research
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Prof. Chong Unveils New Human Movement Model
A KAIST research team headed by Prof. Song Chong of the School of Electrical Engineering and Computer Science has developed a new statistical model that simulates human mobility patterns, mimicking the way people move over the course of a day, a month or longer, university sources said on Tuesday (May 12).
The model, developed in collaboration with scientists at North Carolina State University, is the first to represent the regular movement patterns of humans using statistical data.
The model has a variety of potential uses, ranging from land use planning to public health studies on epidemic disease.
The researchers gave global positioning system (GPS) devices to approximately 100 volunteers at five locations in the U.S. and South Korea and tracked the participants" movements over time. By tracing the points where the study participants stopped, and their movement trajectories, researchers were able to determine patterns of mobility behavior.
The researchers were then able to emulate these fundamental statistical properties of human mobility into a model that could be used to represent the regular daily movement of humans. The model, called Self-similar Least Action Walk (SLAW), will have a wide array of practical applications.
The research, "SLAW: A Mobility Model for Human Walks," was presented on April 20 at the 28th IEEE Conference on Computer Communications in Rio de Janeiro, Brazil. The National Science Foundation of the U.S. funded the research.
2009.05.13 View 12830 -
KAIST Professor Unveils New Method of Manufacturing Complex Nano-wire
A KAIST research team led by Prof. Sang-Ouk Kim of the Department of Materials Science and Engineering has discovered a new nanowire manufacturing method, university sources said on Monday (May 11).
The KAIST researchers successfully demonstrated soft graphoepitaxy of block copolymer assembly as a facile, scalable nanolithography for highly ordered sub-30-nm scale features. Graphoepitaxy is a new technique that uses artificial surface relief structure to induce crystallographic orientation in thin films.
Various morphologies of hierarchical block copolymer assembly were achieved by means of disposable topographic confinement of photoresist pattern. Unlike usual graphoepitaxy, soft graphoepitaxy generates the functional nanostrutures of metal and semiconductor nanowire arrays without any trace of structure-directing topographic pattern.
The discovery was featured in the May 7 edition of Nano-Letters. Application has been made for the domestic patent of the new method.
The new method is expected to be advantageous for multi-layer overlay processing required for complex device architecture, the sources said.
2009.05.12 View 10019 -
KAIST Research Team Discovers Process for Rapid Growth of N-Doped CNT Arrays
A team of scientists led by Profs. Sang-Ouk Kim, Won-Jong Lee and Duck-Hyun Lee of the Department of Materials Science and Engineering has found a straightforward process for rapid growth of wall-number selected, nitrogen-doped carbon nanotube (CNT) arrays, university officials said on Monday (March 16).
KAIST researchers prepared highly uniform nanopatterned iron catalyst arrays by tilted deposition through block copolymer nanotemplates. This remarkably fast growth of highly uniform N-doped CNTs, whose material properties and chemical functionalizability are reinforced by N-doping, offers a new area of a large-scale nanofabrication, potentially useful for diverse nano-devices.
Carbon nanotubes (CNTs) are of broad technical interest in electronics, photonics, energy devices, and other applications. However, establishing a straightforward process for mass production of uniform CNTs with desired structure and properties has been a long-standing challenge.
In particular, it was strongly desired to precisely control the numbers of walls and diameter of CNTs, which are decisive parameters for the physical properties of CNTs. In this respect, the preparation of monodisperse catalyst array having a narrow size distribution is generally considered an effective pathway to produce well-defined CNTs, since the number of walls and diameter of the produced CNTs are closely related to the catalyst size.
The finding was featured in the March 13 edition of Nano Letters, a leading journal in the nano technology field.
2009.03.20 View 13108 -
Prof. Song Develops Nano-Structure to Enhance Power of Rechargeable Lithium-ion Battery
A team of scientists led by Prof. Hyun-Joon Song of the Department of Chemistry, KAIST, developed a nano-structure that could increase the power of rechargeable lithium-ion batteries, university sources said on Monday (Feb. 16).
The research team found that a nano-structured material using copper oxide (CuO) could produce lithium-ion batteries with some 50 percent more capacity than conventional products. The study was published in the online edition of peer-review journal Advanced Materials.
In rechargeable lithium-ion batteries, lithium ions move between the battery"s anode and cathode. The high-energy density of the batteries led to their common use in consumer electronics products, expecially portable devices. Their demand in automotive and aerospace applications is growing, and nano-structured, or nano-enabled batteries are emerging as the new generation of lithium-ion batteries for their edge in recharging time, capacity and battery life.
Graphite has been a popular material for cathodes in lithium-ion batteries. However, graphite cathodes are also blamed for lost capacity due to their consumption of lithium ions, which are linked to shorter battery life.
As such, scientists have been looking for materials that could replace graphite in cathodes, and silicon and metal oxide have been studied as possible alternatives.
2009.02.17 View 11231
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Prof. Cho Identifies Dynamics of Signal Transportation System in Control of Cell Proliferation
KAIST, Jan. 22, 2009 -- A research team led by Prof. Kwang-Hyun Cho of the Department of Bio and Brain Engineering, KAIST, has identified a hidden mechanism of the dynamic behavior of signal transportation system involved in the control of cell proliferation, university authorities said.
The finding is expected to provide a clue to appropriately controlling the pathway of ERK protein which is known to play a significant role in causing and spreading cancer. The research was featured as the cover paper of the latest online edition of the Journal of Cell Science.
The Ras-Raf-MEK-ERK pathway (or ERK pathway) is an important signal transduction system involved in the control of cell proliferation, survival and differentiation. However, the dynamic regulation of the pathway by positive- and negative-feedback mechanism, in particular the functional role of Raf kinase inhibitor protein (RKIP) are still incompletely understood. RKIP is a physiological endogenous inhibitor of MEK phosphorylation by Raf kinases, but also participates in a positive-feedback loop in which ERK can inactivate RKIP.
"We attempted to unearth the hidden dynamics of these feedback mechanisms and to identify the functional role of RKIP through combined efforts of biochemical experiments and computer simulations based on an experimentally validated mechanical model," Prof. Cho was quoted as saying.
2009.02.03 View 11122 -
KAIST Scientists Creates Transparent Memory Chip
--See-Through Semis Could Revolutionize Displays
A group of KAIST scientists led by Prof. Jae-Woo Park and Koeng-Su Lim has created a working computer chip that is almost completely clear -- the first of its kind.
The new chip, called "transparent resistive random access memory (TRRAM), is similar in type to an existing technology known as complementary metal-oxide semiconductor (CMOS) memory -- common commercial chips that provide the data storage for USB flash drives and other devices. Like CMOS devices, the new chip provides "non-volatile" memory, meaning that it stores digital information without losing data when it is powered off. Unlike CMOS devices, however, the new TRRAM chip is almost completely clear.
The paper on the new technology, entitled "Transparent resistive random access memory and its characteristics for non-volatile resistive switching," was published in the December issue of the Applied Physics Letters (APL), and the American Institute of Physics, the publisher of APL, issued a press release about this breakthrough.
"It is a new milestone of transparent electronic systems," says researcher Jung-Won Seo, who is the first author of the paper. "By integrating TRRAM devices with other transparent electronic components, we can create a totally see-through embedded electronic system."
Technically, TRRAM devices rely upon an existing technology known as resistive random access memory (RRAM), which is already in commercial development for future electronic data storage devices. RRAM is built using metal oxide materials between equally transparent electrodes and substrates.
According to the research team, TRRAM devices are easy to fabricate and may be commercially available in just 3-4 years.
"We are sure that TRRAM will become one of alternative devices to current CMOS-based flash memory in the near future after its reliability is proven and once any manufacturing issues are solved," says Prof. Jae-Woo Park, who is the co-author on the paper. He adds that the new devices have the potential to be manufactured cheaply because any transparent materials can be utilized as substrate and electrode. They also may not require incorporating rare elements such as Indium.
2008.12.17 View 15839 -
Prof. Kwon Unveils Home-Made Lunar Module
A KAIST research team led by Prof. Se-Jin Kwon at the Department of Aerospace Engineering has unveiled a small lunar module developed in cooperation with engineers at a local company, Space Solutions, university authorities said on Thursday (Nov. 27).
The home-made lunar module, the vehicle that conducts survey on the surface of the moon, is 40 centimeters tall and weighs 25 kg. Equipped with a liquid-fuel rocket engine with a maximum thrust of 350 newtons (N), it is capable of carrying objects weighing around 20 kg to the lunar space from the space ship. Professor Kwon"s team held a demonstration of the lander for journalists at a KAIST lab on Friday (Nov. 28).
Lunar landers are critical in developing lunar spacecraft, and countries with advanced aerospace technologies have been careful to protect their core technologies.
According to Prof. Kwon, every part of the rocket engine, including the catalyst, was home made. The rocket"s propulsion system features a state-of-the-art propellant valve developed by Space Solutions, which enables thrust control.
Lunar modules between the 100 and 200 kilogram range, developed by NASA (U.S. National Aeronautics and Space Administration), costs around $100 million, said Kwon. "It is expensive to guarantee the safety of developers of an American module because the fuel contains carcinogens. But the rocket engine created by KAIST team could cut development costs to about half that because it is powered by environmentally friendly fuel," he said.
The lander, product of a six-year-long effort, represents remarkable advancement in the technology for developing spacecraft for lunar missions.
2008.12.01 View 11269 -
Method to Synthesize New Lithium Ion Battery Cathode Material Identified
A KAIST research team headed by Prof. Do-Kyung Kim at the Department of Materials Science and Engineering developed a technology to synthesize a new lithium ion battery spinel cathode which is regarded as a core part of hybrid and lithium battery cars.
The research was conducted in collaboration with a research team of Prof. Yi Cui at Stanford University"s Department of Chemistry. Their findings were introduced in the November issue of Nano Letters, one of the leading academic journals in nano-science.
The newly synthesized lithium ion battery spinel cathode known as spinel LiMn2O4 nanorods is attracting interests as an alternative cathode material since it is a low-cost, environmentally friendly substance for Li-ion battery cathodes. Its raw material is also highly available.
Lithium ion batteries with high energy and power density are important for consumer electronic devices, portable power tools, and vehicle electrification. LixCoO2 is a commonly used cathode material in commercial lithium iron batteries. However, the high cost, toxicity, and limited abundance of cobalt have been recognized to be disadvantageous.
2008.11.20 View 11790 -
KAIST Research Team Unveils Method to Fabricate Photonic Janus Balls
A research team led by Prof. Seung-Man Yang of the Department of Chemical and Biomolecular Engineering has found a method to fabricate photonic Janus balls with isotropic structural colors.
The finding draws attention since the newly-fabricated photonic balls may prove useful pigments for the realization of e-paper or flexible electronic displays.
The breakthrough was published in the Nov. 3 edition of the science journal "Advanced Materials." The Nov. 6 issue of "Nature" also featured it as one of the research highlights under the title of "Future Pixels."
Prof. Yang"s research team found that tiny marbles, black on one side and colored on the other, can be made by "curing" suspensions of silica particles with an ultraviolet lamp. When an electric field is applied, the marbles line up so that the black sides all face upwards, which suggests they may prove useful pigments for flexible electronic displays.
The researchers suspended a flow of carbon-black particles mixed with silica and a transparent or colored silica flow in a resin that polymerizes under ultraviolet light. They then passed the mixture through a tiny see-through tube. The light solidified the silica and resin as balls with differently colored regions, each about 200 micrometers in diameter.
Over the last decades, the development of industrial platforms to artificially fabricate structural color pigments has been a pressing issue in the research areas of materials science and optics. Prof. Yang, who is also the director of the National Creative Research Initiative Center for Integrated Optofluidic Systems, has led the researches focused on fabrication of functional nano-materials through the process of assembling nano-building blocks into designed patterns.
The "complementary hybridization of optical and fluidic devices for integrated optofluidic systems" research was supported by a grant from the Creative Research Initiative Program of the Ministry of Education, Science & Technology.
2008.11.12 View 12951 -
KAIST Team Identifies Nano-scale Origin of Toughness in Rare Earth-added Silicon Carbide
A research team led by Prof. Do-Kyung Kim of the Department of Materials Science and Engineering of KAIST has identified the nano-scale origin of the toughness in rare-earth doped silicon carbide (RE-SiC), university sources said on Monday (Oct. 6).
The research was conducted jointly with a U.S. team headed by Prof. R. O. Ritchie of the Department of Materials Science and Engineering, University of California, Berkeley.
The findings were carried in the online edition of Nano Letters published by the American Chemical Association.
Silicon carbide, a ceramic material known to be one of the hardest substances, are potential candidate materials for many ultrahigh-temperature structural applications. For example, if SiC, instead of metallic alloys, is used in gas-turbine engines for power generation and aerospace applications, operating temperatures of many hundred degrees higher can be obtained with a consequent dramatic increase in thermodynamic efficiency and reduced fuel consumption. However, the use of such ceramic materials has so far been severely limited since the origin of the toughness in RE-SiC remained unknown thus far.
In order to investigate the origin of the toughness in RE-SiC, the researchers attempted to examine the mechanistic nature of the cracking events, which they found to occur precisely along the interface between SiC grains and the nano-scale grain-boundary phase, by using ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy. The research found that for optimal toughness, the relative elastic modulus across the grain-boundary phase and the interfacial fracture toughness are the most critical material parameters; both can be altered with appropriate choice of rare-earth elements.
In addition to identifying the nano-scale origin of the toughness in RE-SiC, the findings also contributed to precisely predicting how the use of various rare-earth elements lead to difference in toughness.
University sources said that the findings will significantly advance the date when RE-SiC will replace metallic alloys in gas-turbine engines for power generation and aerospace applications.
2008.10.08 View 13880 -
KAIST Professor Exposes Structural Dynamics of Protein in Solution
-- Dr. Hyot-Cherl Ihee"s 3-Year Research Is Valuable in Pharmaceutical Application
Prof. Hyot-Cherl Ihee and his team at the Department of Chemistry, KAIST, has successfully unveiled the structural dynamics of protein in solution as a result of more than three years" research work.
Nature Methods, a sister publication of the authoritative science magazine Nature, published the treatise, titled "Tracking the structural dynamics of proteins in solution using time-resolved wide-angle X-ray scattering" in its Sept. 22 online edition. The research paper will be carried in the magazine"s printed version in its October edition, according to Dr. Lee who is its correspondence author.
In May 2005, Prof. Ihee successfully photographed the structural dynamics of protein in solid state and his findings were published in the Proceedings of National Academy of Science of the United States. As protein normally exists in human body in solution, not in solid state, he directed his research to developing the technology to capture protein"s dynamics in resolved state.
In July that year, Prof. Ihee succeeded in measuring the structural changes of simple organic molecules in real time. He further developed the technology to uncover the structural dynamics of hemoglobin, myoglobin and cytochrome C.
Prof. Ihee"s research, helped with the Education-Science-Technology Ministry"s Creative Research Promotion Fund, can be applied to new pharmaceutical development projects as well as nanotechnology development, according to KAIST officials.
Prof. Ihee who earned his doctorate at California Institute of Technology in 1994 began teaching at KAIST in 2003. He won the Young Scientist Award given by the Korean government in 2006.
2008.09.22 View 12565 -
KAIST Professor Finds Paradox in Human Behaviors on Road
-Strange as it might seem, closing roads can cut delays
A new route opened to ease traffic jam, but commuting time has not been reduced.Conversely, motorists reached their destinations in shorter times after a big street was closed. These paradoxical phenomena are the result of human selfishness, according to recent findings of a research team led by a KAIST physics professor.
Prof. Ha-Woong Jeong, 40, at the Department of Physics, conducted a joint research with a team from Santa Fe Institute of the U.S. to analyze the behaviors of drivers in Boston, New York and London. Their study found that when individual drivers, fed with traffic information via various kinds of media, try to choose the quickest route, it can cause delays for others and even worsen congestion.
Prof. Jeong and his group"s study will be published in the Sept. 18 edition of the authoritative Physical Review Letters. The London-based Economist magazine introduced Prof. Jeong"s finding in its latest edition.
Prof. Jeong, a pioneer in the study of "complex system," has published more than 70 research papers in the world"s leading science journals, including Nature, PNAS and Physical Review Letters. "Initially, my study was to reduce annoyance from traffic jam during rush hours," Prof. Jeong said. "Ultimately, it is purposed to eliminate inefficiency located in various corners of social activities, with the help of the network science."
The Economist article read (in part):
"...when individual drivers each try to choose the quickest route it can cause delays for others and even increase hold-ups in the entire road network.
"The physicists give a simplified example of how this can happen: trying to reach a destination either by using a short but narrow bridge or a longer but wide motorway. In their hypothetical case, the combined travel time of all the drivers is minimized if half use the bridge and half the motorway. But that is not what happens. Some drivers will switch to the bridge to shorten their commute, but as the traffic builds up there the motorway starts to look like a better bet, so some switch back. Eventually the traffic flow on the two routes settles into what game theory calls a Nash equilibrium, named after John Nash, the mathematician who described it. This is the point where no individual driver could arrive any faster by switching routes.
"The researchers looked at how this equilibrium could arise if travelling across Boston from Harvard Square to Boston Common. They analysed 246 different links in the road network that could be used for the journey and calculated traffic flows at different volumes to produce what they call a “price of anarchy” (POA). This is the ratio of the total cost of the Nash equilibrium to the total cost of an optimal traffic flow directed by an omniscient traffic controller. In Boston they found that at high traffic levels drivers face a POA which results in journey times 30% longer than if motorists were co-ordinated into an optimal traffic flow. Much the same thing was found in London (a POA of up to 24% for journeys between Borough and Farringdon Underground stations) and New York (a POA of up to 28% from Washington Market Park to Queens Midtown Tunnel).
"Modifying the road network could reduce delays. And contrary to popular belief, a simple way to do that might be to close certain roads. This is known as Braess’s paradox, after another mathematician, Dietrich Braess, who found that adding extra capacity to a network can sometimes reduce its overall efficiency.
"In Boston the group looked to see if the paradox could be created by closing any of the 246 links. In 240 cases their analysis showed that a closure increased traffic problems. But closing any one of the remaining six streets reduced the POA of the new Nash equilibrium. Much the same thing was found in London and New York. More work needs to be done to understand these effects, say the researchers. But even so, planners should note that there is now evidence that even a well intentioned new road may make traffic jams worse."
2008.09.18 View 13252