Search results for: Subhankar Sen

Authors: Niru Chowdhury, Subhankar Bedanta, Alexander Weber, Thomas Brueckel

Abstract:

We show the effect of interlayer coupling on magnetization reversal in purely dipolar coupled magnetic multilayers. Longitudinal magneto-optic Kerr microscopy (LMOKE) has been performed on [Co(10nm)/Al2O3(t)/Co(10nm)] for various thicknesses of Al2O3(t). We will show that inter-layer coupling interactions lead to layer-by-layer reversal in the magnetic multilayers. Also transverse component of magnetization was observed for higher thickness of the spacer layer.

Keywords: Interlayer coupling, Magnetic domains, Magneto – Optic Kerr effect microscopy, Magnetization reversal, Magnetic thin film

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Authors: Sherly M. A., Varsha Vijaykumar, Subhankar Karmakar, Terence Chan, Christian Rau

Abstract:

This study aims at proposing an indicator-based framework for assessing social vulnerability of any coastal megacity to floods. The final set of indicators of social vulnerability are chosen from a set of feasible and available indicators which are prepared using a Geographic Information System (GIS) framework on a smaller scale considering 1-km grid cell to provide an insight into the spatial variability of vulnerability. The optimal weight for each individual indicator is assigned using data envelopment analysis (DEA) as it avoids subjective weights and improves the confidence on the results obtained. In order to de-correlate and reduce the dimension of multivariate data, principal component analysis (PCA) has been applied. The proposed methodology is demonstrated on twenty four wards of Mumbai under the jurisdiction of Municipal Corporation of Greater Mumbai (MCGM). This framework of vulnerability assessment is not limited to the present study area, and may be applied to other urban damage centers.

Keywords: urban floods, vulnerability, data envelopment analysis, principal component analysis

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Authors: Amit K. Singh, Subhankar Sen

Abstract:

The bifurcation curve of separation in steady two-dimensional viscous flow past an elliptic cylinder is studied by varying the angle of incidence (α) with different aspect ratio (ratio of minor to major axis). The solutions are based on numerical investigation, using finite element analysis, of the Navier-Stokes equations for incompressible flow. Results are presented for Reynolds number up to 50 and angle of incidence varies from 0° to 90°. Range of aspect ratio (Ar) is from 0.1 to 1 (in steps of 0.1) and flow is considered as unbounded flow. Bifurcation curve represents the locus of Reynolds numbers (Res) at which flow detaches or separates from the surface of the body at a given α and Ar. In earlier studies, effect of Ar on laminar separation curve or bifurcation curve is limited for Ar = 0.1, 0.2, 0.5 and 0.8. Some results are also available at α = 90° and 45°. The present study attempts to provide a systematic data and clear understanding on the effect of Ar at bifurcation curve and its point of maxima. In addition, issues regarding location of separation angle and maximum ratio of coefficient of lift to drag are studied. We found that nature of curve, separation angle and maximum ratio of lift to drag changes considerably with respect to change in Ar.

Keywords: aspect ratio, bifurcation curve, elliptic cylinder, GMRES, stabilized finite-element

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Authors: Triloki Prasad, Subhankar Ghosh, Asis Goswami

Abstract:

The information received from visual organ plays an important role in human locomotion and human beings generally veer from the straight line in the absence of visual cue. Since in case of visually impaired persons this support is unavailable they are expected to have a different type of locomotion behaviour than the sighted persons. Higher degree of veering can result in accident or injury during indoor and outdoor activities. Hence, it is important to know the degree of veering that may happen in case of a sighted individual loosing the visual input. The present study was conducted on fifty three volunteers who walked with open and closed eyes, at their comfortable pace, in a grid marked area of 17m by 10m space. The volunteers had to walk in a straight line from a central starting point during three trials and their walking path was marked with a pair of sponge absorbed with three different colours. All volunteers had walked expectedly in straight line during open eye condition but had varied degree of veering during closed eye state. The correlation between the first step side and the side of deviation was not significant in closed eye condition. The number of steps taken in open eye and closed eye condition were significantly different while travelling similar distances. This study reveals that sighted persons become cautious during walking if the visual cue is not available and they reduce the step length so there is increase in step number.

Keywords: Closed eye, Open eye, Footprint, Veering

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Authors: Sherly M. A., Subhankar Karmakar, Terence Chan, Christian Rau

Abstract:

Floods are one of the most frequent natural disasters, causing widespread devastation, economic damage and threat to human lives. Hydrologic impacts of climate change and intensification of urbanization are two root causes of increased flood occurrences, and recent research trends are oriented towards understanding these aspects. Due to rapid urbanization, population of cities across the world has increased exponentially leading to improperly planned developments. Climate change due to natural and anthropogenic activities on our environment has resulted in spatiotemporal changes in rainfall patterns. The combined effect of both aggravates the vulnerability of urban populations to floods. In this context, an efficient and effective flood risk management with its core component as flood risk mapping is essential in prevention and mitigation of flood disasters. Urban flood risk mapping involves zoning of an urban region based on its flood risk, which depicts the spatiotemporal pattern of frequency and severity of hazards, exposure to hazards, and degree of vulnerability of the population in terms of socio-economic, environmental and infrastructural aspects. Although vulnerability is a key component of risk, its assessment and mapping is often less advanced than hazard mapping and quantification. A synergic effort from technical experts and social scientists is vital for the effectiveness of flood risk management programs. Despite an increasing volume of quality research conducted on urban flood risk, a comprehensive multidisciplinary approach towards flood risk mapping still remains neglected due to which many of the input parameters and definitions of flood risk concepts are imprecise. Thus, the objectives of this review are to introduce and precisely define the relevant input parameters, concepts and terms in urban flood risk mapping, along with its methodology, current status and limitations. The review also aims at providing thought-provoking insights to potential future researchers and flood management professionals.

Keywords: flood risk, flood hazard, flood vulnerability, flood modeling, urban flooding, urban flood risk mapping

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Authors: Subhankar Kumar Sarkar

Abstract:

Beetles of the subfamily Dynastinae under the family Scarabaeidae of the insect order Coleoptera are popularly known as ‘Rhinoceros beetles’ because of the characteristic horn borne by the males on their head. These horns are dedicated in mating battle against other males and have evolved as a result of phenotypic plasticity. Scarabaeidae is the largest of all families under Coleoptera and is composed of 11 subfamilies, of which the subfamily Dynastinae is represented by approximately 300 species. Some of these beetles have been reported to cause considerable damage to agriculture and forestry both in their larval and adult stages, while many of them are beneficial as they pollinate plants and recycle plant materials. Eastern Himalayas is regarded as one of the 35 biodiversity hotspot zones of the world and one of the four of India, which is exhibited by its rich and megadiverse tropical forests. However, our knowledge on the faunal diversity of these forests is very limited, particularly for the insect fauna. One such tropical forest of Eastern Himalayas is the ‘Buxa Tiger Reserve’ located between latitudes 26°30” to 26°55” North and Longitudes 89°20” to 89˚35” East of India and occupies an area of about 759.26 square kilometers. It is with this background an attempt has been made to explore the insect fauna of the forest. Insect sampling was carried out in each beat and range of Buxa Tiger Reserve in all the three seasons viz, Premonsoon, Monsoon, and Postmonsoon. Sample collections were done by sweep nets, hand picking technique and pit fall traps. UV light trap was used to collect the nocturnal insects. Morphological examinations of the collected samples were carried out with Stereozoom Binocular Microscopes (Zeiss SV6 and SV11) and were identified up to species level with the aid of relevant literature. Survey of the insect fauna of the forest resulted in the recognition of 76 scarab species, of which 8 belong to the subfamily dealt herein. Each of the 8 species represents a separate genus. The forest is dominated by the members of Xylotrupes gideon (Linnaeus) as is represented by highest number of individuals. The recorded taxa show about 12% endemism and are of mainly oriental in distribution. Premonsoon is the most favorable season for their occurrence and activity followed by Monsoon and Postmonsoon.

Keywords: Dynastinae, Scarabaeidae, diversity, Buxa Tiger Reserve

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Authors: Subhankar Karmakar, Madhan Kumar Vasudevan, Manivannan Muniyandi

Abstract:

Thermal Grill Illusion (TGI) elicits a strong and often painful sensation of burn when interlacing warm and cold stimuli that are individually non-painful, excites thermoreceptors beneath the skin. Among several theories of TGI, the “disinhibition” theory is the most widely accepted in the literature. According to this theory, TGI is the result of the disinhibition or unmasking of the pain-sensitive HPC (Heat-Pinch-Cold) nerve fibers due to the inhibition of cold-sensitive nerve fibers that are responsible for masking HPC nerve fibers. Although researchers focused on understanding TGI throughexperiments and models, none of them investigated the prediction of TGI pain intensity through a computational model. Furthermore, the comparison of psychophysically perceived TGI intensity with neurophysiological models has not yet been studied. The prediction of pain intensity through a computational model of TGI can help inoptimizing thermal displays and understanding pathological conditions related to temperature perception. The current studyfocuses on developing a computational model to predict the intensity of TGI pain and experimentally observe the perceived TGI pain. The computational model is developed based on the disinhibition theory and by utilizing the existing popular models of warm and cold receptors in the skin. The model aims to predict the neuronal activity of the HPC nerve fibers. With a temperature-controlled thermal grill setup, fifteen participants (ten males and five females) were presented with five temperature differences between warm and cold grills (each repeated three times). All the participants rated the perceived TGI pain sensation on a scale of one to ten. For the range of temperature differences, the experimentally observed perceived intensity of TGI is compared with the neuronal activity of pain-sensitive HPC nerve fibers. The simulation results show a monotonically increasing relationship between the temperature differences and the neuronal activity of the HPC nerve fibers. Moreover, a similar monotonically increasing relationship is experimentally observed between temperature differences and the perceived TGI intensity. This shows the potential comparison of TGI pain intensity observed through the experimental study with the neuronal activity predicted through the model. The proposed model intends to bridge the theoretical understanding of the TGI and the experimental results obtained through psychophysics. Further studies in pain perception are needed to develop a more accurate version of the current model.

Keywords: thermal grill Illusion, computational modelling, simulation, psychophysics, haptics

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Authors: Subhankar Kumar Sarkar

Abstract:

Scarab beetles composing the family Scarabaeidae is one of the largest families in the order Coleoptera. The family is comprised of 11 subfamilies. Of these, the subfamily Scarabaeinae includes 13 tribes globally. Indian species are however considered within 2 tribes Scarabaeini and Coprini. Scarab beetles under this subfamily also known as Coprophagus beetles play an indispensable role in forestry and agriculture. Both adults and larvae of these beetles do a remarkable job of carrying excrement into the soil thus enriching the soil to a great extent. Eastern and North Eastern states of India are heavily rich in diversity of organisms as this region exhibits the tropical rain forests of the eastern Himalayas, which exhibits one of the 18 biodiversity hotspots of the world and one of the three of India. Buxa Tiger Reserve located in Dooars between latitudes 26°30” to 26°55” North & longitudes 89°20” to 89°35” East is one such fine example of rain forests of the eastern Himalayas. Despite this, the subfamily is poorly known, particularly from this part of the globe and demands serious revisionary studies. It is with this background; the attempt is being made to assess the Scarabaeinae fauna of the forest. Both extensive and intensive surveys were conducted in different beats under different ranges of Buxa Tiger Reserve. For collection sweep nets, bush beating and collection in inverted umbrella, hand picking techniques were used. Several pit fall traps were laid in the collection localities of the Reserve to trap ground dwelling scarabs. Dung of various animals was also examined to make collections. In the evening hours UV light, trap was used to collect nocturnal beetles. The collected samples were studied under Stereozoom Binocular Microscopes Zeiss SV6, SV11 and Olympus SZ 30. The faunistic investigation of the forest revealed in the recognition of 19 species under 6 genera distributed over 2 tribes. Of these Heliocopris tyrannus Thomson, 1859 was recorded new from the Country, while Catharsius javanus Lansberge, 1886, Copris corpulentus Gillet, 1910, C. doriae Harold, 1877 and C. sarpedon Harold, 1868 from the state. 4 species are recorded as endemic to India. The forest is dominated by the members of the Genus Onthophagus, of which Onthophagus (Colobonthophagus) dama (Fabricius, 1798) is represented by highest number of individuals. Their seasonal distribution is most during Premonsoon followed by Monsoon and Postmonsoon. Zoogeographically all the recorded species are of oriental distribution.

Keywords: buxa tiger reserve, diversity, India, new records, scarabaeinae, scarabaeidae

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