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Monday, 20 June 2016

Introducing Alice

Hello all, I’m Alice and I’m the new SEPnet intern at Things We Don’t Know. I’ve just finished my third year studying physics at Royal Holloway, University of London, so I’ve just got my masters year left to go.

photograph of Alice Wayne

My interest in physics started in secondary school when I was taught about fundamental particles and forces. At that time, science had found neither the Higgs boson nor the Graviton, and I decided then that I would study physics and contribute toward the search. We’ve now found the Higgs boson, but as the Graviton still eludes us, I am writing my Research Review on the work that has been done so far at CERN to find it, or at least, to find where it isn’t.

Saturday, 18 June 2016

The Case of the Jumping Carbons

Imagine you are inside a nuclear reactor, a UK design. Not only are you inside it, but you are part of it; a carbon atom inside the graphite core which houses the control rods and fuel rods (the ‘moderator’). Around you the environment is glowing with heat and radiation, all given off in the splitting (fission) of uranium-235 nuclei. The temperature of 450°C is no problem, and you remain tightly bound in a lattice arrangement with your fellow carbons.

However, when the uranium nuclei split, they spit out more neutrons which pelt towards you at high speeds. One slams into you, and you slow it down, as is your job, so it travels at a suitable speed to cause more fission events. In this process you absorb the neutron’s energy, and get knocked out of your slot in the lattice. You whiz towards your fellow carbon atoms, knocking more out of their spaces like a billiard ball, wreaking havoc in the strict order of the graphite crystal. Eventually you transfer all of your extra energy to your neighbours and come to rest, filling a vacancy left by another displaced carbon or squeezing in between the orderly lattice layers (as an ‘interstitial’). Here you wait, ready to absorb the excess energy of the next neutron. The upheaval is routine to you, as during your life in the reactor you may switch places up to 30 times.

A finite element model of a graphite sample and how the model behaves when irradiated or heated. Image credit: Dr Graham Hall. Manchester University

This is just one atom, but what are the consequences of millions jumping around like this?

Well, the effects are unpredictable. The radiation barrage that the graphite endures can cause it to change its material properties; its thermal expansion, strength and even its dimensions, in strange ways. Even to the human eye, these changes would be noticeable. The moderator can change shape by up to 2%, depending on the grade of graphite; a surface that started smooth may finish rough. The dimensions may warp so that the control rods used to restrain the nuclear reaction may no longer fit into their channels. It is clearly important to completely understand how the graphite will change when designing new reactors or maintaining the existing ones. The problem is that we don’t.

Sunday, 12 June 2016

Face blindness

How do we recognise faces?

Most humans can recognise hundreds of faces, and tell the identity of each one, even in different lighting conditions or when someone has changed their hair colour or aged considerably. But how this works, and how our brain codes for individual people’s identity isn’t known. I spoke to Dr Meike Ramon from the University of Glasgow and University of Louvain, who studies face recognition, to uncover why we still don’t understand this seemingly simple ability.

One famous study using single cell recordings from people undergoing brain surgery claimed to discover a ‘Jennifer Aniston Neuron’[1]. The neuroscientists believed they had found a neuron that responded specifically to pictures of the movie star, suggesting information about the identity of a face may be stored in a single cell. However, these findings should be taken with caution. First, an experiment is always limited in terms of the number and type of stimuli it can test for. Second, we don’t have enough individual cells in our brains to assign one to each of the people we have come into contact with, meaning it can’t be as simple as one cell for each person. It was also discovered that the so called ‘Jennifer Aniston cell’ responded to information relating to her, as well as images, suggesting identity is more complex than was first thought.

Prosopagnosia, or face blindness, is an impairment of the ability to recognise faces that have been seen before.
Image © Yelisa van der Bij (CC BY)

Since the invention of brain-scanning techniques, researchers have tried to find regions of the brain that are involved in face processing; probably the best studied of these is the Fusiform Face Area (FFA)[2]. But while this area is activated more when subjects are looking at faces than at other objects, it is also activated in chess grand masters viewing chess board layouts[3], suggesting that the area might be engaged when looking at anything we are experts in, which for most of us includes faces. It also shows increased activation towards curved and symmetrical images[4], leading to the idea that this area is involved in extracting global patterns for discrimination. As important as this region may be, it is now clear that it alone is not sufficient for face recognition, which seems to depend on a network of regions[5].

One way of studying our normal ability to recognise the faces of people we know is to look at people who don’t have this ability. These people suffer from a condition known as prosopagnosia, or ‘face-blindness’, which can be present from birth or brought on by brain damage. While they may be unaffected in other areas of cognition, prosopagnosia cannot recognise celebrities, their loved ones, or even themselves without using other clues like voice and posture. This is an ability most of us take for granted, but losing it can have a huge impact on a person’s life.