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Diagnostic techniques for photonic materials based on Raman and Brillouin spectroscopies

The elastic and vibrational properties of a material,bulk or planar waveguide,are studied by Brillouin and Raman spectroscopy to follow the process of nanocrystals growth in glass-ceramics. The nanoparticles cause the appearance,in the low fre-quency Raman spectrum,of characteristic peaks,whose position depends on the size of the crystals. At the same time,sharp crystal peaks,due to optical phonons,appear in the Raman spectra,allowing the determination of the nucleated phase,and a frequency shift of the Brillouin peaks is observed.     

Modelling the time-dependent transmission rate for porcine circovirus type 2 (PCV2) in pigs using data from serial transmission experiments

Six successive transmission trials were carried out from 4 to 39 days post inoculation (DPI) to determine the features of the infectious period for PCV2-infected pigs. The infectiousness of inoculated pigs, assessed from the frequency of occurrence of infected pigs in susceptible groups in each contact trial, increased from 4 to 18 DPI (0, 7 and 8 infected pigs at 4, 11 and 18 DPI, respectively) and then decreased slowly until 39 days post infection (4, 2 and 1 pigs infected at 25, 32 and 39 DPI, respectively). The estimated time-dependent infectiousness was fitted to three unimodal function shapes (gamma, Weibull and lognormal) for comparison. The absence of infected pigs at 4 DPI revealed a latency period between 4 and 10 DPI. A sensitivity analysis was performed to test whether the parametric shape of the transmission function influenced the estimations. The estimated time-dependent transmission rate was implemented in a deterministic SEIR model and validated by comparing the model prediction with external data. The lognormal-like function shape evidenced the best quality of fit, leading to a latency period of 8 days, an estimated basic reproduction ratio of 5.9 [1.8,10.1] and a mean disease generation time of 18.4 days [18.2, 18.5].     

Insight into silicate-glass corrosion mechanisms

The remarkable chemical durability of silicate glass makes it suitable for a wide range of applications. The slowdown of the aqueous glass corrosion kinetics that is frequently observed at long time is generally attributed to chemical affinity effects (saturation of the solution with respect to silica). Here, we demonstrate a new mechanism and highlight the impact of morphological transformations in the alteration layer on the leaching kinetics. A direct correlation between structure and reactivity is revealed by coupling the results of several structure-sensitive experiments with numerical simulations at mesoscopic scale. The sharp drop in the corrosion rate is shown to arise from densification of the outer layers of the alteration film, leading to pore closure. The presence of insoluble elements in the glass can inhibit the film restructuring responsible for this effect. This mechanism may be more broadly applicable to silicate minerals.     

Evaluation of cross‐linking after accelerated photo‐ageing of silicone rubber

Silicone formulations based on polydimethylsiloxane (PDMS) were investigated by using a number of analytical techniques. Horizontal attenuated total reflectance Fourier‐transform infrared (HATR‐FTIR) spectroscopy studies have confirmed the stability of these materials towards photo‐oxidation. No significant oxygenated products were detected after 5000 h of accelerated photo‐ageing. However, by using thermoporosimetry, hardness measurements and densitometry, an important vulnerability of these formulations towards the cross‐linking reactions provoked by UV visible radiation was identified. Thermoporosimetry, using the solid‐solid cyclohexane transition as a textural probe, was also used to visualize the profile of cross‐linking inside the materials by calculation of the mesh size distribution in successive slices of 40 µm in thickness. Copyright © 2003 Society of Chemical Industry     

Comparison of visible and near infrared reflectance spectroscopy to discriminate between pasture-fed and concentrate-fed lamb carcasses

We compared visible and near infrared spectroscopy to distinguish pasture-fed (P) from stall concentrate-fed (S) lamb carcasses. A total of 120 P and 139 S lambs were used. The reflectance spectrum of perirenal fat was measured at wavelengths between 400 and 700 nm using a portable spectrophotometer, and at wavelengths between 400 and 2500 nm using a laboratory monochromator NIRSystem. In method W_450–510, the reflectance data were used at wavelengths between 450 and 510 nm. In methods W_400–700 and W_400–2500, a multivariate analysis was performed over the full set of reflectance data, at wavelengths in the range 400–700 nm and 400–2500 nm, respectively. The proportion of correctly classified P lambs was 89.1%, 90.8% and 97.5% for W_450–510, W_400–700 and W_400–2500, W_400–2500 performing best. The proportion of correctly classified S lambs was not significantly different between methods (98.6%, 98.6% and 97.8% for W_450–510, W_400–700 and W_400–2500, respectively).     

Er^3＋-activated silica inverse opals synthesized by the solgel method

We present the details of the sol-gel processing used to realize inverse silica opal,where the silica was activated with 0.3 mol% of Er3 ions. The template(direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3 -activated silica inverse opal was obtained infiltrating,into the void of the template,the silica sol doped with Er3 ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess a fcc structure with a air hollows of about 210 nm and a photonic band gap,in the visible range,was observed from reflectance measurements. Spectroscopic properties of Er3 -activated silica inverse opal were investigated by luminescence spectroscopy,where,upon excitation at 514.5 nm,an emission of 4I13/2 → 4I15/2 of Er3 ions transition with a 21 nm bandwidth was observed. Moreover the 4I13/2 level decay curve presents a single-exponential profile,with a measured lifetime of 18 ms,corresponding a high quantum efficiency of the system.