2,365 research outputs found
Two-point derivative dispersion relations
A new derivation is given for the representation, under certain conditions,
of the integral dispersion relations of scattering theory through local forms.
The resulting expressions have been obtained through an independent procedure
to construct the real part, and consist of new mathematical structures of
double infinite summations of derivatives. In this new form the derivatives are
calculated at the generic value of the energy and separately at the
reference point that is the lower limit of the integration. This new form
may be more interesting in certain circumstances and directly shows the origin
of the difficulties in convergence that were present in the old truncated forms
called standard-DDR. For all cases in which the reductions of the double to
single sums were obtained in our previous work, leading to explicit
demonstration of convergence, these new expressions are seen to be identical to
the previous ones. We present, as a glossary, the most simplified explicit
results for the DDR's in the cases of imaginary amplitudes of forms
, that cover the cases of practical interest in
particle physics phenomenology at high energies. We explicitly study the
expressions for the cases with negative odd integers, that require
identification of cancelation of singularities, and provide the corresponding
final results.Comment: The final publication is available at
http://scitation.aip.org/content/aip/journal/jm
A new approach to the epsilon expansion of generalized hypergeometric functions
Assumed that the parameters of a generalized hypergeometric function depend
linearly on a small variable , the successive derivatives of the
function with respect to that small variable are evaluated at
to obtain the coefficients of the -expansion of the function. The
procedure, quite naive, benefits from simple explicit expressions of the
derivatives, to any order, of the Pochhammer and reciprocal Pochhammer symbols
with respect to their argument. The algorithm may be used algebraically,
irrespective of the values of the parameters. It reproduces the exact results
obtained by other authors in cases of especially simple parameters. Implemented
numerically, the procedure improves considerably the numerical expansions given
by other methods.Comment: Some formulae adde
The direct boundary element method: 2D site effects assessment on laterally varying layered media (methodology)
The Direct Boundary Element Method (DBEM) is presented to solve the elastodynamic field equations in 2D, and a complete comprehensive implementation is given. The DBEM is a useful approach to obtain reliable numerical estimates of site effects on seismic ground motion due to irregular geological configurations, both of layering and topography. The method is based on the discretization of the classical Somigliana's elastodynamic representation equation which stems from the reciprocity theorem. This equation is given in terms of the Green's function which is the full-space harmonic steady-state fundamental solution. The formulation permits the treatment of viscoelastic media, therefore site models with intrinsic attenuation can be examined. By means of this approach, the calculation of 2D scattering of seismic waves, due to the incidence of P and SV waves on irregular topographical profiles is performed. Sites such as, canyons, mountains and valleys in irregular multilayered media are computed to test the technique. The obtained transfer functions show excellent agreement with already published results
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