IMPROVING ATOMIC CLOCKS

FROM:  NATIONAL SCIENCE FOUNDATION
The challenge of building a better atomic clock and why it matters

Prior to the mid-18th century, it was tough to be a sailor. If your voyage required east-west travel, you couldn't set out to a specific destination and have any real hope of finding it efficiently.

At the time sailors had no reliable method for measuring longitude, the coordinates that measure a point's east-west position on the globe. To find longitude, you need to know the time in two places--the ship you're on, and the port you departed from. By calculating the difference between those times, sailors got a rough estimate of their position. The problem: The clocks back then just couldn't keep time that well. They lost their home port's time almost immediately after departing.

Today, time is just as important to navigation, only instead of calculating positioning with margins of errors measured in miles and leagues, we have GPS systems that are accurate within meters. And instead of springs and gears, our best timepieces rely on cesium atoms and lasers.

But given the history, it's fitting that scientists like Clayton Simien, a National Science Foundation (NSF)-funded physicist at the University of Alabama at Birmingham who works on atomic clocks, was inspired by the story of John Harrison, an English watchmaker who toiled in the 1700s to come up with the first compact marine chronometer. This device marked the beginning of the end for the "longitude problem" that had plagued sailors for centuries.

"If you want to measure distances well, you really need an accurate clock," Simien said.

Despite the massive leaps navigation technology has made since Harrison's time, scientists--many NSF-funded--are looking for new ways to make clocks more accurate, diminishing any variables that might distort precise timekeeping. Some, for example, are looking for ways to better synchronize atomic clocks on earth with GPS satellites in orbit, where atmospheric distortion can limit signal accuracy to degrees that seem minute, but are profound for the precise computer systems that govern modern navigation.

The National Institute of Standards and Technology, Department of Defense, join NSF in the search for even better atomic clocks. But today's research isn't just about building a more accurate timepiece. It's about foundational science that has other ramifications.

'One Mississippi,' or ~9 billion atom oscillations

Atomic clocks precisely measure the ticks of atoms, essentially tossing cesium atoms upward, much like a fountain. Laser-beam photons "cool down" the atoms to very low temperatures, so the atoms can transfer back and forth between a ground state and an excited state.

The trick to this process is finding just the right frequency to move directly between the two states and overcome Doppler shifts that distort rhythm. (Doppler shifts are increases or decreases in wave frequency as the waves move closer or further away -- much like the way a siren's sound changes depending on its distance.)

Laser improvements have helped scientists control atoms better and address the Doppler issue. In fact, lasers helped to facilitate something known as an optical lattice, which can layer atoms into "egg cartons" to immobilize them, helping to eliminate Doppler shifts altogether.

That shift between ground state and excited state (better known as the atomic transition frequency) yields something equivalent to the official definition of a second: 9,192,631,770 cycles of the radiation that gets a cesium atom to vibrate between those two energy states. Today's atomic clocks mostly still use cesium.

NSF-funded physicist Kurt Gibble, of Pennsylvania State University, has an international reputation for assessing accuracy and improving atomic clocks, including some of the most accurate ones in the world: the cesium clocks at the United Kingdom's National Physical Laboratory and the Observatory of Paris in France.

But accurate as those are, Gibble says the biggest advance in atomic clocks will be a move from current-generation microwave frequency clocks -- the only kind currently in operation -- to optical frequency clocks.

The difference between the two types of clocks lies in the frequencies they use to measure the signals their atoms' electrons emit when they change energy levels. The microwave technology keeps reliable time, but optical clocks offer significant improvements. According to Gibble, they're so accurate they would lose less than a second over the lifetime of the universe, or 13.8 billion years.

Despite that promise of more accurate performance, the optical frequency clocks don't currently keep time.

"So far, optical standards don't run for long enough to keep time," Gibble said. "But they will soon."

Optical frequency clocks operate on a significantly higher frequency than the microwave ones, which is why many researchers are exploring their potential with new alkaline rare earth elements, such as ytterbium, strontium and gadolinium.

"The higher frequency makes it a lot easier to be more accurate," Gibble said.

Gibble is starting work on another promising elemental candidate: cadmium. Simien, whose research employs gadolinium, has focused on minimizing--or eliminating if possible--key issues that limit accuracy.

"Nowadays, the biggest obstacle, in my opinion is the black body radiation shift," Simien said. "The black body radiation shift is a symptomatic effect. We live in a thermal environment, meaning its temperature fluctuates. Even back in the day, a mechanical clock had pieces that would heat up and expand or cool down and contract.

"A clock's accuracy varied with its environment. Today's system is no longer mechanical and has better technology, but it is still susceptible to a thermal environment's effects. Gadolinium is predicted to have a significantly reduced black body relationship compared to other elements implemented and being proposed as new frequency standards."

While Simien and Gibble agree that optical frequency research represents the next generation of atomic clocks, they recognize that most people don't really care if the Big Bang happened 13 billion years ago or 13 billion years ago plus one second.

"It's important to understand that one more digit of accuracy is not always just fine tuning something that is probably already good enough," said John Gillaspy, an NSF program director who reviews funding for atomic clock research for the agency's physics division. "Extremely high accuracy can sometimes mean a qualitative breakthrough which provides the first insight into an entirely new realm of understanding--a revolution in science."

Gillaspy cited the example of American physicist Willis Lamb, who in the middle of the last century measured a tiny frequency shift that led theorists to reformulate physics as we know it, and earned him a Nobel Prize. While research to improve atomic clocks is sometimes dismissed as trying to make ultra-precise clocks even more precise, the scientists working in the field know their work could potentially change the world in profound, unexpected ways.

"Who knows when the next breakthrough will come, and whether it will be in the first digit or the 10th?" Gillaspy continued. "Unfortunately, most people cannot appreciate why more accuracy matters."

From Wall Street to 'Interstellar'

Atomic clock researchers point to GPS as the most visible application of the basic science they study, but it's only one of this foundational work's potential benefits.

Many physicists expect it to provide insight that will illuminate our understanding of fundamental physics and general relativity. They say new discoveries will also advance quantum computing, sensor development and other sensitive instrumentation that requires clever design to resist natural forces like gravity, magnetic and electrical fields, temperature and motion.

The research also has implications beyond the scientific world. Financial analysts worry that worldwide markets could lose millions due to ill-synchronized clocks.

On June 30 th at 7:59:59 p.m. EDT, the world adds what is known as a "leap second" to keep solar time within 1 second of atomic time. History has shown, however, that this adjustment to clocks around the world is often done incorrectly. Many major financial markets are taking steps ranging from advising firms on how to deal with the adjustment to curtailing after-hours trading that would occur when the change takes place.

Gibble says the goal of moving to ever more accurate clocks isn't to more precisely measure time over a long period.

"It's the importance of being able to measure small time differences."

GPS technology, for example, looks at the difference of the propagation of light from multiple satellites. To provide location information, several GPS satellites send out signals at the speed of light--or one foot per nanosecond--saying where they are and what time they made their transmissions.

"Your GPS receiver gets the signals and looks at the time differences of the signals--when they arrive compared to when they said they left," Gibble said. "If you want to know where you are to a couple of feet, you need to have timing to a nanosecond--a billionth of a second."

In fact, he said, if you want that system to continue to accurately operate for a day, or for weeks, you need timing significantly better than that. Getting a GPS to guide us in deserts, tropical forests, oceans and other areas where roads aren't around to help as markers along the way--one needs clocks with nanosecond precision in GPS satellites to keep us from getting lost.

And if you're not traveling to those locales, then there's still the future to think about.

"Remember the movie, 'Interstellar,'" Simien said. "There is someone on a spaceship far away, and Matthew McConaughey is on a planet in a strong gravitational field. He experiences reality in terms of hours, but the other individual back on the space craft experiences years. That's general relativity. Atomic clocks can test this kind of fundamental theory and its various applications that make for fascinating science, and as you can see, they also expand our lives."

-- Ivy F. Kupec,
Investigators
Kurt Gibble
Clayton Simien
Related Institutions/Organizations
University of Alabama at Birmingham
Pennsylvania State Univ University Park

DISCOVERING HOW ROMULAN CLOAKING TECHNOLOGY WORKS THROUGH MATH

FROM:  THE NATIONAL SCIENCE FOUNDATION
Hidden from view
Mathematicians formulate equations, bend light and figure out how to hide things

The idea of cloaking and rendering something invisible hit the small screen in 1966 when a Romulan Bird of Prey made an unseen, surprise attack on the Starship Enterprise on Star Trek. Not only did it make for a good storyline, it likely inspired budding scientists, offering a window of technology's potential.

Today, between illusionists who make the Statue of Liberty disappear to Harry Potter's invisibility cloak that not only hides him from view but also protects him from spells, pop culture has embraced the idea of hiding behind force fields and magical materials. And not too surprisingly, National Science Foundation (NSF)-funded mathematicians, scientists and engineers are equally fascinated and looking at how and if they can transform science fiction into, well, just science.

"Cloaking is about detection and rendering something--and the cloak itself--not detectable or seen," said Michael Weinstein, an NSF-funded mathematician at Columbia University. "An object is seen when waves are bounced off it and observed by a detector."

In recent years, researchers have developed new ways in which light can move around and even through a physical object, making it invisible to parts of the electromagnetic spectrum and undetectable by sensors. Additionally, mathematicians, theoretical physicists and engineers are exploring how and whether it's feasible to cloak against other waves besides light waves. In fact, they are investigating sound waves, sea waves, seismic waves and electromagnetic waves including microwaves, infrared light, radio and television signals.

Successful outcomes have far-reaching results--like protecting deep-water oil rigs from earthquakes and vulnerable beaches from tsunamis.

Uncloaking cloaking's math and science history

Partial differential equations, coordinate invariance, wave equations--when you start talking to researchers about cloaking, it soon starts sounding a lot like math. And that's because at the very heart of this scientific question lies a mathematical one.

"There are very nice mathematical problems associated with this, and some of the ideas are mathematically very, very simple," said Michael Vogelius, NSF's division director for mathematical sciences and whose own research at Rutgers University has contributed significantly to this field. "But that doesn't mean they are simple to implement. In transformation cloaking the materials with the desired cloaking properties are found by singular or nearly singular change of variables in the energy expression--these material coefficients are sometimes referred to as the push-forward (or pull-back) of the original background. Basically, mathematicians ask, 'what do the equations have to look like to get this effect?' The thing that will be very hard--and is very hard--is to build these materials. They are singular in all kinds of ways."

That is why throughout cloaking research history, mathematicians, theoretical physicists and engineers have looked at the problem together.

According to Graeme Milton, an NSF-funded mathematician at the University of Utah, cloaking's start is rooted in math.

"Mathematicians and theoretical physicists basically had the idea independently for transformation-based cloaking," he said, adding that other mathematicians along the way--including himself--have taken the same wave equations and developed them further.

Milton and his collaborators created superlens cloaking, where cloaking occurs near lenses with capabilities far greater than traditional ones, and active exterior cloaking, where cloaking is created by active devices, and the cloak does not completely surround the object.

While cloaking has made considerable theoretical strides, its triumphs have been fairly limited for those awaiting real-world applications.

"Essentially, all the cloaking that has been done successfully in experiment involves a fixed frequency or small band of frequencies," Weinstein said. "So, it's a bit like--suppose you detect things by shining a light on them, and we all agree you're only allowed to shine blue light. I can construct a cloak that will conceal it under blue light, but if you vary the color--that is the wavelength--of the probing light, it will then be detectable. So far, we are unable to cloak something that is invisible to all colors. And because white light is composed of a broad spectrum of colors, no one has come near to making things truly undetectable."

Even with those limitations, there have been distinct milestones in cloaking research.

One of the best examples is actually widely available but probably not commonly thought of as cloaking technology, yet it applies the same sort of math. It involves sounds waves.

"Noise-cancelling headphones are basically cloaking the sounds from outside so they don't reach your ears," Milton said. "Active cloaking is very much along these same lines."

In 2006, as Milton published a key paper that expanded on the superlens cloaking he developed more than a decade earlier, a group of Duke University physicists created the first-ever microwave invisibility cloak using specially engineered "metamaterials," which can manipulate wavelengths, such as light, in a way that naturally occurring materials cannot do alone. However, it only cloaked microwaves and only in two dimensions.

And in 2014, a group in France actually did some experiments with a company to drill 5-meter-deep holes in strategic locations that would modify the earth's density and then measure effectiveness in cloaking. The experiments man-made vibrations that were at a given frequency, not earthquakes. They were able to deflect the seismic waves, showing some possibility to develop this application further.

"Science needs to figure out how to cloak against multiple frequencies before there can be any 'real' cloaking, however," Milton said. "Earthquakes and tsunamis involve a mixture of frequencies, so they are particularly challenging problems."

Passive and active approaches to cloaking research

To understand cloaking, one must first understand where the idea comes from.

When light encounters an object, it is either reflected, refracted or absorbed. Reflection means light waves bounce off an object, like a mirror. Refraction bends light waves, much like looking at a straw in a glass of water seems to break the straw into two pieces. When waves are absorbed, they are stopped, neither bouncing back nor transmitting through the object--although perhaps heating it. Objects which absorb light appear opaque or dark. These interactions between light and objects are what allow us to see those objects.

For cloaking to occur, light must be tricked into doing unusual things that reduce our ability to "see" or detect the object. Mathematicians look for how to control the flow of waves, using wave equations to characterize their behavior. Wave equations are an example of partial differential equation (PDE); PDEs are the language of the fundamental laws of physics. (Just this year, John Nash and Louis Nirenberg received the prestigious Abel Prize for their work in partial differential equations. Their contributions have had a major impact on how mathematicians analyze the PDEs used to understand phenomena such as cloaking.)

"All wave phenomena are predictable from these wave equations--at least in principle," Weinstein said. "That is, light waves, sound waves, elastic waves, quantum waves, gravitational waves. But the problem is that these equations are not so easily solved, so one tries to come up with guiding principles, useful approximations and rules of thumb. Coming to the question of cloaking, there's a mathematical property of wave equations, governing, for example, light, called coordinate invariance. That's basically a way of saying that you can change coordinates and perspectives of viewing the object, and the equations themselves don't change their essential form. By exploiting this idea of coordinate invariance, scientists have come up with prescriptions for optical properties that can cloak arbitrary objects."

In 2009, Milton and colleagues first introduced exterior active cloaking. Scientists in this field describe their research as involving either active or passive cloaking. Active cloaking uses devices that actively generate electromagnetic fields that distort waves. Passive cloaking employs metamaterials that passively shield objects from electromagnetic waves rather than intervening.

"The term 'metamaterial' is a bit deceptive," Weinstein noted. "Metamaterials are roughly composite materials. You take a bunch of building blocks, made from naturally occurring materials, and put them together in interesting ways to create some emergent property--some collective property of this novel arrangement not in naturally occurring materials. That new collective material is a metamaterial. But it's more like a device that actually interacts actively with waves moving through it."

With new metamaterial designs come new cloaking capabilities. NSF-funded engineer Andrea Alù won NSF's Waterman award in 2015 for creating metamaterials that can cloak a three-dimensional object. He and his team developed two methods--plasmonic cloaking and mantle cloaking--that take advantage of different light-scattering effects to hide an object.

Weinstein is exploring, through his research on the partial differential equations governing light, electromagnetism, sound, etc.--different ways of controlling the flow of energy, cloaking being one example, by using novel media such as metamaterials. Vogelius is known for bringing credibility to the transformation optics that serve as a backbone to cloaking broadly.

Where's my invisibility cloak?

But most fans of stealthful space ships, submarines and cloaks will still wonder: how close are we to really having any of this technology?

"I think that from the perspective of lay people, the most misunderstood thing is thinking this technology is right around the corner," Milton said. "Realistic Harry Potter cloaks are still a long way off."

Unfortunately, addressing multi-frequency cloaking will take time.

"What I do see is a merging of mathematical, physical and engineering principles to more effectively enable isolation of objects from harmful environments--there will be movement in that direction," Weinstein said. "Also, there will be important experimental advances resulting from attempts to achieve what is only theoretically possible at this time."

In the meantime, these mathematicians often look at other issues--sometimes similar ones that offer the potential to rethink their approaches.

"Right now, we're working on the opposite sort of problem--on the limitations to cloaking," Milton said. "Cloaking is just one of the many avenues I work on. Honestly, it's always stimulating to explore the limitations of what's possible and what's impossible."

-- Ivy F. Kupec
Investigators
Andrea Alu
Graeme Milton
Michael Vogelius
Michael Weinstein
Related Institutions/Organizations
Rutgers University
University of Utah
Columbia University
University of Texas at Austin

NSF VIDEO: Interstellar, meet Large Hadron Collider (SPOILER ALERT!)

VERY PROMISING QUANTUM DOTS

FROM:  NATIONAL SCIENCE FOUNDATION
Many uses in researching quantum dots

These nanoparticles can achieve higher levels of energy when light stimulates them.

It's easier to dissolve a sugar cube in a glass of water by crushing the cube first, because the numerous tiny particles cover more surface area in the water than the cube itself. In a way, the same principle applies to the potential value of materials composed of nanoparticles.

Because nanoparticles are so small, millions of times smaller than the width of a human hair, they have "tremendous surface area," raising the possibility of using them to design materials with more efficient solar-to-electricity and solar-to-chemical energy pathways, says Ari Chakraborty, an assistant professor of chemistry at Syracuse University.

"They are very promising materials," he says. "You can optimize the amount of energy you produce from a nanoparticle-based solar cell."

Chakraborty, an expert in physical and theoretical chemistry, quantum mechanics and nanomaterials, is seeking to understand how these nanoparticles interact with light after changing their shape and size, which means, for example, they ultimately could provide enhanced photovoltaic and light-harvesting properties. Changing their shape and size is possible "without changing their chemical composition," he says. "The same chemical compound in different sizes and shapes will interact differently with light."

Specifically, the National Science Foundation (NSF)-funded scientist is focusing on quantum dots, which are semiconductor crystals on a nanometer scale. Quantum dots are so tiny that the electrons within them exist only in states with specific energies. As such, quantum dots behave similarly to atoms, and, like atoms, can achieve higher levels of energy when light stimulates them.

Chakraborty works in theoretical and computational chemistry, meaning "we work with computers and computers only," he says. "The goal of computational chemistry is to use fundamental laws of physics to understand how matter interacts with each other, and, in my research, with light. We want to predict chemical processes before they actually happen in the lab, which tells us which direction to pursue."

These atoms and molecules follow natural laws of motion, "and we know what they are," he says. "Unfortunately, they are too complicated to be solved by hand or calculator when applied to chemical systems, which is why we use a computer."

The "electronically excited" states of the nanoparticles influence their optical properties, he says.

"We investigate these excited states by solving the Schrödinger equation for the nanoparticles," he says, referring to a partial differential equation that describes how the quantum state of some physical system changes with time. "The Schrödinger equation provides the quantum mechanical description of all the electrons in the nanoparticle.

"However, accurate solution of the Schrödinger equation is challenging because of large number of electrons in system," he adds. "For example, a 20 nanometer CdSe quantum dot contains over 6 million electrons. Currently, the primary focus of my research group is to develop new quantum chemical methods to address these challenges. The newly developed methods are implemented in open-source computational software, which will be distributed to the general public free of charge."

Solar voltaics, "requires a substance that captures light, uses it, and transfers that energy into electrical energy," he says. With solar cell materials made of nanoparticles, "you can use different shapes and sizes, and capture more energy," he adds. "Also, you can have a large surface area for a small amount of materials, so you don't need a lot of them."

Nanoparticles also could be useful in converting solar energy to chemical energy, he says. "How do you store the energy when the sun is not out?" he says. "For example, leaves on a tree take energy and store it as glucose, then later use the glucose for food. One potential application is to develop artificial leaves for artificial photosynthesis. There is a huge area of ongoing research to make compounds that can store energy."

Medical imaging presents another useful potential application, he says.

"For example, nanoparticles have been coated with binding agents that bind to cancerous cells," he says. "Under certain chemical and physical conditions, the nanoparticles can be tuned to emit light, which allows us to take pictures of the nanoparticles. You could pinpoint the areas where there are cancerous cells in the body. The regions where the cancerous cells are located show up as bright spots in the photograph."

Chakraborty is conducting his research under an NSF Faculty Early Career Development (CAREER) award. The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organization. NSF is funding his work with $622,123 over five years.

As part of the grant's educational component, Chakraborty is hosting several students from a local high school--East Syracuse Mineoa High School--in his lab. He also has organized two workshops for high school teachers on how to use computational tools in their classrooms "to make chemistry more interesting and intuitive to high school students," he says.

"The really good part about it is that the kids can really work with the molecules because they can see them on the screen and manipulate them in 3-D space," he adds. "They can explore their structure using computers. They can measure distances, angles, and energies associated with the molecules, which is not possible to do with a physical model. They can stretch it, and see it come back to its original structure. It's a real hands-on experience that the kids can have while learning chemistry."

-- Marlene Cimons, National Science Foundation
Investigators
Arindam Chakraborty
Related Institutions/Organizations
Syracuse University

LANL: ADVANCED MODELING, SIMULATION TECH USED IN LIGHT-WATER REACTOR RESEARCH

FROM:  LOS ALAMOS NATIONAL LABORATORY
Los Alamos Boosts Light-Water Reactor Research with Advanced Modeling and Simulation Technology
Simulated nuclear reactor project benefits from funding extension

LOS ALAMOS, N.M., March 2, 2015, 2014—Hard on the heels of a five-year funding renewal, modeling and simulation (M&S) technology developed at Los Alamos National Laboratory as part of the Consortium for the Advanced Simulation of Light Water Reactors (CASL) will now be deployed to industry and academia under a new inter-institutional agreement for intellectual property.

“This agreement streamlines access to the reactor simulation research tools,” said Kathleen McDonald, software business development executive for the Laboratory, “and with a single contact through UT-Battelle, we have a more transparent release process, the culmination of a lengthy effort on the part of all the code authors,” she said.

CASL is a US Department of Energy “Energy Innovation Hub” established in 2010 to develop advanced M&S capabilities that serve as a virtual version of existing, operating nuclear reactors. As announced by DOE in January, the hub would receive up to $121.5 million over five years, subject to congressional appropriations. Over the next five years, CASL researchers will focus on extending the M&S technology built during its first phase to include additional nuclear reactor designs, including boiling water reactors and pressurized water reactor-based small modular reactors.

CASL’s Virtual Environment for Reactor Applications (VERA) – essentially a “virtual” reactor – has currently been deployed for testing to CASL’s industrial partners. Created with CASL Funding, VERA consists of CASL Physics Codes and the software that couples CASL Physics Codes to create the computer models to predict and simulate light water reactor (LWR) nuclear power plant operations. VERA is being validated with data from a variety of sources, including operating pressurized water reactors such as the Watts Bar Unit 1 Nuclear Plant in Tennessee, operated by the Tennessee Valley Authority (TVA)

As one of the original founding CASL partners, Los Alamos will continue to play an important role in Phase 2 of CASL.  Specifically, Los Alamos has leadership roles in three technical focus areas: Thermal Hydraulics Methods (THM), Fuel, Materials and Chemistry (FMC) and Validation and Modeling Applications (VMA).

Thermal-Hydraulics applications range from fluid-structure interaction to boiling multiphase flows. The Los Alamos-led THM team is targeting a number of industry-defined CASL “challenge problems” related to corrosion, fretting and departure from nucleate boiling.

The Fuel, Materials and Chemistry (FMC) Focus Area aims to develop improved materials performance models for fuel and cladding, and integrate those models via constitutive relations and behavioral models into VERA.  In particular, Los Alamos will bring to bear experience in structure-property relations, mechanical deformation and chemical kinetics to address several key aspects of nuclear fuel performance.

The Validation and Modeling Applications (VMA) Focus Area applies the products developed by CASL to address essential industry issues for achieving the CASL objectives of power uprates, lifetime extension, and fuel burn up limit increases, while ensuring the fuel performance and safety limits are met.

Los Alamos will continue to provide functions that are essential for achieving credible, science-based predictive modeling and simulation capabilities, including verification, validation, calibration through data assimilation, sensitivity analysis, discretization error analysis and control, and uncertainty quantification.

The new IIA agreement makes one of the Los Alamos-developed software tools, MAMBA, available for research, subject to agreements through the consortium partners. In addition, the Hydra-TH application is provided under an open-source license in VERA for advanced, scalable single and multiphase computational fluid dynamics simulations.

CASL, which is led by and headquartered at Oak Ridge National Laboratory (ORNL), has created hundreds of technical reports and publications and wide engagement with nuclear reactor technology vendors, utilities, and the advanced computing industry.

Doug Kothe, CASL Director at ORNL, notes that “CASL has benefitted tremendously from the innovative technical contributions and leadership provided by Los Alamos technical staff and is fortunate to have these contributions continuing as CASL moves into its second five-years of execution.”

NSF VIDEO: Torque - Science of NFL Football

COMPUTER SCIENTIST LOOKS AT LIMITS OF COMPUTER SCALING

FROM:  NATIONAL SCIENCE FOUNDATION 

Can our computers continue to get smaller and more powerful?

University of Michigan computer scientist reviews frontier technologies to determine fundamental limits of computer scaling

From their origins in the 1940s as sequestered, room-sized machines designed for military and scientific use, computers have made a rapid march into the mainstream, radically transforming industry, commerce, entertainment and governance while shrinking to become ubiquitous handheld portals to the world.

This progress has been driven by the industry's ability to continually innovate techniques for packing increasing amounts of computational circuitry into smaller and denser microchips. But with miniature computer processors now containing millions of closely-packed transistor components of near atomic size, chip designers are facing both engineering and fundamental limits that have become barriers to the continued improvement of computer performance.

Have we reached the limits to computation?

In a review article in this week's issue of the journal Nature, Igor Markov of the University of Michigan reviews limiting factors in the development of computing systems to help determine what is achievable, identifying "loose" limits and viable opportunities for advancements through the use of emerging technologies. His research for this project was funded in part by the National Science Foundation (NSF).

"Just as the second law of thermodynamics was inspired by the discovery of heat engines during the industrial revolution, we are poised to identify fundamental laws that could enunciate the limits of computation in the present information age," says Sankar Basu, a program director in NSF's Computer and Information Science and Engineering Directorate. "Markov's paper revolves around this important intellectual question of our time and briefly touches upon most threads of scientific work leading up to it."

The article summarizes and examines limitations in the areas of manufacturing and engineering, design and validation, power and heat, time and space, as well as information and computational complexity.​

"What are these limits, and are some of them negotiable? On which assumptions are they based? How can they be overcome?" asks Markov. "Given the wealth of knowledge about limits to computation and complicated relations between such limits, it is important to measure both dominant and emerging technologies against them."

Limits related to materials and manufacturing are immediately perceptible. In a material layer ten atoms thick, missing one atom due to imprecise manufacturing changes electrical parameters by ten percent or more. Shrinking designs of this scale further inevitably leads to quantum physics and associated limits.

Limits related to engineering are dependent upon design decisions, technical abilities and the ability to validate designs. While very real, these limits are difficult to quantify. However, once the premises of a limit are understood, obstacles to improvement can potentially be eliminated. One such breakthrough has been in writing software to automatically find, diagnose and fix bugs in hardware designs.

Limits related to power and energy have been studied for many years, but only recently have chip designers found ways to improve the energy consumption of processors by temporarily turning off parts of the chip. There are many other clever tricks for saving energy during computation. But moving forward, silicon chips will not maintain the pace of improvement without radical changes. Atomic physics suggests intriguing possibilities but these are far beyond modern engineering capabilities.

Limits relating to time and space can be felt in practice. The speed of light, while a very large number, limits how fast data can travel. Traveling through copper wires and silicon transistors, a signal can no longer traverse a chip in one clock cycle today. A formula limiting parallel computation in terms of device size, communication speed and the number of available dimensions has been known for more than 20 years, but only recently has it become important now that transistors are faster than interconnections. This is why alternatives to conventional wires are being developed, but in the meantime mathematical optimization can be used to reduce the length of wires by rearranging transistors and other components.

Several key limits related to information and computational complexity have been reached by modern computers. Some categories of computational tasks are conjectured to be so difficult to solve that no proposed technology, not even quantum computing, promises consistent advantage. But studying each task individually often helps reformulate it for more efficient computation.

When a specific limit is approached and obstructs progress, understanding the assumptions made is key to circumventing it. Chip scaling will continue for the next few years, but each step forward will meet serious obstacles, some too powerful to circumvent.

What about breakthrough technologies? New techniques and materials can be helpful in several ways and can potentially be "game changers" with respect to traditional limits. For example, carbon nanotube transistors provide greater drive strength and can potentially reduce delay, decrease energy consumption and shrink the footprint of an overall circuit. On the other hand, fundamental limits--sometimes not initially anticipated--tend to obstruct new and emerging technologies, so it is important to understand them before promising a new revolution in power, performance and other factors.

"Understanding these important limits," says Markov, "will help us to bet on the right new techniques and technologies."

-NSF-

Media Contacts
Steve Crang, University of Michigan

BEETLE INSPIRES NEW MATERIALS DEVELOPED TO TRAP AND CHANNEL SMALL AMOUNTS OF FLUIDS

FROM:  NATIONAL SCIENCE FOUNDATION 

Quenching the world's water and energy crises, one tiny droplet at a time

In pursuit of beetle biomimicry, NSF-funded engineers develop new, textured materials to trap and channel small amounts of liquid

In the Namib Desert of Africa, the fog-filled morning wind carries the drinking water for a beetle called the Stenocara.

Tiny droplets collect on the beetle's bumpy back. The areas between the bumps are covered in a waxy substance that makes them water-repellant, or hydrophobic (water-fearing). Water accumulates on the water-loving, or hydrophilic, bumps, forming droplets that eventually grow too big to stay put, then roll down the waxy surface.

The beetle slakes its thirst by tilting its back end up and sipping from the accumulated droplets that fall into its mouth. Incredibly, the beetle gathers enough water through this method to drink 12 percent of its body weight each day.

More than a decade ago, news of this creature's efficient water collection system inspired engineers to try and reproduce these surfaces in the lab.

Small-scale advances in fluid physics, materials engineering and nanoscience since that time have brought them close to succeeding.

These tiny developments, however, have the prospect to lead to macro-scale changes. Understanding how liquids interact with different materials can lead to more efficient, inexpensive processes and products, and might even lead to airplane wings impervious to ice and self-cleaning windows.

Beetle bumps in the lab

Using various methods to create intricately patterned surfaces, engineers can make materials that closely mimic the beetle's back.

"Ten years ago no one had the ability to pattern surfaces like this at the nanoscale," says Sumanta Acharya, a National Science Foundation (NSF) program director. "We observed naturally hydrophobic surfaces like the lotus leaf for decades. But even if we understood it, what could we do about it?"

What researchers have done is create surfaces that so excel at repelling or attracting water they've added a "super" at the front of their description: superhydrophobic or superhydrophilic.

Many superhydrophobic surfaces created by chemical coatings are already in the marketplace (water-repellant shoes! shirts! iPhones!).

However, many researchers focus on materials with physical elements that make them superhydrophobic.

These materials have micro or nano-sized pillars, poles or other structures that alter the angles at which water droplets contact their surface. These contact angles determine whether a water droplet beads up like a teeny crystal ball or relaxes a bit and rests on the surface like a spilled milkshake.

By varying the layout of these surfaces, researchers can now trap, direct and repulse small amounts of water for a variety of new purposes.

"We can now do things with fluids we only imagined before," says mechanical engineer Constantine Megaridis at the University of Illinois at Chicago. Megaridis and his team have two NSF grants from the Engineering Directorate's Division of Chemical, Bioengineering, Environmental and Transport Systems.

"The developments have enabled us to create devices -- devices with the potential to help humanity -- that do things much better than have ever been done before," he says.

Megaridis has used his beetle-inspired designs to put precise, textured patterns on inexpensive materials, making microfluidic circuits.

Plastic strips with superhydrophilic centers and superhydrophobic surroundings that combine or separate fluids have the potential to serve as platforms for diagnostic tests (watch "The ride of the water droplets").

"Imagine you want to bring drops of blood or water or any liquid to a certain location," Megaridis explains. "Just like a highway, the road is the strip for the liquid to travel down, and it ends up collecting in a fluid storage tank on the surface." The storage tank could hold a reactive agent. Medical personnel could use the disposable strips to field-test water samples for E. coli, for example.

Devices such as these -- created in engineering labs -- are now working their way to the marketplace.

Water, water in the air

NBD Nanotechnologies, a Boston-based company funded by NSF's Small Business Technology Transfer program, aims to scale up the durability and functionality of surface coatings for industrial use.

One of the most impactful applications for superhydrophobic or hydrophobic research is improved condensation efficiency. When water vapor condenses to a liquid, it typically forms a film. That film is a barrier between the vapor and the surface, making it more difficult for other droplets to form. If that film can be prevented by whisking away droplets immediately after they condense--say, with a superhydrophobic surface--the rate of condensation increases.

Condensers are everywhere. They're in your refrigerator, car and air conditioner. More efficient condensation would let all this equipment function with less energy. Better efficiency is especially important in places where large-scale cooling is paramount, such as power plants.

"NBD makes more durable coatings that span large surface areas," says NBD Nanotechnologies senior scientist Sara Beaini. "Durability is an important factor, because when you're working on the micro level you depend on having a pristine surface structure. Any mechanical or chemical abrasion that distorts the surface structures can significantly reduce or eliminate the advantageous surface properties quickly."

NBD, which you might have guessed stands for Namib Beetle Design, has partnered with Megaridis and others to improve durability, the main challenge in commercializing superhydrophobic research. Power plant condensers with durable hydrophobic or superhydrophobic coatings could be more efficient. And with water and energy shortages looming, partnerships such as theirs that help to transfer this breakthrough from the lab to the outside world are increasingly valuable.

Other groups have applied hydrophobic patterning methods in clever ways.

Kripa Varanasi, mechanical engineer at MIT and NSF CAREER awardee, has applied superhydrophobic coatings to metal, ceramics and glass, including the insides of ketchup bottles. Julie Crockett and Daniel Maynes at Brigham Young University developed extreme waterproofing by etching microscopic ridges or posts onto CD-sized wafers.

With all these cross-country efforts, many are optimistic for a future where people in dry areas can harvest fresh water from a morning wind, and lower their energy needs dramatically.

"If someone comes up with a really cheap solution, then applications are waiting," said Rajesh Mehta, NSF Small Business Innovation Research/Small Business Technology Transfer program director.
-- Sarah Bates
Investigators
Constantine Megaridis
Sara Beaini
Julie Crockett
Kripa Varanasi
Brent Webb
R Daniel Maynes
Related Institutions/Organizations
University of Illinois at Chicago
Iowa State University
Brigham Young University
NBD Nanotechnologies, Inc.
Massachusetts Institute of Technology

SCIENTISTS RESEARCHING A WAY TO BETTER USE SUPERCONDUCTING MATERIALS

FROM:  NATIONAL SCIENCE FOUNDATION 
Researcher studies unsolved problem of interacting objects
Insights could enable more widespread use of superconducting materials

One of science's biggest puzzles is figuring out how interacting objects behave collectively. Take water, for example. "It's a molecule, but it's also a liquid with specific properties," says Daniel Sheehy, an assistant professor of physics at Louisiana State University. "How does the liquid come from the microscopic action of these water molecules?"

Sheehy doesn't study water, but he likes to use it to describe what he does study, which is many-particle quantum mechanics, that is, how atoms organize themselves at very low temperatures when they become trapped in beams of laser light, and whether they reach a superfluid state, a phenomenon that occurs only when it is extremely cold.

In a superconductor, the electrons form a superfluid which "is like a liquid, but better," Sheehy says. "It never slows down and the electrical resistance is zero, meaning none of the energy is lost."

The down side, however, is that this requires very cold temperatures to achieve, on the order of 10 kelvins (minus 263 C, minus 442 F), for conventional superconductors, which is why they generally only are used in special applications, such as in MRI machines, where they are kept cold with liquid helium.

"This is why they are not used in power lines," he says. "You would need refrigerators, which isn't very practical."

Sheehy's goal is to gain further insights that could enable more widespread uses for superconducting materials. "Might it be possible to make material that is a superconductor at ambient temperatures?" he asks. "No one knows. It is a very difficult goal, a very big goal. But we would like to use superconductors in places where they are not used now."

He is performing theoretical calculations regarding clouds of extremely cold atoms--imagine very dilute particles of gases trapped in a laser field--to see how they behave and whether they show superconducting properties. "All I want to know is if I put a million atoms in a small region and watch them interact, what can they do?" he says.

He is examining the activities of different alkali gases--those in the first column of the Periodic Table--because "they have only one outermost electron, making them easier to control," he says. "First, let's understand the simplest system we can think of so we can develop the theory. Let's fundamentally understand nature and this unsolved problem of interacting objects."

He does not conduct actual physical experiments, but is a theorist "who uses a computer, as well as paper and pencil calculations," to determine the properties of these clouds of atoms. "I am interested in the superfluid states of these atoms, which is where the particles don't have any viscosity; they flow without resistance," he says.

Sheehy is conducting his research under a National Science Foundation (NSF) Faculty Early Career Development (CAREER) award, which he received in 2012. The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education, and the integration of education and research within the context of the mission of their organization. NSF is funding his work with $428,200 over five years.

The grant's educational component includes developing more interactive materials in large-size physics classes so that they go beyond the "lecture" format, "with more hands-on activities that get them thinking," he says. "We will be trying to use Internet applications with certain computer programs that demonstrate the principles of quantum mechanics. This, hopefully, will get them to better learn physics, and get them excited about a future in science."

He also plans an outreach project to the public, and to high school and middle school students, including an in-school demonstration program aimed at inspiring the interest of minority students in science, and in pursuing science careers.

"The field of cold atoms is growing rapidly, fueled by numerous recent experimental breakthroughs, making it an ideal area for students to work in," he says. "We're working on fundamental problems that are conceptually simple but yet still intellectually stimulating and experimentally relevant."

-- Marlene Cimons, National Science Foundation
Investigators
Daniel Sheehy
Related Institutions/Organizations
Louisiana State University & Agricultural and Mechanical College

ARTIFICIAL ANTI-GRAVITY AT THE NAVAL RESEARCH LABORATORY

FROM:  U.S. DEPARTMENT OF DEFENSE "ARMED WITH SCIENCE"

Written on July 25, 2012 at 7:20 am by jtozer
Artificial Anti-Gravity-How NRL Is Simulating Space
Precision honed to within +/-0.0018 inches tolerance across its surface, the Gravity Offset Table (shown right) will allow scientists to emulate the inertia of space in the laboratory using full-size spacecraft and robotic arms like the Front-End Robotic Enabling Near-Term Demonstration (FREND) arm pictured center.Photo: U.S. Naval Research Laboratory
The U.S. Naval Research Laboratory Spacecraft Engineering Department‘s space robotics research facility recently took possession of a one-of-a-kind 75,000 pound Gravity Offset Table (GOT) made from a single slab of solid granite.
I know what you’re thinking. "TACOS!" Oh wait, that’s what I’m thinking.
Actually, the idea that a slab that weighs 37 and a 1/2 tons (which is, oh, maybe half a dozen elephants? Give or take?) could be associated with something that has no gravity is pretty impressive. And intuitively confusing. So let’s read on…
While the idea of building a space simulator is pretty cool (see: AWESOME), the concept conjures up thoughts of holodecks and space walks and whatnot. Obviously I’m getting ahead of myself here (crawl, walk, run), but why are we starting off at the quarry? Why the slab of granite?
Apparently, emulating the classical mechanics of physics found in space on a full-scale replica on Earth requires not only a hefty amount of air to ‘float’ the object, but a precision, frictionless, large surface area that will allow researchers to replicate the effects of inertia on man-made objects in space.

Ah. A hover table. But wait a minute, how is this even possible?
"We accomplish this by floating models of spacecraft and other resident space objects on air bearings — similar to the dynamics of an upside-down air hockey table," said Dr. Gregory P. Scott, space robotics scientist. "Based on the inertia of the ‘floating’ system, a realistic spacecraft response can be measured when testing thrusters, attitude control algorithms, and responses to contact with other objects."
Currently, the grappling, or capture, of spacecraft in orbit is accomplished by specifically engineered pre-configured couplers and mating mechanisms. Why space station, we hardly know each other. Still, this is assuming all things are right and true in the universe and everything is where it’s supposed to be and all that.
But if TV and movies have taught me anything, it’s that space circumstances rarely ever qualify as smooth sailing. Also the word Raxacoricofallapatorius. But that’s beside the point.
So, in order to capture and service a ‘free-flying’ orbiting spacecraft that has no conventional coupling mechanism, researchers must first be able to demonstrate minimal rates of error in a cost effective and efficient manner using many spacecraft configurations here on Earth. And how are they going to do that? Enter the hover slab!

Honed by Precision Granite<sup>® to federal ‘AAA’ specifications, the 20 feet by 15 feet, 1.5-foot thick single piece of granite is within +/- 0.0018 inches flat across its surface. Now that’s my kind of granite slab.

The precision GOT will allow NRL researchers to precisely simulate the frictionless motion of objects in space and understand the dynamics of docking and servicing satellites on-orbit. This function is of increasing importance as rising launch costs and the addition of new orbiting spacecraft can be offset by the repair or updating of assets already in Earth orbit.

Quarried from the Raymond Granite Quarry, Clovis, Calif., the 450 cubic-foot, 37.5 ton GOT slab is thought to be the largest, single slab, precision granite table in the world with tolerances capable of allowing engineers to simulate service of full-scale satellite spacecraft with significant structural flexibility to a degree of accuracy unmatched by any other space robotics facility.

They want to float a full-scale satellite spacecraft. Over a slab of granite. To study robotics. That’s…well that’s terrific, actually. I mean really, I thought the floating magnet toy on my desk was cool, but NRL has managed to acquire a thing that will allow them to literally simulate space in a lab. Talk about a controlled environment.</sup>