For the First Time, Researchers Use an Atom Interferometer to Measure Aircraft Acceleration

Atom Interferometry Explained Geiger et al. via arXiv

Atom interferometers are neat little devices that exploit the wave characters of atoms to make highly precise measurements of things like distance and or the force of gravity. But because they are fickle by nature--even the smallest vibrations distort their results--atom interferometers have been mostly limited to highly controlled experiments that take place in either underground labs or in free-falling zero-g experiments. But a team of French researchers has announced today the first use of an atom interferometer to measure the acceleration of an airplane.

This is useful because atom interferometers are super sensitive, more so than the inertial sensors used widely on modern aircraft. Those inertial sensors have been known to fail with potentially disastrous results, but more frequently they cause slight errors to creep into navigation systems that must later be corrected. With no moving parts and a high degree of accuracy, atom interferometers could mitigate these problems, recording inertial effects 300 times weaker than the normal fluctuations in the acceleration in a standard aircraft.

But the vibrations in an aircraft have previously made deployment of atom interferometers in planes unfeasible. That’s where Remi Geiger at the Laboratoire Charles Fabry in Paris comes in. He and his colleagues have created a system that compensates for the effects of vibrations via mechanical accelerometers that record the movements of the aircraft itself.

Using that vibration data, their system recalculates the interferometer’s data to compensate for any vibration that might be skewing its final result. By stripping out the vibration noise, they end up with a clean, high-resolution atom interferometer result. The system could go a long way toward delivering better acceleration data to the cockpits of large jets. Geiger and company have already tested their system successfully on an Airbus A300.

But an atom interferometer that can operate free of laboratory constraints isn’t limited to jetliner applications. The researchers hope their method will lead to more precise measurements of geodesy and of gravity itself, enabling some fundamental experiments that have been previously very difficult to conduct and challenging some existing principles of physics with more and better data. More at arXiv.

[Technology]

View the original article here

New sensor to measure structural stresses can heal itself when broken

ScienceDaily (June 17, 2011) — Researchers from North Carolina State University have designed a sensor that can measure strain in structural materials and is capable of healing itself -- an important advance for collecting data to help us make informed decisions about structural safety in the wake of earthquakes, explosions or other unexpected events.

Engineers use sensors to measure the strain, or forces, exerted on materials used to build everything from airplanes to civil infrastructure. For example, these sensors can tell us how an airplane wing is performing in flight, and give maintenance authorities advance notice when the wing may be near failure. In other words, it gives you a chance to address an issue before it becomes a problem.

Historically, one flaw in such sensors is that they can break under stress. That means the sensor can no longer provide information to users, but it doesn't necessarily mean that the material they were monitoring has been irreparably harmed. And, as in the airplane example, the sensors may be inaccessible -- making them difficult or impossible to replace.

"To address this problem, we've developed a sensor that automatically repairs itself, in the event that it is broken," says Dr. Kara Peters, an associate professor of mechanical and aerospace engineering at NC State and co-author of a paper describing the research.

The sensor can stretch and compress along with the material it monitors. An infrared (IR) light wave runs through the sensor and detects these changes in length, which tells us how much strain the material is undergoing.

The sensor contains two glass optical fibers that run through a reservoir filled with ultraviolet(UV)-curable resin. The ends of the glass fibers are aligned with each other, but separated by a small gap. Focused beams of IR and UV light run through one of the fibers. When the tightly focused UV beam hits the resin, the resin hardens, creating a thin polymer filament that connects the glass fibers -- creating a closed circuit for the IR light. The rest of the resin in the reservoir remains in liquid form, surrounding the filament.

The remaining liquid resin is important. If the polymer filament breaks under stress, more liquid resin rushes into the gap, comes into contact with the UV beam and hardens -- repairing the sensor automatically.

"Events that can break a sensor, but don't break the structure being monitored, are important," Peters says. "These events could be bird strikes to an airplane wing or earthquake damage to a building. Collecting data on what has happened to these structures can help us make informed decisions about what is safe and what is not. But if those sensors are broken, that data isn't available. Hopefully, this new sensor design will help us collect this sort of data in the future."

The paper, "A self-repairing polymer waveguide sensor," is published in the June issue of Smart Materials And Structures and was co-authored by Peters and NC State Ph.D. student Young Song. The research was funded by the National Science Foundation.

NC State's Department of Mechanical and Aerospace Engineering is part of the university's College of Engineering.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by North Carolina State University.

Journal Reference:

Young J Song, Kara J Peters. A self-repairing polymer waveguide sensor. Smart Materials and Structures, 2011; 20 (6): 065005 DOI: 10.1088/0964-1726/20/6/065005

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New sensor to measure structural stresses can heal itself when broken

ScienceDaily (June 17, 2011) — Researchers from North Carolina State University have designed a sensor that can measure strain in structural materials and is capable of healing itself -- an important advance for collecting data to help us make informed decisions about structural safety in the wake of earthquakes, explosions or other unexpected events.

Engineers use sensors to measure the strain, or forces, exerted on materials used to build everything from airplanes to civil infrastructure. For example, these sensors can tell us how an airplane wing is performing in flight, and give maintenance authorities advance notice when the wing may be near failure. In other words, it gives you a chance to address an issue before it becomes a problem.

Historically, one flaw in such sensors is that they can break under stress. That means the sensor can no longer provide information to users, but it doesn't necessarily mean that the material they were monitoring has been irreparably harmed. And, as in the airplane example, the sensors may be inaccessible -- making them difficult or impossible to replace.

"To address this problem, we've developed a sensor that automatically repairs itself, in the event that it is broken," says Dr. Kara Peters, an associate professor of mechanical and aerospace engineering at NC State and co-author of a paper describing the research.

The sensor can stretch and compress along with the material it monitors. An infrared (IR) light wave runs through the sensor and detects these changes in length, which tells us how much strain the material is undergoing.

The sensor contains two glass optical fibers that run through a reservoir filled with ultraviolet(UV)-curable resin. The ends of the glass fibers are aligned with each other, but separated by a small gap. Focused beams of IR and UV light run through one of the fibers. When the tightly focused UV beam hits the resin, the resin hardens, creating a thin polymer filament that connects the glass fibers -- creating a closed circuit for the IR light. The rest of the resin in the reservoir remains in liquid form, surrounding the filament.

The remaining liquid resin is important. If the polymer filament breaks under stress, more liquid resin rushes into the gap, comes into contact with the UV beam and hardens -- repairing the sensor automatically.

"Events that can break a sensor, but don't break the structure being monitored, are important," Peters says. "These events could be bird strikes to an airplane wing or earthquake damage to a building. Collecting data on what has happened to these structures can help us make informed decisions about what is safe and what is not. But if those sensors are broken, that data isn't available. Hopefully, this new sensor design will help us collect this sort of data in the future."

The paper, "A self-repairing polymer waveguide sensor," is published in the June issue of Smart Materials And Structures and was co-authored by Peters and NC State Ph.D. student Young Song. The research was funded by the National Science Foundation.

NC State's Department of Mechanical and Aerospace Engineering is part of the university's College of Engineering.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by North Carolina State University.

Journal Reference:

Young J Song, Kara J Peters. A self-repairing polymer waveguide sensor. Smart Materials and Structures, 2011; 20 (6): 065005 DOI: 10.1088/0964-1726/20/6/065005

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Taking the 3-D measure of macromolecules

ScienceDaily (June 17, 2011) — The world's first three-dimensional plasmon rulers, capable of measuring nanometer-scale spatial changes in macrmolecular systems, have been developed by researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with researchers at the University of Stuttgart, Germany. These 3D plasmon rulers could provide scientists with unprecedented details on such critical dynamic events in biology as the interaction of DNA with enzymes, the folding of proteins, the motion of peptides or the vibrations of cell membranes.

"We've demonstrated a 3D plasmon ruler, based on coupled plasmonic oligomers in combination with high-resolution plasmon spectroscopy, that enables us to retrieve the complete spatial configuration of complex macromolecular and biological processes, and to track the dynamic evolution of these processes," says Paul Alivisatos, director of Berkeley Lab and leader of this research.

Alivisatos, who is also the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC), Berkeley, is the senior author of a paper in the journal Science describing this research. The paper is titled "Three-Dimensional Plasmon Rulers." Co-authoring this paper were Laura Na Liu, who at the time the work was done was a member of Alivisatos' research group but is now with Rice University, and Mario Hentschel, Thomas Weiss and Harald Giessen with the University of Stuttgart.

The nanometer scale is where the biological and materials sciences converge. As human machines and devices shrink to the size of biomolecules, scientists need tools by which to precisely measure minute structural changes and distances. To this end, researchers have been developing linear rulers based on the electronic surface waves known as "plasmons," which are generated when light travels through the confined dimensions of noble metal nanoparticles or structures, such as gold or silver.

"Two noble metallic nanoparticles in close proximity will couple with each other through their plasmon resonances to generate a light-scattering spectrum that depends strongly on the distance between the two nanoparticles," Alivisatos says. "This light-scattering effect has been used to create linear plasmon rulers that have been used to measure nanoscale distances in biological cells."

Compared to other types of molecular rulers, which are based on chemical dyes and fluorescence resonance energy transfer (FRET), plasmon rulers neither blink nor photobleach, and also offer exceptional photostability and brightness. However, until now plasmon rulers could only be used to measure distances along one dimension, a limitation that hampers any comprehensive understanding of all the biological and other soft-matter processes that take place in 3D.

"Plasmonic coupling in multiple nanoparticles placed in proximity to each other leads to light scattering spectra that are sensitive to a complete set of 3D motions," says Laura Na Liu, corresponding author of the Science paper. "The key to our success is that we were able to create sharp spectral features in the otherwise broad resonance profile of plasmon-coupled nanostructures by using interactions between quadrupolar and dipolar modes."

Liu explains that typical dipolar plasmon resonances are broad because of radiative damping. As a result, the simple coupling between multiple particles produces indistinct spectra that are not readily converted into distances. She and her co-authors overcame this problem with a 3D ruler constructed from five gold nanorods of individually controlled length and orientation, in which one nanorod is placed perpendicular between two pairs of parallel rod nanorods to form a structure that resembles the letter H.

"The strong coupling between the single nanorod and the two parallel nanorod pairs suppresses radiative damping and allows for the excitation of two sharp quadrupolar resonances that enable high-resolution plasmon spectroscopy," Liu says. "Any conformational change in this 3D plasmonic structure will produce readily observable changes in the optical spectra."

Not only did conformational changes in their 3D plasmon rulers alter light scattering wavelengths, but the degrees of spatial freedom afforded its five nanorod structure also enabled Liu and her colleagues to distinguish the direction as well as the magnitude of structural changes.

"As a proof of concept, we fabricated a series of samples using high-precision electron beam lithography and layer-by-layer stacking nanotechniques, then embedded them with our 3D plasmon rulers in a dielectric medium on a glass substrate," Liu says. "Experimental results were in excellent agreement with the calculated spectra."

Alivisatos, Liu and their Stuttgart collaborators envision a future in which 3D plasmon rulers would, through biochemical linkers, be attached to a sample macromolecule, for example, to various points along a strand of DNA or RNA, or at different positions on a protein or peptide. The sample macromolecule would then be exposed to light and the optical responses of the 3D plasmon rulers would be measured via dark field microspectroscopy.

"The realization of 3D plasmon rulers using nanoparticles and biochemical linkers is challenging, but 3D nanoparticle assemblies with desired symmetries and configurations have been already been demonstrated," Liu says. "We believe these exciting experimental achievements along with the introduction of our new concept will pave the road toward the realization of 3D plasmon rulers in biological and other soft-matter systems."

This research was supported by grants from the National Institutes of Health Plasmon Rulers Project and the German Ministry of Science.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Na Liu, Mario Hentschel, Thomas Weiss, A. Paul Alivisatos and Harald Giessen. Three-Dimensional Plasmon Rulers. Science, 17 June 2011: 1407-1410 DOI: 10.1126/science.1199958

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Taking the 3-D measure of macromolecules

ScienceDaily (June 17, 2011) — The world's first three-dimensional plasmon rulers, capable of measuring nanometer-scale spatial changes in macrmolecular systems, have been developed by researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with researchers at the University of Stuttgart, Germany. These 3D plasmon rulers could provide scientists with unprecedented details on such critical dynamic events in biology as the interaction of DNA with enzymes, the folding of proteins, the motion of peptides or the vibrations of cell membranes.

"We've demonstrated a 3D plasmon ruler, based on coupled plasmonic oligomers in combination with high-resolution plasmon spectroscopy, that enables us to retrieve the complete spatial configuration of complex macromolecular and biological processes, and to track the dynamic evolution of these processes," says Paul Alivisatos, director of Berkeley Lab and leader of this research.

Alivisatos, who is also the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC), Berkeley, is the senior author of a paper in the journal Science describing this research. The paper is titled "Three-Dimensional Plasmon Rulers." Co-authoring this paper were Laura Na Liu, who at the time the work was done was a member of Alivisatos' research group but is now with Rice University, and Mario Hentschel, Thomas Weiss and Harald Giessen with the University of Stuttgart.

The nanometer scale is where the biological and materials sciences converge. As human machines and devices shrink to the size of biomolecules, scientists need tools by which to precisely measure minute structural changes and distances. To this end, researchers have been developing linear rulers based on the electronic surface waves known as "plasmons," which are generated when light travels through the confined dimensions of noble metal nanoparticles or structures, such as gold or silver.

"Two noble metallic nanoparticles in close proximity will couple with each other through their plasmon resonances to generate a light-scattering spectrum that depends strongly on the distance between the two nanoparticles," Alivisatos says. "This light-scattering effect has been used to create linear plasmon rulers that have been used to measure nanoscale distances in biological cells."

Compared to other types of molecular rulers, which are based on chemical dyes and fluorescence resonance energy transfer (FRET), plasmon rulers neither blink nor photobleach, and also offer exceptional photostability and brightness. However, until now plasmon rulers could only be used to measure distances along one dimension, a limitation that hampers any comprehensive understanding of all the biological and other soft-matter processes that take place in 3D.

"Plasmonic coupling in multiple nanoparticles placed in proximity to each other leads to light scattering spectra that are sensitive to a complete set of 3D motions," says Laura Na Liu, corresponding author of the Science paper. "The key to our success is that we were able to create sharp spectral features in the otherwise broad resonance profile of plasmon-coupled nanostructures by using interactions between quadrupolar and dipolar modes."

Liu explains that typical dipolar plasmon resonances are broad because of radiative damping. As a result, the simple coupling between multiple particles produces indistinct spectra that are not readily converted into distances. She and her co-authors overcame this problem with a 3D ruler constructed from five gold nanorods of individually controlled length and orientation, in which one nanorod is placed perpendicular between two pairs of parallel rod nanorods to form a structure that resembles the letter H.

"The strong coupling between the single nanorod and the two parallel nanorod pairs suppresses radiative damping and allows for the excitation of two sharp quadrupolar resonances that enable high-resolution plasmon spectroscopy," Liu says. "Any conformational change in this 3D plasmonic structure will produce readily observable changes in the optical spectra."

Not only did conformational changes in their 3D plasmon rulers alter light scattering wavelengths, but the degrees of spatial freedom afforded its five nanorod structure also enabled Liu and her colleagues to distinguish the direction as well as the magnitude of structural changes.

"As a proof of concept, we fabricated a series of samples using high-precision electron beam lithography and layer-by-layer stacking nanotechniques, then embedded them with our 3D plasmon rulers in a dielectric medium on a glass substrate," Liu says. "Experimental results were in excellent agreement with the calculated spectra."

Alivisatos, Liu and their Stuttgart collaborators envision a future in which 3D plasmon rulers would, through biochemical linkers, be attached to a sample macromolecule, for example, to various points along a strand of DNA or RNA, or at different positions on a protein or peptide. The sample macromolecule would then be exposed to light and the optical responses of the 3D plasmon rulers would be measured via dark field microspectroscopy.

"The realization of 3D plasmon rulers using nanoparticles and biochemical linkers is challenging, but 3D nanoparticle assemblies with desired symmetries and configurations have been already been demonstrated," Liu says. "We believe these exciting experimental achievements along with the introduction of our new concept will pave the road toward the realization of 3D plasmon rulers in biological and other soft-matter systems."

This research was supported by grants from the National Institutes of Health Plasmon Rulers Project and the German Ministry of Science.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Na Liu, Mario Hentschel, Thomas Weiss, A. Paul Alivisatos and Harald Giessen. Three-Dimensional Plasmon Rulers. Science, 17 June 2011: 1407-1410 DOI: 10.1126/science.1199958

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Quantum physics first: Physicists measure without distorting

ScienceDaily (June 3, 2011) — Quantum mechanics is famous for saying that a tree falling in a forest when there's no one there doesn't make a sound. Quantum mechanics also says that if anyone is listening, it interferes with and changes the tree. And so the famous paradox: how can we know reality if we cannot measure it without distorting it?

An international team of researchers, led by University of Toronto physicist Aephraim Steinberg of the Centre for Quantum Information and Quantum Control, has found a way to do just that by applying a modern measurement technique to the historic two-slit interferometer experiment in which a beam of light shone through two slits results in an interference pattern on a screen behind.

That famous experiment, and the 1927 Neils Bohr and Albert Einstein debates, seemed to establish that you could not watch a particle go through one of two slits without destroying the interference effect: you had to choose which phenomenon to look for.

"Quantum measurement has been the philosophical elephant in the room of quantum mechanics for the past century," says Steinberg, who is lead author of Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer, to be published in Science on June 2. "However, in the past 10 to 15 years, technology has reached the point where detailed experiments on individual quantum systems really can be done, with potential applications such as quantum cryptography and computation."

With this new experiment, the researchers have succeeded for the first time in experimentally reconstructing full trajectories which provide a description of how light particles move through the two slits and form an interference pattern. Their technique builds on a new theory of weak measurement that was developed by Yakir Aharonov's group at Tel Aviv University. Howard Wiseman of Griffith University proposed that it might be possible to measure the direction a photon (particle of light) was moving, conditioned upon where the photon is found. By combining information about the photon's direction at many different points, one could construct its entire flow pattern ie. the trajectories it takes to a screen.

"In our experiment, a new single-photon source developed at the National Institute for Standards and Technology in Colorado was used to send photons one by one into an interferometer constructed at Toronto. We then used a quartz calcite, which has an effect on light that depends on the direction the light is propagating, to measure the direction as a function of position. Our measured trajectories are consistent, as Wiseman had predicted, with the realistic but unconventional interpretation of quantum mechanics of such influential thinkers as David Bohm and Louis de Broglie," said Steinberg.

The original double-slit experiment played a central role in the early development of quantum mechanics, leading directly to Bohr's formulation of the principle of complementarity. Complementarity states that observing particle-like or wave-like behaviour in the double-slit experiment depends on the type of measurement made: the system cannot behave as both a particle and wave simultaneously. Steinberg's recent experiment suggests this doesn't have to be the case: the system can behave as both.

"By applying a modern measurement technique to the historic double-slit experiment, we were able to observe the average particle trajectories undergoing wave-like interference, which is the first observation of its kind. This result should contribute to the ongoing debate over the various interpretations of quantum theory," said Steinberg. "It shows that long-neglected questions about the different types of measurement possible in quantum mechanics can finally be addressed in the lab, and weak measurements such as the sort we use in this work may prove crucial in studying all sorts of new phenomena.

"But mostly, we are all just thrilled to be able to see, in some sense, what a photon does as it goes through an interferometer, something all of our textbooks and professors had always told us was impossible."

Research partners include the University of Toronto's Centre for Quantum Information and Quantum Control, Department of Physics and Institute for Optical Sciences, the National Institute of Standards and Technology in Boulder, Colorado, the Institute for Quantum Computing at the University of Waterloo, Griffith University, Australia, and the Laboratoire Charles Fabry in Orsay, France. Research was funded by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, and Quantum Works.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Toronto, via EurekAlert!, a service of AAAS.

Journal Reference:

Sacha Kocsis, Boris Braverman, Sylvain Ravets, Martin J. Stevens, Richard P. Mirin, L. Krister Shalm, Aephraim M. Steinberg. Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer. Science, 2011; 332 (6034): 1170-1173 DOI: 10.1126/science.1202218

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here