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Sound waves

Shamit Shrivastava, a post-doctoral researcher in the Department of Engineering Science, writes about a recent finding that has far-reaching consequences for the fundamental understanding of the physics of the brain. The research was conducted in partnership with Professor Matthias F Schneider at the Technical University in Dortmund, Germany.

The findings, published in the Journal of Royal Society Interface, provide the experimental evidence that sound waves propagating in artificial lipid systems that mimic the neuron membrane can annihilate each other upon collision – a remarkable property of signals propagating in neurons that was considered to be inaccessible to an acoustic phenomenon.

Nerve impulses are believed to propagate in a manner similar to the conduction of current in an electrical cable. However, for as long as the electrical theory has been around, scientists have also been measuring various other physical signals that are equally characteristic of a nerve impulse, such as changes in the mechanical and optical properties that propagate in sync with the electrical signal. Furthermore, several studies have reported reversible temperature changes that accompany a nerve impulse, which is inconsistent with the electrical understanding from a thermodynamic standpoint.

To address these inconsistencies, researchers had previously proposed that nerve pulse propagation results from the same fundamental principles that cause the propagation of sound in a material and not the flow of ions or current. In this framework, the electromechanical nature of the nerve impulse, also known as an action potential, emerges naturally from the collective properties of the plasma membrane, in which the sound or the compression wave propagates. Thus the characteristics of the wave are derived from the principles of condensed matter physics and thermodynamics, unlike the emphasis on molecular biology in the electrical theory.

The suggestion has been highly controversial because of the well-accepted and widely successful nature of the electrical basis of nerve pulse propagation in spite of its few inconsistencies. As a wave phenomenon, nerve pulse propagation has remarkable properties, such as a threshold for excitation, non-dispersive (solitary) and all-or-none propagation, and annihilation of two pulses that undergo head-on collision. Moreover, sound waves are generally not associated with such characteristics, rather sound waves are known to spread out, disperse, dissipate, superimpose and interfere, which is counter-intuitive given the properties of nerve impulses.

Therefore, experimental evidence for such a phenomenon was crucial, which was provided by us in 2014. We showed that sound or compression waves can indeed propagate within a molecular thin film of lipid molecules, mimicking action potentials in the plasma membrane. Remarkably, even in such a minimalistic system that is devoid of any proteins and macromolecules other than lipids, these waves behave strikingly similar to nerve impulses in a neuron, including the solitary electromechanical pulse propagation, the velocity of propagation and all-or-none excitation. These characteristics were shown to be a consequence of the conformational change or a phase transition in the lipid molecules that accompany the sound wave. Thus only when sufficient energy is provided to cause a phase change in the lipids (fluid to gel-like), the entire pulse propagates otherwise nothing propagates, the so-called all-or-none propagation.

Now, in research published in the Journal of Royal Society Interface, we have shown that these waves can even annihilate each other upon collision, just like nerve impulses. Even from a purely acoustic physics perspective, this is a remarkable finding. The amplitudes of two sound pulses colliding head-on typically superimpose linearly before passing each other unaffected. Even nonlinear sound pulses, such as solitons, typically remain unaffected upon collision, which was a major criticism of the proposed acoustic theory of nerve pulse propagation.

With the observation of annihilation of colliding sound pulses in the model lipid system, we have shown that qualitative characteristics of the entire phenomena of nerve pulse propagation can be derived solely from the principles of condensed matter physics and thermodynamics without the need for molecular models or fit parameters of the electrical theory. We have demonstrated a unique acoustic phenomenon that combines all the observable characteristics that define the propagation of nerve impulses. This strongly suggests that the underlying physics of propagation of sound and nerve impulses is indeed one and the same.

Sound wave propagationSound waves propagating in artificial lipid systems that mimic the neuron membrane can annihilate each other upon collision.

Image credit: Shutterstock

As MPs give Heathrow Airport's proposed third runway the green light, Professor David Banister, Emeritus Professor of Transport studies at Oxford University, sheds light on the issue of transport inequality and just why the proposed expansion has sparked such controversy.

London Heathrow (LHR) is the busiest airport in the UK with 48 million passengers beginning or ending their journeys in London, and an additional 28 million passengers making interconnecting flights to other destinations. The 3rd Runway will increase the total capacity to 130 million (+71%) and the number of flights will increase to 740,000 per annum (+56%). But who will be the new passengers flying from LHR?

About half the population of Great Britain has flown in the last year (47%), and this figure has been stable over the last 15 years. Most of those that do fly make one or two trips a year (31%). This means that 10% make about 60% of all flights, and as might be expected these people are mainly from the highest income groups. The richest 10% make 6.7 times as many trips by air as the poorest 10% of the population. The inequality in air travel in Great Britain is far higher than any other form of travel with the exception of High Speed Rail (10.3 times). Figures for the other forms of transport are much lower, with the difference for car travel being 2.75 times and for the bus the poor make more trips than the rich.

Some might argue that low cost airlines have helped rebalance this inequality, but the evidence would suggest that cheaper flights have enabled those already flying to travel more frequently and possibly to save money. Inequality is important as it reflects on societal values and the argument that society as a whole should gain. But it is equally important to identify who are the winners and who are the losers – it is about fairness and justice. This is particularly the case when large amounts of public money are involved. The new runway is estimated to cost £14 billion, with a similar amount being needed to improve road and rail links to the airport. A substantial part of this funding will come from Government and Transport for London.

It is likely that low income people will make only limited use of the new runway, but they will also be impacted by it indirectly through additional CO2 emissions. Overall, the richest 10% of households produced 3 times the levels of CO2 emissions than those from the poorest 10% of households, but for transport the difference is between 7-8 times and 10 times for aviation. New runway capacity at LHR will increase this difference, as more rich people fly further and more frequently. Local pollutants (e.g. NOx) and the noise impact are also likely to increase from the additional planes (and traffic). This means that it becomes much harder to meet CO2 reduction targets and improve local air quality, and air quality around LHR is already very poor.

Even the argument about the importance of increased airport to the local and national economies is weak. Business air travel accounts for about 20% of all passengers in Great Britain, with the figure for LHR being higher (30%). This market has been relatively stable, as the growth in air travel has come from leisure travel and visiting friends and relatives. In addition, UK residents are spending more overseas than others do coming to the UK. In 2016, there were 71 million overseas visits from UK residents and the total spend was £43.8 billion. There were 38 million visits to the UK and the total spend was £22.5 billion.

The clear conclusion is that on grounds of inequality, environment and spend, building additional airport capacity at LHR does not add up, as it will enable the richest 10% to fly even more and spend their money overseas. It will be the poorest 10% that stay in the UK, and they will suffer from even higher levels of CO2 emissions and poorer levels of air quality.

This analysis is based on National Travel Survey data (2002-2012) and Air Passenger Surveys carried out for the Civil Aviation Authority.

Read the full article on The Conversation here

This analysis of air travel in the UK forms part of Professor Banister’s new book Inequality in Transport, which will be published by Alexandrine Press on 12th July.

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Engineering a better world

Lanisha Butterfield | 22 Jun 2018

Despite being one of the most fast evolving sciences in many ways, gender equality is one area where the field of engineering is playing catch-up. But, in spite of this continued imbalance, little by little, female engineers are shaping the world around us with their research achievements, developing scientific solutions to real world challenges.

In celebration of International Women in Engineering Day (June 23) – an initiative intended to raise the profile of women in engineering and physical sciences and encourage other budding scientists to join them, we wanted to shine a light on a female academic engineering a difference at Oxford.

Dr. Dong Liu is an independent research fellow at Oxford’s Department of Materials and a Soapbox Science ambassador. Specialising in materials sciences, physical sciences and mechanical engineering, Dr Liu’s research is focused on better understanding of new materials for nuclear reactors and how this can drive further developments in nuclear energy production.

For those that are not familiar, what is Materials Science – and how does it differ from Engineering in general?

To make any effective device, structure or product, you need the right material(s). Materials Science is the study of all materials – from the things you use every day like plastics, glass and sports and health care equipment, to more industrial appliances in aircrafts, space shuttles and nuclear reactors. 

I am interested in how materials react to extreme conditions, for example, inside a jet engine or a reactor core, where heat and irradiation is a problem. Understanding how and why the materials degrade and break is key to designing and making stronger materials. Compared with Engineering, Materials Science focuses more on the mechanisms of the material failure. By gaining this knowledge, we can understand their engineering behaviour better.

 By understanding a material’s strengths and weaknesses we can optimise its use and eventually make our nuclear energy sources more efficient and effective.

Which material does your research focus on?

My primary research interest is on ceramic-like materials used in aero-engines, e.g. ceramic coatings on turbine blades protecting them from the heat of the engine, and a material called graphite used in the core of nuclear reactors at power plants in the UK and some other countries.

What is graphite?
Nuclear grade graphite is used as the core of all 14 operating reactors that provide about 20% of the total electricity in the UK. It is much purer than materials used day to day, such as lead in pencils, so it’s ideal for building the core of nuclear reactors - a lesser material would interfere with the reactions.

Image credit: Dong LiuDr Liu hard at work in the lab.

 What does your research involve?

Once installed, the graphite core cannot be taken out or replaced, so if it becomes unstable or develops cracks, we have to shut down the reactor. I study these cracks and work to understand why stability issues occur in general. By understanding a material’s strengths and weaknesses we can optimise its use and eventually make our nuclear energy sources more efficient and effective.

Working together with my colleagues at Lawrence Berkeley National Laboratory in California, we heated our nuclear graphite to more than 1000°C to test the tolerance of the material. We found that the material actually becomes stronger in high temperature environments and was less likely to fracture when heated up.

What impact has this research achievement had on your career?

Publishing our paper in Advance Science has boosted my reputation in the nuclear graphite research community and allowed me more international research opportunities.

The material is used in nuclear reactors in many other countries, including Europe, USA and China, where they are working to build the next generation of reactors, which are more powerful and environmentally friendly than previous models. I am supporting this work, analysing different grades of graphite material so that we can understand and use their tolerance levels to create a superior nuclear reactor that enables clean energy.

Image credit: Dong LuiDr. Dong Liu is an independent research fellow at Oxford’s Department of Materials, her research focuses on testing and better understanding materials used in nuclear reactor cores to make our energy sources more effective and sustainable.

How did you come to specialise in this area?
I am excited by research that has an industrial imperative, it makes me feel that I am solving a real problem that is related to everyday life and helps our society.

Some people assume that research is dull, but scientific engineering is all about getting your hands dirty. Taking things apart and blasting them with boiling hot X-rays is all in a day’s work for me, and I love it.

What drew you towards a career in science?
Education is very important in China and my parents played an important role in my passion for academia. Even at primary school my mum said to me; ‘you have to get a Doctorate degree when you are older’, so I have always had that goal.

I’ve always believed that a burning desire to learn is the most powerful driving force in life. When I look at where I am now, I know that I have made the right decisions.

What has surprised you most in your career?

I used to think that working in science would be lonely and I would be stuck in a lab on my own 24/7. But, communication is a big part of the job, and collaboration is key to overcoming challenges.

Some people assume that research is dull, but scientific engineering is all about getting your hands dirty. Taking things apart and blasting them with boiling hot X-rays is all in a day’s work for me, and I love it!

What advice would you give to anyone beginning or considering a career in academic science?
Be brave, take as many opportunities as you can and keep an open mind. Being a scientist is about more than publishing papers and experiments. You are part of a community that has a responsibility for influencing people’s science perceptions and understanding. 

I am involved in the Nuclear Institute’s Woman in Nuclear (WiN) initiative and in organising Oxford Soapbox Science events - the national initiative to make science more accessible to the general public and raise the profile of female scientists.

Another tip is to be aware of independent research opportunities – such as funded research fellowships. I have had two while at Oxford: 1851 Royal Commission Research Fellow (Brunel) and another with the Engineering and Physical Sciences Research Council (EPSRC).

Fellowships have been key to my career, and helped me to grow as an independent young academic. You are the leader, the worker and the negotiator for your own research – effectively you ‘run the show.’ Applications can be competitive and time consuming, but the pay-off is worth it.

How has your experience as a women in engineering shaped your career?
For me, being a young woman in Engineering has shaped my career. It is great to be young, but in academia youth isn’t always a good thing. People often assume that you must be older to practice good science, or to have a senior position. Male or female, being or looking younger can lead to your work being challenged, so you need to really know your stuff and prove yourself

From a positive perspective being challenged only makes you get better at what you do. Before I came to Oxford as an independent researcher, if someone had asked me if I was ready for a permanent position I would have panicked. But, my experience has improved my confidence in my teaching.

Image credit: Carlyn SamuelDr Liu is one of the core organisers for the Oxford branch of Soapbox Science - the national initiative to make science more accessible to the general public and raise the profile of female scientists.

 What do you think are the barriers to entry for women in STEM?

Stereotypes are a big issue. A student of mine once told me that her mother has a doctorate degree, but people always assume that the Doctor in her family must be her father.

Statistically less women are applying for jobs in science and engineering compared to men, which is why it’s so important to mentor young people to encourage them to take a science / engineering career. 

I believe that everyone is equal and can make important contributions to science. A diverse workforce is needed to represent the multiple facets of knowledge, perspectives and values required to uncover the most significant findings.

How do you balance the stresses of work and home life?

Any work - science or otherwise, is like a marathon rather than a sprint. My philosophy is work hard play hard and I do lots of sports like kickboxing and hiking with friends in the sunshine.

What is next for you?
I am coming to the end of my Fellowships and will soon start a permanent Lectureship position with the School of Physics at Bristol University.

I feel really lucky to have been able to stay in academic science as long as I have and I feel it is my duty to raise awareness of women working in the sciences, sharing our cool research and letting others know that they can do this too.

What will you miss most about Oxford?
There is so much I will miss, but especially the people that I work with in the Materials Department - they are like extended family. I have lots of collaborative research coming up, so I will continue to be a visiting academic at Oxford.

I’ll miss the delicious, formal Mansfield College dinners, which are out of this world and great for networking - you never know who you are going to meet at the table. I recently met Professor Katherine Blundell who specialises in Astrophysics. She is so inspiring person and good at explaining complex science, she makes me think about how I can better communicate my own work.

View Dr Liu's paper 'Damage tolerance of nuclear graphite at elevated temperatures' here


Next week, a conference hosted at Oxford will explore the latest research into ‘intact’ forests – large forested areas that remain mostly unharmed by human activity. Co-organiser Dr Alexandra Morel, a postdoctoral researcher in Oxford’s Environmental Change Institute, explains why these threatened landscapes are so important to the future of the planet.

‘Forests are among the most ecologically important landscapes on Earth. Some 1.6 billion people depend on them, and 80% of animals and plants on land live in them. Preserving forests is one of the most cost-effective solutions to mitigating climate change and could help meet 30-50% of the Paris goal of keeping Earth’s temperature rise below 2°C by 2050.

‘In particular, “intact” forests – the large, unbroken swaths of forests whose ecological functions remain unharmed by human activity – provide extraordinary benefits for protecting wildlife, human health, water supplies and indigenous communities. Furthermore, intact forests play a significant role in the fight against climate change, the most pressing environmental threat facing our planet today.

‘Despite these extraordinary benefits, intact forests are disappearing. Since 2000, intact forests have diminished by over 9% – twice the rate of overall forest clearance. If destruction continues at this pace, half of today’s intact forests will be gone by 2100.

‘For the purposes of this conference, we are defining intact forests as forests that are free of significant human-generated degradation, including loss of wildlife. That doesn’t mean a forest must be free of all human presence to be considered intact, but ecosystem science is increasingly showing that forest function is impacted by “edge effects” – the changes that take place at the boundaries between landscapes – and over-hunting. Therefore, significant areas of contiguous forest with minimal human disturbance and a large core area behave differently from smaller areas of forest within a highly fragmented landscape.

‘As for why these landscapes are important, we are keen for this conference to highlight the latest science on this question – specifically with respect to intact forest areas in tropical, temperate and boreal, or northern, regions. Some of the key values that are derived from a forest’s intactness relate to its ability to store and sequester carbon, its resilience to fire, local to regional climate regulation, watershed protection, and the ability to protect local communities from animal-borne diseases.

‘Threats to forest landscapes are manifold, primarily because their protection has not been made an international priority due to the focus on the current hotspots of deforestation and forest degradation. The fact that intact forest areas remain that way is due to their not previously being under direct threat. However, like other forest areas, intact forests are suffering hunting pressure, selective logging, mining and clearance for commodity production, which has significantly reduced their total area since 2000.

‘A multi-pronged approach will be necessary to mitigate these threats. Our conference sessions have been organised around some large topics, such as attempting to maintain intactness in logged forests, the relevance of international policies and financial instruments in incentivising intactness, and the effectiveness of protected areas, including indigenous reserves, for maintaining intact forest area. The fundamental responsibility to protect these areas lies with national and sub-national governments – however, it is increasingly recognised that these actors need additional support, both technical and financial, to achieve adequate protection of intact forests.’

The ‘Intact Forests in the 21st Century’ conference will be held in Oxford from 18-20 June.

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Professor David Macdonald and Dr Merryl Gelling of Oxford’s Wildlife Conservation Research Unit (WildCRU) discuss recent work which questions the efficacy of the mitigation technique and looks at ways to better protect one of Britain’s most endangered wild mammals, the water vole. 

The water vole, forever immortalised as ‘Ratty’ in Kenneth Grahams’ classic tale Wind in the Willows, was formerly a common sight on waterways throughout mainland Britain. However, catastrophic declines due to invasive American mink combined with habitat loss and fragmentation have resulted in the water vole now being considered one of Britain’s most endangered wild mammals. As such, water voles and their burrows are fully protected under the Wildlife and Countryside Act. Despite these measures, development works affecting the bankside have created an additional pressure on remaining populations and while we might hope Toad is safe in Toad Hall, Ratty has been in peril. However, our research, conducted in collaboration with Natural England, Mammal Society and PTES, amongst others, offers a simple, practical solution.

Natural England created a licence to permit intentional disturbance of water voles - with the idea of giving the voles a chance to move to safety before development work begins. This involved encouraging the voles to relocate by removing any riverside vegetation, and then, once they were thought to be safely out of harm’s way, strategically destroying their burrows to prevent the animals’ return. Such activities, which are intended to conserve the water voles while enabling approved development, are licensed between mid-February and mid-April and must not exceed 50m of bankside length.

However, while the goal of the approach is to displace the animals, our research found that the voles had other ideas. Radio-tracking water voles subjected to this procedure found that they often steadfastly stayed put.

These findings, published today in Conservation Evidence, revealed no overall movement of water voles out of areas where displacement works had occurred. On the contrary, many voles remained faithful to their burrows. The guidelines had always insisted that destruction of burrows should be undertaken cautiously and only during spring, in the hope of saving the lives of any water voles remaining. However, that was in the expectation that at most, only a few bankside denizens would stubbornly refuse to shift. Now it seems the majority stand firm, shifting the balance of risks. This behaviour does not alter between spring and autumn, when vole populations are at their highest.

While labour intensive, the solution proposed in our study - which includes careful excavation of burrows left exposed by vegetation, and then removing the water voles by hand, is worth the effort. With this vole-sensitive and life-saving approach, we believe the displacement method can be a pragmatic and proportional solution for small-scale developments where water voles are present.

Water voles often remained in their burrows after vegetation removal, highlighting the need for burrow excavation to proceed with caution to allow animals to relocate prior to development works starting. There was no difference in behaviour in either spring or autumn, suggesting that works under this licence could occur outside of the current mid-February to mid-April window, potentially reducing costly delays for development works.

It's a particular pleasure to have been able to work with the government’s statutory agency, Natural England, to solve this practical problem, along with leading wildlife charities – a splendid example of all pulling together, and now we hope and expect developers will follow suit.

Not to exhaust the Wind in the Willows reference, but, Toad is in a mess too. However, that’s another story, and one we are busily researching.

The research was carried out in the Upper Thames region and predominantly funded by a partnership between Natural England, Peoples’ Trust for Endangered Species, The Mammal Society, Universities Federation for Animal Welfare, and Thames Water, with additional support from M&H Ecology Ltd, RSK Ltd, Arcadis, ERM Ltd, Ecosulis and the Environment Agency.