Streamer initiation in atmospheric pressure gas discharges by direct particle simulation.

A two-dimensional particle code that simulates electrical breakdown of gases by modeling avalanche evolution from the initial ion-electron pair up to the development of a streamer is presented. Trajectories of individual particles are followed, the self-field is included consistently and collision processes are accurately modeled using experimentally determined cross sections. It is emphasized that the tadpolelike structure of well-formed streamer heads is present throughout the avalanche phase, and that the transition to the self-similar evolution characteristic of the streamer phase merely reflects the continued development of this structure.

Identification and sequence of an unstable DNA element in the entomopathogenic bacteria Photorhabdus temperata strain K122.

Aims: A search was conducted for a difference in genome composition between phenotypic variants of the insect pathogenic bacteria, Photorhabdus temperata.

Methods: An unstable 300 bp fragment of DNA was identified by amplified fragment length polymorphism (AFLP) analysis, which was not, however, associated with phenotypic variation.

Results: During prolonged culturing of the bacteria, one copy of the repeated fragment was deleted and a restriction site linked to one of the copies was lost or gained.

The ner gene of Photorhabdus: effects on primary-form-specific phenotypes and outer membrane protein composition.

The nematode-bacterium complex of Heterorhabditis-Photorhabdus is pathogenic to insect larvae. The bacteria undergo a form of phenotypic switching whereby the primary form, at the stationary phase of the growth cycle, makes a range of products and has the capacity to support nematode growth, whereas the secondary form does not express these phenotypes. The work described here investigated the mechanism regulating phenotypic variation by transforming the primary cells with secondary-form DNA on a low-copy-number vector and screening for colonies which did not produce the yellow pigment characteristic of primaries.

Acid stress in the food pathogen Bacillus cereus.

Aims: The pathogen Bacillus cereus, which is associated with a number of foods including dairy products, was studied for its response to acid stress during the exponential phase.

Methods And Results: Bacillus cereus was found to adapt to acid stress (pH 4.6) when pre-exposed to a non-lethal, inducing pH of 6.

Heat and salt stress in the food pathogen Bacillus cereus.

Aims: The effects of stresses imposed on bacterial contaminants during food processing and treatment of packaging material were evaluated on the food pathogen Bacillus cereus.

Methods And Results: Conditions were established which allowed the cells to adapt to heat, ethanol and hydrogen peroxide stresses, but not to osmotic shock. Cross protection between stresses indicated a clear hierarchy of resistance with salt protecting against hydrogen peroxide, which protected against ethanol, which protected against heat shock.

Students' philosophical assumptions and psychology in the classroom.

The current study investigated the underlying philosophical assumptions, or world views, that undergraduate nursing students bring to the psychology classroom. It was hypothesized that students would most prefer mechanistic explanations of behavior, explanations derived from an analytical, linear, cause-and-effect model. It was also hypothesized that they would least prefer contextualistic explanations of behavior, i.

Xenorhabdus and Photorhabdus spp.: bugs that kill bugs.

Xenorhabdus and Photorhabdus spp. are gram negative gamma proteobacteria that form entomopathogenic symbioses with soil nematodes. They undergo a complex life cycle that involves a symbiotic stage, in which the bacteria are carried in the gut of the nematodes, and a pathogenic stage, in which susceptible insect prey are killed by the combined action of the nematode and the bacteria.

Entry into the health care system: the family's decision-making process.

Background And Objectives: Prior work has demonstrated the importance of family members in deciding whether or not to consult a physician. This study investigated how such decisions are made and what dimensions are important in the decision-making process.

Methods: Thirty middle-class couples each role-played four hypothetical illness situations.

Development and initial validation of a scale to measure self-efficacy beliefs in patients with chronic pain.

The present study describes the development of the Chronic Pain Self-Efficacy Scale (CPSS), a 22-item questionnaire designed to measure chronic pain patients' perceived self-efficacy to cope with the consequences of chronic pain. The CPSS and other measures of psychosocial functioning were administered to 141 consecutive patients who were referred to an outpatient multidisciplinary pain treatment program. An exploratory factor analysis of the CPSS responses identified 3 factors: self-efficacy for pain management (PSE), self-efficacy for coping with symptoms (CSE), and self-efficacy for physical function (FSE).

The oxidative stress response in Bacillus subtilis.

Bacillus subtilis undergoes a typical bacterial stress response when exposed to low concentrations (0.1 mM) of hydrogen peroxide. Protection is thereby induced against otherwise lethal, challenge concentrations (10 mM) of this oxidant and a number of proteins are induced including the scavenging enzymes, catalase and alkyl hydroperoxide reductase, and a putative DNA binding and protecting protein.

Gene structure and amino acid sequences of alcohol dehydrogenases of Bacillus stearothermophilus.

Partial amino acid sequences of the two alcohol dehydrogenases of Bacillus stearothermophilus and the oligonucleotide sequence of a cloned fragment containing the gene for ADH 2334 were determined and compared with the known, derived ADH 1503 amino acid sequence. The two proteins are identical at 244 of 349 positions. ADH 2334 is encoded in a transcription unit containing an aldehyde dehydrogenase.

The gene coding for polynucleotide phosphorylase in Photorhabdus sp. strain K122 is induced at low temperatures.

Photorhabdus sp. strain K122 was found to produce higher levels of the protein CAP87K when cultured at 9 degrees C than when cultured at 28 degrees C. NH2-terminal sequencing of this protein revealed homology with the NH2 terminus of Escherichia coli polynucleotide phosphorylase.

Isolation and characterization of a hydrogen peroxide resistant mutant of Bacillus subtilis.

A mutant of Bacillus subtilis has been isolated by continuous selection in increasing concentrations of H2O2. It grew with a doubling time of 85 min in minimal medium containing 150 mM H2O2, whereas the wild-type parent lysed in 100 mM H2O2. The mutant was also more resistant to organic peroxides than the wild-type.

The citrulline biosynthetic operon, argC-F, and a ribose transport operon, rbs, from Bacillus subtilis are negatively regulated by Spo0A.

A method is described here that can be used to identify operons whose expression is controlled by any particular regulator protein. This method was used to identify operons whose expression is negatively regulated by Spo0A in Bacillus subtilis. Twenty-eight strains were identified, each of which contains an operon-lacZ transcriptional fusion, negatively regulated, either directly or indirectly, by Spo0A.

Phase variation in Xenorhabdus luminescens: cloning and sequencing of the lipase gene and analysis of its expression in primary and secondary phases of the bacterium.

The phenomenon of phase variation in the insect-pathogenic bacterium Xenorhabdus luminescens was investigated. Differential activity of the lipase enzyme (EC 3.1.

Cloning and characterization of genes induced by hydrogen peroxide in Bacillus subtilis.

Transcriptional fusions of Bacillus subtilis DNA to the lacZ gene were screened for induction, initially by ethanol and then by hydrogen peroxide (H2O2). Two fusions were identified which were induced late following treatment with sublethal concentrations of H2O2 (100 microM). The oxy-1 promoter was induced 4-5-fold and mapped to 11 degrees while the oxy-2 promoter was induced 20-fold and mapped close to the right of the defective prophage PBSX, at about 120 degrees.

Regulation of the oxidative stress response by the hpr gene in Bacillus subtilis.

Bacillus subtilis mutants with null mutations in the spo0 A gene are resistant to oxidative stress during the exponential phase of growth. This resistance phenotype can be suppressed by mutations in the abrB gene, or in the hpr gene. Both of these gene products are negative regulatory proteins which are over-produced in a spo0 A strain, and the over-production of the hpr gene product results from over-production of the abrB gene product.

Multigene families of Cellulomonas flavigena encoding endo-beta-1,4-glucanases (CM-cellulases).

Multiple genes coding for endo-beta-1,4-glucanases (CM-cellulases) have been isolated from a newly discovered highly cellulolytic strain of Cellulomonas flavigena. Clones of C. flavigena DNA were isolated in Escherichia coli and screened for gene expression on CM-cellulose plates staining with congo red.

Cloning and characterization of the gene for a methanol-utilising alcohol dehydrogenase from Bacillus stearothermophilus.

The cloning and characterization of the alcohol dehydrogenase (ADH) gene (adh) from Bacillus stearothermophilus strain DSM2334, an obligate aerobe, are described. The clone directed the synthesis of ADH as judged on Western blots, activity gels and tetrazolium plates. It specified an enzyme that oxidised methanol as well as ethanol.

A new alcohol dehydrogenase, reactive towards methanol, from Bacillus stearothermophilus.

An NAD+-dependent alcohol dehydrogenase (ADH) was purified to homogeneity from an aerobic strain of Bacillus stearothermophilus, DSM 2334 (ADH 2334), and compared with the ADH from B. stearothermophilus NCA 1503 (ADH 1503). When an antibody raised against ADH 2334 was used, no cross-reactivity with ADH 1503 was observed on Western blots; by means of an enzyme-linked-immunoabsorbent-assay ('e.

Relationship among oxidative stress, growth cycle, and sporulation in Bacillus subtilis.

The sensitivity of Bacillus subtilis to hydrogen peroxide (oxidative stress) was found to vary with the position of the culture in the growth cycle. The most dramatic change occurred at the stationary phase, when the cells became totally resistant to 10 mM H2O2, in contrast to the loss of 3 to 4 log units of viability when treated at the early log phase. Two of the eight proteins induced by a protective concentration of H2O2 (50 muM) were also induced (in the absence of oxidative stress) on entry into the late log phase of growth.