Adsorption and co-adsorption of CH<Subscript>3</Subscript> and H on flat and defective nickel (111) surfaces

We use a periodic density functional theory (DFT) code to study the adsorption of CH₃ and H, as well as their co-adsorption on a Ni(111) surface with and without Ni ad-atom, at a surface coverage of 0.25 monolayer (ML). We systematically investigate the site preference for CH₃ and H. Then we combine CH₃ and H in many co-adsorbed configurations on both surfaces. Methyl and hydrogen adsorption on a flat Ni(111) surface favours the hollow site over the top site. The presence of a Ni ad-atom stabilizes the adsorption of CH₃ better than a flat surface, while hydrogen is more stable on a flat Ni(111) surface. When H and CH₃ are co-adsorbed at nearest Ni neighbours on the (111) surface, their interaction is always repulsive. However, the dissociative adsorption of CH₄ is stabilised when the fragments are infinitely separated. For the co-adsorbed fragments CH₃ and H, in the presence of an ad-atom, the repulsive interaction is lowered, so that the dissociative form of CH₄ is locally stable.     

A critical experimental study of the classical tactile threshold theory

Background  

The tactile sense is being used in a variety of applications involving tactile human-machine interfaces. In a significant number of publications the classical threshold concept plays a central role in modelling and explaining psychophysical experimental results such as in stochastic resonance (SR) phenomena. In SR, noise enhances detection of sub-threshold stimuli and the phenomenon is explained stating that the required amplitude to exceed the sensory threshold barrier can be reached by adding noise to a sub-threshold stimulus. We designed an experiment to test the validity of the classical vibrotactile threshold. Using a second choice experiment, we show that individuals can order sensorial events below the level known as the classical threshold. If the observer's sensorial system is not activated by stimuli below the threshold, then a second choice could not be above the chance level. Nevertheless, our experimental results are above that chance level contradicting the definition of the classical tactile threshold.     

Niobian iron oxides as heterogeneous Fenton catalysts for environmental remediation

Heterogeneous Fenton or Fenton-like reagents consist of a mixture of an iron-containing solid matrix and a liquid medium with H₂O₂. The Fenton system is based on the reaction between Fe^2?+? and H₂O₂ to produce highly reactive intermediate hydroxyl radicals (^???OH), which are able to oxidize organic contaminants, whereas the Fenton-like reaction is based on the reaction between Fe^3?+? and H₂O₂. These heterogeneous systems offer several advantages over their homogeneous counterparts, such as no sludge formation, operation at near-neutral pH and the possibility of recycling the iron promoter. Some doping transition cations in the iron oxide structure are believed to enhance the catalytic efficiency for the oxidation of organic substrates in water. In this work, goethites synthesized in presence of niobium served as precursors for the preparation of magnetites (niobian magnetites) via chemical reduction with hydrogen at 400°C. These materials were used as Fenton-like catalysts. Both groups of (Nb, Fe)-oxide samples were characterized by ⁵⁷Fe Mössbauer spectroscopy at 298 K. The results show that increasing niobium contents raise the catalytic potential for decomposition of methylene blue, which was, in this work, used as a model molecule for organic substrates in water.     

Actualism and Modal Semantics

According to actualism, modal reality is constructed out of valuations (combinations of truth values for all propositions). According to possibilism, modal reality consists in a set of possible worlds, conceived as independent objects that assign truth values to propositions. According to possibilism, accounts of modal reality can intelligibly disagree with each other even if they agree on which valuations are contained in modal reality. According to actualism, these disagreements (possibilist disagreements) are completely unintelligible. An essentially actualist semantics for modal propositional logic specifies which sets of valuations are compatible with the meanings of the truth-functional connectives and modal operators without drawing on formal resources that would enable us to represent possibilist disagreements. The paper discusses the availability of an essentially actualist semantics for modal propositional logic. I argue that the standard Kripkean semantics is not essentially actualist and that other extant approaches also fail to provide a satisfactory essentially actualist semantics. I end by describing an essentialist actualist semantics for modal propositional logic.     

Existence and fractional regularity of solutions for a doubly nonlinear differential inclusion

This article considers the issues of existence and regularity of solutions to the following doubly nonlinear differential inclusion $$\omega_t+\alpha (\omega_t)-\Delta \omega-\Delta_p{\omega} \ni f$$ where α is a maximal monotone operator in ${\mathbb{R}^2}$ and Δ _p denotes the p-Laplacian with p > 2. The investigation on fractional regularity is based on the Galerkin method combined with a suitable basis for W ^1,p , which we exhibit as a preliminary result. This approach also allows the obtaining of estimates in the so-called Nikolskii spaces, since it balances the interplay between the maximal monotone operator with the appearing higher order nonlinear terms.     

Preparation of CeO2 by a simple microwave–hydrothermal method

Cerium carbonate hydroxide (orthorhombic Ce(OH)CO₃) hexagonal-shaped microplates were synthesized by a simple and fast microwave–hydrothermal method at 150 °C for 30 min. Cerium nitrate, urea and cetyltrimethylammonium bromide were used as precursors. Ceria (cubic CeO₂) rhombus-shape was obtained by a thermal decomposition oxidation process at 500 °C for 1 h using as- synthesized Ce(OH)CO₃. The products were characterized by X-ray powder diffraction, field-emission scanning electron microscopy, thermogravimetric analysis and Fourier transformed infrared spectroscopy. The use of microwave–hydrothermal method allowed to obtain cerium compounds at low temperature and shorter time compared to other synthesis methods.     

Consequences of weak Allee effect on prey in the May–Holling–Tanner predator–prey model

In this work, a modified Holling–Tanner predator–prey model is analyzed, considering important aspects describing the interaction such as the predator growth function is of a logistic type; a weak Allee effect acting in the prey growth function, and the functional response is of hyperbolic type. Making a change of variables and time rescaling, we obtain a polynomial differential equations system topologically equivalent to the original one in which the non‐hyperbolic equilibrium point (0,0) is an attractor for all parameter values. An important consequence of this property is the existence of a separatrix curve dividing the behavior of trajectories in the phase plane, and the system exhibits the bistability phenomenon, because the trajectories can have different ω ? limit sets; as example, the origin (0,0) or a stable limit cycle surrounding an unstable positive equilibrium point. We show that, under certain parameter conditions, a positive equilibrium may undergo saddle‐node, Hopf, and Bogdanov–Takens bifurcations; the existence of a homoclinic curve on the phase plane is also proved, which breaks in an unstable limit cycle. Some simulations to reinforce our results are also shown. Copyright © 2015 John Wiley & Sons, Ltd.     

A mean value theorem for metric spaces

We present a form of the Mean Value Theorem (MVT) for a continuous function f between metric spaces, connecting it with the possibility to choose the relation of f in a homeomorphic way. We also compare our formulation of the MVT with the classic one when the metric spaces are open subsets of Banach spaces. As a consequence, we derive a version of the Mean Value Propriety for measure spaces that also possesses a compatible metric structure.