Three methods are described in order to solve the canonical problem of the onedimensional reflection by a semi-infinite periodic row of identical scatterers. The exact reflection coefficient R is determined. The first method is associatedwith shifting the domain by a single period and subsequently considering two scatterers, one being a single scatterer and the second being the entire semi-infi...

−∞ log(z− s)d(log(1−|r(s)|2))+ π 4 + argΓ(iν(z))− argr(z). Here z0 = −x/(4t), Γ is the gamma function and the function r is the so-called reflection coefficient associated to the initial data q0, as described later in this section. Estimates on the size of the error term E (x,t) depend on the smoothness assumptions on q0. The above asymptotic form was first obtained in [10]. The nonlinear steep...

We derive dispersion estimates for solutions of the one-dimensional discrete perturbed Schrödinger and wave equations. In particular, we improve upon previous works and weaken the conditions on the potentials. To this end we also provide new results concerning scattering for one-dimensional discrete perturbed Schrödinger operators which are of independent interest. Most notably we show that the...

Using the conformal invariance of the SL(2, IR) ⊗ SO(1, 1) d−2 /SO(1, 1) coset models we calculate the conformally exact metric and dilaton, to all orders in the 1/k expansion. We consider both vector and axial gauging. We find that these cosets represent two different space–time geometries: (2d black hole)⊗IR d−2 for the vector gauging and (3d black string)⊗IR d−3 for the axial one. In particu...

The results of a measurement campaign conducted to determine the wideband behaviour of the radio channel assigned to Multimedia Wireless Systems are described in this paper. It has been found that small multipath components are present in the impulsive response of radio channels operating at 40 GHz with 80 MHz bandwidths. Multipath and delay spread are limited by the spatial filtering of direct...

The paper presents the results of a series of experiments conducted on physical models of Quarter-circle breakwater (QBW) in a two dimensional monochromatic wave flume. The purpose of the experiments was to evaluate the reflection coefficient Kr of QBW models of different radii (R) for different submergence ratios (d/hc), where d is the depth of water and hc is the height of the breakwater cres...