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Near the interface of two contacting metallic bodies in relative motion, the microstructure changes. This modified microstructure leads to changes in material properties and thereby influences the tribological behavior of the entire contact. Tribological properties such as the friction coefficient and wear rate are controlled by the microstructure, while the elementary mechanisms for microstructural changes are not sufficiently understood. In this paper, the influence of the normal load and the size of the counter body on the initiation of a tribologically induced microstructure in copper after a single sliding pass is revealed. A systematic variation in the normal load and sphere diameter resulted in maximum Hertzian contact pressures between 530 MPa and 1953 MPa. Scanning electron microscopy, focused ion beam, and transmission electron microscopy were used to probe the subsurface deformation. Irrespective of the normal load and the sphere diameter, a sharp line-like feature consisting of dislocations, the so-called dislocation trace line, was identified in the subsurface area at depths between 100 nm and 400 nm. For normal loads below 6.75 N, dislocation features are formed below this line. For higher normal loads, the microstructure evolution directly underneath the surface is mainly confined to the area between the sample surface and the dislocation trace line, which itself is located at increasing depth. Transmission Kikuchi diffraction and transmission electron microscopy demonstrate that the misorientation is predominantly concentrated at the dislocation trace line. The results disclose a material rotation around axes roughly parallel to the transverse direction. This study demonstrates the generality of the trace line phenomena over a wide range of loads and contact pressures and the complexity of subsurface processes under a sliding contact and provides the basis for modeling the early stages in the microstructure evolution.

Nonequilibrium molecular dynamics (NEMD) simulations have provided unique insights into the nanoscale behaviour of lubricants under shear. This review discusses the early history of NEMD and its progression from a tool to corroborate theories of the liquid state, to an instrument that can directly evaluate important fluid properties, towards a potential design tool in tribology. The key methodological advances which have allowed this evolution are also highlighted. This is followed by a summary of bulk and confined NEMD simulations of liquid lubricants and lubricant additives, as they have progressed from simple atomic fluids to ever more complex, realistic molecules. The future outlook of NEMD in tribology, including the inclusion of chemical reactivity for additives, and coupling to continuum methods for large systems, is also briefly discussed.

In Uruguay, reforestations with Eucalyptussp. is of fundamental importance to supply paper, pulp, and wood production. This study investigates genetic, productivity, stability, and adaptability parameters in the selection of Eucalypts grandis x Eucalyptus globulusfull-sib hybrid clones. The study was conducted in a clonal test, repeated in two different soils types, in Rio Negro State, Uruguay. The population was characterized phenotypically for diameter at breast height (dbh) and genotyped for SNP markers (EuCHIP60K chip). Mean dbh was similar between sites and the genotype–environment interaction was simple. We found high genotype correlation in clone performance between environments (0.708), indicating the possibility of selecting the same clones for both study locations. Mean heritability between clones (0.724), coefficient of individual genetic variation (10.9 %), and relative variation (0.916), suggest the possibility of gains (estimated at 3.1 % for both sites together) by selecting clones with higher growth rates. A total of 15,196 SNPs were used to confirm parentage and test a genomic selection model for dbh. The predictive capacity was negative (-0.15) given the small population size (78 individuals). The most adaptable material among the tested study sites presented higher values for SNP heterozygosity. Thus, using molecular markers to identify clones responsive to environmental changes can act as a powerful tool in Eucalyptusbreeding programs. The hybrid population showed greater adaptability than E. globulusfor this region.

Surface roughness affects several tribological phenomena like adhesion. In this work, JKR-like experimental tests were performed between Polydimethylsiloxane (PDMS) spherical samples and flat glass substrates with different surface roughness properties. Data were interpreted in the light of classical JKR theory. We find that adhesion is destroyed by roughness in agreement with the most common and well-known results in the literature. However, from the analysis of the Power Spectral Density (PSD) of the surfaces, it emerges that the smaller scales of roughness have a greater influence on the surface adhesion energy in the range of the high fractal dimensions (D> 2.5). In this range, for surfaces with the same root mean square (RMS) roughness amplitude hrms, which is mainly affected by large scale roughness, the pull-off force (i.e., the maximum tensile force reached during the retracting phase) is observed reducing by increasing the RMS slope of the surface roughness hrms′, that is by changing the roughness content at the small scales. This result agrees with recent theoretical findings and has never been shown experimentally in the literature to the best of our knowledge.

Viscoelastic contacts are present in countless industrial components including tires, dampers and rubber seals. The effective design of such components requires a full knowledge of viscoelastic contact mechanics in terms of stresses, strains and hysteric dissipation. To assess some of these issues, this paper describes a series of experiments on the contact area and penetration in a rolling contact between a nitrile rubber ball and a glass disk. The experimental results are compared with the theory proposed by Carbone and Putignano1showing close agreement at low speeds. However, discrepancies arise at speeds above 100 mm/s because of the frictional heating. In order to evaluate this effect, the temperature of the sliding interface is measured for different rolling speeds using infrared microscopy. Thermal results showed that interfacial temperature remained constant at low rolling speeds before rising significantly when speeds above 100 mm/s were reached. These temperature effects are incorporated into the numerical simulations by means of an approximated approach, which corrects the viscoelastic modulus based on the mean measured temperature in the contact. The result of this approach is to extend the region of agreement between experimental and numerical outcomes to higher speeds.

A computationally efficient classical molecular simulation technique is derived for ranking the pKavalues of a set of chemically similar congeneric molecules in an implicit solvent model of water. This uses the deprotonation free energy of the titratable group in the gas and aqueous phases obtained by thermodynamic integration (TI). For a series of alcohols and acids a strong linear correlation is demonstrated between the experimental pKaand the deprotonation free energy difference in the gas and liquid phases. These calculations also show that classical TI is more efficient than slow-growth TI in calculating deprotonation free energies for the series of molecules considered herein.

It is well known that the gas turbine blade vibrations can give rise to catastrophic failures and a reduction of the blades life because of fatigue related phenomena[1]-[3]. In last two decades, the adoption of piezoelectric elements, has received considerable attention by many researcher for its potential applicability to different areas of mechanical, aerospace, aeronautical and civil engineering. Recently, a number of studies of blades vibration control via piezoelectric plates and patches have been reported[4]-[6]. It was reported that the use of piezoelectric elements can be very effective in actively controlling vibrations. In one of their previous contributions[7], the authors of the present manuscript studied a model to control the blade vibrations by piezoelectric elements and validated their results using a multi-physics finite elements package (COMSOL) and results from the literature. An optimal placement method of piezoelectric plate has been developed and applied to different loading scenarios for realistic configurations encountered in gas turbine blades. It has been demonstrated that the optimal placement depends on the spectrum of the load, so that segmented piezoelectric patches have been considered and, for different loads, an optimal combination of sequential and/or parallel actuation and control of the segments has been studied. In this paper, an experimental investigation carried out by the authors using a simplified beam configuration is reported and discussed. The test results obtained by the investigators are then compared with the numerical predictions [7].

Recently, a class of widely linear (augmented) complex-valued Kalman filters (KFs), that make use of augmented complex statistics, have been proposed for sequential state space estimation of the generality of complex signals. This was achieved in the context of neural network training, and has allowed for a unified treatment of both second-order circular and noncircular signals, that is, both those with rotation invariant and rotation-dependent distributions. In this paper, we revisit the augmented complex KF, augmented complex extended KF, and augmented complex unscented KF in a more general context, and analyze their performances for different degrees of noncircularity of input and the state and measurement noises. For rigor, a theoretical bound for the performance advantage of widely linear KFs over their strictly linear counterparts is provided. The analysis also addresses the duality with bivariate real-valued KFs, together with several issues of implementation. Simulations using both synthetic and real world proper and improper signals support the analysis.

The contact problem of a driving tyred wheel, pressed and rolling over an elastically similar half-plane, is considered. Although applicable to a wide range of shrink-fitted assemblies, the simplified model is solved to study the practical case of an elastically similar steel tyre mounted on a locomotive steel wheel subjected to tractive rolling. The behaviour of the system at the tyre—substrate interface is studied using closed-form solutions to calculate the state of stress within the tyre. Conditions leading to incipient slip and/or plasticity are identified and mapped for different loads and geometries.

This paper provides a set of ‘maps’ showing the response of three example frictional complete contacts (with edge angle of 60°, 90°, and 120°) subject to a constant normal load and the subsequent application of cyclic shear and bulk tension, the latter present in only one body. The maps define the region of full adhesion, the nature of violations, and conditions under which they arise.

The characteristics of a semi-infinite flat and rounded contact, subject to constant normal load and oscillating shear, are found. These include the slip displacement and frictional energy expenditure, together with the process of frictional shakedown. The set of solutions is applied to the problem of a D shaped punch having a very small radius at the notionally sharp corner. The possible application of the methodology outlined in this paper to a range of fretting fatigue problems is also discussed.

Electrically induced light emission from conjugated organic molecules in a condensed phase has constituted one of the most investigated phenomena in the recent past for a variety of reasons. The considerable development achieved in this field has been mainly based on the search of new configurations for luminescent devices such as flexible large area light-emitting diodes, and in the synthesis of improved light-emitting organic materials. In the present review a particular aspect of electrically induced light-emission phenomena from organic materials is considered, namely, organic electrochemiluminescence, which is the phenomenon of light emission from excited organic molecules generated upon occurrence of electrochemically driven redox reactions. Such processes can produce luminescence in the visible range if the resulting oxidized/reduced forms of the conjugated organic molecules form excited species capable of emitting photons within the energy range 1.5−3.5 eV. Electrochemiluminescence from organic emitters in a condensed phase has led to the creation of devices such as light-emitting electrochemical cells, whose realization was decisive in the development of effective light-emitting devices. In the present review the description of the phenomena at the basis of organic electrochemiluminescence is given together with the description of materials and devices configurations for light-emitting electrochemical cells.

In the present contribution, we show that long‐lived electrochemically generated chemiluminescence (ECL) from conjugated polymers can be achieved in both anodic and cathodic polarizations of poly[2‐(2′‐ethylethoxy)‐5‐methoxy‐1,4‐phenylene vinylene] (MEH–PPV), when the appropriate electrochemical conditions are adopted and an adequate degree of purity for the active polymer, solvent, and supporting electrolyte is achieved. The quantum efficiency is generally higher during the anodic polarization of MEH–PPV, whereas the ECL vs. time profile depends on the nature of the supporting electrolyte. Such findings led to the conclusion that the kinetics of the doping/undoping processes in MEH–PPV represents a crucial factor in determining the emissive properties of the conjugated polymer. A comparison of the ECL emission from analogous polymeric systems, namely poly[2,5‐bis‐(triethoxymethoxy)‐1,4‐phenylene vinylene] (BTEM–PPV) and poly[2,3‐dibutoxy‐1,4‐phenylene vinylene] (DB–PPV), is also reported.

In this paper we present a systematic study of the effect of the substitution pattern in the starting monomers on the resulting properties of some electrodeposited polydidodecylterthiophenes. The compared characterization of p-doping processes in regioregular electropolymerized poly-3‘,4‘- and 3,3‘ ‘-didodecyl-2,2‘:5‘,2‘ ‘-terthiophene is here reported for the first time. The in situ variations of the optical, magnetic, and electrical transport properties have been measured and correlated with the effects associated to the substituent position. An important result was the verification of absorption fine structures in the wavelength range 500 < λ < 620 nm for the optical spectra of the electropolymerized polydidodecylterthiophenes thus confirming the typical features of regioregular polymers. Visible spectra and cyclic voltammetries verified that poly-3,3‘ ‘-didodecyl-2,2‘:5‘,2‘ ‘-terthiophene possessed a more effective electronic conjugation with respect of the other isomer poly-3‘,4‘-didodecyl-2,2‘:5‘,2‘ ‘-terthiophene. On the other hand the latter polymer showed a higher value of the electronic conductivity (33 vs 21 S cm^-1). Such differences were discussed in terms of the effect of the substituent position on the polymers packing and the separation between chains.

Abstract:  We report on the study of the electropolymerization of 3-methylthiophene onto Pt, p-Si and indium-tin oxide deposited on polyester using quartz crystal microgravimetry, electrochemical and spectroelectrochemical measurements. We observe that potential variation during the galvanostatic electrodeposition is correlated with the nucleation process. The mass variation of poly(3-methylthiophene) is linear with the amount of the electrochemical charge whereas the absorbance variation curve shows two distinct slopes. The latter result has been explained in terms of conjugation length variation during polymer growth. Scanning electron microscopy analysis allowed the detection of morphological changes from a dense and compact structure to an open morphology when the poly(3-methylthiophene) film thickness increases. The roughness of the films did not change considerably with the substrate, as observed by atomic force microscopy. Absorption and photocurrent spectra at different film thicknesses show a shift of the peaks to lower wavelengths when the thickness increased, thus confirming the decrease of mean conjugation length in thicker films.

The electrochromic response of W03 thin films under electrochemical insertion from nonaqueous electrolytes of one of the three different ions: protons, lithium and sodium cations is reported. In spite of the common belief that the nature of the ion does not change the electrochromic effect, we show that the sample colouring and bleaching are dependent on the intercalant ion and on the insertion rate. The facile insertion of protons is responsible for the highest optical contrast and the quickest response time of this intercalation electrode. Lithium and sodium-intercalated electrodes do not show large optical difference from the proton-intercalated tungsten trioxide unless large charging currents are used. Subtle changes in electrochromic efficiency and in the optical contrast in the red part of the spectrum can be detected; these are larger for the sodium than for the lithium intercalant. According to our analysis, the slow insertion kinetics of Na+ and the formation of a new MxWO3 (M=Li, Na) compound is responsible for most of the observed differences.

Si anodic dissolution in acidic fluoride medium has been investigated in different regimes (porous silicon formation, electropolishing under stationary and oscillating current) by probe beam deflection (PBD) or the “mirage” technique. Evolution of deflection signal allows monitoring of dissolution processes both under polarization and at open circuit, providing for example an estimate of the oxide etch-back times during open circuit corrosion. The time evolution of deflection signal during current oscillations reveals components resulting from electrochemical film formation and chemical dissolution. The PBD technique shows larger etching rates for the less passivating film (low potential) and smaller etching rates for the better passivating film (high potential). Our observations are compared with those obtained from spectroscopic investigations of the oxide layer and their relevance for models of oxide formation, and dissolution is here discussed.

The electrochemical doping and undoping processes of poly-(3,3‘‘-didodecyl-2,2‘:5‘,2‘‘-terthiophene) (poly(33‘‘DDTT)) were studied by scanning electrochemical microscopy (SECM) to characterize the electron transfer of the polymer with a redox mediator in solution when the polymer was at different oxidation levels. SECM showed that electron exchange processes of oxidized poly(33‘‘DDTT) were localized at the polymer/solution interface rather than inside the film. Poly(33‘‘DDTT) in the neutral state did not allow the permeation of redox species to the underlying metal and behaved like a completely passivating film. A modified expression for the effective electron-transfer rate constant, keff, was obtained by grouping the terms concerned with charge transport across the polymeric film, and the values of keff were calculated from SECM approach curves. The values of keff for the electron transfer between poly(33‘‘DDTT) film and methyl viologen (MV^+/2+) as the redox couple ranged between 10^-5 and 10^-1 cm s^-1, depending on polymer thickness, substrate potential, and MV concentration. Under the proper experimental conditions, keff could be directly correlated with the conductance of the polymer film, where poly(33‘‘DDTT) thin films in the conducting state showed a metallic character.

The study recalls some mathematical aspects of the dynamics of a non-rigid satellite spin stabilized taking into consideration the behaviour of the liqiid propellant. In particular the two main cases of quasi-full tanks under large satellite maneuvers and of perturbation on a quasi-staedy spin motion are discussed and general analytical models are established. The study has provided the mathematical frame for the experimental work in order to make the identification of the system possible.