Science.gov

Sample records for high turnover rates

  1. The Distribution of Dropout and Turnover Rates among Urban and Suburban High Schools.

    ERIC Educational Resources Information Center

    Rumberger, Russell W.; Thomas, Scott L.

    2000-01-01

    Examines the distribution of dropout and turnover rates among 247 U.S. urban and suburban high schools to study school effectiveness. Finds that dropout and turnover rates can be attributed to student background, student composition, school resources, and school processes. (Contains references.) (CMK)

  2. High concentrations and turnover rates of DMS, DMSP and DMSO in Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Asher, Elizabeth C.; Dacey, John W. H.; Mills, Matthew M.; Arrigo, Kevin R.; Tortell, Philippe D.

    2011-12-01

    The vast Antarctic sea-ice zone (SIZ) is a potentially significant source of the climate-active gas dimethylsulfide (DMS), yet few data are available on the concentrations and turnover rates of DMS and the related compounds dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) in sea ice environments. Here we present new measurements characterizing the spatial variability of DMS, DMSP, and DMSO concentrations across the Antarctic SIZ, and results from tracer experiments quantifying the production rates of DMS from various sources. We observed extremely high concentrations (>200 nM) and turnover rates (>100 nM d-1) of DMS in sea-ice brines, indicating intense cycling of DMS/P/O. Our results demonstrate a previously unrecognized role for DMSO reduction as a major pathway of DMS production in Antarctic sea ice.

  3. High Gene Family Turnover Rates and Gene Space Adaptation in the Compact Genome of the Carnivorous Plant Utricularia gibba.

    PubMed

    Carretero-Paulet, Lorenzo; Librado, Pablo; Chang, Tien-Hao; Ibarra-Laclette, Enrique; Herrera-Estrella, Luis; Rozas, Julio; Albert, Victor A

    2015-05-01

    Utricularia gibba is an aquatic carnivorous plant with highly specialized morphology, featuring fibrous floating networks of branches and leaf-like organs, no recognizable roots, and bladder traps that capture and digest prey. We recently described the compressed genome of U. gibba as sufficient to control the development and reproduction of a complex organism. We hypothesized intense deletion pressure as a mechanism whereby most noncoding DNA was deleted, despite evidence for three independent whole-genome duplications (WGDs). Here, we explore the impact of intense genome fractionation in the evolutionary dynamics of U. gibba's functional gene space. We analyze U. gibba gene family turnover by modeling gene gain/death rates under a maximum-likelihood statistical framework. In accord with our deletion pressure hypothesis, we show that the U. gibba gene death rate is significantly higher than those of four other eudicot species. Interestingly, the gene gain rate is also significantly higher, likely reflecting the occurrence of multiple WGDs and possibly also small-scale genome duplications. Gene ontology enrichment analyses of U. gibba-specific two-gene orthogroups, multigene orthogroups, and singletons highlight functions that may represent adaptations in an aquatic carnivorous plant. We further discuss two homeodomain transcription factor gene families (WOX and HDG/HDZIP-IV) showing conspicuous differential expansions and contractions in U. gibba. Our results 1) reconcile the compactness of the U. gibba genome with its accommodation of a typical number of genes for a plant genome, and 2) highlight the role of high gene family turnover in the evolutionary diversification of U. gibba's functional gene space and adaptations to its unique lifestyle and highly specialized body plan. PMID:25637935

  4. High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice

    NASA Astrophysics Data System (ADS)

    Fripiat, François; Sigman, Daniel M.; Massé, Guillaume; Tison, Jean-Louis

    2015-04-01

    We report concentration and nitrogen and oxygen isotopic measurements of nitrate, total dissolved nitrogen, and particulate nitrogen from Antarctic landfast sea ice, covering almost the complete seasonal cycle of sea ice growth and decay (from April to November). When sea ice forms in autumn, ice algae growth depletes nitrate and accumulates organic N within the ice. Subsequent low biological activity in winter imposes minor variations in the partitioning of fixed N. In early spring, the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed N within sea ice, up to 20 times higher than in the underlying seawater. At this time, remineralization and nitrification also accelerate, yielding nitrate concentrations up to 5 times higher than in seawater. Nitrate δ15N and δ18O are both elevated, indicating a near-balance between nitrification and nitrate assimilation. These findings require high microbially mediated turnover rates for the large fixed N pools, including nitrate. When sea ice warms in the spring, ice algae grow through the full thickness of the ice. The warming stratifies the brine network, which limits the exchange with seawater, causing the once-elevated nitrate pool to be nearly completely depleted. The nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment, affecting its N cycling (e.g., allowing for nitrification) and impacting algal physiology (e.g., as reflected in the N and O isotope effects of nitrate assimilation).

  5. Should I Stay or Should I Go? A Comparison Study of Intention to Leave among Public Child Welfare Systems with High and Low Turnover Rates

    ERIC Educational Resources Information Center

    Strolin-Goltzman, Jessica

    2008-01-01

    This comparison study analyzes the commonalties, similarities, and differences on supervisory and organizational factors between a group of high turnover systems and a group of low turnover systems. Significant differences on organizational factors, but not on supervisory factors, emerged from the statistical analysis. Additionally, this study…

  6. Forest turnover rates follow global and regional patterns of productivity

    USGS Publications Warehouse

    Stephenson, N.L.; van Mantgem, P.J.

    2005-01-01

    Using a global database, we found that forest turnover rates (the average of tree mortality and recruitment rates) parallel broad-scale patterns of net primary productivity. First, forest turnover was higher in tropical than in temperate forests. Second, as recently demonstrated by others, Amazonian forest turnover was higher on fertile than infertile soils. Third, within temperate latitudes, turnover was highest in angiosperm forests, intermediate in mixed forests, and lowest in gymnosperm forests. Finally, within a single forest physiognomic type, turnover declined sharply with elevation (hence with temperature). These patterns of turnover in populations of trees are broadly similar to the patterns of turnover in populations of plant organs (leaves and roots) found in other studies. Our findings suggest a link between forest mass balance and the population dynamics of trees, and have implications for understanding and predicting the effects of environmental changes on forest structure and terrestrial carbon dynamics. ??2005 Blackwell Publishing Ltd/CNRS.

  7. Investigating Histone Acetylation Stoichiometry and Turnover Rate.

    PubMed

    Fan, J; Baeza, J; Denu, J M

    2016-01-01

    Histone acetylation is a dynamic epigenetic modification that functions in the regulation of DNA-templated reactions, such as transcription. This lysine modification is reversibly controlled by histone (lysine) acetyltransferases and deacetylases. Here, we present methods employing isotopic labeling and mass spectrometry (MS) to comprehensively investigate histone acetylation dynamics. Turnover rates of histone acetylation are determined by measuring the kinetics of labeling from (13)C-labeled precursors of acetyl-CoA, which incorporates (13)C-carbon onto histones via the acetyltransferase reaction. Overall histone acetylation states are assessed from complete protease digestion to single amino acids, which is followed by MS analysis. Determination of site-specific acetylation stoichiometry is achieved by chemically acetylating endogenous histones with isotopic acetic anhydride, followed by trypsin digestion and LC-MS analysis. Combining metabolic labeling with stoichiometric analysis permits determination of both acetylation level and acetylation dynamics. When comparing genetic, diet, or environmental perturbations, these methods permit both a global and site-specific evaluation of how histone acetylation is dynamically regulated. PMID:27423860

  8. American and Danish Police "Dropout" Rates: Denmark's Force as a Case Study in High Job Satisfaction, Low Stress, and Low Turnover.

    ERIC Educational Resources Information Center

    DeLey, Warren W.

    1984-01-01

    Compares actual turnover rates of a sample of U.S. police departments from large cities (N=87) and small cities (N=39) with that of the Danish police force. Results showed rates of early leaving to be lower for the Danish police than for the U.S. sample. (LLL)

  9. Mitochondrial protein turnover: methods to measure turnover rates on a large scale

    PubMed Central

    Chan, X’avia CY; Black, Caitlin M; Lin, Amanda J; Ping, Peipei; Lau, Edward

    2016-01-01

    Mitochondrial proteins carry out diverse cellular functions including ATP synthesis, ion homeostasis, cell death signaling, and fatty acid metabolism and biogenesis. Compromised mitochondrial quality control is implicated in various human disorders including cardiac diseases. Recently it has emerged that mitochondrial protein turnover can serve as an informative cellular parameter to characterize mitochondrial quality and uncover disease mechanisms. The turnover rate of a mitochondrial protein reflects its homeostasis and dynamics under the quality control systems acting on mitochondria at a particular cell state. This review article summarizes some recent advances and outstanding challenges for measuring the turnover rates of mitochondrial proteins in health and disease. PMID:25451168

  10. Differences in Bone Quality between High versus Low Turnover Renal Osteodystrophy

    SciTech Connect

    Porter, Daniel S.; Pienkowski, David; Faugere, Marie-Claude; Malluche, Hartmut H.

    2012-01-01

    Abnormal bone turnover is common in chronic kidney disease (CKD), but its effects on bone quality remain unclear. This study sought to quantify the relationship between abnormal bone turnover and bone quality. Iliac crest bone biopsies were obtained from CKD-5 patients on dialysis with low (n=18) or high (n=17) turnover, and from volunteers (n=12) with normal turnover and normal kidney function. Histomorphometric methods were used to quantify the microstructural parameters; Fourier transform infrared spectroscopy and nanoindentation were used to quantify the material and mechanical properties in bone. Reduced mineral-to-matrix ratio, mineral crystal size, stiffness and hardness were observed in bone with high turnover compared to bone with normal or low turnover. Decreased cancellous bone volume and trabecular thickness were seen in bone with low turnover compared to bone with normal or high turnover. Bone quality, as defined by its microstructural, material, and mechanical properties, is related to bone turnover. These data suggest that turnover related alterations in bone quality may contribute to the known diminished mechanical competence of bone in CKD patients, albeit from different mechanisms for bone with high (material abnormality) vs. low (microstructural alteration) turnover. The present findings suggest that improved treatments for renal osteodystrophy should seek to avoid low or high bone turnover and aim for turnover rates as close to normal as possible.

  11. Proteins with High Turnover Rate in Barley Leaves Estimated by Proteome Analysis Combined with in Planta Isotope Labeling1[W][OPEN

    PubMed Central

    Nelson, Clark J.; Alexova, Ralitza; Jacoby, Richard P.; Millar, A. Harvey

    2014-01-01

    Protein turnover is a key component in cellular homeostasis; however, there is little quantitative information on degradation kinetics for individual plant proteins. We have used 15N labeling of barley (Hordeum vulgare) plants and gas chromatography-mass spectrometry analysis of free amino acids and liquid chromatography-mass spectrometry analysis of proteins to track the enrichment of 15N into the amino acid pools in barley leaves and then into tryptic peptides derived from newly synthesized proteins. Using information on the rate of growth of barley leaves combined with the rate of degradation of 14N-labeled proteins, we calculate the turnover rates of 508 different proteins in barley and show that they vary by more than 100-fold. There was approximately a 9-h lag from label application until 15N incorporation could be reliably quantified in extracted peptides. Using this information and assuming constant translation rates for proteins during the time course, we were able to quantify degradation rates for several proteins that exhibit half-lives on the order of hours. Our workflow, involving a stringent series of mass spectrometry filtering steps, demonstrates that 15N labeling can be used for large-scale liquid chromatography-mass spectrometry studies of protein turnover in plants. We identify a series of abundant proteins in photosynthesis, photorespiration, and specific subunits of chlorophyll biosynthesis that turn over significantly more rapidly than the average protein involved in these processes. We also highlight a series of proteins that turn over as rapidly as the well-known D1 subunit of photosystem II. While these proteins need further verification for rapid degradation in vivo, they cluster in chlorophyll and thiamine biosynthesis. PMID:25082890

  12. High School Band Students' Perspectives of Teacher Turnover

    ERIC Educational Resources Information Center

    Kloss, Thomas E.

    2013-01-01

    Teacher turnover remains an important issue in education. The least researched perspectives, though, are those of the students who experience teacher turnover. The purpose of this study was to examine how high school band students experience teacher turnover. A total of twelve students were interviewed, representing three schools that experienced…

  13. Bed occupancy, turnover interval and MRSA rates in Northern Ireland.

    PubMed

    Cunningham, Joseph B; Kernohan, W George; Rush, Thomas

    The data describe bed turnover intervals (TI), bed percentage occupancy (PO) and methicillin-resistant Staphylococcus aureus (MRSA) rates per 1000 bed days of patient episodes. It was collected from annual hospital statistics in Northern Ireland (NI) and from the Communicable Diseases Surveillance Centre (CDSC) NI. The descriptive data show 6 of the general 11 surgical Trusts, out of a total of 12 Trusts examined, had PO greater than 85%; and all 11 medical facilities in these Trusts had occupancy rates greater than 85%. A significant correlation was established between turnover interval and MRSA per 1000 bed days of patient episodes in acute services beds. The correlation of PO with MRSA rates was 0.49 (ns). The conclusions drawn from the study are that in many Trusts the rates of bed occupancy for general surgery and general medicine is in excess of national guidelines and rapid turnover of patients is related to rates of MRSA infection. The implications for nurses and managers are discussed. PMID:16628168

  14. Explaining the Gap in Charter and Traditional Public School Teacher Turnover Rates

    ERIC Educational Resources Information Center

    Stuit, David A.; Smith, Thomas M.

    2012-01-01

    This study uses national survey data to examine why charter school teachers are more likely to turnover than their traditional public school counterparts. We test whether the turnover gap is explained by different distributions of factors that are empirically and theoretically linked to turnover risk. We find that the turnover rate of charter…

  15. An Exploration of Job, Organizational, and Environmental Factors Associated with High and Low Nursing Assistant Turnover

    ERIC Educational Resources Information Center

    Brannon, Diane; Zinn, Jacqueline S.; Mor, Vincent; Davis, Jullet

    2002-01-01

    Purpose: This article examines factors that distinguish nursing facilities with very high and very low nursing assistant turnover rates from a middle referent group, exploring the possibility that high and low turnover are discrete phenomena with different antecedents. Design and Methods: Data from a stratified sample of facilities in eight…

  16. Inorganic pyrophosphate pool size and turnover rate in arthritic joints.

    PubMed

    Camerlain, M; McCarty, D J; Silcox, D C; Jung, A

    1975-06-01

    Recent studies have shown elevated inorganic pyrophosphate (PPi) levels in most knee joint fluid supernates from patients with pseudogout (PG) or osteoarthritis (OA) and more modestly elevated levels in some supernates from patients with gout or rheumatoid arthritis (RA) relative to PPi levels found in the venous blood plasma of normal or arthritic subjects. We measured the intraarticular PPi pool and its rate of turnover to better understand the significance of the joint fluid-plasma PPi gradient. Preliminary studies in rabbits showed that (32-P)PPi passed from joint space to blood and vice versa without detectable hydrolysis. Incubation of natural or synthetic calcium pyrophosphate dihydrate (CPPD) microcrystals with synovial fluid in vitro in the presence of (32P)PPi tracer showed no change in PPi specific activity in the supernate over a 19-h period so that exchange of PPi in solution with that in CPPD microcrystals could be ignored. Clearance rates of (32P)PPi and of (33P)Pi, as determined by serially sampling the catheterized knee joints of volunteers with various types of arthritis over a 3-h period, were nearly identical. The (32P)PPi/(32P)Pi was determined in each sample. A mixture of a large excess of cold PPi did not influence the clearance rate of either nuclide. The quantity of PPi turned over per hous was calculated from the pool size as determined by isotope dilution and the turnover rate. The residual joint fluid nuclide was shown to be (32P)PPi. The PPi pool was generally smaller and the rate of turnover was greater in clinically inflamed joints. The mean plus or minus SEM pool size (mu-moles) and turnover rate (percent/hour) in PG knees was 0.23 plus or minus 0.07 and 117 plus or minus 11.9, hydrolysis rate (%/h) to Pi was 27.7 plus or minus 13.2; in OA knees: 0.45 plus or minus 0.26 and 72 plus or minus 9.2, hydrolysis 6.9 plus or minus 0.9; in gouty knees: 0.8 plus or minus 0.41 and 50 plus or minus 11.6, hydrolysis 9.8 plus or minus 2.8; and in

  17. Factors influencing the rate of job turnover among hospital pharmacists.

    PubMed

    Smith, S N; Stewart, J E; Grussing, P G

    1986-08-01

    Factors influencing the rate of job turnover among hospital pharmacists were studied. In June 1982, pharmacists and pharmacy directors in acute-care hospitals in the Chicago area with more than 100 beds were asked both open-ended and multiple-choice questions pertaining to reasons for accepting and staying at current jobs, reasons for leaving previous and possibly current jobs, career goals, and demographic data. From the sample of 529 pharmacists, 217 (41%) usable responses were received. Pharmacy directors' responses indicated that the turnover rate for pharmacists was 14.4% and that relocation and layoffs or job termination were the most common reasons for job turnover. Overall, pharmacists' pay and benefits and opportunity for promotion or advancement were the reasons pharmacists cited most frequently both for leaving a job and for staying at a job. Men ranked pay and benefits as the most important reason for taking and staying at a position and for leaving, whereas women cited hospital location as the most important reason for taking, staying at, or leaving a job. Other factors cited as important were working hours, professional challenge, job duties, and continuation of education. Pharmacists who had been in the current job for more than two years were less likely to leave. Pregnancy of the employee or spouse was not a strong reason for leaving, and relocation was a more important reason for women than for men. Approximately half the respondents indicated they had a career goal; promotion to management and continuation of education were the goals most frequently mentioned. Regional or national studies should be conducted to gain further understanding of why pharmacists accept, remain in, and change jobs. PMID:3752133

  18. Enhancer regions show high histone H3.3 turnover that changes during differentiation

    PubMed Central

    Deaton, Aimee M; Gómez-Rodríguez, Mariluz; Mieczkowski, Jakub; Tolstorukov, Michael Y; Kundu, Sharmistha; Sadreyev, Ruslan I; Jansen, Lars ET; Kingston, Robert E

    2016-01-01

    The organization of DNA into chromatin is dynamic; nucleosomes are frequently displaced to facilitate the ability of regulatory proteins to access specific DNA elements. To gain insight into nucleosome dynamics, and to follow how dynamics change during differentiation, we used a technique called time-ChIP to quantitatively assess histone H3.3 turnover genome-wide during differentiation of mouse ESCs. We found that, without prior assumptions, high turnover could be used to identify regions involved in gene regulation. High turnover was seen at enhancers, as observed previously, with particularly high turnover at super-enhancers. In contrast, regions associated with the repressive Polycomb-Group showed low turnover in ESCs. Turnover correlated with DNA accessibility. Upon differentiation, numerous changes in H3.3 turnover rates were observed, the majority of which occurred at enhancers. Thus, time-ChIP measurement of histone turnover shows that active enhancers are unusually dynamic in ESCs and changes in highly dynamic nucleosomes predominate at enhancers during differentiation. DOI: http://dx.doi.org/10.7554/eLife.15316.001 PMID:27304074

  19. Hibernation, stress, intestinal functions, and catecholoamine turnover rate in hamsters and gerbils

    NASA Technical Reports Server (NTRS)

    Musacchia, X. J.

    1973-01-01

    Bioenergetic studies on hamsters during depressed metabolic states are reported. External support of blood glucose extended the survival times of hibernating animals. Radioresistance increased in hibernating as well as in hypothermic hamsters. Marked changes in hamster catecholamine turnover rates were observed during acclimatization to high temperature stress. High radioresistance levels of the gerbil gastrointestinal system were attributed in part to the ability of the gut to maintain functional integrity.

  20. Uptake, distribution, and turnover rates of selenium in barley.

    PubMed

    Huang, K X; Clausen, J

    1994-03-01

    The present communication elucidates initially the topographic distribution of selenium in barley grains. Then by the fluorimetric method the uptake of selenium (selenite) in 8-16 d old germinating barley was estimated. Finally by means of 75Se the anabolic and catabolic rates (turnover) of 75Se (selenite) was compared. The distribution of selenium in barley was evaluated after micro-dissection of barley grains. In dried grains the highest concentration was found in husk and pericarp with about 0.6 ppm Se. Then followed Scutellum with 0.4 and 0.3 ppm in embryon. The aleurone layer, embryonic leaves, and initial root did only have 0.2 ppm Se. In order to know more about the uptake and distribution of selenium in 8-d-old barley, the plants were cultivated for a further 8 d in the culture medium with variation in selenite concentration. In roots and leaves, the uptake did not arrive at saturation during the period studied since the dose-response curve increased up to 0.34 mM selenite in the medium, whereas the selenium levels were about 200 ppm in roots and 30 ppm in leaves. However, the uptake was linear, with concentration during 8 d of cultivation up to 0.84 microM selenite for grain and stem. At higher concentrations the dose-response curve diminished its slope. At 0.34 mM selenite the concentration in grain increased to 6.87 ppm and in the stem to 8.13 ppm. The uptake, distribution, and catabolic rate of selenium components in germinating barley were further evaluated by exposing the plants to 0.0492 microCi 75Se (12.6 microM selenite) for up to 4 d. Then the plants were moved to a selenium deficient medium for further 4 d. Then finally the medium was supplemented with high doses of cold selenite (0.126 mM selenite) for further 4 d. The first third period made it possible to estimate the rate of uptake. It was highest in roots (313 fmol/h/mg dw), i.e., about 10 times those of grains, stems, and leaves. The intermediate period where the barley was transferred to a

  1. Acetate in recent anoxic sediments: Direct and indirect measurements of concentration and turnover rates

    NASA Astrophysics Data System (ADS)

    Shaw, David G.; McIntosh, Douglas J.

    1990-12-01

    While acetate is generally regarded as an important intermediate in the mineralization of organic matter in anoxic sediment systems, some quantitative studies in marine systems (including our own) have measured acetate oxidation rates in excess of sulphate reduction rates where sulphate is known to be the principal electron acceptor. We revisited Skan Bay, Alaska, where we had previously made such observations, for a reexamination of acetate turnover. Measurements of acetate concentrations, production rate, oxidation rate and sulphate reduction rate as well as bioenergetic considerations led to the conclusion that acetate oxidation rate in 15-18-cm deep sediment is 1·1-1·5 μM h -1. The possibility that previous measurements were high because of a non-citric-acid-cycle pathway of acetate oxidation (suggested by recent laboratory studies) was excluded. It appears that our previous turnover measurements were high mainly because of high acetate concentrations. Procedures used for the isolation of porewater for acetate determination may influence results to an extent not previously recognized.

  2. Tissue Turnover Rates and Isotopic Trophic Discrimination Factors in the Endothermic Teleost, Pacific Bluefin Tuna (Thunnus orientalis)

    PubMed Central

    Madigan, Daniel J.; Litvin, Steven Y.; Popp, Brian N.; Carlisle, Aaron B.; Farwell, Charles J.; Block, Barbara A.

    2012-01-01

    Stable isotope analysis (SIA) of highly migratory marine pelagic animals can improve understanding of their migratory patterns and trophic ecology. However, accurate interpretation of isotopic analyses relies on knowledge of isotope turnover rates and tissue-diet isotope discrimination factors. Laboratory-derived turnover rates and discrimination factors have been difficult to obtain due to the challenges of maintaining these species in captivity. We conducted a study to determine tissue- (white muscle and liver) and isotope- (nitrogen and carbon) specific turnover rates and trophic discrimination factors (TDFs) using archived tissues from captive Pacific bluefin tuna (PBFT), Thunnus orientalis, 1–2914 days after a diet shift in captivity. Half-life values for 15N turnover in white muscle and liver were 167 and 86 days, and for 13C were 255 and 162 days, respectively. TDFs for white muscle and liver were 1.9 and 1.1‰ for δ15N and 1.8 and 1.2‰ for δ13C, respectively. Our results demonstrate that turnover of 15N and 13C in bluefin tuna tissues is well described by a single compartment first-order kinetics model. We report variability in turnover rates between tissue types and their isotope dynamics, and hypothesize that metabolic processes play a large role in turnover of nitrogen and carbon in PBFT white muscle and liver tissues. 15N in white muscle tissue showed the most predictable change with diet over time, suggesting that white muscle δ15N data may provide the most reliable inferences for diet and migration studies using stable isotopes in wild fish. These results allow more accurate interpretation of field data and dramatically improve our ability to use stable isotope data from wild tunas to better understand their migration patterns and trophic ecology. PMID:23145128

  3. Tissue turnover rates and isotopic trophic discrimination factors in the endothermic teleost, pacific bluefin tuna (Thunnus orientalis).

    PubMed

    Madigan, Daniel J; Litvin, Steven Y; Popp, Brian N; Carlisle, Aaron B; Farwell, Charles J; Block, Barbara A

    2012-01-01

    Stable isotope analysis (SIA) of highly migratory marine pelagic animals can improve understanding of their migratory patterns and trophic ecology. However, accurate interpretation of isotopic analyses relies on knowledge of isotope turnover rates and tissue-diet isotope discrimination factors. Laboratory-derived turnover rates and discrimination factors have been difficult to obtain due to the challenges of maintaining these species in captivity. We conducted a study to determine tissue- (white muscle and liver) and isotope- (nitrogen and carbon) specific turnover rates and trophic discrimination factors (TDFs) using archived tissues from captive Pacific bluefin tuna (PBFT), Thunnus orientalis, 1-2914 days after a diet shift in captivity. Half-life values for (15)N turnover in white muscle and liver were 167 and 86 days, and for (13)C were 255 and 162 days, respectively. TDFs for white muscle and liver were 1.9 and 1.1‰ for δ(15)N and 1.8 and 1.2‰ for δ(13)C, respectively. Our results demonstrate that turnover of (15)N and (13)C in bluefin tuna tissues is well described by a single compartment first-order kinetics model. We report variability in turnover rates between tissue types and their isotope dynamics, and hypothesize that metabolic processes play a large role in turnover of nitrogen and carbon in PBFT white muscle and liver tissues. (15)N in white muscle tissue showed the most predictable change with diet over time, suggesting that white muscle δ(15)N data may provide the most reliable inferences for diet and migration studies using stable isotopes in wild fish. These results allow more accurate interpretation of field data and dramatically improve our ability to use stable isotope data from wild tunas to better understand their migration patterns and trophic ecology. PMID:23145128

  4. Support Effects on Bronsted acid site densities and alcohol dehydration turnover rates on tungsten oxide domains

    SciTech Connect

    Macht, Josef; Baertsch, Chelsey D.; May-Lozano, Marcos; Soled, Stuart L.; Wang, Yong; Iglesia, Enrique

    2005-03-01

    Initial activity and acid site density of several WAl, WSi (MCM41) and one WSn sample were determined. Trans/cis 2-butene selectivity is dependent on the support. Presumably, these differences are due to subtle differences in base strengths. 2-Butanol dehydration rates (per W-atom) reached maximum values at intermediate WOx surface densities on WAl, as reported for 2-butanol dehydration reactions on WZr. Titration results indicate that Bronsted acid sites are required for 2-butanol dehydration on WAl, WSi and WSn. UV-visible studies suggest that WAl is much more difficult to reduce than WZr. The detection of reduced centers on WAl, the number of which correlates to Bronsted acid site density and catalyst activity, as well as the temperature dependence of Bronsted acid site density indicate the in-situ formation of these active sites. We infer that this mechanism is common among all supported WOx samples described in this study. Turnover rates are a function of Bronsted acid site density only. High acid site densities lead to high turnover rates. Higher active site densities may cause stronger conjugate bases, as a higher electron density has to be stabilized, and thus weaker acidity, enabling a faster rate of product desorption. The maximum achievable active site density is dependent on the support. WZr reaches a higher active site density than WAl.

  5. High Classroom Turnover: How Children Get Left Behind.

    ERIC Educational Resources Information Center

    Hartman, Chester

    This book chapter discusses the problem of transiency, or high classroom turnover, in education. Research shows that a disproportionate number of schools with predominantly low-income African American and Hispanic students have low stability, and that such students are much more likely than white, middle-income students to switch schools in the…

  6. Local extinction and turnover rates at the edge and interior of species' ranges

    USGS Publications Warehouse

    Doherty, P.F., Jr.; Boulinier, T.; Nichols, J.D.

    2003-01-01

    One hypothesis for the maintenance of the edge of a species' range suggests that more central (and abundant) populations are relatively stable and edge populations are less stable with increased local extinction and turnover rates. To date, estimates of such metrics are equivocal due to design and analysis flaws. Apparent increased estimates of extinction and turnover rates at the edge of range, versus the interior, could be a function of decreased detection probabilities alone, and not of a biological process. We estimated extinction and turnover rates for species at the interiors and edges of their ranges using an approach which incorporates potential heterogeneity in species detection probabilities. Extinction rates were higher at the edges (0.17 ' 0.03 [SE]) than in the interiors (0.04 ' 0.01), as was turnover. Without taking the probability of detection into account these differences would be artificially magnified. Knowledge of extinction and turnover rates is essential in furthering our understanding of range dynamics, and in directing conservation efforts. This study further illustrates the practical application of methods proposed recently for estimating extinction rates and other community dynamic parameters.

  7. Local extinction and turnover rates at the edge and interior of species' ranges

    USGS Publications Warehouse

    Doherty, P.F., Jr.; Boulinier, T.; James., D., Nichols

    2003-01-01

    One hypothesis for the maintenance of the edge of a species' range suggests that more central (and abundant) populations are relatively stable and edge populations are less stable with increased local extinction and turnover rates. To date, estimates of such metrics are equivocal due to design and analysis flaws. Apparent increased estimates of extinction and turnover rates at the edge of range, versus the interior, could be a function of decreased detection probabilities alone, and not of a biological process. We estimated extinction and turnover rates for species at the interiors and edges of their ranges using an approach which incorporates potential heterogeneity in species detection probabilities. Extinction rates were higher at the edges (0.17 ?? 0.03 []) than in the interiors (0.04 ?? 0.01), as was turnover. Without taking the probability of detection into account these differences would be artificially magnified. Knowledge of extinction and turnover rates is essential in furthering our understanding of range dynamics, and in directing conservation efforts. This study further illustrates the practical application of methods proposed recently for estimating extinction rates and other community dynamic parameters.

  8. Blind Spots: Small Rural Communities and High Turnover in the Superintendency

    ERIC Educational Resources Information Center

    Kamrath, Barry; Brunner, C. Cryss

    2014-01-01

    This article examines high superintendency turnover through rural community members' perceptions of such attrition in their districts. Findings indicate that community members perceived high turnover as negative and believed that turnover was created by financial pressures, rural community resistance to educational trends, and bias against…

  9. Sources of variation in extinction rates, turnover, and diversity of marine invertebrate families during the Paleozoic

    USGS Publications Warehouse

    Nichols, J.D.; Morris, R.W.; Brownie, C.; Pollock, K.H.

    1986-01-01

    The authors present a new method that can be used to estimate taxonomic turnover in conjunction with stratigraphic range data for families in five phyla of Paleozoic marine invertebrates. Encounter probabilities varied among taxa and showed evidence of a decrease over time for the geologic series examined. The number of families varied substantially among the five phyla and showed some evidence of an increase over the series examined. There was no evidence of variation in extinction probabilities among the phyla. Although there was evidence of temporal variation in extinction probabilities within phyla, there was no evidence of a linear decrease in extinction probabilities over time, as has been reported by others. The authors did find evidence of high extinction probabilities for the two intervals that had been identified by others as periods of mass extinction. They found no evidence of variation in turnover among the five phyla. There was evidence of temporal variation in turnover, with greater turnover occurring in the older series.

  10. Proteome Scale-Protein Turnover Analysis Using High Resolution Mass Spectrometric Data from Stable-Isotope Labeled Plants.

    PubMed

    Fan, Kai-Ting; Rendahl, Aaron K; Chen, Wen-Ping; Freund, Dana M; Gray, William M; Cohen, Jerry D; Hegeman, Adrian D

    2016-03-01

    Protein turnover is an important aspect of the regulation of cellular processes for organisms when responding to developmental or environmental cues. The measurement of protein turnover in plants, in contrast to that of rapidly growing unicellular organismal cultures, is made more complicated by the high degree of amino acid recycling, resulting in significant transient isotope incorporation distributions that must be dealt with computationally for high throughput analysis to be practical. An algorithm in R, ProteinTurnover, was developed to calculate protein turnover with transient stable isotope incorporation distributions in a high throughput automated manner using high resolution MS and MS/MS proteomic analysis of stable isotopically labeled plant material. ProteinTurnover extracts isotopic distribution information from raw MS data for peptides identified by MS/MS from data sets of either isotopic label dilution or incorporation experiments. Variable isotopic incorporation distributions were modeled using binomial and beta-binomial distributions to deconvolute the natural abundance, newly synthesized/partial-labeled, and fully labeled peptide distributions. Maximum likelihood estimation was performed to calculate the distribution abundance proportion of old and newly synthesized peptides. The half-life or turnover rate of each peptide was calculated from changes in the distribution abundance proportions using nonlinear regression. We applied ProteinTurnover to obtain half-lives of proteins from enriched soluble and membrane fractions from Arabidopsis roots. PMID:26824330

  11. Turnover Rates of Hepatic Collagen and Circulating Collagen-Associated Proteins in Humans with Chronic Liver Disease

    PubMed Central

    Li, Kelvin; Gatmaitan, Michelle; Luo, Flora; Cattin, Jerome; Nakamura, Corelle; Holmes, William E.; Angel, Thomas E.; Peters, Marion G.; Turner, Scott M.; Hellerstein, Marc K.

    2015-01-01

    Accumulation and degradation of scar tissue in fibrotic liver disease occur slowly, typically over many years. Direct measurement of fibrogenesis, the rate of scar tissue deposition, may provide valuable therapeutic and prognostic information. We describe here results from a pilot study utilizing in vivo metabolic labeling to measure the turnover rate of hepatic collagen and collagen-associated proteins in plasma for the first time in human subjects. Eight subjects with chronic liver disease were labeled with daily oral doses of 2H2O for up to 8 weeks prior to diagnostic liver biopsy and plasma collection. Tandem mass spectrometry was used to measure the abundance and fractional synthesis rate (FSR) of proteins in liver and blood. Relative protein abundance and FSR data in liver revealed marked differences among subjects. FSRs of hepatic type I and III collagen ranged from 0.2–0.6% per day (half-lives of 4 months to a year) and correlated significantly with worsening histologic fibrosis. Analysis of plasma protein turnover revealed two collagen-associated proteins, lumican and transforming growth factor beta-induced-protein (TGFBI), exhibiting FSRs that correlated significantly with FSRs of hepatic collagen. In summary, this is the first direct measurement of liver collagen turnover in vivo in humans and suggests a high rate of collagen remodeling in advanced fibrosis. In addition, the FSRs of collagen-associated proteins in plasma are measurable and may provide a novel strategy for monitoring hepatic fibrogenesis rates. PMID:25909381

  12. Estimating soil turnover rate from tree uprooting during hurricanes in Puerto Rico

    USGS Publications Warehouse

    Lenart, M.T.; Falk, D.A.; Scatena, F.N.; Osterkamp, W.R.

    2010-01-01

    Soil turnover by tree uprooting in primary and secondary forests on the island of Puerto Rico was measured in 42 study plots in the months immediately after the passage of a Category 3 hurricane. Trunk basal area explained 61% of the variability of mound volume and 53% of the variability of mound area. The proportion of uprooted trees, the number of uprooted trees, or the proportion of uprooted basal area explained 84-85% of the variation in hurricane-created mound area. These same variables explain 79-85% of the variation in mound volume. The study indicates that the soil turnover period from tree uprooting by Puerto Rican hurricanes is between 1600 and 4800 years. These rates are faster than soil turnover by landslides and background treefall in the same area and provide a useful age constraint on soil profile development and soil carbon sequestration in these dynamic landscapes. ?? 2009 Elsevier B.V.

  13. Metabolic turnover rates of carbon and nitrogen stable isotopes in captive juvenile snakes.

    PubMed

    Fisk, Aaron T; Sash, Kim; Maerz, John; Palmer, William; Carroll, John P; Macneil, M Aaron

    2009-01-01

    Metabolic turnover rates (m) of delta(15)N and delta(13)C were assessed in different tissues of newly hatched captive-raised corn snakes (Elaphe guttata guttata) fed maintenance diets consisting of earthworms (Eisenia foetida) that varied substantially in delta(15)N (by 644 per thousand) and delta(13)C (by 5.0 per thousand). Three treatments were used during this 144 day experiment that consisted of the same diet throughout (control), shifting from a depleted to an enriched stable isotope signature diet (uptake), and shifting from an enriched to depleted stable isotope signature diet (elimination). Values of delta(13)C in the liver, blood, and muscle of the control snakes reached equilibrium with and were, respectively, 1.73, 2.25 and 2.29 greater than in their diet, this increase is called an isotopic discrimination factor (Deltadelta(13)C = delta(13)C(snake) - delta(13)C(food)). Values of delta(15)N in snake tissues did not achieve equilibrium with the diets in any of the exposures and thus Delta(15)N could not be estimated. Values of metabolic turnover rates (m) for delta(13)C and delta(15)N were greater in liver than in muscle and blood, which were similar, and relative results remained the same if the fraction of (15)N and (13)C were modeled. Although caution is warranted because equilibrium values of stable isotopes in the snakes were not achieved, values of m were greater for delta(13)C than delta(15)N, resulting in shorter times to dietary equilibrium for delta(13)C upon a diet shift, and for both stable isotopes in all tissues, greater during an elimination than in an uptake shift in diet stable isotope signature. Multiple explanations for the observed differences between uptake and elimination shifts raise new questions about the relationship between animal and diet stable isotope concentrations. Based on this study, interpretation of feeding ecology using stable isotopes is highly dependent on the kind of stable isotope, tissue, direction of diet switch

  14. The effect of the social organization of work on the voluntary turnover rate of hospital nurses in the United States.

    PubMed

    Bloom, J R; Alexander, J A; Nuchols, B A

    1992-06-01

    In light of current concerns over nursing shortages and productivity, voluntary turnover among hospital nurses in the United States has assumed renewed importance as a managerial issue. This study examines the thesis that the social organization of work in hospitals is an important determinant of the voluntary turnover rate among registered nurses. This perspective differs from previous work in this area in that both turnover and its determinants are conceptualized at the organizational rather than individual level, thus opening the way for administrative intervention to reduce turnover. The conceptual model is tested using multiple regression techniques on a sample of 435 hospitals. Results suggest that organizational characteristics and environmental conditions are important contributors to turnover. Organizational characteristics are stronger predictors of turnover than are economic factors. PMID:1529379

  15. Massive turnover rates of fine root detrital carbon in tropical Australian mangroves.

    PubMed

    Robertson, Alistar I; Alongi, Daniel M

    2016-03-01

    Dead fine roots are the major component of organic carbon (C) stored in mangrove forests. We measured the mass and decomposition of fine root detritus in three mangrove forests along an intertidal gradient in tropical Australia to provide the first integrated estimates of the rate of turnover of fine root detritus. The grand mean dry masses of dead fine roots in the forests decreased in the order mid-intertidal Rhizophora (mean 28.4 kg m(-2)), low-intertidal Rhizophora (16.3 kg m(-2)) and high-intertidal Ceriops (mean 8.9 kg m(-2)), and were some of the highest on record. The first-order decay coefficients (day(-1)) for dead fine roots in the low Rhizophora, mid Rhizophora and high Ceriops forest sites were 0.0014, 0.0017 and 0.0007, respectively, and were the lowest on record. The estimated mean fluxes of C via decomposition of dead fine roots were very high in all forests, decreasing in the order mid Rhizophora (18.8 g C m(-2) day(-1)), low Rhizophora (8.4 g C m(-2) day(-1)) and high Ceriops (2.5 g C m(-2) day(-1)). There were relatively low levels of uncertainty in these estimates when all sources of error were considered. The fluxes of C for the two Rhizophora sites integrate all losses from saprophytic decay and leaching of dissolved C and were 50-200 % higher than the estimated total annual loss of C derived by summing rates of bacterial metabolism and export via groundwater and surface waters in these forests. The significant difference reflects both the very high dead root masses and the incorporation of the impact of fungi in our estimates. PMID:26581419

  16. Changes in turnover and vacancy rates of care workers in England from 2008 to 2010: panel analysis of national workforce data.

    PubMed

    Hussein, Shereen; Ismail, Mohamed; Manthorpe, Jill

    2016-09-01

    The combination of growing demand for long-term care and higher expectations of care staff needs to be set in the context of long-standing concerns about the sustainability of recruitment and retention of front-line staff in the United Kingdom. Organisational and work environment factors are associated with vacancy levels and turnover rates. The aim of the current analysis was to investigate changes in turnover and vacancy rates over time experienced by a sample of social care employers in England. Taking a follow-up approach offers potentially more accurate estimates of changes in turnover and vacancy rates, and enables the identification of any different organisational characteristics which may be linked to reductions in these elements over time. The study constructed a panel of 2964 care providers (employers) using 18 separate data sets from the National Minimum Data Set for Social Care during 2008-2010. The findings indicate slight reductions in vacancy rates but the presence of enduring, high turnover rates among direct care workers over the study period. However, the experience of individual employers varied, with home-care providers experiencing significantly higher turnover rates than other parts of the sector. These findings raise questions around the quality and motivations of new recruits and methods of reducing specific vacancy levels. At a time of increased emphasis on care at home, it is worthwhile examining why care homes appear to have greater stability of staff and fewer vacancies than home-care agencies. PMID:25736156

  17. Campanian to Maastrichtian pollen biostratigraphy and floral turnover rates, Colville River region, north slope of Alaska

    SciTech Connect

    Frederiksen, N.O.; Schindler, K.S.

    1987-05-01

    This study is based on occurrence data for 104 angiosperm pollen taxa from 83 pollen-bearing outcrop and core samples taken along the Colville River and stratigraphically distributed from the base of the Sentinel Hill Member of the Schrader Bluff Formation to the top of the Cretaceous section. Many of the pollen taxa are highly useful for intraregional correlations because they have remarkably short stratigraphic ranges and are consistently present within these ranges. Important similarities are present between North Slope pollen assemblages and those of western Canada, Siberia, and China. The Campanian-Maastrichtian boundary is approximately marked by the range bases of Wodehouseia edmontonicola and Senipites drummhellerensis and is nearly as far south (downsection) as Sentinel Hill core test 1. Based on pollen correlations with Alberta, the marine beds at Ocean Point are probably within the middle part of the Maastrichtian, and strata north of Ocean Point that contain Aquilapollenites conatus are uppermost Maastrichtian. Thus, if the Cretaceous-Tertiary boundary in the study area is represented by an unconformity as their data suggest, the lowermost Paleocene is missing, not the uppermost Cretaceous. Maximum diversities of species of the stratigraphically significant Triprojectacites and Expressipollis groups are in the upper Campanian. Major turnovers of angiosperm taxa occurred late in the Campanian and in the Maastrichtian, but high rates of first appearances coincided with high rates of last appearances. Thus, once a fairly high overall angiosperm diversity was established in the middle(.) Campanian, the diversity remained relatively constant until at or near the end of the Maastrichtian.

  18. Turnover rate of cerebrospinal fluid in female sheep: changes related to different light-dark cycles

    PubMed Central

    Thiéry, Jean-Claude; Lomet, Didier; Bougoin, Sylvain; Malpaux, Benoit

    2009-01-01

    Background Sheep are seasonal breeders. The key factor governing seasonal changes in the reproductive activity of the ewe is increased negative feedback of estradiol at the level of the hypothalamus under long-day conditions. It has previously been demonstrated that when gonadotropin secretions are inhibited during long days, there is a higher concentration of estradiol in the cerebrospinal fluid (CSF) than during short days. This suggests an involvement of the CSF and choroid plexus in the neuroendocrine regulatory loop, but the mechanisms underlying this phenomenon remain unknown. One possible explanation of this difference in hormonal content is an effect of concentration or dilution caused by variations in CSF secretion rate. The aim of this study was thus to investigate changes in the CSF turnover rate related to light-dark cycles. Methods The turnover rate of the CSF was estimated by measuring the time taken for the recovery of intraventricular pressure (IVP) after removal of a moderate volume (0.5 to 2 ml) of CSF (slope in mmHg/min). The turnover rate was estimated three times in the same group of sheep: during a natural period of decreasing day-length corresponding to the initial period when gonadotropin activity is stimulated (SG1), during a long-day inhibitory period (IG), and finally during a short-day stimulatory period (SG2). Results The time taken and the speed of recovery of initial IVP differed between groups: 8 min 30 sec, 0.63 ± 0.07 mmHg/min(SG1), 11 min 1 sec, 0.38 ± 0.06 mmHg/min (IG) and 9 min 0 sec, 0.72 ± 0.15 mmHg/min (SG2). Time changes of IVP differed between groups (ANOVA, p < 0.005, SG1 different from IG, p < 0.05). The turnover rate in SG2: 183.16 ± 23.82 μl/min was not significantly different from SG1: 169. 23 ± 51.58 μl/min (Mann-Whitney test, p = 0.41), but was significantly different from IG: 71.33 ± 16.59 μl/min (p = 0.016). Conclusion This study shows that the turnover rate of CSF in ewes changes according to the light

  19. Spectroelectrochemical investigation of intramolecular and interfacial electron-transfer rates reveals differences between nitrite reductase at rest and during turnover.

    PubMed

    Krzemiński, Łukasz; Ndamba, Lionel; Canters, Gerard W; Aartsma, Thijs J; Evans, Stephen D; Jeuken, Lars J C

    2011-09-28

    A combined fluorescence and electrochemical method is described that is used to simultaneously monitor the type-1 copper oxidation state and the nitrite turnover rate of a nitrite reductase (NiR) from Alcaligenes faecalis S-6. The catalytic activity of NiR is measured electrochemically by exploiting a direct electron transfer to fluorescently labeled enzyme molecules immobilized on modified gold electrodes, whereas the redox state of the type-1 copper site is determined from fluorescence intensity changes caused by Förster resonance energy transfer (FRET) between a fluorophore attached to NiR and its type-1 copper site. The homotrimeric structure of the enzyme is reflected in heterogeneous interfacial electron-transfer kinetics with two monomers having a 25-fold slower kinetics than the third monomer. The intramolecular electron-transfer rate between the type-1 and type-2 copper site changes at high nitrite concentration (≥520 μM), resulting in an inhibition effect at low pH and a catalytic gain in enzyme activity at high pH. We propose that the intramolecular rate is significantly reduced in turnover conditions compared to the enzyme at rest, with an exception at low pH/nitrite conditions. This effect is attributed to slower reduction rate of type-2 copper center due to a rate-limiting protonation step of residues in the enzyme's active site, gating the intramolecular electron transfer. PMID:21863850

  20. Unit-level voluntary turnover rates and customer service quality: implications of group cohesiveness, newcomer concentration, and size.

    PubMed

    Hausknecht, John P; Trevor, Charlie O; Howard, Michael J

    2009-07-01

    Despite substantial growth in the service industry and emerging work on turnover consequences, little research examines how unit-level turnover rates affect essential customer-related outcomes. The authors propose an operational disruption framework to explain why voluntary turnover impairs customers' service quality perceptions. On the basis of a sample of 75 work units and data from 5,631 employee surveys, 59,602 customer surveys, and organizational records, results indicate that unit-level voluntary turnover rates are negatively related to service quality perceptions. The authors also examine potential boundary conditions related to the disruption framework. Of 3 moderators studied (group cohesiveness, group size, and newcomer concentration), results show that turnover's negative effects on service quality are more pronounced in larger units and in those with a greater concentration of newcomers. PMID:19594245

  1. Large-scale variation in boreal and temperate forest carbon turnover rate related to climate

    NASA Astrophysics Data System (ADS)

    Thurner, Martin; Beer, Christian; Carvalhais, Nuno; Forkel, Matthias; Santoro, Maurizio; Tum, Markus; Schmullius, Christiane

    2016-05-01

    Vegetation carbon turnover processes in forest ecosystems and their dominant drivers are far from being understood at a broader scale. Many of these turnover processes act on long timescales and include a lateral dimension and thus can hardly be investigated by plot-level studies alone. Making use of remote sensing-based products of net primary production (NPP) and biomass, here we show that spatial gradients of carbon turnover rate (k) in Northern Hemisphere boreal and temperate forests are explained by different climate-related processes depending on the ecosystem. k is related to frost damage effects and the trade-off between growth and frost adaptation in boreal forests, while drought stress and climate effects on insects and pathogens can explain an elevated k in temperate forests. By identifying relevant processes underlying broadscale patterns in k, we provide the basis for a detailed exploration of these mechanisms in field studies, and ultimately the improvement of their representations in global vegetation models (GVMs).

  2. Predicting rates of isotopic turnover across the animal kingdom: a synthesis of existing data.

    PubMed

    Thomas, Stephen M; Crowther, Thomas W

    2015-05-01

    The stable isotopes of carbon ((12)C, (13)C) and nitrogen ((14)N, (15)N) represent powerful tools in food web ecology, providing a wide range of dietary information in animal consumers. However, identifying the temporal window over which a consumer's isotopic signature reflects its diet requires an understanding of elemental incorporation, a process that varies from days to years across species and tissue types. Though theory predicts body size and temperature are likely to control incorporation rates, this has not been tested empirically across a morphologically and phylogenetically diverse range of taxa. Readily available estimates of this relationship would, however, aid in the design of stable isotope food web investigations and improve the interpretation of isotopic data collected from natural systems. Using literature-derived turnover estimates from animal species ranging in size from 1 mg to 2000 kg, we develop a predictive tool for stable isotope ecologists, allowing for estimation of incorporation rates in the structural tissues of entirely novel taxa. In keeping with metabolic scaling theory, we show that isotopic turnover rates of carbon and nitrogen in whole organisms and muscle tissue scale allometrically with body mass raised approximately to the power -0.19, an effect modulated by body temperature. This relationship did not, however, apply to incorporation rates in splanchnic tissues, which were instead dependent on the thermoregulation tactic employed by an organism, being considerably faster in endotherms than ectotherms. We believe the predictive turnover equations we provide can improve the design of experiments and interpretation of results obtained in future stable isotopic food web studies. PMID:25482029

  3. Effect of dietary protein and iron on the fractional turnover rate of rat liver xanthine oxidase

    SciTech Connect

    Cherry, D.M.; Amy, N.K.

    1987-12-01

    Rat liver xanthine oxidase activity is regulated in response to dietary protein and iron. To investigate whether the change in activity was mediated by a change in the rate of protein degradation, we measured the fractional turnover rate using the double-isotope technique with (/sup 3/H)- and (/sup 14/C)leucine and calculated the apparent half-life of xanthine oxidase in rats fed diets containing either 20 or 5% casein with either 35 or 5 mg iron/kg diet. Under control conditions, xanthine oxidase had an apparent half-life of 4.8 d and approximately 65% of the enzyme subunits were active. Rats fed diets with low dietary protein had lower xanthine oxidase activity, but the enzyme had a slower fractional turnover rate, resulting in an apparent half-life of 6.4 d, and only 15-20% of the enzyme was active. The apparent half-life of xanthine oxidase increased to 7.5 d in rats fed diets with low dietary iron, but dietary iron did not affect the specific activity of the enzyme or the percentage of active subunits. These results suggest that the loss of enzyme activity is not due to loss of enzyme protein by increased degradation, but rather to inactivation of the enzyme.

  4. The High Cost of Teacher Turnover. Policy Brief

    ERIC Educational Resources Information Center

    National Commission on Teaching and America's Future, 2007

    2007-01-01

    In 2007, the National Commission on Teaching and America's Future (NCTAF) completed an 18-month study of the costs of teacher turnover in five school districts. The selected districts varied in size, location, and demographics enabling exploration of how these variations affected costs. Costs of recruiting, hiring, processing, and training…

  5. A Ministudy of employee turnover in US hospitals.

    PubMed

    Collins, Sandra K; McKinnies, Richard C; Matthews, Eric P; Collins, Kevin S

    2015-01-01

    A ministudy was conducted to collect self-reported employee turnover rates in US hospitals. The results indicate many hospitals are struggling with high employee turnover rates. Widespread variances in ratings were observed across hospitals, which may be due to lack of consistency in how they each calculate their employee turnover. This makes benchmarking for the purposes of performance improvement challenging. PMID:25627851

  6. Estimation of water turnover rates of captive West Indian manatees (Trichechus manatus) held in fresh and salt water

    NASA Technical Reports Server (NTRS)

    Ortiz, R. M.; Worthy, G. A.; Byers, F. M.

    1999-01-01

    The ability of West Indian manatees (Trichechus manatus) to move between fresh and salt water raises the question of whether manatees drink salt water. Water turnover rates were estimated in captive West Indian manatees using the deuterium oxide dilution technique. Rates were quantified in animals using four experimental treatments: (1) held in fresh water and fed lettuce (N=4), (2) held in salt water and fed lettuce (N=2), (3) acutely exposed to salt water and fed lettuce (N=4), and (4) chronically exposed to salt water with limited access to fresh water and fed sea grass (N=5). Animals held in fresh water had the highest turnover rates (145+/-12 ml kg-1 day-1) (mean +/- s.e.m.). Animals acutely exposed to salt water decreased their turnover rate significantly when moved into salt water (from 124+/-15 to 65+/-15 ml kg-1 day-1) and subsequently increased their turnover rate upon re-entry to fresh water (146+/-19 ml kg-1 day-1). Manatees chronically exposed to salt water had significantly lower turnover rates (21+/-3 ml kg-1 day-1) compared with animals held in salt water and fed lettuce (45+/-3 ml kg-1 day-1). Manatees chronically exposed to salt water and fed sea grass had very low turnover rates compared with manatees held in salt water and fed lettuce, which is consistent with a lack of mariposia. Manatees in fresh water drank large volumes of water, which may make them susceptible to hyponatremia if access to a source of Na+ is not provided.

  7. Low brain serotonin turnover rate (low CSF 5-HIAA) and impulsive violence.

    PubMed Central

    Virkkunen, M; Goldman, D; Nielsen, D A; Linnoila, M

    1995-01-01

    The findings of a series of studies by the authors support the idea that most impulsive offenders who have a tendency to behave aggressively while intoxicated have a low brain serotonin turnover rate. The impulsive violent offenders with the lowest CSF 5-HIAA concentrations have diurnal activity rhythm disturbances, and are also prone to hypoglycemia after an oral glucose challenge. Low CSF 5-HIAA combined with hyoglycemic tendency also predicts future violence under the influence of alcohol. Sons of alcoholic fathers, who have committed violent crimes, have very low CSF 5-HIAA concentrations. Vagal tone does not correlate significantly with CSF 5-HIAA but correlates with enhanced insulin secretion, which is most prominent in subjects with intermittent explosive disorder. A polymorphism of tryptophan hydroxylase (TPH) gene is associated with low CSF 5-HIAA and a history of suicide attempts. PMID:7544158

  8. Regional processes in mangrove ecosystems: Spatial scaling relationships, biomass, and turnover rates following catastrophic disturbance

    USGS Publications Warehouse

    Ward, G.A.; Smith, T. J., III; Whelan, K.R.T.; Doyle, T.W.

    2006-01-01

    Physiological processes and local-scale structural dynamics of mangroves are relatively well studied. Regional-scale processes, however, are not as well understood. Here we provide long-term data on trends in structure and forest turnover at a large scale, following hurricane damage in mangrove ecosystems of South Florida, U.S.A. Twelve mangrove vegetation plots were monitored at periodic intervals, between October 1992 and March 2005. Mangrove forests of this region are defined by a -1.5 scaling relationship between mean stem diameter and stem density, mirroring self-thinning theory for mono-specific stands. This relationship is reflected in tree size frequency scaling exponents which, through time, have exhibited trends toward a community average that is indicative of full spatial resource utilization. These trends, together with an asymptotic standing biomass accumulation, indicate that coastal mangrove ecosystems do adhere to size-structured organizing principles as described for upland tree communities. Regenerative dynamics are different between areas inside and outside of the primary wind-path of Hurricane Andrew which occurred in 1992. Forest dynamic turnover rates, however, are steady through time. This suggests that ecological, more-so than structural factors, control forest productivity. In agreement, the relative mean rate of biomass growth exhibits an inverse relationship with the seasonal range of porewater salinities. The ecosystem average in forest scaling relationships may provide a useful investigative tool of mangrove community biomass relationships, as well as offer a robust indicator of general ecosystem health for use in mangrove forest ecosystem management and restoration. ?? Springer 2006.

  9. Carbon and nitrogen stable isotope turnover rates and diet-tissue discrimination in Florida manatees (Trichechus manatus latirostris).

    PubMed

    Alves-Stanley, Christy D; Worthy, Graham A J

    2009-08-01

    The Florida manatee (Trichechus manatus latirostris) is a herbivorous marine mammal that occupies freshwater, estuarine and marine habitats. Despite being considered endangered, relatively little is known about its feeding ecology. The present study expands on previous work on manatee feeding ecology by providing critical baseline parameters for accurate isotopic data interpretation. Stable carbon and nitrogen isotope ratios were examined over a period of more than 1 year in the epidermis of rescued Florida manatees that were transitioning from a diet of aquatic forage to terrestrial forage (lettuce). The mean half-life for (13)C turnover was 53 and 59 days for skin from manatees rescued from coastal and riverine regions, respectively. The mean half-life for (15)N turnover was 27 and 58 days, respectively. Because of these slow turnover rates, carbon and nitrogen stable isotope analysis in manatee epidermis is useful in summarizing average dietary intake over a long period of time rather than assessing recent diet. In addition to turnover rate, a diet-tissue discrimination value of 2.8 per thousand for (13)C was calculated for long-term captive manatees on a lettuce diet. Determining both turnover rate and diet-tissue discrimination is essential in order to accurately interpret stable isotope data. PMID:19617427

  10. Environmental and historical imprints on beta diversity: insights from variation in rates of species turnover along gradients

    PubMed Central

    Fitzpatrick, Matthew C.; Sanders, Nathan J.; Normand, Signe; Svenning, Jens-Christian; Ferrier, Simon; Gove, Aaron D.; Dunn, Robert R.

    2013-01-01

    A common approach for analysing geographical variation in biodiversity involves using linear models to determine the rate at which species similarity declines with geographical or environmental distance and comparing this rate among regions, taxa or communities. Implicit in this approach are weakly justified assumptions that the rate of species turnover remains constant along gradients and that this rate can therefore serve as a means to compare ecological systems. We use generalized dissimilarity modelling, a novel method that accommodates variation in rates of species turnover along gradients and between different gradients, to compare environmental and spatial controls on the floras of two regions with contrasting evolutionary and climatic histories: southwest Australia and northern Europe. We find stronger signals of climate history in the northern European flora and demonstrate that variation in rates of species turnover is persistent across regions, taxa and different gradients. Such variation may represent an important but often overlooked component of biodiversity that complicates comparisons of distance–decay relationships and underscores the importance of using methods that accommodate the curvilinear relationships expected when modelling beta diversity. Determining how rates of species turnover vary along and between gradients is relevant to understanding the sensitivity of ecological systems to environmental change. PMID:23926147

  11. Greater carbon stocks and faster turnover rates with increasing agricultural productivity

    NASA Astrophysics Data System (ADS)

    Sanderman, J.; Fallon, S.; Baisden, T. W.

    2013-12-01

    H.H. Janzen (2006) eloquently argued that from an agricultural perspective there is a tradeoff between storing carbon as soil organic matter (SOM) and the soil nutrient and energy benefit provided during SOM mineralization. Here we report on results from the Permanent Rotation Trial at the Waite Agricultural Institute, South Australia, indicating that shifting to an agricultural management strategy which returns more carbon to the soil, not only leads to greater carbon stocks but also increases the rate of carbon cycling through the soil. The Permanent Rotation Trial was established on a red Chromosol in 1925 with upgrades made to several treatments in 1948. Decadal soil samples were collected starting in 1963 at two depths, 0-10 and 10-22.5 cm, by compositing 20 soil cores taken along the length of each plot. We have chosen to analyze five trials representing a gradient in productivity: permanent pasture (Pa), wheat-pasture rotation (2W4Pa), continuous wheat (WW), wheat-oats-fallow rotation (WOF) and wheat-fallow (WF). For each of the soil samples (40 in total), the radiocarbon activity in the bulk soil as well as size-fractionated samples was measured by accelerator mass spectrometry at ANU's Radiocarbon Dating Laboratory (Fallon et al. 2010). After nearly 70 years under each rotation, SOC stocks increased linearly with productivity data across the trials from 24 to 58 tC ha-1. Importantly, these differences were due to greater losses over time in the low productivity trials rather than gains in SOC in any of the trials. Uptake of the bomb-spike in atmospheric 14C into the soil was greatest in the trials with the greatest productivity. The coarse size fraction always had greater Δ14C values than the bulk soil samples. Several different multi-pool steady state and non-steady state models were used to interpret the Δ14C data in terms of SOC turnover rates. Regardless of model choice, either the decay rates of all pools needed to increase or the allocation of C to

  12. Metabolic rate and rates of protein turnover in food-deprived cuttlefish, Sepia officinalis (Linnaeus 1758).

    PubMed

    Lamarre, Simon G; MacCormack, Tyson J; Sykes, Antonio V; Hall, Jennifer R; Speers-Roesch, Ben; Callaghan, Neal I; Driedzic, William R

    2016-06-01

    To determine the metabolic response to food deprivation, cuttlefish (Sepia officinalis) juveniles were either fed, fasted (3 to 5 days food deprivation), or starved (12 days food deprivation). Fasting resulted in a decrease in triglyceride levels in the digestive gland, and after 12 days, these lipid reserves were essentially depleted. Oxygen consumption was decreased to 53% and NH4 excretion to 36% of the fed group following 3-5 days of food deprivation. Oxygen consumption remained low in the starved group, but NH4 excretion returned to the level recorded for fed animals during starvation. The fractional rate of protein synthesis of fasting animals decreased to 25% in both mantle and gill compared with fed animals and remained low in the mantle with the onset of starvation. In gill, however, protein synthesis rate increased to a level that was 45% of the fed group during starvation. In mantle, starvation led to an increase in cathepsin A-, B-, H-, and L-like enzyme activity and a 2.3-fold increase in polyubiquitin mRNA that suggested an increase in ubiquitin-proteasome activity. In gill, there was a transient increase in the polyubiquitin transcript levels in the transition from fed through fasted to the starved state and cathepsin A-, B-, H-, and L-like activity was lower in starved compared with fed animals. The response in gill appears more complex, as they better maintain rates of protein synthesis and show no evidence of enhanced protein breakdown through recognized catabolic processes. PMID:27053650

  13. Slow isotope turnover rates and low discrimination values in the American alligator: implications for interpretation of ectotherm stable isotope data.

    PubMed

    Rosenblatt, Adam E; Heithaus, Michael R

    2013-01-01

    Stable isotope analysis has become a standard ecological tool for elucidating feeding relationships of organisms and determining food web structure and connectivity. There remain important questions concerning rates at which stable isotope values are incorporated into tissues (turnover rates) and the change in isotope value between a tissue and a food source (discrimination values). These gaps in our understanding necessitate experimental studies to adequately interpret field data. Tissue turnover rates and discrimination values vary among species and have been investigated in a broad array of taxa. However, little attention has been paid to ectothermic top predators in this regard. We quantified the turnover rates and discrimination values for three tissues (scutes, red blood cells, and plasma) in American alligators (Alligator mississippiensis). Plasma turned over faster than scutes or red blood cells, but turnover rates of all three tissues were very slow in comparison to those in endothermic species. Alligator δ(15)N discrimination values were surprisingly low in comparison to those of other top predators and varied between experimental and control alligators. The variability of δ(15)N discrimination values highlights the difficulties in using δ(15)N to assign absolute and possibly even relative trophic levels in field studies. Our results suggest that interpreting stable isotope data based on parameter estimates from other species can be problematic and that large ectothermic tetrapod tissues may be characterized by unique stable isotope dynamics relative to species occupying lower trophic levels and endothermic tetrapods. PMID:23303328

  14. Serum biomarker profile associated with high bone turnover and BMD in postmenopausal women.

    PubMed

    Bhattacharyya, Sudeepa; Siegel, Eric R; Achenbach, Sara J; Khosla, Sundeep; Suva, Larry J

    2008-07-01

    Early diagnosis of the onset of osteoporosis is key to the delivery of effective therapy. Biochemical markers of bone turnover provide a means of evaluating skeletal dynamics that complements static measurements of BMD by DXA. Conventional clinical measurements of bone turnover, primarily the estimation of collagen and its breakdown products in the blood or urine, lack both sensitivity and specificity as a reliable diagnostic tool. As a result, improved tests are needed to augment the use of BMD measurements as the principle diagnostic modality. In this study, the serum proteome of 58 postmenopausal women with high or low/normal bone turnover (training set) was analyzed by surface enhanced laser-desorption/ionization time-of-flight mass spectrometry, and a diagnostic fingerprint was identified using a variety of statistical and machine learning tools. The diagnostic fingerprint was validated in a separate distinct test set, consisting of serum samples from an additional 59 postmenopausal women obtained from the same Mayo cohort, with a gap of 2 yr. Specific protein peaks that discriminate between postmenopausal patients with high or low/normal bone turnover were identified and validated. Multiple supervised learning approaches were able to classify the level of bone turnover in the training set with 80% sensitivity and 100% specificity. In addition, the individual protein peaks were also significantly correlated with BMD measurements in these patients. Four of the major discriminatory peaks in the diagnostic profile were identified as fragments of interalpha-trypsin-inhibitor heavy chain H4 precursor (ITIH4), a plasma kallikrein-sensitive glycoprotein that is a component of the host response system. These data suggest that these serum protein fragments are the serum-borne reflection of the increased osteoclast activity, leading to the increased bone turnover that is associated with decreasing BMD and presumably an increased risk of fracture. In conjunction with the

  15. Estimating rates of local species extinction, colonization and turnover in animal communities

    USGS Publications Warehouse

    Nichols, J.D.; Boulinier, T.; Hines, J.E.; Pollock, K.H.; Sauer, J.R.

    1998-01-01

    Species richness has been identified as a useful state variable for conservation and management purposes. Changes in richness over time provide a basis for predicting and evaluating community responses to management, to natural disturbance, and to changes in factors such as community composition (e.g., the removal of a keystone species). Probabilistic capture-recapture models have been used recently to estimate species richness from species count and presence-absence data. These models do not require the common assumption that all species are detected in sampling efforts. We extend this approach to the development of estimators useful for studying the vital rates responsible for changes in animal communities over time; rates of local species extinction, turnover, and colonization. Our approach to estimation is based on capture-recapture models for closed animal populations that permit heterogeneity in detection probabilities among the different species in the sampled community. We have developed a computer program, COMDYN, to compute many of these estimators and associated bootstrap variances. Analyses using data from the North American Breeding Bird Survey (BBS) suggested that the estimators performed reasonably well. We recommend estimators based on probabilistic modeling for future work on community responses to management efforts as well as on basic questions about community dynamics.

  16. Influence of beta-adrenoceptor blocking agents on the turnover rate of cardiac and splenic noradrenaline in rats.

    PubMed Central

    Alexandre, J. M.; Chevillard, C.

    1980-01-01

    1 The effects of (+) and (+/-)-propranolol, pindolol, alprenolol, practolol, acebutolol and bretylium were studied on the turnover rate of noradrenaline in heart and spleen of rats. 2 Bretylium (8 mg/kg) greatly reduced the turnover rate of noradrenaline in both organs. 3 (+)-Propranolol (4 and 10 mg/kg) also diminished the turnover rate of noradrenaline, but its effects were smaller than those of (+/-)-propranolol (4 and 10 mg/kg). 4 Pindolol (300 micrograms/kg) greatly increased the turnover rate of noradrenaline; this effect was especially important in the spleen. 5 Alprenolol (4 and 10 mg/kg) acebutolol (20 and 40 mg/kg) practolol (10 mg/kg) did not produce any significant change. 6 These effects are compatible with the view that beta-adrenoceptor blocking agents may affect noradrenaline release in different manners: anaesthetic properties of some of these drugs and blockade of beta 2 prejunctional adrenoceptors produce a diminished release of transmitter, whereas the intrinsic sympathomimetic action of pindolol causes the opposite effect. PMID:6103727

  17. Estrogen regulates the rate of bone turnover but bone balance in ovariectomized rats is modulated by prevailing mechanical strain

    NASA Technical Reports Server (NTRS)

    Westerlind, K. C.; Wronski, T. J.; Ritman, E. L.; Luo, Z. P.; An, K. N.; Bell, N. H.; Turner, R. T.

    1997-01-01

    Estrogen deficiency induced bone loss is associated with increased bone turnover in rats and humans. The respective roles of increased bone turnover and altered balance between bone formation and bone resorption in mediating estrogen deficiency-induced cancellous bone loss was investigated in ovariectomized rats. Ovariectomy resulted in increased bone turnover in the distal femur. However, cancellous bone was preferentially lost in the metaphysis, a site that normally experiences low strain energy. No bone loss was observed in the epiphysis, a site experiencing higher strain energy. The role of mechanical strain in maintaining bone balance was investigated by altering the strain history. Mechanical strain was increased and decreased in long bones of ovariectomized rats by treadmill exercise and functional unloading, respectively. Functional unloading was achieved during orbital spaceflight and following unilateral sciatic neurotomy. Increasing mechanical loading reduced bone loss in the metaphysis. In contrast, decreasing loading accentuated bone loss in the metaphysis and resulted in bone loss in the epiphysis. Finally, administration of estrogen to ovariectomized rats reduced bone loss in the unloaded and prevented loss in the loaded limb following unilateral sciatic neurotomy in part by reducing indices of bone turnover. These results suggest that estrogen regulates the rate of bone turnover, but the overall balance between bone formation and bone resorption is influenced by prevailing levels of mechanical strain.

  18. Estrogen regulates the rate of bone turnover but bone balance in ovariectomized rats is modulated by prevailing mechanical strain

    PubMed Central

    Westerlind, Kim C.; Wronski, Thomas J.; Ritman, Erik L.; Luo, Zong-Ping; An, Kai-Nan; Bell, Norman H.; Turner, Russell T.

    1997-01-01

    Estrogen deficiency induced bone loss is associated with increased bone turnover in rats and humans. The respective roles of increased bone turnover and altered balance between bone formation and bone resorption in mediating estrogen deficiency-induced cancellous bone loss was investigated in ovariectomized rats. Ovariectomy resulted in increased bone turnover in the distal femur. However, cancellous bone was preferentially lost in the metaphysis, a site that normally experiences low strain energy. No bone loss was observed in the epiphysis, a site experiencing higher strain energy. The role of mechanical strain in maintaining bone balance was investigated by altering the strain history. Mechanical strain was increased and decreased in long bones of ovariectomized rats by treadmill exercise and functional unloading, respectively. Functional unloading was achieved during orbital spaceflight and following unilateral sciatic neurotomy. Increasing mechanical loading reduced bone loss in the metaphysis. In contrast, decreasing loading accentuated bone loss in the metaphysis and resulted in bone loss in the epiphysis. Finally, administration of estrogen to ovariectomized rats reduced bone loss in the unloaded and prevented loss in the loaded limb following unilateral sciatic neurotomy in part by reducing indices of bone turnover. These results suggest that estrogen regulates the rate of bone turnover, but the overall balance between bone formation and bone resorption is influenced by prevailing levels of mechanical strain. PMID:9108129

  19. Retaining your high performers: moderators of the performance-job satisfaction-voluntary turnover relationship.

    PubMed

    Nyberg, Anthony

    2010-05-01

    Two divergent ideas explain the relationship between performance and voluntary turnover. One suggests that higher performing employees, who are rewarded for their superior work product, will desire to remain with an organization that values their performance and will, consequently, be less likely than lower performing employees to voluntarily leave. An alternative idea suggests that higher performing employees, who are more desirable to external companies as a result of their superior work product, will have more external job opportunities and will, consequently, be more likely than their lower performing colleagues to voluntarily leave. The current study evaluated the behaviors and attitudes of 12,545 insurance employees over a 3-year period to examine how these 2 divergent expectations influence the performance-voluntary turnover relationship. Results show that both pay growth and the relevant unemployment rate interact with performance to influence the performance-voluntary turnover relationship and that they work independently of employee job satisfaction influences. PMID:20476825

  20. Turn-over rate of academic faculty at the College of Health Sciences, Addis Ababa University: a 20-year analysis (1991 to 2011)

    PubMed Central

    2013-01-01

    Background Faculty turn-over affects both workers and organizations. Turnover of faculty and researchers is increasing alarmingly and costing the universities and the country at large. Fast turnover of health professionals from the health system and from academic institutions has recently received substantial attention from both academia and health sector managers. This paper calculates the faculty turnover rate at the College of Health Sciences of Addis Ababa University during the period of September 1991 to August 2011. Methods The study was conducted at the College of Health Sciences, Addis Ababa University. Retrospective analysis of employee records was done. All records of the faculty that were working in the College during the 20-year period, starting from September 1991 to August 2011 were retrospectively reviewed. Data were collected from the employee records accessed from the College’s human resources database and supplemented by payroll sheets and different reports. A structured checklist was used to extract the required data from the database. The crude turnover rate for academic faculty was calculated. Results Within the 20-year period of September 1991 to August 2011, a total of 120 faculty members left. The overall turn-over rate was 92.8 %. The rate in the most recent five years (172 %) is 8.5 times higher than the rate for the first five years (20 %). The average retention period before the termination of an employment contract was 4.9 years. The top five departments where employment contracts were relatively higher include: Nursing 15 (15.6 %), Internal Medicine 12 (12.5%), Public Health 10 (10.4%), Pediatrics 9 (9.4%) and Surgery 9 (9.4%). About two thirds (66.6%) of the faculty who were leaving were at the ranks of assistant professorship and above. Conclusion This study revealed that outflow of faculty has been continuously increasing in the period reviewed. This implies that the College had been losing highly skilled professionals with

  1. Novel oligonucleotide primers reveal a high diversity of microbes which drive phosphorous turnover in soil.

    PubMed

    Bergkemper, Fabian; Kublik, Susanne; Lang, Friederike; Krüger, Jaane; Vestergaard, Gisle; Schloter, Michael; Schulz, Stefanie

    2016-06-01

    Phosphorus (P) is of central importance for cellular life but likewise a limiting macronutrient in numerous environments. Certainly microorganisms have proven their ability to increase the phosphorus bioavailability by mineralization of organic-P and solubilization of inorganic-P. On the other hand they efficiently take up P and compete with other biota for phosphorus. However the actual microbial community that is associated to the turnover of this crucial macronutrient in different ecosystems remains largely anonymous especially taking effects of seasonality and spatial heterogeneity into account. In this study seven oligonucleotide primers are presented which target genes coding for microbial acid and alkaline phosphatases (phoN, phoD), phytases (appA), phosphonatases (phnX) as well as the quinoprotein glucose dehydrogenase (gcd) and different P transporters (pitA, pstS). Illumina amplicon sequencing of soil genomic DNA underlined the high rate of primer specificity towards the respective target gene which usually ranged between 98% and 100% (phoN: 87%). As expected the primers amplified genes from a broad diversity of distinct microorganisms. Using DNA from a beech dominated forest soil, the highest microbial diversity was detected for the alkaline phosphatase (phoD) gene which was amplified from 15 distinct phyla respectively 81 families. Noteworthy the primers also allowed amplification of phoD from 6 fungal orders. The genes coding for acid phosphatase (phoN) and the quinoprotein glucose dehydrogenase (gcd) were amplified from 20 respectively 17 different microbial orders. In comparison the phytase and phosphonatase (appA, phnX) primers covered 13 bacterial orders from 2 different phyla respectively. Although the amplified microbial diversity was apparently limited both primers reliably detected all orders that contributed to the P turnover in the investigated soil as revealed by a previous metagenomic approach. Genes that code for microbial P transporter

  2. Proteome-wide Changes in Protein Turnover Rates in C. elegans Models of Longevity and Age-Related Disease.

    PubMed

    Visscher, Marieke; De Henau, Sasha; Wildschut, Mattheus H E; van Es, Robert M; Dhondt, Ineke; Michels, Helen; Kemmeren, Patrick; Nollen, Ellen A; Braeckman, Bart P; Burgering, Boudewijn M T; Vos, Harmjan R; Dansen, Tobias B

    2016-09-13

    The balance between protein synthesis and protein breakdown is a major determinant of protein homeostasis, and loss of protein homeostasis is one of the hallmarks of aging. Here we describe pulsed SILAC-based experiments to estimate proteome-wide turnover rates of individual proteins. We applied this method to determine protein turnover rates in Caenorhabditis elegans models of longevity and Parkinson's disease, using both developing and adult animals. Whereas protein turnover in developing, long-lived daf-2(e1370) worms is about 30% slower than in controls, the opposite was observed in day 5 adult worms, in which protein turnover in the daf-2(e1370) mutant is twice as fast as in controls. In the Parkinson's model, protein turnover is reduced proportionally over the entire proteome, suggesting that the protein homeostasis network has a strong ability to adapt. The findings shed light on the relationship between protein turnover and healthy aging. PMID:27626671

  3. Large-Scale Variation in Forest Carbon Turnover Rate and its Relation to Climate - Remote Sensing vs. Global Vegetation Models

    NASA Astrophysics Data System (ADS)

    Carvalhais, N.; Thurner, M.; Beer, C.; Forkel, M.; Rademacher, T. T.; Santoro, M.; Tum, M.; Schmullius, C.

    2015-12-01

    While vegetation productivity is known to be strongly correlated to climate, there is a need for an improved understanding of the underlying processes of vegetation carbon turnover and their importance at a global scale. This shortcoming has been due to the lack of spatially extensive information on vegetation carbon stocks, which we recently have been able to overcome by a biomass dataset covering northern boreal and temperate forests originating from radar remote sensing. Based on state-of-the-art products on biomass and NPP, we are for the first time able to study the relation between carbon turnover rate and a set of climate indices in northern boreal and temperate forests. The implementation of climate-related mortality processes, for instance drought, fire, frost or insect effects, is often lacking or insufficient in current global vegetation models. In contrast to our observation-based findings, investigated models from the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), including HYBRID4, JeDi, JULES, LPJml, ORCHIDEE, SDGVM, and VISIT, are able to reproduce spatial climate - turnover rate relationships only to a limited extent. While most of the models compare relatively well to observation-based NPP, simulated vegetation carbon stocks are severely biased compared to our biomass dataset. Current limitations lead to considerable uncertainties in the estimated vegetation carbon turnover, contributing substantially to the forest feedback to climate change. Our results are the basis for improving mortality concepts in global vegetation models and estimating their impact on the land carbon balance.

  4. Turnover Begets Turnover

    ERIC Educational Resources Information Center

    Castle, Nicholas G.

    2005-01-01

    Purpose: This study examined the association between turnover of caregivers and turnover of nursing home top management. The top managers examined were administrators and directors of nursing, and the caregivers examined were registered nurses, licensed practical nurses, and nurse aides. Design and Methods: The data came from a survey of 419…

  5. The High Cost of Leaving: An Analysis of the Cost of Teacher Turnover

    ERIC Educational Resources Information Center

    Watlington, Eliah; Shockley, Robert; Guglielmino, Paul; Felsher, Rivka

    2010-01-01

    The cost of teacher turnover to schools and school districts has only recently been studied. This research reveals that when high-quality teachers leave the classroom, the effect on both student performance and school and district fiscal operations is significant and deleterious. The implications for study in this area include the planning of…

  6. Teacher Turnover in High-Poverty Schools: What We Know and Can Do

    ERIC Educational Resources Information Center

    Simon, Nicole S.; Johnson, Susan Moore

    2015-01-01

    Background/Context: Over the past three decades, teacher turnover has increased substantially in U.S. public schools, especially in those serving large portions of low-income students of color. Teachers who choose to leave high-poverty schools serving large numbers of students of color usually transfer to schools serving wealthier, Whiter student…

  7. Calvarial doughnut lesions associated with high-turnover osteoporosis presenting in childhood.

    PubMed

    Stock, J L; Coderre, J A; Overdorf, J H; Fitzpatrick, L A; Shapiro, J R

    1999-01-01

    Osteogenesis imperfecta and juvenile osteoporosis are two well-described syndromes of osteoporosis presenting in childhood. There are also several references in the radiology literature to calvarial doughnut lesions (CDLs), areas of radiolucency surrounded by a dense and well-defined area of sclerotic bone, either as an incidental finding or associated with childhood fracture. We have characterized the metabolic abnormalities in a 13-yr-old boy with CDLs and multiple fractures and followed him during his progression through puberty. The patient's paternal grandmother; father; and paternal aunt, uncle, and first cousin were similarly affected, and a mandibular lesion in the uncle was pathologically described as fibrous dysplasia. The subject's physical examination was significant for bony protuberances of the skull and normal hearing, sclearal hue, dentition, and joint flexibility. Radiographs revealed calvarial CDLs and osteopenia which was confirmed by bone mineral density (BMD) testing. Biochemical markers of bone formation and resorption were elevated compared to normal adult and a transiliac crest bone biopsy confirmed high-turnover osteoporosis. Over 6 yr, with no specific therapy, BMD gradually normalized, but the CDLs increased in size, bone turnover remained elevated by biochemical markers, and he continued to fracture. The subject's affected father and maternal grandmother had normal BMD and no history of adult fracture. CDLs with high-turnover osteoporosis should be considered in the differential diagnosis of pediatric osteoporosis. During puberty the BMD normalizes but the high-turnover state persists, and the propensity to fracture eventually decreases in older affected adults. The CDLs may be a variant of fibrous dysplasia, and further study is necessary in order to elucidate the stimulus for increased bone turnover and the familial nature of this syndrome. PMID:23547313

  8. Characteristics of Teacher Induction Programs and Turnover Rates of Beginning Teachers

    ERIC Educational Resources Information Center

    Kang, Seok; Berliner, David C.

    2012-01-01

    The federal School and Staffing Survey (SASS) and Teacher Follow-up Survey (TFS) were used to examine the impacts of induction activities on beginning teacher turnover. This study excluded those teachers who moved or left schools for unavoidable and involuntary reasons, a confounding factor in previous research. This analysis revealed that three…

  9. Overworked RNs, social workers cause high nursing assistant turnover in nursing homes.

    PubMed

    1999-04-01

    Using benchmarking to stanch the loss of employees. Many nursing homes and long-term care facilities have a burdensome employee turnover rate, in some cases approaching 400% annually. A benchmarking study conducted by Southern University and the Louisiana State Nursing Home Association revealed that the factors widely believed to cause the problem--wages, benefits, and workload--are not to blame. Take a look at the results. PMID:10557961

  10. Turnover among High School Physics Teachers. Focus On

    ERIC Educational Resources Information Center

    White, Susan; Tesfaye, Casey Langer

    2011-01-01

    In the fall of 2008 the authors contacted a representative sample of over 3,600 high schools in the United States, both public and private, to determine whether or not physics was taught there. They received responses from over 99% of the schools. For the schools which indicated they were offering physics, the authors obtained contact information…

  11. Employee Turnover: Evidence from a Case Study.

    ERIC Educational Resources Information Center

    Borland, Jeff

    1997-01-01

    Patterns of employee turnover from a medium-sized law firm in Australia were examined in regard to theories of worker mobility (matching, sectoral shift, and incentive). Results support a role for matching effects, but personnel practices affect the timing of turnover. Matching and incentive-based theories do not explain the high rates of turnover…

  12. Role of TGF-β in a Mouse Model of High Turnover Renal Osteodystrophy†

    PubMed Central

    Liu, Shiguang; Song, Wenping; Boulanger, Joseph H; Tang, Wen; Sabbagh, Yves; Kelley, Brian; Gotschall, Russell; Ryan, Susan; Phillips, Lucy; Malley, Katie; Cao, Xiaohong; Xia, Tai-He; Zhen, Gehua; Cao, Xu; Ling, Hong; Dechow, Paul C; Bellido, Teresita M; Ledbetter, Steven R; Schiavi, Susan C

    2014-01-01

    Altered bone turnover is a key pathologic feature of chronic kidney disease-mineral and bone disorder (CKD-MBD). Expression of TGF-β1, a known regulator of bone turnover, is increased in bone biopsies from individuals with CKD. Similarly, TGF-β1 mRNA and downstream signaling is increased in bones from jck mice, a model of high-turnover renal osteodystropy. A neutralizing anti-TGF-β antibody (1D11) was used to explore TGF-βs role in renal osteodystrophy. 1D11 administration to jck significantly attenuated elevated serum osteocalcin and type I collagen C-telopeptides. Histomorphometric analysis indicated that 1D11 administration increased bone volume and suppressed the elevated bone turnover in a dose-dependent manner. These effects were associated with reductions in osteoblast and osteoclast surface areas. μCT confirmed the observed increase in trabecular bone volume and demonstrated improvements in trabecular architecture and increased cortical thickness. 1D11 administration was associated with significant reductions in expression of osteoblast marker genes (Runx2, alkaline phosphatase, osteocalcin) and the osteoclast marker gene, Trap5. Importantly, in this model, 1D11 did not improve kidney function or reduce serum PTH levels indicating that 1D11 effects on bone are independent of changes in renal or parathyroid function. 1D11 also significantly attenuated high turnover bone disease in the adenine-induced uremic rat model. Antibody administration was associated with a reduction in pSMAD2/SMAD2 in bone but not bone marrow as assessed by quantitative immunoblot analysis. Immunostaining revealed pSMAD staining in osteoblasts and osteocytes but not osteoclasts, suggesting 1D11 effects on osteoclasts may be indirect. Immunoblot and whole genome mRNA expression analysis confirmed our previous observation that repression of Wnt/β catenin expression in bone is correlated with increased osteoclast activity in jck mice and bone biopsies from CKD patients. Furthermore

  13. Arthritis Induces Early Bone High Turnover, Structural Degradation and Mechanical Weakness

    PubMed Central

    Vidal, Bruno; Cascão, Rita; Vale, Ana Catarina; Cavaleiro, Inês; Vaz, Maria Fátima; Brito, José Américo Almeida; Canhão, Helena; Fonseca, João Eurico

    2015-01-01

    Background We have previously found in the chronic SKG mouse model of arthritis that long standing (5 and 8 months) inflammation directly leads to high collagen bone turnover, disorganization of the collagen network, disturbed bone microstructure and degradation of bone biomechanical properties. The main goal of the present work was to study the effects of the first days of the inflammatory process on the microarchitecture and mechanical properties of bone. Methods Twenty eight Wistar adjuvant-induced arthritis (AIA) rats were monitored during 22 days after disease induction for the inflammatory score, ankle perimeter and body weight. Healthy non-arthritic rats were used as controls for compar-ison. After 22 days of disease progression rats were sacrificed and bone samples were collected for histomorphometrical, energy dispersive X-ray spectroscopical analysis and 3-point bending. Blood samples were also collected for bone turnover markers. Results AIA rats had an increased bone turnover (as inferred from increased P1NP and CTX1, p = 0.0010 and p = 0.0002, respectively) and this was paralleled by a decreased mineral content (calcium p = 0.0046 and phos-phorus p = 0.0046). Histomorphometry showed a lower trabecular thickness (p = 0.0002) and bone volume (p = 0.0003) and higher trabecular sepa-ration (p = 0.0009) in the arthritic group as compared with controls. In addition, bone mechanical tests showed evidence of fragility as depicted by diminished values of yield stress and ultimate fracture point (p = 0.0061 and p = 0.0279, re-spectively) in the arthritic group. Conclusions We have shown in an AIA rat model that arthritis induc-es early bone high turnover, structural degradation, mineral loss and mechanical weak-ness. PMID:25617902

  14. RpoS synthesis is growth rate regulated in Salmonella typhimurium, but its turnover is not dependent on acetyl phosphate synthesis or PTS function.

    PubMed

    Cunning, C; Elliott, T

    1999-08-01

    The RpoS sigma factor of enteric bacteria is either required for or augments the expression of a number of genes that are induced during nutrient limitation, growth into stationary phase, or in response to stresses, including high osmolarity. RpoS is regulated at multiple levels, including posttranscriptional control of its synthesis, protein turnover, and mechanisms that affect its activity directly. Here, the control of RpoS stability was investigated in Salmonella typhimurium by the isolation of a number of mutants specifically defective in RpoS turnover. These included 20 mutants defective in mviA, the ortholog of Escherichia coli rssB/sprE, and 13 mutants defective in either clpP or clpX which encode the protease active on RpoS. An hns mutant was also defective in RpoS turnover, thus confirming that S. typhimurium and E. coli have identical genetic requirements for this process. Some current models predict the existence of a kinase to phosphorylate the response regulator MviA, but no mutants affecting a kinase were recovered. An mviA mutant carrying the D58N substitution altering the predicted phosphorylation site is substantially defective, suggesting that phosphorylation of MviA on D58 is important for its function. No evidence was obtained to support models in which acetyl phosphate or the PTS system contributes to MviA phosphorylation. However, we did find a significant (fivefold) elevation of RpoS during exponential growth on acetate as the carbon and energy source. This behavior is due to growth rate-dependent regulation which increases RpoS synthesis at slower growth rates. Growth rate regulation operates at the level of RpoS synthesis and is mainly posttranscriptional but, surprisingly, is independent of hfq function. PMID:10438755

  15. ON THE ORIGIN OF THE HIGH COLUMN DENSITY TURNOVER IN THE H I COLUMN DENSITY DISTRIBUTION

    SciTech Connect

    Erkal, Denis; Gnedin, Nickolay Y.; Kravtsov, Andrey V.

    2012-12-10

    We study the high column density regime of the H I column density distribution function and argue that there are two distinct features: a turnover at N{sub H{sub I}} Almost-Equal-To 10{sup 21} cm{sup -2}, which is present at both z = 0 and z Almost-Equal-To 3, and a lack of systems above N{sub H{sub I}} Almost-Equal-To 10{sup 22} cm{sup -2} at z = 0. Using observations of the column density distribution, we argue that the H I-H{sub 2} transition does not cause the turnover at N{sub H{sub I}} Almost-Equal-To 10{sup 21} cm{sup -2} but can plausibly explain the turnover at N{sub H{sub I}} {approx}> 10{sup 22} cm{sup -2}. We compute the H I column density distribution of individual galaxies in the THINGS sample and show that the turnover column density depends only weakly on metallicity. Furthermore, we show that the column density distribution of galaxies, corrected for inclination, is insensitive to the resolution of the H I map or to averaging in radial shells. Our results indicate that the similarity of H I column density distributions at z = 3 and 0 is due to the similarity of the maximum H I surface densities of high-z and low-z disks, set presumably by universal processes that shape properties of the gaseous disks of galaxies. Using fully cosmological simulations, we explore other candidate physical mechanisms that could produce a turnover in the column density distribution. We show that while turbulence within giant molecular clouds cannot affect the damped Ly{alpha} column density distribution, stellar feedback can affect it significantly if the feedback is sufficiently effective in removing gas from the central 2-3 kpc of high-redshift galaxies. Finally, we argue that it is meaningful to compare column densities averaged over {approx} kpc scales with those estimated from quasar spectra that probe sub-pc scales due to the steep power spectrum of H I column density fluctuations observed in nearby galaxies.

  16. Measurement of the rates of oxindole-3-acetic acid turnover, and indole-3-acetic acid oxidation in Zea mays seedlings

    NASA Technical Reports Server (NTRS)

    Nonhebel, H. M.; Bandurski, R. S. (Principal Investigator)

    1986-01-01

    Oxindole-3-acetic acid is the principal catabolite of indole-3-acetic acid in Zea mays seedlings. In this paper measurements of the turnover of oxindole-3-acetic acid are presented and used to calculate the rate of indole-3-acetic acid oxidation. [3H]Oxindole-3-acetic acid was applied to the endosperm of Zea mays seedlings and allowed to equilibrate for 24 h before the start of the experiment. The subsequent decrease in its specific activity was used to calculate the turnover rate. The average half-life of oxindole-3-acetic acid in the shoots was found to be 30 h while that in the kernels had an average half-life of 35h. Using previously published values of the pool sizes of oxindole-3-acetic acid in shoots and kernels from seedlings of the same age and variety, and grown under the same conditions, the rate of indole-3-acetic acid oxidation was calculated to be 1.1 pmol plant-1 h-1 in the shoots and 7.1 pmol plant-1 h-1 in the kernels.

  17. Performance and carbon turnover in fast- and slow-growing broilers submitted to cyclic heat stress and fed on high-protein diets.

    PubMed

    Campos, D M B; Macari, M; Fernadez-Alarcon, M F; Nogueira, W C L; de Souza, F A; Hada, F H; Lunedo, R; Denadai, J C

    2016-01-01

    Two experiments were conducted to test the hypothesis that when using similar protein/amino acid diets and environment temperature conditions, the performance and carbon turnover in muscle and liver tissues, as measured by the incorporation of stable isotopes ((13)C/(12)C), must be different between fast-growing Cobb 500® and slow-growing Label Rouge broilers. For both experiments (Cobb and Label Rouge), 21-d-old birds were distributed in a completely randomised, 3 × 3 factorial design; three environmental temperatures (cyclic heat stress ad libitum, 22°C ad libitum, and 22°C restricted) and three crude protein concentrations (189.1, 210 and 220 g/kg CP) were used. The Cobb 500® had better performance with higher concentrations of crude protein. Cyclic heat stress (a temperature factor), negatively affected this genetic strain's performance. For the Label Rouge birds, the crude protein concentrations in the diet presented inconsistent results and cyclic heat stress did not affect the performance. The carbon turnover rate was affected in the Cobb 500® strain, with a high protein content reducing carbon turnover in the evaluated tissues (liver and muscles). Feed intake had a greater impact on carbon turnover rates than cyclic heat stress. The Label Rouge birds were not affected by the evaluated factors, suggesting that genetic improvement has a leading role on tissue carbon turnover. There is a genetic influence on carbon turnover in the liver and muscle tissues of broiler chickens. In addition, genetically fast-growing broilers are more susceptible to variations in diet composition and environmental temperature than less rapidly growing animals. PMID:26634283

  18. Familial resemblance of bone turnover rate in men aged 40 and over-the MINOS study.

    PubMed

    Nagy, Hoda; Feyt, Clément; Chapurlat, Roland; Szulc, Pawel

    2013-03-01

    Familial resemblance of bone mineral density (BMD) is well known in both sexes. Fewer data concern the familial resemblance of bone turnover markers (BTMs) and bone size in men. Our aim was to assess the correlation of BMD, bone size, BTM levels and hormones regulating bone turnover in 50 pairs of brothers aged ≥ 40 and 50 pairs of unrelated men matched for age, weight and height. BMD was measured at the lumbar spine, hip, forearm and whole body. We measured serum osteocalcin (OC), bone-specific alkaline phosphatase (bone ALP), N-terminal propeptide of type I procollagen (PINP) and C-terminal telopeptide of type I collagen (CTX-I) as well as urinary free and total deoxypyridinoline (DPD) and CTX-I. After adjustment for age, weight, bioavailable 17β-estradiol, and parathyroid hormone, all the BTMs (except bone ALP) were significantly correlated in the brothers (ICC = 0.36-0.64). Most of these correlations were significantly stronger than in the unrelated men. Bone size correlated significantly between the brothers (ICC = 0.55-0.65). These correlations were significantly stronger than in the unrelated men. BMD correlated between the brothers at most of the skeletal sites and, for some of them, more strongly than in the unrelated men. Serum levels of LDL-cholesterol and triglycerides were significantly correlated in the brothers, but not more strongly than in the unrelated men. BTM levels correlated independently in the brothers aged ≥ 40, when their shared environment was limited. These data suggest a substantial hereditary determinism of the BTM levels in men. PMID:23179229

  19. Opposite control of frontocortical 2-arachidonoylglycerol turnover rate by cannabinoid type-1 receptors located on glutamatergic neurons and on astrocytes.

    PubMed

    Belluomo, Ilaria; Matias, Isabelle; Pernègre, Camille; Marsicano, Giovanni; Chaouloff, Francis

    2015-04-01

    This study examined the respective influences of cannabinoid type-1 (CB1) receptors expressed either in forebrain GABAergic neurons, in cortical glutamatergic neurons, or in astrocytes on the turnover rates of the endocannabinoids N-arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), and the non-cannabinoid N-acylethanolamides, palmitoylethanolamide (PEA), and oleoylethanolamide (OEA), in mouse forebrain regions. To this end, conditional mutant mice lacking CB1 receptors from either of these cell types were pre-treated systemically with JZL195, a dual inhibitor of fatty acid amide hydrolase, the enzyme degrading AEA, PEA, and OEA, and of monoacylglycerol lipase, the main 2-AG-degrading enzyme. The analyses of frontocortical, hippocampal, and striatal AEA, 2-AG, PEA, and OEA concentrations revealed that their respective baseline concentrations were not influenced by the mouse genotype. On the other hand, the accumulation of frontocortical and/or hippocampal 2-AG levels in JZL195-pre-treated mice was dependent on the mouse genotype. Thus, JZL195-induced 2-AG accumulation rates were diminished in the frontal cortex of mice lacking CB1 receptors in glutamatergic neurons while their respective values were increased in the frontal cortex and hippocampus of mice lacking these receptors in astrocytes. These genotypic differences occurred with parallel and proportionate changes in the fractional rate constants for degradation of 2-AG, thus providing a mechanism whereby the baseline levels of 2-AG remained constant between genotypes. Besides suggesting a cell-type-specific control of frontocortical and/or hippocampal 2-AG synthesis and degradation rates by CB1 receptors, this study highlights the interest of assessing endocannabinoid turnover rates when questioning the status of the endocannabinoid system. PMID:25626460

  20. The cellular growth rate controls overall mRNA turnover, and modulates either transcription or degradation rates of particular gene regulons

    PubMed Central

    García-Martínez, José; Delgado-Ramos, Lidia; Ayala, Guillermo; Pelechano, Vicent; Medina, Daniel A.; Carrasco, Fany; González, Ramón; Andrés-León, Eduardo; Steinmetz, Lars; Warringer, Jonas; Chávez, Sebastián; Pérez-Ortín, José E.

    2016-01-01

    We analyzed 80 different genomic experiments, and found a positive correlation between both RNA polymerase II transcription and mRNA degradation with growth rates in yeast. Thus, in spite of the marked variation in mRNA turnover, the total mRNA concentration remained approximately constant. Some genes, however, regulated their mRNA concentration by uncoupling mRNA stability from the transcription rate. Ribosome-related genes modulated their transcription rates to increase mRNA levels under fast growth. In contrast, mitochondria-related and stress-induced genes lowered mRNA levels by reducing mRNA stability or the transcription rate, respectively. We also detected these regulations within the heterogeneity of a wild-type cell population growing in optimal conditions. The transcriptomic analysis of sorted microcolonies confirmed that the growth rate dictates alternative expression programs by modulating transcription and mRNA decay. The regulation of overall mRNA turnover keeps a constant ratio between mRNA decay and the dilution of [mRNA] caused by cellular growth. This regulation minimizes the indiscriminate transmission of mRNAs from mother to daughter cells, and favors the response capacity of the latter to physiological signals and environmental changes. We also conclude that, by uncoupling mRNA synthesis from decay, cells control the mRNA abundance of those gene regulons that characterize fast and slow growth. PMID:26717982

  1. The cellular growth rate controls overall mRNA turnover, and modulates either transcription or degradation rates of particular gene regulons.

    PubMed

    García-Martínez, José; Delgado-Ramos, Lidia; Ayala, Guillermo; Pelechano, Vicent; Medina, Daniel A; Carrasco, Fany; González, Ramón; Andrés-León, Eduardo; Steinmetz, Lars; Warringer, Jonas; Chávez, Sebastián; Pérez-Ortín, José E

    2016-05-01

    We analyzed 80 different genomic experiments, and found a positive correlation between both RNA polymerase II transcription and mRNA degradation with growth rates in yeast. Thus, in spite of the marked variation in mRNA turnover, the total mRNA concentration remained approximately constant. Some genes, however, regulated their mRNA concentration by uncoupling mRNA stability from the transcription rate. Ribosome-related genes modulated their transcription rates to increase mRNA levels under fast growth. In contrast, mitochondria-related and stress-induced genes lowered mRNA levels by reducing mRNA stability or the transcription rate, respectively. We also detected these regulations within the heterogeneity of a wild-type cell population growing in optimal conditions. The transcriptomic analysis of sorted microcolonies confirmed that the growth rate dictates alternative expression programs by modulating transcription and mRNA decay.The regulation of overall mRNA turnover keeps a constant ratio between mRNA decay and the dilution of [mRNA] caused by cellular growth. This regulation minimizes the indiscriminate transmission of mRNAs from mother to daughter cells, and favors the response capacity of the latter to physiological signals and environmental changes. We also conclude that, by uncoupling mRNA synthesis from decay, cells control the mRNA abundance of those gene regulons that characterize fast and slow growth. PMID:26717982

  2. Turnover-Dependent Inactivation of the Nitrogenase MoFe-Protein at High pH

    PubMed Central

    2013-01-01

    Proton uptake accompanies the reduction of all known substrates by nitrogenase. As a consequence, a higher pH should limit the availability of protons as a substrate essential for turnover, thereby increasing the proportion of more highly reduced forms of the enzyme for further study. The utility of the high-pH approach would appear to be problematic in view of the observation reported by Pham and Burgess [(1993) Biochemistry 32, 13725–13731] that the MoFe-protein undergoes irreversible protein denaturation above pH 8.65. In contrast, we found by both enzyme activity and crystallographic analyses that the MoFe-protein is stable when incubated at pH 9.5. We did observe, however, that at higher pHs and under turnover conditions, the MoFe-protein is slowly inactivated. While a normal, albeit low, level of substrate reduction occurs under these conditions, the MoFe-protein undergoes a complex transformation; initially, the enzyme is reversibly inhibited for substrate reduction at pH 9.5, yet in a second, slower process, the MoFe-protein becomes irreversibly inactivated as measured by substrate reduction activity at the optimal pH of 7.8. The final inactivated MoFe-protein has an increased hydrodynamic radius compared to that of the native MoFe-protein, yet it has a full complement of iron and molybdenum. Significantly, the modified MoFe-protein retains the ability to specifically interact with its nitrogenase partner, the Fe-protein, as judged by the support of ATP hydrolysis and by formation of a tight complex with the Fe-protein in the presence of ATP and aluminum fluoride. The turnover-dependent inactivation coupled to conformational change suggests a mechanism-based transformation that may provide a new probe of nitrogenase catalysis. PMID:24392967

  3. Docosahexaenoate-containing molecular species of glycerophospholipids from frog retinal rod outer segments show different rates of biosynthesis and turnover

    SciTech Connect

    Louie, K.; Wiegand, R.D.; Anderson, R.E.

    1988-12-13

    The authors have studied the de novo synthesis and subsequent turnover of major docosahexaenoate-containing molecular species in frog rod outer segment (ROS) phospholipids following intravitreal injection of (2-/sup 3/H)glycerol. On selected days after injection, ROS were prepared and phospholipids extracted. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) were isolated and converted to diradylglycerols with phospholipase C. Diradylglycerols were derivatized with benzoic anhydride and resolve into diacylglycerobenzoates and ether-linked glycerobenzoates. The diacylglycerobenzoates were fractionated into molecular species by HPLC, quantitated, and counted for radioactivity. Label was incorporated into ROS phospholipids by day 1 and was followed up through the eighth day. The dipolyenoic species 22:6-22:6 from PC showed 1 3-5 times higher radiospecific activity than the same species from either PE or PS. The rate of decline was determined by calculating the half-life of each molecular species, which was used as a measure of the turnover of the species. The percent distribution of radioactivity in the molecular species of PC and PE was quite different from the relative mass distribution at day 1. However, percent dpm approached the mole percent by 31 days. In PS, percent dpm and mole percent were the same at all time points. These results indicate that the molecular species composition of PC and PE in frog retinal ROS is determined by a combination of factors, which include rate of synthesis, rate of degradation, and selective interconversions. In contrast, PS composition appears to be determined at the time of synthesis.

  4. Effects of F/G-actin ratio and actin turn-over rate on NADPH oxidase activity in microglia

    PubMed Central

    2010-01-01

    Background Most in vivo studies that have addressed the role of actin dynamics in NADPH oxidase function in phagocytes have used toxins to modulate the polymerization state of actin and mostly effects on actin has been evaluated by end point measurements of filamentous actin, which says little about actin dynamics, and without consideration for the subcellular distribution of the perturbed actin cytoskeleton. Results Here, we in addition to toxins use conditional expression of the major actin regulatory protein LIM kinase-1 (LIMK1), and shRNA knock-down of cofilin to modulate the cellular F/G-actin ratio in the Ra2 microglia cell line, and we use Fluorescence Recovery after Photobleaching (FRAP) in β-actin-YFP-transduced cells to obtain a dynamic measure of actin recovery rates (actin turn-over rates) in different F/G-actin states of the actin cytoskeleton. Our data demonstrate that stimulated NADPH oxidase function was severely impaired only at extreme actin recovery rates and F/G-actin ratios, and surprisingly, that any moderate changes of these parameters of the actin cytoskeleton invariably resulted in an increased NADPH oxidase activity. Conclusion moderate actin polymerization and depolymerization both increase the FMLP and PMA-stimulated NADPH oxidase activity of microglia, which is directly correlated with neither actin recovery rate nor F/G- actin ratio. Our results indicate that NADPH oxidase functions in an enhanced state of activity in stimulated phagocytes despite widely different states of the actin cytoskeleton. PMID:20825680

  5. Preliminary results on the influence of mineralogy on the turnover rates of SOM from different Hungarian soils

    NASA Astrophysics Data System (ADS)

    Zacháry, Dóra; Szalai, Zoltán; Jakab, Gergely; Németh, Tibor; Sipos, Péter; Filep, Tibor

    2016-04-01

    Fine textured soils generally considered containing more microbial biomass, and having a lower rate of biomass turnover and organic matter decomposition than coarse textured soils. In spite of this, several recent studies have shown contradicting trends. For example, the relative importance of different clay minerals for stabilizing SOM remains an open question. The aim of this study is to evaluate soil mineralological effect on the turnover of SOM by identifying and quantifying soil phyllosilicates. Our samples are derived from C3 forests and C3 croplands from different sites of Hungary. C4 maize residues are added to the soils in order to get natural 13C enrichment as tracer for the young carbon. Bulk samples of the soils from 0 to 20 cm depth were collected. The samples were dried at room temperature and preincubated in the dark for 4 months at 20 °C. The basic soil properties (pH, cation exchange capacity) were analysed after 2 mm sieving and homogenization. The amount of total C and N in the soils and maize residues were analysed using NDIR-chemiluminescent analyzer (Tekmar Dohrman Apollo 9000N). Particle size distribution was determined by laser diffraction (Fritsch Analysette MicroTec 22 plus) and particle imaging method (Malvern Morphologi G3-ID). The mineralological composition of the samples was determined by X-ray diffraction (Philips PW 1730 X-ray diffractometer). Moist soil equivalent to 400 g dry soil mixed with 2 g maize leaves is kept in air tight glass chambers for 183 days at 20°C. The leaves had previously been dried at 60 °C, were cut into pieces and sieved through a 2 mm mesh. The evolved CO2 is trapped by 10 mL 2 M NaOH, which is exchanged on day 1, 3, 5, 7, 10, 14, 21, 28 and subsequently every 31 days. The fractional abundance of 13C of the soils, the plant material and the evolved CO2 is measured with isotope ratio mass spectrometer (Thermo Scientific Delta V IRMS). Our work show the preliminary results on the link between phyllosilicate

  6. Comparison of Faunal Equilibrium Turnover Rates on a Tropical Island and a Temperate Island

    PubMed Central

    Diamond, Jared M.

    1971-01-01

    Rates of immigration and extinction of bird species on a tropical island, Karkar in the southwest Pacific Ocean, have been estimated from surveys made in 1914 and in 1969. Compared to a temperate-zone island of similar size and isolation (Santa Cruz off southern California), Karkar has a similar extinction rate, but a lower immigration rate expressed as a fraction of the mainland species pool, due to the sedentariness of many tropical forest birds. The probability of extinction is highest for species that are rare (due to narrow habitat requirements, large territory size, competition, recency of colonization, or marginal suitability of habitat), species with “in-and-out” tactics, and populations on small islands. PMID:16591954

  7. Turnover rate, reaction order, and elementary steps for the hydrodechlorination of chlorofluorocarbon compounds on palladium catalysts

    SciTech Connect

    Thompson, C.D.; Rioux, R.M.; Chen, N.; Ribeiro, F.H.

    2000-04-13

    The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H{sub 2}, and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H{sub 2}, gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF{sub 3}-CF{sub 2}Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF{sub 3}-CFClH), 1,1-dichlorotetrafluoroethane (CF{sub 3}-CFCl{sub 2}), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF{sub 3}-CCl{sub 3}).

  8. Turnover intention in new graduate nurses: a multivariate analysis

    PubMed Central

    Beecroft, Pauline C; Dorey, Frederick; Wenten, Madé

    2008-01-01

    recruitment of new graduate nurses, particularly in the United States of America. Historically, new graduate nurses have a high turnover rate within the first year of employment. What this paper adds When new graduate nurses are satisfied with their jobs and pay and feel committed to the organization, the odds of turnover intent decrease. Increased seeking social support to cope with the transition from student to competent Registered Nurse is related to turnover intent. Older graduates (>30) are 4·5 times more likely to have turnover intent if they do not get their ward of choice. PMID:18352963

  9. Assimilation efficiencies and turnover rates of trace elements in marine bivalves: A comparison of oysters, clams and mussels

    USGS Publications Warehouse

    Reinfelder, J.R.; Wang, W.-X.; Luoma, S. N.; Fisher, N.S.

    1997-01-01

    Assimilation efficiencies (AEs) and physiological turnover-rate constants (k) of six trace elements (Ag, Am, Cd, Co, Se, Zn) in four marine bivalves (Crassostrea virginica Gmelin,Macoma balthica Linnaeus, Mercenaria mercenaria Linnaeus, and Mytilus edulis Linnaeus) were measured in radiotracer-depuration experiments. Egestion rates of unassimilated elements were highest during the first 24 h of depuration and declined thereafter. Significant egestion of unassimilated Co, however, continued for up to 5 d in Macoma balthica,Mercenaria mercenaria and Mytilus edulis. With the exception of the extremely low values for110 mAg, 109Cd, and 65Zn in C. virginica, physiological turnover-rate constants (k) showed no general pattern of variation among elements, bivalve species or food types, and were relatively invariant. Values from  ≤0.001 to 0.1 d−1 were observed, but excluding those for Co, most values were  ≤0.04 d−1. In all four species, the AEs of Ag, Am, and Co were generally lower than those of Cd, Se, and Zn. The AEs of Ag, Cd, Se, and Zn in these bivalves are directly related to the proportion of each element in the cytoplasmic fraction of ingested phytoplankton, indicating that >80% of elements in a prey alga's cytoplasm was assimilated. C. virginica, Macoma balthica, and Mercenaria mercenaria assimilated ∼36% of the Ag and Cd associated with the non-cytoplasmic (membrane/organelle) fraction of ingested cells in addition to the cytoplasmic fraction. The ratio of AE:k, which is proportional to the consumer–prey trace-element bioaccumulation factor (concentration in consumer:concentration in prey) was generally greater for Cd, Se, and Zn than for Ag, Am, and Co. This ratio was lowest in Mytilus edulis, suggesting that this bivalve, the most widely employed organism in global biomonitoring, is relatively inefficient at accumulating important elements such as Ag, Cd, and Zn from ingested phytoplankton.

  10. Rate turnover in mechano-catalytic coupling: A model and its microscopic origin

    SciTech Connect

    Roy, Mahua; Grazioli, Gianmarc; Andricioaei, Ioan

    2015-07-28

    A novel aspect in the area of mechano-chemistry concerns the effect of external forces on enzyme activity, i.e., the existence of mechano-catalytic coupling. Recent experiments on enzyme-catalyzed disulphide bond reduction in proteins under the effect of a force applied on the termini of the protein substrate reveal an unexpected biphasic force dependence for the bond cleavage rate. Here, using atomistic molecular dynamics simulations combined with Smoluchowski theory, we propose a model for this behavior. For a broad range of forces and systems, the model reproduces the experimentally observed rates by solving a reaction-diffusion equation for a “protein coordinate” diffusing in a force-dependent effective potential. The atomistic simulations are used to compute, from first principles, the parameters of the model via a quasiharmonic analysis. Additionally, the simulations are also used to provide details about the microscopic degrees of freedom that are important for the underlying mechano-catalysis.

  11. In search of the elusive U-shaped performance-turnover relationship: are high performing Swiss bankers more liable to quit?

    PubMed

    Salamin, Alain; Hom, Peter W

    2005-11-01

    This project revisits the perennial debate over the relationship between job performance and turnover. Disputing traditional findings, C. Trevor, B. Gerhart, and J. Boudreau (1997) observed that high and low performers quit more than do average performers. They further challenged received wisdom by showing that promotions can induce turnover, especially among poor performers, by signaling ability. The authors sought to replicate and extend these unconventional findings by exploring curvilinear and moderating effects on the performance-exit relationship among 11,098 Swiss nationals employed in a bank. Survival regression revealed that performance is curvilinearly related to quits and that bonus pay deterred superior performers from leaving more than did pay increases. Further, the average number of job levels advanced per promotion rather than promotion rate increased quit risks. Cultural and organizational moderators of performance-termination associations and effective strategies for retaining top performers are discussed. PMID:16316274

  12. Hypothalamic norepinephrine turnover response to a single low protein, high carbohydrate meal in the male Wistar rat

    SciTech Connect

    Raum, W.; Glick, Z.

    1986-03-01

    A single meal stimulates norepinephrine turnover (NET) by approximately 4-fold in the brown adipose tissue (BAT). In this experiment the role of the hypothalamus in regulating this response was examined. NET was measured in the cortex (C), ventro-medial (VMH), and the lateral hypothalamus (LH). A total of 48 male Wistar rats (200 g body weight) were trained to eat during two feeding sessions per day. On the experimental day, one group (N = 24) was meal deprived and the other (N = 24) was given a low protein, high carbohydrate test meal for 2 hours. NET was determined by the synthesis inhibition method using alpha-methyltyrosine (AMT) injected within one hour after the meal. Norepinephrine (NE) content in each brain section was measured by radioimmunoassay at 4 time points (0, 1, 2, 3 hours) after AMT. The turnover rate (TR) was calculated as the slope of the decline in NE content over time (ng/mg protein/hr) following AMT. The fraction of the total pool of NE released/hr (k) was calculated by dividing the slope (TR) by the Y intercept (NE content at zero time). NET (TR) increased significantly (p < .05) in the VMH following a meal (9.36 +/- .67 vs 8.04 +/- .98 ng/hr; fed vs deprived). There was no change in TR in the C or LH, or in k in any brain section. The marked (4-fold) increase in BAT NET and minimal increase in VMH NET suggests that the meal has a direct effect on BAT with the VMH playing a secondary or modulatory role.

  13. Response of the Fine Root Production, Phenology, and Turnover Rate of Six Shrub Species from a Subtropical Forest to a Soil Moisture Gradient and Shading

    NASA Astrophysics Data System (ADS)

    Fu, X.; Dai, X.; Wang, H.

    2015-12-01

    Knowledge of the fine root dynamics of different life forms in forest ecosystems is critical to understanding how the overall belowground carbon cycling is affected by climate change. However, our current knowledge regarding how endogenous or exogenous factors regulate the root dynamics of understory vegetation is limited. We selected a suite of study sites representing different habitats with gradients of soil moisture and solar radiation (shading or no shading). We assessed the fine root production phenology, the total fine root production, and the turnover among six understory shrub species in a subtropical climate, and examined the responses of the fine root dynamics to gradients in the soil moisture and solar radiation. The shrubs included three evergreen species, Loropetalum chinense, Vaccinium bracteatum, and Adinandra millettii, and three deciduous species, Serissa serissoides, Rubus corchorifolius, and Lespedeza davidii. We observed that variations in the annual fine root production and turnover among species were significant in the deciduous group but not in the evergreen group. Notably, V. bracteatum and S. serissoides presented the greatest responses in terms of root phenology to gradients in the soil moisture and shading: high-moisture habitat led to a decrease and shade led to an increase in fine root production during spring. Species with smaller fine roots of the 1st+2nd-order diameter presented more sensitive responses in terms of fine root phenology to a soil moisture gradient. Species with a higher fine root nitrogen-to -carbon ratio exhibited more sensitive responses in terms of fine root annual production to shading. Soil moisture and shading did not change the annual fine root production as much as the turnover rate. The fine root dynamics of some understory shrubs varied significantly with soil moisture and solar radiation status and may be different from tree species. Our results emphasize the need to study the understory fine root dynamics

  14. Carbon turnover rates in the One Tree Island reef: A 40-year perspective

    NASA Astrophysics Data System (ADS)

    Silverman, J.; Kline, D. I.; Johnson, L.; Rivlin, T.; Schneider, K.; Erez, J.; Lazar, B.; Caldeira, K.

    2012-09-01

    During November-December 2009 community rates of gross photosynthesis (Pg), respiration (R) and net calcification (Gnet) were estimated from low-tide slack water measurements of dissolved oxygen, dissolved inorganic carbon and total alkalinity at the historical station DK13 One Tree Island reef, Great Barrier Reef, Australia. Compared to measurements made during the 1960s-1970s at DK13 in the same season,Pg increased from 833 to 914 mmol O2·m-2·d-1 and Pg:R increased from 1.14 to 1.30, indicating that the reef has become more autotrophic. In contrast, Gnet decreased from 133 mmol C·m-2·d-1 to 74 ± 24 mmol C·m-2·d-1. This decrease stems primarily from the threefold increase in nighttime CaCO3 dissolution from -2.5 mmol·m-2·h-1 to -7.5 mmol·m-2·h-1. Comparison of the benthic community survey results from DK13 and its vicinity conducted during this study and in studies from the 1970s, 1980s and 1990s suggest that there have been no significant changes in the live coral coverage during the past 40 years. The reduced Gnet most likely reflects the almost threefold increase in dissolution rates, possibly resulting from increased bioerosion due to changes in the biota (e.g., sea cucumbers, boring organisms) and/or from greater chemical dissolution produced by changing abiotic conditions over the past 40 years associated with climate change, such as increased temperatures and ocean acidification. However, at this stage of research on One Tree Island the effects of these changes are not entirely understood.

  15. Turnover Rate of NS3 Proteins Modulates Bluetongue Virus Replication Kinetics in a Host-Specific Manner

    PubMed Central

    Ftaich, Najate; Ciancia, Claire; Viarouge, Cyril; Barry, Gerald; Ratinier, Maxime; van Rijn, Piet A.; Breard, Emmanuel; Vitour, Damien; Zientara, Stephan; Palmarini, Massimo; Terzian, Christophe

    2015-01-01

    ABSTRACT Bluetongue virus (BTV) is an arbovirus transmitted to livestock by midges of the Culicoides family and is the etiological agent of a hemorrhagic disease in sheep and other ruminants. In mammalian cells, BTV particles are released primarily by virus-induced cell lysis, while in insect cells they bud from the plasma membrane and establish a persistent infection. BTV possesses a ten-segmented double-stranded RNA genome, and NS3 proteins are encoded by segment 10 (Seg-10). The viral nonstructural protein 3 (NS3) plays a key role in mediating BTV egress as well as in impeding the in vitro synthesis of type I interferon in mammalian cells. In this study, we asked whether genetically distant NS3 proteins can alter BTV-host interactions. Using a reverse genetics approach, we showed that, depending on the NS3 considered, BTV replication kinetics varied in mammals but not in insects. In particular, one of the NS3 proteins analyzed harbored a proline at position 24 that leads to its rapid intracellular decay in ovine but not in Culicoides cells and to the attenuation of BTV virulence in a mouse model of disease. Overall, our data reveal that the genetic variability of Seg-10/NS3 differentially modulates BTV replication kinetics in a host-specific manner and highlight the role of the host-specific variation in NS3 protein turnover rate. IMPORTANCE BTV is the causative agent of a severe disease transmitted between ruminants by biting midges of Culicoides species. NS3, encoded by Seg-10 of the BTV genome, fulfills key roles in BTV infection. As Seg-10 sequences from various BTV strains display genetic variability, we assessed the impact of different Seg-10 and NS3 proteins on BTV infection and host interactions. In this study, we revealed that various Seg-10/NS3 proteins alter BTV replication kinetics in mammals but not in insects. Notably, we found that NS3 protein turnover may vary in ovine but not in Culicoides cells due to a single amino acid residue that, most

  16. Employee Turnover among Full-time Public Librarians.

    ERIC Educational Resources Information Center

    Rubin, Richard

    1989-01-01

    A study of employee turnover in 31 public libraries in the American Midwest established baseline turnover rates and examined the relationship of gender to turnover behavior. Findings showed that: turnover rates are low compared to other occupations; and turnover rates of males and females are similar. (28 references) (Author/MES)

  17. The high turnover Drosophila multidrug resistance-associated protein shares the biochemical features of its human orthologues.

    PubMed

    Szeri, Flóra; Iliás, Attila; Pomozi, Viola; Robinow, Steven; Bakos, Eva; Váradi, András

    2009-02-01

    DMRP, an ABC transporter encoded by the dMRP/CG6214 gene, is the Drosophila melanogaster orthologue of the "long" human multidrug resistance-associated proteins (MRP1/ABCC1, MRP2/ABCC2, MRP3/ABCC3, MRP6/ABCC6, and MRP7/ABCC10). In order to provide a detailed biochemical characterisation we expressed DMRP in Sf9 insect cell membranes. We demonstrated DMRP as a functional orthologue of its human counterparts capable of transporting several human MRP substrates like beta-estradiol 17-beta-D-glucuronide, leukotriene C4, calcein, fluo3 and carboxydichlorofluorescein. Unexpectedly, we found DMRP to exhibit an extremely high turnover rate for the substrate transport as compared to its human orthologues. Furthermore, DMRP showed remarkably high basal ATPase activity (68-75 nmol Pi/mg membrane protein/min), which could be further stimulated by probenecid and the glutathione conjugate of N-ethylmaleimide. Surprisingly, this high level basal ATPase activity was inhibited by the transported substrates. We discussed this phenomenon in the light of a potential endogenous substrate (or activator) present in the Sf9 membrane. PMID:19059376

  18. Modeling the rate of turnover of DOC and particulate organic carbon in a UK, peat-hosted stream: Including diurnal cycling in short-residence time systems

    NASA Astrophysics Data System (ADS)

    Worrall, F.; Moody, C. S.

    2014-10-01

    This study proposes a multicomponent, multiprocess scheme to explain the turnover of organic matter (particulate and dissolved organic matter) in streams. The scheme allows for production and degradation of organic matter by both photic and aphotic processes with transformation of dissolved organic carbon (DOC) to increasingly refractory forms. The proposed scheme was compared to 10 months of experimental observations of the turnover and fate of particulate and dissolved organic matter in stream water from a peat-covered catchment. The scheme was able to explain average decline in DOC concentration of 65% over 70 h with a 13% mean average percentage error based on turnover in three types of organic matter (particulate, labile dissolved, and refractory dissolved) although the order and rate of reactions did change between sets of experimental observations. The modeling suggests that activation energies are low for all except the most refractory forms of DOC in turn, suggesting that processes are not sensitive to temperature change. Application of the modeling scheme to organic matter turnover in the River Tees, northern England, showed that annual removal of total organic carbon was equivalent to between 13 and 33 t C/km2/yr from an at source export of between 22 and 56 t C/km2/yr giving a total in-stream loss rate of between 53 and 62% over a median in-stream residence time of 35 h.

  19. Tackling Teacher Turnover in Child Care: Understanding Causes and Consequences, Identifying Solutions

    ERIC Educational Resources Information Center

    Hale-Jinks, Claudia; Knopf, Herman; Kemple, Kristen

    2006-01-01

    "Teacher turnover," the number of teachers who leave a program during a year has numerous detrimental effects that can lower the quality of care received by children and families. High rates of teacher turnover, high child-to-adult ratios, and poorly trained staff characterize poor-quality child care in the United States. In fact, high rates of…

  20. Effects of norepinephrine infusion on myocardial high-energy phosphate content and turnover in the living rat.

    PubMed Central

    Bittl, J A; Balschi, J A; Ingwall, J S

    1987-01-01

    Using 31P-nuclear magnetic resonance, we studied the relationship between myocardial high-energy phosphate content and flux values for the creatine kinase reaction in the living rat under inotropic states achieved during norepinephrine infusion and halothane anesthesia. Under 2% halothane anesthesia (n = 4), 1% halothane anesthesia (n = 5) and norepinephrine infusion (n = 4), rats developed rate-pressure products of 19.5 +/- 1.6, 32.0 +/- 3.5, and 48.5 +/- 2.0 X 1,000 mmHg/min, respectively. Adenosine triphosphate content was not affected by inotropic state, ranging from 24.3 +/- 1.1 to 25.6 +/- 1.1 mumol/g dry weight, but creatine phosphate content varied inversely and reversibly with cardiac performance from 45.6 +/- 6.0 under 2% halothane to 26.0 +/- 6.5 mumol/g dry weight during norepinephrine infusion. The flux values for the creatine kinase reaction were 15.4 +/- 4.6, 20.5 +/- 2.0, and 30.1 +/- 7.9 mumol/g dry weight per s under 2% halothane, 1% halothane, and 1% halothane with norepinephrine, respectively. These results suggest that the turnover of myocardial high-energy phosphate compounds, not their tissue contents, matches cardiac performance during inotropic stimulation. Images PMID:3584473

  1. Mice expressing markedly reduced striatal dopamine transporters exhibit increased locomotor activity, dopamine uptake turnover rate, and cocaine responsiveness.

    PubMed

    Rao, Anjali; Sorkin, Alexander; Zahniser, Nancy R

    2013-10-01

    Variations in the expression levels of the dopamine transporter (DAT) can influence responsiveness to psychostimulant drugs like cocaine. To better understand this relationship, we studied a new DAT-low expresser (DAT-LE) mouse model and performed behavioral and biochemical studies with it. Immunoblotting and [(3) H]WIN 35,428 binding analyses revealed that these mice express ∼35% of wildtype (WT) mouse striatal DAT levels. Compared to WT mice, DAT-LE mice were hyperactive in a novel open-field environment. Despite their higher basal locomotor activity, cocaine (10 or 20 mg/kg, i.p.) induced greater locomotor activation in DAT-LE mice than in WT mice. The maximal velocity (Vmax ) of DAT-mediated [(3) H]DA uptake into striatal synaptosomes was reduced by 46% in DAT-LE mice, as compared to WT. Overall, considering the reduced number of DAT binding sites (Bmax ) along with the reduced Vmax in DAT-LE mice, a 2-fold increase in DA uptake turnover rate (Vmax /Bmax ) was found, relative to WT mice. This suggests that neuroadaptive changes have occurred in the DAT-LE mice that would help to compensate for their low DAT numbers. Interestingly, these changes do not include a reduction in tyrosine hydroxylase levels, as was previously reported in DAT knockout homozygous and heterozygous animals. Further, these changes are not sufficient to prevent elevated novelty- and cocaine-induced locomotor activity. Hence, these mice represent a unique model for studying changes of in vivo DAT function and regulation that result from markedly reduced levels of DAT expression. PMID:23564231

  2. Modulation of the Active Complex Assembly and Turnover Rate by Protein–DNA Interactions in Cre–LoxP Recombination†,‡

    PubMed Central

    Martin, Shelley S.; Chu, Victor C.; Baldwin, Enoch

    2010-01-01

    Cre promotes recombination at the 34 bp LoxP sequence. Substitution of a critical C-G base pair in LoxP with an A-T base pair, to give LoxAT, reduced Cre binding in vitro and abolished recombination in vivo. We demonstrated that LoxAT can be recombined in vitro. However, Cre discriminates against this substrate both before and after DNA binding. The preference for LoxP over LoxAT is the result of reduced binding and a slower turnover rate, amplified by changes in cooperativity of complex assembly. With LoxAT, similar levels of substrate turnover required 2–2.5-fold higher protein–DNA concentrations compared to LoxP, but the sigmoidal behavior of the concentration dependence was more pronounced. Further, the Cre–LoxAT complexes reacted 4–5-fold more slowly. In the 2.3 Å resolution Cre–LoxAT complex structure, the major groove Arg259–guanine interaction was disrupted, explaining the reduced binding. Overall structural shifts and mobility changes indicate more favorable interactions between subunits, providing a hypothesis for the reduced turnover rate. Concomitant with the displacement of Arg259 from the DNA, adjacent charged residues Glu262 and Glu266 shifted to form salt bridges with the Arg259 guanidinium moiety. Substitution of Glu262 and Glu266 with glutamine increased Cre complex assembly efficiency and reaction rates with both LoxAT and LoxP, but diminished Cre’s ability to distinguish them. The increased rate of this variant suggests that DNA substrate binding and turnover are coupled. The improved efficiency, made at some expense of sequence discrimination, may be useful for enhancing recombination in vivo. PMID:12779336

  3. High Rate Digital Demodulator ASIC

    NASA Technical Reports Server (NTRS)

    Ghuman, Parminder; Sheikh, Salman; Koubek, Steve; Hoy, Scott; Gray, Andrew

    1998-01-01

    The architecture of High Rate (600 Mega-bits per second) Digital Demodulator (HRDD) ASIC capable of demodulating BPSK and QPSK modulated data is presented in this paper. The advantages of all-digital processing include increased flexibility and reliability with reduced reproduction costs. Conventional serial digital processing would require high processing rates necessitating a hardware implementation in other than CMOS technology such as Gallium Arsenide (GaAs) which has high cost and power requirements. It is more desirable to use CMOS technology with its lower power requirements and higher gate density. However, digital demodulation of high data rates in CMOS requires parallel algorithms to process the sampled data at a rate lower than the data rate. The parallel processing algorithms described here were developed jointly by NASA's Goddard Space Flight Center (GSFC) and the Jet Propulsion Laboratory (JPL). The resulting all-digital receiver has the capability to demodulate BPSK, QPSK, OQPSK, and DQPSK at data rates in excess of 300 Mega-bits per second (Mbps) per channel. This paper will provide an overview of the parallel architecture and features of the HRDR ASIC. In addition, this paper will provide an over-view of the implementation of the hardware architectures used to create flexibility over conventional high rate analog or hybrid receivers. This flexibility includes a wide range of data rates, modulation schemes, and operating environments. In conclusion it will be shown how this high rate digital demodulator can be used with an off-the-shelf A/D and a flexible analog front end, both of which are numerically computer controlled, to produce a very flexible, low cost high rate digital receiver.

  4. Determination of the Na+/Glucose Cotransporter (SGLT1) Turnover Rate Using the Ion-Trap Technique

    PubMed Central

    Longpré, Jean-Philippe; Lapointe, Jean-Yves

    2011-01-01

    The Na+/glucose cotransporter (SGLT1) is a membrane protein that couples the transport of two Na+ ions and one glucose molecule using the so-called alternating access mechanism. According to this principle, each cotransporter molecule can adopt either of two main conformations: one with the binding sites accessible to the extracellular solution and one with the binding sites facing the intracellular solution. The turnover rate (TOR) is the number of complete cycles that each protein performs per second. Determination of the TOR has important consequences for investigation of the cotransport mechanism, as none of the rate constants involved in mediating transport in a given direction (conformational changes and binding and unbinding reactions) can be slower than the TOR measured under the same conditions. In addition, the TOR can be used to estimate the number of cotransporter molecules involved in generating a given ensemble activity. In this study, we obtain an independent estimation of the TOR for human SGLT1 expressed in Xenopus laevis oocytes applying the ion-trap technique. This approach detects the quantity of ions released in or taken up from the restricted space existing between the oocyte plasma membrane and the tip of a large ion-selective electrode. Taking advantage of the fact that hSGLT1 in the absence of Na+ can cotransport glucose with protons, we used a pH electrode to determine a TOR of 8.00 ± 1.3 s−1 in the presence of 35 mM α-methyl-glucose at −150 mV (pH 5.5). For the same group of oocytes, a TOR of 13.3 ± 2.4 s−1 was estimated under near-Vmax conditions, i.e., in the presence of 90 mM Na+ and 5 mM α-methyl-glucose. Under these circumstances, the average cotransport current was −1.08 ± 0.61 μA (n = 14), and this activity was generated by an average of 3.6 ± 0.7 × 1011 cotransporter molecules/oocyte. PMID:21190656

  5. A high protein diet upregulated whole-body protein turnover during energy deficit

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effects of higher protein diets and sustained energy deficit (ED) on whole-body protein turnover (WBPTO) are not well described. This study examined whether dietary protein level influences whole-body protein breakdown (Ra), non-oxidative leucine disposal (NOLD), and oxidation (Ox) during ED. ...

  6. Subtle Ecological Gradient in the Tropics Triggers High Species-Turnover in a Local Geographical Scale

    PubMed Central

    Nguyen, Dinh T.

    2016-01-01

    Our perception of diversity, including both alpha- and beta-diversity components, depends on spatial scale. Studies of spatial variation of the latter are just starting, with a paucity of research on beta-diversity patterns at smaller scales. Understanding these patterns and the processes shaping the distribution of diversity is critical to describe this diversity, but it is paramount in conservation too. Here, we investigate the diversity and structure of a tropical community of herbivorous beetles at a reduced local scale of some 10 km2, evaluating the effect of a small, gradual ecological change on this structure. We sampled leaf beetles in the Núi Chúa National Park (S Vietnam), studying changes in alpha- and beta-diversity across an elevation gradient up to 500 m, encompassing the ecotone between critically endangered lowland dry deciduous forest and mixed evergreen forest at higher elevations. Leaf beetle diversity was assessed using several molecular tree-based species delimitation approaches (with mtDNA cox1 data), species richness using rarefaction and incidence-based diversity indexes, and beta-diversity was investigated decomposing the contribution of species turnover and nestedness. We documented 155 species in the area explored and species-richness estimates 1.5–2.0x higher. Species diversity was similar in both forest types and changes in alpha-diversity along the elevation gradient showed an expected local increase of diversity in the ecotone. Beta-diversity was high among forest paths (average Sørensen's dissimilarity = 0.694) and, tentatively fixing at 300 m the boundary between otherwise continuous biomes, demonstrated similarly high beta-diversity (Sørensen's dissimilarity = 0.581), with samples clustering according to biome/elevation. Highly relevant considering the local scale of the study, beta-diversity had a high contribution of species replacement among locales (54.8%) and between biomes (79.6%), suggesting environmental heterogeneity

  7. Subtle Ecological Gradient in the Tropics Triggers High Species-Turnover in a Local Geographical Scale.

    PubMed

    Nguyen, Dinh T; Gómez-Zurita, Jesús

    2016-01-01

    Our perception of diversity, including both alpha- and beta-diversity components, depends on spatial scale. Studies of spatial variation of the latter are just starting, with a paucity of research on beta-diversity patterns at smaller scales. Understanding these patterns and the processes shaping the distribution of diversity is critical to describe this diversity, but it is paramount in conservation too. Here, we investigate the diversity and structure of a tropical community of herbivorous beetles at a reduced local scale of some 10 km2, evaluating the effect of a small, gradual ecological change on this structure. We sampled leaf beetles in the Núi Chúa National Park (S Vietnam), studying changes in alpha- and beta-diversity across an elevation gradient up to 500 m, encompassing the ecotone between critically endangered lowland dry deciduous forest and mixed evergreen forest at higher elevations. Leaf beetle diversity was assessed using several molecular tree-based species delimitation approaches (with mtDNA cox1 data), species richness using rarefaction and incidence-based diversity indexes, and beta-diversity was investigated decomposing the contribution of species turnover and nestedness. We documented 155 species in the area explored and species-richness estimates 1.5-2.0x higher. Species diversity was similar in both forest types and changes in alpha-diversity along the elevation gradient showed an expected local increase of diversity in the ecotone. Beta-diversity was high among forest paths (average Sørensen's dissimilarity = 0.694) and, tentatively fixing at 300 m the boundary between otherwise continuous biomes, demonstrated similarly high beta-diversity (Sørensen's dissimilarity = 0.581), with samples clustering according to biome/elevation. Highly relevant considering the local scale of the study, beta-diversity had a high contribution of species replacement among locales (54.8%) and between biomes (79.6%), suggesting environmental heterogeneity

  8. Comparative Genomics Uncovers Unique Gene Turnover and Evolutionary Rates in a Gene Family Involved in the Detection of Insect Cuticular Pheromones

    PubMed Central

    Torres-Oliva, Montserrat; Almeida, Francisca C.; Sánchez-Gracia, Alejandro; Rozas, Julio

    2016-01-01

    Chemoreception is an essential process for the survival and reproduction of animals. Many of the proteins responsible for recognizing and transmitting chemical stimuli in insects are encoded by genes that are members of moderately sized multigene families. The members of the CheB family are specialized in gustatory-mediated detection of long-chain hydrocarbon pheromones in Drosophila melanogaster and play a central role in triggering and modulating mating behavior in this species. Here, we present a comprehensive comparative genomic analysis of the CheB family across 12 species of the Drosophila genus. We have identified a total of 102 new CheB genes in the genomes of these species, including a functionally divergent member previously uncharacterized in D. melanogaster. We found that, despite its relatively small repertory size, the CheB family has undergone multiple gain and loss events and various episodes of diversifying selection during the divergence of the surveyed species. Present estimates of gene turnover and coding sequence substitution rates show that this family is evolving faster than any known Drosophila chemosensory family. To date, only other insect gustatory-related genes among these families had shown evolutionary dynamics close to those observed in CheBs. Our findings reveal the high adaptive potential of molecular components of the gustatory system in insects and anticipate a key role of genes involved in this sensory modality in species adaptation and diversification.

  9. Estimating tissue-specific discrimination factors and turnover rates of stable isotopes of nitrogen and carbon in the smallnose fanskate Sympterygia bonapartii (Rajidae).

    PubMed

    Galván, D E; Jañez, J; Irigoyen, A J

    2016-08-01

    This study aimed to estimate trophic discrimination factors (TDFs) and metabolic turnover rates of nitrogen and carbon stable isotopes in blood and muscle of the smallnose fanskate Sympterygia bonapartii by feeding six adult individuals, maintained in captivity, with a constant diet for 365 days. TDFs were estimated as the difference between δ(13) C or δ(15) N values of the food and the tissues of S. bonapartii after they had reached equilibrium with their diet. The duration of the experiment was enough to reach the equilibrium condition in blood for both elements (estimated time to reach 95% of turnover: C t95%blood  = 150 days, N t95%blood  = 290 days), whilst turnover rates could not be estimated for muscle because of variation among samples. Estimates of Δ(13) C and Δ(15) N values in blood and muscle using all individuals were Δ(13) Cblood = 1·7‰, Δ(13) Cmuscle = 1·3‰, Δ(15) Nblood = 2·5‰ and Δ(15) Nmuscle = 1·5‰, but there was evidence of differences of c.0·4‰ in the Δ(13) C values between sexes. The present values for TDFs and turnover rates constitute the first evidence for dietary switching in batoids based on long-term controlled feeding experiments. Overall, the results showed that S. bonapartii has relatively low turnover rates and isotopic measurements would not track seasonal movements adequately. The estimated Δ(13) C values in S. bonapartii blood and muscle were similar to previous estimations for elasmobranchs and to generally accepted values in bony fishes (Δ(13) C = 1·5‰). For Δ(15) N, the results were similar to published reports for blood but smaller than reports for muscle and notably smaller than the typical values used to estimate trophic position (Δ(15) N c. 3·4‰). Thus, trophic position estimations for elasmobranchs based on typical Δ(15) N values could lead to underestimates of actual trophic positions. Finally, the evidence of differences in TDFs between sexes reveals a need for more

  10. Bayesian inference of decomposition rate of soil organic carbon using a turnover model and a hybrid method of particle filter and MH algorithm

    NASA Astrophysics Data System (ADS)

    Sakurai, G.; Jomura, M.; Yonemura, S.; Iizumi, T.; Shirato, Y.; Yokozawa, M.

    2010-12-01

    The soils of terrestrial ecosystems accumulate large amounts of carbon and the response of soil organic carbon (SOC) to global warming is of great concern in projections of future carbon cycling. While many theoretical and experimental studies have suggested that the decomposition rates of soil organic matters depend upon the physical and chemical conditions, land managements and so on, there has not yet been consensus in the dependencies. Most of the soil carbon turnover models for describing the SOC dynamics do not assume the differences in decomposition rates. The purpose of this study is to evaluate the decomposition rates of SOC based on a soil carbon turnover model, RothC, which describes SOC dynamics dividing it into compartments with different decomposition rates. In this study, reflecting that decomposition rate could change with time due to the fertility management in arable land, we used time-dependent Bayesian inference methods to allow time-change variation of the parameters. Thus, we used a hybrid method of particle filtering methods and MH algorithm. We applied this method to datasets obtained from three long-term experiments on time changes in total SOC at five sites over the Japan mainland. For each dataset, three treatments were examined: no N applied, chemical fertilizer applied, and chemical fertilizer and farmyard manure applied. We estimated parameters on the temperature and water dependent functions as well as the intrinsic decomposition rate for each compartment of RothC and for each treatment. As a result, it was shown that the temperature dependencies tended to decreased with the decomposability of the compartment, i.e. lower temperature dependency for more recalcitrant compartment of the model. On the other hand, the water dependencies were not determined with the SOC turnover rates of the compartments. Additionally, the intrinsic decomposition rates tended to increase with time especially in no N applied treatment. This result reflects

  11. Effect of phenmetrazine, aminorex and (±) p-chloramphetamine on the motor activity and turnover rate of brain catecholamines

    PubMed Central

    Costa, E.; Naimzada, K. M.; Revuelta, A.

    1971-01-01

    1. The minimal doses (μmol/kg i.v.) of phenmetrazine, (±)-p-chloramphetamine, and aminorex which increase motor activity are 5·6, 3·5, and 1·5, respectively. We detected stereotype behaviour neither in rats receiving intravenous doses 3 times greater nor in animals injected intraperitoneally with 44, 62 and 112 μmol/kg of (±)-p-chloramphetamine, aminorex and phenmatrazine, respectively. 2. The latter doses of the three amphetamine congeners were tested for their action on tissue monoamine content. Only (±)-p-chloramphetamine decreased the concentration of tel-diencephalon 5-hydroxytryptamine (5-HT) and this decrease lasted longer than 24 hours. This and the other two amphetamine congeners failed to affect the concentration of noradrenaline (NA) in brain, heart and lung. 3. Aminorex (1·5 μmol/kg i.v.) and (±)-p-chloramphetamine (3·5 μmol/kg i.v.) decreased the turnover time of striatum dopamine (DM) but failed to change the turnover time of tel-diencephalon and brainstem NA. Phenmetrazine (5·6 μmol/kg i.v.) changed neither the turnover time of striatum DM nor that of NA in the two brain areas assayed. PMID:5157723

  12. Director Turnover: An Australian Academic Development Study

    ERIC Educational Resources Information Center

    Fraser, Kym; Ryan, Yoni

    2012-01-01

    Although it can be argued that directors of central academic development units (ADUs) are critical to the implementation of university teaching and learning strategies, it would appear there is a high director turnover rate. While research in the USA, the UK, and Australia illustrates that ADUs are frequently closed or restructured, that research…

  13. The Presence of Thyroid-Stimulation Blocking Antibody Prevents High Bone Turnover in Untreated Premenopausal Patients with Graves’ Disease

    PubMed Central

    Cho, Sun Wook; Bae, Jae Hyun; Noh, Gyeong Woon; Kim, Ye An; Moon, Min Kyong; Park, Kyoung Un; Song, Junghan; Yi, Ka Hee; Park, Do Joon; Chung, June-Key; Cho, Bo Youn; Park, Young Joo

    2015-01-01

    Osteoporosis-related fractures are one of the complications of Graves’ disease. This study hypothesized that the different actions of thyroid-stimulating hormone receptor (TSHR) antibodies, both stimulating and blocking activities in Graves’ disease patients might oppositely impact bone turnover. Newly diagnosed premenopausal Graves’ disease patients were enrolled (n = 93) and divided into two groups: patients with TSHR antibodies with thyroid-stimulating activity (stimulating activity group, n = 83) and patients with TSHR antibodies with thyroid-stimulating activity combined with blocking activity (blocking activity group, n = 10). From the stimulating activity group, patients who had matched values for free T4 and TSH binding inhibitor immunoglobulin (TBII) to the blocking activity group were further classified as stimulating activity-matched control (n = 11). Bone turnover markers BS-ALP, Osteocalcin, and C-telopeptide were significantly lower in the blocking activity group than in the stimulating activity or stimulating activity-matched control groups. The TBII level showed positive correlations with BS-ALP and osteocalcin levels in the stimulating activity group, while it had a negative correlation with the osteocalcin level in the blocking activity group. In conclusion, the activation of TSHR antibody-activated TSH signaling contributes to high bone turnover, independent of the actions of thyroid hormone, and thyroid-stimulation blocking antibody has protective effects against bone metabolism in Graves’ disease. PMID:26650844

  14. The Presence of Thyroid-Stimulation Blocking Antibody Prevents High Bone Turnover in Untreated Premenopausal Patients with Graves' Disease.

    PubMed

    Cho, Sun Wook; Bae, Jae Hyun; Noh, Gyeong Woon; Kim, Ye An; Moon, Min Kyong; Park, Kyoung Un; Song, Junghan; Yi, Ka Hee; Park, Do Joon; Chung, June-Key; Cho, Bo Youn; Park, Young Joo

    2015-01-01

    Osteoporosis-related fractures are one of the complications of Graves' disease. This study hypothesized that the different actions of thyroid-stimulating hormone receptor (TSHR) antibodies, both stimulating and blocking activities in Graves' disease patients might oppositely impact bone turnover. Newly diagnosed premenopausal Graves' disease patients were enrolled (n = 93) and divided into two groups: patients with TSHR antibodies with thyroid-stimulating activity (stimulating activity group, n = 83) and patients with TSHR antibodies with thyroid-stimulating activity combined with blocking activity (blocking activity group, n = 10). From the stimulating activity group, patients who had matched values for free T4 and TSH binding inhibitor immunoglobulin (TBII) to the blocking activity group were further classified as stimulating activity-matched control (n = 11). Bone turnover markers BS-ALP, Osteocalcin, and C-telopeptide were significantly lower in the blocking activity group than in the stimulating activity or stimulating activity-matched control groups. The TBII level showed positive correlations with BS-ALP and osteocalcin levels in the stimulating activity group, while it had a negative correlation with the osteocalcin level in the blocking activity group. In conclusion, the activation of TSHR antibody-activated TSH signaling contributes to high bone turnover, independent of the actions of thyroid hormone, and thyroid-stimulation blocking antibody has protective effects against bone metabolism in Graves' disease. PMID:26650844

  15. Turnover Time

    EPA Science Inventory

    Ecosystems contain energy and materials such as carbon, nitrogen, phosphorus, and water, and are open to their flow-through. Turnover time refers to the amount of time required for replacement by flow-through of the energy or substance of interest contained in the system, and is ...

  16. High Data Rate Instrument Study

    NASA Technical Reports Server (NTRS)

    Schober, Wayne; Lansing, Faiza; Wilson, Keith; Webb, Evan

    1999-01-01

    The High Data Rate Instrument Study was a joint effort between the Jet Propulsion Laboratory (JPL) and the Goddard Space Flight Center (GSFC). The objectives were to assess the characteristics of future high data rate Earth observing science instruments and then to assess the feasibility of developing data processing systems and communications systems required to meet those data rates. Instruments and technology were assessed for technology readiness dates of 2000, 2003, and 2006. The highest data rate instruments are hyperspectral and synthetic aperture radar instruments which are capable of generating 3.2 Gigabits per second (Gbps) and 1.3 Gbps, respectively, with a technology readiness date of 2003. These instruments would require storage of 16.2 Terebits (Tb) of information (RF communications case of two orbits of data) or 40.5 Tb of information (optical communications case of five orbits of data) with a technology readiness date of 2003. Onboard storage capability in 2003 is estimated at 4 Tb; therefore, all the data created cannot be stored without processing or compression. Of the 4 Tb of stored data, RF communications can only send about one third of the data to the ground, while optical communications is estimated at 6.4 Tb across all three technology readiness dates of 2000, 2003, and 2006 which were used in the study. The study includes analysis of the onboard processing and communications technologies at these three dates and potential systems to meet the high data rate requirements. In the 2003 case, 7.8% of the data can be stored and downlinked by RF communications while 10% of the data can be stored and downlinked with optical communications. The study conclusion is that only 1 to 10% of the data generated by high data rate instruments will be sent to the ground from now through 2006 unless revolutionary changes in spacecraft design and operations such as intelligent data extraction are developed.

  17. A new method combining soil oxygen concentration measurements with the quantification of gross nitrogen turnover rates and associated formation of N2O and N2 emissions

    NASA Astrophysics Data System (ADS)

    Gütlein, Adrian; Dannenmann, Michael; Sörgel, Christoph; Meier, Rudi; Meyer, Astrid; Kiese, Ralf

    2014-05-01

    Climate change and the expansion of land use have led to significant changes in terrestrial ecosystems. These include changes in the biogeochemical cycle of nitrogen and therewith implications for biodiversity, water cycle and pedosphere-atmosphere exchange. To understand these impacts detailed research on nitrogen turnover and fluxes are conducted at various (semi-) natural and managed ecosystems in the Mt. Kilimanjaro region. In this context, we execute 15N tracing analyses on soil samples in our stable isotope laboratory including a new experimental setup. The soils were sampled from different forest ecosystems of Mt. Kilimanjaro varying in altitude (1600 - 4500 m) and will be analyzed for gross rates of ammonification and nitrification, gross rates of microbial inorganic N uptake as well as for the gaseous losses of ^15N2 and ^15N2O using ^15NH4+ and ^15NO3- tracing and pool dilution approaches. Since nitrogen turnover of nitrification and denitrification is dependent on soil oxygen concentrations we developed an incubation method which allows to adjust soil samples to different oxygen concentrations. For this purpose, soil is incubated in glass bottles with side tubes to ensure a constant gas flow over the whole incubation time. To adjust the oxygen levels in the laboratory experiment as close as possible to the natural conditions, we started to monitor soil oxygen concentrations with a FirestingO2 Sensor (Pyroscience) connected to a timer and a datalogger (MSR 145 IP 60 E3333) at a Mt. Kilimanjaro rainforest site. The equipment is complemented with soil temperature, moisture and pressure sensors (MSR 145 IP 60). A solar panel connected to an energy source guarantees a working time for over 2 years by a measuring frequency of 20 seconds each 30 minutes. The new laboratory incubation method together with in-situ oxygen concentration measurements in soils will facilitate laboratory incubations with realistic oxygen concentrations and thus will allow for a better

  18. Changes in floral diversities, floral turnover rates, and climates in Campanian and Maastrichtian time, North Slope of Alaska

    USGS Publications Warehouse

    Frederiksen, N.O.

    1989-01-01

    One-hundred-and-ten angiosperm pollen taxa have been found in upper Campanian to Masstrichtian rocks of the Colville River region, North Slope of Alaska. These are the highest paleolatitude Campanian and Maastrichtian floras known from North America. Total angiosperm pollen diversity rose during the Campanian and declined toward the end of the Maastrichtian. However, anemophilous porate pollen of the Betulaceae-Myricaceae-Ulmaceae complex increased gradually in diversity during the late Campanian and Maastrichtian and into the Paleocene. Turnover of angiosperm taxa was active throughout most of late Campanian and Maastrichtian time; rapid turnover affected mainly the taxa of zoophilous herbs, representing an bundant but ecologically subordinate element of the vegetation. Last appearances of pollen taxa during the late Campanian and Maastrichtian probably represented mainly extinctions rather than emigrations; end- Cretaceous angiosperm extinctions in the North American Arctic began well before the Cretaceous-Tertiary boundary event. The last appearances in the late Maastrichtian took place in bursts; they appear to represent stepwise rather than gradual events, which may indicate the existence of pulses of climatic change particularly in late Maastrichtian time. ?? 1989.

  19. What are the reasons for high turnover in nursing? A discussion of presumed causal factors and remedies.

    PubMed

    Currie, Elizabeth J; Carr Hill, Roy A

    2012-09-01

    Problems with high turnover in nursing and of maintaining adequate numbers of nurses to supply clinical staffing requirements have a long history and have therefore attracted a commensurate literature with time. An overview and discussion of the situation internationally, with an emphasis on Organisation for Economic Co-operation and Development (OECD) countries and the UK, finds that job satisfaction is often a consistent underlying determinant interacting with workplace factors and personal reasons in complex ways. Effective and adaptive retention strategies are required to meet and mitigate the problem as reasons for it may vary over time. Solutions must be flexible and targeted to meet the individual circumstances identified. PMID:22321821

  20. Subtle Changes to Peripheral Ligands Enable High Turnover Numbers for Photocatalytic Hydrogen Generation with Supramolecular Photocatalysts.

    PubMed

    Kowacs, Tanja; O'Reilly, Laura; Pan, Qing; Huijser, Annemarie; Lang, Philipp; Rau, Sven; Browne, Wesley R; Pryce, Mary T; Vos, Johannes G

    2016-03-21

    The photocatalytic generation of hydrogen (H2) from protons by two cyclometalated ruthenium-platinum polypyridyl complexes, [Ru(bpy)2(2,5-bpp)PtIS](2+) (1) and [Ru(dceb)2(2,5-bpp)PtIS](2+) (2) [where bpy = 2,2'-bipyridine, 2,5-bpp = 2,2',5',2″-terpyridine, dceb = 4,4'-di(carboxyethyl)bipyridine, and S = solvent], is reported. Turnover numbers (TONs) for H2 generation were increased by nearly an order of magnitude by the introduction of carboxyethyl ester units, i.e., from 80 for 1P to 650 for 2P after 6 h of irradiation, with an early turnover frequency (TOF) increasing from 15 to 200 h(-1). The TON and TOF values for 2P are among the highest reported to date for supramolecular photocatalysts. The increase correlates with stabilization of the excited states localized on the peripheral ligands of the light-harvesting Ru(II) center. PMID:26925834

  1. Glucose utilization in the medial prefrontal cortex correlates with serotonin turnover rate and clinical depression in alcoholics.

    PubMed

    Williams, Wendol; Reimold, Matthias; Kerich, Michael; Hommer, Dan; Bauer, Michael; Heinz, Andreas

    2004-12-30

    We measured the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF), regional cerebral glucose uptake (rCMRglc) as assessed with positron emission tomography in the medial prefrontal cortex (PFC) and severity of clinical depression (Beck's Depression Inventory, BDI) in detoxified male alcoholics and age-matched healthy men. In alcoholics, the severity of clinical depression was negatively correlated with rCMRglc in the medial PFC and positively with CSF 5-HIAA concentrations. A voxel-based analysis showed that the strongest correlation between CSF 5-HIAA levels and rCMRglc was found in alcoholics in the left orbitofrontal and medial PFC (BA10 and BA11); no significant correlations were observed among healthy control subjects. This pilot study indicates that a dysfunction of medial PFC may interact with central serotonin turnover and negative mood states during early abstinence. PMID:15664793

  2. Plant Trait Variation along an Altitudinal Gradient in Mediterranean High Mountain Grasslands: Controlling the Species Turnover Effect

    PubMed Central

    Pescador, David S.; de Bello, Francesco; Valladares, Fernando; Escudero, Adrián

    2015-01-01

    Assessing changes in plant functional traits along gradients is useful for understanding the assembly of communities and their response to global and local environmental drivers. However, these changes may reflect the effects of species composition (i.e. composition turnover), species abundance (i.e. species interaction), and intra-specific trait variability (i.e. species plasticity). In order to determine the relevance of the latter, trait variation can be assessed under minimal effects of composition turnover. Nine sampling sites were established along an altitudinal gradient in a Mediterranean high mountain grassland community with low composition turnover (Madrid, Spain; 1940 m–2419 m). Nine functional traits were also measured for ten individuals of around ten plant species at each site, for a total of eleven species across all sites. The relative importance of different sources of variability (within/between site and intra-/inter-specific functional diversity) and trait variation at species and community level along the considered gradients were explored. We found a weak individual species response to altitude and other environmental variables although in some cases, individuals were smaller and leaves were thicker at higher elevations. This lack of species response was most likely due to greater within- than between-site species variation. At the community level, inter-specific functional diversity was generally greater than the intra-specific component except for traits linked to leaf element content (leaf carbon content, leaf nitrogen content, δ13C and δ15N). Inter-specific functional diversity decreased with lower altitude for four leaf traits (specific leaf area, leaf dry matter content, δ13C and δ15N), suggesting trait convergence between species at lower elevations, where water shortage may have a stronger environmental filtering effect than colder temperatures at higher altitudes. Our results suggest that, within a vegetation type encompassing

  3. Collagen synthesis and degradation in vivo. Evidence for rapid rates of collagen turnover with extensive degradation of newly synthesized collagen in tissues of the adult rat.

    PubMed

    McAnulty, R J; Laurent, G J

    1987-06-01

    Collagen turnover is now known to occur more rapidly in body tissues than traditionally believed, but the kinetics and mechanisms for degradation are still poorly understood. Here we measure collagen synthesis rates and the proportion of newly synthesized collagen (probably procollagen) which is rapidly degraded, in tissues of the adult rat after injection of [14C]-proline with a large "flooding" dose of unlabelled proline. Incorporation of [14C]-proline into lung, heart, skeletal muscle and skin collagen and its appearance as hydroxy [14C]-proline, free or in small molecular weight moieties, at various times up to one hour, suggested extremely rapid synthesis and degradation for some tissues of the adult rat. Values in heart, lung, skeletal muscle and skin (with the proportion of degradation of newly synthesized collagen shown in parentheses) were 5.2 +/- 0.7%/day (53 +/- 5%), 9.0 +/- 0.7%/day (37 +/- 2%), 2.2 +/- 0.3%/day (38 +/- 7%) and 4.4 +/- 1.3%/day (8.8 +/- 0.5%). These data provide in vivo evidence, which are consistent with the observation in isolated cells, that a proportion of newly synthesized collagen is degraded rapidly, and probably intracellularly, after its synthesis. They also indicate that collagen may be synthesized and degraded rapidly in normal rat tissues, but the mean turnover rates and the proportions of collagen degraded intracellularly vary widely between tissues. PMID:3497767

  4. Using Turnover as a Recruitment Strategy

    ERIC Educational Resources Information Center

    Duncan, Sandra

    2009-01-01

    Teacher turnover is notoriously high in the field of early childhood education with an estimated 33% of staff exiting the workplace each year. Turnover is costly. Not only do high levels of turnover negatively impact children's growth and development, it also erodes the program's economic stability and wherewithal to provide effective operations…

  5. High rate manure supernatant digestion.

    PubMed

    Bergland, Wenche Hennie; Dinamarca, Carlos; Toradzadegan, Mehrdad; Nordgård, Anna Synnøve Røstad; Bakke, Ingrid; Bakke, Rune

    2015-06-01

    The study shows that high rate anaerobic digestion may be an efficient way to obtain sustainable energy recovery from slurries such as pig manure. High process capacity and robustness to 5% daily load increases are observed in the 370 mL sludge bed AD reactors investigated. The supernatant from partly settled, stored pig manure was fed at rates giving hydraulic retention times, HRT, gradually decreased from 42 to 1.7 h imposing a maximum organic load of 400 g COD L(-1) reactor d(-1). The reactors reached a biogas production rate of 97 g COD L(-1) reactor d(-1) at the highest load at which process stress signs were apparent. The yield was ∼0.47 g COD methane g(-1) CODT feed at HRT above 17 h, gradually decreasing to 0.24 at the lowest HRT (0.166 NL CH4 g(-1) CODT feed decreasing to 0.086). Reactor pH was innately stable at 8.0 ± 0.1 at all HRTs with alkalinity between 9 and 11 g L(-1). The first stress symptom occurred as reduced methane yield when HRT dropped below 17 h. When HRT dropped below 4 h the propionate removal stopped. The yield from acetate removal was constant at 0.17 g COD acetate removed per g CODT substrate. This robust methanogenesis implies that pig manure supernatant, and probably other similar slurries, can be digested for methane production in compact and effective sludge bed reactors. Denaturing gradient gel electrophoresis (DGGE) analysis indicated a relatively fast adaptation of the microbial communities to manure and implies that non-adapted granular sludge can be used to start such sludge bed bioreactors. PMID:25776915

  6. Analysis of a Mentoring Program to Change Attitudes Related to Turnover of Special Needs Teachers

    ERIC Educational Resources Information Center

    Eson-Brizo, Jaimie

    2010-01-01

    High teacher turnover was a problem at the preschool for students with autism where this study took place. The primary purpose of this project was to create and implement a mentor program that would effectively decrease turnover rates of newly hired teachers. The secondary purpose was to determine whether newly hired teachers changed their…

  7. Understanding Job Satisfaction and Turnover in the Home Aide Work Force.

    ERIC Educational Resources Information Center

    Feldman, Penny Hollander; Sapienza, Alice M.

    Increasing demands for home health aides to the frail elderly and disabled, coupled with a high rate of turnover among these aides, has led to growing concerns over worker recruitment and retention in the home care industry. This paper therefore describes a model developed to explain job satisfaction and turnover among home health aides. The model…

  8. Mobility-Related Teacher Turnover and the Unequal Distribution of Experienced Teachers in Turkey

    ERIC Educational Resources Information Center

    Özoglu, Murat

    2015-01-01

    This study investigates the issue of mobility-related teacher turnover in Turkey through both quantitative and qualitative methods. The quantitative findings derived from descriptive and correlational analyses of countrywide teacher-assignment and transfer data indicate that a high rate of mobility-related turnover is observed in the…

  9. On-call work and physicians' turnover intention: the moderating effect of job strain.

    PubMed

    Heponiemi, Tarja; Presseau, Justin; Elovainio, Marko

    2016-01-01

    Physician shortage and turnover are major problems worldwide. On-call duties may be among the risk factors of high turnover rates among physicians. We investigated whether having on-call duties is associated with physicians' turnover intention and whether job strain variables moderate this association. The present study was a cross-sectional questionnaire study among 3324 (61.6% women) Finnish physicians. The analyses were conducted using analyses of covariance adjusted for age, gender, response format, specialization status and employment sector. The results showed that job strain moderated the association between being on-call and turnover intention. The highest levels of turnover intention were among those who had on-call duties and high level of job strain characterized by high demands and low control opportunities. The lowest levels of turnover intention were among those who were not on-call and who had low strain involving low demands and high control. Also, job demands moderated the association between being on-call and turnover intention; turnover intention levels were higher among those with on-call duties and high demands than those being on-call and low demands. To conclude, working on-call was related to physicians' turnover intention particularly in those with high job strain. Health care organizations should focus more attention on working arrangements and scheduling of on-call work, provide a suitable working pace and implement means to increase physicians' participation and control over their job. PMID:26072662

  10. Fast demographic traits promote high diversification rates of Amazonian trees

    PubMed Central

    Baker, Timothy R; Pennington, R Toby; Magallon, Susana; Gloor, Emanuel; Laurance, William F; Alexiades, Miguel; Alvarez, Esteban; Araujo, Alejandro; Arets, Eric J M M; Aymard, Gerardo; de Oliveira, Atila Alves; Amaral, Iêda; Arroyo, Luzmila; Bonal, Damien; Brienen, Roel J W; Chave, Jerome; Dexter, Kyle G; Di Fiore, Anthony; Eler, Eduardo; Feldpausch, Ted R; Ferreira, Leandro; Lopez-Gonzalez, Gabriela; van der Heijden, Geertje; Higuchi, Niro; Honorio, Eurídice; Huamantupa, Isau; Killeen, Tim J; Laurance, Susan; Leaño, Claudio; Lewis, Simon L; Malhi, Yadvinder; Marimon, Beatriz Schwantes; Marimon Junior, Ben Hur; Monteagudo Mendoza, Abel; Neill, David; Peñuela-Mora, Maria Cristina; Pitman, Nigel; Prieto, Adriana; Quesada, Carlos A; Ramírez, Fredy; Ramírez Angulo, Hirma; Rudas, Agustin; Ruschel, Ademir R; Salomão, Rafael P; de Andrade, Ana Segalin; Silva, J Natalino M; Silveira, Marcos; Simon, Marcelo F; Spironello, Wilson; ter Steege, Hans; Terborgh, John; Toledo, Marisol; Torres-Lezama, Armando; Vasquez, Rodolfo; Vieira, Ima Célia Guimarães; Vilanova, Emilio; Vos, Vincent A; Phillips, Oliver L; Wiens, John

    2014-01-01

    The Amazon rain forest sustains the world's highest tree diversity, but it remains unclear why some clades of trees are hyperdiverse, whereas others are not. Using dated phylogenies, estimates of current species richness and trait and demographic data from a large network of forest plots, we show that fast demographic traits – short turnover times – are associated with high diversification rates across 51 clades of canopy trees. This relationship is robust to assuming that diversification rates are either constant or decline over time, and occurs in a wide range of Neotropical tree lineages. This finding reveals the crucial role of intrinsic, ecological variation among clades for understanding the origin of the remarkable diversity of Amazonian trees and forests. PMID:24589190

  11. High Resolution, High Frame Rate Video Technology

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Papers and working group summaries presented at the High Resolution, High Frame Rate Video (HHV) Workshop are compiled. HHV system is intended for future use on the Space Shuttle and Space Station Freedom. The Workshop was held for the dual purpose of: (1) allowing potential scientific users to assess the utility of the proposed system for monitoring microgravity science experiments; and (2) letting technical experts from industry recommend improvements to the proposed near-term HHV system. The following topics are covered: (1) State of the art in the video system performance; (2) Development plan for the HHV system; (3) Advanced technology for image gathering, coding, and processing; (4) Data compression applied to HHV; (5) Data transmission networks; and (6) Results of the users' requirements survey conducted by NASA.

  12. High accuracy optical rate sensor

    NASA Technical Reports Server (NTRS)

    Uhde-Lacovara, J.

    1990-01-01

    Optical rate sensors, in particular CCD arrays, will be used on Space Station Freedom to track stars in order to provide inertial attitude reference. An algorithm to provide attitude rate information by directly manipulating the sensor pixel intensity output is presented. The star image produced by a sensor in the laboratory is modeled. Simulated, moving star images are generated, and the algorithm is applied to this data for a star moving at a constant rate. The algorithm produces accurate derived rate of the above data. A step rate change requires two frames for the output of the algorithm to accurately reflect the new rate. When zero mean Gaussian noise with a standard deviation of 5 is added to the simulated data of a star image moving at a constant rate, the algorithm derives the rate with an error of 1.9 percent at a rate of 1.28 pixels per frame.

  13. Understanding the factors that determine registered nurses' turnover intentions.

    PubMed

    Osuji, Joseph; Uzoka, Faith-Michael; Aladi, Flora; El-Hussein, Mohammed

    2014-01-01

    Turnover among registered nurses (RNs) produces a negative impact on the health outcomes of any health care organization. It is also recognized universally as a problem in the nursing profession. Little is known about the turnover intentions and career orientations of RNs working in Calgary, Alberta, Canada. The aim of this study is to contribute to the knowledge of and to advance the discussion on the turnover of nursing professionals. The study population consisted of RNs employed in the five major hospitals in Calgary. There were 193 surveys returned, representing a response rate of 77.2%. The results show that age and education have a negative effect on turnover intention. Education was found to have a significant negative effect on career satisfaction but not on job satisfaction and organizational commitment. Length of service has a significant negative effect on turnover intention. Role ambiguity has significant highly negative effect on career satisfaction. Growth opportunity and supervisor support have a very significant positive effect on job satisfaction, career satisfaction, and organizational commitment. External career opportunities and organizational commitment do not seem to have a significant effect on turnover intention. Career satisfaction, on the other hand, had negative significant effects on turnover intention. PMID:25087326

  14. Chronic Teacher Turnover in Urban Elementary Schools

    ERIC Educational Resources Information Center

    Guin, Kacey

    2004-01-01

    This study examines the characteristics of elementary schools that experience chronic teacher turnover and the impacts of turnover on a school's working climate and ability to effectively function. Based on evidence from staff climate surveys and case studies, it is clear that high turnover schools face significant organizational challenges.…

  15. Estimating Teacher Turnover Costs: A Case Study

    ERIC Educational Resources Information Center

    Levy, Abigail Jurist; Joy, Lois; Ellis, Pamela; Jablonski, Erica; Karelitz, Tzur M.

    2012-01-01

    High teacher turnover in large U.S. cities is a critical issue for schools and districts, and the students they serve; but surprisingly little work has been done to develop methodologies and standards that districts and schools can use to make reliable estimates of turnover costs. Even less is known about how to detect variations in turnover costs…

  16. Understanding Turnover Intentions and Behavior of Indian Information Systems Professionals: A Study of Organizational Justice, Job Satisfaction and Social Norms

    ERIC Educational Resources Information Center

    Iyer, Vidya V.

    2011-01-01

    Despite the phenomenal growth projected for the Indian information technology (IT) industry, one of the biggest challenges it faces is the high rate of turnover in offshore supplier firms based in India (Everest Research Group 2011). According to recent estimates, turnover rates among Indian information systems (IS) professionals have been…

  17. Diet-tissue discrimination factors (Δ(13) C and Δ(15) N) and turnover rate in somatic tissues of a neotropical detritivorous fish on C3 and C4 diets.

    PubMed

    Sacramento, P A; Manetta, G I; Benedito, E

    2016-07-01

    In this study, diet-tissue discrimination factors and turnover rates were determined from the somatic tissues of a detritivorous fish Prochilodus lineatus. The carbon (Δ(13) C) and nitrogen (Δ(15) N) diet-tissue discrimination factors varied for all feed rations with a range of Δ(13) C values between -1·9 and 3·6‰ and Δ(15) N between 3·3 and 5·7‰. Carbon turnover rate in the blood was 23·1 days for the C3 ration and 34·7 days for the C4 ration, in the liver was 9·9 days under the C3 ration and nitrogen turnover rate was the same (23·1 days) in the liver for both C4 and C3 -C4 rations, and 13·9 days in the muscle for C3 -C4 ration. PMID:26728338

  18. Gaussian Process Modeling of Protein Turnover.

    PubMed

    Rahman, Mahbubur; Previs, Stephen F; Kasumov, Takhar; Sadygov, Rovshan G

    2016-07-01

    We describe a stochastic model to compute in vivo protein turnover rate constants from stable-isotope labeling and high-throughput liquid chromatography-mass spectrometry experiments. We show that the often-used one- and two-compartment nonstochastic models allow explicit solutions from the corresponding stochastic differential equations. The resulting stochastic process is a Gaussian processes with Ornstein-Uhlenbeck covariance matrix. We applied the stochastic model to a large-scale data set from (15)N labeling and compared its performance metrics with those of the nonstochastic curve fitting. The comparison showed that for more than 99% of proteins, the stochastic model produced better fits to the experimental data (based on residual sum of squares). The model was used for extracting protein-decay rate constants from mouse brain (slow turnover) and liver (fast turnover) samples. We found that the most affected (compared to two-exponent curve fitting) results were those for liver proteins. The ratio of the median of degradation rate constants of liver proteins to those of brain proteins increased 4-fold in stochastic modeling compared to the two-exponent fitting. Stochastic modeling predicted stronger differences of protein turnover processes between mouse liver and brain than previously estimated. The model is independent of the labeling isotope. To show this, we also applied the model to protein turnover studied in induced heart failure in rats, in which metabolic labeling was achieved by administering heavy water. No changes in the model were necessary for adapting to heavy-water labeling. The approach has been implemented in a freely available R code. PMID:27229456

  19. High turnover drives prolonged persistence of influenza in managed pig herds

    PubMed Central

    Aguas, Ricardo; Riley, Steven; Loeffen, Willie L. A.; Wood, James L. N.; Grenfell, Bryan T.

    2016-01-01

    Pigs have long been hypothesized to play a central role in the emergence of novel human influenza A virus (IAV) strains, by serving as mixing vessels for mammalian and avian variants. However, the key issue of viral persistence in swine populations at different scales is ill understood. We address this gap using epidemiological models calibrated against seroprevalence data from Dutch finishing pigs to estimate the ‘critical herd size’ (CHS) for IAV persistence. We then examine the viral phylogenetic evidence for persistence by comparing human and swine IAV. Models suggest a CHS of approximately 3000 pigs above which influenza was likely to persist, i.e. orders of magnitude lower than persistence thresholds for IAV and other acute viruses in humans. At national and regional scales, we found much stronger empirical signatures of prolonged persistence of IAV in swine compared with human populations. These striking levels of persistence in small populations are driven by the high recruitment rate of susceptible piglets, and have significant implications for management of swine and for overall patterns of genetic diversity of IAV. PMID:27358277

  20. High turnover drives prolonged persistence of influenza in managed pig herds.

    PubMed

    Pitzer, Virginia E; Aguas, Ricardo; Riley, Steven; Loeffen, Willie L A; Wood, James L N; Grenfell, Bryan T

    2016-06-01

    Pigs have long been hypothesized to play a central role in the emergence of novel human influenza A virus (IAV) strains, by serving as mixing vessels for mammalian and avian variants. However, the key issue of viral persistence in swine populations at different scales is ill understood. We address this gap using epidemiological models calibrated against seroprevalence data from Dutch finishing pigs to estimate the 'critical herd size' (CHS) for IAV persistence. We then examine the viral phylogenetic evidence for persistence by comparing human and swine IAV. Models suggest a CHS of approximately 3000 pigs above which influenza was likely to persist, i.e. orders of magnitude lower than persistence thresholds for IAV and other acute viruses in humans. At national and regional scales, we found much stronger empirical signatures of prolonged persistence of IAV in swine compared with human populations. These striking levels of persistence in small populations are driven by the high recruitment rate of susceptible piglets, and have significant implications for management of swine and for overall patterns of genetic diversity of IAV. PMID:27358277

  1. Supervisory Turnover in Outpatient Substance Abuse Treatment

    PubMed Central

    Knight, Danica K.; Broome, Kirk M.; Edwards, Jennifer R.; Flynn, Patrick M.

    2009-01-01

    Staff turnover is a significant issue within substance abuse treatment, with implications for service delivery and organizational health. This study examined factors associated with turnover among supervisors in outpatient substance abuse treatment. Turnover was conceptualized as being an individual response to organizational-level influences, and predictors represent aggregate program measures. Participants included 532 staff (including 467 counselors and 65 clinical/program directors) from 90 programs in four regions of the USA. Using logistic regression, analyses of structural factors indicated that programs affiliated with a parent organization and those providing more counseling hours to clients had higher turnover rates. When measures of job attitudes were included, only parent affiliation and collective appraisal of satisfaction were related to turnover. Subsequent analyses identified a trend toward increased supervisory turnover when satisfaction was low following the departure of a previous supervisor. These findings suggest that organizational-level factors can be influential in supervisory turnover. PMID:19949883

  2. Sweat rate and fluid turnover in American football players compared with runners in a hot and humid environment

    PubMed Central

    Godek, S; Bartolozzi, A; Godek, J; Roberts, W

    2005-01-01

    Objectives: To determine sweat rate (SwR) and fluid requirements for American footballers practicing in a hot, humid environment compared with cross country runners in the same conditions. Methods: Fifteen subjects, 10 footballers and five runners, participated. On the 4th and 8th day of preseason two a day practices, SwR during exercise was determined in both morning and afternoon practices/runs from the change in body mass adjusted for fluids consumed and urine produced. Unpaired t tests were used to determine differences between groups. Results: Overall SwR measured in litres/h was higher in the footballers than the cross country runners (2.14 (0.53) v 1.77 (0.4); p<0.01). Total sweat loss in both morning (4.83 (1.2) v 1.56 (0.39) litres) and afternoon (4.8 (1.2) v 1.97 (0.28) litres) practices/runs, and daily sweat losses (9.4 (2.2) v 3.53 (0.54) litres) were higher in the footballers (p<0.0001). The footballers consumed larger volumes of fluid during both morning and afternoon practices/runs (23.9 (8.9) v 5.5 (3.1) ml/min and 23.5 (7.3) v 13.6 (5.6) ml/min; p<0.01). For complete hydration, the necessary daily fluid consumption calculated as 130% of daily sweat loss in the footballers was 12.2 (2.9) litres compared with 4.6 (0.7) litres in the runners (p<0.0001). Calculated 24 hour fluid requirements in the footballers ranged from 8.8 to 19 litres. Conclusions: The American footballers had a high SwR with large total daily sweat losses. Consuming large volumes of hypotonic fluid may promote sodium dilution. Recommendations for fluid and electrolyte replacement must be carefully considered and monitored in footballers to promote safe hydration and avoid hyponatraemia. PMID:15793087

  3. Whole-body protein turnover response to short-term high-protein diets during weight loss: a randomized controlled trial

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Objective: Determine whole-body protein turnover responses to high protein diets during weight loss. Design: Thirty-nine adults (age, 21 ± 1 yr; VO2peak, 48 ± 1 ml'kg-1'min-1; body mass index, 25 ± 1 kg•m2) were randomized to diets providing protein at the recommend dietary allowance (RDA), 2X-RD...

  4. Altered carbon turnover processes and microbiomes in soils under long-term extremely high CO2 exposure.

    PubMed

    Beulig, Felix; Urich, Tim; Nowak, Martin; Trumbore, Susan E; Gleixner, Gerd; Gilfillan, Gregor D; Fjelland, Kristine E; Küsel, Kirsten

    2016-01-01

    There is only limited understanding of the impact of high p(CO2) on soil biomes. We have studied a floodplain wetland where long-term emanations of temperate volcanic CO2 (mofettes) are associated with accumulation of carbon from the Earth's mantle. With an integrated approach using isotope geochemistry, soil activity measurements and multi-omics analyses, we demonstrate that high (nearly pure) CO2 concentrations have strongly affected pathways of carbon production and decomposition and therefore carbon turnover. In particular, a promotion of dark CO2 fixation significantly increased the input of geogenic carbon in the mofette when compared to a reference wetland soil exposed to normal levels of CO2. Radiocarbon analysis revealed that high quantities of mofette soil carbon originated from the assimilation of geogenic CO2 (up to 67%) via plant primary production and subsurface CO2 fixation. However, the preservation and accumulation of almost undegraded organic material appeared to be facilitated by the permanent exclusion of meso- to macroscopic eukaryotes and associated physical and/or ecological traits rather than an impaired biochemical potential for soil organic matter decomposition. Our study shows how CO2-induced changes in diversity and functions of the soil community can foster an unusual biogeochemical profile. PMID:27571979

  5. Effects of the turnover rate on the size distribution of firms: An application of the kinetic exchange models

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Anindya S.

    2012-12-01

    We address the issue of the distribution of firm size. To this end we propose a model of firms in a closed, conserved economy populated with zero-intelligence agents who continuously move from one firm to another. We then analyze the size distribution and related statistics obtained from the model. There are three well known statistical features obtained from the panel study of the firms i.e., the power law in size (in terms of income and/or employment), the Laplace distribution in the growth rates and the slowly declining standard deviation of the growth rates conditional on the firm size. First, we show that the model generalizes the usual kinetic exchange models with binary interaction to interactions between an arbitrary number of agents. When the number of interacting agents is in the order of the system itself, it is possible to decouple the model. We provide exact results on the distributions which are not known yet for binary interactions. Our model easily reproduces the power law for the size distribution of firms (Zipf’s law). The fluctuations in the growth rate falls with increasing size following a power law (though the exponent does not match with the data). However, the distribution of the difference of the firm size in this model has Laplace distribution whereas the real data suggests that the difference of the log of sizes has the same distribution.

  6. Short-term immobilization-induced cancellous bone loss is limited to regions undergoing high turnover and/or modeling in mature rats.

    PubMed

    Shen, V; Liang, X G; Birchman, R; Wu, D D; Healy, D; Lindsay, R; Dempster, D W

    1997-07-01

    remodeling sites when a high turnover state is provided by either estrogen or dietary calcium deficiency. These results suggest that the presence of a risk factor, such as immobilization, which in the short-term causes inhibition of bone formation, does not predispose the skeleton to rapid cancellous bone loss except when accompanied by modeling or high turnover. PMID:9213010

  7. Addressing employee turnover and retention: keeping your valued performers.

    PubMed

    McConnell, Charles R

    2011-01-01

    Employee turnover and employee retention are inextricably linked; to control turnover is to enhance retention. Turnover is a relatively simple concept; however, considerable confusion often results when addressing turnover because of differences in how it is defined; that is, what is counted, how it is counted, and how the turnover rates are expressed. Turnover is also costly, although not enough attention is paid to its cost because so much of it is indirect and thus not readily visible. There are a variety of causes of turnover, some that can be corrected and some that cannot be avoided. Reducing or otherwise controlling turnover requires continuing management attention to its causes and constant recognition of what can and should be controlled and what cannot be controlled. Ongoing attention to turnover is an essential part of the department manager's role; every improvement in turnover is a direct improvement in retention, with eventual positive effects on the bottom line. PMID:21808181

  8. Production rates and turnover of triiodothyronine in rat-developing cerebral cortex and cerebellum. Responses to hypothyroidism

    SciTech Connect

    Silva, J.E.; Matthews, P.S.

    1984-09-01

    Local 5'-deiodination of serum thyroxine (T4) is the main source of triiodothyronine (T3) for the brain. Since we noted in previous studies that the cerebral cortex of neonatal rats tolerated marked reductions in serum T4 without biochemical hypothyroidism, we examined the in vivo T4 and T3 metabolism in that tissue and in the cerebellum of euthyroid and hypothyroid 2-wk-old rats. We also assessed the contribution of enhanced tissue T4 to T3 conversion and decreased T3 removal from the tissues to the T3 homeostasis in hypothyroid brain. Congenital and neonatal hypothyroidism was induced by adding methimazole to the drinking water. Serum, cerebral cortex (Cx), cerebellum (Cm), liver (L) and kidney (R) concentrations of 125I-T4, 125I-T3(T4), and 131I-T3 were measured at various times after injecting 125I-T4 and 131I-T3. The rate of T3 removal from the tissues was measured after injecting an excess of anti-T3-antibody to rats previously injected with tracer T3. In hypothyroidism, the fractional removal rates and clearances were reduced in all tissues, in cortex and cerebellum by 70%, and in liver and kidney ranging from 30 to 50%. While greater than 80% of the 125I-T3(T4) in the brain tissues of euthyroid rats was locally produced, in hypothyroid cerebral cortex and cerebellum the integrated concentrations of 125I-T3(T4) were 2.7- and 1.5-fold greater than in euthyroid rats.

  9. On the chlorophyll a fluorescence yield in chloroplasts upon excitation with twin turnover flashes (TTF) and high frequency flash trains.

    PubMed

    Vredenberg, Wim; Durchan, Milan; Prasil, Ondrej

    2007-01-01

    Chlorophyll fluorescence is routinely taken as a quantifiable measure of the redox state of the primary quinone acceptor Q(A) of PSII. The variable fluorescence in thylakoids increases in a single turnover flash (STF) from its low dark level F (o) towards a maximum F (m) (STF) when Q(A) becomes reduced. We found, using twin single turnover flashes (TTFs) that the fluorescence increase induced by the first twin-partner is followed by a 20-30% increase when the second partner is applied within 20-100 micros after the first one. The amplitude of the twin response shows a period-of-four oscillation associated with the 4-step oxidation of water in the Kok cycle (S states) and originates from two different trapped states with a life time of 0.2-0.4 and 2-5 ms, respectively. The oscillation is supplemented with a binary oscillation associated with the two-electron gate mechanism at the PSII acceptor side. The F(t) response in high frequency flash trains (1-4 kHz) shows (i) in the first 3-4 flashes a transient overshoot 20-30% above the F (m) (STF) = 3*F (o) level reached in the 1st flash with a partial decline towards a dip D in the next 2-3 ms, independent of the flash frequency, and (ii) a frequency independent rise to F (m) = 5*F (o) in the 3-60 ms time range. The initial overshoot is interpreted to be due to electron trapping in the S(0) fraction with Q(B)-nonreducing centers and the dip to the subsequent recovery accompanying the reoxidation of the double reduced acceptor pair in these RCs after trapping. The rise after the overshoot is, in agreement with earlier findings, interpreted to indicate a photo-electrochemical control of the chlorophyll fluorescence yield of PSII. It is anticipated that the double exciton and electron trapping property of PSII is advantageous for the plant. It serves to alleviate the depression of electron transport in single reduced Q(B)-nonreducing RCs, associated with electrochemically coupled proton transport, by an increased electron

  10. The Effects of Intradistrict School Mobility and High Student Turnover Rates on Early Reading Achievement

    ERIC Educational Resources Information Center

    LeBoeuf, Whitney A.

    2013-01-01

    A number of studies have identified school mobility as one form of school disengagement that is disproportionately harmful for young children enrolled in large urban districts. However, there is substantial variation in these findings, with some studies actually evidencing positive associations between school mobility and academic outcomes (Mehana…

  11. Concurrent and Lagged Effects of Registered Nurse Turnover and Staffing on Unit-Acquired Pressure Ulcers

    PubMed Central

    Park, Shin Hye; Boyle, Diane K; Bergquist-Beringer, Sandra; Staggs, Vincent S; Dunton, Nancy E

    2014-01-01

    Objective We examined the concurrent and lagged effects of registered nurse (RN) turnover on unit-acquired pressure ulcer rates and whether RN staffing mediated the effects. Data Sources/Setting Quarterly unit-level data were obtained from the National Database of Nursing Quality Indicators for 2008 to 2010. A total of 10,935 unit-quarter observations (2,294 units, 465 hospitals) were analyzed. Methods This longitudinal study used multilevel regressions and tested time-lagged effects of study variables on outcomes. Findings The lagged effect of RN turnover on unit-acquired pressure ulcers was significant, while there was no concurrent effect. For every 10 percentage-point increase in RN turnover in a quarter, the odds of a patient having a pressure ulcer increased by 4 percent in the next quarter. Higher RN turnover in a quarter was associated with lower RN staffing in the current and subsequent quarters. Higher RN staffing was associated with lower pressure ulcer rates, but it did not mediate the relationship between turnover and pressure ulcers. Conclusions We suggest that RN turnover is an important factor that affects pressure ulcer rates and RN staffing needed for high-quality patient care. Given the high RN turnover rates, hospital and nursing administrators should prepare for its negative effect on patient outcomes. PMID:24476194

  12. Vertebrate Dissimilarity Due to Turnover and Richness Differences in a Highly Beta-Diverse Region: The Role of Spatial Grain Size, Dispersal Ability and Distance

    PubMed Central

    Calderón-Patrón, Jaime M.; Moreno, Claudia E.; Pineda-López, Rubén; Sánchez-Rojas, Gerardo; Zuria, Iriana

    2013-01-01

    We explore the influence of spatial grain size, dispersal ability, and geographic distance on the patterns of species dissimilarity of terrestrial vertebrates, separating the dissimilarity explained by species replacement (turnover) from that resulting from richness differences. With data for 905 species of terrestrial vertebrates distributed in the Isthmus of Tehuantepec, classified into five groups according to their taxonomy and dispersal ability, we calculated total dissimilarity and its additive partitioning as two components: dissimilarity derived from turnover and dissimilarity derived from richness differences. These indices were compared using fine (10 x 10 km), intermediate (20 x 20 km) and coarse (40 x 40 km) grain grids, and were tested for any correlations with geographic distance. The results showed that total dissimilarity is high for the terrestrial vertebrates in this region. Total dissimilarity, and dissimilarity due to turnover are correlated with geographic distance, and the patterns are clearer when the grain is fine, which is consistent with the distance-decay pattern of similarity. For all terrestrial vertebrates tested on the Isthmus of Tehuantepec both the dissimilarity derived from turnover and the dissimilarity resulting from richness differences make important contributions to total dissimilarity, and dispersal ability does not seem to influence the dissimilarity patterns. These findings support the idea that conservation efforts in this region require a system of interconnected protected areas that embrace the environmental, climatic and biogeographic heterogeneity of the area. PMID:24324840

  13. Inhibition of cell wall turnover and autolysis by vancomycin in a highly vancomycin-resistant mutant of Staphylococcus aureus.

    PubMed

    Sieradzki, K; Tomasz, A

    1997-04-01

    A highly vancomycin-resistant mutant (MIC = 100 microg/ml) of Staphylococcus aureus, mutant VM, which was isolated in the laboratory by a step-pressure procedure, continued to grow and synthesize peptidoglycan in the presence of vancomycin (50 microg/ml) in the medium, but the antibiotic completely inhibited cell wall turnover and autolysis, resulting in the accumulation of cell wall material at the cell surface and inhibition of daughter cell separation. Cultures of mutant VM removed vancomycin from the growth medium through binding the antibiotic to the cell walls, from which the antibiotic could be quantitatively recovered in biologically active form. Vancomycin blocked the in vitro hydrolysis of cell walls by autolytic enzyme extracts, lysostaphin and mutanolysin. Analysis of UDP-linked peptidoglycan precursors showed no evidence for the presence of D-lactate-terminating muropeptides. While there was no significant difference in the composition of muropeptide units of mutant and parental cell walls, the peptidoglycan of VM had a significantly lower degree of cross-linkage. These observations and the results of vancomycin-binding studies suggest alterations in the structural organization of the mutant cell walls such that access of the vancomycin molecules to the sites of wall biosynthesis is blocked. PMID:9098053

  14. Inhibition of cell wall turnover and autolysis by vancomycin in a highly vancomycin-resistant mutant of Staphylococcus aureus.

    PubMed Central

    Sieradzki, K; Tomasz, A

    1997-01-01

    A highly vancomycin-resistant mutant (MIC = 100 microg/ml) of Staphylococcus aureus, mutant VM, which was isolated in the laboratory by a step-pressure procedure, continued to grow and synthesize peptidoglycan in the presence of vancomycin (50 microg/ml) in the medium, but the antibiotic completely inhibited cell wall turnover and autolysis, resulting in the accumulation of cell wall material at the cell surface and inhibition of daughter cell separation. Cultures of mutant VM removed vancomycin from the growth medium through binding the antibiotic to the cell walls, from which the antibiotic could be quantitatively recovered in biologically active form. Vancomycin blocked the in vitro hydrolysis of cell walls by autolytic enzyme extracts, lysostaphin and mutanolysin. Analysis of UDP-linked peptidoglycan precursors showed no evidence for the presence of D-lactate-terminating muropeptides. While there was no significant difference in the composition of muropeptide units of mutant and parental cell walls, the peptidoglycan of VM had a significantly lower degree of cross-linkage. These observations and the results of vancomycin-binding studies suggest alterations in the structural organization of the mutant cell walls such that access of the vancomycin molecules to the sites of wall biosynthesis is blocked. PMID:9098053

  15. Is gastrectomy-induced high turnover of bone with hyperosteoidosis and increase of mineralization a typical osteomalacia?

    PubMed

    Ueyama, Takashi; Yamamoto, Yuta; Ueda, Kazuki; Yajima, Aiji; Maeda, Yoshimasa; Yamashita, Yasunobu; Ito, Takao; Tsuruo, Yoshihiro; Ichinose, Masao

    2013-01-01

    Gastrectomy (GX) is thought to result in osteomalacia due to deficiencies in Vitamin D and Ca. Using a GX rat model, we showed that GX induced high turnover of bone with hyperosteoidosis, prominent increase of mineralization and increased mRNA expression of both osteoclast-derived tartrate-resistant acid phosphatase 5b and osteocalcin. The increased 1, 25(OH)2D3 level and unchanged PTH and calcitonin levels suggested that conventional bone and Ca metabolic pathways were not involved or changed in compensation. Thus, GX-induced bone pathology was different from a typical osteomalacia. Gene expression profiles through microarray analysis and data mining using Ingenuity Pathway Analysis indicated that 612 genes were up-regulated and 1,097 genes were down-regulated in the GX bone. These genes were related functionally to connective tissue development, skeletal and muscular system development and function, Ca signaling and the role of osteoblasts, osteoclasts and chondrocytes. Network analysis indicated 9 genes (Aldehyde dehydrogenase 1 family, member A1; Aquaporin 9; Interleukin 1 receptor accessory protein; Very low density lipoprotein receptor; Periostin, osteoblast specific factor; Aggrecan; Gremlin 1; Angiopoietin-like 4; Wingless-type MMTV integration site family, member 10B) were hubs connected with tissue development and immunological diseases. These results suggest that chronic systemic inflammation might underlie the GX-induced pathological changes in bone. PMID:23776526

  16. Taking It or Leaving It. Instability and Turnover in a High-Tech Firm.

    ERIC Educational Resources Information Center

    Schellenberg, Kathryn

    1996-01-01

    Interviews and other data collected from a high-tech firm found that organizational instability raises workers' inclination to quit, independent of whether their job security is threatened. Instability undermines trust and impairs the usefulness of incentives intended to increase commitment. (SK)

  17. Lack of 13C-label incorporation suggests low turnover rates of thaumarchaeal intact polar tetraether lipids in sediments from the Iceland Shelf

    NASA Astrophysics Data System (ADS)

    Lengger, S. K.; Lipsewers, Y. A.; de Haas, H.; Sinninghe Damsté, J. S.; Schouten, S.

    2013-08-01

    Thaumarchaeota are amongst the most abundant microorganisms in aquatic environments, however, their metabolism in marine sediments is still debated. Labeling studies in marine sediments have previously been undertaken, but focused on complex organic carbon substrates which Thaumarchaeota have not yet been shown to take up. In this study, we investigated the activity of Thaumarchaeota in sediments by supplying different 13C-labeled substrates which have previously been shown to be incorporated into archaeal cells in water incubations and/or enrichment cultures. We determined the incorporation of 13C-label from bicarbonate, pyruvate, glucose and amino acids into thaumarchaeal intact polar lipid-glycerol dibiphytanyl glycerol tetraethers (IPL-GDGTs) during 4-6 day incubations of marine sediment cores from three different sites on the Iceland Shelf. Thaumarchaeal intact polar lipids were detected at all stations and concentrations remained constant or decreased slightly upon incubation. No 13C incorporation in any IPL-GDGT was observed at stations 2 (clay-rich sediment) and 3 (organic-rich sediment). In bacterial/eukaryotic IPL-derived fatty acids at station 3, contrastingly, a large uptake of 13C label (up to +80‰) was found. 13C was also respired during the experiment as shown by a substantial increase in the 13C content of the dissolved inorganic carbon. In IPL-GDGTs recovered from the sandy sediments at station 1, however, some enrichment in 13C (1-4‰) was detected after incubation with bicarbonate and pyruvate. The low incorporation rates suggest a low activity of Thaumarchaeota in marine sediments and/or a low turnover rate of thaumarchaeal IPL-GDGTs due to their low degradation rates. Cell numbers and activity of sedimentary Thaumarchaeota based on IPL-GDGT measurements may thus have previously been overestimated.

  18. Lack of 13C-label incorporation suggests low turnover rates of thaumarchaeal intact polar tetraether lipids in sediments from the Iceland shelf

    NASA Astrophysics Data System (ADS)

    Lengger, S. K.; Lipsewers, Y. A.; de Haas, H.; Sinninghe Damsté, J. S.; Schouten, S.

    2014-01-01

    Thaumarchaeota are amongst the most abundant microorganisms in aquatic environments, however, their metabolism in marine sediments is still debated. Labeling studies in marine sediments have previously been undertaken, but focused on complex organic carbon substrates which Thaumarchaeota have not yet been shown to take up. In this study, we investigated the activity of Thaumarchaeota in sediments by supplying different 13C-labeled substrates which have previously been shown to be incorporated into archaeal cells in water incubations and/or enrichment cultures. We determined the incorporation of 13C-label from bicarbonate, pyruvate, glucose and amino acids into thaumarchaeal intact polar lipid-glycerol dibiphytanyl glycerol tetraethers (IPL-GDGTs) during 4-6 day incubations of marine sediment cores from three sites on the Iceland shelf. Thaumarchaeal intact polar lipids, in particular crenarchaeol, were detected at all stations and concentrations remained constant or decreased slightly upon incubation. No 13C incorporation in any IPL-GDGT was observed at stations 2 (clay-rich sediment) and 3 (organic-rich sediment). In bacterial/eukaryotic IPL-derived fatty acids at station 3, contrastingly, a large uptake of 13C label (up to + 80‰ ) was found. 13C was also respired during the experiment as shown by a substantial increase in the 13C content of the dissolved inorganic carbon. In IPL-GDGTs recovered from the sandy sediments at station 1, however, some enrichment in δ13C (1-4‰ ) was detected after incubation with bicarbonate and pyruvate. The low incorporation rates suggest a low activity of Thaumarchaeota in marine sediments and/or a low turnover rate of thaumarchaeal IPL-GDGTs due to their low degradation rates. Cell numbers and activity of sedimentary Thaumarchaeota based on IPL-GDGT measurements may thus have previously been overestimated.

  19. Modifying the high rate algal pond light environment and its effects on light absorption and photosynthesis.

    PubMed

    Sutherland, Donna L; Montemezzani, Valerio; Howard-Williams, Clive; Turnbull, Matthew H; Broady, Paul A; Craggs, Rupert J

    2015-03-01

    The combined use of high rate algal ponds (HRAPs) for wastewater treatment and commercial algal production is considered to be an economically viable option. However, microalgal photosynthesis and biomass productivity is constrained in HRAPs due to light limitation. This paper investigates how the light climate in the HRAP can be modified through changes in pond depth, hydraulic retention time (HRT) and light/dark turnover rate and how this impacts light absorption and utilisation by the microalgae. Wastewater treatment HRAPs were operated at three different pond depth and HRT during autumn. Light absorption by the microalgae was most affected by HRT, significantly decreasing with increasing HRT, due to increased internal self-shading. Photosynthetic performance (as defined by Pmax, Ek and α), significantly increased with increasing pond depth and decreasing HRT. Despite this, increasing pond depth and/or HRT, resulted in decreased pond light climate and overall integrated water column net oxygen production. However, increased light/dark turnover was able to compensate for this decrease, bringing the net oxygen production in line with shallower ponds operated at shorter HRT. On overcast days, modelled daily net photosynthesis significantly increased with increased light/dark turnover, however, on clear days such increased turnover did not enhance photosynthesis. This study has showed that light absorption and photosynthetic performance of wastewater microalgae can be modified through changes to pond depth, HRT and light/dark turnover. PMID:25514661

  20. High frequency of herpesvirus-specific clonotypes in the human T cell repertoire can remain stable over decades with minimal turnover.

    PubMed

    Neller, M A; Burrows, J M; Rist, M J; Miles, J J; Burrows, S R

    2013-01-01

    High-throughput T cell receptor sequencing on sequentially banked blood samples from healthy individuals has shown that high-frequency clonotypes can remain relatively stable for up to 18 years, with minimal inflation, deflation, or turnover. These populations included T cell expansions specific for Epstein-Barr virus. Thus, in spite of exposure to a barrage of microorganisms over the course of life, the dominant clonotypes in the mature peripheral T cell repertoire can alter surprisingly little. PMID:23077319

  1. High dose sapropterin dihydrochloride therapy improves monoamine neurotransmitter turnover in murine phenylketonuria (PKU).

    PubMed

    Winn, Shelley R; Scherer, Tanja; Thöny, Beat; Harding, Cary O

    2016-01-01

    Central nervous system (CNS) deficiencies of the monoamine neurotransmitters, dopamine and serotonin, have been implicated in the pathophysiology of neuropsychiatric dysfunction in phenylketonuria (PKU). Increased brain phenylalanine concentration likely competitively inhibits the activities of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH), the rate limiting steps in dopamine and serotonin synthesis respectively. Tetrahydrobiopterin (BH4) is a required cofactor for TH and TPH activity. Our hypothesis was that treatment of hyperphenylalaninemic Pah(enu2/enu2) mice, a model of human PKU, with sapropterin dihydrochloride, a synthetic form of BH4, would stimulate TH and TPH activities leading to improved dopamine and serotonin synthesis despite persistently elevated brain phenylalanine. Sapropterin (20, 40, or 100mg/kg body weight in 1% ascorbic acid) was administered daily for 4 days by oral gavage to Pah(enu2/enu2) mice followed by measurement of brain biopterin, phenylalanine, tyrosine, tryptophan and monoamine neurotransmitter content. A significant increase in brain biopterin content was detected only in mice that had received the highest sapropterin dose, 100mg/kg. Blood and brain phenylalanine concentrations were unchanged by sapropterin therapy. Sapropterin therapy also did not alter the absolute amounts of dopamine and serotonin in brain but was associated with increased homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), dopamine and serotonin metabolites respectively, in both wild type and Pah(enu2/enu2) mice. Oral sapropterin therapy likely does not directly affect central nervous system monoamine synthesis in either wild type or hyperphenylalaninemic mice but may stimulate synaptic neurotransmitter release and subsequent metabolism. PMID:26653793

  2. Dynamics of Cell Generation and Turnover in the Human Heart.

    PubMed

    Bergmann, Olaf; Zdunek, Sofia; Felker, Anastasia; Salehpour, Mehran; Alkass, Kanar; Bernard, Samuel; Sjostrom, Staffan L; Szewczykowska, Mirosława; Jackowska, Teresa; Dos Remedios, Cris; Malm, Torsten; Andrä, Michaela; Jashari, Ramadan; Nyengaard, Jens R; Possnert, Göran; Jovinge, Stefan; Druid, Henrik; Frisén, Jonas

    2015-06-18

    The contribution of cell generation to physiological heart growth and maintenance in humans has been difficult to establish and has remained controversial. We report that the full complement of cardiomyocytes is established perinataly and remains stable over the human lifespan, whereas the numbers of both endothelial and mesenchymal cells increase substantially from birth to early adulthood. Analysis of the integration of nuclear bomb test-derived (14)C revealed a high turnover rate of endothelial cells throughout life (>15% per year) and more limited renewal of mesenchymal cells (<4% per year in adulthood). Cardiomyocyte exchange is highest in early childhood and decreases gradually throughout life to <1% per year in adulthood, with similar turnover rates in the major subdivisions of the myocardium. We provide an integrated model of cell generation and turnover in the human heart. PMID:26073943

  3. Job Turnover and Job Satisfaction among Nursing Home Aides.

    ERIC Educational Resources Information Center

    Waxman, Howard M.; And Others

    1984-01-01

    Interviewed 234 aides in seven nursing homes concerning job turnover rate, job satisfaction, and perception of milieu. A positive association found between turnover rate and aides' perceptions of the homes' order, organization, and control suggested that job turnover would lessen with more involvement in the decision-making process. (JAC)

  4. Salary and Ranking and Teacher Turnover: A Statewide Study

    ERIC Educational Resources Information Center

    Garcia, Cynthia Martinez; Slate, John R.; Delgado, Carmen Tejeda

    2009-01-01

    This study examined three years of data obtained from the Academic Excellence Indicator System of the State of Texas regarding teacher turnover rate and teacher salary. Across all public school districts, teacher salary was consistently negatively related to teacher turnover; that is, where salary was lower, turnover rate was higher When data were…

  5. Principal Turnover. Information Capsule. Volume 0914

    ERIC Educational Resources Information Center

    Blazer, Christie

    2010-01-01

    Recent studies indicate that school districts are facing increasing rates of principal turnover. Frequent principal changes deprive schools of the leadership stability they need to succeed, disrupt long-term school reform efforts, and may even be linked to increased teacher turnover and lower levels of student achievement. This Information Capsule…

  6. Staff turnover in statewide implementation of ACT: relationship with ACT fidelity and other team characteristics

    PubMed Central

    Rollins, Angela L.; Salyers, Michelle P.; Tsai, Jack; Lydick, Jennifer M.

    2010-01-01

    Staff turnover on assertive community treatment (ACT) teams is a poorly understood phenomenon. This study examined annual turnover and fidelity data collected in a statewide implementation of ACT over a 5-year period. Mean annual staff turnover across all observations was 30.0%. Turnover was negatively correlated with overall fidelity at Year 1 and 3. The team approach fidelity item was negatively correlated with staff turnover at Year 3. For 13 teams with 3 years of follow-up data, turnover rates did not change over time. Most ACT staff turnover rates were comparable or better than other turnover rates reported in the mental health and substance abuse literature. PMID:20012481

  7. High burn rate solid composite propellants

    NASA Astrophysics Data System (ADS)

    Manship, Timothy D.

    High burn rate propellants help maintain high levels of thrust without requiring complex, high surface area grain geometries. Utilizing high burn rate propellants allows for simplified grain geometries that not only make production of the grains easier, but the simplified grains tend to have better mechanical strength, which is important in missiles undergoing high-g accelerations. Additionally, high burn rate propellants allow for a higher volumetric loading which reduces the overall missile's size and weight. The purpose of this study is to present methods of achieving a high burn rate propellant and to develop a composite propellant formulation that burns at 1.5 inches per second at 1000 psia. In this study, several means of achieving a high burn rate propellant were presented. In addition, several candidate approaches were evaluated using the Kepner-Tregoe method with hydroxyl terminated polybutadiene (HTPB)-based propellants using burn rate modifiers and dicyclopentadiene (DCPD)-based propellants being selected for further evaluation. Propellants with varying levels of nano-aluminum, nano-iron oxide, FeBTA, and overall solids loading were produced using the HTPB binder and evaluated in order to determine the effect the various ingredients have on the burn rate and to find a formulation that provides the burn rate desired. Experiments were conducted to compare the burn rates of propellants using the binders HTPB and DCPD. The DCPD formulation matched that of the baseline HTPB mix. Finally, GAP-plasticized DCPD gumstock dogbones were attempted to be made for mechanical evaluation. Results from the study show that nano-additives have a substantial effect on propellant burn rate with nano-iron oxide having the largest influence. Of the formulations tested, the highest burn rate was a 84% solids loading mix using nano-aluminum nano-iron oxide, and ammonium perchlorate in a 3:1(20 micron: 200 micron) ratio which achieved a burn rate of 1.2 inches per second at 1000

  8. Employee Turnover in the Federal Government. A Special Study.

    ERIC Educational Resources Information Center

    Musell, R. Mark

    A study of employee turnover in the Federal government showed that in 1984, about 195,000 full-time, nonpostal Federal workers with permanent appointments left Federal jobs or transferred to other Federal agencies--representing a turnover rate of 11.5 percent. The turnover was about three percentage points higher for white-collar workers than for…

  9. Multichannel analyzers at high rates of input

    NASA Technical Reports Server (NTRS)

    Rudnick, S. J.; Strauss, M. G.

    1969-01-01

    Multichannel analyzer, used with a gating system incorporating pole-zero compensation, pile-up rejection, and baseline-restoration, achieves good resolution at high rates of input. It improves resolution, reduces tailing and rate-contributed continuum, and eliminates spectral shift.

  10. High-rate lithium thionyl chloride cells

    NASA Technical Reports Server (NTRS)

    Goebel, F.

    1982-01-01

    A high-rate C cell with disc electrodes was developed to demonstrate current rates which are comparable to other primary systems. The tests performed established the limits of abuse beyond which the cell becomes hazardous. Tests include: impact, shock, and vibration tests; temperature cycling; and salt water immersion of fresh cells.

  11. ISS Update: High Rate Communications System

    NASA Video Gallery

    ISS Update Commentator Pat Ryan interviews Diego Serna, Communications and Tracking Officer, about the High Rate Communications System. Questions? Ask us on Twitter @NASA_Johnson and include the ha...

  12. Tracking in high-frame-rate imaging.

    PubMed

    Wu, Shih-Ying; Wang, Shun-Li; Li, Pai-Chi

    2010-01-01

    Speckle tracking has been used for motion estimation in ultrasound imaging. Unlike conventional Doppler techniques, which are angle-dependent, speckle tracking can be utilized to estimate velocity vectors. However, the accuracy of speckle-tracking methods is limited by speckle decorrelation, which is related to the displacement between two consecutive images, and, hence, combining high-frame-rate imaging and speckle tracking could potentially increase the accuracy of motion estimation. However, the lack of transmit focusing may also affect the tracking results and the high computational requirement may be problematic. This study therefore assessed the performance of high-frame-rate speckle tracking and compared it with conventional focusing. The effects of the signal-to-noise ratio (SNR), bulk motion, and velocity gradients were investigated in both experiments and simulations. The results show that high-frame-rate speckle tracking can achieve high accuracy if the SNR is sufficiently high. In addition, its computational complexity is acceptable because smaller search windows can be used due to the displacements between frames generally being smaller during high-frame-rate imaging. Speckle decor-relation resulting from velocity gradients within a sample volume is also not as significant during high-frame-rate imaging. PMID:20690428

  13. Superintendent Turnover in Texas, Connecticut, Kentucky, and Oregon Public School Districts: Contributing Factors and Trends

    ERIC Educational Resources Information Center

    Berryhill, Kathy S.

    2009-01-01

    School district administrator openings are occurring across Texas and many other states at an increasing rate. The high rate of turnover in the superintendency has become a national problem. Texas was chosen for the study due to the total number of school districts in the state and the high percent of rural districts. The other selected states,…

  14. Systematic review of the use of bone turnover markers for monitoring the response to osteoporosis treatment: the secondary prevention of fractures, and primary prevention of fractures in high-risk groups.

    PubMed Central

    Burch, Jane; Rice, Stephen; Yang, Huiqin; Neilson, Aileen; Stirk, Lisa; Francis, Roger; Holloway, Paul; Selby, Peter; Craig, Dawn

    2014-01-01

    BACKGROUND There is currently no standard practice for the monitoring of patients receiving treatment for osteoporosis. Repeated dual-energy X-ray absorptiometry (DXA) is commonly used for monitoring treatment response, but it has its limitations. Bone turnover markers have advantages over DXA as they are non-invasive, relatively cheap and can detect changes in bone turnover rates earlier. However, they do have disadvantages, particularly high within- and between-patient variability. The ability of bone turnover markers to identify treatment non-responders and predict future fracture risk has yet to be established. OBJECTIVES We aimed to determine the clinical effectiveness, test accuracy, reliability, reproducibility and cost-effectiveness of bone turnover markers for monitoring the response to osteoporosis treatment. DATA SOURCES We searched 12 electronic databases (including MEDLINE, EMBASE, The Cochrane Library and trials registries) without language restrictions from inception to March 2012. We hand-searched three relevant journals for the 12 months prior to May 2012, and websites of five test manufacturers and the US Food and Drug Administration (FDA). Reference lists of included studies and relevant reviews were also searched. REVIEW METHODS A systematic review of test accuracy, clinical utility, reliability and reproducibility, and cost-effectiveness of two formation and two resorption bone turnover markers, in patients being treated for osteoporosis with any of bisphosphonate [alendronate (Fosamax, MSD), risedronate (Actonel, Warner Chilcott Company), zolendronate (Zometa, Novartis)], raloxifene (Evista, Eli Lilly and Company Ltd), strontium ranelate (Protelos, Servier Laboratories Ltd), denosumab (Prolia, Amgen Ltd) or teriparatide (Forsteo, Eli Lilly and Company Ltd), was undertaken according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Given the breadth of the review question, a range of study designs

  15. Staff turnover: occasional friend, frequent foe, and continuing frustration.

    PubMed

    McConnell, C R

    1999-09-01

    Turnover appears to be a relatively simple concept. However, considerable confusion results when discussing turnover because of differences in how it is defined--what is counted, how it is counted, and how the rate of turnover is expressed. Turnover is also costly, although not enough attention is paid to turnover's cost because so much of it is indirect and thus not readily visible. There are a variety of causes of turnover, some which can be corrected and some which cannot be avoided. Reducing or otherwise controlling turnover requires continuing management attention to its causes and constant recognition of what can and should be controlled and what cannot be controlled. Ongoing attention to turnover is an essential part of the department manager's role. PMID:10747463

  16. Fine root turnover: a story of root production and root phenology

    NASA Astrophysics Data System (ADS)

    McCormack, M. L.; Adams, T. S.; Smithwick, E. A.; Eissenstat, D. M.

    2012-12-01

    Fine root turnover in terrestrial ecosystems partially controls carbon flow from plants into soils as well the amount of roots available for nutrient and water uptake. However, we have poor understanding of basic patterns and variability in fine root turnover. We address this shortfall through the use of a heuristic model and analysis of a multi-year minirhizotron dataset exploring the impacts of fine root phenology and production on fine root turnover rates across 12 temperate tree species in a common garden experiment. The heuristic model allowed us to calculate fine root turnover given different patterns of root production and different fine root lifespans. Using the model we found that patterns of phenology characterized by a single, concentrated peak resulted in slower calculated root turnover rates while broader and bi-modal production patterns resulted in faster turnover rates. For example, for roots with median lifespans of 91 days, estimates of root turnover increased from 1.5 yr-1 to 4.0 yr-1 between the pattern of concentrated root production and the pattern with root production spread equally throughout the year. Turnover rates observed in the common garden ranged from 0.75 yr-1 to 1.33 yr-1 and 0.93 yr-1 to 2.14 yr-1 when calculated as annual production divided by maximum standing root crop or average standing root crop, respectively. Turnover varied significantly across species and interannual variability in root production and turnover was high. Patterns of root phenology observed at the common garden included concentrated root production in late spring as well as several examples of bi-modal and broader patterns of root production with roots produced across spring, summer and fall. Overall, both phenology and total root production impacted estimates of root turnover, particularly for short-lived fine roots with median lifespans of less than one year. Our results suggest that better understanding fine root phenology and production will improve our

  17. High Strain Rate Rheology of Polymer Melts

    NASA Astrophysics Data System (ADS)

    Kelly, Adrian; Gough, Tim; Whiteside, Ben; Coates, Phil D.

    2009-07-01

    A modified servo electric injection moulding machine has been used in air-shot mode with capillary dies fitted at the nozzle to examine the rheology of a number of commercial polymers at wall shear strain rates of up to 107 s-1. Shear and extensional flow properties were obtained through the use of long and orifice (close to zero land length) dies of the same diameter. A range of polyethylene, polypropylene and polystyrene melts have been characterized; good agreement was found between the three techniques used in the ranges where strain rates overlapped. Shear viscosity of the polymers studied was found to exhibit a plateau above approximately 1×106 s-1. A relationship between the measured high strain rate rheological behaviour and molecular structure was noted, with polymers containing larger side groups reaching the rate independent plateau at lower strain rates than those with simpler structures.

  18. A high-strain-rate superplastic ceramic.

    PubMed

    Kim, B N; Hiraga, K; Morita, K; Sakka, Y

    2001-09-20

    High-strain-rate superplasticity describes the ability of a material to sustain large plastic deformation in tension at high strain rates of the order of 10-2 to 10-1 s-1 and is of great technological interest for the shape-forming of engineering materials. High-strain-rate superplasticity has been observed in aluminium-based and magnesium-based alloys. But for ceramic materials, superplastic deformation has been restricted to low strain rates of the order of 10-5 to 10-4 s-1 for most oxides and nitrides with the presence of intergranular cavities leading to premature failure. Here we show that a composite ceramic material consisting of tetragonal zirconium oxide, magnesium aluminate spinel and alpha-alumina phases exhibits superplasticity at strain rates up to 1 s-1. The composite also exhibits a large tensile elongation, exceeding 1,050 per cent for a strain rate of 0.4 s-1. The tensile flow behaviour and deformed microstructure of the material indicate that superplasticity is due to a combination of limited grain growth in the constitutive phases and the intervention of dislocation-induced plasticity in the zirconium oxide phase. We suggest that the present results hold promise for the application of shape-forming technologies to ceramic materials. PMID:11565026

  19. High Bit Rate Experiments Over ACTS

    NASA Technical Reports Server (NTRS)

    Bergman, Larry A.; Gary, J. Patrick; Edelsen, Burt; Helm, Neil; Cohen, Judith; Shopbell, Patrick; Mechoso, C. Roberto; Chung-Chun; Farrara, M.; Spahr, Joseph

    1996-01-01

    This paper describes two high data rate experiments chat are being developed for the gigabit NASA Advanced Communications Technology Satellite (ACTS). The first is a telescience experiment that remotely acquires image data at the Keck telescope from the Caltech campus. The second is a distributed global climate application that is run between two supercomputer centers interconnected by ACTS. The implementation approach for each is described along with the expected results. Also. the ACTS high data rate (HDR) ground station is also described in detail.

  20. Altered bone turnover during spaceflight

    NASA Technical Reports Server (NTRS)

    Turner, R. T.; Morey, E. R.; Liu, C.; Baylink, D. J.

    1982-01-01

    Modifications in calcium metabolism during spaceflight were studied, using parameters that reflect bone turnover. Bone formation rate, medullary area, bone length, bone density, pore size distribution, and differential bone cell number were evaluated in growing rate both immediately after and 25 days after orbital spaceflights aboard the Soviet biological satellites Cosmos 782 and 936. The primary effect of space flight on bone turnover was a reversible inhibition of bone formation at the periosteal surface. A simultaneous increase in the length of the periosteal arrest line suggests that bone formation ceased along corresponding portions of that surface. Possible reasons include increased secretion of glucocorticoids and mechanical unloading of the skeleton due to near-weightlessness, while starvation and immobilization are excluded as causes.

  1. A Prospective Examination of Clinician and Supervisor Turnover Within the Context of Implementation of Evidence-Based Practices in a Publicly-Funded Mental Health System.

    PubMed

    Beidas, Rinad S; Marcus, Steven; Wolk, Courtney Benjamin; Powell, Byron; Aarons, Gregory A; Evans, Arthur C; Hurford, Matthew O; Hadley, Trevor; Adams, Danielle R; Walsh, Lucia M; Babbar, Shaili; Barg, Frances; Mandell, David S

    2016-09-01

    Staff turnover rates in publicly-funded mental health settings are high. We investigated staff and organizational predictors of turnover in a sample of individuals working in an urban public mental health system that has engaged in a system-level effort to implement evidence-based practices. Additionally, we interviewed staff to understand reasons for turnover. Greater staff burnout predicted increased turnover, more openness toward new practices predicted retention, and more professional recognition predicted increased turnover. Staff reported leaving their organizations because of personal, organizational, and financial reasons; just over half of staff that left their organization stayed in the public mental health sector. Implications include an imperative to focus on turnover, with a particular emphasis on ameliorating staff burnout. PMID:26179469

  2. High Rate for Type IC Supernovae

    SciTech Connect

    Muller, R.A.; Marvin-Newberg, H.J.; Pennypacker, Carl R.; Perlmutter, S.; Sasseen, T.P.; Smith, C.K.

    1991-09-01

    Using an automated telescope we have detected 20 supernovae in carefully documented observations of nearby galaxies. The supernova rates for late spiral (Sbc, Sc, Scd, and Sd) galaxies, normalized to a blue luminosity of 10{sup 10} L{sub Bsun}, are 0.4 h{sup 2}, 1.6 h{sup 2}, and 1.1 h{sup 2} per 100 years for SNe type la, Ic, and II. The rate for type Ic supernovae is significantly higher than found in previous surveys. The rates are not corrected for detection inefficiencies, and do not take into account the indications that the Ic supernovae are fainter on the average than the previous estimates; therefore the true rates are probably higher. The rates are not strongly dependent on the galaxy inclination, in contradiction to previous compilations. If the Milky Way is a late spiral, then the rate of Galactic supernovae is greater than 1 per 30 {+-} 7 years, assuming h = 0.75. This high rate has encouraging consequences for future neutrino and gravitational wave observatories.

  3. Baltimore District Tackles High Suspension Rates

    ERIC Educational Resources Information Center

    Maxwell, Lesli A.

    2007-01-01

    This article reports on how the Baltimore District tackles its high suspension rates. Driven by an increasing belief that zero-tolerance disciplinary policies are ineffective, more educators are embracing strategies that do not exclude misbehaving students from school for offenses such as insubordination, disrespect, cutting class, tardiness, and…

  4. Understanding High School Graduation Rates in Illinois

    ERIC Educational Resources Information Center

    Alliance for Excellent Education, 2009

    2009-01-01

    Graduation rates are a fundamental indicator of whether or not the nation's public school system is doing what it is intended to do: enroll, engage, and educate youth to be productive members of society. Since almost 90 percent of the fastest-growing and highest-paying jobs require some postsecondary education, having a high school diploma and the…

  5. Understanding High School Graduation Rates in Delaware

    ERIC Educational Resources Information Center

    Alliance for Excellent Education, 2009

    2009-01-01

    Graduation rates are a fundamental indicator of whether or not the nation's public school system is doing what it is intended to do: enroll, engage, and educate youth to be productive members of society. Since almost 90 percent of the fastest-growing and highest-paying jobs require some postsecondary education, having a high school diploma and the…

  6. High rate vacuum deposited silicon layers

    NASA Astrophysics Data System (ADS)

    Kipperman, A. H. M.; van Zolingen, R. J. C.

    1982-08-01

    Silicon layers were deposited in vacuum at high rates (up to 50 microns/min) on aluminum-, silicon oxide-, and silicon nitride-coated stainless steel, pyrex, and silicon substrates. The morphological, crystallographic, and electrical properties of the layers were studied in as-grown and annealed conditions. Layers as-grown on aluminum-coated substrates had unsatisfactory electrical properties and too high an aluminum concentration to be acceptable for solar cells. Thermal annealing of layers on SiO2- and on Si3N4-coated substrates markedly improved their crystallographic and electrical properties. In all cases, silicon layers deposited at about 550 C showed a columnar structure which, after prolonged etching, was found to be composed of fibrils of about 0.3 microns in diameter extending over the entire thickness of the layer. It is suggested that further tests should be carried out at a substrate temperature of about 800 C maintaining the high deposition rates.

  7. The Cost of Teacher Turnover in Five School Districts: A Pilot Study

    ERIC Educational Resources Information Center

    Barnes, Gary; Crowe, Edward: Schaefer, Benjamin

    2007-01-01

    In this paper, we report the results of a pilot study of the cost of teacher turnover in five school districts. We examine the rate of turnover, the relationship between turnover and teacher and school characteristics, and the costs associated with recruiting, hiring, and training replacement teachers. We find evidence that turnover costs,…

  8. High strain rate behaviour of polypropylene microfoams

    NASA Astrophysics Data System (ADS)

    Gómez-del Río, T.; Garrido, M. A.; Rodríguez, J.; Arencón, D.; Martínez, A. B.

    2012-08-01

    Microcellular materials such as polypropylene foams are often used in protective applications and passive safety for packaging (electronic components, aeronautical structures, food, etc.) or personal safety (helmets, knee-pads, etc.). In such applications the foams which are used are often designed to absorb the maximum energy and are generally subjected to severe loadings involving high strain rates. The manufacture process to obtain polymeric microcellular foams is based on the polymer saturation with a supercritical gas, at high temperature and pressure. This method presents several advantages over the conventional injection moulding techniques which make it industrially feasible. However, the effect of processing conditions such as blowing agent, concentration and microfoaming time and/or temperature on the microstructure of the resulting microcellular polymer (density, cell size and geometry) is not yet set up. The compressive mechanical behaviour of several microcellular polypropylene foams has been investigated over a wide range of strain rates (0.001 to 3000 s-1) in order to show the effects of the processing parameters and strain rate on the mechanical properties. High strain rate tests were performed using a Split Hopkinson Pressure Bar apparatus (SHPB). Polypropylene and polyethylene-ethylene block copolymer foams of various densities were considered.

  9. Norepinephrine turnover in heart and spleen of 7-, 22-, and 34 C-acclimated hamsters

    NASA Technical Reports Server (NTRS)

    Jones, S. B.; Musacchia, X. J.

    1976-01-01

    The relationship of norepinephrine (NE) concentration and endogenous turnover rates in both myocardial and spleen tissues in the golden hamster is examined as a function of chronic exposure to either high or low ambient temperatures. Changes in myocardial and spleen NE turnover values are discussed in terms of functional alterations in sympathetic nerve activity and the importance of such changes in temperature acclimation. It is found that acclimation of hamsters to 7 C for 7-10 weeks results in decreased myocardial NE concentration and an apparent increase in myocardial NE turnover. In contrast, exposure to 34 C for 6-8 weeks results in increased myocardial NE concentration and an apparent decrease in NE turnover in both myocardial and spleen tissues. The implication of altered NE synthesis is that sympathetic nerve activity is reduced with heat acclimation and is enhanced with cold acclimation.

  10. Sustained high prevalence of sexually transmitted infections among female sex workers in Cambodia: high turnover seriously challenges the 100% condom use programme

    PubMed Central

    Sopheab, Heng; Morineau, Guy; Neal, Joyce J; Saphonn, Vonthanak; Fylkesnes, Knut

    2008-01-01

    Background Cambodia's 100% Condom-Use Programme (CUP), implemented nationally in 2001, requires brothel-based female sex workers (FSWs) to use condoms with all clients. In 2005, we conducted a sexually transmitted infection (STI) survey among FSWs. This paper presents the STI prevalence and related risk factors, and discusses prevalence trends in the context of the 100% CUP in Cambodia. Methods From March-May, 1079 FSWs from eight provinces consented to participate, provided specimens for syphilis, chlamydia, and gonorrhoea testing, and were interviewed. Univariate and multivariate logistic regression analysis was used to determine factors associated with STIs. STI prevalence was compared with data from the 1996 and 2001 STI surveys. Results Most FSWs were young (55% aged 15–24) and new to sex work (60% had worked 12 ≤ months). Consistent condom use with clients was reported by 80% of FSWs, but only 38% of FSWs always used condoms with sweethearts or casual partners. Being new to sex work was the only factor significantly associated with "any STI" (OR = 2.1). Prevalence of syphiliwas 2.3%; chlamydia, 14.4%; gonorrhoea, 13.0%; and any STI, 24.4%. Prevalence of each STI in 2005 was significantly lower than in 1996, but essentially the same as prevalence observed in 2001. Conclusion New FSWs were found to have substantially higher prevalence than those with longer experience. The percent of FSWs who used condoms consistently was high with clients but remained low with non-paying sex partners. Because of the high turnover of FSWs, the prevention needs of new FSWs should be ascertained and addressed. Despite 100% CUP implementation, the prevalence of STIs among FSWs was the same in 2005 as it was in 2001. Limited coverage and weak implementation capacity of the programme along with questionable quality of the STI services are likely to have contributed to the sustained high prevalence. The programme should be carefully reviewed in terms of intensity, quality and

  11. Faunal turnover in Neogene to Recent Caribbean reef corals and region environmental change

    SciTech Connect

    Budd, A.F. . Geology Dept.); Johnson, K.G. . Palaeontology Dept.); Stemann, T.A. . Geologisches Inst.)

    1993-03-01

    Quantitative analyses of species richness and species extinction and origination rates in the Neogene to Recent Caribbean reef coral fauna show that a major episode of turnover occurred during middle to late Pliocene time (4--1 Ma). The data for the authors analyses consist of a new compilation of occurrences of 175 species and 49 genera in reef sequences in the Dominican Republic and Costa Rica and in 21 scattered sites ranging in age from 22 Ma to present. The results show that: (1) during turnover, more than 75% of all species living between 6--4 Ma (n = 82) became extinct; (2) during turnover, extinction and origination rates were equally and simultaneously high, and a relatively constant number of species was maintained in the fauna; (3) the taxonomic composition of Caribbean reefs remained relatively constant before (10--4 Ma) and after (1--0 Ma) turnover. Turnover therefore preceded the high frequency sea level oscillations of late Pleistocene time, and appears related to long-term, unidirectional changes in climate and/or ocean circulation across the Caribbean region in association with closure of the Isthmus of Panama. The observed correspondence between high origination and extinction rates indicates that the same environmental factors may have been associated with increases in both rates, and that local habitat differentiation and fragmentation may have been involved. Stability persisted in the region despite the severe environmental stresses associated with Pleistocene climate change.

  12. Actin Turnover-Mediated Gravity Response in Maize Root Apices

    PubMed Central

    Mancuso, Stefano; Barlow, Peter W; Volkmann, Dieter

    2006-01-01

    The dynamic actin cytoskeleton has been proposed to be linked to gravity sensing in plants but the mechanistic understanding of these processes remains unknown. We have performed detailed pharmacological analyses of the role of the dynamic actin cytoskeleton in gravibending of maize (Zea mays) root apices. Depolymerization of actin filaments with two drugs having different mode of their actions, cytochalasin D and latrunculin B, stimulated root gravibending. By contrast, drug-induced stimulation of actin polymerization and inhibition of actin turnover, using two different agents phalloidin and jasplakinolide, compromised the root gravibending. Importantly, all these actin drugs inhibited root growth to similar extents suggesting that high actin turnover is essential for the gravity-related growth responses rather than for the general growth process. Both latrunculin B and cytochalasin D treatments inhibited root growth but restored gravibending of the decapped root apices, indicating that there is a strong potential for effective actin-mediated gravity sensing outside the cap. This elusive gravity sensing outside the root cap is dependent not only on the high rate of actin turnover but also on weakening of myosin activities, as general inhibition of myosin ATPases induced stimulation of gravibending of the decapped root apices. Collectively, these data provide evidence for the actin turnover-mediated gravity sensing outside the root cap. PMID:19521476

  13. Highly stable high-rate discriminator for nuclear counting

    NASA Technical Reports Server (NTRS)

    English, J. J.; Howard, R. H.; Rudnick, S. J.

    1969-01-01

    Pulse amplitude discriminator is specially designed for nuclear counting applications. At very high rates, the threshold is stable. The output-pulse width and the dead time change negligibly. The unit incorporates a provision for automatic dead-time correction.

  14. High temperature electrochemical corrosion rate probes

    SciTech Connect

    Bullard, Sophie J.; Covino, Bernard S., Jr.; Holcomb, Gordon R.; Ziomek-Moroz, M.

    2005-09-01

    Corrosion occurs in the high temperature sections of energy production plants due to a number of factors: ash deposition, coal composition, thermal gradients, and low NOx conditions, among others. Electrochemical corrosion rate (ECR) probes have been shown to operate in high temperature gaseous environments that are similar to those found in fossil fuel combustors. ECR probes are rarely used in energy production plants at the present time, but if they were more fully understood, corrosion could become a process variable at the control of plant operators. Research is being conducted to understand the nature of these probes. Factors being considered are values selected for the Stern-Geary constant, the effect of internal corrosion, and the presence of conductive corrosion scales and ash deposits. The nature of ECR probes will be explored in a number of different atmospheres and with different electrolytes (ash and corrosion product). Corrosion rates measured using an electrochemical multi-technique capabilities instrument will be compared to those measured using the linear polarization resistance (LPR) technique. In future experiments, electrochemical corrosion rates will be compared to penetration corrosion rates determined using optical profilometry measurements.

  15. High strain rate damage of Carrara marble

    NASA Astrophysics Data System (ADS)

    Doan, Mai-Linh; Billi, Andrea

    2011-10-01

    Several cases of rock pulverization have been observed along major active faults in granite and other crystalline rocks. They have been interpreted as due to coseismic pervasive microfracturing. In contrast, little is known about pulverization in carbonates. With the aim of understanding carbonate pulverization, we investigate the high strain rate (c. 100 s-1) behavior of unconfined Carrara marble through a set of experiments with a Split Hopkinson Pressure Bar. Three final states were observed: (1) at low strain, the sample is kept intact, without apparent macrofractures; (2) failure is localized along a few fractures once stress is larger than 100 MPa, corresponding to a strain of 0.65%; (3) above 1.3% strain, the sample is pulverized. Contrary to granite, the transition to pulverization is controlled by strain rather than strain rate. Yet, at low strain rate, a sample from the same marble displayed only a few fractures. This suggests that the experiments were done above the strain rate transition to pulverization. Marble seems easier to pulverize than granite. This creates a paradox: finely pulverized rocks should be prevalent along any high strain zone near faults through carbonates, but this is not what is observed. A few alternatives are proposed to solve this paradox.

  16. High Rate Data Delivery Thrust Area

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul

    2000-01-01

    In this paper, a brief description of the high rate data delivery (HRDD) thrust area, its focus and current technical activities being carried out by NASA centers including JPL, academia and industry under this program is provided. The processes and methods being used to achieve active participation in this program are presented. The developments in space communication technologies, which will shape NASA enterprise missions in the 21 st. century, are highlighted.

  17. HIGH ENERGY RATE EXTRUSION OF URANIUM

    DOEpatents

    Lewis, L.

    1963-07-23

    A method of extruding uranium at a high energy rate is described. Conditions during the extrusion are such that the temperature of the metal during extrusion reaches a point above the normal alpha to beta transition, but the metal nevertheless remains in the alpha phase in accordance with the Clausius- Clapeyron equation. Upon exiting from the die, the metal automatically enters the beta phase, after which the metal is permitted to cool. (AEC)

  18. Reserve, flowing electrolyte, high rate lithium battery

    NASA Astrophysics Data System (ADS)

    Puskar, M.; Harris, P.

    Flowing electrolyte Li/SOCl2 tests in single cell and multicell bipolar fixtures have been conducted, and measurements are presented for electrolyte flow rates, inlet and outlet temperatures, fixture temperatures at several points, and the pressure drop across the fixture. Reserve lithium batteries with flowing thionyl-chloride electrolytes are found to be capable of very high energy densities with usable voltages and capacities at current densities as high as 500 mA/sq cm. At this current density, a battery stack 10 inches in diameter is shown to produce over 60 kW of power while maintaining a safe operating temperature.

  19. Optimization of coplanar high rate supercapacitors

    NASA Astrophysics Data System (ADS)

    Sun, Leimeng; Wang, Xinghui; Liu, Wenwen; Zhang, Kang; Zou, Jianping; Zhang, Qing

    2016-05-01

    In this work, we describe two efficient methods to enhance the electrochemical performance of high-rate coplanar micro-supercapacitors (MSCs). Through introducing MnO2 nanosheets on vertical-aligned carbon nanotube (VACNT) array, the areal capacitance and volumetric energy density exhibit tremendous improvements which have been increased from 0.011 mF cm-2 to 0.017 mWh cm-3 to 0.479 mF cm-2 and 0.426 mWh cm-3 respectively at an ultrahigh scan rate of 50000 mV s-1. Subsequently, by fabricating an asymmetric MSC, the energy density could be increased to 0.167 mWh cm-3 as well. Moreover, as a result of applying MnO2/VACNT as the positive electrode and VACNT as the negative electrode, the cell operating voltage in aqueous electrolyte could be increased to as high as 2.0 V. Our advanced planar MSCs could operate well at different high scan rates and offer a promising integration potential with other in-plane devices on the same substrate.

  20. Optimization of coplanar high rate supercapacitors

    NASA Astrophysics Data System (ADS)

    Sun, Leimeng; Wang, Xinghui; Liu, Wenwen; Zhang, Kang; Zou, Jianping; Zhang, Qing

    2016-05-01

    In this work, we describe two efficient methods to enhance the electrochemical performance of high-rate coplanar micro-supercapacitors (MSCs). Through introducing MnO2 nanosheets on vertical-aligned carbon nanotube (VACNT) array, the areal capacitance and volumetric energy density exhibit tremendous improvements which have been increased from 0.011 mF cm-2 to 0.017 mWh cm-3 to 0.479 mF cm-2 and 0.426 mWh cm-3 respectively at an ultrahigh scan rate of 50000 mV s-1. Subsequently, by fabricating an asymmetric MSC, the energy density could be increased to 0.167 mWh cm-3 as well. Moreover, as a result of applying MnO2/VACNT as the positive electrode and VACNT as the negative electrode, the cell operating voltage in aqueous electrolyte could be increased to as high as 2.0 V. Our advanced planar MSCs could operate well at different high scan rates and offer a promising integration potential with other in-plane devices on the same substrate.

  1. Civilian residential fire fatality rates: Six high-rate states versus six low-rate states

    NASA Astrophysics Data System (ADS)

    Hall, J. R., Jr.; Helzer, S. G.

    1983-08-01

    Results of an analysis of 1,600 fire fatalities occurring in six states with high fire-death rates and six states with low fire-death rates are presented. Reasons for the differences in rates are explored, with special attention to victim age, sex, race, and condition at time of ignition. Fire cause patterns are touched on only lightly but are addressed more extensively in the companion piece to this report, "Rural and Non-Rural Civilian Residential Fire Fatalities in Twelve States', NBSIR 82-2519.

  2. High rate pulse processing algorithms for microcalorimeters

    SciTech Connect

    Rabin, Michael; Hoover, Andrew S; Bacrania, Mnesh K; Tan, Hui; Breus, Dimitry; Henning, Wolfgang; Sabourov, Konstantin; Collins, Jeff; Warburton, William K; Dorise, Bertrand; Ullom, Joel N

    2009-01-01

    It has been demonstrated that microcalorimeter spectrometers based on superconducting transition-edge-sensor can readily achieve sub-100 eV energy resolution near 100 keV. However, the active volume of a single microcalorimeter has to be small to maintain good energy resolution, and pulse decay times are normally in the order of milliseconds due to slow thermal relaxation. Consequently, spectrometers are typically built with an array of microcalorimeters to increase detection efficiency and count rate. Large arrays, however, require as much pulse processing as possible to be performed at the front end of the readout electronics to avoid transferring large amounts of waveform data to a host computer for processing. In this paper, they present digital filtering algorithms for processing microcalorimeter pulses in real time at high count rates. The goal for these algorithms, which are being implemented in the readout electronics that they are also currently developing, is to achieve sufficiently good energy resolution for most applications while being (a) simple enough to be implemented in the readout electronics and (b) capable of processing overlapping pulses and thus achieving much higher output count rates than the rates that existing algorithms are currently achieving. Details of these algorithms are presented, and their performance was compared to that of the 'optimal filter' that is the dominant pulse processing algorithm in the cryogenic-detector community.

  3. High Strain Rate Behavior of Polyurea Compositions

    NASA Astrophysics Data System (ADS)

    Joshi, Vasant; Milby, Christopher

    2011-06-01

    Polyurea has been gaining importance in recent years due to its impact resistance properties. The actual compositions of this viscoelastic material must be tailored for specific use. It is therefore imperative to study the effect of variations in composition on the properties of the material. High-strain-rate response of three polyurea compositions with varying molecular weights has been investigated using a Split Hopkinson Pressure Bar arrangement equipped with titanium bars. The polyurea compositions were synthesized from polyamines (Versalink, Air Products) with a multi-functional isocyanate (Isonate 143L, Dow Chemical). Amines with molecular weights of 1000, 650, and a blend of 250/1000 have been used in the current investigation. The materials have been tested up to strain rates of 6000/s. Results from these tests have shown interesting trends on the high rate behavior. While higher molecular weight composition show lower yield, they do not show dominant hardening behavior. On the other hand, the blend of 250/1000 show higher load bearing capability but lower strain hardening effects than the 600 and 1000 molecular weight amine based materials. Refinement in experimental methods and comparison of results using aluminum Split Hopkinson Bar is presented.

  4. High strain rate behavior of polyurea compositions

    NASA Astrophysics Data System (ADS)

    Joshi, Vasant S.; Milby, Christopher

    2012-03-01

    High-strain-rate response of three polyurea compositions with varying molecular weights has been investigated using a Split Hopkinson Pressure Bar arrangement equipped with aluminum bars. Three polyurea compositions were synthesized from polyamines (Versalink, Air Products) with a multi-functional isocyanate (Isonate 143L, Dow Chemical). Amines with molecular weights of 1000, 650, and a blend of 250/1000 have been used in the current investigation. These materials have been tested to strain rates of over 6000/s. High strain rate results from these tests have shown varying trends as a function of increasing strain. While higher molecular weight composition show lower yield, they do not show dominant hardening behavior at lower strain. On the other hand, the blend of 250/1000 show higher load bearing capability but lower strain hardening effects than the 600 and 1000 molecular weight amine based materials. Results indicate that the initial increase in the modulus of the blend of 250/1000 may lead to the loss of strain hardening characteristics as the material is compressed to 50% strain, compared to 1000 molecular weight amine based material.

  5. High strain-rate magnetoelasticity in Galfenol

    NASA Astrophysics Data System (ADS)

    Domann, J. P.; Loeffler, C. M.; Martin, B. E.; Carman, G. P.

    2015-09-01

    This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW/m3 ), comparable to explosively driven ferromagnetic pulse generators (500 MW/m3 ). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.

  6. High strain rate deformation of layered nanocomposites.

    PubMed

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A; Thomas, Edwin L

    2012-01-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers. PMID:23132014

  7. High strain rate deformation of layered nanocomposites

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P.; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A.; Thomas, Edwin L.

    2012-11-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

  8. High frame-rate digital radiographic videography

    SciTech Connect

    King, N.S.P.; Cverna, F.H.; Albright, K.L.; Jaramillo, S.A.; Yates, G.J.; McDonald, T.E.; Flynn, M.J.; Tashman, S.

    1994-09-01

    High speed x-ray imaging can be an important tool for observing internal processes in a wide range of applications. In this paper we describe preliminary implementation of a system having the eventual goal of observing the internal dynamics of bone and joint reactions during loading. Two Los Alamos National Laboratory (LANL) gated and image intensified camera systems were used to record images from an x-ray image convertor tube to demonstrate the potential of high frame-rate digital radiographic videography in the analysis of bone and joint dynamics of the human body. Preliminary experiments were done at LANL to test the systems. Initial high frame-rate imaging (from 500 to 1000 frames/s) of a swinging pendulum mounted to the face of an X-ray image convertor tube demonstrated high contrast response and baseline sensitivity. The systems were then evaluated at the Motion Analysis Laboratory of Henry Ford Health Systems Bone and Joint Center. Imaging of a 9 inch acrylic disk with embedded lead markers rotating at approximately 1000 RPM, demonstrated the system response to a high velocity/high contrast target. By gating the P-20 phosphor image from the X-ray image convertor with a second image intensifier (II) and using a 100-microsecond wide optical gate through the second II, enough prompt light decay from the x-ray image convertor phosphor had taken place to achieve reduction of most of the motion blurring. Measurement of the marker velocity was made by using video frames acquired at 500 frames/s. The data obtained from both experiments successfully demonstrated the feasibility of the technique. Several key areas for improvement are discussed along with salient test results and experiment details.

  9. High-frame-rate digital radiographic videography

    NASA Astrophysics Data System (ADS)

    King, Nicholas S. P.; Cverna, Frank H.; Albright, Kevin L.; Jaramillo, Steven A.; Yates, George J.; McDonald, Thomas E.; Flynn, Michael J.; Tashman, Scott

    1994-10-01

    High speed x-ray imaging can be an important tool for observing internal processes in a wide range of applications. In this paper we describe preliminary implementation of a system having the eventual goal of observing the internal dynamics of bone and joint reactions during loading. Two Los Alamos National Laboratory (LANL) gated and image intensified camera systems were used to record images from an x-ray image convertor tube to demonstrate the potential of high frame-rate digital radiographic videography in the analysis of bone and joint dynamics of the human body. Preliminary experiments were done at LANL to test the systems. Initial high frame-rate imaging (from 500 to 1000 frames/s) of a swinging pendulum mounted to the face of an X-ray image convertor tube demonstrated high contrast response and baseline sensitivity. The systems were then evaluated at the Motion Analysis Laboratory of Henry Ford Health Systems Bone and Joint Center. Imaging of a 9 inch acrylic disk with embedded lead markers rotating at approximately 1000 RPM, demonstrated the system response to a high velocity/high contrast target. By gating the P-20 phosphor image from the X-ray image convertor with a second image intensifier (II) and using a 100 microsecond wide optical gate through the second II, enough prompt light decay from the x-ray image convertor phosphor had taken place to achieve reduction of most of the motion blurring. Measurement of the marker velocity was made by using video frames acquired at 500 frames/s. The data obtained from both experiments successfully demonstrated the feasibility of the technique. Several key areas for improvement are discussed along with salient test results and experiment details.

  10. High-Turnover Aromatic C-H Borylation Catalyzed by POCOP-Type Pincer Complexes of Iridium.

    PubMed

    Press, Loren P; Kosanovich, Alex J; McCulloch, Billy J; Ozerov, Oleg V

    2016-08-01

    The catalytic C-H borylation of arenes with HBpin (pin = pinacolate) using POCOP-type pincer complexes of Ir has been demonstrated, with turnover numbers exceeding 10 000 in some cases. The selectivity of C-H activation was based on steric preferences and largely mirrored that found in other Ir borylation catalysts. Catalysis in the (POCOP)Ir system depends on the presence of stoichiometric quantities of sacrificial olefin, which is hydrogenated to consume the H2 equivalents generated in the borylation of C-H bonds with HBpin. Smaller olefins such as ethylene or 1-hexene were more advantageous to catalysis than sterically encumbered tert-butylethylene (TBE). Olefin hydroboration is a competing side reaction. The synthesis and isolation of multiple complexes potentially relevant to catalysis permitted examination of several key elementary reactions. These experiments indicate that the C-H activation step in catalysis ostensibly involves oxidative addition of an aromatic C-H bond to the three-coordinate (POCOP)Ir species. The olefin is mechanistically critical to gain access to this 14-electron, monovalent Ir intermediate. C-H activation at Ir(I) here is in contrast to the olefin-free catalysis with state-of-the-art Ir complexes supported by neutral bidentate ligands, where the C-H activating step is understood to involve trivalent Ir-boryl intermediates. PMID:27327895

  11. Fuel droplet burning rates at high pressures.

    NASA Technical Reports Server (NTRS)

    Canada, G. S.; Faeth, G. M.

    1973-01-01

    Combustion of methanol, ethanol, propanol-1, n-pentane, n-heptane, and n-decane was observed in air under natural convection conditions, at pressures up to 100 atm. The droplets were simulated by porous spheres, with diameters in the range from 0.63 to 1.90 cm. The pressure levels of the tests were high enough so that near-critical combustion was observed for methanol and ethanol. Due to the high pressures, the phase-equilibrium models of the analysis included both the conventional low-pressure approach as well as high-pressure versions, allowing for real gas effects and the solubility of combustion-product gases in the liquid phase. The burning-rate predictions of the various theories were similar, and in fair agreement with the data. The high-pressure theory gave the best prediction for the liquid-surface temperatures of ethanol and propanol-1 at high pressure. The experiments indicated the approach of critical burning conditions for methanol and ethanol at pressures on the order of 80 to 100 atm, which was in good agreement with the predictions of both the low- and high-pressure analysis.

  12. Microalgal separation from high-rate ponds

    SciTech Connect

    Nurdogan, Y.

    1988-01-01

    High rate ponding (HRP) processes are playing an increasing role in the treatment of organic wastewaters in sunbelt communities. Photosynthetic oxygenation by algae has proved to cost only one-seventh as much as mechanical aeration for activated sludge systems. During this study, an advanced HRP, which produces an effluent equivalent to tertiary treatment has been studied. It emphasizes not only waste oxidation but also algal separation and nutrient removal. This new system is herein called advanced tertiary high rate ponding (ATHRP). Phosphorus removal in HRP systems is normally low because algal uptake of phosphorus is about one percent of their 200-300 mg/L dry weights. Precipitation of calcium phosphates by autofluocculation also occurs in HRP at high pH levels, but it is generally not complete due to insufficient calcium concentration in the pond. In the case of Richmond where the studies were conducted, the sewage is very low in calcium. Therefore, enhancement of natural autoflocculation was studied by adding small amounts of lime to the pond. Through this simple procedure phosphorus and nitrogen removals were virtually complete justifying the terminology ATHRP.

  13. High Rate Pulse Processing Algorithms for Microcalorimeters

    NASA Astrophysics Data System (ADS)

    Tan, Hui; Breus, Dimitry; Hennig, Wolfgang; Sabourov, Konstantin; Collins, Jeffrey W.; Warburton, William K.; Bertrand Doriese, W.; Ullom, Joel N.; Bacrania, Minesh K.; Hoover, Andrew S.; Rabin, Michael W.

    2009-12-01

    It has been demonstrated that microcalorimeter spectrometers based on superconducting transition-edge-sensors can readily achieve sub-100 eV energy resolution near 100 keV. However, the active volume of a single microcalorimeter has to be small in order to maintain good energy resolution, and pulse decay times are normally on the order of milliseconds due to slow thermal relaxation. Therefore, spectrometers are typically built with an array of microcalorimeters to increase detection efficiency and count rate. For large arrays, however, as much pulse processing as possible must be performed at the front end of readout electronics to avoid transferring large amounts of waveform data to a host computer for post-processing. In this paper, we present digital filtering algorithms for processing microcalorimeter pulses in real time at high count rates. The goal for these algorithms, which are being implemented in readout electronics that we are also currently developing, is to achieve sufficiently good energy resolution for most applications while being: a) simple enough to be implemented in the readout electronics; and, b) capable of processing overlapping pulses, and thus achieving much higher output count rates than those achieved by existing algorithms. Details of our algorithms are presented, and their performance is compared to that of the "optimal filter" that is currently the predominantly used pulse processing algorithm in the cryogenic-detector community.

  14. High-Rate Digital Receiver Board

    NASA Technical Reports Server (NTRS)

    Ghuman, Parminder; Bialas, Thomas; Brambora, Clifford; Fisher, David

    2004-01-01

    A high-rate digital receiver (HRDR) implemented as a peripheral component interface (PCI) board has been developed as a prototype of compact, general-purpose, inexpensive, potentially mass-producible data-acquisition interfaces between telemetry systems and personal computers. The installation of this board in a personal computer together with an analog preprocessor enables the computer to function as a versatile, highrate telemetry-data-acquisition and demodulator system. The prototype HRDR PCI board can handle data at rates as high as 600 megabits per second, in a variety of telemetry formats, transmitted by diverse phase-modulation schemes that include binary phase-shift keying and various forms of quadrature phaseshift keying. Costing less than $25,000 (as of year 2003), the prototype HRDR PCI board supplants multiple racks of older equipment that, when new, cost over $500,000. Just as the development of standard network-interface chips has contributed to the proliferation of networked computers, it is anticipated that the development of standard chips based on the HRDR could contribute to reductions in size and cost and increases in performance of telemetry systems.

  15. Analysis of the Educational Personnel System: IV. Teacher Turnover.

    ERIC Educational Resources Information Center

    Keeler, Emmett B.

    This report attempts to predict the rates of teacher turnover in the 1970s, which teachers will leave the profession, and what the effects of turnover will be on the educational personnel system. The overall termination rate has varied from six to 11 percent over the last 15 years. An analysis of recent changes in the teaching profession is used…

  16. Organizational commitment and turnover of nursing home administrators.

    PubMed

    Castle, Nicholas G

    2006-01-01

    In this investigation, the associations between organizational commitment (OC), intent-to-turnover, and actual turnover of a large sample of nursing home administrators (NHAs) are examined. Data used come from a mail survey, from which 632 responses were received from the NHAs (response rate = 63%). The one-year turnover rate of NHAs was 39 percent, and in almost all cases (87%) these NHAs had also exhibited low OC scores. The intent-to-turnover results show thinking about quitting comes before searching for a new position, which in turn both comes before the intention to quit. Multivariate analyses show work overload has a strong and robust association with both intent-to-turnover and turnover of NHAs, and may indicate that NHAs are leaving their positions because they are understaffed. PMID:16648695

  17. Dynamics of Adipocyte Turnover in Humans

    SciTech Connect

    Spalding, K; Arner, E; Westermark, P; Bernard, S; Buchholz, B; Bergmann, O; Blomqvist, L; Hoffstedt, J; Naslund, E; Britton, T; Concha, H; Hassan, M; Ryden, M; Frisen, J; Arner, P

    2007-07-16

    Obesity is increasing in an epidemic fashion in most countries and constitutes a public health problem by enhancing the risk for cardiovascular disease and metabolic disorders such as type 2 diabetes. Owing to the increase in obesity, life expectancy may start to decrease in developed countries for the first time in recent history. The factors determining fat mass in adult humans are not fully understood, but increased lipid storage in already developed fat cells is thought to be most important. We show that adipocyte number is a major determinant for the fat mass in adults. However, the number of fat cells stays constant in adulthood in lean and obese and even under extreme conditions, indicating that the number of adipocytes is set during childhood and adolescence. To establish the dynamics within the stable population of adipocytes in adults, we have measured adipocyte turnover by analyzing the integration of {sup 14}C derived from nuclear bomb tests in genomic DNA. Approximately 10% of fat cells are renewed annually at all adult ages and levels of body mass index. Neither adipocyte death nor generation rate is altered in obesity, suggesting a tight regulation of fat cell number that is independent of metabolic profile in adulthood. The high turnover of adipocytes establishes a new therapeutic target for pharmacological intervention in obesity.

  18. Study on high rate MRPC for high luminosity experiments

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Huang, X.; Lv, P.; Zhu, W.; Shi, L.; Xie, B.; Cheng, J.; Li, Y.

    2014-08-01

    Multi-gap Resistive Plate Chambers (MRPC) has been used to construct time-of-flight system in the field of nuclear and particle physics, due to their high-precision timing properties, high efficiency, reliability and coverage of large area. With the increase of accelerator luminosity, MRPCs have to withstand particle fluxes up to several tens of kHz/cm2 in view of the next generation physics experiments, such as the SIS-100/300 at FAIR-CBM, SoLID at JLab and NICA at JINR. But the MRPC assembled with float glass has very low rate capability not exceeding some hundreds of Hz/cm2. Two possible solutions for increasing rate capability, one is to reduce the bulk resistivity of glass and the other is to reduce the electrode thickness. Tsinghua University has done R&D on high rate MRPC for many years. A special low resistive glass with bulk resistivity around 1010Ω.cm was developed. We also studied the rate capability changes with glass thickness. In this paper we describe the performance of low resistive glass and two kinds of high rate MRPC (Pad readout and Strip readout) tested by deuterium beams. The results show that the tolerable particle flux can reach 70 kHz/cm2. In the mean time, MRPCs assembled with three thickness (0.7 mm, 0.5 mm and 0.35 mm) of float glass were also tested with deuteron beams, the results show that the three detectors can afford particle rate up to 500 Hz/cm2, 0.75 kHz/cm2 and 3 kHz/cm2, respectively.

  19. Microbial carbon turnover in the plant-rhizosphere-soil continuum

    NASA Astrophysics Data System (ADS)

    Malik, Ashish; Dannert, Helena; Griffiths, Robert; Thomson, Bruce; Gleixner, Gerd

    2014-05-01

    Soil microbial biomass contributes significantly to maintenance of soil organic matter (SOM). It is well known that biochemical fractions of soil microorganisms have varying turnover and therefore contribute differentially to soil C storage. Here we compare the turnover rates of different microbial biochemical fractions using a pulse chase 13CO2 plant labelling experiment. The isotope signal was temporally traced into rhizosphere soil microorganisms using the following biomarkers: DNA, RNA, fatty acids and chloroform fumigation extraction derived microbial biomass size classes. C flow into soil microbial functional groups was assessed through phospholipid and neutral lipid fatty acid (PLFA/NLFA) analyses. Highest 13C enrichment was seen in the low molecular weight (LMW) size class of microbial biomass (Δδ13C =151) and in nucleic acids (DNA: 38o RNA: 66) immediately after the pulse followed by a sharp drop. The amount of 13C in the high molecular weight (HMW) microbial biomass (17-81) and total fatty acids (32-54) was lower initially and stayed relatively steady over the 4 weeks experimental period. We found significant differences in turnover rates of different microbial biochemical and size fractions. We infer that LMW cytosolic soluble compounds are rapidly metabolized and linked to respiratory C fluxes, whereas mid-sized products of microbial degradation and HMW polymeric compounds have lower renewal rate in that order. The turnover of cell wall fatty acids was also very slow. DNA and RNA showed faster turnover rate; and as expected RNA renewal was the fastest due to its rapid production by active microorganisms independent of cell replication. 13C incorporation into different functional groups confirmed that mutualistic arbuscular mycorrhizal fungi rely on root C and are important in the initial plant C flux. We substantiated through measurements of isotope incorporation into bacterial RNA that rhizosphere bacteria are also important in the initial C conduit

  20. Application of high-rate cutting tools

    NASA Astrophysics Data System (ADS)

    Moriarty, John L., Jr.

    1989-03-01

    Widespread application of the newest high-rate cutting tools to the most appropriate jobs is slowed by the sheer magnitude of developments in tool types, materials, workpiece applications, and by the rapid pace of change. Therefore, a study of finishing and roughing sizes of coated carbide inserts having a variety of geometries for single point turning was completed. The cutting tools were tested for tool life, chip quality, and workpiece surface finish at various cutting conditions with medium alloy steel. An empirical wear-life data base was established, and a computer program was developed to facilitate technology transfer, assist selection of carbide insert grades, and provide machine operating parameters. A follow-on test program was implemented suitable for next generation coated carbides, rotary cutting tools, cutting fluids, and ceramic tool materials.

  1. A high data rate recorder for astronomy

    NASA Technical Reports Server (NTRS)

    Hinteregger, H. F.; Rogers, A. E. E.; Cappallo, R. J.; Webber, J. C.; Petrachenko, W. T.

    1991-01-01

    A magnetic tape recorder developed for the special requirements of radio astronomy and geodesy is described. These requirements include a high bit packing density and long record times. The current version of this longitudinal recorder used by the Very Long Baseline Array (VLBA) records 5.5 Terabits on a 14-in diameter reel of inch-wide tape. A maximum record rate of 256 Mb/s is achieved in the VLBA configuration with one recorder operating at 4 ms and utilizing 32 of the heads in a single stack. The VLBA recorders have been tested using a longitudinal density of 2.25 fr/micron; 448 data + 56 system tracks are recorded in 14 passes, each lasting 50 min, for a total record time (at 128 Mb/s) of 12 h on 14-in diameter reel of inch-wide 13-microns-thick D1-equivalent tape.

  2. Spatial turnover in the global avifauna

    PubMed Central

    Gaston, Kevin J; Davies, Richard G; Orme, C. David L; Olson, Valerie A; Thomas, Gavin H; Ding, Tzung-Su; Rasmussen, Pamela C; Lennon, Jack J; Bennett, Peter M; Owens, Ian P.F; Blackburn, Tim M

    2007-01-01

    Despite its wide implications for many ecological issues, the global pattern of spatial turnover in the occurrence of species has been little studied, unlike the global pattern of species richness. Here, using a database on the breeding distributions of birds, we present the first global maps of variation in spatial turnover for an entire taxonomic class, a pattern that has to date remained largely a matter of conjecture, based on theoretical expectations and extrapolation of inconsistent patterns from different biogeographic realms. We use these maps to test four predictions from niche theory as to the form that this variation should take, namely that turnover should increase with species richness, towards lower latitudes, and with the steepness of environmental gradients and that variation in turnover is determined principally by rare (restricted) species. Contrary to prediction, we show that turnover is high both in areas of extremely low and high species richness, does not increase strongly towards the tropics, and is related both to average environmental conditions and spatial variation in those conditions. These results are closely associated with a further important and novel finding, namely that global patterns of spatial turnover are driven principally by widespread species rather than the restricted ones. This complements recent demonstrations that spatial patterns of species richness are also driven principally by widespread species, and thus provides an important contribution towards a unified model of how terrestrial biodiversity varies both within and between the Earth's major land masses. PMID:17472910

  3. Consideration of wear rates at high velocity

    NASA Astrophysics Data System (ADS)

    Hale, Chad S.

    The development of the research presented here is one in which high velocity relative sliding motion between two bodies in contact has been considered. Overall, the wear environment is truly three-dimensional. The attempt to characterize three-dimensional wear was not economically feasible because it must be analyzed at the micro-mechanical level to get results. Thus, an engineering approximation was carried out. This approximation was based on a metallographic study identifying the need to include viscoplasticity constitutive material models, coefficient of friction, relationships between the normal load and velocity, and the need to understand wave propagation. A sled test run at the Holloman High Speed Test Track (HHSTT) was considered for the determination of high velocity wear rates. In order to adequately characterize high velocity wear, it was necessary to formulate a numerical model that contained all of the physical events present. The experimental results of a VascoMax 300 maraging steel slipper sliding on an AISI 1080 steel rail during a January 2008 sled test mission were analyzed. During this rocket sled test, the slipper traveled 5,816 meters in 8.14 seconds and reached a maximum velocity of 1,530 m/s. This type of environment was never considered previously in terms of wear evaluation. Each of the features of the metallography were obtained through micro-mechanical experimental techniques. The byproduct of this analysis is that it is now possible to formulate a model that contains viscoplasticity, asperity collisions, temperature and frictional features. Based on the observations of the metallographic analysis, these necessary features have been included in the numerical model, which makes use of a time-dynamic program which follows the movement of a slipper during its experimental test run. The resulting velocity and pressure functions of time have been implemented in the explicit finite element code, ABAQUS. Two-dimensional, plane strain models

  4. Talc lubrication at high strain rate

    NASA Astrophysics Data System (ADS)

    Doan, M.; Hirose, T.; Andreani, M.; Boullier, A.; Calugaru, D.; Boutareaud, S.

    2012-12-01

    Talc is a very soft material that has been found in small quantities in active fault zones. Its presence, even in small amount, has been demonstrated in numerous weak faults where microseismicity activity may also occur. Although talc properties have been investigated at low slip rate, its effects at coseismic rate have not been investigated. Here we show that a few weight percents of talc are enough to significantly alter the frictional behavior of natural serpentinite gouge at seismic slip rate. We performed high velocity friction experiments on wet powders mixing talc and serpentinite in varying proportions. At 1.3 m/s, pure natural serpentinite starts sliding with a high friction peak of 0.5 that falls exponentially to a steady-state value of ~0.2 over slip greater than 5 m. By introducing only 5%wt of talc, the initial peak in friction of serpentinite is cut-off: friction levels to 0.35 below 2 m of displacement before merging the exponential decay curve observed for pure serpentinite. For a larger amount of talc, friction curve becomes closer to the talc behavior, which exhibits a friction of 0.2, regardless of displacement. Increasing the amount of talc not only alters the mechanical properties of the mixture, it also changes deformation mechanism and the resulting microstructure. Below 5%wt of talc, deformation is accommodated by cataclastic comminution of serpentine grains, without any thermal decomposition. When talc is present in larger proportion, it accommodates slip with intense delamination. Principal slip zone is composed of serpentine grains smaller than 0.5 μm, 40 times smaller than the size of the initials serpentine grains. Talc grains inserted within the mixture shows extensive delamination after only 3 m of displacement. Talc lamellae are observed along the microscopic shear planes that pervade the principal slip zone and the remaining gouge. We infer that easy delamination of talc multiplies the number of talc grains and increases its

  5. On gigahertz spectral turnovers in pulsars

    NASA Astrophysics Data System (ADS)

    Rajwade, K.; Lorimer, D. R.; Anderson, L. D.

    2016-01-01

    Pulsars are known to emit non-thermal radio emission that is generally a power-law function of frequency. In some cases, a turnover is seen at frequencies around 100 MHz. Kijak et al. have reported the presence of a new class of `Gigahertz Peaked Spectrum' (GPS) pulsars that show spectral turnovers at frequencies around 1 GHz. We apply a model based on free-free thermal absorption to explain these turnovers in terms of surrounding material such as the dense environments found in H II regions, pulsar wind nebulae, or in cold, partially ionized molecular clouds. We show that the turnover frequency depends on the electron temperature of the environment close to the pulsar, as well as the emission measure along the line of sight. We fitted this model to the radio fluxes of known GPS pulsars and show that it can replicate the GHz turnover. From the thermal absorption model, we demonstrate that normal pulsars would exhibit a GPS-like behaviour if they were in a dense environment. We discuss the application of this model in the context of determining the population of neutron stars within the central parsec of the Galaxy. We show that a non-negligible fraction of this population might exhibit high-frequency spectral turnovers, which has implications on the detectability of these sources in the Galactic Centre.

  6. A National Issue: Whether the Teacher Turnover Effects Students' Academic Performance?

    ERIC Educational Resources Information Center

    Terry, Loretta A.; Kritsonis, William Allan

    2008-01-01

    The high teacher turnover rate and low student academic performance are two urgent issues that threaten the education of America's children--our greatest resource. The technical core of schools nationally is to provide a quality education to produce literate generations to function in our global society. If the United States is to equip its young…

  7. The Causes and Effects of English Teachers' Turnover: A Case from Afghanistan

    ERIC Educational Resources Information Center

    Khawary, Omidullah; Ali, Sajid

    2015-01-01

    One of the challenging issues that educational organizations in developing countries face in staffing classrooms with qualified teachers is the high rate of teachers' turnover. It creates problems for schools, which eventually leads to substandard instruction and low student achievement. This research explores the causes of English teachers'…

  8. High rate PLD of diamond-like-carbon utilizing high repetition rate visible lasers

    SciTech Connect

    McLean, W. II; Fehring, E.J.; Dragon, E.P.; Warner, B.E.

    1994-09-15

    Pulsed Laser Deposition (PLD) has been shown to be an effective method for producing a wide variety of thin films of high-value-added materials. The high average powers and high pulse repetition frequencies of lasers under development at LLNL make it possible to scale-up PLD processes that have been demonstrated in small systems in a number of university, government, and private laboratories to industrially meaningful, economically feasible technologies. A copper vapor laser system at LLNL has been utilized to demonstrate high rate PLD of high quality diamond-like-carbon (DLC) from graphite targets. The deposition rates for PLD obtained with a 100 W laser were {approx} 2000 {mu}m{center_dot}cm{sup 2}/h, or roughly 100 times larger than those reported by chemical vapor deposition (CVD) or physical vapor deposition (PVD) methods. Good adhesion of thin (up to 2 pm) films has been achieved on a small number of substrates that include SiO{sub 2} and single crystal Si. Present results indicate that the best quality DLC films can be produced at optimum rates at power levels and wavelengths compatible with fiber optic delivery systems. If this is also true of other desirable coating systems, this PLD technology could become an extremely attractive industrial tool for high value added coatings.

  9. Species Turnover through Time: Colonization and Extinction Dynamics across Metacommunities.

    PubMed

    Nuvoloni, Felipe Micali; Feres, Reinaldo José Fazzio; Gilbert, Benjamin

    2016-06-01

    Island biogeography and metacommunity theory often use equilibrium assumptions to predict local diversity, yet nonequilibrium dynamics are common in nature. In nonequilibrium communities, local diversity fluctuates through time as the relative importance of colonization and extinction change. Here, we test the prevalence and causes of nonequilibrium dynamics in metacommunities of mites associated with rubber trees distributed over large spatial (>1,000 km) and temporal (>30-60 generations) scales in Brazil. We measured colonization and extinction rates to test species turnover and nonequilibrium dynamics over a growing season. Mite metacommunities exhibited nonequilibrium dynamics for most months of the year, and these dynamics tracked climatic conditions. Monthly shifts in temperature of more than 1°C resulted in nonequilibrium dynamics, as did mean temperatures outside of two critical ranges. Nonequilibrium dynamics were caused by a change in colonization with temperature change and changes in both colonization and extinction with absolute temperature. Species turnover showed different trends; high relative humidity increased both colonization and extinction rates, increasing turnover but not nonequilibrium dynamics. Our study illustrates that testing nonequilibrium dynamics can provide new insights into the drivers of colonization, extinction, and diversity fluctuations in metacommunities. PMID:27172597

  10. High-pressure, High-strain-rate Materials Effects

    SciTech Connect

    Kalantar, D; Belak, J; Bringa, E; Budil, K; Colvin, J; Kumar, M; Meyers, M; Rosolankova, K; Rudd, R; Schneider, M; Stolken, J; Wark, J

    2004-03-04

    A 3-year LDRD-ER project to study the response of shocked materials at high pressure and high strain rate has concluded. This project involved a coordinated effort to study single crystal samples that were shock loaded by direct laser irradiation, in-situ and post-recovery measurements, and molecular dynamics and continuum modeling. Laser-based shock experiments have been conducted to study the dynamic response of materials under shock loading materials at a high strain-rate. Experiments were conducted at pressures above the published Hugoniot Elastic Limit (HEL). The residual deformation present in recovered samples was characterized by transmission electron microscopy, and the response of the shocked lattice during shock loading was measured by in-situ x-ray diffraction. Static film and x-ray streak cameras recorded x-rays diffracted from lattice planes of Cu and Si both parallel and perpendicular to the shock direction. Experiments were also conducted using a wide-angle detector to record x-rays diffracted from multiple lattice planes simultaneously. This data showed uniaxial compression of Si (100) along the shock direction and 3-dimensional compression of Cu (100). In the case of the Si diffraction, there was a multiple wave structure observed. We present results of shocked Si and Cu obtained with a new large angle diffraction diagnostic, and discuss the results in the context of detailed molecular dynamics simulations and post-processing.

  11. High voltage high repetition rate pulse using Marx topology

    NASA Astrophysics Data System (ADS)

    Hakki, A.; Kashapov, N.

    2015-06-01

    The paper describes Marx topology using MOSFET transistors. Marx circuit with 10 stages has been done, to obtain pulses about 5.5KV amplitude, and the width of the pulses was about 30μsec with a high repetition rate (PPS > 100), Vdc = 535VDC is the input voltage for supplying the Marx circuit. Two Ferrite ring core transformers were used to control the MOSFET transistors of the Marx circuit (the first transformer to control the charging MOSFET transistors, the second transformer to control the discharging MOSFET transistors).

  12. Dislocation Mechanics of High-Rate Deformations

    NASA Astrophysics Data System (ADS)

    Armstrong, Ronald W.; Li, Qizhen

    2015-10-01

    Four topics associated with constitutive equation descriptions of rate-dependent metal plastic deformation behavior are reviewed in honor of previous research accomplished on the same issues by Professor Marc Meyers along with colleagues and students, as follow: (1) increasing strength levels attributed to thermally activated dislocation migration at higher loading rates; (2) inhomogeneous adiabatic shear banding; (3) controlling mechanisms of deformation in shock as compared with shock-less isentropic compression experiments and (4) Hall-Petch-based grain size-dependent strain rate sensitivities exhibited by nanopolycrystalline materials. Experimental results are reviewed on the topics for a wide range of metals.

  13. HIgh Rate X-ray Fluorescence Detector

    SciTech Connect

    Grudberg, Peter Matthew

    2013-04-30

    The purpose of this project was to develop a compact, modular multi-channel x-ray detector with integrated electronics. This detector, based upon emerging silicon drift detector (SDD) technology, will be capable of high data rate operation superior to the current state of the art offered by high purity germanium (HPGe) detectors, without the need for liquid nitrogen. In addition, by integrating the processing electronics inside the detector housing, the detector performance will be much less affected by the typically noisy electrical environment of a synchrotron hutch, and will also be much more compact than current systems, which can include a detector involving a large LN2 dewar and multiple racks of electronics. The combined detector/processor system is designed to match or exceed the performance and features of currently available detector systems, at a lower cost and with more ease of use due to the small size of the detector. In addition, the detector system is designed to be modular, so a small system might just have one detector module, while a larger system can have many you can start with one detector module, and add more as needs grow and budget allows. The modular nature also serves to simplify repair. In large part, we were successful in achieving our goals. We did develop a very high performance, large area multi-channel SDD detector, packaged with all associated electronics, which is easy to use and requires minimal external support (a simple power supply module and a closed-loop water cooling system). However, we did fall short of some of our stated goals. We had intended to base the detector on modular, large-area detectors from Ketek GmbH in Munich, Germany; however, these were not available in a suitable time frame for this project, so we worked instead with pnDetector GmbH (also located in Munich). They were able to provide a front-end detector module with six 100 m^2 SDD detectors (two monolithic arrays of three elements each) along with

  14. Bipolar high-repetition-rate high-voltage nanosecond pulser

    SciTech Connect

    Tian Fuqiang; Wang Yi; Shi Hongsheng; Lei Qingquan

    2008-06-15

    The pulser designed is mainly used for producing corona plasma in waste water treatment system. Also its application in study of dielectric electrical properties will be discussed. The pulser consists of a variable dc power source for high-voltage supply, two graded capacitors for energy storage, and the rotating spark gap switch. The key part is the multielectrode rotating spark gap switch (MER-SGS), which can ensure wider range modulation of pulse repetition rate, longer pulse width, shorter pulse rise time, remarkable electrical field distortion, and greatly favors recovery of the gap insulation strength, insulation design, the life of the switch, etc. The voltage of the output pulses switched by the MER-SGS is in the order of 3-50 kV with pulse rise time of less than 10 ns and pulse repetition rate of 1-3 kHz. An energy of 1.25-125 J per pulse and an average power of up to 10-50 kW are attainable. The highest pulse repetition rate is determined by the driver motor revolution and the electrode number of MER-SGS. Even higher voltage and energy can be switched by adjusting the gas pressure or employing N{sub 2} as the insulation gas or enlarging the size of MER-SGS to guarantee enough insulation level.

  15. High data rate systems for the future

    NASA Technical Reports Server (NTRS)

    Chitwood, John

    1991-01-01

    Information systems in the next century will transfer data at rates that are much greater than those in use today. Satellite based communication systems will play an important role in networking users. Typical data rates; use of microwave, millimeter wave, or optical systems; millimeter wave communication technology; modulators/exciters; solid state power amplifiers; beam waveguide transmission systems; low noise receiver technology; optical communication technology; and the potential commercial applications of these technologies are discussed.

  16. High rates of molecular evolution in hantaviruses.

    PubMed

    Ramsden, Cadhla; Melo, Fernando L; Figueiredo, Luiz M; Holmes, Edward C; Zanotto, Paolo M A

    2008-07-01

    Hantaviruses are rodent-borne Bunyaviruses that infect the Arvicolinae, Murinae, and Sigmodontinae subfamilies of Muridae. The rate of molecular evolution in the hantaviruses has been previously estimated at approximately 10(-7) nucleotide substitutions per site, per year (substitutions/site/year), based on the assumption of codivergence and hence shared divergence times with their rodent hosts. If substantiated, this would make the hantaviruses among the slowest evolving of all RNA viruses. However, as hantaviruses replicate with an RNA-dependent RNA polymerase, with error rates in the region of one mutation per genome replication, this low rate of nucleotide substitution is anomalous. Here, we use a Bayesian coalescent approach to estimate the rate of nucleotide substitution from serially sampled gene sequence data for hantaviruses known to infect each of the 3 rodent subfamilies: Araraquara virus (Sigmodontinae), Dobrava virus (Murinae), Puumala virus (Arvicolinae), and Tula virus (Arvicolinae). Our results reveal that hantaviruses exhibit short-term substitution rates of 10(-2) to 10(-4) substitutions/site/year and so are within the range exhibited by other RNA viruses. The disparity between this substitution rate and that estimated assuming rodent-hantavirus codivergence suggests that the codivergence hypothesis may need to be reevaluated. PMID:18417484

  17. Cheetah: A high frame rate, high resolution SWIR image camera

    NASA Astrophysics Data System (ADS)

    Neys, Joel; Bentell, Jonas; O'Grady, Matt; Vermeiren, Jan; Colin, Thierry; Hooylaerts, Peter; Grietens, Bob

    2008-10-01

    A high resolution, high frame rate InGaAs based image sensor and associated camera has been developed. The sensor and the camera are capable of recording and delivering more than 1700 full 640x512pixel frames per second. The FPA utilizes a low lag CTIA current integrator in each pixel, enabling integration times shorter than one microsecond. On-chip logics allows for four different sub windows to be read out simultaneously at even higher rates. The spectral sensitivity of the FPA is situated in the SWIR range [0.9-1.7 μm] and can be further extended into the Visible and NIR range. The Cheetah camera has max 16 GB of on-board memory to store the acquired images and transfer the data over a Gigabit Ethernet connection to the PC. The camera is also equipped with a full CameralinkTM interface to directly stream the data to a frame grabber or dedicated image processing unit. The Cheetah camera is completely under software control.

  18. Turnover of dhurrin in green sorghum seedlings. [Sorghum bicolor

    SciTech Connect

    Adewusi, S.R.A. )

    1990-11-01

    The turnover of dhurrin in green seedlings of Sorghum bicolor (Linn) Moench var Redland x Greenleaf, Sudan 70 has been investigated using glyphosate and pulse-labeling studies with {sup 14}C-tyrosine and ({sup 14}C)shikimic acid. The rate of dhurrin breakdown was 4.8 nanomoles per hour in the shoot and 1.4 nanomoles per hour in the root. The rate of dhurrin accumulation in the shoot of 4- to 5-day-old seedlings was high but decreased with age until at the peak period of dhurrin accumulation, the rates of dhurrin synthesis and breakdown were equal. Using a first order equation (an approximation) the rate of dhurrin synthesis (which equals accumulation plus breakdown rates) was 17.4 nanomoles per hour in the shoot and 4.1 nanomoles per hour in the root. In both tissues, the breakdown rate was between 27 and 34% of their synthetic capacity within the experimental period. Dhurrin synthesis in green sorghum seedlings occurred in both the light and dark photoperiods but was faster in the dark period. The result is discussed in relation to the possible metabolic roles of the turnover.

  19. Exceptionally large entropy contributions enable the high rates of GTP hydrolysis on the ribosome

    PubMed Central

    Åqvist, Johan; Kamerlin, Shina C.L.

    2015-01-01

    Protein synthesis on the ribosome involves hydrolysis of GTP in several key steps of the mRNA translation cycle. These steps are catalyzed by the translational GTPases of which elongation factor Tu (EF-Tu) is the fastest GTPase known. Here, we use extensive computer simulations to explore the origin of its remarkably high catalytic rate on the ribosome and show that it is made possible by a very large positive activation entropy. This entropy term (TΔS‡) amounts to more than 7 kcal/mol at 25 °C. It is further found to be characteristic of the reaction mechanism utilized by the translational, but not other, GTPases and it enables these enzymes to attain hydrolysis rates exceeding 500 s−1. This entropy driven mechanism likely reflects the very high selection pressure on the speed of protein synthesis, which drives the rate of each individual GTPase towards maximal turnover rate of the whole translation cycle. PMID:26497916

  20. Smoking Rates Still High in Some Racial Groups, CDC Reports

    MedlinePlus

    ... page: https://medlineplus.gov/news/fullstory_160256.html Smoking Rates Still High in Some Racial Groups, CDC ... lot of progress in getting Americans to stop smoking, some groups still have high smoking rates, a ...

  1. Turnover and dispersal of prairie falcons in southwestern Idaho

    USGS Publications Warehouse

    Lehman, Robert N.; Steenhof, Karen; Carpenter, L.B.; Kochert, Michael N.

    2000-01-01

    We studied Prairie Falcon (Falco mexicanus) breeding dispersal, natal dispersal, and turnover at nesting areas in the Snake River Birds of Prey National Conservation Area (NCA) from 1971- 95. Of 61 nesting areas where falcons identified one year were known to be present or absent the following year, 57% had a different falcon. This turnover rate was 2-3 times higher than that reported elsewhere for large falcons, and may have been related to high nesting densities in the NCA. Turnover at nesting areas was independent of nesting success in the previous year, but was significantly higher for females nesting on large cliffs. Mean distance between natal and breeding locations for 26 falcons banded as nestlings and later encountered as nesting adults was 8.9 km. Natal dispersal distances were similar for males and females, but more than twice as many males marked as nestlings were later encountered nesting in the NCA. Fourteen adult falcons found on different nesting areas in successive years moved an average of 1.5 km between nesting areas; males dispersed significantly farther than females. Natal and breeding dispersal distances in the NCA were lower than those reported for Prairie Falcons in other study areas. Only four falcons banded as nestlings were found outside NCA boundaries during the breeding period, and only one of these birds was known to be occupying a nesting area. We encountered no falcons banded outside the NCA occupying nesting areas in the NCA during this study.

  2. Constituent attachment and voluntary turnover in low-wage/low-skill service work.

    PubMed

    Ellingson, Jill E; Tews, Michael J; Dachner, Alison M

    2016-01-01

    This paper draws on life stage theory, ethnographic research conducted in the service sector, and evidence for secondary segmentation within the low-wage/low-skill labor force to offer evidence that social bond development with coworkers can help reduce the high rate of turnover observed in low-wage/low-skill service work. Contrary to the belief that these employees will leave before social ties can develop, constituent attachment was found to be the only significant predictor of turnover in 2 samples of front-line service workers in a casual dining, national restaurant chain after controlling for other aspects of work that can create a sense of attachment to a job, and other job attitudes, such as satisfaction and commitment. However, the effect was dependent on developmental life stage. Constituent attachment reduced turnover among workers classified as emerging adults, whereas constituent attachment did little to affect turnover among nonemerging adults. Implications of the results are discussed with respect to the value of considering segmentation in future research on turnover in the service sector and the use of life stage theory for understanding the leaving behavior of workers in different stages of adulthood. PMID:26121092

  3. High frame rate fluorescence lifetime imaging

    NASA Astrophysics Data System (ADS)

    Agronskaia, A. V.; Tertoolen, L.; Gerritsen, H. C.

    2003-07-01

    A fast time-domain based fluorescence lifetime imaging (FLIM) microscope is presented that can operate at frame rates of hundreds of frames per second. A beam splitter in the detection path of a wide-field fluorescence microscope divides the fluorescence in two parts. One part is optically delayed with respect to the other. Both parts are viewed with a single time-gated intensified CCD camera with a gate width of 5 ns. The fluorescence lifetime image is obtained from the ratio of these two images. The fluorescence lifetime resolution of the FLIM microscope is verified both with dye solutions and fluorescent latex beads. The fluorescence lifetimes obtained from the reference specimens are in good agreement with values obtained from time correlated single photon counting measurements on the same specimens. The acquisition speed of the FLIM system is evaluated with a measurement of the calcium fluxes in neonatal rat myocytes stained with the calcium probe Oregon Green 488-Bapta. Fluorescence lifetime images of the calcium fluxes related to the beating of the myocytes are acquired with frame rates of up to 100 Hz.

  4. Program Needs and Change Orientation: Implications for Counselor Turnover

    PubMed Central

    Knight, Danica K.; Landrum, Brittany; Becan, Jennifer E.; Flynn, Patrick M.

    2011-01-01

    While evidence suggests that turnover rates are higher in high-stress/high-needswork environments, it is unclear whether agencies’ attempts at improving practices influence individuals’ decisions to stay at or leave a job. The purpose of this study is to examine whether program needs and change orientation influence individual decisions to quit. A sample of 206 counselors from 25 outpatient substance abuse treatment programs completed the Survey of Organizational Functioning, rating the organization on program needs, leadership, and change. They also rated themselves on stress, burnout, and job satisfaction. Multilevel modeling indicated a significant interaction between program needs and change orientation, even after controlling for stress, burnout, job satisfaction, tenure, and selected program characteristics. When perceptions of program needs were high, counselors were more likely to stay if they felt that the organization was making progress toward change. These findings suggest that an orientation toward change can counteract negative effects of perceived need within the workplace. PMID:22154025

  5. Glucosidase II, a protein of the endoplasmic reticulum with high mannose oligosaccharide chains and a rapid turnover

    SciTech Connect

    Strous, G.J.; Van Kerkhof, P.; Brok, R.; Roth, J.; Brada, D.

    1987-03-15

    Glucosidase II is regarded as a resident protein of the endoplasmatic reticulum. The enzyme removes alpha-1-3-linked glucose from high mannose oligosaccharides N-linked to asparagine residues of glycoproteins. Monospecific antibodies raised against the pig kidney enzyme are used to study the metabolism of the enzyme in a rat hepatoma cell line. These antiglucosidase II antibodies specifically immune precipitate glucosidase II as a 100,000-Da species from (/sup 35/S)methionine-labeled cells. In addition, protein blotting and immune staining of cell extracts from both rat liver and human and rat hepatoma cell lines show identity in apparent Mr (100,000). Glucosidase II synthesized in the presence of tunicamycin is approximately 94,000 Da, indicating the presence of one or more N-linked oligosaccharide chains. Cell-free protein synthesis of rat hepatoma total RNA demonstrates that glucosidase II is synthesized as a slightly higher molecular weight species as compared to the polypeptide synthesized in whole cells in the presence of tunicamycin, indicating that the enzyme has a cleavable signal sequence. Using a pulse-chase protocol, the apparent molecular weight does not change upon longer chase periods. In addition, the 100,000-Da protein remains sensitive to endo-beta-N-acetylglucosaminidase H regardless of prolonged chase periods. The cells incorporate (/sup 3/H)mannose into the enzyme; after release with endo-beta-N-acetylglucosaminidase H, most of the radioactivity comigrates with Glc1-Man9-GlcNAc on a gel filtration column.

  6. High Count Rate Electron Probe Microanalysis

    PubMed Central

    Geller, Joseph D.; Herrington, Charles

    2002-01-01

    Reducing the measurement uncertainty of quantitative analyses made using electron probe microanalyzers (EPMA) requires a careful study of the individual uncertainties from each definable step of the measurement. Those steps include measuring the incident electron beam current and voltage, knowing the angle between the electron beam and the sample (takeoff angle), collecting the emitted x rays from the sample, comparing the emitted x-ray flux to known standards (to determine the k-ratio) and transformation of the k-ratio to concentration using algorithms which includes, as a minimum, the atomic number, absorption, and fluorescence corrections. This paper discusses the collection and counting of the emitted x rays, which are diffracted into the gas flow or sealed proportional x-ray detectors. The representation of the uncertainty in the number of collected x rays collected reduces as the number of counts increase. The uncertainty of the collected signal is fully described by Poisson statistics. Increasing the number of x rays collected involves either counting longer or at a higher counting rate. Counting longer means the analysis time increases and may become excessive to get to the desired uncertainty. Instrument drift also becomes an issue. Counting at higher rates has its limitations, which are a function of the detector physics and the detecting electronics. Since the beginning of EPMA analysis, analog electronics have been used to amplify and discriminate the x-ray induced ionizations within the proportional counter. This paper will discuss the use of digital electronics for this purpose. These electronics are similar to that used for energy dispersive analysis of x rays with either Si(Li) or Ge(Li) detectors except that the shaping time constants are much smaller. PMID:27446749

  7. Infant mortality rates declining, but still high.

    PubMed

    Hoffman, M

    1992-10-01

    Family planning can improve infant survival. Specifically, use of family planning methods can minimize family size, increase birth spacing, and reduce the likelihood of pregnancy for teenagers and women aged 40 or older. Immunizations and oral rehydration are responsible for the falling infant mortality rats since 1977 in developing countries, especially among 1-12 month old infants. Yet, neonatal mortality in developing countries had not changed. WHO intends to step up efforts to improve newborn survival. Accurate data are needed, however. Even in developed countries which keep good statistics, infant mortality bias exists. For example, in Japan, some infant deaths are called fetal deaths. In developing countries, much of the data come from hospitals, yet most birth do not occur in hospitals. Even in surveys, bias exists, such as problems with recall. Many researchers use traditional birth attendants (TBAs) to follow up on all births in an area which may eliminate some biases. Such a prospective and longitudinal study in Trairi county in northeastern Brazil shows the infant mortality rate to be less than half of the official rate (65 vs. 142). The major causes of infant death in developed countries, which tends to occur in the neonatal period, are low birth weight, prematurity, birth complications, and congenital defects; developing countries; they are vaccine preventable infectious diseases, diarrhea and dehydration, and respiratory illnesses, all complicated by malnutrition. To make further strides in reducing infant mortality, public health workers must concentrate on the neonatal period. Training TBAs in sterile techniques, appropriate technology, resuscitation of infants, and identification of potential problems is a positive step. Yet, unpredictable conditions (e.g., AIDS) exist and/or will arise which erode improvements. For example, in Nicaragua, within 1 year after the new government introduced health budget cuts which resulted in the poor paying for

  8. Social Disadvantage and Network Turnover

    PubMed Central

    2015-01-01

    Objectives. Research shows that socially disadvantaged groups—especially African Americans and people of low socioeconomic status (SES)—experience more unstable social environments. I argue that this causes higher rates of turnover within their personal social networks. This is a particularly important issue among disadvantaged older adults, who may benefit from stable networks. This article, therefore, examines whether social disadvantage is related to various aspects of personal network change. Method. Social network change was assessed using longitudinal egocentric network data from the National Social Life, Health, and Aging Project, a study of older adults conducted between 2005 and 2011. Data collection in Wave 2 included a technique for comparing respondents’ confidant network rosters between waves. Rates of network losses, deaths, and additions were modeled using multivariate Poisson regression. Results. African Americans and low-SES individuals lost more confidants—especially due to death—than did whites and college-educated respondents. African Americans also added more confidants than whites. However, neither African Americans nor low-SES individuals were able to match confidant losses with new additions to the extent that others did, resulting in higher levels of confidant network shrinkage. These trends are partly, but not entirely, explained by disadvantaged individuals’ poorer health and their greater risk of widowhood or marital dissolution. Discussion. Additional work is needed to shed light on the role played by race- and class-based segregation on group differences in social network turnover. Social gerontologists should examine the role these differences play in explaining the link between social disadvantage and important outcomes in later life, such as health decline. PMID:24997286

  9. High-rate counting efficiency of VLPC

    SciTech Connect

    Hogue, H.H.

    1998-11-01

    A simple model is applied to describe dependencies of Visible Light Photon Counter (VLPC) characteristics on temperature and operating voltage. Observed counting efficiency losses at high illumination, improved by operating at higher temperature, are seen to be a consequence of de-biasing within the VLPC structure. A design improvement to minimize internal de-biasing for future VLPC generations is considered. {copyright} {ital 1998 American Institute of Physics.}

  10. Dispersal, niche, and isolation processes jointly explain species turnover patterns of nonvolant small mammals in a large mountainous region of China.

    PubMed

    Wen, Zhixin; Quan, Qing; Du, Yuanbao; Xia, Lin; Ge, Deyan; Yang, Qisen

    2016-02-01

    Understanding the mechanisms that govern the spatial patterns of species turnover (beta diversity) has been one of the fundamental issues in biogeography. Species turnover is generally recognized as strong in mountainous regions, but the way in which different processes (dispersal, niche, and isolation) have shaped the spatial turnover patterns in mountainous regions remains largely unexplored. Here, we explore the directional and elevational patterns of species turnover for nonvolant small mammals in the Hengduan Mountains of southwest China and distinguish the relative roles of geographic distance, environmental distance, and geographic isolation on the patterns. The spatial turnover was assessed using the halving distance (km), which was the geographic distance that halved the similarity (Jaccard similarity) from its initial value. The halving distance was calculated for the linear, logarithmic, and exponential regression models between Jaccard similarity and geographic distance. We found that the east-west turnover is generally faster than the south-north turnover for high-latitudinal regions in the Hengduan Mountains and that this pattern corresponds to the geographic structure of the major mountain ranges and rivers that mainly extend in a south-north direction. There is an increasing trend of turnover toward the higher-elevation zones. Most of the variation in the Jaccard similarity could be explained by the pure effect of geographic distance and the joint effects of geographic distance, environmental distance, and average elevation difference. Our study indicates that dispersal, niche, and isolation processes are all important determinants of the spatial turnover patterns of nonvolant small mammals in the Hengduan Mountains. The spatial configuration of the landscape and geographic isolation can strongly influence the rate of species turnover in mountainous regions at multiple spatial scales. PMID:26941938