Large Number Of Cycles Research Articles

Model-based comparison of sequencing batch reactors and continuous-flow activated sludge processes for biological wastewater treatment

This study compares, based on mathematical modelling, continuous-flow activated sludge processes (CAS) and sequencing batch reactors (SBR). The steady-state or periodic steady-state of CAS and SBR processes is compared for a feed composed of readily or slowly biodegradable substrates, for carbon and for carbon and nitrogen removal. The simulations are carried out for different values of the SRT (solids residence time), HRT (hydraulic residence time), number of cycles and internal recycle. If the SRT is large enough, the SBR can remove the influent biodegradable COD completely, while the CAS has a residual effluent COD concentration. For carbon and nitrogen removal, the SBR can remove the ammonia completely while the CAS has a residual effluent ammonia concentration. For typical values of the operating parameters, the CAS gives higher total nitrogen removal than the SBR, which becomes comparable to the CAS only for a large number of cycles per day.

Identification of highly active surface iron sites on Ni(OOH) for the oxygen evolution reaction by atomic layer deposition

Atomic layer deposition (ALD) has become a versatile tool in catalysis, allowing for precise synthesis of catalysts useful for gaining fundamental understanding of complex systems. In this work, ALD was used to perform surface-directed modification of Ni(OH)2/Ni(OOH) electrocatalysts for the oxygen evolution reaction (OER) to elucidate the different roles of iron as a surface dopant and of iron distributed throughout the NiOOH structure. Electrochemical and material characterization of FeOx ALD-modified Ni(OH)2 indicates that iron is deposited on the surface of Ni(OH)2 sheets without modifying its bulk properties. Sub-monolayer amounts of iron were deposited on the surface of Ni(OH)2 using low cycle numbers of ALD. This surface iron results in high OER activity, characteristic of Ni-Fe(OOH) catalysts. Ni(OH)2/Ni(OOH) catalysts modified to incorporate iron throughout the structure were prepared by depositing large cycle numbers of FeOx ALD, which results in the deposition of a Fe2O3 overlayer. Corrosion of this Fe2O3 overlayer during electrochemical cycling in alkaline electrolyte leads to the incorporation of iron throughout the structure of Ni(OH)2/Ni(OOH) while leaving some iron at the surface. Incorporation of iron throughout the Ni(OH)2/Ni(OOH) structure was found to increase OER geometric activity for thick, high surface area Ni(OH)2/Ni(OOH) catalysts. Lastly, Ni-FeOx electrocatalysts synthesized fully by ALD were investigated for the OER; these catalysts demonstrated high OER activity and potential for photocatalysis applications.

Geometric detection of hierarchical backbones in real networks

Hierarchies permeate the structure of real networks, whose nodes can be ranked according to different features. However, networks are far from tree-like structures and the detection of hierarchical ordering remains a challenge, hindered by the small-world property and the presence of a large number of cycles, in particular clustering. Here, we use geometric representations of undirected networks to achieve an enriched interpretation of hierarchy that integrates features defining popularity of nodes and similarity between them, such that the more similar a node is to a less popular neighbor the higher the hierarchical load of the relationship. The geometric approach allows us to measure the local contribution of nodes and links to the hierarchy within a unified framework. Additionally, we propose a link filtering method, the similarity filter, able to extract hierarchical backbones containing the links that represent statistically significant deviations with respect to the maximum entropy null model for geometric heterogeneous networks. We applied our geometric approach to the detection of similarity backbones of real networks in different domains and found that the backbones preserve local topological features at all scales. Interestingly, we also found that similarity backbones favor cooperation in evolutionary dynamics modelling social dilemmas.

Cyclic and creep combination effects on the long-term undrained behavior of overconsolidated clay

Soft soil subjected to cyclic loading typically exhibits an increase in excess pore pressure under undrained condition which brings the soil to an overconsolidated state. Then, under a subsequent large number of cycles (e.g. more than one million) which also takes time, the creep at overconsolidated state influences the cyclic effect and thus results in a complicated long-term undrained behavior. This paper aims to clarify this long-term undrained behavior of overconsolidated clay. The reconstituted samples are prepared from natural samples retrieved in the north of France. First, the shear strength characteristics along monotonic triaxial stress paths are identified. Then load control cyclic tests on overconsolidated specimens are conducted in fully saturated and undrained conditions. Small cyclic deviatoric stresses are applied in order to investigate more particularly the behavior under a very large number of cycles, during which an unusual pore pressure evolution is observed. To explain this, undrained triaxial creep tests are performed on reconstituted specimens with different values of OCRs under some specified stress states. The evolutions of axial strain, excess pore pressure, stress ratio, stress path, plastic strain rates and stress dilatancy during undrained creep are discussed. The additional undrained creep tests also show that two processes are simultaneously acting in a competitive manner: increase in the pore pressure due to the cyclic loading and decrease in the pore pressure because of creep.

Elastoplastic modeling of cyclic behavior of natural structured clay with large number of cycles

Subgrade soils may be subjected to tens of thousands of traffic loading at a given stress level over a long period of time. Its long-term performance is therefore one of the major concerns of traffic geotechnical engineers. Up to now, it is still a challenge in constitutive modeling for describing the stress–strain responses with large number of cycles. For this, an elastoplastic model is proposed in this study to predict the undrained cyclic behavior of natural structured clay with large number of cycles. The proposed model includes three yield surfaces, an inner yield surface, an outer yield surface and an intrinsic yield surface. A hardening law associated with the inner yield surface is employed to computer the elaso-plastic transition inside the outer yield surface. Meanwhile, the elastic anisotropy, small-strain stiffness and structure degradation are considered in this model. In particular, a new hardening law of the inner yield surface which can flexibly control the hardening rate of the soil during cyclic loadings is adopted. Monotonic and cyclic (up to 50,000 cycles) undrained triaxial tests on Wenzhou clay are employed to verify the feasibility of the model. All comparisons demonstrate that the accumulative strains and pore water pressures during cyclic loadings are well captured by the model.

Precursor-surface interactions revealed during plasma-enhanced atomic layer deposition of metal oxide thin films by in-situ spectroscopic ellipsometry

We find that a five-phase (substrate, mixed native oxide and roughness interface layer, metal oxide thin film layer, surface ligand layer, ambient) model with two-dynamic (metal oxide thin film layer thickness and surface ligand layer void fraction) parameters (dynamic dual box model) is sufficient to explain in-situ spectroscopic ellipsometry data measured within and across multiple cycles during plasma-enhanced atomic layer deposition of metal oxide thin films. We demonstrate our dynamic dual box model for analysis of in-situ spectroscopic ellipsometry data in the photon energy range of 0.7–3.4 eV measured with time resolution of few seconds over large numbers of cycles during the growth of titanium oxide (TiO2) and tungsten oxide (WO3) thin films, as examples. We observe cyclic surface roughening with fast kinetics and subsequent roughness reduction with slow kinetics, upon cyclic exposure to precursor materials, leading to oscillations of the metal thin film thickness with small but positive growth per cycle. We explain the cyclic surface roughening by precursor-surface interactions leading to defect creation, and subsequent surface restructuring. Atomic force microscopic images before and after growth, x-ray photoelectron spectroscopy, and x-ray diffraction investigations confirm structural and chemical properties of our thin films. Our proposed dynamic dual box model may be generally applicable to monitor and control metal oxide growth in atomic layer deposition, and we include data for SiO2 and Al2O3 as further examples.

Assessment of fatigue life and reliability of high-mast luminaire structures

Recent failures of high-mast luminaire poles have showcased the vulnerability of such structures to wind loading. High mast luminaire poles are long slender structures with low damping and highly susceptible to wind-induced vibrations that over a large number of cycles can result in fatigue failures during the life cycle of the structure. Such poles are constructed from sets of components that include base plate, reinforced cut-out hand holes, weld details and a hollow tubular pole supporting the luminaire. Among all these components, the base-to-tube connection was identified to have the lowest fatigue resistance through static analysis and previous fatigue experiments, so this study focuses on estimating the fatigue life of the base-to-tube connection under wind loading. Wind time histories were generated for different mean wind speeds and used to analyze fatigue performance in terms of stress cycle, failure, and damage indices. Simulated results were collected to build a damage fraction function to show the fatigue damage created in a certain period at different mean wind speeds. Local wind probability data was combined with the fatigue damage fraction function to estimate the fatigue life at different locations. Also, reliability analysis was carried out through running Monte Carlo simulations. The results provide a general framework for helping designers and fabricators to better determine the fatigue life and probability of failure of high-mast luminaire poles.

An energy-based stability analysis of misfit dislocations in two-phase electrode particles: A planar model and implications for LiFePO4

It is well known that cycling induced capacity fading in phase transforming intercalation materials is critically linked to the severity of misfit strain between the phases which could result in the emergence of a variety of defects in the material. Here, adopting a planar model and making use of a well-established energy-based framework, we examine stability of a misfit dislocation lying at the phase boundary within a two-phase electrode particle. Within this framework, the stability criterion emerges as a result of competition between the work that must be done against the image forces with the work that is supplied by the phase transformation induced stresses, as the dislocation is pulled from free surface of the solid toward interior. A numerical model accounting for anisotropy of both misfit strain between the phases and elastic properties of the solid is developed. The model is in particular applied to the electrode particles of LiFePO4, a highly promising cathode material for lithium-ion battery applications in which misfit dislocations as a result of phase transformation have also been experimentally observed. The analysis is revealing of size effects on the stability of a misfit dislocation in the electrode particle. Most notably, it is shown that below a critical particle size, no misfit dislocation at the interphase can remain stable within the particle as it becomes energetically more favorable for the dislocation to be driven out of the particle through absorption by the free surfaces. Numerical estimates of the critical size are presented and discussed with reference to available experiments. Through providing a guideline for suppressing misfit dislocations, results of this work could have potentially important implications for disabling a wide range of dislocation-based fatigue mechanisms which could otherwise become active and result in capacity fading upon a large number of cycles.

A Parametric Study on the Evolution of Cyclic Clay-Pile Interface Friction for Large Numbers of Cycles

The present experimental study investigates the influence of cyclic displacement amplitude and effective consolidation stress on the evolution of mobilized local shaft friction along piles submitted to large number of cycles (up to 105 cycles). Two-way cyclic displacement-controlled tests were performed on an instrumented pile-probe installed and loaded in a calibration chamber. Tests were performed on reconstituted specimens of saturated clay to examine the shaft friction evolution in the soil-pile interface during cyclic loading. Displacement-controlled static tests were also performed before and after the cyclic loading in order to quantify the influence of cyclic parameters on post-cyclic static response. It was found that the amplitude of cyclic displacement and the initial state of stress have an influence on the evolution of local friction during cyclic loading. The degradation rate of local friction increased for larger cyclic displacement amplitudes whereas with increasing the effective consolidation stress, the degradation rate decreased. The application of displacement- controlled cycles resulted in a modification in the behaviour of the interface. A significant peak of static friction followed by strain softening was observed during post cyclic static tests, which was not the case for pre-cyclic static tests. The peak value of friction obtained upon post-cyclic static loadings found to be more important for higher values of applied displacement amplitude during cyclic loading. Finally, a brief synthesis of the results is given.

Hospital-based or home-based administration of oncology drugs? A micro-costing study comparing healthcare and societal costs of hospital-based and home-based subcutaneous administration of trastuzumab

ObjectiveTo investigate resource use and time investments of healthcare professionals, patients and their family and to compare healthcare and societal costs of one single hospital-based and one single home-based subcutaneous administration of trastuzumab in The Netherlands. MethodWe conducted a bottom-up micro-costing study. Patients diagnosed with HER2+ early or metastatic breast cancer were recruited in four Dutch hospitals. For healthcare costs, data were collected on drug use, consumables, use of healthcare facilities, time of healthcare professionals, and travelling distance of the nurse. For societal costs, data were collected on patient and family costs (including travelling expenses and time of informal caregivers) and productivity losses of paid and unpaid work. ResultsSocietal costs of one single administration of SC trastuzumab were €1753 within the home-based and €1724 within the hospital-based setting. Drug costs of trastuzumab were identical in both settings (€1651). Healthcare costs were higher for home-based administration (€91 versus €47) mainly because of more time of healthcare professionals (110 versus 38 minutes). Costs for patient and family were, however, lower for home-based administration due to travelling expenses (€7 versus €0) and time of informal caregivers (€14 versus €4). Costs for productivity losses were similar for both settings. ConclusionsHome-based subcutaneous administration of trastuzumab is more time consuming for healthcare professionals and therefore more costly than hospital-based administration. The total budget impact can be large considering that a large number of patients receive a large number of cycles of oncology treatments. If home-based administration is the way forward, novel approaches are crucial for ensuring efficiency of home-based care.

Parametric study of the evolution of shaft friction of a model pile in calibration chamber subjected to cyclic loading at a large number of cycles

Pile foundations are usually subjected to cyclic loading which could possibly causes a significant degradation of the friction mobilised along the pile shaft. Most of the experimental studies devoted to analysing the behaviour of the pile-soil interfaces under cyclic loading tests are performed at a few hundred of cycles. However, a large number of cycles of the order of hundreds of thousands may cause a severe degradation of pile capacity. The present work aims to study the effect of cyclic loading parameters on the evolution of shaft friction of pile subjected to a large number of cycles. The experimental study is based on a physical modelling in a calibration chamber of axial cyclic loading of single pile jacked into sand under a large number of cycles, up to 105. It is found that cyclic amplitude, confining pressure and soil density have a significant effect on the evolution of skin friction along the pile shaft at a large number of cycles.

Effect of drainage states on dynamic behaviours of Ningbo clay under uniform cyclic loading

In this study, the actual drainage condition of in situ soft clay is partially drained and the natural soft soil was subjected to long-term uniform cyclic loading. Cyclic triaxial tests were conducted on remoulded samples to analyse the effect of drainage condition on the dynamic behaviour of Ningbo clay. The results showed that when the cyclic stress ratio (CSR) was small, the accumulated axial strain under undrained conditions was larger than that under partially drained conditions; however, when the CSR was high, the accumulated axial strain in the undrained condition reduced. The resilient strain gradually decreased after a large number of cycles under partially drained conditions, while it increased more significantly with an increase in CSR during the experiments under undrained conditions. With increasing cycle numbers, the pore pressure initially increased and then decreased with a peak value under partially drained conditions, while the pore pressure tended to become stable under undrained conditions. On the basis of the test results, equations for permanent axial strain and pore pressure considering the effect of drainage conditions are proposed, which can predict the dynamic responses of in situ subsoils under long-term uniform cyclic loading.

Time constant of the transverse-field demagnetization of superconducting stacks of tapes

Stacks of REBCO tapes can trap large amounts of magnetic fields and can stay magnetized for long periods of times. This makes them an interesting option for major engineering applications such as motors, generators and magnetic bearings. When subjected to alternating magnetic fields transverse to the magnetization (or cross fields), superconducting tapes face a reduction in the trapped field, and thus it is the goal of this paper to understand the influence of all parameters in the cross field demagnetization of stacks of tapes. Major parameter dependencies considered for the scope of this paper are cross field amplitude and frequency, tape width, tape thickness (from 1 to 20 µm), and number of tapes (up to 20). This article also provides a systemic study of the relaxation time constant τ, which can be used to estimate the cross-field demagnetization decay for high number of cycles. Modeling is based on the Minimum Electro-Magnetic Entropy Production method, and it is shown that the 2D model gives very accurate results for long samples when compared with 3D model. Analytical formulas for large number of cycles have been devised. The results show that when the cross field amplitude is above the penetration field of one tape, the stack always fully demagnetizes, roughly in exponential decay. Increasing the number of tapes only increases the relaxation time. The formulas derived also hold when validated against numerical results, and can be used for quick approximation of decay constant. They also show that the cause of the decreases of cross field demagnetization with number of tapes is the increase in the self-inductance of the magnetization currents. The trends and insights obtained for cross field demagnetization for stacks are thus very beneficial for engineers and scientists working with superconducting magnet design and applications.

Reprocessing of High-Density Polyethylene Reinforced with Carbon Nanotubes

High-density polyethylene (HDPE) was compounded with 3 wt% carbon nanotubes (CNTs). In order to simulate mechanical recycling, both the nanocomposite and neat HDPE were repeatedly extruded and subsequently analysed by tensile tests, Charpy impact strength, differential scanning calorimetry (DSC), oxidation induction time (OIT), Gel Performance Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR) and TEM After 10 cycles of extrusion, thermal, mechanical, and rheological tests did not reveal any significant degradation. In order to better study the effect of the CNTs, a large number of cycles were simulated by processing the materials for up to 200 min. After 200 min of processing, the neat HDPE was significantly degraded whereas the nanocomposite was almost unaffected.

Post-cycling Interface Strength Test of Geogrids

Geosynthetic-reinforced soil structures are commonly used in seismic design in regions. The performance of GRES under seismic conditions can be found to range from very good to catastrophic. This paper presents the implementation of a test to evaluate the influence of pre-cycling on the post-cycling resistance of a soil–geogrid system. Tests were performed on a PVE uniaxial geogrid with a tensile strength of 400 kN/m and a clean sand with 89% compaction and friction angle of 37.5°. The system was subjected to cyclic pullout tests at 40 and 80% of the monotonic strength. After the pre-cycling, a posterior monotonic pullout test was performed to evaluate the influence of the previous cycling on the final post-cycling strength. A test protocol was established to apply 50, 100, 500 and 5000 cycles with 40% and 80% pullout resistance amplitudes. At the 40% amplitude, the system exhibited stable increasing behavior in terms of resistance and cyclic displacement. Failure was not reached during the pre-cycling stage at 40% amplitude. At the 80% amplitude, the system failed at 250 cycles, and cyclic displacement was found to be erratic for all pre-cycling cases. The results suggest a general tendency of the pre-cycling to increase the post-cycling resistance. However, a combination of high cyclic amplitude with large number of cycles may lead to failure. Exposure to seismic events could be considered in the design of GRES though a rationally chosen reduction factor is applied.

Mechanical, acoustic, and fracture behaviors of yellow sandstone specimens under triaxial monotonic and cyclic loading

The mechanical, acoustic, and fracture behaviors of sandstone play important roles in design and stability analysis in rock engineering applications. In this research, a series of triaxial monotonic and cyclic tests was conducted on yellow sandstone. The results of triaxial monotonic experiments were used to analyze the influence of the confining pressure on the mechanical parameters of the sandstone. The strength and deformation parameters depended strongly on the confining pressure. The triaxial strength of the sandstone specimens under cyclic loading was approximately equal to that under monotonic loading, whereas the fatigue loading led to a reduction in triaxial strength. Under lower deviatoric stress levels, the specimen was highly resistant to fatigue loading; however, higher deviatoric stress level lead to fatigue failure of the specimen even though after large cycle numbers. The influence of the cycle number on the deformation and crack damage parameters of the sandstone was also investigated. The internal damage of the sandstone specimens were characterized on basis of the recorded P-wave velocity and acoustic emission (AE) counts during triaxial monotonic loading, and the effect of the cycle number on the AE behaviors was explored under triaxial cyclic loading. Finally, the fractured yellow sandstone specimens were further analyzed by using X-ray micro computerized tomography (CT) scanning. The internal fracture characteristics of the sandstone specimens were investigated by cross-section analysis and three-dimentional (3D) reconstruction of the CT scanning, which revealed the fracture mechanism of the sandstone.

Soil behavior under low- and high-cycle loading—Element tests vs. constitutive models

The first part of the paper deals with high-cycle loading and presents a parametric study with numerous drained cyclic tests with a large number of cycles (N≥104). The dependence of the strain accumulation rate on initial relative density, amplitude, average stress and cyclic preloading is addressed. These test series form the basis of the calibration of a high-cycle accumulation (HCA) model, which is briefly explained. Furthermore, the influences of the grain size distribution curve, particle shape and the sample preparation method on the cumulative strains are discussed. In further test series the effects of multiple changes of the direction of the cycles, of frequently changing amplitudes, and of changes of the average stress between bundles of cycles were investigated. The second part of the paper is dedicated to low-cycle loading. A data base with a large number of undrained cyclic triaxial tests performed on a fine sand is presented. The test conditions comprise stress or strain-controlled cycles, performed from isotropic or anisotropic initial stresses and involving different densities and amplitudes. The predictions of three sophisticated constitutive models for sand, namely hypoplasticity with intergranular strain, ISA and Sanisand, are tested against the experimental data. Finally, a second data base concerning a large number of cyclic tests on kaolin is briefly introduced.

Water Recovery from Floor Cleaning Operations of Industrial or Public Areas: The Results of a Field Test

Water resources are increasingly under pressure because of human activities and economic development. Moreover, accelerated urbanization and the expansion of drinking water supply and sanitation systems contribute to this rising demand. The development of water reuse solutions is an urgent issue. This study presents a solution for the reuse of wastewaters generated from floor cleaning operations of industrial or public areas. A portable device containing a grid, for coarse filtration, and a 300-L reaction chamber to carry out the sequential processes of coagulation, flocculation and settling, was employed for a field test. In the field test the wastewater coming from the tank of a cleaning machine, used for floor cleaning in an industrial site, was treated and reused for the same purpose for a total of 110 times. The quality of the treated wastewater was monitored cycle after cycle and the results of the test demonstrated that the treated water was suitable to be reused for the same purpose, even after a large number of cycles, provided that a finishing treatment was eventually supplemented in order to reduce the residual concentration of organic substances. It was demonstrated that, under standard operating conditions, that is a wastewater with a total suspended solid (TSS) content of 800 mg/L, and on the grounds of the results found in the test, that is a TSS removal efficiency of 98% and a sludge total solid (TS) content of 6%, the whole volume of the cleaning machine tank was completely renewed with fresh water after 60 cycles. Eventually, the combination of treatment and reuse operations allowed to save approximately 18,000 L of fresh water over a series of 60 cleaning cycles. The proposed treatment allowed not only to save fresh water but even to reduce the cost of water usage by approximately 50%. In fact, thanks to this treatment, the cost of a single cubic meter of water decreased from approximately 6 €/m3, which included supply of fresh water and discharge to the public sewer, to approximately 3 €/m3.

Microstructural and Mechanical Stability of a Ti-50.8 at.% Ni Shape Memory Alloy Achieved by Thermal Cycling with a Large Number of Cycles

The influence of thermal cycling (TC) with a large number of cycles on the microstructure, the parameters of martensitic transformations (MTs), and the mechanical properties of a Ti-50.8 at.% Ni shape-memory alloy in coarse-grained (CG) and ultrafine-grained (UFG) states was investigated. The effect of microstructural and mechanical stability was found in both coarse-grained and ultrafine-grained states starting from the 100th cycle of martensitic transformations. In addition, an unusual temperature change was observed in martensitic transformations occurring with the formation of an intermediate R phase.

Aspects of the thermodynamic behavior of salt caverns used for gas storage

New evidence supporting views previously expressed in a paper dedicated to the thermodynamic behavior of gas storage caverns (Bérest, 2019, Heat transfer in salt caverns, Int. J. Rock Mech. Rock Eng. Sci. 120, 82–95. https://doi.org/10.1016/j.ijrmms.2019.06.009) is provided. In a fluid-filled cavern, conditions for the onset of natural convection are always met, at least in principle. In fact, for gas storage caverns, convection is present in the upper part of a cavern, where gas temperature and moisture content tend to homogenize. In the lower part of a cavern, below the temperature-gradient inversion depth, temperature is a decreasing function of depth, and no convection is observed. The reason is that brine trapped in the cavern sump remains consistently colder than the rock mass, even decades after cavern creation. Sump brine is cooled during each gas pressure cycle: most often, during depressurization, condensation of water vapor occurs; it is spread in the entire gas body from which latent heat is withdrawn, resulting in “raining” in the cavern. During re-pressurization, vaporization takes place at the gas-brine interface, where latent heat is provided by the brine sump, resulting, during a cycle, in net cooling of the brine sump. This process is more effective when a larger number of cycles per year is run. The buffer created above the brine-gas interface hinders vapor diffusion to the cavern main body. It is hypothetized that, when cavern pressure is cycled more frequently, water content in the withdrawn gas is smaller. This might be an advantage in natural gas caverns, as hydrate formation is lessened, and in hydrogen or compressed air caverns, as less dehydration efforts are required.