Statistical similarity between the compression of a porous material and earthquakes

It has been long stated that there are profound analogies between fracture experiments and earthquakes; however, few works attempt a complete characterization of the parallelisms between these so separate phenomena. We study the Acoustic Emission events produced during the compression of Vycor (SiO2). The Gutenberg-Richter law, the modified Omori's law, and the law of aftershock productivity are found to 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.Comment: 4 pages and a bit more, 4 figure

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 dissipation and 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.Comment: preprint, Main article: 7 pages, 3 figures. Supplementary material included in \anc folder: 6 pages, 3 figure

Informe final. Gestió de grans grups en les tutories dels Treballs de Fi de Grau a Història Contemporània

Projecte: 2017PID-UB/041El punt de sortida d'aquest projecte és el gran nombre de Treballs de Fi de Grau que son tutoritzats des de la Secció d'Història Contemporània. En el curs 2017-2018, dels 219 TFG's matriculats al Grau d'Història, 105 foren d'Història Contemporània (el 47,9%). Aquesta tendència és creixent en termes absoluts i relatius. En el present curs 2018-2019, són 122 d'Història Contemporània respecte un total de 236 (el 51,7%). Malgrat el gran nombre de docents dedicats a la tutorització, alguns d'aquests docents assumeixen fins a uns 15 alumnes tutoritzats. L'objectiu principal del projecte ha estat el construir una eina de treball que permeti fer un seguiment de qualitat d'aquests treballs. Així s'ha previst l'elaboració d'un protocol de tutorització que inclou la potenciació de les eines disponibles a traves del campus virtual. Amb això es tracta de que l'alumnat rebi una tutorització de qualitat a partir de l'ús d'unes eines metodològiques orientades a l'aprofitament dels recursos col·lectius i a l'optimització del temps. Els resultats previstos consistien en l'elaboració d'un calendari de reunions plenàries i de tutories individualitzades, així com en l'elaboració d'unes guies (en total 5) corresponents a cadascuna de les fases del procés d'elaboració d'un Treball de Fi de Grau. En el desenvolupament del projecte hem assolit tots els resultats previstos

Acoustic emission across the magnetostructural transition of the giant magnetocaloric Gd5Si2Ge2 compound

We report on the existence of acoustic emission during the paramagnetic-monoclinic to ferromagnetic-orthorhombic magnetostructural phase transition in the giant magnetocaloric Gd5Si2Ge2 compound. The transition kinetics have been analyzed from the detected acoustic signals. It is shown that this transition proceeds by avalanches between metastable states.Comment: 5 pages, 4 figure

On the evolution of cell size distribution during bacterial growth cycle: Experimental observations and individual-based model simulations

Postprint (published version

Statistical similarity between the compression of a porous material and earthquakes

"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 (SiO2). 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.

Disorder induced critical phenomena in magnetically glassy Cu-Al-Mn alloys

Measurements of magnetic hysteresis loops in Cu-Al-Mn alloys of different Mn content at low temperatures are presented. The loops are smooth and continuous above a certain temperature, but exhibit a magnetization discontinuity below that temperature. Scaling analysis suggest that this system displays a disorder induced phase transition line. Measurements allow to determine the critical exponents $\beta=0.03\pm 0.01$ and $\beta \delta = 0.4 \pm 0.1$ in agreement with those reported recently [Berger et al., Phys. Rev. Lett. {\bf 85}, 4176 (2000)]Comment: 4 pages, 5 figure

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.The group from Barcelona acknowledges financial support from CICyT (Spain), Projects No. MAT2013-40590-P and No. MAT2015-69777-REDT. E.K.H.S. is grateful to EPSRC for support under Grant No. EP/K009702/1. I.J. gratefully acknowledges support from the National Science Foundation (NSF) the DMR Program Grant No. 15-07169

CD148, a membrane protein tyrosine phosphatase, is able to induce tyrosine phosphorylation on human lymphocytes

Producción CientíficaCD148 is a new cluster of differentiation defined in the VI International Workshop on Leucocyte Differentiation Antigens. It has been identified as the hematopoietic form of a formerly described membrane protein tyrosine phosphatase called HPTP eta/ DEP-1. Previous data have demonstrated that this molecule is able to give rise to [Ca2+]i increase. In the present work we show its capability to induce protein tyrosine phosphorylation in human lymphocytes in spite of its intrinsic protein tyrosine phosphatase activity. The induction of kinase activity suggests the involvement of some protein tyrosine kinase based signaling pathway. The activation of this postulated kinase could be carried out through a direct association or via an adapter molecule

Introductory analysis of human upper body after stroke

The most reliable prognostic factors associated with Upper Extremity (UE) recovery are localized motor impairments, especially in the musculature of the hand and abduction of the shoulder in the first days after a stroke. Evaluation of the biomechanics of the hand allows an accurate identification of the motion arcs of the digital joints. Objective: Assess the prognostic value of the range of motion of the finger joints using an instrumental glove (CyberGlove II®) one week after stroke for UE functional recovery at 6 months. Methodology: A prospective, longitudinal, observational study with follow-ups at 3-4 days, 1 week, 3 and 6months of patients with UE motor impairment. Variables collected included: demographic data, level of stroke severity (NIHSS), deep sensitivity, sphincter incontinence, Fugl Meyer Assessment of UE (FM-UE), muscle balance with the Medical Research Council (MRC), muscle tone (Modified Ashworth Scale) and pre- and post-stroke functional ability (Barthel Index and Modified Rankin Scale). Active range of motion of the metacarpophalangeal and interphalangeal joints of the index, middle finger, annulary, and little finger was assessed with CyberGlove II® without and against gravity. The dependent variable UE function was evaluated with the Action Research Arm Test (ARAT) categorized as good function (ARAT=10) and poor function (ARAT<10). Results: 31 patients were included, 18 of which completed the 6-month follow-up. Mean age was 68.2 years (SD = 9.1) and 72.2 % were men. A total of 77.8 % of strokes were ischemic, and 50 % of these were lacunar. Mean NIHSS score was 9.2 (SD = 5.5). Motor NIHSS of UE, FM-UE and MRC of the flexion-extension musculature of the digits and wrist were prognostic factors for the recovery of UE function.Peer ReviewedPostprint (author's final draft