Condensation, involving nucleation, growth, and ripening from a metastable state, is an important but complex phase transition process. The effect of physical parameters, including temperature, on condensation dynamics, the competition between homogeneous and heterogeneous (seeding) nucleation, and the separation of polymorphs are among several issues of practical interest. We present a model based on population dynamics that describes the time evolution of the particle size distributions for condensation of the fluid phase and consequent decline in supersaturation. The crucial effect of interfacial curvature on energy, and hence on particle size (Gibbs-Thomson effect), causes larger particles to be less soluble, so that smaller particles dissolve and eventually vanish (denucleate). Numerical solutions of the governing equations show the transition from nucleation and growth to ripening occurs over a relatively long time period. The influence of temperature on these phenomena is primarily through its effect on interfacial energy, growth rate coefficients, and equilibrium solubility. Temperature programming is proposed as a potential method to control the size distribution during the phase transition. The model suggests conditions to suppress homogeneous nucleation by seeding. We also explore how a temperature program for cooling crystallization based on different properties of the crystal forms can separate two crystal polymorphs. 相似文献
The UHF signals are generated due to PD formed by particle movement in liquid nitrogen under AC voltages. The levitation voltage of a particle in liquid nitrogen measured through UHF technique and by conventional PD measurement technique is the same, confirming the sensitivity of UHF technique for identification of PD activity. The frequency content of UHF signal generated due to particle movement in liquid nitrogen, under AC voltages, lies in the range 0.5–1.5 GHz. The characteristics of UHF signal generated due to particle movement between the barrier and high voltage/ground electrode is much similar to the signal generated by particle movement in clean electrode gap. Pseudo resonance phenomena can occur in liquid nitrogen due to particle movement. It is also observed that the partial discharge magnitude, in general, be high when the particle moves between the barrier and high voltage electrode when compared to the barrier and the ground electrode. Percentage of clay in epoxy nanocomposites has not altered the levitation voltage of the particle in the electrode gap. Zero span analysis clearly indicates that pseudo resonance occurs when particle moves (in a short gap) between the barrier and high voltage/ground electrode. 相似文献
Dimension and morphology of photocatalysts has extensive interest in order to use the effective concurrence of photon. Despite TiO2 and ZnO, WO3 has also been considered as a promising candidate in terms of remediation and purification that owes to its visible light absorption and non-toxic environmental friendliness. In this study, we report the preparation of nanostructured WO3 with different morphologies for the photocatalytic degradation of organic pollutants without the presence of any sacrificial agents. The study envisages the effect of the aspect ratio of WO3 particles on the photochemical process and their inherent reactive species mechanism. Mechanistic reasoning revealed that, apart from the hole and hydroxyl radicals as the participating species in both structures, a significant contribution from superoxide radicals takes place in the presence of nanorods and promotes the photochemical reaction. High aspect ratio facilitates the absorption coefficient and resultant efficiency. Both the catalysts retain its reactivity after regeneration and confirms the consistent catalytic reusability. Reactivity enhancement of any photocatalyst is possible through tuning the inherent structure of the material. 相似文献
Text document clustering is used to separate a collection of documents into several clusters by allowing the documents in a cluster to be substantially similar. The documents in one cluster are distinct from documents in other clusters. The high-dimensional sparse document term matrix reduces the clustering process efficiency. This study proposes a new way of clustering documents using domain ontology and WordNet ontology. The main objective of this work is to increase cluster output quality. This work aims to investigate and examine the method of selecting feature dimensions to minimize the features of the document name matrix. The sports documents are clustered using conventional K-Means with the dimension reduction features selection process and density-based clustering. A novel approach named ontology-based document clustering is proposed for grouping the text documents. Three critical steps were used in order to develop this technique. The initial step for an ontology-based clustering approach starts with data pre-processing, and the characteristics of the DR method are reduced with the Info-Gain collection. The documents are clustered using two clustering methods: K-Means and Density-Based clustering with DR Feature Selection Process. These methods validate the findings of ontology-based clustering, and this study compared them using the measurement metrics. The second step of this study examines the sports field ontology development and describes the principles and relationship of the terms using sports-related documents. The semantic web rational process is used to test the ontology for validation purposes. An algorithm for the synonym retrieval of the sports domain ontology terms has been proposed and implemented. The retrieved terms from the documents and sport ontology concepts are mapped to the retrieved synonym set words from the WorldNet ontology. The suggested technique is based on synonyms of mapped concepts. The proposed ontology approach employs the reduced feature set in order to clustering the text documents. The results are compared with two traditional approaches on two datasets. The proposed ontology-based clustering approach is found to be effective in clustering the documents with high precision, recall, and accuracy. In addition, this study also compared the different RDF serialization formats for sports ontology.
The solubility of tri-iso-amyl phosphate (TiAP) in supercritical carbon dioxide (SCCO2) was determined at 313–333 K with pressure ranging from 10 to 25 MPa. The solubility data of TiAP in SCCO2 medium were correlated using four semi-empirical models. Selective extraction of uranium from simulated dissolver solution was demonstrated using SCCO2 modified with TiAP. The extraction efficiency of uranium was found to be 95 ± 5%. The influence of temperature, pressure and acidity on the extraction of uranium was studied. An attempt was made to explain the plausible extraction mechanism. 相似文献