Optimization of the nonoverlap length in decanano MOS devices with 2-D QM simulations

Two-dimensional quantum-mechanical simulations of nonoverlapped MOS devices are presented, and validated through comparison against experimental data. Simulations are used to highlight the electrical characteristics of these devices, explore their design tradeoffs and optimize the performance with respect to the nonoverlap length. Simulations show that a minimum switching time is always achieved by adopting a nonoverlapped structure if the MOS device is operating properly. This approach can effectively improve the performance of decananometer MOSFETs.     

Effects of structural nonlinearity and along-span wind coherence on suspension bridge aerodynamics: Some numerical simulation results

The response of suspension bridges to wind excitation is studied by means of numerical simulations with a specifically developed finite element program implementing full structural nonlinearities. A pure time-domain load model, linearized around the average configuration, is considered. The self-excited effects are included through the indicial function formulation, whereas the buffeting is considered according to the quasi-steady model. The response under turbulent wind, both fully and partially correlated, is evaluated through a Monte Carlo approach. A simplified structural model is considered, where only two cross-sections are modeled. This allows a high reduction of the number of degrees of freedom (DoFs) but maintains many characteristics of the true bridge, precluded to the classical 2-DoF sectional-model (e.g. considering more than two modes, including structural nonlinearities, introducing along-span wind coherence). The case studies of a long-span suspension bridge and a light suspension footbridge are analyzed. It is observed that structural nonlinearities deemphasize the presence of a critical flutter wind velocity, as they limit the oscillation amplitudes. On the other hand, fully correlated flow may produce an important underestimation of the structural response.     

Creep properties of austenitic stainless-steel weld metals

The creep behavior of two austeitic stainless-steel weld metals was investigated. Two AISI 316L stainless-steel base plates were welded together using the submerged arc-welding process. Creep tests were carried out on the welds at constant load, over a stress range of 100 to 400 MPa, and in the temperature range of 600 to 700 °C. The relationships between stress and minimum secondary creep rate at a constant temperature were obtained with Norton’s law. The results showed that AISI 347 weld metal presented a higher creep resistance with lower values of the minimum strain rate, and, consequently, it exhibited a longer life before rupture than AISI 316L weld metal. However, this weld metal showed a lower ductility value than AISI 316L weld metal. The weld-metal microstructure survey, performed before and after the creep testing, has shown different amounts of delta ferrite, which was strongly dependent on time, temperature, and stress level.     

The influences of macrosegregation, intermetallic particles, and dendritic spacing on the electrochemical behavior of hypoeutectic Al-Cu alloys

The purpose of this research is (1) to investigate the influence of Al(2)Cu intermetallic particles associated with the dendritic arm spacing on the corrosion resistance of different hypoeutectic Al-Cu alloys and (2) to evaluate the electrochemical behavior of a hypoeutectic Al-Cu alloy directionally solidified under unsteady-state heat flow. The as-cast samples were produced using vacuum arc remelting and vertical upward water-cooled solidification. Microscopic examinations were carried out with optical microscopy and scanning electron microscopy + energy dispersiveX-ray analyses. To evaluate the surface corrosion behavior of such alloys, all corrosion tests were performed in a 0.5-M NaCl solution at 25 degrees C using an electrochemical impedance spectroscopy technique and potentiodynamic polarization curve analysis. Based on the tests, corrosion rate and impedance parameters were obtained. The present research has underlined the use of appropriate techniques of characterization for determining Al(2)Cu distribution, morphology, and fraction within the typical microstructures of Al-Cu alloys. The experimental results have established correlations between the Al-rich phase dendritic arm size, the intermetallic particles distribution in the eutectic mixture, the macrosegregation profile, and the resulting corrosion resistance.     

In-service testing of wind turbine towers using a microwave sensor

A remote-sensing technique based on microwave interferometry is applied to dynamic testing of wind turbine towers for power generation. A high-speed interferometric radar is able to sample the structure at a rate high enough for modal and transient analysis. An experimental campaign is reported carried out on wind turbine towers of a power plant in north Sardinia, Italy.     

Reconstruction of upper cranial and cranial base defects utilizing the scalping flap

Reconstruction of midfacial defects by means of a scalping flap has been widely practiced and described in the literature. The advantages of the flap are familiar to surgeons who perform extirpations and reconstruction of the head and neck and include contiguous availability, simplicity of application, and a robust and redundant blood supply. Despite these merits, the flap has not been widely used for reconstructions of large anterior cranial defects or defects of the cranial base. A retrospective review of 11 patients who underwent reconstructions between 1990 and 1995 was performed. In each case, a reconstruction of a large anterior cranial or cranial base defect was carried out. The resulting soft-tissue defect was restored via the scalping flap. In six cases, this was carried out in a single procedure. In five cases, flap division and insetting were carried out in a subsequent procedure, following a 1- to 2-week delay. In all cases, the extirpation and reconstruction were well tolerated, and the average time of hospitalization was 5.9 days and ranged from 3 to 11 days. No major surgical complications occurred. One of 11 patients had a minor complication not requiring surgical intervention. There was one recurrence of a cranial base tumor approximately 2 years following the initial resection and reconstruction. In all cases, the final aesthetic and functional results were acceptable to excellent. Follow-up ranged from 11 months to 5 years. In conclusion, the scalping flap can be effectively utilized for soft-tissue coverage in the reconstruction of anterior cranial and cranial base defects. Use of this simple and versatile flap in craniofacial reconstruction is well tolerated and is associated with a low morbidity, a good aesthetic result, and a short hospital stay.