MIT probes secret of bone's strength

New research at MIT has revealed for the first time the role of bone's atomistic structure in a toughening mechanism that incorporates two theories previously proposed by researchers eager to understand the secret behind the material's lightweight strength.

Past experimental studies have revealed a number of different mechanisms at different scales of focus, rather than a single theory. The combination mechanism uncovered by the MIT researchers allows for the sacrifice of a small piece of the bone in order to save the whole, helps explain why bone tolerates small cracks, and seems to be adapted specifically to accommodate bone's need for continuous rebuilding from the inside out.

"The newly discovered molecular mechanism unifies controversial attempts of explaining sources of the toughness of bone, because it illustrates that two of the earlier explanations play key roles at the atomistic scale," said the study's author, Esther and Harold E. Edgerton Professor Markus Buehler of MIT's Department of Civil and Environmental Engineering.

"It's quite possible that each scale of bone--from the molecular on up--has its own toughening mechanism," said Buehler. "This hierarchical distribution of toughening may be critical to explaining the intriguing properties of bone and laying the foundation for new materials design that includes the nanostructure as a specific design variable."

Unlike synthetic building materials, which tend to be homogenous throughout, bone is heterogeneous living tissue whose cells undergo constant change. Scientists have classified bone's basic structure into a hierarchy of seven levels of increasing scale. Level 1 bone consists of bone's two primary components: chalk-like hydroxyapatite and collagen fibrils, which are strands of tough, chewy proteins. Level 2 bone comprises a merging of these two into mineralized collagen fibrils that are much stronger than the collagen fibrils alone. The hierarchical structure continues in this way through increasingly larger combinations of the two basic materials until reaching level 7, or whole bone.

Buehler scaled down his model to the atomistic level, to see how the molecules fit together--and equally important for materials scientists and engineers--how and when they break apart. More precisely, he looked at how the chemical bonds within and between molecules respond to force. Last year, he analyzed for the first time the characteristic staggered molecular structure of collagen fibrils, the precursor to level 1 bone.

In his newer research, he studied the molecular structure of the mineralized collagen fibrils that make up level 2 bone, hoping to find the mechanism behind bone's strength, which is considerable for such a lightweight, porous material.

At the molecular level, the mineralized collagen fibrils are made up of strings of alternating collagen molecules and consistently sized hydroxyapatite crystals. These strings are "stacked" together in a staggered fashion such that the crystals appear in stair-step configurations. Weak bonds form between the crystals and molecules in the strings and between the strings.

When pressure is applied to the fabric-like fibrils, some of the weak bonds between the collagen molecules and crystals break, creating small gaps or stretched areas in the fibrils. This stretching spreads the pressure over a broader area, and in effect, protects other, stronger bonds within the collagen molecule itself, which might break outright if all the pressure were focused on them. The stretching also lets the tiny crystals shift position in response to the force, rather than shatter, which would be the likely response of a larger crystal.

Previously, some researchers suggested that the fundamental key to bone's toughness is the "molecular slip" mechanism that allows weak bonds to break and "stretch" the fabric without destroying it. Others have cited the characteristic length of bone's hydroxyapatite crystals (a few nanometers) as an explanation for bone's toughness; the crystals are too small to break easily.

At the atomistic scale, Buehler sees the interplay of both these mechanisms. This suggests that competing explanations may be correct; bone relies on different toughening mechanisms at different scales.

Buehler also discovered something very notable about bone's ability to tolerate gaps in the stretched fibril fabric. These gaps are of the same magnitude--several hundred micrometers--as the basic multicellular units or BMUs associated with bone's remodeling. BMUs are a combination of cells that work together like a small boring tool that eats away old bone at one end and replaces it at the other, forming small crack-like cavities in between as it works its way through the tissue.

Thus, the mechanism responsible for bone's strength at the molecular scale also explains how bone can remain so strong--even though it contains those many tiny cracks required for its renewal.

This could prove very useful information to civil engineers, who have always used materials like steel that gain strength through density. Nature, however, creates strength in bone by taking advantage of the gaps, which themselves are made possible by the material's hierarchical structure.

"Engineers typically over-dimension structures in order to make them robust. Nature creates robustness by hierarchical structures," said Buehler.

This work was funded by a National Science Foundation CAREER award and a grant from the Army Research Office.

Photo / Donna Coveney MIT Professor Markus Buehler has helped reveal why bones are so tough. The object on the screen is a triple helical tropocollagen molecule, a fundamental building block of bone. Next to the molecule are nanosized hydroxyapatite chalk-like crystals. In his work he simulates the behavior of the composite of tropocollagen and hydroxyapatite during deformation. Enlarge image CONTACT Elizabeth A. Thomson MIT News Office Phone: 617-258-5402 E-mail: thomson@mit.edu RELATED Model helps students visualize nanoscale problems - An educational experiment during IAP demonstrated that students can learn to apply sophisticated atomistic modeling techniques to traditional materials research in just a few classes, an advance that could dramatically change the way civil engineers learn to model the mechanical properties of materials. 4/2/2007 Markus Buehler - MIT Department of Civil and Environmental Engineering More: Biology More: Civil engineering More: Materials science

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Virtual schooling growing at K-12 level

24 hours news Students get their lessons online and communicate with their teachers and each other through chat rooms, e-mail, telephone and instant messaging

As a seventh-grader, Kelsey-Anne Hizer was getting mostly D's and F's and felt the teachers at her Ocala middle school were not giving her the help she needed. But after switching to a virtual school for eighth grade, Kelsey-Anne is receiving more individual attention and making A's and B's. She's also enthusiastic about learning, even though she has never been in the same room as her teachers.

Kelsey-Anne became part of a growing national trend when she transferred to Orlando-based Florida Virtual School. Students get their lessons online and communicate with their teachers and each other through chat rooms, e-mail, telephone and instant messaging.

"It's more one-on-one than regular school," Kelsey-Anne said. "It's more they're there; they're listening."

Virtual learning is becoming ubiquitous at colleges and universities but remains in its infancy at the elementary and secondary level, where skeptics have questioned its cost and effect on children's socialization.

However, virtual schools are growing fast - at an annual rate of about 25 percent. There are 25 statewide or state-led programs and more than 170 virtual charter schools across the nation, according to the North American Council for Online Learning.

Estimates of elementary and secondary students taking virtual classes range from 500,000 to 1 million nationally compared to total public school enrollment of about 50 million.

Online learning is used as an alternative for summer school and for students who need remedial help, are disabled, being home schooled or suspended for behavioral problems. It also can help avoid overcrowding in traditional classrooms and provide courses that local schools, often rural or inner-city, do not offer.

Advocates say those niche functions are fine, but that virtual learning has almost unlimited potential. Many envision a blending of virtual and traditional learning.

"We hope that it becomes just another piece of our public schools' day rather than still this thing over here that we're all trying to figure out," said Julie Young, Florida Virtual's president and CEO.

Florida Virtual is one of the nation's oldest and largest online schools, with more than 55,000 students in Florida and around the world, most of them part-time. Its motto is "Any Time, Any Place, Any Path, Any Pace."

Struggling students such as Kelsey-Anne, who suffers from attention deficit disorder, can take more time to finish courses while those who are gifted can go at a faster speed.

Casey Hutcheson, 17, finished English and geometry online in the time it would have taken to complete just one of those courses at his regular high school in Tallahassee.

"I like working by myself because of no distractions, and I can go at my own pace rather than going at the teacher's pace," he said.

For all its potential, virtual schooling has its critics and skeptics.

"There is something to be said for having kids in a social situation learning how to interact in society," said state Rep. Shelley Vana. "I don't think you get that if you're at home."

But virtual students get a different kind of social experience that is just as valuable, said Susan Patrick, president and CEO of the North American Council for Online Learning in Vienna, Va.

"We should socialize them for the world that they live in," she said, suggesting that people spend much of their time interacting via computer these days.

Many policymakers approach virtual learning with dollar signs in their eyes, expecting big savings from schools that do not need buildings, buses and other traditional infrastructure.

"We should not, as stewards of public money, be automatically paying the same or even close to the same amount of money for a virtual school day as we pay for a conventional school day," said Florida Senate Education Committee Chairman Don Gaetz.

Florida Virtual this year is slated to get $6,682 for every full-time equivalent student, just slightly less than the average of $7,306 for all of the state's public schools. Young said her school has expenses that traditional schools do not.

"Our data infrastructure is our building," she said.

Teacher unions have opposed spending public dollars on some virtual schools, mainly those that are privately operated or function as charter schools.

Indiana lawmakers this year refused to fund virtual charter schools. Opponents argued they are unproven and would have siphoned millions of dollars from traditional public schools.

Florida Virtual's Young said she plans to recommend that her state follow the example of Michigan, which passed a requirement that students complete some type of online experience to earn a high school diploma.

If "we do not give them an opportunity to take an online course, we're doing them a tremendous disservice," she said. "It's become the way of the world."

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The high-tech savvy

24 hours news .

education era

Students at Hamilton's McMaster University can hear the first lecture of the year for introductory psychology this week without going anywhere near a classroom.

In a break with tradition, the course's main lectures will be prerecorded and posted on the Web, available for students to watch when they have a free half hour and an Internet connection.

The online lectures, on topics such as colour perception and sexual motivation, are available only to students and, to ward off procrastination, are posted for a limited time. They include interactive slides, practice quizzes and a search function.

Students can pause or rewind, join chat groups or e-mail questions.

"I want them to think psychology is cool," says the course's creator, Professor Joe Kim.

"The old lecture model, that is what we are used to, but in a large hall it is not the most satisfying experience."

Prof. Kim, 35, has spent long hours this summer redesigning a course which, with upward of 3,000 students, is easily the largest on campus. He's already recorded all 13 of his fall lectures in a studio, with the help of a homemade teleprompter and a sizable support crew.

Such online, on-demand instruction is a far cry from the standard lecture format, and it's the latest development in a long line of changes in the classroom.

Higher education is becoming increasingly high-tech as professors look for ways to engage a generation raised on the Internet and video games.

The burgeoning use of technology also raises questions about the nature of university education, as schools use it to cope with growing class sizes and limited resources.

The only required face-to-face contact at the McMaster course, for instance, are tutorial groups of 40 to 45 students led by third- or fourth-year undergraduates that meet twice a week.

Is the tech wave a way to enhance education, or simply to make do with less?

"This generation of students, they expect teachers to be more than a talking head," says Veselin Jungic, a math professor at Simon Fraser University in Burnaby.

Prof. Jungic says he has overhauled his teaching style since he came to Canada from his native Bosnia. Along the way, he also has created a superhero - Math Girl - and two animated short films to help explain difficult concepts to his first-year calculus class.

The early morning introductory course is likely the hardest thing his students will face during their fall term, so he created the cartoons - available on YouTube by searching Math Girl - as an unthreatening way to introduce difficult topics, he says.

"At 8:30, you make 500 people laugh. That is a good start. That creates a chance for a teacher to reach those students," he explains.

After showing the cartoon, he spends his lecture discussing the concept and then finishes by playing the cartoon again.

Preliminary studies show that students who watch the cartoons - inspired by a former top student - have a better grasp on the material. "There is something, I call it magic, in that pop culture. It really reaches young people," Prof. Jungic says.

He is working on his third instalment with local artist Lou Crockett, which will focus on pi.

Across the country, professors are experimenting with other approaches to get their messages across.

Many are putting lectures on podcasts for students to listen to at their leisure. A handful have gone one step further than Prof. Kim at McMaster and are using video podcasting, offering all their lectures and course material online without any face-to-face meetings.

Others have introduced "clickers" in the classroom that allow them to poll students as a way of increasing interaction in large lecture halls. At the University of British Columbia, technology is being used to increase student feedback, with the rollout of online professor-evaluation forms.

Julia Christensen Hughes, head of the business department at the University of Guelph and a long-time champion of improving teaching practices, applauds these attempts to enrich the old lecture model.

"The classroom should be a value-added experience. It should not be just a straight transmission of information," she says.

At the same time, she cautions that "technology is not a panacea" and cannot be a substitute for face-to-face contact. "For me, learning is a social activity."

At McMaster, Prof. Kim agrees. In addition to his online lectures, he plans to give optional "live" talks on special topics.

He also plans to spice up his online offerings with hidden features that his students can discover and game shows involving students and tutorial assistants from the course. He's thinking he'll model it after Who Wants to Be a Millionaire.

He says given the number of students who enroll in his course, teaching in person would mean cramming thousands of them into a large lecture hall.

In past years, students in the course went to tutorials and watched a videotape of the lecture. This new format allows more time for discussion in class and forces them to become involved as they listen, he says.

While most of the personal instruction will come from undergraduates, Prof. Kim says his new job is designed with an emphasis on teaching, and the majority of his time will be devoted to this course.

He will be dropping in on tutorials, he says, and holding regular office hours if students prefer to ask questions in person.

Finally, as a professor of psychology, he's hoping to use the new course design to study how this new generation of students learns. The real test, he says, will be whether the combination of interactive, online learning and small group meetings will allow students to take in difficult concepts more easily.

"I'll be watching how they perform," he says.

CALCULUS SUPERHERO

How does a math professor create a cartoon superhero?

Veselin Jungic says he got the idea from watching the way his two sons, now grown, were captivated by characters in pop culture. "These superhero characters, they are able to bring a message to young people," said Prof. Jungic, 52, in English that carries the accent of his native Bosnia.

He started thinking that he could use a superhero to turn learning calculus into a positive experience for his first-year students. One day in 2003, as he handed back mid-term tests to students, he found his inspiration. Only one student got 100 per cent and, when he asked her to stand up, he saw a tiny young woman reluctantly rise in the large lecture hall. "That was my math girl," he said.

Prof. Jungic says he still has lots to learn about being a writer. The cartoons, filled with formulas and complicated concepts, are not likely to make it into a Saturday morning time slot. Still, there have been refinements. The first Math Girl episode, for example, didn't have a villain, but one was created for the sequel at the advice of his students. Prof. Jungic says he also has gained inspiration from old episodes of the Batman television series and predicts Math Girl 3, now in production, will be his best yet.

"I am just warming up,"

Cool tools

The latest crop of university students share many characteristics that professors can use to improve the teaching experience, says University of Guelph professor Julia Christensen Hughes. They are generally tech-savvy, are comfortable communicating online and are more willing to learn through trial and error than their parents.

"When they get a new piece of technology," she said, "they aren't going to look at the manual."

The same goes for the wave of young professors arriving on Canadian campuses. But just because technology is available doesn't mean every learning experience needs lots of bells and whistles, Prof. Christensen Hughes says. Posing questions and encouraging discussion is also a great way to foster different kinds of learning, she says.

"Some students find it very refreshing to go into a course without PowerPoint because it is a break," she said.

The trick, she believes, is to offer students a variety of learning options so that they can pick the style that works for them.

Some of the techniques now being used include:

Course websites: There are lots of developments on this front as websites evolve from a source of general information such as lecture outlines and assignment schedules to interactive hubs with discussion groups, professor blogs and links to journal articles or other sources.

Podcasts: Making lectures available in MP3 format is becoming a popular feature of many courses. The option means students can catch up on a missed class, review material at exam time or go over difficult concepts at their own pace. Many podcasts are also available to the general public. But some scholars worry students will forgo class altogether and just listen online.

Video podcasts: A few professors have gone one step further and created recordings with pictures and text that can be downloaded onto computers, MP3 players or even video-game consoles. They also allow students to review material and go at their own pace, but also provide charts, slides, video and other features for students who are visual learners.

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Intel Socket Xeon 7300 quad-core processor-

24 hours news. Santa Clara, Calif.-based Intel Corp. officially announced its new four-socket, quad-core Xeon 7300 Series this week, code-named Tigerton -- just five days before Advanced Micro Devices Inc. (AMD)'s quad-core processor Barcelona is to be introduced.

Compared with the company's previous-generation four-socket, dual-core products, the new quad-core Xeon 7300 series processors pack more than twice the performance and more than three times the performance per watt - and at the same price, Intel says. The Xeon 7300 completes Intel's transition to Core microarchitecture, a move that Intel first announced in June 2006.

Intel's consolidation mission
Intel is pushing users to move away from the phased-out single-core processors onto the quad-core platform, saying the Intel Xeon 7300 is designed for server consolidation. It has four times the memory capacity of the previous generation: a four-socket, dual-core code-named Tulsa.

"We are not charging a premium for quad-core, so all of our dual-core processor pricing is replaced with quad-core prices," said Kirk Skaugen, Intel vice president and general manager of the Server Products Group. "We've eliminated every reason not to go to quad core. Many [users] have single-core servers that are utilized only 15% to 20%. Now we have a platform with five times the performance of single core, so you can take dozens of underutilized systems, create virtual partitions and increase utilization dramatically."

The more energy-efficient Xeon 7300 series includes frequencies up to 2.93 GHz at 130 watts; several 80-watt processors; as well as a 50-watt version, or 12.5 watts per core, with a frequency of 1.86 GHz for ultradense deployments, such as four-socket blade servers.

It's also possible to upgrade the Xeon 7300 to Intel's next-generation chips. Code-named Dunnington, the 45-nanometer (nm) processor with four or more cores is due out next year, Skaugen said. In mid-2008, Intel plans to ship its Nehalem family of processors, which will include one to eight cores per product. In 2009, Intel plans to introduce its 32-nm manufacturing process.

In addition, the Xeon 7300 includes a new Data Traffic Optimizations feature that enhances data movement between processors, memory and I/O connections, Intel said. While previously an interconnect was shared, each processor will now have its own interconnect, Skaugen said.

The previously announced Intel VT FlexMigration will assist in the seamless upgrade of virtual machines to Intel's next-generation 45-nm Core microarchitecture-based platforms.
VMware Inc. of Palo Alto, Calif., and Intel worked together to optimize VMware ESX Server on the Xeon 7300 for live migration with VMotion between Intel processor families. This means users with Intel Xeon processors can perform live migrations of virtual machines to servers with future-generation Intel processors.

Users won't be able to do live migrations between AMD and Intel-based servers, however.

AMD's two cents on Tigerton
When AMD of Sunnyvale, Calif., releases its first quad-core processor next week, the two-, four- and eight-socket versions of the chip, code-named Barcelona, will surpass performance of Intel's Xeon quad-core processor line.
"Tigerton has the unfortunate distinction of being near last in a line of a dying architecture based on a front-side bus bottleneck," said Bruce Shaw, director of server and workstation product marketing. "Nowhere are the limitations of a front-side bus architecture more keenly felt than in the high-end multiprocessor server market. So while Intel may publicly 'celebrate' the arrival of Tigerton, it is in fact the final inadequate attempt by Intel to make the front-side bus architecture scale."

AMD's quad-core processor will be on one die, making it the first "native" quad-core processor. Intel's quad-core processors are two dual cores stuck together.

"Tigerton is still a dual-core processor design, just as Penryn will be, said AMD's Shaw. "To achieve full-performance scaling on real-world multithreaded workloads, real design work is needed. Packaging dual-cores together into quad cores is insufficient, as Intel itself clearly understands. Why else transition to native quad core in late 2008?"

Intel spokesperson Nick Knupffer said Intel's Xeon quad-core processor performance is the same as if it were on a single piece of silicon. He did not confirm any plans to move to a single die in the future.

"We are interested in end-user performance, and we are proud of the performance we have been delivering," Knupffer said.

Since November 2006, Intel has introduced more than 20 quad-core processors in the server and desktop market segments.

Vendors add servers designed for Xeon 7300
Starting today, servers based on the Xeon 7300 series processors are available from more than 50 system manufacturers, including Dell Inc., Egenera Inc., Fujitsu, Fujitsu Siemens, Hitachi, IBM Corp., NEC Corp., Sun Microsystems Inc., Super Micro Computer Inc., and Unisys Corp.
Today, for example, Hewlett-Packard Co. announced its enhanced lineup of multiprocessor-based server systems based on the Xeon 7300.

The rack-based HP ProLiant DL580 G5 server and the HP ProLiant BL680c G5, HP's first four-processor, quad-core server blade, offer increased performance with double the number of processor cores.

Pricing for the new Intel Xeon quad-core processors depends on the speed, features and volume ordered, and cost ranges from $856 to $2,301 in quantities of 1,000. For additional details on the performance characteristics of the quad-core Intel Xeon 7300 series, visit Intel's Web site.

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