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Continuous Period (continuous + period)

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Medical Sciences	50%

Selected Abstracts

Modelling the hydrology of a catchment using a distributed and a semi-distributed model

HYDROLOGICAL PROCESSES, Issue 3 2005
Ahmed Abu El-Nasr
Abstract Various hydrological models exist that describe the phases in the hydrologic cycle either in an empirical, semi-mechanistic or fully mechanistic way. The way and level of detail for the different processes of the hydrologic cycle that needs to be described depends on the objective, the application and the availability of data. In this study the performance of two different models, the fully distributed MIKE SHE model and the semi-distributed SWAT model, was assessed. The aim of the comparative study was to examine if both models are equally able to describe the different phases in the hydrologic cycle of a catchment, given the availability of hydrologic data in the catchment. For the comparison, historic data of the Jeker river basin, situated in the loamy belt region of Belgium, was used. The size of the catchment is 465 km2. The landscape is rolling, the dominant land use is farmland, and the soils vary from sandy-loam to clay-loam. The daily data of a continuous period of 6 years were used for the calibration and validation of both models. The results were obtained by comparing the performance of the two models using a qualitative (graphical) and quantitative (statistical) assessment, such as graphical representation of the observed and simulated river discharge, performance indices, the hydrograph maxima, the baseflow minima, the total accumulated volumes and the extreme value distribution of river flow data. The analysis revealed that both models are able to simulate the hydrology of the catchment in an acceptable way. The calibration results of the two tested models, although they differ in concept and spatial distribution, are quite similar. However, the MIKE SHE model predicts slightly better the overall variation of the river flow. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Temporal fluctuations in heat waves at Prague,Klementinum, the Czech Republic, from 1901,97, and their relationships to atmospheric circulation

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2002
Jan Kyselý
Abstract Temporal fluctuations in heat wave occurrence and severity are analysed in long-term daily temperature series at Prague,Klementinum, the Czech Republic. Although the observations have been continuous since 1775, the period 1901,97 with the most credible data is mainly examined. Most of the warmest summers of the 20th century appeared within the periods 1943,52 and 1992,95; the temporal distribution of heat waves corresponds to this pattern and shows two maxima, in the 1940s to early 1950s and in the 1990s. A very low occurrence of heat waves was typical of the beginning of the 20th century and around 1980. The peak of heat wave severity in the 1940s,early 1950s, as well as their almost total absence in the first two decades of the 20th century, may be a common feature for a large area, as indicated by the comparison between two stations within central Europe, Prague,Klementinum and Basel (Switzerland), and by other studies. An extraordinary heat wave occurred in July and August 1994. It greatly exceeded other heat waves, mainly in the much higher cumulative temperature excess above 30°C and a record-breaking duration of a continuous period of tropical days. Relationships between heat wave characteristics in warm and cold decades and circulation conditions were analysed using the subjective Hess,Brezowsky catalogue of weather types (Grosswetterlagen). The link to the atmospheric circulation is evident, e.g. situations with an anticyclone or a ridge over central Europe were more (less) frequent during all the warm (cold) decades. Moreover, the occurrence of long and severe heat waves in the 1990s may reflect an enhanced persistence of the atmospheric circulation over Europe in the summer season because all groups of weather types have considerably increased residence times in 1988,97 compared with long-term means. Copyright © 2002 Royal Meteorological Society [source]

Urinary fluoride excretion in children drinking fluoridated school milk

INTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 4 2000
C.E. Ketley
Summary.Objective. To determine fluoride excretion under various conditions of fluoride intake and to estimate the fractional urinary excretion of fluoride in individual children participating in a school milk fluoridation scheme. Design. In the first part of the study, individual urine samples were collected from each of eight 4 to 5-year-old children for a continuous period of 55 h. For each child (n = 8) and for each day (n = 3) the maximum urinary fluoride concentration (p.p.m.F), the maximum fluoride excretion rate (,gF/h) and the total daily fluoride excretion (mg) were calculated. The second part of the study was carried out to determine the 24 h fractional percentage of fluoride excreted following administration of a known dose of fluoride in the absence of other sources. Results. Under usual conditions of fluoride intake (i.e. milk containing 0·5 mg fluoride, customary diet and toothbrushing with fluoride toothpaste) the children's daily fluoride excretion was 0·33 mg. The fractional urinary fluoride excretion of a 0·5-mg fluoride tablet was 30%. Conclusions. It is concluded that the children's mean 24 h fluoride excretion was somewhere between that reported in low fluoride conditions and that reported in optimally fluoridated areas. The fractional urinary fluoride excretion was found to be in agreement with the findings of other workers. [source]

Hypothermic insult to the periodontium: a model for the study of aseptic tooth resorption

DENTAL TRAUMATOLOGY, Issue 1 2000
C. W. Dreyer
Abstract , The aim of the current investigation was to define an animal model for the study of hard tissue resorption by examining the responses of the periodontal ligament (PDL) to both single and multiple episodes of hypothermic injury to the crowns of rat teeth. A group of 12 male rats weighing 200,250 g were anesthetized, and pellets of dry ice (CO2) were applied once to the crowns of the right first maxillary molars for continuous periods of 10 or 20 min. Animals were sacrificed at 2, 7, 14 and 28 days and tissues were processed for routine histological examination. A second group of eight animals and a third group of 12 animals were subjected to three applications of dry ice over a period of 1 week and sacrificed at 2 and 14 days respectively after the final application. In addition to thermal insult, the periodontium of teeth from a fourth group of six rats was subjected to mechanical trauma. Examination of the sections from the group undergoing a single freezing episode revealed that, by 1 week, shallow resorption lacunae had appeared on the root surface. These became more extensive after 14 days. At the same time hyaline degeneration was evident in the PDL. Within this group, teeth subjected to the longer 20-min application times generally showed more extensive injuries. By 28 days, evidence of repair was observed with reparative cementum beginning to line the resorption lacunae in the root dentin. Sections from animals subjected to multiple episodes of thermal trauma and those subjected to additional mechanical insult showed more extensive external root resorption than those from single-injury animals. It was concluded that low temperature stimuli applied to the crowns of rat molars were capable of eliciting a sterile degenerative response in the PDL which, in turn, resulted in external root resorption. Furthermore, the degree of this tissue injury was commensurate with the duration and number of exposures to the trauma. The results also indicated that progression of the resorptive process required periodic exposure to the injury, in the absence of which repair to the damaged root occurred. [source]