15MV电子加速器机头感生放射性的Monte Carlo计算

加速器停机后的感生放射性是工作人员所受内外照射的首要来源。Monte Carlo模拟计算是进行感生放射性预测分析的重要方法之一。该文应用Monte Carlo软件FLUKA对同方威视技术股份有限公司一台15MV电子加速器的机头屏蔽结构进行了模拟。给出了2个测点的吸收剂量率和周围剂量当量率随冷却时间的变化曲线及其与实验测量结果的对比,并给出了各个区域放射性核素产额随时间的变化。模拟计算与实验测量的结果在量级和衰减趋势上吻合。该文提供了一种通过Monte Carlo模拟预测感生放射性问题的方法,也可应用于其他高能粒子加速器的活化分析。     

利用MONTE CARLO方法分析高能电子加速器中中子引起的感生放射性——微观分析

在高能电子加速器中,高能电子与物质相互作用产生电磁簇射,生成的高能光子与 介质发生光核反应,其后的中子、介子又引发核反应,并引发感生辐射场.本系列文章利用 Monte Carlo方法分析了高能电子加速器中中子引起的感生放射性以及对加速器周围环境的 影响,对于制定关于停机后等待时间的规定具有指导性意义.在微观上利用多步动力学模型 （Many Stage Dynamical Model,MSDM）计算了中子与不同靶材Fe、Cu、Ni的辐射损伤总截 面,然后计算了能量为10、140和700 MeV的中子与加速器相互作用所产生的放射性同位素的 分布及生成截面,并且对3种情况进行了比较和分析.     

医用电子加速器中的光中子产额计算

计算了电子加速器中不同能量的电子垂直入射到钨靶和金靶上时的光中子产额。采用 Monte Carlo 程序EGS4对电子光子簇在靶中的输运进行模拟 ,计算出光子在靶中的径迹长度 ,从而求出光中子产额。对电子加速器钨靶和金靶中的光中子产额进行了计算 ,得到了电子加速器中光中子产额随打靶电子能量变化的规律及随靶厚度变化的规律 ,为加速器靶和屏蔽系统的设计提供依据 ,并为计算光中子的剂量分布和复合靶中的光中子产额奠定基础     

低能电子加速器的感生放射性

运行在１０ＭｅＶ能量以上的放射治疗和工业辐照用的电子加速器，均可能产生感生放射性，其强度取决于加速电子能量，束功率和被照材料的类型。电子能量在阈能或近似于２５ＭｅＶ之间，中子基本上产生于“巨光核共振”。医用加速器的Ｘ射线靶，固定和可变准直辐照容器等也是感生放射性的主要来源。     

Monte Carlo方法在靶尺寸分析中的应用

对于电子直线加速器而言,当电子束的能量一定时,X射线的剂量场分布与很多因素相关,其中靶的尺寸和材料便是重要的因素。目前最经常采用的靶材料是钨,靶尺寸的选取则由加速器的能量等条件来决定。该文采用Monte Carlo通用程序包Geant4,对靶的尺寸进行了一系列的分析。结果表明:靶厚度对X射线剂量场分布影响很大,为得到理想的加速器输出剂量,需要选取合适的靶厚度;相对而言,靶直径的影响则很小。     

医用加速器场所中子和感生γ光子剂量当量的计算分析

医用高能加速器在广泛应用的同时,也存在着相关的辐射屏蔽问题,特别是迷宫内剂量的快速估算。该文对当前典型的迷宫内中子及感生γ光子剂量当量的计算方法进行了汇总,将其应用于多折迷宫的计算案例中,并与基于MCNP(Monte Carlo N-particle transport code)的Monte Carlo模拟值进行对比。结果表明:这些计算方法基本能够较为精确的估算迷道内不同点的中子和感生γ光子剂量当量,与Monte Carlo模拟值的偏差在1个数量级以内,但可能会低于模拟值。在实际应用中,可通过乘以安全系数以防止剂量低估。     

高能X射线整车原木辐照检疫中的感生放射性

利用加速器产生的高能电子束或者高能X射线进行原木辐照处理过程中,原木和车厢有可能会产生感生放射性,从而可能会对工作人员或后续的消费者带来不必要的辐射照射风险。采用Monte Carlo方法,使用FLUKA程序结合解析经验公式,以25 MeV和35 MeV高能X射线装置为例,建立了高能X射线整车原木辐照检疫中的感生放射性计算模型,并比较了16、20、25、35MeV的辐照装置可能产生的感生放射性核素的剂量率。结果表明:由于木材的感生放射性核素多为短寿命核素,故不需要考虑原木被辐照后的感生放射性的影响;但只有16MeV辐照装置能够满足工作人员每年20 mSv的剂量限值要求,因此需要对车厢经过辐照后对工作人员的长期辐照进行防护。     

质疑爱因斯坦力学和传统加速器理论的三个实验

用直线加速器精出的高速电子轰击铅靶,浏量铅靶的温升.用直线加速器输出的高速电子垂直封入均匀磁场,测量电子受洛伦茨力偏转而作圆周运动的半径.实验结果不符合爱因斯坦的质速会式和动能公式,而且表明被加速的电子没有获得加速器的全部工作能量.显然,爱因斯坦力学和传统的加速器理论都是可疑的.作者还做了电子在均匀电场内加速的实验,测量了电子获得的速度,并按照爱因斯坦力学计算了电子获得的动能,这个动能竟然大于加速器的工作能量,从而再次证明爱因斯坦力学可疑.     

用极限分析方法计算边坡可靠度上限值

为了减小边坡可靠度计算在模型建立、参数估计和算法选取上的误差,建立了基于极限分析上限定理的边坡可靠度分析模型,采用最大熵原理推断边坡结构参数的统计特征,并采用Monte Carlo模拟法计算边坡的结构可靠度上限值。最后将结果与其他方法进行了比较。研究结果表明：利用最大熵原理、Monte Carlo模拟法和基于上限定理的边坡可靠度分析模型所计算的可靠度值是边坡可靠度的一个严格上限值,该模型与极限平衡法模型、R.Jimenez-Rodriguez等模型计算的结果比较接近。     

挑战传统电磁加速理论和爱因斯坦力学的两个实验

用直线加速器输出的高速电子轰击铅靶,测量铅靶的温升.用直线加速器输出的高速电子垂直射入均匀磁场,测量电子受洛伦兹力偏转而作圆周运动的半径.两个实验都证明:(1)加速器的效率随着电子速度增加而急剧下降,电子的实际速度远低于按传统的电磁加速理论和爱因斯坦力学计算的理论速度.(2)实验结果不符合爱因斯坦力学的质速公式和动能公式,而与光速可变的新相对论力学的质速公式和动能公式高度相符.(3)电子偏转实验还证明洛伦兹力与电子速度之间不是线性关系.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that