Pseudo Sources Research Articles

Distributed source scheme for Poisson equation using finite element method

The finite-element method (FEM) is one of the most versatile numerical techniques to solve partial differential equations (PDEs). The approximations in FEM result in numerous errors and various techniques are available to reduce the errors. Distributed Source Scheme (DSS) is a recently proposed method to reduce error around a single source of field which obeys the Poisson equation using the 3-D finite-difference method (FDM). DSS achieves this feat by introducing pseudo sources around the singular source. In this article, the proposed method is studied for single and bulk sources using 2-D FEM along with experimental validation. The numerical solution from FEM is compared with the approximate solution from integral equations over the whole computational domain for the error analysis. The error due to boundary values are isolated by considering the solution of integral equations on boundary elements in FEM. The maximum error in the numerical solution of a single source is reduced from 4.96% to 3.28×10−4% using DSS and to 0.55% using Truncated Distributed Source Scheme (TDSS) with a truncation number of 5. The mean difference in numerical and approximate potential at the boundaries of bulk sources is reduced from 1.21×105 Volt to 2.69×104 Volt using DSS.

A novel odor source localization system based on particle filtering and information entropy

So far, gas leakage caused by natural or human factors has led to serious consequences in terms of social security. Previous strategies for locating the odor sources appear to be either defective or incomplete. For enhancing the success rate and rapidity, this paper aims to present a novel and complete strategy in search of lurking gas sources. Particle filtering and information entropy are both employed to track the plume information. To improve the tracking efficiency in this process, a novel objective function is designed by considering the entropy gains of the suspected targets as well as the repeated exploration scores. Considering the pseudo sourced caused by obstacles, a statistics-based source determine algorithm is proposed to confirm the source’s authenticity, while the artificial potential field method is subsequently applied to eliminate the distractions introduced by the pseudo sources. Simulations and on-site tests are both carried out while results showed that the proposed scheme is competent to complete sources localization task in the scene that contains randomly distributed obstacles and pseudo source.

Minimum-cost forest for uncertain multicast with delay constraints

The use of multicast transmission can efficiently reduce the consumption of network resources by jointly serving multiple destinations with a single source node. Currently, many multicast applications impose the constraint wherein multicast flows must be processed by a series of Virtual Network Functions (VNFs) before reaching their destinations. Given a multicast transmission, there are usually multiple server nodes, each of which is able to host all the required VNFs. Thus, the multicast flow should be initially steered to one or a few selected server nodes that act as pseudo sources, and the destinations will then retrieve new flow from any of these pseudo sources. In this paper, we model this kind of multicast as an uncertain multicast with multiple pseudo sources, whose routing structure is usually a forest consisting of multiple isolated trees. We then characterize and construct the Delay-guaranteed Minimum Cost Forest (D-MCF) such that each path from the source to the destination satisfies the end-to-end delay constraint. To tackle this NP-hard problem, we design two efficient methods, the Partition Algorithm (PA) and the Combination Algorithm (CA), to approximate the optimal solution. Theoretical analyses and evaluations indicate that these two methods can generate the desired routing forest for any multicast transfer. Moreover, the PA method achieves a better balance between performance and time consumption than the CA method. The evaluation results show that PA-(Ω+ 20) can reduce total cost by 49:02% while consuming 12:59% more time, thus significantly outperforming the CA-(Ω+ 20) method.

Current source reconstructing and magnetic imaging of cardiac electrical activity during P-wave

<sec> The current source reconstruction and magnetic imaging is a new technique to non-invasively obtain spatial information regarding cardiac electrical activity using magnetocardiogram (MCG) signals measured by the superconducting quantum interference device (SQUID) on the human thorax surface. Using MCG signals to reconstruct distributed current sources needs to solve the inverse problem of magnetic field. The beamforming is a type of spatial filter method that has been used for distributed source reconstruction and source imaging in electroencephalogram (EEG) and magnetoencephalogram (MEG). In this paper, the dipole moment of distributed current source is estimated with corresponding each spatial filter based on the cardiac source field model. The purpose is to enhance the intensity contrast of the dipole moment of distributed current sources in distributed source spatial spectrum estimation with beamforming, so that the reconstructed-pseudo sources beyond the heart can be removed for imaging cardiac electric activity well.</sec><sec> A new beamforming method of improving intensity contrast (IIC) of distributed source spatial spectrum estimation is developed for imaging cardiac electric activity in P-wave, due to cardiac magnetic signals in P-wave lower than that of the peak value of R-wave, which has a relatively low signal-to-noise ratio (SNR). For enhancing the accuracy of current source reconstruction in P-wave, the IIC divided into two steps: firstly, to introduce the lead-field matrix, which represents the measurement sensor-array sensitivity to magnetic field current sources, into a weight matrix of the spatial filter for making the output estimation of the filter more sensitive to the current sourcedistribution, so as to improve the intensity contrast of the reconstructed distributed sources.Secondly, by setting a threshold of source intensity from experience, to extract the reconstructed source with locally-maximal dipole strength at each time for eliminating the relatively weak pseudo sources in other locations, so as to enhance the accuracy of current source reconstruction during P-wave. In this paper, the IIC and three other methods, including minimum variance beamforming (MVB), suppressing spatial filter output noise-power gain (SONG) and trust region reflective (TRR), are compared by using the theoretical analysis and simulation experiments of MCG current source reconstruction during P-wave. The results show that the IIC has higher intensity contrast of the single source spatial spectrum estimation, and possesses better accuracy of the current source reconstruction. The 61-channel MCG signals of two healthy subjects and their imaging of cardiac electrical activity during P-wave also are analyzed. The result shows that the IIC is better than the other three methods. It is indicated that two healthy subjects have stronger electrical activity in the atrium than that in the ventricle at Ppeak time, also that the electrical activity has the direction feature when the right-atrium is depolarized during P-wave. </sec><sec> In summary, the IIC is useful for imaging the cardiac electrical activity. However, it is needed to carry out a further research on patients with local myocardial ischemia and left or right coronary artery stenosis, and to establish the evaluation index for imaging of cardiac electrical activity in such patients.</sec>

Analysing historical enquiry in school history textbooks

According to the South African curriculum, two of the aims of learning history are to learn the process of historical enquiry and to understand historical concepts such as the use of historical sources and examining evidence. This paper explores how a sample of seven social science South African textbooks uses historical sources to enable learners to learn the process of historical enquiry. The findings show that there were no primary sources presented in the Grade 3 – 6 textbooks, although there were many generic pictures and texts. There is an increase in the number and use of sources in the Grade 7 to Grade 9 textbooks, but issues of contextualisation and lack of provenance remain a challenge to the process of developing historical thinking. ‘Pseudo sources’ (a picture or text recreated to look like a primary source) and generic sources of information do not support historical thinking. The multi-perspective approach, which means understanding the diverse ways of interpreting the same event, is poorly developed in the lower grade textbooks but became more evident in the Grade 9 books. Thus, specialised procedural knowledge is only introduced to learners in Grade 9, suggesting that the primary school textbooks analysed in this study are not fully supporting the aims of the official history curriculum.

Evaluation of the Effect of Linear Scattering Anisotropy and Boundary Shape on the Calculation of K ∞ for VVER-1000 Cells with Mixed Uranium-Plutonium Power-Grade Fuel

The method of surface pseudo sources for solving the multigroup neutron transport equation with scattering anisotropy and different boundary conditions by the operator splitting method was developed previously. The method was implemented in the RATsIYa option of the WIMS-SH-2.0 complex. The impact of scattering anisotropy and the form of the boundary conditions on K ∞ of VVER-1000 reactor cells with uranium-plutonium power-grade fuel was investigated. The calculations showed that the impact of each of these two effects is about 0.5%; they have different signs, as a result of which they largely compensate one another.

Source apportionment using reconstructed mass calculations

A long-term study was undertaken to investigate the air quality of the Islamabad/Rawalpindi area. In this regard fine and coarse particulate matter were collected from 4 sites in the Islamabad/Rawalpindi region from 1998 to 2010 using Gent samplers and polycarbonate filters and analyzed for their elemental composition using the techniques of Neutron Activation Analysis (NAA), Proton Induced X-ray Emission/Proton Induced Gamma-ray Emission (PIXE/PIGE) and X-ray Fluorescence (XRF) Spectroscopy. The elemental data along with the gravimetric measurements and black carbon (BC) results obtained by reflectance measurement were used to approximate or reconstruct the particulate mass (RCM) by estimation of pseudo sources such as soil, smoke, sea salt, sulfate and black carbon or soot. This simple analysis shows that if the analytical technique used does not measure important major elements then the data will not be representative of the sample composition and cannot be further utilized for source apportionment studies or to perform transboundary analysis. In this regard PIXE/PIGE and XRF techniques that can provide elemental compositional data for most of the major environmentally important elements appear to be more useful as compared to NAA. Therefore %RCM calculations for such datasets can be used as a quality assurance (QA) measure to treat data prior to application of chemometrical tools such as factor analysis (FA) or cluster analysis (CA).

Single-channel bearing vibration signal blind source separation method based on morphological filter and optimal matching pursuit (MP) algorithm

A novel method to solve the single-channel source separation problem is proposed, which is based on a morphological filter to remove noise and the optimal matching pursuit (MP) algorithm to create pseudo sources. The signal is first purified by the morphological filter. Then, the purified signal is decomposed by the MP method, the Gabor atoms of the MP are selected by genetic algorithm in order to be less time-consuming. The selected atoms and the purified signal are combined into multi-dimensional signals, and the underdetermined problem of single-channel source separation is solved. The singular value decomposition method is used to estimate the number of new constructed signals. Then, the fast independent component analysis algorithm is used to achieve the separation of the signals. The proposed method is applied to the separation of the simulated signals and the mixed faults of bearing, the results indicate that the method can well solve the single-channel signal separation problem.

Size-fractionated airborne particulate matter characterization of a residential area near Islamabad airport by IBA methods

Size fractionated PM2.5 and PM2.5–10 airborne particulates collected from the airport housing society site in Rawalpindi were characterized using the non destructive ion beam analysis method. Proton induced X-ray emission and Proton induced gamma ray emission were employed to quantify 28 trace elements in fine and coarse filter samples. The average PM2.5 and PM2.5–10 masses were found to be 15.7 and 144 μg/m3, respectively which, when combined exceed the Pakistani limit for PM10 of 100 μg/m3. The average black carbon (BC) content was found to be 3.49 and 5.95 μg/m3 corresponding to 23.8 and 4.30% of the fine and coarse masses, respectively. The reconstructed mass (RCM) was calculated for both particle modes using 5 pseudo sources, namely soil, sulfate, smoke, sea salt and BC. It was found that 5 sources could account for 80.6 and 49.0% of the fine and coarse masses, respectively. The low value of RCM for the coarse mode may imply a much higher organic content. The major sources contributing to the fine mode were soil, sulfate and BC. Similarly for the coarse mass fraction it was found that soil was the major source whereas the sulfate and BC sources did not contribute as much.

Non-cavitating propeller noise source inversion

Ship's propeller cavitation generates major inboard noise and vibration over the aft body surface of a ship. During the last decade, cavitation-induced hull pressure forces have been reduced considerably leading to reduced noise and vibration levels owing to cavitation, in which case the non-cavitating components of propeller excitations have to be considered: pressure fluctuations due to blade loading and blade thickness. In this work, an algorithm to invert for the non-cavitating propeller noise source parameters based on the experimental data in a cavitation tunnel is shown. The fluctuating hull pressure is estimated by forward modeling based on acoustic boundary element method (BEM). The propeller blade loading and thickness noise sources are modeled using rings of dipoles and quadrupoles, respectively. The inversion for these pseudo sources are carried out by matching the data obtained from a cavitation tunnel experiment, where several hydrophone are flush mounted on the ship's surface near the propeller. Proper inversion results are obtained when six or more dipole and quadrupole rings are placed at each blade. Using the inverted source parameters, hull pressures were estimated, which show good agreement with the experiment data.

A calibration approach to acoustic emission energy measurement

An approximate method for the quantitative characterization of acoustic emission sources whose signals are recorded with traditional instrumentation has been developed to evaluate the emission from a Fe-Ni alloy undergoing martensitic transformations. The calibration principle is based upon using pseudo sources of known elastic strain energy to produce a calibration curve relating a parameter of the acoustic emission signal measured (envelope strength) to the strain energy of the source. The curve can then be used to determine the strain energy of naturally occurring sources during martensitic transformations.

Simulation of Angular and Energy Distributions of the PTB Beta Secondary Standard

Calculations and measurements have been performed to assess radiation doses delivered by the PTB Secondary Standard that employs 147Pm, 204Tl, and 90Sr:90Y sources in prescribed geometries, and features "beam-flattening" filters to assure uniformity of delivered doses within a 5-cm radius of the axis from source to detector plane. Three-dimensional, coupled, electron-photon Monte Carlo calculations, accounting for transmission through the source encapsulation and backscattering from the source mounting, led to energy spectra and angular distributions of electrons penetrating the source encapsulation that were used in the representation of pseudo sources of electrons for subsequent transport through the atmosphere, filters, and detectors. Calculations were supplemented by measurements made using bare LiF TLD chips on a thick polymethyl methacrylate phantom. Measurements using the 204Tl and 90Sr:90Y sources revealed that, even in the absence of the beam-flattening filters, delivered dose rates were very uniform radially. Dosimeter response functions (TLD:skin dose ratios) were calculated and confirmed experimentally for all three beta-particle sources and for bare LiF TLDs ranging in mass thickness from 10 to 235 mg cm-2.

Numerical Optimization Techniques in Air Quality Modeling: Objective Interpolation Formulas for the Spatial Distribution of Pollutant Concentration

Abstract A technique is proposed for objection interpolation of the air quality distribution over a region in terms of sparse measurement data. Empirical information provided by the latter is effectively combined with knowledge of atmospheric dispersion functions of the type commonly used in source-oriented air quality models, to provide improved estimates of the concentration distribution over an extended region. However, the technique is not primarily source-oriented since, in contrast to the real source distribution of a source-oriented model, it utilizes fictitious or pseudo sources that are estimated in terms of the measured air quality data. This involves the use of interpolation functions that are computed using numerical optimization techniques based on the method of least squares. Due to the large number of different “weather” states that affect the atmospheric dispersion of pollution, considerable computation is required, although the bulk of this can be done in advance, so that the final interp...