Source Distribution Model Research Articles

Cosmic-ray propagation under consideration of a spatially resolved source distribution

Cosmic rays (CRs) are an integral component of the interstellar medium, producing broadband emission while interacting with other Galactic matter components like the interstellar gas or magnetic fields. In addition to observations, numerical simulations of CR propagation through the Galaxy help to increase the level of understanding of Galactic CR transport and diffuse γ-ray emission as seen by different experiments. Up to now, the standard approach at modelling source distributions used as input for such transport simulations often rely on radial symmetry and analytical functions rather than individual, observation-based sources. We aim at a redefinition of existing CR source distributions by combining sources observed with the H.E.S.S. experiment and simulated random sources, which follow the matter density in the Milky Way. As a result, H.E.S.S.-inspired Galactic CR source distributions are inferred.We use the PICARD code to perform 3D-simulations of nuclei and electrons in CR propagation using our hybrid source distribution models. Furthermore, also gamma-ray maps and spectra, simulated with the redefined source models, are evaluated in different regions in the Galaxy and compared with each other to determine the statistical scatter of the underlying distributions. We find global consistency between our models and in comparison to previous simulations, with only some localised fluctuations, e.g. in the spiral arms.This implementation of a three-dimensional source model based on observations and simulations enables a new quality of propagation modelling. It offers possibilities for more realistic CR transport scenarios beyond radial symmetry and delivers meaningful results in both the arm and interarm regions of the Galaxy. This gives a more realistic picture of the Galactic γ-ray sky by including structures from the source model and not just the gas distributions.

Numerical and Experimental Investigations of Modal Coherence Characteristics for the Determination of Broadband Noise in Flow Ducts

This paper presents a detailed investigation about the modal coherence characteristics of turbomachinery noise. The modal coherence characteristics of ducted noise at high frequencies are investigated by establishing three kinds of ducted sound source distribution models. The results are consistent with the acoustic experimental results of a single-stage axial fan. The results show that acoustic modes of different orders are mutually incoherent, and radial modes within the same circumferential mode have a great degree of coherence. This paper successfully conducted an acoustic measurement on turbomachinery noise by rotating microphone arrays. The acoustic experimental results show that the coherence of some modes has little impact on the measurement of incident acoustic waves in the flow duct, while it leads to about 3 dB deviation in the prediction of the reflected modal sound power and has little influence on the spectral shape of reflected acoustic waves. It was demonstrated that the experimentally measured modal coherence functions give an inner sense of the spatial noise source distribution and enable the investigation of mode scattering within the propagation. Based on the modal coherence characteristics obtained in this paper, more theoretical and methodological studies can be carried out for the turbomachinery broadband noise test.

The Rapid ASKAP Continuum Survey Paper II: First Stokes I Source Catalogue Data Release

Abstract The Rapid ASKAP Continuum Survey (RACS) is the first large sky survey using the Australian Square Kilometre Array Pathfinder (ASKAP), covering the sky south of $+41^\circ$ declination. With ASKAP’s large, instantaneous field of view, ${\sim}31\,\mathrm{deg}^2$ , RACS observed the entire sky at a central frequency of 887.5 MHz using 903 individual pointings with 15 minute observations. This has resulted in the deepest radio survey of the full Southern sky to date at these frequencies. In this paper, we present the first Stokes I catalogue derived from the RACS survey. This catalogue was assembled from 799 tiles that could be convolved to a common resolution of $25^{\prime\prime}$ , covering a large contiguous region in the declination range $\delta=-80^{\circ}$ to $+30^\circ$ . The catalogue provides an important tool for both the preparation of future ASKAP surveys and for scientific research. It consists of $\sim$ 2.1 million sources and excludes the $|b|<5^{\circ}$ region around the Galactic plane. This provides a first extragalactic catalogue with ASKAP covering the majority of the sky ( $\delta<+30^{\circ}$ ). We describe the methods to obtain this catalogue from the initial RACS observations and discuss the verification of the data, to highlight its quality. Using simulations, we find this catalogue detects 95% of point sources at an integrated flux density of $\sim$ 5 mJy. Assuming a typical sky source distribution model, this suggests an overall 95% point source completeness at an integrated flux density $\sim$ 3 mJy. The catalogue will be available through the CSIRO ASKAP Science Data Archive (CASDA).

Galactic cosmic ray propagation models using Picard

We will give an overview of recent developments in numerical modelling of CR transport in our Galaxy with the PICARD code. Corresponding numerical models aim at reproducing CR spectra and also diffuse gamma-ray emission from the Galaxy by solving the cosmic-ray transport problem in a three-dimensional model of the Galaxy. We address the impact of different transport physics processes on the flux and distribution of diffuse Galactic gamma rays: we investigate CR transport using different cosmic-ray source distribution models ranging from smooth source distributions to localised sources related to high-energy gamma-ray observations. Additionally, we consider anisotropic cosmic-ray diffusion in an improved Galactic magnetic field model. The choice of changing the different transport parameters is most readily visible in the inverse-Compton channel, which shows features not present in commonly-used axisymmetric transport models.

Fractal Dimension of the Cosmic Microwave Background as a Test of "Planck" Spacecraft Data

The fractal dimensions of cosmic microwave background (CMB) maps and other sources obtained by the “Planck” mission are investigated. It is shown that the choice of source distribution models used in data processing can significantly affect the fractal dimension of CMB.

Analysis and evaluation of tomographic gamma scanning image reconstruction algorithm

Abstract Tomographic Gamma Scanning (TGS) is a nondestructive analysis technique for accurately measuring the content of radioactive material in sealed containers. It has important applications in the fields of nuclear safety assurance and the measurement and analysis of radioactive waste drums. As the key of TGS technique, the quality of the emission image reconstruction algorithm will directly affect the accuracy of measurement results. In this paper, a computer simulation platform for TGS technique is established. The application of four emission image reconstruction algorithms in TGS technique is systematically studied by using 6 · 6 · 6 sample voxel model. Three representative sample media and radioactive source distribution models are established and the applicability of the four reconstruction algorithms is analyzed and evaluated in the presence and absence of detector noise interference. Computer simulation and experimental results show that ML-EM algorithm is the most applicable in the process of TGS image reconstruction.

Theoretical and experimental study of temperature field in noncircular high-speed grinding

A study of a noncircular workpiece grinding mechanism for improving the quality of noncircular grinding was conducted. By combining the principle of heat transfer, the geometry, and the kinematics in the high-speed grinding of noncircular workpiece, a variable heat flow distribution model was developed to evaluate the temperature field. Through a reasonable hypothesis and simplification, a three-dimensional (3D) finite element (FE) simulation model was established based on the variable heat source distribution model. The temperature field in the workpiece was simulated with a 3D transient thermal FE code. The grinding temperature test platform using an infrared thermal imager was established. Experimental results were compared with the results of a simulation; the comparison results showed that the temperature field obtained from ANSYS and the infrared thermal imager were nearly identical, the maximum error was 5.91%, and the simulation results truly reflected noncircular high-speed grinding heat conditions. Based on the analysis of experimental and simulation results, the influence of grinding process parameters on the grinding temperature in high-speed grinding of the noncircular workpiece was revealed. This work should be helpful in solving the problem of thermal damage on the surface of noncircular workpieces during high-speed grinding.

Study on Heat Source Distribution Model of High-order Function in Grinding Arc Area

Study on Heat Source Distribution Model of High-order Function in Grinding Arc Area

Tracking and Positioning Technology of Chemical Plumes by Underwater Robots Based on Source Distribution Model

Tracking and Positioning Technology of Chemical Plumes by Underwater Robots Based on Source Distribution Model

Research on force and temperature characteristics of novel point grinding wheels

We propose a novel point grinding wheel (NPGW) with coarse grinding zone angle θ. According to earlier studies, this type of grinding wheel has high grinding efficiency, long service life, and generates very little surface roughness. The contact zone between the grinding wheel and workpiece is modified by the addition of the NPGW with the coarse grinding zone angle θ and the inclined angle α of point grinding process, and as a result, grinding force and grinding zone temperature are also altered. The grinding force theoretical model of NPGW was established and the grinding zone temperature was simulated by the finite element method, based on the theory of grinding heat generation and distribution and triangular heat source distribution model. At the same time, seven pieces of NPGW with different angles θ used for grinding experiments were fabricated. The theoretical model of grinding force and the simulation of grinding temperature coincided with experimental results. Therefore, the grinding force theoretical model and the grinding temperature simulation provide an auxiliary and predictive method for the actual process. Moreover, the influence of parameters on grinding force and grinding zone temperature can be obtained, and the results indicate that the NPGW and point grinding process can reduce grinding force and grinding zone temperature. Finally, plastic deformation is attributed to the production of compressive stress and grinding heat is attributed to the production of tensile stress. Therefore, the residual stress is influenced by the grinding force and the grinding temperature coupled. The residual stress of workpiece surface and subsurface was studied. In conclusion, the NPGW and point grinding process can reduce residual stress of workpiece surface and subsurface, in the case of tensile and compressive stress.

Investigation of the grinding temperature and subsurface quality of a novel point grinding wheel

In this paper, a novel point grinding wheel (NPGW) with coarse grinding area angle θ is proposed. According to earlier studies, this type of grinding wheel has the advantages of high grinding efficiency, a long service life, and very little surface roughness generated. The contact zone between the grinding wheel and workpiece is modified by the addition of the NPGW with the coarse grinding area angle θ and the inclining angle α of the point grinding process, and as a result, the grinding zone temperature is also altered. Using the finite element method, the grinding zone temperature can be simulated based on the theory of grinding heat generation and distribution, and the triangular heat source distribution model. From this, the distribution of the point grinding temperature field and influence of different grinding parameters on the grinding zone temperature were obtained. To verify the simulation, thermocouple measurements for different NPGWs were taken during the grinding experiments. The simulation provides an auxiliary and predictive method for the actual process. Moreover, an L16(45) orthogonal experiment was designed. Analyzing this range, primary and secondary factors affecting grinding zone temperature, and the optimum combination of parameters for reducing the grinding zone temperature, are determined. Finally, the grinding heat can affect the quality of the workpiece subsurface; therefore, the influence of the various parameters on subsurface quality, including metallographic structure, work hardening, and residual stress, was studied. In conclusion, the NPGW and point grinding process can reduce the degree of work hardening and residual stress of the subsurface of the workpiece, and it was demonstrated that the residual stress changes from compressive to tensile with increasing depth.

A dosimetric model for the heterogeneous delivery of radioactive nanoparticles In vivo: a feasibility study

ᅟAccurate and quantitative dosimetry for internal radiation therapy can be especially challenging, given the heterogeneity of patient anatomy, tumor anatomy, and source deposition. Internal radiotherapy sources such as nanoparticles and monoclonal antibodies require high resolution imaging to accurately model the heterogeneous distribution of these sources in the tumor. The resolution of nuclear imaging modalities is not high enough to measure the heterogeneity of intratumoral nanoparticle deposition or intratumoral regions, and mathematical models do not represent the actual heterogeneous dose or dose response. To help answer questions at the interface of tumor dosimetry and tumor biology, we have modeled the actual 3-dimensional dose distribution of heterogeneously delivered radioactive nanoparticles in a tumor after systemic injection.Methods24 h after systemic injection of dually fluorescent and radioactive nanoparticles into a tumor-bearing mouse, the tumor was cut into 342 adjacent sections and imaged to quantify the source distribution in each section. The images were stacked to generate a 3D model of source distribution, and a novel MATLAB code was employed to calculate the dose to cells on a middle section in the tumor using a low step size dose kernel.ResultsThe average dose calculated by this novel 3D model compared closely with standard ways of calculating average dose, and showed a positive correlation with experimentally determined cytotoxicity in vivo. The high resolution images allowed us to determine that the dose required to initiate radiation-induced H2AX phosphorylation was approximately one Gray. The nanoparticle distribution was further used to model the dose distribution of two other radionuclides.ConclusionsThe ability of this model to quantify the absorbed dose and dose response in different intratumoral regions allows one to investigate how source deposition in different tumor areas can affect dose and cytotoxicity, as well as how characteristics of the tumor microenvironment, such as hypoxia or high stromal areas, may affect the potency of a given dose.

A Mobile Agent Routing Protocol for Data Aggregation in Wireless Sensor Networks

Mobile agent data aggregation routing forwards mobile agents in wireless sensor network to collect and aggregate data. The key objective of data aggregation routing is to maximise the number of collected data samples at the same time as minimising network resource consumption and data collection delay. This paper proposes a mobile agent routing protocol, called zone-based mobile agent aggregation. This protocol utilises a bottom-up mobile agent migration scheme in which the mobile agents start their journeys from the centre of the event regions to the sink aiming to reduce the MA itinerary cost and delay and increase data aggregation routing accuracy. In addition, the proposed protocol reduces the impact of network architecture, event source distribution model and/or data heterogeneity on the performance of data aggregation routing.

CBA: A cluster-based client/server data aggregation routing protocol

Client/server routing forwards data samples from the source nodes to the sink through single or multi-hop paths which are formed over a flat or hierarchical infrastructure. Depending on the routing infrastructure, the intermediate nodes may perform in-network data aggregation to collect and combine the data samples which are measures of the environmental events. Minimising energy consumption is a vital requirement due to resource constraints in wireless sensor networks. Data collection delay should be minimised as it is the key to data freshness. At the same time, the number of collected data samples should be maximised, as it should lead to increased accuracy and robustness in data collection. Owing to these, we define the system objective to be maximising the number of delivered data samples, while minimising energy consumption and data collection delay. We propose a cluster-based client/server data aggregation routing protocol called Cluster-Based client/server data Aggregation routing protocol (CBA). It dynamically partitions the network into a set of data-centric clusters using a lightweight clustering approach based on the Hamming distance. The cluster-heads then form a Minimum Spanning Tree (MST) as the network backbone to forward aggregated results to the sink. A parallel collision-guided technique is used to minimise the establishment cost of the tree infrastructure. Compared with the conventional routing protocols like MR-LEACH and Directed DiFFusion, CBA reduces energy consumption and data collection delay and increases accuracy (the number of captured data samples). In addition, our protocol reduces the impacts of the network architecture and the event source distribution model (distributed and centralised) on the performance of data aggregation routing.

Numerical simulation and experimental validation of arc welding of DMR-249A steel

Abstract The thermo-mechanical attributes of DMR-249A steel weld joints manufactured by shielded metal arc welding (SMAW) and activated gas tungsten arc welding (A-GTAW) processes were studied using Finite Element Model (FEM) simulation. The thermal gradients and residual stresses were analyzed with SYSWELD software using double ellipsoidal heat source distribution model. The numerically estimated temperature distribution was validated with online temperature measurements using thermocouples. The predicted residual stresses profile across the weld joints was compared with the values experimentally measured using non-destructive techniques. The measured and predicted thermal cycles and residual stress profile was observed to be comparable. The residual stress developed in double sided A-GTAW joint were marginally higher in comparison to five pass SMAW joint due to phase transformation associated with high heat input per weld pass for A-GTAW process. The present investigations suggest the applicability of numerical modeling as an effective approach for predicting the thermo-mechanical properties influenced by welding techniques for DMR-249A steel weld joints. The tensile, impact and micro-hardness tests were carried to compare the welds. Considering benefits of high productivity and savings of labor and cost associated with A-GTAW compared to SMAW process, the minor variation in residual stress build up of A-GTAW joint can be neglected to develop A-GTAW as qualified alternative welding technique for DMR-249A steel.

Investigation of temperature and residual stresses field of submerged arc welding by finite element method and experiments

This article reports on a numerical and experimental investigation to understand and improve computer methods in application of the Goldak model for predicting thermal distribution in submerged arc welding (SAW) of APIX65 pipeline steel. Accurate prediction of the thermal cycle and residual stresses will enable control of the fusion zone geometry, microstructure, and mechanical properties of the SAW joint. In this study, a new Goldak heat source distribution model for SAW is presented first. Both 2D and 3D finite element models are developed using the solution of heat transfer equations in ABAQUS Standard implicit. The obtained results proved that the 2D axi-symmetric model can be effectively employed to simulate the thermal cycles and the welding residual stresses for the test steel. As compared to the 3D analysis, the 2D model significantly reduced the time and cost of the FE computation. The numerical accuracy of the predicted fusion zone geometry is compared to the experimentally obtained values for bead-on-plate welds. The predictions given by the present model were found to be in good agreement with experimental measurements.

Propagation in 3D spiral-arm cosmic-ray source distribution models and secondary particle production using Picard

We study the impact of possible spiral-arm distributions of Galactic cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our Galaxy. We investigate model cosmic-ray spectra at the nominal position of the sun and at different positions within the Galaxy. The modelling is performed using the recently introduced numerical cosmic ray propagation code Picard. Assuming non-axisymmetric cosmic-ray source distributions yields new insights on the behaviour of primary versus secondary nuclei.We find that primary cosmic rays are more strongly confined to the vicinity of the sources, while the distribution of secondary cosmic rays is much more homogeneous compared to the primaries. This leads to stronger spatial variation in secondary to primary ratios when compared to axisymmetric source distribution models. A good fit to the cosmic-ray data at Earth can be accomplished in different spiral-arm models, although leading to decisively different spatial distributions of the cosmic-ray flux. These lead to different cosmic ray anisotropies, where even reproducing the data becomes possible. Consequently, we advocate directions to seek best fit propagation parameters that take into account the higher complexity introduced by the spiral-arm structure on the cosmic-ray distribution. We specifically investigate whether the flux at Earth is representative for a large fraction of the Galaxy. The variance among possible spiral-arm models allows us to quantify the spatial variation of the cosmic-ray flux within the Galaxy in presence of non-axisymmetric source distributions.

The spatial coherence function in scanning transmission electron microscopy and spectroscopy.

We investigate the implications of the form of the spatial coherence function, also referred to as the effective source distribution, for quantitative analysis in scanning transmission electron microscopy, and in particular for interpreting the spatial origin of imaging and spectroscopy signals. These questions are explored using three different source distribution models applied to a GaAs crystal case study. The shape of the effective source distribution was found to have a strong influence not only on the scanning transmission electron microscopy (STEM) image contrast, but also on the distribution of the scattered electron wavefield and hence on the spatial origin of the detected electron intensities. The implications this has for measuring structure, composition and bonding at atomic resolution via annular dark field, X-ray and electron energy loss STEM imaging are discussed.

Numerical Simulation of Air Distribution of Lateral Supply and Return Pattern Affected by Indoor Heated Source Distribution Models

In this paper, the numerical simulation was adopted to explore indoor air distribution affected by three typical heated source distribution models, included spatially homogeneous heated source in the room, the heated source distributed evenly at the bottom and the local heated source at the bottom of the room. The characteristics of air distribution effected by three typical heated source models were studied in the air conditioning room with the pattern of lateral supply and return, the scope of rational arrangement in relatively comfortable environment of indoor personnel occupied zone was obtained. The result indicated that, the air distribution with the setting of the spatially homogeneous heated source pattern and the heated source distributed evenly at the bottom pattern were more satisfying than the setting of the local heated source at the bottom pattern.

Measurements and kernels for source-structure inversions in noise tomography

Seismic noise cross-correlations are used to image crustal structure and heterogeneity. Typically, seismic networks are anisotropically illuminated by seismic noise, a consequence of the non-uniform distribution of sources. Here, we study the sensitivity of such a seismic network to structural heterogeneity in a 2-D setting. We compute finite-frequency cross-correlation sensitivity kernels for traveltime, waveform-energy and waveform-difference measurements. In line with expectation, wave speed anomalies are best imaged using traveltimes and the source distribution using cross-correlation energies. Perturbations in attenuation and impedance are very difficult to image and reliable inferences require a high degree of certainty in the knowledge of the source distribution and wave speed model (at least in the case of transmission tomography studied here). We perform single-step Gauss-Newton inversions for the source distribution and the wave speed, in that order, and quantify the associated Cramér-Rao lower bound. The inversion and uncertainty estimate are robust to errors in the source model but are sensitive to the theory used to interpret of measurements. We find that when classical source–receiver kernels are used instead of cross-correlation kernels, errors appear in the both the inversion and uncertainty estimate, systematically biasing the results. We outline a computationally tractable algorithm to account for distant sources when performing inversions.