The aim of our study was to describe an effective technique for mastoid cavity obliteration in canal wall down tympanomastoidectomy for chronic otitis media and to review its efficacy in producing a ...dry, low-maintenance, small mastoid cavity.
A retrospective clinical study of 56 consecutive patients undergoing procedures for active chronic otitis media with cholesteatoma has been carried out. All surgical interventions involved partial mastoid obliteration and restoration of the middle ear space by use of cartilage reconstruction of the tympanic membrane. Ossicular reconstruction was achieved with either a partial or total ossicular replacement prosthesis.
A completely dry cavity was achieved in 49 of 56 patients (approx. 88%, 95% confidence interval 77-95%). An overall statistically significant improvement in hearing (p < 0.05) was obtained, with the mean pure-tone average air-bone gap decreasing from 33.4 ± 8.2 dB (average ± SD) to 18.3 ± 9.7 dB. There were no residual or recurrent cholesteatomas.
Cartilage reconstruction of the tympanic membrane proved to be a useful adjunct in the surgical management of the chronically draining cavity.
This article aims to provide an interactive in-house tool to quickly asses the stress in the critical points of the aeronautical structures. The software compares the results between the stress ...values obtained from the experimental tests using the resistive electrical tensometry technique (RET) and the stress values calculated with FEM software. RET refers to the stress and strains measured by strain gauges applied to the critical points of the structures. The finite element analysis was carriedout with MSC. PATRAN/ NASTRAN using shell and solid elements in order to identify the critical points based on the stress and strain results. The validation of the results obtained by the finite element modelling has been made experimentally using the resistive electrical tensometry method. The results from these two methods have been compared with the in-house software developed in Visual Basic with Excel interface. The program evaluates the relative error between the experimental and calculated data at critical points.
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Thermal barrier coatings (TBC) are designed to protect metal surfaces from extreme temperatures and improve their resistance to oxidation during service. Currently, the most commonly used systems are ...those that have the TBC structure bond coat (BC) / top coat (TC) layers. The top coat layer is a ceramic layer. Oxidation tests are designed to identify the dynamics of the thermally oxide layer (TGO) growth at the interface of bond coat / top coat layers, delamination mechanism and the TBC structural changes induced by thermal conditions. This paper is a short study on the evolution of aluminum oxide protective layer along with prolonged exposure to the testing temperature. There have been tested rectangular specimens of metal super alloy with four surfaces coated with a duplex thermal barrier coating system. The specimens were microscopically and EDAX analyzed before and after the tests. In order to determine the oxide type, the samples were analyzed using X-ray diffraction. The results of the investigation are encouraging for future studies. The results show a direct relationship between the development of the oxide layer and long exposure to the test temperature. Future research will focus on changing the testing temperature to compare the results.
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The article presents a mathematical modeling of aileron actuation that uses piezo V-shaped stacks. The aim of the actuation is the increasing of flutter speed in the context of a control law, in ...order to widen the flight envelope. In this way the main advantage of such a piezo actuator, the bandwidth is exploited. The mathematical model is obtained based on free body diagrams, and the numerical simulations allow a preliminary sizing of the actuator.
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Random vibrations occur during the launch at the fastening interface between thruster brackets and basic support of satellite. These are generated in the launcher by the motion of some mechanical ...parts, combustion phenomena or structural elements excited by the acoustic environment. The goal of this comparative study is to find a simplified and efficient validation method using FEM PATRAN-NASTRAN software for thruster brackets in the random vibrations environment for space applications. The random vibration analysis requests complex pre/ post processing efforts and large hardware resources for various geometrical shapes. The PATRAN-NASTRAN random vibration analysis consists of frequency response analysis (111 solver) and Acceleration Spectral Density (ASD) diagram, taking into account the natural frequencies of the bracket. The Miles method computes the root mean square acceleration (aRMS) using the natural frequencies and the ASD diagram as input. As a conservative hypothesis in the random analysis, the three sigma standard deviation criteria in normal Gaussian distribution is applied at these RMS acceleration values, which means to multiply the aRMS by a load factor of three. Simplified method consists of using linear static PATRAN-NASTRAN analysis (101 solver) where the aRMS are introduced as loads. For validation of the simplified method, a comparative study was made between the random vibration and the linear static analysis. The final results are presented in detail in this article.
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In the space sector the most decisive elements are: mass reduction, cost saving and minimum lead time; here, structural optimization and additive layer manufacturing (ALM) fit best. The design must ...be driven by stiffness, because an important requirement for spacecraft (S/C) structures is to reduce the dynamic coupling between the S/C and the launch vehicle. The objective is to create an end-to-end process, from the input given by the customer to the manufacturing of an aluminum part as light as possible but at the same time considerably stiffer while taking the full advantage of the design flexibility given by ALM. To design and optimize the parts, a specialized in-house tool was used, guaranteeing a load-sufficient material distribution. Using topological optimization, the iterations between the design and the stress departments were diminished, thus greatly reducing the lead time. In order to improve and lighten the obtained structure a design with internal cavities and hollow beams was considered. This implied developing of a procedure for powder evacuation through iterations with the manufacturer while optimizing the design for ALM. The resulted part can be then manufactured via ALM with no need of further design adjustments. To achieve a high-quality part with maximum efficiency, it is essential to have a loop between the design team and the manufacturer. Topological optimization and ALM work hand in hand if used properly. The team achieved a more efficient structure using topology optimization and ALM, than using conventional design and manufacturing methods.
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This paper presents an algorithm that calculates the nominal torque for friction grip joints, followed by its implementation in a Microsoft Excel worksheet that is automated by a macro written in ...Visual Basic. The algorithm outputs not only the optimum nominal torque (the value for which the margin of safety is maximum) but also the interval of acceptable values so that the user can easily choose the torque according to his preferences.
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The paper presents several types of mobile robots (MR) with 4, 6 and 8 wheels adapted for moving on uneven terrain. In the case of MR on 4 wheels, their diameter is limited and the chassis is raised, ...the ground clearance being higher than the height of a bump. MRs on 4 or 6 wheels have the chassis linked to the motor wheels by articulated bars as a dyad or tetrad variable geometry suspension. MR on 8 wheels use 4 planetary motor gear sets in tristar shape.
The paper focuses on the multidisciplinary optimisation and preliminary design of a twostage microlauncher capable of inserting a small 50 kg payload into Low Earth Orbit. The microlauncher is ...obtained using a MDO approach, where the lightest configuration capable of reaching the target orbit is considered to be optimal. For this paper, the propulsion system of the microlauncher is based on a non-cryogenic bipropellant combination.
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