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发信人: sagayao (才子佳人(美国巴灵蹲大学计算机博士)), 信区: Biology
标 题: Re: [转载] 关于DNA的弹性---by space(供讨论)
发信站: Unknown Space - 未名空间 (Sun Oct 12 21:38:56 2003) WWW-POST
http://www.nytimes.com/2003/10/11/science/11DOCT.html
Doctor Disputes Winners of Nobel in Medicine
By NICHOLAS WADE
Published: October 11, 2003
n inventor who feels he was unfairly excluded has mounted an unusual and
vigorous protest against the award this year of the Nobel Prize in Medicine.
The inventor, Dr. Raymond V. Damadian, president of the Fonar Corporation in
Melville, N.Y., took a first step toward the development of M.R.I., or
magnetic resonance imaging, a now widespread medical technique for imaging the
body without the use of radiation. But the Nobel Prize in Medicine was given
this week to two others, Dr. Paul C. Lauterbur of the University of Illinois
and Sir Peter Mansfield of the University of Nottingham in England.
The Nobel Prize committee committed "a shameful wrong that must be righted,"
according to a full-page advertisement taken out in this newspaper yesterday
by the Fonar Corporation. A similar ad appeared earlier in The Washington
Post. Ads of this size in The New York Times generally cost around $100,000,
and in the Post about $80,000.
Dr. Damadian holds a basic patent on the technique, which was upheld by the
Supreme Court in 1997, and which the General Electric Company was ordered to
pay $129 million for infringing, Dr. Damadian said in an interview. He has
also received the National Medal of Technology and an award for inventors, the
Lemelson Prize from the Massachusetts Institute of Technology.
He said he would have been willing to share the prize but felt it was unfair
to have been excluded, especially because historians and textbook writers tend
to follow the Nobel committees' verdicts. "I have hoped for 30 years of my
life for some moment of vindication," Dr. Damadian said. "To wake up on Monday
morning and see that I had been written out of history is an agony I cannot
live with."
Dr. Hans Ringertz, the chairman of the Nobel Assembly at the Karolinska
Institute, which awards the prize established by Alfred Nobel's will, said the
Swedish assembly stood by its decision. "We have had world experts evaluating
this issue for years and this has been our final conclusion," Dr. Ringertz
said.
The issue has been the subject of a dispute between Dr. Damadian and Dr.
Lauterbur and has been known for years in academic circles, with some fearing
that the Nobel committee would steer clear of magnetic resonance imaging
altogether because of the Swedes' supposed distaste for controversial
discoveries.
Dr. Lauterbur, 74, is not in good health, and the committee may have decided
that its prize, which cannot be given posthumously, needed to be awarded for
the discovery now or never.
The prestigious awards are disputed with some regularity, notably when those
who have made acknowledged contributions to a discovery find their names are
not included in the three-winner maximum allowed by Nobel's will
The M.R.I. case is unusual because the omission of Dr. Damadian, when there
were only two winners, is seen by him and others as a pointed oversight. Also,
his contribution, though one in a series of advances required to make M.R.I.
machines a reality, has been widely acknowledged outside of the academic
community.
In the academic community, including the circles whose advice probably reached
the Nobel committee, some experts believe that the conceptual work required to
make the discovery a practical reality was undertaken by Dr. Lauterbur and
others, and that Dr. Damadian's contribution was less significant.
It is also the case that Dr. Damadian, who sees himself as an outsider, has
sometimes flouted the behavioral norms of the scientific community, as when he
held a news conference in 1977 at which he announced his new M.R.I. machine
could detect cancer anywhere in the human body. Even today, M.R.I. machines
are usually used to delineate cancers detected by other means.
It took a series of steps to make the machines practical. Essentially, Dr.
Damadian and his supporters, backed by the patent courts, view the first of
those steps, which he took, as being of critical importance, a view not shared
by the Nobel committee and many academic experts.
"If you could take a poll of the research community, they would come out very
seriously in agreement with the Nobel committee," said Dr. Charles Springer,
an M.R.I. expert at the Oregon Health and Science University.
Dr. Damadian "made an important observation that set people thinking about
moving N.M.R. to medicine," Dr. Springer said, referring to nuclear magnetic
resonance, the basic technique that underlies M.R.I. machines. Until 1970, the
technique had been used only by chemists and physicists.
Dr. Damadian's idea was to look at N.M.R. signals from excised lumps of tissue
to see if they were cancerous. But it was Dr. Lauterbur, Dr. Springer said,
who showed how to use the signal to generate an image of the body.
【 在 space (排骨教主) 的大作中提到: 】
: 【 在 space (排骨教主) 的大作中提到: 】
: : 【 在 space (排骨教主) 的大作中提到: 】
: : : 根据前面所说,当x接近L的时候,下述公式可以很好的在这个范围描述DNA的力学响
应:
: : : F=(k*T)/(2*b) * [1-(x/L)]^(-2),
: : : 当x接近L.
: : : 这个响应如何解释是个大问题. 其实也并不难. 解释这个响应导致的一个模型,叫
作
: : : DNA的蠕虫模型. 下面就来介绍这个模型. 由于涉及的数学细节太多, 所以主要介
绍
: : : 思想. 实际上这个思想应该是很广泛并且有典型意义的一种处理方法.
: : : 我们要处理的问题实际上是: 一根被拉扯的弹性线,在溶液中. 它的运动受受两方
面
: : : 的影响: 1. 热运动; 2. 外部的拉力.
: : : 可以想象拉力很小的时候, 热运动起决定作用, 这根线就可以用无规行走作良好描
述;
: : : 但是拉力比较大, 两端距离接近总长度的时候, 很显然拉力的作用扮演非常大的角
色.
: : : 这时候的力学相应一定是热运动和拉力竞争的结果. 实际上很直观可以想见, 我们
: : : 需要无穷大的力才可能把把线完全拉直, 彻底杜绝热振动. 就跟你在一根绳子之间
: : : 挂个重物,然后打算把线拉直是一个道理.
: : : 如果把这根线看成是个总长不可拉伸的, 具有弯曲弹性的线, 建立相应的统计物理
: : : 学描述,就是所谓的 worm-like chain. 偶这个定义可能不准确, 但是也差不远.下
: : : 面进行具体说明.
: : 进行统计物理学描述,就是考虑系统能量和热运动影响之间的关系. 比如说在这里,这
根
: : 线的不同构型就对应了不同(弯曲)能量. 很显然,如果没有热运动,这样一根棒自由的
情
: : 况,应该是直的,可以定义这时候的能量为零. 在溶液中, 受热运动影响, 它不可能是
直
: : 的, 那是因为环境中的微观颗粒随机碰撞这个链, 使它的形状偏离直线, 它的弹性能
因此
: : 升高(升高的能量来自外不碰撞它的颗粒作的功). 很显然这根线在溶液中就有各种可
能
: : 的形状. 每种形状的构型出现的几率不同. 如果形状对应的能量高, 就说明需要外部
: : 作功大,因此出现的几率就小. 出现某种能量的构型的几率大家都是知道的,
由Boltzmann
: : 分布描述:
: : P(E)=Z*EXP[-E/(K*T)]
: : E是能量, K是Boltzmann常数, T是环境温度, Z是归一化常数.
: : 前面说了, worm-like chain模型里面, 线的能量只考虑弯曲弹性能. 一根线段可以
看作
: : 是无穷多小园弧相连而成. 没个园弧都有个曲率半径(就是圆半径). 这个曲率半径
: : 的倒数就是曲线的曲率. 很显然直线的曲率为零. 什么地方弯曲越厉害,这曲率就越
大.
: : 线段的完全弹性能量最后就是曲率平方的积分:
: : E=(1/2)*A*(K*T)*Integrate[C(s)^2,(s,0,L)]
: : 其中C(s)是曲线的曲率.s是曲线的弧长参数;A是个弹性刚度常数,具有长度量纲,
: : 经常称为: persistence length".对DNA来说, A大概是50(nm).
:
: 下面就是数学处理了:
:
: 就统计物理来说, 只要知道这根线的能量分布,一切事情都已经定下来了. 困难经常来
自
: 数学. 我们这里完全的能量表述,除了上面的弹性弯曲能量外,还有拉力作的功.所以最
后
: 的能量是:
:
: E=(1/2)*A*(KT)*Integrate[C(s)^2,(s,0,L)]-F.(R(L)-R(0))
:
: F是(矢量)外力, R(L)是末端(矢量)位置,R(0)是头端位置.(.)表示矢量的内积.
:
: -F.(R(L)-R(0))就是外力作的功了.
:
: 对上面这个能量作统计物理学计算是非常困难的.但是对于我们要讨论的情况(X/L约等
于
: 1), 曲线的弯曲波动不会大: 虽然它不可能是完全直的, 但是也不可能非常弯.也就是
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