Full Monte Research Articles

PIN POWER CALCULATION SCHEME FOR REACTOR PRESSURE VESSEL FAST NEUTRON FLUENCE ESTIMATION

The estimation of the neutron fluence at the Reactor Pressure Vessel (RPV) is classically carried out by a two-step approach. The first step is to estimate the full core neutron source term whether the second step of the calculation consists in the transport of neutrons from the core (source term) to the RPV using the neutron fission distribution determined in the previous step. For this purpose, the neutron fission distribution is to be accurately determined at the fuel pin level for the assemblies on the border of the core. To achieve this goal, two methods are evaluated in this study. The first method considered is a full core 2D Monte Carlo calculation using the MNCP6 code. The second method is based on a deterministic approach using the CASMO5 multi-segment option, allowing a full 2D transport calculation at the pin level with an expected accuracy similar to a stochastic method. The comparison of the two methods shows an overall good agreement with differences within the statistical uncertainty for different cores: homogeneous UOX core, mixed UOX-MOX loading and the effect of the hafnium rods used in the assemblies in the periphery of the core. The modelling limitation and the associated calculational time are discussed for the comparison of the two approaches.

Crash Modification Functions for Passing Relief Lanes on Two-Lane Rural Roads

Passing relief lanes on two-lane rural roads provide passing opportunities that would otherwise be scarce where there are extensive no-passing zones, high opposing traffic volumes, or both. This paper addresses the safety effects of installing a passing lane or lengthening an existing one. It stands to reason that the effect of installing a passing lane will depend on the actual length of that lane. By extension, it is also reasonable to expect that the safety effects of lengthening an existing one will depend not only on the amount of the lengthening, but also on the original length. Yet, knowledge that can be applied to estimate these two sets of effects in a design process is lacking. The crash modification factors (CMFs) in the Highway Safety Manual (HSM) and in the CMF Clearinghouse for installing a passing lane are all single-valued, of the order of 0.75. And neither source provides CMFs for lengthening an existing passing lane. This paper seeks to address these voids by developing continuous crash modification functions (CMFunctions) for both sets of design decisions using Michigan, U.S., and Ontario, Canada, crash, geometric, and traffic data for passing lane and reference sections. Generalized linear modeling and full Bayes Markov Chain Monte Carlo (FB MCMC) simulation are used to develop cross-section regression models from which crash modification functions are derived and compared. The results are consistent with those from credible before-after studies, so are recommended for implementation in practice, in particular for HSM applications.

The Honeymoon, A Novel

The Honeymoon, A Novel

Abstract ID: 5 Monte Carlo simulation studies on a beam monitor based on MPGD detectors for hadron therapy

Remarkable scientific and technological progress during the last years has led to the construction of accelerator based facilities dedicated to hadron therapy. This kind of technology requires precise and continuous control of position, intensity and shape of the ions or protons used to irradiate cancers. Patient safety, accelerator operation and dose delivery should be optimized by a real time monitoring of beam intensity and profile before and during the treatment, by using non-destructive, high spatial resolution detectors. The authors have studied, developed and initially tested a beam monitor based on Micro Pattern Gaseous Detectors (MPGDs) called TPC-GEM (TPG) detector, characterized by high spatial resolution and rate capability. Due to the low amount of material in the active volume, it is “not invasive”, therefore the beam characteristics are preserved, so minimizing the uncertainties on beam position, intensity, energy and stability. Computer simulation could be done as a preliminary step for analyzing the basic characteristics of a detector, and Monte Carlo simulation is one approach that can be established. For a better understanding of the first TPG prototype design, and its further improvements, several Monte Carlo simulations were performed. The aim of this presentation is to give an overview of the full and specific Monte Carlo simulation framework, including different tools (GEANT4, FLUKA/FLAIR, Garfield++, ANSYS and ROOT), developed in order to study in detail the interaction of a therapeutic proton beam with the detector sensitive volume in a typical hadron therapy environment and the performance of the chamber, especially for the calculation of the primary ionization, charge transport through the amplification stages and signal creation. The results obtained will be presented, as well as the future perspectives.

The Role of the Base Stack on the AC Performance of GaN Hot Electron Transistor

In this letter, we provide guidelines for the design of the base stack of a GaN-base HET suitable for high-frequency operation, through full band cellular Monte Carlo device simulations. The experimental curves are matched by our model and the transmission coefficient through the base is confirmed to be 0.2. We found that upon moderate reduction of the base thickness and collector barrier height, the transmission coefficient reaches values well above 0.5, hence allowing current amplification. The cutoff frequency of the scaled devices is then calculated from the short circuit current gain and is found to be larger than 100 GHz. Moreover, the cutoff frequency is seen to increase roughly proportionally to the transmission coefficient. This result, and the calculation of the base capacitance, suggests that the cutoff frequency can be well described by the intrinsic delay time $C_{b}/$ gm.

P530 Comparison between liposomial iron and ferrous sulfate in patients with iron deficiency anemia and inflammatory bowel disease. A pilot controlled study

Background: Vedolizumab (VDZ), currently in development for treating ulcerative colitis (UC) and Crohn's disease (CD), exhibits target-mediated drug disposition. Described here are a VDZ population pharmacokinetic (PK) model, an estimation of typical VDZ parameter values, and effects of covariates that may be predictors of VDZ PK variability. Methods: The population PK data set included data from 5 VDZ clinical studies (1 phase 1 study in healthy subjects and 1 phase 2 study and 3 phase 3 studies [GEMINI 1, 2, and 3] in UC or CD patients). Analysis of repeatedmeasures was conducted via nonlinear mixed-effects modeling, using NONMEM (Version 7.2). The population PK base model was developed using firstorder conditional estimation with an η-e interaction method and extensively sampled phase 1 and 2 data. Results from the base model were used to develop the full covariate model, which was fit to sparse phase 3 data using the full Bayesian Markov Chain Monte Carlo method. Model selection was based on standard goodness-of-fit criteria. A full covariate modeling approach, emphasizing parameter estimation rather than stepwise hypothesis testing, was implemented for the population PK analysis. Results: The data set comprised 2554 individuals with 18,427 evaluable VDZ serum concentrations. VDZ PK was best described by a 2-compartmentmodel with parallel linear and nonlinear elimination. Reference covariates for the final PK model included baseline age, weight, albumin, disease activity scores (Crohn's Disease Activity Index score [CD]; partial Mayo Clinic score [UC]), prior anti-tumor necrosis factor α treatment, and inflammatory bowel disease diagnosis (CD or UC). Presence of anti-VDZ antibodies and use of adjuvant therapy (immunomodulator or aminosalicylate) were also evaluated. Overall, PK parameter estimates for patients with UC and CD were similar using reference values for individual covariates. At steady state, VDZ half-life estimate was 25 days for the linear elimination phase. Linear clearance of VDZ (CLL) was 0.159 L/day for UC and 0.155 L/day for CD. Volume of distribution for the central compartment (Vc) was 3.19 L and 1.66 L for the peripheral compartment. Interindividual variabilities (coefficients of variation) in CLL and Vc were 35% and 19%, respectively; proportional residual variance estimate was 24%. While baseline albumin had the potential to have a clinically relevant effect on VDZ CLL, defined as an effect size of more than ±25% from the reference value, effects of other covariates tested were not considered clinically meaningful. Conclusions: Population PK parameters were similar in patients with UC and CD. No change in dosing recommendations is needed based on baseline covariates (eg, age, gender, weight, presence of anti-VDZ antibodies, and albumin).

Linear-scaling and parallelisable algorithms for stochastic quantum chemistry

For many decades, quantum chemical method development has been dominated by algorithms which involve increasingly complex series of tensor contractions over one-electron orbital spaces. Procedures for their derivation and implementation have evolved to require the minimum amount of logic and rely heavily on computationally efficient library-based matrix algebra and optimised paging schemes. In this regard, the recent development of exact stochastic quantum chemical algorithms to reduce computational scaling and memory overhead requires a contrasting algorithmic philosophy, but one which when implemented efficiently can achieve higher accuracy/cost ratios with small random errors. Additionally, they can exploit the continuing trend for massive parallelisation which hinders the progress of deterministic high-level quantum chemical algorithms. In the Quantum Monte Carlo community, stochastic algorithms are ubiquitous but the discrete Fock space of quantum chemical methods is often unfamiliar, and the methods introduce new concepts required for algorithmic efficiency. In this paper, we explore these concepts and detail an algorithm used for Full Configuration Interaction Quantum Monte Carlo (FCIQMC), which is implemented and available in MOLPRO and as a standalone code, and is designed for high-level parallelism and linear-scaling with walker number. Many of the algorithms are also in use in, or can be transferred to, other stochastic quantum chemical methods and implementations. We apply these algorithms to the strongly correlated chromium dimer to demonstrate their efficiency and parallelism.

An energy-loss model for low- and intermediate-energy carbon projectiles in water

Purpose: To model interaction cross sections and energy loss for carbon projectiles C0–C6+ of 1–104 keV/u (u: atomic mass unit) in water.Materials and methods: The classical trajectory Monte Carlo method was used to calculate the ionisation and charge-transfer cross sections. The excitation cross sections were scaled from proton data using equilibrium charges determined from the charge-transfer cross sections. Energy loss was obtained from the singly differential cross sections, and ionisation potentials of the target and projectile.Results: The calculated total ionisation cross sections are consistent with measured data, while the calculated electron-capture cross sections are larger than experimental data by a factor of 3. By scaling the latter to the measured data, the cross sections were made consistent with these data for 1–10 keV/u energies. The present stopping cross sections agree well with experimental data below 10 keV/u, and with other model calculations above 2 MeV/u. Deviation from the latter is found where electron capture is competitive with ionisation, and also arises from different energy-transfer calculations.Conclusions: In this paper we report our efforts in the developments of full slowing-down Monte Carlo track structure calculations for carbon ions. Further development and refinement of the model are currently underway.

EXTRACTION OF GATE CAPACITANCE OF HIGH-FREQUENCY AND HIGH-POWER GaN HEMTs BY MEANS OF CELLULAR MONTE CARLO SIMULATIONS

A high-frequency a high-power GaN HEMT was analyzed using our full band Cellular Monte Carlo (CMC) simulator, in order to extract small signal parameters and figures of merit, and to correlate them to carrier dynamics and distribution inside the device. A complete RF and DC characterization of the device was performed using experimental data to calibrate the few adjustable parameters of the simulator. Then, gate-related capacitances, such as Cg, Cgd, and Cgs, were directly and indirectly extracted combining small-signal analysis and DC characterization.

SiGe:C HBT transit time analysis based on hydrodynamic modeling using doping, composition and strained dependent SiGe:C carriers mobility and relaxation time

We present an original method for the detailed evaluation of different device region contributions to the whole SiGe:C heterojunction bipolar transistor transit time in the frame of modeling studies. This method is based on AC analysis with structures of several base widths. The two-dimensional hydrodynamic solver relies on analytical models of electron and hole mobilities, and of energy relaxation times, calculated from results of the Boltzmann Transport Equation in highly acceptor doped and strained SiGe:C, using a full band Monte Carlo solver. The simulation results are compared to DC and AC measurements and exhibit good agreement. The proposed transit time analysis scheme and the analytical model for mobilities and energy relaxation times may be used for device optimization, toward highest dynamic performances.

Electron transport property in wurtzite GaN at high electric field with Monte Carlo simulation

We present the results of the electron transport property in wurtize GaN using an ensemble full band Monte Carlo simulation. The data of wurtzite GaN band structure calculated with the first-principles total-energy pseudopotential method is used in the simulations. The impact ionization scattering rate is calculated based on Cartier’s method. The average electron drift velocity and the average electron energy each as a function of electric field are computed. The electron impact ionization coefficient is calculated as a function of applied electric field. The analysis of the impact ionization coefficient shows that when the applied electric field is greater than 1 MV/cm, the obvious impact ionization events occur. The analysis of the quantum yield shows that when the electron energy is greater than 7 eV, the quantum yield increases rapidly with electron energy increasing. We study the occupancy of the electrons in the eight conduction bands at the applied electric field ranging from 0 to 4 MV / cm. For the case of the low applied electric field all of the electrons are located in the 1st conduction band. With the increase of the applied electric field, some of the electrons move to high index conduction bands. For the whole range of the applied electric field, most of the electrons are located in the 1st conduction band and 2nd conduction band, a small number of the electrons are located in the 3rd, 4th and 5th conduction band, and very few electrons are located in the 7th and 8th conduction band.

SU-FF-T-619: Electron Dose Kernels to Account For Secondary Particle Doses in Deterministic Simulations

Purpose: We developed a hybrid deterministic‐Monte Carlo methodology called EDK‐SN, or “Electron Dose Kernel‐Discrete Ordinates”. This methodology rapidly and accurately computes organ and whole body doses in human phantoms attributed to high energy photon irradiation from external beam therapy. Methods and Materials: Full physics Monte Carlo(MC) calculations from MCNP5 were used to pre‐compute electron dose kernels (EDKs) in energy bins to obtain the dose due to electrons in voxels (i′, j′, k′), generated as a result of incident primary photons at (i, j, k). Then, we employ voxelized phantoms to compute doses efficiently in two steps. First, we rapidly solve for the photon transport over the entire phantom using 3‐D discrete ordinates (SN) radiation transport on parallel computers using the PENTRAN‐MP code system. Then, the detailed global SN solution angular data throughout the phantom maps the dose to surrounding voxels; the dose is accumulated on each mesh, scaled by SNphoton fluence, using pre‐computed EDKs. Results: EDK‐SN and independent MCNP5 organ results are in good agreement; the largest statistical uncertainty (2σ) of the MC simulation near the source was less than 6%, and 200 hrs for equivalent statistical uncertainty). Conclusions: A new methodology for accurate whole body or organ‐specific 3D dose calculations has been developed based on SN computations coupled to pre‐computed EDKs based on full physics MC calculations. With the proper discretization and appropriate application of the EDK‐SN method, efficient and accurate 3D whole body doses can be determined for high energy photon beams.

Probability Distribution of Peaks for Nonlinear Combination of Vector Gaussian Loads

The problem of approximating the probability distribution of peaks, associated with a special class of non-Gaussian random processes, is considered. The non-Gaussian processes are obtained as nonlinear combinations of a vector of mutually correlated, stationary, Gaussian random processes. The Von Mises stress in a linear vibrating structure under stationary Gaussian loadings is a typical example for such processes. The crux of the formulation lies in developing analytical approximations for the joint probability density function of the non-Gaussian process and its instantaneous first and second time derivatives. Depending on the nature of the problem, this requires the evaluation of a multidimensional integration across a possibly irregular and disjointed domain. A numerical algorithm, based on first order reliability method, is developed to evaluate these integrals. The approximations for the peak distributions have applications in predicting the expected fatigue damage due to combination of stress resultants in a randomly vibrating structure. The proposed method is illustrated through two numerical examples and its accuracy is examined with respect to estimates from full scale Monte Carlo simulations of the non-Gaussian process.

On the Diffusion of Electromagnetic Waves and Applicability of Diffusion Equation to Multipath Random Media

The diffusion behavior of electromagnetic (EM) waves in two dimensional (2-D) multipath media is studied through integral equation based full wave Monte Carlo simulations. The influences of some physical factors are explored, among which the area density of the embedded obstacles manifests itself to be the most important one in determining wave diffusion. A lossy system starts to behave diffusively when the area density approximately exceeds 5%, and the diffusion equations are generally applicable for predicting power decay. At low densities, the power-distance relation of the waves appears to follow power laws. The sizes and shapes of the obstacles have a secondary effect on the diffusion of waves. Whenever a system contains small objects or objects with reflecting sides, the waves therein are more diffusive and the diffusion equation approximates the reality more accurately. Absorption loss decreases wave diffusion in general, but our results show that the diffusion equation for a system with very lossy but small obstacles can work very well for predicting power decay.

Full band Monte Carlo simulation of dislocation effects on 250 nm AlGaN-GaN HEMT

In this work, we present a full band Monte Carlo simulation of the effects of dislocation scattering on the performance of a 0.25 μm AlGaN/GaN HEMT (high electron mobility transistor). We performed a full characterization of the device and validated the simulation results with experimental data (Lee et al. in IEEE Electron. Dev. Lett. 24:613–615, [2003]). Here we show a study of the DC device performance as a function of the density of thread dislocations.

Quantum Boltzmann equation solved by Monte Carlo method for nano-scale semiconductor devices simulation

A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC) method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to extend the MC method to the study of nano-scale semiconductor devices with obvious quantum mechanical (QM) effects. The quantum effects both in real space and momentum space in nano-scale semiconductor devices can be simulated. The effective mobility in the inversion layer of n and p channel MOSFET is simulated and compared with experimental data to verify this method. With this method 50nm ultra thin body silicon on insulator MOSFET are simulated. Results indicate that this method can be used to simulate the 2D QM effects in semiconductor devices including tunnelling effect.

Monte Carlo simulation of the hole transport properties for wurtzite GaN

The simulation of the hole transport properties of wurtzite phase GaN are performed by the full band ensemble Monte Carlo approach. The band structure data of GaN used in the simulation are obtained by the empirical pseudopotential method. The scattering mechanisms included in the simulation are acoustic phonon scattering, optical phonon scattering, polar optical phonon scattering, piezoelectronic scattering, ionized impurity scattering, as well as the intervalley scattering. The dependence of the hole average drift velocity and average energy in three main symmetry directions for wurtzite GaN on the electric field are obtained. At room temperature, the velocity-field relation shows the non-saturated characteristics. The maximum drift velocity is about 6×106 cm s-1, and the maximum average energy is 0.12 eV in the range of the field of this work. These values are much smaller than the corresponding parameters of the electrons in GaN. Furthermore, the dependence of the diffusion mobility on the impurity density is reported.

Non-destructive method of characterisation of radioactive waste containers using gamma spectroscopy and Monte Carlo techniques

During the decommissioning of the SATURNE accelerator at CEA Saclay (France), a number of concrete containers with radioactive materials of low or very low activity had to be characterised before their final storage. In this paper, a non-destructive approach combining gamma ray spectroscopy and Monte Carlo simulations is used in order to characterise massive concrete blocks containing some radioactive waste. The limits and uncertainties of the proposed method are quantified for the source term activity estimates using 137Cs as a tracer element. A series of activity measurements with a few representative waste containers were performed before and after destruction. It has been found that neither was the distribution of radioactive materials homogeneous nor was its density unique, and this became the major source of systematic errors in this study. Nevertheless, we conclude that by combining gamma ray spectroscopy and full scale Monte Carlo simulations one can estimate the source term activity for some tracer elements such as 134Cs, 137Cs, 60Co, etc. The uncertainty of this estimation should not be bigger than a factor of 2-3.

Computing large signal distortions and bit-error ratios in DPSK transmission systems

We demonstrate the application of importance sampling (IS) to the simulation of a soliton-based differential phase-shift-keyed optical transmission system. We use an approximation to the pulse evolution given by perturbation theory and optimized with calculus of variations to guide full numerical Monte Carlo simulations employing IS. The method not only directly determines the bit-error ratio, but also predicts the manner in which large signal distortions occur.

Comparison of Monte Carlo and NEGF Simulations of Double Gate MOSFETs

The present work compares the simulation results of the two-dimensional full band Monte Carlo simulator (MOCA) developed at the University of Illinois at Urbana-Champaign and the two-dimensional quantum simulator (NanoMOS) developed at Purdue University. Double-gate MOSFETs of three body thicknesses – tSi = 4, 3 and 2 nm—were considered in this study. For a body thickness of 4 nm, the conduction band profiles and sheet charge densities obtained from MOCA and NanoMOS almost overlap, particularly for high gate and drain-to-source biases. However, as the body thickness is reduced, quantum effects are captured more naturally in NanoMOS since MOCA only uses a simple quantum correction scheme, with an otherwise semi-classical model. However, even for thinner devices, since MOCA makes use of a detailed band structure and scattering model, high energy transport is better reproduced by the Monte Carlo procedure. A particle description is appealing for nanoscale simulation, in order to reproduce the granularity aspects of the transport. Comparisons with a quantum model based on continuum flow equations as in NanoMOS should provide valuable insight to better incorporate the quantum mechanical aspects in a practical particle-based model.