Category Archives: Physics

Klingon style cloaking device, now a little closer

Invisibility cloaking devices have been the subject of science fiction for a long time; for example the famous Klingon and Romulan devices of Star Trek.

klingon

Image courtesy of http://en.memory-alpha.org

This started to become reality in two papers in 2006. John Pendry of Imperial College London and David Schurig & David Smith of Duke University laid out the theory of “transformation optics” in [1]. Shortly after the principle was demonstrated using microwaves [2].

Perfect cloaking?

No-one so far has created a perfect cloaking device that works in a range of frequencies. Although one can make an object invisible, reflections from the cloak make the scene a little darker and the presence of the object is clear.

Now Nathan Landy & David R. Smith [3] have developed a diamond-shaped cloak, with properties carefully matched at the diamond’s corners, so that light passes around the cloak completely with no reflections.

Here, we design and experimentally characterize a two-dimensional, unidirectional cloak that makes no approximations to the underlying transformation optics formulation, yet is capable of reducing the scattering of an object ten wavelengths in size. We demonstrate that this approximation-free design regains the performance characteristics promised by transformation optics.

Extracted from the abstract of [3]

Applications

It would be very difficult to extend this technique to visible light, so hiding large objects from our view is a little way off. However, microwaves are important in telecommunications and it is possible that cloaking devices could be applied here.

Reference

[1] J. B. Pendry, D. Schurig, D. R. Smith, Controlling Electromagnetic Fields, Science 23 June 2006:
Vol. 312 no. 5781 pp. 1780-1782.

[2] D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, D. R. Smith, Metamaterial Electromagnetic Cloak at Microwave Frequencies, Science 10 November 2006: Vol. 314 no. 5801 pp. 977-980

[3] Nathan Landy & David R. Smith, A full-parameter unidirectional metamaterial cloak for microwaves, Nature Materials (2012) doi:10.1038/nmat3476

IOP comments on George Osborne’s speech

Professor Paul Hardaker, Institute of Physics  Chief Executive, has commented on a speech made by the Chancellor of the Exchequer, George Osborne, at the Royal Society, London.

George

George Osborne,Chancellor of the Exchequer

It is really encouraging to know that the Chancellor of the Exchequer recognises the central role that science can play in creating robust economic growth for the UK. The proposed framework for capital investment includes some key features that will be vital to keep this country at the forefront of innovation and research.

Paul Hardaker

Link

Institute of Physics comments on George Osborne’s speech at the Royal Society (IOP News)

Another dimension to Latin America

Dimensional regularization, that is compute in “4 + ε space-time dimensions” and take the limit ε→0 at the end, is a powerful tool in quantum field theory. In fact, Veltman and ’t Hooft won the 1999 Physics Nobel Prize, for dimensional regularization and its application to Yang-Mills theory. The work of Veltman and ‘t Hooft dates back to 1971 and was published in 1972 [3].

However, the original idea may have come from two physicist working in Argentina. According to Wolfgang Bietenholz & Lilian Prado, it was Juan Jose Giambiagi and Carlos Guido Bollini [1] in a paper submitted before Veltman and ‘t Hooft, who first proposed dimensional regularization [2].

The paper of Giambiagi and Bollini, although submitted for publication earlier, was actually published after the paper of Veltman and ‘t Hooft.

Juan José Giambiagi (1924 – 1996)

Read the short preprint by Bietenholz & Prado, which is available on the arXiv, for more details.

Carlos Guido Bollini

Links

Juan José Giambiagi (ICTP biography)

Carlos Guido Bollini (Fundación Konex)

References
[1]Wolfgang Bietenholz & Lilian Prado,40 Years of Calculus in 4 + epsilon Dimensions,(2012) arXiv:1211.1741v1 [physics.hist-ph]

[2]C.G. Bollini and J.J. Giambiagi, Lowest order ‘divergent’ graphs in n-dimensional space, Phys. Lett. 40B (1972) 566-568.

[3] G. ’t Hooft & M. Veltman, Regularization and renormalization of gauge fields Nucl. Phys. B44 (1972) 189-213.

Indian monsoons may regularly fail in the future

New research suggests that the rate of failure in Indian summer monsoon will increase over the next two centuries, due to global warming [1].

The Indian farmers rely on the monsoons to disperse freshwater on agricultural land. Failure of the summer monsoons could be very detrimental to India’s economy.

Walker Circulation

The Walker circulation is a vast loop of winds that influences climate across much of the globe, including the Indian summer monsoons.

Walker

Image courtesy of NOAA

Walker circulation describes the air flow in the tropics in the lower atmosphere. The Walker circulation is generated by the pressure gradient that results from a high pressure system over the eastern Pacific ocean, and a low pressure system over Indonesia.

El Niño

The Southern Oscillation is the natural variation in the temperature of the surface of the tropical eastern Pacific Ocean and the surface air pressure. This occurs across the tropical Pacific Ocean roughly every five years. The extremes of this climate pattern’s oscillations, El Niño (warm) and La Niña (cool), cause extreme weather events across many regions of the world.

The Walker circulation brings areas of high pressure to the western Indian Ocean, bringing the monsoons. However, in years when El Niño occurs, the winds get shifted eastward, bringing high pressure over India and the effect is to suppress the monsoons.

The predictions

Jacob Schewe and Anders Levermann simulations suggest that as temperatures increase in the future, the Walker circulation, will on average bring more high pressure over India; even though the occurrence of El Niño doesn’t increase.

The effect of this will be an increase in the occurrence of monsoons failing to form and an increase in drought across India.

Reference

Jacob Schewe and Anders Levermann (2012), A statistically predictive model for future monsoon failure in India, Environ. Res. Lett. 7 044023

Link

Indian monsoon failure more frequent with warming, IOP News

Italian earthquake scientists found guilty

Six Italian scientists and an ex-government official have been sentenced to six years in prison over the 2009 earthquake in L’Aquila, about 100 km north-east of Rome.

The 6.3 magnitude quake, that struck on 6 April 2009, heavily damaged the city of L’Aquila and killed 309 people.

The prosecution argued that the scientists gave false reassurances before the earthquake. The defense argued that earthquake prediction is difficult and that it is impossible to make an accurate prediction of major quakes.

The convicted

  • Franco Barberi, head of Serious Risks Commission
  • Enzo Boschi, former president of the National Institute of Geophysics
  • Giulio Selvaggi, director of National Earthquake Centre
  • Gian Michele Calvi, director of European Centre for Earthquake Engineering
  • Claudio Eva, physicist
  • Mauro Dolce, director of the the Civil Protection Agency’s earthquake risk office
  • Bernardo De Bernardinis, former vice-president of Civil Protection Agency’s technical department

All seven have been sentenced to six years in prison for issuing false reassurances.

Before the convictions, more than 5,000 scientists, organised by the American Association for the Advancement of Science, signed an open letter to the Italian President Napolitano in support of the accused. The letter can be found here (pdf).

The aftermath

The worry is that science itself has been put on trial. Scientists should not have to make statements or not, in worry of being subject to lawsuits. This could discourage scientists becoming involved in public engagement.

Links

IOP News

Lack of investment in nuclear physics, says IOP

Current funding of nuclear physics research is insufficient for the UK to take advantage of developing technologies needed in such areas as healthcare, the nuclear industry and defense, according to an international panel of nuclear physicists.

IOP website

A new report by the Institute of Physics, A Review of UK Nuclear Physics Research, has been published to help produce a strategy to help guide nuclear physics in the UK for the next decade [1].

Reference

[1] A Review of UK Nuclear Physics Research (PDF, 10 MB)

Link

Nuclear physics ‘compromised by lack of investment’, IOP News

Cauliflower and fractals

Researchers have published a mathematical formula to describe the processes that dictate how cauliflower-like fractals form [1].

flower

The team grew thin films using a technique known as chemical vapour deposition (CVD). They adapted the CVD process so that the film would grow into shapes similar to those seen on a cauliflower. These structures were on the submicron scale.

From this work the team were able to derive the formula which describes how the cauliflower-like patterns develop over time.

Theory verses Experiment

Below are some graphics comparing the theory with experimental observations. The close agreement is clear.

simulations

Taken from the paper [1], courtesy of IOP publishing

Reference

[1] Mario Castro et al (2012) Universality of cauliflower-like fronts: from nanoscale thin films to macroscopic plants New J. Phys. 14 103039 (online here)

Link

IOP News

One step closer to a Star Trek tractor beam

Professor David Grier and David Ruffner (graduate student), working at the Department of Physics and Centre for Soft Matter Research have published a paper announcing that they have experimentally demonstrated a class of tractor beams[1]. They were able to move microscopic spheres of silica suspended in water over distances of about 30 micrometres.

david

David G. Grier

The definition of a tractor beam (quoted from the paper) is: A tractor beam is a traveling wave that can transport illuminated material along its length back to its source.

By this definition things like optical tweezers or optical conveyor belts are not technically tractor beams.

The problem

If you think about it, in order for a particle to be pulled by a beam of light, rather than pushed, it has to redirect the momentum of enough photons to overcome the force due to the radiation pressure of the beam.

This can happen if the intensity of light beam changes sufficiently along the axis of the beam. For example, one can use a beam with tightly focused areas.

The method

The tractor beam demonstrated by Ruffner and Grier uses a special kind of laser beam called a Bessel beam laser– the amplitude is given by a Bessel function of the first kind. A perfect Bessel beam would not diffract and spread out as it propagates. (For those that are interested, there is a lot of classical mathematical physics behind Bessel functions)

The team produced two Bessel beams side by side using a lens to angle them so they overlapped. Then by varying the relative phase of the two beams, the particle becomes trapped in an “optical conveyor” which allows the particle to be transported in three dimensions.

beam

Cross-section of the Bessel beam and graph of intensity

Applications

No-one is about to start pulling space craft about using this technique. However, it may find applications in biology rather quickly.

Reference

[1] Optical conveyors: A class of active tractor beams, D. B. Ruffner and D. G. Grier, Physical Review Letters, in press (2012) (download)

Link

David Grier’s Home Page

Global Weirding in the UK

One of the predicted outcomes of global climate change is the phenomena of “global weirding”. This basically says that extremes of weather will become more common.

rain

Image by Bidgee

Of course, there is rather natural expected variation in the weather and extreme phenomena have always occurred. The claim is that global warming is making record breaking weather more and more common.

In the UK

The Environment Agency, Met Office and Centre for Ecology & Hydrology (CEH) held a joint briefing in London. They warned that a the UK must get ready for for regular swings of drought conditions and flooding.

This summer?

This summer was the wettest in the UK for 100 years, according to Met Office figures. The Environment Agency issued over 1,000 river flood alerts and warnings for the period of the 1st June at 15th July. This was the most alerts issued in a summer since 2007.

Then in August the hottest temperature recorded was 32.4°C at Cavendish, Suffolk, on 18 August.

The UK mean temperature was 0.4 °C above the 1981-2010 average. It was a wet month in south-west England and south Wales and in northern England, southern and eastern Scotland, with a few areas having over twice the average rainfall. In contrast much of East Anglia and south-east England and parts of north-west Scotland and the west of Northern Ireland were drier than normal. Many areas were somewhat duller than usual, the sunnier exceptions being Northern Ireland and the western side of Scotland.

http://www.metoffice.gov.uk/climate/uk/2012/august.html

Cold winters

The winter of 2010-2011 came early, with snow in the United Kingdom falling in November 2010. This was the earliest snowfall in 17 years. A night time low temperature of −9.1 °C was recorded on the 25th/26th at Redesdale Camp, Northumberland. From January on the winter conditions were more normal.

The winter of 2009–2010 was known as “The Big Freeze” here in the UK and was part of the severe winter weather in Europe. It was the coldest winter since 1978-79, with a mean temperature of 1.5 °C.

The question

The BIG question must be is this all due to global weirding, or is this normal variations?

Links

BBC News

One million jobs in the UK rely on physics

Physics is central to the economy of the UK. Whether through the application of novel research and technologies, or through the skills and abilities of physics-trained workers, physics drives businesses and innovation.

Professor Sir Peter Knight President, Institute of Physics

According to a new report by the Institute of Physics, about 4% of of employees in the UK work in companies that could not exist without a knowledge of physics.

spectrum

Image by Bill Bertram

Of course, the definition of a “physics based company” is wide. Supermarket checkouts would not work without laser physics, for example. However, the study only takes into account the companies that would be unable to exist without ability to respond and adapt to latest advances in research.

A good example here would be Oxford Instruments, whose annual turnover of £337 million is almost entirely “physics based”.

The full report The Importance of Physics to the UK Economy can be found here (opens a PDF).

Links

One million UK jobs depend on physics, IOP News