Science

Guest Post by Sarah Jensen from the Ask an Engineer series, published by MIT’s School of Engineering

Photo: Reggie35

Photo: Reggie35

Since the time of Aristotle, researchers and amateur scientists alike have batted about the counter-intuitive theory that hot water freezes faster than cold. The notion even has a name: the Mpemba effect, named for a Tanzanian schoolboy who in 1963 noticed that the ice cream he and his classmates made from warm milk froze quicker than that made from cool milk.

“No matter what the initial temperature of water is, it must be brought to the freezing point before it will change state and become ice,” says Prakash Govindan, most recently a postdoctoral associate in MIT’s Mechanical Engineering Department. It will actually take more time and energy to freeze hot water because it must be brought down further in temperature until it reaches the freezing point, about 0°C.

Govindan suggests conducting a simple experiment to demonstrate that hot and cold water will behave as logic predicts. “Fill two identical containers with hot and cold tap water from the kitchen sink and see which freezes first,” he says. Interestingly, he points out, the rates of change in this experiment will not be the same. “When you set them in the freezer, the freezer will work harder to bring the temperature of the hot water down, so initially the rate of heat transfer will be faster in the hot water.” However, the other container will be cooling at the same time (if not at quite the same rate).

When the temperature of the water in each container reaches just about 0°C it will undergo the same changes as it moves from a liquid to a solid, and it will take the same amount of time to begin forming tiny ice crystals. At that point, each mixture of liquid and ice will be at a uniform temperature, and as more heat is taken from the mixtures, the thermodynamic principle of latent heat kicks in: The water continues to convert to a solid state, but no longer changes in temperature. “As long as you have a mixture of liquid water and solid ice, the temperature will remain at 0 until all the water is frozen,” says Govindan.

It’s never been convincingly proven than hot water and cold water behave differently from each other at any step of the freezing process, despite the ongoing fascination with the Mpemba effect. In early 2013, Europe’s Royal Society of Chemistry even held a competition for the best explanation of the theory. The winner speculated that hot water indeed freezes more quickly if the cold water is first supercooled. But logic triumphs when it comes the plain ordinary water that comes from the household faucet. Most likely to impact the freezing point of water is the presence of impurities such as salt, dissolved solids, and gases—and the ingredients of homemade ice cream. 

Thanks to Khubaib Mukhtar of Pakistan for this question. Visit the MIT School of Engineering’s Ask an Engineer site for answers to more of your questions.

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Once again, MIT has been ranked the best graduate engineering school by U.S. News & World Report, the position MIT has held since 1990 in the magazine’s annual ratings of graduate schools. Who’s next in line? Stanford, UC Berkeley, and Caltech.

How the world sees MIT.

MIT from above.

In the School of Engineering, top-ranked graduate engineering programs include aerospace engineering; chemical engineering; materials engineering; computer engineering; electrical engineering (tied); mechanical engineering (tied); and nuclear engineering (tied).

USNews and World Report does not rank all disciplines annually. In the first sciences evaluations in several years, the School of Science took the top spot in biological sciences (tied); chemistry (tied) plus an additional top ranking in the specialty of inorganic chemistry; computer science (tied); mathematics (tied) plus top ranking in discrete mathematics and combinations; and physics.

The MIT Sloan School of Management’s graduate programs in information systems, production/operations, and supply chain/logistics were again ranked first this year; Sloan was ranked the #5 business school.

Read the MIT News article to see which other MIT disciplines scored in the top five nationally and the contenders in the ties.

 

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A month ago today, the European Space Agency’s Rosetta spacecraft awoke from a 31-month-long nap and transmitted a simple message back to Earth, 420 million miles away: “Hello, world.”

Artist impression of the lander approaching the comet. (Courtesy ESA)

Artist impression of the lander approaching the comet. (Courtesy ESA)

Philippe Kletzkine SM ’83 smiled when he heard the news. The last time Kletzkine saw Rosetta was at its launch, on March 2, 2004. As ESA’s manager for the Rosetta Philae Lander, he had great hopes but he knew he would need great patience, too.

And the Rosetta team’s patience has been tried, especially for the past three years. Since Rosetta was so far away from the sun, gathering momentum for its trip to a comet, it was programmed to power down for 31 months to conserve energy. Whether it awoke from that nap in January was quite literally a long shot.

The orbiter did wake, but now Kletzkine hopes his comet landing probe, still in hibernation on the orbiter, will awaken too. In November, it has a date to become the first such probe to land on a comet.

“The next big milestone will be the awakening of the Lander, in a few weeks, so its own housekeeping telemetry can be analyzed on ground for a thorough health check,” says Kletzkine. “And then, on to the comet phase. If all goes well, it will land in late 2014, and with a bit of luck more science [will come] from the surface of the comet thereafter. Lots to look forward to, even for those, like me, who are no longer in the driver’s seat.”

Like many who joined the Rosetta project before its launch, Kletzkine has moved on. He is currently project manager for the ESA’s Solar Orbiter, an even more ambitious effort aimed at traveling closer to the sun than ever before (though still 27 million miles from it). Scheduled for a 2017 launch, the orbiter aims to photograph the sun’s two poles for the first time.

When he joined the Rosetta team in 2000, Kletzkine was uncertain that Rosetta would even make it to liftoff. Landing a satellite on a comet millions of miles away from one’s lab can be daunting.

“The greatest difficulty was to design to an unknown environment,” Kletzine says. “How do you specify the elements of a landing gear when you don’t know whether you will land on compact hard rock, porous terrain, or fluffy regolith? Is the danger to rebound, or maybe to sink into the surface? If you try to cover all worst cases, you create a versatile but enormously bulky and costly monster. If you cover too few possibilities, your chances of mission success dwindle. Remember, too, that all this was done with 1990s technology and a limited budget.”

Why land on a comet? From flybys of other comets, satellite photographs have revealed that comets have a great deal of ice. That’s prompted the question of whether water on earth is a result of a comet collision. Ultimately, comets may also hold secrets to where water—and possibly life—exist elsewhere in the universe.

Kletzkine is not the only alum working at ESA. Anne Pacros SM ’02, a payload systems engineer, works alongside Kletzkine on the Solar Orbiter project.

Pacros still remembers vividly the day ESA launched Rosetta.

“I was thrilled to hear about Rosetta’s successful ‘wake-up,’” she says, “but also thought, wow—already 10 years have passed.”

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If it’s possible to lase Jello for your party guests, Stephen Wilk ’77 can tell you how. He can also tell you the best ingredients for a laser gin-and-tonic.

In his recently published book How the Ray Gun Got Its Zap, published by Oxford University Press in the fall, Wilk provides dozens of inquiries into such geeky interests.208397

Consider this volume The Anarchist’ Cookbook for MIT alums. If you’ve ever wondered why cats’ eyes are reflective, why the moon is blue every so often, whether autopsies of murder victims’ retinas will reveal images of their assailants, or who the first spectacle-wearers were in history, this is your book.

Besides some hard science and math, Wilk is a student of pop culture, too. As he discusses here, Hollywood has done some good in popularizing science over the years.

“My concentration is on optics,” Wilk says in this podcast. “I’ve been a great admirer of science popularizers like Stephen Jay Gould, L. Sprague de Camp, and Carl Sagan. And I wanted to write the same sort of thing that I was reading, with the emphasis on my own particular background.”

Capture

Hear more by listening to this podcast interview and add your comments below.

Note to MIT alumni: This podcast presents alumni authors discussing their latest books. Help us keep up with recent books or send along names of alumni authors you’d like to hear interviewed.

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Exoplanets_Slice

Update: Watch the Feb. 11 webcast.

The study of exoplanets can be portrayed as a single-minded quest for habitable, Earth-like planets. But the most remarkable discoveries have been exoplanets with unanticipated properties that can make habitation impossible.

In the Feb. 2014 Faculty Forum Online, Associate Professor Joshua Winn ’94, SM ’94, PhD ’01 described these new worlds—and shared research discoveries about the formation and evolution of planets.

Following his comments, Winn took questions from the worldwide MIT community via interactive chat. Watch the archived webcast then return to Slice of MIT and continue the conversation in the comments.

About Joshua Winn ’94, SM ’94, PhD ’01

Joshua Winn

Joshua Winn

Associate Professor Joshua Winn’s research explores the properties of planets around other stars, how planets form and evolve, and seeks to answer if there are other planets capable of supporting life.

His research group uses optical and infrared telescopes to study exoplanetary systems—particularly those in which the star and planet eclipse one another—and pursues topics in stellar astronomy, planetary dynamics, radio interferometry, gravitational lensing, and photonic band-gap materials.

Winn is the deputy science director of the Transiting Exoplanet Survey Satellite, a NASA mission scheduled for launch in 2017. He earned his bachelor’s degree, master’s degree, and doctorate for MIT and spent one year as a Fulbright Scholar at Cambridge University. He is a contributor to the science section of the Economist and held postdoctoral fellowships with the National Science Foundation and NASA. He joined the MIT Department of Physics in January 2006.

Related

Searching for solar systems like our own,” MIT News, March 13, 2013
Learning from Hot Jupiters,” MIT News, December 15, 2010
MIT Department of Physics Faculty Profile: Joshua Winn

About Faculty Forum Online

Eight times per season, the Faculty Forum Online presents compelling interviews with faculty on timely and relevant topics. Viewers watch and participate in live 30-minute interviews via interactive chat. Since its inception in 2011, archival editions of these programs have been viewed more than 50,000 times.

For the 2013-2014 season, the Alumni Association will produce three public service-themed evening editions centered titled “One Community Together in Service.”

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Despite the cold outside, inside MIT’s CityFarm bell peppers, eggplants, and tomatoes are ripening for an early February harvest. Unlike conventional farming methods, many of CityFarm’s plants are being grown with air.

Photo: Aleszu Bajak

Founded by Caleb Harper MArch ’14, CityFarm is an MIT Media Lab initiative designed to explore the large-scale adoption of both aeroponics and hydroponics to “invent the future of agriculture,” according to their website. Unlike traditional farming, which irrigates and uses soil as structural support, an aeroponic plant’s roots are fed a mineral-enriched mist and protected in boxlike chambers. Plants are exposed to spectrally-optimized LED lights and are constantly evaluated to ensure optimum growing conditions.

The results? A head of romaine lettuce can grow in 19 days. By comparison, it takes 80 days to grow the same lettuce through traditional farming and 22 days using hydroponics, which submerges the roots in water.

Aeroponics uses 98 percent less water than conventional farming, and plants can grow 365 days a year inside and in much smaller areas. That’s a whole lot more veggies even during Boston’s chilliest winters.

Harper and his team of farmers celebrate their first harvest this past November.

Harper and his team of farmers celebrate their first harvest this past November.
Photo: Aleszu Bajak

With recent estimates that 60 percent of the world’s population will reside in cities by 2030, aeroponics might be an increasingly common growing method in cities. Harper predicts city dwellers will be able to pick up their berries, lettuce, and vegetables at local growing sites right in their neighborhoods.

Back at CityFarm, the lab’s 1,500 plants provide Harper’s team with detailed data on embodied energy—exactly how much energy a plant needs to grow. Small radio transmitters on the lights, misters, and other equipment submit information on each kilowatt of energy used. Eventually equipment will tweet this data.

Such detailed tracking of energy inputs and produce outputs is new to farming. Often the energy required to power the tractor or transport tomatoes to the grocery store is rarely factored into the true energy requirements to grow produce. Harper hopes to change that.

Harper envisions launching an Open Agriculture Initiative in the next couple months with CityFarm hosting an open source platform of farming data to improve the evaluation of aeroponics and other farming methods. “We’re providing an economic and data-driven back bone for fundamental agricultural change,” he said.

Caleb Harper checks on lettuce plants in the CityFarm. Photo: Kent Larson

He sees MIT leading the way in the new technology-agriculture space and encouraging cross-discipline scholarship between tech and agriculture universities. “I’m not competing with agriculture, I’m really providing networked intelligence and technological optimization that wasn’t there before.”

For now, Harper continues to taste test his lettuce plants in preparation for the upcoming harvest. “I have become a lettuce connoisseur,” he jokes.

For farm updates and news on the latest harvest event follow CityFarm on Twitter at @MITCityFARM.

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MIT’s Department of Earth, Atmospheric and Planetary Sciences takes the pulse of the weather and planetary changes from the ocean depths to deep space. Learn what phenomena influence today’s weather as well as the future of the planet. Here are a few research highlights:

oceans-EArthBigger Storms Ahead

For the past 40 years—as far back as satellite records show—the frequency and intensity of tropical cyclones has remained relatively stable: About 90 of these storms spin through the world each year. But according to a report by MIT’s Kerry Emanuel, the coming century may whip up stronger and more frequent storms.

Not Too Hot, Not Too Cold?

Some 40 billion Earth-like planets have been discovered in the so-called Goldilocks Zone. NPR’s On Point with Tom Ashbrook reports on research by Sara Seager, astrophysicist and planetary scientist, and colleauges in “Earth 2.0? Billions of Reasons Why It’s Possible.”

Weather in a Tank

Fluid dynamics plays a central role in determining Earth’s climate. Ocean currents and eddies stir up contents from the deep, while atmospheric winds and weather systems steer temperature and moisture around the globe. A demonstration called Weather in a Tank—a clear circular basin of water on a rotating platform that simulates Earth’s spin—illustrates weather phenomena such as atmospheric cyclones, fronts, jets, and ocean currents and eddies.

And for a little history…

Modern meteorology arrives at MIT.

Modern meteorology arrives at MIT.

Wind, War and Weathermen

Learn how a Swedish bon vivant let MIT introduce modern meteorology to America—just in time to help the Allies win World War II.

When the Butterfly Effect Took Flight

While simulating weather patterns 50 years ago, Edward Lorenz, SM ′43, ScD ′48, overthrew the idea of the clockwork universe with his ground-breaking research on chaos.

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If squirrels had written American history, it’s likely that they would have stayed as wild as wolves and as rare a sight in cities as coyotes or deer.

But as Etienne Benson PhD ’08 points out in a recent Journal of American History issuesquirrels came to cities by invitation.

Photo: Inhabitat.

Photo: Inhabitat.

The eastern gray squirrel, which Benson focuses on, was plucked from his native forest habitat as landscape architects designed the country’s greatest city parks in the late 19th century. Because industrialization had stripped away their daily encounters with beasts of burden, Americans found spotting squirrels in city parks a pleasant substitute.

We can learn a lot from our history with squirrels, says Benson, an assistant professor in the department of history and sociology of science at the University of Pennsylvania.

“The way urban Americans thought about squirrels [in the 19th c.] was definitely condescending and rooted in a hierarchical understanding of nature and society,” he told Popular Science.  At first, squirrels were “a novel and much-commented-upon feature of the American urban scene,” first introduced in Philadelphia and Boston and then in other major parks around the country.

We all know how that history changed.

Squirrels soon became known for spreading diseases and parasites. In big cities, they occupied dumpsters, harassed tourists, and chewed electric lines. “No feeding wildlife” signs popped up from Central Park to Yellowstone. As cities developed more holistic attitudes towards ecology, Benson notes, squirrels found themselves in trouble.

“The killing of squirrels by hawks, while perhaps distasteful, was natural and a sign of the city’s ecological revival,” writes Benson.

As for squirrels in Cambridge, Benson cites Mt. Auburn Cemetery as the first area park where they were introduced. They migrated eastward and were first observed in Harvard Square in 1902. The only squirrels native to MIT’s campus, it turns out, might be robotic ones or those employed for various tasks on Scratch.

Benson’s interests go beyond squirrels. He studies the way humans interact with nature around the world, particularly in terms of technology. In a 2008 essay, Benson expressed concern for the overexposure many species get in the wild from scientific surveillance. His 2010 book, Wired Wilderness: Technologies of Tracking and the Making of Modern Wildlife, expands that argument.

Benson’s interest in squirrels predates MIT, but in studying for a PhD at SHASS, he found a welcoming place for his curiosity.

“My PhD advisor at MIT, Harriet Ritvo, is one of the people who have made it possible to take human-animal relationships seriously as a historical topic,” says Benson. “Without her model and support I don’t think I would have had the courage to take on the topic or to submit the paper to a journal like this.”

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Guest Post from the Ask an Engineer series, published by MIT’s School of Engineering
Both. They work as a team—and Santa is an incredible pilot…

Great question. I haven’t seen the technical specifications for Santa’s sleigh, so I can’t say for certain, but I think there are a few things we can deduce on the basis of reliable reports of the sleigh in flight. The poem “A Visit From St. Nicholas” (also known as “’Twas the Night Before Christmas”) gives a detailed picture of Santa’s sleigh in flight, and as the evidence presented has been largely unchallenged for many decades, we can assume that, even if we have not ourselves seen Santa’s sleigh, those who have would also support the descriptions given in this poem.The poem tells us that when the reindeer approach the roof of the house, an observer can hear “on the roof/the prancing and pawing of each little hoof.” This tells us that the reindeer generally move their legs and feet when the sleigh is moving. Because reindeer are moving their legs, we know they are using energy. As nothing else on the sleigh seems to be actively producing energy, we can safely deduce that reindeer constitute the propulsion subsystem of Santa’s sleigh.

The question of steering the sleigh is a trickier problem. Steering a flying vehicle is usually split into three separate processes: navigation, guidance, and control. Navigation is the process of finding the current location and speed of a vehicle (in this case, the sleigh). Guidance is the process of figuring out where that vehicle should go next (in this case, the next house on Santa’s list) and how to get there. Control is actually getting there by performing specific maneuvers. So if Santa is trying to land on a rooftop, navigation for him is seeing that he is too high and too far left, guidance is realizing that he needs to move the sleigh down and to the right, and control is how he does the moving.

When we read the poem, we note that Santa calls all his reindeer by name and orders them onward. However, it’s not clear that the reindeer are sitting in harness in the order that Santa calls their names. His slight variations in timing as he calls their names provide another hint. When control is implemented on a flying vehicle, it is often a matter of firing engines in different directions at different times. If a spaceship has many different rocket thruster engines pointing in many different directions, it can fire one or two of them at a time to make itself point in a slightly new direction. When we look at how Santa calls his reindeer (“Now Dancer! Now Prancer and Vixen!”), we realize that he is probably telling them to run just a little bit harder, and by calling their names in different pairings, different orders, and at different times, he can turn the sleigh in different directions. Santa isn’t reminding himself of his reindeer’s names – he’s making a course correction so he can make a safe landing.

Furthermore, Santa provides explicit landing information to the reindeer (“To the top of the porch! To the top of the wall!”), indicating that he delivers both guidance and control information to the reindeer. From this it is clear that Santa provides the navigation and guidance, although he may share control responsibilities with the reindeer. After all, if given the guidance information “to the top of the wall,” the reindeer could conceivably figure out how to arrive there using their own abilities to take turns running faster or slower.

The question of how Santa navigates—that is, how he makes sure he reaches each house from the North Pole—is even more difficult, and a testament to Santa’s flying skills. He navigates by a vision-based method, which is made clear by Santa’s inability to operate the sleigh in whiteout conditions (evidenced by that fact that he once added a ninth red-nosed reindeer to his sleigh for the express purpose of illuminating his surrounding environment).

Applying logical thinking to known, observed phenomena is the surest way to figure out how things work—it’s what engineers do every day. I, for instance, often wonder how Santa manages his gift list. With so many requests to manage, he probably has to use advanced wide-scale data collection techniques to figure out what to give everyone, and pretty advanced supply-chain analytics to be sure he can deliver on those requests. My own theory is that he has a special staff of elf data managers.

Authored by Phillip M. Cunio, a graduate student in Aeronautics and Astronautics. Thanks to John Simpson from Providence, RI, for this question. Visit the MIT School of Engineering’s Ask an Engineer site for answers to more of your questions, and ask your own. 

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Guest Post from the Ask an Engineer series, published by MIT’s School of Engineering

Sure it can—but sadly, the bee isn’t likely to survive the experience…

Honeybee

Photo: Turnbud

Anything moving faster than the speed of sound (about 770 miles per hour) can create a sonic boom, including bullets, bullwhips—and yes, really fast bees. A honeybee would definitely cause a sonic boom if it was moving fast enough, but the question is: can it move fast enough?

Now, we’re engineers, not beekeepers, but we’ve heard a bee’s top speed is about 15 miles per hour. That may look fast for such a little guy, but it’s not—and he’s not alone. The fastest people can reach speeds only twice as high as the bee’s. Even the fastest animal on the planet, the peregrine falcon, can only get up to 200 miles per hour, far slower than the 770 miles per hour needed to create a sonic boom.

So what would happen if we could somehow get a honeybee to move that fast? Well, the bee would probably not survive. When something is moving that fast, all the wind around it pushes back on it and makes it heat up a lot (this is what destroyed the Space Shuttle Columbia back in 2003). For the sake of our honeybee, we would only want him to be sonic-booming for a split second, and we would want to protect him. Maybe we could invent a metal bee-suit, and dip him in something that would keep him cool as he picks up speed…

So let’s do it—we’ve got our honeybee, he’s wearing his bee-suit and he’s soaked in something nice and cool, and we’ve tied him to the end of a bullwhip for the first supersonic bee flight… Ready to hear the sonic boom? Unfortunately, our sonic bee will make more of a “crack” than a “boom.” He’s just a little bee after all, and although technically speaking, he’ll cause a sonic boom if he goes fast enough, it’s going to be a smaller, quieter sonic boom than what planes and space shuttles make.

Authored by H.N. Slater Associate Professor of Aeronautics and Astronautics Paulo Lozano, and Aeronautics and Astronautics graduate student Thomas Chiasson. Thanks to 10-year-old Reno Colburn from Big Rock, IL, for this question. Visit the MIT School of Engineering’s Ask an Engineer site for answers to more of your questions, and ask your own. 

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