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Study of classical Be stars in open clusters older than 100 Myr
We performed the slitless spectroscopic survey to identify classical Be (CBe) stars in open clusters older than 100 Myr. Observing a sample of 71 open clusters, we identified 13 CBe stars in 11 open clusters, one of, which (TYC 2679-432-1) is a new detection. The 13 CBe stars show both H? in emission and IR excess, which confirm that they possess gaseous circumstellar discs. Two more CBe stars are found to exhibit H? in absorption for the first time, indicating that might be passing through disc-less episode presently. The spectral-type estimation is done for all these 15 stars and it is noticed that they belong to B0.5B8 type. Moreover, we found that the distribution of our sample is peaking near late B-types as expected. 2021, Indian Academy of Sciences. -
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Study of Classical Be Stars in Open Clusters in the Galaxy
Classical Be stars (CBe) in open clusters older than 100 Myr are identifed. The objective is to study their characteristics relating to age, spectral type and evolutionary state. This study compliments with that of Mathew et al. (2008), where they identifed and characterized emission-line stars in open clusters younger than 100 Myr. For this research, we surveyed a sample of newline71 open clusters older than 100 Myr using the slitless spectroscopy technique, with the Himalayan Chandra Telescope (HCT). From the survey we identifed 15 CBe stars from the 11 open clusters older than 100 Myr. Out of 15 CBe stars, 13 CBe stars show Hand#945; in emission. Among these CBe stars, TYC 2679-432-1 is a new detection, belonging to Berkeley 50 open newlinecluster. Two more CBe stars, out of 15 CBe stars, are found to exhibit Hand#945; in absorption for the frst time. This suggests that they might be passing through a disc-loss episode (or transient phase). Apart from our survey of 71 old open clusters, we found additional 16 Be stars from 6 open clusters older than 100 Myr in the literature (which was not observed in the slitless survey due to observation limitations). In addition to HFOSC instrument mounted on HCT, we used Opto Mechanics Research (OMR) spectrograph newlinemounted on 2.3-m Vainu Bappu Telescope (VBT) for taking the slit spectra of CBe stars. We performed the optical spectroscopy of 16 classical Be stars in 11 open clusters older than 100 Myr. Among these 16 stars, 15 newlinewere identifed from our previous slitless spectroscopic study. The remaining one, LS III +47 37b is a new detection, which is confrmed through the present study. Our analysis also suggests that one out of these 16 stars, [KW97] 35-12 might be a weak Hand#945; emitter in nature showing Hand#945; EW of -0.5 Moreover, it is found that the Hand#945; EW for 15 stars is lt -40 in agreement with previous works. Interestingly, we did not observe any FeII emission line or even the OI 8446 emission feature in any of our sample stars. -
Study of chaos in the Darcy-Bard convection problem with Robin boundary condition on the upper surface
Possibility of chaos is studied in Darcy-Bard convection using the Dirichlet and the Robin boundary condition at the lower and upper boundaries, respectively. Comparison is made with the results of Dirichlet (classical-Darcy-Bard convection, CDBC) and Neumann boundary condition (Barletta-Darcy-Bard convection, BDBC). It is found that the cell size at onset is bigger in the case of BDBC compared to the generalized-Darcy-Bard convection (GDBC) and much bigger compared to CDBC. The critical-Darcy-Rayleigh number of BDBC is found to be the least and that of CDBC is the largest. Nonlinear-stability-analysis is performed leading to the scaled-generalized-Vadasz-Lorenz model (SGVLM). In deriving this model, help is sought from a local-nonlinear-stability-analysis that yields the form of the convective-mode. The SGVLM is shown to be dissipative and conservative, with its bounded solution trapped within an ellipsoid. Onset of chaos and its characteristics are studied using the Hopf-Rayleigh-number, the Lorenz-butterfly-diagram, and the plot of the amplitude of the convective-mode vs the control-parameter, R, which is the eigenvalue. Chaos sets in earlier in CDBC and much later in BDBC when compared to that in GDBC. Beyond the onset of chaos is seen a sequence of chaotic and periodic motions, with the latter sometimes being present for an extended period. 2024 Author(s). -
Study of candidate Be stars in the Magellanic Clouds using near-infrared photometry and optical spectroscopy
Mennickent et al. and Sabogal et al. identified a large number of classical Be (CBe) candidates (?3500) in the Large and Small Magellanic Clouds (LMC and SMC) based on their photometric variability using the OGLEII data base. They classified these stars into four different groups based on the appearance of their variability. In order to refine and understand the nature of this large number of stars, we studied the infrared properties of the sample and the spectroscopic properties of a subsample. We cross-correlated the optical sample with the IRSF-MCPS catalogue to obtain the J, H, K s magnitudes of all the four types of stars (?2500) in the LMC and SMC. Spectra of 120 stars belonging to the types 1, 2 and 3 were analysed to study their spectral properties. Among the four types, the type 4 stars are the dominant group, with ?60 and ?65 per cent of the total sample in the LMC and SMC, respectively. The near-infrared (NIR) colour-colour diagrams suggest that the type 4 stars in the LMC have a subclass, which is not found in our Galaxy or in the SMC. This subclass is ?18 per cent of the type 4 sample. The main type 4 sample which is ?49 per cent of the total sample has NIR properties similar to the Galactic CBe stars and the SMC type 4 stars. Though the new subclass of type 4 stars have high E(B-V) ? 0.75, they are not located close to regions with high reddening. The type 3 stars (?6 per cent and 7.3 per cent in the LMC and SMC) are found to have large H? equivalent width (EW) in the SMC and some are found to have large NIR excess. This small fraction of stars are unlikely to be CBe stars. Three stars among the type 3 stars in the LMC are found to be double periodic variables. The type 2 stars are found in larger fraction in the SMC (?14.5 per cent), when compared to the LMC (?6 per cent). The spectroscopic and the NIR properties suggest that these could be CBe stars. The type 1 stars are relatively more in the LMC (?24 per cent) when compared to the SMC (?13 per cent). The SMC type 1 stars have relatively large H? EW and this class has properties similar to CBe stars. The spectroscopic sample of type 1 stars which show H? in emission and are confirmed as CBe stars are more abundant in the SMC by a factor of 2.6. If the effect of metallicity is to cause more CBe stars in the SMC, when compared to the LMC, then type 1, type 2 and type 4 stars follow this rule, with an enhancement of 2.6, 2.4 and 1.3, respectively. 2012 The Authors Monthly Notices of the Royal Astronomical Society 2012 RAS. -
Study of Candidate be Stars in the Magellanic Clouds using near-Infrared Photometry and Optical Spectroscopy
Monthly Notices of the Royal Astronomical Society Vol. 421, Issue 4, pp. 3622-3640, ISSN No. 1365-2966 -
Study of buoyancy and surface tension driven convention in nanaofluid
This thesis presents a detail study of linear and non-linear analysis of buoyancy and surface tension driven convection in nanofluid. The linear Rayleigh-Bard / Rayleigh- Bard Marangoni convection in nanofluids in the presence of external constraints like magnetic field, rotation and newlineinternal heat generation is investigated. The effect of temperature and volumetric concentration modulation of nanoparticles at the boundary and gravity modulation are studied on the onset of Rayleigh- Bard newlineconvection. The obtained results are discussed qualitatively and presented newlinegraphically. The problem discussed have important applications in the field of oceanography, geophysics, nuclear fuel, astrophysics, geothermal reservoirs, engineering and space situations with g-jitter connected with gravity simulation studies.Given the rising relevance of nanofluid application, we discuss four newlineproblems in this thesis whose detail summary is presented below: (i) LINEAR AND WEAKLY NON-LINEAR ANALYSIS OF GRAVITY MODULATION ON THE ONSET OF RAYLEIGH BARD CONVECTION IN NANOFLUID The effect of modulation of gravity or time-periodic body force on newlinethe onset of Rayleigh-Bard convection in nanofluid is studied using newlinelinear and non-linear analysis. The stability of the fluid layer heated from newlinebelow is analysed by considering time-periodic body acceleration. This newlinehappens generally in the vehicles and satellites associated with studies of newlinemicro gravity simulation. In order to study the effect of gravity modulation newlineon the system stability limit, linear and weakly non-linear analysis is performed. Normal mode technique and perturbation method is applied to study linear stability. The critical Rayleigh number and wave number is newlinecalculated by taking modulation of small amplitude. It is found that the critical thermal Rayleigh number can be increase or decrease by a massive amount depending upon the distribution of nanoparticles.In this thesis we considered bottom heavy distribution of nanoparticles. -
Study of buoyancy and surface tension driven convection in nanofluid
This thesis presents a detail study of linear and non-linear analysis of buoyancy and surface tension driven convection in nanofluid. The linear Rayleigh-Bernard / Rayleigh-Bernard Marangoni convection in nanofluids in the presence of external constraints like mangnetic feild, rotation and internal heat generation is investigated. -
Study of BrinkmanBard nanofluid convection with idealistic and realistic boundary conditions and by considering the effects of shape of nanoparticles
This study deals with linear and weakly non-linear stability analyses of BrinkmanBard convection in nanoliquid-saturated porous enclosures. Water with a dilute concentration of molybdenum disulfide nanoparticles with 0.06 volume fraction and 30% glass fiber-reinforced polycarbonate as a porous medium with porosity 0.88 are considered to be a working medium. The analytical solution is obtained in the present study for idealistic and realistic boundary conditions, and their results are compared. An analytically intractable Lorenz model with quadratic nonlinearities is reduced to a tractable GinzburgLandau amplitude equation with cubic nonlinearity using the multiscale method. Nanoparticles with different shapesare considered in the study, and their effects on the onset and heat transfer are discussed in great detail graphically in the presence of other parameters arising in the problem. 2021 Wiley Periodicals LLC -
STUDY OF BOUND AND CONTINUUM STATE BETA DECAY RATES OF A FEW BARE NUCLEI
Beta decay is one of the most widely studied research problems in nuclear physics. There has been a growing interest in understanding the dynamics of beta decay transitions for many decades. Many research groups have invested a lot of time, money and effort in experiments as well as developing the theory for the same. Lot of work was done using Fermis theory and huge amount of data is available in that domain of nuclear physics. But recently, standard model has gained a lot of attention in the eyes of theoretical nuclear physicists and particle physicists to understand nuclear transitions with more importance to gluons mixing and quark mixing by incorporating CKM matrix and PMNS matrix elements. Subsequently, the standard model theory is applied to beta decay to gain a better insight with the application of standard weak interaction Hamiltonian to compute decay rates. The half life and stability of these nuclei depends on decay rates. Also, it gives us an idea about the kind of transitions which happen and which dont. Recent interest in comparison of two modes of beta decay namely, continuum and bound state for same mother and daughter set, paved way for a lot of interesting calculations by various research groups. It is exciting to understand as to how their differences are compared. The aim of this work is to predict continuum and bound state beta decay rates using approach incorporating standard weak theory for some new transitions, which has not been done so far and also compare few decay rates with existing experimental values done by various groups all over the globe. -
Study of Bard-Marangoni Convection in a Microfluid with Coriolis Force
The convection of micro-structured fluid particles and the Coriolis force has been investigated in the problem. The eigenvalues are calculated for upper free velocity and adiabatic temperature boundary conditions and lower rigid velocity and isothermal temperature boundary conditions. The analysis is based on solving linear disturbance equations. The impact of different micropolar fluid variables and the Taylor number based on the convection has also been investigated. The study could observe that while the coupling and micropolar heat conduction parameters along with rotational parameters have a stabilizing effect, the couple stress parameter results in a destabilizing effect. The Author(s), under exclusive license to Springer Nature Switzerland AG 2024. -
Study of 1s internal bremsstrahlung spectrum from 57Co
The internal bremsstrahlung contribution from the electron capture of 57Co has been measured in coincidence with K-X-ray of the residual atom. The end-point energy (EPE) is extracted from the data using the linearised Jauch plot. The transition energy obtained using the (EPE) is 842.7keV, which is close to the value given by Audi and Wapstra. The measured intensity and shape factor from 300 to 600keV are found to be in good agreement with the Glauber and Martin theory. 2002 Elsevier Science Ltd. All rights reserved. -
Studies on Uniaxial Compressive Strength of Laterite Masonry Prisms
Vol-04, No.02, April ISNN: 0974-5904 -
Studies on thermal, structural, electrical and optical properties of Se-Te-Sb chalcogenide glasses /
Glasses, an intriguing state of matter, known to mankind since ages, have seen systematically reported investigations only in the 20th century. Of the various kinds of glasses such as silicates, oxides, halides, chalcogenide etc., a large spectrum of commercial and technological applications of chalcogenide glasses(ChG), have made them a subject of great interest and studied for more than four decades now. -
Studies on the Fresh Water Algal Floria in Chimmony Wildlife Sanctuary
Algae is a crucial organism in the environment. They help in maintaining the balance among different ecosystems. According to the geography and climatic conditions, newlineKerala has a suitable environment for algal growth. However, the algal biodiversity newlinestudies conducted in Kerala are significantly less. The wildlife sanctuary comprises a newlineconsiderable scope for algal biodiversity. The Chimmony wildlife sanctuary is situated in Mukundapuram taluk of Thrissur district. It spreads over 85.067 km2 with a water spread area of 10.1 km2. Ten different sampling stations were selected across newlinethe wildlife sanctuary, and extensive field visits were conducted to identify and newlinedocument the algae with respect to three seasons (pre-monsoon, monsoon, and post- newlinemonsoon). The physicochemical parameters of water like dissolved oxygen, temperature, pH, alkalinity, total dissolved solids, light intensity, and rainfall amount were estimated seasonally. In this present study, a total of 121 taxa belonging to 60 genera, 38 families, 24 orders, and 5 classes, namely Chlorophyceae, Bacillariophyceae, Euglenineae, Rhodophyceae, and Cyanophyceae, were identified from 10 different stations. The Bacillariophyceae and Chlorophyceae were the most dominant class in the study area. The algal multiplication will be more in the pre monsoon season and it was observed that the Chlorophyceaen members were dominant, while the Bacillariophyceae were dominant during the post-monsoon season. Cyanophyceae was dominant only during the monsoon season because of its sensitivity toward light. The ANOVA (Two-way) analysis showed no significant difference between stations, and there is a considerable difference between seasons for dissolved oxygen, alkalinity, temperature, and total dissolved solids. While pH, showed no significant difference between seasons and stations, light intensity showed a substantial difference between stations and seasons. The temperature and dissolved oxygen showed a negative correlation. -
Studies on the Culture Conditions, Nutritional Value of the Black Soldier Fly, Hermetia illucens (Diptera : Stratiomyid) and its Suitability as Aquaculture Feed
The Black Soldier Fly (BSF), Hermetia illucens, has emerged as a promising newlinesolution in aquaculture due to its remarkable ability to convert organic waste into newlineprotein-rich biomass. This has garnered interest among aquaculturists seeking costeffective and sustainable alternative ingredients for aqua feed. However, fully newlineharnessing the potential of this insect requires a deeper understanding of its life cycle and nutritional composition. A key challenge in utilising BSF larvae (BSFL) for newlineaquafeed production is the lack of standardized culture systems. This study addresses this gap by establishing a comprehensive culture system using two common organic wastes, fruit waste (FW) and vegetable waste (VW), as rearing substrates. By evaluating the growth performance of BSFL reared on these substrates, the research sheds light on optimal conditions for large-scale BSF production. The study investigated the impact of FW and VW substrates on BSFL growth through a thorough analysis of growth performance, morphometric measurements and newlineScanning Electron Microscopy (SEM). Results showed that BSFL reared on FW exhibited better growth (40 days) than those reared on VW (46 days). Morphometric analysis and SEM identified five larval stages and the prepupa, pupa, and adult stages. Additionally, the study analysed the nutritional composition of BSFL at different newlinedevelopmental stages, such as Instar 3 through instar 5, prepupa and pupa, including newlineprotein, carbohydrate, lipid, amino acids and fatty acids. This provided insights into newlinehow variations in substrate impact the nutritional quality of BSFL at different stages, which is crucial for ensuring that BSFL-derived feed meets the dietary requirements of target aquaculture species. Significant differences were found in the proximate composition of the substrates (FW and VW), resulting in significant variations in BSFL nutrition. BSFL reared on FW exhibited higher nutritional content especially crude newlineprotein (54.160.64%), than those reared on VW, except for crude lipids (2.200.01%). -
Studies on the characterisation of thiophene substituted 1,3,4-oxadiazole derivative for the highly selective and sensitive detection of picric acid
A novel thiophene substituted 1,3,4-oxadiazole based chemosensor namely 2-(4-(5-(5-hexylthiophen-2-yl) thiophen-2-yl)phenyl) -5-(5-(5-(5-hexylthiophen-2-yl) thiophen-2-yl)thiophen-2-yl)-1,3,4-oxadiazole [TKO] has been characterised for the efficient detection of picric acid (PA) based on fluorescence quenching mechanism. In this regard, the electronic absorption spectra, fluorescence spectra, and fluorescence lifetime of TKO are recorded in the presence of different nitroaromatic compounds (NACs) in ethanol at room temperature. The absorption studies exhibited a blue shift in the absorption maxima with the increase in the concentration of PA. In the fluorescence titration studies, TKO shows a remarkable fluorescence quenching with picric acid as compared to other nitroaromatic compounds. Using the Benesi-Hildebrand plot, the binding constant value of PA with TKO is determined and is of the order of 6.467 104 M?1. Job's plot analysis confirms the 1:1 binding stoichiometry ratio between TKO and PA and is supported by the 1H NMR studies. The detection limit is determined and is of the order of 10.08 M. The competitive studies revealed that TKO is highly selective for recognizing PA without the interference of other NACs. The theoretical studies were also carried out to understand the binding mechanisms of PA with TKO. The fluorescence quenching of TKO by PA may be attributed to photo induced electron transfer (PET). Overall, the experimental findings suggest that, the novel probe TKO may be used as a highly selective and sensitive chemosensor for the detection of explosives like picric acid. 2022 Elsevier B.V. -
Studies on the antifungal activity of biotemplated gold nanoparticles over Candida albicans
Green synthesis and applications of gold nanoparticles are more fascinating research area due to their unique optical properties and high X-ray attenuation power. In this study, we have synthesized gold nanoparticles of uniform size (5 nm) with spherical shape. UVvis spectroscopy, Transmission Electron Microscopy and Atomic Force Microscopy were employed to characterize the synthesized gold nanoparticles. The biomedical applications of the synthesized gold nanoparticles were carried out against most prevalent human fungal pathogen, Candida albicans. Broth micro dilution assay was used to determine minimum inhibitory concentration (MIC). We observed that 0. 5 mM concentration was effective in inhibiting the growth of fungal cells which was later confirmed by spot assay. 2019 Elsevier Ltd -
Studies on Tensile Properties of Graphene Hydroxyl Reinforced Aluminium 6061 Composites for Vehicle Structures Applications
Aluminium composite plays a significant role in the mechanical structures. Low tensile strength of the aluminium alloy limits its application in mechanical structures. Graphene hydroxyl (GrOH) is a noble emerging material which is an allotropic form of carbon. It has high cohesive strength, good bonding ability with other materials. Carbon bonds processes high compatibility when it reinforced with other material. Reinforcement of GrOH with aluminium composites enhances the wear strength of composite material. This paper focused on analysis of tensile properties and percentage elongation of aluminium composites reinforced with GrOH with various weight percentage (wt. %). The characteristics of aluminium composites, particularly related to its tensile properties are very much important for its use in vehicle structures applications. 2022. MechAero Foundation for Technical Research & Education Excellence.