Temperature-driven micro-fracturing in granite: The interplay between microstructure, mineralogy and tensile strength.

High temperatures exert a significant influence on the mechanical and fluid flow properties of rocks and minerals. In crystalline rocks, differential thermal expansion of minerals is known to induce microfracture damage leading to changes in bulk volume and tensile strength. Here we report new data from thermally treated core samples of Devon Granite in order to constrain the interplay between tensile strength and thermally-induced damage with respect to the background mineralogy. A series of core samples was cyclically heated at temperatures ranging from 25 to 800 °C, with P-wave velocity and porosity measured after each cycle. Tensile strength decreased significantly from 9 MPa to less than 3 MPa as thermal treatment increased from 25 to 800 °C. The mechanical data were then compared to fracture density values obtained by optical maps of microfracture damage to assess the quantity and degree of linkage of intergranular and intragranular fractures using the FraqPaQ toolbox. The fracture density increased from 0.02 m m - 2 to 2.0 m m - 2 which is consistent with results obtained from direct physical parameters as calculated from elastic wave data. We conclude that the combined effects of thermal expansion and the α - ß phase transition within quartz crystals has a pronounced effect on tensile strength.

A novel neurocognitive rehabilitation tool in the recovery of hemiplegic hand grip after stroke: a case report.

Stroke has significant physical, psychological and social consequences. Recent rehabilitation approaches suggest that cognitive exercises with dual-task (sensory-motor) exercises positively influence the recovery and function of the hemiplegic hand grip. The purpose of this study was to describe a rehabilitation protocol involving the use of a new neurocognitive tool called "UOVO" for hand grip recovery after stroke. A 58-year-old right-handed male patient in the chronic stage of stroke, presenting with left-sided hemiparesis and marked motor deficits at the level of the left hand and forearm, was treated with the UOVO, a new rehabilitation instrument based on the neurocognitive rehabilitation theory of Perfetti. The patient was evaluated at T0 (before treatment), T1 (after treatment) and T2 (2 months of follow-up). At T2, the patient showed improvements of motor functions, shoulder, elbow and wrist spasticity, motility and performance. This case report explores the possibility of improving traditional rehabilitation through a neurocognitive approach with a dual-task paradigm (including motor and somato-sensory stimulation), specifically one involving the use of an original rehabilitation aid named UOVO, which lends itself very well to exercises proposed through the use of motor imagery. The results were encouraging and showed improvements in hemiplegic hand grip function and recovery. However, further studies, in the form of randomized controlled trials, will be needed to further explore and confirm our results.

Analysis of self-organized criticality in the Olami-Feder-Christensen model and in real earthquakes.

We perform an analysis on the dissipative Olami-Feder-Christensen model on a small world topology considering avalanche size differences. We show that when criticality appears, the probability density functions (PDFs) for the avalanche size differences at different times have fat tails with a q-Gaussian shape. This behavior does not depend on the time interval adopted and is found also when considering energy differences between real earthquakes. Such a result can be analytically understood if the sizes (released energies) of the avalanches (earthquakes) have no correlations. Our findings support the hypothesis that a self-organized criticality mechanism with long-range interactions is at the origin of seismic events and indicate that it is not possible to predict the magnitude of the next earthquake knowing those of the previous ones.

Folded fabric tunes rock deformation and failure mode in the upper crust.

The micro-mechanisms of brittle failure affect the bulk mechanical behaviour and permeability of crustal rocks. In low-porosity crystalline rocks, these mechanisms are related to mineralogy and fabric anisotropy, while confining pressure, temperature and strain rates regulate the transition from brittle to ductile behaviour. However, the effects of folded anisotropic fabrics, widespread in orogenic settings, on the mechanical behaviour of crustal rocks are largely unknown. Here we explore the deformation and failure behaviour of a representative folded gneiss, by combining the results of triaxial deformation experiments carried out while monitoring microseismicity with microstructural and damage proxies analyses. We show that folded crystalline rocks in upper crustal conditions exhibit dramatic strength heterogeneity and contrasting failure modes at identical confining pressure and room temperature, depending on the geometrical relationships between stress and two different anisotropies associated to the folded rock fabric. These anisotropies modulate the competition among quartz- and mica-dominated microscopic damage processes, resulting in transitional brittle to semi-brittle modes under P and T much lower than expected. This has significant implications on scales relevant to seismicity, energy resources, engineering applications and geohazards.

Cellular versus myocardial basis for the contractile dysfunction of hypertrophied myocardium.

Contractile dysfunction has been demonstrated in many previous studies of experimental right ventricular pressure-overload hypertrophy; however, given the complex changes that occur both in the cardiac muscle cell and in the multiple components of the cardiac interstitium, it is not clear whether the contractile dysfunction observed is an intrinsic property of the cardiac muscle cell or whether it is the result of a mechanically normal cardiac muscle cell contracting within an abnormal interstitial environment. The purpose of the present study was to examine the contractile behavior of cardiac muscle cells, or cardiocytes, isolated from seven cat right ventricles that were pressure-overloaded by banding the pulmonary artery; right ventricular cardiocytes from seven sham-operated cats served as controls. Cardiocytes were obtained from these cats via standard cell isolation procedures; contractile function of the cardiocytes in response to graded viscous external loads was defined by laser diffraction. The cells were stimulated to contract at a frequency of 0.25 Hz, using 100-microA direct current pulses of alternating polarity. Hypertrophied right ventricular cardiocytes obtained from banded cats showed marked systolic contractile abnormalities in comparison with right ventricular cardiocytes from sham-operated cats. The peak velocity of sarcomere shortening for the control and hypertrophied cardiocytes in 1-cp superfusate was 3.6 +/- 0.2 and 2.1 +/- 0.1 microns/sec, respectively (p less than 0.001); the maximum extent of sarcomere shortening for the control and hypertrophied cardiocytes was 0.21 +/- 0.01 and 0.14 +/- 0.01 microns, respectively (p less than 0.001). Further, the time to peak shortening in the 1-cp superfusate was significantly longer for the hypertrophied cardiocytes (150.1 +/- 3.3 versus 160.4 +/- 3.7 msec; p less than 0.04). When the relengthening properties of the cells were examined in the 1-cp superfusate, there were significant differences between cardiocyte groups. The peak rate of sarcomere relengthening was 3.5 +/- 0.2 microns/sec in the control cardiocytes and 2.2 +/- 0.17 microns/sec in the hypertrophied cardiocytes (p less than 0.001). Similarly, the time to peak velocity of sarcomere relengthening (48.8 +/- 1.8 versus 57.9 +/- 2.9 msec) and the time to 50% maximal sarcomere relengthening (57.1 +/- 3.1 versus 67.1 +/- 3.1 msec) were both significantly prolonged for the hypertrophied cardiocytes (p less than 0.02). This study shows for the first time that the contractile defect in this model of right ventricular pressure-overload hypertrophy is intrinsic to the cardiac muscle cell itself. This finding provides a basis for further, more focused investigations designed to determine the mechanisms responsible for the contractile dysfunction observed in this form of experimental cardiac hypertrophy.

[Echopolycardiographic evaluation of left ventricular function after hemodialysis]. / Valutazione eco-policardiografica della funzionalità ventricolare sinistra dopo emodialisi.

The acute effects of haemodialysis on left ventricular (LV) function were studied by echocardiography and systolic time intervals in 19 patients maintained on long-term haemodialysis. Dialysis resulted in a significant reduction in body weight, an increase in heart rate and a small reduction in systolic blood pressure. A significant decrease was observed in LV diastolic and systolic dimensions, with an increase in the mean rate of circumferential shortening (mean VCF). The LV ejection time (LVET) decreased significantly, while changes in the pre-ejection period (PEP) were insignificant. The PEP/LVET ratio increased in all patients. Haemodialysis reduced the serum potassium levels; an increase was noted in the serum calcium concentrations, with a significant, although small, correction of blood pH. The major haemodynamic change induced by dialysis was a decrease in blood volume with a reduction in LV pre-load. These changes are suggested by the reduction in body weight and by the shortening in LV end-diastolic dimension and LVET. There was also a reduction in after-load, as expressed by the shortening in LV systolic diameter and by the decrease in systolic blood pressure. It should be emphasized that the study of LV function in patients on chronic dialysis is greatly influenced by the loading conditions. In such patients the assessment of LV function by echocardiography and systolic time intervals provides information regarding the haemodynamic changes induced by dialysis; however, no direct evidence can be derived about the functional state of the left ventricle.