Communication technologies including smartphones and laptops could now be 1,000 times faster, new study suggests

 Many of the communication tools of today rely on the function of light or, more specifically, on applying information to a light wave. Up until now, studies on electronic and optical devices with materials that are the foundations of modern electronics -- such as radio, TV, and computers -- have generally relied on nonlinear optical effects, producing devices whose bandwidth has been limited to the gigahertz (GHz) frequency region. (Hertz stands for cycles per second of a periodic phenomenon, in this case 1billion cycles).

Thanks to research performed at the University of Pittsburgh, a physical basis for terahertz bandwidth (THz, or 1 trillion cycles per second) -- the portion of the electromagnetic spectrum between infrared and microwave light -- has now been demonstrated.

In a paper published March 4 in Nature Photonics, Hrvoje Petek, a professor of physics and chemistry in Pitt's Kenneth P. Dietrich School of Arts and Sciences, and his colleague Muneaki Hase, a professor of applied physics at the University of Tsukuba in Japan and a visiting scientist in Petek's lab, detail their success in generating a frequency comb -- dividing a single color of light into a series of evenly spaced spectral lines for a variety of uses -- that spans a more than 100 terahertz bandwidth by exciting a coherent collective of atomic motions in a semiconductor silicon crystal.

"The ability to modulate light with such a bandwidth could increase the amount of information carried by more than 1,000 times when compared to the volume carried with today's technologies," says Petek. "Needless to say, this has been a long-awaited discovery in the field."

To investigate the optical properties of a silicon crystal, Petek and his team investigated the change in reflectivity after excitation with an intense laser pulse. Following the excitation, the team observed that the amount of reflected light oscillates at 15.6 THz, the highest mechanical frequency of atoms within a silicon lattice. This oscillation caused additional change in the absorption and reflection of light, multiplying the fundamental oscillation frequency by up to seven times to generate the comb of frequencies extending beyond 100 THz. Petek and his team were able to observe the production of such a comb of frequencies from a crystalline solid for the first time.

"Although we expected to see the oscillation at 15.6 THz, we did not realize that its excitation could change the properties of silicon in such dramatic fashion," says Petek. "The discovery was both the result of developing unique instrumentation and incisive analysis by the team members."

Petek notes the team's achievements are the result of developing experimental and theoretical tools to better understand how electrons and atoms interact in solids under intense optical excitation and of the invested interest by Pitt's Dietrich School in advanced instrumentation and laboratory infrastructure.

The team is currently investigating the coherent oscillation of electrons, which could further extend the ability of harnessing light-matter interactions from the terahertz- to the petahertz-frequency range. Petahertz is a unit of measure for very fast frequencies (1 quadrillion hertz).

This research was funded by a grant from the National Science Foundation.

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The above story is reprinted from materials provided by University of Pittsburgh.

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Journal Reference:

Muneaki Hase, Masayuki Katsuragawa, Anca Monia Constantinescu, Hrvoje Petek. Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon. Nature Photonics, 2012; DOI: 10.1038/nphoton.2012.35

The secret life of proteins: Researchers discover dual role of key player in immune system

That protein, STIM1, was previously known to sense a change in calcium within immune cells, a process that occurs when the body confronts a pathogen. Upon sensing this change, STIM1 opens a type of pore in the cell membrane, called a CRAC channel, to allow the flow of calcium ions — a vital step in activating the immune system.

The Feinberg team, led by Murali Prakriya, assistant professor of molecular pharmacology and biological chemistry, discovered that STIM1 not only opens these pores but is responsible for determining the exquisite selectivity for calcium ions within the CRAC channels, a critical factor in kick starting the body's immune system. These findings were recently reported in the journal Nature.

"People have generally thought that selectivity of ion channels is fixed and that selectivity and opening are separate processes; this is a fundamental shift in the way scientists believe ion channels operate," says Prakriya, referring to the 'pores' that STIM1 regulates. "CRAC channels and STIM1 are absolutely vital to activating the immune system. As is observed in some human patients, you can block key parts of the system by blocking these molecules in immune cells. These finding reveal not only a novel mechanism by which CRAC channels operate, but also new ways in which it encodes biological information. This represents exciting new possibilities to develop therapeutics to treat a broad range of conditions."

To determine that STIM1 is responsible for selectivity and opening, the researchers created a mutated CRAC channel designed to keep the pore open without the assistance of STIM1. When the channel was opened without STIM1, multiple types of ions were passed through the pore, including sodium and potassium. When STIM1 was added back in, the channel became very selective for calcium ions again, like the normal channel. Even at low doses of STIM1, the unmutated channel lost its normally high calcium selectivity, allowing the entry of multiple types of ions.

Conditions that might benefit from immune suppression are likely targets for future CRAC channel targeted therapy, including autoimmune diseases and many types of allergies. Additionally, targeting CRAC channels could provide improvements for existing immune suppression therapies such as those used during transplantation.

"The CRAC channel is emerging to be incredibly important for the immune system," says Prakriya. "But we have been solely focused on its calcium conducting mode that occurs in response to STIM1. It is certainly possible that there could be other players in the cell that open the CRAC channel pore to permit the flux of other ions to stimulate different cell functions. That's the next question."

Also in the Nature article, Prakriya's team identified the location of the barrier, or gate, within the CRAC channel that controls its opening and closing.

"The identification of the molecular and structural regions of the pore that controls opening and closing is highly valuable for facilitating drug design targeting CRAC channels for the treatment of immune disorders," he adds.

Provided by Northwestern University (news : web)

Envelope for an artificial cell

Neal Devaraj, assistant professor of chemistry at the University of California, San Diego, and Itay Budin, a graduate student at Harvard University, report their success in the Journal of the American Chemical Society.

“One of our long term, very ambitious goals is to try to make an artificial cell, a synthetic living unit from the bottom up – to make a living organism from non-living molecules that have never been through or touched a living organism,” Devaraj said. “Presumably this occurred at some point in the past. Otherwise life wouldn’t exist.”

By assembling an essential component of earthly life with no biological precursors, they hope to illuminate life’s origins.

“We don’t understand this really fundamental step in our existence, which is how non-living matter went to living matter,” Devaraj said. “So this is a really ripe area to try to understand what knowledge we lack about how that transition might have occurred. That could teach us a lot – even the basic chemical, biological principles that are necessary for life.”

Molecules that make up cell membranes have heads that mix easily with water and tails that repel it. In water, they form a double layer with heads out and tails in, a barrier that sequesters the contents of the cell.

Devaraj and Budin created similar molecules with a novel reaction that joins two chains of lipids. Nature uses complex enzymes that are themselves embedded in membranes to accomplish this, making it hard to understand how the very first membranes came to be.

“In our system, we use a sort of primitive catalyst, a very simple metal ion,” Devaraj said. “The reaction itself is completely artificial. There’s no biological equivalent of this chemical reaction. This is how you could have a de novo formation of membranes.”

They created the synthetic membranes from a watery emulsion of an oil and a detergent. Alone it’s stable. Add copper ions and sturdy vesicles and tubules begin to bud off the oil droplets. After 24 hours, the oil droplets are gone, “consumed” by the self-assembling membranes.

Although other scientists recently announced the creation of a “synthetic cell,” only its genome was artificial. The rest was a hijacked bacterial cell. Fully artificial life will require the union of both an information-carrying genome and a three-dimensional structure to house it.

The real value of this discovery might reside in its simplicity. From commercially available precursors, the scientists needed just one preparatory step to create each starting lipid chain.

“It’s trivial and can be done in a day,” Devaraj said. “New people who join the lab can make membranes from day one.”

Provided by University of California - San Diego (news : web)

Chemists to develop new materials for hydrogen storage in vehicles

The U.S. Department of Energy recently awarded Berkeley Lab a three-year, $2.1 million grant for the project, which will also include contributions by the National Institute of Standards and Technology (NIST) and General Motors (GM). The grant was part of more than $7 million awarded by DOE last month for hydrogen storage technologies in fuel cell electric vehicles.

“We’re working on materials called metal-organic frameworks to increase the capacity of hydrogen gas in a pressure cylinder, which would be the fuel tank,” said Jeffrey Long, a Berkeley Lab scientist who co-leads the project along with Berkeley Lab chemist Martin Head-Gordon. “With these materials, we’re working on storing the hydrogen without the use of very high pressures, which will be safer and also more efficient without the significant compression energy losses.”

Metal-organic frameworks (MOFs) are three-dimensional sponge-like framework structures that are composed primarily of carbon atoms and are extremely lightweight. “What’s very special about these materials is that you can use synthetic chemistry to modify the surfaces within the materials and make it attractive for hydrogen to stick on the surface,” Long explained.

Separately, Long is also using MOFs in a carbon capture project, in which the material would selectively absorb carbon dioxide over nitrogen. For the fuel cell project, the trick lies not in getting the MOF to select hydrogen out of a mixture but to store as much hydrogen as possible.

Currently, vehicles using hydrogen fuel cells can achieve a range of close to 300 miles—but only if the hydrogen is stored at extremely high pressures (600 to 700 bar), which is expensive and potentially unsafe. It is also energy intensive to pressurize the hydrogen.

So far Long has succeeded in more than doubling hydrogen capacity, but only at very low temperatures (around 77 Kelvin, or -321 Fahrenheit). “It’s still very much basic research on how to create revolutionary new materials that would boost the capacity by a factor of four or five at room temperature,” he said. “We have an idea of what kinds of frameworks we might make to do this.”

Long’s approach is to create frameworks with lightweight metal sites on the surface, making it attractive for hydrogen molecules to bind to the sites. “Our approach has been to make some of the first metal-organic frameworks that have exposed metal cations on the surface,” he said. “Now we need to figure out ways of synthesizing the materials so that instead of one hydrogen molecule we can get two or three or even four hydrogen molecules per metal site. Nobody’s done that.”

This is where Head-Gordon, a computational chemist, comes in. He will work on theoretical understanding of MOFs so that he can try to predict their hydrogen storage properties and then instruct Long’s team as to what kind of material to synthesize. “He can do calculations on a lot of different target structures and say, here’s the best one for you guys to spend time trying to make, because synthetic chemistry is very cost and labor intensive,” Long said.

The scientist at GM will aid in providing accurate high-pressure measurements. The NIST scientist is an expert in neutron diffraction and neutron spectroscopy, which will allow Long and his team to pinpoint where exactly the hydrogen is going and verify that it is binding to the metals.

Provided by University of California - Berkeley (news : web)

Portable device will quickly detect pathogens

Using synthetic DNA, Dan Luo, professor of biological and environmental engineering, has devised a method of "amplifying" very small samples of pathogen DNA, RNA or proteins. Edwin Kan, professor of electrical and computer engineering, has designed a computer chip that quickly responds to the amplified samples targeted by Luo's method. They will combine these to make a handheld device, usable under harsh field conditions, that can report in about 30 minutes what would ordinarily require transporting samples to a laboratory and waiting days for results.

The work will be supported by the Bill & Melinda Gates Foundation as part of the Grand Challenge program to develop "point-of-care diagnostics" for developing countries. The foundation has distributed $25 million to 12 teams, selected from more than 700 applicants. Various teams are working on different aspects of the technology, and eventually their work will be integrated to make a practical, low-cost testing kit, Luo said.

Luo's research group has found that DNA can be used like molecular-level Lego blocks. A single strand of DNA will lock onto another single strand that has a complementary genetic code. By synthesizing DNA strands that match over just part of their length, his team can assemble unusual shapes -- in this case, a Y. Attached to the base of the Y is a DNA strand or antibody designed to lock onto a pathogen. Attached to one of the upper arms is a molecule that will polymerize -- chain up with other similar molecules -- when exposed to ultraviolet light.

When a pathogen is added to a solution of these Y-DNA molecules, the matching receptors on the stem of the Y will lock onto pathogen molecules, but only onto part of them; the mix will contain two different Y-structures, each tagged to lock onto a different part of the pathogen molecule. The result, when the targeted pathogen is present, is the formation of many double-Ys linked together by a pathogen molecule, each assembly carrying two molecules capable of polymerizing.

When the mixture is exposed to a portable ultraviolet light, the polymer molecules at the ends of each double-Y link to those on other double-Ys, forming long chains that clump up into larger masses. This polymerization won't happen, the researchers emphasize, unless a targeted pathogen is present to link two Ys together. A single Y with only one polymer molecule attached can only link to one other single Y, and no chain will form.

Kan's new chip measures both the mass and charge of molecules that fall on it. The large clumps of Y-DNA have a much larger mass and charge than single molecules, and trigger the detector. The chip uses the popular and inexpensive CMOS technology compatible with other common electronic devices. A detector might, for example, be controlled and powered by a mobile phone, Luo suggested.

All this can be combined with nanofluidics to make a robust battery-operated testing kit, the researchers said. After further development they plan to conduct tests simulating field conditions in the developing world. Along with surviving hot or cold weather, Luo said, "It has to work in dirty water."

Provided by Cornell University (news : web)