IS QUALITY ENGINEERING AN OXYMORON?

It is my purpose in this editorial to offer some highly personal and likely controversial views on the state of statistics and the quality profession. These views are based on my personal experiences and prejudices-especially those of my 10 years as an independent statistical consultant. I wish to particularly absolve my current employer, Merck and Company, and my colleagues there of any guilt by association. The opinions rendered here are entirely my own and in no way represent Merck's practices or policies, Mea culpa.     

Capillary zone electrophoresis with laser-induced fluorescence detection for the determination of nanomolar concentrations of noradrenaline and dopamine: application to brain microdialysate analysis

Determination of catecholamines by capillary zone electrophoresis with laser-induced fluorescence detection was performed on low-concentration samples, which were derivatized with naphthalene-2,3-dicarboxaldehyde to give highly fluorescent compounds. When the borate concentration in the derivatization medium was decreased from 130 to 13 mM, sensitivity for noradrenaline (NA) and dopamine (DA) was greatly enhanced while resolution between these two compounds decreased. A 50 mM borate concentration in derivatization medium was chosen since it provided maximal resolution between NA and DA, together with a high separation efficiency (3.1 million theoretical plates per meter for DA). The injection of 2.4 nL of a NA and DA solution derivatized at 10(-9) M produced peaks with signal-to-noise ratio of 8:1 and 3:1, respectively, corresponding to 1.8 amol of each catecholamine. The calibration curves were linear when NA and DA solutions were derivatized at concentrations ranging from 10(-6) to 10(-9) M. This method was used to determine NA in brain extracellular fluid: a peak corresponding to a basal level of 5 x 10(-9) M endogeneous NA was observed in microdialysates from the medial frontal cortex of the rat, and its nature was confirmed by both electrophoretic and pharmacological validations.     

On the stress function approach in three-dimensional elasticity

Summary Stress function-based solution procedures in elasticity require the knowledge of those stress functions that give zero complementary strain energy. In the two-dimensional case, the structure of the zero-energy first-order stress functions is as simple as that of the zero-energy displacements, and the number of the zero-energy modes is three [1]. This paper investigates the more complicated three-dimensional case and, considering a possible set of six independent first-order stress functions, derives the zero-energy stress functions in polynomial form. It is pointed out that the number of the zero-energy stress function modes in the three-dimensional case is infinite.     

Housing market change in Amsterdam: Some trends

This article resulted from a research project sponsored by the Vereniging Amsterdamse Bouwbedrijven. We want to thank Arno Bongenaar for this assistance during the project.     

Modelling the effect of superatmospheric oxygen concentrations on in vitro mushroom PPO activity

The kinetics of polyphenol oxidase (PPO, EC 1.14.18.1) with respect to oxygen concentrations from 5 to 100% using chlorogenic acid (CGA) as substrate was examined. In vitro mushroom PPO activity was determined by measuring the consumption of oxygen during the oxidation reaction. A differential Michaelis–Menten model was fitted to the obtained total depletion curves. The product concentration as well as the concentration of oxygen had a clear inhibitory effect on the reaction rate. However, the inhibitory effect of oxygen was more evident at low product concentration. A linear mixed inhibition model that considered both the product (oxidised CGA) and oxygen as inhibitors was developed. A model with the product as a competitive inhibitor and oxygen as an uncompetitive inhibitor was the most appropriate to explain the reaction kinetics. The values of the inhibition constants calculated from the model were 0.0032 mmol L⁻¹ for K_m (Michaelis–Menten constant related to oxygen), 0.023 mmol L⁻¹ for K_mc (constant for competitive inhibition due to the product), 1.630 mmol L⁻¹ for K_mu (constant for uncompetitive inhibition due to oxygen) and 1.77 × 10⁻⁴ mmol L⁻¹ s⁻¹ for V_max (maximum reaction rate). The results indicate that superatmospheric oxygen concentrations could be effective in preventing enzymatic browning by PPO. Copyright © 2006 Society of Chemical Industry     

Make computer assisted instruction smarter

It is argued in this paper that the quality of computer assisted instruction can only increase if more research is directed towards the development of generative intelligent CAI systems. Characteristics of these systems are described and the state-of-the-art is assessed. Finally the design of one such future system is presented.     

Fundamental frequency analysis of laminated rectangular plates by differential quadrature method

In this paper a differential quadrature method is presented for computation of the fundamental frequency of a thin laminated rectangular plate. The partial differential equations of motion for free vibration are solved for the boundary conditions by approximating them by substituting weighted polynomials functions for the differential operator. By doing this, the coupled partial differential equations of motion are reduced to sets of homogeneous algebraic equations. These sets of homogeneous algebraic equations are combined to give a set of general eigenvalue equations for the problem. Three types of laminated plate problems, which include symmetric, antisymmetric cross-ply, and symmetric, balanced angle-ply laminates, are analysed by the method and the results obtained are compared with solutions reported in the literature for other numerical methods. The effects of the level of discretization on the accuracy and rate of convergence of the results are also discussed. The method presented gives accurate results and is found to use not much computer time.