Research Stories

Search article
  • Development of Ultrafast H2 Sensors that Requires No Additional Electrical Apparatus

    Chemical Engineering Prof. PANG, CHANGHYUN

    Development of Ultrafast H2 Sensors that Requires No Additional Electrical Apparatus

    By imitating the antennae of insects, ultrafast H2 sensors that requires no additional electrical apparatus was developed. The new sensors that realizes high hydrogen detection performance and safety simultaneously can be widely applied from precise measuring equipment to simple leak alarms, so it is expected to have a great ripple effect across the industry and households in the future. Hydrogen is used as an essential material in many industries such as petroleum, chemical, and steel, and its usage is increasing every year in everyday life. However, the use of a hydrogen leak detection system is essential because it can explode easily even when the concentration exceeds only 4% in the air. An existing commercialized hydrogen sensors such as electrochemical sensor, catalytic sensor, acoustic sensor, ceramic sensor and semiconductor sensor require additional apparatus such as display and speaker. These also requires a power supply for hydrogen detection, which increases the risk of explosion when hydrogen is leaked. In order to overcome these limitations, sensors that use optical signals instead of electrical signals and make it possible to detect the leakage of hydrogen visually have been developed. However, because these are usually based on chemical reactions between hydrogen and reactive materials, response time is slow. In addition, since these have irreversible characteristics at room temperature, the possibility of actual commercialization is very low. In order to develop a hydrogen sensor with high sensitivity and high response rate without the need for power, the researchers developed a nano/microactuators that changes its shape in response to hydrogen by imitating the antenna structure of insects. This nano/microactuators is made by coating palladium on the flexible polymer asymmetrically, and hydrogen gas stimulation can be detected with visually without additional display and power supply by maximizing the changes in the optical characteristics of the dev ice due to changes in the shape of the nano/microactuators by hydrogen. Furthermore, the researchers developed a new type of hydrogen sensors such as wetting-controllable H2-selective smart surfaces, a hydrogen sensitive locking device capable of controlling adhesion by hydrogen. The results of this research can be applied not only to existing industries such as petroleum, chemical, steel, but also to everyday life such as hydrogen stations, hydrogen vehicles, and fuel cell distributed generation systems. Especially, because of its distinguishable advantage such as non-power source, non-explosive, ultrasensitive, its high demand is expected with the explosive growth of the hydrogen fuel cell market. Also the factor that it is produced at low cost compared with existing hydrogen sensors although it requires no additional electrical apparatus and makes it possible to detect a hydrogen the naked eye is competitiveness both at home and abroad.

  • Development of X-ray Material with Almost No Radiation Using Microcrystalline Halide Perovskites

    Chemical Engineering Prof. PARK, NAM-GYU

    Development of X-ray Material with Almost No Radiation Using Microcrystalline Halide Perovskites

    A collaborative research project with Samsung Electronics A semiconductor material that can reduce the amount of radiation exposure while taking medical X-ray images to less than 1/10 has been developed. On the 11th, it was announced that an ‘X-ray detector’ that can increase sensitivity by over 20 times more than conventional flat X-rays by using perovskites semiconductor material was developed. An X-ray detector is a kind of image sensor that absorbs X-rays. The new material developed by the research team has high sensitivity, so it is possible to obtain a clear medical image while reducing the radiation dose. The cost of production is also low. Unlike conventional detectors, which are made by vacuum processing used in semiconductor manufacturing, the new detector can be made through a liquid process, so a large screen can be made. If this technology is commercialized, it will be possible to make X-ray devices that can take an image of the whole body at once. Perovskite has excellent characteristics of converting light into an electric current, so it is a material that is very popular in the fields of solar cells and X-rays. X-ray devices are widely used for medical purposes because they can convert X-rays transmitted through the human body into pictures and images, but they are expensive and result in large doses of radiation. For this reason, research and development projects to reduce X-ray exposure are being widely carried out in the United States, European Union, etc. The research team expects that X-ray devices that can dramatically reduce X-ray exposure will be developed in a few years. If the remaining technical problems are improved, X-ray medical imaging technology that reduces the radiation dose to less than 1/10 is expected to be available in the practical field of medicine. The results of this research have been published in the online edition of the worldwide scientific journal Nature, titled "Printable organometallic perovskite enables large-area, low-dose X-ray imaging."

  • Prof. Gi Ra YI Develops New Method for Mass Production of Patchy Particles

    Chemical Engineering Prof. YI, GI RA

    Prof. Gi Ra YI Develops New Method for Mass Production of Patchy Particles

    □ Associate Professor Gi-Ra YI in School of Chemical Engineering, Sungkyunkwan University and Assistant Professor Stefano SACANNA at chemistry department of New York University developed together new method for mass production of patchy particles which can be assembled as do molecules. □ Researchers began with a set of four large solid polystyrene spheres arranged in a tetrahedral manner around a smaller, softer silicone oil droplet. These two components are oppositely charged and thus spontaneously assemble into clusters. They then add a plasticiser (terahydrofuran), which allows the polystyrene spheres to flow and reconfigure into a single, bigger sphere thanks to surface tension. This process can be likened to the way balls of playdough can be squashed together. As the outer spheres fuse together to form a single sphere, the inner silicone oil droplet in fact deforms to fill the spaces inside the sphere. It is eventually pushed out to form a tetrahedral pattern of patches on the sphere’s surface. These patchy spherical-shaped particles are produced in over 90% yield. □ Adding patches to self-assembling systems in this way could allow us to produce colloidal nanostructures. Until now, however, it was not easy to yield enough particles to make a material big enough to hold in their hands. □ On the other hand, at low pH, oil droplets surrounded with four spheres can be stayed in the center during deformation by adding plasicitizer, in which oil droplets are first faceted into tetrahedra and then become spheres. Researchers can polymerized in the middle of deformation which produced uniform tetraheron particles. □ The research is detailed in Nature doi:10.1038/nature23901. □ “Mass production of patchy particles has been one of most important problem in fabricating nanostructured materials by self-assembly” says Prof. Gi-Ra Yi. This will be used now for builidng up new colloidal structures which may be used for even 3D printers with complex internal nanostructures.

  • Next Generation Perovskite Solar Cell with Improved the Efficiency and Stability

    Chemical Engineering Prof. PARK, NAM-GYU

    Next Generation Perovskite Solar Cell with Improved the Efficiency and Stability

    Solar energy is an expected source of energy that can play an important role in energy supply in the future of the world. As part of the response to changes in the environment due to global climate change, there is an ongoing effort to increase the proportion of power generation from renewable energy. It is expected that solar cells will take the largest proportion in such a flow. Recently, researchers have focused on organic-inorganic composite material having a perovskite structure that would allow low-cost and high-efficiency solar cell as a new photo-active material. Perovskite solar cells, one of the ten scientific breakthroughs in 2013, are in close proximity to the efficiency of crystalline silicon (~ 25 %) solar cells by the rapid improvement of the efficiency (from 2.2 % in 2008 to 22% in 2016). It, as next-generation solar cell with superior performance in low-cost materials that are based on cheap solution process, are expected to be able to replace the conventional silicon solar cells. Perovskites are materials described by the formula ABX3, where X is an anion and A and B are cations of different sizes (A being larger than B). Perovskite which is used for solar cells has methylammonium in the A site, B site is lead or tin ion, and X site is composed of halide ions. It simply shows the following attractive properties as a photo-active materials; a bandgap of around 1.6 eV, high extinction coefficient, with long electron-hole diffusion length (0.1 ~ 1mm). The most successful architecture of the perovskite solar cells has adopted the titanium oxide and the Spiro-OMeTAD(2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene) as charge transfer layer. Despite the high efficiency, however, the current - voltage hysteresis (asymmetry result in current-voltage measurement between forward and revers scan) has dropped reliability of the device. Meanwhile, perovskite solar cells using PEDOT: PSS (poly (3,4-ethylenedioxythiophene) poly (styrene sulfonate)) and PCBM (phenyl C61 butyric acid methyl ester) also can be manufactured. Current-voltage hysteresis that reduces the reliability of the solar cells was significantly suppressed when producing a solar cell in this structure. Another problem of the perovskite solar cells is low stability. This material is highly vulnerable to moisture and heat. The efficiency of the solar cell can be rapidly decreased within a few hours to exposure in the air. Therefore, it is an important issue for practical use to improve the stability of the perovskite solar cells. The researchers reported highly efficient perovskite solar cell based on chemically stable Nickel Oxide (NiO) with 16.40 % of power conversion efficiency by replacing PEDOT:PSS, organic charge transporting material. Although PEDOT:PSS has superior functionality to extract charges selectively from the perovskite layer, PEDOT:PSS promotes the decomposition of the perovskite which is moisture-sensitive due to its hygroscopic nature. On the other hand, nickel oxide, can improve the stability of the perovskite solar cells by retaining the chemical stability. Perovskite solar cells based on NiO, however, have suffered from relatively lower performance with smaller fill factor and photocurrent density compared to devices based on PEDOT:PSS. The researchers prepared the ultrathin NiO films (a few nanometers in thickness) deposited by atomic layer deposition (ALD) method for highly efficient perovskite solar cells. The Ultrathin Nickel Oxide showed an improved hole transport property compared to the bulk Nickel Oxide films. In addition to this, high transparency of such a thin nickel oxide helps the perovskite to exhibit the high power conversion efficiency. Further, the solar cell has maintained 90% of the initial efficiency over 500 hours when stored under inert gas atmosphere. The result is expected to be the basis for the development of highly efficient and reliable perovskite solar cell for future commercialization. The research was published in ‘Nanoscale’.

  • Profs. Gi-Ra YI & Jaeyun KIM's Study on Vanishing Colloidal Mesoporous Nanoparticles to Heal Wounds

    Chemical Engineering Prof. YI, GI RA

    Profs. Gi-Ra YI & Jaeyun KIM's Study on Vanishing Colloidal Mesoporous Nanoparticles to Heal Wounds

    The research team under Profs. Gi-Ra YI and Jaeyun KIM at Sungkyunkwan University's Department of Chemical Engineering have developed a colloidal mesporous nanoparticle solution that has the potential to rapidly and and effectively close wounds in the skin when it spreads, then degrades away after the wound heals. Figure 1. Schematic illustration of wound healing process on mouse skin by applying mesoporous nanoparticles The fundamental research behind the rapid wound closure is the high surface area of the colloidal mesoporous silica nanoparticles in which extracellular matrixes within biological tissues are strongly absorbed on the surface of the nanoparticles; therefore, the wound is rapidly closed. By introducing the mesopores and controlling the average diameters on the surface, the research team has shown increases of up to 10 times more adhesion energy compared to nonporous silica nanoparticles, even at 10 times lower concentration. Figure 2. Graphical illustration of extracellular matrixes interacting on the surface of mesoporous nanoparticles The team has also compared the use of colloidal mesoporous silica nanoparticles with conventional suturing and chemically treating agents in wound closure. The result confirmed that the colloidal mesoporous silica nanoparticles are much more convenient to use, the adhesion was stronger, and most importantly, there were no signs of inflammation or scars. Figure 3. In vivo comparison of wound healing on mice by methods and time Once the wound is closed and healed, the colloidal mesoporous silica nanoparticles degrade easily in biological media. The fact that colloidal silica nanoparticles degrade is advantageous, confirming the possibility of being used as biocompatible adhesive material. The research was supported by the Engineering Research Center and the Bank of Porous Nanoparticles from the National Research Foundation (NRF) of Korea, and was published in the journal ACS Applied Materials and Interfaces (Impact Factor 7.504) on August 24th, 2017. Title: Colloidal Mesoporous Silica Nanoparticles as Strong Adhesives for Hydrogels and Biological Tissues Authors: Joo-Hyung KIM (Research Assistant), Hodae KIM (M.S.), Youngjin CHOI (Ph.D), Doo Sung LEE (Professor), Jaeyun KIM (Associate Professor), and Gi-Ra YI (Associate Professor) The research team is currently continuing this study to combine wound healing agents for colloidal mesoporous silica nanoparticles capable of dual rapid closure/healing treatments.

  • A Multimediation Model of Learning by Exporting: Analysis of Export-Induced Productivity Gains

    Prof. TSE, CALEB

    A Multimediation Model of Learning by Exporting: Analysis of Export-Induced Productivity Gains

    Learning-by-exporting describes the phenomenon that firms can learn as a result of engaging in exporting to other countries, and this learning helps the exporting firms to become more productive. The phenomenon has been studied in different contexts by international business, economics, and strategic management scholars. Some scholars have found empirical evidence in support of it, while others have not. As global markets continue to rise in competitiveness, a more complete understanding of learning-by-exporting will provide useful knowledge to researchers, firm managers, and policy makers. In a recently published article, Professor Caleb H. TSE, along with his co-authors, argue that previous studies only sought to uncover whether the learning-by-exporting effect exists or not, and have overlooked the exact mechanisms that may cause the learning-by-exporting effect. The team created a theoretical model that examines the mediating mechanisms of the learning-by-exporting effect, and theorized that by exporting, firms acquire knowledge, learn and become more productive through the specific mechanisms of innovativeness, production capability improvements, as well as improvements in human capital. Using data from 250,000 Chinese firms over a 7-year period (2001-2007), the team found strong empirical evidence not only for the learning-by-exporting effect, but also for these mediating mechanisms. They also uncovered various boundary conditions to the learning-by-exporting effect. Non-state-owned enterprises and firms in industries with a moderate level of export intensity, as well as firms in industries with a medium to high level of new product development intensity, are able to effectuate more learning through these mechanisms than their counterparts. The study sheds light on the specific knowledge benefits that firms can gain from exporting which lead to increases in productivity. It also points out how policy makers can promote environments that encourage firms and industries to capitalize on this learning-by-exporting effect.

  • Prof. Cham Na YOON Estimates Dynamic Games of Electoral Competition to Evaluate Term Limits

    Economics Prof. YOON, CHAMNA

    Prof. Cham Na YOON Estimates Dynamic Games of Electoral Competition to Evaluate Term Limits

    Elections serve an important function in modern democracies by allowing voters to express their support for politicians who share their ideological views and plan to pursue the policies they prefer. In addition, elections provide voters the opportunity to remove from office incumbents that are not adequately performing the duties of their office. Over the last decade, much progress has been made in modeling electoral competition as a dynamic game with asymmetric information. One important qualitative finding of the theoretical literature is that the institutional design of election rules (e.g., term limits) can have a large impact on election outcomes and voters' welfare. However, few attempts have been made to quantify these welfare effects. This paper shows how to identify and estimate, using standard semi-parametric techniques, a class of dynamic games with perfect monitoring that have been at the frontier of recent research in political economy. Using US gubernatorial election data, they estimate the model to study the consequences of term limits. The team finds that the benefits from holding office are significant and large in magnitude. As a consequence, the prospects of reelection provide strong incentives for moderate governors to move towards the center of the ideological spectrum during their first term in office. Voters are willing to accept significant trade-offs in ideology to obtain a more capable governor. They find that there are significant differences in ideology across states and between parties within states. In contrast, there are only small differences in ability across states and no significant differences in the ability across parties. Term limits reduce welfare in the baseline model by six percent. They also find that tenure effects are negative for both parties. Consequently, term limits have the capacity to be constructive. The team show that with moderate levels of negative tenure effects term limits can be welfare improving.

  • Space Experiment Instrument Developed by SKKU Research Team will be bound Internation Space Station

    Physics Prof. PARK, IL HUNG

    Space Experiment Instrument Developed by SKKU Research Team will be bound Internation Space Station

    Space experiment instrument developed by Sungkyunkwan university research team will be bound for the International Space Station. Sungkyunkwan university announced a silicon charge detector(SCD) developed by research team of Prof. Ilheung PARK of department of physics will be delivered to the International Space Station on 15th, at 1:31 pm(Korea time) at the Kennedy Space Center in the United States. The space experiment instrument will be delivered to space by a SpaceX rocket ‘Dragon’. It will be installed on an outside module of the International Space Station and be expected to perform space mission for at least three years. The silicon charge detector is instrument to measure component of cosmic rays which is particles falling to Earth from space. It is made by using Semiconductor sensor technology. Cosmic rays is first detected in 1912, but its origins or spread processes have not been identified for more than 100 years. So, The Cosmic Ray Energetics And Mass mission destined for the International Space Station (ISS-CREAM) is designed to measure the highest-energy cosmic rays by National Aeronautics and Space Administration (NASA). The Republic of Korea, the United States, Mexico and France are participating in the experiment. According to Sungkyunkwan University, the silicon charge detector will play a key role in the ISS-CREAM. It is made of pure domestic technology and has an area of 1 ㎡ and a weight of 150 ㎏, which is the maximum size of a detector used in space. Four layers of silicon sensors measure component of cosmic rays. (Accuracy 99%) This detector was developed by Sungkyunkwan University in cooperation with Korea Electronics and Telecommunications Research Institute and small and medium enterprises, and Korea Institute of Industrial Technology did space environment experiment. The whole process was conducted in Korea. Prof. PARK said “This is the first time that domestic high-tech instrument is used in large space experiment of the International Space Station.”, and “This is a case we make the core instrument for main space project of NASA, and participate as main partner.”

  • Prof. Do Hyun RYU Develops the First Catalytic Asymmetric Synthesis of 2,5-dihydrooxepine

    Chemistry Prof. RYU, DOHYUN

    Prof. Do Hyun RYU Develops the First Catalytic Asymmetric Synthesis of 2,5-dihydrooxepine

    A research team led by Prof. Do Hyun RYU (Dept. of Chemistry) has developed the first catalytic synthetic method of chiral 2,5-dihydrooxepine. 2,5-Dihydrooxepine, seven-membered cyclic compound containing oxygen atom, is a structural core of many important natural products. Therefore, a variety of synthetic methods have been widely developed for several decades. However, there has been no example of catalytic asymmetric synthesis of 2,5-dihydrooxepines and multiple synthetic steps were required to prepare corresponding starting materials. The research team developed asymmetric synthetic method of highly functionalized 2,5-dihydrooxepine with chiral Lewis acid catalyst through cyclopropanation/retro-Claisen rearrangement tandem reaction to give good yields and high enantioselectivity. Developed methodology exhibits excellent atom economy because this utilizes simple starting materials and nitrogen gas (N2) is the only by-product. Since there are various bioactive natural products which possess dihydrooxepine as a key structure, chiral 2,5-dihydrooxepine derivatives synthesized with developed method are expected to be used in bio- or medicinal chemistry fields. Prof. RYU said "the value of this work is to synthesize enantioenriched 2,5-dihydrooxeines from simple starting materials using catalyst. Furthermore, this work is highly valuable because this suggests experimental results to support computational calculation data about reaction mechanism of retro-Claisen rearrangement of cyclopropane to 2,5-dihydrooxepine." This research was published in the Angewandte Chemie International Edition (IF : 11.709) as of April 18th, with the title of "Catalytic Enantioselective Synthesis of 2,5-Dihydrooxepines" (doi: 10.1002/anie.201700890). This work was selected as a Very Important Paper (VIP) and front cover page of July 17th.

  • Prof. Young Han KIM Finds the Relationship between Media Appearances and Compensation

    Business Administration Prof. KIM, YOUNGHAN

    Prof. Young Han KIM Finds the Relationship between Media Appearances and Compensation

    New research that examined 4,452 CEOs from 2,666 U.S. firms, as well as 104,129 news articles and 6,567 CNBC interviews, found that CEOs who appeared in CNBC interviews could expect their compensation to increase by $210,239 on average, notwithstanding firm performance and other mitigating factors. The research will be published in the upcoming volume of the INFORMS journal Organization Science. The research authors, Jingoo KANG of the Nanyang Business School and Andy Han KIM of the SKKU Business School, found the relationship between media appearances and compensation between 1997 and 2009 was strongest when the CEO was from a smaller firm or one that demonstrated a strong stock market performance in the wake of increased media visibility. Improved stock performance serves as strong supporting evidence to the employer of the CEO’s role in increasing the company’s visibility and that of its stock. This in turn provided the CEO with increased bargaining power for greater compensation, up to $130,925 more than their counterparts in larger firms. “For highly visible CEOs of larger firms, media appearances will only have a small visibility-enhancing effect,” said KANG. “On the other hand, for CEOs of smaller companies who are less well known, media appearances will have a strong visibility-enhancing effect.” For CEOs in larger, well-known companies that already have a high degree of visibility, the additional visibility-enhancing effect of media appearances was weaker for those CEOs, as there was little additional growth that corresponded to the CEO’s presence in the media. In addition, when the CEO had a high equity ownership or was the founding CEO, that positive relationship disappeared. The tone of media coverage also had an impact on the relationship between CEO media appearance and compensation, but primarily when the coverage was a CNBC interview. “When the tone of the media is more negative, the positive relationship between the media appearance and compensation becomes weaker,” said KIM. “In contrast, in the CEO news article models, we did not find a statistically significant interaction.” The full study can be found here. To cite this study: Jingoo KANG and Andy Y. Han KIM (2017). “The Relationship Between CEO Media Appearance and Compensation” forthcoming in the INFORMS journal Organization Science. About INFORMS and Organization Science INFORMS is the leading international association for operations research and analytics professionals. Organization Science, one of 14 journals published by INFORMS, is a leading academic journal that covers groundbreaking research about organizations, including their processes, structures, technologies, identities, capabilities, forms, and performance. More information is available at http://www.informs.orgor @informs.

  • Prof. Jong San CHANG Develops a Study on Selective Nitrogen Capture by Porous Hybrid Materials

    Chemistry Prof. CHANG, JONGSAN

    Prof. Jong San CHANG Develops a Study on Selective Nitrogen Capture by Porous Hybrid Materials

    Prof. Jong San CHANG (dual-appointed professor, Dept. of Chemistry, SKKU and KRICT) and his colleagues have recently published an important article, titled “Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites’’ in Nature Materials (doi:10.1038/nmat4825). It is known that selective dinitrogen binding to transition metal ions mainly covers two strategic domains: the biological nitrogen fixation, catalyzed by metalloenzyme nitrogenases, and the adsorptive purification of natural gas and air. Many transition metal-dinitrogen complexes have been envisaged for biomimetic nitrogen fixation to produce ammonia. Inspired by this concept, Prof. CHANG's group developed the first-ever adsorbent, a mesoporous Metal-Organic Framework (MOF) material containing accessible Cr(III) sites, able to thermodynamically capture N2 over CH4 and O2. This study resulted from cooperative international research, mainly between the research group for nanocatalysts at KRICT and several groups at the National Center for Scientific Research (CNRS) in France. The study presents a major breakthrough in the domain of the selective capture of nitrogen (here N2 mixed with CH4 and O2) using a porous hybrid solid, called a metal-organic framework (MOF), which contains accessible chromium (III) ion sites. The selective adsorption of N2 is a strategic issue, with the related applications, such as the upgrading of natural gas (for the production of pipelined natural gas (PNG) and compressed natural gas (CNG) as alternative fuels) and the purification of air being amongst the most critical challenges facing the industry today. For the moment, the discovery of a porous adsorbent sufficient for such purposes had not yet been achieved because these solids typically exhibit a better affinity for gases such as CH4 or O2 than N2. In this context, Prof. CHANG's group has first introduced the utilization of the concept of cationic unsaturated sites (CUS) for generating drastic changes in host-guest interactions (a general problem in materials science), which is useful to induce an unprecedented affinity for N2 with respect to other gases, far above the performances of materials currently used for the target application. The porous adsorbent material that combines a high selective adsorption, large uptake, easy regeneration, excellent recyclability, and good chemical/thermal stability offers a unique opportunity to achieve highly-efficient N2 capture that is difficult to attain using conventional approaches. From the results, they could identify a clear and striking advance in fundamental understanding or material design. They evidenced the unique property of this solid through a multidisciplinary approach combining state-of-the-art experimental and computational methods. This included structural aspects, infrared spectroscopy, equilibrium and breakthrough adsorption experiments and quantum/force field-based molecular simulations. Inspired by biomimetic and metal dinitrogen chemistry concepts, this multidisciplinary fundamental study revealed that designing MOFs with unsaturated metal sites into their cages offers a unique opportunity to achieve unprecedented, highly efficient N2 capture. It is believed that this publication will pave the way towards unprecedented adsorption-based technologies in the fields of energy, environment, medicine and catalysis by pushing the limits of our current knowledge on porous materials chemistry. In addition to this, the manipulation of multifunctional MOFs possessing both selective N2 binding and catalytic sites may propel forward progress in developing future enzymatic catalysts for N2 fixation, which is a dream of chemists, to produce nitrogen-containing chemicals.

  • Taller People Are Thinner, a Study by Prof. Beom Jun KIM

    Physics Prof. KIM, BEOMJUN

    Taller People Are Thinner, a Study by Prof. Beom Jun KIM

    If the human body is stretched in three directions of width, length and height, the weight of a human body is proportional to the cube of its height. However, this is not valid in reality, and the body-mass index (BMI) is often calculated from the weight divided by the square of the height. From such definition of the BMI, Prof. Beom Jun KIM has shown that the waist circumference of a human is not proportional to the height, but proportional to the square root of the height. In other words, if the body-mass index is the same, the taller person is thinner. “This is the reason why many fashion models are tall,” Prof. KIM says. By analyzing the data of the length and weight of a variety of fishes, whales, and quadrupedal land mammals, Prof. KIM has shown that weight is proportional to the square of the height only for humans. In the case of other animals, the weight is proportional to the cube of the height. He presumed the reason why the calculation of the body-mass index of a human differs from that of other animals is that humans are bipedal, standing and walking upright. From this, he predicted that in the case of infants who cannot walk yet, their weight should be proportional to the cube of their height, but children older than about one year old should have a weight proportional to the square of their height. This prediction was tested for data from Sweden, Korea, and the World Health Organization, and was confirmed to be correct. If we consider the human body as the form of a simple cylinder and apply the condition that the torque by gravity and the torque by muscle must be in balance, we can show that the weight of a human should be proportional to the square of the height using Newtonian mechanics of physics. Prof. KIM also said that if we measure the size of the pelvis and the height from human fossil records, we will be able to deduce the time when mankind started to walk upright. Figure 1. Graphs of the relationship between the height (H) and the weight (M) of pale chub fish, whales and land mammals. All three graphs show that the animals’ weight is proportional to the cube (p = 3) of the height. For land animals, the height (H) can be measured in two ways: shoulder height and head-to-tail length. Both ways to measure the height meet the relationship (M is proportional to the cube of H). Figure 2. Graphs of the relationship between the height (H) and the weight (M) of children from Sweden and Korea. In this figure, the purple dots represent infants younger than one year old, and the orange dots represent children older than one year old. At one year of age, the time when a child begins to walk, the relationship between the height and weight is changed. Before one year, the weight is close to the cube of the height as with the other animals in Figure 1 above, but after one year, weight is close to the square of the height. Figure 3. A simple model of a human body. By applying the equilibrium condition of the torque by gravity (Fg) and the torque by muscle (Fm), we can show that the weight of a human being should be proportional to the square of the height. Figure 4. According to the body-mass index calculation method, the waist circumference of a human being is proportional to the square root of the height. The figure shows how body somatotype is changed according to the height if the body-mass index is the same. The taller the person is, the thinner it becomes. In the figure, when the height doubles, the waist circumference is about 1.4 times (or the square root of 2) smaller. Figure 5. Unlike a human body, when the length of a fish doubles, the height of the torso also doubles. In other words, it is difficult to know the actual fish size only from fish pictures without comparisons because both big fish and small fish look the same. This is because the weight (or volume) of the fish is proportional to the cube of its length.

  • Content Manager