Break opening times for axial rupture of a gas-pressurised pipe

The consequences of a major rupture of a pressurised pipe are strongly influenced by the break characteristics (i.e. fracture orientation, opening time and final breah area). For example, the amplitude of the blast wave generated in the external atmosphere is dictated by the rate at which energy is released through the developing breach and hence is a function of opening time. A pipe is assumed to be fully open when the breach area is twice the cross-sectional area of the pipe, thus allowing full flow from each leg of the pipe.This paper describes experiments where the development of an axial rupture in large gas-pressurised steel pipes was observed by high speed photography. The tests were performed on 610 mm diameter pipes, with wall thicknesses of either 6.2 mm or 9.3 mm, apart from the final test where a 915 mm diameter, 12.5 mm wall thickness pipe was ruptured. Rupture pressures ranged from 19 bar to 40 bar.Measured breach opening times are compared with data from earlier small scale tests (102 mm diameter pipes with 1.6 mm wall thickness) where rupture pressure ranged from 50 bar to 120 bar. Both sets of data are shown to be in general agreement with a theoretical model which combines an upper limit ductile fracture propagation velocity with a simple inertia model for the displacement of the free edges of the breach. For large pipes the measured and predicted opening times are significantly longer than the maximum of 1 ms specified in the current US design codes.     

Untersuchungen vollsynthetischer Kohlenwasserstoff-Wachse

Investigation of Fully Synthetic Hydrocarbon Waxes Methods for the structural investigation of synthetic hydrocarbon waxes of a new series of Ruhrwaxes are reported. Besides the molecular weight distribution, which is determined by fractional extraction of the hydrocarbon waxes with an organic solvent and characterization of the fractions by means of molecular weights, solidification points and refractive indices, properties like ability to form adducts with urea, dilatometric and calorimetric measurements as well as assay of IR spectra serve for elucidating the structure and composition.     

Scattering and absorption property database for nonspherical ice particles in the near- through far-infrared spectral region

The single-scattering properties of ice particles in the near- through far-infrared spectral region are computed from a composite method that is based on a combination of the finite-difference time-domain technique, the T-matrix method, an improved geometrical-optics method, and Lorenz-Mie theory. Seven nonspherical ice crystal habits (aggregates, hexagonal solid and hollow columns, hexagonal plates, bullet rosettes, spheroids, and droxtals) are considered. A database of the single-scattering properties for each of these ice particles has been developed at 49 wavelengths between 3 and 100 microm and for particle sizes ranging from 2 to 10,000 microm specified in terms of the particle maximum dimension. The spectral variations of the single-scattering properties are discussed, as well as their dependence on the particle maximum dimension and effective particle size. The comparisons show that the assumption of spherical ice particles in the near-IR through far-IR region is generally not optimal for radiative transfer computation. Furthermore, a parameterization of the bulk optical properties is developed for mid-latitude cirrus clouds based on a set of 21 particle size distributions obtained from various field campaigns.     

RNA helicases: versatile ATP-driven nanomotors

RNA helicases are a large family of molecular motors that utilize nucleoside triphosphates to unwind RNA duplexes and to remodel RNA protein complexes. In this review, we discuss the structure and function of RNA helicases with an emphasis on the potential application of these enzymes to control conformational changes in nanoassemblies that contain RNA.     

Aktuelle Probleme bei der Ultraschallprüfung von Freiformschmiedestücken

Die routinemäßige Ultraschallprüfung von Schmiedestücken und ihre Grenzen. Festlegungen in Regelwerken, Forderungen hinsichtlich Registrier- und Zulässigkeitsgrenzen. Prüfung austenitischer Bauteile, Einsatz spezieller Prüfköpfe und Geräte. Möglichkeiten der Automatisierung, Ausblick auf zukünftige Entwicklungen.     

The effect of hemodilution on regional myocardial function in the presence of coronary stenosis

Hemodilution decreases blood viscosity and circulatory input impedance and thus reduces afterload. Its use in treatment of LV power failure has been advocated, but the safe limits of isovolemic hemodilution are not known. Compensation of the reduced O2-capacity of the blood was therefore studied with normal and impaired coronary reserve. In 20 dogs the LAD was stenosed to a degree just not affecting the supplied region and central and coronary hemodynamics were studied. Regional myocardial function was assessed by ultrasound transit time between transducers implanted in the LV wall. Lowering the hematocrit to 15% by isovolumic exchange of blood for Dextran 60 increased CVP (18%), PAP (47%), LAP (64%), LVedP (46%), CO (67%), and flow to the intact area (LCA: 211%). Flow in the stenosed LAD increased slightly. Enddiastolic length (EDL) of LAD dependent muscle segments rose to 120% and their contraction amplitude deltaL was decreased by 46%. Whereas non-ischemic segments showed compensatory rise in deltaL (38%) at almost constant EDL (+9%). After release of the LAD stenosis EDL and deltaL returned to normal. During progressive anemia myocardial O2-demand is not adequately met if coronary reserve capacity is depleted. Reversion of hypokinesia after removal of the stenosis shows unimpaired myocardial function at a hematocrit as low as 15% provided the coronary circulation is intact.