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Home » Page 1863

UK tackles student shortage

Fifteen recommendations designed to bolster undergraduate physics are contained in the report. The inquiry panel believes that more must be done to promote physics to young people and that the critical shortage of physics teachers in schools must be addressed at a national level. In the report, the panel says that MPhys and BSc courses must remain the primary source of highly qualified physicists, but it believes that there is a case for less mathematically demanding physics degrees. The report also states that the funding of physics departments must be addressed and the provision of physics courses throughout the UK safeguarded.

How much maths?

One of the central themes of the report is the shortage of physics graduates, at a time when their intellectual and practical skills are eagerly sought by employers. Since 1990, when the Institute published a report that led to the introduction of the four-year MPhys degrees, the total number of students entering higher education in the UK has increased significantly. The number taking physics degrees, however, has remained static – indeed only one in 20 students studying physics at A-level goes on to study the subject at university.

One physicist with direct experience of this shortage is Derek Raine of Leicester University. “I can’t remember a time when so many firms have come to me looking for physicists,” he says. “Physics has a great economic as well as cultural importance.”

One of the skills most prized by employers is students’ mathematical ability. The report recognizes the value of the current MPhys and BSc degrees in this regard, but points out that the mathematical skills of new undergraduates tend be weaker because of a less rigorous mathematical training at A-level. Indeed, many 18 year olds with good physics grades go on to study less mathematical courses at university, such as IT, engineering and biomedical sciences. The report says that there is therefore “an opportunity to develop courses that provide the intellectual education of physics, with its analytical, modelling and practical aspects, but in a broader context” (see Physics World October 2001 pp16-17, print version only).

“It’s no good moaning that we should go back to the old A-levels,” says Raine. “Universities should adjust their courses to suit the students coming in. We have to develop a degree for people not training to become researchers, such as those who want to work in financial services or management.”

The panel supports the idea of a new degree that would be open to students with limited mathematical training, which would allow students to build up their mathematical knowledge during the degree. It believes that such a qualification would meet the demands of employers looking to recruit graduates in shortage areas, including teaching. The panel recommends that a working group should look into the content and level of such a degree, and explore the demand and funding available for it.

“It would be a great benefit for the country if university physics departments could be a source of two kinds of graduates,” says Bob Lambourne of the Open University. “They would be differently skilled and differently schooled, but would complement one another and each could make an important contribution to the UK.”

Reversing the teacher shortage

In addition to discussing undergraduate shortages, the report also focuses on the need to increase enthusiasm for physics among younger people. It calls on the government to do more to promote science and science-based careers, and recommends that the Institute should set up a programme to encourage girls to study physics and women to take up physics careers.

Part of the problem when trying to interest young people in physics is the severe shortage of qualified physics teachers in schools, the panel believes. In fact, only about a third of people teaching A-level physics have a degree in the subject. “The critical shortage of physics teachers in schools and colleges is the greatest threat to the future supply of skilled scientists and engineers,” says the report. “It is crucial that it is addressed at a national level.”

The panel urges parliament to address what it considers to be the five factors that deter graduates from becoming teachers: pay, conditions, status, workload and technical provision. It says that the government must “accept and respond to market forces that dictate differential salaries for teachers in shortage subjects”. And, in particular, it thinks that the government should set targets for the proportion of science classes taught to 14-19 year olds by subject specialists.

The report goes on to say that university physics departments must improve their links with schools and teachers by offering support, advice and access to equipment. Ian Aitchison of Oxford University shares this view, but points out that departments will have to be given extra money to do so. “University departments have an obligation to be a resource to teachers,” he says, “but they cannot do it for nothing. A few hundred thousand pounds should allow a department to run a school liaison service, for example.”

Physics in the regions

Another area of concern to the panel is the provision of university physics courses throughout the regions of the UK. The report points out that since 1994 the number of universities offering degrees in physics has dropped from 79 to 58. One consequence of such a decline, it says, is the emergence of “deserts” in undergraduate physics teaching – regions of the UK not served by a local department. The panel is concerned about this because the introduction of student loans means that students are now more likely to study at home, as are the increasing numbers of mature students. The report points out that cutbacks also threaten contact between teachers and universities, and deprive local industry of trained personnel and access to research expertise.

The report also says that the Institute, together with the Standing Conference of Physics Professors, must use its influence with government and pan-European educational bodies to ensure that the MPhys degree is recognized as a masters qualification in a more integrated European education system (Physics World October 2000 pp8-9).

Heavy water tests body water

In trials, patients drank a measure of heavy water – the exact amount depended on their weight – mixed with tap water. Davies and team then collected breath samples from the patients every four minutes for the next two hours. Heavy water is formed when two deuterium atoms replace the hydrogen atoms in a water molecule. Deuterium is chemically identical to hydrogen, but it is heavier because it contains an extra neutron.

The exhaled moisture consisted of ordinary water, heavy water, and a small amount of water containing the naturally occurring isotope oxygen-18. Each sample was mixed with protonated water to create ions of the three types of water, which all have different ratios of charge to mass. Their relative abundances were measured using a technique known as ‘flowing afterglow mass spectrometry’. Since the fraction of oxygen-18 in ordinary water vapour is well known, Davies and team were able to calculate the proportion of deuterium in their breath samples.

The researchers found that the levels of deuterium in the patients’ breath became stable two hours after drinking the heavy water, and this indicates that the heavy water is evenly distributed in the body. This measurement, together with each patient’s heavy water dose, is used to calculate the total amount of body water. “We are now developing a user-friendly instrument that should be ready for hospitals in 2002”, team member David Smith told PhysicsWeb.

Until now, doctors have gauged the level of water in a patient’s body using methods that required blood samples and took several days to complete. Other techniques are based on measurements of the electrical resistance of body tissue, but these are unreliable, partly because the formulae used for converting the data are based on healthy people.

City air pollution becomes clear

The ability of airborne particles to absorb water – that is, their hygroscopicity – strongly affects their optical properties, and these properties have many consequences for the environment. The amount of light that particles scatter determines how much they reduce visibility, and – en masse – affects the proportion of sunlight that the atmosphere reflects back into space. Water absorption also influences how easily airborne material can be inhaled.

Heintzenberg’s team collected samples of atmospheric particles from 12 metres above the ground during December 2000 and January 2001 in central Leipzig. After segregating the particles – which were around 300 nanometres in size – according to their moisture content, the researchers measured the amount of light scattered by each class of particles. They were surprised to find a group of highly water-repellent particles that were transparent. Heintzenberg and co-workers are not sure what they are, but speculate that they could be glassy materials or lighter organic compounds.

The discovery could benefit studies that predict the composition of pollutants from their optical properties. But Heintzenberg stresses that it is too early to say if the result is good news for the environment: “We just don’t know yet – we didn’t expect to see particles that are both clear and water-repellent”, he told PhysicsWeb.

New Year’s Eve fireworks caused the only significant variation in Leipzig’s atmosphere during the course of the study – they greatly boosted the proportion of hygroscopic particles in the air.

Collider costs shake CERN

An increase of 25% in the cost of a large high-tech project like the LHC is not unusual, according to Roger Cashmore, CERN’s director for collider programmes. But such rises are usually factored into the original price. No such allowance was made in the case of the LHC. “In the US you would take the base price and add 40%,” says Cashmore. “So these overruns are what prudent people would expect. I’m afraid the chickens are coming home to roost.”

It is not clear at this stage how the extra costs – which came to light at a meeting of CERN’s finance committee last week – will be met. Cashmore says that there are no technical problems with the LHC and that CERN still intends to collide the machine’s first protons in April 2006, although he admits that problems with civil engineering could delay this. By sticking to its schedule, CERN will therefore have to enlarge its annual SFr1bn budget by a few per cent over the next five to ten years, or add to the loans that it originally took out to pay for part of the project.

The issue will be discussed at a meeting of CERN’s finance committee in November and then at a council meeting of the member states the following month. Cashmore says that by this time there will have to be “very clear statements” about the budget.

Entanglement leaps to larger scales

Entanglement is a feature of quantum mechanics that allows particles to share a much closer relationship than classical physics permits. A measurement on one part of an entangled system reveals the properties of the other part, even if they are physically separated.

Polzik and co-workers injected the caesium atoms into two cylindrical glass cells lying end to end, but separated by a few millimetres of air. The team then shone a pulse of right-handed circularly polarized light through one cylinder so that the spins of the atoms in that cell were aligned with each other. A left-handed pulse aligned the spins in the other cell in the opposite direction.

To entangle the atoms in the cells, a single polarized laser pulse passed through both cells. The momentum of the light changes the spin of the atoms in each cell slightly, by an equal and opposite amount. This means they are entangled – the exact spin of the atoms in each cell is unknown, but a measurement of the spin of one sample would reveal the spin of the other sample.

Since the spins of the atoms also change the momentum of the light as it passes through, a measurement of the light as it exits the second cell revealed the average spin of the two samples. This showed that entanglement had taken place.

Half a millisecond later, Polzik and colleagues sent a second pulse of linearly polarized light through both cells. Again, this changed the spins slightly, but the researchers found that the average spin was the same – this revealed that the entangled state was still intact. Systems containing just a few atoms have been entangled for longer periods, but the Aarhus result is a record for macroscopic objects.

‘We have achieved entanglement with a single pulse of light, so in theory the samples can be placed at a considerable distance apart’, Polzik told PhysicsWeb. ‘This makes it the first type of entanglement useful for teleportation of atomic states and other types of quantum communication’.

Excitons take charge of optoelectronics

When light falls on a semiconductor, electrons are excited from the ‘valence band’ – where they are tightly bound to their parent atom – into the ‘conduction band’, where they can move and contribute to current flow. Each electron leaves a ‘positive hole’ in the valence band, and the electron stays close to this hole in a bound system called an exciton. The exciton can move through the semiconductor, but it is not influenced by electric fields because it has no net charge.

But an exciton can have an overall negative charge if it attracts an extra electron to form a ‘trion’. To encourage trions to form, Shields and colleagues added extra electrons, in the form of silicon ‘donor’ atoms, to a gallium arsenide structure. When they applied a voltage across the structure, they found that the trions drifted several micrometres towards the positive terminal. This overturns the long-held idea that trions are held still – or ‘pinned’ – by the attraction of positive ions in the semiconductors.

‘Previous research had suggested that trions are localised by the potential of donor ions’, Shields told PhysicsWeb, ‘although the results of some experiments could be best explained by a model in which the excitons are free’.

Electrons emit their excess energy as light when they recombine with positive holes, and this means that excitons are the source of light in semiconductors. ‘We have shown that charged excitons can be controlled using applied voltages’, says Shields. ‘Since these excitons produce light, this gives us another handle to control optoelectronic devices such as light-emitting diodes.’

Electron laser packs a punch

Conventional lasers amplify the radiation that is emitted when electrons move between certain energy levels in atoms or molecules. But the radiation in a free electron laser is generated by a beam of accelerated electrons. Magnets makes the electron beam follow a zigzag path, and the acceleration the electrons experience each time they change direction makes them emit radiation. Mirrors direct this radiation back into the electron beam and this leads to further emission. This self-amplifying effect can take place at any wavelength, and the free electron laser can be tuned by altering the speed of the electrons.

The DESY experiment successfully amplified light at ultraviolet wavelengths ranging from 80 to 180 nanometres, with its peak amplification at 98 nanometres. The international team of scientists at the Hamburg centre aim to achieve a similar gain with soft X-rays – that is, radiation with a wavelength below six nanometres – within a year. To do this, they will need to extend the current linear accelerator from 50 metres to 300 metres in length.

The free electron laser programme at DESY is part of the TESLA project proposal to build a next-generation linear collider for particle physics.

Interference makes super-sensitive ruler

Interferometers work by splitting a coherent beam and then recombining the different components at a detector, such as a screen. If the components are in phase when they recombine, they reinforce each other, and if they are out of phase they cancel each other out – the exact phase relationship depends on the distance each component has travelled. This leads to a characteristic pattern of bright and dark fringes on the screen, and the spacing between the fringes can be used to measure small distances and movements. The minimum spacing is half the wavelength of the light used, and this is the best resolution the device can have.

To increase this resolution, Ovchinnikov and Pfau shone a helium-neon laser at an oblique angle into the cavity between two narrowly spaced parallel mirrors. The light can take many different paths through this ‘waveguide’, and each one has a different angle of reflection from the mirrors. This means there are very many beams – or ‘modes’ – of light propagating at the same time. Each one takes a different amount of time to travel through the waveguide, which depends on its angle of reflection.

Each time a single mode of light is reflected, its phase shifts by a tiny amount. The phases of the other modes change by a slightly different amount. This means that the light waves have a very complex phase relationship when they reach the end of the waveguide. In the experiment conducted by Ovchinnikov and Pfau, this led to a diffraction pattern in which the fringes were separated by just a ninth of the wavelength of light.

The researchers plan to modify their device – known as a multimode waveguide interferometer – to increase its sensitivity even further. The fringes in the diffraction pattern get closer together as the light undergoes more reflections. This means that a narrower cavity would lead to a higher resolution, because the light would undergo more reflections as it passes through the waveguide.

“Pfau and I have been using the multimode waveguide since early 2000, but it took us six months to realise that it was a new type of interferometer”, Ovchinnikov told PhysicsWeb.

British firms lag the world in R&D

British firms ploughed back just 2.1% of sales into R&D, compared to an international average of 4.2%. Only in three sectors – health (7.2%), aerospace (7.7%) and pharmaceuticals (14.8%) – does the UK have a higher R&D intensity than its competitors. In sectors such as engineering (1.3%), electronics (3.0%), and software (4.2%), meanwhile, British investment is well behind international levels.

Over a quarter of the US companies analysed have an R&D intensity greater than 10%, compared with just 4% of the UK companies studied.

Friction riddle is cracked

Over two hundred years ago, Amontons and Coulomb found that the force needed to push an object across a surface depends on the mass of the object, but does not appear to depend on the area in contact with the surface. Microscopic bumps – or ‘asperities’ – on the surfaces have traditionally been blamed for these effects. The asperities make the true contact area much smaller than it seems, and also difficult to measure. The mass of the object creates pressure at the interface and compresses the asperities, increasing this contact area.

To reach a better understanding of how microscopic effects determine macroscopic behaviour, Marder and Gerde extended an existing theory that describes how cracks arise and propagate in other materials. They found that ‘micro-cracks’ – similar to dislocations in crystalline materials – emerge in the lattice structure of the materials at the boundary between two surfaces. Although these cracks seem to move – like wrinkles in a rug – as the object is pushed along, the back edge of each crack actually ‘heals’ while the front edge grows. Like the ridges in a rug, the micro-cracks reduce the contact area between the surfaces and make it easier for them to slide across each other.

The atom-level simulation also confirmed that the force needed to slide one object over another is proportional to the compressive force at the boundary, which is determined by the mass of the object on top. This relationship was also described by the earlier theory based on asperities.

Micro-cracks could even solve a long-standing geophysical puzzle, according to Marder and Gerde. If micro-cracks existed between tectonic plates, they would reduce the contact area and explain why earthquakes generate much less heat than calculations predict.

Marder also speculates that the theory could have implications at the other end of the scale: “It may help us to understand frictional sliding in nanomachines”, he told PhysicsWeb. “Non-destructive sliding is highly desirable and our mechanism for friction produces no wear.”

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