Point Source Model Research Articles

Gamma-Ray Emission of 60Fe and 26Al Radioactivity in Our Galaxy

Abstract The isotopes 60Fe and 26Al originate from massive stars and their supernovae, reflecting ongoing nucleosynthesis in the Galaxy. We studied the gamma-ray emission from these isotopes at characteristic energies 1173, 1332, and 1809 keV with over 15 yr of SPI data, finding a line flux in 60Fe combined lines of and the Al line flux of above the background and continuum emission for the whole sky. Based on the exponential disk grid maps, we characterize the emission extent of 26Al to find scale parameters and kpc; however, the 60Fe lines are too weak to spatially constrain the emission. Based on a point-source model test across the Galactic plane, the 60Fe emission would not be consistent with a single strong point source in the Galactic center or somewhere else, providing a hint of a diffuse nature. We carried out comparisons of emission morphology maps using different candidate source tracers for both 26Al and 60Fe emissions and suggest that the 60Fe emission is more likely to be concentrated toward the Galactic plane. We determine the 60Fe/26Al γ-ray flux ratio at 18.4% ± 4.2% when using a parameterized spatial morphology model. Across the range of plausible morphologies, it appears possible that 26Al and 60Fe are distributed differently in the Galaxy. Using the best-fitting maps for each of the elements, we constrain flux ratios in the range 0.2–0.4. We discuss the implications for massive star models and their nucleosynthesis.

Estimation of Path Attenuation Effect from Ground Motion in the Korean Peninsula using Stochastic Point-source Model

Estimation of Path Attenuation Effect from Ground Motion in the Korean Peninsula using Stochastic Point-source Model

What is the most ``non-point'' gravitating or electrically charged object?

In this paper we search the shape of an aspherical body and the direction in space, for which the greatest deviations from the point mass field (the difference from the inverse-square law) take place for large distances from the field source. It turns out to be a system of two equal point-like masses at the poles of a fixed sphere (giving the greatest positive deviations from the point mass field) and uniform distribution of point-like masses (discrete or continuous) around the sphere equator (giving the greatest negative deviations from the point mass field). In these cases the extremal direction of the field measurement respectively passes through point-like particles and coincides with the axis of symmetry of a ring, which is perpendicular to its plane. Our numerical estimations show that any body can be considered with reasonable accuracy (the relative error in the determination of the field strength is less than $5 \%$) as point-like mass if the distance to the observation point is more than an order of magnitude larger than its characteristic sizes. The problem considered in this paper can help readers to probe the limits of applicability of the field point source model.

Estimating Rupture Dimensions of Three Major Earthquakes in Sichuan, China, for Early Warning and Rapid Loss Estimates

ABSTRACTLarge earthquakes, such as Wenchuan in 2008, Mw 7.9, Sichuan, China, provide an opportunity for earthquake early warning (EEW), as many heavily shaken areas are far (∼50 km) from the epicenter and warning times could be sufficient (≥5 s) to take preventive action. On the other hand, earthquakes with magnitudes larger than ∼M 6.5 are challenging for EEW because source dimensions need to be defined to adequately estimate shaking. Finite-fault rupture detector (FinDer) is an approach to identify fault rupture extents from real-time seismic records. In this study, we playback local and regional onscale strong-motion waveforms of the 2008 Mw 7.9 Wenchuan, 2013 Mw 6.6 Lushan, and 2017 Mw 6.5 Jiuzhaigou earthquakes to study the performance of FinDer for the current layout of the China Strong Motion Network. Overall, the FinDer line-source models agree well with the observed spatial distribution of aftershocks and models determined from waveform inversion. However, because FinDer models are constructed to characterize seismic ground motions (as needed for EEW) instead of source parameters, the rupture length can be overestimated for events radiating high levels of high-frequency motions. If the strong-motion data used had been available in real time, 50%–80% of sites experiencing intensity modified Mercalli intensity IV–VII (light to very strong) and 30% experiencing VIII–IX (severe to violent) could have been issued a warning with 10 and 5 s, respectively, before the arrival of the S wave. We also show that loss estimates based on the FinDer line source are more accurate compared to point-source models. For the Wenchuan earthquake, for example, they predict a four to six times larger number of fatalities and injured, which is consistent with official reports. These losses could be provided 1/2∼3 hr faster than if they were based on more complex inversion rupture models.

Revision of Boore (2018) Ground-Motion Predictions for Central and Eastern North America: Path and Offset Adjustments and Extension to 200 m/s≤VS30≤3000 m/s

AbstractThe three sets of ground-motion predictions (GMPs) of Boore (2018; hereafter, B18) are compared with a much larger dataset than was used in deriving the predictions. The B18 GMPs work well for response spectra at periods between ∼0.15 and 4.0 s after an adjustment accounting for a path bias at distances beyond 200 km—this was the maximum distance used to derive the stress parameters on which the simulations in B18 are based. An additional offset adjustment is needed in the B18 predictions for short and long periods. The adjustment at short periods may be because the κ0 of 0.006 s stipulated by the Next Generation Attenuation-East (NGA-East) project to be used in deriving the GMPs is inconsistent with the observations on rock sites. The explanation for the offset adjustment at long periods is not clear, but it could be a combination of limitations of the point-source stochastic model for longer period motions, as well as a decreasing number of observations at longer periods available to constrain the simulations on which the predictions are based.The predictions of B18, developed for very-hard-rock sites (VS30 of 2000 and 3000 m/s), have here been extended down to VS30 values as low as 200 m/s. I find, as have others, that for a given VS30, there is generally less site amplification for central and eastern North America (CENA) than for the active crustal region dataset used for the Boore, Stewart, et al. (2014; hereafter, BSSA14) GMP equations. This might have an impact on conclusions of several previous studies of CENA GMPs that used the site amplifications in BSSA14 in comparing data and predictions.An additional finding is that the κ0 implied by recordings on a subset of stations in the Charlevoix region located on rock (data from these stations were not used in the analysis described earlier) is more consistent with a value near 0.014 s than the 0.006 s value used in B18 and the NGA-East project.

Evaluation of Liquefaction Potential of Soil at a Power Plant Site in Chittagong, Bangladesh

This study presents an evaluation of liquefaction potential for combined cycle power plant site located in the Chittagong district, Bangladesh, using standard penetration test blow counts (SPT-N values). The peak ground acceleration (PGA) values at a bedrock level were estimated deterministically using both linear and point source models as well as different ground motion prediction equations (GMPEs). The surface level hazard was estimated using amplification factors for the soil conditions present and the response spectrum at the center of the plant site was plotted. The liquefaction potential for the site was arrived at by using the SPT-N values of 33 boreholes in the site and at every 3-meter interval from the ground level to a depth of 30 meters. The results from the LPI contours at successive depths indicate that in the majority of the borehole locations, the soil up to 15 meters depth had a significant hazard of liquefaction. These findings from the present study can prove to be crucial from the structural point of view, for any future construction activities in the area.

Full Field Radiant Flux Distribution of Multiple Tilted Flat Lambertian Light Sources

The emergence of visible light communication (VLC) as a subset of optical wireless communication (OWC) in the early 2000s has turned any light-emitting diode (LED) source into a potential data transmitter. The design process for any VLC or OWC system typically involves a link budget analysis performed by studying the signal-to-noise ratio (SNR) at the receiver. Since this SNR strongly depends on the radiant flux collected by the receiver, an accurate model for this parameter is required. The point-source model has been widely used since 1979 and generally provides a good approximation of the received radiant flux. However, it might be less accurate for typical extended lighting sources like LED panels or large-area organic LEDs. In this paper, the radiant flux distribution of flat Lambertian rectangular or circular sources is derived from a vector analysis of their irradiance. It is then validated through actual measurements in the case of a circular source. The resulting extended-source models thus better capture the light beam pattern of such transmitters to enable a more accurate link budget. It provides at the same time almost identical results to the point-source model for small sources and can, therefore, be seen as a natural extension of this already widely used model. INDEX TERMS LED pattern, irradiance pattern, light power pattern, non-imaging optics, link budget, optical wireless communication, visible light communication.

Improvement of Instantaneous Point Source Model for Simulating Radionuclide Diffusion in Oceans under Nuclear Power Plant Accidents

Simulation methods have become an important tool to reveal radionuclide migration during accidental radionuclide releases and predict influences of accidents on the marine environment. The instantaneous point source model is a useful method to simulate the large-scale radionuclide diffusion in marine areas. However, the simulation accuracy of this method requires improvement as it didn’t take radionuclide decay into account. In this study, an improved instantaneous point source model considering radionuclide decay was proposed on the basis of the original model. Furthermore, the instantaneous point source model and the improved version were used to simulate the concentrations of 131I and 137Cs following the Fukushima Dai-ichi nuclear power plant accident. The results showed that the relative error of 131I concentrations decreased from 136.03% to 37.59% when using the improved model; and improvements in relative errors for 137Cs concentrations were not apparent as the simualtion period was much shorter than its half-life period. Therefore, the improved model can accurately simulate the diffusion process for radionuclides following an accident and provides an efficient decision support tool for risk assessment managers and for use in safety guarantees of nuclear power plants during siting and operational phases.

Thermal radiation model for the buoyancy-controlled diffusion plumes from rectangular fire sources

This study investigated the thermal radiation from a rectangular fire source with different aspect ratios. Fire experiments with burners of the same surface area but different aspect ratios were conducted. The flame was split into several sub-flames as the aspect ratio of burner increased. Compared with the axis-symmetric fire source, the flame split in the rectangular fire source led to a change in the thermal radiation mechanism. Thus, a multi-cuboid flame model was developed to estimate the radiant heat flux from a rectangular fire source. The number of sub-cuboid flames considered in the proposed model depended on the aspect ratio of the rectangular fire source. Compared with experimental results and data available in the literature, the standard error of estimation by the developed model was 0.505, indicating that the proposed model outperformed the cuboid flame and point source models found in the literature. This developed model has better prediction for the thermal radiation from rectangular fire source with large aspect ratio. Based on sensitivity analysis of model parameter, the ratio of the aspect ratio of the burner to the number of sub-cuboid flames could be considered as a constant. Thus, this proposed model can be applied to risk assessment of rectangular fire.

Simulation of acoustic fields emitted by ultrasonic phased array in austenitic steel weld**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474308, 11574343, and 11774377).

Ultrasonic inspection of austenitic steel weld is a great challenge due to skewed and distorted beam in such a highly anisotropic and inhomogeneous material. To improve the ultrasonic measurement in this situation, it is essential to have an in-depth understanding of ultrasound characteristics in austenitic steel weld. To meet such a need, in the present study we propose a method which combines the weld model, Dijkstra’s path-finding algorithm and Gaussian beam equivalent point source model to calculate the acoustic fields from ultrasonic phased array in such a weld. With this method, the acoustic field in a steel-austenitic weld-steel three-layered structure for a linear phase array transducer is calculated and the propagation characteristics of ultrasound in weld are studied. The research results show that the method proposed here is capable of calculating the acoustic field in austenitic weld. Additionally, beam steering and focusing can be still realized in the austenitic steel weld and the beam distortion is more severe in the middle of weld than at other positions.

Examination of radiative fraction of small-scale pool fires at reduced pressure environments

Determining flame radiative fraction is necessary in the estimation of radiation heat transfer of a fire, while the radiative fraction for a given fuel is usually regarded as constant, even at sub-atmospheric pressures. To ascertain the factors affecting this parameter, a series of small-scale n-heptane pool fires with diameters of 4–10 cm are performed at low pressures by means of an altitude chamber in this work. Based on a point source model, the radiative fractions of tested pool fires are determined, and coupled effects of pressure and pool diameter on this parameter are observed. A dimensional scaling theory is further proposed to interpret these effects, i.e. Xr~P0.3−0.175αD0.15, and the experimental results can be well correlated with this model. The findings will be helpful in evaluating the radiative heat fluxes of pool fires at reduced pressures more accurately, further providing guidance on the detection of incipient fires at sub-atmospheric pressure environments.

Equivalent multipolar point-source modeling of small spheres for fast and accurate electromagnetic wave scattering computations

In this paper, we develop reduced models to approximate the solution of the electromagnetic scattering problem in an unbounded domain which contains a small perfectly conducting sphere. Our approach is based on the method of matched asymptotic expansions. This method consists in defining an approximate solution using multi-scale expansions over outer and inner fields related in a matching area. We make explicit the asymptotics up to the second order of approximation for the inner expansion and up to the fifth order for the outer expansion. We validate the results with numerical experiments which illustrate theoretical orders of convergence for the asymptotic models requiring negligible computational cost.

Self-propulsion of symmetric chemically active particles: Point-source model and experiments on camphor disks.

Solid undeformable particles surrounded by a liquid medium or interface may propel themselves by altering their local environment. Such nonmechanical swimming is at work in autophoretic swimmers, whose self-generated field gradient induces a slip velocity on their surface, and in interfacial swimmers, which exploit unbalance in surface tension. In both classes of systems, swimmers with intrinsic asymmetry have received the most attention but self-propulsion is also possible for particles that are perfectly isotropic. The underlying symmetry-breaking instability has been established theoretically for autophoretic systems but has yet to be observed experimentally for solid particles. For interfacial swimmers, several experimental works point to such a mechanism, but its understanding has remained incomplete. The goal of this work is to fill this gap. Building on an earlier proposal, we first develop a point-source model that may be applied generically to interfacial or phoretic swimmers. Using this approximate but unifying picture, we show that they operate in very different regimes and obtain analytical predictions for the propulsion velocity and its dependence on swimmer size and asymmetry. Next, we present experiments on interfacial camphor disks showing that they indeed self-propel in an advection-dominated regime where intrinsic asymmetry is irrelevant and that the swimming velocity increases sublinearly with size. Finally, we discuss the merits and limitations of the point-source model in light of the experiments and point out its broader relevance.

Landing gear interwheel tonal noise characterization with the Boundary Element Method

Landing gear noise is mainly broadband in nature, but it can also feature some tonal contributions. Tonal noise significantly increases noise annoyance and can originate from facing cavities in landing gear wheels. The present work aims at using the Boundary Element Method (BEM) with a simple harmonic point source model to characterize the resonance between the two facing cylindrical cavities in the wheels of the generic nose landing gear LAGOON, where a flow independence of the tonal noise emission has been reported experimentally. Three configurations of increasing complexity are successively considered: a single wheel, the two facing wheels linked by an axle, and finally the whole landing gear, including the main strut. In terms of resonant frequencies, the BEM is shown to give results in very good agreement with analytical formulae and CFD/CAA computations from the literature. Some acoustic measurements are also performed for the whole LAGOON configuration and a very good agreement is observed between BEM results and the experimental database. The directivity of the resonant modes is detailed for each case and compared with success to CFD/CAA results, except for convective amplification effects. The amplification of each resonant mode is quantified through a so-called scattering factor and it is shown that the facing cavities present much sharper resonances than the single cavity, and that the presence of the main strut only increases the amplification of the axisymmetric mode. Finally, the modelisation of the interwheel space by an annular duct is discussed and a parametric study is conducted on the axle diameter. The results of this parametric study shed light on the annular duct model domain of validity while demonstrating the ability of the BEM to treat geometries of arbitrary complexity with low computational cost when analytical models are unavailable.

Earthquake Early Warning: Advances, Scientific Challenges, and Societal Needs

Earthquake early warning (EEW) is the delivery of ground shaking alerts or warnings. It is distinguished from earthquake prediction in that the earthquake has nucleated to provide detectable ground motion when an EEW is issued. Here we review progress in the field in the last 10 years. We begin with EEW users, synthesizing what we now know about who uses EEW and what information they need and can digest. We summarize the approaches to EEW and gather information about currently existing EEW systems implemented in various countries while providing the context and stimulus for their creation and development. We survey important advances in methods, instrumentation, and algorithms that improve the quality and timeliness of EEW alerts. We also discuss the development of new, potentially transformative ideas and methodologies that could change how we provide alerts in the future. ▪ Earthquake early warning (EEW) is the rapid detection and characterization of earthquakes and delivery of an alert so that protective actions can be taken. ▪ EEW systems now provide public alerts in Mexico, Japan, South Korea, and Taiwan and alerts to select user groups in India, Turkey, Romania, and the United States. ▪ EEW methodologies fall into three categories, point source, finite fault, and ground motion models, and we review the advantages of each of these approaches. ▪ The wealth of information about EEW uses and user needs must be employed to focus future developments and improvements in EEW systems.

Ground motion acceleration and response spectra of Al-Mashair area, Makkah Al-Mukarramah, Saudi Arabia

The residential buildings of Makkah Al-Mukarramah constructed mostly on a soft Quaternary deposits with various thicknesses reaching to more than 30 m in most districts. The spatial variation of ground motion in Al-Mashair area has been assessed by synthetic ground motion acceleration using a point source model coupled by a site response analysis. The bedrock level acceleration time histories have been generated at 27 sites within Al-Mashair area generated by earthquake of 5.0 moment magnitude, using a synthetic ground motion model. While, the ground surface response spectral curves with 5% of the critical damping were assessed using shear-wave velocity profiles of multichannel analysis of surface waves besides the earthquake time histories. Surface ground response spectra were mapped using the ArcGIS platform for 1.5 Hz, 3.0 Hz, 5.0 Hz, 8 Hz, and 10 Hz where this frequency range includes the range of natural frequencies of tall to single story buildings. The surface ground motion maps display that the hazard level ranges from low to moderate, where peak spectral acceleration varies between 13 cm/s2 and 124 cm/s2. The maximum surface ground motion values are calculated with 5% damped horizontal spectral acceleration at 10 Hz, which is equal to the natural frequency of low-rise buildings. These results should be taken into consideration from decision-makers, urban planners, and civil engineers during the design of earthquake-resistant structures in Makkah Al-Mukarramah city in general and Al-Mashair zone in particular.

A Bayesian Analysis of SDSS J0914+0853, a Low-mass Dual AGN Candidate

Abstract We present the first results from Bayesian AnalYsis of Multiple AGN in X-rays (BAYMAX), a tool that uses a Bayesian framework to quantitatively evaluate whether a given Chandra observation is more likely a single or dual point source. Although the most robust method of determining the presence of dual active galactic nuclei (AGNs) is to use X-ray observations, only sources that are widely separated relative to the instrument's point-spread function are easy to identify. It becomes increasingly difficult to distinguish dual AGNs from single AGNs when the separation is on the order of Chandra's angular resolution (<1″). Using likelihood models for single and dual point sources, BAYMAX quantitatively evaluates the likelihood of an AGN for a given source. Specifically, we present results from BAYMAX analyzing the lowest-mass dual AGN candidate to date, SDSS J0914+0853, where archival Chandra data shows a possible secondary AGN ∼ 0.″3 from the primary. Analyzing a new 50 ks Chandra observation, results from BAYMAX shows that SDSS J0914+0853 is most likely a single AGN with a Bayes factor of 13.5 in favor of a single point source model. Further, posterior distributions from the dual point source model are consistent with emission from a single AGN. We find a very low probability of SDSS J0914+0853 being a dual AGN system with a flux ratio f > 0.3 and separation r > 0.″3. Overall, BAYMAX will be an important tool for correctly classifying candidate dual AGNs in the literature, as well as studying the dual AGN population where past spatial resolution limits have prevented systematic analyses.

Estimation of source and site characteristics in the North-West Himalaya and its adjoining area using generalized inversion method

A site constraint generalized inversion technique (GINV) has been used in the present study to develop source and site spectra for the regions in and around north-west Himalaya. Database consists of 156 earthquake (EQ) records corresponding to 21 EQ events [2.5<magnitude <5.8], recorded at 78 recording stations. Source parameters like scalar moment( ), corner frequency( ), stress drop( ), apparent stress drop( , and seismic energy ) are computed for each EQ event by fitting the point source model to the obtained source spectra. Calculated and values for all events are found in the range of 4.96×10 13 Nm-2.91×10 16 Nm and 1.50Hz-5.50Hz respectively. Further, regression analysis between the above two parameters lead to the relation: for the study area. Value of computed in the study varies from 1.86×10 8 J-1.75×10 12 J. Further, value of is found varying from 0.65MPa-21.13MPa while is found in the range of 0.07MPa-2.76MPa. It is observed that both and approximately follow the theoretical relation as; = . Another outcome of the study is the site amplification curves developed based on the GINV results of horizontal and vertical components for all the recording stations. Further, site transfer function (STF) for all the recording stations characterised by the ratio of horizontal and vertical site amplification components is computed and, amplification function (A peak ) and predominant frequency (f peak ) are determined. Comparison of estimated STFs based on GINV and results of Horizontal to Vertical Spectral Ratio method (HVSR) show similarity in terms of the f peak values.

Experiments in unmanned aerial vehicle/unmanned ground vehicle radiation search

AbstractThis paper discusses the results of a field experiment conducted at Savannah River National Laboratory to test the performance of several algorithms for the localization of radioactive materials. In this multirobot system, both an unmanned aerial vehicle, a custom hexacopter, and an unmanned ground vehicle (UGV), the ClearPath Jackal, equipped with γ‐ray spectrometers, were used to collect data from two radioactive source configurations. Both the Fourier scattering transform and the Laplacian eigenmap algorithms for source detection were tested on the collected data sets. These algorithms transform raw spectral measurements into alternate spaces to allow clustering to detect trends within the data which indicate the presence of radioactive sources. This study also presents a point source model and accompanying information‐theoretic active exploration algorithm. Field testing validated the ability of this model to fuse aerial and ground collected radiation measurements, and the exploration algorithm’s ability to select informative actions to reduce model uncertainty, allowing the UGV to locate radioactive material online.

Optimal Safe Layout of Fuel Storage Tanks Exposed to Pool Fire: One Dimensional Deterministic Modelling Approach

Fire hazard is one of the main risks associated to fuel storage tanks in petroleum and in the petrochemical industries. Such a hazard includes pool fires in the storage tanks or in the bunds, fire propagation from the source tank to target tanks both in absence and in presence of wind, and also the cascading/domino effect due to confined and unconfined vapour cloud explosion and or BLEVE associated with the source tank. In the present work, a radiation shield of flowing water has been introduced at a distance from the source fuel storage tank to prevent the domino effect originating from this source tank, under fire, to the target fuel storage tanks in a tank farm. A simple one dimensional model has been developed from the steady state energy balance to simulate the safe distances (i.e. rim–rim distance) between fuel storage tanks containing class-I fuel (e.g. gasoline), both in presence and absence of a water-shield under no-wind and cross-wind conditions. The model predictions have shown that the maximum safe inter-tank separation distance of 28.42 m is anticipated at a wind velocity of 6 m/s, compared to 16.34 m in no-wind condition, beyond which the centroid of the parallelepiped (a solid-flame geometry) falls outside the base of the tilted flame geometry causing flattening of flame and a very sluggish increase in the flame tilt angle as the inverse of the Richardson number in the presence of wind velocity vector increases. Furthermore, the present one dimensional mathematical model has also been extended to show that introduction of a water-shield with an appropriate thickness (δopt) is able to prevent the propagation of radiation heat flux under both no-wind and cross-wind conditions to a much lower distance close to 8.34 m between tanks (measured from the centre of the source tank), than those predicted from the existing empirical models; viz. Point Source model and Shokrie-Beyler’s model.