Dry Sliding Wear Properties of Ultra-high Molecular Weight Polyethylene Parts Made by the Injection Molding Process

The objective of this study was to investigate the effects of various sliding wear test conditions on the tribological properties of UHMWPE. The results indicated that the wear resistance of UHMWPE in the sliding direction perpendicular to the melt flow direction was stronger than that in the sliding direction parallel with the melt flow direction. It was found that the X-Z plane obtains more serious incomplete molecular bondings and cracks than the Y-Z plane. The main wear mechanisms were plastic deformations and wrinkled formations. The UHMWPE hardness increases or decreases as the applied load and sliding frequency increases or decreases.     

An analytical computation method for statistical tolerance analysis of assemblies with truncated normal mean shift

This paper proposes an analytical solution for fast tolerance analysis of the assembly of components with a mean shift or drift in the form of a doubly-truncated normal distribution. The assembly of components with a mean shift or drift in the form of a uniform distribution (the Gladman model) can be calculated by this method as well since the uniform distribution is a special form of the doubly-truncated normal distribution. Integration formulae of the first four moments of the truncated normal distribution are first derived. The first four moments of the resultant tolerance distribution are then calculated. As a result, the resultant tolerance specification is represented as a function of the standard deviation and the coefficient of kurtosis of the resultant distribution. Based on this method, the calculated resultant tolerance specification is more accurate than that predicted by the Gladman's model or the simplified truncated normal model. The difference between this model and the Monte Carlo method with 1,000,000 simulation samples is less than 0.5%. The merit of the proposed method is that it is fast and accurate which is crucial for engineering applications in tolerance analysis.     

Improving biodegradation behavior of calcium sulfate bone graft tablet by using water vapor treatment

The biodegradation rate of calcium sulfate hemihydrate (CSH) tablets is extremely rapid. This study adopts a water vapor treatment to modify the surface structure of a CSH tablet. After the treatment, a small amount of calcium sulfate dihydrate (CSD) forms on the surface; the porosity near the surface region decreases, consequently enhancing tablet strength and surface hardness. Because of the decrease in porosity at the surface, the time for complete disintegration increases from 1.2 h to 7.2 h; the time for complete dissolution increases from 7 days to 25 days.     

Anti-Inflammatory Activity of N-(3-Florophenyl) ethylcaffeamide in Mice

In this study, we evaluated the anti-inflammatory activity of one synthetic product, N-(3-Florophenyl)ethylcaffeamide (abbrev. FECA), by using animal model of λ-carrageenan-induced paw edema in mice. The anti-inflammatory mechanism of FECA was determined by measuring the levels of cyclooxygenase-2 (COX-2), nitric oxide (NO), tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), and malondialdehyde (MDA) in the edema paw tissue, and the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GRd) in the liver. The results showed that FECA reduced the paw edema at three, four and five hours after λ-carrageenan administration. The levels of COX-2, NO, TNF-α, and MDA in the λ-carrageenan-induced edema paws were reduced and the activities of SOD, GPx, and GRd in liver tissues were raised by FECA. These results suggested that FECA possessed anti-inflammatory activities and the anti-inflammatory mechanisms might be related to the decrease of the levels of COX-2, NO, and TNF-α in inflamed tissues and the increase in the MDA level by increasing the activities of SOD, GPx, and GRd.     

Preparation and characterization of novel ultra‐high molecular weight polyethylene composite fibers filled with nanosilica particles

Ultrahigh molecular weight polyethylene (UHMWPE)/nanosilica (F₂S_y) and UHMWPE/modified nanosilica (F₂S_mx‐y) as‐prepared fibers were prepared by spinning of F₂S_y and F₂S_mx‐y gel solutions, respectively. Modified nanosilica particles were prepared by grafting maleic anhydride grafted polyethylenes onto nanosilica particles. The achievable draw ratios (D_ra) of F₂S_y and F₂S_mx‐y as‐prepared fibers approached a maximal value as the original and modified nanosilica contents reached corresponding optimum values; the maximal D_ra value obtained for F₂S_mx‐y as‐prepared fiber specimens was significantly higher than that of the F₂S_y as‐prepared fiber specimens prepared at the optimum nanosilica content. The melting temperature and evaluated lamellar thickness values of F₂S_y and F₂S_mx‐y as‐prepared fiber series specimens decrease, but crystallinity values increase significantly, as their original and modified nanosilica contents respectively increase. Similar to the achievable drawing properties of the as‐prepared fibers, the orientation factor, tensile strength (σ_f) and initial modulus (E) values of both drawn F₂S_y and F₂S_mx‐y fiber series specimens with a fixed draw ratio reach a maximal value as the original and/or modified nanosilica contents approach the optimum values; the σ_f and E values of the drawn F₂S_mx‐y fiber specimens are significantly higher than those of the corresponding drawn F₂S_y fiber specimens prepared at the same draw ratios and nanosilica contents but without being modified. To understand the interesting ultradrawing, thermal, orientation and tensile properties of F₂S_y and F₂S_mx‐y fiber specimens, Fourier transform infrared, specific surface area and transmission electron microscopy analyses of the original and modified nanosilica were performed in this study. © 2012 Society of Chemical Industry     

NURBS machining and feed rate adjustment for high-speed cutting of complex sculptured surfaces

Owing to the enormous engineering advancement in modern industry, the competition in the development of advanced manufacturing technologies has been increasingly intense as can be seen in automobile, aerospace and various industries. Not only has product quality improved tremendously, but also the demand over production speed has become higher. Therefore, high-speed and high-accuracy production has become a very important goal of modern manufacturing companies. Thanks to ever increasing computer speed and the open architecture of new controllers in computer-controlled machines, the capability and flexibility of today's CNC machines allow us to machine contoured geometry using non-uniform rational B-spline (NURBS) curves directly from the free-form surfaces of a complex CAD/CAM model. As a result, machining accuracy and product quality can be greatly improved while machining time is also significantly reduced. This paper proposes a post-processing approach to convert G1 NC codes from most CAD/CAM systems to NURBS NC paths for highspeed contour machining. The NURBS interpolation strategy that takes into account the optimized cutting feed rate based on machine dynamic response and curvature of the NURBS curve is also developed. Experiments show that the implemented NURBS cutting can significantly improve machining accuracy and reduce cutting time and therefore satisfies the requirements of today's highspeed and-accuracy machining needs.     

Frequency domain analysis for stability robustness of multivariable feedback systems

Abstract

This paper presents techniques for analyzing stability robustness of multivariable control systems. The upper bounds for each element of the allowable perturbation matrices can be obtained whether highly structural information is available or not. Approaching from testing the nonsingularity of a matrix by its eigenvalues instead of using matrix norms, the main algorithm involved is the computation of the spectral radii of certain nonnegative matrices. Due to the fact that any matrix norm is never less than the spectral radius of the same matrix, less conservative results are obtained using our criteria as compared with those obtained by utilizing matrix norms.     

A hybrid swarm intelligence algorithm for the travelling salesman problem

Abstract: We present a hybrid model named HRKPG that combines the random‐key search method and an individual enhancement scheme to thoroughly exploit the global search ability of particle swarm optimization. With a genetic algorithm, we can expand the area of exploration of individuals in the solution space. With the individual enhancement scheme, we can enhance the particle swarm optimization and the genetic algorithm for the travelling salesman problem. The objective of the travelling salesman problem is to find the shortest route that starts from a city, visits every city once, and finally comes back to the start city. With the random‐key search method, we can search the ability of the particle and chromosome. On the basis of the proposed hybrid scheme of HRKPG, we can improve solution quality quite a lot. Our experimental results show that the HRKPG model outperforms the particle swarm optimization and genetic algorithm in solution quality.     

ILS双载波干扰测试的处理方法

描述了针对RTCA/DO-195（Radio Commission for Aeronautics/Document-195）标准要求中提到的双载波测试干扰问题所采取的措施方法。重点介绍了在频域内如何处理带内信号干扰并提高解算精度的过程，这种设计方法为类似的无线电带内信号干扰问题提供了一种有效实用的解决方案。     

A universal design chart for linear time-invariant continuous-timeand discrete-time compensators

Recently, design charts were given for various conventional compensators. In particular, a design chart was developed for the phase-lead-lag compensator to eliminate the trial-and-error nature of the design. In this paper, it is shown that a single universal design chart can be generated for all the various types of conventional compensators. This chart allows compensator parameters to be determined readily and is applicable to the design of both continuous-time and discrete-lime compensators. A detailed example is given to illustrate the use of the chart. This universal chart may be computerized for ease of design