Smart windows offer an opportunity to reduce energy consumption. However, the use of multiple optical elements, such as low emittance coatings and electrochromic devices, is detrimental to the ...luminous transmittance of these high performance windows. Although the addition of antireflective coatings has helped to reduce this problem, some elements, such as high index of refraction materials still give rise to loss of light. We show that replacing the single WO
3 active coating, the main component of an electrochromic device, by an appropriately designed electrochromic interference filter can significantly increase the transmittance. This active filter is based on a stack of dense and porous WO
3 layers. We first study the effect of porosity on the physical and electrochromic properties of WO
3 prepared by radio frequency magnetron sputtering. We demonstrate that the overlying dense coating does not inhibit the coloration of the underlying porous coating. The best performing films are combined into a 27 layer quarter-wave interference filter which is shown to cycle between bleached and colored states, while providing attractive transmission. Finally, we discuss various filter designs which can increase the transmission of an electrochromic device in its bleached state, as well as the potential use of active filters for optical security devices possessing two levels of authentication.
Bryophytes are ecologically essential to northern ecosystem restoration after disturbance. In this study, native bryophytes were used to revegetate two Arctic restoration sites. Different propagation ...types (small, medium, large fragments) and substrates (crushed rock, lake sediment, processed kimberlite in Canada; volcanic silt loam and crushed lava rock in Iceland) with two erosion control treatments (with and without cheesecloth) were evaluated. After two growing seasons, large bryophyte fragments resulted in the greatest density and total and live cover with erosion control and medium fragments resulted in the highest density and species occurrence without erosion control. Erosion control significantly increased live cover, total cover, species occurrence, and density, including a tempering effect on soil volumetric water content and temperature. Substrates with more heterogeneous surfaces (crushed rock, volcanic silt loam, crushed lava rock) yielded higher live cover, density, and spontaneous colonization than more homogeneous substrates (processed kimberlite, lake sediment) and can be more suitable for use in arctic ecosystems revegetation. The positive outcomes in both Canada and Iceland led to the conclusion that bryophyte propagation with large to medium fragments, erosion control with cheesecloth, and substrates with heterogeneous surfaces would be effective restoration approaches where bryophyte revegetation is a focus.
Gold nanoparticles embedded in a silica matrix were irradiated with 2 to 40MeV Cu or Si ions at fluences ranging from 1×1013 to 4×1015 ions/cm2, and their deformation from spheres to prolate ...ellipsoids with major axis parallel to the ion beam was studied using P and S polarized light. For fixed ion energy, the longitudinal surface plasmon resonance (SPR) at 520nm is red-shifted with an increase of the ion fluence up to a certain value where it reaches a plateau indicating that a maximum aspect ratio is obtained. This saturation in the wavelength shift was found to depend on the ion energy and reaches a maximum of 40nm. The SPR shift was also used to measure the electronic stopping power dependent deformation rate and to deduce the electronic stopping power threshold of (1.9±1.3) keV/nm required for shape transformation of the embedded gold nanoparticles. Ion track diameters of 0.18 to 1.4nm were inferred from the fluence dependence of the SPR shift. Analysis by transmission electron microscopy shows that large (d>10nm) particles are more elongated than smaller ones. Our data are consistent with a mechanism of gold nanoparticle elongation requiring both the silica matrix and the nanoparticles to melt following the passage of the swift heavy ion and with elongation being due to the relief of stress in the gold nanoparticle which had built up as a consequence of the deformation of the surrounding silica matrix.
► We irradiated gold nanoparticles embedded in silica with swift heavy ions. ► Such treatment changes the shape of the particles, from spherical to nano-rods. ► Irradiation of the silica matrix leads to anisotropic growth, so-called hammering. ► Stress applied by the deformed silica onto the gold nanoparticles deforms them.
The High Frequency Instrument of Planck will map the entire sky in the millimeter and sub-millimeter domain from 100 to 857 GHz with unprecedented sensitivity to polarization (ΔP/Tcmb ~ 4 × 10-6 ...for P either Q or U and Tcmb $\simeq$ 2.7 K) at 100, 143, 217 and 353 GHz. It will lead to major improvements in our understanding of the cosmic microwave background anisotropies and polarized foreground signals. Planck will make high resolution measurements of the E-mode spectrum (up to $\ell$ ~ 1500) and will also play a prominent role in the search for the faint imprint of primordial gravitational waves on the CMB polarization. This paper addresses the effects of calibration of both temperature (gain) and polarization (polarization efficiency and detector orientation) on polarization measurements. The specific requirements on the polarization parameters of the instrument are set and we report on their pre-flight measurement on HFI bolometers. We present a semi-analytical method that exactly accounts for the scanning strategy of the instrument as well as the combination of different detectors. We use this method to propagate errors through to the CMB angular power spectra in the particular case of Planck-HFI, and to derive constraints on polarization parameters. We show that in order to limit the systematic error to 10% of the cosmic variance of the E-mode power spectrum, uncertainties in gain, polarization efficiency and detector orientation must be below 0.15%, 0.3% and 1° respectively. Pre-launch ground measurements reported in this paper already fulfill these requirements.
Spider silks exhibit remarkable properties, among which the so-called supercontraction, a physical phenomenon by which fibers undergo a longitudinal shrinkage and a radial swelling when exposed to ...water. The process is marked by a significant decrease in chain orientation resulting from plasticisation of the amorphous phase. Despite several studies that determined the Hermans orientation function, more quantitative data are required to be able to describe theoretically the macroscopic water-induced shrinkage from molecular reorganization. Here, we have examined the supercontraction of the major ampullate silk single fibers of Nephila clavipes (Nc) and Araneus diadematus (Ad) using polarized Raman spectromicroscopy. We determined the order parameters, the orientation distribution and the secondary structure content. Our data suggest that supercontraction induces a slight increase in β-sheet content, consistently with previous works. The β-sheet orientation is slightly affected by supercontraction compared to that of the amorphous phase, which becomes almost isotropic with shrinkage. Despite an initially lower orientation level, the Ad fiber shows a larger orientation decrease than Nc, consistently with its higher shrinkage amplitude. Although they share similar trends, absolute values of the orientation parameters from this work differ from those found in the literature. We took advantage of having determined the distribution of orientation to estimate the amplitude of shrinkage from changes in macromolecular size resulting from molecular disorientation. Our calculations show that more realistic models are needed to correlate molecular reorientation/refolding to macroscopic shrinkage. This work also underlines that more accurate data relative to molecular orientation are necessary.
We present submillimetre observations obtained using the balloon-borne experiment PRONAOS/SPM, from 200 to 600 μm with an angular resolution of 2–3.5′, of a quiescent dense filament (typically $A_{V} ...\sim 4$) in the Taurus molecular complex. This filament, like many other molecular clouds, presents a deficit in its IRAS $I_{\rm 60 \,\mu m}/I_{\rm 100 \,\mu m}$ flux ratio in comparison with the diffuse interstellar medium. We show, from the combination of the PRONAOS/SPM and IRAS data, that, inside the filament, there is no evidence for emission from the transiently heated small particles responsible for the 60 μm emission, and that the temperature of large grains in thermal equilibrium with the radiation field is reduced in the inner parts of the filament. The temperature is as low as 12.1$^{+0.2}_{-0.1}$ K with $\beta=1.9\pm 0.2$ (or 12.0$^{+0.2}_{-0.1}$ K using $\beta=2$) toward the filament centre. These phenomena are responsible for the IRAS colour ratio observed toward the filament. In order to explain this cold temperature, we have developed a model for the emission from the filament using star counts from the 2MASS catalog as an independent tracer of the total column density and a radiative transfer code. We first use the optical properties of the dust from the standard model of Désert et al. (CITE). The computed brightness profiles fail to reproduce the data inside the filament, showing that the dust properties change inside the filament. An agreement between data and model can be found by removing all the transiently heated particles from the densest parts of the filament, and multiplying the submillimetre emissivity by a significant factor, 3.4$^{+0.3}_{-0.7}$ (for typically $n_{H}> 3 \pm 1\times 10^3$ cm-3, $A_{V} > 2.1\pm 0.5$). We show that grain-grain coagulation into fluffy aggregates may occur inside the filament, explaining both the deficit of small grain abundance and the submillimetre emissivity enhancement of the large grains.
The Planck High Frequency Instrument (HFI) surveyed the sky continuously from August 2009 to January 2012. Its noise and sensitivity performance were excellent (from 11 to 40 aW Hz-1), but the rate ...of cosmic-ray impacts on the HFI detectors was unexpectedly higher than in other instruments. Furthermore, collisions of cosmic rays with the focal plane produced transient signals in the data (glitches) with a wide range of characteristics and a rate of about one glitch per second. A study of cosmic-ray impacts on the HFI detector modules has been undertaken to categorize and characterize the glitches, to correct the HFI time-ordered data, and understand the residual effects on Planck maps and data products. This paper evaluates the physical origins of glitches observed by the HFI detectors. To better understand the glitches observed by HFI in flight, several ground-based experiments were conducted with flight-spare HFI bolometer modules. The experiments were conducted between 2010 and 2013 with HFI test bolometers in different configurations using varying particles and impact energies. The bolometer modules were exposed to 23 MeV protons from the Orsay IPN Tandem accelerator, and to 241Am and 244Cm α-particle and 55Fe radioactive X-ray sources. The calibration data from the HFI ground-based preflight tests were used to further characterize the glitches and compare glitch rates with statistical expectations under laboratory conditions. Test results provide strong evidence that the dominant family of glitches observed in flight are due to cosmic-ray absorption by the silicon die substrate on which the HFI detectors reside. Glitch energy is propagated to the thermistor by ballistic phonons, while thermal diffusion also contributes. The average ratio between the energy absorbed, per glitch, in the silicon die and thatabsorbed in the bolometer is equal to 650. We discuss the implications of these results for future satellite missions, especially those in the far-infrared to submillimeter and millimeter regions of the electromagnetic spectrum.
Measurement of cosmic microwave background polarization is today a major goal of observational cosmology. The level of the signal to measure, however, makes it very sensitive to various systematic ...effects. In the case of Planck, which measures polarization by combining data from various detectors, the beam asymmetry can induce a conversion of temperature signals to polarization signals or a polarization mode mixing. In this paper, we investigate this effect using realistic simulated beams and propose a first-order method to correct the polarization power spectra for the induced systematic effect.
Planck is a European Space Agency (ESA) satellite, launched in May 2009, which will map the cosmic microwave background anisotropies in intensity and polarisation with unprecedented detail and ...sensitivity. It will also provide full-sky maps of astrophysical foregrounds. An accurate knowledge of the telescope beam patterns is an essential element for a correct analysis of the acquired astrophysical data. We present a detailed description of the optical design of the High Frequency Instrument (HFI) together with some of the optical performances measured during the calibration campaigns. We report on the evolution of the knowledge of the pre-launch HFI beam patterns when coupled to ideal telescope elements, and on their significance for the HFI data analysis procedure.
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