arXiv subjects

Monika

Publications and source records attributed to Monika.

9 recordsLinked to original sources

arXiv2026

Dimensional Crossover of Mass Anisotropy in Ta-doped WTe2

The observation of extremely large magnetoresistance in WTe2 has attracted considerable attention towards understanding its underlying origin. With its layered van der Waals structure, the question that remains largely unexplored is whether the three-dimensional anisotropic transport characteristics of WTe2 persists under chemical substitution. Here, we present a systematic angle-dependent magneto-transport study of single-crystalline TaxW1-xTe2 (x = 0, 0.05, 0.1). The results are analysed within a mass anisotropy scaling framework to extract the mass anisotropy parameter {\gamma} as a function of temperature and doping. It is observed that Ta substitution leads to monotonic increase of {\gamma} across all temperatures, indicating a progressive deepening of quasi-two-dimensional Fermi surface character. Ta doping also leads to a substantial improvement in crystalline quality, reflected in a pronounced increase in the residual resistivity ratio. Despite weakening electron-hole compensation, the magnetoresistance rises sharply to ~58,211% at x = 0.1, which is assigned to a substantial enhancement in carrier mobility. Rietveld refinement confirms a systematic c-axis contraction with Ta content, identifying the structural origin of the enhanced anisotropy. The mass anisotropy scaling that holds for x = 0 and x = 0.05 breaks down for x = 0.1, where the angular magneto-resistance anisotropy substantially exceeds single-ellipsoid predictions, pointing to a multi-pocket Fermi surface with distinct anisotropies. Nonlinear Hall resistivity provides independent evidence for the underlying multiband character of transport in this system. These findings demonstrate that Fermi surface anisotropy, carrier compensation, and mobility are independent parameters that can lead to tuneable control of large magnetoresistance in topological semimetal WTe2.

cond-mat.mtrl-sci↗

arXiv2026

The Bishop--Phelps--Bollob\'as Property for Extremally Disconnected Ranges: Separable and Low-Density Domains

We prove a Bishop--Phelps--Bollob\'as theorem for operators into spaces of continuous scalar-valued functions on extremally disconnected compact Hausdorff spaces over both the real and complex scalar fields. The main result applies whenever the density character of the domain is strictly smaller than the Baire number of the underlying compact space. The proof also yields an explicit quadratic Bishop--Phelps--Bollob\'as modulus. In particular, every separable Banach space paired with such a function space has the Bishop--Phelps--Bollob\'as property for operators.

math.FA↗

arXiv2026

Role of Asymmetry in the Performance Optimization of a Relativistic Quantum Otto Engine

We present an analytical study of the relativistic quantum Otto cycle driven by a time-dependent harmonic oscillator. By imposing an asymmetry on the two adiabatic processes of this cycle, we obtain distinct scenarios of sudden compression and sudden expansion, and analyze how asymmetry affects the performance of the relativistic quantum Otto engine. By leveraging the Omega function as a unified performance metric, we analytically characterize the efficiency in both scenarios. Our findings demonstrate that the efficiency approaches unity in the sudden compression case, while it is restricted to one-half for the sudden expansion case. Furthermore, we investigate the impact of increasing oscillator velocity on the extracted work and identify parameter regimes where either sudden compression or sudden expansion dominates. Additionally, we examine the optimal operating point using parametric efficiency-work plots, whose loop-shaped structure shows that increasing oscillator velocity enhances both work output and efficiency. Finally, through a detailed phase diagram analysis of the Otto cycle, we observe that the operational region corresponding to the engine mode expands with increasing oscillator velocity, while the refrigeration regime shrinks correspondingly.

quant-ph↗

arXiv2026

On the Convergence of Numerical Index via Operator Openings and Ultraproducts

The numerical index of a Banach space is a geometric constant relating the numerical radius of bounded linear operators to their standard operator norm. In this paper, we study the continuity of the numerical index under two distinct notions of subspace convergence. First, we establish a full limit theorem in the operator opening topology: if $\{X_n\}_{n \in \mathbb{N}}$ and $X$ are closed subspaces of a Banach space $Y$ with $X_n \to X$ in the operator opening, then $\lim_{n \to \infty} n(X_n) = n(X)$. Second, we develop ultraproduct methods for the numerical index, proving that the numerical radius is exactly preserved by ultraproduct operators, i.e., $v((T_n)_{\mathcal{U}}) = \lim_{\mathcal{U}} v(T_n)$. As a consequence, we show that $n(X_{\mathcal{U}}) \le n(X)$ for every ultrapower $\mathcal{U}$.

math.FA↗

arXiv2025

Projections in the Algebra generated by an n-Potent Operator

This paper investigates the projection operators that lie in the algebra generated by powers of an $n$-potent operator $T$ on a complex Banach space, where $T^n = T$. We give a complete description of all projections in the algebra $\operatorname{comb}(T) = \text{span}\{T, T^2, \dots, T^{n-1}\}$, and prove that each such projection is uniquely determined by, and in bijection with, a subset of the nonzero spectrum of $T$. As a consequence, the family of projections in $\operatorname{comb}(T)$ forms a Boolean algebra isomorphic to the power set of $\sigma(T)\setminus\{0\}$. We also establish a spectral decomposition for $n$-potent operators in terms of their Riesz projections and derive explicit formulas for the associated Riesz projections using resolvent expansions. We give an illustration of the theory for $5$-potent operators, which highlights the algebraic and spectral structure of finite-order operators on Banach spaces.

math.FA↗

arXiv2025

Optimal Performance of an Asymmetric Quantum Harmonic Otto Engine and Refrigerator

We study a quantum Otto cycle operating with a time-dependent harmonic oscillator as the working material. We examine the asymmetry present between the two adiabatic processes of the Otto cycle, focusing on cases of sudden expansion and sudden compression. We analytically derive the efficiency and coefficient of performance for an asymmetric Otto cycle, employing the Omega function, which represents the balance between the maximum useful energy and minimum lost energy. Notably, our findings reveal that the efficiency (coefficient of performance) of an asymmetric engine (refrigerator) is higher during the sudden compression case compared to the sudden expansion case. Furthermore, we derive the results for the maximum work efficiency and observe that efficiency at the maximum Omega function consistently exceeds the maximum work efficiency. Finally, we compute the fractional loss of work in both cases to thoroughly examine the performance of asymmetric Otto engine.

quant-ph↗

arXiv2024

Asymmetric Quantum Harmonic Otto Engine Under Hot Squeezed Thermal Reservoir

We study a quantum harmonic Otto engine under a hot squeezed thermal reservoir with asymmetry between the two adiabatic branches introduced by considering different speeds of the driving protocols. In the first configuration, the driving protocol for the expansion stroke is sudden-switch in nature and compression stroke is driven adiabatically, while the second configuration deals with the converse situation. In both cases, we obtain analytic expressions for the upper bound on efficiency and efficiency at optimal work output, which reveals a significant difference between the two configurations. Additionally, we find that the maximum achievable efficiency in sudden expansion case is 1/2 only while it approaches unity for the sudden compression stroke. Further, we study the effect of increasing degree of squeezing on the efficiency and work output of the engine and indicate the optimal operational regime for both configurations under consideration. Finally, by studying the full phase-diagram of the Otto cycle we observe that the operational region of the engine mode grows with increasing squeezing at the expense of refrigeration regime.

quant-ph↗

arXiv2023

GeoCovaxTweets: COVID-19 Vaccines and Vaccination-specific Global Geotagged Twitter Conversations

Social media platforms provide actionable information during crises and pandemic outbreaks. The COVID-19 pandemic has imposed a chronic public health crisis worldwide, with experts considering vaccines as the ultimate prevention to achieve herd immunity against the virus. A proportion of people may turn to social media platforms to oppose vaccines and vaccination, hindering government efforts to eradicate the virus. This paper presents the COVID-19 vaccines and vaccination-specific global geotagged tweets dataset, GeoCovaxTweets, that contains more than 1.8 million tweets, with location information and longer temporal coverage, originating from 233 countries and territories between January 2020 and November 2022. The paper discusses the dataset's curation method and how it can be re-created locally, and later explores the dataset through multiple tweets distributions and briefly discusses its potential use cases. We anticipate that the dataset will assist the researchers in the crisis computing domain to explore the conversational dynamics of COVID-19 vaccines and vaccination Twitter discourse through numerous spatial and temporal dimensions concerning trends, shifts in opinions, misinformation, and anti-vaccination campaigns.

cs.SI↗

arXiv2021

The Existence of Linear Selection and the Quotient Lifting Property

Lifting properties for Banach spaces are studied. An alternate version of the lifting property due to Lindenstrass and Tzafriri is proposed and a characterization, up to isomorphism, is given. The quotient lifting property for pairs of Banach spaces $(X,J)$, with $J$ proximinal in $X$, is considered and several conditions for the property to hold are given.

math.FA↗