Discrete Sources Research Articles

Hydrogeochemical controls on contrasting co-occurrence of geogenic Arsenic (As) and Fluoride (F−) in complex aquifer system of Upper Indus Basin, (UIB) western Himalaya

Arsenicosis and fluorosis have become severe health hazards associated with the drinking of Arsenic (As) and Fluoride (F−) contaminated groundwater across south-east Asia. Although, significant As and F− concentration is reported from major Himalayan river basins but, the hydrogeochemical processes and mechanisms controlling their contrasting co-occurrence in groundwater is still poorly explored and understood. In the present study, groundwater samples were collected from phreatic and confined aquifers of Upper Indus Basin (UIB), India to understand the hydrogeochemical processes controlling the distribution and co-occurrence of geogenic As and F− in this complex aquifer system. Generally, the groundwater is circum-neutral to alkaline with Na+-HCO3-, Ca2+-Na+-HCO3- and Ca2+-Mg2+-HCO3- water facies signifying the dominance of silicate and carbonate dissolution. The poor correlation of As and F− in groundwater depicted that these geogenic elements have discrete sources of origin with distinct mechanisms controlling their distribution. As enrichment in groundwater is associated with high pH, Fe, Mn and NH4-N suggesting dominance of metal oxide/hydroxide reduction with organic matter degradation. However, F− enrichment in groundwater is associated with high pH, HCO3− and Na+, which is assisted by the incessant dissolution of fluorinated minerals. The study also revealed that high HCO3− facilitates the exchange of hydroxides (OH−) with As and F− on sediment surfaces that contribute to As and F− enrichment in groundwater through desorption. 70% groundwater samples have As and F− concentration above the permissible limit given by WHO. Therefore, continuous exposure to these contaminants may pose severe health hazard of arsenicosis and fluorosis to people living in the region and downstream. The study provides insights into geological sources, hydrogeochemical processes and mechanisms controlling distribution of As and F− in groundwater that will help in developing the appropriate measures to mitigate the impact these contaminants on human health.

Implementing the finite element numerical approach to optimize thermosolutal convection (TSC) energy imparted by discrete heat and solute sources in generalized Newtonian fluid flow in square enclosure

AbstractMesmerizing utilizations of thermosolutal convection (TSC) have been found in metallurgical and petrochemical procedures, crystal growth, thermal exchangers, nuclear waste disposal, and building environment control. In the current study, we considered three heat and solute sources on the left boundary of the cavity, which raises the significance of studying multiple chemical and civil engineering phenomena. Therefore, the prime motivation to commence this work is to attain the optimization of thermosolutal attributes characterized by non-Newtonian (power–law) liquid in the presence of installed sources. For this purpose, the natural convective flow governed by the nonpersistent impact of buoyancy forces is encompassed in the square enclosure. In addition to the source location, the vertical boundaries are considered to be cold, whereas the horizontal boundaries are kept insulated. Owing to the free convective flow, no compositional and thermal gradients are induced by lid movement, and all walls are prescribed with no-slip constraints. To examine the transport mechanism, structuring of problem is attained in the form of dimensional governing expressions by employing conservation laws. Subsequently, constitutive equations in a dimensionless format are accessed through similar variables. The finite element approach is employed to find the solution using COMSOL Multiphysics software. The deviations in the thermal and solutal fields are examined against the involved physical parameters by illustrating graphs and tables. Quantities of interest, such as the mean Nusselt and Sherwood numbers, are also computed against sundry parameters. The assurance of the computed results is validated by constructing a comparison with published studies. A grid sensitivity test is also executed to ensure the credibility of the built-in software (COMSOL). It is observed that the averaged heat and mass flux coefficient diminishes with an elevation in the magnitude of the power-law index (n), irrespective of the change in other involved parameters. The average Sherwood number tends to increase for a positive magnitude of (N) in contrast to negative values of (N). The average heat flux and average mass flux coefficients increase until the Prandtl number (Pr) reaches a value of 5 in shear thinning case at $$Ra\ge {10}^{5},$$ R a ≥ 10 5 , whereas, for n > 1 there is no substantial effect on either the average heat flux coefficient or average mass flux coefficient.

Geomorphological and morphometric characterization of subglacial channels on Devon Island, Nunavut, Canada

Subglacial channels are morphologically and morphometrically distinct in comparison to fluvial channels, yet their identification from remote sensing data is still problematic. To contribute to the current set of criteria used to identify such channels, we performed a detailed analysis of two subglacial channel networks on Devon Island, Nunavut, Canada. In planform, these channels are isolated, finger-like networks that drain into a main stem and have distinct cross-sectional and longitudinal profiles. Cross-sections are flat-bottomed with steep walls and longitudinal profiles are convex and exhibit undulations, typical of pressurized water flow (i.e., subglacial flow). To facilitate remote sensing identification, we interrogated how well-known scaling relationships capturing hydraulics and mass balance dynamics of fluvial systems differ in subglacial channels. Scaling relationships typically used to discern connections between discharge and channel and catchment size in fluvial systems were applied to both networks, yielding trends distinct from the fluvial literature. We suggest that the weakly correlated relationship we found between channel discharge and the size of the drainage area indicates a discrete point or line source of water, such as a moulin or crevasse.

Tracing sources of inorganic suspended particulate matter in the Great Barrier Reef lagoon, Australia

Water clarity on the inshore Great Barrier Reef (GBR) is greatly influenced by terrestrial runoff of suspended particulate matter (SPM). Catchment sediment tracing studies often do not extend into the marine environment, preventing the analysis of preferential marine transport. This study employs novel collection and sediment tracing techniques to examine the transport of the terrigenous ‘mineral’ component of plume SPM within the GBR lagoon for two flood events. Utilising geochemical, radionuclide and clay mineral analysis, we trace terrigenous mineral sediments > 100 km from the river mouth. We show that the SPM geochemistry is highly influenced by particle-size fractionation, desorption, and dilution within the plume, rendering traditional tracing methods unviable. However, the ratios of rare earth elements (REE) to thorium (Th) provide stable tracers of mineral SPM transported across the catchment to marine continuum and allow the identification of discrete catchment sources for each flood event. Plume sediment radionuclides are also stable and consistent with sub-surface erosion sources.

Sensitive 3 mm Imaging of Discrete Sources in the Fields of Thermal Sunyaev–Zel’dovich Effect–Selected Galaxy Clusters

In this paper, we present the results of a blind survey for compact sources in 243 Galaxy clusters that were identified using the thermal Sunyaev–Zel'dovich effect (tSZ). The survey was carried out at 90 GHz using MUSTANG2 on the Green Bank Telescope and achieved a 5σ detection limit of 1 mJy in the center of each cluster. We detected 24 discrete sources. The majority (18) of these correspond to known radio sources, and of these, five show signs of significant variability, either with time or in spectral index. The remaining sources have no clear counterparts at other wavelengths. Searches for galaxy clusters via the tSZ strongly rely on observations at 90 GHz, and the sources found have the potential to bias mass estimates of clusters. We compare our results to the Websky simulation that can be used to estimate the source contamination in galaxy cluster catalogs. While the simulation shows a good match to our observations at the clusters’ centers, it does not match our source distribution further out. Sources over 104″ from a cluster’s center bias the tSZ signal high, for some of the sources found, by over 50%. When averaged over the whole cluster population, the effect is smaller but still at a level of 1%–2%. We also discovered that unlike previous measurements and simulations, we see an enhancement of source counts in the outer regions of the clusters and fewer sources than expected in the centers of this tSZ-selected sample.

Estimation of temperature in a computer mother board with discrete heat sources by numerical analysis

Estimation of temperature in a computer mother board with discrete heat sources by numerical analysis

Improved source classification and performance analysis using Gaia DR3

The Discrete Source Classifier (DSC) provides probabilistic classification of sources in Gaia Data Release 3 (GDR3) using a Bayesian framework and a global prior. The DSC Combmod classifier in GDR3 achieved for the extragalactic classes (quasars and galaxies) a high completeness of 92%, but a low purity of 22% (all sky, all magnitudes) due to contamination from the far larger star class. However, these single metrics mask significant variation in performance with magnitude and sky position. Furthermore, a better combination of the individual classifiers that comprise Combmod is possible. Here we compute two-dimensional (2D) representations of the completeness and the purity as a function of Galactic latitude and source brightness, and also exclude the Magellanic Clouds where stellar contamination significantly reduces the purity. Reevaluated on a cleaner validation set and without introducing changes to the published GDR3 DSC probabilities themselves, we here achieve for Combmod average 2D completenesses of 92% and 95% and average 2D purities of 55% and 89% for the quasar and galaxy classes, respectively. Since the relative proportions of extragalactic objects to stars in Gaia is expected to vary significantly with brightness and latitude, we then introduce a new prior that is a continuous function of brightness and latitude, and compute new class probabilities from the GDR3 DSC component classifiers, Specmod and Allosmod. Contrary to expectations, this variable prior only improves the performance by a few percentage points, mostly at the faint end. Significant improvement, however, is obtained by a new additive combination of Specmod and Allosmod. This classifier, Combmod-α, achieves average 2D completenesses of 82% and 93% and average 2D purities of 79% and 93% for the quasar and galaxy classes, respectively, when using the global prior. Thus, we achieve a significant improvement in purity for a small loss of completeness. The improvement is most significant for faint quasars (G≥20) where the purity rises from 20% to 62%.

Experimental verification of double-four-ring-type aluminosilicate molecule as a single-source precursor for zeolite synthesis

Abstract While a variety of functional zeolites have been synthesized using hydrothermal methods with conventional discrete Al and Si sources, control of the composition, structure, and function of the targeted zeolites often involves expensive and time-consuming trial-and-error approaches. Despite ongoing efforts to manipulate zeolite formation by adjusting Al and Si sources and reaction conditions, limited attention has been given to studies on zeolite synthesis using molecular precursors (MPs) with preorganized Al–O–Si bonds. Here, we demonstrate the synthesis of LTA-type zeolites using [TMA]4[Al4Si4O12(OH)8]·13H2O ([MP]; TMA = tetramethylammonium cation) with a double-four-ring (D4R)-type core structure, which is known to be a secondary building unit in the LTA-type zeolite, as a MP. Here, we demonstrate the successful synthesis of LTA-type zeolites using [MP] under hydrothermal conditions at 100 to 200 °C in the presence of 1 equiv. of NaOH or NaCl. Notably, when discrete Al and Si sources were used instead of [MP] under otherwise identical conditions (the same Si/Al ratio, Na+ content, and temperature), GIS-, SOD-, and FAU-type zeolites lacking the D4R structure were obtained in addition to the LTA-type zeolites.

Impact of different numerical approaches on the magnetocaloric effect modeling

As an ecological alternative to the conventional refrigeration technology, magnetocaloric refrigeration is still facing scientific and technological challenges hindering their application. Magnetocaloric devices rely on the magnetocaloric effect, where temperature variations result from magnetic field changes. The correct implementation of the magnetocaloric effect in numerical models is crucial before prototyping the related solutions. Here, we present a comparison between the three most used numerical methods to simulate the magnetocaloric effect: continuous temperature change, discrete temperature change step and heat source obtained from adiabatic temperature. By varying the time and space steps, it was observed that the continuous temperature change method is the most appropriate for small time steps, but has the largest computational cost. The discrete method can only be applied to small time steps, but is the fastest method. Finally, the adiabatic temperature change power source method can be applied in the entire range and is the one that presents the best results for larger time steps.

Unidirectional focusing Rayleigh waves EMAT for plate surface defect Inspection

ABSTRACT Electromagnetic ultrasonic Rayleigh waves are commonly used for detecting surface or near-surface defects, but they still exhibit the drawback of low energy conversion efficiency. In this study, based on the Huygens principle and the discrete point source method, a double curving meander line coils EMAT (DC-MLCs EMAT) which generate unidirectional focusing Rayleigh waves is designed. Firstly, a simulation model of the transducer is established using COMSOL Multiphysics. Then, the impacts of magnet and coise defect detection efficiency is validated by numerical simulation method. Finally, a physical transducer is made, an experimental system is built, and the defect specimens are tested using this experimental system. The simulation and experimental results show that the optimised DC-MLCs EMAT significantly improves ultrasound focusing effect. Compared with the existing single constant length meander line coil（SCL-MLC）EMAT, the signal strength increases by 164.36%. This DC-MLCs EMAT shows good application prospects in the field of fixed focal length measurement.

High-visibility ghost imaging with phase-controlled discrete classical light sources

Abstract We take phase modulation to create discrete phase-controlled sources and realize the super-bunching effect by a phase-correlated method. From theoretical and numerical simulations, we find the space translation invariance of the bunching effect is a key point for the ghost imaging realization. Experimentally, we create the orderly phase-correlated discrete sources which can realize high-visibility second-order ghost imaging than the result with chaotic sources. Moreover, some factors affecting the visibility of ghost image are discussed in detail.

A New Version of the Adaptive Fast Gauss Transform for Discrete and Continuous Sources

A New Version of the Adaptive Fast Gauss Transform for Discrete and Continuous Sources

Effects of measured and simulated diffraction from a plate on sound source localization.

In daily life, natural or man-made structures influence sound propagation, causing reflections and diffraction with potential effects on auditory spatial perception. While the effect of isolated reflections on binaural localization has been investigated, consequences of edge diffraction on spatial perception have received less attention. Here, effects of edge diffraction on the horizontal localization of a sound source were assessed when a flat square plate occludes the direct sound or produces a reflection in an otherwise anechoic environment. Binaural recordings were obtained with an artificial head for discrete sound source positions along two horizontal trajectories in the vicinity of the plate, including conditions near the incident and reflection shadow boundary. In a listening test, the apparent source position was matched for conditions with and without the plate, resulting in azimuth offsets between the apparent and physical source of up to 12°. The perceived direction of occluded frontal sound sources was laterally shifted to the visible region near the edge of the plate. Geometrical-acoustics-based simulations with different methods to binaurally render diffracted sound paths were technically and perceptually compared to the measurements. The observed localization offset was reproduced with the acoustic simulations when diffraction was rendered considering the individual ear positions.

A3COSMOS and A3GOODSS: Continuum source catalogues and multi-band number counts

Context. Galaxy submillimetre number counts are a fundamental measurement in our understanding of galaxy evolution models. Most early measurements are obtained via single-dish telescopes with substantial source confusion, whereas recent interferometric observations are limited to small areas. Aims. We used a large database of ALMA continuum observations to accurately measure galaxy number counts in multiple (sub)millimetre bands, thus bridging the flux density range between single-dish surveys and deep interferometric studies. Methods. We continued the Automated Mining of the ALMA Archive in the COSMOS Field project (A3COSMOS) and extended it with observations from the GOODS-South field (A3GOODSS). The database consists of ∼4000 pipeline-processed continuum images from the public ALMA archive, yielding 2050 unique detected sources, including sources with and without a known optical counterpart. To infer galaxy number counts, we constructed a method to reduce the observational bias inherent to targeted pointings that dominate the database. This method comprises a combination of image selection, masking, and source weighting. The effective area was calculated by accounting for inhomogeneous wavelengths, sensitivities, and resolutions and for the spatial overlap between images. We tested and calibrated our method with simulations. Results. We derived the number counts in a consistent and homogeneous way in four different ALMA bands covering a relatively large area. The results are consistent with number counts retrieved from the literature within the uncertainties. In Band 7, at the depth of the inferred number counts, ∼40% of the cosmic infrared background is resolved into discrete sources. This fraction, however, decreases with increasing wavelength, reaching ∼4% in Band 3. Finally, we used the number counts to test models of dusty galaxy evolution, and find a good agreement within the uncertainties. Conclusions. By continuing the A3COSMOS and A3GOODSS archival effort, we obtained the deepest archive-based (sub)millimetre number counts measured to date over such a wide area. This database proves to be a valuable resource that, thanks to its substantial size, can be used for statistical analyses after having applied certain conservative restrictions.

Pulsar timing array source ensembles

The stochastic gravitational wave background for pulsar timing arrays is often modeled by a Gaussian ensemble which is isotropic and unpolarized. However, the Universe has a discrete set of polarized gravitational wave sources at specific sky locations. Can we trust that the Gaussian ensemble is an accurate description? To investigate this, we explicitly construct an ensemble containing N individual binary sources with circular orbits. The orbital inclination angles are randomly distributed, hence the individual sources are elliptically polarized. We then compute the first two moments of the Hellings and Downs correlation, as well as the pulsar-averaged correlation mean and (cosmic) variance. The first moments are the same as for a previously studied ensemble of circularly polarized sources. However, the second moments, and hence the variances, are different for the two ensembles. While neither discrete source model is exactly described by a Gaussian ensemble, we show that in the limit of large N, the differences are small. Published by the American Physical Society 2024

Constraints on UHECR Sources and Extragalactic Magnetic Fields from Directional Anisotropies

A dipole anisotropy in ultra–high-energy cosmic ray (UHECR) arrival directions, of extragalactic origin, is now firmly established at energies E > 8 EeV. Furthermore, the UHECR angular power spectrum shows no power at smaller angular scales than the dipole, apart from hints of possible individual hot or warm spots for energy thresholds ≳40 EeV. Here we exploit the magnitude of the dipole and the limits on smaller-scale anisotropies to place constraints on two quantities: the extragalactic magnetic field (EGMF) and the number density of UHECR sources or the volumetric event rate if UHECR sources are transient. We also vary the bias between the extragalactic matter and the UHECR source densities, reflecting whether UHECR sources are preferentially found in over- or underdense regions, and find that little or no bias is favored. We follow Ding et al. (2021) in using the CosmicFlows-2 density distribution of the local universe as our baseline distribution of UHECR sources, but we improve and extend that work by employing an accurate and self-consistent treatment of interactions and energy losses during propagation. Deflections in the Galactic magnetic field are treated using either the full JF12 magnetic field model, with both random and coherent components, or just the coherent part, to bracket the impact of the GMF on the dipole anisotropy. This large-scale structure model gives good agreement with both the direction and magnitude of the measured dipole anisotropy and forms the basis for simulations of discrete sources and the inclusion of EGMF effects.

Frequency-domain distribution of astrophysical gravitational-wave backgrounds

The superposition of many astrophysical gravitational wave (GW) signals below typical detection thresholds baths detectors in a stochastic gravitational wave background (SGWB). In this work, we present a Fourier space approach to compute the frequency-domain distribution of stochastic gravitational wave backgrounds produced by discrete sources. Expressions for the moment-generating function and the distribution of observed (discrete) Fourier modes are provided. The results are first applied to the signal originating from all the mergers of compact stellar remnants (black holes and neutron stars) in the Universe, which is found to exhibit a −4 power-law tail. This tail is verified in the signal-to-noise ratio distribution of Gravitational-Wave Transient Catalogue (GWTC) events. The extent to which the subtraction of bright (loud) mergers gaussianizes the resulting confusion noise of unresolved sources is then illustrated. The power-law asymptotic tail for the unsubtracted signal, and an exponentially decaying tail in the case of the SGWB, are also derived analytically. Our results generalize to any background of gravitational waves emanating from discrete, individually coherent, sources. Published by the American Physical Society 2024

Constraints on the Origins of the Galactic Neutrino Flux Detected by IceCube

Galactic and extragalactic objects in the Universe are sources of high-energy neutrinos that may contribute to the astrophysical neutrino signal seen by IceCube. Recently, a study done using cascade-like events seen by IceCube reported neutrino emission from the Galactic plane with >4σ significance. In this work, we put a lower limit on the number of Galactic sources required to explain this emission. To achieve this, we use a simulation package created to simulate point sources in the Galaxy along with the neutrino and gamma-ray flux emissions originating from them. Along with using past IceCube discovery potential curves, we also account for Eddington bias effects due to Poisson fluctuations in the number of detected neutrino events. We present a toy Monte Carlo simulation to show that there must be at least eight sources, each with luminosity less than 1.6 × 1035 erg s−1, responsible for the Galactic neutrino emission. Our results constrain the number of individual point-like emission regions, which apply both to discrete astrophysical sources and to individual points of diffuse emission.

Balanceable data structure with element priorities in the problem of discrete information source modeling

Balanceable data structure with element priorities in the problem of discrete information source modeling

GRID-STEP OPTIMIZATION OF THE PARAMETERS OF THERMAL IMPACT ON THE TECHNICAL SYSTEM

The article solves applied problems of optimizing the parameters of technical systems under the influence of concentrated, discrete sources of thermal load. To improve the accuracy and speed of solving applied optimization problems, the authors propose a generalized procedure for finding the optimal thermal load parameters. This procedure consists of well-known computational methods for solving boundary value problems and ensuring the optimization of the objective function and its parameters. To calculate the values of the temperature field, it is necessary to solve a nonlocal boundary value problem of a system of nonlinear differential heat transfer equations. In order to find the conditions for the correctness of boundary value problems, the authors used the theory of pseudo-differential operators in the space of generalized slow power functions. This made it possible to guarantee the correctness of computational and applied optimization mathematical models. The procedure for grid-step optimization of the parameters of thermal action on a multilayer material proposed by the authors is based on a grid approach with discretization of the main parameters of thermal load and grinding of a large uniform grid in the vicinity of the selected node of the large grid. The directed search for local extremes of the mesh model is carried out by the nodes of the crushed mesh. The search for local extrema is performed by selecting the next node of a large grid. This approach will increase the accuracy of solving applied optimization problems by allowing further mesh refinement and refinement of the values of local extremes, and, consequently, refinement of the values of the global extremum of the objective function. The optimization of the thermal impact parameters was carried out according to the criterion of reducing damage to the test material. This makes it possible to increase the accuracy of the technological process of thermal action on a multilayer material.