1. Crystallizing covalent organic frameworks from metal organic framework through chemical induced-phase engineeringAbdul Khayum Mohammed, Safa Gaber, Jesus Raya, Tina Škorjanc, Nada Elmerhi, Sasi Stephen, Pilar Pena-Sánchez, Felipe Gándara, Steven Hinder, Mark A. Baker, Kyriaki Polychronopoulou, Dinesh Shetty, 2023, original scientific article Abstract: The ordered porous frameworks like MOFs and COFs are generally constructed using the monomers through distinctive metal-coordinated and covalent linkages. Meanwhile, the inter-structural transition between each class of these porous materials is an under-explored research area. However, such altered frameworks are expected to have exciting features compared to their pristine versions. Herein, we have demonstrated a chemical-induction phase-engineering strategy to transform a two dimensional conjugated Cu-based SA-MOF (Cu-Tp) into 2D-COFs (Cu-TpCOFs). The structural phase transition offered in-situ pore size engineering from 1.1 nm to 1.5–2.0 nm. Moreover, the Cu-TpCOFs showed uniform and low percentage-doped (~ 1–1.5%) metal distribution and improved crystallinity, porosity, and stability compared to the parent Cu-Tp MOF. The construction of a framework from another framework with new linkages opens interesting opportunities for phase-engineering. Keywords: metal organic framework, covalent organic framework, phase engineering, chemical transformation, porous materials Published in RUNG: 10.11.2023; Views: 750; Downloads: 5 Full text (3,64 MB) This document has many files! More... |
2. Time series and mel frequency analyses of wet and dry cough signals : a neural net classificationAmmini Renjini, Mohanachandran Nair Sindhu Swapna, K. Satheesh Kumar, Sankaranarayana Iyer Sankararaman, 2023, original scientific article Keywords: time series, mel frequency, cough signal, wet cough, dry cough, phase portrait, mel coefficients, fractal dimension, neural network Published in RUNG: 29.09.2023; Views: 793; Downloads: 5 Link to file This document has many files! More... |
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4. ULTRAFAST ELECTRON DYNAMICS IN CORRELATED SYSTEMS PROBED BY TIME-RESOLVED PHOTOEMISSION SPECTROSCOPYTanusree Saha, 2023, doctoral dissertation Abstract: Complex systems in condensed matter are characterized by strong coupling
between different degrees of freedom constituting a solid. In materials
described by many-body physics, these interactions may lead to
the formation of new ground states such as excitonic insulators, Mott
insulators, and charge and spin density waves. However, the inherent
complexity in such materials poses a challenge to identifying the
dominant interactions governing these phases using equilibrium studies.
Owing to the distinct timescales associated with the elementary interactions,
such complexities can be readily addressed in the non-equilibrium
regime. Additionally, these materials might also show the emergence
of new, metastable “hidden“ phases under non-equilibrium. The thesis
investigates the ultrafast timescales of fundamental interactions in candidate
systems by employing time-and angle-resolved photoemission spectroscopy
in the femtosecond time domain. In the (supposed) excitonic
insulator model system Ta2NiSe5, the timescale of band gap closure
and the dependence of rise time (of the photoemission signal) on the
photoexcitation strength point to a predominantly electronic origin of
the band gap at the Fermi level. The charge density wave (CDW) -
Mott insulator 1T-TaS2 undergoes photoinduced phase transition to two
different phases. The initial one is a transient phase which resembles
the systems’s high temperature equilibrium phase, followed by a long-lived
“hidden“ phase with a different CDW amplitude and is primarily
driven by the CDW lattice order. For the spin density wave system
CaFe2As2 where multiple bands contribute in the formation of Fermi surfaces,
selective photoexcitation was used to disentangle the role played
by different electron orbitals. By varying the polarization of photoexcitation
pulses, it is observed that dxz/dyz orbitals primarily contribute to
the magnetic ordering while the dxy orbitals have dominant role in the
structural order. The findings of the present study provide deeper perspectives
on the underlying interactions in complex ground phases of
matter, therefore, initiating further experimental and theoretical studies
on such materials. Keywords: complex systems, charge density wave, excitonic insulator, metastable phase, Mott insulator, non-equilibrium, spin density wave, timescales, time- and angle-resolved photoemission, ultrafast dynamics Published in RUNG: 01.06.2023; Views: 1378; Downloads: 27 Full text (13,34 MB) |
5. Electronic and chemical surface properties of Bi2Se3 derived compoundsZipporah Rini Benher, doctoral dissertation Keywords: Bismuth selenide derived compounds, surface chemical and electronic properties, topological insulators, single crystals, phase separation, inorganic bulk heterostructures, ix
Bridgman method, X-ray powder diffraction, scanning electron microscopy, photoelectron spectroscopy Published in RUNG: 16.12.2022; Views: 1594; Downloads: 22 Full text (9,56 MB) |
6. Photopyroelectric spectroscopy and calorimetryD Dadarlat, C Tripon, Iain R. White, Dorota Korte, 2022, review article Abstract: In this tutorial, we present an overview of the development of the photopyroelectric (PPE) technique, from its beginnings in 1984, through to the present day. The tutorial is organized in five sections, exploring both theoretical and experimental aspects of PPE detection, as well as some important spectroscopic and calorimetric applications. In the “Introduction” section we present the fundamental basics of photothermal phenomena and the state-of-the-art of the photopyroelectric technique. In the “Theoretical aspects” section we describe some specific cases of experimental interest, with examples in both back and front detection configurations. Several mathematical expressions for the PPE signal in specific detection modes (combined back-front configurations and PPE-IRT methods) are also deduced. The “Instrumentation and experiment” section contains two sub-sections. The first describes several examples of set-ups used for both room temperature and temperature-controlled experiments. The second sub-section is dedicated to the configuration of detection cells and to the various sensor/sample assemblies that are currently used in spectroscopic and calorimetric experiments for both liquid and solid samples. The “Applications” section is in fact a collection of experimental results dedicated to the thermal characterization of a wide range of solid and liquid samples. At the end of this section we present some examples that have been selected to convey that the PPE technique is not only useful in the investigation of optical and thermal properties of a variety of condensed matter samples, but also to study physical and chemical processes such as molecular associations, food adulteration or phase transitions. In “Concluding remarks” we summarize the advantages of this technique in spectroscopic and calorimetric applications. Keywords: photopyroelectric spectroscopy, photopyroelectric calorimetry, phase transitions, condensed matter samples, thermal parameters Published in RUNG: 16.11.2022; Views: 1174; Downloads: 22 Full text (2,87 MB) |
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9. Phase Portrait for High Fidelity Feature Extraction and Classification: A Surrogate ApproachMohanachandran Nair Sindhu Swapna, 2020, original scientific article Abstract: 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. Keywords: Phase Portrait, time series, feature extraction, pleural rub Published in RUNG: 05.07.2022; Views: 1109; Downloads: 0 This document has many files! More... |
10. Neural net pattern recognition based auscultation of croup cough and pertussis using phase portrait featuresMohanachandran Nair Sindhu Swapna, 2021, original scientific article Abstract: 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. Keywords: Croup cough
Pertussis
Fractal dimension
Phase portrait
Sample entropy
Machine learning techniques Published in RUNG: 04.07.2022; Views: 1051; Downloads: 0 This document has many files! More... |