Friday, September 19, 2008

Opening the door to Hogwarts
[This is how I originally wrote my latest story for Nature’s online news. It is about another piece of creative thinking from this group at Shanghai Jiao Tong University. I was particularly struck by the milk-bottle effect that John Pendry told me about – I’d never thought about it before, but it’s actually quite a striking thing. (The same applies to water in a glass, but it’s more effective with milk.) John says that it is basically because, as one can show quite easily, no light ray can pass through the glass wall that does not also pass through some milk.

Incidentally, I have to suspect that John Pendry must be a candidate for some future Nobel for his work in this area, though probably not yet, as the committee would want to see metamaterials prove their worth. The same applies to Eli Yablonovitch and Sajeev John for their work on photonic crystals. Some really stimulating physics has come out of both of these ideas.

The photo, by the way, was Oliver Morton’s idea.]

Scientists show how to make a hidden portal

In a demonstration that the inventiveness of physicists is equal to anything fantasy writers can dream up, scientists in China have unveiled a blueprint for the hidden portal in King’s Cross railway station through which Harry Potter and his chums catch the train to Hogwarts.

Platform Nine and Three Quarters already exists at King’s Cross in London, but visitors attempting the Harry Potter manoeuvre of running at the wall and trusting to faith will be in for a rude shock.

Xudong Luo and colleagues at Shanghai Jiao Tong University have figured out what’s missing. In two preprints, they describe a method for concealing an entrance so that what looks like a blank wall actually contains invisible openings [1,2].

Physicist John Pendry of Imperial College in London, whose theoretical work laid the foundations of the trick, agrees that there is a whiff of wizardry about it all. “It’s just magic”, he says.

This is the latest stunt of metamaterials, which have already delivered invisibility cloaks [3] and other weird manipulations of light. Metamaterials are structures pieced together from ‘artificial atoms’, tiny electrical devices that allow the structure to interact with light in way that are impossible for ordinary substances.

Some metamaterials have a negative refractive index, meaning that they bend light the ‘wrong’ way. This means that an object within the metamaterial can appear to float above it. A metamaterial invisibility shield, meanwhile, bends light smoothly around an object at its centre, like water flowing around a rock in a river. The Shanghai group recently showed how the object can be revealed again with an anti-invisibility cloak [4].

Now they have worked out in theory how to hide a doorway. The trick is to create an object that, because of its unusual interactions with light, looks bigger than it really is. A pillar made of such stuff, placed in the middle of an opening in a wall, could appear to fill the gap completely, whereas in fact there are open spaces to each side.

Pendry and his coworker S. Anantha Ramakrishna demonstrated the basic principle in 2003, when they showed that a cylinder of metamaterial could act as a magnifying lens for an object inside it [5].

“When you look at a milk bottle, you don’t see the glass”, Pendry explains. Because of the way in which the milk scatters light, “the milk seems to go right to the edge of the bottle.” He and Ramakrishna showed that with a negative-refractive index metamaterial, an object in the bottle could be magnified on the surface.

And now Luo and colleagues have shown that an even more remarkable effect is possible: the milk can appear to be outside the bottle. “It’s like a three-dimensional projector”, says Pendry. “I call it a super-milk bottle.”

The Chinese team opt for the rather more prosaic term “superscatterer”. They show that such an object could be made from a metal core surrounded by a metamaterial with a negative refractive index [1].

The researchers have calculated how light interacts with a rectangular superscatterer placed in the middle of a wide opening in a wall, and find that, for the right choice of sizes and metamaterial properties, the light bounces back just as it does if there was no opening [2].

If someone passes through the concealed opening, they find, it becomes momentarily visible before disappearing again once they are on the other side.

So “platform nine and three-quarters is realizable”, the Shanghai team says. “This is terrific fun”, says Pendry. He feels that the effect is even more remarkable than the invisibility cloak, because it seems so counter-intuitive that an object can project itself into empty space.

But the calculations so far only show concealment for microwave radiation, not visible light. Pendry says that the problem in using visible-light metamaterials – which were reported last month [6,7] – is that currently they tend to absorb some light rather than scattering it all into the magnified image, making it hard to project the image a significant distance beyond the object’s surface. So openings hidden from the naked eye aren’t likely “until we get on top of these materials”, he says.


References
1. Yang, T. et al. http://arxiv.org/abs/0807.5038 (2008).
2. Luo, X. et al. http://arxiv.org/abs/0809.1823 (2008).
3. Schurig, D. et al., Science 314, 977-980 (2006).
4. Chen, H., Luo, X., Ma, H. & Chan, C. T. http://arxiv.org/abs/0807.4973 (2008).
5. Pendry, J. B. & Ramakrishna, S. A. J. Phys.: Condens. Matter 15, 6345-6364 (2003).
6. Valentine, J. et al., Nature doi:10.1038/nature07247 (2008).
7. J. Yao et al., Science 321, 930 (2008).

2 comments:

uhfdf said...

歐美a免費線上看,熊貓貼圖區,ec成人,聊天室080,aaa片免費看短片,dodo豆豆聊天室,一對一電話視訊聊天,自拍圖片集,走光露點,123456免費電影,本土自拍,美女裸體寫真,影片轉檔程式,成人視訊聊天,貼圖俱樂部,辣妹自拍影片,自拍電影免費下載,電話辣妹視訊,情色自拍貼圖,卡通做愛影片下載,日本辣妹自拍全裸,美女裸體模特兒,showlive影音聊天網,日本美女寫真,色情網,台灣自拍貼圖,情色貼圖貼片,百分百成人圖片 ,情色網站,a片網站,ukiss聊天室,卡通成人網,3級女星寫真,080 苗栗人聊天室,成人情色小說,免費成人片觀賞,

傑克論壇,維納斯成人用品,免費漫畫,內衣廣告美女,免費成人影城,a漫,國中女孩寫真自拍照片,ut男同志聊天室,女優,網友自拍,aa片免費看影片,玩美女人短片試看片,草莓論壇,kiss911貼圖片區,免費電影,免費成人,歐美 性感 美女 桌布,視訊交友高雄網,工藤靜香寫真集,金瓶梅免費影片,成人圖片 ,女明星裸體寫真,台灣處女貼圖貼片區,成人小遊戲,布蘭妮貼圖片區,美女視訊聊天,免費情色卡通短片,免費av18禁影片,小高聊天室,小老鼠論壇,免費a長片線上看,真愛love777聊天室,聊天ukiss,情色自拍貼圖,寵物女孩自拍網,免費a片下載,日本情色寫真,美女內衣秀,色情網,

liwo said...

av自拍,臺灣18歲成人免費,avon,正妹強力牆,免費線上成人影片,免費遊戲,a片貼圖,正妹圖片,3d美女圖,杜蕾斯免費a片,蓬萊仙山寫真集,a片網站,哈拉網路成人區,sex女優王國,性感美女,自拍密錄館,18禁卡通,爽翻天成人網,go2av,網拍模特兒應徵,台灣18成人,制服美女,小老鼠成人,成人光碟,金瓶影片交流區,85cc免費影城,成人交友,蓬萊仙山寫真集,無碼,正妹強力牆,嘟嘟情色網,影片轉檔程式,免費成人片觀賞,拓網交友,松島楓免費影片,色美眉部落格,18成人avooo,美腿論壇,辣媽辣妹,露點寫真,哈雷聊天室,18禁影片,看a片,美女工廠,影音城論壇,美女影片,免費遊戲,免費算,小魔女貼影片,a片貼圖,美腿褲襪高跟鞋,av女優王國,觀月雛乃影片,性感美女,

女優王國,免費無碼a片,0800a片區,免費線上遊戲,無名正妹牆,成人圖片,寫真美女,av1688影音娛樂網,dodo豆豆聊天室,網拍模特兒,成人文學,免費試看a片,a片免費看,成人情色小說,美腿絲襪,影片下載,美女a片,人體寫真模特兒,熊貓成人貼,kiss情色,美女遊戲區,104 貼圖區,線上看,aaa片免費看影片,天堂情色,躺伯虎聊天室,洪爺情色網,kiss情色網,貼影區,雄貓貼圖,080苗栗人聊天室,都都成人站,尋夢園聊天室,a片線上觀看,無碼影片,情慾自拍,免費成人片,影音城論壇,情色成人,最新免費線上遊戲,a383影音城,美腿,色情寫真,xxx383成人視訊,視訊交友90739,av女優影片,