Estimation Of Absorption Coefficient Research Articles

Estimating absorption coefficients of colored dissolved organic matter (CDOM) using a semi-analytical algorithm for southern Beaufort Sea waters: application to deriving concentrations of dissolved organic carbon from space

Estimating absorption coefficients of colored dissolved organic matter (CDOM) using a semi-analytical algorithm for southern Beaufort Sea waters: application to deriving concentrations of dissolved organic carbon from space

Sound absorption modeling of thin woven fabrics backed by an air cavity

A theoretical model for the oblique incidence sound absorption coefficient of thin woven fabrics backed by an air cavity is presented where the fabric is acoustically described by its specific airflow resistance and its surface mass density. The theoretical model is illustrated by an equivalent electrical circuit and validated in the case of normal sound incidence by experimental results obtained from impedance tube measurements on three fabric types. The influence of the surface mass density on the absorption coefficient is discussed and recommendations for practical applications are derived. Further, a simple formula to predict the specific airflow resistance of woven fabrics based on geometrical parameters is deduced. The normal incidence absorption coefficient and geometrical parameters of a set of 24 fabrics with a large range of interyarn porosities and specific airflow resistances were measured and used to validate the proposed geometry-based model to predict the absorption coefficient. Measured and estimated absorption coefficients show excellent agreement, with mean value and standard deviation of the differences of 0.03 ± 0.10. The model is therefore suitable for the design of new fabrics with an intended absorption coefficient.

Rating of the loudest college basketball arenas for Entertainment Sports Network (ESPN) magazine.

A recent ESPN magazine article [“These go to 11,” ESPN the Magazine 15 Nov (2010)] ranked the top collegiate basketball arenas according to “noise potential.” The top five arenas were listed as Kansas University, Duke University, New Mexico University, Kentucky University, and Florida University. The rankings were established by a team of Penn State Acoustics students using the theory for sound buildup in large rooms, since actual measurements were infeasible. Both diffuse field and direct field contributions of the sound pressure were estimated at center court for octave band frequencies from 125 Hz to 4 kHz. Seating geometries, materials, and other relevant information were collected for each arena and used with estimated absorption coefficients to determine the room constant and critical distance. The diffuse field contributions were then combined with approximate sources terms based on the seating capacity of the arena, the proximity of the fans to the court, and whether they were students. The sound pressures were then combined into a total A‐weighted sound pressure level and used to determine the ranking. The direct and reverberant contributions of each arena were then compared to establish the positive and negative aspects of each arena in terms of noise potential. This comparison reveals how Kansas and Duke reached the top of the ranking, despite having drastically different arena geometry and capacity.

Quantitative photoacoustic imaging: correcting for heterogeneous light fluence distributions using diffuse optical tomography

The specificity of molecular and functional photoacoustic (PA) images depends on the accuracy of the photoacoustic absorption spectroscopy. The PA signal is proportional to the product of the optical absorption coefficient and local light fluence; quantitative PA measurements of the optical absorption coefficient therefore require an accurate estimation of optical fluence. Light-modeling aided by diffuse optical tomography (DOT) can be used to map the required fluence and to reduce errors in traditional PA spectroscopic analysis. As a proof-of-concept, we designed a tissue-mimicking phantom to demonstrate how fluence-related artifacts in PA images can lead to misrepresentations of tissue properties. To correct for these inaccuracies, the internal fluence in the tissue phantom was estimated by using DOT to reconstruct spatial distributions of the absorption and reduced scattering coefficients of multiple targets within the phantom. The derived fluence map, which only consisted of low spatial frequency components, was used to correct PA images of the phantom. Once calibrated to a known absorber, this method reduced errors in estimated absorption coefficients from 33% to 6%. These results experimentally demonstrate that combining DOT with PA imaging can significantly reduce fluence-related errors in PA images, while producing quantitatively accurate, high-resolution images of the optical absorption coefficient.

Optical absorption red and blue shifts in ZnFe 2O 4 nanoparticles

Nanoparticles of zinc ferrite (ZnFe 2O 4) prepared by both wet- and dry-high-energy ball milling (HEBM), have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), surface area and pore size distribution (BET) and wavelength-dependent diffuse reflectance and scattering turned into absorption coefficient estimation using the Kubelka–Munk theory. It was found that after 72 h of HEBM, the particle size was decreased from 220 nm for the initial material to 16.5 nm and 9.4 nm for the wet- and dry-milled samples, respectively. The optical absorption analysis revealed that the energy gap is increased (blue shift) for wet-milled and decreased (“anomalous” red shift) for dry-milled samples of ZnFe 2O 4 as the particle size decreased. The likely origins for the phenomena, namely the blue and red shifts as large as 0.45 eV and 0.14 eV, respectively, are proposed and discussed, and the effects are quantitatively estimated.

Design and construction of a small sound testing room in an office building

A small sound-testing room has been constructed in the basement of an office building located within 50 ft. of railroad tracks. The room was designed to be multifunctional with both reverberant and semianechoic settings. The sound isolation of the room was designed with the expectation of conducting active noise reduction tests with sound-pressure levels of 120 dB and higher. The room is also being used to roughly estimate absorption coefficients of various materials. The room is 10.5×9.75×7.5 ft. with a volume of 768 ft3. It is composed of a concrete floor and gypsum walls and ceiling. The walls are isolated from the floor with rubber isolation pads. The ceiling is constructed of 5/8-in. gypsum, 1/2-in. plywood, and a 2-in. layer of sand. The wall construction is 2×4 wood studs, two layers of 5/8-in. gypsum resiliently attached, and 3 in. of fiberglass. The entrance to the room is made of double solid core wood doors with a composite isolation and absorption layer in between both doors. Other design components, actual sound transmission testing results, reverberation times, modal issues, and uses for the room are discussed.

Compensation for geometric mismodelling by anisotropies in optical tomography

We propose an approach for the estimation of the optical absorption coefficient in medical optical tomography in the presence of geometric mismodelling. We focus on cases in which the boundaries of the measurement domain or the optode positions are not accurately known. In general, geometric distortion of the domain produces anisotropic changes for the material parameters in the model. Hence, geometric mismodelling in an isotropic case may correspond to an anisotropic model. We seek to approximate the errors due to geometric mismodelling as extraneous additive noise and to pose a simple anisotropic model for the diffusion coefficient. We show that while geometric mismodelling may deteriorate the estimates of the absorption coefficient significantly, using the proposed model enables the recovery of the main features.

Influence Factors and Slope Coefficients of Spectral Absorption of Coloured Dissolved Organic Matter (CDOM) in East Taihu Lake, China

CDOM吸收特性是湖泊水色遥感的重要研究内容之一,影响着水体的遥感反射率;吸收光谱的形状一般符合波长的负指数关系,但不同水体的形态因子即S值是不同的.实地采集东太湖水样,实验室测量叶绿素、悬浮物质以及黄色物质的组份含量,室内测试计算水样的CDOM吸收光谱,根据光谱曲线形状,把样点分为三组,分别进行考察,结果发现对东太湖春季水体而言,浮游植物的降解对CDOM吸收具有重要甚至主导作用;水体中有机悬浮颗粒占有一定的比例,在测试或计算东太湖总的吸收或散射系数时,必须充分考虑有机悬浮颗粒的吸收与散射特性,否则会带来较大的误差;以500nm为分界点,把300-700nm的波段范围分为两个部分即300-500nm和500-700nm,分别定义CDOM吸收光谱的曲线斜率即S值,可以提高CDOM吸收光谱的估测精度,把S值定义为随波长线性变化的函数,可以进一步提高CDOM吸收光谱的估测精度,对东太湖春季水体而言,当:300≤λ<500nm时,S(μm^-1)=-0.0193×λ+20.821,当500≤λ≤700nm时,S(μm^-1)=-0.0121×λ+16.003.;Absorption property of CDOM(coloured dissolved organic matter),which influences remote sensing reflectance of waterbody,is one of the important contents to remote sensing of water colour.Generally, the absorption spectra curves follow the minus-exponential function with wavelength.But the shapes have some difference in different water-body.Consequently, the spectral slope co-efficients,viz.S-values,are different to different water-bodies.So,if we only use the S-value from some different literatures,the error for estimating absorption coefficient of CDOM will be great.Accordingly, we have to determine the S-value of absorption curves of CDOM in Taihu Lake,a large shallow lake with average depth 1.9 meters (max.2.6m),68.5km length from south to north,average 34km width from east to west (max.56km),covering an area of 2427.8 km² (including 51 islands),one among the five fresh-water lakes of China and positioned in the Yangtze Della (30°55'40-31°32'58N,119°52'32-l20°36'10E),east of China. One campaign was taken for 14 water-samples in East Taihu Lake,on April 4,2004.Surface water-samples were collected in situ in the vertical direction with a standard 2 liter polyethylene water-fetched instrument.Then they were brought from the deepfreeze to the laboratory using 2 liter polyethylene bottles for further analysis according to correlated investigation criterions about lakes of China.The parameters analyzed in the lab included concentrations of chlorophyll-a (CHL), suspended substance (SS)and yellow substance (DOC).Then the absorption spectra of CDOM were also measured with the spectrophotometer in the lab according to some measurement criterion by NASA,and the final results were revised in scattering influences. According to the shapes of spectra curves measured f all the samples were divided into three groups for analyzing further, denoting the different water-quality environment.And the results show that influence factors of CDOM absorption are different in different water-quality environment.To tlie water-body of East Taihu Lake in spring,decomposition of phytoplankton plays an important role in absorption of CDOM.When phytoplankton is decomposed into organic suspended matter, its role to absorption of CDOM isnt evi-dent.However,when it continues decomposing and decays,the decayed matter plays a dominant role in absorption of CDOM.Accordingly, the organic suspended matter takes a relative staled proportion in total suspended matter.And the absorption and scatter properties of suspended matter should be taken fully into ac count when we measure or estimate the total absorption and scatter coefficients of the water-body in East Taihu Lake.Otherwise,great error will be caused. The wavelength range from 300 to 700nm is divided into two parts,one from 300 to 500nm and the other from 500 to 710nm, and then the different S-values are quantitated,which can improve the estimation of CDOM absorption,proved by their comparative analysis results. In facl,S-value here is a linear function following with wavelength.So when we use the appropriate linear function to define S-value.the estimation precision of CDOM absorplion can be improved farther.To the water-body of East Taihu Laihu Lake in Spring, when the wavelength A is more than 300nm and less than 500nm,S(μm^-1)=-0.0193×λ+20.821.And when the wave-length λ is more than 500 nm and less than 700 nm, S(μm^-1)=-0,0121×λ+16.003.

A modelling error approach for the estimation of optical absorption in the presence of anisotropies

Optical tomography is an emerging method for non-invasive imaging of human tissues using near-infrared light. Generally, the tissue is assumed isotropic, but this may not always be true. In this paper, we present a method for the estimation of optical absorption coefficient allowing the background to be anisotropic. To solve the forward problem, we model the light propagation in tissue using an anisotropic diffusion equation. The inverse problem consists of the estimation of the absorption coefficient based on boundary measurements. Generally, the background anisotropy cannot be assumed to be known. We treat the uncertainties in the background anisotropy parameter values as modelling error, and include this in our model and reconstruction. We present numerical examples based on simulated data. For reference, examples using an isotropic inversion scheme are also included. The estimates are qualitatively different for the two methods.

The dispersal of the Amazon and Orinoco River water in the tropical Atlantic and Caribbean Sea: Observation from space and S-PALACE floats

Abstract The temporal evolution of spatial patterns of the colored water mass associated with the discharges of the Amazon and Orinoco Rivers between 1997 and 2002 was examined using concurrent in situ and satellite observations in the region bounded by 0°N–24°N and 70°W–40°W. Patches of low-salinity (∼32–34) surface waters were frequently observed with Salinity Profiling Autonomous LAgrangian Current Explorer (S-PALACE) floats as far as 2000 km away from the mouths of the Amazon and Orinoco Rivers. Ocean-color data collected with the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) show that these patches originate with these rivers. Chlorophyll (Chl) and colored dissolved organic matter (CDOM) distribution estimated with SeaWiFS data are well correlated with low sea-surface salinity (SSS) throughout the observation period (average correlation coefficients for monthly observations of −0.6 for the SSS–CDOM relationship and −0.5 for the SSS–Chl relationship). The color of the water in the river plumes is dominated by CDOM rather than Chl light absorption, in contrast to adjacent open-ocean and equatorial upwelling regions, where optical properties are primarily controlled by Chl. The mean CDOM absorption coefficient for the area covered by the Amazon's plume showed a peak in July for the 1998–2001 period, which lagged the Amazon's hydrograph by one month. The timing of the CDOM peak along different sections of the Amazon River plume implies an estimated advection speed of ∼35 cm s−1 within the plume. Anti-cyclonic rings (eddies) with diameters of 400–500 km were observed moving along the northeastern coast of South America every year and in all seasons, at a frequency of about one every 30–60 days. These eddies moved to the northwest at a speed of 8–20 cm s−1, with higher speeds observed during the first half of each calendar year. The average depth of the Amazon plume for SSS ranging from 32 to 35 was 20–30 m, and the total fresh-water volume contained in the plume was consistent with discharge rates. Due to uncertainties in the Chl and CDOM absorption coefficient estimates in river plumes, accurate estimation of the rivers’ impact on regional primary production remains a challenge. The paired SeaWiFS and S-PALACE float observations validate the hypothesis that the coherent surface color patches seen annually far offshore in the tropical North Atlantic are caused by dispersal of Amazon and Orinoco River water. In contrast, wind-driven upwelling near the edge of the North Brazil Current retroflection, another mechanism causing color enhancement, is not suggested by these data sets.

Estimation of the absorption performance of multiple layer perforated panel systems by transfer matrix method

The absorption performance of single layer perforated panel system has been usually estimated by equivalent electro-acoustic circuit analysis based upon the analogy between electric circuit and acoustic system. In the case of multiple layer perforated panel system, however, the transfer matrix method is more convenient than the equivalent circuit analysis. Hence, in this paper the transfer matrix method widely used for the one-dimensional acoustic analysis of engine exhaust muffler is presented. The absorption coefficient is estimated from the overall transfer matrix obtained by multiplying unit transfer matrices for perforated panels or airspaces. The proposed transfer matrix method is confirmed by comparing the estimated absorption coefficient with the measured value. In addition, the effect of dimension and arrangement of the perforated panels on the acoustical performance is discussed.

The quantitative filter technique for measuring phytoplankton absorption: Interference by MAAs in the UV waveband

The absorption of suspended particulate material is commonly estimated with the filter pad technique, which requires a correction for pathlength amplification. The pathlength amplification factor (β) varies among different studies and phytoplankton species or communities. It remains the largest source of uncertainty in estimated absorption coefficients. Recently, several empirical models estimating this correction were developed but mostly for visible range. In this study, β was calculated empirically from the ratio of filtered to suspension absorption between 280 and 850 nm for cultures of two dinoflagellates and one diatom. Results show that in the visible waveband, β values are relatively constant and fall within the published range (averages between 2.4 and 2.8). These values remain flat over the UV waveband for the diatom tested. However, below 400 nm, the presence of mycosporine‐like amino acids (MAAs) strongly influences the absorbance measurements. For the dinoflagellates studied, the ultraviolet (UV) absorbance measured on frozen filters (stored in liquid nitrogen) reveals a large peak (Sosik 1999) caused by high concentrations of MAAs, which is much smaller on absorbance scans of suspended cells. This amplified UV peak adds to the true amplification effect caused by the extended pathlength of light in filter pads. This artifact, caused by the extracellular release of the water‐soluble MAAs during freezing, also was observed to a lower degree with measurements performed on fresh filters (immediate scanning), precluding the use of this method to estimate UV absorption in the species tested.

Resonant photothermal bending spectroscopy at variable temperature 25–150 °C and its application to hydrogenated microcrystalline silicon films

Resonant photothermal bending spectroscopy (RPBS) at various measurement temperatures has been developed for estimating absorption coefficient (α) spectra of thin film semiconductors. The experimentally obtained sensitivity of RPBS was about ten times larger than nonresonant PBS. In vacuum, this technique has been applied to estimate the α spectrum of hydrogenated microcrystalline silicon (μc-Si:H) films at the measurement temperatures from 25 to 150 °C. It is demonstrated that the temperature coefficient of an indirect optical absorption at 1.2–1.8 eV caused by Si microcrystallite is almost the same as that of single crystalline silicon, and the temperature coefficient of below-gap absorption intensity is negative. The reason for the negative temperature coefficient and the energy level of the localized state resulting in the below gap absorption are discussed.

전달행렬법을 이용한 다중 다공판 시스템의 흡음성능 예측

A practical method of predicting the sound absorption coefficient for multiple perforated-plate sound absorbing system was developed using transfer matrix method. The proposed method was validated by comparing the calculated absorption coefficients of a single layer perforated plate with the values measured by the two-microphone impedance tube method for various porosity and spacing of the perforated plate. The developed transfer matrix method was further applied to estimate the multiple layer perforated plates and it is shown that the estimated absorption coefficients agree well with the measured values.

Temperature dependence of absorption coefficient spectra for μc-Si films by resonant photothermal bending spectroscopy

Abstract Resonant photothermal bending spectroscopy (R-PBS) has been developed for estimating absorption coefficient spectra of thin film semiconductors. This technique has been applied to hydrogenated microcrystalline silicon (μc-Si:H) films at different measurement temperatures. It is found that absorption coefficient of μc-Si:H films at 0.7–1.1 eV is relevant for the localized states and decreases with increasing measurement temperature. The localized state exists at ∼0.7 eV in the band gap from the band edge. The origin of the absorption is also discussed.

Method for Measuring Cellular Optical Absorption and Scattering Evaluated Using Dilute Cell Suspension Phantoms

The opal glass method (OGM) is a standard technique used by the ocean optics community to measure the spectral absorption coefficients of algal suspensions. We present and evaluate this method for its potential application to measurements of the inherent optical properties (optical absorption and scattering coefficients) of dilute mammalian cell suspensions, as an alternative to the integrating sphere method. In a series of controlled experiments on absorbing and scattering phantoms (Evans blue dye and polystyrene spheres 1–20 μm in diameter), separation of absorption and scattering was possible with less than 20% error in absorption coefficient estimates for particles with major scattering components in the size range of 2–5 μm.

Light absorption by phytoplankton and the filter amplification correction: cell size and species effects.

Filter amplification corrections are presented for eight marine centric diatoms. These functions are required to correct the amplified optical path-length associated with the glass-fiber filter used in the measurement of phytoplankton absorption. Correction factors constructed from phytoplankton cultures in the laboratory are often applied to phytoplankton assemblages in the field. This study demonstrates significant differences in the filter amplification correction correlated to species and cell volume. This variation in the filter amplification correction can result in significant error in estimated absorption coefficients, compromising subsequent estimates of quantum yield and primary production.

Dermal pharmacokinetics of microemulsion formulations determined by in vivo microdialysis.

To investigate the potential of improving dermal drug delivery of hydrophilic and lipophilic substances by formulation in microemulsion vehicles and to establish a reliable pharmacokinetic model to analyze cutaneous microdialysis data. After a topical application of microemulsions, commercially available creams, and a hydrogel, unbound cutaneous concentrations of lidocaine and prilocaine were determined by in vivo microdialysis in rats. Recovery was monitored during the experiments via retrodialysis by calibrator. The presented pharmacokinetic model provided an excellent fit of the microdialysis concentration-time curves with reliable estimation of absorption coefficient and lag time. The microemulsion formulations were shown to increase the absorption coefficient of lidocaine more than eight times (753 microg/l/min) compared with a conventional oil-in-water emulsion-based cream (89 microg/l/min) and prilocaine hydrochloride almost two times (8.9 microg/l/min) compared with hydrogel (5.2 microg/l/min). The microemulsion formulations can be applied to increase dermal drug delivery of both the hydrophilic and lipophilic model drug. The pharmacokinetic model presented in this report is, to the author's knowledge, the first example in the literature, providing reliable estimation of cutaneous absorption coefficient and lag time from microdialysis data of topically applied substances.

Theoretical estimation of absorption coefficients of various polymers at 13 nm

The linear absorption coefficients at 13 nm were calculated for more than 150 polymers. The results indicate that an aromatic substitution lowers the absorption coefficient. This is because oxygen has a larger atomic absorption than carbon or hydrogen and the substitution reduces the relative oxygen content. Furthermore, the Ohnishi parameters for the polymers were calculated in order to investigate the relationship between the absorption at 13 nm and the etching resistance. This showed that polymers with aromatic groups tend to exhibit a lower absorption and a higher etching resistance than those without aromatic groups. This suggests that, regarding resist processes for EUV (extreme ultraviolet) lithography, a single-layer resist process employing no hard-mask layer is another promising candidate in addition to one that uses both an unltrathin resist layer (∼100 nm thick) and a hard-mask layer

Shadowgraphic and interferometric investigations on Nd:YAG laser-induced vapor/plasma plumes for different processing wavelengths

Shadowgraphic and interferometric images of vapor/plasma plumes generated by pulses of a ns-Nd:YAG laser reveal the distinctive behavior of the shock wave expansion for each of three processing wavelengths (1064 nm, 532 nm, and 355 nm), indicating that different mechanisms dominate the interaction between the optical fields and the material vapor/plasma. Electron density distributions within the plasma plumes calculated from interferometrically obtained refractive index distributions allow us to describe the regions of absorption and the absorption mechanisms using a simple model of inverse bremsstrahlung and photoionization, which allows us to estimate absorption coefficients.