Role of Rubber Stiffness and Surface Roughness in the Tribological Performance on Ice

The aim of this work is to investigate the effect of slider surface roughness and stiffness on the friction between rubber compounds and ice surfaces in order to provide insight into rubber–ice friction generation mechanisms. For this purpose, rubber compounds were designed to have different levels of macroscopic roughness and cured stiffness by modifying the filler system and plasticizer loading. In order to accurately evaluate the effects of surface and bulk rubber property on ice friction, linear friction tests were performed on laboratory ice with varied frictional heat buildup by modifying the friction test protocol. The results showed that the friction force was in general increased through the ploughing effect of a rough rubber block sliding on smooth ice. The increase in friction by ploughing was more pronounced when the contacting rubber block had sufficiently low stiffness and when the accumulation of frictional heat on ice was sufficiently high. It was also evidenced that a sufficiently hard rubber with test conditions leading to low heat buildup on ice could nevertheless lead to an opposite influence of roughness on rubber–ice friction; that is, lower friction force with a slider with a higher roughness.     

Interactions at fiber/matrix interface in short fiber reinforced amorphous thermoplastic composites modified with micro- and nano-fillers

This study aims at systematically extracting fiber/matrix interfacial strength in short-glass fiber-reinforced polymer composites using an experimental micromechanics approach which employs mechanical properties and residual fiber length distributions to derive the apparent interfacial shear strength. We started from neat high-impact polystyrene matrix short-glass fiber-reinforced composites (HIPS/GF) with varying fiber loading and proceeded toward HIPS/GF hybrid composites containing micro- and nano-fillers where complex fiber/matrix interfacial interactions exist. It was found that apparent interfacial shear strength does not vary with fiber content, while the presence of fillers with different length-scales alters fiber/matrix interactions depending on their influence on physical properties of the polymer matrix, particularly in the vicinity of reinforcing fiber surfaces.     

Probabilistic Assessment of Stress Normalization for CPT Data

Currently available cone penetration test (CPT) stress normalization schemes exhibit no consensus on the estimation of the stress normalization component. Depending on which power law stress normalization exponent is used, very different interpretations may result in the analyses where normalized CPT data are used (e.g., CPT-based soil classification and seismic soil liquefaction initiation assessment). Within the confines of this paper, it is intended to clarify and resolve some of these differences, and to propose improved recommendations for CPT stress normalization. For this purpose, available stress normalization databases from theoretical, numerical, and field data analyses approaches were compiled. For the soil types, and stress conditions where compiled database is not conclusive, additional finite element simulations have been performed. The resulting relationship not only eliminates several sources of bias intrinsic to previous, similar correlations, and provides greatly reduced overall uncertainty and variance, it also helps to establish a consensus to the stress normalization issue that have long been difficult and controversial. Key elements in the development of these new correlations are: (1) accumulation of a significantly expanded database of analytical/numerical CPT simulation results, as well as field and chamber test data from homogeneous soil layers; (2) use of improved knowledge and understanding of factors affecting CPT and stress normalization; and (3) use of high-order probabilistic tools (Bayesian updating).     

Sorption and desorption behaviours of 2,4‐D and glyphosate in calcareous soil from Antalya,Turkey

2,4‐Dichlorophenoxyl acetic acid (2,4‐D) and glyphosate are used extensively as a herbicide in vicinity of Antalya, Turkey. Laboratory batch experiments were conducted to investigate the sorption isotherm and sorption‐desorption characteristics of 2,4‐D and glyphosate. Results indicated that degree of sorption of glyphosate was approximately 50 times higher than 2,4‐D (K_d= 34.43 vs. 0.66 L/Kg). The sorption of 2,4‐D and glyphosate was described by linear and rate‐limited processes for soil. Organic carbon content was most likely responsible for sorption behaviour of 2,4‐D and glyphosate. The rapid desorption can be attributed to soft carbon fraction (humic/fluvic acid and lipids) whereas slower desorption can be responsible by hard carbon fraction (black carbon, kerogen) of soils that led to chemically nonideal behaviour (hysteresis). Sorption of 2,4‐D was low due to most likely deactivation of organic carbon surfaces by excess carbonate fraction, whereas strong binding of glyphosate onto organic carbon causing high sorption behaviour.     

Transesterification reaction between acetylated wood and trialkoxysilane coupling agents

A novel dibutyltin oxide‐catalyzed transesterification reaction between acetylated maritime pine sapwood (Pinus pinaster Soland) and methyltrimethoxysilane (MTMS) was studied. The transesterification exchange between the acetyl moities and MTMS was confirmed by weight percent gain calculations, Fourier‐transform infrared spectroscopy, as well as solid state ¹³C and ²⁹Si crosspolarization with magic‐angle spinning nuclear magnetic resonance spectroscopy. The silicon atoms in the MTMS‐transesterified wood were found to exist in the form of more or less condensed structures, concurrently formed by condensation between neighboring Si(OMe)₃ groups. An increase in the acetyl/MTMS exchange rate was also noted when the catalyst amount, temperature, or reaction time were increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Finite state automata resulting from temporal information maximization and a temporal learning rule

We extend Linkser's Infomax principle for feedforward neural networks to a measure for stochastic interdependence that captures spatial and temporal signal properties in recurrent systems. This measure, stochastic interaction, quantifies the Kullback-Leibler divergence of a Markov chain from a product of split chains for the single unit processes. For unconstrained Markov chains, the maximization of stochastic interaction, also called Temporal Infomax, has been previously shown to result in almost deterministic dynamics. This letter considers Temporal Infomax on constrained Markov chains, where some of the units are clamped to prescribed stochastic processes providing input to the system. Temporal Infomax in that case leads to finite state automata, either completely deterministic or weakly nondeterministic. Transitions between internal states of these systems are almost perfectly predictable given the complete current state and the input, but the activity of each single unit alone is virtually random. The results are demonstrated by means of computer simulations and confirmed analytically. It is furthermore shown numerically that Temporal Infomax leads to a high information flow from the input to internal units and that a simple temporal learning rule can approximately achieve the optimization of temporal interaction. We relate these results to experimental data concerning the correlation dynamics and functional connectivities observed in multiple electrode recordings.     

Implementation of a closed loop sliding mode observer for speed sensorless control of an indirect field oriented induction motor drives

A new sliding mode flux and speed observer is proposed for indirect field oriented induction motor drive system. The error between the actual and observed currents converges to zero, which guarantees the accuracy of the flux observer. The rotor speed and the rotor time constant are estimated based on the estimated stator currents and rotor flux. The estimated rotor time constant is used in slip calculation and observer structures. The estimated speed is used as feedback to the speed regulation. Simulation and experimental results of the speed control verify the validity of the proposed speed estimation algorithm.