Micromachined, kHz-frequency resonators are now routinely employed as testing structures to characterize the fatigue degradation properties of thin film materials such as polycrystalline silicon (polysilicon). In addition to stress-life (S–N) fatigue curves, important properties such as crack propagation rates may be inferred from proper resonant frequency measurements throughout a fatigue test. Consequently, any nonlinear dynamic behavior that would complicate the interpretation of resonant frequency changes should be avoided. In this paper, nonlinear frequency–response curves of a polysilicon fatigue structure are measured in a vacuum environment. Finite element models of the structure are used to identify the source of geometric nonlinearity leading to a Duffing-type cubic stiffness. Given the origin of the behavior, a parametric optimization strategy is performed to minimize the cubic stiffness. This study highlights the importance of considering the dynamic behavior when designing resonating structures, especially when they are used for mechanistic studies in various environments.
Novel results and experiments are presented on the application of cellular neural networks to binocular stereo vision. A cellular neural network (CNN) universal machine (UM) algorithm is described for depth estimation as part of a stereo-vision-based guidance system for autonomous vehicles. Being most amenable to revealing stereo correspondence, extraction of vertical edges is performed first. Then their distance from the observer in 3D space is established through a stereo matching scheme. The performance of the algorithm is demonstrated on real-life highway imagery and it is shown that very low latency real-time operation is attainable via the CNN-UM.
Productivity growth is slowing around the world. In 2015, the growth of total factor productivity (TFP) hovered around zero for the fourth straight year, down from 1 percent in 1996–2006 and 0.5 percent in 2007–12. In this paper we identify previous episodes of sharp and sustained decelerations in TFP growth using data for a large sample of countries and years. TFP slumps are ubiquitous: We find as many as 77 such episodes, depending on definition, in low-, middle- and high-income countries. Low levels of educational attainment and unusually high investment rates are among the significant country-specific correlates of TFP slumps, and energy-price shocks are among the significant global factors.
The electronic properties of palladium supported on SiO/sub 2/ and La/sub 2/O/sub 3/ were investigated by X-ray photoelectron spectroscopy. Spectra were collected after each stage of catalyst preparation: deposition of the palladium chloride precursor, oxidation in air at 623 K, and reduction in H/sub 2/ at 573 K. The Pd 3d/sub 5/2/ binding energies recorded following precursor deposition and oxidation were the same on both catalysts. However, after reduction the Pd 3d/sub 5/2/ binding energies of the Pd/La/sub 2/O/sub 3/ samples shifted below the corresponding values for metallic Pd, while the Pd 3d/sub 5/2/ binding energies of the Pd/SiO/sub 2/ samples did not. Furthermore, the binding energies for the Pd/La/sub 2/O/sub 3/ samples decreased with increasing metal loading, the largest Pd particles apparently exhibiting the greatest interaction. A maximum shift of -0.7 eV relative to the Pd foil value was observed for 8.8% Pd/La/sub 2/O/sub 3/. This binding energy shift is interpreted as arising from a change in the chemical state of Pd, i.e., that Pd supported on La/sub 2/O/sub 3/ is more electronegative than zero-valent Pd alone. A model is proposed which suggests that a thin covering of the La/sub 2/O/sub 3/ support lies on a portion of themore » Pd surface. The exact composition of the support depended strongly on the reduction temperature and the amount of Pd deposited. 49 references, 13 figures, 9 tables.« less
An olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the Siberian flood basalt province (SFBP) yielded a 40 Ar/ 39 Ar plateau age of 253.3 ± 2.6 million years, distinctly older than the main tholeiitic pulse of the SFBP at 250.0 million years. Olivine phenocrysts of this rock showed 3 He/ 4 He ratios up to 12.7 times the atmospheric ratio; these values suggest a lower mantle plume origin. The neodymium and strontium isotopes, rare earth element concentration patterns, and cerium/lead ratios of the associated rocks were also consistent with their derivation from a near-chondritic, primitive plume. Geochemical data from the 250-million-year-old volcanic rocks higher up in the sequence indicate interaction of this high- 3 He SFBP plume with a suboceanic-type upper mantle beneath Siberia.
Theoretical and experimental investigations for fundamental understanding of the passivation process and its kinetics could lead to the prediction of the electrochemical behavior of the third-generation Al-Li alloy 2098. In this paper, the kinetics of the passive film formation on AA2098-T851 in 0.1M NaHCO 3 in a CO 2 atmosphere at 25°C, at potentials with both metal dissolution and hydrogen evolution reaction (HER) was investigated. This was done by performing electrochemical impedance spectroscopy (EIS) on the passive layer after each potentiostic steps in the anodic direction that followed by stepping in the opposite direction. The optimization of the EIS data was done by applying the previously developed Mixed Potential Model (MPM) that considers the Point Defect Model (PDM) for dissolution and passivation of the metal along with the Butler-Volmer equation for the cathodic reaction. It was shown that the inequality of certain kinetic processes of passive layer formation leads to the irreversibility of the metallic passivation in opposite potential scanning directions. Also, considering that the hydrogen evolution reaction incorporates quantum mechanical tunneling of the charge carriers through the barrier oxide layer on the passive metal surface, a cathodic Tafel constant ( β c ) was calculated. The estimated β c was in accord with the predicted value for the HER according to the slow discharge of protons mechanism.
Asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid catalyst, generates an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity.
