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Significance: Numerous optical imaging and spectroscopy techniques are used to study the tissue-optical properties; the majority of them are limited in information regarding the penetration depth. A simple, safe, easily applicable diagnostic technique is required to get deeper tissue information in a multilayer structure. Aim: A fiber-based diffuse reflectance (DR) technique is used to extract and quantify the bottom layer absorption coefficients in two-layer (2L) tissue-mimicking solid phantoms. We determine the Indian black ink concentrations in a deep-hidden layer that is sandwiched between agar and silicone-based phantom layers. Approach: A fiber-based DR experiment was performed to study the optical properties of the tissue at higher penetration depth, with different fiber core diameters and a constant numerical aperture (0.5 NA). The optimal core diameter of the fiber was chosen by measuring solid phantoms. In 2L phantoms, the thickness of the top layer was kept 5.5 mm with a constant absorption and reduced scattering coefficients (μa = 0.045 mm − 1 and μs ′ = 2.622 mm − 1), whereas the absorption coefficients of the bottom layers were varied from 0.014 to 0.037 mm − 1 keeping the μs ′ the same as the top layer. A unique crossover point (Cp) was found in the DR intensity profile against distance. We examined the slope before and after the Cp. These two slopes indicate the difference between the optical properties of the top and bottom layers. Our technique got further verification, as we successfully determined the Cp with different Indian black ink concentrations, placed at the junction between the agar and silicone-based phantom layers. Results: The DR measurements were applied to 2L phantoms. Two different slopes were found in 2L phantoms compared to the one-layer (optical properties equal to the top layer of 2L). We extracted the slopes before and after the Cp in the 2L phantoms. The calculated absorption coefficients before the Cp were 0.014 ± 0.0004, 0.022 ± 0.0003, 0.028 ± 0.0003, and 0.036 ± 0.0014 mm − 1, and the absorption coefficients after the Cp were 0.019 ± 0.0013, 0.013 ± 0.0004, 0.014 ± 0.0006, and 0.031 ± 0.0001 mm − 1, respectively. The calculated absorption coefficients before the Cp were in good agreement with the optical properties of the bottom layer. The calculated absorption coefficients after the Cp were not the same as the top layer. Our DR system successfully determines the crossover points 12.14 ± 0.11 and 11.73 ± 0.15 mm for 70% and 100% ink concentrations placed at the junction of the agar and silicone layers. Conclusions: In a 2L tissue structure, the Cp depends on the absorption coefficients of top and bottom layers and the thickness of the top layer. With the help of the Cp and the absorption coefficients, one can determine the thickness of the top layer or vice versa. The slope value before the Cp in the DR profile allowed us to determine the absorption properties of the bottom layer instead of having the average behavior of the 2L phantom in the far detection range (11.0 to 17.0 mm).

The optical properties of human tissues are an important parameter in medical diagnostics and therapy. The knowledge of these parameters can encourage the development of automated, computer-driven optical tissue analysis methods. We determine the absorption coefficient μa and scattering coefficient μs′ of different tissue types obtained during parotidectomy in the wavelength range of 250 to 800 nm. These values are determined by high precision integrating sphere measurements in combination with an optimized inverse Monte Carlo simulation. To conserve the optical behavior of living tissues, the optical spectroscopy measurements are performed immediately after tissue removal. Our study includes fresh samples of the ear, nose, and throat (ENT) region, as muscle tissue, nervous tissue, white adipose tissue, stromal tissue, parotid gland, and tumorous tissue of five patients. The measured behavior of adipose corresponds well with the literature, which sustains the applied method. It is shown that muscle is well supplied with blood as it features the same characteristic peaks at 430 and 555 nm in the absorption curve. The parameter μs′ decreases for all tissue types above 570 nm. The accuracy is adequate for the purposes of providing μa and μs′ of different human tissue types as muscle, fat, nerve, or gland tissue, which are embedded in large complex structures such as in the ENT area. It becomes possible for the first time to present reasonable results for the optical behavior of human soft tissue located in the ENT area and in the near-UV, visual, and near-infrared areas.

Carotenoid biosynthesis is one of the most important biochemical changes occurring during mango ripening. Carotenoids are responsible for the yellow-orange pulp colour, which is one of the best maturity indices for mangoes, notwithstanding it is a destructive method. Time-resolved reflectance spectroscopy (TRS) is a non-destructive technique which simultaneously quantifies the internal optical properties of fruit related to pigments (absorption coefficient, mu(a)) and to structure (reduced scattering coefficient, mu(s)') by probing the pulp to a depth of 1-2 cm with no or limited influence from the skin. In previous works, it was found that TRS is able to predict with good accuracy the pulp colour of mangoes and then to sort fruit with different maturity degrees. The aim of this research was to study the relationships among TRS optical properties, total carotenoids content and pulp colour parameters of two cultivars of Brazilian mangoes transported by plane to Italy. Fruit were measured by TRS in the 540-690 nm range for 'Palmer' cultivar and in the 540-780 nm range for 'Haden' and analyzed for pulp colour and total carotenoids content. Total carotenoids ranged from 5.2 to 32.7 mg kg(-1) FW for 'Palmer' and from 5.9 to 56.2 mg kg(-1) FW for 'Haden'. By using partial least squares regression, good correlations were obtained between TRS absorption spectra and total carotenoids content (R-cv(2)=0.83 and 0.93 for 'Haden' and 'Palmer', respectively) and pulp colour parameters (R-cv(2)=0.78-0.96).

Significance: In laser therapy and diagnosis of skin diseases, the irradiated light distribution, which is determined by the absorption coefficient μa and reduced scattering coefficient μs′ of the epidermis, dermis, and subcutaneous fat, affects the treatment outcome and diagnosis accuracy. Although values for μa and μs′ have been reported, detailed analysis for Asian skin tissues is still lacking. Aim: We present μa and μs′ measurements of Asian skin tissues in the 400- to 1100-nm wavelength range for evaluating optical penetration depth and energy deposition. Approach: The measurements with Asian human skin samples are performed employing a double integrating sphere spectrometric system and an inverse Monte Carlo technique. Using the measured parameters, the optical penetration depth and energy deposition are quantitatively analyzed. Results: The μa of the epidermis layer varies among different ethnic groups, while the μa of the other layers and the μs′ of all of the layers exhibit almost no differences. The analysis reveals that the optical penetration depth and the energy deposition affect the photodynamic therapy treatment depth and the heat production in skin tissue, respectively. Conclusions: The experimentally measured values of μa and μs′ for Asian skin tissues are presented, and the light behavior in Asian skin tissues is analyzed using a layered tissue model.

We applied terahertz (THz)-pulsed spectroscopy to study ex vivo the refractive index and absorption coefficient of human brain gliomas featuring different grades, as well as perifocal regions containing both intact and edematous tissues. Glioma samples from 26 patients were considered and analyzed according to further histological examination. In order to fix tissues for the THz measurements, we applied gelatin embedding, which allows for sustaining their THz response unaltered, as compared to that of the freshly excised tissues. We observed a statistical difference between the THz optical constants of intact tissues and gliomas of grades I to IV, while the response of edema was similar to that of tumor. The results of this paper justify a potential of THz technology in the intraoperative label-free diagnosis of human brain gliomas for ensuring the gross-total resection.

International audience; Soleimanzad Haleh, Gurden Hirac, Pain Frédéric, "Optical properties of mice skull bone in the 455-to 705-nm range," J. Abstract. Rodent brain is studied to understand the basics of brain function. The activity of cell populations and networks is commonly recorded in vivo with wide-field optical imaging techniques such as intrinsic optical imaging, fluo-rescence imaging, or laser speckle imaging. These techniques were recently adapted to unrestrained mice carrying transcranial windows. Furthermore, optogenetics studies would benefit from optical stimulation through the skull without implanting an optical fiber, especially for longitudinal studies. In this context, the knowledge of bone optical properties is requested to improve the quan-titation of the depth and volume of imaged or stimulated tissues. Here, we provide experimental measurements of absorption and reduced scattering coefficients of freshly excised mice skull for wavelengths between 455 and 705 nm. Absorption coefficients from 6 to 8 months mice skull samples range between 1.67 AE 0.28 mm −1 at 455 nm and 0.47 AE 0.07 mm −1 at 705 nm, whereas reduced scattering coefficients were in the range of 2.79 AE 0.26 mm −1 at 455 nm up to 2.29 AE 0.12 mm −1 at 705 nm. In comparison, measurements carried out on 4 to 5 weeks mice showed similar spectral profiles but smaller absorption and reduced scattering coefficients by a factor of about 2 and 1.5, respectively. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication , including its DOI.

© 2015 SPIE. We present a review of short-wave infrared (SWIR, defined here as ∼1000 to 2000 nm) spectroscopy and imaging techniques for biological tissue optical property characterization. Studies indicate notable SWIR absorption features of tissue constituents including water (near 1150, 1450, and 1900 nm), lipids (near 1040, 1200, 1400, and 1700 nm), and collagen (near 1200 and 1500 nm) that are much more prominent than corresponding features observed in the visible and near-infrared (VIS-NIR, defined here as ∼400 to 1000 nm). Furthermore, the wavelength dependence of the scattering coefficient has been observed to follow a power-law decay from the VIS-NIR to the SWIR region. Thus, the magnitude of tissue scattering is lower at SWIR wavelengths than that observed at VIS or NIR wavelengths, potentially enabling increased penetration depth of incident light at SWIR wavelengths that are not highly absorbed by the aforementioned chromophores. These aspects of SWIR suggest that the tissue spectroscopy and imaging in this range of wavelengths have the potential to provide enhanced sensitivity (relative to VIS-NIR measurements) to chromophores such as water and lipids, thereby helping to characterize changes in the concentrations of these chromophores due to conditions such as atherosclerotic plaque, breast cancer, and burns.

Terahertz (THz) frequency generation via nonlinear optical techniques is of particular interest due to the immense potential of this type of radiation in various scientific fields, ranging from medicine to telecommunications. Selecting suitable nonlinear media for laser frequency down-conversion presents a challenging task. Considering an approach that uses nonlinear crystals with high radiation resistance, pumped by intense laser pulses near their damage threshold, we suggest the crystal of bismuth triborate (BiB3O6, BIBO). Compared to other borate-class crystals, BIBO exhibits relatively high coefficients of quadratic susceptibility. In this paper, we have studied the optical properties of BIBO samples in a wide spectral range from 0.1 to 2.1 THz at temperatures of 473, 383, 295, and 77 K using Terahertz Time-Domain Spectroscopy (THz-TDS). Furthermore, we simulated collinear three-wave interactions with nonzero efficiency for difference frequency generation (DFG) in the THz range. For the pump wavelengths of about 800 nm, we determined phase-matching (PM) conditions and compared the generation efficiency for different crystal cuts. The potential of utilizing BIBO crystal for terahertz frequency generation is discussed.

International audience; AbstractIn this paper, the intersubband optical properties of strained InAsSb/AlGaAs single quantum well structure have been investigated in a detailed way as depending on the structure parameters. For this aim, first, we have computed the energy eigenvalues and their corresponding wave functions of this structure by means of the solution of the Schrodinger equation in envelope function effective mass approximation. Second, we have calculated some important parameters as strain, band gap energy, effective mass and the conduction band (CB) offset ratio. Finally, the intersubband absorption coefficient properties have been determined as a function of the composition, well thickness and the emission wavelength.

One of the most vulnerable issues in the technical protection of information is to obtain data via leakage through the opto-electronic channel. In this paper, studies of the protective capabilities of glass from laser sounding depending on its elemental composition were carried out using such indicators as the coefficients of reflection and absorption of the laser beam by the window glass. As a result of the work, an experimental installation based on a continuous solid-state laser was assembled. The study of the elemental composition of window glass, which is produced by modern industry, X-ray fluorescence method and the study of the coefficients of reflection and absorption of glass samples in the experimental setup showed that the studied window glass chemically belongs to quartz (silicate). All chemical elements involved in its formation can be divided into 3 groups: glass-forming, transitional, modifiers, which affects the optical properties of the studied glasses, as the elements used have different not only qualitative but also quantitative parameters. Absorption increases if the number of chemical elements that exhibit amphoteric and non-metallic properties and have (-charge) decreases, and increases if the number of chemical elements in the glass that exhibit the most alkaline, alkaline earth properties and in which the radius of cations (+ions) increases. Systematization of the elemental and quantitative composition of the studied window glass in accordance with the periods and groups of the periodic table of chemical elements, enabled the relationship between the electronic structure of chemical elements and the protective properties of glass

The paper presents the results of optical and photoelectric measurements and their analysis for Tl1-xIn1-xDIVxSe2 (DIV – Si, Ge, Sn) crystalline compounds in the wavelength range 0.41.4 μm at a temperature T = 300 K. The work aims to investigate the influence of mole fraction DIVSe2 on the mechanisms of interband transitions and the basic photon parameters of crystals of ТlInSe2–DIVSe2 solid solutions. It was found that the change in the physical properties of the mole fraction of the components x associated with the rearrangement of the band structure significantly expands the functionality of the Tl1-xIn1-x(Si, Ge, Sn)xSe2 (x0.25) crystalline compounds as promising materials for optoelectronic devices.

International audience; The paper presents the sound absorption coefficient of acoustic absorbers fabricated from natural durian husk fibers, which are currently still considered as agricultural wastes, especially in Malaysia. Samples were fabricated with different fiber densities and thicknesses and the sound absorption performance was measured using the impedance tube method. The results reveal that the durian husk fibers can have absorption coefficient of more than 0.5 above 1 kHz for a minimum thick sample of 20 mm and with minimum density of 160 kg/m3. The optimised macroscopic parameters for various densities were calculated using the inverse method employing the well-known Johnson-Champoux-Allard (JCA) model for porous material.

The creation of van der Waals heterostructures with tunable properties from various combinations of modern 2D materials is one of the promising tasks of nanoelectronics, focused on improving the parameters of electronic nanodevices. In this paper, using ab initio methods, we theoretically predict the existence of new three-layer van der Waals zinc oxide/blue phosphorus/zinc oxide (ZnO/BlueP/ZnO) heterostructure with AAA, ABA, ABC layer packing types. It is found that AAA-, ABA-, and ABC-stacked ZnO/BlueP/ZnO heterostructures are semiconductors with a gap of about 0.7 eV. The dynamic conductivity and absorption spectra are calculated in the wavelength range of 200–2000 nm. It is revealed that the BlueP monolayer makes the greatest contribution to the formation of the profiles the dynamic conductivity and absorption coefficient spectrums of the ZnO/BlueP/ZnO heterostructure. This is indicated by the fact that, for the ZnO/BlueP/ZnO heterostructure, conductivity anisotropy is observed at different directions of wave polarization, as for blue phosphorus. It has been established that the absorption maximum of the heterostructure falls in the middle ultraviolet range, and, starting from a wavelength of 700 nm, there is a complete absence of absorption. The type of layer packing has practically no effect on the regularities in the formation of the spectra of dynamic conductivity and the absorption coefficient, which is important from the point of view of their application in optoelectronics.

In recent years, the possibility of combining graphene and carbon nanotubes has attracted much attention from researchers attempting to obtain new multifunctional hybrid materials with promising properties. Optoelectronics shows potential as a field of application for such hybrid structures. The variety of existing structural configurations of graphene-nanotube hybrids requires preliminary detailed studies of their optical properties by computer simulation methods. In this paper, we consider island-type graphene-nanotube hybrid films formed by AB-stacked bilayer graphene and single-walled carbon nanotubes (SWCNTs). In this case, bilayer graphene is located above the surface of the nanotube, forming areas with an increased density of carbon atoms, creating so-called “islands.” To meet the conditions of a real experiment, we chose chiral SWCNTs (12,6) with a diameter of 1.2 nm, which are most often synthesized in real experiments. All constructed atomistic models of bilayer graphene-chiral SWCNT films were tested for thermodynamic stability at room temperature and proved their suitability for research. Using Kubo-Greenwood formalism, we calculated the complex optical conductivity tensor and absorbance coefficient in the wavelengths of ultraviolet, visible, and near-infrared radiations. The photocurrent spectra are calculated based on the obtained absorption spectra and solar radiation spectra on the earth’s surface (AM1.5) and outside the earth’s atmosphere (AM0). The results of calculations revealed regularities in the influence of structural parameters (nanotube diameter, graphene width) on the optical and optoelectronic properties of graphene-chiral SWCNT (12,6) with an island structure.

"© 2020 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited", The generation and manipulation of small aqueous droplets is an important issue for nano- and biotechnology, particularly, when using microfluidic devices. The production of very small droplets has been frequently carried out by applying intense local electric fields to the fluid, which requires power supplies and metallic electrodes. This procedure complicates the device and reduces its versatility. In this work, we present a novel and flexible, to the best of our knowledge, electrodeless optoelectronic method for the production of tiny droplets of biologically friendly aqueous fluids. Our method takes advantage of the photoinduced electric fields generated by the bulk photovoltaic effect in iron-doped lithium niobate crystals. Two substrate configurations, presenting the polar ferroelectric axis either parallel or perpendicular to the active surface, have been successfully tested. In both crystal geometries, small droplets on the femtoliter scale have been obtained, although with a different spatial distributions correlated with the symmetry of the photovoltaic fields. The overall results demonstrate the effectiveness of the optoelectronic method to produce femtoliter droplets, both with pure water and with aqueous solutions containing biological material, Ministerio de Ciencia, Innovación y Universidades of Spain (MAT2017-83951-R); Marie Sklodowska-Curie Action COFUND (713366-InterTalentum)

This paper is concerned with the stability issue in determining absorption and diffusion coefficients in quantitative photoacoustic imaging. Assuming that the optical wave is generated by point sources in a region where the optical coefficients are known, we derive pointwise H{\"o}lder stability estimate of the inversion. This result shows that the reconstruction of the optical coefficients is stable in the region close to the optical illumination sources and deteriorate exponentially far away. Our stability estimate is therefore in accordance with known experimental observations. Mathematics subject classification : 35R30.

International audience; Recently, a large variety of photothermal agents have been developed and are currently under study, owing to their wide range of applications. Nonetheless, a comparison of their relative performances remains a challenge, and it appears that no tool is yet available for rationalizing the data reported in the literature. Indeed, we demonstrate in this paper that neither the temperature increase (Delta T) nor the photothermal efficiency (eta) are sufficient to account for the performance of a photothermal agent. From this observation, we propose that a new index, I-PTmax, could be used, in order to properly rank molecular photothermal agents according to their efficacy for converting light into heat, in a similar fashion that brilliance is used to compare luminescence properties.

In this paper, the plasmonic property of triple layered ZnO@M@Au (M = spacer) spherical core-shell nanostructures embedded in a dielectrics host medium is investigated by varying core size, spacer thickness, shell thickness and dielectrics function of the host medium within the framework of the qausi-static approximation method. The absorption coefficient of ZnO@M@Au spherical triple layered core-shell nanostructures is effectively studied by optimizing the parameters with range of nano-inclusion size mainly in between 18 and 23 nm. In this triple layered core-shell nanostructure two plasonic resonances are found associated with spacer@Au and Au@medium interfaces. The tunability of the plasmon resonances of the composite systems enables it to exhibit very interesting material properties in a variety of applications extending from near-UV to near-infrared spectral region.

International audience; This paper deals with thermal attenuation of a transmitted THz signal (165 GHz) across a POM polymer sample subjected to a thermal gradient in the thickness direction. The paper describes the experimental setup, including a THz sensor, a system to impose thermal loading and an infrared camera used to measure temperature variations at the surface. The thermal dependence of the transmitted THz signal through the sample was studied along a spatial profile. A simple polynomial model, validated through finite element analysis and thermal imaging measurement, was used to estimate temperature variations in the thickness direction. The correspondence between the 2D transmitted THz signal and the 3D temperature distribution allowed us to estimate the thermal sensitivity of the absorption coefficient in the THz range. This study showed that the THz sensor was sensitive enough to measure THz signal variations due to small temperature variations. The mean temperature may be determined along the thickness direction once the thermodependence of the transmission and reflection coefficients are known.

Next generation in-to-out-of body biomedical applications have adopted optical wireless communications (OWCs). However, by delving into the published literature, a gap is recognized in modeling the in-to-out-of channel, since most published contributions neglect the particularities of different types of tissues. In this paper, we present a novel pathloss and scattering models for in-to-out-of OWC links. Specifically, we derive extract analytical expressions that accurately describe the absorption of the five main tissues’ constituents, namely fat, water, melanin, and oxygenated and de-oxygenated blood. Moreover, we formulate a model for the calculation of the absorption coefficient of any generic biological tissue. Next, by incorporating the impact of scattering in the aforementioned model, we formulate the complete pathloss model. The developed model is verified by means of comparisons between the estimated pathloss and experimental measurements from independent research works. Finally, we illustrate the accuracy of the proposed model in estimating the optical properties of any generic tissue based on its constitution. The extracted channel model is expected to enable link budget analysis, performance analysis, and theoretical framework development, which will boost the design of optimized communication protocols for a plethora of biomedical applications.

This paper proposes an algorithm that utilizes a macroscopic approach to calculate the amplitude of the total acoustic signal generated by an alternating magnetic field in ribbon-shaped nanocrystalline magnets (NCMs) with polydomain nanofibers at reversible displacements of domain boundaries. The calculations are made for the case with the wave vector directed along the magnetic field parallel to the tape plane. At the same time, the influence of anharmonicity on the displacements of the domain boundaries is considered for the carrier frequency. The orientation and frequency dependences for the wave vector and the signal absorption coefficient are found under the assumption that the rotation processes can be neglected. It is shown that the residual internal stresses in the (poly- or monodomain) nanograin NCMs have a significant effect on the absorption coefficient and the amplitude of the generated DG signal. The magnetic anisotropy constants decrease along with the size of the nanograins. In this case, the generation process due to the rotation of the spontaneous magnetization vectors is also significant, which must be considered in relation to the displacement processes. The proposed algorithm for calculating the amplitudes of the signals generated by a nanocrystalline magnet can be used to predict the friction properties of the developed promising NCM and calculate the amplitudes of the generated signals at the carrier frequency and harmonics., Предложен алгоритм расчета амплитуды суммарного акустического сигнала, генерируемого переменным магнитным полем в нанокристаллических магнетиках в форме ленты с полидоменными нанозернами при обратимых смещениях доменных границ с использованием макроскопического подхода. Расчет произведен для случая, когда волновой вектор kв направлен вдоль магнитного поля, параллельного плоскости ленты. При этом для несущей частоты учтено влияние ангармонизма в смещениях доменных границ. Найдены ориентационная и частотные зависимости для волнового вектора и коэффициента поглощения сигнала в предположении, что процессами вращений можно пренебречь. Показано существенное влияние остаточных внутренних напряжений в НКМ, состоящих из нанозерен (поли- или монодоменных), на коэффициент поглощения и амплитуду генерируемого ДГ сигнала. С уменьшением размеров нанозерен происходит уменьшение констант магнитной анизотропии, в этом случае существенным является и процесс генерации за счет вращений векторов спонтанной намагниченности, который надо учитывать во взаимосвязи с процессами смещения. Предложенный алгоритм расчета амплитуд сигналов, генерируемых нанокристаллическим магнетиком, может быть использован для прогнозирования стрикционных свойств разрабатываемых перспективных НКМ, расчета амплитуд генерируемых сигналов на несущей частоте и гармониках.

This paper reports on absorption properties of thin films of hydrogenated amorphous and microcrystalline silicon considered for absorption-based applications, such as solar cell, photodetectors, filters, sensors, etc. A series of four amorphous and four microcrystalline samples PECVD deposited under varied hydrogen dilution was under consideration. Various absorption metrics, based separately on the absorption coefficient and the refractive index (single pass absorption, optical path length, classical light trapping limit) or direct absorptance calculated by the Yablonovitch concept based on a mutual role of them were examined and compared. Differences in absorption abilities are related to the evolving thin film microstructure.

Building further upon the high spatial resolution offered by ultrasonic imaging and the high optical contrast yielded by laser excitation of photoacoustic imaging, and exploiting the temperature dependence of photoacoustic signal amplitudes, this paper addresses the question whether the rich information given by multispectral optoacoustic tomography (MSOT) allows to obtain 3D temperature images. Numerical simulations and experimental results are reported on agarose phantoms containing gold nanoparticles and the effects of shadowing, reconstruction flaws, etc. on the accuracy are determined. Keywords: Photoacoustic imaging, Multispectral optoacoustic tomography, Absorption coefficient, Finite difference

Funding Information: The authors greatly acknowledge the support of the Academy of Finland under grant no. 314487 and the Finnish Fire Protection Fund (Palosuojelurahasto). The authors would also like to thank Dr. Isaac Leventon for providing the original sample of black PMMA. Publisher Copyright: © 2022 The Author(s) In-depth radiation absorption significantly affects the ignition time and burning rate of flammable translucent materials. To improve the accuracy of flammability predictions by pyrolysis models, the spectral dependency of radiation sources and the depth of the computational cell in the sample should be considered. This paper provides the absorption spectra of black Poly(methyl methacrylate) (PMMA) in a wide spectral range of 0.25 to 25 μm by measuring the high-resolution spectral transmissivity of thin samples. Compared to clear PMMA, black PMMA has a higher spectral absorption coefficient in the UV–Vis–NIR region (

Представлен обзор перспективных моделей бортовых чёрных тел на основе фазовых переходов высокочистых веществ или эвтектических соединений и углеродных нанотрубок, применяемых в аэрокосмических аппаратах для радиометрической калибровки аппаратуры наблюдения Земли. Рассмотрены устройство и характеристики этих моделей, недостатки и преимущества, а также примеры их использования или испытания, The paper presents promising models of onboard blackbodies based on phase transitions of high-purity substances or eutectic compositions and carbon nanotubes used in aerospace vehicles for the radiometric calibration measurement of the equipment to observe the Earth. Their design and technical specifications, advantages and disadvantages as well as the examples of their use and tests are described here, Вестник НПО им. С.А. Лавочкина, Выпуск 3 (53) 2021, Pages 54-59

Recently, Dai et al. published a paper in Research Materials 2019; 22(5): e20190311. They have investigated the visible-light photocatalytic activity of the synthesized Bi2WO6 powders1. In the context of determining of band gap energy based on diffuse reflectance measurements, the cited authors make some mistakes, which are clarified in the present letter.

This paper is concerned with the nonexistence of global solutions to fractional in time nonlinear Schr&ouml, dinger equations of the form i &alpha, &part, t &alpha, &omega, ( t , z ) + a 1 ( t ) &Delta, ( t , z ) + i &alpha, a 2 ( t ) &omega, ( t , z ) = &xi, ( t , z ) | p , ( t , z ) &isin, ( 0 , &infin, ) &times, R N , where N &ge, 1 , &xi, &isin, C ∖ { 0 } and p &gt, 1 , under suitable initial data. To establish our nonexistence theorem, we adopt the Pohozaev nonlinear capacity method, and consider the combined effects of absorption and dispersion terms. Further, we discuss in details some special cases of coefficient functions a 1 , a 2 &isin, L l o c 1 ( [ 0 , &infin, ) , R ) , and provide two illustrative examples.

International audience; This paper aims at consolidating research dealing with vibroacoustics of periodic media. The main goal of this work is to develop and to validate tools for the design of global vibroacoustic treatments based on periodic patterns, allowing passive control of acoustic paths in layered concepts. To this aim, some enhancements are introduced to the state of the art on the the study and the design of Biot-modeled foams, in order to obtain desired acoustics performances through embedded periodic inclusions. At first, the properties of the studied acoustic package, constituted by a poro-elastic 3D unit cell, is introduced. Successively, through the use of the acoustic-structure coupling that comes from the implementation of Biot model, a non-rigid inclusion test campaign is carried out by considering some solid (but still nonperfectly-rigid) inclusions in a 3D-modeled unit cell; in particular, six setups are discussed herein. Then, some design guidelines are provided in order to predict at which frequency the first performance peak appears, together with its amplitude, as functions of unit cell dimensions, airflow resistivity, tortuosity, viscous and thermal characteristic lengths, frame density, Young modulus and loss factor; conversely, it is shown also the link between the unit cell dimensions and the first performance peak amplitude as functions of the design frequency.

To facilitate optical design of energy-efficient materials and devices, a detailed knowledge of their basic optical parameters is necessary. In this paper we present a novel method for determining scattering (S) and absorption (K) coefficients from total transmittance and reflectance measurements by inversion of the Kubelka-Munk theory. The reflectance parameters appearing in this theory depend on the angular distribution of scattered light inside the material. The versatility of our method is demonstrated by a reanalysis of experimental data for several materials of interest in energy-related applications. Specifically, we report spectra of S and K for: (a) pigmented polymer foils for radiative cooling applications; (b) suspended particle devices for smart windows; (c) solar reflecting TiO2-pigmented paints and (d) selective solar absorbing paints for solar collectors.

Cork is a sustainable material and at the end of its useful life it can be disposed of into the environment without causing damage. This paper analyzes an acoustic correction system made of cork sheets mounted at an opportune distance from the walls inside a room. The cork sheets have a thickness equal to 1.5 mm. The sound absorption coefficients of the cork sheets were initially evaluated by mounting samples inside an impedance tube, then creating a back cavity at a suitable distance from a rigid wall. The distances considered were: 3, 5, 10 and 15 cm. A room used as an office with a volume of about 90 m3 and plastered walls was considered as a case-study. In this type of environment, suitable acoustic comfort conditions are required. The acoustic characteristics were analyzed through a virtual model with an architectural acoustics software in an empty room and then with the introduction of sound-absorbing cork sheets. Measurements of the acoustic characteristics of the empty room were taken and subsequently with the walls lined with cork panels mounted at a distance of 3.0 cm from the rigid rear wall. A configuration was analyzed, in line with what was carried out in the numerical model, covering a surface of 5m2 of the room. The results of the numerical simulations as well as the experimental measurements are discussed.

This article deals with data for oxygen in the Schumann–Runge band, stored in world databases NIST and Glushko. My program NKrov2 compares this data in order to calculate the most important part of the absorption coefficient: The H–function. I developed the program NKrov2 for H– function calculation and database comparison.

PhD (Science with Atmospheric Chemistry), North-West University, Potchefstroom Campus Atmospheric aerosols affect the earth’s radiative budget in two ways: firstly, particles directly absorb and scatter short- and long-wave radiation and, secondly, particles indirectly influence the lifetime and physical properties of clouds. There are many uncertainties associated with these effects of atmospheric aerosols on the earth’s radiative budget due to their high spatial and temporal variability of aerosol optical properties, particularly on regional scales. Consequently, high-resolution long-term, regional scale aerosol optical property measurements are required in order to decrease the uncertainties. Southern Africa is an important sub-source region of Africa where open biomass burning produces significant amounts of aerosols, especially during the dry season. Within southern Africa, South Africa is the largest economy with numerous primary and secondary sources of aerosols. Only a few papers have been published on aerosol optical properties in South Africa. Therefore, to partially address this knowledge gap, i.e. long-term ground level in situ aerosol optical data, aerosol optical properties, which include scattering and absorption coefficients (σSP and σAP), single scattering albedo (ω0), and Ångström exponent (αSP), are investigated based on in situ measurements conducted from September 2011 to November 2016 at the Welgegund measurement station. The σSP was measured with a three wavelength light scattering Nephelometer and the σAP with a multi-angle absorption photometer. The αSP and ω0 were calculated from the σSP and σSP and σAP, respectively. Relatively well-defined seasonal and diurnal patterns were observed, which indicated the influence of open biomass burning frequencies, other possible sources (e.g. industrial emissions, domestic combustion, wind-blown dust) and meteorological effects (e.g. temperature, relative humidity, planetary boundary layer daily evolution and air mass circulation patterns). Two main approaches, i.e. auto-generated source maps and defined source regions, were used to identify more unambiguously the sources and source areas that influenced the aerosol optical properties. From these two approaches, the contributions of seasonal sources (e.g. open biomass burning, domestic combustion for space heating, wind-blown dust) and continuous emission sources (e.g. industrial emissions and domestic combustion for cooking) were observed. From the auto-generated source maps, considering all aerosol optical properties for the entire measurement period, anthropogenic activities such as emissions from the Vaal Triangle, Mpumalanga Highveld, and Johannesburg-Pretoria megacity, as well as the aging and recirculation of pollution over the dominant anti-cyclonic recirculation pattern, in addition to high open biomass burning frequencies especially over eastern Zimbabwe and central Mozambique had the most significant effects on the aerosol optical properties (e.g. higher σSP and σAP), if compared to the background sector between west-southwest and south-southwest of Welgegund. The auto-generated source maps for defined periods, i.e. warmest/wettest, coldest and driest, peak open biomass burning, indicated the contributions from sources and/or source areas even better. From the warmest/wettest period for all aerosol optical properties, the contribution of air masses that had passed over industrial activities and the dominant anti-cyclonic recirculation pattern were evident. The coldest period mostly indicated the contribution of higher population densities (more domestic combustion for space heating) in addition to industrial activities that contribute year-round. From the driest period, the contributions of open biomass burning frequencies of air masses that had passed over eastern Zimbabwe and central Mozambique were evident for all aerosol optical properties. The defined source regions approach was subdivided into three different methods that further improved the understanding of possible sources and source regions influencing aerosol optical properties. The predefined eastern and western sectors method allowed the comparison of aerosol optical properties for air masses that had passed over the eastern (higher industry population densities and open biomass burning frequencies), and western (very few industries, lower population densities and lower open biomass burning frequencies) sectors during the warmest/wettest and driest periods. From this comparison, the significant differences between the two defined sectors and contributions of open biomass burning to all aerosol optical properties during the driest period were evident. The predefined source regions approach allowed the comparison of aerosol optical properties for air masses that had passed over the anthropogenic source regions in the eastern sector. From this approach, it was evident that the aerosol optical properties were significantly altered (if compared to the regional background) in air masses that had passed over the anthropogenic influenced source regions in the South African interior. For example, the σSP and αSP indicated the extent of pollution of air masses that had passed over the Vaal Triangle (VaalT), as well as the occurrence of wind-blown dust that travelled over the VaalT from the eastern Free State to Welgegund. In the last method, information obtained by the predefined and auto-generated source map region methods was applied, which allowed the comparison between two separate background regions, i.e. Karoo and Kalahari, and two anthropogenically influenced regions, i.e. anti-cyclonic recirculation pattern and the industrial hub, during different periods, i.e. warmest/wettest, coldest and driest periods. From these aerosol optical properties results, it was evident that air masses that had passed over the Karoo were typically cleaner (e.g. lower σSP and σAP) than air masses that had passed over the Kalahari, and that air masses that had passed over the industrial hub during the coldest period were the most polluted (e.g. highest σSP and σAP). To contextualise the aerosol optical properties measured at Welgegund, mean values were compared with other sites. The highest mean aerosol optical property values during all periods were lower than the mean values reported for polluted sites. The mean aerosol optical property values measured in air masses that had passed over the Karoo region during all periods were similar and/or higher to mean values reported for true background sites. The mean ω0 for Welgegund over the entire measurement period was comparable with the mean ω0 reported for Elandsfontein in the Mpumalanga Highveld. However, it was not that straightforward to contextualise the Welgegund ω0 values with other sites, since the climatological effect of ω0 depends on the albedo of the underlying surface. Lastly, a statistical approach, i.e. multi-linear regression analysis, was applied to serve as an additional, independent analysis to support the source deductions made in the earlier chapters. Although the interpretations of the meaning of parameters included in the optimum multi-linear regression equations, and the signs (positive or negative) associated with them, were somewhat speculative, it did indicate that the earlier source deductions were plausible. Doctoral

This paper presents an analysis of optical properties of cubic titanium dioxide (TiO2) using Orthogonalized Linear Combinations of Atomic Orbitals (OLCAO) basis set under the framework of Density Functional Theory (DFT). Many optical properties such as refractive index, extinction coefficient, reflectivity, absorption coefficient, photoconductivity, and loss coefficient have been studied and analyzed thoroughly. From the analysis of optical properties, it is seen that cubic TiO2 supports interband transition between states. The reflectivity of pyrite structure TiO2 lies within IR- visible- UV region due to which it qualifies for coating industry. Furthermore, the results are compared with previous theoretical as well as with experimental results. It is found that DFT based simulation produces results which are the close approximation to experimental results.

The paper is devoted to the development of a mathematical model for high-pressure hydro vortex inertial kinematic dust suppression. The suppression can significantly improve the efficiency of localization of man-made accidents and reduce the level of occupational pulmonary diseases. The dynamics of improving the technology and technical means of dust suppression in the mining and metallurgical complex of Russia shows their lack of effectiveness in ensuring sanitary conditions, especially in localization of dust mixture explosions. A further increase in the efficiency of coal mining and mineral processing is significantly limited by the imperfection of the technology for localizing and eliminating explosions of coal dust. The method of high-pressure hydro vortex dedusting is developed based on the theory of attached vortices. A mathematical model of hydro vortex inertial, kinematic heterocoagulation, which significantly increases the energy efficiency of dust suppression, is proposed. The graphical model of the interaction in the contact zone at the time of the collision in the liquid-solid system is refined. Stokes and Reynolds criteria equations are obtained with hydro vortex inertial orthokinetic heterocoagulation. An equation is obtained which allows to calculate the magnitude of the reduction in the required energy of the total absorption of dust particles as a function of the circulation of liquid droplets. Equations for calculation of effective wetting angle and the minimum diameter of absorbed dust particles are obtained as a function of the angular velocity of rotation of liquid droplets. It is shown that hydro vortex coagulation significantly reduces the size of the dispersed dust composition, water consumption, increasing the efficiency of dust suppression. A significant decrease in the size of the absorbed dust particles increases the efficiency of localization of coal dust explosions, reduces the incidence of silicosis and anthracosis. Certification tests using patent-protected vortex nozzles confirmed that there was a reduction in the minimum size of absorbed dust in four times, increase in dust collection efficiency of up to 99 %, reduce in water consumption by 20 % compared to classic high-pressure spray cleaning. The proposed technology of dust suppression can be used in mining companies when fine explosive dust mixtures are formed.

One of the urgent tasks of modern materials science is the search for new materials with improved optoelectronic properties for various applications of optoelectronics and photovoltaics. In this paper, using ab initio methods, we investigate the possibility of forming new types of van der Waals heterostructures based on monolayers of triangulated borophene, and monolayers of rhenium sulfide (ReS), and rhenium selenide (ReSe2), and predict their optoelectronic properties. Energy stable atomic configurations of borophene/ReS2 and borophene/ReSe2 van der Waals heterostructures were obtained using density functional theory (DFT) calculations in the Siesta software package. The results of calculating the density of electronic states of the obtained supercells showed that the proposed types of heterostructures are characterized by a metallic type of conductivity. Based on the calculated optical absorption and photocurrent spectra in the wavelength range of 200 to 2000 nm, it is found that borophene/ReS2 and borophene/ReSe2 heterostructures demonstrate a high absorption coefficient in the near- and far-UV(ultraviolet) ranges, as well as the presence of high-intensity photocurrent peaks in the visible range of electromagnetic radiation. Based on the obtained data of ab initio calculations, it is predicted that the proposed borophene/ReS2 and borophene/ReSe2 heterostructures can be promising materials for UV detectors and photosensitive materials for generating charge carriers upon absorption of light.

This paper reports an InAs/InAsSb strained-layer superlattice (SLS) mid-wavelength infrared detector and a focal plane array particularly suited for high-temperature operation. Utilizing the nBn architecture, the detector structure was grown by molecular beam epitaxy and consists of a 5.5 &micro, m thick n-type SLS as the infrared-absorbing element. Through detailed characterization, it was found that the detector exhibits a cut-off wavelength of 5.5 um, a peak external quantum efficiency (without anti-reflection coating) of 56%, and a dark current of 3.4 &times, 10-4 A/cm2, which is a factor of 9 times Rule 07, at 160 K temperature. It was also found that the quantum efficiency increases with temperature and reaches ~56% at 140 K, which is probably due to the diffusion length being shorter than the absorber thickness at temperatures below 140 K. A 320 &times, 256 focal plane array was also fabricated and tested, revealing noise equivalent temperature difference of ~10 mK at 80 K with f/2.3 optics and 3 ms integration time. The overall performance indicates that these SLS detectors have the potential to reach the performance comparable to InSb detectors at temperatures higher than 80 K, enabling high-temperature operation.

Nowadays, micro-perforated absorbers are one of the structures that are widely used nowadays. The sound absorption mechanism is performed by viscous energy losses in the cavities on the plate. This paper examined the effect of the surface shape on the micro perforated absorber performance at low frequencies (less than 500 Hz). The three-dimensional finite element method was used to predict the absorption coefficient of this group of adsorbents. Also, the results obtained from the shaped absorbers were compared with the flat micro perforated absorbers. After validating the numerical results, six different designs were defined as the surface shape of the micro perforated plates in the COMSOL Multiphysics, Ver. 5.3a software. The results reflected the fact that the factor of the surface shape can be used as a contributing factor in some frequencies. In general, the dented or concave shapes provide better outcomes than other flat designs and shapes and the convex or outward shapes bring the weakest results.

В работе предложена методика обоснования электродинамических и конструктивных параметров материалов волноводного типа, основанная на разработанной модели поглощения СВЧизлучения на импедансных стенках и диэлектрическом наполнителе конструкционных поглощающих материалов замкнутых волноводных структур. Сущность модели, основанной на методах теории дифракции электромагнитных волн в слоистых средах, законах распространения сверхвысокочастотного излучения в волноводах, заключается в том, что электромагнитное поле перед решеткой рассматривается в виде суперпозиции полей падающей плоской волны, зеркально отраженной от границы раздела среда материал, и рассеянной на стенках решетки материала. Электромагнитная волна, падающая на материал, по мере распространения вглубь него взаимодействует с радиопоглощающими стенками. Предложен подход определения коэффициента отражения материала, особенностью которого является то, что в выражение для расчета коэффициента отражения введено слагаемое, описывающее экспоненциальное снижение уровня амплитуды (плотности потока мощности) рассеянной составляющей электромагнитного поля при распространении ее вглубь материала и обратно от конструктивных и электродинамических параметров импедансных стенок и диэлектрического наполнителя замкнутых волноводных структур (закороченных волноводных отрезков), и позволяющий установить закономерности между отражательными характеристиками конструкционного поглощающего материала и его электродинамическими и конструктивными параметрами., The paper proposes a method for substantiating the electrodynamic and structural parameters of waveguidetype materials, based on the developed model for the absorption of microwave radiation on impedance walls and the dielectric filler of structural absorbing materials of closed waveguide structures. The essence of the model, based on the methods of the theory of diffraction of electromagnetic waves in layered media, the laws of propagation of microwave radiation in waveguides, is that the electromagnetic field in front of the grating is considered as a superposition of the fields of the incident plane wave, mirrored from the mediummaterial interface, and scattered on the walls of the lattice material. An electromagnetic wave incident on the material, as it propagates deep into it, interacts with radioabsorbing walls. An approach is proposed for determining the reflection coefficient of a material, a feature of which is that a term is introduced in the expression for calculating the reflection coefficient describing an exponential decrease in the amplitude level (power flux density) of the diffuse component of the electromagnetic field when it propagates deep into the material and back impedance walls and dielectric filler of closed waveguide structures (shortcircuited waveguide segments), and allowing becoming patterns between reflection characteristics of the structural material and the absorbent electrodynamic and design parameters., №2(25) (2019)

In recent years low frequency measurements in building and room acoustics fields gained attention. Moreover the low frequency sound absorption coefficient (below 100 Hz) has always been difficult to determine and the results coming from different laboratories cannot always be compared. This paper describes the principles at the basis of the round robin test carried out in the framework of the DENORMS cost action (Designs for Noise Reducing Materials and Structures). The same samples have been measured in reverberation rooms and in impedance tube by the different laboratories participating to the Round Robin Test. ispartof: Online ispartof: International Congress on Sound and Vibration (ICSV26) location:Montreal date:7 Jul - 11 Jul 2019 status: accepted

Made available in DSpace on 2021-06-25T10:33:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Previous studies have shown the challenges in using a single model to estimate chlorophyll-a concentration (Chl-a) in water bodies with widely differing characteristics. A single model based on remote sensing to map the Chl-a distribution across the entire Tietê River Cascade System (TRCS) serves as a cost and time-efficient alternative to the conventional monitoring by providing trophic status over space and time. The Tietê River contains one of the largest cascade reservoir systems in the world, which sustains important ecological and socio-economic activities in the São Paulo State, Brazil. Surplus nutrients in water draining its surrounding catchments have been the main cause of eutrophication in the reservoirs of the TRCS. To assess the trophic state of the reservoirs, Chl-a has been regularly monitored by sampling points. However, they are limited by operational costs and dependent on weather conditions. Moreover, the current sampling method only produces point-based measurements. In this paper, we calibrate remote sensing images based on the absorption coefficient to map the spatial distribution patterns of Chl-a levels in the reservoirs. Mapping is done by estimating the Chl-a concentration. The absorption coefficients were retrieved from OLI/Landsat images using the Quasi-Analytical Algorithm (QAA). The total absorption (at) in 482 nm and 655 nm retrieved by QAA presented NRMSE of 17% and 18.5%, respectively. Both at (482 and 655 nm) were used in the model calibration and presented a satisfactory result covering all data ranges, with R2 of 0.646 and NRMSE of 15.3%. The proposed model in this study to retrieve Chl-a maps with relatively high accuracy can be incorporated into the operational monitoring system of the TRCS at a low cost that can provide timely information for reservoir managers to carry out necessary actions. This may include mitigating environmental impacts caused by sudden algae blooms. São Paulo State University – Unesp Department of Cartography São Paulo State University – Unesp Department of Environmental Engineering National Institute of Education and Asian School of the Environment Nanyang Technological University São Paulo State University – Unesp Department of Cartography São Paulo State University – Unesp Department of Environmental Engineering

International audience; In this paper, we present, to the best of our knowledge, the first low-loss vacuum-compatible thermally controlled Faraday isolator able to retain a good isolation factor under high-vacuum working conditions. The throughput that can be obtained with the developed device is as high as 99%, retaining an isolation factor higher than 40 dB. That very high isolation ratio can be kept over long time periods independently from external temperature conditions with a few Celsius degrees of variation due to thermal active control. The mechanical and optical configuration is detailed, and the performances achieved with this device are presented.

V tento příspěvek pojednává o výsledcích experimentu z transmisní optické spektroskopie doplněných o data ze strukturní rentgenové analýzy na určení optických vlastností série deponovaných a tepelně zpracovaných (na 900°C) vrstev BaSrTiO3 (BST) vytvořených RF magnetronovým naprašováním. Vzorky v sérii se liší teplotou substrátu v průběhu depozice a dodatečným dodáním kyslíku k argonu do depoziční komory. Perovskitová struktura s nevýraznou přednostní orientací krystalitů ve směru [110] byla zjištěna ve vzorkách tepelně zpracovaných, zatím co vzorky v původním stavu byly amorfní. Disperzivní optické vlastnosti – indexy lomu, absorpční koeficienty a optické šířky zakázaného pásma energií byly určeny ze spekter transmitance. Indexy lomu vzorků po tepelném zpracování se zvýšily potvrzujíc zhuštění materiálu spojené se smrštěním tloušťky vrstev. Optické šířky zakázaného pásma energií určeny Taucovou procedurou jako iso-absorpční hladiny byly rovněž shledány v závislosti na parametrech depozice. In this paper we report results from optical transmittance spectroscopy complemented with data on structure from XRD measurements to determine optical properties of a series of as-deposited and annealed (at 900 C) BaSrTiO3 (BST) thin films deposited by RF magnetron sputtering. The members of the series differ by the substrate temperature and additional oxygen to accompany argon in the deposition chamber. The perovskite structure with weak preferred [110] orientation was detected for annealed BST thin films whilst the as-deposited films were amorphous. Dispersive optical properties – refractive indices, absorption coefficients and optical band gaps were determined from transmittance spectra. After annealing refractive indices increase to prove the densification of material accompanied by the thickness shrinkage. Optical band gaps calculated either by Tauc procedure or determined as iso-absorption levels are also found to be deposition dependent.

In this paper the influence of non-acoustic properties on the sound absorption coefficient of polyurethane foams as a porous medium is investigated. Biot’s equations with transfer matrix method, as the solution approach are employed to evaluate the sound absorption coefficient of selected polyurethane foams. The major issue is the dependency of non-acoustic properties on each other which makes difficulties to examine the effect of parameters individually. Some facts from the results of previous works are used in order to overcome this prominent obstacle. The results show that increasing the porosity doesn’t have a great influence on the sound absorption coefficient and only for highly porous foams, raising porosity decreases the sound absorption performance. The increase of air flow resistivity up to an optimized value, intensifies the absorption capability. Furthermore, for partially reticulated (partially open cell) foams, the increase of tortuosity improves the sound absorption efficiency at lower frequencies.

The acoustic correction of large places for low frequency components can be obtained by inserting acoustic resonators. This paper reports the realization and the experimental verification of acoustic resonators obtained with ceramic material. The sound absorption is obtained by drilling the specimens of ceramic material with a hole size of 2 mm and 5 mm and a thickness of 3.0 cm, 2.0 cm and 0.6 cm. The sound absorption of perforated plates is based on the principle of Helmholtz resonators, which, however, are effective only on narrow frequency bands; so to make the phenomenon of absorption more effective and to increase the range in absorption frequency perforated panels are made, mounted at a suitable distance from a rigid surface. The measurements of the sound absorption coefficient were performed with an impedance tube (Kundt tube) with an internal diameter of 10 cm and with the validity of the measurement of the absorption coefficient in the range of 100 Hz – 1.0 kHz. The measurements of the absorption coefficient were performed, for each specimen, creating a cavity of air between the sample and the behind rigid surface, with the following thicknesses: 25 cm, 20 cm, 15 cm, 10 cm and 5 cm. As expected, for the same specimen, the peak of the absorption coefficient shifts to higher frequencies on decreasing size of the cavity between the specimen and the rigid wall.

Tento článek uvádí výsledky výzkumu z optické transmitanční spektrofotometrie spolu s daty ze strukturní rentgenové difrakce za účelem určení optických vlastností série vzorků tenkých vrstev perovskitu ZnTiO3 deponovaných na skle reaktivním magnetronovým naprašováním. Jednotlivé vzorky ze série se navzájem liší množstvím titanu, což posloužilo jako zdroj změn ne jenom struktury, nýbrž i změn disperzních optických vlastností. Nízká porosita materiálu byla zjištěna použitím Bruggemanovy aproximací efektivního média. Se stoupajícím množstvím titanu ve vrstvách byl pozorován zjevný „modrý“ posun optické šířky zakázaného pásma. Pozorované změny zakázaného pásma energií je dobrý potenciál pro optoelektronické a foto-katalytické aplikace ZnTiO3. In this paper we report results from optical transmittance spectroscopy complemented with data on structure from XRD measurements to determine optical properties of a series of ZnTiO3 perovskite thin films deposited on glass by reactive magnetron co-sputtering. The members of the series differ by the titanium content that was revealed as an origin of the changes not only in structure but also in dispersive optical properties. Low porosity has been discovered and calculated using the Bruggeman effective medium approximation. An apparent blue-shift of the optical band gap energies with increasing titanium content was observed. The observed band gap engineering is a good prospective for eg optoelectronic and photocatalytic applications of ZnTiO3.

In this paper, two composite silicon solar cells n+-ii-p+ based on hydrogenated amorphous - nanocrystalline silicon (a-Si:H/nc-Si:H) have been simulated by using computer modeling and simulation program (AMPS-1D - Analysis of Microelectronic and Photonic Structures). Various factors that affect cell performance have been studied, such as spectral light irradiation (flux flow), front and back contacts potential, work function and reflection coefficients of Transparent Conducting Oxide (TCO), layers absorption coefficients, band gap and layer thickness up to 1500nm of the homogenous and heterogeneous intrinsic absorber layer of silicon solar cells. It was found that in case of standard solar cell conditions a layers absorption coefficient has a major contribution to solar cell performance. It is demonstrated that, for homogenous intrinsic absorber layer with crystal fraction Xc=33% cell efficiency is higher than in case heterogeneous intrinsic absorber layer which contains of arbitrary crystal fractions depending of layer thickness. Second case scenario of silicon thin film composite structure is more common in solar cells production according to PECVD deposition technique proven by earlier X-ray diffraction and high resolution electron microscopy measurements.

In this paper, a computational approach based on decoupled study for different directions in the analysis of minibands structure and absorption coefficient for cuboid quantum dot superlattices is described and used. Analysis is focused on zinc-blende semiconductors (such as InAs and GaAs) and wurtzite InGaN. Nowadays, the latter represents a promising material for light emission, but it could become an interesting semiconductor for devices based on optical absorption, too.

Airflow resistance is one of the main non-acoustic parameters, which shows the behaviour of porous materials used in sound-absorbing systems. The standard SRPS ISO 9053 specifies two methods for measuring airflow resistance: a steady-state airflow method and an alternating airflow method. The paper presents the possibility of realization of the measurement system for measuring airflow resistance by using the existing laboratory equipment. The constant airflow is provided by a vacuum pump. The advantage of using this measurement system is a considerably lower price in comparison to commercial solutions, whereas the processing of measurement results which is not completely automated is regarded as a weakness.

There have recently been several studies published involving terahertz (THz) imaging of frozen biomedical samples. In this paper, we investigate the effects of the freeze-thaw cycle on THz properties of porcine muscle and fat samples. For ordinary freezing, there was a significant change in the THz properties after thawing for muscle tissue but not for fat tissue. However, if snap-freezing was combined with fast-thawing instead of ordinary freezing and ordinary thawing, then the freeze-thaw hysteresis was removed. Refereed/Peer-reviewed

In this paper, a model to estimate minibands and theinterminiband absorption coefficient for a wurtzite (WZ) indium gallium nitride (InGaN) self-assembled quantum dot superlattice (QDSL) is developed. It considers a simplified cuboid shape for quantum dots (QDs). The semi-analytical investigation starts from evaluation through the three-dimensional (3D) finite element method (FEM) simulations of crystal mechanical deformation derived from heterostructure lattice mismatch under spontaneous and piezoelectric polarization effects. From these results, mean values in QDs and barrier regions of charge carriers’ electric potentials and effective masses for the conduction band (CB) and three valence sub-bands for each direction are evaluated. For the minibands’ investigation, the single-particle time-independent Schrödinger equation in effective mass approximation is decoupled in three directions and resolved using the one-dimensional (1D) Kronig–Penney model. The built-in electric field is also considered along the polar axis direction, obtaining Wannier–Stark ladders. Then, theinterminiband absorption coefficient in thermal equilibrium for transverse electric (TE) and magnetic (TM) incident light polarization is calculated using Fermi’s golden rule implementation based on a numerical integration into the first Brillouin zone. For more detailed results, an absorption coefficient component related to superlattice free excitons is also introduced. Finally, some simulation results, observations and comments are given.