Dissolution rate measurements of sea water soluble pigments for antifouling paints: ZnO

The dissolution of soluble pigments from both tin-based and tin-free chemically active antifouling (AF) paints is a key process influencing their polishing and biocide leaching rates. In this context, a low time- and resources-consuming method capable of screening the pigment behaviour in the search for the most promising materials or mixtures is of great interest. A preliminary attempt to develop such a method is presented in this paper based on the widely used ZnO pigments.

While highly pure, nano-polished, monocrystalline ZnO substrates yielded very low dissolution rates in the order of 17.3 ± 3.7 μg Zn²⁺ cm⁻² day⁻¹, pellets prepared by compacting and sintering technical grade ZnO pigments dissolved about three times faster according to inductively-coupled plasma mass spectrometry (ICP-MS) measurements. The rougher and more porous surface exposed, together with the larger number of defects in the lattice structure, are hypothesised to be responsible for the faster sea water attack of the pellets compared to the ZnO crystals. In any case, the ZnO dissolution rates reported in this paper are markedly lower than those associated with the sea water dissolution of cuprous oxide (Cu₂O) particles which are also used in AF paints. Experimental performance testing of model antifouling paints formulated with ZnO and/or Cu₂O demonstrates that the binder/pigment interaction should not be disregarded if the leaching of sea water soluble pigments from paint systems is to be determined.     

Single-shot electron bunch length measurements using a spatial electro-optical autocorrelation interferometer

A spatial, electro-optical autocorrelation (EOA) interferometer using the vertically polarized lobes of coherent transition radiation (CTR) has been developed as a single-shot electron bunch length monitor at an optical beam port downstream the 100 MeV preinjector LINAC of the Swiss Light Source. This EOA monitor combines the advantages of step-scan interferometers (high temporal resolution) [D. Mihalcea et al., Phys. Rev. ST Accel. Beams 9, 082801 (2006) and T. Takahashi and K. Takami, Infrared Phys. Technol. 51, 363 (2008)] and terahertz-gating technologies [U. Schmidhammer et al., Appl. Phys. B: Lasers Opt. 94, 95 (2009) and B. Steffen et al., Phys. Rev. ST Accel. Beams 12, 032802 (2009)] (fast response), providing the possibility to tune the accelerator with an online bunch length diagnostics. While a proof of principle of the spatial interferometer was achieved by step-scan measurements with far-infrared detectors, the single-shot capability of the monitor has been demonstrated by electro-optical correlation of the spatial CTR interference pattern with fairly long (500 ps) neodymium-doped yttrium aluminum garnet (Nd:YAG) laser pulses in a ZnTe crystal. In single-shot operation, variations of the bunch length between 1.5 and 4 ps due to different phase settings of the LINAC bunching cavities have been measured with subpicosecond time resolution.     

Synthesis,characterization and thiol-ene polymerization of hydrolyzed/condensed norbornenyl silic acid ester

Summary Bicyclo[2.2.1]hept-2-ene-5-yl (norborn-2-ene-5-yl) derivatives of silic acid were synthesized by the Diels-Alder reaction, of the corresponding (meth)acryloxypropyl silanes with cyclopentadiene monomer. The norbornenyl silanes were characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR and ²⁹Si NMR spectroscopy. The hydrolysis and condensation of norbornene-funktionalized silic acid esters yield polysiloxanes which can be crosslinked by the photoinitiated reaction with multifunctional thiols. The shrinking behaviour of the bulk materials which are obtained by this combination of the sol-gel process with the thiol-ene polymerization were investigated.     

Varying bending eigenfrequencies in BTA deep hole drilling: mechanical modeling using statistical parameter estimation

One serious problem in deep-hole drilling is the formation of a dynamic disturbance called spiralling which causes a multi-lobe shaped distortion of the bore hole cross section. An important factor governing the occurrence of spiralling is the coincidence of a bending eigenfrequency of the boring tool with a multiple of the spindle rotation frequency. This article presents a discrete dynamic model of the tool/boring-bar assembly including a Lanchester-damper and containing free parameters for the unknown stiffness of the tools lateral supports. Furthermore, a method for estimating these parameters by determining the changing eigenfrequencies over the drilling depth from spectrogram data using the maximum likelihood method is proposed. The work presented in this paper is financially supported by the ‘Deutsche Forschungsgemeinschaft (DFG)’ within the ‘Sonderforschungs-bereich (SFB)’ 475. It is conducted in cooperation with Lehrstuhl Computergestützte Statistik, University of Dortmund.     

Stahlbeton‐Verbundkonstruktionen – Ein Bemessungskonzept für schubbeanspruchte Fugen. Teil 2: Normative Empfehlungen für Neubau und Revitalisierungsmaßnahmen

R/C Composite Constructions – A Design Concept for Shear Loaded Joints – Part 2: Normative Recommendations for New Building and Retrofit Measures In the modern engineering practice composite constructions are often used. This constructions consisting of prefabricated R/C components and in situ concrete are marked by the interaction of concrete interfaces with different age and different strength. With various examinations will be show, that the present designing practice and the distribution of reinforcement is not effective and leads to high reinforcement concentrations in uncritical joint sections and also to an unbalanced reinforcement along the joint. This paper is divided into 2 parts: Part 1 summarizes the state‐ofthe‐ art, a special structural model and important results. A design concept, continued in part 2, will be presented for the practical use according to European standard EC 2 which enables the differentiation between narrow and broad bond surfaces for the first time. Additional, the new concept considers the non‐rigid bond and also decisive parameter in a subtly differentiated, nearly realistic and bearing structure referred way.     

Vergleich statischer und dynamischer Methoden zur Zustandsbewertung von Stahlbeton‐ und Spannbetontragwerken

Risse in Stahlbeton‐ und Spannbetontragwerken führen zu einem Steifigkeitsverlust, der die statischen und dynamischen Eigenschaften der jeweiligen Struktur beeinflusst. Eine klassische Methode zur Bestimmung statischer Kennwerte sind Probebelastungen, bei denen gemessene Verformungen mit rechnerischen Werten abgeglichen werden und somit einen Rückschluss auf die Tragfähigkeit der Struktur ermöglichen. Bei Bauwerken wie Brücken können derartige Tests sehr kosten‐, zeit‐ und materialaufwändig sein und erfordern häufig eine längerfristige Sperrung. Des Weiteren müssen die gemessenen Verformungen vor Ort durch erfahrene Ingenieure überwacht werden, um gegebenenfalls bei Überschreiten kritischer Werte den Test abzubrechen. Auch die dynamischen Eigenschaften von Strukturen werden maßgeblich durch die Steifigkeit beeinflusst und können in vielen Fällen schnell und mit wenig Aufwand bestimmt werden. Im Rahmen dieses Aufsatzes werden die Ergebnisse statischer und dynamischer Untersuchungen zur Zustandsbewertung, durchgeführt an Stahlbeton‐ und Spannbetonbauteilen im Labor und an einer schrittweise geschädigten Spannbetonbrücke, hinsichtlich ihrer Sensibilität auf Schäden und Handhabbarkeit in der praktischen Anwendung gegenübergestellt. Comparison of Static and Dynamic Methods to Assess the State of Reinforced and Prestressed Concrete Structures Cracks in reinforced and prestressed concrete structures lead to a reduction in stiffness and therefore to an influence on the static and dynamic properties. A conventional method to assess the static characteristics are static load tests which enable to correlate measured deformations with calculated values and to draw conclusions about the loading capacity. In case of bridges, these tests can be very cost‐intensive and time‐consuming and often require a closure of the bridge. Furthermore the measured deformations have to be examined in situ, in order to abort the test if the deformations exceed critical values. As well, the dynamic properties are affected by changes in stiffness and in many cases they can be quickly determined without large effort. Within this article the results of static and dynamic tests with laboratory reinforced and prestressed concrete structures and tests on a gradually damaged prestressed concrete bridge are presented. The results are compared with regard to the sensitivity of the different methods to damage.     

Systems toxicology approaches for understanding the joint effects of environmental chemical mixtures

Environmental mixtures of chemicals constitute a prevalent issue in ecotoxicology and the development of new methods to reduce the uncertainties associated with their ecological risk assessment is a critical research need. Historically, a number of models have been explored to predict the potential combined effects of chemicals on species. These models, especially concentration addition and the independent action, have been applied to a number of mixtures. While often providing a good prediction of joint effect, there are cases where these models can have limitations: notably in cases where there are interactions for which they fail to adequately predict joint effects. To support the better mechanistic understanding of interactions in mixture toxicology a framework to support experimental studies to investigate the basis of observed interactions is proposed. The conceptual framework is derived from the extension of a three stage scheme which has previously been applied to understand chemical bioavailability. The framework considers that interactions in mixtures result from processes related to 1) the speciation, binding and transport of chemicals in the exposure medium (external exposure); 2) the adsorption, distribution, metabolism and excretion of chemicals within the organisms (toxicokinetics); 3) associations governing the binding and toxicity of the chemical(s) at the target site (toxicodynamics). The current state of the art in (eco)toxicology in relation to investigation of the mechanisms of interactions between chemicals is discussed with particular emphasis towards the multi-disciplinary tools and techniques within environmental chemistry; toxicology; biochemistry and systems biology that can be used to address such effects.