多轴加工提高生产效率

经济性和适用性是对加工大型零件加工中心的主要要求。Handtmann公司推出的双主轴高速加工机床,为生产力设定了新的标准。任何一家企业要想在市场上取得成功,就必须按用户要求不断改进其产品。Handtmann公司推出的UBZ龙门式加工中心不仅扩展了该公司的产品系列,而且在整个产品设计过程中与用户保持合作。同等占地面积,金属切除率提高一倍采用模块化设计,利用经过结构优化的不同模块可构成能满足用户要求的高效生产系统。由于机床占用空间已构成工厂规划的重要因素,在此情况下,必须寻求考虑到这个方面的解决办法,这就是转向双主轴的原因。…     

ZF-ECOLIFE-适用于城市公共汽车的、现代化的动力换档变速器

除了内燃机和车桥系统外,道路车辆的传动系统主要由变速器所决定.目前城市公共汽车中主要采用动力换档的自动变速器,特别是因为它们具有舒适性高和操纵便捷的特点.今天变速器系统的新挑战源自于内燃机的改进,特别是受制于排放法规使得内燃机提高转矩和冷却温度.另一方面,车辆的全寿命成本正变得更加重要,并由此带来技术方面的挑战,例如更高的可靠性和更佳的燃油经济性等.将诸如成本、舒适性最优等各种要求合并,形成了相当复杂的需求内容.而且这些需求对车辆制造商和诸如操作人员的最终用户有所不同.因此ZF公司开发新一代动力换档变速器,将长期目标与诸如更广的车辆应用场合、降低全寿命成本、简化使用条件等用户需求相结合.采用QFD(质量功能展开)方法分析后发现,由液力变矩器、行星齿轮机构和初级缓速器组成的动力换档变速器是满足各种不同需求的最佳方案.我们开发的新变速器在设计和制造的各个细节方面均采用了特殊和全新的解决方案.将最新的开发工具和方法应用与概念定义中.最终形成的动力换档变速器是一个6档行星齿轮变速器、带锁止离合器的液力变矩器,并可选装扭转减振器.新的冷却系统有两个热交换器,以提高系统的可靠性和改善城市公共汽车初级缓速器的制动转矩以适应更重的车辆、较高平均速度、长时间性能和舒适性等方面的要求.新型ECU直接安装在变速器上,其电气安装界面做到最小.其结论是,新型动力换档变速器的优势非常突出,因为它们体现了当代和今后动力传动系统应有的高性能,以及更佳的全寿命成本和优越的舒适性;并且在安全性和环保方面都相当出色.最后强调一下,我们将其取名为EcoLife,象征着更高的经济性和生态效益以及寿命.     

Combined Mutagenesis and Kinetics Characterization of the Bilin‐Binding GAF Domain of the Protein Slr1393 from the Cyanobacterium Synechocystis PCC6803

The gene slr1393 from Synechocystis sp. PCC6803 encodes a protein composed of three GAF domains, a PAS domain, and a histidine kinase domain. GAF3 is the sole domain able to bind phycocyanobilin (PCB) as chromophore and to accomplish photochemistry: switching between a red‐absorbing parental and a green‐absorbing photoproduct state (λ_max=649 and 536 nm, respectively). Conversions in both directions were followed by time‐resolved absorption spectroscopy with the separately expressed GAF3 domain of Slr1393. Global fit analysis of the recorded absorbance changes yielded three lifetimes (3.2 μs, 390 μs, and 1.5 ms) for the red‐to‐green conversion, and 1.2 μs, 340 μs, and 1 ms for the green‐to‐red conversion. In addition to the wild‐type (WT) protein, 24 mutated proteins were studied spectroscopically. The design of these site‐directed mutations was based on sequence alignments with related proteins and by employing the crystal structure of AnPixJg2 (PDB ID: 3W2Z), a Slr1393 orthologous from Anabaena sp. PCC7120. The structure of AnPixJg2 was also used as template for model building, thus confirming the strong structural similarity between the proteins, and for identifying amino acids to target for mutagenesis. Only amino acids in close proximity to the chromophore were exchanged, as these were considered likely to have an impact on the spectral and dynamic properties. Three groups of mutants were found: some showed absorption features similar to the WT protein, a second group showed modified absorbance properties, and the third group had lost the ability to bind the chromophore. The most unexpected result was obtained for the exchange at residue 532 (N532Y). In vivo assembly yielded a red‐absorbing, WT‐like protein. Irradiation, however, not only converted it into the green‐absorbing form, but also produced a 660 nm, further‐red‐shifted absorbance band. This photoproduct was fully reversible to the parental form upon green light irradiation.     

Multiphase materials with lignin. XII. Blends of poly(vinyl chloride) with lignin–caprolactone copolymers

A previously described starlike copolymer consisting of a lignin derivative (hydroxypropyl lignin) and caprolactone has been blended with poly(vinyl chloride) (PVC) over a composition range of 0–100%. Solvent-cast films of the blends were examined with regard to thermal, mechanical, crystallinity, and morphological characteristics. In addition, the blends were examined with regard to aging effects. The results suggest that the lignin/caprolactone copolymer forms either a miscible (by thermal analysis) or a nearly miscible (with phase dimensions in the order of 10–30 nm) system in which physical properties are modified over a wide range of modulus and elongation. Blends with copolymer content exceeding 50% reveal partial caprolactone crystallinity that increases with age. Lignin derivative not copolymerized with caprolactone, by contrast, produces macrophase-separated structures with exceedingly poor properties. Lignin caprolactone starlike copolymers are materials ideally suited as plasticizers for PVC. © 1994 John Wiley & Sons, Inc.     

Nondestructive and noncontact method for determining the spring constant of rectangular cantilevers

We present here an experimental setup and suggest an extension to the long existing added-mass method for the calibration of the spring constant of atomic force microscope cantilevers. Instead of measuring the resonance frequency shift that results from attaching particles of known masses to the end of cantilevers, we load them with water microdrops generated by a commercial inkjet dispenser. Such a device is capable of generating drops, and thus masses, of extremely reproducible size. This makes it an ideal tool for calibration tasks. Moreover, the major advantage of water microdrops is that they allow for a nearly contactless calibration: no mechanical micromanipulation of particles on cantilevers is required, neither for their deposition nor for removal. After some seconds the water drop is completely evaporated, and no residues are left on the cantilever surface or tip. We present two variants: we vary the size of the drops and deposit them at the free end of the cantilever, or we keep the size of the drops constant and vary their position along the cantilever. For the second variant, we implemented also numerical simulations. Spring constants measured by this method are comparable to results obtained by the thermal noise method, as we demonstrate for six different cantilevers.     

Promoted Fe/ZSM-5 catalysts prepared by sublimation: de-NOx activity and durability in H2O-rich streams

Fe/ZSM-5 catalysts with an Fe/Al ratio 1:0, were prepared by sublimation of FeCl3 into H/ZSM-5. They display high activity and durability for the selective catalytic reduction of NOx to N2, both in dry and wet gas flows. These catalysts have now been modified by exchanging a second cation into the zeolite. Mere neutralization of zeolite protons by Na⁺ lowers the selectivity for NOx reduction to N2, but the cations Ce₃ ⁺ and La₃ ⁺ act as true catalyst promoters. With isobutane as the reductant in a simulated vehicular emission gas, almost 90% of NOx is reduced to N2 at 350°C over the La-promoted catalyst. The presence of 10% H2O in the feed does not impair the catalyst performance at high temperature; in the temperature region below 350°C it even increases the N2 yield. The beneficial effect of La is due to its lowering of the catalyst activity for the undesired combustion of the hydrocarbon. No signs of zeolite destruction are evident after 100 h TOS in a wet gas flow at 350°C. Carbonaceous deposits causing a slight deactivation are easily removed in an O2/He flow at 500°C; this in situ regeneration fully restores the original activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Untersuchungen zur Sorptionsreversibilität von organischen Schadstoffen in Aktivkohle, Holzkohle und Zeolith Y-200

Numerous studies have shown that sorption of organic contaminants in soils is dominated by the natural organic carbon content (C _org) of the soil. However, it is still under discussion whether sorption processes are fully reversible or whether an irreversibly sorbed contaminant fraction remains in the soil. This is especially important when considering soil remediation measures and its targets. In multi-stage sorption-desorption batch experiments with TCE, PCE, ortho-xylene and para-xylene and with the sorbents activated carbon, charcoal and a hydrophobic zeolite Y-200, the reversibility of sorption was studied. It could be shown that the structural features of the sorbents are of ample importance for the occurrence of a desorption-resistant fraction. While sorption was mainly reversible for the micro-porous zeolite Y-200 with a rigid pore network, charcoal and the activated carbon showed significant desorption hysteresis. However, following a subsequent sorption step, this fraction eventually desorbs and is re-mobilized.     

Sport Stadia, Sporting Events and Urban Development: International Experience and the Ambitions of Durban

The paper considers the stadium construction and infrastructure projects underway for World Cup 2010. We ask whether and under which conditions hosting such an event (along with the new facilities and infrastructural development required) will have positive effects on urban development. By analysing the stadium project in Durban, the paper also presents evidence on whether such positive effects may be enhanced by the attempt to create an image effect by seeking outstanding architectural quality of the new stadia.

Reductive electrochemical remediation of emerging and regulated disinfection byproducts

Long-term exposure to low concentrations of disinfection byproducts (DBPs) in drinking water has been associated with increased human-health risks of bladder cancer and adverse reproductive outcomes. In this study, we investigated electrochemical reduction utilizing a resin-impregnated graphite cathode for the degradation of 17 DBPs (i.e. halomethanes, haloacetonitriles, halopropanones, chloral hydrate and trichloronitromethane) at low μg L⁻¹ concentration levels. The reduction experiments were potentiostatically controlled at cathode potentials −700, −800 and −900 mV vs Standard Hydrogen Electrode (SHE) during 24 h. At the lowest potential applied (i.e. −900 mV vs SHE), the disappearance of DBPs from the solution after 24 h of reduction was >70%, except for chloroform (32%), 1,1-dichloropropanone (48%), and chloral hydrate (31%). Due to the participation of several removal mechanisms (e.g. electrochemical reduction, adsorption, volatilization and/or hydrolysis) it was not possible to distinguish the removal efficiencies of electrochemical reduction of individual compounds. Adsorption of the more hydrophilic DBPs (i.e. haloacetonitriles, chloral hydrate, and 1,1-dichloropropanone) onto the electrode seems to be affected by the cathode polarization, as the removals observed in the open circuit experiments were significantly higher than the ones obtained in electrochemical reduction under the same conditions. The overall efficiency of reduction was estimated based on the analyses of the released Cl⁻, Br⁻ and I⁻ ions. Nearly complete C-I bond cleavage was achieved at all three potentials applied, and from the theoretically predicted release of I⁻ ions, calculated based on the removed DBPs, 86 ± 9 to 92 ± 1% was measured in the catholyte solution at −700 to −900 mV vs SHE. Debromination efficiencies obtained were 74 ± 3, 79 ± 6 and 68 ± 4% at −700, −800 and −900 mV vs SHE, while for C-Cl bond cleavage the obtained values were 69 ± 1, 72 ± 1 and 76 ± 4%, respectively. Nevertheless, dechlorination efficiencies are to be considered as approximate, since an increase in Cl⁻ concentration was observed in the open circuit experiments due to the hydrolysis of some of the chlorine-containing DBPs. Although the Coulombic efficiencies for DPBs dehalogenation were only 1.9 ± 0.3 (−900 mV vs SHE) -4.1 ± 0.2% (−700 mV vs SHE), relatively low energy consumption of the process was observed, estimated at 72 ± 2 Wh m⁻³ at −900 mV vs SHE for the concentration range of DBPs in this study (i.e. 65.3-129.7 μg L⁻¹). The study demonstrated that reductive electrochemical treatment has the potential to be a modern remediation technology for the removal of low concentrations of halogenated DBPs in water.