Photocatalytic H2 generation using semiconductor photocatalysts is considered as a cost-effective and eco-friendly technology for solar to energy conversion; however, the present photocatalysts have been recognized to depict low efficiency. Currently, porous coordination polymers known as metal-organic frameworks (MOFs) constituting flexible and modifiable porous structure and having excess active sites are considered to be appropriate for photocatalytic H2 production. This review highlights current progress in structural development of MOF materials along with modification strategies for enhanced photoactivity. Initially, the review discusses the photocatalytic H2 production mechanism with the concepts of thermodynamics and mass transfer with particular focus on MOFs. Elaboration of the structural categories of MOFs into Type I, Type II, Type III and classification of MOFs for H2 generation into transition metal based, post-transition metal based, noble-metal based and hetero-metal based has been systematically discussed. The review also critically deliberate various modification approaches of band engineering, improvement of charge separation, efficient irradiation utilization and overall efficiency of MOFs including metal modification, heterojunction formation, Z-scheme formation, by introducing electron mediator, and dye based composites. Also, the MOF synthesized derivatives for photocatalytic H2 generation are elaborated. Finally, future perspectives of MOFs for H2 generation and approaches for efficiency improvement have been suggested. 相似文献
Telecommunication Systems - This paper proposes two algorithms for hybrid (Analog–Digital) beamforming in a single-user millimeter-wave (mm-wave) multi-input multi-output (MIMO) systems under... 相似文献
Safety and reliability are absolutely important for modern sophisticated systems and technologies. Therefore, malfunction monitoring capabilities are instilled in the system for detection of the incipient faults and anticipation of their impact on the future behavior of the system using fault diagnosis techniques. In particular, state-of-the-art applications rely on the quick and efficient treatment of malfunctions within the equipment/system, resulting in increased production and reduced downtimes. This paper presents developments within Fault Detection and Diagnosis (FDD) methods and reviews of research work in this area. The review presents both traditional model-based and relatively new signal processing-based FDD approaches, with a special consideration paid to artificial intelligence-based FDD methods. Typical steps involved in the design and development of automatic FDD system, including system knowledge representation, data-acquisition and signal processing, fault classification, and maintenance related decision actions, are systematically presented to outline the present status of FDD. Future research trends, challenges and prospective solutions are also highlighted.
The correlations between structural and optical properties of magnetite (Fe3O4) nanoparticles were analyzed by using X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. The magnetite was synthesised from the iron sand using NaOH, HCl, and NaCl as a solvent. From the quantitative analysis of XRD spectra, the crystallite size (D), strain (), stress (), energy deformation (u), porosity, and specific surface area were determined. The Kramers Kronig (K–K) relations was applied to the FTIR spectra to determine the optical properties: refractive index (n), extinction coefficient (k), the complex dielectric function (), and the energy loss function (Im(-1/ε)). The uniform strain was produced from the NaOH and HCl as the solvent. The magnetite had higher porosity with NaCl as a solvent and was directly proportional to the optical phonon vibration. We found a perfect correlation; when the difference between two optical phonon increases, the crystallite size decreases, and the strain will be uniform. 相似文献
Pure silica MCM-41 mesoporous molecular sieve material was synthesised and characterised by in situ synchrotron XRD, TEM,
TGA/DTA and DRIFTS techniques. In situ energy dispersive XRD (EDXRD) confirmed the exact nature of the pore diameter of MCM-41
and the change in crystal structure on calcination. The IR band at 1057 cm-1 of as-synthesised MCM-41 was shifted by 14 cm-1 on heating to 673 K due to increased condensation of silanol groups to form Si-O-Si bridges. Calcined MCM-41 materials were
used to support Pd, and the catalytic activities for 1-hexene and benzene selective hydrogenation were investigated. The Pd/MCM-41
catalyst showed high activity in hydrogenation of 1-hexene at an inlet reaction temperature of 298 K, but did not show any
activity in hydrogenation for benzene. TEM results for the reduced Pd/MCM-41 catalysts revealed that the average Pd particle
size was around 2-2.5 nm and these particles were located in the pores of MCM-41 and showed good distribution. TPR measurements
showed that about 70% of palladium oxide (PdO) loading in the calcined catalysts was reduced at sub-ambient temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Automatic onset detection and picking algorithm has been proposed by applying the spectro-ratio on time–frequency sub-band. The proposed algorithm does not need any parameter settings as it will work on data generated by either short or very broad band seismometers. Our algorithm is applied on local events from Cairo region recorded by three stations of the Egyptian National Seismic Network (ENSN). Maximum standard deviation is observed to be 0.113 s of the corresponding manual picks made by analysts. 相似文献
This paper introduces a software tool based on illustrative applications for the development, analysis and application of multiobjective evolutionary algorithms. The multiobjective evolutionary algorithms tool (MOEAT) written in C# using a variety of multiobjective evolutionary algorithms (MOEAs) offers a powerful environment for various kinds of optimization tasks. It has many useful features such as visualizing of the progress and the results of optimization in a dynamic or static mode, and decision variable settings. The performance measurements of well-known multiobjective evolutionary algorithms in MOEAT are done using benchmark problems. In addition, two case studies from engineering domain are presented. 相似文献
In this paper, a novel inverse random under sampling (IRUS) method is proposed for the class imbalance problem. The main idea is to severely under sample the majority class thus creating a large number of distinct training sets. For each training set we then find a decision boundary which separates the minority class from the majority class. By combining the multiple designs through fusion, we construct a composite boundary between the majority class and the minority class. The proposed methodology is applied on 22 UCI data sets and experimental results indicate a significant increase in performance when compared with many existing class-imbalance learning methods. We also present promising results for multi-label classification, a challenging research problem in many modern applications such as music, text and image categorization. 相似文献
Multi-walled carbon nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first efforts to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbon nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, elongation at break and hardness were studied. Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR studied by Transmission Electron Microscopy (TEM) in order to understand the morphology of the resulting system 相似文献
The study of near-nanocrystalline cermet composite coating was performed by depositing near-nanocrystalline WC-17Co powder
using the high velocity oxy-fuel spraying technique. The WC-17Co powder consists of a core with an engineered near-nano-scale
WC dispersion with a mean grain size 427 nm. The powder particle contains 6 wt pct of the ductile phase Co matrix mixed into
the core to ensure that the reinforcing ceramic phase WC material is discontinuous to limit debridement during wear, while
the remainder of the binding phase (11 wt pct) is applied as a coating on the powder particle to improve the ductility. The
tribological properties of the coating, in terms of corrosion resistance, microhardness, and sliding abrasive wear, were studied
and compared with those of an industrially standard microcrystalline WC-10Co-4Cr coating with a WC mean grain size 3 μm. Results indicated that the WC-17Co coating had superior wear and corrosion resistance compared to the WC-10Co-4Cr coating.
The engineered WC-17Co powder with a duplex Co layer had prevented significant decarburization of the WC dispersion in the
coating, thereby reducing the intersplat microporosity necessary for initiating microgalvanic cells. The improved wear resistance
was attributed to the higher hardness value of the near-nanocrystalline WC-17Co coating. 相似文献