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The rational design and synthesis of multimetallic hollow nanostructures (HNSs) have been attracting great attention due to their structural and compositional advantages for application in electrocatalysis. Herein, the one-pot synthesis of Pd-Pt-Ag ternary alloy HNSs with controllable morphologies through a self-templating approach without any pre-synthesized templates is reported. Simultaneous reduction of multiple metal precursors by ascorbic acid in the presence of cetyltrimethylammonium chloride (CTAC) yielded initially metastable Pd-Ag nanocrystals, which can act as a self-template, and subsequent galvanic replacement and reduction led to the formation of final Pd-Pt-Ag HNSs. The size and hollowness (the ratio of inner cavity diameter to outer diameter) of the HNSs could be tuned through control over the concentration of CTAC. This can be attributed to the manipulated reduction kinetics of multiple metal precursors with the change in the CTAC concentration. The prepared Pd-Pt-Ag HNSs exhibited improved catalytic performance for ethanol electro-oxidation due to their large active surface areas and ternary alloy composition.

We review the history of space mission in Korea focusing on the field of astronomy and astrophysics. For each mission, scientific motivation and achievement are reviewed together with some technical details of the program including mission schedule. This review includes the ongoing and currently approved missions as well as some planned ones. Within the admitted limitations of authors' perspectives, some comments on the future direction of space program for astronomy and astrophysics in Korea are made at the end of this review., 29 pages, 31 figures, and 4 tables. To be published in the special issue of Journal of Korean Physical Society (JKPS) to celebrate the 25th anniversary of Astrophysics Division of Korean Physical Society (KPS)

Multi-walled carbon nanotube (MWCNT)-supported PtRuNi catalysts were synthesized using a microwave heating process. The particle sizes and structures of the catalysts were analyzed using X-ray diffraction and transmission electron microscopy (TEM). The electrocatalytic activities of the catalysts for methanol electrooxidation were evaluated by cyclic voltammetry, chronoamperometry, and impedance spectroscopy. The TEM results revealed that the MWCNT-supported PtRuNi catalyst synthesized via microwave heating for 10 min showed a uniform distribution of nanoparticles with an average size of about 5 nm. The catalyst showed an electrochemically active surface area of 62.2 m2 g−1 and a mass activity of 148.64 mA gpt−1. A decrease in the microwave heating time increased the dispersion and reduced the size of the PtRuNi nanoparticles. Moreover, the improved performance of the catalysts can be attributed to their high proton and electronic conductivity due to nickel hydroxides. Nickel hydroxides produced on the surface of metallic Ni in the Pt lattice contribute to the catalytic activity of PtNi catalysts in direct methanol fuel cells.

As of July 2013, the Republic of Korea (ROK) has been operating a total of 23 nuclear power reactors at four sites with five new reactors under construction. In addition, the country has been planned to construct two more units at two candidate sites. But, at now, due to change the energy policy, only one candidate site has been constructed and one nuclear power plant has been decommissioned. Otherwise, ROK has also been exporting nuclear power plants to the United Arab Emirates (UAE) and building a research reactor to Jordan. These performances have made the nation’s nuclear industry by far the fastest growing industry in the world. While Korea has focused on improvements in the field of nuclear safety (especially after the Fukushima accident), it continues to strengthen nuclear security as well. This was demonstrated when the country hosted the 2012 Nuclear Security Summit and in a speech made by nation’s president emphasizing the need for nuclear and cyber security during the 2014 Nuclear Security Summit (NSS). The paper examined the approaches leading to the establishment of the physical protection systems applied at the nuclear facilities in ROK based on CPPNM. Also, the paper will offer recommendations for further steps to improve the ROK’s existing nuclear security apparatus.

Globular clusters (GCs) play an important role in the formation and evolution of the Milky Way. New candidates are continuously found, particularly in the high-extinction low-latitude regions of the bulge, although their existence and properties have yet to be verified. In order to investigate the new GC candidates, we performed high-resolution NIR spectroscopy of stars toward the bulge using the IGRINS instrument at the Gemini-South telescope. We selected 15 and 10 stars near Camargo 1103 and 1106, respectively, which have recently been reported as metal-poor GC candidates in the bulge. In contrast to the classical approaches used in optical spectroscopy, we determined stellar parameters from a combination of line-depth ratios and the equivalent width of a CO line. The stellar parameters of the stars follow the common trends of nearby APOGEE stars in a similar magnitude range. We also determined the abundances of Fe, Na, Mg, Al, Si, S, K, Ca, Ti, Cr, Ni, and Ce through spectrum synthesis. There is no clear evidence of a grouping in RV-[Fe/H] space that would indicate the characterization of either object as metal-poor GCs. This result emphasizes the necessity of follow-up spectroscopy for new GC candidates toward the bulge, although we cannot completely rule out a low probability that we only observed nonmember stars. We also note discrepancies between the abundances of Al, Ca, and Ti when derived from the H- vs. the K-band spectra. Although the cause of this discrepancy is not clear, the effects of atmosphere parameters or NLTE are discussed. Our approach and results demonstrate that IGRINS spectroscopy is a useful tool for studying the chemical properties of stars toward the Galactic bulge with a statistical uncertainty in [Fe/H] of 0.03 dex, while the systematic error through uncertainties of atmospheric parameter is slightly larger than in measurements from optical spectroscopy., Comment: 16 pages, 9 figures, accepted for publication in A&A

The exploration of efficient nanocatalysts with high activity and stability towards water electrolysis and fuel cell applications is extremely important for the advancement of electrochemical reactions. However, it remains challenging. Controlling the morphology of bimetallic Pd–Pt nanostructures can be a great way to improve their electrocatalytic properties compared with previously developed catalysts. Herein, we synthesize bimetallic Pd–Pt nanodendrites, which consist of a dense matrix of unsaturated coordination atoms and high porosity. The concentration of cetyltrimethylammonium chloride was significant for the morphology and size of the Pd–Pt nanodendrites. Pd–Pt nanodendrites prepared by cetyltrimethylammonium chloride (200 mM) showed higher activities towards both the hydrogen evolution reaction and methanol oxidation reaction compared to their different Pd–Pt nanodendrite counterparts, commercial Pd, and Pt catalysts, which was attributed to numerous unsaturated surface atoms in well-developed single branches.

The one-pot synthesis strategy of Au@Pd dendrites nanoparticles (Au@Pd DNPs) was simply synthesized in a high-temperature aqueous solution condition where cetyltrimethylammonium chloride (CTAC) acted as a reducing and capping agent at a high temperature. The Au@Pd DNPs with highly monodisperse were shown in high yields by the Au:Pd rate. The nanostructure and optical and crystalline properties of the Au@Pd DNPs were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction. The Au@Pd DNPs showed an efficient electrochemical catalytic performance rate toward the ethanol oxidation reaction (EOR) due to their nanostructures and Au:Pd rate.

The durability of catalysts in fuel cells is a longstanding issue that needs to be resolved. Catalyst stability of the fuel cell has always been a problem, studies are underway to address them. Herein, to address this issue, we synthesize a hybrid structure consisting of SP carbon (SP) as the graphitic carbon and TiO2 as the metal oxide using a microwave method for use as a support for Pt nanoparticles. Anatase TiO2 and Pt nanoparticles with sizes of ~5 and 3.5 ± 1.4 nm, respectively, are uniformly dispersed on a modified graphitic SP carbon support (Pt-TiO2-SP). This supported Pt catalyst exhibits significantly improves durability in the oxygen reduction reaction (ORR). Furthermore, the Pt-TiO2-SP carbon hybrid catalyst manifests superior electrocatalytic stability and higher onset potential in ORR than those exhibited by Pt-SP carbon without TiO2. Pt-TiO2-SP exhibits an activity loss of less than 68 mV after 5000 electrochemical cycles, whereas an activity loss of ~100 mV is observed for Pt-SP carbon in a stability test. These results suggest that the strong metal–support interaction in TiO2-supported Pt catalyst significantly enhances the activity of Pt nanocatalyst.

The solid oxide membrane (SOM) process is an environmentally friendly and innovative technology that can produce valuable metals directly from their oxides. In the SOM process, a yttria-stabilized zirconia (YSZ) tube is normally immersed the molten salt containing dissolved metal oxides and oxygen anions that move to the SOM tube where they are reduced without any emission. However, the YSZ phase transition and yttrium dissolution by the reaction with the flux reduce the SOM stability and lifetime. Here, we investigated the effect of powder characteristics on YSZ stability in the SOM electrolysis environment. Thus, powder with good formability such as high flowability and tap/untap density showed a 2% decrease in electrical conductivity, but a 17% decrease in low formability powders. The cause of the degradation is the penetration of salt ions into the lattice and the elution of yttrium ions, which results in a phase transition.

One of the important challenges with a bifunctional electrocatalyst is reducing the large overpotential involved in the slow kinetics of the oxygen evolution reaction (OER) and oxygen reduction rea...

Pt-based multimetallic nanocrystals (NCs) have attracted tremendous research interest because of their excellent catalytic properties in various electrocatalysis fields. However, the development of rational synthesis approaches that can give multimetallic NCs with desirable compositional structures is still a radical issue. In the present work, we devised an efficient strategy for the systematic control of the spatial distribution of constituent elements in Pt-based trimetallic core-shell NCs, through which NCs with distinctly different compositional structures, such as Au@PdPt, Au@Pd@Pt, AuPd@Pt, and AuPdPt@Pt core-shell NCs, could selectively be generated. The adjustment of the amount of a reducing agent, hydrazine, which can provide control over the relative reduction kinetics of multiple metals, is the key to the selective formation of NCs. Through extensive studies on the effect of the compositional structure of the trimetallic NCs on their catalytic function toward the methanol electro-oxidation reaction, we found that the Au@Pd@Pt NCs exhibited considerably enhanced catalytic performance in comparison to the other trimetallic NCs as well as to their binary counterparts, a commercial catalyst, and reported Pt-based nanocatalysts due to the optimized surface electronic structure. The present strategy will be useful to design and construct multicomponent catalytic systems for various energy and environmental applications.

Recent analyses of Lee et al. (2018, 2019) have confirmed that Galactic bulge consists of stellar populations originated from Milky Way globular clusters (MWGCs). Motivated by this, here we present the evolutionary population synthesis (EPS) for the Galactic bulge and early-type galaxies (ETGs) with the realistic treatment of individual variations in light elements observed in the MWGCs. We have utilized our model with GC-origin populations to explain the CN spread observed in ETGs, and the results show remarkable matches with the observations. We further employ our model to estimate the age of ETGs, which are considered as good analogs for the MW bulge. We find that, without the effect of our new treatments, EPS models will almost always underestimate the true age of ETGs. Our analysis indicates that the EPS with GC-origin populations is an essential constraint in determining the ETG formation epoch and is closely related to understanding the evolution of the Universe.

Design of heteronanostructures with controlled topologies and configurations is receiving ever-increasing attention for developing practical photocatalytic and photoelectrochemical systems. Herein, we present a promising solar energy conversion platform constructed using the intimate contact of a plasmonic metal (octahedral Au nanocrystals), semiconductor (TiO2), and graphene with a well-defined configuration. The shell engineering of Au nanocrystals with TiO2 and graphene through sequential sol–gel, self-assembly, and post-calcination processes could allow the generation of graphene-encapsulated (octahedral Au nanocrystals)@(anatase TiO2) core–shell nanostructures. The prepared ternary heteronanostructures exhibited superior photocatalytic hydrogen evolution activity over their binary counterparts, single-component catalysts, and physical mixtures of the constituents under visible-light irradiation (λ > 400 nm). Furthermore, they effectively utilized the red-light region for photocatalytic reactions. Detailed mechanism studies on the photocatalysis revealed that the prominent photocatalytic performance of the heteronanostructures can be attributed to the transfer of plasmon-induced hot electrons from Au nanocrystals to TiO2 and the subsequent migration of the photogenerated electrons to graphene, which could be facilitated by the intimate contact between the constituent materials. This study can provide a new insight into devising heteronanostructures for efficient light harvesting.

Herein, gold nanoparticles (Au NPs) were synthesized by pulsed laser ablation (PLA) in a mixed-phase solvent of acetonitrile and water. The size of Au NPs and the number of graphitic carbon (GC) layers were controlled by varying the ratio of the solvent mixture. The surface-enhanced Raman scattering (SERS) of the Au NPs was investigated using 10−3 M 4-aminobenzenethiol and 10−4 M 4-nitrobenzenethiol as probe molecules. The SERS activity strongly depended on the nanogaps between particles owing to the formation of hot spots. In the present work, the nanogaps were controlled by changing the amount of GC layers. No GC layers were produced in water, resulting low SERS intensity. In contrast, Au NPs prepared in 30 vol% of acetonitrile showed significant SERS enhancement, which was attributed to the optimal size of the GC-coated NPs and a reasonable gap between them. The obtained results revealed that Au NPs produced by PLA in liquid could be applied in SERS-based microsensors.

We performed low-resolution spectroscopy for the red giant branch stars in an intriguing globular cluster (GC) NGC 2808, which hosts subpopulations with extreme helium and light-element abundances. In order to trace N, C, and Ca abundance differences among subpopulations, we measured CN, CH, and Ca II H&K spectral indices, respectively. We identified four subpopulations (G1, G2, G3, and G4) from CN and CH strength, with CN-weak/CH-strong G1, CN-intermediate/CH-strong G2, CN-strong/CH-intermediate G3, and CN-strong/CH-weak G4. Compared to [Na/O] from high-resolution spectroscopy, we show that CN index can more clearly separate G1 and G2. Since CN traces N abundance in a GC, it implies that G1 and G2 would show a larger difference in [N/Fe] compared to [Na/Fe], as predicted by chemical evolution models. Later generation stars G3 and G4, however, are better separated with high-resolution spectroscopy. We also found that G4 shows a stronger Ca II H&K line strength compared to that of G1, but we suspect this to be a result of unusually strong He enhancement and/or Mg depletion in G4 of this GC. This work illustrates that combining low- and high-resolution spectroscopic studies can improve the separation of subpopulations in GCs., Accepted for publication in AJ

A few dozen dwarf satellite galaxies of the Milky Way have been discovered, which are often viewed as the remaining building blocks of our Galaxy. The follow-up spectroscopy showed that dwarf galaxies have a sizeable spread in their metallicities. Several scenarios were suggested to explain the metallicity spread, which can be tested by the structural patterns of stellar subpopulations with distinct metallicities. However, such chemical plus structural examination, to which we refer to as "chemostructural study" is hindered by the lack of stars with spectroscopic metallicity. Here we propose the Ca$-$$by$ photometry as an alternative way to secure metallicities for a 2$-$3 orders of magnitude larger stellar sample than the spectroscopic sample and thus enable us to perform a chemostructural study on dwarf galaxies. In particular, we use the $hk$ index [$\equiv($Ca$-b)-(b-y)$], whose validity as a photometric metallicity indicator (and crass insensitivity to age) for red-giant-branch stars was upheld via Galactic globular clusters, and observe three dwarf spheroidal galaxies$-$Draco, Sextans, and Canes Venatici I (CVnI)$-$with Subaru/Suprime-Cam. We find that in all the galaxies the metal-rich stellar populations are more centrally concentrated than the metal-poor counterparts, suggesting that the central regions of the galaxies underwent extended star formation. Such a negative radial metallicity gradient for Sextans and CVnI opposes to the traditional spectroscopic results. We also find that their metallicity distribution functions (MDFs) can be characterized by a unimodal, skewed Gaussian shape with a metal-rich peak and a metal-poor tail. We discuss their features in the chemostructure and MDF in terms of dwarf galaxy formation theories., Accepted for publication in ApJS, data will be available at http://vo.kasi.re.kr/Phot_dSphs/

The most direct and strongest evidence for the presence of dark energy is provided by the measurement of galaxy distances using SNe Ia. This result is based on the assumption that the corrected brightness of SN Ia through the empirical standardization would not evolve with look-back time. Recent studies have shown, however, that the standardized brightness of SN Ia is correlated with host morphology, host mass, and local star formation rate (SFR), suggesting a possible correlation with stellar population property. To understand the origin of these correlations, we have continued our spectroscopic observations to cover most of the reported nearby early-type host galaxies. From high-quality (signal-to-noise ratio ~175) spectra, we obtained the most direct and reliable estimates of population age and metallicity for these host galaxies. We find a significant correlation between SN luminosity (after the standardization) and stellar population age at a 99.5 % confidence level. As such, this is the most direct and stringent test ever made for the luminosity evolution of SN Ia. Based on this result, we further show that the previously reported correlations with host morphology, host mass, and local SFR are most likely originated from the difference in population age. This indicates that the light-curve fitters used by the SNe Ia community are not quite capable of correcting for the population age effect, which would inevitably cause a serious systematic bias with look-back time. Notably, taken at face values, most of the Hubble residual used in the discovery of the dark energy appears to be affected by the luminosity evolution., Comment: To be published in 20 January 2020 issue of ApJ; see Figure 16 for the luminosity evolution mimicking dark energy

Supernova (SN) cosmology is based on the assumption that the corrected luminosity of SN Ia would not evolve with redshift. Recently, our age dating of stellar populations in early-type host galaxies (ETGs) from high-quality spectra has shown that this key assumption is most likely in error. It has been argued though that the age-Hubble residual (HR) correlation from ETGs is not confirmed from two independent age datasets measured from multi-band optical photometry of host galaxies of all morphological types. Here we show, however, that one of them is based on highly uncertain and inappropriate luminosity-weighted ages derived, in many cases, under serious template mismatch. The other dataset employs more reliable mass-weighted ages, but the statistical analysis involved is affected by regression dilution bias, severely underestimating both the slope and significance of the age-HR correlation. Remarkably, when we apply regression analysis with a standard posterior sampling method to this dataset comprising a large sample ($N=102$) of host galaxies, very significant ($> 99.99 \%$) correlation is obtained between the global population age and HR with the slope ($-0.047 \pm 0.011$~mag/Gyr) highly consistent with our previous spectroscopic result from ETGs. For the local age of the environment around the site of SN, a similarly significant ($> 99.96 \%$) correlation is obtained with a steeper slope ($-0.057 \pm 0.016$ mag/Gyr). Therefore, the SN luminosity evolution is strongly supported by the age dating based on multi-band optical photometry and can be a serious systematic bias in SN cosmology., 7 pages, 3 figures, Accepted for publication in ApJ

To develop high-performance bimetallic catalysts, fine control over both the ligand and strain effects of secondary elements on the catalytic function of primary elements is crucial. Here we introduce an approach to produce Pd–Ag bimetallic core–shell nanocatalysts with synergistic regulation of the ligand and strain effects of Ag. Through precise core–shell engineering, (PdAg alloy core)@(ultrathin Pd shell) nanocrystals with controlled core compositions and shell thicknesses in addition to a well-defined octahedral morphology could be realized. The prepared octahedral PdAg@Pd core–shell nanocrystals exhibited pronounced catalytic performance toward hydrogen production from formic acid decomposition. The maximum catalytic activity was achieved with PdAg@Pd nanocrystals consisting of PdAg alloy cores with an average Pd/Ag atomic ratio of 3.5:1 and 1.1 atomic layer of Pd shells, which showed a record high turnover frequency of 21 500 h–1 at 50 °C. This catalytic function could be attributed to the optimize...

For floating buildings may float on the water for a long time, they are constantly affected by various environmental loads such as wind and wave loads. In this study to find the wave effect on the floating building, five models are designed using steel moment resisting frame. It is assumed that the lower part of the floating building is a reinforced concrete pontoon, while the upper part is a three-story steel frame. To analyze floating buildings affected by wind and wave loads, hydro-dynamic and substructure analysis are performed. As input loads, this study set limits that the mean wind velocity is 35 m/s and the significant wave height is 0.5 m for the residential building. From the hydrodynamic analysis, the time-history acceleration of building is obtained and transformed into a base ground input for a substructure analysis of the superstructure of the building. Finally the mean of the maximum from 30 dynamic analysis of the floating buildings are used to be compared with the results of the same model on the ground. It was shown that the dynamic results with wind and wave loads are not always lesser than the static results which are calculated with static equivalent wind load for a building that is located on the ground.

In this work, a facile synthetic method for site-selectively Pt-decorated PdPt bimetallic nanosheets (S-Pt-PdPtBN) has been described. The size, structure, and composition distribution of the synthesized S-Pt-PdPtBN were determined by transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The electrocatalytic activity of these bimetallic nanosheets was examined for the oxidation of methanol in an acidic solution. The electrochemically active surface area (ECSA) of S-Pt-PdPtBN was 0.842 cm2. This value is slightly lower than the ECSA (1.012 cm2) of the commercial Pt/C (Alpha, Pt 10%) electrode. Interestingly, even though the ECSA of the S-Pt-PdPtBN/C was smaller than that of the commercial Pt/C, the forward peak current density of the former (2.95 mA cm−2) was ca. 1.5 times higher than that of the latter (2.05 mA cm−2). Moreover, the current density of the S-Pt-PdPtBN/C catalysts was high even after 800 s of continuous electrocatalysis at 0.5 V. This current density is six times that of commercial Pt/C catalysts. Thus, the synthesized S-Pt-PdPtBN exhibited significantly enhanced electrocatalytic activity and better stability than the commercial Pt/C catalyst for methanol oxidation.

In order to investigate the origin of multiple populations in globular clusters (GCs), we have constructed new chemical evolution models for proto-GCs where the supernova blast waves undergo blowout without expelling the ambient gas. Chemical enrichments in our models are then dictated by the winds of massive stars together with the asymptotic-giant-branch stars ejecta. We find that the observed Na-O anti-correlation can be reproduced when multiple episodes of starburst and enrichment are allowed to continue in proto-GCs. The “mass budget problem” is mostly resolved by our models without ad-hoc assumptions on star formation efficiency, initial mass function, and significant loss of first-generation stars. Interestingly, ages and chemical abundances predicted by this chemical evolution model are in good agreements with those independently obtained from our stellar evolution model for the horizontal-branch. We also discuss observational evidence for the GC-like multiple populations in the Milky Way bulge.

Electric vehicles (EVs) require high operating voltages as well as high-capacity batteries. One candidate material that has received a great deal of attention is the nickel-substituted “high-voltage” spinel LiMn1.5Ni0.5O4, which offers the advantages of both higher capacity and higher operating voltage than spinel LiMn2O4. These features, along with the relatively benign constituent elements, have made this material a top choice for the next generation of high-power batteries. In this study, LiMn1.5Ni0.5O4−δ materials were synthesized by a microwave-assisted hydrothermal method. Analyses show that microwave irradiation enables the tuning of the Mn3+ concentration, which is related to the degree of disorder and enhances the electrochemical performance. However, with increasing synthesis time, the material limit of the elastic strain was exceeded, and the structure became morphologically unstable, which deteriorated the electrochemical performance. Thus, further efforts are necessary to improve its intrinsic stability. The LiMn1.5Ni0.5O4−δ cathode active material may be suitable for the rapid charging of electric vehicle batteries.

The beech mushrooms have customarily been revered by oriental societies for their nutritional and health benefits. We explored the mass spectrometry (MS) based spatial metabolomic variations between parts (cap and stipe) of two beech mushroom strains (brown and white). The principal component analysis (PCA) revealed their distinct primary (cap and stipe: PC1, 25.5%; strains: PC2, 12.5%) and secondary (cap and stipe: PC1, 10.3%; strains: PC2, 7.6%) metabolite patterns. The caps were rich in amino acids, fatty acids, and N-acetylglucosamine with higher protein and nitrogen contents. The stipes had abundant β-glucans, malic acid, and fructose. The discriminant secondary metabolites, especially, hypsiziprenols were higher in caps from brown strains. A fatty acid derivative, azelaic acid, was abundant in white strains (cap>stipe). We established a positive correlation for the cytotoxic activities of hypsiziprenols against ACHN cells. These spatial inter-strain metabolomic distinctions are potentially helpful for mushroom selection and improvement.

Summary Noble metal nanocrystals (NCs) with controlled morphologies and compositions have shown great applicable potentials as electrocatalytic materials. Recently, the incorporation of plasmonic function into NC-based electrocatalysts has been considered as a highly promising approach to promote the electrocatalytic activity and stability due to the synergism between plasmonic and catalytic functions. This review highlights the latest advancements in plasmon-enhanced electrocatalysis with multi-metallic heteronanostructures with integrated plasmonic and catalytic functions. We also provide a perspective for designing new types of heteronanostructures for plasmon-enhanced electrocatalysis, which can be useful to the development of a new class of energy conversion systems.

Reduced graphene oxide (rGO) functionalized with organic capping agents has gained increasing attention as a promising metal-free catalyst. To optimize the properties of rGO for target applications, comprehending the link between the catalytic function of rGO and the chemical and structural characteristics of capping agents is critical. Herein, we report a systematic study on the effect of capping agents on the catalytic function of rGO for redox reactions using nitrogen-containing surface modifiers with distinctly different chemical structures, such as poly(diallyldimethylammonium chloride), cetyltrimethylammonium chloride, and poly(allylamine hydrochloride), which have the capability to endow rGO with improved suspension stability, enhanced reactant adsorption, and modified electronic properties. Functionalized rGOs were facilely prepared by the reduction of graphene oxide with hydrazine in the presence of the capping agents. The results of model redox reactions, that is, 4-nitrophenol and ferricyanide reduction reactions, catalyzed by the functionalized rGOs corroborated that the way the capping agents functionalize rGO, which is highly correlated with their chemical structure, drastically influences the overall reaction kinetics, including induction time, reduction rate, total reaction time, and reaction order. This strongly suggests that the judicious selection of capping agents is crucial to fully harness the catalytic function of rGO and thus to design novel rGO-based non-metallic catalysts with controllable reaction kinetics.

Recent stellar evolution models for globular clusters (GCs) in multiple population paradigm suggest that horizontal-branch (HB) morphology and mean period of type ab RR Lyrae variables are mostly determined by He & CNO abundances and relative ages for subpopulations. These parameters are also provided by chemical evolution models constructed to reproduce the Na-O anti-correlation. Therefore, a consistency check is possible between the synthetic HB and chemical evolution models. Furthermore, by combining them, a better constraint might be attained for star formation history and chemical abundances of subpopulations in GCs. We find, from such efforts made for four GCs, M4, M5, M15, and M80, that consistent results can be obtained from these two independent studies. In our unified model, He and Na abundances gradually increase over the generation, and therefore, the various extensions observed in both HB morphology and Na-O chemical pattern depend on the presence of later generation stars after the second generation. It is schematically shown that this observed diversity, however, would not be naturally explained by the models requiring dilution. Further spectroscopic observations are required, for metal-poor GCs in particular, to obtain a more detailed constraint from this approach., Accepted for publication in ApJ