71. Concentration-dependent thermal duality of hafnium carbide nanofluid for heat transfer applications : a mode mismatched thermal lens studyVijayakumar 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 confirm 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 v RUNG: 04.07.2022; Ogledov: 1124; Prenosov: 0
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72. Boron carbide Nanowires from castor oil for optronic applications: A low-temperature greener approachMohanachandran Nair Sindhu Swapna, 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 v RUNG: 04.07.2022; Ogledov: 1057; Prenosov: 0
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73. Thermal diffusivity of molybdenum oxide nanowire film: a photothermal beam deflection studyMohanachandran Nair Sindhu Swapna, 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 v RUNG: 04.07.2022; Ogledov: 1149; Prenosov: 0
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74. Laser-induced thermal lens study of the role of morphology and hydroxyl group in the evolution of thermal diffusivity of copper oxideRiya Sebastian, Mohanachandran Nair Sindhu Swapna, Vimal Raj, Sankaranarayana Iyer Sankararaman, 2022, izvirni znanstveni članek Opis: The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity
using the single beam thermal lens (TL) technique. For this purpose, the decomposition of Cu(OH)2 into CuO is studied in a
time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time
evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the
reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications,
from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement
of base fluid’s thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of
CuO.
Ključne besede: thermal diffusivity, CuO, thermal lens, morphology, hydroxyl group
Objavljeno v RUNG: 04.07.2022; Ogledov: 1012; Prenosov: 0
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76. Neural net pattern recognition based auscultation of croup cough and pertussis using phase portrait featuresMohanachandran Nair Sindhu Swapna, 2021, izvirni znanstveni članek Opis: Cough signal analysis for understanding the pathological condition has become important from the outset of the exigency posed by the epidemic COVID-19. The present work suggests a surrogate approach for the classification of cough signals - croup cough (CC) and pertussis (PT) – based on spectral, fractal, and nonlinear time-series techniques. The spectral analysis of CC reveals the presence of more frequency components in the short duration cough sound compared to PT. The musical nature of CC is unveiled not only through the spectral analysis but also through the phase portrait features – sample entropy (S), maximal Lyapunov exponent (L), and Hurst exponent (Hb). The modifications in the internal morphology of the respiratory tract, giving rise to more frequency components associated with the complex airflow dynamics, get staged through the higher fractal dimension of CC. Among the two supervised classification tools, cubic KNN (CKNN) and neural net pattern recognition (NNPR), used for classifying the CC and PT signals based on nonlinear time series parameters, NNPR is found better. Thus, the study opens the possibility of identification of pulmonary pathological conditions through cough sound signal analysis.
Ključne besede: Croup cough
Pertussis
Fractal dimension
Phase portrait
Sample entropy
Machine learning techniques
Objavljeno v RUNG: 04.07.2022; Ogledov: 996; Prenosov: 0
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77. Evolution of fractal dimension in pulsed laser deposited MoO3 film with ablation time and annealing temperatureMohanachandran Nair Sindhu Swapna, 2021, izvirni znanstveni članek Opis: The multifractal analysis is a potential method for assessing thin flm surface morphology and its changes due to diferent
deposition conditions and post-deposition treatments. In this work, the multifractal analysis is carried out to understand the
surface morphology—root mean square (RMS) surface roughness—of nanostructured MoO3 flms prepared by pulsed laser
deposition technique by varying the ablation time and post-deposition annealing. The XRD analysis shows the evolution of
crystalline nature with annealing temperature. The XRD pattern of all the annealed flms shows the characteristic peak of
the orthorhombic MoO3 phase. The FESEM and AFM analysis reveals the morphological modifcation with ablation time
and annealing temperature. The multifractal analysis of the AFM images shows that the box—counting, information and
correlation dimension varies with the annealing temperature. The study also reveals the inverse relation between the fractal
dimension and the RMS surface roughness due to the annealing induced particle size variation and reorientation. The fractal
dimension’s evolution in the pulsed laser deposited MoO3 flm with ablation time and annealing temperature is also investigated. Thus, the study reveals the potential of multifractal analysis in the thin flm surface characterizatio
Ključne besede: Multifractal analysis · Pulsed laser deposition · Molybdenum oxide · Atomic force microscopy · Fractal
dimension
Objavljeno v RUNG: 04.07.2022; Ogledov: 1186; Prenosov: 0
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78. Acclimatisation through thermal diffusivity tuning of coconut oil – A mode mismatched dual-beam thermal lens studyMohanachandran Nair Sindhu Swapna, 2022, izvirni znanstveni članek Opis: Background: Ayurvedic medicinal oils traditionally prepared by blending herbal extracts in different
compositions are commonly used for treatment and improving health. The estimation of the thermal
properties of medicinal oils is essential for practical applications.
Objective: The present work aims to expound the ability of medicinal oils for the acclimatization of body
temperature by determining its thermal diffusivity and thereby providing a validation to the traditional
knowledge.
Materials and methods: The medicinal oils are prepared by incorporating black pepper (Piper nigrum),
aloe vera (Aloe barbadensis), hibiscus bud (Hibiscus rosa-sinensis) and Ocimum sanctum in coconut oil
base. The samples are subjected to thermal diffusivity study using the mode-mismatched dual-beam
thermal lens technique.
Results: The study reveals that the incorporation of black pepper (Piper nigrum), having hot potency
(Ushna veerya), to the base fluid lowers the thermal diffusivity value, suggesting its potential in heat-trapping. The addition of aloe vera (Aloe barbadensis), hibiscus bud (Hibiscus rosa-sinensis), and
O. sanctum dissipates heat energy quickly, thus increases the thermal diffusivity of coconut oil revealing a
cold potency (Sheeta veerya). The study provides a validation for traditional knowledge and delineates
the possiblity of thermal diffusivity tuning of the base fluids.
Conclusion: The thermal diffusivity tuning through incorporation of herbal extracts can effectively be
used to acclimatize the human body temperature with the surroundings. A higher thermal diffusivity
value induces a cooling effect and the lower value causes heating effect. This, opens up the possibility of
using thermally tuned oils depending on climate and geographical location.
Ključne besede: Ayurveda, Acclimatization, Medicinal oils, Thermal lens spectroscopy
Thermal diffusivity
Objavljeno v RUNG: 04.07.2022; Ogledov: 1014; Prenosov: 0
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79. Tunable fluorescence from natural carbon source- PandanusMohanachandran Nair Sindhu Swapna, SARITHA DEVI H V, AMBADAS G, Sankararaman S, 2019, izvirni znanstveni članek Opis: Carbon materials possessing photoluminescence properties are considered as potential candidates in a
wide range of photonic and optoelectronic applications. In this work, the cellulose derived from the natural source,
Pandanus, is autoclave-treated for the synthesis of fluorescent carbon. The natural fibres are greatly preferred
over synthetic ones due to their cost-effectiveness, easy processability, non-abrasivity, non-toxic and environment-friendly characteristics along with high mechanical strength and damage tolerance. These properties enable them
to be used as templates for synthesis, as important reinforcement materials for commercial thermoplastics and
for making value-added products. In this study, the synthesised sample is subjected to structural, morphological,
elemental and optical characterisations. These studies reveal that the sample can be used as a low-cost tunable
light-emitting source for photonic, biomedical and biosensing applications.
Ključne besede: Fluorescence, Pandanus, natural carbon, cellulose
Objavljeno v RUNG: 04.07.2022; Ogledov: 1026; Prenosov: 0
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80. Allotropic transformation instigated thermal diffusivity of soot nanofluid: Thermal lens studyMohanachandran Nair Sindhu Swapna, RAJ VIMAL, Sankararaman S, 2019, izvirni znanstveni članek Opis: This paper employs the sensitive single-beam thermal lens technique for analyzing the thermal behavior of gasoline soot containing allotropes of carbon by preparing its nanofluid (NF). The soot, annealed at different temperatures up to 400 ○C (the samples), used for preparing the NF, is found to enhance the thermal diffusivity (α) up to 95% without changing the solid volume fraction, suggesting its possible use in
coolants. The thermal induced modifications are understood from the field emission scanning electron microscopic, X-ray diffraction (XRD),thermogravimetric, and Raman spectroscopic analyses. The variation of α of the sample is found to exhibit similar variations observed in XRD and Raman spectroscopic analyses. The study stresses the significance of the optimum temperature (300 ○C) for the soot NF above which morphological and structural modifications may lead to thermal energy trapping rather than dissipation or cooling.
Ključne besede: petrol soot, thermal lens, thermal diffusivity
Objavljeno v RUNG: 04.07.2022; Ogledov: 1136; Prenosov: 0
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