New Worlds: Crystal, heal thyself! [pg. 7]

May 14, 2006 07:43
4 minute read.


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We thought that only living cells and tissues can heal themselves. But researchers at the Technion Institute in Haifa have demonstrated how a photonic quasicrystal heals itself using interactions with light. The researchers, whose article was published in Nature, have created a nonlinear photonic quasi-crystal that responds to light in a dynamic fashion. They deliberately introduced a defect into the crystal and then observed in real time how the crystal heals itself by dynamically interacting with light. The research was conducted by doctoral student Barak Freedman, under the supervision of Prof. Mordechai Segev of the physics department. The other authors are Guy Bartal ( also Segev's PhD student); Jason Fleischer (formerly a postdoctoral fellow with Segev's group and currently a professor at Princeton); Prof. Demetri Christodoulides of the University of Central Florida; and Tel Aviv University Prof. Ron Lifshitz. Alongside this paper by Segev and his associates, Nature published a piece (in the section called "Quantified: Israel") on Segev's lab and the research atmosphere there. "An ordinary periodic crystal consists of a single repeating unit, with which you can fill space periodically, like the square tiles in your bathroom floor," the researchers explain. "But nature has found other ways to fill space, usually with more than a single repeating unit, which are still perfectly ordered but not periodic. These structures are called quasi-crystals (short for "Equasiperiodic crystals"), and they possess some unique and remarkable physical properties. Quasi-crystals were discovered in 1982 by another Technion staffer, Prof. Dan Shechtman, of the materials engineering department, whose discovery that crystals need not be periodic triggered a scientific revolution. Shechtman, who was working in the NBS labs in Maryland when he made his discovery, was ignored for some time by his NBS colleagues. He was even told that his work had "shamed" his team, and was asked to transfer to another. But he was fully vindicated when they admitted their unfair assessment. Light waves passing through the new dynamic ("nonlinear") photonic quasi-crystal created by the Technion team behave just like electrons and atoms do in the material (atomic) quasi-crystals discovered by Shechtman; the quasi-crystal created by the Technion researchers changes its optical properties while light passes through it. That is, the light passing through this quasi-crystal causes a change in its properties, which in return changes the light beam. This process repeats itself dynamically. The important difference between the dynamic photonic quasi-crystal and material quasi-crystals is that, unlike electrons and atoms, the light beams can be observed individually in real time, as in the defect-healing experiment. Thus, the new photonic quasi-crystal allows the Technion researchers to study quasi-periodic order in ways that were impossible before. E-MAIL AND INFO MOST POPULAR WEB USES Seventy-one percent of Israelis have a computer at home, and 60% are online at home, most of them via a broadband connection. These were some of the statistics revealed by the latest half-year survey conducted for Tel Aviv University's Netvision Institute for Internet Research (whose professional director is Eli Hacohen). Of all those connected to the Internet, 22% use it at least four times a day, while 39% used it once to three times a day (moderate users) and the rest were light users, going into the Web or e-mail less than daily. The share of moderate users rose from the last survey (from 23%), while that of heavy users declined from 28%. The most popular use of the Internet is for information searches (69%, compared to 59% in the previous survey) and e-mail, and there was a slight rise in the share of those using it for news. Listening to radio, watching TV or reading blogs were the least popular uses, according to the poll of 5,009 adults who were a representative sample of Israelis (4.5% sampling error) taken by the Smith Polling Institute. Only 6% go into the Internet via slow dialup, with the rest using ADSL or cables. Among adults over 50, 44% say they have no computer at home; the figure was 42% among haredim and other religious Jews, 63% of people with a low educational level and 45% of those with a low income. Twenty-three percent of haredim and other religious Jews said they had a computer at home but were not connected to the Internet. In the general population, 10% who have a computer and are connected to the Internet said they do not "surf" it. BIU TO HIRE 24 MORE SCIENTISTS

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