Browsing by Author "Pankaj Kumar Tripathi"

Now showing 1 - 18 of 18

An Extensive Investigation on Lyapunov Optimization-based Task Offloading Techniques in Multi-access Edge Computing
(Springer, 2025) Vandna Rani Verma; Pushkar; Bablu Kumar; Anshul Verma; Vishnu Sharma; Pankaj Kumar Tripathi
Technological advancements have heightened the demand for real-time applications with minimal energy consumption on resource-constrained devices, often facing storage, computational power, and battery life limitations. Multi-access edge computing mitigates these challenges by offloading data and computational tasks to nearby edge servers, improving task execution efficiency. Despite the progress in task-offloading techniques, real-time processing and energy consumption issues remain. Lyapunov optimization offers a promising approach to address these challenges by optimizing task allocation and resource management in dynamic environments. This paper provides a comprehensive review of task offloading techniques using Lyapunov optimization, focusing on energy consumption and latency. It examines these techniques through classification, theoretical frameworks, and mathematical analyses, while also detailing Lyapunov optimization algorithms, workflows, advantages, and metrics. The paper includes an in-depth comparative analysis of Lyapunov-based algorithms in the context of task offloading, highlighting their benefits and challenges. Finally, it identifies emerging research opportunities and suggests future directions based on recent advancements in the field. © The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2025.
Application of thermodynamic model to study the phase transition properties of surface stabilized ferroelectric liquid crystals
(Elsevier B.V., 2017) Shubha Singh; Pankaj Kumar Tripathi; Shri Singh
In this work, we have considered the application of thermodynamic model, as developed by us, to investigate, under electric field, the variation of relative temperature(T − Tc), where Tc represents Sm C* − Sm A* transition temperature, and spontaneous polarization with tilt angle of Sm C* phase near Sm A* − Sm C* phase transition in surface stabilized ferroelectric liquid crystals (SSFLCs). Based on the concept of Landau-de-Gennes formalism, the free-energy density of the system has been written as an expansion series in powers of relevant order parameters and their coupling terms. Adopting usual method, we have evaluated the values of spontaneous polarization (Ps) and relative temperature (T − Tc) as a function of tilt angle for seven SSFLCs materials. In case of materials exhibiting second-order transition a wide temperature variation in the tilt angle has clearly been observed. For materials showings first-order transition, the transition enthalpy has been found to be directly related to the Landu coefficient (b) associated with cubic power of orientational order parameter. We have found a close agreement between theory and experiment. © 2017 Elsevier B.V.
Dielectric and electro-optical properties of polymer-stabilized liquid crystal system
(Springer Verlag, 2016) Mukti Pande; Pankaj Kumar Tripathi; Abhishek Kumar Misra; Shashwati Manohar; Rajiv Manohar; Shri Singh
In this work, we report the results of dielectric and electro-optical properties as a function of temperature for both pure liquid crystal matrix and polymer-stabilized liquid crystal (PSLC). The threshold and saturation voltages have been determined from transmission–voltage curves. We have studied the polymer domains formation in PSLC with variation of concentration of polymer in liquid crystal matrix. It is observed that the dielectric anisotropy of PSLC is significantly influenced by the polar order present in the polymer domains environment. A delicate interplay between the orientational order of liquid crystal and polymeric domains determines the molecular orientations of PSLC with respect to the director of the LC system. © 2016, Springer-Verlag Berlin Heidelberg.
Dielectric and electro-optical properties of polymer-stabilized liquid crystal. II. Polymer PiBMA dispersed in MBBA
(Springer Verlag, 2016) Pankaj Kumar Tripathi; Mukti Pande; Shri Singh
In continuation of our earlier work (Pande et al. in Appl Phys A 122:217–226, 2016), we report the results of dielectric and electro-optical properties of pure MBBA and PSLC (polymer PiBMA dispersed in MBBA) systems. The polymer networks domains formed are found to be anisotropic and are oriented in the direction of electric field for both the planar and homeotropic alignment cells. The dielectric anisotropy, optical anisotropy, response time, threshold voltage, splay elastic constant and rotational viscosity were observed for both the LC and PSLC systems with electric field. The liquid crystal properties are affected significantly with increasing concentration of polymer in pure LC material. It has been observed that the polymer networks interaction plays a major role in changing the properties of PSLC system. The effect of dielectric loss and dielectric permittivity on both pure LC and PSLC systems is also discussed. © 2016, Springer-Verlag Berlin Heidelberg.
Dielectric Relaxation Spectroscopy of Liquid Crystal in Nematogenic Mesophase
(Taylor and Francis Inc., 2016) Pankaj Kumar Tripathi; Rajiv Manohar; Shri Singh
In the present study, we report the dielectric behavior of a high temperature nematic liquid crystal (NLC) in both the planar as well as homeotropic alignments. To understand the mechanism of such high temperature NLC, we have performed dielectric spectroscopy in frequency range 100 Hz to 10 MHz. The different dielectric parameters, viz., effective dielectric permittivity and dielectric anisotropy of the sample have been determined with the variation of frequency and temperature. It is found that the dielectric parameters depend on dipole moment and rotation of side chain of molecule. The phase transition of this high temperature NLC has been confirmed by the DSC study. © 2016 Taylor & Francis Group, LLC.
Dielectric Study of Multiwall Carbon Nanotube Dispersed Nematic Liquid Crystal Mixture
(Elsevier Ltd, 2018) Pankaj Kumar Tripathi; Anil Kumar; Kamal Kumar Pandey
In the present work, multiwall carbon nanotube dispersed/doped nematic liquid crystal mixture have been synthesized by ultrasonication technique and studied using dielectric spectroscopy tools in the frequency range of 10 kHz-40 MHz. We have observed that the dielectric permittivity, loss and relaxation frequency of a nematic liquid crystal (MBBA) are influenced by the presence of multiwall carbon nanotube as a function of frequency and temperature. The value of dielectric permittivity increases with the dispersion of multiwall carbon nanotube due to π-π interaction of MWCNT and LC molecules. However, an increase in relaxation frequency is also found in dispersed samples. The MWCNT with almost identical size within themselves are dispersed at 0.5% concentration into nematic LC. The MWCNT-nematic LC composites are not only of fundamental importance, but also useful materials for device applications such as liquid crystal displays. © 2018 Elsevier Ltd.
Effect of UV light irradiation on the dielectric behaviour of liquid crystal/nano composite
(Taylor and Francis Inc., 2017) Kamal Kumar Pandey; Alok Chandra Dixit; M. Saleem khan; Pankaj Kumar Tripathi; Abhishek Kumar Misra; Rajiv Manohar
In this work, we investigate the effect of UV light irradiation on the dielectric parameters of the nematic liquid crystal (5CB) containing dispersed ZnO nanoparticles. With addition of nanoparticles, nematic LC's are promising new materials for a variety of applications in energy harvesting, displays and photonics including the liquid crystal laser. To realize many applications, however one must optimize the properties of liquid crystal and understand how UV light irradiation interacts with the nanoparticles and LC molecules in dispersed/doped LC. The dielectric permittivity and loss factor are discussed for the pure nematic LC and dispersed/doped system after, during and before UV light exposure. Dielectric relaxation spectroscopy was carried out in the frequency range 100 Hz-10 MHz in the nematic mesophase. © 2017 Taylor & Francis Group, LLC.
Electro-optic switching and memory effect in suspension of ferroelectric liquid crystal and iron oxide nanoparticles
(Institute of Physics Publishing, 2019) Abhishek Kumar Misra; Pankaj Kumar Tripathi; Kamal Kumar Pandey; Fanindra Pati Pandey; Shri Singh; Abhilasha Singh
In this work, impact of dispersion of iron oxide nanoparticles (Fe2O3 NPs) into ferroelectric liquid crystal (FLC) SCE-13 mixture on the electro-optical and dielectric properties has been studied. It has been found that the dispersion of Fe2O3 NPs in host FLC matrix exhibits pronounced influence on response time, spontaneous polarization, rotational viscosity and voltage required for switching the FLC molecules. Also dispersed system shows memory effect as confirmed by the optical texture and dielectric permittivity studies. Effort has been made to explain the experimental results as for as possible. © 2019 IOP Publishing Ltd.
Enhancement of birefringence of liquid crystals with dispersion of poly (n-butyl methacrylate) (PBMA)
(Taylor and Francis Ltd., 2015) Mukti Pande; Pankaj Kumar Tripathi; Swadesh Kumar Gupta; Rajiv Manohar; Shri Singh
In this work, we have reported the temperature dependence of birefringence for pure liquid crystals (LCs) and liquid crystal-polymer composite (LC-PC) systems. The enhancement of the electro-optical performances is higher in LC with poly (n-butyl methacrylate) polymer. The temperature dependence of the birefringence (Δn) were determined from the transmitted intensity. Dielectric study of pure LC system and LC-PC system has also been presented as a function of frequency. The observed results may be attributed to the occurrence of polymeric domains (chains) formed in LCs. The complete study reveals that the use of polymeric materials in nematic LCs is effective to improve the response in phase shifters devices. © 2015 Taylor & Francis.
Exploring a solid polymorphism and phase transitions in 4-cyano-4′-pentylbiphenyl (5CB) and rGO-doped 5CB using temperature dependent Raman spectroscopy
(Elsevier B.V., 2025) Ummer Bashir Khoja; Chandan Bhai Patel; Pankaj Kumar Tripathi; Rajesh Kumar; Soni Mishra; Sachin Kumar Singh; Ranjan Kumar Singh; Kunwar Vikram
Raman spectroscopy is used to examine the temperature-dependent phase transition behaviour of the liquid crystalline system 4-cyano-4′-pentylbiphenyl (5CB) and its nanocomposite with reduced graphene oxide (5CB@rGO) over the temperature range of −160 °C to 90 °C. First time, such a broad temperature range study of 5CB and 5CB@rGO has been reported. The structural and intermolecular interaction characteristics of the liquid crystal 5CB and its behaviour in the presence of reduced graphene oxide (rGO) are examined in depth by the temperature-induced Raman spectra and DFT calculations. To assess the phase transitions in 5CB and 5CB@rGO, the significant bands associated with the polar C[tbnd]N group and phenyl rings were thoroughly examined. A new crystal-crystal (solid polymorphism) phase transition is investigated first time, occurring between −120 °C and −100 °C. Another significant new crystal-crystal phase transition in 5CB and 5CB@rGO is also exposed, taking place between −20 °C and −10 °C. Differential scanning calorimeter (DSC) measurements confirm this new phase transition in 5CB and temperature sensitivity fairly matches Raman analysis. To evaluate the structural as well as change in intermolecular interactions in each phase, the detailed DFT study is performed on the 5CB molecule to establish the spectra-structure relation. The detailed spectra-structure correlation is discussed in this study. The spectra-structure correlation and change in spectral parameters are used to investigate the structure and intermolecular interaction of each phase. © 2025 Elsevier B.V.
Exploring the photoluminescence behavior of antiferroelectric liquid crystals through graphene oxide dispersion
(Elsevier B.V., 2025) Shishir Shukla; Pankaj Kumar Tripathi; Ayushi Rastogi; Ehsan Shakerzadeh; Vijay Singh; V. K. Mishra; Thakur Prasad Yadav; Mithlesh Tiwari; Abhishek Kumar Misra
The photoluminescence properties of antiferroelectric liquid crystal (AFLC) dispersed with graphene oxide (GO) were studied. AFLC-based composites were prepared by dispersing various weight concentrations (0.1 % and 0.3 % wt./wt.) of GO into AFLC. UV absorbance studies were performed using spectrum, time scan, and overlay modes. The decrease in UV absorbance was observed in all of these modes. Red shifts in absorbance bands were observed for both pure AFLC sample and GO/AFLC composite. The UV absorbance maxima for AFLC dispersed with GO shifted from 317.27 nm to 324.57 nm. This shift was attributed to the varying concentrations of GO in the AFLC medium. A significant improvement in the luminescence intensity of AFLC dispersed with GO nanoparticles mixtures was observed. The luminescence intensity increased from 0.3 (pure AFLC) to 1.0 (0.3 % wt./wt.). Furthermore, the luminescence intensity of the AFLC mixture was observed to increase with the concentration of GO for the fixed weight of the AFLC sample. © 2025 Korean Physical Society
Fluorescent dye doped ferroelectric liquid crystal: An anchoring energy, electro-optical and fluorescence study
(Elsevier B.V., 2016) Abhishek Kumar Misra; Pankaj Kumar Tripathi; Rajiv Manohar
In this study anchoring energy parameters, electro-optical (E-O) study along with UV absorption and fluorescence study have been performed for pure ferroelectric liquid crystal (FLC) and three different concentrations i.e. 1%, 3% and 5% of fluorescent dye in pure FLC. The UV absorption has been shifted towards lower frequency side for fluorescent dye doped system in comparison to the pure FLC. Excitation wavelength, emission wavelength and quantum yield have been determined for all the mixtures from fluorescence study. Anchoring energy parameters, spontaneous polarization and response time have been determined by E-O study. The values of these parameters are strongly changed by the concentration of fluorescent dye. © 2015 Elsevier B.V.
Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal
(Taylor and Francis Ltd., 2018) Pankaj Kumar Tripathi; Satya Prakash Yadav; Shri Singh
The present work concerns with the investigation of the effect of dispersion of Silica (SiO2) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO2 NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO2 NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation Ps and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions. © 2017 Informa UK Limited, trading as Taylor & Francis Group.
Investigation of phase transition in the binary mixture of thermotropic liquid crystalline systems 4-(Heptylox) benzoic acid and 4-(Undecyloxy) benzoic acid using Raman and DFT studies
(Elsevier B.V., 2023) Chandan Bhai Patel; K. Vikram; Pankaj Kumar Tripathi; Rajib Nandi; K. Ummer; Shashank Shekhar; Ranjana Singh; Ranjan K. Singh
A binary mixture Uba@Hba of liquid crystalline systems; 4-(Undecyloxy) benzoic acid and 4-(Heptylox) benzoic acid was prepared, and their liquid crystalline properties were investigated through differential scanning calorimetry and polarized optical microscopy at the bulk level and temperature dependent Raman spectroscopic technique as well as density functional calculations at molecular level. The polarized optical microscopic studies revealed crystal, smectic A, nematic and isotropic phases in the Uba@Hba. The phase transition temperatures of the binary mixture Uba@Hba was identified by the temperature dependent Raman study which was found almost close to phase transitions observed in differential scanning calorimetry and polarized optical microscopy. The detailed Raman & DFT studies provide information occurring in phase transitions at molecular level. The changes in inter/intra-molecular interactions at crystal → smectic A and smectic A → nematic transitions have been discussed in detail. © 2023 Elsevier B.V.
Molecular geometries, vibrational spectra and electronic properties of biphenyl nematic liquid crystals: a quantum chemical analysis
(Taylor and Francis Ltd., 2023) Nagendra Prasad Yadav; Anil Kumar Vishwkarma; Ajit Kumar Maddheshiya; Tarun Yadav; Srikanta Moharana; Rajneesh Kumar; Amit Pathak; Pankaj Kumar Tripathi
The present work reports the vibrational spectroscopic signature, thermodynamics, and natural bond orbital analysis (NBO) of 4-Cyano-4-pentylbiphenyl (5CB) and 4-Cyano-4'-hexyl diphenyl (6CB) liquid crystals. The optimization of both compounds (5CB and 6CB) has been performed at DFT/B3LYP/6-31++G(d, p) level of theory. Most of the vibrational modes have wavenumbers in the expected range. The comparison of vibrational frequencies of both compounds has been made. Subsequently, the different thermodynamical parameters and electronic properties have been calculated and discussed in detail. The NBO analysis has been performed to check the stability of the electronic structures. The UV visible, HOMO- LUMO, MEP, and charge analysis has been performed. Moreover, the strong electronic transition from HOMO to LUMO (97% of MO contribution) has been predicted for 5CB and 6CB at 289 nm with oscillator strengths of 0.7242 and 0.7286, respectively. The MEP plots of both 5CB and 6CB are almost the same and show that strong electrophilic substitution would take place near the N atom attached to the CN group. The energy gap of 5CB and 6CB compounds is found to be 4.65eV. Molecules with large energy gaps are less polarizable and are termed as hard molecules, having low chemical reactivity and high kinetic stability. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Pristine and quantum dots dispersed nematic liquid crystal: Impact of dispersion and applied voltage on dielectric and electro-optical properties
(Elsevier B.V., 2017) Pankaj Kumar Tripathi; Bipin Joshi; Shri Singh
In this work, we have dispersed Cd1-xZnxS/ZnS quantum dots (QDs) in nematic liquid crystal (LC) BBHA which shows negative dielectric anisotropy (Δε = −2.90) [1]. The impact of QDs dispersion, applied bias and concentration of QDs on the dielectric permittivity, dielectric loss, response time, transmittance and birefringence as a function of frequency and temperature for planar alignment has been studied. We have observed that dispersion of QDs in pure nematic LC influences these properties. Due to QDs dispersion the birefringence increases and this helps in the alignment and ordering of nematic molecules. Under applied bias the ionic contributions to the dielectric loss as observed in low frequency region are suppressed and the relaxation frequency is shifted towards higher frequency side. We have made an effort to explain the observed behaviour of pristine and dispersed systems on the basis of interactions between QDs and nematic molecules. © 2017
Structural investigations on nickel substituted zinc magnesium ferrites nanoparticles formed via co-precipitation method
(Elsevier B.V., 2024) Farhana Naaz; Preeti Lahiri; Vijay Kumar Mishra; Hemant Kumar Dubey; Pankaj Kumar Tripathi; Ehsan Shakerzadeh
The present study provides a comprehensive structural investigation on Mg0.5Zn0.5−xNixFe2O4 nano-ferrites. Nano-crystalline Mg0.5Zn0.5−xNixFe2O4 (x = 0.0,0.1,0.2,0.3,0.4) powder samples were synthesized using co-precipitation process followed by calcinations at 600 °C for 6 h. The purity and phase of thus prepared samples were confirmed using X-ray Diffraction, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy techniques. The average crystallite size, determined using the Debye-Scherrer method, was estimated to be between 17 and 26 nm. The average particle size ranged from 26.9 nm to 13.1 nm. It was evident that as the nickel concentration increases in Mg-Zn-Ni ferrite, the average grain size decreases from 26.1 nm to 10.9 nm, indicating denser samples with higher nickel concentrations. The ferrites were found to be porous and at the nanoscale, with sizes less than 30 nm. Raman studies supported the presence of iron-oxide phases, confirming the spinel structure with tetrahedrally and octahedrally occupied iron sites. The low coercivity (Hc) values observed in the hysteresis loops indicate soft magnetic characteristics for all samples. This is advantageous for applications in recording heads, inductor and transformer cores, magnetic shielding, the high-frequency range, particularly in deflection yoke rings, microwave devices, and drug delivery. © 2024 Elsevier B.V.
Structural Modeling, Spectroscopic Signature and NBO Analysis of Octopamine and Its Radical
(John Wiley and Sons Inc, 2024) Nagendra Yadav; Tarun Yadav; Anil Kumar Vishwkarma; Subhendu Chakroborty; Pankaj Kumar Tripathi; Fanindra Pati Pandey; Amit Pathak; Mariyam Ansari
The present communication deals with theoretical vibrational spectroscopic signature (IR and Raman) of octopamine molecule and its radical. All theoretical calculations for octopamine and its radical are performed at DFT/B3LYP/6-31++G (d, p) level. Besides, the vibrational frequencies of these two structures has been compared. Most of the vibrational frequencies agree well with experimental ones. It has been documented how the geometrical characteristics and vibrational frequencies of octopamine are affected when hydrogen is removed from the oxygen atom's site. The HOMO-LUMO energy gap in the case of neutral form of octopamine is computed to be 5.42 eV while for deprotonated octopamine this gap has been increased by 0.78 eV. The NBO analysis is also performed to ensure stability of radical of octopamine. The magnitude of occupancy at bonding orbitals within the 0.997–0.885e, and 0.996–0.885e range in octopamine and octopamine, respectively, is calculated. © 2024 Wiley-VCH GmbH.