Accurate total-energy calculations are used to study the structures and formation energies of oxygen chains as models for thermal double donors (TDD's) in Si. We find that the first three TDD's (TDD0-TDD2) consist of one four-member ring, with one or two adjacent interstitial O atoms. These metastable TDD's form bistable negative-U systems with the corresponding stable, electrically inactive st...

introduction: complicated crown- root fractures, extended caries and iatrogenic destruction often result in insufficient sound tooth structures and compromise the biologic width. two common options for re-establishing flap with osseous surgery. although some advantages are related to these two options, but coronal movement of gingival and alveolar bone in orthodontic extrusion, esthetic problem...

a considerable amount of energy is released in the form of shock wave from explosive charge detonation. shock wave energy is responsible for the creation of crushing and fracture zone around the blast hole. the rest of the shock wave energy is transferred to rock mass as ground vibration. ground vibration is conveyed to the adjacent structures by body and surface waves. geological structures li...

several lesions (inflammatory, neoplastic and congenital) can involve in the skull base. the role of imaging is to detect the location and extension of lesion, determine mass and mass like lesions, differentiate benign from malignant tumors, detect invasion to adjacent structures and make decision in surgical planning. skull base divides to anterior, middle and posterior cranial fossa and some ...

myoepithelioma is an uncommon benign neoplasm that most likely occurs in the parotid gland. extra-salivary myoepitheliomas are rare, with less than 10 cases reported in the sinonasal cavity. we present a rare case of benign myoepithelioma with recurrent behavior, abundant extensions to adjacent structures, and resistant to treat clinical course, which influenced the patient’s quality of life fo...