Elastocaloric Waste/Natural Rubber Materials with Various Crosslink Densities.

The characterization of the mechanical behavior of elastocaloric materials is essential to identify their viability in heating/cooling devices. Natural rubber (NR) is a promising elastocaloric (eC) polymer as it requires low external stress to induce a wide temperature span, ΔT. Nonetheless, solutions are needed to further improve DT, especially when targeting cooling applications. To this aim, we designed NR-based materials and optimized the specimen thickness, the density of their chemical crosslinks, and the quantity of ground tire rubber (GTR) used as reinforcing fillers. The eC properties under a single and cyclic loading conditions of the resulting vulcanized rubber composites were investigated via the measure of the heat exchange at the specimen surface using infrared thermography. The highest eC performance was found with the specimen geometry with the lowest thickness (0.6 mm) and a GTR content of 30 wt.%. The maximum temperature span under single interrupted cycle and multiple continuous cycles were equal to 12 °C and 4 °C, respectively. These results were assumed to be related to more homogeneous curing in these materials and to a higher crosslink density and GTR content which both act as nucleating elements for the strain-induced crystallization at the origin of the eC effect. This investigation would be of interest for the design of eC rubber-based composites in eco-friendly heating/cooling devices.

Philippistenia, a new Disteniini genus from the Philippines (Coleoptera: Disteniidae).

A new genus from the Philippines, Philippistenia, is proposed to gather three species previously allocated in Distenia (Distenia) Lepeletier Audinet-Serville, 1828: Philippistenia heterotarsalis (Heller, 1923) comb. nov.; P. levitemporalis (Heller, 1924) comb. nov.; and P. halconensis (Vives, 2012) comb. nov. Distenia samarensis Villiers, 1959 is proposed as a junior synonym of P. heterotarsalis. Photographs of Philippistenia species are provided. A key to species of the new genus is proposed and the male terminalia are illustrated. Notes on the localization of the type material of Distenia heterotarsalis and Distenia levitemporalis are provided and lectotypes are designated for both species. Additionally, the geographical distribution of the species is expanded.

New species and subspecies of Laoechinophorus from China and Thailand (Coleoptera, Cerambycidae, Lamiinae, Morimopsini).

Two new species with a new subspecies of the genus Laoechinophorus Gouverneur, 2016 are described: L. thailandicus thailandicus ssp. nov. and L. thailandicus tsuyukii ssp. nov. from Thailand, and L. yunnanus sp. nov. from China. A description of male genitalia of the type species, L. unifasciatus Gouverneur, 2016, from Laos, and a key to the species of the genus are provided.

A new genus and species of the tribe Oemini (Coleoptera, Cerambycidae, Cerambycinae) from the Sundaic region, Southeastern Asia.

A new genus and species of the subtribe Oemina of the tribe Oemini (Cerambycidae: Cerambycinae) is described from the Sundaic region, Southeastern Asia. Relationships with other oemine genera are discussed.

Avalanche mixing and the simultaneous collapse of two media under uniaxial stress.

Avalanches in coal and sandstone samples under common uniaxial stress serve as a model for mixing of avalanche exponents in ceramics, multiferroics, and alloys. The two media are sandwiched together and subjected to common uniaxial stress using high- and low-stress compression. Each medium collapses individually through avalanches that often coincide with secondary avalanches into the other medium. The total avalanche time sequence allows a detailed investigation of the mixing by superposition and delayed coincidence. Correlations can be described by an inter-media Båth's law.

Criticality in failure under compression: Acoustic emission study of coal and charcoal with different microstructures.

A systematic study of acoustic emission avalanches in coal and charcoal samples under slow uniaxial compression is presented. The samples exhibit a range of organic composition in terms of chemical elements as well as different degrees of heterogeneity in the microstructure. The experimental analysis focuses on the energies E of the individual acoustic emission events as well as on the time correlations between successive events. The studied samples can be classified into three groups. The more homogeneous samples (group I) with pores in the micro and nanoscales, with signatures of hardening effects in the stress-strain curves, exhibit the cleanest critical power-law behavior for the energy distributions g(E)dE∼E^{-ε}dE with a critical exponent ε=1.4. The more heterogeneous samples with voids, macropores, and granular microstructures (group III), show signatures of weakening effects and a larger effective exponent close to the value ε=1.66, but in some cases truncated by exponential damping factors. The rest of the samples (group II) exhibit a mixed crossover behavior still compatible with an effective exponent ε=1.4 but clearly truncated by exponential factors. These results suggest the existence of two possible universality classes in the failure of porous materials under compression: one for homogeneous samples and another for highly heterogeneous samples. Concerning time correlations between avalanches, all samples exhibit very similar waiting time distributions although some differences for the Omori aftershock distributions cannot be discarded.

Notes on the genus Leptostrangalia Nakane Ohbayashi, 1959 (Coleoptera: Cerambycidae: Lepturinae: Lepturini) with description of a new species from Damingshan, Guangxi, south China.

Taxonomic notes on the lepturine genus Leptostrangalia Nakane Ohbayashi, 1959 are provided and a new species from China, Leptostrangalia rufithorax nov. sp., is described. A key to the world species of the genus is provided.

Universality of power-law exponents by means of maximum-likelihood estimation.

Power-law-type distributions are extensively found when studying the behavior of many complex systems. However, due to limitations in data acquisition, empirical datasets often only cover a narrow range of observation, making it difficult to establish power-law behavior unambiguously. In this work we present a statistical procedure to merge different datasets, with two different aims. First, we obtain a broader fitting range for the statistics of different experiments or observations of the same system. Second, we establish whether two or more different systems may belong to the same universality class. By means of maximum likelihood estimation, this methodology provides rigorous statistical information to discern whether power-law exponents characterizing different datasets can be considered equal among them or not. This procedure is applied to the Gutenberg-Richter law for earthquakes and for synthetic earthquakes (acoustic emission events) generated in the laboratory: labquakes. Different earthquake catalogs have been merged finding a Gutenberg-Richter law holding for more than eight orders of magnitude in seismic moment. The value of the exponent of the energy distribution of labquakes depends on the material used in the compression experiments. By means of the procedure proposed in this manuscript, we find that the Gutenberg-Richter law for earthquakes and charcoal labquakes can be characterized by the same power-law exponent, whereas Vycor labquakes exhibit a significantly different exponent.

Experimental Evidence of Accelerated Seismic Release without Critical Failure in Acoustic Emissions of Compressed Nanoporous Materials.

The total energy of acoustic emission (AE) events in externally stressed materials diverges when approaching macroscopic failure. Numerical and conceptual models explain this accelerated seismic release (ASR) as the approach to a critical point that coincides with ultimate failure. Here, we report ASR during soft uniaxial compression of three silica-based (SiO_{2}) nanoporous materials. Instead of a singular critical point, the distribution of AE energies is stationary, and variations in the activity rate are sufficient to explain the presence of multiple periods of ASR leading to distinct brittle failure events. We propose that critical failure is suppressed in the AE statistics by mechanisms of transient hardening. Some of the critical exponents estimated from the experiments are compatible with mean field models, while others are still open to interpretation in terms of the solution of frictional and fracture avalanche models.

Increasing power-law range in avalanche amplitude and energy distributions.

Power-law-type probability density functions spanning several orders of magnitude are found for different avalanche properties. We propose a methodology to overcome empirical constraints that limit the range of truncated power-law distributions. By considering catalogs of events that cover different observation windows, the maximum likelihood estimation of a global power-law exponent is computed. This methodology is applied to amplitude and energy distributions of acoustic emission avalanches in failure-under-compression experiments of a nanoporous silica glass, finding in some cases global exponents in an unprecedented broad range: 4.5 decades for amplitudes and 9.5 decades for energies. In the latter case, however, strict statistical analysis suggests experimental limitations might alter the power-law behavior.

Crossover from three-dimensional to two-dimensional systems in the nonequilibrium zero-temperature random-field Ising model.

We present extensive numerical studies of the crossover from three-dimensional to two-dimensional systems in the nonequilibrium zero-temperature random-field Ising model with metastable dynamics. Bivariate finite-size scaling hypotheses are presented for systems with sizes L×L×l which explain the size-driven critical crossover from two dimensions (l=const, L→∞) to three dimensions (l∝L→∞). A model of effective critical disorder R_{c}^{eff}(l,L) with a unique fitting parameter and no free parameters in the R_{c}^{eff}(l,L→∞) limit is proposed, together with expressions for the scaling of avalanche distributions bringing important implications for related experimental data analysis, especially in the case of thin three-dimensional systems.

Avalanche criticality in thermal-driven martensitic transitions: the asymmetry of the forward and reverse transitions in shape-memory materials.

Martensitic transitions take place intermittently as a sequence of avalanches which are accompanied by the emission of acoustic waves. The study of this acoustic emission (AE) reveals the scale-free nature of the avalanches. In a number of shape memory materials undergoing a martensitic transition it has been found that, in spite of relatively low hysteresis, the dynamics of forward and reverse transitions are different, which may explain the fact that the AE activity is different in both forward and reverse transitions. The asymmetry could be a consequence of the fact that, while nucleation is required for the transition from the parent to martensitic phase to take place, reverse transition occurs by fast shrinkage of martensitic domains. We have analysed in detail the distribution of avalanches in cooling and heating runs in Fe-Pd and Cu-Zn-Al shape-memory alloys. In the former, the martensitic transition is weakly first order while it shows a significant first order character in the latter. We have found that in Fe-Pd the distributions are power law for the forward and reverse transitions characterized by the same critical exponents. For Cu-Zn-Al the distribution of avalanches is critical in forward transitions but exponentially damped in the reverse transition. It is suggested that this different behaviour could originate from the different dynamic mechanisms in forward and reverse transitions.

Dominance of Metric Correlations in Two-Dimensional Neuronal Cultures Described through a Random Field Ising Model.

We introduce a novel random field Ising model, grounded on experimental observations, to assess the importance of metric correlations in cortical circuits in vitro. Metric correlations arise from both the finite axonal length and the heterogeneity in the spatial arrangement of neurons. The experiments consider the response of neuronal cultures to an external electric stimulation for a gradually weaker connectivity strength between neurons, and in cultures with different spatial configurations. The model can be analytically solved in the metric-free, mean-field scenario. The presence of metric correlations precipitates a strong deviation from the mean field. Null models of the same networks that preserve the distribution of connections recover the mean field. Our results show that metric-inherited correlations in spatial networks dominate the connectivity blueprint, mask the actual distribution of connections, and may emerge as the asset that shapes network dynamics.

New species of Callichromatini Swainson, 1840. (Coleoptera, Cerambycidae). New Cerambycidae from Vietnam. Part 6.

Three new species of Cerambycidae, Callichromatini from Vietnam are described: Aphrodisium lingafelteri sp. nov., Mimochelidonium vietnamicum sp. nov., and Polyzonus (Striatopolyzonus) tonkinensis sp. nov. The genus Mimochelidonium Bentanachs & Drouin is recorded as new for the fauna of Vietnam.

Geometrical model for martensitic phase transitions: Understanding criticality and weak universality during microstructure growth.

A simple model for the growth of elongated domains (needle-like) during a martensitic phase transition is presented. The model is purely geometric and the only interactions are due to the sequentiality of the kinetic problem and to the excluded volume, since domains cannot retransform back to the original phase. Despite this very simple interaction, numerical simulations show that the final observed microstructure can be described as being a consequence of dipolar-like interactions. The model is analytically solved in 2D for the case in which two symmetry related domains can grow in the horizontal and vertical directions. It is remarkable that the solution is analytic both for a finite system of size L×L and in the thermodynamic limit L→∞, where the elongated domains become lines. Results prove the existence of criticality, i.e., that the domain sizes observed in the final microstructure show a power-law distribution characterized by a critical exponent. The exponent, nevertheless, depends on the relative probabilities of the different equivalent variants. The results provide a plausible explanation of the weak universality of the critical exponents measured during martensitic transformations in metallic alloys. Experimental exponents show a monotonous dependence with the number of equivalent variants that grow during the transition.

Analysis of crackling noise using the maximum-likelihood method: Power-law mixing and exponential damping.

Crackling noise can be initiated by competing or coexisting mechanisms. These mechanisms can combine to generate an approximate scale invariant distribution that contains two or more contributions. The overall distribution function can be analyzed, to a good approximation, using maximum-likelihood methods and assuming that it follows a power law although with nonuniversal exponents depending on a varying lower cutoff. We propose that such distributions are rather common and originate from a simple superposition of crackling noise distributions or exponential damping.

Avalanches and force drops in displacement-driven compression of porous glasses.

Similarities between force-driven compression experiments of porous materials and earthquakes have been recently proposed. In this paper, we measure the acoustic emission during displacement-driven compression of a porous glass. The energy of acoustic-emission events shows that the failure process exhibits avalanche scale-invariance and therefore follows the Gutenberg-Richter law. The resulting exponents do not exhibit significant differences with respect the force-driven case. Furthermore, the force exhibits an avalanche-type behavior for which the force drops are power-law distributed and correlated with the acoustic emission events.

Avalanche criticality during compression of porcine cortical bone of different ages.

Crack events developed during uniaxial compression of cortical bones cut from femurs of developing pigs of several ages (4, 12, and 20 weeks) generate avalanches. These avalanches have been investigated by acoustic emission analysis techniques. The avalanche energies are power-law distributed over more than four decades. Such behavior indicates the absence of characteristic scales and suggests avalanche criticality. The statistical distributions of energies and waiting times depend on the pig age and indicate that bones become stronger, but less ductile, with increasing age. Crack propagation is equally age-dependent. Older pigs show, on average, larger cracks with a time distribution similar to those of aftershocks in earthquakes, while younger pigs show only statistically independent failure events.

Influence of the aspect ratio and boundary conditions on universal finite-size scaling functions in the athermal metastable two-dimensional random field Ising model.

This work studies universal finite size scaling functions for the number of one-dimensional spanning avalanches in a two-dimensional (2D) disordered system with boundary conditions of different nature and different aspect ratios. To this end, we will consider the 2D random field Ising model at T=0 driven by the external field H with athermal dynamics implemented with periodic and forced boundary conditions. We have chosen a convenient scaling variable z that accounts for the deformation of the distance to the critical point caused by the aspect ratio. In addition, assuming that the dependence of the finite size scaling functions on the aspect ratio can be accounted for by an additional multiplicative factor, we have been able to collapse data for different system sizes, different aspect ratios, and different types of the boundary conditions into a single scaling function Q̂.

Avalanches in compressed Ti-Ni shape-memory porous alloys: An acoustic emission study.

Mechanical avalanches during compression of martensitic porous Ti-Ni have been characterized by high-frequency acoustic emission (AE). Two sequences of AE signals were found in the same sample. The first sequence is mainly generated by detwinning at the early stages of compression while fracture dominates the later stages. Fracture also determines the catastrophic failure (big crash). For high-porosity samples, the AE energies of both sequences display power-law distributions with exponents ɛ≃2 (twinning) and 1.7 (fracture). The two power laws confirm that twinning and fracture both lead to avalanche criticality during compression. As twinning precedes fracture, the observation of twinning allows us to predict incipient fracture of the porous shape memory material as an early warning sign (i.e., in bone implants) before the fracture collapse actually happens.