Accurate Source Model Research Articles

Behavior of I-section steel beam welding reinforced while under load

An experimental study was conducted to investigate the mechanical behavior of four I-section steel beams, which were reinforced by welding a plate to the bottom and top flange, respectively. For all welding reinforced specimens, the ultimate capacity was obviously enhanced relative to that of the original beams. Preload while the beam is reinforced is proved to be an adverse factor for the capacity if the failure of the beam is controlled by lateral–torsional buckling. During the welding process, larger vertical deflection and web curvature were generated. The torsional section angle decreased if the appropriate welding procedure was adopted. In addition to the experimental study, a type of thermo-mechanical coupling analysis by ANSYS, considering the welding process, was conducted. A generally good agreement between FE analysis and the experiments could be observed from the comparison of the load versus deflection curves obtained from FE and the experiments. It was proved that the FE analysis is reasonable and can allow for the prediction of residual deflection after welding reinforcement. The FE analysis presented in this paper is a reasonable method for simulating the behavior of the steel beams reinforced while under load. With more accurate material parameters and heat source models, the simulation can be further enhanced.

113 逆音響解析によるエンジン音源モデルの構築と防音構造への適用(OS4 機械の振動・騒音および制御に関する新技術(2),研究討論セッション)

Engine enclosures are one of the methods that reduce air borne noise from engine. It is effective to predict the sound pressure by numerical simulation, when we design the enclosure. However, accurate sound source model is needed for the numerical simulation. Inverse-numerical acoustic analysis (INA) has been proposed as a method of constructing sound source model. In this study, the sound source model of diesel engine was constructed using INA. In addition, using the sound source model and boundary element method, the surrounding noise of engine enclosure was predicted, and the effectiveness of sound source model was shown.

Stress changes induced by the 2008 [formula omitted] Wenchuan earthquake, China

We invert the background stress fields of the Longmenshan and its adjacent regions before and after the 2008 great Wenchuan earthquake from focal mechanism data. Our results show that the stress orientations after the 2008 great Wenchuan earthquake are more coherent than those before this event at the epicentral zone. This result includes twofold implications: one is that the Wenchuan event altered the local stress field, the other is that the strength of the Wenchuan fault zone is very high and the characteristic of the seismogenic fault is consistent with the asperity model. We also estimate the stress changes caused by the Wenchuan event using an accurate source model and exhaustive receiver faults. The stress changes of >10kPa mainly occur in the nearby areas of the Longriba, east Kunlun, Qingchuan, Lushan faults and the southeastern section of the Xianshuihe fault, indicating that there is high earthquake hazard in these areas. The seismicity before and after the great Wenchuan earthquake in the Longmenshan and its adjacent regions shows that some subsequent earthquakes in the stress shadow area may be delayed and the 2013 Lushan earthquake may be advanced.

Lamp emission and quartz sleeve modelling in slurry photocatalytic reactors

Modelling of incident radiation intensity in a reaction medium or at catalyst surface is a necessity for kinetics modelling of pollutant degradation in photocatalytic reactors. In slurry photoreactors, the incident radiation within the reacting medium is calculated via the radiative transport equation (RTE) which considers the absorption and scattering of light due to the catalyst particles. As a result, a proper lamp emission model is required so as to obtain boundary conditions of the incident radiation entering the reacting medium. In this paper, we examine the validity of line, surface and volumetric source models at describing the incident radiation around a UV lamp. We then examine the effects of different lamp length to lamp radius ratios (2L/rlamp) and lamp ageing on the lamp emission model, with respect to the more descriptive and accurate volume source model. Finally, computational fluid dynamics (CFD) simulations are performed to determine the effect of light reflection, refraction and absorption at the air–quartz–water interfaces on incident radiation entering the reaction medium, for three quartz tube radius to lamp radius ratios (rquartz/rlamp) and two typical quartz tube thicknesses. The results obtained in this study are conveniently presented in dimensionless form and could be used as correction factors in the setting up of the radiation boundary condition in the modelling of cylindrical slurry photocatalytic reactors.

Revisiting the 7Li(p,n)7Be reaction near threshold

In this work we review all the available experimental neutron data for the 7Li(p,n) reaction near threshold which is necessary to obtain an accurate source model for Monte Carlo simulations in Boron Neutron Capture Therapy. Scattered published experimental results such as cross sections, differential neutron yields and total yields were collected and analyzed, exploring the sensitivity of the fitting parameters to the different possible variables and deriving a consistent working set of parameters to evaluate the neutron source near threshold.

Joint Source-Filter Optimization for Accurate Vocal Tract Estimation Using Differential Evolution

In this work, we present a joint source-filter optimization approach for separating voiced speech into vocal tract (VT) and voice source components. The presented method is pitch-synchronous and thereby exhibits a high robustness against vocal jitter, shimmer and other glottal variations while covering various voice qualities. The voice source is modeled using the Liljencrants-Fant (LF) model, which is integrated into a time-varying auto-regressive speech production model with exogenous input (ARX). The non-convex optimization problem of finding the optimal model parameters is addressed by a heuristic, evolutionary optimization method called differential evolution. The optimization method is first validated in a series of experiments with synthetic speech. Estimated glottal source and VT parameters are the criteria used for comparison with the iterative adaptive inverse filter (IAIF) method and the linear prediction (LP) method under varying conditions such as jitter, fundamental frequency (f0) as well as environmental and glottal noise. The results show that the proposed method largely reduces the bias and standard deviation of estimated VT coefficients and glottal source parameters. Furthermore, the performance of the source-filter separation is evaluated in experiments using speech generated with a physical model of speech production. The proposed method reliably estimates glottal flow waveforms and lower formant frequencies. Results obtained for higher formant frequencies indicate that research on more accurate voice source models and their interaction with the VT is necessary to improve the source-filter separation. The proposed optimization approach promises to be a useful tool for future research addressing this topic.

Groundwave Propagation at Short Ranges and Accurate Source Modeling [Testing Ourselves

Radiowave propagation models have long been used in long-range communication and/or radar systems. Different models use different sources. Observed and calculated results are therefore usually normalized, either against maximum or free-space values, or against values obtained above a non-penetrable flat Earth. This is acceptable and useful because excitation differences become negligible at long ranges. Today's interests and priorities in propagation modeling have shifted to quite short ranges, which necessitates accurate source modeling. Short-range propagation problems, modeling, and simulation challenges and accurate source modeling, are discussed, and several useful MATLAB codes are presented.

A source model for modulated electron radiation therapy using dynamic jaw movements

The development of fast and accurate source models (SMs) might be of crucial importance for the future clinical implementation of modulated electron radiation therapy (MERT). In this study, a SM is presented for reconstructing phase-space information of modulated electron beams using a few-leaf electron collimator (FLEC) and the photon jaws. During a FLEC-based delivery, two collimation devices (jaws and FLEC) modulate the electron beam characteristics dynamically. The SM separates the beam into a primary and a scattered component. The primary component is derived by a fast Monte Carlo (MC) transport calculation in air using the EGSnrc/BEAMnrc code. The scattered beam is modeled analytically. The accelerator was decomposed into its individual leaf components and the scattered beam was characterized at various levels of the accelerator. Scattered particles are assigned an energy and position by sampling pre-calculated probability distributions. The direction is estimated by geometrical arguments. Particles were assumed to emerge from tunable virtual sources on the side of each collimator leaf. A leaf-hit algorithm was developed to dynamically reject particles that are incident on any collimating leaf. Electron transport in air between the two collimation levels was calculated based on a MC-modified version of the Fermi-Eyges scattering theory. Correlations between direction and position were observed and taken into account at the final collimation level. To validate the model, reconstructed phase-space data were compared with the full accelerator MC phase-space data. The model accurately reproduced the beam characteristics and preserved important correlations. Depth and profile dose distributions in water were derived for square, rectangular, and off-axis field sizes and for a range of clinical energies. Discrepancies in the dose distributions and dose output were within 3% in all cases. Fast and accurate SMs open the possibility for fast treatment planning in MERT, based on an inverse optimization MC treatment planning scheme.

Sci-Thur AM: Planning - 07: A fast and accurate source model for energy and intensity modulated electron beams.

The purpose of this study is to develop a highly accurate and fast method for calculating electron beam dose distributions in Modulated Electron Radiation Therapy (MERT). An algorithm has been developed for creating phase-space files at the exit of a linear accelerator for any arbitrary intensity and energy electron beam without the need of full Monte Carlo simulations. The model assigns each particle to one of the 3 following sources: primary, secondary collimator and electron collimator scatter. The primary component is derived by fast MC transport in air. The scatter components are derived by the use of MC pre-calculated leaf kernels. Each kernel includes the fluence distribution, energy distribution and scatter probability of generating an electron from a leaf. The original position is sampled from tunable Gaussian or uniform distributions. The direction is estimated by geometrical means. According to the projection of the direction a particle is rejected if it is expected to suffer a leaf-hit. A leaf-hit counter is used to calculate the output of scatter particles based on the pre-calculated scatter probabilities. To account for multiple coulomb scattering in air a MC-corrected version of the Fermi-Eyges scattering theory was implemented. Depth and profile dose distributions were derived for the largest and smallest square field sizes, as well as for irregular and off-axis fields. The model agreed with full MC dose distributions within 3 % in all cases. Output at the depth of maximum dose exhibited discrepancies less than 2.6 % in all cases. The model was 16-22 times faster in generating a phase-space file than a full MC simulation with the BEAMnrc code.

WE‐C‐BRB‐04: Fast and Accurate Hybrid Source Model for Modulated Electron Radiotherapy

Purpose: To develop a highly accurate and fast method for calculating electron beam dose distributions in Modulated Electron Radiation Therapy (MERT). Method: An algorithm has been developed for creating phase‐ space files at the exit of a linear accelerator for any arbitrary intensity and energy electron beam without the need of full Monte Carlo simulations. The model assigns each particle to one of the 3 following sources: primary, secondary collimator and electron collimator scatter. The primary component is derived by fast MC transport in air. The scatter components are derived by the use of MC pre‐calculated leaf kernels. Each kernel includes the fluence distribution, energy distribution and scatter probability of generating an electron from a leaf. The original position is sampled from Gaussian or uniform distributions. The direction is estimated by geometrical means. According to the projection of the direction, a particle is rejected if it is expected to suffer a leaf‐hit. A leaf‐hit counter is used to calculate the output of scatter particles based on the pre‐calculated scatter probabilities. To account for multiple coulomb scattering in air a MC‐corrected version of the Fermi‐Eyges scattering theory was implemented. Results: Depth and profile dose distributions were derived for the largest and smallest square field sizes, as well as for irregular and off‐axis fields. The model agreed with full MC dose distributions within 3% in all cases. Output at the depth of maximum dose exhibited discrepancies less than 2.6% in all cases. The model was 16–22 times faster in generating a phase‐space file than a full MC simulation with the BEAMnrc code. Conclusions: Fast, dynamic electron beam calculations open up the possibility for real time delivery of MERT in the clinic and renew interest in electron beam therapy.

One-Sided $\rho$-GGD Source Modeling and Rate-Distortion Optimization in Scalable Wavelet Video Coder

We develop an accurate source model, one-sided ρ-generalized Gaussian distribution (GGD), for approximating the residual signals in scalable wavelet video coding. An efficient piecewise linear expression is suggested to estimate the shape parameter of the one-sided ρ-GGD. We also improve the model accuracy in matching the real data by modifying the ρ parameter estimation formula. Continuing our previous work on developing the motion information gain metric to measure the motion information efficiency, we now incorporate the one-sided ρ -GGD model in the cost function, which is used for deciding the motion vectors and motion estimation mode in scalable wavelet video coding. Compared with the conventional Lagrangian optimization, our simulation results show that the new mode decision method generally improves the peak signal-to-noise ratio performance in the combined signal-to-noise ratio and temporal scalability cases.

Retinotopic mapping of the primary visual cortex - a challenge for MEG imaging of the human cortex

Magnetoencephalography (MEG) can be used to reconstruct neuronal activity with high spatial and temporal resolution. However, this reconstruction problem is ill-posed, and requires the use of prior constraints in order to produce a unique solution. At present there are a multitude of inversion algorithms, each employing different assumptions, but one major problem when comparing the accuracy of these different approaches is that often the true underlying electrical state of the brain is unknown. In this study, we explore one paradigm, retinotopic mapping in the primary visual cortex (V1), for which the ground truth is known to a reasonable degree of accuracy, enabling the comparison of MEG source reconstructions with the true electrical state of the brain. Specifically, we attempted to localize, using a beanforming method, the induced responses in the visual cortex generated by a high contrast, retinotopically varying stimulus. Although well described in primate studies, it has been an open question whether the induced gamma power in humans due to high contrast gratings derives from V1 rather than the prestriate cortex (V2). We show that the beanformer source estimate in the gamma and theta bands does vary in a manner consistent with the known retinotopy of V1. However, these peak locations, although retinotopically organized, did not accurately localize to the cortical surface. We considered possible causes for this discrepancy and suggest that improved MEG/magnetic resonance imaging co-registration and the use of more accurate source models that take into account the spatial extent and shape of the active cortex may, in future, improve the accuracy of the source reconstructions.

Flow dynamics and characterization of a cough

Airborne disease transmission has always been a topic of wide interests in various fields for decades. Cough is found to be one of the prime sources of airborne diseases as it has high velocity and large quantity of droplets. To understand and characterize the flow dynamics of a cough can help to control the airborne disease transmission. This study has measured flow dynamics of coughs with human subjects. The flow rate variation of a cough with time can be represented as a combination of gamma-probability-distribution functions. The variables needed to define the gamma-probability-distribution functions can be represented by some medical parameters. A robust multiple linear regression analysis indicated that these medical parameters can be obtained from the physiological details of a person. However, the jet direction and mouth opening area during a cough seemed not related to the physiological parameters of the human subjects. Combining the flow characteristics reported in this study with appropriate virus and droplet distribution information, the infectious source strength by coughing can be evaluated. There is a clear need for the scientific community to accurately predict and control the transmission of airborne diseases. Transportation of airborne viruses is often predicted using Computational Fluid Dynamics (CFD) simulations. CFD simulations are inexpensive but need accurate source boundary conditions for the precise prediction of disease transmission. Cough is found to be the prime source for generating infectious viruses. The present study was designed to develop an accurate source model to define thermo-fluid boundary conditions for a cough. The model can aid in accurately predicting the disease transmission in various indoor environments, such as aircraft cabins, office spaces and hospitals.

SU‐GG‐T‐358: Monte Carlo Characterization of a Medical Linear Accelerator for Small Animal Irradiation

Purpose: Characterize a medical linear accelerator using Monte Carlo methods to investigate the precision and exactitude of dose delivery on small animal irradiation, particularly Wistar rat species. Method and Materials: A dedicated 6.0 MV linear accelerator (Novalis®, BrainLAB, Germany) for stereotactic radiosurgery (SRS) was simulated using BEAMnrc. A phase space (PS) data file was generated. The Monte Carlo (MC) calculations were tuned and validated to match depth and off‐axis dose profile data measured using a shielded diode detector (PFD3G, IBA‐dosimetry, Germany) for a 15.0 mm circular collimator. The animal model was based on a computed tomography (CT) scan of a Wistar rat for medullar trauma lesion model. An in‐house mask fixation system compatible with the treatment planning system (TPS) was developed to immobilize the rat. The CT scan images were imported to DOSXYZnrc using ctcreate tool and to the TPS via DICOM network. Dose distribution was calculated by the TPS using 2 non‐coplanar circular (NCAs). The NCAs were simulated using 20 static beams. The MC dose calculations were exported for analysis and compared with TPS dose calculations. On the other hand, absolute dose measurements were performed using the PFD3G inter calibrated using a Farmer type ionization chamber. Results: Absolute dose measurements showed that dose difference between TPS and treatment delivery is less than 4.3% on the selected points. Difference between TPS and MC dose calculations showed an over‐estimation by the TPS up to 15.0%. However, in the spinal cord lesion there is a good agreement between TPS and MC calculated data. Conclusion: Dose delivered by the dedicated linear accelerator is reliable to perform spinal cord irradiation in trauma lesion models. These preliminary results must be improved including an accurate source model of an arc radiation beam instead of the 20 discrete static beams.

SU-FF-T-227: Extra-Focal Analytical Source Model for the Radiation Output From a Linear Accelerator

Purpose: To describe in detail the recently improved extra-focal photon source component of an accurate analytical source model for the radiation output from a linear accelerator. Method and Materials: In the Anisotropic Analytical Algorithm used in the Eclipse™ Integrated Treatment Planning System (Varian Medical Systems Inc.) the radiation output from a linear accelerator is modeled using a multiple-source model with separate sub-sources for primary photon radiation, extra-focal photon radiation and electron contamination. Closely related to this, analytical models for accessories such as hard wedges and dynamic wedges are included. We describe in detail the extra-focal photon source component. A recent improvement to the extra-focal source leading to enhanced accuracy in cases of small MLC apertures that are common during IMRT treatments is discussed. Another related improvement significantly improves the modeling of the Varian Enhanced Dynamic Wedge (EDW). Results: The new extra-focal source model significantly improves the modeling of small MLC apertures that occur during dynamic IMRT treatments. In our test case to water phantom the maximum error (disregarding the buildup region) in depth dose curves has been reduced to 1% of dose maximum. Modeling of the Varian Enhanced Dynamic Wedge has been significantly improved also: in our example dataset the worst case deviation of local value at CAX has been reduced by more than 50%. Conclusion: The analytical source and accessory models used in the Anisotropic Analytical Algorithm in combination with a scheme to optimize the free parameters of the model has been already shown to be clinically acceptable. In this work we discuss two improvements related to the extra-focal source model which further improve its accuracy. Conflict of Interest: The authors are employed by Varian Medical Systems Finland Oy.

SU‐FF‐T‐445: Use of the Monte Carlo Method as a Comprehensive Tool for SMLC and DMLC‐Based IMRT Delivery and Quality Assurance (QA)

Purpose: To report on use of a thoroughly benchmarked MC dose calculation algorithm as an accurate tool for IMRT delivery and QA, in patient‐like media, where direct measurements for routine QA are impractical. Methods and material: We have developed a source model to investigate dosimetric effects related to MLC based delivery techniques such as step‐and‐shoot and sliding window using the DPM MC code. The model incorporates details of the Varian, 120‐leaf MLC and has been comprehensively verified against measurements in homogeneous and heterogeneous phantoms. As part of this development, we have investigated an efficient algorithm, using adaptive kernel density estimation for sampling phase space files. Using this accurate source model, we have studied beams that were sequenced with 1% and 10% fluence intervals for prostate, brain, head and neck and breast IMRT beams. Dose differences between SMLC and DMLC delivery types were evaluated in homogeneous and heterogeneous media (bone, lung and low‐density slabs) using DPM. We have also investigated dosimetric differences between optimized planned leaf sequences and actual delivered sequences, using machine log (Dynalog) files, which capture the physical leaf positions during delivery. Results: Benchmarking of the source model showed average agreement with measurements within 1%/2 mm. For a given fluence interval, calculated dose differences between SMLC and DMLC delivery techniques are different in homogeneous and heterogeneous media. Dose differences of up to 10% were found between plans developed with 1% and 10% fluence intervals for either SMLC or DMLC delivered sequences. Calculated dose differences of up to ±3cGy were observed between planned and delivered sequences (computed using the Dynalog files) for a prostate beam; these differences were in good agreement with film measurements. Conclusions: A well commissioned MC‐based dose algorithm provides a useful tool to study dosimetric issues related to fluence modulation and static versus dynamic delivery in IMRT.

MCNPX benchmark for cosmic ray interactions with the Moon

The MCNPX radiation transport code is used to simulate cosmic ray interactions within the Moon. Accurate source, geometric, and physics models are developed to successfully benchmark neutron density results with Apollo 17 measurements. The peak of the MCNPX lunar neutron density profile is shown to be within a few percent of the measured value, using a galactic cosmic rays modulation parameter that is consistent with the timeframe of the Apollo 17 mission. Sensitivity of the density profile to various input parameters and physics options is considered. Details of the simulation input are provided, along with neutron production and flux results, to facilitate additional benchmark efforts in the future.

Photon‐beam subsource sensitivity to the initial electron‐beam parameters

One limitation to the widespread implementation of Monte Carlo (MC) patient dose-calculation algorithms for radiotherapy is the lack of a general and accurate source model of the accelerator radiation source. Our aim in this work is to investigate the sensitivity of the photon-beam subsource distributions in a MC source model (with target, primary collimator, and flattening filter photon subsources and an electron subsource) for 6- and 18-MV photon beams when the energy and radial distributions of initial electrons striking a linac target change. For this purpose, phase-space data (PSD) was calculated for various mean electron energies striking the target, various normally distributed electron energy spread, and various normally distributed electron radial intensity distributions. All PSD was analyzed in terms of energy, fluence, and energy fluence distributions, which were compared between the different parameter sets. The energy spread was found to have a negligible influence on the subsource distributions. The mean energy and radial intensity significantly changed the target subsource distribution shapes and intensities. For the primary collimator and flattening filter subsources, the distribution shapes of the fluence and energy fluence changed little for different mean electron energies striking the target, however, their relative intensity compared with the target subsource change, which can be accounted for by a scaling factor. This study indicates that adjustments to MC source models can likely be limited to adjusting the target subsource in conjunction with scaling the relative intensity and energy spectrum of the primary collimator, flattening filter, and electron subsources when the energy and radial distributions of the initial electron-beam change.

A GACS Modeling Approach for MPEG Broadcast Video

Accurate MPEG source models are needed to support high speed networks such as ATM and Internet. In this paper, we propose a video model called Gaussian auto-regressive and chi-square processes (GACS) for MPEG coded video traffic. The GACS models the sizes of MPEG I, P, and B frames according to the MPEG syntax I-frame>P-frame>B-frame. This is done by decomposing the process of each frame size into a weighted sum of a number of chi-square sequences. Each chi-square sequence is then obtained by squaring a Gaussian process, which is efficiently generated by using an auto-regressive (AR) model whose parameters are determined from an estimated covariance matrix. We evaluate the effectiveness of our model by conducting a series of experiments using a wide variety of long empirical video sequences. The results show that the proposed model leads to excellent data fit and accurate prediction of queuing performance.

Source location variability and volcanic vent mapping with a small-aperture infrasound array at Stromboli Volcano, Italy

Stromboli Volcano in Italy is a persistently active, complex volcanic system. In May 2002 activity was confined to 3 major summit craters within which several active vents hosted multiple explosions each hour. During a 5-day field campaign an array of 3 low-frequency microphones was installed to investigate the coherent infrasound produced by degassing from these vents. Consistent phase lags across the 3 stations indicate distinct sources that are subsequently investigated to determine the associated vent location, apparent depth, and origin time. The cross-correlation routine allows for variations in comparison window length, waveform filtering bandwidth, and correlation and consistency thresholds, allowing for improved detection of certain types of degassing sources. Identification of activity at the various vents could be subsequently corroborated with 3 channels of synchronously acquired thermal data and video. During the May 2002 experiment persistent, energetic infrasound was observed from a passive degassing source within the Central Crater (CC) and transient infrasound, produced by discrete Strombolian explosions, was identified at 4 additional vents. The continuous infrasound produced by the CC exhibits variable frequency-dependent correlation lag times that are interpreted as a diffraction effect due to the acoustic radiator’s recessed location within a steep-walled crater. Such dispersion has important implications for accurate eruption source modeling because it indicates that infrasonic waveforms may be significantly filtered during propagation. Transient explosion signals from the Northeast Crater (NEC) and Southwest Crater (SWC) vents also exhibit dynamic correlation lag times, but this scatter may be more reasonably attributed to variable epicentral locations. Explosions from the NEC west vent, for instance, appear to emanate from a diffuse zone with a lateral extent in excess of 10 m.