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Temporary gains - While the U.S. economy struggles, one form of employment is on the rise: Temporary jobs. In December, the country lost 85,000 jobs overall, but added 47,000 temp positions, according to the Bureau of Labor Statistics. Increasingly America relies on these contingent employees — or “disposable workers,” as BusinessWeek put it in a recent cover story.
 
For many workers, these jobs are stop-gap measures, but social scientists have long floated another idea: That temp positions help low-skill workers to acquire experience and eventually join the permanent workforce in better long-term jobs. Now, a new working paper co-authored by MIT economist David Autor throws cold water on that notion. Not only do many temp employees struggle to find long-term or “direct-hire” work, the study says, but holding a temp job generally lowers a worker’s employment and income prospects over time.
 
“Temp jobs have some initial positive impact,” says Autor. “But not only do they end quickly, they tend to displace what a person would have done instead, either taking a direct-hire job or engaging in the kind of search that could lead to a direct-hire job.”
 
Autor and his co-author, Susan Houseman of the W.E. Upjohn Institute for Employment Research in Kalamazoo, Mich., came to this conclusion after examining a welfare-to-work program in Detroit called Work First. The program offers some job-seeking training and attempts to put people in either temporary or long-term positions. Using Work First data for over 37,000 cases from 1999 to 2003, combined with state employment information, Autor and Houseman examined how workers fared in the two years before and after they participated in Work First.   
 
Their findings showed that workers placed into direct-hire jobs increased their earnings by about $2,000 per year, compared to their earnings before trying the Work First program. By contrast, workers initially placed into temp jobs saw their earnings lowered by about $1,000 per year, compared to their previous average income.
 
The study, “Do Temporary-Help Jobs Improve Labor Market Outcomes for Low-Skilled Workers? Evidence from ‘Work First,’” (PDF) which will be published in the American Economic Journal: Applied Economics, has clear policy implications. “Work First as a model is not a bad idea, but I think these programs should be more focused on getting people into direct-hire positions,” says Autor. “In terms of what state agencies should be spending their money on, it should not be temporary-help placements, at least for this part of the population.”

Workplace experiment
 
The study’s surprising results have already gained notice among labor researchers, who have often assumed a solid correlation between temp employment and better job prospects. “I would have expected them to find a positive result, but they didn’t,” says Mary Corcoran, a professor of political science, public policy, social work, and women's studies at the University of Michigan, who is conducting her own study of temporary employment in Michigan. Corcoran thinks the Autor-Houseman paper is “one of the best pieces out there on the effects of using temp agencies, because it’s more like an experiment than other studies.”

Indeed, the study uses a key feature of Work First to create what economists call a “quasi-experiment” — research that uses a random element found in data to duplicate the structure of a laboratory trial. In general, it is hard to separate the employment status of people from their skills and motivation; temp workers might have temp jobs because they are less predisposed to have long-term jobs. But in Detroit, Work First arbitrarily rotated job-seekers through different job-placement contractors which themselves had varying tendencies in terms of placing workers in temp positions or long-term jobs. Because each group of job-hunters assigned to each job placement contractor was essentially identical, Autor and Houseman could rule out differences in workers as the primary explanation of differences in workers’ employment trajectories; in this case, even some workers who were highly motivated to find full-time work started out in temp jobs.
 
To be sure, a valid question is how broadly these findings apply, given Michigan’s acute economic struggles. However, as Autor notes, the study’s data starts when the state economy was growing in the late 1990s, then continues through the slump of the early 2000s and the subsequent rebound; it ends before the current recession began.
 
Moreover, Autor and Houseman believe there is no regional bias in the study because the overall figures for people finding both temporary and long-term jobs through Work First in Detroit closely match the equivalent data for other regions, including North Carolina and Missouri. The researchers also say temp workers fared no differently in the production-line jobs associated with Michigan than in the kinds of clerical jobs found everywhere.
 
“I don’t think it’s anything specific about Detroit, or the type of work in which temps are placed,” says Autor. “In terms of the external validity of the conclusions, my main concern is how this relates to a more skilled population. There we don’t have a clear answer yet.” It is possible that temp jobs for people with college degrees do lead to greater opportunities and earnings — something the researchers would study if the right data set presents itself, Autor says. Given the way America’s temporary workforce keeps growing, there may be plenty of those numbers for Autor to scrutinize in the future.



Reporter’s Notebook: Workshop seeks answers to Haiti crisis - Guided by the principle that the first step in solving a problem is to define it, members of the MIT community held back-to-back conference calls Wednesday afternoon with experts from around the United States to better understand both the scope of the earthquake catastrophe in Haiti and how their talents and knowledge could best be put to use in relief and reconstruction efforts.

Sponsored by the MIT Media Lab and the Center for Future Civic Media, and open to the Institute community and the broader public, the discussion was part of a four-day Independent Activities Period workshop that began Tuesday and is aimed at developing innovative technologies to alleviate the crisis caused by the Jan. 12 earthquake that is estimated to have killed more than 200,000 people. The workshop is being held from 2 to 7 p.m. through Friday in E15-363.

“Our interest is that MIT is better engaged in responding to the earthquake and relief effort in a way that is more empowering for the Haitian people,” said Chris Csikszentmihalyi, director of CFCM, who is running the IAP workshop with Dale Joachim, a Media Lab visiting scientist. Although the workshop will analyze the current situation in Haiti, including what technologies might be appropriate to implement in the short term, the goal of the class is to look at the transition period following the earthquake as Haitians try to rebuild their government, infrastructure and society.

“The representation we see of Haiti is done by the international media and journalists,” Csikszentmihalyi said. “Dale’s idea is to get Haitian voices out so we understand their stake and opinion in the recovery.” How they attempt to do that remains a work in progress that will extend beyond Friday when the group has a better sense of which ideas may actually be developed into seeding projects.

Until then, workshop participants are gathering and processing as much information as possible. On Wednesday, the group of about 15 professors, graduate students and volunteers spoke to Kate Stanton, of the U.S. State Department’s Office of Innovation, about her involvement in efforts to establish a telephone number that people could text to donate money to the Red Cross; Tim Schwartz, a San Diego-based artist who helped build an online database to help Haitians locate their missing relatives; and Robert Munro, a content management specialist in San Francisco who is coordinating volunteers around the world to translate and process text messages requesting specific relief for survivors in Haiti.

The IAP group asked each source what technological assistance his or her organization needs. Stanton identified a technological need for fundraising operations that are continuous, effective and transparent. Schwartz said the challenge for his group was communicating the information gathered by the database to people back in Haiti. He also mentioned developing part of the online application that will catalog names, and possibly pictures, of the deceased.

In addition to seeking information outside MIT, the workshop is tapping the wealth of knowledge available at the Institute. Erica James, an associate professor of anthropology, whose research includes the psychosocial experience of Haitian torture survivors targeted during a coup period in the 90s, spoke to the group about her work with Haitian trauma victims, and her fears about what could go wrong in trying to shift the population away from the earthquake zone.

“The key thing is coordination of relief,” James answered when a student asked her to propose a positive model for the Haitian recovery.

The attempt to improve and sustain that coordination by a part of the MIT community is being heard and recognized. “I’m grateful for your reaching out and being a force and a clear voice in a sea of noise,” Stanton told the workshop participants.

For more information about the workshop, please visit http://krikkrak.media.mit.edu/IAP2010.



Extreme makeovers in space - Astronomers have worried about the impact that asteroids could have on Earth ever since a theory was proposed in the 1980s that a giant asteroid likely caused the extinction of the dinosaurs 65 million years ago. New research by MIT Professor of Planetary Science Richard Binzel examines the opposite scenario: that Earth has considerable influence on asteroids — and from a distance much larger than previously thought.

By analyzing telescopic measurements of near-Earth asteroids (NEAs), or asteroids that come within 30 million miles of Earth, Binzel has determined that if an NEA travels within a certain range of Earth, roughly one-quarter of the distance between Earth and the moon, it can experience a “seismic shake” strong enough to bring fresh material called “regolith” to its surface. These rarely seen “fresh asteroids” have long interested astronomers because their spectral fingerprints, or how they reflect different wavelengths of light, match 80 percent of all meteorites that fall to Earth, according to a paper by Binzel appearing in the Jan. 21 issue of Nature. The paper suggests that Earth’s gravitational pull and tidal forces create these seismic tremors.

By hypothesizing about the cause of the fresh surfaces of some NEAs, Binzel and his colleagues have tried to solve a decades-old conundrum about why these fresh asteroids, known as Q-types, are not seen in the main asteroid belt, which is between Mars and Jupiter. They believe this is because the fresh surfaces are the result of a close encounter with Earth, which obviously wouldn’t be the case with an object in the main asteroid belt. Only those few objects that have ventured recently inside the moon’s orbital distance, about one-quarter of the distance between Earth and the moon, and have experienced a “fresh shake” match freshly fallen meteorites measured in the laboratory, Binzel says.

Clark Chapman, a planetary scientist at the Southwest Research Institute in Colorado, believes Binzel’s work is part of a “revolution in asteroid science” over the past five years that considers the possibility that something other than collisions can affect asteroid surfaces. “For decades, it was thought that the sizes, shapes and spin period of asteroids were all caused by collisions between asteroids, and that this could explain everything that has happened to them in the past 4 billion years,” he says. “This work is one more perspective in this revolution of thinking about these very weird rubble piles, and what’s affecting them.”

The ordinary chondrite problem

Although it is believed that meteorites come from asteroids, astronomers and meteorite scientists have struggled for 30 years to figure out why asteroids matching the majority of all meteorites that fall to the Earth, known as ordinary chondrites, could not be found in space. The discrepancy emerged when scientists began measuring the spectral fingerprints of meteorites in the lab to determine their mineral constituents based on how they reflect light of different wavelengths. Around the same time, astronomers began using telescopes to measure how asteroids reflect light of varying wavelengths. Because meteorites are thought to originate from asteroids, it was expected that the spectral fingerprints would match.

Instead, scientists found asteroids with spectral fingerprints that were muted and had a reddish tint. These asteroids, known as S-types, appear “sunburned,” according to Binzel, due to the space weathering process of solar wind that physically damages their mineral structure.

It wasn’t until last year that astronomers could estimate the exposure time of the space weathering process when co-author Pierre Vernazza determined that it takes solar wind a million years to redden an asteroid. “In astronomy, this is nothing, it’s like yesterday,” Binzel explains. Vernazza’s findings, he notes, suggested that astronomers should never see fresh asteroids, since the weathering process is so “brief.”

And yet they’ve been observing Q-types among NEAs for 25 years — suggesting there is something about their proximity to Earth that freshens their surface at a rate that is faster than the space weathering process. That something, Binzel believes, is the seismic shake-up caused by Earth’s tidal stress and gravitational pull.

Making the connection

For a decade, Binzel’s team has used a large NASA telescope in Hawaii to collect information on NEAs, including a huge amount of spectral fingerprint data. Using this data, as well as estimates based on numerical calculations, Binzel’s team examined where a sample of 95 NEAs had been during the past 500,000 years, tracing their orbits to see how close they’d come to Earth. They discovered that 75 NEAs in the sample had passed well inside the moon’s distance within the past 500,000 years, including all 20 Q-types in the sample.

Using a calculation known as Minimum Orbit Intersection Distance (MOID), Binzel next determined that an asteroid traveling within a distance equal to 16 times the Earth’s radius (about one-quarter of the distance to the moon) appears to experience vibrations strong enough to create fresh surface material. He reached that figure based on his finding that one-quarter of NEAs are fresh, as well as two known facts — that space weathering can happen in less than one million years, and that about one-quarter of all NEAs come within 16 Earth radii in one million years.

Before now, people thought an asteroid had to come within one to two Earth radii, a distance known as the Roche limit, to undergo significant physical change.

Shaking up asteroid seismology

Many details about the shaking process remain unknown, including what exactly it is about Earth that shakes the asteroids, and why this happens from a distance as far away as 16 Earth radii. What is certain is that the conditions depend on complex factors such as the velocity and duration of the encounter; the asteroid’s shape, internal structure, surface gravity and rotation rate; and the nature of the preexisting regolith. “The exact trigger distance depends on all those seismology factors that are the totally new and interesting area for cutting edge research,” Binzel says.

Further research might include computer simulations, ground observations and sending probes to look at the surfaces of asteroids. “We don’t know yet what more than a handful of these objects look like,” Chapman says of the Q-types. He predicts theoreticians will put together models about the behavior of these asteroids to help scientists better understand Binzel’s research.

Binzel’s next steps will be to try to discover counterexamples to his findings or additional examples to support it. He may also investigate whether other planets like Venus or Mars affect asteroids that venture close to them.

His research will be tested in 2029 when the asteroid Apophis is expected to travel within a distance equal to six times the Earth’s radius. Anyone with binoculars in Europe or Africa will be able to conduct a simple test to see whether the close encounter makes the surface of the weathered asteroid appear less red. “It should certainly be changed in this fashion if the Binzel observation is interpreted correctly,” Chapman says.




Explained: Gallager codes - This is the second part of a two-part Explained about information theory. The first part, on the Shannon limit, appeared on Tuesday.

In the 1948 paper that created the field of information theory, MIT grad (and future professor) Claude Shannon threw down the gauntlet to future generations of researchers. In those predigital days, communications channels — such as phone lines or radio bands — were particularly susceptible to the electrical or electromagnetic disruptions known as “noise.” Shannon proved the counterintuitive result that no matter how noisy a channel, information could be sent over it error free. All you needed was a way to add enough redundancy to the information so that errors could be corrected. He also demonstrated that there was a hard limit on how efficient those error-correcting codes could be — a minimum amount of extra information that would guarantee near-zero error. Since longer codes take longer to send, a minimum code length implied a maximum transmission rate — the Shannon limit. Finally, Shannon proved that codes approaching that limit must exist. But he didn’t show how to find them.

For the next 45 years, researchers sought those codes. Along the way, there were improvements of the kind that helped increase modem speeds from 9.6 kilobits per second to 14.4 kilobits per second in the early 1980s. But according to Muriel Médard, a professor of computer science and electrical engineering at MIT, proposed codes tended to run up against a limit called the computational cutoff rate. That rate varied according to the transmission power and noise characteristics of a channel, but in practical communications systems, it might be only halfway to the Shannon limit.

Then, in 1993, at the Institute of Electrical and Electronics Engineers’ International Communications Conference, Alain Glavieux and Claude Berrou of the École Nationale Supérieure des Télécommunications de Bretagne presented a new set of codes that they claimed came very close to the Shannon limit. “People almost laughed them out of the room,” Médard says, “especially because they were not coming from the coding side; they were coming from the electronics side.” The researchers had developed their codes — dubbed “turbo codes” — largely through trial and error and had no elegant formal explanation for why they worked so well. Nonetheless, subsequent investigation quickly confirmed their results.

Turbo codes are so-called iterative codes, which means that the decoder makes a series of guesses about what the encoded message is supposed to be. Each successive guess is fed back into the decoder, and the result is a more refined guess. Ideally, repeating the process over and over will get the error rate as low as you want.

The startling performance of turbo codes mobilized researchers to try to explain why they worked so well. Within a few years, investigation of iterative coding schemes had yielded a perhaps even more surprising result: a set of codes that worked at least as well as turbo codes had been around since 1960, when they were introduced in the MIT doctoral thesis of Robert Gallager.

Quiet revolution

The power of Gallager’s codes went unappreciated for so long because the decoding process he proposed was simply too complicated for 1960s-era technology. Which is ironic, since simplifying the decoding process was his motive in creating the codes. “The crux of the whole thing was, How do you design a good decoding algorithm?” says Gallager, who taught at MIT from 1960 to 2001 and still supervises graduate students as a professor emeritus. “And then given that idea for how to do that, how do you generate codes that you can actually decode in this way?” At the time, however, research on new coding schemes frequently depended on statistical claims about the performance of hypothetical ideal decoders. For researchers like Gallager, who were trying to develop codes that approached the Shannon limit, specifying a concrete decoding algorithm at all was already an uncommon step in the direction of practical deployment.

Gallager’s codes use so-called parity bits — extra bits that contain information about message bits. One parity bit might indicate, say, whether the sum of message bits 1, 2, and 4 is even or odd; the next parity bit might do the same for message bits 3, 4, and 6; and so on, through successive triplets of bits. Reliable information about any two bits in a triplet conveys reliable information about the third. “Iterative techniques involve making a first guess of what a received bit might be and giving it a weight according to how reliable it was,” says David Forney, an adjunct professor in MIT’s Laboratory for Information and Decision Systems. “Then maybe you get more information about it because it’s involved in parity checks with other bits, and so that gives you an improved estimate of its reliability — might go the same way, might go the opposite way — and through a series of computations like this, hopefully the thing will converge to where all the bits are known highly reliably.” Problems arise, Forney says, “if you begin to confuse yourself because you’re just feeding back reliabilities that you’ve already used in the same computation, so you get a false positive increase in reliability. It’s like a rumor mill. If you keep hearing the same rumor from the same people again and again, you can all begin to think it’s true, when it’s really just a closed circuit.” The trick to the design of Gallager’s codes, Forney says, was to minimize the likelihood of such closed loops. “It should take a long time for the telephone chain to go all around the world before it gets back to you again,” he says.

To date, Gallager’s codes have enabled the closest approaches to the Shannon limit for a given communications channel — closer even than turbo codes. They’ve been integrated into standards for wireless data transmissions, and computer chips dedicated to decoding Gallager’s codes can be found in commercial cell phones. During their long eclipse, did Gallager have any inkling of how good they were?

“I had a little bit of an inkling, but I also had a suspicion that they well might not be,” Gallager says. “And I spent a long time trying to resolve whether they were or weren’t.” His conclusion was equivocal: “What I showed is that with different classes of these codes, you could achieve positive [transmission] rates. As you change the class to make it more complicated, the rate would continue to increase. If you made it complicated enough, you could reach capacity — but you would probably never decode it. What’s happened since is that people have found ways of somewhat streamlining the way you choose the codes to make them better codes.”




3 Questions: Lawrence Vale on rebuilding Haiti - The human and economic toll of this month's earthquake in Haiti has yet to be fully measured, but it is clear that the country faces an enormous rebuilding task. Lawrence Vale, MIT's Ford Professor of Urban Design and Planning, is an expert on the reconstruction of cities devastated by natural disasters or warfare; a 2005 book he co-edited on the subject, The Resilient City, explores how and why modern societies choose to rebuild ruined metropolises. MIT News asked Vale about Haiti's long-term prospects for renewal.

Q. In The Resilient City, you write that throughout history, devastated cities have almost always "risen again like the mythic phoenix" and "are among humankind's most durable artifacts." What are the crucial first steps that could allow Haiti, and the Port-au-Prince area, to rebuild?

A. Before 1800, it was more common for cities to be destroyed and abandoned, leaving the world with "lost cities" later to be recovered only as touristic ruins. In the last 200 years or so, however, it has been rare for governments to let their cities die, even after massive annihilation from war — think of Hiroshima or Warsaw in WW II. Similarly, cities tend to be rebuilt in the same location even after massive natural disasters — half a million people may well have died in Tangshan, China from an earthquake in 1976, yet that city regained its population numbers within a decade. More generally, the combination of nation-states, insurance industries and global philanthropy have all made "caring-at-a-distance" much more prevalent. Cities are no longer left on their own.

That said, the thing we loosely term "rebuilding" is at least a three-part challenge.  There is physical rebuilding, both in terms of the necessities of daily life such as basic shelter and in terms of more symbolic structures — civic institutions such as a destroyed cathedral or palace. Then there is socio-economic rebuilding, an especially difficult challenge in a place like Haiti where poverty was so broad and deep even before this particular disaster struck. Finally, there is the challenge of emotional rebuilding, the need to cope with great personal losses. Each of these entails a form of resilience. 

For Haitians, resilience may well be substantially undergirded by faith, and the restoration of the Cathedral and other houses of worship will surely be regarded as key symbolic milestones signaling recovery. The leaders of most societies have also chosen to use disasters as opportunities to "build back better," and I hope that it will become possible to enforce safer building practices in Haiti.

Q. And yet you note that an exception to the universality of rebuilding is from the Caribbean, as well: When St. Pierre, Martinique, was buried by a volcano in 1902, it was not reconstructed. Are there any comparable cases of equally small, poor countries like Haiti rebuilding major cities?

A. There is another, more recent, Caribbean example. Between 1995 and 1997, volcanic activity rendered Plymouth, the capital of Montserrat, completely uninhabitable, and forced construction of a new city on a less vulnerable part of the island. So, that's an example of rebuilding, even though it has entailed relocation. But Port-au-Prince is several hundred times larger than Plymouth, so there are limits to the comparison. Perhaps the near-continual rebuilding that occurs in Bangladesh after floods and storms is a better parallel, since this is a place that regularly endures large losses of life, and continues to rebuild at high densities. If so, the comparison is not an auspicious one, since vulnerabilities are still increasing.

Q. Rebuilding a devastated city often has a political dimension, and serves an expression of national identity — but Haiti has had political chaos for years, and weak governmental institutions. How do you think Haiti's past, and its lack of strong civic institutions, will affect the type of reconstruction that occurs in the future?

A. It is hard to imagine a place with more factors working against it than Haiti, especially given that its political landscape has been literally destroyed. A lot of the more storied recoveries from major disasters have been in places that were otherwise poised for significant economic growth when catastrophe struck — think of Chicago in 1871 or San Francisco in 1906. Other places have gained from an influx of aid from the non-devastated parts of the country, a luxury that Haitians do not have. Disasters — even those we call "natural disasters" — always reflect poorly on governments, and often increase the power of social movements in support of alternative political leadership. The politics of redevelopment in Haiti will reveal the priorities of the government (and also the priorities of global aid organizations), and this can easily spark enhanced unrest among citizens, leading to further destabilization. Ultimately, the physical rebuilding of Port-au-Prince and its environments may prove to be the least of Haiti's problems. At the same time, I can only hope that the remarkable emotional resilience of the Haitian people will once again prevail.



Picture-driven computing - Until the 1980s, using a computer program meant memorizing a lot of commands and typing them in a line at a time, only to get lines of text back. The graphical user interface, or GUI, changed that. By representing programs, program functions, and data as two-dimensional images — like icons, buttons and windows — the GUI made intuitive and spatial what had been memory intensive and laborious.

But while the GUI made things easier for computer users, it didn’t make them any easier for computer programmers. Underlying GUI components is a lot of computer code, and usually, building or customizing a program, or getting different programs to work together, still means manipulating that code. Researchers in MIT’s Computer Science and Artificial Intelligence Lab hope to change that, with a system that allows people to write programs using screen shots of GUIs. Ultimately, the system could allow casual computer users to create their own programs without having to master a programming language.

The system, designed by associate professor Rob Miller, grad student Tsung-Hsiang Chang, and the University of Maryland’s Tom Yeh, is called Sikuli, which means “God’s eye” in the language of Mexico’s Huichol Indians. In a paper that won the best-student-paper award at the Association for Computing Machinery’s User Interface Software and Technology conference last year, the researchers showed how Sikuli could aid in the construction of “scripts,” short programs that combine or extend the functionality of other programs. Using the system requires some familiarity with the common scripting language Python. But it requires no knowledge of the code underlying the programs whose functionality is being combined or extended. When the programmer wants to invoke the functionality of one of those programs, she simply draws a box around the associated GUI, clicks the mouse to capture a screen shot, and inserts the screen shot directly into a line of Python code.

Suppose, for instance, that a Python programmer wants to write a script that automatically sends a message to her cell phone when the bus she takes to work rounds a particular corner. If the transportation authority maintains a web site that depicts the bus’s progress as a moving pin on a Google map, the programmer can specify that the message should be sent when the pin enters a particular map region. Instead of using arcane terminology to describe the pin, or specifying the geographical coordinates of the map region’s boundaries, the programmer can simply plug screen shots into the script: when this (the pin) gets here (the corner), send me a text.

“When I saw that, I thought, ‘Oh my God, you can do that?’” says Allen Cypher, a researcher at IBM’s Almaden Research Center who specializes in human-computer interactions. “I certainly never thought that you could do anything like that. Not only do they do it; they do it well. It’s already practical. I want to use it right away to do things I couldn’t do before.”

In the same paper, the researchers also presented a Sikuli application aimed at a broader audience. A computer user hoping to learn how to use an obscure feature of a computer program could use a screen shot of a GUI — say, the button that depicts a lasso in Adobe Photoshop — to search for related content on the web. In an experiment that allowed people to use the system over the web, the researchers found that the visual approach cut in half the time it took for users to find useful content.

In the same way that a programmer using Sikuli doesn’t need to know anything about the code underlying a GUI, Sikuli doesn’t know anything about it, either. Instead, it uses computer vision algorithms to analyze what’s happening on-screen. “It’s a software agent that looks at the screen the way humans do,” Miller says. That means that without any additional modification, Sikuli can work with any program that has a graphical interface. It doesn’t have to translate between different file formats or computer languages because, like a human, it’s just looking at pixels on the screen.

In a new paper to be presented this spring at CHI, the premier conference on human-computer interactions, the researchers describe a new application of Sikuli, aimed at programmers working on large software development projects. On such projects, new code accumulates every day, and any line of it could cause a previously developed GUI to function improperly. Ideally, after a day’s work, testers would run through the entire application, clicking virtual buttons and making sure that the right windows or icons still pop up. Since that would be prohibitively time consuming, however, broken GUIs may not be detected until the application has begun the long and costly process of quality assurance testing.

The new Sikuli application, however, lets programmers create scripts that automatically test an application’s GUI components. Visually specifying both the GUI and the window it’s supposed to pull up makes writing the scripts much easier; and once written, they can be run every night without further modification.

But the new application has an added feature that’s particularly heartening to non-programmers. Like its predecessors, it allows users to write their scripts — in this case, GUI tests — in Python. But of course, writing scripts in Python still requires some knowledge of Python — at the very least, an understanding of how to use commands like “dragDrop” or “assertNotExist,” which describe how the GUI components should be handled.

The new application gives programmers the alternative of simply recording the series of keystrokes and mouse clicks that define the test procedure. For instance, instead of typing a line of code that includes the command “dragDrop,” the programmer can simply record the act of dragging a file. The system automatically generates the corresponding Python code, which will include a cropped screen shot of the sample file; but if she chooses, the programmer can reuse the code while plugging in screen shots of other GUIs. And that points toward a future version of Sikuli that would require knowledge neither of the code underlying particular applications nor of a scripting language like Python, giving ordinary computer users the ability to intuitively create programs that mediate between other applications.




New ‘nanoburrs’ could help fight heart disease - Building on their previous work delivering cancer drugs with nanoparticles, MIT and Harvard researchers have turned their attention to cardiovascular disease, designing new particles that can cling to damaged artery walls and slowly release medicine.

The particles, dubbed “nanoburrs,” are coated with tiny protein fragments that allow them to stick to damaged arterial walls. Once stuck, they can release drugs such paclitaxel, which inhibits cell division and helps prevent growth of scar tissue that can clog arteries.

“This is a very exciting example of nanotechnology and cell targeting in action that I hope will have broad ramifications,” says MIT Institute Professor Langer, senior author of a paper describing the nanoparticles in this week’s issue of the Proceedings of the National Academy of Sciences.

Langer and Omid Farokhzad, associate professor at Harvard Medical School and another senior author of the paper, have previously developed nanoparticles that seek out and destroy tumors. Their nanoburrs, however, are among the first particles that can zero in on damaged vascular tissue.

Mark Davis, professor of chemical engineering at Caltech, says the work is a promising step towards new treatments for cardiovascular and other diseases. “If they could do this in patients — target particles to injured areas — that could open up all kinds of new opportunities,” says Davis, who was not involved in this research.

On target

Currently, one of the standard ways to treat clogged and damaged arteries is by implanting a vascular stent, which holds the artery open and releases drugs such as paclitaxel. The researchers hope that their new nanoburrs could be used alongside such stents — or in lieu of them — to treat damage located in areas not well suited to stents, such as near a fork in the artery.

The nanoburrs are targeted to a structure known as the basement membrane, which lines the arterial walls but is only exposed when those walls are damaged. To build their nanoparticles, the team screened a library of short peptide sequences to find one that binds most effectively to molecules on the surface of the basement membrane. They used the most successful, a seven-amino-acid sequence called C11, to coat the outer layer of their nanoparticles.

The inner core of the 60-nanometer-diameter particles carries the drug, which is bound to a polymer chain called PLA. A middle layer of soybean lecithin, a fatty material, lies between the core and the outer shell, which consists of a polymer called PEG that protects the particles as they travel through the bloodstream.

The drug can only be released when it detaches from the PLA polymer chain, which occurs gradually by a reaction called ester hydrolysis. The longer the polymer chain, the longer this process takes, so the researchers can control the timing of the drug’s release by altering the chain length. So far, they have achieved drug release over 12 days, in tests in cultured cells.

Uday Kompella, professor of pharmaceutical sciences at the University of Colorado, says the nanoburr’s structure could make it easier to manufacture, because the targeted peptides are attached to an outer shell and not directly to the drug-carrying core, which would require a more complicated chemical reaction. The design also reduces the risk of the nanoparticles bursting and releasing drugs prematurely, says Kompella, who was not involved in this research.

Another advantage of the nanoburrs is that they can be injected intravenously at a site distant from the damaged tissue. In tests in rats, the researchers showed that nanoburrs injected near the tail are able to reach their intended target — walls of the injured carotid artery but not normal carotid artery. The burrs bound to the damaged walls at twice the rate of nontargeted nanoparticles.

Because the particles can deliver drugs over a longer period of time, and can be injected intravenously, patients would not have to endure repeated and surgically invasive injections directly into the area that requires treatment, says Juliana Chan, a graduate student in Langer’s lab and lead author of the paper.

The team is now testing the nanoburrs in rats over a two-week period to determine the most effective dose for treating damaged vascular tissue. The particles may also prove useful in delivering drugs to tumors.

 “This technology could have broad applications across other important diseases, including cancer and inflammatory diseases where vascular permeability or vascular damage is commonly observed," says Farokhzad.



Explained: The Shannon limit - It’s the early 1980s, and you’re an equipment manufacturer for the fledgling personal-computer market. For years, modems that send data over the telephone lines have been stuck at a maximum rate of 9.6 kilobits per second: if you try to increase the rate, an intolerable number of errors creeps into the data.

Then a group of engineers demonstrates that newly devised error-correcting codes can boost a modem’s transmission rate by 25 percent. You scent a business opportunity. Are there codes that can drive the data rate even higher? If so, how much higher? And what are those codes?

In fact, by the early 1980s, the answers to the first two questions were more than 30 years old. They’d been supplied in 1948 by Claude Shannon SM ’37, PhD ’40 in a groundbreaking paper that essentially created the discipline of information theory. “People who know Shannon’s work throughout science think it’s just one of the most brilliant things they’ve ever seen,” says David Forney, an adjunct professor in MIT’s Laboratory for Information and Decision Systems.

Shannon, who taught at MIT from 1956 until his retirement in 1978, showed that any communications channel — a telephone line, a radio band, a fiber-optic cable — could be characterized by two factors: bandwidth and noise. Bandwidth is the range of electronic, optical or electromagnetic frequencies that can be used to transmit a signal; noise is anything that can disturb that signal.

Given a channel with particular bandwidth and noise characteristics, Shannon showed how to calculate the maximum rate at which data can be sent over it with zero error. He called that rate the channel capacity, but today, it’s just as often called the Shannon limit.

In a noisy channel, the only way to approach zero error is to add some redundancy to a transmission. For instance, if you were trying to transmit a message with only three bits, like 001, you could send it three times: 001001001. If an error crept in, and the receiver received 001011001 instead, she could be reasonably sure that the correct string was 001.

Any such method of adding extra information to a message so that errors can be corrected is referred to as an error-correcting code. The noisier the channel, the more information you need to add to compensate for errors. As codes get longer, however, the transmission rate goes down: you need more bits to send the same fundamental message. So the ideal code would minimize the number of extra bits while maximizing the chance of correcting error.

By that standard, sending a message three times is actually a terrible code. It cuts the data transmission rate by two-thirds, since it requires three times as many bits per message, but it’s still very vulnerable to error: two errors in the right places would make the original message unrecoverable.

But Shannon knew that better error-correcting codes were possible. In fact, he was able to prove that for any communications channel, there must be an error-correcting code that enables transmissions to approach the Shannon limit.

His proof, however, didn’t explain how to construct such a code. Instead, it relied on probabilities. Say you want to send a single four-bit message over a noisy channel. There are 16 possible four-bit messages. Shannon’s proof would assign each of them its own randomly selected code — basically, its own serial number.

Consider the case in which the channel is noisy enough that a four-bit message requires an eight-bit code. The receiver, like the sender, would have a codebook that correlates the 16 possible four-bit messages with 16 eight-bit codes. Since there are 256 possible sequences of eight bits, there are at least 240 that don’t appear in the codebook. If the receiver receives one of those 240 sequences, she knows that an error has crept into the data. But of the 16 permitted codes, there’s likely to be only one that best fits the received sequence — that differs, say, by only a digit.

Shannon showed that, statistically, if you consider all possible assignments of random codes to messages, there must be at least one that approaches the Shannon limit. The longer the code, the closer you can get: eight-bit codes for four-bit messages wouldn’t actually get you very close, but two-thousand-bit codes for thousand-bit messages could.

Of course, the coding scheme Shannon described is totally impractical: a codebook with a separate, randomly assigned code for every possible thousand-bit message wouldn’t begin to fit on all the hard drives of all the computers in the world. But Shannon’s proof held out the tantalizing possibility that, since capacity-approaching codes must exist, there might be a more efficient way to find them.

The quest for such a code lasted until the 1990s. But that’s only because the best-performing code that we now know of, which was invented at MIT, was ignored for more than 30 years. That, however, is a story for the next installment of Explained.




Y chromosomes evolving rapidly - The Y chromosome is often considered somewhat of a genetic oddball. Short and stubby, it carries hardly any genes, most of which are related to traits associated with maleness. Most of the chromosome consists of highly repetitive sequences of DNA, known as massive palindrome sequences, whose function is unknown.

Evolutionary biologists have long believed that the mammalian Y chromosome is essentially stagnant, having lost most of its genes hundreds of millions of years ago. But new research from MIT's Whitehead Institute, published in this week's issue of Nature, overturns that theory. The research team, led by Whitehead Institute director and MIT biology professor David Page, showed that the Y chromosome is actually evolving rapidly and continuously remaking itself.

For the first time, the researchers sequenced the Y chromosome of the chimpanzee, allowing for the first interspecies comparison of the chromosome. They found significant differences between the two species' Y chromosomes, suggesting that those chromosomes have evolved faster than other chromosomes during the six million years since humans and chimpanzees emerged from a common ancestor.

The findings offer the first evidence that a Y chromosome as evolutionarily old as the human Y is in fact still evolving, says Andrew Clark, a genetics professor at Cornell University who studies Y chromosome evolution in fruit flies.

"There's a dramatic amount of turnover, and it's not just degeneration — it's gain and loss of genes that do something on the Y chromosome," says Clark, adding that the new sequence comparison may also help researchers study male infertility, which is often driven by defects in the Y chromosome.

Hundreds of millions of years ago, the Y diverged from its sister X chromosome and became specialized for male-specific traits. Evolutionary biologists have theorized that it quickly lost most of its genes through a process known as degeneration, then lapsed into a fairly static state.

However, this theory was difficult to test because all of those repetitive DNA stretches make the Y chromosome very tricky to sequence, says Jennifer Hughes, a postdoctoral associate at the Whitehead Institute and lead author of the Nature paper. Most genome sequencing studies completely exclude the Y chromosome.

In 2003, Page's laboratory and collaborators at the Genome Center at Washington University (who were also involved in the new chimpanzee study) were the first team to sequence the human Y chromosome. They found that the Y carries 78 genes, more than expected, but still far fewer than the 1,000 or so located on the X chromosome.

"Having the human sequence tells us quite a bit, but to obtain information about the evolution of the Y, we needed to do a comparative analysis," says Hughes.

As its next target, the Whitehead team chose the chimpanzee, humans' closest living relative. Human and chimpanzees genomes differ very little: 98.8 percent of DNA base pairs are identical between the two species.

Page's team expected that the chimpanzee and human Y chromosomes would also be very similar. To their surprise, they found that chimp and human Y chromosomes differ considerably — far more than the rest of the chromosomes. During the six million years of separation, the chimp Y has lost one-third to one-half of the human Y chromosome genes. However, the chimp Y has twice as many massive palindrome sequences as the human Y.

Page compares the Y chromosome changes to a home undergoing continual renovation. "People are living in the house, but there's always some room that's being demolished and reconstructed," says Page, who is also a Howard Hughes Medical Institute investigator. "And this is not the norm for the genome as a whole."

The researchers suspect several factors are at play in the divergent evolution of human and chimp Y chromosomes, including differences in mating behaviors. Because a female chimpanzee may mate with many male chimpanzees around the same time, any genes on the Y chromosome that lead to enhanced sperm production offer a distinct competitive advantage.

If a Y chromosome with genes for enhanced sperm production also carries mutations that alter or eliminate a gene not related to sperm production, those less advantageous mutations also get passed on, resulting in a Y chromosome with far fewer genes than the human Y.

"The gene loss seen in chimps and the possibility that this has been driven by the influence of sperm competition in chimps but not humans is interesting, and we will be able to judge this more readily once we have functional information about the gene products, which is still sketchy in many cases," says Mark Jobling, professor of genetics at the University of Leicester, who studies the evolution of the Y chromosome.

Researchers in the Page lab and the Washington University Genome Center are now sequencing and examining the Y chromosomes of several other mammals, to investigate whether rapid evolution is occurring in species other than humans and chimpanzees.



Human immune cells — in mice - In 1796, English physician Edward Jenner decided to investigate a tale he had often heard — that milkmaids infected with cowpox became immune to smallpox, a much more dangerous affliction. To test this theory, Jenner inoculated an eight-year-old boy with pus from the blisters of a milkmaid who had caught cowpox. Two months later, Jenner injected the boy with material from a smallpox lesion. The boy did not become ill, nor did the 22 people on whom Jenner later performed the same procedure.

Jenner had just made one of the most significant discoveries in medical history — a vaccine against smallpox, one of the greatest scourges humans have faced. But, his methodology would not make it past the ethical review boards that now govern research on human subjects.

Today, scientists testing experimental vaccines usually rely on laboratory experiments, measuring the immune responses of cells grown in Petri dishes, or animal studies, which don't always offer an accurate picture of the human immune response. Once vaccines become promising enough to test in humans, researchers can vaccinate volunteer subjects but can't purposely expose them to the pathogen. For example, in a recent study of an AIDS vaccine, researchers administered either the vaccine or a placebo to more than 16,000 volunteers in Thailand, then followed them for three years to see how many became infected. 

That kind of study is useful but doesn't allow researchers to fully control the experimental conditions. Now, researchers at MIT and elsewhere are trying a new tactic — recreating the human immune system in a mouse. With mice that have human immune cells, you can "study immune response to pathogens that you can't give to people," says Jianzhu Chen, the MIT biology professor leading this effort.

Chen and his colleagues recently reported that they have engineered, for the first time, strains of mice that produce several types of human immune cells. Though the mice still do not express the full complement of immune cells, the work, published in December in the Proceedings of the National Academy of Sciences, represents a big advance in generating so-called "humanized" mice, says Andrew Tager, an immunologist who works on humanized mouse models for HIV.

Chen's new technique offers "a big advantage in terms of really filling a glaring hole in the human immune system in humanized mice," says Tager, an assistant professor at Harvard Medical School, who was not involved in this research.

Such humanized mice could be used to test potential vaccines against HIV and other human diseases such as tuberculosis, malaria and Dengue fever.

A complicated system

The human immune system is a vastly complicated network with multiple layers of defenses, exquisitely suited to combat the huge range of pathogens — bacterial, viral and fungal — to which humans can be exposed. Reproducing that complex system is no easy task.

Most of the critical players are white blood cells. B and T cells roam the bloodstream looking for specific pathogens, and launch an attack when they encounter a bacterium or virus that match receptors on the immune cell surfaces. Natural killer (NK) cells seek out and destroy cells that have been infected with a pathogen, and macrophages and dendritic cells engulf pathogens and recruit other immune cells if necessary.

To get a comprehensive picture of the body's immune response to a pathogen or vaccine, you need all of those components. All of those cells originate from hematopoietic stem cells (HSCs), which are hard to come by; the most plentiful and easily obtainable source is umbilical cord blood.

In the early 2000s, scientists induced mice to create B and T cells by injecting them with human HSCs from cord blood, but the mice lacked human NK cells and other cells important to the immune response.

In 2008, Chen and his colleagues at the Singapore-MIT Alliance in Research and Technology (SMART) set out to create mice with not just B and T cells, but also NK cells, macrophages and red blood cells. The team realized that in order to get mice to produce those humanized cells, they would have to express human cytokines that promote stem cell differentiation into NK cells and myeloid cells such as macrophages.

Rather than injecting the mice with cytokines, a laborious process that would have to be done daily to have any effect, Chen's team delivered a single injection containing genes for human cytokines, which were taken up and expressed by the mouse livers. Within two to three weeks, the mice were producing human cytokines and significant numbers of human NK cells.

The team also engineered mice that can generate human macrophages, dendritic cells and red blood cells.

Chen's team is now working on a new way to boost the number of hematopoietic stem cells generated from a single umbilical cord, which now only provides enough cells for about 10 mice. Their new technique increases the stem cell population by 20- to 150-fold, allowing them to generate enough genetically identical mice to do the large-scale studies necessary for vaccine testing.

Though any vaccine developed and tested in humanized mice would still need to be studied in humans before approval, this kind of model would allow researchers to select only the most promising candidates before moving to human trials, which are expensive and time-consuming, says Tager. "That would be tremendously helpful to vaccine efforts," he says.