Accelerated wear testing with a microfabricated surface to evaluate the lubrication ability of biomolecules on polyethylene

Wear of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and wear‐particle‐induced osteolysis and bone resorption are the major factors causing the failure of total joint replacements. It is feasible to improve the lubrication and reduce the wear of artificial joints. We need further understanding of the lubrication mechanism of the synovial fluid. The objective of this study is to evaluate the lubricating ability of three major components in the synovial fluid: albumin, globulin, and phospholipids. An accelerated wear testing procedure in which UHMWPE is rubbed against a microfabricated surface with controlled asperities has been developed to evaluate the lubrication behavior. An analysis of the wear particle dimensions and wear amount of the tests has provided insights for comparing their lubrication performance. It is concluded that the presence of biomolecules at the articulating interface may reduce friction. A higher concentration of a biological lubricant leads to a decrease in the wear particle width. In addition, in combination with the wear results and mechanical analysis, the roles of individual biomolecules contributing to friction and wear at the articulating interface are discussed. These results can help us to identify the role of the biomolecules in the boundary lubrication of artificial joints, and further development of lubricating additives for artificial joints may be feasible. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Invasive group A streptococcal disease in Taiwan is not associated with the presence of streptococcal pyrogenic exotoxin genes

We reviewed the clinical features of 44 patients with invasive group A streptococcal (GAS) disease who were treated at two teaching hospitals in southern Taiwan from 1991 to 1994. Genes encoding streptococcal pyrogenic exotoxin types A (speA), B (speB), C (speC), and F (speF) and serotypes of M1, M6, and M12 were determined by polymerase chain reaction to target specific sequences in the 44 isolates recovered from these patients and in 28 isolates recovered from upper respiratory sites in 28 additional patients during the study period. The protease activity of these isolates was tested by using the casein plate method. Of the 44 patients with invasive diseases, 25 (57%) had no obvious underlying diseases, and 14 (32%) had preexisting neoplastic diseases or had previously used steroids. Twenty-five patients (57%) presented with cellulitis or necrotizing fasciitis, 24 (55%) had bacteremia, and eight (18%) had streptococcal toxic shock syndrome (STSS). Eight patients (18%) died of invasive GAS disease; seven had STSS, and seven had underlying diseases. All eight patients died within 48 hours after hospitalization. The presence of speA, speC, or speF was not implicated in any particular clinical syndrome in patients with invasive GAS disease. High-level protease activity and the M1 serotype of the isolates were significantly associated with the clinical signs of STSS and with mortality. M1 serotype and protease activity, as well as host immune status, might play significant roles in the pathogenesis of invasive GAS disease in Taiwan.     

Mathematical model for the pultrusion of blocked PU–UP matrix composites

The thermokinetic behavior of blocked polyurethane (PU)–unsaturated polyester (UP)–based composites during the pultrusion of glass‐fiber‐reinforced composites was investigated utilizing a mathematical model that accounted for the heat transfer and heat generation during curing. The equations of continuity and energy balance, coupled with a kinetic expression for the curing system, were solved using a finite difference method to calculate the temperature profiles and conversion profiles in the thickness direction in a rectangular pultrusion die. A kinetic model, dP/dt = A exp(?E/RT)P^m(1 ? P)ⁿ, was proposed to describe the curing behavior of a blocked PU–UP resin. Kinetic parameters for the model were obtained from dynamic differential scanning calorimetry scans using a multiple regression technique, which was able to predict the effects of processing parameters on the pultrusion. The effects of processing parameters including pulling speed, die wall temperature, and die thickness on the performance of the pultrusion also were evaluated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1996–2002, 2003     

Structural topology optimization using ant colony optimization algorithm

The ant colony optimization (ACO) algorithm, a relatively recent bio-inspired approach to solve combinatorial optimization problems mimicking the behavior of real ant colonies, is applied to problems of continuum structural topology design. An overview of the ACO algorithm is first described. A discretized topology design representation and the method for mapping ant's trail into this representation are then detailed. Subsequently, a modified ACO algorithm with elitist ants, niche strategy and memory of multiple colonies is illustrated. Several well-studied examples from structural topology optimization problems of minimum weight and minimum compliance are used to demonstrate its efficiency and versatility. The results indicate the effectiveness of the proposed algorithm and its ability to find families of multi-modal optimal design.     

Synergistic effects of micro-/nano-fillers on conductive and electromagnetic shielding properties of polypropylene nanocomposites

This study presents the synergistic effects of graphene nanosheets (GNSs) and carbon fibers (CFs) additions on the electrical and electromagnetic shielding properties of GNS/CF/polypropylene (PP) composites. These composites were fabricated by the melt blending of different ratios of GNSs and CFs (20:0, 15:5, 10:10, 5:15 and 0:20 wt/wt%) into a PP polymer matrix using a Brabender mixer. Besides, the chemical and crystalline structures and the thermal stability of the resultant GNS/CF/PP composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). FT-IR and XRD showed that with the addition of GNSs content, transmittances at 1373.4?cm^?1 and 1454.4?cm^?1 became smaller and the characteristic peak at 26.82° became stronger. TGA showed that the GNS/CF/PP composite can be used at high temperature below 456°C. Blending 10?wt% CFs and 10?wt% GNSs into the PP polymer resulted in excellent conductivity (0.397 S/cm), which indicated the occurrence of the critical percolation threshold phenomenon, and also reached the maximum electromagnetic shielding effectiveness (EMSE) of 20?dB at 1.28–2.00?GHz. Laminated with five layers of composites, its EMSE achieved 25–38?dB at 0.3–3.0?GHz, corresponding to blocking of 94.38–98.74% electromagnetic waves.     

An innovative framework of collaborative-based workflow in Development Chain Management

Currently, most product development procedures have been characterized as unnecessarily complicated. To maintain a competitive edge and to simplify the procedures, joint efforts from different functional groups play such crucial role. Specifically, information from marketing, sales, engineering, sourcing, and manufacturing should be cross-referenced. In addition, adopting pre-defined workflows contributes to efficient collection of distributed information. Moreover, unlike traditional workflow, a collaborative-based workflow (CWF) in product development process boasts of complicated workflow forms with manifold views for a workflow execution. Traditional workflow solutions, for instance, can only transmit a workflow form through different actors. Such workflow solutions merely offer modeling approval-based workflow (AWF), such as drawing reviews or absence applications.     

Biomimetic Engineering of a Scavenger‐Free Nitric Oxide‐Generating/Delivering System to Enhance Radiation Therapy

Nitric oxide (NO) is a potent tumor‐cell radiosensitizer but it can be readily scavenged by hemoglobin (Hb) in vivo. A biomimetic incubator that can generate and deliver NO in a scavenger (Hb)‐free environment to enhance its radiosensitizing effect to maximize its efficacy in radiotherapy is proposed. This NO incubator comprises a poly(lactic‐co‐glycolic acid) (PLGA) hollow microsphere (HM) that contains an NO donor (NONOate) and a surfactant molecule (sodium caprate, SC) in its aqueous core. In acidic tumorous environments, the PLGA shell of the HM allows the penetration of protons from the outside, activating the hydrolytic cleavage of NONOate, spontaneously generating NO bubbles, which are immediately trapped/stabilized by SC. The SC‐stabilized NO bubbles in the HM are then squeezed through the spaces of its PLGA matrices by the elevated internal pressure. Upon leaving the HM, the entrapped NO molecules may passively diffuse through their SC‐stabilized/protected layer gradually to the tumor site, having a long‐lasting radiosensitizing effect and inhibiting tumor growth. The entire process of NO generation and delivery is conducted in a scavenger (Hb)‐free environment, mimicking the development of young ovoviviparous fish inside their mothers' bodies in the absence of predators before birth.     

Decomposition of singular large sparse matrix by adding dummy links and dummy degrees

Abstract

This paper proposes a simple scheme to decompose an n×n nonpositive definite matrix, A, associated with simultaneous equations, A X = B, into a triple‐factors (lower triangular, diagonal, and upper triangular matrices), i.e., Å = L D U, without interchanging rows or columns of A, but with A expanded with new rows and new columns to an m×m matrix Å. Whenever a near‐zero diagonal element, say ā_ii , is encountered and used as a pivoting element, an appropriate positive real number, say p, is added to this diagonal element, and a new term —px_k is also added to the i‐th equation, where x_k is a new variable called “dummy variable'’. If we also add a new equation —px_i + px_k = 0 to enforce the new added variable x_k equal to x_i then the modified i‐th equation has the same effect as the original equation. Therefore, the original solution X can be found directly from the expanded solution of the modified expanded equation. The method is very useful in solving the following problems: (1) nonlinear problems near the limit state, (2) postbuckling analysis, (3) system equations with constraint conditions, and (4) getting eigenvectors from eigenvalues.     

Improving proton exchange membrane fuel cell performance with carbon nanotubes as the material of cathode microporous layer

The cathode microporous layer (MPL) is fabricated by various multiwall carbon nanotubes (CNTs), and its influence on the performance of a proton exchange membrane fuel cell (PEMFC) is evaluated. Three types of CNT with different dimensions are employed in the experiments, and the conventional MPL made by acetylene black (AB) is also considered for the purpose of comparison. The results show that the employment of CNT as MPL composition indeed may improve fuel cell performance significantly in comparison with the case of AB. The type of CNT with the largest tube diameter and straight cylinder in shape exhibits the highest cell performance. The corresponding optimal CNT loading and polytetrafluoroethylene (PTFE) content in the MPL are also evaluated. Results show that the case of cathode MPL composed of 1.5 mg cm^?2 CNT and 20 wt% PTFE exhibits the best performance in all the experimental cases. The present data reveal that the application of CNT for MPL fabrication is beneficial to promote PEMFC performance. Copyright © 2015 John Wiley & Sons, Ltd.