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The gas leakage dynamic flow in nanoporous silica aerogel under different pressure
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.The dynamic gas flow in silica aerogel caused by ambient pressure change is an important factor to influence the thermal conductivity performance. Due to the ultrafine pore size, the flow in the silica aerogel is non-continuum. The direct simulation Monte Carlo method is selected to simulate the transient behavior of gas dynamic flow in nanoporous silica aerogel caused by pressure difference. The influences of pressure ratio and porosity on the unsteady dynamic response and the magnitude of the macroscopic parameters are investigated. The results show that the response processes under different pressure ratio and porosity conditions are similar. The effect of the pressure ratio and porosity are mainly reflected on the magnitude of the macro parameters and response time
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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
Search for lepton flavor violating decays of a heavy neutral particle in p-pbar collisions at root(s)=1.8 TeV
We report on a search for a high mass, narrow width particle that decays
directly to e+mu, e+tau, or mu+tau. We use approximately 110 pb^-1 of data
collected with the Collider Detector at Fermilab from 1992 to 1995. No evidence
of lepton flavor violating decays is found. Limits are set on the production
and decay of sneutrinos with R-parity violating interactions.Comment: Figure 2 fixed. Reference 4 fixed. Minor changes to tex
Casimir Dispersion Forces and Orientational Pairwise Additivity
A path integral formulation is used to study the fluctuation-induced
interactions between manifolds of arbitrary shape at large separations. It is
shown that the form of the interactions crucially depends on the choice of the
boundary condition. In particular, whether or not the Casimir interaction is
pairwise additive is shown to depend on whether the ``metallic'' boundary
condition corresponds to a ``grounded'' or an ``isolated'' manifold.Comment: 6 pages, RevTe
Phase shift experiments identifying Kramers doublets in a chaotic superconducting microwave billiard of threefold symmetry
The spectral properties of a two-dimensional microwave billiard showing
threefold symmetry have been studied with a new experimental technique. This
method is based on the behavior of the eigenmodes under variation of a phase
shift between two input channels, which strongly depends on the symmetries of
the eigenfunctions. Thereby a complete set of 108 Kramers doublets has been
identified by a simple and purely experimental method. This set clearly shows
Gaussian unitary ensemble statistics, although the system is time-reversal
invariant.Comment: RevTex 4, 5 figure
Ubiquitous e-learning System for dynamic mini-courseware assembling and delivering to mobile terminals
From 2000, mobile Learning (m-Learning) and ubiquitous Learning (u-Learning) has been the hottest research topic in e-learning, and now, integrating ubiquitous learning into mainstream of education and train has been the direction in the area, which demand new generational e-learning system. The paper introduces our research efforts in this direction. Based on the key concepts, such as ubiquitous learning object, mini-courseware, a new generational ubiquitous e-learning system is designed, which can be used for new requirements in m-Learning and u-Learning environments. In the system, learning resource related to a course is encapsulated into different ubiquitous learning objects, and mini-courseware can be assembled dynamically with learning resource extracted from these ubiquitous learning objects, accordingly, a mini-courseware player is designed for the situation. Based on these work, a resource based ubiquitous e-Learning system is designed considering pedagogical requirements under m-Learning and u-Learning environment
Effect of Anisotropy on the Localization in a Bifractal System
Bifractal is a highly anisotropic structure where planar fractals are stacked
to form a 3-dimensional lattice. The localization lengths along fractal
structure for the Anderson model defined on a bifractal are calculated. The
critical disorder and the critical exponent of the localization lengths are
obtained from the finite size scaling behavior. The numerical results are in a
good agreement with previous results which have been obtained from the
localization lengths along the perpendicular direction. This suggests that the
anisotropy of the embedding lattice structure is irrelevant to the critical
properties of the localization.Comment: 3 pages, source TeX file and 3 epsi figures. submitted to PR
Effect of Greening Trees on Thermal Comfort of the Pedestrian Streets in Hot Summer and Cold Winter Regions in China
The thermal environment problems of pedestrian streets space are becoming increasingly important with the growing rate of urbanization, especially in regions with hot summers and cold winters. Taking Cinnamomum camphora as an example, several urban design scenarios with dynamic setting parameters of streets orientation (N-S, E-W), aspect ratio (0.5, 1,1.5, 2) are simulated by ENVI-met to analyze the impact of the green coverage on the thermal comfort of the street canyons in Shanghai. Results showed that: (1) green coverage has an impact on the thermal comfort of the street both in summer and winter and the significance of this effect is affected by the orientation and aspect ratio of the streets. (2) In summer, with the increase in aspect ratio, N-S orientation streets need more and more green coverage to bring a significant impact on thermal comfort, while E-W orientation streets only need 24 % green coverage. (3) In winter, with the increase in aspect ratio, N-S orientation streets also need more green coverage to significantly reduce thermal comfort. For E-W orientation, only when the aspect ratio is 1/2, the green coverage can effectively reduce the thermal comfort of the street. (4) The planting layout had no significant effect on the thermal comfort effect of trees. Based on the above conclusions, the greening strategy was proposed for pedestrian streets in the hot summer and cold winter region in China
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