正极性操作冲击电压下长短空气间隙放电特性

现场真型试验是考核长空气间隙绝缘性能的关键环节,但由于电板结构各异、布置复杂等实际条件限制,试验对象一般为典型间隙结构,并不能涵盖所有实际工程问题.中外学者均在努力探索长、短间隙试验的内在联系,通过研究不同间隙距离下放电各阶段异同点,实现对放电特性的精细掌握.搭建了由光电倍增管、电场传感器组成的光电联合测量系统,获得了操作冲击电压下5 cm和3 m针-板间隙放电发展过程中的空间场强、瞬时光功率等信号,分析得到了初始流注起始时延、暗期持续时间、初始流注电场跃升幅值和初始流注光功率跃升幅值等关键特征参数.结果 表明:5 cm与3m针-板间隙流注起始时延、暗期持续时间、场强跃升幅值相近,且光功率跃升幅值均与场强跃升幅值呈正相关的关系,长、短间隙在初始流注和暗期阶段呈现一定相似性;另外,5 cm间隙的特征参数方差均小于3 m间隙,短间隙下的放电随机性较小.获得的5 cm和3 m间隙距离下放电发展过程特征参数及各特征参量变化规律,为后期长、短间隙放电特性的电磁学仿真提供了准确的计算参数.     

Effect of Co substitution on the structural,dielectric and optical properties of KBiFe2O5

Cobalt (Co)-modified brownmillerite KBiFe2O5 (KBFO; [KBiFe2(1?x)Co2xO5 (x = 0, 0.05)]) polycrystalline is synthesized following the solid-state reaction route. Rietveld refinement of X-ray diffraction data confirmed the phase purity of KBFO and KBiFe1.9Co0.1O5 (KBFCO). The optical bandgap energy (Eg) of KBFO decreased from 1.59 to 1.51 eV because of Co substitution. The decrease in bandgap can be attributed to the tilting of the Fe–O tetrahedral structure of KBFCO. The observed room-temperature Raman peaks of KBFCO shifted by 3 cm?1 toward a lower wavenumber than that of KBFO. The shift in Raman active modes can be attributed to the change in the bond angles and bond lengths of the Fe–O tetrahedral structure and modification in response to oxygen deficiency in KBFO because of Co doping. Compared with that of KBFO, the frequency-dependent dielectric constant and dielectric loss of KBFCO decrease at room temperature, which is a con-sequence of the reduction in oxygen migration and modification in response to vibrational modes present in the sample.     

Dielectric relaxation and conduction mechanism in Aurivillius ceramic Bi5Ti3FeO15

For this study, we synthesized Aurivillius Bi5Ti3FeO15 ceramic using the generic solid-state reaction route and then performed room-temperature X-ray diffraction to confirm that the compound had a single phase with no impurities. The surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2 μm in size. The dielectric properties of the sample were determ-ined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures (303 K ≤ T ≤ 773 K). Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region, which is explained by the equivalent electrical circuit (R1C1)(R2QC2), where R1 and R2 represent the resistances associated with the grains and grain boundaries, respectively, C1 and C2 are the re-spective capacitances, and Q is the constant phase element (CPE), which accounts for non-Debye type of behavior. Our results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the grains. The alternating current (ac) conductiv-ity data were analyzed based on the Jonscher universal power law, which indicated that the conduction process is dominated by the hopping mechanism. The calculated activation energies of the relaxation and conduction processes were very similar (0.32 to 0.53 eV), from which we conclude that the same type of charge carriers are involved in both processes.     

石杉碱甲片联合丁苯酞软胶囊对轻度阿尔茨海默病患者认知功能的疗效观察

目的 评价石杉碱甲片联合丁苯酞软胶囊对阿尔茨海默病患者认知功能的临床疗效.方法 将100例轻度阿尔茨海默病(Alzheimer's disease,AD)患者随机分为石杉碱甲片联合丁苯酞软胶囊组(治疗组)及单独应用石杉碱甲组(对照组).治疗前及治疗90 d后分别评价两组患者简易智力状态检查(Mini-mental State Examination,MMSE)量表、事件诱发电位P300潜伏期、波幅及不良反应.结果 石杉碱甲片联合丁苯酞软胶囊组治疗90 d后,MMSE评分和P300潜伏期、波幅与治疗前比较差异均具有统计学意义(P<0.05);与单独应用石杉碱甲组比较差异具有统计学意义(P<0.05).结论 石杉碱甲片联合丁苯酞软胶囊对轻度阿尔茨海默病患者认知功能有明显改善,且优于单独应用石杉碱甲片组.     

Prion protein cleavage fragments regulate adult neural stem cell quiescence through redox modulation of mitochondrial fission and SOD2 expression

Neurogenesis continues in the post-developmental brain throughout life. The ability to stimulate the production of new neurones requires both quiescent and actively proliferating pools of neural stem cells (NSCs). Actively proliferating NSCs ensure that neurogenic demand can be met, whilst the quiescent pool makes certain NSC reserves do not become depleted. The processes preserving the NSC quiescent pool are only just beginning to be defined. Herein, we identify a switch between NSC proliferation and quiescence through changing intracellular redox signalling. We show that N-terminal post-translational cleavage products of the prion protein (PrP) induce a quiescent state, halting NSC cellular growth, migration, and neurite outgrowth. Quiescence is initiated by the PrP cleavage products through reducing intracellular levels of reactive oxygen species. First, inhibition of redox signalling results in increased mitochondrial fission, which rapidly signals quiescence. Thereafter, quiescence is maintained through downstream increases in the expression and activity of superoxide dismutase-2 that reduces mitochondrial superoxide. We further observe that PrP is predominantly cleaved in quiescent NSCs indicating a homeostatic role for this cascade. Our findings provide new insight into the regulation of NSC quiescence, which potentially could influence brain health throughout adult life.     

A new twist to the No Miracles Argument for the success of science

J. D. Trout has recently developed a new defense of scientific realism, a new version of the No Miracles Argument. I critically evaluate Trout's novel defense of realism. I argue that Trout's argument for scientific realism and the related explanation for the success of science are self-defeating. In the process of arguing against the traditional realist strategies for explaining the success of science, he inadvertently undermines his own argument.     

Robust model rankings of forecasting performance

This paper investigates robust model rankings in out‐of‐sample, short‐horizon forecasting. We provide strong evidence that rolling window averaging consistently produces robust model rankings while improving the forecasting performance of both individual models and model averaging. The rolling window averaging outperforms the (ex post) “optimal” window forecasts in more than 50% of the times across all rolling windows.     

Rediscovery of Disepyris semiruber (Kieffer) (Hymenoptera: Bethylidae) in Southern Africa,with first description of the male

Holepyris semiruber Kieffer is redescribed and illustrated based on freshly collected specimens. Holepyris semiruber var. striatipleura Kieffer is considered a colour variant of this species and therefore a junior synonym of H. semiruber syn. nov. This species is transferred to Disepyris, D. semiruber (Kieffer) comb. nov., based on the possession of a short 2r-rs&Rs vein in the fore wing and presence of long flat spine-shaped setae on the outer (posterior) surface of the protarsi. The male is described for the first time from new specimens collected in South Africa. This species is recorded for the first time from Namibia and Zimbabwe. All photographs are available on www.waspweb.org.