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通过对γ射线暴能源机制研究，讨论了宇宙学距离处γ射线暴的能量来自奇异星相变的可能性，认识了奇异星模型的独特优势．火球模型被认为是γ暴的标准模型，而火球产生的机制是多方面的，其中之一就是奇异星相变，它既解释了γ暴的短时标、高能量特征，又避免了火球的重子污染这一最大难题。 相似文献
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随着X荧光检测方法的广泛应用,作为核心的探测器性能显得尤其重要。国内研制的Si(Li)X射线探测器,部分性能指标达到并超过了国外水平,为我国X荧光仪整体性能的提升,打下了良好基础。另外,碲锌镉(CZT)晶体作为一种新型半导体材料,由于原子序数高、禁带宽、密度大,制成低能γ射线和X射线探测器不需液氮冷却就能得到相当好的能量分辨率,且有相当高的探测效率。因此近年来发展迅速。我们实验室已制成Φ8×1.7mm3灵敏体积的CZT探测器,室温22℃下对241Am放射源、59.54keV能量的γ射线能量分辨率可以达到/2.06keV(FWHM)(未使用准直器),连续测量没有极化效应,并且具有很好的长期稳定性。 相似文献
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γ射线通过物质时,会在一次碰撞中整个地丢失能量．这与带电粒子通过逐次碰撞丢失能量的方式是不同的．在物质中它主要发生3种效应：（1）光电效应．光子把它的全部能量交给孩外束缚电子,使之脱离原子而成为光电子．它主要发生在γ射线能量低、吸收物质原子序数Z高的情况下．（2）康普顿效应．光子被原子中的束缚电子或自由电子所散射,其飞行方向发生偏转,同时电子受到反冲．这是一种非相干散射,主要发生在中能γ射线能量（几个MeV）的范围．（3）电子偶效应．能量大于2mec2的光子在原子核或电子的库仑场中会产生电子一正电子对γ→e… 相似文献
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《课堂内外(高中版)》2013,(9):61
金子常被看作财富象征。马克思说:"货币天然是金银。"那么,金子来自哪里?美国研究人员说,地球上所有金子可能都是中子星碰撞爆炸的产物。金子不仅在地球上罕见,在宇宙中同样罕见。科学家此前已知道,恒星内部的聚变反应可产生碳与氧等轻元素,却无法产生金这样的重元素。美国研究人员的一项天文观测则揭开了金子这一重元素的身世。中子星是巨大恒星发生超新星爆发后留下的密度超大核心,两颗中子星的碰撞会产生伽马射线暴。美国哈佛·史密森天体物理学中心研究人员说,2013年6月,他们借助美国航天局SWIFT卫星,观测到一次伽 相似文献
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李帮军 《中国现代教育装备》2007,(10):104-105
γ射线与物质原子相互作用时,发生一次相互作用就导致损失其大部分或全部能量(大能量转移),光子不是完全消失就是大角度散射。γ射线穿过物质时强度按指数规律衰减,没有射程概念。在此研究的主要是窄束γ射线在物质中的吸收规律。研究并测定某一能量γ光子在不同材料物质中的吸收系数。 相似文献
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《中国科教创新导刊》1997,(10)
哥伦比亚大学首次测量了中子星的质量借助于爱因斯坦的广义相对论，哥伦比亚大学的天体物理学家研究组通过测量中子星正在闪烁的Ｘ射线，第一次测出中子星的质量。正如广义相对论所预言的，此结果首次证实了在致密星附近有不稳定轨道存在。此前其他研究者测过中子星的质量... 相似文献
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陈砥柱 《中学物理教学参考》1994,(3)
某省1992年高中毕业生复习统一测试题中有这样一道题: 下列说法中,哪一些是正确的? A.放射性元素存放射α、β、γ射线时,不可能独立地只放出其中一种射线; B.玻尔理论成功地解释了原子光谱规律; C.核子结合成原子核时必须吸收能量; D.可见光和γ射线都是原子从高能级跃迁到低能级时放出的光子所形成的电磁波. 显然,所给的四个答棠中,B、C、D均不正确,就只 相似文献
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戴子高:1993年6月获南京大学理学博士学位,现为南京大学天文系教授、博士生导师、中国天文学会副理事长。主要研究理论天体物理和高能天体物理,包括伽玛射线暴、中子星物理、脉冲星辐射和超新星爆发机制等。1998年获国家杰出青年科学基金,2002年被聘为“长江学者奖励计划”特聘教授,2004年获江苏省五一劳动奖章和第八届中国青年科技奖。 相似文献
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Li Ju Chen 《欧洲特需教育杂志》2019,34(1):1-19
This research identified the potential special education transition development trajectories by tracing the priorities and hierarchical structure of published transition issues in special education. Social network analysis (SNA) of the 1900–2015 data from the Web of Science (WOS) database achieves a transition exploration flow by citation-based main path analysis (MPA). The first main finding was that 517 papers were published relating to special education transition over the past 60 years. Special education transition literature emerged in 1957, was systematically explored after 1987, and grew rapidly in the 1990s. The second main finding was that the trajectories contained various topics that can be broken down into two mainstream fields: curriculum and employment. The third main finding was that there are five sub-branches of the mainstream fields: legislation; team working; accountability; individualised transition programmes (ITP); and self-determination. This research is the first to use MPA techniques in SNA for special education transition. The findings indicate that more foci deserve to be explored to attain the transition working exhaustively and smooth transitions between each career stage for individuals with disabilities. 相似文献
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本文采用微分方程的李群方法，研究了外噪声影响下的Ｓｃｈｌｏｇｌ二级相变模型对应的Ｆ－Ｐ几率密度Ｐ（ｘ，ｔ）的严格表达式；讨论了最可几值ｘ随时间的变化。在时间ｔ→∞时，给出了几率密度的定态解Ｐｓｔ（ｘ）以及此时的最可几值ｘ与确定性描述的区别。 相似文献
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本文采用微分方程的李群方法,求解了外噪声影响下的非平衡二级相变模型对应的F—P方程,得出含时概率密度P（x.t）的严格表达式,讨论了最概然值x随时间的变化。在时间t→∞时,给出概率的定态解Pst(x)以及此时的最概然值;得出了它与确定性描述的差别。 相似文献
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孙建新 《雁北师范学院学报》2011,27(2)
对中子星状态方程作了简介,对核物质能量密度的计算的近似方法作了说明。以此为基础,研究了相互能对总能量的贡献,把相互能引入计算中,得到中子星质量、半径及密度的关系。 相似文献
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Charlotte L. Bagnall Claire L. Fox Yvonne Skipper 《Journal of Research in Special Educational Needs》2021,21(2):156-167
Primary–secondary school transition encompasses multiple social, academic and environmental changes which can negatively impact children’s emotional well-being. Children with Social, Emotional and Mental Health difficulties (SEMH) are believed to be especially vulnerable during this time. However, the voices of children with SEMH are heavily underrepresented in this field within practice and research. The present case study examined how children with SEMH difficulties within one special school experience primary–secondary school transition and how they are supported, in order to make recommendations to improve this period. The case study was qualitative and longitudinal, conducted over 18-months and methodologies included ethnographic observations, child photo-elicitation focus groups (with 11 Year 6 children) and three adult interviews. Findings demonstrated that over primary–secondary school transition children with SEMH difficulties (a) negotiate significant structural changes in support (often unanticipated) and (b) need to feel a sense of safety and belonging. To manage this effectively, transition provision for children with SEMH difficulties needs to consider their short-term emotional well-being whilst still in primary school, in addition to their long-term well-being looking ahead to secondary school. Greater collaboration and communication across schools and stakeholders can help ensure children receive continuity in standards and support. 相似文献
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Boron-doped diamond (BDD) film electrodes using Ta as substrates were employed for anodic oxidation of salicylic acid (SA). The effects of operational variables including initial concentration,current density,temperature and pH were examined. The results showed that BDD films deposited on the Ta substrates had high electrocatalytic activity for SA degradation. There was little effect of pH on SA degradation. The current efficiency (CE) was found to be dependent mainly on the initial SA concentration,current density and temperature. Chemical oxygen demand (COD) was reduced from 830 mg/L to 42 mg/L under a current density of 200 A/m2 at 30 °C. 相似文献
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ZHANG Juan CHEN Xue-ming YAO Pei-dong CHEN Guo-hua 《浙江大学学报(A卷英文版)》2007,8(9):1457-1461
Boron-doped diamond （BDD） film electrodes using Ta as substrates were employed for anodic oxidation of salicylic acid （SA）. The effects of operational variables including initial concentration, current density, temperature and pH were examined. The results showed that BDD films deposited on the Ta substrates had high electrocatalytic activity for SA degradation. There was little effect ofpH on SA degradation. The current efficiency （CE） ,aas fbund to be dependent mainly on the initial SA concentration, current density and temperature. Chemical oxygen demand （COD） was reduced from 830 mg/L to 42 mg/L under a current density of200A/m^2 at 30℃. 相似文献
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Inhibitory effects of jujuboside A on EEG and hippocampal glutamate in hyperactive rat 总被引：3，自引：0，他引：3
Lu YJ Zhou J Zhang SM Zhang HY Zheng XX 《Journal of Zhejiang University. Science. B》2005,6(4):265-271
In this study, the inhibitory effect ofjujuboside A (JuA) on a penicillin sodium (Na-PCN) induced hyperactivity model was investigated. Cortical EEG (electroencephalogram) and the concentration of hippocampal Glutamate (Glu) were monitored simultaneously in vivo as indicators of rat's excitatory state. Power spectral density (PSD) and gravity frequency of PSD were calculated. JuA (0.05 g/L and 0.1 g/L) inhibited the EEG excitation effect caused by Na-PCN by increasing the power of δ1 and δ2bands (P＜0.01 vs model) and lowering the gravity frequency of PSD (P＜0.01 vs model). JuA also remarkably reduced the Glu elevation induced by Na-PCN (P＜0.05 vs model). Diazepam also depressed Glu concentration and lowered the gravity frequency,but it showed a different EEG pattern in increased β2-activity (P＜0.01 vs model). EEG excitation caused by Na-PCN correlated with Glu elevation during the first hour. Neurophysiological inhibitory effects of JuA and diazepam were more persistent than their Glu inhibitoty effects. 相似文献
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余剑 《柳州职业技术学院学报》2007,7(3):78-82
文主要介绍了基于IDEA(Internation Data Encryption Algorithm)加密方法的网络中一种密钥分配方案。它将整个网络系统中的密钥不会以明文的形式出现进行传送,而是以被高级密钥加密的形式传输和保存。从而较好的提供了一种安全稳定的密钥管理方案。 相似文献
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为了拓展渐变槽线天线的工作频带,提出一种采用共面波导新型馈电结构的双面印刷对跖型渐变槽线天线.基于对渐变槽线天线之宽频带特性受限于现有馈电方式的分析,改用蚀刻于背板的共面波导至双面印刷对跖渐变槽线的行波式转接.其仿真和实验结果一致表明:该馈电方式使天线的阻抗具有高通频响特性,且保持较好的辐射方向性图,在3 GHz以上的... 相似文献