The behaviour of the dispersed phase in liquid-liquid cocurrent flow through a packed bed

The drop size distributions produced by the cocurrent flow of kerosene dispersed in water through a vertical column packed with spheres have been measured at different levels of flow rate, volume fraction dispersed phase, packing diameter and height of packed bed. The drop size measurements were made by isolating and photographing a portion of the dispersion as it emerged from the packing. The Sauter mean diameter is predicted by: where C is a constant, f(?) is the phase fraction effect, ∈ is the power input per unit volume, τ is the residence time and d_p is the packing diameter.     

The effect of loading rate and temperature on fracture initiation in 1020 hot-rolled steel

Fracture initiation experiments were conducted to determine the fracture toughness of an AISI 1020 hot-rolled steel under quasi-static and dynamic loading conditions. The dynamic tests were performed on specimens consisting of notched round bars loaded in tension by means of a stress pulse, thus giving an effective value of $\text{/.K}{}_{\mathrm{I}}\text{= 2 · 10}{}^6\text{ksi √in. s}{}^{\mathrm{?1}}\text{(2.2 · 10}{}^6\text{MPa √m s}{}^{\mathrm{?1}}\text{)}$. The tests were conducted over the temperature range ?157 to 121°C, and results are compared to those obtained in quasi-static tests with like specimens. Parallel tests were conducted to determine static and dynamic flow stresses of the material over the temperature range. Finally, a comparison is made with the behavior of an AISI 1018 cold-rolled steel previously tested in the same apparatus.     

Epitaxial growth and piezoelectric properties of A1N,GaN, and GaAs on sapphire or spinel

Heteroepitaxial films of the III-V compounds, A1N, GaN and GaAs have been grown on insulating substrates by reactions involving Group III metal-organic compounds and Group V hydrides. The films were examined with respect to crystallography, surface topography, uniformity, residual strain, and electrical and acoustic properties with emphasis on those orientations which are of particular interest to surface acoustic wave (SAW) device applications. Aluminum nitride films up to 10 μm in thickness were grown on 1″ diameter sapphire substrates with a 5% to 10% thickness variation. The films, though characterized as single crystal by x-ray means, exhibited a grain-like structure and considerable surface faceting. The residual strain in the films depends on the crystallographic direction and increases substantially with film thickness. These films exhibit useful surface acoustic properties. Epitaxial GaN films are more easily prepared than A1N films but by contrast are semiconducting unless “doped” with Zn or Li during the growth process. Films of this material are similar crystallographically to A1N and preliminary results show that they exhibit piezoelectric properties. The lack of published data on the acoustic properties of GaN films is probably due to the difficulty in compensating the films to provide insulating layers in device structures. Preliminary results obtained on GaAs epitaxial layers are discussed briefly because of the semiconducting properties of this material. Research jointly sponsored by the Air Force Materials Laboratory, Wright-Patterson Air Force Base, under Contract F33615-70-C-1536     

Mercury concentrations in muscle, brain and bone of Western Alaskan waterfowl

Total mercury (THg), which includes both inorganic (Hg(2+)) and methylmercury (MeHg) species, has been reported for seabirds in the North Pacific and Alaska. For the Yup'ik and Aleut people of Alaska, waterfowl are a small but important seasonal component of the diet, but many Alaskan species have not been studied extensively for the presence of mercury. Birds are good subjects for examination of mercury concentrations because they feed at different trophic levels, they can be long-lived, and many are both abundant and widely distributed. In this study, we present the levels of mercury in muscle, brain, and bone tissue of 140 birds taken by subsistence food users across Western Alaska. THg wet weight mean concentrations in the 18 species of waterfowl surveyed ranged from 0.8 to 268.6 ng/g in muscle, from 0.4 to 197.7 ng/g in brain and from 0.7 to 422.9 ng/g in bone. The null hypothesis that there are no interspecific differences in the level of total mercury in the 18 species of Alaska birds surveyed was not supported. We found interspecific differences with the Lesser Scaup (Aythya affinis), and the Black Scoter (Melanitta nigra), having the highest muscle tissue levels of THg. In general, THg mean levels were higher in muscle than in brain with the exceptions of the Bar-tailed Godwit and Northern Shoveler. Bone THg were highest in the Black Scoter. The mean values for THg in the species studied are unlikely to cause adverse reproductive or behavioral effects in the birds.     

Electron transfer and intershell spectroscopic parameters of Pb2+: Changes when lead halide films interact with alkali halide substrates

UV spectral data for Pb²⁺ highly diluted in alkali halide crystals and in lead halide thin films are shown to be consistent in the context of current inorganic spectroscopy. For Pb²⁺ in (i) alkali halides and (ii) lead halides the optical electronegativities are 1.2 and 1.4 respectively, while for the ¹S₀→³P₁ frequency (v_s?p) relationship (v_s?p = v_f?v_fmh where h is the nephelauxetic parameter of the complexing halide ion), the values of v_f are 60 700 cm^-1 and 64 400 cm^-1 and the values of m are 0.20 and 0.22 respectively. The results indicate that the modified Pb²⁺ ion model used for Pb²⁺ ions in alkali halide crystals can be extended to Pb²⁺ halide salts. These rationalizations indicate the usefulness of UV spectroscopic measurements for studying the penetration of lead halide thin films into crystalline alkali halides. Spectral changes occuring when sandwiches of lead halide films between NaCl and KBr substrates are maintained at 300°C indicate substantial evaporation of the lead halide film and preference of Pb²⁺ to diffuse into KBr rather than into NaCl.     

The National Ignition Facility neutron time-of-flight system and its initial performance (invited)

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.     

Effect of organic chelates on the performance of hybrid sol–gel coated AA 2024-T3 aluminium alloys

Sol–gels are organic–inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, primarily silanes, which have found applications as electronic, optical and protective coatings. These coatings possess important characteristics such as chemical stability, physical strength and scratch resistance. Further performance improvement is achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through the sol–gel process. However due to the inherent difference in the reactivity of the precursors, the hydrolysis of each precursor must be carried out separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acids, prior to hydrolysis, to lower the hydrolysis rate.In this body of work various ligands such as organic acids, acetyl acetone (AcAc) and 2,2′-bipyridine (Bipy) were used to control the zirconium hydrolysis reaction and form nanoparticles within the silane sol matrix.Nanoparticle modified coatings formed from the silane sol on AA 2024-T3 aluminium were characterised spectroscopically, electrochemically and calorimetrically to evaluate the potential effect of the different chelates on the final film properties while neutral salt spray tests were performed to study their anti-corrosion performance. Results indicate that the acid ligand modified coatings provided the best performance followed by AcAc, while Bipy was the poorest. In all cases the zirconium nanoparticle improved the protective properties of the sol–gel coating.     

Development and validation of a probabilistic second-order exposure assessment model for Escherichia coli O157:H7 contamination of beef trimmings from Irish meat plants

A second-order quantitative Monte Carlo simulation model was developed for Escherichia coli O157:H7 contamination of beef trimmings in Irish abattoirs. The assessment considers initial contamination levels, cross-contamination and decontamination events during the cattle slaughter process. The mean simulated prevalence of E. coli O157:H7 on trimmings was 2.36% and the mean simulated counts of E. coli O157:H7 on contaminated trimmings was -2.69log(10)CFU/g. A parallel validation survey provided some confidence in the model predictions. An uncertainty analysis indicated that microbial test sensitivity is a significant factor contributing to model uncertainty and requires further investigation while also indicating that risk reduction measures should be directed towards reducing the hide to carcass transfer (correlation coefficient 0.25) during dehiding and reducing the initial prevalence and counts on bovine hides (correlation coefficients 0.19 and 0.16, respectively). A characterisation of uncertainty and variability indicating that further research is required to reduce parameter uncertainty and to achieve better understanding of microbial transfer in meat plants. The model developed in this study highlights the need for further development of quantitative risk assessments in the food industry.     

Altered hydrophobicity and membrane composition in stress-adapted Listeria innocua

Exposure of Listeria innocua to acid and starvation stress decreases sensitivity to the quaternary ammonium compound cetrimide, whereas exposure to cold and heat stress increases sensitivity to this compound. Changes in membrane lipids occur in response to certain types of stress, and these changes likely impact cell sensitivity to chemical sanitizers. The present study included an assessment of the effects of acid, starvation, cold, and heat stress on net cell hydrophobicity and fatty acid composition in L. innocua. Net cell hydrophobicity was determined by measuring absorbance of stress-adapted cell suspensions after partitioning with the nonpolar solvent n-hexadecane. Free fatty acids extracted from stress-adapted suspensions were analyzed by gas chromatography. Adaptation to acid and starvation increased net cell hydrophobicity and decreased membrane fluidity, which was correlated with reductions in anteiso fatty acids and in ratios of anteiso to iso fatty acids. Conversely, cold-stressed populations exhibited decreased net cell hydrophobicity and increased membrane fluidity with a corresponding increase in C15:C17 and anteiso:iso ratios and in C18 unsaturated fatty acids. No significant changes in net cell hydrophobicity or membrane fluidity were observed in heat-stressed cells, which exhibited increased sensitivity to cetrimide, suggesting another mechanism for altered cell sensitivity. These findings indicate that the efficacy of cetrimide against Listeria is partially dependent on the physiological state of the organism following exposure to various environmental stresses.