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Monte carlo

He Tie, Zheng Pu, Xiao Jun, Zhu Chuanxin, Yang Jian, Guo Haiping
The measurements of iron, beryllium and carbon sphere neutron leakage spectra using BC501A detector by DT neutron source are presented. The experiments were carried out in Institute of Nuclear Physics and Chemistry (INPC), China. Neutron leakage spectra in a wide energy range at angles of 0° and 30° from the direction of incident deuteron beam were obtained. The results show the leakage neutron flux decreases notably with the spherical shell increasing when neutron energy >10MeV. When neutron energy <6MeV the leakage neutron distribution tends to lower energy side with the shell increase...
December 20, 2016: Applied Radiation and Isotopes
Y Ozaki, H Watanabe, A Kaida, M Miura, K Nakagawa, K Toda, R Yoshimura, Y Sumi, T Kurabayashi
Early stage oral cancer can be cured with oral brachytherapy, but whole-body radiation exposure status has not been previously studied. Recently, the International Commission on Radiological Protection Committee (ICRP) recommended the use of ICRP phantoms to estimate radiation exposure from external and internal radiation sources. In this study, we used a Monte Carlo simulation with ICRP phantoms to estimate whole-body exposure from oral brachytherapy. We used a Particle and Heavy Ion Transport code System (PHITS) to model oral brachytherapy with 192Ir hairpins and 198Au grains and to perform a Monte Carlo simulation on the ICRP adult reference computational phantoms...
February 24, 2017: Journal of Radiation Research
Manh-Huong Phan, Javier Alonso, Hafsa Khurshid, Paula Lampen-Kelley, Sayan Chandra, Kristen Stojak Repa, Zohreh Nemati, Raja Das, Óscar Iglesias, Hariharan Srikanth
The exploration of exchange bias (EB) on the nanoscale provides a novel approach to improving the anisotropic properties of magnetic nanoparticles for prospective applications in nanospintronics and nanomedicine. However, the physical origin of EB is not fully understood. Recent advances in chemical synthesis provide a unique opportunity to explore EB in a variety of iron oxide-based nanostructures ranging from core/shell to hollow and hybrid composite nanoparticles. Experimental and atomistic Monte Carlo studies have shed light on the roles of interface and surface spins in these nanosystems...
November 23, 2016: Nanomaterials
Feng Gong, Hai M Duong, Dimitrios V Papavassiliou
Here, we present a review of recent developments for an off-lattice Monte Carlo approach used to investigate the thermal transport properties of multiphase composites with complex structure. The thermal energy was quantified by a large number of randomly moving thermal walkers. Different modes of heat conduction were modeled in appropriate ways. The diffusive heat conduction in the polymer matrix was modeled with random Brownian motion of thermal walkers within the polymer, and the ballistic heat transfer within the carbon nanotubes (CNTs) was modeled by assigning infinite speed of thermal walkers in the CNTs...
July 30, 2016: Nanomaterials
Helene Ruffieux, Anthony C Davison, Jorg Hager, Irina Irincheeva
Combined inference for heterogeneous high-dimensional data is critical in modern biology, where clinical and various kinds of molecular data may be available from a single study. Classical genetic association studies regress a single clinical outcome on many genetic variants one by one, but there is an increasing demand for joint analysis of many molecular outcomes and genetic variants in order to unravel functional interactions. Unfortunately, most existing approaches to joint modeling are either too simplistic to be powerful or are impracticable for computational reasons...
March 16, 2017: Biostatistics
Aubree M Kees, Andrea R Hefty, Robert C Venette, Steven J Seybold, Brian H Aukema
The walnut twig beetle, Pityophthorus juglandis Blackman, and associated fungus Geosmithia morbida Kolařík, Freeland, Utley, & Tisserat constitute the insect-fungal complex that causes thousand cankers disease in walnut, Juglans spp., and wingnut, Pterocarya spp. Thousand cankers disease is responsible for the decline of Juglans species throughout the western United States and more recently, the eastern United States and northern Italy. We examined the flight capacity of P. juglandis over 24-h trials on a flight mill in the laboratory...
March 16, 2017: Environmental Entomology
Yujin Chung, Jody Hey
We present a new Bayesian method for estimating demographic and phylogenetic history using population genomic data. Several key innovations are introduced that allow the study of diverse models within an Isolation with Migration framework. The new method implements a 2-step analysis, with an initial Markov chain Monte Carlo (MCMC) phase that samples simple coalescent trees, followed by the calculation of the joint posterior density for the parameters of a demographic model. In step 1, the MCMC sampling phase, the method uses a reduced state space, consisting of coalescent trees without migration paths, and a simple importance sampling distribution without the demography of interest...
February 25, 2017: Molecular Biology and Evolution
Georgios I Angelis, William Ryder, John Gillam, Frederic Boisson, Andre Kyme, Roger Fulton, Steven Meikle, Peter Kench
Awake and/or freely moving small animal single photon emission imaging allows the continuous study of molecules exhibiting slow kinetics without the need to restrain or anaesthetise the animals. Estimating motion free projections in freely moving small animal planar imaging can be considered as a limited angle tomography problem, except that we wish to estimate the 2D planar projections rather than the 3D volume, where the angular sampling in all three axes depends on the rotational motion of the animal. In this study, we hypothesise that the motion corrected planar projections estimated by reconstructing an estimate of the 3D volume using an iterative motion compensating reconstruction algorithm and integrating it along the projection path, will closely match the true, motion-less, planar distribution regardless of the object motion...
March 23, 2017: Physics in Medicine and Biology
Leith J Rankine, Stewart Mein, Bin Cai, Austen Curcuru, Titania Juang, Devin Miles, Sasa Mutic, Yuhe Wang, Mark Oldham, H Harold Li
PURPOSE: To validate the dosimetric accuracy of a commercially available magnetic resonance guided intensity modulated radiation therapy (MRgIMRT) system using a hybrid approach: 3-dimensional (3D) measurements and Monte Carlo calculations. METHODS AND MATERIALS: We used PRESAGE radiochromic plastic dosimeters with remote optical computed tomography readout to perform 3D high-resolution measurements, following a novel remote dosimetry protocol. We followed the intensity modulated radiation therapy commissioning recommendations of American Association of Physicists in Medicine Task Group 119, adapted to incorporate 3D data...
April 1, 2017: International Journal of Radiation Oncology, Biology, Physics
Tron Vedul Tronstad
OBJECTIVE: The aim of this study is to present a new tool that can be used in the prevention of noise-induced hearing loss. Even in most countries where noise levels are well regulated, many workers are still exposed to high levels of noise and suffer from permanent threshold shifts. It is necessary to develop a new strategy to prevent such damage. METHOD: A statistical process control (SPC) scheme is presented that is able to detect both large and small hearing threshold shifts...
March 23, 2017: International Journal of Audiology
Ge Li, Xue Zhao, Shimin Wu, Hongying Hua, Qiang Wang, Zhiheng Zhang
Youtiao is a typical, traditional, and widely consumed fried food in China. Fermentation of Youtiao involves the use of aluminium potassium sulphate (alum). There are health concerns related to the levels of aluminium in food; therefore, we aimed to determine the aluminium concentrations of Youtiao from various locations, and estimate the dietary exposure by different age groups in Southern and Northern China. The aluminium content of Youtiao samples varied considerably (range: 4.46 to 852.69 Both the mean and median aluminium contents of Youtiao exceeded 100 mg...
March 23, 2017: Food Additives & Contaminants. Part A, Chemistry, Analysis, Control, Exposure & Risk Assessment
Manu N Lakshmanan, Joel A Greenberg, Ehsan Samei, Anuj J Kapadia
Although transmission-based x-ray imaging is the most commonly used imaging approach for breast cancer detection, it exhibits false negative rates higher than 15%. To improve cancer detection accuracy, x-ray coherent scatter computed tomography (CSCT) has been explored to potentially detect cancer with greater consistency. However, the 10-min scan duration of CSCT limits its possible clinical applications. The coded aperture coherent scatter spectral imaging (CACSSI) technique has been shown to reduce scan time through enabling single-angle imaging while providing high detection accuracy...
January 2017: Journal of Medical Imaging
Lixin Yang, Jing Liu, Yun Xing, Lichuan Du, Jing Chen, Xin Liu, Jianyu Hao
Hyperlipidemic acute pancreatitis (HLAP) is characterized by critical condition and high recurrence rate compared with non-HLAP. We conducted this study to investigate the value of body mass index and waist-hip ratio in predicting severity and local complications in HLAP. 96 patients with HLAP were categorized by body mass index and waist-hip ratio, respectively. According to the body mass index, they were divided into 3 groups, including normal weight, overweight, and obesity. According to the waist-hip ratio, they were divided into central obesity group and no central obesity group...
2017: Gastroenterology Research and Practice
Robert J B Goudie, Sach Mukherjee
We propose a Gibbs sampler for structure learning in directed acyclic graph (DAG) models. The standard Markov chain Monte Carlo algorithms used for learning DAGs are random-walk Metropolis-Hastings samplers. These samplers are guaranteed to converge asymptotically but often mix slowly when exploring the large graph spaces that arise in structure learning. In each step, the sampler we propose draws entire sets of parents for multiple nodes from the appropriate conditional distribution. This provides an efficient way to make large moves in graph space, permitting faster mixing whilst retaining asymptotic guarantees of convergence...
April 2016: Journal of Machine Learning Research: JMLR
J F Kamenik, G Perez, M Schlaffer, A Weiler
We examine, using the analyses of the 750 GeV diphoton resonance as a case study, the methodology for estimating the dominant backgrounds to diphoton resonance searches. We show that close to the high energy tails of the distributions, where background estimates rely on functional extrapolations or Monte Carlo predictions, large uncertainties are introduced, in particular by the challenging photon-jet background. Analyses with loose photon and low photon [Formula: see text] cuts and those susceptible to high photon rapidity regions are especially affected...
2017: European Physical Journal. C, Particles and Fields
Harini Pattabhiraman, Marjolein Dijkstra
Using Monte Carlo simulations and free-energy calculations, we study the phase behaviour of a two-dimensional system of particles interacting with a hard core of diameter σHD and a repulsive square shoulder potential. The interest in this system lies in the formation of quasicrystals of different symmetries at specific square-shoulder widths δ as previously reported by Dotera et al. [Nature 506, 208 (2014)]. However, an insight into other possible periodic phases formed in these systems and the thermodynamic stability of both the periodic and quasicrystal phases is yet to be addressed...
March 21, 2017: Journal of Chemical Physics
Joanne Bates, Darryl McClymont, Irvin Teh, Peter Kohl, Jurgen Schneider, Vicente Grau
A model of cardiac microstructure and diffusion MRI is presented, and compared with experimental data from ex vivo rat hearts. The model includes a simplified representation of individual cells, with physiologically correct cell size and orientation, as well as intra- to extracellular volume ratio. Diffusion MRI is simulated using a Monte Carlo model and realistic MRI sequences. The results show good correspondence between the simulated and experimental MRI signals. Similar patterns are observed in the eigenvalues of the diffusion tensor, the mean diffusivity (MD) and the fractional anisotropy (FA)...
March 10, 2017: IEEE Transactions on Medical Imaging
Yu Liu, Craig K Enders
In Ordinary Least Square regression, researchers often are interested in knowing whether a set of parameters is different from zero. With complete data, this could be achieved using the gain in prediction test, hierarchical multiple regression, or an omnibus F test. However, in substantive research scenarios, missing data often exist. In the context of multiple imputation, one of the current state-of-art missing data strategies, there are several different analogous multi-parameter tests of the joint significance of a set of parameters, and these multi-parameter test statistics can be referenced to various distributions to make statistical inferences...
March 22, 2017: Multivariate Behavioral Research
Helio F Dos Santos, Marcelo Chagas, Leonardo De Souza, Willian Rocha, Mauro V De Almeida, Cleber P A Anconi, Wagner Batista De Almeida
In this paper, density functional theory calculations of nuclear magnetic resonance (NMR) chemical shifts for L-quebrachitol isomer, previously studied in our group (Mag. Res. Chem. 50 (2012) 608-614) are reported aiming to investigate in more details the water solvent effect on the prediction of 1H NMR spectra. In order to include explicit water molecules, twenty water-L-quebrachitol configurations obtained from Monte Carlo simulation were selected to perform geometry optimizations using the effective fragment potential method encompassing 60 water molecules around the solute...
March 22, 2017: Journal of Physical Chemistry. A
Sivaramakrishnan Ramadurai, Marco Werner, Nigel K H Slater, Aaron Martin, Vladimir A Baulin, Tia E Keyes
Deeper understanding of the molecular interactions between polymeric materials and the lipid membrane is important across a range of applications from permeation for drug delivery to encapsulation for immuno-evasion. Using highly fluidic microcavity supported lipid bilayers, we studied the interactions between amphiphilic polymer PP50 and a DOPC lipid bilayer. As the PP50 polymer is pH responsive the studies were carried out at pH 6.5, 7.05 and 7.5, corresponding to fully, partly protonated (pH = pKa = 7.05) and fully ionized states of the polymer, respectively...
March 22, 2017: Soft Matter
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