Magnetoresistance of composites based on graphitic discs and cones

We have studied the magnetotransport of conical and disc-shaped nanocarbon particles in magnetic fields |B| ≤ 9 T at temperatures 2 ≤ T ≤ 300 K to characterize electron scattering in a three-dimensional (3D) disordered material of multilayered quasi 2D and 3D carbon nanoparticles. The microstructure of the particles was modified by graphitization at temperatures of 1600 and 2700 °C. We find clear correlations between the microstructure as seen in transmission electron microscopy and the magnetotransport properties of the particles. The magnetoresistance measurements showed a metallic nature of samples and positive magnetoconductance which is a signature of weak localization in disordered systems. We find that the magnetoconductance at low temperatures resembles quantum transport in single-layer graphene despite the fact that the samples are macroscopic and 3D, consisting of stacked and layered particles, which are randomly oriented in the bulk sample. This graphene-like behaviour is attributed to the very weak interlayer coupling between the graphene layers

Reaction kinetics of protons and oxide ions in LSM/lanthanum tungstate cathodes with Pt nanoparticle activation

Composite electrodes of La0.8Sr0.2MnO3 (LSM)/La28–xW4+xO54+3x/2 (x = 0.85, “LWO56”) on LWO56 electrolytes have been characterized by use of electrochemical impedance spectroscopy vs. pO2 and temperature from 900°C, where LWO56 is mainly oxide ion conducting, to 450°C, where it is proton conducting in wet atmospheres. The impedance data are analyzed in a model which takes into account the simultaneous flow of oxide ions and protons across electrolyte and electrodes, allowing extraction of activation energies and pre-exponential factors for the partial electrode reactions of protons and oxide ions. One composite electrode was infiltrated with Pt nanoparticles with average diameter of 5 nm, lowering the overall electrode polarization resistance (Rp) at 650°C from 260 to 40 Ω cm2. The Pt-infiltrated electrode appears to be rate limited by surface reactions with activation energy of ∼90 kJ mol−1 in the low temperature proton transport regime and ∼150 kJ mol−1 in the high temperature oxide ion transport regime. The charge transfer reaction, which makes a minor contribution to Rp, exhibits activation energies of ∼85 kJ mol−1 for both oxide ion and proton charge transfer

The roles of Eu during the growth of eutectic Si in Al-Si alloys

Controlling the growth of eutectic Si and thereby modifying the eutectic Si from flake-like to fibrous is a key factor in improving the properties of Al-Si alloys. To date, it is generally accepted that the impurity-induced twinning (IIT) mechanism and the twin plane re-entrant edge (TPRE) mechanism as well as poisoning of the TPRE mechanism are valid under certain conditions. However, IIT, TPRE or poisoning of the TPRE mechanism cannot be used to interpret all observations. Here, we report an atomic-scale experimental and theoretical investigation on the roles of Eu during the growth of eutectic Si in Al-Si alloys. Both experimental and theoretical investigations reveal three different roles: (i) the adsorption at the intersection of Si facets, inducing IIT mechanism, (ii) the adsorption at the twin plane re-entrant edge, inducing TPRE mechanism or poisoning of the TPRE mechanism, and (iii) the segregation ahead of the growing Si twins, inducing a solute entrainment within eutectic Si. This investigation not only demonstrates a direct experimental support to the well-accepted poisoning of the TPRE and IIT mechanisms, but also provides a full picture about the roles of Eu atoms during the growth of eutectic Si, including the solute entrainment within eutectic Si

Bilayer graphene formed by passage of current through graphite: evidence for a three-dimensional structure

The passage of an electric current through graphite or few-layer graphene can result in a striking structural transformation, but there is disagreement about the precise nature of this process. Some workers have interpreted the phenomenon in terms of the sublimation and edge reconstruction of essentially flat graphitic structures. An alternative explanation is that the transformation actually involves a change from a flat to a three-dimensional structure. Here we describe detailed studies of carbon produced by the passage of a current through graphite which provide strong evidence that the transformed carbon is indeed three-dimensional. The evidence comes primarily from images obtained in the scanning transmission electron microscope using the technique of high-angle annular dark-field imaging, and from a detailed analysis of electron energy loss spectra. We discuss the possible mechanism of the transformation, and consider potential applications of “three-dimensional bilayer graphene”

Atomic-Scale Spectroscopic Imaging of the Extreme-UV Optical Response of B- and N-Doped Graphene

Abstract Substitutional doping of graphene by impurity atoms such as boron and nitrogen, followed by atom-by-atom manipulation via scanning transmission electron microscopy, can allow for accurate tailoring of its electronic structure, plasmonic response, and even the creation of single atom devices. Beyond the identification of individual dopant atoms by means of ?Z contrast? imaging, spectroscopic characterization is needed to understand the modifications induced in the electronic structure and plasmonic response. Here, atomic scale spectroscopic imaging in the extreme UV-frequency band is demonstrated. Characteristic and energy-loss-dependent contrast changes centered on individual dopant atoms are highlighted. These effects are attributed to local dopant-induced modifications of the electronic structure and are shown to be in excellent agreement with calculations of the associated densities of states

Biological and genetic interaction between Tenascin C and Neuropeptide S receptor 1 in allergic diseases

Neuropeptide S receptor 1 (NPSR1, GPRA 154, GPRA) has been verified as a susceptibility gene for asthma and related phenotypes. The ligand for NPSR1, Neuropeptide S (NPS), activates signalling through NPSR1 and microarray analysis has identified Tenascin C (TNC) as a target gene of NPS-NPSR1 signalling. TNC has previously been implicated as a risk gene for asthma. We aimed therefore to study the genetic association of TNC in asthma- and allergy-related disorders as well as the biological and genetic interactions between NPSR1 and TNC. Regulation of TNC was investigated using NPS stimulated NPSR1 transfected cells. We genotyped 12 TNC SNPs in the cross-sectional PARSIFAL study (3113 children) and performed single SNP association, haplotype association and TNC and NPSR1 gene-gene interaction analyses. Our experimental results show NPS-dependent upregulation of TNC-mRNA. The genotyping results indicate single SNP and haplotype associations for several SNPs in TNC with the most significant association to rhinoconjunctivitis for a haplotype, with a frequency of 29% in cases (P = 0.0005). In asthma and atopic sensitization significant gene-gene interactions were found between TNC and NPSR1 SNPs, indicating that depending on the NPSR1 genotype, TNC can be associated with either an increased or a decreased risk of disease. We conclude that variations in TNC modifies, not only risk for asthma, but also for rhinoconjunctivitis. Furthermore, we show epistasis based on both a direct suggested regulatory effect and a genetic interaction between NPSR1 and TNC. These results suggest merging of previously independent pathways of importance in the development of asthma- and allergy-related trait

Effect of composition on the structure of lithium- and manganese-rich transition metal oxides

The choice of chemical composition of lithium- and manganese-rich transition metal oxides used as cathode materials in lithium-ion batteries can significantly impact their long-term viability as storage solutions for clean energy automotive applications. Their structure has been widely debated: conflicting conclusions drawn from individual studies often considering different compositions have made it challenging to reach a consensus and inform future research. Here, complementary electron microscopy techniques over a wide range of length scales reveal the effect of lithium-to-transition metal-ratio on the surface and bulk structure of these materials. We found that decreasing the lithium-to-transition metal-ratio resulted in a significant change in terms of order and atomic-level local composition in the bulk of these cathode materials. However, throughout the composition range studied, the materials consisted solely of a monoclinic phase, with lower lithium content materials showing more chemical ordering defects. In contrast, the spinel-structured surface present on specific crystallographic facets exhibited no noticeable structural change when varying the ratio of lithium to transition metal. The structural observations from this study warrant a reexamination of commonly assumed models linking poor electrochemical performance with bulk and surface structure

Is cash king or dead money? : an empirical study of Norwegian firms and the effect of cash on firm performance

This thesis explores the relationship between cash and rm performance. Additionally, the thesis provides insight into how this relationship varies across di erent time periods and industries. Using instrumental variable multiple regression analysis, the thesis analyzes accounting data for a sample of Norwegian rms from 2005-2015. After correcting for a non-linear relationship between cash and rm performance we nd that i) rm performance for our sample of Norwegian rms is less a ected by cash than US manufacturing rms, ii) cash has a positive, but weakly diminishing e ect on rm performance throughout the entire sample period, iii) the relationship between cash and rm performance is most pronounced pre-recession, iv) rms with high knowledge intensity have higher cash ratios than rms with lower knowledge intensity, v) cash has less e ect on rm performance for rms with high knowledge intensity compared to rms with low knowledge intensity for cash ratios up to 0.4, and vi) cash has a greater e ect on rm performance for rms in labor intensive industries than in capital intensive industries. In addition to our analysis results, we provide a thorough discussion of potential pitfalls of OLS regression and how we account for these. We also attempt to explain all our results in great detail, focusing on understanding the underlying causality behind the regression estimates. We conclude that cash indeed has a substantial impact on rm performance and that the importance of cash is understated in much of the current strategy and nance theory.nhhma