arXiv subjects

Amit Verma

Publications and source records attributed to Amit Verma.

At least 19 recordsLinked to original sources

arXiv2026

Multi-probe detection of domain nucleation across the metal-insulator transition in VO$_2$

Electronic and structural degrees of freedom are often intimately coupled in strongly correlated systems, which result in intriguing macroscopic and microscopic phenomena. Using the well-studied material VO$_2$ as a prototype, here we explore the domain distribution across the metal-insulator transition (MIT). We use macroscopic as well as microscopic techniques, such as first-order reversal curve (FORC) and infrared imaging, to probe the domain distributions across the MIT. This study compares MIT in thin films of VO$_2$ with different grain sizes grown by pulsed laser deposition and dc sputtering. We explore the relation between the nature of the FORC distribution and the corresponding thermal hysteresis due to interactions between the supercooled metallic domains and surrounding insulating matrix. Our multi-probe study with quantitative analysis provides a correlation between the growth, domain interaction, and domain nucleation process in MIT.

cond-mat.str-el↗

arXiv2026

The role of radiation-induced segregation in defect-phase formation in Ni-Ge and Ni-Si alloys

The interactions between chemical phase fields and structural defects play a key role in the properties of alloys. We illustrate the importance of these interactions in driven alloys, where defects are continuously being created, with particular focus on systems where radiation-induced segregation occurs. Specifically, we compare the microstructural evolution in undersaturated Ni-Si and Ni-Ge alloys during both 100 keV He and 2 MeV Ti irradiations. While the equilibrium phase diagrams of these systems are similar, and both systems show strong radiation-induced segregation, the evolving defect structures are remarkably different. Ni-Si reveals a high density of Frank loops, while Ni-Ge shows a complex array of dislocations. Moreover, a Ni3Ge precipitate shell is observed to coat He bubbles, while no segregation of Si is observed at such bubbles. We explain these differences in behaviors to solute drag by interstitial fluxes in Ni-Si vs solute drag by vacancy fluxes in Ni-Ge.

cond-mat.mtrl-sci↗

arXiv2024

Enhancing Fluorescence Lifetime Parameter Estimation Accuracy with Differential Transformer Based Deep Learning Model Incorporating Pixelwise Instrument Response Function

Fluorescence Lifetime Imaging (FLI) is a critical molecular imaging modality that provides unique information about the tissue microenvironment, which is invaluable for biomedical applications. FLI operates by acquiring and analyzing photon time-of-arrival histograms to extract quantitative parameters associated with temporal fluorescence decay. These histograms are influenced by the intrinsic properties of the fluorophore, instrument parameters, time-of-flight distributions associated with pixel-wise variations in the topographic and optical characteristics of the sample. Recent advancements in Deep Learning (DL) have enabled improved fluorescence lifetime parameter estimation. However, existing models are primarily designed for planar surface samples, limiting their applicability in translational scenarios involving complex surface profiles, such as \textit{in-vivo} whole-animal or imaged guided surgical applications. To address this limitation, we present MFliNet (Macroscopic FLI Network), a novel DL architecture that integrates the Instrument Response Function (IRF) as an additional input alongside experimental photon time-of-arrival histograms. Leveraging the capabilities of a Differential Transformer encoder-decoder architecture, MFliNet effectively focuses on critical input features, such as variations in photon time-of-arrival distributions. We evaluate MFliNet using rigorously designed tissue-mimicking phantoms and preclinical in-vivo cancer xenograft models. Our results demonstrate the model's robustness and suitability for complex macroscopic FLI applications, offering new opportunities for advanced biomedical imaging in diverse and challenging settings.

eess.IV↗

arXiv2024

Parallel Online Directed Acyclic Graph Exploration for Atlasing Soft-Matter Assembly Configuration Spaces

The paper formalizes a version of parallel online directed acyclic graph (DAG) exploration, general enough to be readily mapped to many computational scenarios. In both the offline and online versions, vertices are weighted with the work units required for their processing, at least one parent must be completely processed before a child is processed, and at any given time only one processor can work on any given vertex. The online version has the following additional natural restriction: only after a vertex is processed, are its required work units or its children known. Using the Actor Model of parallel computation, it is shown that a natural class of parallel online algorithms meets a simple competitive ratio bound. We demonstrate and focus on the problem's occurrence in the scenario of energy landscape roadmapping or atlasing under pair-potentials, a highly compute-and-storage intensive modeling component integral to diverse applications involving soft-matter assembly. The method is experimentally validated using a C++ Actor Framework (CAF) software implementation built atop EASAL (Efficient Atlasing and Search of Assembly Landscapes), a substantial opensource software suite, running on multiple CPU cores of the HiperGator supercomputer, demonstrating linear speedup results.

cs.DC↗

arXiv2024

Low-Temperature Electron Transport in [110] and [100] Silicon Nanowires: A DFT - Monte Carlo study

The effects of very low temperature on the electron transport in a [110] and [100] axially aligned unstrained silicon nanowires (SiNWs) are investigated. A combination of semi-empirical 10-orbital tight-binding method, density functional theory (DFT), and Ensemble Monte Carlo (EMC) methods are used. Both acoustic and optical phonons are included in the electron-phonon scattering rate calculations covering both intra-subband and inter-subband events. A comparison with room temperature (300 K) characteristics shows that for both nanowires, the average electron steady-state drift velocity increases at least 2 times at relatively moderate electric fields and lower temperatures. Furthermore, the average drift velocity in [110] nanowires is 50 percent more than that of [100] nanowires, explained by the difference in their conduction subband effective mass. Transient average electron velocity suggests that there is a pronounced streaming electron motion at low temperature which is attributed to the reduced electron-phonon scattering rates.

cond-mat.mes-hall↗

arXiv2024

Nonclassicality in Two-Mode New Generalized Binomial State

The study of nonclassical properties of two-mode quantum states is particularly useful in quantum information theory because of the possibilities of obtaining entanglement and other two-mode quantum correlations in these states. Here we have investigated the possibilities of the existence of nonclassicality in a two-mode New generalized binomial state (TMNGBS). Specifically two-mode antibunching, Quadrature squeezing, sum \& difference squeezing, and various entanglement criteria e.g Shchukin-Vogel entanglement criterion, the uncertainty relation of SU(1,1) Algebra and EPR entanglement criterion are explored in two mode particular example of quantum state named as New generalized binomial state. Earlier we studied nonclassicality in single-mode NGBS, here we are extending our study toward the two-mode version of a quantum state. Here we provide the general expressions of moments for a two-mode quantum state (Fock basis) and explore the quantification in a particular example NGBS. It is found that antibunching, squeezing, and SV entanglement are possible with different limits of depending parameters but the entanglement criteria (EPR, SU (1,1) algebra and Cauchy - Schwarz inequality based)for NGBS are not possible. This study opens up the possibility of exploring the two-mode nonclassicality in other states too.

quant-ph↗

arXiv2024

Dynamic Multi Color Switching using Ultrathin Vanadium Oxide on Aluminium based Asymmetric Fabry-Perot Resonant Structure

Vanadium dioxide ($VO_{2}$) exhibits strong infrared optical switching due to its insulator-metal phase-transition property. However, in the visible wavelengths, it's intrinsic optical switching is quite low. Current research explores solutions like multilayering, intricate structural patterning, high thermal budget processes and costly metals for improved color switching. Nonetheless, the color gamut coverage with these methodologies remains notably limited. This work overcomes these limitations and demonstrates dynamic multi-colour switching covering a large color gamut using a simple, unpatterned, ultrathin ($\sim$ $\frac{\lambda}{14}$, where wavelength $\lambda$ is taken as 575 nm at the center of visible spectrum) asymmetric Fabry-P\'{e}rot structure of $VO_{2}$ on Aluminium (Al). We use the transfer matrix method to design the $VO_{2}/Aluminium\,(Al)/Sapphire$ structure for maximum visible reflectance switching. $VO_{2}$ films are synthesized using a simple, low thermal budget atmospheric oxidation of Vanadium (V). With varying oxidation durations, different colors of the oxidized samples are observed. Consistent and reversible color-switching is observed visibly and in reflectance measurements with the change in temperature from low (RT $\sim$ 30$^{\circ}$C) to high (HT $\sim$ 100$^{\circ}$C) or vice versa due to the phase transition property of the $VO_{2}$ layer in the structure. Compared to the existing studies, this work shows a significant change in chromaticities and covers a large color gamut when plotted on the CIE chromaticity diagram. This work has potential applications in the fields of display, thermochromic structures, and visible camouflage.

physics.app-ph↗

arXiv2023

Bilayer Vanadium Dioxide Thin Film with Elevated Transition Temperatures and High Resistance Switching

Despite widespread interest in the phase-change applications of vanadium dioxide (VO$_2$), the fabrication of high-quality VO$_2$ thin films with elevated transition temperatures (TIMT) and high Insulator-Metal-Transition resistance switching still remains a challenge. This study introduces a two-step atmospheric oxidation approach to fabricate bilayer VO$_{2-x}$/VO$_2$ films on a c-plane sapphire substrate. To quantify the impact of the VO$_2$ buffer layer, a single-layer VO$_2$ film of the same thickness was also fabricated. The bilayer VO$_{2-x}$/VO$_2$ films wherein the top VO$_{2-x}$ film was under-oxidized demonstrated an elevation in TIMT reaching ~97 $^\circ$C, one of the highest reported to date for VO$_2$ films and is achieved in a doping-free manner. Our results also reveal a one-order increase in resistance switching, with the optimum bilayer VO$_2$/VO$_2$ film exhibiting ~3.6 orders of switching from 25 $^\circ$C to 110 $^\circ$C, compared to the optimum single-layer VO$_2$ reference film. This is accompanied by a one-order decrease in the on-state resistance in its metallic phase. The elevation in TIMT, coupled with increased strain extracted from the XRD characterization of the bilayer film, suggests the possibility of compressive strain along the c-axis. These VO$_{2-x}$/VO$_2$ films also demonstrate a significant change in the slope of their resistance vs temperature curves contrary to the conventional smooth transition. This feature was ascribed to the rutile/monoclinic quasi-heterostructure formed due to the top VO$_{2-x}$ film having a reduced TIMT. Our findings carry significant implications for both the lucid fabrication of VO$_2$ thin film devices as well as the study of phase transitions in correlated oxides.

cond-mat.mtrl-sci↗

arXiv2022

Parallel Exploration of Directed Acyclic Graphs using the Actor Model

In this paper we describe a generic scheme for the parallel exploration of directed acyclic graphs starting from one or more `roots' of the graph. Our scheme is designed for graphs with the following properties, (i) discovering neighbors at any node requires a non-trivial amount of computation, it is not a simple lookup; (ii) once a node is processed, all its neighbors are discovered; (iii) each node can be discovered through multiple paths, but should only be processed once. Several computational problems can be reduced to traversing such graphs, where the goal is to explore the graph and build a traversal roadmap. As a proof of concept for the effectiveness of our scheme at achieving speedup due to parallelism, we implement the scheme for the parallel exploration of assembly landscape using the EASAL methodology.

cs.DC↗

arXiv2022

Multi Spectral Switchable Infra-Red Reflectance Resonances in Highly Subwavelength Partially Oxidized Vanadium Thin Films

Phase transition materials are promising for realization of switchable optics. In this work, we show reflectance resonances in the near-infrared and long-wave infrared wavelengths in highly subwavelength partially oxidized Vanadium thin films. These partially oxidized films consist of a multilayer of Vanadium dioxide and Vanadium as shown using Raman spectroscopy and four-probe measurements. As Vanadium dioxide is a phase transition material that shows insulator to metal phase transition at 68 C, the observed infra-red resonances can be switched with temperature into a high-reflectance state. The wavelength of these resonances are passively tunable as a function of the oxidation duration. The obtained reflectance resonance at near-infrared wavelength red shifts from 1.78 um to 2.68 um with increasing oxidation duration while the long-wavelength infrared resonance blue shifts from 12.68 um to 9.96 um. To find the origin of the reflectance resonances, we model the reflectance spectra as a function of the oxidation duration using the transfer matrix method. The presented model captures the dual reflectance resonances reasonably well. These passive wavelength-tunable and switchable resonances with easy to fabricate lithography-free multilayer structure will be useful for multispectral applications such as camouflage, spectral selective microbolometer, and thermal management.

physics.optics↗

arXiv2021

Kramers' escape problem for white noise driven switching in ferroelectrics

A simulation-based study of stochastic resonance (SR) in a ferroelectric capacitor is presented. The SR phenomenon involves the detection of weak signals by adding an optimal amount noise to a non-linear system. This is linked with Kramers' escape problem, which deals with the escape of a particle undergoing Brownian motion over an energy barrier. The position of the particle is analogous to the polarisation dynamics of a ferroelectric. Within this framework, we numerically investigate SR in single domain ferroelectrics using the Landau-Ginzburg-Devonshire (LGD) theory. In addition, we use a model for multidomain ferroelectrics to demonstrate feasibility in real world applications. Our results show that SR in ferroelectrics is promising for the purpose of weak signal detection, given that these materials are widely used for various applications in the semiconductor industry.

cond-mat.stat-mech↗

arXiv2021

An examination of skill requirements for Augmented Reality and Virtual Reality job advertisements

The field of Augmented Reality (AR) and Virtual Reality (VR) has seen massive growth in recent years. Numerous degree programs have started to redesign their curricula to meet the high market demand of such job positions. In this paper, we performed a content analysis of online job postings hosted on Indeed.com and provided a skill classification framework for AR/VR job positions. Furthermore, we present a ranking of the relevant skills for the job position. Overall, we noticed that technical skills like UI/UX design, software design, asset design and graphics rendering are highly desirable for AR/VR positions. Our findings regarding prominent skill categories could be beneficial for the human resource departments as well as enhancing existing course curricula to tailor to the high market demand.

cs.CY↗

arXiv2021

Efficient QUBO transformation for Higher Degree Pseudo Boolean Functions

Quadratic Unconstrained Binary Optimization (QUBO) is recognized as a unifying framework for modeling a wide range of problems. Problems can be solved with commercial solvers customized for solving QUBO and since QUBO have degree two, it is useful to have a method for transforming higher degree pseudo-Boolean problems to QUBO format. The standard transformation approach requires additional auxiliary variables supported by penalty terms for each higher degree term. This paper improves on the existing cubic-to-quadratic transformation approach by minimizing the number of additional variables as well as penalty coefficient. Extensive experimental testing on Max 3-SAT modeled as QUBO shows a near 100% reduction in the subproblem size used for minimization of the number of auxiliary variables.

math.OC↗

arXiv2021

Effect of Vanadium Thickness and Deposition Temperature on VO2 Synthesis using Atmospheric Pressure Thermal Oxidation

Vanadium dioxide (VO2) is a phase transition material that undergoes a reversible insulator-metal phase transition at ~ 68 C. Atmospheric pressure thermal oxidation (APTO) of vanadium (V) is a simple VO2 synthesis method in which V thin film is oxidized in open air. For an optimum oxidation duration, VO2 films are obtained with good phase transition properties. We recently reported a modified APTO process using a step temperature profile for oxidation (Thin Solid Films 706, 138003 (2020)). We demonstrated an ultra-low thermal budget synthesis of VO2 thin films with good electrical and optical phase transition properties. For a 130 nm room-temperature RF sputtered V thin film, an optimum oxidation duration of ~ 30 s was obtained. In this work, we study how the starting V film thickness and deposition temperature affects the optimum oxidation duration. V thin films of varying thickness (15-212 nm) and 120 nm thick V films with varying deposition temperature (~27-450 C) are prepared using RF magnetron sputtering. These films are oxidized for different oxidation durations and characterized using Raman and four-probe measurements to find the optimum oxidation duration for each deposition condition. We find that the optimum oxidation duration increases with the increase in V film thickness and V deposition temperature. We model the effect of V film thickness and deposition temperature on the optimal oxidation time using a parabolic law which can be used to obtain the optimal oxidation times for intermediate V thicknesses/deposition temperatures.

cond-mat.mtrl-sci↗

arXiv2021

High Infrared Reflectance Modulation in VO2 Films Synthesized on Glass and ITO coated Glass substrates using Atmospheric Oxidation of Vanadium

Vanadium Dioxide (VO2) is a strongly correlated material, which exhibits insulator to metal transition at ~68 C along with large resistivity and infrared optical reflectance modulation. In this work, we use atmospheric pressure thermal oxidation of Vanadium to synthesize VO2 films on glass and ITO coated glass substrates. With the optimized short oxidation durations of 2 min and 4 min, the synthesized VO2 film shows high optical reflectance switching in long-wavelength infrared on glass substrates and mid-wavelength infrared on ITO coated glass substrates, respectively. Peak reflectance switching values of ~76% and ~79% are obtained on the respective substrates, which are among the highest reported values. Using the reflectance data, we extract VO2 complex refractive index in infrared wavelengths, in both the insulating and metallic phases. The extracted refractive index shows good agreement with VO2 synthesized using other methods. This demonstration of high optical reflectance switching in VO2 thin films, grown on low cost glass and ITO coated glass substrates, using a simple low thermal budget process will aid in enhancing VO2 applications in the optical domain.

physics.app-ph↗

arXiv2021

QUBO transformation using Eigenvalue Decomposition

Quadratic Unconstrained Binary Optimization (QUBO) is a general-purpose modeling framework for combinatorial optimization problems and is a requirement for quantum annealers. This paper utilizes the eigenvalue decomposition of the underlying Q matrix to alter and improve the search process by extracting the information from dominant eigenvalues and eigenvectors to implicitly guide the search towards promising areas of the solution landscape. Computational results on benchmark datasets illustrate the efficacy of our routine demonstrating significant performance improvements on problems with dominant eigenvalues.

math.OC↗

arXiv2021

Predicting 3D RNA Folding Patterns via Quadratic Binary Optimization

The structure of an RNA molecule plays a significant role in its biological function. Predicting structure given a one dimensional sequence of RNA nucleotide bases is a difficult and important problem. Many computer programs (known as in silico) are available for predicting 2-dimensional (secondary) structures however 3-dimensional (tertiary) structure prediction is much more difficult mainly due to the far greater number of feasible solutions and fewer experimental data on the thermodynamic energies of 3D structures. It is also challenging to verify the most likely three dimensional structure even with the availability of sophisticated x-ray crystallography and nuclear magnetic resonance imaging technologies. In this paper we develop three dimensional RNA folding predictions by adding penalty and reward parameters to a previous two dimensional approach based on Quadratic Unconstrained Binary Optimization (QUBO) models. These parameters provide flexibility in the amount of three dimensional folding allowed. We address the problem of multiple near-optimal structures via a new weighted similarity structure measure and illustrate folding pathways via progressively improving local optimal solutions. The problems are solved via a new commercial QUBO solver AlphaQUBO (Meta-Analytics, 2020) that solves problems having hundreds of thousands of binary variables.

q-bio.BM↗

arXiv2021

An exploratory study of skill requirements for social media positions: A content analysis of job advertisements

There has been considerable debate about the comparative advantages of marketing education emphasizing theoretical knowledge and applied skills. The current study investigated the skills necessary for entry-level marketing positions, specifically that of Social Media Manager (SMMgr) and Social Media Marketer (SMMkt). Data was collected from Indeed.com using a web crawler to extract job postings for SMMgr and SMMkt. A total of 766 and 654 entry-level jobs for SMMgr and SMMkt, respectively, across the entire United States, was collected. Independent raters separately analyzed the data for keywords and categories. Findings suggest that the most desired skills are occupational digital marketing skills. Other relevant skill categories included communication, employee attributes, problem-solving, and information technology skills. This study extends the current literature by highlighting the desired skills prevalent across the social media industry. The findings also have relevance in designing the marketing education curriculum, specifically in isolating core skills that could be integrated into the marketing courses.

cs.CY↗