Graphene quantum dots: structural integrity and oxygen functional groups for high sulfur/sulfide utilization in lithium sulfur batteries

Park, Jungjin,Moon, Joonhee,Kim, Chunjoong,Kang, Jin Hyoun,Lim, Eunhak,Park, Jaesung,Lee, Kyung Jae,Yu, Seung-Ho,Seo, Jung-Hye,Lee, Jouhahn,Heo, Jiyoung,Tanaka, Nobuo,Cho, Sung-Pyo,Pyun, Jeffrey,Caban Nature Publishing Group 2016 NPG Asia Materials Vol.8 No.-

<P>Lithium-sulfur (Li-S) batteries are expected to overcome the limit of current energy storage devices by delivering high specific energy with low material cost. However, the potential of Li-S batteries has not yet been realized because of several technical barriers. Poor electrochemical performance is mainly attributed to the low electrical conductivity of the fully charged and discharged species, the irreversible loss of polysulfide anions and the decrease in the number of electrochemically active reaction sites during battery operation. Here, we report that the introduction of graphene quantum dots (GQDs) into the sulfur cathode dramatically enhanced sulfur/sulfide utilization, yielding high performance. In addition, the GQDs induced structural integrity of the sulfur-carbon electrode composite by oxygen-rich functional groups. This hierarchical architecture enabled fast charge transfer while minimizing the loss of lithium polysulfides, which is attributed to the physicochemical properties of GQDs. The mechanisms through which excellent cycling and rate performance are achieved were thoroughly studied by analyzing capacity versus voltage profiles. Furthermore, experimental observations and theoretical calculations further clarified the role played by GQDs by proving that C-S bonding occurs. Thus, the introduction of GQDs into Li-S batteries will provide an important breakthrough allowing their use as high-performance and low-cost batteries for next-generation energy storage systems.</P>

Cooperativity of E-cadherin and Smad4 Loss to Promote Diffuse-Type Gastric Adenocarcinoma and Metastasis

Park, Jun Won,Jang, Seok Hoon,Park, Dong Min,Lim, Na Jung,Deng, Chuxia,Kim, Dae Yong,Green, Jeffrey E.,Kim, Hark Kyun American Association for Cancer Research 2014 Molecular Cancer Research Vol.12 No.8

<P>Loss of E-cadherin (<I>CDH1</I>), Smad4, and p53 has been shown to play an integral role in gastric, intestinal, and breast cancer formation. Compound conditional knockout mice for Smad4, p53, and E-cadherin were generated to define and compare the roles of these genes in gastric, intestinal, and breast cancer development by crossing with <I>Pdx-1-Cre</I>, <I>Villin-Cre</I>, and <I>MMTV-Cre</I> transgenic mice. Interestingly, gastric adenocarcinoma was significantly more frequent in <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> mice than in <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1</I><SUP>+/+</SUP> mice, demonstrating that <I>Cdh1</I> heterozygosity accelerates the development and progression of gastric adenocarcinoma, in combination with loss of Smad4 and p53. <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> mice developed gastric adenocarcinomas without E-cadherin expression. However, intestinal and mammary adenocarcinomas with the same genetic background retained E-cadherin expression and were phenotypically similar to mice with both wild-type <I>Cdh1</I> alleles. Lung metastases were identified in <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> mice, but not in the other genotypes. Nuclear β-catenin accumulation was identified at the invasive tumor front of gastric adenocarcinomas arising in <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> mice. This phenotype was less prominent in mice with intact E-cadherin or Smad4, indicating that the inhibition of β-catenin signaling by E-cadherin or Smad4 downregulates signaling pathways involved in metastases in <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> mice. Knockdown of β-catenin significantly inhibited the migratory activity of <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> cell lines. Thus, loss of E-cadherin and Smad4 cooperates with p53 loss to promote the development and metastatic progression of gastric adenocarcinomas, with similarities to human gastric adenocarcinoma.</P><P><B>Implications:</B> This study demonstrates that inhibition of β-catenin is a converging node for the antimetastatic signaling pathways driven by E-cadherin and Smad4 in <I>Pdx-1-Cre;Smad4<SUP>F/F</SUP>;Trp53<SUP>F/F</SUP>;Cdh1<SUP>F</SUP></I><SUP>/+</SUP> mice, providing novel insights into mechanisms for gastric cancer metastasis. <I>Mol Cancer Res; 12(8); 1088–99. ©2014 AACR</I>.</P>

Aerosol concentrations and composition in the North Pacific marine boundary layer

Choi, Yongjoo,Rhee, Tae Siek,Collett Jr., Jeffrey L.,Park Jr., Taehyun,Park Jr., Seung-Myung,Seo Jr., Beom-Keun,Park Jr., Gyutae,Park Jr., Keyhong,Lee Jr., Taehyoung Elsevier 2017 Atmospheric environment Vol.171 No.-

<P>Ship-borne measurements of inorganic and organic aerosols, including methanesulfonic acid (MSA), were conducted over the Northern Pacific using a High Resolution Time of Flight Aerosol Mass Spectrometer (AMS). This study, conducted aboard the Korean ice breaker R/V Araon, was part of the SHIP borne Pole-to-Pole Observations (SHIPPO) project. Based on air mass source region, the cruise track could be divided into five sections. Overall, the South Asia and Northern Japan ship transects showed higher aerosol concentrations due to continental pollution and biomass burning sources, respectively. In all five regions, the average mass concentrations of sulfate and organic aerosols (OA) were much higher than concentrations of nitrate and ammonium. Positive matrix factorization (PMF) analysis distinguished two organic aerosol factors as hydrocarbon-like and oxidized OA (HOA and OOA). HOA peaked in South Asia under the influence of anthropogenic pollution source areas, such as China and Korea, and generally decreased with increasing latitude across the full study region. OOA concentrations peaked in Northern Japan near the Tsugaru Strait and appear to reflect fine particle contributions from biomass burning. The mean HOA concentration in the clean marine area (Aleutian Island to Siberia) was 0.06 mu g/m(3) and comprised approximately 8% of the OA mass fraction. The highest MSA concentrations peaked in the Aleutian Islands at nearly 15 mu g/m(3), suggesting influence from higher dimethyl sulfide (DMS) emissions resulting from biological nutrient uptake during summer. The MSA/sulfate ratio, an indicator of the relative fine particle contributions of DMS and anthropogenic sources, revealed a sharp gradient as the ship approached the clean marine areas where the dominance of DMS increased. The patterns in OOA, HOA, and MSA concentrations found in this study provide a better understanding of the characteristics of inorganic and organic aerosols in the Northern Pacific Ocean. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Reduction in programmed cell death and improvement in functional outcome of transient focal cerebral ischemia after administration of granulocyte-macrophage colony-stimulating factor in rats

Kong, TaeHo,Choi, Jung-Kyoung,Park, Hyeonseon,Choi, Byung Hyune,Snyder, Brian Jeffrey,Bukhari, Shefqat,Kim, Na-Kyeong,Huang, Xian,Park, So Ra,Park, Hyung Chun,Ha, Yoon Journal of Neurosurgery Publishing Group 2009 Journal of Neurosurgery Vol.111 No.1

<B>Object</B><P>Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a potent hematopoietic growth factor that both enhances the survival and drives the differentiation and proliferation of myeloid lineage cells. Recent studies have suggested that GM-CSF has a neuroprotective effect against CNS injury. In this paper, the authors investigated the neuroprotective effect of GM-CSF on neuron survival and locomotor behavior in a rat model of focal cerebral ischemic injury.</P><B>Materials</B><P>To understand its neuroprotective effect in vitro, GM-CSF was administered to a glutamate-induced excitotoxicity neuronal injury cell culture model that mimics the pathophysiology of focal hypoxic cerebral injury. In the animal study, the authors prepared a rat focal cerebral ischemia model by occluding the unilateral middle cerebral artery. They then examined the effects of GM-CSF administration on changes in infarct volume, apoptosis-related gene expression, and improvement in locomotor behavior.</P><B>Results</B><P>Treatment with GM-CSF significantly increased cell viability in a cell culture model of glutamate-induced neuronal injury. Furthermore, in vivo administration of GM-CSF at 60 μg/kg body weight daily for 5 consecutive days beginning immediately after injury decreased infarction volume, altered the expression of several apoptosis-related genes (<I>Bcl-2, Bax, caspase 3,</I> and <I>p53</I>), and improved locomotor behavior in the focal cerebral ischemia model.</P><B>Conclusions</B><P>The GM-CSF had neuroprotective effects in in vitro and in vivo experiments and resulted in decreased infarction volume and improved locomotor behavior. Although the specific mechanism involved in stroke recovery was not fully elucidated as it was not the primary focus of this study, administration of GM-CSF appeared to decrease the extent of neuronal apoptosis by modulating the expression of several apoptosis-related genes such as <I>Bcl-2, Bax, caspase 3, and p53</I>. Further investigations are necessary to better understand the role of GM-CSF on neural regeneration during the recovery phase of a stroke, as well as the intracellular signal transduction pathways that mediate neuroprotection.</P>

Prophylactic effect of trimethoprim-sulfamethoxazole for pneumocystis pneumonia in patients with rheumatic diseases exposed to prolonged high-dose glucocorticoids

Park, Jun Won,Curtis, Jeffrey R,Moon, Jinyoung,Song, Yeong Wook,Kim, Suhnggwon,Lee, Eun Bong H. K. Lewis 2018 Annals of the rheumatic diseases Vol. No.

<P><B>Objectives</B></P><P>To investigate the efficacy and safety of trimethoprim/sulfamethoxazole (TMP-SMX) as primary prophylaxis for pneumocystis pneumonia (PCP) in patients with rheumatic diseases receiving high-dose steroids.</P><P><B>Methods</B></P><P>The study included 1522 treatment episodes with prolonged (≥4 weeks) high-dose (≥30 mg/day prednisone) steroids in 1092 patients over a 12-year period. Of these, 262 treatment episodes involved TMP-SMX (prophylaxis group) while other episodes involved no prophylaxis (control group). Differences in 1-year PCP incidence and its mortality between the two groups were estimated using Cox regression. To minimise baseline imbalance, propensity score matching was performed and efficacy outcome was mainly assessed in the postmatched population (n=235 in both groups).</P><P><B>Results</B></P><P>During a total of 1474.4 person-years, 30 PCP cases occurred with a mortality rate of 36.7%. One non-fatal case occurred in the prophylaxis group. TMP-SMX significantly reduced the 1-year PCP incidence (adjusted HR=0.07(95% CI 0.01 to 0.53)) and related mortality (adjusted HR=0.08 (95% CI 0.0006 to 0.71)) in the postmatched population. The result of the same analysis performed in the whole population was consistent with that of the primary analysis. Incidence rate of adverse drug reactions (ADR) related to TMP-SMX was 21.2 (14.8–29.3)/100 person-years. Only two serious ADRs (including one Stevens-Johnson syndrome case) occurred. The number needed to treat for preventing one PCP (52 (33–124)) was lower than the number needed to harm for serious ADR (131 (55–∞)).</P><P><B>Conclusion</B></P><P>TMP-SMX prophylaxis significantly reduces the PCP incidence with a favourable safety profile in patients with rheumatic disease receiving prolonged, high-dose steroids.</P>

THE TIMING OF EXCHANGE REGIME COLLAPSE UNDER CAPITAL CONTROLS

PARK, DAE KEUN,SACHS, JEFFREY D . 한국국제경제학회 1996 International Economic Journal Vol.10 No.4

Auger Recombination of Biexcitons and Negative and Positive Trions in Individual Quantum Dots

Park, Young-Shin,Bae, Wan Ki,Pietryga, Jeffrey M.,Klimov, Victor I. American Chemical Society 2014 ACS NANO Vol.8 No.7

<P>Charged exciton states commonly occur both in spectroscopic studies of quantum dots (QDs) and during operation of QD-based devices. The extra charge added to the neutral exciton modifies its radiative decay rate and also opens an additional nonradiative pathway associated with an Auger process whereby the recombination energy of an exciton is transferred to the excess charge. Here we conduct single-dot spectroscopic studies of Auger recombination in thick-shell (“giant”) CdSe/CdS QDs with and without an interfacial alloy layer using time-tagged, time-correlated single-photon counting. In photoluminescence (PL) intensity trajectories of some of the dots, we resolve three distinct states of different emissivities (“bright”, “gray”, and “dark”) attributed, respectively, to the neutral exciton and negative and positive trions. Simultaneously acquired PL lifetime trajectories indicate that the positive trion is much shorter lived than the negative trion, which can be explained by a high density of valence band states and a small hole localization radius (defined by the QD core size), factors that favor an Auger process involving intraband excitation of a hole. A comparison of trion and biexciton lifetimes suggests that the biexciton Auger decay can be treated in terms of a superposition of two independent channels associated with positive- and negative-trion pathways. The resulting interdependence between Auger time constants might simplify the studies of multicarrier recombination by allowing one, for example, to infer Auger lifetimes of trions of one sign based on the measurements of biexciton decay and dynamics of the trions of the opposite sign or, alternatively, estimate the biexciton lifetime based on studies of trion dynamics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-7/nn5023473/production/images/medium/nn-2014-023473_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5023473'>ACS Electronic Supporting Info</A></P>

Atomic Layer-by-Layer Deposition of Platinum on Palladium Octahedra for Enhanced Catalysts toward the Oxygen Reduction Reaction

Park, Jinho,Zhang, Lei,Choi, Sang-Il,Roling, Luke T.,Lu, Ning,Herron, Jeffrey A.,Xie, Shuifen,Wang, Jinguo,Kim, Moon J.,Mavrikakis, Manos,Xia, Younan American Chemical Society 2015 ACS NANO Vol.9 No.3

<P>We systematically evaluated two different approaches to the syntheses of Pd@Pt<SUB><I>n</I>L</SUB> (<I>n</I> = 2–5) core–shell octahedra. We initially prepared the core–shell octahedra using a polyol-based route by titrating a Pt(IV) precursor into the growth solution containing Pd octahedral seeds at 200 °C through the use of a syringe pump. The number of Pt atomic layers could be precisely controlled from two to five by increasing the volume of the precursor solution while fixing the amount of seeds. We then demonstrated the synthesis of Pd@Pt<SUB><I>n</I>L</SUB> octahedra using a water-based route at 95 °C through the one-shot injection of a Pt(II) precursor. Due to the large difference in reaction temperature, the Pd@Pt<SUB><I>n</I>L</SUB> octahedra obtained <I>via</I> the water-based route showed sharper corners than their counterparts obtained through the polyol-based route. When compared to a commercial Pt/C catalyst based upon 3.2 nm Pt particles, the Pd@Pt<SUB><I>n</I>L</SUB> octahedra prepared using both methods showed similar remarkable enhancement in terms of activity (both specific and mass) and durability toward the oxygen reduction reaction. Calculations based upon periodic, self-consistent density functional theory suggested that the enhancement in specific activity for the Pd@Pt<SUB><I>n</I>L</SUB> octahedra could be attributed to the destabilization of OH on their Pt<SUB><I>n</I>L</SUB>*/Pd(111) surface relative to the {111} and {100} facets exposed on the surface of Pt/C. The destabilization of OH facilitates its hydrogenation, which was found to be the rate-limiting step of the oxygen reduction reaction on all these surfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-3/nn506387w/production/images/medium/nn-2014-06387w_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn506387w'>ACS Electronic Supporting Info</A></P>

Superlattice-induced ferroelectricity in charge-ordered La_1/3Sr_2/3FeO₃

Park, Se Young,Rabe, Karin M.,Neaton, Jeffrey B. National Academy of Sciences 2019 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.116 No.48

<P><B>Significance</B></P><P>Charge-order–driven ferroelectrics are an emerging class of materials with promise for high-frequency electron-dominated polarization switching, distinct from conventional ferroelectrics. However, only a few systems exhibiting this behavior have been experimentally realized thus far. With continued development of layer-by-layer growth techniques with a high level of composition control, the exploration of charge-ordered ferroelectrics can be extended to artificially structured superlattices. Here, we use density-functional theory to explore an experimentally realized bulk perovskite iron-oxide solid solution with robust charge ordering and find that in superlattices formed by layered cation ordering, bulk charge ordering is maintained and can lead to charge-order–driven ferroelectricity. Our results suggest that other broad classes of mixed valence materials may be promising candidates for discovery of electronic ferroelectrics.</P><P>Charge-order–driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La<SUB>1/3</SUB>Sr<SUB>2/3</SUB>FeO<SUB>3</SUB> (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 [Formula]C/[Formula], a significant value arising from electron transfer between [Formula] octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order–induced ferroelectricity.</P>

Carbohydrate microarrays

Park, Sungjin,Gildersleeve, Jeffrey C.,Blixt, Ola,Shin, Injae The Royal Society of Chemistry 2013 Chemical Society reviews Vol.42 No.10

<P>In the last decade, carbohydrate microarrays have been core technologies for analyzing carbohydrate-mediated recognition events in a high-throughput fashion. A number of methods have been exploited for immobilizing glycans on the solid surface in a microarray format. This microarray-based technology has been widely employed for rapid analysis of the glycan binding properties of lectins and antibodies, the quantitative measurements of glycan-protein interactions, detection of cells and pathogens, identification of disease-related anti-glycan antibodies for diagnosis, and fast assessment of substrate specificities of glycosyltransferases. This review covers the construction of carbohydrate microarrays, detection methods of carbohydrate microarrays and their applications in biological and biomedical research.</P>