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11.
A time series generator is presented, employing a robust three-level multivariate scheme for stochastic simulation of correlated processes. It preserves the essential statistical characteristics of historical data at three time scales (annual, monthly, daily), using a disaggregation approach. It also reproduces key properties of hydrometeorological and geophysical processes, namely the long-term persistence (Hurst–Kolmogorov behaviour), the periodicity and intermittency. Its efficiency is illustrated through two case studies in Greece. The first aims to generate monthly runoff and rainfall data at three reservoirs of the hydrosystem of Athens. The second involves the generation of daily rainfall for flood simulation at five rain gauges. In the first emphasis is given to long-term persistence – a dominant characteristic in the management of large-scale hydrosystems, comprising reservoirs with carry-over storage capacity. In the second we highlight to the consistent representation of intermittency and asymmetry of daily rainfall, and the distribution of annual daily maxima. 相似文献
12.
A fracture mechanics approach to accelerated life testing of cathodic delamination between steel and polyurea is presented. This required the hyperelastic behavior of the polyurea to be described by the Marlow model based on uniaxial tension and plane strain compression tests. Time-dependence was also considered but could be neglected if proper test protocols were followed in cathodic delamination tests using a strip blister specimen. The variation of J-integral with specimen geometry and loading parameter was obtained, which allowed the resistance to cathodic delamination to be expressed in terms the J-integral and the crack speeds obtained from the tests at several temperatures. The approach established that both temperature and stress can be used to accelerate the cathodic delamination, thereby providing a quantitative and rational basis for conducting accelerated testing. In addition, the discriminating nature of the approach for design purposes was exemplified by quantitatively establishing differences in the delamination resistance of three surface treatments. 相似文献
13.
In this paper, the thermoelectric properties of ZnO doped with Al, Bi and Sn were investigated by combining experimental and theoretical methods. The average Seebeck coefficient of Bi doped ZnO over the measured temperature range is improved from −90 to −497 μV/K. However, segregation of Bi2O3 in ZnO:Bi sample, confirmed by FESEM, lead to enormous grain growth and low electrical conductivity, which makes Bi is not a good dopant to improve ZT value of ZnO. As a 4+ valence cation, Sn doping actually show an increase in carrier concentration to 1020 cm−3, further enhancing the electrical conductivity. Unfortunately, the Seebeck coefficient of ZnO:Sn samples is even lower than pure ZnO sample, which lead to a low ZT value. As for ZnO:Al sample, with nearly no change in lattice thermal conductivity, electrical conductivity and Seebeck coefficient were both enhanced. Threefold enhancement in ZT value has been achieved in ZnO:Al sample at 760 °C compared with pure ZnO. 相似文献
14.
测试分析钛矿渣和页岩的矿物组成、化学成分,把钛矿渣加入到页岩中制备烧结砖。研究钛矿渣与页岩的配比及其烧成制度对烧结制品抗压强度的影响,并利用X射线衍射仪、扫描电子显微镜对烧结砖进行微观结构分析。通过正交实验确定了各因素对烧结砖抗压强度的影响程度由大到小顺序为:烧结温度﹥钛矿渣掺量﹥保温时间,烧结砖制备的最佳工艺条件:钛矿渣掺量为10%,烧结温度为1 100℃,保温时间为2h。钛矿渣-页岩烧结制品结构致密,并有大量长石类矿物相生成,使得制品抗压强度增强。 相似文献
15.
《Carbon》2014
The characteristics of network formation of multiwall carbon nanotubes (MWCNTs) inside ethylene–octene copolymer (EOC) melts under an alternating current (AC) electric field and the resulting electrical conductivity improvements are studied by combining dynamic and steady state resistivity measurements. Fine MWCNT dispersion during melt compounding of the samples is accomplished by means of a novel non-specific, non-covalent functionalization method. It is found that the electrified composite films exhibit nanotube assembly into columnar structures parallel to the electric field, accompanied by dramatic increases in electrical conductivity up to eight orders of magnitude. Experimentally acquired resistivity data are used to derive correlations between the characteristic insulator-to-conductor transition times of the composites and process parameters, such as electric field strength (E), polymer viscosity (η) and nanotube volume fraction (ϕ). Finally, a criterion for the selection of (η, E, C) conditions that enable MWCNT assembly under an electric field controlled regime (i.e., minimal Brownian motion-driven aggregation effects) is developed. The correlations presented herein not only provide insights in the MWCNT assembly process, but can also guide the experimental design in future studies on electrified composites or assist in the selection of process parameters in composites manufacturing. 相似文献
16.
《International Journal of Hydrogen Energy》2019,44(50):27483-27491
Exploring earth-abundant electrocatalyst with active and stable hydrogen evolution reaction (HER) properties is desirable but still challengeable. Herein, WP2 nanosheets are seamlessly grown on W foil (WP2 NSs/W) through phosphorization of WO3/W. This seamless WP2/W structure is beneficial to reducing the resistance between WP2 and W. Along with the exposed large density of active sites, WP2 NSs/W displays outstanding HER activity with a lower onset potential of about 0 V, a smaller overpotential of 90 mV for the current density of 10 mA/cm2 in basic media. Notably, WP2 NSs/W electrode also catalyzes HER efficiently in acid. The synthesis of WP2 NSs/W provides us a straightforward strategy to gain more cost-effective cathode for HER. 相似文献
17.
《Ceramics International》2016,42(14):15876-15880
The influence of ZnO nanoseeds on the formation of ZnO nanorods from ε-Zn(OH)2 in NaOH solution at 80 °C was investigated, using ZnO nanoparticles with a diameter of 4–10 nm as the seeds. The experimental results indicated that the presence of ZnO nanoseeds promoted the rapid heterogeneous formation of ultrathin ZnO nanorods. Compared with the ZnO submicron rods with a diameter of 0.5–1.0 µm, the ultrathin ZnO nanorods with a diameter of 10–15 nm were found to be more sensitive for detecting NO2 at room temperature owing to their higher variation of channel conduction to the diameter. 相似文献
18.
A precise control of the morphology and crystallization of perovskite thin-films is well-correlated to higher perovskite solar cells performances. Ionic liquids (ILs) can retard perovskite crystallization to aid the formation of films with uniform morphology to realize highly efficient perovskite solar cells. Herein, we attempt to control the nanostructural growth of CH3NH3PbI3 thin films by adding ILs to the perovskite spin-coating solution and investigate the effect of IL viscosity on the resulting CH3NH3PbI3 nanoparticle (NP) thin films. NPs with desirable morphology were obtained using ILs with a low viscosity that completely dissolved in the CH3NH3PbI3 solution. In particular, the IL tetrabutylammonium chloride yielded NPs with a diameter of 500 nm and controllable morphology, crystallinity, and absorption behavior, which led to improved photovoltaic performance compared with that of solar cells containing NPs produced using other ILs. Our findings revealed a pathway to obtain uniformly distributed CH3NH3PbI3 NP thin films for use in perovskite solar cells. The developed method is well suited for large-scale production of perovskite thin films on flexible substrates. 相似文献
19.
Novel TiO2–Ag core–shell micro‐/nanowires (TiO2 shell coating on Ag core) have been successfully prepared via a solvent–thermal method. Energy dispersive spectroscopy and X‐ray diffraction analyses revealed that the micro‐/nanowires were composed of Ag, Ti and O elements, and Ag was face‐centered cubic whereas TiO2 was mainly amorphous. Interestingly, scanning electron microscopy (SEM) and transmission electron microscopy results showed that most of the TiO2 bristles were perpendicular to and uniformly studded on the surface of the Ag cores. Subsequently, TiO2–Ag/poly(arylene ether nitrile) (PEN) composite films were prepared via a solution‐casting method in order to investigate the effect of TiO2–Ag on the PEN matrix. SEM images showed that there was good interfacial adhesion between fillers and PEN matrix owing to the special bristle‐like structure. Thermal analysis results showed that the TiO2–Ag/PEN composite films possessed excellent thermal properties endowed by the PEN matrix. The dielectric constant of the composite films increased to 9.3 at 100 Hz when the TiO2–Ag loading reached 40 wt%. Rheology measurements revealed that the network formed by TiO2–Ag was sensitive to shear stress and nearly time independent. © 2013 Society of Chemical Industry 相似文献
20.
Formation of intermetallic compounds (IMCs) in solder joints is closely associated with the mechanical reliability of the system. Though internal voids formed in Ni/Sn solder joints are known to be related to the formation of Ni3Sn4 IMC, a detailed study on the mechanical reliability has not yet been reported. In this study, the mechanical reliability of Ni/Sn joints was investigated using two different soldering systems: Ni/Ag-Ag/Sn/Ni bilayers and Ni/Sn/Ag-Ag/Sn/Ni sandwich structures. The failure mode was found to be closely related to the formation and growth of an Ag3Sn phase. Filling of the voids with Ag3Sn IMC resulted in maximum shear strength, with a failure locus through Ni3Sn4 and Ag3Sn. However, formation of a large amount of Ag3Sn decreased the shear strength once again. 相似文献