Point Source Research Articles

Vertical line time domain green function and its applications in numerical simulation of ship seakeeping performance

In present study, a vertical line source time domain Green function is proposed and the subsequent numerical evaluation methods are described in detail. For which, Taylor expansion and Chebyshev approximation algorithms are originally extended from point source to line source for small parameters, as well as asymptotic expansions are extended for large parameters. Meanwhile, polynomials are originally proposed to replace the asymptotic expansions to improve the computational efficiency. The accuracy and stability of the proposed method are validated through several cases and good agreement can be obtained.Furthermore, a hybrid Green function method based on the vertical line source Green function and Rankine source is developed for time domain simulation of seakeeping performances of ships. With respect to the hybrid method, the flow domain is divided into inner part and outer part by an artificial control surface. The first-order Taylor Expansion Boundary Element Method (TEBEM) based on the Rankine panel distribution is applied in the inner part, while three-dimensional panel method based on the vertical line source Green function distribution is adopted in the outer part. Under this circumstance, motions of the single-ship (Slender Wigley and Blunt Wigley) and two-ship (two side-by-side ships) in head waves are numerically investigated. The numerical results agree well with the experimental data, which proved the feasibility and the accuracy of present hybrid Green function method for motion prediction of both single-ship and two-ship.

A deep neural network for positioning and inter-crystal scatter identification in multiplexed PET detectors: a simulation study.


High-resolution PET relies on the accurate positioning of annihilation photons impinging the crystal array. However, conventional positioning algorithms in light-sharing PET detectors are often limited due to edge effects and/or the absence of additional information for identifying and correcting scattering within the crystal array (known as inter-crystal scattering). Using GATE simulations, this study explores the feasibility of deep neural network techniques for more precise event positioning in finely segmented and highly multiplexed PET detectors with light-sharing. 
Approach:
Initially, the spatial and statistical properties of inter-crystal scatter (ICS) events in finely segmented LYSO PET detectors were investigated. Next, a deep neural network (DNN) for crystal localisation was designed, trained and tested with light distributions of photoelectric (P) and Compton + photoelectric (CP) events simulated using optical GATE and an analytical method to speed up data generation. Using the statistical properties of ICS events, an energy-guided positioning algorithm was then built into the DNN. The positioning algorithm enables selection of the unique or first crystal of interaction in P and CP events, respectively. Performance of the DNN was compared with Anger logic using light distributions from simulated 511-keV point sources placed at different locations around a single PET detector module. 
Main results: The fraction of events forward and backward scattered in the LYSO detector was 0.54 and 0.46, respectively, whereas naïve application of the Klein-Nishina formulation predicts 70% forward scatter. Despite coarse photodetector data due to signal multiplexing, the DNN demonstrated a crystal classification accuracy of 90% for P events and 82% for CP events. For crystal positioning, the DNN outperformed Anger logic by at least 34% and 14% for P and CP events, respectively. Further improvement is somewhat constrained by the physics - specifically, the ratio of backward to forward scattering of gamma rays within the crystal array being close to 1. This prevents selecting the first crystal of interaction in CP events with a high degree of certainty.
Significance: Light sharing and multiplexed PET detectors are common in high-resolution PET, yet their traditional positioning algorithms often underperform due to edge effects and/or the difficulty in correcting ICS events. Our study indicates that energy-guided DNN-based event positioning has the potential to enhance 2D coincidence event positioning accuracy by nearly a factor of 3 compared to Anger logic. However, further improvements are difficult to foresee without additional information such as event timing.

Self-purification in tropical upland rivers as affected by environmental factors: the case of Balili River in Benguet, Philippines

A major data gap in tropical river ecology is the limited documentation of natural water purification of upstream rivers. This study documented the improvement of water quality of downstream Balili River as affected by environmental factors and macrophyte diversity using a mixed-method approach (water quality assessment, plant inventory, field observation, canonical correspondence analysis, community interview). Results showed that the distance from pollution plays a significant role in the self-purification of the river while the floral diversity maintains the riparian from further contaminating the water and at the same time absorbing air pollutants. Generally, the pollution reduction and %change is exponential at 2 and 3 km from point source then taper at 4 and 5 km. At 3 km from the point source, 30% improvement in TDS, BOD and salinity, 25% for EC, 20% in TSS, 35% in WQI, 36% in CPI, and 50% for DO were noted. Key factors that influence the self-purification process in the river were distance from pollution source, elevation, human disturbance (as indicated by %tree canopy) and temperature. These findings highlight the importance of distance from pollution sources and floral diversity in driving water quality improvements, with implications for sustainable water resource management in tropical regions.

A Posteriori Error Analysis of Defect Correction Method for Singular Perturbation Problems With Discontinuous Coefficient and Point Source

Abstract The paper presents a defect correction method to solve singularly perturbed problems with discontinuous coefficient and point source. The method combines an inexpensive, lower-order stable, upwind difference scheme and a higher-order, less stable central difference scheme over a layer-adapted mesh. The mesh is designed so that most mesh points remain in the regions with rapid transitions. A posteriori error analysis is presented. The proposed numerical method is analyzed for consistency, stability, and convergence. The error estimates of the proposed numerical method satisfy parameter-uniform second-order convergence on the layer-adapted grid. The convergence obtained is optimal because it is free from any logarithmic term. The numerical analysis confirms the theoretical error analysis.

Revisiting γ-Ray Emission of the Supernova Remnant RCW 103

We analyze more than 15 yr of γ-ray data obtained with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) for the region of the young supernova remnant (SNR) RCW 103, since the nearby source 4FGL J1616.2−5054e, counterpart to HESS J1616−518 and ≃13′ away from the SNR, is determined to be extended in the more recent Fermi-LAT source catalog. Different templates for 4FGL J1616.2−5054e and RCW 103 are tested, and we find that a point source (PS) with a power-law (PL) spectrum at the southern limb of the SNR best describes the detected γ-ray emission. The photon index of the PL emission is Γ ≃ 2.31 (or α ≃ 2.4 in a log-parabola model), softer than the previously reported Γ ≃ 2.0 when the counterpart to HESS J1616−518 was considered to be a PS (which likely caused misidentification of extended emission at RCW 103). In order to produce the γ-ray emission in a hadronic scenario, we estimate that protons with an index ∼2.4 PL energy distribution are needed. These results fit with those from multiwavelength observations that have indicated the remnant at the southern limb is interacting with a molecular cloud.

Unraveling the birthplaces of NGC 2070's massive stars, tracked with MUSE and revealed with JWST

The formation of massive O-type stars cannot be simply explained as a scaled-up version of the accretion mechanisms observed in lower-mass stars. Understanding these processes necessitates systematic studies of their early stages, which are challenging to identify. Forming massive stars remain embedded in their dense nursery clouds, and IR instruments with high spatial resolution capabilities are needed to better observe them. Despite these challenges, MUSE optical observations of the massive cluster NGC 2070 successfully detected potential star-forming regions through spatially resolved electron density maps. To further explore these regions, the James Webb Space Telescope (JWST) utilized its NIRCam and MIRI instruments to penetrate optically obscured areas. This study examines two specific regions in the southeast part of the NGC 2070 MUSE density map, where tracks of highly dense point sources were identified. NIRCam, partially overlapped with MIRI, resolved these MUSE findings, revealing a procession of stellar point sources in the projected images. The detections are associated with elongated clouds, suggesting greater proper motions compared to the surrounding interstellar medium. These findings may indicate the presence of runaway candidates in the early stages of their evolution that are following common escape routes. This would support the notion that dynamical ejection is an efficient mechanism for the formation of massive runaway stars during early stages and likely plays a significant role in the origin of O-type field stars. However, additional data are required to confirm this scenario and rule out other ionizing feedback mechanisms, such as those observed in the formation of pillar-like structures around HII regions in the Milky Way. MUSE electron density mapping effectively captures the complexity of NGC 2070's interstellar medium and highlights targets for subsequent spectroscopic follow-ups, as demonstrated by the JWST data in the two fields studied.

Mixed Boundary Value Problem for a Monotone Equation with a Lower Order Term and Point Sources on the Right Side

Mixed Boundary Value Problem for a Monotone Equation with a Lower Order Term and Point Sources on the Right Side

Acute exposure to environmentally relevant concentrations of pharmaceutical pollutants induces neurobehavioral toxicity in zebrafish (Danio rerio)

Pharmaceutical waste from point and non-point sources enters, persists, or disseminates in the environment and is known as environmentally persistent pharmaceutical pollutants. Understanding the impacts of pharmaceutical pollutants on the environment and health is essential. This study investigates the behavioral impacts of pharmaceutical pollutants on aquatic organisms and delineates the possible nexus of oxidative stress. The male zebrafish were exposed to four major representative pharmaceutical pollutants, viz., acetaminophen, carbamazepine, metformin, and trimethoprim at environmentally relevant concentrations individually as well as in a mixture for seven days. Substantial alterations in social interaction, aggressive nature, novel tank exploration, and light and dark zone preferences were recorded and the degree varied to different pharmaceutical pollutants. The activity of oxidative stress markers, superoxide dismutase, glutathione-S-transferase, and catalase, was found to be suppressed to 66–20%, 42–25%, and 59–20% respectively with the elevated malondialdehyde generation (180–260%) compared to control. The activity level of acetylcholine esterase was found to be increased to 200–500% across all treatment groups. Despite the synergistic impacts of pharmaceutical pollutants on the whole system that could not be ascertained, this comprehensive study highlights their toxicity nature to induce neurobehavioral toxicity in zebrafish through oxidative stress mechanisms and altered cholinergic systems.

Open dumping site as a point source of microplastics and plastic additives: A case study in Thailand

Microplastics (MPs) and plastic additive chemicals are emerging pollutants of great concerns around the world. Open dumping sites can be important sources of those pollutants in emerging countries, but little is known about their occurrence, distribution, transport pathway, and remediation approach. This study aimed to obtain the comprehensive dataset on plastic pollution in an open dumping site in Thailand, including (1) the polymer types and organic/inorganic plastic additives in plastic garbage, (2) horizontal distribution of MPs and plastic additives in the surface soil, (3) the effects of soil-capping treatment, and (4) the vertical transport. First, thirty-two plastic garbage collected from the dumping site were analyzed, and a total of 40 organic chemicals (mean: 1400,000 ng/g dw) and 7 heavy metals (mean: 2,030,000 ng/g dw) were identified. The burdens stored in the dumping site were estimated to reach to 3.3–18 tons for organic additives and 4.9–26 tons for heavy metals. In the surface soil analysis, 13 types of polymers in MPs, 20 elements, and 37 organic plastic additives were detected. The pollution levels were significantly higher near the dumping site than at control sites, indicating that the open dumping site is a point source of MPs and plastic additives. Interestingly, a significantly positive correlation was found between the concentrations of MPs and organic additives in soil. This suggests that MPs act as carriers of plastic-derived chemicals. Soil-capping treatment (including removal of some trash) drastically mitigated the contaminant levels in the surface soil, indicating this treatment is one of the effective approaches to control the horizontal distribution of MPs and plastic additives. However, soil core analyzes implied that the vertical transport is still continued even after soil-capping treatment. Our findings provided the comprehensive dataset to support for understanding plastic pollution in the open dumping site.

Extended legality of curved boundary integral method

The angular spectrum method is an efficient approach for synthesizing electromagnetic beams from planar electric field distributions. The electric field definition is restricted to a plane, which can introduce inaccuracy when applying the synthesized beam to curved surface features. The angular spectrum method can also be interpreted as a pure source method defining the field symmetrically with respect to the creation plane. Recently, we generalized that symmetric field method to arbitrary source distributions, which are valid at any point on compact, regular surface Ω in R3. We call this approach the Curved Boundary Integral method. The electromagnetic fields synthesized with this method satisfy the Helmholtz equation and are adjusted via amplitude and phase at the desired surface. The fields are obtained as a relatively simple integral. However, restrictions on where in space the synthesized field is valid were included in the mathematical proof length to avoid obscuring the main points. These restrictions can be significant depending on the shape and degree of curvature of surface Ω. In this article, we remove these restrictions so that the integral representation of the electromagnetic beam becomes valid at all points r∈R3∖Ω, with a minor restriction. Its modification can work even on Ω. We demonstrate the importance of this extended legality with a source field parametrized into the torus surface. The electromagnetic radiation of this structure would not be valid at any point in space without this extension. Finally, we show that by changing the order of integration, the field singularity at each source point is eliminated.

Retroreflective optical ISAC using OFDM: channel modeling and performance analysis

In this Letter, we propose and investigate a retroreflective optical integrated sensing and communication (RO-ISAC) system using orthogonal frequency division multiplexing (OFDM) and corner cube reflector (CCR). To accurately model the reflected sensing channel of the RO-ISAC system, both a point source model and an area source model are proposed according to the two main types of light sources that are widely used. Detailed theoretical and experimental results are presented to verify the accuracy of the proposed channel models and evaluate the communication and sensing performance of the considered RO-ISAC system.

Production of Sustainable Methanol from Industrial Exhaust Gases

AbstractCarbon capture and utilization (CCU) is part of the European Union (EU)’s strategy to become climate‐neutral by 2050. CO2 is needed as a feedstock for the production of climate‐friendly base chemicals and sustainable fuels. Although CO2 capture from industrial point sources is technically feasible and requires less energy than direct air capture, its integration into the circular economy is challenging due to only the temporary recognition of fossil CO2 as a source for the production of climate‐friendly renewable fuels. In this article, CO2 sources such as waste incineration plants, lime production, and steel production are analyzed based on process simulation in terms of their energy demand for CCU and compliance with current EU legislation on renewable fuels over the service life of a CCU plant.

Evaluating NOx stack plume emissions using a high-resolution atmospheric chemistry model and satellite-derived NO2 columns

Abstract. This paper presents large-eddy simulations with atmospheric chemistry of four large point sources world-wide, focusing on the evaluation of NOx (NO + NO2) emissions with the TROPOspheric Monitoring Instrument (TROPOMI). We implemented a condensed chemistry scheme to investigate how the emitted NOx (95 % as NO) is converted to NO2 in the plume. To use NOx as a proxy for CO2 emission, information about its atmospheric lifetime and the fraction of NOx present as NO2 is required. We find that the chemical evolution of the plumes depends strongly on the amount of NOx that is emitted, as well as on wind speed and direction. For large NOx emissions, the chemistry is pushed in a high-NOx chemical regime over a length of almost 100 km downwind of the stack location. Other plumes with lower NOx emissions show a fast transition to an intermediate-NOx chemical regime, with short NOx lifetimes. Simulated NO2 columns mostly agree within 20 % with TROPOMI, signalling that the emissions used in the model were approximately correct. However, variability in the simulations is large, making a one-to-one comparison difficult. We find that temporal wind speed variations should be accounted for in emission estimation methods. Moreover, results indicate that common assumptions about the NO2 lifetime (≈ 4 h) and NOx:NO2 ratios (≈ 1.3) in simplified methods that estimate emissions from NO2 satellite data need revision.

Numerical Computation of 2D Domain Integrals in Boundary Element Method by (α, β) Distance Transformation for Transient Heat Conduction Problems

When the time-dependent boundary element method, also termed the pseudo-initial condition method, is employed for solving transient heat conduction problems, the numerical evaluation of domain integrals is necessitated. Consequently, the accurate calculation of the domain integrals is of crucial importance for analyzing transient heat conduction. However, as the time step decreases progressively and approaches zero, the integrand of the domain integrals is close to singular, resulting in large errors when employing standard Gaussian quadrature directly. To solve the problem and further improve the calculation accuracy of the domain integrals, an (α, β) distance transformation is presented. Distance transformation is a simple and efficient method for eliminating near-singularity, typically applied to nearly singular integrals. Firstly, the (α, β) coordinate transformation is introduced. Then, a new distance transformation for the domain integrals is constructed by replacing the shortest distance with the time step. With the new method, the integrand of the domain integrals is substantially smoothed, and the singularity arising from small time steps in the domain integrals is effectively eliminated. Thus, more accurate results can be obtained by the (α, β) distance transformation. Different sizes of time steps, positions of source point, and shapes of integration elements are considered in numerical examples. Comparative studies of the numerical results for the domain integrals using various methods demonstrate that higher accuracy and efficiency are achieved by the proposed method.

Assessment of risk intensity in the triffa plain aquifer: Integration of hazard quantification, land use analysis, dynamic vulnerability GCITF, and DRASTIC method

This study aims to assess the level of groundwater pollution risk in the Triffa Plain, stemming from various pollution sources, with a specific focus on agricultural intensification and excessive pesticide use. Data were collected from ABHM (the Moulouya Hydraulic Basin Agency) and ORMVAM (Regional Office of Moulouya Agricultural Development), and a field visit was conducted in July 2023. The study utilized two main methodologies for mapping risk intensity: the COST 620 action and overlaying vulnerability maps with the land use (LU) factor. Vulnerability maps were generated using the original DRASTIC method and the new dynamic vulnerability assessment method, GCITF.The research approach involved comparing the COST 620 risk index (Ri) and the land use risk index (LU) to identify the most suitable method for the study area. Due to challenges in inventorying various point sources of pollution, the study focused on mapping the primary sources of pollution (diffuse, point, and linear). The key findings indicate that the predominant pollution intensity in the region is high, covering 60.66% of the total surface area. These results closely align with those obtained using the European COST 620 approach and the spatial distribution of nitrates. The study demonstrates the reliability of integrating the GCITF method in assessing groundwater contamination risk, highlighting the significant negative impacts of agricultural activities on the Triffa Plain aquifer, primarily due to uncontrolled pesticide and fertilizer use and point sources of pollution.This study suggests that implementing targeted technical solutions for specific pollution sources is crucial for reducing contamination in the Triffa Plain. These pollution risk intensity maps can assist planners and decision-makers in understanding the origin of pollution and identifying necessary actions to minimize contamination risk, contributing to better groundwater management and protection in the region.

Dynamic response mechanism of the hole subjected to the 3D point source disturbance in an isotropic formation

Accurate estimation of the effects of dynamic disturbances on stress concentration is crucial for the stability of rock engineering and the corresponding analytical approaches are needed. This study presents an analytical approach to calculate the relative stress distribution with a point source inside and outside a hole using the linear theory of elasticity. The Helmholtz potentials and Sommerfeld integral are employed to describe the displacement and stress components, and then formulate the equilibrium equations to solve the equivalent stress distribution around the hole. Numerical examples demonstrate the impact of model parameters on the equivalent stress, such as frequency, hole radius, source location, etc. It is found that sometimes high frequencies can make the equivalent stress greater far from the source than that close to the source. Additionally, when the ratio of the distance between the source and the hole axis to the hole radius exceeds ten, the equivalent stress distribution around the hole remains nearly constant. This approach can be used for the design and assessment of underground engineering structures' stability under dynamic disturbances.

Potential of 14C-based vs. ΔCO-based ΔffCO2 observations to estimate urban fossil fuel CO2 (ffCO2) emissions

Abstract. Atmospheric transport inversions are a powerful tool for independently estimating surface CO2 fluxes from atmospheric CO2 concentration measurements. However, additional tracers are needed to separate the fossil fuel CO2 (ffCO2) emissions from non-fossil CO2 fluxes. In this study, we focus on radiocarbon (14C), the most direct tracer of ffCO2, and the continuously measured surrogate tracer carbon monoxide (CO), which is co-emitted with ffCO2 during incomplete combustion. In the companion paper by Maier et al. (2024), we determined discrete 14C-based and continuous ΔCO-based estimates of the ffCO2 excess concentration (ΔffCO2) compared with a clean-air reference for the urban Heidelberg observation site in southwestern Germany. The ΔCO-based ΔffCO2 concentration was calculated by dividing the continuously measured ΔCO excess concentration by an average 14C-basedΔCO/ΔffCO2 ratio. Here, we use the CarboScope inversion framework adapted for the urban domain around Heidelberg to assess the potential of both types of ΔffCO2 observations to investigate ffCO2 emissions and their seasonal cycle. We find that, although they are more precise, 14C-based ΔffCO2 observations from almost 100 afternoon flask samples collected in the 2 years of 2019 and 2020 are not well suited for estimating robust ffCO2 emissions in the main footprint of this urban area, which has a very heterogeneous distribution of sources including several point sources. The benefit of the continuous ΔCO-based ΔffCO2 estimates is that they can be averaged to reduce the impact of individual hours with an inadequate model performance. We show that the weekly averaged ΔCO-based ΔffCO2 observations allow for a robust reconstruction of the seasonal cycle of the area source ffCO2 emissions from temporally flat a priori emissions. In particular, the distinct COVID-19 signal – with a steep drop in emissions in spring 2020 – is clearly present in these data-driven a posteriori results. Moreover, our top-down results show a shift in the seasonality of the area source ffCO2 emissions around Heidelberg in 2019 compared with the bottom-up estimates from the Netherlands Organization for Applied Scientific Research (TNO). This highlights the huge potential of ΔCO-based ΔffCO2 to validate bottom-up ffCO2 emissions at urban stations if the ΔCO/ΔffCO2 ratios can be determined without biases.

Time-modulated planar frequency diverse array for multi-target detection

The frequency diverse array (FDA) is a very interesting technique in wireless communications. Many research papers are introduced in this field. A lot of them is concerned with linear point sources array. In this paper, a design of a time-modulated planar frequency diverse array architecture is proposed for tracking single or multi-target for the first time. The time-modulation array (TMA) and FDA are combined for detecting single and multi-target. The effectiveness of this combined scheme is demonstrated through simulation results that compared with a point source case to show its superior performance. Authors introduce planar FDA array instead of linear FDA array and realize the planar array using cylindrical dielectric resonator antenna array (CDRA). A planar array consists of 8 × 8 CDRA is used to enable the detection of single target/multi-target. The operating frequency of the antenna is set at 10 GHz, aligning with its applications in the FDA radar. The radiation characteristics of the CDRA antenna element are introduced. High maximum gain of 6 dBi is achieved with a remarkably high efficiency. A set of representative results is reported and analyzed to assess the effectiveness of the proposed approach.

The Nature of Pointer States and Their Role in Macroscopic Quantum Coherence

This article begins with an interdisciplinary review of a hydrodynamic approach to understanding the origins and nature of macroscopic quantum phenomena in high-temperature superconductivity, superfluidity, turbulence and biological systems. Building on this review, we consider new theoretical insights into the origin and nature of pointer states and their role in the emergence of quantum systems. The approach includes a theory of quantum coherence underpinned by turbulence, generated by a field of pointer states, which take the form of recirculating, spin-1/2 vortices (toroids), interconnected via a cascade of spin-1 vortices. Decoherence occurs when the bosonic network connecting pointer states is disrupted, leading to their localisation. Building further on this work, we explore how quantum particles (in the form of different vortex structures) could emerge as the product of a causal dynamic process, within a turbulent (fractal) spacetime. The resulting particle structures offer new insights into intrinsic spin, the probabilistic nature of the wave function and how we might consider pointer states within the standard “point source” representation of a quantum particle, which intuitively requires a more complexed description.

Thermal Spreading Resistance of Near Surface Localized Heating-Induced Size Effects in Semiconductors

Abstract Localized heating is encountered in various scenarios, including the operation of transistors, light-emitting diodes, and some thermal spectroscopy techniques. When localized heating occurs on a scale comparable to the mean free path of the dominant energy carriers, additional thermal resistance is observed due to ballistic effects. The main objective of this study is to find a relation between this resistance, problem geometry, and material thermal properties in situations involving localized heating. Models based on the solution of the Fourier heat diffusion equation and the gray phonon Boltzmann Transport Equation are solved simultaneously to calculate the additional thermal resistances that arise from localized heating. Subsequently, the results are analyzed to derive the desired relationship. It is noted that in the context of localized heating resistance, the effects of geometrical variables are non-linear and substantial, particularly when the Knudsen numbers for the boundary and heat source exceed certain thresholds. Specifically, when the Knudsen number for the heat source becomes comparable to 1 localized heating resistance is observed. However, when the Knudsen number based on heat source height and width surpasses 8 and 20, respectively the heat source behaves akin to a point source, no longer significantly affecting the localized heating resistance. At this juncture, the maximum resistance limit is reached.