The Role of Catalyst Support, Diluent and Co-Catalyst in Chromium-Mediated Heterogeneous Ethylene Trimerisation.

Sequential treatment of a previously-calcined solid oxide support (i.e. SiO2, γ-Al2O3, or mixed SiO2-Al2O3) with solutions of Cr{N(SiMe3)2}3 (0.71 wt% Cr) and a Lewis acidic alkyl aluminium-based co-catalyst (15 molar equivalents) affords initiator systems active for the oligomerisation and/or polymerisation of ethylene. The influence of the oxide support, calcination temperature, co-catalyst, and reaction diluent on both the productivity and selectivity of the immobilised chromium initiator systems have been investigated, with the best performing combination (SiO2-600, modified methyl aluminoxane-12 {MMAO-12}, heptane) producing a mixture of hexenes (61 wt%; 79% 1-hexene), and polyethylene (16 wt%) with an activity of 2403 g gCr -1 h-1. The observed product distribution is rationalised by two competing processes: trimerisation via a supported metallacycle-based mechanism and polymerisation through a classical Cossee-Arlman chain-growth pathway. This is supported by the indirect observation of two distinct chromium environments at the surface of the oxide support by a solid-state 29Si NMR spectroscopic study of the Cr{N(SiMe3)2}x/SiO2-600 pro-initiator.

Fruit and vegetable intake and cardiovascular risk factors in people with newly diagnosed type 2 diabetes.

BACKGROUND/OBJECTIVES: The cardiovascular benefit of increasing fruit and vegetable (F&V) intake following diagnosis of diabetes remains unknown. We aimed to describe how quantity and variety of F&V intake, and plasma vitamin C, change after diagnosis of type 2 diabetes and examine whether these changes are associated with improvements in cardiovascular risk factors. SUBJECTS/METHODS: A total of 401 individuals with screen-detected diabetes from the ADDITION-Cambridge study were followed up over 5 years. F&V intake was assessed by food frequency questionnaire and plasma vitamin C at baseline, at 1 year and at 5 years. Linear mixed models were used to estimate associations of changes in quantity and variety of F&V intake, and plasma vitamin C, with cardiovascular risk factors and a clustered cardiometabolic risk score (CCMR), where a higher score indicates higher risk. RESULTS: F&V intake increased in year 1 but decreased by year 5, whereas variety remained unchanged. Plasma vitamin C increased at 1 year and at 5 years. Each s.d. increase (250g between baseline and 1 year and 270g between 1 and 5 years) in F&V intake was associated with lower waist circumference (-0.92 (95% CI: -1.57, -0.27) cm), HbA1c (-0.11 (-0.20, -0.03) %) and CCMR (-0.04 (-0.08, -0.01)) at 1 year and higher high-density lipoprotein (HDL)-cholesterol (0.04 (0.01, 0.06) mmol/l) at 5 years. Increased plasma vitamin C (per s.d., 22.5 µmol/l) was associated with higher HDL-cholesterol (0.04 (0.01, 0.06) mmol/l) and lower CCMR (-0.07 (-0.12, -0.03)) between 1 and 5 years. CONCLUSIONS: Increases in F&V quantity following diagnosis of diabetes are associated with lower cardiovascular risk factors. Health promotion interventions might highlight the importance of increasing, and maintaining increases in, F&V intake for improved cardiometabolic health in patients with diabetes.

Glycaemic control of Type 1 diabetes in clinical practice early in the 21st century: an international comparison.

AIMS: Improving glycaemic control in people with Type 1 diabetes is known to reduce complications. Our aim was to compare glycaemic control among people with Type 1 diabetes using data gathered in regional or national registries. METHODS: Data were obtained for children and/or adults with Type 1 diabetes from the following countries (or regions): Western Australia, Austria, Denmark, England, Champagne-Ardenne (France), Germany, Epirus, Thessaly and Thessaloniki (Greece), Galway (Ireland), several Italian regions, Latvia, Rotterdam (The Netherlands), Otago (New Zealand), Norway, Northern Ireland, Scotland, Sweden, Volyn (Ukraine), USA and Wales) from population or clinic-based registries. The sample size with available data varied from 355 to 173 880. Proportions with HbA1c < 58 mmol/mol (< 7.5%) and ≥ 75 mmol/mol (≥ 9.0%) were compared by age and sex. RESULTS: Data were available for 324 501 people. The proportions with HbA1c 58 mmol/mol (< 7.5%) varied from 15.7% to 46.4% among 44 058 people aged < 15 years, from 8.9% to 49.5% among 50 766 people aged 15-24 years and from 20.5% to 53.6% among 229 677 people aged ≥ 25 years. Sex differences in glycaemic control were small. Proportions of people using insulin pumps varied between the 12 sources with data available. CONCLUSION: These results suggest that there are substantial variations in glycaemic control among people with Type 1 diabetes between the data sources and that there is room for improvement in all populations, especially in young adults.

Kalpha yields from Ti foils irradiated with ultrashort laser pulses.

We have studied the emission of Kalpha radiation from Ti foils irradiated with ultrashort (45 fs) laser pulses. We utilized the fundamental (800 nm) light from a Ti:sapphire laser on bare foils and foils coated with a thin layer of parylene E (CH). The focusing was varied widely to give a range of intensities from approximately 10(15) - 10(19) W cm(-2). Our results show a conversion efficiency of laser to Kalpha energy of approximately 10(-4) at tight focus for both types of targets. In addition, the coated targets exhibited strong secondary peaks of conversion at large defocus, which we believe are due to modification of the extent of preformed plasma due to the dielectric nature of the plastic layer. This in turn affects the level of resonance absorption. A simple model of Kalpha production predicts a much higher conversion than seen experimentally and possible reasons for this are discussed.

[Epigenetic heredity in evolution]. / Epigeneticheskaia nasledstvennost' v évoliutsii.

We discuss the role of cell memory in heredity and evolution. We describe the properties of the epigenetic inheritance systems (EISs) that underlie cell memory and enable environmentally and developmentally induced cell phenotypes to be transmitted in cell lineages, and argue that transgenerational epigenetic inheritance is an important and neglected part of heredity. By looking at the part EISs have played in the evolution of multicellularity, ontogeny, chromosome organization, and the origin of some post-mating isolating mechanisms, we show how considering the role of epigenetic inheritance can sometimes shed light on major evolutionary processes.

Treatment of flexor tendon injuries: surgeons' perspective.

Medical researchers continue to explore the flexor tendon's response to injury and repair. In recent years, hand surgery and therapy publications have focused on the biomechanics of suture techniques and the benefits of early postoperative motion on surgically repaired flexor tendons. Laboratory and clinical studies have shown that stronger suture techniques can withstand the strain of immediate active motion without a significant risk of tendon rupture or gap formation. Newly proposed therapy techniques and anatomic studies defining the effects of wrist and digital position on tendon excursion share the goals of achieving early motion and reducing restrictive adhesions. Clinical studies have evaluated the various imaging modalities used to diagnose postoperative adhesions. Other clinical surveys have detailed the use of pedicled autograft and allograft tendons in staged reconstruction. Histologic and immunologic researchers have concentrated on cellular activation patterns following tendon injury and the effects of pharmacologic agents, such as hyaluronan and aprotinin, on tendon healing and adhesion formation.

'Lamarckian' mechanisms in darwinian evolution.

Since the Modern Synthesis, evolutionary biologists have assumed that the genetic system is the sole provider of heritable variation, and that the generation of heritable variation is largely independent of environmental changes. However, adaptive mutation, epigenetic inheritance, behavioural inheritance through social learning, and language-based information transmission have properties that allow the inheritance of induced or learnt characters. The role of induced heritable variation in evolution therefore needs to be reconsidered, and the evolution of the systems that produce induced variation needs to be studied.

Comparison of two methods for teaching advanced arrhythmias to nurses.

An experimental study to compare the effectiveness of assisted self-directed learning (ASD) and traditional lecture methods (TLM) in acquiring competency for electrocardiogram interpretation was conducted within a conceptual framework of developmental and adult learning theory (Erickson, Tomlin & Swain, 1983; Knowles, 1980). After two teaching units were designed and an EKG posttest was constructed (r = .75) from actual patient records, registered nurse volunteers (N = 19) were randomly assigned to groups for simultaneous instruction. Because of the small sample size, statistical procedures were used to determine the effectiveness of randomization and to justify statistical procedures. EKG post-test scores for the experimental group (ASD, M = 81) and the control group (TLM, M = 71) were significantly different (one-tailed t = 1.79; p = .045); however, participants' prior knowledge of basic arrhythmias was not independent of method (ANCOVA, F[1, 16] = 21.373, p = .0003, covariate; F[1.16] = 2.312, p = .1479, main effects). EKG post-test scores were not related to critical care experience, cardiac monitoring experience, education level, or course satisfaction. While both methods are effective, ASD had higher mean scores and is more cost- and time-efficient.

Sex chromosomes and speciation.

Studies of reproductive isolation between animal species have shown (i) that if one sex of the hybrids between two species is sterile or inviable, it is usually the heterogametic sex (Haldane's rule), and (ii) the genes on the sex chromosomes play a particularly large role in hybrid sterility and inviability. We propose an explanation for these two observations which is based on the changes in chromosome conformation which take place during gametogenesis. These changes are far greater in sex chromosomes than in autosomes. They are also greater in the heterogametic than in the homogametic sex. We suggest that the sensitivity of hybrids of the heterogametic sex to the genetic divergence that occurs during periods of population isolation is partly the result of the failure of their sex chromosomes to undergo appropriate conformational changes. This hypothesis explains why the sex chromosomes play a disproportionate role in post-zygotic, but not in pre-zygotic, isolation, and why often only the germ line is sensitive to hybridization.

The evolution of heteromorphic sex chromosomes.

The facts and ideas which have been discussed lead to the following synthesis and model. 1. Heteromorphic sex chromosomes evolved from a pair of homomorphic chromosomes which had an allelic difference at the sex-determining locus. 2. The first step in the evolution of sex-chromosome heteromorphism involved either a conformational or a structural difference between the homologues. A structural difference could have arisen through a rearrangement such as an inversion or a translocation. A conformational difference could have occurred if the sex-determining locus was located in a chromosomal domain which behaved as a single control unit and involved a substantial segment of the chromosome. It is assumed that any conformational difference present in somatic cells would have been maintained in meiotic prophase. 3. Lack of conformational or structural homology between the sex chromosomes led to meiotic pairing failure. Since pairing failure reduced fertility, mechanisms preventing it had a selective advantage. Meiotic inactivation (heterochromatinization) of the differential region of the X chromosome in species with heterogametic males and euchromatinization of the W in species with heterogametic females are such mechanisms, and through them the pairing problems are avoided. 4. Structural and conformational differences between the sex chromosomes in the heterogametic sex reduced recombination. In heterogametic males recombination was reduced still further by the heterochromatinization of the X chromosome, which evolved in response to selection against meiotic pairing failure. 5. Suppression of recombination resulted in an increase in the mutation rate and an increased rate of fixation of deleterious mutations in the recombination-free chromosome regions. Functional degeneration of the genetically isolated regions of the Y and W was the result. In XY males this often led to further meiotic inactivation of the differential region of the X chromosome, and in this way an evolutionary positive-feedback loop may have been established. 6. Structural degeneration (loss of material) followed functional degeneration of Y or W chromosomes either because the functionally degenerate genes had deleterious effects which made their loss a selective advantage, or because shorter chromosomes were selectively neutral and became fixed by chance. 7. The evolutionary routes to sex-chromosome heteromorphism in groups with female heterogamety are more limited than in those with male heterogamety. Oocytes are usually large and long-lived, and are likely to need the products of X- or Z-linked genes. Meiotic inactivation of these chromosomes is therefore unlikely. In the oocytes of ZW females, meiotic pairing failure is avoided through euchromatinization of the W rather than heterochromatinization of the Z chromosome.(ABSTRACT TRUNCATED AT 400 WORDS)

Lamarckism and ageing.

Although it is usually assumed that Lamarckian inheritance does not and cannot occur, molecular mechanisms by which non-mutational changes acquired in one generation can be transmitted to the next are now known. These mechanisms involve changes in chromatin structure, rather than changes in DNA base sequence. It is argued that some parentalage effects and Lansing effects may be due to inherited changes in chromatin structure. Methods of testing this idea are suggested.

The inheritance of acquired epigenetic variations.

There is evidence that the functional history of a gene in one generation can influence its expression in the next. In somatic cells, changes in gene activity are frequently associated with changes in the pattern of methylation of the cytosines in DNA; these methylation patterns are stably inherited. Recent work suggests that information about patterns of methylation and other epigenetic states can also be transmitted from parents to offspring. This evidence is the basis of a model for the inheritance of acquired epigenetic variations. According to the model, an environmental stimulus can induce heritable chromatin modifications which are very specific and predictable, and might result in an adaptive response to the stimulus. This type of response probably has most significance for adaptive evolution in organisms such as fungi and plants, which lack distinct segregation of the soma and germ line. However, in all organisms, the accumulation of specific and random chromatin modifications in the germ line may be important in speciation, because these modifications could lead to reproductive isolation between populations. Heritable chromatin variations may also alter the frequency and distribution of classical mutations and meiotic recombination. Therefore, inherited epigenetic changes in the structure of chromatin can influence neo-Darwinian evolution as well as cause a type of "Lamarckian" inheritance.

Meiotic pairing constraints and the activity of sex chromosomes.

The state of activity and condensation of the sex chromosomes in gametocytes is frequently different from that found in somatic cells. For example, whereas the X chromosomes of XY males are euchromatic and active in somatic cells, they are usually condensed and inactive at the onset of meiosis; in the somatic cells of female mammals, one X chromosome is heterochromatic and inactive, but both X chromosomes are euchromatic and active early in meiosis. In species in which the female is the heterogametic sex (ZZ males and ZW females), the W chromosome, which is often seen as a condensed chromatin body in somatic cells, becomes euchromatic in early oocytes. We describe an hypothesis which can explain these changes in the activity and condensation of sex chromosomes in gametocytes. It is based on the fact that normal chromosome pairing seems to be essential for the survival of sex cells; chromosomal anomalies resulting in incomplete pairing during meiosis usually result in gametogenic loss. We argue that the changes seen in the sex chromosomes reflect the need to avoid pairing failure during meiosis. Pairing normally requires structural and conformational homology of the two chromosomes, but when the regions is avoided when these regions become heterochromatinized. This hypothesis provides an explanation for the changes found in gametocytes both in species with male heterogamety and those with female heterogamety. It also suggests possible reasons for the frequent origin of large supernumerary chromosomes from sex chromosomes, and for the reported lack of dosage compensation in species with female heterogamety.

Influence of age and diet on DNA synthesis and the DNA content of mid-gut cells in the dipteran Sarcophaga carnaria.

Virgin female Sarcophaga carnaria maintained on a diet of sugar and water had shorter lifespans than those maintained on a liver, sugar and water diet; there was no significant different between the lifespans of mated females or mated males kept on the two diets. Autoradiographs of mid-gut sections from virgin females which had been fed with [3H]thymidine showed substantial amounts of DNA synthesis in the nuclei during at least the first 14-15 days of adult life. Cytophotometric measurements of Feulgen-stained mid-gut nuclei of 0--1-, 2--3-, and 14--15-day-old females showed that the integrated absorbances peaked at values corresponding approximately to 2 C, 4 C, 8 C, 16 C and 32 C. The proportion of nuclei with the higher Feulgen-DNA values increased with age, and was greater in flies maintained on the liver, sugar and water diet. It is suggested that the DNA synthesis observed is associated with polytenization rather than mitotic cell division, and that the level of polyteny reached may reflect age- and diet-related differences in the functional demand made on mid-gut cells.

Molecular sieve generation of aviator's oxygen: Performance of a prototype system under simulated flight conditions.

The molecular sieve method of generating an enriched-oxygen breathing gas is one of several candidate onboard oxygen generation (OBOG) systems under joint Army-Navy-Air Force development for application in tactical aircraft. The performance of a nominal two-man-capacity molecular sieve oxygen generation system was characterized under simulated flight conditions. Data are given on the composition of the molecular sieve-generated breathing gas (oxygen, nitrogen, carbon dioxide, and argon) as a function of inlet air pressure, altitude, breathing gas flow rate, and ambient temperature. The maximum oxygen concentration observed was 95%, with the balance argon. At low demand flow rates and certain conditions of pressure and altitude, the argon enrichment factor exceeded that of oxygen giving a maximum argon concentration of 6.6% with the balance oxygen. The structural integrity of the unit was verified by vibration and centrifuge testing. The performance of the molecular sieve unit is discussed in the context of aircraft operating envelopes using both diluter-demand and 100% delivery subsystems.

An investigation of some genetic toxicological effects of the fungicide benomyl.

The widely used fungicide benomyl (methyl-1-(butylcarbamoyl)-2-benzimidazole carbamate) and its breakdown product methyl-2-benzimidazole carbamate (MBC) have been reported to have mutagenic activity in some organisms. In experiments with Drosophila melanogaster we found (i) there was no significant increase in recessive lethal frequency after feeding adult flies with Benlate did not increase chromosome breakage or loss significantly; (ii) there was a relatively high incidence of sterility when males of one strain (Oregon R) were fed Benlate or MBC. In experiments in which cultures of human lymphocytes were exposed in vitro to 0.5 mg/ml MBC we observed extreme contraction of the chromosomes but found no evidence of an increase in the number of cells with chromosome aberrations. We conclude that benomyl and MBC are unlikely to be strong mutagens, but more research is needed to exclude the possibility that they are capable of inducing genetic damage in the germ cells of higher organisms.

Relationship between linguistic performance and memory deficits in retarded children.

Performance of retarded children was measured on four tests of linguistic ability and two memory tests. Subjects were 50 retarded children: 10 each at mental ages 3, 4, 5, 6, and 7. The relationship between linguistic performance and memory was assessed by correlational analysis. Multiple and partial correlations were computed using a measure of language comprehension and a measure of memory span as predictor variables and three measures of language production as criterion variables. Different patterns of correlation were found with the three production as criterion variables. Different patterns of correlation were found with the three production measures, suggesting that the relative importance of memory span in language production depends on the specific production task.