Characterization of flexural and compressive behavior in polylactic acid composites for low-cost transtibial prosthetic applications: Influence of reinforcements

Loss of a lower limb leads to immobility, necessitating the use of prosthetic foot and socket as substitutes for lost limbs. However, the production of these prosthetic devices poses challenges due to the wide array of printing settings, materials, and post-processing techniques involved. The objectives of this study were to examine the compression and flexural behavior of polylactic acid reinforced with carbon fiber fabricated via fused filament fabrication (FFF) and to investigate the effects of process constraints, namely nozzle hole diameter (0.20, 0.40, and 0.60 mm) and internal filling pattern (rectilinear, honeycomb, and triangle). The study employed compression and flexural tests, along with the analysis of failure morphology, on build samples. The resulting data were analyzed using Taguchi ANOVA and response surface methodology (RSM) to determine how compression and flexural behavior vary with the specified process constraints. The research findings demonstrate that the prosthetic socket and foot prosthesis created using FFF exhibit superior flexural and compressive behavior and strength, respectively. These results signify the potential for cost reduction in the production of prosthetic devices. The significance of these results lies in the improvement of prosthetic device production, enabling enhanced mobility and independence for amputees.     

Properties of nanocomposites based on maleate‐vinyl ether donor—acceptor UV‐curable systems

UV‐curable nanocomposites based on donor–acceptor crosslinking chemistry were prepared containing organically modified montmorillonites. The coatings were characterized for thermal, mechanical, and morphological properties. X‐ray diffraction and transmission electron microscopy showed that nanocomposites were formed in all samples. Results showed that an increase in the percentage of clay caused an increased modulus and glass‐transition temperature. It was also seen that tensile modulus showed dramatic improvement when compared with the unmodified polyester sample. Real time IR kinetic data showed that higher conversions were obtained at higher clay loadings. Pendulum hardness values and tensile modulus values showed different trends in properties depending on the combination of polymer matrix and organomodification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Direct numerical simulations of HCCI/SACI with ethanol

Two and three dimensional direct numerical simulations (DNS) of an autoignitive premixture of air and ethanol in Homogeneous Charge Compression Ignition (HCCI) mode have been conducted. A special feature of these simulations is the use of compression heating through mass source/sink terms to emulate the compression and expansion due to piston motion. Furthermore, combustion phasing is adjusted such that peak heat release occurs after Top Dead Center (TDC) during the expansion stroke, as in a real engine. Zero dimensional simulations were first conducted to identify important parameters for the higher dimensional simulations. They showed that for ethanol, temperature and dilution are the parameters the problem is most sensitive to. One set of two dimensional simulations were conducted with a uniform mixture composition and different levels of temperature stratification, both with and without compression heating. Another set of simulations varied the mixture stratification with constant temperature stratification. Both sets showed considerable differences in ignition delay, heat release and peak temperature and peak pressure. Compression heating was also found to have a significant effect on the heat release profile. A three dimensional simulation was conducted for Spark-Assisted HCCI (SACI). It was initiated with a small spark kernel, which evolved into a premixed flame. The entire mixture eventually underwent autoignition. Distance function based analysis showed a strongly attenuating flame. Analysis of scalar mixing frequencies shows that differential diffusion and reaction induced mixing play an important role in predicting the mixing of reactive scalars. This has significant implications for mixing models for reactive flows. Chemical explosive mode analysis (CEMA) was applied to the 3D simulation and showed promise in identifying the transition from flame propagation to autoignition.     

An efficient and unbiased method for sensitivity analysis of stochastic reaction networks

We consider the problem of estimating parameter sensitivity for Markovian models of reaction networks. Sensitivity values measure the responsiveness of an output with respect to the model parameters. They help in analysing the network, understanding its robustness properties and identifying the important reactions for a specific output. Sensitivity values are commonly estimated using methods that perform finite-difference computations along with Monte Carlo simulations of the reaction dynamics. These methods are computationally efficient and easy to implement, but they produce a biased estimate which can be unreliable for certain applications. Moreover, the size of the bias is generally unknown and hence the accuracy of these methods cannot be easily determined. There also exist unbiased schemes for sensitivity estimation but these schemes can be computationally infeasible, even for very simple networks. Our goal in this paper is to present a new method for sensitivity estimation, which combines the computational efficiency of finite-difference methods with the accuracy of unbiased schemes. Our method is easy to implement and it relies on an exact representation of parameter sensitivity that we recently proved elsewhere. Through examples, we demonstrate that the proposed method can outperform the existing methods, both biased and unbiased, in many situations.     

Molecular modelling and competition binding study of Br-noscapine and colchicine provide insight into noscapinoid-tubulin binding site

We have previously discovered the tubulin-binding anti-cancer properties of noscapine and its derivatives (noscapinoids). Here, we present three lines of evidence that noscapinoids bind at or near the well studied colchicine binding site of tubulin: (1) in silico molecular docking studies of Br-noscapine and noscapine yield highest docking score with the well characterised colchicine-binding site from the co-crystal structure; (2) the molecular mechanics-generalized Born/surface area (MM-GB/SA) scoring results ΔΔG(bind-cald) for both noscapine and Br-noscapine (3.915 and 3.025 kcal/mol) are in reasonably good agreement with our experimentally determined binding affinity (ΔΔG(bind-Expt) of 3.570 and 2.988 kcal/mol, derived from K(d) values); and (3) Br-noscapine competes with colchicine binding to tubulin. The simplest interpretation of these collective data is that Br-noscapine binds tubulin at a site overlapping with, or very close to colchicine-binding site of tubulin. Although we cannot rule out a formal possibility that Br-noscapine might bind to a site distinct and distant from the colchicine-binding site that might negatively influence the colchicine binding to tubulin.     

Score level fusion of multimodal biometrics using triangular norms

A multimodal biometric system that alleviates the limitations of the unimodal biometric systems by fusing the information from the respective biometric sources is developed. A general approach is proposed for the fusion at score level by combining the scores from multiple biometrics using triangular norms (t-norms) due to Hamacher, Yager, Frank, Schweizer and Sklar, and Einstein product. This study aims at tapping the potential of t-norms for multimodal biometrics. The proposed approach renders very good performance as it is quite computationally fast and outperforms the score level fusion using the combination approach (min, mean, and sum) and classification approaches like SVM, logistic linear regression, MLP, etc. The experimental evaluation on three databases confirms the effectiveness of score level fusion using t-norms.     

Permeability of concrete with fiber reinforcement and service life predictions

In the context of its long-term durability, permeability of concrete to water remains one of the most important characteristics. In the study reported here, water permeability of plain and fiber reinforced concrete (FRC) was measured with and without an applied compressive stress. For the stressed specimens, two levels of the applied stress, 0.3f _u and 0.5f _u , where f _u is the ultimate strength of concrete in compression, were investigated. A collated cellulose fiber at volume fractions of 0.1, 0.3 and 0.5% was used. Results indicate that for the unstressed concrete, fiber reinforcement reduces the permeability. For the stressed concrete, initially as the applied stress was increased, a reduction in the permeability for both plain and fiber reinforced concrete was observed. This reduction, however, occurred only to a certain threshold value of stress. Beyond this threshold, a rapid increase in the permeability occurred for plain concrete. For fiber reinforced concrete, while an increase in the permeability was noticed beyond the threshold value of stress, the magnitude of the increase remained small and the permeability remained well below the unstressed level. In the later part of the paper, some Service Life Predictions were carried out by first relating the measured permeability coefficients to chloride diffusion coefficients and then using available mathematical models. Results from the modeling exercise indicate that at least in qualitative terms, fiber reinforced concrete will depict a better durability in service than plain concrete.     

Anisotropic organic glasses

While the last decades have seen considerable efforts to control molecular packing in organic crystals, the idea of controlling packing in organic glasses is relatively unexplored. Glasses have many advantageous properties that crystals lack, such as macroscopic homogeneity and compositional flexibility, but packing in organic glasses is generally considered to be isotropic and highly disordered. Here we review and compare four areas of recent research activity showing control over anisotropic packing in organic glasses: (1) anisotropic glasses of low molecular weight organic semiconductors prepared by physical vapor deposition, (2) the use of mesogens to produce anisotropic glasses by cooling equilibrium liquid crystal phases, (3) the preparation of highly anisotropic glassy solids by vapor-depositing low molecular weight mesogens, and (4) anisotropic films of polymeric semiconductors prepared by spin-coating or solution casting. We delineate the connections between these areas with the hope of cross-fertilizing progress in the development of anisotropic glassy materials.