Internal Feedback Research Articles

Nitrogen limitation of microbial activity in alpine tundra soils along an environmental gradient: Intra-seasonal variations and effect of rising temperature

Alpine tundra ecosystems exhibit one of the most limited availabilities of nitrogen. Furthermore, climate change may potentially stimulate not only soil organic matter decomposition, but also N mineralization; therefore, a better understanding of the response of microorganisms to increasing N availability is crucial for evaluating soil C cycling under warmer climate scenarios. In this study, we suggested that the degree of N limitation of microbial activity in the surface and subsurface soil horizons of a N-poor dwarf-shrub heath (DSH) and an N-rich graminoid meadow (GM) during a single active growing season. We conducted three series of laboratory incubations under natural (+10 °C) and high (+20 °C) temperatures with soil samples collected at the beginning, peak, and end of the growing season to examine the effects of rising temperature and intra-seasonal variations on the N limitation of microbial activity. We measured the contents of microbial C and N, microbial respiration, and the potential activity of peroxidase and β-1.4-glucosidase (enzymes that play a key role in the SOM turnover processes). It was found that the N limitation of microorganism activity could be dynamic and demonstrate temporal (depending on the season) and spatial (depending on the soil horizon) variations. The results disputed the universality of previous conclusions about the high degree of N limitation of microorganisms in alpine tundra soils, thereby suggesting that N is not always a limiting factor for microbial activity, even in the N-poor DSH. We found that warming could increase the N limitation of microorganisms, even in the N-rich GM soil, thereby limiting the effect of warming on the mineralization of soil organic matter. These data demonstrate the importance of further understanding the internal feedback mechanisms that control soil organic matter mineralization and microbial activity for accurately predicting the effects of global climate change in the Arctic.

The role of internal feedbacks in shifting deep lake mixing regimes under a warming climate

Abstract Climate warming is causing changes in the physics of deep lakes, such as longer summer stratification, increased water column stability, reduced ice cover, and a shallower depth of winter overturns. An ultimate consequence of warming would be a transition to a different mixing regime. Here we investigate the role of physical, chemical, and biological feedback mechanisms that unfold during a shift in mixing regime, and whether these feedbacks could prompt and stabilise the new regime. Although climate, interannual temperature variation, and lake morphometry are the main determinants of a mixing regime, when climate change causes shifts in mixing regime, internal feedback mechanisms may gain in importance and modify lake ecosystem functioning. We review the role of these feedbacks in three mixing regime shifts: from polymictic to seasonally stratified, from dimictic to monomictic, and from holomictic to oligomictic or meromictic. Polymictic lakes of intermediate depth (c. 3–10 m mean depth) could experience seasonal stratification if a stratification event triggers phytoplankton blooms or dissolved organic matter release, reducing transparency and therefore further heating the surface layer. However, this feedback is only likely to have influence in small and clear lakes, it would be easily disturbed by weather conditions, and the resulting stratified state does not remain stable in the long term, as stratification is lost in winter. The ice‐albedo feedback might cause an accelerated shift from ice‐covered (dimictic) to ice‐free (monomictic) winters in sufficiently deep (mean depth 50 m or more) lakes, where temperature memory is carried over from one winter to the next. Nevertheless, there is an ongoing debate into whether this process can persist during natural weather variations and overcome self‐stabilising mechanisms such as thermal insulation by snow. The majority of studies suggest that a gradual transition from dimictic to monomictic is more likely than an abrupt transition. A shift from a holomictic to a meromictic regime can occur if anoxia is triggered by incomplete mixing and an increase in deep‐water density—through the accumulation of solutes—exceeds a density decrease by hypolimnetic warming. A shift to meromixis would strongly alter the biology of a lake and might be difficult to reverse. If solutes accumulate only minimally in the hypolimnion, an oligomictic regime is formed, in which years with complete and incomplete mixing alternate. Understanding the importance of feedback mechanisms and the role of biogeochemistry when lakes shift in mixing regime could lead to a better understanding of how climate change affects lake ecosystems.

Spontaneous Patterning during Frontal Polymerization.

Complex patterns integral to the structure and function of biological materials arise spontaneously during morphogenesis. In contrast, functional patterns in synthetic materials are typically created through multistep manufacturing processes, limiting accessibility to spatially varying materials systems. Here, we harness rapid reaction-thermal transport during frontal polymerization to drive the emergence of spatially varying patterns during the synthesis of engineering polymers. Tuning of the reaction kinetics and thermal transport enables internal feedback control over thermal gradients to spontaneously pattern morphological, chemical, optical, and mechanical properties of structural materials. We achieve patterned regions with two orders of magnitude change in modulus in poly(cyclooctadiene) and 20 °C change in glass transition temperature in poly(dicyclopentadiene). Our results suggest a facile route to patterned structural materials with complex microstructures without the need for masks, molds, or printers utilized in conventional manufacturing. Moreover, we envision that more sophisticated control of reaction-transport driven fronts may enable spontaneous growth of structures and patterns in synthetic materials, inaccessible by traditional manufacturing approaches.

Trend correlations for coastal eutrophication and its main local and whole-sea drivers - Application to the Baltic Sea.

Coastal eutrophication is a major environmental issue worldwide. In the Baltic Sea, eutrophication affects both the coastal waters and the open sea. Various policy frameworks aim to hinder its progress but eutrophication-relevant water quality variables, such as chlorophyll-a concentrations, still exhibit opposite temporal trends in various Baltic Sea marine and coastal waters. In this study, we investigate the temporal-trend linkages of measured water quality variables and their various anthropogenic, climatic and hydrospheric drivers over the period 1990-2020 with focus on the Swedish coastal waters and related marine basins in the Baltic Sea. We find that it is necessary to distinguish more and less isolated coastal waters, based on their water exchanges with the open sea, to capture different coastal eutrophication dynamics. In less isolated coastal waters, eutrophication is primarily related to nitrogen concentrations, while it is more related to phosphorus concentrations in more isolated coastal waters. In the open sea, trends in eutrophication conditions correlate best with trends in climatic and hydrospheric drivers, like wind speed and water salinity, respectively. In the coastal waters, driver signals are more mixed, with considerable influences from anthropogenic land-based nutrient loads and sea-ice cover duration. Summer chlorophyll-a concentration in the open sea stands out as a main change driver of summer chlorophyll-a concentration in less isolated coastal waters. Overall, coastal waters are a melting pot of driver influences over various scales, from local land-based drivers to large-scale total catchment and open sea conditions. The latter in turn depend on long-term integration of pathway-dependent influences from the various coastal parts of the Baltic Sea and their land-based nutrient load drivers, combined with overarching climate conditions and internal feedback loops. As such, our results challenge any unidirectional local source-to-sea paradigm and emphasize a need for concerted local land-catchment and whole-sea measures for robust coastal eutrophication management.

Fractional Sliding-Mode Control for Microgyroscope Based on Multilayer Recurrent Fuzzy Neural Network

In this article, an approximation-based adaptive fractional sliding-mode control (SMC) scheme is proposed for a microgyroscope, where a double-loop recurrent fuzzy neural network (DLRFNN) is employed to approximate system uncertainties and disturbance. A fractional-order term is incorporated into the sliding surface that could add an extra degree of freedom and combine the advantages of fractional calculus and SMC. A new four-layer fuzzy neural network (FNN) is studied, which has two feedback loops (internal feedback loop and external feedback loop) to capture the weights and output signal calculated in the previous step and use it as a feedback signal for the next step. On the one hand, the proposed DLRFNN structure combines a fuzzy system to process uncertain information with a neural network to learn from the process. On the other hand, both the internal state information and the output signal are acquired and stored so that better approximation performance is obtained compared with a regular FNN system. Furthermore, the adaptive laws of DLRFNN parameters are derived, which can automatically update free parameters with a bound. Finally, the effectiveness of the proposed adaptive fractional SMC using the DLRFNN strategy is identified by the simulations’ analysis with different fractional orders, whereby tracking errors are uniformly ultimately bounded. The proposed adaptive fractional SMC using the DLRFNN strategy can achieve remarkably superior tracking performance in terms of high precision and fast response by comprehensive comparisons.

Integrating Non-spiking Interneurons in Spiking Neural Networks.

Researchers working with neural networks have historically focused on either non-spiking neurons tractable for running on computers or more biologically plausible spiking neurons typically requiring special hardware. However, in nature homogeneous networks of neurons do not exist. Instead, spiking and non-spiking neurons cooperate, each bringing a different set of advantages. A well-researched biological example of such a mixed network is a sensorimotor pathway, responsible for mapping sensory inputs to behavioral changes. This type of pathway is also well-researched in robotics where it is applied to achieve closed-loop operation of legged robots by adapting amplitude, frequency, and phase of the motor output. In this paper we investigate how spiking and non-spiking neurons can be combined to create a sensorimotor neuron pathway capable of shaping network output based on analog input. We propose sub-threshold operation of an existing spiking neuron model to create a non-spiking neuron able to interpret analog information and communicate with spiking neurons. The validity of this methodology is confirmed through a simulation of a closed-loop amplitude regulating network inspired by the internal feedback loops found in insects for posturing. Additionally, we show that non-spiking neurons can effectively manipulate post-synaptic spiking neurons in an event-based architecture. The ability to work with mixed networks provides an opportunity for researchers to investigate new network architectures for adaptive controllers, potentially improving locomotion strategies of legged robots.

Lake thermal structure drives interannual variability in summer anoxia dynamics in a eutrophic lake over 37 years

Abstract. The concentration of oxygen is fundamental to lake water quality and ecosystem functioning through its control over habitat availability for organisms, redox reactions, and recycling of organic material. In many eutrophic lakes, oxygen depletion in the bottom layer (hypolimnion) occurs annually during summer stratification. The temporal and spatial extent of summer hypolimnetic anoxia is determined by interactions between the lake and its external drivers (e.g., catchment characteristics, nutrient loads, meteorology) as well as internal feedback mechanisms (e.g., organic matter recycling, phytoplankton blooms). How these drivers interact to control the evolution of lake anoxia over decadal timescales will determine, in part, the future lake water quality. In this study, we used a vertical one-dimensional hydrodynamic–ecological model (GLM-AED2) coupled with a calibrated hydrological catchment model (PIHM-Lake) to simulate the thermal and water quality dynamics of the eutrophic Lake Mendota (USA) over a 37 year period. The calibration and validation of the lake model consisted of a global sensitivity evaluation as well as the application of an optimization algorithm to improve the fit between observed and simulated data. We calculated stability indices (Schmidt stability, Birgean work, stored internal heat), identified spring mixing and summer stratification periods, and quantified the energy required for stratification and mixing. To qualify which external and internal factors were most important in driving the interannual variation in summer anoxia, we applied a random-forest classifier and multiple linear regressions to modeled ecosystem variables (e.g., stratification onset and offset, ice duration, gross primary production). Lake Mendota exhibited prolonged hypolimnetic anoxia each summer, lasting between 50–60 d. The summer heat budget, the timing of thermal stratification, and the gross primary production in the epilimnion prior to summer stratification were the most important predictors of the spatial and temporal extent of summer anoxia periods in Lake Mendota. Interannual variability in anoxia was largely driven by physical factors: earlier onset of thermal stratification in combination with a higher vertical stability strongly affected the duration and spatial extent of summer anoxia. A measured step change upward in summer anoxia in 2010 was unexplained by the GLM-AED2 model. Although the cause remains unknown, possible factors include invasion by the predacious zooplankton Bythotrephes longimanus. As the heat budget depended primarily on external meteorological conditions, the spatial and temporal extent of summer anoxia in Lake Mendota is likely to increase in the near future as a result of projected climate change in the region.

Performance Improvement of a Two-Stage Proportional Valve With Internal Hydraulic Position Feedback

Abstract The present research concentrates on the performance improvement of a two-stage proportional valve with internal hydraulic position feedback which is named as the Valvistor valve. In this paper, the performance constraint of this valve is identified and a novel electronic closed-loop control strategy with an integral-separation fuzzy proportional-integral-derivative controller is proposed to improve the valve performance, including the static characteristics and the dynamic characteristics. The results show that in the Valvistor valve, the comparison point and the feedback loop for the internal hydraulic position feedback is only in the main stage, while the input is in the pilot stage. This leads to the poor performance of this valve. The control strategy is very effective and the performance of the Valvistor valve is improved. With the control strategy, the error of the poppet displacement is reduced from 4.9% to 2.1% by adjusting the spool displacement in the pilot stage in real-time and the flow error is reduced from 5.3% to 2.3%. The dead zone of the poppet displacement and the flow is eliminated. The hysteresis is reduced from 5.3% to 2.6% and the linearity is improved. The overshoot is reduced from 0.06 to 0.02 mm and the settling time is reduced from 0.5 to 0.2 s. Moreover, the bandwidth is increased from 8 to 16 Hz.

Pacific Decadal Oscillation-like variability at a millennial timescale during the Holocene

Sea surface temperatures (SSTs) in the North Pacific exert a great influence on global climate and ecosystem changes. The Pacific Decadal Oscillation (PDO) is the leading mode of decadal SST variability in the North Pacific. The PDO-like variability at a millennial timescale during the Holocene is still poorly understood. In this study, the millennial-scale PDO-like variability during the Holocene is explored using model–data comparisons. To reduce the uncertainties caused by differential age controls, this study reconstructs the Holocene PDO-like index using two types of published proxy records, including 1) east–west SST contrast in the extratropical North Pacific and 2) PDO-related precipitation anomalies in East Asia. These two reconstructions reveal coherent changes in the PDO-like pattern during the Holocene, showing positive phases at 10.4–8.5 ka BP and 3.5–3.0 ka BP, and negative phases at 8.5–3.5 ka BP and 3.0–0.2 ka BP. Climate simulations suggest that the millennial-scale PDO-like variability is predominantly controlled by orbital forcing during the Holocene, leading to a positive phase of the PDO-like regime during the early Holocene. The positive phase of the PDO-like regime between 3.5 and 3.0 ka BP was probably caused by the internal feedback of the climate system, which the climate simulations fail to capture.

Internal positive feedback promotes water quality improvement for a recovering hyper-eutrophic lake: A three-dimensional nutrient flux tracking model

Nutrient dynamics in lakes are determined by the combined effects of external and internal nutrient fluxes. However, the feedback loop of nutrient fluxes and water quality changes is still an open question. An integrated three-dimensional flux tracking approach based on the Environmental Fluid Dynamics Code model was established to quantify the long-term dynamic changes in external and internal processes in Lake Dianchi (one of the three most hyper-eutrophic lakes in China), and to explore the potential causes of water quality improvement during 2012–2018. The long-term trends and relative influences of nutrient fluxes on water quality were identified. The results showed that the inflow flux was the largest input source and declined by 50% between 2003 and 2012, which was followed by a stable trend from 2012 to 2018. The second largest input source was benthic release, which exhibited a significant interannual reduction. Algae sedimentation was the largest removal process, and declined by 45% between 2012 and 2018. An integrated analysis demonstrated that, following an external loading reduction prior to 2012, the positive feedback of internal fluxes promoted water quality improvement during 2012–2018. Considering the long timescale of the nutrient-flux feedback mechanism, reducing external loading is still the top priority for a long-term virtuous cycle of water quality in the process of eutrophic lake restoration.

Utilizing four-node tetrahedra-shaped Hopfield neural network configurations in the local magnetization assessment of 3d objects exhibiting hysteresis

There is no doubt that the accurate assessment of local magnetization in three-dimensional objects exhibiting hysteresis is crucial to accurate performance estimation of a variety of electromagnetic devices. Recently, it has been demonstrated that a Stoner-Wohlfarth-like elementary hysteresis operator may be constructed using two-node Hopfield neural network (HNN) having internal positive feedback. Based upon the previously mentioned approach, this paper presents a methodology using which local magnetization in 3D objects exhibiting hysteresis may be assessed. The approach utilizes a four-node tetrahedron-shaped HNN with activation functions constructed using a weighted superposition of a step and sigmoidal functions in accordance with the M − H curve of the material under consideration. In this approach, the internal feedback factors between the different nodes for any tetrahedron are dependent on its geometrical configuration. Hence, shape configuration effects on the magnetization patterns of any three-dimensional object approximated by an ensemble of tetrahedra are implicitly taken into consideration. To demonstrate the applicability of the proposed approach, computations were carried out for different three-dimensional magnetized bodies having different M − H curves. Theoretical and computational details of the approach are given in the paper.

Spatial patterns in a vegetation model with internal competition and feedback regulation

The vegetation patterns are a characteristic particularity of semiarid zones, which can be the future of modern ecology for its importance. This paper aims to study a diffusive vegetation model for the subject of studying the complex patterns generated by the presence of Turing-Hopf bifurcation. The main focus is on analyzing the effect of the locative internal rivalry between plants and feedback regulation on the pattern formations. The cross-diffusion produced by the positive feedback regulation generates surprising dynamics such as Hopf bifurcation, Turing bifurcation, Turing-Hopf bifurcation, which confirms the imbalance of the distribution of the vegetation in the semi-desert regions. For analyzing the spatiotemporal behavior near the Turing-Hopf bifurcation point, the Amplitude equation restricted at this point is used. Further, by using numerical simulations, the complex dynamics induced by the positive feedback redistribution and inner competition are explored.

Застосування зворотного зв’язку в автономному навчанні іншомовного спілкування

The article deals with the use of feedback in the autonomous learning of foreign language communication of students in higher education institutions. The authors analyzed the scientific and methodological literature on the research topic, identified the main methodological fundamentals for the feedback application and provided recommendations for the use of feedback in the autonomous learning of foreign language communication of students in higher education institutions. The article identifies the levels of student autonomy, reveals the essence of the outcome and cognitive feedback, as well as the features of internal and external feedback. According to the developed abilities, the levels of student’s autonomy can be the following: a high / advanced level, a moderate / intermediate level, a low / beginning level. It is cleared out that the most frequent outcome feedback gives learners little advice on their own self-study. Scientists often compare cognitive feedback with outcome feedback. The latter also recommends some ways of dealing with difficulties. It is stated that the internal feedback is invoked by students’ monitoring of themselves and links their past outcomes with the expected. Simultaneously, students get external feedback from numerous sources. It can be spontaneous or conscious and intended. Feedback has been found to be a prerequisite for effective foreign language learning for students with different levels of autonomy.

The meaning of feedback: medical students’ view

Abstract: Introduction: The teaching-learning process in health involves a binomial: on the one hand, teaching (the teacher and the institution) and, on the other hand, the students and their ability to adequately interact in this context. Just as teaching requires specific skills, learning also requires students to be able to master the necessary skills for learning. Feedback should also be understood in this regard. Although feedback is a frequent topic in the literature, few studies have addressed its meaning and impact from the students’ perspective. Moreover, a gap has been identified between theory and practice regarding the real power of feedback in the teaching-learning process. Objective: This study aimed to assess medical students’ understanding of feedback. Method: This is a qualitative research with a descriptive and exploratory focus, carried out using in the case study modality, with the focus group technique in data collection and thematic content analysis. The participants were medical students attending the fourth-year or eighth-semester at three schools located in the state of Goiás, Brazil. Results: The following categories emerged: understanding of feedback, frequency of received feedback, impact of feedback on the teaching-learning process and perception about the received feedback. Students understood in part the concept of feedback, not recognizing the internal feedback. A low frequency of feedback was reported and depended on the teacher, subject and year/semester of the course related to the type of curriculum. Even so, the participants recognized the points of feedback that impact on the teaching-learning process and were receptive to effective feedback. Conclusion: Even though they knew the meaning of feedback only partially and experienced it irregularly, medical students recognized the impact of this tool on the teaching-learning process. In a context of students trained to know about their own knowledge, truly empowering them in the teaching-learning process, they will develop a constant reflective practice of generating internal feedback, allowing the actual impact of feedback on the teaching-learning process to be observed in practice, as described in the literature.

A Self-Tuning Congestion Tracking Control for TCP/AQM Network for Single and Multiple Bottleneck Topology

In this work a self-tuning rate and queue based proportional and integral controller called SRQ-PI is proposed to efficiently control the queue length with small overshoot and faster settling time. SRQ-PI proposes a new control tracking function that maps level of congestion to the packet drop probability dynamically. In SRQ-PI, the incoming traffic rate is estimated and used with the proportional and integral controller. The SRQ-PI tunes itself and stabilizes the system with internal feedback without requiring any external feedback. Furthermore, the stability of the SRQ-PI is analyzed using control theory and presents systematic guidelines to select the control gain parameters. NS2 is used to carry out the simulation work. The simulation result demonstrates that SRQ-PI is stable and gets faster transient response due to lower average delay jitter and robust against dynamic network parameters. The SRQ-PI outperforms proportional integral (PI), Intelligent adaptive PI (IAPI) and Random exponential marking (REM) algorithm.

The meaning of feedback: medical students’ view

Abstract: Introduction: The teaching-learning process in health involves a binomial: on the one hand, teaching (the teacher and the institution) and, on the other hand, the students and their ability to adequately interact in this context. Just as teaching requires specific skills, learning also requires students to be able to master the necessary skills for learning. Feedback should also be understood in this regard. Although feedback is a frequent topic in the literature, few studies have addressed its meaning and impact from the students’ perspective. Moreover, a gap has been identified between theory and practice regarding the real power of feedback in the teaching-learning process. Objective: This study aimed to assess medical students’ understanding of feedback. Method: This is a qualitative research with a descriptive and exploratory focus, carried out using in the case study modality, with the focus group technique in data collection and thematic content analysis. The participants were medical students attending the fourth-year or eighth-semester at three schools located in the state of Goiás, Brazil. Results: The following categories emerged: understanding of feedback, frequency of received feedback, impact of feedback on the teaching-learning process and perception about the received feedback. Students understood in part the concept of feedback, not recognizing the internal feedback. A low frequency of feedback was reported and depended on the teacher, subject and year/semester of the course related to the type of curriculum. Even so, the participants recognized the points of feedback that impact on the teaching-learning process and were receptive to effective feedback. Conclusion: Even though they knew the meaning of feedback only partially and experienced it irregularly, medical students recognized the impact of this tool on the teaching-learning process. In a context of students trained to know about their own knowledge, truly empowering them in the teaching-learning process, they will develop a constant reflective practice of generating internal feedback, allowing the actual impact of feedback on the teaching-learning process to be observed in practice, as described in the literature.

Continuous assessment for learning: issues of multiple instances of peer feedback in a university course

In the context of continuous assessment for learning in a university course in French-speaking Switzerland, this article studies students’ perception when they receive multiple instances of peer feedback on a written academic assignment carried out in small collaborative groups. How do students, who are both assessees and assessors, perceive these multiple instances of feedback, especially when they are led to compare them to regulate their own initial work and their assessment skills? This article analyses in detail the processes and feelings at play when students notice similarities and differences between the instances of feedback they received and produced. Conceptual considerations are proposed around the notions of feedback, internal feedback, comprehensive feedback, and metafeedback, seen as contributing to the regulation and learning processes involved.

Design of digital regulated power supply based on feedback control

This paper studies and designs a multi-functional digital regulated power supply, which can realize the switch between the two functions of numerical control current source and numerical control voltage source, and can set the relevant current parameters and voltage parameters through the keyboard. The idea of feedback control is fully adopted to establish the internal and external double negative feedback structures, so as to improve the precision of the regulated power supply. The digital regulator has the advantages of convenient control, large amount of display data, stable performance and so on. It is suitable for various applications of small capacity power supply.

Delay Margin Optimization for Systems with Internal Delayed Feedback

In this brief paper, controller design for delay margin optimization is considered for systems with internal feedback delays (systems with delays in the state variables). Similar to existing results on delay margin optimization for finite dimensional systems with I/O delays, it is shown that the problem considered can be solved by using Nevanlinna-Pick interpolation involving non-minimum phase zeros of the plant.

Experience in monitoring the educational activities of students

Today, digital technologies allow creating and operated a virtual (online) platform that facilitates synchronous and asynchronous interaction with available resources between all parties to the learning process. In distance or blended learning, students independently organize, control, direct and regulate their activities. At the same time, monitoring, in particular by the teacher, plays a crucial role in creating internal feedback and, thus, in adopting appropriate rules. However, students may have unsatisfactory self-regulated learning outcomes due to poor monitoring. Therefore, external feedback between all actors involved in the various electronic learning management platforms is important. The article analyzes the possibilities of monitoring the educational activities of students in the study of disciplines in the system of higher education for technical and economic specialties. The main components of the study and the possibility of obtaining information about the activity and success of student learning in the learning management systems Moodle and Microsoft Teams are considered. A detailed description of obtaining information about the student's actions on the page of the discipline in the Moodle system using the blocks "Action Reports" and "Monitoring" are presented. Opportunities for monitoring all active student groups with which the teacher works, using the Insights tab and other Microsoft Teams applications are presented. The mechanisms of obtaining statistical information about the work of students during classroom and extracurricular work are described.