科学美国人60秒 SSS Knot Not Easy to Knot
时间：2018-12-24 作者：英语课 分类：2017年Scientific American(一)月
Of the many puzzles mathematicians 1 ponder, one is new ways to tie knots. "There are more than six billion different types of knots that have been tabulated 2 by mathematicians. Six billion." David Leigh, a chemist at the University of Manchester in the U.K.
The hard part, he says, is actually making them. "Just because I can see a knitted jumper doesn't mean I can actually make one." Because what Leigh and his colleagues are interested in, is tying molecular 3 knots—using strands 4 that are 10,000 times thinner than a human hair.
"With a molecule 5 you can't just grab hold of the ends and tie them like you would a shoelace. They're too small for that. Instead you've got to use chemistry to make the molecules 6 fold themselves round into the precise way you need to form the knot."
Continuing the shoelace analogy—remember when you were learning to tie your shoes, your mom or dad put a finger in the middle of the knot, to make it easier to tie? Leigh and his team did something similar, but used metal ions as the "fingers" to keep the knot tying organized. Then tiny molecular strands, just 192 atoms long, assembled themselves around the ions.
"And then mum pulls her finger out—we extract the metal ions out—and you're left with just the knot at the end." The most complex molecular knot ever synthesized. The study is in the journal Science. [Jonathan J. Danon et al., Braiding a molecular knot with eight crossings]
Knots were hugely useful to our ancestors in the stone age: "fishing nets, axes with blades tied to the handles, how to weave fabrics 7 to keep him warm." And Leigh says knots could be just as helpful in the molecular world—like for stronger braided polymers—maybe a better Kevlar.
After all, we do have six billion knots to choose from. "As every Boy Scout 8 knows, different types of knots have different characteristics that make them more or less suited to particular tasks." And yes, Leigh himself was once a Scout. "I found knots difficult to tie then, and it hasn't gotten easier as I've gotten older."
—Christopher Intagliata
[The above text is a transcript 9 of this podcast.]
- Do you suppose our mathematicians are unequal to that? 你以为我们的数学家做不到这一点吗？ 来自英汉文学
- Mathematicians can solve problems with two variables. 数学家们可以用两个变数来解决问题。 来自哲学部分
- Results for the test program haven't been tabulated. 试验的结果还没有制成表格。
- A large number of substances were investigated and the relevant properties tabulated. 已经研究了多种物质，并将有关性质列成了表。
- The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
- For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时，分子的碰撞就停止了。
- Twist a length of rope from strands of hemp. 用几股麻搓成了一段绳子。 来自《简明英汉词典》
- She laced strands into a braid. 她把几股线编织成一根穗带。 来自《简明英汉词典》
- A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈̬f婘̬ 妈̬成的。
- This gives us the structural formula of the molecule.这种方式给出了分子的结构式。
- The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
- Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。
- cotton fabrics and synthetics 棉织物与合成织物
- The fabrics are merchandised through a network of dealers. 通过经销网点销售纺织品。
- He was mistaken for an enemy scout and badly wounded.他被误认为是敌人的侦察兵，受了重伤。
- The scout made a stealthy approach to the enemy position.侦察兵偷偷地靠近敌军阵地。
- A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
- They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。