Qijing Huang, Ruolong Lian, Andrew Canis, Jongsok Choi, R. Xi, S. Brown, J. Anderson
We consider the impact of compiler optimizations on the quality of high-level synthesis (HLS)-generated FPGA hardware. Using a HLS tool implemented within the state-of-the-art LLVM [1] compiler, we study the effect of compiler optimizations on the hardware metrics of circuit area, execution cycles, Fmax, and wall-clock time. We evaluate 56 different compiler optimizations implemented within LLVM and show that some optimizations significantly affect hardware quality. Moreover, we show that hardware quality is also affected by the order in which optimizations are applied. We then present a new HLS-directed approach to compiler optimizations, wherein we execute partial HLS and profiling at intermittent points in the optimization process and use the results to judiciously undo the impact of optimization passes predicted to be damaging to the generated hardware quality. Results show that our approach produces circuits with 16% better speed performance, on average, versus using the standard -O3 optimization level.
{"title":"The Effect of Compiler Optimizations on High-Level Synthesis for FPGAs","authors":"Qijing Huang, Ruolong Lian, Andrew Canis, Jongsok Choi, R. Xi, S. Brown, J. Anderson","doi":"10.1109/FCCM.2013.50","DOIUrl":"https://doi.org/10.1109/FCCM.2013.50","url":null,"abstract":"We consider the impact of compiler optimizations on the quality of high-level synthesis (HLS)-generated FPGA hardware. Using a HLS tool implemented within the state-of-the-art LLVM [1] compiler, we study the effect of compiler optimizations on the hardware metrics of circuit area, execution cycles, Fmax, and wall-clock time. We evaluate 56 different compiler optimizations implemented within LLVM and show that some optimizations significantly affect hardware quality. Moreover, we show that hardware quality is also affected by the order in which optimizations are applied. We then present a new HLS-directed approach to compiler optimizations, wherein we execute partial HLS and profiling at intermittent points in the optimization process and use the results to judiciously undo the impact of optimization passes predicted to be damaging to the generated hardware quality. Results show that our approach produces circuits with 16% better speed performance, on average, versus using the standard -O3 optimization level.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121452588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work we aim to strike a balance between performance, power consumption and design effort for complex digital signal processing within the power and size constraints of embedded systems. Looking across the design stack, from algorithm formulation down to accelerator microarchitecture, we show that a high degree of flexibility and design reuse can be achieved without much performance sacrifice. The foundation of our design is a numerical accelerator template. Extensively parameterized, it allows us to develop the design while postponing microarchitectural decisions until program is known. Statically scheduling compiler provides a link between the algorithm and template instantiation parameters. Results show that the derived design can significantly outperform embedded processors for similar power cost and also approach the high-performance processor performance for a fraction of the power cost.
{"title":"Hardware-Software Codesign for Embedded Numerical Acceleration","authors":"Ranko Sredojevic, A. Wright, V. Stojanović","doi":"10.1109/FCCM.2013.27","DOIUrl":"https://doi.org/10.1109/FCCM.2013.27","url":null,"abstract":"In this work we aim to strike a balance between performance, power consumption and design effort for complex digital signal processing within the power and size constraints of embedded systems. Looking across the design stack, from algorithm formulation down to accelerator microarchitecture, we show that a high degree of flexibility and design reuse can be achieved without much performance sacrifice. The foundation of our design is a numerical accelerator template. Extensively parameterized, it allows us to develop the design while postponing microarchitectural decisions until program is known. Statically scheduling compiler provides a link between the algorithm and template instantiation parameters. Results show that the derived design can significantly outperform embedded processors for similar power cost and also approach the high-performance processor performance for a fraction of the power cost.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125512557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper we describe a technique for scheduling memory accesses to improve effective memory bandwidth on the Convey HC-1 platform.
在本文中，我们描述了一种调度内存访问的技术，以提高传输HC-1平台上的有效内存带宽。
{"title":"Memory Access Scheduling on the Convey HC-1","authors":"Zheming Jin, J. Bakos","doi":"10.1109/FCCM.2013.55","DOIUrl":"https://doi.org/10.1109/FCCM.2013.55","url":null,"abstract":"In this paper we describe a technique for scheduling memory accesses to improve effective memory bandwidth on the Convey HC-1 platform.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115679441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
SYLVA is a System Level Architectural Synthesis Framework that translates Synchronous Data Flow (SDF) models of DSP sub-systems like modems and codecs into hardware implementation in ASIC/Standard Cells, FPGAs or CGRAs (Coarse Grain Reconfigurable Fabric).
{"title":"Global Control and Storage Synthesis for a System Level Synthesis Approach","authors":"Shuo Li, Nasim Farahini, A. Hemani","doi":"10.1109/FCCM.2013.61","DOIUrl":"https://doi.org/10.1109/FCCM.2013.61","url":null,"abstract":"SYLVA is a System Level Architectural Synthesis Framework that translates Synchronous Data Flow (SDF) models of DSP sub-systems like modems and codecs into hardware implementation in ASIC/Standard Cells, FPGAs or CGRAs (Coarse Grain Reconfigurable Fabric).","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131189903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Double-precision computations operating on inputs with uncertainty margins can be compiled to lower precision fixed-point datapaths with no loss in output accuracy. We observe that ideal SPICE model equations based on device physics include process parameters which must be matched with real-world measurements on specific silicon manufacturing processes through a noisy data-fitting process. We expose this uncertainty information to the open-source FX-SCORE compiler to enable automated error analysis using the Gappa++ backend and hardware circuit generation using Vivado HLS. We construct an error model based on interval analysis to statically identify sufficient fixedpoint precision in the presence of uncertainty as compared to reference double-precision design. We demonstrate 1-16× LUT count improvements, 0.5-2.4× DSP count reductions and 0.9-4× FPGA power reduction for SPICE devices such as Diode, Level-1 MOSFET and an Approximate MOSFET designs. We generate confidence in our approach using Monte-Carlo simulations with auto-generated Matlab models of the SPICE device equations.
{"title":"Exploiting Input Parameter Uncertainty for Reducing Datapath Precision of SPICE Device Models","authors":"Nachiket Kapre","doi":"10.1109/FCCM.2013.28","DOIUrl":"https://doi.org/10.1109/FCCM.2013.28","url":null,"abstract":"Double-precision computations operating on inputs with uncertainty margins can be compiled to lower precision fixed-point datapaths with no loss in output accuracy. We observe that ideal SPICE model equations based on device physics include process parameters which must be matched with real-world measurements on specific silicon manufacturing processes through a noisy data-fitting process. We expose this uncertainty information to the open-source FX-SCORE compiler to enable automated error analysis using the Gappa++ backend and hardware circuit generation using Vivado HLS. We construct an error model based on interval analysis to statically identify sufficient fixedpoint precision in the presence of uncertainty as compared to reference double-precision design. We demonstrate 1-16× LUT count improvements, 0.5-2.4× DSP count reductions and 0.9-4× FPGA power reduction for SPICE devices such as Diode, Level-1 MOSFET and an Approximate MOSFET designs. We generate confidence in our approach using Monte-Carlo simulations with auto-generated Matlab models of the SPICE device equations.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114678121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, we propose a novel architecture for DWT that can be reconfigured to be adapted to different kinds of filter banks and different sizes of inputs. High flexibility and generality are achieved by using the MAC loop based filter(MLBF). Classic methods, such as polyphase structure and fragment-based sample consumption, are used to enhance the parallelism of the system. The architecture can be reconfigured to 3 modes to deal with 1-D or 2-D DWT with different bandwidth and throughput requirements.
{"title":"A Reconfigurable Architecture for 1-D and 2-D Discrete Wavelet Transform","authors":"Qing Sun, Jiang Jiang, Yongxin Zhu, Yuzhuo Fu","doi":"10.1109/FCCM.2013.23","DOIUrl":"https://doi.org/10.1109/FCCM.2013.23","url":null,"abstract":"In this paper, we propose a novel architecture for DWT that can be reconfigured to be adapted to different kinds of filter banks and different sizes of inputs. High flexibility and generality are achieved by using the MAC loop based filter(MLBF). Classic methods, such as polyphase structure and fragment-based sample consumption, are used to enhance the parallelism of the system. The architecture can be reconfigured to 3 modes to deal with 1-D or 2-D DWT with different bandwidth and throughput requirements.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115721599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The data-intensive applications that will shape computing in the coming decades require scalable architectures that incorporate scalable data and compute resources and can support random requests to unstructured (e.g., logs) and semi-structured (e.g., large graph, XML) data sets. To explore the suitability of FPGAs for these computations, we are constructing an FPGAbased system with a memory capacity of 512 GB from a collection of 32 Virtex-5 FPGAs spread across 8 enclosures. This paper describes our work in exploring alternative interconnect technologies and network topologies for FPGA-based clusters. The diverse interconnects combine inter-enclosure high-speed serial links and wide, single-ended intra-enclosure on-board traces with network topologies that balance network diameter, network throughput, and FPGA resource usage. We discuss the architecture of high-radix routers in FPGAs that optimize for the asymmetry between the interand intra-enclosure links. We analyze the various interconnects that aim to efficiently utilize the prototype's total switching capacity of 2.43 Tb/s. The networks we present have aggregate throughputs up to 51.4 GB/s for random traffic, diameters as low as 845 nanoseconds, and consume less than 12% of the FPGAs' logic resources.
{"title":"Latency-Optimized Networks for Clustering FPGAs","authors":"Trevor Bunker, S. Swanson","doi":"10.1109/FCCM.2013.49","DOIUrl":"https://doi.org/10.1109/FCCM.2013.49","url":null,"abstract":"The data-intensive applications that will shape computing in the coming decades require scalable architectures that incorporate scalable data and compute resources and can support random requests to unstructured (e.g., logs) and semi-structured (e.g., large graph, XML) data sets. To explore the suitability of FPGAs for these computations, we are constructing an FPGAbased system with a memory capacity of 512 GB from a collection of 32 Virtex-5 FPGAs spread across 8 enclosures. This paper describes our work in exploring alternative interconnect technologies and network topologies for FPGA-based clusters. The diverse interconnects combine inter-enclosure high-speed serial links and wide, single-ended intra-enclosure on-board traces with network topologies that balance network diameter, network throughput, and FPGA resource usage. We discuss the architecture of high-radix routers in FPGAs that optimize for the asymmetry between the interand intra-enclosure links. We analyze the various interconnects that aim to efficiently utilize the prototype's total switching capacity of 2.43 Tb/s. The networks we present have aggregate throughputs up to 51.4 GB/s for random traffic, diameters as low as 845 nanoseconds, and consume less than 12% of the FPGAs' logic resources.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124484267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emerging non-volatile memory (NVM) technologies have DRAM-like latency with storage-like density, offering unique capability to analyze large data sets significantly faster than flash or disk storage. However, the hybrid nature of these NVM technologies such as phase-change memory (PCM) make it difficult to use them to best advantage in the memory-storage hierarchy. These NVMs lack the fast write latency required of DRAM and are thus not suitable as DRAM equivalent on the memory bus, yet their low latency even in random access patterns is not easily exploited over an I/O bus. In this work, we describe an FPGA-based system to execute application-specific operations in the NVM controller and evaluate its performance on two microbenchmarks and a keyvalue store. Our system Minerva1extends the conventional solidstate drive (SSD) architecture to offload data or I/O intensive application code to the SSD to exploit the low latency and high internal bandwidth of NVMs. Performing computation in the FPGA-based NVM storage controller significantly reduces data traffic between the host and storage and serves as an offload engine for data analysis workloads. A runtime library enables the programmer to offload computations to the SSD without dealing with the complications of the underlying architecture and inter-controller communication management. We have implemented a prototype of Minerva on the BEE3 FPGA system. We compare the performance of Minerva to a state of the art PCIe-attached PCM-based SSD. Minerva improves performance by an order of magnitude on two microbenchmarks. Minerva based key-value store performs up to 5.2 M get operations/s and 4.0 M set operations/s which is 7.45× and 9.85× higher than the PCM-based SSD that uses the conventional I/O architecture. This huge improvement comes from the reduction of data transfer between the storage to the host and the FPGA-based data processing in the SSD.
新兴的非易失性内存(NVM)技术具有类似dram的延迟和类似存储的密度，提供了独特的能力，可以比闪存或磁盘存储更快地分析大型数据集。然而，这些NVM技术(如相变存储器(PCM))的混合性质使得很难在内存-存储层次结构中充分利用它们。这些nvm缺乏DRAM所需的快速写入延迟，因此不适合作为内存总线上的DRAM等效，然而，即使在随机访问模式下，它们的低延迟也不容易在I/O总线上被利用。在这项工作中，我们描述了一个基于fpga的系统，用于在NVM控制器中执行特定于应用程序的操作，并在两个微基准测试和一个键值存储上评估其性能。我们的系统minerva1扩展了传统的固态硬盘(SSD)架构，将数据或I/O密集型应用程序代码卸载到SSD上，以利用nvm的低延迟和高内部带宽。在基于fpga的NVM存储控制器中执行计算，可以显著减少主机和存储之间的数据流量，并作为数据分析工作负载的卸载引擎。运行时库使程序员能够将计算卸载到SSD上，而无需处理底层体系结构和控制器间通信管理的复杂性。我们已经在BEE3 FPGA系统上实现了Minerva的原型。我们将Minerva的性能与最先进的pcie连接的基于pcm的SSD进行比较。Minerva在两个微基准测试上提高了一个数量级的性能。基于Minerva的键值存储的get操作次数为5.2 M /s, set操作次数为4.0 M /s，分别比采用传统I/O架构的基于pcm的SSD高7.45倍和9.85倍。这种巨大的改进来自于减少了存储到主机之间的数据传输和SSD中基于fpga的数据处理。
{"title":"Minerva: Accelerating Data Analysis in Next-Generation SSDs","authors":"Arup De, M. Gokhale, Rajesh K. Gupta, S. Swanson","doi":"10.1109/FCCM.2013.46","DOIUrl":"https://doi.org/10.1109/FCCM.2013.46","url":null,"abstract":"Emerging non-volatile memory (NVM) technologies have DRAM-like latency with storage-like density, offering unique capability to analyze large data sets significantly faster than flash or disk storage. However, the hybrid nature of these NVM technologies such as phase-change memory (PCM) make it difficult to use them to best advantage in the memory-storage hierarchy. These NVMs lack the fast write latency required of DRAM and are thus not suitable as DRAM equivalent on the memory bus, yet their low latency even in random access patterns is not easily exploited over an I/O bus. In this work, we describe an FPGA-based system to execute application-specific operations in the NVM controller and evaluate its performance on two microbenchmarks and a keyvalue store. Our system Minerva1extends the conventional solidstate drive (SSD) architecture to offload data or I/O intensive application code to the SSD to exploit the low latency and high internal bandwidth of NVMs. Performing computation in the FPGA-based NVM storage controller significantly reduces data traffic between the host and storage and serves as an offload engine for data analysis workloads. A runtime library enables the programmer to offload computations to the SSD without dealing with the complications of the underlying architecture and inter-controller communication management. We have implemented a prototype of Minerva on the BEE3 FPGA system. We compare the performance of Minerva to a state of the art PCIe-attached PCM-based SSD. Minerva improves performance by an order of magnitude on two microbenchmarks. Minerva based key-value store performs up to 5.2 M get operations/s and 4.0 M set operations/s which is 7.45× and 9.85× higher than the PCM-based SSD that uses the conventional I/O architecture. This huge improvement comes from the reduction of data transfer between the storage to the host and the FPGA-based data processing in the SSD.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116611081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Embedded signal processing is facing the challenges of increased performance as well as to achieve energy efficiency. Massively parallel processor arrays (MPPAs) consisting of hundreds of processing cores offer the possibility of meeting the growing performance demand in an energy efficient way by exploiting parallelism instead of scaling the clock frequency of a single processor. In this paper we evaluate two selected commercial architectures belonging to the category of MPPA. The adopted approach for the evaluation is to implement a real, industrial application in the form of compute-intensive parts of Synthetic Aperture Radar (SAR) systems.
{"title":"An Evaluation of High-Performance Embedded Processing on MPPAs","authors":"Zain-ul-Abdin, B. Svensson","doi":"10.1109/FCCM.2013.44","DOIUrl":"https://doi.org/10.1109/FCCM.2013.44","url":null,"abstract":"Embedded signal processing is facing the challenges of increased performance as well as to achieve energy efficiency. Massively parallel processor arrays (MPPAs) consisting of hundreds of processing cores offer the possibility of meeting the growing performance demand in an energy efficient way by exploiting parallelism instead of scaling the clock frequency of a single processor. In this paper we evaluate two selected commercial architectures belonging to the category of MPPA. The adopted approach for the evaluation is to implement a real, industrial application in the form of compute-intensive parts of Synthetic Aperture Radar (SAR) systems.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134233826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper designed a MPI-like Message Passing Engine (MPE) as part of the on-chip network, providing point-to-point and collective communication primitives in hardware. On one hand, the MPE offloads the communication workload from the general processing elements. On the other hand, the MPE provides direct interface to the heterogeneous processing elements which can eliminate the data path going around the OS and libraries. The experimental results have shown that the MPE can significantly reduce the communication time and improve the overall performance, especially for heterogeneous computing systems.
{"title":"The Impact of Hardware Communication on a Heterogeneous Computing System","authors":"Shanyuan Gao, Bin Huang, R. Sass","doi":"10.1109/FCCM.2013.43","DOIUrl":"https://doi.org/10.1109/FCCM.2013.43","url":null,"abstract":"This paper designed a MPI-like Message Passing Engine (MPE) as part of the on-chip network, providing point-to-point and collective communication primitives in hardware. On one hand, the MPE offloads the communication workload from the general processing elements. On the other hand, the MPE provides direct interface to the heterogeneous processing elements which can eliminate the data path going around the OS and libraries. The experimental results have shown that the MPE can significantly reduce the communication time and improve the overall performance, especially for heterogeneous computing systems.","PeriodicalId":269887,"journal":{"name":"2013 IEEE 21st Annual International Symposium on Field-Programmable Custom Computing Machines","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2013-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127057712","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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