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"Ali, Mohammad"
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Exceptional points in optics and photonics
Many complex systems operate with loss. Mathematically, these systems can be described as non-Hermitian. A property of such a system is that there can exist certain conditions—exceptional points—where gain and loss can be perfectly balanced and exotic behavior is predicted to occur. Optical systems generally possess gain and loss and so are ideal systems for exploring exceptional point physics. Miri and Alù review the topic of exceptional points in photonics and explore some of the possible exotic behavior that might be expected from engineering such systems. Science , this issue p. eaar7709 Exceptional points are branch point singularities in the parameter space of a system at which two or more eigenvalues, and their corresponding eigenvectors, coalesce and become degenerate. Such peculiar degeneracies are distinct features of non-Hermitian systems, which do not obey conservation laws because they exchange energy with the surrounding environment. Non-Hermiticity has been of great interest in recent years, particularly in connection with the quantum mechanical notion of parity-time symmetry, after the realization that Hamiltonians satisfying this special symmetry can exhibit entirely real spectra. These concepts have become of particular interest in photonics because optical gain and loss can be integrated and controlled with high resolution in nanoscale structures, realizing an ideal playground for non-Hermitian physics, parity-time symmetry, and exceptional points. As we control dissipation and amplification in a nanophotonic system, the emergence of exceptional point singularities dramatically alters their overall response, leading to a range of exotic optical functionalities associated with abrupt phase transitions in the eigenvalue spectrum. These concepts enable ultrasensitive measurements, superior manipulation of the modal content of multimode lasers, and adiabatic control of topological energy transfer for mode and polarization conversion. Non-Hermitian degeneracies have also been exploited in exotic laser systems, new nonlinear optics schemes, and exotic scattering features in open systems. Here we review the opportunities offered by exceptional point physics in photonics, discuss recent developments in theoretical and experimental research based on photonic exceptional points, and examine future opportunities in this area from basic science to applied technology.
Journal Article
Weak gravity conjecture validation with photon spheres of quantum corrected Reissner–Nordstrom–AdS black holes in Kiselev spacetime
In this study, we investigate the Weak Gravity Conjecture (WGC) in the context of quantum-corrected Reissner–Nordstrom–AdS (RN-AdS) black holes within Kiselev spacetime. Our focus is on photon spheres, which serve as markers for stable and unstable photon spheres. We confirm the validity of the WGC by demonstrating that quantum corrections do not alter the essential charge-to-mass ratio, thereby supporting the conjecture’s universality. Our analysis reveals that black holes with a charge greater than their mass
(
Q
>
M
)
possess photon spheres or exhibit a total topological charge of the photon sphere
(
PS
=
-
1
)
,
which upholds the WGC. This finding is significant as it reinforces the conjecture’s applicability even in the presence of quantum corrections. Furthermore, we examine various parameter configurations to understand their impact on the WGC. Specifically, we find that configurations with
ω
=
-
1
3
and
ω
=
-
1
maintain the conjecture, indicating that these values do not disrupt the charge-to-mass ratio required by the WGC. However, for
ω
=
-
4
3
,
the conjecture does not hold, suggesting that this particular parameter value leads to deviations from the expected behavior. These results open new directions for research in quantum gravity, as they highlight the importance of specific parameter values in maintaining the WGC. The findings suggest that while the WGC is robust under certain conditions, there are scenarios where it may be challenged, prompting further investigation into the underlying principles of quantum gravity.
Journal Article
A flexible piezoresistive strain sensor based on laser scribed graphene oxide on polydimethylsiloxane
Flexible strain sensors are an important constituent in soft robotics, health care devices, and in the defence industry. Strain sensors are characterized by their sensitivity (gauge factor-GF) and sensing range. In flexible strain sensors, simultaneously achieving consistency and high sensitivity has always been challenging. A number of materials and their derivatives have been explored to achieve balanced sensitivity with respect to sensing range with limited results. In this work, a low-cost flexible piezoresistive strain sensor has been developed using reduced graphene oxide (rGO) on polydimethylsiloxane (PDMS). The reduction has been performed using laser scribing, which enables the fabrication of arbitrary structures. After lead-out, the devices were again sandwiched in a layer of PDMS to secure the structures before performing their testing using a locally developed testing rig. Compared to previously reported graphene strain sensors, the devices fabricated in this work show relatively high GF with respect to sensing range. The GF calculated for stretching, bending and torsion was 12.1, 3.5, and 90.3 respectively, for the strain range of 0–140%, 0–130%, and 0–11.1%. A hand test was performed for the detection of joint movement. Change of resistance has been observed indicating muscle motion.
Journal Article
Internet of Things intrusion detection systems: a comprehensive review and future directions
The Internet of Things (IoT) is a paradigm that connects objects to the Internet as a whole and enables them to work together to achieve common objectives, such as innovative home automation. Potential attackers see the scattered and open IoT service structure as an appealing target for cyber-attacks. So, security cannot be dealt with independently. Security must be designed and built-in to every layer of the IoT system. IoT security concerns not only network and data security but also human health and life attacks. Therefore, the development of the loT system to provide security through resistance to attacks is a de facto requirement to make the loT safe and operational. Protecting these things is very important for system security. Plus, it is important to integrate the Intrusion Detection System (IDS) with IoT systems. IDS intends to track and analyze network traffic from different resources and detect malicious activities. It is a significant part of cybersecurity technology. In short, IDS is a process used to detect malicious activities against victims by several methods. Besides, the method of Systematic Literature Review (SLR) is used to classify, review, and incorporate results from all similar research that answers one or more IDS research topics and perform a detailed empirical research analysis on IDS techniques. Furthermore, depending on the detection technique, we classify IDS approaches in IoT as signature-based, anomaly-based, specification-based, and hybrid. Also, for the IDS approaches, the authors give a parametric comparison. The benefits and drawbacks of the chosen mechanisms are then addressed. Eventually, there is an analysis of open problems as well as potential trend directions.
Journal Article
