Frequency Selective Surfaces as Near Infrared Electro-Magnetic Filters for Thermophotovoltaic Spectral Control

Frequency selective surfaces (FSS) effectively filter electromagnetic radiation in the microwave band (1 mm to 100 mm). Interest exists in extending this technology to the near infrared (1 {micro}m to 10 {micro}m) for use as a filter of thermal radiation in thermophotovoltaic (TPV) direct energy conversion. This paper assesses the ability of FSS to meet the strict spectral performance requirements of a TPV system. Inherent parasitic absorption, which is the result of the induced currents in the FSS metallization, is identified as a significant obstacle to achieving high spectral performance

Growth and characterization of semiconductor nanoparticles in porous sol-gel films

Published versio

Thermal decomposition as route for silver nanoparticles

Single crystalline silver nanoparticles have been synthesized by thermal decomposition of silver oxalate in water and in ethylene glycol. Polyvinyl alcohol (PVA) was employed as a capping agent. The particles were spherical in shape with size below 10 nm. The chemical reduction of silver oxalate by PVA was also observed. Increase of the polymer concentration led to a decrease in the size of Ag particles. Ag nanoparticle was not formed in the absence of PVA. Antibacterial activity of the Ag colloid was studied by disc diffusion method

Further evidence for a variable fine-structure constant from Keck/HIRES QSO absorption spectra

[Abridged] We previously presented evidence for a varying fine-structure constant, alpha, in two independent samples of Keck/HIRES QSO spectra. Here we present a detailed many-multiplet analysis of a third Keck/HIRES sample containing 78 absorption systems. We also re-analyse the previous samples, providing a total of 128 absorption systems over the redshift range 0.2<z_abs<3.7. All three samples separately yield consistent, significant values of da/a. The analyses of low- and high-z systems rely on different ions/transitions with very different dependencies on alpha, yet they also give consistent results. We identify additional random errors in 22 high-z systems characterized by transitions with a large dynamic range in apparent optical depth. Increasing the statistical errors on da/a for these systems gives our fiducial result, a weighted mean da/a=(-0.543+/-0.116)x10^-5, representing 4.7-sigma evidence for a smaller weighted mean alpha in the absorption clouds. Assuming that da/a=0 at z_abs=0, the data marginally prefer a linear increase in alpha with time: dota/a=(6.40+/-1.35)x10^-16 yr^-1. The two-point correlation function for alpha is consistent with zero over 0.2-13 Gpc comoving scales and the angular distribution of da/a shows no significant dipolar anisotropy. We therefore have no evidence for spatial variations in da/a. We extend our previous searches for possible systematic errors, identifying atmospheric dispersion and isotopic structure effects as potentially the most significant. However, overall, known systematic errors do not explain the results. Future many-multiplet analyses of QSO spectra from different telescopes and spectrographs will provide a now crucial check on our Keck/HIRES results.Comment: 31 pages, 25 figures (29 EPS files), 8 tables. Accepted by MNRAS. Colour versions of Figs. 6, 8 & 10 and text version of Table 3 available at http://www.ast.cam.ac.uk/~mim/pub.htm