Primary Control Mechanism Research Articles

Long-term nitrogen application decreased mineral-associated organic carbon while increasing particulate organic carbon in purple soil in southwest China

In recent years, anthropogenic activities have increased nitrogen (N) input into terrestrial ecosystems, profoundly impacting soil organic carbon (SOC) sequestration. However, the potential mechanisms through which N affects mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) remain unclear. To address this gap, we conducted a 12-year field trial applying continuous N application (0, 90, 180, 270, and 360 kg N·ha−1) in a maize agro-ecosystem. We assessed plant biomass (yield, straw, and root biomass), microbial properties (enzyme activity, biomass, and diversity), soil chemistry (pH, N availability, and base ions), mineralogy (oxides and silicates), and SOC fractions to elucidate the primary control mechanisms influencing MAOC and POC. Our findings showed that N application increased SOC and POC by 6.56%–10.4% and 43.1%–54.0%, respectively, but decreased MAOC by 7.31%–17.1%. And N application increased plant biomass, but decreased soil pH (pH from 6.7 to 5.6), base ion concentrations (K⁺, Na⁺, Ca2⁺, Mg2⁺), amorphous oxides, and illite content. Partial least squares path model (PLS-PM) and correlation analyses indicated that N application enhances root biomass while increasing microbial decomposition, and ultimately their combined effect increased POC. The decline in MAOC is primarily attributed to soil acidification decreasing the C input from microbial residues, altering mineral composition and diminishing the minerals' capacity to protect SOC. Thus, our study demonstrates that N addition predominantly increases POC through enhanced root biomass, while reducing MAOC by decreasing microbial biomass and weakening mineral protection. These insights provide a deeper understanding of the mechanisms governing SOC fraction dynamics in answer to N inputs in agroecosystems.

Integrated study on CO2 enhanced oil recovery and geological storage in tight oil reservoirs

Carbon utilization, and sequestration (CUS) in tight oil reservoirs stands as a pivotal strategy for enhancing oil recovery and mitigating CO2 emissions. Research on CUS mainly focuses on the calculation of overall displacement efficiency and the total sequestration amount. However, the primary control and sequestration mechanisms throughout the life cycle of CUS, as well as the contribution of each mechanism at different development stages and under various injection and production parameters, are not clear, which limits effective guidance for oilfield development. Therefore, this paper studies the entire life cycle of tight oil reservoirs, from water flooding to CO2 flooding and CO2 sequestration after reservoir abandonment. The contribution degree changes of dissolution, structural, residual gas and mineralized sequestration mechanisms during the whole life cycle are analyzed. The results show that the main sequestration mechanism during CO2 flooding stage and injection sequestration stage after shutting down production wells is structural sequestration, which accounts for 84.75%. In the 2000 years following the cessation of CO2 injection, the proportion of structural sequestration gradually decreases, with a cumulative decrease of 12.41%, and it is mainly converted to the other three sequestration modes, with the largest increase in mineralization sequestration, reaching 8.81%, mainly due to the reaction of dicalcium silicate with CO2 to produce more stable calcite. When the injection pressure was increased from 23 MPa to 44 MPa, the sequestration efficiency increased by 18.45%. An interesting finding is that the solubility of CO2 in water in the target reservoir reaches its lowest point at 80 °C, and both warming and cooling at this point are conducive to the dissolution and sequestration of CO2. The initial pH value of formation water mainly affects mineralization and sequestration. The rate of calcite production and the contribution of CO2 dissolution and sequestration are positively correlated with water saturation. The findings underscore the importance of understanding dynamic contributions of various sequestration mechanisms and optimizing conditions to enhance CO2 sequestration efficiency.

Thermal Response Characteristics of Concrete-Filled Steel Tube Columns with Flame Encapsulation Thickness

In order to elucidate the influence of flame encapsulation thickness on the thermal response characteristics of concrete-filled steel tube columns in a fire environment, a study was conducted focusing on the primary control mechanism of heat radiation power from fire——the thickness of fire encapsulation. The thermal resistance effect at the interface between the steel tube and concrete, as well as the temperature rise characteristics of the flame, were comprehensively considered. A calculation method was established for the thermal response characteristics of concrete-filled steel tube columns under different flame encapsulation thickness conditions, providing support for the simulation of thermal response and temperature rise prediction of concrete-filled steel tube columns in fires. The results indicate that the flame emissivity and radiant heat power increase with the increase of flame encapsulation thickness. As the flame encapsulation thickness gradually increases, the growth trend of flame radiant power slows down. When the flame encapsulation thickness L < 1 m, the temperature rise rate of the concrete-filled steel tube column is significant. When the flame encapsulation thickness L ≥ 1 m, the temperature rise rate of the concrete-filled steel tube column tends towards a constant value.

A new perspective on frequency control in conventional and future interconnected power systems

In the interconnected power systems, the frequency change during disturbances may manifest differently in certain areas in the initial moments after the disturbance. Due to wave propagation, generating units located in distant areas contribute to primary frequency control (PFC) with a certain time delay. To address this issue, this study presents a novel primary frequency control (PFC) mechanism that enables generators in remote areas to adjust their output power before the disturbance wave propagates to that area. This mechanism leverages the use of PMU systems to enable early power adjustments. The proposed PFC mechanism is applicable to both conventional interconnected power systems and future systems with a significant share of converter-based technologies. The effectiveness of the method is demonstrated through simulations conducted on a two-area power system model, showing a 15 % reduction in maximum frequency deviation compared to the conventional method. This improvement results in a lower frequency nadir, offering the potential for a decrease of frequency nadir of up to 0.2 Hz when the disturbance causes the frequency drop to 49 Hz.

Measuring knowledge exploration and exploitation in universities and the relationship with global ranking indicators

This study examines the primary external control mechanism of universities (i.e. international rankings) to assess their knowledge exploration and exploitation performance. A taxonomy of indicators from the perspective of ambidexterity is presented. The most prestigious global university rankings are assessed within this theoretical framework. Exploration and exploitation indicators in the rankings are analysed in relation to the input, output and outcomes of universities. The results indicate a predominance of exploitation indicators in rankings. The potential managerial implications of this imbalance in indicators are discussed.

Visualizing Mitophagy with Fluorescent Dyes for Mitochondria and Lysosome.

Mitochondria, being the powerhouses of the cell, play important roles in bioenergetics, free radical generation, calcium homeostasis, and apoptosis. Mitophagy is the primary mechanism of mitochondrial quality control and is generally studied using microscopic observation, however in vivo mitophagy assays are difficult to perform. Evaluating mitophagy by imaging live organelles is an alternative and necessary method for mitochondrial research. This protocol describes the procedures for using the cell-permeant green-fluorescent mitochondria dye MitoTracker Green and the red-fluorescent lysosome dye LysoTracker Red in live cells, including the loading of the dyes, visualization of the mitochondria and the lysosome, and expected outcomes. Detailed steps for the evaluation of mitophagy in live cells, as well as technical notes about microscope software settings, are also provided. This method can help researchers observe mitophagy using live-cell fluorescent microscopy. In addition, it can be used to quantify mitochondria and lysosomes and assess mitochondrial morphology.

Control and Performance of 240-Clamped Space Vector PWM in Three-Phase Grid-Connected Photovoltaic Converters Under Adverse Grid Conditions

This article evaluates the performance of a relatively new pulsewidth modulation (PWM) method i.e., 240 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> -clamped space vector PWM (240CPWM), in three-phase grid-connected photovoltaic (PV) converters under various grid voltage conditions. 240CPWM is a minimum switching loss PWM method that reduces the switching loss by 85% at unity power factor and has better total harmonic distortion (THD) as compared to conventional space vector PWM. A unique six-pulse dynamically varying dc-link voltage is required for 240CPWM. Typically, a three-phase grid-connected PV system consists of a dc–dc stage followed by a dc–ac stage. In this article, the dc–dc stage is operated in closed-loop control to shape the dynamic dc-link voltage required for 240CPWM. The dc–ac stage is operated in the current control mode using a proportional–integral controller along with a harmonic compensator to ensure sinusoidal grid currents along with maximum power point tracking. The modulation index of the dc–ac stage is uncontrolled and fixed at the maximum value, and the primary control mechanism changes the magnitude, phase, and wave shape of the dc-link voltage. The coordinated control of dc–dc and dc–ac stages is ensured for better dynamic performance and grid support functions. Finally, the performance of the grid-connected PV converter with 240CPWM is validated using a three-phase 3-kW 208-V hardware prototype under nonunity power factors, voltage unbalance, and voltage sag/swell conditions for the first time. The implemented control with 240CPWM achieves smooth operation under nonunity power factor and grid voltage disturbance conditions with THD as low as 3.5% and peak combined efficiency of dc–dc and dc–ac stages as 96.4%.

Experimental study on interaction mechanism on the mass burning rate in two n-heptane fires with cross airflows

This work aims to interpret the flame interaction mechanisms of the mass burning rates of two pool fires in a cross-airflow. The flame morphology, mass burning rate, and heat feedback components are measured. The results show that the mass burning rates of the two pool fires increase rapidly, then decrease, and finally increase slowly with wind speed. Owing to the blockage and air entrainment restriction effect of the upstream flame on cross airflow, the critical transition (from increasing to decaying) of the mass burning rate of the downstream flame corresponds to a relatively larger cross airflow speed under the same experimental conditions. In general, with increasing fire spacing, the dominant mechanism of flame interaction transitions from interactive blockage and air entrainment restriction to heat feedback enhancement to monopolar blockage and air entrainment restriction. The process of the primary control mechanism from radiation dominance to convection dominance with the increase of airflow speed is revealed. Finally, based on the stagnant layer theory, a model of the mass burning rates is developed for the convection-dominated multiple pool fires in the non-merging stage.

Numerical Study of Stream-wise and Span-wise Nanosecond DBD Plasma Actuators Effects on Supersonic Flow Separation

The current paper aimed to investigate the primary control mechanism of various Nanosecond Dielectric Barrier Discharge (NS-DBD) plasma actuators on the Shock Wave/Boundary Layer Interaction (SWBLI). For this purpose, the effects of the NS-DBD actuator have been investigated on an M=2.8 supersonic flow numerically. The Reynolds Averaged Navier-Stokes (RANS) equations and SST turbulence model were used as the governing equations to simulate the supersonic flow characteristics. The numerical simulation of the baseline flow (without plasma actuator) was verified using an investigation on wall pressure distribution and the size of SWBLI. Then, NS-DBD phenomenological model based on the energy deposition model in accordance with experimental data was applied to the baseline simulation. Moreover, various stream-wise and span-wise NS-DBD plasma actuator models were used to investigate the actuator effects on the studied flow’s low-density separation zone. Comparing the numerical results of the stream-wise and span-wise actuations revealed that both actuator types cause a momentum transferred to the flow, consequently decreasing the SWBLI region’s size and the boundary layer’s thickness. The results showed that the presence of the NS-DBD actuator increased the local temperature of flow over the insulated electrode. In this regard, a stream-wise NS-DBD actuator with a length of 90 mm upstream of the SWBLI increased the separation flow velocity by 33.7% and decreased the length of the separation region by 5 mm. Also, in this case, after 170 microseconds from the start of actuation, the size of SWBLI decreased by 4.2 mm. Therefore, it can be concluded that the stream-wise type of actuation was more effective in reducing the flow separation and SWBLI size than the span-wise type due to vortex generation into the inlet flow and suppressing the SWBLI region. The proposed NS-DBD actuators were mainly capable of applying the momentum to the boundary layer and reducing the velocity of separated flow in the SWBLI zone. The micro shock wave propagation through the flow associated with the NS-DBD discharge of the actuators can produce more effective high-speed flow control.

A theoretical model for flow regulation in the cerebral cortex: role of penetrating arterioles

Activation of a region of the brain results in a local increase in blood flow, a process known as neurovascular coupling (NVC). Here, a theoretical model of blood flow regulation in the cerebral cortex is utilized to investigate the potential role of penetrating arterioles as the primary mechanism for local control of blood flow. Penetrating arterioles connect pial arterioles with the capillary meshwork deeper in the cortex and have a typical length of approximately 600 μm. This is about one‐sixth of the length of corresponding small arterioles in skeletal muscle. The question arises whether these relatively short arterioles can achieve the range of flow modulation observed in the cerebral cortex. A previously developed compartmental model for flow regulation in skeletal muscle was modified to represent the structure of cerebral microvasculature. A compartment consisting of penetrating arterioles with a reference diameter of 14.8 μm and a length of 600 μm is assumed to provide active control of blood flow. Smooth muscle tone in these arterioles is assumed to depend on a combination of signals representing myogenic, shear‐dependent, and metabolic responses. The metabolic response is represented by a change in endothelial cell membrane potential, propagated upstream along arterioles by conducted responses. Sensitivity of diameter to membrane potential was determined based on experimental data. According to the model, a hyperpolarization of 40 mV can result in an increase in local blood flow by approximately 70%. Since increases in local blood flow of 50% with activation have been observed, these results imply that vasoconstriction and vasodilation by penetrating arterioles can provide typical levels of blood flow control seen in neurovascular coupling.

Modelling the structure and functioning of an upwelling ecosystem in the Southern Taiwan Strait, China

A first mass balance food web model was developed to parameterize and characterize the structure and functioning of the upwelling ecosystem in the Southern Taiwan Strait ( STWS ). The model representing the ecosystem state and trophic flows in 2001 includes 50 functional groups from primary producer to marine mammal and 6 fishing fleets. The basic outputs and trophic flows in the ecosystem are analyzed using ecological indicators. Results indicate that phytoplankton, zooplankton, benthos and shrimps are structuring groups while dolphins, top predatory fishes, seabirds, lizard fish, hairtail and mantis shrimps are the keystone groups within the ecosystem. Based on the maturity indicators, STWS is at a mature state. An analysis of control mechanisms indicates that the top-down effect was the primary ecosystem control mechanism, although bottom-up effect was also in play. In addition, fishing impacts were analyzed throughout the food web. Such modelling of the structure and functioning of ecosystem provides basic information for stakeholders and policy-makers to implement ecosystem-based management. • The first mass balance model in Southern Taiwan Strait (STWS) is developed. • The structure and functioning of STWS are characterized. • The top-down effect is the main mechanism of ecosystem control in STWS. • The bottom-up effect can be enhanced in the STWS due to the upwelling effect.

Observer-based Purge Estimation for Robust Air Fuel Ratio Control of Internal Combustion Engines

This paper presents a purge estimation method for a robust air fuel ratio control of internal combustion engines. The air fuel ratio control is a primary emission control mechanism of gasoline engines, and purge is one of the most critical disturbances that can lead to significant air fuel ratio excursions. In this work, Luenberger-like unknown input observers are proposed to estimate purge flow rate and purge fuel fraction using existing sensors available in production engine management systems. The convergence properties of the proposed observers are investigated analytically and numerically. The estimation method allows to improve accuracy of the air fuel ratio control by compensating for the purged fuel, thereby it allows aggressive purge in a wide range of operational conditions to meet stringent evaporative emission standards.

An optimization‐based congestion control for constrained application protocol

SummaryThe Constrained Application Protocol (CoAP) is a lightweight web transfer protocol designed based on the REST architecture standardized by the Internet Engineering Task Force (IETF) to meet and accommodate the requirements of the constrained Internet of Things (IoT) environments. Managing congestion control in a resource‐constrained lossy network with a high bit error rate is a significantly challenging task that needs to be addressed. The primary congestion control mechanism defined by CoAP specification leverages on basic binary exponential backoff and often fails to utilize the network dynamics to the best of its traffic conditions. As a result, CoCoA has been introduced for better IoT resource utilization. In addition, CoCoA retransmission timeout (RTO) for network dynamics is based on constant coefficient values. The resource‐constrained nature of IoT networks poses new design challenges for congestion control mechanisms. In this paper, we propose a new particle swarm optimization (PSO)‐based congestion control approach called psoCoCoA as a variation of CoCoA. The psoCoCoA applies random and optimal parameter‐driven simulation to optimize default CoAP parameters and update the fitness and velocity positions to adapt to the traffic conditions. This process is performed for different traffic scenarios by varying the retransmission and max‐age values by using the optimization‐based algorithm. We carried out extensive simulations to validate the congestion control performance for CoAP with Observe, CoCoA, and psoCoCoA with different network topologies. The results indicate that psoCoCA outperforms or very similar to CoCoA and achieves better performance compared to CoAP with Observe under different network scenarios.

Self-assembly of multi-component mitochondrial nucleoids via phase separation.

Mitochondria contain an autonomous and spatially segregated genome. The organizational unit of their genome is the nucleoid, which consists of mitochondrial DNA (mtDNA) and associated architectural proteins. Here, we show that phase separation is the primary physical mechanism for assembly and size control of the mitochondrial nucleoid (mt-nucleoid). The major mtDNA-binding protein TFAM spontaneously phase separates in vitro via weak, multivalent interactions into droplets with slow internal dynamics. TFAM and mtDNA form heterogenous, viscoelastic structures in vitro, which recapitulate the dynamics and behavior of mt-nucleoids in vivo. Mt-nucleoids coalesce into larger droplets in response to various forms of cellular stress, as evidenced by the enlarged and transcriptionally active nucleoids in mitochondria from patients with the premature aging disorder Hutchinson-Gilford Progeria Syndrome (HGPS). Our results point to phase separation as an evolutionarily conserved mechanism of genome organization.

Admins, mods, and benevolent dictators for life: The implicit feudalism of online communities

Online platforms train users to interact with each other through certain widespread interface designs. This article argues that an “implicit feudalism” informs the available options for community management on the dominant platforms for online communities. It is a pattern that grants user-administrators absolutist reign over their fiefdoms, with competition among them as the primary mechanism for quality control, typically under rules set by platform companies. Implicit feudalism emerged from technical conditions dating to early online networks. In light of alternative management mechanisms with more democratic features, it becomes all the more clear that implicit feudalism is not a necessary condition.

Dynamic Moral Hazard and Optimal Accruals

We investigate the impact of accrual accounting on contracting and the characteristics of optimal accrual policies in a continuous-time moral hazard framework. An agent who controls unobservable fundamental performance is compensated via a contract written on cash flows, which contain timing errors, and accounting earnings, which correct timing errors at the expense of introducing measurement errors. Deferred incentives and accruals are substitutes in solving the incentive problems created by cash flow timing errors, and accruals dominate deferred incentives as measurement becomes more precise. If cash flows and earnings are sufficiently informative, then accruals are the primary control mechanism late in the agency relationship when the most efficient accrual policy is time-invariant and standardized - it is driven by measurability rather than agency-specific parameters. By contrast, deferred incentives are the primary control mechanism early in the agency relationship, when the most efficient accrual policy changes over time, is non-standardized, and corrects fewer timing errors than the standardized policy. Overall, our model links optimal long-term incentives to accrual accounting policies and generates novel predictions about dynamic contracting and accounting practices.

Knowledge, Attitudes, Practices and Information Needs During the COVID-19 Pandemic in Indonesia.

IntroductionIn the absence of vaccines and specific drugs, prevention effort has been attributed as the primary control mechanism of COVID-19. Knowledge, attitude, and practice are used to determine the current situation and formulate appropriate control interventions as well as risk communication. This study, therefore, aims to assess knowledge, attitude, practice and information needs about COVID-19 in Indonesian society.MethodsA cross-sectional study was conducted through an online survey in the third week of August 2020. Purposive and random sampling was used to select the respondents. People with a minimum age of 18 years and residing in Indonesia were allowed to participate in this study. The survey was conducted with an online questionnaire that spread on several platforms such as WhatsApp, Instagram and Facebook by distributing the link and continuous chain messages on that platform. Data were analysed using descriptive, chi-square and logistic regression test.ResultsA total of 816 respondents were included in this study. In general, public knowledge about COVID-19 was sufficient, but some topic areas were still low. Most people had a positive attitude about the COVID-19, but they provided a negative response to government policies. Most of the community has taken preventive measures for COVID-19. However, some behaviours received a low percentage. Information about how to prevent COVID-19 was the most wanted information during this pandemic. Social media was a favourite source of information, with the most popular type of visualisation was a table containing numbers. Age and education were significantly associated with knowledge. Some attitudes were affected by age and occupation scope. Gender and health insurance ownership significantly associated with preventive measures.ConclusionThis research highlights the importance of providing valid, effective, efficient, and continuous information to the public through appropriate channels to increase understanding about COVID-19 precautions.

The Integrated UPR and ERAD in Oligodendrocytes Maintain Myelin Thickness in Adults by Regulating Myelin Protein Translation.

Myelin proteins, which are produced in the endoplasmic reticulum (ER), are essential and necessary for maintaining myelin structure. The integrated unfold protein response (UPR) and ER-associated degradation (ERAD) are the primary ER quality control mechanism. The adaptor protein Sel1L (Suppressor/Enhancer of Lin-12-like) controls the stability of the E3 ubiquitin ligase Hrd1 (hydroxymethylglutaryl reductase degradation protein 1), and is necessary for the ERAD activity of the Sel1L-Hrd1 complex. Herein, we showed that Sel1L deficiency specifically in oligodendrocytes caused ERAD impairment, the UPR activation, and attenuation of myelin protein biosynthesis; and resulted in late-onset, progressive myelin thinning in the CNS of adult mice (both male and female). The pancreatic ER kinase (PERK) branch of the UPR functions as the master regulator of protein translation in ER-stressed cells. Importantly, PERK inactivation reversed attenuation of myelin protein biosynthesis in oligodendrocytes and restored myelin thickness in the CNS of oligodendrocyte-specific Sel1L-deficient mice (both male and female). Conversely, blockage of proteolipid protein production exacerbated myelin thinning in the CNS of oligodendrocyte-specific Sel1L-deficient mice (both male and female). These findings suggest that impaired ERAD in oligodendrocytes reduces myelin thickness in the adult CNS through suppression of myelin protein translation by activating PERK.SIGNIFICANCE STATEMENT Myelin is an enormous extended plasma membrane of oligodendrocytes that wraps and insulates axons. Myelin structure, including thickness, was thought to be extraordinarily stable in adults. Myelin proteins, which are produced in the endoplasmic reticulum (ER), are essential and necessary for maintaining myelin structure. The integrated unfolded protein response (UPR) and ER-associated degradation (ERAD) are the primary mechanism that maintains ER protein homeostasis. Herein, we explored the role of the integrated UPR and ERAD in oligodendrocytes in regulating myelin protein production and maintaining myelin structure using mouse models. The results presented in this study imply that the integrated UPR and ERAD in oligodendrocytes maintain myelin thickness in adults by regulating myelin protein production.

Great Blue Hole (Lighthouse Reef, Belize): A continuous, annually-resolved record of Common Era sea surface temperature, Atlantic Multidecadal Oscillation and cyclone-controlled run-off

The Holocene (<11.7 kyr BP) is characterized by several periods of distinct climate changes. Some of these climate variations had extensive effects on mankind and coincided with demises of extinct high civilizations. Annually-resolved climate reconstructions will certainly play an increasingly important role in public perception, when applying these past patterns to the recent climate debate. The future consequences of the ongoing climate crisis are still challenging to predict, due to the lack of comprehensive, annually-resolved and continuous sea-surface temperature (SST) data. Our 8.55 m long sediment core from the bottom of the Great Blue Hole (Lighthouse Reef, Belize) provides an annually-resolved, continuous and unique south-western Caribbean climate record for the last 1885 years. The varved, “lake-like” sinkhole successions of marine carbonates encompass approximately the entire Common Era (0 CE-modern), a time window, which is key for studying climatic variations and their effects on human society. Our SST record is based on stable isotopes (δ18O) and molecular proxy applications (TEX86). Throughout the Common Era, oxygen isotopes (δ18O) and TEX86 data imply a general SST rise of 0.5 °C and 1.3 °C, respectively, within the south-western Caribbean. The modulation of SST within the Common Era time series likely operated on two different time levels: (1) Solar (e.g., “Gleissberg Cycles”) and volcanic activity triggered climate changes, which in turn induced responses of the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO) and the El-Niño-Southern Oscillation (ENSO). Their changing mode of action has been identified as a likely origin of the primary, i.e., centennially scaled SST variability. We suspect long-term positive AMO and NAO modes as the primary key control mechanisms of the Dark Ages Cold and Medieval Warm Period SST patterns. ENSO mode modulation likely exerted primary control on regional SST variability during the Little Ice Age and the Modern Global Warming. (2) Our δ18O data further indicate a striking secondary control on multi-decadal time scales: δ18O variations occur with 32–64 years periodicity. This signal is clearly evidence of SST modulation controlled by AMO phase changes (50–70 years) over almost the entire Common Era. Our carbon isotope record (δ13C) exhibits two remarkable negative anomalies and a long-term up-core decreasing trend. The first excursion (drop of 0.5‰) occurred with the onset of the Medieval Warm Period, which is reconstructed to be a peak time in south-western Caribbean tropical cyclone (TC) activity. This overlap is stressing a potential context between TC activity, enhanced coastal run-off and increased soil-erosion reflected by 13C-depleted carbon isotopes. A second anomaly (>1900 CE) is more likely the result of the “Suess Effect” (anthropogenic impact of the Industrial Revolution on carbon isotopes composition) than another reflection of a TC peak activity interval.

Modulation of driving signals in flow control over an airfoil with synthetic jet

A new skill of modulating driving signals of a synthetic jet with low frequency is introduced to enhance the control authority. Based on dynamic mesh technique, the effect of flow control over a NACA0015 airfoil with a Synthetic Jet Actuator (SJA) has been investigated. The SJA is located at x/c = 10%, and two jet injection angles of 90° and 30° have been considered. Flow structures indicate that modulation with low frequency can reduce the dissipation rate of vortices after they shed off the surface. Thus aerodynamic performance of the airfoil could be improved. For the injection angle of 90°, modulation can increase the control authority of the SJA. Compared to the unmodulated case, increment of lift-to-drag ratio is up to 15%. The modulating frequency corresponding to the largest increment is FM+≈1. For the injection angle of 30°, improvement of aerodynamic forces positively relates to momentum coefficient of the SJA. Due to the decrease of effective momentum, modulation degrades the effect of flow control. The opposite responses to modulation are believed to have a relationship with the variation of primary control mechanism. When jet injection angle varies from 90° to 30°, the primary mechanism changes from the interaction of vortices and waves to the direct momentum addition. The skill of modulation of driving signals is very useful for applications of SJA.