Fatigue Life Prediction of Edge-Welded Metal Bellows Using Neural Networks and Multiple Linear Regression

Edge-welded metal bellows present an ongoing challenge: the prediction of an accurate cycle life. Current methods rely on physical leak detection to determine a bellow\u27s cycle life to failure. It is known, however, that crack initiation begins many cycles before a leak path is present. Bellows manufacturers require a method for detection of fatigue cracks when they initiate but before they result in leak rates large enough to contaminate a process. Acoustic emission (AE) testing is one method which can meet this need and is a proven, reliable technique for detecting crack initiation and monitoring fatigue crack growth. Four sets of metal bellows samples were fatigue tested and AE parameter data recorded. The data sets were analyzed and the determination made that amplitude, duration, and time of occurrence were the AE data variables required for separation of the various failure mechanisms. For two of the four materials, an expanded set of tests were performed. Fourteen tests were used to train and test a back-propagation neural network for prediction of bellows cycle life. The input data consisted of a material identifier, AE parameter data consisting of the amplitude distribution (50-100 dB) of the first 250 hits, and the final cycle life. The network was structured with an input layer consisting of the identifier and amplitude data, two hidden layers for mapping failure mechanisms, and an output layer for predicting cycle life. The network required training on four samples for the Inconel 718 and five samples for the 350 stainless steel. Once trained the network was able to predict cycle life with a worst case error of-4.45 percent and 2.66 percent for the Inconel 718 and 350 stainless steel, respectively. Finally, through the use of multiple linear regression, a statistical analysis was made to develop a model capable of accurate prediction. Applying a natural log transformation to the independent variables of amplitude and energy resulted in a model capable of explaining 95 percent of the variability in cycle life prediction

The Economic Impact of Substantial Sea-Level Rise

Using the FUND model, an impact assessment is conducted over the 21st century for rises in sea level of up to 2-m/century and a range of socio-economic scenarios downscaled to the national level, including the four SRES storylines. This model balances the costs of retreat with the costs of protection, including the effects of coastal squeeze. While the costs of sea-level rise increase with greater rise due to greater damage and protection costs, the model suggests that an optimum response in a benefit-cost sense remains widespread protection of developed coastal areas, as identified in earlier analyses. The socio-economic scenarios are also important in terms of influencing these costs. In terms of the four components of costs considered in FUND, protection dominates, with substantial costs from wetland loss under some scenarios. The regional distribution of costs shows that a few regions experience most of the costs, especially East Asia, North America, Europe and South Asia. Importantly, this analysis suggests that protection is much more likely and rational than is widely assumed, even with a large rise in sea level. This is underpinned by the strong economic growth in all the SRES scenarios: without this growth, the benefits of protection are significantly reduced. It should also be noted that some important limitations to the analysis are discussed, which collectively suggest that protection may not be as widespread as suggested in the FUND results. Equity weighting allows the damages to be modified to reflect the wealth of those impacted by sea-level rise. Taking these distributional issues into account increases damage estimates by a factor of three, reflecting that the costs of sea-level rise fall disproportionately on poorer developing countries.Sea-level rise;Socio-economic scenarios;costs;protection;equity weighting

Electrical and optical characterisation of low temperature grown InGaAs for photodiode applications

Dilute bismide and nitride alloys are promising semiconductors for bandgap engineering, opening additional design freedom for devices such as infrared photodiodes. Low growth temperatures are required to incorporate bismuth or nitrogen into III V semiconductors. However, the effects of low growth temperature on dark current and responsivity are not well understood. In this work, a set of InGaAs p i n wafers were grown at a constant temperature of 250, 300, 400 and 500 °C for all p, i and n layers. A second set of wafers was grown where the p and n layers were grown at 500 °C while the i-layers were grown at 250, 300 and 400 °C. Photodiodes were fabricated from all seven wafers. When constant growth temperature was employed (for all p, i and n layers), we observed that photodiodes grown at 500 °C show dark current density at 1 V that is 6 orders of magnitude lower while the responsivity at an illumination wavelength of 1520 nm is 4.5 times higher than those from photodiodes grown at 250 °C. Results from the second set of wafers suggest that performance degradation can be recovered by growing the p and n layers at high temperature. For instance, comparing photodiodes with i-layers grown at 250 °C, photodiodes showed dark current density at -1 V that is 5 orders of magnitude lower when the p and n layer were grown at 500 °C. Postgrowth annealing, at 595 °C for 15 minutes, on the two wafers grown at 250 and 300 °C showed recovery of diode responsivity but no significant improvement in the dark current. Our work suggests that growth of the cap layer at high temperature is necessary to maintain the responsivity and minimise the dark current degradation, offering a pathway to developing novel photodiode materials that necessitate low growth temperatures

Demonstration of large ionization coefficient ratio in AlAs0.56Sb0.44 lattice matched to InP

The electron and hole avalanche multiplication characteristics have been measured in bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes, lattice matched to InP, with nominal avalanche region thicknesses of ~0.6 μm, 1.0 μm and 1.5 μm. From these and data from two much thinner devices, the bulk electron and hole impact ionization coefficients (α and β respectively), have been determined over an electric-field range from 220-1250 kV/cm for α and from 360-1250 kV/cm for β for the first time. The α/β ratio is found to vary from 1000 to 2 over this field range, making it the first report of a wide band-gap III-V semiconductor with ionization coefficient ratios similar to or larger than that observed in silicon

Mission Concept for the Single Aperture Far-Infrared (SAFIR) Observatory

The Single Aperture Far-InfraRed (SAFIR) Observatory's science goals are driven by the fact that the earliest stages of almost all phenomena in the universe are shrouded in absorption by and emission from cool dust and gas that emits strongly in the far-infrared and submillimeter. Over the past several years, there has been an increasing recognition of the critical importance of this spectral region to addressing fundamental astrophysical problems, ranging from cosmological questions to understanding how our own Solar System came into being. The development of large, far-infrared telescopes in space has become more feasible with the combination of developments for the James Webb Space Telescope and of enabling breakthroughs in detector technology. We have developed a preliminary but comprehensive mission concept for SAFIR, as a 10 m-class far-infrared and submillimeter observatory that would begin development later in this decade to meet the needs outlined above. Its operating temperature (<4K) and instrument complement would be optimized to reach the natural sky confusion limit in the far-infrared with diffraction-limited peformance down to at least 40 microns. This would provide a point source sensitivity improvement of several orders of magnitude over that of Spitzer or Herschel, with finer angular resolution, enabling imaging and spectroscopic studies of individual galaxies in the early universe. We have considered many aspects of the SAFIR mission, including the telescope technology, detector needs and technologies, cooling method and required technology developments, attitude and pointing, power systems, launch vehicle, and mission operations. The most challenging requirements for this mission are operating temperature and aperture size of the telescope, and the development of detector arrays.Comment: 36 page

Polarization-Correlated Photon Pairs from a Single Quantum Dot

Polarization correlation in a linear basis, but not entanglement, is observed between the biexciton and single-exciton photons emitted by a single InAs quantum dot in a two-photon cascade. The results are well described quantitatively by a probabilistic model that includes two decay paths for a biexciton through a non-degenerate pair of one-exciton states, with the polarization of the emitted photons depending on the decay path. The results show that spin non-degeneracy due to quantum-dot asymmetry is a significant obstacle to the realization of an entangled-photon generation device.Comment: 4 pages, 4 figures, revised discussio

Multimodal Aerial Locomotion:An Approach to Active Tool Handling

The research focus in aerial robotics is shifting from contactless inspection toward interaction and manipulation, with the number of potential applications rapidly increasing [1]. Eventually, aerial manipulators, i.e., unmanned aerial vehicles (UAVs) equipped with manipulators, will likely take on hazardous maintenance tasks now performed by humans. For this to happen, aerial manipulators must be able to perform all the different operations required in these maintenance routines

Outcome of Patients After Transcatheter Aortic Valve Embolization

ObjectivesThis study aims to assess the mid- to long-term follow-up of patients after valve embolization at the time of transcatheter aortic valve implantation (TAVI).BackgroundTranscatheter heart valve (THV) embolization is a rare but serious complication during TAVI. Although various techniques have been developed to manage acute complications and reduce periprocedural morbidity/mortality, long-term clinical and hemodynamic consequences after these events are unknown.MethodsPatients who developed THV embolization after TAVI were prospectively assessed. Clinical and echocardiographic characteristics were recorded at baseline and after successful TAVI/surgical aortic valve replacement. The THV migration and strut fractures/degeneration were assessed by computed tomography.ResultsA total of 7 patients had THV embolization, all of which occurred immediately after valve deployment. The embolized THV was repositioned in the aortic arch proximal to the left subclavian artery (n = 2), immediately distal to the left subclavian artery (n = 2), and in the abdominal aorta (n = 3). A second THV was implanted successfully at the same sitting in 4 patients and at the time of a second procedure in 2 patients. Elective conventional aortic valve replacement was performed in 1 patient. Median follow-up was 1,085 days. One patient died during follow-up from an unrelated cause. The remaining 6 survivors were in New York Heart Association functional class I or II at final follow-up. Mid-term computed tomography follow-up (n = 4,591 to 1,548 days) showed that the leaflets of the embolized THV remain open in all phases of the cardiac cycle. There was also no strut fracture or migration of these valves.ConclusionsClinical outcomes remain good when THV embolization is managed effectively. There are no apparent hemodynamic consequences of a second valve placed in the series. These embolized valves remain in a stable position with no evidence of strut fractures at mid-term follow-up

Ground-based walking training improves quality of life and exercise capacity in COPD

This study was designed to determine the effect of ground-based walking training on health-related quality of life and exercise capacity in people with chronic obstructive pulmonary disease (COPD). People with COPD were randomised to either a walking group that received supervised, ground-based walking training two to three times a week for 8–10 weeks, or a control group that received usual medical care and did not participate in exercise training. 130 out of 143 participants (mean±SD age 69±8 years, forced expiratory volume in 1 s 43±15% predicted) completed the study. Compared to the control group, the walking group demonstrated greater improvements in the St George’s Respiratory Questionnaire total score (mean difference -6 points (95% CI -10– -2), p<0.003), Chronic Respiratory Disease Questionnaire total score (mean difference 7 points (95% CI 2–11), p<0.01) and endurance shuttle walk test time (mean difference 208 s (95% CI 104–313), p<0.001). This study shows that ground-based walking training is an effective training modality that improves quality of life and endurance exercise capacity in people with COPD