Tuesday, March 2, 2010

CANCER BREAKTHROUGH COULD SAVE CHILDRENS LIVES

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A cancer which claims the lives of thousands of children worldwide every year is a step closer to being cured thanks to a breakthrough by scientists at Newcastle University.

New research, published in the current edition of the American publication Clinical Cancer Research, could offer hope to parents whose children suffer relapses after being treated for neuroblastoma.

Neuroblastoma, a cancer mainly affecting children under the age of 5 years, arises from the sympathetic nervous system and can occur anywhere from the neck to the groin but is commonest in the abdomen.

It is the second biggest cancer killer of children in the world and it remains one of the most difficult childhood cancers to cure.

Every year in the UK 100 children will develop the disease and of those about half are in the high risk category.

High risk neuroblastomas have spread to distant sites when discovered in children over a year or 18 months of age, or have unfavourable genetics.

While most neuroblastomas initially respond to treatment, relapsed high risk neuroblastoma is very difficult to cure and in the UK about 30 children die every year from the disease.

But it is hoped the new discovery, which has identified abnormalities in a particular gene called p53, may be one reason why relapses are so hard to cure.

p53 is a tumour suppressor gene which activates cell death or stops cells reproducing after DNA damage, including that from cancer chemotherapy.

Abnormalities of the p53 gene pathway were detected in almost 1/2 of the 41 cases of relapsed neuroblastoma that were studied.

Experts hope they will now be able to develop new types of therapies that target the rogue gene which prevents the resurgent cancer being successfully treated.

Dr Deborah Tweddle, Clinical Senior Lecturer at the Northern Institute for Cancer Research at Newcastle University and Honorary Consultant Paediatric Oncologist at Newcastle upon Tyne Hospitals NHS Trust, who led the research, said: “Over half of all children who get high risk neuroblastoma will relapse and the chances of surviving a relapse are at present very small.

“This research is one of the first to investigate the cause of relapsed neuroblastoma and finding this link is an important breakthrough in developing new treatments”.

“We are currently developing drugs that reactivate the p53 gene at Newcastle University and elsewhere these types of drugs are now going into clinical trials and may help patients with neuroblastoma”.

“By understanding more about the biology of neuroblastoma at relapse we may be able to prevent it and reduce the deaths of many young children, with its devastating effect on families.

Newcastle University

NASA'S FERMI CLOSES ON SOURCE OF COSMIC RAYS

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New images from NASA's Fermi Gamma-ray Space Telescope show where supernova remnants emit radiation a billion times more energetic than visible light. The images bring astronomers a step closer to understanding the source of some of the universe's most energetic particles -- cosmic rays.

Cosmic rays consist mainly of protons that move through space at nearly the speed of light. In their journey across the galaxy, the particles are deflected by magnetic fields. This scrambles their paths and masks their origins.

"Understanding the sources of cosmic rays is one of Fermi's key goals," said Stefan Funk, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), jointly located at SLAC National Accelerator Laboratory and Stanford University, Calif.

When cosmic rays collide with interstellar gas, they produce gamma rays.

"Fermi now allows us to compare emission from remnants of different ages and in different environments," Funk added. He presented the findings Monday at the American Physical Society meeting in Washington, D.C.

Fermi's Large Area Telescope (LAT) mapped billion-electron-volt (GeV) gamma-rays from three middle-aged supernova remnants -- known as W51C, W44 and IC 443 -- that were never before resolved at these energies. (The energy of visible light is between 2 and 3 electron volts.) Each remnant is the expanding debris of a massive star that blew up between 4,000 and 30,000 years ago.

In addition, Fermi's LAT also spied GeV gamma rays from Cassiopeia A (Cas A), a supernova remnant only 330 years old. Ground-based observatories, which detect gamma rays thousands of times more energetic than the LAT was designed to see, have previously detected Cas A.

"Older remnants are extremely bright in GeV gamma rays, but relatively faint at higher energies. Younger remnants show a different behavior," explained Yasunobu Uchiyama, a Panofsky Fellow at SLAC. "Perhaps the highest-energy cosmic rays have left older remnants, and Fermi sees emission from trapped particles at lower energies."

In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of gas clouds. In the decades that followed, astronomers showed that supernova remnants are the galaxy's best candidate sites for this process.

Young supernova remnants seem to possess both stronger magnetic fields and the highest-energy cosmic rays. Stronger fields can keep the highest-energy particles in the remnant's shock wave long enough to speed them to the energies observed.

The Fermi observations show GeV gamma rays coming from places where the remnants are known to be interacting with cold, dense gas clouds.

"We think that protons accelerated in the remnant are colliding with gas atoms, causing the gamma-ray emission," Funk said. An alternative explanation is that fast-moving electrons emit gamma rays as they fly past the nuclei of gas atoms. "For now, we can't distinguish between these possibilities, but we expect that further observations with Fermi will help us to do so," he added.

Either way, these observations validate the notion that supernova remnants act as enormous accelerators for cosmic particles.

"How fitting it is that Fermi seems to be confirming the bold idea advanced over 60 years ago by the scientist after whom it was named," noted Roger Blandford, director of KIPAC.

(Photo: NASA/DOE/Fermi LAT Collaboration)

NASA

UPSIDE-DOWN ANSWER FOR DEEP EARTH MYSTERY

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When Earth was young, it exhaled the atmosphere. During a period of intense volcanic activity, lava carried light elements from the planet's molten interior and released them into the sky. However, some light elements got trapped inside the planet. In this week's issue of Nature, a Rice University-based team of scientists is offering a new answer to a longstanding mystery: What caused Earth to hold its last breath?

For some time, scientists have known that a large cache of light elements like helium and argon still reside inside the planet. This has perplexed scientists because such elements tend to escape into the atmosphere during volcanism. However, because these elements are depleted in the Earth's upper mantle, Earth scientists are fairly certain the retained elements lie in a deeper portion of the mantle. Researchers have struggled to explain why some gases would be retained while others would rise and escape into the air. The dominant view has been that the lowermost mantle has been largely isolated from the upper mantle and therefore retains its primordial composition.

In the new study, a team of researchers from Rice, the University of Michigan and the University of California-Berkeley suggests that a particular set of geophysical conditions that existed about 3.5 billion years ago -- when Earth's interior was much warmer -- led to the formation of a "density trap" about 400 kilometers below the planet's surface. In the trap, a precise combination of heat and pressure led to a geophysical rarity, an area where liquids were denser than solids.

Today, liquids generated in the mantle are less dense than solids and therefore rise to the surface to form volcanoes. However, several billion years ago, a hotter mantle permitted deeper melting and generated dense liquids that stalled, crystallized and eventually sank to the bottom of the mantle.

"When something melts, we expect the gas to get out, and for that reason people have suggested that the trapped elements must be in a primordial reservoir that has never melted," said lead author Cin-Ty Lee, associate professor of Earth science at Rice. "That idea's become problematic in recent decades, because there's evidence that suggests all the mantle should have melted at least once. What we are suggesting is a mechanism where things could have melted but where the gas does not escape because the melted material never rises to the surface."

Lee said the rise of less dense, melted material from Earth's interior is the process that created Earth's crust. Suggesting that melted material might sink instead literally turns conventional wisdom on its head. But the "upside-down" model can explain several geochemical and geophysical oddities in addition to the trapped gases, which suggests that it is a plausible hypothesis.

"I hope this generates a lot of interest," Lee said. "There are seismic methods that can be used to test our idea. Even if we turn out to be wrong, the tests that would be needed to falsify our hypothesis would generate a lot of new information."

Rice University

JURASSIC SPACE: ANCIENT GALAXIES COME TOGETHER AFTER BILLIONS OF YEARS

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Imagine finding a living dinosaur in your backyard. Astronomers have found the astronomical equivalent of prehistoric life in our intergalactic backyard: a group of small, ancient galaxies that has waited 10 billion years to come together. These "late bloomers" are on their way to building a large elliptical galaxy.

Such encounters between dwarf galaxies are normally seen billions of light-years away and therefore occurred billions of years ago. But these galaxies, members of Hickson Compact Group 31, are relatively nearby, only 166 million light-years away.

New images of this foursome by NASA's Hubble Space Telescope offer a window into the universe's formative years when the buildup of large galaxies from smaller building blocks was common.

Astronomers have known for decades that these dwarf galaxies are gravitationally tugging on each other. Their classical spiral shapes have been stretched like taffy, pulling out long streamers of gas and dust. The brightest object in the Hubble image is actually two colliding galaxies. The entire system is aglow with a firestorm of star birth, triggered when hydrogen gas is compressed by the close encounters between the galaxies, and collapses to form stars.

The Hubble observations have added important clues to the story of this interacting group, allowing astronomers to determine when the encounter began and to predict a future merger.

"We found the oldest stars in a few ancient globular star clusters that date back to about 10 billion years ago. Therefore, we know the system has been around for a while," says astronomer Sarah Gallagher of The University of Western Ontario in London, Ontario, leader of the Hubble study. "Most other dwarf galaxies like these interacted billions of years ago, but these galaxies are just coming together for the first time. This encounter has been going on for at most a few hundred million years, the blink of an eye in cosmic history. It is an extremely rare local example of what we think was a quite common event in the distant universe."

Everywhere the astronomers looked in this group they found batches of infant star clusters and regions brimming with star birth. The entire system is rich in hydrogen gas, the stuff of which stars are made. Gallagher and her team used Hubble's Advanced Camera for Surveys to resolve the youngest and brightest of those clusters, which allowed them to calculate the clusters' ages, trace the star-formation history, and determine that the galaxies are undergoing the final stages of galaxy assembly.

The analysis was bolstered by infrared data from NASA's Spitzer Space Telescope and ultraviolet observations from the Galaxy Evolution Explorer (GALEX) and NASA's Swift satellite. Those data helped the astronomers measure the total amount of star formation in the system. "Hubble has the sharpness to resolve individual star clusters, which allowed us to age-date the clusters," Gallagher adds.

Hubble reveals that the brightest clusters, hefty groups each holding at least 100,000 stars, are less than 10 million years old. The stars are feeding off of plenty of gas. A measurement of the gas content shows that very little has been used up — further proof that the "galactic fireworks" seen in the images are a recent event. The group has about five times as much hydrogen gas as our Milky Way Galaxy.

"This is a clear example of a group of galaxies on their way toward a merger because there is so much gas that is going to mix everything up," Gallagher says. "The galaxies are relatively small, comparable in size to the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Their velocities, measured from previous studies, show that they are moving very slowly relative to each other, just 134,000 miles an hour (60 kilometers a second). So it's hard to imagine how this system wouldn't wind up as a single elliptical galaxy in another billion years."

Adds team member Pat Durrell of Youngstown State University: "The four small galaxies are extremely close together, within 75,000 light-years of each other — we could fit them all within our Milky Way."

Why did the galaxies wait so long to interact? Perhaps, says Gallagher, because the system resides in a lower-density region of the universe, the equivalent of a rural village. Getting together took billions of years longer than it did for galaxies in denser areas.

Hickson Compact Group 31 is one of 100 compact galaxy groups catalogued by Canadian astronomer Paul Hickson.

(Photo: NASA, ESA, S. Gallagher (The University of Western Ontario), and J. English (University of Manitoba))

The University of Western Ontario

OCEAN GEOENGINEERING SCHEME NO EASY FIX FOR GLOBAL WARMING

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Pumping nutrient-rich water up from the deep ocean to boost algal growth in sunlit surface waters and draw carbon dioxide down from the atmosphere has been touted as a way of ameliorating global warming. However, a new study led by Professor Andreas Oschlies of the Leibniz Institute of Marine Sciences (IFM-GEOMAR) in Kiel, Germany, pours cold water on the idea.

"Computer simulations show that climatic benefits of the proposed geo-engineering scheme would be modest, with the potential to exacerbate global warming should it fail," said study co-author Dr Andrew Yool of the National Oceanography Centre, Southampton (NOCS).

If international governmental policies fail to reduce emissions of carbon dioxide to levels needed to keep the impacts of human-induced climate change within acceptable limits it may necessary to move to 'Plan B'. This could involve the implementation of one or more large-scale geo-engineering schemes proposed for reducing the carbon dioxide increase in the atmosphere.

One possible approach is to engineer the oceans to facilitate the long-term sequestration of carbon dioxide from the atmosphere. It has been suggested that this could be done by pumping of nutrient-rich water from a depth of several hundred metres to fertilize the growth of phytoplankton, the tiny marine algae that dominate biological production in surface waters.

The aim would be to mimic the effects of natural ocean upwelling and increase drawdown of atmospheric carbon dioxide by phytoplankton through the process of photosynthesis. Some of the sequestered carbon would be exported to the deep ocean when phytoplankton die and sink, effectively removing it from the system for hundreds or thousands of years.

A previous study, of which Yool was lead author, used an ocean general circulation model to conclude that literally hundreds of millions of pipes would be required to make a significant impact on global warming. But even if the technical and logistical difficulties of deploying the vast numbers of pipes could be overcome, exactly how much carbon dioxide could in principle be sequestered, and at what risk?

In the new study, the researchers address such questions using a more integrated model of the whole Earth system. The simulations show that, under most optimistic assumptions, three gigatons of carbon dioxide per year could be captured. This is under a tenth of the annual anthropogenic carbon dioxide emissions, which currently stand at 36 gigatons per year. A gigaton is a million million kilograms.

One surprising feature of the simulations was that the main effect occurred on land rather than the ocean. Cold water pumped to the surface cooled the atmosphere and the land surface, slowing the decomposition of organic material in soil, and ultimately resulting in about 80 per cent of the carbon dioxide sequestered being stored on land. "This remote and distributed carbon sequestration would make monitoring and verification particularly challenging," write the researchers.

More significantly, when the simulated pumps were turned off, the atmospheric carbon dioxide levels and surface temperatures rose rapidly to levels even higher than in the control simulation without artificial pumps. This finding suggests that there would be extra environmental costs to the scheme should it ever need to be turned off for unanticipated reasons.

"All models make assumptions and there remain many uncertainties, but based on our findings it is hard to see the use of artificial pumps to boost surface production as being a viable way of tackling global warming," said Yool.

(Photo: IFM-GEOMAR)

National Oceanography Centre, Southampton

ORANGE PEELS, NEWSPAPERS MAY LEAD TO CHEAPER, CLEANER ETHANOL FUEL

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Scientists may have just made the breakthrough of a lifetime, turning discarded fruit peels and other throwaways into cheap, clean fuel to power the world's vehicles.

University of Central Florida professor Henry Daniell has developed a groundbreaking way to produce ethanol from waste products such as orange peels and newspapers. His approach is greener and less expensive than the current methods available to run vehicles on cleaner fuel – and his goal is to relegate gasoline to a secondary fuel.

Daniell's breakthrough can be applied to several non-food products throughout the United States, including sugarcane, switchgrass and straw.

"This could be a turning point where vehicles could use this fuel as the norm for protecting our air and environment for future generations," he said.

Daniell's technique – developed with U.S. Department of Agriculture funding -- uses plant-derived enzyme cocktails to break down orange peels and other waste materials into sugar, which is then fermented into ethanol.

Corn starch now is fermented and converted into ethanol. But ethanol derived from corn produces more greenhouse gas emissions than gasoline does. Ethanol created using Daniell's approach produces much lower greenhouse gas emissions than gasoline or electricity.

There's also an abundance of waste products that could be used without reducing the world's food supply or driving up food prices. In Florida alone, discarded orange peels could create about 200 million gallons of ethanol each year, Daniell said.

More research is needed before Daniell's findings, published this month in the highly regarded Plant Biotechnology Journal, can move from his laboratory to the market. But other scientists conducting research in biofuels describe the early results as promising.

"Dr. Henry Daniell's team's success in producing a combination of several cell wall degrading enzymes in plants using chloroplast transgenesis is a great achievement," said Mariam Sticklen, a professor of crop and soil sciences at Michigan State University. In 2008, she received international media attention for her research looking at an enzyme in a cow's stomach that could help turn corn plants into fuel.

Daniell said no company in the world can produce cellulosic ethanol – ethanol that comes from wood or the non-edible parts of plants.

Depending on the waste product used, a specific combination or "cocktail" of more than 10 enzymes is needed to change the biomass into sugar and eventually ethanol. Orange peels need more of the pectinase enzyme, while wood waste requires more of the xylanase enzyme. All of the enzymes Daniell's team uses are found in nature, created by a range of microbial species, including bacteria and fungi.

Daniell's team cloned genes from wood-rotting fungi or bacteria and produced enzymes in tobacco plants. Producing these enzymes in tobacco instead of manufacturing synthetic versions could reduce the cost of production by a thousand times, which should significantly reduce the cost of making ethanol, Daniell said.

Tobacco was chosen as an ideal system for enzyme production for several reasons. It is not a food crop, it produces large amounts of energy per acre and an alternate use could potentially decrease its use for smoking.

(Photo: UCF)

University of Central Florida

MOST PRECISE TEST YET OF EINSTEIN'S GRAVITATIONAL REDSHIFT

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While airplane and rocket experiments have proved that gravity makes clocks tick more slowly — a central prediction of Albert Einstein's general theory of relativity — a new experiment in an atom interferometer measures this slowdown 10,000 times more accurately than before, and finds it to be exactly what Einstein predicted.

The result shows once again how well Einstein's theory describes the real world, said Holger Müller, an assistant professor of physics at the University of California, Berkeley.

"This experiment demonstrates that gravity changes the flow of time, a concept fundamental to the theory of general relativity," Müller said. The phenomenon is often called the gravitational redshift because the oscillations of light waves slow down or become redder when tugged by gravity.

A report describing the experiment appears in the Feb. 18 issue of the journal Nature.

Müller tested Einstein's theory by taking advantage of a tenet of quantum mechanics: that matter is both a particle and a wave. The cesium atoms used in the experiment can be represented by matter waves that oscillate 3x10^25 times per second, that is, nearly a million billion billion times per second.

When the cesium atom matter wave enters the experiment, it encounters a carefully tuned flash of laser light. The laws of quantum mechanics step in, and each cesium atom enters two alternate realities, Müller said. In one, the laser has pushed the atom up one-tenth of a millimeter – 4/1000 of an inch – giving it a tiny boost out of Earth’s gravitational field. In the other, the atom remains unmoved inside Earth’s gravitational well, where time flies by less quickly.

While the frequency of cesium matter waves is too high to measure, Müller and his colleagues used the interference between the cesium matter waves in the alternate realities to measure the resulting difference between their oscillations, and thus the redshift.

The equations of general relativity predicted precisely the measured slowing of time, to an accuracy of about one part in 100 million (7x10^-9) — 10,000 times more accurate than the measurements made 30 years ago using two hydrogen maser clocks, one on Earth and the other launched via rocket to a height of 10,000 kilometers.

The mirrors and lenses on this optical bench prepare six lasers to capture cold atoms in the atom interferometer (at rear). (Damon English/UC Berkeley)"Two of the most important theories in all of physics are Quantum Mechanics and the General Theory of Relativity," noted Müller's collaborator, Steven Chu, a former UC Berkeley professor of physics and former director of Lawrence Berkeley National Laboratory (LBNL). Chu was one of the originators of the atom interferometer, which is based on his Nobel Prize-winning development of cold laser traps. "The paper that we are publishing in Nature uses two fundamental aspects of the quantum description of matter to perform one of the most precise tests of The General Theory of Relativity."

Far from merely theoretical, the results have implications for Earth's global positioning satellite system, for precision timekeeping and for gravitational wave detectors, Müller said.

"If we used our best clocks, with 17-digit precision, in global positioning satellites, we could determine position to the millimeter," he said. "But lifting a clock by 1 meter creates a change in the 16th digit. So, as we use better and better clocks, we need to know the influence of gravity better."

Müller also noted that the experiment demonstrates very clearly "Einstein’s profound insight, that gravity is a manifestation of curved space and time, which is among the greatest discoveries of humankind."

This insight means that what we think of as the influence of gravity — planets orbiting stars, for example, or an apple falling to Earth — is really matter following the quickest path through spacetime. In a flat geometry, the quickest route is a straight line. But in Einstein’s theory, the flow of time becomes a function of location, so the quickest path could now be an elliptical orbit or a plumb line to the ground.

Experiments have tested the theory to higher and higher precision, but direct measurements of the gravitational redshift have had to struggle with the minimal size of the effect in Earth’s gravitational field. These measurements culminated in the 1976 experiment by NASA and the Harvard Smithsonian Astrophysical Observatory using hydrogen maser clocks. That precision was 7x10^-5.

Just as an optical interferometer uses interfering light waves to measure time or distance to within to a fraction of a wavelength, an atom interferometer uses interfering matter waves. Because matter waves oscillate at a much higher frequency than light waves, they can be used to measure correspondingly smaller times and distances.

Cesium atom matter waves oscillate more slowly along the lower path because the gravitational field is stronger, which means time passes more slowly. In the experiment, laser pulses kicked half the atoms 0.1 mm higher than the others; a second laser sent them on a course to merge; and a third laser measured the phase difference between the interfering matter waves. (Courtesy of Nature magazine)Since 1991, when Chu was at Stanford University, he and former members of his lab have used Chu's technique of cooling and trapping atoms with lasers to build the most precise atom interferometers. In 1999, one of those students, Achim Peters, now at Humboldt University in Berlin, performed such an experiment on cesium atoms in free fall to precisely measure the acceleration of gravity.

Müller, who was Peters' graduate student at Humboldt University, subsequently worked in Steve Chu’s group at Stanford as a postdoctoral fellow, although Chu left Stanford during that time to become the director of LBNL and later U.S. Secretary of Energy. After joining the UC Berkeley faculty in July 2008, Müller attended a conference on frequency and time measurement where he realized that Peters' experimental data could also yield the most precise measure yet of the gravitational redshift. Müller approached Chu about the experiment and received an enthusiastic response.

Peters' experiment involved capturing a million cesium atoms in a cold laser trap chilled to a few millionths of a degree above absolute zero and zapping them with a vertical laser beam tuned to give them a kick upwards, with 50 percent probability. A split second later, a second laser pulse sends the high-flying matter waves downward and the stationary ones upward to merge. A third laser pulse recombines the two. Measuring the amplitude of the recombined matter waves reveals the phase difference between the two.

Müller and Chu noted that the contribution of the rest mass to the frequency of matter wave oscillations is normally ignored in quantum mechanical calculations, because the resulting frequencies are too fast to measure. But in this experiment, that high "Compton" frequency allowed an extremely precise measurement of the different clock rates.

"In conceiving of this research, we realized that relativity theory demands that the energy E also includes the energy due to the rest mass of the atom, given by Einstein's famous equation E = mc^2," Chu wrote in an e-mail. "The energy due to the rest mass of the atoms is enormous, resulting in an atomic clock that ticks at 3x10^25 Hertz."

During the approximately 0.3 seconds of freefall, the matter waves on the higher route feel that a little more time elapsed: just 2x10^-20 seconds compared to the lower route. But because of the sheer magnitude of the Compton frequency, Müller said, they oscillated about a million times more often. Since the atom interferometer could measure the difference to within a thousandth of an oscillation, the experiment produced a 9-digit accuracy. This corresponds to measuring the time difference to 10^-28 seconds.

To put these numbers in perspective, Müller said, "if the time of freefall was extended to the age of the universe, 14 billion years, the time difference between the upper and lower routes would be a mere 1/100th second, and the accuracy of the measurement would be 60 picoseconds, the time it takes for light to travel about 1/2 inch."

Müller is building ever more precise atom interferometers, and hopes this year to measure the gravitational redshift more precisely with a millimeter separation. One future milestone will be a separation of a meter or more.

"If we could separate the atoms by a meter, we could build an experiment to observe gravity waves," he said. Gravity waves are tiny fluctuations in gravity propagating through spacetime theoretically generated by interactions between massive stars or black holes.

To filter out noise from Earth's gravity and other perturbations, like a passing truck, such an experiment would have to involve at least two atom interferometers separated by a large distance. An ideal spot for the experiment, he said, would be the Deep Underground Science and Engineering Laboratory at the former Homestake mine in South Dakota.

(Photo: Damon English/UC Berkeley)

University of California, Berkeley

THE COST OF BEING ON YOUR TOES

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Humans, other great apes and bears are among the few animals that step first on the heel when walking, and then roll onto the ball of the foot and toes. Now, a University of Utah study shows the advantage: Compared with heel-first walking, it takes 53 percent more energy to walk on the balls of your feet, and 83 percent more energy to walk on your toes.

"Our heel touches the ground at the start of each step. In most mammals, the heel remains elevated during walking and running," says biology Professor David Carrier, senior author of the new study being published online Friday, Feb. 12 and in the March 1 print issue of The Journal of Experimental Biology.

"Most mammals - dogs, cats, raccoons - walk and run around on the balls of their feet. Ungulates like horses and deer run and walk on their tiptoes," he adds. "Few species land on their heel: bears and humans and other great apes - chimps, gorillas, orangutans."

"Our study shows that the heel-down posture increases the economy of walking but not the economy of running," says Carrier. "You consume more energy when you walk on the balls of your feet or your toes than when you walk heels first."

Economical walking would have helped early human hunter-gatherers find food, he says. Yet, because other great apes also are heel-first walkers, it means the trait evolved before our common ancestors descended from the trees, he adds.

"We [human ancestors] had this foot posture when we were up in the trees," Carrier says. "Heel-first walking was there in the great apes, but great apes don't walk long distances. So economy of walking probably doesn't explain this foot posture [and why it evolved], even though it helps us to walk economically."

Carrier speculates that a heel-first foot posture "may be advantageous during fighting by increasing stability and applying more torque to the ground to twist, push and shove. And it increases agility in rapid turning maneuvers during aggressive encounters."

The study concludes: "Relative to other mammals, humans are economical walkers but not economical runners. Given the great distances hunter-gatherers travel, it is not surprising that humans retained a foot posture, inherited from our more arboreal [tree-dwelling] great ape ancestors, that facilitates economical walking."

Carrier conducted the study with Christopher Cunningham, a doctoral student in biology at the University of Utah; Nadja Schilling, a zoologist at Friedrich Schiller University of Jena, Germany; and Christoph Anders, a physician at University Hospital Jena. The study was funded by the National Science Foundation, Friedrich Schiller University of Jena and a German food industry insurance group interested in back pain.

The study involved 27 volunteers, mostly athletes in their 20s, 30s and 40s. Each subject walked or ran three different ways, with each step either heel-first, ball-of-foot first with the heel a bit elevated or toes first with the heel even more elevated.
In his lab, Carrier and colleagues measured oxygen consumption - and thus energy use - as 11 volunteers wore face masks while walking or running on a treadmill. They also walked on a "force plate" to measure forces exerted on the ground.

Part of the study was conducted at Anders' lab in Germany, where 16 people walked or ran on a treadmill as scientists monitored activity of muscles that help the ankles, knees, hips and back do work during walking and running.

Findings of the experiments included:

•"You consume more energy when you walk on the balls of your feet or your toes than when you walk heels-first," Carrier says. Compared with heels-first walkers, those stepping first on the balls of their feet used 53 percent more energy, and those stepping toes-first expended 83 percent more energy.

•"The activity of the major muscles of the ankle, knee, hip and back all increase if you walk on the balls of your feet or your toes as opposed to landing on your heels," says Carrier. "That tells us the muscles increase the amount of work they are producing if you walk on the balls of your feet."

•"When we walk on the balls of our feet, we take shorter, more frequent strides," Carrier says. "But this did not make walking less economical." Putting the heel down first and pivoting onto the ball of the foot makes the stride longer because the full length of the foot is added to the length of the step. But that has no effect on energy use.

•The researchers wondered if stepping first on the balls of the feet took more energy than walking heel-first because people are less stable on their toes or balls of the feet. But increased stability did not explain why heel-first walking uses less energy.

•Stepping heel-first reduced the up-and-down motion of the body's center of mass during walking and required less work by the hips, knees and ankles. Stepping first onto the balls of the feet slows the body more and requires more re-acceleration.

•Heels-first steps also made walking more economical by increasing the transfer of movement or "kinetic" energy to stored or "potential" energy and back again. As a person starts to step forward and downward, stored energy is changed to motion or kinetic energy. Then, as weight shifts onto the foot and the person moved forward and upward, their speed slows down, so the kinetic energy of motion is converted back into stored or potential energy. The study found that stepping first onto the balls of the feet made this energy exchange less efficient that walking heels-first.

•Heel-first walking also reduced the "ground reaction force moment" at the ankle. That means stepping first onto the ball of the foot "decreases the leverage, decreases the mechanical advantage" compared with walking heel-first, Carrier says.
In sum, walking heel-first is not more economical because it is more stable or involves fewer, longer strides, but because when we land on our heels, less energy is lost to the ground, we have more leverage, and kinetic and potential energy are converted more efficiently.

If heel-first walking is so economical, why do so many animals walk other ways?

"They are adapted for running," Carrier says. "They've compromised their economy of walking for the economy of running."

"Humans are very good at running long distances. We are physiologically and anatomically specialized for running long distances. But the anatomy of our feet is not consistent with economical running. Think of all the animals that are the best runners - gazelles, deer, horses, dogs - they all run on the ball of their feet or the tips of their toes."

When people run, why is there no difference in the amount of energy they expend when stepping first onto their heels versus the balls of their feet or toes?

The answer is unknown, but "if you land on your heel when you run, the force underneath the foot shoots very quickly to the ball of your foot," Carrier says. "Even when we run with a heel plant, most of the step our weight is supported by the ball of our foot. Lots of elite athletes, whether sprinters or distance runners, don't land on their heel. Many of them run on the balls of their feet," as do people who run barefoot. That appears to be the natural ancestral condition for early human runners, he adds.
"The important thing is we are remarkable economical walkers," Carrier says. "We are not efficient runners. In fact, we consume more energy to run than the typical mammal our size. But we are exceptionally economical walkers."

"This study suggests that one of the things that may explain such economy is the unusual structure of our foot," he adds. "The whole foot contacts the ground when we walk. We have a big heel. Our big toe is as long as our other toes and is much more robust. Our big toe also is parallel to and right next to the second toe."

"These features are distinct among apes, and provide the mechanical basis for economical walking. No other primate or mammal could fit into human shoes."

(Photo: David Carrier, The University of Utah)

University of Utah

HUMAN GENOME BREAKTHROUGH

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An international team of scientists, led by researchers from Children’s Cancer Institute Australia for Medical Research (CCIA), the University of New South Wales (UNSW) and Penn State University in the US, sequenced the genomes of indigenous southern Africans and found them to be among the world’s most genetically diverse people.

The genomes of four Kalahari Desert Bushmen and an ethnic Bantu are the first to be sequenced from an indigenous population. More than 1.3 million new genetic variants have been added to databases of Human Genome Variation which until now have been largely Eurocentric.

Featured as the cover story in the prestigious journal Nature, the discovery has important implications for medical research, providing potential markers for the origins, treatments and cures for many of the most complex diseases, including cancer. It also raises questions about current scientific assumptions regarding the genetic causes of many diseases.

“The indigenous hunter-gatherer peoples of southern Africa are believed to be the oldest known lineage of modern humans,” said study co-leader Dr Vanessa Hayes from the CCIA and UNSW.

“On average, we found as many genetic differences between two Bushmen, than between a European and an Asian.

“This research now provides us with the tools to read the story of human evolution and specifically the story of disease evolution,” Dr Hayes said.

Significantly, the genomes are personalised, with all participants named and their medical histories recorded. Among the participants was Nobel Peace Laureate Archbishop Desmond Tutu – a representative of the Bantu community and a Global Elder. The genome sequences will be released to the public and freely accessible online.

“Human variation is vital in determining disease risk and drug response for complex genetic diseases. It is important to include genetic differences from all global populations in research efforts,” Dr Hayes said.

“It has been well established that the African continent is the cradle of civilisation and therefore the origin of disease, we just haven’t known to what extent.

“We can predict there will be just as much genetic diversity in Australia’s Aboriginal community and that would tell another important story of our genetic heritage.”

Dr Hayes said the African data is already contributing to the development of a new test based on the human variation found in the study. These 'arrays' will soon be available globally for medical research efforts.

Read more about the background to the study and Dr Hayes' work in a feature story published in the Sydney Morning Herald.

(Photo: UNSW)

University of New South Wales

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