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Cycling
Kinds of Cycling Terms modified by Cycling Selected AbstractsMEIOTIC DRIVE AND SEX CHROMOSOME CYCLINGEVOLUTION, Issue 5 2004David W. Hall Abstract , Sex-linked meiotic drive is found in a broad variety of taxa, including insects, birds, and mammals. In populations of some species, we see four types of sex chromosomes segregating: normal and driving X chromosomes and susceptible and resistant Y chromosomes. A theoretical analysis shows that a stable four-chromosome equilibria is a more common outcome in these systems than previously recognized. Cycling of sex chromosome frequencies and associated changes in the sex ratio are other predicted outcomes. The absence of cycling in nature may be due to migration among populations. [source] Redox Cycling of Ni-Based Solid Oxide Fuel Cell Anodes: A ReviewFUEL CELLS, Issue 3 2007D. Sarantaridis Abstract The published literature relating to damage to SOFCs caused by redox cycling of Ni-based anodes is reviewed. The review covers the kinetics of Ni oxidation and NiO reduction (as single phases and as constituents of composites with yttria-stabilised zirconia, YSZ), the dimensional changes associated with redox cycling and the effect of this on the mechanical integrity and electrical performance of cells and stacks. A critical parameter is the expansion strain that is caused by oxidation. Several studies report that the first complete oxidation of a Ni/YSZ composite causes a linear expansion of the order of 1%, but the actual values vary substantially between different investigations. The oxidation strain is the result of microstructural irreversibility during the redox process and leads to strain accumulation over several redox cycles. This can cause mechanical disruption to an anode, anode support or other cell components attached to the anode. A simplified mechanical model of the stress and damage that are likely to be caused by anode expansion is proposed and applied to anode-supported, electrolyte-supported and inert substrate-supported cell configurations. This allows the maximum oxidation strain to avoid damage in each configuration to be estimated. [source] Micro-scale sulphur isotope evidence for sulphur cycling in the late Archean shallow oceanGEOBIOLOGY, Issue 1 2007B. S. KAMBER ABSTRACT We report in situ secondary ion mass spectrometer sulphur isotope data for sedimentary pyrite from the 2.52 Ga Upper Campbellrand Subgroup, Transvaal, South Africa. The analysed sedimentary rocks represent a transition in depositional environment from very shallow to deeper water, with strong sedimentological, facies distribution and geochemical evidence for the presence of a shallow redox chemocline. Data were obtained directly in thin section in order to preserve petrographic context. They reveal a very large extent of isotopic fractionation both in mass-independent (MIF) and in mass-dependent fractionation (MDF) on unprecedentedly small scale. In the shallow-water microbical carbonates, three types of pyrite were identified. The texturally oldest pyrite is found as small, isotopically little fractionated grains in the microbial mats. Large (several mm) spheroidal pyrite concretions, which postdate the mat pyrite, record strong evidence for an origin by bacterial sulphate reduction. Rare pyrite surrounding late fenestral calcite is inferred to have formed from recycled bacterial pyrite on account of the slope of its correlated MIF and MDF array. This latter type of pyrite was also found in an interbedded black shale and a carbonate laminite. In a deeper water chert, pyrite with very heavy sulphur indicates partial to almost complete sulphate reduction across a chemocline whose existence has been inferred independently. The combined picture from all the studied samples is that of a sulphate availability-limited environment, in which sulphur was cycled between reservoirs according to changing redox conditions established across the chemocline. Cycling apparently reduced the extent of recorded sulphur isotope fractionation relative to what is expected from projection in the correlated MIF and MDF arrays. This is consistent with regionally relatively high free oxygen concentrations in the shallow water, permitting locally strong MDF. Our new observations add to the growing evidence for a complex, fluctuating evolution of free atmospheric oxygen between c. 2.7 Ga and 2.3 Ga. [source] Potassium cycling and losses in grassland systems: a reviewGRASS & FORAGE SCIENCE, Issue 3 2005M. Kayser Abstract Cycling of potassium in grassland systems has received relatively little attention in research and practice in recent years. Balanced nutrient systems require consideration of nutrients other than nitrogen (N). Potassium (K) is needed in large amounts and is closely related to N nutrition. In intensive dairy farming, surpluses of K arise from the input of concentrates and fertilizer and are returned to the grassland and may lead to increasing K content in the soil. Organic farming, on the other hand, is characterized by limitations in input of nutrient sources and quantities. Leaching of K from grassland is usually low, but high levels of available soil K, high K input from fertilizer or at urine patches lead to increasing losses. High K inputs have a negative influence on Mg and Ca uptake by plants and can cause accelerated leaching of these cations. High levels of K have been associated with inducing nutrition-related dairy cow health problems such as milk fever (hypocalcaemia) and grass tetany (hypomagnesaemia). This review gives an overview of the cycling of potassium and related cations in grassland systems especially with regard to leaching losses and identifies limitations to knowledge. [source] Reversible Low-Field Magnetoresistance in Sr2Fe2,xMoxO6,, by Oxygen Cycling and the Role of Excess Mo (x,>,1) in Grain-Boundary RegionsADVANCED MATERIALS, Issue 7 2006L. MacManus-Driscoll Oxygen cycling of Sr2Fe2,xMoxO6,, (SFMO) samples allows the resistivity and low-field magnetoresistance (LFMR) to be precisely cycled. TEM shows that the change in resistivity with oxygen is not only a consequence of the change in oxygen stoichiometry of SFMO, but also a concomitant change in the Fe/Mo ratio in SFMO. The figure shows the change in MR and resistivity (values in m,,cm above the data points for samples D1,D7) with increasing post-annealing time. [source] Comparison of Effect of Aerobic Cycle Training and Progressive Resistance Training on Walking Ability After Stroke: A Randomized Sham Exercise,Controlled StudyJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 6 2008Mi-Joung Lee PhD OBJECTIVES: To determine whether changes in strength or cardiorespiratory fitness after exercise training improve walking ability in individuals who have had a stroke. DESIGN: A sham exercise-controlled, randomized two-by-two factorial design, in which the two factors investigated were cycle training (AEROBIC) and resistance training (STRENGTH). SETTING: University exercise laboratory. PARTICIPANTS: Fifty-two individuals with a history of stroke (aged 63±9; time since stroke, 57±54 months). INTERVENTION: Participants undertook 30 exercise sessions over 10 to 12 weeks. Depending on group allocation, individuals underwent aerobic cycling plus sham progressive resistance training (PRT) (n=13), sham cycling plus PRT (n=13), aerobic cycling plus PRT (n=14), or sham cycling plus sham PRT (n=12). MEASUREMENTS: Primary outcomes were 6-minute walk distance, habitual and fast gait velocities, and stair climbing power. Secondary outcomes included measures of cardiorespiratory fitness; muscle strength, power, and endurance; and psychosocial attributes. RESULTS: Neither AEROBIC nor STRENGTH improved walking distance or gait velocity significantly more than sham exercise, although STRENGTH significantly improved participants' stair climbing power by 17% (P=.009), as well as their muscle strength, power, and endurance; cycling peak power output; and self-efficacy. Conversely, AEROBIC improved indicators of cardiorespiratory fitness only. Cycling plus PRT produced larger effects than either single modality for mobility and impairment outcomes. CONCLUSION: Single-modality exercises targeted at existing impairments do not optimally address the functional deficits of walking but do ameliorate the underlying impairments. The underlying cardiovascular and musculoskeletal impairments are significantly modifiable years after stroke with targeted robust exercise. [source] Ni,YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical CharacterizationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Trine Klemensø Nickel (Ni),yttria-stabilized zirconia (YSZ) cermets are a prevalent material used for solid oxide fuel cells. The cermet degrades upon redox cycling. The degradation is related to microstructural changes, but knowledge of the mechanisms has been limited. Direct current conductivity measurements were performed on cermets and cermets where the Ni component was removed. Measurements were carried out before, during, and after redox cycling the cermet. The cermet conductivity degraded over time due to sintering of the nickel phase. Following oxidizing events, the conductivity of the cermets improved, whereas the conductivity of the YSZ phase decreased. An improved model of the redox degradation mechanism was established based on the measurements. [source] The Effect of Using Variable Frequency Trains During Functional Electrical Stimulation CyclingNEUROMODULATION, Issue 3 2008Simona Ferrante PhD ABSTRACT Objectives., This paper describes an experimental investigation of variable frequency stimulation patterns as a means of increasing torque production and, hence, performance in cycling induced by functional electrical stimulation. Materials and Methods., Experiments were conducted on six able-bodied subjects stimulating both quadriceps during isokinetic trials. Constant-frequency trains (CFT) with 50-msec interpulse intervals and four catchlike-inducing trains (CIT) were tested. The CITs had an initial, brief, high-frequency burst of two pulses at the onset of or within a subtetanic low-frequency stimulation train. Each stimulation train consisted of the same number of pulses. The active torques produced by each train were compared. Parametric main effect ANOVA tests were performed on the active torque-time integral (TTI), on the active torque peaks and on the time needed to reach those peaks (T2P). Results., The electrical stimulation of the quadriceps produced active torques with mean peak values in the range of 1.6,3.5 Nm and a standard error below 0.2 Nm. CITs produced a significant increase of TTI and torque peaks compared with CFTs in all the experimental conditions. In particular, during the postfatigue trials, the CITs with the doublet placed in the middle of the train produced TTIs and torque peaks about 61% and 28% larger than the CFT pattern, respectively. In addition, the CITs showed the lowest reduction of the performance between prefatigue and postfatigue conditions. Conclusions., The use of CITs improves the functional electrical stimulation cycling performance compared with CFT stimulation. This application might have a relevant clinical importance for individuals with stroke where the residual sensation is still present and thus the maximization of the performance without an excessive increase of the stimulation intensity is advisable. Therefore, exercise intensity can be increased yielding a better muscle strength and endurance that may be beneficially for later gait training in individuals with stroke. [source] Induction of Persistent Double Strand Breaks Following Multiphoton Irradiation of Cycling and G1 -arrested Mammalian Cells,Replication-induced Double Strand BreaksPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2008Jane V. Harper DNA double strand breaks (DSBs) are amongst the most deleterious lesions induced within the cell following exposure to ionizing radiation. Mammalian cells repair these breaks predominantly via the nonhomologous end joining pathway which is active throughout the cell cycle and is error prone. The alternative pathway for repair of DSBs is homologous recombination (HR) which is error free and active during S- and G2/M-phases of the cell cycle. We have utilized near-infrared laser radiation to induce DNA damage in individual mammalian cells through multiphoton excitation processes to investigate the dynamics of single cell DNA damage processing. We have used immunofluorescent imaging of ,-H2AX (a marker for DSBs) in mammalian cells and investigated the colocalization of this protein with ATM, p53 binding protein 1 and RAD51, an integral protein of the HR DNA repair pathway. We have observed persistent DSBs at later times postlaser irradiation which are indicative of DSBs arising at replication, presumably from UV photoproducts or clustered damage containing single strand breaks. Cell cycle studies have shown that in G1 cells, a significant fraction of multiphoton laser-induced prompt DSBs persists for >4 h in addition to those induced at replication. [source] Ovum Pick-up in Cycling and Lactating Postpartum Swamp Buffaloes (Bubalis bubalis)REPRODUCTION IN DOMESTIC ANIMALS, Issue 2 2005A Promdireg Contents The objective of this study was to evaluate the efficiency of Ovum Pick Up (OPU) in cycling (n = 5) and lactating, postpartum, swamp buffaloes (n = 6) with and without gonadotropin stimulation. The OPU was performed every two weeks in all groups of animals, for a total of six sessions. Thirty collections were performed in five cycling buffaloes and 36 collections in six lactating postpartum buffaloes. Buffaloes that received hormonal stimulation were given a total of 400 mg, follicle stimulating hormone (FSH), administered twice daily over 3 days in decreasing doses, together with 100 ,g of GnRH, 24 h after the last FSH injection. Following a resting period of 1 month, the two groups of buffaloes, were subjected to the same OPU regimen, but without any hormonal treatment for an additional six OPU sessions. The number of aspirated follicles recorded from the hormonal stimulated, cycling animals and lactating, postpartum buffaloes was not significantly different, 7.2 ± 3.7 and 9.0 ± 3.2, respectively (p > 0.05). Recovered oocytes collected from the two groups of hormonally stimulated animals were also not statistically different: 3.7 ± 2.7 in the cycling and 5.9 ± 3.5 in the lactating postpartum group (p > 0.05). In the two groups of buffaloes not receiving hormonal stimulation, the number of aspirated follicles was not significantly different: 2.1 ± 1.4 and 1.4 ± 0.7 in cycling and lactating postpartum buffaloes respectively (p > 0.05). Recovered oocytes in the non-treated groups were also similar: 1.4 ± 1.3 vs 0.7 ± 0.8 in cycling and lactating buffaloes (p > 0.05). Among stimulated buffaloes, most aspirated follicles were small in size (,5 mm), whereas they were mostly medium and large sizes in the non-treated buffaloes. The oocyte recovery rate in both the groups, cycling and lactating postpartum, were 51.6% and 69.5% in stimulated groups and 55.0% and 53.1% in non-stimulated groups (p > 0.05). The majority of recovered oocytes were single- and multi-layered, and the number was greater in the cycling than in the lactating, postpartum buffaloes. The number and quality of recovered oocytes was similar in all groups of buffaloes whether they were received or did not receive hormonal stimulation. Moreover no difference was found in multi- and single-layered oocytes between cycling and lactating, postpartum buffaloes. In conclusion, OPU can be performed successfully in swamp buffalo in different reproductive status and FSH administration was shown to increase the number of aspirated oocytes in both cycling and lactating, postpartum buffaloes. [source] ORIGINAL ARTICLE: Lipopolysaccharide Alters the Vaginal Electrical Resistance in Cycling and Pregnant MiceAMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 2 2009Varkha Agrawal Problem, Lipopolysaccharide (LPS) has been postulated to exert harmful biologic effects during pregnancy. The objective of present investigation is to measure the vaginal electrical resistance (VER) in LPS-treated normal cycling and pregnant female mice. Method of study, Minimum dose (MD) of LPS (250 ,g/kg body weight) was injected in pregnant female mice through i.p. route on day 0.5 of pregnancy. VER was measured during different phases of reproductive cycle in female mice, which were pre-exposed to LPS and in untreated cycling female mice. VER was also measured in control pregnant female mice (saline-treated mice) through whole pregnancy and LPS-treated female mice in early stages of pregnancy. Results, Vaginal electrical resistance was significantly higher during proestrous or early estrous stage as compared with any other stages of reproductive cycle in mouse. One peak of VER was observed during peri-implantation period of pregnancy in control female mice. The significant differences in the pattern of VER were found between LPS-treated and control female mice during peri-implantation period of pregnancy, and between cycling female mice, which were pre-exposed to LPS and untreated cycling female mice during proestrus. Conclusion, The presented results demonstrate, for the first time, that LPS exposure during pregnancy may be determined by measuring VER in mothers without any adverse effect on ongoing pregnancy and may help in refining the assisted reproduction techniques. [source] A Personal User's View of Functional Electrical Stimulation CyclingARTIFICIAL ORGANS, Issue 3 2002Roger Fitzwater Abstract: Two years of functional electrical stimulation cycling (FESC) as a researcher and subject have given me an insight into the direction that future FESC should take as well as providing me with significant health benefits and an enjoyable and functional ability to cycle. If FESC is to benefit spinal cord injured persons (SCIPs), researchers must turn their attention to making the activity convenient and enjoyable. What follows is a personal view and will be less scientifically rigorous than other presentations but hopefully still of value. It calls upon my experience as a general medical practitioner with a special interest in the value of exercise, a human powered vehicle enthusiast, an amateur FES researcher, but most importantly, an SCIP and FES cyclist. [source] Cycling and Thermal Stability of Nanostructured MgH2,Cr2O3 Composite for Hydrogen Storage.CHEMINFORM, Issue 7 2003Z. Dehouche Abstract For Abstract see ChemInform Abstract in Full Text. [source] The theory of cosy NMR experiments revisited: Application to an AX spin system of quadrupolar nucleiCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2010P. Kempgens Abstract The two-dimensional nuclear magnetic resonance correlation spectroscopy (2D NMR COSY) spectrum of an AX spin system of spin-1 has been calculated by numerical density matrix calculations. The mathematical expressions found are valid for an AX spin system of any spins. These expressions should be used to calculate the 2D NMR COSY spectrum of an AX spin system of high spin nuclei as their use will significantly simplify the calculations. More precisely, one needs to calculate only one set of coefficients despite the need of two steps in the phase cycling to achieve phase modulation during t1. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 170,177, 2010. [source] Cardiac basal metabolism: energetic cost of calcium withdrawal in the adult rat heartACTA PHYSIOLOGICA, Issue 3 2010P. Bonazzola Abstract Aim:, Cardiac basal metabolism upon extracellular calcium removal and its relationship with intracellular sodium and calcium homeostasis was evaluated. Methods:, A mechano-calorimetric technique was used that allowed the simultaneous and continuous measurement of both heat rate and resting pressure in arterially perfused quiescent adult rat hearts. Using pharmacological tools, the possible underlying mechanisms related to sodium and calcium movements were investigated. Results:, Resting heat rate (expressed in mW g,1dry wt) increased upon calcium withdrawal (+4.4 ± 0.2). This response was: (1) unaffected by the presence of tetrodotoxin (+4.3 ± 0.6), (2) fully blocked by both, the decrease in extracellular sodium concentration and the increase in extracellular magnesium concentration, (3) partially blocked by the presence of either nifedipine (+2.8 ± 0.4), KB-R7943 (KBR; +2.5 ± 0.2), clonazepam (CLO; +3.1 ± 0.3) or EGTA (+1.9 ± 0.3). The steady heat rate under Ca2+ -free conditions was partially reduced by the addition of Ru360 (,1.1 ± 0.2) but not CLO in the presence of EGTA, KBR or Ru360. Conclusion:, Energy expenditure for resting state maintenance upon calcium withdrawal depends on the intracellular rise in both sodium and calcium. Our data are consistent with a mitochondrial Ca2+ cycling, not detectable under normal calcium diastolic levels. The experimental condition here analysed, partially simulates findings reported under certain pathological situations including heart failure in which mildly increased levels of both diastolic sodium and calcium have also been found. Therefore, under such pathological conditions, hearts should distract chemical energy to fuel processes associated with sodium and calcium handling, making more expensive the maintenance of their functions. [source] Cerebral oxygenation is reduced during hyperthermic exercise in humansACTA PHYSIOLOGICA, Issue 1 2010P. Rasmussen Abstract Aim:, Cerebral mitochondrial oxygen tension (PmitoO2) is elevated during moderate exercise, while it is reduced when exercise becomes strenuous, reflecting an elevated cerebral metabolic rate for oxygen (CMRO2) combined with hyperventilation-induced attenuation of cerebral blood flow (CBF). Heat stress challenges exercise capacity as expressed by increased rating of perceived exertion (RPE). Methods:, This study evaluated the effect of heat stress during exercise on PmitoO2 calculated based on a Kety-Schmidt-determined CBF and the arterial-to-jugular venous oxygen differences in eight males [27 ± 6 years (mean ± SD) and maximal oxygen uptake (VO2max) 63 ± 6 mL kg,1 min,1]. Results:, The CBF, CMRO2 and PmitoO2 remained stable during 1 h of moderate cycling (170 ± 11 W, ,50% of VO2max, RPE 9,12) in normothermia (core temperature of 37.8 ± 0.4 °C). In contrast, when hyperthermia was provoked by dressing the subjects in watertight clothing during exercise (core temperature 39.5 ± 0.2 °C), PmitoO2 declined by 4.8 ± 3.8 mmHg (P < 0.05 compared to normothermia) because CMRO2 increased by 8 ± 7% at the same time as CBF was reduced by 15 ± 13% (P < 0.05). During exercise with heat stress, RPE increased to 19 (19,20; P < 0.05); the RPE correlated inversely with PmitoO2 (r2 = 0.42, P < 0.05). Conclusion:, These data indicate that strenuous exercise in the heat lowers cerebral PmitoO2, and that exercise capacity in this condition may be dependent on maintained cerebral oxygenation. [source] Impact of carbohydrate supplementation during endurance training on glycogen storage and performanceACTA PHYSIOLOGICA, Issue 2 2009L. Nybo Abstract Aim:, Glucose ingestion may improve exercise endurance, but it apparently also influences the transcription rate of several metabolic genes and it alters muscle metabolism during an acute exercise bout. Therefore, we investigated how chronic training responses are affected by glucose ingestion. Methods:, In previously untrained males performance and various muscular adaptations were evaluated before and after 8 weeks of supervised endurance training conducted either with (n = 8; CHO group) or without (n = 7; placebo) glucose supplementation. Results:, The two groups achieved similar improvements in maximal oxygen uptake and peak power output during incremental cycling (both parameters elevated by 17% on average) and both groups lost ,3 kg of fat mass during the 8 weeks of training. An equal reduction in respiratory exchange ratio (0.02 units) during submaximal exercise was observed in both groups. Beta-hydroxyacyl-CoA-dehydrogenase activity was increased in both groups, however, to a larger extent in the placebo group (45 ± 11%) than CHO (23 ± 9%, P < 0.05). GLUT-4 protein expression increased by 74 ± 14% in the placebo group and 45 ± 14% in CHO (both P < 0.05), while resting muscle glycogen increased (P < 0.05) to a larger extent in the placebo group (96 ± 4%) than CHO (33 ± 2%). Conclusion:, These results show that carbohydrate supplementation consumed during exercise training influences various muscular training adaptations, but improvements in cardiorespiratory fitness and reductions in fat mass are not affected. [source] Increased fat oxidation and regulation of metabolic genes with ultraendurance exerciseACTA PHYSIOLOGICA, Issue 1 2007J. W. Helge Abstract Aim:, Regular endurance exercise stimulates muscle metabolic capacity, but effects of very prolonged endurance exercise are largely unknown. This study examined muscle substrate availability and utilization during prolonged endurance exercise, and associated metabolic genes. Methods:, Data were obtained from 11 competitors of a 4- to 5-day, almost continuous ultraendurance race (seven males, four females; age: 36 ± 11 years; cycling o2peak: males 57.4 ± 5.9, females 48.1 ± 4.0 mL kg,1 min,1). Before and after the race muscle biopsies were obtained from vastus lateralis, respiratory gases were sampled during cycling at 25 and 50% peak aerobic power output, venous samples were obtained, and fat mass was estimated by bioimpedance under standardized conditions. Results:, After the race fat mass was decreased by 1.6 ± 0.4 kg (11%; P < 0.01). Respiratory exchange ratio at the 25 and 50% workloads decreased (P < 0.01) from 0.83 ± 0.06 and 0.93 ± 0.03 before, to 0.71 ± 0.01 and 0.85 ± 0.02, respectively, after the race. Plasma fatty acids were 3.5 times higher (from 298 ± 74 to 1407 ± 118 ,mol L,1; P < 0.01). Muscle glycogen content fell 50% (from 554 ± 28 to 270 ± 25 nmol kg,1 d.w.; n = 7, P < 0.01), whereas the decline in muscle triacylglycerol (from 32 ± 5 to 22 ± 3 mmol kg,1 d.w.; P = 0.14) was not statistically significant. After the race, muscle mRNA content of lipoprotein lipase and glycogen synthase increased (P < 0.05) 3.9- and 1.7-fold, respectively, while forkhead homolog in rhabdomyosarcoma, pyruvate dehydrogenase kinase 4 and vascular endothelial growth factor mRNA tended (P < 0.10) to be higher, whereas muscle peroxisome proliferator-activated receptor , co-activator-1, mRNA tended to be lower (P = 0.06). Conclusion:, Very prolonged exercise markedly increases plasma fatty acid availability and fat utilization during exercise. Exercise-induced regulation of genes encoding proteins involved in fatty acid recruitment and oxidation may contribute to these changes. [source] Aporias, Webs, and Passages: Doubt as an Opportunity to LearnCURRICULUM INQUIRY, Issue 2 2000Nicholas C. Burbules This article offers an exploration of the idea, and the experience, of aporia (usually translated as ,doubt') in Plato's dialogue, the Meno, and in other teaching/learning contexts. A metaphor that moves throughout the article is the experience of being lost when exploring the World Wide Web and other weblike or hypertextual environments. The article represents the experience of movement, following uncertain connections, and cycling back through certain points by way of the form in which it is written. Through a series of interlinked passages, the article explores the ideas of webs, passages, and paths of connection as models of discovery, getting lost, making unexpected connections, and learning. It explores different types of aporia and shows how aporia can be seen, not as a barrier to knowledge, or as simply ,clearing the ground' for new learning, but as an integral dimension of learning (and of teaching) itself. By design, it offers not an argument but a way of exploring complex ideas; in a different medium, it could have been produced as a hypertextual article itself (and in this way might also spark reflection on the possibilities and limits of hypertextual writing within a print medium). [source] Association between fatigue and failure to preserve cerebral energy turnover during prolonged exerciseACTA PHYSIOLOGICA, Issue 1 2003L. Nybo Abstract Aim: This study evaluated if the fatigue and apathy arising during exercise with hypoglycaemia could relate to a lowering of the cerebral metabolic rates of glucose and oxygen. Methods and results: Six males completed 3 h of cycling with or without glucose supplementation in random order. Cerebral blood flow, metabolism and interleukin-6 (IL-6) release were evaluated with the Kety,Schmidt technique. Blood glucose was maintained during the glucose trial, while it decreased from 5.2 ± 0.1 to 2.9 ± 0.3 mmol L,1 (mean ± SE) after 180 min of exercise in the placebo trial with a concomitant increase in perceived exertion (P < 0.05). During hypoglycaemia, the cerebral glucose uptake was reduced from 0.34 ± 0.05 to 0.28 ± 0.04 ,mol g,1 min,1, while the cerebral uptake of , -hydroxybutyrate increased to 5 ± 1 pmol g,1 min,1 (P < 0.05). The reduced glucose uptake was accompanied by a lowering of the cerebral metabolic rate of oxygen from 1.84 ± 0.19 mmol g,1 min,1 during exercise with glucose supplementation to 1.60 ± 0.16 mmol g,1 min,1 during hypoglycaemia (P < 0.05). In addition, the cerebral IL-6 release was reduced from 0.4 ± 0.1 to 0.0 ± 0.1 pg g,1 min,1 (P < 0.05). Conclusions: Exercise-induced hypoglycaemia limits the cerebral uptake of glucose, exacerbates exercise, reduces the cerebral metabolic rate of oxygen and attenuates the release of IL-6 from the brain. [source] Lithium and KB-R7943 effects on mechanics and energetics of rat heart muscleACTA PHYSIOLOGICA, Issue 1 2002P. Bonazzola ABSTRACT The role of calcium influx on energy expenditure during cardiac contraction was studied. For this purpose, the described ability of lithium and KB-R 7943 (KBR) to diminish Ca entry through Na,Ca exchanger (Ponce-Hornos & Langer, J Mol Cell Cardiol 1980, 12, 1367, Satoh et al., Circulation 2000, 101, 1441) were used. In isolated contractions (contractions elicited after at least 5 min of rest) LiCl 45 mmol L,1 decreased pressure developed and pressure,time integral from 42.3 ± 2.7 and 14.5 ± 1.2 to 32.1 ± 3.4 mN mm,2 and 8.3 ± 0.9 mN mm,2 s, respectively. A similar effect was observed in regular contractions (at 0.16 Hz stimulation). The presence of KBR (5 ,mol L,1) in the perfusate induced a slight but not significant decrease in pressure developed and pressure,time integral in steady-state contractions. As it was previously described, the heat involved in a heart muscle contraction can be decomposed into several components (H1, H2, H3 and H4), but only one (H3) was associated with force generation. While H3 decreased with lithium in both types of contractions, H3/PtI ratio remained unaltered, indicating that the economy for pressure maintenance was unaffected. To further investigate the role of Ca entry on force development, a condition in which the contraction is mainly dependent on extracellular calcium was studied. An ,extra' stimulus applied 200 ms after the regular one in a muscle stimulated at 0.16 Hz induces a contraction with this characteristic (Marengo et al., Am J Physiol 1999, 276, H309). Lithium induced a strong decrease in pressure,time integral and H3 associated with this contraction (43 and 45%, respectively) with no change in H3/PtI ratio. Lithium also reduced (53%) an energy component (H2) associated with Ca cycling. The use of KBR showed qualitatively similar results [i.e. a 33% reduction in pressure,time integral associated with the extrasystole (ES) with no changes in H3/PtI ratio and a 30% reduction in the H2 component]. Li and KBR effects appear to be additive and in the presence of 45 mmol L,1 Li and 5 ,mol L,1 KBR the extrasystole was abolished in 77%. Lithium and KBR effects particularly for the extrasystole can be explained through the inhibition of Ca entry via Na,Ca exchange giving support to the participation of the Na,Ca exchanger in the Ca influx from the extracellular space. In addition, the results also suggest the possibility of an effect of Li on an additional Ca sensitive locus (different than the Na,Ca exchanger). In this connection, in isolated contractions lithium decreased the energy release fraction related to mitochondrial processes (H4) increasing the economy of the overall cardiac contraction. [source] Traumatic dental injuries in an urban adolescent population in Tirana, AlbaniaDENTAL TRAUMATOLOGY, Issue 5 2010Dorina Sula Thelen Material & methods: A cross-sectional survey was carried out to acquire epidemiological data about TDI in the permanent incisors of Albanian adolescents. Participants (n = 2789) were adolescents of both genders, aged 16,18 years, attending public high schools in Tirana. Results: The occurrence of TDI in the incisors ranged from 8.9% of 16-year-olds to 10.5% of 18-year-olds. A greater proportion of boys (12.4%) had TDI compared with girls (7.7). The most commonly reported causes were collisions (27.5%) followed by physical leisure activities and sports (mainly cycling and swimming/diving) (14.1%) and falls (13.4%). Of the adolescents affected by TDI, 32% had unmet treatment need because of no or inadequate treatment. Adolescents living in districts with low socio-economic level had significantly more TDI with unmet treatment need than those living in districts with high socio-economic level. Conclusion: The occurrence of TDI among Albanian adolescents was moderate. Adolescents who came from low socio-economic districts had a greater probability of having TDI with unmet treatment need. [source] Dental trauma in children presenting for treatment at the Department of Dentistry for Children and Orthodontics, Budapest, 1985,1999DENTAL TRAUMATOLOGY, Issue 3 2001Katalin Gábris Abstract , Data on children with dental trauma who presented for treatment at the Department of Dentistry for Children and Orthodontics in Budapest over a period of 15 years were analysed. The WHO guidelines were used to classify the traumatic injuries. A total of 590 children were involved, 810 teeth being affected. Children aged 7,14 years made up 88% of the cohort. The male:female ratio was 58:42. The permanent:primary ratio for the affected teeth was 90:10. The teeth most commonly affected were the maxillary central incisors. In 70% of the cases, only one tooth was traumatised. The incidence of dental trauma peaked at 10 years of age. The most common injury type observed was enamel-dentin crown fracture. The decreasing sequence of frequency of etiological factors was playing, sports, falls, cycling, road accidents and fighting. Of the accidents, 65% occurred at school or at home. Seventy seven per cent of the patients presented for medical care in the first 3 days after the accident. [source] Somatic H1 histone accumulation and germ layer determination in amphibian embryosDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 8 2006Reed A. Flickinger The induction of mesoderm and/or endoderm from prospective ectoderm and dorsalization of the marginal zone mesoderm may be linked to inhibition of cell cycling and DNA synthesis in early amphibian embryos. In turn, this may lead to reduction of somatic H1 histone accumulation. A greater number of cell cycles and rounds of DNA synthesis characterizes the induction of neural tissue. This is correlated with an increase of somatic H1 histone accumulation. The number of rounds of DNA replication may regulate the level of H1 histone accumulation and this may have a role in germ layer determination. [source] Health-promoting physical activity of adults with mental retardationDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 1 2006Heidi I. Stanish Abstract This literature review describes the physical activity behavior of adults with mental retardation consistent with the U.S. Surgeon General's recommendation of 30 minutes of moderate intensity physical activity on 5 or more days per week. The proportion of participants achieving this criterion ranges from 17.5 to 33%. These data are likely to be generous estimates of activity as individuals included in physical activity studies to date have been relatively young and healthy volunteers with mild to moderate limitations. Major sources of physical activity were walking and cycling for transport, chores and work, dancing, and Special Olympics. There is a pressing need to conduct studies using appropriately powered representative samples and to validate measures that assess physical activity less directly; including methodologies in which proxy respondents are used. Accurate information about existing patterns of behavior will enhance the development of effective strategies to promote physical activity among persons with mental retardation. MRDD Research Reviews 2006;12:13,21. © 2006 Wiley-Liss, Inc. [source] Cell proliferation during blastema formation in the regenerating teleost finDEVELOPMENTAL DYNAMICS, Issue 2 2002Leonor Santos-Ruiz Abstract Epimorphic regeneration in teleost fins occurs through the establishment of a balanced growth state in which a blastema gives rise to all the mesenchymal cells, whereas definite areas of the epidermis proliferate leading to its extension, thus, allowing the enlargement of the whole structure. This type of regeneration involves specific mechanisms that temporally and spatially regulate cell proliferation. To understand how the blastema is formed and how this growth situation is set up, we investigated cell proliferation patterns in the regenerating fin of the goldfish Carassius auratus from the time of amputation to that of blastema formation by using proliferating cell nuclear antigen immunostaining and bromodeoxyuridine labeling. Wound closure and apical epidermal cap formation took place by epidermal migration and re-arrangement, without the contribution of cell proliferation. As soon as the apical cap had formed, the epidermis started to proliferate at its lateral surfaces, in which all layers maintained cycling for the duration of the studied process. The distal epidermal cap, on the contrary, presented very few cycling cells, and its cytoarchitecture was indicative of continuous remodeling due to ray growth. The basal layer of this epidermal cap showed a typical morphology and remained nonproliferative whilst in contact with the proliferating blastema. Proliferation in the mesenchymal compartment of the ray started far from the amputation plane. Subsequently, cycling cells approached that location, until they formed the blastema in contact with the apical epidermal cap. Differences observed between the epidermis and mesenchyma, regarding activation of the cell cycle and the establishment of proliferative patterns, suggest that differential mechanisms regulate cell proliferation in each of these compartments during the initial stages of regeneration. © 2002 Wiley-Liss, Inc. [source] Interpretation of urinary concentrations of pseudoephedrine and its metabolite cathine in relation to doping controlDRUG TESTING AND ANALYSIS, Issue 5 2009K. Deventer Abstract Until the end of 2003 a urinary concentration of pseudoephedrine exceeding 25 µg/mL was regarded as a doping violation by the World Anti-Doping Agency. Since its removal from the prohibited list in 2004 the number of urine samples in which pseudoephedrine was detected in our laboratory increased substantially. Analysis of 116 in-competition samples containing pseudoephedrine in 2007 and 2008, revealed that 66% of these samples had a concentration of pseudoephedrine above 25 µg/mL. This corresponded to 1.4% of all tested in competition samples in that period. In the period 2001,2003 only 0.18% of all analysed in competition samples contained more than 25 µg/mL. Statistical comparison of the two periods showed that after the removal of pseudoephedrine from the list its use increased significantly. Of the individual sports compared between the two periods, only cycling is shown to yield a significant increase. Analysis of excretion urine samples after administration of a therapeutic daily dose (240 mg pseudoephedrine) in one administration showed that the threshold of 25 µg/mL can be exceeded. The same samples were also analysed for cathine, which has currently a threshold of 5 µg/mL on the prohibited list. The maximum urinary concentration of cathine also exceeded the threshold for some volunteers. Comparison of the measured cathine and pseudoephedrine concentrations only indicated a poor correlation between them. Hence, cathine is not a good indicator to control pseudopehedrine intake. To control the (ab)use of ephedrines in sports it is recommended that WADA reintroduce a threshold for pseudoephedrine. Copyright © 2009 John Wiley & Sons, Ltd. [source] Temporal and spatial variations in periglacial soil movements on alpine crest slopesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2005Norikazu Matsuoka Abstract This paper describes up to ten years of continuous monitoring of frost heave, creep and associated parameters on high mountain crest slopes in the Japanese and Swiss Alps, aiming to evaluate spatial and interannual variations in the rates and controls of soil movement. Shallow frost creep re,ecting diurnal frost heave activity dominates the crest slopes that lack a vegetation mat and have a thin debris mantle with good drainage. Seasonal frost heave activity can induce slightly deeper movement where ,ne soil exists below the depth reached by diurnal freeze,thaw penetration, although the shallow bedrock impedes movements below 20 cm depth. As a result, downslope velocity pro,les display strong concavity with surface velocities of 2,50 cm a,1. The frost creep rates vary spatially, depending on the soil texture, slope gradient, frequency of temperature cycling across 0 °C and moisture availability during freeze,thaw periods. Soil movements recur in every freeze,thaw period, although with some interannual variations affected by the length of seasonal snow cover and the occurrence of precipitation during freeze,thaw periods. The Swiss Alps encounter more signi,cant interannual variations than the Japanese Alps, re,ecting the large variability of the annual snow regime. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effects of summer grazing by reindeer on composition of vegetation, productivity and nitrogen cyclingECOGRAPHY, Issue 1 2001Johan Olofsson In this study, we investigated the effect of reindeer grazing on tundra heath vegetation in northern Norway. Fences, erected 30 yr ago, allowed us to compare winter grazed, lightly summer grazed and heavily summer grazed vegetation at four different sites. At two sites, graminoids dominated the heavily grazed zone completely, while ericoid dwarf shrubs had almost disappeared. In the other two areas, the increase of graminoids was almost significant. At one of the sites where graminoids dominated the heavily grazed area, we also measured plant biomass, primary production and nitrogen cycling. In this site, heavy grazing increased primary production and rate of nitrogen cycling, while moderate grazing decreased primary production. These results were inconsistent with the view that the highest productivity is found at intermediate grazing pressure. These results rather support the hypothesis that intensive grazing can promote a transition of moss-rich heath tundra into productive, graminoid-dominated steppe-like tundra vegetation. Moreover the results suggests that intermittent intensive reindeer grazing can enhance productivity of summer ranges. [source] Woody plants modulate the temporal dynamics of soil moisture in a semi-arid mesquite savanna,ECOHYDROLOGY, Issue 1 2010Daniel L. Potts Abstract Climate variability and human activities interact to increase the abundance of woody plants in arid and semi-arid ecosystems worldwide. How woody plants interact with rainfall to influence patterns of soil moisture through time, at different depths in the soil profile and between neighboring landscape patches is poorly known. In a semi-arid mesquite savanna, we deployed a paired array of sensors beneath a mesquite canopy and in an adjacent open area to measure volumetric soil water content (,) every 30 min at several depths between 2004 and 2007. In addition, to quantify temporally dynamic variation in soil moisture between the two microsites and across soil depths we analysed , time-series using fast Fourier transforms (FFT). FFT analyses were consistent with the prediction that by reducing evaporative losses through shade and reducing rainfall inputs through canopy interception of small rainfall events, the mesquite canopy was associated with a decline in high-frequency (hour-to-hour and day-to-day) variation in shallow ,. Finally, we found that, in both microsites, high-frequency , variation declined with increasing soil depth as the influence of evaporative losses and inputs associated with smaller rainfall events declined. In this case, we argue that the buffering of shallow soil moisture against high-frequency variations can enhance nutrient cycling and alter the carbon cycle in dryland ecosystems. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||