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51.
We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO) nanostructured AlGaN/GaN high electron mobility transistors (HEMTs). The ZnO nanorods (NRs) are selectively grown on the gate area by using hydrothermal method. It is shown that ZnO nanorod (NR)-gated UV detectors exhibit much superior performance in terms of response speed and recovery time to those of seed-layer-gated detectors. It is also found that the best response speed (~10 and~190 ms) and responsivity (~1.1×105 A/W) were observed from detectors of the shortest gate length of 2 µm among our NR-gated devices of three different gate dimensions, and this responsivity is about one order higher than the best performance of ZnO NR-based UV detectors reported to date. 相似文献
52.
Regime shifts observed in Lake Kasumigaura,a large shallow lake in Japan: Analysis of a 40‐year limnological record 下载免费PDF全文
Lake Kasumigaura, which is composed of the two basins (Nishiura and Kitaura), is a large, shallow, hypereutrophic lake. Phytoplankton and water quality records from the past forty years were analysed to elucidate whether or not, when, and what type of certain regime shifts may have occurred, based on using inferential regime shift detectors. Characteristics of the phytoplankton and water quality changes were similar at 6 sampling sites in the two basins, with 20 water quality parameters being classified into four groups, based on cluster analysis. Shifts in dominant plankton groups (DPGs) and water quality occurring almost concomitantly, concentration on the period from 1987 to 1992 (Shift A) and from 1997 to 2001 (Shift B), with those observed for the two basins usually being similar with small differences. Two types of inferential regime shift detectors (sequential t‐test type; Rodionov's RSD and sequential F‐test type: package strucchange in R) yielded similar timings and significances of the shifts. Furthermore, changes in skewness and conditional heteroskedasticity (package early warnings in R) usually represented early warning signals before the shifts. Correlation analysis and ratios of dissolved inorganic nitrogen (DIN) vs. total phosphorus (TP) supported the hypothesis that phosphorus was the phytoplankton biomass limiting nutrient, except for one period for the Nishiura basin. Neither the nitrogen:phosphorus (N/P) ratio hypothesis and ammonia–nitrate (NH4‐N/NO3‐N) hypothesis satisfactorily explain the DPGs before and after Shift A (Microcystis spp. and Planktothrix spp., respectively), although it may be possible that these ratios triggered the DPG change in this shift. A considerable increase in silicon was observed for Shift B when the DPGs changed from cyanobacteria to diatoms. Further studies on the accurate types and triggers of the regime shifts are necessary to better understand the interactions between ecosystem and water quality for this and similar lakes elsewhere. 相似文献
53.
《核技术(英文版)》2016,(4):50-59
A Monte Carlo method to study the response of portable detector to terrestrial gamma ray is proposed. This method is based on two-stage Monte Carlo simulation.First, the probability distributions of the phase space coordinates of the events that are most likely to be detected are reconstructed at the phase space shell level. The phase space shell is a closed surface enclosing the detector. The detector response to events originating from the phase space shell is then studied. The full absorption spectra as well as the partial absorption spectra are obtained for natural radionuclides uniformly distributed in the ground. For validation, this method is applied to a Hp Ge portable detector previously studied. The previous study is based on a semiempirical model. Good agreement is achieved when we compare the full-energy peak efficiencies and the total in situ spectra obtained by the two methods. As an application, the effective depth of the activity of the~(137) Cs artificial radionuclide in the soil is determined from the low-energy part of the total in situ spectrum. 相似文献
54.
《Optical Materials》2014,36(12):2480-2485
Recent study revealed that single crystal Ce:Gd3(Al,Ga)5O12 (Ce:GAGG) showed good scintillation response under γ-ray exposure. We discover here that ceramic Ce:GAGG scintillator exhibited better performance than the single crystal counterpart. We developed Ce 1% doped ceramic and single crystal GAGG scintillators with 1 mm thick and compared their properties. In radioluminescence spectra, they showed intense emission peaking at 530 nm due to Ce3+ 5d–4f transition. The 137Cs γ-ray induced light yields of ceramic and single crystal resulted 70 000 ph/MeV and 46 000 ph/MeV with primary decay times of 165 and 143 ns, respectively. At present, the observed light yield was the brightest in oxide scintillators. 相似文献
55.
钒自给能探测器(VSPND)输出电流信号的慢响应特性严重影响反应堆内中子通量的实时测量,不利于反应堆的控制和安全管理。采用反函数计算或各种补偿方法改进其响应特性,有利于VSPND的使用。本文研究了前向差分变换法、后向差分变换法、阶跃响应不变法及双线性变换法等4种数字处理算法,提出了两次处理的方法,有效缩短了VSPND输出信号的响应时间,时间常数由325.47 s减少到7 s以内,其中阶跃响应不变法算法的时间常数最小为5.2 s。设计了数字实验系统,验证了算法的正确性,为该探测器用于反应堆内中子通量测量的快速响应提供了可行性。 相似文献
56.
在投入运行的地铁项目中尽管按照现行的标准规范设置了火灾自动报警系统.但在系统设备选型、现场设备设置及电气火灾监测预防等方面尚存在一定问题.通过对现场出现的问题进行调研分析,并结合工程实践经验提出相应的解决对策。 相似文献
57.
58.
Chizuo Mori 《Journal of Nuclear Science and Technology》2013,50(9):891-897
Macro-autoradiographs of alpha emitters in environmental materials were obtained with solid-state nuclear track detector CR-39. This method is applicable only to alpha particles, and because their penetration ranges are very short, the obtained images are very clear. Since the method is simple and inexpensive, it can be used even at the high-school level. From the etch pit density obtained by microscopic observation, the radioactivity density of materials can be determined by using some theoretical calculations. 相似文献
59.
Sergey V. Polyakov 《Journal of Modern Optics》2013,60(9):1045-1052
We review radiometric techniques that take advantage of photon counting and stem from the quantum laws of nature. We present a brief history of metrological experiments and review the current state of experimental quantum radiometry. 相似文献
60.
O.V. Dudnik E.V. KurbatovV.A. Tarasov L.A. AndryushenkoA.Yu. Boyarintsev E. Valtonen 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2012,664(1):148-153
Response and noise properties of scintillation detectors were investigated using a 137Cs radioactive source. The experimental setup consisted of a scintillator, photodetector, amplifier, and spectrometric analog-to-digital converter. Small-sized, cubic crystals were manufactured of stilbene, p-terphenyl and thallium-doped cesium iodide, as well as of a plastic scintillator material based on polystyrene. Vacuum and solid-state photomultipliers and a silicon PIN photodiode were used as photodetectors. The energy equivalent noise was determined for all used photodetectors. The response of various scintillators when using vacuum and semiconductor photomultipliers was found to be closely similar. 相似文献