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- 实验方案
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Optical Diagnosis of the Geometry of an Axisymmetric Controlled Nozzle of a Gas-Turbine Engine
摘要： Modern aviation industry solves the problem of developing multifunction engines capable of ?ying both at subsonic and supersonic speeds. An important part in such engines is a variable area nozzle, which allows varying the geometry of the engine exhaust unit and, accordingly, its technical characteristics. This study touches upon an computer vision based optical noncontact method for reconstructing a nozzle shape. The reconstruction requires data recorded by two optical three-dimensional recorders directed toward the inner part of the nozzle when the engine is subjected to ground tests. The diagnosis is complicated by the presence of a hot jet being in the way of the sensor vision, the regime-dependent variation of the nozzle glow brightness, and intense mechanical vibrations. The performed bench tests con?rm the e?ciency of the proposed method. According to their results, in a low-gas regime, the standard deviation of the diagnosed diameters of the exhaust unit and critical sections for each frame does not exceed 0.3% of the corresponding sizes. The data obtained as a result of this diagnosis can be taken into account when upgrading the exhaust unit of the engine and the thrust control system of a gas turbine engine.
关键词： 3D scan,GTE exhaust unit geometry,optical diagnosis,stereo vision,stereo reconstruction,ground tests
更新于2025-09-23 15:21:01
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Highly Conjugated, Fused-Ring, Quadrupolar Organic Chromophores with Large Two-Photon Absorption Cross-Sections in the Near-Infrared
摘要： The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as non-fullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 103 GM) in the near infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (7 rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement and their moderate magnitudes (ca. 10-21 m2) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.
关键词： pump-probe spectroscopy,Nonlinear optics,Z-scan,organic optoelectronics,ultrafast spectroscopy,two-photon absorption
更新于2025-09-23 15:21:01
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Nonlinear optical properties of core shell type II quantum dot structures
摘要： In this study, CdSe/CdTe Type-II quantum dots (QDs) were synthesized using dropwise method. The core/shell nanocrystals have been characterized by UV–Vis absorption and photoluminescence (PL) spectroscopies, transmission electron microscopy and z-scan technique. Nonlinear properties of each type of quantum dots were studied using femtosecond(fs) z-scan method at 800 nm wavelength with different laser intensities. Fs laser z-scan experimental set-up are used to determine two photon absorption coefficient (β ?10?12 cm/W) and nonlinear optical Kerr coefficient (n2 ? 10?20 cm2/W. The imaginary and real parts of third order susceptibility (X(3)) were calculated based on β and n2 under different laser intensities for seven different core/shell QDs. Third order susceptibility for CdSe/CdTe type II QDs was found to be about 10?12 esu.
关键词： Femtosecond Z-scan,CdSe/CdTe,Type-II quantum dots
更新于2025-09-23 15:21:01
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Influence of soil texture on the estimation of bare soil moisture content using MODIS images
摘要： Spectral behaviour of soil is strongly influenced by the soil texture as well as its nutrient content. Many attempts have so far been made to assess the soil moisture using soil reflectance in different bands of satellite images. In this paper, the investigations showed that the coarse texture soils did not show a profound relationship with the reflectance values that was in part due to its weak water storage capacity. Fine texture soils, on the contrary, showed better results which could be attributed to their higher water storage capacity and the capillary phenomenon. Finally, a linear regression model made of a combination of Land Surface Temperature (LST), Normalized Difference Water Index (NDWI) and Visible and Short-wave infrared Drought Index (VSDI) indices was proposed. The suggested method has improved the accuracy of the soil moisture content estimation up to 1% in general and the medium texture soil in particular. The results were compared with the performance of seven conventional soil moisture estimators method all using the Moderate Resolution Imaging Spectroradiometer (MODIS) data.
关键词： Soil moisture content,MODIS,soil texture,US-SCAN
更新于2025-09-23 15:21:01
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Tunable thermo-piezo-plasmonic effect on core/shell nanoparticles under laser irradiation and external electric field
摘要： This work is focused on the characterization of the opto-heating generation in thermo-piezo-plasmonic solutions of gold-PbZrTiO3 (PZT) core/shell nanoparticles. Core/shell nanoparticles have been prepared by the laser ablation in liquid method. Linear and nonlinear optical properties of proposed nanoparticles were studied by optical spectroscopy and the Z-scan technique under external voltage to investigate the piezo-photonic effect. Furthermore, the linear optical properties of these nanostructures were calculated vie dipole approximation method with different core size and different shell thickness of samples immersed in water and poly-vinyl-pyrrolidone. In addition, thermo-plasmonic effects of samples are investigated theoretically and experimentally by the finite element method of COMSOL multiphysics V5.4 and infrared camera under laser irradiation and external electric field. The results revealed a clear tunable and adjustable linear and nonlinear behavior and thermo-piezo-plasmonic properties under external effects. The temperature elevation is ranging of ?T = 3.7–14.1 °C under different external effects. Accordingly, these results encourage to uses proposed samples for the cancer treatment and the different biomedical applications.
关键词： Nonlinear refractive index,External electric field,Core/shell NPs,Laser irradiation,Thermoplasmonic,Piezoelectric,Z-scan technique,Schottky barrier
更新于2025-09-23 15:21:01
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Smart Line Scan Measurement Systems
摘要： Current industrial machine vision applications mostly rely on PC-based image processing. Smart camera systems, which incorporate an image sensor and computing capabilities, were initially restricted to very simple tasks like barcode reading and interpretation. But as the computing capabilities of embedded systems increased, smart cameras are now able to handle a wide range of applications. Especially when machine vision has to be integrated into an existing automation system, this is often more easily done with a smart camera solution than with a PC-based vision system. Smart camera solutions are smaller, they generally generate less heat, and, therefore, can be a better choice if localized sorting tasks pass / fail decision making or process control is requested.
关键词： Smart Line Scan Measurement Systems,analysis,image acquisition,machine vision,automation
更新于2025-09-23 15:21:01
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Third-order NLO properties and power limiting behavior of (E)-3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one under CW laser excitation
摘要： A novel chalcone derivative (E)-3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one abbreviated as FMC was synthesized using Claisen-Schmidt condensation reaction method. Single crystals were grown using slow evaporation solution growth technique. The UV-Visible spectrum reveals that crystals are transparent in the visible region. The third order NLO properties of grown crystals in DMF (0.01m) have been studied using single beam z-scan technique with continuous wave DPSS laser operating at 532nm wavelength and 200mW power. The calculated values of non linear R.I, non linear absorption coefficient and magnitude of 3rd order susceptibility are of the order -0.1466×10-8 cm2W-1, 4.5×10-5cmW-1 and 1.26×10-8e.s.u respectively. The hyperpolarizability value obtained is of the order 1.044×10-27e.s.u. The crystal shows optical limiting behavior with limiting threshold of 11.2 KJcm-2. The results suggest that this material is considered as a promising candidate for future nonlinear optical device applications for continuous wave laser excitation.
关键词： chalcone derivatives,crystal growth,NLO materials,z-scan
更新于2025-09-23 15:21:01
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density functional
摘要： It was recently reported in experiments that at temperatures below 2500 K liquid nitrogen (N) remains molecular up to 120 GPa [Phys. Rev. Lett. 119, 235701 (2017)], which contradicts a liquid-liquid transition at 88 GPa and 2000 K predicted by PBE-GGA density functional. To clarify this, we perform extensive ?rst principles molecular dynamics using SCAN meta-GGA density functional, which captures the intermediate-range part of the van der Waals interaction better than PBE-GGA. It is found that SCAN gives more accurate bond energy and length of an isolated N2 molecule than PBE. SCAN, as well as PBE, is capable of reproducing the ?rst-order molecular-to-polymeric phase transition, but in contrast to PBE, it predicts a wider stability range for ?uid N2. The boundary of this range is 15 GPa higher than the one predicted with PBE, which is in closer agreement with experiments. In addition, SCAN predicts a higher amount of threefold coordinated atoms in the polymeric phase than PBE, which is expected from experiments in amorphous N. These improvements indicate that SCAN is more accurate than PBE in predicting the phase transition from molecular to polymeric ?uid N.
关键词： phase transition,density functional,molecular dynamics,SCAN meta-GGA,liquid nitrogen
更新于2025-09-23 15:21:01
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A new method of mark detection for software-based optical mark recognition
摘要： Software optical mark recognition (SOMR) is the process whereby information entered on a survey form or questionnaire is converted using specialized software into a machine-readable format. SOMR normally requires input fields to be completely darkened, have no internal labels, or be filled with a soft pencil, otherwise mark detection will be inaccurate. Forms can also have print and scan artefacts that further increase the error rate. This article presents a new method of mark detection that improves over existing techniques based on pixel counting and simple thresholding. Its main advantage is that it can be used under a variety of conditions and yet maintain a high level of accuracy that is sufficient for scientific applications. Field testing shows no software misclassification in 5695 samples filled by trained personnel, and only two misclassifications in 6000 samples filled by untrained respondents. Sensitivity, specificity, and accuracy were 99.73%, 99.98%, and 99.94% respectively, even in the presence of print and scan artefacts, which was superior to other methods tested. A separate direct comparison for mark detection showed a sensitivity, specificity, and accuracy respectively of 99.7%, 100.0%, 100.0% (new method), 96.3%, 96.0%, 96.1% (pixel counting), and 99.9%, 99.8%, 99.8% (simple thresholding) on clean forms, and 100.0%, 99.1%, 99.3% (new method), 98.4%, 95.6%, 96.2% (pixel counting), 100.0%, 38.3%, 51.4% (simple thresholding) on forms with print artefacts. This method is designed for bubble and box fields, while other types such as handwriting fields require separate error control measures.
关键词： Software optical mark recognition,pixel counting,mark detection,print and scan artefacts,simple thresholding
更新于2025-09-23 15:21:01
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Enhanced nonlinear optical behavior of graphene-CuO nanocomposites investigated by Z-scan technique
摘要： Graphene-CuO nanocomposites were synthesized by the solvothermal method, and graphene (G) were prepared for comparison. The morphologies and structures of samples were investigated by x-ray diffraction, scanning electron microscopy, Raman spectroscopy and ultraviolet-visible absorption spectroscopy. The nonlinear optical (NLO) properties were tested by the Z-scan technology with 1030 nm laser pulses (340 fs, 1000 Hz). The analyse demonstrates that the NLO properties of the graphene-CuO nanocomposites are significantly enhanced compared with graphene, the doping of CuO increases the time of the electron transfer and the photon transition, suppress the recombination between electrons and holes, and prolong the working time of the free carrier, ultimately enhance the nonlinear optical properties of nanocomposites. The results provide a facile approach of doping CuO in graphene to obtain nanocomposites with excellent NLO properties, and the nanocomposites exhibited potential applications in optical devices such as optical switch and optical sensors, etc.
关键词： Nonlinear optical properties,Z-scan technology,Nanocomposites
更新于2025-09-23 15:21:01