arXiv subjects

Manish K. Tiwari

Publications and source records attributed to Manish K. Tiwari.

8 recordsLinked to original sources

arXiv2026

Dynamic compensation of diffusion-limited oxygen sensing with deep learning

Luminescence-based oxygen sensors suffer from a fundamental trade-off between mechanical robustness and temporal response; polymers that encapsulate the sensing dye also act as diffusion barriers that compromise real-time monitoring. Here, we show that this bottleneck can be computationally mitigated using spatially resolved imaging and deep learning. We develop a Temporal Vision Transformer (TViT) architecture that processes consecutive frames from a low-cost platform consisting of a Raspberry Pi camera, UV LED, and porous PtOEP/polystyrene film. Trained against a high-speed reference sensor, the TViT reduced mean absolute error (MAE) by up to 96% and improved T90 response times by 91%, relative to the classical two-site Stern-Volmer model. We benchmarked seven neural architectures, including physics-informed and curriculum-learning variants. Physical plausibility of predictions was also assessed using a Rauch-Tung-Striebel Kalman smoother. The data-driven TViT achieved the highest performance and strongest physical plausibility, suggesting temporal attention can implicitly capture Fickian diffusion, but physics-informed models minimised temporal lag. Validated under both gaseous and biofouled aqueous conditions, the framework demonstrated robust generalisation across different setups, environments, biofilm states, and dynamic unstructured oxygen conditions. These capabilities are fundamentally beyond classical sensor operation, establishing a new IoT-compatible paradigm for computationally compensated diffusion-limited chemical sensing.

eess.IV↗

arXiv2026

Deep Learning-Enabled Dissolved Oxygen Sensing in Biofouling Environments for Ocean Monitoring

The escalating climate crisis and ecosystem degradation demand intelligent, low-cost sensors capable of robust, long-term monitoring in real-world environments. Absolute dissolved oxygen (DO) concentration is a key parameter for predicting climate tipping points. Inexpensive optoelectronic sensors based on microstructured polymer films doped with phosphorescent dyes could be readily deployable; however, signal drift and marine biofouling remain major challenges. Here, we introduce a sensing paradigm that combines camera-based DO sensors with a visual transformer (ViT)-based physics-informed neural network (PINN) for high-fidelity sensing under biofouling conditions. Training and testing data were obtained from an algae-laden water tank over 14 days to capture accelerated biofouling. The ViT-PINN, which embeds the Stern-Volmer (SV) equation into the loss function, reduces mean average error (MAE) by 92% and 89% compared to classical statistical and ML approaches, achieving ~2 umol/L absolute error. A deep ensemble further quantifies predictive uncertainty, enabling self-diagnostic sensing.

eess.IV↗

arXiv2023

Infrared thermochromic antenna composite for self-adaptive thermoregulation

Self-adaptive thermoregulation, the mechanism living organisms use to balance their temperature, holds great promise for decarbonizing cooling and heating processes. The functionality can be effectively emulated by engineering the thermal emissivity of materials to adapt to background temperature variations. Yet, solutions that marry large emissivity switching ($Δε$) with scalability, cost-effectiveness and design freedom are still lacking. Here, we fill this gap by introducing infrared dipole antennas made of tunable thermochromic materials. We demonstrate that non-spherical antennas (rods, stars and flakes) made of vanadium-dioxide can exhibit a massive (~200-fold) increase in their absorption cross-section as temperature rises. Embedding these antennas in polymer films, or simply spraying them directly, creates free-form thermoregulation composites, featuring an outstanding $Δε\sim0.6$ in spectral ranges that can be tuned at will. Our research paves the way for versatile self-adaptive heat management solutions (coatings, fibers, membranes and films) that could find application in radiative-cooling, heat-sensing, thermal-camouflage, and other.

physics.optics↗

arXiv2023

Atmospheric water vapor condensation on engineered interfaces: Busting the myths

Condensing atmospheric water vapor on surfaces is a sustainable approach to potentially address the potable water crisis. However, despite extensive research, a key question remains: what is the physical mechanism governing the condensation from humid air and how significantly does it differ from pure steam condensation? The answer may help define an optimal combination of the mode and mechanism of condensation as well as the surface wettability for best possible water harvesting efficacy. Here we show that this lack of clarity is due to the differences in heat transfer characteristics during condensation from pure vapor and humid air environments. Specifically, during condensation from humid air, the thermal resistance across the condensate is non-dominant and the energy transfer is controlled by vapor diffusion and condensate drainage. This leads to filmwise condensation on superhydrophilic surfaces, offering the highest water collection efficiency. To demonstrate this, we measured condensation rate on different sets of superhydrophilic and superhydrophobic surfaces in a wide degree of subcooling (10 - 26 C) and humidity-ratio differences (5 - 45 g/kg of dry air). The resulting condensation rate is enhanced by 57 - 333 % on the superhydrophilic surfaces as compared to the superhydrophobic ones. The findings of this study challenges the nearly century-old scientific ambiguity about the mechanism of vapor condensation from humid air. Our findings will lead to the design of efficient atmospheric water harvesting systems.

physics.flu-dyn↗

arXiv2021

A route to engineered high aspect-ratio silicon nanostructures through regenerative secondary mask lithography

Silicon nanostructuring imparts unique material properties including antireflectivity, antifogging, anti-icing, self-cleaning, and/or antimicrobial activity. To tune these properties however, a good control over features size and shape is essential. Here, a versatile fabrication process is presented to achieve tailored silicon nanostructures (thin/thick pillars, sharp/truncated/re-entrant cones), of pitch down to ~50 nm, and high-aspect ratio (>10). The approach relies on pre-assembled block copolymer (BCP) micelles and their direct transfer into a glass hard mask of an arbitrary thickness, now enabled by our recently reported regenerative secondary mask lithography. During this pattern transfer, not only the mask diameter can be decreased but also uniquely increased; constituting the first method to achieve such tunability without necessitating a different molecular weight BCP. Consequently, the hard mask modulation (height, diameter) advances the flexibility in attainable inter-pillar spacing, aspect ratios, and re-entrant profiles (= glass on silicon). Combined with adjusted silicon etch conditions, the morphology of nanopatterns can be highly customized. The process control and scalability enable uniform patterning of a 6-inch wafer which is verified through cross-wafer excellent antireflectivity (<5%) and water-repellency (advancing contact angle 158°; hysteresis 1°). It is envisioned the implementation of this approach to silicon nanostructuring to be far-reaching, facilitating fundamental studies and targeting applications spanning solar panels, antifogging/antibacterial surfaces, sensing, amongst many others.

physics.chem-ph↗

arXiv2021

Pre-impact dynamics of a droplet impinging on a deformable surface

The non-linear interaction between air and a water droplet just prior to high-speed impingement on a surface is a phenomenon that has been researched extensively and occurs in a number of industrial settings. The role that surface deformation plays in an air cushioned impact of a liquid droplet is considered here. In a two-dimensional framework, assuming small density and viscosity ratios between the air and the liquid, a reduced system of integro-differential equations is derived governing the liquid droplet free-surface shape, the pressure in the thin air film and the deformation of the surface, assuming the effects of surface tension, compressibility and gravity to be negligible. The deformation of the surface is first described in a rather general form, based on previous membrane-type models. The coupled system is then investigated in two cases: a soft viscoelastic case where the substrate stiffness and (viscous) damping are considered and a more general flexible surface where all relevant parameters are retained. Numerical solutions are presented, highlighting a number of key consequences of substrate deformability on the pre-impact phase of droplet impact, such as reduction in pressure buildup, increased air entrapment and considerable delay to touchdown. Connections (including subtle dependence of the size of entrapped air on the droplet velocity, reduced pressure peaks and droplet gliding) with recent experiments and a large deformation analysis are also presented.

physics.flu-dyn↗

arXiv2015

Electrostatic Potential as a Descriptor of Anti-Bacterial Activities of Some Anacardic Acid Derivatives: A Study Using Density Functional Theory

Structures and minimum molecular electrostatic potential (MEP) distributions in anacardic acid and some of its derivatives have been studied by full geometry optimization at the M06-2X/6-31G(d,p), WB97XD/6-31G(d,p) and B3LYP/6-31G(d,p) levels of density functional theory (DFT) in gas phase as well as in DMSO and aqueous solutions. Solvent effect was treated employing the integral equation formalism of the polarizable continuum model. Effects of modifications of the C1-side chain on the minimum MEP values in various regions were studied. Minimum MEP values near the oxygen atoms of the C2-OH group, oxygen or sulfur atoms of the C1-attached urea or thiourea groups and above or below the ring plane considered to be involved in interaction with the receptor were used to perform multiple linear regression. Experimentally observed anti-bacterial activities of these molecules against S. aureus are thus shown to be related to minimum MEP values in the above mentioned regions. Among the three DFT functionals used in the study, the M06-2X functional is found to yield most reliable results. Anti-bacterial activities have been predicted for certain molecules of the class which need to be verified experimentally.

physics.chem-ph↗

arXiv2013

What am I? Supercooled droplet or ice?

In this fluid dynamics video we show the trick played by a supercooled liquid water drop against a superhydrophobic surface. The water drop shows a double personality, impacting onto the surface the first time while still in the liquid state, and then re-impacting as a frozen ice crystal.

physics.flu-dyn↗