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
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
The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on cli- mate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. ...The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on cli- mate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. A multi-wavelength (405 rim, 532 nm, 780 nm) aerosol absorption meter based on photoacoustic spectroscopy (PAS) invovling a single cylin- drical acoustic resonator is developed for measuring the aerosol optical absorption coefficients (OACs). A sensitivity of 1.3 Mm-l (at 532 nm) is demonstrated. The aerosol absorption meter is successfully tested through measuring the OACs of atmospheric nigrosin and ambient aerosols in the suburbs of Hefei city. The absorption cross section and absorption Angstrom exponent (AAE) for ambient aerosol are determined for characterizing the component of the ambient aerosol.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
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 diffusion coefficient of the minority charge carriers in the base of a silicon solar cell under temperature and subjected to a magnetic field, passes in reso-nance at temperature (T<sub>opt</sub>). For...The diffusion coefficient of the minority charge carriers in the base of a silicon solar cell under temperature and subjected to a magnetic field, passes in reso-nance at temperature (T<sub>opt</sub>). For this same magnetic field, the diffusion coeffi-cient of the photogenerated carriers by a monochromatic light in frequency modulation enters into resonance, at the frequency (ω<sub>c</sub>). Under this double resonance in temperature and frequency, the diffusion coefficient is used in the expression of the recombination velocity of the minority charge carriers on the back side of the base of the solar cell (n<sup>+</sup>/p/p<sup>+</sup>), to obtain, by a graphical method, the optimum thickness. A modeling of the results obtained shows a material saving (Si), in the development of the solar cell.展开更多
Accurate determination of the optical properties of biological tissues enables quantitative understanding of light propagation in these tissues for optical diagnosis and treatment applications.The absorption(μa)and s...Accurate determination of the optical properties of biological tissues enables quantitative understanding of light propagation in these tissues for optical diagnosis and treatment applications.The absorption(μa)and scattering(μs)coe±cients of biological tissues are inversely analyzed from their diffuse re°ectance(R)and total transmittance(T),which are measured using a double integrating spheres(DIS)system.The inversion algorithms,for example,inverse adding doubling method and inverse Monte Carlo method,are sensitive to noise signals during the DIS measurements,resulting in reduced accuracy during determination.In this study,we propose an arti ficial neural network(ANN)to estimateμa andμs at a target wavelength from the R and T spectra measured via the DIS to reduce noise in the optical properties.Approximate models of the optical properties and Monte Carlo calculations that simulated the DIS measurements were used to generate spectral datasets comprisingμa,μs,R and T.Measurement noise signals were added to R and T,and the ANN model was then trained using the noise-added datasets.Numerical results showed that the trained ANN model reduced the effects of noise inμa andμs estimation.Experimental veri fication indicated noise-reduced estimation from the R and T values measured by the DIS with a small number of scans on average,resulting in measurement time reduction.The results demonstrated the noise robustness of the proposed ANN-based method for optical properties determination and will contribute to shorter DIS measurement times,thus reducing changes in the optical properties due to desiccation of the samples.展开更多
The bifacial silicon solar cell, placed at temperature (T) and illuminated from the back side by monochromatic light in frequency modulation (ω), is studied from the frequency dynamic diffusion equation, relative to ...The bifacial silicon solar cell, placed at temperature (T) and illuminated from the back side by monochromatic light in frequency modulation (ω), is studied from the frequency dynamic diffusion equation, relative to the density of excess minority carriers in the base. The expressions of the dynamic recombination velocities of the minority carriers on the rear side of the base Sb1(D(ω, T);H) and Sb2(α, D(ω, T);H), are analyzed as a function of the dynamic diffusion coefficient (D(ω, T)), the absorption coefficient (α(λ)) and the thickness of the base (H). Thus their graphic representation makes it possible to go up, to the base optimum thickness (Hopt(ω, T)), for different temperature values and frequency ranges of modulation of monochromatic light, of strong penetration. The base optimum thickness (Hopt(ω, T)) decreases with temperature, regardless of the frequency range and allows the realization of the solar cell with few material (Si).展开更多
The actual treatise represents a synopsis of six important previous contributions of the author, concerning atmospheric physics and climate change. Since this issue is influenced by politics like no other, and since t...The actual treatise represents a synopsis of six important previous contributions of the author, concerning atmospheric physics and climate change. Since this issue is influenced by politics like no other, and since the greenhouse-doctrine with CO<sub>2</sub> as the culprit in climate change is predominant, the respective theory has to be outlined, revealing its flaws and inconsistencies. But beyond that, the author’s own contributions are focused and deeply discussed. The most eminent one concerns the discovery of the absorption of thermal radiation by gases, leading to warming-up, and implying a thermal radiation of gases which depends on their pressure. This delivers the final evidence that trace gases such as CO<sub>2</sub> don’t have any influence on the behaviour of the atmosphere, and thus on climate. But the most useful contribution concerns the method which enables to determine the solar absorption coefficient β<sub>s</sub> of coloured opaque plates. It delivers the foundations for modifying materials with respect to their capability of climate mitigation. Thereby, the main influence is due to the colouring, in particular of roofs which should be painted, preferably light-brown (not white, from aesthetic reasons). It must be clear that such a drive for brightening-up the World would be the only chance of mitigating the climate, whereas the greenhouse doctrine, related to CO<sub>2</sub>, has to be abandoned. However, a global climate model with forecasts cannot be aspired to since this problem is too complex, and since several climate zones exist.展开更多
The development of optical methods in modern medicine in the areas of diagnostics,therapy,and surgery has stimulated the investigation of optical properties of various biological tissues,since the efficacy of laser tr...The development of optical methods in modern medicine in the areas of diagnostics,therapy,and surgery has stimulated the investigation of optical properties of various biological tissues,since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues.In this work,an overview of published absorption and scattering properties of skin and subcutaneous tissues measured in wide wavelength range is presented.Basic principles of measurements of the tissue optical properties and techniques used for processing of the measured data are outlined.展开更多
Data from three cruises conducted in the Zhujiang River (ZR), coastal waters of Guangdong (CWGD) and the northern South China Sea (NSCS) during 2003 and 2004 were examined for assessing the relative importance o...Data from three cruises conducted in the Zhujiang River (ZR), coastal waters of Guangdong (CWGD) and the northern South China Sea (NSCS) during 2003 and 2004 were examined for assessing the relative importance of pigment composition and packaging effect in modifying the specific absorption coefficients of phytoplankton. The three survey regions differ widely in their phytoplankton community with large cells dominating the ZR and CWGD waters and small cells dominating the NSCS region. Variations in the size structure and the accessory pigments have much effect on the chlorophyll a-specific absorption coefficient of phytoplankton. The size index accounted for about 42% and 33% of the variation of the specific absorption coefficient at 440 and 675 nm, respectively. Using the multiple regression analysis approach, pigment concentrations for each sample were calculated. The accessory pigments other than chlorophyll a contribute to absorption mainly in the blue - to - green region of the spectrum and their absorptions account for about 44%, 43% and 53% on the average of the total phytoplankton absorption at 440 nm for the ZR, CWGD and NSCS regions. Among the accessory pigments, the photosynthetic carotenoids (noted PSC) play a dominant role in the ZR and CWGD waters, while in the NSCS the nonphotosynthetic carotenoids (noted PPG) as well as PSC have important contributions. Because the variations of both the size structure and accessory pigments in algal populations contributed to the variability of the specific absorption coefficient in the study regions, these factors may be considered explicitly in future bio - optical algorithms to derive chlorophyll a concentration more accurately.展开更多
The quantum yield is an important factor to evaluate the efficiency of photoreactor. This article gives an overall calculation method of the quantum efficiency( Φ ) and the apparent quantum efficiency( Φ a) to...The quantum yield is an important factor to evaluate the efficiency of photoreactor. This article gives an overall calculation method of the quantum efficiency( Φ ) and the apparent quantum efficiency( Φ a) to the TiO 2/UV photocatalysis system. Furthermore, for the immobility system (IS), the formulation of the faction of light absorbed by the TiO 2 thin film is proposed so as to calculate the quantum efficiency by using the measured value and theoretic calculated value of transmissivity (T). For the suspension system(SS), due to the difficulty to obtain the absorption coefficient ( α ) of TiO 2 particulates, the quantum efficiency is calculated by means of the relative photonic efficiency ( ζ r) and the standard quantum yield ( Φ standard ).展开更多
Based on sound absorption mechanism of material,the special sound absorption material CEMCOM for road sound insulation is introduced.This high sound absorption material is mainly composed of expanded perlite.Using mul...Based on sound absorption mechanism of material,the special sound absorption material CEMCOM for road sound insulation is introduced.This high sound absorption material is mainly composed of expanded perlite.Using multiple sound absorption structure can improve sound absorption property of material.According to the preparation principle and durability design of material,a new kind of material with low cost and high durability is developed.展开更多
The multilayer impedance composite sound absorption structure of the new muffler is proposed by combining the microporous plate structure with the resonant sound absorption structure of the porous material.Firstly,the...The multilayer impedance composite sound absorption structure of the new muffler is proposed by combining the microporous plate structure with the resonant sound absorption structure of the porous material.Firstly,the acoustic impedance and acoustic absorption coefficient of the new muffler structure are calculated by acoustic electric analogy method,and then the noise attenuation is calculated.When the new muffler structure parameters change,the relationship among the noise frequency,the sound absorption coefficient and the noise attenuation is calculated by using MATLAB.Finally,the calculated results are compared with the experimental data to verify the correctness of the theoretical calculation.The variation of resonance peak,resonance frequency and attenuation band width of each structural parameter is analyzed by the relation curve.The conclusion shows that it is feasible to use multilayer sound absorbing materials as the body structure of the new muffler.And the influence relationship between the change of various parameters of the sound absorption structure with the sound absorption coefficient and noise attenuation is obtained.展开更多
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 Open Research Fund of Key Laboratory of Atmospheric Composition and Optical Radiation,Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant Nos.41175036 and 41205120)
文摘The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on cli- mate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. A multi-wavelength (405 rim, 532 nm, 780 nm) aerosol absorption meter based on photoacoustic spectroscopy (PAS) invovling a single cylin- drical acoustic resonator is developed for measuring the aerosol optical absorption coefficients (OACs). A sensitivity of 1.3 Mm-l (at 532 nm) is demonstrated. The aerosol absorption meter is successfully tested through measuring the OACs of atmospheric nigrosin and ambient aerosols in the suburbs of Hefei city. The absorption cross section and absorption Angstrom exponent (AAE) for ambient aerosol are determined for characterizing the component of the ambient aerosol.
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.
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.
文摘The diffusion coefficient of the minority charge carriers in the base of a silicon solar cell under temperature and subjected to a magnetic field, passes in reso-nance at temperature (T<sub>opt</sub>). For this same magnetic field, the diffusion coeffi-cient of the photogenerated carriers by a monochromatic light in frequency modulation enters into resonance, at the frequency (ω<sub>c</sub>). Under this double resonance in temperature and frequency, the diffusion coefficient is used in the expression of the recombination velocity of the minority charge carriers on the back side of the base of the solar cell (n<sup>+</sup>/p/p<sup>+</sup>), to obtain, by a graphical method, the optimum thickness. A modeling of the results obtained shows a material saving (Si), in the development of the solar cell.
基金supported by the Japan Society for the Promotion of Science KAKENHI(Grant numbers:20H04549 and 19K12822)the Japan Science and Technology Agency ACT–X(Grant Number:JPMJAX21K7).
文摘Accurate determination of the optical properties of biological tissues enables quantitative understanding of light propagation in these tissues for optical diagnosis and treatment applications.The absorption(μa)and scattering(μs)coe±cients of biological tissues are inversely analyzed from their diffuse re°ectance(R)and total transmittance(T),which are measured using a double integrating spheres(DIS)system.The inversion algorithms,for example,inverse adding doubling method and inverse Monte Carlo method,are sensitive to noise signals during the DIS measurements,resulting in reduced accuracy during determination.In this study,we propose an arti ficial neural network(ANN)to estimateμa andμs at a target wavelength from the R and T spectra measured via the DIS to reduce noise in the optical properties.Approximate models of the optical properties and Monte Carlo calculations that simulated the DIS measurements were used to generate spectral datasets comprisingμa,μs,R and T.Measurement noise signals were added to R and T,and the ANN model was then trained using the noise-added datasets.Numerical results showed that the trained ANN model reduced the effects of noise inμa andμs estimation.Experimental veri fication indicated noise-reduced estimation from the R and T values measured by the DIS with a small number of scans on average,resulting in measurement time reduction.The results demonstrated the noise robustness of the proposed ANN-based method for optical properties determination and will contribute to shorter DIS measurement times,thus reducing changes in the optical properties due to desiccation of the samples.
文摘The bifacial silicon solar cell, placed at temperature (T) and illuminated from the back side by monochromatic light in frequency modulation (ω), is studied from the frequency dynamic diffusion equation, relative to the density of excess minority carriers in the base. The expressions of the dynamic recombination velocities of the minority carriers on the rear side of the base Sb1(D(ω, T);H) and Sb2(α, D(ω, T);H), are analyzed as a function of the dynamic diffusion coefficient (D(ω, T)), the absorption coefficient (α(λ)) and the thickness of the base (H). Thus their graphic representation makes it possible to go up, to the base optimum thickness (Hopt(ω, T)), for different temperature values and frequency ranges of modulation of monochromatic light, of strong penetration. The base optimum thickness (Hopt(ω, T)) decreases with temperature, regardless of the frequency range and allows the realization of the solar cell with few material (Si).
文摘The actual treatise represents a synopsis of six important previous contributions of the author, concerning atmospheric physics and climate change. Since this issue is influenced by politics like no other, and since the greenhouse-doctrine with CO<sub>2</sub> as the culprit in climate change is predominant, the respective theory has to be outlined, revealing its flaws and inconsistencies. But beyond that, the author’s own contributions are focused and deeply discussed. The most eminent one concerns the discovery of the absorption of thermal radiation by gases, leading to warming-up, and implying a thermal radiation of gases which depends on their pressure. This delivers the final evidence that trace gases such as CO<sub>2</sub> don’t have any influence on the behaviour of the atmosphere, and thus on climate. But the most useful contribution concerns the method which enables to determine the solar absorption coefficient β<sub>s</sub> of coloured opaque plates. It delivers the foundations for modifying materials with respect to their capability of climate mitigation. Thereby, the main influence is due to the colouring, in particular of roofs which should be painted, preferably light-brown (not white, from aesthetic reasons). It must be clear that such a drive for brightening-up the World would be the only chance of mitigating the climate, whereas the greenhouse doctrine, related to CO<sub>2</sub>, has to be abandoned. However, a global climate model with forecasts cannot be aspired to since this problem is too complex, and since several climate zones exist.
文摘The development of optical methods in modern medicine in the areas of diagnostics,therapy,and surgery has stimulated the investigation of optical properties of various biological tissues,since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues.In this work,an overview of published absorption and scattering properties of skin and subcutaneous tissues measured in wide wavelength range is presented.Basic principles of measurements of the tissue optical properties and techniques used for processing of the measured data are outlined.
基金This work was supported by the National Natural Science Foundation of China under contract Nos 40476019,40576078 and 5210266the Knowledge Innovation Program of the Chinese Academy of Sciences under contract No.KZCX2-YW-215.
文摘Data from three cruises conducted in the Zhujiang River (ZR), coastal waters of Guangdong (CWGD) and the northern South China Sea (NSCS) during 2003 and 2004 were examined for assessing the relative importance of pigment composition and packaging effect in modifying the specific absorption coefficients of phytoplankton. The three survey regions differ widely in their phytoplankton community with large cells dominating the ZR and CWGD waters and small cells dominating the NSCS region. Variations in the size structure and the accessory pigments have much effect on the chlorophyll a-specific absorption coefficient of phytoplankton. The size index accounted for about 42% and 33% of the variation of the specific absorption coefficient at 440 and 675 nm, respectively. Using the multiple regression analysis approach, pigment concentrations for each sample were calculated. The accessory pigments other than chlorophyll a contribute to absorption mainly in the blue - to - green region of the spectrum and their absorptions account for about 44%, 43% and 53% on the average of the total phytoplankton absorption at 440 nm for the ZR, CWGD and NSCS regions. Among the accessory pigments, the photosynthetic carotenoids (noted PSC) play a dominant role in the ZR and CWGD waters, while in the NSCS the nonphotosynthetic carotenoids (noted PPG) as well as PSC have important contributions. Because the variations of both the size structure and accessory pigments in algal populations contributed to the variability of the specific absorption coefficient in the study regions, these factors may be considered explicitly in future bio - optical algorithms to derive chlorophyll a concentration more accurately.
文摘The quantum yield is an important factor to evaluate the efficiency of photoreactor. This article gives an overall calculation method of the quantum efficiency( Φ ) and the apparent quantum efficiency( Φ a) to the TiO 2/UV photocatalysis system. Furthermore, for the immobility system (IS), the formulation of the faction of light absorbed by the TiO 2 thin film is proposed so as to calculate the quantum efficiency by using the measured value and theoretic calculated value of transmissivity (T). For the suspension system(SS), due to the difficulty to obtain the absorption coefficient ( α ) of TiO 2 particulates, the quantum efficiency is calculated by means of the relative photonic efficiency ( ζ r) and the standard quantum yield ( Φ standard ).
文摘Based on sound absorption mechanism of material,the special sound absorption material CEMCOM for road sound insulation is introduced.This high sound absorption material is mainly composed of expanded perlite.Using multiple sound absorption structure can improve sound absorption property of material.According to the preparation principle and durability design of material,a new kind of material with low cost and high durability is developed.
基金National Natural Science Foundation of China(Nos.51705545 and 15A460041)。
文摘The multilayer impedance composite sound absorption structure of the new muffler is proposed by combining the microporous plate structure with the resonant sound absorption structure of the porous material.Firstly,the acoustic impedance and acoustic absorption coefficient of the new muffler structure are calculated by acoustic electric analogy method,and then the noise attenuation is calculated.When the new muffler structure parameters change,the relationship among the noise frequency,the sound absorption coefficient and the noise attenuation is calculated by using MATLAB.Finally,the calculated results are compared with the experimental data to verify the correctness of the theoretical calculation.The variation of resonance peak,resonance frequency and attenuation band width of each structural parameter is analyzed by the relation curve.The conclusion shows that it is feasible to use multilayer sound absorbing materials as the body structure of the new muffler.And the influence relationship between the change of various parameters of the sound absorption structure with the sound absorption coefficient and noise attenuation is obtained.