Non‐Radial Growth of Helical Homopolymer Crystals: Breaking the Paradigm of the Polymer Spherulite Microstructure

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X‐ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat‐on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.

     

Memristive port-Hamiltonian Systems

The port-Hamiltonian modelling framework is extended to a class of systems containing memristive elements and phenomena. First, the concept of memristance is generalised to the same generic level as the port-Hamiltonian framework. Second, the underlying Dirac structure is augmented with a memristive port. The inclusion of memristive elements in the port-Hamiltonian framework turns out to be almost as straightforward as the inclusion of resistive elements. Although a memristor is a resistive element, it is also a dynamic element since the associated Ohmian laws are rather expressed in terms of differential equations. This means that the state space manifold, as naturally defined by the storage elements, is augmented by the states associated with the memristive elements. Hence the order of complexity is, in general, defined by the number of storage elements plus the number of memristors in the system. Apart from enlarging our repertoire of modelling building blocks, the inclusion of memristive elements in the existing port-Hamiltonian formalism possibly opens up new ideas for controller synthesis and design.     

Versatile mass excited impact oscillator

Nonlinear Dynamics - This paper presents the design and the initial experimental results of a novel impact oscillator rig developed by the Centre of Applied Dynamic Research at the University of...     

Direct Synthesis of N-Heterocyclic Carbene-Stabilized Copper Nanoparticles from an N-Heterocyclic Carbene–Borane

N-Heterocyclic carbene (NHC)-stabilized copper nanoparticles (NPs) were synthesized from an NHC–borane adduct and mesitylcopper(I) under thermal conditions (refluxing toluene for 2.5 h). NPs with a size distribution of 11.6±1.8 nm were obtained. The interaction between Cu NPs and NHC ligands was probed by X-ray photoelectron spectroscopy, which showed covalent binding of the NHC to the surface of the NPs. Mechanistic studies suggested that NHC–borane plays two roles: contributing to the reduction of [CuMes]₂ to release Cu⁰ species and providing NHC ligands to stabilize the copper NPs.     

Enantioselective,Stereodivergent Hydroazidation and Hydroamination of Allenes Catalyzed by Acyclic Diaminocarbene (ADC) Gold(I) Complexes

The gold‐catalyzed enantioselective hydroazidation and hydroamination reactions of allenes are presented herein. ADC gold(I) catalysts derived from BINAM were critical for achieving high levels of enantioselectivity in both transformations. The sense of enantioinduction is reversed for the two different nucleophiles, allowing access to both enantiomers of the corresponding allylic amines using the same catalyst enantiomer.     

Self-Assembly of Low-Molecular-Weight Asymmetric Linear Triblock Terpolymers: How Low Can We Go?

The synthesis of two (2) novel triblock terpolymers of the ABC type and one (1) of the BAC type, where A, B and C are chemically different segments, such as polystyrene (PS), poly(butadiene) (PB_1,4) and poly(dimethylsiloxane) (PDMS), is reported; moreover, their corresponding molecular and bulk characterizations were performed. Very low dimensions are evident from the characterization in bulk from transmission electron microscopy studies, verified by small-angle X-ray data, since sub-16 nm domains are evident in all three cases. The self-assembly results justify the assumptions that the high Flory–Huggins parameter, χ, even in low molecular weights, leads to significantly well-ordered structures, despite the complexity of the systems studied. Furthermore, it is the first time that a structure/properties relationship was studied for such systems in bulk, potentially leading to prominent applications in nanotechnology and nanopatterning, for as low as sub-10 nm thin-film manipulations.     

Compact fluidized bed sorber for CO2 capture

Multiphase CFD is used to design a compact fluidized bed sorber for CO2 removal from flue gases using sodium or potassium carbonate pellets. The sorber sizes are much smaller than commercial amine absorbers and smaller than other proposed dry adsorbers. The size reduction is due to the elimination of dilute regions that cause bypassing. With proper solids feeding we eliminated the usual core-annular regime found in circulating fluidized beds.     

Thermodynamic and kinetic analysis of the reaction between biological catecholamines and chlorinated methylperoxy radicals

The antiradical potency of catecholamines (dopamine, epinephrine, norepinephrine, L-DOPA), metabolites of dopamine (homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid) and catechol towards substituted methylperoxy radicals is investigated. The thermodynamic parameters, together with the kinetic approach, are used to determine the most probable mechanism of action. The natural bond orbital and quantum theory of atoms in molecules are utilised to explain the highest reactivity of trichloromethylperoxy radical. The preferred mechanism is dependent both on the thermodynamic and kinetic parameters . The number of chlorine atoms on radical, the presence of intra-molecular hydrogen bond and number of hydroxy groups attached to the aromatic ring significantly influence the mechanism. The results suggest that sequential proton loss electron transfer (SPLET) is the most probable for reaction with methylperoxy and hydrogen atom transfer (HAT) for reaction with trichloromethylperoxy radicals, with a gradual transition between SPLET and HAT for other two radicals. Due to the significant deprotonation of molecules containing the carboxyl group, the respective anions are also investigated. The HAT and SPLET mechanisms are highly competitive in reaction with MP radical, while the dominant mechanism towards chlorinated radicals is HAT. The reactions in methanol and benzene are also discussed.     

Phase diagrams and magnetic properties of CaCu3Fe2Os2O12 quadruple perovskite: Monte Carlo study

In this paper, a Monte Carlo Simulation (MCS) has been used to study the quadruple perovskite oxide CaCu₃Fe₂Os₂O₁₂. The system has been conceived as a mixture of atoms with the magnetic moments Cu (±1/2), Fe (±5/2, ±3/2, ±1/2) and Os (±3/2, ±1/2). Phase diagrams depending on reduced exchange couplings and reduced crystal fields have been established. A stable ferromagnetic phase at the ground state has been found. Investigation of magnetic properties has been focused on the finite size analysis of magnetization and magnetic susceptibility according to reduced temperatures. Critical temperature has been calculated through simulation and the compound has been found to belong in the three-dimensional Ising model universality class.     

Realistic Type IIB supersymmetric Minkowski flux vacua

We show that there exist supersymmetric Minkowski vacua on Type IIB toroidal orientifold with general flux compactifications where the RR tadpole cancellation conditions can be relaxed elegantly. Then we present a realistic Pati–Salam like model. At the string scale, the gauge symmetry can be broken down to the Standard Model (SM) gauge symmetry, the gauge coupling unification can be achieved naturally, and all the extra chiral exotic particles can be decoupled so that we have the supersymmetric SMs with/without SM singlet(s) below the string scale. The observed SM fermion masses and mixings can also be obtained. In addition, the unified gauge coupling, the dilaton, the complex structure moduli, the real parts of the Kähler moduli and the sum of the imaginary parts of the Kähler moduli can be determined as functions of the four-dimensional dilaton and fluxes, and can be estimated as well.