Lattice Boltzmann simulation of magnetic field effects on nanofluid

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, the magnetic field effects on natural convection heat transfer in an enclosure filled with nanofluid are numerically investigated by using lattice Boltzmann method. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. A uniform external magnetic field with different angles was applied. A series of simulation cases were carried out for different governing parameters including Hartmann number, Rayleigh number, the nanoparticle volume fractions and magnetic field angles. The results show that the increasing Rayleigh number and nanoparticle volume fraction improve the heat transfer in the enclosure. However, the heat transfer has been suppressed when Hartmann number increases. The results also indicate there are critical values for the Raleigh number and also the magnetic field orientation, at which the impacts of the solid volume fraction and magnetic field effects are the most pronounced

Numerical simulation of microflow over superhydrophobic surfaces by lattice Boltmann method

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The superhydrophobicity of a microchannel is determined by not only the wettability of channel wall but also the surface topography. Recent experiments have found that superhrydrophobic surfaces can be achieved by pattering roughness on hydrophobic surfaces. In this paper, the dynamics of two-phase flow in microchannel with different wettability and topography is studied numerically by the lattice Boltzmann method (LBM). The mechanism of drag reduction resulted from the superhydrophobicity is investigated. In particular, the effect of different rough surfaces on superhydrophobicity is analyzed. It is found that flow behaviours are strongly affected by the wall wettability and topography. The results show that the LBM has a good application prospect in the study of drag reduction in microchannels.The UK Royal Society-NSFC (China) International Joint Project (2009-2011), China NSFC under grant (50920105504), and China Scholarship Council (CSC)

Effects of relative orientation of the molecules on electron transport in molecular devices

Effects of relative orientation of the molecules on electron transport in molecular devices are studied by non-equilibrium Green's function method based on density functional theory. In particular, two molecular devices, with the planer Au$_{7}$ and Ag$_{3}$ clusters sandwiched between the Al(100) electrodes are studied. In each device, two typical configurations with the clusters parallel and vertical to the electrodes are considered. It is found that the relative orientation affects the transport properties of these two devices completely differently. In the Al(100)-Au$_7$-Al(100) device, the conductance and the current of the parallel configuration are much larger than those in the vertical configuration, while in the Al(100)-Ag$_{3}$-Al(100) device, an opposite conclusion is obtained

Suppressing longitudinal double-layer oscillations by using elliptically polarized laser pulses in the hole-boring radiation pressure acceleration regime

It is shown that well collimated mono-energetic ion beams with a large particle number can be generated in the hole-boring radiation pressure acceleration regime by using an elliptically polarized laser pulse with appropriate theoretically determined laser polarization ratio. Due to the $\bm{J}\times\bm{B}$ effect, the double-layer charge separation region is imbued with hot electrons that prevent ion pileup, thus suppressing the double-layer oscillations. The proposed mechanism is well confirmed by Particle-in-Cell simulations, and after suppressing the longitudinal double-layer oscillations, the ion beams driven by the elliptically polarized lasers own much better energy spectrum than those by circularly polarized lasers.Comment: 6 pages, 5 figures, Phys. Plasmas (2013) accepte

Exact solution of gyration radius of individual's trajectory for a simplified human mobility model

Gyration radius of individual's trajectory plays a key role in quantifying human mobility patterns. Of particular interests, empirical analyses suggest that the growth of gyration radius is slow versus time except the very early stage and may eventually arrive to a steady value. However, up to now, the underlying mechanism leading to such a possibly steady value has not been well understood. In this Letter, we propose a simplified human mobility model to simulate individual's daily travel with three sequential activities: commuting to workplace, going to do leisure activities and returning home. With the assumption that individual has constant travel speed and inferior limit of time at home and work, we prove that the daily moving area of an individual is an ellipse, and finally get an exact solution of the gyration radius. The analytical solution well captures the empirical observation reported in [M. C. Gonz`alez et al., Nature, 453 (2008) 779]. We also find that, in spite of the heterogeneous displacement distribution in the population level, individuals in our model have characteristic displacements, indicating a completely different mechanism to the one proposed by Song et al. [Nat. Phys. 6 (2010) 818].Comment: 4 pages, 4 figure

The extraction, identification and quantification of hypoglycemic active ingredients from stinging nettle (Urtica angustifolia)

Urtica angustifolia is a traditional medicinal material which has hypoglycemic function. The objectives of this study were to isolate and identify hypoglycemic active ingredients from it. Three groups of mice were gavaged with the decoction of Urtica root, stem and leaf for 14 days at a dose of 20 mg/(kg·d). Area under the curve (AUC) values were 24.62±5.24, 24.33±4.66 and 25.51±4.25, respectively. The AUC in leaf decoction group was significantly lower than the other two groups (P < 0.05), which indicated the leaf extracts did have significant hypoglycemic action. Four kinds of extractions were obtained from leaves and fed to mice. AUC values were 33.44±3.58, 34.24±3.64, 30.44±2.57 and 9.93±1.98, respectively. AUC in group U3 (P < 0.05) and U4 (P < 0.01) were significantly lower than in the group of U1 and U2, which indicated that extraction U3 and U4 obviously decreased the blood sugar. Also, U3 was flavonoid and U4 was daucosterol, which was identified by thin-layer chromatography test, IR and ESI-MS spectral analysis.Key words: Urtica angustifolia, active component, glucose tolerance test, hypoglycemic

Absolute orientation based on distance kernel functions

© 2016 by the authors. The classical absolute orientation method is capable of transforming tie points (TPs) from a local coordinate system to a global (geodetic) coordinate system. The method is based only on a unique set of similarity transformation parameters estimated by minimizing the total difference between all ground control points (GCPs) and the fitted points. Nevertheless, it often yields a transformation with poor accuracy, especially in large-scale study cases. To address this problem, this study proposes a novel absolute orientation method based on distance kernel functions, in which various sets of similarity transformation parameters instead of only one set are calculated. When estimating the similarity transformation parameters for TPs using the iterative solution of a non-linear least squares problem, we assigned larger weighting matrices for the GCPs for which the distances from the point are short. The weighting matrices can be evaluated using the distance kernel function as a function of the distances between the GCPs and the TPs. Furthermore, we used the exponential function and the Gaussian function to describe distance kernel functions in this study. To validate and verify the proposed method, six synthetic and two real datasets were tested. The accuracy was significantly improved by the proposed method when compared to the classical method, although a higher computational complexity is experienced

Longevity of the Permian Emeishan mantle plume (SW China): 1 Ma, 8 Ma or 18 Ma?

After the formation of the ∼ 260 Ma Emeishan large igneous province, there were two volumetrically minor magmatic pulses at ∼ 252 Ma and ∼ 242 Ma, respectively. Alkaline mafic dykes intruding both 260 Ma and 252 Ma felsic plutons in the Panxi region, southwestern China, have compositions similar to the Emeishan flood basalts. One dyke is dated using the SHRIMP zircon U-Pb technique at 242 ± 2 Ma, ∼ 18 Ma younger than the start of Emeishan magmatism. The dykes have enriched light rare earth element patterns (La/YbN = 4.4-18.8) and trace element patterns similar to the Emeishan flood basalts and average ocean-island basalts. Some trace element ratios of the dykes (Zr/Nb = 3.8-8.2, La/Nb = 0.4-1.7, Ba/La = 7.5-25.6) are somewhat similar to EM1 source material, however, there are differences. Their εNd values (εNd = +2.6 and +2.7) and ISr( ISr = 0.704542 and 0.704554) ratios are indicative of a mantle source. Thus Emeishan magmatism may have lasted for almost 20 Ma after the initial eruption. However, geological evidence precludes the possibility that the post-260 Ma magmatic events were directly related to Emeishan magmatism, which began at and ended shortly after 260 Ma. The 252 Ma plutons and 242 Ma dykes represent volumetrically minor melting of the fossil Emeishan plume-head beneath the Yangtze crust. The 252 Ma magmatic event was likely caused by post-flood basalt extension of the Yangtze crust, whereas the 242 Ma event was caused by decompressional melting associated with the collision between the South China and North China blocks during the Middle Triassic. © 2008 Cambridge University Press.published_or_final_versio