Sustainable Power Sources Based on High Efficiency Thermopower Wave Devices

In this time-lapse series of photos, progressing from top to bottom, a coating of sucrose (ordinary sugar) over a wire made of carbon nanotubes is lit at the left end, and burns from one end to the other. As it heats the wire, it drives a wave of electrons along with it, thus converting the heat into electricity.

Engineers from MIT have developed an alternative system for generating electricity, which harnesses heat and uses no metals or toxic materials.

The batteries that power the ubiquitous devices of modern life, from smartphones and computers to electric cars, are mostly made of toxic materials such as lithium that can be difficult to dispose of and have limited global supplies. Now, researchers at MIT have come up with an alternative system for generating electricity, which harnesses heat and uses no metals or toxic materials.

The new approach is based on a discovery announced in 2010 by Michael Strano, the Carbon P. Dubbs Professor in Chemical Engineering at MIT, and his co-workers: A wire made from tiny cylinders of carbon known as carbon nanotubes can produce an electrical current when it is progressively heated from one end to the other, for example by coating it with a combustible material and then lighting one end to let it burn like a fuse.

That discovery represented a previously unknown phenomenon, but experiments at the time produced only a minuscule amount of current in a simple laboratory setup. Now, Strano and his team have increased the efficiency of the process more than a thousandfold and have produced devices that can put out power that is, pound for pound, in the same ballpark as what can be produced by today’s best batteries. The researchers caution, however, that it could take several years to develop the concept into a commercializable product.

The new results were published in the journal Energy & Environmental Science, in a paper by Strano, doctoral students Sayalee Mahajan PhD ’15 and Albert Liu, and five others.

Catching the wave

Strano says “it’s actually remarkable that this [phenomenon] hasn’t been studied before.” Much of his team’s work on the project has focused on not just improving the efficiency of the process but also “developing the theory of how these things work.” And the latest experiments, he says, show good agreement between theory and experimental results, providing strong confirmation of the underlying mechanism.

Basically, the effect arises as a pulse of heat pushes electrons through the bundle of carbon nanotubes, carrying the electrons with it like a bunch of surfers riding a wave.

One key finding that helped to verify the theory is that sometimes the wave of heat produces a single voltage, but sometimes it produces two different voltage regions at the same time. “Our mathematical model can describe why that occurs,” Strano says, whereas alternative theories cannot account for this. According to the team’s theory, the thermopower wave “divides into two different components,” which sometimes reinforce one another and sometimes counter each other.

The improvements in efficiency, he says, “brings [the technology] from a laboratory curiosity to being within striking distance of other portable energy technologies,” such as lithium-ion batteries or fuel cells. In their latest version, the device is more than 1 percent efficient in converting heat energy to electrical energy, the team reports — which is “orders of magnitude more efficient than what’s been reported before.” In fact, the energy efficiency is about 10,000 times greater than that reported in the original discovery paper.

“It took lithium-ion technology 25 years to get where they are” in terms of efficiency, Strano points out, whereas this technology has had only about a fifth of that development time. And lithium is extremely flammable if the material ever gets exposed to the open air — unlike the fuel used in the new device, which is much safer and also a renewable resource.

A spoonful of sugar

While the initial experiments had used potentially explosive materials to generate the pulse of heat that drives the reaction, the new work uses a much more benign fuel: sucrose, otherwise known as ordinary table sugar. But the team believes that other combustion materials have the potential to generate even higher efficiencies. Unlike other technologies that are specific to a particular chemical formulation, the carbon nanotube-based power system works just on heat, so as better heat sources are developed they could simply be swapped into a system to improve its performance, Strano says.

Already, the device is powerful enough to show that it can power simple electronic devices such as an LED light. And unlike batteries that can gradually lose power if they are stored for long periods, the new system should have a virtually indefinite shelf life, Liu says. That could make it suitable for uses such as a deep-space probe that remains dormant for many years as it travels to a distant planet and then needs a quick burst of power to send back data when it reaches its destination.

In addition, the new system is very scalable for use in the increasingly tiny wearable devices that are emerging. Batteries and fuel cells have limitations that make it difficult to shrink them to tiny sizes, Mahajan says, whereas this system “can scale down to very small limits. The scale of this is unique.”

This work is “an important demonstration of increasing the energy and lifetime of thermopower wave-based systems,” says Kourosh Kalantar-Zadeh, a professor of electrical and computer engineering at RMIT University in Australia, who was not involved in this research. “I believe that we are still far from the upper limit that the thermopower wave devices can potentially reach,” he says. “However, this step makes the technology more attractive for real applications.”

He adds that with this technology, “We can obtain phenomenal bursts of power, which is not possible from batteries. For instance, the thermopower wave systems can be used for powering long-distance transmission units in micro- and nano-telecommunication hubs.”

The team also included Anton Cottrill, Yuichiro Kunai, David Bender, Javier Castillo Jr., and Stephen Gibbs. The work was supported by the Air Force Office of Scientific Research and the Office of Naval Research.

Publication: Sayalee G. Mahajan, et al., “Sustainable power sources based on high efficiency thermopower wave devices,” Energy Environ. Sci., 2016, DOI: 10.1039/C5EE03651H

Engineers Design Calcium-Based Multi-Element for Liquid Batteries

An artist’s rendering of a calcium liquid battery.

In a newly published study, MIT researchers show that calcium can form the basis for both the negative electrode layer and the molten salt that forms the middle layer of the three-layer battery.

Liquid metal batteries, invented by MIT professor Donald Sadoway and his students a decade ago, are a promising candidate for making renewable energy more practical. The batteries, which can store large amounts of energy and thus even out the ups and downs of power production and power use, are in the process of being commercialized by a Cambridge-based startup company, Ambri.

Now, Sadoway and his team have found yet another set of chemical constituents that could make the technology even more practical and affordable, and open up a whole family of potential variations that could make use of local resources.

The latest findings are reported in the journal Nature Communications, in a paper by Sadoway, who is the John F. Elliott Professor of Materials Chemistry, and postdoc Takanari Ouchi, along with Hojong Kim (now a professor at Penn State University) and PhD student Brian Spatocco at MIT. They show that calcium, an abundant and inexpensive element, can form the basis for both the negative electrode layer and the molten salt that forms the middle layer of the three-layer battery.

That was a highly unexpected finding, Sadoway says. Calcium has some properties that made it seem like an especially unlikely candidate to work in this kind of battery. For one thing, calcium easily dissolves in salt, and yet a crucial feature of the liquid battery is that each of its three constituents forms a separate layer, based on the materials’ different densities, much as different liqueurs separate in some novelty cocktails. It’s essential that these layers not mix at their boundaries and maintain their distinct identities.

It was the seeming impossibility of making calcium work in a liquid battery that attracted Ouchi to the problem, he says. “It was the most difficult chemistry” to make work but had potential benefits due to calcium’s low cost as well as its inherent high voltage as a negative electrode. “For me, I’m happiest with whatever is most difficult,” he says — which, Sadoway points out, is a very typical attitude at MIT.

Another problem with calcium is its high melting point, which would have forced the liquid battery to operate at almost 900 degrees Celsius, “which is ridiculous,” Sadoway says. But both of these problems were solvable.

First, the researchers tackled the temperature problem by alloying the calcium with another inexpensive metal, magnesium, which has a much lower melting point. The resulting mix provides a lower operating temperature — about 300 degrees less than that of pure calcium — while still keeping the high-voltage advantage of the calcium.

The other key innovation was in the formulation of the salt used in the battery’s middle layer, called the electrolyte, that charge carriers, or ions, must cross as the battery is used. The migration of those ions is accompanied by an electric current flowing through wires that are connected to the upper and lower molten metal layers, the battery’s electrodes.

The new salt formulation consists of a mix of lithium chloride and calcium chloride, and it turns out that the calcium-magnesium alloy does not dissolve well in this kind of salt, solving the other challenge to the use of calcium.

But solving that problem also led to a big surprise: Normally there is a single “itinerant ion” that passes through the electrolyte in a rechargeable battery, for example, lithium in lithium-ion batteries or sodium in sodium-sulfur. But in this case, the researchers found that multiple ions in the molten-salt electrolyte contribute to the flow, boosting the battery’s overall energy output. That was a totally serendipitous finding that could open up new avenues in battery design, Sadoway says.

And there’s another potential big bonus in this new battery chemistry, Sadoway says. “There’s an irony here. If you’re trying to find high-purity ore bodies, magnesium and calcium are often found together,” he says. It takes great effort and energy to purify one or the other, removing the calcium “contaminant” from the magnesium or vice versa. But since the material that will be needed for the electrode in these batteries is a mixture of the two, it may be possible to save on the initial materials costs by using “lower” grades of the two metals that already contain some of the other.

“There’s a whole level of supply-chain optimization that people haven’t thought about,” he says.

Sadoway and Ouchi stress that these particular chemical combinations are just the tip of the iceberg, which could represent a starting point for new approaches to devising battery formulations. And since all these liquid batteries, including the original liquid battery materials from his lab and those under development at Ambri, would use similar containers, insulating systems, and electronic control systems, the actual internal chemistry of the batteries could continue to evolve over time. They could also adapt to fit local conditions and materials availability while still using mostly the same components.

“The lesson here is to explore different chemistries and be ready for changing market conditions,” Sadoway says. What they have developed “is not a battery; it’s a whole battery field. As time passes, people can explore more parts of the periodic table” to find ever-better formulations, he says.

“This paper brings together innovative engineering advances in cell design and component materials within a strategic framework of ‘cost-based discovery’ that is amenable to the massive scale-up required of grid-scale applications,” says Richard Alkire, a professor of Chemical and Biomolecular Engineering at the University of Illinois, who was not involved in this research.

Because this work builds on a base of well-developed electrochemical systems used for aluminum production, Alkire says, “the path forward to grid-scale applications can therefore take advantage of a large body of existing engineering experience in areas of sustainability, environmental, life cycle, materials, manufacturing cost, and scale-up.”

The research was supported by the U.S. Department of Energy’s Advanced Research Projects Energy (ARPA-E) and by the French energy company Total S.A.

Publication: Takanari Ouchi, et al., “Calcium-based multi-element chemistry for grid-scale electrochemical energy storage,” Nature Communications 7, Article number: 10999; doi:10.1038/ncomms10999

MIT Researchers Create Perfect Nanoscrolls from Graphene Oxide

An electron microscopy image shows many examples of nanoscrolls. The insert zooms in on a single nanoscroll and reveals its conical nature.

Using both low- and high-frequency ultrasonic techniques, scientists have fabricated nanoscrolls made from graphene oxide flakes.

Water filters of the future may be made from billions of tiny, graphene-based nanoscrolls. Each scroll, made by rolling up a single, atom-thick layer of graphene, could be tailored to trap specific molecules and pollutants in its tightly wound folds. Billions of these scrolls, stacked layer by layer, may produce a lightweight, durable, and highly selective water purification membrane.

But there’s a catch: Graphene does not come cheap. The material’s exceptional mechanical and chemical properties are due to its very regular, hexagonal structure, which resembles microscopic chicken wire. Scientists take great pains in keeping graphene in its pure, unblemished form, using processes that are expensive and time-consuming, and that severely limit graphene’s practical uses.

Seeking an alternative, a team from MIT and Harvard University is looking to graphene oxide — graphene’s much cheaper, imperfect form. Graphene oxide is graphene that is also covered with oxygen and hydrogen groups. The material is essentially what graphene becomes if it’s left to sit out in open air. The team fabricated nanoscrolls made from graphene oxide flakes and was able to control the dimensions of each nanoscroll, using both low- and high-frequency ultrasonic techniques. The scrolls have mechanical properties that are similar to graphene, and they can be made at a fraction of the cost, the researchers say.

“If you really want to make an engineering structure, at this point it’s not practical to use graphene,” says Itai Stein, a graduate student in MIT’s Department of Mechanical Engineering. “Graphene oxide is two to four orders of magnitude cheaper, and with our technique, we can tune the dimensions of these architectures and open a window to industry.”

Stein says graphene oxide nanoscrolls could also be used as ultralight chemical sensors, drug delivery vehicles, and hydrogen storage platforms, in addition to water filters. Stein and Carlo Amadei, a graduate student at Harvard University, have published their results in the journal Nanoscale.

This sketch illustrates how a nanoscroll forms from a graphene oxide flake as a result of ultrasonic irradiation.

Getting away from crumpled graphene

The team’s paper originally grew out of an MIT class, 2.675 (Micro/Nano Engineering), taught by Rohit Karnik, associate professor of mechanical engineering. As part of their final project, Stein and Amadei teamed up to design nanoscrolls from graphene oxide. Amadei, as a member of Professor Chad Vecitis’ lab at Harvard University, had been working with graphene oxide for water purification applications, while Stein was experimenting with carbon nanotubes and other nanoscale architectures, as part of a group led by Brian Wardle, professor of aeronautics and astronautics at MIT.

The researchers’ graphene nano scroll research originated in this MIT classes 2.674 and 2.675 (Micro/Nano Engineering Laboratory). Video: Department of Mechanical Engineering

“Our initial idea was to make nanoscrolls for molecular adsorption,” Amadei says. “Compared to carbon nanotubes, which are closed structures, nanoscrolls are open spirals, so you have all this surface area available to manipulate.”

“And you can tune the separation of a nanoscroll’s layers, and do all sorts of neat things with graphene oxide that you can’t really do with nanotubes and graphene itself,” Stein adds.

When they looked at what had been done previously in this field, the students found that scientists had successfully produced nanoscrolls from graphene, though with very complicated processes to keep the material pure. A few groups had tried doing the same with graphene oxide, but their attempts were literally deflated.

“What was out there in the literature was more like crumpled graphene,” Stein says. “You can’t really see the conical nature. It’s not really clear what was made.”

Collapsing bubbles

Stein and Amadei first used a common technique called the Hummers’ method to separate graphite flakes into individual layers of graphene oxide. They then placed the graphene oxide flakes in solution and stimulated the flakes to curl into scrolls, using two similar approaches: a low-frequency tip-sonicator, and a high-frequency custom reactor.

The tip-sonicator is a probe made of piezoelectric material that shakes at a low, 20Hz frequency when voltage is applied. When placed in a solution, the tip-sonicator produces sound waves that stir up the surroundings, creating bubbles in the solution.

Similarly, the group’s reactor contains a piezoelectric component that is connected to a circuit. As voltage is applied, the reactor shakes — at a higher, 390 Hz frequency compared with the tip-sonicator — creating bubbles in the solution within the reactor.

Stein and Amadei applied both techniques to solutions of graphene oxide flakes and observed similar effects: The bubbles that were created in solution eventually collapsed, releasing energy that caused the flakes to spontaneously curl into scrolls. The researchers found they could tune the dimensions of the scrolls by varying the treatment duration and the frequency of the ultrasonic waves. Higher frequencies and shorter treatments did not lead to significant damage of the graphene oxide flakes and produced larger scrolls, while low frequencies and longer treatment times tended to cleave flakes apart and create smaller scrolls.

While the group’s initial experiments turned a relatively low number of flakes — about 10 percent — into scrolls, Stein says both techniques may be optimized to produce higher yields. If they can be scaled up, he says the techniques can be compatible with existing industrial processes, particularly for water purification.

“If you can make this in large scales and it’s cheap, you could make huge bulk samples of filters and throw them out in the water to remove all sorts of contaminants,” Stein says.

This work was supported, in part, by the Department of Defense through the National Defense Science and Engineering Graduate (NDSEG) fellowship program.

Publication: Carlo A. Amadei, et al., “Fabrication and morphology tuning of graphene oxide nanoscrolls,” Nanoscale, 2016,8, 6783-6791; DOI: 10.1039/C5NR07983G

New Microfluidic Screening Device May Speed Up DNA Insertion in Bacteria

In search of the ideal bacteria for use in a microbial fuel cell, researchers from MIT have developed a new microfluid device to quickly sort and identify the various strains. This technology, which could lead to a carbon-neutral method of harvesting energy for the grid from wastewater, may also be useful to doctors in identifying deadly infections more quickly.

Genetically engineering any organism requires first getting its cells to take in foreign DNA. To do this, scientists often perform a process called electroporation, in which they expose cells to an electric field.

If that field is at just the right magnitude, it will open up pores within the cell membrane, through which DNA can flow. But it can take scientists months or even years to figure out the exact electric field conditions to reversibly unlock a membrane’s pores.

A new microfluidic device developed by MIT engineers may help scientists quickly home in on the electric field “sweet spot” — the range of electric potentials that will harmlessly and temporarily open up membrane pores to let DNA in. In principle, the simple device could be used on any microorganism or cell, significantly speeding up the first step in genetic engineering.

“We’re trying to reduce the amount of experimentation that’s needed,” says Cullen Buie, the Esther and Harold E. Edgerton Associate Professor of mechanical engineering at MIT. “Our big vision for this device and future iterations is to be able to take a process that usually takes months or years, and do it in a day or two.”

Buie and his colleagues, including postdoc Paulo Garcia, graduate student Zhifei Ge, and lecturer Jeffrey Moran, have published their results this week in the journal Scientific Reports.

Hear about MIT Associate Professor Cullen Buie’s research into a novel method to quickly sort and identify various bacteria strains, which could be useful in identifying deadly infections more quickly. Video: Department of Mechanical Engineering/MIT

“A shot in the dark”

Currently, scientists can order various electroporation systems — simple instruments that come with a set of instructions for penetrating an organism’s cell membranes. Each system may include instructions for roughly 100 different organisms, such as strains of bacteria and yeast, each of which requires a unique electric field and set of experimental conditions for permeation. However, Buie says the number of organisms for which these instructions are known is but a fraction of what actually exists in nature.

“There’s a tremendous amount of biodiversity we’re unable to access,” Buie says. “Part of the problem is, we can’t even get the DNA in, much less get it expressed by the organism. And for electroporation, the search for the conditions that might work is like a shot in the dark.”

For electroporation to work, the applied electric field must be strong enough to puncture the membrane temporarily, but not so strong as to do so permanently, which would cause a cell to die.

“It’s like surgery — this is pretty invasive,” Buie says. “There’s a sweet spot between killing them and not affecting them at all, that you need to find to be able to open them reversibly, just enough so that DNA gets in and they reseal on their own.”

Whether an electric field penetrates a membrane also depends on a cell’s surrounding conditions. Scientists have also had to experiment with parameters such as the composition of a cell’s solution and the way in which the electric field is applied.

“For a novel organism, it could take you months or years to develop new conditions so that the cell is happy and will survive the poration process, and it will uptake the DNA,” Buie says.

A range in one

The group’s new microfluidic device may significantly shorten the time it takes to identify these ideal conditions. The device consists of a channel created using soft lithography. The channel narrows in the middle. When an electric field is applied to the device, the channel’s geometry causes the field to exhibit a range of electric potentials, the highest being at the channel’s narrowest region.

The researchers flowed several strains of bacterial cells through the device and exposed the cells to an electric field. They then added a fluorescent marker that lights up in the presence of DNA. If cells were successfully permeated by the electric field, they would let in the fluorescent marker, which would then light up in response to the cell’s own genetic material. To identify the magnitude of the electric potential that was able to open a cell membrane, the researchers simply marked the location of each fluorescent cell along the channel.

“In one experiment, you can test a range of electric fields and get some information almost instantly, in terms of whether there’s been something successful in opening pores,” Buie says. “So now, in your searching process, you don’t need to run a bunch of different experiments and test different electric fields separately. You can do it in one go, and it literally lights up. ”

The researchers successfully permeated strains of E. coli and Mycobacterium smegmatis, a bacterium in the same family as the organism that causes tuberculosis — a family whose membranes, Buie says, are “notoriously difficult” to penetrate.

The group’s first set of experiments involved opening up pores to take in the fluorescent marker — a molecule that is slightly smaller than DNA. The researchers also ran experiments in which they applied an electric field to bacterial cells in the presence of DNA encoded for antibiotic resistance. The team checked that the cells took up the DNA by removing them from the device and growing them on a separate plate with antibiotics — a standard procedure known as a streak test. They found that the cells were able to reproduce — a sign that the DNA was successfully incorporated, and the membranes closed back up.

“At present, only a limited number of cell types can be genetically modified due to limitations in the technologies available for introducing DNA into cells,” says Garcia. “We have developed a microfluidic device that will facilitate genetic engineering of many different cell types. By mediating genetic engineering of novel cell types, this technology will contribute to the areas of drug discovery, regenerative medicine, cancer therapy, and DNA vaccination.”

This research was supported, in part, by DARPA and the National Science Foundation.

Publication: Paulo A. Garcia, et al., “Microfluidic Screening of Electric Fields for Electroporation,” Scientific Reports 6, Article number: 21238 (2016); doi:10.1038/srep21238

NASA to Build a Quieter Supersonic Passenger Jet

This is an artist’s concept of a possible Low Boom Flight Demonstration Quiet Supersonic Transport (QueSST) X-plane design. The award of a preliminary design contract is the first step towards the possible return of supersonic passenger travel – but this time quieter and more affordable.

NASA’s award of a contract for the preliminary design of a “low boom” flight demonstration aircraft brings the return of supersonic passenger air travel is one step closer to reality. This is the first in a series of ‘X-planes’ in NASA’s New Aviation Horizons initiative, introduced in the agency’s Fiscal Year 2017 budget.

NASA Administrator Charles Bolden announced the award at an event Monday at Ronald Reagan Washington National Airport in Arlington, Virginia.

“NASA is working hard to make flight greener, safer and quieter – all while developing aircraft that travel faster, and building an aviation system that operates more efficiently,” said Bolden. “To that end, it’s worth noting that it’s been almost 70 years since Chuck Yeager broke the sound barrier in the Bell X-1 as part of our predecessor agency’s high speed research. Now we’re continuing that supersonic X-plane legacy with this preliminary design award for a quieter supersonic jet with an aim toward passenger flight.”

NASA selected a team led by Lockheed Martin Aeronautics Company of Palmdale, California, to complete a preliminary design for Quiet Supersonic Technology (QueSST). The work will be conducted under a task order against the Basic and Applied Aerospace Research and Technology (BAART) contract at NASA’s Langley Research Center in Hampton, Virginia.

After conducting feasibility studies and working to better understand acceptable sound levels across the country, NASA’s Commercial Supersonic Technology Project asked industry teams to submit design concepts for a piloted test aircraft that can fly at supersonic speeds, creating a supersonic “heartbeat” — a soft thump rather than the disruptive boom currently associated with supersonic flight.

“Developing, building and flight testing a quiet supersonic X-plane is the next logical step in our path to enabling the industry’s decision to open supersonic travel for the flying public,” said Jaiwon Shin, associate administrator for NASA’s Aeronautics Research Mission.

Lockheed Martin will receive about $20 million over 17 months for QueSST preliminary design work. The Lockheed Martin team includes subcontractors GE Aviation of Cincinnati and Tri Models Inc. of Huntington Beach, California.

The company will develop baseline aircraft requirements and a preliminary aircraft design, with specifications, and provide supporting documentation for concept formulation and planning. This documentation would be used to prepare for the detailed design, building and testing of the QueSST jet. Performance of this preliminary design also must undergo analytical and wind tunnel validation.

In addition to design and building, this Low Boom Flight Demonstration (LBFD) phase of the project also will include validation of community response to the new, quieter supersonic design. The detailed design and building of the QueSST aircraft, conducted under the NASA Aeronautics Research Mission Directorate’s Integrated Aviation Systems Program, will fall under a future contract competition.

NASA’s 10-year New Aviation Horizons initiative has the ambitious goals of reducing fuel use, emissions and noise through innovations in aircraft design that departs from the conventional tube-and-wing aircraft shape.

The New Aviation Horizons X-planes will typically be about half-scale of a production aircraft and likely are to be piloted. Design-and-build will take several years with aircraft starting their flight campaign around 2020, depending on funding.

New Debugging Method Finds 23 Undetected Security Flaws in Popular Web Applications

A new debugging system found 23 previously undiagnosed security flaws in 50 popular Web applications, and it took no more than 64 seconds to analyze any given program.

By exploiting some peculiarities of the popular Web programming framework Ruby on Rails, MIT researchers have developed a system that can quickly comb through tens of thousands of lines of application code to find security flaws.

In tests on 50 popular Web applications written using Ruby on Rails, the system found 23 previously undiagnosed security flaws, and it took no more than 64 seconds to analyze any given program.

The researchers will present their results at the International Conference on Software Engineering, in May.

According to Daniel Jackson, professor in the Department of Electrical Engineering and Computer Science, the new system uses a technique called static analysis, which seeks to describe, in a very general way, how data flows through a program.

“The classic example of this is if you wanted to do an abstract analysis of a program that manipulates integers, you might divide the integers into the positive integers, the negative integers, and zero,” Jackson explains. The static analysis would then evaluate every operation in the program according to its effect on integers’ signs. Adding two positives yields a positive; adding two negatives yields a negative; multiplying two negatives yields a positive; and so on.

“The problem with this is that it can’t be completely accurate, because you lose information,” Jackson says. “If you add a positive and a negative integer, you don’t know whether the answer will be positive, negative, or zero. Most work on static analysis is focused on trying to make the analysis more scalable and accurate to overcome those sorts of problems.”

With Web applications, however, the cost of accuracy is prohibitively high, Jackson says. “The program under analysis is just huge,” he says. “Even if you wrote a small program, it sits atop a vast edifice of libraries and plug-ins and frameworks. So when you look at something like a Web application written in language like Ruby on Rails, if you try to do a conventional static analysis, you typically find yourself mired in this huge bog. And this makes it really infeasible in practice.”

That vast edifice of libraries, however, also gave Jackson and his former student Joseph Near, who graduated from MIT last spring and is now doing a postdoc at the University of California at Berkeley, a way to make to make static analysis of programs written in Ruby on Rails practical.

A library is a compendium of code that programmers tend to use over and over again. Rather than rewriting the same functions for each new program, a programmer can just import them from a library.

Ruby on Rails — or Rails, as it’s called for short — has the peculiarity of defining even its most basic operations in libraries. Every addition, every assignment of a particular value to a variable, imports code from a library.

Near rewrote those libraries so that the operations defined in them describe their own behavior in a logical language. That turns the Rails interpreter, which converts high-level Rails programs into machine-readable code, into a static-analysis tool. With Near’s libraries, running a Rails program through the interpreter produces a formal, line-by-line description of how the program handles data.

In his PhD work, Near used this general machinery to build three different debuggers for Ruby on Rails applications, each requiring different degrees of programmer involvement. The one described in the new paper, which the researchers call Space, evaluates a program’s data access procedures.

Near identified seven different ways in which Web applications typically control access to data. Some data are publicly available, some are available only to users who are currently logged in, some are private to individual users, some users — administrators — have access to select aspects of everyone’s data, and so on.

For each of these data-access patterns, Near developed a simple logical model that describes what operations a user can perform on what data, under what circumstances. From the descriptions generated by the hacked libraries, Space can automatically determine whether the program adheres to those models. If it doesn’t, there’s likely to be a security flaw.

Using Space does require someone with access to the application code to determine which program variables and functions correspond to which aspects of Near’s models. But that isn’t an onerous requirement: Near was able to map correspondences for all 50 of the applications he evaluated. And that mapping should be even easier for a programmer involved in an application’s development from the outset, rather than coming to it from the outside as Near did.

NASA to Begin Historic New Era of X-Plane Research

The Quiet Supersonic Technology, or QueSST, concept is in the preliminary design phase and on its way to being one of NASA’s first X-planes.

NASA’s aeronautical innovators are preparing to put in the sky an array of new experimental aircraft, each intended to carry on the legacy of demonstrating advanced technologies that will push back the frontiers of aviation.

History is about to repeat itself.

There have been periods of time during the past seven decades – some busier than others – when the nation’s best minds in aviation designed, built and flew a series of experimental airplanes to test the latest fanciful and practical ideas related to flight.

Short wings. Long wings. Delta-shaped wings. Forward swept wings. Scissor wings. Big tails. No tails. High speed. Low speed. Jet propulsion. Rocket propulsion. Even nuclear propulsion – although that technology was never actually flown.

Individually each of these pioneering aircraft has its own story of triumph and setback – even tragedy. Each was made by different companies and operated by a different mix of government organizations for a myriad of purposes.

Together they are known as X-planes – or X-vehicles, since some were missiles or spacecraft – and the very mention of them prompts a warm feeling and a touch of nostalgia among aviation enthusiasts worldwide.

“They certainly are all interesting in their own way. Each one of them has a unique place in aviation that helps them make their mark in history,” said Bill Barry, NASA’s chief historian. “And they are really cool.”

And now, NASA’s aeronautical innovators once again are preparing to put in the sky an array of new experimental aircraft, each intended to carry on the legacy of demonstrating advanced technologies that will push back the frontiers of aviation.

Goals include showcasing how airliners can burn half the fuel and generate 75 percent less pollution during each flight as compared to now, while also being much quieter than today’s jets – perhaps even when flying supersonic.

NASA’s renewed emphasis on X-planes is called, “New Aviation Horizons,” an initiative announced in February as part of the President’s budget for the fiscal year that begins Oct. 1, 2016. The plan is to design, build and fly the series of X-planes during the next 10 years as a means to accelerate the adoption of advanced green aviation technologies by industry.

“If we can build some of these X-planes and demonstrate some of these technologies, we expect that will make it much easier and faster for U.S. industry to pick them up and roll them out into the marketplace” said Ed Waggoner, NASA’s Integrated Aviation Systems Program director.

It’s something NASA has known how to do going way back to the days of its predecessor organization, the National Advisory Committee for Aeronautics (NACA), and the very first X-plane, fittingly called the X-1, a project the NACA worked on with the then newly formed U.S. Air Force.

Experiment Supersonic

Built by Bell Aircraft, the X-1 was the first plane to fly faster than the speed of sound, thus breaking the “sound barrier,” a popular but fundamentally misleading term that spoke more to the romantic notion of the challenges of high speed flight than an insurmountable physical wall in the sky.

As colorfully recounted in books and movies such as “The Right Stuff,” it was Oct. 14, 1947 when Air Force Capt. Chuck Yeager, dinged-up ribs and all, climbed into the bright orange Glamorous Glennis and flew the X-1 into its moment in history.

On that day the Antelope Valley, home to Edwards Air Force Base in California, reportedly echoed with its first sonic boom. But whether or not anyone there actually heard a sonic boom, thousands more echoed over the valley in the decades to come as supersonic flight over the military base became routine.

The X-1 also marked the first in what became a long line of experimental aircraft programs managed by the NACA (and later NASA), the Air Force, the Navy, and other government agencies.

The current list of X-planes that have been assigned numbers by the Air Force stands at 56, but that doesn’t mean there have been 56 X-planes.

Some had multiple models using the same number. And still more experimental vehicles were designed, built and flown but were never given X-numbers. And some X-vehicles received numbers but were never built.

The X-52 was skipped altogether because no one wanted to confuse that aircraft with the B-52 bomber.

Moreover, some X-planes weren’t experimental research planes at all, but rather prototypes of production aircraft or spacecraft, further muddying the waters over what is truly considered an X-plane and what isn’t, Barry said.

“They weren’t necessarily thinking there would be a series of X vehicles at the time of the X-1 because you wound up with several modifications, for example, including the A, the B models – which were very different vehicles in many ways,” Barry said.

Examples of experimental aircraft not called X-planes include some of NASA’s lifting bodies, and the Navy’s D-558-II Skyrocket, which pilot Scott Crossfield flew in 1953 to become the first airplane to travel twice the speed of sound, or Mach 2.

And it gets even more confusing: some of the early X-planes were called the XS-1, XS-2 and so on – the XS being short for “experiment, supersonic.” Although it’s not clearly documented, at some point XS became X, because XS sounded too much like “excess,” as in something you don’t need, Barry said.

There also have been airplanes like the XB-70, a supersonic jet demonstrator considered an X-plane in most circles, but officially not part of the 56 X-planes numbered to date by the Air Force.

“In any case, while the X-plane designation has become a very amorphous term through history, it’s a term that people today now identify as being a cutting edge research sort of plane,” Barry said.

Perhaps of all the X-planes NASA has been associated with, none was more cutting edge and became more famous – rivaling even the X-1 – than the X-15 rocket plane.

“The X-1 was certainly the most historic for being the first and for what it did for supersonic flight. But the X-15 was probably the most productive model of an X-plane,” Barry said.

Flown 199 times between 1959 and 1968, the winged X-15 reached beyond the edge of space at hypersonic speeds, trailblazing design concepts and operational procedures that directly contributed to the development of the Mercury, Gemini, and Apollo piloted spaceflight programs, as well as the space shuttle.

Another component of the X-15 success story beyond its contributions to high-speed aviation, Barry explained, is that it was a great example of collaboration between NASA, the rival military services of the Air Force and the Navy.

“This kind of major aeronautical research, which the X-15 represented, often is best done when several organizations contribute to a common goal,” Barry said. “We’re already seeing that as we prepare to fly this next wave of X-planes.”

Three-Legged Stool

But in this age of high-speed computers capable of generating sophisticated simulations, and with the availability of world-class wind tunnels to test high-fidelity models, why still the need to fly something like an X-plane?

“It’s a valid question,” Waggoner said.

The answer has to do with what Waggoner describes as the necessity of a “three legged stool” when it comes to aviation research.

One leg represents computational capabilities. This involves the high-speed super computers that can model the physics of air flowing over an object – be it a wing, a rudder or a full airplane – that exists only in the ones and zeros of a simulation.

A second leg represents experimental methods. This is where scientists put what is most often a scale model of an object or part of an object – be it a wing, a rudder or an airplane – in a wind tunnel to take measurements of air flowing over the object.

Measurements taken in the wind tunnel can help improve the computer model, and the computer model can help inform improvements to the airplane design, which can then be tested again in the wind tunnel.

“Each of these is great on its own and each helps the other, but each also can introduce errors into the inferences that might be made based on the results,” Waggoner said. “So the third leg of the stool is to go out and actually fly the design.”

Whether it’s flying an X-plane or a full-scale prototype of a new aircraft, the data recorded in actual flight can then be applied to validate and improve the computational and experimental methods used in developing the design in the first place.

“Now you’ve got three different ways to look at the same problem,” Waggoner said. “It’s only through doing all that together that we will ever get to the point where we’ve lowered the risk enough to completely trust what our numbers are telling us.”

“Que” the Supersonic Technology

Although it may not wind up being the first of the New Aviation Horizons X-planes to actually fly as part of the three-legged stool of research, design work already has begun on QueSST, short for Quiet Supersonic Technology

A preliminary design contract was awarded in February to a team led by Lockheed Martin. If schedule and congressional funding holds, this new supersonic X-plane could fly in the 2020 timeframe.

QueSST aims to fix something the X-1 first introduced to the flying world nearly 70 years ago – the publicly annoying loud sonic boom.

Recent research has shown it is possible for a supersonic airplane to be shaped in such a way that the shock waves it forms when flying faster than the speed of sound generate a sonic boom so quiet it hardly will be noticed by the public, if at all.

The resulting sonic “boom” has variously been described as like distant thunder, the sound of your neighbor forcefully shutting his car door outside while you are inside, or as the thump of a “supersonic” heartbeat.

“We know the concept is going to work, but now the best way to continue our research is to demonstrate the capability to the public with an X-plane,” said Peter Coen, NASA’s supersonic project manager.

It is hoped data gathered from flying QueSST will help the Federal Aviation Administration and its international counterparts establish noise-related regulations that will make it possible for commercial supersonic airliners to fly over land across country.

“Providing that data will be a key step in bringing accessible and affordable supersonic flight to the traveling public,” Coen said.

Meanwhile, other experimental aircraft also are under consideration, including those with novel shapes that break the mold of the traditional tube and wing airplane, and others that are propelled by hybrid electric power.

Exactly what these X-planes will look like, how they will be operated and where they will be flown all have yet to be precisely defined.

“We’re going to let the marketplace and the community help us inform our decisions on the direction we want to go,” Waggoner said. “But we’re really excited about all of the things we might demonstrate.”

Interestingly, despite these future test aircraft being referred to as X-planes, it is entirely possible only some of them will actually get an official X-plane number designation – or perhaps none of them will.

“We just don’t know yet,” Waggoner said. “That decision likely won’t take place for each aircraft until we’re about to award the construction contract.”

So whether NASA winds up calling these new planes by an X-number or a catchy acronym – or both – one thing is clear: NASA’s flight research program is on its way to creating a renaissance of an exciting era in aviation research.

Source: Jim Banke, NASA Aeronautics Research Mission Directorate