Use of a range scaling method to determine alanine/water stopping power ratios

A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level).     

Application of INAA to reveal the chemical evolution of selected volcanic eruptiva from Santorini, Greece

The pumiceous products of the large-scale explosive eruptions at Santorini show a high grade of similarity in their optical appearance as well as in their chemical composition. The demand for a clear classification of these eruption products was raised from archaeological research, where pumice can be interpreted as a “post-eruption” time marker. The aim of this work was to find elements that underwent significant changes because of geochemical processes and that could be indicative for a distinction of pumice produced by the five major explosive eruptions. INAA of 25 elements allows a clear classification and contributes new information to the chemical evolution of Santorini volcano. This revised version was published online in July 2006 with corrections to the Cover Date.     

Absorption and propagation of light in quaterthiophene crystals

We examine absorption of light in quaterthiophene crystals for different directions of the ray and wave-normal vector after refraction on the vacuum/crystal interface. Experimental non-normal incidence spectra are reported where different absorption bands show different behaviour as a function of the angle of incidence. This allows to identify those originating from the b_u Frenkel exciton state.     

Enhancement of measurement sensitivity in determination of changes in the shape of a wavefront by holographic lateral-shearing interferometry

A method for increasing measurement sensitivity in the visualization of dynamics of changes in wavefront shape with the use of holographic lateral-shearing interferometry is considered. At the first stage of this method, a photograph of a reference shear interferogram obtained with tuning to closely spaced fringes is recorded under linear conditions. After chemical treatment, the photograph of the reference shear interferogram is installed in exactly its initial position. At the second stage, a series of photographs of lateral-shear interferograms of the wavefront under study is recorded under nonlinear conditions using the photograph of the reference interferogram. The photographs of the lateral-shear interferograms are optically processed by two coherent beams with selection of the highest diffraction orders, which makes it possible to visualize the dynamic component of the wavefront deformation with an increase in the measurement sensitivity (the static component is excluded in this case). The effect of the degree of nonlinearity of photograph recording on the range in which the measurement sensitivity can be controlled during the optical processing of a pair of matched photographs or one double-exposure photograph of interferograms recorded at different values of a lateral shift is analyzed.     

Study of the dynamic structure factor of strong glasses

The dynamic structure factors (DSFs) of several strong glasses (SF6, SF10, BK7, SUPRASIL) measured by Brillouin light scattering spectroscopy are reported. Spectra have been collected, at and above room temperature, at two scattering angles, θ=90° and θ=180° corresponding to exchanged wavevector q values ranging from 0.0256 to 0.0448 nm⁻¹. In particular we find that the isotropic spectral lineshapes are in all cases well described by the simple hydrodynamic theory of an amorphous solid. The width of the Brillouin peaks are found to be consistent with the predicted q² dependence at both investigated temperatures. This damping is however found to account only partially for the strong asymmetry of the Brillouin line clearly visible on a logarithmic intensity scale. As a matter of fact there is an excess intensity in the very low frequency plateau underlying the central component. The height of this plateau and hence the entire lineshape is well reproduced if a relaxation process is taken into account in the hydrodynamic equations. Owing to the intense elastic scattering we are able to determine unambiguously only the ratio between amplitude and characteristic time of this process which quantifies the sound dispersion to be of the order of a few percent in all samples. The temperature dependence of the parameters indicates that this relaxation cannot be attributed to thermally activated relaxation phenomena. These general findings favorably compare with molecular dynamics simulation results on similar systems.     

On Non-Continuous Dirichlet Processes

We introduce here some Itô calculus for non-continuous Dirichlet processes. Such calculus extends what was known for continuous Dirichlet processes or for semimartingales. In particular we prove that non-continuous Dirichlet processes are stable under C ¹ transformation.     

Scattering of excited atoms due to ion bombardment of metals

The spectrum and the spatial distribution of the emission of scattered particles upon bombardment of Be, Ti, Ta, and W with H and He ions were studied. The quantum yield and the velocity and angular distributions of the scattered excited particles were measured. Computer simulation of the scattering of H ions and He ions from the metals under study was performed with the use of the program TRIM-95. Agreement is observed between the calculated and experimentally measured angular distributions of the scattered particles.     

Design of a wideband microstrip antenna and the use of artificial neural networks in parameter calculation

This paper deals with the design of a multi-slot hole-coupled microstrip antenna on a substrate of 2 mm thickness that gives multi-frequency (wideband) characteristics. The Method of Moments (MoM)-based IE3D software was used to simulate the results for return loss, VSWR, the Smith chart, and the radiation patterns. A tunnel-based artificial neural network (ANN) was also developed to calculate the radiation patterns of the antenna. The radiation patterns were measured experimentally at 10.5 GHz and 12 GHz. The experimental results were in good agreement with the simulated results from IE3D and those of the artificial neural network. A new method of using a genetic algorithm (GA) in an artificial neural network is also discussed. This new method was used to calculate the resonant frequency of a single-shorting-post microstrip antenna. The resonant frequency calculated using the genetic-algorithm-coupled artificial neural network was compared with the analytical and experimental results. The results obtained were in very good agreement with the experimental results.     

Terahertz characterisation of building materials

To obtain realistic models for propagation channels in future pico-cellular indoor terahertz communication systems it is necessary to know the reflective properties of building materials found in a typical office environment. The angular dependent reflection coefficients of different building materials were determined using terahertz time-domain spectroscopy in transmission geometry and Fresnel's equations. This approach is more efficient than a set of measurements in reflection geometry for different angles. Verification of the method with a set of such reflection measurements shows an excellent agreement.     

An efficient nonlinear circuit simulation technique

This paper proposes a novel method for the analysis and simulation of integrated circuits (ICs) with the potential to greatly shorten the IC design cycle. The circuits are assumed to be subjected to input signals that have widely separated rates of variation, e.g., in communication systems, an RF carrier modulated by a low-frequency information signal. The proposed technique involves two stages. Initially, a particular order result for the circuit response is obtained using a multiresolution collocation scheme involving cubic spline wavelet decomposition. A more accurate solution is then obtained by adding another layer to the wavelet series approximation. However, the novel technique presented here enables the reuse of results acquired in the first stage to obtain the second-stage result. Therefore, vast gains in efficiency are obtained. Furthermore, a nonlinear model-order reduction technique can readily be used in both stages making the calculations even more efficient. Results will highlight the efficacy of the proposed approach