Scanning transmission electron microscopy (STEM) has been widely used for characterization of materials; to identify micro- and nano-structures within a sample and to analyze crystal and defect structures. High-angle annular dark field (HAADF) STEM imaging using atomic number (Z) contrast has proven capable of resolving atomic structures with better than 2 A lateral resolution. In this work, the HAADF STEM imaging mode is used in combination with multislice simulations. This combination is applied to the investigation of the temperature dependence of the intensity collected by the HAADF detector in silicon, and to convergent beam electron diffraction (CBED) to measure the degree of chemical order in intermetallic nanoparticles. The experimental and simulation results on the high–angle scattering of 300 keV electrons in crystalline silicon provide a new contribution to the understanding of the temperature dependence of the HAADF intensity. In the case of 300 keV, the average high-angle scattered intensity slightly decreases as the temperature increases from 100 K to 300 K, and this is different from the temperature dependence at 100 keV and 200 keV where HAADF intensity increases with temperature, as had been previously reported by other workers. The L10 class of hard magnetic materials has attracted continuous attention as a candidate for high-density magnetic recording media, as this phase is known to have large magnetocrystalline anisotropy, with magnetocrystalline anisotropy constant, Ku, strongly dependent on the long-range chemical order parameter, S. A new method is developed to assess the degree of chemical order in small FePt L10 nanoparticles by implementing a CBED diffraction technique. Unexpectedly, the degree of order of individual particles is highly variable and not a simple function of particle size or sample composition. The particle-to-particle variability observed is an important new aspect to the understanding of phase transformations in nanoparticle systems.

BSCCO-2212 is a high-temperature cuprate superconductor whose microscopic behavior is currently poorly understood. In particular, it is unclear whether its order parameter is consistent with s-wave or d-wave symmetry. It has been suggested that its order parameter might take one of several forms that are consistent with d-wave behavior. We present some calculations using the many-body theory approach to superconductivity that suggest that such order parameters would lead to a suppression of the critical temperature in the presence of impurities. Because some experiments have suggested the critical temperature of BSCCO-2212 is relatively independent of the concentration of impurities, this lends support to the hypothesis that its order parameter has s-wave symmetry.

The interactions between cholesterol and other membrane molecules determine important membrane properties. It was shown that even small changes in the molecular structure of cholesterol have a crucial influence on these interactions. We recently reported that in addition to alterations in the tetracyclic ring structure, the iso-branched side chain of cholesterol also has a significant impact on membrane properties (Scheidt H. et al. 2013 Angew. Chem. Int. Ed. Engl. 52, 12848-12851). Here we used synthetic cholesterol analogs to investigate the influence of an unbranched aliphatic side chain of different length. The 2H NMR order parameter of the phospholipid chains and therefore the molecular packing of the phospholipid molecules shows a significant dependence on the sterol’s alkyl side chain length, while , membrane permeation studied by a dithionite ion permeation assay and lateral diffusion measured by 1H MAS pulsed field gradient NMR are less influenced. To achieve the same molecular packing effect similar to that of an iso-branched aliphatic side chain, a longer unbranched side chain (n-dodecyl instead of n-octyl) at C17 of cholesterol is required. Obviously, sterols having a branched iso- alkyl chain with two terminal methyl groups exhibit altered cholesterol-phospholipid-interactions compared to analogous molecules with a straight unbranched chain.

In contrast to the static snapshots provided by protein crystallography, G protein-coupled receptors constitute a group of proteins with highly dynamic properties, which are required in the receptors’ function as signaling molecule. Here, the human neuropeptide Y2 receptor was reconstituted into a model membrane composed of monounsaturated phospholipids and solid-state NMR was used to characterize its dynamics. Qualitative static 15N NMR spectra and quantitative determination of 1H-13C order parameters through measurement of the 1H-13C dipolar couplings of the CH, CH2 and CH3 groups revealed axially symmetric motions of the whole molecule in the membrane and molecular fluctuations of varying amplitude from all molecular segments. The molecular order parameters (Sbackbone = 0.59-0.67, SCH2 = 0.41-0.51 and SCH3 = 0.22) obtained in directly polarized 13C NMR experiments demonstrate that the Y2 receptor is highly mobile in the native-like membrane. Interestingly, according to these results the receptor was found to be slightly more rigid in the membranes formed by the monounsaturated phospholipids than by saturated phospholipids as investigated previously. This could be caused by an increased chain length of the monounsaturated lipids, which may result in a higher helical content of the receptor. Furthermore, the incorporation of cholesterol, phosphatidylethanolamine, or negatively charged phosphatidylserine into the membrane did not have a significant influence on the molecular mobility of the Y2 receptor.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Experimental data show that the dissolved impurities of the Mn presents a magnetic moment when substitute the Ni atom in pseudoquaternary borocarbide Y (Ni(1−x)Mx)2B2C, this is not observed if the impurities are Fe and Co. In this work we do a theoretical study of the superconducting order parameter variation and a possible formation of impurities magnetic moment to T < Tc. We have used the LAPW method, based in Density Functional Theory, to calculate the density of state of pure compound. To describe the superconductor system it was used the attractive Hubbard model. To describe the effects of the disorder induced by the dissolved impurities was used the coherent potential approximation. Using the Nambu s formalism to represent the Hamiltonian and the Green s functions of the effective medium (g) and of the perturbed system (G), we calculate the magnetic moment of the impurities from the diagonal terms and the variation of the order parameter from the off-diagonal one. The calculated date to magnetic moment show a qualitative agreement with the experimental results to Mn impurities. To the Fe and Co cases no magnetic moment was observed, in agreement with the experimental results too. The calculated order parameter shows a decrease with concentration to the Mn and Fe atoms. We investigate, through of the a calculation first principles (LAPW), the possible formation of the magnetic moment in this compound to concentration of 25 and 12.5%. The obtained results show that to concentration of 25%, both the impurities, Mn and Fe, presents a magnetic moment. The magnetization on the Co site was small when compared with the above cases. In this way we conclude that the Co atom not present a magnetic moment in this system. / Medidas experimentais mostram que impurezas de Mn formam momento magnético quando substituem o Ni no borocarbeto pseudoquaternário Y (Ni(1−x)Mx)2B2C, enquanto que as impurezas de Fe e de Co não exibem tal comportamento. Neste trabalho foi feito um estudo teórico da variação do parâmetro de ordem supercondutor e da possível formação de momento magnético nos sítios dessas impurezas para T < Tc. Para isso, utilizamos o m´etodo LAPW, baseado na Teoria do Funcional da Densidade, para calcular a densidade de estados do composto puro. Para descrever o sistema supercondutor foi utilizado o modelo de Hubbard atrativo. Os efeitos de desordem induzidos pela adição de impurezas de metais de transição M no material, foram tratados dentro da aproximação do potencial coerente. Usando o formalismo de Nambu para representar o hamiltoniano e as funções de Green associadas aos propagadores do sistema efetivo (g) e do sistema perturbado (G), calculamos o momento magn´etico das impurezas através dos termos diagonais e as variações do parâmetro de ordem efetivo a partir do termo fora da diagonal. Os resultados obtidos comprovam o que é observado experimentalmente, ou seja, o Mn forma momento magn´etico que aumenta com a concentração, enquanto que nas impurezas de Fe e Co nenhuma magnetização foi observada. Além disso, o parâmetro de ordem diminui com a concentração de Mn e Fe. Além desse estudo, também investigamos, através de um cálculo de primeiros princípios (LAPW), a possível formação de momento magnético neste composto para concentrações de 25 e 12.5%. Os resultados obtidos mostraram que para x = 25%, tanto as impurezas de Mn quanto as de Fe, apresentaram um momento magnético. A magnetização no síıtio do Co foi bastante pequena comparada com as duas anteriores e dessa forma pode-se concluir que esta impureza não forma momento quando diluída neste sistema.

No description available.

In part to search for a possible critical point (CP) in the phase diagram of hot nuclear matter, a beam energy scan was performed at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory. The Solenoidal Tracker at RHIC (STAR) collected Au+Au data sets at beam energies, √sNN , of 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV. Such a scan produces hot nuclear matter at different locations in the phase diagram. Lattice and phenomenological calculations suggest that the presence of a CP might result in divergences of the thermodynamic susceptibilities and correlation lengths. The statistical moments of the identified-particle multiplicity distributions directly depend on both the thermodynamic susceptibilities and correlation lengths, possibly making the shapes of these multiplicity distributions sensitive tools for the search for the critical point. The statistical moments of the multiplicity distributions of a number of different groups of identified particle species were analyzed. Care was taken to remove a number of experimental artifacts that can modify the shapes of the multiplicity distributions. The observables studied include the lowest four statistical moments (mean, variance, skewness, kurtosis) and some products of these moments. These observables were compared to the predictions from several approaches lacking critical behavior, such as the Hadron Resonance Gas model, mixed events, (negative) binomial, and Poisson statistics. In addition, the data were analyzed after gating on the event-by-event antiproton-to-proton ratio, which is expected to more tightly constrain the event trajectories on the phase diagram.

This thesis is devoted to several aspects of geometry and morphology in wetting problems and hard sphere packings. First, we propose a new method to simulate wetting and slip on nanostructured substrates: a phase field model associated with a dynamical density theory approach. We showed omniphobicity, meaning repellency, no matter the chemical properties of the liquid on monovalued surfaces, i.e. surfaces without overhangs, which is in contradiction with the macroscopic Cassie-Baxter-Wenzel theory, can produce so-called We checked systematically the impact of the surface parameters on omniphobic repellency, and we show that the key ingredient are line tensions, which emerge from needle shaped surface structures. Geometrical effects have also an important influence on glassy or jammed systems, for example amorphous hard sphere systems in infinite pressure limit. Such hard sphere packings got stuck in a so-called jammed phase, and we shall demonstrate that the local structure in such systems is universal, i.e. independent of the protocol of the generation. For this, robust order parameters - so-called Minkowski tensors - are developed, which overcome robustness deficiencies of widely used order parameters. This leads to a unifying picture of local order parameters, based on geometrical principles. Furthermore, we find with the Minkowski tensor analysis crystallization in jammed sphere packs at the random closed packing point

The interactions between cholesterol and other membrane molecules determine important membrane properties. It was shown that even small changes in the molecular structure of cholesterol have a crucial influence on these interactions. We recently reported that in addition to alterations in the tetracyclic ring structure, the iso-branched side chain of cholesterol also has a significant impact on membrane properties (Scheidt H. et al. 2013 Angew. Chem. Int. Ed. Engl. 52, 12848-12851). Here we used synthetic cholesterol analogs to investigate the influence of an unbranched aliphatic side chain of different length. The 2H NMR order parameter of the phospholipid chains and therefore the molecular packing of the phospholipid molecules shows a significant dependence on the sterol’s alkyl side chain length, while , membrane permeation studied by a dithionite ion permeation assay and lateral diffusion measured by 1H MAS pulsed field gradient NMR are less influenced. To achieve the same molecular packing effect similar to that of an iso-branched aliphatic side chain, a longer unbranched side chain (n-dodecyl instead of n-octyl) at C17 of cholesterol is required. Obviously, sterols having a branched iso- alkyl chain with two terminal methyl groups exhibit altered cholesterol-phospholipid-interactions compared to analogous molecules with a straight unbranched chain.

In contrast to the static snapshots provided by protein crystallography, G protein-coupled receptors constitute a group of proteins with highly dynamic properties, which are required in the receptors’ function as signaling molecule. Here, the human neuropeptide Y2 receptor was reconstituted into a model membrane composed of monounsaturated phospholipids and solid-state NMR was used to characterize its dynamics. Qualitative static 15N NMR spectra and quantitative determination of 1H-13C order parameters through measurement of the 1H-13C dipolar couplings of the CH, CH2 and CH3 groups revealed axially symmetric motions of the whole molecule in the membrane and molecular fluctuations of varying amplitude from all molecular segments. The molecular order parameters (Sbackbone = 0.59-0.67, SCH2 = 0.41-0.51 and SCH3 = 0.22) obtained in directly polarized 13C NMR experiments demonstrate that the Y2 receptor is highly mobile in the native-like membrane. Interestingly, according to these results the receptor was found to be slightly more rigid in the membranes formed by the monounsaturated phospholipids than by saturated phospholipids as investigated previously. This could be caused by an increased chain length of the monounsaturated lipids, which may result in a higher helical content of the receptor. Furthermore, the incorporation of cholesterol, phosphatidylethanolamine, or negatively charged phosphatidylserine into the membrane did not have a significant influence on the molecular mobility of the Y2 receptor.