Front dynamics in catalytic surface reactions

A variety of pattern formation phenomena in catalytic surface reactions can be attributed to the dynamics of interfaces, or fronts, separating distinct uniform states. The states may represent surface coverages by different adsorbates or in the case of forced oscillations, different phases of oscillation. The dynamics of fronts are strongly affected by front instabilities and by diffusion anisotropy. We identify two new pattern formation mechanisms associated with different front behaviors in orthogonal directions: an ordering process by which stationary labyrinths in an isotropic system evolve into ordered stationary stripes, and confinement of isotropic spatiotemporal chaos to one space dimension, a state we term stratified chaos.     

Probabilistic analysis of pipelines with corrosion defects by using FITNET FFS procedure

A probabilistic method based on the corrosion module of the FITNET FFS procedure is presented to perform the structural integrity analysis for pipelines. The comparison of the failure pressure determined by both deterministic and probabilistic methods shows that even for a high safety factor, the deterministic method may predict nonconservative results. FITNET FFS procedure predicts a similar probability to that given by the Shell-92 model. The sensitivity analysis of both the uncertainty of the variables and the underlying model shows that the corrosion depth has the most significant contribution to the pipeline failure at an inspection interval of 8 years.     

State space modeling of non-proportional passive damping in machine tools

In the context of virtual development processes of mechatronic systems like machine tools, the preventive assessment of the effects of lightweight structural components on the characteristics of controlled feed systems and therefore on the power and energy requirement of machine tools is of great importance. The modeling of the damping is often limited in practical computation of real machine tools, because they are mostly limited to proportional damping characteristics. Yet the presence of discrete dampers, as for instance, in damping units in guides, or known diverse material damping in construction (components made of glass or carbon fiber-reinforced plastic), demands that the possibility of observance of non-proportional damping, in regard to later model updating, has to be given. The article demonstrates the theoretical state-space modeling of non-proportional damped mechanics using the example of a biaxial vertical lathe.     

Structure-property relations in molded, nucleated isotactic polypropylene

The influence of molecular characteristics and nucleating agents on the morphology distribution and properties of injection molded isotactic polypropylene (iPP) is investigated using optical microscopy, X-ray diffraction and mechanical testing. To have better control over the thermo-mechanical history, instead of a reciprocating screw, a capillary rheometer is used to drive the melt into the simple rectangular mold. Molecular weight (MW), molecular weight distribution (MWD) and addition of ethylene via copolymerization all influence the thickness of the oriented shear layer, the crystallinity, the type and amount of crystal phases, and the lamellar thickness. The addition of a nucleating agent (DMDBS), dictates the crystallization process, and resulting morphology, and samples with an oriented morphology over the full thickness are created without changing other morphological features, by applying a thermal treatment to the melt prior to injection, which is based on the specific phase behavior of the iPP-DMDBS system. The thermally treated samples show a considerable improvement in mechanical properties.     

Controlled-release system for the insect growth regulator cyromazine

An encapsulation system designed to give long-lasting effectiveness of the insect growth regulator (IGR) cyromazine (Neporex) against Culex pipiens (Culicidae) mosquito larvae was developed. The main thrust of the research was to develop a simple method for preparing controlled-release formulations by means of an extrusion technique in combination with a supplementary coating and to study the release characteristics and effectiveness of the formulations. A series of formulations were prepared with low-density polyethylene (LDPE 600) for the matrix and with polyurea or one of four types of polyurethane for the coating. The rate of release of the active material from the controlled-release formulations was determined in an in vitro dissolution system. The biological activity of the controlled-release formulations was tested in vivo against C. pipiens larvae. Received: 3 August 2000 / Accepted: 22 December 2000     

Planktonic food web structure and potential carbon flow in the Lower River Rhine with a focus on the role of protozoans

Studies during the last two decades have revealed the importance of planktonic micro‐organisms in the aquatic matter flux. However, studies on the planktonic food web structure have mostly concentrated on lentic waters. In the present study the biomass partitioning of the major plankton groups (bacteria, algae, heterotrophic flagellates (HF), ciliates and metazoans) in a large river (Lower River Rhine) has been analysed for a complete annual cycle and calculations on potential carbon flow within the planktonic food web were conducted for the four seasons. The plankton biomass was dominated by phytoplankton followed by bacterioplankton. The zooplankton was dominated by HF, contributing more than 65% of the total zooplankton biomass in all seasons. A significant part of the HF biomass was contributed by large flagellates (> 20 µm). In accordance with the dominance of the HF and their high growth rates, this group contributed the largest part of the planktonic matter turnover within the zooplankton. The calculations suggest that the HF were able to consume between 11 and 65% of the seasonal mean bacterial production and that the HF consumed a larger amount of phytoplankton than both ciliates and metazoans. According to these calculations, only a small part of the total potential production of the phytoplankton as well as that of the total zooplankton was consumed by planktonic predators. Since the plankton abundance did not generally increase during the downstream passage, the present data suggest that a large part of the plankton production is lost by other means. The role of benthic predators has been discussed in this context. Copyright © 2005 John Wiley & Sons, Ltd.