Part feeders, which separate and orient parts prior to packing and insertion, are critical components of an assembly line. Existing feeders utilize off-plane vibrations of a rigid structure to convey parts along a track. Repeated part hopping/landing phases are concerns if parts are delicate and/or high positioning accuracy is required. Here we consider a simpler feeder design in which parts are in permanent contact with a horizontally-vibrating flat plate. Each vibration is a "pump-like" motion along a single degree of freedom: the plate spends more time moving forward than backward. Parts are propelled forward since dynamic friction is fixed and independent of the relative velocity at the interface. In designing plate vibration profiles we consider issues of waveform simplicity, bandwidth, and feed rate performance. Both bang-bang and sinusoidal control waveforms are analyzed. Expressions are derived for equilibrium feed rates for both waveforms; dynamic simulation is used to verify the analysis. A prototype of the proposed feeder has been implemented with cheap mechanical parts. A simple experiment with the device is presented.
The relationship between the peak deformations of inelastic and corresponding linear single-degree-of-freedom (SDF) systems is investigated. Presented are the median of the inelastic deformation ratio for 214 ground motions organized into 11 ensembles of ground motions, representing large or small earthquake magnitude and distance, and National Earthquake Hazards Reduction Program (NEHRP) site classes B, C, and D; near-fault ground motions are also included. Two sets of results are presented for bilinear nondegrading systems over the complete range of elastic vibration period, Tn:Cμ for systems with known ductility factor, μ, and CR for systems with known yield-strength reduction factor, Ry. The influence of postyield stiffness on the inelastic deformation ratios Cμ and CR is investigated comprehensively. All data are interpreted in the context of acceleration-sensitive, velocity-sensitive, and displacement-sensitive regions of the spectrum for broad applications. The median Cμ versus Tn and CR versus Tn plots are demonstrated to be essentially independent of the earthquake magnitude and distance (over their ranges considered), and of site class. In the acceleration-sensitive spectral region, the median inelastic deformation ratio for near-fault ground motions is systematically different when plotted against Tn; however, when plotted against normalized period Tn/Tc (where Tc is the period separating the acceleration- and velocity-sensitive regions) they become very similar in all spectral regions. Determined by regression analysis of the data, two equations—one for Cμ and the other for CR—have been developed as a function of Tn/Tc, and μ or Ry, respectively, and are valid for all ground motion ensembles considered. These equations for Cμ and CR should be useful in estimating the inelastic deformation of new or rehabilitated structures—where the global ductility capacity can be estimated—and existing structures with known lateral strength.
We report highly enantioselective intramolecular, silylations of unactivated, primary C(sp<sup>3</sup>)-H bonds. The reactions form dihydrobenzosiloles in high yields with excellent enantioselectivities by functionalization of enantiotopic methyl groups under mild conditions. The reaction is catalyzed by an iridium complex generated from [Ir(COD)OMe]<sub>2</sub> and chiral dinitrogen ligands that we recently disclosed. The C-Si bonds in the enantioenriched dihydrobenzosiloles were further transformed to C-Cl, C-Br, C-I, and C-O bonds in final products. The potential of this reaction was illustrated by sequential C(sp<sup>3</sup>)-H and C(sp<sup>2</sup>)-H silylations and functionalizations, as well as diastereoselective C-H silylations of a chiral, natural-product derivative containing multiple types of C-H bonds. Preliminary mechanistic studies suggest that C-H cleavage is the rate-determining step.
Abstract In 2000, a regional rule governing maximum individual cancer risk from stationary facilities in Southern California was dramatically altered, reducing allowable risk levels by 75%. This article uses a case study approach to explore the role of a community‐based participatory research (CBPR) partnership, the Southern California Environmental Justice Collaborative, in producing research and helping spearhead policy advocacy leading to this policy change. It also highlights the role of the collaborative in helping to change the framing of the issue from individual to cumulative risk assessment, so that the regulatory agencies began to reflect this broader thinking in their policymaking. The collaborative's structure and methodology, regional focus, relationships with key decision makers, and its reputation as an important source of both credible science and “people power” were seen as contributing to its effectiveness. The role of contextual factors including a recovering and more regulation‐friendly economy also is highlighted, as are key barriers faced. Implications for other community–academic partnerships working to address regional and statewide public policy are discussed.
