and centrifuges, for example, to predict performance and provide insights into process optimisation.


Biography: A/Prof Anthony Stickland is an academic in Chemical Engineering at The University of Melbourne, where he lectures ‘Fluid Mechanics’, ‘Particle Technology’, and ‘Sustainable Minerals and Recycling’.  He is a Chief Investigator in the ARC Centre of Excellence for Enabling Eco-Efficient Mineral Beneficiation and leads the Sludge Group, which undertakes research in particulate suspension rheology and solid-liquid separation. This research covers (1) material characterisation techniques and analysis tools to be able to adequately describe particle and suspension behaviour, (2) models of processes to be able to predict performance for design and optimisation, and (3) development and commercialisation of novel technologies for suspension dewatering and handling. The Sludge Group works closely with industries such as water treatment and minerals processing.

Recording of the seminar here.