Effect of temperature on hydration kinetics and polymerization of tricalcium silicate in stirred suspensions of CaO-saturated solutions

Tricalcium silicate was hydrated at 274, 278, 283, 298, and 313 K in stirred suspensions of saturated CaO solutions under a nitrogen-gas atmosphere until the end of deceleratory period. The suspension conductivities and energy flows were measured continuously. The individual reaction rates for tricalcium silicate dissolution, calcium silicate hydrate precipitation, and calcium hydroxide precipitation were calculated from these measurements. The results suggest that the proportion of tricalcium silicate dissolved was determined by the rate of tricalcium silicate dissolution and the time to very rapid calcium hydroxide precipitation. The time to very rapid calcium hydroxide precipitation was more sensitive to changes in temperature than was the rate of tricalcium silicate dissolution, so that the proportion of tricalcium silicate hydration dissolved by the deceleratory period increased with decreasing temperature. The average chain length of the calcium silicate hydrate ascertained by magic-angle spinning nuclear magnetic resonance spectroscopy increased with increasing temperature.     

The thermal springs of bockfjord, svalbard: occurrence and major ion hydrochemistry

The Troll and Jotun thermal springs of northern Svalbard, with temperatures of up to 25.6°C, are derived from a major fault forming the junction between Devonian sandstones and Proterozoic marbles, mica schists and gneisses. The Troll waters are dominated by Na–HCO₃ compositions and the Jotun waters by Na–Cl compositions. The pristine thermal water source has a sub-neutral pH and is highly reducing. Taken at face value, common geothermometers suggest temperatures at depth of 130–180°C for the Troll springs (corresponding to a depth of 1.6–2.3 km), with 10–30% thermal water diluted by 70–90% cold water. Such geothermometers may, however, be inappropriate to the cool, high CO₂ waters of Bockfjord, and real temperatures at depth and dilution factors are probably considerably lower. The salinity of the thermal water appears to be only partially derived from water–rock interaction; Br\Cl ratios suggest that seawater or possibly evaporites may be a source of chloride salinity.     

Lessons learned from full-spectral modeling of signatures of an estuary front

Previously, we have modeled radar signatures, involving large variations (/spl sim/10-15 dB) in radar cross section (RCS), that have been observed at strongly convergent ocean fronts and at an estuarine front. In each of these cases, we obtained quantitative agreement with measurement but only by including wave-breaking (WB) effects in an approximate manner. However, in each case, we used the composite scattering (CS) model at a frequency (9.4 GHz) where this model may be deficient. For this reason, questions remain concerning the importance of WB effects in these simulations. In the present study, we monitor the sensitivity of the simulations with respect to this CS approximation by comparing the results of this model with those from an alternative theory, based on simulations of RCS, derived from a common wave spectrum. The spectrum is calculated using a full-spectral treatment of wave-current interaction. The resulting simulations are used to model the radar signature of the buoyant plume associated with the efflux of fresh water from the Chesapeake Bay that was observed during the Chesapeake Outflow Plume Experiment 2 (COPE-II). In both cases, it is possible to simulate this signature, in quantitative agreement with experiment, but only by including WB effects. We find that the CS model predictions for the behavior of the signature do not agree with the comparable predictions from the remaining model. Additional simulations indicate the difference between the two models, which is rather large because of the large (60/spl deg/) angle of incidence, occurs because the CS model includes higher order terms that are not included in the Kirchoff Approximation.     

Application of the finite element method to off-shore structures

The merits of finite element methods in connection with the design of offshore structures are discussed using the Ekofisk Tank as an example. Various design approaches and procedures are evaluated on the same basis and some of the experiences gained are mentioned. The conclusion is drawn that the finite element method is a very powerful tool in the evaluation of new designs, but to be successful, it requires good planning and experienced personnel.The procedures presently applied for determination of wave loads do not represent a very realistic modelling of the actual storm conditions. To show what improvements can be made in this field, an outline of how the irregular wave system may be formulated and how the calculated loads may be applied in the stress analysis is given. The procedure is described with reference to a semisubmersible drilling platform but the principle may be applied to any offshore structure.     

The acute phase serum amyloid A protein (SAA) in the horse: isolation and characterization of three isoforms

Serum amyloid A (SAA) from acute phase horse serum was isolated using hydrophobic interaction chromatography, gel filtration and ion exchange chromatography. Three SAA isoforms with different isoelectric points, i.e. SAA pI 8.0, SAA pI 9.0 and SAA pI 9.7, were identified by two-dimensional electrophoresis and further characterized with amino acid sequence analysis. These isoforms were found in similar concentrations in all animals investigated, with SAA pI 9.7 constituting about half of the total SAA content. Partial amino acid sequence analysis verified the previously published heterogeneous SAA sequence. SAA pI 8.0 was found to have isoleucine in Position 16, glutamine in Position 44 and glycine in Position 59. SAA pI 9.0 had leucine, glutamine and alanine in the corresponding positions. In SAA pI 9.7 leucine, lysine and alanine were detected. The three isoforms characterized in this study are all acute phase SAAs. SAA pI 9.0 and 9.7 correspond to amyloid A protein variants previously isolated from amyloid deposits of equine liver, while there are no reports on an amyloid A variant corresponding to SAA pI 8.0.     

Long-haul pilots use in-flight napping as a countermeasure to fatigue

The aim of this study was to examine the effects of fatigue on the amount of in-flight sleep obtained by airline pilots during long-haul duty periods. A total of 301 pilots collected sleep/wake and work/rest data for a period of at least 2 weeks each. Fatigue likelihood, i.e. low, moderate, high, or extreme, was estimated for each duty period based on a pilot’s sleep/wake behaviour prior to duty and the time of day that the duty period occurred. Participants obtained 1.8 h of sleep (i.e. 27% of their rest time) during duty periods with low fatigue likelihood and 3.7 h of sleep (i.e. 54% of their rest time) during duty periods with extreme fatigue likelihood. These results indicate that (i) long-haul pilots obtain substantially more sleep during duty periods when fatigue is likely to be extreme than when fatigue is likely to be low and (ii) long-haul pilots use in-flight napping as a fatigue countermeasure, but more could be done to increase its efficacy.     

Serum amyloid A protein in humans and four animal species: a comparison by two dimensional electrophoresis

Two-dimensional electrophoresis and N-terminal analysis were used to study serum amyloid A protein (SAA) from humans, mink, fox, goat and rabbit. Previously uncharacterized SAA variants were demonstrated in fox, goat and rabbit, and considerable interspecies homology was seen. In rabbit, two novel SAAs were characterized, and SAA1 and SAA2 were demonstrated in mink and rabbit sera. The results confirm previous cDNA studies and indicate that SAA do possess an important function also in fox and goat.     

Multipath scattering in ultrawide-band radar sea spikes

This paper presents sea scatter data collected with an ultrawide-band (UWB) polarimetric radar system that indicates that multipath scattering plays an important role in the generation of sea spikes. The radar system used in this study produces short pulses with a bandwidth of approximately 3 GHz centered at 9 GHz for a range resolution of approximately 4 cm. Pulse-to-pulse switching allows collection of the microwave echoes produced by all four combinations of linear transmit and receive polarizations [vertical-transmit vertical-receive (VV), horizontal-transmit horizontal-receive (HH), horizontal-transmit vertical receive (HV), and vertical-transmit horizontal-receive (VH)] each of which is collected by a sampling oscilloscope utilizing equivalent time sampling. In June 1996, upwind sea scatter data at grazing angles of 10°, 20°, and 30° were collected while the system was deployed on a research pier on the Outer Banks of North Carolina. An analysis of the strongest echoes (sea spikes) from this data set is presented and discussed. First, the cumulative distribution functions are presented. Second, an increase of approximately 5 dB is shown to occur in the polarization ratio (HH/VV) of the strongest echoes as the grazing angle decreases from 30° to 10°. Third, differences in the spatial and spectral characteristics of the VV and HH spikes are described. Through comparisons with laboratory results and a simple scattering model, these observations are explained by the presence of a multibounce scattering mechanism. The use of the model to extract wave height from the sea-spike frequency response is also explored