Increased risk for falling associated with obesity: mathematicalmodeling of postural control

Recent epidemiological studies report that obesity is positively related to fracture incidence. In the present experiment, a model of postural control was used to examine the impact of an abnormal distribution of body fat in the abdominal area upon postural stability. Obese and lightweight humanoids were destabilized by imposing a small initial angular speed from a neutral standing position. To avoid a loss of stability yielding a stepping reaction or a fall, an ankle torque is necessary to counteract the perturbation. Three torque parameters-ankle torque onset, time to peak torque, and muscular ankle torque-were entered in a program to simulate the intrinsic variability of the human postural control system. A loss of stability was detected when the center of pressure exceeded stability margins. The most striking observation is the nonlinear increase of torque needed to stabilize the humanoid when the motor response was chararterized by delayed temporal parameters. The effect was more pronounced when an anterior position of the center of mass was included in the simulations. This suggests that, when submitted to daily postural stresses and perturbations, obese persons (particularly those with an abnormal distribution of body fat in the abdominal area) may be at higher risk of falling than lightweight individuals     

Intrinsic properties of the optical coupling between axisymmetric Gaussian beams

On the basis of the overlap integral method, an approximate analytical model is derived to estimate the coupled optical power between axisymmetric Gaussian beams when transverse, axial, and angular misalignments simultaneously exist in three dimensions. Seven optical properties are derived from a detailed analysis of the model. Because the model is an approximate analytical solution to the overlap integral method, the existence of each property is also investigated by a numerical solution. Results show that all seven properties are intrinsic to the optical coupling phenomenon between Gaussian beams. Because numerous single-mode device-to-fiber coupling systems can be well described by use of Gaussian beams, the seven properties provide a solid basis to develop model-based algorithms for single-mode device-to-fiber alignment automation.     

Chemistry of the Interface Between Aluminum and Polyester Films

It has been observed that the adhesion between vacuum-evaporated aluminum and poly(ethylene isophthalate-co-ethylene sodium sulfoisophthalate) copolymer is approximately five times greater than the adhesion between vacuum-evaporated aluminum and biaxially-oriented poly(ethylene terephthalate) film. To describe the interface between the aluminum and these polymeric substrates, thermoanalytical, spectroscopic and microscopic techniques have been applied. Definite changes in surface elemental composition and chemical functionality occur upon metallization of the polymer films. Aluminized samples contained two new oxygen functionalities; one due to the aluminum oxide and the other due to an organoaluminum species. Thermal degradation, as may occur during vacuum evaporation, would be expected to yield a carboxylic acid endgroup and a vinyl endgroup for each chain scission reaction that occurred. Reaction of aluminum with these carboxylic acid endgroups is thought to be responsible for the organoaluminum oxygen peak that was observed. Based on the XPS data, however, the level of this new functionality was comparable for both types of polyester film. Thus, this new functionality may be involved in promoting aluminum/polyester adhesion, but by itself cannot explain the differences in the level of adhesion that are attained. It appears, based on the transmission electron micrographs, that the aluminum deposit penetrates the copolymer coating to a greater depth than it does the PET. The greater level of penetration could be responsible for the greater adhesion obtained between vacuum-evaporated aluminum and the copolymer film compared with the level of adhesion obtained with the PET film. Based on this work, it appears that the adhesion of the vacuum-evaporated aluminum to both polyesters has a similar chemical component (type and amount) but a different extent of the mechanical component.     

Metal ion additive–polyimide interactions employing thermogravimetry

Solutions of poly(amic acid), a polyimide precursor prepared from 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride and 4,4′-oxydianiline, containing metal ions such as Pd, Pt, and Sn in a variety of chemical states were prepared. The polymer–metal ion solutions and each component thereof were analyzed by thermogravimetry. Summation of the calculated contribution of each component of the polymer solution mass loss curve yields a calculated TG curve. Subtraction of the calculated curve from the actual curve for the polyamic acid–metal ion solution results in a difference TG curve. From the difference TG curve information about polymer/additive interactions can be obtained.     

Bayesian inference theory applied to hyperfine parameter distribution extraction in Mössbauer spectroscopy

We present an effective direct extraction method for hyperfine parameter distributions based on Bayesian inference theory with free-form model and give an example of application to quadrupole splitting distribution analysis in an Fe-57 Mössbauer spectrum of an Fe³⁺-chlorite. The technique gives a unique solution to the distribution with arbitrary shape and is not sensitive to the elemental doublet parameters. In addition full error analysis of the distribution is obtained for the first time in Mössbauer spectroscopy.     

Ellipsometric study of thermally evaporated germanium thin film

The optical properties of thermally evaporated germanium thin films in the spectral range 0.3-1.7 mum were studied with spectroscopic ellipsometry. The microstructure of these films, including their crystallinity, density, surface morphology, and surface oxidation, was analyzed with x-ray diffraction, Rutherford backscattering spectrometry, atomic force microscopy (AFM), and Auger electron spectrometry (AES). Parameters such as the surface roughness and surface-oxidation-layer thickness, derived from AFM and AES measurements, were incorporated into our optical model. The complex index of refraction (n and k) of the films was determined throughout the above spectral range and compared with that of single-crystal germanium.     

A single step process to design a custom mattress that relieves trunk shear forces

Back pain is a common complaint that may result from the use of an inappropriate mattress. It can be minimized by using a well suited mattress. This paper presents a method for designing a custom foam mattress in an attempt to reduce back pain for the lateral lying position. Body three-dimensional profile and its mass distribution are both estimated by a simple photographic method. Finite element models are established and precalculated to characterize and predict the interaction between the body and the mattress surface. The process is based on two design performance criteria: a spine curvature in the frontal plane similar to a standing one and a given load distribution along the mattress. The process is validated with three mattresses customized to three individuals. Results show a good fit with numerical predictions according to the two performance design criteria.     

Sorption and diffusion of a brake fluid in EPDM elastomers

This article reports on an investigation into how the morphology of four commercially available ethylene propylene diene monomer (EPDM) elastomers was affected by exposure to a brake fluid. The sorption and diffusion coefficients as a function of carbon‐black content as well as the EPDM type were determined at 23°C, 60°C, 100°C and 150°C. It was found that variation in carbon‐black loading showed an effect on the transport characteristics of EPDM elastomers. The sorption data at room temperature were not reported since these took too long a time. The leaching out of the indigenous additives might be due to the paraffin oil migrating to the surface of the specimens. The diffusion of the brake fluid in the EPDM membranes follows non‐Fickian transport. The results of this investigation are discussed in terms of the morphological differences in the EPDM formulations. The diffusion coefficients showed a dependence on the morphology of EPDM, as studied by the glass‐transition temperature of the elastomers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 000–000, 2001