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At least 775 records · Page 43Linked to original sources
PubMed2001

Measurement of B(0)(d)-B_(0)(d) mixing rate from the time evolution of dilepton events at the upsilon(4S).

We report a determination of the B(0)(d)-&B_(0)(d) mixing parameter Deltam(d) based on the time evolution of dilepton yields in Upsilon(4S) decays. The measurement is based on a 5.9 fb(-1) data sample collected by the Belle detector at KEKB. The proper-time difference distributions for same-sign and opposite-sign dilepton events are simultaneously fitted to an expression containing Deltam(d) as a free parameter. Using both muons and electrons, we obtain Deltam(d) = 0.463+/-0.008 (stat)+/-0.016 (syst) ps(-1). This is the first determination of Deltam(d) from time evolution measurements at the Upsilon(4S). We also place limits on possible CPT violations.

Journal Article↗
PubMed1967

Effects of Metabolic Inhibitors on the Rates of CO(2) Evolution in Light and in Darkness by Detached Spruce Twigs, Wheat, and Soybean Leaves.

Detached spruce twigs, wheat and soybean leaves were infiltrated with various metabolic inhibitors, placed in a closed system in CO(2)-free air and the amounts of CO(2) evolved in either light or darkness were determined with an infra-red CO(2) analyzer. In light, metabolic inhibitors always greatly suppressed evolution of CO(2), the magnitude of suppression varying between 50 to 80% of that without an inhibitor. This depressing effect became less pronounced with increasing oxygen. In darkness, metabolic inhibitors sometimes suppressed and sometimes stimulated CO(2) evolution. These observations have been taken as further support for a conclusion made earlier, that evolution of CO(2) in light and darkness is not the same process.

Journal Article↗
PubMed1983

Evolution and design of 'rate controlled' osmotic forms.

A new type of therapeutic system, the precision release osmotic form, has recently been developed. This new dosage form has been referred to in other publications as the gastro-intestinal therapeutic system (GITS). Its action is based on the principles of osmosis as a means of delivering precise amounts of drug over prolonged periods of time. The precision release form has evolved from a prototype design through a simplification and miniaturization process into the elementary osmotic pump, a simple, elegant delivery form that permits controlled drug release by osmosis. Sodium indomethacin trihydrate is the first drug to be incorporated into this precision release form ('Osmosin'). Comparisons with conventional drug forms have shown 'Osmosin' to produce more sustained and constant drug release profiles, thus aiming to improve the therapeutic applicability of a drug through a reduction in dose-related side-effects and allowing once-daily dosing.

Delayed-Action Preparations↗
PubMed1988

Evolution of erythrocyte sedimentation rate as predictor of early relapse in posttherapy early-stage Hodgkin's disease.

A retrospective study was undertaken at the Institut Gustave Roussy (IGR) to determine the predictive ability of changes in the erythrocyte sedimentation rate (ESR) during posttherapy periods for early relapse (within 18 months from start of therapy) and long-term survival in Hodgkin's disease (HD). Three hundred one patients with clinical stages (CS) I or II HD entered in the European Organization for Research and Treatment of Cancer (EORTC) clinical trials were included in this study. All relevant data and long-term follow-up were available for these patients. A stepwise logistic regression was performed to assess the prognostic value of ESR changes independent of other prognostic parameters and treatment. The incidence of early relapse was found to be significantly increased in patients in whom ESR remained elevated (greater than 30 mm at one hour) after completion of therapy, regardless of the value before therapy. This was true whether the ESR was elevated in plateau fashion, oscillating between normal and abnormal, or was lower than at onset, but still abnormal. Moreover, early relapse predicted by elevated ESR posttherapy was associated with poor survival despite subsequent initiation of combination chemotherapy. Thus, the persistence of an abnormal ESR appears to be a reliable indicator for high probability of early relapse and subsequent poor prognosis. This might be introduced as a prognostic variable in the design of future therapy programs for HD.

Adult↗
PubMed2006

Estimating the genomewide rate of adaptive protein evolution in Drosophila.

When polymorphism and divergence data are available for multiple loci, extended forms of the McDonald-Kreitman test can be used to estimate the average proportion of the amino acid divergence due to adaptive evolution--a statistic denoted alpha. But such tests are subject to many biases. Most serious is the possibility that high estimates of alpha reflect demographic changes rather than adaptive substitution. Testing for between-locus variation in alpha is one possible way of distinguishing between demography and selection. However, such tests have yielded contradictory results, and their efficacy is unclear. Estimates of alpha from the same model organisms have also varied widely. This study clarifies the reasons for these discrepancies, identifying several method-specific biases in widely used estimators and assessing the power of the methods. As part of this process, a new maximum-likelihood estimator is introduced. This estimator is applied to a newly compiled data set of 115 genes from Drosophila simulans, each with each orthologs from D. melanogaster and D. yakuba. In this way, it is estimated that alpha approximately 0.4+/-0.1, a value that does not vary substantially between different loci or over different periods of divergence. The implications of these results are discussed.

Adaptation, Physiological↗
PubMed1984

[Evolution of the mortality rate of newborn infants transferred to a Parisian intensive care service from 1969 to 1978].

This study reports on the trend in neonatal death rates in a Paris intensive care unit between 1969 and 1978. Three time-periods were compared: 1969-1971, 1972-1974, and 1975-1978. These limits were chosen to take into account the introduction of continuous airway positive pressure in the unit in 1972, and the gradual implementation, from 1972 onwards, of a new perinatal care policy in France. The mortality rate was significantly lower in the second period than in the first, after adjustment on birthweight and type of disease. This trend varied according to type of disease: the death decreased significantly in case of membrane disease or foetal distress, but not in case of admission for amniotic inhalation or congenital anomalies. The gradual improvement in newborn's condition on arrival in the unit played a part in the improvement in survival, as well as the use of the continuous airway positive pressure.

Critical Care↗
PubMed2002

Fitness evolution and the rise of mutator alleles in experimental Escherichia coli populations.

We studied the evolution of high mutation rates and the evolution of fitness in three experimental populations of Escherichia coli adapting to a glucose-limited environment. We identified the mutations responsible for the high mutation rates and show that their rate of substitution in all three populations was too rapid to be accounted for simply by genetic drift. In two of the populations, large gains in fitness relative to the ancestor occurred as the mutator alleles rose to fixation, strongly supporting the conclusion that mutator alleles fixed by hitchhiking with beneficial mutations at other loci. In one population, no significant gain in fitness relative to the ancestor occurred in the population as a whole while the mutator allele rose to fixation, but a substantial and significant gain in fitness occurred in the mutator subpopulation as the mutator neared fixation. The spread of the mutator allele from rarity to fixation took >1000 generations in each population. We show that simultaneous adaptive gains in both the mutator and wild-type subpopulations (clonal interference) retarded the mutator fixation in at least one of the populations. We found little evidence that the evolution of high mutation rates accelerated adaptation in these populations.

Adenosine Triphosphatases↗
PubMed1999

Natural selection promotes divergence of transferrin among salmonid species.

Transferrin is an iron-binding protein that plays an important role in iron metabolism and resistance to bacterial infection in a variety of organisms. A comparison of transferrin coding sequences from four salmonid species shows that the rate of evolution at nonsynonymous sites is significantly higher than the rate at synonymous sites, suggesting that positive natural selection for new alleles has played an important role in the evolution of transferrin in some salmon species. We hypothesize that the selective agent driving rapid divergence is interactions between host transferrin and the iron-scavenging proteins of pathogenic bacteria.

Alleles↗
PubMed1997

Cloning and characterisation of the gene encoding red deer (Cervus elaphus) growth hormone: implications for the molecular evolution of growth hormone in artiodactyls.

In mammals the structure of pituitary GH is generally strongly conserved, indicating a slow basal rate of molecular evolution. However, on two occasions, during the evolution of primates and of artiodactyls, the rate of evolution has increased dramatically (25- to 50-fold) so that the sequences of human and ruminant GHs differ markedly from those of other mammalian GHs. In order to define further the burst of GH evolution that occurred in artiodactyls we have cloned and characterised the GH gene of red deer (Cervus elaphus) using genomic DNA and a polymerase chain reaction technique. The deduced sequence for the mature GH from red deer is identical to that of bovine GH, indicating that the burst of rapid evolution of GH that occurred in Artiodactyla must have been completed before the divergence of Cervidae and Bovidae and suggesting that the rate of evolution during this burst must have been greater than previously estimated. In other aspects (signal sequence, 5' and 3' sequences, introns and synonymous substitutions in the coding sequence) the red deer GH gene differs considerably from the GH genes of other ruminants. Differences between the signal peptide sequences of red deer and bovid GHs probably explain why N-terminal heterogeneity is seen in bovine, ovine and caprine GHs but not GH from red deer, pig or most other mammals.

Amino Acid Sequence↗
PubMed2005

Natural selection in neoplastic progression of Barrett's esophagus.

Neoplasms progress to cancer through a process of natural selection. The rate of evolution, and thus progression is determined by three parameters: mutation rate, population size of the evolving neoplastic cells, and intensity of selection or rate of clonal expansion. All three parameters are reviewed in the context of Barrett's esophagus, a pre-malignant neoplasm. Although Barrett's esophagus is an ideal model for the study of neoplastic clonal evolution, similar studies may be carried out in a wide variety of human neoplasms. Evolutionary analyses provide insights for clinical management, including rates of progression to cancer and emergence of resistance to interventions.

Barrett Esophagus↗
PubMed1999

Evolution of stepping-stone dispersal rates.

We present a general model of the evolution of dispersal in a population with any distribution of dispersal distance. We use this model to analyse evolutionarily stable (ES) dispersal rates for the classical island model of dispersal and for three different stepping-stone models. Using general techniques to compute relatedness coefficients in the different dispersal models which we consider, we find that the distribution of dispersal distance may affect the ES dispersal rate when the cost of dispersal is low. In this case the ES dispersal rate increases with the number of demes that can be reached by one dispersal event. However, for increasing cost the ES dispersal rate converges to a value independent of the distribution of dispersal distance. These results are in contrast to previous analyses of similar models. The effects of the size (number of demes) and shape (ratio between the width and the length) of the population on the evolution of dispersal are also studied. We find that larger and more elongated populations lead generally to higher ES dispersal rates. However, both of these effects can only be observed for extreme parameter values (i.e. for very small and very elongated populations). The direct fitness method and the analytical techniques used here to compute relatedness coefficients provide an efficient way to analyse ES strategies in subdivided populations.

Animals↗
PubMed1996

[Evolution modes of eukaryote retrotransposons].

A number of general problems of molecular macroevolution of retroposons were examined, including the question of the ratio of the contributions of genomic replication and retrotransposition to mutational variability of retrotransposons, as well as that of the influence of stress-induced transpositional variability on the rate of evolution and the phylogenetic trees of retrotransposons. It is thought that the substitution fixation rate in genes of retrotransposons is determined by the transposition rate and the probability of mutation upon replication of copies of retransposons in the genome and upon retrotransposition, as well as by selection stabilizing the function of proteins of the retroreplicative mechanism. By means of molecular-evolutionary parameters, estimated for Drosophila retrotransposons and animal retroviruses, it was shown that spontaneous retrotransposition makes the dominant contribution to the frequency of mutation, and the expected fixation rate of nucleotide substations is on the order of 2 x 10(-8) per position per year. This version of evolution of retrotransposons agrees with the results of phylogenetic analysis of trees of macroevolution. Another version, associated with stress-induced transpositions, gives a very high rate of evolution, on the order 3 x 10(-6) fixations of nucleotide substitutions per position per year. This version seems improbable, as it leads to a significant hidden genetic load.

Animals↗
PubMed2005

The evolutionary ecology of seed germination of Arabidopsis thaliana: variable natural selection on germination timing.

Germination timing of Arabidopsis thaliana displays strong plasticity to geographic location and seasonal conditions experienced by seeds. We identified which plastic responses were adaptive using recombinant inbred lines in a field manipulation of geographic location (Kentucky, KY; Rhode Island, RI), maternal photoperiod (14-h and 10-h days), and season of dispersal (June and November). Transgressive segregation created novel genotypes that had either higher fitness or lower fitness in certain environments than either parent. Natural selection on germination timing and its variation explained 72% of the variance in fitness among genotypes in KY, 30% in June-dispersed seeds in RI, but only 4% in November-dispersed seeds in RI. Therefore, natural selection on germination timing is an extremely efficient sieve that can determine which genotypes can persist in some locations, and its efficiency is geographically variable and depends on other aspects of life history. We found no evidence for adaptive responses to maternal photoperiod during seed maturation. We did find adaptive plasticity to season of seed dispersal in RI. Seeds dispersed in June postponed germination, which was adaptive, while seeds dispersed in November accelerated germination, which was also adaptive. We also found maladaptive plasticity to geographic location for seeds dispersed in June, such that seeds dispersed in KY germinated much sooner than the optimum time. Consequently, bet hedging in germination timing was favorable in KY; genotypes with more variation in germination timing had higher fitness because greater variation was associated with postponed germination. Selection on germination timing varied across geographic location, indicating that germination timing can be a critical stage in the establishment of genotypes in new locations. The rate of evolution of germination timing may therefore strongly influence the rate at which species can expand their range.

Adaptation, Physiological↗