Dr Hess envisages a ray of light travelling down an optical fibre made from two materials: a core with a negative refractive index and an outer sheath with a positive one.

赫斯博士构想出一个画面，即一道光正穿越于一个由两种材料制作的光导纤维，一种是具有正折射指数的纤维核，另一种则是具有正折射指数的外围。

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We were short of equipment, including laboratory materials and spare parts for X-ray machines.

我们缺乏设备，包括缺乏化验材料和X光机的零部件。

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There is also a lack of bed sheets, mattresses and other consumable medical equipment such as sterile kits for surgeries, stitching materials and X-ray films.

那里还缺乏被褥、床垫和其它诸如外科手术消毒包、缝合材料和X光片等其它消费性医疗用品。

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It is also important to make sure that operators of Explosive Detection Systems (EDS) and Trace Detection Systems (TDS) learn to identify specific X-ray transmission properties of the materials they are called upon to identify.

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"It's very desirable for cultural heritage conservation because with a lot of other techniques like X-ray or ultraviolet, there is some molecular breakdown in the materials, " Dr Jackson told the meeting.

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