RePAST: A ReRAM-based PIM Accelerator for Second-order Training of DNN

The second-order training methods can converge much faster than first-order optimizers in DNN training. This is because the second-order training utilizes the inversion of the second-order information (SOI) matrix to find a more accurate descent direction and step size. However, the huge SOI matrices bring significant computational and memory overheads in the traditional architectures like GPU and CPU. On the other side, the ReRAM-based process-in-memory (PIM) technology is suitable for the second-order training because of the following three reasons: First, PIM's computation happens in memory, which reduces data movement overheads; Second, ReRAM crossbars can compute SOI's inversion in $O\left(1\right)$ time; Third, if architected properly, ReRAM crossbars can perform matrix inversion and vector-matrix multiplications which are important to the second-order training algorithms. Nevertheless, current ReRAM-based PIM techniques still face a key challenge for accelerating the second-order training. The existing ReRAM-based matrix inversion circuitry can only support 8-bit accuracy matrix inversion and the computational precision is not sufficient for the second-order training that needs at least 16-bit accurate matrix inversion. In this work, we propose a method to achieve high-precision matrix inversion based on a proven 8-bit matrix inversion (INV) circuitry and vector-matrix multiplication (VMM) circuitry. We design \archname{}, a ReRAM-based PIM accelerator architecture for the second-order training. Moreover, we propose a software mapping scheme for \archname{} to further optimize the performance by fusing VMM and INV crossbar. Experiment shows that \archname{} can achieve an average of 115.8$\times$/11.4$\times$ speedup and 41.9$\times$/12.8$\times$energy saving compared to a GPU counterpart and PipeLayer on large-scale DNNs.Comment: 13pages, 13 figure

Development and Verification of Performance Analysis Code for Fuel Element of Sodium-cooled Fast Reactor

For many years, sodium-cooled fast reactors have occupied the most important part of the closed fuel cycle. In order to improve the economy of sodium-cooled fast reactors, the nuclear industry around the world is actively increasing fuel burnup as much as possible. The behavior simulation of fuel elements under high fuel burnup is a key issue in the design and reliability of fuel elements. In this case, it is necessary to develop computer code that can accurately analyze fuel behavior to evaluate the behavior and reliability of high-fuel fuels, and as a safety analysis tool to evaluate the performance and behavioral evolution of fuel elements under steady-state, transient and accident conditions. For the above reasons, the Chinese Institute of Atomic Energy has developed FIBER, a performance analysis code for fuel elements of sodium-cooled fast reactor. The code consists of two main parts:The first part is used to analyze the temperature distribution, the thermal deformation and fission gas release; The other part is used to analyze the mechanical behavior of fuel elements. In the thermal analysis part, the axisymmetric finite volume method is applied to the entire length of the fuel element. The code has the ability to calculate thermal conductivity, gap heat transfer, coolant heat transfer, fission gas release, fuel restructure, solid fission product migration, and plenum pressure. In the mechanical analysis part, the axisymmetric finite element method is applied to the entire length of the fuel elements. The code can simulate the phenomena of thermal expansion, densification, irradiation swelling, pellet cracking, elasticity, plasticity, creep, and PCMI. The thermal analysis part and the mechanical analysis part are coupled, and the convergence of temperature and deformation is obtained in each time step through iteration. FIBER code consists of many theoretical models, empirical models, and parameters that control the calculation process. However, fuel behavior cannot be explained only by a simple combination of these models, because fuel behavior is the result of the coupling of many phenomena. Therefore, as many cases as possible must be used for code verification to determine the appropriate model and parameter selection. The irradiation data of UO2 and MOX of the Russian BN600 reactor were obtained through research. The two fuel elements operated in the Russian BN600 for 559 days, with maximum fuel burnup of 11.8at% and maximum irradiation damage of 78 dpa. The FIBER code was used to analyze the above two fuel elements. the calculation results of fission gas release rate, irradiation deformation, gap, columnar region, are compared with the irradiation data. The comparison results show that the FIBER code is effective for evaluating the irradiation deformation, columnar crystal region, and fission gas release performance of high burnup fuel elements

Estimation of Surface Air Specific Humidity and Air–Sea Latent Heat Flux Using FY-3C Microwave Observations

Latent heat flux (LHF) plays an important role in the global hydrological cycle and is therefore necessary to understand global climate variability. It has been reported that the near-surface specific humidity is a major source of error for satellite-derived LHF. Here, a new empirical model relating multichannel brightness temperatures ( T B ) obtained from the Fengyun-3 (FY-3C) microwave radiometer and sea surface air specific humidity ( Q a ) is proposed. It is based on the relationship between T B , Q a , sea surface temperature (SST), and water vapor scale height. Compared with in situ data, the new satellite-derived Q a and LHF both exhibit better statistical results than previous estimates. For Q a , the bias, root mean square difference (RMSD), and the correlation coefficient (R2) between satellite and buoy in the mid-latitude region are 0.08 g/kg, 1.76 g/kg, and 0.92, respectively. For LHF, the bias, RMSD, and R2 are 2.40 W/m2, 34.24 W/m2, and 0.87, respectively. The satellite-derived Q a are also compared with National Oceanic and Atmospheric Administration (NOAA) Cooperative Institute for Research in Environmental Sciences (CIRES) humidity datasets, with a bias, RMSD, and R2 of 0.02 g/kg, 1.02 g/kg, and 0.98, respectively. The proposed method can also be extended in the future to observations from other space-borne microwave radiometers

Understanding Land Use and Rural Development in the National Scheme of Village Relocation and Urbanization in China: A Case Study of Two Villages in Jiangsu Province

Large-scale village relocation and urbanization, one of the most significant social changes in China, bring villages both development opportunities and social risks. The social risks mainly stem from the government’s strong position in land expropriation and policy preference for urban development. We observe the amalgamation of Anyang and Bomu Village in China and explore the specific role of land policies in the social change and restructuring of the two villages. We find that clan gentries challenge the government’s “absolute” authority over land and landless villagers start the trend of “de-urbanization.” Our research presents targeted policy recommendations in terms of weakening the role of the government in urbanization, strengthening dialogues between the government and clans and coordinating urban and rural land use

Back Analysis and Calculation of Dynamic Mechanical Parameters of Rock Mass with Measured Blasting Vibration Signals

How to obtain dynamic parameters of rock masses quickly and precisely is a popular and difficult problem, which plays a very important part in engineering design or construction. Currently, the methods used to obtain these parameters are in situ testing method, empirical formula, and so on. However, these methods have some shortcomings, such as large investment and long construction period, which cannot obtain the dynamic parameters precisely and quickly in the engineering scale. In this study, a new method of estimating the rock parameters based on the measured field blasting vibration signals is proposed according to theory of elastic stress wave. In addition, an improved method for S-wave identification used in engineering scale was proposed and then the numerical simulation is given to verify the feasibility. Comparison of the numerical identification results and theoretical results clearly show that the improved method is available in S-wave identification with errors less than 2%. By identifying the arrival times of P and S waves, the propagation velocities of P and S waves are calculated and the parameters of rock mass can be obtained at last. Through analyzing the measured field blasting vibration signals in Fengning pumped-storage power station, the dynamic elastic modulus of rock mass inversed by vibration signals is about 2.2~2.9 times of its static elastic modulus, while the inversed dynamic Poisson's ratio is 0.9~0.975 times of the static

An evaluation of numerical approaches for S-wave component simulation in rock blasting

The shear wave (S-wave) component of the total blast vibration always plays an important role in damage to rock or adjacent structures. Numerical approach has been considered as an economical and effective tool in predicting blast vibration. However, S-wave has not yet attracted enough attention in previous numerical simulations. In this paper, three typical numerical models, i.e. the continuum-based elastic model, the continuum-based damage model, and the coupled smooth particle hydrodynamics (SPH)-finite element method (FEM) model, were first introduced and developed to simulate the blasting of a single cylindrical charge. Then, the numerical results from different models were evaluated based on a review on the generation mechanisms of S-wave during blasting. Finally, some suggestions on the selection of numerical approaches for simulating generation of the blast-induced S-wave were put forward. Results indicate that different numerical models produce different results of S-wave. The coupled numerical model was the best, for its outstanding capacity in producing S-wave component. It is suggested that the model that can describe the cracking, sliding or heaving of rock mass, and the movement of fragments near the borehole should be selected preferentially, and priority should be given to the material constitutive law that could record the nonlinear mechanical behavior of rock mass near the borehole

Fabrication of nitrogen-doped graphene decorated with organophosphor and lanthanum towards high-performance polymer nanocomposites

Despite substantial advances, it remains imperative but challenging to develop high-performance polymer/graphene nanocomposites combining with excellent mechanical, thermal, and fire-retardant properties. In this work, a novel kind of graphene-based multifunctional nanofiller (La@PN-RGO) was fabricated via the nitrogen doping and the decoration with organophosphorus and lanthanum based on graphene oxide, which is then incorporated into acrylonitrile−butadiene−styrene (ABS) resin via melt blending to obtain resultant ABS nanocomposites. As expected, the La@PN-RGO nanosheets were well dispersed in ABS composites. Attractively, with only 1.0 wt % of La@PN-RGO incorporated into ABS matrix, the peak heat release rate (PHRR) and total smoke production (TSP) were significantly reduced by 38% and 36%, which is much superior to its counterparts at the same nanofillers loading level. The notably enhanced fire safety was primarily attributed to the rare earth catalysis accompanied by the lamellae blocking effect and intumescent flame retardancy of La@PN-RGO. Additionally, ABS/La@PN-RGO composite exhibited a 16% enhancement in tensile strength without at the expense of extensibility. This effective and promising method may open a new pathway to obtain high-performance polymer/graphene nanocomposites