Wechselwirkungen in Kristallen. 136. Protonierte Di(pyrid-2-yl)amin-Salze mit verschiedenen Anionen: Monomeres Tetraphenylborat sowie Bis(trifluormethylsulfonat), dimeres Squarat und polymeres Chlorid-Dihydrat

Interactions in Crystals. 136. Protonated Dipyridylamine Salts with Different Anions: Monomeric Tetraphenylborate as well as Bis(trifluormethylsulfonate), Dimeric Squarate and Polymeric Chloride Dihydrate Di(pyrid-2-yl)amine is monoprotonated by acetic, squaric as well as hydrochloric acid and diprotonated by trifluoromethylsulfonic acid. To explore the anion and hydrogen-bridge dependency of its salts, crystals of the monomeric tetraphenylborate, the dimeric squarate as well as the bis(trifluoromethylsulfonate) and the polymeric chloride hydrate have been grown and their structures determined: Separated by bulky tetraphenylborate anions, pyrid-2-yl(2′-pyridinium) amine cation contains an intramolecular hydrogen bridge N^⊕H…︁N and is slightly folded. The squarate salt dimer exhibits additional bridges, N H…︁O^⊖ and O H…︁O. The severely twisted di(2-pyridinium)amine dication is connected to its trifluormethylsulfonate counter anions by altogether three H-bridges, two N^⊕H…︁O and one N H…︁O. The chloride dihydrate crystallizes in layers of 16-membered rings, formed from three Cl anions and five water molecules. The diversity of the hydrogen-bridge dominated salt structures is discussed based on comparison with selected literature examples and on PM3 calculations.     

Lead Zirconate Titanate Hollow-Sphere Transducers

Millimeter-sized, hollow spheres of lead zirconate titanate were fabricated by blowing gas through a fine-grained slurry of PZT-5. After they were sintered, the spheres were poled in two ways: radially between inside and outside electrodes, and tangentially between two outside electrodes. The capacitance and vibration modes were modeled and measured for these two poling configurations. The two principal modes of vibration were a breathing mode near 700 kHz and a wall thickness mode near 10 MHz. These spheres have potential uses in medical ultrasound, nondestructive testing, and low-density transducer arrays.     

Comparison of analytical and theoretical pharmaceutical concentrations in human urine in Germany

Urine is considered as a valuable plant fertiliser due to its high nutrient content. However, urine also contains pharmaceuticals. Currently, little is known regarding expected pharmaceutical concentrations in urine and the resulting risks. Through series of analyses in Hamburg and Berlin and results from the development of a concentration prediction model this knowledge gap was intended to be filled. To which extent the theoretical calculations can substitute analyses of pharmaceuticals was also tested. Results showed that the model fits well for bezafibrate, carbamazepine, diclofenac, ibuprofen, phenazone, and pentoxifylline. In Hamburg an R(2) value of 0.98 and in Berlin of 0.90 was achieved for correlations between predicted and analysed concentrations. Additionally, it was shown that a sufficient number of people discharging their urine to the respective collection system are important to allow for reasonable predictions via calculation. Also, comparisons of predicted pharmaceutical concentrations to those determined in other projects showed good correlations. Overall, it can be concluded that in any case the calculated concentrations exceed the measured ones and are therefore conservative. This overestimation can be explained by several factors discussed in this article.     

Querkraftwiderstand betonstabbewehrter Bauteile ohne Querkraftbewehrung

Shear Strength of Concrete Elements reinforced by prestressed Concrete Bars The shear strength of commonly reinforced concrete elements without shear reinforcement has been extensively studied and several semi‐empirical approaches for the determination of ultimate shear loads have been published. It seems to be necessary to prove the validity of these approaches for concrete elements reinforced with materials with a bi‐linear stress‐strain diagram in the elastic range. Prestressed Concrete Bars (PCB) show a distinct non‐linear behavior after decompression. Thus, they are especially suitable for a comparison with common reinforcement. The present article describes tests on the shear strength of concrete elements reinforced with PCBs. The results obtained are compared with the code DIN 1045‐1.     

Sorption materials for arsenic removal from water: a comparative study

Five different sorption materials were tested in parallel for the removal of arsenic from water: activated carbon (AC), zirconium-loaded activated carbon (Zr-AC), a sorption medium with the trade name 'Absorptionsmittel 3' (AM3), zero-valent iron (Fe(0)), and iron hydroxide granulates (GIH). Batch and column tests were carried out and the behavior of the two inorganic species (arsenite and arsenate) was investigated separately. The sorption kinetics of arsenate onto the materials followed the sequence Zr-AC > GIH = AM3 > Fe(0) > AC. A different sequence was obtained for arsenite (AC > Zr-AC = AM3 = GIH = Fe(0)). AC was found to enhance the oxidation reaction of arsenite in anaerobic batch experiments. The linear constants of the sorption isotherms were determined to be 377, 89 and 87 for Zr-AC, AM3 and GIH, respectively. The uptake capacities yielded from the batch experiment were about 7gl(-1) for Zr-Ac and 5gl(-1) for AM3. Column tests indicated that arsenite was completely removed. The best results were obtained with GIH, with the arsenate not eluting before 13100 pore volumes (inflow concentration 1 mg l(-1) As) which corresponds to a uptake capacity of 2.3 mg g(-1) or 3.7 g l(-1).     

Mechanical Forces Induce Changes in VEGF and VEGFR-1/sFlt-1 Expression in Human Chondrocytes

Expression of the pro-angiogenic vascular endothelial growth factor (VEGF) stimulates angiogenesis and correlates with the progression of osteoarthritis. Mechanical joint loading seems to contribute to this cartilage pathology. Cyclic equibiaxial strains of 1% to 16% for 12 h, respectively, induced expression of VEGF in human chondrocytes dose- and frequency-dependently. Stretch-mediated VEGF induction was more prominent in the human chondrocyte cell line C-28/I2 than in primary articular chondrocytes. Twelve hours of 8% stretch induced VEGF expression to 175% of unstrained controls for at least 24 h post stretching, in promoter reporter and enzyme-linked immunosorbent assay (ELISA) studies. High affinity soluble VEGF-receptor, sVEGFR-1/sFlt-1 was less stretch-inducible than its ligand, VEGF-A, in these cells. ELISA assays demonstrated, for the first time, a stretch-mediated suppression of sVEGFR-1 secretion 24 h after stretching. Overall, strained chondrocytes activate their VEGF expression, but in contrast, strain appears to suppress the secretion of the major VEGF decoy receptor (sVEGFR-1/sFlt-1). The latter may deplete a biologically relevant feedback regulation to inhibit destructive angiogenesis in articular cartilage. Our data suggest that mechanical stretch can induce morphological changes in human chondrocytes in vitro. More importantly, it induces disturbed VEGF signaling, providing a molecular mechanism for a stress-induced increase in angiogenesis in cartilage pathologies.     

On differences and similarities of applied wind comfort criteria

This paper presents the comparison of different wind comfort criteria presently used at European wind engineering institutions. In the framework of the European COST Action C14, Working Group 1 has gathered various wind comfort criteria with the purpose of discussing the present state-of-the-art, identifying differences, and initiating a common criterion or code of good practice. The paper focuses on the comparison of comfort criteria. In the last three decades, various comparative studies have been performed on the same topic and this paper puts the gathered information in context to earlier works. The comparison reveals a change occurred in the conceptual design of the different criteria over the last decade. The study distinguishes between two groups of criteria; first those using the hourly mean wind speed as the relevant parameter to assess human wind comfort, and secondly those criteria based on gust wind speeds. Regarding criteria based on hourly mean wind speeds, the comparison allows for the identification of relationships between the different comfort approaches and was used to propose a more general formulation. The comfort criteria using gust wind speeds prove to be more complex in design and application. The main difficulties in the application could be identified through theoretical comparison and through a case study. Possible improvements are discussed. The paper is intended to give information about the spectrum of presently used methods to assess wind comfort in urban environments, and to identify the differences and similarities. Suggestions concerning a possible future code of good practice are made.     

Hydrophobic recovery of atmospheric pressure plasma treated surfaces of Wood-Polymer Composites (WPC)

In this study, the behavior of atmospheric pressure plasma treated surfaces of Wood-Polymer Composites (WPC) was investigated as a function of time and environmental conditions. The surfaces of injection molded WPC based on polypropylene (PP) and polyethylene (PE) were treated by a dielectric barrier discharge (DBD) and subsequently aged under various conditions. The wettability as an indicator for change of the composite surface was assessed using water contact angle. In addition, a calculation for half-time of the contact angles was developed to predict the time span which is needed for recovery of hydrophobicity. The results showed a major influence of temperature and time, whereas the humidity only at storing conditions of 60?°C and 75% relative humidity showed a distinct effect on the activated surface. The effect of DBD treatment was stable for more than one week in the climates 20?°C and 0% RH and 20?°C and 65% RH.     

PF-bonded particleboards from AKD-modified chips

Alkyl ketene dimer (AKD) was used as a hydrophobic agent for PF-bonded particleboards. In contrast to conventionally used paraffin, AKD can be covalently bonded to the chip surface by esterification with wood hydroxyl groups. FTIR analyses before and after toluene extractions indicated that only a small amount of the applied AKD is chemically bonded. Wettability studies on veneer strips suggested that particularly the bonded AKD accounts for the surface hydrophobicity. A subsequent spraying of AKD and PF resin on the chips that were pressed for 15, 30, and 60 s?mm^-1 (Process 1) did not result in decreased thickness swelling and water uptake as compared to the control boards. In Process 2, chips were cured (130 °C/6, 12, 24 h) prior to pressing (15 s?mm^-1) which did not impart significant hydrophobicity either. The low efficacy of AKD as hydrophobic agent in Process 1 is attributed to the hydrolysis of AKD by water vapor during pressing. The low hydrophobic effect of AKD in Process 2 is ascribed to a saponification of esters between AKD and wood hydroxyl groups by the alkaline PF resin.