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A classification method for double-walled carbon nanotubes is proposed taking account of the geometric constraints. The different possibilities of interlayer interactions are examined.

A band structure model for carbon nanotubes taking into account the deformation potential characterizing the conformal mapping of graphene to tubules is presented and overlap is introduced in the π band calculations. This model corresponds to the study of a one-dimensional (1D) system and is not simply the limit of a 2D system becoming quasi-1D. While development is explicitly made for the zigzag tubules, the method itself can also be applied to the armchair and chiral configurations by modifying the structure factor and boundary conditions.

Summary An unusual case of upper gastrointestional hemorrhage caused by gallstone impaction in the duodenal bulb (Bouveret's syndrome) is reported. Endoscopy was used to make the diagnosis rapidly and surgery was performed to provide definitive treatment. Bouveret's syndrome must be kept in mind as a rare cause of upper gastrointestinal hemorrhage.

We present nine patients (five men and four women) who underwent surgical excision of clinically significant heterotopic ossification at the elbow. They also received perioperative radiation therapy using total doses between 600 and 1000 cGy. Five received fractionated radiotherapy, with two fractions of 500 cGy applied on the first two postoperative days, and the remaining four were irradiated with single doses of 600 and 700 cGy.After a mean period of observation of 7.7 months (6 to 13) none had radiological recurrence of heterotopic ossification and eight showed clinical improvement. Assessment of the functional outcome showed a mean improvement in the Morrey score from 33.3 to 84.5 points indicating a high therapeutic efficacy of prophylactic irradiation.