Parameters influencing pressure during pumping of self-compacting concrete

The main difference between conventional vibrated concrete (CVC) and self-compacting concrete (SCC) is observed in the fresh state, as SCC has a significantly lower yield stress. On the other hand, the placement of SCC by means of pumping is done with the same equipment and following the same practical guidelines developed for CVC. It can be questioned whether the flow behaviour in pipes of SCC is different and whether the developed practical guidelines can still be applied. This paper describes the results of full-scale pumping tests carried out on several SCC mixtures. It shows primarily that the slump or yield stress of the concrete is no longer a dominating factor for SCC, as it is for CVC. Instead, the pressure losses are well related to the viscosity and the V-funnel flow time of SCC. Secondly, bends cause an additional pressure loss for SCC, which is in contrast to the observations of Kaplan and Chapdelaine and the estimation of the practical guidelines is not always on the safe side. Finally, due to the specific mix design of SCC, blocking is less likely to occur during pumping operations, but the same rules as for CVC must be applied during start-up.     

Effects of environmental stress on the condition of Littorina littorea along the Scheldt estuary (The Netherlands)

The condition of the periwinkle Littorina littorea, expressed in terms of its shell morphology, reproductive impairment (i.e. female sterility/intersex, male penis shedding), trematode infestation load, lipid reserves and dry/wet weight ratio, was determined in function of environmental stress along the polluted Western and relatively clean Eastern Scheldt estuary (The Netherlands). The upstream increasing pollution and decreasing salinity levels along the Western Scheldt estuary (Fig. 1) are reflected in the dry/wet weight ratio and lipid content of the periwinkles. Compared to the Eastern Scheldt, female intersex (i.e. indicator of TBT pollution) and sterility occurred more frequently in the Western Scheldt estuary, while male penis shedding was even restricted to the latter estuary. The highest population intersex and sterility incidence was found near the harbour of Vlissingen and reflects potential nautical activities. The number of trematode infested periwinkles did not differ between both estuaries, although local sampling site differences were detected within each estuary, reflecting the complex interactions that exist among parasites, hosts and the local environment. Finally, both estuaries were maximally discriminated from each other based on the shell weight of the periwinkles using a canonical discriminant analysis. Periwinkles with the heaviest shells were found in the Western Scheldt estuary and may reflect growth rate or structural population differences caused by the less favourable living conditions in the Western Scheldt estuary.     

微控制器灵活的外设可提高设计的经济性和能源效率

嵌入式控制应用的快速增长,对当今的微控制器提出了极为苛刻的要求.由于大量的数字/模拟输入信号的复杂控制算法都必须在一个界定的较短响应时间内进行处理,而且生成适当的输出信号.     

Ultrasonic spray coating and flash lamp annealing of silicon nanoparticle dispersions for silicon thin film formation

Ultrasonic spray coating is reported as a deposition method for thin silicon films using a mixture of silicon nanoparticles and organosilicon compounds. The as-deposited films were treated by flash lamp annealing (FLA) using xenon light in order to obtain polycrystalline silicon. The nanoparticles were characterized by diffuse reflection infrared Fourier transform spectroscopy, transmission electron microscopy, and powder X-ray diffraction prior to deposition and film formation. The effect of FLA on the morphology of silicon films obtained from these silicon nanoparticles is investigated. Thin polycrystalline films up to 4 µm with a silicon content up to 95 % were prepared by combining the use of ultrasonic spray coating and FLA.     

KnowVolution of a Fungal Laccase toward Alkaline pH

To date, commercial laccase preparations are used in the food, textile, and paper and pulp industries (mild pH). Laccases are attractive in the synthesis of dye molecules or oxidative lignin treatment, which take place at high pH (≥8.0). So far, one fungal laccase has been reported to be active at alkaline pH. Herein, engineering of the fungal laccase from Melanocarpus albomyces (MaL) for increased activity toward the substrate 2,6-dimethoxyphenol at pH (≥9.0) is reported. Through a knowledge-gaining directed evolution (KnowVolution) campaign, the key positions Leu365 and Leu513 were identified to increase alkaline tolerance. Both positions are located in close proximity of the T1Cu site. Molecular docking and simulations studies reveal that both substitutions act in a synergic way to stabilize and improve laccase activity at higher pH. Kinetic characterization of the final variant MaL-M1 (L365E/L513M) revealed at pH 9.8 a threefold improved k_cat (k_cat=(6.0±0.2) s⁻¹) compared with that of wild-type M. albomyces laccase (k_cat=(2.11±0.07) s⁻¹).     

Side Chain Orientation of Tryptophan Analogues Determines Agonism and Inverse Agonism in Short Ghrelin Peptides

We describe two synthetic amino acids with inverted side chain stereochemistry, which induce opposite biological activity. Phe⁴ is an important part of the activation motif of ghrelin, and in short peptide inverse agonists such as KwFwLL-NH₂, the aromatic core is necessary for inactivation of the receptor. To restrict indole/phenyl mobility and simultaneously strengthen the interaction between peptide and receptor, we exchanged the natural monoaryl amino acids for diaryl amino acids derived from tryptophan. By standard solid-phase peptide synthesis, each of them was inserted into ghrelin or in the aromatic core of the inverse agonist. Both ghrelin analogues showed nanomolar activity, indicating sufficient space to accommodate the additional side chain. In contrast, diaryl amino acids in the inverse agonist had considerable influence on receptor signaling. Whereas the introduction of Wsf maintains inverse agonism of the peptide, Wrf shifts the receptor more to active states and can induce agonism depending on its introduction site.     

Einfluss der Plattendicke auf die Kontaktzeit beim elastischen Stoßvorgang

Using a free fall apparatus, the coefficient of restitution and the contact time of steel spheres at impact on thin gold‐coated glass plates were measured experimentally. The influence of the impact velocity, the particle size, and the plate thickness has been investigated. The measurements were evaluated using the Zener model. However, since the model merely considers energy dissipation due to elastic flexural waves and ignores additional energy dissipation by friction and viscous damping, the experimental values remain slightly below the theoretical Zener curve.