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- [Engineering/Technology] New technology to improve performance of graphene
- Professor Jongill Hong Department of Materials Science and Engineering, Yonsei University ■ Engineering & Technology / New technology to improve performance of graphene Establishes foundation for commercialization of graphene-based electronic devices A research team led by Yonsei Materials Science and Engineering Professor Jongill Hong has developed a new technology that improves the performance of graphene, a remarkable carbon allotrope that is the basic structural element of other allotropes, such as graphite, charcoal, carbon nanotubes, and fullerenes. The research, which has progressed over four years, promises to have important applications in the production of various electronic devices. The results were published November 10, 2016 in Nature Communications under the title “Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor.” In the words of Professor Hong: “It is anticipated that this research will make a significant contribution to groundbreaking development and commercialization in the field of carbon-based electronics, in particular, transparent electronic devices, which have hitherto been devised only theoretically.” He added: “We will continue to engage in collaborative research with experts in other fields to make pioneering efforts to develop the devices of the future, using promising new materials.” Updated in Feb 2017 Reference Son, J., Lee, S., Kim, S. J., Park, B. C., Lee, H.-K., Kim, S., Kim, J. H., Hong, B. H., Hong, J., “Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor” Nature Communications, doi: 10.1038/ncomms13261
- 통합관리자 2017.02.13
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- [Natural Sciences] Aromaticity reversal in the lowest triplet state
- Professor Dongho Kim Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University ■ Natural Sciences / Aromaticity reversal in the lowest triplet state A group of Yonsei researchers demonstrates that bis-rhodium hexaphyrins containing [26] and [28] π-electron peripheries show properties consistent with Baird’s rule As any organic chemist will tell you, aromaticity is a fundamental concept because it relates to the chemical properties and reactivities of a wide range of species. At the most basic level, a compound (more specifically, a planar ring molecule) can be classified as aromatic, antiaromatic, or non-aromatic. The quantum mechanical basis for this classification was described by Hückel, whose [4n+2] rule defined a compound as being aromatic when its number of π-electrons is equal to 4n+2, where “n” is any positive integer. Since the introduction of this rule, various concepts of aromaticity have been reported, and a new rule for the lowest triplet state was proposed by Baird, where the Hückel (anti)aromaticity in the ground state would be reversed in the excited state. Despite the potential of excited-state aromaticity for application in areas such as photonic devices, there has been no report on the comparison between the electronic structures of the ground (closed-shell singlet) and excited (triplet excited) states of a pair of aromatic and antiaromatic congeners. Indeed, such studies would be useful to test Baird’s rule and experimentally confirm the reversal of (anti)aromaticity in the excited state. Congeneric expanded porphyrins R26H and R28H With the aforementioned background, the researchers analyzed a pair of congeneric expanded porphyrins (bis-rhodium [26]- and [28]hexaphyrins, R26H and R28H) with well-defined [4n+2] and [4n]π-electron systems in the ground state. These compounds are particularly useful as they can release or capture two pyrrolic protons following two-electron reduction or oxidation of the macrocycle, and hence can be employed to examine molecular aromaticity. Specifically, the photophysical properties of expanded porphyrins can be employed to determine aromaticity in [4n]/[4n+2]π-electron heteroannulenes. Generally, when compared to aromatic expanded porphyrins, the antiaromatic congeners exhibit broad, weak, and featureless absorption spectra. Moreover, they display a lack of fluorescence intensity and rapid decay from the excited state to the ground state. Indeed, as R26H and R28H represent Hückel aromatic and antiaromatic compounds, respectively, the intensities and spectral shapes of their transient absorption (TA) spectra differ greatly, and as such, they are considered suitable to explore the validity of Baird’s prediction. Moreover, the presence of coordinated bis-rhodium metals helps rigidify the nearly planar conformations of these chemically stable species, while the two coordinated rhodium metal cations should accelerate the intersystem crossing processes required to populate the corresponding excited triplet states through the heavy atom effect. Meanwhile, disturbance of the excited state dynamics should be minimized because of the closed-shell configuration of the rhodium(I) centers. Spectral data and calculations In contrast to the intense bands observed in the ground-state absorption spectrum of R26H, R28H exhibited relatively broad and weak spectra. Furthermore, the singlet excited-state lifetimes of these compounds were shorter than those of metal-free hexaphyrins due to efficient intersystem crossing (Sn→Tn). The decay-associated spectra reflecting the excited-state absorption (ESA) and ground-state bleaching of the transient species corresponding to the S1 and T1 states were obtained, and the extinction coefficients were estimated to compare the absorbance differences between the two states. The obtained ESA spectra of the T1 states of the two hexaphyrins further indicated reversal of the (anti)aromaticity: the spectrum of R26H was comparable to the spectra observed for antiaromatic porphyrinoids, while the spectrum of R28H resembled the spectra of canonical aromatic porphyrinoids. As expected, the calculated vertical energy transitions of R26H and R28H revealed that the transitions of the triplet state R26H resembled those of the ground state R28H, and vice versa. Calculated nucleus-independent chemical shift (NICS) values for the T1 states of R26H and R28H indicated that diatropic and paratropic ring currents were present in the ground and T1 states of R26H, respectively. The opposite was true for R28H; hence, the NICS values accurately reflected the magnitude of the global or macrocycle-derived aromaticity. This was supported by the ACID (anisotropy of the induced current density) plots, where the overall directions of the ring current densities induced by external magnetic fields changed from clockwise (aromatic) to anticlockwise (antiaromatic) in the ground and T1 states of R26H, respectively. Again, the opposite trend was observed for R28H. Finally, the HOMA (harmonic oscillator model of aromaticity) values for all available 26- and 28-π-electronic circuits of R26H and R28H further confirmed the proposed reversal of (anti)aromaticity in the T1 state. Reversal of aromaticity The authors concluded that the spectroscopic and calculated features of Hückel aromatic and antiaromatic hexaphyrins in their T1 states demonstrate the reversal of Hückel (anti)aromaticity. These findings are consistent with previous theoretical analyses of simple annulenes, such as benzene. As such, the study proposes the possibility of manipulating (anti)aromaticity through the selection of a desired electronic state to provide novel tools for modulating the chemical features and reactivity of highly conjugated systems. This could facilitate the development of fast saturable absorbers, novel molecular magnets, and photoswitchable devices that operate in both visible and NIR regions. Updated in Feb 2017 Reference Y. M. Sung, M. C. Yoon, J. M. Lim, H. Rath, K. Naoda, A. Osuka, D. Kim, “Reversal of Hückel (anti)aromaticity in the lowest triplet states of hexaphyrins and spectroscopic evidence for Baird’s rule”, Nature Chemistry, doi: 10.1038/NCHEM.2233
- 통합관리자 2017.02.13
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- [Natural Sciences] Changing the Properties of a Topologically Insulating Film through Bending
- Professor Mann-Ho Cho Department of Physics, Yonsei University ■ Natural Sciences / Changing the Properties of a Topologically Insulating Film through Bending A group of researchers, including Prof. Mann-Ho Cho, examines the effects of strain on three-dimensional topological insulators Can the properties of a topologically insulating film be tuned by bending? And are such changes reversible? Park, Chae, Jeong, Kim, Choi, Cho, Hwang, Bae, and Kang (2015) have answered these questions in their paper, “Reversible Fermi Level Tuning of a Sb2Te3 Topological Insulator by Structural Deformation,” published in Nano Letters. Building on previous theoretical and experimental work showing the influence of structural deformation on three-dimensional (3D) topological insulators, the authors examined the effect of bending on the band gap and Fermi level of Sb2Te3 film, a chalcogenide p-type 3D topological insulator. Topological insulators have a wide range of important potential applications, for example, in quantum computing, terahertz (THz) generators, magneto–electronic sensors, and superconductors. Therefore, various attempts at tuning the properties of these materials (in particular, their Fermi levels) have been made in the past. One of the most common approaches involves chemical doping. Unfortunately, the changes obtained through this approach are irreversible; therefore, reversible tuning techniques are in high demand. In their study, the authors investigated the changes to the band gap and Fermi level of Sb2Te3, which has weak bonding between its layers, under the influence of bending. Sb2Te3 film specimens were placed within a 500-µm-thick polyimide sheet, which was then bent to generate a low strain of less than 2%. This strain was confirmed using transmittance X-ray scattering analysis. Further, the influence of the applied strain on the Sb2Te3 topological properties was examined using magneto-resistance and temperature-dependent resistance measurements, terahertz-time domain spectroscopy, and density functional theory calculations. The results of these tests showed that the application of tensile strain via bending lowers the bulk carrier density and enhances the transport properties of the topological surface state of the Sb2Te3. Most strikingly, the Fermi level tuning can be reversed, as the examined sheets could be folded and unfolded repeatedly. This finding introduces the possibility of using structural deformation to achieve reversible control of a topological surface state device. Let’s take a look at some of the key results of the current study in greater detail. In-plane strain causes Fermi level shift Different in-plane strains were applied to the sheets using different degrees of bending; then, the sheet resistance was measured. A reversible increase in this property was recorded under increased in-plane strain, which was interpreted as being due to a shift in the Fermi level towards a lower binding energy (the midgap region). In addition, noticeable differences were observed in the sheet resistance dependence on temperature for flat and bent films, e.g., a higher maximum conductance temperature shift under bending. Increased bending also corresponded to an increased rate of change in the conductance with temperature. From these tests, the authors concluded that the bending of the Sb2Te3 film caused the Fermi level to move to a lower binding energy, which led to increased sheet resistance, enhanced topological surface state transport, and decreased bulk carrier density. The results of a 2D transport theory analysis also showed that the electron screening factor decreased with increased bending. Further, density functional theory calculations and Hall measurements supported the conclusions that the Fermi level shifted under bending and that the carrier density was decreased. Bending causes magneto-resistance enhancement Another striking effect generated by the shift in the Fermi level was an enhanced change in the magneto-resistance of the Sb2Te3. Both flat and bent films were examined under a vertical magnetic field and at the same temperature. Under this magnetic field, the difference in magneto-resistance for the bent film was significantly higher than that for the flat specimen. This behavior is associated with the weak antilocalization effect and carrier density, again indicating that the greater the strain applied via bending, the lower the carrier density of the Sb2Te3 film. Topologically insulating properties are conserved A final important finding of the study was that the strain did not have a significant effect on the topological surface state of the Sb2Te3 film. To obtain this result, the researchers measured the THz generations of the film, finding the same spectral shape up to ~1% strain. Conclusion The current study has revealed that mechanical deformation, i.e., bending of a chalcogenide 3D topologically insulating material, allows the Fermi level and bulk carrier density to be tuned. The most noteworthy result is that the change in sheet resistance, which is related to the above properties, is reversible, as bending and unbending of the film lead to respective increases and decreases in this property. The findings reported by the authors have important implications for future research on 3D topological insulators. More specifically, the topological surface state transport mechanism revealed by their investigations is interesting and worthy of further study. Updated in Feb 2017 Reference S.H. Park, J. Chae, K.S. Jeong, T.-H. Kim, H. Choi, M.-H. Cho, I. Hwang, M.-H. Bae, C. Kang, “Reversible Fermi Level Tuning of a Sb2Te3 Topological Insulator by Structural Deformation”, Nano Letters, doi: 10.1021/acs.nanolett.5b00553
- 통합관리자 2017.02.13
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- [Social Sciences/Business] Dependence on Search Engines May Cause Business Failure
- Professor Kyung Min Park School of Business, Yonsei University ■ Social Sciences & Business / Dependence on Search Engines May Cause Business Failure Research conducted at Yonsei examines the burdensome effect of dependence on other organizations Internet portals (i.e., search engines) play a significant role in leading potential customers to access for-profit online companies. However, this dependence on portals places a burden on deficient firms, especially when the dependency is asymmetric. Seung-Hyun Lee, Hee Jin Mun, and Kyung Min Park explore this hypothesis in their 2015 publication, “When is dependence on other organizations burdensome? The effect of asymmetric dependence on internet firm failure.” They show that online businesses depend on such portals to provide web traffic and build on a well-established asymmetric dependence model to show that dependence on portals increases the likelihood of business failure. The researchers use Nielson KoreanClick data (which collects tracking information of approximately 5,000 internet users) to demonstrate that overdependence on one portal poses significant business risk to online companies. Portals are beneficial for a website, but firms need to be wary of dependence While portals are beneficial to internet-based firms, asymmetric dependence on one portal increases failure rates due to the power imbalance between firms and portals. Online businesses must be listed among the first five pages of search results, which are accessed by approximately 90% of potential customers, to outmaneuver competitors. Search engines use algorithms to establish the order of search results and a company listed outside the first five pages faces a higher risk of business failure. The asymmetric and dominant position of portals is only weakened when a well-known brand is absent from the first few pages, causing portals to lose credibility. This visibility spillover effect from market leaders may have a further negative impact on comparatively unknown internet-based firms. While past research made significant contributions in understanding competitive interdependence among firms, there was room for improvement in examining competitive interdependence at the firm level with asymmetric dependence. Lee, Mun, and Park measure asymmetric resource dependence between internet-based firms and portals based on web traffic. Firm vulnerability is more significant when portals can avoid sales-channel specific investments. Moreover, portals face significantly lower costs in terminating relationships.This study uses data from the Korean search engines Naver and Daum, which represent around 95% of the country’s online search queries; Google has a comparatively small market presence. The authors consulted the Nielson KoreanClick database and used data from April 2002 to August 2011. This data was collected from Korean internet users’ monthly web traffic data from the leading 96 firms in four categories (blog or social network service, music, open market, and video sharing). Relying on one portal has consequences Lee, Mun, and Park advance the existing measure of asymmetric dependence that was previously used to study the impact of buyer–supplier relationships on the survival of suppliers. SWNi represents the traffic weight of an online firm i on the Naver portal. An increase in SWNi is accompanied by a decrease in the firm’s bargaining power, implying that the firm’s dependence on portals is high. For example, if a firm depends on only one portal, then the numerator has 1 as its maximum value, while it becomes 0.5 if a firm has the same number of transactions from two portals. BWNi represents the traffic weight of firm i’s traffic flow from Naver. If a firm has web traffic only with a single portal that has two equal referrals with two firms, then the bargaining factor is 0.5 and the value of asymmetric dependence is 2. The figure above shows that W and Z are satellite internet firms that depend on one portal, whereas X and Y distribute the entry points from both Daum and Naver. Results show that ADw (2.75) and ADz (2.39) have a higher asymmetric dependence than ADx (1.82) and ADy (1.31). World famous brands weaken portals’ power With stronger asymmetric dependence on portals, internet-based firms suffer from opportunistic portal behavior when relative autonomy is low. Business failure rates are higher with a stronger relationship between asymmetric dependence and portal dependence intensity. When a site is a category leader, there is a weaker relationship between asymmetric dependence and failure rates. Consumer loyalty, then, could offer the firm a sustainable competitive advantage by suppressing the adverse effect of asymmetric dependence. Conclusion Lee, Mun, and Park develop a new tool to measure resource dependence at the firm level. They recommend that firms balance their dependence on online portals but recognize that consumers rarely use multiple portals. This study presents a clear view of the burden imposed on online businesses as result of their dependence on search engines, and online businesses could benefit by formulating business strategies based on the results of this study. Overall, this is an engaging exploration into the potentially negative consequences faced by relatively weaker firms because of their asymmetric dependence on external organizations. Updated in Feb 2017 Reference Lee, S.-H. Mun, H. J., Park, K. M., “When is dependence on other organizations burdensome? The effect of asymmetric dependence on internet firm failure”, Strategic Management Journal, doi: 10.1002/smj.2330
- 통합관리자 2017.02.13
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- [Humanities] The World’s Most Authoritative Biblical Meeting held at Yonsei
- ■ Humanities / The world’s most authoritative biblical meeting held at Yonsei “Crossing Borders”: Biblical studies in today’s multifaceted world Between July 3 and 7 of 2016, the Society of Biblical Literature (SBL) International Meeting was held at Yonsei University. SBL is known as “the oldest and largest learned society devoted to the critical investigation of the Bible from a variety of academic perspectives.” With the subject of “Crossing Borders”, the meeting brought together more than 600 Biblical scholars from 30 different countries to explore biblical issues and their relation to such fields as theology, philosophy, psychology, anthropology, and sociology. Heated debates in every session became an opportunity to confirm the position of the Biblical Studies in today’s society. Dr. John Kutsko, the Executive Director of SBL, commented that “the 2016 International Meeting will go down in SBL’s history as having set a new mark for academic excellence.” In the past, the international meeting was usually held in Europe; in 2005, it took place in Asia for the first time, in Singapore. This year’s meeting served to increase Yonsei’s visibility as an important hub for biblical studies, while giving Korean scholars the opportunity to network with colleagues from around the world and discuss potential joint research projects. Updated in Feb 2017
- 통합관리자 2017.02.13
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- [Social Sciences/Business] How Your Childhood Advantage May Become a Mortality-related Disadvantage
- Photographed by Yonyoung Associate Professor Jeong-han Kang Department of Sociology, Yonsei University ■ Social Sciences & Business / How Your Childhood Advantage May Become a Mortality-related Disadvantage Yonsei sociologist investigates mortality, marriage longevity, and childhood family structure Does growing up in a home with both parents actually help you live longer? If so, does it remain true regardless of one’s own marital history in adulthood? Kang et al.’s (2016) “Marital status and mortality: Does family structure in childhood matter?” broadens existing research on the relationship between marital status and mortality risk by digging up the past: how our childhood family structure can affect the relationship. Using the General Social Survey (from an 8-year period)—which gathers data on contemporary American society in order to monitor and explain trends and constants in attitudes, behaviors, and attributes—merged with the National Death Index (GSS-NDI), the authors explore the effects of the connections between marital status and childhood family structure on mortality, as well as gendered patterns of these processes. Previous studies have already shown that married people demonstrate higher levels of psychological and physical well-being as well as lower levels of mortality risks than people with other marital statuses; in addition, parental marital disruption in childhood has also been shown to influence an individual’s own mortality in later life. It has not previously been investigated, however, how childhood family structure and adulthood marital status interplay in terms of mortality. Using Cox proportional hazard models to examine the effects of marital status and living with both parents in childhood, marital status was measured in this study by a set of dummy variables. Those married for the first time were used as the reference group and four dummies were created for other statuses: remarried, widowed, divorced or separated, and never married. Family structure at age 16 was measured by one dummy for having lived with both biological parents, to which about 70% of all respondents belonged. Although Kang et al.’s study has potential to be taken further—perhaps to include detailed family types such as living with single fathers—its contribution to existing literature is undeniable, and key interactive effects found through the study, among both men and women, are highlighted below. Family: A prescription for personal health? While this study agrees with previous findings that married people have significantly lower levels of mortality risk than widowed people, family structure in childhood is also significantly associated with mortality risk in adulthood. This study found that people who lived with both biological parents in childhood had a 19.5% lower mortality risk than their counterparts, as a disadvantaged family structure indicates exposure to a range of stressors (e.g., economic, psychological, social), which can negatively affect health over an individual’s life span. So good it’s bad Ironically, having a stable family structure throughout childhood can actually work against both men and women if they experience marital disruption later in life, such as the death of a spouse. Spending one’s childhood with both parents generally equates to more resources, care, and support, but also creates a vulnerability in a lack of coping mechanisms to deal with unwanted or unanticipated events later in life. As such, the context of spousal loss matters, because family structures in childhood provide a different background to widowed people’s psychological adjustments following spousal loss. Widowed subjects who lived with both parents in childhood suffered from a 43.2% higher hazard of death than married people who had also lived with both parents. Gender neutral, with a few exceptions Although findings were marginally significant for women, the study found that the general interaction effect between marital status and family structure in childhood was largely similar for both men and women. Of course, the introduction of variables such as education, income, and marital status (e.g., being widowed) can tilt the scales and result in gender-based significance. One of the more striking findings in this vein was that the coefficient of the interaction effect for men who were widowed and lived with both parents in childhood was about twice as large as that for women in the same situation. In fact, widowed men who lived with both parents in childhood had the highest mortality risk among all respondents, or 66.3% greater than their married counterparts, who had the lowest mortality risk. Conclusion This study’s inclusion of childhood family structure into existing models of linking marital status and mortality shows surprising disparities in its subsample analyses by gender. In addition, the finding that living with both parents in childhood does not have protective effects for widowed people (particularly widowed men) raises the question of why widowed adults do not benefit from an advantaged family structure during their formative years. Overall, this is an engaging look into how research on these contextual effects are related to gender as well as other life-course factors, and how our past can be used to predict our vulnerabilities in the future. Updated in Feb 2017 Reference J.-H. Kang, J. Kim, M.-A. Lee, “Marital status and mortality: Does family structure in childhood matter?” Social Science & Medicine, doi:http://dx.doi.org/10.1016/j.socscimed.2016.05.010
- 통합관리자 2017.02.13
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- [Humanities] First Korean Translation of the Complete Works of Shakespeare Published
- ■ Humanities / First Korean Translation of the Complete Works of Shakespeare Published “All’s well that ends well” for honorary professor as 10 years of work finally pays off “Shakespeare is a poet. Most of his plays are written in verse. That makes him both a poet and a playwright,” says Yonsei University Department of English Language and Literature honorary professor Lee Sang-seop, who recently published the complete works of the world’s greatest playwright from England, William Shakespeare. The Complete Works of William Shakespeare (셰익스피어 전집) is Korea’s first compilation of all forty-four works in one book, with 2016 marking 400 years since Shakespeare’s death. Though collectively his plays have all been published by various publishers in separate volumes, this is the first book to include the complete collection. Professor Lee who oversaw the translation project emphasizes moving past the notion of Shakespeare the playwright and focusing on Shakespeare the poet. To encourage this approach, Lee included extensive explanations of the poetic characteristics of the works in his publication. The translation of the famous soliloquy from Hamlet was altered for this same purpose. The well-known line, “To be or not to be, that is the question,” was translated to simultaneously maintain metered rhythm in Korean while appropriately convey young Hamlet’s philosophical anguish about existence that the author intended. Likewise, the spirit of Shakespeare’s play on words in the original English text, such as the rhyming of “tide” and “tied,” was preserved through careful substitution with Korean expression. The content of Lee’s book is an accumulation of ten years’ worth of work late in life, nearly seventy years after he encountered his first Shakespearean play. In the words of William Shakespeare, “all’s well that ends well.” Updated in Feb 2017
- 통합관리자 2017.02.01
