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Plasmaphysik III : von den kapazitiv gekoppelten Plasmen bis zur Plasmadiagnostik
Full text linkInhalt: Kapazitiv gekoppelte Plasmen; Streuprozesse; Hoch-Dichte-Plasmen; CCP-Entladungen vs. ICP-Entladungen; Magnetfeldunterstützte Einkopplung; Ionenstrahlsysteme; Trockenätzverfahren I-V; Plasma-Analyti
Quantenphysik : Festkörperphysik
Full text linkInhalt: Festkörpermodelle; Metalle; Elektronen im realen Festkörper; Halbleite
Vom Hörsaal in den Kindergarten : Berufseinmündung von KindheitspädagogInnen
Full text linkVom Hörsaal in den Kindergarten. Berufseinmündung von KindheitspädagogInne
Alloplastic Reconstruction of the Extensor Mechanism after Resection of Tibial Sarcoma
No full textReconstruction of the extensor mechanism is essential for good extremity function after endoprosthetic knee replacement following tumor resection. Only a few biological methods have been able to reliably restore a functional extensor mechanism, but they are often associated with significant complication rates. Reattachment of the patellar tendon to the prosthesis using an alloplastic patellar ligament (Trevira cord) can be an appropriate alternative. In vivo and in vitro studies have already shown that complete fibrous ingrowth in polyethylene chords can be seen after a period of six months. However, until now, no biomechanical study has shown the efficacy of an alloplastic cord and its fixation device in providing sufficient stability and endurance in daily life-activity until newly formed scar tissue can take over this function. In a special test bench developed for this study, different loading regimes were applied to simulate loads during everyday life. Failure loads and failure modes were evaluated. The properties of the cord were compared before and after physiological conditioning. It was shown that rubbing was the mode of failure under dynamic loading. Tensile forces up to 2558N did not result in material failure. Thus, using an artificial cord together with this fixation device, temporary sufficient stable fixation can be expected
Monolithical serial interconnects of large CIS solar cells with picosecond laser pulses
No full textThe production of CIS thin film solar cells is still employing some mechanical steps of structuring, where thin layers have to be selectively separated in three patterns (P1 to P3) for the monolithic serial interconnection. We report on the high speed structuring of these patterns by picosecond laser ablation at 1064 nm. We demonstrate on 100x100 mm2 samples, that the molybdenum back electrode can be structured with a process speed of up to 15 m/s. The ZnO front electrode film can be line separated with up to 15 m/s, the CIS absorber layer is structured with up to 4 m/s. Furthermore we extended our laser processes to 300 x 300 mm2 pilot line samples which were displaying efficiencies of 13.4%
Using a variance-based sensitivity analysis for analyzing the relation between measurements and unknown parameters of a physical model
No full textAn implementation of uncertainty analysis (UA) and quantitative global sensitivity analysis (SA) is applied to the non-linear inversion of gravity changes and three dimensional displacement data which were measured in and active volcanic area. A didactic example is included to il lustrate the computational procedure. The main emphasis is placed on the problem of extended Fourier amplitude sensi tivity test (E-FAST). This method produces the total sensi tivity indices (TSIs), so that all interactions between the un known input parameters are taken into account. The possible correlations between the output an the input parameters can be evaluated by uncertainty analysis. Uncertainty analysis re sults indicate the general fi between the physical model and the measurements. Results of the sensitivity analysis show quite different sensitivities for the measured changes as they relate to the unknown parameters of a physical model for an elastic-gravitational source. Assuming a fi ed number of ex ecutions, thirty different seeds are observed to determine the stability of this method
Improved fiber orientation predictions for injection molded composites
No full textShort fibers are commonly utilized to reinforce the polymer matrix for injection molded parts. Fibers suspended in the molten polymer matrix are oriented by the flow during the mold filling process, and acquire a preferential orientation pattern in the final part. The fiber orientation introduces anisotropy to the mechanical and thermal properties of the material, including the elastic modulus, the tensile strength, and the thermal expansion. A final part is stronger and stiffer in the direction along which the most fibers align, while it is weaker and more compliant in the other directions. An accurate prediction of fiber orientation in injection molding is crucial for designing a mold and controlling part properties.
The well-established Folgar, Advani, and Tucker model is widely used to predict fiber orientation. However, recent experiments indicate that this theory overestimates the change rate of the fiber orientation tensor, and therefore predicts a similar orientation pattern in injection-molded parts regardless of the flow length, the part thickness, or the mold filling speed. A strain reduction factor (SRF) was introduced by Huynh (2001) to decrease the change rate of orientation tensor. Though it produces an excellent agreement with experimental data, the SRF model is not objective and encounters difficulty in complex flows.
Inspired by the idea of reducing the growth rates of the eigenvalues of the orientation tensor by a scalar factor, a new orientation model was built, in which we modified the closure and fiber-fiber interactions terms accordingly. A possible approach to reduce the rotation rates of the eigenvectors was also explored, but no successful model with this feature was found. A finite difference program was developed and used to simulate the filling process for two simple geometries: end-gated strips and center-gated disks. The program is based upon the Hele-Shaw approximation to solve the velocity field, and implements the new orientation model to predict the fiber orientation. The results using the same scalar factor as the SRF model show an excellent agreement with experimental measurements, for both strips and disks, in small thicknesses and at different filling speeds. A special treatment was proposed for thick strips, to account for the radial flow front that is observed in short-shot experiments and is different from the almost flat flow front in thin strips. The finite difference program was also extended to simulate the filling process of injection molds with rotation, compression, and expansion (RCEM). The comparison of the predicted and measured fiber orientation demonstrates again the usefulness of our new orientation model.
The new orientation theory was further implemented to model complex flows where the full equations of motion must be solved. The solver of fiber orientation equations was added to FIDAP™, a commercial finite element software, through user subroutines. The final program is able to solve for velocity, temperature, pressure, and fiber orientation in any two- or three-dimensional geometry. Flow through the gate of our end-gated strips was simulated, and the fiber orientation was calculated. The orientation results were compared to the measured values at a region just inside the gate, and then were used as inlet conditions for the finite difference program to successfully predict the downstream orientation.
Our new orientation model is a phenomenological theory, and the value of the scalar factor to reduce the orientation change rate is determined by matching experimental data. Since the rheology of a fiber suspension is affected by the fiber orientation, a rheological experiment measuring the shear viscosity and the normal stress difference is one approach to determine the phenomenological parameters. The formulations were worked out for the shear stress and the normal stress difference with respect to the fiber orientation in a parallel-disk rotational rheometer, and the model was fit to the measured values in a least square sense by adjusting the model parameters. This provides a convenient and viable route for determining the parameters of the orientation model