Tag Archives: tigers

Red to blue

Some research has a very long incubation time.  Last month, we published a short paper that describes the initial results of research that started just after I arrived in Liverpool in 2011.  There are various reasons for our slow progress, including our caution about the validity of the original idea and the challenges of working across discipline boundaries.  However, we were induced to rush to publication by the realization that others were catching up with us [see blog post and conference paper].  Our title does not give much away: ‘Characterisation of metal fatigue by optical second harmonic generation‘.

Second harmonic generation or frequency doubling occurs when photons interact with a non-linear material and are combined to produce new photons with twice the energy, and hence, twice the frequency and half the wavelength of the original photons.  Photons are discrete packets of energy that, in our case, are supplied in pulses of 2 picoseconds from a laser operating at a wavelength of 800 nanometres (nm).  The photons strike the surface, are reflected, and then collected in a spectrograph to allow us to evaluate the wavelength of the reflected photons.  We look for ones at 400 nm, i.e. a shift from red to blue.

The key finding of our research is that the second harmonic generation from material in the plastic zone ahead of a propagating fatigue crack is different to virgin material that has experienced no plastic deformation.  This is significant because the shape and size of the crack tip plastic zone determines the rate and direction of crack propagation; so, information about the plastic zone can be used to predict the life of a component.  At first sight, this capability appears similar to thermoelastic stress analysis that I have described in Instructive Update on October 4th, 2017; however, the significant potential advantage of second harmonic generation is that the component does not have to be subject to a cyclic load during the measurement, which implies we could study behaviour during a load cycle as well as conduct forensic investigations.  We have some work to do to realise this potential including developing an instrument for routine measurements in an engineering laboratory, rather than an optics lab.

Last week, I promised weekly links to posts on relevant Thermodynamics topics for students following my undergraduate module; so here are three: ‘Emergent properties‘, ‘Problem-solving in Thermodynamics‘, and ‘Running away from tigers‘.


Our place in the web of life

140-4032_IMGThe seven billion human beings who live on this planet weigh in about 300 million tonnes in total and if you add in our domesticated animals then the scales would hit about 700 million tonnes. Whereas if you weighed all of the animals left in the wild then their total weight would be less than 100 million tonnes, according to Yuval Noah Harari in his book ‘Sapiens: a brief history of mankind’. This explains why many of our landscapes appear empty and barren – they are, at least at the level of large mammals. That’s why you are unlikely to be chased by a tiger or any other predator, see last week’s post entitled ‘Running away from tigers’.

These landscapes are not really barren. We just can’t see what is there. Bacteria are too small for us to see but they have dominated the landscape for most of evolutionary time. They ‘invented’ all of life’s essential biotechnologies including fermentation, photosynthesis, nitrogen fixation, respiration and devices for rapid motion plus probably a few we have haven’t discovered yet. Bacteria exchange up to 15% of their genetic material on a daily basis across all strains so that they could be considered to form a single microscopic web of life.

This web of bacterial life is all around us as well as inside us. If you like to learn more than you probably ever want to know about the bacteria inside us then read Giulia Enders’book ‘Gut: The inside story of our bodies most underrated organ’. We are not alone in being immersed in this web of bacterial life; so is every other living thing which implies we are all intimately connected in a vast ecological network. This microbial web of life in which we are embedded is self-organising – there are no leaders, presidents, generals or CEOs – instead bacteria empower one another. It appears to be one of the secrets of their success.

In an interconnected world, power and control over others in a hierarchy is less appropriate than empowering one another in the network. Many people would find this approach difficult because they identify themselves with their position of power and, hence would tend to resist any attempt to empower the network. To them it begins to sound like anarchy, particularly in the narrow context of human society, but others might suggest it offers a better prospect for addressing the challenges posed by global climate change than world leaders have so far proposed. Well-informed individuals intimately connected in a network are likely to take decisions that support the network, and hence themselves. But, now we are straying into game theory…


Yuval Noah Harari, Sapiens: A brief history of mankind. London: Vintage (Penguin, Random House), 2014.

Capri F. & Luisi, P.L., The systems view of life: a unifying vision. Cambridge: Cambridge University Press, 2014.

Enders, G, Gut: the inside story of our bodies most underrated organ. Vancouver: Greystone Books, 2013.

Running away from tigers

rsph graphicToday, the probability that you will have to run away from a tiger is very small, no matter where you live.  Tigers have lost 93% of their historical range that used to stretch from Turkey across Asia to Eastern China and southwards to Indonesia.  Tigers have no problem with the first law of thermodynamics – they instinctively know that if they take in more energy than they expend then the excess energy will be stored as fat and when they become overweight they won’t be able to catch you or whatever else they decided to chase for their next meal.

As a species we seem to have lost that understanding of energy balances.   Obesity is increasing in many parts of the world.  The situation is so serious in the UK, where more than two-thirds of the adult population are overweight or obese, that the Royal Society for Public Health has proposed that food should be labelled with the amount of exercise required to burn-off the calories it contains and they have suggested using the infographic in the thumbnail.  Of course, the Royal Society’s position paper does not mention explicitly thermodynamics (or tigers!) though it does effectively cite the first law by stating ‘the cause of obesity is excess energy consumption relative to energy expenditure‘.  By coincidence, this week I interviewed Professor Graham Kemp, in the Institute of Ageing and Chronic Disease in Liverpool, about energy flows through our bodies for a MOOC on Energy: Thermodynamics in Everyday Life.

If you wathermolectures posternt to listen to that interview or learn more about the thermodynamics underpinning the energy balances controlling our weight, climate change and your electricity charges, then you need to join the more than 4,500 people who have already enrolled on the MOOC that will run for five weeks from February 8th, 2016.  I will also be giving an accompanying series of lectures in London.

I was astonished to discover that there are fewer tigers in the world than people signed up for our MOOC.  Less than 3,200 tigers exist in the wild mainly because our growing population and prolifigate use of the world’s resources has destroyed their habitat and those of the other species with which we share this planet.