SpaceX, founded by Elon Musk, has landed it’s Falcon 9 rocket after launching it into space. The rocket is part of an attempt to develop a credible relaunch-able platform for sending satellites into space.
According to SpaceX’s youtube page:
“With this mission, SpaceX’s Falcon 9 rocket will deliver 11 satellites to low-Earth orbit for ORBCOMM, a leading global provider of Machine-to-Machine communication and Internet of Things solutions. The ORBCOMM launch is targeted for an evening launch from Space Launch Complex 40 at Cape Canaveral Air Force Station, Fla. If all goes as planned, the 11 satellites will be deployed approximately 20 minutes after liftoff, completing a 17-satellite, low Earth orbit constellation for ORBCOMM. This mission also marks SpaceX’s return-to-flight as well as its first attempt to land a first stage on land. The landing of the first stage is a secondary test objective.”
A new Stanford study found that renewable energy can make a major and increasingly cost-effective contribution to alleviating climate change.
BY TERRY NAGEL
Stanford energy experts have released a study that compares the experiences of three large economies in ramping up renewable energy deployment and concludes that renewables can make a major and increasingly cost-effective contribution to climate change mitigation.
The report from Stanford’s Steyer-Taylor Center for Energy Policy and Finance analyzes the experiences of Germany, California and Texas, the world’s fourth, eighth and 12th largest economies, respectively. It found, among other things, that Germany, which gets about half as much sunshine as California and Texas, nevertheless generates electricity from solar installations at a cost comparable to that of Texas and only slightly higher than in California.
The report was released in time for the United Nations Climate Change Conference that started this week, where international leaders are gathering to discuss strategies to deal with global warming, including massive scale-ups of renewable energy.
“As policymakers from around the world gather for the climate negotiations in Paris, our report draws on the experiences of three leaders in renewable-energy deployment to shed light on some of the most prominent and controversial themes in the global renewables debate,” said Dan Reicher, executive director of the Steyer-Taylor Center, which is a joint center between Stanford Law School and Stanford Graduate School of Business. Reicher also is interim president and chief executive officer of the American Council on Renewable Energy.
“Our findings suggest that renewable energy has entered the mainstream and is ready to play a leading role in mitigating global climate change,” said Felix Mormann, associate professor of law at the University of Miami, faculty fellow at the Steyer-Taylor Center and lead author of the report.
Other conclusions of the report, “A Tale of Three Markets: Comparing the Solar and Wind Deployment Experiences of California, Texas, and Germany,” include:
Germany’s success in deploying renewable energy at scale is due largely to favorable treatment of “soft cost” factors such as financing, permitting, installation and grid access. This approach has allowed the renewable energy policies of some countries to deliver up to four times the average deployment of other countries, despite offering only half the financial incentives.
Contrary to widespread concern, a higher share of renewables does not automatically translate to higher electricity bills for ratepayers. While Germany’s residential electric rates are two to three times those of California and Texas, this price differential is only partly due to Germany’s subsidies for renewables. The average German household’s electricity bill is, in fact, lower than in Texas and only slightly higher than in California, partly as a result of energy-efficiency efforts in German homes.
An increase in the share of intermittent solar and wind power need not jeopardize the stability of the electric grid. From 2006 to 2013, Germany tripled the amount of electricity generated from solar and wind to a market share of 26 percent, while managing to reduce average annual outage times for electricity customers in its grid from an already impressive 22 minutes to just 15 minutes. During that same period, California tripled the amount of electricity produced from solar and wind to a joint market share of 8 percent and reduced its outage times from more than 100 minutes to less than 90 minutes. However, Texas increased its outage times from 92 minutes to 128 minutes after ramping up its wind-generated electricity sixfold to a market share of 10 percent.
The study may inform the energy debate in the United States, where expanding the nation’s renewable energy infrastructure is a top priority of the Obama administration and the subject of debate among presidential candidates.
The current share of renewables in U.S. electricity generation is 14 percent – half that of Germany. Germany’s ambitious – and controversial – Energiewende (Energy Transition) initiative commits the country to meeting 80 percent of its electricity needs with renewables by 2050. In the United States, 29 states, including California and Texas, have set mandatory targets for renewable energy.
In California, Gov. Jerry Brown recently signed legislation committing the state to producing 50 percent of its electricity from renewables by 2030. Texas, the leading U.S. state for wind development, set a mandate of 10,000 megawatts of renewable energy capacity by 2025, but reached this target 15 years ahead of schedule and now generates over 10 percent of the state’s electricity from wind alone.
The Epoch of Reionisation (EoR) is the time in the early Universe when the first stars and galaxies formed and re-ionised the neutral hydrogen. Indirect information about the EoR has been obtained from the Cosmic Microwave Background and spectra of the distant quasars. However, the bulk of information about the physical parameters of the EoR is encoded in the 21cm line (1420 MHz) from neutral hydrogen redshifted into the low radio frequency range 200 – 50 MHz, for redshifts of 6 < z < 30.
The observational approaches range from large interferometer arrays to single antenna experiments. The latter, so-called global EoR experiments, spatially average the signal from the entire visible sky and try to identify the tiny signature of the EoR (of order 100 milliKelvin, which is a few orders of magnitude smaller than the Galactic foregrounds) in the sky-averaged spectrum. This extremely challenging precision requires very long observations (hundreds of hours) to achieve a sufficiently high signal-to-noise ratio. Moreover, ground-based global EoR experiments are affected by frequency-dependent effects (i.e. absorption and refraction) due to the propagation of radio-waves in the Earth’s ionosphere. The amplitude of these effects changes in time. There has therefore been an ongoing discussion in the literature on the importance of ionospheric effects and whether the global EoR signature can feasibly be detected from the ground.
The team of CAASTRO researches at Curtin University, led by Dr Marcin Sokolowski, used three months’ worth of 2014/2015 data collected with the BIGHORNS system with a conical log-spiral antenna deployed at the Murchison Radio-astronomy Observatory to study the impact of the ionosphere on its capability to detect the global EoR signal. Comparison of data collected on different days at the same sidereal time enabled the researchers to infer some properties of the ionosphere, such as electron temperature (Te≈470 K at night-time) and amplitude and variability of ionospheric absorption of radio waves. Furthermore, the data sample shows that the sky-averaged spectrum indeed varies in time due to fluctuations of these ionospheric properties. Nevertheless, the data analysis indicates that averaging over very long observations (several days or even several weeks) suppresses the noise and leads to an improved signal-to-noise ratio. Therefore, the ionospheric effects and fluctuations are not fundamental impediments that prevent ground-based instruments, such as BIGHORNS, from integrating down to the precision required for global EoR experiments, provided that the ionospheric contribution is properly accounted for in the data analysis.
System that replaces human intuition with algorithms outperforms 615 of 906 human teams.
By Larry Hardesty
Big-data analysis consists of searching for buried patterns that have some kind of predictive power. But choosing which “features” of the data to analyze usually requires some human intuition. In a database containing, say, the beginning and end dates of various sales promotions and weekly profits, the crucial data may not be the dates themselves but the spans between them, or not the total profits but the averages across those spans.
MIT researchers aim to take the human element out of big-data analysis, with a new system that not only searches for patterns but designs the feature set, too. To test the first prototype of their system, they enrolled it in three data science competitions, in which it competed against human teams to find predictive patterns in unfamiliar data sets. Of the 906 teams participating in the three competitions, the researchers’ “Data Science Machine” finished ahead of 615.
In two of the three competitions, the predictions made by the Data Science Machine were 94 percent and 96 percent as accurate as the winning submissions. In the third, the figure was a more modest 87 percent. But where the teams of humans typically labored over their prediction algorithms for months, the Data Science Machine took somewhere between two and 12 hours to produce each of its entries.
“We view the Data Science Machine as a natural complement to human intelligence,” says Max Kanter, whose MIT master’s thesis in computer science is the basis of the Data Science Machine. “There’s so much data out there to be analyzed. And right now it’s just sitting there not doing anything. So maybe we can come up with a solution that will at least get us started on it, at least get us moving.”
Between the lines
Kanter and his thesis advisor, Kalyan Veeramachaneni, a research scientist at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL), describe the Data Science Machine in a paper that Kanter will present next week at the IEEE International Conference on Data Science and Advanced Analytics.
Veeramachaneni co-leads the Anyscale Learning for All group at CSAIL, which applies machine-learning techniques to practical problems in big-data analysis, such as determining the power-generation capacity of wind-farm sites or predicting which students are at risk fordropping out of online courses.
“What we observed from our experience solving a number of data science problems for industry is that one of the very critical steps is called feature engineering,” Veeramachaneni says. “The first thing you have to do is identify what variables to extract from the database or compose, and for that, you have to come up with a lot of ideas.”
In predicting dropout, for instance, two crucial indicators proved to be how long before a deadline a student begins working on a problem set and how much time the student spends on the course website relative to his or her classmates. MIT’s online-learning platform MITxdoesn’t record either of those statistics, but it does collect data from which they can be inferred.
Kanter and Veeramachaneni use a couple of tricks to manufacture candidate features for data analyses. One is to exploit structural relationships inherent in database design. Databases typically store different types of data in different tables, indicating the correlations between them using numerical identifiers. The Data Science Machine tracks these correlations, using them as a cue to feature construction.
For instance, one table might list retail items and their costs; another might list items included in individual customers’ purchases. The Data Science Machine would begin by importing costs from the first table into the second. Then, taking its cue from the association of several different items in the second table with the same purchase number, it would execute a suite of operations to generate candidate features: total cost per order, average cost per order, minimum cost per order, and so on. As numerical identifiers proliferate across tables, the Data Science Machine layers operations on top of each other, finding minima of averages, averages of sums, and so on.
It also looks for so-called categorical data, which appear to be restricted to a limited range of values, such as days of the week or brand names. It then generates further feature candidates by dividing up existing features across categories.
Once it’s produced an array of candidates, it reduces their number by identifying those whose values seem to be correlated. Then it starts testing its reduced set of features on sample data, recombining them in different ways to optimize the accuracy of the predictions they yield.
“The Data Science Machine is one of those unbelievable projects where applying cutting-edge research to solve practical problems opens an entirely new way of looking at the problem,” says Margo Seltzer, a professor of computer science at Harvard University who was not involved in the work. “I think what they’ve done is going to become the standard quickly — very quickly.”
Researchers use engineered viruses to provide quantum-based enhancement of energy transport.
By David Chandler
CAMBRIDGE, Mass.–Nature has had billions of years to perfect photosynthesis, which directly or indirectly supports virtually all life on Earth. In that time, the process has achieved almost 100 percent efficiency in transporting the energy of sunlight from receptors to reaction centers where it can be harnessed — a performance vastly better than even the best solar cells.
One way plants achieve this efficiency is by making use of the exotic effects of quantum mechanics — effects sometimes known as “quantum weirdness.” These effects, which include the ability of a particle to exist in more than one place at a time, have now been used by engineers at MIT to achieve a significant efficiency boost in a light-harvesting system.
Surprisingly, the MIT researchers achieved this new approach to solar energy not with high-tech materials or microchips — but by using genetically engineered viruses.
This achievement in coupling quantum research and genetic manipulation, described this week in the journal Nature Materials, was the work of MIT professors Angela Belcher, an expert on engineering viruses to carry out energy-related tasks, and Seth Lloyd, an expert on quantum theory and its potential applications; research associate Heechul Park; and 14 collaborators at MIT and in Italy.
Lloyd, a professor of mechanical engineering, explains that in photosynthesis, a photon hits a receptor called a chromophore, which in turn produces an exciton — a quantum particle of energy. This exciton jumps from one chromophore to another until it reaches a reaction center, where that energy is harnessed to build the molecules that support life.
But the hopping pathway is random and inefficient unless it takes advantage of quantum effects that allow it, in effect, to take multiple pathways at once and select the best ones, behaving more like a wave than a particle.
This efficient movement of excitons has one key requirement: The chromophores have to be arranged just right, with exactly the right amount of space between them. This, Lloyd explains, is known as the “Quantum Goldilocks Effect.”
That’s where the virus comes in. By engineering a virus that Belcher has worked with for years, the team was able to get it to bond with multiple synthetic chromophores — or, in this case, organic dyes. The researchers were then able to produce many varieties of the virus, with slightly different spacings between those synthetic chromophores, and select the ones that performed best.
In the end, they were able to more than double excitons’ speed, increasing the distance they traveled before dissipating — a significant improvement in the efficiency of the process.
The project started from a chance meeting at a conference in Italy. Lloyd and Belcher, a professor of biological engineering, were reporting on different projects they had worked on, and began discussing the possibility of a project encompassing their very different expertise. Lloyd, whose work is mostly theoretical, pointed out that the viruses Belcher works with have the right length scales to potentially support quantum effects.
In 2008, Lloyd had published a paper demonstrating that photosynthetic organisms transmit light energy efficiently because of these quantum effects. When he saw Belcher’s report on her work with engineered viruses, he wondered if that might provide a way to artificially induce a similar effect, in an effort to approach nature’s efficiency.
“I had been talking about potential systems you could use to demonstrate this effect, and Angela said, ‘We’re already making those,’” Lloyd recalls. Eventually, after much analysis, “We came up with design principles to redesign how the virus is capturing light, and get it to this quantum regime.”
Within two weeks, Belcher’s team had created their first test version of the engineered virus. Many months of work then went into perfecting the receptors and the spacings.
Once the team engineered the viruses, they were able to use laser spectroscopy and dynamical modeling to watch the light-harvesting process in action, and to demonstrate that the new viruses were indeed making use of quantum coherence to enhance the transport of excitons.
“It was really fun,” Belcher says. “A group of us who spoke different [scientific] languages worked closely together, to both make this class of organisms, and analyze the data. That’s why I’m so excited by this.”
While this initial result is essentially a proof of concept rather than a practical system, it points the way toward an approach that could lead to inexpensive and efficient solar cells or light-driven catalysis, the team says. So far, the engineered viruses collect and transport energy from incoming light, but do not yet harness it to produce power (as in solar cells) or molecules (as in photosynthesis). But this could be done by adding a reaction center, where such processing takes place, to the end of the virus where the excitons end up.
The research was supported by the Italian energy company Eni through the MIT Energy Initiative. In addition to MIT postdocs Nimrod Heldman and Patrick Rebentrost, the team included researchers at the University of Florence, the University of Perugia, and Eni.
On Aug. 7, 1972, in the heart of the Apollo era, an enormous solar flare exploded from the sun’s atmosphere. Along with a gigantic burst of light in nearly all wavelengths, this event accelerated a wave of energetic particles. Mostly protons, with a few electrons and heavier elements mixed in, this wash of quick-moving particles would have been dangerous to anyone outside Earth’s protective magnetic bubble. Luckily, the Apollo 16 crew had returned to Earth just five months earlier, narrowly escaping this powerful event.
In the early days of human space flight, scientists were only just beginning to understand how events on the sun could affect space, and in turn how that radiation could affect humans and technology. Today, as a result of extensive space radiation research, we have a much better understanding of our space environment, its effects, and the best ways to protect astronauts—all crucial parts of NASA’s mission to send humans to Mars.
“The Martian” film highlights the radiation dangers that could occur on a round trip to Mars. While the mission in the film is fictional, NASA has already started working on the technology to enable an actual trip to Mars in the 2030s. In the film, the astronauts’ habitat on Mars shields them from radiation, and indeed, radiation shielding will be a crucial technology for the voyage. From better shielding to advanced biomedical countermeasures, NASA currently studies how to protect astronauts and electronics from radiation – efforts that will have to be incorporated into every aspect of Mars mission planning, from spacecraft and habitat design to spacewalk protocols.
“The space radiation environment will be a critical consideration for everything in the astronauts’ daily lives, both on the journeys between Earth and Mars and on the surface,” said Ruthan Lewis, an architect and engineer with the human spaceflight program at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “You’re constantly being bombarded by some amount of radiation.”
Radiation, at its most basic, is simply waves or sub-atomic particles that transports energy to another entity – whether it is an astronaut or spacecraft component. The main concern in space is particle radiation. Energetic particles can be dangerous to humans because they pass right through the skin, depositing energy and damaging cells or DNA along the way. This damage can mean an increased risk for cancer later in life or, at its worst, acute radiation sickness during the mission if the dose of energetic particles is large enough.
Fortunately for us, Earth’s natural protections block all but the most energetic of these particles from reaching the surface. A huge magnetic bubble, called the magnetosphere, which deflects the vast majority of these particles, protects our planet. And our atmosphere subsequently absorbs the majority of particles that do make it through this bubble. Importantly, since the International Space Station (ISS) is in low-Earth orbit within the magnetosphere, it also provides a large measure of protection for our astronauts.
“We have instruments that measure the radiation environment inside the ISS, where the crew are, and even outside the station,” said Kerry Lee, a scientist at NASA’s Johnson Space Center in Houston.
This ISS crew monitoring also includes tracking of the short-term and lifetime radiation doses for each astronaut to assess the risk for radiation-related diseases. Although NASA has conservative radiation limits greater than allowed radiation workers on Earth, the astronauts are able to stay well under NASA’s limit while living and working on the ISS, within Earth’s magnetosphere.
But a journey to Mars requires astronauts to move out much further, beyond the protection of Earth’s magnetic bubble.
“There’s a lot of good science to be done on Mars, but a trip to interplanetary space carries more radiation risk than working in low-Earth orbit,” said Jonathan Pellish, a space radiation engineer at Goddard.
A human mission to Mars means sending astronauts into interplanetary space for a minimum of a year, even with a very short stay on the Red Planet. Nearly all of that time, they will be outside the magnetosphere, exposed to the harsh radiation environment of space. Mars has no global magnetic field to deflect energetic particles, and its atmosphere is much thinner than Earth’s, so they’ll get only minimal protection even on the surface of Mars.
Throughout the entire trip, astronauts must be protected from two sources of radiation. The first comes from the sun, which regularly releases a steady stream of solar particles, as well as occasional larger bursts in the wake of giant explosions, such as solar flares and coronal mass ejections, on the sun. These energetic particles are almost all protons, and, though the sun releases an unfathomably large number of them, the proton energy is low enough that they can almost all be physically shielded by the structure of the spacecraft.
Since solar activity strongly contributes to the deep-space radiation environment, a better understanding of the sun’s modulation of this radiation environment will allow mission planners to make better decisions for a future Mars mission. NASA currently operates a fleet of spacecraft studying the sun and the space environment throughout the solar system. Observations from this area of research, known as heliophysics, help us better understand the origin of solar eruptions and what effects these events have on the overall space radiation environment.
“If we know precisely what’s going on, we don’t have to be as conservative with our estimates, which gives us more flexibility when planning the mission,” said Pellish.
The second source of energetic particles is harder to shield. These particles come from galactic cosmic rays, often known as GCRs. They’re particles accelerated to near the speed of light that shoot into our solar system from other stars in the Milky Way or even other galaxies. Like solar particles, galactic cosmic rays are mostly protons. However, some of them are heavier elements, ranging from helium up to the heaviest elements. These more energetic particles can knock apart atoms in the material they strike, such as in the astronaut, the metal walls of a spacecraft, habitat, or vehicle, causing sub-atomic particles to shower into the structure. This secondary radiation, as it is known, can reach a dangerous level.
There are two ways to shield from these higher-energy particles and their secondary radiation: use a lot more mass of traditional spacecraft materials, or use more efficient shielding materials.
The sheer volume of material surrounding a structure would absorb the energetic particles and their associated secondary particle radiation before they could reach the astronauts. However, using sheer bulk to protect astronauts would be prohibitively expensive, since more mass means more fuel required to launch.
Using materials that shield more efficiently would cut down on weight and cost, but finding the right material takes research and ingenuity. NASA is currently investigating a handful of possibilities that could be used in anything from the spacecraft to the Martian habitat to space suits.
“The best way to stop particle radiation is by running that energetic particle into something that’s a similar size,” said Pellish. “Otherwise, it can be like you’re bouncing a tricycle off a tractor-trailer.”
Because protons and neutrons are similar in size, one element blocks both extremely well—hydrogen, which most commonly exists as just a single proton and an electron. Conveniently, hydrogen is the most abundant element in the universe, and makes up substantial parts of some common compounds, such as water and plastics like polyethylene. Engineers could take advantage of already-required mass by processing the astronauts’ trash into plastic-filled tiles used to bolster radiation protection. Water, already required for the crew, could be stored strategically to create a kind of radiation storm shelter in the spacecraft or habitat. However, this strategy comes with some challenges—the crew would need to use the water and then replace it with recycled water from the advanced life support systems.
Polyethylene, the same plastic commonly found in water bottles and grocery bags, also has potential as a candidate for radiation shielding. It is very high in hydrogen and fairly cheap to produce—however, it’s not strong enough to build a large structure, especially a spacecraft, which goes through high heat and strong forces during launch. And adding polyethylene to a metal structure would add quite a bit of mass, meaning that more fuel would be required for launch.
“We’ve made progress on reducing and shielding against these energetic particles, but we’re still working on finding a material that is a good shield and can act as the primary structure of the spacecraft,” said Sheila Thibeault, a materials researcher at NASA’s Langley Research Center in Hampton, Virginia.
One material in development at NASA has the potential to do both jobs: Hydrogenated boron nitride nanotubes—known as hydrogenated BNNTs—are tiny, nanotubes made of carbon, boron, and nitrogen, with hydrogen interspersed throughout the empty spaces left in between the tubes. Boron is also an excellent absorber secondary neutrons, making hydrogenated BNNTs an ideal shielding material.
“This material is really strong—even at high heat—meaning that it’s great for structure,” said Thibeault.
Remarkably, researchers have successfully made yarn out of BNNTs, so it’s flexible enough to be woven into the fabric of space suits, providing astronauts with significant radiation protection even while they’re performing spacewalks in transit or out on the harsh Martian surface. Though hydrogenated BNNTs are still in development and testing, they have the potential to be one of our key structural and shielding materials in spacecraft, habitats, vehicles, and space suits that will be used on Mars.
Physical shields aren’t the only option for stopping particle radiation from reaching astronauts: Scientists are also exploring the possibility of building force fields. Force fields aren’t just the realm of science fiction: Just like Earth’s magnetic field protects us from energetic particles, a relatively small, localized electric or magnetic field would—if strong enough and in the right configuration—create a protective bubble around a spacecraft or habitat. Currently, these fields would take a prohibitive amount of power and structural material to create on a large scale, so more work is needed for them to be feasible.
The risk of health effects can also be reduced in operational ways, such as having a special area of the spacecraft or Mars habitat that could be a radiation storm shelter; preparing spacewalk and research protocols to minimize time outside the more heavily-shielded spacecraft or habitat; and ensuring that astronauts can quickly return indoors in the event of a radiation storm.
Radiation risk mitigation can also be approached from the human body level. Though far off, a medication that would counteract some or all of the health effects of radiation exposure would make it much easier to plan for a safe journey to Mars and back.
“Ultimately, the solution to radiation will have to be a combination of things,” said Pellish. “Some of the solutions are technology we have already, like hydrogen-rich materials, but some of it will necessarily be cutting edge concepts that we haven’t even thought of yet.”
CAMBRIDGE, Mass. – Comparing the genomes of different species — or different members of the same species — is the basis of a great deal of modern biology. DNA sequences that are conserved across species are likely to be functionally important, while variations between members of the same species can indicate different susceptibilities to disease.
The basic algorithm for determining how much two sequences of symbols have in common — the “edit distance” between them — is now more than 40 years old. And for more than 40 years, computer science researchers have been trying to improve upon it, without much success.
At the ACM Symposium on Theory of Computing (STOC) next week, MIT researchers will report that, in all likelihood, that’s because the algorithm is as good as it gets. If a widely held assumption about computational complexity is correct, then the problem of measuring the difference between two genomes — or texts, or speech samples, or anything else that can be represented as a string of symbols — can’t be solved more efficiently.
In a sense, that’s disappointing, since a computer running the existing algorithm would take 1,000 years to exhaustively compare two human genomes. But it also means that computer scientists can stop agonizing about whether they can do better.
“This edit distance is something that I’ve been trying to get better algorithms for since I was a graduate student, in the mid-’90s,” says Piotr Indyk, a professor of computer science and engineering at MIT and a co-author of the STOC paper. “I certainly spent lots of late nights on that — without any progress whatsoever. So at least now there’s a feeling of closure. The problem can be put to sleep.”
Moreover, Indyk says, even though the paper hasn’t officially been presented yet, it’s already spawned two follow-up papers, which apply its approach to related problems. “There is a technical aspect of this paper, a certain gadget construction, that turns out to be very useful for other purposes as well,” Indyk says.
Edit distance is the minimum number of edits — deletions, insertions, and substitutions — required to turn one string into another. The standard algorithm for determining edit distance, known as the Wagner-Fischer algorithm, assigns each symbol of one string to a column in a giant grid and each symbol of the other string to a row. Then, starting in the upper left-hand corner and flooding diagonally across the grid, it fills in each square with the number of edits required to turn the string ending with the corresponding column into the string ending with the corresponding row.
Computer scientists measure algorithmic efficiency as computation time relative to the number of elements the algorithm manipulates. Since the Wagner-Fischer algorithm has to fill in every square of its grid, its running time is proportional to the product of the lengths of the two strings it’s considering. Double the lengths of the strings, and the running time quadruples. In computer parlance, the algorithm runs in quadratic time.
That may not sound terribly efficient, but quadratic time is much better than exponential time, which means that running time is proportional to 2N, where N is the number of elements the algorithm manipulates. If on some machine a quadratic-time algorithm took, say, a hundredth of a second to process 100 elements, an exponential-time algorithm would take about 100 quintillion years.
Theoretical computer science is particularly concerned with a class of problems known as NP-complete. Most researchers believe that NP-complete problems take exponential time to solve, but no one’s been able to prove it. In their STOC paper, Indyk and his student Artūrs Bačkurs demonstrate that if it’s possible to solve the edit-distance problem in less-than-quadratic time, then it’s possible to solve an NP-complete problem in less-than-exponential time. Most researchers in the computational-complexity community will take that as strong evidence that no subquadratic solution to the edit-distance problem exists.
Can’t get no satisfaction
The core NP-complete problem is known as the “satisfiability problem”: Given a host of logical constraints, is it possible to satisfy them all? For instance, say you’re throwing a dinner party, and you’re trying to decide whom to invite. You may face a number of constraints: Either Alice or Bob will have to stay home with the kids, so they can’t both come; if you invite Cindy and Dave, you’ll have to invite the rest of the book club, or they’ll know they were excluded; Ellen will bring either her husband, Fred, or her lover, George, but not both; and so on. Is there an invitation list that meets all those constraints?
In Indyk and Bačkurs’ proof, they propose that, faced with a satisfiability problem, you split the variables into two groups of roughly equivalent size: Alice, Bob, and Cindy go into one, but Walt, Yvonne, and Zack go into the other. Then, for each group, you solve for all the pertinent constraints. This could be a massively complex calculation, but not nearly as complex as solving for the group as a whole. If, for instance, Alice has a restraining order out on Zack, it doesn’t matter, because they fall in separate subgroups: It’s a constraint that doesn’t have to be met.
At this point, the problem of reconciling the solutions for the two subgroups — factoring in constraints like Alice’s restraining order — becomes a version of the edit-distance problem. And if it were possible to solve the edit-distance problem in subquadratic time, it would be possible to solve the satisfiability problem in subexponential time.
An international team of scientists studying ultrafast physics have solved a mystery of quantum mechanics, and found that quantum tunneling is an instantaneous process.
The new theory could lead to faster and smaller electronic components, for which quantum tunneling is a significant factor. It will also lead to a better understanding of diverse areas such as electron microscopy, nuclear fusion and DNA mutations.
“Timescales this short have never been explored before. It’s an entirely new world,” said one of the international team, Professor Anatoli Kheifets, from The Australian National University (ANU).
“We have modelled the most delicate processes of nature very accurately.”
At very small scales quantum physics shows that particles such as electrons have wave-like properties – their exact position is not well defined. This means they can occasionally sneak through apparently impenetrable barriers, a phenomenon called quantum tunneling.
Quantum tunneling plays a role in a number of phenomena, such as nuclear fusion in the sun, scanning tunneling microscopy, and flash memory for computers. However, the leakage of particles also limits the miniaturisation of electronic components.
Professor Kheifets and Dr. Igor Ivanov, from the ANU Research School of Physics and Engineering, are members of a team which studied ultrafast experiments at the attosecond scale (10-18 seconds), a field that has developed in the last 15 years.
Until their work, a number of attosecond phenomena could not be adequately explained, such as the time delay when a photon ionised an atom.
“At that timescale the time an electron takes to quantum tunnel out of an atom was thought to be significant. But the mathematics says the time during tunneling is imaginary – a complex number – which we realised meant it must be an instantaneous process,” said Professor Kheifets.
“A very interesting paradox arises, because electron velocity during tunneling may become greater than the speed of light. However, this does not contradict the special theory of relativity, as the tunneling velocity is also imaginary” said Dr Ivanov, who recently took up a position at the Center for Relativistic Laser Science in Korea.
The team’s calculations, which were made using the Raijin supercomputer, revealed that the delay in photoionisation originates not from quantum tunneling but from the electric field of the nucleus attracting the escaping electron.
The results give an accurate calibration for future attosecond-scale research, said Professor Kheifets.
“It’s a good reference point for future experiments, such as studying proteins unfolding, or speeding up electrons in microchips,” he said.
The mission will be launched in 2020 and the landing is expected to be in 2021
By Syed Faisal ur Rahman
Recently UAE has announced details of its mission to Mars named ‘Al-Amal’. Amal is an Arabic word and name meaning ‘hope’ or ‘aspiration’ and the program truly represents the desires of many in Arab or even the whole Muslim world to contribute something big in humanity’s endeavors to explore the universe.
There was a time when Muslim and especially Arab astronomers used to contribute or even lead in many areas of science. From algebra to astronomy and medicine, we can find a lot of literature in history highlighting the contribution of Muslim scientists and engineers.
If you look at the star charts and astronomy catalogues, you will find many Arabic names of celestial objects and that’s because some of the early discoveries in astronomy were made by Muslim scientists in a time when Europe was going through dark ages.
Unfortunately, Muslims lost their way into darkness 7-8 centuries ago and the intellectual leadership was taken over by people who pushed us away from the path of learning physical sciences, reasoning and exploring the uncharted territories. According to the details provided by Mohammed Bin Rashid Space Center MBRSC, the mission will be launched in 2020 and the landing is expected to be in 2021. The mission will not only cover the entire Martian atmosphere for the first time but will also acquire critical data which will help in understanding climate and atmosphere on our own planet “Earth”.
The data from the probe will also help in learning more about Exo-planets and so will also help in finding prospects of life beyond Earth. Sheikh Mohammad of UAE rightly said “The Emirates Mars Mission will be a great contribution to human knowledge, a milestone for Arab civilization, and a real investment for future generations.” It is a good thing that after USA, Europe and Russia, Asian countries like India, China, Japan and now UAE are also excelling in space sector.
It will be good if Pakistan can also accelerate its space program and have put more focus on the civilian aspects of space technology. A right path for us will be to bring more scientists into our decision making structure and like India, make science and technology collaboration, especially in civilian or academic areas, as an important part of our foreign policy goals. Currently, our foreign policy goals mainly revolve around security, energy and aid related issues. We need to be pro-active if we want to be among the successful nations of the world.
In the end, I would like to wish best of luck to our brothers and sisters in UAE for their great initiative and hope that their mission will contribute greatly towards humanity’s goal of exploring worlds beyond our own.
Magnet-based setup may help detect the elusive mass of neutrinos.
MIT physicists have developed a new tabletop particle detector that is able to identify single electrons in a radioactive gas.
As the gas decays and gives off electrons, the detector uses a magnet to trap them in a magnetic bottle. A radio antenna then picks up very weak signals emitted by the electrons, which can be used to map the electrons’ precise activity over several milliseconds.
The team worked with researchers at Pacific Northwest National Laboratory, the University of Washington, the University of California at Santa Barbara (UCSB), and elsewhere to record the activity of more than 100,000 individual electrons in krypton gas.
The majority of electrons observed behaved in a characteristic pattern: As the radioactive krypton gas decays, it emits electrons that vibrate at a baseline frequency before petering out; this frequency spikes again whenever an electron hits an atom of radioactive gas. As an electron ping-pongs against multiple atoms in the detector, its energy appears to jump in a step-like pattern.
“We can literally image the frequency of the electron, and we see this electron suddenly pop into our radio antenna,” says Joe Formaggio, an associate professor of physics at MIT. “Over time, the frequency changes, and actually chirps up. So these electrons are chirping in radio waves.”
Formaggio says the group’s results, published in Physical Review Letters, are a big step toward a more elusive goal: measuring the mass of a neutrino.
A ghostly particle
Neutrinos are among the more mysterious elementary particles in the universe: Billions of them pass through every cell of our bodies each second, and yet these ghostly particles are incredibly difficult to detect, as they don’t appear to interact with ordinary matter. Scientists have set theoretical limits on neutrino mass, but researchers have yet to precisely detect it.
“We have [the mass] cornered, but haven’t measured it yet,” Formaggio says. “The name of the game is to measure the energy of an electron — that’s your signature that tells you about the neutrino.”
As Formaggio explains it, when a radioactive atom such as tritium decays, it turns into an isotope of helium and, in the process, also releases an electron and a neutrino. The energy of all particles released adds up to the original energy of the parent neutron. Measuring the energy of the electron, therefore, can illuminate the energy — and consequently, the mass — of the neutrino.
Scientists agree that tritium, a radioactive isotope of hydrogen, is key to obtaining a precise measurement: As a gas, tritium decays at such a rate that scientists can relatively easily observe its electron byproducts.
Researchers in Karlsruhe, Germany, hope to measure electrons in tritium using a massive spectrometer as part of an experiment named KATRIN (Karlsruhe Tritium Neutrino Experiment). Electrons, produced from the decay of tritium, pass through the spectrometer, which filters them according to their different energy levels. The experiment, which is just getting under way, may obtain measurements of single electrons, but at a cost.
“In KATRIN, the electrons are detected in a silicon detector, which means the electrons smash into the crystal, and a lot of random things happen, essentially destroying the electrons,” says Daniel Furse, a graduate student in physics, and a co-author on the paper. “We still want to measure the energy of electrons, but we do it in a nondestructive way.”
The group’s setup has an additional advantage: size. The detector essentially fits on a tabletop, and the space in which electrons are detected is smaller than a postage stamp. In contrast, KATRIN’s spectrometer, when delivered to Karlsruhe, barely fit through the city’s streets.
Furse and Formaggio’s detector — an experiment called “Project 8” — is based on a decades-old phenomenon known as cyclotron radiation, in which charged particles such as electrons emit radio waves in a magnetic field. It turns out electrons emit this radiation at a frequency similar to that of military radio communications.
“It’s the same frequency that the military uses — 26 gigahertz,” Formaggio says. “And it turns out the baseline frequency changes very slightly if the electron has energy. So we said, ‘Why not look at the radiation [electrons] emit directly?’”
Formaggio and former postdoc Benjamin Monreal, now an assistant professor of physics at UCSB, reasoned that if they could tune into this baseline frequency, they could catch electrons as they shot out of a decaying radioactive gas, and measure their energy in a magnetic field.
“If you could measure the frequency of this radio signal, you could measure the energy potentially much more accurately than you can with any other method,” Furse says. “The problem is, you’re looking at this really weak signal over a very short amount of time, and it’s tough to see, which is why no one has ever done it before.”
It took five years of fits and starts before the group was finally able to build an accurate detector. Once the researchers turned the detector on, they were able to record individual electrons within the first 100 milliseconds of the experiment — although the analysis took a bit longer.
“Our software was so slow at processing things that we could tell funny things were happening because, all of a sudden, our file size became larger, as these things started appearing,” Formaggio recalls.
He says the precision of the measurements obtained so far in krypton gas has encouraged the team to move on to tritium — a goal Formaggio says may be attainable in the next year or two — and pave a path toward measuring the mass of the neutrino.
Steven Elliott, a technical staff member at Los Alamos National Laboratory, says the group’s new detector “represents a very significant result.” In order to use the detector to measure the mass of a neutrino, Elliott adds, the group will have to make multiple improvements, including developing a bigger cell to contain a larger amount of tritium.
“This was the first step, albeit a very important step, along the way to building a next-generation experiment,” says Elliott, who did not contribute to the research. “As a result, the neutrino community is very impressed with the concept and execution of this experiment.”
This research was funded in part by the Department of Energy and the National Science Foundation.