Color and Selected Properties of PbO─BiO1.5─GaO1.5 Glasses

The density; molar volume; thermal expansion coefficient; dissolution rate in water, HC1, and NaOH; glass transition and crystallization temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO─BiO1.5─GaO1.5 glasses. The range of compositions investigated was x PbO (100 − (x + y) )BiO_1.5. yGaO_1.5 for x between 20 and 60 cat% and y of 20, 25, 30, and 35 cat%. The glass-forming tendency increased with increased GaO_1.5 and decreased with increased PbO or BiO_1.5. The compositional dependence of these properties was consistent with the weight, size, charge, and bond strength of the cations. The Ga^{3 +} ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi³⁺ and Pb²⁺ ions behave as network-modifying cations. It is suggested that a small friction of the lead ions are present as Pb⁴⁺. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.     

Model-based operating recommendations for high-speed spindles equipped with a self-vibratory drilling head

The drilling of deep holes requires the chips to be evacuated using retreat cycles and lubrication, which is problematic for both productivity and the environment. An alternative response to the chip evacuation problem is the use of a vibratory drilling head, which enables the chip to be split thanks to the axial self-excited drill, and hence it can easily be evacuated from the hole. The vibratory drilling head is composed of a specific tool holder with adjustable axial stiffness. In this paper, a dynamic high-speed spindle/drilling head/tool system model is elaborated on the basis of rotor dynamics predictions. The dynamic properties of interfaces between system components are identified by the receptance coupling method and integrated into the model. The model is validated by comparing the numerical FRF with experimental results. Then adequate self-vibratory cutting conditions are established by integrating the model-based tool tip FRF into the chatter approach of Budak-Altintas. Spindle rolling bearing lifespan is also investigated in order to guarantee a rational use of the spindle-tool set with respect to industrial lifespan.     

Optimal periodic forcing of nonlinear chemical processes for performance improvements

Unsteady-state periodic operations can improve the optimal steady-state performance of nonlinear chemical processes. To examine if the optimal periodic operation is proper and to obtain the optimal forcing functions subject to various control and state constraints it is suggested in this paper to convert the problems into a form which is suitable for constrained nonlinear programming. The adopted numerical optimization method is based on employing the control parametrization technique and is thus capable of dealing with the problem of multiple input forcings and obtaining optimal forcing functions and/or parameters while subject to general constraints. Besides, it provides information about to what extent the process performance can be improved by adopting the optimal periodic control.     

Accelerometers for bridge load testing

This paper describes a load-test procedure using accelerometer response and compares the results with that obtained using the traditionally used strain-gage data. The load rating provides an approximate load capacity of a bridge based on the available capacity of a critical girder for a predefined loading path. The results indicate that the accelerometer can conveniently extract information of bridges independent of their physical conditions. Application of accelerometers can remarkably enhance the response measurement of cracked concrete girders for bridge load rating. The proposed procedure can be useful in monitoring bridge performance over time and measuring the effectiveness of bridge retrofitting by comparing pre- and post-repair capacities.     

Effect of austenitization on austempering of copper alloyed ductile iron

A ductile iron containing 0.6% copper as the main alloying element was austempered at a fixed austempering temperature of 330 °C for a fixed austempering time of 60 min after austenitization at 850 °C for different austenitization periods of 60, 90, and 120 min. The austempering process was repeated after changing austenitization temperature to 900 °C. The effect of austenitization temperature and time was studied on the carbon content and its distribution in the austenite after austenitization. The effect of austenitization parameters was also studied on austempered microstructure, structural parameters like volume fraction of austenite, X _γ , carbon content C _γ , and X _γ C _γ , and bainitic ferrite needle size, d _α after austempering. The average carbon content of austenite increases linearly with austenitization time and reaches a saturation level. Higher austenitization temperature results in higher carbon content of austenite. As regards the austempered structure, the lowering austenitization temperature causes significant refinement and more uniform distribution of austempered structure, and a decrease in the volume fraction of retained austenite.     

High-Performance Switched Reluctance Brushless Drives

Switched reluctance (SR) drives offer the advantages of simple and robust motor construction, high speeds, high overall efficiencies over a wide operating range of torque and speed, simple power converter circuits with a reduced number of switches, and excellent controllability. The basis of these claims is explained. The history of the SR system, in particular the extensive research at Nottingham and Leeds Universities, and the basic operating principles and design considerations for motors and power converters are reviewed. Alternative configurations are discussed. The difficulties of establishing a simple mathematical model for the motor and of calculating torque and inverter VA requirements are examined. A comparison of the VA requirements for SR and pulsewidth modulation (PWM) is given for a 7.85-kW system. Measured drive performance is discussed in terms of efficiency over an operating envelope, specific output, controllability, and power converter ratings. Earlier traction drives, incorporating a constant power range and including regeneration, are reported together with the constant torque industrial drives and more recent traction extensions. The long-term potential of the drive is discussed for a wide range of applications. A comprehensive list of references is provided.     

Enhanced magnetoelectric effect in multiferroic composite beams due to flexoelectricity and transverse deformations

This paper is concerned with the exploration of the role of transverse normal and shear deformations on enhancing the magnetoelectric (ME) coefficient of multiferroic bilayer composite beams composed of a piezoelectric layer and a piezomagnetic layer. Analytical models have been derived based on the displacement field which accounts for both the transverse normal and shear deformations, Timoshenko beam theory and Euler Bernoulli beam theory. The induced flexoelectricity in the piezoelectric layer due to axial strain gradient and transverse shear strain gradient has also been taken into consideration for estimating the ME coefficient. It has been found that the contribution of transverse normal strain in the piezoelectric layer for enhancing the ME coefficient is significantly larger than that due to axial strain, transverse shear strain and flexoelectricity. For the particular values of the thicknesses of the piezoelectric layer and the piezomagnetic layer, the ME coefficient remains invariant for both thick and thin multiferroic composite beams.     

Exact solutions for flexoelectric response in elastic dielectric nanobeams considering generalized constitutive gradient theories

International Journal of Mechanics and Materials in Design - This paper deals with the derivation of the exact solutions for the static flexoelectric response of a simply supported dielectric...     

Rasch measurement in the assessment of amytrophic lateral sclerosis patients

This paper examines the sensitivity to change over time of the Amyotrophic Lateral Sclerosis Assessment Questionnaire (ALSAQ-40). Individuals' health status change was assessed by means of the Rasch-based Reliable Change Index (RCI) for ALSAQ-40 questionnaires completed on two occasions, three months apart. In addition, at follow-up respondents indicated how much change they had experienced since baseline via dimension-specific self reported transition questions. 764 individuals returned questionnaires at baseline and follow-up. For all dimensions, of respondents defined by the RCI as worse, a majority rated themselves as worse. However, on two dimensions over 60% of the respondents who rated themselves as being worse were defined as unchanged by the RCI. As with effect size smaller RCI cut-off points might be needed for subjects with ALS. This study confirms that the ALSAQ-40 is a valid and responsive disease specific health related quality of life instrument for use in studies of patients with ALS or other motor neuron diseases.