385 research outputs found
Ionic conductivity of sodium silicate glasses grown within confined volume of mesoporous silica template
No full textNanodimensional sodium silicate glasses of composition 30Na2O.70SiO2 has been prepared within the pores of 5.5 nm of mesoporous silica as a template using the surfactant P123. The nanocomposite was characterized by X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy. Electrical conductivity of the sample was studied by ac impedance spectroscopy. The activation energy for ionic conduction was found to be 0.13 eV with dc conductivity at room temperature of 10-6 S-cm-1. This is attributed to the creation of oxygen ion vacancies at the interface of mesoporous silica and nanoglass arising out of the presence of Si2+ species in the system. These nanocomposites are expected to be useful for applications in sodiumion battery for storage of renewable energy
Influence of thermal buoyancy on boundary layer separation over a triangular surface
No full textWe endeavour here to elucidate the role of the superimposed thermal buoyancy on the boundary layer separation over a two-dimensional triangular surface. Particular emphasis is given to analyze the response of different orientations of the triangular object with respect to the incoming flow under the action of aiding/opposing thermal buoyancy. The object is placed in a vertical unconfined domain with two different orientations, one when the apex of the object is facing the flow (C1) and the other when one of the bases of the object is exposed to the incoming fluid (C2). A similar study by Chatterjee and Mondal (2014) considering circular and square shaped objects reveals that the steady, laminar and separated flow over the objects at low Reynolds numbers can be degenerated to an attached flow under the action of aiding thermal buoyancy. However, unlike circular/square bodies, the triangular body shows significant deviations in the separation characteristics. The present effort aims at numerically obtaining the critical heating parameters for which the separated boundary layer on the triangular object can be suppressed and analyzing the influence of the object orientation on the thermally induced suppression phenomena. Furthermore, the opposing buoyancy is known to trigger the vortex shedding process at low Reynolds numbers which is already established for circular/square objects. This triggering of vortex shedding over different orientations of a triangular object under the action of opposing buoyancy is numerically demonstrated. The Reynolds number is kept in the range 5 ⩽ Re ⩽ 30 keeping the Prandtl number fixed at Pr = 50 with varying Richardson number. The critical Richardson numbers for the onset of flow suppression as well as the complete suppression of flow separation and the critical Richardson number for the onset of vortex shedding are obtained for the two different orientations of the object. Important inferences are drawn on the fluid dynamic and thermal transport characteristics focussing the separation phenomena. It is observed that the configuration C1 needs more heating than C2 for flow suppression. Also, C1 needs more cooling than C2 for the initiation of the vortex shedding. Such quantification in regard to the critical heating parameters for flow suppression and triggering of vortex shedding over a triangular object is reported for the first time
Calibrated meudon data
No full textThis repository contains calibrated filament data which is made from Meudon hand drawn archive, which consist hand drawn Carrington maps in image format available at BASS2000: Solar Survey Archive at Observatoire de Paris (available at http://bass2000.obspm.fr/lastsynmap.php). The Meudon archive consisting gray scaled images for Carrington rotation 876-1823 and coloured images for Carrington rotation 1824-2008. After downloading the data from the Meudon archive, we have used a automated method (described in our paper which is accepted for publication in APJ and now available at https://arxiv.org/pdf/2106.04320.pdf) to calibrate these data and then we have used these calibrated data for further studeis of solar filaments. These calibrated data from our automated detection is now we are making public and can be used for any further studies only after citing our paper Mazumder et al 2021. Data of gray scaled images for Carrington rotation 876-1823 is kept at gray_scale_image.zip folder and data for coloured images for Carrington rotation 1824-2008 is kept in colour_mages.zip folder.
@misc{mazumder2021solar, title={Solar Cycle Evolution of Filaments over a Century: Investigations with the Meudon and McIntosh Hand-drawn Archives}, author={Rakesh Mazumder and Subhamoy Chatterjee and Dibyendu Nandy and Dipankar Banerjee}, year={2021}, eprint={2106.04320}, archivePrefix={arXiv}, primaryClass={astro-ph.SR} }
This repository contains calibrated filament data which is made from Meudon hand drawn archive, which consist hand drawn Carrington maps in image format available at BASS2000: Solar Survey Archive at Observatoire de Paris (available at http://bass2000.obspm.fr/lastsynmap.php). The Meudon archive consisting gray scaled images for Carrington rotation 876-1823 and coloured images for Carrington rotation 1824-2008. After downloading the data from the Meudon archive, we have used a automated method (described in our paper in https://arxiv.org/pdf/2106.04320.pdf) to calibrate these data and then we have used these calibrated data for further studeis of solar filaments. These calibrated data from our autamated detection is now we are making public and can be used for any further studies only after citing our paper Mazumder et al 2021.
@misc{mazumder2021solar, title={Solar Cycle Evolution of Filaments over a Century: Investigations with the Meudon and McIntosh Hand-drawn Archives}, author={Rakesh Mazumder and Subhamoy Chatterjee and Dibyendu Nandy and Dipankar Banerjee}, year={2021}, eprint={2106.04320}, archivePrefix={arXiv}, primaryClass={astro-ph.SR} }
Our work is accepted for publication in APJ and now available at https://arxiv.org/pdf/2106.04320.pdf and after it get published the refernce of ApJ will be updated here
A Comparison of Numerical Strategies for Modeling the Transport Phenomena in High-Energy Laser Surface Alloying Process
No full textA comparative assessment is done on the effectiveness of some developed and reported macroscopic and mesoscopic models deployed for addressing the three-dimensional thermo-fluidic transport during high-power laser surface alloying process. The macroscopic models include the most celebrated k–ε turbulence model and the large eddy simulation (LES) model, whereas a kinetic theory-based lattice Boltzmann (LB) approach is invoked under the mesoscopic paradigm. The time-dependent Navier–Stokes equations are transformed into the k–ε turbulence model by performing the Reynolds averaging technique, whereas a spatial filtering operation is used to produce the LES model. The models are suitably modified to address the turbulent melt-pool convection by using a modified eddy viscosity expression including a damping factor in the form of square root of the liquid fraction. The LB scheme utilizes three separate distribution functions to monitor the underlying hydrodynamic, thermal and compositional fields. Accordingly, the kinematic viscosity, thermal and mass diffusivities are adjusted independently. A single domain fixed-grid enthalpy-porosity approach is utilized to model the phase change phenomena in conjunction with an appropriate enthalpy updating closure scheme. The performance of these models is recorded by capturing the characteristic nature of the thermo-fluidic transport during the laser material processing. The maximum values of the pertinent parameters in the computational domain obtained from several modeling efforts are compared to assess their capabilities. The comparison shows that the prediction from the k–ε turbulence model is higher than the LES and LB models. In addition, the results from all three models are compared with the available experimental results in the form of dimensionless composition of the alloyed layer along the dimensionless depth of the pool. The comparison reveals that the LB and the LES approaches are better than the k–ε turbulence approach in reproducing the experimental results
Lattice kinetic simulation of buoyancy induced MHD flows
No full textA lattice kinetic model is proposed in this article for simulating buoyancy induced classical magnetohydrodynamic (MHD) flow in the low Mach number incompressible limit. The model is derived by coupling the passive scalar approach of He et al. [X. He, S. Chen, G.D. Doolen, A novel thermal model for the lattice Boltzmann method in incompressible limit, J. Comput. Phys. 146 (1998) 282–300] for the flow and thermal fields and Dellar formalism [P.J. Dellar, Lattice kinetic schemes for magnetohydrodynamics, J. Comput. Phys. 179 (2002) 95–126] for the magnetic field. Accordingly, the underlying hydrodynamics is monitored by a conventional single relaxation time lattice Boltzmann (LB) model through a density distribution function (DF), which obeys a scalar kinetic equation (KE) associated with external force fields (Lorentz and buoyancy forces). The magnetic field is represented by a vector DF, which obeys a corresponding vector KE and the thermal field is obtained from a separate temperature DF through another scalar KE incorporating the Joule heating effect. The three distribution functions are coupled through the macroscopic density, momentum, magnetic and thermal fields evaluated at lattice points. This allows a reduced lattice to be used for the magnetic distribution function, with a corresponding saving in the storage. Furthermore, the fluid viscosity, magnetic resistivity and thermal diffusivity may be adjusted independently that renders the model to be applicable for a wide variety of non-isothermal MHD problems. The novelty of the work is the computation of the thermal field in conjunction with the hydro-magnetic fields in the LB framework for the buoyancy driven non-isothermal MHD flows. A 9-bit 2D (d2q9) lattice scheme is used for the numerical computation of the hydrodynamic and thermal fields, whereas the magnetic field is simulated by a reduced 5-bit 2D (d2q5) lattice. Simulation of the magnetoconvective buoyancy induced flow (a) past a vertical flat plate, (b) between two differentially heated vertical walls provide excellent agreement with analytical results. Finally, the model is utilized to solve a classical problem of buoyancy driven MHD flow in a square cavity
Computational modelling of transport phenomena in high energy materials processing application: large eddy simulation and parallelisation
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The Hindu Religious Tradition: A Philosophical Approach. By Pratima Bowes. London and Boston: Routledge & Kegan Paul, 1978. xii, 322 pp. Notes, Index. $18.95.
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