Performance evaluation of multilayer thin film coatings under mixed rolling–sliding dry contact conditions

This paper focuses on the application of advanced finite element analysis to simulate the response of complex multilayer coatings when subjected to mixed rolling–sliding dry contact conditions, typical of those experienced by heavily loaded gear tooth flanks. In this study, a versatile model is developed to investigate the response of a variety of complex coatings. Through the investigation of three advanced surface coatings the developed model is shown to offer detailed subsurface stress and strain information, quantifying the benefits provided by the application of each coating.A number of rolling contact fatigue tests were also conducted to complement the computational simulations. An adapted twin disc testing machine was used to investigate the progressive wear rates of the three advanced surface coatings when subjected to mixed rolling–sliding contact at high load and in dry conditions. The result is a clear indication that advanced surface coating techniques can provide significant improvements in wear resistance and surface durability. From the rolling contact fatigue experiments conducted in this study, a multilayer tungsten carbide/carbon coating was shown to provide the most significant increase in surface durability with a 16-fold reduction in measured weight loss compared to the uncoated substrate over the 145,000 cycle test duration investigated.     

Temporal location of unsignaled food deliveries: Effects on conditioned withdrawal (inhibition) in pigeon signtracking.

Standard models of Pavlovian conditioning neglect local effects of unsignaled unconditioned stimuli (USs) on learning and performance. Using the approach-withdrawal behavior of pigeons toward keylights as conditioned stimuli (CSs), the authors varied the specific times (5–210 s) that USs occurred before or after a CS. Withdrawal from a CS generally increased as the time between a US before and/or after the CS was lengthened. Combinations of 2 distant USs produced more withdrawal from the CS than either US alone, whereas combinations of a distant and a nearby US yielded behavior intermediate between that for either US alone. Postacquisition retardation tests supported similar conclusions. Based on the temporal isolation of CSs and USs, a tentative model was offered to summarize these data. The results and the model suggest that a more molecular, possibly perceptual approach to Pavlovian excitation and inhibition is needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The elastic properties of lithium oxide and their variation with temperature

The energies of the acoustic phonon modes in a single crystal of ⁷Li₂O have been measured in the temperature range 293–1603 K using the technique of inelastic neutron scattering. The slopes of the phonon energy dispersion curves as they approach the Brillouin zone centre give values for the cubic elastic stiffness constants, C_ij. C₁₁ is found to undergo a sharp decrease above ˜ 1350 K similar to that observed in structurally related compounds, such as CaF₂ and SrCl₂, as they undergo a transition to a fast-ion phase. The Reuss and Voigt averaging methods have been used to calculate the temperature dependence of the adiabatic Young's modulus, shear modulus, bulk modulus and Poisson's ratio of polycrystalline Li₂O. Estimates of the corresponding isothermal values are obtained using an expression for the linear thermal expansion coefficient of Li₂O obtained in this work, together with thermodynamic data available from specific heat measurements. These results represent the first experimental data describing the elastic properties of Li₂O at elevated temperatures and are important in predicting the behaviour of this material in its potential role as a tritium breeding blanket material for future fusion reactors.     

Chemosensory conditioning of Hermissenda crassicornis..

Bite–strike responses of Hermissenda crassicornis, elicited by chemosensory stimulation of the lips, were found to be modified when food extracts were paired with rotation-produced stimulation of the statocysts. Animals that received repeated pairings of an extract of 1 food (conditioned stimulus, CS) with rotation exhibited suppressed bite–strike responses to that food for up to 48 hr after training. This suppression was usually specific to the trained food and was pairing-specific as well. Discriminative conditioning was also demonstrated. Animals trained with 1 CS paired with rotation and a second CS that was unpaired (CS–) showed suppressed bite–strike responses to the first CS. The results demonstrate that Hermissenda can learn to avoid foods that reliably signal an aversive event and may allow an analysis of higher order conditioning phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Running in the real world: adjusting leg stiffness for different surfaces

A running animal coordinates the actions of many muscles, tendons, and ligaments in its leg so that the overall leg behaves like a single mechanical spring during ground contact. Experimental observations have revealed that an animal's leg stiffness is independent of both speed and gravity level, suggesting that it is dictated by inherent musculoskeletal properties. However, if leg stiffness was invariant, the biomechanics of running (e.g. peak ground reaction force and ground contact time) would change when an animal encountered different surfaces in the natural world. We found that human runners adjust their leg stiffness to accommodate changes in surface stiffness, allowing them to maintain similar running mechanics on different surfaces. These results provide important insight into mechanics and control of animal locomotion and suggest that incorporating an adjustable leg stiffness in the design of hopping and running robots is important if they are to match the agility and speed of animals on varied terrain.     

Contingency learning and causal detection in Hermissenda: II. Cellular mechanisms.

Neural correlates of contingency-sensitive behavioral changes in the nudibranch Hermissenda were studied by in vitro conditioning of the isolated nervous system. The additions of unpaired light-alone or hair cell-alone stimulation presentations to sequences of light-hair cell stimulation pairings were found to attenuate the cumulative depolarization of Type B photoreceptors that normally result from pairings. Unpaired light presentations produced a transitory depression of the light-induced depolarizing generator potential of the B cell. Unpaired hair cell stimulation synaptically hyperpolarized the B photoreceptor and thus acted in a retroactive manner to partially reverse the cumulative depolarization owing to prior pairings. Behavioral experiments revealed a striking temporal specificity for the decremental effects of added light and rotational stimulation. The present experiments indicate that contiguity and contingency relations are both encoded and stored in the Type B photoreceptors, and to a first approximation reflect similar biophysical mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mosquitoes or malaria? Rockefeller campaigns in the American South and Sardinia

Most members of the International Health Division of the Rockefeller Foundation remained convinced that diseases were the fundamental cause of human poverty and underdevelopment and that destruction of the larval stages of vector mosquitoes was the cheapest and most effective way to eliminate one of the most important of such diseases, malaria. But the validity of both their assumptions remains in question despite campaigns in the American South and elsewhere during the 1920s and 1930s and an unsuccessful attempt at "species eradication" in Sardinia immediately after World War II.