Numerical simulation of transient roll-waves in two-phase pipe flow

This paper presents a transient roll-wave simulator based on a one-dimensional incompressible two-fluid model. Using an efficient numerical method and a grid cell length of one pipe diameter, the simulator is able to accurately predict experimental data in the roll-wave regime. Essential to obtaining the stable roll-wave solutions is the use of a modified version of the Biberg friction model. Based on an algebraic eddy viscosity model, the Biberg model yields mechanistic expressions for the wall and interfacial shear stresses in stratified two-phase flow. Input to the model is closure relations for the turbulence levels at either side of the interface. In order to model the increased dissipation of energy in breaking wave fronts, we propose to modify the original closures by adding a term proportional to the negative gradient of the liquid height. As the waves grow and come close to breaking, this term redistributes the shear stresses such that the waves are stabilized. The numerical method used in the simulator is an extension of a previously presented pseudospectral Fourier method. In particular, spectral vanishing viscosity terms are introduced to stabilize short wavelengths inconsistent with the long wavelength approximation of the two-fluid model. The result is a simulator that provides reliable and convergent numerical solutions for all stratified flow conditions. In the last part of the paper, the simulator is tested against roll-wave experiments with horizontal and upward inclined flows of water and a dense gas in a 10 cm pipe. Wave heights and speeds as well as mean pressure drops and holdups are predicted within 20% accuracy when compared with 474 experiments. Furthermore, the transient simulations enable us to study the dynamics and interactions between waves. In agreement with experimental observations, two different wave growth mechanisms are identified, and their influence on the evolution of the roll-wave flow regime is analyzed.     

Evaluation of nickel deposition by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy was used to characterize the deposition of nickel from unbuffered acid sulfate electrolytes, from which a wide range of deposit morphologies and current efficiencies are possible. The operating parameters were in the range of 40 to 60 g L^–1 Ni²⁺, 40 to 60 °C, and the pH from 2.0 to 3.5. The resulting impedance spectra for nickel deposition at 20 mA cm^–2 consisted of one or two characteristic loops whose frequency and capacitance were dependent upon the electrowinning conditions and indicative of the resultant deposit morphology. A single high frequency capacitive loop, on the order of 1 kHz, correlated to good quality deposits which were flat, smooth and ductile. The presence of a low frequency loop, on the order of a few hertz, indicated a degraded deposit morphology which showed localized dark, glassy areas and were cracked, curled and brittle. The second loop may be associated with a diffusion controlled component in the reaction mechanism. Deposits of intermediate quality had impedance spectra consisting of both type loops. No apparent trend between the impedance spectra and the deposit current efficiency was determined, but a correlation with deposit quality was clearly established.     

Topology of the stable serpin-protease complexes revealed by an autoantibody that fails to react with the monomeric conformers of antithrombin

Solving the structure of the stable complex between a serine protease inhibitor (serpin) and its target has been a long standing goal. We describe herein the characterization of a monoclonal antibody that selectively recognizes antithrombin in complex with either thrombin, factor Xa, or a synthetic peptide corresponding to residues P14 to P9 of the serpin's reactive center loop (RCL, ultimately cleaved between the P1 and P'1 residues). Accordingly, this antibody reacts with none of the monomeric conformers of antithrombin (native, latent, and RCL-cleaved) and does not recognize heparin-activated antithrombin or antithrombin bound to a non-catalytic mutant of thrombin (S195A, in which the serine of the charge stabilizing system has been swapped for alanine). The neoepitope encompasses the motif DAFHK, located in native antithrombin on strand 4 of beta-sheet A, which becomes strand 5 of beta-sheet A in the RCL-cleaved and latent conformers. The inferences on the structure of the antithrombin-protease stable complex are that either a major remodeling of antithrombin accompanies the final elaboration of the complex or that, within the complex, at the most residues P14 to P6 of the RCL are inserted into beta-sheet A. These conclusions limit drastically the possible locations of the defeated protease within the complex.     

A prospective, population-based study of the demographics, epidemiology, management, and outcome of out-of-hospital pediatric cardiopulmonary arrest

STUDY OBJECTIVEs: To perform a population-based study addressing the demography, epidemiology, management, and outcome of out-of-hospital pediatric cardiopulmonary arrest (PCPA). METHODS: Prospective, population-based study of all children (17 years of age or younger) in a large urban municipality who were treated by EMS personnel for apneic, pulseless conditions. Data were collected prospectively for 3(1/2) years using a comprehensive data collection tool and on-line computerized database. Each child received standard pediatric advanced cardiac life support. RESULTS: During the 3(1/2)-year period, 300 children presented with PCPA (annual incidence of 19. 7/100,000 at risk). Of these, 60% (n=181) were male (P =.0003), and 54% (n=161) were patients 12 months of age or younger (152,500 at risk). Compared with the population at risk (32% black patients, 36% Hispanic patients, 26% white patients), a disproportionate number of arrests occurred in black children (51.6% versus 26.6% in Hispanics, and 17% in white children; P <.0001). Over 60% of all cases (n=181) occurred in the home with family members present, and yet those family members initiated basic CPR in only 31 (17%) of such cases. Only 33 (11%) of the total 300 PCPA cases had a return of spontaneous circulation, and 5 of the 6 discharged survivors had significant neurologic sequelae. Only 1 factor, endotracheal intubation, was correlated positively with return of spontaneous circulation (P =.032). CONCLUSION: This population-based study underscores the need to investigate new therapeutic interventions for PCPA, as well as innovative strategies for improving the frequency of basic CPR for children.     

The anomalous behavior of Al3+ in nickel electrowinning from sulfate electrolytes

The effect of varying concentrations of Al³⁺ on the morphology and current efficiency of electrodeposited nickel from an acid-sulfate electrolyte was studied. Concentrations of Al³⁺ of 20 to 100 ppm significantly degraded the nickel-cathode morphology and current efficiency. However, it was found that higher concentrations of Al³⁺, in the range of 1 to 5 g/L, depending on the electrolyte parameters and operating conditions, improved the deposit morphology compared to deposition from a pure electrolyte. However, the current efficiency remained low. Physical characterization of the nickel revealed that a smoother, more uniform surface resulted from deposition in the presence of 1 g/L or greater of Al³⁺. Impedance analysis indicated the presence of an inhibiting layer on the cathode when low concentrations of Al³⁺ were present. Concentrations of Al³⁺ greater than 1 g/L appeared to modify this layer and the nickel-deposition mechanism, allowing improved nickel morphology and structure.     

Sexually Mature Cuttlefish are Attracted to the Eggs of Conspecifics

Cuttlefish typically are solitary, but form aggregations to spawn. We tested the hypothesis that bioactive factors in the eggs of conspecifics may facilitate the formation of spawning groups of Sepia officinalis. Cuttlefish detected odors from cuttlefish eggs, resulting in an increased ventilation rate. Extracts from female ovaries induced the largest increase in ventilation rate, suggesting that this organ could be a potential source of the bioactive chemicals. In y-maze assays, sexually mature, but not subadult, cuttlefish, were attracted to odors of cuttlefish eggs. These data suggest that Sepia eggs could be a source of reproductive pheromones.     

Options for CO2-lean hydrogen export from Norway to Germany

Norway is a nation with an abundant supply of energy, both from fossil and renewable resources. Due to limited domestic demand, Norway is today exporting large amounts of petroleum products. For the future, various options for export of CO₂-lean energy exist, both from Northern and Southern Norway, and both from fossil sources (including carbon capture and storage), and renewable energies (particularly wind power). Transport vectors are hydrogen pipelines, liquid hydrogen ships and HVDC cables, and a plausible customer is central Europe due to its proximity, high population density and lack of domestic energy resources.     

Evidence that Tn5565, which includes the enterotoxin gene in Clostridium perfringens, can have a circular form which may be a transposition intermediate

The Clostridium perfringens enterotoxin gene is on a transposon-like element, Tn5565, integrated in the chromosome in human food poisoning strains. The flanking IS elements, IS1470 A and B, are related to IS30. The IS element found in the transposon, IS1469, is related to IS200 and has been found upstream of cpe in all Type A strains. PCR and sequencing studies from cell extracts and plasmid isolations of C. perfringens indicate that Tn5565 can form a circular form with the tandem repeat (IS1470)2, similar to the transposition intermediates described for a number of IS elements.