[en] In this paper it is shown how the results of short-term constant strainrate tests can be used to predict deformation and rupture under long term creep conditions. Such tests have been performed on a candidate material for the high temperature reactor in the temperature range 800-900⁰C. Creep curve, isochronous stress-strain curve, rupture life and ductility predictions in the temperature range 800 -1050⁰C involving time extrapolations over more than three orders of magnitude, are presented and compared with available experimental data as well as with extrapolated results obtained by other methods. It is shown that valid predictions can be made using this new and very versatile short term method. The possibility to determine time-dependent allowable stress levels for use in structural design at high temperatures is presented. (author)

[en] In this paper it is shown how the results of short-term constant strainrate tests can be used to predict deformation and rupture under long term creep conditions. Such tests have been performed on a candidate material (α Ni-Cr-Co-Mo superalloy) for the high temperature reactor in the temperature range 800-900⁰C. Creep curve, isochronous stress-strain curve and rupture life extrapolations are presented in the temperature range 800-1050⁰C. These extrapolations all agree favourably with published data. (orig./GL)

[en] A suspension of glass fibers in alcohol has been used to investigate a upward vertical developing pipe flow. The refractive index of the alcohol was matched to that of the glass fibers, making the whole suspension transparent. Laser Doppler Anemometry (LDA) was applied, and fluid velocities could then be measured for consistencies up to c = 12 g/l. Radial profiles of axial U-velocity and turbulence spectra have been recorded at various positions (z/D = 2, 5, 36) downstream of an orifice (step) with 64% open area. Measurements were taken for different consistencies (c = 1.2, 12 g/l), fiber lengths (l = 1, 3 mm) and Reynolds numbers (R_e = 8.5 ⋅ 10³, 6.5 ⋅ 10⁴). The fiber crowding factor (n_f) has been used to discuss the observed effects of the present fibers on momentum transfer and turbulence structure. The results show both an increase (l= 1 mm, c= 1.2 g/l) and decrease (l=3 mm, c = 12 g/l) in turbulence levels in the presence of fibers. Suspensions with long fibers at the highest consistency show plug flow in parts of the core. This causes damping of the turbulence mainly at smaller length scales. For short fibers at low consistency, the increased turbulent energy was mainly observed at small length scales in the spectrum. (author)

No abstract available

[en] Purpose: The aim of this work was to compare the knee coil and the surface coil for the visualisation of the patellar cartilage. Materials and methods: In 28 patients (17 women, 11 men) with an average age of 40 years (range 14-76) with knee pain MR was performed. Transverse images were obtained using a fast spin echo proton density weighted sequence on a Philips Gyroscan Intera 1.5 T clinical system. Transverse images were obtained at the level of the patellar cartilage using both the surface and the knee coil. All images were evaluated by consensus of two radiologists. They evaluated a number of quality criteria on a 4-point scale. Criteria for artefacts were also graded on a 4-point scale. Results: For the visualisation of fluid there was no significant difference between the knee coil and the surface coil (P=0.021). For all other criteria regarding image quality and presence of imaging artefacts there was a significant difference between both coils (P<0.001) with the surface coil obtaining the better result. Conclusion: The use of the surface coil in the visualisation of the patellar cartilage can be recommended at knee MR

[en] A TOF-PET system has been designed and constructed for educational purposes. The aim of this system is to demonstrate the possibilities of positron emission tomography in general and the time-of-flight method in particular to the students of various courses at the Royal Institute of Technology, Stockholm, Sweden. The set-up consists of 48 small BaF₂ crystals coupled to fast photomultipliers placed in a ring geometry. The signals of the photomultipliers are fed into fast constant fraction discriminators (CFD). The outputs of these are directed to a specially designed logic VME unit, which combines the CFD signals of 6 neighbouring channels to one signal by adding a different delay to each channel. The logic circuitry produces a prompt pulse for each event that serves as the start pulse for the 8-channel fast TDC. The delayed pulses act as the stop pulses for the TDC. In a computer, the measured times are converted into information about which the photomultipliers fired with the difference in the time of flight. The set-up is described and the results are presented

[en] A detector system for positron emission tomography with time-of-flight capability has been built to serve as an educational tool for undergraduate students. The set-up consists of 48 BaF₂ scintillator crystals, each coupled to a fast photo-multiplier tube, mounted in a circular geometry. The analogue detector pulses are handled by fast constant fraction discriminators. A dedicated unit reduces the 48 channels to eight channels via delay-line encoding, and the signals are then fed to an eight channel fast time-to-digital converter. A VME processor sorts the events and sends them to a workstation where the coincident events are extracted. The time resolution of the detectors together with fast VME based electronics allows for time-of-flight measurements to improve on the signal-to-noise ratio in the reconstructed images. The system can be used for different types of exercises for the students, varying from the fundamentals of scintillator detectors to advanced image reconstruction. The set-up is described and some results are presented

[en] Constant strainrate tests have been carried out at 800⁰C on three batches of alloy 800H. The imposed strainrates range from 10^-5 to 10^-8 s^-1. The results of the tests are interpreted in the framework of the effective stress description of the creep behaviour. Their application in predicting the creep behaviour is discussed. (orig.)

[en] A commercially available HP-Si₃N₄ has been exposed for 200 hours in a 0.4%H₂S+0.75%H₂O+H₂ bal. environment at 1200 and 1300 C. Subsequently long term constant stress tests have been performed at the exposure temperatures in the uniaxial tensile mode. Strength, toughness and subcritical crack growth tests results obtained in the flexural loading mode presented elsewhere highlight the effect of a reduction in the amount in the intergranular glassy phase. However, the interpretation of flexural test results at high temperature is hampered by time-dependent changes in the stress distribution and a shift of the neutral axis, making it very difficult to derive the constitutive equations without making arbitrary assumptions. This paper therefore deals with the comparison of the long term uniaxial tensile mechanical behaviour of the material in both as-received and exposed conditions. In order not to mask the intrinsic behaviour of the exposed material, all tests are performed in vacuum. (orig.)

[en] Many sensor networks, including large particle detector arrays measuring high-energy cosmic-ray air showers, traditionally rely on centralised trigger algorithms to find spatial and temporal coincidences of individual nodes. Such schemes suffer from scalability problems, especially if the nodes communicate wirelessly or have bandwidth limitations. However, nodes which instead communicate with each other can, in principle, use a distributed algorithm to find coincident events themselves without communication with a central node. We present such an algorithm and consider various design tradeoffs involved, in the context of a potential trigger for the Auger Engineering Radio Array (AERA).