Long term time dependent frequency analysis of chaotic waves in the weakly magnetized spherical Couette system

The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.

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Long-term performance of prestressed concrete continuous box girders in the natural environment

Canadian Journal of Civil Engineering ◽

10.1139/cjce-2018-0447 ◽

2020 ◽

Vol 47 (7) ◽

pp. 856-864

Author(s):

Guohui Cao ◽

Wang Zhang ◽

Jiaxing Hu ◽

Xirong Peng

Keyword(s):

Prestressed Concrete ◽

Load Test ◽

Time Dependent ◽

Material Strength ◽

Practical Calculation ◽

Box Girders ◽

Load Types ◽

In The Beginning ◽

Support Reactions

A long-term load test performed for 470 days on two two-span prestressed concrete (PC) continuous box girders is reported in this paper. Load types were selected as the test variates, and structural responses such as support reactions, deflections, and concrete strains were monitored. Simultaneously, affiliated experiments such as material strength, creep, and shrinkage tests were conducted to investigate the time-dependent performances of the materials. Data obtained from these tests showed that deflections, strains, and support reactions develop rapidly in the beginning and stabilize afterward; the reactions of mid- and end-supports decline and rise over time, respectively. Time-dependent patterns of deflections and support reactions were analyzed on the basis of an effective modulus method, and a practical calculation method for long-term deflections considering reaction redistributions was proposed. The effects of the service environment on the performance of PC girders were evaluated through an incremental analysis method.

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Time-Dependent Changes in Excitability After One-Trial Conditioning of Hermissenda

Journal of Neurophysiology ◽

10.1152/jn.1997.78.6.3460 ◽

1997 ◽

Vol 78 (6) ◽

pp. 3460-3464 ◽

Cited By ~ 13

Author(s):

Terry Crow ◽

Vilma Siddiqi

Keyword(s):

Time Dependent ◽

Control Group ◽

Type B ◽

Control Groups ◽

Phototactic Behavior ◽

Parallel Processes ◽

Short And Long Term ◽

A Site ◽

Different Levels

Crow, Terry and Vilma Siddiqi. Time-dependent changes in excitability after one-trial conditioning of Hermissenda. J. Neurophysiol. 78: 3460–3464, 1997. The visual system of Hermissenda has been studied extensively as a site of cellular plasticity produced by classical conditioning. A one-trial conditioning procedure consisting of light paired with the application of serotonin (5-HT) to the exposed, but otherwise intact, nervous system produces suppression of phototactic behavior tested 24 h after conditioning. Short- and long-term enhancement (STE and LTE) of excitability in identified type B photoreceptors is a cellular correlate of one-trial conditioning. LTE can be expressed in the absence of STE suggesting that STE and LTE may be parallel processes. To examine the development of enhancement, we studied its time-dependent alterations after one-trial conditioning. Intracellular recordings from identified type B photoreceptors of independent groups collected at different times after conditioning revealed that enhanced excitability follows a biphasic pattern in its development. The analysis of spikes elicited by 2 and 30 s extrinsic current pulses at different levels of depolarization showed that enhancement reached a peak 3 h after conditioning. From its peak, excitability decreased toward baseline control levels 5–6 h after conditioning followed by an increase to a stable plateau at 16 to 24 h postconditioning. Excitability changes measured in cells from unpaired control groups showed maximal changes 1 h posttreatment that rapidly decremented within 2 h. The conditioned stimulus (CS) elicited significantly more spikes 24 h postconditioning for the conditioned group as compared with the unpaired control group. The analysis of the time-dependent development of enhancement may reveal the processes underlying different stages of memory for this associative experience.

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Improving the Long-Term Performance of Elastomeric Seals by Material Behavior Design

Journal of Tribology ◽

10.1115/1.3203148 ◽

2009 ◽

Vol 131 (4) ◽

Cited By ~ 1

Author(s):

Ryan B. Sefkow ◽

Nicholas J. Maciejewski ◽

Barney E. Klamecki

Keyword(s):

Energy Density ◽

Contact Pressure ◽

Strain Energy ◽

Applied Pressure ◽

Material Behavior ◽

Time Dependent ◽

Ring Section ◽

Stiff Material ◽

Elastomeric Seals

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior. The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density.

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Neural network-based prediction of the long-term time-dependent mechanical behavior of laminated composite plates with arbitrary hygrothermal effects

Journal of Mechanical Science and Technology ◽

10.1007/s12206-021-0932-2 ◽

2021 ◽

Author(s):

Sy-Ngoc Nguyen ◽

Chien Truong-Quoc ◽

Jang-woo Han ◽

Sunyoung Im ◽

Maenghyo Cho

Keyword(s):

Neural Network ◽

Mechanical Behavior ◽

Laminated Composite ◽

Composite Plates ◽

Time Dependent ◽

Laminated Composite Plates

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Safety Assessment of Long Term Serviced Pressure Vessels: A Case Study of Typical Refining and Chemical Plants in China

10.1115/pvp2021-61470 ◽

2021 ◽

Author(s):

Zhiyuan Han ◽

Guoshan Xie ◽

Haiyi Jiang ◽

Xiaowei Li

Keyword(s):

Pressure Vessel ◽

Safety Assessment ◽

Failure Modes ◽

Pressure Vessels ◽

Time Dependent ◽

Chemical Plants ◽

Safety Specification ◽

Detailed Assessment

Abstract The safety and risk of the long term serviced pressure vessels, especially which serviced more than 20 years, has become one of the most concerned issues in refining and chemical industry and government safety supervision in China. According to the Chinese pressure vessel safety specification TSG 21-2016 “Supervision Regulation on Safety Technology for Stationary Pressure Vessel”, if necessary, safety assessment should be performed for the pressure vessel which reaches the design service life or exceeds 20 years without a definite design life. However, the safety and risk conditions of most pressure vessels have little changes after long term serviced because their failure modes are time-independent. Thus the key problem is to identify the devices with the time-dependent failure modes and assess them based on the failure modes. This study provided a case study on 16 typical refining and chemical plants including 1870 pressure vessels serviced more than 20 years. The quantitative risk and damage mechanisms were calculated based on API 581, the time-dependent and time-independent failure modes were identified, and the typical pressure vessels were assessed based on API 579. Taking the high pressure hydrogenation plant as an example, this study gave the detailed assessment results and conclusions. The results and suggestions in this study are essential for the safety supervision and extending life of long term serviced pressure vessels in China.

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Stochastic semi-continuous simulation for extreme flood estimation in catchments with combined rainfall–snowmelt flood regimes

Natural Hazards and Earth System Science ◽

10.5194/nhess-14-1283-2014 ◽

2014 ◽

Vol 14 (5) ◽

pp. 1283-1298 ◽

Cited By ~ 20

Author(s):

D. Lawrence ◽

E. Paquet ◽

J. Gailhard ◽

A. K. Fleig

Keyword(s):

Frequency Analysis ◽

Probabilistic Model ◽

Extreme Precipitation ◽

Flood Frequency ◽

Flood Frequency Analysis ◽

Continuous Simulation ◽

Weather Patterns ◽

Extreme Flood ◽

Flood Estimation

Abstract. Simulation methods for extreme flood estimation represent an important complement to statistical flood frequency analysis because a spectrum of catchment conditions potentially leading to extreme flows can be assessed. In this paper, stochastic, semi-continuous simulation is used to estimate extreme floods in three catchments located in Norway, all of which are characterised by flood regimes in which snowmelt often has a significant role. The simulations are based on SCHADEX, which couples a precipitation probabilistic model with a hydrological simulation such that an exhaustive set of catchment conditions and responses is simulated. The precipitation probabilistic model is conditioned by regional weather patterns, and a bottom–up classification procedure was used to define a set of weather patterns producing extreme precipitation in Norway. SCHADEX estimates for the 1000-year (Q1000) discharge are compared with those of several standard methods, including event-based and long-term simulations which use a single extreme precipitation sequence as input to a hydrological model, statistical flood frequency analysis based on the annual maximum series, and the GRADEX method. The comparison suggests that the combination of a precipitation probabilistic model with a long-term simulation of catchment conditions, including snowmelt, produces estimates for given return periods which are more in line with those based on statistical flood frequency analysis, as compared with the standard simulation methods, in two of the catchments. In the third case, the SCHADEX method gives higher estimates than statistical flood frequency analysis and further suggests that the seasonality of the most likely Q1000 events differs from that of the annual maximum flows. The semi-continuous stochastic simulation method highlights the importance of considering the joint probability of extreme precipitation, snowmelt rates and catchment saturation states when assigning return periods to floods estimated by precipitation-runoff methods. The SCHADEX methodology, as applied here, is dependent on observed discharge data for calibration of a hydrological model, and further study to extend its application to ungauged catchments would significantly enhance its versatility.

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Selected Contribution: Chronic intermittent hypoxia enhances respiratory long-term facilitation in geriatric female rats

Journal of Applied Physiology ◽

10.1152/japplphysiol.00476.2003 ◽

2003 ◽

Vol 95 (6) ◽

pp. 2614-2623 ◽

Cited By ~ 37

Author(s):

A. G. Zabka ◽

G. S. Mitchell ◽

E. B. Olson ◽

M. Behan

Keyword(s):

Intermittent Hypoxia ◽

Young Female ◽

Time Dependent ◽

Female Rats ◽

Chronic Intermittent Hypoxia ◽

Middle Aged ◽

Short Term ◽

Hypoxic Response ◽

Long Term Facilitation

Age and the estrus cycle affect time-dependent respiratory responses to episodic hypoxia in female rats. Respiratory long-term facilitation (LTF) is enhanced in middle-aged vs. young female rats ( 72 ). We tested the hypothesis that phrenic and hypoglossal (XII) LTF are diminished in acyclic geriatric rats when fluctuating sex hormone levels no longer establish conditions that enhance LTF. Chronic intermittent hypoxia (CIH) enhances LTF ( 41 ); thus we further predicted that CIH would restore LTF in geriatric female rats. LTF was measured in young (3-4 mo) and geriatric (20-22 mo) female Sasco Sprague-Dawley rats and in a group of geriatric rats exposed to 1 wk of nocturnal CIH (11 vs. 21% O2 at 5-min intervals, 12 h/night). In anesthetized, paralyzed, vagotomized, and ventilated rats, time-dependent hypoxic phrenic and XII responses were assessed. The short-term hypoxic response was measured during the first of three 5-min episodes of isocapnic hypoxia (arterial Po2 35-45 Torr). LTF was assessed 15, 30, and 60 min postepisodic hypoxia. Phrenic and XII short-term hypoxic response was not different among groups, regardless of CIH treatment ( P > 0.05). LTF in geriatric female rats was smaller than previously reported for middle-aged rats but comparable to that in young female rats. CIH augmented phrenic and XII LTF to levels similar to those of middle-aged female rats without CIH ( P < 0.05). The magnitude of phrenic and XII LTF in all groups was inversely related to the ratio of progesterone to estradiol serum levels ( P < 0.05). Thus CIH and sex hormones influence the magnitude of LTF in geriatric female rats.

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