396 research outputs found

    A brief review on micro-implants and their use in orthodontics and dentofacial orthopaedics

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    The aim of this study was to review the literature and evaluate the failure rates and factors that affect the stability and success of temporary anchorage devices (TADs) used as orthodontic anchorage. Data was collected from electronic databases: MEDLINE database and Google Scholar. Four combinations of term were used as keywords: \u201cmicro-implant\u201d, \u201cmini-implant\u201d, \u201cmini-screw\u201d, and \u201corthodontics\u201d. The following selection criteria were used to select appropriate articles: articles on implants and screws used as orthodontic anchorage, published in English, with both prospective and retrospective clinical and experimental investigations. The search provided 209 abstracts about TADs used as anchorage. After reading and applying the selection criteria, 66 articles were included in the study. The data obtained were divided into two topics: which factors affected TAD success rate and to what degree and in how many articles they were quoted. Clinical factors were divided into three main groups: patient-related, implant related, and management-related factors. Although all articles included in this meta-analysis reported success rates of greater than 80 percent, the factors determining success rates were inconsistent between the studies analyzed and this made conclusions difficult

    Invisibility in billiards

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    The question of invisibility for bodies with mirror surface is studied in the framework of geometrical optics. We construct bodies that are invisible/have zero resistance in two mutually orthogonal directions, and prove that there do not exist bodies which are invisible/have zero resistance in all possible directions of incidence

    On the connection between the number of nodal domains on quantum graphs and the stability of graph partitions

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    Courant theorem provides an upper bound for the number of nodal domains of eigenfunctions of a wide class of Laplacian-type operators. In particular, it holds for generic eigenfunctions of quantum graph. The theorem stipulates that, after ordering the eigenvalues as a non decreasing sequence, the number of nodal domains Îœn\nu_n of the nn-th eigenfunction satisfies n≄Μnn\ge \nu_n. Here, we provide a new interpretation for the Courant nodal deficiency dn=n−Μnd_n = n-\nu_n in the case of quantum graphs. It equals the Morse index --- at a critical point --- of an energy functional on a suitably defined space of graph partitions. Thus, the nodal deficiency assumes a previously unknown and profound meaning --- it is the number of unstable directions in the vicinity of the critical point corresponding to the nn-th eigenfunction. To demonstrate this connection, the space of graph partitions and the energy functional are defined and the corresponding critical partitions are studied in detail.Comment: 22 pages, 6 figure

    Giant extracranial liposarcoma: Case report

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    Objective: Anaplastic liposarcoma of the head is an extremely rare entity. Seventy-seven cases of head and neck liposarcomas have been reported in the world literature since 1911. Radical surgery is the form of treatment advised.Clinical presentation: Authors report the case of a 62 years old female patient admitted in our institution for a giant extracranial tumor (122/88 mm), developed insidious over a period of 3 years and neglected. The patient agreed surgery only for the epicranial tumor. The lesion was completely removed. Postoperatory outcome was excellent concerning this tumor, although the histopathological result was not that great: high anaplastic liposarcoma.Conclusion: Liposarcoma of the scalp is rare. Diagnosis is made histologically. The histopathologic variant influences clinical behavior and prognosis. The treatment of choice is wide surgical excision.&nbsp

    Tomographie ultrasonore pour les arbres sur pied

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    Ultrasonic tomography on standing trees. Ultrasonic tomography was used for the detection of degradation of transversal section of a beech, attacked by white decay. The image reconstruction of the transversal section of the tree in 2D was obtained with a software, which used the values of ultrasonic velocities measured at different heights from the ground. The attacked wood is characterised by low velocities. The measurements were performed with special transducers of 1 MHz, without damaging the bark of the tree. To improve the readings of the signals, a frequency analysis was performed. The ultrasonic tomographies were compared with the corresponding photographic images and with data obtained with a “Resistograph”. A good agreement between ultrasonic tomographies and photographs was observed. The image resolution is between 4 and 5 cm. Presently, this is the best resolution ever obtained with an acoustic nondestructive method on a standing tree

    Phase field approach to optimal packing problems and related Cheeger clusters

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    In a fixed domain of RN\Bbb{R}^N we study the asymptotic behaviour of optimal clusters associated to α\alpha-Cheeger constants and natural energies like the sum or maximum: we prove that, as the parameter α\alpha converges to the "critical" value (N−1N)+\Big (\frac{N-1}{N}\Big ) _+, optimal Cheeger clusters converge to solutions of different packing problems for balls, depending on the energy under consideration. As well, we propose an efficient phase field approach based on a multiphase Gamma convergence result of Modica-Mortola type, in order to compute α\alpha-Cheeger constants, optimal clusters and, as a consequence of the asymptotic result, optimal packings. Numerical experiments are carried over in two and three space dimensions
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