Measurement Of Absorption Coefficient Research Articles

Experimental investigation on optical and thermal properties of propylene glycol–water based nanofluids for direct absorption solar collectors

Direct absorption solar collectors (DASCs), which absorb solar radiation energy by the working medium, attract considerable attention. Because the addition of nanoparticles can improve the efficiency of solar collectors, nanofluids can be used as the working fluid. The stability, optical properties and thermal conductivity of propylene glycol–water based nanofluids containing TiO2, SiC and multiwalled carbon nanotubes (MWCNTs) are investigated in this paper. The results confirmed that nanofluids with surfactant exhibited good stability. By combining comprehensive transmittance, extinction coefficient and the solar-weighted absorption coefficient (Am) measurements, the transmittance of TiO2 and SiC nanofluids decreased from 65% at 0.025 vol% to about 5% at 0.2 vol%, and the light can hardly pass the MWCNT nanofluids over 0.05 vol%. MWCNT nanofluids had the highest Am, followed by SiC nanofluids and TiO2 nanofluids, which exhibited optimum properties even at low concentration. In addition, thermal conductivity of nanofluids increased with the growing volume fractions and temperature. MWCNT nanofluids had the maximum thermal conductivity (0.508 W/m k at 0.2 vol%) at 20 °C. This work provides valuable insights into the optical and thermal property enhancement of nanofluids for increasing the efficiency of DASCs.

The effect of changes in atmospheric conditions on the measured sound absorption coefficients of materials for scale model tests

The absorption of scale model materials is generally measured in a scaled reverberation chamber, with frequency scaled according to the scale factor. Moreover, the acoustic absorption of the chamber needs to be reduced, especially the absorption of air. It depends not only on the volume of the chamber, but also on the air parameters: pressure, temperature and relative humidity. Most frequently, in order to reduce the air absorption, the air inside the model is dried or replaced with dry nitrogen, or a digital air absorption compensation is used. Air-drying methods are time consuming and require specialised equipment; digital compensation may in turn result in errors, hence the question arises whether scaling the air absorption is really necessary to achieve good accuracy of the sound absorption coefficient measurements. In order to answer this question, the authors firstly ran a theoretical analysis of the issue based on ISO 9613-1 formulas describing air acoustic absorption. Based on this analysis, the influence of particular air parameters on the total air absorption in the model reverberation chamber, Aair (m2), was examined, together with the possibilities of scaling down the Aair values. This indicated, that the Aair may be scaled by manipulating temperature or relative air humidity. For the needs of the study, the relative air humidity was chosen, as it was used by the predecessors and may be easily manipulated. In the next step, the experimental studies of sound absorption coefficient measurements were conducted in a 1:8 scale reverberation chamber for representative specimens at different relative air humidity values (3–45%). The gathered data was then statistically analysed. The results showed that the influence of relative air humidity on the accuracy of sound absorption coefficient measurements in model tests is negligible and therefore such measurements can be performed in the ambient air humidity of the test room. As a consequence, a conclusion was drawn that the Aair value does not need to be scaled. Moreover, an attempt was made to identify the cause of the inaccuracy of the measurements – the analysis indicated that the values of the intensity attenuation coefficient m calculated according to ISO 9613-1, at model frequencies are not sufficiently accurate.

CCN activation properties at a tropical hill station in Western Ghats during south-west summer monsoon: Vertical heterogeneity

Cloud Condensation Nuclei (CCN) concentrations, aerosol number concentrations larger than about 3 nm (CN), and aerosol scattering and absorption coefficient measurements carried out at a hill station (Ponmudi, 8.8°N, 77.1°E, ~960 m amsl) located on Western Ghats and at a nearby coastal location (Thumba, 8.5°N, 76.9°E, ~3 m amsl) in the peninsular India during summer monsoon period are used to investigate the vertical heterogeneity in the activation properties and its association with the aerosol optical properties. CCN concentration over the hill station depicted high values during daytime and low values during nighttime, whereas an opposite pattern in CCN is observed over the coastal site. The intrinsic properties like CCN activation fraction and Twomey's empirical fit (k value) show insignificant diurnal variation over the hill station in contrast to the coastal location where the land-sea breeze circulation modify the prevailing airmasses over the sampling site. The percentage of CN acting as CCN at 0.4% supersaturation is about 25% at Ponmudi and is about 46% at Thumba. The higher scattering angstrom exponent observed at Ponmudi indicates the consistent presence of fine mode particles. CCN concentration at both Ponmudi and Thumba show a good linear correlation with scattering aerosol index. The association between CCN number concentrations and BC mass concentrations suggest that carbonaceous combustion sources influence CCN at Ponmudi. Even though marine airmass prevails over both locations due to the onset of the summer monsoon, CCN activation properties are distinct at the mean sea level and at an altitude of 1 km above the coastal region.

Calibration of an in-water multi-excitation fluorometer for the measurement of phytoplankton chlorophyll-a fluorescence quantum yield.

A multi-excitation fluorometer (MFL, JFE Advantech Co., Ltd.), originally designed to discriminate between phytoplankton species present within a population, has been redirected for use in fluorescence quantum yield (FQY) determination. While this calibration for apparent FQY requires no modification of the MFL, it is necessary to have an independent measurement of the spectral absorption coefficient of the subject fluid. Two different approaches to calibration were implemented. The primary method made use of reference fluorescent dye solutions of known quantum yield. The second method made use of acrylic fluorescent plaques and films. The two methods yielded consistent results, except in the 570 and 590 nm LED channels of the MFL. Application of the MFL in FQY determination is illustrated with an in situ Southern Ocean sample.

Absolute fluorescence and absorption measurements over a dynamic range of 106 with cavity-enhanced laser-induced fluorescence.

We present a novel spectroscopic technique that exhibits high sensitivity and a large dynamic range for the measurement of absolute absorption coefficients. We perform a simultaneous and correlated laser-induced fluorescence and cavity ring-down measurement of the same sample in a single pulsed laser beam. The combined measurement offers a large dynamic range and a lower limit of detection than either technique on its own. The methodology, dubbed cavity-enhanced laser-induced fluorescence, is developed and rigorously tested against the electronic spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell. We outline how the method can be used to determine absolute quantities, such as sample densities, absorption cross sections, and fluorescence quantum yields, particularly in spatially confined samples.

Error Sources and Distinctness of Materials Parameters Obtained by THz-Time Domain Spectroscopy Using an Example of Oxidized Engine Oil.

Gasoline engine oil (SAE 5W-20) was subjected to thermal oxidization (TO) for four periods of time (0 h, 48 h, 96 h and 144 h) and exposed to THz-time domain spectroscopy (TDS) measurement. Error contributions from various error sources, such as repeatability errors, assembly errors of the probe volume and errors caused by the TDS system were evaluated with respect to discernibility and significance of measurement results. The most significant error source was due to modifications of the TDS setup, causing errors in the range of 0.13% of the refractive index for samples with a refractive index around 1.467 and a probe volume length between 5 and 15 mm at 1 THz. The absorption coefficient error was in the range of 8.49% for an absorption around 0.6 cm−1. While the average of measurements taken with different setup configurations did not yield significant differences for different TO times, a single, fixed setup would be able to discern all investigated oil species across the entire frequency range of 0.5–2.5 THz. The absorption coefficient measurement showed greater discernibility than the measurement of the refractive index.

Influence of DC magnetron sputtering reaction gas on structural and optical characteristics of Ce-oxide thin films

The influence of the reaction gas composition during the DC magnetron sputtering process on the structural, chemical and optical properties of Ce-oxide thin films was investigated. X-ray diffraction (XRD) studies confirmed that all thin films exhibited a polycrystalline character with cubic fluorite structure for cerium dioxide. X-ray photoelectron spectroscopy (XPS) analyses revealed that cerium is present in two oxidation states, namely as CeO2 and Ce2O3, at the surface of the films prepared at oxygen/argon flow ratios between 0% and 7%, whereas the films are completely oxidized into CeO2 as the aforementioned ratio increases beyond 14%. Various optical parameters for the thin films (including an optical band gap in the range of 2.25–3.1 eV) were derived from the UV–Vis reflectance. A significant change in the band gap was observed as oxygen/argon flow ratio was raised from 7% to 14% and this finding is consistent with the high-resolution XPS analysis of Ce 3d that reports a mixture of Ce2O3 and CeO2 in the films. Density functional theory (DFT+U) implemented in the Cambridge Serial Total Energy Package (CASTEP) was carried out to simulate the optical constants of CeO2 clusters at ground state. The computed electronic density of states (DOSs) of the optimized unit cell of CeO2 yields a band gap that agrees well with the experimentally measured optical band gap. The simulated and measured absorption coefficient (α) exhibited a similar trend and, to some extent, have similar values in the wavelength range from 100 to 2500 nm. The combined results of this study demonstrate good correlation between the theoretical and experimental findings.

Ab-Initio Calculation of Spectral Absorption Coefficients in Molten Fluoride Salts with Metal Impurities

Molten salts have been proposed as coolants for numerous advanced reactor designs. It is envisioned that these reactors, both fluoride-salt–cooled high-temperature reactors and molten-salt–fueled reactors will operate at high temperatures, where the radiative heat transfer properties of the salts may be required for accurate heat transfer analysis. Experimental challenges have prevented the measurement of absorption coefficients in most salts. In an attempt to fill this gap in data, the Vienna Ab-Initio Simulation Package is used in the present research to calculate the absorption coefficient resulting from photoelectric interactions in numerous molten salts. Ab-initio molecular dynamics is used to generate the amorphous structures of a variety of salts. The pure halide salts LiF, FLiNaK, and FLiBe, are shown to be optically clear through a wide portion of the electromagnetic spectrum. Conversely, the transition metal fluoride salt KF-ZrF4 is shown to be substantially opaque. As chromium is a known impurity of concern from the corrosion of steels in reactor environments, the effect on absorption of low levels of chromium in an otherwise transparent salt is investigated and found to significantly increase absorption at relevant wavelengths.

Assessment of Scattering Error Correction Techniques for AC-S Meter in a Tropical Eutrophic Reservoir

Measurements of absorption coefficients (a(λ), in m−1) collected by spectrophotometers in situ are overestimated due to the scattering of the reflecting tube absorption meter. Accurate correction of these data is essential in order to characterize water bodies bio-optically, as well as retrieve the remote sensing reflectance (Rrs, in sr−1), when applying a forward model. There are various methods of scattering error correction; however, they were all developed for clear water. In this research, different techniques were attempted in order to define the most appropriate method for correcting a(λ) values acquired by an absorption and attenuation spectral (ac-s) meter (WET Labs Inc., Philomath, OR, USA) in a tropical eutrophic reservoir. Three methods recommended by the manufacturer of the ac-s meter were tested: “flat” or “baseline”, “constant fraction”, and “proportional”. These methods were applied to two datasets that were measured in May and October 2014. The flat technique exhibited the lowest errors, with an average normalized root mean square error (NRMSE) of 7.95%, and a mean absolute percentage error (MAPE) of 29.26% for May. Meanwhile, proportional was the most suitable technique for most of the samples in October, with a mean NRMSE of 11.19% and a MAPE of 31.03% for October. In addition, the proportional method maintained the shape of the a(λ) values better than the other methods. Despite that, both the flat and proportional methods gave a similar performance statistically. Moreover, the flat method produced the best estimations of chla content for both datasets. Therefore, this method is recommended to correct ac-s data in retrieving such phytoplankton pigments.

Effects of multiwall carbon nanotube addition on the corrosion resistance and underwater acoustic absorption properties of polyurethane coatings

In this study, the effect of multiwall carbon nanotube (CNT) addition on the anticorrosion and underwater acoustic absorption properties of polyurethane (PU) coatings was studied. The corrosion and mechanical properties of various coatings were characterized through electrochemical impedance spectroscopy, polarization curve measurement, salt spray tests, pull-off tests, and dynamic mechanical analysis. Underwater acoustic absorption properties were evaluated using an underwater acoustic impedance tube system comprising two hydrophones, a sound and vibration data acquisition module, a power amplifier, and a speaker. The results indicated that the corrosion resistance and adhesion strength of the PU coating was enhanced by adding 0.4 wt% CNTs. When additional CNTs were added (1 wt%), however, the corrosion rate of the coating increased. Measurement of the underwater sound absorption coefficient revealed that the underwater acoustic absorption properties of the PU + CNT composite coatings increased as the CNT content increased to 1 wt%.

Effect of the suspended ceiling with low-frequency resonant panel absorber on heavyweight floor impact sound in the building

This study investigated the effect of the suspended ceiling panel with low-frequency resonant panel absorber on heavyweight floor impact sound. The resonant panel absorber was designed with a perforated top panel, an air gap with or without glass wool, and a bottom panel to ensure a high absorption coefficient in the low-frequency range around 100 Hz. Absorption coefficient measurements were carried out first in the reverberation chamber for resonant panel absorbers varying with the hole diameter of the top panel, the thickness of the glass wool and the air gap between the top and bottom board. As a result, the glass wool had the greatest influence on the absorption coefficient, and the highest absorption coefficient of the resonant panel absorber was about 0.6 in the band of 100 Hz. Floor impact sounds after installing the suspended ceiling with the best resonant panel absorber were also measured in test building using heavyweight floor impact sound sources (bang machine and rubber ball) and compared with result for normal suspended ceiling with gypsum board. Heavyweight floor impact sound by the resonant panel absorber was decreased by 2 dB and 4 dB in single number quantity (Li,Fmax,Aw) for bang machine and rubber ball, respectively. In particular, the resonant panel absorber reduced by 6 dB in 125 Hz octave band with the largest absorption coefficient.

Seasonal variability of aerosol absorption parameters at a remote site with high mineral dust loads

Measurements of particulate matter (PM), absorption coefficient (σap) and Absorption Angstrom Exponent (AAE) have been performed during three years (2014–2016) at a remote site (1558 m a.s.l) located in the southeast of the Iberian Peninsula, close to the Mediterranean coast. Mean values ± (standard deviation) of the measured parameters were: PM10 (11.3 ± 19.8 μg⋅m−3), PM1 (3.0 ± 1.9 μg⋅m−3), σap (2.18 ± 1.45 Mm−1/λ = 520 nm) and AAE (1.190 ± 0.225). PM concentrations and σap were maxima during summer, while AAE values were highest during the colder months, as expected for high altitude environments with scarce human activity. The influence that both, air masses coming from the Sahara desert loaded with mineral dust (SDE) and the height of the Planetary Boundary Layer (PBL), had on the studied parameters was also analyzed. During SDEs, σap and AAE levels increased. These increments were slightly higher when the sampling point was located within the free troposphere (FT) and correlated with the intensity of the event. In the case of SDEs with high mineral dust (MD) concentrations, AAE values increased up to 30% and σap values were more than double compared to average values for non-event days. However, the seasonal variability of the optical parameters could not be attributed to these episodes since the MD load at the sampling point did not show significant seasonal differences. For this reason, the different spectral absorption behavior observed between the warmest and the coldest months may be attributed to the seasonal differences in the percentage contribution of Brown Carbon (BrC) to PM levels. These results indicate that for short wavelengths (UV and VIS), the absorption due to non-BC absorbers during the winter was almost twice that registered during summer time.

Laser absorption spectroscopy applied to monitoring of short-lived climate pollutants (SLCPs)

Enhanced mitigation of short-lived climate pollutants (SLCPs) has been recently paid more attention in order to provide more sizeable short-term reductions of global warming effects over the next several decades. We overview in this article our recent progress in the development of spectroscopic instruments for optical monitoring of major SLCPs based on laser absorption spectroscopy. Methane (CH4) and black carbon (BC) are the most important SLCPs contributing to the human enhancement of the global greenhouse effect after CO2. We present optical sensing of these two climate-change related atmospheric species to illustrate how “classical” spectroscopy can help to address today's challenging issues: (1) Photoacoustic measurements of BC optical absorption coefficient in order to determine its radiative-forcing related optical parameters (such as mass absorption coefficient, absorption Ångström coefficient) with higher precision (∼7.4% compared to 12–30% for filter-based methods routinely used nowadays). The 1σ (SNR = 1) minimum measurable volumetric mass density of 21 ng/m3 (in 60 s) for black carbon. (2) Direct absorption spectroscopy-based monitoring of methane (CH4) in field campaign to identify pollution source in conjunction with air mass back-trajectory modeling. Using a White‐type multipass cell (an effective path‐length of 175 m), a 1σ detection limit of 33.3 ppb in 218 s was achieved with a relative measurement precision of 1.1% and an overall measurement uncertainty of about 5.1%.Performance of the custom, lab-based instruments (in terms of detection limits, measurement precision, temporal response, etc.), spectroscopic measurement aspects, experimental details, spectral data processing, analysis and modeling of the observed environmental episode will be presented and discussed.

Design Considerations for Integration of Terahertz Time-Domain Spectroscopy in Microfluidic Platforms

Microfluidic platforms have received much attention in recent years. In particular, there is interest in combining spectroscopy with microfluidic platforms. This work investigates the integration of microfluidic platforms and terahertz time-domain spectroscopy (THz-TDS) systems. A semiclassical computational model is used to simulate the emission of THz radiation from a GaAs photoconductive THz emitter. This model incorporates white noise with increasing noise amplitude (corresponding to decreasing dynamic range values). White noise is selected over other noise due to its contributions in THz-TDS systems. The results from this semiclassical computational model, in combination with defined sample thicknesses, can provide the maximum measurable absorption coefficient for a microfluidic-based THz-TDS system. The maximum measurable frequencies for such systems can be extracted through the relationship between the maximum measurable absorption coefficient and the absorption coefficient for representative biofluids. The sample thickness of the microfluidic platform and the dynamic range of the THz-TDS system play a role in defining the maximum measurable frequency for microfluidic-based THz-TDS systems. The results of this work serve as a design tool for the development of such systems.

Measurement of Absorption Coefficient of Paraformaldehyde and Metaldehyde with Terahertz Spectroscopy

The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as "fingerprints" to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient–mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.

Black Carbon Aerosol in Rome (Italy): Inference of a Long-Term (2001–2017) Record and Related Trends from AERONET Sun-Photometry Data

Surface concentration of black carbon (BC) is a key factor for the understanding of the impact of anthropogenic pollutants on human health. The majority of Italian cities lack long-term measurements of BC concentrations since such a metric is not regulated by EU legislation. This work attempts a long-term (2001–2017) inference of equivalent black carbon (eBC) concentrations in the city of Rome (Italy) based on sun-photometry data. To this end, aerosol light absorption coefficients at the surface are inferred from the ”columnar” aerosol aerosol light absorption coefficient records from the Rome Tor Vergata AERONET sun-photometer. The main focus of this work is to rescale aerosol light absorption columnar data (AERONET) to ground-level BC data. This is done by using values of mixing layer height (MLH) derived from ceilometer measurements and then by converting the absorption into eBC mass concentration through a mass–to–absorption conversion factor, the Mass Absorption Efficiency (MAE). The final aim is to obtain relevant data representative of the BC aerosol at the surface (i.e., in-situ)–so within the MLH– and then to infer a long-term record of “surface” equivalent black carbon mass concentration in Rome. To evaluate the accuracy of this procedure, we compared the AERONET-based results to in-situ measurements of aerosol light absorption coefficients ( α abs) collected during some intensive field campaigns performed in Rome between 2010 and 2017. This analysis shows that different measurement methods, local emissions, and atmospheric conditions (MLH, residual layers) are some of the most important factors influencing differences between inferred and measured α abs. As a general result, ”inferred” and ”measured” α abs resulted to reach quite a good correlation (up to r = 0.73) after a screening procedure that excludes one of the major cause of discrepancy between AERONET inferred and in-situ measured α abs: the presence of highly absorbing aerosol layers at high altitude (e.g., dust), which frequently affects the Mediterranean site of Rome. Long-term trends of “inferred” α abs, eBC, and of the major optical variables that control aerosol’s direct radiative forcing (extinction aerosol optical depth, AODEXT, absorption aerosol optical depth, AODABS, and single scattering albedo, SSA) have been estimated. The Mann-Kendall statistical test associated with Sen’s slope was used to test the data for long-term trends. These show a negative trend for both AODEXT (−0.047/decade) and AODABS (−0.007/decade). The latter converts into a negative trend for the α abs of −5.9 Mm−1/decade and for eBC mass concentration of −0.76 μ g / m 3 /decade. A positive trend is found for SSA (+0.014/decade), indicating that contribution of absorption to extinction is decreasing faster than that of scattering. These long-term trends are consistent with those of other air pollutant concentrations (i.e., PM2.5 and CO) in the Rome area. Despite some limitations, findings of this study fill a current lack in BC observations and may bear useful implications with regard to the improvement of our understanding of the impact of BC on air quality and climate in this Mediterranean urban region.

Characteristics of Mass Absorption Efficiency of Elemental Carbon in Urban Chengdu, Southwest China: Implication for the Coating Effects on Aerosol Absorption

To investigate the mass absorption efficiency (MAE) of elemental carbon (EC) at Chengdu in China’s Sichuan Basin, daily PM2.5 filter samples were collected during the typical month for each season in 2011. PM2.5 samples were subject to chemical analysis for water-soluble inorganic ions, organic carbon and EC, as well as biomass burning organic tracer (i.e., levoglucosan). Additionally, PM2.5 samples were further conducted for aerosol absorption coefficient (bap) measurement at the wavelengths of 370 and 880 nm. To evaluate the seasonal variations of MAEs of EC, linear regression analyses were applied to EC (determined by thermal method), black carbon (BC, determined by optical method) and bap for four seasons. The average BC concentration was 10 µg m−3 when using the manufacturer’s recommended value (16.6 m2 g−1 at the wavelength of 880 nm), which was 1.4 times the mean EC concentration. The MAE of EC at 880 nm was estimated to be 6.1 m2 g−1 in autumn, which was evidently lower than 6.7–6.9 m2 g−1 in other seasons. The higher MAE in other seasons was likely due to more effective light absorption by internally mixed EC with both transparent coatings (e.g., sulfate and nitrate) and organic matters coatings.

Source Apportionment of Black Carbon Aerosol in the North Suburb of Nanjing

Based on one year real-time measurements from a seven-wavelength Aethalometer combined with an Aethalometer model, the measured aerosol absorption coefficients at different wavelengths have been used to apportion the contribution of fossil fuel and biomass burning sources to the total black carbon (BC) mass concentration in the north suburb of Nanjing. Good consistency in the relationship between the Angstrom absorption exponent(α)and the ratio of BC from biomass burning sources to total BC (BB) was obtained during this period. The α was highest in winter and lowest in summer, which indicates the change in the source of the absorbing aerosols and their relative source strength. The BC and the BC from fossil fuel (BCff) and biomass burning (BCbb) mass concentrations exhibit significant diurnal variation, with higher values during 07:00 to 09:00 (local time) and 18:00 to 21:00. The BCff was three to five times higher than the BCbb and contributes greatest to the BC mass concentrations throughout the day. Night time BC values were about a factor of 1.2 higher than day time BC values. Meanwhile, the concentration weighted trajectory (CWT) analysis indicates that the highest value of BC was concentrated in the Zhejiang, Anhui, Jiangxi, and Fujian provinces.

Sound attenuation and absorption by anisotropic fibrous materials: Theoretical and experimental study

This paper describes analytical and experimental studies carried out to examine the attenuation and absorption properties of rigidly-backed fibrous anisotropic materials in contact with a uniform mean flow. The aim is to provide insights for the development of non-locally reacting wall-treatments able to dissipate the noise induced by acoustic excitations over in-duct or external lining systems. A model of sound propagation in anisotropic bulk-reacting liners is presented that fully accounts for anisotropic losses due to heat conduction, viscous dissipation and diffusion processes along and across the material fibres as well as for the convective effect of an external flow. The propagation constant for the least attenuated mode of the coupled system is obtained using a simulated annealing search method. The predicted acoustical performance is validated in the no-flow case for a wide range of fibre diameters. They are assessed against impedance tube and free-field pressure-velocity measurements of the normal incidence absorption coefficient and surface impedance. Parametric studies are then conducted to determine the key constitutive parameters such as the fibres orientation or the amount of anisotropy that mostly influence the axial attenuation or the normal absorption. They are supported by a low-frequency approximation to the axial attenuation under a low-speed flow.

Erratum: “On the infrared absorption coefficient measurement of thick heavily Zn doped GaAs using spectrally resolved modulated photothermal infrared radiometry” [J. Appl. Phys. 122, 135109 (2017)

Erratum: “On the infrared absorption coefficient measurement of thick heavily Zn doped GaAs using spectrally resolved modulated photothermal infrared radiometry” [J. Appl. Phys. <b>122</b>, 135109 (2017)