Multiple Source Model Research Articles

Varian 2100C/D Clinac 18 MV photon phase space file characterization and modeling by using MCNP Code

Multiple points and a spatial mesh based surface source model (MPSMBSS) was generated for 18MV Varian 2100 C/D Clinac phase space file (PSF) and implemented in MCNP code. The generated source model (SM) was benchmarked against PSF and measurements. PDDs and profiles were calculated using the SM and original PSF for different field sizes from 5 × 5 to 20 × 20 cm2. Agreement was within 2% of the maximum dose at 100cm SSD for beam profiles at the depths of 4cm and 15cm with respect to the original PSF. Differences between measured and calculated points were less than 2% of the maximum dose or 2mm distance to agreement (DTA) at 100 cm SSD. Thus it can be concluded that the modified MCNP code can be used for radiotherapy calculations including multiple source model (MSM) and using the source biasing capability of MPSMBSS can increase the simulation speed up to 3600 for field sizes smaller than 5 × 5 cm2.

Linear colour correction for multiple illumination changes and non‐overlapping cameras

Many image processing methods, such as techniques for people re-identification, assume photometric constancy between different images. This paper addresses the correction of photometric variations based upon changes in background areas to correct foreground areas. We assume a multiple light source model where all light sources can have different colors and will change over time. In training mode we learn per-location relations between foreground and background color intensities. In correction mode we apply a double linear correction model based on learned relations. This double linear correction includes a dynamic local illumination correction mapping as well as an inter-camera mapping. We evaluate our illumination correction by computing the similarity between two images based on the Earth Mover’s Distance. We compare the results to a representative auto-exposure (AE) algorithm found in the recent literature plus a color correction one based on the inverseintensity chromaticity. Especially in complex scenarios our method outperforms these state-of-the-art algorithms.

Shaking Scenarios from Multiple Source Models Shed Light on the 8 September 1905Mw 7 Calabria Earthquake (Southern Italy)

Project ISTEGE: “Indagine Sismotettonica del TErremoto dell'8 Settembre 1905 (Mw 7.4) nel Golfo di Sant'Eufemia – offshore tirrenico calabrese”, supported by OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale); Project RITMARE, funded by Dipartimento della Protezione Civile (Italy's National Civil Protection).

Strategy of effective management for small businesses at different stages of innovation activity

Proven by international experience appropriateness of the model of multiple innovation sources determines the urgency of the problem of development of small enterprises innovative activity. This paper examines the theoretical basis for attribution of 'innovation activity' concept i.e. definition, types and stages of innovation, as well as analyzes the methodological aspects of effective management of the small business innovation. This study describes the main negative factors of innovation environment for small business and modern innovation strategies. The authors draw conclusions about effectiveness of application of innovative management strategies at different innovation stages and offer some measures to develop innovative intra-firm behavior.

Analysis of Partially Observed Clustered Data using Generalized Estimating Equations and Multiple Imputation

Clustered data arise in many settings, particularly within the social and biomedical sciences. As an example, multiple-source reports are commonly collected in child and adolescent psychiatric epidemiologic studies where researchers use various informants (e.g. parent and adolescent) to provide a holistic view of a subject's symptomatology. Fitzmaurice et al. (1995) have described estimation of multiple source models using a standard generalized estimating equation (GEE) framework. However, these studies often have missing data due to additional stages of consent and assent required. The usual GEE is unbiased when missingness is Missing Completely at Random (MCAR) in the sense of Little and Rubin (2002). This is a strong assumption that may not be tenable. Other options such as weighted generalized estimating equations (WEEs) are computationally challenging when missingness is non-monotone. Multiple imputation is an attractive method to fit incomplete data models while only requiring the less restrictive Missing at Random (MAR) assumption. Previously estimation of partially observed clustered data was computationally challenging however recent developments in Stata have facilitated their use in practice. We demonstrate how to utilize multiple imputation in conjunction with a GEE to investigate the prevalence of disordered eating symptoms in adolescents reported by parents and adolescents as well as factors associated with concordance and prevalence. The methods are motivated by the Avon Longitudinal Study of Parents and their Children (ALSPAC), a cohort study that enrolled more than 14,000 pregnant mothers in 1991-92 and has followed the health and development of their children at regular intervals. While point estimates were fairly similar to the GEE under MCAR, the MAR model had smaller standard errors, while requiring less stringent assumptions regarding missingness.

Enhanced EEG connectivity in children with febrile seizures

Epilepsy is currently conceptualized as a disturbance of neuronal networks with altered connectivity that persists into the interictal phase. Febrile seizures are sometimes a precursor in childhood of lifelong epilepsy. We investigated whether studying functional connectivity in children with febrile seizures could help understand the mechanisms underlying their long-term seizure susceptibility. EEG was recorded during rest and intermittent photic stimulation (IPS) in 12 FS patients, 5 siblings and 15 control children between 6 and 36 months of age. Original EEG data were transformed into source space using a multiple regional source model. Source coherence values were calculated for the interfrontal, interoccipital and occipito-frontal connections for the delta, theta, alpha, beta and gamma frequency bands. Our results suggest enhanced delta and theta frequency EEG source coherence in patients with FSs compared to siblings and control children, both under resting conditions and during IPS, more consistent for the theta band and the occipito-frontal connections. Enhanced connectivity in patients with FSs could indicate a seizure-prone state and interfere with the maturation of cerebral networks. Further prospective studies are needed to assess whether hyperconnectivity is a risk factor for epileptogenesis and neurodevelopmental disorders.

Evolutionary dynamics of R2 retroelement and insertion inheritance in the genome of bisexual and parthenogenetic Bacillus rossius populations (Insecta Phasmida).

Theoretical and empirical studies have shown differential management of transposable elements in organisms with different reproductive strategies. To investigate this issue, we analysed the R2 retroelement structure and variability in parthenogenetic and bisexual populations of Bacillus rossius stick insects, as well as insertions inheritance in the offspring of parthenogenetic isolates and of crosses. The B. rossius genome hosts a functional (R2Br(fun) ) and a degenerate (R2Br(deg) ) element, their presence correlating with neither reproductive strategies nor population distribution. The median-joining network method indicated that R2Br(fun) duplicates through a multiple source model, while R2Br(deg) is apparently still duplicating via a master gene model. Offspring analyses showed that unisexual and bisexual offspring have a similar number of R2Br-occupied sites. Multiple or recent shifts from gonochoric to parthenogenetic reproduction may explain the observed data. Moreover, insertion frequency spectra show that higher-frequency insertions in unisexual offspring significantly outnumber those in bisexual offspring. This suggests that unisexual offspring eliminate insertions with lower efficiency. A comparison with simulated insertion frequencies shows that inherited insertions in unisexual and bisexual offspring are significantly different from the expectation. On the whole, different mechanisms of R2 elimination in unisexual vs bisexual offspring and a complex interplay between recombination effectiveness, natural selection and time can explain the observed data.

SU-E-T-110: Development of An Independent, Monte Carlo, Dose Calculation, Quality Assurance Tool for Clinical Trials

Purpose: To develop a comprehensive end-to-end test for Varian's TrueBeam linear accelerator for head and neck IMRT using a custom phantom designed to utilize multiple dosimetry devices. Purpose: To commission a multiple-source Monte Carlo model of Elekta linear accelerator beams of nominal energies 6MV and 10MV. Methods: A three source, Monte Carlo model of Elekta 6 and 10MV therapeutic x-ray beams was developed. Energy spectra of two photon sources corresponding to primary photons created in the target and scattered photons originating in the linear accelerator head were determined by an optimization process that fit the relative fluence of 0.25 MeV energy bins to the product of Fatigue-Life and Fermi functions to match calculated percent depth dose (PDD) data with that measured in a water tank for a 10×10cm2 field. Off-axis effects were modeled by a 3rd degree polynomial used to describe the off-axis half-value layer as a function of off-axis angle and fitting the off-axis fluence to a piecewise linear function to match calculated dose profiles with measured dose profiles for a 40×40cm2 field. The model was validated by comparing calculated PDDs and dose profiles for field sizes ranging from 3×3cm2 to 30×30cm2 to those obtained from measurements. A benchmarking study compared calculated data to measurements for IMRT plans delivered to anthropomorphic phantoms. Results: Along the central axis of the beam 99.6% and 99.7% of all data passed the 2%/2mm gamma criterion for 6 and 10MV models, respectively. Dose profiles at depths of dmax, through 25cm agreed with measured data for 99.4% and 99.6% of data tested for 6 and 10MV models, respectively. A comparison of calculated dose to film measurement in a head and neck phantom showed an average of 85.3% and 90.5% of pixels passing a 3%/2mm gamma criterion for 6 and 10MV models respectively. Conclusion: A Monte Carlo multiple-source model for Elekta 6 and 10MV therapeutic x-ray beams has been developed as a quality assurance tool for clinical trials.

Ensemble learning from multiple information sources via label propagation and consensus

Many applications are facing the problem of learning from multiple information sources, where sources may be labeled or unlabeled, and information from multiple information sources may be beneficial but cannot be integrated into a single information source for learning. In this paper, we propose an ensemble learning method for different labeled and unlabeled sources. We first present two label propagation methods to infer the labels of training objects from unlabeled sources by making a full use of class label information from labeled sources and internal structure information from unlabeled sources, which are processes referred to as global consensus and local consensus, respectively. We then predict the labels of testing objects using the ensemble learning model of multiple information sources. Experimental results show that our method outperforms two baseline methods. Meanwhile, our method is more scalable for large information sources and is more robust for labeled sources with noisy data.

The Joint Multivariate Modeling of Multiple Mixed Response Sources: Relating Student Performances with Feedback Behavior

The present study concerns a Dutch computer-based assessment, which includes an assessment process about information literacy and a feedback process for students. The assessment is concerned with the measurement of skills in information literacy and the feedback process with item-based support to improve student learning. To analyze students’ feedback behavior (i.e. feedback use and attention time), test performance, and speed of working, a multivariate hierarchical latent variable model is proposed. The model can handle multivariate mixed responses from multiple sources related to different processes and comprehends multiple measurement components for responses and response times. A flexible within-subject latent variable structure is defined to explore multiple individual latent characteristics related to students’ test performance and feedback behavior. Main results of the computer-based assessment showed that feedback-information pages were less visited by well-performing students when they relate to easy items. Students’ attention paid to feedback was positively related to working speed but not to the propensity to use feedback.

The 1991 Racha earthquake, Caucasus: Multiple source model with compensative type of motion

The source of the 1991 Racha earthquake in the Greater Caucasus generally corresponds to thrusting, which is characteristic of the predominant regional compression stress field. A more adequate view of the rupture process is provided by a complex source model composed of three subsources. This model is reconstructed by the body-wave inversion and consistent with the spatial distribution of the aftershocks. In terms of the suggested model, at the last stage of the rupture process, the opposite slip type (normal faulting) is observed in the source, which seems to be objective. It compensates the rapid (probably short) local redistribution of stresses caused by the thrusts in the first two subsources. The surface deformations observed in the epicentral zones of strong earthquakes are probably the analogs of such a compensative mechanism. For example, in the rear parts of the thrusts associated with the surface ruptures, normal faults trending parallel to the strike of the thrust line occur. Another analog of the compensative motion is probably the peculiarities of the aftershock sources. It has long since been noted (Kuznetsova et al., 1976) that some fault plane solutions in the aftershock sequences of strong earthquakes are close to the main shock solution, while others are different. The explanation of this phenomenon is suggested in (Kuznetsova et al., 1976; Kostrov and Das, 1988). In (Kuznetsova et al., 1976), these events are referred to as the aftershocks due to the fracture growth and aftershocks of relaxation, respectively.

Study on Voltage Stability Weak Buses of Power System with Multiple Power Sources Integrated

To obtain the distribution of voltage stability weak buses (VSWB) for power system with multiple power sources integrated, so as to provide a basis for voltage stability control, an analysis method under full time frame is proposed in this paper. Based on the modeling of multiple power sources, combined with the load prediction, the active power output prediction of wind and photovoltaic power and the generation scheduling of conventional power, considering different patterns of load increase and power output increase and allocation of multiple power sources, within a certain period of time and for the specifically selected time sections, the continuation power flow method is respectively used to get the voltage stability critical point (SNB point), where modal analysis is applied, so that the VSWB are obtained of the certain time section. The same calculation is carried out for all the time sections selected, and then the distribution and occurrence frequency of VSWB are summed up, thereby acquiring the concrete condition of VSWB within such certain time period. Its considered that the condition of VSWB can be affected by the different integration buses and penetration rates of multiple power sources. The proposed method is verified on the IEEE 118-bus system, as well as the fact with practical significance that the condition of VSWB varies with the difference of integration buses and the penetration rates of multiple power sources.

Model-Based Multiple Pitch Tracking Using Factorial HMMs: Model Adaptation and Inference

Robustness against noise and interfering audio signals is one of the challenges in speech recognition and audio analysis technology. One avenue to approach this challenge is single-channel multiple-source modeling. Factorial hidden Markov models (FHMMs) are capable of modeling acoustic scenes with multiple sources interacting over time. While these models reach good performance on specific tasks, there are still serious limitations restricting the applicability in many domains. In this paper, we generalize these models and enhance their applicability. In particular, we develop an EM-like iterative adaptation framework which is capable to adapt the model parameters to the specific situation (e.g. actual speakers, gain, acoustic channel, etc.) using only speech mixture data. Currently, source-specific data is required to learn the model. Inference in FHMMs is an essential ingredient for adaptation. We develop efficient approaches based on observation likelihood pruning. Both adaptation and efficient inference are empirically evaluated for the task of multipitch tracking using the GRID corpus.

Distributed Video Coding Based on Multiple-source Correlation Model

Distributed Video Coding (DVC) is a new video coding paradigm which has the ability to shift coding complexity from encoder to decoder. State-of-art DVC schemes are mainly based on two-source correlation model and only one correlation channel between side information and wyner-ziv frame is considered. In this paper, multiple-source correlation model is introduced into a famous DVC scheme, namely Transform Domain Wyner-Ziv video coder (TDWZ). A soft-input computing algorithm based on multiple-source correlation model is firstly proposed. The correlations a mong multiple side information are separately exploited. Then a new reconstruction function based on multiple source correlation model is also proposed to improve reconstructed image's quality. Experimental results show that the proposed algorithms can effectively improve the coding performance of systems.

Three-dimensional shear and compressional wave propagation of multiple point sources in fluid-saturated elastic porous media

A multiple point source model is developed in this research for studying both shear and compressional spherical wave propagation in a non-viscous fluid-saturated elastic porous medium. Relative displacement between the fluid and solid of the medium is quantified by the spherical wave governing equations, such that the waves described are more representative to that in engineering practices. The shear wave has shown significant influences on the characteristics of superposed shear and compressional waves generated by multiple point sources. Utilization of multiple point sources shows higher efficiency and effectiveness in generating desired waves, in comparing with that of single source. Specifically, the multiple sources model is more energy effective in comparing with the single source model by always producing larger magnitudes of relative displacement than a single source with the same energy, which becomes more significant when the distance between the source and the considered geological particles increases. Multiple point sources also show advantages on duration, direction control and magnitude adjustment for the waves generated. Numerical analyses are performed for comparing different shear, compressional and the superposed wave responses under single and multiple sources.

SU-E-T-462: Energy Modulated Photon Radiotherapy: A Monte Carlo Investigation

Purpose: To investigate the feasibility of energy modulated photon radiation therapy (EMXRT) using Monte Carlo simulations of photon beams of various energies. Methods: An EMXRT plan was generated for a prostate cancer patient treated with 10-MV 5-field intensity modulated radiotherapy (IMRT) optimized using Eclipse treatment planning system. Based on beam characterization of a Varian Clinac with EGS4/BEAM Monte Carlo code, multiple source models were first generated to represent the photon beams with energy of 1, 2, 3, 4, 5, 6, 10 and 15 MV, respectively. Optimal beam energy was then selected based on the effective path-length in the patient via ray-tracing for each beam angle. An inverse planning system based on gradient search algorithm was used to optimize photon beam intensity of various beam energies with pre-simulated Monte Carlo pencil beam dose distributions in patient anatomy. Finally, both EMXRT and IMRT plans were simulated with EGS4/MCSIM for 3D dose distributions in patient and compared. Results: Based on different path-lengths, 5, 6 and 10 MV photons were chosen in our EMXRT plan with lower energy photons used for shorter path-lengths. DVH analysis indicated that the target coverage in EMXRT plan was less uniform with Dmax and Dmin at 111.6% and 92.6% of prescription dose, respectively, as compared to 106.2% and 97.8% in regular IMRT plan. On the other hand, critical structures were much more spared in EMXRT plan than in IMRT plan, with 32% dose reduction in rectum and 40% reduction in bladder, respectively. The integral dose to the surrounding normal tissues was significantly reduced by 56% in EMXRT plan. Conclusion: This work demonstrates the potential of this Monte Carlo based tool for investigating the feasibility and desirability of EMXRT. Further investigation on more complex tumor sites such as head and neck cancer are now in progress.

The Use of Bivariate Spatial Modeling of Questionnaire and Parasitology Data to Predict the Distribution of Schistosoma haematobium in Coastal Kenya

BackgroundQuestionnaires of reported blood in urine (BIU) distributed through the existing school system provide a rapid and reliable method to classify schools according to the prevalence of Schistosoma haematobium, thereby helping in the targeting of schistosomiasis control. However, not all schools return questionnaires and it is unclear whether treatment is warranted in such schools. This study investigates the use of bivariate spatial modelling of available and multiple data sources to predict the prevalence of S. haematobium at every school along the Kenyan coast.MethodologyData from a questionnaire survey conducted by the Kenya Ministry of Education in Coast Province in 2009 were combined with available parasitological and environmental data in a Bayesian bivariate spatial model. This modeled the relationship between BIU data and environmental covariates, as well as the relationship between BIU and S. haematobium infection prevalence, to predict S. haematobium infection prevalence at all schools in the study region. Validation procedures were implemented to assess the predictive accuracy of endemicity classification.Principal FindingsThe prevalence of BIU was negatively correlated with distance to nearest river and there was considerable residual spatial correlation at small (∼15 km) spatial scales. There was a predictable relationship between the prevalence of reported BIU and S. haematobium infection. The final model exhibited excellent sensitivity (0.94) but moderate specificity (0.69) in identifying low (<10%) prevalence schools, and had poor performance in differentiating between moderate and high prevalence schools (sensitivity 0.5, specificity 1).ConclusionsSchistosomiasis is highly focal and there is a need to target treatment on a school-by-school basis. The use of bivariate spatial modelling can supplement questionnaire data to identify schools requiring mass treatment, but is unable to distinguish between moderate and high prevalence schools.

Mapping multiple source effects on the strontium isotopic signatures of ecosystems from the circum‐Caribbean region

A method for mapping strontium isotope ratio (87Sr/86Sr) variations in bedrock and water has been recently developed for use in the interpretation of 87Sr/86Sr datasets for provenance studies. The mapping process adopted the simplifying assumption that strontium (Sr) comes exclusively from weathering of the underlying bedrock. The scope of this bedrock‐only mapping method is thus limited to systems where the contributions of other sources of Sr are minimal. In this paper, we build on this 87Sr/86Sr mapping method by developing a mixing model of Sr fluxes from multiple sources to the bioavailable Sr pool. The new multiple source model includes: (1) quantitative calculations of Sr fluxes from bedrock weathering using an empirical rock weathering model; and (2) addition of sub‐models calculating the contribution of Sr fluxes from atmospheric aerosols based on outputs from global climate model simulations. We compared the performance of the new multiple source model and the bedrock‐only mapping method in predicting observed values from two datasets of bioavailable 87Sr/86Sr from the circum‐Caribbean region (Antilles and Mesoamerica). Although the bedrock‐only method performs relatively well in Mesoamerica (n = 99, MAE = 0.00011, RMSE = 0.00073), its prediction accuracy is lower for the Antillean dataset (n = 287, MAE = 0.0021, RMSE = 0.0027). In comparison, the new multiple source model, which accounts for the deposition of sea salt and mineral dust aerosols, performs comparably well in predicting the observed 87Sr/86Sr values in both datasets (MAE = 0.00040, RMSE = 0.00087 and MAE = 0.00014, RMSE = 0.0010). This study underscores the potential of using process‐oriented spatial modeling to improve the predictive power of Sr isoscapes over large spatial scales and to refine sampling strategies and bioavailable Sr dataset interpretations for provenance studies.

Gravity anomaly modelling of multiple geological sources having differing strike lengths and arbitrary density contrast variations

ABSTRACTA method to compute gravity anomalies of multiple geological sources having variable but finite strike lengths with arbitrary density contrast variations is presented. An ensemble of variable but finite strike limited vertical prisms among which density contrasts vary randomly both with depth and lateral position describes the anomalous source(s). The proposed method has the advantage that it can be applied to compute the gravity anomalies of a variety of geologic sources at both local and crustal scale levels. The applicability of the method is demonstrated with synthetic and real field examples. In the synthetic example, the geology resembles that of a typical rifted sedimentary basin, where thick sectioned sediments with arbitrarily varying density contrasts are concealed under a thick pile of flood basalt. For the real field example, the method is applied to calculate the gravity anomalies of a crustal scale structure across the suture zone between the Superior and Churchill structural provinces in the Canadian Shield. Modelling of real field anomalies reveals that i) the Churchill block is much thicker and ii) the western boundary of the base of the fold belt within the Superior block is shallower than reported in previous studies.

Construct Validity of ADHD/ODD Rating Scales: Recommendations for the Evaluation of Forthcoming DSM-V ADHD/ODD Scales

Exploratory structural equation modeling (SEM) was applied to a multiple indicator (26 individual symptom ratings) by multitrait (ADHD-IN, ADHD-HI and ODD factors) by multiple source (mothers, fathers and teachers) model to test the invariance, convergent and discriminant validity of the Child and Adolescent Disruptive Behavior Inventory with 872 Thai adolescents and the ADHD Rating Scale-IV and ODD scale of the Disruptive Behavior Inventory with 1,749 Spanish children. Most of the individual ADHD/ODD symptoms showed convergent and discriminant validity with the loadings and thresholds being invariant over mothers, fathers and teachers in both samples (the three latent factor means were higher for parents than teachers). The ADHD-IN, ADHD-HI and ODD latent factors demonstrated convergent and discriminant validity between mothers and fathers within the two samples. Convergent and discriminant validity between parents and teachers for the three factors was either absent (Thai sample) or only partial (Spanish sample). The application of exploratory SEM to a multiple indicator by multitrait by multisource model should prove useful for the evaluation of the construct validity of the forthcoming DSM-V ADHD/ODD rating scales.