Distribution Of Point Sources Research Articles

Polybrominated diphenyl ethers and their alternatives in soil cores from a typical flame-retardant production park: Vertical distribution and potential influencing factors

With the prohibition on the production and use of polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE) and organophosphate flame retardants (OPFRs) have emerged as their alternatives. However, the vertical transport and associated influencing factors of these chemicals into soil are not clearly understood. To clarify the vertical distribution of the pollutants and related influencing factors, surface soil and soil core samples were collected at a depth in the range of 0.10–5.00 m in a typical 20-year-old flame-retardant production park and surrounding area. PBDEs and DBDPE show a clear point source distribution around the production park with their central concentrations up to 2.88 × 104 and 8.46 × 104 ng/g, respectively. OPFRs are mainly found in residential areas. The production conversion of PBDEs to DBDPE has obvious environmental characteristics. The vertical distribution revealed that most of the pollutants have penetrated into the soil 5.00 m or even deeper. The median concentrations of deca-BDE and DBDPE reached 50.9 and 9.85 × 103 ng/g, respectively, even at a depth of 5.00 m. Soil organic matter plays a crucial role in determining the vertical distribution, while soil clay particles have a greater impact on the high molecular weight and/or highly brominated compounds.

A dual-reciprocity boundary element method based transient seepage model with nonlinear distributed point source dual-porosity gas reservoir

As a result of advancements in gas reservoir development technologies and a deeper understanding of seepage theory, numerous nonlinear seepage problems have emerged. Consequently, conventional analytical solution models are no longer applicable. Moreover, existing semi-analytical and numerical solution models suffer from issues like high computational complexity and limited flexibility, significantly constraining their practical utility. For this purpose, a gas reservoir transient seepage model is established based on the dual-reciprocity boundary element method (DRBEM). This model couples the wellbore storage coefficients with skin factor and introduces a novel dual-porosity transient interporosity seepage algorithm, enabling the resolution of transient seepage problems in dual-porosity gas reservoirs with nonlinear point source distributions. Additionally, it investigates the dynamic behavior of bottomhole pressure during the early production stage of gas wells, while capturing the dynamic pressure distribution within the seepage field. This approach offers the advantages of semi-analyticity, meshless, and eliminates the need for Laplace transforms, resulting in a significant reduction in computational complexity. Ultimately, the application of our model to well-pattern production with the production system transition issues, in conjunction with the log-log type curves of bottomhole pressure, and the dynamics of gas reservoir pressure, enables the analysis of interference characteristics between injection-production wells. This showcases the practical advantages of the model's application. The findings of this study provide valuable assistance for modeling and solving transient seepage problems in dual-porosity oil and gas reservoirs production. The application of DRBEM in unsteady-state diffusion, heat conduction, stress fields, and other potential field problems is relevant for reference.

NG-DPSM: A neural green-distributed point source method for modelling ultrasonic field emission near fluid-solid interface using physics informed neural network

Distributed point source method (DPSM) is a collocation point-based semi-analytical method to model the scattered ultrasonic fields in isotropic and anisotropic materials. It requires the evaluation of Green's function solutions and its rigorous differentiation for complex geometry problems having a large set of distributed point sources. DPSM is much faster than the finite element method (FEM) however, it is analytically demanding as it requires differentiation of the Green's function. The intricacy associated with differentiation operation hinders the potential application of DPSM in large-scale automation and real-time structural health monitoring. The current paper introduces machine-learning-based strategies within DPSM and yields the proposed Neural Green-DPSM (NG-DPSM) framework. A physics-informed neural network (PINN) is incorporated in the DPSM framework for evaluating the Green's function and its gradients. To train the PINN, displacement Green's function solutions of wave propagation in isotropic solid is used as the governing physics. Once the PINN is trained for displacement Green's function solutions, the NG-DPSM framework leverages the trained network and its automatic differentiation capability to predict displacement and stress fields annihilating the rigorous differentiation of Green's functions. The accuracy and efficacy of NG-DPSM are demonstrated using two numerical experiments. First, the ultrasonic fields are evaluated for the problem geometry of a plate immersed in fluid excited at different angles of incidence. Further, the efficacy of the proposed approach is demonstrated for wave scattering through a circular hole in the plate. The results show a strong agreement between the ultrasonic fields computed using both NG-DPSM and conventional DPSM.

Analysis of the energy transfer process for multiple scattering problems involving lossy media

The energy transfer process for acoustic propagation and scattering in inhomogeneous, lossy media is rigorously investigated. Two problems are considered: an arbitrarily composed cluster of lossy scatterers, excited by a single point source and a layered, lossy medium excited by an internal point-source distribution. Energy conservation laws and optical theorems are established. The connection of active intensity with the scattering cross section and the relation between reactive intensity and Lagrangian density are determined. Furthermore, the influence of the losses of the involved media to the kinetic energy is unveiled. Reductions to lossless media and near-zero frequency values are derived.

Investigation of nonlinear propagation effects on sound from supersonic bullets

ISO standard 17201-4 is a calculation method for sound levels generated by supersonic bullets. The standard takes into account nonlinear propagation effects, including broadening of a sound pulse with increasing propagation distance. Two elements of the ISO method are investigated in this paper: i) the accuracy for various Mach numbers, and ii) the effect of noise barriers. For the first element, calculation results are compared with measurement results. In general the agreement is good, but large deviations occur at Mach numbers near unity. Calculation parameters were varied in order to find an explanation for the deviations. For the second element, propagation paths along the horizontal top edge and the vertical side edges of a barrier of finite length are considered. For the path over the top edge, a possible approach is developed to account for the expected reduction of nonlinear propagation effects in the shadow region behind a barrier. For the paths along the vertical side edges, a simulation model with a dense distribution of point sources is employed. The three propagation paths are explained in terms of pairwise cancellation of Fresnel zones. The results of the simulation model are compared with results of an engineering model.

Surface deformations and gravity changes caused by pressurized finite ellipsoidal cavities

SUMMARY We develop quasi-analytical solutions for the surface deformation field and gravity changes due to the pressurization of a finite (triaxial) ellipsoidal cavity in a half-space. The solution is in the form of a non-uniform distribution of triaxial point sources within the cavity. The point sources have the same aspect ratio, determined by the cavity shape, while their strengths and spacing are determined in an adaptive manner, such that the net point-source potency per unit volume is uniform. We validate and compare our solution with analytical and numerical solutions. We provide computationally efficient MATLAB codes tailored for source inversions. This solution opens the possibility of exploring the geometry of shallow magma chambers for potential deviations from axial symmetry.

Unresolved z ∼ 8 Point Sources and Their Impact on the Bright End of the Galaxy Luminosity Function

The distribution and properties of the first galaxies and quasars are critical pieces of the puzzle in understanding galaxy evolution and cosmic reionization. Previous studies have often excluded unresolved sources as potential low-redshift interlopers. We combine broadband color and photometric redshift analysis with morphological selections to identify a robust sample of candidates consistent with unresolved point sources at redshifts z ∼ 8 using deep Hubble Space Telescope images. We also examine G141 grism spectroscopic data to identify and eliminate dwarf star contaminants. From these analyses, we identify three bright (M UV ≲ −22 AB mag) dropout point sources at 7.5 < z < 8.1. Spectral energy distribution analyses suggest that these sources are either quasars or compact star-forming galaxies. The flux captured by the IRAC 4.5 μm channel suggests that they have moderate Hβ + [O III] equivalent widths. We calculate the number density of point sources at z ∼ 7–8, and find that a double-power-law model well describes the point-source distribution. We then extend our analysis to estimate the combined point-source + galaxy luminosity function and find that the point sources have a nonnegligible contribution to the bright-end excess. The fact that the point sources dominate only at M UV ≲ −22 suggests that their contribution to cosmic reionization is likely limited. While spectroscopic follow-up is needed to confirm the nature of these point sources, this work demonstrates that the inclusion of Lyman-dropout point sources is necessary for a complete census of early galaxies at the epoch of cosmic reionization.

Method for Calculating Thrust Vector Eccentricity Angle of Electric Thruster

The installation of a propulsion device in space missions requires the thrust vector to be in line with the centroid of the satellite platform. If the installation is eccentric, interference torque occurs on the satellite body, which is not conducive for the attitude control of the whole satellite. In this paper, a method for calculating the thrust vector eccentricity angle by Gaussian surface fitting is proposed, which is suitable for a class of electric thrusters, for which the plume is conformed to point source distribution. For the cylindrical-shaped plume that cannot be regarded as a point source, a new weight function is proposed. A Hall thruster is considered an example to experimentally verify the method. Error analysis shows that the calculation accuracy in most of the cases is within 10%. To obtain the result of a small error, a preprocessing procedure is proposed before applying the method for optimization. Moreover, considering the contribution of the ion energy distributed along the angle, the calculation method is corrected and improved; and it is found that the thrust vector eccentricity angle of the Hall thruster is overestimated by about 20–30% when the angular distribution of the ion energy is not considered.

Finite-Difference Simulation for Infrasound Generated by Finite-Extent Ground Motions

Abstract Underground explosions can produce infrasound in the atmosphere, and the wavefield characteristics are often governed by the ground surface motions. Finite-difference methods are popular for infrasound simulation as their generality and robustness allow for complex atmospheric structures and surface topography. A simple point-source approximation is often used because infrasound wavelengths tend to be large relative to the source dimensions. However, this assumption may not be able to capture the complexity of explosion-induced ground motions if the surface area is not compact, and appropriate source models must be incorporated into the finite-difference simulations for accurate infrasound prediction. In this study, we develop a point source representation of the complex ground motions for infrasound sources. Instead of a single point source, we use a series of point sources distributed over the source area. These distributed point sources can be equivalent to air volume changes produced by the ground motions in the atmosphere. We apply the distributed point-source method to a series of buried chemical explosions conducted during the Source Physics Experiment Phase I. Epicentral ground-motion measurements during the experiments provide a way to calculate accurate distributed point sources. We validate and evaluate the accuracy of distributed point source approach for infrasound simulations by direct comparison with acoustic observations in the field experiment.

Modeling of heat transfer from an electrically heated rotating helix in a circular cylindrical channel filled with a biomass moving at a constant velocity

The increasingly popular use of screw conveyors for thermo(chemical) processing of food or waste requires modeling the temperature distribution inside such a device. The purpose of this work is to demonstrate the temperature distribution around an electrically heated rotating helix inside a circular cylindrical channel of infinite length filled with a homogeneous biomass moving at a constant velocity in the axial direction. The non-stationary problem of temperature distribution is solved by replacing the real heat source with continuously distributed point sources, expansion of the given and required functions into a Fourier series over angular coordinate and applying integral Fourier and Laplace transforms over axial coordinate and time, respectively. The exact solution of the problem is represented as the product of the energy source determined by the Joule heat and the influence function in the form of the Fourier-Bessel series, which depends on the thermodynamic characteristics of substance and its velocity, radius, pitch and angular velocity of the helix. The temperature field consists of two components, one proportional to the time and the other forming the micro-structure of the temperature profile. On the basis of numerical calculations the analysis of space–time microstructure of the temperature field in the channel is provided. It is shown that in time the temperature undergoes low-amplitude quasi-monochromatic oscillations, the period of which is determined by the angular velocity of the spiral. The spatial temperature distribution has a plateau-like character formed by the geometry of the helix. In particular, the conditions under which the resonant amplification of the amplitude of temperature fluctuations occurs are established.

Dissecting the inner Galaxy with gamma-ray pixel count statistics

The nature of the GeV gamma-ray Galactic center excess (GCE) in the data of Fermi-LAT is still under investigation. Different techniques, such as template fitting and photon-count statistical methods, have been applied in the past few years in order to disentangle between a GCE coming from sub-threshold point sources or rather from diffuse emissions, such as the dark matter annihilation in the Galactic halo. A major limit to all these studies is the modeling of the Galactic diffuse foreground, and the impact of residual mis-modeled emission on the results’ robustness. We combine for the first time adaptive template fitting and pixel count statistical methods in order to assess the role of sub-threshold point sources to the GCE, while minimizing the mis-modelling of diffuse emission components. We reconstruct the flux distribution of point sources in the inner Galaxy well below the Fermi-LAT detection threshold, and measure their radial and longitudinal profiles. We find that point sources and diffuse emission from the Galactic bulge each contributes about 10% of the total emission therein, disclosing a potential sub-threshold point-source contribution to the GCE.

Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide

Abstract We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst. These measurements of HCN, CS, CH3OH, H2CO, and HNC (along with continuum emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for each molecule and a stringent upper limit for CO. HCN is consistent with direct nucleus release in C/2015 ER61, whereas CS, H2CO, HNC, and potentially CH3OH are associated with distributed sources in the coma. Adopting a Haser model, parent scale lengths determined for H2CO (L p ∼ 2200 km) and HNC (L p ∼ 3300 km) are consistent with previous work in comets, whereas significant extended source production (L p ∼ 2000 km) is indicated for CS, suggesting production from an unknown parent in the coma. The continuum presents a point-source distribution with a flux density implying an excessively large nucleus, inconsistent with other estimates of the nucleus size. It is best explained by the thermal emission of slowly moving outburst ejectas, with total mass 5–8 × 1010 kg. These results demonstrate the power of the ACA for revealing the abundances, spatial distributions, and locations of molecular production for volatiles in moderately bright comets such as C/2015 ER61.

A wave-optical model for chromatic confocal sensing using multimode fibre incoherent illumination

This paper presents a wave-optical model for chromatic confocal signals based on multimode optical fibre data acquisition. It is shown that the emitted light from a multimode fibre can be modelled as a point source grid. The confocal signal can be obtained by incoherent summation of the intensities of the reflected fields in the detector plane. In this manner, this two-dimensional wave-optical model encompasses the temporal incoherence of the light source due to the usage of a broadband light source and the spatial incoherence due to the application of a multimode fibre. In fact, this model enables the modelling of different degrees of coherence. Therefore, to our knowledge, it represents the most thorough modelling tool for chromatic confocal signals. Physical parameters such as the spectral distribution of the polychromatic light source, the lateral distribution of point sources on the grid, and the strength of longitudinal aberrations, and their influences on the chromatic confocal signal have been evaluated in detail. Consideration of all these parameters results in simulated chromatic confocal signals, which almost perfectly match the experimentally recorded chromatic confocal signals. The results obtained will be very useful for the development of a deeper understanding of chromatic confocal sensing, to optimise the setup parameters with regard to a particular application and to reinterpret the results, possibly in combination with artificial intelligence algorithms, in order to increase the measurement precision and to reduce the demands imposed on the manufacturing quality of the optical elements.

Dissecting the Inner Galaxy with γ-Ray Pixel Count Statistics.

We combine adaptive template fitting and pixel count statistics in order to assess the nature of the Galactic Center excess in Fermi-LAT data. We reconstruct the flux distribution of point sources well below the Fermi-LAT detection threshold, and measure their radial and longitudinal profiles in the inner Galaxy. We find that all point sources and the bulge-correlated diffuse emission each contributes O(10%) of the total inner Galaxy emission, and disclose a potential subthreshold point-source contribution to the Galactic Center excess.

Measurement of the anisotropy power spectrum of the radio synchrotron background

ABSTRACT We present the first targeted measurement of the power spectrum of anisotropies of the radio synchrotron background, at 140 MHz, where it is the overwhelmingly dominant photon background. This measurement is important for understanding the background level of radio sky brightness, which is dominated by steep-spectrum synchrotron radiation at frequencies below ν ∼ 0.5 GHz and has been measured to be significantly higher than that produced by known classes of extragalactic sources and most models of Galactic halo emission. We determine the anisotropy power spectrum on scales ranging from 2° to 0.2 arcmin with Low-Frequency Array observations of two 18-deg2 fields – one centred on the Northern hemisphere’s coldest patch of radio sky where the Galactic contribution is smallest and the other offset from that location by 15°. We find that the anisotropy power is higher than that attributable to the distribution of point sources above 100 $\mu$Jy in flux. This level of radio anisotropy power indicates that if it results from point sources, those sources are likely at low fluxes and incredibly numerous, and likely clustered in a specific manner.

Multifractal Analysis of a Seismic Moment Distribution Obtained From InSAR Inversion.

Interferometric synthetic aperture radar (InSAR) interferograms contain valuable information about the fault systems hidden beneath the surface of the Earth. In a new approach, we aim to fit InSAR ground deformation data using a distribution of multiple seismic point sources whose parameters are found by a genetic algorithm. The resulting source distribution could provide another useful tool in solving the difficult problem of accurately mapping earthquake faults. We apply the algorithm to an ALOS‐2 InSAR interferogram and perform a multifractal analysis on the resulting distribution, finding that it exhibits multifractal properties. We report first results and discuss advantages and disadvantages of this approach.

Topological sensitivity analysis revisited for time-harmonic wave scattering problems. Part I: the free space case

PurposeIn this paper, the authors revisit the computation of closed-form expressions of the topological indicator function for a one step imaging algorithm of two- and three-dimensional sound-soft (Dirichlet condition), sound-hard (Neumann condition) and isotropic inclusions (transmission conditions) in the free space.Design/methodology/approachFrom the addition theorem for translated harmonics, explicit expressions of the scattered waves by infinitesimal circular (and spherical) holes subject to an incident plane wave or a compactly supported distribution of point sources are available. Then the authors derive the first-order term in the asymptotic expansion of the Dirichlet and Neumann traces and their surface derivatives on the boundary of the singular medium perturbation.FindingsAs the shape gradient of shape functionals are expressed in terms of boundary integrals involving the boundary traces of the state and the associated adjoint field, then the topological gradient formulae follow readily.Originality/valueThe authors exhibit singular perturbation asymptotics that can be reused in the derivation of the topological gradient function that generates initial guesses in the iterated numerical solution of any shape optimization problem or imaging problems relying on time-harmonic acoustic wave propagation.

Design of a freeform two-reflector system to collimate and shape a point source distribution.

In this paper we propose a method to compute a freeform reflector system for collimating and shaping a beam from a point source. We construct these reflectors such that the radiant intensity of the source is converted into a desired target. An important generalization in our approach compared to previous research is that the output beam can be in an arbitrary direction. The design problem is approached by using a generalized Monge-Ampère equation. This equation is solved using a least-squares algorithm for non-quadratic cost functions. This algorithm calculates the optical map, from which we can then compute the surfaces. We test our algorithm on two cases. First we consider a uniform source and target distribution. Next, we use the model of a laser diode light source and a ring-shaped target distribution.

Revisiting the Source Rupture Process of the Mainshock of the 2016 Kumamoto Earthquake and Implications for the Generation of Near-Fault Ground Motions and Forward-Directivity Pulse

ABSTRACT Strong near-fault ground motions associated with the MJMA 7.3 mainshock of the 2016 Kumamoto, central Kyushu, Japan, earthquake sequence have received attention by seismological and engineering communities. In this study, the kinematic source rupture process was reanalyzed based on an improved approach for the representation of source faults. The slips at densely distributed point sources were defined via the bilinear interpolation of those at surrounding control points. The result shows that the rupture started on the Hinagu fault with a small initial rupture and propagated beyond the junction to the Futagawa fault. The rupture on the Futagawa fault mainly propagated up and northeastward. A large slip area with a peak slip of 4.9 m and peak slip velocity of 3.1 m/s was detected at depths ranging from 3 to 15 km in the central part of the Futagawa fault. This asperity spatially coincides with a body with moderate-seismic velocity (VP∼6 km/s) and low-seismic attenuation. The slips on the Futagawa fault have significant normal-slip components, whereas the slip vectors of the Hinagu fault represent almost pure right-lateral strike slip. The shallower part of the fault segments in the western Aso caldera is characterized by relatively large normal slips. The estimated slip-velocity functions at shallower depths (&amp;lt;3 km) are almost temporally symmetric and relatively long. The shallower portion of the source fault significantly contributes to the velocity and displacement waveforms at near-fault sites. On the contrary, the slip-velocity functions at deeper depths (&amp;gt;3 km) are temporally asymmetric and have a sharp peak. The simulation of the ground-motion evolution suggests that the lateral flow in the Aso Valley was primarily triggered by the strong forward-directivity pulse generated from the asperity on the Futagawa fault.

Modeling and experimental study on CO2 adsorption in fixed-bed columns: Applications to carbon capture and utilization

The concerns towards the rise in carbon dioxide (CO2) concentrations in atmosphere and its impact on climate change have been increasing since past decades. While one of the primary sources of CO2 emissions are power or manufacturing plants (large point sources) that burn fossil fuels to generate electricity, the cumulative emissions from vehicles and humans/animals (small but distributed point sources) can be significant. This necessitates the development of carbon capture technologies not only from flue gases but also directly from the atmosphere. Most of these technologies are based on CO2 adsorption in a fixed-bed reactor. The current work presents the modeling and experimental studies on the topic, where we developed reduced-order model to describe the transport and adsorption of CO2 in a packed-bed reactor and perform the lab-scale experiments to investigate adsorption characteristics. The reduced-order model (ROM) is expressed in multiple concentration modes while capturing the small-scale physics using mass-transfer coefficients. We illustrate that ROM developed here are more accurate than traditional pseudo-homogeneous model and can be utilized for real time optimization and parametric/bifurcation studies. We also show the use of ROM in solving inverse problems to analyze the experimental data in obtaining transport/reaction parameters. Finally, we provide the physical interpretation of the various terms used in the model, perform sensitivity analysis and discuss its use in design/scale-up of the reactor.