Difficulties in Quantifying Financial Losses that Could Be Reduced by Ergonomic Solutions

There is currently a significant amount of discussion regarding new ways to insert ergonomics into the business community through adding financial benefits; however, analysis must be performed to justify this type of investment. Occupational problems that could be reduced by ergonomics solutions can be expressed as financial losses. Although the impact and importance of these losses are high, the difficulties in their quantification prevent adequate cost‐benefit analysis. This article aims to document evidence of the difficulties encountered when quantifying the financial losses that are caused by problems that could be reduced by ergonomic solutions. In this study, we performed a literature review concerning the financial costs related to occupational problems from the perspective of ergonomics. The results indicate that losses that occur mainly concern the productivity of the working process or the workers. The chief barriers documented in the scientific literature are the information cost, the multifactorial nature of the problem, the absence of information, and the methods of measurement. © 2012 Wiley Periodicals, Inc.     

Model reference adaptive control of discrete‐time piecewise linear systems

This article presents a switched model reference adaptive controller for discrete‐time piecewise linear systems. In the spirit of the work by Landau in the late seventies, proof of asymptotic stability of the closed‐loop error system is obtained, recasting its dynamics as a feedback system and showing the feedforward and the feedback paths are both passive. The challenge is that both paths can be piecewise linear. Numerical results show excellent performance of the proposed controller even in the face of sudden variations of the plant parameters. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of HDG Methods for Oseen Equations

We propose a hybridizable discontinuous Galerkin (HDG) method to numerically solve the Oseen equations which can be seen as the linearized version of the incompressible Navier-Stokes equations. We use same polynomial degree to approximate the velocity, its gradient and the pressure. With a special projection and postprocessing, we obtain optimal convergence for the velocity gradient and pressure and superconvergence for the velocity. Numerical results supporting our theoretical results are provided.     

Morphological and porosity changes in primary enamel surface after an in vitro demineralization model

In vitro models are very useful in dentistry, especially to evaluate preventive methods against dental caries. Although they have been used for more than 30 years, specific demineralization models have not been established for primary enamel, which is more prone to demineralization than permanent enamel. This study evaluates porosity changes in primary enamel surface after a demineralization model through a scientifically validated analytical tool. Nine healthy human anterior primary teeth extracted for therapeutic reasons were included in this study, previous informed consent. The samples were randomly assigned to three groups n = 3: G1_2D, G2_4D, and G3_7D. Scanning electron microscopy (SEM) images at ×200 and ×1000 were taken during two stages: before demineralization (BD) and after demineralization (AD). Morphological characterization was observed at ×1000, while porosity (pore count and perimeter) was analyzed by the ImageJ program, using ×200 SEM images previously converted. Several statistical analyses were used to determine differences (p ≤ .05). Morphological characterization AD revealed new pits and cracks on the enamel surface in G1_2D and G2_4D groups. Localized eroded enamel areas were observed in G3_7D. Pore count of enamel surface BD ranged from 64.26 ± 37.62 to 97.93 ± 34.25 and AD ranged from 150.06 ± 64.86 to 256 ± 58.14. AD, G_4D exhibited a decrease in pore perimeter contrary to G_2D and G_7D. Significant differences were observed. Finally, morphological changes were more evident as days of demineralization increased; 7 days of immersion could be employed as an enamel erosive model. The pore count increased after the demineralization model, BD pores perimeter was heterogeneous, and AD varied according to the immersion period.

• Morphological changes were more evident as days of demineralization increased.
• Seven days of immersion could be employed as an enamel erosive model.
• The initial porosity seems to be a determining factor for the final porousness.
• The pore perimeter of the primary enamel varied according to the immersion period on the demineralization model.

     

Fuzzy Theory for the Active Control of the Dynamic Response in Buildings

Abstract: A new fuzzy control method for the reduction of the dynamic response of structures is presented, and is compared with the instantaneous optimal control method. The control forces are determined from preformulated fuzzy rules regarding the velocity and the acceleration of the system. The triangular membership function and the mini-max-gravity method are used in the fuzzyfication and the defuzzyfication process, respectively. In these processes, no material property of the structure such as the mass matrix or the stiffness matrix are needed. This characteristic nature is definitely different from that of optimal control algorithms. Numerical examples are shown in order to compare the performances both of the proposed fuzzy control method and the optimal control method. It appeared that the fuzzy control method is quite useful as regards reliability and robustness.     

Solving Convection-Diffusion Problems on Curved Domains by Extensions from Subdomains

We present a technique for numerically solving convection-diffusion problems in domains $\varOmega $ with curved boundary. The technique consists in approximating the domain $\varOmega $ by polyhedral subdomains $\mathsf{{D}}_h$ where a finite element method is used to solve for the approximate solution. The approximation is then suitably extended to the remaining part of the domain $\varOmega $ . This approach allows for the use of only polyhedral elements; there is no need of fitting the boundary in order to obtain an accurate approximation of the solution. To achieve this, the boundary condition on the border of $\varOmega $ is transferred to the border of $\mathsf{D }_h$ by using simple line integrals. We apply this technique to the hybridizable discontinuous Galerkin method and provide extensive numerical experiments showing that, whenever the distance of $\mathsf{{D}}_h$ to $\partial \varOmega $ is of order of the meshsize $h$ , the convergence properties of the resulting method are the same as those for the case in which $\varOmega =\mathsf{{D}}_h$ . We also show numerical evidence indicating that the ratio of the $L^2(\varOmega )$ norm of the error in the scalar variable computed with $d>0$ to that of that computed with $d=0$ remains constant (and fairly close to one), whenever the distance $d$ is proportional to $\min \{h,Pe^{-1}\}/(k+1)^2$ , where $Pe$ is the so-called Péclet number.     

Some contributions to mechanical behaviors of lacustrine deposit in Bogota,Colombia

This paper presents the mechanical behaviors of the lacustrine deposit,a representative soil in Bogota,Colombia.Initially,the physical characterization of the deposit is performed via laboratory tests(grain size distribution,scanning electron microscopy,Atterberg limits and water content).This characterization intends to explain the special characteristics of the mechanical behaviors of this soil.Then,various triaxial tests are carried out with controlled loading path,strain rate change,relaxation,extensile stress,and cyclic loading.The test results reveal the shape of the yield curve for Bogota soil(in a natural state),and also show that an increasing effect of the strain rate depends on the liquid limit.This effect is also preserved with extensile stresses(which are poorly studied in soil mechanics).Finally,other effects,such as the loss of structure in the reconstituted samples and the effect of shear modulus at low strains,are studied for Bogota soil.     

Kinetic Studies of Mullite Synthesis from Alumina Nanoparticles and a Preceramic Polymer

The crystallization kinetics of mullite formation in a diphasic precursor consisting of a silicone resin filled with commercial γ-alumina nanoparticles (15 nm mean particle size, specific surface area of 100 m²/g), heated in air from 1250° to 1350°C, was studied by X-ray diffraction. Transitional γ-alumina and amorphous silica from the pyrolysis of the preceramic polymer exhibited a remarkable reactivity, as demonstrated by a very low incubation time (from 500 s at 1250°C to 20 s at 1350°C), a high mullite yield (about 80 vol%, after 100 s at 1350°C), and a low activation energy for nucleation (677±60 kJ/mol). The activation energy values found were lower than those reported previously for other diphasic systems, including sol–gel precursors. Besides the high specific surface of nanosized γ-alumina particles, the low energy barrier could be attributed to the highly reactive silica deriving from the oxidation of Si–CH₃ bonds in the silicone and to the homogeneous dispersion of the nanosized filler inside the preceramic polymer. Furthermore, the possibility of applying plastic shaping processing methods to the mixture of a preceramic polymer and nanosized filler makes this approach particularly valuable, in comparison, for instance, with sol–gel based alternatives.     

A stochastic interspecific competition model to predict the behaviour of <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> in the fermentation process of a traditional Sicilian salami

The present article discusses the use of modified Lotka–Volterra equations in order to stochastically simulate the behaviour of Listeria monocytogenes and lactic acid bacteria (LAB) during the fermentation period (168 h) of a typical Sicilian salami. For this purpose, the differential equation system is set considering temperature (T), pH, water activity (aw) as stochastic variables. Each of them is governed by dynamics that involve a deterministic linear decrease as a function of the time t and an “additive noise” term which instantaneously mimics the fluctuations of T, pH and aw. The choice of a suitable parameter accounting for the interaction of LAB on L. monocytogenes as well as the introduction of appropriate noise levels allows to match the observed data, both for the mean growth curves and for the probability distribution of L. monocytogenes concentration at 168 h.