Dynamic reflective color pixels based on molybdenum oxide.

Active materials which show phase transitions, usually known as Phase Change Materials (PCM), have paved the way to a new generation of reconfigurable plasmonic platforms. Tunable color devices have experienced a great development in the recent years. In particular, reflective color filters can take advantage from sunlight to select and reflect a specific resonant wavelength in the visible spectrum range. Reflective displays are usually structural color filters based on asymmetric Fabry-Perot cavities (AFPCs). For a fixed geometry, most of AFPCs filters generate static color, limiting their potential as tunable color devices. Dynamic color is achieved by introducing an active layer whose optical properties can be modulated by an external stimuli. In this paper, we propose AFPCs based on molybdenum oxide (MoOx, 2

Physically meaningful Monte Carlo approach to the four-flux solution of a dense multilayered system.

Due to the complexity of the radiative transfer equation, light transport problems are commonly solved using either models under restrictive assumptions, e.g., N-flux models where infinite lateral extension is assumed, or numerical methods. While the latter can be applied to more general cases, it is difficult to relate their parameters to the physical properties of the systems under study. Hence in this contribution we present, first, a review of a four-flux formalism to study the light transport problem in a plane-parallel system together with a derivation of equations to evaluate the different contributions to the total absorptance and, second, as a complementary tool, a Monte Carlo algorithm with a direct correspondence between its inputs and the properties of the system. The combination of the four-flux model and the Monte Carlo approach provides (i) all convergence warranties since the formalism has been established as a limit and (ii) new added capabilities, i.e., both temporal (transient states) and spatial (arbitrarily inhomogeneous media) resolution. The support between the theoretical model and the numerical tool is reciprocal since the model is utilized to set a Monte Carlo discretization criterion, while the Monte Carlo approach is used to validate the aforementioned model. This reinforces the parallel approach used in this work. Furthermore, we provide some examples to show its capabilities and potential, e.g., the study of the temporal distribution of a delta-like pulse of light.

Raman spectroscopy for wine analyses: A comparison with near and mid infrared spectroscopy.

Routine wine analysis are commonly employed to ensure the quality and safety standards, and to meet consumers' demands and legal requirements. In the last decades, efforts have been done in order to replace the traditional analytical techniques by vibrational spectroscopic techniques such as near infrared (NIR) and mid infrared (MIR) spectroscopy. The potential of these techniques has already been proved by several studies that revealed their ability for the determination of several wine parameters with high levels of precision and accuracy. Raman spectroscopy, (which is also a vibrational technique), was much less explored in the wine industry. In this work, the ability of Raman spectroscopy for routine wine analysis was evaluated and compared to NIR and MIR spectroscopy. Several calibration models were developed aiming the quantitative assessment of alcoholic strength, density, total acidity, volatile acidity, total sugars and pH in white wines. For this purpose, partial least squares (PLS) regression was employed, enabling the correlation between reference results and spectral information obtained by NIR, MIR and Raman spectroscopy. Results revealed the better performance of MIR spectroscopy for the measurement of alcoholic strength (R2P = 0.99, RMSEP=1.77%, and RER=56.41), and total acidity (R2P = 0.98, RMSEP=2.02%, and RER=49.46). Raman spectroscopy was pointed out as the most suitable for the determination of total sugars (R2P = 0.97, RMSEP=5.12%, RER=19.52), and pH (R2P = 0.90, RMSEP=4.92%, RER=20.34). The three techniques presented similar results in what referred the assessment of density (R2P = 0.96, 0.98, and 0.97, RMSEP=4.72%, 3.90%, and 3.80%, for Raman, MIR, and NIR respectively). None of the three techniques seemed to be suitable for the accurate determination of volatile acidity (R2P <0.78, RMSEP>14.32%, and RER<6.98).

Merging vibrational spectroscopic data for wine classification according to the geographic origin.

The wine making procedure is no longer a secret and it is nowadays well described and repeated around the world. Nevertheless, wines present unique features, strongly associated with their geographic origin. Classification systems were developed to catalogue wines according to the provenance, and are currently established by official authorities in order to ensure wine authenticity. The use of near-infrared (NIR), mid-infrared (MIR) and Raman spectroscopy for tracing the origin of wine samples, has been reported with different levels of success. This work evaluated and compared the performance of these techniques, as well as their joint use, in terms of geographic origin classification. NIR, MIR and Raman spectra of wine samples belonging to four Portuguese wine regions (Vinhos Verdes, Lisboa, Açores and Távora-Varosa) were analyzed by partial least squares discriminant analysis (PLS-DA). Results revealed the better suitability of MIR spectroscopy (87.7% of correct predictions) over NIR (60.4%) and Raman (60.8%). The joint use of spectral sets did not improve the predictive ability of the models. The best models were achieved by combining MIR and NIR spectra resulting in 86.7% of correct predictions. Multiblock partial least squares (MB-PLS) models were developed to further explore the combination of spectral data. Although these models did not improve the percentage of correct predictions, they demonstrated the higher contribution of MIR spectroscopic data, in the development of the models.

Extension of the Kubelka-Munk theory to an arbitrary substrate: a Monte Carlo approach.

In this work we review and-to some extent-upgrade one of the main theories of light flux through homogeneous isotropic media, namely, the Kubelka-Munk (K-M) theory, and in particular the later expansion made by Kubelka to obtain the reflectance of a specimen when a substrate lies underneath. We have completed this solution by calculating the transverse energy density in the specimen and the transmission of the whole. We show that this last result-compatible with Kubelka's upgrade for layered media-also allows for the calculation of the specimen/substrate absorption split. In order to validate these expressions, the results were reproduced by means of a Monte Carlo simulation working on a layered medium under the same assumptions as the K-M theory. Interestingly, the numerical procedure introduces new capabilities in the model regarding the history of any absorbed or outgoing elemental light beam, such as the recording of its time-of-flight through a given system.

Enhanced Magneto-Optical Edge Excitation in Nanoscale Magnetic Disks.

We report unexpected enhancements of the magneto-optical effect in ferromagnetic Permalloy disks of diameter D<400 nm. The effect becomes increasingly pronounced for smaller D, reaching more than a 100% enhancement for D=100 nm samples. By means of experiments and simulations, the origin of this effect is identified as a nanoscale ring-shaped region at the disk edges, in which the magneto-optically induced electric polarization is enhanced. This leads to a modification of the electromagnetic near fields and causes the enhanced magneto-optical excitation, independent from any optical resonance.

A simple and sensitive vortex assisted liquid-liquid microextraction method for the simultaneous determination of haloanisoles and halophenols in wines.

A vortex assisted liquid-liquid microextraction (VALLME) method was developed and optimised for the determination of the main compounds that can cause cork taint in wines, 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), 2,4,6-tribromoanisole (TBA) and pentachloroanisole (PCA); and their corresponding halophenolic precursors. Target compounds were determined by gas chromatography combined with a micro-electron capture detector (GC-µECD) system. Halophenol extraction and derivatisation processes were performed at the same time. To optimise the VALLME method, the extraction solvent was selected. Then, the other parameters of influence, such as volume of extraction solvent and derivatisation agent, salt addition and vortex time were optimised using a central composite design combined with desirability functions. Once the optimal conditions had been determined, the method was validated, showing satisfactory linearity (with correlation coefficients over 0.983), repeatability (below 10.0%) and reproducibility (below 11.2%). Detection limits obtained were lower than the olfactory threshold of the studied compounds, being similar or even lower than previously reported with the advantage of reducing the extraction time. The analysis of real wine samples demonstrated the applicability of the method. To our knowledge, this is the first time that VALLME has been applied for the simultaneous determination of haloanisoles and halophenols in wine.

Modulation of the phenolic composition and colour of red wines subjected to accelerated ageing by controlling process variables.

The aim of the present work was to evaluate the effect of the main factors conditioning accelerated ageing processes (oxygen dose, chip dose, wood origin, toasting degree and maceration time) on the phenolic and chromatic profiles of red wines by using a multivariate strategy based on experimental design methodology. The results obtained revealed that the concentrations of monomeric anthocyanins and flavan-3-ols could be modified through the application of particular experimental conditions. This fact was particularly remarkable since changes in phenolic profile were closely linked to changes observed in chromatic parameters. The main strength of this study lies in the possibility of using its conclusions as a basis to make wines with specific colour properties based on quality criteria. To our knowledge, the influence of such a large number of alternative ageing parameters on wine phenolic composition and chromatic attributes has not been studied previously using a comprehensive experimental design methodology.

Influence of pollutants in the magneto-dielectric response of silicon nanoparticles.

The influence of the degree of purity of a silicon nanoparticle on its resonances, either electric or magnetic, is assessed by using Mie theory as well as finite-element simulations. In particular, it is shown that the main effect of the increase of absorption due to the pollutants is observed in the magnetic resonances. Concerning Kerker's conditions for the directionality of the scattering [J. Opt. Soc. Am.73, 765 (1983)], it is found that both are strongly shifted when the material's purity is varied. Resistive losses confirm the quenching of magnetic resonances, showing that the region of influence in the magnetic dipole resonance is much larger than in the electric one, although it has been found that losses are not critical for silicon content over 99.50%.

Experimental design approach to evaluate the impact of oak chips and micro-oxygenation on the volatile profile of red wines.

A chemometric strategy based on combining an experimental design approach and response surface methodology was applied to gain further knowledge on the influence of chip maceration and micro-oxygenation related factors (oxygen doses, chip doses, wood origin, toasting degree and maceration time) on the volatile profile of red wines during the accelerated ageing process. The results obtained indicated that the volatile profile of wines could be modulated by applying different combinations of factor conditions. Thus, these results would be used to obtain wines with specific volatile profiles that would lead to particular olfactory attributes according to consumers' preferences. Moreover, it was shown that combining wood from different origins helped enhance the quality of the elaborated wines. To the best of our knowledge, this is the first time that an experimental design methodology has been applied to simultaneously evaluate the influence of five different ageing parameters on the volatile profile of red wines.

Comprehensive polarimetric analysis of Spectralon white reflectance standard in a wide visible range.

Since polarimetry has extended its use for the study of scattering from surfaces and tissues, Spectralon, a white reflectance standard, is acquiring the role of a polarimetric standard. Both the behavior of Spectralon as a Lambertian surface and its performance as a perfect depolarizer are analyzed in detail. The accuracy of our dynamic polarimeter, together with the polar decomposition to describe the Mueller matrix (MM) depolarizing action, combine to produce a powerful tool for the proper analysis of this scattering surface. Results allowed us to revisit, for confirmation or revision, the role of some MM elements, as described in the bibliography. The conditions under which it can be considered a good Lambertian surface are specified in terms of incidence and scattering angle and verified over a large wavelength range.

Classification of Spanish extra virgin olive oils by data fusion of visible spectroscopic fingerprints and chemical descriptors.

The potential of visible fingerprints and physical-chemical parameters in combination with multivariate data analysis was examined to classify extra virgin olive oils (EVOOs) from different Spanish regions according to their geographical origin. Firstly, spectral and quality parameters matrices were processed separately and subsequently were joined to evaluate the effect of synergy on the information obtained from the different methodologies. Linear discriminant analysis (LDA) and partial least squares discriminant analysis (PLS-DA) were performed as classification methods. The results revealed a perfect discrimination between the defined categories after performing PLS-DA on the Fused matrix, reaching 100% of correct classifications and showed a clear improvement in the overall prediction rates (92.5%), so that the effect of synergy was confirmed. These accurate results emphasise the feasibility of the proposed strategy and encourage the development of similar approaches based on visible spectroscopy in olive oil quality and traceability determination.

Quantum optical response of metallic nanoparticles and dimers.

The optical properties of metallic nanoparticles (NPs) can be described with analytical models based on fundamental quantum mechanical principles, of which the Drude model constitutes the classical limit. Here, we examine the plasmonic properties of silver and gold nanospheres and dimers, with radii ranging from 10 to 1 nm, extending from the classically described regime to the quantum size regime. We have studied the spectral extinction cross section by using the T-matrix method. The results indicate an increasingly substantial change in NP permittivity as the radius is reduced below 5 nm, showing a clear blueshift and weakening of the plasmon resonances for both silver and gold. As a consequence, we observe a dramatic change in the interaction of dimers, especially in the case of gold, where the introduction of quantum mechanically corrected optical properties quenches the plasmonic resonance and predicts an absence of the expected associated redshift.

Simultaneous determination of cork taint and Brett character responsible compounds in wine using ultrasound-assisted emulsification microextraction with solidification of floating organic drop.

In this study, ultrasound-assisted emulsification microextraction combined with solidification of floating organic drop method (USAEME-SFOD) has been proposed as a novel approach for the sensitive determination of haloanisoles and volatile phenols in wines. For this purpose, the influence of the different parameters affecting the procedure (type and volume of extraction solvent, temperature, time and ionic strength) was evaluated in order to optimise the efficiency of the process. Subsequently, the linearity, detection and quantification limits, precision, recoveries and applicability to real samples were studied, obtaining excellent method performance results. Moreover, USAEME-SFOD was compared with other liquid-liquid microextraction methods such as dispersive liquid-liquid microextraction (DLLME) and ultrasound-assisted emulsification microextraction (USAEME). This comparison study proved the suitability of USAEME-SFOD as an alternative to previously reported methods for the simultaneous determination of cork taint and Brett character responsible compounds in wines.

Optimisation of ultrasound-assisted emulsification microextraction method with solidification of floating organic drop for the analysis of cork taint responsible compounds in wine.

This paper presents the optimisation of a method based on ultrasound assisted-emulsification method (USAEME) combined with solidification of floating organic drop (SFOD) for the sensitive determination of cork taint responsible compounds in wine. Haloanisoles (2,4,6-trichloranisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), 2,4,6-tribromoanisole (TBA) and pentachloranisole (PCA)) and their halophenolic precursors were determined by gas chromatography with electron capture detection (GC-ECD). The derivatisation of the halophenols was performed simultaneously with the extraction. To perform the optimisation, the main parameters affecting both extraction and derivatisation were exhaustively studied in different steps. Once the extraction solvent and the pH and time conditions had been determined, experimental design was applied for the simultaneous study of the volumes of acetic anhydride and extraction solvent, temperature and ionic strength conditions. Then, the analytical characteristics of the optimised method were evaluated achieving satisfactory linearity (with correlation coefficients over 0.984), repeatability (below 10.7%) and inter-day precision (below 10.6%) for all target analytes. Moreover, detection limits found were similar or even lower than the olfactory threshold of the studied compounds. Finally, the applicability of the proposed method was tested by analysing real wine samples. To the best of our knowledge, this is the first time that USAEME-SFOD method has been used to determine cork taint responsible compounds in wine.

Ultrasound-assisted emulsification-microextraction for the sensitive determination of Brett character responsible compounds in wines.

In this study, a method based on ultrasound-assisted emulsification-microextraction (USAEME) was optimised for the determination of Brett character responsible compounds (4-ethylguaiacol (EG), 4-ethylphenol (EP), 4-vinylguaiacol (VG) and 4-vinylphenol (VP)) in wines. For this purpose, once the extraction solvent had been selected, the influence on the extraction efficiency of ratio between extraction solvent and sample volumes, temperature, ionic strength and time was studied using experimental design methodology. The optimum conditions found for USAEME of 5mL of wine were 160µL of chlorobenzene at 60°C during 5min without salt addition. Then, the analytical performance of the optimised USAEME procedure was evaluated. For all the studied compounds, the proposed method showed correlation coefficients over 0.984. Satisfactory repeatability (below 10%) and inter-day repeatability (below 11%) were obtained at different concentration levels and the method achieved detection limits similar or even lower than previously reported for these compounds in wines. Moreover, the applicability of the method was evaluated by the analysis of real samples. To our knowledge, this is the first time that USAEME has been applied to the determination of Brett character responsible compounds in wine.

Polar decomposition of the Mueller matrix: a polarimetric rule of thumb for square-profile surface structure recognition.

In this research, the polar decomposition (PD) method is applied to experimental Mueller matrices (MMs) measured on two-dimensional microstructured surfaces. Polarization information is expressed through a set of parameters of easier physical interpretation. It is shown that evaluating the first derivative of the retardation parameter, δ, a clear indication of the presence of defects either built on or dug in the scattering flat surface (a silicon wafer in our case) can be obtained. Although the rule of thumb thus obtained is established through PD, it can be easily implemented on conventional surface polarimetry. These results constitute an example of the capabilities of the PD approach to MM analysis, and show a direct application in surface characterization.

Directionality in scattering by nanoparticles: Kerker's null-scattering conditions revisited.

Since the first studies made by Kerker in the 1970s stating the conditions for null light scattering in certain directions by particles, such conditions have remained unquestioned. The increasing interest in scattering directionality by tuning the optical properties of materials demands a new analysis of this problem. In addition, as has been shown recently, one of Kerker's statements does not comply with the optical theorem. We propose corrected expressions for the null-scattering conditions that satisfy the optical theorem.

Development of a dispersive liquid-liquid microextraction method for the simultaneous determination of the main compounds causing cork taint and Brett character in wines using gas chromatography-tandem mass spectrometry.

A novel dispersive liquid-liquid microextraction (DLLME) method, coupled to gas chromatography-tandem mass spectrometry (GC-MS/MS), was developed for simultaneously determining the main compounds responsible for cork taint (2,4,6-trichloranisole (TCA), 2,3,4,6-tetrachloroanisole (TeCA), 2,4,6-tribromoanisole (TBA) and pentachloranisole (PCA)) and Brett character (4-ethylguaiacol (EG), 4-ethylphenol (EP), 4-vinylguaiacol (VG) and 4-vinylphenol (VP)) in wines. Optimisation of DLLME procedure was performed by evaluating the type of disperser and extraction solvents and the temperature and salt addition effects. The volumes of disperser and extraction solvents were also optimised by means of a central composite design combined with desirability functions. Under optimum conditions, 5 mL of wine were extracted with an extraction mixture consisting of 1.43 mL of acetone, and 173 µL of chloroform at room temperature. The analytical characteristics of the method were evaluated. Satisfactory linearity (with correlation coefficients over 0.992), repeatability (below 11.6%) and between-days precision (below 11.0%) were obtained for all target analytes. Detection limits attained were at similar levels or even lower than the olfactory threshold of the studied compounds. Finally, the developed method was successfully applied to the analysis of wine samples. To our knowledge, this is the first time that DLLME has been applied to simultaneously determine the compounds responsible for cork taint and Brett character in wine.

Recognition of volatile compounds as markers in geographical discrimination of Spanish extra virgin olive oils by chemometric analysis of non-specific chromatography volatile profiles.

Chromatographic profiles obtained by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography (GC) were processed as continuous and non-specific signals through multivariate analysis techniques in order to select and identify the most discriminate volatile marker compounds related to the geographical origin of extra virgin olive oils. The blind analysis of the chromatographic profiles was carried out on several steps including preliminary mathematical treatments, explorative analysis, feature selection and classification. The results obtained through the application of stepwise linear discriminant analysis (SLDA) method revealed a perfect discrimination between the different Spanish geographical regions considered (La Rioja, Andalusia and Catalonia). The assignment success rate was 100% in both classification and prediction by using cross validation procedure. In addition, it must be noted that the proposed strategy was able to verify the geographical origin of the samples involving only a reduced number of discriminate retention times selected by the stepwise procedure. This fact emphasizes the quality of the accurate results obtained and encourages the feasibility of similar procedures in olive oil quality and traceability studies. Finally, volatile compounds corresponding to the predictors retained were identified by gas chromatography-mass spectrometry (GC-MS) for a chemical interpretation of their importance in quality virgin olive oils.