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Department of Computer Science and EngineeringHardware with advanced functionalities and/or improved performance and efficiency has been introduced in modern computer systems. However, there exist several challenges with such emerging hardware. First, the characteristics of emerging hardware are unknown but deriving useful properties through characterization studies is hard because emerging hardware has different effects on applications with different characteristics. Second, sole use of emerging hardware is suboptimal but coordination of emerging hardware and other techniques is hard due to large and complex system state space. To address the problem, we first conduct in-depth characterization studies for emerging hardware based on applications with various characteristics. Guided by the observations from our characterization studies, we propose a set of system software techniques to effectively leverage emerging hardware. The system software techniques combine emerging hardware and other techniques to improve the performance, efficiency, and fairness of computer systems based on efficient optimization algorithms. First, we investigate system software techniques to effectively manage hardware-based last-level cache (LLC) and memory bandwidth partitioning functionalities. For effective memory bandwidth partitioning on commodity servers, we propose HyPart, a hybrid technique for practical memory bandwidth partitioning on commodity servers. HyPart combines the three widely used memory bandwidth partitioning techniques (i.e., thread packing, clock modulation, and Intel MBA) in a coordinated manner considering the characteristics of the target applications. We demonstrate the effectiveness of HyPart through the quantitative evaluation. We also propose CoPart, coordinated partitioning of LLC and memory bandwidth for fairness-aware workload consolidation on commodity servers. We first characterize the impact of LLC and memory bandwidth partitioning on the performance and fairness of the consolidated workloads. Guided by the characterization, we design and implement CoPart. CoPart dynamically profiles the characteristics of the consolidated workloads and partitions LLC and memory bandwidth in a coordinated manner to maximize the fairness of the consolidated workloads. Through the quantitative evaluation with various workloads and system configurations, we demonstrate the effectiveness of CoPart in the sense that it significantly improves the overall fairness of the consolidated workloads. Second, we investigate a system software technique to effectively leverage hardware-based power capping functionality. We first characterize the performance impact of the two key system knobs (i.e., concurrency level of the target applications and cross component power allocation) for power capping. Guided by the characterization results, we design and implement RPPC, a holistic runtime system for maximizing performance under power capping. RPPC dynamically controls the key system knobs in a cooperative manner considering the characteristics (e.g., scalability and memory intensity) of the target applications. Our evaluation results show the effectiveness of RPPC in the sense that it significantly improves the performance under power capping on various application and system configurations. Third, we investigate system software techniques for effective dynamic concurrency control on many-core systems and heterogeneous multiprocessing systems. We propose RMC, an integrated runtime system for adaptive many-core computing. RMC combines the two widely used dynamic concurrency control techniques (i.e., thread packing and dynamic threading) in a coordinated manner to exploit the advantages of both techniques. RMC quickly controls the concurrency level of the target applications through the thread packing technique to improve the performance and efficiency. RMC further improves the performance and efficiency by determining the optimal thread count through the dynamic threading technique. Our quantitative experiments show the effectiveness of RMC in the sense that it outperforms the existing dynamic concurrency control techniques in terms of the performance and energy efficiency. In addition, we also propose PALM, progress- and locality-aware adaptive task migration for efficient thread packing. We first conduct an in-depth performance analysis of thread packing with various synchronization-intensive benchmarks and system configurations and find the root causes of the performance pathologies of thread packing. Based on the characterization results, we design and implement PALM, which supports both of symmetric multiprocessing systems and heterogeneous multiprocessing systems. For efficient thread packing, PALM solves the three key problems, progress-aware task migration, locality-aware task migration, and scheduling period control. Our quantitative evaluation explains the effectiveness of PALM in the sense that it achieves substantially higher performance and energy efficiency than the conventional thread packing. We also present case studies in which PALM considerably improves the efficiency of dynamic server consolidation and the performance under power capping.ope

Comparative Neutronics Analysis of DIMPLE S06 Criticality Benchmark with Contemporary Reactor Core Analysis Computer Code Systems

A high-leakage core has been known to be a challenging problem not only for a two-step homogenization approach but also for a direct heterogeneous approach. In this paper the DIMPLE S06 core, which is a small high-leakage core, has been analyzed by a direct heterogeneous modeling approach and by a two-step homogenization modeling approach, using contemporary code systems developed for reactor core analysis. The focus of this work is a comprehensive comparative analysis of the conventional approaches and codes with a small core design, DIMPLE S06 critical experiment. The calculation procedure for the two approaches is explicitly presented in this paper. Comprehensive comparative analysis is performed by neutronics parameters: multiplication factor and assembly power distribution. Comparison of two-group homogenized cross sections from each lattice physics codes shows that the generated transport cross section has significant difference according to the transport approximation to treat anisotropic scattering effect. The necessity of the ADF to correct the discontinuity at the assembly interfaces is clearly presented by the flux distributions and the result of two-step approach. Finally, the two approaches show consistent results for all codes, while the comparison with the reference generated by MCNP shows significant error except for another Monte Carlo code, SERPENT2open0

Physics Study of Canada Deuterium Uranium Lattice with Coolant Void Reactivity Analysis

This study presents a coolant void reactivity analysis of Canada Deuterium Uranium (CANDU)-6 and Advanced Canada Deuterium Uranium Reactor-700 (ACR-700) fuel lattices using a Monte Carlo code. The reactivity changes when the coolant was voided were assessed in terms of the contributions of four factors and spectrum shifts. In the case of single bundle coolant voiding, the contribution of each of the four factors in the ACR-700 lattice is large in magnitude with opposite signs, and their summation becomes a negative reactivity effect in contrast to that of the CANDU-6 lattice. Unlike the coolant voiding in a single fuel bundle, the 2 ?? 2 checkerboard coolant voiding in the ACR-700 lattice shows a positive reactivity effect. The neutron current between the no-void and voided bundles, and the four factors of each bundle were analyzed to figure out the mechanism of the positive coolant void reactivity of the checkerboard voiding case. Through a sensitivity study of fuel enrichment, type of burnable absorber, and moderator to fuel volume ratio, a design strategy for the CANDU reactor was suggested in order to achieve a negative coolant void reactivity even for the checkerboard voiding case.ope

A Multi-Physics Adaptive Time Step Coupling Algorithm for Light-Water Reactor Core Transient and Accident Simulation

A new reactor core multi-physics system addresses the pellet-to-cladding heat transfer modeling to improve full-core operational transient and accident simulation used for assessment of reactor core nuclear safety. The rigorous modeling of the heat transfer phenomena involves strong interaction between neutron kinetics, thermal-hydraulics and nuclear fuel performance, as well as consideration of the pellet-to-cladding mechanical contact leading to dramatic increase in the gap thermal conductance coefficient. In contrast to core depletion where parameters smoothly depend on fuel burn-up, the core transient is driven by stiff equation associated with rapid variation in the solution and vulnerable to numerical instability for large time step sizes. Therefore, the coupling algorithm dedicated for multi-physics transient must implement adaptive time step and restart capability to achieve prescribed tolerance and to maintain stability of numerical simulation. This requirement is met in the MPCORE (Multi-Physics Core) multi-physics system employing external loose coupling approach to facilitate the coupling procedure due to little modification of constituent modules and due to high transparency of coupling interfaces. The paper investigates the coupling algorithm performance and evaluates the pellet-to-cladding heat transfer effect for the rod ejection accident of a light water reactor core benchmark

Verification and validation of isotope inventory prediction for back-end cycle management using two-step method

This paper presents the verification and validation (V&V) of a calculation module for isotope inventory prediction to control the back-end cycle of spent nuclear fuel (SNF). The calculation method presented herein was implemented in a two-step code system of a lattice code STREAM and a nodal diffusion code RAST-K. STREAM generates a cross section and provides the number density information using branch/ history depletion branch calculations, whereas RAST-K supplies the power history and three history indices (boron concentration, moderator temperature, and fuel temperature). As its primary feature, this method can directly consider three-dimensional core simulation conditions using history indices of the operating conditions. Therefore, this method reduces the computation time by avoiding a recalculation of the fuel depletion. The module for isotope inventory calculates the number densities using the Lagrange interpolation method and power history correction factors, which are applied to correct the effects of the decay and fission products generated at different power levels. To assess the reliability of the developed code system for back-end cycle analysis, validation study was performed with 58 measured samples of pressurized water reactor (PWR) SNF, and code-to-code comparison was conducted with STREAM-SNF, HELIOS-1.6 and SCALE 5.1. The V&V results presented that the developed code system can provide reasonable results with comparable confidence intervals. As a result, this paper successfully demonstrates that the isotope inventory prediction code system can be used for spent nuclear fuel analysis. (c) 2021 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Packaging and Antenna-Assembled Hybrid Stacked PCB with Novel Vertical Transition for 39 GHz 5G Base Stations

This paper proposes a novel packaging and large-scale antenna-assembled structure for a printed circuit board (PCB) that reinforces productivity, facilitates cost reduction, and maintains reliability. This was achieved by splitting the antenna from the main board and packaging it into a radio-frequency integrated circuit. In addition, two innovative solutions—an externally attachable flexible PCB antenna and a PCB-embedded coaxial line—are introduced to overcome the degradation in antenna performance and vertical RF transition loss in the proposed low-cost hybrid PCB. First, the proposed externally attachable flexible PCB antenna and a parasitic air-coupled antenna, which were easily assembled on the PCB, achieved an antenna efficiency of 95% and an impedance bandwidth of 7 GHz. Second, the fabricated coaxial line exhibited enhanced impedance matching over a wide frequency range of 30–40 GHz and improved insertion loss of approximately 1.4 dB. Furthermore, the packaged antenna, composed of 256 dual-polarized antenna elements per stream, incorporated a 39 GHz CMOS-based 16-channel phased-array transceiver IC. The set-level beam-forming measurements were verified considering an effective isotropic radiated power of 55 dBm at boresight and a steering range >±60°. In addition to being suitable for mass production in terms of cost and reliability, the proposed structures and solutions met the required antenna and beam-forming performance for commercial 39 GHz base stations without sacrificing performance