Neue analysenmethode zur quantitativen bestimmung von vinylacetat in äthylen-vinylacetat-copolymeren

A new method for quantitative determination of vinyl acetate in copolymers is described. It is based on the elimination of acetic acid in molten p-toluenesulfonic acid at 160°C. The released acetic acid is potentiometrically titrated in the presence of p-toluenesulfonic acid. The method is applicable to a content of vinyl acetate from 0 to 100% in the copolymers.     

Dynamic studies of molecular imprinting polymerizations

Mechanisms of interaction of a three-dimensional polymer with solutes are of interest in the development and function of synthetic biomimetic polymers. We have investigated the effects of template/monomer interactions and template concentration on conversion and polymerization rates of a molecularly imprinted polymer. Copolymers of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (PEG600DMA) were prepared in the presence of glucose. The polymerization reaction kinetics of non-imprinted networks as well as those imprinted with glucose at concentration ratios of [HEMA]/[Glucose] between 11 and 1 were monitored in situ by ATR-FTIR spectroscopy and differential photocalorimetry (DPC). The rates of polymerization for imprinted polymers showed an early lag period followed by a late autoacceleration, indicative of the complexation between monomer and template. Hydrogen-bonding was also observed using FTIR through the CO (carbonyl) bond of the monomers by FTIR. A significant effect of the template on conversion and polymerization rate of imprinted polymers was observed compared to non-imprinted ones. These values provide guidelines for kinetic models of interacting systems.     

Strain-controlled growth of nanowires within thin-film cracks

There is continued interest in finding quicker and simpler ways to fabricate nanowires, even though research groups have been investigating possibilities for the past decade. There are two reasons for this interest: first, nanowires have unusual properties-for example, they show quantum-mechanical confinement effects, they have a very high surface-to-volume ratio, enabling them to be used as sensors, and they have the ability to connect to individual molecules. Second, no simple method has yet been found to fabricate nanowires over large areas in arbitrary material combinations. Here we describe an approach to the generation of well-defined nanowire network structures on almost any solid material, up to macroscopic sample sizes. We form the nanowires within cracks in a thin film. Such cracks have a number of properties that make them attractive as templates for nanowire formation: they are straight, scalable down to nanometre size, and can be aligned (by using microstructure to give crack alignment via strain). We demonstrate the production of nanowires with diameter <16 nm, both singly and as networks; we have also produced aligned patterns of nanowires, and nanowires with individual contacts.     

Radiation cross-linking in ultra-high molecular weight polyethylene for orthopaedic applications

The motivation for radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is to increase its wear resistance to be used as bearing surfaces for total joint arthroplasty. However, radiation also leaves behind long-lived residual free radicals in this polymer, the reactions of which can detrimentally affect mechanical properties. In this review, we focus on the radiation cross-linking and oxidative stability of first and second generation highly cross-linked UHMWPEs developed in our laboratory.     

安装烤瓷牙后影响牙髓的因素及其防护

随着烤瓷技术的不断改进,安装金属烤瓷牙修复牙齿逐步普及。对于利用活髓基牙安装烤瓷牙,修复原则是尽量保存和保护基牙牙体和牙髓组织,但在修复过程中有诸多原因可引起基牙牙髓组织反应,甚至导致不可逆性牙髓炎。本文主要论述用活髓牙作为基牙安装烤瓷牙后,影响牙髓发生病变的因素及其防护。     

Ultra high molecular weight polyethylene with improved plasticity and toughness by high temperature melting

Our goal was to improve the strength and toughness of ultra high molecular weight polyethylene (UHWMPE), which is the preferred polymeric bearing material in total joint implants. Based on accelerated diffusion of UHMWPE chains at high temperatures, our hypothesis was that high temperature melting could minimize the structural defects and thus improve the toughness of consolidated UHMWPE. Melting of consolidated medical-grade UHMWPE at 280, 300, and 320 °C in inert atmosphere improved the elongation at break, work-to-failure and impact strength, presumably due to chain scissioning and structural defect elimination through self-diffusion. An important finding of this study was that the gain in plasticity and toughness did not sacrifice the wear resistance under optimized melting conditions, which may be promising for next generation high performance UHMWPE materials for joint implant bearing surfaces.     

Millimeter-Wave Antenna of a Travelling-Wave Long Sinusoidal Slot in the Narrow Face of a Rectangular Waveguide

A travelling-wave long sinusoidal slot in the narrow face of a millimeter-wave (Ka-Band) rectangular waveguide is investigated. To the best of our knowledge, a slot of this shape is applied to the narrow face of a rectangular waveguide for the first time at this frequency range. The analytical study is based on the magnetic current model. Experimentally, far-field and S-parameters are measured and a good match is obtained between analytical and measured patterns. Frequency scan rates and velocity ratios of the structure are calculated. The effect of the sinusoidal slot’s geometrical parameters (amplitude, period and number of periods) on the radiation patterns is also investigated. The drawback of the sinusoidal radiator is its cross-polarized beam that is not convenient for antenna applications. These co and cross-polarized beams scan in two different angle regions. To filter/suppress the cross-polarized beam, a grid polarizer is mounted to the sinusoidal slot and a 15 dB suppression level is reached. S-parameters measurement shows that the antenna efficiency increases remarkably after the application of the grid polarizer to the slot.     

Integrating renewable sources of energy into an existing combined heat and power system

In recent years, renewable energy sources have played an increasingly important role in potential energy production. The integration of renewables into energy production plants has therefore become a major challenge for many organizations. This study concerns the modernization of a small power plant in a large hospital. The design criteria include the possibility of utilizing renewable energy sources and providing a potential increase in heat production (with additional heat being supplied to a nearby university campus). The existing boiler conditions (i.e. controls, efficiency, etc.) are unable to satisfy the desired requirements and therefore require an extensive retrofit.     

Bubbly cavitating flow generation and investigation of its erosional nature for biomedical applications

This paper presents a study that investigates the destructive energy output resulting from hydrodynamic bubbly cavitation in microchannels and its potential use in biomedical applications. The research performed in this study includes results from bubbly cavitation experiments and findings showing the destructive effects of bubbly cavitating flow on selected solid specimens and live cells. The bubbles generated by hydrodynamic cavitation are highly destructive at the surfaces of the target medium on which they are carefully focused. The resulting destructive energy output could be effectively used for biomedical treatments, such as destroying kidney stones (renal calculi) or killing cancer cells. Motivated by this potential, the cavitation damage to cancerous cells and material removal from chalk pieces (which possess similar material properties as some kidney stones) was investigated. Our results showed that cavitation could induce damage both on chalk pieces and leukemia/lymphoma cells. We discovered that hydrodynamic cavitation exposure had early and delayed effects on cancer cell survival. Hence, the potential of hydrodynamic bubbly cavitation generated at the microscale for biomedical treatments was revealed using the microchannel configuration as a microorifice (with an inner diameter of 147 μm and a length of 1.52 cm), which acts as the source of bubbly cavitating flows.     

Wear resistant UHMWPE with high toughness by high temperature melting and subsequent radiation cross-linking

The goal of this study was to create wear resistant ultra high molecular weight polyethylene (UHMWPE) with improved strength and toughness. It was previously demonstrated that high temperature melting (HTM) of UHMWPE at 280-320 °C improved its toughness without detrimentally affecting its wear resistance. We hypothesized that radiation cross-linking after high temperature melting could further improve the wear resistance of UHMWPE, and the loss in toughness by radiation cross-linking could be compensated by the improved toughness achieved by the high temperature melting prior to irradiation. In this work, we demonstrated that irradiation after HTM generated UHMWPE with improved toughness compared to the irradiated UHMWPEs without HTM, partly due to the low cross-link density of irradiated HTM UHMWPE. At a given cross-link density, irradiated HTM UHMWPEs showed higher wear resistance than irradiated UHMWPE. Therefore, successive HTM and radiation cross-linking strategy is promising to create UHMWPE materials with low wear and improved mechanical properties for total joint implants.