The calculation of branch flows in a directed network

This paper describes a procedure for the calculation of branch flows in a directed network in which the node-to-node flows are prescribed. The node-to-node paths of the network are enumerated using a combinatorial process. Procedures based on the path list are used to allocate the node-to-node flows to the alternative paths of the network according to Wardrop's first principle. The calculation, although necessarily iterative, is rapidly convergent. The method has been implemented as a computer program and the results obtained for a typical network are discussed. A linear relationship between branch potential and branch flow has been used, but the method can be extended to piece-wise linear and non-linear relationships.     

Microwave detection at 110 Ghz by nanowires with broken symmetry

By using arrays of nanowires with intentionally broken symmetry, we were able to detect microwaves up to 110 GHz at room temperature. This is, to the best of our knowledge, the highest speed that has been demonstrated in different types of novel electronic nanostructures to date. Our experiments showed a rather stable detection sensitivity over a broad frequency range from 100 MHz to 110 GHz. The novel working principle enabled the nanowires to detect microwaves efficiently without a dc bias. In principle, the need for only one high-resolution lithography step and the planar architecture allow an arbitrary number of nanowires to be made by folding a linear array as many times as required over a large area, for example, a whole wafer. Our experiment on 18 parallel nanowires showed a sensitivity of approximately 75 mV dc output/mW of nominal input power of the 110 GHz signal, even though only about 0.4% of the rf power was effectively applied to the structure because of an impedance mismatch. Because this array of nanowires operates simultaneously, low detection noise was achieved, allowing us to detect -25 dBm 110 GHz microwaves at zero bias with a standard setup.     

The influence of nitrate ion on the morphology of zinc electrodeposits

The morphology of zinc electrodeposited from acidic solutions containing nitrate ions was studied as part of a research project entitled “Regeneration of Bright Chromating Baths”. It has been found that in the presence of nitrate ions the usual sequence:sponge, compact, dendritic deposit, as a function of increasing current density, is disturbed so that in almost all cases, spongy deposits are obtained, independent of the cd and hydrodynamic conditions. Possible causes of this phenomenon are discussed.     

Syngas combustion in a chemical-looping combustion system using an impregnated Ni-based oxygen carrier

Chemical-looping combustion (CLC) has emerged as a promising option for CO₂ capture because this gas is inherently separated from the other flue gas components and thus no energy is expended for the separation. This technology would have some advantages if it could be adapted for its use with coal as fuel. In this sense, a process integrated by coal gasification and CLC could be used in power plants with low energy penalty for CO₂ capture. This work presents the results obtained in the combustion of syngas as fuel with a Ni-based oxygen carrier prepared by impregnation in a CLC plant under continuous operation. The effect on the oxygen carrier behaviour and the combustion efficiency of several operating conditions was determined in the continuous CLC plant. High combustion efficiencies (～99%), close to the values limited by thermodynamics, were reached at oxygen carrier-to-fuel ratios higher than 5. The temperature in the FR had a significant influence, although high efficiencies were obtained even at 1073 K. The syngas composition had small effect on the combustion, obtaining high and similar efficiencies with syngas fuels of different composition, even in the presence of high CO concentrations. The low reactivity of the oxygen carrier with CO seemed to indicate that the water gas shift reaction acts as an intermediate step in the global reaction of the syngas in a continuous CLC plant. Neither agglomeration nor carbon deposition problems were detected during 50 h of continuous operation in the prototype. The obtained results showed that the impregnated Ni-based oxygen carrier could be used in a CLC plant for the combustion of syngas produced in an integrated gasification combined cycle (IGCC).     

Impact of preheating on the behavior of Listeria monocytogenes in a broth that mimics Camembert cheese composition

The effect of preheating on the survival of L. monocytogenes in Richard's broth, which mimics the composition of Camembert cheese composition, was examined. Experiments were carried out to reproduce contamination of cheese with environmental heat-stressed cells of L. monocytogenes surviving hot-cleaning procedures. Cells in mid-log phase were heated for 30 min at 56 degrees C before being inoculated into Richard's broth. The pHs and temperatures of Richard's broth were chosen to recreate the conditions of curd dripping (pH 5, 25 degrees C), of the beginning of cheese ripening (pH 5, 12 degrees C), and of the beginning (pH 5, 4 degrees C) and the end (pH 7, 4 degrees C) of cheese storage. Immediately after heat treatment, the viability loss was especially high for strain 306715, which exhibited only 0.6% +/- 0.2% survival, compared with 22% +/- 8.7% for strain EGD. The percentages of the surviving heated cells that were injured were 93% +/- 8% for strain 306715 and 98% +/- 3% for strain EGD. The destruction of the surviving L. monocytogenes cells was accelerated when they encountered the pH and temperature conditions of Camembert cheese during manufacturing, ripening, and cold storage (pH 5 at 25, 12, and 4 degrees C, respectively). The multiplication of the surviving heated cells was retarded under favorable growth conditions similar to those of storage by the distributor and the consumer (pH 7 at 4 and 12 degrees C, respectively).     

The effect of human chorionic gonadotrophin on the expression of progesterone receptors in human luteal cells in vivo and in vitro

The human corpus luteum expresses genomic progesterone receptors (PRs) suggesting that progesterone may have an autocrine or paracrine role in luteal function. We hypothesised that the reduction in luteal PR reported in the late-luteal phase augmented progesterone withdrawal and had a role in luteolysis. We therefore tested the hypothesis that luteal rescue with human chorionic gonadotrophin (hCG) would maintain PR expression. PR was immunolocalised to different cell types in human corpora lutea (n = 35) from different stages of the luteal phase and after luteal rescue with exogenous hCG. There was no change in the staining intensity of theca-lutein cell or stromal cell PR throughout the luteal phase or after luteal rescue. In the late-luteal phase, granulosa-lutein cell PR immunostaining was reduced (P < 0.05) but the trend to reduction was also seen after luteal rescue with hCG (P = 0.055). To further investigate the effect of hCG on granulosa-lutein cell PR expression, an in vitro model system of cultured human luteinised granulosa cells was studied. Cells were cultured for 12-13 days exposed to different patterns of hCG and aminoglutethamide to manipulate progesterone secretion (P < 0.0001). Expression of PR A/B and PR B isoforms was examined by quantitative real-time RT-PCR. PR A/B mRNA was lower (P < 0.05) after 11-13 days of culture than after 7 days of culture. This reduction could not be prevented by hCG in the presence (P < 0.05) or absence (P < 0.05) of stimulated progesterone secretion. The expression of PR B mRNA showed a similar pattern (P = 0.054). Simulated early pregnancy in vivo and hCG treatment of luteinised granulosa cells in vitro did not appear to prevent the down-regulation of PR seen during luteolysis.     

Improved cellulase production by stable Clostridium cellulolyticum mutants

Methods for the production of mutants of the cellulase producer Clostridium cellulolyticum ATCC 35319 were examined using an agar plate screening technique. Spontaneous and UV light-induced mutants were isolated, some of which exhibited a high level of both endoglucanase and exoglucanase activities as assayed using CMC (carboxymethyl cellulose) and PNPCb (paranitrophenyi-β-cellobioside) respectively. The volumetric enzyme activities were up to 2.5 times those of the wild strain.     

Wastewater treatment by radial freezing with stirring effects

Radial freezing experiments on wastewater models were conducted in the presence of imposed stirring in order to remove impurities. The studied samples (dilute Na-montmorillonite suspensions charged with nitrates and with zinc or lead) were placed inside a cylindrical annulus, cooled at a controlled temperature around -7 degrees C at its inner wall which rotated around a vertical axis. The freezing front propagated toward the still outer wall which was maintained at a constant temperature around +1 degrees C. Thanks to stirring, considerable purification rates up to 99.97% were attained. It was also demonstrated that combining radial freezing and stirring ended in residual concentrations which agreed with drinking water standards.     

Boston harbor outfall tunnel: An environmental imperative

In February 1989, the Massachusetts Water Resource Authority (MWRA) began the design and construction of a 15.3-km subsea tunnel and ocean riser system to discharge effluent in conjunction with the design and construction of a large secondary treatment plant. The court-mandated schedule required the tunnel and risers to be completed in July 1995. The paper discusses the project from the viewpoints of management, concept design and construction methods, including the ocean riser system. Key to th success of the project is the accuracy of the location of the risers. The design calls for a final tunnel alignment to be driven within 10 m of the riser shafts, beginning at a distance of 13.1 km from shore.     

Optical properties of rotationally twinned InP nanowire heterostructures

We have developed a technique so that both transmission electron microscopy and microphotoluminescence can be performed on the same semiconductor nanowire over a large range of optical power, thus allowing us to directly correlate structural and optical properties of rotationally twinned zinc blende InP nanowires. We have constructed the energy band diagram of the resulting multiquantum well heterostructure and have performed detailed quantum mechanical calculations of the electron and hole wave functions. The excitation power dependent blue-shift of the photoluminescence can be explained in terms of the predicted staggered band alignment of the rotationally twinned zinc blende/wurzite InP heterostructure and of the concomitant diagonal transitions between localized electron and hole states responsible for radiative recombination. The ability of rotational twinning to introduce a heterostructure in a chemically homogeneous nanowire material and alter in a major way its optical properties opens new possibilities for band-structure engineering.