First conceptualised in Olaf Stapledon's 1937 novel 'Star Maker', before being popularised by Freeman Dyson in the 1960s, Dyson Spheres are structures which surround a civilisation's sun to collect all the energy being radiated. This article presents a discussion of the features of such a feat of engineering, reviews the viability, scale and likely design of a Dyson structure, and analyses details about each stage of its construction and operation. It is found that a Dyson Swarm, a large array of individual satellites orbiting another celestial body, is the ideal design for such a structure as opposed to the solid sun-surrounding structure which is typically associated with the Dyson Sphere. In our solar system, such a structure based around Mars would be able to generate the Earth's 2019 global power consumption of 18.35 TW within fifty years once its construction has begun, which itself could start by 2040 using biennial launch windows. Alongside a 4.17 km2 ground-based heliostat array, the swarm of over 5.5 billion satellites would be constructed on the surface of Mars before being launched by electromagnetic accelerators into a Martian orbit. Efficiency of the Dyson Swarm ranges from 0.74–2.77% of the Sun's 3.85 × 1026 W output, with large potential for growth as both current technologies improve, and future concepts are brought to reality in the time before and during the swarm's construction. Not only would a Dyson Swarm provide a near-infinite, renewable power source for Earth, it would also allow for significant expansions in human space exploration and for our civilisation as a whole.
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Jack Smith 2022 Phys. Scr. 97 122001
S B Dugdale 2016 Phys. Scr. 91 053009
The concept of the Fermi surface is at the very heart of our understanding of the metallic state. Displaying intricate and often complicated shapes, the Fermi surfaces of real metals are both aesthetically beautiful and subtly powerful. A range of examples is presented of the startling array of physical phenomena whose origin can be traced to the shape of the Fermi surface, together with experimental observations of the particular Fermi surface features.
Gerard 't Hooft et al 2024 Phys. Scr. 99 052501
Despite its amazing quantitative successes and contributions to revolutionary technologies, physics currently faces many unsolved mysteries ranging from the meaning of quantum mechanics to the nature of the dark energy that will determine the future of the Universe. It is clearly prohibitive for the general reader, and even the best informed physicists, to follow the vast number of technical papers published in the thousands of specialized journals. For this reason, we have asked the leading experts across many of the most important areas of physics to summarise their global assessment of some of the most important issues. In lieu of an extremely long abstract summarising the contents, we invite the reader to look at the section headings and their authors, and then to indulge in a feast of stimulating topics spanning the current frontiers of fundamental physics from 'The Future of Physics' by William D Phillips and 'What characterises topological effects in physics?' by Gerard 't Hooft through the contributions of the widest imaginable range of world leaders in their respective areas. This paper is presented as a preface to exciting developments by senior and young scientists in the years that lie ahead, and a complement to the less authoritative popular accounts by journalists.
Ulrik L Andersen et al 2016 Phys. Scr. 91 053001
Squeezed light generation has come of age. Significant advances on squeezed light generation have been made over the last 30 years—from the initial, conceptual experiment in 1985 till today's top-tuned, application-oriented setups. Here we review the main experimental platforms for generating quadrature squeezed light that have been investigated in the last 30 years.
Anton Zeilinger 2017 Phys. Scr. 92 072501
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single- and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that nature cannot be local, that objective randomness exists and about the emergence of a classical world. It is suggestive that information plays a fundamental role also in the foundations of quantum physics.
Kaj Sotala and Roman V Yampolskiy 2015 Phys. Scr. 90 018001
Many researchers have argued that humanity will create artificial general intelligence (AGI) within the next twenty to one hundred years. It has been suggested that AGI may inflict serious damage to human well-being on a global scale ('catastrophic risk'). After summarizing the arguments for why AGI may pose such a risk, we review the fieldʼs proposed responses to AGI risk. We consider societal proposals, proposals for external constraints on AGI behaviors and proposals for creating AGIs that are safe due to their internal design.
Gerianne Alexander et al 2020 Phys. Scr. 95 062501
Sounds of Science is the first movement of a symphony for many (scientific) instruments and voices, united in celebration of the frontiers of science and intended for a general audience. John Goodenough, the maestro who transformed energy usage and technology through the invention of the lithium-ion battery, opens the programme, reflecting on the ultimate limits of battery technology. This applied theme continues through the subsequent pieces on energy-related topics—the sodium-ion battery and artificial fuels, by Martin Månsson—and the ultimate challenge for 3D printing, the eventual production of life, by Anthony Atala. A passage by Gerianne Alexander follows, contemplating a related issue: How might an artificially produced human being behave? Next comes a consideration of consciousness and free will by Roland Allen and Suzy Lidström. Further voices and new instruments enter as Warwick Bowen, Nicolas Mauranyapin and Lars Madsen discuss whether dynamical processes of single molecules might be observed in their native state. The exploitation of chaos in science and technology, applications of Bose–Einstein condensates and the significance of entropy follow in pieces by Linda Reichl, Ernst Rasel and Roland Allen, respectively. Mikhail Katsnelson and Eugene Koonin then discuss the potential generalisation of thermodynamic concepts in the context of biological evolution. Entering with the music of the cosmos, Philip Yasskin discusses whether we might be able to observe torsion in the geometry of the Universe. The crescendo comes with the crisis of singularities, their nature and whether they can be resolved through quantum effects, in the composition of Alan Coley. The climax is Mario Krenn, Art Melvin and Anton Zeilinger's consideration of how computer code can be autonomously surprising and creative. In a harmonious counterpoint, his 'Guidelines for considering AIs as coauthors', Roman Yampolskiy concludes that code is not yet able to take responsibility for coauthoring a paper. An interlude summarises a speech by Zdeněk Papoušek. In a subsequent movement, new themes emerge as we seek to comprehend how far we have travelled along the path to understanding, and speculate on where new physics might arise. Who would have imagined, 100 years ago, a global society permeated by smartphones and scientific instruments so sophisticated that genes can be modified and gravitational waves detected?
S Pfalzner et al 2015 Phys. Scr. 90 068001
The solar system started to form about 4.56 Gyr ago and despite the long intervening time span, there still exist several clues about its formation. The three major sources for this information are meteorites, the present solar system structure and the planet-forming systems around young stars. In this introduction we give an overview of the current understanding of the solar system formation from all these different research fields. This includes the question of the lifetime of the solar protoplanetary disc, the different stages of planet formation, their duration, and their relative importance. We consider whether meteorite evidence and observations of protoplanetary discs point in the same direction. This will tell us whether our solar system had a typical formation history or an exceptional one. There are also many indications that the solar system formed as part of a star cluster. Here we examine the types of cluster the Sun could have formed in, especially whether its stellar density was at any stage high enough to influence the properties of today's solar system. The likelihood of identifying siblings of the Sun is discussed. Finally, the possible dynamical evolution of the solar system since its formation and its future are considered.
Michael G Raymer and Ian A Walmsley 2020 Phys. Scr. 95 064002
We review the concepts of temporal modes (TMs) in quantum optics, highlighting Roy Glauber's crucial and historic contributions to their development, and their growing importance in quantum information science. TMs are orthogonal sets of wave packets that can be used to represent a multimode light field. They are temporal counterparts to transverse spatial modes of light and play analogous roles—decomposing multimode light into the most natural basis for isolating statistically independent degrees of freedom. We discuss how TMs were developed to describe compactly various processes: superfluorescence, stimulated Raman scattering, spontaneous parametric down conversion, and spontaneous four-wave mixing. TMs can be manipulated, converted, demultiplexed, and detected using nonlinear optical processes such as three-wave mixing and quantum optical memories. As such, they play an increasingly important role in constructing quantum information networks.
Jawad Mirza et al 2024 Phys. Scr. 99 055513
The spectrum required for future optical communication systems is being extended towards the C-, L- and U-bands, resulting in a significant interest in the spectral region around 2 μm wavelength. Since Holmium doped fiber amplifiers (HDFAs) provide amplification in this spectral region, they have become a focus of researchers working on doped fiber amplifiers. A major factor resulting in the performance degradation of HDFAs is the inhomogeneous energy transfer within Ho3+ ion-pairs in high-concentration Holmium-doped fibers (HDFs), an effect generally known as pair-induced quenching (PIQ). In this paper, we study the luminal and temporal dynamics of pulses of different repetition rates at 2.05 μm in high-concentration HDFs considering the effects of ion-pairs. Input pulses having repetition rates of 25 GHz and 500 kHz are generated using wavelength tunable actively mode-locked Holmium-doped fiber laser (AML-HDFL) based on a single ring cavity and bidirectional pumping. The characteristics of the pulses propagating through high-concentration HDF are analyzed based on different metrics such as average power, peak power, pulse energy, full-width at half maximum (FWHM), and time delay without and with ion-pairs for values of fraction of ion-pairs k = 0 and k = 10%, respectively. The results obtained at optimized length of HDF show that ion-pairs significantly degrade the average power, peak power, and energy of the output pulses for both of the repetition rates. For both k = 0 and k = 10%, the FWHM and shape of the output pulses remain same in the presence of the ion-pairs while, time delay of 4 ps and 19 ns is observed in the output pulses at repetition rates of 25 GHz and 500 kHz, respectively. The effects of increasing the pump and signal power on the average power and energy of the output pulses for k = 0 and k = 10% are also discussed for both repetition rates. This analysis provides important guidelines for designers of 2 μm fiber lasers and amplifiers based on high-concentration HDFs.
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A Davlatov et al 2024 Phys. Scr. 99 075933
In this research, electron energy levels were calculated analytically using Nelson's formula, the shooting method, and Garrett's formula for effective mass. These calculations were performed for a rectangular finite deep potential well, focusing on the InP/InAs/InP heterostructure, which is a narrow-bandgap semiconductor system. Our results demonstrate that the nonparabolicity of the dispersion has a more significant effect on higher energy levels compared to lower ones, with deviations of up to 15% for the third energy level. An equation estimating the number of observable energy levels in the potential well is suggested, revealing that considering nonparabolicity leads to a 20% increase in the number of levels compared to the parabolic dispersion case. The relationship between the widths of infinite and finite potential wells for equivalent energy levels follows a linear behaviour, with bonding coefficients ranging from 95,93% to 97,49% and a maximum difference of 1.5% between parabolic and non-parabolic cases. The transcendental equation for the energy levels is linearized, yielding a fourth-order equation that provides results within 98% accuracy compared to the original equation. These findings contribute to the understanding of the energy distribution in InP/InAs/InP heterostructures with a view to their application in optoelectronic devices such as lasers, light-emitting diodes
Shahzad Hussain et al 2024 Phys. Scr. 99 075938
Multiferroics with strong magnetoelectric coupling can be created by improving the magnetostriction of the ferrite phase and combining it with the best-known piezoelectric. Herein, the ferromagnetic CoFe2O4 was modified with Al incorporation further improve the resistivity, magnetic, and magnetostrictive properties and then combined with (0.5)Ba(Zr0.2Ti0.8)O3−(0.5)(Ba0.7Ca0.3)TiO3 (BCZT) with different weight percentages. XRD results revealed the presence of a mixed spinel cubic phase for CAF (Fd-3m), whereas BCZT crystallized in a tetragonal structure (Amm2) in composite systems. The dielectric response of the materials was studied using impedance spectroscopy and it displayed a typical Maxwell–Wagner polarization of two-phase composites. The magnetic response of the CAF sample improved significantly which is attributed to the preference of Al3+ ions on tetrahedral sites. The magnetization of composites increased as the nonmagnetic BCZT component increased and the (0.75)CAF-(0.25)BCZT system had the highest saturation magnetization. We anticipate that these systems will have significantly improved magnetoelectric characteristics than unmodified CFO-BCZT systems.
H Karim et al 2024 Phys. Scr. 99 075937
In this work, we present computational investigations of the electronic, the optical and the magnetic properties of the Li2BeTMSe4(TM = V, Cr, Mn, Fe) compounds using the first-principle calculations based on the density functional theory. In this respect, we employ the generalized gradient approximation corrected by the Tran-Balaha modified Becke-Johnson exchange potential to obtain more accurate results. Among these outcomes, we first study the electronic properties such as the band energy dispersion and the state densities. Regarding this, the Li2BeTMSe4 quaternary family is found to have an indirect band gap of 1.910 eV, 1.905 eV, 2.223 eV and 1.278 eV for TM = V, Cr, Mn, and Fe, respectively. Further, an examination of the optical properties reveals that the computed optical absorption spectra cover a broad energy range in the visible and the ultraviolet spectrums. Motivated by spintronic applications, we additionally determine the total and the local magnetic moments. Then, we compute the associated Curie temperatures via a linear relation with the total magnetic moments. Among others, the Li2BeTMSe4(TM = V, Cr, Mn, Fe) materials involve acceptable temperatures showing potential applications for high temperature nano-devices activities. Comparing the obtained findings with the available ones, the acquired results indicate that the Li2BeTMSe4(TM = V, Cr, Mn, Fe) materials exhibit a wide range of applications in solar cells, optoelectronics, and other fields.
C A Alonso-Herrera et al 2024 Phys. Scr. 99 075936
The thermal conductivity for the wurtzite ZnO is determined in the temperature range from 300 to 1100 K by using parallel tempering molecular dynamics within the Green-Kubo approach and a classical Morse-Born-Mayer-Coulomb hybrid interaction potential. Compared to other previous calculations for the thermal conductivity of common crystals within the same Green-Kubo and molecular dynamics approach, the used parallel tempering scheme shows some appealing improvements in the calculation of the time self-correlation of the heat flux vector, although at the price of using a relatively large number of total computational steps. However, in spite of the found improvements for the calculation of the self-correlation of the heat flux vector, some statistical problems on this point remain on the particular application of the method. Finally, even with the presence of a clear statistical noise, the obtained values and temperature trend of the calculated thermal conductivity shows the classical 1/T decaying behavior reported in previous works for wurtzite ZnO and other related semiconductor systems using the alternative Boltzmann transport equation theory.
Jasmine Xavier A et al 2024 Phys. Scr. 99 075222
The field of H-IoT is emerging with enormous potential to empower various technologies. Smart cities and advanced manufacturing are a few of the fields where H-IoT is currently used. The issue with H-IoT is its heavy energy consumption while transmitting data, which makes scaling difficult. To overcome such issues, a hybrid approach of Crayfish Optimization (CFO) with FCM and Restricted Boltzmann Machine (RBM) with Soft Sign Activation (SSA) has been proposed. Initially, Node initialization lays the foundation by configuring individual sensor nodes for network participation. After initialization, Fuzzy C Means clustering optimizes data aggregation by categorizing nodes into clusters based on similarity. Gathering Neighbor Node Traffic Data (NNTD) provides insights into communication patterns. Based on the threshold of NNTD, node localization is performed that enhances network accuracy by pinpointing sensor node locations. Integration of CFO into clustering, along with localization further improves cluster head selection for optimal data routing. Classification through the RBM with SSA function enhances anomaly detection, combining data analysis for optimizing energy utilization in heterogeneous IoT environments. The 'combined CFO-FCM and SSA-RBM' has been implemented in MATLAB and achieved an accuracy of 94.50%. As a result, the overall performance of the system is improved.
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Da Zhang et al 2024 Phys. Scr. 99 062010
The arc discharge plasma (ADP) technology has been widely developed in the fields of cutting, welding, spraying and nanomaterials synthesis over the past 20 years. However, during the process of ADP, it is difficult to explain the generation and evolution of arc column, the interaction between arc column and electrodes, as well as the effect of plasma generator structure on the physical characteristics of ADP by experimental means. Therefore, numerical simulation has become an effective mean to explore the physical characteristics of ADP, but also faces severe challenges because it involves multiple physical field coupling, resolution of multiscale features as well as robustness in the presence of large gradients. From the point of view of the construction of ADP mathematical physical models and combined with the practical application of ADP, this paper systematically reviews the researches on physical properties of arc column, near-cathode region, near-anode region as well as the today's state of the numerical simulation of plasma generators. It provides a good reference for further mastering the physical characteristics of plasma, guiding the industrial application of plasma and optimizing the design of plasma generators. Meanwhile, the relevant computational aspects are discussed and the challenges of plasma numerical simulation in the future are summarized.
Muhammad Usman et al 2024 Phys. Scr. 99 062009
Infectious diseases caused by bacterial pathogens are currently a significant problem for global public health. Rapid diagnosis and effective treatment of clinically significant bacterial pathogens can prevent, control, and inhibit infectious diseases. Therefore, there is an urgent need to develop selective and accurate diagnostic methods for bacterial pathogens and clinically effective treatment strategies for infectious diseases. In recent years, developing novel nanoparticles has dramatically facilitated the rapid and accurate diagnosis of bacterial pathogens and the precise treatment of contagious diseases. In this review, we systematically investigated a variety of nanoparticles currently applied in the diagnosis and treatment of bacterial pathogens, from synthesis procedures to structural characterization and then to biological functions. In particular, we first discussed the current progress in applying representative nanoparticles for bacterial pathogen diagnostics. The potential nanoparticle-based treatment for the control of bacterial infections was then carefully explored. We also discussed nanoparticles as a drug delivery method for reducing antibiotic global adverse effects and eradicating bacterial biofilm formation. Furthermore, we studied the highly effective nanoparticles for therapeutic applications in terms of safety issues. Finally, a concise and insightful discussion of nanoparticles' limitations, challenges, and perspectives for diagnosing and eradicating bacterial pathogens in clinical settings was conducted to provide a direction for future development.
M E Semenov et al 2024 Phys. Scr. 99 062008
The Preisach model is a well-known model of hysteresis in the modern nonlinear science. This paper provides an overview of works that are focusing on the study of dynamical systems from various areas (physics, economics, biology), where the Preisach model plays a key role in the formalization of hysteresis dependencies. Here we describe the input-output relations of the classical Preisach operator, its basic properties, methods of constructing the output using the demagnetization function formalism, a generalization of the classical Preisach operator for the case of vector input-output relations. Various generalizations of the model are described here in relation to systems containing ferromagnetic and ferroelectric materials. The main attention we pay to experimental works, where the Preisach model has been used for analytic description of the experimentally observed results. Also, we describe a wide range of the technical applications of the Preisach model in such fields as energy storage devices, systems under piezoelectric effect, models of systems with long-term memory. The properties of the Preisach operator in terms of reaction to stochastic external impacts are described and a generalization of the model for the case of the stochastic threshold numbers of its elementary components is given.
A Srinivasa Rao 2024 Phys. Scr. 99 062007
Over the past 36 years much research has been carried out on Bessel beams (BBs) owing to their peculiar properties, viz non-diffraction behavior, self-healing nature, possession of well-defined orbital angular momentum with helical wave-front, and realization of smallest central lobe. Here, we provide a detailed review on BBs from their inception to recent developments. We outline the fundamental concepts involved in the origin of the BB. The theoretical foundation of these beams was described and then their experimental realization through different techniques was explored. We provide an elaborate discussion on the different kinds of structured modes produced by the BB. The advantages and challenges that come with the generation and applications of the BB are discussed with examples. This review provides reference material for readers who wish to work with non-diffracting modes and promotes the application of such modes in interdisciplinary research areas.
Amrinder Mehta et al 2024 Phys. Scr. 99 062006
Shape Memory Alloys (SMAs) are metallic materials with unique thermomechanical characteristics that can regain their original shape after deformation. SMAs have been used in a range of industries. These include consumer electronics, touch devices, automobile parts, aircraft parts, and biomedical equipment. In this work, we define the current state of the art in SMA manufacturing and distribution across the aerospace, healthcare, and aerospace industries. We examine the effect of manganese on the structure and mechanical and corrosive properties of SMA Cu-Al-Ni and discuss the importance of incorporating small and medium-sized enterprises in the study of cu-Al luminum. This research outlines a fundamental example of SME integration in the analysis of superelasticity, a critical instance of SMA activity. It can also serve as a reference for activities such as medical, aerospace, and other industries that target SMA-based equipment and systems. Also, they can be used to look at SMA activation and material upgrade mechanisms. These FEM simulations are advantageous in optimizing and promoting design in fields such as aerospace and healthcare. FEM simulations identify the stress and strength of SMA-based devices and structures. This would result in minimizing cost and usage and lowering the risk of damage. FEM simulations can also recognize the weaknesses of the SMA designs and suggest improvements or adjustments to SMA-based designs.
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Fouad et al
We studied the X-ray evolution of the core collapse, Type IIb, supernova SN 2008ax. In addition to the four Swift/XRT observations previously published, we included, for the first time, two observations from XMM-NEWTON to our analysis that have not been published before. By focusing on the early observations of the SN 2008ax, we were able to explore the time evolution of both X-ray luminosity (Lx) and temperature (Tx) during the radiative phase. The analysis showed that the evolution of Lx and Tx can be expressed as a power law as Lx ∝ t -0.85 and Tx ∝ t -0.46, respectively. Based on the observed X-ray luminosity, we estimated the mass-loss rate () for the progenitor star to be approximately 0.64 ± 0.15 × 10−5 M⊙ yr -1, for a wind velocity of 10 km s-1. This finding is in good agreement with the previous studies.
Yazdankish
This study examines the shielding properties of polyvinylidene difluoride reinforced with 20%, 40%, and 60% weight fractions of tungsten and compares the findings to those obtained from lead. The mass and linear attenuation coefficient, half-value layer, and effective atomic number were calculated using the Phy-X/PSD software. From the photon interactions with matter point of view, the Photoelectric effect dominates in low-energy photons, while pair production is dominant in high-energy photons; meanwhile, Compton scattering remains almost constant across the energy range. The results show that the mass attenuation coefficient is higher for low-energy photons, and composites with a higher weight fraction of tungsten exhibit higher values of mass attenuation coefficients. The half-value layer decreased as the weight fraction of tungsten increased, and the effective atomic number was higher for lower energy photons. These findings were contrasted against calculations derived for lead. Within the energy interval of 20-200 keV, the mass attenuation coefficient for lead was observed to be approximately two times that of the optimal values recorded for the specific composites under examination, whereas at 2 MeV, this discrepancy diminished. The minimum half-value layer for polyvinylidene difluoride augmented with 60% weight proportions of tungsten in comparison to lead was identified at an energy of 2 MeV. During this interval, the half-value layer for this composite material was threefold greater than that of lead. Although the mass attenuation coefficient is higher for lead, in some energy ranges (about two MeV), the findings from the selected composites are completely comparable to those from lead, demonstrating the ability and performance of the polyvinylidene difluoride composites for radiation shielding.
Lu et al
In terahertz wireless communication systems, flexible wavefront control devices based on various structure metasurfaces have attracted enormous attention for next-generation communication. In general, tunable terahertz metasurfaces integrated with active materials or MEMS technologies are used for dynamic wavefront control. However, most existing metasurfaces suffer from various limitations, including intrinsic properties of active materials, low reliability of MEMS technologies, and single polarization mode of incident waves, which hinders their development and application. To address these challenges, herein, we design two types of reflective graphene-based coding metasurfaces for active wavefront control. The metasurface coding meta-atom is composed of a graphene split-ring resonator, a dielectric layer, and a metal ground plane. By simply rotating the coding meta-atom, independent 2π phase coverage for circularly polarized (CP) or linearly polarized (LP) illumination can be achieved, enabling polarization multiplexing. Thus, a metasurface (MS-1) is constructed based on the vortex phase profile to generate different wavefronts. Moreover, these wavefronts can be actively switched between a vortex beam, a multi-beam, and a specular reflection beam by altering the polarization mode of the incident waves and the Fermi level of the graphene coding regions Additionally, another metasurface (MS-2) is developed according to the parabolic phase profile to create a tunable metalens that allows active control over focal intensity and depth by adjusting the Fermi level of graphene. Such wavefront-controlled metasurfaces have high capacity and integration, making them very promising for potential applications in terahertz communication and imaging systems.
Li et al
This article's purpose is to investigate the inverse scattering transform of the nonlocal long wave-short wave (LW-SW) equation and its multi-soliton solutions via Riemann-Hilbert (RH) approach. By using spectral analysis to the Lax pair of LW-SW equation, the RH problem can be constructed. However, we consider spectral analysis from the time part rather than the usual space part, since it is hard to obtain the analyticity of the space part. Then the RH problem can be solved and the formula of the soliton solutions can be given. We provide several special soliton solutions including Y-shaped solitons, V-shaped solitons, bound-state solitons and mixed four-soliton solutions. Compared with the local case, the solutions of nonlocal LW-SW equation exhibit distinct characteristics that (i) these soliton solutions are strictly symmetric with respect to x=0 under special parameter conditions, (ii) the mixed four-soliton solution, which combines Y-type and bound-state solitons, is novel.
Khademi et al
The advancement of scientific machine learning (ML) techniques has led to the development of methods for approximating solutions to nonlinear partial differential equations (PDE) with increased efficiency and accuracy. Automatic differentiation has played a pivotal role in this progress, enabling the creation of physics-informed neural networks (PINN) that integrate relevant physics into machine learning models. PINN have shown promise in approximating the solutions to the Navier-Stokes equations, overcoming limitations of traditional numerical discretization methods. However, challenges such as local minima and long training times persist, motivating the exploration of domain decomposition techniques to improve it. Previous domain decomposition models have introduced spatial and temporal domain decompositions but have yet to fully address issues of smoothness and regularity of global solution. In this study, we present a novel domain decomposition approach for PINN, termed domain discretized PINN (DD-PINN), which incorporates complementary loss functions, subdomain-specific transformer networks (TRF), and independent optimization within each subdomain. By enforcing continuity and differentiability through interface constraints and leveraging the Sobolev (H1) norm of the mean squared error (MSE), rather than the Euclidean norm (L2), DD-PINN enhances solution regularity and accuracy. The inclusion of TRF in each subdomain facilitates feature extraction and improves convergence rates, as demonstrated through simulations of two test problems: steady-state flow in a two-dimensional lid-driven cavity and the time-dependent cylinder wake. Numerical comparisons highlight the effectiveness of DD-PINN in preserving global solution regularity and accurately approximating complex phenomena, marking a significant advancement over previous domain decomposition methods within the PINN framework.
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Nishith Mohan and Seshadev Padhi 2024 Phys. Scr. 99 075221
The study involves examining the global bifurcation structure associated with the nonconstant steady states of a reaction-diffusion predator-prey system where both the species interact in accordance with the Beddington DeAngelis response and the movement flux of the predator incorporates attractive transition. We consider the magnitude of population flux by attractive transition as the bifurcation parameter and employ the Crandall-Rabinowitz bifurcation theorem to study the global bifurcation structure associated with the problem. We have also derived some a priori estimates associated with the problem and carried out numerical simulations to support our theoretical results. This work can be regarded as the first step towards inclusion of population flux by attractive transition in scenarios where interactions are governed by complex functional responses.
Amirhossein Khademi and Steven Dufour 2024 Phys. Scr.
The advancement of scientific machine learning (ML) techniques has led to the development of methods for approximating solutions to nonlinear partial differential equations (PDE) with increased efficiency and accuracy. Automatic differentiation has played a pivotal role in this progress, enabling the creation of physics-informed neural networks (PINN) that integrate relevant physics into machine learning models. PINN have shown promise in approximating the solutions to the Navier-Stokes equations, overcoming limitations of traditional numerical discretization methods. However, challenges such as local minima and long training times persist, motivating the exploration of domain decomposition techniques to improve it. Previous domain decomposition models have introduced spatial and temporal domain decompositions but have yet to fully address issues of smoothness and regularity of global solution. In this study, we present a novel domain decomposition approach for PINN, termed domain discretized PINN (DD-PINN), which incorporates complementary loss functions, subdomain-specific transformer networks (TRF), and independent optimization within each subdomain. By enforcing continuity and differentiability through interface constraints and leveraging the Sobolev (H1) norm of the mean squared error (MSE), rather than the Euclidean norm (L2), DD-PINN enhances solution regularity and accuracy. The inclusion of TRF in each subdomain facilitates feature extraction and improves convergence rates, as demonstrated through simulations of two test problems: steady-state flow in a two-dimensional lid-driven cavity and the time-dependent cylinder wake. Numerical comparisons highlight the effectiveness of DD-PINN in preserving global solution regularity and accurately approximating complex phenomena, marking a significant advancement over previous domain decomposition methods within the PINN framework.
Sergei Gerasimov et al 2024 Phys. Scr.
The presented data refer to the Shattered Pellet Injector (SPI) experiments carried out at JET in 2019-2020. This paper is a full journal version of the data originally presented as posters at TMPDM_2020 and EPS_2021. This paper presents various aspects of the interaction of pellets with plasma and associated disruptions. The experiment was performed with Ip = (1.1 - 3.1) MA plasmas and mainly with Ne + D2 pellet composition, but also with Ar pellets. The Current Quench (CQ) time, τ80-20, is the key characteristic of mitigation effectiveness. A pellet with a high content of Ne or Ar can reduce the CQ duration below the upper required JET threshold. Plasmas with high (thermal + internal poloidal magnetic) pre-disruptive plasma energy require a high content of Ne pellets to obtain a short CQ duration. Pellets with a small amount of Ne (and accordingly large amount of D), instead of causing a mitigated CQ, create the conditions for a "cold" Vertical Displacement Events (VDE).
The SPI was applied to plasma with different status: mainly to normal ("healthy") plasma, i.e. not prone to disruption, post-disruptive and VDE plasma. This study shows that SPI effectiveness in terms of CQ duration and, accordingly, EM loads does not depend on the state of the plasma, whether it is "healthy" or post-disruptive plasma. SPI has been shown to reduce axisymmetric vertical vessel reaction forces by about (30-40)% compared to unmitigated disruptions.
On JET, the VDE, whether "hot" or "cold", always creates the conditions for a toroidal asymmetry in the plasma, so the VDE on the JET is referred to as Asymmetric VDE (AVDE). The interrupting of VDE and prevention of AVDE with SPI has been demonstrated. Thus, the effectiveness of disruption mitigation using SPI has been confirmed.
George Biswas et al 2024 Phys. Scr. 99 075103
We investigate the fidelity of Haar random bipartite pure states from a fixed reference quantum state and their bipartite entanglement. By plotting the fidelity and entanglement on perpendicular axes, we observe that the resulting plots exhibit non-uniform distributions. The distribution depends on the entanglement of the fixed reference quantum state used to quantify the fidelity of the random pure bipartite states. We find that the average fidelity of typical random pure bipartite qubits within a narrow entanglement range with respect to a randomly chosen fixed bipartite qubit is . Extending our study to higher dimensional bipartite qudits, we find that the average fidelity of typical random pure bipartite qudits with respect to a randomly chosen fixed bipartite qudit remains constant within a narrow entanglement range. The values of these constants are , with d being the dimension of the local Hilbert space of the bipartite qudit system, suggesting a consistent relationship between entanglement and fidelity across different dimensions. The probability distribution functions of fidelity with respect to a product state are analytically studied and used as a reference for the benchmarking of distributed quantum computing devices.
Sheng Liu et al 2024 Phys. Scr. 99 075604
Based on the parameters of the HL-2A experiment, the effect of energetic particles (EPs) on non-resonant high-order harmonics energetic particle modes (EPMs) with qmin>1 is investigated in the present work. Hybrid kinetic-magnetohydrodynamic nonlinear code M3D-K is performed to simulate the linear properties and the nonlinear evolution of the non-resonant EPM during neutral beam injection (NBI). To deeply understand the physical mechanism of interaction resonant between energetic-ions and non-resonant EPM, this work compares the effects of passing energetic particles and trapped energetic particles on the non-resonant EPM instabilities. It is numerically identified that EPs' effects on high n harmonics (m/n = 2/2, 3/3, 4/4) instability are more obvious than the m/n = 1/1 mode. Furthermore, the effects of energetic particles injection energy, the minimum safety factor qmin , toroidal rotation and beam ion distribution on the features of high n harmonics are also investigated specifically. Toroidal rotation is found to suppress high n harmonics, which is more obvious for the modes driven by trapped particles. Nonlinear simulation results show that these non-resonant high n harmonics can induce larger energetic ion transport, which may affect the plasma confinement performance.
Srihari N V et al 2024 Phys. Scr. 99 075917
Bismuth ferrite (BFO) is a prime candidate for room-temperature magnetoelectric coupling and multiferroic applications. The rhombohedral R3c phase of BFO is the source of many properties, but the phase purity and oxygen vacancies are still the biggest obstacles to its real-world application. Considering these facts, the present work investigates the effects of oxygen vacancies on the functional properties through manipulation of drying temperatures of spin-cast films, especially at temperatures around 280 °C, where both the secondary phase and oxygen vacancies are prevalent. One of the biggest sources of oxygen vacancy is bismuth volatilisation, and our work deals with the situation head-on, uncovering the effect of bismuth volatilisation on functional properties. The structural properties were studied using x-ray diffraction (XRD), and deeper insights into the surface topography of the samples were obtained using AFM imaging. The electrical and dielectric characteristics help distinguish and analyse the samples in terms of the presence of resistive switching. PUND studies were performed to determine the ferroelectric properties of the samples. A fifty percent reduction in the oxygen vacancies in the presence of secondary phases was observed when compared with the phase-pure sample, as shown by the XPS analysis. Deeper insights were provided into the valence band spectra by first-principles studies. This work shows that phase purity may not be the singular condition for enhancing functional properties, and fine-tuning the presence of secondary phases and oxygen vacancies may be the way forward. The ferroelectric polarisation in one of the samples exhibits a notably higher value when using chemical solution deposition methods, making it a promising candidate for memory devices.
Chongbin Xi et al 2024 Phys. Scr. 99 075513
In order to reduce the requirement of system bandwidth of Laser Doppler Velocimeter (LDV), a Dual-Doppler signal mixing LDV is proposed in this paper. By transmitting two beams to the moving surface, two Doppler signals are acquired and subsequently mixed to obtain a difference frequency signal. The measured speed can be calculated based on the frequency of this difference frequency signal. This novel structure significantly reduces the bandwidth requirements on the system, which can be further diminished by minimizing the angle between the two beams of the emitted light. Moreover, it exhibits enhanced robustness against variations in launch angle and enables defocusing measurements.
Sayed S.R Moustafa and Sara Said Khodairy 2024 Phys. Scr.
This investigation presents a comprehensive analysis of the historical trajectory of sunspot number (SSN) observations in Egypt, a country renowned for its rich astronomical heritage. Despite Egypt's long-standing practice in solar observation, the local SSN datasets are marred by a significant incidence of missing entries, posing formidable obstacles to the accurate evaluation of solar activity. Addressing this challenge, the study employs dynamic time warping (DTW) as a methodological tool to assess the alignment of local and global SSN datasets. This technique adeptly harmonizes these datasets by reconciling temporal inconsistencies and variations in sampling rates. Subsequent to the application of DTW, the research integrates orthogonal regression for the imputation of the absent values in the Egyptian SSN dataset. This method, preferred for its proficiency in managing errors in both the dependent and independent variables, deviates from conventional linear regression techniques, thereby providing a more nuanced approach to data approximation. The analysis unveils a substantial correlation between the estimated local SSN values and the global SSN indices, with the former consistently exhibiting lower figures. Nevertheless, these local values display parallel trends and seasonal fluctuations akin to those observed in the global dataset, validating the imputation method and highlighting the unique characteristics of the Egyptian SSN data within the global context of solar activity monitoring. The implications of these findings are significant for the discipline of solar physics, especially for regions contending with incomplete datasets. The methodologies advanced in this research offer a robust framework for the enhancement of datasets with missing data, thus broadening the comprehension of solar phenomena.
G Lopardo et al 2024 Phys. Scr. 99 075912
A new cryostat for the realization of the triple-point of the argon (83.8058 K), a defining fixed point of the International Temperature Scale of 1990 (ITS-90), was acquired at Italian National Metrological Institute (INRiM). The new system, manufactured by Fluke, is intended to substitute the current National reference, a model developed at BNM-INM in the 1975. The main difference between the two system is in the way to control the temperature. In the BNM-INM device the temperature is controlled adjusting the pressure of liquid nitrogen bath, in the Fluke system instead, an electrical heater wrapped around the argon cell is used, following cryogenic practice. This paper describes the result of the direct comparison and shows typical phase transitions obtained with the two argon systems. Then, a complete uncertainty budget is evaluated for the new Fluke system and compared with the National standard.
Axel Schulze-Halberg 2024 Phys. Scr. 99 075212
We construct approximate solutions to the stationary, one-dimensional Schrödinger equation for a hyperbolic double-well potential within the Dunkl formalism. Our approximation is applied to an inverse quadratic term contributed by the Dunkl formalism in the effective potential. The solutions we obtain are given in terms of confluent Heun functions. We establish parity of these solutions, discuss their elementary cases, and present an example of a system admitting bound states.