Home About us Contact
|
Home About us Contact | ||
|
|
||
Min Duration (min + duration)
Selected AbstractsEffects of spatially structured vegetation patterns on hillslope erosion in a semiarid Mediterranean environment: a simulation studyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005Matthias Boer Abstract A general trend of decreasing soil loss rates with increasing vegetation cover fraction is widely accepted. Field observations and experimental work, however, show that the form of the cover-erosion function can vary considerably, in particular for low cover conditions that prevail on arid and semiarid hillslopes. In this paper the structured spatial distribution of the vegetation cover and associated soil attributes is proposed as one of the possible causes of variation in cover,erosion relationships, in particular in dryland environments where patchy vegetation covers are common. A simulation approach was used to test the hypothesis that hillslope discharge and soil loss could be affected by variation in the spatial correlation structure of coupled vegetation cover and soil patterns alone. The Limburg Soil Erosion Model (LISEM) was parameterized and verified for a small catchment with discontinuous vegetation cover at Rambla Honda, SE Spain. Using the same parameter sets LISEM was subsequently used to simulate water and sediment fluxes on 1 ha hypothetical hillslopes with simulated spatial distributions of vegetation and soil parameters. Storms of constant rainfall intensity in the range of 30,70 mm h,1 and 10,30 min duration were applied. To quantify the effect of the spatial correlation structure of the vegetation and soil patterns, predicted discharge and soil loss rates from hillslopes with spatially structured distributions of vegetation and soil parameters were compared with those from hillslopes with spatially uniform distributions. The results showed that the spatial organization of bare and vegetated surfaces alone can have a substantial impact on predicted storm discharge and erosion. In general, water and sediment yields from hillslopes with spatially structured distributions of vegetation and soil parameters were greater than from identical hillslopes with spatially uniform distributions. Within a storm the effect of spatially structured vegetation and soil patterns was observed to be highly dynamic, and to depend on rainfall intensity and slope gradient. Copyright © 2005 John Wiley & Sons, Ltd. [source] Changes in direct current (DC) potentials and infra-slow EEG oscillations at the onset of the luteinizing hormone (LH) pulseEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2000Lisa Marshall Abstract An essential function of the neuroendocrine system lies in the coordination of hypothalamo-pituitary secretory activity with neocortical neuronal activity. Cortical direct current (DC) potential shifts and EEG were monitored in conjunction with the circulating concentration of luteinizing hormone (LH) in humans while asleep to assess a hypothalamic,neocortical interaction. The onset of an LH pulse was accompanied (i) at frontocortical locations by a transient positive DC potential shift of ,,3 min duration and peak amplitude 50 ,V; (ii) at frontal and central locations by an increase in power of infra-slow EEG oscillations for periodicities between 64 and 320 s. Results uniquely demonstrate a coupling of hypothalamo-pituitary activity with regulation of neocortical excitability. [source] Mechanosensitive hyaluronan secretion: stimulus,response curves and role of transcription,translation,translocation in rabbit jointsEXPERIMENTAL PHYSIOLOGY, Issue 3 2009A. K. T. Wann Joint movement was recently shown to stimulate the secretion of the lubricant hyaluronan (HA); also, exercise therapy and intra-articular hyaluronan injections are used to treat moderate osteoarthritis. The present study quantifies the stimulus,response curves for HA secretion in vivo and reports a role of transcription,translation,translocation in the secretory response. After washing out endogenous HA from anaesthetized, cannulated rabbit knees, the joints were cycled passively at various frequencies and durations, with or without intra-articular inhibitors of protein synthesis and Golgi processing. Newly secreted HA was harvested for analysis after 5 h. Joints displayed graded, non-linear stimulus,response curves to both duration and frequency of movement; 1 min duration per 15 min or a frequency of 0.17 Hz raised HA secretion by 42,54%, while rapid (1.5 Hz) or prolonged cycling (9 min per 15 min) raised it by 110,130%. Movement-stimulated secretion and phorbol ester-stimulated secretion were partly inhibited by the translation inhibitor cycloheximide, by the transcription,translation inhibitors actinomycin D and puromycin and by the Golgi translocation inhibitor brefeldin A. There is thus a graded coupling between HA secretion and cyclic joint movement that depends partly on new protein synthesis. This is likely to be important for joint homeostasis, providing protection during repetitive cycling and potentially contributing to exercise therapy for osteoarthritis. [source] Effects of Ischaemia on Subsequent Exercise-Induced Oxygen Uptake Kinetics in Healthy Adult HumansEXPERIMENTAL PHYSIOLOGY, Issue 2 2002Michael L. Walsh Leg muscles were occluded (33 kPa) prior to exercise to determine whether the induced metabolic changes, and reactive hyperaemia upon occlusion release just prior to the exercise, would accelerate the subsequent oxygen consumption (V,O2) response. Eight subjects performed double bouts (6 min duration, 6 min rest in-between) of square wave leg cycle ergometry both below and above their lactate threshold (LT). Prior to exercise, large blood pressure cuffs were put around the upper thighs. Occlusion durations were 0 min (control), 5 min and 10 min. Ischaemia was terminated within 5 s prior to exercise onset. Heart rate, V,O2, ventilatory rate (V,E), electromyogram (EMG) and haemoglobin/myoglobin (Hb/Mb) saturation were recorded continuously. Single exponential modelling demonstrated that, compared to control (time constant = 53.9 ± 13.9 s), ischaemia quickened the V,O2 response (P < 0.05) for the first bout of exercise above LT (time constant = 48.3 ± 14.5 s) but not to any other exercise bout below or above LT. The 3-6 min integrated EMG (iEMG) slope was correlated to the 3-6 min V,O2 slope (r = 0.73). Hb/Mb saturation verified the ischaemia but did not show a consistent relation to the V,O2 time course. Reactive hyperaemia induced a faster V,O2 response for work rates above LT. The effect, while significant, was not large considering the expected favourable metabolic and circulatory changes induced by ischaemia. [source] Selective Long-Term Electrical Stimulation of Fast Glycolytic Fibres Increases Capillary Supply but not Oxidative Enzyme Activity in Rat Skeletal MusclesEXPERIMENTAL PHYSIOLOGY, Issue 5 2000S. Egginton Glycolytic fibres in rat extensor digitorum longus (EDL) and tibialis anterior (TA) were selectively activated, as demonstrated by glycogen depletion, by indirect electrical stimulation via electrodes implanted in the vicinity of the peroneal nerve using high frequency (40 Hz) trains (250 ms at 1 Hz) and low voltage (threshold of palpable contractions). This regime was applied 10 times per day, each bout being of 15 min duration with 60 min recovery, for 2 weeks. Cryostat sections of muscles were stained for alkaline phosphatase to depict capillaries, succinate dehydrogenase (SDH) to demonstrate oxidative fibres, and periodic acid-Schiff reagent (PAS) to verify glycogen depletion. Specific activity of hexokinase (HK), 6-phosphofructokinase, pyruvate kinase, glycogen phosphorylase and cytochrome c oxidase (COX) were estimated separately in homogenates of the EDL and the predominantly glycolytic cortex and oxidative core of the TA. Stimulation increased the activity of HK but not that of oxidative enzymes in fast muscles. Comparison of changes in oxidative capacity and capillary supply showed a dissociation in the predominantly glycolytic TA cortex. Here, COX was 3.9 ± 0.68 ,M min-1 (g wet wt)-1 in stimulated muscles compared with 3.7 ± 0.52 ,M min-1 (g wet wt)-1 in contralateral muscles (difference not significant), while the percentage of oxidative fibres (those positively stained for SDH) was also similar in stimulated (14.0 ± 2.8%) and contralateral (12.2 ± 1.9%) muscles. In contrast, the capillary to fibre ratio was significantly increased (2.01 ± 0.12 vs. 1.55 ± 0.04, P < 0.01). We conclude that capillary supply can be increased independently of oxidative capacity, possibly due to haemodynamic factors, and serves metabolite removal to a greater extent than substrate delivery. [source] Water temperature sampling by foraging Brünnich's Guillemots with bird-borne data loggersJOURNAL OF AVIAN BIOLOGY, Issue 2 2001Yutaka Watanuki (correspondence) We describe the features of waters where seabirds were feeding by sampling vertical water temperature profiles with data loggers mounted on five Brünnich's Guillemots in Svalbard, Norway. The guillemots foraged in a cold water (,0.5,0.5°C SST (sea surface temperature)) by making 1.8 dive bouts in short trips (32,257 min duration) as well as in moderate (0.5,2.0°C SST) and warm waters (2.5,4.0°C SST) by making 6.0 dive bouts during long trips (411,688 min duration). Judging from outbound flying time (15.7,24.4 min), time between dive bouts (23.9,43.3 min) and water types, the birds probably fed in fjord or coastal waters during short trips and in both coastal and offshore waters during long trips. Water temperature and diving behaviour can be simultaneously recorded by small data loggers, which therefore will provide useful information on marine features and foraging activity of top predators. [source] POLYPHENOLOXIDASE ACTIVITY OF MINIMALLY PROCESSED ,JONAGORED' APPLES (MALUS DOMESTICA)JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2005A.M.C.N. ROCHA ABSTRACT The influence of three chemical dips using ascorbic acid (AA), citric acid (CA) and calcium chloride (CC) on the polyphenoloxidase (PPO) activity and on the total phenolic content of minimally processed (MP) apple (Malus domestica, cv. Jonagored) during cold storage was evaluated and a potential relationship with enzymatic browning was investigated. An ascorbic acid dip (42.6 mM) of 5 min duration was the most efficient chemical treatment in reducing the PPO activity of apple cubes. A 92% inhibition was achieved after 7 days of storage at 4C. All treatments were advantageous in comparison to the control in reducing color changes. Color changes, determined by absorbance at 420 nm (soluble pigments) and lightness (L) (insoluble pigments) of apple cubes treated with ascorbic acid were correlated with total phenolic content. No correlation was observed between PPO activity and tristimulus color parameters, browning index or total phenolic content of AA-treated apple cubes. [source] A small dose of droperidol decreases postoperative nausea and vomiting in adults but cannot improve an already excellent patient satisfactionACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 4 2001A. Hechler Background: We evaluated whether or not 1) a routine prophylaxis with 20 ,g ,· ,kg,1 body weight of droperidol would efficiently prevent postoperative nausea and vomiting (PONV) after elective surgery in adults and 2) an efficient prophylaxis would improve patient satisfaction. Methods: With approval of the local ethics committe and after having obtained informed written consent, 1334 patients in a randomised, single-blinded fashion either received droperidol (group 1, n=665) or saline intravenously (group 2, n=669) 20 min before the end of a standard O2/N2O/fentanyl/isoflurane anaesthesia of at least 30 min duration. End points: incidence of PONV during the first 24 h; individual episodes of nausea or vomiting, overall patient satisfaction with the procedure. Results: Compared to saline, intravenous injection of droperidol substantially and significantly reduced the incidence of PONV from 30% to 20% (P<0.0001). Women suffered three times more frequently from PONV (10.5% vs. 30%, P<0.0001). Droperidol significantly reduced the incidence of PONV from 35.4% to 24.4% in women (relative risk reduction: 31%, P=0.0002), but not in men (13.1% vs. 8.2%, relative risk reduction: 37%, P=0.159) , without impact on overall patient satisfaction (98.8% vs. 97.1%, P=0.439). Distribution of surgical procedures, sex, age, height, weight and anaesthetic duration were not different between groups. To prevent one woman from suffering PONV, nine had to be treated prophylactically at an individual drug cost (German prices) of about 0.80 per woman. Conclusion: Routine PONV prophylaxis with 20 ,g ,· ,kg,1 body weight of droperidol is cost-efficient and appropriate in women but not in men. [source] Influence of maternal carbohydrate intake on fetal movements at 14 to 16 weeks of gestationPRENATAL DIAGNOSIS, Issue 2 2003Israel Goldstein Abstract Objective Ultrasonographic assessment of fetal movements at 14 to 16 weeks of gestation before and after maternal oral intake of carbohydrate. Design Thirty consecutive healthy pregnant women between 14 and 16 weeks of gestation were scanned transvaginally. Real-time ultrasound recordings of 20 min duration were performed in the fasting state and after an oral intake of 110 g of glucose. The number of fetal movements, body and limb movements and breathing movements were evaluated. Fetal movements were quantified using a digital chronometer, and the percentage of time spent moving and the rate of movements per minute were then calculated. Data was statistically analyzed using the simple and Wilcoxon paired t -test. Results Absolute number of fetal movements, body movements, rotation movements, time spent moving and rate of movements per minute showed a statistically significant increase after maternal intake of carbohydrate (p < 0.0001). Conclusions Maternal oral intake of 110 g of carbohydrate significantly increases fetal movements at 14 to 16 weeks of gestation, thus allowing better ultrasonographic viewing of the fetus. Copyright © 2003 John Wiley & Sons, Ltd. [source] Motor unit recruitment and derecruitment induced by brief increase in contraction amplitude of the human trapezius muscleTHE JOURNAL OF PHYSIOLOGY, Issue 2 2003C. Westad The activity pattern of low-threshold human trapezius motor units was examined in response to brief, voluntary increases in contraction amplitude (,EMG pulse') superimposed on a constant contraction at 4,7% of the surface electromyographic (EMG) response at maximal voluntary contraction (4,7% EMGmax). EMG pulses at 15,20% EMGmax were superimposed every minute on contractions of 5, 10, or 30 min duration. A quadrifilar fine-wire electrode recorded single motor unit activity and a surface electrode recorded simultaneously the surface EMG signal. Low-threshold motor units recruited at the start of the contraction were observed to stop firing while motor units of higher recruitment threshold stayed active. Derecruitment of a motor unit coincided with the end of an EMG pulse. The lowest-threshold motor units showed only brief silent periods. Some motor units with recruitment threshold up to 5% EMGmax higher than the constant contraction level were recruited during an EMG pulse and kept firing throughout the contraction. Following an EMG pulse, there was a marked reduction in motor unit firing rates upon return of the surface EMG signal to the constant contraction level, outlasting the EMG pulse by 4 s on average. The reduction in firing rates may serve as a trigger to induce derecruitment. We speculate that the silent periods following derecruitment may be due to deactivation of non-inactivating inward current (,plateau potentials'). The firing behaviour of trapezius motor units in these experiments may thus illustrate a mechanism and a control strategy to reduce fatigue of motor units with sustained activity patterns. [source] PEELING AND THE PHYSICAL AND CHEMICAL PROPERTIES OF KIWI FRUITJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 4 2003METIN GULDAS Hand peeling of kiwi fruit has some disadvantages such as difficulty during peeling, increase of loss in weight and nutritional value. Peeling of kiwi fruits with alkali (NaOH) was investigated. Some chemical (acidity, pectin, and chlorophyll) and physical properties (Hunter color value and weight loss) of the fruits were determined after selected alkali peeling methods were used. Peeling methods at 80, 90 or 100C temperatures; in 13, 18 or 23% of NaOH solutions and for 3, 4 or 5 min durations were tested and compared with hand peeling. Weight (fruit tissue) loss in hand peeling was higher than alkali peeling. Peeling with alkali was easier. Nutritional value (ascorbic acid content) of alkali peeled fruits was higher than hand peeled kiwi fruit. Because of less weight loss, better green color and high pectin content the method including 15% of NaOH solution at 95C for 4 min was selected as most advantageous peeling method. [source] | ||||||||||