1,803 research outputs found
Resistance to intercompartmental mass transfer limits Ī²2-microglobulin removal by post-dilution hemodiafiltration
Although clearance of Ī²2-microglobulin is greater with hemodiafiltration than with high-flux hemodialysis, Ī²2-microglobulin concentrations after long-term hemodiafiltration are only slightly less than those obtained with high-flux hemodialysis. Resistance to Ī²2-microglobulin transfer between body compartments could explain this observation. Ī²2-Microglobulin kinetics were determined in patients receiving on-line post-dilution hemodiafiltration for 4āh with 18āl of filtration. Plasma Ī²2-microglobulin concentrations were measured during and for 2āh following hemodiafiltration and immediately before the next treatment. The filter clearance of Ī²2-microglobulin was determined from arterial and venous concentrations. The Ī²2-microglobulin generation rate was calculated from the change in the plasma concentration between treatments. The intercompartmental clearance was obtained by fitting the observed concentrations to a two-compartment, variable volume model. The plasma clearance of Ī²2-microglobulin by the filter was 73Ā±2āml/min. Plasma Ī²2-microglobulin concentrations decreased by 68Ā±2% from pre- to post-treatment (27.1Ā±2.2ā8.5Ā±0.7āmg/l), but rebounded by 32Ā±3% over the next 90āmin. The generation rate of Ī²2-microglobulin was 0.136Ā±0.008āmg/min. The model fit yielded an intercompartmental clearance of 82Ā±7āml/min and a volume of distribution of 10.2Ā±0.6āl, corresponding to 14.3Ā±0.7% of body weight. Hemodiafiltration provides a Ī²2-microglobulin clearance of similar magnitude to the intercompartmental clearance within the body. As a result, intercompartmental mass transfer limits Ī²2-microglobulin removal by hemodiafiltration. This finding suggests that alternative strategies, such as increased treatment times or frequency of treatment, are needed to further reduce plasma Ī²2-microglobulin concentrations
A baseline survey of dissolved methane in aquifers in Great Britain
Interest in dissolved methane (CH4) concentrations in aquifers in England, Scotland and Wales (āGreat Britainā or GB) has grown concurrently with interest in the exploitation of unconventional gas sources (UGS). Experience, mainly from North America, has shown the importance of a pre-production baseline against which changes possibly due to UGS extraction can be compared. The British Geological Survey, aided by water utilities, private users and regulators, has compiled a unique dataset for CH4 in groundwaters of GB. This focuses principally on areas where UGS exploration is considered more likely, as indicated by the underlying geology.
All the main water supply aquifers (Principal aquifers) were targeted, plus Secondary aquifers where locally important. The average dissolved CH4 concentration across GB in the aquifers sampled was 45 Ī¼g/l. Out of a total of 343 sites, 96% showed dissolved CH4 concentrations b100 Ī¼g/l, 80% b10 Ī¼g/l, and 43% b 1 Ī¼g/l. No site had a CH4 concentration above the US Department of the Interior suggested risk action level of 10,000 Ī¼g/l.
While most sites were sampled only once, a sub set was monitored quarterly to determine the magnitude of seasonal or other variations. Generally these variations were minor, with 84% of sites showing variations within the range 0.5ā37 Ī¼g/l, but some aquifers where the porosity was primarily fracture-related showed larger changes (0.5ā264 Ī¼g/l). This may have been due to the nature of sampling at these sites which, unlike the others, did not have installed pumps. Since the regulatory compliance monitoring attending UGS operations will include the measurement of parameters such as dissolved CH4, it is essential that sampling methods are tested to ensure that reliable and comparable datasets can be obtained
Validity of a pictorial perceived exertion scale for effort estimation and effort production during stepping exercise in adolescent children
This is the author's PDF version of an article published in European Physical Education Review Ā©2002. The definitive version is available at http://epe.sagepub.com.Recent developments in the study of paediatric effort perception have continued to emphasise the importance of child-specific rating scales. The purpose of this study was to examine the validity of an illustrated 1 ā 10 perceived exertion scale; the Pictorial Childrenās Effort Rating Table (PCERT). 4 class groups comprising 104 children; 27 boys and 29 girls, aged 12.1Ā±0.3 years and 26 boys, 22 girls, aged 15.3Ā±0.2 years were selected from two schools and participated in the initial development of the PCERT. Subsequently, 48 of these children, 12 boys and 12 girls from each age group were randomly selected to participate in the PCERT validation study. Exercise trials were divided into 2 phases and took place 7 to 10 days apart. During phase 1, children completed 5 x 3-minute incremental stepping exercise bouts interspersed with 2-minute recovery periods. Heart rate (HR) and ratings of exertion were recorded during the final 15 s of each exercise bout. In phase 2 the children were asked to regulate their exercising effort during 4 x 4-minute bouts of stepping so that it matched randomly prescribed PCERT levels (3, 5, 7 and 9). Analysis of data from Phase 1 yielded significant (P<0.01) relationships between perceived and objective (HR) effort measures for girls. In addition, the main effects of exercise intensity on perceived exertion and HR were significant (P<0.01); perceived exertion increased as exercise intensity increased and this was reflected in simultaneous significant rises in HR. During phase 2, HR and estimated power output (POapprox) produced at each of the four prescribed effort levels were significantly different (P<0.01). The children in this study were able to discriminate between 4 different exercise intensities and regulate their exercise intensity according to 4 prescribed levels of perceived exertion. In seeking to contribute towards childrenās recommended physical activity levels and helping them understand how to self-regulate their activity, the application of the PCERT within the context of physical education is a desirable direction for future research
A relational database of post-harvest fish losses
The article describes FISHLOSS, a database of post-harvest fish losses devised by the Natural Resources Institute (NRI), UK. The database contains 450 records of post-harvest fish losses from 150 sources. The majority of the estimates are shelf-life estimates. Designed to be a reference for people studying post-harvest fish losses, it draws attention to areas requiring future research to identify significant losses and the factors which cause them. All researchers and users are encouraged to send NRI their own estimates for inclusion in revised versions of FISHLOSS
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Exploring the relation between flapping behaviour and accelerometer signal during ascending flight, and a new approach to calibration
We understand little about the energetic costs of flight in free-ranging birds; in part since current techniques for estimating flight energetics in the wild are limited. Accelerometry is known to estimate energy expenditure through body movement in terrestrial animals, once calibrated using a treadmill with chamber respirometry. The flight equivalent, a wind tunnel with mask respirometry, is particularly difficult to instigate, and has not been applied to calibrate accelerometry. We take the first steps in exploring a novel method for calibrating accelerometers with flight energy expenditure. We collected accelerometry data for Harrisās Hawks Parabuteo unicinctus flying to varying heights up to 4.1 m over a small horizontal distance; the mechanical
energy expended to gain height can be estimated from physical first principles. The relationship between accelerometry and mechanical energy expenditure was strong, and while a simple wing flapping model confirmed that accelerometry is sensitive to both changes in wing beat amplitude and frequency, the relationship was explained predominately by changes in wing beat frequency, and less so by changes in amplitude. Our study provides initial, positive evidence that accelerometry can be calibrated with body power using climbing flights, potentially providing a basis for estimating flapping flight metabolic rate at least in situations of altitude gain
Yield conditions for deformation of amorphous polymer glasses
Shear yielding of glassy polymers is usually described in terms of the
pressure-dependent Tresca or von Mises yield criteria. We test these criteria
against molecular dynamics simulations of deformation in amorphous polymer
glasses under triaxial loading conditions that are difficult to realize in
experiments. Difficulties and ambiguities in extending several standard
definitions of the yield point to triaxial loads are described. Two
definitions, the maximum and offset octahedral stresses, are then used to
evaluate the yield stress for a wide range of model parameters. In all cases,
the onset of shear is consistent with the pressure-modified von Mises
criterion, and the pressure coefficient is nearly independent of many
parameters. Under triaxial tensile loading, the mode of failure changes to
cavitation.Comment: 9 pages, 8 figures, revte
Forage quality, mineral constituents, and performance of beef yearlings grazing two crested wheatgrasses
In the central Great Plains, crested wheatgrasses (Agropyron cristatum
(L.) Gaetner and A. desertorium (Fischer ex Link) Schultes] are
best utilized for early spring and late fall grazing. The principal objective
of this study was to determine if beef (Bos taurus L.) yearlings
grazing 'Ruff' (A. cristatum) during the spring grazing season had
higher average daily gains and gains per hectare than cattle grazing
`Nordan' (A. desertorum). These cultivars were evaluated in grazing
trials (four replications) in eastern Nebraska in 1985, 1986, and 1987.
The 0.8-ha pastures were seeded in the fall of 1983 on a Typic Argiudoll
soil and were fertilized annually with 68 to 90 kg N ha-1. Grazing
was for 6 wk each spring by yearling steers with a beginning average
weight of 250 kg. Averaged over 3 yr, Ruff produced higher gains
per hectare than Nordan (272 vs 245 kg ha-1) probably because it
produced more herbage because of its better persistence. At the end
of the trial, the averge basal cover of Ruff and Nordan were 21 and
6%, respectively. Three-year mean average daily gains were Ruff =
1.28 vs. Nordan = 1.34 kg d-1, which were unexpected, because Ruff
generally had higher forage quality as measured by an array of parameters.
Ruff forage had a higher, less desirable grass tetany ratio
[K/(Mg +Ca)) than Nordan (2.6 vs. 2.3) averaged over 3 yr. Cattle
grazing Ruff had lower blood serum Mg levels than cattle grazing
Nordan (15.4 vs. 16.2 mg L-1, both of which were below the hypomagnesemia
threshold of 18 mg L-1. This condition may have reduced
intake and animal gains. These results indicate the need for evaluating
pasture and range grass cultivars under grazing conditions
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