For years, scientists have labored to reproduce this feat（技艺）.

　　In 2013. they succeeded

　　A team of British and Czech scientists, led by Dr Tomas Cizmar. say

　　they have created a rea-life "tractor beam". like the kind from Star Trek . which uses a line of

　　light to attract objects. at least at a microscopic level

　　Light control techniques have existed since the l970s. but this is thought to be the first

　　time a beam has been used to draw objects towards a light source

　　Usually when microscopic

　　objects are hit by a line of light. they are forced along the direction of the beam

　　After many

　　years' research. Dr Cizmar's team discovered a technique that allows for the radiant force(辐射力) of light to be changed and to use the negative force to draw out certain particles（小颗粒）

　　Dr Cizmar says that even though it is a few years away from practical use. the technology　 has huge potential for medical research

　　In particular. the tractor beam is highly selective in　 the particles it can attract. so it can pick up particles that have specific characteristics. such as　 size or composition. in a mixture

　　"Eventually, this could be used to separate white blood　cells. for example," Dr Cizmar told BBC News

　　It has been a primary plot design in science fiction TV programs and movies to allow ob-

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