446494 research outputs found
Sort by
Janus ZrFX (X = Cl, Br, I) monolayers with giant vertical piezoelectricity exhibiting electronegativity difference ratio effect
No full textThe advancement of piezoelectric materials is often constrained by insufficient understanding of their internal mechanisms and limited out-of-plane piezoelectric response. In this work, Janus ZrFX (X = Cl, Br, or I) monolayers are proposed, and their stress and strain piezoelectric coefficients are systematically investigated. The structural stability of these monolayers is confirmed through analyses of dynamic, thermodynamic, and mechanical properties. The results reveal that breaking mirror symmetry in these structures leads to remarkable vertical piezoelectricity, with piezoelectric strain coefficients exceeding those of other Janus materials by two to three orders of magnitude. The significant enhancement is explained by Bader charge and electronegativity difference ratios. The larger the electronegativity difference ratio is, the stronger the piezoelectricity will be. Furthermore, the superior vertical piezoelectric performance is associated with strong built-in electric fields and high Born effective charges of halogen atoms, providing deeper insight into the underlying physical origin. Additionally, ZrFX monolayers exhibit an intrinsic coupling between piezoelectricity and carrier transport, where a weaker polarization field correlates with higher hole mobility. This study not only identifies promising candidates for energy conversion and tactile sensing but also lays a theoretical foundation for the design of advanced nanoscale piezoelectric devices
Optics in spiral dislocation spacetime: torsion as a geometric waveguide and frequency-filtering mechanism
No full textWe present an exact analytical study of null trajectories and scalar wave propagation in a -dimensional spacetime containing a spiral dislocation, a topological defect characterized by torsion in the absence of curvature. For null rays, the torsion parameter modifies the affine structure, enforcing a finite turning radius , and inducing a torsion-mediated angular deflection that decreases monotonically with increasing . The photon trajectory departs from the curvature-induced lensing paradigm, exhibiting instead a purely topological exclusion zone around the defect core. Moreover, the results can, in principle, be mapped onto laboratory frames and conditions. In the wave regime, we recast the Helmholtz equation into a Schrödinger-like form and extract a spatially and spectrally dependent refractive index . This index approaches unity asymptotically at large distances but diverges strongly and negatively near the dislocation core due to torsion-induced geometric contributions. The resulting refractive index profile governs the transition from propagating to evanescent wave behavior, with low-frequency modes undergoing pronounced localization and suppression. Our findings demonstrate that torsion alone, even in the absence of curvature, can act as a geometric regulator of both classical and quantum propagation, inducing effective anisotropy, frequency filtering, and confinement. This framework provides a rare exact realization of light-matter interaction in a torsion-dominated background, with potential applications in analog gravity systems and photonic metamaterials designed to emulate non-Riemannian geometries
Charged Dirac perturbations on Reissner–Nordström black holes in a cavity: quasinormal modes with Robin boundary conditions
No full textWe investigate charged Dirac quasinormal spectra on Reissner–Nordström black holes in a mirror-like cavity. For this purpose, we first derive charged Dirac equations, and two sets of Robin boundary conditions following the vanishing energy flux principle. The Dirac spectra are then computed both analytically and numerically. Our results reveal a symmetry hidden in the Dirac spectra between two boundary conditions. Moreover, when the cavity is placed close to the event horizon , we identify that, in the neutral background the Dirac spectra asymptote to [] for the first [second] boundary condition; while in the charged background the real part of charged Dirac spectra asymptote to for both boundary conditions; where N is the overtone number, q and Q are charges for the field and for the background. In particular, we uncover a striking anomalous decay pattern, i.e. the excited modes decay slower than the fundamental mode, when the charge coupling qQ is large. Our results further illustrate the robustness of vanishing energy flux principle, which are applicable not only to anti-de Sitter black holes but also to black holes in a cavity
ECCD Studies for a Volumetric Neutron Source (VNS)
No full textWe explore the theoretical capabilities of Electron Cyclotron Current Drive (ECCD) in a volumetric neutron source (VNS), a high-neutron-fluence tokamak for component testing and qualification that is being considered in the frame of the EUROfusion Consortium. Two selected applications are addressed, namely bulk current drive in the plasma centre and stabilization of Neoclassical Tearing Modes (NTMs). It is shown that a current drive efficiency above 50 kA/MW can be reached, close to typical values reported for DEMO central ECCD. Suppression of NTMs should require less than 10 MW, but this power might become marginal in case of significant beam broadening caused by density fluctuations. The optimum launcher parameters for the envisaged applications will be further iterated to find the sweet spot between physics and engineering constraints
Echoes from the dark: Galaxy catalog incompleteness in standard siren cosmology
No full textGravitational wave observations can be combined with galaxy catalogs to constrain cosmology and test modified gravity theories using the standard siren method. However, galaxy catalogs are intrinsically incomplete due to observational limitations, potentially leaving host galaxies undetected, thereby weakening constraints and potentially introducing systematic errors. In this work, we present a self-consistent framework to study catalog incompleteness and host weighting effects, implemented in the publicly available CHIMER
The quest for Magrathea planets
No full textContext. Planetary formation might occur at different stages of the stellar evolution. In particular, theoretical studies have been focusing on addressing whether formation can occur around compact binaries that evolved beyond the main sequence. Formation of second-generation planets has been tested in circumbinary disks formed by the ejection of stellar material from binaries composed of either a main-sequence star and a white dwarf or a double white dwarf (DWD). In the latter case, formation appears to be common and to create sub-Neptunian, Neptunian, and giant planets that can migrate within 1 au of the central binary. Nevertheless, the orbital stability of these systems has yet to be studied.
Aims. We investigate whether planetary systems that formed around compact DWDs in nonresonant and resonant configurations can be dynamically stable over a timescale of a few million years.
Methods. We performed N-body simulations of circumbinary multiplanetary systems that initially hosted two, three, four or five planets by employing a hybrid symplectic integrator made specifically for circumbinary systems. We recorded the catastrophic events that planetary systems experience and employed a variety of metrics, such as orbital spacing, variation in the center of mass, and normalized angular momentum deficit, to explore the outcomes of their long-term evolution. Furthermore, we evaluated the potential for detecting these systems in their final configurations with the Laser Interferometer Space Antenna mission by measuring the overall amplitude shift in the gravitational-wave frequency induced by their planets.
Results. Our results show that planets orbiting DWDs can be stable over the studied timescales. While planetary systems starting with two planets are more likely to survive unaltered, planetary systems with three, four, or five planets experience catastrophic events that cause them to lose some of their original planets. At the end of their phases of dynamical instability, the five-planet population is completely disrupted, and most of the systems host only two surviving planets. This increases the number of two-planet systems by 122% with respect to their initial abundance and creates a single-planet population of 7% of all systems. Additionally, the four-planet population decreases by 56.1% and the three-planet population by 22.5%. Finally, 7.7% of the systems are disrupted; they initially hosted more than two planets. Most of the systems that in the end only host a single planet are potential candidates for the Laser Interferometer Space Antenna mission. A handful of multiplanet systems might be detected. Finally, we provide a formula for estimating the amplitude shift in the gravitational-wave frequency for multiplanet systems orbiting DWDs.
Conclusions. Throughout our analysis, we highlight the importance of characterizing the system orbits and estimating their normalized angular momentum deficit in order to distinguish between the different dynamical scenarios presented above. Ultimately, second-generation systems might represent crucial targets for the Laser Interferometer Space Antenna mission because they reside within its observability range
Research progress in metamaterial-inspired klystrons
No full textMetamaterials are a class of artificial subwavelength structures exhibiting novel electromagnetic properties that are absent or difficult to achieve in natural materials. These novel properties include negative refractive, reversed Doppler effect, reversed Cherenkov radiation, and anomalous radiation pressure, and are primarily determined by the shape, dimensions, and arrangement of their unit cells. Loading metamaterials into klystrons can leverage their subwavelength characteristics to achieve device miniaturization. Based on coherent transition radiation and the subwavelength characteristics of metamaterials, a series of significantly miniaturized and high-efficiency klystrons has been developed. Notably, the first S-band metamaterial-inspired klystron features a high-frequency structure volume approximately 0.44 times that of a conventional klystron, achieving a measured electron efficiency of 57.4%. Compared to conventional klystrons, the first P-band metamaterial-inspired klystron exhibits a 66% reduction in high-frequency structure volume and a 32% reduction in weight, with a measured electron efficiency exceeding 48%. These experimental results validate the miniaturization and high-efficiency advantages of metamaterial-inspired klystrons, which hold significant application prospects in large scientific facilities, radar, communications, medical imaging, microwave heating, and other fields
The Role of Farmer Corporate Actors in Supporting Farm Sustainability (Case Study: PT Sembada Agro Lestari)
No full textThis study aims to analyse the role of multiple actors in supporting farm sustainability within the farmer corporation PT Sembada Agro Lestari (SMILE). Using a descriptive qualitative approach supported by Focus Group Discussions (FGD), the research explores the contributions of key actors including the government, extension workers, farmers, the private sector, and financial institutions in the operation and development of the corporation's business units. The findings show that each actor plays a strategic role: the government provides capital support and regulatory facilitation; extension workers strengthen technical and managerial capacity; farmers ensure participation, land allocation, and product supply; the private sector enhances access to inputs and markets; and financial institutions improve operational capacity through mechanization financing. Collaboration among these actors enables PT SMILE to address challenges in its business sectors such as input procurement, machinery services, grain trading, and seed breeding. Overall, multi-actor synergy significantly improves efficiency, productivity, and resilience, indicating that collaborative governance is essential for achieving sustainable farmer corporations
Economic Resilience of Indonesian Farmers: Statistical and Machine Learning Approach for Sustainable Agribusiness Strategy
No full textFarmers' economic resilience plays a critical role in sustaining agricultural systems and national food security. This study analyzes Indonesia's Farmer Terms of Trade (NTP) from 2022-2025 using a hybrid methodology that integrates descriptive-inferential statistics, cluster analysis, and machine learning. Monthly data for NTP, the price index received (IT), and the price index paid (IB) were examined alongside key input-cost components: fertilizer, transportation energy, and agricultural wages. Statistical tests confirm a significant post-2022 recovery, with NTP rising by 4.76% in 2023 and 6.36% in 2024. K-Means clustering identifies three resilience regimes: a cost-shock phase in 2022, a stabilization phase in 2023, and a commodity-driven boom in 2024. A Random Forest model (R2 = 0.887) highlights transportation costs as the strongest determinant of NTP fluctuations (39.1% importance). The findings show that cost-price dynamics, particularly fuel-related expenses, dominate short-term resilience, while commodity-price cycles shape medium-term adaptive capacity. This study provides an evidence-based framework for strengthening farmer resilience through targeted input-price stabilization, adaptive agribusiness strategies, and long-term structural transformation
Risk Mitigation Priorities in a Sustainable Pasteurized Milk Supply Chain: A House of Risk Approach in a Small-Scale Dairy Company
No full textThe pasteurized milk supply chain plays a strategic role in economic, social, and environmental sustainability, yet is vulnerable to risks at every level. This study aims to identify key risks, prioritize risk agents, and formulate effective mitigation strategies for a pasteurized milk supply chain in Indonesia. The House of Risk was used through a two-stage analysis with input from 9 experts representing farmers, collectors, and processing companies. The mapping yielded 38 risks and 30 risk agents, and a priority assessment was calculated using aggregate risk potential and an effectiveness-to-difficulty ratio. Key findings identified Farmer's error in cattle rearing as the most dominant risk agent with low milk quality and quantity as the next priority. Priority mitigation strategies included education on cattle rearing management, the development of SOPs on farms, and monitoring of on—farm activities. Integrated on-farm activity scheduling and business record-keeping were implemented in the next phase to strengthen efficiency, traceability, and data-driven decision-making. A phased approach focused on the upstream sector increased system resilience, reduced waste, maintained raw material quality, and strengthened partnerships between stakeholders. Practical implications demonstrate the readiness for adoption in small-to medium-scale businesses and the relevance of its application to other fresh food commodities with similar characteristics