Constant Cycle Research Articles

A numerical approach for simulation of stress-controlled cyclic shear loading in a soil column considering partial drainage

Liquefaction strength curves (LSCs) are commonly generated based on undrained stress-controlled cyclic testing to define the liquefaction potential of sands. However, these LSCs do not consider the effect of partial drainage on liquefaction potential. This is mainly because there are very limited experimental techniques to run stress-controlled tests for partially drained sands. This manuscript proposes a procedure to numerically simulate a saturated sand column with a free drainage boundary at the top (or top and bottom), accelerated horizontally at the bottom with constant acceleration cycles of duration designed to generate constant cyclic shear stress histories in the column. This is done for columns subjected to low and high overburden pressures. The paper starts with numerical simulations of a typical undrained cyclic direct simple shear, CDSS tests by applying a stepped velocity wave to a single soil element, an already established approach. This approach only works for a single element in undrained condition which is fixed at the base. Then, the proposed procedure is implemented by applying stepped acceleration time histories at the base of soil columns having one or two drainage boundaries. In these stepped acceleration runs, the durations of the acceleration cycles are controlled to achieve a partially drained stress-controlled CDSS kind-of-loading at specific elevations within the soil columns. The technique is used to show the effect of partial drainage on sand liquefaction behavior at both low and high overburden pressures. The results show that the effect of drainage is much more significant at higher overburden. The existence of both top and bottom drainage boundaries resulted in less liquefaction vulnerability, as compared to having only one drainage boundary at the top of the sand column. The results show that liquefiable sand layers in the field may be less prone to liquefaction under high overburden pressure than predicted by the current state-of-practice, which relies mainly on undrained small-scale cyclic tests.

Do temporal and spatial heterogeneity modulate biodiversity–functioning relationships in com-munities of methanotrophic bacteria?

Positive relationships between biodiversity functioning have been found in communities of plants but also of soil microbes. The beneficial effects of diversity are thought to be driven by niche partitioning among community members, which leads to more complete or more efficient community-level resource use through various mechanisms. An intriguing related question is whether environmentally more heterogeneous habitats provide a larger total niche space and support stronger diversity—functioning relationships because they harbor more species or allow species to partition the available niche space more efficiently. Here, we tested this hypothesis by assembling communities of 1, 2 or 4 methanotrophic isolates and exposing them to temporally (constant or diurnal temperature cycling) and structurally (one or two aggregate size classes) more heterogeneous conditions. In total, we incubated 396 microcosms for 41 days and found that more biodiverse communities consumed more methane (CH4) and tended to have a larger community size (higher pmoA copy numbers). Diurnal temperature cycling strongly reduced CH4 oxidation and growth, whereas soil aggregate composition and diversity had no detectable effect. Biodiversity effects varied greatly with the identity of the community members that were combined. With respect to community level CH4 consumption, strain interactions were positive or neutral but never negative, and could neither be explained by 14 structural and function traits we collected or by the observed competitive hierarchy among the strains. Overall, our results indicate that methanotrophic diversity promotes methanotrophic community functioning. The strains that performed best varied with environmental conditions, suggesting that a high biodiversity is important for maintaining methanotrophic functioning as environmental conditions fluctuate over time.

Barriers and Solutions to Successful Problem-Based Learning Delivery in Developing Countries - A Literature Review.

Problem-based learning (PBL) was introduced in the 1960s as an alternative to traditional teacher-centered and discipline-based preclinical medical education. A literature review was conducted to explore the barriers and solutions to successful PBL uptake and delivery in developing countries. The review involved the search of articles and scientific studies on PubMed, The Lancet, and Scielo. The review focused on the medical education literature, using as a primary search criterion "problem-based learning" in combination with "developing countries" and "education". The search was limited to articles in Spanish and English published between 2011 and November 2021, except for three articles due to their relevance to the subject. Faculty development programs are the cornerstone when implementing a new methodology in developing countries. Early career development, PBL methodology, and the available assessment options should be the primary learning objectives of these programs. Stakeholders will need to plan using available resources following the experience of other countries and institutions encouraging collaborative development. Evaluation and assessment will be crucial to understand the impact of PBL, and considerations should be taken to implement an integrated curriculum. Medical Education Research should be encouraged, appraised, and disseminated to improve evidence-based decision-making, creating a constant development cycle. PBL is innovative and represents many unanswered questions that will develop in the following decade as more schools implement new methodologies and Research on PBL.

Differential locomotor activity responses to day-time light intensity in juvenile and adult solitary Cape mole-rats, Georychus capensis (Rodentia: Bathyergidae)

ABSTRACT The Cape mole-rat (Georychus capensis) is a solitary, strictly subterranean rodent that is responsive to light and entrains to photic cues despite having a reduced visual system. Circadian entrainment is maintained throughout life, but age can alter the amplitude of the response and re-entrainment time. Mole-rats are long-lived for their size which raises questions regarding the robustness of their circadian rhythms and how impacts their locomotor activity rhythms. The locomotor activity rhythms of juvenile and adult Cape mole-rats were investigated. They were exposed to pre-experimental and post-experimental control cycles under fluorescent lights, six 12 h light:12 h dark cycles of decreasing intensities and a constant dark cycle (DD). All animals exhibited more activity during the dark phases of all light regimes. Juveniles were more active than adults and displayed more variable activity during both the light and dark phases. Adults exhibited relatively stable levels of activity under all experimental conditions, whereas juvenile activity decreased as the light intensity was reduced. The amplitude of Cape mole-rat rhythms was consistently low, but similar across light regimes and between adults and juveniles. Cape mole-rats have functional circadian systems, are primarily nocturnal and respond differentially to light intensity depending on their age. Light intensity does not affect the locomotor activity responses of Cape mole-rats in a predictable manner, and could indicate more complex interactions with light wavelengths. The circadian systems of juveniles appear to be more sensitive than those of adults, although the mechanism of the light response remains unclear.

One-step microwave synthesis of FeSe2@CNT as high-performance supercapacitor anode material

In this work, FeSe2@CNT nanocomposite anode materials are fabricated using a convenient and efficient one-step microwave method. The FeSe2@CNT electrode exhibits superior electrochemical performance. The carbon nanotube structure effectively mitigates the severe volume change in the FeSe2@CNT electrode during continuous charge and discharge. Thus, the capacitance value of 573 F g−1 and capacitance retention of 81.9% for 3000 constant current charge and discharge cycles are achieved. In addition, the asymmetric device assembled with FeSe2@CNT as the anode and NiSe2@CNT as the cathode exhibits high Energy density (E can reach 41.32 Wh kg−1 when P is 800 W kg−1), and the device achieves 82.6% capacity retention after 3000 cycles.

Energy Management of Hybrid DC Microgrid with Different Levels of DC Bus Voltage for Various Load Types

This article suggests a hybrid DC microgrid (HDCMG) with different levels of DC bus voltages to use for various types of loads. The available sources in the HDCMG are wind generating systems (WGSs), photovoltaic (PV) systems, battery banks, and the AC grid for emergencies. The various levels of the DC bus voltages are 760 V, 380 V, and 48 V for different application uses such as electric vehicles and home applications. In addition, the controller plays an important role in the proposed system to achieve the desired DC bus voltage levels and extract the maximum power point (MPP) from the WGS and PV systems. In order to check the power continuity for the critical loads and improve the overall system performance, a suggested energy management strategy (SEMS) is developed. The SEMS is based on the optimum generated power and the state-of-charge (SOC) of the battery banks. Further, the SEMS is developed as a way to prevent battery storage from overcharging and deep discharging. The mathematical relations of the proposed HDCMG and MPP tracking are described. The bidirectional 3-Φ inverter connects the 760 V bus voltage to the AC grid for regulating this DC bus by absorbing the excess power or supplying the required power during the shortage in the generation and the low SOC of the battery storage. Buck converters with controlled duty cycles rather than constant duty cycles are used to obtain 380 V and 48 V from 760 V to achieve better dynamic responses. The overall HDCMG is evaluated using the MATLAB/Simulink package under different working cases to verify the capability of the control system and the PEMS. The obtained results are discussed and show the good performance and the capability of the overall system under the different scenarios, including (i) a comparison between variable duty and constant duty; (ii) high/low generated power and the SOC of the battery in the acceptable region; (iii) high/low generated power and the SOC of the battery in the critical region; and (iv) high/low generated power and the SOC of the battery in the overcharging region.

Mechanisms of airway epithelial injury and abnormal repair in asthma and COPD.

The airway epithelium comprises of different cell types and acts as a physical barrier preventing pathogens, including inhaled particles and microbes, from entering the lungs. Goblet cells and submucosal glands produce mucus that traps pathogens, which are expelled from the respiratory tract by ciliated cells. Basal cells act as progenitor cells, differentiating into different epithelial cell types, to maintain homeostasis following injury. Adherens and tight junctions between cells maintain the epithelial barrier function and regulate the movement of molecules across it. In this review we discuss how abnormal epithelial structure and function, caused by chronic injury and abnormal repair, drives airway disease and specifically asthma and chronic obstructive pulmonary disease (COPD). In both diseases, inhaled allergens, pollutants and microbes disrupt junctional complexes and promote cell death, impairing the barrier function and leading to increased penetration of pathogens and a constant airway immune response. In asthma, the inflammatory response precipitates the epithelial injury and drives abnormal basal cell differentiation. This leads to reduced ciliated cells, goblet cell hyperplasia and increased epithelial mesenchymal transition, which contribute to impaired mucociliary clearance and airway remodelling. In COPD, chronic oxidative stress and inflammation trigger premature epithelial cell senescence, which contributes to loss of epithelial integrity and airway inflammation and remodelling. Increased numbers of basal cells showing deregulated differentiation, contributes to ciliary dysfunction and mucous hyperproduction in COPD airways. Defective antioxidant, antiviral and damage repair mechanisms, possibly due to genetic or epigenetic factors, may confer susceptibility to airway epithelial dysfunction in these diseases. The current evidence suggests that a constant cycle of injury and abnormal repair of the epithelium drives chronic airway inflammation and remodelling in asthma and COPD. Mechanistic understanding of injury susceptibility and damage response may lead to improved therapies for these diseases.

Comparison of the characteristics of compressed air energy storage in dome-shaped and horizontal aquifers based on the Pittsfield aquifer field test

Most studies have suggested that aquifers with anticlinal structures are the most favorable structures for compressed air energy storage (CAES) in aquifers because of their trapping ability, but this limits the potential locations for CAES plants, as horizontal aquifers are very common only in offshore areas rich in wind power. The comparison of the characteristics of CAES in dome-shaped and horizontal aquifers can help in understanding the quantitative differences between them. In this study, based on Pittsfield aquifer field test strata and parameters, the characteristics of CAES in dome-shaped and horizontal aquifers were investigated using a numerical simulation method by establishing two comparable conceptual models of a dome-shaped aquifer and a horizontal aquifer. Reasonable matches between the monitored data and simulated results were obtained for the initial air bubble development period of the Pittsfield aquifer field test. Comparisons of the initial air bubble, air cycling performance and energy recovery efficiency were carried out with the same calculation settings for the dome-shaped and horizontal aquifers. In the initial air bubble development period, when the same air volume was injected into the dome-shaped and horizontal aquifers, the radius of the air–water interface in the horizontal aquifer was 16.7% larger than that in the dome-shaped aquifer. In the air cycling period, an isothermal cycle type with a constant injection and production air pressure was designed. The energy recovery efficiency of CAES in aquifers is calculated in terms of the concept of exergy. In the case of isothermal compressor work and ignoring the energy loss in the compressor system, the energy recovery efficiency of the horizontal aquifer can reach approximately 80% of that in the dome-shaped aquifer. The effects of wellbore injection/production length and circulation mode on the performance of CAES in both aquifers were investigated. Wellbore injection/production length has obvious impacts on air mass flow rates during initial air bubble development and subsequent cycling, and a longer wellbore injection/production length can provide greater capacity. A comparison between the daily and weekly circulation periods in the dome-shaped and horizontal aquifers showed that the daily circulation has an efficiency advantage at the same energy storage scale, and the energy recovery efficiency of the horizontal aquifer in the weekly circulation can reach approximately 74% of that of the dome-shaped aquifer. In addition, a constant flow rate injection/production gas daily cycle mode was investigated, and the results showed that this mode has higher energy recovery efficiency than the constant pressure cycle mode, and the horizontal aquifer can reach 88.39% of the efficiency of the dome-shaped aquifer. The comparison of the characteristics of CAES in dome-shaped and horizontal aquifers shows that horizontal aquifers may be a potential choice for the storage media of CAES in the case that there are no suitable aquifers with anticlinal structures in offshore areas.

Technics, Perception, Différance Narrating the Seeing-Machine?

Abstract This article offers a discussion of the intricate relation between the human body and its technological supplementation. It argues that while the physical body may seem to sublimate in the plethora of discourses, it keeps reasserting its materiality via processes of technologization which capture perception and cognition in a constant cycle of disembodiment and re-embodiment. The article offers an analysis of Elizabet Goldring’s work with the Seeing Laser Ophthalmoscope, and her RetinaPrints (a unique form of visualization) to comment on the ways in which lived experiences are inexorably linked to practices of fragmentation, prosthesis and technological mediation.

Layered Titanium Sulfide Cathode for All‐Solid‐State Magnesium Batteries

AbstractMagnesium solid‐state batteries attract significant attention as a future mean of energy storage. Here we present the first cathode study of an inorganic all‐solid‐state magnesium battery using a magnesium metal anode, a nanocomposite electrolyte Mg(BH4)2 ⋅ 1.6NH3‐MgO (75 wt %), and a layered titanium disulfide (TiS2) as cathode active material. The structural transformations of TiS2 particles with different sizes are investigated at different stages of battery life. Reversible Mg2+ intercalation occurs via three structurally distinct phases of MgxTiS2, identified by powder X‐ray diffraction. Magnesium intercalates initially on octahedral sites and at higher depth of discharge on tetrahedral sites in the interlayers of TiS2, which leads to an expansion initially mainly along the c‐axis and later along both the a‐ and c‐axes. A maximum discharge capacity of 172 mAh g−1 (Δx=0.36 in MgxTiS2) is observed for smaller TiS2 particles. Parasitic reactions could be reduced by decreasing the cut‐off voltage by a constant current constant voltage cycling procedure. The chemical diffusion coefficient of the entire cell is found from galvanostatic intermittent titration technique experiments to be in the order of 10−15 to 10−19 cm2 s−1.

Experimental investigation of mechanical behavior of lightweight RC elements under repeated loadings

Today, the use of lightweight structural concrete in earthquake-prone countries of the world has grown more and more. Therefore, it is important to study the behavior of this type of concrete against seismic loads. So far, many studies have been conducted on the behavior of reinforced concrete (RC) elements against cyclic loads caused by earthquakes, but recent observations show that many earthquakes occur consecutively. That is, structural elements and systems may experience several weak earthquakes or aftershocks during their lifetime. It is obvious that a structure that experiences several cyclic vibrations will suffer a degradation of strength and stiffness, and its behavior will change against subsequent earthquakes. The existing structural models consider the cyclic degradation resulting from the cyclic movement during an earthquake, but many of these models do not consider the effects of degradation caused by previous earthquakes; While this degradation can have significant effects on the behavior of structural elements. In this research, the degradation caused by cyclic loading in lightweight concrete structural elements was investigated first, and then their post-degradation behavior under different levels of degradation was studied; For this purpose, 12 specimens of lightweight RC beams and 4 specimens of lightweight RC columns were made with a scale of 50% and subjected to different uniform and cyclic loadings, and three levels of slight, moderate and extensive degradation were defined based on a number of constant fatigue cycles. Then, in the next step, the cyclic behavior of the specimens after degradation was tested in three levels of slight, moderate and extensive degradation. The results of the tests showed that with the increase in the degradation level, the amount of energy absorption of RC beams decreases; Especially in beams with extensive degradation level, the amount of beam energy absorption decreases by more than 40%. Comparing the cyclic behavior after the degradation of the damaged columns with the behavior of the intact specimen shows that the increase in the level of degradation reduces the ductility of the columns.

Theoretical assessment of fatigue life of metal materials at constant cycle stress range

A computational model is proposed for theoretical evaluation of fatigue life of samples made of metallic materials at a constant applied cycle stress range. The total fatigue life is divided into two stages: the stage of crack nucleation, i.e., the number of loading cycles before its initiation (stage 1) and the stage of crack growth (stage 2). Different approaches are used to estimate the duration of each stage. For stage 1, the power law fatigue life equation is obtained from the condition that the accumulated strain energy is equal to the specific cracking energy, and for stage 2, the number of cycles is obtained by integrating the crack growth rate equation, where the effective range of the stress intensity factor (SIF), defined as the difference between the applied "external" range of the SIF and the "internal" range of the SIF, which characterizes the material's resistance to crack growth, is taken as its driving force. The initial data for the calculation, in addition to the loading parameters, are the characteristics of the static strength and microstructure of the initial material. Calculations based on the proposed fatigue life model for steel 0.45%C specimens show good agreement with experimental results.

Condensations on electrowetting surfaces: An electrostatic liquid conveyor from dropwise-filmwise competition

In contrast to the traditional point of view, electrowetting creates a dynamic wetting regime. Hydrophilicity can penetrate or recede from the working surface –depending on the liquid locale rather than the substrate structures. Size regulation forms droplet clusters as condensation accumulates. Coalescence cascades and mass imbalances transfer the liquid from one zone to the next. What ensues is a passive electrostatic liquid conveyor that takes the condensation away from its constant self-stagnating cycles. Each working zone functions independently from one another according to its intended purpose: nucleation and diffusion, accumulation and collection. 40 to 50 percent of the increase in liquid recovery traces its root to the spatial-size regulation of the droplet population. Simultaneously, the gain from higher nucleations runs parabolically with electrostatic voltage. The competition between dropwise and filmwise tendencies determines the migration of condensates. Yet, the autonomy of the two means that nucleations are direct and unhindered as to how high an electrostatic voltage can be: the only limit is the material strength and endurance to sustain this concentration of electric potentials.

Physical Activity, Exercise Capacity and Sedentary Behavior in People with Alpha-1 Antitrypsin Deficiency: A Scoping Review.

Alpha-1 antitrypsin deficiency (AATD) isa hereditary disorder and a genetic risk factor for chronic obstructive pulmonary disease (COPD). Physical activity (PA) is important for the prevention and treatment of chronic disease. Little is known about PA in people with AATD. Therefore, we aimed to map the research undertaken to improve and/or measure PA, sedentary behaviour (SB) or exercise in people with AATD. Searches were conducted in CINAHL, Medline, EMBASE and clinical trial databases for studies published in 2021. Databases were searched for keywords (physical activity, AATD, exercise, sedentary behavior) as well as synonyms of these terms, which were connected using Boolean operators. The search yielded 360 records; 37 records were included for review. All included studies (n = 37) assessed exercise capacity; 22 studies reported the use of the six-minute walk test, the incremental shuttle walk test and cardiopulmonary exercise testing were reported in three studies each. Other objective measures of exercise capacity included a submaximal treadmill test, the Naughton protocol treadmill test, cycle ergometer maximal test, endurance shuttle walk test, constant cycle work rate test, a peak work rate test and the number of flights of stairs a participant was able to walk without stopping. A number of participant self-reported measures of exercise capacity were noted. Only one study aimed to analyze the effects of an intensive fitness intervention on daily PA. One further study reported on an exercise intervention and objectively measured PA at baseline. No studies measured SB. The assessment of PA and use of PA as an intervention in AATD is limited, and research into SB absent. Future research should measure PA and SB levels in people with AATD and explore interventions to enhance PA in this susceptible population.

Styrene-butadiene rubber patterned current collector for improved Li-ion kinetics of the anode for high energy density lithium-ion batteries

The styrene-butadiene rubber (SBR) binder migration caused by the capillary force-driven solvent evaporation during the drying process results in the concentration gradient of SBR binder in the anode, which deteriorates the adhesion strength at the interface between the anode film and Cu current collector and Li-ion kinetics, respectively. Here, we report SBR patterned Cu current collector (SPC) to overcome problems caused by the SBR binder migration behavior. Pre-patterned SBR strongly adheres to the Cu current collector, which suppresses its migration during the drying process. Homogeneous SBR distribution in the longitudinal direction of the anode improves the adhesion strength and Li-ion kinetics. Enhanced adhesion strength enables the reduction of the SBR content in the anode, which further improves Li-ion kinetics. The anode employing SPC exhibits improved constant current charging capacity retention and cycling stability compared to those of the anode with a pristine Cu current collector.

A New Cuk-Based DC-DC Converter with Improved Efficiency and Lower Rated Voltage of Coupling Capacitor

DC-DC converters play a crucial role in recent and advanced applications, enabling efficient power conversion and management for renewable energy systems, electric vehicles, portable devices, and advanced communication systems. In line with this, the objective of this paper is to introduce a new DC-DC configuration based on the Cuk converter named as Mahafzah converter, which utilizes a coupling capacitor with a lower rated voltage. The paper aims to demonstrate the effectiveness of the proposed converter in terms of improved efficiency, reduced size, and reduced semiconductor device currents compared to the conventional Cuk converter. The proposed configuration comprises the same components as the Cuk converter, but in a different arrangement, without any additional elements. The main advantage of the proposed converter is using a coupling capacitor with a much lower rated voltage than the Cuk converter, resulting in a smaller capacitor size, reduced printed circuit board (PCB) size, and manufacturing cost. Additionally, the proposed converter reduces the currents of the semiconductor devices compared to those in the Cuk converter. To demonstrate its effectiveness, the converter is operated under continuous current mode (CCM) with a constant duty cycle and switching frequency. The study provides an in-depth discussion of the various operating modes by making use of equations relating to currents, voltages, duty cycles, and voltage gains. It also provides detailed illustrations of the limits between CCM and discontinuous current mode (DCM). The effectiveness of the proposed converter is demonstrated through a design example with operating parameters of 1 kW, 200 V/−300 V, and 20 kHz. Additionally, a low voltage–low power prototype (12/−18 V, 3.24 W, 20 kHz) is established to verify the operation of the proposed converter. Simulation and experimental verification of the proposed configuration achieved the desired results to improve efficiency and reduce the rate. The results clearly indicate that the efficiency of the proposed converter surpasses that of the conventional Cuk converter under identical operating conditions, reaching approximately 88% at rated load conditions.

The minimal important difference of the constant work rate cycle test in severe COPD

BackgroundThe Constant Work Rate Cycle Test (CWRT) is a commonly used and sensitive test to detect treatment success in patients with Chronic Obstructive Pulmonary Disease (COPD). Earlier, the Minimal Important Difference (MID) of the CWRT was estimated at 101 s (or 34%) change from baseline based on one well executed study. However, this study was performed in a population of patients with mild-to-moderate COPD, and we have learned that MIDs might be quite different in patients with severe COPD. Therefore, we aimed to establish the MID of the CWRT in patients with severe COPD. MethodsWe included 141 patients with severe COPD, who underwent either pulmonary rehabilitation, bronchoscopic lung volume reduction with endobronchial valves, or a sham bronchoscopy as a control group. CWRT workload was set at 75% of the peak work capacity, as determined by an incremental cycle test. We used the change in 6-min walking test (6-MWT), forced expiratory volume in 1s (FEV1), residual volume (RV), and St. George's Respiratory Questionnaire (SGRQ) total score as anchors to calculate the MID. ResultsAll anchors had an association of ≥0.41 with change in CWRT. The MID estimates for the different anchors were: 6-MWT 278 s (95%), FEV1 273 s (90%), RV 240 s (84%), and SGRQ 208 s (71%). The average of these four MID estimates resulted in an MID of 250 s (or 85%). ConclusionWe established the MID for CWRT at 250 s (or 85%) change from baseline in patients with severe COPD.

A two-surface contact model for DEM and its application to model fatigue crack growth in cemented materials

This paper proposes a modelling approach that combines the discrete element method (DEM) and a novel bonded contact model to characterise the fatigue response of cemented materials. While DEM is commonly used to simulate bonded materials undergoing cracking, the centrepiece of the present method is the development of the novel bonded fatigue model. This new model couples damage mechanics and bounding surface plasticity theory to capture fatigue crack growth in cement bridges between aggregates. Thanks to the incorporation of the bounding surface plasticity, the proposed model provides a smooth transition from static to fatigue damages and vice-versa in a unified manner, making it more flexible to capture damage responses of cemented materials under different loading conditions (i.e. monotonic and cyclic loadings). Moreover, the proposed approach automatically captures the hysteretic response in cement bridges between aggregates under fatigue loadings without ad-hoc treatments. More importantly, by removing the direct dependence of the fatigue damage variable on the number of loading cycles, the modelling approach can be applied to simulate the fatigue behaviour of cemented materials under cyclic variable load amplitudes. The proposed modelling approach is evaluated against several strength tests to examine its predictive capability. Satisfactory agreements with fatigue experiments are achieved for flexural modulus degradations, lifetimes and sensitivity of stress levels under constant and variable amplitude cycles. This result suggests that the proposed discrete modelling approach can be used to conduct numerical experiments for insights into the fatigue behaviour of cemented materials.

Anisotropic fatigue performance of directed energy deposited Ti-6Al-4V: Effects of build orientation

Directed energy deposition (DED), an important branch of additive manufacturing technology, has unique processes that attribute to the fatigue performance anisotropy associated with the build orientation of DED materials. However, the mechanism of fatigue performance anisotropy still remains unclear due to multiple factors of the defect and microstructure, which has limited further application of DED materials. This paper investigates the effects of build orientation on the anisotropic fatigue performance of DED Ti-6Al-4V treated with stress relief annealing, specifically the impact of defects and microstructures on fatigue performance anisotropy. The defects in the fully dense DED Ti-6Al-4V are non-directional porosity defects with smooth morphology and high sphericity; the microstructures are mainly characterized by prior-β columnar grains, α colonies and basketweave structures. To represent fatigue performance anisotropy of the material, standard round bar specimens were sampled from three build orientations, i.e., X, Y and Z directions, where Z-direction represents the build direction. These specimens were subsequently subjected to constant amplitude high cycle fatigue tests at the same loading condition and room temperature. The fatigue test results showed that the logarithmic mean fatigue lives of the X- and Y-direction specimens were close to each other, but significantly longer than those of the Z-direction specimens. Fractography and EBSD tests were conducted to explain the causes of fatigue performance anisotropy, suggesting that microstructures are more likely to explain the anisotropy caused by the build orientation than the porosity defects, with crystallographic orientation and α colony being two critical factors.

The Relationship between Chlorophyll Concentration and ENSO Events and Possible Mechanisms off the Changjiang River Estuary

More and more attention has been paid to the study of the impact of extreme climatic events on the ecological environment off the Changjiang River Estuary. In this study, the relationship between the chlorophyll concentration and ENSO (El Niño Southern Oscillation) events was studied. Several potential physical mechanisms between the ENSO and chlorophyll concentration were analyzed using observation and sensitivity experiments from a high-resolution ROMS-CoSiNE coupled model (Regional Ocean Modeling System-Carbon, Oxygen, Silicon, Nitrogen and Ecosystem) off the Changjiang River Estuary. Our results indicated that the April to August averaged chlorophyll concentration off the Changjiang River Estuary was significantly correlated with the December to February averaged ENSO indices in the previous winter. The 10 m wind speed and SST (Sea Surface Temperature) affected by an ENSO event had little effect on the chlorophyll concentration, while the discharge had a significant effect on the chlorophyll concentration off the Changjiang River Estuary, and the discharge was significantly and positively correlated with the ENSO indices. We tested the effect of interannual variations of the discharge and nutrients carried by discharge on the interannual variation in the chlorophyll concentration in the ENSO events. Two sensitivity experiments showed that when the nutrients in the freshwater discharge were kept as a constant seasonal cycle, the composite differences in the chlorophyll concentration between the positive and negative ENSO phases off the Changjiang River Estuary were reduced. When there were no nutrients in the freshwater discharge, the composite differences in the chlorophyll concentration between the positive and negative ENSO phases off the Changjiang River Estuary were reduced by one order of magnitude. The discharge can modify the stratification off the Changjiang River Estuary, and the nutrients carried by the discharge play a dominant role in determining the interannual variation of the chlorophyll concentration associated with the ENSO cycles.