Effect Of Rest Periods Research Articles

Establishment of a universal healing evaluation index for asphalt binder

The healing performance of asphalt binder is important to the overall performance of asphalt pavement. A suitable healing evaluation index is critical in order to compare the healing performance of different asphalt binders and choose the binder with the best healing properties. However, current studies focus primarily on the healing performance of asphalt binder and seem to ignore the importance of the healing evaluation index.In this paper, the healing performance of four different asphalt binders is analyzed. By comparing the healing curve to the initial curve, a ratio that is based on the areas created by the curves is found to reflect the healing performance of asphalt binders. Once the healing evaluation indices are established, they are also used to evaluate the mastics, and the applicability of the indices is analyzed. Also, a healing function for asphalt binder is established. The results show that the HIm-c index (based on the curve of the normalized modulus versus load cycles), the HIem-c index (based on the curve of the elastic modulus versus load cycles) and the HIvm-c index (based on the curve of the viscous modulus versus load cycles) suggest the same rankings for the healing of the studied binders. The healing ranking of the binders is also the same as that of the corresponding mastics evaluated by the HIm-c index. Based on the established healing function, it is found that the effect of terminal cases on the healing performance of asphalt binder is greater than the effect of rest periods.

Refining Conditions of Fatigue Testing of Hot Mix Asphalt

The beam fatigue test of hot-mix asphalt (HMA) has been used for nearly a half century. However, several conflicting results have been recently reported. This study attempts to refine test conditions such as waveform type (haversine versus sinusoidal), incorporating rest periods between loading cycles, and the effect of rest period on the healing of the HMA to minimize (eliminate) gross errors in the data analysis of the fatigue test results. In the deflection-controlled haversine test [ASTM D7460, 2010, “Standard Test Method for Determining Fatigue Failure of Compacted Asphalt Concrete Subjected to Repeated Flexural Bending,” Annual Book of ASTM Standards, Vol. 04.03, ASTM International, West Conshohocken, PA, pp. 1–14] permanent deformations lead to a new equilibrium neutral position of the beam and the force output follows a sinusoidal waveform. This tends to bend the beam in both directions similar to the deflection-controlled sinusoidal test. This would produce erroneous fatigue results since the test assumptions do not match the actual test conditions. In contrast, the deflection-controlled sinusoidal test [AASHTO T-321, 2012, “Standard Method of Test for Determining the Fatigue Life of Compacted Hot Mix Asphalt (HMA) Subjected to Repeated Flexural Bending,” Annual Book of AASHTO Standards, Vol. 32, Washington, DC, pp. T321-1–T321-11] is more consistent than the deflection-controlled haversine test [ASTM D7460, 2010, “Standard Test Method for Determining Fatigue Failure of Compacted Asphalt Concrete Subjected to Repeated Flexural Bending,” Annual Book of ASTM Standards, Vol. 04.03, ASTM International, West Conshohocken, PA, pp. 1–14]. When tests, with and without rest periods, are compared for healing studies, it is even more important to use a deflection-controlled sinusoidal test in order to obtain a fair comparison and accurate healing results. Since neither the haversine waveform nor the sinusoidal waveform in the lab exactly simulates field conditions, it is important to use a sinusoidal waveform in order to obtain consistent results. It is recommended that ASTM changes the ASTM D-7460 designation and test procedure to require a deflection-controlled sinusoidal waveform instead of haversine. Implementing the recommended test conditions is a crucial step in studying the concept of HMA healing and; as a result, estimating the endurance limit which plays an important role in designing sustainable pavements.

Insights into heap bioleaching of low grade chalcopyrite ores — A pilot scale study

Heap bioleaching of low grade chalcopyrite (CuFeS2) was carried out in 1000tons scale over a time period of 383days. Bacterial solution was prepared and re‐circulated in specially designed BACFOX (BACterial Film OXidation) tank. The micro‐organisms used in the pilot scale were a mixed culture of acidophilic bacteria predominantly of the Acidithiobacillus ferrooxidans strain. Effect of rest period, solution recirculation, acid concentration, frequency of solution transfers and seasonal effects on copper recovery were monitored. The leaching studies showed a cumulative copper dissolution rate of 0.14% per day (2.37kgd−1). The overall recovery of the heap was 30%. Variation in leaching efficiency and some of the precautionary measures to improve performance of heap bioleaching are also discussed.

Rest period effect on peak torque in female collegiate and recreational athletes

The purpose of the study was to evaluate the effect of rest period on peak torque in females. Thirty college-aged females (n = 15 collegiate athletes and n = 15 recreational athletes) performed three practice sessions and four experimental sessions using a knee flexion/extension protocol on a CYBEX NORM isokinetic dynamometer. Each session began with a five minute warmup on a cycle ergometer after which the subjects performed four maximal repetitions of knee extension at five isokinetic velocities, 60, 120, 180, 240, and 300°·sec -1 with randomly assigned rest periods of 15, 60, 180, or 300 seconds between velocity sets while knee flexion was held constant at 300°·sec -1 . Peak torque was recorded for each trial. Data were analyzed using a 4 (rest) x 5 (velocity) repeated measures ANOVA (p < 0.05). There were no significant differences in peak torque between any of the rest periods. It was concluded that in females a 60 second rest is adequate for muscle recovery when executing four maximal repetitions.

TAXAS DE APARECIMENTO E ALONGAMENTO DO CAPIM-XARAÉS EM DIFERENTES MANEJOS E NÍVEIS DE ADUBAÇÃO, INTERVALOS DE DESFOLHA E ESTAÇÕES ANUAIS

Objetivou-se avaliar os efeitos de diferentes manejos e doses de adubação, intervalos de desfolha e estações anuais sobre as características morfogênicas do capim-xaraés. O experimento foi conduzido em esquema de parcelas subsubdivididas, tendo nas parcelas um esquema fatorial 2 x 2, duas estações anuais (inverno e verão) e dois manejos de adubação (convencional e fertirrigação), nas subparcelas quatro intervalos de desfolha (21, 28, 35 e 42 dias) e nas subsubparcelas seis níveis de adubação (0, 15, 39, 64, 83 e 100% das doses de 700 e 560 kg de N e K2O, respectivamente), no delineamento inteiramente casualizado, com quatro repetições. As características morfogênicas foram estudadas por meio das taxas de aparecimento de folhas (TApF) e de alongamento de folhas (TAlF) e colmo (TAlC). Os efeitos proporcionados pelos intervalos de desfolha nas características morfogênicas foram dependentes do manejo, dos níveis de adubação e da estação anual. A estação verão proporcionou maiores médias nas características morfogênicas estudadas. O manejo da adubação (convencional e fertirrigação) não afetou os parâmetros avaliados e o aumento da adubação nitrogenada e potássica proporcionaram acréscimos nas TApF e TAlF.

The Influence of Resting Period Length on Jumping Performance

The purpose of this study was to determine a resting interval between countermovement jumps (i.e., volleyball spikes) that allows the maintenance of maximal jumping performance. Ten male volleyball players (1.85 +/- 0.05 m, 77.2 +/- 10.6 kg, 21.6 +/- 5.3 years) performed 6 experimental jumping sessions. In the first and sixth sessions, maximal countermovement jump height was measured, followed by submaximal countermovement jumps to the point of volitional fatigue. The number of countermovement jumps was used as a reference to test the effect of rest period between volleyball spikes. From the second to fifth experimental sessions, 30 maximal volleyball spikes were performed with different resting periods (i.e., 8, 14, 17, and 20 seconds) followed by countermovement jumps. Between the 15th and 30th spikes, the blood lactate concentration and heart rate were measured. Because the performance on the first and sixth sessions was the same, no training effects were noticed. During the 8-second resting interval set, the lactate concentration increased significantly between the 15th and 30th spikes (i.e., from 3.37 +/- 1.16 mmol to 4.94 +/- 1.49 mmol); the number of countermovement jumps decreased significantly after spikes compared to those performed without a previous effort (i.e., from 23 +/- 7 jumps to 17 +/- 9 jumps); and these variables were significantly correlated (r = -0.7). On the other hand, the lactate concentration and number of countermovement jumps were stable across the other resting intervals, without a heart rate steady state. The results indicate that an adequate resting period between spikes allowed participants to achieve a lactate steady state in which the performance was maintained during the exercise. These findings show that resting intervals between 14 and 17 seconds, typical during volleyball matches, are indicated to use in volleyball spike drills due to their capacity to maintain maximal jumping performance.

A Laboratory Investigation of the Effect of Multiple Axle and Truck Configurations on HMA Mixture Rutting

ABSTRACT Few studies have investigated pavement damage resulting from different axle and truck configurations, and they were generally limited to single and tandem axles. The unconfined compression cyclic load test with loading cycles that simulate different axle and truck configurations was used to examine their relative effect on permanent deformation of an asphalt mixture. The laboratory investigation indicates that the rutting damage due to different axle configurations is approximately proportional to the number of axles. However, the effect of rest period between axles groups within a truck configuration is significant. Calculating truck rutting damage by simply summing the vertical permanent deformation corresponding to its constituent axle groups results in erroneous predictions. The application of Miner's rule results in improved truck rutting damage predictions for a wider range of truck configurations, although it does not account for the effect of rest periods within a truck configuration. Finally, unique HMA rutting damage curves, which can be used for any axle or truck configuration, were developed using strain and energy response parameters.

Effects of Short vs. Long Rest Period Between Sets on Elbow-Flexor Muscular Endurance During Resistance Trainingto Failure

This study aimed to examine short-term resistance training effects of resting period length between sets on maximal number of repetitions and mean velocity over a moderate-intensity (60% of the maximum voluntary isometric contraction [MVIC]) set to failure on elbow-flexor muscles. The MVIC and surface electromyographic activity (sEMG) were also measured. Twenty-one untrained subjects were divided into 3 groups: short rest between sets (1 minute; SR), long rest between sets (4 minutes; LR), and nontraining control group (CG). The SR and LR performed 3 sets to failure in an arm-curl machine, 2 days per week for 5 weeks, with moderate loads (60-75% of the MVIC). The LR completed a significantly higher (31.6%, p < 0.05) total training volume than the SR. Both training groups enhanced the maximal number of repetitions to failure, with no significant differences in the magnitude of gains. The posttraining average velocity achieved by the SR at 40, 50, 60, 70, 80, and 90% of the total number of repetitions completed was significantly higher (p < 0.05) than the corresponding average velocity achieved on pretraining conditions, whereas no significant differences were observed in the LR. No significant changes in the MVIC or sEMG were observed in any group. We conclude that short-term elbow-flexor resistance training to failure, allowing 1 or 4 minutes of rest between sets, induces similar gains concerning local muscular endurance. Nevertheless, only the SR training approach reduced the rate of decline in the average repetition velocity during a set to failure. This can be of some importance in sport modalities in which not only the maximal number of repetitions (e.g., muscle endurance), but also a greater maintenance of high repetition velocities, may be critical for performance.

Central fatigue in continuous and intermittent contractions of triceps brachii

Conflicting results have been found across studies concerning the effect of rest periods on the development of central fatigue during prolonged muscle activity. Thus, the aim of the present study was to assess differences in the development of central fatigue between continuous and intermittent elbow extension fatigue tasks in the same subjects. Force and electromyographic data were collected on eight healthy volunteers. The ability to maximally activate the triceps brachii muscle was assessed by delivering trains of electrical stimulation during maximal voluntary efforts. This was done before, during, and after three fatigue tasks involving a maximal contraction in elbow extension. One short-duration ( approximately 55-s) and two long-duration (3-min) fatigue tasks were performed by all subjects on separate sessions. One 3-min task was intermittent (5-s rests every 30 s) and the other was continuous. The main findings were that the development and extent of central fatigue were task-dependent, with a greater decrease in the ability to maximally activate triceps brachii observed for the 3-min continuous task. Also, the voluntary activation (VA) ratio was found to be a more sensitive index of central fatigue than the central activation ratio (CAR). These results suggest that, when assessing central fatigue in patients, conclusions may vary depending on the continuous/intermittent nature of the task performed and the estimate of voluntary activation used.

BPMA rewards pump sector excellence

Heap bioleaching of low grade chalcopyrite (CuFeS2) was carried out in 1000 tons scale over a time period of 383 days. Bacterial solution was prepared and re‐circulated in specially designed BACFOX (BACterial Film OXidation) tank. The micro‐organisms used in the pilot scale were a mixed culture of acidophilic bacteria predominantly of the Acidithiobacillus ferrooxidans strain. Effect of rest period, solution recirculation, acid concentration, frequency of solution transfers and seasonal effects on copper recovery were monitored. The leaching studies showed a cumulative copper dissolution rate of 0.14% per day (2.37 kg d− 1). The overall recovery of the heap was 30%. Variation in leaching efficiency and some of the precautionary measures to improve performance of heap bioleaching are also discussed.

Characterization of Microdamage and Healing of Asphalt Concrete Mixtures

The pseudo-strain concept based on Schapery’s extended nonlinear elastic-viscoelastic correspondence principle is demonstrated by a considerable database to be able to characterize both microdamage and microdamage healing during the damage process. A change in pseudo stiffness can be used to quantify microdamage and healing during the fatigue test. Pseudo stiffness decreases consistently with increasing number of loading cycles, indicating that microdamage occurs during the fatigue test. The significant recovery of pseudo stiffness after rest periods demonstrates a healing effect due to rest periods. Dissipated pseudo-strain energy is a strong and consistent quantifier of damage and healing. High levels of cumulative dissipated pseudo-strain energy are consistent with high levels of fatigue damage, whereas low levels of cumulative pseudo-strain energy are associated with fatigue damage resistance. Pseudo stiffness is the chord slope of the stress-pseudo strain hysteresis loop. Since linear viscoelastic-based time effects are eliminated in this approach, pseudo stiffness and/or pseudo-strain energy are superior indicators of damage than either stiffness or total dissipated strain energy. The effects of rest periods on fatigue life extension due to healing of microcracks are significant. It has been demonstrated that longer rest periods result in more healing, and in turn in greater fatigue life.

Constitutive model of tendon responses to multiple cyclic demands (I)

The work reported here is an extensive study of tendon response to multiple cyclic tests including 3% constant peak strain level test (A-type test), 3% constant peak strain level test with two rest periods (B-type test), and 3–4% different peak strain level test (C-type test). A sufficient number of speciments were tested at each type of the test to statistically evaluate many changes in response during testing and differences in response between each type of the test. In cyclic tests, there were decreses (relaxations) in the peak stresses and hysteresis, increases in the slack strains, and during lower peak strain level (3%) cyclic block after higher peak strain level (4%) cyclic block in the C-type tests. Considering the results of this study and those of the other study of multiple cyclic tests with rest periods by Hubbard and Chun, 1985,recovery phenomena during the rest periods occurred predominantly at the beginning of the rest periods. Consistently in both studies, the effects of rest periods were small and transient compared to the effects of the cyclic extensions. The recovery with cycles at lower peak strain level (3%) after higher peak strain level (4%) in the C-type test has not been previously documented. This recovery seems to be a natural phenomena in tissue behavior so that collagenous structures recover during periods of decreased demand.

Fast-charging of a lead-acid cell: effect of rest period and depolarization pulse

Fast-charging of a lead-acid cell: effect of rest period and depolarization pulse

Fast-charging of a lead–acid cell: effect of rest period and depolarization pulse

Cell behavior is numerically investigated for fast charging of a lead–acid cell under constant current or pulsed current. A model used in the simulation has been developed to predict the cell performance by considering the solid-state reaction at the negative electrode. By incorporating a rest period and a depolarization pulse on high rate charge, it is possible to avoid deterioration of the cell performance due to an increase in internal resistance. Thus, fast charging of a lead–acid cell can be achieved without a loss of cycle-life, despite the fact that higher currents are forced into the cell.

The effect of rest periods on temporary threshold shift (TTS) after noise exposure

In a series of experimental studies the hypothesis that periods of silence reduce the risk of hearing impairment was tested. The noise exposure was comparable to that of workers in the engineering industry: e.g., during 10 minutes' grinding. Two different experiments with rest periods of different lengths and repetition rates were performed. Frequent short periods of silence offered the best protection. Significantly less influence on hearing, temporary threshold shift (TTS), was obtained when repeated 5-second pauses were allowed than during continuous work. The studies also included experiments with impulse noise. This consisted of a different series of sledgehammer impacts, with a peak level of 130 dB(A). Different repetition rates were tested in order to determine whether the reaction time of the acoustic reflex influenced its protective effect. A low repetition rate gave less temporary impairment than a higher repetition rate, although the total number of impacts was the same.

Fatigue crack propagation behaviour of a Ni−Cr−Mo steel due to rest period and overload

The aim of this study is to investigate the effects of an intermittent rest period at 300°C, overload in tension, and the combination of an overload and a subsequent rest period on fatigue crack growth in AISI 4340 steel. The intermittent rest period was found to stop fatigue crack growth completely near threshold level of ΔK. The alleviation effect of a rest period on crack growth was more distinct at the lower level of ΔK. In overload, the greater overload ratio (OLR=3) caused more alleviated effect on crack growth rate. The reduced stress intensity factor by crack branching and enhanced roughness of crack surface are proposed to contribute to the retardation and arrest of fatigue crack growth. The most distinct retardation of fatigue crack growth was found after the combined treatment of a overload and a subsequent rest period.

Effect of rest periods on the endurance of notched duralumin specimens under program loading

Effect of rest periods on the endurance of notched duralumin specimens under program loading

Influence of rest periods on the fatigue strength of structural steel

The effect of rest periods on fatigue life was investigated. Small size specimen and constant load amplitudes were used with a new developed fatigue testing machine in alternating bending. Rest periods of 1.5 min were introduced after each half cycle. The cycling rate was 0.25 cpm. Comparative tests on specimen tested without rest periods showed a substantial increase in fatigue life due to rest periods.

Rheological properties of wheat flour doughs I.—Method for determining the large deformation and rupture properties in simple tension

AbstractA method and an apparatus are described for determining the large deformation and rupture properties of wheat flour doughs in simple tension. Dough rings are submerged in a liquid of matching density to prevent the dough from deforming under its own weight and are stretched at constant rates of extension until rupture occurs. Stress‐strain curves obtained at different temperatures and extension rates on doughs prepared from a medium strength flour and a weak flour are presented, and the effects of rest period, mixing time, and mixing atmosphere on dough properties are discussed.

Effects of Rest Periods of Various Lengths on the Consistency of Maximal Performance on a Muscular Endurance Test

Abstract Thirty-four college men were administered the maximum-dip test during eight consecutive, regularly scheduled physical education class periods. The maximum number of dips possible was measured for continuous, all-out effort and for effort with 5, 7, or 10 sec. of rest between each two dips. Each of these four testing conditions was repeated on the next testing day after original measurement. Coefficients of correlation were computed between maximum-dip performances in the four exercise programs. The degree of relationship became increasingly smaller as the rest period increased in length. More than half of the predictive values of continuous, maximum effort was lost in the program with 10 sec. of rest. Considerable variability was observed in the degree of gain in total dips as rest periods of varying lengths were interjected. The nature of the work load is an important factor in interpreting endurance studies.