446494 research outputs found
Sort by
Further upgrades of the ASDEX Upgrade ICRF system
No full textThe original plans were to operate the tokamak ASDEX Upgrade (AUG) for ten years. The flexibility of the experiment lead to the fact, that AUG is now operating for over three decades. As the Ion Cyclotron range of Frequencies (ICRF) heating was AUG’s first auxiliary heating system, which went into operation in 1992, regular upgrades of different ICRF components are mandatory for different reasons. For example, due to a lack of supply, it became necessary to replace the pre-driver stage tetrode by a widely available triode in the ICRF generators. This change reduced the frequency range of the rf generators from 30 – 120 MHz to 30 – 60 MHz, still covering the experiment requirements. A long-time limitation was the behaviour of the high voltage supply of the driver stage of the rf generator. A new power converter was extensively tested on a test bed with promising results. Further upgrades include a redesign of the antenna vacuum pumping system to replace the maintenance intense cold heads. A redesign of the antenna vacuum feed through has also been made to increase the voltage standoff. For the implementation of a new rf generator in the near future, which will extend the frequency range from 30 MHz down to 24 MHz, changes in the antenna matching systems were made on two of the four ICRF antennas by adding a third stub tuner. For the integration of this rf generator into the AUG ICRF network, additional coaxial switches, which were recycled from a shortwave broadcasting station, are integrated in the ICRF system
Progress in the pre-conceptual design of the auxiliary heating and current drive system for the Tokamak Energy Fusion Pilot Plant
No full textAuxiliary heating and current drive is a crucial aspect of reactor-relevant tokamaks. Tokamak Energy is currently in the design phase of their Fusion Pilot Plant (FPP). Initial investigations for the flat-top phase of plasma scenarios rely exclusively on electron cyclotron (EC) waves as auxiliary heating and current drive source. This work focuses on parametric optimisation of the flat-top EC current drive scheme via ray-tracing simulations for three plasma scenarios, each having different magnetic field and aspect ratio. The purpose of the study is to maximise the normalised current drive efficiency ζ
ECCD. It is shown that EC waves in the O mode polarisation are capable of efficiently driving plasma current throughout the plasma volume, supporting the notion that EC waves can be the single auxiliary power source for flat-top operations
Observational evidence for a possible link between PAH emission and dust trap locations in protoplanetary disks
No full textContext. Polycyclic aromatic hydrocarbons (PAHs) are commonly detected in protoplanetary disks, but it is unclear what causes the wide range of intensities across the samples.
Aims. For this work, the measured PAH intensities of a range of disks were compared with ALMA dust continuum images in order to test whether there is evidence that PAHs are frozen out on pebbles in dust traps and only sublimate under certain conditions.
Methods. A sample was constructed from 26 T Tauri and Herbig disks located within 300 pc, with constraints on the 3.3 μm PAH intensity and with high-resolution ALMA continuum data. The midplane temperature was derived using a power law or via radiative transfer modeling. The warm dust mass was computed by integrating the flux within the 30 K radius and converted to a dust mass.
Results. A strong correlation with a Pearson coefficient of 0.88±0.07 between the 3.3 μm PAH intensity and the warm dust mass was found. The correlation is driven by the combination of deep upper limits and strong detections corresponding to a range of warm dust masses. Possible correlations with other disk properties, for example a far-UV radiation field or total dust mass, are much weaker. Correlations with PAH features at 6.2, 8.6, and 11.3 μm are potentially weaker, but this could be explained by the smaller sample for which these data were available.
Conclusions. The correlation is consistent with the hypothesis that PAHs are generally frozen out on pebbles in disks, and are only revealed in the gas phase if those pebbles have drifted toward warm dust traps inside the 30 K radius and vertically transported upward to the disk atmosphere with sufficiently high temperature to sublimate PAHs into the gas phase. This is similar to previous findings on complex organic molecules in protoplanetary disks, and provides further evidence that the chemical composition of the disk is governed by pebble transport
Research on the Green Construction Evaluation System for Urban Underground Utility Tunnels
No full textTo address issues such as the numerous factors and unreasonable weight allocation in existing green construction evaluation systems for urban underground utility tunnels, this paper systematically reviews relevant domestic and international research and, considering the unique characteristics of underground utility tunnels, proposes evaluation factors encompassing four dimensions: resource utilization, environmental impact, construction management, and technological innovation.Through the Delphi method, the evaluation factors were screened and refined, ultimately leading to the identification of six core indicators: application of trenchless construction techniques, recycling and utilization of spoil, innovation in green construction techniques, application of information technology, conservation of energy and material resources, and integrated control of dust and noise pollution.These core indicators collectively embody the intensive nature, circularity, technological innovation, and environmental sensitivity inherent in the green construction of utility tunnels. Validation results using the fuzzy comprehensive evaluation method demonstrate that the proposed system can effectively assess the green construction performance of different construction methods. This study provides a scientific basis for standardizing and promoting the sustainable development of green construction practices for urban underground utility tunnels, thereby advancing the green transformation of urban infrastructure development
Application of the Combination of High-Density Electrolysis Method and Drilling Method in Bridge Karst Cave Investigation
No full textIn the design and construction of expressway bridges, over-reliance on drilling investigation often suffers from the limitation of “using points to represent the whole area”, making it difficult to fully reveal the spatial structural characteristics of the pile foundation bearing stratum. This discrepancy frequently leads to inconsistencies between actual geological conditions and survey data during construction. Taking the Leicun Bridge of the Guangzhou-Lianzhou Expressway as an example, no karst development was identified in the detailed survey stage of this project; however, a large karst cave was discovered during construction. To clarify the distribution and scale of the karst cave, this study adopted a comprehensive investigation method combining “3D surveying + high-density electrical method + drilling verification”. Through the high-density electrical method, 9,384 measurement points were collected along 13 survey lines (with a total length of 4,435 meters). By integrating RES2DINV inversion and Surfer planar mapping, the identification and interpretation of low-resistivity anomaly areas were realized. Subsequent drilling verification finally confirmed that the karst cave has a length of approximately 120 meters, a width of approximately 25 meters, a height of approximately 11 meters, and a total volume of about 1.68×10⁴ cubic meters. The results show that the high-density electrical method can effectively detect large karst caves that cannot be found by drilling alone, and its combination with drilling significantly improves the accuracy and reliability of geological investigation. This study provides a scientific basis for the design modification and treatment of pile foundations in karst cave areas, and has popularization value for the investigation of bridges in similar karst regions
Advances in the remediation of contaminated soils using combined biochar and microorganisms
No full textHeavy metal pollution represents a critical global environmental challenge. Biochar-microbe synergistic remediation (BMS) has emerged as a promising green strategy, enabling simultaneous removal and stabilization of multiple heavy metals through synergistic biochar-microorganism interactions. Experimental results demonstrate its high remediation efficiency: Cr(VI)-reducing bacteria immobilized on Enteromorpha-derived biochar achieved 94.2% conversion of Cr(VI) with approximately 84% total chromium fixation; Pseudomonas-loaded biochar enhanced plant cadmium accumulation by 1.8–2.4 times; and immobilized bacterial communities removed approximately 65% of arsenic via biotransformation and surface co-precipitation. This review systematically elucidates the underlying synergistic mechanisms of BMS, including soil condition improvement, microbial habitat provision, adsorption gradient enhancement, and enzyme activity elevation, while also highlighting its impacts on heavy metal speciation and plant growth. Finally, key future research directions are outlined
Corrosion Product Filled Paste and Corrosion Layer in Reinforced Concrete Beam at Coastal Atmosphere
No full textThis study investigated the corrosion product filled paste (CP) and corrosion layer (CL) of a beam from a concrete structure at coastal atmospheric environment. The structure was built in 1970s and near the east sea. Part of the beam was cut into several blocks and then polished. The thickness of CP (TCP) and CL (TCL) were observed and measured by scanning electron microscopy. A TCP–TCL model in marine atmosphere is proposed, which provides a mechanistic basis for predicting corrosion evolution and guiding maintenance strategies for aging marine concrete structures. The steel corrosion and values of kT and TCPmax, in the TCP–TCL model of the steel bars, near the windward surface, are larger than those near the leeward surface
A hybrid physics-informed neural network based multiscale solver as a partial differential equation constrained optimization problem
No full textIn this work, we study physics-informed neural networks (PINNs) constrained by partial differential equations (PDEs) and their application in approximating PDEs with two characteristic scales. From a continuous perspective, our formulation corresponds to a non-standard PDE-constrained optimization problem with a PINN-type objective. From a discrete standpoint, the formulation represents a hybrid numerical solver that utilizes both neural networks and finite elements. For the problem analysis, we introduce a proper function space, and we develop a numerical solution algorithm. The latter combines an adjoint-based technique for the efficient gradient computation with automatic differentiation. This new multiscale method is then applied exemplarily to a heat transfer problem with oscillating coefficients. In this context, the neural network approximates a fine-scale problem, and a coarse-scale problem constrains the associated learning process. We demonstrate that incorporating coarse-scale information into the neural network training process via a weak convergence-based regularization term is beneficial. Indeed, while preserving upscaling consistency, this term encourages non-trivial PINN solutions and also acts as a preconditioner for the low-frequency component of the fine-scale PDE, resulting in improved convergence properties of the PINN method. The relevance of our approach to material science is discussed
Spatial exponential decay of perturbations in optimal control of general evolution equations
No full textWe analyze the robustness of optimally controlled evolution equations with respect to spatially localized perturbations.We prove that if the involved operators are domain-uniformly stabilizable and detectable, then these localized perturbations only have a local effect on the optimal solution. We characterize this domain-uniform stabilizability and detectability for the transport equation with constant transport velocity, showing that even for unitary semigroups, optimality implies exponential damping. We extend this result to the case of a space-dependent transport velocity. Finally we leverage the results for the transport equation to characterize domain-uniform stabilizability of the wave equation. Numerical examples in one space dimension complement the theoretical results
Revised optical classification of a sample of gamma-ray-emitting active galactic nuclei with GTC and VLT
No full textWe report the results of the optical follow-up of a sample of γ-ray-emitting active galactic nuclei (AGNs). New high-quality optical spectra were obtained using the Gran Telescopio Canarias with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy and the European Southern Observatory’s Very Large Telescope Unit Telescope 1 with the FOcal Reducer and low dispersion Spectrograph 2. From the analysis of these spectra, we confirmed the previous narrow-line Seyfert 1 (NLS1) classification for four objects and discovered two new NLS1s, bringing the total number of optically confirmed γ-NLS1s to 26. We also identified two ambiguous cases between NLS1 and intermediate Seyfert (IS), three ISs, one broad-line Seyfert 1, and one Seyfert 2. Based on the new spectra, we calculated black hole masses ranging from 106.25 to 109.32 M⊙ and Eddington ratios spanning 0.05 to 2.07. This reclassification provides support for the scenario in which AGNs with relatively low black hole masses are capable of launching powerful relativistic jets and contributes to our broader understanding of γ-ray-emitting AGNs