Indian Institute of Technology Kanpur

The interplay between charge density wave (CDW) formation and electron correlations can lead to the emergence of novel topological phases in materials. In quasi‐2D 1T‐TaS2, below approximately 150 K, the system transitions from a nearly commensurate (NC) to a commensurate (C) CDW phase. Here, it is shown that the NC‐CDW to C‐CDW phase transition is marked by the emergence of a finite planar Hall and nonlinear Hall effect, alongside sign changes in the ordinary Hall and thermoelectric signals, indicating the reconstruction of the Fermi surface in the C‐CDW phase. The theoretical calculations suggest that the C‐CDW phase, stabilized by specific layer stacking, breaks both mirror and inversion symmetries. This leads to finite Berry curvature and a substantial Berry curvature dipole, giving rise to the observed planar Hall and nonlinear Hall effect. This study highlights the nontrivial band geometry‐driven physics of 1T‐TaS2 and opens new possibilities for developing innovative sensors.

Achieving long‐lived charge‐separated states is paramount for advancing perovskite solar cells technology, enhancing efficiency, and enabling kinetically slow processes like photocatalysis. While hole transport materials (HTMs) are essential for efficient charge extraction, conventional materials suffer from high defect densities at the perovskite/HTM interface, leading to severe nonradiative recombination losses. Previous strategies for surface passivation often rely on external treatments, which pose scalability challenges. This work overcomes these limitations by integrating passivation functionality directly into HTMs through targeted molecular engineering of phenazine derivatives. By leveraging the anchoring capability of the 1,10‐phenanthroline (Phen) skeleton and strategically incorporating electron‐donating (─NH2, ─OCH3) and electron‐withdrawing (─NO2, ─Br) groups, electron density is systematically modulated to control charge transfer dynamics. Electron‐donating groups (EDGs) increase charge density on the phenazine core, suppressing trap‐assisted recombination and stabilizing charge‐separated states. In contrast, electron‐withdrawing groups (EWGs) promote dipole formation at perovskite defect sites, leading to prolonged charge separation, as confirmed by observed sustained bleaching in transient absorption spectroscopy. This study reveals the profound impact of substituent electronic effects on interfacial interactions, offering a molecular design strategy for optimizing charge transport and defect mitigation in perovskite optoelectronics. These findings provide a scalable approach to enhancing perovskite‐based photovoltaics and photocatalytic applications.

A FeMnNi equiatomic medium entropy alloy was subjected to high-pressure torsion up to 5 turns under 2 GPa pressure at room temperature to achieve wide range of microstructures comprising of heterogeneous sub-microcrystalline structures to uniform nanocrystalline grains as a function of strain. Heterogeneous intragranular deformation caused by the operation of octahedral and partial slip systems causes rapid grain fragmentation without significant change in aspect ratio. The grain size was reduced from nearly 26 μm, as measured by EBSD, to approximately 59 nm after five turns, as determined by TEM, accompanied by a significant increase in hardness after the first turn, with saturation observed up to five turns. Nanoindentation experiments indicated that the improvement in strength was accompanied with substantial plasticity indicated by the plasticity index Wp/Wt during nanoindentation unloading cycle. This is followed by a decrease in strain rate sensitivity and marginal decrease in activation volume till a shear strain of about εvm ≈ 29, after which both remain almost constant indicating a steady state of microstructural refinement. Microstructural analyses, including EBSD and TEM, confirmed that grain subdivision occurs through dislocation rearrangement, leading to the formation of low-angle grain boundaries that progressively transform to high-angle grain boundaries contributing to grain size refinement by grain subdivision with the increase in strain. The process of grain refinement does not involve nucleation of dislocation free grains as observed for classical discontinuous recrystallization and is attributed to continuous dynamic recrystallization (CDRX) or extended dynamic recovery. Thus, the FeMnNi medium entropy alloy exhibits scope for microstructural engineering in the ultrafine and nanocrystalline regime to achieve optimum combination of strength and ductility. Graphical abstract

This work solves an open question in finite-state compressibility posed by Lutz and Mayordomo about compressibility of real numbers in different bases. Finite-state compressibility, or equivalently, finite-state dimension, quantifies the asymptotic lower density of information in an infinite sequence. Absolutely normal numbers, being finite-state incompressible in every base, are precisely those numbers which have finite-state dimension equal to 1 in every base. At the other extreme, for example, every rational number has finite-state dimension equal to 0 in every base. Generalizing this, Lutz and Mayordomo posed the question: are there numbers which have absolute positive finite-state dimension strictly between 0 and 1 - equivalently, is there a real number ξ and a compressibility ratio s ∈ (0, 1) such that for every base b , the compressibility ratio of the base- b expansion of ξ is precisely s ? It is conceivable that there is no such number. Indeed, some works explore “zero-one” laws for other feasible dimensions - i.e. sequences with certain properties either have feasible dimension 0 or 1, taking no value strictly in between. However, we answer the question of Lutz and Mayordomo affirmatively by proving a more general result. We show that given any sequence of rational numbers $\langle q_b \rangle _{b=2}^{\infty }$ , we can explicitly construct a single number ξ such that for any base b , the finite-state dimension/compression ratio of ξ in base b is q b . As a special case, this result implies the existence of absolutely dimensioned numbers for any given rational dimension between 0 and 1, as posed by Lutz and Mayordomo. In our construction, we combine ideas from Wolfgang Schmidt’s construction of absolutely normal numbers from Schmidt (1962), upper bounds on the discrepancy of certain sequences and several new estimates related to exponential sums.

It is well known from existing literature that the molecular constitutive models face convergence issues in CFD simulations at higher flow rates. Hence, this article investigates the viability of a numerically efficient approximation that potentially replaces such models by a GNF-based approach, by closely mimicking flow and stress profiles. As a test case, we use the flow of polymer solutions, modelled by FENE-P, around a sphere. Note, the FENE-P is frequently used as a constitutive model for polymer solutions. First, the flow fields predicted by FENE-P are compared with an equivalent GNF model (with the Carreau-Yasuda serving as the representative GNF in this study). Despite efforts to align the viscosity-shear rate dependence and thus creating equivalent models, the GNF model exhibits notable shortcomings, particularly due to neglect of chain stretching, especially near the stagnation points. Subsequently, an attempt is made to address this limitation by introducing extensional components to the local viscosity. Various inelastic models exist in literature for this aspect, among which the most recent one, the GNF-X formulation [Journal of Rheology 64, 493 (2020)] is selected. However, this formulation predicts significantly large stresses at the stagnation regions relative to FENE-P as well as fails to exhibit the asymmetry in stress and flow profiles. Consequently, we propose appropriate corrections to be added (termed as GNF-XM), which enables successful predictions. The asymmetry and drag coefficients from the GNF-XM agree well with the predictions from FENE-P across all flow rates. Notably, being inelastic and easier to converge, computational times are significantly lower than those for FENE-P, particularly at higher flow rates. This suggests a promising, highly efficient GNF-based approximation to FENE-P, with potential applicability to other complex constitutive models. Note, such an inelastic model would be helpful for polymer processing applications, particularly for faster design estimates. The corrections are physical in origin and independent of the details of the GNF-X formulation, which can be added to any given inelastic mixed-viscosity formulation.

A series of high-performing C-C bonded nitropyrazole and thiadiazole-based energetic materials (compounds 3-7) were synthesized and thoroughly characterized. SC-XRD studies supported the structure of compounds 3, 4, 6, and 7....

Since the recognition of the area of asymmetric synthesis in 2000, there has been a tremendous focus on the development of heterogeneous catalysts for asymmetric synthesis. Porous organic polymers (POPs) have emerged in recent years as inextricable materials of high physicochemical and hydrolytic stabilities, permitting infinite possibilities to modulate and tune reactivity, engineer porosity, regulate spatial environments and pore attributes, and maneuver material transport. With a diligent design of building blocks and the exploitation of organic reactions judiciously, the synthesis of POPs with BET surface areas of the order of a few thousand cm³/g has been demonstrated. The incorporation of reactive functional groups and chiral centers into the porous matrices of polymers offers opportunities to conduct asymmetric synthesis. Very high enantioselectivities of the order of 99% ee have been exemplified in the reactions mediated by chiral POPs (CPOPs). The design‐driven tunability of POPs allows the development of catalytic materials for targeted applications in a tailor‐made fashion. This review, while placing the development of chiral materials for asymmetric synthesis in the right perspective, delves into different design principles to pave the way for continued research on futuristic CPOP materials by a creative design, limited by one's imagination, for heretofore unprecedented results.

We report on the defect engineering in n-type Bi1.8Sb0.2Te3 end-compound via Te non-stoichiometry (Bi1.8Sb0.2Te3−x) intending to enhance the thermoelectric performance at low and near room temperature regime (10–350 K). Contemplating the asymmetry in electronic and phonon transport, the extrinsic anionic disorders successfully modulate the thermoelectric transport. Systematic manipulation of Te and Bi/Sb vacancies increases the electrical conductivity, leading to the highest power factor of 534 μW mK⁻² at 350 K. The self-doping effect created via anionic disorders resulted in an enhancement in the thermoelectric performance compared to the Bi1.8Sb0.2Te3 compound. Increased ZT values, accompanied by the thermoelectric quality factor, confirm the quality factor as one of the decisive parameters in elevating the thermoelectric performance. The sample with x = 0.08 has the highest ZT value of 0.081 at 350 K. A 174% increase in compatibility factor is also observed, indicating the state-of-the-art applicability of Bi1.8Sb0.2Te3 in segmented thermoelectric generators.

The experimental findings on the properties of an suddenly expanded flow from convergent nozzle is presented in this article. For suddenly expanded subsonic, sonic and underexpanded flows, the effect of passive control in the form of an annular rib on the base pressure distribution along the enlarged duct is examined. The range of the nozzle pressure ratio (NPR) was 1–7. The enlarged duct’s length-to-diameter ratio was adjusted from the base to 0.5D to 6D. The rib’s aspect ratio was adjusted between 0.45 and 1.25. The experimental findings demonstrate that, in the absence of ribs, the base pressure is highly impacted by the flow Mach number, the degree of expansion at the nozzle exit, and the length-to-diameter ratio of the enlarged duct. The base pressure of a sonic jet with NPR 4 rises as the rib aspect ratio does as well. The current study clearly shows that, in a suddenly expanded axi-symmetric duct, the base pressure can be managed passively by using a rib with the proper aspect ratio. This prevents wall pressure oscillations from rising to an unacceptably high level in subsonic and appropriately and underexpanded sonic flow.

We study time-dependent density segregation of granular mixtures flowing over an inclined plane. Discrete element method (DEM) simulations in a periodic box are performed for granular mixtures of same size and different density particles flowing under the influence of gravity. In addition, a continuum model is developed to solve the momentum balance equations along with the species transport equation by accounting for the inter-coupling of segregation and rheology. The particle force-based density segregation theory has been used along with the $\mu {-}I$ rheology to predict evolution of flow properties with time for binary and multicomponent mixtures. The effect of particle arrangements on the transient evolution of flow properties for three different initial configurations is investigated using both continuum and DEM simulations. Continuum predictions for various flow properties of interest such as species concentration, velocity, pressure and shear stress at different time instants are compared with DEM simulations. The results from the discrete and continuum models are found to be in good agreement with each other for well-mixed and heavy-near-base initial configurations. Kinetic theory-based predictions of segregation evolution, however, show good quantitative agreement only for the heavy-near-base configuration with a much slower evolution for the well-mixed case. Interestingly, the continuum model is unable to predict the flow evolution for the light-near-base initial configuration. DEM simulations reveal the presence of an instability driven, quick segregation for this configuration which is not predicted by the one-dimensional model and requires generalisation to three dimensions.

A purely elastic linear instability was recently reported for viscoelastic plane Poiseuille flow in the limit of ultra-dilute (solvent to solution viscosity ratio $\beta \gt 0.99$ ), highly elastic (Weissenberg number $W \sim 1000$ ) polymer solutions, within the framework of the Oldroyd-B model (Khalid et al. , Phys. Rev. Lett., vol. 127, 2021, pp. 134–502). This is the first instance of a purely elastic instability in a strictly rectilinear shearing flow, with the phase speed of the unstable ‘centre mode’ being close to the base-state maximum velocity at the channel centreline. Subsequently, Buza, Page and Kerswell ( J. Fluid Mech., vol. 940, 2022, A11) have shown, using the FENE-P model, that the centre-mode instability persists down to moderate elasticities ( $W \sim O (100)$ ), the reduction in threshold evidently due to the finite extensibility of the polymer molecules. In this work, we augment this latter finding and provide a comprehensive account of the effect of finite extensibility on the centre-mode instability in viscoelastic channel flow, using the FENE-P and FENE-CR models, in both the absence and presence of fluid inertia. In both these models, finite extensibility causes a decrease in the polymer relaxation time at high shear rates, and the resulting weakening of elastic stresses would seem to indicate a stabilising effect. The latter trend has been demonstrated by earlier analyses of hoop-stress-driven instabilities in curvilinear flows, and is indeed borne out for the FENE-CR case, where finite extensibility has a largely stabilising influence on the centre-mode instability. In stark contrast, for the FENE-P model, finite extensibility plays a dual role – a stabilising one at lower values of the elasticity number E , but, surprisingly, a destabilising one at higher E values. Further, the centre-mode instability is predicted over a significantly larger domain of the Re – E – $\beta$ parameter space, compared to the Oldroyd-B model, making it more amenable to experimental observations.

This paper develops a selected survey based on game theory in circular economy (CE) by complementing two perspectives: the CE business strategies and the public schemes (PS) available to implement CE systems. These perspectives are concentrated in six CE business strategies (circular inputs, sharing platforms, product‐as‐a‐service (PaaS), product life extension, product use extension, and resource recovery) and 20 different public incentives. We focus on the game theory literature since firms struggle to select the best CE strategies to adopt considering the public mechanisms in place while the governments fixes the PS to sponsor the implementation of CE systems according to the firms’ capacity to adopt CE strategies. Our results highlight that previous research has most likely focused on resource recovery business strategy, investigating predominantly four schemes: material taxation, environmental producer responsibility on contract duration and conditions, tradable recycling credit schemes, and subsidy. While few game theory papers investigate the product life extension and product use extension strategies, other CE strategies linked to circular inputs, sharing platforms, and PaaS turn out to be fully unexplored, independent of the PS used. Finally, we identify several research gaps that can help future research in game theory to contribute in the crossing domain of CE strategies and PS to implement CE systems.

We developed a CoFe-PBA on surface pre-oxidized copper foam (CoFe-PBA@A-CF) for electrocatalytic benzyl alcohol oxidation reaction. The CoFe-PBA@A-CF reduced a cell voltage of 0.17 V in a two-electrode setup after...

Bistable structures have two non-adjacent equilibrium configurations with minimum total potential energies. Unsymmetrical cross-ply laminate can show bistability if its initial curvature is within a specified range or an inelastic curvature is induced through various actions such as thermal curing, mechanical prestressing, etc. This paper adopts an alternative method to achieve bistability in three-layered sandwich laminates using a mechanically prestressed core. By adjusting the applied prestrain, this sandwich structure can be designed to exhibit bistable or monostable characteristics. A semi-analytical model based on the Rayleigh-Ritz method is developed for bistable laminates with different planform geometries. In the semi-analytical framework, the kinematic variables are approximated using Lagrange polynomials. The accuracy of the semi-analytical model was ascertained by comparing the semi-analytical solutions with those obtained from finite element analyses. In addition, a simplified analytical model is proposed to verify the deformed shape of a square prestressed laminate. Using the semi-analytical model, the post-critical and negative stiffness behavior of bistable sandwich laminates, with various planform geometries, have been studied. Numerical investigations carried out in this work have revealed that the postcritical behavior and negative stiffness characteristics of sandwich prestressed laminates can be tailored by carefully controlling several factors. These factors include the prestrain ratio applied to the core, elastic moduli of the core, the slenderness of the face sheets, and the planform shape of the laminate. Furthermore, the studies show the feasibility to control the bistable response of the laminate by manipulating the prestrain ratio within the core. By adjusting the prestrain ratio, the structural response of the laminate can be tuned, allowing it to exhibit stable configurations under specific conditions. This capability of controlling and inducing bistable or pseudo-bistable states opens up new possibilities for designing advanced materials and structures with tailored mechanical properties and enhanced functionality.

Polymer-based plasmonic metasurfaces containing subwavelength features arranged in one dimension (1D) and two dimensions (2D) are compared for their application in refractive index sensing. The 1D metasurface has parallel linear grooves with a sinusoidal surface profile, while the 2D metasurface has hexagonally periodic nanobumps. Both have a thin gold film on the top for plasmonic effect. Both the designs were optimized using numerical computations. The 1D metasurface exhibits only one plasmonic mode while the 2D metasurface exhibits multiple plasmonic modes for normal incidence of light. For refractive index sensing, both the metasurfaces can be used over a broad range. But in comparison, the 1D metasurface is found to be better in the low- and intermediate-index ranges, and the 2D metasurface works better in the higher-index range. In the low-index range, the 1D metasurface has a sensitivity of 766 nm RIU⁻¹, whereas the mode-1 of the 2D metasurface has a sensitivity of 633 nm RIU⁻¹. In the intermediate-index region, the sensitivity of the 1D metasurface is 714 nm RIU⁻¹, while the sensitivity values of mode-2 and mode-3 of the 2D metasurface are 428 nm RIU⁻¹ and 238 nm RIU⁻¹, respectively. At the higher-index range, the width of the plasmonic mode for 1D metasurfaces widens, thus lowering its figure of merit and quality factor for sensing, but mode-3 of 2D metasurface detects the analyte efficiently. Both the metasurfaces were fabricated using a low-cost two-step soft lithography approach using easily available economical masters, and the label-free sensing ability of the 1D metasurface is experimentally tested using a biomolecular interaction which establishes that micromolar concentrations of the analyte can be detected unambiguously.