The effect of Zr on the low-cycle fatigue behavior of NiAl at 1000 K

The effect of a 0.1 at. % alloying addition of Zr on the low-cycle fatigue behavior of polycrystalline NiAl was determined at 1000 K and compared to that of binary NiAl. Samples of binary NiAl and the Zr-doped alloy were processed by either HIP consolidation or extrusion of prealloyed intermetallic powders. The cyclic stress response, cyclic stress-strain behavior, and strain-life relationships were all significantly influenced by the microalloying addition of Zr, regardless of the processing technique. A detailed examination of the post-tested low-cycle fatigue (LCF) samples was conducted by optical and electron microscopy to determine variations in fracture and deformation modes and to characterize any microstructural changes that occurred during LCF testing. Differences in LCF behavior due to the Zr addition are attributed to the strong effect that Zr has on modifying the deformation behavior of the intermetallic.     

Fretting wear of Ti-48Al-2Cr-2Nb

An investigation was conducted to examine the wear behavior of gamma titanium aluminide (Ti-48Al-2Cr-2Nb in atomic percent) in contact with a typical nickel-base superalloy under repeated microscopic vibratory motion in air at temperatures from 296–823 K. The surface damage observed on the interacting surfaces of both Ti-48Al-2Cr-2Nb and superalloy consisted of fracture pits, oxides, metallic debris, scratches, craters, plastic deformation, and cracks. The Ti-48Al-2Cr-2Nb transferred to the superalloy at all fretting conditions and caused scuffing or galling. The increasing rate of oxidation at elevated temperatures led to a drop in Ti-48Al-2Cr-2Nb wear at 473 K. Mild oxidative wear was observed at 473 K. However, fretting wear increased as the temperature was increased from 473–823 K. At 723 and 823 K, oxide disruption generated cracks, loose wear debris, and pits on the Ti-48Al-2Cr-2Nb wear surface. Ti-48Al-2Cr-2Nb wear generally decreased with increasing fretting frequency. Both increasing slip amplitude and increasing load tended to produce more metallic wear debris, causing severe abrasive wear in the contacting metals.     

Keramische Membranen in der Membrandestillation

TiO₂ membranes were successfully rendered hydrophobic (modified with perfluoroalkyl silanes) and evaluated by liquid entry pressure (LEP) measurements and membrane distillation (MD) tests. It was shown that the LEP is strongly depended on the pore size of the membranes and the feed composition. The obtained permeate fluxes were highest in vacuum MD. None of the membranes showed any sign of wetting during the experiments and salt retentions greater than 99.9 % were recorded and permeate qualities lower than 2 µS cm^?1 were achieved in air gap MD and vacuum MD.     

Effect of Germanium content and strain on the formation of extended defects in ion implanted Silicon/Germanium

We studied the evolution of extended defects in relaxed and strained Si and SiGe structures after an amorphising implant. The investigated structures included three relaxed SiGe alloy layers with various Ge contents (20, 35 and 50 at.%), a 40 nm-thick tensely strained Si layer and a 40 nm-thick compressively strained Si_0.8Ge_0.2 layer. Concerning the compositional effects, we found that the increase of Ge concentration in relaxed SiGe structures leads to: (i) an overall decrease of the defect stability and to (ii) an enhanced {311}-to-loops transformation. As for the strain effects, it is found that: (i) Tensile strain (in Si) retards the transformation of {311} defects into loops; (ii) compressive strain (in SiGe) enhances the transformation of {311}s into loops; (iii) in all cases, the overall defect stability is not strongly modified in the presence of strain. The observed results are discussed in terms of the various mechanisms involved, including the increase of the interstitial diffusivity in relaxed SiGe alloys (with respect to Si) and the strain effects on both interstitial equilibrium concentration and defect formation energy.     

Simultaneous diffusion of Si and Ge in isotopically controlled heterostructures

Experiments on the diffusion of Si and Ge in Si_1-xGe_x-isotope heterostructures with Ge contents x=0, 0.05, and 0.25 were performed at temperatures between 870 and . The concentration profiles of the stable Si- and Ge-isotopes were recorded by means of time-of-flight secondary ion mass spectrometry. For all compositions, an Arrhenius type temperature dependence of diffusion was observed. The activation enthalpy of Si diffusion in SiGe equals the activation enthalpy of Ge diffusion and the pre-exponential factors agree within experimental accuracy. However, the absolute values of the Si and Ge diffusion coefficients indicate a clear trend. In elemental Si the diffusion coefficients of Si and Ge agree, but the difference between the diffusion coefficients of Ge and Si in Si_1-xGe_x increases with x. This indicates that with increasing Ge content the diffusional jumps of Ge atoms become more successful compared to that of Si. This trend is explained with an increasing contribution of vacancies to self-diffusion in Si_1-xGe_x with an increase of the Ge content x.     

Datenschutz im Web 2.0 am Beispiel des sozialen Tagging-Systems BibSonomy

Soziale Tagging-Systeme geh?ren zu den in den vergangenen Jahren entstandenen Web2.0-Systemen. Sie erm?glichen es Anwendern, beliebige Informationen in das Internet einzustellen und untereinander auszutauschen. Je nach Anbieter verlinken Nutzer Videos, Fotos oder Webseiten und beschreiben die eingestellten Medien mit entsprechenden Schlagw?rtern (Tags). Die damit einhergehende freiwillige Preisgabe oftmals pers?nlicher Informationen wirft Fragen im Bereich der informationellen Selbstbestimmung auf. Dieses Grundrecht gew?hrleistet dem Einzelnen, grunds?tzlich selbst über die Preisgabe und Verwendung seiner pers?nlichen Daten zu bestimmen. Für viele Funktionalit?ten, wie beispielsweise Empfehlungsdienste oder die Bereitstellung einer API, ist eine solche Kontrolle allerdings schwierig zu gestalten. Oftmals existieren keine Richtlinien, inwieweit Dienstanbieter und weitere Dritte diese ?ffentlichen Daten (und weitere Daten, die bei der Nutzung des Systems anfallen) nutzen dürfen. Dieser Artikel diskutiert anhand eines konkreten Systems typische, für den Datenschutz relevante Funktionalit?ten und gibt Handlungsanweisungen für eine datenschutzkonforme technische Gestaltung.     

Watershed vulnerability to herbicide transport in northern Missouri and southern Iowa streams

Herbicide contamination of streams has been well documented, but little is currently known about the specific factors affecting watershed vulnerability to herbicide transport. The primary objectives of this study were (1) to document herbicide occurrence and transport from watersheds in the northern Missouri/southern Iowa region; (2) to quantify watershed vulnerability to herbicide transport and relate vulnerability to soil properties; and (3) to compute the contribution of this region to the herbicide load of the Missouri and Mississippi Rivers. Grab samples were collected under baseflow and runoff conditions at 21 hydrologic monitoring stations between April 15 and July 15 from 1996 to 1999. Samples were analyzed for commonly used soil-applied herbicides (atrazine, cyanazine, acetochlor, alachlor, metolachlor, and metribuzin) and four triazine metabolites (deisopropylatrazine, deethylatrazine, hydroxyatrazine, and cyanazine amide). Estimates of herbicide load and relative losses were computed for each watershed. Median parent herbicide losses, as a percentage of applied, ranged from 0.33 to 3.9%; loss rates that were considerably higher than other areas of the United States. Watershed vulnerability to herbicide transport, measured as herbicide load per treated area, showed that the runoff potential of soils was a critical factor affecting herbicide transport. Herbicide transport from these watersheds contributed a disproportionately high amount of the herbicide load to both the Missouri and Mississippi Rivers. Based on these results, this region of the Corn Belt is highly vulnerable to transport of herbicides from fields to streams, and it should be targeted for implementation of management practices designed to reduce herbicide losses in surface runoff.     

Early ductal decompression prevents the progression of biliary pancreatitis: an experimental study in the opossum

BACKGROUND: The value of early endoscopic or surgical interventions to remove bile duct stones and decompress the biliopancreatic ductal system in gallstone pancreatitis is controversial. METHODS: To evaluate this issue, acute hemorrhagic necrotizing pancreatitis was induced in opossums by obstructing the biliopancreatic ductal system with a balloon catheter for 1, 3, or 5 days. RESULTS: A progressive increase in the severity of pancreatitis, as manifested by inflammation, fat necrosis, hemorrhage, acinar cell vacuolization, in vitro lactate dehydrogenase release, and acinar cell necrosis, was noted in these obstructed animals. In contrast, decompression of the obstructed ductal system by removal of the balloon catheter after 1 or 3 days prevented the increase in severity of these parameters of pancreatic injury. CONCLUSIONS: We concluded that the severity of biliary pancreatitis in this model is dependent upon the duration of ductal obstruction and that decompression of the ductal system can prevent progression of the disease. These observations support the practice of early attempts to remove obstructing stones in clinical gallstone pancreatitis.     

Modeling of smart devices

The precise numerical modeling of electromechanical smart structures and devices is reported. This modeling is performed on the basis of finite and boundary element procedures solving coupled field problems arising in transducer technology. Furthermore, the controler is embedded within the simulation process. Therewith, the numerical computation of the closed loop starting with the sensor and ending with the actuator is performed. Results are shown for an electrostatic excited plate as well as an electromagnetic excited tube, which are both actively damped by controlled piezoelectric actuators.