PubMed Health⌕ Search

Biomedical subjects

K Clark

Publications and source records attributed to K Clark.

At least 19 recordsLinked to original sources
PubMed2006

Simulation of special bubble detectors for PICASSO.

The PICASSO project is a cold dark matter (CDM) search experiment relying on the superheated droplet technique. The detectors use superheated freon liquid droplets (active material) dispersed and trapped in a polymerised gel. This detection technique is based on the phase transition of superheated droplets at about room temperature and ambient pressure. The phase transition is induced by nuclear recoils when an atomic nucleus in the droplets interacts with incoming subatomic particles. This includes CDM particles candidate as the neutralino (a yet-to-discover particle predicted in extensions of the standard model of particle physics). Simulations performed to understand the detector response to neutrons and alpha particles are presented along with corresponding data obtained at the Montreal Laboratory.

Computer Simulation↗
PubMed2006

Measurement of the asymmetry in the decay Omega+-->LamdaKappa+-->rhopi+Kappa+.

The asymmetry in the rho angular distribution in the sequential decay Omega+-->LamdaKappa+-->rhopi+Kappa+. has been measured to be alphaOmegaalphaLamda=[+1.16+/-0.18(stat)+/-0.17(syst)]x10(-2) using 1.89x10(6) unpolarized Omega+ decays recorded by the HyperCP (E871) experiment at Fermilab. Using the known value of alphaLamda, and assuming that alphaLamda=-alphaLamda, alphaOmega=[-1.81+/-0.28(stat)+/-0.26(syst)]x10(-2). A comparison between this measurement of alphaOmegaalphaLamda and recent measurements of alphaOmegaalphaLamda made by HyperCP shows no evidence of a violation of CP symmetry.

Journal Article↗
PubMed2006

Direct dark matter search using large-mass superheated droplet detectors in the PICASSO experiment.

The PICASSO experiment investigates the presence and nature of dark matter in the Universe. The experiment is based on the detection of acoustic signals generated in explosive phase transitions induced by dark matter particles. This technique is an alternative more traditional detection technique like scintillation and ionisation, which are largely employed for dark matter search. One of the main advantages of this technique, besides its sensitivity to very low nuclear recoil energies (few keV), is its excellent background suppression features. A pilot experiment consisting of six superheated droplet detectors (40 g of active mass) is presently taking data at the Sudbury Neutrino Observatory (SNO) at a depth of 2000 m. We discuss the operation, calibration and data acquisition of the experiment and also the ongoing work to increase the sensitivity and the active mass of the detectors.

Cosmic Radiation↗
PubMed2006

Growth rates of the blowfly, Lucilia sericata, on different body tissues.

Estimates of post-mortem interval based on forensic analysis of the age of blowfly larvae on a corpse, are generated from standardised larval development curves. These are derived from studies of the growth of larvae reared, usually, on liver and at a range of temperatures. However, it is possible that the species or organ on which the larvae feed, might significantly alter the rate of growth. The present study therefore compared the development of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae) fed on lung, liver and heart, from both cows and pigs. Half of the tissue samples used were liquidised while half were not, to assess whether structural differences in the food source were important. Larvae grew significantly faster and gave rise to larger adults when reared on pig compared to cow tissue and when reared on lung and heart compared to liver. Larvae completed feeding and wandered from the food source 31h earlier and grew 2mm longer when reared on lung compared to liver. Tissue structure had no or little effect on development. For the forensic entomologist, these results highlight the importance of recording the position of larvae removed from a body and the care that should be used when extrapolating development rates from standard curves based on larvae fed on only a single medium, particularly where that is liver.

Animals↗
PubMed2006

Biochemical characterization of Drosophila gamma-glutamyl carboxylase and its role in fly development.

To investigate structure-function relationships in gamma-glutamyl carboxylases, the enzyme from Drosophila melanogaster was characterized. Four cysteine residues were shown to be important determinants for enzymatic activity. Native Drosophila substrates have not yet been identified, but propeptides of human prothrombin and factor IX are recognized by the Drosophila enzyme. The presence of the propeptide region increased apparent affinity by approximately 200-fold, and mutation of a hydrophobic residue of factor IX propeptide (F-16A) decreased carboxylation by 90%, as in the human enzyme. Substrate recognition appears to be highly conserved between the human and Drosophila gamma-glutamyl carboxylases. Inactivation of Drosophila gamma-glutamyl carboxylase by non-sense mutations or insertional mutagenesis by P-element insertion have no apparent effects on growth and fertility under laboratory conditions.

Alanine↗
PubMed2006

Expression of genes related to activity of oxaliplatin and 5-fluorouracil in endoscopic biopsies of primary esophageal cancer in patients receiving oxaliplatin, 5-flourouracil and radiation: characterization and exploratory analysis with survival.

With a goal of identifying relations between gene expression and response (mucosal or pathological) or survival in esophageal cancer patients (stages II to IV) receiving oxaliplatin, 5-fluorouracil (5FU) and radiation, we measured in endoscopic primary tumor biopsies from 38 patients, the expression of seven genes (gammaGCS, gammaGT, MRP-2, ERCC-1, XPA, TS and DPD) prior to treatment, 1 week following oxaliplatin alone and at the end of the combined radio-chemotherapy cycle using real time QRT-PCR. A higher pretreatment level of XPA was related to shorter survival with a hazard ratio of 2.43 (90% confidence interval 1.09 to 5.43) using Cox regression modeling. However, multivariate analysis with a Cox model indicated low expression of XPA or TS and combined stages II and III had a higher probability of survival (for XPA: hazard ratio 3.0 and 90% C.I. of 1.3 to 6.9, with adjustment for stage included; for TS: hazard ratio is 1.98 with 90% C.I. of 0.94 to 4.20. The expression of TS, gammaGCS, ERCC-1 and MRP-2 declined from D 1 to the end of the cycle (p<0.05, sign test). A validation and further understanding of the findings need to be carried out in a larger study with a more homogeneous population of patients.

Aged↗
PubMed2005

Search for the lepton-number-violating decay Xi(-)-->pmu(-)mu(-).

A sensitive search for the lepton-number-violating decay Xi(-)-->pmu(-)mu(-) has been performed using a sample of approximately 10(9) Xi(-) hyperons produced in 800 GeV/c p-Cu collisions. We obtain B(Xi(-)-->pmu(-)mu(-))<4.0x10(-8) at 90% confidence, improving on the best previous limit by 4 orders of magnitude.

Journal Article↗
PubMed2005

Search for DeltaS = 2 nonleptonic hyperon decays.

A sensitive search for the rare decays Omega(-)--> Lambdapi(-) and Xi(0)--> ppi(-) has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |DeltaS| = 2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Omega(-)-->Lambdapi(-)) < 2.9 x 10(-6) and B(Xi(0)--> ppi(-)) < 8.2 x 10(-6), both at 90% confidence level.

Journal Article↗
PubMed2005

Evidence for the decay sigma+ --> pmu+ mu-.

We report the first evidence for the decay Sigma(+)-->pmu(+)mu(-) from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Sigma(+)-->pmu(+)mu(-))=[8.6(+6.6)(-5.4)(stat)+/-5.5(syst)]x10(-8). The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma(+)-->pP(0),P0-->mu(+)mu(-) with a P0 mass of 214.3+/-0.5 MeV/c(2) and branching ratio B(Sigma(+)-->pP(0),P0-->mu(+)mu(-))=[3.1(+2.4)(-1.9)(stat)+/-1.5(syst)]x10(-8).

Journal Article↗
PubMed2005

[Medical hypnosis in cases of herpes labialis improves resistance for recurrence. A pilot study].

The present study examined the effectiveness of a hypnotherapeutic treatment program for patients suffering from recurrent orofacial herpes infections. Twenty-one patients were randomly allocated to either an experimental group (n=10) or a control condition (n=11). During five weekly individual therapy sessions the participants received symptom-oriented treatment. In addition, they learnt how to improve their stress coping skills and their management of aversive emotions. The final assessment took place 6 months after treatment. Besides documentation of the frequency and intensity of symptoms, questionnaires were administered to assess stress coping mechanisms (SVF), skin disease-related subjective strain (MHF) and perceptions of control (KKG). A significant reduction of disease intensity could be confirmed. Individual scales of the SVF and MHF also revealed significant results. For an effective treatment of severe herpes infections a mere focus on physical changes appears to be insufficient. A common reflection of a person's sensuality and expectations of closeness and distance seem to influence treatment success remarkably.

Adult↗
PubMed2004

Search for CP violation in charged-Xi and Lambda hyperon decays.

We have compared the p and p angular distributions in 117 x 10(6) Xi- -->Lambdapi- -->ppi-pi- and 41 x 10(6) Xi+ -->Lambda pi+ -->p pi+pi+ decays using a subset of the data from the HyperCP experiment (E871) at Fermilab. We find no evidence of CP violation, with the direct-CP-violating parameter AXiLambda identical with (alphaXialphaLambda-alpha Xialpha Lambda)/(alphaXialphaLambda+alphaXialphaLambda)=[0.0+/-5.1(stat)+/-4.4(syst)] x 10(-4).

Journal Article↗
PubMed2004

Genome sequence of the enterobacterial phytopathogen Erwinia carotovora subsp. atroseptica and characterization of virulence factors.

The bacterial family Enterobacteriaceae is notable for its well studied human pathogens, including Salmonella, Yersinia, Shigella, and Escherichia spp. However, it also contains several plant pathogens. We report the genome sequence of a plant pathogenic enterobacterium, Erwinia carotovora subsp. atroseptica (Eca) strain SCRI1043, the causative agent of soft rot and blackleg potato diseases. Approximately 33% of Eca genes are not shared with sequenced enterobacterial human pathogens, including some predicted to facilitate unexpected metabolic traits, such as nitrogen fixation and opine catabolism. This proportion of genes also contains an overrepresentation of pathogenicity determinants, including possible horizontally acquired gene clusters for putative type IV secretion and polyketide phytotoxin synthesis. To investigate whether these gene clusters play a role in the disease process, an arrayed set of insertional mutants was generated, and mutations were identified. Plant bioassays showed that these mutants were significantly reduced in virulence, demonstrating both the presence of novel pathogenicity determinants in Eca, and the impact of functional genomics in expanding our understanding of phytopathogenicity in the Enterobacteriaceae.

Base Sequence↗
PubMed2004

Mechanisms of integration of cells and extracellular matrices by integrins.

While it is self-evident that all extracellular molecules are an integral part of a multicellular organism, it is paradoxical that they are often considered to be dissociated from cells. The reality is that a continuum of dynamic, bi-directional interactions links the intracellular environment through cell-surface receptors to multimolecular extracellular assemblies. These interactions not only control the behaviour of individual cells, but also determine tissue architecture. Adhesion receptor function is partly determined by an ability to tether the contractile cytoskeleton to the plasma membrane, but there is also evidence that integrin receptors modulate signalling events that are essential for cellular differentiation. A major challenge is now to integrate work at the atomic, molecular and cellular levels, and obtain holistic insights into the mechanisms controlling cell adhesion. In the present study, we review current knowledge of the molecular mechanisms employed by cells to integrate with the extracellular matrix. Two main topics are covered: the adaptation of integrin structure for bi-directional signalling and the integration of integrin signalling with other receptors.

Binding Sites↗
PubMed2003

Design and standards for genetic evaluation of swine seedstock populations.

The purpose of this article is to describe a program for evaluation of seedstock populations in the swine industry. Differences among seedstock populations for economically important traits must be identified in order for pork producers to efficiently use available genetic resources. National genetic evaluation programs have the potential to identify the important differences among populations and to increase the rate of genetic improvement in a population. Program results provide performance benchmarks that stimulate testing and selection procedures by seedstock suppliers that further increase the rate of genetic improvement. A Terminal Sire Line Genetic Evaluation Program was designed and conducted in the United States by the National Pork Producers Council (Des Moines, IA) to compare seedstock populations for use in crossbreeding systems. High levels of statistical accuracy for program results were established; the ability to detect differences of 0.25 SD per trait, a power of test of 75%, and a 5% significance level were selected. Pure breeds and breeding company sire lines were nominated for the program. Semen was collected from nominated boars and distributed to cooperating commercial producers during eight 1-wk breeding periods. Pigs were produced in 136 commercial herds and transported to testing facilities at 8 to 23 d of age. Nine of the 11 sire lines originally entered in the program completed the sampling requirements for statistical analysis. High levels of statistical accuracy and a large, representative sample of boars with restrictions on genetic relationships ensured that the program results included unbiased, highly accurate sire line data for growth, carcass, meat quality, and eating quality traits of economic importance. This program has shown commercial producers that they have several choices of sire lines for changing their crossbreeding programs in desired trait areas. Commercial product evaluation must be an ongoing process, and this program serves as a model for future testing and evaluation of diverse genetic seedstock populations.

Animals↗
PubMed2002

Observation of the decay K- --> pi(-)mu(+)mu(-) and measurements of the branching ratios for K+/- --> pi(+/-)mu(+)mu(-).

Using data collected with the HyperCP (E871) spectrometer during the 1997 fixed-target run at Fermilab, we report the first observation of the decay K--->pi(-)mu(+)mu(-) and new measurements of the branching ratios for K+/--->pi(+/-)mu(+)mu(-). By combining the branching ratios for the decays K+-->pi(+)mu(+)mu(-) and K--->pi(-)mu(+)mu(-), we measure Gamma(K+/--->pi(+/-)mu(+)mu(-))/Gamma(K+/--->all) = (9.8+/-1.0+/-0.5)x10(-8). The CP asymmetry between the rates of the two decay modes is [Gamma(K+-->pi(+)mu(+)mu(-))-Gamma(K--->pi(-)mu(+)mu(-))]/[Gamma(K+-->pi(+)mu(+)mu(-))+Gamma(K--->pi(-)mu(+)mu(-))] = -0.02+/-0.11+/-0.04.

Journal Article↗
PubMed2002

The ethics of surgery in the elderly demented patient with bowel obstruction.

OBJECTIVE: Little has been written in the medical literature concerning the ethics of treatment of the elderly demented patient with bowel obstruction. It is one example of the issues with which we are becoming increasingly involved. We conducted a survey of our colleagues' opinions to determine current practice. DESIGN: A postal questionnaire study (62% response rate). Questions were posed that related to a case scenario of an elderly demented patient presenting with a presumed sigmoid volvulus. SETTING: The northern region of England. PARTICIPANTS: Thirty seven surgical members of the Association of Coloproctology of Great Britain and Ireland, Northern Chapter. RESULTS: Sixty five per cent of respondents felt that surgery would be inappropriate, and 26% that any intervention at all upon the subject in the case scenario would be inappropriate. More would operate, however, at the request of relatives. An advance directive not to treat would be respected by 70% despite a relative's wishes. CONCLUSIONS: Overall there was a wide variation in the approach of the surgeons to a demented patient with bowel obstruction. In an era of clinical governance, and an increased awareness of the ethics of consent, this study presents one example of the difficult decisions with which we are increasingly faced. The greater use of advance directives may provide one possible solution.

Advance Directives↗