WWW
-
Characteristics of Submesoscale Geophysical Turbulence Reported
A KAIST research team has reported some of unique characteristics and driving forces behind submesoscale geophysical turbulence. Using big data analysis on ocean surface currents and chlorophyll concentrations observed using coastal radars and satellites has brought better understanding of oceanic processes in space and time scales of O(1) kilometer and O(1) hour. The outcomes of this work will lead to improved tracking of water-borne materials and performance in global and regional climate prediction models.
In 2012, United States National Aeronautics and Space Administration (NASA) released a movie clip called “Perpetual Oceans”, which visualized ocean circulation obtained from satellite altimeter-derived sea surface height observations over two and a half years. When the movie was released to the public, it received a great deal of attention because the circulation patterns were strikingly similar to “The Starry Night” by Vincent van Gogh.
“Perpetual Oceans” is full of vortical flow patterns describing the oceanic turbulent motions at mesoscale (a scale of 100 km or larger). Meanwhile, Professor Sung Yong Kim from the Department of Mechanical Engineering and his team focused on the study of the oceanic turbulence at sub-mesoscale (space and time scales of 1 to 100 km and hours).
Sub-mesoscale processes are important because they contribute to the vertical transport of oceanic tracers, mass, buoyancy, and nutrients and rectify both the mixed layer structure and upper ocean stratification. These process studies have been primarily based on numerical simulations because traditional in situ ocean measurements can be limited in their capability to resolve the detailed horizontal and vertical structures of these processes.
The team conducted big data analysis on hourly observations of one-year ocean surface current maps and five-year chlorophyll concentration maps, obtained from remote sensing instruments such as coastal high-frequency radars (HFRs) and geostationary ocean color imagery (GOCI) to examine the unique characteristics of oceanic submesoscale processes.
The team analyzed the slope change of the wavenumber energy spectra of the observations in terms of season and sampling directions. Through the analysis, the team proved that energy cascade (a phenomenon in which large-scale energy transfers to small-scale energy or vice-versa during the turbulent energy transit) occurs in the spatial scale of 10 km in the forward and inverse directions. This is driven by baroclinic instability as opposed to the mesoscale eddy-driven frontogenesis at the O(100) km scale based on the observed regional submesoscale circulations.
This work will contribute to the parameterization of physical phenomenon of sub-mesoscale in the field of global high-resolution modeling within ocean physics and atmospheric as well as climate change. Based on the understanding of the principle of sub-mesoscale surface circulation, practical applications can be further derived for radioactivity, oil spill recovery, and marine pollutant tracking.
Moreover, the data used in this research was based on long-term observations on sub-mesoscale surface currents and concentrations of chlorophyll, which may reflect the submesoscale processes actively generated in the subpolar front off the east coast of Korea. Hence, this study can potentially be beneficial for integrated big data analyses using high-resolution coastal radar-derived surface currents and satellite-derived products and motivate interdisciplinary research between ocean physics and biology.
This research was published as two companion papers in the Journal of Geophysical Research: Oceans on August 6, 2018. (doi:10.1002/2016JC012517; doi:10.1002/2017JC013732)
Figure 1.'The Starry Night' of Van Gogh and the 'Perpetual Ocean' created by NASA's Goddard Space Flight Center.
Figure 2. A schematic diagram of the energy cascades in forward and backward directions and the spatial scale where the energy is injected.
Figure 3. A snapshot of the chlorophyll concentration map derived from geostationary ocean color imagery (GOCI) off the east coast of Korea presenting several examples of sub-mesoscale turbulent flows.
Figure 4. Energy spectra of the HFR-derived surface currents and GOCI-derived chlorophyll concentrations and the temporal variability of spectral decay slopes in the cross-shore and along-shore directions.
2018.12.13 View 6287 -
"Do Not Erect the Wall, But Build the Bridge"
(Mr. Ban gave a lecture on UN and Global Citizenship at KAIST)
“People are saying that multilateralism is under threat, but I believe that it has helped others keep away from wars. There are currently invisible walls among countries. But do not erect the wall, build the bridge!”
On December 7, KAIST invited one of the most admired people by Korea’s younger generation to give a lecture on UN and Global Citizenship, as the final session of the Global Leaders Lecture Series 2018.
He is the 33th Minister of Foreign Affairs and the 8th Secretary-General of the United Nations, Ban Ki-Moon. Mr. Ban is recognized for making significant contributions to world peace and environmental preservation during his term at the UN.
Mr. Ban first opened his lecture by explaining his great expectations for KAIST students. “KAIST is one of the outstanding universities that fosters the world’s best scientists and for that I have a great expectations for your role in the era of the Fourth Industrial Revolution. In this rapidly changing society, acquiring global citizenship is most important,” he said.
Who are global citizens? According to UNESCO, they are ‘active promoters of more peaceful, tolerant, inclusive, secure and sustainable societies’.
He stated that global leaders lacking global citizenship has resulted in so many disputes among countries and concerns for themselves.
This concept of global citizenship came to him when he studied abroad in the U.S as a young man and met John F. Kennedy. He said, “It touched my heart although I was young. He (John F. Kennedy) told me that the world leaders were not getting along well. During the hype of the Cold War, national boundaries were meaningless. The question was whether I could help others. He then encouraged me, telling me that I could change it because I was young.”
Mr. Ban proposed four required mindsets for global citizenship. The first is to have respect, empathy, and trustworthiness for others. He believes that speaking is the foundation of knowledge, while listening is the foundation of wisdom. Although the concept of philosophy might vary between the East and West, listening to others is very important for gaining respect, empathy, and trustworthiness.
The second is to be future-oriented, particularly for scientists who have the potential to change civilization. He encouraged the audience to look to the future by sharing his story about climate change. “During my term, I received strong advice from scientists that led me to prioritize the issue of climate change. I focused on climate change for better living conditions around the world.” He also added, “This cannot be done by one country. We need to all work together to live harmoniously with nature.”
Third, having a critical mindset is important, especially for scientists because it helps with solving problems by taking a scientific approach, without missing any of the small things. It is essential for scientists to find out new things, particularly in the era of the Fourth Industrial Revolution and informatization; however, they need to keep in mind how their findings will affect us. For instance, they need to question how robotics will change humans’ living patterns, as well as their role and how it links to humanity.
Last but not least, passion, which goes along with compassion, is required for helping others. Ban thinks people without passion are like the walking dead. When pursuing policies, they need to have the passion to drive it. At the same time, they need to have compassion for creating a happier life for everyone.
Mr. Ban ended by saying to the students, “You did not lead the era of informatization, but you are the beneficiaries of it. Acquiring global citizenship, you need to think how you can help even out the growth across the globe through the development of science during this era.”
2018.12.13 View 3255 -
AI-based Digital Watermarking to Beat Fake News
(from left: PhD candidates Ji-Hyeon Kang, Seungmin Mun, Sangkeun Ji and Professor Heung-Kyu Lee)
The illegal use of images has been a prevalent issue along with the rise of distributing fake news, which all create social and economic problems. Here, a KAIST team succeeded in embedding and detecting digital watermarks based on deep neural learning artificial intelligence, which adaptively responds to a variety of attack types, such as removing watermarks and hacking. Their research shows that this technology reached a level of reliability for technology commercialization.
Conventional watermarking technologies show limitations in terms of practicality, technology scalability, and usefulness because they require a predetermined set of conditions, such as the attack type and intensity. They are designed and implemented in a way to satisfy specific conditions.
In addition to those limitations, the technology itself is vulnerable to security issues because upgraded hacking technologies are constantly emerging, such as watermark removal, copying, and substitution.
Professor Heung-Kyu Lee from the School of Computing and his team provided a web service that responds to new attacks through deep neural learning artificial intelligence. It also serves as a two-dimensional image watermarking technique based on neural networks with high security derived from the nonlinear characteristics of artificial neural networks. To protect images from varying viewpoints, the service offers a depth-image-based rendering (DIBR) three-dimensional image watermarking technique.
Lastly, they provided a stereoscopic three-dimensional (S3D) image watermarking technique that minimizes visual fatigue due to the embedded watermarks. Their two-dimensional image watermarking technology is the first of its kind to be based upon artificial neural works. It acquires robustness through educating the artificial neural networking on various attack scenarios.
At the same time, the team has greatly improved on existing security vulnerabilities by acquiring high security against watermark hacking through the deep structure of artificial neural networks. They have also developed a watermarking technique embedded whenever needed to provide proof during possible disagreements.
Users can upload their images to the web service and insert the watermarks. When necessary, they can detect the watermarks for proof in any dispute.
Moreover, this technology provides services, including simulation tools, watermark adjustment, and image quality comparisons before and after the watermark is embedded.
This study maximized the usefulness of watermarking technology by facilitating additional editing and demonstrating robustness against hacking.
Hence, this technology can be applied in a variety of contents for certification, authentication, distinction tracking, and copyrights. It can contribute to spurring the content industry and promoting a digital society by reducing the socio-economic losses caused by the use of various illegal image materials in the future.
Professor Lee said, “Disputes related to images are now beyond the conventional realm of copyrights. Recently, their interest has rapidly expanded due to the issues of authentication, certification, integrity inspection, and distribution tracking because of the fake video problem. We will lead digital watermarking research that can overcome the technical limitations of conventional watermarking techniques.”
This technology has only been conducted in labs thus far, but it is now open to the public after years of study. His team has been conducting a test run on the webpage (click).Moving forward from testing the technology under specific lab conditions, it will be applied to a real environment setting where constant changes pervade.
1. Figure. 2D image using the watermarking technique: a) original image b) watermark-embedded image c) signal from the embedded watermark
Figure 2. Result of watermark detection according to the password
Figure 3. Example of a center image using the DIBR 3D image watermarking technique: a) original image b) depth image c) watermark-embedded image d) signal from the embedded watermark
Figure 4. Example of using the S3D image watermarking technique: a) original left image b) original right image c) watermark-embedded left image d) watermark-embedded right image e) signal from the embedded watermark (left) f) signal from the embedded watermark (right)
2018.12.05 View 5898 -
Reducing the Drag Force of a Moving Body Underwater
(from left: Professor Yeunwoo Cho and PhD Jaeho Chung)
Professor Yeunwoo Cho and his team from the Department of Mechanical Engineering developed new technology that reduces the drag force of a moving body in a still fluid by using the supercavitation phenomenon.
When a body moves in air, the frictional drag is lower than that of the same body moving in water. Therefore, the body that moves in water can reduce the drag significantly when it is completely enveloped in a gaseous cavity.
The team used compressed air to create so-called supercavitation, which is a phenomenon created by completely enveloping a body in a single large gaseous cavity. The drag force exerted on the body is then measured.
As a result, the team confirmed that the drag force for a moving body enveloped in air is about 25% of the drag force for a moving body without envelopment.
These results can be applied for developing high-speed underwater vehicles and the development of air-lubricated, high-speed vessels.
The team expects that the results can be applied for developing high-speed underwater vehicles and the development of air lubrication for a ship’s hull.
This research, led by PhD Jaeho Chung, was published in the Journal of Fluid Mechanics as a cover article on November 10, 2018.
Figure 1. The cover article of the Journal of Fluid Mechanics Vol. 854
2018.12.04 View 5038 -
From Concept to Reality: Changing Color of Light Using a Spatiotemporal Boundary
(from left: Professor Bumki Min, PhD candidate Jaehyeon Son and PhD Kanghee Lee)
A KAIST team developed an optical technique to change the color (frequency) of light using a spatiotemporal boundary. The research focuses on realizing a spatiotemporal boundary with a much higher degree of freedom than the results of previous studies by fabricating a thin metal structure on a semiconductor surface. Such a spatiotemporal boundary is expected to be applicable to an ultra-thin film type optical device capable of changing the color of light.
The optical frequency conversion device plays a key role in precision measurement and communication technology, and the device has been developed mainly based on optical nonlinearity.
If the intensity of light is very strong, the optical medium responds nonlinearly so the nonlinear optical phenomena, such as frequency doubling or frequency mixing, can be observed. Such optical nonlinear phenomena are realized usually by the interaction between a high-intensity laser and a nonlinear medium.
As an alternative method frequency conversion is observed by temporally modifying the optical properties of the medium through which light travels using an external stimulus. Since frequency conversion in this way can be observed even in weak light, such a technique could be particularly useful in communication technology.
However, rapid optical property modification of the medium by an external stimulus and subsequent light frequency conversion techniques have been researched only in the pertubative regime, and it has been difficult to realize these theoretical results in practical applications.
To realize such a conceptual idea, Professor Bumki Min from the Department of Mechanical Engineering and his team collaborated with Professor Wonju Jeon from the Department of Mechanical Engineering and Professor Fabian Rotermund from the Department of Physics. They developed an artificial optical material (metamaterial) by arranging a metal microstructure that mimics an atomic structure and succeeded in creating a spatiotemporal boundary by changing the optical property of the artificial material abruptly.
While previous studies only slightly modified the refractive index of the medium, this study provided a spatiotemporal boundary as a platform for freely designing and changing the spectral properties of the medium. Using this, the research team developed a device that can control the frequency of light to a large degree.
The research team said a spatiotemporal boundary, which was only conceptually considered in previous research and realized in the pertubative regime, was developed as a step that can be realized and applied.
Professor Min said, “The frequency conversion of light becomes designable and predictable, so our research could be applied in many optical applications. This research will present a new direction for time-variant media research projects in the field of optics.”
This research, led by PhD Kanghee Lee and PhD candidate Jaehyeon Son, was published online in Nature Photonics on October 8, 2018.
This work was supported by the National Research Foundation of Korea (NRF) through the government of Korea. The work was also supported by the Center for Advanced Meta-Materials (CAMM) funded by the Korea Government (MSIP) as the Global Frontier Project (NRF-2014M3A6B3063709).
Figure 1. The frequency conversion process of light using a spatiotemporal boundary.
Figure 2. The complex amplitude of light at the converted frequency with the variation of a spatiotemporal boundary.
2018.11.29 View 9424 -
KAIST Shows Strong Performance in Crypto Contest Korea 2018
(Awardees at the ceremony for Crypto Contest Korea 2018)
A paper titled “Indifferentiability of Truncated Random Permutations” by PhD candidate Wonseok Choi and MS candidate Byeonghak Lee (under Professor Jooyoung Lee) from the KAIST Graduate School of Information Security (GSIS) won first place in Crypto Contest Korea 2018. Byeonghak Lee became a repeat winner since his paper titled “Tweakable Block Ciphers Secure Beyond the Birthday Bound in the Ideal Cipher Model” also received an award at Crypto Contest Korea 2017.
The contest, hosted by the Korea Cryptography Forum, the Korea Institute of Information Security & Cryptology, and the National Security Research Institute and sponsored by the National Intelligence Service, was held for promoting cryptography in Korea. The total prize money is fifty million won with ten million won going to the first place winners.
The contest was divided into three divisions: paper, problem solving, and idea. Among the three divisions, first place came from the paper division only.
Besides first place, KAIST students showed outstanding performance in the contest. PhD candidate Seongkwang Kim received participation prize while he also received special prizes with MS candidate Yeongmin Lee. The hacking club GoN (under Professor Sang Kil Cha), comprised of undergraduate students from the GSIS was awarded the grand prize in the division of problem solving.
The award ceremony was held during the Future Crypto Workshop 2018 on November 15. The awards ceremony for Crypto Expert Korea 2018 were also held there, and PhD candidate Ji-Eun Lee from the School of Computing and Byeonghak Lee received awards, the grand prize and runner-up prize respectively.
2018.11.27 View 10743 -
Vietnamese Alumni of Korean S&T Universities Gather in Hanoi
(Vietnamese KAIST alumni gather in Hanoi on November 24.)
(Dr.Huong Minh Nguyen at the Institute of Biotechnology in the Vietnam Academy of Science and Technology (VAST). She is the representative of Vietnamese KAIST alumni.)
Some came from Ho Chi Minh and some even flew in from Singapore. For those KAIST alumni who gathered in Hanoi, the trip was well worth it. More than 100 Vietnamese alumni of KAIST, GIST, and UST attended the reunion in Hanoi on November 24. Presidents and vice president from three universities welcomed them and celebrated their successful careers after returning home or starting careers in other countries.
The reunion was co-hosted by KAIST, UST, and GIST in an effort to make a platform for continued networking for scientists who have studied at Korea’s science and technology universities. This joint reunion will be expected to include other science and technology universities and institutes in the future.
Among 1,873 international KAIST alumni from 106 countries, the number of Vietnamese graduates is the most dominant with 262 alumni, 14% of the total international alumni. Welcoming them, KAIST Vice President Soohyun Kim said that he was very impressed that all of the alumni are making a very impressive stride in their fields.
“You will be a big asset to make your country grow. You will also be a bridge for future collaborations with your institutions and KAIST and Korea. Vietnam holds great potential for future prosperity especially in science and technology and we look forward to seeing this network continue to benefit both countries.” Vice President Kim said all of the presidents shared the idea to make this gathering a regular event. “Other S&T universities will join to hold joint reunions in other countries in the future,” he added.
Dr. Huong Minh Nguyen at the Institute of Biotechnology in the Vietnam Academy of Science and Technology (VAST) is one of 22 KAIST alumni who joined the reunion and supported the idea. She is also the representative of Vietnamese KAIST alumni. Dr. Nguyen, who earned her MS and PhD in the Department of Biological Sciences in 2013, spent five and half years at KAIST. “All the members at the lab were taking care of each other. When I joined the lab back then, they treated me as a ‘baby sister’ in a family and our relationship grew like a sister and brotherhood. I still appreciate the bonding relationship we could make with our colleagues.”
She cites a supporting culture, a competent educational system that places a focus on practicality, and rich resources that help researchers try whatever they want as the distinct advantages of a KAIST education.
“I never heard my professor saying “No” to any of my suggestions in conducting research. Professors and lab members put all their efforts, resources, and facilities to getting my research started. They helped me obtain all the resources that I needed. It was a huge encouragement to me,” she added.
She started her Masters, along with four Vietnamese colleagues, right after graduating from the Hanoi University of Natural Sciences, a top science university in Vietnam. Their experience at KAIST during a 4-week exchange program during undergraduates made them decide their academic destination without any doubt. All of them finished their PhDs in 2013. Two of them moved back home and the two others are now in the US and Germany as postdoctoral fellows.
“At that time, I could go to other countries for my further studies. But I already experienced KAIST for a month when I was an undergraduate, so I was not hesitant to go to KAIST. All of the classes are in English so, for students who do not speak in Korean, language does not bring any problems in studying and conducting research.”
She said that KAIST alumni are enjoying very successful careers in Vietnam and many foreign countries. “We do not have any problems choosing our careers back home and other countries we wanted to work in.”
However, like many PhD candidates who feel pressure about their studies and an uncertain future, her days at KAIST also included challenging times while adjusting to Korean culture. She took Korean classes for three semesters voluntarily at the KAIST Language Center to better understand Korea and her lab members. Her efforts paid off well. She could easily communicate with her colleagues and felt she became a real part of the inner group. But the stress remained to prove herself in research and she still had to deal with some bias.
“I know some people think Vietnam is behind Korea. Many people think that we are not as good as Korean students because we are from Vietnam. I desperately wanted to prove that I am as good as my peers.” Studying together with Korean and other international PhD candidates, she realized that everyone has their own purposes and pressures. “Even though there are minor differences, every PhD candidate has the same issues with their uncertain futures. It was quite comforting when we shared that it’s not only my problem. To understand that it’s a problem we all share comforts us a lot and we came to support each other.
To better help students release such pressure and stress, she said the university needs to create more diverse institutional channels to communicate with them. “Looking back, I was younger and less competent to speak up about when we were stressed and needed to ask for help. I hope students can begin to release their pressure and stress through diverse channels and resolve the problems,” she said.
Asked about her future plans, she replied, “I don’t think I can do anything better than what I am doing now. I enjoy what I am doing now at my institute. But in the near very future, I want to visit Korea and KAIST again.”
2018.11.27 View 4626 -
Silk Adhesive Paves the Way for Epidermal Electronics
(from left: Dr. Ji-Won Seo, Professor Hyunjoo Jenny Lee and PhD candidate, Hyojung Kim)
Producing effective epidermal electronics requires a strong, biocompatible interface between a biological surface and a sensor. Here, a KAIST team employed a calcium-modified silk fibroin as a biocompatible and strong adhesive. This technology led to the development of epidermal electronics with strong adhesion for patients who need drug injections and physiological monitoring over a long time.
Recently, biocompatible silk fibroins has been increasingly used for flexible substrates and water-soluble sacrificial layers because they allow structural modifications and are biodegradable. From previous studies, the team discovered the adhesive properties of silk fibroin via metal chelate bonding and the water-capturing of Ca ions.
Professor Hyunjoo Jenny Lee from the School of Electrical Engineering and her team explored ways to develop reusable, water-degradable, biocompatible and conductive epidermal electronics that can be attached to the human skin for long-term use. To overcome the limitations of conventional silk fibroin, the team introduced Ca ions to modify silk fibroin into a strong and biocompatible adhesive.
Calcium ions adopted in silk fibroins serve to capture water and enhance the cohesion force through metal chelation. Therefore, this endows viscoelasticity to previously a firm silk fibroin. This modified silk fibroin exhibits strong viscoelasticity and strong adhesiveness when physically attached to the human skin and various polymer substrates. Their developed silk adhesive is reusable, water-degradable, biocompatible, and conductive.
To test the effectiveness, the team employed the silk adhesive to fabricate an epidermal capacitive touch sensor that can be attached to the human skin. They verified the reusability of the sensor by performing attachment and detachment tests. They also confirmed that the physical adhesion of the Ca-modified silk facilitates its reusability and possesses high peel strength.
Furthermore, they tested the stretchability of the silk adhesive on bladder tissue. Although it is not an epidermal skin, bladder tissue is highly stretchable. Hence, it is a perfect target to measure the resistance-strain characteristic of the silk adhesive. When the bladder tissue was stretched, the resistive strain epidermal sensor corresponded to the tensile strain.
Showing high biocompatibility, the silk adhesive is suitable for interfacing with the human skin for a long period of time. Therefore, it can also be applied to a drug delivery epidermal system as well as an electrocardiogram (ECG) epidermal sensor.
Professor Lee said, “We are opening up a novel use for silk by developing reusable and biodegradable silk adhesive using biocompatible silk fibroin. This technology will contribute to the development of next-generation epidermal electronics as well as drug delivery systems.
This research, led by Dr. Ji-Won Seo and a PhD candidate, Hyojung Kim, was published in Advanced Functional Materials on September 5, 2018.
Figure 1. Schematic and photograph of a hydrogel patch adhered on the human skin through the silk adhesive
Figure 2. Cover page of Advanced Functional Materials
2018.11.21 View 7362 -
Distinguished Professor Lee Re-Appointed As Co-Chair of the Global Future Council on Biotechnology
(Distinguished Professor Sang Yup Lee)
Distinguished Professor Sang Yup Lee from the Department of Chemical and Biomolecular Engineering was re-appointed as the co-chair of the Global Future Council on Biotechnology at the World Economic Forum during the annual GFC meeting in Dubai, UAE last week. Elizabeth O’Day, founder and CEO of Olaris Therapeutics, will co-chair the council with him for two years.
Professor Lee served as the inaugural co-chair of the council for two years from 2016 with Professor Feng Zhang from the Broad Institute of MIT and Harvard.
The World Economic Forum’s Global Future Councils on Biotechnology is comprised of 14 members and aims to identify policy opportunities to help accelerate new biotechnological discoveries and applications while guiding dialogue with consumers about their implications.
Professor Lee, who has made significant research breakthroughs in the field of systems metabolic engineering, received the George Washington Carver Award, the PV Danckwerts Memorial Lecture Award, and the Eni Award this year.
2018.11.19 View 4474 -
Novel Strategies to Transform a Commercially Available Iboga Alkaloid to Post-Iboga Alkaloids
(PhD candidate HyeonggeunLim, Professor Sunkyu Han, PhD candidate Sikwang Seong)
KAIST chemists have synthesized seven different iboga and post-iboga natural products from commercially available catharanthine by mirroring nature’s biosynthetic post-modification of the iboga skeleton. They devised a novel strategy to biosynthesize the natural products via a series of selective and efficient oxidation and rearrangement reactions. This will serve as a stepping stone for developing therapeutic medications against cancer and narcotics addiction.
The research team, led by Professor Sunkyu Han, conceptualized and coined the term “Post-Iboga” alkaloids to describe the natural products that are biosynthetically derived from iboga-type alkaloids, which are composed of rearranged indole and/or isoquinuclidine backbones.
Iboga alkaloids have attracted significant attention from the scientific community due to their intriguing polycyclic structures and potential therapeutic uses against drug addictions. Nature has evolved to add architectural repertoires to this family of secondary metabolites by diversifying the iboga frameworks.
Notable examples are the FDA-approved anticancer drugs vinblastine and vincristine, both derived by the oxidative dimerization of catharanthine and vindoline subunits. Admittedly, synthetic foci toward the biosynthetic iboga-derivatives have historically been on these aforementioned dimeric natural products.
Recent natural product isolation studies on Tabernaemontana corymbosa and Ervatamia officinalis species have resulted in discoveries of various secondary metabolites that are biosynthetically derived from iboga alkaloids. These recent outbursts of iboga-derived natural product isolation reports have kindled interests toward these family of natural products.
The research team utilized (+)-catharanthine, the starting material for the industrial production of the anticancer drug Navelbine®. Well-orchestrated oxidations at the C19 position and the indole moiety of the catharanthine derivative, followed by differential rearrangements under acidic conditions, provided synthetic samples of voatinggine and tabertinggine respectively.
On the other hand, opportune oxidations at the C19 position and the alpha position of the tertiary amine moiety of the catharantine derivative, followed by a transhemiaminalization, produced the first synthetic sample of chippiine/dippinine-type natural product, dippinine B.
It is important to note that the chippiine and dippinine-type alkaloids have been targeted among synthetic chemists for over 30 years but had not succumbed to synthesis prior to this report.
Professor Han believes that their study will serve as a blueprint for further explorations of the synthesis, biosynthesis, and pharmacology of this emerging family of natural products. This study was published in Chem on November 15, 2018 (DOI: 10.1016/j.chempr.2018.10.009).
2018.11.16 View 6591 -
New Anisotropic Conductive Film for Ultra-Fine Pitch Assembly Applications
(Professor Paik(right) and PhD Candidate Yoon)
Higher resolution display electronic devices increasingly needs ultra-fine pitch assemblies. On that account, display driver interconnection technology has become a major challenge for upscaling display electronics.
Researchers have moved to one step closer to realizing ultra-fine resolution for displays with a novel thermoplastic anchoring polymer layer structure. This new structure can significantly improve the ultra-fine pitch interconnection by effectively suppressing the movement of conductive particles. This film is expected to be applied to various mobile devices, large-sized OLED panels, and VR, among others.
A research team under Professor Kyung-Wook Paik in the Department of Materials developed an anchoring polymer layer structure that can effectively suppress the movement of conductive particles during the bonding process of the anisotropic conductive films (ACFs). The new structure will significantly improve the conductive particle capture rate, addressing electrical short problems in the ultra-fine pitch assembly process.
During the ultra-fine pitch bonding process, the conductive particles of conventional ACFs agglomerate between bumps and cause electrical short circuits. To overcome the electrical shortage problem caused by the free movement of conductive particles, higher tensile strength anchoring polymer layers incorporated with conductive particles were introduced into the ACFs to effectively prevent conductive particle movement.
The team used nylon to produce a single layer film with well-distributed and incorporated conductive particles. The higher tensile strength of nylon completely suppressed the movement of conductive particles, raising the capture rate of conductive particles from 33% of the conventional ACFs to 90%. The nylon films showed no short circuit problem during the Chip on Glass assembly. Even more, they obtained excellent electrical conductivity, high reliability, and low cost ACFs during the ultra-fine pitch applications.
Professor Paik believes this new type of ACFs can further be applied not only to VR, 4K and 8K UHD display products, but also to large-size OLED panels and mobile devices.
His team completed a prototype of the film supported by the ‘H&S High-Tech,’ a domestic company and the ‘Innopolis Foundation.’ The study, whose first author is PhD candidate Dal-Jin Yoon, is described in the October issue of IEEE TCPMT.
Figure 1: Schematic process of APL structure fabrication.
Figure 2: Proto-type production of APL ACFs.
2018.11.13 View 7127 -
Faster and More Powerful Aqueous Hybrid Capacitor
(Professor Jeung Ku Kang from the Graduate School of EEWS)
A KAIST research team made it one step closer to realizing safe energy storage with high energy density, high power density, and a longer cycle life. This hybrid storage alternative shows power density 100 times faster than conventional batteries, allowing it to be charged within a few seconds. Hence, it is suitable for small portable electronic devices.
Conventional electrochemical energy storage systems, including lithium-ion batteries (LIBs), have a high voltage range and energy density, but are subject to safety issues raised by flammable organic electrolytes, which are used to ensure the beneficial properties. Additionally, they suffer from slow electrochemical reaction rates, which lead to a poor charging rate and low power density with a capacity that fades quickly, resulting in a short cycle life.
On the other hand, capacitors based on aqueous electrolytes are receiving a great deal of attention because they are considered to be safe and environmentally friendly alternatives. However, aqueous electrolytes lag behind energy storage systems based on organic electrolytes in terms of energy density due to their limited voltage range and low capacitance.
Hence, developing aqueous energy storage with high energy density and a long cycle life in addition to the high power density that enables fast charging is the most challenging task for advancing next-generation electrochemical energy storage devices.
Here, Professor Jeung Ku Kang from the Graduate School of Energy, Environment, Water and Sustainability and his team developed an aqueous hybrid capacitor (AHC) that boasts high energy density, high power, and excellent cycle stability by synthesizing two types of porous metal oxide nanoclusters on graphene to create positive and negative electrodes for AHCs.
The porous metal oxide nanoparticles are composed of nanoclusters as small as two to three nanometers and have mesopores that are smaller than five nanometers. In these porous structures, ions can be rapidly transferred to the material surfaces and a large number of ions can be stored inside the metal oxide particles very quickly due to their small particle size and large surface area.
The team applied porous manganese oxide on graphene for positive electrodes and porous iron oxide on graphene for negative electrodes to design an aqueous hybrid capacitor that can operate at an extended voltage range of 2V.
Professor Kang said, “This newly developed AHC with high capacity and power density driven from porous metal oxide electrodes will contribute to commercializing a new type of energy storage system. This technology allows ultra-fast charging within several seconds, making it suitable as a power source for mobile devices or electric vehicles where solar energy is directly stored as electricity.”
This research, co-led by Professor Hyung Mo Jeong from Kangwon National University, was published in Advanced Functional Materials on August 15, 2018.
Figure 1. Image that shows properties of porous metal oxide nanoparticles formed on graphene in the aqueous hybrid capacitor
2018.11.09 View 8685