Transmission laser welding of amorphous and semi-crystalline poly-ether–ether–ketone for applications in the medical device industry

The use of thermoplastics in the medical device industry is increasing rapidly. This is stimulating the development of manufacturing processes, such as joining techniques, for these materials. Transmission laser welding (TLW) is a fast and efficient method for joining thermoplastics, creating a strong and durable bond. The aim of this study was to determine the influence of laser intensity, scan speed, and material morphology on the lap-joint bond strength of poly-ether–ether–ketone (PEEK) joined using TLW. Clearweld® was used as the infrared absorbing medium at the interface. Two laser powers (10 and 20 W) and five scan speeds (4, 8, 16, 32, 64 mm/s) were assessed for quality of the joint for two PEEK morphologies (amorphous and semi-crystalline). The results showed that the greatest bond strengths were achieved using the two lowest scan speeds of 4 mm/s and 8 mm/s (p < 0.05); ranging from 22 to 25 MPa for semi-crystalline and 12 to 19 MPa for amorphous. The laser intensity had no significant effect on bond strength, for the two intensities tested. The semi-crystalline PEEK bonds were stronger than the amorphous PEEK bonds, at all speeds and power (p < 0.05). Post-fracture surface analysis showed bubbles within the weld line of all samples, possibly due to water vaporisation.     

Stochastic analysis and robust optimization for a deck lid inner panel stamping

FE-simulation and optimization are widely used in the stamping process to improve design quality and shorten development cycle. However, the current simulation and optimization may lead to non-robust results due to not considering the variation of material and process parameters. In this study, a novel stochastic analysis and robust optimization approach is proposed to improve the stamping robustness, where the uncertainties are involved to reflect manufacturing reality. A meta-model based stochastic analysis method is developed, where FE-simulation, uniform design and response surface methodology (RSM) are used to construct meta-model, based on which Monte-Carlo simulation is performed to predict the influence of input parameters variation on the final product quality. By applying the stochastic analysis, uniform design and RSM, the mean and the standard deviation (SD) of product quality are calculated as functions of the controllable process parameters. The robust optimization model composed of mean and SD is constructed and solved, the result of which is compared with the deterministic one to show its advantages. It is demonstrated that the product quality variations are reduced significantly, and quality targets (reject rate) are achieved under the robust optimal solution. The developed approach offers rapid and reliable results for engineers to deal with potential stamping problems during the early phase of product and tooling design, saving more time and resources.     

Dead-time effect and compensations of three-level neutral pointclamp inverters for high-performance drive applications

Due to the use of high-power devices and slow-switching frequency in a three-level neutral point clamp inverter, the dead-time effect may not be compensated sufficiently fast by using methods developed for the two-level inverter. In this paper, the dead-time effect in a three-level inverter with snubber circuits is analyzed to reveal that it does not only depend on load current direction, but also on magnitude. The snubber network also plays an important role in determining the output phase voltage during the dead-time period. Software techniques are proposed to compensate the dead-time effect as soon as it occurs as demanded by the slow-switching frequency. Experimental results show their effectiveness     

Stretchable and Transparent Conductive PEDOT:PSS‐Based Electrodes for Organic Photovoltaics and Strain Sensors Applications

The development of transparent, conducting, and stretchable poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐based electrodes using a combination of a polyethylene oxide (PEO) polymer network and the surfactant Zonyl is reported. The latter improves the ductility of PEDOT:PSS and enables its deposition on hydrophobic surfaces such as polydimethylsiloxane (PDMS) elastomers, while the presence of a 3D matrix offers high electrical conductivity, elasticity, and mechanical recoverability. The resulting electrode exhibits attractive properties such as high electrical conductivity of up to 1230 S cm^?1 while maintaining high transparency of 95% at 550 nm. The potential of the electrode technology is demonstrated in indium‐tin‐oxide (ITO)‐free solar cells using the PBDB‐T‐2F:IT‐4F blend with a power conversion efficiency of 12.5%. The impact of repeated stretch‐and‐release cycles on the electrical resistance is also examined in the effort to evaluate the properties of the electrodes. The interpenetrated morphology of the PEDOT:PSS and polyethylene oxide network is found to exhibit beneficial synergetic effects resulting in excellent mechanical stretchability and high electrical conductivity. By carefully tuning the amount of additives, the ability to detect small changes in electrical resistance as a function of mechanical deformation is demonstrated, which enables the demonstration of stretchable and resilient on‐skin strain sensors capable of detecting small motions of the finger.     

Glutamatergic transmission in the nucleus of the solitary tract modulates memory through influences on amygdala noradrenergic systems.

The authors examined whether glutamate release from the vagus nerve onto the nucleus of the solitary tract (NTS) is one mechanism by which the vagus influences memory and neural activity in limbic structures. Rats trained to drink from a spout were given a footshock (0.35 mA) on Day 5 after approaching the spout. Phosphate-buffered saline or 5.0, 50.0, or 100.0 nmol/0.5 μl glutamate was then infused into the NTS. Glutamate (5.0 or 50.0 nmol) significantly enhanced memory on the retention test. In Experiment 2, this effect was attenuated by blocking noradrenergic receptors in the amygdala with propranolol (0.3 μg/0.5 μl). Experiment 3 used in vivo microdialysis to determine whether footshock plus glutamate (50.0 nmol) alters noradrenergic output in the amygdala. These treatments caused a significant and long-lasting increase in amygdala noradrenergic concentrations. The results indicate that glutamate may be one transmitter that conveys the effects of vagal activation on brain systems that process memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

3D modelling of flexural isostatic deformation

Modelling of the isostatic loading of the earth's crust in three dimensions is a difficult problem due to the length scales involved, the lack of scalability of the underlying equations and the slow convergence of the solution under conventional techniques. In this paper, a new method to solve the three-dimensional (3D) flexure equation has been developed. The long-standing challenge in numerically modelling flexural isostasy at large scale and high rigidity is addressed. The program is capable of modelling both local and regional isostatic compensation. Compared with other schemes, the isostatic model presented here is more robust and computationally efficient.     

Optimal portfolios with regime switching and value-at-risk constraint

We consider the optimal portfolio selection problem subject to a maximum value-at-Risk (MVaR) constraint when the price dynamics of the risky asset are governed by a Markov-modulated geometric Brownian motion (GBM). Here, the market parameters including the market interest rate of a bank account, the appreciation rate and the volatility of the risky asset switch over time according to a continuous-time Markov chain, whose states are interpreted as the states of an economy. The MVaR is defined as the maximum value of the VaRs of the portfolio in a short time duration over different states of the chain. We formulate the problem as a constrained utility maximization problem over a finite time horizon. By utilizing the dynamic programming principle, we shall first derive a regime-switching Hamilton-Jacobi-Bellman (HJB) equation and then a system of coupled HJB equations. We shall employ an efficient numerical method to solve the system of coupled HJB equations for the optimal constrained portfolio. We shall provide numerical results for the sensitivity analysis of the optimal portfolio, the optimal consumption and the VaR level with respect to model parameters. These results are also used to investigating the effect of the switching regimes.     

Book reviews

House as a Mirror of Self: Exploring the Deeper Meanings of Home. Clare Cooper Marcus. Berkeley, California, Conari Press, 1995, 307 pp., US$24.95. ISBN: 0 943233 92 5.

In the Cities of the South: Scenes from a Developing World. Jeremy Seabrook. London, Verso, 1996, £13.95 pbk, £44.95 hbk. ISBN: 1 85984 081 7 (pbk) ISBN: 1 85984 986 5 (hbk).

Households and Housing. William A.V. Clark & Frans M. Dieleman. New Jersey, Center for Urban Policy Research, Rutgers University, 1996, $19.95 pbk. ISBN: 0 88285 156 X.

Modern Housing for America. Policy Struggles in the New Deal Era. Gail Radford. Chicago, University of Chicago Press, 1997, 258 pp., $17.95 pbk. ISBN: 0 226 70223 5.     

Speculations on the possible causes of the Whymper apparition

During the first ascent of the Matterhorn, a remarkable optical effect comprising three crosses surrounded by a great arch was observed by Edward Whymper, the British mountaineer. The authors review previous published explanations of the apparition. There are no photographs, only a woodcut and sketch, so the size of the apparition is not known, and it is not possible to make a definitive conclusion about what caused it. A fogbow and ice crystal arcs could have produced a circle and crosses in a direction consistent with the apparition. Some simulations are presented; one has a form approximating Whymper's sketch. However, while this simulation used a crystal type that can occur, it required an unusual alignment that would be very rare.