Browsing by Author "Vivek Singh"

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A comparative study of dispersion relation of em waves in ternary one-dimensional plasma photonic crystals having two different structures
(2011) S. Prasad; Vivek Singh; A.K. Singh
In this paper, a rigorous theoretical analysis has been made to study the dispersion relation of EM waves in periodic ternary one-dimensional photonic crystal having two different structures. In one case we have chosen glass-plasma and ZnS in one unit cell and in other case we have considered glass-plasma and MgF2 in one unit cell. Using Kronig-Penney model the dispersion relation for proposed structures has been obtained and numerical results are presented in the form of dispersion curves. The dependence of photonic band gap (PBG) characteristics on plasma frequency, plasma width and the width of dielectric media are discussed in the light of frequency gap and cutoffs of binary one-dimensional plasma photonic crystal. An attempt has been made to show how the PBG characteristic of a particular structure changes when the dielectric materials of its unit cell is changed by the other dielectric material. It is found that the structure having glass-plasma-ZnS in unit cell is more useful for broad band filtering and other plasma functioning devices compared to the structure having glass-plasma-MgF2 in one unit cell. © 2010 Elsevier GmbH. All rights reserved.
A novel Bragg fiber waveguide based narrow band inline optical filter
(Elsevier GmbH, 2018) Ritesh Kumar Chourasia; Surendra Prasad; Vivek Singh
Theoretical analysis of Bragg fiber waveguide based inline optical filter having a defect layer is presented. Defect layer is introduced in Bragg fiber waveguide by breaking its cladding layer periodicity. Considering the cylindrical wave equations, the transmittance of proposed waveguide is obtained using transfer matrix method. It is observed that the proposed Bragg waveguide represent photonic band gap and a narrow defect mode (pass band) is present in this band gap region. This defect mode can be obtained in any position between the wavelength ranges 1.241 μm–1.550 μm with the help of incident angle of light. The narrowness of the defect mode depends on the number of unit cell present in the cladding region. This proposed waveguide may be used to design a narrowband transmission filters. © 2018 Elsevier GmbH
A novel tunable metal-clad planar waveguide with 0.62PMN-0.38PT material for detection of cancer cells
(John Wiley and Sons Inc, 2023) Rajiv Maurya; Ankit Mishra; Chandan Singh Yadav; Abhishek Upadhyay; Gaurav Sharma; Sushil Kumar; Vivek Singh
A dynamically tunable metal clad planar waveguide having 0.62PMN-0.38PT material is simulated and optimized for detection of cancer cells. Angular interrogation of the TE0 mode of waveguide shows that critical angle increases greater than the resonance angle with increasing of cover refractive index, which limits the detection range of waveguide. To overcome this limitation, proposed waveguide applies a potential on the PMN-PT adlayer. Although a sensitivity of 105.42 degree/RIU was achieved at 70 Volts in testing the proposed waveguide, it was found that the optimal performance parameters were obtained at 60 Volts. At this voltage, the waveguide demonstrated detection range 1.3330–1.5030, a detection accuracy 2393.33, and a figure of merit 2243.59 RIU−1, which enabled the detection of the entire range of the targeted cancer cells. Therefore, it is recommended to apply a potential of 60 Volts to achieve the best performance from the proposed waveguide. (Figure presented.). © 2023 Wiley-VCH GmbH.
A tumour stage-dependent evolution of drug resistant T cell lymphoma: Role of soluble mediators of tumour and host origin
(2009) Vivek Singh; Sukh Mahendra Singh
The present investigation was carried out to investigate if soluble mediators present in tumour microenvironment and systemic circulation of a tumour-bearing host can regulate growth properties and response of the cells of a T cell lymphoma to chemotherapeutic drug: cisplatin, depending on the stage of tumour progression. In order to investigate this, tumour cells of a murine T cell lymphoma, designated as Dalton's lymphoma (DL), were incubated in vitro for 48 h in the presence of ascitic fluid and serum obtained from cisplatin treated or untreated tumour hosts at early or late tumour-bearing stages and cell survival was estimated. It was observed that tumour serum and ascitic fluid showed a tumour stage-dependent differential ability to regulate tumour cell survival and susceptibility of the tumour cells to the cytotoxic action of cisplatin. A tumour stage-dependent qualitative and quantitative difference in the profile of cell survival regulating cytokines: IL-1, IL-2, IFN-γ, TNF-α, VEGF and TGF-β in the ascitic fluid and serum of the tumour-bearing host was observed to be associated with a tumour stage-dependent differential regulation of survival of tumour cells by modulation in the expression of growth regulating proteins: IL-2R, p53, CAD, Hsp70 and Bcl-2. Further the result also showed that production of IL-1, TNF-α, and NO by macrophages could be implicated in the differential action of tumour sera on the altered survival responses of tumour cells depending on the stage of tumour growth. Possible mechanisms involved in the tumour stage-dependent differential survival response of tumour cells and evolution of drug resistance are discussed. The finding of this investigation will have clinical implications in designing of therapeutic strategies for T cell lymphoma based on manipulation of tumour growth regulatory mediators present in the tumour microenvironment. © 2008 Elsevier Ltd. All rights reserved.
Acoustically induced forbidden electromagnetic band gaps
(Springer, 2023) Suraj Prakash; Souryadipta Maiti; Gaurav Sharma; Vivek Singh
Lamb wave’s perturbation effect on electromagnetic modes propagating in Y − X lithium niobate slab is theoretically investigated. Rayleigh Lamb dispersion curves are estimated to investigate the behaviour of Lamb waves in micrometer order thick slab. Utilizing the information obtained from dispersion curves, acoustic displacement patterns and strain generated along the plate are evaluated. The modification caused to the refractive index of lithium niobate due to Lamb wave induced strain with photoelastic effect is determined. Further, the features of acoustically modified refractive index are examined using the transfer matrix method. It is found that an acoustically modified refractive index offers forbidden electromagnetic band gaps that can be adjusted by tuning the frequency of Lamb waves and by changing the incidence angle of electromagnetic waves. Hence proposed structure is used as a dynamically tunable photonic crystal for various applications like optical filters and optical switches. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Acoustically tunable photonic band gap generation in MgO doped Lithium Niobate micro-dimension plate
(Academic Press, 2018) Suraj Prakash; Gaurav Sharma; Gulab Chand Yadav; Vivek Singh
Refractive index contrast generation in MgO doped LiNbO3 plate via Lamb wave perturbation for induction of acoustically tunable photonic band gap is theoretically studied. Fundamental symmetric Lamb mode is excited in micro dimension thin plate structure to produce symmetric disturbance for periodic contraction and rarefaction along the length of plate. Effect of contraction and rarefaction on production of refractive index contrast is studied using photo–elastic effect. The generated quasi static low–high optical index region in plate modifies electromagnetic wave propagation and provides photonic band gaps, which are investigated using Bloch's theorem and transfer matrix method. The induced photonic band gap shows great dependency on optical contrast and unit cell dimension created by acoustic frequencies. These acoustically tunable photonic band gaps have rewarding applications in acousto optical devices, laser and sophisticated sensing. © 2018 Elsevier Ltd
Addressing stresses in agriculture through bio-priming intervention
(Springer Singapore, 2018) Deepranjan Sarkar; Sumita Pal; M. Mehjabeen; Vivek Singh; Sonam Singh; Subhadip Pul; Jancy Garg; Amitava Rakshit; H.B. Singh
Concurrent occurrences of different stresses, i.e. biotic and abiotic, are very common in the environment of plants which consequently reduce yield. As cost-effective options are very limited, bio-priming is a suitable tool to address the numerous challenges associated with agriculture. Plant growth benefits are easily attainable through this technique while managing the natural resources and enhancing the environmental sustainability. © Springer Nature Singapore Pte Ltd. 2018. All rights reserved.
An analytical study of a doubly clad compressed ellipse optical waveguide
(2014) S.P. Singh; R. Jatan; R. Janma; B.D. Singh; Vivek Singh; M.P.S. Rao
Using an analytical method based on boundary matching technique, the modal behavior and cutoff frequencies of a compressed ellipse doubly clad optical waveguide is studied. The proposed waveguide consists of a core region of higher refractive index with two cladding regions: one is inner cladding and the other is outer cladding. We take appropriate orthogonal coordinates for the proposed structure and impose the boundary conditions to obtain the characteristic equation. The effect of the width of inner cladding layer on the dispersion characteristic is observed. It is found that the width of inner cladding is able to tailor the dispersion characteristic and cutoff condition of the waveguide up to a certain limit. © 2013 Elsevier GmbH.
Analysis of Bragg fiber waveguides having a defect layer for biosensing application
(Elsevier GmbH, 2020) Ritesh Kumar Chourasia; Chandan Singh Yadav; Abhishek Upadhyay; Nitesh Kumar Chourasia; Vivek Singh
A novel hollow core Bragg fiber waveguides having a defect layer are proposed and analyzed theoretically for sensing application. Matching the electric and magnetic fields at various interfaces, a relation between fields of first layer with final layer has been stabilized; hence, the equations for reflectance and transmittance of proposed structure are derived. Due to periodicity of concentric cylindrical structure, a perfect photonic band gap is observed in considered wavelength range. The presence of defect layer in cylindrical periodic structure shows a peak corresponding to defect mode in perfect photonic band gap region. The full width at half maxima of this peak depends on the periodicity of the cladding layers. Also, the spectral position and shift of peak of defect mode depend on the angle of incidence of light, refractive index of core material and design wavelength of structure. Therefore, it is more appropriate to consider this peak of defect mode as sensing signal instead of considering whole photonic band gap as sensing signal. © 2019 Elsevier GmbH
Analysis of dispersion relation of the elliptical dielectric waveguides having M-type refractive index profile
(2013) Y. Prajapati; Vivek Singh; J.P. Saini
The propagation of electromagnetic wave in elliptical waveguide having M-type refractive index profiles is investigated. The considered waveguide consists of an elliptical core which lies between inner cladding region and outer cladding region and it is known as annular waveguide. The possible modes for this structure are numerically calculated by solving a dispersion relation, which is expressed in terms of Mathieu functions. The finding results of this waveguide are compared with another similar waveguide having inner cladding regions filled with air. It is observed that the cutoff V-values shifted toward lower frequency when the inner cladding region is filled with air. © 2012 Elsevier GmbH.
Analysis of reflection spectrum of uniform fiber bragg grating having air holes in the cladding
(International Academy of Microwave and Optical Technology (IAMOT), 2020) M. P. Srinivasa Rao; Vivek Singh
The reflection spectrum of fiber Bragg grating mainly depends on grating length, change in refractive index and profile of the refractive index. In this paper, we propose a uniform fiber Bragg grating having air holes in the cladding to study the reflection spectrum. The air filling fraction of the air holes can affect the reflection spectrum. Fully vectorial effective index method and coupled mode theories are used to analyze the proposed Bragg grating. The results show that the change in air filling fraction affect the reflectivity, full width at half maximum, side lobe strength, group time delay and dispersion. It is concluded that air filling fraction can be used as one of the design parameters of fiber Bragg gratings in practical applications. © 2020 IAMOT.
Analytical solution of the scalar wave equation for slightly deformed optical Bragg waveguide
(2013) Y. Prajapati; J.P. Saini; D.S. Chauhan; Vivek Singh
Using a simple analytical method, we study the electromagnetic-wave propagation in an optical Bragg waveguide which is slightly deformed at one side. We show the results of computations in the form of dispersion curves and provide a comparison with standard circular Bragg waveguides and step-index circular waveguides. We show that the correspondence between the cutoff V values for the standard step-index fiber and the new Bragg waveguide, which is slightly flattened on one side, is quite close for the lowest mode under the weak guidance condition. © 2013 Springer Science+Business Media New York.
Biochemical and histochemical analyses revealing endophytic Alcaligenes faecalis mediated suppression of oxidative stress in Abelmoschus esculentus challenged with Sclerotium rolfsii
(Elsevier Masson SAS, 2016) Shatrupa Ray; Vivek Singh; Surendra Singh; Birinchi Kumar Sarma; Harikesh Bahadur Singh
Sclerotium rolfsii is a highly aggressive pathogen that causes huge economic losses, especially in temperate climates. Alcaligenes faecalis, particularly in endophytic form, has rarely been used to control this fungus. In this study, endophytic Alcaligenes sp. strain BHU 12, BHU 16 (isolated from Abelmoschus esculentus leaf) and BHU M7 (isolated from Andrographis paniculata leaf) were reported to trigger a wide range of host defenses in Okra plant against the collar-rot pathogen S. rolfsii. Endophytic colonization of the strains in ten days old plants was assessed through re-isolation of the rif-tagged strains on rifampicin augmented nutrient agar media. The ability of the endophytic strains to induce systemic defense responses in above-ground organs was assessed by collecting leaf tissues of the Okra plants grown under non-gnotobiotic conditions at different time intervals post seedling bacterization with the endophytic biocontrol agents. The pathogen challenged unprimed plants exhibited flaccidity of the stem and leaves at 48 h post infection (hpi) in contrast to the bioprimed and challenged plants. Biochemical and histochemical analyses explained the above phenomenon as activation of phyto-peroxidases leading to an increased metabolism of the reactive oxygen species (ROS), accompanied by activation of the phenylpropanoid network and a subsequent enhancement in plant phenolics. Interestingly, though the maximum increase in the defense pathways was observed in treatments with native endophytes of Okra plant, yet the enhancement in antioxidant pathway due to A. paniculata borne endophytes was also quite significant. Thus, this work clearly demonstrates how Okra plants respond to the “non-hostile” colonization of bacterial endophytes and how induced defense response can contribute to the biocontrol activity of the endophytic strains. © 2016 Elsevier Masson SAS
Bragg fiber with a doubly defect layer-based tunable multiband optical filter
(The Optical Society, 2022) Chandan Singh Yadav; Abhishek Upadhyay; Sushil Kumar; Vivek Singh
A Bragg fiber waveguide having double-defect layers in its periodic cladding region is investigated and optimized for inline tunable multi-bandpass filter applications. The proposed waveguide is classified in terms of a symmetric waveguide and an asymmetric waveguide depending upon the refractive index of the defect layers. The required reflectance and confinement loss equations are obtained using the boundary matching technique and the transfer matrix method. Due to the presence of the double-defect layer, two sharp passbands in the bandgap region are observed. The separation of the passbands and their intensities can be controlled by introducing the number of unit cells between the defect layers. Our analysis shows that the passband’s intensity, bandwidth, and central wavelength can also be tuned by changing the refractive index of the core material. In addition, the central wavelength for both defect modes are blue shifted with the increase of the core refractive index. In all of our considered cases, the higher tunability with a core refractive index variation in the right defect mode is 25.38 nm/RIU for the symmetric cases having defect layer refractive indices of 1.45. Similarly, the higher tunability with a core refractive index variation in the left defect mode is 16.9 nm/RIU for the asymmetric cases having a refractive index of 1.45 in the first defect layer and 3.42 in the second defect layer. Hence, our proposed waveguide can work as a tunable multi-bandpass inline filter with a narrow bandwidth. © 2022 Optica Publishing Group.
Cell density-dependent alterations in tumorigenic potential of a murine T-cell lymphoma: Implication in the evolution of multidrug resistance in tumor cells
(2008) Vivek Singh; Mahendra Pal Singh; Sukh Mahendra Singh
We have previously demonstrated that cells of murine T-cell lymphoma, when grown in vivo or in vitro in an environment of high cell density, undergo phenotypic alterations, providing them with survival benefits. However, it is unclear whether the acquisition of such growth-related phenotypic alterations is inheritable in successive cell generations and if these alterations are associated with an irreversible alteration in their tumorigenic ability and evolution of multidrug resistance. To investigate this, tumor cells of a murine model of a T-cell lymphoma, designated as Daltons lymphoma, and obtained from high and low cell density environment in vitro and in vivo, were transplanted in mice with or without the administration of anticancer drugs followed by analysis of their phenotypic properties and tumorigenic potential as measured by kinetics of tumor growth and survival of the tumor-bearing host. Kinetics of tumor progression was comparatively rapid in tumor-bearing mice transplanted with tumor cells from a high cell density environment, causing an early death of the host. Moreover, under these conditions the antitumor response of anticancer drugs, cisplatin, doxorubicin, and methotrexate, was found to be less effective compared with mice transplanted with tumor cells from a low cell density environment. The tumor cells from a high cell density source showed a long-term alteration in their survival properties both in vitro and in vivo, indicating that such alterations were sustainable over successive cell cycles. The study also discusses the possible mechanisms indicating the role of MDR1, Hsp70 and 90, Bcl-2, IL-1, IL-6, IL-10, IFNγ, and TGFβ in the evolution of multidrug resistance in tumor cells obtained from a high cell density environment. © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins.
Common path interferometeric analysis of a planar polymer optical waveguide having adlayer of 2D materials for biosensing applications
(Springer, 2021) Abhishek Upadhyay; Chandan Singh Yadav; Gaurav Sharma; Sushil Kumar; Vivek Singh
Sensitivity of a planar polymer optical waveguide having adlayer of MoS2, WS2, MoSe2, WSe2 are estimated using common path Mach-Zehnder interferometer analyses. Dispersion relation and reflectivity equation of proposed waveguide is obtained by matching the electric and magnetic field at various boundaries. The obtained cutoff film thickness of the waveguide is approximately same in the presence of monolayer thickness of transition metal dichalcogenides materials. The cutoff film thickness 84.2 nm of this waveguide is approximately same for TE0, TM0 mode at wavelength 300 nm, these cutoff film thicknesses increases and become 304.6 nm at 1200 nm wavelength. In the proposed common path interferometer analysis, the superposition of TE0 and TM0 modes is considered as sensing signal. It is observed that the difference of their propagation constant is slightly decreased with increase of cover refractive index. Further the maximum phase change is obtained near the propagation constant maxima value hence around this value the output interference signal shows maximum shift with cover refractive index. In the considered wavelength range the maximum sensitivity 0.019 is obtained at wavelength 936nm, when a monolayer of WSe2 material is used as adlayer. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Comparative Analysis of ELM and Sparse Bayesian ELM for Healthcare Diagnosis
(Springer Science and Business Media Deutschland GmbH, 2024) Vivek Singh; Abhishek Pandey; Jyoti Singh Kirar
Extreme Learning Machine is a popular technique that became a center for research because of its easier implementation. It is s faster machine learning algorithm that has shown to have higher accuracy in various classification problems and has proven to be less time-consuming than traditional neural networks. But it also suffers from various drawbacks which are resolved with the help of the Bayesian paradigm along with the use of a Bayesian system known as Automatic Relevance Determination. We have tested how it performs on 3 different kinds of datasets. Various metrics are computed for all the 3 datasets and compared with the results from the conventional ELM. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Comparative analysis of silica fiber Bragg grating and chalcogenide fiber Bragg grating
(Elsevier Ltd, 2021) Souryadipta Maiti; Vivek Singh
Sensing performance of silica fiber Bragg grating (FBG) and chalcogenide FBG are compared in presence of apodization functions. The Bessel and Gaussian apodization functions are chosen in this analysis. These fibers are compared on the basis of their sensitivity, detection accuracy, quality parameter and sidelobe suppression ability. Reflectivity equations established from couple modes equations by matching fields at interfaces. For considered apodization profiles, it is observed that the sidelobe suppression ability and sensitivities are nearly same in both chalcogenide and silica fiber Bragg grating. Chalcogenide-based fiber Bragg grating with Bessel apodization function have narrower full width half maxima (FWHM) value that's why its detection accuracy and quality parameter is maximum in comparison of other considered cases. Hence for sensing application purpose chalcogenide-based fiber Bragg grating in presence of Bessel apodization function is appropriate. © 2021 Elsevier Ltd. All rights reserved.
Comparative analysis of the dispersion characteristic of Bragg fibers having different refractive index contrast
(Optica Publishing Group (formerly OSA), 2016) Ritesh Kumar Chourasia; Vivek Singh
Dispersion characteristics of two Bragg fibers are compared. By matching the Henkel function and its derivative at various boundaries dispersion equations are obtained. In this study the high contrast waveguide guided larger number of modes. © OSA 2016.
Comparative study of defect mode intensity and wavelength modulation in Bragg fiber waveguide sensors
(Elsevier GmbH, 2020) Ritesh Kumar Chourasia; Chandan Singh Yadav; Abhishek Upadhyay; Nitesh K. Chourasia; Vivek Singh
Sensing parameters of Bragg fiber waveguides having a defect layer in the cladding region are studied theoretically for bio-sensing and thickness monitoring applications. A comparison between Bragg fiber waveguides consist of a liquid-core surrounded with alternate high refractive index (R.I.) contrast of claddings and low R.I. contrast of claddings is presented. In non-homogeneous multilayer cylindrical system, the transmittance of proposed waveguide-based sensors is formulated using transfer matrix method and Hankel formalism. Both considered structures show photonic bandgap with a narrow passband in the bandgap region. This narrow passband is treated as sensing signal because its position and intensity depends on the diameter and refractive index of core material. The high refractive index contrast cladding waveguide shows larger intensity shift than low refractive index contrast cladding waveguide. The presence of defect layer in both considered waveguides is able to increase the sensing parameters like detection accuracy and overall performance. © 2020 Elsevier GmbH