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Biomedical subjects

P Jarvis

Publications and source records attributed to P Jarvis.

At least 19 recordsLinked to original sources
PubMed2005

A review of floc strength and breakage.

The main focus of the paper is to review current understanding of floc structure and strength. This has been done by reviewing current theoretical understanding of floc growth and breakage and an analysis of different techniques used for measuring floc strength. An overview has also been made of the general trends seen in floc strength analysis. The rate of floc formation is a balance between breakage and aggregation with flocs eventually reaching a steady-state size for a given shear rate. The steady-state floc size for a particular shear rate can, therefore, be a good indicator of floc strength. This has resulted in the development of a range of techniques to measure floc size at different applied shear levels using a combination of one or more of the following tools: light scattering and transmission; microscopy; photography; video and image analysis software. Floc strength may be simply quantified using the initial floc size for a given shear rate and the floc strength factor. More complex techniques have used theoretical modelling to determine whether flocs break by large-scale fragmentation or smaller-scale surface erosion effects, although this interpretation is open to debate. Impeller-based mixing, ultrasound and vibrating columns have all been used to provide a uniform, accurate and controllable dissipation of energy onto a floc suspension to determine floc strength. Other more recent techniques have used sensitive micromanipulators to measure the force required to break or compress individual flocs, although these techniques have been limited to the measurement of only a few hundred flocs. General trends emerge showing that smaller flocs tend to have greater strength than larger flocs, whilst the use of polymer seems to give increased strength to only some types of floc. Finally, a comparison of the strength of different types of floc (activated sludge flocs, organic matter flocs, sweep flocs and charge neutralised flocs) has been made highlighting differences in relative floc strength.

Bioreactors↗
PubMed2004

Flocs through the looking glass.

The paper describes the investigation of how the make up of raw water influences the physical properties of flocculated suspensions. The work focuses on the properties of four characteristic organic fractions separated as a function of their hydrophobicity. Mesoscale data indicates that the hydrophobic fractions dominate the make up of the water and are the most easily removed. Microscale and nanoscale data reveals that the fulvic acid fraction (FAF) generates statistically smaller and more compact flocs than those formed by the other fractions and the hydrophilic fractions form the most internally open and dendritic structures. The FAF fraction was also seen to dominate the zeta potential response of the raw water.

Benzopyrans↗
PubMed2004

The duplicity of floc strength.

The breakage of flocs is dependent upon the strength of the bonds holding the aggregate together. The present work describes the breakage and re-growth behaviour of three different types of floc, these were: 1) coagulant precipitate flocs, 2) turbidity flocs and 3) organic matter flocs. Floc aggregates were exposed to increased levels of shear on a conventional jar tester and the sizes of the flocs were observed dynamically using a laser diffraction instrument. The organic flocs showed most resistance to breakage across the whole range of shears under investigation. The dynamic procedure provided detailed information on particle size distributions (PSD). Large and small scale degradation events could be identified from analysis of the PSD data. All of the flocs under investigation showed little re-growth potential after breakage. The precipitate and organic flocs showed slightly better re-aggregation of the small floc sizes.

Flocculation↗
PubMed2001

Toc, Tic, and chloroplast protein import.

The vast majority of chloroplast proteins are synthesized in precursor form on cytosolic ribosomes. Chloroplast precursor proteins have cleavable, N-terminal targeting signals called transit peptides. Transit peptides direct precursor proteins to the chloroplast in an organelle-specific way. They can be phosphorylated by a cytosolic protein kinase, and this leads to the formation of a cytosolic guidance complex. The guidance complex--comprising precursor, hsp70 and 14-3-3 proteins, as well as several unidentified components--docks at the outer envelope membrane. Translocation of precursor proteins across the envelope is achieved by the joint action of molecular machines called Toc (translocon at the outer envelope membrane of chloroplasts) and Tic (translocon at the inner envelope membrane of chloroplasts), respectively. The action of the Toc/Tic apparatus requires the hydrolysis of ATP and GTP at different levels, indicating energetic requirements and regulatory properties of the import process. The main subunits of the Toc and Tic complexes have been identified and characterized in vivo, in organello and in vitro. Phylogenetic evidence suggests that several translocon subunits are of cyanobacterial origin, indicating that today's import machinery was built around a prokaryotic core.

Arabidopsis↗
PubMed2001

Intracellular signalling: the chloroplast talks!

Plant cells have a unique problem: the coordination of three different genomes. While the dominance of the nuclear genome is indisputable, it is now clear that organellar signals can have profound effects, not just on nuclear gene expression but, as the Arabidopsis laf6 mutant reveals, also on whole plant morphology.

ATP-Binding Cassette Transporters↗
PubMed2000

Galactolipid deficiency and abnormal chloroplast development in the Arabidopsis MGD synthase 1 mutant.

The lipid monogalactosyl diacylglycerol (MGD) is a major structural component of photosynthetic membranes in chloroplasts. Its formation is catalyzed by the enzyme MGD synthase. In many plants, MGD derives from two different biosynthetic pathways: the prokaryotic pathway, which operates entirely within the plastid, and the eukaryotic pathway, which involves steps in the endoplasmic reticulum. Here, we describe the identification and characterization of an Arabidopsis mutant with a defective MGD synthase gene (MGD1). The mutant was identified in a screen of T-DNA lines for individuals with defects in chloroplast biogenesis. It has a yellow-green phenotype that correlates with a approximately 50% deficiency in total chlorophyll per plant. A single T-DNA insertion is located adjacent to the transcription initiation site of the MGD1 gene, and the abundance of MGD1 mRNA is reduced by 75% compared with wild type. Correlation between steady-state MGD1 transcript levels and MGD synthase activity (also reduced by 75% in mgd1) suggests that MGD1 is the most important MGD synthase in green tissues. The amount of MGD in mutant leaves is reduced by 42% compared with wild type. MGD from the mutant contains 23% less 16:3 fatty acid and 10% more 18:3 fatty acid. Because 16:3 is a characteristic feature of MGD from the prokaryotic pathway, it is possible that MGD1 operates with some preference in the prokaryotic pathway. Finally, the MGD-deficiency of mgd1 is correlated with striking defects in chloroplast ultrastructure, strongly suggesting a unique role for MGD in the structural organization of plastidic membranes.

Amino Acid Sequence↗
PubMed2000

The practitioner-researcher in nursing.

Knowledge is changing rapidly in late modern society which has led to the recognition that no two practice situations are the same. This has been implicit in the perceived gap between theory and practice. In contemporary society, the legitimation of practice knowledge is pragmatic, so that research in this situation is best undertaken by practitioners, and many of them are actually doing this for a variety of different reasons. However, practitioner-researchers can also be a beneficial development in third world countries, such as Zambia, since their practice situations are so different from that of many Western consultants whose expertise is utilized by these countries.

Clinical Nursing Research↗
PubMed2000

Generalized nonlinear models for pharmacokinetic data.

Phase I trials to study the pharmacokinetic properties of a new drug generally involve a restricted number of healthy volunteers. Because of the nature of the group involved in such studies, the appropriate distributional assumptions are not always obvious. These model assumptions include the actual distribution but also the ways in which the dispersion of responses is allowed to vary over time and the fact that small concentrations of a substance are not easily detectable and hence are left censored. We propose that a reasonably wide class of generalized nonlinear models allowing for left censoring be considered now that this is feasible with current computer power and sophisticated statistical packages. These modelling strategies are applied to a Phase I study of the drug flosequinan and its metabolite. This drug was developed for the treatment of heart failure. Because the metabolite also exhibits an active pharmacologic effect, study of both the parent drug and the metabolite is of interest.

Adult↗
PubMed2000

Defective hMSH2/hMLH1 protein expression is seen infrequently in ulcerative colitis associated colorectal cancers.

BACKGROUND: Ulcerative colitis is associated with an increased risk of colorectal cancer above that of the normal population. The relative risk correlates with the extent and duration of the disease but the genetic basis of ulcerative colitis associated cancer risk is not known. AIMS: To assess the prevalence of microsatellite instability and mismatch repair gene abnormalities in ulcerative colitis associated colorectal cancer. PATIENTS: Forty six patients with colorectal cancer, with a previous histological diagnosis of ulcerative colitis. METHODS: The frequency of microsatellite instability and/or immunohistochemical expression of hMSH2 and hMLH1 was assessed. Thirty three cases were investigated using both approaches. RESULTS: Although 6/41 (14.6%) cases showed microsatellite instability at one or more markers, only one case (2. 4%) exhibited high level instability (at least two markers affected). Of 38 cases which were assessed using antibodies against hMSH2 and hMLH1, only one case (2.6%) showed loss of expression. This case, which showed loss of hMSH2 expression, was the same case which exhibited high level microsatellite instability. The 33 cases which were investigated using both approaches showed that loss of expression of either hMSH2 or hMLH1 was not seen in any case which exhibited microsatellite instability in no more than one marker. CONCLUSIONS: This study suggests that both high level microsatellite instability and loss of expression of hMSH2/hMLH1 are infrequent events in ulcerative colitis associated colorectal cancers. Low level microsatellite instability was not associated with loss of expression of either hMSH2 or hMLH1.

Biomarkers↗
PubMed1998

An Arabidopsis mutant defective in the plastid general protein import apparatus.

Elaborate mechanisms have evolved for the translocation of nucleus-encoded proteins across the plastid envelope membrane. Although putative components of the import apparatus have been identified biochemically, their role in import remains to be proven in vivo. An Arabidopsis mutant lacking a new component of the import machinery [translocon at the outer envelope membrane of chloroplasts (Toc33), a 33-kilodalton protein] has been isolated. The functional similarity of Toc33 to another translocon component (Toc34) implies that multiple different translocon complexes are present in plastids. Processes that are mediated by Toc33 operate during the early stages of plastid and leaf development. The data demonstrate the in vivo role of a translocon component in plastid protein import.

Amino Acid Sequence↗
PubMed1997

The globalization of nurse education within higher education.

This paper considers the effect that globalization is having on knowledge and higher education. Having undertaken this, it applies the discussion to the future of nurse education. The paper has a long introduction in which globalization is considered, thereafter it has three parts: the first examines the changing nature of knowledge; the second the changing nature of education; and the final part locates nurse education in this discussion.

Diffusion of Innovation↗
PubMed1997

Inefficient and incorrect processing of the Ac transposase transcript in iae1 and wild-type Arabidopsis thaliana.

As part of the analysis of the Arabidopsis mutant iae1-1 (increased Ac excision), quantitative studies of the Ac transposase transcript were conducted. The primary transcript of Ac contains three small introns (introns 1-3; mean size 89 bp) and one larger intron (intron 4; 387 bp). We analysed the splicing of intron 3 and intron 4 in wild-type Arabidopsis and the iae1-1 mutant. Our results demonstrate that the splicing of Ac introns 3 and 4 is inefficient (splicing efficiencies 57 and 30% respectively) compared with that of an intron of an endogenous Arabidopsis gene (PHYB intron 1; splicing efficiency 90%). The poor splicing efficiency of Ac intron 4 was found to correlate with aberrant processing. Steady state levels of total Ac transcript were higher in the iae1-1 mutant than wild-type, but the same aberrant processing occurred. The inefficient processing of Ac in Arabidopsis prompted us to construct an Ac element lacking introns (Ac::cDNA) in an attempt to increase transposition frequencies. Autonomous activity of the Ac::cDNA element was undetectable in Arabidopsis, despite its ability to transpose at high frequency in response to a strong transposase source (35S::transposase) in trans, and the demonstrable autonomy of the same element in tobacco. A number of smaller transcripts were detected in Arabidopsis lines containing Ac::cDNA or Ac. Analysis of these smaller transcripts revealed a high frequency of premature polyadenylation in exon 2 and splicing of cryptic introns.

Arabidopsis↗
PubMed1997

Increased Ac excision (iae): Arabidopsis thaliana mutations affecting Ac transposition.

The maize transposable element Ac is highly active in the heterologous hosts tobacco and tomato, but shows very much reduced levels of activity in Arabidopsis. A mutagenesis experiment was undertaken with the aim of identifying Arabidopsis host factors responsible for the observed low levels of Ac activity. Seed from a line carrying a single copy of the Ac element inserted into the streptomycin phosphotransferase (SPT) reporter fusion, and which displayed typically low levels of Ac activity, were mutagenized using gamma rays. Nineteen mutants displaying high levels of somatic Ac activity, as judged by their highly variegated phenotypes, were isolated after screening the M2 generation on streptomycin-containing medium. The mutations fall into two complementation groups, iae1 and iae2, are unlinked to the SPT::Ac locus and segregate in a Mendelian fashion. The iae1 mutation is recessive and the iae2 mutation is semi-dominant. The iae1 and iae2 mutants show 550- and 70-fold increases, respectively, in the average number of Ac excision sectors per cotyledon. The IAE1 locus maps to chromosome 2, whereas the SPT::Ac reporter maps to chromosome 3. A molecular study of Ac activity in the iae1 mutant confirmed the very high levels of Ac excision predicted using the phenotypic assay, but revealed only low levels of Ac re-insertion. Analyses of germinal transposition in the iae1 mutant demonstrated an average germinal excision frequency of 3% and a frequency of independent Ac re-insertions following germinal excision of 22%. The iae mutants represents a possible means of improving the efficiency of Ac/Ds transposon tagging systems in Arabidopsis, and will enable the dissection of host involvement in Ac transposition and the mechanisms employed for controlling transposable element activity.

Arabidopsis↗
PubMed1996

Trials to assess equivalence: the importance of rigorous methods.

The aim of an equivalence trial is to show the therapeutic equivalence of two treatments, usually a new drug under development and an existing drug for the same disease used as a standard active comparator. Unfortunately the principles that govern the design, conduct, and analysis of equivalence trials are not as well understood as they should be. Consequently such trials often include too few patients or have intrinsic design biases which tend towards the conclusion of no difference. In addition the application of hypothesis testing in analysing and interpreting data from such trials sometimes compounds the drawing of inappropriate conclusions, and the inclusion and exclusion of patients from analysis may be poorly managed. The design of equivalence trials should mirror that of earlier successful trials of the active comparator as closely as possible. Patient losses and other deviations from the protocol should be minimised; analysis strategies to deal with unavoidable problems should not centre on an "intention to treat" analysis but should seek to show the similarity of results from a range of approaches. Analysis should be based on confidence intervals, and this also carries implications for the estimation of the required numbers of patients at the design stage.

Clinical Trials as Topic↗
PubMed1995

Towards a philosophical understanding of mentoring.

This paper commences with a brief introduction during which the foundations are laid for the ensuing discussion, in which learning, practical knowledge and expertise, and reflective practice are briefly analysed. Thereafter, it is argued that mentorship is best understood as relationship and function, neither of which is necessarily the same as that of the teacher-practitioner.

Clinical Competence↗
PubMed1994

Integration of CAPS markers into the RFLP map generated using recombinant inbred lines of Arabidopsis thaliana.

Konieczny and Ausubel have described a technique whereby Arabidopsis thaliana loci can be rapidly mapped to one of the ten chromosome arms using a small number of F2 progeny from crosses between the ecotypes Landsberg erecta and Columbia. The technique involves the use of 18 co-dominant, cleaved amplified polymorphic sequence (CAPS) markers which are evenly distributed throughout the Arabidopsis genome. We have mapped these 18 markers using recombinant inbred (RI) lines generated in our laboratory. These data enable a better integration of loci mapped relative to the CAPS markers into the restriction fragment length polymorphism (RFLP) map generated using Arabidopsis RI lines.

Arabidopsis↗