School of Physics and Astronomy

The School of Physics & Astronomy had a particularly strong line-up of speakers in this year's Orkney Science Festival, contributing to its outstanding public engagement record.

Peter Higgs' appearance attracted great interest and as expected "Peter Higgs in Conversation" at the Kirkwall Arts Theatre was a complete sell-out. His conversations with fellow particle physicist and science writer Frank Close were followed by the presentation "From Maxwell to Higgs - and Beyond?" by Alan Walker and Victoria Martin. Clive Greated's presentation "Sounds Around Us" at Pier Arts Centre in Stromness was also a sell-out. 

The Particle Physics For Scottish Schools Exhibition (PP4SS) was present throughout the Festival, reaching a total audience of over 2000. 

Physical Review Letters has published a paper on turbulence by PhD student Moritz Linkmann and Alexander Morozov, both of the School of Physics & Astronomy.

Paper summary

Chaotic flows of liquids or gases far away from any boundary, like many atmospheric and oceanic flows, are often viewed by scientists as real-life realisations of the so-called forced isotropic turbulence - a classical idealised description of turbulent motion that dates back to the beginning of the 20th century. In this framework turbulence is driven by a vigorous large-scale stirring and was thought to be featureless at smaller scales: if one would look at the flow through a magnifying glass, one should see the same picture independent of the degree of magnification. This is in contrast with turbulence between boundaries, like flow in a pipe, where recent research showed that the flow is organised by spatially regular, unstable structures. 

Surprisingly, computer simulations performed in the Letter suggest that forced isotropic turbulence is not featureless and is much more similar to wall-bounded flows than was thought previously. We demonstrate that at moderate Reynolds number isotropic turbulence is always metastable and the probability of its sudden disappearance obeys an exponential law, previously found in experiments and simulations on pipe flows. 

The similarities between the two systems suggest a universal scenario in which turbulence is always organized around unstable, spatially regular structures. 

"It was very interesting to find that isotropic turbulence, which is an idealised system that allows the study of fundamental turbulent dynamics without having to consider external influences such as the geometry (and walls) of a container, is connected to real-world flows such as flow through a pipe." Moritz Linkmann, PhD student, School of Physics & Astronomy​

Below, Moritz Linkmann explains the research behind the paper.

Dynamical systems and the transition to turbulence in parallel shear flows

In parallel wall-bounded shear flows (such as flow through a pipe or counter-rotating cylinders) the transition to turbulence does not occur due to a linear instability of the laminar profile. The state space of the system, where each point corresponds to a flow state, is organised by a complicated collection of unstable flow states and the linearly stable laminar profile. Turbulence is then characterised as the system revolving around these unstable flow states (so-called `exact coherent structures'). The important point is that the laminar profile and the turbulent states remain dynamically connected and a sudden `escape' from the turbulent region of state space can occur. Localised turbulence in a flow can therefore suddenly relaminarise and this has been observed in many experiments of parallel shear flows. This relaminarisation is a memoryless process, that is, it does not depend on the amount of time the system has spent in the turbulent region of the state space. A characteristic timescale can be associated with this process which increases with Reynolds number as a double exponential. This implies that there is always a finite probability of relaminarisation, even at high Reynolds numbers: Localised turbulence in wall-bounded shear flows is transient.   

The transition to sustained turbulence then occurs due to a competing process,that is the splitting of a locally turbulent region into two. This process also has a characteristic timescale which now decreases with Reynolds number as a double exponential. The critical Reynolds number for sustained turbulence is then defined at the point where the two timescales are equal.

Collapse of isotropic turbulence

Isotropic turbulence and a parallel wall-bounded shear flow are a priori very different systems, isotropic turbulence being a simplified system studied in order to establish fundamental properties of turbulent flows. It is often thought of as high Reynolds number limit of wall-bounded flows, where the walls have negligible influence on the turbulent dynamics. It is traditionally studied in statistical terms and in numerical simulations, where the decay of turbulence due to viscous dissipation is balanced by an external energy input at the large scales. The emphasis in the simulations is usually on achieving high Reynolds numbers. The dynamics of forced isotropic turbulence has been thought to be as simpler than that of parallel shear flows. In particular, isotropic turbulence is not expected to show transitional behaviour and nothing is known about its phase space structure.

In this study we investigated the same system at low Reynolds numbers and observe a sudden collapse of turbulence in favour of a large-scale ordered flow. This can be seen in the figures, which show streamlines of the flow before and after the collapse of turbulence. A transition from a 'disordered' to an 'ordered' flow is clearly visible. This collapse of turbulence happens despite the continuous stirring of the flow at the large scales and had been observed in a previous study already. Our analysis, which is new in the sense that it is the first time that a dynamical systems approach has been applied to isotropic turbulence, now shows that this collapse has very similar features to relaminarisation events in pipe flow: It is a memoryless process with a characteristic timescale that increases with Reynolds number in much the same way as in wall-bounded shear flows. Furthermore, the base flow appears to be linearly stable. This shows that isotropic turbulence at low Reynolds numbers is transient and it suggests that the phase space dynamics of wall-bounded shear flows and isotropic turbulence may be very similar.

Outlook: the universality class of the transition to turbulence

Recent research suggests that the transition to turbulence in parallel shear flows constitutes a second-order nonequilibrium phase transition belonging to the Directed Percolation universality class. That is, the transition to turbulence in these flows behaves like, for example, the spread of diseases or wildfires. The similarities between relaminarisation in pipe flow and the collapse of isotropic turbulence reported here suggest that this behaviour may in fact be a universal feature of turbulence and plans are under way to investigate this further. 

This work has made use of the resources provided by the Edinburgh Compute and Data Facility (http://www.ecdf.ed.ac.uk). Moritz Linkmann and Alexander Morozov acknowledge support from the UK Engineering and Physical Sciences Research Council (EP/K503034/1 and EP/I004262/1).

Reference: M. Linkmann and A. Morozov, Sudden Relaminarization and Lifetimes in Forced Isotropic Turbulence, Phys. Rev. Lett. 115, 134502

The School of Physics and Astronomy is opening its doors at the end of September.

Coordinated by the Cockburn Association, Doors Open Day is an annual opportunity for the public to visit buildings and institutions across the city that are not available during the rest of the year.

Take a guided tour of the Institute for Condensed Matter and Complex Systems (ICMCS) and go behind the scenes of soft matter research on Saturday 26 September at the James Clerk Maxwell Building on the King’s Building campus. You will have the opportunity to experiment with a variety of hands-on activities alongside staff and students, including having the chance to make and take away your own slime!

On Saturday 26 & Sunday 27 September, you will have the chance to talk to astronomers from the Institute for Astronomy about their work on galaxy evolution, planet formation and computer simulations of the Universe. There will be hands-on craft activities including making your own origami brown dwarf and the chance to try your hand at characterising light curves from stars to spot exoplanets. Relax on the sofa in the astronomers’ corner while discussing the big questions of the Universe and get an insight into the working life of an observatory. These events take place at the Royal Observatory Edinburgh.

Childhood memories of sticky hands from melting ice cream cones could soon become obsolete, thanks to a new food ingredient.

Scientists have discovered a naturally occurring protein that can be used to create ice cream that is more resistant to melting than conventional products. The protein binds together the air, fat and water in ice cream, creating a super-smooth consistency.

The new ingredient could enable ice creams to keep frozen for longer in hot weather. It could also prevent gritty ice crystals from forming, ensuring a fine, smooth texture like those of luxury ice creams. The development could allow products to be manufactured with lower levels of saturated fat – and fewer calories – than at present.

Researchers at the Universities of Edinburgh and Dundee developed a method of producing the new protein – which occurs naturally in some foods – in friendly bacteria. They estimate that ice cream made with the ingredient could be available within three to five years.

The protein works by adhering to fat droplets and air bubbles, making them more stable in a mixture. Using the ingredient could offer significant advantages for ice cream makers. It can be processed without loss of performance, and can be produced from sustainable raw materials.

Manufacturers could also benefit from a reduced need to deep freeze their product, as the ingredient would keep ice cream frozen for longer. The supply chain would also be eased by a reduced need to keep the product very cold throughout delivery and merchandising.

The protein, known as BslA, was developed with support from the Engineering and Physical Sciences Research Council and the Biotechnology and Biological Sciences Research Council.

Professor Cait MacPhee, of the University of Edinburgh’s School of Physics and Astronomy, who led the project, said: “We’re excited by the potential this new ingredient has for improving ice cream, both for consumers and for manufacturers.”

Dr Nicola Stanley-Wall, of the University of Dundee, said: “It has been fun working on the applied use of a protein that was initially identified due to its practical purpose in bacteria.”

Computer models of developing cancers reveal how tiny movements of cells can quickly transform the makeup of a tumour.

The models reinforce laboratory studies of how tumours evolve and spread, and why patients can respond well to therapy, only to relapse later.

Cell changes

Researchers used mathematical algorithms to create three-dimensional simulations of cancers developing over time. They studied how tumours begin with one rogue cell which multiplies to become a malignant mass containing many billions of cells.

Their models took into account changes that occur in cancerous cells as they move within the landscape of a tumour, and as they replicate or die. They also considered genetic variation, which makes some cells more suited to the environment of a tumour than others.

Transforming tumours

They found that movement and turnover of cells in a tumour allows those that are well suited to the environment to flourish. Any one of these can take over an existing tumour, replacing the original mass with new cells quickly - often within several months. This helps explain why tumours are comprised mostly of one type of cell, whereas healthy tissue tends to be made up of a mixture of cell types.

Therapy resistance

However, this mechanism does not entirely mix the cells inside the tumour, the team says. This can lead to parts of the tumour becoming immune to certain drugs, which enables them to resist chemotherapy treatment. Those cells that are not killed off by treatment can quickly flourish and repopulate the tumour as it regrows.

Researchers say treatments that target small movements of cancerous cells could help to slow progress of the disease.

Joint study

The study, a collaboration between the University of Edinburgh, Harvard University and Johns Hopkins University, is published in the journal Nature. The research was supported by the Leverhulme Trust and The Royal Society of Edinburgh.

"Computer modelling of cancer enables us to gain valuable insight into how this complex disease develops over time and in three dimensions.” Dr Bartlomiej Waclaw, School of Physics and Astronomy

A new astrobiology textbook and complementary lectures written by the School's Prof Charles Cockell and published by Wiley-Blackwell will encourage other universities to teach this complex subject.

Astrobiology is an interdisciplinary field that asks profound scientific questions. How did life originate on the Earth? How has life persisted on the Earth for over three billion years? Is there life elsewhere in the Universe? What is the future of life on Earth?

Astrobiology: Understanding Life in the Universe is an introductory text which explores the structure of living things, the formation of the elements for life in the Universe, the biological and geological history of the Earth and the habitability of other planets in our own Solar System and beyond. The book is designed to convey some of the major conceptual foundations of astrobiology that cut across a diversity of traditional fields including chemistry, biology, geosciences, physics and astronomy. It can be used to complement existing courses in these fields or as a stand-alone text for astrobiology courses. The text book also comes with 21 full lectures on astrobiology, allowing anyone to set up a complete astrobiology course.

"The major stumbling block to new astrobiology courses so far has been the difficulty of gathering all the required information for a very diverse subject and making lectures that match an existing textbook. This has been a barrier to new astrobiology courses around the world. This textbook and accompanying lectures now solves this problem." Charles Cockell, Professor of Astrobiology, School of Physics & Astronomy

The intended audience includes undergraduates studying for degrees in earth or life sciences, physics, astronomy and related disciplines, as well as anyone with an interest in grasping some of the major concepts and ideas in astrobiology.

A new video traces the development of the School of Physics & Astronomy and reflects on the achievements of some of its students and staff.

The film opens in the house where James Clerk Maxwell was born, with Sir David Wallace describing the early days when he was a student at Edinburgh. Professors Stuart Pawley, Alan Shotter and Murray Campbell then reflect on early achievements at Edinburgh in high-performance computing, nuclear physics and applied physics, followed by Prof. Peter Brand who describes the symbiosis of Physics with Astronomy and how research methods have changed over the generations.

Finally Nobel Laureate Prof. Peter Higgs talks about how he was inspired to work in the area of theoretical physics, and the relationship between the theoretician and experimentalist.  

Watch the video on YouTube.

The extent to which galaxies consume one another has been revealed in research.

Findings from the study help to explain how galaxies such as the Milky Way were formed.

A team of scientists has used a highly sensitive instrument on one of the world’s largest telescopes to witness a dominant galaxy ingesting the stars of its near neighbours.

Deep images

Astronomers took extremely wide-view, long exposures of a nearby group of galaxies known as the M81 Group, which lies 11.7 million light years from the Milky Way.

They observed the dominant central galaxy, M81, capturing stars from its two nearest neighbouring galaxies.

The gravitational pull of M81 was shown to distort the shapes of the other galaxies, pulling their stars into long tails, in a process called tidal stripping.

The images reveal for the first time how the stars from smaller galaxies are being ingested into M81.

It is expected that eventually the smaller galaxies will be devoured entirely.

Growing evidence

The team, including researchers from the University of Edinburgh, were not surprised to see this process taking place.

However, the degree of interaction witnessed exceeded their expectations.

Findings from the study add to two decades of research during which evidence for this process has been mounting.

In the early 1990s, scientists discovered that our own Milky Way is in the process of subsuming a smaller system known as the Sagittarius dwarf galaxy.

The study, to be published in Astrophysical Journal Letters, was conducted using the Hyper Suprime-Cam on the Subaru Telescope in Hawaii.

It was carried out by astronomers from Shanghai Astronomical Observatory, the National Astronomical Observatory of Japan, the Universities of Edinburgh and Cambridge, and Hiroshima University.

"The extremely faint outer regions of galaxies are challenging to study, but our findings reveal that they contain a wealth of information about how galaxies capture and cannibalise their smaller neighbours. This is important for understanding how large galaxies like our Milky Way have formed and evolved over time." Prof. Annette Ferguson, School of Physics and Astronomy

Astronomers have discovered a planet, likely to be rocky, close to our own solar system.

The planet, which has a three-day orbit round a central star, is joined by a further three planets also newly discovered in the same system. The star at the centre of the system can be seen in the sky close to the Cassiopeia the Queen constellation, near the North Star, and is visible to the naked eye from dark skies.

Future research

At a distance of just 21 light years away, the rocky planet is the nearest confirmed outside our solar system. It is also the closest planet to Earth that has been found to transit across the front of its star which, together with its short orbit, makes it ideal for further study.

The newfound Earth-like planet, designated HD 219134b, was discovered by an international team of astronomers using data from the HARPS-North instrument on the 3.6-metre Telescopio Nazionale Galileo in the Canary Islands. Scientists found that it weighs 4.5 times the mass of Earth, making it what is termed a super-Earth.

"Although this planet is far too hot to be habitable, it is an amazing discovery given how close and bright the star is. This will provide amazing opportunities to learn about and characterise a rocky planet outside our solar system." Dr Eric Lopez, School of Physics & Astronomy, University of Edinburgh 

Images from space

Three additional planets in the system were also found - one planet with a mass at least 2.7 times that of the Earth orbits the star once every 6.8 days. A Neptune-like planet with nine times the mass of Earth circles in a 47-day orbit. Much further out from the star, a hefty fourth world with 62 times the mass of Earth orbits at a distance of about 200 million miles, with a year length of 1,190 days.

Astronomers used NASA’s Spitzer Space Telescope to capture the smallest planet crossing in front of the star. The star was seen to dim slightly as the planet crossed its face. Measuring the depth of the transit gave the planet’s size, enabling the team to calculate the planet’s density, which showed that it is a rocky world.

"This is a fascinating system, not only because it is around a relatively nearby star, but also because we are able to determine the compostion of the closest of the four planets, and because the architecture, with three inner low-mass planets with an outer, more massive companion, is similar to that of our own Solar System." Prof. Ken Rice, School of Physics & Astronomy, University of Edinburgh

Transiting planets

Any of the other three planets might also pass directly in front of the star, so the team plans to search for additional transits across the star in the months ahead. The star which the planets orbit is cooler, smaller and less massive than our Sun, and is known as HD 219134.

Transiting planets are ideal targets for astronomers wanting to know more about planetary compositions and atmospheres. As a planet passes in front of its star, it causes the starlight to dim, and telescopes can measure this effect. If molecules are present in the planet's atmosphere, they can absorb certain wavelengths of light, leaving imprints in the starlight. This type of technique will be used in the future to investigate potentially habitable planets and search for signs of life. 

The study will be published in the journal Astronomy & Astrophysics.

HARPS-North

The HARPS-North project is led by the University of Geneva, and involves the Universities of St Andrews, Edinburgh and Queen’s University Belfast. Other partners are the Harvard-Smithsonian Center for Astrophysics, and the Italian National Institute for Astrophysics.

The St Andrews and Edinburgh contributions were part-funded by the Scottish Funding Council through the Scottish Universities Physics Alliance. Together with funds from Queen’s University Belfast, these contributions funded construction of the telescope interface and instrument control systems at the Science and Technology Facilities Council’s UK Astronomy Technology Centre in Edinburgh.

The UK Astronomy Technology Centre instrument team were responsible for delivering the HARPS-North instrument Front End Unit, Calibration Unit, Instrument control electronics and software, Detector control system and Sequencer software. In addition they helped to install and commission the instrument on the Telescopio Nazionale Galileo (TNG) in partnership with colleagues from the University of Geneva and the TNG.

Professor Peter Higgs has been awarded the world’s oldest scientific prize, the Royal Society’s Copley Medal.

The award has been made for the Professor’s work on the theory of the Higgs boson, a fundamental physical particle.

The particle was discovered in experiments at the European Organization for Nuclear Research (CERN) in 2012.

Prof Higgs was awarded a Nobel Prize in Physics 2013 for his research.

Highly ranked peers

"It is an honour to be the recipient this year of the Copley Medal, the Royal Society’s premier award." Professor Peter Higgs, School of Physics & Astronomy

The Copley medal was first awarded by the Royal Society in 1731.

Previous winners include Charles Darwin, Humphrey Davey and Albert Einstein.

It is awarded for outstanding achievements in scientific research.

In recent times it has been awarded to eminent scientists such as theoretical physicist Stephen Hawking, DNA fingerprinting pioneer Alec Jeffreys and discoverer of graphene Andre Geim.

"Peter Higgs is a most deserving winner of the Copley Medal. I congratulate him. His work, alongside that of Francois Englert, has helped shape our fundamental understanding of the world around us. The search for the Higgs boson completely ignited the public’s imagination, hopefully inspiring the next generation of scientists. The Copley Medal is the highest honour the Royal Society can give a scientist and Peter Higgs joins the ranks of the world’s greatest ever scientists." Professor Sir Paul Nurse, President, The Royal Society