Category: A Level Physics Chapters

‘Critical phase’ for fusion dream

‘Critical phase’ for fusion dream

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Secret of Bolt’s speed unveiled

Secret of Bolt’s speed unveiled


Secret of Usain Bolt’s speed unveiled

By Melissa HogenboomScience reporter, BBC News

Usain Bolt wins the 100mBolt’s 2012 Olympic record of 9.63 seconds in the 100m final was not his fastest 100m sprint

Scientists say they can explain Usain Bolt’s extraordinary speed with a mathematical model.

His 100m time of 9.58 seconds during the 2009 World Championships in Berlin is the current world record.

They say their model explains the power and energy he had to expend to overcome drag caused by air resistance, made stronger by his frame of 6ft 5in.

Writing in the European Journal of Physics, the team hope to discover what makes extraordinary athletes so fast.

According to the mathematical model proposed, Bolt’s time of 9.58 seconds in Berlin was achieved by reaching a speed of 12.2 metres per second, equivalent to about 27mph.

The team calculated that Bolt’s maximum power occurred when he was less than one second into the race and was only at half his maximum speed. This demonstrates the near immediate effect of drag, which is where air resistance slows moving objects.

They also discovered less than 8% of the energy his muscles produced was used for motion, with the rest absorbed by drag.

Jamaica's Usain Bolt celebrates after winning the men's 100m final The 2012 gold medallist became a worldwide sensation

When comparing Bolt’s body mass, the altitude of the track and the air temperature, they found out that his drag coefficient – which is a measure of the drag per unit area of mass – was actually less aerodynamic than that of the average man.

Jorge Hernandez of the the National Autonomous University of Mexico said: “Our calculated drag coefficient highlights the outstanding ability of Bolt. He has been able to break several records despite not being as aerodynamic as a human can be.

“The enormous amount of work that Bolt developed in 2009, and the amount that was absorbed by drag, is truly extraordinary.

“It is so hard to break records nowadays, even by hundredths of a second, as the runners must act very powerfully against a tremendous force which increases massively with each bit of additional speed they are able to develop.

“This is all because of the ‘physical barrier’ imposed by the conditions on Earth. Of course, if Bolt were to run on a planet with a much less dense atmosphere, he could achieve records of fantastic proportions.

“The accurate recording of Bolt’s position and speed during the race provided a splendid opportunity for us to study the effects of drag on a sprinter.

“If more data become available in the future, it would be interesting to see what distinguishes one athlete from another,” added Mr Hernandez.

Bolt 2012Bolt (L) is known to be a

Bolt’s time in Berlin was the biggest increase in the record since electronic timing was introduced in 1968.

John Barrow at Cambridge University who has previously analysed how Bolt could become even faster, explained that his speed came in part due his “extraordinary large stride length”, despite having such an initial slow reaction time to the starting gun.

“He has lots of fast twitch muscle fibres that can respond quickly, coupled with his fast stride is what gives him such an extraordinary fast time.”

He said Bolt has lots of scope to break his record if he responded faster at the start, ran with a slightly stronger tail-wind and at a higher altitude, where there was less drag.

Bolt’s Berlin record was won with a tail wind of only 0.9m per second, which didn’t give him “the advantage of helpful wind assistance”, he added.

“You’re allowed to have a wind no greater than 2m per second to count for record purposes, so without becoming any faster he has huge scope to improve,” Prof Barrow told BBC News.

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Neutrino ‘flavour’ flip confirmed

Neutrino ‘flavour’ flip confirmed


An important new discovery has been made in Japan about neutrinos. These are the ghostly particles that flood the cosmos but which are extremely hard to detect and study. Experiments have now established that one particular type, known as the muon “flavour”, can flip to the electron type during flight. The observation is noteworthy because it allows for the possibility that neutrinos and their anti-particle versions might behave differently. If that is the case, it could be an explanation for why there is so much more matter than antimatter in the Universe. Theorists say the counterparts would have been created in equal amounts at the Big Bang, and should have annihilated each other unless there was some significant element of asymmetry in play.

“The fact that we have matter in the Universe means there have to be laws of physics that aren’t in our Standard Model, and neutrinos are one place they might be,” Prof Dave Wark, of the UK’s Science and Technology Facilities Council (STFC) and Oxford University, told BBC News. The confirmation that muon flavour neutrinos can flip, or oscillate, to the electron variety comes from T2K, an international collaboration involving some 500 scientists. The team works on a huge experimental set-up that is split across two sites separated by almost 300km. At one end is the Japan Proton Accelerator Research Centre (J-Parc) located on the country’s east coast.

The ‘ghostly’ neutrino particle

  • Second most abundant particle in the Universe, after photons of light
  • Means ‘small neutral one’ in Italian; was first proposed by Wolfgang Pauli in 1930
  • Uncharged, and created in nuclear reactions and some radioactive decay chains
  • Shown to have a tiny mass, but hardly interacts with other particles of matter
  • Comes in three flavours, or types, referred to as muon, tau and electron
  • These flavours are able to oscillate – flip from one type to another – during flight
  • Could be a Majorana particle – that is a particle that is equal to its anti-particle

It generates a beam of muon neutrinos that it fires under the ground towards the Super-Kamiokande facility on the west coast. The Super-K, as it is sometimes called, is a tank of 50,000 tonnes of ultra-pure water surrounded by sensitive optical detectors. These photomultiplier tubes pick up the very rare, very faint flashes of light emitted when passing neutrinos interact with the water.

In experiments in early 2011, the team saw an excess of electron neutrinos turning up at Super-K, suggesting the muon types had indeed changed flavour en route. But just as the collaboration was about to verify its findings, the Great Tohoku Earthquake damaged key pieces of equipment and took T2K offline. Months of repairs followed before the project was able then to gather more statistics and show the muon-electron oscillation to be a formal discovery. Details are being reported on Friday at the European Physical Society Conference on High Energy Physics in Stockholm, Sweden.

“Up until now the oscillations have always been measured by watching the types disappear and then deducing that they had turned into another type. But in this instance, we observe muon neutrinos disappearing and we observe electron neutrinos arriving – and that’s a first,” said Prof Alfons Weber, another British collaborator on T2K from the STFC and Oxford.

Neutrino oscillations are governed by a matrix of three angles that can be thought of as the three axes of rotation in an aeroplane – roll, pitch and yaw. Other research has already shown two of the matrix angles to have non-zero values. T2K’s work confirms that the third angle – referred to as theta-one-three – also has to have a non-zero value.

This is critical because it allows for the oscillations of normal neutrinos and their anti-particles, anti-neutrinos, to be different – that they can have enough degrees of freedom to display an asymmetrical behaviour called charge parity (CP) violation. CP-violation has already been observed in quarks, the elementary building blocks of the protons and neutrons that make up atoms, but it is a very small effect – too small to have driven the preference for matter over anti-matter after the Big Bang. However, if neutrinos can also display the asymmetry – and especially if it was evident in the very massive neutrinos thought to have existed in the early Universe – this might help explain the matter-antimatter conundrum. The scientists must now go and look for it. It is likely, though, that much more powerful neutrino laboratories than even T2K will be needed to investigate the issue.

“We have the idea for a Hyper-Kamiokande which will require an upgrade of the accelerator complex,” Prof Weber told BBC News.

“And in America there’s something called the LBNE, which again would have bigger detectors, more sensitive detectors and more intense beams, as well as a longer baseline to allow the neutrinos to travel further.”

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Neutron starbursts can forge gold

Neutron starbursts can forge gold

New evidence has been uncovered of a rare cosmic event that is proposed as a source of heavy elements such as gold. Observations from the Hubble Space Telescope appear to show a distant collision between two neutron stars – the remnants of massive supernovae. Astronomers suggest that such collisions are responsible for ultra-short bursts of gamma rays occasionally seen across the Universe. The work is described in a paper on the pre-print server

Although rare, neutron star collisions would generate the enormous fluxes of neutrons needed to make elements heavier than iron, like platinum, lead and gold, by rapid neutron capture. Prof Edo Berger and colleagues from Harvard University analysed Hubble observations of a short burst of gamma rays, lasting only one fifth of a second, seen from a galaxy 3.9 billion light years away. The infrared afterglow of this burst of gamma-ray light appears to show the characteristics expected during radioactive decay of atomic nuclei generated in a neutron star collision.

This sort of event emits light with an intensity that lies between normal star light and that of a supernova, and the term “kilonova” has been coined to describe it. They appear to be around 1,000 times rarer than supernova explosions, and occur when the remnants of two supernovae collide.

If confirmed, the result represents the first observation of a neutron star collision, and provides an explanation for the rapid “R-process” of atom-building that must generate the heavy elements on the periodic table, such as gold and platinum. Neutron stars are incredibly dense and massive. As well as bursts of light, when they collide they are also expected to send gravity “shock waves” through the Universe. Experiments in America and Europe are now focussed on measuring such waves, and combined with the type of events seen by Hubble in the last month this will provide a further confirmation of neutron star collision. Astronomers are now testing the conclusions of the Harvard group with further detailed analysis of the Hubble data.

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French nuclear tests ‘showered vast area of Polynesia with radioactivity’

French nuclear tests ‘showered vast area of Polynesia with radioactivity’

French nuclear tests ‘showered vast area of Polynesia with radioactivity’

Declassified papers show extent of plutonium fall-out from South Pacific tests of 60s and 70s was kept hidden, says French paper

Tahiti, Polynesia

Tahiti, above, was exposed to 500 times the accepted maximum radiation level from nuclear tests in the 20th century, reports Le Parisien. French nuclear tests in the South Pacific in the 1960s and 1970s were far more toxic than has been previously acknowledged and hit a vast swath of Polynesia with radioactive fallout, according to newly declassified ministry of defence documents which have angered veterans and civilians’ groups.

The papers, seen by the French paper Le Parisien, reportedly reveal that plutonium fallout hit the whole of French Polynesia, a much broader area than France had previously admitted. Tahiti, above, the most populated island, was exposed to 500 times the maximum accepted levels of radiation. The impact spread as far as the tourist island, Bora Bora.

Thousands of veterans, families and civilians still fighting for compensation over health issues have insisted France now reveals the full truth about the notorious tests whose impact was kept secret for decades.

From 1960 to 1996, France carried out 210 nuclear tests, 17 in the Algerian Sahara and 193 in French Polynesia in the South Pacific, symbolised by the images of a mushroom cloud over the Mururoa atoll. For decades, France argued that the controlled explosions were clean.Jacques Chirac, the French president, controversially resumed nuclear atoll explosions in the South Pacific shortly after being elected in 1995.

Le Parisien said the documents “lifted the lid on one of the biggest secrets of the French army”. It said papers showed that on 17 July 1974, a test exposed Tahiti to 500 times the maximum allowed level of plutonium fallout.

Bruno Barillot, who has investigated the impacts of the nuclear tests for the Polynesian government, complained of the high levels of thyroid cancers and leukaemia in Polynesia. He said the declassified documents revealed Tahiti had “literally been showered with plutonium for two days” during the Mururoa test; from the outset France knew the impact spread further than it publicly admitted. But of the 2,050 pages declassified, 114 remained blacked out.

Richard Oldham, a member of the Polynesia nuclear workers’ association Mururoa e Tatou, told Radio New Zealand International : “It’s the right for our future generations to know what has happened in this country.”

In 2006 a French medical research body found nuclear testing had caused an increase in cancer on the nearest inhabited islands. The French judiciary began investigating health implications. It was not until 2010 that France acknowledged that there could be a compensation process for veterans and civilians. But that is complex and limited to a small geographical area and certain ailments.

About 150,000 veterans and civilians worked on, or were present during, nuclear tests, including 127,000 in Polynesia. But of 800 dossiers, only 11 people have received compensation.

Troops who worked on the tests have described a staggering lack of precaution for workers. During the Mururoa tests in French Polynesia in the late 1960s, one veteran described how he was stationed in shorts and a T-shirt on a boat only about 15 miles from the explosion before having to sail immediately to the area of the vast mushroom cloud to examine the damage.

Others on different tests wore shorts and had no sunglasses; they were told simply to shield their eyes and turn their backs at the time of the explosion.

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Graduate recruitment at highest level since 2008

Graduate recruitment at highest level since 2008

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Nasa buys into ‘quantum’ computer

Quantum Computer

Nasa buys into ‘quantum’ computer

The machine does not fit the conventional concept of a quantum computer, but makes use of quantum effects

A $15m computer that uses “quantum physics” effects to boost its speed is to be installed at a Nasa facility.

It will be shared by Google, Nasa, and other scientists, providing access to a machine said to be up to 3,600 times faster than conventional computers.

Unlike standard machines, the D-Wave Two processor appears to make use of an effect called quantum tunnelling.

This allows it to reach solutions to certain types of mathematical problems in fractions of a second.

Effectively, it can try all possible solutions at the same time and then select the best.

Google wants to use the facility at Nasa’s Ames Research Center in California to find out how quantum computing might advance techniques of machine learning and artificial intelligence, including voice recognition.

Geordie Rose Chief technology officer, D-wave

University researchers will also get 20% of the time on the machine via the Universities Space Research Agency (USRA).

Nasa will likely use the commercially available machine for scheduling problems and planning.

Canadian company D-Wave Systems, which makes the machine, has drawn scepticism over the years from quantum computing experts around the world.

Until research outlined earlier this year, some even suggested its machines showed no evidence of using specifically quantum effects.

Quantum computing is based around exploiting the strange behaviour of matter at quantum scales.

Most work on this type of computing has focused on building quantum logic gates similar to the gate devices at the basis of conventional computing.

But physicists have repeatedly found that the problem with a gate-based approach is keeping the quantum bits, or qubits (the basic units of quantum information), in their quantum state.

“You get drop out… decoherence, where the qubits lapse into being simple 1s and 0s instead of the entangled quantum states you need. Errors creep in,” says Prof Alan Woodward of Surrey University.

One gate opens…

Instead, D-Wave Systems has been focused on building machines that exploit a technique called quantum annealing – a way of distilling the optimal mathematical solutions from all the possibilities.

Geordie Rose, D-WaveGeordie Rose believes others have taken the wrong approach to quantum computing

Annealing is made possible by physics effect known as quantum tunnelling, which can endow each qubit with an awareness of every other one.

“The gate model… is the single worst thing that ever happened to quantum computing”, Geordie Rose, chief technology officer for D-Wave, told BBC Radio 4’s Material World programme.

“And when we look back 20 years from now, at the history of this field, we’ll wonder why anyone ever thought that was a good idea.”

Dr Rose’s approach entails a completely different way of posing your question, and it only works for certain questions.

But according to a paper presented this week (the result of benchmarking tests required by Nasa and Google), it is very fast indeed at finding the optimal solution to a problem that potentially has many different combinations of answers.

In one case it took less than half a second to do something that took conventional software 30 minutes.

A classic example of one of these “combinatorial optimisation” problems is that of the travelling sales rep, who needs to visit several cities in one day, and wants to know the shortest path that connects them all together in order to minimise their mileage.

The D-Wave Two chip can compare all the possible itineraries at once, rather than having to work through each in turn.

Reportedly costing up to $15m, housed in a garden shed-sized box that cools the chip to near absolute zero, it should be installed at Nasa and available for research by autumn 2013.

US giant Lockheed Martin earlier this year upgraded its own D-Wave machine to the 512 qubit D-Wave Two.

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Debut for thermal invisibility cloak

Debut for thermal invisibility cloak

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