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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Neutron Electric Dipole Moment and Tensor Charges from Lattice QCD

Here, we present lattice QCD results on the neutron tensor charges including, for the first time, a simultaneous extrapolation in the lattice spacing, volume, and light quark masses to the physical point in the continuum limit. We find that the “disconnected” contribution is smaller than the statistical error in the “connected” contribution. Our estimates in the modified minimal subtraction scheme at 2 GeV, including all systematics, are 𝑔$^{𝑑−𝑢}_𝑇$ =1.020⁢(76), 𝑔$^𝑑_𝑇$ = 0.774⁢(66), 𝑔$^𝑢_𝑇$ = −0.233⁢(28), and 𝑔$^𝑠_𝑇$ = 0.008⁢(9). The flavor diagonal charges determine the size of the neutron electric dipole moment (EDM) induced by quark EDMs that are generated in many new scenarios of 𝐶⁢𝑃 violation beyond the standard model. We use our results to derive model-independent bounds on the EDMs of light quarks and update the EDM phenomenology in split supersymmetry with gaugino mass unification, finding a stringent upper bound of 𝑑 𝑛 < 4 × 1⁢0 −28 𝑒 cm for the neutron EDM in this scenario.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Structure Factors of Neutron Matter at Finite Temperature

Here, we compute continuum and infinite volume limit extrapolations of the structure factors of neutron matter at finite temperature and density. Using a lattice formulation of leading-order pionless effective field theory, we compute the momentum dependence of the structure factors at finite temperature and at densities beyond the reach of the virial expansion. The Tan contact parameter is computed and the result agrees with the high momentum tail of the vector structure factor. All errors, statistical and systematic, are controlled for. This calculation is a first step towards a model-independent understanding of the linear response of neutron matter at finite temperature.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

First Simultaneous Determination of Inclusive and Exclusive | V u b |

The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element V ub using inclusive and exclusive decays is performed with the full Belle data set at the $Υ$(4S) resonance, corresponding to an integrated luminosity of 711 fb -1 . We analyze collision events in which one B meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic X u system of the semileptonic b → $πℓe_ℓ$ decay. We separate exclusive B → $πℓ\overline{ν}_ℓ$ decays from other inclusive B → $X_uℓ\overline{ν}_ℓ$ and backgrounds with a two-dimensional fit that utilizes the number of charged pions in the X u system and the four-momentum transfer q 2 between the B and X u systems. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the B → $πℓe_ℓ$ form factor, we determine |$V^{excl}_{ub}$| = (3.78 ± 0.23 ± 0.16 ± 0.14) × 10 -3 and |$V^{incl}_{ub}$| = (3.88 ± 0.20 ± 0.31 ± 0.09) x 10 -3 , respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of |$V^{excl}_{ub}$|/|$V^{incl}_{ub}$| 0.97 ± 0.12 is compatible with unity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

On the possibility of using X-ray Compton scattering to study magnetoelectrical properties of crystals

The possibility of using X-ray Compton scattering to reveal antisymmetric components of the electron momentum density, as a fingerprint of magnetoelectric sample properties, is investigated experimentally and theoretically by studying the polar ferromagnet GaFeO{sub 3}. This paper discusses the possibility of using Compton scattering – an inelastic X-ray scattering process that yields a projection of the electron momentum density – to probe magnetoelectrical properties. It is shown that an antisymmetric component of the momentum density is a unique fingerprint of such time- and parity-odd physics. It is argued that polar ferromagnets are ideal candidates to demonstrate this phenomenon and the first experimental results are shown, on a single-domain crystal of GaFeO{sub 3}. The measured antisymmetric Compton profile is very small (≃ 10{sup −5} of the symmetric part) and of the same order of magnitude as the statistical errors. Relativistic first-principles simulations of the antisymmetric Compton profile are presented and it is shown that, while the effect is indeed predicted by theory, and scales with the size of the valence spin–orbit interaction, its magnitude is significantly overestimated. The paper outlines some important constraints on the properties of the antisymmetric Compton profile arising from the underlying crystallographic symmetry of the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A cascaded model of spectral distortions due to spectral response effects and pulse pileup effects in a photon-counting x-ray detector for CT

Purpose: Energy discriminating, photon-counting detectors (PCDs) are an emerging technology for computed tomography (CT) with various potential benefits for clinical CT. The photon energies measured by PCDs can be distorted due to the interactions of a photon with the detector and the interaction of multiple coincident photons. These effects result in distorted recorded x-ray spectra which may lead to artifacts in reconstructed CT images and inaccuracies in tissue identification. Model-based compensation techniques have the potential to account for the distortion effects. This approach requires only a small number of parameters and is applicable to a wide range of spectra and count rates, but it needs an accurate model of the spectral distortions occurring in PCDs. The purpose of this study was to develop a model of those spectral distortions and to evaluate the model using a PCD (model DXMCT-1; DxRay, Inc., Northridge, CA) and various x-ray spectra in a wide range of count rates. Methods: The authors hypothesize that the complex phenomena of spectral distortions can be modeled by: (1) separating them into count-rate independent factors that we call the spectral response effects (SRE), and count-rate dependent factors that we call the pulse pileup effects (PPE), (2) developing separate models for SRE and PPE, and (3) cascading the SRE and PPE models into a combined SRE+PPE model that describes PCD distortions at both low and high count rates. The SRE model describes the probability distribution of the recorded spectrum, with a photo peak and a continuum tail, given the incident photon energy. Model parameters were obtained from calibration measurements with three radioisotopes and then interpolated linearly for other energies. The PPE model used was developed in the authors’ previous work [K. Taguchi et al., “Modeling the performance of a photon counting x-ray detector for CT: Energy response and pulse pileup effects,” Med. Phys. 38(2), 1089–1102 (2011)]. The agreement between the x-ray spectra calculated by the cascaded SRE+PPE model and the measured spectra was evaluated for various levels of deadtime loss ratios (DLR) and incident spectral shapes, realized using different attenuators, in terms of the weighted coefficient of variation (COV{sub W}), i.e., the root mean square difference weighted by the statistical errors of the data and divided by the mean. Results: At low count rates, when DLR < 10%, the distorted spectra measured by the DXMCT-1 were in agreement with those calculated by SRE only, with COV{sub W}'s less than 4%. At higher count rates, the measured spectra were also in agreement with the ones calculated by the cascaded SRE+PPE model; with PMMA as attenuator, COV{sub W} was 5.6% at a DLR of 22% and as small as 6.7% for a DLR as high as 55%. Conclusions: The x-ray spectra calculated by the proposed model agreed with the measured spectra over a wide range of count rates and spectral shapes. The SRE model predicted the distorted, recorded spectra with low count rates over various types and thicknesses of attenuators. The study also validated the hypothesis that the complex spectral distortions in a PCD can be adequately modeled by cascading the count-rate independent SRE and the count-rate dependent PPE.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

ARCHER{sub RT} – A GPU-based and photon-electron coupled Monte Carlo dose computing engine for radiation therapy: Software development and application to helical tomotherapy

Purpose: Using the graphical processing units (GPU) hardware technology, an extremely fast Monte Carlo (MC) code ARCHER{sub RT} is developed for radiation dose calculations in radiation therapy. This paper describes the detailed software development and testing for three clinical TomoTherapy® cases: the prostate, lung, and head and neck. Methods: To obtain clinically relevant dose distributions, phase space files (PSFs) created from optimized radiation therapy treatment plan fluence maps were used as the input to ARCHER{sub RT}. Patient-specific phantoms were constructed from patient CT images. Batch simulations were employed to facilitate the time-consuming task of loading large PSFs, and to improve the estimation of statistical uncertainty. Furthermore, two different Woodcock tracking algorithms were implemented and their relative performance was compared. The dose curves of an Elekta accelerator PSF incident on a homogeneous water phantom were benchmarked against DOSXYZnrc. For each of the treatment cases, dose volume histograms and isodose maps were produced from ARCHER{sub RT} and the general-purpose code, GEANT4. The gamma index analysis was performed to evaluate the similarity of voxel doses obtained from these two codes. The hardware accelerators used in this study are one NVIDIA K20 GPU, one NVIDIA K40 GPU, and six NVIDIA M2090 GPUs. In addition, to make a fairer comparison of the CPU and GPU performance, a multithreaded CPU code was developed using OpenMP and tested on an Intel E5-2620 CPU. Results: For the water phantom, the depth dose curve and dose profiles from ARCHER{sub RT} agree well with DOSXYZnrc. For clinical cases, results from ARCHER{sub RT} are compared with those from GEANT4 and good agreement is observed. Gamma index test is performed for voxels whose dose is greater than 10% of maximum dose. For 2%/2mm criteria, the passing rates for the prostate, lung case, and head and neck cases are 99.7%, 98.5%, and 97.2%, respectively. Due to specific architecture of GPU, modified Woodcock tracking algorithm performed inferior to the original one. ARCHER{sub RT} achieves a fast speed for PSF-based dose calculations. With a single M2090 card, the simulations cost about 60, 50, 80 s for three cases, respectively, with the 1% statistical error in the PTV. Using the latest K40 card, the simulations are 1.7–1.8 times faster. More impressively, six M2090 cards could finish the simulations in 8.9–13.4 s. For comparison, the same simulations on Intel E5-2620 (12 hyperthreading) cost about 500–800 s. Conclusions: ARCHER{sub RT} was developed successfully to perform fast and accurate MC dose calculation for radiotherapy using PSFs and patient CT phantoms.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-56: Brain Metastasis Treatment Plans for Contrast-Enhanced Synchrotron Radiation Therapy

Purpose: Iodine-enhanced radiotherapy is an innovative treatment combining the selective accumulation of an iodinated contrast agent in brain tumors with irradiations using monochromatic medium energy x-rays. The aim of this study is to compare dynamic stereotactic arc-therapy and iodineenhanced SSRT. Methods: Five patients bearing brain metastasis received a standard helical 3D-scan without iodine. A second scan was acquired 13 min after an 80 g iodine infusion. Two SSRT treatment plans (with/without iodine) were performed for each patient using a dedicated Monte Carlo (MC) treatment planning system (TPS) based on the ISOgray TPS. Ten coplanar beams (6×6 cm2, shaped with collimator) were simulated. MC statistical error objective was less than 5% in the 50% isodose. The dynamic arc-therapy plan was achieved on the Iplan Brainlab TPS. The treatment plan validation criteria were fixed such that 100% of the prescribed dose is delivered at the beam isocentre and the 70% isodose contains the whole target volume. The comparison elements were the 70% isodose volume, the average and maximum doses delivered to organs at risk (OAR): brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma. Results: The stereotactic dynamic arc-therapy remains the best technique in terms of dose conformation. Iodine-enhanced SSRT presents similar performances to dynamic arc-therapy with increased brainstem and brain parenchyma sparing. One disadvantage of SSRT is the high dose to the skull bone. Iodine accumulation in metastasis may increase the dose by 20–30%, allowing a normal tissue sparing effect at constant prescribed dose. Treatment without any iodine enhancement (medium-energy stereotactic radiotherapy) is not relevant with degraded HDVs (brain, parenchyma and skull bone) comparing to stereotactic dynamic arc-therapy. Conclusion: Iodine-enhanced SSRT exhibits a good potential for brain metastasis treatment regarding the dose distribution and OAR criteria.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-169: Evaluation of Oncentra TPS for Nasopharynx Brachy Using Patient Specific Voxel Phantom and EGSnrc

Purpose: Nasopharnx carcinoma (NPC) treatment is being carried out using Ir-192 HDR seeds in Mehdieh Hospital in Hamadan, Iran. The Oncentra™ TPS is based on optimized TG-43 formalism which disregards heterogeneity in the treatment area. Due to abundant heterogeneity in head and neck, comparison of the Oncentra™ TPS dose evaluation and an accurate dose calculation method in NPC brachytherapy is the objective of this study. Methods: CT DICOMs of a patient with NPC obtained from Mehdieh Hospital used to create 3D voxel phantom with CTCREATE utility of EGSnrc code package. The voxel phantom together with Ir-192 HDR brachytherapy source were the input to DOSXYZnrc to calculate the 3D dose distribution. The sources were incorporate with type 6 source in DOSXYZnrc and their dwell times were taken into account in final dose calculations. Results: The direct comparison between isodoses as well as DVHs for the GTV, PTV and CTV obtained by Oncentra™ and EGSnrc Monte Carlo code are made. EGSnrc results are obtained using 5×10{sup 9} histories to reduce the statistical error below 1% in GTV and 5% in 5% dose areas. The standard ICRP700 cross section library is employed in DOSXYZnrc dose calculation. Conclusion: A direct relationship between increased dose differences and increased material density (hence heterogeneity) is observed when isodoses contours of the TPS and DOSXYZnrc are compared. Regarding the point dose calculations, the differences range from 1.2% in PTV to 5.6% for cavity region and 7.8% for bone regions. While Oncentra™ TPS overestimates the dose in cavities, it tends to underestimate dose depositions within bones.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-356: Accuracy of Eclipse Electron Macro Monte Carlo Dose Algorithm for Use in Bolus Electron Conformal Therapy

Purpose: To evaluate the accuracy of electron dose distribution calculated by the Varian Eclipse electron Monte Carlo (eMC) algorithm for use with recent commercially available bolus electron conformal therapy (ECT). Methods: eMC-calculated electron dose distributions for bolus ECT have been compared to those previously measured for cylindrical phantoms (retromolar trigone and nose), whose axial cross sections were based on the mid-PTV CT anatomy for each site. The phantoms consisted of SR4 muscle substitute, SR4 bone substitute, and air. The bolus ECT treatment plans were imported into the Eclipse treatment planning system and calculated using the maximum allowable histories (2×10{sup 9}), resulting in a statistical error of <0.2%. Smoothing was not used for these calculations. Differences between eMC-calculated and measured dose distributions were evaluated in terms of absolute dose difference as well as distance to agreement (DTA). Results: Results from the eMC for the retromolar trigone phantom showed 89% (41/46) of dose points within 3% dose difference or 3 mm DTA. There was an average dose difference of −0.12% with a standard deviation of 2.56%. Results for the nose phantom showed 95% (54/57) of dose points within 3% dose difference or 3 mm DTA. There was an average dose difference of 1.12% with a standard deviation of 3.03%. Dose calculation times for the retromolar trigone and nose treatment plans were 15 min and 22 min, respectively, using 16 processors (Intel Xeon E5-2690, 2.9 GHz) on a Varian Eclipse framework agent server (FAS). Results of this study were consistent with those previously reported for accuracy of the eMC electron dose algorithm and for the .decimal, Inc. pencil beam redefinition algorithm used to plan the bolus. Conclusion: These results show that the accuracy of the Eclipse eMC algorithm is suitable for clinical implementation of bolus ECT.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-F-BRD-02: Application of ARCHERRT-- A GPU-Based Monte Carlo Dose Engine for Radiation Therapy -- to Tomotherapy and Patient-Independent IMRT

Purpose: As a module of ARCHER -- Accelerated Radiation-transport Computations in Heterogeneous EnviRonments, ARCHER{sub RT} is designed for RadioTherapy (RT) dose calculation. This paper describes the application of ARCHERRT on patient-dependent TomoTherapy and patient-independent IMRT. It also conducts a 'fair' comparison of different GPUs and multicore CPU. Methods: The source input used for patient-dependent TomoTherapy is phase space file (PSF) generated from optimized plan. For patient-independent IMRT, the open filed PSF is used for different cases. The intensity modulation is simulated by fluence map. The GEANT4 code is used as benchmark. DVH and gamma index test are employed to evaluate the accuracy of ARCHER{sub RT} code. Some previous studies reported misleading speedups by comparing GPU code with serial CPU code. To perform a fairer comparison, we write multi-thread code with OpenMP to fully exploit computing potential of CPU. The hardware involved in this study are a 6-core Intel E5-2620 CPU and 6 NVIDIA M2090 GPUs, a K20 GPU and a K40 GPU. Results: Dosimetric results from ARCHER{sub RT} and GEANT4 show good agreement. The 2%/2mm gamma test pass rates for different clinical cases are 97.2% to 99.7%. A single M2090 GPU needs 50~79 seconds for the simulation to achieve a statistical error of 1% in the PTV. The K40 card is about 1.7∼1.8 times faster than M2090 card. Using 6 M2090 card, the simulation can be finished in about 10 seconds. For comparison, Intel E5-2620 needs 507∼879 seconds for the same simulation. Conclusion: We successfully applied ARCHER{sub RT} to Tomotherapy and patient-independent IMRT, and conducted a fair comparison between GPU and CPU performance. The ARCHER{sub RT} code is both accurate and efficient and may be used towards clinical applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

MO-E-17A-03: Monte Carlo CT Dose Calculation: A Comparison Between Experiment and Simulation Using ARCHER-CT

Purpose: To compare the CT doses derived from the experiments and GPU-based Monte Carlo (MC) simulations, using a human cadaver and ATOM phantom. Methods: The cadaver of an 88-year old male and the ATOM phantom were scanned by a GE LightSpeed Pro 16 MDCT. For the cadaver study, the Thimble chambers (Model 10×5−0.6CT and 10×6−0.6CT) were used to measure the absorbed dose in different deep and superficial organs. Whole-body scans were first performed to construct a complete image database for MC simulations. Abdomen/pelvis helical scans were then conducted using 120/100 kVps, 300 mAs and a pitch factor of 1.375:1. For the ATOM phantom study, the OSL dosimeters were used and helical scans were performed using 120 kVp and x, y, z tube current modulation (TCM). For the MC simulations, sufficient particles were run in both cases such that the statistical errors of the results by ARCHER-CT were limited to 1%. Results: For the human cadaver scan, the doses to the stomach, liver, colon, left kidney, pancreas and urinary bladder were compared. The difference between experiments and simulations was within 19% for the 120 kVp and 25% for the 100 kVp. For the ATOM phantom scan, the doses to the lung, thyroid, esophagus, heart, stomach, liver, spleen, kidneys and thymus were compared. The difference was 39.2% for the esophagus, and within 16% for all other organs. Conclusion: In this study the experimental and simulated CT doses were compared. Their difference is primarily attributed to the systematic errors of the MC simulations, including the accuracy of the bowtie filter modeling, and the algorithm to generate voxelized phantom from DICOM images. The experimental error is considered small and may arise from the dosimeters. R01 grant (R01EB015478) from National Institute of Biomedical Imaging and Bioengineering.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-156: Monte Carlo Simulation Using TOPAS for Synchrotron Based Proton Discrete Spot Scanning System

Purpose: This study provides an overview of the design and commissioning of the Monte Carlo (MC) model of the spot-scanning proton therapy nozzle and its implementation for the patient plan simulation. Methods: The Hitachi PROBEAT V scanning nozzle was simulated based on vendor specifications using the TOPAS extension of Geant4 code. FLUKA MC simulation was also utilized to provide supporting data for the main simulation. Validation of the MC model was performed using vendor provided data and measurements collected during acceptance/commissioning of the proton therapy machine. Actual patient plans using CT based treatment geometry were simulated and compared to the dose distributions produced by the treatment planning system (Varian Eclipse 13.6), and patient quality assurance measurements. In-house MATLAB scripts are used for converting DICOM data into TOPAS input files. Results: Comparison analysis of integrated depth doses (IDDs), therapeutic ranges (R90), and spot shape/sizes at different distances from the isocenter, indicate good agreement between MC and measurements. R90 agreement is within 0.15 mm across all energy tunes. IDDs and spot shapes/sizes differences are within statistical error of simulation (less than 1.5%). The MC simulated data, validated with physical measurements, were used for the commissioning of the treatment planning system. Patient geometry simulations were conducted based on the Eclipse produced DICOM plans. Conclusion: The treatment nozzle and standard option beam model were implemented in the TOPAS framework to simulate a highly conformal discrete spot-scanning proton beam system.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Features of the application of the Monte Carlo method to calculations for large RBMK reactors and to model correction on the basis of data from in-core detectors

Statistical errors in sampling neutron fields in physically large systems like an RBMK are analyzed both qualitatively and quantitatively. Recommendations concerning the choice of parameters for calculations are given. A new procedure for Monte Carlo RBMK calculations with model corrections on the basis of data from in-core detectors is proposed. Dedicated software based on the CUDA software and hardware platform is developed for computational research. Results of testing the procedure and software in question via calculations for real RBMK reactors are discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Spin transfer to Λ and Λ-bar hyperons in deep inelastic scattering at HERMES

Preliminary results on the spin transfer to the Λ and Λ-bar hyperons measured by the HERMES Collaboration are presented. Longitudinal spin transfer directed along the virtual-photon momentum in the Λ rest frame is found to be D{sup Λ}{sub LL }= 0.19 ± 0.04{sub stat} ± 0.02{sub syst}, the transverse component being compatible with zero. For Λ-bar both longitudinal and transverse components are compatible with zero within statistical errors of ±0.1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

The origin of the background radioactive isotope {sup 127}Xe in the sample of Xe enriched in {sup 124}Xe

The results of investigation of {sup 127}Xe radioactive isotope production in the xenon sample enriched in {sup 124}Xe, {sup 126}Xe, {sup 128}Xe are presented. The isotope is supposed to be the source of the background events in the low-background experiment on search for 2K-capture of {sup 124}Xe. In this work we consider two channels of {sup 127}Xe production: the neutron knock-out from {sup 128}Xe nucleus by cosmogenic muons and the neutron capture by {sup 126}Xe nucleus. For the first channel the upper limit of the cross section of {sup 127}Xe production was found to be σ ≤ 0.007 × 10{sup −24} cm{sup 2} at 95% C.L. For the second channel the value obtained for the cross section was found to be equal to σ = (2.74 ± 0.4) × 10{sup −24} cm{sup 2}, which coincides well, within the statistical error, with reference value.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2019

Critical Temperature of the Three-Vertex Potts Model on a Kagome Lattice

The Potts model on a Kagome lattice is considered. The Monte Carlo method is used to obtain the temperature dependences of the thermodynamic parameters: heat capacity C, order parameter m, and susceptibility χ. The calculations were performed for systems with periodic boundary conditions. Systems with linear dimensions L × L = N, L = 20–90, were considered. Based on the fourth-order Binder cumulant method, the critical temperature (T{sub c}) was calculated for the three-vertex Potts model on a Kagome lattice. It is shown that the obtained value of T{sub c}, within the statistical error, is in good agreement with the results obtained by the transfer matrix and polynomial approximation methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Heavy-quark meson spectrum tests of the Oktay–Kronfeld action

The Oktay-Kronfeld (OK) action extends the Fermilab improvement program for massive Wilson fermions to higher order in suitable power-counting schemes. It includes dimension-six and -seven operators necessary for matching to QCD through order ${\mathrm{O}}(\Lambda^3/m_Q^3)$ in HQET power counting, for applications to heavy-light systems, and ${\mathrm{O}}(v^6)$ in NRQCD power counting, for applications to quarkonia. In the Symanzik power counting of lattice gauge theory near the continuum limit, the OK action includes all ${\mathrm{O}}(a^2)$ and some ${\mathrm{O}}(a^3)$ terms. To assess whether the theoretical improvement is realized in practice, we study combinations of heavy-strange and quarkonia masses and mass splittings, designed to isolate heavy-quark discretization effects. We find that, with one exception, the results obtained with the tree-level-matched OK action are significantly closer to the continuum limit than the results obtained with the Fermilab action. The exception is the hyperfine splitting of the bottom-strange system, for which our statistical errors are too large to draw a firm conclusion. Lastly, these studies are carried out with data generated with the tadpole-improved Fermilab and OK actions on 500 gauge configurations from one of MILC's $a\approx0.12$~fm, $N_f=2+1$-flavor, asqtad-staggered ensembles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Machine learning based design space exploration for hybrid main-memory design

We develop a machine learning (ML) based design space exploration (DSE) method that builds predictive models for various responses of a hybrid main-memory system. To overcome the challenges associated with latency, capacity, and power of memory systems in future extreme-scale machines, the hybrid memory architectures are being considered in which novel non-volatile memory (NVM) systems augment the traditional DRAM. However, way before their actual design and implementation, these emerging hybrid memory systems need to be simulated and analyzed to fully understand their capabilities and limitations. As the conventional architectural-level memory simulators require significant amounts of computational costs and time, we propose to utilize ML techniques for developing various memory-response models that can instantly provide a predicted response corresponding to any new memory configuration. Specifically, in this work, we apply four supervised ML techniques to build regression models for memory latency, bandwidth, power, and total read/write responses. The training and validation data for the ML methods are generated using NVMain memory simulator for DRAM, NVM, and their hybrid combinations. We demonstrate the results of the ML based memory-DSE method in terms of the learning curve characteristics for hyperparameter tuning and the statistical error analyses of the designed predictive models.

Sen, Satyabrata↗