arXiv subjects

Ahmed Khan

Publications and source records attributed to Ahmed Khan.

3 recordsLinked to original sources

arXiv2026

Assessing the Predictability of $\delta$ Scuti Variable Stars for Spacecraft Navigation

Previous studies have shown that $\delta$ Scuti stars can be used for determining spacecraft position and time similar to X-ray pulsar navigation, but open questions remain regarding the light-curve stability, and, therefore, the navigation accuracy that can be derived from $\delta$ Scuti variable stars. Here, we develop a computational framework to identify $\delta$ Scuti variable stars with light curves that are suitable for spacecraft navigation purposes. Our approach emphasizes quantifying timing uncertainty through developing metrics and evaluating such metrics in the context of spacecraft navigation. We analyze over 110 $\delta$ Scuti variable stars from the Kepler space telescope and 10 additional stars from the K2 mission. For each star, we produce a simple model of its normalized flux as a function of time, along with several metrics used to assess its suitability for navigation. Model quality was further assessed through comparing predictions with observations from the Transiting Exoplanet Survey Satellite (TESS). Out of the 120 $\delta$ Scuti variable stars we investigated in this study, 32 stars were identified as candidates predictable enough to enable spacecraft navigation.

astro-ph.IM↗

arXiv2023

Twisted van der Waals Quantum Materials: Fundamentals, Tunability and Applications

Twisted vdW quantum materials have emerged as a rapidly developing field of 2D semiconductors. These materials establish a new central research area and provide a promising platform for studying quantum phenomena and investigating the engineering of novel optoelectronic properties such as single-photon emission, non-linear optical response, magnon physics, and topological superconductivity. These captivating electronic and optical properties result from, and can be tailored by, the interlayer coupling using moiré patterns formed by vertically stacking atomic layers with controlled angle misorientation or lattice mismatch. Their outstanding properties and the high degree of tunability position them as compelling building blocks for both compact quantum-enabled devices and classical optoelectronics. This article offers a comprehensive review of recent advancements in the understanding and manipulation of twisted van der Waals structures and presents a survey of the state-of-the-art research on moiré superlattices, encompassing interdisciplinary interests. It delves into fundamental theories, synthesis and fabrication, and visualization techniques, and the wide range of novel physical phenomena exhibited by these structures, with a focus on their potential for practical device integration in applications ranging from quantum information to biosensors, and including classical optoelectronics such as modulators, light emitting diodes (LEDs), lasers, and photodetectors. It highlights the unique ability of moiré superlattices to connect multiple disciplines, covering chemistry, electronics, optics, photonics, magnetism, topological and quantum physics. This comprehensive review provides a valuable resource for researchers interested in moiré superlattices, shedding light on their fundamental characteristics and their potential for transformative applications in various fields.

cond-mat.mtrl-sci↗

arXiv2023

HDR image watermarking using saliency detection and quantization index modulation

High-dynamic range (HDR) images are circulated rapidly over the internet with risks of being exploited for unauthorized usage. To protect these images, some HDR image based watermarking (HDR-IW) methods were put forward. However, they inherited the same problem faced by conventional IW methods for standard dynamic range (SDR) images, where only trade-offs among conflicting requirements are managed instead of simultaneous improvement. In this paper, a novel saliency (eye-catching object) detection based trade-off independent HDR-IW is proposed, to simultaneously improve robustness, imperceptibility and payload. First, the host image goes through our proposed salient object detection model to produce a saliency map, which is, in turn, exploited to segment the foreground and background of the host image. Next, the binary watermark is partitioned into the foregrounds and backgrounds using the same mask and scrambled using a random permutation algorithm. Finally, the watermark segments are embedded into selected bit-plane of the corresponding host segments using quantized indexed modulation. Experimental results suggest that the proposed work outperforms state-of-the-art methods in terms of improving the conflicting requirements.

cs.CV↗