MRC Laboratory of Molecular Biology
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Shaping of melting and dissolving solids under natural convection
No full textHow quickly does an ice cube melt or a lump of sugar dissolve? We address the open problem of the shapes of solids left to melt or dissolve in an ambient fluid driven by stable natural convection. The theory forms a convective form of a Stefan problem in which the evolution is controlled by a two-way coupling between the shape of the body and stable convection along its surface. We develop a new model describing the evolution of such bodies in two-dimensional or axisymmetric geometries and analyse it using a combination of numerical and analytical methods. Different initial conditions are found to lead to different fundamental shapes and descent rates. For the cases of initially linear surfaces (wedges or cones), the model admits similarity solutions in which the tip descends from its initial position as, where t is time. It is determined that the evolving shape always forms a parabola sufficiently near the tip. For steeply inclined bodies, we establish a general two-tiered asymptotic structure comprising a broad -power intermediate near-tip region connected to a deeper parabolic region at the finest scale. The model results apply universally for any given relationship between density, viscosity, diffusivity and concentration, including two-component convection. New laboratory experiments involving the dissolution of cones of sugar candy in water are found to collapse systematically onto our theoretically predicted shapes and descent rates with no adjustable parameters
Exploring the impacts and contributions of maintenance function for sustainable manufacturing
No full textThis investigation studies advanced practitioners of maintenance management and seeks to uncover the related impacts and contributions of best practice maintenance toward sustainable manufacturing operations. This exploratory research conducted a novel empirical analysis focused on maintenance functions in nine manufacturing companies from diverse sectors. The analysis uncovered insights related to the economic, environmental, and social benefits of deeper involvement of maintenance function in plant operations and decision-making. We observed links of maintenance function with product competitiveness and with energy management activities that were unexpected. We confirmed benefits from keeping machinery in good working conditions and restoring promptly good working conditions when an issue happens. The depth of maintenance contribution on each area identified in this study will depend on the operational and business context of the manufacturing company; thus, companies need to reflect on these based on their specific processes, business needs and goals. Ultimately, this work can inspire managers in manufacturing companies to organise maintenance functions strategically toward fostering long-term competitive, responsible and sustainable performance
Automatically designing the behaviours of falling paper: The emergence of non-trivial behaviours via interaction with the physical world
No full textBiological systems exhibit extraordinary levels of diversity. Embodied behaviours are the emergent property of many loosely-coupled parallel processes, from the microscopic level, e.g. materials, to more abstracted levels, e.g. organs and limbs. We summarise our investigations into using a synthetic methodology, i.e. an understanding-by-building approach, for designing the complex interactions of falling paper shapes. By studying how simple systems such as a falling paper shape behave, we can analyse the specific characteristics of the interaction between morphology and the environment, and how this leads to programmable non-trivial behaviours. We present current results and discuss the implications on the future of design in robotics
Stress inhomogeneity effect on fluid-induced fracture behavior into weakly consolidated granular systems
No full textWe study the effect of stress inhomogeneity on the behavior of fluid-driven fracture development in weakly consolidated granular systems. Using numerical models we investigate the change in fracture growth rate and fracture pattern structure in unconsolidated granular packs (also referred to as soft-sands) as a function of the change in the confining stresses applied to the system. Soft-sands do not usually behave like brittle, linear elastic materials, and as a consequence, poroelastic models are often not applicable to describe their behavior. By making a distinction between "cohesive"and "compressive"grain-grain contact forces depending on their magnitude, we propose an expression that describes the fluid opening pressure as a function of the mean value and the standard deviation of the "compressive stress"distribution. We also show that the standard deviation of this distribution can be related with the extent to which fracture "branches"reach into the material
A tool for analysis and synthesis of heterogeneous multi-agent systems under rank-deficient coupling
No full textThe Authors The behavior of heterogeneous multi-agent systems is studied when the coupling matrices are possibly all different and/or singular, that is, its rank is less than the system dimension. Rank-deficient coupling allows exchange of limited state information, which is suitable for the study of multi-agent systems under output coupling. We present a coordinate change that transforms the heterogeneous multi-agent system into a singularly perturbed form. The slow dynamics is still a reduced-order multi-agent system consisting of a weighted average of the vector fields of all agents, and some sub-dynamics of agents. The weighted average is an emergent dynamics, which we call a blended dynamics. By analyzing or synthesizing the blended dynamics, one can predict or design the behavior of a heterogeneous multi-agent system when the coupling gain is sufficiently large. For this result, stability of the blended dynamics is required. Since stability of the individual agent is not asked, the stability of the blended dynamics is the outcome of trading off the stability among the agents. It can be seen that, under the stability of the blended dynamics, the initial conditions of the individual agents are forgotten as time goes on, and thus, the behavior of the synthesized multi-agent system is initialization-free and is suitable for plug-and-play operation. As a showcase, we apply the proposed tool to four application problems; distributed state estimation for linear systems, practical synchronization of heterogeneous van der Pol oscillators, estimation of the number of nodes in a network, and a problem of distributed optimization
Extreme values in optical fiber communication systems
No full textExtreme value theory provides a framework to assess rare but extreme events such as network outages or cycle slips. We present the theory of extreme value statistics and its application to optical fiber communication systems
Long-Range Propagation and Interference of d -Wave Superconducting Pairs in Graphene
No full textRecent experiments have shown that proximity with high-temperature superconductors induces unconventional superconducting correlations in graphene. Here, we demonstrate that those correlations propagate hundreds of nanometers, allowing for the unique observation of d-wave Andreev-pair interferences in YBa2Cu3O7-graphene devices that behave as a Fabry-Perot cavity. The interferences show as a series of pronounced conductance oscillations analogous to those originally predicted by de Gennes-Saint-James for conventional metal-superconductor junctions. The present demonstration is pivotal to the study of exotic directional effects expected for nodal superconductivity in Dirac materials
Serine-Selective Bioconjugation
No full textThis Communication reports the first general method for rapid, chemoselective, and modular functionalization of serine residues in native polypeptides, which uses a reagent platform based on the P(V) oxidation state. This redox-economical approach can be used to append nearly any kind of cargo onto serine, generating a stable, benign, and hydrophilic phosphorothioate linkage. The method tolerates all other known nucleophilic functional groups of naturally occurring proteinogenic amino acids. A variety of applications can be envisaged by this expansion of the toolbox of site-selective bioconjugation methods
Suction cup based on particle jamming and its performance comparison in various fruit handling tasks
No full textSuction cups are widely used in pick and place tasks in well-structured and controlled environments with low variance in task requirements. For tasks requiring higher demands and variations, such as quality control of citrus fruits, commercial suction cups do not have the required reliability. The design and performance of a novel suction cup based on particle jamming is presented in this paper. Particle jamming allows operation in two states, a malleable state to adapt to large irregularities in object surfaces, and a stiff state to rigidly hold the object for manipulation and prevent the cup collapsing in on itself. This jamming cup is shown to successfully adapt to surfaces with up to 7 times variations compared to standard suction cups. Additionally, for similar scale cups, the holding force is comparable and has <50% deviation
Novel digital and analogue hybrid radio over fibre system for distributed antenna system (DAS) fronthaul applications
No full textA hybrid digital and analogue radio over fibre (RoF) architecture carrying WCDMA and LTE services with data compression at the digital path is demonstrated. Over 40dB dynamic range is achieved for both services