Effect Of Rest Periods Research Articles

Effect of Rest Period on the Fatigue Characteristics of Unmodified and Modified Bitumen

Effect of Rest Period on the Fatigue Characteristics of Unmodified and Modified Bitumen

Effect of Rest Period and Temperature on the Estimation of Fatigue Life of Bituminous Mixture

This paper reports the experimental investigation conducted to study the influence of temperature and rest period on different methods of estimation of fatigue life of the bituminous mixture. Four-point beam bending tests were conducted on the bituminous mixture prepared with one unmodified binder and two different modified binders (crumb rubber modified and elastomer modified binder). The test was conducted at 20 °C and 0 °C using continuous loading and a rest period between two load cycles. The fatigue life was estimated using stiffness modulus and energy dissipation. The performance of three different bituminous mixtures was ranked—ranking a bituminous mixture based on the fatigue performance varied with temperature and loading condition. In addition, the ranking also varied with different post-processing methods adopted.

Impact of rest period on asphalt concrete permanent deformation

Truck platooning has several advantages including congestion reduction, safety, and fuel efficiency. However, there are concerns regarding its impact on pavement performance due to channelized traffic and reduced spacing. A rest period governed by the distance between each truck can have a significant impact on asphalt pavement performance due to time dependent deformation characteristics of asphalt materials. Despite numerous studies available in the literature explaining the rest period effect on fatigue cracking, the impact on permanent deformations is relatively less studied. In this paper, we present the results to characterize the impact of rest period on the permanent deformation characteristics of two asphalt concrete (AC) mixes using four different types of binders. The experimental program included repeated load permanent deformation experiments coupling rest period with various stress and temperature configurations. Increasing rest periods from 0.18 s to 2.5 s increased permanent deformations consistently for the two mixes. The results are consistent with the hardening-relaxation or hardening–softening mechanisms describing the reorientation of the aggregate structure from a more resistant to less resistant state to deformations as rest duration increases. It was also shown with the customized multiple stress creep recovery experiments that the effect of rest period on mixture level permanent deformations could not be attributed to the binders’ deformation characteristics. Rest period impact was found to be as important as temperature and stress magnitude for asphalt mixture’s permanent deformation resistance. Various truck platoon scenarios can be compared to conventional truck configuration and loading assumptions using the results presented in this paper.

Impact of Relaxation Time on Electrochemical Impedance Spectroscopy Characterization of the Most Common Lithium Battery Technologies—Experimental Study and Chemistry-Neutral Modeling

In electrified vehicle applications, understanding the battery characteristics is of great importance as it is the state-of-art principal energy source. The key battery parameters can be identified by one of the robust and nondestructive characterization techniques, such as electrochemical impedance spectroscopy (EIS). However, relaxing the battery cell before performing the EIS method is crucial for the characterization results to be standardized. In this study, the three most common and commercially available lithium-ion technologies (NMC/graphite, LFP/graphite, NCA/LTO) are investigated at 15–45 °C temperature, in the range of 20–80% state of charge (SoC) and in fresh and aged state of health (SoH) conditions. The analysis shows that the duration of the relaxation time before impedance measurement has an impact on the battery’s nonlinear behavior. A rest time of 2 h can be proposed, irrespective of battery health condition, considering neutral technology-based impedance measurement. An impedance growth in ohmic and charge transfer characteristics was found, due to aging, and the effect of rest periods was also analyzed from an electrochemical standpoint. This experimental data was fitted to develop an empirical model, which can predict the nonlinear dynamics of lithium technologies with a 4–8% relative error for longer rest time.

Impact of Relaxation Time on Electrochemical Impedance Spectroscopy Characterization of the Most Common Lithium Battery Technologies – Experimental Study and Chemistry-Neutral Modeling

In the electrified vehicle application, understanding of the battery characteristics is very important as it is the state-of-art principal energy source. The key battery parameters can be identified by one of the robust and non-destructive characterization techniques as Electrochemical Impedance Spectroscopy (EIS). However, relaxing the battery cell before performing the EIS method, is crucial for characterization results that should be standardized.In this study, the three most common and commercially available lithium-ion technologies (NMC/graphite, LFP/graphite, NCA/LTO) are investigated at 15-45oC temperature, in the range of 20-80% state of charges (SoCs) and with fresh and aged state of health (SoH) conditions. The analysis shows that the duration of the relaxation time spell before impedance measurement has an impact on the battery's non-linear behavior. A rest time of 2h can be proposed irrespective of battery health condition considering neutral technology-based impedance measurement. Impedance growth in ohmic and charge transfer characteristics is found due to aging and the effect of rest periods are analyzed as well, from an electrochemical standpoint. This experimental data is fitted to develop an empirical model, which can predict the non-linear dynamics of lithium technologies with a 4-8% relative error for longer rest time.

Evolution of asphalt binder stiffness during fatigue loading and rest periods and its impact on fatigue life

Fatigue in asphalt materials is evaluated in the laboratory through continuous cyclic loading tests, whereas field loading in pavements is intermittent. Further studies on the effect of rest periods (RPs) on asphalt binder stiffness and fatigue life is of paramount importance. This paper investigates three 50/70 penetration grade binders with respect to their stiffness and fatigue properties. Fatigue was tested at 19 °C using three strain amplitudes. Tests with recovery time (5 RPs of 4 h each) were performed. Results show stiffness recovery during rest, however such recovery is not associated with an increase in the number of cycles to failure.

Recovery capacity of electroconductive asphalt mortars under the influence of magnetic fields

The self-healing capacity of electroconductive asphalt materials can be enhanced by the use of induction heating. The highest enhancement of this self-healing capacity is produced in the early stages of the fatigue life of the material. During the early stages of the fatigue life, micro-cracks appear in the mastics/mortars that compose the asphalt mixture. In this sense, by the use of micromechanics, it could be possible to study the mastics/mortars to characterize the healing performance of asphalt mixtures under induction heating treatments. This study evaluates the recovery capacity of electroconductive asphalt mortars (EM), after multiple applications of induction heating and rest periods. In order to use a representation of materials that can be produced on-site, the EM were manufactured with the smallest sizes of metallic fibres obtained from the recycling process of vehicle tires at the end of their useful life. Results showed that half of the recovery capacity of the EM was produced by the effect of induction heating and the remainder by the effect of rest periods. This recovery capacity generates an extension in the fatigue life of the EM, which along with the use of a high asphalt content (higher than 7%) and fine aggregates (less than 9.5 mm), provides the conditions to use the EM in the construction of interlayer systems. The use of EM as interlayer systems, additionally to delay the reflection of cracks in the surface layers of the pavement, seems to represent a safe strategy to introduce their use on-site.

Abstract P008: Pulse Pressure Following a Brief Patient Rest Period: Age and Gender Variations

Background: Increased pulse pressure (PP) is an independent determinant of cardiovascular disease. The effect of rest period on office-based systolic blood pressure has been previously reported, but not on PP in particular. Whether such rest period impacts the measured pulse pressure, and the variability of such response with age and gender remains unknown. Methods: Patient charts reviewed in University-based cardiology clinic identified 170 encounters which contained blood pressure (BP) re-measurement data due to elevated initial BP of > 130/80 mmHg. BP was measured initially by the nurse, with the patient in a sitting position and the arm resting at the level of the heart. If BP was > 130/80 mmHg, it was repeated by the physician after resting the patient for 15 minutes. There were 112 (66%) elderly patients ≥ 60 years of age and 58 (34%) younger patients < 60 years of age. Among the elderly patients, there were 51 males (46%) and 61 females (54%). Results: Among all encounters, after a brief rest period, initial pulse pressure (PP) of 67 ± 2 mmHg decreased to 62 ± 1 mmHg (5 mmHg; P < 0.01). PP decreased by 8 mmHg in the elderly (72 ± 2 to 64 ± 2 mmHg; P < 0.01) but did not significantly change in the young (56 ± 3 to 58 ± 3 mmHg; P = NS). PP decrease among the elderly was more pronounced in females (11 mmHg; 76 ± 4 to 65 ± 2 mmHg; P < 0.01) compared with males (4 mmHg; 68 ± 3 to 64 ± 2 mmHg; P = 0.03). Conclusion: Hypertension is a challenging public health problem. The new ACC/AHA High Blood Pressure Guidelines have decreased the range for Stage 1 hypertension to systolic blood pressure of 130-139 mmHg, and diastolic blood pressure of 80-89 mmHg, with normal blood pressure as less than 120/80 mmHg. Blood pressure guidelines recommend that prior to BP measurement, persons should be seated quietly for at least 5 minutes in a chair, with feet on the floor, and arm supported at heart level; which resulted in significant decrease in pulse pressure in our patients. We show that while a decrease in pulse pressure was confined to the elderly, elderly females had a more pronounced PP decrease compared to males; both, however, fell to the same level. White coat hypertension may explain this observation, since it is more frequent in elderly females. The implication of this observation is that physicians should take extra care in re-measuring the blood pressure and pulse pressure, especially in elderly females, in whom a more pronounced drop in pressure may be observed after a brief rest period, and thereby, result in reclassifying their risk and need for treatment.

VECD investigation and quantification of rest period healing within pulse-rest loading

ABSTRACT The viscoelastic continuum damage (VECD) model has been widely recognised as a characterisation method for asphalt mixture’s fatigue and damage behaviour. Rest periods between loading cycles can recover stiffness and extend fatigue life. However, there is still a lack of approach to quantify the effect of rest period after each load cycle (pulse-rest loading). In this paper, a series of simplified VECD tests are conducted with different length of rest period. Based on smeared continuum damage method, rest period based damage characteristic curves are produced at two different temperatures, with rest period healing effect critically evaluated. VECD results indicate that longer rest period improves healing effect, and higher temperature incurs greater maximum healing effect when rest period is long. Based on regression fitting technique, a novel rest period damage function has been developed. The new function can be used to overcome laboratory fluctuation of VECD tests with pulse-rest loading, to produce accurate smeared damage characteristic curves with any rest period length. It has benefit of saving experiment time and improving accuracy. This work also proposes laboratory procedures and data processing notices for the production of rest period damage functions for future use.

Effects of intermittent liquid addition on heap hydrodynamics

Heap leaching is a well-known mineral processing technique, whereby crushed low grade ore is used for valuable metal extraction. The technique is typically used to extract precious and base metals, however, the metal extraction efficiency is relatively low. Even though reaction kinetics are extensively studied in heap leaching, the detailed hydrodynamic studies are still required to understand the underlying flow aspects. Heap hydrodynamics plays an important role in the transport of both leaching reagents and dissolved metal species and thus uniform liquid distribution through the ore mass is required. However, liquid channelling within the heaps has been identified as one of the main contributing factors for non-uniform liquid distribution. Since liquid channelling is supposed to be an inherent property in heap leaching systems, this work was primarily designed to explore the suitable techniques to improve liquid distribution and minimise liquid channelling in heaps. Intermittent liquid addition is employed and its effect on liquid channelling is studied, which has not been reported in the literature despite the application of it in industrial heaps. Both narrowly sized ore (16–20 cm) and realistic ore mixtures (2.36–25 cm) were studied in a pseudo 2-D Perspex column and the effect of rest period in intermittent leaching on liquid channelling was studied using out-flow liquid distribution measurements. The experimental results showed improved out-flow liquid distribution profiles and less channelling flow features in intermittent liquid addition conditions. The liquid out-flow profiles in both the packed bed systems were improved by resulting more flow paths through the particles and reduced features of liquid channelling. The narrowly sized fraction formed a near-Gaussian liquid distribution, which is the expected continuous probability based theoretical flow profile with drip emitter based liquid addition in heaps.

Rendimiento de forraje, composición química y morfogénesis de Megathyrsus maximus cv. Mombaça bajo períodos de descanso

The effects of rest periods (14, 21, 28, 35, 42 and 49 days) on green dry matter (GDM) yield, chemical composition and morphogenetic and structural characteristics of Megathyrsus maximus cv. Mombaça were evaluated under natural field conditions. GDM yields and regrowth increased consistently with highest rest periods. The leaf appearance and leaf expansion rates are inversely proportional to the rest periods, occurring the inverse for average leaf length, leaf area index and foliar senescence rate. Maximum GDM yields, regrowth yields, number of leaves tiller-1, average leaf length and leaf area index were obtained with rest periods at 36.4; 39.2; 40.8; 39.6 and 41.3 days. These data suggest that grass grazing at 35 to 42 days of rest period were optimal for obtain maximum yields and regrowth of rich forage.

Abstract 072: Paradoxical Blood Pressure Increase After Brief Patient Rest Period

Background: Office-based blood pressure (BP) measurement is subject to variations which may influence management. Objective: To assess the effect of rest period on repeat BP measurement. Methods: Clinic charts were review identified 200 encounters with BP re-measurement due to initial BP of > 130/80 mmHg. BP was measured initially by a nurse, with the patient in a sitting position and the arm resting at the level of the heart. If BP was > 130/80 mmHg, it was repeated by physician after resting the patient for 15 minutes. Mean age was 64 ± 12 years. Results: Among encounters with BP re-measurement, initial systolic BP (SBP) was 154 ± 25 mmHg, and diastolic BP 87 ± 15 mmHg. Upon re-measurement, 135 of 200 patients (68%) had lower SBP of 144 ± 21 mmHg compared with initial SBP of 161 ± 25 mmHg; a 17 mmHg drop (P < 0.01). However, 53 of 200 patients (27%) had higher SBP of 149 ± 17 mmHg compared with initial SBP of 138 ± 14 mmHg; an 11 mmHg increase (P < 0.01). Twelve patients (6%) had no BP change. In 47% (93/200) of encounters, BP re-measurement necessitated medication changes. Compared with the remaining patients, those with paradoxical increase in BP were younger (60 ± 9 years versus 66 ± 12 years; p < 0.01), and with lower initial SBP (138 ± 14 versus 161 ± 25, p < 0.01). Discussion: Hypertension is a major challenging public health problem. JNC 8 guidelines recommend that prior to BP measurement, patients should be seated quietly for at least 5 minutes in a chair, with feet on the floor, and arm supported at heart level; this may decrease initially elevated BP. However, 27% of our patients exhibited a paradoxical response, with elevation of the SBP after a 15 minute period of rest. The cause of this paradox is not clear, but may have resulted from white-coat hypertension during the rest period, which may be more common in younger patients, as noted in our study. This underscores the importance of ambulatory BP monitoring, especially in subsets of patients prone to having labile or white coat hypertension, to avoid the cost and side effects of BP overtreatment. Studying larger number of patients, and including patient with normal initial BP, may help clarify the mechanism and clinical significance of this observation.

Dinámica de la acumulación del forraje y morfogénesis de Urochloa brizantha cv. Xaraés bajo períodos de descanso

he effects of rest periods (14, 21, 28, 35, 42 and 49 days) on green dry matter (GDM) yield, chemical composition and morphogenetic and structural characteristics of Urochloa brizantha cv. Xaraés were evaluated under natural field conditions. GDM yields and regrowth, medium blade length, leaf elongation and leaf senescence rate increased consistently with highest rest periods however the nitrogen, phosphorus, calcium, magnesium and potassium contents and leaf appearance rate decreased. Maximum GDM yields, number of leaves tiller-1, leaf elongation rate and leaf area index were obtained with rest periods at 40.8; 40.2; 26.2 and 48.2 days. These data suggest that grass grazing at 35 to 42 days of rest period were optimal for obtain maximum yields and regrowth of rich forage.

Investigation on geomechanical behaviour and microstructure of cement-stabilized fly ash

Present laboratory study investigated the geomechanical behaviour of cement-stabilised fly ash. Class F fly ash collected from two different power plants in India was used in the study. Fly ash was stabilised with varying proportions of cement up to 10%, added in the ratio of dry weight of fly ash. Effects of addition of cement were evaluated on compacted fly ash–cement mix at optimum moisture content for rest period of 7, 14, 21 and 28 days. Results showed that the hydraulic conductivity of both the fly ash samples decreased by an order in magnitude when added with 10% cement. Effects of rest periods on hydraulic conductivity of cement-stabilised fly ash were found to be insignificant. Unconfined compressive strength of the cement-stabilised fly ash samples increased with increase in the cement content and rest periods, while the compression index of the stabilised samples decreased with increase in cement content. Different geomechanical behaviour was correlated with the microstructural changes in cement-stabilised fly ash, obtained through Field Emission Scanning Electron Microscope (FMSEM). Test results showed that cement stabilisation improved the engineering behaviour of both the fly ash, which may aid in their application as resource geomaterial.

The Effect of Rest Period on Response Likelihood

The Effect of Rest Period on Response Likelihood

Rigorous solution for 1-D consolidation of a clay layer under haversine cyclic loading with rest period.

Presented in this paper is a rigorous solution of the conventional Terzaghi one-dimensional consolidation under haversine cyclic loading with any rest period. The clay deposit is either permeable at both top and bottom or permeable at the top and impermeable at the bottom. This exact analytical solution was achieved using Fourier harmonic analysis for the periodic function representing the rate of imposition of excess pore water pressure. The double Fourier series in the rigorous solution was found to be rapidly convergent. The analysis of excess pore water pressure and effective stress is done in the Matlab 2010 environment. Both the effects of rest period and frequency of cyclic loading are investigated. The analysis reveals that the excess pore water pressure arrives the steady-state at a time factor T v of about 2. Furthermore, finite element method (FEM) is applied to solve numerically the corresponding consolidation problem and the FEM solution is compared to the analytical solution showing a good match.

Rendimento de forragem e morfogênese de Brachiaria brizantha cv. Marandu sob diferentes períodos de descanso

The effects of rest periods (21, 28, 35, 42 and 49 days) on green dry matter (GDM) yield, chemical composition and morphogenetic and structural characteristics of Brachiaria brizantha cv. Marandu were evaluated under natural field conditions. GDM yields and regrowth, medium blade length, leaf elongation and leaf senescence rate increased consistently with rest period, however the nitrogen, phosphorus, and magnesium contents and leaf appearance rate decreased, while calcium and potassium contents were not affected by rest period. Maximum GDM yields, number of leaves/tiller, leaf elongation rate and leaf area index were obtained with rest periods at 38.8; 38.7; 27.4 and 47.8 days. These data suggest that grass grazing at 35 to 42 days of rest period were optimal for obtain maximum yields and regrowth of rich forage.

Study of loading waveform, loading duration, rest period and stress level on fatigue life of asphalt mixtures

Article history: Received October 6, 2014 Accepted 2 February 2015 Available online 2 February 2015 The main objective of this paper is to study the effects of haversinse and triangular loading waveforms on the fatigue life of Hot Mix Asphalt (HMA) specimens. Effects of load duration, rest period and stress level are also studied for the asphalt mixtures at 25oC. An indirect tensile test with strain control was performed to determine the fatigue life of asphalt. The fatigue tests were performed at two stress levels (170 and 250 kPa), two waveforms (haversine and triangle), three load duration (100, 200, 400 ms), and two rest period to load duration ratios (4 and 9). The obtained results showed that fatigue life of haversine waveform is less than fatigue life of triangle waveform. As the area under the loading curve is increased (stress level is increased or deformed), effect of rest period on the fatigue life decreases. On the other hand, as the tire contact area is increased, the induced tire pressure reduction decreases its destructive effects on the asphalt layer. As the load duration is decreased, fatigue life will increase. This effect is more pronounced for lower stress levels than the higher stress levels. © 2015 Growing Science Ltd. All rights reserved.

Effect of Rest Period on Germination of the Common Reed Seeds from the Water Bodies of the Chornobyl Exclusion Zone

Effect of Rest Period on Germination of the Common Reed Seeds from the Water Bodies of the Chornobyl Exclusion Zone

Abstract 167: Age and Gender Differences in Pulse Pressure Response to Repeat Blood Pressure Measurement After Brief Patient Rest Period

BACKGROUND: Increased pulse pressure (PP) is an independent determinant of cardiac disease. The effect of rest period on office-based systolic blood pressure has been previously reported, but not on PP in particular. OBJECTIVE: To assess the effect of age and gender on repeat PP measurement after a brief rest period in an outpatient cardiology clinic. METHODS: Patient charts reviewed in University-based cardiology clinic identified 170 encounters which contained BP re-measurement data due to elevated initial BP of > 130/80 mmHg. BP was measured initially by a nurse, with the patient in a sitting position and the arm resting at the level of the heart. If BP was > 130/80 mmHg, it was repeated by physician after resting the patient for 15 minutes. There were 112 (66%) elderly patients ≥ 60 years of age and 58 (34%) younger patients < 60 years of age. Among the elderly patients, there were 51 males (46%) and 61 females (54%). RESULTS: Among all encounters, after a brief rest period, initial PP of 67 ± 2 mmHg decreased to 62 ± 1 mmHg (5 mmHg; P < 0.01). PP decreased by 8 mmHg in the elderly (72 ± 2 to 64 ± 2 mmHg; P < 0.01) but did not significantly change in the young (56 ± 3 to 58 ± 3 mmHg; P = 0.3). PP decrease among the elderly was more pronounced in females (11 mmHg; 76 ± 4 to 65 ± 2 mmHg; P < 0.01) compared with males (4 mmHg; 68 ± 3 to 64 ± 2 mmHg; P = 0.03).DISCUSSION: Hypertension is a challenging public health problem. JNC 7 guidelines recommend that prior to BP measurement, persons should be seated quietly for at least 5 minutes in a chair, with feet on the floor, and arm supported at heart level; which resulted in significant decrease in pulse pressure in our patients. We show that while a decrease in pulse pressure was confined to the elderly, elderly females had a more pronounced PP decrease compared to males; both, however, fell to the same level. White coat hypertension may explain this observation, since it is more frequent in elderly females. The implication of this observation is that physicians should take extra care in remeasuring the blood pressure and pulse pressure, especially in elderly females, in whom a more pronounced drop in pressure may be observed after a brief rest period, and thereby, result in reclassifying their risk and need for treatment.