Increase In Cycling Rate Research Articles

Thermomechanical stress analysis and fatigue lifetime evaluation of coal-fired boiler components during peak shaving transient processes: Effects of load cycling rate

The operational flexibility of coal-fired power plants has become a critical concern, but it leads to heightened fatigue damage and reduced operational lifetime as the load cycling rate increases. This study mainly focuses on the fatigue lifetime evaluation of main components within the boiler. Based on the dynamic model of the coal-fired power plants via GSE software, the dynamic characteristics of main thermodynamic parameters within the boiler under different load cycling rates are obtained. Additionally, the equivalent thermomechanical stresses by using the finite difference method are calculated and the fatigue lifetimes in accordance with the ASME design fatigue evaluation code of main components within the boiler are evaluated. It turns out that the maximum load cycling rate is 3.0 % Pe min−1 for the loading up and down processes between 50 % THA and 75 % THA. Moreover, during the loading up process, the panel superheater exhibits the highest equivalent thermomechanical stress, peaking at 171.22 MPa, and is the component with the lowest allowable number of cycles, merely reaching 19458 at a 3.0 % Pe min−1 load cycling rate. Conversely, during the loading down process, the high temperature superheater exhibits the highest equivalent thermomechanical stress at 145.74 MPa and is also the component with the fewest allowable cycles, amounting to 20182 at a 3.0 % Pe min−1 load cycling rate.

A dynamic model of UVR8 photoreceptor signalling in UV-B-acclimated Arabidopsis.

The photoreceptor UVR8 mediates numerous photomorphogenic responses of plants to UV-B wavelengths by regulating transcription. Studies with purified UVR8 and seedlings not previously exposed to UV-B have generated a model for UVR8 action in which dimeric UVR8 rapidly monomerises in response to UV-B exposure to initiate signalling. However, the mechanism of UVR8 action in UV-B-acclimated plants growing under photoperiodic conditions, where UVR8 exists in a dimer/monomer photo-equilibrium, is poorly understood. We examined UVR8 dimer/monomer status, gene expression responses, amounts of key UVR8 signalling proteins and their interactions with UVR8 in UV-B-acclimated Arabidopsis. We show that in UV-B-acclimated plants UVR8 can mediate a response to a 15-fold increase in UV-B without any increase in abundance of UVR8 monomer. Following transfer to elevated UV-B, monomers show increased interaction with both COP1, to initiate signalling and RUP2, to maintain the photo-equilibrium when the dimer/monomer cycling rate increases. Native RUP1 is present in low abundance compared with RUP2. We present a model for UVR8 action in UV-B-acclimated plants growing in photoperiodic conditions that incorporates dimer and monomer photoreception, dimer/monomer cycling, abundance of native COP1 and RUP proteins, and interactions of the monomer population with COP1, RUP2 and potentially other proteins.

Anode material based on nanosized lithium titanate

An anode material based on lithium titanate Li4Ti5O12 with a particle size of 4–5 nm was obtained. Decreasing particle size of lithium titanate significantly changes its electrochemical properties. First of all, the shape of the charge–discharge curve alters and the lithium intercalation–deintercalation rate at high cycling rate increases. At the first cycles of cycling, the charge capacity of the produced material considerably exceeds the calculated value and rapidly decreases while cycling, approaching the discharge capacity, which remains constant.

Stem cell population asymmetry can reduce rate of replicative aging

Cycling tissues such as the intestinal epithelium, germ line, and hair follicles, require a constant flux of differentiated cells. These tissues are maintained by a population of stem cells, which generate differentiated progenies and self-renew. Asymmetric division of each stem cell into one stem cell and one differentiated cell can accomplish both tasks. However, in mammalian cycling tissues, some stem cells divide symmetrically into two differentiated cells and are replaced by a neighbor that divides symmetrically into two stem cells. Besides this heterogeneity in fate (population asymmetry), stem cells also exhibit heterogenous proliferation-rates; in the long run, however, all stem cells proliferate at the same average rate (equipotency). We construct and simulate a mathematical model based on these experimental observations. We show that the complex steady-state dynamics of population-asymmetric stem cells reduces the rate of replicative aging of the tissue—potentially lowering the incidence of somatic mutations and genetics diseases such as cancer. Essentially, slow-dividing stem cells proliferate and purge the population of the fast-dividing – older – cells which had undertaken the majority of the tissue-generation burden. As the number of slow-dividing cells grows, their cycling-rate increases, eventually turning them into fast-dividers, which are themselves replaced by newly emerging slow-dividers. Going beyond current experiments, we propose a mechanism for equipotency that can potentially halve the rate of replicative aging. Our results highlight the importance of a population-level understanding of stem cells, and may explain the prevalence of population asymmetry in a wide variety of cycling tissues.

Behavioral andIn VitroCorrelates of Compulsive-Like Food Seeking Induced by Operant Conditioning inAplysia

Motivated behaviors comprise appetitive actions whose occurrence results partly from an internally driven incentive to act. Such impulsive behavior can also be regulated by external rewarding stimuli that, through learning processes, can lead to accelerated and seemingly automatic, compulsive-like recurrences of the rewarded act. Here, we explored such behavioral plasticity in Aplysia by analyzing how appetitive reward stimulation in a form of operant conditioning can modify a goal-directed component of the animal's food-seeking behavior. In naive animals, protraction/retraction cycles of the tongue-like radula are expressed sporadically with highly variable interbite intervals. In contrast, animals that were previously given a food-reward stimulus in association with each spontaneous radula bite now expressed movement cycles with an elevated frequency and a stereotyped rhythmic organization. This rate increase and regularization, which was retained for several hours after training, depended on both the reward quality and its contingency because accelerated, stereotyped biting was not induced in animals that had previously received a less-palatable food stimulus or had been subjected to nonassociative reward stimulation. Neuronal correlates of these learning-induced changes were also expressed in the radula motor pattern-generating circuitry of isolated buccal ganglia. In such in vitro preparations, moreover, manipulation of the burst frequency of the bilateral motor pattern-initiating B63 interneurons indicated that the regularization of radula motor pattern generation in contingently trained animals occurred separately from an increase in cycle rate, thereby suggesting independent processes of network plasticity. These data therefore suggest that operant conditioning can induce compulsive-like actions in Aplysia feeding behavior and provide a substrate for a cellular analysis of the underlying mechanisms.

Effect of cancer cachexia on triacylglycerol/fatty acid substrate cycling in white adipose tissue

The effect of cancer cachexia on the TAG/FA substrate cycle in white adipose tissue was determined in vivo using the MAC16 murine model of cachexia. When compared with non-tumor-bearing animals, the rate of TAG-glycerol production was found to be increased almost threefold in animals bearing the MAC13 tumor, which does not induce cachexia, but was not further elevated in animals bearing the MAC16 tumor. In both cases TAG-glycerol production and de novo synthesis of TAG-FA were also increased above non-tumor-bearing animals. In animals bearing the MAC16 tumor, the TAG-FA rates were significantly higher than in animals bearing the MAC13 tumor. This suggests that the presence of the tumor alone is sufficient to cause an increase in cycling rate, and in the absence of an elevated energy intake (MAC16) this may contribute to the depletion of adipose tissue.

FORCED MUON CATALYZED FUSION IN HETEROGENEOUS LAYERS OF HYDROGEN ISOTOPES

Muon cycling dynamics for muon catalyzed fusion in heterogeneous solid layers are considered through decay of complex molecule [Formula: see text]. The suggested fusion system consists of three layers which are alternatively repeated. The first layer is D/T (deuterium, tritium) which provides [Formula: see text] molecules. The second layer is T2 molecules which are used to slow down the muonic atoms and the third layer is D2 molecules. The design is in a way in which dtμ, muonic deuterium and tritium molecules, are produced in resonance. It is shown, by considering muonic dynamics theoretically in a suggested heterogeneous system and determining its cycling rate by using a more advanced calculational method, that for equal deuterium, tritium concentration (Cd=Ct=0.5) in D/T layer and ϕ'=ϕ0=ϕ=1 (relative density for each layer respectively and given in liquid hydrogen density LHD=4.25×1022 cm -3), the muon cycling rate is optimum for the suggested heterogeneous system and has 15% enhancement with respect to the conventional D/T system. It is also shown that for ϕ0<0.0003 the muon cycling rate in D2 is almost stopped, and for ϕ0≥1 muon cycling rate increases, but this is not recommended due to low and costly tritium availability.

Cross‐Country Skiing

The purpose was to study the adaptation to speed in the temporal patterns of the movement cycle and determine any differences in velocity, cycle rate and cycle length at the maximum speed level in the different classical style and freestyle cross‐country skiing techniques. Eight skilled male cross‐country skiers were filmed with a digital video camera in the sagittal plane while skiing on a flat cross‐country ski track. The skiers performed three classical style techniques the diagonal stride, kick double poling and the double poling technique and four freestyle techniques paddle dance (gear 2), double dance (gear 3), single dance (gear 4) and combiskate (gear 5) at four different self‐selected speed levels slow, medium, fast and their maximum. Cycle duration, cycle rate, cycle length, and relative and absolute cycle phase duration of the different techniques at the different speed levels were analysed by means of a video analysis system. The cycle rate in all tested classical and freestyle techniques was found to increase significantly (p < .01) with speed from slow to maximum. Simultaneously, there was a significant decrease in the absolute phase durations of all the investigated skiing techniques. A minor, not significant, change in cycle length, and the significant increase in cycle rate with speed showed that the classical and freestyle cross‐country skiing styles are dependent, to a large extent, on an increase in cycle rate for speed adaptation. A striking finding was the constant relative phase duration with speed, which indicates a simplified neural control of the speed adaptation in both cross‐country skiing styles. For the practitioner, the knowledge about the importance of increasing cycle frequency rather than cycle length in the speed adaptation can be used to optimise a rapid increase in speed. The knowledge about the decrease in absolute phase duration, especially the thrust phase duration, points to the need for strength and technique training to enable force production at a high cycle rate and skiing speed. The knowledge that the relative phase duration stays constant with speed may be used to simplify the learning of the different cross‐country skiing techniques.

Stretch-Shortening Cycle in Roller Ski Skating: Effects of Speed

The purpose of this study was to examine the effects of speed on the stretch-shortening cycle (SSC) behavior during roller ski skating. Ten highly skilled male cross-country skiers roller skied at 4.56, 5.33 m · s–1and maximal speed using the V2-alternate technique on a flat terrain. Knee and ankle joint kinematics, and EMG of thevastus lateralis(VL) andgastrocnemius lateralis(GL) muscles were recorded during the last 40 s of each bout of roller skiing. Maximal speed was associated with increases in cycle rate combined with decreases in cycle length. For VL, no significant differences were observed for the integrated EMG eccentric-to-concentric ratio (iEMG Ecc/Conc) and for the stretching velocity over the range of speeds. For GL, stretching velocity and iEMG Ecc/Conc were significantly greater at maximal speed. The analysis of GL EMG activity suggests that speed improved GL stiffness so that more elastic energy was stored, a better force transmission occurred, and coupling time decreased. These findings suggest that the efficiency of roller ski skating locomotion may be increased with speed through a better use of the stretch-shortening cycle pattern in the ankle extensors.

Control of cross-bridge cycling by myosin light chain phosphorylation in mammalian smooth muscle.

This review focuses on experiments in which the single turnover of myosin-bound ADP is used to characterize the regulation of the cross-bridge cycle by myosin light chain phosphorylation in mammalian smooth muscle. Under isometric conditions, at rest, when the myosin light chain is not phosphorylated, myosin cycles very slowly (about 0.004 s-1), while phosphorylation of the light chain results in a 50-fold increase in cycling rate of 0.2 s-1. Experiments consistently show that some myosin does not increase its cycling rate although its light chain is phosphorylated. Studies at low levels of myosin light chain phosphorylation show that phosphorylation also induces an increase in the cycling rate of unphosphorylated myosin. The fast cycling phosphorylated myosin is the main determinant of suprabasal myosin ATPase activity, while the cycling rate of cooperatively activated unphosphorylated myosin is slow and appears to depend on the extent of phosphorylation of the entire thick filament. Single turnover experiments measuring the rate of phosphorylation and dephosphorylation of myosin light chain show that the turnover of light chain phosphate can be very rapid (0.3-0.4 s-1) at suprabasal calcium concentrations. The expected effect of such a rapid turnover of light chain phosphorylation on the turnover of myosin-bound ADP is not observed. The effects of low levels of myosin light chain phosphorylation on the single turnover of myosin suggest that the same small pool of myosin remains phosphorylated for relatively long periods of time rather than the entire pool of myosin spending a small fraction of its cycle time in the phosphorylated state.

Effect of rolling resistance on poling forces and metabolic demands of roller skiing.

To examine the effect of an increase in roller ski rolling resistance on the physiological and upper body demands of roller skiing with the V2-alternate technique. Nine highly skilled cross-country skiers roller skied at three paced speeds on a flat oval loop using roller skis with high (HiR) and low (LowR) rolling resistance. Oxygen uptake (VO2), heart rate, and poling forces were measured during the last 30 s and rating of perceived exertion (RPE) was requested immediately after each 4-min bout of roller skiing. VO2 and all force-related variables increased significantly with speed and were higher (P < 0.01) for HiR at given speeds. Poling time was similar between HiR and LowR, whereas poling recovery time was shorter (P = 0.0002) and cycle rate was higher (P = 0.002) for HiR. For given VO2 levels, peak and average forces, heart rates, and RPE values were similar between HiR and LowR, whereas average poling force across the cycle was greater (P = 0.006) and duty cycle (i.e., percentage of cycle when poling forces were applied) was higher (P = 0.0001) with HiR. 1) The decrease in poling recovery time and increase in cycle rate associated with an increase in roller ski rolling resistance is comparable to the effect previously observed from increasing grade and probably occurs as a means of limiting deceleration. 2) Since changes in rolling resistance do not alter the relationships of RPE and heart rate with VO2, the central cardiovascular adaptations from roller ski training should not be affected by the rolling resistance of the roller skis. 3) Higher resistance roller skis are likely to induce greater upper body aerobic adaptations than lower resistance roller skis.

Pushing Economy and Propulsion Technique of Wheelchair Racers at Three Speeds

Pushing economy and wheelchair propulsion technique were examined for 8 wheelchair racers on a motorized treadmill at 6.0, 6.5, and 7.0 m/s. Kinematic data for the sagittal view were collected by a video camera for two-dimensional analysis. Adaptations to speed changes occurred, initially by a decrease in cycle time and an increase in cycle rate, and later by an increase in the flexion of the elbow. At each speed there were large variations in pushing economy between individuals. The relationship between pushing economy and selected kinematic variables revealed that at 6.0, 6.5, and 7.0 m/s, economy was associated with (a) the lighter athletes (r = .89, .86, .83), (b) a greater range of elbow movement (r = -.85, -.65, -.63), and (c) a lower push rate (r = .73, .81, .63), respectively. Effects of lesion level and wheelchair design may be more important in explaining differences in pushing economy than differences in propulsion technique.

Potentiation of smooth muscle contractility after rapid changes in isotonic force.

The sudden application of step increases in afterload (0.4-3.0 s in duration) arrested the isotonic shortening of electrically stimulated ovarian ligament smooth muscle strips from rabbits. Force steps were chosen to produce, after initial rapid yielding, a quasi-steady state in which muscle length and force remained constant. Removal of the extra afterload allowed renewed shortening that began with a velocity transiently greater than that measured before the force step (at same muscle length). The rate of force redevelopment was also transiently potentiated under isometric conditions after the removal of the extra load. Both types of potentiation depended on force-step duration, and the transients decayed exponentially with a time constant of approximately 0.25 s. The stiffness of the muscle during the force step was initially depressed but then increased along an exponential time course while force and length remained constant. These observations are consistent with an initial detachment of a portion of the cross-bridge array, which then reattached during the course of the force step, with potentiation being due to either a transient increase in cycling rate or a time-dependent reconfiguration of cytoskeletal elements supporting the contractile system.

Effects of thyroid status on glucose cycling by isolated rat hepatocytes

The effects of alterations in thyroid status on glucose metabolism have been investigated in rat hepatocytes. Addition of 10 or 40 mmol/L glucose induced increases in respiration rate that were significantly larger in cells from hyperthyroid rats than from hypothyroid animals. The responses of hepatocytes from euthyroid rats were intermediate. In cells from hyperthyroid rats, most of the increase occurred upon addition of 10 mmol/L glucose, with only a further small stimulation resulting when glucose concentration was increased to 40 mmol/L. For a given glucose concentration, glycolytic rates, determined by measuring release of tritium from [6- 3H]glucose, were comparable in all thyroid states. Studies with 10 mmol/L [2- 3H]glucose showed that cycling between glucose-6-phosphate and glucose was almost twofold higher in euthyroid and hyperthyroid states as compared with the hypothyroid state, although the magnitude of the increase in cycling rate was only approximately 0.2 μmol glucose · min −1 · g −1. When 40 mmol/L [2- 3H]glucose was added, over 44% of the glucose that was phosphorylated to glucose-6-phosphate was cycled back to glucose, but this cycling was independent of thyroid status. Cycling between fructose-1,6-bisphosphate and fructose-6-phosphate was negligible in all thyroid states. Rates of glycogen synthesis were comparable in hypothyroid and hyperthyroid states and slightly less than in the euthyroid state. Glycolytically formed pyruvate was cycled back to glucose in hepatocytes from hypothyroid, euthyroid, and hyperthyroid rats. During a 60-minute incubation period, cycling to glucose in the presence of 10 mmol/L or 40 mmol/L glucose was up to twofold higher in cells from euthyroid and hyperthyroid rats than in hepatocytes from hypothyroid animals. The measured increases in cycling rates induced by thyroid hormone were small and in theory could have been satisfied by a much smaller increase in respiration rate than was observed.

Effect of Velocity on Cycle Rate and Length for Three Roller Skiing Techniques

This investigation examined the adjustments made in cycle rate and length to velocity changes during roller skiing with the double pole (DP), kick double pole (KD), and VI skate (VS) techniques. Eight cross-country ski racers roller skied with each technique on a flat track at submaximal and maximal velocities while being videotaped from a lateral view. Increases in submaximal velocities were associated with increases in cycle rate and cycle length for KD and VS but only with increases in cycle rate for DP. Maximal sprint velocities were approximately 7% lower (p &lt; .01) for KD than for DP and VS and were associated with increases (p &lt; .01) in cycle rate for each technique combined with decreases (p &lt; .01) in cycle length for DP and VS. The findings indicate that there are differences among techniques in the manner in which cycle rate and length are adjusted to change submaximal velocity, but each technique relies upon an increase in cycle rate to achieve maximal velocity.

Muscle enthalpy production and its relationship to actomyosin ATPase.

During a maintained tetanus most of the energy liberated is produced by ATP hydrolysis at the cross-bridge. The energy produced by ATP hydrolysis by the sarcoplasmic reticulum is, however, a significant fraction (0.35) of the total. The energy liberation rate depends on a variety of factors (including the shortening velocity, sarcomere length, temperature, fiber type, and duration of contraction) and is, for the most part, consistent with current cross-bridge models. At the beginning of tetanic stimulation, a significant amount of heat (approximately 30 mJ/g) is produced by calcium binding reactions in the sarcoplasm. In the transition from an isometric to a shortening contraction, the cross-bridge cycling rate increases, and as much as 6 mJ/g of unexplained heat is produced. This unexplained heat appears to involve enthalpy changes accompanying a redistribution of cross-bridge intermediates, and it is reversed by high-energy phosphate splitting after the cessation of shortening. The mechanistic significance of these enthalpy changes remains to be elucidated.

Interfacial properties of arabinofuranosylcytosine diphosphate diacylglycerol, a synthetic liponucleotide

The interfacial properties of a synthetic liponucleotide [1-β- d-arabinofuranosylcytosine 5′-diphosphate 1,2- l-diacylglycerol (ara-CDPdiacylglycerol)] were investigated at 23°C. Surface properties studied included the quasi-equilibrium surface pressure-area (π- A) behavior of solvent-spread monolayers on a Wilhelmy balance, dynamic surface tension lowering at high cycling rate with an oscillating bubble, and the adsorption kinetics of aqueous dispersions. The π- A isotherm of ara-CDPdiacylglycerol was greatly expanded compared with that of egg phosphatidylcholine (egg PC), which had identical fatty acyl chain composition, and this feature was most pronounced at low surface pressures. Molecular areas of the liponucleotide and egg PC were more similar at higher surface pressures with film collapse areas of 60 and 53 Å 2/molecule, respectively. Collapse pressures were 40 dynes/cm for ara-CDPdiacylglycerol and 46 dynes/cm for egg PC at a low cycling rate of 4 Å 2/molecule/min, and these increased only slightly to 44 and 48 dynes/cm, respectively, for a 15-fold increase in cycling rate on the Wilhelmy balance. Maximum surface pressures for these surfactants also did not change significantly in complementary oscillating bubble studies, even at rates as high as 20 cycles/min. Additivity analyses of Wilhelmy balance (π- A) data for mixed monolayers of ara-CDPdiacylglycerol and egg PC suggested that these compounds form ideally miscible films at the air-water interface. Finally, in terms of the additional surface property of adsorption, aqueous dispersions of ara-CDPdiacylglycerol displayed a markedly greater adsorption rate and magnitude than egg PC, correlating with its larger critical micelle concentration. The rapid adsorption found for the synthetic liponucleotide, coupled with its ability to expand phosphatidylcholine monolayers, may give such molecules the potential for biomembrane toxicity.