Piezoelectricity essentially refers to current that accumulates in certain solids in response to applied mechanical stress.

BBC: Sensors

The outer two layers are made up of PZT-5H - a ceramic substance that produces an electrical charge when mechanical stress is applied.

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These two correlations do not by themselves prove that chronic stress damages the memory, but Dr Evans and Dr Schamberg then applied a statistical technique called hierarchical regression to the results.

ECONOMIST: Neuroscience and social deprivation

It measures what HeartMath calls coherence an algorithm applied to heart-rate variability, which the company says can reflect emotional states and stress levels.

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