The Physics Engineering Department at Istanbul Technical University has had a productive year in 2024, publishing research on many topics. This newsletter highlights the key findings and contributions from our researchers, showcasing their innovative work and dedication to science.
Exploring Scalar Field Dynamics: Series Convolution Approach
A collaborative study conducted by Prof. Dr. Tolga Birkandan, Emir Baysazan (MSc student), and İsmail Eyüphan Ünver (undergraduate student) from the Department of Physics Engineering at Istanbul Technical University has been published in The European Physical Journal C. The research examines solutions to scalar field equations in curved spacetimes, focusing on cases where wave equations resist closed-form solutions due to non-polynomial coefficients. By employing series convolutions, the team offers insights into solving such equations analytically.
Prof. Dr. Tolga Birkandan, a faculty member of ITU’s Physics Engineering Department, along with his students Emir Baysazan and İsmail Eyüphan Ünver, has made significant contributions to the field of mathematical physics. Their research, published in The European Physical Journal C (DOI: 10.1140/epjc/s10052-024-13312-5), addresses the analytical challenges posed by scalar field equations in curved spacetimes. The study investigates scenarios where wave equations become unsolvable in closed form due to the non-polynomial nature of their coefficients. Typically, such functions may be transformed or eliminated to yield analytical solutions. However, when such transformations are infeasible, the team proposed examining the convolutions of the series expansions of these functions with power series solutions. Using the background of an Einstein equation solution, they demonstrated this method through a practical example. This work paves the way for future studies in complex spacetime geometries, offering an innovative approach to solving equations that are otherwise analytically intractable.
https://doi.org/10.1140/epjc/s10052-024-13312-5
Development of Optical Thermometers Using Rare Earth Ion-Doped Polymers
A collaborative study by Thami Buhari, Demet Kaya Aktaş, Murat Erdem, and Gönül Eryürek investigates the use of linear and crosslinked polyethylmethacrylate (PEMA) polymer networks doped with Er³⁺/Yb³⁺ rare-earth ions for remote temperature sensing. Published in the Journal of Luminescence the research highlights advancements in optical thermometry through detailed analyses of luminescence properties and thermal sensitivity.
A team of researchers, including Thami Buhari, Demet Kaya Aktaş, Murat Erdem, and Gönül Eryürek, has published a cutting-edge study in the Journal of Luminescence exploring the potential of Er³⁺/Yb³⁺-doped polymer networks for remote temperature sensing. The study focuses on linear and crosslinked polyethylmethacrylate (PEMA) materials synthesized through free-radical polymerization at 60°C. By varying crosslinker content, the researchers created stable and responsive host environments for rare-earth ions, suitable for precise thermal measurements. The analysis employed UV-Visible spectroscopy to determine optical bandgap energies and Urbach energy. Using the Judd-Ofelt (JO) approach, key luminescence parameters such as branching ratios (β), radiative lifetimes (τ), and stimulated emission cross-sections were calculated. Increasing crosslinking content enhanced JO parameters and emission cross-sections while reducing radiative lifetimes, demonstrating the materials’ potential for high-sensitivity applications. Temperature-dependent upconversion (UC) luminescence was studied under 975 nm excitation, with thermal sensing evaluated using the fluorescence intensity ratio (FIR) method. Maximum thermal sensitivity was achieved at lower temperatures as crosslinker content increased, within a broad temperature range of 300–650 K. These findings establish linear and crosslinked PEMA networks as promising candidates for optical thermometry across various fields. This research represents a significant advancement in photonics and materials science, showcasing innovative approaches to using rare-earth ion-doped polymers for remote sensing technologies.
https://doi.org/10.1016/j.jlumin.2024.120928
Non-perpetual Eternal Inflation and the Emergent de Sitter Swampland Conjecture
The study "Non-perpetual Eternal Inflation and the Emergent de Sitter Swampland Conjecture" authored by Dr. Ömer Güleryüz, published in The European Physical Journal C, explores the role of our universe within an infinite cosmic landscape and its connection to eternal inflation. This theory suggests that every quantum fluctuation could give rise to a new universe, positioning our cosmos as part of a much larger structure.
The study introduces a novel framework linking cosmic microwave background (CMB) parameters to the dynamics of eternal inflation. By analyzing quantum fluctuations and the criteria for inflationary phases, the work uncovers how the process of eternal inflation could spawn countless new universes. This suggests that our universe may be part of a "multiverse," a sprawling network of interconnected realms born from quantum processes. Moreover, the study bridges theoretical physics and cosmology by refining the eternal inflation criteria and linking them to the de Sitter swampland conjecture. This reveals a tendency for low-energy effective field theories within the cosmic landscape to favor eternal behavior, hinting at a grander structure in which our universe exists. This research not only advances our understanding of inflation but also opens the door to imagining a universe that is one among many, part of an infinite and dynamic cosmic tapestry.
https://doi.org/10.1140/epjc/s10052-024-13242-2
Machine Learning-Based Tomographic Imaging for Non-Destructive Detection of Internal Tree Defects
The article titled "Machine Learning-Based Tomographic Image Reconstruction Technique to Detect Hollows in Wood", based on the studies conducted by Assoc. Prof. Dr. Burcu Tunga, a faculty member of the Department of Mathematics Engineering; Ecem Nur Yıldızcan, a Mathematics Engineering master's student; and Prof. Dr. Ali Gelir, a faculty member of the Department of Physics Engineering, has been published in the Q1-indexed journal Wood Science and Technology.
Non-destructive detection of internal defects in wood is crucial for forest management and the preservation of trees. This study presents a novel machine learning-based approach for creating tomographic images of tree defects using stress wave propagation data. The proposed two-stage algorithm begins with ray segmentation, accurately modeling stress wave propagation. Subsequently, advanced classification algorithms like K-Nearest Neighbors (KNN) and Gaussian Process Classifier (GPC) are employed to map and visualize defects.
Results demonstrate that this approach effectively addresses challenges in segmentation and classification, achieving over 90% success in accuracy, precision, F1 score, and Dice coefficient across multiple datasets. Comparisons with existing methods highlight significant improvements, ranging from 7% to 22% in key metrics. Synthetic and real-world tree data validated the method's robustness, with visualization revealing intricate defect patterns.
This method is particularly innovative in its use of parameter-free ray segmentation and machine learning integration, setting a benchmark for non-destructive wood analysis. Its adaptability and reliability make it a valuable tool for assessing tree health and ensuring the sustainability of forest ecosystems. Future research could focus on refining thresholding strategies and incorporating additional features to enhance defect detection accuracy further.
https://doi.org/10.1007/s00226-024-01580-z
Probing Cosmic Dynamics: Insights from Stringy Gravity’s O(D, D)-Symmetric Framework
This research explores the cosmological implications of O(D, D)-symmetric Friedmann equations derived from string theory. Phase space and stability analyses uncover novel acceleration dynamics driven by flux contributions. This work contrasts these findings with the phenomenological Chameleon cosmology, offering a compelling framework for addressing key questions about universal evolution and acceleration.
Carried out in collaboration with Prof. Dr. Savaş Arapoğlu from the Physics Department and Prof. Dr. Aybike Çatal-Özer from the Mathematics Department, this study examines the cosmological dynamics governed by O(D, D)-symmetric Friedmann equations derived from Double Field Theory. The research applies a rigorous dynamical systems approach to identify stability regions and critical points, uncovering novel phase space behaviors driven by unique flux contributions.
The findings reveal acceleration phases that do not require the invocation of dark energy, instead pointing to flux-driven dynamics as the key driver of cosmic acceleration. Notably, the study highlights the preference for open universe for some configurations, providing an alternative theoretical perspective to the standard \LambdaCDM model.
A comparative analysis with the phenomenological Chameleon cosmology demonstrates shared features while emphasizing the unique aspects of O(D, D)-symmetric gravity, particularly its capacity to explain early- and late-universe dynamics without ad hoc assumptions. The research underscores the relevance of symmetry in addressing fundamental questions about cosmic evolution, positioning O(D, D)-symmetric gravity as a transformative framework for understanding universal dynamics. These findings offer a foundation for both theoretical exploration and observational validation, fostering further advancements in cosmology and string-inspired gravitational theories.
https://doi.org/10.1140/epjc/s10052-024-13213-7