Given a unitary operator A representing a physical quantity of interest, we employ concepts from group representation theory to define two natural signal energy densities for A. The first is invariant to A and proves useful when the effect of A is to be ignored; the second is covariant to A and measures the “A” content of signals. We also consider joint densities for multiple operators and, in ...

Article history: Available online 18 May 2012

it is well known that ground-shaking site effect caused by an earthquake can vary significantly within a small distance. this is because at sites having soft soil and/or topographic and basement undulations, seismic energy gets trapped, leading to amplification of vibration that may cause considerable damage to man-made structures. theoretical analysis and observational data have shown that eac...

most geologic changes have a seismic response but sometimes this is expressed only in certain spectral ranges hidden within the broadband data. spectral decomposition is one of the methods which can be utilized to help interpreting such cases. there are several time-frequency methods including: short-time fourier transform (stft), continuous wavelet transform (cwt), wigner-ville distribution (w...

the seasonal and diurnal variations in the incidence of hypertension, cerebrovascular accident, coronary heart disease were well documented, but the relation between season and daytime on the onset of aneurysmal subarachnoid hemorrhage (asah) was a subject of controversy. in the present study we aimed to evaluate the role of season of year and diurnal changes on the onset of asah. the time was ...