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Home » Page 1498

Nanoparticles sink or swim in sewage

Scientists in the UK have used neutron scattering studies to develop a new way of separating silica nanoparticles from wastewater — which could prevent millions of tonnes of nanoparticles entering waterways every year.

Just a few tens of nanometres in diameter, such spheres of silica are being used in an increasing number of consumer products including cosmetics, medicines, cleaners and even food. As a result, sewage treatment plants have become a major gateway for nanoparticles entering the environment as treated effluent, sludge or both. Although there is no evidence that such nanoparticles pose an environmental threat, their ultimate fate is a mystery, because monitoring their presence in sewage has so far been impossible.

Now, scientists from the Centre for Ecology & Hydrology (CEH) and the ISIS neutron source have overcome this obstacle using small angle neutron scattering (SANS) — a technique that has been used to study a wide range of nanometre-sized structures. SANS involves firing a beam of low–energy neutrons through a sample and measuring the intensity of neutrons at small deviations from the transmitted beam.

Nanoscale problem

“Detecting nanoparticles in wastewater really is a nanoscale problem”, explains Steve King, from the ISIS neutron source. “One could use an electron microscope, but that would be very laborious, as you would be counting individual particles. Light scattering is made difficult by the background turbidity. SANS, however, is capable of resolving down to a few nanometres, and can quantify the concentration, size, shape and aggregation of the nanoparticles.”

The scientists reproduced the conditions found in a primary sewage treatment plant — microbes and all — and looked at whether the silica nanoparticles remained suspended in the liquid, or dropped into the sludge.

The team studied bare nanoparticles and some that were coated with a surfactant commonly found in consumer products. While the bare nanoparticles remained suspended, the coated particles interacted with other components of the sewage and rapidly formed a solid sludge. The researchers repeated the experiments in pure water, and found that both bare and coated particles remained dispersed.

The SANS measurements also helped the team investigate the mechanism that leads to the rapid aggregation and sedimentation of the coated particles. “Our experiments strongly suggest this must be mediated by interactions between the adsorbed surfactant molecules and organic matter in the sewage,” says King. “Other aggregation mechanisms, such as those promoted by electrolytes, act on much longer time scales.”

Designer Waste

By adding a coating that modifies that surface chemistry, it may be possible to re-route their journey Helen Jarvie, CEH

The difference in behaviour between the coated and uncoated nanoparticles means that they can be separated at primary treatment plants. This opens the possibility of controlling the environmental fate of the nanoparticles at the production stage. “Our research proves that the surface chemistry of nanoparticles influences their likely removal during primary sewage treatment,” says Helen Jarvie from the CEH. “By adding a coating that modifies that surface chemistry, it may be possible to re-route their journey through sewage treatment plants.”

Richard Owen, Chair Environmental Risk Assessment at the University of Westminster, was impressed by the work. “The authors have shown the importance of understanding the relationships between surface functionality of nanoparticles and how they behave in the natural environment and where they end up,” he says. “This is crucial if we are to develop predictive models of fate and behaviour that help us understand the risks engineered nanoparticles pose to the environment.”

Jarvie told physicsworld.com that her team plan to continue their work using SANS, by examining a wider range of nanoparticles, with different classes of surfactants.

The work is described in Environmental Science and Technology.

Binary systems share stardust

Telescopes now routinely yield detailed images of the cosmos, and in the process help unravel some of the mysteries surrounding our own existence. But one big unanswered question is how the Earth and our planetary neighbours were created from the primordial dust surrounding the young Sun.

In the past two decades we have come to understand that stars form “protoplanetary disks” with radii that can reach up to several hundred times the mean distance between the Sun and the Earth. Astrophysicists have studied the structure of such disks at several radiation wavelengths, which has led to a growing understanding of the star-formation process.

However, most stars form in pairs (and sometimes more complex groups) and numerical models produce conflicting results because of the complex dynamical interaction of two cosmological bodies. Our understanding has also been held back by a lack of direct observations of such systems.

This image reveals a rare glimpse of a young multiple protoplanetary disk encircling a two-star system located 160 ps away in the Ophiuchus constellation around the celestial equator. Having pinpointed the binary system, the researchers led by Satoshi Mayama of the Graduate University for Advanced Studies, Japan, placed a coronograph over the Subaru Telescope in Hawaii. This enabled them to filter out the direct light from the twin stars and reveal two individual protoplanetary disks bridged by a complex interaction.

Comparison with numerical models suggests that there could be a channelling of debris from one disk to the other – a finding that the researchers say might reveal where planets can form in binary systems (Science 10.1126/science.1179679).

As the International Year of Astronomy (IYA2009) draws to a close, its organisers must be delighted at the huge attention given over the last 12 months to a field that has come so far since Galileo turned his primitive instrument to the Moon 400 years ago.

Inflation, strings and the anthropic principle

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Alan Guth at the Institute of Physics

By Hamish Johnston

Have you ever wondered what went on in the universe when it was just 10-35 s old — and how this could be related to our special pocket in the multiverse?

If so, you might want to watch a video of the 2009 Newton lecture, which is now available on the Institute of Physics (IOP) website.

The lecture was given in London on 14 October by Alan Guth, who was in town to receive the IOP’s Isaac Newton Medal for his pioneering work on cosmic inflation — a theory that changed the way we think of the early universe.

Entitled “Inflationary Cosmology: Is Our Universe Part of a Multiverse?”, Guth’s talk lasts about one hour. He starts with an explanation of how inflation provides a “simple and natural” explanation for how the universe became what it is today.

He then moves on to dark energy and explains how its discovery has further improved our understanding of the evolution of the universe — but brings with it the “nightmare” of a vacuum energy that is much smaller than that predicted by quantum mechanics.

But inflation offers a way of avoiding this nightmare in a scenario that involves a multiverse of pocket universes, string theory and the anthropic principle…but you’ll have to watch the lecture to find out how!

Quantum poetics in NYC

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Unravelling physics fusing science with art

By James Dacey

“A mash-up of laboratory theatre and laboratory science”. This is how a group of New York thespians are describing their attempt to take theoretical physics to the stage.

Quantum Poetics is seeking to transform recent advances in theoretical physics and neuroscience into performance art, and it’s the latest project of NYC’s Stolen Chair Theatre Company.

A cast of 12, including clowns, stuntmen and musicians will create a “gravity and genre-defying world, which marvels at the complexity and beauty of how the universe’s massive and minuscule forces allow humans to build meaning”.

When I caught up with Liza Green, the theatre company’s spokesperson, she said they hope the performance will “expose audiences to what is beautiful and exciting about mathematical exploration and scientific thought.”

Admitting that the directors still have a lot of homework to do, she says they are determined to avoid “fake science” or “pop math”, citing the film Pi as an example of a production that, whilst name-checking maths and science, doesn’t really engage with academic content.

Of course, this is not the first time that playwrights have looked to theoretical physics for creative inspiration. British writer Tom Stoppard incorporated ideas from thermodynamics and chaos theory in his highly acclaimed play Arcadia (1993), which looked at the life and times of Lord Byron.

In Copenhagen (1998), another British dramatist Michael Frayn built an entire play around the famous 1941 conversation between Neils Bohr and his former protégé Werner Heisenberg in the Nazi-occupied Danish capital.

Earlier this year, the Ransom Theatre Company in Northern Ireland produced the Gentlemen’s Tea Drinking Society — a black comedy centred four alcoholic graduates from Cambridge one of whom has secretly discovered the Higgs boson.

Quantum Poetics will open its pilot season on November 22, which will build towards a full stage production scheduled for the Autumn of 2010.

UK to pull out of Gemini Observatory

The UK is “almost certain” not to continue participating in the Gemini Observatory after 2012 according to a statement by the Gemini board of directors. The UK, which is a founding member of the facility, has a 23% stake in the project with a total of £35m invested to date.

The Gemini Observatory consists of two 8 m telescopes – Gemini North in Hawaii and Gemini South in Chile – that work in the optical and infrared regions. Gemini is operated by a partnership of seven countries including the US, UK, Canada, Chile, Australia, Brazil and Argentina.

Withdrawing from the observatory would save the Science and Technology Facilities Council (STFC), which funds the UK’s involvement in Gemini, around £4m per year in running costs.

“It is regrettable that the UK is likely to pull out of Gemini, which reflects the tight budget of STFC,” says Andrew Fabian, president of the Royal Astronomical Society. “While we do of course have access to southern skies through the European Southern Observatory, we hope that UK astronomers retain access to a large telescope in the northern hemisphere, either through Gemini North or some other agreement.”

In a statement, the STFC said: “The UK has stressed that this is an indicative position only, and does not pre-judge the outcome of the STFC programme prioritization exercise now under way.”

The STFC council will now consider the recommendations from its current programme review with a final decision over whether to withdraw expected in March 2010. However, the statement noted that: “[The Gemini board] unanimously accepted the UK’s position that it is almost certain to not wish to continue beyond the current expiry data [of 2012].”

In late 2007 the UK also threatened to pull out of Gemini, before reinstating itself a few months later after agreeing to sell up to 50% of its observing time to other member states.

Nobel laureates call for open access

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John Mather has called for open access

By Hamish Johnston

It’s a debate that’s been around as long as the Internet — should academic research papers be free to read by one and all (open access) or should university libraries pay for journal subscriptions?

41 Nobel laureates are backing open access, and have written to members of the US Congress to ask them to support a bill calling for the Federal Research Public Access Act (FRPAA). The group includes four physicists — Sheldon Glashow, John Mather, Douglas Osheroff and David Politzer.

I’m not a lawyer, but I believe the the act would require that the results of all federally funded research be freely available online.

But are we well down that road already?

Over the past few years you may have noticed that more and more papers published in prestigious journals such as Nature and Science appear on the open access arXiv preprint server immediately after being published. I don’t know if this is done with the publisher’s blessing, but I’m guessing that it is tolerated in the hope of avoiding the sort of legislation that the US laureates are calling for.

So what about our journals here at IOP Publishing?

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We have an open access journal called the New Journal of Physics, which fits the bill as far as the laureates are concerned. Physicists pay to publish their papers, and if the entire industry went this way, funding would have to be diverted from libraries to the researchers themselves.

Access to most of our other journals is restricted to subscribers — but most articles are open access for 30 days after publication. And I’m told that IOP Publishing is happy for authors to post the text of accepted papers on arXiv, but not the final version that appears in the journal.

So it looks to me like open access publishing is possible already — just make sure you pop your accepted manuscript onto arXiv and the Feds will be happy.

But is this sustainable — if the accepted versions of papers are freely available, why would a scientist pay to publish or a university library bother to subscribe?

In other words, who is going to pay for managing the peer-review process that many scientists believe is essential?

An idealist might argue that scientists themselves could manage peer review — but does a busy physicist really want to be chasing her colleagues for overdue referee reports or field telephone calls from an irate colleague whose paper has been rejected? Who is going to copy edit papers written by authors whose first language is not English? And who is going to ensure that the journal keeps up with the latest advances in information technology?

That brings us back to the New Journal of Physics author pays model…is this the way of the future?

Sorry for all the question marks…and what do you think?

Photo finish in race for strontium condensate

An Austrian group has beaten its US counterpart by a matter of days in a race to create a Bose-Einstein condensate (BEC) of strontium atoms.

Researchers at the Institute of Quantum Optics and Information (IQOQI) at the Austrian Academy of Sciences submitted their paper on a strontium BEC – a mass of ultracold atoms all in the same quantum state – just 10 days before those at Rice University in Houston, Texas. The breakthrough makes way for more precise quantum timekeeping and new studies of the quantum nature of matter.

“We have been in a race to get this done, and once some big unknowns were figured out a couple of years ago it was no mystery how to get here,” says Rice University’s Tom Killian, who adds that the IQOQI is “a great lab”.

Rudi Grimm of the IQOQI says he and his colleagues learnt a lot from the Rice University group, but “were just quicker” with the final cooling stage.

A single state

Bose-Einstein condensation occurs when atoms of integer spin are cooled below a critical temperature. The atoms settle in the same quantum state and move coherently as though they are a single entity.

The first BECs were made in 1995 from alkali metal atoms, such as rubidium, which have one electron in their outer shell. Over the past few years BECs have also come made from atoms that have two outer electrons – ytterbium and more recently calcium. The real prize, however, is strontium – another atom with two outer electrons that has already proved very useful in extremely accurate optical clocks.

Two electron atoms are interesting because they have no magnetic moment in their ground state. This means that a BEC of strontium would not have to be shielded from stray magnetic fields – making it easier to use in applications such as an atom interferometer that could be used to detect tiny changes in the local gravitational field.

Breaking with convention

However, the conventional way of cooling atoms to create a BEC involves trapping them with a magnetic field, and then lowering the field’s potential so the hottest atoms tend to collide with others and are ejected from the trap – a process called “evaporative cooling”. Some researchers had found that lasers could perform both the trapping and evaporative cooling of non-magnetic atoms, but this has proven problematic.

The trouble is related to the scattering length, which effectively marks the distance at which atoms collide. The most abundant isotope of strontium, Sr-88, has a very small scattering length, so the collision rate is too low and evaporative cooling fails. On the other hand, the next most abundant isotope, Sr-86, has a very big scattering length, so collisions occur among too many atoms.

The breakthrough of the two groups was to opt for a much rarer isotope, Sr-84, which has a scattering length somewhere between Sr-88 and Sr-86 – making it just right. The IQOQI group used it to create a BEC of about 1.5 × 105 atoms, while the Rice University group used it to create a larger BEC of 3 × 105 atoms.

“I think it is impressive how the field has matured and that we can now condense atoms which have small natural abundance, and which cannot be magnetically trapped in the ground state,” says Wolfgang Ketterle of the Massachusetts Institute of Technology, who won the Nobel Prize for Physics in 2001 for being one of the first to create a BEC. “The strontium experiment [has] demonstrated an amazing combination of advanced techniques.”

Robust and well defined

Strontium is advantageous because it forms fairly robust condensates that can last longer and be made larger. This makes it easier for studies of quantum degeneracy, in which atomic interactions are tuned, for example, to create novel quantum fluids. Another advantage is that it has several well defined electronic-transition frequencies, which makes it attractive as an atomic clock for more precise metrology studies.

Tilman Pfau, a physicist at the University of Stuttgart who used similar techniques to condense chromium five years ago, called the new work an “interesting” addition to the BECs of ytterbium and calcium. “What is maybe also interesting is that people talked about condensing strontium for years, and now within days two groups have achieved this goal almost simultaneously,” he adds. “Science is a nonlinear process.”

The strontium BECs comes hot on the heels of the first calcium condensate, which was reported in September by Sebastian Kraft and colleagues at Germany’s PTB metrology lab in Braunschweig. Kraft told physicsworld.com long term goal of the PTB team is to create an optical lattice of calcium atoms – in which each lattice site holds precisely one atom. Such a “Mott insulator” could in principle be used as part of an atomic clock that is extremely precise because individual atoms are isolated from each other.

The research is reported in three papers in Physical Review Letters (see restricted links).

The story of Europe's space telescope

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Inspecting the mirror of the Herschel telescope (Courtesy: ESA).

By Hamish Johnston

At 11.00 am GMT today BBC Radio 4 is running the first in a two part series about the Herschel space telescope, which was launched earlier this year.

If you are not in the UK, you should be able to listen online — or listen later to an archived version.

Here’s what the Beeb says about the series:

“Following the engineers and astronomers who are working on the biggest telescope ever sent to space, in one of the most important missions in the history of European spaceflight. Jonathon Amos joins Professor Matt Griffin of Cardiff University and his international team as they aim to peer through the areas in space that are invisible to other telescopes. This is the story of how the team is aiming to solve the mystery of galaxy and star formation, and how these processes eventually gave rise to life-bearing planets like Earth.

“In this episode, the team approach the biggest milestone in their 20-year project – the launch of their work on a rocket from a spaceport in French Guiana. Will it all go safely?

There’s no mention of the Planck microwave observatory, which was launched at the same time as Herschel — but hopefully Amos will touch on its mission to study the cosmic microwave background (CMB) radiation – a remnant of the Big Bang

Holes block light in very thin films

What happens if you drill an array of tiny holes into a metal foil and then measure how much light the holes allow through? It turns out – as physicists discovered back in 1998 – that much more is transmitted than if the light behaved like water passing though a screen. The light is absorbed by electrons on the surface of the metal, creating “surface plasmons” – collective oscillations of conduction electrons – that travel via the holes to the dark side of the foil, where they re-emit the light.

Now, physicists in Germany have discovered that this phenomenon, known as “extraordinary optical transmission”, does not occur in foils that are thin enough to be semi-transparent to light. Instead, Bruno Gompf and colleagues at the University of Stuttgart found that punching holes in such films leads to a significant reduction in the amount of light that gets through. The findings could be useful for creating new kinds of polarization filters and other components for photonic circuits.

Reduced transmission

Gomp’s team began by coating a glass plate with a gold film just 20 nm thick. This should let about half the light through, which was confirmed by measuring the transmission as a function of wavelength. The team then used a beam of argon ions to etch a square array of 200 nm diameter holes with a period of 300 nm. Although this involved removing a significant amount of gold, the amount of transmitted light actually fell by a factor of about five at some wavelengths.

To gain a better understanding of this surprising observation, the team repeated the measurement at various angles of incident light. The researchers found that the wavelength of the transmission minimum shifted at certain angles relative to the square array, which led them to analyse the effect in terms of plasmons propagating on a square lattice. And because the material is so thin, the team also had to assume that surface plasmons on either side of the film were coupled to each other – making them different from the surface plasmons on thicker films responsible for extraordinary optical transmission.

Random holes

Putting all of this together, the team concludes that only certain damped short-range surface plasmons can be excited under these conditions, and that while such plasmons absorb light, they do not re-emit it. Furthermore, the team showed energy of such plasmons corresponds to the energy of light at the dip in the transmission spectrum. Gompf told physicsworld.com that the team is now investigating films with different thicknesses as well as arrays with different periodicities and holes that are randomly positioned.

Because the transmission of such films depends so much on the wavelength and orientation of the incident light, he believes that such materials could be used to create tiny polarization filters and other components for photonic circuits.

The work is reported in Physical Review Letters.

Bend it like Beckham

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Eric Goff testing ball trajectories

By Matin Durrani

Qualification for next summer’s football World Cup in South Africa reaches its climax tomorrow — highlights include France’s return play-off with Ireland and Egypt squaring off against arch-rivals Algeria on the same day.

But some teams, like England, have already secured their passage to the world’s greatest sports tournament and will no doubt be already be dreaming of lifting the famous trophy.

England’s players have a night off tomorrow but if star midfielder David Beckham is feeling a bit bored, he might want to read a new paper in the American Journal of Physics by John Eric Goff of Lynchburg College, Virginia, and Matt Carré of the University of Sheffield in the UK.

Goff and Carré carried out a series of experiments in which soccer balls were launched from a machine while two high-speed cameras recorded portions of their trajectory. The equipment allowed the researchers to vary the balls’ launch speed and spin — balls could be fired either with no spin, topspin, backspin, sidespin or any combination.

From the resulting data, the two physicists then calculated the “lift” drag coefficient on the ball and the “sideways” drag coefficient, CS. If the ball has pure topspin or pure backspin then CS is zero, but if the ball has any other spin, the value of CS is not zero.

All lovely stuff, of course, but where does Beckham come in? Well, Goff and Carré then examined Beckham’s famous 90th-minute free kick taken against Greece in October 2001 that secured England’s qualification for the 2002 World Cup in France. His carefully taken kick bent around the wall before landing plum in the back of the Greek net and secured England a dramatic last-minute equalizer in the 2–2 draw.

Using TV footage of the famous match, the two physicists calculated that the ball left Beckham’s foot at a speed of 36 m/s at which point its “Reynolds number” (air speed times ball diameter, divided by kinematic viscosity) was of 5.1 x 10^5^. The ball had an average rotational velocity of 63 radians per second, rose above the height of the crossbar during the flight and moved about 3 m sideways, before slowing down to about 19 m/s as it dipped into the corner of the goal.

Goff and Carré then did a back-of-the-envelope calculation to estimate a value for CS, which was found to be about 0.2 for the famous shot.

And the punchline? Sorry folks, there isn’t one. But maybe the paper will persuade Becks, who’s currently on loan from LA Galaxy at AC Milan, to swot up on a bit of simple physics before next summer’s tournament. Assuming he makes the team, that is.

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