Amazing Science

How much light has been emitted by all galaxies since the cosmos began? After all, almost every photon (particle of light) from ultraviolet to far infrared wavelengths ever radiated by all galaxies that ever existed throughout cosmic history is still speeding through the Universe today. If we could carefully measure the number and energy (wavelength) of all those photons—not only at the present time, but also back in time—we might learn important secrets about the nature and evolution of the Universe, including how similar or different ancient galaxies were compared to the galaxies we see today. 

That bath of ancient and young photons suffusing the Universe today is called the extragalactic background light (EBL). An accurate measurement of the EBL is as fundamental to cosmology as measuring the heat radiation left over from the Big Bang (the cosmic microwave background) at radio wavelengths. A new paper, called “Detection of the Cosmic γ-Ray Horizon from Multiwavelength Observations of Blazars,” by Alberto Dominguez and six coauthors, just published today by the Astrophysical Journal—based on observations spanning wavelengths from radio waves to very energetic gamma rays, obtained from several NASA spacecraft and several ground-based telescopes—describes the best measurement yet of the evolution of the EBL over the past 5 billion years.

So, astrophysicists developed an ingenious work-around method: measuring the EBL indirectly through measuring the attenuation of—that is, the absorption of—very high energy gamma rays from distant blazars. Blazars are supermassive black holes in the centers of galaxies with brilliant jets directly pointed at us like a flashlight beam. Not all the high-energy gamma rays emitted by a blazar, however, make it all the way across billions of light-years to Earth; some strike a hapless EBL photon along the way. When a high-energy gamma ray photon from a blazar hits a much lower energy EBL photon, both are annihilated and produce two different particles: an electron and its antiparticle, a positron, which fly off into space and are never heard from again. Different energies of the highest-energy gamma rays are waylaid by different energies of EBL photons. Thus, measuring how much gamma rays of different energies are attenuated or weakened from blazars at different distances from Earth indirectly gives a measurement of how many EBL photons of different wavelengths exist along the line of sight from blazar to Earth over those different distances.

Observations of blazars by NASA’s Fermi Gamma Ray Telescope spacecraft for the first time detected that gamma rays from distant blazars are indeed attenuated more than gamma rays from nearby blazars, a result announced on November 30, 2012, in a paper published in Science, as theoretically predicted. 

Now, the big news—announced in today’s Astrophysical Journal paper—is that the evolution of the EBL over the past 5 billion years has been measured for the first time. That’s because looking farther out into the Universe corresponds to looking back in time. Thus, the gamma ray attenuation spectrum from farther distant blazars reveals how the EBL looked at earlier eras. 

A team of researchers has captured images of green alga consuming bacteria, offering a glimpse at how early organisms dating back more than 1 billion years may have acquired free-living photosynthetic cells. This acquisition is thought to have been a critical first step in the evolution of photosynthetic algae and land plants, which, in turn, contributed to the increase in oxygen levels in Earth's atmosphere and ocean and provided one of the conditions necessary for animal evolution.

In a paper that appears in the June 17, 2013 issue of Current Biology and is available online today, researchers identify a mechanism by which a green alga that resembles early ancestors of the group engulfs bacteria, providing conclusive evidence for a process that had been proposed but not definitely shown.

 

"This behavior had previously been suggested but we had not had clear microscopic evidence until this study," said Eunsoo Kim, assistant curator in the Museum's Division of Invertebrate Zoology and corresponding author on the paper. "These results offer important clues to an evolutionary event that fundamentally changed the trajectory of the evolution of not just photosynthetic algae and land plants, but also animals."

In green algae and land plants, photosynthesis, or the conversion of light into food, is carried out by a specialized cell structure known as a chloroplast. The origin of chloroplast is linked to endosymbiosis, a process in which a single-celled eukaryote—an organism whose cells contain a nucleus—captures a free-living photosynthetic cyanobacterium but does not digest it, allowing the photosynthetic cell to eventually evolve into a chloroplast. The specific feeding mechanisms for this process, however, have remained largely unknown until now.

In this study, researchers used transmission electron microscopy and feeding and staining experiments to take conclusive images showing how a basic green alga from the genus Cymbomonas feeds on bacteria. The alga draws bacterial cells into a tubular duct through a mouth-like opening and then transports these food particles into a large, acidic vacuole where digestion takes place. The complexity of this feeding system in photosynthetic modern alga suggests that this bacteria-feeding behavior, and the unique feeding apparatus to support it, descend from colorless ancestors of green algae and land plants and may have played important roles in the evolution of early photosynthetic eukaryotes, the precursors to plants like trees and shrubs that cover the Earth today.

Chinese scientists trace the rare white coloration in Bengal tigers to a single change in a gene that affects a host of animals, including humans.

 

White tigers are a rare variant of the customary orange Bengal sub-species. Today, they are found exclusively in captive programmes where the limited numbers are interbred to maintain the distinctive fur color.

 

Shu-Jin Luo of Peking University and colleagues investigated the genetics of a family of tigers living in Chimelong Safari Park in Panyu, Guangzhou Province. This ambush of tigers included both white and orange individuals.

 

The study zeroed in on the pigment gene called SLC45A2, which has long been associated with the light colouration seen in some human populations, and in a range of other animals including horses, chickens, and fish.

 

The team identified a small alteration in the white-tiger version of SLC45A2 that appears to inhibit the production of red and yellow pigments. This change has no effect on the generation of black pigment - explaining why the whites still have their characteristic dark stripes.

 

A number of the white tigers found in zoos have health issues, such as eyesight problems and some deformities.

 

However, Luo and colleagues say these deficiencies are a consequence of inbreeding by humans and that the white coats are in no way indicative of a more general weakness in the Bengal variant.

 

Establishing this fact means that re-introducing them to the wild under a carefully managed conservation programme might be worth considering.

"The last known free-ranging white tiger was shot in 1958, before which sporadic sightings were made in India," the researchers write.

 

"Reasons for the extinction of wild white tigers were likely the same as those accounting for the dramatic decline in wild tigers in general: uncontrolled trophy hunting, habitat loss, and habitat fragmentation.

 

"However, the fact that many white tigers captured or shot in the wild were mature adults suggests that a white tiger in the wild is able to survive without its fitness being substantially compromised."

Eli Megidish, Hagai Eisenberg, and colleagues at the Hebrew University of Jerusalem have entangled two photons that don't exist at the same time. They start with a scheme known as entanglement swapping. To begin, researchers zap a special crystal with laser light a couple of times to create two entangled pairs of photons, pair 1 and 2 and pair 3 and 4. At the start, photons 1 and 4 are not tangled. But they can be if physicists play the right trick with 2 and 3.

The key is that a measurement "projects" a particle into a definite state -- just as the measurement of a photon collapses it into either vertical or horizontal polarization. So even though photons 2 and 3 start out unentangled, physicists can set up a "projective measurement" that asks, are the two in one of two distinct entangled states or the other? That measurement entangles the photons, even as it absorbs and destroys them. If the researchers select only the events in which photons 2 and 3 end up in, say, the first entangled state, then the measurement also entangles photons 1 and 4. (See diagram, top.) The effect is a bit like joining two pairs of gears to form a four-gear chain: Enmeshing to inner two gears establishes a link between the outer two.

 

In recent years, physicists have played with the timing in the scheme. For example, last year a team showed that entanglement swapping still works even if they make the projective measurement after they've already measured the polarizations of photons 1 and 4. Now, Eisenberg and colleagues have shown that photons 1 and 4 don't even have to exist at the same time.

 

To do that, they first create entangled pair 1 and 2 and measure the polarization of 1 right away. Only after that do they create entangled pair 3 and 4 and perform the key projective measurement. Finally, they measure the polarization of photon 4. And even though photons 1 and 4 never coexist, the measurements show that their polarizations still end up entangled. Eisenberg emphasizes that even though in relativity, time measured differently by observers traveling at different speeds, no observer would ever see the two photons as coexisting.

 

The experiment shows that it's not strictly logical to think of entanglement as a tangible physical property, Eisenberg says. "There is no moment in time in which the two photons coexist," he says, "so you cannot say that the system is entangled at this or that moment." Yet, the phenomenon definitely exists. Anton Zeilinger, a physicist at the University of Vienna, agrees that the experiment demonstrates just how slippery the concepts of quantum mechanics are. "It's really neat because it shows more or less that quantum events are outside our everyday notions of space and time."

 

So what's the advance good for? Physicists hope to create quantum networks in which protocols like entanglement swapping are used to create quantum links among distant users and transmit uncrackable (but slower than light) secret communications. The new result suggests that when sharing entangled pairs of photons on such a network, a user wouldn't have to wait to see what happens to the photons sent down the line before manipulating the ones kept behind, Eisenberg says. Zeilinger says the result might have other unexpected uses: "This sort of thing opens up people's minds and suddenly somebody has an idea to use it in quantum computing or something."

Cardiac stress, for example a heart attack or high blood pressure, frequently leads to pathological heart growth and subsequently to heart failure. Two tiny RNA molecules play a key role in this detrimental development in mice, as researchers at the Hannover Medical School and the Göttingen Max Planck Institute for Biophysical Chemistry have now discovered. When they inhibited one of those two specific molecules, they were able to protect the rodent against pathological heart growth and failure. With these findings, the scientists hope to be able to develop therapeutic approaches that can protect humans against heart failure.

 

The scientists involved in this study had observed that these microRNAs are more prevalent in the cardiac muscle cells of mice suffering from cardiac hypertrophy. To determine the role that the two microRNAs play, the scientists bred genetically modified mice that had an abnormally large number of these molecules in their heart muscle cells. "These rodents developed cardiac hypertrophy and lived for only three to six months, whereas their healthy conspecifics had a normal healthy life-span of several years," explained Kamal Chowdhury, researcher in the Department of Molecular Cell Biology at the Max Planck Institute for Biophysical Chemistry. "For comparison, we also selectively switched off these microRNAs in other mice. These animals had a slightly smaller heart than their healthy conspecifics, but did not differ from them in behaviour or life-span," continued the biologist. The crucial point is when the scientists subjected the hearts of these mice to stress by narrowing the aorta, the mice did not develop cardiac hypertrophy – in contrast to normal mice.

 

The scientists were also able to protect normal mice against the disease. When they gave them a substance that selectively inhibits microRNA-132, no pathological cardiac growth occurred – even when the hearts of these mice were subjected to stress. "Thus, for the first time ever, we have found a molecular approach for treating pathological cardiac growth and heart failure in mice," said the cardiologist Thomas Thum, MD, Director of the Institute for Molecular and Translational Therapy Strategies (IMTTS) at the Hannover Medical School. With these findings, the researchers hope that they will be able to develop therapeutic approaches that can also protect humans against heart failure. "Such microRNA inhibitors, alone or in combination with conventional treatments, could represent a promising new therapeutic approach," said Thum.

 

"In mice with an overdosage of the two microRNAs in their heart muscle cells, the cellular ‘recycling program' is curbed," explained Ahmet Ucar, who together with Shashi K. Gupta was responsible for the experiments. In this recycling process, the cell breaks down components that are damaged or no longer required and reuses their constituents – a vital process that, for example, ensures the organism’s survival under stress conditions. In mice without the microRNAs -212 and 132, this recycling program is more active than in their normal conspecifics. Conceivably, the reduced cellular recycling could be a cause of the observed cardiac hypertrophy. 

Water found in a deep, isolated reservoir in Timmins, Ont., has been trapped there for 1.5 billion to 2.64 billion years — since around the time the first multicellular life arose on the planet — Canadian and British scientists say.

 

The water pouring out of boreholes 2.4 kilometres below the surface in the northern Ontario copper and zinc mine is older than any other free-flowing water ever discovered. It is rich in dissolved gases such as hydrogen and methane that could theoretically provide support for microbial life.

"What we can be sure of is that we have identified a way in which planets can create and preserve an environment friendly to microbial life for billions of years," said a statement from Greg Holland, the Lancaster University geochemist who is the lead author of the study.

His Canadian co-authors included Barbara Sherwood Lollar and Georges Lacrampe-Couloume at the University of Toronto; Greg Slater at McMaster University in Hamilton; and Long Li, who is currently an assistant professor at the University of Alberta, but worked on the project while at the University of Toronto.

 

Some Canadian members of the team are currently testing the water to see if it contains microbial life — if they exist, those microbes may have been isolated from the sun and the Earth's surface for billions of years and may reveal how microbes evolve in isolation.

Microbes that have been isolated for tens of millions of years have been found in water with similar chemistry at even slightly deeper depths below the surface in a South African gold mine, using hydrogen gas as an energy source, the researchers noted.

 

The researchers estimated how old the water was based on an analysis of the xenon gas dissolved in it. Like many other elements, xenon comes in forms with different masses, known as isotopes. The water in the Timmins mine contained an unusually high level of lighter isotopes of xenon that are thought to have come from the Earth's atmosphere at the time it became trapped.

Due to its higher capacity factor and proximity to densely populated areas, offshore wind power with integrated energy storage could satisfy > 20% of U.S. electricity demand. Similar results could also be obtained in many parts of the world. The offshore environment can be used for unobtrusive, safe, and economical utility-scale energy storage by taking advantage of the hydrostatic pressure at ocean depths to store energy by pumping water out of concrete spheres and later allowing it to flow back in through a turbine to generate electricity.

The storage spheres are an ideal complement to energy harvesting machines, such as floating wind turbines (FWTs). The system could provide near-base-load-quality utility-scale renewable energy and do double duty as the anchoring point for the generation platforms. Analysis indicates that storage can be economically feasible at depths as shallow as 200 m, with cost per megawatt hour of storage dropping until 1500 m before beginning to trend upward. The sweet spot occurs when the concrete wall thickness to withstand the hydrostatic pressure provides enough ballast mass, and this will depend on the strength of used concrete and reinforcement. In addition, the required concrete would use significant amounts of fly ash from coal-fired power plants, and the spheres can serve as artificial reefs.

The miniaturization of electronics continues to create unprecedented capabilities in computer and communications applications, enabling handheld wireless devices with tremendous computing performance operating on battery power.

 

A team of researchers at Columbia Engineering has used miniaturized electronics to measure the activity of individual ion-channel proteins with temporal resolution as fine as one microsecond, producing the fastest recordings of single ion channels ever performed. Ion channels are biomolecules that allow charged atoms to flow in and out of cells, and they are an important work-horse in cell signaling, sensing, and energetics.

 

They are also being explored for nanopore sequencing applications. As the "transistors" of living systems, they are the target of many drugs, and the ability to perform such fast measurements of these proteins will lead to new understanding of their functions. The researchers have designed a custom integrated circuit to perform these measurements, in which an artificial cell membrane and ion channel are attached directly to the surface of the amplifier chip.

 

"Scientists have been measuring single ion channels using large rack-mount electronic systems for the last 30 years," says Jacob Rosenstein, the lead author on the paper. Rosenstein was a PhD student in electrical engineering at the School at the time this work was done, and is now an assistant professor at Brown University. "By designing a custom microelectronic amplifier and tightly integrating the ion channel directly onto the amplifier chip surface, we are able to reduce stray capacitances that get in the way of making fast measurements."

 

"This work builds on other efforts in my laboratory to study the properties of individual molecules using custom electronics designed for this purpose," says Ken Shepard, professor of electrical engineering at the School and Rosenstein's adviser. The Shepard group continues to find ways to speed up these single-molecule measurements. "In some cases," he adds, "we may be able to speed things up to be a million times faster than current techniques."

A team of Harvard University physicists has proposed the possible existence of a type of dark matter not described by current physics models. In their paper published in the journal Physical Review Letters, the team suggests it's possible that not all dark matter is cold and collision-less.

In the visible universe, galaxies form into a disk shape—the Milky Way is a good example. All of its members align roughly along a single plane, this due to the forces of gravity and spin. Objects form into masses which, over time, spread out into a disk shape. Dark matter, on the other hand, appears to hover around galaxies like a halo, at least according to current models. It's seen as dark, cold and with so little energy that dark matter particles rarely if ever run into one another. The researchers in this new study suggest there may be other types of matter, however, that behaves more like visible matter. And, because of that, they suggest it could bunch up due to dark-matter-type gravity and form disks as well. These disks, which they describe as dark matter component double-disk dark matter, could represent as much as 5 percent of all existing dark matter.

 

For dark matter to clump, it would need to have other properties similar to visible matter as well. For that reason, the researchers suggest it's possible that there exists dark atoms, dark photons, and likely some form of dark electromagnetic force as well.

 

Research on dark matter over the years has led to a model that describes dark matter as existing in a ball shape—galaxies sit in the middle of the ball, which would mean observers living in a galaxy would "see" it as existing everywhere around them. But it's possible that other types of shapes exist as well, the researchers suggest, because there are other types of matter in the visible universe. They note that baryonic matter (matter made of strongly acting fermions known as baryons) is believed to make up approximately 5 percent of all matter in the known universe. For that reason, they conclude that it would appear likely that similar differences in dark matter would occur as well, and perhaps in nearly equal proportions.

 

If true, it would mean there could be whole dark galaxies out there, undetectable, yet as real as those we can see with the naked eye. Much more research will have to be done in this area before adding such types of dark matter to models in general use, of course. Until then, it will remain an abstract theory.

A genetically modified purple tomato that is tastier than normal varieties and can last for more than a month before going off has been invented by scientists. The GM tomato, which gains its unusual color from a natural pigment known as anthocyanin, could be picked and shipped later due to its longer shelf life, allowing more time for flavour to develop on the vine.

 

Tests showed the shelf life of the tomatoes more than doubled from an average of 21 to 48 days after genetic modification, and they were less likely to go mouldy after harvest.

 

The strain has also been found in earlier studies to fight cancer in mice due to its high levels of antioxidants, and scientists say its qualities could be replicated in other soft fruits like strawberries and raspberries.

 

The tomatoes were modified by scientists at the John Innes Centre in Norfolk to contain two genes from the snapdragon which “switch on” a set of dormant genes in the tomato, causing them to produce more anthocyanin.

 

The pigment occurs naturally in various plants and flowers, and is responsible for many of the blues, reds and purples seen in nature, but also ramps up levels of antioxidants.

The goal of the project was to produce fruit with higher antioxidant levels which could benefit health, and earlier studies have shown that they helped extend the lives of cancer-prone mice by 30 per cent.

Medical researchers think specially tailored RNA sequences could turn off genes in patients’ cells to encourage wound healing or to kill tumor cells. Now researchers have developed a nanocoating for bandages that could deliver these fragile gene-silencing RNAs right where they’re needed (ACS Nano 2013, DOI:10.1021/nn401011n). The team hopes to produce a bandage that shuts down genes standing in the way of healing in chronic wounds.

 

Small interfering RNAs, or siRNAs, derail expression of specific genes in cells by binding to other RNA molecules that contain the code for those genes. Biologists have developed siRNAs that target disease-related genes. But for these siRNAs to reach the clinic, researchers must find a way to deliver the molecules safely to the right cells. Unfortunately, free oligonucleotides like siRNAs don’t fare well inside the body or cells as enzymes and acids quickly chop them up, says Paula T. Hammond, a chemical engineer at Massachusetts Institute of Technology.

 

Other groups have tackled this delivery challenge by attaching siRNAs to chemical carriers that protect the oligonucleotides as they travel through the bloodstream. The pharmaceutical company Sanofi-Aventis asked Hammond to design a vehicle that would work at the site of a wound or tumor, releasing the siRNAs over a long period of time. The company hoped that putting the biomolecules right where they’re needed, without them having to survive a trip through the bloodstream, would increase the efficacy of the treatment.

 

Hammond and her colleagues produced an siRNA-containing nanocoating that could be applied to a wide range of medical materials, such as bandages or biodegradable polymers doctors could implant during surgery to prevent an excised tumor from coming back. As the coating slowly dissolves, it releases siRNA molecules tethered to protective nanoparticles.

 

The thin films consist of two different materials: a peptide called protamine sulfate and calcium phosphate nanoparticles decorated with the therapeutic siRNAs. Other researchers have shown that similar nanoparticles help the nucleotides evade destruction once they’re taken up by cells (J. Controlled Release 2010, DOI: 10.1016/j.jconrel.2009.11.008).

 

The team alternately dips whatever they want to coat in water solutions of the two materials. The RNA and nanoparticles are negatively charged, and the peptides are positively charged. The two substances cling together due to electrostatic force, producing a film when the water dries.

 

To test their delivery method, the researchers coated woven nylon bandages with 80-nm-thick films and applied the bandages to layers of human and animal cells in culture. In one experiment, a bandage loaded with 19 µg of siRNA per square centimeter released two-thirds of its load over 10 days. Other bandages made using siRNAs targeting the gene for fluorescent green protein almost completely shut down the protein’s production in cells expressing the gene. Hammond says the group is now testing bandages that knock down MMP9, a collagen-destroying protein associated with slow healing in chronic wounds.

Gymnosperms are a group of land plants comprising the extant taxa, cycads, Ginkgo, gnetophytes and conifers. Gymnosperms first appeared more than 300 million years ago (Myr ago), well before the angiosperm lineage separated from the stem group of extant gymnosperms. The major radiation of conifer families occurred 250–65 Myr ago, and during their evolution the morphology of conifers has changed relatively little. There are approximately 630 conifer species, representing about 70 currently recognized genera, which dominate many terrestrial ecosystems, especially in the Northern Hemisphere. Conifers also dominated both before and after the major mass extinction events at the end of the Permian and Cretaceous periods, around 250 and 65 Myr ago, respectively. Conifers are of immense ecological and economic value; coniferous forests cover enormous areas in the Northern Hemisphere, and conifers are keystone species in many other ecosystems. Conifers contribute a large fraction of terrestrial photosynthesis and biomass, and the cultural and economic values of conifers are also paramount; early civilizations used conifers for firewood, tools and artefacts and today several national economies depend on commodities produced from conifers. However, despite their abundance and importance, our understanding of conifer genomes is limited. Most conifers have 12 (2n = 24) chromosomes, probably reflecting the ancestral karyotype, which are typically of similar size, each being roughly comparable to the size of the human genome, and containing high proportions of repetitive elements. The gene space of conifer genomes has not been well characterized, although several reports have suggested that gene families in conifers may be larger than their angiosperm counterparts and that conifer genomes contain numerous pseudogenes.

 

Because their genomes are among the largest—typically 20–30 gigabases pairs (Gb)—of all organisms, genome-wide analyses of conifers are particularly challenging. Thus, no full genome sequence of a gymnosperm species is available at present, whereas 30 angiosperm and more basal plant genomes have been sequenced. However, size is not the only challenge to sequencing presented by conifer genomes. Conifers are typically outbreeding, produce wind-dispersed pollen, have very large effective population sizes, and their genomes are highly heterozygous, although their nucleotide substitution rates are lower than those of most angiosperms, perhaps owing to long lifespan (decades to centuries). Furthermore, inbreeding depression negates the production of inbred lines that could facilitate genome assembly.

The failure to replace damaged body parts in adult mammals results from a muted growth response and fibrotic scarring. Although infiltrating immune cells play a major role in determining the variable outcome of mammalian wound repair, little is known about the modulation of immune cell signaling in efficiently regenerating species such as the salamander, which can regrow complete body structures as adults. A comprehensive analysis of immune signaling during limb regeneration in axolotl, an aquatic salamander, revealed a temporally defined requirement for macrophage infiltration in the regenerative process. Although many features of mammalian cytokine/chemokine signaling are retained in the axolotl, they are more dynamically deployed, with simultaneous induction of inflammatory and anti-inflammatory markers within the first 24 h after limb amputation. Systemic macrophage depletion during this period resulted in wound closure but permanent failure of limb regeneration, associated with extensive fibrosis and disregulation of extracellular matrix component gene expression. Full limb regenerative capacity of failed stumps was restored by reamputation once endogenous macrophage populations had been replenished. Promotion of a regeneration-permissive environment by identification of macrophage-derived therapeutic molecules may therefore aid in the regeneration of damaged body parts in adult mammals.

Salamanders are unique in the vertebrate world as they're capable of repairing their hearts, tails, spinal cords, brain, and regrowing limbs. This makes them an obvious candidate for regenerative research. Godwin and the team at ARMI removed the macrophages the Salamanders and found that the animals were no longer able to regenerate limbs. He believes that the cells release chemicals that are vital to the Salamanders' regenerative powers. More research is needed to establish exactly how regeneration works, and Godwin is currently conducting experiments to investigate. "This really gives us somewhere to look for what might be secreted into the wound environment that allows for regeneration," he says.

 

Although understanding the Salamander's abilities may one day lead to impossible-sounding feats like limb regeneration in humans, there are more-immediate benefits that could come from the research. Less ambitious goals such as scarless healing, could be attainable. "The long-term plan is that we'll know exactly what cocktail to add to a wound site to allow salamander-like regeneration under hospital conditions."

Rice University scientists have unveiled a robust new method for arranging metal nanoparticles in geometric patterns that can act as optical processors that transform incoming light signals into output of a different color.

 

Rice's team used the method to create an optical device in which incoming light could be directly controlled with light via a process known as "four-wave mixing." Four-wave mixing has been widely studied, but Rice's disc-patterning method is the first that can produce materials that are tailored to perform four-wave mixing with a wide range of colored inputs and outputs.

 

"Versatility is one of the advantages of this process," said study co-author Naomi Halas, director of LANP and Rice's Stanley C. Moore Professor in Electrical and Computer Engineering and a professor of biomedical engineering, chemistry, physics and astronomy. "It allows us to mix colors in a very general way. That means not only can we send in beams of two different colors and get out a third color, but we can fine-tune the arrangements to create devices that are tailored to accept or produce a broad spectrum of colors."

 

The information processing that takes place inside today's computers, smartphones and tablets is electronic. Each of the billions of transistors in a computer chip uses electrical inputs to act upon and modify the electrical signals passing through it. Processing information with light instead of electricity could allow for computers that are both faster and more energy-efficient, but building an optical computer is complicated by the quantum rules that light obeys.

Researchers of the Fraunhofer Institute for Applied Solid State Physics and the Karlsruhe Institute for Technology have achieved the wireless transmission of 40 Gbit/s at 240 GHz over a distance of one kilometer. Their most recent demonstration sets a new world record and ties in seamlessly with the capacity of optical fiber transmission. In the future, such radio links will be able to close gaps in providing broadband internet by supplementing the network in rural areas and places which are difficult to access.

 

Digital, mobile and networked – changing media usage habits of modern society require the faster transmission of increasing vol-umes of data. Compared to the European standard, Germany lags behind in the expansion of the fiber-optic network, according to statistics from the FTTH Council Europe. Deploying new fiber-optic cables is expensive and difficult when there are natural or urban obstacles such as rivers or traffic junctions. Broadband radio links can help to overcome such critical areas, thereby facilitating the expansion of the network infrastructures. In rural areas they can be a cost-effective and flexible alternative to “Fiber to the Home”.

 

Researchers have now set a new world record in wireless data transmission: For the first time, fully integrated electronic transmit-ters and receivers have been developed for a frequency of 240 GHz, which allows the transmission of data rates of up to 40 Gbit/s. This equals the transmission of a complete DVD in under a second or 2400 DSL16000 internet connections. Distances of over one kilometer have already been covered by using a long range demonstrator, which the Karlsruhe Institute of Technology set up between two skyscrapers as part of the project “Millilink”. “We have managed to develop a radio link based on active electronic circuits, which enables similarly high data rates as in fiber-optic systems, therefore allowing seamless integration of the radio link”, says Prof. Ingmar Kallfass, who coordinated the project at Fraunhofer IAF within the scope of a Shared Professorship between IAF and KIT. Since 2013, Kallfass is with the University of Stuttgart, where he continues to lead the project.

 

Using the high frequency range between 200 and 280 GHz not only enables the fast transmission of large volumes of data, but also results in very compact technical assembly. Since the size of elec-tronic circuits and antennae scales with frequency / wavelength, the transmitter and receiver chip only measures 4 x 1.5 mm⊃2;. The semi-conductor technology developed at Fraunhofer IAF, based on tran-sistors with high carrier mobility (HEMT), makes it possible to use the frequency between 200 and 280 GHz with active transmitters and receivers in the form of compact, integrated circuits. The at-mosphere shows low attenuation in this frequency range, which enables broadband directional radio links. “This makes our radio link easier to install compared to free-space optical systems for data transmission. It also shows better robustness in poor weather condi-tions such as fog or rain”, explains Jochen Antes of KIT.

 

A team of University of Pennsylvania engineers has used a pattern of nanoantennas to develop a new way of turning infrared light into mechanical action, opening the door to more sensitive infrared cameras and more compact chemical-analysis techniques.

 

The research was conducted by assistant professor Ertugrul Cubukcu and postdoctoral researcher Fei Yi, along with graduate students Hai Zhu and Jason C. Reed, all of the Department of Material Scienceand Engineering in Penn’s School of Engineering and Applied Science.  

 

Detecting light in the mid-infrared range is important for applications like night-vision cameras, but it can also be used to do spectroscopy, a technique that involves scattering light over a substance to infer its chemical composition. Existing infrared detectors use cryogenically cooled semiconductors, or thermal detectors known as microbolometers, in which changes in electrical resistance can be correlated to temperatures. These techniques have their own advantages, but both need expensive, bulky equipment to be sensitive enough for spectroscopy applications.

 

“We set out to make an optomechanical thermal infrared detector,” Cubukcu said. “Rather than changes in resistance, our detector works by connecting mechanical motion to changes in temperature.”

 

The advantage to this approach is that it could reduce the footprint of an infrared sensing device to something that would fit on a disposable silicon chip. The researchers fabricated such a device in their study.

 

At the core of the device is a nanoscale structure — about a tenth of a millimeter wide and five times as long — made of a layer of gold bonded to a layer of silicon nitride. The researchers chose these materials because of their different thermal expansion coefficients, a parameter that determines how much a material will expand when heated. Because metals will naturally convert some energy from infrared light into heat, researchers can connect the amount the material expands to the amount of infrared light hitting it.    

 

“A single layer would expand laterally, but our two layers are constrained because they’re attached to one another,” Cubukcu said. “The only way they can expand is in the third dimension. In this case, that means bending toward the gold side, since gold has the higher thermal expansion coefficient and will expand more.”

 

To measure this movement, the researchers used a fiber interferometer. A fiber optic cable pointed upward at this system bounces light off the underside of the silicon nitride layer, enabling the researchers to determine how far the structure has bent upwards. 

 

“We can tell how far the bottom layer has moved based on this reflected light,” Cubukcu said. “We can even see displacements that are thousands of times smaller than a hydrogen atom.”