Environmental tritium measurements and lumped parameter modelling in the Tafilalet aquifer, south-east Morocco

2007 ◽  
Vol 95 (10) ◽  
Author(s):  
S. Bouhlassa ◽  
B. Ammary ◽  
A. Elyahyaoui
Keyword(s):  
Residence Time ◽  
Subsurface Water ◽  
Residence Times ◽  
Transport Modelling ◽  
Lumped Parameter ◽  
The Mean ◽  
Mean Residence Times ◽  
Environmental Tritium ◽  
Future Work

The paper presents a case study for the application of environmental tritium to assess the mean residence time of water in the Tafilalet aquifer. This aquifer corresponds geologically to a tectonic depression with Quaternary fill. The Tafilalet area depends mainly on agriculture and herding. Groundwater is the main source of water supply for domestic, agriculture, and herding purposes.The data on the distribution of tritium in subsurface water indicate the modern water of the Tafilalet aquifer. The tritium transport modelling indicates that Quaternary alluvial waters are likely to have short mean residence times of a few years (14 to 32 years). The study addresses several difficulties concerning the detailed quantitative interpretations of the results, which must be the focus of future work.

Symbolic Equation for the Instantaneous Amount of Substance in Linear Compartmental Systems

2011 ◽  
pp. 348-379
Author(s):  
J.M. Villalba ◽  
R. Varón ◽  
E. Arribas ◽  
R. Diaz-Sierra ◽  
F. Garcia-Sevilla ◽  
...  
Keyword(s):  
Time Course ◽  
Open Systems ◽  
Residence Times ◽  
Transient Phase ◽  
State Equations ◽  
Amount Of Substance ◽  
The Mean ◽  
Symbolic Equation ◽  
Mean Residence Times ◽  
User Friendly

The symbolic time course equations corresponding to a general model of a linear compartmental system, closed or open, with or without traps and with zero input are presented in this chapter. From here, the steady state equations are obtained easily from the transient phase equations by setting the time towards infinite. Special attention is given to the open systems, for which an exhaustive kinetic analysis has been developed to obtain important properties. Besides, the results are particularized to open systems without traps. The software COEFICOM, easy to use and with a user-friendly format of the input of data and the output of results, allows the user to obtain the symbolic expressions of the coefficients involved in the general symbolic equation and all the information necessary to derive the symbolic time course equations for closed or open systems as well as for the derivation of the mean residence times.

scholarly journals Compartment models for estimating attributes of digesta flow in cattle

1988 ◽  
Vol 60 (3) ◽  
pp. 571-595 ◽  
Author(s):  
K. R. Pond ◽  
W. C. Ellis ◽  
J. H. Matis ◽  
H. M. Ferreiro ◽  
J. D. Sutton
Keyword(s):  
Residence Time ◽  
Mean Residence Time ◽  
Residence Times ◽  
Age Dependency ◽  
Faecal Excretion ◽  
Compartment Models ◽  
Equal Rate ◽  
Age Dependent ◽  
The Mean ◽  
Age Independent

1. The basic assumptions involved in one- and two-compartment models with age-independent distributed residence times (exponential, G1) for describing digesta flow are reviewed as the bases for describing families of one- and two-compartment models which assume age-dependent distributions (Gn) of residence times.2. The two-compartment, age-independent model with exponentially distributed residence times (GIGI) yielded estimates of essentially equal rate parameters when fitted to faecal values for all four cows receiving a diet of 500 g coarsely chopped, sodium hydroxide-treated straw /kg and one of four cows receiving the same diet but with ground and pelleted straw. The incorporation of progressively higher orders of age dependency (G2-G6, Gn) into the faster turnover compartment of two-compartment models (GnG1) resulted in a resolution of equal rate parameters estimated by the G1G1 model and a reduction in standard errors for the rate and the initial concentration parameters.3. The occurrence of equal rate parameters in two-compartment models indicated an age-dependent process; a process which could equally well be described by a one-compartment, age-dependent compartment having an order of age dependency equal to the sum of these orders in the two-compartment model with equal rate parameters.4. The age-independent models overestimated time of first appearance in the faeces of a meal's particles. The association of age dependency with the faster turnover compartment resulted in earlier estimates for first appearance of the marked particles; estimates which were more consistent with observed first appearance.5. The faecal excretion pattern from cows fed on the ground and pelleted straw diet exhibited an age-independent distribution of longer residence times which dominated approximately 80% of the later residence times. Age-dependent, one-compartment models gave a poor fit to such data from these cows fed on ground and pelleted straw. In contrast, age-dependent, one-compartment models provided an excellent fit to data from cows fed on chopped straw; data which indicated that age-independent distributions of residence times were much delayed in appearing or were totally absent.6. The mean residence time for the slower turnover, age-independent compartment estimated from faecal excretional of stained particles from either diet was similar to that estimated from duodenal concentrations of the stained particles. This suggests that the slower turnover model compartment was confined to preduodenal sites.7. The mean residence time for the faster turnover, age-dependent compartment estimated from duodenal data was 58–62 % that estimated from faecal data and suggests that the site of this model compartment was both pre- and post-duodenal.8. It is emphasized that the slow and imperfect mixing of particulate matter that occurs in reticulo-rumen digesta is inconsistent with the assumptions of instantaneous and homogeneous mixing made by models having age-independent distributions of residence times. The use of age-dependent distributed residence times can accommodate such imperfect mixing and is consistent with the existence of age-discriminating processes involved in particle flow from the reticulo-rumen. Age dependency also offers improved precision in estimating parameters of digesta flow via processes having inherent uncertainty in their mixing and age-discriminating mechanisms.

Contribution of tissue lipid to long xenon residence times in muscle

1993 ◽  
Vol 74 (5) ◽  
pp. 2127-2134 ◽  
Author(s):  
J. A. Novotny ◽  
E. C. Parker ◽  
S. S. Survanshi ◽  
G. W. Albin ◽  
L. D. Homer
Keyword(s):  
Gas Exchange ◽  
Residence Time ◽  
Compartment Model ◽  
Canine Model ◽  
Inert Gas ◽  
Relative Dispersion ◽  
Residence Times ◽  
Single Compartment ◽  
Single Compartment Model ◽  
The Mean

Experiments demonstrate that the mean residence time of an inert gas in tissue is longer than that predicted by a single-compartment model of gas exchange. Also the relative dispersion (RD, the standard deviation of residence times divided by the mean) is 1 according to this model, but RDs in real tissues are closer to 2, suggesting that a multiple-compartment model might be more accurate. The residence time of a gas is proportional to its solubility in the tissue. Although the noble gases in particular are 10 times more soluble in lipid than in nonlipid tissues, models of gas exchange generally do not incorporate measurements of the lipid in tissue, which may lead to error in the predicted gas residence times. Could a multiple-compartment model that accounts for the lipid in tissue more accurately predict the mean and RD of gas residence times? In this study, we determined the mean and RD of Xe residence times in intact and surgically isolated muscles in a canine model. We then determined the lipid content and the perfusion heterogeneity in each tissue, and we used these measurements with a multiple-compartment model of gas exchange to predict the longest physiologically plausible Xe residence times. Even so, we found the observed Xe mean residence times to be twice as long as those predicted by the model. However, the predicted RDs were considerably larger than the observed RDs. We conclude that lipid alone cannot account for the residence times of Xe in tissue and that a multiple-compartment model is not an accurate representation of inert gas exchange in tissue.

scholarly journals The passage of protozoa from the reticulo-rumen through the omasum of sheep

1986 ◽  
Vol 56 (3) ◽  
pp. 625-634 ◽  
Author(s):  
T. Michalowski ◽  
J. Harmeyer ◽  
G. Breves
Keyword(s):  
Dilution Rate ◽  
Residence Time ◽  
Salt Solution ◽  
Rumen Fluid ◽  
Mineral Salt ◽  
Individual Species ◽  
Residence Times ◽  
Before And After ◽  
Normal Feeding ◽  
The Mean

1. Protozoa in rumen contents and omasal effluent of growing wethers were counted. The wethers were equipped with rumen and abomasal cannulas, and omasal sleeves attached to the omasal-abomasal orifice. Rumen fluid dilution rates were elevated by continuous infusions of hypertonic mineral solutions (34 litres/d) for 24 d. Rumen contents and omasal effluent were sampled between 9 and 21 h during the last 10 d of each experiment.2. Protozoa1 concentrations in omasal effluent were only 0.24.3 those found in the rumen under normal conditions. The ratio of protozoal concentrations in rumen: those in omasal effluent was for small Diplodinium spp. 4.6 (SD 0.9), forOphryoscolexspp. 4.3 (SD 1.0), forDasytricha ruminantium4.0 (SD 0.5), forIsotrichaspp. 3.8 (SD 0.8), forEntodiniumspp. 3.6 (SD 0.9) and forPolyplastron multivesiculatum2.6 (SD 0.5).3. Elevation of rumen fluid dilution rate by 20 and 55% respectively, increased protozoal concentrations in omasal effluents from 22 to 33% and from 31 to 47% those in rumen contents. The apparent residence times of protozoa in the rumen were decreased 50% by the infusion of a mineral-salt solution. The increase in rumen fluid dilution rate had no significant effect on concentrations of protozoa in the rumen or on the differences of the apparent residence times between different species. The apparent residence time of holotrichs remained the same before and after infusion of the mineral-salt solution.4. Apparent residence times of individual species of protozoa in the rumen were, under normal feeding conditions, 2.55 d, and were four to six times longer than the mean residence time of CrEDTA in the rumen.

scholarly journals Pharmacokinetics and tissue residue of toltrazuril in broiler chickens

2015 ◽  
Vol 4 (3) ◽  
pp. 310 ◽  
Author(s):  
Ahmed Soliman
Keyword(s):  
Broiler Chickens ◽  
Animal Health ◽  
Tissue Level ◽  
Residence Times ◽  
Once Daily ◽  
Tissue Residue ◽  
Elimination Half ◽  
The Mean ◽  
Mean Residence Times ◽  
Broiler Feed

<p>The pharmacokinetics and tissue residue of toltrazuril (Baycox<sup>®</sup>, Bayer Animal Health) were investigated in broiler chickens after repeated oral administrations of 7 mg/kg b.wt once daily for two consecutive days. Chickens were subjected to clinical diagnosis to ensure that each one is free from any Eimeria was received a standard broiler feed free from any medications. The results revealed that following repeated oral administration; toltrazuril peaked in blood with [C<sub>max</sub>] of 6.56 and 6.70 μg/ml at [T<sub>max</sub>] of 2.56 and 2.52 hours and the elimination half-life [t<sub>1/2β</sub>] of 14.92 and 16.19 hours and the mean residence times (MRT) were 21.33 and 23.14 hours after first and second doses, respectively. The tissue level concentrations were highest in the kidney and decreased in the following order: liver &gt; lung &gt; heart &gt; muscle &gt; skin and fat. No toltrazuril residues were detected in tissues and plasma after 8 days.</p>

Overloading and removal of N-glycosylation targets on human acetylcholinesterase: effects on glycan composition and circulatory residence time

2002 ◽  
Vol 363 (3) ◽  
pp. 619-631 ◽  
Author(s):  
Theodor CHITLARU ◽  
Chanoch KRONMAN ◽  
Baruch VELAN ◽  
Avigdor SHAFFERMAN
Keyword(s):  
Structural Analysis ◽  
Cell Line ◽  
Residence Time ◽  
Residence Times ◽  
Post Translational Modifications ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
293 Cells ◽  
Mean Residence Times ◽  
Enzyme Species

Optimization of post-translational modifications was shown to affect the ability of recombinant human acetylcholinesterase (rHuAChE) produced in HEK-293 cells to be retained in the circulation for prolonged periods of time [Kronman, Velan, Marcus, Ordentlich, Reuveny and Shafferman (1995) Biochem. J. 311, 959–967; Chitlaru, Kronman, Zeevi, Kam, Harel, Ordentlich, Velan and Shafferman (1998) Biochem. J. 336, 647–658; Chitlaru, Kronman, Velan and Shafferman (2001) Biochem. J. 354, 613–625]. To evaluate the possible contribution of the number of appended N-glycans in determining the pharmacokinetic behaviour of AChE, a series of sixteen recombinant human AChE glycoforms, differing in their number of appended N-glycans (2, 3, 4 or 5 glycans), state of assembly (dimeric or tetrameric) and terminal glycan sialylation (partially or fully sialylated) were generated. Extensive structural analysis of N-glycans demonstrated that the various glycan types associated with all the different rHuAChE glycoforms are essentially similar both in structure and abundance, and that production of the various glycoforms in the sialyltransferase-overexpressing 293ST-2D6 cell line resulted in the generation of enzyme species that carry glycans sialylated to the same extent. Pharmacokinetic profiling of the rHuAChE glycoforms in their fully tetramerized and sialylated state clearly demonstrated that circulatory longevity correlated directly with the number of attached N-glycans (mean residence times for rHuAChE glycoforms harbouring 2, 3, and 4 glycans = 200, 740, and 1055min respectively). This study provides evidence that glycan loading, together with N-glycan terminal processing and enzyme subunit oligomerization, operate in a hierarchical and concerted manner in determining the pharmacokinetic characteristics of AChE.

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