Concept Of Feedback Research Articles

Chemotactic Sensitivity of Escherichia coli to Diffusion Perturbations in Narrow Tubes

Diffusion resistance hinders the free chemotactic motility of bacteria through narrow tubes and capillaries. In many such situations, diffusion is significant and often subject to environmental perturbations. This problem has been analyzed through the sensitivities of Escherichia coli cells, a secreted chemoattractant (aspartase) and a nutrient. Differences and similarities among the sensitivity profiles with respect to the three diffusion coefficients reveal useful information about interactions between diffusion and chemotaxis. The results are consistent with the concept of stabilization created by negative feedback, either within the chemosensory network or from outside. Their implications for some real systems are discussed.

Sarcomere Mechanics in Uniform and Nonuniform Cardiac Muscle

Starling's law and the end-systolic pressure-volume relationship (ESPVR) reflect the effect of sarcomere length (SL) on the development of stress (sigma) and shortening by myocytes in the uniform ventricle. We show here that tetanic contractions of rat cardiac trabeculae exhibit a sigma-SL relationship at saturating [Ca2+] that depends on sarcomere geometry in a manner similar to that of skeletal sarcomeres and the existence of opposing forces in cardiac muscle shortened below slack length. The sigma-SL -[Ca2+](free) relationships (sigma-SL-Ca relationships) at submaximal [Ca2+] in intact and skinned trabeculae were similar, although the sensitivity for Ca2+ of intact muscle was higher. We analyzed the mechanisms underlying the sigma-SL-Ca relationship by using a kinetic model assuming that the rates of Tn-C Ca2+ binding and/or cross-bridge (XB) cycling are determined by either the SL, [Ca2+], or sigma. We analyzed the correlation between the model results and steady-state sigma measurements at varied SL at [Ca2+] from skinned rat cardiac trabeculae to test the hypotheses that the dominant feedback mechanism is SL-, sigma-, or [Ca2+]-dependent, and that the feedback mechanism regulates Tn-C Ca2+ affinity, XB kinetics, or the unitary XB force. The analysis strongly suggests that the feedback of the number of strong XBs to cardiac Tn-C Ca2+ affinity is the dominant mechanism regulating XB recruitment. Using this concept in a model of twitch-sigma accurately reproduced the sigma-SL-Ca relationship and the time courses of twitch sigma and the intracellular [Ca2+]i. The foregoing concept has equally important repercussions for the nonuniformly contracting heart, in which arrhythmogenic Ca2+ waves arise from weakened areas in the cardiac muscle. These Ca2+ waves can reversibly be induced with nonuniform excitation-contraction coupling (ECC) by the cycle of stretch and release in the border zone between the damaged and intact regions. Stimulus trains induced propagating Ca2+ waves and reversibly induced arrhythmias. We hypothesize that rapid force loss by the sarcomeres in the border zone during relaxation causes Ca2+ release from Tn-C and initiates Ca2+ waves propagated by the sarcoplasmic reticulum (SR). Modeling of the response of the cardiac twitch to rapid force changes using the feedback concept uniquely predicts the occurrence of [Ca2+]i transients as a result of accelerated Ca2+ dissociation from Tn-C. These results are consistent with the hypothesis that a force feedback to Ca2+ binding by Tn-C is responsible for Starling's law and the ESPVR in the uniform myocardium and leads to a surge of Ca2+ released by the myofilaments during relaxation in the nonuniform myocardium, which initiates arrhythmogenic propagating Ca2+ release by the SR.

Stability of Model-Based Networked Control Systems with Intermittent Feedback

In this paper, we apply the concept of Intermittent Feedback to a class of networked control systems known as Model-Based Networked Control Systems (MB-NCS). We begin by introducing the basic architecture for model-based control with intermittent feedback, then address the case with output feedback (through the use of a state observer), providing a full description of the state response of the system, as well as a necessary and sufficient condition for stability in each case. Examples are provided to complement the theoretical results. Extensions of our results to cases with nonlinear plants are also presented. Finally, we investigate the situation where the update times τ and h are time-varying, first addressing the case where they have upper and lower bounds, then moving on to the case where their distributions are i.i.d or driven by a Markov chain.

피드백 유전알고리즘 모델 예측 관측기 설계

Observer design for the nonlinear systems is known to be difficult in general. This paper suggests a feedback GA-based model predictive observer for the observable systems. Feedback concept makes on-line design possible for the cases including observer design, where GA is implemented repeatedly every time instant. The effectiveness of our observer is shown by simulation.

Effect of a scratch on curved rail on initiation and evolution of plastic deformation induced rail corrugation

A calculation model is put forward to analyze the effect of a scratch on the running surface of a curved rail on initiation and growth of plastic deformation induced rail corrugation when a wheelset is steadily and repeatedly curving. The numerical method considers a combination of Carter’s two-dimensional contact theory, a two-dimensional elastic–plastic finite element model and a vertical dynamics model of railway vehicle coupled with a curved track. A concept of feedback between the corrugation development and the vertical coupling dynamics of the wheelset and track is involved. The cyclic ratchetting effect of the rail material under repeated contact loadings is taken into account. The numerical results indicate that when a vehicle runs on rails with a scratch the contact vibration between the wheel and rail occurs at large amplitude, and rail corrugation due to plastic deformation initiates and develops. The corrugation has a tendency to move along the running direction and its evolution rate decays as wheelset passages increase. The passing frequencies of the plastic deformation induced corrugation depend on the natural frequencies of the track. The residual stresses stabilize after a limited number of wheelset passages. The residual strains increase at a reduced rate with increasing wheelset passages.

Visualizing feedback‐enhanced contrast in magnetic resonance imaging

AbstractA new approach to magnetic resonance imaging (MRI) contrast enhancement has recently been developed that exploits nonlinear feedback interactions to amplify contrast arising from small variations in the underlying MRI parameters. A unified framework for understanding feedback‐enhanced contrast is presented here based on the concepts of instability and positive feedback. The specific mechanisms governing contrast enhancement under the feedback interactions of radiation damping, the distant dipolar field, and their joint effect are elucidated through numerical simulations illustrating the involved spin dynamics. Experimental demonstrations of feedback‐enhanced contrast are shown on samples of in vitro human brain tissue, and applications to improving lesion detection in disease states such as epilepsy and cancer are discussed. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 378–393, 2007.

Support Vector Machine active learning for 3D model retrieval

In this paper, we present a novel Support Vector Machine active learning algorithm for effective 3D model retrieval using the concept of relevance feedback. The proposed method learns from the most informative objects which are marked by the user, and then creates a boundary separating the relevant models from irrelevant ones. What it needs is only a small number of 3D models labelled by the user. It can grasp the user’s semantic knowledge rapidly and accurately. Experimental results showed that the proposed algorithm significantly improves the retrieval effectiveness. Compared with four state-of-the-art query refinement schemes for 3D model retrieval, it provides superior retrieval performance after no more than two rounds of relevance feedback.

A Control Approach Based on Passive Behavior to Enhance User Interaction

This paper proposes a new control approach for an active (motorized) robotic walking support system based on passive behavior concept. The control approach aims to enhance the interaction between the support system and the user. The passive behavior of a support system allows the user to safely interact with the system since it removes the system's capability to move when there is no user's intention. This passive behavior is realized using imposed apparent dynamics, which uses the user's intention represented by the applied force/torque to derive the system's desired motion. The control approach is extended into a user-oriented motion control algorithm to adapt user's controlling characteristics. This is implemented by varying the point of application of the apparent dynamics. The control approach is further extended to use environment information and realize environment feedback concept. This is implemented by varying the parameters of the apparent dynamics based on environment data. Experimental results are presented to show the validity of the proposed control approach.

‘Why am I doing these things?’: engaging in classroom‐based inquiry around formative assessment

Sponsored by the New Zealand Ministry of Education, the Teaching and Learning Research Initiative has sought to develop teachers’ research capability and to build knowledge about teaching and learning with the intention of improving outcomes for learners. Fortunate to receive a two‐year grant, our research collaboration investigated secondary school teachers’ and students’ conceptions of assessment and feedback. In addition to the ongoing collection and discussion of student achievement data, during the first year a key task for the teacher‐researchers was to develop and implement a tool that could provide them with greater insight into their students’ conceptions of assessment and feedback. This paper reports on how the teacher‐researchers were supported in a continuing manner to achieve this task, and documents their growing understanding of formative assessment through engagement in teacher research. While there was considerable learning for teachers, it is argued that teacher research, even when supported, is complex and problematic.

A time‐delay technique to improve GBW on negative feedback amplifiers

AbstractThis paper presents a new method to improve the GBW (gain‐bandwidth product) on negative feedback amplifiers. The proposed method is based on the introduction of time‐delay elements in the feedback loop, which can be exploited to retrieve significant bandwidth enhancements. This delayed feedback concept is analyzed, and considerations are presented for first‐order amplifiers, based on theoretical analysis. The concept is simulated and further demonstrated in a practical example using a series‐shunt feedback amplifier with a TL081 operational amplifier (OA) and a 36‐m‐long coaxial cable as a delay element. Measured experimental results show a maximum bandwidth improvement of almost 90%, from a theoretical maximum of 141%. Copyright © 2007 John Wiley & Sons, Ltd.

Secondary school students' conceptions of assessment and feedback

This study investigated secondary school students' conceptions of assessment and feedback. Five focus groups were conducted with 41 Year 9 and 10 students (equivalent to Grades 8 and 9 in other countries) from 4 diverse New Zealand schools. Students said that assessment was useful because it led to information and feedback. This information, in the right form, could help students and, to a lesser extent, teachers improve and it could be used to show progress to parents and employers. If assessment and feedback did not provide this information it was irrelevant. There was no indication that students thought assessment or feedback could make them or their school accountable, but some indication that teachers were accountable for student learning.

Multi-Fingered Grasping and Manipulation in Virtual Environments Using an Isometric Finger Device

In this article we present a new isometric input device for multi-fingered grasping in virtual environments. The device was designed to simultaneously assess forces applied by the thumb, index, and middle finger. A mathematical model of grasping, adopted from the analysis of multi-fingered robot hands, was applied to achieve multi-fingered interaction with virtual objects. We used the concept of visual haptic feedback where the user was presented with visual cues to acquire haptic information from the virtual environment. The virtual object corresponded dynamically to the forces and torques applied by the three fingers. The application of the isometric finger device for multi-fingered interaction is demonstrated in four tasks aimed at the rehabilitation of hand function in stroke patients. The tasks include opening the combination lock on a safe, filling and pouring water from a glass, muscle strength training with an elastic torus, and a force tracking task. The training tasks were designed to train patients' grip force coordination and increase muscle strength through repetitive exercises. The presented virtual reality system was evaluated in a group of healthy subjects and two post-stroke patients (early post-stroke and chronic) to obtain overall performance results. The healthy subjects demonstrated consistent performance with the finger device after the first few trials. The two post-stroke patients completed all four tasks, however, with much lower performance scores as compared to healthy subjects. The results of the preliminary assessment suggest that the patients could further improve their performance through virtual reality training.

Design of a New Folded Cascode Op-Amp Using Positive Feedback and Bulk Amplification

In this paper, a new operational amplifier is presented that improves the specifications such as dc gain, common mode rejection ratio. To obtain these improvements, we have used the two important concepts of feedback and bulk amplification.

Some considerations of the concept of climate feedback

AbstractA conceptual study of climate feedbacks is carried out using two simple linear two‐zone models and the commonly‐used zero‐dimensional model to which they reduce under simplifying assumptions. The term ‘feedback’ is used in many different senses in the climate literature. Two prototype usages, stability‐altering feedback (defined in terms of a system's asymptotic response to an impulsive forcing, negative when stability‐enhancing) and sensitivity‐altering feedback (defined in terms of a system's steady‐state response to a step‐function forcing, negative when sensitivity‐diminishing) have been isolated for study. These two climate feedback concepts are viewed against the background of control theory, which provides a generalized feedback perspective embracing all forms of forcing and which is often seen as providing the paradigm for the concept of feedback as used in climate studies.The relationship between the prototype climate feedbacks is simple in the context of the zero‐dimensional model. Here, the stability‐altering and sensitivity‐altering feedbacks provided by a given interaction are of the same sign, and the sign of the stability‐altering feedback as measured by initial tendencies always coincides with its sign as measured by the defining asymptotic tendencies. Even in this simple model, however, the sign of the prototype climate feedbacks can be opposite to the sign of the system's feedback as defined in control theory.In the two‐zone models, the relationship between the prototype climate feedbacks is not so simple. It is shown that, contrary to the common assumption, these feedbacks can be of opposite signs. Moreover, the sign of the stability‐altering feedback as measured by initial tendencies can be opposite to its sign as measured by asymptotic tendencies. It is further shown that there is no simple relationship between the sign of either of the prototype climate feedbacks in the two‐zone models and the sign of these models' feedback as defined in control theory.These results point to the need for greater precision and explicitness in the definition and use of the term ‘climate feedback’, both to facilitate interdisciplinary dialogue in relation to feedback and to guard against erroneous inferences within the climate field. Explicit definitions of the two prototype categories of climate feedback studied here are proposed. Copyright © 2007 Royal Meteorological Society

Erratum. Some considerations of the concept of climate feedback by J. R. Bates. Published in 133, pp 545‐560

Erratum. Some considerations of the concept of climate feedback by J. R. Bates. Published in 133, pp 545‐560

Multirate Output Feedback Based Robust Quasi-Sliding Mode Control of Discrete-Time Systems

Over the last few years, the research on discrete-time sliding mode control has received a considerable attention. Unlike its continuous-time counterpart, discrete-time sliding mode control is not invariant in general. In this note, an algorithm is presented for robust discrete-time sliding mode control using the concept of multirate output feedback

Feedback adaptation in web-based learning systems

Feedback provided by a learning system to its users plays an important role in web-based education. This paper presents an overview of feedback studies and then concentrates on the problem of feedback adaptation in web-based learning systems. We introduce our taxonomy of feedback concept with regard to its functions, complexity, intention, time of occurrence, way of presentation, and level and way of its adaptation. We consider what can be adapted in feedback and how to facilitate feedback adaptation in web-based learning systems.

A Complex Image Rejection Circuit With Sign Detection Only

In direct-conversion receivers, radio frequency (RF) signals are down-converted to low or zero intermediate frequency (IF) using complex in-phase and quadrature (I/Q) mixers with no prior image filtering. Due to I/Q path gain and phase errors, image leaks into the signal band during the down-conversion process. A generic image rejection algorithm is proposed to reject image in the baseband using a zero-forcing sign-sign adaptive feedback concept. The orthonormal property of complex I/Q channels is exploited to update their gain and phase errors by detecting only four signs, and image is corrected with four multiplications and two additions. The proposed image rejection algorithm can be implemented in a digital, analog, or hybrid form. A complex baseband sample and hold (S/H) with a digital error detector, which is a hybrid example, achieves an image rejection of 65 dB while sampling at 40 MS/s. The prototype chip fabricated in 0.18-mum CMOS occupies 800times450 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and consumes 23 mW at 1.8 V

Feedback Loops in Clinical Practice: An Integrative Framework

Practical concepts and interventions for counsellors and their clients are presented based on Maruyama's concept of feedback. Elements of psychodynamic theory, Weinberg's theory and Moreno's role theory are reformulated in terms of feedback. The concept of feedback also links network theory and chaos theory; cognitive challenges and psychodynamic interpretation. This forms an integrative framework for understanding human functioning. Human functioning emerges from the interaction of innumerable intrapersonal and interpersonal feedback loops. The feedback loops organise a network of actions, ideas and feelings, and a network of roles. Some feedback loops tend to intensify life difficulties, while others tend to resolve these difficulties. The counselling interventions evolved from problem gambling counselling practice, and sample interventions are provided based on a composite problem gambler. (author abstract)

Evaluation of an interactive case simulation system in dermatology and venereology for medical students

BackgroundMost of the many computer resources used in clinical teaching of dermatology and venereology for medical undergraduates are information-oriented and focus mostly on finding a "correct" multiple-choice alternative or free-text answer. We wanted to create an interactive computer program, which facilitates not only factual recall but also clinical reasoning.MethodsThrough continuous interaction with students, a new computerised interactive case simulation system, NUDOV, was developed. It is based on authentic cases and contains images of real patients, actors and healthcare providers. The student selects a patient and proposes questions for medical history, examines the skin, and suggests investigations, diagnosis, differential diagnoses and further management. Feedback is given by comparing the user's own suggestions with those of a specialist. In addition, a log file of the student's actions is recorded. The program includes a large number of images, video clips and Internet links. It was evaluated with a student questionnaire and by randomising medical students to conventional teaching (n = 85) or conventional teaching plus NUDOV (n = 31) and comparing the results of the two groups in a final written examination.ResultsThe questionnaire showed that 90% of the NUDOV students stated that the program facilitated their learning to a large/very large extent, and 71% reported that extensive working with authentic computerised cases made it easier to understand and learn about diseases and their management. The layout, user-friendliness and feedback concept were judged as good/very good by 87%, 97%, and 100%, respectively. Log files revealed that the students, in general, worked with each case for 60–90 min. However, the intervention group did not score significantly better than the control group in the written examination.ConclusionWe created a computerised case simulation program allowing students to manage patients in a non-linear format supporting the clinical reasoning process. The student gets feedback through comparison with a specialist, eliminating the need for external scoring or correction. The model also permits discussion of case processing, since all transactions are stored in a log file. The program was highly appreciated by the students, but did not significantly improve their performance in the written final examination.