The Role of Ligand Density in the Enzymatic Glycosylation of Carbohydrates Presented on Self-Assembled Monolayers of Alkanethiolates on Gold

The biological activity of immobilized carbohydrates can show a dramatic dependence on the density of carbohydrate. This is the result of investigations with self-assembled monolayers that present N-acetylglucosamine groups as a model substrate for glycosylation by bovine β-1,4-galactosyltransferase (GalTase; see picture). Surface plasmon resonance spectroscopy and carbohydrate-binding lectins were used to characterize the reaction at the interface. UDP-Gal=uridine diphosphogalactose     

Local structure of core/shell nanocrystalline particles produced by surfactant-assisted ball milling of Fe powder in paraffin

Surfactant-assisted ball milling of the Fe powder in paraffin has been used for fabrication of core–shell nanocrystalline particles. The local atomic structure of the bulk and surface layers of the mechanically milled particles has been studied using X-ray absorption spectroscopic techniques with synchrotron radiation from the DORIS storage ring at DESY, Hamburg. Regardless of milling environment composition, the as-prepared powders were shown to be characterized by a significant drop in the EXAFS signal intensity and coordination numbers of the Fe–Fe pairs due to the formation of nanocrystalline state in the particles. It has been shown that an addition of perfluorononanoic acid as a surfactant has a more prominent effect on the structure of the shell layers. The effect is revealed as an appearance of light element atoms (O, F, C) in the local atomic environment of the Fe atoms due to formation of oxide, carbide and adsorbed structures of different types in the particle shell.     

High-resolution electron microscopy of microstructure of SrTiO3/BaZrO3 bilayer thin films on MgO substrates

SrTiO₃/BaZrO₃ heterofilms as buffer layers are deposited on (0 0 1) MgO substrates by an RF-sputtering technique. The atomic structure and the defect configuration at the interfaces are investigated by means of aberration-corrected high-resolution transmission electron microscopy. At the BaZrO₃/MgO interface, two types of interfacial structures, MgO/ZrO₂-type and MgO/BaO-type, are observed. Antiphase boundaries and dislocations are found at the BaZrO₃/MgO interface. The formation of these lattice defects is discussed in terms of film growth and structural imperfections of the substrate surface. At the SrTiO₃/BaZrO₃ interface, a high density of misfit dislocations is observed with different configurations. The formation of these dislocations contributes both to the relaxation of the large misfit strain and to stopping of the further propagation of lattice defects which are formed in the BaZrO₃ layer into the SrTiO₃ layer.     

Nd:YVO4 crystal growth by Czochralski technique with a submerged plate

This paper is to investigate the growth of Nd:YVO₄ (yttrium vanadate) crystal by the modified Czochralski technique with a submerged plate. Numerical studies are performed to examine melt convection and heat transfer during Nd:YVO₄ growth. The attention is paid to study the effects of initial elevation of the submerged plate, crystal diameter, and melt level on melt inclusions. It is found that the increase in crystal rotation rate and crystal diameter, and the decrease in melt level will increase the axial temperature gradient at the edge and in the center of the crystal, and change the interface shape from convex to flat. The experiments are also carried out to confirm the feasibility of the proposed new technique for controlling melt inclusions in Nd:YVO₄ crystal growth.     

Binding properties between ferroic oxides and metals

Using first principles calculations the binding characteristics of a metallic film covering a piezo-electric oxide is studied. The band structures and the charge densities of interfaces and single compounds are calculated. Comparing the overlaps of the densities of states and the differences in the charge densities, it is found that the interface stabilitydepends on the thickness of the metallic film. The bonding is shown to be a result of charge transfer.     

Reconstruction of a hidden topography by single AFM force–distance curves

Force–distance curves have been acquired with an Atomic Force Microscope on polymethyl methacrylate with embedded glass spheres. The glass spheres provide a stiff substrate with an irregular and complex topography hidden underneath a compliant and even polymer film. This situation is a special case of a mechanical double-layer, which we examined in detail in previous experiments. Up to now uniform and non-uniform polymer films on an even substrate were examined. The film thickness on each point of the sample surface was known and force–distance curves could be averaged in groups according to the film thickness. In this way we were able to develop a semi empirical approach which allows describing the shape of averaged force–distance curves depending on the Young’s moduli of the involved materials and on the film thickness. In this experiment we reconstruct a hidden topography, i.e., we determine the polymer thickness on each point of the sample by analyzing single force–distance curves with our semi empirical equation. The accuracy reached by this approach permits to obtain a reconstruction of the shape and position of the embedded particles limited by a maximum detection depth. Single curves are also analyzed qualitatively in order to locate areas where the adhesion at the polymer/glass interface is weak or the two phases are detached.     

Anticrossing spectroscopy in multi-nanolayer structures

Presently we explored nanosandwich structures with graphite (Gt) and graphene (Gn) nanolayers. We found that in Pt–SiO₂–Gt, Pt–BN–Gt and Pt–SiO₂–Ni–Gn structures the spectra may be decomposed into several components, each corresponding to a different value of the total spin angular momentum S. Only one component was required to describe the Pt–SiO₂–Ni–Gn spectra at 5.3 K, with additional components appearing at higher temperatures. On the other hand, a single component described the Pt–BN–Ni–Gn spectra at all temperatures. Temperature dependence of the spectra of the Pt–SiO₂–Ni–Gn system was studied in the 5.3–75.3 K range. Presently we obtained experimental results for novel sandwich systems, with the Gn layer only two monoatomic layers thick. Thus, we compared experimental spectra of a three-nanolayer sandwich system containing a Gt nanolayer with those of a four-nanolayer system containing a diatomic Gn layer. The experimental results were discussed using a theoretical model of the respective physical mechanisms. We propose an exchange anticrossing mechanism, whereby the spin-state polarization of the given Zeeman?s substate in the Pt nanolayer is transported to Gt or Ni–Gn nanolayer by the exchange interaction between the two layers. As long as exchange interaction coupling spin states in different nanolayers is involved, we term the respective spectra the “spin anticrossing exchange-resonance spectra”. This clarifies the physical origins of some of the model parameters, i.e. the growing external magnetic field shifts the Zeeman?s substates in the different layers differently, producing the anticrossing spectrum. In the frameworks of the developed model, we propose spin–orbit (SO) interaction as the main factor inducing the spin–lattice relaxation, which is one of the important factors determining the line shape. We performed ab initio calculations of the SO interaction in carbon and metal nanolayers, finding that the SO interactions monotonously increase with the atomic number.     

A dislocation density based crystal plasticity finite element model: Application to a two-phase polycrystalline HCP/BCC composites

We present a multiscale model for anisotropic, elasto-plastic, rate- and temperature-sensitive deformation of polycrystalline aggregates to large plastic strains. The model accounts for a dislocation-based hardening law for multiple slip modes and links a single-crystal to a polycrystalline response using a crystal plasticity finite element based homogenization. It is capable of predicting local stress and strain fields based on evolving microstructure including the explicit evolution of dislocation density and crystallographic grain reorientation. We apply the model to simulate monotonic mechanical response of a hexagonal close-packed metal, zirconium (Zr), and a body-centered cubic metal, niobium (Nb), and study the texture evolution and deformation mechanisms in a two-phase Zr/Nb layered composite under severe plastic deformation. The model predicts well the texture in both co-deforming phases to very large plastic strains. In addition, it offers insights into the active slip systems underlying texture evolution, indicating that the observed textures develop by a combination of prismatic, pyramidal, and anomalous basal slip in Zr and primarily {110}〈111〉 slip and secondly {112}〈111〉 slip in Nb.     

Disordered elastic systems and one-dimensional interfaces

We briefly introduce the generic framework of disordered elastic systems (DES), giving a short ‘recipe’ of a DES modeling and presenting the quantities of interest in order to probe the static and dynamical disorder-induced properties of such systems. We then focus on a particular low-dimensional DES, namely the one-dimensional interface in short-ranged elasticity and short-ranged quenched disorder. Illustrating different elements given in the introductory sections, we discuss specifically the consequences of the interplay between a finite temperature T>0$T>0$ and a finite interface width ξ>0$\xi >0$ on the static geometrical fluctuations at different lengthscales, and the implications on the quasistatic dynamics.