Theoretical and Numerical Investigation of Radiative Extinction of Diffusion Flames

The influence of soot radiation on diffusion flames was investigated using both analytical and numerical techniques. Soot generated in diffusion flames dominate the flame radiation over gaseous combustion products and can significantly lower the temperature of the flame. In low gravity situations there can be significant accumulation of soot and combustion products in the vicinity of the primary reaction zone owing to the absence of any convective buoyant flow. Such situations may result in substantial suppression of chemical activities in a flame, and the possibility of a radiative extinction may also be anticipated. The purpose of this work was to not only investigate the possibility of radiative extinction of a diffusion flame but also to qualitatively and quantitatively analyze the influence of soot radiation on a diffusion flame. In this study, first a hypothetical radiative loss profile of the form of a sech(sup 2) was assumed to influence a pure diffusion flame. It was observed that the reaction zone can, under certain circumstances, move through the radiative loss zone and locate itself on the fuel side of the loss zone contrary to our initial postulate. On increasing the intensity and/or width of the loss zone it was possible to extinguish the flame, and extinction plots were generated. In the presence of a convective flow, however, the movement of the temperature and reaction rate peaks indicated that the flame behavior is more complicated compared to a pure diffusional flame. A comprehensive model of soot formation, oxidation and radiation was used in a more involved analysis. The soot model of Syed, Stewart and Moss was used for soot nucleation and growth and the model of Nagle and Strickland-Constable was used for soot oxidation. The soot radiation was considered in the optically thin limit. An analysis of the flame structure revealed that the radiative loss term is countered both by the reaction term and the diffusion term. The essential balance for the soot volume fraction was found to be between the processes of soot convection and soot growth. Such a balance yielded to analytical treatment and the soot volume fraction could be expressed in the form of an integral. The integral was evaluated using two approximate methods and the results agreed very well with the numerical solutions for all cases examined

Dynamically Reconfigurable Online Self-organising Fuzzy Neural Network with Variable Number of Inputs for Smart Home Application

A self-organising fuzzy-neural network (SOFNN) adapts its structure based on variations of the input data. Conventionally in such self-organising networks, the number of inputs providing the data is fixed. In this paper, we consider the situation where the number of inputs to a network changes dynamically during its online operation. We extend our existing work on a SOFNN such that the SOFNN can self-organise its structure based not only on its input data, but also according to the changes in the number of its inputs. We apply the approach to a smart home application, where there are certain situations when some of the existing events may be removed or new events emerge, and illustrate that our approach enhances cognitive reasoning in a dynamic smart home environment. In this case, the network identifies the removed and/or added events from the received information over time, and reconfigures its structure dynamically. We present results for different combinations of training and testing phases of the dynamic reconfigurable SOFNN using a set of realistic synthesized data. The results show the potential of the proposed method

An Experimental and Theoretical Study of Radiative Extinction of Diffusion Flames

In a recent paper on 'Observations of candle flames under various atmospheres in microgravity' by Ross et al., it was found that for the same atmosphere, the burning rate per unit wick surface area and the flame temperature were considerably reduced in microgravity as compared with normal gravity. Also, the flame (spherical in microgravity) was much thicker and further removed from the wick. It thus appears that the flame becomes 'weaker' in microgravity due to the absence of buoyancy generated flow which serves to transport the oxidizer to the combustion zone and remove the hot combustion products from it. The buoyant flow, which may be characterized by the strain rate, assists the diffusion process to execute these essential functions for the survival of the flame. Thus, the diffusion flame is 'weak' at very low strain rates and as the strain rate increases the flame is initially 'strengthened' and eventually it may be 'blown out'. The computed flammability boundaries of T'ien show that such a reversal in material flammability occurs at strain rates around 5 sec. At very low or zero strain rates, flame radiation is expected to considerably affect this 'weak' diffusion flame because: (1) the concentration of combustion products which participate in gas radiation is high in the flame zone; and (2) low strain rates provide sufficient residence time for substantial amounts of soot to form which is usually responsible for a major portion of the radiative heat loss. We anticipate that flame radiation will eventually extinguish this flame. Thus, the objective of this project is to perform an experimental and theoretical investigation of radiation-induced extinction of diffusion flames under microgravity conditions. This is important for spacecraft fire safety

Influence of a Simple Heat Loss Profile on a Pure Diffusion Flame

The presence of soot on the fuel side of a diffusion flame results in significant radiative heat losses. The influence of a fuel side heat loss zone on a pure diffusion flame established between a fuel and an oxidizer wall is investigated by assuming a hypothetical sech(sup 2) heat loss profile. The intensity and width of the loss zone are parametrically varied. The loss zone is placed at different distances from the Burke-Schumann flame location. The migration of the temperature and reactivity peaks are examined for a variety of situations. For certain cases the reaction zone breaks through the loss zone and relocates itself on the fuel side of the loss zone. In all cases the temperature and reactivity peaks move toward the fuel side with increased heat losses. The flame structure reveals that the primary balance for the energy equation is between the reaction term and the diffusion term. Extinction plots are generated for a variety of situations. The heat transfer from the flame to the walls and the radiative fraction is also investigated, and an analytical correlation formula, derived in a previous study, is shown to produce excellent predictions of our numerical results when an O(l) numerical multiplicative constant is employed

Perception of medical teachers towards undergraduate medical theoretical assessment system in a medical college of West Bengal

Background: With change of disease pattern and complexities of therapy globally, medical education become challenging. Problem based learning and self-directed learning became more relevant and occupied its space in medical education. Assessment is very crucial with the change in curriculum for appropriate feedback and learning in the system. Present study evaluated the perception of medical teachers on this issue of theory examination. Assessment or evaluation plays a pivotal role in effectivity of the system. Assessors always guide any system to achieve its objectives.Methods: This is an observational study, done with a questionnaire. It was done by interviewing the faculties of R.G. Kar Medical College, Kolkata, West Bengal who were examiners at University level.Results: Present study comprised faculty of fifteen undergraduate Departments of R. G. Kar Medical College, Kolkata 29.68% faculty supported semester system. 70.32% faculty participated as the study population. 48.4% agreed and 35.93% strongly agreed on the concept of model answers. A majority of the faculties (31.25%) strongly agreed on the issue that answers should be checked by two or more examiners. Regarding the threshold of pass marks, 48.4% strongly agreed and 43.75% agreed that students need to get 50% marks separately in theory examination to get through the examination.Conclusions: Present study evaluated importance of theory assessment system in medical education. It also necessitates further research to improve the objectivity of theory assessment system in medical curriculum at University level, in India

Comparative evaluation of anti-diabetic activity of fresh juice and ethanolic extract of Sunderban mangrove Rhizophora mucronata Lam. leaves in animal model

Background: Mangrove flora possess compounds with potential medicinal values with unique bioactive components. Traditionally Rhizophora mucronata, a mangrove has been used extensively for the treatment of diabetes. Studies revealed that, the leaves of Rhizophora (Bhora) had promising anti-diabetic action in rat model.Methods: A comparative analysis of the anti-diabetic action of fresh juice and ethanolic extract of Rhizophora mucronata leaves was carried out in Streptozotocin induced diabetic model and the different biochemical parameters were evaluated.Results: Present research explored a comparative analysis of the anti-diabetic action of fresh juice and ethanolic extract of leaves of Rhizophora mucronata Lam. in Streptozotocin induced diabetic model. The ethanolic extract showed more potent effect in lowering the elevated blood sugar in the diabetic rats, 200mg/kg was the most effective dose for both the extracts. The ethanol extract was more beneficial having potent lipid lowering action along with anti-hyperglycemic property.Conclusions: This supports the scientific validation for using Rhizophora mucronata leaves in the treatment of diabetes as traditional folk medicine. Identification of the bioactive molecule is under process

UAV Formation Control under Fixed and Variable Adjacency based Directed Network Topologies

The UAV formation control is one of the key aspects in several applications like surveillance, moving target tracking, load-transportation, and delivery systems etc. These situations demand the multiple UAVs to manoeuvre in a desired formation. To address this problem, a distributed formation control scheme is proposed incorporating the details about the state of the neighbouring UAVs. The communication network topology among the UAVs is considered to be directed with the constant and the weighted adjacency matrices. The nonholonomic constraints are considered while deriving the desired Euler angles. Satisfying the conditions of Lyapunov provides necessary proof of stability along the positional and the attitude subsystems. Simulation results demonstrate that the desired tetrahedron, octahedron, and cube shapes are attained and maintained by the UAVs successfully. Also, the designed formation paradigm works proficiently for both the constant and the weighted adjacency matrices based directed network topologies. The performance validation is done through extensive comparative analysis for varying network connections

Kinetička svojstva F-centara pod utjecajem topline

The migration of colour clouds after the electron injection in pure and doped KCl and KBr alkali halides under thermal and field stresses is studied with an anode contact of spherical geometry. The diffusion coefficient of the colour clouds has been obtained using a derived analytical expression and the experimental data, and the activation energy of the colour centre was estimated. The dissociation energy values under thermal and field stresses for doped crystals are deduced through the mobility transport equation. The results indicate the effect of doping in an otherwise pure counterpart of the same crystals.Proučavamo premještanje oblaka boje nakon ubacivanja elektrona u čiste i punjene kristale alkalnih halida KCl i KBr, pod djelovanjem topline i električnog polja, uz primjenu kuglaste elektrode. Pomoću izvedene analitičke relacije i mjernih podataka odredili smo koeficijent difuzije oblaka boje i ocijenili aktivacijsku energiju centara boje. Primjenom jednadžbe pokretljivosti izveli smo vrijednosti disocijacijske energije pod toplinskim i električnim naprezanjem za punjene kristale. Podaci pokazuju učinak punjenja u odnosu na čiste kristale

Kinetička svojstva F-centara pod utjecajem topline

The migration of colour clouds after the electron injection in pure and doped KCl and KBr alkali halides under thermal and field stresses is studied with an anode contact of spherical geometry. The diffusion coefficient of the colour clouds has been obtained using a derived analytical expression and the experimental data, and the activation energy of the colour centre was estimated. The dissociation energy values under thermal and field stresses for doped crystals are deduced through the mobility transport equation. The results indicate the effect of doping in an otherwise pure counterpart of the same crystals.Proučavamo premještanje oblaka boje nakon ubacivanja elektrona u čiste i punjene kristale alkalnih halida KCl i KBr, pod djelovanjem topline i električnog polja, uz primjenu kuglaste elektrode. Pomoću izvedene analitičke relacije i mjernih podataka odredili smo koeficijent difuzije oblaka boje i ocijenili aktivacijsku energiju centara boje. Primjenom jednadžbe pokretljivosti izveli smo vrijednosti disocijacijske energije pod toplinskim i električnim naprezanjem za punjene kristale. Podaci pokazuju učinak punjenja u odnosu na čiste kristale