The weighted sum method for multi-objective optimization: new insights

As a common concept in multi-objective optimization, minimizing a weighted sum constitutes an independent method as well as a component of other methods. Consequently, insight into characteristics of the weighted sum method has far reaching implications. However, despite the many published applications for this method and the literature addressing its pitfalls with respect to depicting the Pareto optimal set, there is little comprehensive discussion concerning the conceptual significance of the weights and techniques for maximizing the effectiveness of the method with respect to a priori articulation of preferences. Thus, in this paper, we investigate the fundamental significance of the weights in terms of preferences, the Pareto optimal set, and objective-function values. We determine the factors that dictate which solution point results from a particular set of weights. Fundamental deficiencies are identified in terms of a priori articulation of preferences, and guidelines are provided to help avoid blind use of the method.     

Phosphorylated Tau in Alzheimer’s Disease and Other Tauopathies

Alzheimer’s disease (AD) is the leading cause of dementia in elderly people. Amyloid beta (Aβ) deposits and neurofibrillary tangles are the major pathological features in an Alzheimer’s brain. These proteins are highly expressed in nerve cells and found in most tissues. Tau primarily provides stabilization to microtubules in the part of axons and dendrites. However, tau in a pathological state becomes hyperphosphorylated, causing tau dysfunction and leading to synaptic impairment and degeneration of neurons. This article presents a summary of the role of tau, phosphorylated tau (p-tau) in AD, and other tauopathies. Tauopathies, including Pick’s disease, frontotemporal dementia, corticobasal degeneration, Alzheimer’s disease, argyrophilic grain disease, progressive supranuclear palsy, and Huntington’s disease, are the result of misprocessing and accumulation of tau within the neuronal and glial cells. This article also focuses on current research on the post-translational modifications and genetics of tau, tau pathology, the role of tau in tauopathies and the development of new drugs targeting p-tau, and the therapeutics for treating and possibly preventing tauopathies.     

One World,Two Realities: Perception Differences between Software Developers and Testers

Strong working relations between software developers and testers are critical to the efficient and effective development of high-quality software. Smooth collaboration must occur as testers find problems and developers fix problems in the software. Prior studies based on anecdotal data have suggested that developers and testers have different personalities, approaches to work, etc., and these differences may have negative impacts on software project outcomes such as software quality and job satisfaction. This study examines the results of a nationwide survey undertaken to empirically examine and to improve our understanding of the pertinent areas where developers and testers differ. Results support that significant differences exist in perceptions between developers and testers. We conclude that these differences must be considered in order to improve software development efficiency and effectiveness.     

Predictive dynamics: an optimization-based novel approach for human motion simulation

Predictive dynamics is a novel approach for simulating human motion. It avoids direct integration of differential-algebraic equations in order to create the resulting simulations for redundant digital human models. Instead, it formulates an optimization problem by defining appropriate performance measures and constraints to recover the real motion of the dynamic system. In the formulation, both kinematics and kinetics parameters serve as unknowns, and equations of motion are treated as equality constraints. Procedures to choose physical performance measures and appropriate constraints based on the available information about the bio-system are presented. The proposed methodology is illustrated and studied by first predicting the swinging motion of a single pendulum with externally applied torque. The pendulum can represent the motion of upper and lower extremities. This simple problem has analytical solutions and is used to gain insights for the predictive dynamics approach. In addition, a complex human walking task is simulated by using the approach, and realistic results are obtained. Such motion prediction capabilities have a wide variety of applications for industries ranging from automotive to military to clinical analysis and design.     

Return Mapping Procedure for Frictional Force Calculation: Some Insights

The return mapping procedure is studied to gain insights for its numerical implementation to calculate the frictional force during contact analysis. A simple quasistatic truss–wall frictional contact analysis problem is used in the study. The problem has closed-form solutions which provide exact target solutions for a numerical algorithm. The penalty method and a true augmented Lagrangian method that automatically determines an accurate value of the penalty parameter are employed in the numerical study. It is determined that the return mapping procedure is not applicable unless the contacting node is constrained to stay at the initial contact point, and the total normal reaction force, the tangential reaction force and the friction limit have been determined. If these requirements are not met, inaccurate or even incorrect solutions are obtained. This characteristic of the procedure is studied by solving slip and stick cases with several different load increments. It is concluded that the return mapping procedure for friction force calculation should be implemented carefully to obtain accurate solutions for contact analysis problems.     

Ferroelectric Phase Stability Studies in Spray Deposited KNO3:PVA Composite Films

The composite films of potassium nitrate (KNO₃):poly(vinyl alcohol) (PVA) have been prepared at different temperatures by spray-deposition technique. Ferroelectric hysteresis loops were traced at room temperature for the composite films using modified Sawyer and Tower circuit. The X-ray diffraction studies confirm the existence of ferroelectric phase III of KNO₃ in the composite films at the room temperature, where this phase in pure KNO₃ films is known to exist in the temperature range 110°–124°C. The composite films deposited at 200°C shows the optimum remanent polarization, P _r∼17 μC/cm². The P _r was studied in the frequency range 10 Hz–1 kHz. The stability of the P _r in the composite films exhibits improved fatigue compared with that of quenched KNO₃ films. The capacitance–voltage ( C – V ) characteristics exhibits butterfly features which supports the presence of ferroelectric phase in the composite films. The atomic force microscopy images show that the composite films have uniform dispersion of KNO₃ particles in the PVA matrix.     

A study of mathematical programmingmethods for structural optimization. Part II: Numerical results

Various mathematical programming methods for structural optimization are studied. In a companion paper, these methods have been studied based on certain theoretical considerations. In this paper, the methods are studied based on solving a set of test problems. The methods that are studied include recursive QP, feasible directions, gradient projection, SUMT and multiplier methods. Various computer codes have been developed, and are studied together with some existing programs such as CONMIN and OPTDYN. The test problems considered have 3–47 design variables and 3–252 constraints. The evaluation criteria consist of studying the accuracy, reliability and efficiency of a code. It turns out that globally convergent algorithms (multiplier methods, in particular) are very reliable but not efficient. Primal algorithms (like CONMIN), which are not proved to be globally convergent, are efficient but not reliable.     

Optimization-based motion prediction of mechanical systems: sensitivity analysis

In this study, we derive sensitivity equations for the problem of optimization-based motion prediction of a mechanical system using the inverse recursive Lagrangian formulation. The simulation and sensitivity formulations are based on Denavit–Hartenberg transformation matrices. External forces and moments are taken into account in the formulation. The sensitivity information is needed in the optimization-based simulation process. The proposed formulation is demonstrated by calculating sensitivities for the optimal time trajectory planning problem of a two-link manipulator. In addition, sensitivities obtained using the proposed algorithm are compared to those obtained using the closed-form equations of motion. The two sensitivities match quite closely. The lifting motion of the two-link manipulator with external loads is also optimized by using the algorithm developed in this paper. More complex applications of the proposed formulation to digital human motion prediction are presented elsewhere.     

Densities, Viscosities, Speeds of Sound, and Refractive Indices of Binary Mixtures of 2-Ethyl-1-hexanol with Benzene and Halobenzenes

Densities, $\rho $ , viscosities, $\eta $ , speeds of sound, $u$ , and refractive indices, $n_\mathrm{D} $ , of binary liquid mixtures of 2-ethyl-1-hexanol with benzene, chlorobenzene, and bromobenzene have been measured over the entire range of composition at 298.15 K, 303.15 K, and 308.15 K and at atmospheric pressure. From the experimental data of the density, speed of sound, viscosity, and refractive index, the values of the excess molar volume, $V^\mathrm{E}$ , isentropic compressibility, ${\kappa _{S}}$ , and deviations in molar refraction, $\Delta R$ , have been calculated. The viscosity data have been correlated using McAllister’s three-body interaction model at different temperatures. The calculated excess and deviation functions have been analyzed in terms of molecular interactions and structural effects.