First-principles modeling of the interactions of iron impurities with graphene and graphite

Results of first principles modelling of interactions graphene and graphite with iron impurities predict the colossal difference between these two carbon allotropes. Insertion of the iron atoms between the planes of graphite is much more energetically favourable than adsorption of the iron adatom at graphite or graphene surface. High mobility of iron adatom over graphite surface and within bulk graphite is reported. Calculated values of formation energies for the substitutional iron impurities suggest that iron is more destructive for graphite than for graphene. This effect caused formation of uniform carbon environment of the iron atom inside the multilayer system. In contrast to graphene segregation of the substitutional iron impurities in graphite at the ambient conditions is not energetically favourable. Enhancement of interlayer bonding in contaminated graphite and purity of graphene from iron impurities are also reported.Comment: 14 pages, 3 figures, to appear in phis. stat. solidi (b

Improvement of Carbon Nanofibers/ZrO2 Composites Properties with a Zirconia Nanocoating on Carbon Nanofibers by Sol–Gel Method

The development of new carbon nanofibers (CNFs)–ceramic nanocomposite materials with excellent mechanical, thermal, and electrical properties is interesting for a wide range of industrial applications. Among the ceramic materials, zirconia stands out for their excellent mechanical properties. The main limitations in the preparation of this kind of nanocomposites are related with the difficulty in obtaining materials with homogeneous distribution of both phases and the dissimilar properties of CNFs and ZrO2 which causes poor interaction between them. CNFs-reinforced zirconia nanocomposites ZrO2/xCNFs (x=1–20 vol%) were prepared by powder mixture and sintered by spark plasma sintering (SPS). ZrO2-reinforced CNFs nanocomposites CNFs/xZrO2 (x=20 vol%) were prepared by powder mixture and a surface coating of CNFs by the wet chemical route with zirconia precursor is proposed as a very effective way to improve the interaction between CNFs and ZrO2. After SPS sintering, an improvement of 50% in fracture strength was found for similar nanocomposite compositions when the surface coating was used. The improved mechanical properties of these nanocomposites are caused by stronger interaction between the CNFs and ZrO2.This work was financially supported by National Plan Projects MAT2006-01783 and MAT2007-30989-E and the Regional Project FICYT PC07-021. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her research grant BES2007-15033.Borrell Tomás, MA.; Rocha, VG.; Torrecillas, R.; Fernandez, A. (2011). Improvement of Carbon Nanofibers/ZrO2 Composites Properties with a Zirconia Nanocoating on Carbon Nanofibers by Sol–Gel Method. Journal of the American Ceramic Society. 94(7):2048-2052. https://doi.org/10.1111/j.1551-2916.2010.04354.xS20482052947Iijima, S. (1991). Helical microtubules of graphitic carbon. Nature, 354(6348), 56-58. doi:10.1038/354056a0Merkoçi, A. (2005). Carbon Nanotubes in Analytical Sciences. 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Mechanical properties of simultaneously synthesized and consolidated carbon nanofiber (CNF)-dispersed SiC composites by pulsed electric-current pressure sintering. Materials Science and Engineering: A, 458(1-2), 216-225. doi:10.1016/j.msea.2006.12.065Dusza, J., Blugan, G., Morgiel, J., Kuebler, J., Inam, F., Peijs, T., … Puchy, V. (2009). Hot pressed and spark plasma sintered zirconia/carbon nanofiber composites. Journal of the European Ceramic Society, 29(15), 3177-3184. doi:10.1016/j.jeurceramsoc.2009.05.030Lee, S.-Y., Kim, H., McIntyre, P. C., Saraswat, K. C., & Byun, J.-S. (2003). Atomic layer deposition of ZrO2 on W for metal–insulator–metal capacitor application. Applied Physics Letters, 82(17), 2874-2876. doi:10.1063/1.1569985Kobayashi, S., & Kawai, W. (2007). Development of carbon nanofiber reinforced hydroxyapatite with enhanced mechanical properties. Composites Part A: Applied Science and Manufacturing, 38(1), 114-123. doi:10.1016/j.compositesa.2006.01.006Sun, J., Gao, L., Iwasa, M., Nakayama, T., & Niihara, K. (2005). Failure investigation of carbon nanotube/3Y-TZP nanocomposites. Ceramics International, 31(8), 1131-1134. doi:10.1016/j.ceramint.2004.11.010Ukai, T., Sekino, T., Hirvonen, A. T., Tanaka, N., Kusunose, T., Nakayama, T., & Niihara, K. (2006). Preparation and Electrical Properties of Carbon Nanotubes Dispersed Zirconia Nanocomposites. Key Engineering Materials, 317-318, 661-664. doi:10.4028/www.scientific.net/kem.317-318.661Duszová, A., Dusza, J., Tomášek, K., Morgiel, J., Blugan, G., & Kuebler, J. (2008). Zirconia/carbon nanofiber composite. Scripta Materialia, 58(6), 520-523. doi:10.1016/j.scriptamat.2007.11.002Wang, X., Padture, N. P., & Tanaka, H. (2004). Contact-damage-resistant ceramic/single-wall carbon nanotubes and ceramic/graphite composites. Nature Materials, 3(8), 539-544. doi:10.1038/nmat1161Zhan, G.-D., Kuntz, J. D., Garay, J. E., & Mukherjee, A. K. (2003). Electrical properties of nanoceramics reinforced with ropes of single-walled carbon nanotubes. Applied Physics Letters, 83(6), 1228-1230. doi:10.1063/1.1600511Yucheng, W., & Zhengyi, F. (2002). Study of temperature field in spark plasma sintering. Materials Science and Engineering: B, 90(1-2), 34-37. doi:10.1016/s0921-5107(01)00780-2Haase, F., & Sauer, J. (1998). The Surface Structure of Sulfated Zirconia:  Periodic ab Initio Study of Sulfuric Acid Adsorbed on ZrO2(101) and ZrO2(001). Journal of the American Chemical Society, 120(51), 13503-13512. doi:10.1021/ja9825534Matsui, K., Suzuki, H., Ohgai, M., & Arashi, H. (1995). Raman Spectroscopic Studies on the Formation Mechanism of Hydrous-Zirconia Fine Particles. Journal of the American Ceramic Society, 78(1), 146-152. doi:10.1111/j.1151-2916.1995.tb08374.xGateshki, M., Petkov, V., Williams, G., Pradhan, S. K., & Ren, Y. (2005). Atomic-scale structure of nanocrystallineZrO2prepared by high-energy ball milling. Physical Review B, 71(22). doi:10.1103/physrevb.71.224107Pyda, W., Haberko, K., & Bulko, M. M. (1991). Hydrothermal Crystallization of Zirconia and Zirconia Solid Solutions. Journal of the American Ceramic Society, 74(10), 2622-2629. doi:10.1111/j.1151-2916.1991.tb06810.xDell’Agli, G., & Mascolo, G. (2000). Hydrothermal synthesis of ZrO2–Y2O3 solid solutions at low temperature. Journal of the European Ceramic Society, 20(2), 139-145. doi:10.1016/s0955-2219(99)00151-xTai, C. Y., Hsiao, B.-Y., & Chiu, H.-Y. (2007). Preparation of silazane grafted yttria-stabilized zirconia nanocrystals via water/CTAB/hexanol reverse microemulsion. Materials Letters, 61(3), 834-836. doi:10.1016/j.matlet.2006.05.068Tai, C. Y., Lee, M.-H., & Wu, Y.-C. (2001). Control of zirconia particle size by using two-emulsion precipitation technique. 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The statistical neuroanatomy of frontal networks in the macaque

We were interested in gaining insight into the functional properties of frontal networks based upon their anatomical inputs. We took a neuroinformatics approach, carrying out maximum likelihood hierarchical cluster analysis on 25 frontal cortical areas based upon their anatomical connections, with 68 input areas representing exterosensory, chemosensory, motor, limbic, and other frontal inputs. The analysis revealed a set of statistically robust clusters. We used these clusters to divide the frontal areas into 5 groups, including ventral-lateral, ventral-medial, dorsal-medial, dorsal-lateral, and caudal-orbital groups. Each of these groups was defined by a unique set of inputs. This organization provides insight into the differential roles of each group of areas and suggests a gradient by which orbital and ventral-medial areas may be responsible for decision-making processes based on emotion and primary reinforcers, and lateral frontal areas are more involved in integrating affective and rational information into a common framework

Inflammatory cytokines and biofilm production sustain Staphylococcus aureus outgrowth and persistence: A pivotal interplay in the pathogenesis of Atopic Dermatitis

Individuals with Atopic dermatitis (AD) are highly susceptible to Staphylococcus aureus colonization. However, the mechanisms driving this process as well as the impact of S. aureus in AD pathogenesis are still incompletely understood. In this study, we analysed the role of biofilm in sustaining S. aureus chronic persistence and its impact on AD severity. Further we explored whether key inflammatory cytokines overexpressed in AD might provide a selective advantage to S. aureus. Results show that the strength of biofilm production by S. aureus correlated with the severity of the skin lesion, being significantly higher (P < 0.01) in patients with a more severe form of the disease as compared to those individuals with mild AD. Additionally, interleukin (IL)-β and interferon γ (IFN-γ), but not interleukin (IL)-6, induced a concentration-dependent increase of S. aureus growth. This effect was not observed with coagulase-negative staphylococci isolated from the skin of AD patients. These findings indicate that inflammatory cytokines such as IL1-β and IFN-γ, can selectively promote S. aureus outgrowth, thus subverting the composition of the healthy skin microbiome. Moreover, biofilm production by S. aureus plays a relevant role in further supporting chronic colonization and disease severity, while providing an increased tolerance to antimicrobials

Clar's Theory, STM Images, and Geometry of Graphene Nanoribbons

We show that Clar's theory of the aromatic sextet is a simple and powerful tool to predict the stability, the \pi-electron distribution, the geometry, the electronic/magnetic structure of graphene nanoribbons with different hydrogen edge terminations. We use density functional theory to obtain the equilibrium atomic positions, simulated scanning tunneling microscopy (STM) images, edge energies, band gaps, and edge-induced strains of graphene ribbons that we analyze in terms of Clar formulas. Based on their Clar representation, we propose a classification scheme for graphene ribbons that groups configurations with similar bond length alternations, STM patterns, and Raman spectra. Our simulations show how STM images and Raman spectra can be used to identify the type of edge termination

An In Silico Modeling Approach to Understanding the Dynamics of Sarcoidosis

BACKGROUND: Sarcoidosis is a polygenic disease with diverse phenotypic presentations characterized by an abnormal antigen-mediated Th1 type immune response. At present, progress towards understanding sarcoidosis disease mechanisms and the development of novel treatments is limited by constraints attendant to conducting human research in a rare disease in the absence of relevant animal models. We sought to develop a computational model to enhance our understanding of the pathological mechanisms of and predict potential treatments of sarcoidosis. METHODOLOGY/RESULTS: Based upon the literature, we developed a computational model of known interactions between essential immune cells (antigen-presenting macrophages, effector and regulatory T cells) and cytokine mediators (IL-2, TNFα, IFNγ) of granulomatous inflammation during sarcoidosis. The dynamics of these interactions are described by a set of ordinary differential equations. The model predicts bistable switching behavior which is consistent with normal (self-limited) and "sarcoidosis-like" (sustained) activation of the inflammatory components of the system following a single antigen challenge. By perturbing the influence of model components using inhibitors of the cytokine mediators, distinct clinically relevant disease phenotypes were represented. Finally, the model was shown to be useful for pre-clinical testing of therapies based upon molecular targets and dose-effect relationships. CONCLUSIONS/SIGNIFICANCE: Our work illustrates a dynamic computer simulation of granulomatous inflammation scenarios that is useful for the investigation of disease mechanisms and for pre-clinical therapeutic testing. In lieu of relevant in vitro or animal surrogates, our model may provide for the screening of potential therapies for specific sarcoidosis disease phenotypes in advance of expensive clinical trials

Targeting HER proteins in cancer therapy and the role of the non-target HER3

Members of the human epidermal growth factor receptor (HER) family have been of considerable interest in the cancer arena due to their potential to induce tumorigenesis when their signalling functions are deregulated. The constitutive activation of these proteins is seen in a number of different common cancer subtypes, and in particular EGFR and HER2 have become highly pursued targets for anti-cancer drug development. Clinical studies in a number of different cancers known to be driven by EGFR or HER2 show mixed results, and further mechanistic understanding of drug sensitivity and resistance is needed to realise the full potential of this treatment modality. Signalling in trans is a key feature of HER family signalling, and the activation of the PI3K/Akt pathway, so critically important in tumorigenesis, is driven predominantly through phosphorylation in trans of the kinase inactive member HER3. An increasing body of evidence shows that HER3 plays a critical role in EGFR- and HER2-driven tumours. In particular, HER3 lies upstream of a critically important tumorigenic signalling pathway with extensive ability for feedback and cross-talk signalling, and targeting approaches that fail to account for this important trans-target of EGFR and HER2 can be undermined by its resiliency and resourcefulness. Since HER3 is kinase inactive, it is not a direct target of kinase inhibitors and not presently an easily drugable target. This review presents the current evidence highlighting the role of HER3 in tumorigenesis and its role in mediating resistance to inhibitors of EGFR and HER2

Measurement of the Dipion Mass Spectrum in X(3872) -> J/Psi Pi+ Pi- Decays

We measure the dipion mass spectrum in X(3872)--> J/Psi Pi+ Pi- decays using 360 pb-1 of pbar-p collisions at 1.96 TeV collected with the CDF II detector. The spectrum is fit with predictions for odd C-parity (3S1, 1P1, and 3DJ) charmonia decaying to J/Psi Pi+ Pi-, as well as even C-parity states in which the pions are from Rho0 decay. The latter case also encompasses exotic interpretations, such as a D0-D*0Bar molecule. Only the 3S1 and J/Psi Rho hypotheses are compatible with our data. Since 3S1 is untenable on other grounds, decay via J/Psi Rho is favored, which implies C=+1 for the X(3872). Models for different J/Psi-Rho angular momenta L are considered. Flexibility in the models, especially the introduction of Rho-Omega interference, enable good descriptions of our data for both L=0 and 1.Comment: 7 pages, 4 figures -- Submitted to Phys. Rev. Let

Top Quark Mass Measurement from Dilepton Events at CDF II with the Matrix-Element Method

We describe a measurement of the top quark mass using events with two charged leptons collected by the CDF II detector from $p\bar{p}$ collisions with $\sqrt s = 1.96$ TeV at the Fermilab Tevatron. The likelihood in top mass is calculated for each event by convoluting the leading order matrix element describing $q\bar{q} \to t\bar{t} \to b\ell\nu_{\ell}\bar{b}\ell'\nu_{\ell'}$ with detector resolution functions. The presence of background events in the data sample is modeled using similar calculations involving the matrix elements for major background processes. In a data sample with integrated luminosity of 340 pb$^{-1}$, we observe 33 candidate events and measure $M_{top} = 165.2 \pm 6.1(\textrm{stat.}) \pm 3.4(\textrm{syst.}) \mathrm{~GeV}/c^2.$ This measurement represents the first application of this method to events with two charged leptons and is the most precise single measurement of the top quark mass in this channel.Comment: 21 pages, 14 figure