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1.
Thermal Lensing of Multi-Walled Carbon Nanotube Solutions as Heat-Transfer Nanofluids
SANKARARAMAN SANKARANARAYANA IYER, CABRERA HUMBERTO, RAJ VIMAL, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2021, izvirni znanstveni članek

Opis: This paper unwraps nanofluids’ particle dynamics with multi-walled carbon nanotubes (MWCNTs) in base fluids such as acetone, water, and ethylene glycol. Having confirmed the morphology and structure of the MWCNTs by field emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopic analyses, the nanofluids are prepared in three different concentrations. The nonzero absorbance at the laser wavelength, revealed through the UV−visible spectrum, makes the thermal diffusivity study of the sample by the sensitive nondestructive single beam thermal lens (TL) technique possible. The TL signal analysis by time series and fractal techniques divulges the complex particle dynamics, through phase portrait, sample entropy, fractal dimension, and Hurst exponent. The study unveils the effect of the amount of nanoparticles and the viscosity of the medium on thermal diffusivity and particle dynamics. The observed inverse relation between thermal diffusivity and viscosity is in good agreement with the Sankar−Swapna model. The complexity of particle dynamics in MWCNT nanofluids reflected through sample entropy, and fractal dimension shows an inverse relation to the base fluid’s viscosity. This paper investigates the role of viscosity of the base fluid on particle dynamics and thermal diffusivity of the nanofluid to explore its applicability in various thermal systems, thereby suggesting a method to tune the sample entropy through proper selection of base fluid.
Najdeno v: osebi
Ključne besede: MWCNT, thermal lens, fractals, nonlinear time series, phase portrait, sample entropy
Objavljeno: 28.06.2022; Ogledov: 147; Prenosov: 0
.pdf Polno besedilo (3,59 MB)

2.
Development of prototype of electronic speckle interferometry based spirometer
SANKARARAMAN SANKARANARAYANA IYER, RAJ VIMAL, SREEJYOTHI S, KUMAR SUNIL, KUMAR ARUN, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2021, izvirni znanstveni članek

Opis: The paper reports the design, construction, and calibration of the prototype of a spirometer based on electronic speckle interferometry (ESPI). The conventional ESPI setup is modified by incorporating a DNM (DiaphragmNozzle-Mouthpiece) module comprising a metallic diaphragm, regulated airflow channel, and a mouthpiece. The exhaled air after a deep breathe is channelled to the DNM module where the diaphragm gets deformed. From the circular fringe pattern obtained by subtracting the speckled images before and after deformation of the metallic diaphragm, the radius of curvature (R) due to deformation is calculated using the principle of Newton’s rings. The value of R and peak expiratory flow rate (PEFR) from the standard spirometer reading are correlated. From the 640 observations spread over the range 100 - 500 L/min in the standard spirometer, an empirical relation is set in terms of R from the scatter plot. The ESPI spirometer (ESPIS) is validated by determining the value of R corresponding to a particular PEFR from the empirical relation and also from the standard spirometer. The PEFR calculated from ESPIS matches well with the standard spirometer reading, which suggests that the system designed and constructed can be used for biomedical applications for assessing lungs’ efficiency.
Najdeno v: osebi
Ključne besede: Speckle, Spirometer, DNM module, ESPIS, Peak expiratory flow rate
Objavljeno: 28.06.2022; Ogledov: 96; Prenosov: 0
.pdf Polno besedilo (2,38 MB)

3.
Unravelling the potential of phase portrait in the auscultation of mitral valve dysfunction
SANKARARAMAN SANKARANARAYANA IYER, RAJ VIMAL, RENJINI A, SREEJYOTHI S, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2021, izvirni znanstveni članek

Opis: The manuscript elucidates the potential of phase portrait, fast Fourier transform, wavelet, and time-series analyses of the heart murmur (HM) of normal (healthy) and mitral regurgitation (MR) in the diagnosis of valve-related cardiovascular diseases. The temporal evolution study of phase portrait and the entropy analyses of HM unveil the valve dysfunctioninduced haemodynamics. A tenfold increase in sample entropy in MR from that of normal indicates the valve dysfunction. The occurrence of a large number of frequency components between lub and dub in MR, compared to the normal, is substantiated through the spectral analyses. The machine learning techniques, K-nearest neighbour, support vector machine, and principal component analyses give 100% predictive accuracy. Thus, the study suggests a surrogate method of auscultation of HM that can be employed cost-effectively in rural health centres.
Najdeno v: osebi
Ključne besede: phase portrait, auscultation, mitral valve dysfunction, heart murmur, nonlinear time series analysis
Objavljeno: 28.06.2022; Ogledov: 104; Prenosov: 0
.pdf Polno besedilo (2,02 MB)

4.
Soot effected sample entropy minimization in nanofluid for thermal system design
Sankaranarayana Iyer Sankararaman, K. Satheesh Kumar, Vimal Raj, Mohanachandran Nair Sindhu Swapna, 2020, izvirni znanstveni članek

Opis: The present work suggests a method of improving the thermal system efficiency, through entropy minimisation, and unveils the mechanism involved by analysing the molecular/particle dynamics in soot nanofluids (SNFs) using the time series, power spectrum, and wavelet analyses of the thermal lens signal (TLS). The photothermal energy deposition in the SNF lowers the refractive index due to the temperature rise. It triggers the particle dynamics that are investigated by segmenting the TLS and analysing the refractive index, phase portrait, fractal dimension (D), Hurst exponent (H), and sample entropy (SampEn). The wavelet analysis gives information about the relation between the entropy and the frequency components. When the phase portrait analysis reflects the complex dynamics from region 1 to 2 for all the samples, the SampEn analysis supports it. The decreasing value of D (from 1.59 of the base fluid to 1.55 and 1.52) and the SampEn (from 1.11 of the base fluid to 0.385 and 0.699) with the incorporation of diesel and camphor soot, indicate its ability to lower the complexity, randomness, and entropy. The increase of SampEn with photothermal energy deposition suggests its relation to the thermodynamic entropy (S). The lowering of thermal diffusivity value of the base fluid from 1.4 × 10−7 m2/s to 1.1 × 10−7 and 0.5 × 10−7 m2 /s upon diesel and camphor soot incorporation suggests the heat-trapping and reduced molecular dynamics in heat dissipation.
Najdeno v: osebi
Ključne besede: soot, entropy, thermal system, photothermal, time series, nanofluid, fractal
Objavljeno: 30.06.2022; Ogledov: 99; Prenosov: 0
.pdf Polno besedilo (2,27 MB)

5.
Downscaling of sample entropy of nanofluids by carbon allotropes
Sankaranarayana Iyer Sankararaman, K. Satheesh Kumar, S. Sreejyothi, Vimal Raj, Mohanachandran Nair Sindhu Swapna, 2020, izvirni znanstveni članek

Opis: The work reported in this paper is the first attempt to delineate the molecular or particle dynamics from the thermal lens signal of carbon allotropic nanofluids (CANs), employing time series and fractal analyses. The nanofluids of multi-walled carbon nanotubes and graphene are prepared in base fluid, coconut oil, at low volume fraction and are subjected to thermal lens study. We have studied the thermal diffusivity and refractive index variations of the medium by analyzing the thermal lens (TL) signal. By segmenting the TL signal, the complex dynamics involved during its evolution is investigated through the phase portrait, fractal dimension, Hurst exponent, and sample entropy using time series and fractal analyses. The study also explains how the increase of the photothermal energy turns a system into stochastic and antipersistent. The sample entropy (S) and refractive index analyses of the TL signal by segmenting into five regions reveal the evolution of S with the increase of enthalpy. The lowering of S in CAN along with its thermal diffusivity (50%–57% below) as a result of heat-trapping suggests the technique of downscaling sample entropy of the base fluid using carbon allotropes and thereby opening a novel method of improving the efficiency of thermal systems.
Najdeno v: osebi
Ključne besede: carbon allotropic nanofluids, time series, entropy, MWCNT, thermal lens signal
Objavljeno: 30.06.2022; Ogledov: 105; Prenosov: 0
.pdf Polno besedilo (4,22 MB)

6.
Time series and fractal analyses of wheezing
Sankaranarayana Iyer Sankararaman, S. Sreejyothi, Vimal Raj, A. Renjini, Mohanachandran Nair Sindhu Swapna, 2020, izvirni znanstveni članek

Opis: Since the outbreak of the pandemic Coronavirus Disease 2019, the world is in search of novel non-invasive methods for safer and early detection of lung diseases. The pulmonary pathological symptoms refected through the lung sound opens a possibility of detection through auscultation and of employing spectral, fractal, nonlinear time series and principal component analyses. Thirty-fve signals of vesicular and expiratory wheezing breath sound, subjected to spectral analyses shows a clear distinction in terms of time duration, intensity, and the number of frequency components. An investigation of the dynamics of air molecules during respiration using phase portrait, Lyapunov exponent, sample entropy, fractal dimension, and Hurst exponent helps in understanding the degree of complexity arising due to the presence of mucus secretions and constrictions in the respiratory airways. The feature extraction of the power spectral density data and the application of principal component analysis helps in distinguishing vesicular and expiratory wheezing and thereby, giving a ray of hope in accomplishing an early detection of pulmonary diseases through sound signal analysis.
Najdeno v: osebi
Ključne besede: auscultation, wheeze, fractals, nonlinear time series analysis, sample entropy
Objavljeno: 30.06.2022; Ogledov: 107; Prenosov: 0
.pdf Polno besedilo (2,46 MB)

7.
Ultralow duty cycle chopper instigated low power continuous wave laser assisted synthesis of silver nanoparticles
Sankaranarayana Iyer Sankararaman, V. P. N. Nampoori, R. A. Krishnanunni, A. S. Ashik, Mohanachandran Nair Sindhu Swapna, 2020, izvirni znanstveni članek

Opis: This paper is the first report of advancement in the drastic reduction of the laser power density from 105 to 7.5 W/cm2 for the synthesis of silver nanoparticles (SNPs) using a low power (60 mW) continuous-wave (cw) laser and a specially designed ultralow duty cycle (3%) optical chopper wheel for modulating the laser beam at low frequencies (2 Hz). The target is irradiated by keeping it in a liquid medium at 40–60 °C to produce quantum dots to SNPs of size less than 40 nm. The UV-visible spectroscopic and electron microscopic analyses confirm the formation of quantum dots and SNPs of size-dependent bandgap energy varying from 1.92 to 2.37 eV. The photoluminescence studies not only support the above observations but also reveal the blue emission upon UV excitation through the chromaticity diagram. The proposed greener approach using the low power cw laser is cost-effective when compared with the high-power laser-assisted synthesis of SNPs reported until now.
Najdeno v: osebi
Ključne besede: cw laser, silver nanoparticle, ultralow duty cycle, chopper
Objavljeno: 30.06.2022; Ogledov: 120; Prenosov: 3
.pdf Polno besedilo (3,49 MB)
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8.
Is SARS CoV-2 a multifractal?
Sankaranarayana Iyer Sankararaman, Vimal Raj, S. Sreejyothi, Mohanachandran Nair Sindhu Swapna, 2021, izvirni znanstveni članek

Opis: A first report of unveiling the fractality and fractal nature of severe acute respiratory syndrome coronavirus (SARS CoV-2) responsible for the pandemic disease widely known as coronavirus disease 2019 (COVID 19) is presented. The fractal analysis of the electron microscopic and atomic force microscopic images of 40 coronaviruses (CoV), by the normal and differential boxcounting method, reveals its fractal structure. The generalised dimension indicates the multifractal nature of the CoV. The higher value of fractal dimension and lower value of Hurst exponent (H) suggest higher complexity and greater roughness. The statistical analysis of generalised dimension and H is understood through the notched box plot. The study on CoV clusters also confirms its fractal nature. The scale-invariant value of the box-counting fractal dimension of CoV yields a value of 1.820. The study opens the possibility of exploring the potential of fractal analysis in the medical diagnosis of SARS CoV-2.
Najdeno v: osebi
Ključne besede: Fractality, SARS CoV, Coronavirus, Fractal dimension, Multifractal
Objavljeno: 30.06.2022; Ogledov: 95; Prenosov: 0
.pdf Polno besedilo (1,48 MB)

9.
Boron‑rich boron carbide from soot
Sankaranarayana Iyer Sankararaman, H. V. Saritha Devi, Mohanachandran Nair Sindhu Swapna, 2020, izvirni znanstveni članek

Opis: Boron carbide is a promising super-hard semiconducting material for refractory applications ranging from the nuclear industry to spacecraft. The present work is the frst report of not only turning futile soot, containing carbon allotropes in varying composition, into boron-rich boron carbide (BC), but also developing it by a low-cost, low-temperature, and green synthesis method. The BC synthesised from gingelly oil soot is subjected to structural, morphological, and optical characterisations. The feld emission scanning electron microscope shows beautiful fower-like morphology, and the thermogravimetric analysis reveals the high-temperature stability of the sample synthesised. The Tauc plot of the sample indicates a 2.38 eV direct bandgap. The formation of BC and boron-rich carbide evidenced by X-ray difraction studies is confrmed through Raman and Fourier transform infrared spectroscopic signatures of B–C and C–B–C bonds. The fuorescence, power spectrum, and CIE analyses carried out suggest the blue light emission for excitation at 350 nm
Najdeno v: osebi
Ključne besede: boron carbide, soot, carbon nanoparticle, refractory, allotropes, green synthesis
Objavljeno: 30.06.2022; Ogledov: 93; Prenosov: 0
.pdf Polno besedilo (1,11 MB)

10.
Weathering induced morphological modification on the thermal diffusivity of natural pyrrhotite
Mohanachandran Nair Sindhu Swapna, V. Gokul, Vimal Raj, R. Manu Raj, S. N. Kumar, Sankaranarayana Iyer Sankararaman, 2021, izvirni znanstveni članek

Opis: Natural pyrrhotites have gained significant attention due to their interesting electronic, antimicrobial, and chemical properties. The present work attempts to explore the morphology-induced modifications in the thermal characteristics of natural pyrrhotite due to ageing. The morphological, elemental, structure, optical, and thermal characterisations help in understanding the effect of ageing. The effects of five years of ageing of the sample are (i) Field Emission Scanning Electron Microscopic analysis reveals a morphological transformation from flakes to agglomerated powder, (ii) elemental analyses suggest the ageing induced compositional modification (iii) the Tauc plot analysis shows a bandgap energy modification from 1.46 eV to 1.92 eV, (iv) X-ray Diffraction (XRD), Fourier Transform Infrared, and X-ray photoelectron spectroscopic studies affirm the formation of oxy-hydroxides (v) the XRD data indicates an increase of dislocation density, and (vi) Photoluminescence study shows a deep violet emission evidenced through the CIE plot. The study by the thermal lens technique shows a lowering of thermal diffusivity study by 23%, due to the morphological modifications, adsorbed/chemisorbed hydroxyl groups, and the formation of secondary compounds due to oxidation and weathering. The phonon boundary scattering, weathering induced smaller grain size, reduced phonon mean free path, and point defects also account for the lowering of the thermal diffusivity value and thereby influencing its properties.
Najdeno v: osebi
Ključne besede: pyrrhotite, thermal diffusivity, thermal lens, ageing, morphology
Objavljeno: 30.06.2022; Ogledov: 125; Prenosov: 1
.pdf Polno besedilo (1,82 MB)
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