Experimentelle Untersuchung des Abwälzverhaltens von Beveloidverzahnungen mit lokal angepassten Verzahnungsdaten entlang der Zahnbreite

Forschung im Ingenieurwesen - Zur Übertragung von Drehmoment und Drehzahl in beliebiger Achsanordnung eignen sich bei kleinem Achswinkel bis 30° Beveloidverzahnungen. Besonders...     

Dynamische Steifigkeit und Dämpfung von Pfahlgruppen

Dynamic stiffness and damping properties of pile groups. The dynamic stiffness and damping properties of pile‐groups have been investigated in this paper. Also, the substantial influence of these properties on an economic structure and foundation design is demonstrated. The analysis has been carried out using the “Thin‐Layer‐Method”, which is a very efficient and powerful analysis procedure in frequency domain.     

Analytical design method for beveloid gears with a small shaft angle and offset

Forschung im Ingenieurwesen - In addition to more sophisticated flank modifications, there is a discernible trend toward special gearing that is reflected in the increased use of beveloid...     

Single-molecule reader for high-throughput bioanalysis

We report here the development of a device for single-molecule imaging on large surface areas. A CCD camera operated in time delay and integration mode is synchronized with the movement of a sample scanning stage, enabling continuous data acquisition. Experiments on single fluorescent lipid molecules in supported lipid bilayers and on stained living cells demonstrate the capabilities of the method. Areas of up to 5 x 5 mm(2) were recorded within 11 min at a pixel size of 129 nm.     

Über regenerative Wärmeübertrager mit poröser Speichermasse

Zusammenfassung Die Untersuchung betrift die Regelung der Ruhetemperatur von überdruck-überschallwindkan?len mittels regenerativer W?rmeübertrager mit por?ser Speichermasse. Für den Regeneratorbetrieb bei konstantem Druck wurde die Aufheizung der Luft unter der Voraussetzung inkompressibler oder kompressibler Luftzust?nde er?rtert. Auf der Grundlage einer linearisierten Theorie gelang es, für verschiedene Speichierwerkstoffe die Speichermasse und das Speichervolum zu bestimmen, die bei gegebenem Luftdurchsatz dazu n?tig sind, im Speicher eine zeitlich ver?nderliche Eintrittstemperaturverteilung der Luft auf ihre ursprünngliche Ruhetemperatur zurückzuführen und so w?hrend der Laufzeit des Windkanals eine konstante Reynoldszahl zu gew?hrleisten.     

Evaluation errors with dust measurements of laminar minerals by scanning electron microscope following German guideline VDI 3492

A number of seemingly fibrous particles are found by evaluation of dust measurements of the industrial mineral vermiculite in accordance with German Guideline VDI 3492, part 2 for “measurements of inorganic fibrous particles- SEM method.” A more thorough investigation based upon an extension of the measuring method proves the nonfibrous morphology of practically all of these particles. The basic idea of this extension is to tilt the filter holder of the electron microscope and to check the exact orientation of the particles on the filter, an examination which is necessary to determine their true length and diameter. The result indicates that only very few fibrous particles actually exist. In the case of vermiculite, these fibrous particles are rolled up and detached flakes called “scrolls.” The systematic error inherent in VDI 3492, part 2, without extension can be quantified in the case of vermiculite to have a factor > 50, that is, fibre counts obtained are more than 50 times too high.     

Theory of self-similar network structures in sedimentary and igneous rocks and their investigation with microscopical and physical methods

Based on self organized growth, a self-similar geometrical model of rock materials is established. The structural mode of the internal surface is carried over to the three-dimensional structure of the pore space and solid phase, which can be described as a fractal network. It is characterized by the fractal dimension of surface, which can be measured by physical and stereological methods. From this, the fractal behaviour of other geometrical properties, relevant for physical processes, such as porosity, number of solid connections, tortuosity and constrictivity of the capillary system and of the solid phase can be derived.     

Quantitative assessment of antioxidant properties of natural colorants and phytochemicals: carotenoids,flavonoids, phenols and indigoids. The role of β‐carotene in antioxidant functions

Reactive oxygen species are potentially damaging molecules. An important function of antioxidants is to intercept harmful triplet states, in order to prevent the formation of singlet oxygen, or to quench singlet oxygen directly. However, antioxidants are also reactive towards other active oxygen species such as the hydroxyl radical, the superoxide anion and the non‐excited oxygen ground state in the presence of radical initiators. It is well known that flavonoids and carotenoids show strong antioxidant properties. Polyenes and carotenoids are the best known among the compounds that quench singlet oxygen by efficient energy transfer. A large number of modified, synthetic analogues and derivatives have been synthesised to prepare even better quenchers than the natural carotenoids. Phenols are also excellent chain‐breaking antioxidants. Recently, many indigoid dyes (including bacterial indigoids) were studied, with the remarkable result that most, but not all, members of this class of chromophores quench singlet oxygen at the diffusion limit and some of them are excellent radical traps. It has been shown in this study that a quantitative assessment of antioxidant properties of flavonoids, carotenoids, phenols and natural indigoids can be achieved using the following three assays: (1) oxygen pressure dependence; (2) peroxide formation; (3) singlet oxygen quenching. Reactivities towards both excited states and ground state radicals can be properly described by these assays. The remarkable role of β‐carotene as an ‘unusual antioxidant’ (Burton GW and Ingold KU, Science 224 : 569–573 (1984)) in reactions using various oxygen pressures becomes clearer. The so‐called ‘pro‐oxidant effects’ concern primarily the antioxidant itself and its degradation, since no or very little damage to the substrate occurs in this type of experiment. Three main categories of antioxidants may be classified: (1) excellent antioxidants that perfectly quench excited states as well as ground state radicals (eg actinioerythrol, astaxanthin); (2) good antioxidants that strongly inhibit peroxide formation but are less efficient in quenching excited states (eg flavonols, tocopherols) or lead to considerable degradation of the antioxidant itself (eg β‐carotene, lycopene); (3) moderate antioxidants that fail to excel in both reactivities (eg ζ‐carotene, flavone). © 2001 Society of Chemical Industry