The Staggered Chiral Perturbation Theory In The Two-Flavor Case And Su(2) Chiral Analysis Of The Milc Data

As a part of the Standard Model: SM), Quantum Chromodynamics: QCD) is a widely accepted theory to describe the physics of quarks and gluons. Formulating QCD on finite discrete lattices in Euclidean space-time not only enables one to study the theory non-perturbatively, but also provides a framework analogous to statistical systems, in which numerical methods can be applied. In this work, we concentrate on one specific fermion formalism, staggered fermions. To interpret the data obtained from numerical simulations with staggered fermions, a particular version of chiral perturbation theory: χPT), rooted staggered χPT: rSχPT), is needed to incorporate the discretization effects, mainly taste-violations, and the fourth root procedure used for the staggered fermion formalism. In the light pseudoscalar sector, I study rSχPT in the two-flavor case. The pion mass and decay constant are calculated through NLO for a partially-quenched theory. In the limit where the strange quark mass is large compared to the light quark masses and the taste splittings, I show that the SU(2) staggered chiral theory emerges from the SU(3) staggered chiral theory, as expected. Explicit relations between SU(2) and SU(3) low energy constants and taste-violating parameters are given. The results are useful for SU(2) chiral fits to asqtad data and allow one to incorporate effects from varying strange quark masses. By using these formulae and continuum NNLO chiral logarithms, I then perform a systematic chiral analysis to the MILC lattice data in the light pseudoscalar sector. Superfine and ultrafine ensembles are used, where light sea quark masses and taste splittings are small compared to the simulated strange quark mass. Correlated fits with Bayesian analysis are done for both the pion mass and the pion decay constant. Physical quantities are obtained by extrapolating the results to the continuum and full QCD case where the light quarks masses are physical. I give results for the pion decay constant, SU(2) low-energy constants and the chiral condensate in the two-flavor chiral limit

DEVELOPMENT OF GPU-BASED MONTE CARLO CODE FOR FAST CT IMAGING DOSE CALCULATION ON CUDA FERMI ARCHITECTURE

ABSTRACT This paper describes the development of a Graphics Processing Unit (GPU) accelerated Monte Carlo photon transport code, ARCHER GPU , to perform CT imaging dose calculations with good accuracy and performance. The code simulates interactions of photons with heterogeneous materials. It contains a detailed CT scanner model and a family of patient phantoms. Several techniques are used to optimize the code for the GPU architecture. In the accuracy and performance test, a 142 kg adult male phantom was selected, and the CT scan protocol involved a whole-body axial scan, 20-mm x-ray beam collimation, 120 kVp and a pitch of 1. A total of 9 × 10 8 photons were simulated and the absorbed doses to 28 radiosensitive organs/tissues were calculated. The average percentage difference of the results obtained by the general-purpose production code MCNPX and ARCHER GPU was found to be less than 0.38%, indicating an excellent agreement. The total computation time was found to be 8,689, 139 and 56 minutes for MCNPX, ARCHER CPU (6-core) and ARCHER GPU , respectively, indicating a decent speedup. Under a recent grant funding from the NIH, the project aims at developing a Monte Carlo code with the capability of sub-minute CT organ dose calculations

I=2 Pion scattering length with improved actions on anisotropic lattices

$\pi\pi$ scattering length in the I=2 channel is calculated within quenched approximation using improved gauge and improved Wilson fermion actions on anisotropic lattices. The results are extrapolated towards the chiral, infinite volume and continuum limit. This result improves our previous result on the scattering length. In the chiral, infinite volume and continuum limit, we obtain $a^{(2)}_0m_\pi=-0.0467(45)$, which is consistent with the result from Chiral Perturbation Theory, the experiment and results from other lattice calculations.Comment: 7 pages, 2 figures, typeset wit elsart.cl

Lattice study on kaon pion scattering length in the I=3/2I=3/2 channel

Using the tadpole improved Wilson quark action on small, coarse and anisotropic lattices, $K\pi$ scattering length in the $I=3/2$ channel is calculated within quenched approximation. The results are extrapolated towards the chiral and physical kaon mass region. Finite volume and finite lattice spacing errors are also analyzed and a result in the infinite volume and continuum limit is obtained. Our result is compared with the results obtained using Roy equations, Chiral Perturbation Theory, dispersion relations and the experimental data.Comment: Latex file typeset with elsart.cls, 9 pages, 3 figure

Lattice study on kaon nucleon scattering length in the I=1 channel

Using the tadpole improved clover Wilson quark action on small, coarse and anisotropic lattices, $KN$ scattering length in the I=1 channel is calculated within quenched approximation. The results are extrapolated towards the chiral and physical kaon mass region. Finite volume and finite lattice spacing errors are also analyzed and a result in the infinite volume and continuum limit is obtained which is compatible with the experiment and the results from Chiral Perturbation Theory.Comment: 15 pages, 4 figures, typeset by latex using elsart.cls,minor change

Sustainable Strategies for Transportation Development in Emerging Cities in China: A Simulation Approach

With the rapid development of emerging cities in China, policy makers are faced with the challenges involved in devising strategies for providing transportation systems to keep pace with development. These challenges are associated with the interactive effects among a number of sophisticated factors involved in transportation systems. This paper presents a system dynamics simulation approach to analyze and select transportation development strategies in order to achieve good sustainability performance once they are implemented. The simulation approach consists of three modules: a socio-economic module, a demand module, and a supply module. The approach is validated through applying empirical data collected from the Shenzhen statistical bulletins. Three types of transport development strategies are selected for the city and examined for their applicability and effects through simulation. The strategies are helpful for reducing decision-making mistakes and achieving the goal of sustainable urban development in most emerging cities

GPU-Accelerated Monte Carlo Electron Transport Methods: Development and Application for Radiation Dose Calculations Using Six GPU cards

An electron-photon coupled Monte Carlo code ARCHER ─