2,555 research outputs found
Stochastic Comparisons of Two-Units Repairable Systems
We consider two models of two-units repairable systems: cold standby system
and warm standby system. We suppose that the lifetimes and repair times of the
units are all independent exponentially distributed random variables. Using
stochastic orders we compare the lifetimes of systems under different
assumptions on the parameters of exponential distributions. We also consider a
cold standby system where the lifetimes and repair times of its units are not
necessarily exponentially distributed
S wave velocity structure below central Mexico using high-resolution surface wave tomography
Shear wave velocity of the crust below central Mexico is estimated using surface wave dispersion measurements from regional earthquakes recorded on a dense, 500 km long linear seismic network. Vertical components of regional records from 90 well-located earthquakes were used to compute Rayleigh-wave group-velocity dispersion curves. A tomographic inversion, with high resolution in a zone close to the array, obtained for periods between 5 and 50 s reveals significant differences relative to a reference model, especially at larger periods (>30 s). A 2-D S wave velocity model is obtained from the inversion of local dispersion curves that were reconstructed from the tomographic solutions. The results show large differences, especially in the lower crust, among back-arc, volcanic arc, and fore-arc regions; they also show a well-resolved low-velocity zone just below the active part of the Trans Mexican Volcanic Belt (TMVB) suggesting the presence of a mantle wedge. Low densities in the back arc, inferred from the low shear wave velocities, can provide isostatic support for the TMVB
Novedades corológicas para la comarca del Andévalo (provincia de Huelva, SO de España). IV
Ministerio de Ciencia y TecnologĂa (España) REN 2002-04478-C03-03/GL
A hierarchy of bound states in the 1D ferromagnetic Ising chain CoNbO investigated by high resolution time-domain terahertz spectroscopy
Kink bound states in the one dimensional ferromagnetic Ising chain compound
CoNbO have been studied using high resolution time-domain terahertz
spectroscopy in zero applied magnetic field. When magnetic order develops at
low temperature, nine bound states of kinks become visible. Their energies can
be modeled exceedingly well by the Airy function solutions to a 1D
Schr\"odinger equation with a linear confining potential. This sequence of
bound states terminates at a threshold energy near two times the energy of the
lowest bound state. Above this energy scale we observe a broad feature
consistent with the onset of the two particle continuum. At energies just below
this threshold we observe a prominent excitation that we interpret as a novel
bound state of bound states -- two pairs of kinks on neighboring chains
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