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Total Synthesis of Flueggenine C via an Accelerated Intermolecular Rauhut-Currier Reaction
The first total synthesis of dimeric securinega alkaloid (-)-flueggenine C was completed via an accelerated intermolecular Rauhut–Currier (RC) reaction. The research team led by Professor Sunkyu Han in the Department of Chemistry succeeded in synthesizing the natural product by reinventing the conventional RC reaction. The total synthesis of natural products refers to the process of synthesizing secondary metabolites isolated from living organisms in the laboratory through a series of chemical reactions. Each stage of chemical reaction needs to be successful to produce the final target molecule, and thus the process requires high levels of patience and creativity. For that reason, the researchers working on natural products total synthesis are often called “molecular artists”. Despite numerous reports on the total synthesis of monomeric securinegas, the synthesis of dimeric securinegas, whose monomeric units are connected by a putative enzymatic RC reaction, has not been reported to date. The team used a Rauhut-Currier (RC) reaction, a carboncarbon bond forming a reaction between two Michael acceptors first reported by Rauhut and Currier in 1963, to successfully synthesize a dimeric natural product, flueggenine C. This new work featured the first application of an intermolecular RC reaction in total synthesis. The conventional intermolecular RC reaction was driven non-selectively by a toxic nucleophilic catalyst at a high temperature of over 150°C and a highly concentrated reaction mixture, and thus has never been applied to natural products total synthesis. To overcome this long-standing problem, the research team placed a nucleophilic moiety at the γ-position of the enone derivative. As a result, the RC reaction could be induced by the simple addition of a base at ambient temperature and dilute solution, without the need of a nucleophilic catalyst. Using this newly discovered reactivity, the team successfully synthesized the natural product (-)-flueggenine C from commercially available amino acid derivative in 12 steps. Professor Han said, “Our key finding regarding the remarkably improved reactivity and selectivity of the intermolecular RC reaction will serve as a significant stepping stone in allowing this reaction to be considered a practical and reliable chemical tool with broad applicability in natural products, pharmaceuticals, and materials syntheses. ” This research was led by Ph.D. candidate Sangbin Jeon and was published in The Journal of the American Chemical Society (JACS) on May 10. This research was funded by KAIST start-up funds, HRHR (High-Risk High-Return), RED&B (Research, Education, Development & Business) projects, the National Research Foundation of Korea, and the Institute for Basic Science. (Figure 1: Representative dimeric/oligomeric securinega alkaloids) (Figure 2: Our reinvented Rauhut-Currier reaction) (Figure 3: Total Synthesis of (-)-flueggenine C)
Processable High Internal Phase Pickering Emulsion Using Depletion Attraction
Professor Siyoung Choi’s research team from the KAIST Department of Chemical & Biomolecular Engineering used physical force to successfully produce a stable emulsion. Emulsions, commonly known as cosmetic products, refer to stably dispersed structures of oil droplets in water (or water droplets in oil). Pickering emulsions refer to emulsions stabilized using solid particles, instead of detergent. Traditionally, it is said that water and oil do not mix. Until recently, detergent was added to mix oil and water for dispersion. Emulsions have traditionally been produced using this technique and are currently used for products such as mayonnaise, sun block, and lotion. On the other hand, Pickering emulsions have been used after stabilization of chemical treatments on solid particle surfaces to enhance adsorption power. However, there were limitations in its application, since the treatment process is complex and its applicable range remains limited. Instead of chemical treatment on Pickering emulsion surfaces, the research team mixed small macromolecules a few nanometer in size with larger solid particles (tens of nanometers to a few micrometers). This induced depletion force was used to successfully stabilize the emulsion. Depletion force refers to the force a large number of small particles induces to aggregate the bigger particles, in order to secure free space for themselves. In short, the force induces an attraction between larger particles. Until now, depletion force could only be applied to solids and solid particles. However, the research team used macromolecules and large particles such as solid particles and oil droplets to show the applicability of depletion force between solids and liquids. By introducing macromolecules that act as smaller particles, hydrophilic solid particles enhanced the adsorption of solid particles to the oil droplet surface, while preventing dissociation from the particle surface, resulting in the maintenance of a stable state. The research team confirmed the possibility of the simple production of various porous macromolecular materials using stable Pickering emulsions. Such porous macromolecules are expected to be applicable in separation film, systems engineering, drug delivery, and sensors, given their large surface area. Professor KyuHan Kim, the first author said, “Until now, depletion force has only been used between solid colloid particles. This research has scientific significance since it is the first example of using depletion force between solid particles and liquid droplets.” Professor Choi said, “Beyond its academic significance, this technology could contribute to industries and national competitiveness.” He continued, “Since this technology uses physical force, not chemical, to produce stable emulsion, it can be used regardless of the type of solid particle and macromolecule. Further, it could be used in customized porous material production for special purposes.” The research was published in Nature Communications online on February 1. In particular, this research is significant since an undergraduate student, Subeen Kim, participated in the project as a second author through the KAIST Undergraduate Research Program (URP). This research was funded by the National Research Foundation of Korea. (Figure 1: Images of the inner structure of porous macromolecules produced using the new technology) (Figure 2: Images showing the measurement of rheological properties of Pickering emulsions and system processability) (Figure 3: Images showing a stable Pickering emulsion system)
Professor Won Do Heo Receives 'Scientist of the Month Award'
Professor Won Do Heo of the Department of Biological Sciences was selected as the “Scientist of the Month” for April 2017 by the Ministry of Science, ICT and Future Planning and the National Research Foundation of Korea. Professor Heo was recognized for his suggestion of a new biological research method developing various optogenetics technology which controls cell function by using light. He developed the technology using lasers or LED light, without the need for surgery or drug administration, to identify the cause of diseases related to calcium ions such as Alzheimer’s disease and cancer. The general technique used in optogenetics, that control cells in the body with light, is the simple activation and deactivation of neurons. Professor Heo developed a calcium ion channel activation technique (OptoSTIM1) to activate calcium ions in the body using light. He also succeeded in increasing calcium concentrations with light to enhance the memory capacity of mice two-fold. Using this technology, the desired amount and residing time of calcium ion influx can be controlled by changing light intensity and exposure periods, enabling the function of a single cell or various cells in animal tissue to be controlled remotely. The experimental results showed that calcium ion influx can be activated in cells that are affected by calcium ions, such as normal cells, cancer cells, and human embryonic stem cells. By controlling calcium concentrations with light, it is possible to control biological phenomena, such as cellular growth, neurotransmitter transmission, muscle contraction, and hormone control. Professor Heo said, “Until now, it was standard to use optogenetics to activate neurons using channelrhodopsin. The development of this new optogenetic technique using calcium ion channel activation can be applied to various biological studies, as well as become an essential research technique in neurobiology. The “Scientist of the Month Award” is given every month to one researcher who made significant contributions to the advancement of science and technology with their outstanding research achievement. The awardee will receive prize money of ten million won.
A Transport Technology for Nanowires Thermally Treated at 700 Celsius Degrees
Professor Jun-Bo Yoon and his research team of the Department of Electrical Engineering at KAIST developed a technology for transporting thermally treated nanowires to a flexible substrate and created a high performance device for collecting flexible energy by using the new technology. Mr. Min-Ho Seo, a Ph.D. candidate, participated in this study as the first author. The results were published online on January 30th in ACS Nano, an international journal in the field of nanoscience and engineering. (“Versatile Transfer of an Ultralong and Seamless Nanowire Array Crystallized at High Temperature for Use in High-performance Flexible Devices,” DOI: 10.1021/acsnano.6b06842) Nanowires are one of the most representative nanomaterials. They have wire structures with dimensions in nanometers. The nanowires are widely used in the scientific and engineering fields due to their prominent physical and chemical properties that depend on a one-dimensional structure, and their high applicability. Nanowires have much higher performance if their structure has unique features such as an excellent arrangement and a longer-than-average length. Many researchers are thus actively participating in the research for making nanowires without much difficulty, analyzing them, and developing them for high performance application devices. Scientists have recently favored a research topic on making nanowires chemically and physically on a flexible substrate and applies the nanowires to a flexible electric device such as a high performance wearable sensor. The existing technology, however, mixed nanowires from a chemical synthesis with a solution and spread the mixture on a flexible substrate. The resultant distribution was random, and it was difficult to produce a high performance device based on the structural advantages of nanowires. In addition, the technology used a cutting edge nano-process and flexible materials, but this was not economically beneficial. The production of stable materials at a temperature of 700 Celsius degrees or higher is unattainable, a great challenge for the application. To solve this problem, the research team developed a new nano-transfer technology that combines a silicon nano-grating board with a large surface area and a nano-sacrificial layer process. A nano-sacrificial layer exists between nanowires and a nano-grating board, which acts as the mold for the nano-transfer. The new technology allows the device undergo thermal treatment. After this, the layer disappears when the nanowires are transported to a flexible substrate. This technology also permits the stable production of nanowires with secured properties at an extremely high temperature. In this case, the nanowires are neatly organized on a flexible substrate. The research team used the technology to manufacture barium carbonate nanowires on top of the flexible substrate. The wires secured their properties at a temperature of 700℃ or above. The team employed the collection of wearable energy to obtain much higher electrical energy than that of an energy collecting device designed based on regular barium titanate nanowires. The researchers said that their technology is built upon a semiconductor process, known as Physical Vapor Deposition that allows various materials such as ceramics and semiconductors to be used for flexible substrates of nanowires. They expected that high performance flexible electric devices such as flexible transistors and thermoelectric elements can be produced with this method. Mr. Seo said, “In this study, we transported nanowire materials with developed properties on a flexible substrate and showed an increase in device performance. Our technology will be fundamental to the production of various nanowires on a flexible substrate as well as the feasibility of making high performance wearable electric devices.” This research was supported by the Leap Research Support Program of the National Research Foundation of Korea. Fig. 1. Transcription process of new, developed nanowires (a) and a fundamental mimetic diagram of a nano-sacrificial layer (b) Fig. 2. Transcription results from using gold (AU) nanowires. The categories of the results were (a) optical images, (b) physical signals, (c) cross-sectional images from a scanning electron microscope (SEM), and (d-f) an electric verification of whether the perfectly arranged nanowires were made on a large surface. Fig. 3. Transcription from using barium titanate (BaTiO3) nanowires. The results were (a) optical images, (b-e) top images taken from an SEM in various locations, and (f, g) property analysis. Fig. 4. Mimetic diagram of the energy collecting device from using a BaTiO3 nanowire substrate and an optical image of the experiment for the miniature energy collecting device attached to an index finger.
An Improved Carbon Nanotube Semiconductor
Professor Yang-Kyu Choi and his research team of the School of Electrical Engineering at KAIST collaborated with Professor Sung-Jin Choi of Kookmin University to develop a large-scale carbon nanotube semiconductor by using a 3-D fin-gate structure with carbon nanotubes on its top. Dong Il Lee, a postdoctoral researcher at KAIST’s Electrical Engineering School, participated in this study as the first author. It was published in ACS Nano on November 10, 2016, and was entitled “Three-Dimensional Fin-Structured Semiconducting Carbon Nanotube Network Transistor.” A semiconductor made with carbon nanotubes operates faster than a silicon semiconductor and requires less energy, yielding higher performance. Most electronic equipment and devices, however, use silicon semiconductors because it is difficult to fabricate highly purified and densely packed semiconductors with carbon nanotubes (CNTs). To date, the performance of CNTs was limited due to their low density. Their purity was also low, so it was impossible to make products that had a constant yield on a large-surface wafer or substrate. These characteristics made the mass production of semiconducting CNTs difficult. To solve these difficulties, the research team used a 3-D fin-gate to vapor-deposit carbon nanotubes on its top. They developed a semiconductor that had a high current density with a width less than 50 nm. The three-dimensional fin structure was able to vapor-deposit 600 carbon nanotubes per micrometer. This structure could have 20 times more nanotubes than the two dimensional structure, which could only vapor-deposit thirty in the same 1 micrometer width. In addition, the research team used semi-conductive carbon nanotubes having a purity rating higher than 99.9% from a previous study to obtain a high yield semiconductor. The semiconductor from the research group has a high current density even with a width less than 50 μm. The new semiconductor is expected to be five times faster than a silicon-based semiconductor and will require five times less electricity during operation. Furthermore, the new semiconductor can be made by or will be compatible with the equipment for producing silicon-based semiconductors, so there will be no additional costs. Researcher Lee said, “As a next generation semiconductor, the carbon nanotube semiconductor will have better performance, and its effectiveness will be higher.” He also added, “Hopefully, the new semiconductor will replace the silicon-based semiconductors in ten years.” This study received support from the Center for Integrated Smart Sensors funded by the Ministry of Science, ICT & Future Planning of Korea as the Global Frontier Project, and from the CMOS (Complementary Metal-Oxide-Semiconductor) THz Technology Convergence Center of the Pioneer Research Center Program sponsored by the National Research Foundation of Korea. Picture 1: 3D Diagram of the Carbon Nanotube Electronic Device and Its Scanning Electron Microscope (SEM) Image Picture 2: 3D Transistor Device on an 8-inch Base and the SEM Image of Its Cross Section
Professor Tae-Eog Lee Receives December's Scientist of the Month Award by the Korean Government
Professor Tae-Eog Lee of the Industrial and Systems Engineering at KAIST received the Scientist of the Month Award for December 2015. The award is sponsored by the Ministry of Science, ICT and Future Planning of Korea, which was hosted by the National Research Foundation of Korea. The award recognizes Professor Lee’s efforts to advance the field of semiconductor device fabrication processing. This includes the development of the most efficient scheduling and controlling of cluster tools. He also created mathematical solutions to optimize the complicated cycle time of cluster tools in semiconductor manufacturing and the process of robot task workload. Professor Lee contributed to the formation of various discrete event systems and automation systems based on his mathematical theories and solutions and advanced a scheduling technology for the automation of semiconductor production. He has published 18 research papers in the past three years and has pioneered to develop Korean tool schedulers through the private sector-university cooperation.
Establishment of System Metabolic Engineering Strategies
Although conventional petrochemical processes have generated chemicals and materials which have been useful to mankind, they have also triggered a variety of environmental problems including climate change and relied too much on nonrenewable natural resources. To ameliorate this, researchers have actively pursued the development of industrial microbial strains around the globe in order to overproduce industrially useful chemicals and materials from microbes using renewable biomass. This discipline is called metabolic engineering. Thanks to advances in genetic engineering and our knowledge of cellular metabolism, conventional metabolic engineering efforts have succeeded to a certain extent in developing microbial strains that overproduce bioproducts at an industrial level. However, many metabolic engineering projects launched in academic labs do not reach commercial markets due to a failure to fully integrate industrial bioprocesses. In response to this, Distinguished Professor Sang Yup Lee and Dr. Hyun Uk Kim, both from the Department of Chemical and Biomolecular Engineering at KAIST, have recently suggested ten general strategies of systems metabolic engineering to successfully develop industrial microbial strains. Systems metabolic engineering differs from conventional metabolic engineering by incorporating traditional metabolic engineering approaches along with tools of other fields, such as systems biology, synthetic biology, and molecular evolution. The ten strategies of systems metabolic engineering have been featured in Nature Biotechnology released online in October 2015, which is entitled "Systems strategies for developing industrial microbial strains." The strategies cover economic, state-of-the-art biological techniques and traditional bioprocess aspects. Specifically, they consist of: 1) project design including economic evaluation of a target bioproduct; 2) selection of host strains to be used for overproduction of a bioproduct; 3) metabolic pathway reconstruction for bioproducts that are not naturally produced in the selected host strains; 4) increasing tolerance of a host strain against the bioproduct; 5) removing negative regulatory circuits in the microbial host limiting overproduction of a bioproduct; 6) rerouting intracellular fluxes to optimize cofactor and precursor availability necessary for the bioproduct formation; 7) diagnosing and optimizing metabolic fluxes towards product formation; 8) diagnosis and optimization of microbial culture conditions including carbon sources; 9) system-wide gene manipulation to further increase the host strain's production performance using high-throughput genome-scale engineering and computational tools; and 10) scale-up fermentation of the developed strain and diagnosis for the reproducibility of the strain's production performance. These ten strategies were articulated with successful examples of the production of L-arginine using Corynebacterium glutamicum, 1,4-butanediol using Escherichia coli, and L-lysine and bio-nylon using C. glutamicum. Professor Sang Yup Lee said, "At the moment, the chance of commercializing microbial strains developed in academic labs is very low. The strategies of systems metabolic engineering outlined in this analysis can serve as guidelines when developing industrial microbial strains. We hope that these strategies contribute to improving opportunities to commercialize microbial strains developed in academic labs with drastically reduced costs and efforts, and that a large fraction of petroleum-based processes will be replaced with sustainable bioprocesses." Lee S. Y. & Kim, H. U. Systems Strategies for Developing Industrial Microbial Strains. Nature Biotechnology (2015). This work was supported by the Technology Development Program to Solve Climate Change on Systems Metabolic Engineering for Biorefineries (NRF-2012M1A2A2026556) and by the Intelligent Synthetic Biology Center through the Global Frontier Project (2011-0031963) from the Ministry of Science, ICT and Future Planning (MSIP), Korea, and through the National Research Foundation (NRF) of Korea. This work was also supported by the Novo Nordisk Foundation. Picture: Concept of the Systems Metabolic Engineering Framework (a) Three major bioprocess stages (b) Considerations in systems metabolic engineering to optimize the whole bioprocess. List of considerations for the strain development and fermentation contribute to improving microbial strain's production performance (red), whereas those for the separation and purification help in reducing overall operation costs by facilitating the downstream process (blue). Some of the considerations can be repeated in the course of systems metabolic engineering.
3D Plasmon Antenna Capable of Focusing Light into Few Nanometers
Professors Myung-Ki Kim and Yong-Hee Lee, both of the Physics Department at KAIST, and their research teams have developed a three dimensional (3D) gap-plasmon antenna which can focus light into a space a few nanometers wide. Their research findings were published in the June 10th issue of Nano Letters. Focusing light into a point-like space is an active research field with many applications. However, concentrating light into a smaller space than its wavelength is often hindered by diffraction. To tackle this problem, many researchers have utilized the plasmonic phenomenon of a metal where light can be confined to a greater extent by overcoming the diffraction limit. Many researchers have focused on developing a two dimensional (2D) plasmon antenna and were able to focus a light under 5 nanometers wide. However, this 2D antenna revealed a challenge: the light disperses to the opposite end regardless of how small its beam was focused. To solve this difficulty, a 3D structure had to be employed to maximize the light's intensity. Adopting the proximal focused-ion-beam milling technology, the KAIST research team developed a 3D four nanometer wide gap-plasmon antenna. By squeezing the photons into a 3D nano space of 4 x 10 x 10 nm3 size, the researchers were able to increase the intensity of light by 400,000 times stronger than that of the incident light. Capitalizing on the enhanced intensity of light within the antenna, they intensified the second-harmonic signal and verified that the light was focused in the nano gap by scanning cathodoluminescent images. The researchers anticipate that this technology will improve the speed of data transfer and processing up to the level of a terahertz (one trillion times per second) and to enlarge the storage volume per unit area on hard disks by 100 times. In addition, high definition images of submolecule size can be taken with actual light, instead of with an electron microscope, while improving the semiconductor process to a smaller size of few nanometers. Professor Kim said, “A simple yet ingenious idea has shifted the research paradigm from 2D gap-plasmon antennas to 3D antennas. This technology will see numerous applications including in the field of information technology, data storage, imaging medical science, and semiconductor processes.” The research was sponsored by the National Research Foundation of Korea. Figure 1: 3D Gap-Plasmon Antenna Structure and Simulation Results Figure 2 – Constructed 3D Gap-Plasmon Antenna Structure Figure 3 – Amplified Second Harmonic Signal Generation and Light Focused in the Nano Gap
Hierarchically-Porous Polymers with Fast Absorption
KAIST's Professor Myungeun Seo and his research team from the Graduate School of Nanoscience and Technology has developed a method to form micropores of less than 2 nanometers within porous polymers where 10 nanometers long mesopores connect like a net. The advantage of the porous polymers is fast absorption of molecules. Porous polymers with micropores of less than 2 nanometers, like a zeolite, have a large surface area. They are used as a means to store hydrogen-based molecules or as a catalytic support that can be used as a surface to convert a material into a desired form. However, because the size of the pores in its path was too small for the molecules, it took a long time to spread into the pores and reach the surface. To reach the surface efficiently, a lung cell or the vein of a leaf has a structure wherein the pores are subdivided into different sizes so that the molecule can spread throughout the organ. A technology that can create not only micropores but also bigger pores was necessary in order to create such structure. The research team solved the issue by implementing a "self-assembly" of block polymers to easily form a net-like nanostructure from mesopores of 10 nanometers. The team created hierarchically-porous polymers consisting of two different types of pores by using a hypercrosslinking reaction along with the "self-assembly" method. The reaction creates micropores within the chain after the polymer chain is confined by a chemical bond. This porous polymer has micropores that are smaller than 2 nanometers on the walls of mesopores while 10 nanometers long mesopores forming 3-dimensional net structures. Because of the "self-assembly" method, the size of mesopores can be adjusted within the range of 6 to 15 nanometers. This is the first case where a porous polymer has both well-defined mesopores and micropores. The research team verified the effect of hierarchically-porous structures on absorption of molecules by confirming that the porous polymer had faster absorption speeds than a polymer consisting only of micropores. Professor Seo said, “The study has found a simple way to create different sizes of pores within a polymer.” He expected that the hierarchically-porous polymers can be used as a catalytic support in which fast diffusion of molecules is essential, or for molecule collection. The research was sponsored by National Research Foundation of Korea and published online in the Journal of the American Chemical Society. Figure 1 – Net-like Structure of Hierarchically-Porous Polymers with Mesopores and Micropores on the walls of Mesopores. Figure 2 - Hierarchically-Porous Polymers Figure 3 – Comparison of Porous-Polymers consisting of Mesopores only (left), and Mesopores and Micropores (right)
A Key Signal Transduction Pathway Switch in Cardiomyocyte Identified
A KAIST research team has identified the fundamental principle in deciding the fate of cardiomyocyte or heart muscle cells. They have determined that it depends on the degree of stimulus in β-adrenergic receptor signal transduction pathway in the cardiomyocyte to control cells' survival or death. The findings, the team hopes, can be used to treat various heart diseases including heart failure. The research was led by KAIST Department of Bio and Brain Engineering Chair Professor Kwang-Hyun Cho and conducted by Dr. Sung-Young Shin (lead author) and Ph.D. candidates Ho-Sung Lee and Joon-Hyuk Kang. The research was conducted jointly with GIST (Gwangju Institute of Science and Technology) Department of Biological Sciences Professor Do-Han Kim’s team. The research was supported by the Ministry of Science, ICT and Future Planning, Republic of Korea, and the National Research Foundation of Korea. The paper was published in Nature Communications on December 17, 2014 with the title, “The switching role of β-adrenergic receptor signalling in cell survival or death decision of cardiomyocytes.” The β-adrenergic receptor signal transduction pathway can promote cell survival (mediated by β2 receptors), but also can result in cell death by inducing toxin (mediated by β1 receptors) that leads to various heart diseases including heart failure. Past attempts to identify the fundamental principle in the fate determining process of cardiomyocyte based on β-adrenergic receptor signalling concluded without much success. The β-adrenergic receptor is a type of protein on the cell membrane of cardiomyocyte (heart muscle cell) that when stimulated by neurohormones such as epinephrine or norepinephrine would transduce signals making the cardiomyocyte contract faster and stronger. The research team used large-scale computer simulation analysis and systems biology to identify ERK* and ICER** signal transduction pathways mediated by a feed-forward circuit as a key molecular switch that decides between cell survival and death. Weak β-adrenergic receptor stimulations activate ERK signal transduction pathway, increasing Bcl-2*** protein expression to promote cardiomyocyte survival. On the other hand, strong β-adrenergic receptor stimulations activate ICER signal transduction pathway, reducing Bcl-2 protein expression to promote cardiomyocyte death. Researchers used a systems biology approach to identify the mechanism of B-blocker****, a common drug prescribed for heart failure. When cardiomyocyte is treated with β1 inhibitor, strong stimulation on β-adrenergic receptor increases Bcl-2 expression, improving the chance of cardiomyocyte survival, a cell protection effect. Professor Kwang-Hyun Cho said, “This research used systems biology, an integrated, convergence research of IT (information technology) and BT (biotechnology), to successfully identify the mechanism in deciding the fate of cardiomyocytes based on the β-adrenergic receptor signal transduction pathway for the first time. I am hopeful that this research will enable the control of cardiomyocyte survival and death to treat various heart diseases including heart failure.” Professor Cho’s team was the first to pioneer a new field of systems biology, especially concerning the complex signal transduction network involved in diseases. Their research is focused on modelling, analyzing simulations, and experimentally proving signal pathways. Professor Cho has published 140 articles in international journals including Cell, Science, and Nature. * ERK (Extracellular signal-regulated kinases): Signal transduction molecule involved in cell survival ** ICER (Inducible cAMP early repressor): Signal transduction molecule involved in cell death *** Bcl-2 (B-cell lymphoma 2): Key signal transduction molecule involved in promotion of cell survival **** β-blocker: Drug that acts as β-adrenergic receptor inhibitor known to slow the progression of heart failure, hence used most commonly in medicine. Picture: A schematic diagram for the β-AR signalling network
Broadband and Ultrathin Polarization Manipulators Developed
Professor Bumki Min from the Department of Mechanical Engineering at KAIST has developed a technology that can manipulate a polarized light in broadband operation with the use of a metamaterial. It is expected that this technology will lead to the development of broadband optical devices that can be applied to broadband communication and display. When an object or its structure is analyzed by using a polarized light such as a laser, the results are generally affected by the polarized state of the light. Therefore, in an optics laboratory, the light is polarized by various methods. In such cases, researchers employ wave plates or photoactive materials. However, the performance of these devices depend vastly on wavelength, and so they are not suitable to be used as a polarizer, especially in broadband. There were many attempts to make artificial materials that are very photoactive by using metamaterials which have a strong resonance. Nonetheless, because the materials had an unavoidable dispersion in the resonance frequency, they were not adequate for broadband operation. Professor Min’s research team arranged and connected helical metamaterials that are smaller than the wavelength of light. They verified theoretically and experimentally that polarized light can be constantly rotated regardless of the wavelength by super-thin materials that have thickness less than one-tenth of the wavelength of the light. The experiment which confirmed the theory was conducted in the microwave band. Broadband polarized rotational 3D metamaterials were found to rotate the polarized microwave within the range of 0.1 GHz to 40 GHz by 45 degrees regardless of its frequency. This nondispersive property is quite unnatural because it is difficult to find a material that does not change in a wide band. In addition, the research team materialized the broadband nondispersive polarized rotational property by designing the metamaterial in a way that it has chirality, which determines the number of rotations proportional to the wavelength. Professor Min said, “As the technology is able to manipulate ultrathin polarization of light in broadband, it will lead to the creation of ultra-shallow broadband optical devices.” Sponsored by the Ministry of Science, ICT and Future Planning of the Republic of Korea and the National Research Foundation of Korea, this research was led by a PhD candidate, Hyun-Sung Park, under the guidance of Professor Min. The research findings were published online in the November 17th issue of Nature Communications. Figure 1 – Broadband and Ultrathin Polarization Manipulators Produced by 3D Printer Figure 2 – Concept of Broadband and Ultrathin Polarization Manipulators
Development of a Photonic Diode with Light Speed, Single-Direction Transfer
A photonic diode using a nitride semiconductor rod can increase the possibility of developing all-optical integrated circuits, an alternative to conventional integrated circuits. Professor Yong-Hoon Cho's research team from the Department of Physics, KAIST, developed a photonic diode which can selectively transfer light in one way, using semiconductor rods. The photonic diode has a diameter of hundreds of nanometers (nm) and a length of few micrometers. This size enables its use in large-scale integration (LSI). The diode’s less sensitivity towards polarized light angle makes it more useful. In an integrated circuit, a diode controls the flow of electrons. If this diode controls light rather than electrons, data can be transferred at high speed, and its loss is minimized to a greater extent. Since these implementations conserve more energy, this is a very promising future technology. However, conventional electronic diodes, made up of asymmetric meta-materials or photonic crystalline structures, are large, which makes them difficult to be used in LSI. These diodes could only be implemented under limited conditions due to its sensitivity towards polarized light angle. The research team used nitride semiconductor rods to develop a highly efficient photonic diode with distinct light intensities from opposite ends. The semiconductor rod yields different amount of energy horizontally. According to the research team, this is because the width of the quantum well and its indium quantity is continuously controlled. Professor Cho said, "A large energy difference in a horizontal direction causes asymmetrical light propagation, enabling it to be operated as a photonic diode." He added that “If light, instead of electrons, were adopted in integrated circuits, the transfer speed would be expected as great as that of light.” The research findings were published in the September 10th issue of Nano Letters as the cover paper. Under the guidance of Professor Cho, two Ph.D. candidates, Suk-Min Ko and Su-Hyun Gong, conducted this research. This research project was sponsored by the National Research Foundation of Korea and KAIST’s EEWS (energy, environment, water, and sustainability) Research Center. Figure Description: Computer simulated image of photonic diode made of semiconductor rod implemented in an all-optical integrated circuit
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