Studies on steam condensation and particle diffusiophoresis in a heat exhanger tube

In this paper, studies on steam condensation and aerosol behaviour in a heat exchanger are presented. The heat exchanger is a model of one single tube of a Passive Containment Condenser (PCC) that is used in the European Simplified Boiling Water Reactor (ESBWR). A hot carrier gas containing nitrogen and steam with Ag and CsOH particles flows through the heat exchanger. The walls of the heat exchanger are cooled with a water jacket, thus causing steam condensation and diffusiophoretic particle deposition. The amount of condensed steam is measured, as well as the temperatures, particle mass concentrations and size distributions before and after the heat exchanger. The experiments are done with different proportions of steam and nitrogen in the carrier gas. Heat and mass transfer in the system are modelled with well known engineering correlations, producing results that agree nicely with the experimental results. The diffusiophoretic particle deposition velocity is shown to be proportional to the steam condensation rate, as expected.     

Research Challenges for 3G and Paving the Way for Emerging New Generations

The first third-generation (3G) systems are going to be implemented within the year 2001. Academia and industry are, however, already looking for means to improve the system performance further. Spectral efficiency and higher data rate are the goal. In order to achieve this goal, several means have to be combined. The most important of these are interference cancellation and multiuser detection, optimum space-time processing and adaptive modulation and coding. In the future several wireless systems having different performance characteristics, system structure and parameters will exist. This heterogeneity will make the seamless handover from system to system difficult if not appropriately solved. 4G (fourth generation) is an acronym without any generally accepted concept. We describe some desirable goals and features of the 4G systems.     

Synthesis of cobalt nanoparticles to enhance magnetic permeability of metal–polymer composites

Metallic cobalt nanoparticles were synthesized by hydrogen reduction method. Particles were coated in situ with carbon by adding ethene to reaction flow. Particles were characterized by transmission electron microscopy, energy dispersive X-ray emission, X-ray diffraction, X-ray fluorescence and BET method. The observed cobalt particle size distributions in different cobalt batches produced with unvarying reaction parameters was reproducible: The mean diameter of primary cobalt particle varied only 5% from the mean value of 76 nm in different batches. Increased carbon precursor concentration decreased mean diameter of cobalt particles to 17 nm. The produced nanoparticles were used as filler material in 0–3 type metal–polymer composites. Composite samples with varying filler loading were fabricated with mixing extrusion and injection moulding techniques. The magnetic properties of the fabricated composites were measured up to 1 GHz. In order to analyse the particle distribution in composite matrix and its effect on magnetic properties the microstructure was studied.     

LZgrep: a Boyer–Moore string matching tool for Ziv–Lempel compressed text

We present a Boyer–Moore (BM) approach to string matching over LZ78 and LZW compressed text. The idea is to search the text directly in compressed form instead of decompressing and then searching it. We modify the BM approach so as to skip text using the characters explicitly represented in the LZ78/LZW formats, modifying the basic technique where the algorithm can choose which characters to inspect. We present and compare several solutions for single and multipattern searches. We show that our algorithms obtain speedups of up to 50% compared to the simple decompress‐then‐search approach. Finally, we present a public tool, LZgrep, which uses our algorithms to offer grep‐like capabilities directly searching files compressed using Unix's Compress, a LZW compressor. LZgrep can also search files compressed with Unix gzip, using new decompress‐then‐search techniques we develop, which are faster than the current tools. This way, users can always keep their files in compressed form and still search them, uncompressing only when they want to see them. Copyright © 2005 John Wiley & Sons, Ltd.     

Toxicological characterization of particulate emissions from straw,Miscanthus, and poplar pellet combustion in residential boilers

Wood pellets have been used in domestic heating appliances for three decades. However, because the share of renewable energy for heating will likely rise over the next several years, alternative biomass fuels, such as short-rotation coppice or energy crops, will be utilized. We tested particulate emissions from the combustion of standard softwood pellets and three alternative pellets (poplar, Miscanthus sp., and wheat straw) for their ability to induce inflammatory, cytotoxic, and genotoxic responses in a mouse macrophage cell line. Our results showed clear differences in the chemical composition of the emissions, which was reflected in the toxicological effects. Standard softwood and straw pellet combustion resulted in the lowest PM₁ mass emissions. Miscanthus sp. and poplar combustion emissions were approximately three times higher. Emissions from the herbaceous biomass pellets contained higher amounts of chloride and organic carbon than the emissions from standard softwood pellet combustion. Additionally, the emissions of the poplar pellet combustion contained the highest concentration of metals. The emissions from the biomass alternatives caused significantly higher genotoxicity than the emissions from the standard softwood pellets. Moreover, straw pellet emissions caused higher inflammation than the other samples. Regarding cytotoxicity, the differences between the samples were smaller. Relative toxicity was generally highest for the poplar and Miscanthus sp. samples, as their emission factors were much higher. Thus, in addition to possible technical problems, alternative pellet materials may cause higher emissions and toxicity. The long-term use of alternative fuels in residential-scale appliances will require technological developments in both burners and filtration.

Copyright © 2016 American Association for Aerosol Research     

Characterization of type IV pilus genes in Pseudomonas syringae pv. tomato DC3000

Many strains of Pseudomonas syringae produce retractile pili that act as receptors for lytic bacteriophage phi 6. As these are also characteristics of type IV pili, it was postulated that P. syringae may possess genes for type IV pilus biogenesis. A cosmid clone bank of P. syringae pv. tomato DC3000 genomic DNA was used to complement a mutant of Pseudomonas aeruginosa defective in the PilD (XcpA) prepilin peptidase gene by selection for restoration of extracellular protein secretion, a function also known to require PilD. A cosmid able to complement this mutant was also able to complement mutations in the pilB and pilC genes, suggesting that, if the organization of these genes is similar to that of P. aeruginosa, the cosmid may contain the P. syringae pilA. This was confirmed by sequencing a region from this plasmid that was shown to hybridize at low stringency to the P. aeruginosa pilA gene. The deduced P. syringae PilA polypeptide possesses the characteristic properties of the type IV pilins. Heterologous expression of the P. syringae pilA in P. aeruginosa was also shown, conferring not only phi 6 phage sensitivity to P. aeruginosa pilA mutants but also sensitivity to PO4, a lytic bacteriophage specific for the pilus of P. aeruginosa. This suggests that additional components might be present in the mature pilus of P. aeruginosa that are the true receptors for this phage. Chromosomal mutations in P. syringae pv. tomato DC3000 pilA and pilD genes were shown to abolish its sensitivity to bacteriophage phi 6. To determine the importance of P. syringae pilus in plant leaf interactions, these mutations were tested under laboratory and field conditions. Although little effect was seen on pathogenicity, culturable leaf-associated population sizes of the pilA mutant were significantly different from those of the wild-type parent. In addition, the expression of the DC3000 pilA gene appears to contribute to the UV tolerance of P. syringae and may play a role in survival on the plant leaf surface.     

Scale coding bag of deep features for human attribute and action recognition

Most approaches to human attribute and action recognition in still images are based on image representation in which multi-scale local features are pooled across scale into a single, scale-invariant encoding. Both in bag-of-words and the recently popular representations based on convolutional neural networks, local features are computed at multiple scales. However, these multi-scale convolutional features are pooled into a single scale-invariant representation. We argue that entirely scale-invariant image representations are sub-optimal and investigate approaches to scale coding within a bag of deep features framework. Our approach encodes multi-scale information explicitly during the image encoding stage. We propose two strategies to encode multi-scale information explicitly in the final image representation. We validate our two scale coding techniques on five datasets: Willow, PASCAL VOC 2010, PASCAL VOC 2012, Stanford-40 and Human Attributes (HAT-27). On all datasets, the proposed scale coding approaches outperform both the scale-invariant method and the standard deep features of the same network. Further, combining our scale coding approaches with standard deep features leads to consistent improvement over the state of the art.     

The effect of materials and obliquity of the impact on the critical velocity of rebound

The critical velocity of rebound was determined for spherical ammonium fluorescein particles in the size range of 0.44–7.3 μm. The method was based on measurements with a variable nozzle area impactor (VNAI) and numerical simulations. A comparison to previous results with spherical silver particles obtained with the same method showed that the critical velocity was approximately two orders of magnitude higher for ammonium fluorescein than for silver at the same size range. Among the hard test materials, including steel, aluminium, molybdenum, and Tedlar, the surface material had no significant effect on the critical velocity of rebound within the accuracy of the method. On the contrary, the critical velocity was observed to be highly dependent on the obliquity of the impact at the onset of rebound. While the ratio of the maximum tangential and normal velocities was defined as a measure for the obliquity, the critical velocity was found to be more than a magnitude smaller for very oblique impacts with the velocity ratio above 9 than for close-to-normal impacts with the velocity ratio below 1.5. The results of this study can be considered as a link between the recently published critical velocity results for nanoparticles and the older results for micron-sized particles.

Copyright © 2017 American Association for Aerosol Research