Feedback Frequency Research Articles

Fast Scanning Nitrogen-Vacancy Magnetometry by Spectrum Demodulation

We demonstrate a spectrum demodulation technique allowing for rapid imaging in scanning nitrogen-vacancy center magnetometry. Our method relies on a periodic excitation of the electron spin resonance by wide-band frequency sweeps at a kilohertz rate combined with a phase-locked detection of the photoluminescence signal. The technique is robust against changes in spectrum shape and photoluminescence intensity, and is readily extended by a frequency feedback to enable real-time tracking of the spin resonance. Fast scanning magnetometry is especially useful for samples where the signal dynamic range is large, of order millitesla, such as for ferromagnets or ferrimagnets. We demonstrate our method by mapping stray fields above the model antiferromagnet $\ensuremath{\alpha}$-${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ (hematite) at pixel rates of up to $100\phantom{\rule{0.2em}{0ex}}\mathrm{Hz}$ and an image resolution exceeding one megapixel.

3.6 mW Active-Electrode ECG/ETI Sensor System Using Wideband Low-Noise Instrumentation Amplifier and High Impedance Balanced Current Driver.

An active electrode (AE) and back-end (BE) integrated system for enhanced electrocardiogram (ECG)/electrode-tissue impedance (ETI) measurement is proposed. The AE consists of a balanced current driver and a preamplifier. To increase the output impedance, the current driver uses a matched current source and sink, which operates under negative feedback. To increase the linear input range, a new source degeneration method is proposed. The preamplifier is realized using a capacitively-coupled instrumentation amplifier (CCIA) with a ripple-reduction loop (RRL). Compared to the traditional Miller compensation, active frequency feedback compensation (AFFC) achieves bandwidth extension using the reduced size of the compensation capacitor. The BE performs three types of signal sensing: ECG, band power (BP), and impedance (IMP) data. The BP channel is used to detect the Q-, R-, and S-wave (QRS) complex in the ECG signal. The IMP channel measures the resistance and reactance of the electrode-tissue. The integrated circuits for the ECG/ETI system are realized in the 180 nm CMOS process and occupy a 1.26 mm2 area. The measured results show that the current driver supplies a relatively high current (>600 μApp) and achieves a high output impedance (1 MΩ at 500 kHz). The ETI system can detect resistance and capacitance in the ranges of 10 mΩ-3 kΩ and 100 nF-100 μF, respectively. The ECG/ETI system consumes 3.6 mW using a single 1.8 V supply.

Efficacy of the 4F Feedback Model: A Game-Based Assessment in University Education

Feedback is a critical aspect of optimised learning design, but there are few, if any, feedback models that map different types of feedback and how they may assist students to increase performance and enhance their learning experience. This research paper outlines a feedback model as an extension of the four-dimensional framework which includes a consideration of the type, the content, the format, and the frequency of feedback, as well as the agent which delivers it. This model is based upon an understanding of learning in the context of designing learning experiences and utilises a game-based model of learning to understand the importance of motivation and autonomy in learners to enhance and accelerate learning. The framework is developed and reflected upon by analysing two cases: a medical triage case in which the timing and frequency of feedback proved critical, and a business simulation which illuminated the need for a range of types of feedback and to be aware of the possibility of different agents (instructor peer and game) that can deliver feedback. The extended model may help game and learning designers alike to discern different types of feedback, both in games and more generally, in more explicit and nuanced ways.

Enhanced PLL-less grid synchronization algorithm amidst unbalanced and distorted three-phase grid conditions

Fast and precise tracking of grid voltage attributes is essential for the smooth and reliable control and operation of grid-side converters. The synchronous reference-frame phase-locked loop (SRF-PLL) approach is commonly used for this purpose, although it has issues related to the stability limit and sluggish transient response. Consequently, PLL-less grid synchronization approaches are becoming increasingly prevalent. In this context, in the present paper, a discrete Fourier transform-based band pass filter (DFT-BPF) is designed in the prefiltering stage for the purpose of extracting the fundamental frequency positive sequence component (FFPS) from unbalanced and distorted grid conditions. Despite being widely used, the SRF-PLL is struggling with stability issues and demands tedious tuning effort. For this objective, a simple frequency estimator has been developed, which is capable of accurately estimating the fundamental frequency. Additionally, a curve fitting based error correction technique is employed to adaptively estimate the amplitude and phase-angle of the fundamental component without using frequency feedback loop. The experimental results validate the efficacy of the proposed scheme.

Can differentiated and personalized mixed-reality simulations transform teacher learning?

Mixed-reality simulations (MRSs) create new opportunities for responsive teacher learning. This experimental study examined, starting from baseline Simulation 0 (Sim0) across three MRSs, the effect of differentiated coaching treatment in Simulation 1 (Sim1), and personalized practice in Simulation 2 (Sim2) on teachers’ provision of high-information feedback to avatar students as measured by the mean of feedback frequency weighted by quality. Motivational-supportive factors of MRS, including teacher perceptions of cognitive load, realism, and task-value were also examined. Participants were teachers at different career points (i.e., preservice: n = 69; early career: n = 66; and in-service: n = 68). Block randomization by grade level taught (elementary and secondary) and assessment of current feedback practices achieved pretreatment equivalence. Quantitative analyses revealed coaching significantly increased teachers’ use of high-information feedback. Teacher-selected personalized practice also impacted feedback. For example, the Sim2 decision to continue where the Sim1 action stopped was significantly related to decreases in clarify and value feedback and increases in pushing student thinking. Overall, differentiated and personalized professional development (PD) through MRS was valued by educators across the career trajectory and led to a complex evolution in teacher practices. However, the effects of the MRS were moderated by teaching experience. Teachers reported the MRS felt realistic and valuable; however, early career teachers’ perceptions were significantly lower than their preservice and in-service peers, especially under the coaching condition. In-service teachers reported greater cognitive load than less experienced teachers. Our discussion explores transforming teacher education across a career trajectory through assessing teaching expertise, differentiating PD, and personalizing practice.

Implementation, Reach, and Effectiveness of the Direct Observation of Residents in Clinic Program.

Direct observation is important, yet medical residents are rarely observed. We implemented and evaluated a direct observation program in resident clinics to increase the frequency of observation and feedback and improve perceptions about direct observation. We assigned faculty as observers in our resident clinics between June 2019 and February 2020. We surveyed residents and faculty before and after the program. Faculty completed a form for each observation performed. We analyzed surveys to examine changes in barriers, frequency and type of observations and feedback, and attitudes toward observation. The analytical sample included 38 and 37 pre- and postresident surveys, respectively, and 20 and 25 pre- and postfaculty surveys, respectively. Resident survey response rates were 32.3% (40/124) pre- and 30.7% (39/127) postintervention. Most residents (76% [pre], 86% [post], P = 0.258) reported being observed in at least one of the four areas: history, examination, counseling, or wrap-up. We received observation tracking forms on 68% of eligible residents. Observed history taking increased from 30% to 79% after the program (P = 0.0010). Survey response rates for faculty were 64.7% (22/34) pre- and 67.5% (25/37) postintervention. Fewer faculty reported time (80% [pre], 52% [post], P = 0.051) and competing demands (65% [pre], 52% [post], P = 0.380) as barriers postintervention. Fewer faculty postintervention viewed observation as a valuable teaching tool (100% [pre], 79% [post], P = 0.0534). All faculty who did not view observation as valuable were the least experienced. Assigning faculty as observers can increase observation, especially in history taking, though data suggest an increase in negative perceptions of observation by faculty.

Does Feedback Seeking Always Improve Performance? Investigating the Roles of Feedback Seeking Content and Frequency in Determining Goal Achievement and Behavior-Related Performance

Abstract We investigated the direct relationship between feedback seeking behavior (FSB) and performance, considering two dimensions of FSB (frequency and content) and two types of performance (goal achievement and behavior-related performance). The purpose is to identify new explanations for the inconclusive results of the direct relationship reported in the literature. FSB is important during performance conversations, which are critical for the effectiveness of performance management. Data from a sample of 306 employees were gathered from two distinct sources on three occasions. Our data were analyzed using the hierarchical regression method. The relationship between FSB frequency and goal achievement was statistically significant. The diagnostic FSB content was positively related to individual work performance (IWP), representing behavior-related performance. We identified no similar relationship with other types of FSB content. This paper provides evidence that while a direct relationship between FSB and performance may not generally exist, it depends on the type of FSB content and expected types of performance. Organizations can use the results to improve the effectiveness of FSB.

Research on generation of stable mid-infrared lasers with narrow linewidths based on optical feedback locking

Mid-infrared precision spectroscopy has important applications in the fields of trace gas detection and the determination of fundamental physical constants. However, due to the limited commercialization of related technologies, there is a lack of narrow linewidth laser sources or linewidth narrowing approaches in the mid-infrared region, as well as stable mid-infrared frequency standards. The most commercialized and widely used mid-infrared laser source is the quantum cascade laser (QCL). But its free-running linewidth is more than MHz scale due to the influence of laser drive current noise and temperature fluctuation. This impedes the development of precision spectroscopy in this region. In this work, we introduce a technique for generating a narrow linewidth, stable mid-infrared laser by using optical feedback frequency locking, with a high-finesse mid-infrared ultrastable Fabry-Pérot cavity as the frequency reference. The optical cavity consists of two high reflectivity mirrors separated by ultra-low expansion (ULE) material with a low temperature expansion coefficient, and its temperature is precisely controlled. And the cavity is also surrounded in a vaccum cavity made of stainless steel. All these measures ensure the cavity length and its longitudinal mode stability. By using optical feecback, a QCL is locked to the cavity, which stabilizes the laser frequency and narrows the laser linewidth. In order to improve the long-term stability of the optical feedback, an active servo is leveraged to control the feedback phase. The error signal for the servo is obtained by using the method similar to the Pound-Derver-Hall locking. In this work, we first theoretically analyze the feasibility of laser to F-P cavity frequency locking by optical feedback. We propose the laser frequency response model with a linear F-P cavity under optical feedback, and analyze the influence of the direct cavity reflection on the laser frequency. Then the experimental demonstration is conducted. Firstly, we measure the reflectivity of the cavity mirror by using cavity ring-down spectroscopy, resulting in a cavity finesse of 30200 and a cavity mode linewidth of 49.7 kHz. After that, we successfully achieve optical feedback frequency locking, and consecutive cavity transmission is observed. The error signal for the control of the optical feedback phase is used to evaluate the locking performance by converting it into the laser frequency noise. By analyzing the noise spectral density, the QCL linewidth is narrowed to 0.3 Hz on a short timescale (< 10 ms). And the long-term stability is suspected to be dedicated by the temperature variation of the optical cavity, resulting in a laser frequency drift 20 kHz/12 h. The narrow linewidth stabilized mid-infrared laser source obtained with this technique is expected to serve as an effective frequency reference source for mid-infrared precision spectroscopic measurements.

Modeling, Stability, and Design of the Single-Phase SOGI-Based Phase-Locked Loop Considering the Frequency Feedback Loop Effect

For single-phase grid-connected inverters, the second-order generalized integrator-based phase-locked loop (SOGI-PLL) is widely used for good harmonics attenuation and frequency adaptability. However, existing studies usually neglect the frequency feedback loop in the modeling and design process, and thus, the potential instability caused by the frequency feedback loop is not well explained. Besides, the improper design of SOGI-PLL can lead to the inverter instability both under ideal and weak grid conditions. Therefore, by fully considering the coupling of the frequency feedback loop, this article establishes an accurate model for SOGI-PLL. Furthermore, effects of different PLL parameters on behaviors of both the SOGI-PLL itself and the inverter are studied, based on which a graphical method for PLL parameters design is proposed. As proved, the frequency feedback loop can deteriorate the stability and performance of both SOGI-PLL itself and inverter system, especially if rapid transient is expected. The modeling method is also extended to the low-pass filter-SOGI-PLL and the improved parameters design is discussed. Experimental results verify the correctness of the proposed PLL model and the abovementioned analysis results. The proposed model is helpful to deeply reveal the instability mechanism and provides a reference for the PLL design under nonideal grid conditions.

Active Power Control of DFIG Wind Turbines for Transient Stability Enhancement

This paper proposes an adaptive Dynamic Power Reduction (aDPR) scheme for Type-3 Wind Turbine-Generators (WTGs) to enhance transient stability of synchronous generators (SGs), with benefits of increasing transfer limits on already fully loaded transmission paths. The scheme consists of three components to deal with a fault close to a SG. Initially, the WTG curtails its active power to a predefined level to act as a dynamic brake for the SG. Then the controller monitors the rate of change of frequency to adaptively ramp the WTG back to its original power output while minimizing the WTG pitch and rotor motion. Finally, to reduce the risk of second-swing instability, the converter uses its reactive current to damp SG power swings. The aDPR scheme can be classified as a remedial action scheme and is enabled if its action can ensure transient stability. To demonstrate the effectiveness of aDPR and to benchmark it against other WTG active current and frequency feedback control techniques, a single-machine infinite-bus system with one WTG is utilized. Next, an aDPR enabled WTG is integrated in the NPCC 68-bus system. Finally, the aDPR controller’s ability to prevent transient instability is demonstrated on the two-area system.

Designing of a quantum TIA to improve FSO signal reception

Free Space Optic Communication (FSO) is one of the communication systems chosen for 5G + / 6G backhaul. Many works were done to improve signal quality either at emission, transmission channel or at reception through photodetector. The aim of this work is to design a new transimpedance amplifier (TIA) to improve Free Space Optic Communication (FSO) photodetector performance. To achieve our purpose, a negative electrical resistance was introduced into conventional TIA. SPICE software and Kirchhoff's laws were used to design and analyze the circuit. The obtained results show that the new TIA has a better amplitude gain response and lower equivalent noise than conventional TIAs. High bandwidth and flat amplitude response in the pass band characterize our TIA. This characteristic is one of the two criteria for a photodetector to be considered as a quantum device. A 3D gain representation highlights different regions of positive and negative feedback resistors and frequencies to be used or avoided in order to ensure TIA stability.

Frecuencia y tipos de retroalimentación sobre la precisión del responder en una tarea de discriminación condicional

Using a conditional discrimination task, the effects of content and frequency of feedback were assessed. Continuous and intermittent feedback was programmed for two groups of students; within groups specific and relational feedback was arranged for two sub. Accuracy was higher for the continuous-feedback group than for intermittent-feedback. We also found that the relational groups showed higher percentages of correct responses than specific feedback groups. Results are consistent with previous findings showing the relevance of the frequency and content of feedback on conditional discrimination learning. Findings are discussed based on their potential application to educational settings.

All-fiber frequency shifted self-mixing interferometry for slow flow measurements

In this study, an all-fiber structure self-mixing sensor using a distributed feedback Bragg (DFB) fiber laser as the light source is proposed to measure flow velocity. In pursuit of slower flow velocity, the external cavity frequency-shifting optical technique is introduced into the optical sensing system to effectively avoid complex noises existing in the low-frequency region. Furthermore, the additional bonus is that the identification of the velocity direction can be obtained by the asymmetric shape near the feedback frequency shift on the spectrum. At the same time, a suitable solution is developed for extraction of the characteristic feature parameters from the asymmetrical spectrum of the flow velocity signal. It was demonstrated the actual conformity of the measurement results by means of this new approach of data processing. According to the practical experimental measurements, the maximum measurable Doppler shift concerning the slow fluid can be obtained as low as 15.37 Hz. This indicates that the designed all-fiber laser self-mixing flow velocity meter can be prospectively extended to slow fluid measurement associated with the related sensing and medical applications.

Quantifying the effect of feedback frequency in interactive reinforcement learning for robotic tasks

Reinforcement learning (RL) has become widely adopted in robot control. Despite many successes, one major persisting problem can be very low data efficiency. One solution is interactive feedback, which has been shown to speed up RL considerably. As a result, there is an abundance of different strategies, which are, however, primarily tested on discrete grid-world and small scale optimal control scenarios. In the literature, there is no consensus about which feedback frequency is optimal or at which time the feedback is most beneficial. To resolve these discrepancies we isolate and quantify the effect of feedback frequency in robotic tasks with continuous state and action spaces. The experiments encompass inverse kinematics learning for robotic manipulator arms of different complexity. We show that seemingly contradictory reported phenomena occur at different complexity levels. Furthermore, our results suggest that no single ideal feedback frequency exists. Rather that feedback frequency should be changed as the agent’s proficiency in the task increases.

Smart Home Tech: an interface to provide feedback to caregivers of persons living with cognitive impairment.

Home-based sensor technologies can detect information on daily activities, such as sleep, activity level, and time spent together. This is relevant information for care partners of individuals with cognitive impairment as it can detect early changes in daily activities and cognition. The challenge is how to present thousands of data points to care partners in real-time, allowing them to make adjustments in their daily routine to help reduce burden. The Collaborative Aging Research using Technology (CART) sensor platform was installed in 4 Ottawa homes of persons with cognitive impairment and their care partner. This system includes contact and motion sensors to assess home activity, a smart watch to record steps and sleep patterns, a bed sensor, and medication tracking pillboxes. Questions regarding areas of stress, the types of information that caregivers would like to receive, and how to receive their data were posed in focus group discussions involving caregivers with and without the sensor platform. An interface was designed based on participant input. Eight care partners (75% female) aged 30 to 81 participated in focus groups that obtained their opinions on the usefulness of a feedback system, its content, layout, and frequency in which care partners would like to receive their sensor information. The majority of participants wished to be sent their sensor information on a weekly basis in easy to interpret graphical formats that summarized information for them. An algorithm that collects sensor data, parses appropriate measures; steps, sleep, time together in a room, and displays it in graphical representation, was developed. The user interface displays the daily summary compared to the weekly average, with the ability to navigate between day and weekly views. Sensor-based data needs to be displayed in an efficient and convenient manner if it is going to be used by care partners to help guide changes in behavior to reduce stress. This project designed an interface, based on user feedback. This system also has the potential to be used by clinicians to evaluate longitudinal cognitive decline. Next, we will provide participants with the CART system with sample visual reports and gather their feedback.

Smart Home Tech: an interface to provide feedback to caregivers of persons living with cognitive impairment

AbstractBackgroundHome‐based sensor technologies can detect information on daily activities, such as sleep, activity level, and time spent together. This is relevant information for care partners of individuals with cognitive impairment as it can detect early changes in daily activities and cognition. The challenge is how to present thousands of data points to care partners in real‐time, allowing them to make adjustments in their daily routine to help reduce burden.MethodThe Collaborative Aging Research using Technology (CART) sensor platform was installed in 4 Ottawa homes of persons with cognitive impairment and their care partner. This system includes contact and motion sensors to assess home activity, a smart watch to record steps and sleep patterns, a bed sensor, and medication tracking pillboxes. Questions regarding areas of stress, the types of information that caregivers would like to receive, and how to receive their data were posed in focus group discussions involving caregivers with and without the sensor platform. An interface was designed based on participant input.ResultEight care partners (75% female) aged 30 to 81 participated in focus groups that obtained their opinions on the usefulness of a feedback system, its content, layout, and frequency in which care partners would like to receive their sensor information. The majority of participants wished to be sent their sensor information on a weekly basis in easy to interpret graphical formats that summarized information for them. An algorithm that collects sensor data, parses appropriate measures; steps, sleep, time together in a room, and displays it in graphical representation, was developed. The user interface displays the daily summary compared to the weekly average, with the ability to navigate between day and weekly views.ConclusionSensor‐based data needs to be displayed in an efficient and convenient manner if it is going to be used by care partners to help guide changes in behavior to reduce stress. This project designed an interface, based on user feedback. This system also has the potential to be used by clinicians to evaluate longitudinal cognitive decline. Next, we will provide participants with the CART system with sample visual reports and gather their feedback.

Frequency-Dependent Network Analysis and Stability Enhanced Design for Voltage-Source Converters Under Weak Grid Conditions

Phase–locked loop (PLL) is commonly used for the grid-connected voltage-source converter (VSC) to synchronize with the grid. Under weak grid conditions, it has been found that the frequency-dependent characteristic of the network impedance inherently introduces a positive feedback loop into PLL. Previous studies focused on the PLL analysis intuitively believe that the positive feedback loop will deteriorate the dynamic performance of the PLL. However, this conclusion is not rigorous since only the dynamic of the PLL is considered and the theoretical analysis is insufficiency to reveal the influence of the positive feedback loop on system stability. In this paper, the impact of the frequency-dependent network on VSC stability is quantified in terms of the overall system based on the damping torque analysis. It is found that the influence of the positive feedback loop on stability depends on the parameters of the PLL and the damping of the dominant eigenvalues. Besides, an angular frequency feedback scheme is proposed to eliminate the adverse effect of the frequency-dependent network and enhance the stability of the VSC under weak grid conditions. Time-domain numerical simulations and reduced-scale experiments are performed to validate the effectiveness of the proposed scheme.

How workplace-based assessments guide learning in postgraduate education: A scoping review.

Competency-based medical education (CBME) led to the widespread adoption of workplace-based assessment (WBA) with the promise of achieving assessment for learning. Despite this, studies have illustrated tensions between the summative and formative role of WBA which undermine learning goals. Models of workplace-based learning (WBL) provide insight, however, these models excluded WBA. This scoping review synthesizes the primary literature addressing the role of WBA to guide learning in postgraduate medical education, with the goal of identifying gaps to address in future studies. The search was applied to OVID Medline, Web of Science, ERIC and CINAHL databases, articles up to September 2020 were included. Titles and abstracts were screened by two reviewers, followed by a full text review. Two members independently extracted and analysed quantitative and qualitative data using a descriptive-analytic technique rooted in Billett's four premises of WBL. Themes were synthesized and discussed until consensus. All 33 papers focused on the perception of learning through WBA. The majority applied qualitative methodology (70%), and 12 studies (36%) made explicit reference to theory. Aligning with Billett's first premise, results reinforce that learning always occurs in the workplace. WBA helped guide learning goals and enhanced feedback frequency and specificity. Billett's remaining premises provided an important lens to understand how tensions that existed in WBL have been exacerbated with frequent WBA. As individuals engage in both work and WBA, they are slowly transforming the workplace. Culture and context frame individual experiences and the perceived authenticity of WBA. Finally, individuals will have different goals, and learn different things, from the same experience. Analysing WBA literature through the lens of WBL theory allows us to reframe previously described tensions. We propose that future studies attend to learning theory, and demonstrate alignment with philosophical position, to advance our understanding of assessment-for-learning in the workplace.

The Effect of Oral Corrective Feedback on Chinese Primary Students’ English Learning Motivation

Oral corrective feedback (OCF) plays a significant role in affecting students’ English learning motivation. However, limited studies were conducted in Chinese classrooms. To address the gap, the current study investigated how OCF influenced Chinese young English learners’ motivation. The participants were 181 students from a Chinese primary school. They were divided into the younger group (98 Grade-three (G3) students) and the older group (84 Grade-five (G5) students). Questionnaires on motivation and OCF were administered first. Ten English lessons (5 for G3 and 5 for G5) were recorded later. Results showed that explicit feedback was more frequent and motivating than implicit feedback. Feedback frequency had no significant correlation with motivation.

Feedback Schedule Effects on Speech Motor Learning in Older Adults

<strong>Purpose:</strong> The Principles of Motor Learning (PML) emerged from studies of limb motor skills in healthy, young adults. The applicability of these principles to speech motor learning, and to older adults, is uncertain. The purpose of this study was to examine one PML, feedback frequency, and to elucidate whether it affects the retention of a speech motor task. <strong>Method:</strong> Thirty older participants were randomly assigned to one of the three feedback frequency groups (every trial, every 5^th, every 10^th) and trained to produce a phrase 2 times and 3 times slower than their habitual rate. Over 100 practice trials, all participants demonstrated a reduction in error, suggesting they understood and acquired the task. Mean absolute error (MAE) was measured to examine delayed 2- to 4- day retention. <strong>Results:</strong> When participants returned for retention testing 2 to 4 days post-training, those receiving feedback every 5^th trial demonstrated significantly lower MAE (enhanced retention) compared to those receiving high frequency feedback following every trial. There were no significant differences between participants receiving feedback following every trial or every 5^th trial versus every 10^th trial. <strong>Conclusions:</strong> Enhanced retention of the trained speech motor task for participants receiving low frequency feedback following every 5^th trial, relative to those receiving high frequency feedback following every trial, is consistent with the extensive limb motor learning literature and the trend of a small number of speech motor learning studies, suggesting provision of low frequency feedback enhances retention of trained novel movements.