Dental implants, what should be known before starting an in vitro study

Dental implant–abutment systems are used as anchors to support single or multi-unit prostheses for partially or fully edentulous patients. In vitro experiments and finite element analyses can be used to investigate their mechanical performance. Accurate information is needed on the geometry, material properties and friction coefficients of different implant-abutment components, on real loading conditions, and elastic properties of human jawbone. Information can be retrieved from previously reported studies or experiments. This paper provides a summary of a small but representative part hereof. Research has shown that the elastic properties of human jawbone are direction dependent and that the Young’s modulus (E) also depends on the bone type. Other studies investigated the maximum bite forces and reported a broad range of results, from 200 to 2000 N. Static experiments are typically performed with axial or bending loads to evaluate the performance of dental implant systems. Dynamic tests simulate chewing cycles and are used to evaluate the fatigue endurance. The supporting structure of the implant system should be representative for the bone structure. Finite element models are ideally suited to evaluate the biomechanical behaviour of implant systems. Accurate representation of the supporting bone and its interaction with the implant is crucial

A very brief description of LOFAR - the Low Frequency Array

LOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30-240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): 1) detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ~5' scale; 2) low-frequency surveys of the sky with of order $10^8$ expected new sources; 3) all-sky monitoring and detection of transient radio sources such as gamma-ray bursts, x-ray binaries, and exo-planets (Farrell et al. 2004); and 4) radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 10^21 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope.Comment: 2 pages, IAU GA 2006, Highlights of Astronomy, Volume 14, K.A. van der Hucht, e

Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function ðð¥with constraintsð ð 𥠥 ðandð´ð¥ = ð. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis