The beautiful symmetry of snowflakes masks the complex physics that governs how ice crystals grow and develop under different environmental conditions, explains Kenneth Libbrecht
Sometimes the simple things in nature can be the most puzzling. Take the humble snowflake, that familiar winter icon immediately recognizable by its beautiful structure and distinctive symmetry. One might think that the process whereby water vapour condenses into crystalline ice would be well understood. A closer look, however, reveals that even some very basic questions about how snow crystals form remain unanswered.
In fact, our understanding of crystal growth in general is remarkably primitive compared with our knowledge of crystal structure. Using X-ray scattering at advanced synchrotron light sources, researchers can routinely determine the exact placement of every constituent atom in crystals made from exceedingly complex biological molecules. Yet because we cannot predict exactly how these crystals will grow under different conditions, producing large samples for analysis remains something of a black art.
The underlying difficulty is that crystal growth is a complex problem of molecular dynamics. The macroscopic development and morphology of a crystal — i.e. whether it forms facets or not, how fast it grows under different conditions and whether it develops into a single large crystal or many smaller ones — is governed by the precise way that the constituent atoms jostle into place as they solidify. While the static problem of crystal structure is relatively easy, the dynamical problem of crystal growth is sufficiently difficult that we cannot yet predict the growth behaviour of even relatively simple crystals — including ice.
To reveal the extent of our ignorance, you need little more than a magnifying glass and a gentle snowfall. The variety of snow crystals that you will see is extraordinary (see "Crystal variety"). For instance, you might first encounter the complex, branched morphologies of stellar snow crystals, which are essentially elaborate thin plates about 50 times thinner than they are wide. In a different snowfall, you might find mostly slender hexagonal columns and needles that are perhaps 20 times longer than they are wide. How can such different forms arise from the same material?
Each column, needle and stellar plate falling from the clouds started out as a simple hexagonal prism — the most basic form of snow crystal — that is defined by two "basal" facets and six "prism" facets. This hexagonal shape, which gives snow crystals their six-fold sym metry, derives from the underlying molecular structure of the ice lattice. But the overall shape of a snow crystal depends on the relative growth rates of the facet surfaces: a columnar crystal forms when water vapour condenses preferentially on the basal surfaces; while plates form when vapour condenses more readily on the prism surfaces. The fact that both columnar and plate-like snowflakes exist means that the ratio of basal and prism growth rates must change by a factor of 1000 under different conditions.
The challenge is to explain how the condensation of water vapour into solid ice can result in such a remarkable variety of crystalline forms. By examining the growth of snow crystals we hope to understand how interactions at the molecular level determine structures at much larger scales. In doing so, we should also gain insights into more general questions about pattern formation and self-assembly in nature.
Crystal morphologies
One of the first people to tackle the science of snowflakes was the physicist Ukichiro Nakaya at the University of Hokkaido in Japan in the 1930s. Nakaya grew his own snowflakes in the lab, which allowed him to study their growth under known conditions. His systematic observations are often summarized in a snow-crystal morphology diagram, which displays crystal shapes as a function of temperature and humidity (see "Morphology dimensions").
Two features in this diagram immediately stand out. First, the crystals become more complex as the humidity increases: simple prisms arise when the humidity is low; while complex, branched forms appear when the humidity is high. Second, the overall morphology behaves peculiarly as a function of temperature, whereby it changes from plate-like to columnar and back again as the temperature is lowered. The latter behaviour has proven particularly difficult to explain, even at a qualitative level. Indeed, after 75 years we still cannot explain why snow crystals grow so differently when the temperature changes by just a few degrees.
In fact, the snow-crystal morphology diagram is but a single 2D slice through a much higher-dimensional "morphology space". For instance, one could also add a time axis, which would reveal that the crystals become larger and more complex with time, or an axis showing the background gas pressure. In 1975 Takehiko Gonda at the Science University of Tokyo found that growing snow crystals in a low-pressure inert gas results in simple prisms, while higher pressures yield more complex crystals. A comprehensive model of snow-crystal growth could explain all the dimensions of morphology space, but many vital pieces of such a model are still missing. As a result, our investigation of the underlying physics of snow-crystal morphology is very much a work in progress.
The morphology diagram clearly shows that snowcrystal growth depends sensitively on temperature and humidity, and this explains why stellar snow crystals develop structures that are complex yet symmetrical. As a growing crystal descends through the clouds, it encounters different temperatures, humidities and other conditions that affect its growth. The particular path that a crystal follows through the turbulent atmosphere determines its final form, so no two crystals end up exactly alike. However, the six arms of a single crystal all travel together, so they all grow in synchrony. Because the growth is very sensitive to temperature and humidity, each falling crystal develops a unique and intricate structure with a recognizable symmetry.
Diffusion-limited growth
The complexity seen in a snow crystal ultimately arises from the way water molecules are transported to it. As a crystal grows, the surrounding air becomes depleted of water vapour, which must then diffuse in from afar. Water molecules are more likely to diffuse to a protruding point on a crystal, essentially because it sticks out farther into the surrounding humid air. This causes the protrusion to grow more rapidly than other parts of the crystal, which, in turn, increases the relative size of the protrusion. This positive feedback results in a growth instability that produces complex structures spontaneously. In particular, the instability is responsible for the dendritic branching and side branching seen in stellar snow crystals.
In 1947 the Russian mathematician G P Ivantsov discovered a family of dynamically stable solutions to the diffusion equation (a differential equation that describes how the density of a material changes while undergoing diffusion) that shed considerable light on the growth of dendritic structures. The solutions correspond to needle-shaped paraboloids in 3D or simple parabolas in 2D. As diffusion transports particles that condense onto the solid surface, the needles grow longer while preserving their parabolic shapes exactly. In other words, both the radius of curvature of a needle tip and its growth velocity remain constant with time.
With snow crystals, the branch tip of a growing stellar dendrite is a rough approximation of the 2D Ivantsov solution, since the crystal is nearly flat and the tip is roughly parabolic in shape. The branched shape of the dendrite is more complex than a simple parabola, but the added complexity is a relatively small perturbation on the behaviour near the tip. Measurements show that the tip radius and growth velocity are essentially constant with time, just as the Ivantsov solutions predict.
Interestingly, ice forms nearly the same dendritic structures whether it is grown from water vapour in air or from freezing liquid water. In the latter case, the growth is mainly limited by the diffusion of latent heat generated at the solid–liquid interface. In a snow crystal, on the other hand, growth is mainly limited by the diffusion of water-vapour molecules through the surrounding air. The resulting dendritic structures are similar in both cases because both are described by the diffusion equation.
The Ivantsov needles are a family of solutions because any tip radius is mathematically allowed, and for each needle the growth velocity is inversely proportional to the radius. For a given system we therefore need additional physics beyond the diffusion equation to be able to select a single, physical solution from the Ivantsov family. This turns out to be a surprisingly subtle problem that depends on details of the molecular dynamics during solidification. Even this easily measurable macroscopic effect — the tip velocity of a growing dendrite — depends on complex physics at the molecular level.
Growing snow crystals in high electric fields adds an interesting twist to the Ivantsov solutions for diffusionlimited growth. By producing an isolated ice dendrite on the end of a wire, one can easily induce novel growth behaviour by applying a high voltage. As there is a negligible flow of current into the surrounding air, the ice surface quickly becomes charged. As a result, the high field gradients near the electrified dendrite tip enhance the diffusion of the polar water molecules, thus pulling molecules in and increasing the growth rate. (The growth is also affected in important ways by electrically induced changes in the equilibrium vapour pressure.)
Plugging these effects into normal dendrite theory yields a new type of growth instability whereby the tip radius becomes considerably smaller and the needle grows markedly faster above a threshold voltage. Experimentally, this can result in "electric needle" crystals with tip radii as small as 100 nm and growth velocities 10 times faster than normal dendrites. These electrically grown ice needles provide useful pedestals for growing isolated snow crystals in the lab, thus allowing us to make controlled measurements of ice-crystal growth dynamics. Once a needle has been grown and the applied voltage removed, normal growth commences and a single plate-like or columnar crystal forms on the end of the needle (see "Electric ice"). As such, the thin ice needle supports the growing crystal while barely perturbing its development.
Digital snowflakes
Although much work has gone into developing an analytical theory of dendrite growth based on the Ivantsov solutions, numerical modelling is necessary to reproduce the complex structures that appear in diffusion-limited growth. This approach is particularly useful when both faceting and branching are present, since the corresponding anisotropy in growth dynamics is not easily included in an analytical theory.
This problem has received considerable attention from metallurgists, since freezing a metal from its melt often produces micro- or even nano-scale dendritic structures that can profoundly affect the strength, ductility and other properties of the final material. To numerically model the solidification process, we must first solve the diffusion equation of the growing surface, then use that solution to propagate the growth, before solving the diffusion equation again with the new solid boundary, and so on. Since errors in each step propagate to all subsequent steps, the challenge is to develop robust computational techniques that include enough relevant physics to model realistic situations.
Several popular numerical approaches have been championed over the years. These include "fronttracking" techniques, which specify the solid–liquid or solid–vapour interface explicitly; "phase-field" techniques, which digitally smooth the interface; and cellular-automaton methods that replace numerical differential-equation solvers (available via commercial software) with a grid of pixels that interact with one another according to well-defined rules. The techniques have different merits, but all have yielded acceptable results for simple dendrite growth. In the case of structures like snow crystals, however, the numerical problems become considerably harder, because the surface dynamics are highly anisotropic.
In 2006 mathematicians David Griffeath at the University of Wisconsin and Janko Gravner of the University of California at Davis, both in the US, showed that cellular automata are especially powerful for solving the problem of snow-crystal growth. The intrinsic anisotropy of the cellular-automata grid, on which individual cells are fixed, seems to stabilize the propagation of numerical errors, although exactly how this works is not yet known. Using this method, Griffeath and Gravner were able to generate the first simulated snow crystals that exhibit complex forms with realistic branching and faceting (see "Model crystals"). The underlying surface physics in these models is still somewhat ad hoc, but this recent work appears to provide the long-sought answer to the question of how one can simulate the growth of solids with highly anisotropic growth dynamics.
Subtleties of the surface
The biggest hurdle preventing researchers from constructing a comprehensive model of snow-crystal formation is knowing with certainty the rate at which water molecules condense at the ice surface. This question is vital because the varying growth rates of the basal and prism surfaces are what ultimately determine the temperature dependence seen in the morphology diagram. Unfortunately, so far no-one has been able to measure these growth rates with sufficient accuracy, nor do we have a model of the ice surface that allows us to calculate condensation rates.
Once again, the detailed molecular dynamics of ice make it difficult to observe and model ice surfaces. At temperatures near the freezing point, for example, water molecules in the air bombard the surface at such a rate that a single molecular layer of ice would be deposited every millisecond if the impinging molecules all stuck to the surface. Using molecular-dynamics simulations to model the growth of such agitated surfaces is not feasible, and the molecular motions are too fast to be imaged using scanning probe microscopy.
Fortunately, it is not necessary to comprehend every detail of the surface dynamics in order to model growth behaviour. As is usually the case in condensed-matter physics, one need only possess a reasonably accurate caricature of the underlying physics to make progress. For crystal growth, this caricature is called the "surface attachment kinetics", where one uses statistical theory to parametrize the growth velocity as a function of temperature, humidity and perhaps other conditions at the surface. The parametrized theory is then constrained using empirical measurements of growth velocities.
Obtaining suitable measurements is surprisingly difficult because one must carefully control the growth conditions to reduce systematic errors. For example, the most accurate measurements are made in low-pressure environments, where the growth is not complicated much by diffusion, and laser interferometry is used to measure the growth rates of individual facets on single, isolated crystals. Researchers are now building up precise measurements of ice-growth rates as a function of temperature, humidity and other parameters, but new puzzles appear as the data improve.
For instance, recent results from my group at the California Institute of Technology show that in these lowpressure environments the prism and basal facets grow at roughly the same rates, with no dramatic dependence on temperature. The data are especially puzzling near a temperature of –15 °C, which is where the thinnest plate-like crystals form. These measurements naively suggest that thin plates would not form at –15 °C, in stark contrast to numerous observations. With these new data, we have only deepened the mystery of the morphology diagram: not only can we not explain the well-known morphological changes with temperature, but now we cannot adequately explain even the formation of thin plates at just one temperature!
There are several ways to reconcile the different observations. One possibility is that the attachment kinetics is strongly affected by the presence of air at the ice surface, which was removed for our growth measurements. Another is that the attachment kinetics depends on the surface structure itself, so that the growth of large facet surfaces differs from the narrow edges of plate-like crystals. Unfortunately, these and other suggestions are all speculative, and to date none has emerged as the correct explanation of the conflicting data sets. How perplexing it is that such a simple phenomenon — the growth of thin, plate-like ice crystals — can be so difficult to understand. For now at least, we are left with the unsettling fact that we still cannot explain, even at a qualitative level, some of the most basic characteristics of snowflakes.
Crystalline conundrums
In many ways, the growth of snow crystals is an excellent case study for the general problem of crystal-growth dynamics. Ice is a relatively simple, monomolecular material with well-characterized intermolecular interactions, and growing ice crystals from water vapour is straightforward and inexpensive. Yet, even simple experiments yield a rich variety of interesting morphologies that cannot be readily understood.
Explaining how snow crystals grow involves a variety of physical processes that take place on a range of length scales. At the small scale, the challenge is to work out the molecular dynamics of growing surfaces and to understand how surface processes vary with temperature and other parameters. At larger scales, one must describe the transport of heat and particles via diffusion and large-scale flows. In order to successfully model morphologies, computational techniques must be developed that incorporate the relevant physics at all these scales. Moreover, trace amounts of chemically active gases have been found to dramatically alter snow-crystal formation, adding a largely unexplored chemical dimension to the morphology diagram.
The lowly snowflake exhibits an impressive phenomenology that stems from the subtle interactions between seemingly simple physical processes. There may be no direct industrial applications for snow crystals, but understanding them requires us to explore fundamental questions about how solids form and how structures arise during crystal growth. This basic research could lead to new discoveries in metallurgy, nano-scale self-assembly and other areas.
However, beyond the intrinsic scientific questions, beyond the practical applications of crystal growth, and beyond the meteorological significance of atmospheric ice, we who ponder snowflakes are motivated by a simple and essential desire to comprehend the natural world around us. These marvellous ice sculptures, so elaborate and beautiful, simply fall from the sky in great abundance. We ought to understand how they are created.
About the author
Kenneth Libbrecht is a physicist at the California Institute of Technology, US
Credits:
http://physicsworld.com/cws/article/print/32277;jsessionid=6F1D49D8119762F8815959C326B5A2DB
Chakradhar
www.chakradhar.net
Showing posts with label General Science. Show all posts
Showing posts with label General Science. Show all posts
Sunday, January 20, 2008
Magnets May Pose Serious Risks For Patients With Pacemakers And ICDs
Magnets may interfere with the operation of pacemakers and implantable cardioverter defibrillators (ICDs), according to a study published in the December 2006 edition of Heart Rhythm.
Researchers found that while common magnets for home and office use with low magnetic strength posed little risk, stronger magnets made from neodymium-iron-boron (NdFeB) may cause interference with cardiac devices and pose potential hazards to patients. NdFeB magnets are increasingly being used in homes and office products, toys, jewelry and even clothing.
"Physicians should caution patients about the risks associated with these magnets," says Thomas Wolber, a cardiologist at the University Hospital of Zurich in Switzerland and lead author of the study. "We also recommend that the packaging include information on the potential risks that may be associated with these types of magnets."
Two spherical magnets of eight and 10 millimeters in diameter and one necklace made of 45 spherical magnets were tested on 70 patients, 41 with pacemakers and 29 with ICDs. Magnetic interference was observed in all patients. The cardiac devices resumed normal function after the magnets were removed.
In an accompanying editorial, Huagui Li, M.D., a cardiologist at the Minnesota Heart Clinic in Edina, MN., writes, "This study is timely and important to attract the attention of both the public and the medical profession about the potentially serious health consequences of magnets used in decoration products... for an ICD patient, the magnet interference can be fatal."
Dr. Li concludes that manufacturers who use magnets should be required to put warning labels on their products for optimal patient safety.
About the Heart Rhythm Society
The Heart Rhythm Society is the international leader in science, education and advocacy for cardiac arrhythmia professionals and patients, and the primary information resource on heart rhythm disorders. Its mission is to improve the care of patients by promoting research, education and optimal health care policies and standards. Incorporated in 1979 and based in Washington, DC, it has a membership of over 4,000 heart rhythm professionals in more than 60 countries around the world.
About Heart Rhythm
Heart Rhythm provides rapid publication of the most important science developments in the field of arrhythmias and cardiovascular electrophysiology. As the Official Journal of the Heart Rhythm Society, Heart Rhythm publishes both basic and clinical subject matter of scientific excellence devoted to the electrophysiology (EP) of the heart and blood vessels, as well as therapy. The journal is the only EP publication serving the entire electrophysiology community from basic to clinical academic researchers, private practitioners, technicians, industry and trainees. Heart Rhythm received a debut Impact Factor of 2.6 and was ranked 21st out of 72 cardiovascular medicine journals by the Institute for Scientific Information. Additionally, the journal ranks fifth in the Immediacy Index among cardiology publications. It is also the official publication of the Cardiac Electrophysiology Society.
Adapted from materials provided by Heart Rhythm Society, via EurekAlert!, a service of AAAS.
Credits: http://www.sciencedaily.com/releases/2006/11/061130081343.htm
Chakradhar
www.chakradhar.net
Researchers found that while common magnets for home and office use with low magnetic strength posed little risk, stronger magnets made from neodymium-iron-boron (NdFeB) may cause interference with cardiac devices and pose potential hazards to patients. NdFeB magnets are increasingly being used in homes and office products, toys, jewelry and even clothing.
"Physicians should caution patients about the risks associated with these magnets," says Thomas Wolber, a cardiologist at the University Hospital of Zurich in Switzerland and lead author of the study. "We also recommend that the packaging include information on the potential risks that may be associated with these types of magnets."
Two spherical magnets of eight and 10 millimeters in diameter and one necklace made of 45 spherical magnets were tested on 70 patients, 41 with pacemakers and 29 with ICDs. Magnetic interference was observed in all patients. The cardiac devices resumed normal function after the magnets were removed.
In an accompanying editorial, Huagui Li, M.D., a cardiologist at the Minnesota Heart Clinic in Edina, MN., writes, "This study is timely and important to attract the attention of both the public and the medical profession about the potentially serious health consequences of magnets used in decoration products... for an ICD patient, the magnet interference can be fatal."
Dr. Li concludes that manufacturers who use magnets should be required to put warning labels on their products for optimal patient safety.
About the Heart Rhythm Society
The Heart Rhythm Society is the international leader in science, education and advocacy for cardiac arrhythmia professionals and patients, and the primary information resource on heart rhythm disorders. Its mission is to improve the care of patients by promoting research, education and optimal health care policies and standards. Incorporated in 1979 and based in Washington, DC, it has a membership of over 4,000 heart rhythm professionals in more than 60 countries around the world.
About Heart Rhythm
Heart Rhythm provides rapid publication of the most important science developments in the field of arrhythmias and cardiovascular electrophysiology. As the Official Journal of the Heart Rhythm Society, Heart Rhythm publishes both basic and clinical subject matter of scientific excellence devoted to the electrophysiology (EP) of the heart and blood vessels, as well as therapy. The journal is the only EP publication serving the entire electrophysiology community from basic to clinical academic researchers, private practitioners, technicians, industry and trainees. Heart Rhythm received a debut Impact Factor of 2.6 and was ranked 21st out of 72 cardiovascular medicine journals by the Institute for Scientific Information. Additionally, the journal ranks fifth in the Immediacy Index among cardiology publications. It is also the official publication of the Cardiac Electrophysiology Society.
Adapted from materials provided by Heart Rhythm Society, via EurekAlert!, a service of AAAS.
Credits: http://www.sciencedaily.com/releases/2006/11/061130081343.htm
Chakradhar
www.chakradhar.net
Listening In On The Whispering Heart
A new implantable device that could send an early-warning signal to your doctor before heart rhythm problems arise, may now be possible thanks to research described in the latest issue of the Institute of Physics journal, Physiological Measurement.
More than five million people worldwide have been diagnosed with the heart disorder atrial fibrillation (AF). In AF, the upper chambers of the heart, the atria, quiver and beat rapidly: a condition that can often lead to heart failure and stroke, making AF a major cause of hospital admission. Similarly, another disorder of the heart's rhythm, ventricular fibrillation (VF) can be just as bad for your health. Biomedical engineer Kityee Au-Yeung of Duke University, in North Carolina, says there is an urgent need to find a safe and effective treatment for AF.
Au-Yeung and her colleagues Chad Johnson and Patrick Wolf, have now developed an implantable electronic device that could help doctors listen in to the whispering heart, and prevent serious attacks of AF before it happens.
AF can often be stopped by a short, sharp electrical shock to the heart, a method known as electrical cardioversion, or defibrillation, a method familiar to anyone who watches TV hospital dramas. The method is designed to resynchronize the heart beat and restore its normal rhythm. Cardioversion is very successful in stopping an AF or VF episode and there are calls for the installation of defibrillators in many public places. But, the electrical shocks delivered to the patient can be very painful.
"AF is not an immediately life-threatening condition, and does not require immediate attention like VF does," explains Au-Yeung, "Defibrillating an AF episode, if not done properly, could itself lead to a fatal ventricular arrhythmia."
Au-Yeung and her colleagues are investigating a new version of electrical defibrillation that uses lower energy shocks, which they say would be far less painful for the patient as well as carrying less risk of complications. "We want to determine if AF can be terminated by using a series of lower energy electrical shocks, instead of a single high energy one," explain Au-Yeung, who is a graduate researcher in Wolf's laboratory at Duke.
To test the concept the team has designed and built a device that can be implanted under the skin close to the heart, like a pacemaker. Sensors on the implantable cardiac telemetry system pick up the heart's electrical pattern and send out a continuous radio signal, which is picked up by a notebook computer fitted with a receiver. With this set up, the researchers could record an electrocardiogram directly on to the computer without the need for external sensors and wiring.
This is not a one-way system though. The computer can send a signal back to the device telling it to deliver a short burst of electrical pulses directly to the heart. The sensors measure the effect on the heartbeat and send the information straight back to the computer. "We hope that with this novel system, we can learn more about AF and subsequently, find a more effective way to treat it," Au-Yeung says.
"A version of this device would most likely be targeted at patients who have already been implanted with a pacemaker or an ICD (implantable cardioverter defibrillator)," adds Au-Yeung, "For example, the remote monitoring and low energy pacing techniques could be incorporated into a pacemaker design." Remote monitoring from a patient's home could alert their doctor to an AF episode and the doctor could then administer appropriate pacing therapy and monitor its effects.
Credits : http://www.sciencedaily.com/releases/2004/08/040815232121.htm
Chakradhar
www.chakradhar.net
More than five million people worldwide have been diagnosed with the heart disorder atrial fibrillation (AF). In AF, the upper chambers of the heart, the atria, quiver and beat rapidly: a condition that can often lead to heart failure and stroke, making AF a major cause of hospital admission. Similarly, another disorder of the heart's rhythm, ventricular fibrillation (VF) can be just as bad for your health. Biomedical engineer Kityee Au-Yeung of Duke University, in North Carolina, says there is an urgent need to find a safe and effective treatment for AF.
Au-Yeung and her colleagues Chad Johnson and Patrick Wolf, have now developed an implantable electronic device that could help doctors listen in to the whispering heart, and prevent serious attacks of AF before it happens.
AF can often be stopped by a short, sharp electrical shock to the heart, a method known as electrical cardioversion, or defibrillation, a method familiar to anyone who watches TV hospital dramas. The method is designed to resynchronize the heart beat and restore its normal rhythm. Cardioversion is very successful in stopping an AF or VF episode and there are calls for the installation of defibrillators in many public places. But, the electrical shocks delivered to the patient can be very painful.
"AF is not an immediately life-threatening condition, and does not require immediate attention like VF does," explains Au-Yeung, "Defibrillating an AF episode, if not done properly, could itself lead to a fatal ventricular arrhythmia."
Au-Yeung and her colleagues are investigating a new version of electrical defibrillation that uses lower energy shocks, which they say would be far less painful for the patient as well as carrying less risk of complications. "We want to determine if AF can be terminated by using a series of lower energy electrical shocks, instead of a single high energy one," explain Au-Yeung, who is a graduate researcher in Wolf's laboratory at Duke.
To test the concept the team has designed and built a device that can be implanted under the skin close to the heart, like a pacemaker. Sensors on the implantable cardiac telemetry system pick up the heart's electrical pattern and send out a continuous radio signal, which is picked up by a notebook computer fitted with a receiver. With this set up, the researchers could record an electrocardiogram directly on to the computer without the need for external sensors and wiring.
This is not a one-way system though. The computer can send a signal back to the device telling it to deliver a short burst of electrical pulses directly to the heart. The sensors measure the effect on the heartbeat and send the information straight back to the computer. "We hope that with this novel system, we can learn more about AF and subsequently, find a more effective way to treat it," Au-Yeung says.
"A version of this device would most likely be targeted at patients who have already been implanted with a pacemaker or an ICD (implantable cardioverter defibrillator)," adds Au-Yeung, "For example, the remote monitoring and low energy pacing techniques could be incorporated into a pacemaker design." Remote monitoring from a patient's home could alert their doctor to an AF episode and the doctor could then administer appropriate pacing therapy and monitor its effects.
Credits : http://www.sciencedaily.com/releases/2004/08/040815232121.htm
Chakradhar
www.chakradhar.net
Computer Scientists Create New Technology For Elderly Home Owners
Computer scientists have designed technologies to help the elderly maintain their independence. One device uses optical sensors to oversee people as they pick up and use items. Another device uses radio frequency identification technology to track which medications have been taken and when. Additionally a variety of sensors at a house can send information on the weather, activity of a person, and other information over the internet to another house, where a picture frame displays the findings graphically.
The United States is in the middle of a longevity revolution. The average person is expected to live to be 77. Boomers will hit 65 in 2011. Homes are going high tech to help us as we grow older.
After 70 years of marriage Ross and Helen Tipton still make beautiful music together. They're just two of more than 60 million seniors in America facing new technology head on!
"We are very fortunate and lucky to have found each other," Helen told Ivanhoe. "He's learned computer at his age, well I think that's a miracle."
His computer may come in handy. Computer scientists and human factors psychologists at Georgia Tech have developed the 'technology coach.' It takes complicated tasks such as checking your glucose level and breaks it down step-by-step on the computer.
"On the box it says it's as easy as 1-2-3 but when you fold out the list of instructions, it's actually 53 steps," Brian Jones, a computer researcher at Georgia Tech, told Ivanhoe.
The technology coach uses optical sensors on an overhead camera. It can tell if a person has picked up the wrong bottle, or if they are doing the steps out of order. The screen then reveals the problem and shows how to fix it. One day this technology may be used for more than just medicine. It could be applied to programming DVD players, TVs and answering machines.
Another problem for seniors is remembering and taking their medication. This 'memory mirror' may be the answer. "The memory mirror allows people to manage medication by showing them what they've done, what they need to do, but it does not force them to do it," Elizabeth Mynatt, human centered computing expert at Georgia Tech, told Ivanhoe.
It uses radio frequency barcodes to track what medication has been taken and when.
And new technology is not just keeping track of medication ... but it's also keeping track of people. "One of the things we talked to older adults about, would you be accepting of having people monitor your home and one common response is, 'well, if I know who is doing the monitoring.'" Wendy Rogers, PhD, professor of psychology at Georgia Tech, told Ivanhoe.
You can get something that looks like a portrait of Mom -- but it will actually say so much more. Butterflies around the portrait show how active she has been during the day. The bigger the butterfly, the more movement; the movement is picked up by sensors placed around the house. It can show up to 28 days of information; so family members can see patterns.
"You don't just want to know how your Mom is doing on a particular day, but you're concerned maybe there are a few days in a row where things seem pretty quiet, maybe your Mom is sick," Rogers explained. Just a few new ideas that will help seniors like Helen and Ross Tipton keep living and loving life.
Credits : http://www.sciencedaily.com/videos/2007/1102-digital_grandparents.htm
Chakradhar
www.chakradhar.net
The United States is in the middle of a longevity revolution. The average person is expected to live to be 77. Boomers will hit 65 in 2011. Homes are going high tech to help us as we grow older.
After 70 years of marriage Ross and Helen Tipton still make beautiful music together. They're just two of more than 60 million seniors in America facing new technology head on!
"We are very fortunate and lucky to have found each other," Helen told Ivanhoe. "He's learned computer at his age, well I think that's a miracle."
His computer may come in handy. Computer scientists and human factors psychologists at Georgia Tech have developed the 'technology coach.' It takes complicated tasks such as checking your glucose level and breaks it down step-by-step on the computer.
"On the box it says it's as easy as 1-2-3 but when you fold out the list of instructions, it's actually 53 steps," Brian Jones, a computer researcher at Georgia Tech, told Ivanhoe.
The technology coach uses optical sensors on an overhead camera. It can tell if a person has picked up the wrong bottle, or if they are doing the steps out of order. The screen then reveals the problem and shows how to fix it. One day this technology may be used for more than just medicine. It could be applied to programming DVD players, TVs and answering machines.
Another problem for seniors is remembering and taking their medication. This 'memory mirror' may be the answer. "The memory mirror allows people to manage medication by showing them what they've done, what they need to do, but it does not force them to do it," Elizabeth Mynatt, human centered computing expert at Georgia Tech, told Ivanhoe.
It uses radio frequency barcodes to track what medication has been taken and when.
And new technology is not just keeping track of medication ... but it's also keeping track of people. "One of the things we talked to older adults about, would you be accepting of having people monitor your home and one common response is, 'well, if I know who is doing the monitoring.'" Wendy Rogers, PhD, professor of psychology at Georgia Tech, told Ivanhoe.
You can get something that looks like a portrait of Mom -- but it will actually say so much more. Butterflies around the portrait show how active she has been during the day. The bigger the butterfly, the more movement; the movement is picked up by sensors placed around the house. It can show up to 28 days of information; so family members can see patterns.
"You don't just want to know how your Mom is doing on a particular day, but you're concerned maybe there are a few days in a row where things seem pretty quiet, maybe your Mom is sick," Rogers explained. Just a few new ideas that will help seniors like Helen and Ross Tipton keep living and loving life.
Credits : http://www.sciencedaily.com/videos/2007/1102-digital_grandparents.htm
Chakradhar
www.chakradhar.net
Amoebas Anticipate Climate Change
A new experiment shows that amoebas will slow their motion in synch with periodic adverse changes in their environment, and will, as if in anticipation, even slow down when the adverse condition is not delivered. A team of scientists from Hokkaido University and the ATR Wave Engineering Laboratories in Japan cultured the single-celled slime mold Physarum polycephalum (a member of the amoeba clan) in a bed of oat flakes on agar. Every ten minutes the air was made slightly cooler and drier, which had the effect of slowing the movement of the amoebas down a narrow lane. Then more favorable air would be restored and the motion continued as before.
After several cycles, the amoebas slowed even when the adverse conditions did not materialize. Later still, when the organisms have been tricked into anticipating impending climate change several times, they refrain from slowing without an actual change in conditions. One of the researchers, Toshiyuki Nakagaki from Hokkaido (nakagaki@es.hokudai.ac.jp), cautions that amoebas do not have a brain and that this is not example of classic “Pavlovian” conditioned response behavior. Nevertheless, it might represent more evidence for a primitive sensitivity or “intelligence” based on the dynamic behavior of the tubular structures deployed by the amoeba. (Saigusa et al., Physical Review Letters;11 January 2008)
Credits : http://www.aip.org/pnu/2008/split/852-1.html
Chakradhar
www.chakradhar.net
After several cycles, the amoebas slowed even when the adverse conditions did not materialize. Later still, when the organisms have been tricked into anticipating impending climate change several times, they refrain from slowing without an actual change in conditions. One of the researchers, Toshiyuki Nakagaki from Hokkaido (nakagaki@es.hokudai.ac.jp), cautions that amoebas do not have a brain and that this is not example of classic “Pavlovian” conditioned response behavior. Nevertheless, it might represent more evidence for a primitive sensitivity or “intelligence” based on the dynamic behavior of the tubular structures deployed by the amoeba. (Saigusa et al., Physical Review Letters;11 January 2008)
Credits : http://www.aip.org/pnu/2008/split/852-1.html
Chakradhar
www.chakradhar.net
Friday, January 18, 2008
Ancient Cave Behavior
People have been acting like people—in other words, they've been making tools, creating rituals, and sharing food—for a long time. That's the conclusion of a recent study from South Africa's southern coast.
There, in a cave perched above the sea, researchers from Arizona State University in Tempe have found evidence that humans were behaving in surprisingly complex ways as early as 164,000 years ago. Our species, Homo sapiens, emerged an estimated 200,000 years ago.
The cave held three important clues about the behavior of these Stone Age people.
First, the researchers found the remains of a variety of shellfish, including mussels, giant periwinkles, and limpets. The cave dwellers probably collected these creatures from rocky shores and tide pools and brought them to the cave to eat.
The researchers propose that the early Africans moved to the South African coast between 195,000 and 130,000 years ago. Around that time, the climate inland turned relatively cold and dry. As a result, there were fewer plants and animals to eat away from the coast.
When these ancient people moved to the coast, they probably experienced a major cultural shift, the researchers suspect. That's because observations of modern hunter-gatherer societies suggest that men are more likely to hunt for big animals when people live inland. On the coast, women play a more important role in providing food by gathering plants and shellfish.
As for the second clue, the researchers unearthed 57 pieces of reddish pigment. The researchers think that the cave dwellers used the pigment for coloring their bodies or for other rituals. Symbolic behavior is a distinctly human trait.
Finally, the search turned up more than 1,800 stone tools, including well-crafted blades. These double-edged blades came in a variety of sizes. The smallest were just less than a half-inch wide. Ancient people may have attached these blades to the end of a stick to make spears or other tools. Until now, the earliest evidence of similar blades dates back just 70,000 years.
The new discoveries support the theory that modern human behavior developed gradually, starting about 285,000 years ago, say some experts.
An alternative theory proposes that people developed modern behavior much more recently—perhaps around 45,000 years ago. It's also possible that complex behavior developed at different rates in different places.—Emily Sohn
Credits: http://www.sciencenewsforkids.org/articles/20071024/Note2.asp
Chakradhar
www.chakradhar.net
There, in a cave perched above the sea, researchers from Arizona State University in Tempe have found evidence that humans were behaving in surprisingly complex ways as early as 164,000 years ago. Our species, Homo sapiens, emerged an estimated 200,000 years ago.
The cave held three important clues about the behavior of these Stone Age people.
First, the researchers found the remains of a variety of shellfish, including mussels, giant periwinkles, and limpets. The cave dwellers probably collected these creatures from rocky shores and tide pools and brought them to the cave to eat.
The researchers propose that the early Africans moved to the South African coast between 195,000 and 130,000 years ago. Around that time, the climate inland turned relatively cold and dry. As a result, there were fewer plants and animals to eat away from the coast.
When these ancient people moved to the coast, they probably experienced a major cultural shift, the researchers suspect. That's because observations of modern hunter-gatherer societies suggest that men are more likely to hunt for big animals when people live inland. On the coast, women play a more important role in providing food by gathering plants and shellfish.
As for the second clue, the researchers unearthed 57 pieces of reddish pigment. The researchers think that the cave dwellers used the pigment for coloring their bodies or for other rituals. Symbolic behavior is a distinctly human trait.
Finally, the search turned up more than 1,800 stone tools, including well-crafted blades. These double-edged blades came in a variety of sizes. The smallest were just less than a half-inch wide. Ancient people may have attached these blades to the end of a stick to make spears or other tools. Until now, the earliest evidence of similar blades dates back just 70,000 years.
The new discoveries support the theory that modern human behavior developed gradually, starting about 285,000 years ago, say some experts.
An alternative theory proposes that people developed modern behavior much more recently—perhaps around 45,000 years ago. It's also possible that complex behavior developed at different rates in different places.—Emily Sohn
Credits: http://www.sciencenewsforkids.org/articles/20071024/Note2.asp
Chakradhar
www.chakradhar.net
Hued Afterglow: Fingerprinting diamonds via phosphorescence
Sid Perkins
The eerie phosphorescence displayed by a rare form of blue diamond can be used as an easy, cheap, and nondestructive way to identify individual gemstones and to distinguish natural blue diamonds from synthetic ones, analyses suggest.
Phosphorescence, a "glow-in-the-dark" process in which energy previously absorbed by a substance is released slowly in the form of light, is common in a certain type of blue diamond. After exposure to light, these type IIb diamonds, which have boron- and nitrogen-containing impurities, softly glow in colors ranging from blue through pink to fiery red, says Sally Eaton-Magaña, a chemical engineer at the Gemological Institute of America in Carlsbad, Calif. The orange-red glow from the 45.52-carat Hope Diamond, a type IIb gemstone on display at the Smithsonian Institution in Washington, D.C., is visible for as long as a minute after the lights go out.
Although millions of visitors to the Smithsonian's National Museum of Natural History see the Hope Diamond each year, the gem has received remarkably little scientific attention. While a set of 239 colored diamonds known as the Aurora Heart Collection was on loan to the museum in 2005, Eaton-Magaña and her colleagues studied the set's type IIb diamonds as well as the Hope Diamond and the museum's 30.62-carat Blue Heart Diamond. They also studied the blue diamonds in the Aurora Butterfly Collection in New York City. In all, the researchers studied 67 natural blue diamonds, 3 synthetic ones, and a gray diamond that other researchers had turned blue via treatments at high temperature and high pressure. In some of their tests, the scientists shone a high-intensity ultraviolet light on each gemstone for 20 seconds and then measured its phosphorescence at various wavelengths.
Reddish phosphorescence in diamonds was thought to be rare, says Eaton-Magaña. However, the tests showed that all natural type IIb diamonds glow for several seconds at two visible wavelengths—a 500-nanometer, greenish-blue light and a 660-nm reddish one. The relative strengths of the phosphorescence at the two wavelengths dictate the hue of a stone's overall glow. Differences in the peak intensities of those emissions and the rates at which they wane provide a virtual fingerprint for each stone, the researchers report in the January Geology.
Neither the synthetic stones nor the color-enhanced gray gemstone glowed at the 660-nm wavelength. The new technique's ability to distinguish between artificial diamonds and the true blue gems "solves one of the big problems in diamond markets," says Stephen E. Haggerty, a geologist at Florida International University in Miami.
Tests on the Hope Diamond suggest that variations in phosphorescence from one part of a large gem to another are negligible, says Eaton-Magaña. Scientists would therefore still be able to identify the pieces of a large diamond if it were stolen and cut into smaller stones.
Credits : http://www.sciencenews.org/articles/20080112/fob2.asp
Chakradhar
www.chakradhar.net
The eerie phosphorescence displayed by a rare form of blue diamond can be used as an easy, cheap, and nondestructive way to identify individual gemstones and to distinguish natural blue diamonds from synthetic ones, analyses suggest.
Phosphorescence, a "glow-in-the-dark" process in which energy previously absorbed by a substance is released slowly in the form of light, is common in a certain type of blue diamond. After exposure to light, these type IIb diamonds, which have boron- and nitrogen-containing impurities, softly glow in colors ranging from blue through pink to fiery red, says Sally Eaton-Magaña, a chemical engineer at the Gemological Institute of America in Carlsbad, Calif. The orange-red glow from the 45.52-carat Hope Diamond, a type IIb gemstone on display at the Smithsonian Institution in Washington, D.C., is visible for as long as a minute after the lights go out.
Although millions of visitors to the Smithsonian's National Museum of Natural History see the Hope Diamond each year, the gem has received remarkably little scientific attention. While a set of 239 colored diamonds known as the Aurora Heart Collection was on loan to the museum in 2005, Eaton-Magaña and her colleagues studied the set's type IIb diamonds as well as the Hope Diamond and the museum's 30.62-carat Blue Heart Diamond. They also studied the blue diamonds in the Aurora Butterfly Collection in New York City. In all, the researchers studied 67 natural blue diamonds, 3 synthetic ones, and a gray diamond that other researchers had turned blue via treatments at high temperature and high pressure. In some of their tests, the scientists shone a high-intensity ultraviolet light on each gemstone for 20 seconds and then measured its phosphorescence at various wavelengths.
Reddish phosphorescence in diamonds was thought to be rare, says Eaton-Magaña. However, the tests showed that all natural type IIb diamonds glow for several seconds at two visible wavelengths—a 500-nanometer, greenish-blue light and a 660-nm reddish one. The relative strengths of the phosphorescence at the two wavelengths dictate the hue of a stone's overall glow. Differences in the peak intensities of those emissions and the rates at which they wane provide a virtual fingerprint for each stone, the researchers report in the January Geology.
Neither the synthetic stones nor the color-enhanced gray gemstone glowed at the 660-nm wavelength. The new technique's ability to distinguish between artificial diamonds and the true blue gems "solves one of the big problems in diamond markets," says Stephen E. Haggerty, a geologist at Florida International University in Miami.
Tests on the Hope Diamond suggest that variations in phosphorescence from one part of a large gem to another are negligible, says Eaton-Magaña. Scientists would therefore still be able to identify the pieces of a large diamond if it were stolen and cut into smaller stones.
Credits : http://www.sciencenews.org/articles/20080112/fob2.asp
Chakradhar
www.chakradhar.net
Monkey Brains In U.S. Make Robot Walk In Japan
Researchers believe their latest work will be used to develop prototypes of robotic leg braces for human use.
By K.C. Jones InformationWeek January 16, 2008 11:37 AM
Researchers at Duke University Medical Center have used a monkey's brain activity to control a robot on the other side of the globe.
In what researchers tout as a first-of-its-kind experiment, monkeys' thoughts controlled the walking patterns of a robot in Japan.
"They can walk in complete synchronization," said Dr. Miguel Nicolelis, who also is the Anne W. Deane Professor of Neuroscience at Duke. "The most stunning finding is that when we stopped the treadmill and the monkey ceased to move its legs, it was able to sustain the locomotion of the robot for a few minutes -- just by thinking -- using only the visual feedback of the robot in Japan."
Implanted electrodes gathered feedback from brain cells of two rhesus monkeys as they walked forward and backward at different paces on a treadmill. Sensors on the monkeys' legs tracked walking patterns while researchers used math models to analyze the relationship between leg movement and activity in the brain's motor and sensory cortex. From there, researchers in North Carolina and Japan determined how well brain cell activity predicted speed and stride.
"We found that certain neurons in multiple areas of the brain fire at different phases and at varying frequency, depending on their role in controlling the complex, multi-muscle process of motion," senior research investigator Nicolelis said in a statement.
Researchers recorded brain activity, predicted the pattern of locomotion, and sent the signal from the motor commands of the animal to the robot, he said.
"We also created a real-time transmission of information that allowed the brain activity of the monkey in North Carolina to control the commands of a robot in Japan," Nicolelis said. "Each neuron provides us with a small piece of the puzzle that we compile to predict the walking pattern of the monkeys with high accuracy."
The research, funded by the Anne W. Deane Endowed Chair Fund, expanded on previous experiments in Nicolelis' laboratory that showed monkeys could control the reaching and grasping movements of a robotic arm with their brain signals. Researchers believe that, within a year, their latest work will be used to develop prototypes of robotic leg braces for human use. They hope that robotic braces can help severely paralyzed patients walk again.
"In essence, we are seeking to capture the information that the foot sends to your brain when it touches the ground as you walk," Nicolelis said.
Mitsuo Kawato, M.E., Ph.D., director of ATR Computational Neuroscience Laboratories and research director of the Computational Brain Project of the Japan Science and Technology Agency, said the findings will be used to advance research on how the brain processes information.
http://www.informationweek.com/internet/showArticle.jhtml?articleID=205801020
Chakradhar
www.chakradhar.net
By K.C. Jones InformationWeek January 16, 2008 11:37 AM
Researchers at Duke University Medical Center have used a monkey's brain activity to control a robot on the other side of the globe.
In what researchers tout as a first-of-its-kind experiment, monkeys' thoughts controlled the walking patterns of a robot in Japan.
"They can walk in complete synchronization," said Dr. Miguel Nicolelis, who also is the Anne W. Deane Professor of Neuroscience at Duke. "The most stunning finding is that when we stopped the treadmill and the monkey ceased to move its legs, it was able to sustain the locomotion of the robot for a few minutes -- just by thinking -- using only the visual feedback of the robot in Japan."
Implanted electrodes gathered feedback from brain cells of two rhesus monkeys as they walked forward and backward at different paces on a treadmill. Sensors on the monkeys' legs tracked walking patterns while researchers used math models to analyze the relationship between leg movement and activity in the brain's motor and sensory cortex. From there, researchers in North Carolina and Japan determined how well brain cell activity predicted speed and stride.
"We found that certain neurons in multiple areas of the brain fire at different phases and at varying frequency, depending on their role in controlling the complex, multi-muscle process of motion," senior research investigator Nicolelis said in a statement.
Researchers recorded brain activity, predicted the pattern of locomotion, and sent the signal from the motor commands of the animal to the robot, he said.
"We also created a real-time transmission of information that allowed the brain activity of the monkey in North Carolina to control the commands of a robot in Japan," Nicolelis said. "Each neuron provides us with a small piece of the puzzle that we compile to predict the walking pattern of the monkeys with high accuracy."
The research, funded by the Anne W. Deane Endowed Chair Fund, expanded on previous experiments in Nicolelis' laboratory that showed monkeys could control the reaching and grasping movements of a robotic arm with their brain signals. Researchers believe that, within a year, their latest work will be used to develop prototypes of robotic leg braces for human use. They hope that robotic braces can help severely paralyzed patients walk again.
"In essence, we are seeking to capture the information that the foot sends to your brain when it touches the ground as you walk," Nicolelis said.
Mitsuo Kawato, M.E., Ph.D., director of ATR Computational Neuroscience Laboratories and research director of the Computational Brain Project of the Japan Science and Technology Agency, said the findings will be used to advance research on how the brain processes information.
http://www.informationweek.com/internet/showArticle.jhtml?articleID=205801020
Chakradhar
www.chakradhar.net
Subscribe to:
Posts (Atom)