Evaluation of TiAl and 40Cr diffusion bonding quality using ultrasonic reflection spectrum

Combined with ultrasonic pulse-echo technique, reflection spectrum analysis was introduced to evaluate TiAl and 40Cr diffusion bonding quality. Frequency dependence of reflection coefficient was used to distinguish perfect bonding from imperfect bonding. It is found that the reflection coefficient from perfect bonding interface does not vary with frequency. When the size of imperfections is much smaller than the wavelength of ultrasound, the reflection coeffwient depends on frequency. When the size of imperfections is the same order of or even larger than the wavelength of ultrasound, the reflection coeffwient does not exhibit frequency dependence. However the amplitude of imperfect interface is higher than the amplitude of perfect bonding interface. A combination of reflection spectrum analysis and ultrasonic pulse-echo technique provides more accurate information about the bonding quality of dissimilar materials.

Cultivar,Nitrogen and Irrigation Influence on Grain Quality and Its Forecasting Methods by In situ Reflected Spectrum of Winter Wheat

Field experiments were conducted to examine the influence factors of cultivar, nitrogen application and irrigation on grain protein content, gluten content and grain hardness in three winter wheat cultivars under four levels of nitrogen and irrigation treatments. Firstly, the influence of cultivars and environment factors on grain quality were studied, the effective factors were cultivars, irrigation, fertilization, etc. Secondly, total nitrogen content around winter wheat anthesis stage was proved to be significantly correlative with grain protein content, and spectral vegetation index significantly correlated to total nitrogen content around anthesis stage were the potential indicators for grain protein content. Accumulation of total nitrogen content and its transfer to grain is the physical link to produce the final grain protein, and total nitrogen content at anthesis stage was proved to be an indicator of final grain protein content. The selected normalized photochemical reflectance index (NPRI) was proved to be able to predict grain protein content on the close correlation between the ratio of total carotenoid to chlorophyll a and total nitrogen content. The method contributes towards developing optimal procedures for predicting wheat grain quality through analysis of their canopy reflected spectrum at anthesis stage. Regression equations were established to forecast grain protein and dry gluten content by total nitrogen content at anthesis stage, so it is feasible for forecasting grain quality by establishing correlation equations between biochemical constitutes and canopy reflected spectrum.

New Vegetation Index and Its Application in Estimating Leaf Area Index of Rice

Leaf area index （LAI） is an important characteristic of land surface vegetation system, and is also a key parameter for the models of global water balancing and carbon circulation. By using the reflectance values of Landsat-5 blue, green and red channels simulated from rice reflectance spectrum, the sensitivities of the bands to LAI were analyzed, and the response and capability to estimate LAI of various NDVIs （normalized difference vegetation indices）, which were established by substituting the red band of general NDVI with all possible combinations of red, green and blue bands, were assessed. Finally, the conclusion was tested by rice data at different conditions. The sensitivities of red, green and blue bands to LAI were different under various conditions. When LAI was less than 3, red and blue bands were more sensitive to LAI. Though green band in the circumstances was less sensitive to LAI than red and blue bands, it was sensitive to LAI in a wider range. When the vegetation indices were constituted by all kinds of combinations of red, green and blue bands, the premise for making the sensitivity of these vegetation indices to LAI be meaningful was that the value of one of the combinations was greater than 0.024, i.e. visible reflectance （VIS）〉0.024. Otherwise, the vegetation indices would be saturated, resulting in lower estimation accuracy of LAI. Comparison on the capabilities of the vegetation indices derived from all kinds of combinations of red, green and blue bands to LAI estimation showed that GNDVI （Green NDVI） and GBNDVI （Green-Blue NDVI） had the best relations with LAI. The capabilities of GNDVI and GBNDVI to LAI estimation were tested under different circumstances, and the same result was acquired. It suggested that GNDVI and GBNDVI performed better to predict LAI than the conventional NDVI.

Model of Reflection Spectra of Rock Surface in 2π Space

This paper deals with reflection spectra and polarized reflection spectra of 20 sorts of rock in 2π space, and then creates a model of reflection spectra of rock surface in 2π space. We measured the change of reflection and polarized reflection spectra as altering the incidence angle, vertex angle, azimuth angle, band and polarization. The results show that influence of the incidence angle on spectral curves is very strong. And when the vertex angle is constant, the horizontal azimuth polarizes rock spectra, and distorts the circular spectrum to become elliptic. The polarization influences the reflection intensity of rock spectra, but has no evident influence on the characteristics of wave forms of rock in 2π space. Therefore, we can describe the whole reflection spectral characteristics, including polarization, of rock surface in 2π space by measuring and calculating the e and p values in several key directions.

Diagnosis of Nitrogen Status in Rice Leaves with Canopy Spectral Reflectance

The investigation was made on the relationship of seasonal time-course canopy spectral reflectance and ratio index to total leaf nitrogen accumulation (leaf nitrogen content per unit ground area) in rice under different nitrogen treatments. The results showed there was a close correlation between the canopy spectral reflectance and total leaf nitrogen accumulation. Ratio of near infrared to green band (R810/R560) was linearly related with total leaf nitrogen accumulation. independent of nitrogen levels and development stages. Different datasets were used to test the linear regression equation, with average estimation accuracy of 91. 22%, RMSE of 1.09 and average relative error of 0. 026. Thus, the ratio index R810/R560 of canopy spectral reflectance should be useful for non-destructive monitoring and diagnosis of nitrogen status in rice plants.

A Preliminary Stndy on Identification of Clay Minerals in Soils with Reference to Reflectance Spectra

The characteristics of the reflectance spectra of clay minerals and their influences on the reflectancespectra of soils are dealt with in the paper. The results showed that dominant clay minerals in soils couldbe distinguished in light of the spectral-form parameters of the reflectance spectra of soils, thus making itpossible to develop a quick method to determine clay minerals by means of reflectance spectra of soils in thelab. and providing a theoretic basis for retnote sensing of clay minerals in soils with a high resolution imagingspectrometer.

Application of Short-wave Near-infrared Reflectance Spectroscopy in Controlling Extract of Fructus Cnidii Using Supercritical Carbon Dioxide

Fructus cnidii （Chinese name shechuangzi） is the fruit produced by Cnidium monnieri （L.） Cusson （Umbelliferae）. It is a perennial herb that is used to treat skin-related diseases and gynecopathyell. Recent pharmacological studies have revealed crude extracts or components isolated from fructus cnidii possess antiallergic, antipruritic, antidermatophytic, antibacterial, antifungal, and antiosteoporotic activities. Osthole and imperatorin are the major compounds present in shechuangzi. They are often used as standards for the evaluation of the quality of shechuangzi products.

Inversion of Biochemical Parameters by Selection of Proper Vegetation Index in Winter Wheat

Recent studies have demonstrated the application of vegetation indices from canopy reflectedspectrum for inversion of chlorophyll concentration. Some indices are both response tovariations of vegetation and environmental factors. Canopy chlorophyll concentration, anindicator of photosynthesis activity, is related to nitrogen concentration in green vegetationand serves as an indicator of the crop response to soil nitrogen fertilizer application. Thecombination of normalized difference vegetation index (NDVI) and photochemical reflectanceindex (PRI) can reduce the effect of leaf area index (LAI) and soil background. The canopychlorophyll inversion index (CCII) was proved to be sensitive to chlorophyll concentration andvery resistant to the other variations. This paper introduced the ratio of TCARI/OSAVI to makeaccurate predictions of winter wheat chlorophyll concentration under different cultivars. Itindicated that canopy chlorophyll concentration could be evaluated by some combined vegetationindices.

Canopy Spectral Reflectance Characteristics of Rice with Different Cultural Practices and Their Fuzzy Cluster Analysis

The influence of major cultural practices including different nitrogen application rates, population densities, transplanting leaf ages of seedling, and water regimes on rice canopy spectral reflectance was investigated. Results showed that increased nitrogen rates, water regimes and population densities and decreased seedling ages could enhance reflectance at NIR （near infrared） bands and reduce reflectance at visible bands. Using reflectance of green, red and NIR band and ratio index of 810-560 nm could distinguish the different type of rice by fuzzy cluster analysis,

Effects of Nanoparticle Size and Morphology on IR Diffuse Reflection Spectra

Two kinds of nanopowders were studied.One is NiFe 2O 4 spherical nanopowders which have different particle sizes.Another is ZnO nanopowders including two series of spherical particles and tetrapod nanowhiskers.Through measuring the infrared diffuse reflection spectra of nanopowders,it can be found that the particle size and morphology affect the infrared diffuse reflection spectra.For the NiFe 2O 4 nanopowders the smaller the particle size,the larger the K-M value.And when the particle size is large enough,the effect of the particle size on infrared diffuse reflection spectra would disappear.For the ZnO nanopowders the effects of the particle size and morphology are more special.The effect of the particle sizes of tetrapod whisker nanopowders on infrared diffuse reflection spectra is more than that of spherical nanopowders.

Influence of Sedimentation on Crystallization of Charged Colloidal Particles

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions on dynamic behavior of a colloidal system. Experiments on crystallization of charged colloidal microspheres with di- ameter of 98 nm dispersed in density-matched and -unmatched media （mixtures of H20 and D20 in proper proportion） are compared to examine the influence of sedimentation. Reflection spectra of colloidal suspensions were used to monitor the crystallization process. Results showed that the crystal size of the density-unmatched （namely, in the presence of sedimentation） sample grew faster than that of the density-matched （in the absence of sedi- mentation） case at the initial stage of the crystallization, and then the latter overtook and outstripped the former. To explain these observations, we assume that in the settling of crystals sedimentation facilitates result in more particles getting into the crystal structures. However, as the crystals increase to varying sizes, the settling velocities become large and hydrodynamic friction strips off some particles from the delicate crystal structures. Overall, the sedimentation appears to accelerate the crystal size growth initially and then retard the growth. In addition, the crystal structures formed under microgravity were more closely packed than that in normal gravity.

Wear monitoring method of water-lubricated polymer thrust bearing based on ultrasonic reflection coefficient amplitude spectrum

The water-lubricated thrust bearings of the marine rim-driven thruster(RDT)are usually composed of polymer composites,which are prone to serious wear under harsh working conditions.Ultrasonic is an excellent non-destructive monitoring technology,but polymer materials are characterized by viscoelasticity,heterogeneity,and large acoustic attenuation,making it challenging to extract ultrasonic echo signals.Therefore,this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient.The effects of bearing parameters,objective function,and algorithm parameters on the identification results are simulated and analyzed.Taking the correlation coefficient and root mean square error as the matching parameters,the thickness,sound velocity,density,and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm(DEA),and the wear measurement system is constructed.In order to verify the identification accuracy of this method,an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-etherketone(PEEK)fixed pad and stainless-steel thrust collar as the object.The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system,respectively.Ultimately,the results demonstrate that the thickness identification error of this method is approximately 1%,and in-situ monitoring ability will be realized in the future,which is of great significance to the life prediction of bearings.

Canopy Spectral Reflectance Characteristics of Rice with Different Cultural Practices and Their Fuzzy Cluster Analysis

The influence of major cultural practices including different nitrogen application rates, population densities, transplanting leaf ages of seedling, and water regimes on rice canopy spectral reflectance was investigated. Results showed that increased nitrogen rates, water regimes and population densities and decreased seedling ages could enhance reflectance at NIR （near infrared） bands and reduce reflectance at visible bands. Using reflectance of green, red and NIR band and ratio index of 810-560 nm could distinguish the different type of rice by fuzzy cluster analysis,

Multi－diffused Reflection Spectroscopy of Rare Earths Doped LaOCl Powder Samples and the Calculation of Quantum Efficiency

The excitation and emission spectra, the relaxation time of principal spectral lines and multi-diffused reflection spectra in LaOCl: Er, LaOCl: Ho powder samples were measured. The diffused absorption spectrum was derived from the multi-diffused reflection spectrum. According to Judd-Ofelt theory,the intensity parameters, radiative transition probabilities and quantum efficiencies of luminescence emission were calculated. Then comparison with erbium and holmium doped floride glass and other matrices were made.

P-type AlAs/[GaAs/AlAs] Semiconductor/Superlattice DBR Grown by MBE

A p-type AlAs(70.2 nm)/16.5 period [GaAs(3 nm)/AlAs(0.7 nm)] semiconductor/superlatice distributed Bragg reflector (DBR) has been grown on n +-GaAs(100) substrate by V80H molecular beam epitaxy system. Experimental reflection spectrum shows that its central wavelength is 820 nm, with the peak reflectivity for 10-pair DBR of as high as 96 %, and the reflection bandwidth of as wide as 90 nm. We formed a 20×20 μm 2 square mesa to measure the series resistance using wet chemical etching. From the measurement result, the series resistance of about 50 Ω is obtained at a moderate doping (3×10 18 cm -3 ). Finally, the dependence of the resistance of the DBR on the temperature is analyzed. From the experimental result, it is found that the mechanism of the low series resistance of this kind of DBR may increase the tunneling current in the semiconductor/superlattice mirror structure, which will result in a decrease in series resistance.

Highly efficient photo-thermal synergistic catalysis of CO_(2)methanation over La_(1-x)Ce_(x)NiO_(3)perovskite-catalyst

Solar-driven photo-thermal catalytic CO_(2)methanation reaction is a promising technology to alleviate the problems posed by greenhouse gases emissions.However,designing advanced photo-thermal catalysts remains a research challenge for CO_(2)methanation reaction.In this work,a series of ABO3(A=lanthanide,B=transition metal)perovskite catalysts with Ce-substituted LaNiO3(La_(1-x)Ce_(x)NiO_(3),x=0,0.2,0.5,0.8,1)were synthesized for CO_(2)methanation.The La_(0.2)Ce_(0.8)NiO_(3) exhibited the highest CH_(4) formation rate of 258.9 mmol·g^(-1)·hcat-1,CO_(2)conversion of 55.4%and 97.2%CH_(4) selectivity at 300℃with the light intensity of 2.9 W·cm^(-2).Then the catalysts were thoroughly analyzed by physicochemical structure and optical properties characterizations.The partial substitution of the A-site provided more active sites for the adsorption and activation of CO_(2)/H_(2).The sources of the active sites were considered to be the oxygen vacancies(O_(v))created by lattice distortions due to different species of ions(La^(3+),Ce^(4+),Ce^(3+))and exsolved Ni0 by H_(2)reduction.The catalysts have excellent light absorption absorbance and low electron-hole(e^(-)/h^(+))recombination rate,which greatly contribute to the excellent performance in photo-thermal synergistic catalysis(PTC)CO_(2)methanation.The results of in situ irradiated electron paramagnetic resonance spectrometer(ISI-EPR)and ISI-X-ray photoelectron spectroscopy(XPS)indicated that the aggregation of unpaired electrons near the defects and Ni metal(from La and Ce ions to Ov and Ni0)accelerated adsorption and activation of CO_(2)/H_(2).At last,the catalyst properties and structure were correlated with the proposed reaction mechanism from the in situ diffuse reflection infrared Fourier transform spectrum(DRIFTS)measurements.The in situ precipitation of the B-site enhanced the dispersion of Ni,while its enriched photoelectrons upon illumination further promote hydrogen dissociation.More H^(*)spillover accelerated the rate-determining step(RDS)of HCOO*hydrogenation.This work provides the theoretical basis for the development of catalysts and industrial application.

Bionic Leaves Imitating the Transpiration and Solar Spectrum Reflection Characteristics of Natural Leaves

A novel thin film organic bionic leaf was prepared by a solution-casting method to simulate the thermal effect of transpi- ration and solar spectrum reflection characteristics of plant leaves. The main components of the bionic leaf are polyvinyl alcohol （PVA）, lithium chloride （LiCl） and chromium sesquioxide （Cr2O3）. The thin film was modified by chemical cross-linking, and its surface was modified by alkylsilane to prevent excessive swelling. The thin film can simulate the thermal effect of natural leaf transpiration because that the hygroscopic PVA and LiCI can absorb and desorb water due to the high and low humidity of the ambient air at night and day, respectively. The thin film has the similar solar spectrum reflection characteristics to those of plant leaves due to the Cr2O3 and the water content of the hygroscopic materials. The measured diurnal maximum radiation temperature difference between the organic bionic leaf and the Osmanthus fragrans leaf was only 0.55 ℃. In addition, the solar spectrum reflection measurements revealed that the organic bionic leaf could precisely simulate the key solar spectrum reflec- tion characteristics of plant leaves.

Biomimetic Material Simulating Solar Spectrum Reflection Characteristics of Yellow Leaf

To counter the threat of hyperspectral detection, it is necessary to develop biomimetic materials to simulate the solar spectral re- flection characteristics of plant leaf accurately. Two kinds ofmembranaceous yellow biomimetic materials were prepared by dispersing the particles of chrome titanium yellow and iron oxide yellow as fillers in polyvinyl alcohol films respectively. Reflectance and transmittance of the biomimetic materials were measured, and absorption and scattering coefficients of the biomimetic materials were inverted with a four-flux model. Results indicate that the biomimetic material adopting chrome titanium yellow particles can simulate the solar spectrum reflection characteristics of yellow leaf because of the similar absorption and scattering characteristics. The biomimetic material adopting iron oxide yellow particles cannot simulate the spectrum reflection characteristics of yellow leaf near the wavelength of 900 nm due to the characteristic absorption of the iron oxide. When the volume fraction of the chrome titanium yellow particles is lower than 2.12%, the absorption and scattering coefficients both increase approximately linearly with the volume fraction, indicating that the particles can scatter radiation independently. Therefore, the reflectance of the biomimetic material can be regulated through linearly changing of the volume fraction of the chrome titanium yellow particles.

Chlorophyll Fluorescence Detected Passively by Difference Reflectance Spectra of Wheat （Triticum aestivum L.） Leaf

The chlorophyll fluorescence （CF） signature emitted from vegetation provides an abundance of information regarding photosynthetics activity and has been used as a powerful tool to obtain physiological information of plant leaves in a non-invasive manner. CF is difficult to quantify because the CF signal is obscured by reflected light. In the present study, the apparent reflectance spectra of wheat （Triticum aestivum L.） leaves were measured under illuminations with and without filtering by three specially designed long-wave pass edge filters; the cut-off wavelengths of the three filters were 653.8, 678.2, and 694. l nm at 50% of maximum transmittance. The CF spectra could be derived as the reflectance difference spectra of the leaves under illuminations with and without the long wave pass edge filters. The ratio of the reflectance difference at 685 and 740 nm （Dif685/Dif740） was linear correlated with the CF parameters （maximal photochemical efficiency Fv/Fm, and the yield of quantum efficiency） measured by the modulated fluorometer. In addition, the ratio reflected the water stress status of the wheat leaf, which was very high when water deficiency was serious. This method provides a new approach for detecting CF and the physiological state of crops.

Spectra Power and Bandwidth of Fiber Bragg Grating Under Influence of Gradient Strain

The reflective spectrum power and the bandwidth of the fiber Bragg grating （FBG） under gradient strain are researched and experimentally demonstrated. The gradient strain is applied on the FBG, which can induce FBG bandwidth broadening, resulting in the variation of reflective power. Based on the coupled-mode theory and transfer matrix method, the segmental linear relationship between the gradient strain, the reflective power, and the bandwidth is simulated and analyzed, and the influence of the FBG length on the reflective spectrum is analyzed. In the experiment, the strict gradient stain device is designed; the experimental results indicate that the reflective optic power and the bandwidth of the FBG under gradient stain are concerned with the length of the FBG. Experimental results are well consistent with the theoretical analysis, which have important guiding significance in the FBG dynamic sensing.