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Zootaxa 2021 Oct 1;5047(4):465-476. Epub 2021 Oct 1.

San Antoni, 73, 08221, Terrassa, Spain.

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.

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http://dx.doi.org/10.11646/zootaxa.5047.4.6 | DOI Listing |

October 2021

Zootaxa 2021 Mar 5;4941(1):zootaxa.4941.1.5. Epub 2021 Mar 5.

Institute for Agro-Environmental Sciences, NARO, Kannondai 3-1-3, Tsukuba, Ibaraki 305-8604, Japan.

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.

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http://dx.doi.org/10.11646/zootaxa.4941.1.5 | DOI Listing |

March 2021

Zootaxa 2020 Mar 25;4755(3):zootaxa.4755.3.7. Epub 2020 Mar 25.

Bioindicator Co., Ltd., Nikkô-Kagurazaka Building, Iwato-chô 18, Shinjuku, Tokyo, 162‒0832 Japan..

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.

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http://dx.doi.org/10.11646/zootaxa.4755.3.7 | DOI Listing |

March 2020

Phys Rev E 2019 Dec;100(6-1):062106

Centre de Recerca Matemàtica, Edifici C, Campus Bellaterra, E-08193 Bellaterra, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.100.062106 | DOI Listing |

December 2019

Phys Rev E 2019 Mar;99(3-1):033001

Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.99.033001 | DOI Listing |

March 2019

Phys Rev E 2019 Feb;99(2-1):023002

School of Civil Engineering, Chongqing University, 400044 Chongqing, People's Republic of China.

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.

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http://dx.doi.org/10.1103/PhysRevE.99.023002 | DOI Listing |

February 2019

Zootaxa 2019 Jan 14;4544(3):429-436. Epub 2019 Jan 14.

Key Laboratory of Insect Evolution and Pest Management for Higher Education in Hunan Province, Central South University of Forestry and Technology, Changsha, Hunan 410004, 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.

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http://dx.doi.org/10.11646/zootaxa.4544.3.8 | DOI Listing |

January 2019

Phys Rev Lett 2018 Jun;120(24):245501

Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Martí i Franquès, 1. 08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevLett.120.245501 | DOI Listing |

June 2018

Phys Rev E 2018 Feb;97(2-1):022134

Departament de Matèria Condensada, Facultat de Física, Universitat de Barcelona, Martí Franquès 1, 08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.97.022134 | DOI Listing |

February 2018

Phys Rev E 2018 Jan;97(1-1):012109

Departament de Matèria Condensada, Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.97.012109 | DOI Listing |

January 2018

Phys Rev E 2017 Oct 11;96(4-1):042122. Epub 2017 Oct 11.

Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Martí i Franquès,1, E-08028 Barcelona, Catalonia.

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.

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http://dx.doi.org/10.1103/PhysRevE.96.042122 | DOI Listing |

October 2017

J Phys Condens Matter 2017 Aug 12;29(33):334001. Epub 2017 Jun 12.

Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Catalonia.

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.

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http://dx.doi.org/10.1088/1361-648X/aa78d7 | DOI Listing |

August 2017

Phys Rev Lett 2017 May 18;118(20):208101. Epub 2017 May 18.

Departament de Física de la Matèria Condensada, Universitat de Barcelona, Barcelona 08028, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevLett.118.208101 | DOI Listing |

May 2017

Zootaxa 2017 Feb 21;4236(1):zootaxa.4236.1.12. Epub 2017 Feb 21.

Department of Animal Biology. University of Barcelona, Spain..

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.

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http://dx.doi.org/10.11646/zootaxa.4236.1.12 | DOI Listing |

February 2017

Phys Rev E 2017 Jan 3;95(1-1):013001. Epub 2017 Jan 3.

Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Catalonia.

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.

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http://dx.doi.org/10.1103/PhysRevE.95.013001 | DOI Listing |

January 2017

Phys Rev E 2016 Sep 30;94(3-1):033005. Epub 2016 Sep 30.

Departament de Matèria Condensada, Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.94.033005 | DOI Listing |

September 2016

Phys Rev E 2016 May 2;93(5):053001. Epub 2016 May 2.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física. Universitat de Barcelona, Diagonal, 647, E-08028 Barcelona, Catalonia.

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.

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http://dx.doi.org/10.1103/PhysRevE.93.053001 | DOI Listing |

May 2016

Phys Rev E 2016 Feb 18;93(2):022129. Epub 2016 Feb 18.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.93.022129 | DOI Listing |

February 2016

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Jun 17;91(6):060401. Epub 2015 Jun 17.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Diagonal 647, E-08028 Barcelona, Catalonia, Spain.

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.

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http://dx.doi.org/10.1103/PhysRevE.91.060401 | DOI Listing |

June 2015

Zookeys 2015 4(502):39-60. Epub 2015 May 4.

Facultat de Biologia, Departament de Biologia Animal, Avda. Diagonal, 643, 08028 Barcelona, Spain.

The ten species of the genus Trypogeus Lacordaire are revised. Trypogeusapicalis Fisher, 1936, is proposed as a new synonym of Trypogeusjavanicus Aurivillius, 1925. A neotype for Trypogeussericeus (Gressitt, 1951) and lectotypes for Toxotusfuscus Nonfried, 1894 and Trypogeusjavanicus are designated. Trypogeusfuscus auct. nec Nonfried is a misidentification of Philusophthalmicus Pascoe. All the species are described and keys are given for distinguishing the species. Photographs of the types of all the Trypogeus species are published for the first time.

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http://dx.doi.org/10.3897/zookeys.502.9049 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4443589 | PMC |

May 2015

Phys Rev E Stat Nonlin Soft Matter Phys 2014 Aug 15;90(2):022405. Epub 2014 Aug 15.

Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom.

The failure dynamics in SiO(2)-based porous materials under compression, namely the synthetic glass Gelsil and three natural sandstones, has been studied for slowly increasing compressive uniaxial stress with rates between 0.2 and 2.8 kPa/s. The measured collapsed dynamics is similar to Vycor, which is another synthetic porous SiO(2) glass similar to Gelsil but with a different porous mesostructure. Compression occurs by jerks of strain release and a major collapse at the failure point. The acoustic emission and shrinking of the samples during jerks are measured and analyzed. The energy of acoustic emission events, its duration, and waiting times between events show that the failure process follows avalanche criticality with power law statistics over ca. 4 decades with a power law exponent ɛ≃ 1.4 for the energy distribution. This exponent is consistent with the mean-field value for the collapse of granular media. Besides the absence of length, energy, and time scales, we demonstrate the existence of aftershock correlations during the failure process.

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http://dx.doi.org/10.1103/PhysRevE.90.022405 | DOI Listing |

August 2014

J Phys Condens Matter 2014 Jul 11;26(27):275401. Epub 2014 Jun 11.

Department d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Catalonia. INP Grenoble, 38031 Grenoble Cédex 1, France.

Acoustic emission has been measured and statistical characteristics analyzed during the stress-induced collapse of porous berlinite, AlPO4, containing up to 50 vol% porosity. Stress collapse occurs in a series of individual events (avalanches), and each avalanche leads to a jerk in sample compression with corresponding acoustic emission (AE) signals. The distribution of AE avalanche energies can be approximately described by a power law p(E)dE = E(-ε)dE (ε ~ 1.8) over a large stress interval. We observed several collapse mechanisms whereby less porous minerals show the superposition of independent jerks, which were not related to the major collapse at the failure stress. In highly porous berlinite (40% and 50%) an increase of energy emission occurred near the failure point. In contrast, the less porous samples did not show such an increase in energy emission. Instead, in the near vicinity of the main failure point they showed a reduction in the energy exponent to ~ 1.4, which is consistent with the value reported for compressed porous systems displaying critical behavior. This suggests that a critical avalanche regime with a lack of precursor events occurs. In this case, all preceding large events were 'false alarms' and unrelated to the main failure event. Our results identify a method to use pico-seismicity detection of foreshocks to warn of mine collapse before the main failure (the collapse) occurs, which can be applied to highly porous materials only.

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http://dx.doi.org/10.1088/0953-8984/26/27/275401 | DOI Listing |

July 2014

J Phys Condens Matter 2014 Mar 6;26(12):125401. Epub 2014 Mar 6.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Diagonal, 647, E-08028 Barcelona, Catalonia, Spain.

The existence of temporal correlations during the intermittent dynamics of a thermally driven structural phase transition is studied in a Cu-Zn-Al alloy. The sequence of avalanches is observed by means of two techniques: acoustic emission and high sensitivity calorimetry. Both methods reveal the existence of event clustering in a way that is equivalent to the Omori correlations between aftershocks in earthquakes as are commonly used in seismology.

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http://dx.doi.org/10.1088/0953-8984/26/12/125401 | DOI Listing |

March 2014

J Phys Condens Matter 2013 Jul 2;25(29):292202. Epub 2013 Jul 2.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Catalonia, Spain.

We study acoustic emission avalanches during the process of failure of porous alumina samples (Al2O3) under compression. Specimens with different porosities ranging from 30% to 59% have been synthesized from a mixture of fine-grained alumina and graphite. The compressive strength as well as the characteristics of the acoustic activity have been determined. The statistical analysis of the recorded acoustic emission pulses reveals, for all porosities, a broad distribution of energies with a fat tail, compatible with the existence of an underlying critical point. In the region of 35%-55% porosity, the energy distributions of the acoustic emission signals are compatible with a power-law behaviour over two decades in energy with an exponent ϵ = 1.8 ± 0.1.

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http://dx.doi.org/10.1088/0953-8984/25/29/292202 | DOI Listing |

July 2013

Zookeys 2013 4(275):67-75. Epub 2013 Mar 4.

Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beichen West Road, Chaoyang Dist., Beijing, 100101, China ; Museu de Ciuències Naturals de Barcelona, c/Sant Antoni, 73, 08221 Terrassa (Barcelona) Spain.

One new species, Schwarzerium yunnanum sp. n. is described from Yunnan Province, China. And a new subgenus Rugosochroma subgen. n. is erected for it. Additionally, Seven species of the tribe Callichromatini are newly recorded from China: Aphrodisium niisatoi Vives & Bentanachs, 2007, Aphrodisium tricoloripes Pic, 1925, Chelidonium violaceimembris Gressitt & Rondon, 1970 (new from Vietnam too), Chloridolum grossepunctatum Gressitt & Rondon, 1970 (new from Vietnam too), Chloridolum semipunctatum Gressit & Rondon 1970, Embrikstrandia vivesi Bentanachs, 2005 and Laosaphrodisium subplicatum (Pic, 1937).

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http://dx.doi.org/10.3897/zookeys.275.4576 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3677327 | PMC |

June 2013

Phys Rev Lett 2013 Feb 19;110(8):088702. Epub 2013 Feb 19.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Catalonia, Spain.

It has long been stated that there are profound analogies between fracture experiments and earthquakes; however, few works attempt a complete characterization of the parallels between these so separate phenomena. We study the acoustic emission events produced during the compression of Vycor (SiO(2)). The Gutenberg-Richter law, the modified Omori's law, and the law of aftershock productivity hold for a minimum of 5 decades, are independent of the compression rate, and keep stationary for all the duration of the experiments. The waiting-time distribution fulfills a unified scaling law with a power-law exponent close to 2.45 for long times, which is explained in terms of the temporal variations of the activity rate.

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http://dx.doi.org/10.1103/PhysRevLett.110.088702 | DOI Listing |

February 2013

Phys Rev E Stat Nonlin Soft Matter Phys 2012 Jun 19;85(6 Pt 2):066121. Epub 2012 Jun 19.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Diagonal 647, E-08028 Barcelona, Catalonia, Spain.

Maximum-likelihood exponent maps have been studied as a technique to increase the understanding and improve the fit of power-law exponents to experimental and numerical simulation data, especially when they exhibit both upper and lower cutoffs. The use of the technique is tested by analyzing seismological data, acoustic emission data, and avalanches in numerical simulations of the three-dimensional random field Ising model. In the different examples we discuss the nature of the deviations observed in the exponent maps and some relevant conclusions are drawn for the physics behind each phenomenon.

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http://dx.doi.org/10.1103/PhysRevE.85.066121 | DOI Listing |

June 2012

Phys Rev E Stat Nonlin Soft Matter Phys 2009 Jul 6;80(1 Pt 1):011105. Epub 2009 Jul 6.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Catalonia.

Avalanche dynamics and related power-law statistics are ubiquitous in nature, arising in phenomena such as earthquakes, forest fires, and solar flares. Very interestingly, an analogous behavior is associated with many condensed-matter systems, such as ferromagnets and martensites. Bearing it in mind, we study the prototypical random-field Ising model at T=0. We find a finite correlation between waiting intervals and the previous avalanche size. This correlation is not found in other models for avalanches but it is experimentally found in earthquakes and in forest fires. Our study suggests that this effect occurs in critical points that are at the end of a first-order discontinuity separating two regimes: one with high activity from another with low activity.

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http://dx.doi.org/10.1103/PhysRevE.80.011105 | DOI Listing |

July 2009

Phys Rev E Stat Nonlin Soft Matter Phys 2009 Jun 19;79(6 Pt 1):061116. Epub 2009 Jun 19.

Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Catalonia, Spain.

We present a numerical study of the zero-temperature response of the Gaussian random-field Ising model to a slowly varying external field, allowing the system to be trapped in microscopic configurations that are not fully metastable. This modification of the standard single-spin-flip dynamics results in an increase in dissipation (hysteresis) somewhat similar to that observed with a finite driving rate. We then study the distribution of avalanches along the hysteresis loop and perform a finite-size scaling analysis that shows good evidence that the critical exponents associated to the disorder-induced phase transition are not modified.

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http://dx.doi.org/10.1103/PhysRevE.79.061116 | DOI Listing |

June 2009

Phys Rev E Stat Nonlin Soft Matter Phys 2009 Feb 19;79(2 Pt 1):021123. Epub 2009 Feb 19.

Department of Applied Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland.

We perform a numerical study of the three-dimensional random-field Ising model at T=0. We compare work distributions along metastable trajectories obtained with the single-spin flip dynamics with the distribution of the internal energy change along equilibrium trajectories. The goal is to investigate the possibility of extending the Crooks fluctuation theorem [G. E. Crooks, Phys. Rev. E. 60, 2721 (1999)] to zero temperature when, instead of the standard ensemble statistics, one considers the ensemble generated by the quenched disorder. We show that a simple extension of Crooks fails close to the disordered induced equilibrium phase transition due to the fact that work and internal energy distributions are very asymmetric.

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February 2009

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