An application of the requirement vs capability analysis to estimating design reliability of solid rocket motors

Design reliability parameters for solid propellant rocket engine

Currents under land-fast ice in the Canadian Arctic Archipelago Part 1: Vertical velocities

A 614 kHz acoustic Doppler current profiler was deployed through land-fast ice in Resolute Passage, in the Canadian Archipelago for 30 days in April and May 1992. It was demonstrated that in the mean, at tidal and at high frequencies the instrument was stable and aligned within 0.5° of vertical, permitting unambiguous measurement of the horizontal, and more importantly, the vertical velocity structure. The flow was dominated by tidal and high frequency (15 min period) oscillations. The K1 and M2 tidal currents were both approximately 10.0 cm s−1, oriented along-channel. The K1 component was constant with depth while the M2 component changed in magnitude and its sense of rotation. The corresponding vertical velocities showed maximum spectral power density in the semi-diurnal frequency band but were insignificant in the diurnal band. At high frequencies, 31 events, or groups of oscillations with vertical velocities greater than 3.5 cm s−1 were found. They were identified as finite amplitude internal waves trapped to the pycnocline, finite amplitude internal waves at greater depth (corresponding to a change in the density structure) and linear internal waves. The horizontal kinetic energy of the oscillations was dependent on the spring-neap tidal cycle. It is proposed that many were generated through interaction of the tidal flow with a compression ridge in the ice, located approximately 15 km from the measurement site

Currents under land-fast ice in the Canadian Arctic Archipelago Part 2: Vertical mixing

During an acoustic Doppler current profiler (ADCP) study of the velocity field under land-fast ice, coincident CTD casts showed three instances of pronounced instability in the water column, immediately above and below the pycnocline. In this paper we demonstrate that the density inversions are associated with the passage of high frequency linear internal waves and finite amplitude waves. Contours of ADCP acoustic return intensity display pronounced vertical eddy-like features which may indicate overturning. A Richardson number calculation showed that even the most highly stratified portion of the pycnocline had sufficient vertical velocity shear to promote dynamic instability. Finally, we calculate that the vertical nutrient flux, resulting from the high frequency internal wave field, could supply a significant portion of the ice-algae nutrient budget

Nicotine Enemas for Active Crohn's Colitis: An Open Pilot Study

Background. Smoking has a detrimental effect in Crohn's disease (CD), but this may be due to factors in smoking other than nicotine. Given that transdermal nicotine benefits ulcerative colitis (UC), and there is a considerable overlap in the treatment of UC and CD, the possible beneficial effect of nicotine has been examined in patients with Crohn's colitis. Aims. To assess the efficacy and safety of nicotine enemas in active Crohn's colitis. Patients. Thirteen patients with active rectosigmoid CD; 3 patients were excluded because they received antibiotics. Methods. Subjects were given 6 mg nicotine enemas, each day for 4 weeks, in an open pilot study. At the beginning and end of the trial, a Crohn's disease activity index (CDAI) score was calculated, sigmoidoscopy was performed, and haematological inflammatory markers measured. Results. Mean CDAI decreased from 202 to 153—the score was reduced in 6 patients, unchanged in 3, and increased in one. Frequency of bowel movements decreased in 8 patients and the sigmoidoscopy grade was reduced in 7. Mean C-reactive protein decreased from 22.0 to 12.3 mg/L. There were no withdrawals due to adverse events. Conclusions. In this relatively small study of patients with active Crohn's colitis, 6 mg nicotine enemas appeared to be of clinical benefit in most patients. They were well tolerated and safe

Using Fluid Curtains to Improve Sealing Performance in Turbomachinery Applications

The results from an investigation into the physics of how fluid curtains can be applied to improve the aerodynamic performance of conventional turbomachinery shaft and rotor seals are described in this paper. Computational fluid dynamics and testing on two experimental facilities are used in the study. In the first part of the work, computational fluid dynamics simulations validated against experimental test data demonstrate the fundamental mechanism by which the presence of the curtain can act to reduce leakage flow through conventional seals. These results are consolidated into a single performance carpet map, showing how the leakage reduction performance and the curtain supply pressure needed to achieve it vary with changes in values of key geometrical parameters. In the second part of the work the effect of swirl in the seal inlet flow, as is often encountered in turbomachinery applications, on the performance of the fluid curtain is investigated experimentally. Test results show that if the swirl momentum in the inlet flow is greater than the momentum of the curtain flow, the performance benefit from applying the curtain is greatly diminished. Overall, the results provide some fundamental design rules for applying fluid curtains to enhance turbomachinery sealing performance for the general type of leakage path geometry (cylindrical channel, 45-degree jet angle, curtain upstream of a conventional seal) and working fluid type and conditions (air, ambient temperature, subsonic leakage channel flow), used in the study

Matrix controlled channel diffusion of sodium in amorphous silica

To find the origin of the diffusion channels observed in sodium-silicate glasses, we have performed classical molecular dynamics simulations of Na$_2$O--4SiO$_2$ during which the mass of the Si and O atoms has been multiplied by a tuning coefficient. We observe that the channels disappear and that the diffusive motion of the sodium atoms vanishes if this coefficient is larger than a threshold value. Above this threshold the vibrational states of the matrix are not compatible with those of the sodium ions. We interpret hence the decrease of the diffusion by the absence of resonance conditions.Comment: 5 pages, 4 figure

Comparing plasma and faecal measures of steroid hormones in Adelie penguins Pygoscelis adeliae

Physiological measurements of both stress and sex hormones are often used to estimate the consequences of natural or human-induced change in ecological studies of various animals. Different methods of hormone measurement exist, potentially explaining variation in results across studies; methods should be cross-validated to ensure that they correlate. We directly compared faecal and plasma hormone measurements for the first time in a wild free-living species, the Adelie penguin (Pygoscelis adeliae). Blood and faecal samples were simultaneously collected from individual penguins for comparison and assayed for testosterone and corticosterone (or their metabolites). Sex differences and variability within each measure, and correlation of values across measures were compared. For both hormones, plasma samples showed greater variation than faecal samples. Males had higher mean corticosterone concentrations than females, but the difference was only statistically significant in faecal samples. Plasma testosterone, but not faecal testosterone, was significantly higher in males than females. Correlation between sample types was poor overall, and weaker in females than in males, perhaps because measures from plasma represent hormones that are both free and bound to globulins, whereas measures from faeces represent only the free portion. Faecal samples also represent a cumulative measure of hormones over time, as opposed to a plasma ‘snapshot’ concentration. Our data indicate that faecal sampling appears more suitable for assessing baseline hormone concentrations, whilst plasma sampling may best define immediate responses to environmental events. Consequently, future studies should ensure that they select the most appropriate matrix and method of hormone measurement to answer their research questions

A Distributed Multilevel Force-directed Algorithm

The wide availability of powerful and inexpensive cloud computing services naturally motivates the study of distributed graph layout algorithms, able to scale to very large graphs. Nowadays, to process Big Data, companies are increasingly relying on PaaS infrastructures rather than buying and maintaining complex and expensive hardware. So far, only a few examples of basic force-directed algorithms that work in a distributed environment have been described. Instead, the design of a distributed multilevel force-directed algorithm is a much more challenging task, not yet addressed. We present the first multilevel force-directed algorithm based on a distributed vertex-centric paradigm, and its implementation on Giraph, a popular platform for distributed graph algorithms. Experiments show the effectiveness and the scalability of the approach. Using an inexpensive cloud computing service of Amazon, we draw graphs with ten million edges in about 60 minutes.Comment: Appears in the Proceedings of the 24th International Symposium on Graph Drawing and Network Visualization (GD 2016

The influence of intercalating perfluorohexane into lipid shells on nano and microbubble stability

Microbubbles are potential diagnostic and therapeutic agents. In vivo stability is important as the bubbles are required to survive multiple passages through the heart and lungs to allow targeting and delivery. Here we have systematically varied key parameters affecting microbubble lifetime to significantly increase in vivo stability. Whilst shell and core composition are found to have an important role in improving microbubble stability, we show that inclusion of small quantities of C6F14 in the microbubble bolus significantly improves microbubble lifetime. Our results indicate that C6F14 inserts into the lipid shell, decreasing surface tension to 19 mN m-1, and increasing shell resistance, in addition to saturating the surrounding medium. Surface area isotherms suggest that C6F14 incorporates into the acyl chain region of the lipid at a high molar ratio, indicating ∼2 perfluorocarbon molecules per 5 lipid molecules. The resulting microbubble boluses exhibit a higher in vivo image intensity compared to commercial compositions, as well as longer lifetimes