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Home » Page 1861

Lasers illuminate the flight of the bumblebee

The apocryphal story about bees not being able to fly arose because the roughness and flexibility of their wings was neglected in a quick calculation. The wings of a bumblebee bend to create vortices that provide lift on both the upward and downward strokes, and a full analysis of the bee’s flight involves many factors: wing angle, wing deformation, aerodynamic and inertial forces on the wing, and so on. All of these parameters are expressed in terms of ‘body vector’ – that is, the exact orientation of the insect’s body.

Existing methods for measuring the body vectors of insects in free flight assume that the wings act symmetrically, but this only happens if the insect is flying in a straight line. To measure body vector more accurately, Zeng and colleagues developed technique that accounts for more realistic curved flight paths.

The team glued a sliver of glass weighing just 0.8 milligrams to the top of a bumblebee’s body, between its wings. The bumblebee was then allowed to fly freely inside a small clear box, illuminated from above by an array of 49 lasers. As the bumblebee changed direction and orientation, the laser beams bounced off the glass onto a trapezoidal screen suspended above the box.

Synchronized cameras above and at the side of the box monitored the position of the bumblebee and this allowed the team to calculate the angle of reflection of the laser light and then the body vector. Coupled with velocity and acceleration data provided by the cameras, the technique should allow biologists to model insect flight much more precisely. Using the new method, Zeng’s team found that the bumblebee’s body vector varied considerably, even as it flew in their small experimental chamber.

Diamond comes under the microscope

Scanning tunnelling microscopy is a powerful tool for mapping the contours of surfaces on the atomic scale. A fine metallic tip hovers just above the surface of the sample, and a voltage is applied across the tip and the sample. This makes the electrons quantum mechanically ‘tunnel’ across the gap between the tip and the sample, and this registers a current that depends on the size of the gap. The current measurements obtained as the tip moves across the material allow a picture of the surface to be built up. But the technique is unsuitable for insulators because they do not allow this current to flow.

But Bobrov and colleagues found that they could image certain planes of the diamond crystal if they applied a much higher voltage between the tip and the sample. Diamond has a ‘work function’ of 5.3 volts – that is, a voltage of 5.3 volts is needed to eject electrons from the material. When the team applied a higher voltage, they found that electrons jumped from the tip of the scanning tunnelling microscope into the conduction band of the diamond, allowing it to conduct electricity. The scanning tunnelling microscope registered a current of about 1 nanoamp and the team were able to obtain an image of the diamond surface.

According to the Paris team, this ‘resonant electron injection’ technique should allow physicists to map the surfaces of other insulators and determine their electrical characteristics, if they have a suitable band gap structure.

Nanotubes win Euro prize

Iijima, currently at Meijo University, and colleagues discovered in 1991 that sheets of graphite can be rolled into seamless tubes just nanometres in diameter. Ebbesen, now at the NEC Research Institute, and team devised a method of producing large numbers of the tubes, and found that they have surprising degree of elasticity that makes them very strong.

Groups led by Dekker, currently at Delft University, and McEuen, now at Cornell University, subsequently discovered the unusual electrical properties of carbon nanotubes, including their ability to behave as quantum wires – that is, two-dimensional semiconductors. Dekker’s team also confirmed that the tubes can act as either metals or semiconductors depending on the angle at which the graphite sheets are rolled.

Many devices based on nanotubes have emerged in the last few years. Dekker and co-workers created a single-molecule transistor made from a single tube, while McEuen and colleagues showed that junctions made from the tubes can behave as diodes. Very recently, a single-electron transistor and the first digital logic circuits based on carbon nanotubes were unveiled, both of which represent significant steps into the world of nano-electronics.

Chaotic lasers decode data

The intensity of light from a laser can vary unpredictably – or ‘chaotically’ – if a tiny portion of the laser output is fed back into the laser cavity. A message ‘imprinted’ onto this complex signal can only be recovered by a receiver if the chaotic signal can be subtracted. This means the chaotic signal must be reproduced in another laser at the receiving end.

Identical chaotic conditions can be created in the transmitter and receiver lasers if they are linked. But on its way to the receiver, the intensity of the encrypted signal continues to vary chaotically. By the time it reaches the receiver laser, the signal no longer matches the signal generated by the receiver laser. The receiver laser therefore needs to predict the variations that take place in the encrypted signal as it travels between the lasers.

To tackle this problem, Shore and team sent a single feedback signal from their transmitter laser to the receiver laser, and also back to the transmitter laser. This created identical conditions in both lasers. But Shore’s team sent the feedback signal on a short route to the receiver and a longer route to the transmitter, so the chaotic signal produced by the receiver laser was 3.5 nanoseconds ahead of that produced by the transmitter. This delay corresponded exactly with the extra time the feedback signal took to reach the receiver. Such ‘anticipating synchronization’ allows the receiver laser to create a chaotic signal identical to the one in the encoded signal, so the message can be retrieved.

Shore and colleagues now plan to investigate how the technique – which some experts are sceptical about – would work in real optical communications systems. They are also optimistic that their theory may have diverse applications. “The process of synchronization could also be used to control different types of chaos in non-physical systems, including biological or economical systems”, Shore told PhysicsWeb. Such systems have a certain response time, which is analogous to the time it takes the signal to reach the transmitter in the laser experiment.

“The work by Shore’s group is a nice experimental demonstration of the idea proposed by Voss [Phys. Rev. E 61 5115],” Edward Ott of the University of Maryland told PhysicsWeb. “I anticipate that people will come up with schemes to exploit this phenomenon”.

Nobel Prize for Bose condensates

Bose-Einstein condensation was first predicted in 1924 by the Indian physicist, Satyendra Nath Bose, and Albert Einstein. In a Bose condensate the de Broglie wavelength of the atoms is comparable with the average interatomic spacing, which causes all the atoms to condense into the same quantum ground state. All the atoms are described by the same quantum wavefunction, which gives the condensate many unusual properties.

Cornell, Wieman and colleagues in Boulder produced the first condensate in an ultracold gas of rubidium atoms in 1995. Later that year Ketterle and co-workers at MIT achieved condensation in a gas of sodium atoms. Since then there has been an explosion of interest in Bose condensation as physicists have probed the properties of this unique state of matter. Bose condensates have been used to produce atom lasers – laser-like beams in which photons are replaced by atoms – and study fundamental processes such as superfluidity.

The winners will share the cash prize of 10 million Swedish kroner – around £730 000 – and will receive their gold medals and diplomas at an Award Ceremony in Stockholm on 10 December. The Swedish capital celebrates the centenary with an exhibition, a programme of lectures and a students’ essay contest.

First nanotube circuits get logical

Carbon nanotubes are rolled-up sheets of graphite about a nanometre in diameter. They have previously been used to make a variety of electronic components, including diodes and field-effect transistors (FETs). A FET can be made from a nanotube by attaching gate, source and drain electrodes to it. Dekker’s group has now placed several of these FETs on a single silicon chip to form different circuits.

Their simple inverter device consists of a nanotube FET and a large bias resistance: it converts a high input voltage to a low one – that is, “one” to “zero” – and vice versa. By adding an extra FET in parallel, the researchers made a NOR gate. This device needs two “zero” inputs to give a “one” output, or two “ones” to give a “zero”.

Any of the standard logic gates – AND, OR, NAND and so on – can be created using different arrangements of these FETs. The team also created a ‘static random access memory’ and an oscillator that generates an ac signal. The devices have gains of a factor of ten.

The Delft group used electron beam lithography to deposit aluminium gate electrodes onto a silicon wafer, placed the nanotubes on top, and added gold electrodes by an evaporation technique. Despite their achievement, Dekker and colleagues admit that there are still challenges to overcome, such as the difficulty in positioning the nanotubes accurately on the wafer. But the team hopes that emerging techniques – including a way to grow nanotubes directly onto the chip – may solve this problem.

Condensate control could lead to ‘atom circuits’

A Bose-Einstein condensate is a super-cold cloud of gas atoms that are all in the same quantum state. This means that a single wave function describes the behaviour of all the atoms, and the quantum properties of the atoms can be seen in the macroscopic behaviour of the condensate.

To make the atom chip, Reichel’s team deposited two parallel gold wires, each 50 micrometres wide, onto the surface of a chip just under two centimetres across. The team confined a gas of rubidium atoms in a conventional magneto-optical trap and then transferred them to the microtrap generated by the atom chip. The magnetic fields of the microtrap are generated by electric currents of a few amps that flow through the gold wires on the atom chip.

After a strong magnetic field compressed the gas, a blast of radio waves was then applied to cool the atoms and create a Bose-Einstein condensate containing about half a million atoms. The condensate hovers a few micrometres above the surface of the chip, held in place by the magnetic field.

Once the condensate is trapped, Reichel and co-workers sent a series of electrical pulses along the parallel gold wires, which pushed the magnetic field along. This ‘magnetic conveyor belt’ dragged the condensate 1.6 millimetres across the surface of the chip – a huge distance in quantum terms.

The small scale of the new technique means that clouds of gas atoms can be chilled to the correct temperature ten times faster than is possible with conventional traps. Such rapid cooling means that a perfect vacuum – which is difficult to maintain – is unnecessary. The proximity of the condensate to the surface is also an important achievement because physicists believed that this would destroy the fragile quantum state. Bose-Einstein condensates are usually created inside relatively large vacuum chambers to shield them from collisions with other atoms.

Modern lithography can create structures smaller than 100 nanometres in size, and this makes the new technique extremely versatile. This will allow physicists to manipulate Bose-Einstein condensates in many different ways, which could benefit fields as diverse as interferometry, holography, microscopy and quantum information processing.

Biological physics hits the high life

About half a century ago, physicists like Max Delbrück and Erwin Schrödinger discovered the fascination of tackling problems in biology with physics. Indeed, the increasing overlap of physics, biology and chemistry that followed led to the foundation in 1961 of the International Union of Pure and Applied Biophysics. And as the 700 delegates at the 4th International Conference on Biological Physics in Kyoto, Japan, back in August demonstrated, the trend towards biological physics is escalating.

The opening highlight of the conference was a talk by Gerald Edelman of the Scripps Research Institute in the US about brain dynamics and consciousness – the first time that the subject has been discussed at an international conference on biological physics. Edelman, who shared the Nobel Prize for Medicine in 1971, guided the audience into the world of neuroscience and philosophy. He outlined various strands of evidence that suggest the brain’s response follows a set of selection principles analogous to Darwin’s theory of evolution. And he emphasized that the brain is by no means an organic computer that is controlled by the same concepts as electronic computers.

In the October issue of Physics World, Fritz G Parak of the Technical University of Munich, Germany, outlines the other diverse roles of physics in biology that were discussed at the conference.

Career options for physicists

If there’s one thing that physicists are good at, it’s being able to apply their skills and knowledge to new areas. Whether they realize it or not, physicists have many of the transferable skills that are highly valued by employers. They are analytical, creative and persistent. They are also experts at problem solving and have an eye for detail.

Even the so-called soft skills that physicists may have lacked in the past – the ability to communicate effectively or to work in a team – are increasingly being taught in undergraduate courses (p40, print version only). As this special issue highlights, a physics degree can open the door to a huge variety of jobs.

A wealth of opportunities

Despite the dot.com meltdown and the fall from grace of several high-tech high-flyers, many of today’s brightest physics graduates still follow a well trodden path to the giants of the computer and telecoms world. Physicists learn fast and are snapped up quickly by employers, as Eugene Loh of Sun Microsystems discovered (p33, print version only). He was on his way to a physics conference when he met someone from a small computer company who was looking to hire a PhD physicist. Loh took the plunge and has been surprised to find that the computing industry can be as intellectually stimulating as his research was. Bigger budgets and better facilities are among the other advantages that industrial R&D has over academic life, as Emma Walton of Sharp Research Labs reports on page 34 (print version only).

Other major employment sectors for physicists include the defence industry and medicine. Physicists, after all, were the brains behind radar plus a host of medical-imaging devices. On page 35 (print version only), Jennifer Morrison describes her experiences with BAE SYSTEMS, while John Kotre of Newcastle General Hospital explains that opportunities abound in medical physics (p46, print version only). And physicists hold many glamorous jobs in the media (p44, print version only).

Love and money

Most people who choose to study physics do so because they are fascinated by the world around us and not because they want to earn big bucks. That’s one reason why many physicists are happy to carve out careers in academia, where the money is good, but not great. The first step on the academic ladder is generally a stint as a post-doc – and on page 43 (print version only) Danny Hill, who left Britain for Spain, describes the virtues of a doing research in another country.

Some academic physicists, however, are so committed to their research that it literally becomes their life – so much so that they often end up in relationships with other physicists. While that can be rewarding – both partners understand the frustration and rewards of research – it can lead to difficulties. Particularly tricky is the so-called two-body problem, the challenge of finding two physics jobs in the same place (see article). Some couples spend years working hundreds of miles apart in order to further their careers, only seeing each other at weekends and at conferences. Another couple even marketed themselves as “a package with 24-hour lines of communication” as a way of staying together.

But if a job with a big pay packet comes your way, it’s going to be hard to ignore. That explains why many young and talented PhD physicists are lured away from academia for high-paying positions as “rocket scientists” and computer experts in the City and Wall Street (p47, print version only). Indeed, the latest salary survey from the Institute of Physics shows that financial services is the most lucrative sector for British and Irish physicists, who earn an average of £40 000 a year (see article). Meanwhile, we compare the earnings of physicists with scientists and engineers in the other fields (see article).

Calling all teachers

If there’s one profession that is crying out for physicists, it’s teaching. Last autumn just 205 graduates in England and Wales registered on teacher-training courses – down from almost 570 in 1993. Teaching certainly suffers from a bad image – 80% of graduates in the UK regard it as hard, unrewarding work. But teaching can be satisfying in ways that other jobs are not, as Kate Searle explains on page 36 (print version only). And the pay – in the UK at least – is not as bad as people might think.

But if you’re fed up with your job – maybe you’re a post-doc who cannot see a permanent job on the horizon or you work in industry and are worried about redundancy – then there is hope. Finding out what makes you tick is one of the keys to finding your dream job, say careers experts, who offer tips for CVs and interviews (see article). As one careers consultant says in our article on how to change career, physicists have “a far wider range of options than they often thought”.

Just ask Queen rock legend Brian May or world-record triple jumper Jonathan Edwards – two celebrities whose degree in physics has done them no harm (p52, print version only).

Isaac Newton: the gifted genius

It seems unlikely that we will ever lose our fascination for the man whom David Berlinski calls “the largest figure in the history of Western science” and the author of “the greatest of scientific theories”. Indeed, there have been many biographies of Isaac Newton over the last two decades. What is important for Berlinski, however, are not the details of Newton’s life – fascinating though these may be – but the understanding of his “gift”. By this he means Newton’s revelation of the “book of Nature” and his unlocking of the “system of the world”. The biographical details only become important to Berlinski when the singularities of Newton’s personality contribute in some way to the equal singularity of his work in physics.

Of course, the key moments of Newton’s life are all here. Berlinski describes the “marvellous year” of 1665-1666, in which Newton laid the foundation for his work in mathematics, mechanics and optics. He notes Newton’s discovery that the Earth’s gravitation extends to the Moon, and describes his invention of the reflecting telescope and the subsequent controversy over his optics. He covers the correspondence with Hooke, which resulted in Newton exchanging a balance of forces for a single attractive force, and the dramatic growth of the Principia following the visit of Halley to Cambridge in 1684.

Berlinski is not always correct in his statements. He says that Newton made no mathematical discoveries after the invention of calculus. He occasionally accepts the truth of a dubious anecdote, like the one about the dog Diamond accidentally causing the fire that consumed Newton’s optical papers. He also makes one or two unsupported statements, such as Newton having Hooke’s portrait destroyed. However, his graphic descriptions of events have an authentic feel, and give the impression that the author understands the period as well as the science. Where necessary, he fills in detail imaginatively and with credibility.

He is also very convincing on the character analysis. His Newton was secret and suspicious, hypersensitive, an indifferent speaker, incapable of intellectual generosity, but possessed of many intellectual and organizational gifts, and lacking only in the capacity and desire to analyse himself. A few incidents help to soften the image of unrelieved austerity. Newton, for example, is shown to have displayed a kind of “alien tenderness” in dealing with his niece, Catherine, during her affair with his close friend, the statesman and politician Lord Halifax. However, the real point of the book is elsewhere.

The key point in Berlinski’s analysis is the sheer strangeness of Newton’s ideas, even in the prior context of the discoveries of such predecessors as Kepler and Galileo. A ruthless simplifier and abstract thinker, Newton had the remarkable ability of striking at the fundamentals. His laws of physics have a transcendent quality that cannot be fully explained in terms of the world’s matter. By extending gravity to the Moon, he destroyed the prospects of a mechanical philosophy of nature, such as Descartes had dreamed of.

There was, however, a great price in intellectual coherence in Newton’s decision to create accessible solutions, while leaving problems that could not be solved for the future. Counterintuitive and intellectually daring, his invocation of forces that acted at a distance served to fill space with mystery.

Berlinski provides fascinating discussions of Newton’s “five” laws of motion, which include his “law” of absolute space and time. The fact that Newton was able to develop an appropriate mathematics in calculus (as also did his contemporary Leibniz) showed that there was an element of fortune in his timing. This is emphasized by the parallel story of his unsuccessful pursuit of alchemy. The alchemists were on the right track, but, through bad luck, they guessed wrong and failed to find equivalent chemical laws.

Despite the importance of mathematics in his work, Newton was not in his heart a pure mathematician. He was essentially a physicist and was already thinking beyond calculus in the act of creating it. After he had created his great masterwork, the Principia, he saw no point in developing further deductive results in what we now call Newtonian mechanics.

Newton’s abstract vision needed no pictures, as were required by a mechanistic philosopher such as Hooke. Yet Berlinski asserts, in a different sense, that Newton was a “painter”, with each diagram in the Principia having a secret to be revealed. This was not always easily done. For example, an anecdote tells how an initially confident Richard Feynman got into a hopeless tangle while trying to explain a diagram to a group of freshman students. Indeed, the only creator whom the author can find to compare to Newton and the Principia is another painter – Michelangelo – at work on the Sistine Chapel. Not even Einstein is of equal standing.

Berlinski himself variously uses words, symbols and pictures. He takes on the difficult task of explaining mathematical ideas to readers, who he clearly hopes will include some who are without mathematical training. Co-ordinate geometry, Cartesian axes, calculus, vectors and differential equations are explained in terms of their meaning and significance, though there is also a technical appendix. Mathematically trained people will find a wealth of metaphors here to use in their own explanations.

Berlinski does not try – like some authors of popular books on physics – to make science sound mysterious. But he does demonstrate convincingly that Newtonian mechanics is a great deal more than a set of routine procedures. For Berlinski, there is no mystery about the way in which we use Newton’s theory. The mystery is in what it is.

The urgency of such books is in the desire to find a fully unified theory of physics, and to comprehend what we have already achieved on the road to it. All the great theories are singular, like Newton’s. Maxwell’s electromagnetic theory, Einstein’s relativity and quantum mechanics are the only comparable ones. Whatever form the ultimate unified theory may take, its origin will be in the scientific style created by Newton.

Berlinski’s book is thought-provoking and stimulating, and a thoroughly enjoyable read. His prose is shot through with brilliant images. It is nowhere more remarkable than in the vivid metaphors he conjures up to explain fundamental aspects of mathematics.

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