Cast no shadows

Cast no shadows 抹去影子How to weave a cloak that makes you invisible 如何编织一件让你隐身的斗篷IN NORSE mythology,a magic cloak granted invisibility to Sigurd,a demi-god andskilled warrior with superhuman strength。Millennia later,a similar garmentbestowed invisibility on Harry Potter,a schoolboy wizard。In the mortal (orMuggle) realm,engineers have for years tried with varying degrees of successto build such a device。This week a team of physicists and materials scientistsannounced it had devised a pattern for a potentially perfect invisibility cloak。在挪威神话中,善战的具有超人能力的半神战士西格德曾被授予一件能让他隐身的魔法斗篷。一千年后,类似的服装赋予了还是男巫师学童哈利波特隐身的能力。在凡人（或麻瓜）的国度,工程师已花费数年终于成功做成这样的装置。本周一些物理学家和材料学家声称他们设计了一种可能让人完美隐身的斗篷。Light is an electromagnetic wave,with a longer wavelength than X-rays andultraviolet,and a shorter wavelength than infra-red,microwaves and radiowaves。All these electromagnetic waves are governed by four mathematical expressionsestablished almost 150 years ago by James Clerk Maxwell。These equationsrepresent one of the most elegant and concise ways to state the behaviour ofelectric and magnetic fields and how they interact with matter。However,because they are so concise,they also embody a high level of mathematicalsophistication。光是一种比X光和紫外线波长长,比红外线,微波和无线电波波长短的电磁波。大概一百五十年前,杰姆斯。克拉克。麦克斯维尔发现了描述所有这些电磁波关系的四条数学表达式。这些等式代表了一种最为优美和精确的阐述电,磁场行为的方式以及他们是如何相互影响彼此的。但是,因为他们过于精确,他们也体现了高度的数学复杂性。The team—Sir John Pendry of Imperial College London with David Schurig and DavidSmith of Duke University in North Carolina—used the equations to devise a wayto cloak an object with a material that would deflect the rays that would havestruck it,guide them around it and return them to their original trajectory。Maxwell's equations conserve certain properties—the magnetic field intensity,the electric displacement field and the Poynting vector that describes theelectric flux of an electromagnetic field。These properties remain the samewhen others are altered。The team showed how these fields could be manipulatedto flow around objects like a fluid,returning undisturbed to their originalpaths。The findings were published online this week by Science。一只由伦敦帝国学院的约翰。潘最先生和北卡罗里娜公爵大学的戴维德。希瑞格和戴维德。史密斯组成的团队用这些等式给设计了一种斗篷,其材料可以让本会射来的射线偏转,引导它们回到它们来时的轨道。麦克斯维尔的公式维持了一些特定属性--磁场强度,电位移,描述电磁场中电通量的坡印亭矢量。当其他属性被改变的时候,这些属性维持不变,团队揭示了这些场可被人为控制像流体一样围绕物体流动,不受干扰的话能回到原先的轨道。该发现已于这周由科学（杂志）网上发表。