A novel multiscale approach to brittle fracture of nano/micro‐sized components

Principles and advantages of a new concept based on the ab initio aided strain gradient elasticity theory are shown in comparison with the classical Barenblatt cohesive model. The method is applied to the theoretical prediction of the critical energy release rate and the crack tip opening displacement at the crack instability in nanopanels made of germanium and molybdenum crystals. The necessary length scale parameter l₁ is determined for germanium and molybdenum by the best gradient elasticity fits of ab initio computed screw dislocation displacements and phonon dispersions. Values of ab initio computed critical energy release rates and crack opening profiles revealed that the length l₁ is related to inflexion points of profiles. A novel ab initio method in combination with continuum mechanics was successfully tested to replace molecular statics dependent of availability of interatomic potentials. The asymptotic strain gradient elasticity solution for displacement components near the crack tip in materials with cubic lattice was also derived.     

Predictor‐based tracking for neuromuscular electrical stimulation

We present a new tracking controller for neuromuscular electrical stimulation (NMES), which is an emerging technology that artificially stimulates skeletal muscles to help restore functionality to human limbs. The novelty of our work is that we prove that the tracking error globally asymptotically and locally exponentially converges to zero for any positive input delay, coupled with our ability to satisfy a state constraint imposed by the physical system. Also, our controller only requires sampled measurements of the states instead of continuous measurements and allows perturbed sampling schedules, which can be important for practical purposes. Our work is based on a new method for constructing predictor maps for a large class of time‐varying systems, which is of independent interest. Copyright © 2014 John Wiley & Sons, Ltd.     

Greener assembling of MoO3 nanoparticles supported on gum arabic: cytotoxic effects and catalytic efficacy towards reduction of p-nitrophenol

Clean Technologies and Environmental Policy - An economical and easy one-step method for the biosynthesis of highly stable molybdenum trioxide (MoO3) nanoparticles was developed using gum arabic as...     

One-pot preparation of surface-functionalized barium titanate nanoparticles for high-K polystyrene composite films prepared via floating method

An advanced and inexpensive one-pot method to prepare polystyrene (PS)–barium titanate (BT) films by solution mixing is reported. The process was developed to obtain free-standing films with an increased dielectric constant (ε′). Since PS is soluble in apolar solvents, BT nanoparticles (BT-NPs) were surface-modified with palmitic acid (PAc) and embedded within the polymer matrix without affecting homogeneity and smoothness of the composite. The films were prepared by floating method consisting in dropping BT-NPs dispersed in PS/toluene solution on the water surface. After the evaporation of toluene, smooth, free-standing and thermally stable films were obtained with a markedly higher ε′ compared to the neat PS. PAc modification improved the dispersion of BT-NPs in the apolar phase and prevented their diffusion into the aqueous phase during the toluene evaporation. The proposed film-forming technique makes it possible to modulate the thickness and shape of the films by selecting the quantity and concentration of the organic phase and using various templates, thus opening up a broad range of applications.     

Twinned Growth of Metal‐Free,Triazine‐Based Photocatalyst Films as Mixed‐Dimensional (2D/3D) van der Waals Heterostructures

Design and synthesis of ordered, metal‐free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed‐dimensional (2D/3D) metal‐free van der Waals (vdW) heterostructures based on triazine (C₃N₃) linkers grow as large area, transparent yellow‐orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E _g,opt = 1.91 eV, E _g,elec = 1.84 eV) and are moderately porous (124 m² g^?1). The material consists of a crystalline 2D phase that is fully sp² hybridized and provides structural stability, and an amorphous, porous phase with mixed sp²–sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one‐pot reaction mixture: unprecedented for metal‐free frameworks and a direct consequence of on‐catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal‐free, light‐induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h^?1 g^?1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of “wet” chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.     

Achieving IT‐based synergies through regulation‐oriented and consensus‐oriented IT governance capabilities

This study aims at exploring the IT governance capabilities that enable organizations to achieve IT‐based synergies. Following existing work on the contextualization of theories and drawing on the resource‐based view of the firm (RBV), we develop an RBV of IT‐based synergies in two steps. First, we adopt existing context‐specific constructs and relationships from prior work on IT governance capabilities, IT relatedness, and synergies to develop a preliminary contextualization of the RBV. Second, to further refine our theoretical framework, we conduct an exploratory field study that includes interviews with 26 CIOs and other IT executives from 21 multibusiness firms. Our findings suggest that IT governance capabilities lead to IT‐based synergies through IT relatedness and business process relatedness. We found regulation‐oriented IT governance capabilities (IT roles and IT processes) to increase IT relatedness, while consensus‐oriented IT governance capabilities (IT groups and relational capabilities) had a positive effect on business process relatedness. Our results suggest that, in isolation, IT and business process relatedness lead to IT cost synergies, while collectively enabling IT‐induced business synergies. Our study is among the first to treat IT relatedness as an endogenous construct and to explicitly integrate business process relatedness into the IT governance domain. Our context‐specific decomposition of IT governance capabilities helps to better explain their links to IT and business process relatedness. These findings contribute to a better understanding of the tension between IT‐based synergies and business‐IT alignment. Decision‐makers are guided in developing IT governance capabilities to achieve IT‐based synergies.     

Towards probabilistic synchronisation of local controllers

The traditional use of global and centralised control methods fails for large, complex, noisy and highly connected systems, which typify many real-world industrial and commercial systems. This paper provides an efficient bottom-up design of distributed control in which many simple components communicate and cooperate to achieve a joint system goal. Each component acts individually so as to maximise personal utility whilst obtaining probabilistic information on the global system merely through local message-passing. This leads to an implied scalable and collective control strategy for complex dynamical systems, without the problems of global centralised control. Robustness is addressed by employing a fully probabilistic design, which can cope with inherent uncertainties, can be implemented adaptively and opens a systematic rich way to information sharing. This paper opens the foreseen direction and inspects the proposed design on a linearised version of coupled map lattice with spatio-temporal chaos. A version close to linear quadratic design gives an initial insight into possible behaviours of such networks.     

Formation of nanostructured epoxy networks containing polyhedral oligomeric silsesquioxane (POSS) blocks

Nanostructured epoxy networks, based on DGEBA and poly(oxypropylene)diamine (Jeffamine D), containing nano-sized inorganic blocks, polyhedral oligomeric silsesquioxanes (POSS), were investigated. The POSS were incorporated in the network as crosslinks or as pendant units by using octa- or monoepoxy-POSS monomers, respectively, as well as diepoxides with pendant POSS. The authors focused on investigating the relationship between the network formation process and the final product properties. The reactivity of the epoxy-functional POSS monomers, the hybrid systems' time of gelation, the gel fractions and the phase structure of the networks were determined using ¹H or ¹³C NMR spectroscopy, chemorheology experiments, sol-gel analysis and transmission electron microscopy (TEM).All the POSS epoxides tested show a reduced reactivity if compared to their respective model compounds due to sterical crowding in the neighborhood of their functional groups and due to reduced epoxy group mobility. The incorporation of pendant POSS into networks of the type DGEBA-Jeffamine D-monoepoxy-POSS hence took place only in the late reaction stage. Together with the high tendency of these POSS to aggregation, the kinetics favors the formation of small nano-phase-separated POSS domains, which act as physical crosslinks due to their covalent bonds to the organic matrix. At POSS loadings higher than 70%, topological constraint by POSS leads to a strongly reduced elastic chain mobility, thus additionally strongly reinforcing the networks. The network build-up and gelation of the octaepoxy-POSS-Jeffamine D system were slow compared to the reference DGEBA-Jeffamine D network due to a low octaepoxy-POSS reactivity and due to its strong tendency to cyclization reactions with primary amines. The topology of the amino groups is shown to be very important. In contrast to monoepoxy-POSS, the octaepoxy-POSS becomes dispersed as oligomeric junctions (purely chemical crosslinks) of the network in the cured product. The octaepoxide's reinforcing effect is small and is given only by its high functionality and not by its inorganic nature. The functionality effect is reduced by the mentioned cyclizations.     

Anionic polymerization of acrylates. XIV. Synthesis of MMA/acrylate block copolymers initiated with ester-enolate/tert-alkoxide complex

Diblock copolymers of methyl methacrylate (MMA) with 2-ethylhexyl, butyl, ethyl or tert-butyl acrylate (EtHA, BuA, EtA, t-BuA) have been prepared by the ligated anionic polymerization initiated with methyl 2-lithioisobutyrate (MIB-Li) in the presence of an excess of Li tert-butoxide (t-BuOLi) in toluene/THF mixture at −60 or −78 °C. The copolymers, prepared at −60 °C, show MWD with a hint of bimodality, indicating partial deactivation of the living PMMA upon addition of acrylic monomer. At −78 °C, the extent of this deactivation is distinctly lower, the formed block copolymers, in particular, poly(MMA-b-EtHA), have unimodal MWD and exhibit tails only in the lower-molecular-weight region. Poly(MMA-b-EtHA)s were extracted with acetonitrile dissolving PMMA; very small parts of the crude products dissolved, whereas prevailing parts remained as solids documenting thus formation of block copolymer in a high yield. Surprisingly, the highest amount of self terminated PMMA was found in block copolymerization of MMA with t-BuA at both the temperatures, the products of which had clearly bimodal MWDs. This finding is shortly discussed on the basis of relatively slow propagation of t-BuA in comparison with EtHA, BuA and EtA.