David Johnson

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Simulation has been the dominant research methodology in wireless and sensor networking. When mobility is added, real-world experimentation is especially rare. However, it is becoming clear that simulation models do not sufficiently capture radio and sensor irregularity in a complex, real-world environment, especially indoors. Unfortunately, the high labor(More)
This paper describes a text chunking system based on a generalization of the Winnow algorithm. We propose a general statistical model for text chunking which we then convert into a classification problem. We argue that the Winnow family of algorithms is particularly suitable for solving classification problems arising from NLP applications, due to their(More)
The microbial composition of acid streamers (macroscopic biofilms) in acidic, metal-rich waters in two locations (an abandoned copper mine and a chalybeate spa) in north Wales was studied using cultivation-based and biomolecular techniques. Known chemolithotrophic and heterotrophic acidophiles were readily isolated from disrupted streamers, but they(More)
Phenotypic and genotypic analysis was carried out on four iron- and sulfur-oxidizing acidophilic bacteria (the “NO-37 group”) isolated from different parts of the world. 16S rRNA phylogeny showed that they are highly related to each other, but are less related to the type strain of Acidithiobacillus ferrooxidans. The NO-37 group isolates are obligate(More)
Microorganisms were enumerated and isolated on selective solid media from a pilot-scale stirred-tank bioleaching operation in which a polymetallic sulfide concentrate was subjected to biologically accelerated oxidation at 45 degrees C. Four distinct prokaryotes were isolated: three bacteria (an Acidithiobacillus caldus-like organism, a thermophilic(More)
Acid mine drainage (AMD) causes environmental pollution that affects many countries having historic or current mining industries. Preventing the formation or the migration of AMD from its source is generally considered to be the preferable option, although this is not feasible in many locations, and in such cases, it is necessary to collect, treat, and(More)
Type 2 innate lymphoid cells (ILC2s, nuocytes, NHC) require RORA and GATA3 for their development. We show that human ILC2s express skin homing receptors and infiltrate the skin after allergen challenge, where they produce the type 2 cytokines IL-5 and IL-13. Skin-derived ILC2s express the IL-33 receptor ST2, which is up-regulated during activation, and are(More)
Acidic, metal-rich waters generated by the microbially accelerated dissolution of pyrite and other sulfide minerals, are frequently encountered in derelict mine sites, including many that have been long-abandoned. While these waters are major causes of environmental pollution and are toxic to the majority of prokaryotic and eukaryotic organisms, some life(More)
An extremely acidic (pH 2.5-2.75) metal-rich stream draining an abandoned mine in the Iberian Pyrite Belt, Spain, was ramified with stratified macroscopic gelatinous microbial growths ('acid streamers' or 'mats'). Microbial communities of streamer/mat growths sampled at different depths, as well as those present in the stream water itself, were analysed(More)
Biomining, the use of micro-organisms to recover precious and base metals from mineral ores and concentrates, has developed into a successful and expanding area of biotechnology. While careful considerations are made in the design and engineering of biomining operations, microbiological aspects have been subjected to far less scrutiny and control. Biomining(More)