A wide-band,high-precision CMOS rectifier

A novel architecture for a precision rectifier is introduced. A new arrangement of a MOS switch and an amplifier has been developed for better precision and higher switching speed. The precision rectifier can rectify signals as low as 10 mV and frequencies up to 20 MHz with excellent linearity.     

Two-phase biomass air-steam gasification model for fluidized bed reactors: Part III—model validation

The developed two-phase air-steam gasification model (Biomass Bioenergy, xxxxx) was validated using the experimental results obtained from a dual distributor fluidized bed reactor. The reactor was operated on wheat straw at various fluidization velocities, steam flow rates and biomass to steam ratios. A good agreement between the model predictions and experimental data was obtained under all operating conditions studied. The model predicted the temperatures of the bubble, emulsion and solid phases, the mole fractions of methane, hydrogen, carbon monoxide, carbon dioxide and nitrogen, and the higher heating value of the producer gas with high accuracy (R²=0.88–0.98). The correlation coefficient (R²) for the gas production was somewhat lower (0.75), which could be attributed to the assumption that the gases behaved ideally.     

Hybrid Au-CdSe and Ag-CdSe nanoflowers and core-shell nanocrystals via one-pot heterogeneous nucleation and growth

A general approach, based on heterogeneous nucleation and growth of CdSe nanostructures on Au or Ag nanocrystals, for the synthesis of Au-CdSe and Ag-CdSe hybrid nanostructures is developed. The new approach provides a versatile one-pot route for the synthesis of hybrid nanoflowers consisting of a gold or silver core and multipod CdSe rods or an intact CdSe shell with controlled thickness, depending on the nucleation and growth parameters. At lower growth temperatures such as 150 °C, the CdSe clusters are adsorbed on the surface of the metal cores in their surface defects, then multiple arms and branches form, resulting in nanoflower-shaped hybrid structures. Increasing the size of the metal core through the choice of the reducing and capping agents results in an improvement of the interface between the metal and CdSe domains, producing core-shell structures. The growth temperature appears to be the most important factor determining the nature of the interface between the metal and CdSe domains. At relatively high temperatures such as 300 °C, the formation of large, faceted Au cores creates preferential growth sites for the CdSe nanocrystalline shell, thus resulting in well-defined Au-CdSe core-shell structures with large interfaces between the Au and CdSe domains. The present approach is expected to foster systematic studies of the electronic structures and optical properties of the metal-semiconductor hybrid materials for potential applications in photovoltaic and nanoelectronic devices.     

Experimental Study of Four-Point Contact Ball Bearing with Deformable Rings

When a ball bearing is designed with thin rings or is mounted in a flexible housing, the assumption of rigid rings is not true anymore. In this article, an experimental study is presented and a comparison with a numerical model is performed. The numerical approach is based on the coupling between a semi-analytical code and a finite element (FE) model that computes the deformation of the rings and housings. The numerical model accounts for ring ovalization, raceway opening, change of conformity, and structural displacements of the whole assembly. The experimental setup allows investigation of the load–displacement behavior of a four-point contact ball bearing submitted to a static thrust loading. Displacements are measured by an optical method (stereo-correlation) that enables comparison of the surface deformation of the two tested bearings and computation of the rigid-body displacement of the inner ring with respect to the outer ring. A comparison between experimental results, numerical results, with and without consideration of ring and housing stiffness, is presented. The numerical results show the importance of the housing stiffness in the modeling, even with standard ball bearings with relatively large and thick rings. Good agreement between measured quantities and numerical results was found. This permits the prediction of the real nonlinear bearing stiffness (load–displacement curve) with a reasonable margin of error.     

The Influence of the Preparation Conditions on Initial Permeability of Cu0.5Zn0.5Fe2?xRxO4

Samples with the chemical formula Cu_0.5Zn_0.5Fe_2−x R _x O₄ (x = 0.0 and 0.02; R = Sm and Gd) were prepared using a conventional ceramic method. x-ray analysis revealed the formation of a single spinel phase. The porosity decreases with an increase in the pressing pressure and the pre-sintering time during the preparation. The initial permeability, Curie temperature, and the homogeneity of the samples are increased with the pressing pressure and the pre-sintering time. This improvement of initial permeability is a novel result for different applications at a normal frequency range. The electrical resistivity is increased by a decrease of the pressing pressure. This is another novel result for the technology especially at a high-frequency range. The results are explained according to the increase of the stoichiometry of the samples.     

Modeling of natural sit-to-stand movement based on minimum jerk criterion for natural-like assistance and rehabilitation

Designing a sit-to-stand (STS) assistive system that mimics the normal transfer is important for improving the quality of life for elderly and mobility impaired people while reducing the burden on the caregivers. This paper presents a robotic-based STS assisting system that can provide assistance at the shoulder and the buttock. The minimum jerk criterion is used to model the natural STS motion. Anthropometry and characteristics of the natural STS motion are used to increase the simplicity and applicability of the STS motion model. This model can generate the shoulder and hip trajectories during STS. This enables the system to provide assistance either at the upper trunk or at the upper trunk and the hip simultaneously without inducing abnormal motion kinematics. The assisting system is used to assist subjects with different heights using the trajectories generated by the proposed motion model. In addition, the proposed trajectory is compared to the one that is resulted from a commercial lifter. The results show that the proposed method can accurately replicate the natural STS motion and results in a lower interaction force. Moreover, the subjects are more satisfied when they are assisted using the proposed method as indicated by the results of the post-experiment questionnaire.