问题 问答题 简答题

重离子束有哪些重要特点?

答案

参考答案:

重离子与X或γ射线及电子束等低LET辐射相比具有以下特点:传能线密度LET高,能在生物介质中产生高密度的电离和激发事件或能量沉积事件。在能量沉积过程中,其射程末端存在一个尖锐的能量损失峰,称为布拉格峰,在布拉格峰后剂量基本上趋于0,使剂量主要集中于组织的特定深度。

因此重离子与机体相互作用产生明显效应的区域是局部的和可选择的。相对生物效应RBE较大。氧增强比较小(OER),组织中含氧量对辐射效应影响较小,在应用方面能降低癌组织因缺氧引起的辐射抗拒问题。射程歧离与横向散射小。辐射敏感性不依赖细胞周期时相,对DNA损伤的可修复性较小。可利用重离子电性,在磁场诱导下三维扫描,利用正电子发射断层照相技术,实时在线监测。

阅读理解

There are many theories about the beginning of drama in ancient Greece. The one most widely accepted today is based on the assumption that drama came from ritual (宗教仪式). The argument for this view goes as follows. In the beginning, human beings viewed the natural forces of the world, even the seasonal changes, as unpredictable, and they sought through various means, to control these unknown and feared powers. Those measures which appeared to bring the desired results were then kept and repeated until they hardened into fixed rituals. Eventually stories arose which explained the mysteries of the rites. As time passed some rituals were abandoned, but the stories, later called myths (神话), coutinued to exist and provided material for art and drama.

Those who believe that drama came from ritual also argue that those rites contained the seed of theater because music, dance, masks, and costumes were almost always used. Furthermore, a suitable site had to be provided for performances and when the entire community did not participate, a clear division was usually made between the “acting area” and the “watching area.” In addition, there were performers, and, since considerable importance was attached to avoiding mistakes in performing, religious leaders usually undertook that task. Wearing masks and costumes, they often imitated other people, animals, or supernatural beings, and used gestures about the desired effect, success in hunt or battle, the coming rain, the revival (复活) of the Sun. Eventually such dramatic representations were separated from religious activities.

Another theory traces the theater’s origin from the human interest in storytelling. According to this view, tales about the hunt, war, or other feats are gradually added in detail, at first through imitation, action, and dialogue by a narrator and then through the assumption of each of the roles by a different person. A closely-related theory traces theater to those dances that are primarily rhythmical and gymnastic or that are imitations of animal movements and sounds.

小题1:What does the passage mainly discuss?

A.The origins of theater.

B.The role of ritual in modern dance.

C.The importance of storytelling.

D.The variety of early religious activities.小题2:What aspect of drama does the author discuss in the first parapraph?

A.The reason why drama is often unpredictable.

B.The seasons in which dramas were performed.

C.The connection between myths and dramatic plots.

D.The importance of costumes in early drama.小题3:Which of the following is NOT mentioned as a common element of theater and ritual?

A.Dance.

B.Costumes.

C.Music.

D.Magic.小题4:According to the passage, what is the main difference between ritual and drama?

A.Ritual uses music whereas drama does not.

B.Ritual is shorter than drama.

C.Ritual requires fewer performers than drama.

D.Ritual has a religious purpose and drama does not.

单项选择题