2,458 research outputs found
Towards a Reconfigurable Sense-and-Stimulate Neural Interface Generating Biphasic Interleaved Stimulus
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Pressure stimulated currents in rocks and their correlation with mechanical properties
The spontaneous electrification of marble samples was studied while they were subjected to uniaxial stress. The Pressure Stimulated Current (PSC) technique was applied to measure the charge released from compressed Dionysos marble samples, while they were subjected to cyclic loading. The experimental results demonstrate that, in the linear elastic region of the sample, no PSC is recorded, while beyond the stress limit (s>0.60), observable variations appear, which increase considerably in the vicinity of sample failure, reaching a maximum value just before the failure. The emitted current is reduced on each loading cycle and it has a reciprocal dependence to the normalized Young modulus. The MCD model, applied out of the vicinity of sample failure explains successfully the above findings. The existence of a "memory-like" behavior of the sample, could justify the weakness or absence of electrical earthquake precursors, during an aftershock sequence
Piezo stimulated currents in marble samples: precursory and concurrent-with-failure signals
International audienceThe Earth?s electric field transient variations are promising candidates of earthquake precursors. In order to study the physical mechanisms of such precursory signals, laboratory experiments of uniaxial compression were carried out. More specifically the behaviour of stressed marble samples from Penteli Mountain was investigated. The samples were subjected to a time-varying uniaxial compression at both variable and constant stress rates. During the first set of experiments weak electric currents were detected during pressure variations. Such Piezo Stimulated Currents (PSC) were detected while stress steps, both positive and negative were applied, the maximum stress never being greater than the elasticity limit. During the second set of experiments stress was applied at a constant rate starting from zero-stress and ending in fracture. In the region beyond the elastic limit a PSC was detected which after reaching a peak suffered a reversal in its polarity just before fracture. In a third set of experiments the same procedure was applied to previously structurally damaged samples taking care not to fracture them. In all cases the PSC followed the variation of stress and moreover it was observed that a linear relationship existed between the PSC maxima and the corresponding stress-rate maxima. The mechanism responsible for the described phenomena can be ascribed to the Moving Charged Dislocations model
Pressure Stimulated Currents (PSC)in marble samples
The electrical behaviour of marble samples from Penteli Mountain was studied while they were subjected to uniaxial stress. The application of consecutive impulsive variations of uniaxial stress to thirty connatural samples produced Pressure Stimulated Currents (PSC). The linear relationship between the recorded PSC and the applied variation rate was investigated. The main results are the following: as far as the samples were under pressure corresponding to their elastic region, the maximum PSC value obeyed a linear law with respect to pressure variation. In the plastic region deviations were observed which were due to variations of Young s modulus. Furthermore,
a special burst form of PSC recordings during failure is presented. The latter is emitted when irregular longitudinal
splitting is observed during failure
Correlation of pressure stimulated currents in rocks with the damage parameter
Pressure Stimulated Current (PSC) experiments were conducted on marble samples to correlate PSC with the
damage parameter, D. The phenomena and procedures taking place in the vicinity of the fracture limit were observed
and analytically described. PSC recordings were conducted by application of uniaxial compressional
stress, both at a constant stress rate and at a constant deformation rate. A linear relationship was shown to exist
between the emitted PSC and the damage parameter which quantifies the deviation from linear elasticity and the
concentration of microcracks
Wavelet analysis on pressure stimulated currents emitted by marble samples
International audienceThis paper presents a wavelet based method of analysis of experimentally recorded weak electric signals from marble specimens which have undergone successive abrupt step loadings. Experimental results verify the existence of "memory effects" in rocks, as far as the current emission is concerned, akin to the "Kaiser effect" in acoustic emissions, which accompany rock fracturing. Macroscopic signal processing shows similarities and differences between the currents emitted during successive loading and wavelet analysis can reveal significant differences between the currents of each loading cycle that contain valuable information for the micro and macro cracks in the specimen as well as information for the remaining strength of the material. Wavelets make possible the time localization of the energy of the electric signal emitted by stressed specimens and can serve as method to differentiate between compressed and uncompressed samples, or to determine the deformation level of specimens
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Making Sense of Electrical Stimulation: A Meta-analysis for Wound Healing
Electrical stimulation as a mode of external enhancement factor in wound healing has been explored widely. It has proven to have multidimensional effects in wound healing including antibacterial, galvanotaxis, growth factor secretion, proliferation, transdifferentiation, angiogenesis, etc. Despite such vast exploration, this modality has not yet been established as an accepted method for treatment. This article reviews and analyzes the approaches of using electrical stimulation to modulate wound healing and discusses the incoherence in approaches towards reporting the effect of stimulation on the healing process. The analysis starts by discussing various processes adapted in in vitro, in vivo, and clinical practices. Later it is focused on in vitro approaches directed to various stages of wound healing. Based on the analysis, a protocol is put forward for reporting in vitro works in such a way that the outcomes of the experiment are replicable and scalable in other setups. This work proposes a ground of unification for all the in vitro approaches in a more sensible manner, which can be further explored for translating in vitro approaches to complex tissue stimulation to establish electrical stimulation as a controlled clinical method for modulating wound healing
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