To minimize the calculation errors in the sound absorption coefficient resulting from inaccurate measurements of flow resistivity,a simple method for determining the sound absorption coefficient of soundabsorbing mate...To minimize the calculation errors in the sound absorption coefficient resulting from inaccurate measurements of flow resistivity,a simple method for determining the sound absorption coefficient of soundabsorbing materials is proposed.Firstly,the sound absorption coefficients of a fibrous sound-absorbing material are measured at two different frequencies using the impedance tube method.Secondly,utilizing the empirical formulas for the wavenumber and acoustic impedance in the fibrous material,the flow resistivity and porosity of the sound-absorbing materials are calculated using the MATLAB cycle program.Thirdly,based on the values obtained through reverse calculations,the sound absorption coefficient,the real and the imaginary parts of the acoustic impedance of the sound-absorbing material at different frequencies are theoretically computed.Finally,the accuracy of these theoretical calculations is verified through experiments.The experimental results indicate that the calculated values are basically consistent with the measured values,demonstrating the feasibility and reliability of this method.展开更多
Establishing the remote sensing algorithm of retrieving the absorption coefficient of seawater petroleum substances is an efficient way to improve the accuracy of retrieving a seawater petroleum concentration using a ...Establishing the remote sensing algorithm of retrieving the absorption coefficient of seawater petroleum substances is an efficient way to improve the accuracy of retrieving a seawater petroleum concentration using a remote sensing technology. A remote sensing reflectance is a basic physical parameter in water color remote sensing. Apply it to directly retrieve the absorption coefficient of seawater petroleum substances is of potential advantage. The absorption coefficient of waters containing petroleum [ACWCP, a_o（λ）], consists of the absorption coefficient of pure water [ACPW, a_w（λ）], plankton [ACP, a_（ph）（λ）], colored scraps [ACCS, a_（d,g）（λ）], and petroleum substance [ACPS, a_（oil）（λ）]. Among those, ACCS consists of the absorption coefficient of nonalgal particle [ACNP, a_d（λ）] and colored dissolved organic matter [ACCDOM, a_g（λ）]. For waters containing petroleum, the retrieved ACCS using the existing method is a combination absorption coefficient of ACNP,ACCDOM and ACPA [CAC, a_（d,g,oil）（λ）]. Therefore, the principle question is how to extract ACPS from CAC.Through the analysis of the three proportion tests conducted between the year of 2013 and 2015 and the corresponding remote sensing data, an algorithm of retrieving the absorption coefficient of petroleum substances is proposed based on remote sensing reflectance. First of all, ACPS and CAC are retrieved from the reflectance using the quasi-analytical algorithm（QAA）, with some parameter modified. Secondly, given the fact that the backscatter coefficient [BC, b_（bp）（555）] of total particles at 555 nm can be obtained completely from the reflectance, the relation between BC and ACNP in petroleum contaminated water can be established. As a result, ACNP can be calculated. Then, combining the remote sensing retrieving algorithm of a_g（440）, the method of achieving the spectral slope of the absorption coefficient can be established, from which ACCDOM,can be calculated. Finally, ACPS can be computed as the residual. The accuracy of ACPS based on this algorithm is 86% compared with the in situ measurements.展开更多
This paper suggests a group of statistical algorithms for calculating the total absorption coefficients based on in situ data of apparent optical property and inherent optical property collected with strict quality as...This paper suggests a group of statistical algorithms for calculating the total absorption coefficients based on in situ data of apparent optical property and inherent optical property collected with strict quality assurance according to NASA ocean bio-optic protocols in the Yellow Sea and the East China Sea in spring 2003. The band-ratios ofRrs412/Rrs555, Rrs49o/Rrs555 are used in the algorithms to derive the total absorption coefficients （at） at 412, 440, 488, 510, 532 and 555nm bands, respectively. The average relative errors between inversed and measured values are less than 25.8%, with the correlative coefficients （R2） being 0.75-0.85. Error sensitivity analysis shows that the maximum retrieval error is less than 24.0% at ＋5% error in Rrs＇s. So the statistical algorithms of this paper are practicable. In this paper, the relations between the total absorption coefficients at 412, 488, 510, 532, 555 nm and that of 440nm are also studied. The results show that the relations between the total absorption coefficients of 400-600 nm and that of 440 nm are correlated well and all of their correlative coefficients R2 are greater than 0.99. Furthermore, a regression analysis is also done for the slope of the linear relations and wavelengths, and the R2 is also 0.99. Thus it is possible to retrieve other bands＇ total absorption coefficients with only one band absorption value, which significantly reduce the number of unknown parameters in studying other ocean color related problems.展开更多
The East China Sea （ECS）, one of the largest continental seas, has dynamic hydrology and complex optical characteristics that make ocean color remote-sensing retrieval difficult. The distributions and proportions of...The East China Sea （ECS）, one of the largest continental seas, has dynamic hydrology and complex optical characteristics that make ocean color remote-sensing retrieval difficult. The distributions and proportions of the light absorption coefficients of major ocean color components based on two large-scale investigations in the ECS are presented, showing these features in typical summer and winter seasons. The absorption coefficient aCDOM, aNAp and aphy of colored dissolved organic matter, non-algal particle, and pigment of phytoplankton show a decreasing trend from the coast to the outer shelf. According to the aeDOM distribution at 440 nm, the Changjiang River plume shows an abnormal southeastward transport. An extremely high aNaP value patch at 440 nm is present in the middle coast. The chlorophyll-a-specific phytoplankton pigment absorption （a^hy） is much higher in winter than in summer, which may cause serious underestimated results when applying the averaged aphy into remote-sensing algorithms for chlorophyll concentration retrieval. The importance of phytoplankton size was evident in outer shelf waters. The absorption of aCDOM （440） is a dominant component accounting for over half of the total seawater absorption in summer. The aNAP（440） accounts for 64% of the absorption of the ECS coastal area in winter.展开更多
The temporal and spatial variabilities of phytoplankton absorption coefficients （a ph （λ）） and their relationships with physical processes in the northern South China Sea were examined, based on in situ data coll...The temporal and spatial variabilities of phytoplankton absorption coefficients （a ph （λ）） and their relationships with physical processes in the northern South China Sea were examined, based on in situ data collected from two cruise surveys during May 14 to 25, 2001 and November 2 to 21, 2002. Significant changes in the surface water in a ph values and B/R ratios （a ph （440）/a ph （675）） were observed in May, which were caused by a phytoplankton bloom on the inner shelf stimulated by a large river plume due to heavy precipitation. This is consistent with the observed one order of magnitude elevation of chlorophyll a and a shift from a pico/nano dominated phytoplankton community to one dominated by micro-algae. Enhanced vertical mixing due to strengthened northeast monsoon in November has been observed to result in higher surface a ph （675） （0.002–0.006 m-1 higher） and less pronounced subsurface maximum on the outer shelf/slope in November as compared with that in May. Measurements of a ph and B/R ratios from three transects in November revealed a highest surface a ph （675） immediately outside the mouth of the Zhujiang （Pearl） River Estuary, whereas lower a ph （675） and higher B/R ratios were featured in the outer shelf/slope waters, demonstrating the respective influence of the Zhujiang River plume and the oligotrophic water of the South China Sea. The difference in spectral shapes of phytoplankton absorption （measured by B/R ratios and bathochromic shifts） on these three transects infers that picoprocaryotes are the major component of the phytoplankton community on the outer shelf/slope rather than on the inner shelf. A regional tuning of the phytoplankton absorption spectral model （Carder et al., 1999） was attempted, demonstrating a greater spatial variation than temporal variation in the lead parameter a 0 （λ）. It was thus implicated that region-based parameterization of ocean color remote sensing algorithms in the northern South China Sea was mandatory.展开更多
Temporal and spatial patterns of inherent optical properties in the Bohai Sea are very complex. In this paper, we used 77 groups of field data of AOPs （apparent optical properties） and IOPs （inherent optical proper...Temporal and spatial patterns of inherent optical properties in the Bohai Sea are very complex. In this paper, we used 77 groups of field data of AOPs （apparent optical properties） and IOPs （inherent optical properties） collected in June, August, and September of 2005 in the Bohai Sea, to retrieve the spectral total absorption coefficient a（2） with the quasi-analytical algorithm （QAA）. For QAA implementation, different bands in the region 680-730 nm （in 5 nm intervals） were selected and compared, to determine the optimal band domain of the reference wavelength. On this basis, we proposed a new algorithm （QAA-Com）, a combination of QAA-685 and QAA-715, according to turbidity characterized by a（440）. The percentage difference of model retrievals in the visible domain was between 4.5%-45.1%, in average of 18.8% for a（2）. The QAA model was then applied to Medium Resolution Imaging Spectrometer （MERIS） radiometric products, which were temporally and spatially matched with in-situ optical measurements. Differences between MERIS retrievals and in-situ values were in the range 9.2%-27.8% for a（2） in the visible domain. Major errors in satellite retrieval are attributable to uncertainties of QAA model parameters and in-situ measurements, as well as imperfect atmospheric correction of MERIS data by the European Space Agency （ESA）. During a storm surge in April 2009, time series of MERIS images together with the QAA model were used to analyze spatial and temporal variability of the total absorption coefficient pattern in the Bohai Sea. It is necessary to collect more independent field data to improve this algorithm.展开更多
The monochromatic absorption coefficient of silicon, inducing the light penetration depth into the base of the solar cell, is used to determine the optimum thickness necessary for the production of a large photocurren...The monochromatic absorption coefficient of silicon, inducing the light penetration depth into the base of the solar cell, is used to determine the optimum thickness necessary for the production of a large photocurrent. The absorption-generation-diffusion and recombination (bulk and surface) phenomena are taken into account in the excess minority carrier continuity equation. The solution of this equation gives the photocurrent according to ab</span><span style="font-family:Verdana;">sorption and electronic parameters. Then from the obtained short circuit</span><span style="font-family:Verdana;"> photocurrent expression, excess minority carrier back surface recombination velocity is determined, function of the monochromatic absorption coefficient at a given wavelength. This latter plotted versus base thickness yields the optimum thickness of an n</span><sup><span style="font-family:Verdana;">+</span></sup><span style="font-family:Verdana;">-p-p</span><sup><span style="font-family:Verdana;">+</span></sup><span style="font-family:Verdana;"> solar cell, for each wavelength, which is in the range close to the energy band gap of the silicon material. This study provides a tool for improvement solar cell manufacture processes, through the mathematical relationship obtained from the thickness limit according to the absorption coefficient that allows base width optimization.展开更多
This paper discusses the principle and mathematical method to measure the phase fractions of multiphase flows by using a dual-energy gamma-ray system. The dual-energy gamma-ray device is composed of radioactive isotop...This paper discusses the principle and mathematical method to measure the phase fractions of multiphase flows by using a dual-energy gamma-ray system. The dual-energy gamma-ray device is composed of radioactive isotopes of 241Am and 137Cs with emission energies of 59.5 keV and 662 keV respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The statistical error has been analyzed on the basis of the accurate absorption coefficient which enables determination phrase fractions almost independent of the flow regime. Improvement has been achieved on the measurement accuracy of phase fractions.展开更多
The band structures of rectangular GaN/AlGaN quantum wires are modeled by using a parabolic effective-mass theory. The absorption coefficients are calculated in a contact-density matrix approach based on the band stru...The band structures of rectangular GaN/AlGaN quantum wires are modeled by using a parabolic effective-mass theory. The absorption coefficients are calculated in a contact-density matrix approach based on the band structure. The results obtained indicate that the peak absorption coefficients augment with the increase of the injected carrier density, and the optical gain caused by interband transition is polarization anisotropic. For the photon energy near 1.55 eV, we can obtain relatively large peak gain. The calculations support the previous results published in the recent literature.展开更多
The absorption coefficient of magnesium-doped near-stoichiometric lithium niobate crystal is measured by terahertz time-domain spectroscopy in a frequency range of 0.2 THz^0.9 THz at room temperature. The absorption c...The absorption coefficient of magnesium-doped near-stoichiometric lithium niobate crystal is measured by terahertz time-domain spectroscopy in a frequency range of 0.2 THz^0.9 THz at room temperature. The absorption coefficient is modulated by external optical pump fields. Experimental results show that the absorption coefficient of near-SLN：Mg crystal is approximately in a range of 22 cm- 1_35 cm- 1 in a frequency range of 0.2 THz-0.9 THz and tunable up to nearly 15%. Further theoretical analysis reveals that the variation of absorption coefficient is related to the number of light-induced carriers, domain reversal process, and OH- absorption in this crystal.展开更多
The nonlinear refractive index and absorption coefficient of single\|shell semiconductor carbon nanotubes(CN s ) are calculated based on the two\|band approximation and Genkin\|Mednis approach. The results of nonlin...The nonlinear refractive index and absorption coefficient of single\|shell semiconductor carbon nanotubes(CN s ) are calculated based on the two\|band approximation and Genkin\|Mednis approach. The results of nonlinear refractive index and absorption coefficient reach the order of 10 -8 and 10 -4 cm 2\5W -1 separately, which indicates that CN s have wonderful nonlinear optical properties. Taking into account the temperature effect and overlapping of σ and π orbits, the effect of relaxation term and chiral angle is discussed. The results show that the smaller the relaxation term, the larger the nonlinear absorption coefficient and refractive index. At the same time, CN s with different chiral angles have different results due to their different energy gap.展开更多
The absorption coefficient is usually considered as a constant for certain materials at the given wavelength.However,recent experiments demonstrated that the absorption coefficient could be enhanced a lot by the PN ju...The absorption coefficient is usually considered as a constant for certain materials at the given wavelength.However,recent experiments demonstrated that the absorption coefficient could be enhanced a lot by the PN junction.The absorption coefficient varies with the thickness of the intrinsic layer in a PIN structure.Here,we interpret the anomalous absorption coefficient from the competition between recombination and drift for non-equilibrium carriers.Based on the Fokker-Planck theory,a non-equilibrium statistical model that describes the relationship between absorption coefficient and material thickness has been proposed.It could predict the experimental data well.Our results can give new ideas to design photoelectric devices.展开更多
Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foa...Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foam to absorb sound at a given frequency,and then fabricate it through sintering,it is expected to have optimized metal foams for the best sound absorption.Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient.In this study,the Lu model was used to optimize the morphological parameters of aluminum metal foam for the best sound absorption coefficient.For this purpose,the Lu model was numerically solved using written codes in MATLAB software.After validating the proposed codes with benchmark data,the genetic algorithm(GA)was applied to optimize the affecting morphological parameters on the sound absorption coefficient.The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz.The optimized parameters ranged from 50%to 95%for porosity,0.1 mm to 4.5 mm for pore size,and 0.07 mm to 0.6 mm for pore opening size.The result of this study was applied to fabricate the desired aluminum metal foams for the best sound absorption.The novel approach applied in this study,is expected to be successfully applied in for best sound absorption in desired frequencies.展开更多
This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a freque...This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.展开更多
The active sound absorption technique excels in mitigating low-frequency sound waves,yet it falls short when dealing with medium and high-frequency sound waves.To enhance the sound-absorbing effect of medium and high-...The active sound absorption technique excels in mitigating low-frequency sound waves,yet it falls short when dealing with medium and high-frequency sound waves.To enhance the sound-absorbing effect of medium and high-frequency sound waves,a novel semi-active sound absorption method has been introduced.This method modulates the surface impedance of a loudspeaker positioned behind the sound-absorbing material,thereby altering the sound absorption coefficient.The theoretical sound absorption coefficient is calculated using MATLAB and compared with the experimental one.Results show that the method can effectively modulates the absorption coefficient in response to varying incident sound wave frequencies,ensuring that it remains at its peak value.展开更多
Determining the optical properties of media remains an important part of scientific research. Knowledge of these optical properties, particularly absorption and diffusion coefficients, has direct applications in biome...Determining the optical properties of media remains an important part of scientific research. Knowledge of these optical properties, particularly absorption and diffusion coefficients, has direct applications in biomedical therapeutic diagnostics. The determination of these coefficients was previously reserved for optically dilute media. Recently, a technique called Structured Laser Illumination Planar Imaging (SLIPI) has been developed for measuring extinction coefficients in dense media. For such a medium and technique, no study has reported the determination of absorption and scattering coefficients. In this study, we have developed a simple calculation method based on the combination of Kubelka-Munk relations and extinction, both functions of the medium’s absorption and diffusion coefficients. The equations thus developed enable absorption and diffusion coefficients to be easily calculated from extinction coefficient measurements alone, using the SLIPI technique. The analysis method thus developed was applied to ten (10) milk solutions of different concentrations considered to be predominantly diffusive, and to ten (10) coffee solutions of different concentrations considered to be predominantly absorbent. The coefficient values obtained have been analysed and compared to the literature ones and they would be satisfactory.展开更多
The temperature-dependent absorption coefficient and thermal conductivity of a quartz window are obtained through experimental tests at a wide range of temperatures.A Fourier transform infrared spectrometer with a hea...The temperature-dependent absorption coefficient and thermal conductivity of a quartz window are obtained through experimental tests at a wide range of temperatures.A Fourier transform infrared spectrometer with a heated cavity is used for performing the transmittance measurements.The spectral absorption coefficient of the quartz window is inverted by the transmittance information at different temperatures using a genetic algorithm.Then,a quartz window-graphite plate-quartz window multilayer structure is designed,and the transient response of the structure subjected to high-temperature heating is recorded by a self-designed setup.Cooperating with the above absorption coefficient,a non-gray radiative-conductive heat transfer model is built for the multilayer structure,and the intrinsic thermal conductivity of the quartz window is identified.Finally,the effects of the temperature-dependent absorption coefficient and spectral selective features of the medium on the heat transfer characteristics are discussed.The results show that the absorption coefficient gradually increases with temperature.The intrinsic thermal conductivity of the quartz window varies from 1.35 to 2.52 W/(m·K)as the temperature rises,while the effective thermal conductivity is higher than the intrinsic thermal conductivity due to thermal radiation,specifically 26.4%higher at 1100 K.In addition,it is found that the influence of the temperature-dependent absorption coefficient on temperature of unheated side shows a trend of first increasing and then decreasing.When the absorption coefficient varies greatly with wavelength,a non-gray radiative-conductive heat transfer model should be built for the semitransparent materials.展开更多
Special attention is paid to the characteristics of microperforated panel absorbers (MPA) in a sa-called random or diffuse sound field. Preliminary analysis based on the theory of “normal model” are given. Measureme...Special attention is paid to the characteristics of microperforated panel absorbers (MPA) in a sa-called random or diffuse sound field. Preliminary analysis based on the theory of “normal model” are given. Measurements for different kinds of MPA in the reveberation chamber have been carried out and useful results have been obtained. For the theoretical predictions, PC-software has been developed. The further stuides in the near future are proposed.展开更多
Narrow-band transmissivities in the spectral range of 150 to 9300 cml and at a uniform resolution of 25 cm-1 were calculated using the statistical narrow-band （SNB） model with the band parameters of Soufiani and Tai...Narrow-band transmissivities in the spectral range of 150 to 9300 cml and at a uniform resolution of 25 cm-1 were calculated using the statistical narrow-band （SNB） model with the band parameters of Soufiani and Taine, the more recent parameters of Andr6 and Vaillon, and the line-by-line （LBL） method along with the HITEMP-2010 spectroscopic database. Calculations of narrow-band transmissivity were conducted for gas columns of different lengths and containing different isothermal and non-isothermal CO2-H20-N2 mixtures at 1 atm. Narrow-band transmissivities calculated by the SNB model are in large relative error at many bands. The more recent SNB model parameters of Andr6 and Vaillon are more accurate than the earlier parameters of Soufiani and Taine. The Planck mean absorption coefficients of CO2, H20, CO, and CH4 in the temperature range of 300 to 2500K were calculated using the LBL method and different versions of the high resolution transmission （HITRAN） and high-temperature spectroscopic absorption parameters （HITEMP） spectroscopic databases. The SNB model was also used to calculate the Planck mean absorption coefficients of these four radiating gases. The LBL results of the Planck mean absorption coefficient were compared with the classical results of Tien and those from the SNB model.展开更多
The numerical simulation is used in this work to study the nearfield radiation pressure of a piston projector, the smooth effect on the pressure field by using a 'big' receiver and the influence of the nearfie...The numerical simulation is used in this work to study the nearfield radiation pressure of a piston projector, the smooth effect on the pressure field by using a 'big' receiver and the influence of the nearfield and in the transition region on measurement of sound absorption coefficient. The result indicates that the big error would appear when using usual absorption coefficient measurement method. According to the reason causing the error, the method eliminating nearfield effect (MENE) is proposed and some digital results are given for a / λ= 3, 9 and b = 0, 0.5a, a (a and b are the transducer and receiver radii respectively). The calculation results show that the method not only widens measurement range in nearfield, but also gives accurate results.展开更多
基金National Natural Science Foundation of China(No.51705545)。
文摘To minimize the calculation errors in the sound absorption coefficient resulting from inaccurate measurements of flow resistivity,a simple method for determining the sound absorption coefficient of soundabsorbing materials is proposed.Firstly,the sound absorption coefficients of a fibrous sound-absorbing material are measured at two different frequencies using the impedance tube method.Secondly,utilizing the empirical formulas for the wavenumber and acoustic impedance in the fibrous material,the flow resistivity and porosity of the sound-absorbing materials are calculated using the MATLAB cycle program.Thirdly,based on the values obtained through reverse calculations,the sound absorption coefficient,the real and the imaginary parts of the acoustic impedance of the sound-absorbing material at different frequencies are theoretically computed.Finally,the accuracy of these theoretical calculations is verified through experiments.The experimental results indicate that the calculated values are basically consistent with the measured values,demonstrating the feasibility and reliability of this method.
基金The National Natural Science Foundation of China under contract No.41271364the Key Projects in the National Science and Technology Pillar Program of China under contract No.2012BAH32B01-4the Program for Scientific Research Start-up Funds of Guangdong Ocean University under contract No.E16187
文摘Establishing the remote sensing algorithm of retrieving the absorption coefficient of seawater petroleum substances is an efficient way to improve the accuracy of retrieving a seawater petroleum concentration using a remote sensing technology. A remote sensing reflectance is a basic physical parameter in water color remote sensing. Apply it to directly retrieve the absorption coefficient of seawater petroleum substances is of potential advantage. The absorption coefficient of waters containing petroleum [ACWCP, a_o（λ）], consists of the absorption coefficient of pure water [ACPW, a_w（λ）], plankton [ACP, a_（ph）（λ）], colored scraps [ACCS, a_（d,g）（λ）], and petroleum substance [ACPS, a_（oil）（λ）]. Among those, ACCS consists of the absorption coefficient of nonalgal particle [ACNP, a_d（λ）] and colored dissolved organic matter [ACCDOM, a_g（λ）]. For waters containing petroleum, the retrieved ACCS using the existing method is a combination absorption coefficient of ACNP,ACCDOM and ACPA [CAC, a_（d,g,oil）（λ）]. Therefore, the principle question is how to extract ACPS from CAC.Through the analysis of the three proportion tests conducted between the year of 2013 and 2015 and the corresponding remote sensing data, an algorithm of retrieving the absorption coefficient of petroleum substances is proposed based on remote sensing reflectance. First of all, ACPS and CAC are retrieved from the reflectance using the quasi-analytical algorithm（QAA）, with some parameter modified. Secondly, given the fact that the backscatter coefficient [BC, b_（bp）（555）] of total particles at 555 nm can be obtained completely from the reflectance, the relation between BC and ACNP in petroleum contaminated water can be established. As a result, ACNP can be calculated. Then, combining the remote sensing retrieving algorithm of a_g（440）, the method of achieving the spectral slope of the absorption coefficient can be established, from which ACCDOM,can be calculated. Finally, ACPS can be computed as the residual. The accuracy of ACPS based on this algorithm is 86% compared with the in situ measurements.
基金Supported by the Subsystem of Calibration and Validation, HY-1 Ground Application System, National Satellite Ocean Application Ser-vice (NSOAS). China High-Tech "863" Project (Nos. 2001AA636010, 2002AA639160 and 2002AA639200). The Ocean Science Fund Sponsor Project for the Youth, State Oceanic Administration (No. 2005415). The Director’s Science and Technology Fund Sponsor Project for the Youth, NSOAS.
文摘This paper suggests a group of statistical algorithms for calculating the total absorption coefficients based on in situ data of apparent optical property and inherent optical property collected with strict quality assurance according to NASA ocean bio-optic protocols in the Yellow Sea and the East China Sea in spring 2003. The band-ratios ofRrs412/Rrs555, Rrs49o/Rrs555 are used in the algorithms to derive the total absorption coefficients （at） at 412, 440, 488, 510, 532 and 555nm bands, respectively. The average relative errors between inversed and measured values are less than 25.8%, with the correlative coefficients （R2） being 0.75-0.85. Error sensitivity analysis shows that the maximum retrieval error is less than 24.0% at ＋5% error in Rrs＇s. So the statistical algorithms of this paper are practicable. In this paper, the relations between the total absorption coefficients at 412, 488, 510, 532, 555 nm and that of 440nm are also studied. The results show that the relations between the total absorption coefficients of 400-600 nm and that of 440 nm are correlated well and all of their correlative coefficients R2 are greater than 0.99. Furthermore, a regression analysis is also done for the slope of the linear relations and wavelengths, and the R2 is also 0.99. Thus it is possible to retrieve other bands＇ total absorption coefficients with only one band absorption value, which significantly reduce the number of unknown parameters in studying other ocean color related problems.
基金The National Basic Research Program ("973" Program) of China under contract No.2009CB421202the National Natural Science Foundation of China under contract Nos 40976110 and 40706061the National High Technology Research and Development Program ("863" Program) of China under contract No.2008AA09Z104
文摘The East China Sea （ECS）, one of the largest continental seas, has dynamic hydrology and complex optical characteristics that make ocean color remote-sensing retrieval difficult. The distributions and proportions of the light absorption coefficients of major ocean color components based on two large-scale investigations in the ECS are presented, showing these features in typical summer and winter seasons. The absorption coefficient aCDOM, aNAp and aphy of colored dissolved organic matter, non-algal particle, and pigment of phytoplankton show a decreasing trend from the coast to the outer shelf. According to the aeDOM distribution at 440 nm, the Changjiang River plume shows an abnormal southeastward transport. An extremely high aNaP value patch at 440 nm is present in the middle coast. The chlorophyll-a-specific phytoplankton pigment absorption （a^hy） is much higher in winter than in summer, which may cause serious underestimated results when applying the averaged aphy into remote-sensing algorithms for chlorophyll concentration retrieval. The importance of phytoplankton size was evident in outer shelf waters. The absorption of aCDOM （440） is a dominant component accounting for over half of the total seawater absorption in summer. The aNAP（440） accounts for 64% of the absorption of the ECS coastal area in winter.
基金The National Basic Research Program of China under contract Nos 2009CB421200, 2009CB421201the National Natural Science Foundation of China under contract No40821063High-Tech R&D Program of China under contract Nos2006AA09A302 and 2008AA09Z108
文摘The temporal and spatial variabilities of phytoplankton absorption coefficients （a ph （λ）） and their relationships with physical processes in the northern South China Sea were examined, based on in situ data collected from two cruise surveys during May 14 to 25, 2001 and November 2 to 21, 2002. Significant changes in the surface water in a ph values and B/R ratios （a ph （440）/a ph （675）） were observed in May, which were caused by a phytoplankton bloom on the inner shelf stimulated by a large river plume due to heavy precipitation. This is consistent with the observed one order of magnitude elevation of chlorophyll a and a shift from a pico/nano dominated phytoplankton community to one dominated by micro-algae. Enhanced vertical mixing due to strengthened northeast monsoon in November has been observed to result in higher surface a ph （675） （0.002–0.006 m-1 higher） and less pronounced subsurface maximum on the outer shelf/slope in November as compared with that in May. Measurements of a ph and B/R ratios from three transects in November revealed a highest surface a ph （675） immediately outside the mouth of the Zhujiang （Pearl） River Estuary, whereas lower a ph （675） and higher B/R ratios were featured in the outer shelf/slope waters, demonstrating the respective influence of the Zhujiang River plume and the oligotrophic water of the South China Sea. The difference in spectral shapes of phytoplankton absorption （measured by B/R ratios and bathochromic shifts） on these three transects infers that picoprocaryotes are the major component of the phytoplankton community on the outer shelf/slope rather than on the inner shelf. A regional tuning of the phytoplankton absorption spectral model （Carder et al., 1999） was attempted, demonstrating a greater spatial variation than temporal variation in the lead parameter a 0 （λ）. It was thus implicated that region-based parameterization of ocean color remote sensing algorithms in the northern South China Sea was mandatory.
基金Supported by the National Natural Science Foundation of China(Nos. 60802089,40801176,40706060)the National High Technology Research and Development Program of China(863 Program)(No. 2007AA092102)
文摘Temporal and spatial patterns of inherent optical properties in the Bohai Sea are very complex. In this paper, we used 77 groups of field data of AOPs （apparent optical properties） and IOPs （inherent optical properties） collected in June, August, and September of 2005 in the Bohai Sea, to retrieve the spectral total absorption coefficient a（2） with the quasi-analytical algorithm （QAA）. For QAA implementation, different bands in the region 680-730 nm （in 5 nm intervals） were selected and compared, to determine the optimal band domain of the reference wavelength. On this basis, we proposed a new algorithm （QAA-Com）, a combination of QAA-685 and QAA-715, according to turbidity characterized by a（440）. The percentage difference of model retrievals in the visible domain was between 4.5%-45.1%, in average of 18.8% for a（2）. The QAA model was then applied to Medium Resolution Imaging Spectrometer （MERIS） radiometric products, which were temporally and spatially matched with in-situ optical measurements. Differences between MERIS retrievals and in-situ values were in the range 9.2%-27.8% for a（2） in the visible domain. Major errors in satellite retrieval are attributable to uncertainties of QAA model parameters and in-situ measurements, as well as imperfect atmospheric correction of MERIS data by the European Space Agency （ESA）. During a storm surge in April 2009, time series of MERIS images together with the QAA model were used to analyze spatial and temporal variability of the total absorption coefficient pattern in the Bohai Sea. It is necessary to collect more independent field data to improve this algorithm.
文摘The monochromatic absorption coefficient of silicon, inducing the light penetration depth into the base of the solar cell, is used to determine the optimum thickness necessary for the production of a large photocurrent. The absorption-generation-diffusion and recombination (bulk and surface) phenomena are taken into account in the excess minority carrier continuity equation. The solution of this equation gives the photocurrent according to ab</span><span style="font-family:Verdana;">sorption and electronic parameters. Then from the obtained short circuit</span><span style="font-family:Verdana;"> photocurrent expression, excess minority carrier back surface recombination velocity is determined, function of the monochromatic absorption coefficient at a given wavelength. This latter plotted versus base thickness yields the optimum thickness of an n</span><sup><span style="font-family:Verdana;">+</span></sup><span style="font-family:Verdana;">-p-p</span><sup><span style="font-family:Verdana;">+</span></sup><span style="font-family:Verdana;"> solar cell, for each wavelength, which is in the range close to the energy band gap of the silicon material. This study provides a tool for improvement solar cell manufacture processes, through the mathematical relationship obtained from the thickness limit according to the absorption coefficient that allows base width optimization.
文摘This paper discusses the principle and mathematical method to measure the phase fractions of multiphase flows by using a dual-energy gamma-ray system. The dual-energy gamma-ray device is composed of radioactive isotopes of 241Am and 137Cs with emission energies of 59.5 keV and 662 keV respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The statistical error has been analyzed on the basis of the accurate absorption coefficient which enables determination phrase fractions almost independent of the flow regime. Improvement has been achieved on the measurement accuracy of phase fractions.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2009AA03Z405)the National Natural Science Foundation of China (Grant Nos. 60908028,60971068 and 60644004)
文摘The band structures of rectangular GaN/AlGaN quantum wires are modeled by using a parabolic effective-mass theory. The absorption coefficients are calculated in a contact-density matrix approach based on the band structure. The results obtained indicate that the peak absorption coefficients augment with the increase of the injected carrier density, and the optical gain caused by interband transition is polarization anisotropic. For the photon energy near 1.55 eV, we can obtain relatively large peak gain. The calculations support the previous results published in the recent literature.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10974063,61205096,and 61177095)the Natural Science Foundation of Hubei Province,China (Grant Nos.02-16-230008,2010CDA001,and 2012FFA074)+2 种基金the Research Foundation of Huazhong University of Science and Technology,China (Grant No.01-09-230904)the Ph.D.Program Foundation of Ministry of Education of China (Grant No.20100142110042)the Fundamental Research Funds for the Central Universities,China (Grant Nos.2010MS041 and 2011TS001)
文摘The absorption coefficient of magnesium-doped near-stoichiometric lithium niobate crystal is measured by terahertz time-domain spectroscopy in a frequency range of 0.2 THz^0.9 THz at room temperature. The absorption coefficient is modulated by external optical pump fields. Experimental results show that the absorption coefficient of near-SLN：Mg crystal is approximately in a range of 22 cm- 1_35 cm- 1 in a frequency range of 0.2 THz-0.9 THz and tunable up to nearly 15%. Further theoretical analysis reveals that the variation of absorption coefficient is related to the number of light-induced carriers, domain reversal process, and OH- absorption in this crystal.
文摘The nonlinear refractive index and absorption coefficient of single\|shell semiconductor carbon nanotubes(CN s ) are calculated based on the two\|band approximation and Genkin\|Mednis approach. The results of nonlinear refractive index and absorption coefficient reach the order of 10 -8 and 10 -4 cm 2\5W -1 separately, which indicates that CN s have wonderful nonlinear optical properties. Taking into account the temperature effect and overlapping of σ and π orbits, the effect of relaxation term and chiral angle is discussed. The results show that the smaller the relaxation term, the larger the nonlinear absorption coefficient and refractive index. At the same time, CN s with different chiral angles have different results due to their different energy gap.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61804176,61991441,and 62004218)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB01000000)the Youth Innovation Promotion Association of Chinese Academy of Sciences.
文摘The absorption coefficient is usually considered as a constant for certain materials at the given wavelength.However,recent experiments demonstrated that the absorption coefficient could be enhanced a lot by the PN junction.The absorption coefficient varies with the thickness of the intrinsic layer in a PIN structure.Here,we interpret the anomalous absorption coefficient from the competition between recombination and drift for non-equilibrium carriers.Based on the Fokker-Planck theory,a non-equilibrium statistical model that describes the relationship between absorption coefficient and material thickness has been proposed.It could predict the experimental data well.Our results can give new ideas to design photoelectric devices.
基金paper was the output of a research project(Registration No.9597/22)which was financially supported by Shahid Beheshti University of Medical Sciences.
文摘Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foam to absorb sound at a given frequency,and then fabricate it through sintering,it is expected to have optimized metal foams for the best sound absorption.Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient.In this study,the Lu model was used to optimize the morphological parameters of aluminum metal foam for the best sound absorption coefficient.For this purpose,the Lu model was numerically solved using written codes in MATLAB software.After validating the proposed codes with benchmark data,the genetic algorithm(GA)was applied to optimize the affecting morphological parameters on the sound absorption coefficient.The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz.The optimized parameters ranged from 50%to 95%for porosity,0.1 mm to 4.5 mm for pore size,and 0.07 mm to 0.6 mm for pore opening size.The result of this study was applied to fabricate the desired aluminum metal foams for the best sound absorption.The novel approach applied in this study,is expected to be successfully applied in for best sound absorption in desired frequencies.
文摘This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.
基金National Natural Science Foundation of China(No.51705545)。
文摘The active sound absorption technique excels in mitigating low-frequency sound waves,yet it falls short when dealing with medium and high-frequency sound waves.To enhance the sound-absorbing effect of medium and high-frequency sound waves,a novel semi-active sound absorption method has been introduced.This method modulates the surface impedance of a loudspeaker positioned behind the sound-absorbing material,thereby altering the sound absorption coefficient.The theoretical sound absorption coefficient is calculated using MATLAB and compared with the experimental one.Results show that the method can effectively modulates the absorption coefficient in response to varying incident sound wave frequencies,ensuring that it remains at its peak value.
文摘Determining the optical properties of media remains an important part of scientific research. Knowledge of these optical properties, particularly absorption and diffusion coefficients, has direct applications in biomedical therapeutic diagnostics. The determination of these coefficients was previously reserved for optically dilute media. Recently, a technique called Structured Laser Illumination Planar Imaging (SLIPI) has been developed for measuring extinction coefficients in dense media. For such a medium and technique, no study has reported the determination of absorption and scattering coefficients. In this study, we have developed a simple calculation method based on the combination of Kubelka-Munk relations and extinction, both functions of the medium’s absorption and diffusion coefficients. The equations thus developed enable absorption and diffusion coefficients to be easily calculated from extinction coefficient measurements alone, using the SLIPI technique. The analysis method thus developed was applied to ten (10) milk solutions of different concentrations considered to be predominantly diffusive, and to ten (10) coffee solutions of different concentrations considered to be predominantly absorbent. The coefficient values obtained have been analysed and compared to the literature ones and they would be satisfactory.
基金supported by the National Natural Science Foundation of China(No.51806046)the China Postdoctoral Science Foundation(2020T130145)。
文摘The temperature-dependent absorption coefficient and thermal conductivity of a quartz window are obtained through experimental tests at a wide range of temperatures.A Fourier transform infrared spectrometer with a heated cavity is used for performing the transmittance measurements.The spectral absorption coefficient of the quartz window is inverted by the transmittance information at different temperatures using a genetic algorithm.Then,a quartz window-graphite plate-quartz window multilayer structure is designed,and the transient response of the structure subjected to high-temperature heating is recorded by a self-designed setup.Cooperating with the above absorption coefficient,a non-gray radiative-conductive heat transfer model is built for the multilayer structure,and the intrinsic thermal conductivity of the quartz window is identified.Finally,the effects of the temperature-dependent absorption coefficient and spectral selective features of the medium on the heat transfer characteristics are discussed.The results show that the absorption coefficient gradually increases with temperature.The intrinsic thermal conductivity of the quartz window varies from 1.35 to 2.52 W/(m·K)as the temperature rises,while the effective thermal conductivity is higher than the intrinsic thermal conductivity due to thermal radiation,specifically 26.4%higher at 1100 K.In addition,it is found that the influence of the temperature-dependent absorption coefficient on temperature of unheated side shows a trend of first increasing and then decreasing.When the absorption coefficient varies greatly with wavelength,a non-gray radiative-conductive heat transfer model should be built for the semitransparent materials.
基金The work supported by National Natural Science Foundation of ChinaDoctor Foundation of NEC
文摘Special attention is paid to the characteristics of microperforated panel absorbers (MPA) in a sa-called random or diffuse sound field. Preliminary analysis based on the theory of “normal model” are given. Measurements for different kinds of MPA in the reveberation chamber have been carried out and useful results have been obtained. For the theoretical predictions, PC-software has been developed. The further stuides in the near future are proposed.
文摘Narrow-band transmissivities in the spectral range of 150 to 9300 cml and at a uniform resolution of 25 cm-1 were calculated using the statistical narrow-band （SNB） model with the band parameters of Soufiani and Taine, the more recent parameters of Andr6 and Vaillon, and the line-by-line （LBL） method along with the HITEMP-2010 spectroscopic database. Calculations of narrow-band transmissivity were conducted for gas columns of different lengths and containing different isothermal and non-isothermal CO2-H20-N2 mixtures at 1 atm. Narrow-band transmissivities calculated by the SNB model are in large relative error at many bands. The more recent SNB model parameters of Andr6 and Vaillon are more accurate than the earlier parameters of Soufiani and Taine. The Planck mean absorption coefficients of CO2, H20, CO, and CH4 in the temperature range of 300 to 2500K were calculated using the LBL method and different versions of the high resolution transmission （HITRAN） and high-temperature spectroscopic absorption parameters （HITEMP） spectroscopic databases. The SNB model was also used to calculate the Planck mean absorption coefficients of these four radiating gases. The LBL results of the Planck mean absorption coefficient were compared with the classical results of Tien and those from the SNB model.
文摘The numerical simulation is used in this work to study the nearfield radiation pressure of a piston projector, the smooth effect on the pressure field by using a 'big' receiver and the influence of the nearfield and in the transition region on measurement of sound absorption coefficient. The result indicates that the big error would appear when using usual absorption coefficient measurement method. According to the reason causing the error, the method eliminating nearfield effect (MENE) is proposed and some digital results are given for a / λ= 3, 9 and b = 0, 0.5a, a (a and b are the transducer and receiver radii respectively). The calculation results show that the method not only widens measurement range in nearfield, but also gives accurate results.
