- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Effects of different complexing agents on the physical properties of ZnO nanoparticles
摘要： ZnO nanoparticles have been synthesised via a co-precipitation method using different complexing agents. X-ray diffraction (XRD) analysis revealed that ZnO nanoparticles were composed of a single hexagonal wurtzite phase. Transmission electron microscopy (TEM) analysis indicates that the samples prepared without any complexing agent have slight agglomeration characteristics presenting a prismatic morphology and a wider size distribution from 22 to 72 nm, which provides good material packing density. However, samples synthesised using urea and glycine are similar and show spherical-like morphology. XRD and TEM analyses indicate that complexing agents also have an important role in the size of the ZnO nanoparticles, where the average particle size of 47 and 22 nm were obtained using urea and glycine, respectively.
关键词： size distribution,glycine,ZnO,complexing agents,co-precipitation,urea,morphology,nanoparticles
更新于2025-09-23 15:19:57
-
Examining Storm Asymmetries in Hurricane Irma (2017) Using Polarimetric Radar Observations
摘要： Dual-polarization radar observations of Hurricane Irma (2017) provide new insight into the microphysical structure of a mature tropical cyclone that can be tied to the cyclone dynamics. The primary eyewall exhibited a radar signature of hydrometeor size sorting, which implied that large drops fell out near persistent upward motion in the front-right quadrant of the storm, while smaller drops were advected downstream. In the outer rainbands, convective initiation was also preferred in the front-right quadrant, whereas stratiform precipitation was predominant downwind. For both the primary eyewall and outer rainbands, the preferred quadrant for convective initiation was consistent with the expected kinematic asymmetry of a tropical cyclone in weak environmental wind shear but with moderate translation speed. The developing secondary eyewall exhibited a different asymmetry that indicated a stratiform-to-convective transition associated with heavy precipitation in the rear quadrants. This transition is consistent with hypothesized dynamical theories for secondary eyewall formation.
关键词： hydrometeor size sorting,stratiform precipitation,microphysical structure,Hurricane Irma,tropical cyclone,convective initiation,dual-polarization radar,secondary eyewall formation
更新于2025-09-23 15:19:57
-
Ammonium oxalate-assisted synthesis of Gd2O3 nanopowders
摘要： The impacts of co-precipitation reaction temperature and duration, as well as calcination temperature and duration, on the particle morphology and properties of gadolinia (Gd2O3) nanopowders were investigated. Thermogravimetric curve of thermally treated gadolinium oxalate (Gd2(C2O4)3) showed that pure stable cubic phase Gd2O3 nanopowders could be obtained by calcining at 640 °C and higher. This finding was also supported by results obtained from Fourier Transform Infrared Spectrometry (FTIR) and Raman spectrometry. This study also shows that uniform spherules of Gd2O3 nanopowders could be obtained under controlled synthesis conditions. However, with an increase in both the co-precipitation reaction temperature and duration, the extent of agglomeration of Gd2O3 nanopowders increased, as observed under a Field Emission Scanning Electron Microscope (FESEM). The FESEM images and X-ray Diffraction (XRD) patterns also revealed accelerated grain growth and increased average crystallite size at high calcination temperatures and holding times. It was determined that the most favourable Gd2O3 particle morphology was achieved when Gd2(C2O4)3 was co-precipitated at 40 °C, then thermally degraded at 650°C, for 1 h and 4 h, respectively. Estimated Scherrer’s average crystallite size of the resulting Gd2O3 nanopowders was 16.54 nm, which was further affirmed with the transmission electron microscope (TEM) image, where crystallite sizes of 3 to 27.5 nm were observed in the Gd2O3 sample. This specimen also demonstrated a considerably large specific surface area of 9.16 m2/g, as measured using a Brunauer–Emmett–Teller (BET) analyser.
关键词： Ammonium oxalate,Gadolinium oxide,Nanopowders,Co-precipitation,Gadolinia
更新于2025-09-19 17:15:36
-
[IEEE 2019 IEEE International Ultrasonics Symposium (IUS) - Glasgow, United Kingdom (2019.10.6-2019.10.9)] 2019 IEEE International Ultrasonics Symposium (IUS) - Simultaneous dictionary learning and reconstruction from subsampled data in photoacoustic microscopy
摘要： The Global Precipitation Measurement (GPM) Core Observatory will carry a Dual-frequency Precipitation Radar (DPR) consisting of a Ku-band precipitation radar (KuPR) and a Ka-band precipitation radar (KaPR). In this study, “at-launch” codes of DPR precipitation algorithms, which will be used in GPM ground systems at launch, were evaluated using synthetic data based upon the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data. Results from the codes (Version 4.20131010) of the KuPR-only, KaPR-only, and DPR algorithms were compared with “true values” calculated based upon drop size distributions assumed in the synthetic data and standard results from the TRMM algorithms at an altitude of 2 km over the ocean. The results indicate that the total precipitation amounts during April 2011 from the KuPR and DPR algorithms are similar to the true values, whereas the estimates from the KaPR data are underestimated. Moreover, the DPR estimates yielded smaller precipitation rates for rates less than about 10 mm/h and greater precipitation rates above 10 mm/h. Underestimation of the KaPR estimates was analyzed in terms of measured radar re?ectivity ( ) of the KaPR at an altitude of 2 km. The underestimation of the KaPR data was most pronounced during strong precipitation events of (high attenuation cases) over heavy precipitation areas in the Tropics, whereas the underestimation was less pronounced when the (moderate attenuation cases). The results suggest that the underestimation is caused by a problem in the attenuation correction method, which was veri?ed by the improved codes.
关键词： simulation,spaceborne radar,rain,Global Precipitation Measurement (GPM),snow,Tropical Rainfall Measuring Mission (TRMM),Algorithms,attenuation
更新于2025-09-19 17:13:59
-
Nondestructive Evaluation of Thermal Aging in Al6061 Alloy by Measuring Acoustic Nonlinearity of Laser-Generated Surface Acoustic Waves
摘要： The structures in high-temperature environments are prone to undergo hardening and embrittlement as a result of thermal aging; this can cause variations in their mechanical properties. Because these changes occur at the microstructural level, it is difficult to evaluate them through linear ultrasonic techniques. In this work, a surface acoustic wave (SAW) was used to measure and compare the acoustic nonlinearity and mechanical properties of Al6061 alloys heat-treated at 220°C for different durations (0 min, 20 min, 40 min, 1 h, 2 h, 10 h, 100 h, 1000 h). The SAW was generated by a pulsed laser and then received by an interferometer. Moreover, the yield strength, ultimate strength, and elongation to failure were measured by tensile tests. The results demonstrate that the critical variations in the mechanical properties can be detected by monitoring the variation features in the acoustic nonlinearity. Transmission electron microscopy images were captured to observe the microstructural changes, which shows that the acoustic nonlinearity varied according to the change in the precipitation phase. This supports the acoustic nonlinearity measurement using the laser-generated SAW being an effective technique for the fully noncontact nondestructive evaluation of material degradations as well as changes in mechanical properties.
关键词： surface acoustic wave,material degradation,laser,heat treatment,mechanical property,thermal aging,nonlinear parameter,precipitation,acoustic nonlinearity
更新于2025-09-19 17:13:59
-
AIP Conference Proceedings [AIP Publishing THE 7TH INTERNATIONAL CONFERENCE ON APPLIED SCIENCE AND TECHNOLOGY (ICAST 2019) - Karbala City, Iraq (27–28 March 2019)] THE 7TH INTERNATIONAL CONFERENCE ON APPLIED SCIENCE AND TECHNOLOGY (ICAST 2019) - Investigations of ZnO-NiO/PSi heterojunction for solar cell application
摘要： In this paper, ZnO-NiO nanocomposite has been successfully synthesized using chemical precipitation method .The structural properties were investigated using X-ray diffraction ( XRD) and field emission scanning electron microscope (FESEM) . XRD measurements confirms the formation of polycrystalline ZnO and NiO nanoparticles with a hexagonal and cubic structure respectively. The average grain size of ZnO-NiO nanocoposite estimated from FESEM was 60 nm . Heterojunction solar cell fabricated using ZnO-NiO nanocomposite on porous silicon by spray pyrolysis method shows open-circuit voltage (VOC) of 470 mV, short-circuit current density (ISC) of 39 mA/cm2, fill factor (FF) of 78.72% , and efficiency of 14.43%.
关键词： porous silicon,solar cell,chemical precipitation,ZnO-NiO nanocomposite,spray pyrolysis
更新于2025-09-19 17:13:59
-
Structural Analysis of Calcium Phosphate-Based Submicrospheres with Internally-Crystallized Iron Oxide Nanoparticles Fabricated by a Laser-Assisted Precipitation Process
摘要： Calcium phosphate (CaP)-based submicrospheres containing magnetic iron oxide (IO) nanoparticles (IO–CaP submicrospheres) have potential for various biomedical applications. We recently achieved facile one-pot fabrication of IO–CaP submicrospheres using a laser-assisted precipitation process in which weak pulsed laser irradiation was applied to a labile CaP reaction mixture supplemented with ferrous ions under adequate pH. In this study, we performed the resulting IO–CaP cross-sectional submicrospheres. The cross-sectional TEM analysis revealed that the IO–CaP submicrospheres were heterogeneous in their internal nanostructures and could be categorized into two types, namely types A and B. The type A submicrospheres contained single nano-sized IO nanoparticles homogeneously dispersed throughout the CaP-based matrix. The type B submicrospheres contained larger IO nanoparticles with an irregular or spherical shape, which were mostly a few tens of nanometers in size along with one or two submicron-sized domains. These findings provide new insight into the formation mechanism of IO–CaP submicrospheres in this fabrication technique as well as future applications of the resulting IO–CaP submicrospheres.
关键词： laser-assisted precipitation process,submicrospheres,calcium phosphate,cross-sectional analysis,iron oxide nanoparticles
更新于2025-09-19 17:13:59
-
Novel Square-Waveguide Dual-Mode Two-Way Reactive Power Divider
摘要： Vertically and horizontally inhomogeneous distributions of hydrometeors are often observed in precipitating clouds. The 3-D characteristics can then cause errors in the passive microwave rainfall measurements with the current off-nadir viewing sensors’ specific specifications. This result is due to the fact that the same surface rainfall could be associated with different amounts of hydrometeors depending on the sensors’ viewing paths. In this paper, we confirmed that the plane-parallel radiative treatment to the atmosphere leaves a notable deficiency in the microwave radiometric signatures, particularly at the higher frequency channels for different viewing directions when largely inhomogeneous precipitating clouds are accompanied by significant ice particles. The mean differences between the two brightness temperature fields with two opposite azimuthal viewing directions were up to approximately 40 ?K for the vertically polarized channel at 85.5 GHz in the case study. The impact of the 3-D effect on the passive microwave rainfall estimations was also examined by synthetic retrievals employing a Bayesian methodology. The results showed that the uncertainty in the rainfall estimations due to the 3-D effect depended on the viewing directions considered in the a priori information. It was also found that taking more viewing angles or the azimuth angles in the a priori information into consideration tended to moderate the retrieval difference that resulted from the different viewing directions. In addition, the retrieval uncertainty related to the 3-D effect appeared to be more significant for heavy rainfall cases with large amounts of ice particles, as expected.
关键词： 3-D radiative transfer,precipitation,3-D effect,Passive microwave remote sensing
更新于2025-09-19 17:13:59
-
Microstructure control, competitive growth and precipitation rule in faceted Al2O3/Er3Al5O12 eutectic in situ composite ceramics prepared by laser floating zone melting
摘要： Microstructure control and competitive growth of Al2O3/Er3Al5O12 eutectic/off-eutectics are explored over wide ranges of solidification rates and compositions. Gradual transformation phenomenon of microstructure morphology from complete eutectic to eutectic + coarse Er3Al5O12 phase and to eutectic + Er3Al5O12 dendrite is observed and the corresponding influence factors are evaluated. Competitive growth between single-phase Al2O3 (or Er3Al5O12) dendrite and eutectic is analyzed and coupled growth zone is mapped through comparing interface temperatures of different patterns of microstructures. The complete eutectic microstructure could be obtained at Al2O3/Er3Al5O12 hypoeutectic (Al2O3-17.5 mol% Er2O3) under fast solidification rate and the onset growth rate (~0.94 × 104 μm/s) estimated from the measured eutectic spacing (~150 nm) fits well with the result calculated on the basis of competitive growth (~1.27 × 104 μm/s). Transformation of microstructure from irregular eutectic to regular eutectic and probable adjustment mechanism of eutectic spacings are discussed when the eutectic spacings refined from micron-scale (< 10 μm) to nano-scale (~20 nm).
关键词： Competitive growth,Directional solidification,Microstructure control,Precipitation rule,Oxide ceramic
更新于2025-09-19 17:13:59
-
Highly stable CdTe quantum dots hosted in gypsum <i>via</i> a flocculation–precipitation method
摘要： Poor stability hinders the practical application of aqueous CdTe quantum dots (QDs) in optoelectronic devices. In this work, a flocculation–precipitation method is demonstrated to host aqueous CdTe QDs in gypsum to form CdTe–gypsum nanocomposites, which is simple, effective and environmental-friendly. Ascribed to gypsum acting as a tight and robust matrix protection agent, the photo-, thermal-, anti-acid and long-term stability of CdTe QDs were remarkably improved. Moreover, this approach solved the problem of incompatibility between aqueous QDs and epoxy resin, allowing for the application of aqueous QDs in white light emitting diodes (WLEDs), based on which a WLED with the red-emission nanocomposites used as a color-conversion layer was successfully fabricated. These results indicate the potential of this technique in stabilizing aqueous QDs as well as their practical application in optoelectronic devices.
关键词： optoelectronic devices,stability,flocculation–precipitation method,CdTe quantum dots,gypsum
更新于2025-09-16 10:30:52