In this paper, we have reported the fabrication of two-dimensional photonic crystals, using a direct writing method in azo polymers. Periodic structures have been fabricated using the interference patterns of two coherent laser beams. The frequency response of the initial one-dimensional structure shows an attenuation of 19.3dB at 1554nm. The twodimensional structure shows 8.3dB and 11.3dB of a...

introduction: monte carlo (mc) is the most common method for simulating virtual spect projections. it is useful for optimizing procedures, evaluating correction algorithms and more recently image reconstruction as a forward projector in iterative algorithms; however, the main drawback of mc is its long run time. we introduced a model based method considering the effect of body attenuation and i...

introduction: the photoelectric attenuation coefficient of substances is known to depend upon the energy e of the photon and the effective atomic number of substances (zeff) as (zeff x /e y ).  no definitive values about these indices x, y are given in the literature. the index x is said to lie between, 3.0 and 4.0, while for ‘y’ different values have been assigned, between 3.0 and 4.0. methodo...

background: radiation shielding properties is an important for a material wish can be used the photon attenuation coefficients of clay produced using different rate of boron have been measured for the purpose of radioactive waste disposal. materials and methods: the measurement has been performed using gamma spectrometer contains nai (tl) detector at the photon energies of 662, 1173 and 1332 ke...

A new formulation for wave propagation in an anelastic medium is developed. The phenomenological theory of linear viscoelasticity provides the basis for describing the attenuation and dispersion of seismic waves. The concept of a spectrum of relaxation mechanisms represents a convenient description of the constitutive relation of linear viscoelastic solids; however, Boltzmann's superposition pr...

According to the ‘environmental selection’ hypothesis, the physical characteristics of environments influence the evolution of long-range acoustic signals by favouring those properties that decrease sound attenuation and distortion with distance. Different environments could favour different acoustic properties and therefore contribute to the intraand interspecific variation of calls. In the pr...

I present a frequency-independent 3D seismic attenuation model (indicated by Q−1 P ) for the crust of the Salton trough and the adjacent regions in southeastern southern California. The simul2000 tomographic algorithm was used to invert the frequency-independent attenuation operator t values measured from amplitude spectra of 23,378 P-wave arrivals of 1203 events through a recently developed 3D...