Off-the-shelf electronics turn up gain on spectroscopy

Now, a new twist on spectroscopy, described in the American Institute of Physics' in journalReview of Scientific Instruments, allows for an unprecedented level of such filtering -- one that could transform everything from the search for extraterrestrial intelligence to super-sensitive spy gear to scan hotel rooms for hidden microphones or cameras.

The technique was demonstrated on the slice of theelectromagnetic spectrumcontaining frequencies on which terrestrial radio stations broadcast music. Currentspectroscopytechniques can take suchradio signalsand tell you, in effect, the average volume and pitch of each moment of the music. However, if a given moment is made up of several notes played simultaneously -- a chord, say -- that fact is more or less invisible.

Or rather, it was invisible before the recent work of doctoral student Sebastian Starosielec and professor Daniel Hagele, both at Germany's Ruhr University Bochum. By stitching together a MHz-sampling card–- a radio-frequency version of a sound card -- and a multi-core graphics CPU, the two combed through a broad band of the radio spectrum in extra-fine detail. Their technical achievement, which determined in real time correlations among many thousands of pairs of frequencies, for the first time makes it easy to distinguish between a soloist and an ensemble based only on analysis of spectra.

Beyond the search for E.T. and illicit bugs, the technique could prove useful"for detecting anything that is not pure noise,"says Hägele. Other applications could include better measurements of various physical systems, particularly in atomic and solid state physics, and the possibility of better communication signal recovery to be used on and off the planet's surface.

Hägele gives the following example to illustrate the power of the the technology: Imagine a TV show was broadcast daily from Mars, and the signal was received, along with a vast amount of background noise, here on Earth. After a few days"we would be able to reconstruct the show's introduction, including the theme song and images, just from spectroscopic data,"he says.

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'Liquid pistons' could drive new advances in camera lenses and drug delivery (w/ Video)

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Engineering researchers at Rensselaer Polytechnic Institute have developed liquid pistons, in which oscillating droplets of ferrofluid precisely displace a surrounding liquid. The pulsating motion of the ferrofluid droplets, which are saturated with metalnanoparticles, can be used to pump small volumes of liquid. The study also demonstrated how droplets can function as liquid lenses that constantly move, bringing objects into and out of focus.

These liquid pistons are highly tunable, scalable, and– because they lack any solid moving parts– suffer no wear and tear. The research team, led by Rensselaer Professor Amir H. Hirsa, is confident this new discovery can be exploited to create a host of new devices ranging from micro displacement pumps and liquid switches, to adaptive lenses and advanced drug delivery systems.

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Researchers at Rensselaer Polytechnic Institute have developed liquid pistons, which can be used to precisely pump small volumes of liquid. Comprising the pistons are droplets of nanoparticle-infused ferrofluids, which can also function as liquid lenses that vibrate at high speeds and move in and out of focus as they change shape. Seen here is a video taken through a liquid lens driven by liquid pistons. As the droplet oscillates, the picture moves in and out of focus. These liquid pistons could enable a new generation of mobile phone cameras, medical imaging equipment, implantable drug delivery devices, and possibly even implantable eye lenses. Credit: Rensselaer/Hirsa

"It is possible to make mechanical pumps that are small enough for use in lab-on-a-chip applications, but it's a very complex, expensive proposition,"said Hirsa, a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer."Our electromagnetic liquid pistons present a new strategy for tackling the challenge of microscale liquid pumping. Additionally, we have shown how these pistons are well-suited for chip-level, fast-acting adaptive liquid lenses."

Results of the study are detailed in the paper"Electromagnetic liquid pistons for capillarity-based pumping,"recently published online by the journalLab on a Chip. The paper will be featured on the cover of the journal's February 2011 issue, and can be readonline.

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Researchers at Rensselaer Polytechnic Institute have developed liquid pistons, which can be used to precisely pump small volumes of liquid. Comprising the pistons are droplets of nanoparticle-infused ferrofluids, which can also function as liquid lenses that vibrate at high speeds and move in and out of focus as they change shape. These liquid pistons could enable a new generation of mobile phone cameras, medical imaging equipment, implantable drug delivery devices, and possibly even implantable eye lenses. Credit: Rensselaer/Hirsa

Hirsa's team developed a liquid piston that is comprised of two ferrofluid droplets situated on a substrate about the size of a piece of chewing gum. The substrate has two holes in it, each hosting one of the droplets. The entire device is situated in a chamber filled with water.

Pulses from an electromagnet provoke one of the ferrofluid droplets, the driver, to vibrate back and forth. This vibration, in turn, prompts a combination of magnetic, capillary, and inertial forces that cause the second droplet to vibrate in an inverted pattern. The two droplets create a piston, resonating back and forth with great speed and a spring-like force. Researchers can finely control the strength and speed of these vibrations by exposing the driver ferrofluid to different magnetic fields.

In this way, the droplets become a liquid resonator, capable of moving the surrounding liquid back and forth from one chamber to another. Similarly, the liquid piston can also function as a pump. The shift in volume, as a droplet moves, can displace from the chamber an equal volume of the surrounding liquid. Hirsa said he can envision the liquid piston integrated into an implantable device that very accurately releases tiny, timed doses of drugs into the body of a patient.

As the droplets vibrate, their shape is always changing. By passing light through these droplets, the device is transformed into a miniature camera lens. As thedropletsmove back and forth, the lens automatically changes its focal length, eliminating the usual chore of manually focusing a camera on a specific object. The images are captured electronically, so software can be used to edit out any unfocused frames, leaving the user with a stream of clear, focused video.

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Researchers at Rensselaer Polytechnic Institute have developed liquid pistons, which can be used to precisely pump small volumes of liquid. Comprising the pistons are droplets of nanoparticle-infused ferrofluids, which can also function as liquid lenses that vibrate at high speeds and move in and out of focus as they change shape. These liquid pistons could enable a new generation of mobile phone cameras, medical imaging equipment, implantable drug delivery devices, and possibly even implantable eye lenses.

The speed and quality of video captured from these liquid lenses has surpassed 30 hertz, which is about the quality of a typical computer web cam. Liquid lenses could mean lighter camera lenses that require only a fraction of the energy demanded by today's digital cameras. Along with handheld and other electronic devices, and homeland security applications, Hirsa said this technology could even hold the key to replacement eye lenses that can be fine-tuned using only high-powered magnets.

"There's really a lot we can do with these liquid pistons. It's an exciting new technology with great potential, and we're looking forward to moving the project even further along,"he said.

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Advance makes MRI scans more than seven times faster

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In a paper that appeared Dec. 20 in the journalPLoS ONE,a University of California, Berkeley, physicist and colleagues from the University of Minnesota and Oxford University in the United Kingdom describe two improvements that allow full three-dimensional brain scans in less than half a second, instead of the typical 2 to 3 seconds.
"When we made the first images, it was unbelievable how fast we were going,"said first author David Feinberg, a physicist and adjunct professor in UC Berkeley's Helen Wills Neuroscience Institute and president of the company Advanced MRI Technologies in Sebastopol, Calif."It was like stepping out of a prop plane into a jet plane. It was that magnitude of difference."

For neuroscience, in particular, fast scans are critical for capturing the dynamic activity in the brain.

"When a functional MRI study of the brain is performed, about 30 to 60 images covering the entire 3-D brain are repeated hundreds of times like the frames of a movie but, with fMRI, a 3-D movie,"Feinberg said."By multiplexing theimage acquisitionfor higher speed, a higher frame rate is achieved for more information in a shorter period of time."

"The brain is a moving target, so the more refined you can sample this activity, the better understanding we will have of the real dynamics of what's going on here,"added Dr. Marc Raichle, a professor of radiology, neurology, neurobiology, biomedical engineering and psychology at Washington University in St. Louis who has followed Feinberg's work.

In addition to broadly advancing the field of neural-imaging, the discovery will have an immediate impact on the Human Connectome Project, funded last year by the National Institutes of Health (NIH) to map the connections of the human brain through functional MRI (fMRI) and structural MRI scans of 1,200 healthy adults.
"At the time we submitted our grant proposal for the Human Connectome Project, we had aspirations of acquiring better quality data from our study participants, so this discovery is a tremendous step in helping us accomplish the goals of the project,"said Dr. David Van Essen, a neurobiologist at Washington University and co-leader of the project."It's vital that we get the highest quality imaging data possible, so we can infer accurately the brain's circuitry– how connections are established, and how they perform."

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The new technique accelerates diffusion MRI as well. The colored tracks show the direction of nerve fiber bundles, providing a 3-D image of the axonal pathways in the white matter (cortex) of a resting human brain. A normal structural cross sectional image of the brain bisects the diffusion 3-D fibertrack image. The entire 3-D image was scanned in 8.5 minutes instead of 30 minutes. (David Feinberg)

The faster scans are made possible by combining two technical improvements invented in the past decade that separately boosted scanning speeds two to four times over what was already the fastest MRI technique, echo planar imaging (EPI). Physical limitations of each method prevented further speed improvements,"but together their image accelerations are multiplied,"Feinberg said. The team can now obtain brain scans substantially faster than the time reductions reported in their paper and many times faster than the capabilities of today's machines.

Probing the brain with radio waves

Magnetic resonance imagingworks by using a magnetic field and radio waves to probe the environment of hydrogen atoms in water molecules in the body. Because hydrogen atoms in blood, for example, respond differently than atoms in bone or tissue, computers can reconstruct the body's interior landscape without the use of penetrating X-rays.

Nearly 20 years ago, however, a new type of MRI called functional MRI (fMRI) was developed to highlight areas of the brain using oxygen, and thus presumably engaged in neuronal activity, such as thinking .Using echo planar imaging (EPI), fMRI vividly distinguishes oxygenated blood funneling into working areas of the brain from deoxygenated blood in less active areas.

As with standard MRI, fMRI machines create magnetic fields that vary slightly throughout the brain, providing a different magnetic environment for hydrogen atoms in different areas. The differing magnetic field strengths make the spin of each hydrogen atom precess at different rates, so that when a pulse of radio waves is focused on the head, the atoms respond differently depending on location and on their particular environment. Those that absorb radio energy and then release the energy are detected by magnetic coils surrounding the head, and these signals, or"echoes,"are used to produce an image of the brain.

With EPI, a single pulse of radio waves is used to excite the hydrogen atoms, but the magnetic fields are rapidly reversed several times to elicit about 50 to 100 echoes before the atoms settle down. The multiple echoes provide a high-resolution picture of the brain.

In 2002, Feinberg proposed using a sequence of two radio pulses to obtain two times the information in the same amount of time. Dubbed simultaneous image refocusing (SIR) EPI, it has proved useful in fMRI and for 3-D imaging of neuronal axonal fiber tracks, though the improvement in scanning speed is limited because with a train of more than four times as many echoes, the signal decays and the image resolution drops.

Another acceleration improvement, multiband excitation of several slices using multiple coil detection, was developed in the U.K. at about the same time by David Larkmann for spinal imaging. The technique was recently pioneered for fMRI by Steen Moeller and colleagues at the University of Minnesota. This technique, too, had limitations, primarily because the multiple coils are relatively widely spaced and cannot differentiate very closely spaced images.

In collaboration with Essa Yacoub, senior author on the paper, and Kamil Ugurbil, director of the University of Minnesota's Center for Magnetic Resonance Research and co-leader of the Human Connectome Project, Feinberg combined these techniques to get significantly greater acceleration than either technique alone while maintaining the same image resolution.

"With the two methods multiplexed, 10, 12 or 16 images the product of their two acceleration factors were read out in one echo train instead of one image,"Feinberg said.

fMRI moving closer to speed of EEG

The ability to scan the brain in under 400 milliseconds moves fMRI closer to electroencephalography (EEG) for capturing very rapid sequences of events in the brain.

"Other techniques which capture signals derived from neuronal activity, EEG or MEG, have much higher temporal resolution; hundred microsecond neuronal changes. But MRI has always been very slow, with 2 second temporal resolution,"Feinberg said."Now MRI is getting down to a few hundred milliseconds to scan the entire brain, and we are beginning to see neuronal network dynamics with the high spatial resolution of MRI."

The development will impact general fMRI as well as diffusion imaging of axonal fibers in the brain, both of which are needed to achieve the main goal of the Human Connectome Project. Diffusion imaging reveals the axonal fiber networks that are the main nerve connections between areas of the brain, while fMRI shows which areas of the brain are functionally connected, that is, which areas are active together or sequentially during various activities.

"While it simply is not possible to show the billions of synaptic connections in the live human brain, the hope is that understanding patterns of how the normal brain is functionally interacting and structurally connected will lead to insights about diseases that involve miswiring in the brain,"Feinberg said.

"We suspect several neurologic and psychiatric disorders, such as autism and schizophrenia, could be brain connectivity disorders, but we don't know what normal connectivity is,"Feinberg added."Although the fMRI and neuronal fiber images do not have the resolution of an electron microscope, the MRI derived Connectome reveals the live human brain and can be combined with genetic and environmental information to identify individual differences in brain circuitry."

Raichle, a collaborator in the NIH Human Connectome project, is one of the pioneers of"resting state"MRI, in which brain scans are taken of patients not involved in any specific task. He believes that the ongoing spontaneous activity discovered during such scans will tell us about how the brain remains flexible and maintains a degree of homeostatis so that"you know who you are."

"Being able to sample this ongoing activity at increasing temporal fidelity and precision becomes really important for understanding how thebrainis doing this,"Raichle said."David is superclever at this kind of technical stuff, and I have been cheering him along, saying that the faster we can go, the better we can understand the brain's spontaneous activity."

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Scientists make holograms of atoms using electrons

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The scientists, Ymkje Huismans from the FOM-Institute AMOLF in Amsterdam, The Netherlands, and an international research team have published their study in a recent issue ofScience Express.

“What we have experimentally demonstrated is that it is possible to make holograms by taking an electron out of a molecule and, using a laser field, redirect the electron toward the molecule,” coauthor Marc Vrakking, of the FOM-Institute AMOLF and the Max Born Institute in Berlin, toldPhysOrg.com.

In their experiments, the scientists beamed an intense infrared laser light at an atom or molecule, which resulted in the atom or molecule becoming ionized and releasing an electron. The laser field causes the liberated electron to oscillate away from and toward the ion. Sometimes, an electron and ion collide, releasing a very short burst of radiation.

Because theelectron motionis fully coherent, meaning it always has the same phase, the scientists realized that they could apply holographic techniques to record information about the ion and electron. The key to holographic electron imaging is to observe the interference between a reference wave (which is emitted by the electron and doesn’t interact with the ion) and a signal wave (which scatters off the ion and encodes its structure). When the reference wave and signal wave interfere on a detector, the encoded information about the electron and ion is stored and can be viewed in the future. As the scientists explained, the result is a hologram of an atom produced by its own electrons.

The researchers also developed theoretical models to simulate their measurements, confirming that the hologram had stored spatial and temporal information about theelectronsand ions. By using the holographic structures to develop a new kind of ultra-fastphotoelectron spectroscopy, researchers could be able to directly measure electron andionmovements on the attosecond timescale. This ability would be useful for understanding chemical reactions at the most basic level, particularly inmoleculesthat cannot be easily studied by other methods.

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New ways to tune electrical conductivity revealed by electron interaction

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The difference between anelectrical conductorand an insulator is thatelectronsin the latter cannot move freely through the crystal. This is because insulators have a gap in their energy spectrum that electrons cannot overcome. Hiroshi Watanabe, Tomonori Shirakawa and Seiji Yunoki from the RIKEN Advanced Science Institute in Wako and the Japan Science and Technology Agency have now uncovered how the electronic gap in Sr2IrO4arises. Other RIKEN scientists had shown previously that the compound is aninsulator.

Sr₂IrO₄is a member of the oxygen-containing compounds based on transition metals that have high atomic numbers. In these transition metals, the electrons of elements such as nickel, copper or cobalt strongly interact with each other, which results in effects such assuperconductivityor magnetism.

In compounds made from the heavier transition metals, the outermost electrons circle the atoms in the so-called‘5d electron shell’, which is relatively distant from the core. For electrons that occupy this shell there is an unusually strong interaction between their magnetic property, called spin, and the orbital motion around the atomic nucleus. The energy of this spin–orbit interaction is as large as the electron’s energy of motion or the energy arising from the electrostatic interaction between the electrons. This has dramatic consequences on their electronic properties, according to Yunoki, who led the research team.“Literally anything can happen in 5d electron systems because of the subtle balance of those three fundamental energy scales.”

How this energetic interplay modifies the electron conducting behavior in Sr2IrO4 became evident from the researchers’ calculations. The strong spin–orbit interaction in Sr₂IrO₄shifts some of the electronic states to higher energies, which is sufficiently strong to create an energy gap in the electronic states.

Furthermore, the calculations reveal an intriguing connection to the family of high-temperature superconductors that have a similar gap in their electronic states. In these compounds, superconductivity is achieved through a small addition of atoms introducing an electron surplus. The researchers are now investigating the possibility that this could also be the case here.“It would have an enormous impact if one can make Sr₂IrO₄superconducting,” says Yunoki.“We hope that our theoretical calculations will be of help to experimentalists.”

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The 'mad' Egyptian scholar who proved Aristotle wrong

January'sPhysics Worldfeatures a fanciful re-imagining of the 10-year period in the life of the medieval Muslim polymath, written by Los Angeles-based science writer Jennifer Ouellette.

The feature covers the time when al-Haytham -- banished from society and deprived of books -- came up with his revolutionary theories about the form and passage of light.

Ouellette brings detail to the skeletal plot of al-Haytham's life, from the awe and intimidation felt when he was summoned by the Caliph to use his engineering prowess to overcome the annual flooding of the Nile, to his fear of punishment when he realised he had failed in his task.

Al-Haytham was only able to escape a death sentence from the notoriously brutal Caliph by pretending he had gone mad. The Caliph instead incarcerated Al-Haytham, imprisoning him under house arrest to a cell. Confined and alone, it was here that Al-Haytham carried out the work that was to make him famous.

In 11th-century Egypt, Aristotle's ancient thought that visible objects and our own eyes emit rays of light to enable our vision still held.

Ouellette imagines al-Haytham lying alone in his darkened room questioning why the objects in the room are not emitting light and asking 'Is it possible that the ancients were mistaken?'

The question providing the crux, al-Haytham was spurred into experimental action with the candles and copper in his bare room to conclude that there is no mysterious"form"that all objects emit; rather there are sources of primary light that are reflected by other objects.

As Ouellette writes,"This is a work of fiction– a fanciful re-imagining of a 10-year period in the life of Ibn al-Haytham, considered by many historians to be the father of modern optics. Living at the height of the golden age of Arabic science, al-Haytham developed an early version of the scientific method 200 years before scholars in Western Europe."

Released from prison after the Caliph's death, Al-Haytham (AD 965-1040) went on to make contributions to astronomy, mathematics, engineering and medicine, as well as physics. But it his seven-volume Book of Optics, which he wrote while imprisoned, that remain his most famous contributions to science, covering visual perception, psychology and physical optics.

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Newly developed cloak hides underwater objects from sonar

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Led by mechanical science and engineering professor Nicholas Fang, Illinois researchers have demonstrated an acoustic cloak, a technology that renders underwater objects invisible to sonar and other ultrasound waves.

"We are not talking about science fiction. We are talking about controlling sound waves by bending and twisting them in a designer space,"said Fang, who also is affiliated with the Beckman Institute for Advanced Science and Technology."This is certainly not some trick Harry Potter is playing with."

While materials that can wrap sound around an object rather than reflecting or absorbing it have been theoretically possible for a few years, realization of the concept has been a challenge. In a paper accepted for publication in the journalPhysical Review Letters, Fang's team describe their working prototype, capable of hiding an object from a broad range of sound waves.

The cloak is made of metamaterial, a class ofartificial materialsthat have enhanced properties as a result of their carefully engineered structure. Fang's team designed a two-dimensional cylindrical cloak made of 16 concentric rings of acoustic circuits structured to guide sound waves. Each ring has a differentindex of refraction, meaning that sound waves vary their speed from the outer rings to the inner ones.

"Basically what you are looking at is an array of cavities that are connected by channels. The sound is going to propagate inside those channels, and the cavities are designed to slow the waves down,"Fang said."As you go further inside the rings, sound waves gain faster and faster speed."

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Illinois professor Nick Fang developed a two-dimensional acoustic cloak that makes objects in the center invisible to sonar and other ultrasound waves. Credit: L. Brian Stauffer

Since speeding up requires energy, the sound waves instead propagate around the cloak's outer rings, guided by the channels in the circuits. The specially structured acoustic circuits actually bend thesound wavesto wrap them around the outer layers of the cloak.

The researchers tested their cloak's ability to hide a steel cylinder. They submerged the cylinder in a tank with an ultrasound source on one side and a sensor array on the other, then placed the cylinder inside the cloak and watched it disappear from their sonar.

Curious to see if the hidden object's structure played a role in the cloaking phenomenon, the researchers conducted trials with other objects of various shapes and densities.

"The structure of what you're trying to hide doesn't matter,"Fang said."The effect is similar. After we placed the cloaked structure around the object we wanted to hide, the scattering or shadow effect was greatly reduced."

An advantage of the acoustic cloak is its ability to cover a broad range of sound wavelengths. The cloak offers acoustic invisibility toultrasound wavesfrom 40 to 80 KHz, although with modification could theoretically be tuned to cover tens of megahertz.

"This is not just a single wavelength effect. You don't have an invisible cloak that's showing up just by switching the frequencies slightly,"Fang said."The geometry is not theoretically scaled with wavelengths. The nice thing about the circuit element approach is that you can scale the channels down while maintaining the same wave propagation technology."

Next, the researchers plan to explore how the cloaking technology could influence applications from military stealth to soundproofing to health care. For example, ultrasound and other acoustic imaging techniques are common in medical practice, but many things in the body can cause interference and mar the image. A metamaterial bandage or shield could effectively hide a troublesome area so the scanner could focus on the region of interest.

The cloaking technology also may affect nonlinear acoustic phenomena. One problem plaguing fast-moving underwater objects is cavitation, or the formation and implosion of bubbles. Fang and his group believe that they could harness their cloak's abilities to balance energy in cavitation-causing areas, such as the vortex around a propeller.

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