ABSTRACT
The electron scattering from periodic line defects on the surface of topological insulators with hexagonal warping effect is investigated theoretically by means of a transfer matrix method. The influence of surface line defects, acting as structural ripples on propagation of electrons are studied in two perpendicular directions due to the asymmetry of warped energy contour under momentum exchange. The transmission profiles and the details of resonant peaks which vary with the number of defects and the strength of their potentials are strongly dependent on the direction in which the line defects extend. At low energies, the quantum interference between the incident and reflected propagating electrons has the dominant contribution in transmission resonances, while at high energies the multiple scattering processes on the constant-energy contour also appear because of the strong warping effect. By increasing the spatial separation between the line defects, the minimum value of electrical conductance remains significantly high at low incident energies, while the minimum value may approach zero at high energies as the number of defects is increased. Our findings suggest that the potential ripples on the surface of topological insulators can be utilized to control the local electronic properties of these materials.
ABSTRACT
The influence of local magnetic moment formation around three kinds of vacancies on the electron conduction through metallic single-wall carbon nanotubes is studied by use of the Landauer formalism within the coherent regime. The method is based on the single-band tight-binding Hamiltonian, a surface Green function calculation, and the mean-field Hubbard model. The numerical results show that the electronic transport is spin polarized due to the localized magnetic moments and it is strongly dependent on the geometry of the vacancies. For all kinds of vacancies, by including the effects of local magnetic moments the electron scattering increases with respect to the nonmagnetic vacancies case and, hence, the current-voltage characteristic of the system changes. In addition, a high value for the electron spin polarization can be obtained by applying a suitable gate voltage.
ABSTRACT
INTRODUCTION: Position of medical devices has increased for last 30 years in otorhinolaryngology. Legal directive of use, main indications and perspectives are presented. RESULTS AND DISCUSSION: Biomaterials are medical devices planned for tissue reconstruction or substitution. The approval labelling are planned in Europe by the European Community certification (marquage CE) and overseen by a postmarket medical device safety (matériovigilance), that are completely independent from the Food and Drug Administration certification. Indications of biomaterials are likely competitive to those of autografts; their advantage is to limit the morbidity due to autograft harvesting. Benefits are aesthetics, functional or complementary. Main indications are presented in otology, rhinology, face traumatology, laryngology, anti-aging surgery, implants and epithesis. Research fields are scanned (increased therapeutic properties, drug delivery systems, tissue engineering...). CONCLUSION: Biomaterials are increasingly implanted in ENT surgery. The surgical success of their use require a strict legal label and well-defined indications.
Subject(s)
Biocompatible Materials , Bone Substitutes , Facial Bones/surgery , Maxilla/surgery , Otorhinolaryngologic Surgical Procedures/methods , Plastic Surgery Procedures/methods , Head , Humans , NeckABSTRACT
The purpose of this article is to report the clinical course and follow-up of a child with ectodermal dysplasia who was treated with implants surgery very early. Different possibilities for prosthetic restoration in the anodontic child are reviewed. Tolerance was excellent. Good cover of the implant was achieved at four years. We propose early implantation reconstruction surgery for these exceptional cases. A prospective multicentric study of this condition would be useful.
Subject(s)
Anodontia/rehabilitation , Dental Implants , Ectodermal Dysplasia/complications , Tooth, Deciduous/abnormalities , Child, Preschool , Dental Abutments , Denture Retention , Denture, Complete, Lower , Follow-Up Studies , Humans , MaleABSTRACT
MATERIAL AND METHODS: This series included 60 patients operated on between 1996 and 1998. Preoperative work-up included a x-ray study bone quality, preparation of the buccal cavity and assessment of the rhinosinus. We used the surgical technique described by Boynes and Tatum with modifications. The bone graft, mean 16 cm2 was fixed with a stud and clamp assemble or a long screw through the gingival crest, or with a microscrew on the lateral wall of the maxillary sinus. Minimal follow-up was two years. RESULTS: Mean age was 54 years (range 20-80). There were only two minor (hematoma) donor site problems. At the receiver site, there were 30 perforations of the mucosa that had no effect on the graft vitality. During the postoperative period, there were 2 hematomas that resolved spontaneously and 20 cases of dysesthesia in the V2 territory. Mid-term outcome (15 days to 6 months postoperatively) showed: 4 graft infections requiring removal in 3 cases and 6 partial resorptions requiring a new parietal bone graft in 3 cases. DISCUSSION: The iliac bone graft provided abundant cancellous tissue. The mid-term outcome was satisfactory although the postoperative problems resolved more slowly and were more painful than when harvesting a parietal graft. Mucosal perforations were frequent but reparable and did not increase postoperative morbidity. Infection was the most severe complication. Our incidence (3%) was slightly higher than reported in the literature. A possible explanation would be the mean height of the graft (18-20 mm) and the severity of the atrophies treated.
