Indian Institute of Technology Goa

Abstract The search for single-ion magnetism (SIM) has been largely focused on hybrid metal-organic systems. Here, we experimentally demonstrate the spin-relaxation mechanism of SIM in a pure inorganic transition-metal oxide, Sr2Ca2Mn2CoO9, an Ising-chain magnet, employing neutron diffraction and inelastic neutron scattering (INS), complemented by SpinW simulations and a machine-learning framework. Interestingly, SIM mechanism persists even in the presence of long-range magnetic ordering, a phenomenon that is rarely observed. This pioneering investigation shows that bistability between the two quantum states Ms=±3/2 is maintained at zero magnetic field, driven by a dominant Orbach spin-relaxation mechanism with an effective energy barrier, U=4.4 meV. This behaviour arises from strong spin-phonon coupling in the presence of negative axial anisotropy (D approx -2.2meV) and the high-spin state S=3/2 of the Co(II) ion. Furthermore, we observe that magnon excitations persist up to room temperature, reflecting low-dimensional magnetic interactions and extended magnetic correlations within the oxide lattice. This interplay between single-ion magnetism and room-temperature spin excitations underscores the chemical tunability of magnetic anisotropy in oxide lattices.

Constitutive models are essential for describing the complex constitutive response of elastoplastic materials, often requiring a numerical integration scheme for solution. Neural networks have emerged as potential substitutes for approximating the ent

ABSTRACT Sodium azide has long been employed as a gas generant in airbag inflators; however, concerns regarding its environmental impact, toxicity, and disposal have prompted the development of alternative formulations, notably ammonium nitrate (AN) based gas generants and, more recently, guanidine nitrate (GN) and basic copper nitrate (BCN) gas generants. In this study, differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were performed to analyze their redox decomposition of GN/BCN gas generants. Three samples were prepared based on the oxygen balance. The overall redox reaction was initiated by the local thermal decomposition of GN, while the fuel‐rich mixture exhibited behavior more akin to pyrolysis. The highest mass loss rate from the derivative thermogravimetry (DTG) plots was observed for the sample with 0% oxygen balance. Kinetic parameters were obtained using the Friedman isoconversional method. The average activation energies of 156.5 ± 44, 207.6 ± 65, and 233.4 ± 102 kJ/mol were calculated for 0%, +10%, and ‐10% oxygen balance samples, respectively. Deconvolution was performed on the DTG curves to discern individual steps using the Lorentz function. The simulated curves derived from the kinetic parameters and reaction models of each step were in good agreement with the experimental data, thus validating the results. Flame propagation velocity studies imparted further insights into flame propagation and its dependence on the oxygen balance. The results demonstrate how oxygen balance influences the multistep redox mechanism, including pyrolysis and the performance of energetic gas generants.

The aim of the current research work was to develop simple, precise and accurate UV spectrophotometric methods for quantitative estimation of amlodipine besylate (AMLO) and nebivolol hydrochloride (NEBI) in binary mixtures and their fixed dose combination. The principle employed was based on isobestic point, area under curve (AUC) and dual wavelength approach. In isobestic point method, wavelength for AMLO and NEBI was found to be 268nm. Concentration of NEBI was determined at isobestic wavelength 268nm while AMLO was determined at 360nm and 268nm as there was no interference of NEBI. In AUC, wavelength of maximum absorption for AMLO and NEBI was found to be 360nm and 280nm. The measurements of AUC were carried out at wavelength range of 348-372nm for AMLO and 268-292 nm for NEBI. In case of dual wavelength, two wavelengths were selected for each drug so that the difference in absorbance would be zero for another drug. The wavelengths selected for determination of AMLO were 272.42nm and 292.42nm, whereas, the wavelengths selected for determination of NEBI were 234.37nm and 239.97nm. Validation of methods were carried out as per ICH Q2(R2) guidelines. Linearity was established over concentration range of 14-30µg/mL for AMLO (r2 = 0.999 at 268nm and r2 = 0.999 at 360nm) and NEBI (r2 = 0.999 at 268nm) in isobestic point method, whereas in case of AUC, it was established at concentration range of 5-25µg/mL for AMLO (r2 = 0.999) and NEBI (r2 = 0.980). However, in dual wavelength method, linearity was determined at concentration range of 10-26µg/mL for AMLO (r2 = 0.999 at 272.42 – 292.42nm) and NEBI (r2 = 0.993 at 234.37 – 239.97nm). Percentage relative standard deviation (%RSD) value of less than 2% for intra-day and inter-day precision confirmed the precision of the methods. Accuracy of the methods was found to be in range of 98-102%. The assay results pertaining to the methods were within the range of pharmacopoeial limits. The greenness of the method was assessed using AGREE and ComplexGAPI tools. The routine analysis of fixed dose combination in terms of time and cost renders the method suitable and valid as compared to other expensive techniques using sophisticated instruments. The developed analytical methods stand out not only for its accuracy and efficiency but also for its profound commitment to sustainability and environmental safekeeping.