Local Feedback Research Articles

Dynamic control of eye-head gaze shifts by a spiking neural network model of the superior colliculus.

To reorient gaze (the eye's direction in space) towards a target is an overdetermined problem, as infinitely many combinations of eye- and head movements can specify the same gaze-displacement vector. Yet, behavioral measurements show that the primate gaze-control system selects a specific contribution of eye- and head movements to the saccade, which depends on the initial eye-in-head orientation. Single-unit recordings in the primate superior colliculus (SC) during head-unrestrained gaze shifts have further suggested that cells may encode the instantaneous trajectory of a desired straight gaze path in a feedforward way by the total cumulative number of spikes in the neural population, and that the instantaneous gaze kinematics are thus determined by the neural firing rates. The recordings also indicated that the latter is modulated by the initial eye position. We recently proposed a conceptual model that accounts for many of the observed properties of eye-head gaze shifts and on the potential role of the SC in gaze control. Here, we extend and test the model by incorporating a spiking neural network of the SC motor map, the output of which drives the eye-head motor control circuitry by linear cumulative summation of individual spike effects of each recruited SC neuron. We propose a simple neural mechanism on SC cells that explains the modulatory influence of feedback from an initial eye-in-head position signal on their spiking activity. The same signal also determines the onset delay of the head movement with respect to the eye. Moreover, the downstream eye- and head burst generators were taken to be linear, as our earlier work had indicated that much of the non-linear main-sequence kinematics of saccadic eye movements may be due to neural encoding at the collicular level, rather than at the brainstem. We investigate how the spiking activity of the SC population drives gaze to the intended target location within a dynamic local gaze-velocity feedback circuit that yields realistic eye- and head-movement kinematics and dynamic SC gaze-movement fields.

Urban Heat Island High Water-Vapor Feedback Estimates and Heatwave Issues: A Temperature Difference Approach to Feedback Assessments

The goal of this paper is to provide an initial assessment of water-vapor feedback (WVF) in humid urban heat island (UHI) environments based on temperature difference data. To achieve this, a novel temperature difference WVF model was developed that can analyze global and UHI local temperature difference data. Specifically, the model was applied to a comparative temperature literature study of similar cities located in humid versus dry climates. The literature study found that the daytime UHI ΔT was observed to be 3.3 K higher in humid compared to dry climates when averaged over thirty-nine cities. Since the direct measurement of WVF in UHI areas could prove challenging due to variations in the temperature lapse rates from tall buildings, modeling provides an opportunity to make a preliminary assessment where measurements may be difficult. Thus, the results provide the first available UHI ΔT WVF model assessment. The preliminary results find local water-vapor feedback values for wet-biased cities of 3.1 Wm−2K−1, 3.4 Wm−2K−1, and 4 Wm−2K−1 for 5 °C, 15 °C, and 30 °C UHI average temperatures, respectively. The temperature difference model could also be used to reproduce literature values. This capability helps to validate the model and its findings. Heatwave assessments are also discussed, as they are strongly affected by UHI water-vapor feedback and support the observation that humid regions amplify heat higher than UHIs in dry regions, exacerbating heatwave problems. Furthermore, recent studies have found that urbanization contributions to global warming more than previously anticipated. Therefore, cities in humid environments are likely larger contributors to such warming trends compared to cities in dry environments. These preliminary modeling results show concern for a strong local UHI water-vapor feedback issue for cities in humid environments, with results possibly over a factor of two higher than the global average. This assessment also indicates that albedo management would likely be an effective way to reduce the resulting WVF temperature increase.

A design methodology for audio amplifiers with no global negative feedback: proposal and validation

This paper proposes a structured methodology for the design of high-performance audio amplifiers without the use of global negative feedback. This type of amplifier is being suggested in order to minimize supposed deleterious effects on audio quality. The proposed methodology uses a minimum number of stages with local negative feedback operating in a high voltage range in order to minimize harmonic distortion without the need to use global feedback. As an example of applying the methodology, a 50W power amplifier is designed and built. In this design example, three stages are used with field effect transistors operating with a symmetrical voltage of }90V in the voltage gain stages and }45V in the output stage. The practical results obtained satisfied the design requirements, such as: Slew Rate above 3.6V/μs (14V/μs), Upper Cutoff Frequency above 40kHz (125kHz), THD+N below 0.5% (0.2%). Also, to ensure that the designed amplifier has a good linearity, the IMD intermodulation distortion was measured. The value of −62.5dB was obtained. In this way, the effectiveness of the proposed method for the design of audio amplifiers without global negative feedback was proven.

What Mainly Drives the Interannual Climate Variability Over the Barents‐Kara Seas in Boreal Early Autumn?

AbstractYear‐to‐year forecasts of the Arctic climate conditions have drawn much interest in recent decades. This study investigates the primary drivers responsible for interannual variations (without multi‐decadal trends) of air temperature at 2 m (T2m) and sea ice concentration (SIC) over the Barents‐Kara Seas (BKS) during September from 1950 to 2021. The Arctic Dipole (AD), a leading factor in the BKS variability, plays an important role via influencing large‐scale atmospheric circulations and local thermodynamical feedbacks (i.e., vapor and albedo feedbacks). During a negative AD phase, the positive surface air temperature advection anomalies warm up the BKS region and promote sea ice melting, which in turn maintains the below‐normal sea ice and warmer‐than‐normal conditions via positive vapor and albedo feedbacks. Moreover, our results suggest that the sea surface temperature (SST) variability in the midlatitudes of the North Atlantic in the preceding month could also be an important driver of the SIC variability over the BKS area. The anomalous temperature advections from the surface to the upper troposphere are accompanied by a Rossby wave‐type atmospheric response, which intensifies the energy exchanges between the ocean and the atmosphere. Local SST anomalies associated with the surface heat flux anomalies further persist in the following month and influence sea ice variations due to their long‐lasting memory. A better understanding of the mechanisms of interannual climate variabilities over the BKS region in boreal early autumn is helpful to improving the Arctic regional climate predictions.

Vegetation phenology and its ecohydrological implications from individual to global scales

The Earth is experiencing unprecedented climate change. Vegetation phenology has already showed strong response to the global warming, which alters mass and energy fluxes on terrestrial ecosystems. With technology and method developments in remote sensing, computer science and citizen science, many recent phenology-related studies have been focused on macrophenology. In this perspective, we 1) reviewed the responses of vegetation phenology to climate change and its impacts on carbon cycling, and reported that the effect of shifted phenology on the terrestrial carbon fluxes is substantially different between spring and autumn; 2) elaborated how vegetation phenology affects ecohydrological processes at different scales, and further listed the key issues for each scale, i.e., focusing on seasonal effect, local feedbacks and regional vapor transport for individual, watershed and global respectively); 3) envisioned the potentials to improve current hydrological models by coupling vegetation phenology-related processes, in combining with machine learning, deep learning and scale transformation methods. We propose that comprehensive understanding of climate-macrophenology-hydrology interactions are essential and urgently needed for enhancing our understanding of the ecosystem response and its role in hydrological cycle under future climate change.

Cooperative evolution under the joint influence of local popularity and global popularity

Motivated by the realistic situation that local and global information feedbacks maybe influence on the cooperative behavior, a new model of spatial prisoner’s dilemma game is proposed to consider the local popularity and global popularity based on the number of players who hold the same strategy with the central or target agent in the local and global environments. The weight of local popularity and the scaling index of the popularity are introduced to the fitness calculation. Numerical experiments show that the information of local popularity and global popularity have different effects on cooperative behavior when the scaling index of the popularity changes from positive to negative. And when the scaling index of the popularity is negative, the greater the absolute value of the scaling index is, the more conducive it is to the cooperation; but there exists the optimal value of the scaling index for the cooperative behavior when the scaling index is positive. These results maybe offer sights to a comprehensive understanding of the influence of the popularity on promoting cooperation.

Students’ uptake and perspectives on teacher and peer feedback on written assignments

PurposeThe purpose of this study is to examine the uptake of peer vs. instructor feedback provided on written essays by undergraduates in a writing course at a public university in Saudi Arabia.Design/methodology/approachThis was a classroom intervention exploratory study with 16 pairs of students attending a writing class over a period of 14 weeks.FindingsAnalysis of feedback and uptake indicated that the students incorporated a high rate (85.21%) of feedback in revising their essays. The results also showed that the quantity of students’ uptake of instructor feedback (88.77%) was higher than that of peer feedback (82.17%). In terms of the rate of uptake of global feedback focusing on content and organization vs. local feedback focusing on language and formatting, the rate of uptake of local feedback (85.34%) was slightly higher than the uptake of global feedback (84.90%). The current results also showed that the quality of feedback (peer vs. instructor feedback and global vs. local feedback) also varied. Students’ perspectives on feedback underlined their perceived value of feedback on writing, their preference for instructor feedback and the perceived benefits of providing and receiving feedback.Originality/valueThis study investigated an area that has been under-researched in the Saudi higher education context and it has direct implications for the provision of feedback in writing classes.

Acute effects of local vibration and visual feedback on the pelvic floor muscle training in Japanese healthy adults: A cross-over study

BACKGROUND: Those undergoing pelvic floor muscle training (PFMT) often experience difficulty in perception; therefore, an easier PFMT method should be devised. OBJECTIVE: To determine the effectiveness of combining PFMT with either vibration stimulation or visual feedback provided by a branded cushion (not a prototype) in increasing PFM muscle activity. Since PFM does not involve large joint movements, muscle activity was a suitable indicator. METHODS: Twenty healthy adults were included in this study. All participants performed PFMT under three conditions using a branded cushion: vibration stimulation, visual feedback, and a control. All three conditions were provided separately. PFM activity of the midline of the perineum at two points was recorded as the root mean square measured using PFM electromyography, measured twice for each condition. Muscle activity ratio was obtained by calculating maximum voluntary contraction of PFM in pre- and post-PFMT conditions. RESULTS: PFM activity and muscle activity ratio were both significantly higher following PFMT under vibration stimulation and visual feedback conditions (p< 0.01, p< 0.01, respectively). CONCLUSIONS: PFMT accompanied by vibration stimulation or visual feedback could immediately raise PFM muscle activity. We believe this study contributes to improving PFMT efficiency by suggesting more suitable PFMT methods.

A Stacked Multi-Sensor Platform for Real-Time MRI Guided Interventions

We present a stacked temperature, pressure, and localization platform, targeted for minimally invasive surgical and diagnostic applications under Magnetic Resonance Imaging. The platform comprises a micro-fabricated three-layer (Titanium-Parylene-Titanium) membrane pressure sensor, a Gallium Arsenide band-gap temperature sensor, and a magnetic material on double prism retro-reflector that benefits from Magneto-Optic Kerr effect as a magnetic field sensor, to provide localization feedback under Magnetic Resonance Imaging. All sensors can be addressed with a single fiber optic cable, where the collected light is directed to a spectrometer and a polarimeter. For the three-layer microfabricated membrane sensor, an analytical formulation is derived, linking the pressure to optical intensity. Moreover, finite-element simulation results are provided, verifying analytical findings. Wavelength division multiplexing is exploited to address the sensors simultaneously. We measured sensitivities of 0.025 millidegree/Gauss rotation of polarization, 1.5 nm/mmHg displacement (in agreement with simulation results and analytical findings), 0.36 nm/°C bandgap wavelength shift for magnetic field, pressure, and temperature sensors; respectively. With further development, the proposed device can be adapted to a clinical setting for use in Magnetic Resonance assisted surgical procedures.

Influence of boreal spring sea surface temperature anomalies over the tropical South Atlantic on the Meiyu onset

This study investigates the impact of boreal spring tropical South Atlantic surface sea temperature anomalies (TSA-SSTA) on the anticyclone over the western North Pacific (WNPAC) and the Meiyu onset date (MOD) based on reanalysis data and numerical experiments. The results indicate an intimate linkage between the MOD and TSA-SSTA, in which warmer spring TSA-SSTA are associated with an earlier MOD and vice versa, and the underlying mechanism is identified. Warm TSA-SSTA can trigger a Gill-type response and anomalous equatorial Walker circulation, which leads to anomalous upward motion and latent heating over the Maritime Continent. This anomalous condition over the Maritime Continent strengthens local Hadley circulation accordingly accompanied by anomalous descending motion over the western North Pacific. This descending motion reduces the local rainfall and enhances the equatorward northerly wind at low level. Further analysis reveals that local Sverdrup positive feedback between the anomalous diabatic cooling owing to reduced rainfall and the lower-level equatorward northerly wind is critical for sustaining the well-developed anomalous WNPAC. The abundant water vapor transport embedded in the northwestern flank of the anomalous WNPAC eventually favors an earlier MOD. Atmospheric conditions corresponding to cold TSA-SSTA produce the opposite effect. The spring TSA-SSTA can therefore prominently communicate with the subsequent East Asian MOD via the aforementioned mechanism, and the spring TSA-SSTA can be interpreted as a precursor signal of the East Asian MOD.

Many-to-Many Data Aggregation Scheduling Based on Multi-Agent Learning for Multi-Channel WSN

Many-to-many data aggregation has become an indispensable technique to realize the simultaneous executions of multiple applications with less data traffic load and less energy consumption in a multi-channel WSN (wireless sensor network). The problem of how to efficiently allocate time slot and channel for each node is one of the most critical problems for many-to-many data aggregation in multi-channel WSNs, and this problem can be solved with the new distributed scheduling method without communication conflict outlined in this paper. The many-to-many data aggregation scheduling process is abstracted as a decentralized partially observable Markov decision model in a multi-agent system. In the case of embedding cooperative multi-agent learning technology, sensor nodes with group observability work in a distributed manner. These nodes cooperated and exploit local feedback information to automatically learn the optimal scheduling strategy, then select the best time slot and channel for wireless communication. Simulation results show that the new scheduling method has advantages in performance when comparing with the existing methods.

Stabilization of traveling waves on dissipative system near subcritical bifurcation through a combination of global and local feedback

Stabilization of traveling waves on dissipative system near subcritical bifurcation through a combination of global and local feedback

Activating Interneurons in Local Inhibitory Circuits by High-Frequency Stimulations at the Efferent Fibers of Pyramidal Neurons in Rat Hippocampal CA1 Region.

Stimulation-induced inhibition is one of the important effects of high-frequency stimulation (HFS) utilized by the therapy of deep brain stimulation (DBS) to treat certain neurological diseases such as epilepsy. In order to explore the stimulation sites to induce inhibition, this study investigated the activation effect of HFS of efferent fibers on the local inhibitory interneurons (IN). Antidromic HFS (A-HFS) of 100 Hz pulses was applied for 2 min at the efferent fibers—the alveus (i.e., the axons of pyramidal neurons) in the hippocampal CA1 region of anesthetized rats. Single unit spikes of INs in local feedback inhibitory circuits, as well as antidromically-evoked population spikes (APS) of pyramidal neurons, were recorded simultaneously in the CA1 region upstream of the stimulation site. Results showed that during the late 60 s of A-HFS, with a substantial suppression in APS amplitudes, the mean firing rate of INs was still significantly greater than the baseline level even when the A-HFS was applied with a weak pulse intensity of 0.08 ± 0.05 mA (9 rats). With a strong pulse intensity of 0.33 ± 0.08 mA (10 rats), the mean firing rate of INs was able to keep at a high level till the end of A-HFS. In addition, the mean latency of IN firing was significantly prolonged during the sustained A-HFS, indicating that alterations had been generated in the pathway to activate INs by the stimulations at efferent fibers. The results suggested that HFS at efferent fibers with various stimulation intensities can modulate the firing of local inhibitory neurons. The finding provides new clues for selecting stimulation sites to enhance inhibition in neural circuits by DBS.

Digital governance in rural Chengdu, China: Its potential for social-ecological resilience

In this study, we echo the call from the UN to interpret Sustainable Development Goals (SDGs) in their regional context—in this case, the linpan (wooded lot) landscape of the Chengdu Plain, in Sichuan, China, where the shocks and stresses of recent, rapid administrative-economic urbanization are testing the resilience of some of the world's most sustainably productive and long- and densely-settled agrarian environments. In recent years, fine-grained information and communications technology (ICT) governance tools in Chengdu, such as “grid management”, present opportunities to sustain and scale up the collection of data necessary to validate and refine indicators of landscape resilience, and use them to regulate development, in accordance with SDG goal 11 to enhance legislation, governance, and capacity via information gathering and sharing. ICT-based governance in combination with traditional place-based knowledge can play a critical role in ensuring the resilience of urban-rural co-development. To realize this potential, however, ICT-enabled governance needs to incorporate greater transparency and more local feedback loops and enable greater participation from older farmers and women, to inform household and community-level land-use choices and initiatives. It also needs to link regulatory functions with marketing and pricing functions so that farmers may benefit from the sustainable practices they are encouraged to adopt.

A quantitative 3D intravital look at the juxtaglomerular renin-cell-niche reveals an individual intra/extraglomerular feedback system.

The juxtaglomerular niche occupied by renin cells (RCN) plays an important role in glomerular repair but the precise temporal and spatial interrelations remain unclear. This study proposes the hypothesis of a local intra-extraglomerular regenerative feedback system and establishes a new quantifiable system for RCN responses in individual glomeruli in vivo. A strictly intraglomerular two-photon laser-induced injury model was established. Labeled renin cells (RC) in transgenic renin reporter mice were fate-traced in healthy and injured glomeruli over several days by intravital microscopy and quantified via new three-dimensional image processing algorithms based on ray tracing. RC in healthy glomeruli demonstrated dynamic extraglomerular protrusions. Upon intraglomerular injury the corresponding RCN first increased in volume and then increased in area of dynamic migration up to threefold compared to their RCN. RC started migration reaching the site of injury within 3 hours and acquired a mesangial cell phenotype without losing physical RCN-contact. During intraglomerular repair only the corresponding RCN responded via stimulated neogenesis, a process of de novo differentiation of RC to replenish the RCN. Repeated continuous intravital microscopy provides a state-of-the-art tool to prove and further study the local intraglomerular RCN repair feedback system in individual glomeruli in vivo in a quantifiable manner.

Distributed multi-agent collision avoidance using robust differential game

This paper proposes a novel robust differential game scheme to solve the collision avoidance problem for networked multi-agent systems (MASs), subject to linear dynamics, external disturbances and limited observation capabilities. Compared with the existing differential game approaches only considering obstacle avoidance objectives, we explicitly incorporate the trajectory optimization target by penalizing the deviation from reference trajectories, based on the artificial potential field (APF) concept. It is proved that the strategies of each agent defined by individual optimization problems will converge to a local robust Nash equilibrium (R-NE), which further, with a fixed strong connection topology, will converge to the global R-NE. Additionally, to cope with the limited observation for MASs, local robust feedback control strategies are constructed based on the best approximate cost function and distributed robust Hamilton–Jacobi–Isaacs (DR-HJI) equations, which does not require global information of agents as in the traditional Riccati equation form. The feedback gains of the control strategies are found via the ant colony optimization (ACO) algorithm with a non-dominant sorting structure with convergence guarantees. Finally, simulation results are provided to verify the efficacy and robustness of the novel scheme. The agents arrived at the targeted position collision-free with a reduced arrival time, and reached the targeted positions under disturbance.

Distributed containment control of networked uncertain MIMO pure‐feedback nonlinear systems via quantized state feedback and communication

AbstractThis article presents a distributed adaptive containment control strategy using quantized state feedback and communication for uncertain multiple‐input‐multiple‐output pure‐feedback nonlinear multi‐agent systems with state quantization. It is assumed that quantized state variables of multiple followers and quantized outputs of multiple dynamic leaders are only available for constructing local adaptive feedback controllers of followers under a directed network. Compared with existing containment control approaches, the primary contribution of this study is dealing with discontinuously quantized state feedback and communication problems for containment control design in the presence of unknown nonaffine nonlinearities. Based on quantized state and communication information, local adaptive neural network trackers of followers and their adaptive tuning laws are developed to guarantee that the trajectories of all followers converge to the dynamic convex hull spanned by the multiple leaders regardless of unknown pure‐feedback nonlinearities. By analyzing the stability of the local quantization errors between quantized signals and original signals, we prove the boundedness of all closed‐loop signals and the convergence of the containment errors to a sufficiently small domain around the origin. Simulation examples involving flexible‐joint manipulators are presented to validate the proposed quantized feedback scheme.

Sensory-thresholded switch of neural firing states in a computational model of the ventromedial hypothalamus.

The mouse ventromedial hypothalamus (VMH) is both necessary and sufficient for defensive responses to predator and social threats. Defensive behaviors typically involve cautious approach toward potentially threatening stimuli aimed at obtaining information about the risk involved, followed by sudden avoidance and flight behavior to escape harm. In vivo neural recording studies in mice have identified two major populations of VMH neurons that either increase their firing activity as the animal approaches the threat (called Assessment+ cells) or increase their activity as the animal flees the threat (called Flight+ cells). Interestingly, Assessment+ and Flight+ cells abruptly decrease and increase their firing activity, respectively, at the decision point for flight, creating an escape-related “switch” in functional state. This suggests that the activity of the two cell types in VMH is coordinated and could result from local circuit interactions. Here, we used computational modeling to test if a local inhibitory feedback circuit could give rise to key features of the neural activity seen in VMH during the approach-to-flight transition. Starting from a simple dual-population inhibitory feedback circuit receiving repeated trains of monotonically increasing sensory input to mimic approach to threat, we tested the requirement for balanced sensory input, balanced feedback, short-term synaptic plasticity, rebound excitation, and inhibitory feedback exclusivity to reproduce an abrupt, sensory-thresholded reciprocal firing change that resembles Assessment+ and Flight+ cell activity seen in vivo. Our work demonstrates that a relatively simple local circuit architecture is sufficient for the emergence of firing patterns similar to those seen in vivo and suggests that a reiterative process of experimental and computational work may be a fruitful avenue for better understanding the functional organization of mammalian instinctive behaviors at the circuit level.

A Simulated Study of 65 nm CMOS 2GHz Front-End Preamplifier Circuit for Optical Fiber Applications

In this research a new design of the transimpedance amplifier (TIA) with the current mirror was employed by the technique (65nm). The TIA consists of a common gate transistor amplifier (CG TIA) and a common source amplifier as an input stage with local active feedback with a second stage of a current mirror and local active feedback to increase gain. In order to verify the performance of the proposed TIA, a circuit simulation was carried out in the LT spice program using coefficients with the technique (65nm CMOS). The simulation results indicate that the interfacial impedance gain is (41 dBΩ) at a bandwidth frequency of (2.0 GHz-3dB) for an input capacitor of (100 fF) and an input referred noise current spectral density of (14 pA/√Hz) and a power consumption value of (0.091 mw) at an applied voltage (1V). The main focus of this research is low consumption of power and voltage compared to another research.

Adaptive Bipartite Time-Varying Output Formation Control for Multiagent Systems on Signed Directed Graphs.

The issue of bipartite time-varying formation (BTVF) tracking for linear multiagent systems (MASs) with a leader of unknown input on signed digraphs is investigated. An adaptive nonsmooth protocol is taken in this article that utilizes only the local output feedback information among neighbors and, thus, can avoid employing the eigenvalue information of the Laplacian matrix of the graph. It is proven that if the interaction network of agents containing a spanning tree is structurally balanced, the BTVF tracking can be achieved with a leader of the bounded input via the proposed scheme. This leader-following BTVF includes two time-varying subformations, whose relationship is antagonistic. A convergence analysis of the proposed protocol for MASs is reflected by the Lyapunov method. Finally, the validly numerical simulations are illustrated to show the performance of the proposed schemes.