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        • KCI등재

          Impact of Multiple Satellite Ocean Color Samplings in a Day on Assessing Phytoplankton Dynamics

          ZhongPing Lee,Mingshun Jiang,Curtiss Davis,Nima Pahlevan,안유환,Ronghua Ma 한국해양과학기술원 2012 Ocean science journal Vol.47 No.3

          Ocean-color imagers on conventional polar-orbiting satellites have a revisit time of ~2 days for most regions, which is further reduced if the area is frequently cloudy. The Geostationary Ocean Color Imager (GOCI), the first ocean-color imager on a geostationary satellite, provides measurements 8times a day, thus significantly improving the frequency of measurements for studies of ocean environments. Here, we use results derived from GOCI measurements over Taihu Lake to demonstrate that the extra sampling can be used to improve the accuracy of statistically averaged longer-term (daily) measurements. Additionally, using numerical simulations, we demonstrate that the coupling of diurnal variations of both biomass and photosynthetic available radiation can improve the accuracy of daily primary production estimates. These results echo that higher sampling frequency can improve our estimates of longer-term dynamics of biogeochemical processes and highlights the value of ocean color measurements from geostationary satellites.

        • SCISCIESCOPUS

          Review—Understanding and Mitigating Some of the Key Factors that Limit Non-Aqueous Lithium-Air Battery Performance

          Lu, Jun,Lau, Kah Chun,Sun, Yang-Kook,Curtiss, Larry A,Amine, Khalil The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.14

          <P>In this article, we have reviewed our work on understanding and mitigating some of the key factors that limit non-aqueous Li-air battery performance. Advances in Li-air battery technology require fundamental understanding of the discharge and charge processes. We first summarize an investigation of Li-air batteries based on a well-defined cathode surfaces having size-selected silver clusters. This work provided key insight into the nucleation and growth mechanism of the discharge product and its relationship to lowering charge potentials. We then describe the development of new cathode materials including ones based on Pd and Mo<SUB>2</SUB>C nanoparticles that give very low charge potentials. This work has shown that it is possible to achieve very good round-trip efficiencies as well as up to 100 cycles in a Li-air cell. Finally, we discuss investigations of likely sources of electrolyte decomposition at the cathode and anode, which need to be resolved in order to achieve the long cycle life that is necessary to enable Li-air batteries.</P>

        • A Mo<sub>2</sub>C/Carbon Nanotube Composite Cathode for Lithium–Oxygen Batteries with High Energy Efficiency and Long Cycle Life

          Kwak, Won-Jin,Lau, Kah Chun,Shin, Chang-Dae,Amine, Khalil,Curtiss, Larry A,Sun, Yang-Kook American Chemical Society 2015 ACS NANO Vol.9 No.4

          <P>Although lithium oxygen batteries are attracting considerable attention because of the potential for an extremely high energy density, their practical use has been restricted owing to a low energy efficiency and poor cycle life compared to lithium-ion batteries. Here we present a nanostructured cathode based on molybdenum carbide nanoparticles (Mo2C) dispersed on carbon nanotubes, which dramatically increase the electrical efficiency up to 88% with a cycle life of more than 100 cycles. We found that the Mo2C nanoparticle catalysts contribute to the formation of well-dispersed lithium peroxide nanolayers (Li2O2) on the Mo2C/carbon nanotubes with a large contact area during the oxygen reduction reaction (ORR). This Li2O2 structure can be decomposed at low potential upon the oxygen evolution reaction (OER) by avoiding the energy loss associated with the decomposition of the typical Li2O2 discharge products.</P>

        • Interactions of Dimethoxy Ethane with Li<sub>2</sub>O<sub>2</sub> Clusters and Likely Decomposition Mechanisms for Li–O<sub>2</sub> Batteries

          Assary, Rajeev S.,Lau, Kah Chun,Amine, Khalil,Sun, Yang-Kook,Curtiss, Larry A. American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.16

          <P>One of the major problems facing the successful development of Li–O<SUB>2</SUB> batteries is the decomposition of nonaqueous electrolytes, where the decomposition can be chemical or electrochemical during discharge or charge. In this paper, the decomposition pathways of dimethoxy ethane (DME) by the chemical reaction with the major discharge product, Li<SUB>2</SUB>O<SUB>2</SUB>, are investigated using theoretical methods. The computations were carried out using small Li<SUB>2</SUB>O<SUB>2</SUB> clusters as models for potential sites on Li<SUB>2</SUB>O<SUB>2</SUB> surfaces. Both hydrogen and proton abstraction mechanisms were considered. The computations suggest that the most favorable decomposition of ether solvents occurs on certain sites on the lithium peroxide surfaces involving hydrogen abstraction followed by reaction with oxygen, which leads to oxidized species such as aldehydes and carboxylates as well as LiOH on the surface of the lithium peroxide. The most favorable site is a Li–O–Li site that may be present on small nanoparticles or as a defect site on a surface. The decomposition route initiated by the proton abstraction from the secondary position of DME by the singlet cluster (O–O site) requires a much larger enthalpy of activation, and subsequent reactions may require the presence of oxygen or superoxide. Thus, pathways involving proton abstraction are less likely than that involving hydrogen abstraction. This type of electrolyte decomposition (electrolyte with hydrogen atoms) may influence the cell performance including the crystal growth, nanomorphologies of the discharge products, and charge overpotential.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-16/jp400229n/production/images/medium/jp-2013-00229n_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp400229n'>ACS Electronic Supporting Info</A></P>

        • KCI등재

          The Mycobacterium tuberculosis relBE toxin:antitoxin genes are stress-responsive modules that regulate growth through translation inhibition

          Shaleen B. Korch,Vandana Malhotra,Heidi Contreras,Josephine E. Clark-Curtiss 한국미생물학회 2015 The journal of microbiology Vol.53 No.11

          Toxin-antitoxin (TA) genes are ubiquitous among bacteria and are associated with persistence and dormancy. Following exposure to unfavorable environmental stimuli, several species (Escherichia coli, Staphylococcus aureus, Myxococcus xanthus) employ toxin proteins such as RelE and MazF to downregulate growth or initiate cell death. Mycobacterium tuberculosis possesses three Rel TA modules (RelMtb): RelBEMtb, RelFGMtb and RelJKMtb (Rv1246c-Rv1247c, Rv2865-Rv2866, and Rv3357-Rv3358, respectively), which inhibit mycobacterial growth when the toxin gene (relE, relG, relK) is expressed independently of the antitoxin gene (relB, relF, relJ). In the present study, we examined the in vivo mechanism of the RelEMtb toxin protein, the impact of RelEMtb on M. tuberculosis physiology and the environmental conditions that regulate all three relMtb modules. RelEMtb negatively impacts growth and the structural integrity of the mycobacterial envelope, generating cells with aberrant forms that are prone to extensive aggregation. At a time coincident with growth defects, RelEMtb mediates mRNA degradation in vivo resulting in significant changes to the proteome. We establish that relMtb modules are stress responsive, as all three operons are transcriptionally activated following mycobacterial exposure to oxidative stress or nitrogen-limiting growth environments. Here we present evidence that the relMtb toxin:antitoxin family is stress-responsive and, through the degradation of mRNA, the RelEMtb toxin influences the growth, proteome and morphology of mycobacterial cells.

        • Innate immunity mediated by MyD88 signal is not essential for induction of lipopolysaccharide-specific B cell responses but is indispensable for protection against Salmonella enterica serovar Typhimurium infection.

          Ko, Hyun-Jeong,Yang, Jin-Young,Shim, Doo-Hee,Yang, Hyungjun,Park, Sung-Moo,Curtiss, Roy,Kweon, Mi-Na Williams Wilkins 2009 JOURNAL OF IMMUNOLOGY Vol.182 No.4

          <P>Salmonella organisms are Gram negative and facultative anaerobic bacteria that cause typhoid fever in humans. In this study, we evaluated LPS-specific adaptive immunity in innate immune-deficient mice after oral administration of attenuated Salmonella enterica serovar Typhimurium (S. Typhimurium) strains. Of interest, identical levels of LPS-specific IgG and IgA Abs were elicited in the systemic (i.e., serum and spleen) and mucosal (i.e., fecal extract and small intestine) compartments of wild-type, TLR4(-/-), and MyD88(-/-) mice following oral vaccination with recombinant attenuated S. Typhimurium (RASV). Depletion of CD4(+) T cells during RASV vaccination completely abrogated the generation of LPS-specific Abs in MyD88(-/-) mice. In addition, mRNA expression levels of a B cell-activating factor of the TNF family were significantly increased in the spleens of MyD88(-/-) mice after oral administration, implying that T cell-independent B cell switching might be also enhanced in the MyD88 signal-deficient condition. Of most interest, orally vaccinated MyD88(-/-) mice that possessed high levels of LPS-specific IgG and IgA, which had a neutralizing effect against Salmonella, died earlier than nonvaccinated wild-type mice following lethal oral challenge with virulent Salmonella species. These results suggest that innate immunity mediated by MyD88 signal is dispensable for induction of LPS-specific Ab responses following oral administration of attenuated Salmonella strains but indispensable for efficient protection.</P>

        • SCISCIESCOPUS

          Study on the Catalytic Activity of Noble Metal Nanoparticles on Reduced Graphene Oxide for Oxygen Evolution Reactions in Lithium–Air Batteries

          Jeong, Yo Sub,Park, Jin-Bum,Jung, Hun-Gi,Kim, Jooho,Luo, Xiangyi,Lu, Jun,Curtiss, Larry,Amine, Khalil,Sun, Yang-Kook,Scrosati, Bruno,Lee, Yun Jung American Chemical Society 2015 NANO LETTERS Vol.15 No.7

          <P>Among many challenges present in Li–air batteries, one of the main reasons of low efficiency is the high charge overpotential due to the slow oxygen evolution reaction (OER). Here, we present systematic evaluation of Pt, Pd, and Ru nanoparticles supported on rGO as OER electrocatalysts in Li–air cell cathodes with LiCF<SUB>3</SUB>SO<SUB>3</SUB>–tetra(ethylene glycol) dimethyl ether (TEGDME) salt-electrolyte system. All of the noble metals explored could lower the charge overpotentials, and among them, Ru-rGO hybrids exhibited the most stable cycling performance and the lowest charge overpotentials. Role of Ru nanoparticles in boosting oxidation kinetics of the discharge products were investigated. Apparent behavior of Ru nanoparticles was different from the conventional electrocatalysts that lower activation barrier through electron transfer, because the major contribution of Ru nanoparticles in lowering charge overpotential is to control the nature of the discharge products. Ru nanoparticles facilitated thin film-like or nanoparticulate Li<SUB>2</SUB>O<SUB>2</SUB> formation during oxygen reduction reaction (ORR), which decomposes at lower potentials during charge, although the conventional role as electrocatalysts during OER cannot be ruled out. Pt-and Pd-rGO hybrids showed fluctuating potential profiles during the cycling. Although Pt- and Pd-rGO decomposed the electrolyte after electrochemical cycling, no electrolyte instability was observed with Ru-rGO hybrids. This study provides the possibility of screening selective electrocatalysts for Li–air cells while maintaining electrolyte stability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-7/nl504425h/production/images/medium/nl-2014-04425h_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl504425h'>ACS Electronic Supporting Info</A></P>

        • Pathogenicity of <i>Yersinia pestis</i> Synthesis of 1-Dephosphorylated Lipid A

          Sun, Wei,Six, David A.,Reynolds, C. Michael,Chung, Hak Suk,Raetz, Christian R. H.,Curtiss 3rd, Roy American Society for Microbiology 2013 Infection and immunity Vol.81 No.4

          <P>Synthesis of <I>Escherichia coli</I> LpxL, which transfers a secondary laurate chain to the 2′ position of lipid A, in <I>Yersinia pestis</I> produced bisphosphoryl hexa-acylated lipid A at 37°C, leading to significant attenuation of virulence. Our previous observations also indicated that strain χ10015(pCD1Ap) (Δ<I>lpxP32</I>::P<SUB>lpxL</SUB> <I>lpxL</I>) stimulated a strong inflammatory reaction but sickened mice before recovery and retained virulence via intranasal (i.n.) infection. The development of live, attenuated <I>Y. pestis</I> vaccines may be facilitated by detoxification of its lipopolysaccharide (LPS). Heterologous expression of the lipid A 1-phosphatase, LpxE, from <I>Francisella tularensis</I> in <I>Y. pestis</I> yields predominantly 1-dephosphorylated lipid A, as confirmed by mass spectrometry. Results indicated that expression of LpxE on top of LpxL provided no significant reduction in virulence of <I>Y. pestis</I> in mice when it was administered i.n. but actually reduced the 50% lethal dose (LD<SUB>50</SUB>) by 3 orders of magnitude when the strain was administered subcutaneously (s.c.). Additionally, LpxE synthesis in wild-type <I>Y. pestis</I> KIM6+(pCD1Ap) led to slight attenuation by s.c. inoculation but no virulence change by i.n. inoculation in mice. In contrast to <I>Salmonella enterica</I>, expression of LpxE does not attenuate the virulence of <I>Y. pestis</I>.</P>

        • SCISCIESCOPUS

          A Physical Pulverization Strategy for Preparing a Highly Active Composite of CoO<sub><i>x</i></sub> and Crushed Graphite for Lithium–Oxygen Batteries

          Ming, Jun,Kwak, Won‐,Jin,Park, Jin‐,Bum,Shin, Chang‐,Dae,Lu, Jun,Curtiss, Larry,Amine, Khalil,Sun, Yang‐,Kook WILEY‐VCH Verlag 2014 CHEMPHYSCHEM -WEINHEIM- Vol.15 No.10

          <P>A new physical pulverization strategy has been developed to prepare a highly active composite of CoOx and crushed graphite (CG) for the cathode in lithium-oxygen batteries. The effect of CoOx loading on the charge potential in the oxygen evolution reaction (Li2O2 -> 2Li(+) + O-2 + 2e(-)) was investigated in coin-cell tests. The CoOx (38.9 wt%)/CG composite showed a low charge potential of 3.92 V with a delivered capacity of 2 mAh cm(-2) under a current density of 0.2 mA cm(-2). The charge potential was 4.10 and 4.15 V at a capacity of 5 and 10 mAh cm(-2), respectively, with a current density of 0.5 mA cm(-2). The stability of the electrolyte and discharge product on the gas-diffusion layer after the cycling were preliminarily characterized by H-1 nuclear magnetic resonance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The high activity of the composite was further analyzed by electrochemical impedance spectroscopy, cyclic voltammetry, and potential-step chronoamperometry. The results indicate that our near-dry milling method is an effective and green approach to preparing a nanocomposite cathode with high surface area and porosity, while using less solvent. Its relative simplicity compared with the traditional solution method could facilitate its widespread application in catalysis, energy storage, and materials science.</P>

        • Interaction of NADPH oxidase 1 with Toll-like receptor 2 induces migration of smooth muscle cells

          Lee, Jee Hyun,Joo, Jung Hee,Kim, Jinoh,Lim, Hee Jung,Kim, Sunah,Curtiss, Linda,Seong, Je Kyung,Cui, Wenhao,Yabe-Nishimura, Chihiro,Bae, Yun Soo Oxford University Press 2013 Cardiovascular research Vol.99 No.3

          <P><B>Aims</B></P><P>NADPH oxidase (Nox) isozymes that generate intracellular reactive oxygen species (ROS) and Toll-like receptor 2 (TLR2), an inflammatory mediator, are both involved in the development of atherosclerotic lesions. To identify the molecular connection between TLR2 and Nox isozymes in vascular remodelling, we analysed generation of ROS and pro-inflammatory cytokines in aortic smooth muscle cells from Nox1-deficient mice in response to the synthetic triacylated lipoprotein Pam3CSK, a TLR2 agonist.</P><P><B>Methods and results</B></P><P>We showed that TLR2 signalling stimulates progression of the pro-inflammatory phenotype in mouse aortic smooth muscle cells (MASMCs) through activation of Nox1. We demonstrated the interaction of TLR2 with Nox1 using yeast two-hybrid and co-immunoprecipitation assays. MASMCs from Nox1-deficient mice failed to generate of ROS in response to Pam3CSK4, indicating that Nox1 is essential for TLR2-dependent production of ROS. We also found that Pam3CSK4 stimulated migration of MASMCs from wild-type mice in a Transwell system, but MASMCs from Nox1-deficient mice failed to show this response. Wild-type MASMCs produced matrix metalloprotease 2 in response to Pam3CSK4, whereas Nox1-deficient MASMCs failed to generate this protease. Moreover, stimulation of MASMCs with Pam3CSK4 resulted in increased expression of the pro-inflammatory cytokine macrophage inflammatory protein 2 in a Nox1-dependent manner, leading to enhanced monocyte-endothelial cell adhesion and trans-endothelial migration of U937 cells.</P><P><B>Conclusion</B></P><P>These data suggest that Nox1 plays an important role in TLR2-mediated intracellular H<SUB>2</SUB>O<SUB>2</SUB> generation, activation of matrix metalloprotease 2, and secretion of pro-inflammatory cytokines, which in turn stimulate MASMC migration and vascular remodelling.</P>

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