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#Engineers Develop Optical devices That Shape Light in Exotic Ways Engineers from the Jet propulsion laboratory and the California Institute of technology have developed innovative flat,

optical lenses that are capable of manipulating light in ways that are difficult or impossible to achieve with conventional optical devices.

Instead, silicon nanopillars are arranged precisely into a honeycomb pattern to create a etasurfacethat can control the paths and properties of passing light waves.

Applications of these devices include advanced microscopes, displays, sensors, and cameras that can be mass-produced using the same techniques used to manufacture computer microchips. hese flat lenses will help us to make more compact and robust imaging assemblies,

said Mahmood Bagheri, a microdevices engineer at JPL and co-author of a new Nature Nanotechnology study describing the devices. urrently,

optical systems are made one component at a time, and the components are assembled often manually, said Andrei Faraon, an assistant professor of applied physics and materials science at Caltech,

and the study principal investigator. ut this new technology is very similar to the one used to print semiconductor chips onto silicon wafers,

so you could conceivably manufacture millions of systems such as microscopes or cameras at a time. Seen under a scanning electron microscope

the new metasurfaces that the researchers created resemble a cut forest where only the stumps remain.

Each silicon stump, or pillar, has an elliptical cross section, and by carefully varying the diameters of each pillar

Manipulating the polarization of light is essential for the operation of advanced microscopes, cameras and displays;

the control of polarization also enables simple gadgets such as 3-D glasses and polarized sunglasses. f you think of a modern microscope,

Semiconductor lasers typically emit into elliptical beams that are really hard to work with and the new metasurface optical components could replace expensive optical systems used to circularize the beams.

The current work was supported by the Caltech/JPL President and Director Fund and the Defense Advanced Research Projects Agency (DARPA.

Yu Horie was supported by the Department of energy Energy Frontier Research center program and a Japan Student Services Organization fellowship.

The device nanofabrication was performed in the Kavli Nanoscience Institute at Caltech. JPL is a division of Caltech.

Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission, Nature Nanotechnology (2015;

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a Yale postdoctoral researcher in applied physics. xamples include more sensitive biological and chemical sensors, lasers with higher output power,

The other co-lead authors of the research are Bo Zhen of MIT and Yuichi Igarashi of Smart energy Research Laboratories, in Japan

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#New Technique Could Enable Chips with Thousands of Cores Researchers from MIT have unveiled the first fundamentally new approach to cache coherence in more than three decades,

a memory-management scheme that could help enable chips with thousands of cores. In a modern, multicore chip, every core or processor has its own small memory cache, where it stores frequently used data.

But the chip also has shared a larger cache, which all the cores can access. If one core tries to update data in the shared cache,

other cores working on the same data need to know. So the shared cache keeps a directory

of which cores have copies of which data. That directory takes up a significant chunk of memory:

In a 64-core chip, it might be 12 percent of the shared cache. And that percentage will only increase with the core count.

Envisioned chips with 128,256, or even 1, 000 cores will need a more efficient way of maintaining cache coherence.

At the International Conference on Parallel Architectures and Compilation Techniques in October, MIT researchers unveil the first fundamentally new approach to cache coherence in more than three decades.

Whereas with existing techniques, the directory memory allotment increases in direct proportion to the number of cores, with the new approach, it increases according to the logarithm of the number of cores.

In a 128-core chip that means that the new technique would require only one-third as much memory as its predecessor.

With Intel set to release a 72-core high-performance chip in the near future, that a more than hypothetical advantage.

But with a 256-core chip, the space savings rises to 80 percent, and with a 1, 000-core chip, 96 percent.

When multiple cores are simply reading data stored at the same location, there no problem.

Conflicts arise only when one of the cores needs to update the shared data. With a directory system, the chip looks up

which cores are working on that data and sends them messages invalidating their locally stored copies of it. irectories guarantee that

when a write happens, no stale copies of the data exist, says Xiangyao Yu, an MIT graduate student in electrical engineering and computer science and first author on the new paper. fter this write happens,

no read to the previous version should happen. So this write is ordered after all the previous reads in physical-time order. ime travelwhat Yu and his thesis advisor Srini Devadas,

the Edwin Sibley Webster Professor in MIT Department of Electrical engineering and Computer science realized was that the physical-time order of distributed computations doesn really matter,

so long as their logical-time order is preserved. That is core A can keep working away on a piece of data that core B has provided

since overwritten that the rest of the system treats core A work as having preceded core B. The ingenuity of Yu

and Devadasapproach is in finding a simple and efficient means of enforcing a global logical-time ordering. hat we do is we just assign time stamps to each operation,

and we make sure that all the operations follow that time stamp order, Yu says. With Yu and Devadassystem, each core has its own counter,

and each data item in memory has associated an counter, too. When a program launches, all the counters are set to zero.

When a core reads a piece of data, it takes out a easeon it, meaning that it increments the data item counter to,

say, 10. As long as the core internal counter doesn exceed 10, its copy of the data is valid.

The particular numbers don matter much; what matters is their relative value. When a core needs to overwrite the data,

however, it takes wnershipof it. Other cores can continue working on their locally stored copies of the data,

but if they want to extend their leases, they have to coordinate with the data item owner.

The core that doing the writing increments its internal counter to a value that higher than the last value of the data item counter.

Say, for instance, that cores A through D have all read the same data, setting their internal counters to 1

and incrementing the data counter to 10. Core E needs to overwrite the data so it takes ownership of it

and sets its internal counter to 11. Its internal counter now designates it as operating at a later logical time than the other cores:

Theye way back at 1, and it ahead at 11. The idea of leaping forward in time is

what gives the system its name Tardis, after the time-traveling spaceship of The british science fiction hero Dr. Who.

Now, if core A tries to take out a new lease on the data, it will find it owned by core E, to

which it sends a message. Core E writes the data back to the shared cache,

and core A reads it, incrementing its internal counter to 11 or higher. Unexplored potentialin addition to saving space in memory

Tardis also eliminates the need to broadcast invalidation messages to all the cores that are sharing a data item.

In massively multicore chips, Yu says, this could lead to performance improvements as well. e didn see performance gains from that in these experiments,

Yu says. ut that may depend on the benchmarksthe industry-standard programs on which Yu and Devadas tested Tardis. heye highly optimized,

so maybe they already removed this bottleneck, Yu says. here have been other people who have looked at this sort of lease idea,

says Christopher Hughes, a principal engineer at Intel Labs, ut at least to my knowledge, they tend to use physical time.

You would give a lease to somebody and say, K, yes, you can use this data for,

say, 100 cycles, and I guarantee that nobody else is going to touch it in that amount of time.

But then youe kind of capping your performance, because if somebody else immediately afterward wants to change the data,

then theye got to wait 100 cycles before they can do so. Whereas here, no problem, you can just advance the clock.

That is something that, to my knowledge has never been done before. That the key idea that really neat. ughes says,

however, that chip designers are conservative by nature. lmost all mass-produced commercial systems are based based on directory protocols,

he says. e don mess with them because it so easy to make a mistake

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including plastics and metals. Simultaneously, the cost of 3-D printers has fallen sufficiently to make them household consumer items.

Now a team of MIT researchers has opened up a new frontier in 3-D printing:

the ability to print optically transparent glass objects. The new system, described in the Journal of 3d printing and Additive manufacturing, was developed by Neri Oxman, an associate professor at the MIT Media Lab;

Peter Houk, director of the MIT Glass Lab; MIT researchers John Klein and Michael Stern;

From the discovery of core-forming process for bead-making in ancient Egypt, through the invention of the metal blow pipe during Roman times, to the modern industrial Pilkington process for making large-scale flat glass;

Like other 3-D printers now on the market, the device can print designs created in a computer-assisted design program,

producing a finished product with little human intervention. In the present version molten glass is loaded into a hopper in the top of the device after being gathered from a conventional glassblowing kiln.

When completed, the finished piece must be cut away from the moving platform on which it is assembled.

far higher than the temperatures used for other 3-D printing. The stream of glowing molten glass from the nozzle resembles honey as it coils onto a platform,

with a lot of trial-and-error. lass is inherently a very difficult material to work with, Klein says:

e can control solar transmittance. Unlike a pressed or blown-glass part, which necessarily has a smooth internal surface,

and generate an all-in-one building skin that is at once structural and transparent? she asks. ecause glass is at once structural and transparent,

Additional work will focus on the use of colors in the glass, which the team has demonstrated already in limited testing.

Klein says the printing system is an example of multidisciplinary work facilitated by MIT flexible departmental boundaries in this case

which is part of the Department of Materials science and engineering. At MIT, members of the research team also included Markus Kayser, Chikara Inamura,

They were joined by James Weaver of Harvard university Wyss Institute for Biologically Inspired Engineering and Giorgia Franchin and Paolo Colombo of the University of Padova in Italy b

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#Pillared Graphene structures Gain Strength, Toughness and Ductility In a newly published study, scientists from Rice university reveal that putting nanotube pillars between sheets of graphene could create hybrid structures with a unique balance of strength, toughness

and ductility throughout all three dimensions. Carbon nanomaterials are common now as flat sheets, nanotubes and spheres,

and theye being eyed for use as building blocks in hybrid structures with unique properties for electronics,

heat transport and strength. The Rice team is laying a theoretical foundation for such structures by analyzing how the blocksjunctions influence the properties of the desired materials.

particularly between carbon nanotubes and graphene, would affect the final hybrid properties in all directions. They found that introducing junctions would add extra flexibility

Carbon nanotubes are rolled-up arrays of perfect hexagons of atoms; graphene is a rolled out sheet of the same.

the way the atoms are arranged can influence all those properties. ome labs are actively trying to make these materials or measure properties like the strength of single nanotubes and graphene sheets,

and quantitatively predict the properties of hybrid versions of graphene and nanotubes. These hybrid structures impart new properties

and functionality that are absent in their parent structures graphene and nanotubes. To that end the lab assembled three-dimensional computer models of illared graphene nanostructures, akin to the boron nitride structures modeled in a previous study to analyze heat transfer between layers. his time we were interested in a comprehensive understanding of the elastic and inelastic properties

of 3-D carbon materials to test their mechanical strength and deformation mechanisms, Shahsavari said. e compared our 3-D hybrid structures with the properties of 2-D stacked graphene sheets and 1-D carbon nanotubes.

Layered sheets of graphene keep their properties in-plane, but exhibit little stiffness or thermal conductance from sheet to sheet,

But pillared graphene models showed far better strength and stiffness and a 42 percent improvement in out-of-plane ductility,

The latter allows pillared graphene to exhibit remarkable toughness along out-of-plane directions, a feature that is not possible in 2-D stacked graphene sheets or 1-D carbon nanotubes,

The researchers calculated how the atomsinherent energies force hexagons to take on or lose atoms to neighboring rings,

Turning the nanotubes in a way that forced wrinkles in the graphene sheets added further flexibility and shear compliance,

When the material did fracture, the researchers found it far more likely for this to happen at the eight-member rings,

That leads to the notion the hybrids can be tuned to fail under particular circumstances. his is the first time anyone has created such a comprehensive atomistic ensto look at the junction-mediated properties of 3-D carbon nanomaterials

Shahsavari said. e believe the principles can be applied to other low-dimensional materials such as boron nitride and molybdenum/tungsten or the combinations thereof.

Shahsavari is an assistant professor of civil and environmental engineering and of materials science and nanoengineering at Rice.

Rice university, the National Science Foundation (NSF), the National institutes of health and IBM-shared University Research Award supported the research.

The researchers used the NSF-supported DAVINCI supercomputer administered by Rice Ken Kennedy Institute for Information technology n

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Possible stem cell therapies often are limited by low survival of transplanted stem cells and the lack of precise control over their differentiation into the cell types needed to repair

a core faculty member at Harvard Wyss Institute, has developed now a strategy that has improved experimentally bone repair by boosting the survival rate of transplanted stem cells

In addition to Mooney, the team included Georg Duda, a Wyss associate faculty member and director of the Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration at Charité Universitätsmedizin in Berlin,

Mooney is also the Robert P. Pinkas Family Professor of Bioengineering at the Harvard John A. Paulson School of engineering and Applied sciences.

Stem cell therapies have potential for repairing many tissues and bones, or even for replacing organs.

a graduate student who worked with Mooney and who is the study first author. ased on our experience with mechanosensitive stem cells,

By coupling the bulk gel with a small eptidederived from the extracellular environment of genuine stem cell niches,

cross-disciplinary work was supported by the Harvard university Materials Research Science and Engineering Center (MRSEC), which is funded by the National Science Foundation (NSF).

Additional funding was provided by the National institutes of health; the Belgian American Education Foundation; the Einstein Foundation Berlin;

the Berlin-Brandenburg School for Regenerative Therapies; the Harvard College Research Program; and NSF Graduate Research, Einstein Visiting, Harvard College PRISE, Herchel-Smith and Pechet Family Fund Fellowships e

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#Scientists Develop an Ultrathin Invisibility Cloak for Visible light A team of scientists have invented an ultra-thin invisibility cloak that can conform to the shape of an object

and conceal it from detection with visible light. Invisibility cloaks are a staple of science fiction and fantasy, from Star trek to Harry potter,

but don exist in real life, or do they? Scientists at the U s. Department of energy (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have devised an ultra-thin invisibility kincloak that can conform to the shape

of an object and conceal it from detection with visible light. Although this cloak is only microscopic in size,

Working with brick-like blocks of gold nanoantennas, the Berkeley researchers fashioned a kin cloakbarely 80 nanometers in thickness,

that was wrapped around a three-dimensional object about the size of a few biological cells and arbitrarily shaped with multiple bumps and dents.

director of Berkeley Lab Materials sciences Division and a world authority on metamaterials artificial nanostructures engineered with electromagnetic properties not found in nature. ur ultra-thin cloak now looks like a coat.

and is a member of the Kavli Energy Nanosciences Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper describing this research in Science.

This short video clip shows how the activation of a metasurface cloak made from an ultrathin layer of nanoantennas can render a 3d object invisible.

It is the scattering of light be infrared it visible , X-ray, etc.,from its interaction with matter that enables us to detect

The rules that govern these interactions in natural materials can be circumvented in metamaterials whose optical properties arise from their physical structure rather than their chemical composition.

For the past ten years, Zhang and his research group have been pushing the boundaries of how light interacts with metamaterials,

In the past, their metamaterial-based optical carpet cloaks were bulky and hard to scale up and entailed a phase difference between the cloaked region

what it concealed was not. reating a carpet cloak that works in air was so difficult we had embed to it in a dielectric prism that introduced an additional phase in the reflected light,

a recent member of Zhang research group who is now an assistant professor at Penn State university. ecent developments in metasurfaces,

however, allow us to manipulate the phase of a propagating wave directly through the use of subwavelength-sized elements that locally tailor the electromagnetic response at the nanoscale,

300 square microns in area that was wrapped conformally in the gold nanoantenna skin cloak, the light reflected off the surface of the skin cloak was identical to light reflected off a flat mirror,

The cloak can be turned nor ffsimply by switching the polarization of the nanoantennas. phase shift provided by each individual nanoantenna fully restores both the wavefront

and metamaterials offers tantalizing future prospects for technologies such as high resolution optical microscopes and superfast optical computers.

At the macroscale, among other applications, invisibility cloaks could prove useful for 3d displays. This research was funded by the DOE Office of Science a

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Scientists at the U s. Department of energy (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have devised an ultra-thin invisibility kincloak that can conform to the shape