基于EOF的雅鲁藏布江流域干湿季降水变化的时空分异研究

根据2000年~2010年雅鲁藏布江流域的15个气象站点的月值降水数据,采用经验正交函数分解法(EOF),分别计算出雅鲁藏布江流域干湿季降水的时空分布特征和时间系数序列。结果表明:应用EOF方法可以很好地揭示降水场的时空分布特征,且对雅鲁藏布江流域而言前4种模态揭示了四种分布场,干季降水的累计贡献率达99.84%,湿季降水的累计贡献率达89.81%。雅鲁藏布江流域干湿季降水的主要空间分布特征是“东–西差异分布”,即表现出西部偏少东部偏多的特点,尤其是在喜马拉雅山脉最东端的米林宽谷地带降水最为丰富,分析其原因是季风气候和印度洋的暖湿气流对东部影响较大,西部由于海拔高,水汽很难到达,因此西部降水较东部少。

Investigation on LCF Behavior of Welded Joint at Di erent Temperatures for Bainite Steel

The current research of low cycle fatigue(LCF) is mainly focused on the components with uniform microstructure.Compared with these typical components, LCF behavior of welded components are more complex due to their great gradient microstructure, especially for di erent temperature. In this paper, LCF properties were conducted on the welded joint at di erent temperatures for bainite steel, and the failure mechanism was systematically discussed.Fatigue parameters derived from fitting curves indicated that welded joint had worse plastic deformation resistance and experienced more significantly strain hardening e ect at 300 °C. The joint failed in the weld metal at room temperature, which attributed to the softening in weld metal combined with cyclic strain hardening e ect in heata ected zone, which meant the joint was more sensitive with the hardness at this condition. When it came to 300 °C,more cracks appeared near to HAZ and the heterogeneous distributed surface inclusion was responsible for the fracture transition to HAZ adjacent to bainite steel rather than the softest zone in HAZ, reflecting the joint was more sensitive with the surface inclusion at 300 °C. This research could support the design on loading of welded component at di erent temperature, and further ensure the safe operation.

Hainan; Nandu River; Soil nutrient; Spatial distribution

[Objectives] Within a research area on basin scale, soil nutrient distribution characteristics and main causes were analyzed, to provide a basis for soil nutrient management on basin scale.[Methods] With the Nandu River Basin of Hainan Island as the research area, by means of geostatistics and spatial analysis methods, the distribution available of soil pH, organic matter, alkali-hydrolyzale nitrogen, available phosphorus, available potassium and available trace elements were studied.[Results] The cultivated land in the Nandu River Basin of Hainan Province is overall acidic, with an average pH of 5.2. The soil organic matter content is overall lower, and its spatial differences are also significant. Soil alkali-hydrolyzable nitrogen, exchangeable calcium and exchangeable magnesium content are at a medium level, but the soil lacks available phosphorus and available potassium.[Conclusions] The differences in pH within the research area might be related to parent materials distribution and fertilizer applications. The main reasons for the low soil organic matter content are inadequate and uneven input of organic fertilizer and high-temperate rainy climate. The lack of soil phosphorus and potassium is mainly caused by unreasonable fertilizer application and climatic and terrain factors.

Local field potentials,spiking activity,and receptive fields in human visual cortex

The concept of receptive field(RF) is central to sensory neuroscience. Neuronal RF properties have been substantially studied in animals,while those in humans remain nearly unexplored. Here, we measured neuronal RFs with intracranial local field potentials(LFPs) and spiking activity in human visual cortex(V1/V2/V3). We recorded LFPs via macro-contacts and discovered that RF sizes estimated from lowfrequency activity(LFA, 0.5–30 Hz) were larger than those estimated from low-gamma activity(LGA, 30–60 Hz) and high-gamma activity(HGA, 60–150 Hz). We then took a rare opportunity to record LFPs and spiking activity via microwires in V1 simultaneously. We found that RF sizes and temporal profiles measured from LGA and HGA closely matched those from spiking activity. In sum, this study reveals that spiking activity of neurons in human visual cortex could be well approximated by LGA and HGA in RF estimation and temporal profile measurement, implying the pivotal functions of LGA and HGA in early visual information processing.

Laminar Distribution of Neurochemically-Identified Interneurons and Cellular Co-expression of Molecular Markers in Epileptic Human Cortex

Inhibitory GABAergic interneurons are fundamental elements of cortical circuits and play critical roles in shaping network activity. Dysfunction of interneurons can lead to various brain disorders, including epilepsy,schizophrenia, and anxiety. Based on the electrophysiological properties, cell morphology, and molecular identity,interneurons could be classified into various subgroups. In this study, we investigated the density and laminar distribution of different interneuron types and the coexpression of molecular markers in epileptic human cortex.We found that parvalbumin(PV) and somatostatin(SST)neurons were distributed in all cortical layers except layer I, while tyrosine hydroxylase(TH) and neuropeptide Y(NPY) were abundant in the deep layers and white matter.Cholecystokinin(CCK) neurons showed a high density in layers IV and VI. Neurons with these markers constituted*7.2%(PV), 2.6%(SST), 0.5%(TH), 0.5%(NPY), and4.4%(CCK) of the gray-matter neuron population. Doubleand triple-labeling revealed that NPY neurons were also SST-immunoreactive(97.7%), and TH neurons were more likely to express SST(34.2%) than PV(14.6%). A subpopulation of CCK neurons(28.0%) also expressed PV, but none contained SST. Together, these results revealed the density and distribution patterns of different interneuron populations and the overlap between molecular markers in epileptic human cortex.

Transition and fracture shift behavior in LCF test of dissimilar welded joint at elevated temperature

This work focused on the low-cycle fatigue （LCF） behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding （NG-SAW） process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R = -1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain （CSS） curve and Manson-Coffin （M-C） curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal （BM） at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone （OTZ） at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV- OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude.

Controller Design-oriented Analysis of Grid-forming Converters for Stability Robustness Enhancement

Grid-forming converters can suffer from control interaction problems in grid connections that can result in small-signal instability.Their inner-loop voltage controller tends to interact with the outer-loop power controller,rendering the controller design more difficult.To conduct a design-oriented analysis,a control-loop decomposition approach for grid-forming converters is proposed.Combined with impedance-based stability analysis,the control-loop decomposition approach can reveal how different control loops affect the converter-grid interaction.This results in a robust controller design enabling grid-forming converters to operate within a wider range of grid short-circuit ratios.Finally,simulation and experimental results,which validate the approach,are presented.

Microstructure characterization and HCF fracture mode transition for modified 9Cr-1Mo dissimilarly welded joint at different elevated temperatures

The high cycle fatigue（HCF） tests of modified 9 Cr-1 Mo dissimilarly welded joint were carried out at different elevated temperatures and the fracture mechanism was systematically revealed. The fatigue strength at 108 cycles based on S-N curve can be estimated as a half of weld joint＇s yield strength for all conducted temperatures, which can be a reliable criterion in predicting the fatigue life. The results show that the inter-critical heat affected zones（IC-HAZs） of both sides are the weak zones due to their low hardness and inferior fatigue resistance property. HAZ of COST-FB2（BM2） is the weakest zone at room temperature due to the existence of numerously distributed defects and the initiation of cracks, either in the surface or interior zone, impacting a crucial effect on the fatigue life of the joint. While at elevated temperatures, fatigue life was controlled mostly by the intrusion-extrusion mechanism at the specimen surface under high stress level and subsurface non-defect fatigue crack origin（SNDFCO） from the interior material under low stress amplitude. With increasing temperature, more and more fatigue failures began to occur at the HAZ of COST-E（BM1） due to its higher susceptibility of temperature. Besides, it is found that the-ferrite in the BM1 has no harm to the HCF behavior of the joint at the conducted temperatures.

Editorial for the Special Issue on Operation and Control of Power Electronics Dominated Power Systems

With the ever increasing penetration of renewable energy and power electronics,the current energy network is being transformed to power electronics dominated power system(PEDPS).Different from conventional power grid,PEDPS has its own characteristics such as much lower inertia,lower short circuit capacity,multi-timescale dynamic behavior,etc.These features bring tremendous challenges to the analysis,design,modeling and control of the modem power grid systems.