Scaling exponents for fracture surfaces in homogenous glass and glassy ceramics

We investigate the scaling properties of post-mortem fracture surfaces in silica glass and glassy ceramics. In both cases, the 2D height-height correlation function is found to obey Family-Viseck scaling properties, but with two sets of critical exponents, in particular a roughness exponent $\zeta\simeq 0.75$ in homogeneous glass and $\zeta\simeq 0.4$ in glassy ceramics. The ranges of length-scales over which these two scalings are observed are shown to be below and above the size of process zone respectively. A model derived from Linear Elastic Fracture Mechanics (LEFM) in the quasistatic approximation succeeds to reproduce the scaling exponents observed in glassy ceramics. The critical exponents observed in homogeneous glass are conjectured to reflect damage screening occurring for length-scales below the size of the process zone

Block to granular-like transition in dense bubble flows

We have experimentally investigated 2-dimensional dense bubble flows underneath inclined planes. Velocity profiles and velocity fluctuations have been measured. A broad second-order phase transition between two dynamical regimes is observed as a function of the tilt angle $\theta$. For low $\theta$ values, a block motion is observed. For high $\theta$ values, the velocity profile becomes curved and a shear velocity gradient appears in the flow.Comment: Europhys. Lett. (2003) in pres

Two-dimensional scaling properties of experimental fracture surfaces

The morphology of fracture surfaces encodes the various complex damage and fracture processes occurring at the microstructure scale that have lead to the failure of a given heterogeneous material. Understanding how to decipher this morphology is therefore of fundamental interest. This has been extensively investigated over these two last decades. It has been established that 1D profiles of these fracture surfaces exhibit properties of scaling invariance. In this paper, we present deeper analysis and investigate the 2D scaling properties of these fracture surfaces. We showed that the properties of scaling invariance are anisotropic and evidenced the existence of two peculiar directions on the post-mortem fracture surface caracterized by two different scaling exponents: the direction of the crack growth and the direction of the crack front. These two exponents were found to be universal, independent of the crack growth velocity, in both silica glass and aluminum alloy, archetype of brittle and ductile material respectively. Moreover, the 2D structure function that fully characterizes the scaling properties of the fracture surface was shown to take a peculiar form similar to the one predicted by some models issued from out-of-equilibrium statistical physics. This suggest some promising analogies between dynamic phase transition models and the stability of a crack front pinned/unpinned by the heterogenities of the material.Comment: 4 page

Some aspects of electrical conduction in granular systems of various dimensions

We report on measurements of the electrical conductivity in both a 2D triangular lattice of metallic beads and in a chain of beads. The voltage/current characteristics are qualitatively similar in both experiments. At low applied current, the voltage is found to increase logarithmically in a good agreement with a model of widely distributed resistances in series. At high enough current, the voltage saturates due to the local welding of microcontacts between beads. The frequency dependence of the saturation voltage gives an estimate of the size of these welded microcontacts. The DC value of the saturation voltage (~ 0.4 V per contact) gives an indirect measure of the number of welded contact carrying the current within the 2D lattice. Also, a new measurement technique provides a map of the current paths within the 2D lattice of beads. For an isotropic compression of the 2D granular medium, the current paths are localized in few discrete linear paths. This quasi-onedimensional nature of the electrical conductivity thus explains the similarity between the characteristics in the 1D and 2D systems.Comment: To be published in The European Physical Journal

Morphology of two dimensional fracture surface

We consider the morphology of two dimensional cracks observed in experimental results obtained from paper samples and compare these results with the numerical simulations of the random fuse model (RFM). We demonstrate that the data obey multiscaling at small scales but cross over to self-affine scaling at larger scales. Next, we show that the roughness exponent of the random fuse model is recovered by a simpler model that produces a connected crack, while a directed crack yields a different result, close to a random walk. We discuss the multiscaling behavior of all these models.Comment: slightly revise

Effect of the position of the antenna on the reading efficiency of different types of electronic identification devices in cattle in Argentina

Animal identification by means of radiofrequency devices allows to capture and transfer data automatically eliminating errors. The system is composed of an electronic identifier device, which has a microchip with a numerical code, unique and unrepeatable, that must be placed in the body of the animals to be read from a distance and a fixed reader with an antenna, which is placed in the catwalk, emits a radiofrequency wave and captures the response of the identifier. The efficiency of the reading of the different types of identifiers and in the different categories of animals depends on the positioning of the antenna, constituting a critical point to optimize the results of the system. The objective of the work was to determine the reading efficiency of different positions of the fixed antenna with respect to electronic identifiers of ruminal bolus and auricular button in adult Angus cows. 116 Angus cows, frame 3 with an average weight of 420 Kg, were used, 20 with intraruminal bolus type and 96 with auricular button type identifiers. There were 196 dynamic readings (bolus, n = 100 and button, n = 96) with the animals in a movement when they passed through the sleeve. A fixed reader (EditID Reader®, NZ) was used with an antenna 87 cm high x 65 cm wide x 2.5 cm thick placed in 3 positions defined by the orientation and height from the ground to the upper edge of the antenna: P1 = vertical at 132 cm from the ground, P2 = vertical at 148 cm from the ground, P3 = horizontal, at 130 cm from the ground. The reading efficiency was defined as: transponders read on the number of readable transponders * 100. The results were for P1: 99.48%, P2: 84.69%, P3: 56.12%, all being significantly different. The differences were especially due to the reading efficiency of ruminal bolus type identifiers

Fracture of glassy materials as detected by real-time Atomic Force Microscopy (AFM) experiments

We have studied the low speed fracture regime for different glassy materials with variable but controlled length scales of heterogeneity in a carefully mastered surrounding atmosphere. By using optical and atomic force (AFM) microscopy techniques we tracked in real-time the crack tip propagation at the nanometer scale on a wide velocity range (1 mm/s and 0.1 nm/s and below). The influence of the heterogeneities on this velocity is presented and discussed. Our experiments revealed also -for the first time- that the crack advance proceeds through nucleation, growth and coalescence of nanometric damage cavities inside the amorphous phase, which generate large velocity fluctuations. The implications of the existence of such a nano-ductile fracture mode in glass are discussed.Comment: 6 pages, 5 figures, submitted to Applied surface Scienc

Introducing a novel online observation of parenting behavior: reliability and validation

Objective. Observations of parents with their children are important for better understanding the critical role that parents play in their children’s adjustment, but resource limitations commonly compromise assessment. A novel online observation tool, Etch-a-Sketch Online (ESO), is introduced that allows resource-efficient observations in the family home. Design. Study 1 was a preliminary, cross-sectional study of 20 mothers with their singleton children (M = 5.96 years). Mothers were observed using both ESO (recorded via Skype) and a traditional Etch-a Sketch task recorded during a home-visit; mothers’ positive and negative parenting was coded from these observations. Study 2 was a longitudinal study of 119 mothers and their young twins. Mothers’ ESO-observed positive parenting and negative parenting at Time 1 (M = 5.51 years) were examined as predictors of children’s disruptive behavior at Time 2 (M = 6.04 years) controlling for mothers’ Time 2 self-reported positive and negative parenting. Results. Study 1 provided preliminary evidence of inter-rater reliability and convergent validity of ESO-observations. Study 2 supported this evidence of inter-rater reliability and ESO’s convergent validity as well as providing predictive validity. ESO-observed parenting at Time 1 was associated with children’s disruptive behavior at Time 2, over and above concurrent maternal reports of their own parenting. Conclusions. ESO shows promise in providing the means for detailed assessment of parenting processes in the home