Cumulative Degradation Research Articles

Cumulative degradation in estuaries: contribution of individual species to community recovery

Cumulative degradation in estuaries: contribution of individual species to community recovery

(Invited) Reliability of SiGe HBTs in Long-Term Operation

The main reliability issue in SiGe HBTs is the cumulative degradation of the base current occurring during combined high collector voltage, high emitter current stress. This ageing is the result of the interplay between oxide interface trap creation and annihilation. Long-term stress tests show that the ageing rate varies significantly over time, reveals saturation behavior, and depends in a much more complex way on stress load as previously assumed. At high enough junction temperatures degradation can be reversed leading to efficient thermal recovery of the HBTs. With simple duty cycles switching between ageing and recovering states it could be demonstrated that pure DC stress represents an upper limit for degradation in SiGe HBTs.

Protected areas in the Atlantic facing the hazards of micro-plastic pollution: First diagnosis of three islands in the Canary Current

Coastal zones and the biosphere as a whole show signs of cumulative degradation due to the use and disposal of plastics. To better understand the manifestation of plastic pollution in the Atlantic Ocean, we partnered with local communities to determine the concentrations of micro-plastics in 125 beaches on three islands in the Canary Current: Lanzarote, La Graciosa, and Fuerteventura. We found that, in spite of being located in highly-protected natural areas, all beaches in our study area are exceedingly vulnerable to micro-plastic pollution, with pollution levels reaching concentrations greater than 100g of plastic in 1l of sediment. This paper contributes to ongoing efforts to develop solutions to plastic pollution by addressing the questions: (i) Where does this pollution come from?; (ii) How much plastic pollution is in the world’s oceans and coastal zones?; (iii) What are the consequences for the biosphere?; and (iv) What are possible solutions?

Double Crossed Step-Down-Stress Accelerated Life Testing for Pneumatic Cylinder Based on Cumulative Damage Model

Double Crossed Step-Down-Stress Accelerated Life Testing (DCSDS-ALT) discussed in this paper was implemented by switch down the double stresses alternately. Compared to constant stress test, step-stress test decreased specimen numbers, time and cost, and eventually well improve the accelerated testing efficiency. For pneumatic cylinder, the step-down-stress testing failure physics can be described as cumulative degradation model. By use of cumulative damage General Log-Linear relationship and Weibull assumption, the failure data obtained were equivalently converted to failure data under constant stress testing. Then the reliability specifications can be derived with better accuracy. The 5% of average lifetime estimation error and 1.85% of the characteristic lifetime error are very satisfying for pneumatic industrial lifetime prediction.

Effect of different buffer agents on in-vessel composting of food waste: Performance analysis and comparative study

This study investigated the performance and feasibility for application of different buffer agent combinations, including K2HPO4/MgSO4, KH2PO4/MgSO4 and NaAc, in composting of food waste. The variations of temperature, pH, O2 consumption, organic mass and ammonia release were monitored. The results showed that addition of all these three types of agents could prolong the thermophilic stage during composting. The amendments of KH2PO4/MgSO4 and NaAc could increase and decrease the final pH levels, respectively. Application of K2HPO4/MgSO4 and NaAc would lead to a peak daily oxygen uptake rate of 10.0 and 12.4 mg/(g·h) respectively, which were all higher than that with KH2PO4/MgSO4 amendment. Similarly, the reactors with K2HPO4/MgSO4 and NaAc were also associated with a higher cumulative oxygen uptake and total organic degradation rate. The amendment of NaAc resulted in a higher ammonia loss than the other two agents. More inorganic nitrogen contents were observed in the series with K2HPO4/MgSO4 and NaAc. It can be concluded that K2HPO4/MgSO4 additive showed the most favorable influence on composting performance. The results of this study will have important implications for developing appropriate treatment approach for food waste composting.

Photocatalytic Degradation of Phytotoxic Substances in Waste Nutrient Solution by Various Immobilized Levels of Nano-TiO2

The photocatalytic degradation effectiveness of six selected typical phytotoxic substances (ferulic, benzoic, gallic, salicylic, tannic, and acetic acid) by two levels of 10 nm TiO2 (11 and 22 g/m2) immobilized on tiles under 254 nm of UV light irradiation was investigated. The results showed that the immobilized nano-TiO2 significantly degraded all phytotoxic substances dissolved in distilled water, and the cumulative degradation rates of ferulic, benzoic, gallic, salicylic, tannic, and acetic acid reached 22.2, 33.6, 48.2, 56.9, 57.5, and 76.0 % after 6 h of treatment, respectively. Furthermore, the cumulative degradation rates of six phytotoxic substances by immobilized nano-TiO2 were different remarkably, i.e., salicylic acid > benzoic acid, gallic acid > ferulic acid, acetic acid > tannic acid. The maximal photocatalytic degradation efficiencies of all phytotoxic substances appeared at the first 2 h in the three experiments. During the 6-h treatment period, the photocatalytic degradation efficiency of all phytotoxic substances decreased gradually. There was no significant difference in the photocatalytic degradation of benzoic acid and ferulic acid between the two levels of immobilized nano-TiO2 treatments, whereas a significant difference was found in the photocatalytic degradation of salicylic acid, gallic acid, tannic acid, and acetic acid. In a word, nano-TiO2 photocatalysis is an effective method to degrade phytotoxic substances. And the photocatalytic degradation effectiveness of six typical phytotoxic substances may be related to their structures.

Increase of long-chain branching by thermo-oxidative treatment of LDPE: Chromatographic, spectroscopic, and rheological evidence

Low-density polyethylene was thermo-oxidatively degraded at 170 °C, i.e., degraded in the presence of air, by a one thermal cycle (1C) treatment during times between 30 and 90 min, and by a two thermal cycles (2C) treatment, i.e., after storage at room temperature, an already previously degraded sample was further degraded during times between 15 and 45 min. Characterization methods include gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, as well as linear and nonlinear rheology. A reduction of molar mass was detected for all degraded samples by GPC, as well as an increase of the high molar mass fraction of the 1C sample degraded for the longest time. Intrinsic viscosity measurements indicate also a reduction of molar mass with increasing degradation times for both 1C and 2C samples. Thermo-oxidation is confirmed for 1C and 2C samples by analyzing specific indices in FTIR. Linear viscoelasticity seems to be in general only marginally affected by thermo-oxidative exposure, while the enhanced strain-hardening effect observed in uniaxial extension experiments presents a clear evidence for an increased long-chain branching (LCB) content in both 1C and 2C samples. Elongational viscosity data were analyzed by the molecular stress function (MSF) model as well as the Wagner-I model, and for both models, quantitative description of the experimental data for all samples was achieved by fit of only one nonlinear model parameter. Time-deformation separability was confirmed for all samples degraded, 1C as well as 2C, for cumulative degradation times of up to 90 min. The characterization by GPC was confronted with the characterization obtained from nonlinear rheology. It can be stated that elongational rheology is a powerful method to detect structural changes due to thermo-oxidative degradation, especially the formation of enhanced LCB. It has the further advantage that experimental data can be quantified by a single nonlinear model parameter of constitutive equations like the MSF or the Wagner-I model.

Equivalent constitutive model of steel with cumulative degradation and damage

To accurately predict the response of steel frames subjected to strong earthquakes, a uniaxial equivalent constitutive model of structural steel under cyclic loading is proposed for fiber beam element model, considering cumulative degradation and damage of strength and stiffness. The model consists of three types of skeleton curves, hysteresis criteria and degraded criteria, and each criterion is described by mathematical expressions with related dimensional parameters. By using the user subroutine interfaces UMAT provided by finite element software ABAQUS, the equivalent model was implemented as fiber beam element model. The proposed model was proved correct and available with comparison of typical experimental results including static cyclic loading tests of members and non-linear time history tests of structures. In the last, the model was applied in a four-storey frame for dynamic time history analysis with comparison of traditional bilinear model. The research shows that: the proposed model is independent of tests and three-dimensional models well simulate the degraded characteristics of strength and stiffness and accurately predict the failure modes. The model balances both computational accuracy and efficiency, which provides a powerful tool for nonlinear analysis of steel frames subjected to strong seismic excitation.

OPTIMAL REPLACEMENT POLICIES UNDER ENVIRONMENT-DRIVEN DEGRADATION

We examine the problem of optimally maintaining a stochastically degrading system using preventive and reactive replacements. The system's rate of degradation is modulated by an exogenous stochastic environment process, and the system fails when its cumulative degradation level first reaches a fixed deterministic threshold. The objective is to minimize the total expected discounted cost of preventively and reactively replacing such a system over an infinite planning horizon. To this end, we present and analyze a Markov decision process model. It is shown that, for each environment state, there exists an optimal threshold-type replacement policy. Additionally, empirical evidence suggests that, when the environment process is monotone, and the state-dependent degradation rates are totally ordered, the optimal threshold is monotone. Lastly, we derive closed-form bounds on the optimal thresholds.

Structural reliability of offshore platforms considering fatigue damage and different failure scenarios

Structural systems will normally fail as a consequence of a chain of different components failure es. In this paper, fatigue reliability of fixed offshore platforms is investigated by analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, it is divided into a finite number of sub-scenarios. All combinations of time sequences are generated for a given sequence of failures, using a specially developed program.In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. A large number of sub-scenarios should be analyzed, therefore implementing time consuming traditional methods for evaluating fatigue reliability may be unrealistic, and a simplified and accurate method is required. Herein, an “Artificial transfer function” is used to calculate the cumulative fatigue degradation in components. The preciseness of the proposed method is evaluated using a numerical model, and then, it is used to calculate the occurrence probability of each sub-scenario. Based on the calculated values, probability of occurrence is obtained for each scenario, and finally, the failure probability of entire system is calculated. The proposed method can be used in inspection planning and evaluating the life extension of existing offshore platforms.

A Geographic Model to Assess and Limit Cumulative Ecological Degradation from Marcellus Shale Exploitation in New York, USA

Davis, J. B., and G. R. Robinson. 2012. A geographic model to assess and limit cumulative ecological degradation from Marcellus Shale exploitation in New York, USA. Ecology and Society 17(2): 25. https://doi.org/10.5751/ES-04822-170225

Long-term potential performance degradation analysis method based on dynamical probability model

With the increment of lifetimes of functional components in complex system, it is difficult or costly to monitor the degradation process for these components directly. In this paper, we propose a novel method to indirectly track the degradation process. The continuous failure time data of associated components is considered as a time series with implications of potential performance degradation information of the long-lifetime functional components (LLFC), which are connected with these associated components. Firstly, in order to compute the mean time-to-failure (MTTF), we present a dynamic probability model based on nonparametric kernel estimator. In this model, the sliding time-window technique is used to extract statistical samples, and conditional probability function of failure time is acquired by kernel estimation, subsequently the MTTF is calculated. Secondly, we apply the elementary renewal theorem to present a mapping model between the cumulative degradation degree of LLFC and the MTTF of the associated component are described. Thirdly, in order to quantitatively evaluate the degradation level of LLFC, we introduce two indicators, probability entropy and relative degradation rate. We apply our method to evaluate the performance degradation of the crystallizer vibro-bench. Results show that the method is available to evaluate the degrees of performance degradation of LLFC even though the degradation data cannot be obtained directly. Meanwhile, the method can auto-adjust itself to meet the different statistical sample to overcome the limitation of parameter distribution model. Furthermore, the method can help us to identify the main reason of breakdown and make correct maintenance decision.

Double-Crossed Step-Stress Accelerated Life Testing for Pneumatic Cylinder

This paper discusses the principle and method of Double-Crossed Step-Down-Stress Accelerated Life Testing (DCSDS-ALT) for pneumatic cylinders. As to pneumatic cylinder, the step-down-stress testing failure physics can be described as cumulative degradation model. Temperature and frequency are normally chosen as the test stresses. The failure data obtained under DCSDS-ALT testing steps can be converted to those under constant stress testing. And the reliability specifications can be derived accordingly. To compare Double-stress ALTs with traditional constant stress testing shows Double-stress ALTs can meet the accuracy demand. The 5% of average lifetime estimation error and 1.85% of the characteristic lifetime error are very satisfying for pneumatic industrial lifetime prediction.

Optimal maintenance policies for systems subject to a Markovian operating environment

Many stochastic models of repairable equipment deterioration have been proposed based on the physics of failure and the characteristics of the operating environment, but they often lead to time to failure and residual life distributions that are quite complex mathematically. The first objective of our study is to investigate the potential for approximating these distributions with traditional time to failure distribution. We consider a single-component system subject to a Markovian operating environment such that the system’s instantaneous deterioration rate depends on the state of the environment. The system fails when its cumulative degradation crosses some random threshold. Using a simulation-based approach, we approximate the time to first failure distribution for this system with a Weibull distribution and assess the quality of this approximation. The second objective of our study is to investigate the cost benefit of applying a condition-based maintenance paradigm (as opposite to a scheduled maintenance paradigm) to the repairable system of interest. Using our simulation model, we assess the cost benefits resulting from condition-based maintenance policy, and also the impact of the random prognostic error in estimating system condition (health) on the cost benefits of the condition-based maintenance policy.

Evaluation of high‐temperature exposure of photovoltaic modules

ABSTRACTPhotovoltaic (PV) modules operate at temperatures above ambient owing to the thermal energy of sunlight. The operating temperature primarily depends on the ambient temperature, incident sunlight, mounting configuration, packaging configuration, and wind speed. In this paper, the cumulative thermal degradation is modeled to follow Arrhenius behavior. The data are analyzed to determine the constant temperature that would give average aging equivalent to the variable temperatures observed in the field. These equivalent temperatures are calculated for various locations using six configurations, providing a technical basis for defining accelerated thermal‐endurance and ‐degradation testing. This data may also be useful as a starting point for studies of the combined effects of elevated temperature and other factors such as UV, moisture, and mechanical stress. Copyright © 2011 John Wiley & Sons, Ltd.

Investigation of polypropylene degradation during melt processing using a profluorescent nitroxide probe: A laboratory-scale study

Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescence technique. The profluorescent nitroxide probe, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was added to PP during melt processing to act as a sensor for carbon-centred radicals. Trapping of carbon-centred radicals, formed during degradation of PP, led to an increase in fluorescence emission from TMDBIO adducts. Through analysis of viscosity changes during processing cumulative chain scission degradation was estimated. At processing temperatures of 210°C or below, fluorescence emission from TMDBIO adducts could be correlated with cumulative chain scissions when the number of chain scissions was small. At higher temperatures, a correlation was not observed most probably due to radical-trap instability rather than decomposition of the TMDBIO. Thus, TMDBIO may be used as a profluorescent sensor for degradation of PP during melt processing when the processing temperature is 210°C or below.

Controle de tráfego agrícola e atributos físicos do solo em área cultivada com cana-de-açúcar

O objetivo deste trabalho foi avaliar o efeito do controle de tráfego agrícola na compactação do solo em áreas cultivadas com cana-de-açúcar no sistema de colheita mecanizada. O trabalho foi realizado em delineamento de blocos ao acaso, em parcelas subsubdivididas com os tratamentos: colheita mecanizada tradicional; corte mecanizado com controle de tráfego; e corte mecanizado com controle de tráfego e uso do piloto automático. Os atributos físicos do solo foram avaliados nas camadas de 0,0-0,1, 0,1-0,2 e 0,2-0,3 m de profundidade, na linha de plantio, no local em que o rodado passa e no entrerrodado. Avaliaram-se também os efeitos desses tratamentos sobre a produtividade da cana-de-açucar, respectivamente. O tráfego das máquinas agrícolas aumenta a densidade do solo e diminui o diâmetro médio ponderado dos agregados e a macroporosidade na linha de rodado em relação à linha de plantio, o que causa a degradação cumulativa da qualidade física do solo, ao longo dos anos de cultivo. Os dois anos de controle de tráfego agrícola da colheita não influenciaram os atributos físicos do solo estudados.

Land-use changes and their impacts on soil degradation and surface runoff of two catchments of Northern Ethiopia

Land-use/land-cover changes and their associated impact on environment in the period from 1964 to 2006 was studied in two catchments located in the highland of Tigray using geographic information system and remote-sensing approaches supplemented with field measurements. Results show that, for all periods, cultivated land constitutes the most prevalent (>60%) land-use type and shows a total increase of 1.7 ha y−1 at Gum Selassa and a decrease of 5.5 ha y−1 at Maileba. Forest and woodland suffered more damage in both areas losing 32.8 ha (100%) and 53 ha (100%), respectively at Gum Selassa; and 1.74 ha (96.7%) and 52.7 ha (100%) at Maileba over four decades. At Gum Selassa, shrubland decreased by 1.26 ha y−1 while at Maileba it showed a slight positive increment of 0.38 ha y−1. Area under settlement increased by a greater magnitude at Maileba (6.3 ha y−1) and a slight increase at Gum Selassa (1.4 ha y−1) in response to the rapid population increase. These changes in land uses/cover brought significant deleterious impacts on land degradation and surface runoff. The cumulative degradation index (DI) was negative for all land uses, with a higher value under Eucalyptus plantation (DI=−282) followed by cultivated land (DI=−260) at Maileba. Changes in land use/cover also decreased the water-storage capacity of soils by 1.63 and 1.09 mm y−1 at Gum Selassa and Maileba, respectively, with a corresponding increase in surface runoff by 2.7 and 2.3 mm y−1. Generally, the observed changes in land degradation and surface runoff are highly linked to the change in land use/land cover.

Dependence of facet stress on reliability of AlGaInAs edge-emitting lasers

The relationship between facet stress and reliability of AlGaInAs edge-emitting lasers is unclear despite it being an important issue. We prepared two 1.3 μm AlGaInAs Fabry–Pérot buried-heterostructure (BH) lasers that were identical except that they had tensile and compressive stress at the facet. The magnitude of the facet stress was controlled to be approximately 200 MPa in both lasers. We performed three reliability tests. In forward-biased electrostatic discharge tests, which can evaluate the resistance to optical damage, the cumulative degradation ratio of the compressive stressed laser was 33% lower than that of the tensile stressed laser. This result indicates a reduction in the optical absorption due to enlargement of the energy band gap at the facet. In the long-term aging of the light output power of 8 mW at 85 °C over 5 000 h, no dependence of the facet stress on the lifetime was observed. Since a major limitation of InP-based BH lasers is the BH interface, the aging results are reasonable. In the accelerated aging of a large current of 200 mA at 85 °C over 800 h, degradation (defined as an increase in the threshold current of over 10%) was observed only in the tensile stressed laser. This degradation differed completely from that caused by optical absorption; dislocation loops covered the entire active layer at the facet. To the best of our knowledge, this is the first time such degradation has been reported. We found the degradation depends on the facet stress and that compressive stress can suppress the degradation.

Biodegradation of rhamnolipid, EDTA and citric acid in cadmium and zinc contaminated soils

Rhamnolipid, a metal sequestering agent produced by Pseudomonas Sp., has been effective in the removal of metals in soil washing technologies. Rhamnolipid has a strong affinity for cadmium (Cd) compared to some other metals (e.g. cobalt (Co), nickel (Ni)) and might also be useful in chelate-assisted phytoextraction. There have been many studies investigating the formation of metal–rhamnolipid complexes and the ability of rhamnolipid to remove metals from soil. However, to date, the longevity of rhamnolipid in soil has not been measured. Therefore, this study investigated the rate of rhamnolipid degradation in soils of varying physicochemical properties and contaminated with varying concentrations of Cd and zinc (Zn). The rate of rhamnolipid degradation was compared with ethylene diamine tetraacetic acid (EDTA) and citric acid. Our results indicate that citric acid was rapidly degraded, with 20% degradation occurring between 1 and 4 d depending on the level of soil contamination and 70% degradation within 20 d. EDTA was more persistent in the soils; only 14% of the EDTA was degraded after 20 d. Rhamnolipid had cumulative degradation between those of citric acid and EDTA. In most contaminated soils, cumulative degradation of the chelates and ligands were lower than in the uncontaminated soils. These results show that rhamnolipid may remain in the soil long enough to enhance metal phytoextraction, but not remain long enough to raise concerns regarding metal transport in the long-term.