Search Results (20)

Thermal relics with masses in the GeV to TeV range remain possible candidates for the Universe’s dark matter (DM). These neutral particles are often assumed to have vanishing electric and magnetic dipole moments so that they do not interact with single real photons, but the anapole moment, a static electromagnetic property whose features are akin to that of a classical toroidal solenoid, can still be non-zero, permitting interactions with single virtual photons. In some models, DM predominantly annihilates into charged standard model particles through a p-wave process mediated by the anapole moment. The anapole moment is also responsible for another interaction of interest. If a DM medium were subjected to an electric current, a DM particle whose anapole moment was aligned with the current would have lower energy than the state with an antialigned anapole moment. Given these interactions, if a collection of initially unpolarized DM particles were subjected to an electric current, then the DM medium would become partially polarized, according to the Boltzmann distribution. In such a polarized medium, DM annihilation into photons, a subdominant s-wave process realizable through higher order interactions, would be somewhat suppressed. If the local electric current existed during a time in which the DM begins to drop out of thermal equilibrium with the rest of the Universe, the suppressed annihilation could lead to a small local excess in the relic DM density relative to a current-free region. This mechanism by which the local DM density can be perturbed is novel. Using effective interactions to model a DM particle’s anapole moment and polarizabilities (responsible for s-wave annihilation into two photons), we compute the changes in the DM density produced by long- and short-lived currents around freeze out. If we employ the most stringent constraints on DM annihilation into two photons, we find that long-lived currents can result in a fractional change in the DM density on the order of ${10}^{-17}$ for DM masses around 100 GeV; for short-lived currents, this fractional change in local DM density is on the order of ${10}^{-23}$ for the same DM mass. Full article

Background/Objectives: Advancements in oral imaging technology are continually shaping the landscape of dental diagnosis and treatment planning. Among these, photon-counting computed tomography (PCCT), introduced in 2021, has emerged as a promising, high-quality oral technology. Dental imaging typically requires a resolution beyond the standard CT systems achievable with the specialized cone-beam CT. PCCT can offer up to 100 µm resolution, improve soft-tissue contrast, and provide faster scanning times, which are crucial for detailed dental diagnosis and treatment planning. Using semiconductor detectors, PCCT produces sharper images and can potentially reduce the number of scans required, thereby decreasing patient radiation exposure. This review aimed to explore the potential benefits of PCCT in dental imaging. Methods: This review analyzed the literature on PCCT in dental imaging from January 2010 to February 2024, sourced from PubMed, Scopus, and Web of Science databases, focusing on high-resolution, patient safety, and diagnostic efficiency in dental structure assessment. We included English-language articles, case studies, letters, observational studies, and randomized controlled trials while excluding duplicates and studies unrelated to PCCT’s application in dental imaging. Results: Studies have highlighted the superiority of PCCT in reducing artifacts, which are often problematic, compared to conventional CBCT and traditional CT scans, due to metallic dental implants, particularly when used with virtual monoenergetic imaging and iterative metal artifact reduction, thereby improving implant imaging. This review acknowledges limitations, such as the potential for overlooking other advanced imaging technologies, a narrow study timeframe, the lack of real-world clinical application data in this field, and costs. Conclusions: PCCT represents a promising advancement in dental imaging, offering high-resolution visuals, enhanced contrast, and rapid scanning with reduced radiation exposure. Full article

Contributions to the radiation-induced dispersion energy shift between two interacting particles dependent on the electric octupole moment are calculated using a physical picture in which moments induced by applied fluctuating electromagnetic fields are coupled via retarded interaction tensors. The specific potentials evaluated include those found between an electric dipole-polarisable molecule and either a mixed electric dipole–octupole- or purely octupole-polarisable molecule, and those between two mixed electric dipole–octupole-polarisable molecules. Interaction energies are obtained for molecular and pair orientationally averaged situations. Terms dependent on the octupole weight-1 moment may be viewed as higher-order corrections to the leading dipole–dipole interaction energy as also found in energy transfer and dispersion forces. A comprehensive polarisation analysis is carried out for linearly and circularly polarised laser light incident parallel and perpendicular to the inter-particle axis. Contributions to the optical binding energy arising when one of the pair is polar and characterised by either a permanent electric dipole or octupole moment are also evaluated. Neither of these energy shifts survive orientational averaging. Full article

The impact of the COVID-19 pandemic on education has accelerated the shift in learning paradigms toward synchronous and asynchronous online approaches, significantly reducing students’ social interactions. This study introduces CollabVR, as a social virtual reality (SVR) platform designed to improve social interaction among remote university students through extracurricular activities (ECAs). Leveraging technologies such as Unity3D for the development of the SVR environment, Photon Unity Networking for real-time participant connection, Oculus Quest 2 for immersive virtual reality experience, and AWS for efficient and scalable system performance, it aims to mitigate this social interaction deficit. The platform was tested using the sociability scale of Kreijns et al., comparing it with traditional online platforms. Results from a focus group in Lima, Peru, with students participating in online ECAs, demonstrated that CollabVR significantly improved participants perceived social interaction, with a mean of 4.65 ± 0.49 compared to traditional platforms with a mean of 2.35 ± 0.75, fostering a sense of community and improving communication. The study highlights the potential of CollabVR as a powerful tool to overcome socialization challenges in virtual learning environments, suggesting a more immersive and engaging approach to distance education. Full article

This article presents an analysis of an electro-optical up-converter relying on a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI). The pulsed control signal is generated by an optical pulse clock (OPC) with a repetition rate of $f_s=$ 19.5 GHz. The intermediate frequency (IF) signal, which carries the modulation format known as quadratic phase shift keying (QPSK) at a frequency $f_{IF}$, is shifted at the output of the SOA-MZI to high outlet mixing frequencies ${nf}_s\pm f_{IF}$, where $n$ represents the harmonic order of the OPC. To examine the characteristics of the sampled QPSK signals, we employ the Virtual Photonics Inc. (VPI) emulator and evaluate them using significate metrics like error vector magnitudes (EVMs), conversion gains, and bit error rates (BERs). The up-mixing process is mainly achieved through the cross-phase modulation (XPM) effect in the SOA-MZI, which operates within a 195.5 GHz ultrahigh frequency (UHF). The electro-optical SOA-MZI up-converter demonstrates consistent uplifting conversion gains across the scope of the output mixing frequencies. The simulated conversion gain deteriorates from 38 dB at 20 GHz to 13 dB at 195.5 GHz. The operational efficiency of the electro-optical SOA-MZI design, employing the standard modulation approach, is also evaluated by measuring the EVM values. The EVM attains a 24% performance level at a data rate of 5 Gbit/s in conjunction with the UHF of 195.5 GHz. To corroborate our results, we compare them with real-world experiments conducted with the UHF of 59 GHz. The maximum frequency range of 1 THz is attained by increasing the OPC repetition rate. Ultimately, through elevating the control frequency to 100 GHz, the generation of terahertz replicas of the 4096-QAM (quadrature amplitude modulation) compound signal becomes achievable at heightened UHF, extending 1 THz, while maintaining a data transmission rate of 120 Gbit/s and upholding exceptional performance characteristics. Full article

Specific properties of quantum field theory are described by considering the combination of the system under investigation and the cloud of virtual or real particles associated with the field. Such a structure is called a “dressed system”, in contrast with the bare one in the absence of the interaction with the field. The description of the properties of such clouds in various physical situations is, today, an active research area. Here, we present the main features associated with virtual and real dressings, focusing on photon dressing. In analogy to virtual photon clouds dressing electrons in vacuum, virtual phonon clouds appear in solid-state physics. The interaction between real photons and the schematized two-level structure of an atom paves the way to flexible quantum control. Here, a unifying Floquet engineering approach is applied to describe single- and multiple-dressed atom configurations. Connections with the past and present atomic physics experiments are presented. Full article

Digital hydraulics is a discrete technology that integrates advanced dynamic system controls, digital electronics, and machine learning to enhance fluid power systems’ performance, overall efficiency, and controllability. A mechanically actuated inline three-piston variable displacement digital pump was previously proposed and designed. The inline three-piston pump incorporates complex mechanical and hydraulic subsystems and highly coupled mechanisms. The complexity of the utilized subsystems poses challenges when assessing the viability of the conceptual design. Therefore, this work focuses on designing, developing, and implementing a collaborative virtual platform involving a digitized module showcasing the internal mechanical structure of the digital pump utilizing mixed reality (MR) technology. MR technology is acknowledged as the forthcoming evolution of the human–machine interface in the real–virtual environment utilizing computers and wearables. This technology permits running simulations that examine the complexity of highly coupled systems, like the digital pump, where understanding the physical phenomenon is far too intricate. The developed MR platform permits multiple users to collaborate in a synchronized immersive MR environment to study and analyze the applicability of the pump’s design and the adequacy of the operated mechanisms. The collaborative MR platform was designed and developed on the Unity game engine, employing Microsoft Azure and Photon Unity Networking to set up the synchronized MR environment. The platform involves a fully interactive virtual module on the digital pump design, developed in multiple stages using Microsoft’s Mixed Reality Tool Kit (MRTK) for Unity and deployed in the synchronized MR environment through a HoloLens 2 MR headset. A research study involving 71 participants was carried out at Purdue University. The study’s objective was to explore the impact of the collaborative MR environment on understanding the complexity and operation of the digital pump. It also sought to assess the effectiveness of MR in facilitating collaboration among fluid power stakeholders in a synchronized digital reality setting to study, diagnose, and control their complex systems. Surveys were designed and completed by all 71 participants after experiencing the MR platform. The results indicate that approximately 75% of the participants expressed positive attitudes toward their overall MR platform experience, with particular appreciation for its immersive nature and the synchronized collaborative environment it provided. More than 70% of the participants agreed that the pump’s collaborative MR platform was essential for studying and understanding the complexity and intricacy of the digital pump’s mechanical structure. Overall, the results demonstrate that the MR platform effectively facilitates the visualization of the complex pump’s internal structure, inspection of the assembly of each of the involved subsystems, and testing the applicability of the complicated mechanisms. Full article

Quantum mechanics is a physical theory that describes the behavior of microscopic matter. According to quantum theory, a microscopic particle may be described as either a particle or a wave, called wave–particle duality. Many students in high school or college (BC level) find it difficult to imagine that microscopic particles have both particle and wave properties. This is mainly caused by the scale of the world they see since quantum mechanics deals with things that are too small, while the wave and particle phenomena at the microscopic scale are difficult to understand, measure, or verify in the real world. In this study, virtual reality technology was used to develop teaching modules on quantum mechanics, allowing learners to see the particles and wave phenomena of electrons and photons in the microscopic world through interactive operation in virtual experiments. A teaching experiment was conducted by recruiting 60 high school students as research subjects. The control group (30 students) used physics textbooks, and the experimental group (30 students) used the virtual teaching modules for learning quantum mechanics. The analysis results show that the experimental group’s learning effectiveness is higher than the control group. The questionnaire results show that students were satisfied with the learning experience using virtual teaching modules with high learning motivation and low cognitive load because virtual reality can visualize the abstract concepts of wave–particle duality and help them understand quantum mechanics. Full article

The growing interest in augmented reality applications has led to an in-depth look at the performance of head-mounted displays and their testing in numerous domains. Other devices for augmenting the real world with virtual information are presented less frequently and usually focus on the description of the device rather than on its performance analysis. This is the case of projected augmented reality, which, compared to head-worn AR displays, offers the advantages of being simultaneously accessible by multiple users whilst preserving user awareness of the environment and feeling of immersion. This work provides a general evaluation of a custom-made head-mounted projector for the aid of precision manual tasks through an experimental protocol designed for investigating spatial and temporal registration and their combination. The results of the tests show that the accuracy ($0.6\pm 0.1$ mm of spatial registration error) and motion-to-photon latency ($113\pm 12$ ms) make the proposed solution suitable for guiding precision tasks. Full article

In an atom, the interaction of a bound electron with the vacuum fluctuations of the electromagnetic field leads to complex shifts in the energy levels of the electron, with the real part of the shift corresponding to a shift in the energy level and the imaginary part to the width of the energy level. The most celebrated radiative shift is the Lamb shift between the $2s_{1/2}$ and the $2p_{1/2}$ levels of the hydrogen atom. The measurement of this shift in 1947 by Willis Lamb Jr. proved that the prediction by Dirac theory that the energy levels were degenerate was incorrect. Hans Bethe’s non-relativistic calculation of the shift using second-order perturbation theory demonstrated the renormalization process required to deal with the divergences plaguing the existing theories and led to the understanding that it was essential for theory to include interactions with the zero-point quantum vacuum field. This was the birth of modern quantum electrodynamics (QED). Numerous calculations of the Lamb shift followed including relativistic and covariant calculations, all of which contain a nonrelativistic contribution equal to that computed by Bethe. The semi-quantitative models for the radiative shift of Welton and Power, which were developed in an effort to demonstrate physical mechanisms by which vacuum fluctuations lead to the shift, are also considered here. This paper describes a calculation of the shift using a group theoretical approach which gives the shift as an integral over frequency of a function, which is called the “spectral density of the shift.“ The energy shift computed by group theory is equivalent to that derived by Bethe yet, unlike in other calculations of the non-relativistic radiative shift, no sum over a complete set of states is required. The spectral density, which is obtained by a relatively simple computation, reveals how different frequencies of vacuum fluctuations contribute to the total energy shift. The analysis shows, for example, that half the radiative shift for the ground state 1S level in H comes from virtual photon energies below 9700 eV, and that the expressions of Power and Welton have the correct high-frequency behavior, but not the correct low-frequency behavior, although they do give approximately the correct value for the total shift. Full article

In this paper, we present a real and simulated study of a frequency up mixing employing an electro-optical sampling semiconductor optical amplifier Mach–Zehnder interferometer (SOA–MZI) along with the differential modulation schema. The sampling signal is generated by an optical pulse clock (OPC) at a frequency of $f_s=$ 19.5 GHz. The quadratic phase shift keying (QPSK) signal at an intermediate frequency (IF) $f_{IF}$ is shifted to high frequencies $n{f}_s \pm f_{IF}$ at the SOA–MZI output. Using a simulator entitled Virtual Photonics Inc. (VPI), we generate sampled QPSK signals and analyze their merits during conversion gains and error vector magnitudes (EVMs). We conducted simulations of mixing in the SOA–MZI operating in a high-frequency band up to 195.5 GHz. The positive conversion gain is accomplished over the mixing frequencies. The EVM is used to evaluate the performance of the electro-optical sampling up-convertor. The EVM reaches 14% at a data rate of 5 Gbit/s at 195.5 GHz. During the experimental work, the results obtained in simulations are set side by side with the factual ones in the frequency range up to 59 GHz. Thus, the comparison between them confirms that they have approximately the same performance. Full article

Simulation and experimental performance analyses of simultaneous up-converted signals, for the first time, were investigated utilizing a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI) sampling mixer in co- and counter-directions for standard and differential modulation modes. An optical pulse source at a sampling frequency of f_s = 15.6 GHz was used as a sampling signal. The IF signal channels carrying quadrature phase shift keying (QPSK) data at frequencies f_m were up-converted at different mixing frequencies up to 195.5 GHz. Using the Virtual Photonics Inc. (VPI) simulator, we realized mixed QPSK signals and studied their characteristics through a conversion gain and an error vector magnitude (EVM). Simulations of up mixing operated in a frequency range up to 158 GHz. For the standard modulation in the co-direction, the conversion gain decreased from 43.3 dB at the mixing frequency of 16.6 GHz to 21.8 dB at 157 GHz for the first channel and from 43 dB at 17.6 GHz to 21 dB at 158 GHz for the second channel. The use of the differential modulation principle improved the conversion gain by about 10 dB at 195.5 GHz compared to standard modulations in co- and counter-directions. The EVM reached, respectively, 15.5 and 17.5% for the differential modulation in both configurations, at the bit rate of 100 Gbit/s at 195.5 GHz. The benefit provided by the differential modulation was that EVM values were shifted by 20% for all channels in both configurations at 100 Gbit/s. In the real measurement, we confirmed that co-directional conversion exhibited a better performance than the counter-directional operation. In addition, the real mixed signal exhibited lower efficiency and quality in comparison with simulated signals due to the sensitivity of the receiver. Full article

This study focuses on a novel concept of transmitting of a quadrature phase shift keying (QPSK) modulation by an electro-optical frequency up-conversion using a cascaded Mach–Zehnder modulators (MZMs) link. Furthermore, we conduct and compare the results obtained by simulations using the Virtual Photonics Inc. (VPI) (Berlin, Germany) simulator and real-world experiments. The design and operating regime peculiarities of the MZM used as a sampling up-converter mixer in a radio over fiber (RoF) system are also analyzed. Besides, the simulation and experimental results of static and dynamic characteristics of the MZM have approximately the same behavior. The conversion gain of the cascaded MZMs link is simulated over many mixing frequencies and it can decrease from 17.5 dB at 8.3 GHz to −4.5 dB at 39.5 GHz. However, in real world settings, it may decrease from 15.5 dB at 8.3 GHz to −6 dB at 39.5 GHz. The maximum frequency range is attained at 78.5 GHz for up-conversion through simulations. Error vector magnitude (EVM) values have been done to evaluate the performance of our system. An EVM of 16% at a mixing frequency of 39.5 GHz with a bit rate of 12.5 Gbit/s was observed with the considering sampling technique, while it reached 19% in real-world settings with a sampling frequency of 39.5 GHz and a bit rate of 12.5 Gbit/s. Full article

Temporal modulation of the quantum vacuum through fast motion of a neutral body or fast changes of its optical properties is known to promote virtual into real photons, the so-called dynamical Casimir effect. Empowering modulation protocols with spatial control could enable the shaping of spectral, spatial, spin, and entanglement properties of the emitted photon pairs. Space–time quantum metasurfaces have been proposed as a platform to realize this physics via modulation of their optical properties. Here, we report the mechanical analog of this phenomenon by considering systems in which the lattice structure undergoes modulation in space and in time. We develop a microscopic theory that applies both to moving mirrors with a modulated surface profile and atomic array meta-mirrors with perturbed lattice configuration. Spatiotemporal modulation enables motion-induced generation of co- and cross-polarized photon pairs that feature frequency-linear momentum entanglement as well as vortex photon pairs featuring frequency-angular momentum entanglement. The proposed space–time dynamical Casimir effect can be interpreted as induced dynamical asymmetry in the quantum vacuum. Full article

In the presence of a thermal medium or an external electro-magnetic field, neutrinos can interact with photon, mediated by the corresponding charged leptons (real or virtual). The effect of a medium or an electromagnetic field is two-fold—to induce an effective $\nu \gamma$ vertex and to modify the dispersion relations of all the particles involved to render the processes kinematically viable. It has already been noted that, in a medium, neutrinos acquire an effective charge, which in the standard model of electroweak interaction comes from the vector type vertex of weak interaction. On the other hand, in a magnetized plasma, the axial vector part also starts contributing to the effective charge of a neutrino. This contribution corresponding to the axial vector part in the interaction Lagrangian is denoted as the axial polarisation tensor. In this note, we outline the calculation of the axial polarization tensor to odd and even powers in $e\mathcal{B}$. We further show its gauge invariance properties. Finally, we infer upon the zero external momentum limit of this axial polarisation tensor. Full article