A Review of Fatigue Crack Growth for Pipeline Steels Exposed to Hydrogen

Hydrogen pipeline systems offer an economical means of storing and transporting energy in the form of hydrogen gas. Pipelines can be used to transport hydrogen that has been generated at solar and wind farms to and from salt cavern storage locations. In addition, pipeline transportation systems will be essential before widespread hydrogen fuel cell vehicle technology becomes a reality. Since hydrogen pipeline use is expected to grow, the mechanical integrity of these pipelines will need to be validated under the presence of pressurized hydrogen. This paper focuses on a review of the fatigue crack growth response of pipeline steels when exposed to gaseous hydrogen environments. Because of defect-tolerant design principles in pipeline structures, it is essential that designers consider hydrogen-assisted fatigue crack growth behavior in these applications.     

Image processing techniques for 3-D chromosome analysis

3-D karyotype analysis is developing rapidly due to the availability of confocal microscopes and CCD video cameras, and the development of 3-D processing techniques. Here, image enhancement and visualization techniques specifically designed for 3-D karyotype analysis are described. To facilitate a good comparison between the different techniques, the same 3-D image, obtained with a confocal scanning laser microscope (CSLM), of a mitotic prophase nucleus of a root-tip cell of Crepis capillaris was used throughout. Besides well-known stereoscopic presentation, another means of improving depth perception is shown, i.e. a solid modelling algorithm, which simulates the process of fluorescence. An interactive routine to dissect objects in the image is presented as an alternative for automated segmentation algorithms, which cannot be applied to closely apposed or merging objects. As an example of a convenient way to reduce the vast amount of data (2 Mbyte per image), a partly automated 3-D cursor is presented in detail. This cursor is used to trace the central axes of chromosomes and record them as strings of Cartesian coordinates. The advantages of a computer graphics display, which facilitates real-time rotation and hence is a powerful tool in studying 3-D features of chromosomes, are also shown.     

SYNCHRONIZED RETROPERFUSION COMBINED WITH CORONARY SINUS OCCLUSION: EXPERIMENTAL MEASUREMENTS COMPARED WITH SIMULATION RESULTS AND MODEL PREDICTIONS

A mathematical model has been developed to investigate the hemodynamic effects of different modes of coronary sinus interventions. To compare the predictions of this model with experimentally derived results, six open chested dogs with coronary artery occlusions were studied. Aortic pressure, coronary venous pressure, and LAD pressure distal to the occlusion were measured. Throughout each experiment, retroperfusion of arterial blood into the coronary sinus, synchronized to diastole (SRP), was performed at flow rates of 25, 50, 75, and 100 ml/min. In each dog, two modes of superimposed coronary sinus occlusion were investigated: mode 1, the coronary sinus was occluded only during diastole; mode 2, coronary sinus occlusion was extended until coronary sinus pressure reached a plateau. The validity of the model was confirmed by a satisfactory agreement between the experimentally and mathematically derived     

A COMPUTER MODEL OF MYOCARDIAL SQUEEZING AND INTRAMYOCARDIAL FLOW DURING GRADED CORONARY ARTERY STENOSIS IN THE PRESENCE OF CORONARY SINUS INTERVENTIONS

A mathematical model of the left coronary circulation is used to calculate phasic arterial and intramyocardial flows under normal conditions, gradual stenosis, and full occlusion of the left anterior descending coronary artery. Experimental data reported in literature are compiled to derive a mathematical formula for the physiologic link between two model parameters: the resistance across the stenosis and the extravasal squeezing pressure within the LAD-dependent region of the myocardium. Matching pairs of resistance and decrease in squeezing form “infarction traces.” Model simulations yield the changes in coronary and intramyocardial flows along these infarction traces. The model was applied to alternating brief coronary sinus occlusions and coronary sinus release. The retrograde blood flow from the coronary veins to the capillaries during coronary sinus occlusion was estimated to range between 47% and 88% of the forward blood flow under patent coronary sinus conditions.     

Image cytometric method for quantifying the relative amount of DNA in bacterial nucleoids using Escherichia coli

An image cytometric method for quantifying integrated fluorescence was developed to measure the relative DNA contents of bacterial nucleoids. Image analysis was performed with newly developed macros in combination with the program Object-Image, all downloadable from http://simon.bio.uva.nl/object-image.html. Four aspects of the method were investigated. (i) Good linearity was found over a ten-fold range of fluorescence intensity in a test with a calibration kit of fluorescent latex spheres. (ii) The accuracy of the method was tested with a narrowly distributed Escherichia coli population, which was obtained by growing cells into stationary phase. The width of the image cytometric distribution was approximately 6%, in good agreement with results obtained by flow cytometry. (iii) The error contribution of manual focusing could be kept below 2%, although a strong dependency between integrated fluorescence and focus position was observed. (iv) The results were verified with a flow cytometer, which gave similar distributions for the DNA contents per cell expressed in chromosome equivalents (4.8 fg of DNA). We used the presented method to evaluate whether the DNA conformation had any effect on the total fluorescence of bacterial nucleoids. Experiments using nucleoids with the same amount of DNA in either a dispersed or a compact conformation showed no significant difference in integrated fluorescence, indicating that it is possible to determine the DNA content per nucleoid independently of the actual organization of the DNA.     

The relationship between extrusion die line roughness and high cycle fatigue life of an AA6082 alloy

The effect of surface finish on the fatigue life of hollow extruded AA6082 was studied by comparing results from specimens with as-extruded surfaces to results from specimens with polished surfaces. Extrusion die lines are the main contributor to surface roughening, and since die lines are parallel to the extrusion direction, distinct variations exist between fatigue lives of as-extruded specimens taken longitudinal and transverse to the extrusion direction [Nanninga N, White C, Furu T, Anderson O, Dickson R. Effect of orientation and extrusion welds on the fatigue life of an Al–Mg–Si–Mn alloy. Int J Fatigue 2008;30(9):1569–78]. Polishing specimen surfaces eliminated much of the variation between specimen orientations. Fatigue lives of polished specimens containing extrusion seam welds transverse to the loading direction were also studied. The seam weld did not appear to significantly affect the fatigue life. Die lines were modeled as notches and finite element analysis (FEA) was used to estimate a linear-elastic stress concentration factor for approximating fatigue run-out values for specimens with as-extruded surfaces loaded transverse to the die lines. The predicted run-out stress values based on the FEA match well with those obtained experimentally.     

Silent hydronephrosis, a hazard revisited

A rapid treatment approach to common sexual dysfunctions has been used in treating 59 couples, including 74 symptomatic individuals. Using a multidisciplinary team approach in an intensive 2 1/2 day workshop format, symptom improvement has been obtained in 86.5% of the dysfunctional individuals, with complete symptom reversal in 63.5%. The intensive workshop format has resulted in a saving of both patient and professional time and is seen as a viable and successful alternative to more time-consuming approaches of treating various sexual dysfunctions.