VALLEY RESEARCH

Research News is a digest of science and technology news items arising from research and development magazines, newspapers, trade magazines, newsletters, and other news sources that Valley Research processes daily for the benefit of its customers everywhere. It is provided freely to our customers who are free in turn to post or transmit it to other interested researchers provided only that credit to Valley Research is given. Research News is updated approximately once a week.

Rodolfo Carrera, Editor

WEEK OF JULY 26, 2010 [No. 855]

Single-molecule DNA translocation through one-atom thick nanopores shown:   researchers at the Kavli Institute in Delft have made graphene nanopores with length comparable to the distance between two bases in a DNA molecule (0.5 nm for single stranded DNA) and then have demonstrated that DNA goes through them. They create the pores (with diameters from 5 to 25 nm) by placing mono-layer flakes of graphene over a SiN membrane and drilling nanosized holes in the graphene using an electron beam. A 200 mV voltage is applied along the graphene surface as DNA strands are passed through the slit one base at a time. As individual DNA molecules translocate (a biochemical process that allows the DNA molecule to slide through the hole) through the nanopore, characteristic temporary conductance changes and concomitant spikes are observed in the ionic current across the nanopore. Each of the four DNA bases (A, C, G, and T) has a unique effect on the conductance of graphene across the gap which provides the bases for sequencing using this technique. The group has demonstrated that DNA goes through nanopores in graphene and that it does so with high speed. These are important advancements towards using graphene for DNA sequencing and then greatly lower cost of genomic sequencing.

For more information: Physicsworld, July 21 (2010); ACS Nano Lett., June 7 (2010).

WEEK OF JULY 19, 2010 [No. 854]

A better Arsenic remover based on graphene made:   Korean researchers at Pohang University have created a new type of magnetite composite based on reduced graphene oxide, RGO. The hybrid material (superparamagnetic at room temperature) is capable of removing 99.9% of As in water and reduce its concentration to below 1 ppb. The composite is ideal for removal of As (and perhaps other heavy metals) compared with bare magnetite because the presence of the graphene flakes among the magnetite particles increases the number of As adsorption sites. The M-RGO increases the stability of magnetite so that it can be used in continuous-flow water systems.

For more information: Physicsworld, July 7 (2010); ACS Nano Lett., June 16 (2010).

Nano-direct- write technique for 3D wiring and bonding shown:   researchers at the University of Illinois have developed a way to produce and bond in-situ tiny pure metal nanowires. They load a micropipette with a Cu electrolyte solution. In close contact a liquid bridge forms between the notched-nozzle tip and the bonding pad. An electric current causes the Cu to deposit as solid. As the tip moves through space at the right speed, Cu continuously deposits from the pipette solution creating a wire. This allows for a leap forward in orders of magnitude both in wire diameter and bonding area over present microelectronics prefabricated fine-wire bonding.

For more information: ScienceDaily, July 16 (2010); Science, to be published.

WEEK OF JULY 12, 2010 [No. 853]

The proton measured to be smaller than previously thought:   an international group lead by scientists from the Max Planck Institute for Quantum Optics in Garching, has found the proton radius to be 0.8418 fm with uncertainty 0.0007 fm, which is smaller by approximately 5 standard deviations of the accepted value to date (0.877 fm with an uncertainty of 0.007 fm). The result was obtained from the measurement of the Lamb shift in muonic H. The Lamb shift is a result of the interactions between the electron (in this case the muon, with same charge and some 207 times the mass of the electron) and the constituent quarks of the proton as described by QED. These interactions are slightly different for electrons occupying the 2S and the 2P energy levels and the resulting energy shift depends in part on the radius of the proton. The team measured the shift using a proton accelerator to create a beam of muons, which they fired at H gas. Whenever a muon collides with a H₂, it knocks the molecule apart and replaces the electron to create a muonic H. About 1% of the time the muon finds itself in the 2S state, where it is excited to the 2P state by a laser pulse, decaying with the emission of an X-ray. By counting the X-rays while scanning the frequency of the laser pulse, the photon energy required to drive the 2S-2P transition was measured and then used on a QED calculation to obtain the radius of the proton.

For more information: Nature, July 8 (2010) pages 213 and 195; Physicsworld, July 7 (2010).

WEEK OF JULY 5, 2010 [No. 852]

Intrinsic neuronal plasticity by the Axon Initial Segment shown:   scientists at King's College London and Kyoto University have identified bi-directional and reversible mechanisms for modulating neuronal excitability: displacement and extension of the AIS (axon initial segment, the initiation site of the action potential). The excitability of a neuron (responsiveness to synaptic input) can be altered by experience adding to the plasticity of synapses connections between neurons. They have shown that the AIS, a highly organized, ion-channel-enriched matrix of proteins situated close to the soma, can be modified to make the cell more or less responsive to inputs. They find that when extracellular K levels are chronically elevated, mimicking increased neuronal activity, the AIS shifts away from the cell body, making the neuron less excitable and requiring stronger stimulation to fire. They also find that in the neurons of deaf avian subjects, the audio input deprivation makes the AIS to elongate to near double size with no changes in the density and composition of Na channels in the AIS and increased total Na currents in the axons. This allows refining neuronal computation during strong sensory deprivation. This novel form of activity-dependent plasticity may fine-tune neuronal excitability during development.

For more information: Science, June 24 (2010) pages 1070, 1075, and 1022.

WEEK OF JUNE 28, 2010 [No. 851]

Regenerated rat lungs implanted:   scientists at Yale and Duke Universities have regenerated fully functional lung tissue that can exchange gas. They have successfully implanted tissue-engineered lungs, cultured in vitro, that serve the lung's primary function of exchanging O₂ and CO₂. They took adult rat lungs and first removed their existing cellular components, preserving the extracellular matrix and hierarchical branching structures of the airways and vascular system to use later as scaffolds for the growth of new lung cells. This advance should help improve the present organ rejection and infection rate for lungs with just 10-20% survival at 10 years.

For more information: ScienceDaily, June 24 (2010); Wall Street Journal, June 25 (2010), page A3; Science, to be published.

High-efficiency solar cells based on hot-electron transfer shown:   researchers at the Universities of Minnesota and Texas have demonstrated a way to increase the current limit of 30% in the efficiency of solar cells to over 60%. They have built on previous work at the University of Chicago probing that hot electrons produced by the photons with energies over the semiconductor's bandgap, can be slowed down in semiconductor nanocrystals. The group has figured out the way to capture these electrons before their energy is lost. They transfer the electrons from quantum dots (PbSe crystals) to an adjacent electronic conductor made of TiO₂.

For more information: Science, June 18 (2010) page 1543; Physicsworld, June 24 (2010).

WEEK OF JUNE 21, 2010 [No. 850]

A laser that mixes dark and bright pulses is built:   scientists at NIST in Boulder have created a new type of laser that emits dark pulses (intensity dips in a continuous beam of light which are the opposite of the bright bursts in a normal pulsed laser). This acts as a continuous-wave laser that has really fast shutter in front of it, only that the dark pulses form inside the laser itself. The laser is based on a quantum-dot diode laser with the laser beam amplified in a specially tailored cavity next to the dot where electrons and holes recombine. An InGaAs dot is topped with a 5 mm semiconductor waveguide to produce a train of dark pulses each 90 ps wide.

For more information: Physicsworld, June 16 (2010).

Thermochemical nanolithography shown:   an international team lead by NRL researchers has developed a new technique to write electrically conducting nanowires onto graphene oxide using a heated AFM tip. The oxidized form of graphene is reduced as the tip is moved to open 12-nm channels that act as low-friction, low-electrical resistance wires. It is believed that the rest of the graphene oxide sample remains insulating. Writing with different temperatures above 130 C allows the tuning of the electronic properties over four orders of magnitude, from semiconducting to metallic nanoribbons. This is a cold lithographic process for the sample.

For more information: Chem. Eng. News, June 14 (2010) page 12; Physicsworld, June 11 (2010).

WEEK OF JUNE 14, 2010 [No. 849]

Diffusive random-walk ground motion established:   work at Fermilab has revealed that apart from motion due to tides, seismic activity and other geophysical phenomena, the ground also moves entirely at random in time and space, generally ~100 nm / minute in any direction, over scales ranging from meters to Kms. Vladimir Shiltsev came to this conclusion after using data from particle accelerator facilities in EU, Japan and US collected over two decades. He has proposed a simple formula to estimate how the distance between two points along a linear accelerator, that would focus their particle beams to just a few nm across, will change over time.

For more information: Physicsworld, June 4 (2010); Phys. Rev. Letts., June 7 (2010) page 238501.

Electrical source of entangled photons pairs:   researchers in Cambridge, England have constructed an entangled light-emitting diode (ELED) using semiconductor techniques utilized in fabrication of LEDs. The device converts electrical current directly into entangled light rather than relying on laser power as conventionally. They grew semiconductor layers using MBE and then defined the active area of the LED and added electrical contacts. The ELED differs from an LED in that it contains quantum dots. The thickness of the semiconductor material surrounding the quantum dot is optimized to control the supply of current to it, to prevent electrons from tunneling into the quantum dot from the n-doped region, which would destroy the entanglement.

For more information: Nature, June 3 (2010) page 594; Physicsworld, June 5 (2010).

WEEK OF JUNE 7, 2010 [No. 848]

Practical assay to detect serum single protein molecules:   the company Quanterix from Boston has developed an assay that is 1,700 times mores sensitive for detecting a cancer biomarker than existing tests. The single molecule array technology uses femtoliter-sized chambers to individually isolate antibody-coated microbeads that trap single biomarker molecules. Labeling the biomarker with an enzyme permits its detection by fluorescence microscopy. The enzyme-linked immunosorbent assay allows prostate-specific antigen (PSA) detection in blood at concentrations of 10^-15 M versus current assays that measure PSA concentrations at 10^-12 M.

For more information: Chem. Eng. News, May 31 (2010) page 51; Nature Biotechnology, on line May 23 (2010).

Quantum dot lithography technique on graphene proposed:   researchers at Rice University in Houston have proposed a technique for patterning the hydrogenated form of graphene (graphane) with quantum dots. They have found that removing hydrogen atoms from 2D sheets of graphane (which is formed by simply adding H atoms to both sides of the graphene matrix) opens up clusters of vacancies with sharp hexagonal graphene-graphane interfaces that behave like quantum dots (3D semiconductors whose electronic properties can be changed simply changing its size). Little charge leaks across from the graphene dots into the graphane host material.

For more information: Physicsworld, June 3 (2010); ScienceDaily, May 27 (20100; ACS Nano, on line May 13 (2010).

WEEK OF MAY 31, 2010 [No. 847]

In vitro astroglia made to mature into fully functional neurons:   a group at the Ludwig-Maximilians University in Munich has made astroglia to become synapse-forming neurons. The researchers manipulated gene expression in astroglia taken from the brains of newborn mice. They generated neurons by inducing higher and more persistent expression of certain gene-regulation proteins that had been induced in previous studies. They showed that astroglia from the postnatal cortex can be reprogrammed in vitro to generate neurons with action potential synaptic generation by following forced expression of neurogenic transcription factors.

For more information: Nature, May 27 (2010) page 400; PLoS Biology, May 18 (2010).

Hemispherical asymmetry of Earth's inner core explained:   French researchers have shown that the growth of the solid core implies an eastward drift of the material three times faster than the rate of growth, driven by crystallization in the western hemisphere and melting on the eastern hemisphere. This self-sustained translational motion generates an asymmetric distribution of sizes of iron crystals, which grow during their translation. The scientists use multiple-scattering modeling of seismic velocity and attenuation measurements sampling the uppermost inner core.

For more information: Science, May 21 (2010) pages 1014, 1018, and 982.

WEEK OF MAY 24, 2010 [No. 846]

A new bacteria with a computer manufactured genome created:   a group from the Craig Venter Institute in Rockville and San Diego have designed, synthesized, and assembled the 1.08 Mbp Mycoplasma mycoides JCV-syn1.0 genome starting from digitized genome sequence information and its transplantation into a Mycoplasma capricolum recipient cell to create new Mycoplasma mycoides cells that are controlled only by the synthetic chromosome. The only DNA in the cells is the designed synthetic DNA sequence, including identification watermark sequences and other designed gene deletions and polymorphisms, and mutations acquired during the building process. They wrote the entire genetic code as a digital file that was later used to synthesize hundreds of DNA pieces that were finally assembled by natural bacteria into the complete synthetic genome. The master set of genes was transplanted into an emptied cell where it converted the cell into a different species. The cell generates the proteins and organelles specified by the synthetic DNA's genetic information. The new cells have expected phenotypic properties and are capable of continuous self-replication. This is the first time that artificial cells has been generated with predetermined properties which opens the door to the creation of other strains of bacteria with commercial potential for generation of vaccines, biofuels, and others.

For more information: Science, May 20 (2010) on line; Wall Street Journal, May 21 (2010) page A1

WEEK OF MAY 17, 2010 [No. 845]

Gas in galaxy groups is displaced away in grand scale by black holes:   a group lead by scientists from the Max Planck Institute for Extraterrestrial Physics in Garching have quantified the importance of the mechanical energy released by radio galaxies inside galaxy groups. They show that the jets produced by the in-fall of surrounding matter into a black hole eject matter not only from their host galaxies but even the gas between the galaxy group members. It is known that active galaxies transport huge amounts of materials with their jets which are particularly luminous at radio wavelengths, into the intra-cluster gas. By comparing the jet energy output to the host galaxy group's gravitational binding energy, they find that radio galaxies produce sufficient energy to unbind a significant fraction of the intragroup gas. The amount of gas observed in galaxy groups is much smaller than expected and the work here explains why for the first time. In galaxy groups the gas is contained by gravity. The black holes produce so much energy that it outweighs the gravitational capacity of the group to hold its gas and a large part of the gas is removed. No similar effect is observed in more massive galaxy clusters where the huge gravitational pull of deeper potential wells restrains the intracluster gas from being removed.

For more information: ScienceDaily, May 14 (2010); The Astrophys. J., May 1 (2010) page 34.

WEEK OF MAY 10, 2010 [No. 844]

Water ice covers an asteroid in the main asteroid belt between Mars and Jupiter:   two independent teams led by scientists from the University of Central Florida and Johns Hopkins University have analyzed data collected at NASA's Infrared Telescope on Mauna Kea, Hawaii observing the asteroid 24 Themis. They have found an absorption feature at 3.1 µ that is indicative of water ice, plus features at longer wavelengths that correlate with organic compounds. Although researchers had previously observed hydrated minerals in asteroids, finding actual water on an asteroid surface was surprising because at temperatures of 150-200 K surface ice should have sublimated away long ago due to the relatively short lifetime of exposed ice at this distance (~3.2 AU) from the Sun. The researchers propose that there is a reservoir of ice inside the asteroid (meters below the surface where it could survive for billions of years) that is constantly sublimating (and additionally brought to the surface by small comet impacting). As the material diffuses up and out of the core, some of it recondenses on the surface frosting it. 24 Themis belongs to the same dynamical family as three of the five known main-belt comets and the presence of ice on 24 Themis provides strong evidence that is also in the main-belts comets.

For more information: Nature, April 29 (2010) pages 1320, 1322, and 1286; Chem. Eng. News, May 3 (2010) page 34.

WEEK OF MAY 3, 2010 [No. 843]

Spread of local signals across large distances in the neocortex clarified:   scientists at the Howard Hughes Medical Institute in Virginia have shown how selective stimulation of neurons in a specified area of the mouse neocortex affects the spatial distribution of excitatory and inhibitory signals both locally and farther afield within the cortex. Two-photon calcium imaging is used to monitor activity of spatially defined neuronal ensembles in the cortex. Specifically this technique is applied to the motor cortex of mice performing a choice behavior. Activity in approximately half of the imaged neurons distinguished trial types associated with different actions. Many neurons showed modulation coinciding with or preceding of action, consistent with their involvement in motor control. Neurons with different response types were spatially intermingled. It is concluded that correlated activity in specific ensembles of functionality related neurons is a signature of learning-related circuit plasticity. There is a fine-scale and dynamic organization of the frontal cortex that underlies flexible behavior. The study not only achieves selective analysis of a single neuronal population in the brain of a live animal but also shows the way in which neuronal signals spread within the less known horizontal plane of the cortex.

For more information: Nature, April 22 (2010) pages 1182 and 1134.

WEEK OF APRIL 26, 2010 [No. 842]

AFM adapted for biological topology:   LBNL scientists in Berkeley have developed nano-sized cantilevers with gentle touch to help discern the workings of living cells and their natural, liquid environment. Rather than measuring the cantilever's deflection by bouncing a laser off it, the group placed a nanowire cantilever in the focus of a laser beam and detected the resulting light pattern, pinpointing the nanowire's position with high resolution. By using non-interferometric high sensitivity detection of nanowires, the researchers expect to probe the assembly and dynamics (association and disassociation) of protein complexes in the cell membrane.

For more information: ScienceDaily, April 22 (2010); Phys. Rev. Lett., April 6 (2010) page 147203.

3D cloaking demonstrated in the NIR range:   a team led by researchers at the KIT at Karlsruhe, have designed and realized a 3D invisibility-cloaking structure operating at optical wavelengths based on transformation optics. They use a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in an Au reflector. The group fabricated structure and controls by direct laser writing and characterized them by simultaneous high-numerical aperture, far-field optical microscopy and spectroscopy. A cloaking operation with a large bandwidth of unpolarized light from 1.4 to 2.7 µ is demonstrated for viewing angles up to 60 deg.

For more information: Science, April 16 (2010) page 337.

WEEK OF APRIL 19, 2010 [No. 841]

New system jumps direct imaging capability of exoplanets:   scientists at JPL have developed a new technique that combines adaptive optics and vortex coronography to allow exoplanet detection with much more precision than before. They used the system to detect the three planets known to HR 8799 at 120 light years in the Pegasus constellation. They did the direct imaging with a clear view of 300 marsec of the star using a 1.5 m portion of the Palomar telescope (that vs. the 10 m Keck telescope used in their discovery in 2008). The light from the star is filtered out after been focused in the center of a glass phase plate that applies a spiral phase shift to it.

For more information: Nature, April 15 (2010) page 1018; Physicsworld, April 15 (2010); ScienceDaily, April 14 (2010).

Genetic process behind the creation of experience-based synaptic connections uncovered:   a team led by researchers at Harvard and Children's Hospital Boston has discovered that a particular set of RNA molecules usually considered just a genetic oddity are actually major players in brain development. They are essential for regulating the process by which neurons absorb the outside world experience into their genetic machinery. Activity-excited neurons release neurotransmitters that in turn activate DNA enhancer regions that induce gene expression in a wide genomic range and create their own eRNA, resulting in new synaptic connections.

For more information: ScienceDaily, April 14 (2010); Nature, published on line, April 14 (2010).

WEEK OF APRIL 12, 2010 [No. 840]

Microlaser built using an electric resonator:   researchers at ETH-Zurich have developed the smallest electrically pumped laser in the world to date. It is 30µ long, 8µ high and it has a wavelength of 200µ. It is a first in being much smaller than the wavelength of the light that it emits. Instead of using the usual optical resonator, they used an electrical resonant circuit made up of two semi-circular capacitors that are connected via a linear inductor. The light is effectively captured in it and induced into self-sustaining electromagnetic oscillations on the spot using an optical amplifier. The resonator can be scaled down regardless of the light wavelength.

For more information: ScienceDaily, April 6 (2010); Science, to be published (2010).

Extragalatic magnetic fields detected:   scientists at the Geneva Observatory have obtained evidence for the existence of intergalactic magnetic fields (seed fields for larger µG galactic fields) and have derived a lower limit for their strength, based on an analysis of data from the Fermi Large Area telescope. The results place constraints on magnetogenesis cosmological models and suggest that magnetic fields originated in the early universe before galaxy formation took place. The lower bound B > 0.3 fG stems from the non-observation of GeV gamma-ray emission from electromagnetic cascades initiated by TeV gamma-rays in intergalactic medium.

For more information: Science, April 2 (2010) pages 73 and 13.

WEEK OF APRIL 5, 2010 [No. 839]

A genetic variant shown to lead to schizophrenia by disrupting a specific brain circuit:   researchers at Columbia University have illuminated how a genetic defect carried by many schizophrenic patients causes a disruption in communication between the hippocampus and prefrontal cortex regions of the brain which are responsible for carrying out working memory. The loss of working memory and its associated impact on cognitive abilities are symptoms of schizophrenia. They use a mouse model with the 22q11.2 deletion (this microedeletion on the human chromosome 22, is one of the largest known genetic risk factors for schizophrenia). To examine functional connectivity in these mice, the group recorded the synchronization of neural activity between the hippocampus and the prefrontal cortex of the mice while they performed a cognitive task of working memory and found that their performance was either completely disrupted, or was impaired, compared to that of the healthy mice. The conclusion is that impaired long-range synchrony of neural activity is one consequence of the 22q11.2 deletion and may be a fundamental component of the pathophysiology underlying schizophrenia. Restoration of the disruption of communication between these two brain regions may help cure schizophrenia.

For more information: Nature, April 1 (2010) page 763; ScienceDaily, March 31 (2010).

WEEK OF MARCH 29, 2010 [No. 838]

Supernova Ia with mass over the Chandrasekhar limit identified:   an international team lead by scientists of Yale university have reported that the white dwarf linked with SN 2007if, an established type Ia supernova, has mass of 2.1 ± 0.2 solar masses. They arrive at this result after examining the dimming which is occurring at a slower rate than would be expected for a supernova of this type. The remnants of the supernova were analyzed using ground-based telescopes in Chile, Hawaii and California. Type Ia supernovas have been used as standard candles to measure distances in the Universe and in the prediction of the existence of dark energy.

For more information: Phyisicsworld, March 19 (2010); Astrophysical Journal, to be published.

Self-assembly of non-coated colloidal particles demonstrated:   researchers in New York University have invented a lock and key technique that causes small particles to assemble themselves into a variety of tiny structures. The new control technique does not depend on the surface chemistry of particles but on their complementary shapes. The absence of chemical bonds means that assembly is reversible. Clusters can be taken apart by changing the temperature. This spontaneous assembly method can provide a simple way to create micro and nano structures plus induce well-defined structured clusters of particles to self-replicate.

For more information: Physicsworld, March 25 (2010); Nature, March 25 (2010) page 575 and 496.

WEEK OF MARCH 22, 2010 [No. 837]

General relativity accounting for dark energy experimentally confirmed at cosmic scales:   researchers from Princeton University and the University of Zurich have confirmed on cosmic scales far beyond those of our Solar System (those larger than galaxies and clusters of galaxies) Einstein's theory of general relativity. Results exclude some but not all alternative theories of gravity. They used imaging and spectroscopy of 30 million background galaxies in the Sloan Digital Sky Survey. This first experimental test of general relativity as a valid theory of gravity at cosmological scales has been based on the determination of a quantity Eg that combines measures of large-scale gravitational lensing, galaxy clustering, and structure growth rate. The team obtains a measurement of Eg= 0.39±0.06 which is consistent with the value of 0.4 predicted by general relativity. A fivefold decrease in uncertainty of Eg would be needed to rule out incorrect gravity models. This technique when applied using billions of galaxies may allow for a determination of whether the Universe expansion acceleration is caused by dark energy (with the cosmological model been a combination of general relativity and the standard model) or a manifestation of a modification of gravity on scales 10⁸ times larger than the Solar System.

For more information: Nature, March 11 (2010) pages 256 and 172

WEEK OF MARCH 15, 2010 [No. 836]

Protective Earth's magnetosphere on at 3.45 Byrs ago:   a group lead by scientists at the University of Rochester have used a custom modified SQUID magnetometer to obtain paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo3.4 to 3.45 Byrs ago. That is some 250 Myrs earlier than previously thought and modifies timing for early life conditions. The measured field strength is ~50 to 70% of the present day field. When combined with a greater Paleoarchean solar wind pressure, the paleofield strength data suggest steady-state magnetopause standoff distances of <5 Earth radii, about half of the present-day extension and similar to values observed during recent coronal mass ejection events. The data also suggest lower-altitude aurora and increases in polar cap area, as well as heating, expansion, and volatile loss from the exosphere that would have affected long-term atmospheric composition. These conditions would have stripped away vast quantities of water vapor before the water cycle became stabilized. It is concluded that the young planet prior to the onset of a magnetic field (when the conducting liquid core convection developed) would have contained more water than previously thought and significantly more than it does today.

For more information: Science, March 5 (2010) page 1238 and 1206; Physicsworld, March 9 (2010).

WEEK OF MARCH 8, 2010 [No. 835]

A step closer to the exaflop (10¹⁸ flops) computer level:   researchers at the IBM Watson Research Center in New York have built an array of Ge nanophotonic APDs (avalanche photodetector) on a Si chip that converts optical to electronical signals at a record speed of 40 Gps operating at just 1.5 V. That compares with 10 GHz at 25 v of previous devices. The APD has built-in Si/Ge waveguides that concentrate incoming light at the Ge detector (30 nm thick, holding very high electric fields at 1.5v biases). The avalanche is produced much faster and over shorter distances than before with a 70% reduction in noise caused by random fluctuations.

For more information: Physicsworld, March 4 (2010); Wall Street Journal, March 4 (2010) page B8; Nature, March 4 (2010) page 80.

A transistor with no doping gradient in the source-drain interface:   Irish researchers at the University College Cork have made a transistor consisting of a Si nanowire in which current flow is perfectly controlled by a Si gate that is separated from the nanowire by a thin insulating layer. There is no need to alter the doping over very short distances. Instead, the entire Si nanowire is heavily n-doped, making it an excellent conductor. However, the gate is p-doped and its presence has the effect of depleting the number of electrons in the region under the nanowire. If a voltage is simply applied along the nanowire, current cannot flow through this depleted region. If a voltage is applied to the gate, the squeezing effect is reduced and current can flow.

For more information: Physicsworld, March 1 (2010); Nature Nanotechnology, March (2010) page 225.

WEEK OF MARCH 1, 2010 [No. 834]

Stimulated sound amplification by stimulated emission of phonons:   two separate groups at Caltech and the University of Nottingham have created the first phonon lasers that emit coherent sound waves (sasers). The idea of extending the laser process to phonons have stumbled against the difficulty of finding materials in which stimulated emission, rather than random spontaneous emission, is the dominant decay process. The Caltech group has used two silica 6µ-diameter microwave resonators separated by 1 µ gap to form a two-state quantum system coupled by light waves. The system is pumped to a higher energy state by a laser and MHz phonons are emitted that stimulate further emission of phonons. Sound in a narrow frequency range is emitted only after a pumping energy threshold is past. The Nottingham device is made of alternating layers of the semiconductor GaAs and the insulator AlAs. Applying a voltage between layers, electrons hop between GaAs quantum wells across the AlAs barrier emitting a phonon in the process that is capable of stimulating another hop. The layer interdistance resonates with the phonon wavelength so that the process is sustained. A femtosecond laser is used to initiate the stimulated emission. The intensity of coherent phonons is increased by increasing the bias voltage up to 160 mV where the photon wavelength (~400 GHz) resonates with the device configuration. A Terahertz saser with phonons ~1 nm wavelength would allow for 3D probing of nanostructures.

For more information: Physicsworld, February 25 (2010); Phys. Rev. Lett., to be published (2010).

WEEK OF FEBRUARY 22, 2010 [No. 833]

Optical clock with Al ion beats time accuracy record:   researchers at NIST in Colorado have built a single Aluminum optical clock that remains accurate to within one second over 3.7 Byrs (precision 8.6 x 10^-18).The previous record was held by a clock with a single Hg ion which is good to one second in 1.7 Byrs. The team begins by trapping an Mg ion using electric fields and then cooling it using a laser. They then introduce the Al ion into the chamber, which interacts with the Mg via electrical forces. These interactions allow the team to chill the Al ion. The local-oscillator laser is then fired at the Al ion (QLS, quantum logic spectroscopy, is used to determine the absorption efficiency) that tunes the laser frequency which is then precisely measured.

For more information: Physicsworld, February 12 (2010); Phys. Rev. Lett., to be published (2010).

Gamma rays become relativistic long after emission from blazars:   an international group lead by scientists at SLAC have used the Fermi Gamma-ray Space Telescope and other telescopes to measure the radiation emitted from a supermassive black hole that fires an intense beam of radiation directly at Earth. They conclude that the beam has to travel several light years before being accelerated to nearly the speed of light. They spotted a big change in polarization which they think occurs as a huge blob of ejected material encounters a bend in the jet located at 10 light-years from the black hole (a thousand times further away than previously thought).

For more information: Physicsworld, February 18 (2010); Nature, February 18 (2010) pages 919 and 886.

WEEK OF FEBRUARY 15, 2010 [No. 823]

First Germanium laser fabricated:   researchers at MIT have made an important next step in the quest for a useful (low cost optoelectronics integration) electrically pumped laser on silicon by creating the first infrared-emitting Ge laser. They have shown that lasers can be made that exploit direct-gap transitions in Ge by overcoming the energy difference between indirect and direct bandgap with doping and thermal strain. The group stimulated light emission at room temperature with a separate pulsed 1064 nm pump laser. Lasing around 1600 nm occurred with pumping power over 6 µJ / pulse. The group has developed an electrically pumped laser too.

For more information: Physicsworld, February 10 (2010); Optics Letters, to be published (2010).

Mass of a trans-uranium element directly measured:   European researchers at the GSI in Darmstadt have for the first time made direct mass measurements of an element heavier than Uranium. They produced Nobelium (102 protons) by firing isotopes of Ca at a Pb target whose fusion process produces No isotopes. They slowed down the energetic No ions through a cloud of He atoms and guided them into a magnetic Penning trap. After the ions were picked up in the magnetic field lines their masses were determined from their orbital rotational frequencies. Results are accurate to a precision of 0.05 ppm and confirm previous indirect evaluations.

For more information: Physicsworld, February 11 (2010); Nature, February 11 (2010) pages 785 and 740.

WEEK OF FEBRUARY 8, 2010 [No. 831]

Test of synchronous neural interactions diagnoses PTSD:   researchers at the University of Minnesota have been able to diagnose post-traumatic stress disorder (PTSD) using a magnetoencephalograpy (MEG) technique to analyze patterns of neural interactions. It is particularly difficult to tell whether someone has the condition or not because this disease has no clear pathology that other psychiatric diseases have and is a purely functional brain disorder instead. MEG data were acquired within an electromagnetically shielded chamber in just a minute using a 248-channel axial gradiometer system. The near-real time non-invasive measurements are done using superconducting LHe-cooled quantum interference device sensors (SQUID) capable of measuring the femtoTesla magnetic fields created by currents flowing in and around neurons. A significant difference between people with a disorder and healthy controls is found in the interaction between the different signals. The idea is that MEG can diagnose brain diseases from patterns of neural interactions. The technique could be used both for initial diagnosis and for monitoring of evolution and remission of the disorder. It allows to identify genuine PTSD sufferers and without the need for patients to relive painful past memories.

For more information: Physicsworld, February 2 (2010); Journal of Neural Engineering, January 20 (2010).

WEEK OF FEBRUARY 1, 2010 [No. 830]

Single organic transistor behaves like a brain synapse:   CNRS and CEA researchers have made the first transistor that mimics connections in the human brain. They added Au nanoparticles to the interface between an insulating layer (dielectric gate) and an organic transistor made of pentacene. A nanoparticle organic memory field effect transistor (NOMFET) was built by fixing 5, 10 and 20 nm diameter particles into the source-drain channel of the device and covering the structure with a 35 nm thick film of pentacene. The transistor mimics the short-term plasticity of synaptic junctions. Previous neural nets required at least 7 transistors to build just one electronic-based synapse. In the NOMFET the pre-synaptic signal is the pulse voltage applied to the device and the output signal is the drain current. The holes are trapped in the nanoparticles and act like the neurotransmitters. A certain number of holes are trapped for each incoming voltage spike and in the absence of pulses, the holes escape in a matter of seconds. The time delay is precisely adjusted by the researchers by optimizing the nanoparticle number and the device geometry. Depending on the frequency of the applied voltage spikes, the output of the NOMFET reproduces either the decreasing or the amplifying behavior typical of a synapse.

For more information: Physicsworld, January 28 (2010); Advanced Functional Materials (2010), to be published.

WEEK OF JANUARY 25, 2010 [No. 829]

Color e-paper using in-plane electrophoresis made:   researchers at Philips have designed an electronic paper that can change color and does not require backlights. Present e-paper is black and white (it reflects ambient light with no need for backlight as needed in LCDs). They apply a voltage across two electrodes on the face of the e-paper rather than into the display as in conventional top-down electrophoresis. Different colored pigments are combined in each pixel (cyan, magenta, yellow, and black all stacked away in the corner of each pixel site leaving a transparent display) and a third electrode controls the spread of the particles across the display.

For more information: Physicsworld, January 20 (2010); J. Soc. Information Display (2010), to be published.

Spin polarization controlled by an electric field alone:   a group lead by scientists of the CNRS has controlled the polarization of a spin current by applying an electric field across an insulator. The electric-only control has been demonstrated in a hybrid material made by coupling a ferroelectric to a ferromagnet. They made tunnel junctions that combine two ferromagnetic electrodes (iron and the ferromagnetic oxide LSMO) separated by a layer of ferroelectric BaTiO₃ just 1 nm thick. The technique requires much less energy than previous schemes for flipping spin. This opens the way to controlling all spintronics devices by purely electric means.

For more information: Physicsworld, January 15 (2010); Science, to be published (2010).

WEEK OF JANUARY 18, 2010 [No. 828]

Precise neural silencing on behaviorally relevant time scales shown:   MIT researchers have shown that members of the class of light-driven outward proton pumps can mediate powerful, safe, multiple-color silencing of neural activity. The gene archaerhodopsin-3 from Halorubrum sodomense enables near-100% silencing of neurons in the awake brain when virally expressed in the mouse cortex and illuminated with yellow light. This ability to silence the activity of genetically specified neurons in a temporally precise fashion should allow investigation of the causal role of specific cell classes in neural computations, behaviors, and pathologies.

For more information: Nature, January 7 (2010) page 98.

Superluminal speeds observed in space:   researchers at the University of Texas at Brownsville have witnessed anomalous dispersion in radio pulses that have traveled from a distant pulsar. They used the Arecibo Observatory in Puerto Rico to take radio data of the pulsar PSR B1937+21 at 1,420.4 MHz (resonance of H₂) with a 1.5 MHz bandwidth for three days. The pulses close to the center frequency value arrived earlier than would be expected given the pulsar's normal timing, and therefore appeared to have traveled faster than the speed of light.

For more information: Physicsworld, January 11 (2010); Astrophys. J., to be published (2010).

Fish-tetrapod transition reassessed:   scientists from Warsaw University have presented well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 Myrs older than the earliest tetrapod body fossils and 10 Myrs earlier than the oldest elpistostegids. They force a significant reassessment of the timing, ecology, and environmental setting of the fish-tetrapod transition.

For more information: Nature, January 7 (2010) page 43.

WEEK OF JANUARY 11, 2010 [No. 827]

Particle quantum trembling observed:   European researchers have observed for the first time zitterbewegung, the violent trembling motion of an elementary particle predicted by Schrodinger in 1930. It is currently impossible to detect the quivering of a free electron, which has amplitude of just 10^-13m and a frequency of 10²¹ Hz. Instead the team simulated the behavior of a free electron with a single, visible wavelength laser manipulated Ca ion trapped in an electrodynamic trap. When the right conditions are met, the Schrodinger equation that describes this ion as a quantum system looks identical to the Dirac equation of the free electron.

For more information: Physicsworld, January 6 (2010); Nature, January 7 (2010) pages 68, 37, and 5

Darwinian evolution active on non-living prions:   scientists at the Scripps Research Institute in Florida have shown that prion proteins, devoid of all genetic materials, can change to suit their environment and go on to develop drug resistance. They transferred prion populations from brain cells to other cells in culture and observed the prions that adapted to the new cellular environment out-competed their brain-adapted counterparts by natural selection. When returned to the brain cells, the brain-adapted prions again took over the population. They found the same process of mutation and adaptive change in prions (and protein folding) as one sees in viruses.

For more information: BBC News, January 1 (2010); ScienceDaily, January 3 (2010); Science, to be published.

WEEK OF JANUARY 4, 2009 [No. 826]

Single-molecule solid state transistor using orbital gating shown:   Korean researchers have fabricated transistors from single molecules, where the flow of electrons is controlled by modulating the energy of the molecular orbitals of the molecule. Their technique is based purely on electrostatic modulation of the molecular-orbital energy of a single molecule. This is the first demonstration of a single molecule being electrically connected to two electrodes. Each device consists of a fractured Au nanowire overlaid on a strip of Al₂O₃. They coated Au nanowires with alkane and aromatic dithiol molecules, then broke the wire (through electromigration) producing a nanogap filled by a single dithiol molecule through which electrons can tunnel. The broken ends form the source and drain electrodes connected by a single molecule and the dielectric strip forms the gate electrode. The electric field created by the gate electrode modulates the energies of molecular orbitals in the dithiol, which in turn control the amount of current that flows through the source and drain electrodes. In situ spectroscopy firmly shows that the IV curves are caused by the single molecule transistor as intended (and are not caused by either impurities or defects in the system) and a steep linear relationship between gate voltage and molecular-orbital energy.

For more information: Nature, December 31 (2009) pages 1039 and 994.

NOTE: previous Research News (since WEEK OF MARCH 1, 1994 [No. 1], around the time when the Quantum Cascade Lasers were demonstrated at AT&T Bell Laboratories in Murray Hill, N.J., as promising MIR solid-state room temperature sources that would enable laser spectroscopy in the spectral region where fundamental rotational-vibrational transitions of most molecules take place) not posted.