̽��ֱ�� of Cambridge - light

Flashes bright when squeezed tight: how single-celled organisms light up the oceans

sc604 — Mon, 06 Jul 2020 06:30:00 +0000

Every few years, a bloom of microscopic organisms called dinoflagellates transforms the coasts around the world by endowing breaking waves with an eerie blue glow. This year’s spectacular bloom in southern California was a particularly striking example. In a new study published in the journal Physical Review Letters, researchers have identified the underlying physics that results in light production in one species of these organisms.

̽��ֱ��international team, led by the ̽��ֱ�� of Cambridge, developed unique experimental tools based on micromanipulation and high-speed imaging to visualise light production on the single-cell level. They showed how a single-celled organism of the species Pyrocystis lunula produces a flash of light when its cell wall is deformed by mechanical forces. Through systematic experimentation, they found that the brightness of the flash depends both on the depth of the deformation and the rate at which it is imposed.

Known as a ‘viscoelastic’ response, this behaviour is found in many complex materials such as fluids with suspended polymers. In the case of organisms like Pyrocystis lunula, known as dinoflagellates, this mechanism is most likely related to ion channels, which are specialised proteins distributed on the cell membrane. When the membrane is stressed, these channels open up, allowing calcium to move between compartments in the cell, triggering a biochemical cascade that produces light.

“Despite decades of scientific research, primarily within the field of biochemistry, the physical mechanism by which fluid flow triggers light production has remained unclear,” said Professor Raymond E. Goldstein, the Schlumberger Professor of Complex Physical Systems in the Department of Applied Mathematics and Theoretical Physics, who led the research.

“Our findings reveal the physical mechanism by which the fluid flow triggers light production and show how elegant decision-making can be on a single-cell level,” said Dr Maziyar Jalaal, the paper’s first author.

Bioluminescence has been of interest to humankind for thousands of years, as it is visible as the glow of night-time breaking waves in the ocean or the spark of fireflies in the forest. Many authors and philosophers have written about bioluminescence, from Aristotle to Shakespeare, who in Hamlet wrote about the ‘uneffectual fire’ of the glow-worm; a reference to production of light without heat:

"…To prick and sting her. Fare thee well at once / ̽��ֱ��glowworm shows the matin to be near / And 'gins to pale his uneffectual fire. / Adieu, adieu, adieu. Remember me.”

̽��ֱ��bioluminescence in the ocean is, however, not ‘uneffectual.’ In contrast, it is used for defence, offense, and mating. In the case of dinoflagellates, they use light production to scare off predators.

̽��ֱ��results of the current study show that when the deformation of the cell wall is small, the light intensity is small no matter how rapidly the indentation is made, and it is also small when the indentation is large but applied slowly. Only when both the amplitude and rate are large is the light intensity maximised. ̽��ֱ��group developed a mathematical model that was able to explain these observations quantitatively, and they suggest that this behaviour can act as a filter to avoid spurious light flashes from being triggered

In the meantime, the researchers plan to analyse more quantitatively the distribution of forces over the entire cells in the fluid flow, a step towards understanding the light prediction in a marine context.

Other members of the research team were postdoctoral researcher Hélène de Maleprade, visiting students Nico Schramma from the Max-Planck Institute for Dynamics and Self-Organization in Göttingen, Germany and Antoine Dode from the Ècole Polytechnique in France, and visiting professor Christophe Raufaste from the Institut de Physique de Nice, France.

̽��ֱ��work was supported by the Marine Microbiology Initiative of the Gordon and Betty Moore Foundation, the Schlumberger Chair Fund, the French National Research Agency, and the Wellcome Trust.

Reference:
M. Jalaal, N. Schramma, A. Dode, H. de Maleprade, C. Raufaste, and R.E. Goldstein. ‘Stress-Induced Dinoflagellate Bioluminescence at the Single Cell Level.’ Physical Review Letters (2020). DOI: 10.1103/PhysRevLett.125.028102

Research explains how a unicellular marine organism generates light as a response to mechanical stimulation, lighting up breaking waves at night.

Our findings show how elegant decision-making can be on a single-cell level

Maziyar Jalaal

̽��ֱ�� of Cambridge

̽��ֱ��Dinoflagellate Pyrocystis lunula

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Petals produce a 'blue halo' that helps bees find flowers

fpjl2 — Wed, 18 Oct 2017 09:54:15 +0000

Latest research has found that several common flower species have nanoscale ridges on the surface of their petals that meddle with light when viewed from certain angles.

These nanostructures scatter light particles in the blue to ultraviolet colour spectrum, generating a subtle optical effect that scientists have christened the ‘blue halo’.

By manufacturing artificial surfaces that replicated ‘blue halos’, scientists were able to test the effect on pollinators, in this case foraging bumblebees. They found that bees can see the blue halo, and use it as a signal to locate flowers more efficiently.

While the ridges and grooves on a petal surface line up next to each other “like a packet of dry spaghetti”, when analysing different flower species the researchers discovered these striations vary greatly in height, width and spacing – yet all produce a similar ‘blue halo’ effect.

In fact, even on a single petal these light-manipulating structures were found to be surprisingly irregular. This is a phenomenon physicists describe as ‘disorder’.

̽��ֱ��researchers conclude that these “messy” petal nanostructures likely evolved independently many times across flowering plants, but reached the same luminous outcome that increases visibility to pollinators – an example of what’s known as ‘convergent evolution’.

̽��ֱ��study was conducted by a multidisciplinary team of scientists from the ̽��ֱ�� of Cambridge’s departments of plant sciences, chemistry and physics along with colleagues from the Royal Botanic Gardens Kew and the Adolphe Merkele Institute in Switzerland.

̽��ֱ��findings are published today in the journal Nature.

“We had always assumed that the disorder we saw in our petal surfaces was just an accidental by-product of life – that flowers couldn’t do any better,” said senior author Prof Beverley Glover, plant scientist and director of Cambridge’s Botanic Garden.

“It came as a real surprise to discover that the disorder itself is what generates the important optical signal that allows bees to find the flowers more effectively.”

“As a biologist, I sometimes find myself apologising to physicist colleagues for the disorder in living organisms – how generally messy their development and body structures can seem.”

“However, the disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees,” Glover said.

All flowering plants belong to the ‘angiosperm’ lineage. Researchers analysed some of the earliest diverging plants from this group, and found no halo-producing petal ridges.

However, they found several examples of halo-producing petals among the two major flower groups (monocots and eudicots) that emerged during the Cretaceous period over 100 million years ago – coinciding with the early evolution of flower-visiting insects, in particular nectar-sucking bees.

“Our findings suggest the petal ridges that produce ‘blue halos’ evolved many times across different flower lineages, all converging on this optical signal for pollinators,” said Glover.

Species which the team found to have halo-producing petals included Oenothera stricta (a type of Evening Primrose), Ursinia speciosa (a member of the Daisy family) and Hibiscus trionum (known as ‘Flower-of-the-hour’).

All the analysed flowers revealed significant levels of apparent ‘disorder’ in the dimensions and spacing of their petal nanostructures.

“ ̽��ֱ��huge variety of petal anatomies, combined with the disordered nanostructures, would suggest that different flowers should have different optical properties,” said Dr Silvia Vignolini, from Cambridge’s Department of Chemistry, who led the study’s physics team.

“However, we observed that all these petal structures produce a similar visual effect in the blue-to-ultraviolet wavelength region of the spectrum – the blue halo.”

Previous studies have shown that many species of bee have an innate preference for colours in the violet-blue range. However, plants do not always have the means to produce blue pigments.

“Many flowers lack the genetic and biochemical capability to manipulate pigment chemistry in the blue to ultraviolet spectrum,” said Vignolini. “ ̽��ֱ��presence of these disordered photonic structures on their petals provides an alternative way to produce signals that attract insects.”

̽��ֱ��researchers artificially recreated ‘blue halo’ nanostructures and used them as surfaces for artificial flowers. In a “flight arena” in a Cambridge lab, they tested how bumblebees responded to surfaces with and without halos.

Their experiments showed that bees can perceive the difference, finding the surfaces with halos more quickly – even when both types of surfaces were coloured with the same black or yellow pigment.

Using rewarding sugar solution in one type of artificial flower, and bitter quinine solution in the other, the scientists found that bees could use the blue halo to learn which type of surface had the reward.

“Insect visual systems are different to human ones,” explains Edwige Moyroud, from Cambridge’s Department of Plant Sciences and the study’s lead author. “Unlike us, bees have enhanced photoreceptor activity in the blue-UV parts of the spectrum.”

“Humans can identify some blue halos – those emanating from darkly pigmented flowers. For example the ‘black’ tulip cultivar, known as ‘Queen of the night’.”

“However, we can’t distinguish between a yellow flower with a blue halo and one without – but our study found that bumblebees can,” she said.

̽��ֱ��team say the findings open up new opportunities for the development of surfaces that are highly visible to pollinators, as well as exploring just how living plants control the levels of disorder on their petal surfaces. “ ̽��ֱ��developmental biology of these structures is a real mystery,” added Glover.

New study finds “messy” microscopic structures on petals of some flowers manipulate light to produce a blue colour effect that is easily seen by bee pollinators. Researchers say these petal grooves evolved independently multiple times across flowering plants, but produce the same result: a floral halo of blue-to-ultraviolet light.

̽��ֱ��disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees

Beverley Glover

Tobias Wenzel/ Edwige Moyroud

Top: petals of Ursinia speciosa, a daisy, contain a dark pigment that appears blue due to 'disordered' striations. Bottom: close-up top and side view of microscopic striations.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

World’s 'smallest magnifying glass' makes it possible to see individual chemical bonds between atoms

sc604 — Thu, 10 Nov 2016 19:00:00 +0000

For centuries, scientists believed that light, like all waves, couldn’t be focused down smaller than its wavelength, just under a millionth of a metre. Now, researchers led by the ̽��ֱ�� of Cambridge have created the world’s smallest magnifying glass, which focuses light a billion times more tightly, down to the scale of single atoms.

In collaboration with European colleagues, the team used highly conductive gold nanoparticles to make the world’s tiniest optical cavity, so small that only a single molecule can fit within it. ̽��ֱ��cavity – called a ‘pico-cavity’ by the researchers – consists of a bump in a gold nanostructure the size of a single atom, and confines light to less than a billionth of a metre. ̽��ֱ��results, reported in the journal Science, open up new ways to study the interaction of light and matter, including the possibility of making the molecules in the cavity undergo new sorts of chemical reactions, which could enable the development of entirely new types of sensors.

According to the researchers, building nanostructures with single atom control was extremely challenging. “We had to cool our samples to -260°C in order to freeze the scurrying gold atoms,” said Felix Benz, lead author of the study. ̽��ֱ��researchers shone laser light on the sample to build the pico-cavities, allowing them to watch single atom movement in real time.

“Our models suggested that individual atoms sticking out might act as tiny lightning rods, but focusing light instead of electricity,” said Professor Javier Aizpurua from the Center for Materials Physics in San Sebastian in Spain, who led the theoretical section of this work.

“Even single gold atoms behave just like tiny metallic ball bearings in our experiments, with conducting electrons roaming around, which is very different from their quantum life where electrons are bound to their nucleus,” said Professor Jeremy Baumberg of the NanoPhotonics Centre at Cambridge’s Cavendish Laboratory, who led the research.

̽��ֱ��findings have the potential to open a whole new field of light-catalysed chemical reactions, allowing complex molecules to be built from smaller components. Additionally, there is the possibility of new opto-mechanical data storage devices, allowing information to be written and read by light and stored in the form of molecular vibrations.

̽��ֱ��research is funded as part of a UK Engineering and Physical Sciences Research Council (EPSRC) investment in the Cambridge NanoPhotonics Centre, as well as the European Research Council (ERC) and the Winton Programme for the Physics of Sustainability, and supported by the Spanish Council for Research (CSIC) and the ̽��ֱ�� of the Basque Country (UPV/EHU).

Reference:
Felix Benz et al. ‘Single-molecule optomechanics in ‘pico-cavities’.’ Science (2016). DOI: 10.1126/science.aah5243

Inset image: ̽��ֱ��presence of the sharp metal tip on a plasma sphere concentrates the electric field into its vicinity, initiating a spark. Credit: NanoPhotonics Cambridge

Using the strange properties of tiny particles of gold, researchers have concentrated light down smaller than a single atom, letting them look at individual chemical bonds inside molecules, and opening up new ways to study light and matter.

Single gold atoms behave just like tiny metallic ball bearings in our experiments, with conducting electrons roaming around, which is very different from their quantum life.

Jeremy Baumberg

NanoPhotonics Cambridge/Bart deNijs

Artist's impression

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Scientists "squeeze" light one particle at a time

tdk25 — Tue, 01 Sep 2015 04:04:46 +0000

A team of scientists has successfully measured particles of light being “squeezed”, in an experiment that had been written off in physics textbooks as impossible to observe.

Squeezing is a strange phenomenon of quantum physics. It creates a very specific form of light which is “low-noise” and is potentially useful in technology designed to pick up faint signals, such as the detection of gravitational waves.

̽��ֱ��standard approach to squeezing light involves firing an intense laser beam at a material, usually a non-linear crystal, which produces the desired effect.

For more than 30 years, however, a theory has existed about another possible technique. This involves exciting a single atom with just a tiny amount of light. ̽��ֱ��theory states that the light scattered by this atom should, similarly, be squeezed.

Unfortunately, although the mathematical basis for this method – known as squeezing of resonance fluorescence – was drawn up in 1981, the experiment to observe it was so difficult that one established quantum physics textbook despairingly concludes: “It seems hopeless to measure it”.

So it has proven – until now. In the journal Nature, a team of physicists report that they have successfully demonstrated the squeezing of individual light particles, or photons, using an artificially constructed atom, known as a semiconductor quantum dot. Thanks to the enhanced optical properties of this system and the technique used to make the measurements, they were able to observe the light as it was scattered, and proved that it had indeed been squeezed.

Professor Mete Atature, from the Cavendish Laboratory, Department of Physics, and a Fellow of St John’s College at the ̽��ֱ�� of Cambridge, led the research. He said: “It’s one of those cases of a fundamental question that theorists came up with, but which, after years of trying, people basically concluded it is impossible to see for real – if it’s there at all.”

“We managed to do it because we now have artificial atoms with optical properties that are superior to natural atoms. That meant we were able to reach the necessary conditions to observe this fundamental property of photons and prove that this odd phenomenon of squeezing really exists at the level of a single photon. It’s a very bizarre effect that goes completely against our senses and expectations about what photons should do.”

Like a lot of quantum physics, the principles behind squeezing light involve some mind-boggling concepts.

It begins with the fact that wherever there are light particles, there are also associated electromagnetic fluctuations. This is a sort of static which scientists refer to as “noise”. Typically, the more intense light gets, the higher the noise. Dim the light, and the noise goes down.

But strangely, at a very fine quantum level, the picture changes. Even in a situation where there is no light, electromagnetic noise still exists. These are called vacuum fluctuations. While classical physics tells us that in the absence of a light source we will be in perfect darkness, quantum mechanics tells us that there is always some of this ambient fluctuation.

"If you look at a flat surface, it seems smooth and flat, but we know that if you really zoom in to a super-fine level, it probably isn't perfectly smooth at all," Atature said. " ̽��ֱ��same thing is happening with vacuum fluctuations. Once you get into the quantum world, you start to get this fine print. It looks like there are zero photons present, but actually there is just a tiny bit more than nothing."

Importantly, these vacuum fluctuations are always present and provide a base limit to the noise of a light field. Even lasers, the most perfect light source known, carry this level of fluctuating noise.

This is when things get stranger still, however, because, in the right quantum conditions, that base limit of noise can be lowered even further. This lower-than-nothing, or lower-than-vacuum, state is what physicists call squeezing.

In the Cambridge experiment, the researchers achieved this by shining a faint laser beam on to their artificial atom, the quantum dot. This excited the quantum dot and led to the emission of a stream of individual photons. Although normally, the noise associated with this photonic activity is greater than a vacuum state, when the dot was only excited weakly the noise associated with the light field actually dropped, becoming less than the supposed baseline of vacuum fluctuations.

Explaining why this happens involves some highly complex quantum physics. At its core, however, is a rule known as Heisenberg’s uncertainty principle. This states that in any situation in which a particle has two linked properties, only one can be measured and the other must be uncertain.

In the normal world of classical physics, this rule does not apply. If an object is moving, we can measure both its position and momentum, for example, to understand where it is going and how long it is likely to take getting there. ̽��ֱ��pair of properties – position and momentum – are linked.

In the strange world of quantum physics, however, the situation changes. Heisenberg states that only one part of a pair can ever be measured, and the other must remain uncertain.

In the Cambridge experiment, the researchers used that rule to their advantage, creating a tradeoff between what could be measured, and what could not. By scattering faint laser light from the quantum dot, the noise of part of the electromagnetic field was reduced to an extremely precise and low level, below the standard baseline of vacuum fluctuations. This was done at the expense of making other parts of the electromagnetic field less measurable, meaning that it became possible to create a level of noise that was lower-than-nothing, in keeping with Heisenberg’s uncertainty principle, and hence the laws of quantum physics.

Plotting the uncertainty with which fluctuations in the electromagnetic field could be measured on a graph creates a shape where the uncertainty of one part has been reduced, while the other has been extended. This creates a squashed-looking, or “squeezed” shape, hence the term, “squeezing” light.

Atature added that the main point of the study was simply to attempt to see this property of single photons, because it had never been seen before. “It’s just the same as wanting to look at Pluto in more detail or establishing that pentaquarks are out there,” he said. “Neither of those things has an obvious application right now, but the point is knowing more than we did before. We do this because we are curious and want to discover new things. That’s the essence of what science is all about.”

Additional image: ̽��ֱ��left diagram represents electromagnetic activity associated with light at what is technically its lowest possible level. On the right, part of the same field has been reduced to lower than is technically possible, at the expense of making another part of the field less measurable. This effect is called “squeezing” because of the shape it produces.

Reference:
Schulte, CHH, et al. Quadrature squeezed photons from a two-level system. Nature (2015). DOI: 10.1038/nature14868.

A team of scientists have measured a bizarre effect in quantum physics, in which individual particles of light are said to have been “squeezed” – an achievement which at least one textbook had written off as hopeless.

It’s just the same as wanting to look at Pluto in more detail or establishing that pentaquarks are out there. Neither of those things has an obvious application right now, but the point is knowing more than we did before. We do this because we are curious and want to discover new things. That’s the essence of what science is all about.

Mete Atature

An image from an experiment in the quantum optics laboratory in Cambridge. Laser light was used to excite individual tiny, artificially constructed atoms known as quantum dots, to create “squeezed” single photons

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Trapping the light fantastic

lw355 — Mon, 16 Jun 2014 08:13:42 +0000

Jeremy Baumberg and his 30-strong team of researchers are master manipulators of light. They are specialists in nanophotonics – the control of how light interacts with tiny chunks of matter, at scales as small as a billionth of a metre. It’s a field of physics that 20 years ago was unknown.

At the heart of nanophotonics is the idea that changing the structure of materials at the scale of a few atoms can be used to alter not only the way light interacts with the material, but also its functional properties.

“ ̽��ֱ��goal is to design materials with really intricate architecture on a really small scale, so small it’s smaller than the wavelength of light,” said Baumberg, Professor of Nanophotonics in the Department of Physics. “Whether the starting material is polystyrene or gold, changing the shape of its nanostructure can give us extraordinary control over how light energy is absorbed by the electrons locked inside. We’re learning how to use this to develop new functionality.”

One of their recent achievements is to develop synthetic materials that mimic some of nature’s most striking colours, among them the iridescent hue of opals. Naturally occurring opals are formed

‘Polymer opals’, however, are plastic – like the polystyrene in drinking cups – and formed within a matter of minutes. With some clever chemistry, the researchers have found a way of making polysterene spheres coated in a soft chewing-gum-like outer shell.

As these polymer opals are twisted and stretched, ‘metallic’ blue–green colours ripple across their surface. Their flexibility and the permanence of their intense colour make them ideal materials for security cards and banknotes or to replace toxic dyes in the textile industry.

“ ̽��ֱ��crucial thing is that by assembling things in the right way you get the function you want,” said Baumberg, who developed the polymer opals with collaborators in Germany (at the DKI, now the Fraunhofer Institute for Structural Durability and System Reliability). “If the spheres are random, the material looks white or colourless, but if stacked perfectly regularly you get colour. We’ve found that smearing the spheres against each other magically makes them fall into regular lines and, because of the chewing gum layer, when you stretch it the colour changes too.

“It’s such a good example of nanotechnology – we take a transparent material, we cut it up in the right form, we stack it in the right way and we get completely new function.”

Although nanophotonics is a comparatively new area of materials research, Baumberg believes that within two decades we will start to see nanophotonic materials in anything from smart textiles to buildings and food colouring to solar cells.

Now, one of the team’s latest discoveries looks set to open up applications in medical diagnostics.

“We’re starting to learn how we can make materials that respond optically to the presence of individual molecules in biological fluids,” he explained. “There’s a large demand for this. GPs would like to be able to test the patient while they wait, rather than sending samples away for clinical testing. And cheap and reliable tests would benefit developing countries that lack expensive diagnostic equipment.”

A commonly used technique in medical diagnostics is Raman spectroscopy, which detects the presence of a molecule by its ‘optical signature’. It measures how light is changed when it bounces off a molecule, which in turn depends on the bonds within the molecule. However, the machines need to be very powerful to detect what can be quite weak effects.

Baumberg has been working with Dr Oren Scherman, Director of the Melville Laboratory for Polymer Synthesis in the Department of Chemistry, on a completely new way to sense molecules they have developed using a barrel-shaped molecular container called cucurbituril (CB). Acting like a tiny test tube, CB enables single molecules to enter its barrel shape, effectively isolating them from a mixture of molecules.

In collaboration with researchers in Spain and France, and with funding from the European Union, Baumberg and Scherman have found a way to detect what’s in each barrel using light, by combining the barrels with particles of gold only a few thousand atoms across.

“Shining light onto this gold–barrel mixture focuses and enhances the light waves into tiny volumes of space exactly where the molecules are located,” Baumberg explained. “By looking at the colours of the scattered light, we can work out which molecules are present and what they are doing, and with very high sensitivity.”

Whereas most sensing equipment requires precise conditions that can only really be achieved in the laboratory, this new technology has the potential to be a low-cost, reliable and rapid sensor for mass markets. ̽��ֱ��amount of gold required for the test is extremely small, and the gold particles self-assemble with CB at room temperature.

Now, with funding from the Engineering and Physical Sciences Research Council, and working with companies and potential end users (including the NHS), Baumberg and Scherman have begun the process of developing their ‘plasmonic sensors’ to test biological fluids such as urine and tears, for uses such as detecting neurotransmitters in the brain and protein incompatibilities between mother and fetus.

“At the same time, we want to understand how we can go further with the technology, from controlling chemical reactions happening inside the barrel, to making captured molecules inside ‘flex’ themselves, and detecting each of these modifications through colour change,” added Baumberg.

“ ̽��ֱ��ability to look at small numbers of molecules in a sea of others has appealed to scientists for years. Soon we will be able to do this on an unprecedented scale: watching in real time how molecules come together and undergo chemical reactions, and even how they form a bond. This has huge implications for optimising catalysis in industrially relevant processes and is therefore at the heart of almost every product in our lives.”

Baumberg views nanophotonics technology as a whole new toolbox. “ ̽��ֱ��excitement for me is the challenge of how difficult the task is combined with the fact that you can see that, if only you could do it, you can get things out that are incredible.

“At the moment we are capable of assembling new structures with different optical properties in a highly controlled way. Eventually, though, we will be able to build things with light itself.”

̽��ֱ��development of a ‘nanobarrel’ that traps and concentrates light onto single molecules could be used as a low-cost and reliable diagnostic test.

Eventually... we will be able to build things with light itself

Jeremy Baumberg

Gen Kamita and Jeremy Baumberg

Light can be manipulated at the nanoscale, as in this elastic material which has been folded like nano-origami

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Yes

Nanotubes used to create smallest ever hologram pixels

bjb42 — Fri, 21 Sep 2012 15:17:31 +0000

Scientists have generated holograms from carbon nanotubes for the first time, which could lead to much sharper holograms with a vastly increased field of view.

̽��ֱ��researchers from the ̽��ֱ��’s Centre of Molecular Materials for Photonics and Electronics (CMMPE) have harnessed the extraordinary conductive and light scattering abilities of these tubes - made from several sheets of carbon atoms rolled into a cylinder - to diffract high resolution holograms.

Carbon nanotubes are one billionth of a metre wide, only a few nanometres, and the scientists have used them as the smallest ever scattering elements to create a static holographic projection of the word CAMBRIDGE.

Many scientists believe that carbon nanotubes will be at the heart of future industry and human endeavour, with anticipated impact on everything from solar cells to cancer treatments, as well as optical imaging. One of their most astonishing features is strength - about 100 times stronger than steel at one-sixth the weight.

̽��ֱ��work on using these nanotubes to project holograms, the 2D images that optically render as three-dimensional, has been published in the journal Advanced Materials.

“Smaller pixels allow the diffraction of light at larger angles - increasing the field of view. Essentially, the smaller the pixel, the higher the resolution of the hologram,” said Dr Haider Butt from CMMPE, who conducted the work along with Yunuen Montelongo.

“We used carbon nanotubes as diffractive elements - or pixels - to produce high resolution and wide field of view holograms.”

̽��ֱ��multi-walled nanotubes used for this work are around 700 times thinner than a human hair, and grown vertically on a layer of silicon in the manner of atomic chimney stacks.

̽��ֱ��researchers were able to calculate a placement pattern that expressed the name of this institution using various colours of laser light - all channelled out (scattered) from the nano-scale structures.

For Haider Butt this is just the start - as these pixels and their subsequent displays are not only of the highest resolution, but ultra-sensitive to changes in material and incoming light.

"A new class of highly sensitive holographic sensors can be developed that could sense distance, motion, tilt, temperature and density of biological materials,” said Butt.

“What’s certain is that these results pave the way towards utilising nanostructures to producing 3D holograms with wide field of view and the very highest resolution.”

For the researchers, there are two key next steps for this emerging technology. One is to find a less expensive alternative to nanotubes, which are financially prohibitive: “Alternative materials should be explored and researched, we are going to try zinc oxide nanowires to achieve the same effects.”

̽��ֱ��other is to investigate movement in the projections. Currently, these atomic scale pixels can only render static holograms. Butt and his team will look at different techniques such as combining these pixels with the liquid crystals found in flat-screen technology to create fluid displays - possibly leading to changeable pictures and even razor-sharp holographic video.

A breakthrough in the use of carbon nanotubes as optical projectors has enabled scientists to generate holograms using the smallest ever pixels.

These results pave the way towards utilising nanostructures to producing 3D holograms with wide field of view and the very highest resolution.

Haider Butt

Dr Haider Butt

Hologram

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Yes

“Echo” of light augurs new era in study of black holes

bjb42 — Thu, 31 May 2012 21:00:24 +0000

̽��ֱ��findings open up new opportunities for scientists trying to map and understand what happens on the brink of “active galactic nuclei”, or AGNs; monster black holes that exist at the heart of most big galaxies.

These black holes contain millions of times the sun’s mass. As matter streams towards them, the centre of the galaxy lights up, emitting billions of times more energy than the sun and illuminating the disk of matter that forms at the hole’s edge.

One of the most important tools for astronomers studying these black holes is something called the “iron K line”. This is a shape which appears as very distinctive X-rays created by iron atoms, which, when excited, emit energies of around 6,000 to 7,000 electron volts – several thousand times the energy in visible light.

̽��ֱ��line brightens as the result of a mysterious and intense X-ray source near to the black hole. This source shines on to the accumulated matter, causing the iron atoms to radiate their K-line energy. In effect, when the source flares, a light “echo” sweeps across the disk of matter and the iron K line lights up accordingly, after a delay corresponding to how long the X-rays took to reach the disk. ̽��ֱ��process is called relativistic reverberation.

Although observing this process carries the promise of a much better understanding of what is happening around supersized black holes, neither the European Space Agency, nor NASA, have telescopes powerful enough to spot the reverberations of single flares coming from the source.

To get round this problem, the researchers, from the Universities of Maryland and Cambridge, reasoned that it might be possible to detect the combined echoes from several flares, if a large amount of data from a particular object in space could be analysed.

This object turned out to be the galaxy NGC 4151, which is located about 45 million light-years away in the constellation Canes Venatici. ̽��ֱ��galaxy has one of the brightest AGNs in X-rays and astronomers think that it is powered by a black hole weighing 50 million solar masses. ̽��ֱ��sheer scale of this black hole suggests that it also has a large accretion disk of matter, capable of producing particularly long-lived and detectable echoes of light coming from the X-ray source.

̽��ֱ��data needed to identify the light echoes came from observations carried out using the European Space Agency’s XMM-Newton satellite. By analysing the data, the researchers were able to uncover numerous X-ray echoes, demonstrating the reality of relativistic reverberation for the first time. Their findings are published in the May 8 issue of the Monthly Notices of the Royal Astronomical Society.

̽��ֱ��study shows that the echoes lagged behind the original flares by a little more than 30 minutes. Moving at the speed of light, the X-rays associated with the echo must have travelled an additional 400 million miles – about four times the Earth’s average distance from the sun, to reach the accretion disk.

“This tells us that the mysterious X-ray source in the AGN hovers at some height above the accretion disk,” Chris Reynolds, a professor of astronomy at the ̽��ֱ�� of Maryland at College Park and a co-author on the study, said. Jets of accelerated particles are often found around AGNs, and the finding appears to endorse an idea which has already been postulated that whatever the X-ray source is, it may be located near to the bases of these jets.

“ ̽��ֱ��data show that the earliest echo comes from the most broadened iron line emission,” Andy Fabian, from the Institute of Astronomy at the ̽��ֱ�� of Cambridge, and another co-author, added. “This line originates from closest to the black hole, and fits well with what we were expecting.”

̽��ֱ��detection of X-ray echoes in the AGN opens up a new way of studying black holes and the disks of matter that accrete around them. Astronomers anticipate that the next generation of X-ray telescopes will have collecting areas large enough to detect the echo produced by a single flare from the X-ray source, giving them an even better tool for testing relativity and probing the immediate surroundings of massive black holes.

“Our analysis allows us to probe black holes through a different window,” Abderahmen Zoghbi, a postdoctoral research associate at the ̽��ֱ�� of Maryland at College Park and the report’s lead author, said. “It confirms some long-held ideas about AGN and gives us a sense of what we can expect when a new generation of space-based X-ray telescopes eventually becomes available.”

A long-sought “echo” of light that promises to reveal more about supersized black holes in distant galaxies has been identified by an international team of astronomers.

Our analysis allows us to probe black holes through a different window.

Abderahmen Zoghbi

NASA.

̽��ֱ��galaxy NGC 4151. Researchers were able to use this galaxy to accumulate data about flares coming from a mysterious X-ray source close to the giant black hole at its centre.

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Physics of sustainability programme launched

bjb42 — Thu, 24 Mar 2011 12:12:33 +0000

An innovative programme which will focus on using physics to meet the growing demand on our natural resources was launched today at the ̽��ֱ�� of Cambridge’s Cavendish Laboratory.

̽��ֱ��programme is the brainchild of David Harding, the founder, chairman and head of research of Winton Capital Management, who has pledged to donate £20 million to the Cavendish, Cambridge's Department of Physics, to set up and fund ̽��ֱ��Winton Programme for the Physics of Sustainability.

His gift, the largest donation to the lab since its creation in 1874, will create a new programme for the physics of sustainability to make new technologies available which address the challenges facing society. There will be a strong emphasis upon fundamental physics research into such areas as renewable energy - to include photovoltaics, electrical storage, etc - that will have important implications for the sustainability agenda in the long-term.

David Willetts, Minister for Universities and Science, visited the Cavendish this morning to mark the launch. As of today, the ̽��ֱ�� is also inviting applications for up to four advanced research fellowships with the Winton Programme, as well as scholarships for PhD students. ̽��ֱ��advanced research fellowships will support outstanding scientists and will allow them to develop an independent research career. Details can be found at: https://www.winton.phy.cam.ac.uk/

"Cambridge has a slogan: ' ̽��ֱ��Freedom to Discover' and I am hoping I can give the scientists of the Cavendish more freedom to discover," says David Harding. "I studied theoretical physics at Cambridge, and the Cavendish has always had the reputation of attracting the finest minds in the world.

"While it is not quite as simple as using physics to save the world, this is an opportunity to use, for example, quantum physics to develop materials with seemingly miraculous properties that could combat the growing effect humans are having on the planet. I want to encourage research to keep the skies blue."

David's donation will help the Cavendish Laboratory, the birthplace of molecular biology and nuclear physics, cement its position at the forefront of the next revolution in physics. ̽��ֱ��donation will support programmes that explore basic science that can generate the new technologies and new industries that will be needed to meet the demands of a growing population on our already strained natural resources.

Some of the areas which will be explored as part of the Winton Programme include:

Designer Materials - Atom by atom manipulation and growth for the creation of new chemical environments with desirable properties. Using materials chemistry for molecular engineering, the scientists hope to change the properties of materials by applying extreme conditions of temperature, pressure, and magnetic and electric fields to search for emergent properties such as superconductivity or magnetism. ̽��ֱ��ultimate goals might include: a room temperature superconductor; a new material which would revolutionise refrigeration; electrical storage densities to rival gasoline; and new mechanisms for thermoelectricity to scavenge heat from the environment.

Light and matter - ̽��ֱ��primary source of energy on our planet is sunlight. Converting light to useful stored energy needs materials with controlled quantum chemistry, delivered on a vast scale in cheap and robust devices. One possibility is the use of photovoltaics, which convert solar radiation into energy. However, they require both strong optical absorption and good electrical transport, two challenging physics problems which the programme will explore.

Self-assembly - Energy applications will need nanoscale engineering that can be delivered by the tonne and will therefore require the invention of new manufacturing methods. Biology currently holds the only examples of functional and interacting structures at the nanoscale, using nanomachines for everything from photosynthesis to the transfer of energy through cells. ̽��ֱ��scientists will strive to replace top-down fabrication by bottom-up self-assembly of structures, using natural systems for inspiration and exploiting a mixture of physical processes and programmed methods.

Multiscale modelling - Developing novel sustainable materials and technologies will require an understanding of how quantum mechanical models on atomic scales can be melded with classical modelling on large scales, and to model physical processes on time scales from picoseconds to seconds. Advances in computational techniques will enable massive simulations of large-scale systems to be carried out at the quantum level. Work will strive to integrate modelling with experiment, and eventually use it to design complex devices.

̽��ֱ��Vice-Chancellor, Professor Sir Leszek Borysiewicz, said: " ̽��ֱ�� ̽��ֱ�� is most grateful to David for this donation, which is truly exceptional both in its generosity and in its vision of translating fundamental discoveries in physics, to meet one of the most pressing needs of our generation."

̽��ֱ��programme's inaugural director is Sir Richard Friend, the Cavendish Professor of Physics and a world-renowned leading expert on the physics, materials science and engineering of semiconductor devices.

Remarking on the impact of the donation, Sir Richard said: "Advances in fundamental physics have always had the capacity to solve very real problems. This programme will support the people with the radical ideas that bring practical solutions - very much the Cambridge way of doing science."

Since graduating from Cambridge in 1982, David Harding has become one of the most successful fund managers in the world. Early on he recognised the advantages of hiring individuals with science backgrounds. Winton currently employs over 90 researchers with PhDs or Master's Degrees in subjects including extragalactic astrophysics, mathematics, statistics, particle physics, planetary science and artificial intelligence.

̽��ֱ��programme will provide PhD studentships, research fellowships, and support for new academic staff as well as investment in research infrastructure of the highest level, pump-priming for novel research projects, support for collaborations within the ̽��ֱ�� and outside, and sponsorship for meetings and outreach activities.

Further details regarding the now advertised fellowships and scholarships can be found at https://www.winton.phy.cam.ac.uk/ and enquires can be addressed to winton@phy.cam.ac.uk

Funded by a £20 million donation from David Harding, the Winton Programme for the Physics of Sustainability aims to address some of the major challenges affecting the modern world.

While it is not quite as simple as using physics to save the world, this is an opportunity to develop materials with seemingly miraculous properties that could combat the growing effect humans are having on the planet.

David Harding

Phil Mynott

Sir Richard Friend and David Harding

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