A method for computing heuristics in problem solving

The purpose of this paper is to propose a formal framework for structuring and embedding the heuristic information, in order to allow an algorithmic computation, in quite general cases, of the evaluation function $\text{f}\text{?}\text{(n)}$ of the classical Hart-Nilsson-Raphael algorithm. The notion of semantic graph is first introduced, in which the atomic notion of node is expanded by associating to it an internal structure where the heuristic information is inserted. It is proved that $\text{h}\text{?}\text{(n)}$ can be computed by solving an auxiliary problem, obtained from the original one by adding new arcs, and of smaller complexity than that onw. A new algorithm is then defined for the computation of $\text{h}\text{?}\text{(n)}$ and for the determination of minimal solutions. The validity of the model proposed is discussed in detail.     

Toughening high density polyethylene submitted to extreme ambient temperatures

The use of polyethylene is limited due to its low impact strength among other mechanical properties at extreme ambient temperatures, for example at ?46 °C and 66 °C. In this work, different polymer components, such as ultra-high molecular weight polyethylene (UHMWPE) and ethylene-vinyl acetate (EVA), were incorporated in high density polyethylene (HDPE) to test their ability to improve toughness of HDPE at extreme ambient temperatures. The polymer blends were processed by extrusion and injection molding and characterized by rotational rheometry, electron microscopy, thermal analysis, tensile, impact and dynamic mechanical tests. The results showed that low concentrations of EVA and UHMWPE in HDPE increased substantially the impact strength of HDPE at room temperature as well as in extreme ambient temperatures (?46 °C and 66 °C). This result indicates that these HDPE blends can be considered good candidates to replace pure HDPE in applications in which high values of toughness are required at extreme ambient temperatures.     

Coumarin Differentially Affects the Morphology of Different Root Types of Maize Seedlings

The effects of coumarin on the length, diameter, and branching density of different root types in maize seedlings (Zea mays L. cv. Cecilia) were investigated. The maize root system represents a useful model for morphological studies, as it consists of radicle, seminal, and nodal roots whose origin and development are quite different. Maize seedlings were grown in a hydroponic culture for 6 days, and then coumarin (at concentrations of 0, 25, 100, and 400 microM) was added to the nutrient solution. Coumarin inhibited root length, but effects differed depending on the root type. C 1/2 values, representing the coumarin concentration causing a 50% inhibition of the root length, were calculated by nonlinear regression. Six, 1, and 0.25 mM coumarin were sufficient to reduce the radicle, seminal, and nodal root lengths by 50%, respectively. At the highest coumarin concentration, the subapical root zone showed swelling. The degree recorded by average diameter was higher in nodal roots than in seminal and radicle roots. Furthermore, coumarin decreased the number of lateral roots and branching density more in the seminal than in the radicle roots. These results suggest the following order of sensitivity to coumarin: nodal > seminal > radicle roots. The observed spatial effects of coumarin could be ecologically significant, since taprooted species could benefit at the disadvantage of fibrous-rooted species and could modify community composition.     

An updated version of wannier90: A tool for obtaining maximally-localised Wannier functions

wannier90  is a program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch energy bands that may or may not be attached to or mixed with other bands. The formalism works by minimising the total spread of the MLWFs in real space. This is done in the space of unitary matrices that describe rotations of the Bloch bands at each k-point. As a result, wannier90  is independent of the basis set used in the underlying calculation to obtain the Bloch states. Therefore, it may be interfaced straightforwardly to any electronic structure code. The locality of MLWFs can be exploited to compute band-structure, density of states and Fermi surfaces at modest computational cost. Furthermore, wannier90  is able to output MLWFs for visualisation and other post-processing purposes. Wannier functions are already used in a wide variety of applications. These include analysis of chemical bonding in real space; calculation of dielectric properties via the modern theory of polarisation; and as an accurate and minimal basis set in the construction of model Hamiltonians for large-scale systems, in linear-scaling quantum Monte Carlo calculations, and for efficient computation of material properties, such as the anomalous Hall coefficient. We present here an updated version of wannier90, wannier90  2.0, including minor bug fixes and parallel (MPI) execution for band-structure interpolation and the calculation of properties such as density of states, Berry curvature and orbital magnetisation. wannier90  is freely available under the GNU General Public License from http://www.wannier.org/.     

EVA‐Montmorillonite Nanocomposites: Effect of Processing Conditions

Summary: The aim of this study is to examine the effect of the compounding apparatus and of processing conditions on the properties of an organoclay‐poly[ethylene‐co‐(vinyl acetate)] (EVA) nanocomposite. The filled materials were prepared using either a discontinuous batch mixer, a single screw extruder, a counter rotating intermeshing twin‐screw compounder or a corotating intermeshing twin‐screw extruder. The characterization of the obtained nanocomposites was performed by XRD, thermogravimetry, mechanical and rheological measurements. The study has shown the possibility of producing nanocomposites based on EVA and a commercial organoclay (Cloisite 15A) by several mixing equipments. In fact all the prepared composite materials exhibit a larger interlayer clay spacing in comparison with the pristine organoclay. Moreover their elastic modulus is significantly increased from 50 to 100% depending on the processing conditions.

X‐ray diffraction of the master (Sample A) and the clay used for its preparation (Cloisite 15A).     

Analysis of non-linear response of the human body to vertical whole-body vibration

The human response to vibration is typically studied using linear estimators of the frequency response function, although different literature works evidenced the presence of non-linear effects in whole-body vibration response. This paper analyses the apparent mass of standing subjects using the conditioned response techniques in order to understand the causes of the non-linear behaviour. The conditioned apparent masses were derived considering models of increasing complexity. The multiple coherence function was used as a figure of merit for the comparison between the linear and the non-linear models. The apparent mass of eight male subjects was studied in six configurations (combinations of three vibration magnitudes and two postures). The contribution of the non-linear terms was negligible and was endorsed to the change of modal parameters during the test. Since the effect of the inter-subject variability was larger than that due to the increase in vibration magnitude, the biodynamic response should be more meaningfully modelled using a linear estimator with uncertainty rather than looking for a non-linear modelling.     

Valuation of R&D Investment Opportunities with the Threat of Competitors Entry in Real Option Analysis

This paper provides a real option methodology in order to value a pioneer’s R&D investment opportunity allowing for more potential competitors to enter in the market. To incorporate this competitive dimension, we assume that the pioneer may lose the “competitive dividends”   if the real option is not exercised. According to Majd and pindyck (1987) (Journal of Financial Economics 18(1):7–27), in a real options context, “dividends”   are the opportunity costs inherent in the decision to defer an investment project and so deferment implies the loss of project’s cash flows. Concerning this, Trigeorgis (1996) (Real Options: Managerial Flexibility and Strategy in Resource Allocation, The MIT Press, Cambridge, (1996) incorporates the preemption effect through the “competitive dividends”  which are the cash flows that can be eroded by anticipated competitive arrivals. In particular way, we propose the valuation of a pioneer’s R&D investment assuming that the Development cost can be spent in two moments: $t_2$ or $t_3$ . If the Development cost is realized in $t_2$ no firms enters in the market since the rivals’ R&D plan is not yet concluded otherwise, if the Development cost is delayed until time $t_3$ waiting better market conditions, other rivals may enter in the market and so the opportunity costs, namely dividends, increase. Moreover, we analyze the optimal timing to realize the Development investment, i.e. we determine the conditions for which the pioneer prefers to invest the Development cost at time $t_2$ or $t_3$ .     

Mesitylene solvated platinum atoms in the preparation of efficient supported catalysts for the dehydrogenation of methylcyclohexane to toluene

Mesitylene solvated platinum atoms have been conveniently used for the deposition of active Pt particles on -Al₂O₃ supports. The so prepared catalysts have been compared with traditionally obtained Pt/-Al₂O₃ catalysts in the dehydrogenation of methylcyclohexane to toluene, at 200 and 250 °C, showing, at low Pt loadings, a much greater specific activity.     

Regenerative Recycling of Automotive Polymer Components: Poly(propylene) Based Car Bumpers

There is a dramatic loss in the mechanical performances at the end of the first life application of bumpers made by a poly(propylene) matrix (PP) and an ethylene‐propylene rubber copolymer as dispersed phase. The use of specific additives during the recycling strongly enhances the mechanical properties of these items. The on purpose designed additive contained a regenerative agent and an antioxidant system. The mixing action of the recycling process re‐establishes the phase compatibility; the antioxidants inhibit oxidation, which speeds up the degradation reactions in the recycling process; eventually the regenerative agent joins short chains possessing suitable reactive groups. These three effects play a different role in restoring original material performance in dependence of the recycling process: for instance the regenerative agent may be nearly useless if chain scission is not the dominant process in the recycling operation and the interfacial adhesion between rubber and the matrix does not assure automatically a ductile mechanical behaviour under impact conditions.

SEM micrograph of the fractured surface of the used bumper recycled with additives.     

Controlled Microfabrication of High‐Aspect‐Ratio Structures in Silicon at the Highest Etching Rates: The Role of H2O2 in the Anodic Dissolution of Silicon in Acidic Electrolytes

In this work the authors report on the controlled electrochemical etching of high‐aspect‐ratio (from 5 to 100) structures in silicon at the highest etching rates (from 3 to 10 µm min^?1) at room temperature. This allows silicon microfabrication entering a previously unattainable region where etching of high‐aspect‐ratio structures (beyond 10) at high etching rate (over 3 µm min^?1) was prohibited for both commercial and research technologies. Addition of an oxidant, namely H₂O₂, to a standard aqueous hydrofluoric (HF) acid electrolyte is used to dramatically change the stoichiometry of the silicon dissolution process under anodic biasing without loss of etching control accuracy at the higher depths (up to 200 µm). The authors show that the presence of H₂O₂ reduces the valence of the dissolution process to 1, thus rendering the electrochemical etching more effective, and catalyzes the etching rate by opening a more efficient path for silicon dissolution with respect to the well‐known Gerischer mechanism, thus increasing the etching speed at both shorter and higher depths.