Category Archives: MyResearch

Size matters

3 Replies

Most of us have a sub-conscious understanding of the forces that control the interaction of objects in the size scale in which we exist, i.e. from millimetres through to metres.  In this size scale gravitational and inertial forces dominate the interactions of bodies.  However, at the size scale that we cannot see, even when we use an optical microscope, the forces that the dominate the behaviour of objects interacting with one another are different.  There was a hint of this change in behaviour observed in our studies of the diffusion of nanoparticles [see ‘Slow moving nanoparticles‘ on December 13th, 2017], when we found that the movement of nanoparticles less than 100 nanometres in diameter was independent of their size.  Last month we published another article in one of the Nature journals, Scientific Reports, on ‘The influence of inter-particle forces on diffusion at the nanoscale‘, in which we have demonstrated by experiment that Van der Waals forces and electrostatic forces are the dominant forces at the nanoscale.  These forces control the diffusion of nanoparticles as well as surface adhesion, friction and colloid stability.  This finding is significant because the ionic strength of the medium in which the particles are moving will influence the strength of these forces and hence the behaviour of the nanopartices.  Since biological fluids contain ions, this will be important in understanding and predicting the behaviour of nanoparticles in biological applications where they might be used for drug delivery, or have a toxicological impact, depending on their composition.

Van der Waals forces are weak attractive forces between uncharged molecules that are distance dependent.  They are named after a Dutch physicist, Johannes Diderik van der Waals (1837-1923).  Electrostatic forces occur between charged particles or molecules and are usually repulsive with the result that van der Waals and electrostatic forces can balance each other, or not depending on the circumstances.

Sources:

Giorgi F, Coglitore D, Curran JM, Gilliland D, Macko P, Whelan M, Worth A & Patterson EA, The influence of inter-particle forces on diffusion at the nanoscale, Scientific Reports, 9:12689, 2019.

Coglitore D, Edwardson SP, Macko P, Patterson EA, Whelan MP, Transition from fractional to classical Stokes-Einstein behaviour in simple fluids, Royal Society Open Science, 4:170507, 2017. doi: 10.1098/rsos.170507.

Patterson EA & Whelan MP, Tracking nanoparticles in an optical microscope using caustics. Nanotechnology, 19 (10): 105502, 2009.

Image: from Giorgi et al 2019, figure 1 showing a photograph of a caustic (top) generated by a 50 nm gold nanoparticle in water taken with the optical microscope adjusted for Kohler illumination and closing the condenser field aperture to its minimum following method of Patterson and Whelan with its 2d random walk over a period of 3 seconds superimposed and a plot of the same walk (bottom).

Thought leadership in fusion engineering

3 Replies

The harnessing of fusion energy has become something of a holy grail – sought after by many without much apparent progress.  It is the energy process that ‘powers’ the stars and if we could reproduce it on earth in a controlled environment then it would offer almost unlimited energy with very low environmental costs.  However, understanding the science is an enormous challenge and the engineering task to design, build and operate a fusion-fuelled power station is even greater.  The engineering difficulties originate from the combination of two factors: the emergent behaviour present in the complex system and that it has never been done before.  Engineering has achieved lots of firsts but usually through incremental development; however, with fusion energy it would appear that it will only work when all of the required conditions are present.  In other words, incremental development is not viable and we need everything ready before flicking the switch.  Not surprisingly, engineers are cautious about flicking switches when they are not sure what will happen.  Yet, the potential benefits of getting it right are huge; so, we would really like to do it.  Hence, the holy grail status: much sought after and offering infinite abundance.

Last week I joined the search, or at least offered guidance to those searching, by publishing an article in Royal Society Open Science on ‘An integrated digital framework for the design, build and operation of fusion power plants‘.  Working with colleagues at the Culham Centre for Fusion Energy, Richard Taylor and I have taken our earlier work on an integrated nuclear digital environment for the nuclear energy using fission [see ‘Enabling or disruptive technology for nuclear engineering?‘ on january 28th, 2015] and combined it with the hierarchical pyramid of testing and simulation used in the aerospace industry [see ‘Hierarchical modelling in engineering and biology‘ on March 14th, 2018] to create a framework that can be used to guide the exploration of large design domains using computational models within a distributed and collaborative community of engineers and scientists.  We hope it will shorten development times, reduce design and build costs, and improve credibility, operability, reliability and safety.  It is a long list of potential benefits for a relatively simple idea in a relatively short paper (only 12 pages).  Follow the link to find out more – it is an open access paper, so it’s free.

References

Patterson EA, Taylor RJ & Bankhead M, A framework for an integrated nuclear digital environment, Progress in Nuclear Energy, 87:97-103, 2016.

Patterson EA, Purdie S, Taylor RJ & Waldon C, An integrated digital framework for the design, build and operation of fusion power plants, Royal Society Open Science, 6(10):181847, 2019.

On the trustworthiness of multi-physics models

Leave a reply

I stayed in Sheffield city centre a few weeks ago and walked past the standard measures in the photograph on my way to speak at a workshop.  In the past, when the cutlery and tool-making industry in Sheffield was focussed around small workshops, or little mesters, as they were known, these standards would have been used to check the tools being manufactured.  A few hundred years later, the range of standards in existence has extended far beyond the weights and measures where it started, and now includes standards for processes and artefacts as well as for measurements.  The process of validating computational models of engineering infrastructure is moving slowly towards establishing an internationally recognised standard [see two of my earliest posts: ‘Model validation‘ on September 18th, 2012 and ‘Setting standards‘ on January 29th, 2014].  We have guidelines that recommend approaches for different parts of the validation process [see ‘Setting standards‘ on January 29th, 2014]; however, many types of computational model present significant challenges when establishing their reliability [see ‘Spatial-temporal models of protein structures‘ on March 27th, 2019].  Under the auspices of the MOTIVATE project, we are gathering experts in Zurich on November 5th, 2019 to discuss the challenges of validating multi-physics models, establishing credibility and the future use of data from experiments.  It is the fourth in a series of workshops held previously in Shanghai, London and Munich.  For more information and to register follow this link. Come and join our discussions in one of my favourite cities where we will be following ‘In Einstein’s footprints‘ [posted on February 27th, 2019].

The MOTIVATE project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 754660.

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

When an upgrade is downgrading

5 Replies

I had slightly surreal time last week.  I visited the USA to attend a review of a research programme sponsored by the US Government and reported on two of our research projects.  When I arrived in the USA on Monday evening, I went to collect my rental car and was told that I had been upgraded to a pick-up truck because the rental company did not have left any of the compact cars that had been booked for me.  I gingerly manoeuvred the massive vehicle, a Toyota Tacoma, out of the parking garage and on to the freeway.  I should admit to having owned a large SUV when we lived in the USA and so driving along the freeway was not a totally new experience, except that the white bonnet in front of me seemed huge.

The following morning, I drove to the location of the review and strategically selected a parking space with empty spaces all around it so that I could drive through into the space and avoid needing to reverse the behemoth.  As I was walking across the parking lot, someone accosted me and said: ‘Nice truck, how do you like it?’  Embarrassed at driving such an environmental-unfriendly vehicle, I responded that it was a rental car that I just picked up.  To which he replied that the best protection against my Tacoma, was his Tacoma. And, that it was his dream car.  Then, I noticed that he had parked his black one alongside mine.

Our children learnt to drive in our ancient Ford Explorer and loved it.  We all knew that it was wrong to drive something that consumed fuel so voraciously even if it did get us effortlessly through the most horrendous winter storms.  However, we have left all that behind and now either use public transport or drive cars that achieve 60 mpg or more on good days. But here I was being admitted to a club that worshipped their pick-up trucks.

We walked together into the review which was held in a small lecture theatre equipped with comfortable armchairs, which was just as well because we sat there from 8.30 to 4.30 for two days listening to half-hour presentations with only short breaks.  We were presented with some stunning research based on brilliant innovative thinking, such as materials that can undergo 90% deformation and fully recover their shape and how the rippling motion of covert feathers on a bird’s wings could help us design more efficient aeroplanes.  More on that in later posts.  Of course, there were some less good presentations that had many us reaching for our mobile phones to catch up on the endless flow of email [see: ‘Compelling Presentations‘ on March 21st, 2018).  At the end of each day, we dispersed to different hotels scattered across town in our rental cars.  On Thursday, I drove back to the airport and topped up the fuel tank before returning my truck.  I worked out that it had achieved only 19 mpg (US) or 23 mpg (UK), despite my gentle driving – that’s almost three times the consumption of my own car!  On the plane home I started reading ‘Overstory‘ by Richard Powers, a novel about our relationship to trees and the damage we are doing to the environment on which trees, and us, are dependent.