Scattering of gravitational radiation

Aims.The effect of gravitational microlensing on the intensity of gravitational radiation as it propagates through an inhomogeneous medium is considered. Lensing by both stars and a power law spectrum of density perturbations is examined. Methods.The long wavelengths characteristic of gravitational radiation mandate a statistical, physical-optics approach to treat the effect of the lensing. Results.A model for the mass power spectrum of a starfield, including the effects of clustering and allowing for a distribution of stellar masses, is constructed and used to determine both the amplitude of fluctuations in the gravitational wave strain and its associated temporal fluctuation spectrum. For a uniformly distributed starfield the intensity variance scales linearly with stellar density, σ, but is enhanced by a factor \ga$\sigma r_{\rm F}^2$ when clustering is important, where rF is the Fresnel scale. The effect of lensing by a power law mass spectrum, applicable to lensing by small scale fluctuations in gas and dark matter, is also considered. For power law mass density spectra with indices steeper than -2 the wave amplitude exhibits rms fluctuations $1.3 \langle \Delta \Sigma^2\rangle^{1/4} (D_{\rm eff}/1\,{\rm Gpc})^{1/2}$%, where $\langle \Delta \Sigma^2 \rangle$ is the variance in the mass surface density measured in $M_\odot^2 \,{\rm pc}^{-4}$ and Deff is the effective distance to the lensing medium. For shallower spectra the amplitude of the fluctuations depends additionally on the inner length scale and power law index of the density fluctuations. The intensity fluctuations are dominated by temporal fluctuations on long timescales. For lensing material moving at a speed v across the line of sight the fluctuation timescale exceeds $v^{-1} (D_{\rm eff} \lambda)^{1/2}$. Lensing by small scale structure induces at most ≈15% rms variations if the line of sight to a gravitational wave source intersects a region with densities ~$100~M_\odot\,{\rm pc}^{-2}$, which are typically encountered in the vicinity of galaxy clusters

Reflexões sobre a cor na conservação/restauração

This paper presents some research possibilities related to Colour as a main issue. Some examples of the study of colour in textiles and modern art are given. Architecture related issues are not covered.Este texto apresenta algumas possibilidades de pesquisa do tema Cor dentro das áreas de conservaçÃo/restauraçÃo de bens móveis. SÃo apresentados alguns exemplos do tema Cor relacionado aos tecidos e às artes contemporâneas. Questões específicas à Arquitetura nÃo sÃo abordadas

Expanding frontiers in materials chemistry and physics with multiple anions

During the last century, inorganic oxide compounds laid foundations for materials synthesis, characterization, and technology translation by adding new functions into devices previously dominated by main-group element semiconductor compounds. Today, compounds with multiple anions beyond the single-oxide ion, such as oxyhalides and oxyhydrides, offer a new materials platform from which superior functionality may arise. Here we review the recent progress, status, and future prospects and challenges facing the development and deployment of mixed-anion compounds, focusing mainly on oxide-derived materials. We devote attention to the crucial roles that multiple anions play during synthesis, characterization, and in the physical properties of these materials. We discuss the opportunities enabled by recent advances in synthetic approaches for design of both local and overall structure, state-of-the-art characterization techniques to distinguish unique structural and chemical states, and chemical/physical properties emerging from the synergy of multiple anions for catalysis, energy conversion, and electronic materials