From nozzles and diffusers to stars and stripes

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Schematic diagram of explanation in textAt the end of a lecture on energy flows in my first year undergraduate course on thermodynamics, I talk about nozzles and diffusers as examples of practical applications of the rest of the material in the lecture.  It is hazardous to sit in the front row of the lecture theatre because I take in a water bottle with a trigger spray to demonstrate how the nozzle increases the velocity of the fluid at the expense of pressure while gently sprinkling water on the front row.  I am always intrigued by the symmetry of nozzles and diffusers.  Diffusers increase pressure of a fluid at the expense of its velocity, i.e., a mirror image of the action of a nozzle.  The cross-sections are also mirror images because a nozzle has a cross-section that decreases in the flow direction while a diffuser has a cross-section that increases in the flow direction.  At least for sub-sonic flows, because the shapes are reversed for super-sonic flow; so a sub-sonic nozzle looks like a super-sonic diffuser and a sub-sonic diffuser looks like a super-sonic nozzle.  If that all sounds like fluid mechanics then the thermodynamic message is that, in nozzles and diffusers, the rates of heat and work transfer are approximately zero while the change in the kinetic energy of the fluid is very large.  I finish the lecture with a video clip of a school quartet of trombones playing ‘Stars and Stripes Forever’ which wakes up the students who have slept through the lecture and allows me to point out the diffusers (bell of the trombone) transmitting acoustic pressure.

You can watch the video clip on YouTube at https://www.youtube.com/watch?v=mHw8P8NnUvI

Time travel and rewriting history

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decorative paintingI have written in the past about consciousness being an accumulation of sensory experiences [see ‘Is there are real ‘you’ or ‘I’? on March 6th, 2019].  Our memory consists of fragments of images, sounds, smells and feelings from the past that we can re-assemble into a complete experience often triggered by something in the present that resembles a fragment of a past experience.  We can time travel in our minds by thinking about the past.  It is so ubiquitous that we barely stop to think about it. Yet, we are fascinated by the possibility of time travel into the future.  However, our subconscious minds are constantly time traveling into the future [see ‘Predicting the future through holistic awareness’ on January 6th, 2021].  They are constantly making predictions about what will happen next, whether anticipating the path taken by a ball so that your hand can be positioned to catch it or picking up an umbrella as you leave the house so that you do not get soaked when it rains later in the day.  The further we attempt travel into the future the less dependable our predictions become and I suspect the same is true for travel backwards in time.  The reliability of our recollection of past experiences become less as time and entropy erode the connections between the fragments in our mind so that we struggle to reassemble all of the fragments in the correct order and our personal history is unintentional rewritten.

Source:

Stefan Klein, We are all stardust, Melbourne: Scribe, 2015  (a conversation with Hannah Monyer on memory entitled ‘Do You Remember?’).

Reflecting on the lack of women in engineering

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It was International Women’s Day last week which caused me to reflect on parlous state of the engineering profession.  Despite many initiatives and substantial expenditure of resources, the percentage of women in engineering in many Western countries has remained around 20% for most of my career.  For instance, in the UK, women made up 14.5% of all engineers in 2021 according to the Women in Engineering Society and 21.8% of women work in the engineering sector; while in the USA women secured 22% of all Bachelor’s degrees in engineering in 2018 (wwwstemwomen.com).  So, why have the many apparently well-supported initiatives made so little progress towards creating a gender-balanced profession?  Perhaps, they are not as well-supported within the engineering profession as they appear to be; or they are the wrong solutions for the problem because we do not understand the problem.  I suspect that both of these reasons for failure are relevant.  The lack of progress would suggest that most men in engineering are not worried that their profession is unrepresentative of the society it claims to serve and if they are concerned then they do not understand the issues sufficiently well to be able see a viable solution.  We can start to gain a better understanding by listening to women in science and engineering.  This can be done in everyday conversations, by attending events such as those organised on International Women’s Day, or by reading about women’s experiences such as in ‘Invisible Women: exposing data bias in a world designed by men’ by Caroline Criado Perez or in ‘A Fly Girl’s Guide to University: being a woman of colour at Cambridge and other institutions of power and elitism’ by Lola Olufemi, Odelia Younge, Waithera Sebatindira and Suhaiymah Manzoor-Khan.

Separating yourself from existence

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The French novelist Michel Houellebecq has written of the power of literature to separate yourself from your existence. It is something that I experience when reading an absorbing novel or occasionally when reading an outstanding scientific paper on a subject that interests me. However, it happens more often when I am writing and perhaps is a reason why I write regularly and frequently. Houellebecq has also written that ‘only literature can give you the sensation of contact with another human mind’ [in Submission, 2015]. Is it only literature that can produce this sensation? Or, does it occur when you listen to an in-depth interview or even when you read posts regularly from a blogger? Perhaps after 500 posts [see ‘500th post‘ on February 2nd, 2022] you have a sensation of contact with some part of my mind.

Source: Jonathan Derbyshire, France’s ‘enfant misérable’.  FT Weekend, 29/30 January 2022.