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Four Dimensional Mapping of Vegetation Moisture Content Using Dual-Wavelength Terrestrial Laser Scanning
摘要： Recently, terrestrial laser scanning (TLS) has shown potential in measuring vegetation biochemical traits in three dimensions (3D) by using reflectance derived from backscattered intensity data. The 3D estimates can provide information about the vertical heterogeneity of canopy biochemical traits which affects canopy reflectance but cannot be measured from spaceborne and airborne optical remote sensing data. Leaf equivalent water thickness (EWT), a metric widely used in vegetation health monitoring, has been successfully linked to the normalized difference index (NDI) of near and shortwave infrared wavelengths at the leaf level. However, only two previous studies have linked EWT to NDI at the canopy level in field campaigns. In this study, an NDI consisting of 808 and 1550 nm wavelengths was used to generate 3D EWT estimates at the canopy level in a broadleaf mixed-species tree plot during and after a heatwave. The relative error in EWT estimates was 6% across four different species. Temporal changes in EWT were measured, and the accuracy varied between trees, a factor of the errors in EWT estimates on both dates. Vertical profiles of EWT were generated for six trees and showed vertical heterogeneity and variation between species. The change in EWT vertical profiles during and after the heatwave differed between trees, demonstrating that trees reacted in different ways to the drought condition.
关键词： drought,leaf water content,vegetation,Lidar,water stress
更新于2025-09-11 14:15:04
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Theoretical and experimental study of artificially controlled backscattering fiber using femtosecond laser fabrication
摘要： Thirteen alloys including high- and low-strength nickel-base alloys, austenitic stainless steels, and ferritic alloys were irradiated using 2 MeV protons to a damage level of 2.5 dpa at 360 °C and assessed for their susceptibility to irradiation assisted stress corrosion cracking (IASCC) in both BWR normal water chemistry (NWC) and PWR primary water. Cracking susceptibility was highest for high strength nickel-base alloys, followed by the low strength nickel-base alloys and then the low strength iron-base alloys. Cracking in the nickel-based alloys was worst in normal water chemistry, which was reversed for the iron-based alloys. In general, cracking correlated with the degree of microstructure changes, though no single feature could be linked to cracking. IGSCC occurred in both the unirradiated and irradiated conditions in high strength nickel-base alloys with susceptibility being considerably higher following irradiation. In all cases, slip was planar, and the degree of slip localization correlated with the probability of IG crack initiation. Low strength nickel-base alloys showed the same dependence on environment as high strength alloys but were considerably less susceptible to IASCC initiation. Among the low strength iron-base alloys, alloy 800 was most susceptible to IASCC initiation in both BWR NWC and PWR primary water, which also correlated with grain boundary chromium depletion and silicon segregation. Across all alloys, cracking correlated with both the degree of localized deformation and the hardness in the irradiated condition. The agreement is expected as increased hardening also correlates with localized deformation, which is likely a necessary, though insufficient condition for cracking.
关键词： PWR primary water,Hardening,Irradiation assisted stress corrosion cracking,Radiation,BWR NWC,Structural materials
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC) - Waikoloa Village, HI (2018.6.10-2018.6.15)] 2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC) - 10.3% Efficient CuIn(S,Se)<inf>2</inf> Solar Cells from DMF Molecular Solution with the Absorber Selenized under High Argon Pressure
摘要： Owing to the transformation of the biomedical model of health, more and more professionals pay close attention to the occupational social psychological factors, such as occupational stress. Due to the socioeconomic impact of occupational stress and the petroleum workers stationed in the unique environment in Xinjiang, a cross-sectional study was carried out between May and December 2016 to investigate the relationship between occupational stress and demographic characteristics. A total of 1480 workers were selected. Occupational stress was evaluated with the Occupational Stress Inventory-Revised Edition. The findings of the present study revealed that the values of the Occupational Roles Questionnaire results (t = 9.266, P < .001) and Personal Strain Questionnaire results (t = 21.381, P < .001) were found to be higher than the national normal. Personal Resources Questionnaire values (t = (cid:1)17.575, P < .001) were found to be lower than the national normal in petroleum workers stationed in the arid desert, and suggested a strong correlation between occupational stress and demographic characteristics. These data provide evidence that different demographic characteristics are associated with different occupational stress levels in petroleum workers stationed in the arid desert.
关键词： occupational stress,petroleum workers,arid desert,demographic characteristics
更新于2025-09-11 14:15:04
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Stresses and fatigue of laser welds
摘要： The paper deals with the specific properties of laser welds in fine-grained high-strength steels. The main topic, however, are residual stresses in laser welds, their impact on the mechanical properties and fatigue behaviour of such welds. As documented, fatigue cracks initiate mainly on micropores or other subsurface defects. From X-ray diffraction studies it follows that thermal expansion is primarily responsible for the longitudinal tensile stresses, whereas transverse compressive stresses are caused by phase transformations. The behaviour of transverse stresses also explains why fractures in laser welds occur completely outside the weld metal and the heat-affected zone.
关键词： welding,laser,residual stress,fatigue
更新于2025-09-11 14:15:04
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Thermo-Mechanical Analysis of Laser Additive Manufacturing for Metals
摘要： The aim of this study is to develop a finite element analysis technique to characterize the distributions of temperature and stress in the process of multilayer deposition of metallic powders by laser additive manufacturing (LAM). Simulation results indicate the residual normal stress in the laser moving direction is greater than that in other directions due to a larger temperature gradient, and it increases with number of deposited layers. Highly residual stresses are present in the LAM build and at the base nearby the interface between the build and base.
关键词： laser additive manufacturing,temperature gradient,finite element analysis,metal,residual stress
更新于2025-09-11 14:15:04
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Stress Evolution during Ge Nanoparticles Growth in a SiO <sub/>2</sub> Matrix
摘要： Superstructures are explored that were obtained by multilayer magnetron deposition at room temperature of 20 SiO2 and SiO2:Ge bilayers, each 2 × 4 nm thick, and subsequently annealed in inert N2 atmosphere at different temperatures in the range of 500?750 °C. The structural and optical changes induced by annealing and the formation and growth of Ge nanoparticles (nps) from early clusters to their full growth and final dissolution were studied by the simultaneous grazing-incidence small- and wide-angle X-ray scattering, transmission electron microscopy, and (time-resolved) photoluminescence (PL). It is shown that in as-deposited multilayers aggregation of small clusters already occurred, and the clusters were reasonably well intercorrelated in the lateral plane. During annealing at Ta = 550 °C or higher temperatures, Ge nps start to form and remain partly amorphous at lower Ta but crystallize completely at about 600 °C. At even higher temperatures, the Ge nps dissolve and Ge diffuses out almost completely, leaving voids in the SiO2 matrix. Visible PL from the samples was detected and attributed to defects in the nps/matrix interface layers rather than to the nps itself because PL persisted even after Ge nps dissolution.
关键词： GIWAXS,photoluminescence,Ge nanoparticles,GISAXS,stress evolution,SiO2 matrix,TEM
更新于2025-09-11 14:15:04
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Handbook of Mechanics of Materials || Surface/Interface Stress and Thin Film Stress
摘要： Thin ?lm stress is critical for the reliability and electronic/optoelectronic properties of thin ?lm devices. In this chapter, we systematically discussed the effects of surface and interface stresses on the ?lm stress development during growth of polycrystalline ?lms at the initial and ?nal growth stage. We demonstrate that surface stress plays an important role at the initial stage of ?lm growth (island growth stage), and conventional stress analysis technology such as wafer curveture experiments may not be applicable at this stage. At the late stage of ?lm growth, we also show that adatom insertion into the grain boundaries is the primary mechanism of compressive stress development.
关键词： interface stress,Thin ?lm stress,adatom insertion,wafer curvature,grain boundaries,surface stress,polycrystalline ?lms
更新于2025-09-10 09:29:36
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Residual Stress Analysis Based on Acoustic and Optical Methods
摘要： Co-application of acoustoelasticity and optical interferometry to residual stress analysis is discussed. The underlying idea is to combine the advantages of both methods. Acoustoelasticity is capable of evaluating a residual stress absolutely but it is a single point measurement. Optical interferometry is able to measure deformation yielding two-dimensional, full-field data, but it is not suitable for absolute evaluation of residual stresses. By theoretically relating the deformation data to residual stresses, and calibrating it with absolute residual stress evaluated at a reference point, it is possible to measure residual stresses quantitatively, nondestructively and two-dimensionally. The feasibility of the idea has been tested with a butt-jointed dissimilar plate specimen. A steel plate 18.5 mm wide, 50 mm long and 3.37 mm thick is braze-jointed to a cemented carbide plate of the same dimension along the 18.5 mm-side. Acoustoelasticity evaluates the elastic modulus at reference points via acoustic velocity measurement. A tensile load is applied to the specimen at a constant pulling rate in a stress range substantially lower than the yield stress. Optical interferometry measures the resulting acceleration field. Based on the theory of harmonic oscillation, the acceleration field is correlated to compressive and tensile residual stresses qualitatively. The acoustic and optical results show reasonable agreement in the compressive and tensile residual stresses, indicating the feasibility of the idea.
关键词： electronic speckle-pattern interferometry,residual stress analysis,acoustoelasticity,scanning acoustic microscopy
更新于2025-09-10 09:29:36
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Analysis of multiple edge cracks in a non-homogeneous piezoelectric layer
摘要： This study is concerned with the treatment of the several edge cracks in a functionally graded piezoelectric (FGP) layer under anti-plane mechanical and in-plane electrical loading. The edge crack is assumed to be either electrically impermeable or permeable. The problem is formulated by using distributed dislocation technique. The integral equations are constructed for the analysis of a FGP layer, in which the unknown variables are dislocation densities. By use of the dislocation densities, the field intensity factors are calculated. Numerical examples are provided to show the effect of the location and orientations of edge crack upon the stress intensity factors.
关键词： functionally graded piezoelectric,distributed dislocation technique,edge cracks,stress intensity factors
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Synthetic aperture radar observations of interannual ocean-atmosphere coupling over the Somali Current
摘要： The covariability of wind stress and sea surface temperature is observed at high resolution over the Western Arabian Sea. Synthetic aperture radar data were acquired over the Somali Current in 2016 and 2017 during the summer monsoon season. The Somali Current, the Southern Gyre and the Great Whirl were all observed at the time of these acquisitions. Wind stress curl derived from the synthetic aperture radar data show the effects of the cold upwelled coastal water and the Somali Current on the wind stress. Significant organized large eddies are also observed east of the Somali Current.
关键词： ocean-atmosphere coupling,wind stress,synthetic aperture radar
更新于2025-09-10 09:29:36