Three-dimensional multi-level heat transfer model of silica aerogel

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this paper, a 3-D multi-level heat transfer model is developed in consideration of the tortuous path of heat conduction in solid skeleton and the fractal characteristic of silica aerogel. The heat conduction is analyzed for both the secondary particle model and the cluster model. The expression of effective thermal conductivity of a multi-level model is derived. The theoretical predictions from the proposed multi-level model are compared with three sets of experimental data with different densities and porosities. The results from the proposed model show good agreement with the experimental data

Risk assessment using transfer learning for grassland fires

© 2019 A new direction of risk assessment research in grassland fire management is data-driven prediction, in which data are collected from particular regions. Since some regions have rich datasets that can easily generate knowledge for risk prediction, and some have no data available, this study addresses how we can leverage the knowledge learned from one grassland risk assessment to assist with a current assessment task. In this paper, we first introduce the transfer learning methodology to map and update risk maps in grassland fire management, and we propose a new grassland fire risk analysis method. In this study, two major grassland areas (Xilingol and Hulunbuir) in northern China are selected as the study areas, and five representative indicators (features) are extracted from grassland fuel, fire climate, accessibility, human and social economy. Taking Xilingol as the source domain (where sufficient labelled data are available) and Hulunbuir as the target domain (which contains insufficient data but requires risk assessment/prediction), we then establish the mapping relationship between grassland fire indicators and the degrees of grassland fire risk by using a transfer learning method. Finally, the fire risk in the Hulunbuir grassland is assessed using the transfer learning method. Experiments show that the prediction accuracy reached 87.5% by using the transfer learning method, representing a significant increase over existing methods

Legged robot gait locus generation based on genetic algorithms

Achieving an effective gait locus for legged robots is a challenging task. It is often done manually in a laborious way due to the lack of research in automatic gait locus planning. Bearing this problem in mind, this article presents a gait locus planning method using inverse kinematics while incorporating genetic algorithms. Using quadruped robots as a platform for evaluation, this method is shown to generate a good gait locus for legged robots. Copyright © held by author

Decision Support for Temperate Grasslands: Challenges and Pitfalls

Key points Successful adoption of decision support tools (DS tools) to address grassland management issues requires careful attention in design to ensure ease-of-use, accuracy in prediction and the flexibility to simulate actual practices. DS tools must handle spatial variability and where possible include facilities for automatic sourcing of essential information for initialisation. Advances in the development of DS tools will depend on resolution of scientific issues in grassland biology including investment in dedicated experiments to determine parameter values for model equations. The use of mechanistic models, the integration of remote sensing technology and cooperation between research groups to develop modular simulation frameworks to share models will enhance the value of DS tools in grassland management

Document image retrieval based on density distribution feature and key block feature

Document image retrieval is an important part of many document image processing systems such as paperless office systems, digital libraries and so on. Its task is to help users find out the most similar document images from a document image database. For developing a System of document image retrieval among different resolutions, different formats document images with hybrid characters of multiple languages,. a new retrieval method based on document image density distribution features and key block features is proposed in this paper. Firstly, the density distribution and key block features of a document image are defined and extracted based on documents' print-core. Secondly, the candidate document images are attained based on the density distribution features. Thirdly, to improve reliability of the retrieval results, a confirmation procedure using key block features is applied to those candidates. Experimental results on a large scale document image database, which contains 10385 document images, show that the proposed method is efficient and robust to retrieve different kinds of document images in real time.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000232022600204&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Computer Science, Artificial IntelligenceComputer Science, Information SystemsCPCI-S(ISTP)

Bio-Inspired Aggregation Control of Carbon Nanotubes for Ultra-Strong Composites

High performance nanocomposites require well dispersion and high alignment of the nanometer-sized components, at a high mass or volume fraction as well. However, the road towards such composite structure is severely hindered due to the easy aggregation of these nanometer-sized components. Here we demonstrate a big step to approach the ideal composite structure for carbon nanotube (CNT) where all the CNTs were highly packed, aligned, and unaggregated, with the impregnated polymers acting as interfacial adhesions and mortars to build up the composite structure. The strategy was based on a bio-inspired aggregation control to limit the CNT aggregation to be sub 20--50 nm, a dimension determined by the CNT growth. After being stretched with full structural relaxation in a multi-step way, the CNT/polymer (bismaleimide) composite yielded super-high tensile strengths up to 6.27--6.94 GPa, more than 100% higher than those of carbon fiber/epoxy composites, and toughnesses up to 117--192 MPa. We anticipate that the present study can be generalized for developing multifunctional and smart nanocomposites where all the surfaces of nanometer-sized components can take part in shear transfer of mechanical, thermal, and electrical signals

Study on the distribution regularity of gas volume in multiphase pump

In order to reduce the phase separation, air plug and turbulence vortex in the multiphase pump. The two-fluid model and the standard k-¦ turbulence model are selected, the distribution regularity of gas phase volume within the multiphase pump is researched using the CFD software about air-liquid two-phase under the different working conditions. The results of the study showed that the gas phase gathers at the rim when the gas-liquid two-phase enter into the impeller inlet, and the gas phase is gradually increased at the rim with the increase of the flow rate, the gas is concentrated in the hub at the second half of the impeller, and the most serious aggregation is the small flow rate condition. When the flow is constant, the gas obviously increases in the guide vane hub with the increase of the gas volume fraction. With the increase of the gas volume fraction, the uniformity of the gas phase in the circumferential direction is deteriorated in the inlet and the middle of impeller, and the lower gas volume fraction region is decreased in the impeller. The results of the study reveal the distribution regularity of gas volume within the multiphase pump, provide the reference basis for the design of the multiphase pump under the higher gas volume fraction

Effect of gas volume fraction on vortex motion in hydraulic turbine

In order to analyze the vortex motion in the flow channel of the hydraulic turbine impeller during the gas volume fraction change. Now, the pump with a specific speed of 55.7 is chosen as hydraulic turbine. On the basis of considering the gas compressibility, to take numerical calculation on the model under different flow rates and different gas volume fraction, to analyze the influence of gas volume fraction on vortex motion law in the impeller flow channel. Findings: When the flow rate is small, the relative velocity distribution in the impeller flow channel is uneven, the velocity field is chaotic, and there are obvious vortices, with the increase of the gas volume fraction, the vortices in the impeller flow channel gradually move to the inlet direction of the blade; With the increase of the flow rate, the flow in the channel of the hydraulic turbine impeller is unstable. Both the pressure surface and the suction surface of the blade appear vortices, the vortex region in the impeller flow channel is enlarged, and all of them are concentrated on the back of the blade. The results provide a theoretical basis for the optimal design of hydraulic turbine structures

Effect of gas volume fraction on the vortex motion within the oil-gas multiphase pump

In order to research the regular pattern of the vortex within the oil-gas multiphase pump with the gas volume fraction changes, the standard K-epsilon turbulence model is selected, the gas-liquid two-phase flow field within the multiphase pump is calculated by the CFD software under the different gas volume fraction, the regular pattern of the vortex motion within the multiphase pump is analyzed under the different gas volume fraction. The results show that, from the impeller hub to the rim, the vortex in the guide vane is gradually become smaller, the vortex within the impeller is gradually obvious, and with the increase of the gas volume fraction, the flow separation, the backflow and the vortex phenomenon within the impeller and the guide vane are gradually increased. It is also found that the flow separation has a greater influence on the turbulent dissipation within the whole flow field, that is, the more serious the area of off flow, the greater the energy loss. The results provide an important theoretical basis for the optimal design of the structure of oil-gas multiphase pump