71. Generalized Theory of Thermal Conductivity for Different Media: Solids to NanofluidsSANKARARAMAN S, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2019, izvirni znanstveni članek Opis: The advent of nanotechnology in the 21st
century opened a new branch of nanoscience known as
nanofluids, finding a wide range of industrial applications
especially in heat transfer. Though the theory of thermal
conductivity of solids is well established, there is no such
conclusive model to explain the thermal conductivity of
nanofluids. In the present work we propose a generalized
theory for thermal conductivity applicable to materials ranging
from heterogeneous solids, porous materials, nanofluids, and
ferrofluids. The model could explain the effective thermal
conductivity of not only the combination of solids but also
solid−fluid mixtures. The proposed theory could successfully
link the existing models for porous solid materials and
nanofluids as its special cases. The proposed model is verified against experimental data by simulating the theoretical equations Ključne besede: thermal conductivity, generalised model, Sankar-Loeb model Objavljeno: 05.07.2022; Ogledov: 126; Prenosov: 0
Polno besedilo (3,99 MB) |
72. Time series analysis of duty cycle induced randomness in thermal lens systemSWAPNA MOHANACHANDRAN NAIR SINDHU, 2020, izvirni znanstveni članek Opis: The present work employs time series analysis, a proven powerful mathematical tool, for investigating the complex molecular dynamics of the thermal lens (TL) system induced by the duty
cycle (C) variation. For intensity modulation, TL spectroscopy commonly uses optical choppers.
The TL formation involves complex molecular dynamics that vary with the input photothermal
energy, which is implemented by varying the duty cycle of the chopper. The molecular dynamics
is studied from the fractal dimension (D), phase portrait, sample entropy (S), and Hurst exponent
(H) for different duty cycles. The increasing value of C is found to increase D and S, indicating
that the system is becoming complex and less deterministic, as evidenced by the phase portrait
analysis. The value of H less than 0.5 conforms the evolution of the TL system to more antipersistent nature with C. The increasing value of C increases the enthalpy of the system that
appears as an increase in full width at half maximum of the refractive index profile. Thus the
study establishes that the sample entropy and thermodynamic entropy are directly related. Ključne besede: Time series analysis
Fractal analysis
Photothermal lens spectroscopy
Fractal dimension
Hurst exponent
Sample entropy Objavljeno: 05.07.2022; Ogledov: 92; Prenosov: 0
Polno besedilo (1,30 MB) |
73. Cost-effective Green Synthesis of Boron rich Carbide Coatings for IR Windows and Night Vision OpticsSWAPNA MOHANACHANDRAN NAIR SINDHU, 2020, izvirni znanstveni članek Opis: The increasing demand for infrared (IR) window materials for various applications
in optical imaging systems necessitates the development of cost-effective green
techniques. Herein, the synthesis of refractory boron carbide (BC) using castor oil,
as carbon precursor, and the preparation of IR transparent films by thermal vapor
deposition technique is reported. Films are prepared with 1:3, 1:4, and 1:5 ratios of
boric acid and castor oil, respectively. The X-ray diffraction (XRD) and Fouriertransform IR (FTIR) analyses reveal the structure of films prepared to be BC. The
morphology of the films is analyzed by the atomic force microscopy (AFM) technique, and its dependence on precursor’s ratio is also studied. The spectroscopic
characterization by the ultraviolet–visible–near IR (UV–vis–NIR) transmittance
study reveals the potential of the films for IR window applications. The bandgap
energy of the BC films determined from the Tauc plot yields a value of 2.33 eV. The
absorption coefficient, extinction coefficient, refractive index, dissipation factor, and
optical conductivity are also studied from the reflectance and transmittance data. Ključne besede: Green Synthesis, Boron rich Carbide, coatings, IR Windows Objavljeno: 05.07.2022; Ogledov: 78; Prenosov: 0
Polno besedilo (1,49 MB) |
74. Phase Portrait for High Fidelity Feature Extraction and Classification: A Surrogate ApproachSWAPNA MOHANACHANDRAN NAIR SINDHU, 2020, izvirni znanstveni članek Opis: This paper proposes a novel surrogate method of classification of breath sound signals for auscultation through the principal component
analysis (PCA), extracting the features of a phase portrait. The nonlinear parameters of the phase portrait like the Lyapunov exponent, the
sample entropy, the fractal dimension, and the Hurst exponent help in understanding the degree of complexity arising due to the turbulence
of air molecules in the airways of the lungs. Thirty-nine breath sound signals of bronchial breath (BB) and pleural rub (PR) are studied
through spectral, fractal, and phase portrait analyses. The fast Fourier transform and wavelet analyses show a lesser number of high-intense,
low-frequency components in PR, unlike BB. The fractal dimension and sample entropy values for PR are, respectively, 1.772 and 1.041, while
those for BB are 1.801 and 1.331, respectively. This study reveals that the BB signal is more complex and random, as evidenced by the fractal
dimension and sample entropy values. The signals are classified by PCA based on the features extracted from the power spectral density (PSD)
data and the features of the phase portrait. The PCA based on the features of the phase portrait considers the temporal correlation of the signal
amplitudes and that based on the PSD data considers only the signal amplitudes, suggesting that the former method is better than the latter
as it reflects the multidimensional aspects of the signal. This appears in the PCA-based classification as 89.6% for BB, a higher variance than
the 80.5% for the PR signal, suggesting the higher fidelity of the phase portrait-based classification. Ključne besede: Phase Portrait, time series, feature extraction, pleural rub Objavljeno: 05.07.2022; Ogledov: 102; Prenosov: 0
Polno besedilo (2,47 MB) |
75. Speckle interferometric investigation of argon pressure-induced surface roughness modifications in RF-sputtered MoO[sub]3 filmS. Soumya, R. Arun Kumar, S. Sreejyothi, Vimal Raj, Mohanachandran Nair Sindhu Swapna, Sankaranarayana Iyer Sankararaman, 2021, izvirni znanstveni članek Opis: Film quality analysis is of more considerable signifcance due to its diversifed applications in various felds of technology.
The present work reports the speckle interferometric analysis of the argon pressure-induced surface roughness modifcations
of RF sputtered MoO3 flms. The paper suggests a new method of surface quality analysis of thin flms through a parameter
δ, which is the diference between the initial and fnal inertia moment values in the study of the thermal-induced dynamic
speckle pattern. The limitations of root mean square surface roughness analysis of the atomic force microscopic image of the
flms is also exemplifed. The research suggests that argon pressure plays a vital role in the surface property of RF sputtered
flms and also that the dynamic speckle analysis can give precise information about the quality of flms. The contour plot of
particle displacement vector under thermal stress, suggests the degree of uniformity in the distribution of particles in the flm. Ključne besede: speckle pattern interferometry, time history of speckle pattern, cross correlation, inertia moment Objavljeno: 04.07.2022; Ogledov: 117; Prenosov: 0
Polno besedilo (10,20 MB) |
76. Hidden periodicity in Stripe 82 with Saraswati supercluster—a fractal analysisVimal Raj, Mohanachandran Nair Sindhu Swapna, Sankaranarayana Iyer Sankararaman, 2021, izvirni znanstveni članek Opis: The manuscript attempts to explore the periodicity in the distribution of galaxies in the recently
reported Saraswati supercluster and the Stripe 82 region containing it as an example. The report
of 120 Mpc periodicity in the Abell galaxy clusters by power spectrum analysis is the motivation
behind the study. The power spectral analysis across the central part of the Stripe 82 region
shows a periodic variation of 3.09° or 71 Mpc in fractal dimension whereas an average angular
periodicity of 3.45° or 94 Mpc is observed across the Stripe 82 region. This refers to the
periodicity of complexity or cluster density of galaxy distribution. The texture of the distribution
pattern understood through lacunarity analysis indicates a near symmetric distribution. Fractal
dimensions like box-counting dimension, information dimension and correlation dimension are
also found through multifractal analysis. While the information dimension tells about the
distribution density of galactic points, the correlation dimension details the distribution of
galaxies in the neighbourhood Ključne besede: galaxy distribution, fractal analysis, multifractals, lacunarity, Saraswati supercluster, Stripe 82 Objavljeno: 04.07.2022; Ogledov: 113; Prenosov: 0
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77. Thermal diffusivity downscaling of molybdenum oxide thin film through annealing temperature-induced nano-lamelle formation: a photothermal beam deflection studyS. Soumya, Vimal Raj, Mohanachandran Nair Sindhu Swapna, Sankaranarayana Iyer Sankararaman, 2021, izvirni znanstveni članek Opis: The present work proposes a method of downscaling the thermal diffusivity (α)
of MoO3 thin films through annealing temperature-induced nano-lamelle formation. The
thermal diffusivity modification of the MoO3 films, prepared by the doctor blade method,
is investigated by the sensitive transverse photothermal beam deflection technique. The Xray diffraction analysis confirms the structural phase transformation from monoclinic to
orthorhombic in the films annealed from 300 to 450 °C. The thermal induced anisotropy of
the film is evident from the variation of the morphology index and texture coefficient. The
field emission scanning electron microscopic analysis unveils the morphology modifications
from blocks to the nano-lamelle structure with layers of average thickness ~ 77 nm. The
thermal diffusivity measurement reveals a 53% reduction upon annealing the film to 450 °C.
The drastic reduction is achieved through the annealing temperature-induced nano-lamelle
formation and the phase transformation from monoclinic to orthorhombic in the MoO3 films. Ključne besede: thermal diffusivity, molybdenum oxide, thin film, nano-lamelle, photothermal beam deflection Objavljeno: 04.07.2022; Ogledov: 85; Prenosov: 3
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78. Concentration-dependent thermal duality of hafnium carbide nanofluid for heat transfer applicationsV. Gokul, Mohanachandran Nair Sindhu Swapna, Vimal Raj, H. V. Saritha Devi, Sankaranarayana Iyer Sankararaman, 2021, izvirni znanstveni članek Opis: he mode mismatch dual-beam thermal lens technique is a sensitive tool for studying the nanofuids’ thermal difusivity in thermal engineering. The work reports
the low-temperature green synthesis of hafnium carbide (HfC) using rice four as a
natural carbon precursor and its potential in heat transfer nanofuids by studying the
concentration-dependent thermal difusivity. The structure characterisations confrm
the formation of HfC, whose refractory nature is revealed through the high thermal
stability observed in the thermogravimetric analysis. The Tauc plot analysis shows
direct bandgap energy of 2.92 eV. The fuorescence study suggests bluish-pink emission with CIE coordinates (0.271, 0.263). The existence of the critical concentration
of HfC in the nanofuid decides its suitability for heat transfer or heat trap applications indicating a concentration-dependent thermal duality. Thus, the study is signifcant as it overcomes the major drawbacks of the existing methods of the synthesis of refractory HfC, using toxic chemical and costly equipment for heat transfer
applications. Ključne besede: hafnium carbide, hydrothermal synthesis, rice flour, thermal lens spectroscopy Objavljeno: 04.07.2022; Ogledov: 84; Prenosov: 0
Polno besedilo (1,50 MB) |
79. Boron carbide Nanowires from castor oil for optronic applications: A low-temperature greener approachSWAPNA MOHANACHANDRAN NAIR SINDHU, 2021, izvirni znanstveni članek Opis: The development of one-dimensional nanostructures has revolutionized electronic and photonic industries because of their unique properties. The present
paper reports the low-temperature green synthesis of boron carbide nanowires,
of diameter 14 nm and length 2 lm, by the condensation method using castor
oil as the carbon precursor. The nanowires synthesized exhibit beaded chain
morphology, and bandgap energy of 2.08 eV revealed through the Tauc plot
analysis. The structure of boron carbide nanowires is revealed by micro-Raman,
Fourier transform infrared spectroscopic, and X-ray diffraction analyses. The
thermogravimetric analysis of the sample reveals the excellent thermal stability.
The photoluminescence study reveals the nanowire’s blue light emission
capability under ultraviolet excitation, which is substantiated by the CIE plot
suggesting its potential in photonic applications. Ključne besede: Boron carbide, Nanowires, castor oil, green synthesis Objavljeno: 04.07.2022; Ogledov: 87; Prenosov: 0
Polno besedilo (1,56 MB) |
80. Thermal diffusivity of molybdenum oxide nanowire film: a photothermal beam deflection studySWAPNA MOHANACHANDRAN NAIR SINDHU, 2021, izvirni znanstveni članek Opis: The paper reports the preparation of thin film with MoO3 nanowires (NWs) by the doctor blade method and the
study of its thermal diffusivity (α) by the sensitive photothermal beam deflection (PTD) method. When the Field
Emission Scanning Electron Microscopic and Atomic Force Microscopic analysis unveil its morphology as NW
bundles, the X-ray diffraction analysis reveals the structure to be orthorhombic. The NWs formed are of diameter
~ 20 nm and length up to 5 μm. The standardization of the transverse PTD setup is done by determining the
value of α of iron, which agrees well with literature reports. The thermal diffusivity of MoO3 NW film is obtained
as 0.0036 cm2
/s, which is 9.48% of its bulk counterpart. The reduction in the thermal diffusivity of NW makes it
a suitable candidate for thermoelectric applications. Ključne besede: Nanowires
Molybdenum oxide
Photothermal beam deflection
Thermal diffusivity Objavljeno: 04.07.2022; Ogledov: 110; Prenosov: 0
Polno besedilo (3,64 MB) |