Dynamical behaviors of Rb-E2F pathway including negative feedback loops involving miR449.

Science.gov (United States)

Yan, Fang; Liu, Haihong; Hao, Junjun; Liu, Zengrong

2012-01-01

MiRNAs, which are a family of small non-coding RNAs, regulate a broad array of physiological and developmental processes. However, their regulatory roles have remained largely mysterious. E2F is a positive regulator of cell cycle progression and also a potent inducer of apoptosis. Positive feedback loops in the regulation of Rb-E2F pathway are predicted and shown experimentally. Recently, it has been discovered that E2F induce a cluster of miRNAs called miR449. In turn, E2F is inhibited by miR449 through regulating different transcripts, thus forming negative feedback loops in the interaction network. Here, based on the integration of experimental evidence and quantitative data, we studied Rb-E2F pathway coupling the positive feedback loops and negative feedback loops mediated by miR449. Therefore, a mathematical model is constructed based in part on the model proposed in Yao-Lee et al. (2008) and nonlinear dynamical behaviors including the stability and bifurcations of the model are discussed. A comparison is given to reveal the implication of the fundamental differences of Rb-E2F pathway between regulation and deregulation of miR449. Coherent with the experiments it predicts that miR449 plays a critical role in regulating the cell cycle progression and provides a twofold safety mechanism to avoid excessive E2F-induced proliferation by cell cycle arrest and apoptosis. Moreover, numerical simulation and bifurcation analysis shows that the mechanisms of the negative regulation of miR449 to three different transcripts are quite distinctive which needs to be verified experimentally. This study may help us to analyze the whole cell cycle process mediated by other miRNAs more easily. A better knowledge of the dynamical behaviors of miRNAs mediated networks is also of interest for bio-engineering and artificial control.

Closed-loop multiple antenna aided wireless communications using limited feedback

OpenAIRE

Yang, Du

2010-01-01

The aim of this thesis is to study the design of closed-loop multiple antenna aided wireless communications relying on limited feedback. Multiple antennas may be employed either/both at the transmitter or/and at the receiver, here the latter periodically feeds back some information about the time-varying wireless channel using a limited number of bits. Furthermore, the transmitter then pre-processes the signals to be transmitted according to the received feedback information. This closed-loop...

Finding Positive Feedback Loops in Environmental Models: A Mathematical Investigation

Science.gov (United States)

Sheikholeslami, R.; Razavi, S.

2016-12-01

Dynamics of most earth and environmental systems are generally governed by interactions between several hydrological (e.g., soil moisture and precipitation), geological (e.g., and erosion), geochemical (e.g., nutrient loading), and atmospheric (e.g., temperature) processes which operate on a range of spatio-temporal scales. These interactions create numerous feedback mechanisms with complex behaviours, and their understanding and representation can vary depending on the scale in space and/or time at which the system is analyzed. One of the most crucial characteristics of such complex systems is the existence of positive feedback loops. The presence of positive feedbacks may increase complexity, accelerate change, or trigger multiple stable states in the underlying dynamical system. Furthermore, because of the inherent non-linearity, it is often very difficult to obtain a general idea of their complex dynamics. Feedback loops in environmental systems have been well recognized and qualitatively discussed. With a quantitative/mathematical view, in this presentation, we address the question of how the positive feedback loops can be identified/implemented in environmental models. We investigate the nature of different feedback mechanisms and dynamics of simple example case studies that underlie fundamental processes such as vegetation, precipitation and soil moisture. To do this, we apply the concept of "interaction graph" from mathematics which is built from the Jacobian matrix of the dynamical system. The Jacobian matrix contains information on how variations of one state variable depends on variations of other variables, and thus can be used to understand the dynamical possibilities of feedback mechanisms in the underlying system. Moreover, this study highlights that there are some situations where the existence of positive feedback loops can cause multiple stable states, and thereby regime shifts in environmental systems. Systems with multiple stable states are

No evidence for an elephant-termite feedback loop in Sand Forest, South Africa

NARCIS (Netherlands)

Lagendijk, D. D G; Davies, A. B.; Eggleton, P.; Slotow, R.

2016-01-01

Termites and mammalian herbivores might derive mutual benefit from each other through positive feedback loops, but empirical evidence is lacking. One suggested positive feedback loop is between termites and elephant, both ecosystem engineers. Termites, as decomposer organisms, contribute to nutrient

The double-loop feedback for active learning with understanding

DEFF Research Database (Denmark)

Christensen, Hans Peter

2004-01-01

Learning is an active process, and in engineering education authentic projects is often used to activate the students and promote learning. However, it is not all activity that leads to deep learning; and in a rapid changing society deep understanding is necessary for life-long learning. Empirical...... findings at DTU question the direct link between high activity and a deep approach to learning. Active learning is important to obtain engineering competencies, but active learning requires more than activity. Feedback and reflection is crucial to the learning process, since new knowledge is built...... on the student’s existing understanding. A model for an active learning process with a double-loop feedback is suggested - the first loop gives the student experience through experimentation, the second conceptual understanding through reflection. Students often miss the second loop, so it is important...

MiR-192-Mediated Positive Feedback Loop Controls the Robustness of Stress-Induced p53 Oscillations in Breast Cancer Cells.

Directory of Open Access Journals (Sweden)

Richard Moore

2015-12-01

Full Text Available The p53 tumor suppressor protein plays a critical role in cellular stress and cancer prevention. A number of post-transcriptional regulators, termed microRNAs, are closely connected with the p53-mediated cellular networks. While the molecular interactions among p53 and microRNAs have emerged, a systems-level understanding of the regulatory mechanism and the role of microRNAs-forming feedback loops with the p53 core remains elusive. Here we have identified from literature that there exist three classes of microRNA-mediated feedback loops revolving around p53, all with the nature of positive feedback coincidentally. To explore the relationship between the cellular performance of p53 with the microRNA feedback pathways, we developed a mathematical model of the core p53-MDM2 module coupled with three microRNA-mediated positive feedback loops involving miR-192, miR-34a, and miR-29a. Simulations and bifurcation analysis in relationship to extrinsic noise reproduce the oscillatory behavior of p53 under DNA damage in single cells, and notably show that specific microRNA abrogation can disrupt the wild-type cellular phenotype when the ubiquitous cell-to-cell variability is taken into account. To assess these in silico results we conducted microRNA-perturbation experiments in MCF7 breast cancer cells. Time-lapse microscopy of cell-population behavior in response to DNA double-strand breaks, together with image classification of single-cell phenotypes across a population, confirmed that the cellular p53 oscillations are compromised after miR-192 perturbations, matching well with the model predictions. Our study via modeling in combination with quantitative experiments provides new evidence on the role of microRNA-mediated positive feedback loops in conferring robustness to the system performance of stress-induced response of p53.

Dynamical behaviors of Rb-E2F pathway including negative feedback loops involving miR449.

Directory of Open Access Journals (Sweden)

Fang Yan

Full Text Available MiRNAs, which are a family of small non-coding RNAs, regulate a broad array of physiological and developmental processes. However, their regulatory roles have remained largely mysterious. E2F is a positive regulator of cell cycle progression and also a potent inducer of apoptosis. Positive feedback loops in the regulation of Rb-E2F pathway are predicted and shown experimentally. Recently, it has been discovered that E2F induce a cluster of miRNAs called miR449. In turn, E2F is inhibited by miR449 through regulating different transcripts, thus forming negative feedback loops in the interaction network. Here, based on the integration of experimental evidence and quantitative data, we studied Rb-E2F pathway coupling the positive feedback loops and negative feedback loops mediated by miR449. Therefore, a mathematical model is constructed based in part on the model proposed in Yao-Lee et al. (2008 and nonlinear dynamical behaviors including the stability and bifurcations of the model are discussed. A comparison is given to reveal the implication of the fundamental differences of Rb-E2F pathway between regulation and deregulation of miR449. Coherent with the experiments it predicts that miR449 plays a critical role in regulating the cell cycle progression and provides a twofold safety mechanism to avoid excessive E2F-induced proliferation by cell cycle arrest and apoptosis. Moreover, numerical simulation and bifurcation analysis shows that the mechanisms of the negative regulation of miR449 to three different transcripts are quite distinctive which needs to be verified experimentally. This study may help us to analyze the whole cell cycle process mediated by other miRNAs more easily. A better knowledge of the dynamical behaviors of miRNAs mediated networks is also of interest for bio-engineering and artificial control.

An oncogenic MYB feedback loop drives alternate cell fates in adenoid cystic carcinoma

Science.gov (United States)

Drier, Yotam; Cotton, Matthew J.; Williamson, Kaylyn E.; Gillespie, Shawn M.; Ryan, Russell J.H.; Kluk, Michael J.; Carey, Christopher D.; Rodig, Scott J.; Sholl, Lynette M; Afrogheh, Amir H.; Faquin, William C.; Queimado, Lurdes; Qi, Jun; Wick, Michael J.; El-Naggar, Adel K.; Bradner, James E.; Moskaluk, Christopher A.; Aster, Jon C.; Knoechel, Birgit; Bernstein, Bradley E.

2016-01-01

Translocation events are frequent in cancer and may create chimeric fusions or ‘regulatory rearrangements’ that drive oncogene overexpression. Here we identify super-enhancer translocations that drive overexpression of the oncogenic transcription factor MYB as a recurrent theme in adenoid cystic carcinoma (ACC). Whole-genome sequencing data and chromatin maps reveal distinct chromosomal rearrangements that juxtapose super-enhancers to the MYB locus. Chromosome conformation capture confirms that the translocated enhancers interact with the MYB promoter. Remarkably, MYB protein binds to the translocated enhancers, creating a positive feedback loop that sustains its expression. MYB also binds enhancers that drive different regulatory programs in alternate cell lineages in ACC, cooperating with TP63 in myoepithelial cells and a Notch program in luminal epithelial cells. Bromodomain inhibitors slow tumor growth in ACC primagraft models in vivo. Thus, our study identifies super-enhancer translocations that drive MYB expression and provides insight into downstream MYB functions in the alternate ACC lineages. PMID:26829750

Construction and modelling of an inducible positive feedback loop stably integrated in a mammalian cell-line.

Directory of Open Access Journals (Sweden)

Velia Siciliano

2011-06-01

Full Text Available Understanding the relationship between topology and dynamics of transcriptional regulatory networks in mammalian cells is essential to elucidate the biology of complex regulatory and signaling pathways. Here, we characterised, via a synthetic biology approach, a transcriptional positive feedback loop (PFL by generating a clonal population of mammalian cells (CHO carrying a stable integration of the construct. The PFL network consists of the Tetracycline-controlled transactivator (tTA, whose expression is regulated by a tTA responsive promoter (CMV-TET, thus giving rise to a positive feedback. The same CMV-TET promoter drives also the expression of a destabilised yellow fluorescent protein (d2EYFP, thus the dynamic behaviour can be followed by time-lapse microscopy. The PFL network was compared to an engineered version of the network lacking the positive feedback loop (NOPFL, by expressing the tTA mRNA from a constitutive promoter. Doxycycline was used to repress tTA activation (switch off, and the resulting changes in fluorescence intensity for both the PFL and NOPFL networks were followed for up to 43 h. We observed a striking difference in the dynamics of the PFL and NOPFL networks. Using non-linear dynamical models, able to recapitulate experimental observations, we demonstrated a link between network topology and network dynamics. Namely, transcriptional positive autoregulation can significantly slow down the "switch off" times, as compared to the non-autoregulated system. Doxycycline concentration can modulate the response times of the PFL, whereas the NOPFL always switches off with the same dynamics. Moreover, the PFL can exhibit bistability for a range of Doxycycline concentrations. Since the PFL motif is often found in naturally occurring transcriptional and signaling pathways, we believe our work can be instrumental to characterise their behaviour.

Construction and modelling of an inducible positive feedback loop stably integrated in a mammalian cell-line.

Science.gov (United States)

Siciliano, Velia; Menolascina, Filippo; Marucci, Lucia; Fracassi, Chiara; Garzilli, Immacolata; Moretti, Maria Nicoletta; di Bernardo, Diego

2011-06-01

Understanding the relationship between topology and dynamics of transcriptional regulatory networks in mammalian cells is essential to elucidate the biology of complex regulatory and signaling pathways. Here, we characterised, via a synthetic biology approach, a transcriptional positive feedback loop (PFL) by generating a clonal population of mammalian cells (CHO) carrying a stable integration of the construct. The PFL network consists of the Tetracycline-controlled transactivator (tTA), whose expression is regulated by a tTA responsive promoter (CMV-TET), thus giving rise to a positive feedback. The same CMV-TET promoter drives also the expression of a destabilised yellow fluorescent protein (d2EYFP), thus the dynamic behaviour can be followed by time-lapse microscopy. The PFL network was compared to an engineered version of the network lacking the positive feedback loop (NOPFL), by expressing the tTA mRNA from a constitutive promoter. Doxycycline was used to repress tTA activation (switch off), and the resulting changes in fluorescence intensity for both the PFL and NOPFL networks were followed for up to 43 h. We observed a striking difference in the dynamics of the PFL and NOPFL networks. Using non-linear dynamical models, able to recapitulate experimental observations, we demonstrated a link between network topology and network dynamics. Namely, transcriptional positive autoregulation can significantly slow down the "switch off" times, as compared to the non-autoregulated system. Doxycycline concentration can modulate the response times of the PFL, whereas the NOPFL always switches off with the same dynamics. Moreover, the PFL can exhibit bistability for a range of Doxycycline concentrations. Since the PFL motif is often found in naturally occurring transcriptional and signaling pathways, we believe our work can be instrumental to characterise their behaviour.

Interleukin 6 promotes endometrial cancer growth through an autocrine feedback loop involving ERK–NF-κB signaling pathway

Energy Technology Data Exchange (ETDEWEB)

Che, Qi; Liu, Bin-Ya; Wang, Fang-Yuan; He, Yin-Yan; Lu, Wen; Liao, Yun [Department of Obstetrics and Gynecology, Shanghai First People’s Hospital Affiliated to Shanghai Jiao Tong University, Shanghai (China); Gu, Wei, E-mail: krisgu70@163.com [Department of Obstetrics and Gynecology, International Peace Maternity and Child Health Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai (China); Wan, Xiao-Ping, E-mail: wanxp@sjtu.edu.cn [Department of Obstetrics and Gynecology, Shanghai First Maternity and Infant Hospital Affiliated to Tong Ji University, Shanghai (China)

2014-03-28

Highlights: • IL-6 could promote endometrial cancer cells proliferation. • IL-6 promotes its own production through an autocrine feedback loop. • ERK and NF-κB pathway inhibitors inhibit IL-6 production and tumor growth. • IL-6 secretion relies on the activation of ERK–NF-κB pathway axis. • An orthotopic nude endometrial carcinoma model confirms the effect of IL-6. - Abstract: Interleukin (IL)-6 as an inflammation factor, has been proved to promote cancer proliferation in several human cancers. However, its role in endometrial cancer has not been studied clearly. Previously, we demonstrated that IL-6 promoted endometrial cancer progression through local estrogen biosynthesis. In this study, we proved that IL-6 could directly stimulate endometrial cancer cells proliferation and an autocrine feedback loop increased its production even after the withdrawal of IL-6 from the medium. Next, we analyzed the mechanism underlying IL-6 production in the feedback loop and found that its production and IL-6-stimulated cell proliferation were effectively blocked by pharmacologic inhibitors of nuclear factor-kappa B (NF-κB) and extra-cellular signal-regulated kinase (ERK). Importantly, activation of ERK was upstream of the NF-κB pathways, revealing the hierarchy of this event. Finally, we used an orthotopic nude endometrial carcinoma model to confirm the effects of IL-6 on the tumor progression. Taken together, these data indicate that IL-6 promotes endometrial carcinoma growth through an expanded autocrine regulatory loop and implicate the ERK–NF-κB pathway as a critical mediator of IL-6 production, implying IL-6 to be an important therapeutic target in endometrial carcinoma.

Biodiversity maintenance in food webs with regulatory environmental feedbacks.

Science.gov (United States)

Bagdassarian, Carey K; Dunham, Amy E; Brown, Christopher G; Rauscher, Daniel

2007-04-21

Although the food web is one of the most fundamental and oldest concepts in ecology, elucidating the strategies and structures by which natural communities of species persist remains a challenge to empirical and theoretical ecologists. We show that simple regulatory feedbacks between autotrophs and their environment when embedded within complex and realistic food-web models enhance biodiversity. The food webs are generated through the niche-model algorithm and coupled with predator-prey dynamics, with and without environmental feedbacks at the autotroph level. With high probability and especially at lower, more realistic connectance levels, regulatory environmental feedbacks result in fewer species extinctions, that is, in increased species persistence. These same feedback couplings, however, also sensitize food webs to environmental stresses leading to abrupt collapses in biodiversity with increased forcing. Feedback interactions between species and their material environments anchor food-web persistence, adding another dimension to biodiversity conservation. We suggest that the regulatory features of two natural systems, deep-sea tubeworms with their microbial consortia and a soil ecosystem manifesting adaptive homeostatic changes, can be embedded within niche-model food-web dynamics.

Smart Braid Feedback for the Closed-Loop Control of Soft Robotic Systems.

Science.gov (United States)

Felt, Wyatt; Chin, Khai Yi; Remy, C David

2017-09-01

This article experimentally investigates the potential of using flexible, inductance-based contraction sensors in the closed-loop motion control of soft robots. Accurate motion control remains a highly challenging task for soft robotic systems. Precise models of the actuation dynamics and environmental interactions are often unavailable. This renders open-loop control impossible, while closed-loop control suffers from a lack of suitable feedback. Conventional motion sensors, such as linear or rotary encoders, are difficult to adapt to robots that lack discrete mechanical joints. The rigid nature of these sensors runs contrary to the aspirational benefits of soft systems. As truly soft sensor solutions are still in their infancy, motion control of soft robots has so far relied on laboratory-based sensing systems such as motion capture, electromagnetic (EM) tracking, or Fiber Bragg Gratings. In this article, we used embedded flexible sensors known as Smart Braids to sense the contraction of McKibben muscles through changes in inductance. We evaluated closed-loop control on two systems: a revolute joint and a planar, one degree of freedom continuum manipulator. In the revolute joint, our proposed controller compensated for elasticity in the actuator connections. The Smart Braid feedback allowed motion control with a steady-state root-mean-square (RMS) error of [1.5]°. In the continuum manipulator, Smart Braid feedback enabled tracking of the desired tip angle with a steady-state RMS error of [1.25]°. This work demonstrates that Smart Braid sensors can provide accurate position feedback in closed-loop motion control suitable for field applications of soft robotic systems.

Depression as a systemic syndrome: mapping the feedback loops of major depressive disorder.

Science.gov (United States)

Wittenborn, A K; Rahmandad, H; Rick, J; Hosseinichimeh, N

2016-02-01

Depression is a complex public health problem with considerable variation in treatment response. The systemic complexity of depression, or the feedback processes among diverse drivers of the disorder, contribute to the persistence of depression. This paper extends prior attempts to understand the complex causal feedback mechanisms that underlie depression by presenting the first broad boundary causal loop diagram of depression dynamics. We applied qualitative system dynamics methods to map the broad feedback mechanisms of depression. We used a structured approach to identify candidate causal mechanisms of depression in the literature. We assessed the strength of empirical support for each mechanism and prioritized those with support from validation studies. Through an iterative process, we synthesized the empirical literature and created a conceptual model of major depressive disorder. The literature review and synthesis resulted in the development of the first causal loop diagram of reinforcing feedback processes of depression. It proposes candidate drivers of illness, or inertial factors, and their temporal functioning, as well as the interactions among drivers of depression. The final causal loop diagram defines 13 key reinforcing feedback loops that involve nine candidate drivers of depression. Future research is needed to expand upon this initial model of depression dynamics. Quantitative extensions may result in a better understanding of the systemic syndrome of depression and contribute to personalized methods of evaluation, prevention and intervention.

Closing the sensorimotor loop: haptic feedback facilitates decoding of motor imagery

Science.gov (United States)

Gomez-Rodriguez, M.; Peters, J.; Hill, J.; Schölkopf, B.; Gharabaghi, A.; Grosse-Wentrup, M.

2011-06-01

The combination of brain-computer interfaces (BCIs) with robot-assisted physical therapy constitutes a promising approach to neurorehabilitation of patients with severe hemiparetic syndromes caused by cerebrovascular brain damage (e.g. stroke) and other neurological conditions. In such a scenario, a key aspect is how to reestablish the disrupted sensorimotor feedback loop. However, to date it is an open question how artificially closing the sensorimotor feedback loop influences the decoding performance of a BCI. In this paper, we answer this issue by studying six healthy subjects and two stroke patients. We present empirical evidence that haptic feedback, provided by a seven degrees of freedom robotic arm, facilitates online decoding of arm movement intention. The results support the feasibility of future rehabilitative treatments based on the combination of robot-assisted physical therapy with BCIs.

Interlinked dual-time feedback loops can enhance robustness to stochasticity and persistence of memory.

Science.gov (United States)

Smolen, Paul; Baxter, Douglas A; Byrne, John H

2009-03-01

Multiple interlinked positive feedback loops shape the stimulus responses of various biochemical systems, such as the cell cycle or intracellular Ca2+ release. Recent studies with simplified models have identified two advantages of coupling fast and slow feedback loops. This dual-time structure enables a fast response while enhancing resistances of responses and bistability to stimulus noise. We now find that (1) the dual-time structure similarly confers resistance to internal noise due to molecule number fluctuations, and (2) model variants with altered coupling, which better represent some specific biochemical systems, share all the above advantages. We also develop a similar bistable model with coupling of a fast autoactivation loop to a slow loop. This model's topology was suggested by positive feedback proposed to play a role in long-term synaptic potentiation (LTP). The advantages of fast response and noise resistance are also present in this autoactivation model. Empirically, LTP develops resistance to reversal over approximately 1h . The model suggests this resistance may result from increased amounts of synaptic kinases involved in positive feedback.

Analysis of beam feedback loops of RF acceleration system at TARN II

International Nuclear Information System (INIS)

Katayama, Takeshi.

1992-08-01

Two beam-feedback-loops are prepared for the frequency control of RF acceleration system at cooler-synchrotron TARN II. One is the phase-loop and the other the radial-position-loop. In the present paper, the effects of these loops on the beam dynamics in the synchrotron are studied on the basis of Laplace transformation approach as well as the numerical values for the synchrotron acceleration at TARN II. (author)

Benefits of Subliminal Feedback Loops in Human-Computer Interaction

OpenAIRE

Walter Ritter

2011-01-01

A lot of efforts have been directed to enriching human-computer interaction to make the user experience more pleasing or efficient. In this paper, we briefly present work in the fields of subliminal perception and affective computing, before we outline a new approach to add analog communication channels to the human-computer interaction experience. In this approach, in addition to symbolic predefined mappings of input to output, a subliminal feedback loop is used that provides feedback in evo...

Computational Model of a Positive BDNF Feedback Loop in Hippocampal Neurons Following Inhibitory Avoidance Training

Science.gov (United States)

Zhang, Yili; Smolen, Paul; Alberini, Cristina M.; Baxter, Douglas A.; Byrne, John H.

2016-01-01

Inhibitory avoidance (IA) training in rodents initiates a molecular cascade within hippocampal neurons. This cascade contributes to the transition of short- to long-term memory (i.e., consolidation). Here, a differential equation-based model was developed to describe a positive feedback loop within this molecular cascade. The feedback loop begins…

A social feedback loop for speech development and its reduction in autism.

Science.gov (United States)

Warlaumont, Anne S; Richards, Jeffrey A; Gilkerson, Jill; Oller, D Kimbrough

2014-07-01

We analyzed the microstructure of child-adult interaction during naturalistic, daylong, automatically labeled audio recordings (13,836 hr total) of children (8- to 48-month-olds) with and without autism. We found that an adult was more likely to respond when the child's vocalization was speech related rather than not speech related. In turn, a child's vocalization was more likely to be speech related if the child's previous speech-related vocalization had received an immediate adult response rather than no response. Taken together, these results are consistent with the idea that there is a social feedback loop between child and caregiver that promotes speech development. Although this feedback loop applies in both typical development and autism, children with autism produced proportionally fewer speech-related vocalizations, and the responses they received were less contingent on whether their vocalizations were speech related. We argue that such differences will diminish the strength of the social feedback loop and have cascading effects on speech development over time. Differences related to socioeconomic status are also reported. © The Author(s) 2014.

How short RNAs impact the human ribonuclease Dicer activity: putative regulatory feedback-loops and other RNA-mediated mechanisms controlling microRNA processing.

Science.gov (United States)

Koralewska, Natalia; Hoffmann, Weronika; Pokornowska, Maria; Milewski, Marek; Lipinska, Andrea; Bienkowska-Szewczyk, Krystyna; Figlerowicz, Marek; Kurzynska-Kokorniak, Anna

2016-01-01

Ribonuclease Dicer plays a pivotal role in RNA interference pathways by processing long double-stranded RNAs and single-stranded hairpin RNA precursors into small interfering RNAs (siRNAs) and microRNAs (miRNAs), respectively. While details of Dicer regulation by a variety of proteins are being elucidated, less is known about non-protein factors, e.g. RNA molecules, that may influence this enzyme's activity. Therefore, we decided to investigate the question of whether the RNA molecules can function not only as Dicer substrates but also as its regulators. Our previous in vitro studies indicated that the activity of human Dicer can be influenced by short RNA molecules that either bind to Dicer or interact with its substrates, or both. Those studies were carried out with commercial Dicer preparations. Nevertheless, such preparations are usually not homogeneous enough to carry out more detailed RNA-binding studies. Therefore, we have established our own system for the production of human Dicer in insect cells. In this manuscript, we characterize the RNA-binding and RNA-cleavage properties of the obtained preparation. We demonstrate that Dicer can efficiently bind single-stranded RNAs that are longer than ~20-nucleotides. Consequently, we revisit possible scenarios of Dicer regulation by single-stranded RNA species ranging from ~10- to ~60-nucleotides, in the context of their binding to this enzyme. Finally, we show that siRNA/miRNA-sized RNAs may affect miRNA production either by binding to Dicer or by participating in regulatory feedback-loops. Altogether, our studies suggest a broad regulatory role of short RNAs in Dicer functioning.

Interlinked Dual-Time Feedback Loops can Enhance Robustness to Stochasticity and Persistence of Memory

OpenAIRE

Smolen, Paul; Baxter, Douglas A.; Byrne, John H.

2012-01-01

Multiple interlinked positive feedback loops shape the stimulus responses of various biochemical systems, such as the cell cycle or intracellular Ca2+ release. Recent studies with simplified models have identified two advantages of coupling fast and slow feedback loops. This dual-time structure enables a fast response while enhancing resistances of responses and bistability to stimulus noise. We now find that: 1) the dual-time structure similarly confers resistance to internal noise due to mo...

MicroRNA miR-308 regulates dMyc through a negative feedback loop in Drosophila

Directory of Open Access Journals (Sweden)

Kaveh Daneshvar

2012-10-01

The abundance of Myc protein must be exquisitely controlled to avoid growth abnormalities caused by too much or too little Myc. An intriguing mode of regulation exists in which Myc protein itself leads to reduction in its abundance. We show here that dMyc binds to the miR-308 locus and increases its expression. Using our gain-of-function approach, we show that an increase in miR-308 causes a destabilization of dMyc mRNA and reduced dMyc protein levels. In vivo knockdown of miR-308 confirmed the regulation of dMyc levels in embryos. This regulatory loop is crucial for maintaining appropriate dMyc levels and normal development. Perturbation of the loop, either by elevated miR-308 or elevated dMyc, caused lethality. Combining elevated levels of both, therefore restoring balance between miR-308 and dMyc levels, resulted in lower apoptotic activity and suppression of lethality. These results reveal a sensitive feedback mechanism that is crucial to prevent the pathologies caused by abnormal levels of dMyc.

A dynamic-biased dual-loop-feedback CMOS LDO regulator with fast transient response

International Nuclear Information System (INIS)

Wang Han; Sun Maomao

2014-01-01

This paper presents a low-dropout regulator (LDO) for portable applications with dual-loop feedback and a dynamic bias circuit. The dual-loop feedback structure is adopted to reduce the output voltage spike and the response time of the LDO. The dynamic bias circuit enhances the slew rate at the gate of the power transistor. In addition, an adaptive miller compensation technique is employed, from which a single pole system is realized and over a 59° phase margin is achieved under the full range of the load current. The proposed LDO has been implemented in a 0.6-μm CMOS process. From the experimental results, the regulator can operate with a minimum dropout voltage of 200 mV at a maximum 300 mA load and I Q of 113 μA. The line regulation and load regulation are improved to 0.1 mV/V and 3.4 μV/mA due to the sufficient loop gain provided by the dual feedback loops. Under a full range load current step, the voltage spikes and the recovery time of the proposed LDO is reduced to 97 mV and 0.142 μs respectively. (semiconductor integrated circuits)

Practical Loop-Shaping Design of Feedback Control Systems

Science.gov (United States)

Kopasakis, George

2010-01-01

An improved methodology for designing feedback control systems has been developed based on systematically shaping the loop gain of the system to meet performance requirements such as stability margins, disturbance attenuation, and transient response, while taking into account the actuation system limitations such as actuation rates and range. Loop-shaping for controls design is not new, but past techniques do not directly address how to systematically design the controller to maximize its performance. As a result, classical feedback control systems are designed predominantly using ad hoc control design approaches such as proportional integral derivative (PID), normally satisfied when a workable solution is achieved, without a good understanding of how to maximize the effectiveness of the control design in terms of competing performance requirements, in relation to the limitations of the plant design. The conception of this improved methodology was motivated by challenges in designing control systems of the types needed for supersonic propulsion. But the methodology is generally applicable to any classical control-system design where the transfer function of the plant is known or can be evaluated. In the case of a supersonic aerospace vehicle, a major challenge is to design the system to attenuate anticipated external and internal disturbances, using such actuators as fuel injectors and valves, bypass doors, and ramps, all of which are subject to limitations in actuator response, rates, and ranges. Also, for supersonic vehicles, with long slim type of structures, coupling between the engine and the structural dynamics can produce undesirable effects that could adversely affect vehicle stability and ride quality. In order to design distributed controls that can suppress these potential adverse effects, within the full capabilities of the actuation system, it is important to employ a systematic control design methodology such as this that can maximize the

An evaluation of the feedback loops in the poverty focus of world bank operations.

Science.gov (United States)

Fardoust, Shahrokh; Kanbur, Ravi; Luo, Xubei; Sundberg, Mark

2018-04-01

The World Bank Group in 2013 made the elimination of extreme poverty by 2030 a central institutional focus and purpose. This paper, based on an evaluation conducted by the Independent Evaluation Group of the World Bank Group, examines how, and how well, the Bank uses feedback loops to enhance the poverty focus of its operations. Feedback loops are important for every element of the results chain running from data, to diagnostics, to strategy formulation and finally to strategy implementation. The evaluation uses a range of instruments, including surveys of stakeholders and World Bank staff, focus group meetings, country case studies and systematic reviews of Bank lending and non-lending operations. We find that while the Bank generates useful information on poverty reduction from its projects and programs, the feedback loops - from outcomes to data analysis to diagnostics to strategy formulation and implementation - have generally been weak, with sizable variation across countries. Copyright © 2017 The World Bank. Published by Elsevier Ltd.. All rights reserved.

Beam stability in synchrotrons with digital filters in the feedback loop of a transverse damper

International Nuclear Information System (INIS)

Zhabitskij, V.M.

2009-01-01

The stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper is treated. Solving the characteristic equation allows one to calculate the achievable damping rates as a function of instability growth rate, feedback gain and parameters of the signal processing. A transverse feedback system (TFS) is required in synchrotrons to stabilize the high intensity ion beams against transverse instabilities and to damp the beam injection errors. The TFS damper kicker (DK) corrects the transverse momentum of a bunch in proportion to its displacement from the closed orbit at the location of the beam position monitor (BPM). The digital signal processing unit in the feedback loop between BPM and DK ensures a condition to achieve optimal damping. Damping rates of the feedback systems with digital notch, Hilbert and all-pass filters are analyzed in comparison with those in an ideal feedback system

Closed loop kinesthetic feedback for postural control rehabilitation.

Science.gov (United States)

Vérité, Fabien; Bachta, Wael; Morel, Guillaume

2014-01-01

Postural control rehabilitation may benefit from the use of smart devices providing biofeedback. This approach consists of increasing the patients perception of their postural state. Namely, postural state is monitored and fed back in real time to the patients through one or more sensory channels. This allows implementing rehabilitation exercises where the patients control their posture with the help of additional sensory inputs. In this paper, a closed loop control of the Center-Of-Pressure (CoP) based on kinesthetic feedback is proposed as a new form of biofeedback. The motion of a one Degree of Freedom (DoF) translational device, lightly touched by the patient's forefinger, is servoed to the patient's CoP position extracted from the measurements of a force plate on which he/she stands. As a result, the patient's CoP can be controllably displaced. A first set of experiments is used to prove the feasibility of this closed-loop control under ideal conditions favoring the perception of the kinesthetic feedback, while the subject is totally unaware of the context. A second set of experiments is then proposed to evaluate the robustness of this approach under experimental conditions that are more realistic with regards to the clinical context of a rehabilitation program involving biofeedback-based exercises.

P53-miR-191-SOX4 regulatory loop affects apoptosis in breast cancer.

Science.gov (United States)

Sharma, Shivani; Nagpal, Neha; Ghosh, Prahlad C; Kulshreshtha, Ritu

2017-08-01

miRNAs have emerged as key participants of p53 signaling pathways because they regulate or are regulated by p53. Here, we provide the first study demonstrating direct regulation of an oncogenic miRNA, miR-191-5p, by p53 and existence of a regulatory feedback loop. Using a combination of qRT-PCR, promoter-luciferase, and chromatin-immunoprecipitation assays, we show that p53 brings about down-regulation of miR-191-5p in breast cancer. miR-191-5p overexpression brought about inhibition of apoptosis in breast cancer cell lines (MCF7 and ZR-75) as demonstrated by reduction in annexin-V stained cells and caspase 3/7 activity, whereas miR-191-5p down-regulation showed the opposite. We further unveiled that SOX4 was a direct target of miR-191-5p. SOX4 overexpression was shown to increase p53 protein levels in MCF7 cells. miR-191-5p overexpression brought about down-regulation of SOX4 and thus p53 levels, suggesting the existence of a regulatory feedback loop. Breast cancer treatment by doxorubicin, an anti-cancer drug, involves induction of apoptosis by p53; we thus wanted to check whether miR-191-5p affects doxorubicin sensitivity. Interestingly, Anti-miR-191 treatment significantly decreased the IC50 of the doxorubicin drug and thus sensitized breast cancer cells to doxorubicin treatment by promoting apoptosis. Overall, this work highlights the importance of the p53-miR-191- SOX4 axis in the regulation of apoptosis and drug resistance in breast cancer and offers a preclinical proof-of-concept for use of an Anti-miR-191 and doxorubicin combination as a rational approach to pursue for better breast cancer treatment. © 2017 Sharma et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.

Extended Cognition: Feedback Loops and Coupled Systems

Directory of Open Access Journals (Sweden)

Olga Markic

2017-12-01

Full Text Available The article explores two waves of active externalism. I first introduce the distinction between passive and active externalism and analyse a proposal of active externalism based on the principle of parity proposed by Clark and Chalmers. There are two main obstacles, causal-constitution fallacy and cognitive bloat, that threaten the extended cognition hypothesis. The second wave of discussions based on the complementarity principle deals with cognitive systems with feedback loops between internal and external elements and is a more radical departure from functionalism and traditional thinking about cognition. I conclude with some remarks on potential ethical considerations of extended cognition.

A transimpedance amplifier using a novel current mode feedback loop

CERN Document Server

Anghinolfi, Francis; Delagnes, E; Jarron, Pierre; Scharfetter, L H H

1995-01-01

We present a transimpedance amplifier stage based on a novel current mode feedback topology. This circuit employs NMOS and PMOS transistors exclusively and requires neither capacitor for stabilizing the transimpedance loop nor resistor for the transresistance feedback and transistor loading. This amplifier circuit is fully compatible with submicron digital CMOS processes. The active feedback network consists of two grounded-gate MOS devices which split the output current in both the feedback and output branches. The transresistance and the phase margin are adjustable through external DC signals. The measured rise time of the impulse response of the amplifier implemented in an industrial 0,7µm CMOS process is 18 ns for a transresistance of 180 k‡ and 30 ns for a transresistance of 560 k‡. The measured Equivalent Noise Charge (ENC) is 800 rms e¯ for an input capacitance of 20 pF with the transresistance adjusted to 560 k‡.

How are things going. Obtaining feedback in a regulatory environment

International Nuclear Information System (INIS)

McGuire, J.V.; Walsh, M.E.; Boegel, A.J.; Morisseau, D.S.; Persendky, J.J.

1984-08-01

This study tested two procedures to gather feedback for a federal agency about its regulatory actions and its licensees' practices. The procedures, a workshop and a mailed survey, targeted a data source new to the agency. Results to date find the feedback workshop useful and the new data source cooperative and valuable. Participation in the workshops is surprising, given their historical backdrop, structure, and psychological literatures. These findings suggest that agencies may be ignoring important data sources for ill-informed reasons. Also, the findings suggest a possible need to restructure existing channels of communication between a regulatory agency and its licensees

Asymmetric dual-loop feedback to suppress spurious tones and reduce timing jitter in self-mode-locked quantum-dash lasers emitting at 155 μm

Science.gov (United States)

Asghar, Haroon; McInerney, John G.

2017-09-01

We demonstrate an asymmetric dual-loop feedback scheme to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single and dual-loop feedback. In this letter, we achieved optimal suppression of spurious tones by optimizing the length of second delay time. We observed that asymmetric dual-loop feedback, with large (~8x) disparity in cavity lengths, eliminates all external-cavity side-modes and produces flat RF spectra close to the main peak with low timing jitter compared to single-loop feedback. Significant reduction in RF linewidth and reduced timing jitter was also observed as a function of increased second feedback delay time. The experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This interesting asymmetric dual-loop feedback scheme provides simplest, efficient and cost effective stabilization of side-band free optoelectronic oscillators based on mode-locked lasers.

Asymmetric positive feedback loops reliably control biological responses.

Science.gov (United States)

Ratushny, Alexander V; Saleem, Ramsey A; Sitko, Katherine; Ramsey, Stephen A; Aitchison, John D

2012-04-24

Positive feedback is a common mechanism enabling biological systems to respond to stimuli in a switch-like manner. Such systems are often characterized by the requisite formation of a heterodimer where only one of the pair is subject to feedback. This ASymmetric Self-UpREgulation (ASSURE) motif is central to many biological systems, including cholesterol homeostasis (LXRα/RXRα), adipocyte differentiation (PPARγ/RXRα), development and differentiation (RAR/RXR), myogenesis (MyoD/E12) and cellular antiviral defense (IRF3/IRF7). To understand why this motif is so prevalent, we examined its properties in an evolutionarily conserved transcriptional regulatory network in yeast (Oaf1p/Pip2p). We demonstrate that the asymmetry in positive feedback confers a competitive advantage and allows the system to robustly increase its responsiveness while precisely tuning the response to a consistent level in the presence of varying stimuli. This study reveals evolutionary advantages for the ASSURE motif, and mechanisms for control, that are relevant to pharmacologic intervention and synthetic biology applications.

A theory of how active behavior stabilises neural activity: Neural gain modulation by closed-loop environmental feedback.

Directory of Open Access Journals (Sweden)

Christopher L Buckley

2018-01-01

Full Text Available During active behaviours like running, swimming, whisking or sniffing, motor actions shape sensory input and sensory percepts guide future motor commands. Ongoing cycles of sensory and motor processing constitute a closed-loop feedback system which is central to motor control and, it has been argued, for perceptual processes. This closed-loop feedback is mediated by brainwide neural circuits but how the presence of feedback signals impacts on the dynamics and function of neurons is not well understood. Here we present a simple theory suggesting that closed-loop feedback between the brain/body/environment can modulate neural gain and, consequently, change endogenous neural fluctuations and responses to sensory input. We support this theory with modeling and data analysis in two vertebrate systems. First, in a model of rodent whisking we show that negative feedback mediated by whisking vibrissa can suppress coherent neural fluctuations and neural responses to sensory input in the barrel cortex. We argue this suppression provides an appealing account of a brain state transition (a marked change in global brain activity coincident with the onset of whisking in rodents. Moreover, this mechanism suggests a novel signal detection mechanism that selectively accentuates active, rather than passive, whisker touch signals. This mechanism is consistent with a predictive coding strategy that is sensitive to the consequences of motor actions rather than the difference between the predicted and actual sensory input. We further support the theory by re-analysing previously published two-photon data recorded in zebrafish larvae performing closed-loop optomotor behaviour in a virtual swim simulator. We show, as predicted by this theory, that the degree to which each cell contributes in linking sensory and motor signals well explains how much its neural fluctuations are suppressed by closed-loop optomotor behaviour. More generally we argue that our results

A theory of how active behavior stabilises neural activity: Neural gain modulation by closed-loop environmental feedback.

Science.gov (United States)

Buckley, Christopher L; Toyoizumi, Taro

2018-01-01

During active behaviours like running, swimming, whisking or sniffing, motor actions shape sensory input and sensory percepts guide future motor commands. Ongoing cycles of sensory and motor processing constitute a closed-loop feedback system which is central to motor control and, it has been argued, for perceptual processes. This closed-loop feedback is mediated by brainwide neural circuits but how the presence of feedback signals impacts on the dynamics and function of neurons is not well understood. Here we present a simple theory suggesting that closed-loop feedback between the brain/body/environment can modulate neural gain and, consequently, change endogenous neural fluctuations and responses to sensory input. We support this theory with modeling and data analysis in two vertebrate systems. First, in a model of rodent whisking we show that negative feedback mediated by whisking vibrissa can suppress coherent neural fluctuations and neural responses to sensory input in the barrel cortex. We argue this suppression provides an appealing account of a brain state transition (a marked change in global brain activity) coincident with the onset of whisking in rodents. Moreover, this mechanism suggests a novel signal detection mechanism that selectively accentuates active, rather than passive, whisker touch signals. This mechanism is consistent with a predictive coding strategy that is sensitive to the consequences of motor actions rather than the difference between the predicted and actual sensory input. We further support the theory by re-analysing previously published two-photon data recorded in zebrafish larvae performing closed-loop optomotor behaviour in a virtual swim simulator. We show, as predicted by this theory, that the degree to which each cell contributes in linking sensory and motor signals well explains how much its neural fluctuations are suppressed by closed-loop optomotor behaviour. More generally we argue that our results demonstrate the dependence

Interaction between beam control and rf feedback loops for high Q cavities an heavy beam loading. Revision A

International Nuclear Information System (INIS)

Mestha, L.K.; Kwan, C.M.; Yeung, K.S.

1994-04-01

An open-loop state space model of all the major low-level rf feedback control loops is derived. The model has control and state variables for fast-cycling machines to apply modern multivariable feedback techniques. A condition is derived to know when exactly we can cross the boundaries between time-varying and time-invariant approaches for a fast-cycling machine like the Low Energy Booster (LEB). The conditions are dependent on the Q of the cavity and the rate at which the frequency changes with time. Apart from capturing the time-variant characteristics, the errors in the magnetic field are accounted in the model to study the effects on synchronization with the Medium Energy Booster (MEB). The control model is useful to study the effects on beam control due to heavy beam loading at high intensities, voltage transients just after injection especially due to time-varying voltages, instability thresholds created by the cavity tuning feedback system, cross coupling between feedback loops with and without direct rf feedback etc. As a special case we have shown that the model agrees with the well known Pedersen model derived for the CERN PS booster. As an application of the model we undertook a detailed study of the cross coupling between the loops by considering all of them at once for varying time, Q and beam intensities. A discussion of the method to identify the coupling is shown. At the end a summary of the identified loop interactions is presented

Self-reinforcing feedback loop in financial markets with coupling of market impact and momentum traders

Science.gov (United States)

Zhong, Li-Xin; Xu, Wen-Juan; Chen, Rong-Da; Zhong, Chen-Yang; Qiu, Tian; Ren, Fei; He, Yun-Xing

2018-03-01

By incorporating market impact and momentum traders into an agent-based model, we investigate the conditions for the occurrence of self-reinforcing feedback loops and the coevolutionary mechanism of prices and strategies. For low market impact, the price fluctuations are originally large. The existence of momentum traders has little impact on the change of price fluctuations but destroys the equilibrium between the trend-following and trend-rejecting strategies. The trend-following herd behaviors become dominant. A self-reinforcing feedback loop exists. For high market impact, the existence of momentum traders leads to an increase in price fluctuations. The trend-following strategies of rational individuals are suppressed while the trend-following strategies of momentum traders are promoted. The crowd-anticrowd behaviors become dominant. A negative feedback loop exists. A theoretical analysis indicates that, for low market impact, the majority effect is beneficial for the trend-followers to earn more, which in turn promotes the trend-following strategies. For high market impact, the minority effect causes the trend-followers to suffer great losses, which in turn suppresses the trend-following strategies.

Pulse energy control through dual loop electronic feedback

CSIR Research Space (South Africa)

Jacobs, Cobus

2006-07-01

Full Text Available University of Stellenbosch WWW.LASER-RESEARCH.CO.ZA University of Stellenbosch Pulse Energy Control Through Dual Loop Electronic Feedback Cobus Jacobs, Steven Kriel Christoph Bollig, Thomas Jones Cobus Jacobs et al. Overview head2righthead2right...What is Laser Pulse Energy Control? head2righthead2rightWhy do we need it? head2righthead2rightHow do we get it? head2righthead2rightSimulation head2righthead2rightExperimental Setup head2righthead2rightResults Cobus Jacobs et al. head2righthead2right...

Can we observe open loop transfer functions in a stochastic feedback system ?

International Nuclear Information System (INIS)

Kishida, Kuniharu; Suda, Nobuhide.

1991-01-01

There are two kinds of problems concerning open loop and closed loop transfer functions in a feedback system. One is a problem even in the deterministic case, and the other is in the stochastic case. In the deterministic case it is guaranteed under a necessary and sufficient condition that total sum of degrees of sub-transfer functions coincides to the degree of the total system. In the stochastic case a systematic understanding of a physical state model, a theoretical innovation model and a data-oriented innovation model is indispensable for determination of open loop transfer functions from time series data. Undesirable factors appear in determination of open loop transfer functions, since a transfer function matrix from input noises to output variables has a redundancy factor of diagonal matrix. (author)

Pdlim7 is required for maintenance of the mesenchymal/epidermal Fgf signaling feedback loop during zebrafish pectoral fin development

Directory of Open Access Journals (Sweden)

Klosowiak Julian

2010-10-01

Full Text Available Abstract Background Vertebrate limb development involves a reciprocal feedback loop between limb mesenchyme and the overlying apical ectodermal ridge (AER. Several gene pathways participate in this feedback loop, including Fgf signaling. In the forelimb lateral plate mesenchyme, Tbx5 activates Fgf10 expression, which in turn initiates and maintains the mesenchyme/AER Fgf signaling loop. Recent findings have revealed that Tbx5 transcriptional activity is regulated by dynamic nucleocytoplasmic shuttling and interaction with Pdlim7, a PDZ-LIM protein family member, along actin filaments. This Tbx5 regulation is critical in heart formation, but the coexpression of both proteins in other developing tissues suggests a broader functional role. Results Knock-down of Pdlim7 function leads to decreased pectoral fin cell proliferation resulting in a severely stunted fin phenotype. While early gene induction and patterning in the presumptive fin field appear normal, the pectoral fin precursor cells display compaction and migration defects between 18 and 24 hours post-fertilization (hpf. During fin growth fgf24 is sequentially expressed in the mesenchyme and then in the apical ectodermal ridge (AER. However, in pdlim7 antisense morpholino-treated embryos this switch of expression is prevented and fgf24 remains ectopically active in the mesenchymal cells. Along with the lack of fgf24 in the AER, other critical factors including fgf8 are reduced, suggesting signaling problems to the underlying mesenchyme. As a consequence of perturbed AER function in the absence of Pdlim7, pathway components in the fin mesenchyme are misregulated or absent, indicating a breakdown of the Fgf signaling feedback loop, which is ultimately responsible for the loss of fin outgrowth. Conclusion This work provides the first evidence for the involvement of Pdlim7 in pectoral fin development. Proper fin outgrowth requires fgf24 downregulation in the fin mesenchyme with subsequent

Sp1-CD147 positive feedback loop promotes the invasion ability of ovarian cancer.

Science.gov (United States)

Zhao, Jing; Ye, Wei; Wu, Juan; Liu, Lijuan; Yang, Lina; Gao, Lu; Chen, Biliang; Zhang, Fanglin; Yang, Hong; Li, Yu

2015-07-01

CD147 is a novel cancer biomarker that has been confirmed to be overexpressed in ovarian carcinoma, which is significantly associated with poor prognosis. Although the Sp1 protein regulates the expression level of CD147, it remains unclear whether Sp1 phosphorylation plays a role in this regulation. A dual-luciferase assay revealed that T453 and T739 mutations decreased the activity of Sp1 binding to the promoter of CD147, followed by a decrease in CD147 mRNA and protein expression. Western blot analysis showed that CD147 promoted Sp1 phosphorylation at T453 and T739 through the PI3K/AKT and MAPK/ERK pathways. In addition, blocking the Sp1-CD147 positive feedback loop reduced the invasion ability of HO-8910pm cells. Immunohistochemical staining showed that the components of the feedback loop were overexpressed in ovarian cancer tissues. The correlation analysis revealed a significant correlation between phospho-Sp1 (T453), phospho-Sp1 (T739) and CD147 expression levels, with correlation coefficients of r=0.477 and r=0.461, respectively. Collectively, our results suggest that a Sp1-CD147 positive feedback loop plays a critical role in the invasion ability of ovarian cancer cells.

Autonomous feedback loop of RUNX1-p53-CBFB in acute myeloid leukemia cells.

Science.gov (United States)

Morita, Ken; Noura, Mina; Tokushige, Chieko; Maeda, Shintaro; Kiyose, Hiroki; Kashiwazaki, Gengo; Taniguchi, Junichi; Bando, Toshikazu; Yoshida, Kenichi; Ozaki, Toshifumi; Matsuo, Hidemasa; Ogawa, Seishi; Liu, Pu Paul; Nakahata, Tatsutoshi; Sugiyama, Hiroshi; Adachi, Souichi; Kamikubo, Yasuhiko

2017-11-30

Although runt-related transcription factor 1 (RUNX1) and its associating core binding factor-β (CBFB) play pivotal roles in leukemogenesis, and inhibition of RUNX1 has now been widely recognized as a novel strategy for anti-leukemic therapies, it has been elusive how leukemic cells could acquire the serious resistance against RUNX1-inhibition therapies and also whether CBFB could participate in this process. Here, we show evidence that p53 (TP53) and CBFB are sequentially up-regulated in response to RUNX1 depletion, and their mutual interaction causes the physiological resistance against chemotherapy for acute myeloid leukemia (AML) cells. Mechanistically, p53 induced by RUNX1 gene silencing directly binds to CBFB promoter and stimulates its transcription as well as its translation, which in turn acts as a platform for the stabilization of RUNX1, thereby creating a compensative RUNX1-p53-CBFB feedback loop. Indeed, AML cells derived from relapsed cases exhibited higher CBFB expression levels compared to those from primary AML cells at diagnosis, and these CBFB expressions were positively correlated to those of p53. Our present results underscore the importance of RUNX1-p53-CBFB regulatory loop in the development and/or maintenance of AML cells, which could be targeted at any sides of this triangle in strategizing anti-leukemia therapies.

A closed-loop analysis of the tubuloglomerular feedback mechanism

DEFF Research Database (Denmark)

Holstein-Rathlou, N H

1991-01-01

The tubuloglomerular feedback (TGF) mechanism is of importance in the regulation of glomerular filtration rate (GFR). A second mechanism of potential importance is the change in proximal pressure caused by a change, for example, in the rate of proximal fluid reabsorption. The quantitative contrib...... and the late proximal flow rate, with changes in the proximal pressure of lesser importance. Furthermore, under closed-loop conditions the operating point for the TGF mechanism is at or close to the point of maximal sensitivity....... nl/min in steps of 5 nl/min. The open-loop gain (OLG) was 3.1 (range 1.5-9.9, n = 13) at the unperturbed tubular flow rate, and decreased as the tubular flow rate was either increased or decreased. The proximal pressure increased by 0.21 +/- 0.03 mmHg per unit increase in late proximal flow rate (nl...

Feedback versus open-loop leader/fringe models of the oil supply market

International Nuclear Information System (INIS)

Pelot, R.P.; Fuller, J.D.

1991-01-01

A multiperiod feedback Stackelberg model of exhaustible resources is presented. The results of the feedback model are compared with those from a corresponding open-loop formulation to determine whether the solution to the latter, and much simpler, model produces the same or similar outcomes. An analysis of the world oil market with OPEC as leader dictating the price to a competitive fringe comprised of the remaining oil suppliers demonstrates the features of the model. It permits variable length periods and cumulative extraction cost functions

Closed-Loop Hybrid Gaze Brain-Machine Interface Based Robotic Arm Control with Augmented Reality Feedback

Directory of Open Access Journals (Sweden)

Hong Zeng

2017-10-01

Full Text Available Brain-machine interface (BMI can be used to control the robotic arm to assist paralysis people for performing activities of daily living. However, it is still a complex task for the BMI users to control the process of objects grasping and lifting with the robotic arm. It is hard to achieve high efficiency and accuracy even after extensive trainings. One important reason is lacking of sufficient feedback information for the user to perform the closed-loop control. In this study, we proposed a method of augmented reality (AR guiding assistance to provide the enhanced visual feedback to the user for a closed-loop control with a hybrid Gaze-BMI, which combines the electroencephalography (EEG signals based BMI and the eye tracking for an intuitive and effective control of the robotic arm. Experiments for the objects manipulation tasks while avoiding the obstacle in the workspace are designed to evaluate the performance of our method for controlling the robotic arm. According to the experimental results obtained from eight subjects, the advantages of the proposed closed-loop system (with AR feedback over the open-loop system (with visual inspection only have been verified. The number of trigger commands used for controlling the robotic arm to grasp and lift the objects with AR feedback has reduced significantly and the height gaps of the gripper in the lifting process have decreased more than 50% compared to those trials with normal visual inspection only. The results reveal that the hybrid Gaze-BMI user can benefit from the information provided by the AR interface, improving the efficiency and reducing the cognitive load during the grasping and lifting processes.

Closed-Loop Hybrid Gaze Brain-Machine Interface Based Robotic Arm Control with Augmented Reality Feedback

Science.gov (United States)

Zeng, Hong; Wang, Yanxin; Wu, Changcheng; Song, Aiguo; Liu, Jia; Ji, Peng; Xu, Baoguo; Zhu, Lifeng; Li, Huijun; Wen, Pengcheng

2017-01-01

Brain-machine interface (BMI) can be used to control the robotic arm to assist paralysis people for performing activities of daily living. However, it is still a complex task for the BMI users to control the process of objects grasping and lifting with the robotic arm. It is hard to achieve high efficiency and accuracy even after extensive trainings. One important reason is lacking of sufficient feedback information for the user to perform the closed-loop control. In this study, we proposed a method of augmented reality (AR) guiding assistance to provide the enhanced visual feedback to the user for a closed-loop control with a hybrid Gaze-BMI, which combines the electroencephalography (EEG) signals based BMI and the eye tracking for an intuitive and effective control of the robotic arm. Experiments for the objects manipulation tasks while avoiding the obstacle in the workspace are designed to evaluate the performance of our method for controlling the robotic arm. According to the experimental results obtained from eight subjects, the advantages of the proposed closed-loop system (with AR feedback) over the open-loop system (with visual inspection only) have been verified. The number of trigger commands used for controlling the robotic arm to grasp and lift the objects with AR feedback has reduced significantly and the height gaps of the gripper in the lifting process have decreased more than 50% compared to those trials with normal visual inspection only. The results reveal that the hybrid Gaze-BMI user can benefit from the information provided by the AR interface, improving the efficiency and reducing the cognitive load during the grasping and lifting processes. PMID:29163123

Evidence of extra-telomeric effects of hTERT and its regulation involving a feedback loop

International Nuclear Information System (INIS)

Lai, Serene R.; Cunningham, Amanda P.; Huynh, Vu Q.; Andrews, Lucy G.; Tollefsbol, Trygve O.

2007-01-01

The human telomerase reverse transcriptase (hTERT) is the catalytic subunit of the enzyme telomerase which is responsible for telomeric maintenance and extension. Using RNA interference to knock down hTERT mRNA expression, we provide evidence that hTERT exerts extra-telomeric effects on the cell cycle and on its own regulatory proteins, specifically: p53 and p21. We tested our hypothesis that hTERT regulates its own expression through effects on upstream regulatory genes using transformed human embryonic kidney (HEK 293) cells, p53 and p16 INK4a null human ovarian cancer SKOV-3 cells, and p53-null MDA-MB-157 human mammary cancer cells. In HEK 293 cells, hTERT knockdown resulted in elevated p53 and p21 transcription and a decrease in cellular proliferation. Similar results were observed in the MDA-MB-157 cell line where p21 was upregulated, correlating with cell growth inhibition. In contrast, we observed a decrease in expression of p21 in SKOV-3 cells with hTERT knockdown and cell growth appeared to be unaffected. These findings suggest that hTERT may be involved in a feedback loop system, thereby playing a role in its own regulation

Uncovering the spatially distant feedback loops of global trade: A network and input-output approach.

Science.gov (United States)

Prell, Christina; Sun, Laixiang; Feng, Kuishuang; He, Jiaying; Hubacek, Klaus

2017-05-15

Land-use change is increasingly driven by global trade. The term "telecoupling" has been gaining ground as a means to describe how human actions in one part of the world can have spatially distant impacts on land and land-use in another. These interactions can, over time, create both direct and spatially distant feedback loops, in which human activity and land use mutually impact one another over great expanses. In this paper, we develop an analytical framework to clarify spatially distant feedbacks in the case of land use and global trade. We use an innovative mix of multi-regional input-output (MRIO) analysis and stochastic actor-oriented models (SAOMs) for analyzing the co-evolution of changes in trade network patterns with those of land use, as embodied in trade. Our results indicate that the formation of trade ties and changes in embodied land use mutually impact one another, and further, that these changes are linked to disparities in countries' wealth. Through identifying this feedback loop, our results support ongoing discussions about the unequal trade patterns between rich and poor countries that result in uneven distributions of negative environmental impacts. Finally, evidence for this feedback loop is present even when controlling for a number of underlying mechanisms, such as countries' land endowments, their geographical distance from one another, and a number of endogenous network tendencies. Copyright © 2017 Elsevier B.V. All rights reserved.

Q-factor enhancement for self-actuated self-sensing piezoelectric MEMS resonators applying a lock-in driven feedback loop

International Nuclear Information System (INIS)

Kucera, M; Bittner, A; Schmid, U; Manzaneque, T; Sánchez-Rojas, J L

2013-01-01

This paper presents a robust Q-control approach based on an all-electrical feedback loop enhancing the quality factor of a resonant microstructure by using the self-sensing capability of a piezoelectric thin film actuator made of aluminium nitride. A lock-in amplifier is used to extract the feedback signal which is proportional to the piezoelectric current. The measured real part is used to replace the originally low-quality and noisy feedback signal to modulate the driving voltage of the piezoelectric thin-film actuator. Since the lock-in amplifier reduces the noise in the feedback signal substantially, the proposed enhancement loop avoids the disadvantage of a constant signal-to-noise ratio, which an analogue feedback circuit usually suffers from. The quality factor was increased from the intrinsic value of 1766 to a maximum of 34 840 in air. These promising results facilitate precise measurements for self-actuated and self-sensing MEMS cantilevers even when operated in static viscous media. (paper)

Power flow control based solely on slow feedback loop for heart pump applications.

Science.gov (United States)

Wang, Bob; Hu, Aiguo Patrick; Budgett, David

2012-06-01

This paper proposes a new control method for regulating power flow via transcutaneous energy transfer (TET) for implantable heart pumps. Previous work on power flow controller requires a fast feedback loop that needs additional switching devices and resonant capacitors to be added to the primary converter. The proposed power flow controller eliminates these additional components, and it relies solely on a slow feedback loop to directly drive the primary converter to meet the heart pump power demand and ensure zero voltage switching. A controlled change in switching frequency varies the resonant tank shorting period of a current-fed push-pull resonant converter, thus changing the magnitude of the primary resonant voltage, as well as the tuning between primary and secondary resonant tanks. The proposed controller has been implemented successfully using an analogue circuit and has reached an end-to-end power efficiency of 79.6% at 10 W with a switching frequency regulation range of 149.3 kHz to 182.2 kHz.

Stress-specific response of the p53-Mdm2 feedback loop

Directory of Open Access Journals (Sweden)

Jensen Mogens H

2010-07-01

Full Text Available Abstract Background The p53 signalling pathway has hundreds of inputs and outputs. It can trigger cellular senescence, cell-cycle arrest and apoptosis in response to diverse stress conditions, including DNA damage, hypoxia and nutrient deprivation. Signals from all these inputs are channeled through a single node, the transcription factor p53. Yet, the pathway is flexible enough to produce different downstream gene expression patterns in response to different stresses. Results We construct a mathematical model of the negative feedback loop involving p53 and its inhibitor, Mdm2, at the core of this pathway, and use it to examine the effect of different stresses that trigger p53. In response to DNA damage, hypoxia, etc., the model exhibits a wide variety of specific output behaviour - steady states with low or high levels of p53 and Mdm2, as well as spiky oscillations with low or high average p53 levels. Conclusions We show that even a simple negative feedback loop is capable of exhibiting the kind of flexible stress-specific response observed in the p53 system. Further, our model provides a framework for predicting the differences in p53 response to different stresses and single nucleotide polymorphisms.

Investigation, development and application of optimal output feedback theory. Volume 2: Development of an optimal, limited state feedback outer-loop digital flight control system for 3-D terminal area operation

Science.gov (United States)

Broussard, J. R.; Halyo, N.

1984-01-01

This report contains the development of a digital outer-loop three dimensional radio navigation (3-D RNAV) flight control system for a small commercial jet transport. The outer-loop control system is designed using optimal stochastic limited state feedback techniques. Options investigated using the optimal limited state feedback approach include integrated versus hierarchical control loop designs, 20 samples per second versus 5 samples per second outer-loop operation and alternative Type 1 integration command errors. Command generator tracking techniques used in the digital control design enable the jet transport to automatically track arbitrary curved flight paths generated by waypoints. The performance of the design is demonstrated using detailed nonlinear aircraft simulations in the terminal area, frequency domain multi-input sigma plots, frequency domain single-input Bode plots and closed-loop poles. The response of the system to a severe wind shear during a landing approach is also presented.

Trade typhoon over Japan: Turbulence metaphor and spatial production cycles feedback loops of the Japanese economy, 1980–85–90

Directory of Open Access Journals (Sweden)

M. Sonis

2002-01-01

Full Text Available This paper deals with the turbulence similitude between whirlpool structure of atmosphere disturbances and the spatial production cycles. Such an analogy leads to the production cycles feedback loops superposition analysis of trade feedbacks reflecting the economic phenomena of horizontal and vertical trade specifications. Moreover, the visualization of this process is achieved with the help of coloring the different permutation matrices presenting the hierarchy of production cycles feedback loops. In this manner the qualitative presentation of Japan inter-regional and inter-industry trade, 1980–85–90, is visualized and interpreted.

A feedback regulatory loop involving microRNA-9 and nuclear receptor TLX in neural stem cell fate determination.

Science.gov (United States)

Zhao, Chunnian; Sun, GuoQiang; Li, Shengxiu; Shi, Yanhong

2009-04-01

MicroRNAs have been implicated as having important roles in stem cell biology. MicroRNA-9 (miR-9) is expressed specifically in neurogenic areas of the brain and may be involved in neural stem cell self-renewal and differentiation. We showed previously that the nuclear receptor TLX is an essential regulator of neural stem cell self-renewal. Here we show that miR-9 suppresses TLX expression to negatively regulate neural stem cell proliferation and accelerate neural differentiation. Introducing a TLX expression vector that is not prone to miR-9 regulation rescued miR-9-induced proliferation deficiency and inhibited precocious differentiation. In utero electroporation of miR-9 in embryonic brains led to premature differentiation and outward migration of the transfected neural stem cells. Moreover, TLX represses expression of the miR-9 pri-miRNA. By forming a negative regulatory loop with TLX, miR-9 provides a model for controlling the balance between neural stem cell proliferation and differentiation.

LncRNA FIRRE/NF-kB feedback loop contributes to OGD/R injury of cerebral microglial cells.

Science.gov (United States)

Zang, Yunhua; Zhou, Xiyan; Wang, Qun; Li, Xia; Huang, Hailiang

2018-04-28

Stroke is one of the leading causes for serious long-term neurological disability. LncRNAs have been investigated to be dysregulated in ischemic stroke. However, the underlying mechanisms of some specific lncRNAs have not been clearly clarified. To determine lncRNA-mediated regulatory mechanism in ischemic stroke, we constructed OGD/R injury model of cerebral microglial cells. Microarray analysis was carried out and analyzed that lncRNA functional intergenic repeating RNA element (FIRRE) was associated with OGD/R injury. Based on the molecular biotechnology, we demonstrated that FIRRE could activate NF-kB signal pathway. Meanwhile, the activated NF-kB promoted FIRRE expression in OGD/R-treated cerebral microglial cells. Therefore, FIRRE and NF-kB formed a positive feedback loop to promote the transcription of NLRP3 inflammasome, thus contributed to the OGD/R injury of cerebral microglial cells. All findings in this study may help to explore novel and specific therapeutic target for ischemic stroke. Copyright © 2018. Published by Elsevier Inc.

A Platform for Closing the Open Data Feedback Loop Based on Web2.0 Functionality

Directory of Open Access Journals (Sweden)

Charalampos Alexopoulos

2014-11-01

Full Text Available One essential element of open data ecosystems concerns their development through feedback loops, discussions and dynamic supplier and user interactions. These user-centric features communicate the users’ needs to the open data community as well to the public sector bodies responsible for data publication. Addressing these needs by the corresponding public sector bodies or even by utilising the power of the community as ENGAGE supports will actually accelerate innovation. However, these elements appear barely to be part of existing open data practices. We conducted a survey which showed that most professional open data users did not know at least one open data infrastructure that enabled five specific types of discussion and feedback mechanisms. The survey showed that much can still be done to improve feedback and discussion on open data infrastructures. In this paper we discuss an open data platform which has started to contribute to filling this gap and present a usage scenario explaining the sequence of the underlined functionality. The discussed ENGAGE open data infrastructure combines functionalities to close the feedback loop and to return information to public authorities for better open data use and publication as well as establishing communication channels between stakeholders. This may effectively lead to the stimulation and facilitation of value generation from open data, as such functionality position the user at the centre of the open data publication process.

Designing Dialogic E-Learning in Pharmacy Professionalism Using Calibrated Feedback Loops (CFLs

Directory of Open Access Journals (Sweden)

Sue Roff

2013-09-01

Full Text Available The feedback analytics of online software including Articulate and Bristol Online Surveys can be used to facilitate dialogic learning in a community of practice such as Pharmacy and, thereby, promote reflective learning by the creation of formative calibrated feedback loops. Based on work with medical, dental, nursing, osteopathic, and social work students, trainees, and registrants, the paper shows how an online learning community can be created along the continuum from undergraduate to registrant to develop authentic dialogic e-learning around standards of Professionalism. The Dundee PolyProfessionalism inventories and Situational Judgement Scenarios (SJSs can be customised for Pharmacy Professionalism learning to support evidence-based curriculum design along benchmarked learning curves and to profile Professionalism learning in individuals and cohorts.

MicroRNA-Mediated Positive Feedback Loop and Optimized Bistable Switch in a Cancer Network Involving miR-17-92

Science.gov (United States)

Li, Yichen; Li, Yumin; Zhang, Hui; Chen, Yong

2011-01-01

MicroRNAs (miRNAs) are small, noncoding RNAs that play an important role in many key biological processes, including development, cell differentiation, the cell cycle and apoptosis, as central post-transcriptional regulators of gene expression. Recent studies have shown that miRNAs can act as oncogenes and tumor suppressors depending on the context. The present work focuses on the physiological significance of miRNAs and their role in regulating the switching behavior. We illustrate an abstract model of the Myc/E2F/miR-17-92 network presented by Aguda et al. (2008), which is composed of coupling between the E2F/Myc positive feedback loops and the E2F/Myc/miR-17-92 negative feedback loop. By systematically analyzing the network in close association with plausible experimental parameters, we show that, in the presence of miRNAs, the system bistability emerges from the system, with a bistable switch and a one-way switch presented by Aguda et al. instead of a single one-way switch. Moreover, the miRNAs can optimize the switching process. The model produces a diverse array of response-signal behaviors in response to various potential regulating scenarios. The model predicts that this transition exists, one from cell death or the cancerous phenotype directly to cell quiescence, due to the existence of miRNAs. It was also found that the network involving miR-17-92 exhibits high noise sensitivity due to a positive feedback loop and also maintains resistance to noise from a negative feedback loop. PMID:22022595

Regulation of Trib2 by an E2F1-C/EBPα feedback loop in AML cell proliferation

DEFF Research Database (Denmark)

Rishi, Loveena; Hannon, Maura; Salomè, Mara

2014-01-01

α (C/EBPα)-p42, occurs in acute myeloid leukemia (AML), resulting in the perturbation of cell cycle and apoptosis, emphasizing its importance in the molecular pathogenesis of AML. Here we show that E2F family members directly regulate Trib2 in leukemic cells and identify a feedback regulatory loop......The loss of regulation of cell proliferation is a key event in leukemic transformation, and the oncogene tribbles (Trib)2 is emerging as a pivotal target of transcription factors in acute leukemias. Deregulation of the transcription factor E2F1, normally repressed by CCAAT enhancer-binding protein...... for E2F1, C/EBPα, and Trib2 in AML cell proliferation and survival. Further analyses revealed that E2F1-mediated Trib2 expression was repressed by C/EBPα-p42, and in normal granulocyte/macrophage progenitor cells, we detect C/EBPα bound to the Trib2 promoter. Pharmacological inhibition of the cell cycle...

Feedback loops and temporal misalignment in component-based hydrologic modeling

Science.gov (United States)

Elag, Mostafa M.; Goodall, Jonathan L.; Castronova, Anthony M.

2011-12-01

In component-based modeling, a complex system is represented as a series of loosely integrated components with defined interfaces and data exchanges that allow the components to be coupled together through shared boundary conditions. Although the component-based paradigm is commonly used in software engineering, it has only recently been applied for modeling hydrologic and earth systems. As a result, research is needed to test and verify the applicability of the approach for modeling hydrologic systems. The objective of this work was therefore to investigate two aspects of using component-based software architecture for hydrologic modeling: (1) simulation of feedback loops between components that share a boundary condition and (2) data transfers between temporally misaligned model components. We investigated these topics using a simple case study where diffusion of mass is modeled across a water-sediment interface. We simulated the multimedia system using two model components, one for the water and one for the sediment, coupled using the Open Modeling Interface (OpenMI) standard. The results were compared with a more conventional numerical approach for solving the system where the domain is represented by a single multidimensional array. Results showed that the component-based approach was able to produce the same results obtained with the more conventional numerical approach. When the two components were temporally misaligned, we explored the use of different interpolation schemes to minimize mass balance error within the coupled system. The outcome of this work provides evidence that component-based modeling can be used to simulate complicated feedback loops between systems and guidance as to how different interpolation schemes minimize mass balance error introduced when components are temporally misaligned.

Integration of Bacterial Small RNAs in Regulatory Networks.

Science.gov (United States)

Nitzan, Mor; Rehani, Rotem; Margalit, Hanah

2017-05-22

Small RNAs (sRNAs) are central regulators of gene expression in bacteria, controlling target genes posttranscriptionally by base pairing with their mRNAs. sRNAs are involved in many cellular processes and have unique regulatory characteristics. In this review, we discuss the properties of regulation by sRNAs and how it differs from and combines with transcriptional regulation. We describe the global characteristics of the sRNA-target networks in bacteria using graph-theoretic approaches and review the local integration of sRNAs in mixed regulatory circuits, including feed-forward loops and their combinations, feedback loops, and circuits made of an sRNA and another regulator, both derived from the same transcript. Finally, we discuss the competition effects in posttranscriptional regulatory networks that may arise over shared targets, shared regulators, and shared resources and how they may lead to signal propagation across the network.

Silicon photonic dynamic optical channel leveler with external feedback loop.

Science.gov (United States)

Doylend, J K; Jessop, P E; Knights, A P

2010-06-21

We demonstrate a dynamic optical channel leveler composed of a variable optical attenuator (VOA) integrated monolithically with a defect-mediated photodiode in a silicon photonic waveguide device. An external feedback loop mimics an analog circuit such that the photodiode directly controls the VOA to provide blind channel leveling within +/-1 dB across a 7-10 dB dynamic range for wavelengths from 1530 nm to 1570 nm. The device consumes approximately 50 mW electrical power and occupies a 6 mm x 0.1 mm footprint per channel. Dynamic leveling is accomplished without tapping optical power from the output path to the photodiode and thus the loss penalty is minimized.

An HIV feedback resistor: auto-regulatory circuit deactivator and noise buffer.

Science.gov (United States)

Weinberger, Leor S; Shenk, Thomas

2007-01-01

Animal viruses (e.g., lentiviruses and herpesviruses) use transcriptional positive feedback (i.e., transactivation) to regulate their gene expression. But positive-feedback circuits are inherently unstable when turned off, which presents a particular dilemma for latent viruses that lack transcriptional repressor motifs. Here we show that a dissipative feedback resistor, composed of enzymatic interconversion of the transactivator, converts transactivation circuits into excitable systems that generate transient pulses of expression, which decay to zero. We use HIV-1 as a model system and analyze single-cell expression kinetics to explore whether the HIV-1 transactivator of transcription (Tat) uses a resistor to shut off transactivation. The Tat feedback circuit was found to lack bi-stability and Tat self-cooperativity but exhibited a pulse of activity upon transactivation, all in agreement with the feedback resistor model. Guided by a mathematical model, biochemical and genetic perturbation of the suspected Tat feedback resistor altered the circuit's stability and reduced susceptibility to molecular noise, in agreement with model predictions. We propose that the feedback resistor is a necessary, but possibly not sufficient, condition for turning off noisy transactivation circuits lacking a repressor motif (e.g., HIV-1 Tat). Feedback resistors may be a paradigm for examining other auto-regulatory circuits and may inform upon how viral latency is established, maintained, and broken.

The Double Feedback Loop and the Parameter Theory of Text Genres

DEFF Research Database (Denmark)

Bundgaard, Peer; Østergaard, Svend

2014-01-01

on the first feedback loop: the way genres develop as deviations from existing text types and then stabilize as text types proper with a normative import. The second scope of this article consists in developing a typological apparatus consistent with the dynamic approach to the emergence of genres. This is our...... parameter theory of genres which is presented in Section 3. Here we consider genres as governed by parameters external to them and intrinsic to the situations they are dynamically related to. Genres should thus be understood not simply in terms of inherent textual or formal traits, but also relative...

An Integrated Loop Model of Corrective Feedback and Oral English Learning: A Case of International Students in the United States

Science.gov (United States)

Lee, Eun Jeong

2017-01-01

The author in this study introduces an integrated corrective feedback (CF) loop to schematize the interplay between CF and independent practice in L2 oral English learning among advanced-level adult ESL students. The CF loop integrates insights from the Interaction, Output, and Noticing Hypotheses to show how CF can help or harm L2 learners'…

Detection of the dominant direction of information flow and feedback links in densely interconnected regulatory networks

Directory of Open Access Journals (Sweden)

Ispolatov Iaroslav

2008-10-01

Full Text Available Abstract Background Finding the dominant direction of flow of information in densely interconnected regulatory or signaling networks is required in many applications in computational biology and neuroscience. This is achieved by first identifying and removing links which close up feedback loops in the original network and hierarchically arranging nodes in the remaining network. In mathematical language this corresponds to a problem of making a graph acyclic by removing as few links as possible and thus altering the original graph in the least possible way. The exact solution of this problem requires enumeration of all cycles and combinations of removed links, which, as an NP-hard problem, is computationally prohibitive even for modest-size networks. Results We introduce and compare two approximate numerical algorithms for solving this problem: the probabilistic one based on a simulated annealing of the hierarchical layout of the network which minimizes the number of "backward" links going from lower to higher hierarchical levels, and the deterministic, "greedy" algorithm that sequentially cuts the links that participate in the largest number of feedback cycles. We find that the annealing algorithm outperforms the deterministic one in terms of speed, memory requirement, and the actual number of removed links. To further improve a visual perception of the layout produced by the annealing algorithm, we perform an additional minimization of the length of hierarchical links while keeping the number of anti-hierarchical links at their minimum. The annealing algorithm is then tested on several examples of regulatory and signaling networks/pathways operating in human cells. Conclusion The proposed annealing algorithm is powerful enough to performs often optimal layouts of protein networks in whole organisms, consisting of around ~104 nodes and ~105 links, while the applicability of the greedy algorithm is limited to individual pathways with ~100

How Attributes of the Feedback Message affect Subsequent Feedback Seeking: The interactive effects of feedback sign and type

OpenAIRE

Medvedeff, Megan; Gregory, Jane Brodie; Levy, Paul E

2008-01-01

In the current study, we examined the interactive effects of feedback type and sign on feedback-seeking behaviour, as well as the moderating role of regulatory focus. Using a behavioural measure of feedback seeking, we demonstrated a strong interaction between feedback type and sign, such that individuals subsequently sought the most feedback after they were provided with negative process feedback. Additionally, results suggested that an individual's chronic regulatory focus has implications ...

Feedback systems in the SLC

International Nuclear Information System (INIS)

Thompson, K.A.; Jobe, R.K.; Johnson, R.; Phinney, N.

1987-02-01

Two classes of computer-controlled feedback have been implemented to stabilize parameters in subsystems of the SLC: (1) ''slow'' (time scales ∼ minutes) feedback, and (2) ''fast'', i.e., pulse-to-pulse, feedback. The slow loops run in a single FEEDBACK process in the SLC host VAX, which acquires signals and sets control parameters via communication with the database and the network of normal SLC microprocessors. Slow loops exist to stabilize beam energy and energy spread, beam position and angle, and timing of kicker magnets, and to compensate for changes in the phase length of the rf drive line. The fast loops run in dedicated microprocessors, and may sample and/or feedback on particular parameters as often as every pulse of the SLC beam. The first implementations of fast feedback are to control transverse beam blow-up and to stabilize the energy and energy spread of bunches going into the SLC arcs. The overall architecture of the feedback software and the operator interface for controlling loops are discussed

Experimental test of an eco-evolutionary dynamic feedback loop between evolution and population density in the green peach aphid.

Science.gov (United States)

Turcotte, Martin M; Reznick, David N; Daniel Hare, J

2013-05-01

An eco-evolutionary feedback loop is defined as the reciprocal impacts of ecology on evolutionary dynamics and evolution on ecological dynamics on contemporary timescales. We experimentally tested for an eco-evolutionary feedback loop in the green peach aphid, Myzus persicae, by manipulating initial densities and evolution. We found strong evidence that initial aphid density alters the rate and direction of evolution, as measured by changes in genotype frequencies through time. We also found that evolution of aphids within only 16 days, or approximately three generations, alters the rate of population growth and predicts density compared to nonevolving controls. The impact of evolution on population dynamics also depended on density. In one evolution treatment, evolution accelerated population growth by up to 10.3% at high initial density or reduced it by up to 6.4% at low initial density. The impact of evolution on population growth was as strong as or stronger than that caused by a threefold change in intraspecific density. We found that, taken together, ecological condition, here intraspecific density, alters evolutionary dynamics, which in turn alter concurrent population growth rate (ecological dynamics) in an eco-evolutionary feedback loop. Our results suggest that ignoring evolution in studies predicting population dynamics might lead us to over- or underestimate population density and that we cannot predict the evolutionary outcome within aphid populations without considering population size.

Efficient phase locking of two dual-wavelength fiber amplifiers by an all-optical self-feedback loop

Science.gov (United States)

Lei, Bing; Chen, Keshan; Yao, Tianfu; Shi, Jianhua; Hu, Haojun

2017-10-01

Efficient phase locking of two dual-wavelength fiber amplifiers has been demonstrated by using a self-feedback coupling and intracavity filtering configuration, and the effect of bandwidth and wavelength spacing on their phase locking performances have been investigated in experiment. Two independent fiber lasers with different operating wavelength were combined incoherently by a 3 dB fiber coupler to form a dual-wavelength seed source laser, which was injected into the fiber amplifiers' coupling array through the self-feedback loop. The effect of bandwidth and wavelength spacing was researched by altering the seed laser's pump power and operating wavelengths respectively. As long as the feedback loop and the single-mode fiber filtering configuration were well constructed in the unidirectional ring laser cavity, stable phase locking states and high fringe visibility interference patterns could always be obtained in our experiment. When the spacing of two operating wavelength was varied from 1.6 nm to 19.6 nm, the fringe visibility decreased slightly with the increase of wavelength spacing, and the corresponding fringe visibility was always larger than 0.6. In conclusion, we believe that efficient phase locking of several multi-wavelength laser sources is also feasible by passive self-adjusting methods, and keeping the component laser beams' phase relationship stable and fixed is more important than controlling their operating wavelengths.

Analytically exploiting noise correlations inside the feedback loop to improve locked-oscillator performance

CSIR Research Space (South Africa)

Sastrawan, J

2016-08-01

Full Text Available (2016) Analytically exploiting noise correlations inside the feedback loop to improve locked-oscillator performance J. Sastrawan,1 C. Jones,1 I. Akhalwaya,2 H. Uys,2 and M. J. Biercuk1,* 1ARC Centre for Engineered Quantum Systems, School of Physics...) that probes and is locked to the atomic transition. The LO frequencymay evolve randomly in time due to intrinsic noise processes in the underlying hardware [10,11], leading to time-varying deviations of the LO frequency from that of the stable atomic reference...

Closed-loop control of grasping with a myoelectric hand prosthesis: which are the relevant feedback variables for force control?

Science.gov (United States)

Ninu, Andrei; Dosen, Strahinja; Muceli, Silvia; Rattay, Frank; Dietl, Hans; Farina, Dario

2014-09-01

In closed-loop control of grasping by hand prostheses, the feedback information sent to the user is usually the actual controlled variable, i.e., the grasp force. Although this choice is intuitive and logical, the force production is only the last step in the process of grasping. Therefore, this study evaluated the performance in controlling grasp strength using a hand prosthesis operated through a complete grasping sequence while varying the feedback variables (e.g., closing velocity, grasping force), which were provided to the user visually or through vibrotactile stimulation. The experiments were conducted on 13 volunteers who controlled the Otto Bock Sensor Hand Speed prosthesis. Results showed that vibrotactile patterns were able to replace the visual feedback. Interestingly, the experiments demonstrated that direct force feedback was not essential for the control of grasping force. The subjects were indeed able to control the grip strength, predictively, by estimating the grasping force from the prosthesis velocity of closing. Therefore, grasping without explicit force feedback is not completely blind, contrary to what is usually assumed. In our study we analyzed grasping with a specific prosthetic device, but the outcomes are also applicable for other devices, with one or more degrees-of-freedom. The necessary condition is that the electromyography (EMG) signal directly and proportionally controls the velocity/grasp force of the hand, which is a common approach among EMG controlled prosthetic devices. The results provide important indications on the design of closed-loop EMG controlled prosthetic systems.

Study of an accelerating superconducting module and its feedback loop systems for the MYRRHA project

International Nuclear Information System (INIS)

Bouly, F.

2011-11-01

The MYRRHA ( Multi-purpose hybrid Research Reactor for High-tech Applications ) project aims at constructing an accelerator driven system (ADS) demonstrator (50 a 100 MWth) to explore the feasibility of nuclear waste transmutation. Such a subcritical reactor requires an extremely reliable accelerator which delivers a CW high power protons beam (600 MeV, 4 mA). The reference solution for this machine is a superconducting linear accelerator. This thesis presents the work - undertaken at IPN Orsay in October 2008 - on the study of a prototypical superconducting module and the feedback control systems of its cavity for the high energy part of the MYRRHA linac. First, the optimization and the design of 5-cell elliptical cavities (β=0,65), operating at 704.4 MHz, are presented. Then, the experimental work focuses on a reliability oriented study of the 'cryo-module' which hold a prototypical 5-cell cavity (β=0,47). In this study, the dynamic behavior of the fast tuning system of the cavity was measured and qualified. The 'field flatness' issue in 'low beta' multi-cell cavity was also brought to light. Finally, a fault-tolerance analysis of the linac was carried out. Toward this goal, a model of the cavity, its RF feedback loop system and its tuning system feedback loop was developed. This study enabled to determine the RF power needs, the tuning system requirements and as well as to demonstrate the feasibility of fast fault-recovery scenarios to minimize the number of beam interruptions in the MYRRHA linac. (author)

miR-137 forms a regulatory loop with nuclear receptor TLX and LSD1 in neural stem cells.

Science.gov (United States)

Sun, GuoQiang; Ye, Peng; Murai, Kiyohito; Lang, Ming-Fei; Li, Shengxiu; Zhang, Heying; Li, Wendong; Fu, Chelsea; Yin, Jason; Wang, Allen; Ma, Xiaoxiao; Shi, Yanhong

2011-11-08

miR-137 is a brain-enriched microRNA. Its role in neural development remains unknown. Here we show that miR-137 has an essential role in controlling embryonic neural stem cell fate determination. miR-137 negatively regulates cell proliferation and accelerates neural differentiation of embryonic neural stem cells. In addition, we show that the histone lysine-specific demethylase 1 (LSD1), a transcriptional co-repressor of nuclear receptor TLX, is a downstream target of miR-137. In utero electroporation of miR-137 in embryonic mouse brains led to premature differentiation and outward migration of the transfected cells. Introducing a LSD1 expression vector lacking the miR-137 recognition site rescued miR-137-induced precocious differentiation. Furthermore, we demonstrate that TLX, an essential regulator of neural stem cell self-renewal, represses the expression of miR-137 by recruiting LSD1 to the genomic regions of miR-137. Thus, miR-137 forms a feedback regulatory loop with TLX and LSD1 to control the dynamics between neural stem cell proliferation and differentiation during neural development.

Mode Selection Rules for a Two-Delay System with Positive and Negative Feedback Loops

Science.gov (United States)

Takahashi, Kin'ya; Kobayashi, Taizo

2018-04-01

The mode selection rules for a two-delay system, which has negative feedback with a short delay time t1 and positive feedback with a long delay time t2, are studied numerically and theoretically. We find two types of mode selection rules depending on the strength of the negative feedback. When the strength of the negative feedback |α1| (α1 0), 2m + 1-th harmonic oscillation is well sustained in a neighborhood of t1/t2 = even/odd, i.e., relevant condition. In a neighborhood of the irrelevant condition given by t1/t2 = odd/even or t1/t2 = odd/odd, higher harmonic oscillations are observed. However, if |α1| is slightly less than α2, a different mode selection rule works, where the condition t1/t2 = odd/even is relevant and the conditions t1/t2 = odd/odd and t1/t2 = even/odd are irrelevant. These mode selection rules are different from the mode selection rule of the normal two-delay system with two positive feedback loops, where t1/t2 = odd/odd is relevant and the others are irrelevant. The two types of mode selection rules are induced by individually different mechanisms controlling the Hopf bifurcation, i.e., the Hopf bifurcation controlled by the "boosted bifurcation process" and by the "anomalous bifurcation process", which occur for |α1| below and above the threshold value αth, respectively.

Negative feedback loops leading to nitrate homeostasis and oscillatory nitrate assimilation in plants and fungi.

OpenAIRE

Huang, Yongshun

2011-01-01

Master's thesis in Biological Chemistry Nitrate is an important nutrient for plants and fungi. For plants it has been shown that cytosolic nitrate levels are under homeostatic control. Here we describe two networks that can obtain robust, i.e. perturbation independent, homeostatic behavior in cytosolic nitrate concentration. One of the networks, a member in the family of outflow controllers, is based on a negative feedback loop containing a nitrate-induced activation of a controller molecu...

Pulse oximeter improvement with an ADC-DAC feedback loop and a radial reflectance sensor.

Science.gov (United States)

Thompson, David; Wareing, Austin; Day, Dwight; Warren, Steve

2006-01-01

Pulse oximeter circuitry must meet several design constraints, including the ability to separate a small pulsatile signal component from a large signal baseline. This paper describes pulse oximeter design changes that produced order-of-magnitude improvements in signal quality. The primary changes were (a) the replacement of an analog sample-and-hold-based differentiator circuit with an ADC-DAC feedback loop and (b) the replacement of a side-by-side reflectance sensor design with a radial sensor arrangement that maximizes the pulsatile-to-baseline signal ratio.

Quality-factor amplification in piezoelectric MEMS resonators applying an all-electrical feedback loop

International Nuclear Information System (INIS)

Manzaneque, T; Hernando-García, J; Sánchez-Rojas, J L; Ababneh, A; Schwarz, P; Seidel, H; Schmid, U

2011-01-01

An all-electrical velocity feedback control to enhance the quality factor of piezoelectric aluminium nitride (AlN)-based microcantilevers and microbridges was implemented. Two alternatives to obtain a velocity-proportional signal were demonstrated depending on the top electrode configuration. For a straightforward electrode design in one-port configuration (i.e. self-actuation and self-sensing), a velocity signal, proportional to the piezoelectric current, was used in the feedback loop by cancelling out the dielectric current electronically. For top electrodes allowing a two-port configuration (i.e. one for actuation and one for sensing), the piezoelectric current is directly extracted and its relationship with velocity is analysed taking the symmetry of the modal shape into account. Standard operational amplifier-based configurations for the feedback circuits were implemented on a printed circuit board. Quality factors were determined from the transient electrical response of the devices. Comparable results were obtained from the displacement spectrum applying a laser Doppler vibrometer. Quality factors as high as 2 × 10 5 , corresponding to an enhancement factor of about 200, were achieved in air for the lowest gain margin achievable before the circuit becomes unstable, making this kind of device more competitive for mass sensor applications due to enhanced spectral resolution.

Electro-optic chaotic system based on the reverse-time chaos theory and a nonlinear hybrid feedback loop.

Science.gov (United States)

Jiang, Xingxing; Cheng, Mengfan; Luo, Fengguang; Deng, Lei; Fu, Songnian; Ke, Changjian; Zhang, Minming; Tang, Ming; Shum, Ping; Liu, Deming

2016-12-12

A novel electro-optic chaos source is proposed on the basis of the reverse-time chaos theory and an analog-digital hybrid feedback loop. The analog output of the system can be determined by the numeric states of shift registers, which makes the system robust and easy to control. The dynamical properties as well as the complexity dependence on the feedback parameters are investigated in detail. The correlation characteristics of the system are also studied. Two improving strategies which were established in digital field and analog field are proposed to conceal the time-delay signature. The proposed scheme has the potential to be used in radar and optical secure communication systems.

The paracrine feedback loop between vitamin D₃ (1,25(OH)₂D₃) and PTHrP in prehypertrophic chondrocytes

NARCIS (Netherlands)

Bach, Frances C; Rutten, Kirsten; Hendriks, Kristyanne; Riemers, Frank M; Cornelissen, Peter; de Bruin, Alain; Arkesteijn, Ger J; Wubbolts, Richard; Horton, William A; Penning, Louis C; Tryfonidou, Marianna A

2014-01-01

The endocrine feedback loop between vitamin D3(1,25(OH)2D3) and parathyroid hormone (PTH) plays a central role in skeletal development. PTH-related protein (PTHrP) shares homology and its receptor (PTHR1) with PTH. The aim of this study was to investigate whether there is a functional paracrine

Closed-loop feedback control for microfluidic systems through automated capacitive fluid height sensing.

Science.gov (United States)

Soenksen, L R; Kassis, T; Noh, M; Griffith, L G; Trumper, D L

2018-03-13

Precise fluid height sensing in open-channel microfluidics has long been a desirable feature for a wide range of applications. However, performing accurate measurements of the fluid level in small-scale reservoirs (sensor contact needs to be avoided. In particular, gravity-driven systems used in several microfluidic applications to establish pressure gradients and impose flow remain open-loop and largely unmonitored due to these sensing limitations. Here we present an optimized self-shielded coplanar capacitive sensor design and automated control system to provide submillimeter fluid-height resolution (∼250 μm) and control of small-scale open reservoirs without the need for direct fluid contact. Results from testing and validation of our optimized sensor and system also suggest that accurate fluid height information can be used to robustly characterize, calibrate and dynamically control a range of microfluidic systems with complex pumping mechanisms, even in cell culture conditions. Capacitive sensing technology provides a scalable and cost-effective way to enable continuous monitoring and closed-loop feedback control of fluid volumes in small-scale gravity-dominated wells in a variety of microfluidic applications.

Transcription factor trapping by RNA in gene regulatory elements.

Science.gov (United States)

Sigova, Alla A; Abraham, Brian J; Ji, Xiong; Molinie, Benoit; Hannett, Nancy M; Guo, Yang Eric; Jangi, Mohini; Giallourakis, Cosmas C; Sharp, Phillip A; Young, Richard A

2015-11-20

Transcription factors (TFs) bind specific sequences in promoter-proximal and -distal DNA elements to regulate gene transcription. RNA is transcribed from both of these DNA elements, and some DNA binding TFs bind RNA. Hence, RNA transcribed from regulatory elements may contribute to stable TF occupancy at these sites. We show that the ubiquitously expressed TF Yin-Yang 1 (YY1) binds to both gene regulatory elements and their associated RNA species across the entire genome. Reduced transcription of regulatory elements diminishes YY1 occupancy, whereas artificial tethering of RNA enhances YY1 occupancy at these elements. We propose that RNA makes a modest but important contribution to the maintenance of certain TFs at gene regulatory elements and suggest that transcription of regulatory elements produces a positive-feedback loop that contributes to the stability of gene expression programs. Copyright © 2015, American Association for the Advancement of Science.

Robustness and accuracy in sea urchin developmental gene regulatory networks

Directory of Open Access Journals (Sweden)

Smadar eBen-Tabou De-Leon

2016-02-01

Full Text Available Developmental gene regulatory networks robustly control the timely activation of regulatory and differentiation genes. The structure of these networks underlies their capacity to buffer intrinsic and extrinsic noise and maintain embryonic morphology. Here I illustrate how the use of specific architectures by the sea urchin developmental regulatory networks enables the robust control of cell fate decisions. The Wnt-βcatenin signaling pathway patterns the primary embryonic axis while the BMP signaling pathway patterns the secondary embryonic axis in the sea urchin embryo and across bilateria. Interestingly, in the sea urchin in both cases, the signaling pathway that defines the axis controls directly the expression of a set of downstream regulatory genes. I propose that this direct activation of a set of regulatory genes enables a uniform regulatory response and a clear cut cell fate decision in the endoderm and in the dorsal ectoderm. The specification of the mesodermal pigment cell lineage is activated by Delta signaling that initiates a triple positive feedback loop that locks down the pigment specification state. I propose that the use of compound positive feedback circuitry provides the endodermal cells enough time to turn off mesodermal genes and ensures correct mesoderm vs. endoderm fate decision. Thus, I argue that understanding the control properties of repeatedly used regulatory architectures illuminates their role in embryogenesis and provides possible explanations to their resistance to evolutionary change.

Positive and negative feedback loops in nutrient phytoplankton interactions related to climate dynamics factors in a shallow temperate estuary (Vistula Lagoon, southern Baltic)

Science.gov (United States)

Kruk, Marek; Kobos, Justyna; Nawrocka, Lidia; Parszuto, Katarzyna

2018-04-01

This study aims to demonstrate that factors associated with climate dynamics, such as temperature and wind, affect the ecosystem of the shallow Vistula Lagoon in the southern Baltic and cause nutrient forms phytoplankton interactions: the growth of biomass and constraints of it. This occurs through a network of direct and indirect relationships between environmental and phytoplankton factors, including interactions of positive and negative feedback loops. Path analysis supported by structural equation modeling (SEM) was used to test hypotheses regarding the impact of climate factors on algal assemblages. Increased phytoplankton biomass was affected directly by water temperature and salinity, while the wind speed effect was indirect as it resulted in increased concentrations of suspended solids (SS) in the water column. Simultaneously, the concentration of SS in the water was positively correlated with particulate organic carbon (POC), particulate nitrogen (PN), and particulate phosphorus (PP), and was negatively correlated with the total nitrogen to phosphorus (N:P) ratio. Particulate forms of C, N, and phosphorus (P), concentrations of soluble reactive phosphorus (SRP) and nitrate and nitrite nitrogen (NO3-N + NO2-N), and ratios of the total N:P and DIN:SRP, all indirectly effected Cyanobacteria C concentrations. These processes influence other phytoplankton groups (Chlorophyta, Bacillariophyceae and the picophytoplankton fraction). Increased levels of SRP associated with organic matter (POC), which stemmed from reduced DIN:SRP ratios, contributed to increased Cyanoprokaryota and picophytoplankton C concentrations, which created a positive feedback loop. However, a simultaneous reduction in the total N:P ratio could have inhibited increases in the biomass of these assemblages by limiting N, which likely formed a negative feedback loop. The study indicates that the nutrients-phytoplankton feedback loop phenomenon can intensify eutrophication in a temperate lagoon

[Leptin and the feedback regulation of body weight].

Science.gov (United States)

Wang, X; Ye, G; Sun, J

1999-09-30

Body weight may be controlled by a negative feedback loop. Recent studies have identified that the ob gene product, leptin, apparently and exclusively expressed in adipose tissue, is a part of the negative feedback loop. Leptin is proposed to act as an afferent signal in the negative feedback loop to hypothalamus that limiting food-intake, controlling energy homeostasis and regulating the mass of adipose tissue. The dificiency of or resistance to leptin causes severe obesity.

Irradiation-induced angiogenesis is associated with an MMP-9-miR-494-syndecan-1 regulatory loop in medulloblastoma cells.

Science.gov (United States)

Asuthkar, S; Velpula, K K; Nalla, A K; Gogineni, V R; Gondi, C S; Rao, J S

2014-04-10

Matrix metalloproteinase-9 (MMP-9) represents one of the most prominent proteins associated with tumorigenesis and is a modulator of the tumor microenvironment during angiogenesis. Recently, syndecan-1 (SDC1), a transmembrane heparan sulfate-bearing proteoglycan, was also speculated to have a critical role in contributing to angiogenesis when associated with MMP-9. However, the mechanism behind their synergistic regulation is not fully understood. In the current study, we report for the first time that ionizing radiation (IR)-induced MMP-9 enhances SDC1 shedding, corroborating to tube-inducing ability of medulloblastoma (MB) cells. Furthermore, we observed that the tumor angiogenesis is associated with higher MMP-9-SDC1 interactions on both the cell surface and extracellular medium. Our results also revealed the existence of a novel regulatory mechanism where MMP-9 drives the suppression of miR-494, resulting in enhanced SDC1 shedding and angiogenesis. From the in situ hybridization analysis, we found that MMP-9-specific shRNA (shMMP-9) treatment of mouse intracranial tumors resulted in elevated expression of miR-494. This negative correlation between MMP-9 and miR-494 levels was observed to be dependent on the methylation status of a miR-494 promoter-associated CpG island region (-186 to -20), which was confirmed by bisulfite-sequencing and methylation-specific PCR (MSP) analysis. Further, validation of MMP-9 and SDC1 3'-untranslated region (3'-UTR) targets with luciferase reporter assay provided a more favorable result for miR-494-mediated regulation of SDC1 but not of MMP-9, suggesting that the 3'-UTR of SDC1 mRNA is a direct target of miR-494. Overall, our results indicate that angiogenesis induced by radiotherapy is associated with an MMP-9-miR-494-SDC1 regulatory loop and that MMP-9-SDC1 activity creates a negative feedback loop by regulating the expression of miR-494.

RF feedback development for the PEP-II B Factory

Energy Technology Data Exchange (ETDEWEB)

Corredoura, P.; Sapozhnikov, L.; Tighe, R.

1994-06-01

In PEP-II heavy beam loading along with a relatively long revolution period combine to strongly drive lower coupled-bunch modes through interaction with the fundamental cavity mode. Feedback techniques can be applied to reduce the cavity impedance seen by the beam. Several RF feedback loops are planned to reduce the growth rates down to a level which can be damped by the relatively low power bunch-by-bunch longitudinal feedback system. This paper describes the RF feedback loops as well as hardware tests using a 500 kW klystron, analog and digital feedback loops, and a low power test cavity.

RF feedback development for the PEP-II B Factory

International Nuclear Information System (INIS)

Corredoura, P.; Sapozhnikov, L.; Tighe, R.

1994-06-01

In PEP-II heavy beam loading along with a relatively long revolution period combine to strongly drive lower coupled-bunch modes through interaction with the fundamental cavity mode. Feedback techniques can be applied to reduce the cavity impedance seen by the beam. Several RF feedback loops are planned to reduce the growth rates down to a level which can be damped by the relatively low power bunch-by-bunch longitudinal feedback system. This paper describes the RF feedback loops as well as hardware tests using a 500 kW klystron, analog and digital feedback loops, and a low power test cavity

Time Optimal Synchronization Procedure and Associated Feedback Loops

CERN Document Server

Angoletta, Maria Elena; CERN. Geneva. ATS Department

2016-01-01

A procedure to increase the speed of currently used synchronization loops in a synchrotron by an order of magnitude is presented. Beams dynamics constraint imposes an upper limit on excursions in stable phase angle, and the procedure presented exploits this limit to arrive in the synchronized state from an arbitrary initial state in the fastest possible way. Detailed corrector design for beam phase loop, differential frequency loop and final synchronization loop is also presented. Finally, an overview of the synchronization methods currently deployed in some other CERN’s machines is provided, together with a brief comparison with the newly proposed time-optimal algorithm.

Are Success and Failure Experiences Equally Motivational? An Investigation of Regulatory Focus and Feedback

Science.gov (United States)

Shu, Tse-Mei; Lam, Shui-fong

2011-01-01

The present study extended regulatory focus theory (Idson & Higgins, 2000) to an educational setting and attempted to identify individuals with high motivation after both success and failure feedback. College students in Hong Kong (N = 180) participated in an experiment with a 2 promotion focus (high vs. low) x 2 prevention focus (high vs.…

Closed-loop mechanical ventilation for lung injury: a novel physiological-feedback mode following the principles of the open lung concept.

Science.gov (United States)

Schwaiberger, David; Pickerodt, Philipp A; Pomprapa, Anake; Tjarks, Onno; Kork, Felix; Boemke, Willehad; Francis, Roland C E; Leonhardt, Steffen; Lachmann, Burkhard

2018-06-01

Adherence to low tidal volume (V T ) ventilation and selected positive end-expiratory pressures are low during mechanical ventilation for treatment of the acute respiratory distress syndrome. Using a pig model of severe lung injury, we tested the feasibility and physiological responses to a novel fully closed-loop mechanical ventilation algorithm based on the "open lung" concept. Lung injury was induced by surfactant washout in pigs (n = 8). Animals were ventilated following the principles of the "open lung approach" (OLA) using a fully closed-loop physiological feedback algorithm for mechanical ventilation. Standard gas exchange, respiratory- and hemodynamic parameters were measured. Electrical impedance tomography was used to quantify regional ventilation distribution during mechanical ventilation. Automatized mechanical ventilation provided strict adherence to low V T -ventilation for 6 h in severely lung injured pigs. Using the "open lung" approach, tidal volume delivery required low lung distending pressures, increased recruitment and ventilation of dorsal lung regions and improved arterial blood oxygenation. Physiological feedback closed-loop mechanical ventilation according to the principles of the open lung concept is feasible and provides low tidal volume ventilation without human intervention. Of importance, the "open lung approach"-ventilation improved gas exchange and reduced lung driving pressures by opening atelectasis and shifting of ventilation to dorsal lung regions.

Controlling Unknown Saddle Type Steady States of Dynamical Systems with Latency in the Feedback Loop

DEFF Research Database (Denmark)

Tamasevicius, Arunas; Bumeliene, Skaidra; Tamaseviciute, Elena

2009-01-01

We suggest an adaptive control technique for stabilizing saddle type unstable steady states of dynamical systems. The controller is composed of an unstable and a stable high-pass filters operating in parallel. The mathematical model is considered analytically and numerically. The conjoint...... controller is sufficiently robust to time latencies in the feedback loop. In addition, it is not sensitive to the damping parameters of the system and is relatively fast. Experiments have been performed using a simplified version of the electronic Young-Silva circuit imitating behavior of the Duffing...

Belgian class II nuclear facilities such as irradiators and accelerators. Regulatory Body attention points and operating experience feedback

Energy Technology Data Exchange (ETDEWEB)

Minne, Etienne; Peters, Christelle; Mommaert, Chantal; Kennes, Christian; Cortenbosch, Geert; Schmitz, Frederic; Haesendonck, Michel van [Bel V, Brussels (Belgium); Carlier, Pascal; Schrayen, Virginie; Wertelaers, An [Federal Agency for Nuclear Control, Brussels (Belgium)

2016-11-15

The aim of this paper is to present the Regulatory Body attention points and the operating experience feedback from Belgian ''class IIA'' facilities such as industrial and research irradiators, bulk radionuclides producers and conditioners. Reinforcement of the nuclear safety and radiation protection has been promoted by the Federal Agency for Nuclear Control (FANC) since 2009. This paper is clearly a continuation of the former paper [1] presenting the evolution in the regulatory framework relative to the creation of Bel V, the subsidiary of the FANC, and to the new ''class IIA'' covering heavy installations such as those mentioned above. Some lessons learnt are extracted from the operating experience feedback based on the events declared to the authorities. Even though a real willingness to meet the new safety requirements is observed among the ''class IIA'' licensees, promoting the safety culture, the nuclear safety and radiation protection remains an endless challenge for the Regulatory Body.

Operating nuclear plant feedback to ASME and French codes

International Nuclear Information System (INIS)

Journet, J.; O'Donnell, W.J.

1996-01-01

The French have an advantage in nuclear plant operating experience feedback due to the highly centralized nature of their nuclear industry. There is only one utility in charge of design as well as operations (EDF) and only one reactor vendor (Framatome). The ASME Code has played a key role in resolving technical issues in the design and operation of nuclear plants since the inception of nuclear power. The committee structure of the Code brings an ideal combination of senior technical people with both broad and specialized experience to bear on complex how safe is safe enough technical issues. The authors now see an even greater role for the ASME Code in a proposed new regulatory era for the US nuclear industry. The current legalistic confrontational regulatory era has been quite destructive. There now appears to be a real opportunity to begin a new era of technical consensus as the primary means for resolving safety issues. This change can quickly be brought about by having the industry take operating plant problems and regulatory technical issues directly to the ASME Code for timely resolution. Surprisingly, there is no institution in the US nuclear industry with such a mandate. In fact, the industry is organized to feedback through the Nuclear Regulatory Commission issues which could be far better resolved through the ASME Code. Major regulatory benefits can be achieved by closing this loop and providing systematic interaction with the ASME Code. The essential elements of a new regulatory era and ideas for organizing US institutional industry responsibilities, taken from the French experience, are described in this paper

Net Metering and Market Feedback Loops: Exploring the Impact of Retail Rate Design on Distributed PV Deployment

Energy Technology Data Exchange (ETDEWEB)

Darghouth, Naïm R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Wiser, Ryan [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Barbose, Galen [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Mills, Andrew [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2015-01-13

The substantial increase in deployment of customer-sited solar photovoltaics (PV) in the United States has been driven by a combination of steeply declining costs, financing innovations, and supportive policies. Among those supportive policies is net metering, which in most states effectively allows customers to receive compensation for distributed PV generation at the full retail electricity price. The current design of retail electricity rates and the presence of net metering have elicited concerns that the possible under-recovery of fixed utility costs from PV system owners may lead to a feedback loop of increasing retail prices that accelerate PV adoption and further rate increases. However, a separate and opposing feedback loop could offset this effect: increased PV deployment may lead to a shift in the timing of peak-period electricity prices that could reduce the bill savings received under net metering where time-varying retail electricity rates are used, thereby dampening further PV adoption. In this paper, we examine the impacts of these two competing feedback dynamics on U.S. distributed PV deployment through 2050 for both residential and commercial customers, across states. Our results indicate that, at the aggregate national level, the two feedback effects nearly offset one another and therefore produce a modest net effect, although their magnitude and direction vary by customer segment and by state. We also model aggregate PV deployment trends under various rate designs and net-metering rules, accounting for feedback dynamics. Our results demonstrate that future adoption of distributed PV is highly sensitive to retail rate structures. Whereas flat, time-invariant rates with net metering lead to higher aggregate national deployment levels than the current mix of rate structures (+5% in 2050), rate structures with higher monthly fixed customer charges or PV compensation at levels lower than the full retail rate can dramatically erode aggregate customer

Dynamics of nonlinear feedback control.

Science.gov (United States)

Snippe, H P; van Hateren, J H

2007-05-01

Feedback control in neural systems is ubiquitous. Here we study the mathematics of nonlinear feedback control. We compare models in which the input is multiplied by a dynamic gain (multiplicative control) with models in which the input is divided by a dynamic attenuation (divisive control). The gain signal (resp. the attenuation signal) is obtained through a concatenation of an instantaneous nonlinearity and a linear low-pass filter operating on the output of the feedback loop. For input steps, the dynamics of gain and attenuation can be very different, depending on the mathematical form of the nonlinearity and the ordering of the nonlinearity and the filtering in the feedback loop. Further, the dynamics of feedback control can be strongly asymmetrical for increment versus decrement steps of the input. Nevertheless, for each of the models studied, the nonlinearity in the feedback loop can be chosen such that immediately after an input step, the dynamics of feedback control is symmetric with respect to increments versus decrements. Finally, we study the dynamics of the output of the control loops and find conditions under which overshoots and undershoots of the output relative to the steady-state output occur when the models are stimulated with low-pass filtered steps. For small steps at the input, overshoots and undershoots of the output do not occur when the filtering in the control path is faster than the low-pass filtering at the input. For large steps at the input, however, results depend on the model, and for some of the models, multiple overshoots and undershoots can occur even with a fast control path.

Spatiotemporal network motif reveals the biological traits of developmental gene regulatory networks in Drosophila melanogaster

Directory of Open Access Journals (Sweden)

Kim Man-Sun

2012-05-01

Full Text Available Abstract Background Network motifs provided a “conceptual tool” for understanding the functional principles of biological networks, but such motifs have primarily been used to consider static network structures. Static networks, however, cannot be used to reveal time- and region-specific traits of biological systems. To overcome this limitation, we proposed the concept of a “spatiotemporal network motif,” a spatiotemporal sequence of network motifs of sub-networks which are active only at specific time points and body parts. Results On the basis of this concept, we analyzed the developmental gene regulatory network of the Drosophila melanogaster embryo. We identified spatiotemporal network motifs and investigated their distribution pattern in time and space. As a result, we found how key developmental processes are temporally and spatially regulated by the gene network. In particular, we found that nested feedback loops appeared frequently throughout the entire developmental process. From mathematical simulations, we found that mutual inhibition in the nested feedback loops contributes to the formation of spatial expression patterns. Conclusions Taken together, the proposed concept and the simulations can be used to unravel the design principle of developmental gene regulatory networks.

Generalized fast feedback system in the SLC

International Nuclear Information System (INIS)

Hendrickson, L.; Allison, S.; Gromme, T.; Himel, T.; Krauter, K.; Rouse, F.; Sass, R.; Shoaee, H.

1991-11-01

A generalized fast feedback system has been developed to stabilize beams at various locations in the SLC. The system is designed to perform measurements and change actuator settings to control beam states such as position, angle and energy on a pulse to pulse basis. The software design is based on the state space formalism of digital control theory. The system is database-driven, facilitating the addition of new loops without requiring additional software. A communications system, KISNet, provides fast communications links between microprocessors for feedback loops which involve multiple micros. Feedback loops have been installed in seventeen locations throughout the SLC and have proven to be invaluable in stabilizing the machine

Pulsed feedback defers cellular differentiation.

Directory of Open Access Journals (Sweden)

Joe H Levine

2012-01-01

Full Text Available Environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well-characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable "polyphasic" positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a "timer" that operates over timescales much longer than a cell cycle.

In vivo argon laser vascular welding using thermal feedback: open and closed loop patency and collagen crosslinking

Energy Technology Data Exchange (ETDEWEB)

Small, W., LLNL

1997-02-28

An in vivo study of vascular welding with a fiber-delivered argon laser was conducted using a canine model. Longitudinal arteriotomies and venotomies were treated on femoral vein and artery. Laser energy was delivered to the vessel wall via a 400 {micro}m optical fiber. The surface temperature at the center of the laser spot was monitored in real time using a hollow glass optical fiber-based two-color infrared thermometer. The surface temperature was limited by either a room-temperature saline drip or direct feedback control of the laser using a mechanical shutter to alternately pass and block the laser. Acute patency was evaluated either visually (leak/no leak) or by in vivo burst pressure measurements. Biochemical assays were performed to investigate the possible laser-induced formation or destruction of enzymatically mediated covalent crosslinks between collagen molecules. Viable welds were created both with and without the use of feedback control. Tissues maintained at 50 C using feedback control had an elevated crosslink count compared to controls, while those irradiated without feedback control experienced a decrease. Differences between the volumetric heating associated with open and closed loop protocols may account for the different effects on collagen crosslinks. Covalent mechanisms may play a role in argon laser vascular fusion.

Generalized fast feedback system in the SLC

International Nuclear Information System (INIS)

Hendrickson, L.; Allison, S.; Gromme, T.; Himel, T.; Krauter, K.; Rouse, F.; Sass, R.; Shoaee, H.

1992-01-01

A generalized fast feedback system has been developed to stabilize beams at various locations in the SLC. The system is designed to perform measurements and change actuator settings to control beam states such as position, angle and energy on a pulse to pulse basis. The software design is based on the state space formalism of digital control theory. The system is database-driven, facilitating the addition of new loops without requiring additional software. A communications system, KISNet, provides fast communications links between microprocessors for feedback loops which involve multiple micros. Feedback loops have been installed in seventeen locations throughout the SLC and have proven to be invaluable in stabilizing the machine. (author)

Model-based rational feedback controller design for closed-loop deep brain stimulation of Parkinson's disease

Science.gov (United States)

Gorzelic, P.; Schiff, S. J.; Sinha, A.

2013-04-01

Objective. To explore the use of classical feedback control methods to achieve an improved deep brain stimulation (DBS) algorithm for application to Parkinson's disease (PD). Approach. A computational model of PD dynamics was employed to develop model-based rational feedback controller design. The restoration of thalamocortical relay capabilities to patients suffering from PD is formulated as a feedback control problem with the DBS waveform serving as the control input. Two high-level control strategies are tested: one that is driven by an online estimate of thalamic reliability, and another that acts to eliminate substantial decreases in the inhibition from the globus pallidus interna (GPi) to the thalamus. Control laws inspired by traditional proportional-integral-derivative (PID) methodology are prescribed for each strategy and simulated on this computational model of the basal ganglia network. Main Results. For control based upon thalamic reliability, a strategy of frequency proportional control with proportional bias delivered the optimal control achieved for a given energy expenditure. In comparison, control based upon synaptic inhibitory output from the GPi performed very well in comparison with those of reliability-based control, with considerable further reduction in energy expenditure relative to that of open-loop DBS. The best controller performance was amplitude proportional with derivative control and integral bias, which is full PID control. We demonstrated how optimizing the three components of PID control is feasible in this setting, although the complexity of these optimization functions argues for adaptive methods in implementation. Significance. Our findings point to the potential value of model-based rational design of feedback controllers for Parkinson's disease.

Perspectives on Regulatory T Cell Therapies.

Science.gov (United States)

Probst-Kepper, Michael; Kröger, Andrea; Garritsen, Henk S P; Buer, Jan

2009-01-01

Adoptive transfer in animal models clearly indicate an essential role of CD4+ CD25+ FOXP3+ regulatory T (T(reg)) cells in prevention and treatment of autoimmune and graft-versus-host disease. Thus, T(reg) cell therapies and development of drugs that specifically enhance T(reg) cell function and development represent promising tools to establish dominant tolerance. So far, lack of specific markers to differentiate human T(reg) cells from activated CD4+ CD25+ effector T cells, which also express FOXP3 at different levels, hampered such an approach. Recent identification of the orphan receptor glycoprotein-A repetitions predominant (GARP or LRRC32) as T(reg) cell-specific key molecule that dominantly controls FOXP3 via a positive feedback loop opens up new perspectives for molecular and cellular therapies. This brief review focuses on the role of GARP as a safeguard of a complex regulatory network of human T(reg) cells and its implications for regulatory T cell therapies in autoimmunity and graft-versus-host disease.

A regulatory transcriptional loop controls proliferation and differentiation in Drosophila neural stem cells.

Directory of Open Access Journals (Sweden)

Tetsuo Yasugi

Full Text Available Neurogenesis is initiated by a set of basic Helix-Loop-Helix (bHLH transcription factors that specify neural progenitors and allow them to generate neurons in multiple rounds of asymmetric cell division. The Drosophila Daughterless (Da protein and its mammalian counterparts (E12/E47 act as heterodimerization factors for proneural genes and are therefore critically required for neurogenesis. Here, we demonstrate that Da can also be an inhibitor of the neural progenitor fate whose absence leads to stem cell overproliferation and tumor formation. We explain this paradox by demonstrating that Da induces the differentiation factor Prospero (Pros whose asymmetric segregation is essential for differentiation in one of the two daughter cells. Da co-operates with the bHLH transcription factor Asense, whereas the other proneural genes are dispensible. After mitosis, Pros terminates Asense expression in one of the two daughter cells. In da mutants, pros is not expressed, leading to the formation of lethal transplantable brain tumors. Our results define a transcriptional feedback loop that regulates the balance between self-renewal and differentiation in Drosophila optic lobe neuroblasts. They indicate that initiation of a neural differentiation program in stem cells is essential to prevent tumorigenesis.

Klystron equalization for RF feedback

International Nuclear Information System (INIS)

Corredoura, P.

1993-01-01

The next generation of colliding beam storage rings support higher luminosities by significantly increasing the number of bunches and decreasing the spacing between respective bunches. The heavy beam loading requires large RF cavity detuning which drives several lower coupled bunch modes very strongly. One technique which has proven to be very successful in reducing the coupled bunch mode driving impedance is RF feedback around the klystron-cavity combination. The gain and bandwidth of the feedback loop is limited by the group delay around the feedback loop. Existing klystrons on the world market have not been optimized for this application and contribute a large portion of the total loop group delay. This paper describes a technique to reduce klystron group delay by adding an equalizing filter to the klystron RF drive. Such a filter was built and tested on a 500 kill klystron as part of the on going PEP-II R ampersand D effort here at SLAC

Current control loop design and analysis based on resonant regulators for microgrid applications

DEFF Research Database (Denmark)

Federico, de Bosio; Pastorelli, Michelle; de Sousa Ribeiro, Luiz Antonio

2015-01-01

Voltage and current control loops play an important role in the performance of microgrids employing power electronics voltage source inverters. Correct design of feedback loops is essential for the proper operation of these systems. This paper analyzes the influence of state feedback cross......-coupling in the design of resonant regulators for inner current loops in power converters operating in standalone microgrids. It is also demonstrated that the effect of state feedback cross-coupling degrades the performance of the control loops by increasing the steady-state error. Different resonant regulators...

Fault Tolerant Feedback Control

DEFF Research Database (Denmark)

Stoustrup, Jakob; Niemann, H.

2001-01-01

An architecture for fault tolerant feedback controllers based on the Youla parameterization is suggested. It is shown that the Youla parameterization will give a residual vector directly in connection with the fault diagnosis part of the fault tolerant feedback controller. It turns out...... that there is a separation be-tween the feedback controller and the fault tolerant part. The closed loop feedback properties are handled by the nominal feedback controller and the fault tolerant part is handled by the design of the Youla parameter. The design of the fault tolerant part will not affect the design...... of the nominal feedback con-troller....

The light cycle controls the hatching rhythm in Bombyx mori via negative feedback loop of the circadian oscillator.

Science.gov (United States)

Tao, Hui; Li, Xue; Qiu, Jian-Feng; Liu, Heng-Jiang; Zhang, Da-Yan; Chu, Feng; Sima, Yanghu; Xu, Shi-Qing

2017-10-01

Hatching behavior is a key target in silkworm (Bombyx mori) rearing, especially for the control of Lepidoptera pests. According to previous research, hatching rhythms appear to be controlled by a clock mechanism that restricts or "gates" hatching to a particular time. However, the underlying mechanism remains elusive. Under 12-h light:12-h dark photoperiod (LD) conditions, the transcriptional levels of the chitinase5 (Cht5) and hatching enzyme-like (Hel) genes, as well as the enzymatic activities of their gene products, oscillated in time with ambient light cycles, as did the transcriptional levels of the cryptochrome 1, cryptochrome 2, period (per), and timeless genes, which are key components of the negative feedback loop of the circadian rhythm. These changes were related to the expression profile of the ecdysteroid receptor gene and the hatching behavior of B. mori eggs. However, under continuous light or dark conditions, the hatching behavior, the expression levels of Cht5 and Hel, as well as the enzymatic activities of their gene products, were not synchronized unlike under LD conditions. In addition, immunohistochemistry experiments showed that light promoted the translocation of PER from the cytoplasm to the nucleus. In conclusion, LD cycles regulate the hatching rhythm of B. mori via negative feedback loop of the circadian oscillator. © 2017 Wiley Periodicals, Inc.

Feedback control of atomic motion in an optical lattice

International Nuclear Information System (INIS)

Morrow, N.V.; Dutta, S.K.; Raithel, G.

2002-01-01

We demonstrate a real-time feedback scheme to manipulate wave-packet oscillations of atoms in an optical lattice. The average position of the atoms in the lattice wells is measured continuously and nondestructively. A feedback loop processes the position signal and translates the lattice potential. Depending on the feedback loop characteristics, we find amplification, damping, or an entire alteration of the wave-packet oscillations. Our results are well supported by simulations

Regulation of Trib2 by an E2F1-C/EBPα feedback loop in AML cell proliferation.

LENUS (Irish Health Repository)

Rishi, Loveena

2014-04-10

The loss of regulation of cell proliferation is a key event in leukemic transformation, and the oncogene tribbles (Trib)2 is emerging as a pivotal target of transcription factors in acute leukemias. Deregulation of the transcription factor E2F1, normally repressed by CCAAT enhancer-binding protein α (C\\/EBPα)-p42, occurs in acute myeloid leukemia (AML), resulting in the perturbation of cell cycle and apoptosis, emphasizing its importance in the molecular pathogenesis of AML. Here we show that E2F family members directly regulate Trib2 in leukemic cells and identify a feedback regulatory loop for E2F1, C\\/EBPα, and Trib2 in AML cell proliferation and survival. Further analyses revealed that E2F1-mediated Trib2 expression was repressed by C\\/EBPα-p42, and in normal granulocyte\\/macrophage progenitor cells, we detect C\\/EBPα bound to the Trib2 promoter. Pharmacological inhibition of the cell cycle or Trib2 knockdown resulted in a block in AML cell proliferation. Our work proposes a novel paradigm whereby E2F1 plays a key role in the regulation of Trib2 expression important for AML cell proliferation control. Importantly, we identify the contribution of dysregulated C\\/EBPα and E2F1 to elevated Trib2 expression and leukemic cell survival, which likely contributes to the initiation and maintenance of AML and may have significant implications for normal and malignant hematopoiesis.

Coherent-feedback-induced controllable optical bistability and photon blockade

International Nuclear Information System (INIS)

Liu, Yu-Long; Liu, Zhong-Peng; Zhang, Jing

2015-01-01

It is well known that some nonlinear phenomena such as strong photon blockade are difficult to observe in optomechanical systems with current experimental technology. Here we present a coherent feedback control strategy in which a linear cavity is coherently controlled by an optomechanical controller in a feedback manner. The coherent feedback loop transfers quantum nonlinearity from the controller to the controlled cavity causing destructive quantum interference to occur, and making it possible to observe strong nonlinear effects. With the help of the coherent feedback loop, large and tunable bistability and strong photon blockade of the cavity modes can be achieved even in the optomechanical weak coupling regime. Additionally, the coherent feedback loop leads to two-photon and multiphoton tunnelings for the controlled linear cavity, which are also typical quantum nonlinear phenomena. We hope that our work can give new perspectives on engineering nonlinear interactions in quantum systems. (paper)

Control of conducting polymer actuators without physical feedback: simulated feedback control approach with particle swarm optimization

International Nuclear Information System (INIS)

Xiang, Xingcan; Mutlu, Rahim; Alici, Gursel; Li, Weihua

2014-01-01

Conducting polymer actuators have shown significant potential in articulating micro instruments, manipulation devices, and robotics. However, implementing a feedback control strategy to enhance their positioning ability and accuracy in any application requires a feedback sensor, which is extremely large in size compared to the size of the actuators. Therefore, this paper proposes a new sensorless control scheme without the use of a position feedback sensor. With the help of the system identification technique and particle swarm optimization, the control scheme, which we call the simulated feedback control system, showed a satisfactory command tracking performance for the conducting polymer actuator’s step and dynamic displacement responses, especially under a disturbance, without needing a physical feedback loop, but using a simulated feedback loop. The primary contribution of this study is to propose and experimentally evaluate the simulated feedback control scheme for a class of the conducting polymer actuators known as tri-layer polymer actuators, which can operate both in dry and wet media. This control approach can also be extended to other smart actuators or systems, for which the feedback control based on external sensing is impractical. (paper)

Multi-bunch Feedback Systems

OpenAIRE

Lonza, M.; Schmickler, H.

2016-01-01

Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. Advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides importa...

FOXP3: required but not sufficient. the role of GARP (LRRC32) as a safeguard of the regulatory phenotype.

Science.gov (United States)

Probst-Kepper, M; Balling, R; Buer, J

2010-08-01

FOXP3 is essential for the development and function of regulatory CD4(+)CD25(hi) T (T(reg)) cells. However, recent evidence suggests that FOXP3 alone is not sufficient to completely explain the regulatory phenotype of these key players in autoimmunity and inflammation: after being activated, conventional human CD4(+) T cells transiently up-regulate FOXP3 without acquiring a regulatory function. Researchers have recently found that glycoprotein A repetitions predominant (GARP, or LRRC32) is a T(reg)-specific receptor that binds latent TGF-beta and dominantly controls FOXP3 and the regulatory phenotype via a positive feedback loop. This finding provides a missing link in our molecular understanding of FOXP3 in T(reg) cells. This viewpoint focuses on GARP as safeguard of FOXP3 and the regulatory phenotype.

Generalized modal analysis for closed-loop piezoelectric devices

International Nuclear Information System (INIS)

Giraud-Audine, Christophe; Giraud, Frédéric; Amberg, Michel; Lemaire-Semail, Betty

2015-01-01

Stress in a piezoelectric material can be controlled by imposing an electrical field. Thanks to feedback, this electrical field can be a function of some strain-related measurement so as to confer on the piezoelectric device a closed-loop macroscopic behaviour. In this paper we address the modelling of such a system by extending the modal decomposition methods to account for the closed loop. To do so, the boundary conditions are modified to include the electrical feedback circuit, hence allowing a closed-loop modal analysis. A case study is used to illustrate the theory and to validate it. The main advantage of the method is that design issues such as the coupling factor of the device and closed-loop stability are simultaneously captured. (paper)

The effect of sensory feedback on crayfish posture and locomotion: II. Neuromechanical simulation of closing the loop.

Science.gov (United States)

Bacqué-Cazenave, Julien; Chung, Bryce; Cofer, David W; Cattaert, Daniel; Edwards, Donald H

2015-03-15

Neuromechanical simulation was used to determine whether proposed thoracic circuit mechanisms for the control of leg elevation and depression in crayfish could account for the responses of an experimental hybrid neuromechanical preparation when the proprioceptive feedback loop was open and closed. The hybrid neuromechanical preparation consisted of a computational model of the fifth crayfish leg driven in real time by the experimentally recorded activity of the levator and depressor (Lev/Dep) nerves of an in vitro preparation of the crayfish thoracic nerve cord. Up and down movements of the model leg evoked by motor nerve activity released and stretched the model coxobasal chordotonal organ (CBCO); variations in the CBCO length were used to drive identical variations in the length of the live CBCO in the in vitro preparation. CBCO afferent responses provided proprioceptive feedback to affect the thoracic motor output. Experiments performed with this hybrid neuromechanical preparation were simulated with a neuromechanical model in which a computational circuit model represented the relevant thoracic circuitry. Model simulations were able to reproduce the hybrid neuromechanical experimental results to show that proposed circuit mechanisms with sensory feedback could account for resistance reflexes displayed in the quiescent state and for reflex reversal and spontaneous Lev/Dep bursting seen in the active state. Copyright © 2015 the American Physiological Society.

Closing the Feedback Loop: Physics Undergraduates' Use of Feedback Comments on Laboratory Coursework

Science.gov (United States)

Donovan, Pam

2014-01-01

The laboratory notebooks of physics undergraduates taking two second-year practical courses were audited to discover whether they had used feedback comments in their subsequent coursework. Ninety-five per cent of the 37 students on the first course and 100% of the 14 students on the second course whose work was audited had used feedback. The…

Closed orbit feedback with digital signal processing

International Nuclear Information System (INIS)

Chung, Y.; Kirchman, J.; Lenkszus, F.

1994-01-01

The closed orbit feedback experiment conducted on the SPEAR using the singular value decomposition (SVD) technique and digital signal processing (DSP) is presented. The beam response matrix, defined as beam motion at beam position monitor (BPM) locations per unit kick by corrector magnets, was measured and then analyzed using SVD. Ten BPMs, sixteen correctors, and the eight largest SVD eigenvalues were used for closed orbit correction. The maximum sampling frequency for the closed loop feedback was measured at 37 Hz. Using the proportional and integral (PI) control algorithm with the gains Kp = 3 and K I = 0.05 and the open-loop bandwidth corresponding to 1% of the sampling frequency, a correction bandwidth (-3 dB) of approximately 0.8 Hz was achieved. Time domain measurements showed that the response time of the closed loop feedback system for 1/e decay was approximately 0.25 second. This result implies ∼ 100 Hz correction bandwidth for the planned beam position feedback system for the Advanced Photon Source storage ring with the projected 4-kHz sampling frequency

Simulating closed- and open-loop voluntary movement: a nonlinear control-systems approach.

Science.gov (United States)

Davidson, Paul R; Jones, Richard D; Andreae, John H; Sirisena, Harsha R

2002-11-01

In many recent human motor control models, including feedback-error learning and adaptive model theory (AMT), feedback control is used to correct errors while an inverse model is simultaneously tuned to provide accurate feedforward control. This popular and appealing hypothesis, based on a combination of psychophysical observations and engineering considerations, predicts that once the tuning of the inverse model is complete the role of feedback control is limited to the correction of disturbances. This hypothesis was tested by looking at the open-loop behavior of the human motor system during adaptation. An experiment was carried out involving 20 normal adult subjects who learned a novel visuomotor relationship on a pursuit tracking task with a steering wheel for input. During learning, the response cursor was periodically blanked, removing all feedback about the external system (i.e., about the relationship between hand motion and response cursor motion). Open-loop behavior was not consistent with a progressive transfer from closed- to open-loop control. Our recently developed computational model of the brain--a novel nonlinear implementation of AMT--was able to reproduce the observed closed- and open-loop results. In contrast, other control-systems models exhibited only minimal feedback control following adaptation, leading to incorrect open-loop behavior. This is because our model continues to use feedback to control slow movements after adaptation is complete. This behavior enhances the internal stability of the inverse model. In summary, our computational model is currently the only motor control model able to accurately simulate the closed- and open-loop characteristics of the experimental response trajectories.

A Theory of Circular Organization and Negative Feedback: Defining Life in a Cybernetic Context

Science.gov (United States)

Tsokolov, Sergey

2010-12-01

All life today incorporates a variety of systems controlled by negative feedback loops and sometimes amplified by positive feedback loops. The first forms of life necessarily also required primitive versions of feedback, yet surprisingly little emphasis has been given to the question of how feedback emerged out of primarily chemical systems. One chemical system has been established that spontaneously develops autocatalytic feedback, the Belousov-Zhabotinsky (BZ) reaction. In this essay, I discuss the BZ reaction as a possible model for similar reactions that could have occurred under prebiotic Earth conditions. The main point is that the metabolism of contemporary life evolved from primitive homeostatic networks regulated by negative feedback. Because life could not exist in their absence, feedback loops should be included in definitions of life.

Particle tracking code of simulating global RF feedback

International Nuclear Information System (INIS)

Mestha, L.K.

1991-09-01

It is well known in the ''control community'' that a good feedback controller design is deeply rooted in the physics of the system. For example, when accelerating the beam we must keep several parameters under control so that the beam travels within the confined space. Important parameters include the frequency and phase of the rf signal, the dipole field, and the cavity voltage. Because errors in these parameters will progressively mislead the beam from its projected path in the tube, feedback loops are used to correct the behavior. Since the feedback loop feeds energy to the system, it changes the overall behavior of the system and may drive it to instability. Various types of controllers are used to stabilize the feedback loop. Integrating the beam physics with the feedback controllers allows us to carefully analyze the beam behavior. This will not only guarantee optimal performance but will also significantly enhance the ability of the beam control engineer to deal effectively with the interaction of various feedback loops. Motivated by this theme, we developed a simple one-particle tracking code to simulate particle behavior with feedback controllers. In order to achieve our fundamental objective, we can ask some key questions: What are the input and output parameters? How can they be applied to the practical machine? How can one interface the rf system dynamics such as the transfer characteristics of the rf cavities and phasing between the cavities? Answers to these questions can be found by considering a simple case of a single cavity with one particle, tracking it turn-by-turn with appropriate initial conditions, then introducing constraints on crucial parameters. Critical parameters are rf frequency, phase, and amplitude once the dipole field has been given. These are arranged in the tracking code so that we can interface the feedback system controlling them

A review of control strategies in closed-loop neuroprosthetic systems

Directory of Open Access Journals (Sweden)

James Wright

2016-07-01

Full Text Available It has been widely recognized that closed-loop neuroprosthetic systems achieve more favorable outcomes for users then equivalent open-loop devices. Improved performance of tasks, better usability and greater embodiment have all been reported in systems utilizing some form of feedback. However the interdisciplinary work on neuroprosthetic systems can lead to miscommunication due to similarities in well established nomenclature in different fields. Here we present a review of control strategies in existing experimental, investigational and clinical neuroprosthetic systems in order to establish a baseline and promote a common understanding of different feedback modes and closed-loop controllers. The first section provides a brief discussion of feedback control and control theory. The second section reviews the control strategies of recent Brain Machine Interfaces, neuromodulatory implants, neuroprosthetic systems and assistive neurorobotic devices. The final section examines the different approaches to feedback in current neuroprosthetic and neurorobotic systems.

Closed loop identification of a piezoelectrically controlled radial gas bearing: Theory and experiment

DEFF Research Database (Denmark)

Sekunda, André Krabdrup; Niemann, Hans Henrik; Poulsen, Niels Kjølstad

2018-01-01

Gas bearing systems have extremely small damping properties. Feedback control is thus employed to increase the damping of gas bearings. Such a feedback loop correlates the input with the measurement noise which in turn makes the assumptions for direct identification invalid. The originality...... of this article lies in the investigation of the impact of using different identification methods to identify a rotor-bearing systems’ dynamic model when a feedback loop is active. Two different identification methods are employed. The first method is open loop Prediction Error Method, while the other method...

An Actomyosin-Arf-GEF Negative Feedback Loop for Tissue Elongation under Stress.

Science.gov (United States)

West, Junior J; Zulueta-Coarasa, Teresa; Maier, Janna A; Lee, Donghoon M; Bruce, Ashley E E; Fernandez-Gonzalez, Rodrigo; Harris, Tony J C

2017-08-07

In response to a pulling force, a material can elongate, hold fast, or fracture. During animal development, multi-cellular contraction of one region often stretches neighboring tissue. Such local contraction occurs by induced actomyosin activity, but molecular mechanisms are unknown for regulating the physical properties of connected tissue for elongation under stress. We show that cytohesins, and their Arf small G protein guanine nucleotide exchange activity, are required for tissues to elongate under stress during both Drosophila dorsal closure (DC) and zebrafish epiboly. In Drosophila, protein localization, laser ablation, and genetic interaction studies indicate that the cytohesin Steppke reduces tissue tension by inhibiting actomyosin activity at adherens junctions. Without Steppke, embryogenesis fails, with epidermal distortions and tears resulting from myosin misregulation. Remarkably, actomyosin network assembly is necessary and sufficient for local Steppke accumulation, where live imaging shows Steppke recruitment within minutes. This rapid negative feedback loop provides a molecular mechanism for attenuating the main tension generator of animal tissues. Such attenuation relaxes tissues and allows orderly elongation under stress. Copyright © 2017 Elsevier Ltd. All rights reserved.

Grid-Current-Feedback Control for LCL-Filtered Grid Converters With Enhanced Stability

DEFF Research Database (Denmark)

Xin, Zhen; Wang, Xiongfei; Loh, Poh Chiang

2017-01-01

This paper proposes a Second-Order-Generalized- Integrator (SOGI)-based time delay compensation method for extending the stable region of dual-loop Grid-Current-Feedback (GCF) control system. According to the analysis, stable region of the dual-loop system should be designed below a certain...... critical frequency, before time delay compensation method can be applied. To always meet the requirement, relationship between single-loop converter-current-feedback and dual-loop GCF control is clarified, before a robust inner-loop gain for the dualloop GCF scheme is determined. Enforcing this gain allows...

Numerical study on identification of transfer functions in a feedback system and model reduction

International Nuclear Information System (INIS)

Kishida, Kuniharu

1997-01-01

Identification of transfer function matrices in a feedback system is discussed by using the singular value decomposition of Hankel matrix from the viewpoint of inverse problems. A method of model reduction is considered, and selection criteria are proposed for identification of them. Transformation formula between open loop and closed loop transfer function matrices are determined from the feedback loop structure, and they are needed for identification of open loop transfer function matrices under such a condition where the feedback system is in a minimum phase. Though the identifiability of open loop transfer function matrices can be examined in the framework of innovation model equivalent to the feedback system, there are pole-zero cancellations in the identification of them. The method to reduce a model order of an open loop transfer function is discussed by using the singular value decomposition of a gramian given by the open loop transfer function with higher degree. To check reliability of the present algorithm, a simulation study is performed for an example. (author)

Tutorial on beam-based feedback systems for linacs

International Nuclear Information System (INIS)

Hendrickson, L.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T.; Krauter, K.; MacKenzie, R.; Ross, M.; Sass, R.; Shoaee, H.

1994-08-01

A generalized fast feedback system stabilizes beams in the SLC. It performs measurements and modifies actuator settings to control beam states such as position, angle, energy and intensity on a pulse to pulse basis. An adaptive cascade feature allows communication between a series of linac loops, avoiding overcorrection problems. The system is based on the state space formalism of digital control theory. Due to the database-driven design, new loops are added without requiring software modifications. Recent enhancements support the monitoring and control of nonlinear states such as beam phase using excitation techniques. In over three years of operation, the feedback system has grown from its original eight loops to more than fifty loops, and it has been invaluable in stabilizing the machine

Computational investigation of feedback loop as a potential source of neuromechanical wave speed discrepancy in swimming animals

Science.gov (United States)

Patel, Namu; Patankar, Neelesh A.

2017-11-01

Aquatic locomotion relies on feedback loops to generate the flexural muscle moment needed to attain the reference shape. Experimentalists have consistently reported a difference between the electromyogram (EMG) and curvature wave speeds. The EMG wave speed has been found to correlate with the cross-sectional moment wave. The correlation, however, remains unexplained. Using feedback dependent controller models, we demonstrate two scenarios - one at higher passive elastic stiffness and another at lower passive elastic stiffness of the body. The former case becomes equivalent to the penalty type mathematical model for swimming used in prior literature and it does not reproduce neuromechanical wave speed discrepancy. The latter case at lower elastic stiffness does reproduce the wave speed discrepancy and appears to be biologically most relevant. These findings are applied to develop testable hypotheses about control mechanisms that animals might be using at during low and high Reynolds number swimming. This work is supported by NSF Grants DMS-1547394, CBET-1066575, ACI-1460334, and IOS-1456830. Travel for NP is supported by Institute for Defense Analyses.

The Y-located gonadoblastoma gene TSPY amplifies its own expression through a positive feedback loop in prostate cancer cells

Energy Technology Data Exchange (ETDEWEB)

Kido, Tatsuo; Lau, Yun-Fai Chris, E-mail: Chris.Lau@UCSF.edu

2014-03-28

Highlights: • Y-encoded proto-oncoprotein TSPY amplifies its expression level via a positive feedback loop. • TSPY binds to the chromatin/DNA at exon 1 of TSPY gene. • TSPY enhances the gene expression in a TSPY exon 1 sequence dependent manner. • The conserved SET/NAP-domain is essential for TSPY transactivation. • Insights on probable mechanisms on TSPY exacerbation on cancer development in men. - Abstract: The testis-specific protein Y-encoded (TSPY) is a repetitive gene located on the gonadoblastoma region of the Y chromosome, and has been considered to be the putative gene for this oncogenic locus on the male-only chromosome. It is expressed in spermatogonial cells and spermatocytes in normal human testis, but abundantly in gonadoblastoma, testicular germ cell tumors and a variety of somatic cancers, including melanoma, hepatocellular carcinoma and prostate cancer. Various studies suggest that TSPY accelerates cell proliferation and growth, and promotes tumorigenesis. In this report, we show that TSPY could bind directly to the chromatin/DNA at exon 1 of its own gene, and greatly enhance the transcriptional activities of the endogenous gene in the LNCaP prostate cancer cells. Domain mapping analyses of TSPY have localized the critical and sufficient domain to the SET/NAP-domain. These results suggest that TSPY could efficiently amplify its expression and oncogenic functions through a positive feedback loop, and contribute to the overall tumorigenic processes when it is expressed in various human cancers.

The feed-back regulation of erythropoietin production in healthy humans

International Nuclear Information System (INIS)

Klausen, T.

1998-01-01

The proposed oxygen-dependent feed-back loop regulation of EPO (erythropoietin) production is mainly supported by data from studies in animals and cell cultures. The feed-back loop and its dependence on oxygen was therefore challenged by studies in healthy humans: Exposure of humans to different levels of acute and continued altitude hypobaria provided evidence for an oxygen dependence of the EPO response. This response is consistent with the proposed feed-back loop regulation of EPO production; Exposure to continued altitude hypobaria demonstrated that the decline in human EPO production is initiated before an EPO-induced erythopoiesis is detectable, and that this decline is related to a concomitant decrease in the haemoglobin-oxygen affinity. Contrary to the feed-back loop, this time-relation indicate that the feed-back regulation of EPO production during continued hypobaric hypoxia is exerted primarily through a decrease in the haemoglobin-oxygen affinity, rather than by the effects of an EPO-stimulated erythropoiesis; Increased circulating levels of the proinflammatory cytokine IL-6 was found in healthy humans during four days of altitude exposure as compared with sea level. The other proinflammatory cytokines IL-1 beta, and TNF alpha remained unchanged, and the increased serum IL-6 did not induce production of c-reactive protein; Comparable circadian variations in human EPO production were shown in sedentary subjects, athletes, and healthy but hypoxaemic subjects. Human EPO production could not be triggered by one hour of high-intensity exercise, whereas longitudinal changes in exercise showed a trend of relation between human EPO production, serum concentration of free testosterone, and indices of body composition. These results have demonstrated and endogenous, probably hormonal, and oxygen-independent regulation of human EPO production, which is at variance with the oxygen dependent feed-back loop regulation of EPO production. Conclusively, the present

Peatland plant communities under global change: negative feedback loops counteract shifts in species composition.

Science.gov (United States)

Hedwall, Per-Ola; Brunet, Jörg; Rydin, Håkan

2017-01-01

Mires (bogs and fens) are nutrient-limited peatland ecosystems, the vegetation of which is especially sensitive to nitrogen deposition and climate change. The role of mires in the global carbon cycle, and the delivery of different ecosystem services can be considerably altered by changes in the vegetation, which has a strong impact on peat-formation and hydrology. Mire ecosystems are commonly open with limited canopy cover but both nitrogen deposition and increased temperatures may increase the woody vegetation component. It has been predicted that such an increase in tree cover and the associated effects on light and water regimes would cause a positive feed-back loop with respect to the ground vegetation. None of these effects, however, have so far been confirmed in large-scale spatiotemporal studies. Here we analyzed data pertaining to mire vegetation from the Swedish National Forest Inventory collected from permanent sample plots over a period of 20 yr along a latitudinal gradient covering 14°. We hypothesized that the changes would be larger in the southern parts as a result of higher nitrogen deposition and warmer climate. Our results showed an increase in woody vegetation with increases in most ericaceous dwarf-shrubs and in the basal area of trees. These changes were, in contrast to our expectations, evenly distributed over most of the latitudinal gradient. While nitrogen deposition is elevated in the south, the increase in temperatures during recent decades has been larger in the north. Hence, we suggest that different processes in the north and south have produced similar vegetation changes along the latitudinal gradient. There was, however, a sharp increase in compositional change at high deposition, indicating a threshold effect in the response. Instead of a positive feed-back loop caused by the tree layer, an increase in canopy cover reduced the changes in composition of the ground vegetation, whereas a decrease in canopy cover lead to larger changes

Contributions of the European Operating Experience Feedback Project to Support Regulatory Bodies

International Nuclear Information System (INIS)

Heitsch, M.

2016-01-01

Operating Experience Feedback (OEF) is one of the ways of improving the nuclear safety of operating nuclear power plants. The EC-Clearinghouse initiative was set up in 2008 to support nuclear regulatory authorities of EU Member States, but also Technical Support Organizations, international organizations and the broader nuclear community, to enhance nuclear safety. The differing regulatory regimes in the EU member countries and a significant diversity of the nuclear power plant (NPP) designs have been a challenge in the establishment of the European Clearinghouse. The European Clearinghouse is organized as a Network operated by a Central Office located at the Institute for Energy and Transport (IET) which is part of Joint Research Centre (JRC) of the European Commission. It gathers 17 European regulatory authorities and 3 major European Technical Support organizations (TSO). The Clearinghouse aims at providing lessons learned, recommendations and best practices from operational experience of NPPs based on support and commitment from the EU nuclear regulatory authorities. One of the objectives of the European Clearinghouse is to establish European best practices for the assessment of unusual events in NPPs. The paper will present the main activities of the European Clearinghouse. These include: • Topical studies providing in-depth assessment of selected topics important for the safe operation of NPPs. Statistical tools help to identify interesting subjects for these studies; • Quarterly reports on operating experience; • Training courses in the field of root cause analysis and event investigation; • Development, maintenance and population of a database for storage of operating experience related information; • Collaboration with international organizations such as IAEA and OECD/NEA on all aspects of OEF. All activities of the Clearinghouse initiative focus on providing an added value for nuclear regulation. (author)

Active fault diagnosis in closed-loop systems

DEFF Research Database (Denmark)

Niemann, Hans Henrik; Poulsen, Niels Kjølstad

2005-01-01

Active fault diagnosis (AFD) of parametric faults is considered in connection with closed loop feedback systems. AFD involves auxiliary signals applied on the closed loop system. A fault signature matrix is introduced in connection with AFD and it is shown that if a limited number of faults can...

Interrogation of inhibitor of nuclear factor κB α/nuclear factor κB (IκBα/NF-κB) negative feedback loop dynamics: from single cells to live animals in vivo.

Science.gov (United States)

Moss, Britney L; Elhammali, Adnan; Fowlkes, Tiffanie; Gross, Shimon; Vinjamoori, Anant; Contag, Christopher H; Piwnica-Worms, David

2012-09-07

Full understanding of the biological significance of negative feedback processes requires interrogation at multiple scales as follows: in single cells, cell populations, and live animals in vivo. The transcriptionally coupled IκBα/NF-κB negative feedback loop, a pivotal regulatory node of innate immunity and inflammation, represents a model system for multiscalar reporters. Using a κB(5)→IκBα-FLuc bioluminescent reporter, we rigorously evaluated the dynamics of ΙκBα degradation and subsequent NF-κB transcriptional activity in response to diverse modes of TNFα stimulation. Modulating TNFα concentration or pulse duration yielded complex, reproducible, and differential ΙκBα dynamics in both cell populations and live single cells. Tremendous heterogeneity in the transcriptional amplitudes of individual responding cells was observed, which was greater than the heterogeneity in the transcriptional kinetics of responsive cells. Furthermore, administration of various TNFα doses in vivo generated ΙκBα dynamic profiles in the liver resembling those observed in single cells and populations of cells stimulated with TNFα pulses. This suggested that dose modulation of circulating TNFα was perceived by hepatocytes in vivo as pulses of increasing duration. Thus, a robust bioluminescent reporter strategy enabled rigorous quantitation of NF-κB/ΙκBα dynamics in both live single cells and cell populations and furthermore, revealed reproducible behaviors that informed interpretation of in vivo studies.

Operation of the transverse feedback system at the CERN SPS

International Nuclear Information System (INIS)

Bossart, R.; Louwerse, R.; Mourier, J.; Vos, L.

1987-01-01

To prevent transverse instabilities at high beam intensity in the SPS, the transverse feedback system for damping the betatron oscillations has been upgraded for larger damping decrements and for increased system's bandwidth. The feedback loop now contains a digital delay line cancellor, so that the damper works with a velocity feedback Δx/Δt, unaffected by the closed orbit position x at the pick-up station. The digital processing of the feedback signal facilitates nonlinear feedback techniques such as antidamping and ''band-bang'' feedback. The ''bang-bang'' feedback provides the maximum possible damping rate of the injection oscillations in the SPS-collider, in order to minimize the emittance increase caused by filamentation. The antidamping nonlinearity provides small continuous beam oscillations of 50 μm amplitude for tracking the machine tune Q with a phase locked loop

Adaptive Sliding Mode Control of Dynamic Systems Using Double Loop Recurrent Neural Network Structure.

Science.gov (United States)

Fei, Juntao; Lu, Cheng

2018-04-01

In this paper, an adaptive sliding mode control system using a double loop recurrent neural network (DLRNN) structure is proposed for a class of nonlinear dynamic systems. A new three-layer RNN is proposed to approximate unknown dynamics with two different kinds of feedback loops where the firing weights and output signal calculated in the last step are stored and used as the feedback signals in each feedback loop. Since the new structure has combined the advantages of internal feedback NN and external feedback NN, it can acquire the internal state information while the output signal is also captured, thus the new designed DLRNN can achieve better approximation performance compared with the regular NNs without feedback loops or the regular RNNs with a single feedback loop. The new proposed DLRNN structure is employed in an equivalent controller to approximate the unknown nonlinear system dynamics, and the parameters of the DLRNN are updated online by adaptive laws to get favorable approximation performance. To investigate the effectiveness of the proposed controller, the designed adaptive sliding mode controller with the DLRNN is applied to a -axis microelectromechanical system gyroscope to control the vibrating dynamics of the proof mass. Simulation results demonstrate that the proposed methodology can achieve good tracking property, and the comparisons of the approximation performance between radial basis function NN, RNN, and DLRNN show that the DLRNN can accurately estimate the unknown dynamics with a fast speed while the internal states of DLRNN are more stable.

Quantifying the ice-albedo feedback through decoupling

Science.gov (United States)

Kravitz, B.; Rasch, P. J.

2017-12-01

The ice-albedo feedback involves numerous individual components, whereby warming induces sea ice melt, inducing reduced surface albedo, inducing increased surface shortwave absorption, causing further warming. Here we attempt to quantify the sea ice albedo feedback using an analogue of the "partial radiative perturbation" method, but where the governing mechanisms are directly decoupled in a climate model. As an example, we can isolate the insulating effects of sea ice on surface energy and moisture fluxes by allowing sea ice thickness to change but fixing Arctic surface albedo, or vice versa. Here we present results from such idealized simulations using the Community Earth System Model in which individual components are successively fixed, effectively decoupling the ice-albedo feedback loop. We isolate the different components of this feedback, including temperature change, sea ice extent/thickness, and air-sea exchange of heat and moisture. We explore the interactions between these different components, as well as the strengths of the total feedback in the decoupled feedback loop, to quantify contributions from individual pieces. We also quantify the non-additivity of the effects of the components as a means of investigating the dominant sources of nonlinearity in the ice-albedo feedback.

Regenerative feedback resonant circuit

Science.gov (United States)

Jones, A. Mark; Kelly, James F.; McCloy, John S.; McMakin, Douglas L.

2014-09-02

A regenerative feedback resonant circuit for measuring a transient response in a loop is disclosed. The circuit includes an amplifier for generating a signal in the loop. The circuit further includes a resonator having a resonant cavity and a material located within the cavity. The signal sent into the resonator produces a resonant frequency. A variation of the resonant frequency due to perturbations in electromagnetic properties of the material is measured.

Dynamics of nonlinear feedback control

OpenAIRE

Snippe, H.P.; Hateren, J.H. van

2007-01-01

Feedback control in neural systems is ubiquitous. Here we study the mathematics of nonlinear feedback control. We compare models in which the input is multiplied by a dynamic gain (multiplicative control) with models in which the input is divided by a dynamic attenuation (divisive control). The gain signal (resp. the attenuation signal) is obtained through a concatenation of an instantaneous nonlinearity and a linear low-pass filter operating on the output of the feedback loop. For input step...

Cytokine loops driving senescence

Czech Academy of Sciences Publication Activity Database

Bartek, Jiří; Hodný, Zdeněk; Lukáš, Jan

2008-01-01

Roč. 10, č. 8 (2008), s. 887-889 ISSN 1465-7392 Institutional research plan: CEZ:AV0Z50520514 Keywords : cellular senescence * cytokines * autocrine feedback loop Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 17.774, year: 2008

Approximate Models for Closed-Loop Trajectory Tracking in Underactuated Systems

Data.gov (United States)

National Aeronautics and Space Administration — Control of robotic systems, as a field, spans both traditional closed-loop feedback techniques and modern machine learning strategies, which are primarily open-loop....

Feedback Augmented Sub-Ranging (FASR) Quantizer

Science.gov (United States)

Guilligan, Gerard

2012-01-01

This innovation is intended to reduce the size, power, and complexity of pipeline analog-to-digital converters (ADCs) that require high resolution and speed along with low power. Digitizers are important components in any application where analog signals (such as light, sound, temperature, etc.) need to be digitally processed. The innovation implements amplification of a sampled residual voltage in a switched capacitor amplifier stage that does not depend on charge redistribution. The result is less sensitive to capacitor mismatches that cause gain errors, which are the main limitation of such amplifiers in pipeline ADCs. The residual errors due to mismatch are reduced by at least a factor of 16, which is equivalent to at least 4 bits of improvement. The settling time is also faster because of a higher feedback factor. In traditional switched capacitor residue amplifiers, closed-loop amplification of a sampled and held residue signal is achieved by redistributing sampled charge onto a feedback capacitor around a high-gain transconductance amplifier. The residual charge that was sampled during the acquisition or sampling phase is stored on two or more capacitors, often equal in value or integral multiples of each other. During the hold or amplification phase, all of the charge is redistributed onto one capacitor in the feedback loop of the amplifier to produce an amplified voltage. The key error source is the non-ideal ratios of feedback and input capacitors caused by manufacturing tolerances, called mismatches. The mismatches cause non-ideal closed-loop gain, leading to higher differential non-linearity. Traditional solutions to the mismatch errors are to use larger capacitor values (than dictated by thermal noise requirements) and/or complex calibration schemes, both of which increase the die size and power dissipation. The key features of this innovation are (1) the elimination of the need for charge redistribution to achieve an accurate closed-loop gain of two

Robust fault detection in open loop vs. closed loop

DEFF Research Database (Denmark)

Niemann, Hans Henrik; Stoustrup, J.

1997-01-01

The robustness aspects of fault detection and isolation (FDI) for uncertain systems are considered. The FDI problem is considered in a standard problem formulation. The FDI design problem is analyzed both in the case where the control input signal is considered as a known external input signal (o...... (open loop) and when the input signal is generated by a feedback controller...

A new discrete dynamic model of ABA-induced stomatal closure predicts key feedback loops.

Directory of Open Access Journals (Sweden)

Réka Albert

2017-09-01

several predictions of the model with regard to reactive oxygen species, cytosolic Ca2+ (Ca2+c, and heterotrimeric G-protein signaling. We analyzed dynamics-determining positive and negative feedback loops, thereby elucidating the attractor (dynamic behavior repertoire of the system and the groups of nodes that determine each attractor. Based on this analysis, we predict the likely presence of a previously unrecognized feedback mechanism dependent on Ca2+c. This mechanism would provide model agreement with 10 additional experimental observations, for a validation rate of 85%. Our research underscores the importance of feedback regulation in generating robust and adaptable biological responses. The high validation rate of our model illustrates the advantages of discrete dynamic modeling for complex, nonlinear systems common in biology.

A new discrete dynamic model of ABA-induced stomatal closure predicts key feedback loops.

Science.gov (United States)

Albert, Réka; Acharya, Biswa R; Jeon, Byeong Wook; Zañudo, Jorge G T; Zhu, Mengmeng; Osman, Karim; Assmann, Sarah M

2017-09-01

of the model with regard to reactive oxygen species, cytosolic Ca2+ (Ca2+c), and heterotrimeric G-protein signaling. We analyzed dynamics-determining positive and negative feedback loops, thereby elucidating the attractor (dynamic behavior) repertoire of the system and the groups of nodes that determine each attractor. Based on this analysis, we predict the likely presence of a previously unrecognized feedback mechanism dependent on Ca2+c. This mechanism would provide model agreement with 10 additional experimental observations, for a validation rate of 85%. Our research underscores the importance of feedback regulation in generating robust and adaptable biological responses. The high validation rate of our model illustrates the advantages of discrete dynamic modeling for complex, nonlinear systems common in biology.

A prototype framework for models of socio-hydrology: identification of key feedback loops and parameterisation approach

Science.gov (United States)

Elshafei, Y.; Sivapalan, M.; Tonts, M.; Hipsey, M. R.

2014-06-01

It is increasingly acknowledged that, in order to sustainably manage global freshwater resources, it is critical that we better understand the nature of human-hydrology interactions at the broader catchment system scale. Yet to date, a generic conceptual framework for building models of catchment systems that include adequate representation of socioeconomic systems - and the dynamic feedbacks between human and natural systems - has remained elusive. In an attempt to work towards such a model, this paper outlines a generic framework for models of socio-hydrology applicable to agricultural catchments, made up of six key components that combine to form the coupled system dynamics: namely, catchment hydrology, population, economics, environment, socioeconomic sensitivity and collective response. The conceptual framework posits two novel constructs: (i) a composite socioeconomic driving variable, termed the Community Sensitivity state variable, which seeks to capture the perceived level of threat to a community's quality of life, and acts as a key link tying together one of the fundamental feedback loops of the coupled system, and (ii) a Behavioural Response variable as the observable feedback mechanism, which reflects land and water management decisions relevant to the hydrological context. The framework makes a further contribution through the introduction of three macro-scale parameters that enable it to normalise for differences in climate, socioeconomic and political gradients across study sites. In this way, the framework provides for both macro-scale contextual parameters, which allow for comparative studies to be undertaken, and catchment-specific conditions, by way of tailored "closure relationships", in order to ensure that site-specific and application-specific contexts of socio-hydrologic problems can be accommodated. To demonstrate how such a framework would be applied, two socio-hydrological case studies, taken from the Australian experience, are presented

Self-oscillating loop based piezoelectric power converter

DEFF Research Database (Denmark)

2013-01-01

The present invention relates to a piezoelectric power converter comprising an input driver electrically coupled directly to an input or primary electrode of the piezoelectric transformer without any intervening series or parallel inductor. A feedback loop is operatively coupled between an output......- oscillation loop within a zero-voltage-switching (ZVS) operation range of the piezoelectric transformer....

Activation of TGF-β1-CD147 positive feedback loop in hepatic stellate cells promotes liver fibrosis.

Science.gov (United States)

Li, Hai-Yan; Ju, Di; Zhang, Da-Wei; Li, Hao; Kong, Ling-Min; Guo, Yanhai; Li, Can; Wang, Xi-Long; Chen, Zhi-Nan; Bian, Huijie

2015-11-12

Activation of hepatic stellate cells (HSCs) by transforming growth factor-β1 (TGF-β1) initiates HBV-associated fibrogenesis. The mechanism of TGF-β1 modulating HSC activation is not fully uncovered. We hypothesized a positive feedback signaling loop of TGF-β1-CD147 promoting liver fibrogenesis by activation of HSCs. Human HSC cell line LX-2 and spontaneous liver fibrosis model derived from HBV transgenic mice were used to evaluate the activation of molecules in the signaling loop. Wound healing and cell contraction assay were performed to detect the CD147-overexpressed HSC migration and contraction. The transcriptional regulation of CD147 by TGF-β1/Smad4 was determined using dual-luciferase reporter assay and chromatin immunoprecipitation. We found that a positive reciprocal regulation between TGF-β1 and CD147 mediated HSC activation. CD147 over-expression promoted HSC migration and accelerated TGF-β1-induced cell contraction. Phosphorylation of Smad2 and Smad3 in cooperation with Smad4 mediated the TGF-β1-regulated CD147 expression. Smad4 activated the transcription by direct interaction with CD147 promoter. Meanwhile, CD147 modulated the activated phenotype of HSCs through the ERK1/2 and Sp1 which up-regulated α-SMA, collagen I, and TGF-β1 synthesis. These findings indicate that TGF-β1-CD147 loop plays a key role in regulating the HSC activation and combination of TGF-β receptor inhibitor and anti-CD147 antibody might be promised to reverse fibrogenesis.

Hierarchical structure and modules in the Escherichia coli transcriptional regulatory network revealed by a new top-down approach

Directory of Open Access Journals (Sweden)

Buer Jan

2004-12-01

Full Text Available Abstract Background Cellular functions are coordinately carried out by groups of genes forming functional modules. Identifying such modules in the transcriptional regulatory network (TRN of organisms is important for understanding the structure and function of these fundamental cellular networks and essential for the emerging modular biology. So far, the global connectivity structure of TRN has not been well studied and consequently not applied for the identification of functional modules. Moreover, network motifs such as feed forward loop are recently proposed to be basic building blocks of TRN. However, their relationship to functional modules is not clear. Results In this work we proposed a top-down approach to identify modules in the TRN of E. coli. By studying the global connectivity structure of the regulatory network, we first revealed a five-layer hierarchical structure in which all the regulatory relationships are downward. Based on this regulatory hierarchy, we developed a new method to decompose the regulatory network into functional modules and to identify global regulators governing multiple modules. As a result, 10 global regulators and 39 modules were identified and shown to have well defined functions. We then investigated the distribution and composition of the two basic network motifs (feed forward loop and bi-fan motif in the hierarchical structure of TRN. We found that most of these network motifs include global regulators, indicating that these motifs are not basic building blocks of modules since modules should not contain global regulators. Conclusion The transcriptional regulatory network of E. coli possesses a multi-layer hierarchical modular structure without feedback regulation at transcription level. This hierarchical structure builds the basis for a new and simple decomposition method which is suitable for the identification of functional modules and global regulators in the transcriptional regulatory network of E

Investigation of Inner Loop Flight Control Strategies for High-Speed Research

Science.gov (United States)

Newman, Brett; Kassem, Ayman

1999-01-01

This report describes the activities and findings conducted under contract NAS1-19858 with NASA Langley Research Center. Subject matter is the investigation of suitable flight control design methodologies and solutions for large, flexible high-speed vehicles. Specifically, methodologies are to address the inner control loops used for stabilization and augmentation of a highly coupled airframe system possibly involving rigid-body motion, structural vibrations, unsteady aerodynamics, and actuator dynamics. Techniques considered in this body of work are primarily conventional-based, and the vehicle of interest is the High-Speed Civil Transport (HSCT). Major findings include 1) current aeroelastic vehicle modeling procedures require further emphasis and refinement, 2) traditional and nontraditional inner loop flight control strategies employing a single feedback loop do not appear sufficient for highly flexible HSCT class vehicles, 3) inner loop flight control systems will, in all likelihood, require multiple interacting feedback loops, and 4) Ref. H HSCT configuration presents major challenges to designing acceptable closed-loop flight dynamics.

Feedback regulation between autophagy and PKA.

Science.gov (United States)

Torres-Quiroz, Francisco; Filteau, Marie; Landry, Christian R

2015-01-01

Protein kinase A (PKA) controls diverse cellular processes and homeostasis in eukaryotic cells. Many processes and substrates of PKA have been described and among them are direct regulators of autophagy. The mechanisms of PKA regulation and how they relate to autophagy remain to be fully understood. We constructed a reporter of PKA activity in yeast to identify genes affecting PKA regulation. The assay systematically measures relative protein-protein interactions between the regulatory and catalytic subunits of the PKA complex in a systematic set of genetic backgrounds. The candidate PKA regulators we identified span multiple processes and molecular functions (autophagy, methionine biosynthesis, TORC signaling, protein acetylation, and DNA repair), which themselves include processes regulated by PKA. These observations suggest the presence of many feedback loops acting through this key regulator. Many of the candidate regulators include genes involved in autophagy, suggesting that not only does PKA regulate autophagy but that autophagy also sends signals back to PKA.

Error analysis of acceleration control loops of a synchrotron

International Nuclear Information System (INIS)

Zhang, S.Y.; Weng, W.T.

1991-01-01

For beam control during acceleration, it is conventional to derive the frequency from an external reference, be it a field marker or an external oscillator, to provide phase and radius feedback loops to ensure the phase stability, radial position and emittance integrity of the beam. The open and closed loop behaviors of both feedback control and their response under the possible frequency, phase and radius errors are derived from fundamental principles and equations. The stability of the loops is investigated under a wide range of variations of the gain and time delays. Actual system performance of the AGS Booster is analyzed and compared to commissioning experiences. Such analysis is useful for setting design criteria and tolerances for new proton synchrotrons. 4 refs., 13 figs

Gastric Cancer Cell Proliferation and Survival Is Enabled by a Cyclophilin B/STAT3/miR-520d-5p Signaling Feedback Loop.

Science.gov (United States)

Li, Ting; Guo, Hanqing; Zhao, Xiaodi; Jin, Jiang; Zhang, Lifeng; Li, Hong; Lu, Yuanyuan; Nie, Yongzhan; Wu, Kaichun; Shi, Yongquan; Fan, Daiming

2017-03-01

Molecular links between inflammation and cancer remain obscure despite their great pathogenic significance. The JAK2/STAT3 pathway activated by IL6 and other proinflammatory cytokines has garnered attention as a pivotal link in cancer pathogenesis, but the basis for its activation in cancer cells is not understood. Here we report that an IL6-triggered feedback loop involving STAT3-mediated suppression of miR-520d-5p and upregulation of its downstream target cyclophilin B (CypB) regulate the growth and survival of gastric cancer cells. In clinical specimens of gastric cancer, we documented increased expression of CypB and activation of STAT3. Mechanistic investigations identified miR-520d-5p as a regulator of CypB mRNA levels. This signaling axis regulated gastric cancer growth by modulating phosphorylation of STAT3. Furthermore, miR-520d-5p was identified as a direct STAT3 target and IL6-mediated inhibition of miR-520d-5p relied upon STAT3 activity. Our findings define a positive feedback loop that drives gastric carcinogenesis as influenced by H. pylori infections that involve proinflammatory IL6 stimulation. Cancer Res; 77(5); 1227-40. ©2016 AACR . ©2016 American Association for Cancer Research.

Study of CMOS micromachined self-oscillating loop utilizing a phase-locked loop-driving circuit

International Nuclear Information System (INIS)

Li, Hsin-Chih; Tseng, Sheng-Hsiang; Lu, Michael S.-C.; Huang, Po-Chiun

2012-01-01

This work describes the design and characterization of integrated CMOS (complementary metal oxide semiconductor) oscillators comprising a capacitively transduced micromechanical resonator and a phase-locked loop (PLL) driving circuit. Three oscillator schemes are studied and compared, including direct feedback, direct feedback containing a PLL and hybrid direct feedback plus a PLL. PLL is known for its capability in automatic tuning and tracking of a reference signal. Inclusion of a PLL is beneficial for sustaining oscillations at resonant frequencies within its capture range. The micromechanical resonator has a measured resonant frequency of 117.3 kHz. The CMOS PLL circuit has a closed-loop bandwidth of 1.8 kHz with a capture range between 111 kHz and 118.4 kHz. The start-up times for oscillation are shortened in the two schemes utilizing a PLL, since it provides an initial driving signal at its free-running frequency. The lock-in time is also reduced by increasing the proportion of PLL drive in the hybrid scheme. The measured noises for the three oscillator schemes are similar with a value of −75 dB below the resonant peak at a 10 Hz offset. (paper)

Digital limiter for a self-excited loop

International Nuclear Information System (INIS)

Joshi, G.; Singh, P.; Agarwal, V.; Kumar, G.

2015-01-01

Limiter is one of the main signal processing modules of a self-excited loop (SEL). It plays a crucial role in initiating and stabilizing the amplitude of the RF field in a free running SEL. In a recently reported implementation of a self excited loop in digital domain, the limiter has been realized at based band in the form of a feedback loop. This feedback loop stabilizes the amplitude of the RF phasor present at its input without affecting its phase. In the present work we study the suitability of this implementation of limiter through analysis and simulations. An approximate equivalent model of an SEL, incorporating the digital limiter, is created in analog domain. It is demonstrated that even in the presence for large transients, such as, at the start up of oscillations, SEL continues to exhibit smooth and predictable response. In free running mode of operation the coupling from loop oscillation frequency change to resonator field amplitude change is absent, thus avoiding instability due to electro-mechanical coupling. In the locked mode, the transmission of amplitude jitter through the limiter is far exceeded by that through the controller gain thereby keeping the behavior of the digital SEL close to its analog counterpart. (author)

ProMES: A method for "accepted control loops"

NARCIS (Netherlands)

Tuijl, van H.F.J.M.

1997-01-01

ProMES, a method for the measurement and feedback of performance data is related to the concepts of goal setting and feedback (Locke, 1991; Locke and Latham, 1990), and to the concept of self-control (Bandura, 1991). The result is a model for self-management: the "accepted control loop". Whether

Supporting graduate nurse transition to practice through a quality assurance feedback loop.

Science.gov (United States)

Phillips, Craig; Kenny, Amanda; Esterman, Adrian

2017-11-01

This mixed-method study focused on new graduate nurses and their transition to practice. Transition to practice can be a time of heightened stress and anxiety, leaving many new graduates disillusioned and dissatisfied with their work. The study explored how satisfaction levels with transition may improve during their first year, using a unique approach of a continuous quality assurance feedback loop. This assurance framework is utilised in hospitality, automotive and supply chain logistics and in health, primarily to monitor patient outcomes. However, an association with graduate nurse satisfaction has not been previously reported. Graduate nurses from two health services completed a short survey questionnaire every four weeks for 12 months. De-identified aggregated data was sent to health service management, giving them an opportunity to integrate the findings with the objective of potentially increasing graduate satisfaction ratings. Quantitative findings showed no statistical significance of graduate nurse satisfaction scores between health services, however, one health service consistently outperformed the other. Qualitative findings drawn from a seminar and interviews confirmed that one health service took a more proactive stance with the monthly reports, communicating the results to ward managers. Outcomes reflected a greater commitment of support and an overall increase of satisfaction scores. Copyright © 2017 Elsevier Ltd. All rights reserved.

Virtual sensory feedback for gait improvement in neurological patients

Directory of Open Access Journals (Sweden)

Yoram eBaram

2013-10-01

Full Text Available We review a treatment modality for movement disorders by sensory feedback. The natural closed-loop sensory-motor feedback system is imitated by a wearable virtual reality apparatus, employing body-mounted inertial sensors and responding dynamically to the patient’s own motion. Clinical trials have shown a significant gait improvement in patients with Parkinson's disease using the apparatus. In contrast to open-loop devices, which impose constant-velocity visual cues in a treadmill fashion, or rhythmic auditory cues in a metronome fashion, requiring constant vigilance and attention strategies, and in some cases, instigating freezing in Parkinson’s patients, the closed-loop device improved gait parameters and eliminated freezing in most patients, without side effects. Patients with multiple sclerosis, previous stroke, senile gait and cerebral palsy using the device also improved their balance and gait substantially. Training with the device has produced a residual improvement, suggesting virtual sensory feedback for the treatment of neurological movement disorders.

Quantum feedback for rapid state preparation in the presence of control imperfections

International Nuclear Information System (INIS)

Combes, Joshua; Wiseman, Howard M

2011-01-01

Quantum feedback control protocols can improve the operation of quantum devices. Here we examine the performance of a purification protocol when there are imperfections in the controls. The ideal feedback protocol produces an x-eigenstate from a mixed state in the minimum time, and is known as rapid state preparation. The imperfections we examine include time delays in the feedback loop, finite strength feedback, calibration errors and inefficient detection. We analyse these imperfections using the Wiseman-Milburn feedback master equation and related formalism. We find that the protocol is most sensitive to time delays in the feedback loop. For systems with slow dynamics, however, our analysis suggests that inefficient detection would be the bigger problem. We also show how system imperfections, such as dephasing and damping, can be included in a model via the feedback master equation.

A Negative Feedback Loop Between Autophagy and Immune Responses in Mycobacterium leprae Infection.

Science.gov (United States)

Ma, Yuelong; Zhang, Li; Lu, Jie; Shui, Tiejun; Chen, Jia; Yang, Jun; Yuan, Joanna; Liu, Yeqiang; Yang, Degang

2017-01-01

The obligate intracellular bacterium Mycobacterium leprae is the causative agent of leprosy and primarily infects macrophages, leading to irreversible nerve damage and deformities. So far, the underlying reasons allowing M. leprae to persist and propagate in macrophages, despite the presence of cellular immunity, are still a mystery. Here, we investigated the role of autophagy, a cellular process that degrades cytosolic materials and intracellular pathogens, in M. leprae infection. We found that live M. leprae infection of macrophages resulted in significantly elevated autophagy level. However, macrophages with high autophagy levels preferentially expressed lower levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, IL-12, and tumor necrosis factor-α, and preferentially primed anti-inflammatory T cells responses, characterized by high IL-10 and low interferon-γ, granzyme B, and perforin responses. These anti-inflammatory T cells could suppress further induction of autophagy, leading to improved survival of intracellular M. leprae in infected macrophages. Therefore, these data demonstrated that although autophagy had a role in eliminating intracellular pathogens, the induction of autophagy resulted in anti-inflammatory immune responses, which suppressed autophagy in a negative feedback loop and allowed the persistence of M. leprae.

RF feedback simulation results for PEP-II

International Nuclear Information System (INIS)

Tighe, R.; Corredoura, P.

1995-06-01

A model of the RF feedback system for PEP-II has been developed to provide time-domain simulation and frequency-domain analysis of the complete system. The model includes the longitudinal beam dynamics, cavity fundamental resonance, feedback loops, and the nonlinear klystron operating near saturation. Transients from an ion clearing gap and a reference phase modulation from the longitudinal feedback system are also studied. Growth rates are predicted and overall system stability examined

Explicit knowledge about the availability of visual feedback affects grasping with the left but not the right hand.

Science.gov (United States)

Tang, Rixin; Whitwell, Robert L; Goodale, Melvyn A

2014-01-01

Previous research (Whitwell et al. in Exp Brain Res 188:603-611, 2008; Whitwell and Goodale in Exp Brain Res 194:619-629, 2009) has shown that trial history, but not anticipatory knowledge about the presence or absence of visual feedback on an upcoming trial, plays a vital role in determining how that feedback is exploited when grasping with the right hand. Nothing is known about how the non-dominant left hand behaves under the same feedback regimens. In present study, therefore, we compared peak grip aperture (PGA) for left- and right-hand grasps executed with and without visual feedback (i.e., closed- vs. open-loop conditions) in right-handed individuals under three different trial schedules: the feedback conditions were blocked separately, they were randomly interleaved, or they were alternated. When feedback conditions were blocked, the PGA was much larger for open-loop trials as compared to closed-loop trials, although this difference was more pronounced for right-hand grasps than left-hand grasps. Like Whitwell et al., we found that mixing open- and closed-loop trials together, compared to blocking them separately, homogenized the PGA for open- and closed-loop grasping in the right hand (i.e., the PGAs became smaller on open-loop trials and larger on closed-loop trials). In addition, the PGAs for right-hand grasps were entirely determined by trial history and not by knowledge of whether or not visual feedback would be available on an upcoming trial. In contrast to grasps made with the right hand, grasps made by the left hand were affected both by trial history and by anticipatory knowledge of the upcoming visual feedback condition. But these effects were observed only on closed-loop trials, i.e., the PGAs of grasps made with the left hand on closed-loop trials were smaller when participants could anticipate the availability of feedback on an upcoming trial (alternating trials) than when they could not (randomized trials). In contrast, grasps made with the

Closed-loop feedback of MHD instabilities on DIII-D

Energy Technology Data Exchange (ETDEWEB)

Fredrickson, E.D.; Johnson, L.C.; Manickam, J.; Okabayashi, M. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Bialek, J.; Garofalo, A.M.; Navratil, G.A. [Columbia University, New York, NY 10027 (United States); La Haye, R.J.; Scoville, J.T.; Strait, E.J. [General Atomics, La Jolla, CA 92186 (United States); Lazarus, E.A. [Oak Ridge National Laboratory, Oak Ridge, TN 37830 (United States)

2001-03-01

A system of coils, sensors and amplifiers has been installed on the DIII-D tokamak to study the physics of feedback stabilization of low-frequency MHD modes such as the resistive wall mode (RWM). Experiments are being performed to assess the effectiveness of this minimal system and benchmark the predictions of theoretical models and codes. In the last campaign the experiments had been extended to a regime where the RWM threshold is lowered by a fast ramp of the plasma current. In these experiments the onset time of the RWM is very reproducible. With this system, the onset of the RWM had been delayed by up to 100 ms without degrading the plasma performance. The growth rate of the mode increases proportional to the length of the delay, suggesting that the plasma is evolving towards a more unstable configuration. The present results have suggested directions for improving the feedback system, including better sensors and improved feedback algorithms. (author)

Numerical Simulation of the Oscillations in a Mixer: An Internal Aeroacoustic Feedback System

Science.gov (United States)

Jorgenson, Philip C. E.; Loh, Ching Y.

2004-01-01

The space-time conservation element and solution element method is employed to numerically study the acoustic feedback system in a high temperature, high speed wind tunnel mixer. The computation captures the self-sustained feedback loop between reflecting Mach waves and the shear layer. This feedback loop results in violent instabilities that are suspected of causing damage to some tunnel components. The computed frequency is in good agreement with the available experimental data. The physical phenomena are explained based on the numerical results.

Bidirectional neural interface: Closed-loop feedback control for hybrid neural systems.

Science.gov (United States)

Chou, Zane; Lim, Jeffrey; Brown, Sophie; Keller, Melissa; Bugbee, Joseph; Broccard, Frédéric D; Khraiche, Massoud L; Silva, Gabriel A; Cauwenberghs, Gert

2015-01-01

Closed-loop neural prostheses enable bidirectional communication between the biological and artificial components of a hybrid system. However, a major challenge in this field is the limited understanding of how these components, the two separate neural networks, interact with each other. In this paper, we propose an in vitro model of a closed-loop system that allows for easy experimental testing and modification of both biological and artificial network parameters. The interface closes the system loop in real time by stimulating each network based on recorded activity of the other network, within preset parameters. As a proof of concept we demonstrate that the bidirectional interface is able to establish and control network properties, such as synchrony, in a hybrid system of two neural networks more significantly more effectively than the same system without the interface or with unidirectional alternatives. This success holds promise for the application of closed-loop systems in neural prostheses, brain-machine interfaces, and drug testing.

Switching of the positive feedback for RAS activation by a concerted function of SOS membrane association domains.

Science.gov (United States)

Nakamura, Yuki; Hibino, Kayo; Yanagida, Toshio; Sako, Yasushi

2016-01-01

Son of sevenless (SOS) is a guanine nucleotide exchange factor that regulates cell behavior by activating the small GTPase RAS. Recent in vitro studies have suggested that an interaction between SOS and the GTP-bound active form of RAS generates a positive feedback loop that propagates RAS activation. However, it remains unclear how the multiple domains of SOS contribute to the regulation of the feedback loop in living cells. Here, we observed single molecules of SOS in living cells to analyze the kinetics and dynamics of SOS behavior. The results indicate that the histone fold and Grb2-binding domains of SOS concertedly produce an intermediate state of SOS on the cell surface. The fraction of the intermediated state was reduced in positive feedback mutants, suggesting that the feedback loop functions during the intermediate state. Translocation of RAF, recognizing the active form of RAS, to the cell surface was almost abolished in the positive feedback mutants. Thus, the concerted functions of multiple membrane-associating domains of SOS governed the positive feedback loop, which is crucial for cell fate decision regulated by RAS.

Open loop thanks to direct torque control (DTC). Motor control without feedback loop; Open loop dank direkter Drehmomentregelung (DTC). Hochwertige Motorregelung ohne Rueckfuehrung

Energy Technology Data Exchange (ETDEWEB)

Link, Michael [ABB Automation Products GmbH, Ladenburg (Germany)

2009-07-01

Servo drives are used in various applications. The range of applications is huge and thus also requirements to the drive system. Mainly, a fast torque and speed control is required. This is the domaine of direct torque control (DTC). In many applications DTC can meet this challenge to control the motor with full torque at zero speed. The servo converter based on DTC technology provides a control concept for synchronous and asynchronous motors for both closed loop and open loop control. DTC controlled drives support the whole range from open loop up to high performance motion control applications. (orig.)

Closed-loop model identification of cooperative manipulators holding deformable objects

Science.gov (United States)

Alkathiri, A. A.; Akmeliawati, R.; Azlan, N. Z.

2017-11-01

This paper presents system identification to obtain the closed-loop models of a couple of cooperative manipulators in a system, which function to hold deformable objects. The system works using the master-slave principle. In other words, one of the manipulators is position-controlled through encoder feedback, while a force sensor gives feedback to the other force-controlled manipulator. Using the closed-loop input and output data, the closed-loop models, which are useful for model-based control design, are estimated. The criteria for model validation are a 95% fit between the measured and simulated output of the estimated models and residual analysis. The results show that for both position and force control respectively, the fits are 95.73% and 95.88%.

Watch what you type: the role of visual feedback from the screen and hands in skilled typewriting.

Science.gov (United States)

Snyder, Kristy M; Logan, Gordon D; Yamaguchi, Motonori

2015-01-01

Skilled typing is controlled by two hierarchically structured processing loops (Logan & Crump, 2011): The outer loop, which produces words, commands the inner loop, which produces keystrokes. Here, we assessed the interplay between the two loops by investigating how visual feedback from the screen (responses either were or were not echoed on the screen) and the hands (the hands either were or were not covered with a box) influences the control of skilled typing. Our results indicated, first, that the reaction time of the first keystroke was longer when responses were not echoed than when they were. Also, the interkeystroke interval (IKSI) was longer when the hands were covered than when they were visible, and the IKSI for responses that were not echoed was longer when explicit error monitoring was required (Exp. 2) than when it was not required (Exp. 1). Finally, explicit error monitoring was more accurate when response echoes were present than when they were absent, and implicit error monitoring (i.e., posterror slowing) was not influenced by visual feedback from the screen or the hands. These findings suggest that the outer loop adjusts the inner-loop timing parameters to compensate for reductions in visual feedback. We suggest that these adjustments are preemptive control strategies designed to execute keystrokes more cautiously when visual feedback from the hands is absent, to generate more cautious motor programs when visual feedback from the screen is absent, and to enable enough time for the outer loop to monitor keystrokes when visual feedback from the screen is absent and explicit error reports are required.

PNRA Process for Utilizing Experience Feedback for Enhancing Nuclear Safety

International Nuclear Information System (INIS)

Shah, Z.H.

2016-01-01

One of the elements essential for any organization to become a learning organization is to learn from its own and others experience. The importance of utilizing experience feedback for enhancing operational safety is highlighted in nuclear industry again and again and this has resulted in establishment of several national and international forums. In addition, IAEA action plan on nuclear safety issued after Fukushima accident further highlighted the importance of experience sharing among nuclear community to enhance global nuclear safety regime. PNRA utilizes operating experience feedback gathered through different sources in order to improve its regulatory processes. During the review of licensing submissions, special emphasis is given to utilize the lessons learnt from experience feedback relating to nuclear industry within and outside the country. This emphasis has gradually resulted in various safety improvements in the facilities and processes. Accordingly, PNRA has developed a systematic process of evaluation of international operating experience feedback with the aim to create safety conscious approach. This process includes collecting information from different international forums such as IAEA, regulatory bodies of other countries and useful feedback of past accidents followed by its screening, evaluation and suggesting recommendations both for PNRA and its licensees. As a result of this process, several improvements concerning regulatory inspection plans of PNRA as well as in regulatory decision making and operational practices of licensees have been highlighted. This paper will present PNRA approach for utilizing experience feedback in its regulatory processes for enhancing / improving nuclear safety. (author)

General, database-driven fast-feedback system for the Stanford Linear Collider

International Nuclear Information System (INIS)

Rouse, F.; Allison, S.; Castillo, S.; Gromme, T.; Hall, B.; Hendrickson, L.; Himel, T.; Krauter, K.; Sass, B.; Shoaee, H.

1991-05-01

A new feedback system has been developed for stabilizing the SLC beams at many locations. The feedback loops are designed to sample and correct at the 60 Hz repetition rate of the accelerator. Each loop can be distributed across several of the standard 80386 microprocessors which control the SLC hardware. A new communications system, KISNet, has been implemented to pass signals between the microprocessors at this rate. The software is written in a general fashion using the state space formalism of digital control theory. This allows a new loop to be implemented by just setting up the online database and perhaps installing a communications link. 3 refs., 4 figs

Application of non-linear discretetime feedback regulators with assignable closed-loop dynamics

Directory of Open Access Journals (Sweden)

Dubljević Stevan

2003-01-01

Full Text Available In the present work the application of a new approach is demonstrated to a discrete-time state feedback regulator synthesis with feedback linearization and pole-placement for non-linear discrete-time systems. Under the simultaneous implementation of a non-linear coordinate transformation and a non-linear state feedback law computed through the solution of a system of non-linear functional equations, both the feedback linearization and pole-placement design objectives were accomplished. The non-linear state feedback regulator synthesis method was applied to a continuous stirred tank reactor (CSTR under non-isothermal operating conditions that exhibits steady-state multiplicity. The control objective was to regulate the reactor at the middle unstable steady state by manipulating the rate of input heat in the reactor. Simulation studies were performed to evaluate the performance of the proposed non-linear state feedback regulator, as it was shown a non-linear state feedback regulator clearly outperformed a standard linear one, especially in the presence of adverse disturbance under which linear regulation at the unstable steady state was not feasible.

Passive mode locking and formation of dissipative solitons in electron oscillators with a bleaching absorber in the feedback loop

Energy Technology Data Exchange (ETDEWEB)

Ginzburg, N. S., E-mail: ginzburg@appl.sci-nnov.ru; Kocharovskaya, E. R.; Vilkov, M. N.; Sergeev, A. S. [Russian Academy of Sciences, Institute of Applied Physics (Russian Federation)

2017-01-15

The mechanisms of passive mode locking and formation of ultrashort pulses in microwave electron oscillators with a bleaching absorber in the feedback loop have been analyzed. It is shown that in the group synchronism regime in which the translational velocity of particles coincides with the group velocity of the electromagnetic wave, the pulse formation can be described by the equations known in the theory of dissipative solitons. At the same time, the regimes in which the translational velocity of electrons differs from the group velocity and the soliton being formed and moving along the electron beam consecutively (cumulatively) receives energy from various electron fractions are optimal for generating pulses with the maximal peak amplitudes.

Multi-bunch feedback systems

CERN Document Server

Lonza, M

2008-01-01

Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. The advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. The lecture will first introduce coupled-bunch instabilities analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedbacks systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback sy...

Multi-bunch Feedback Systems

CERN Document Server

Lonza, M.

2014-12-19

Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. Advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. We first introduce coupled-bunch instabilities, analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedback systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback systems. The main co...

Closed-Loop and Robust Control of Quantum Systems

Directory of Open Access Journals (Sweden)

Chunlin Chen

2013-01-01

Full Text Available For most practical quantum control systems, it is important and difficult to attain robustness and reliability due to unavoidable uncertainties in the system dynamics or models. Three kinds of typical approaches (e.g., closed-loop learning control, feedback control, and robust control have been proved to be effective to solve these problems. This work presents a self-contained survey on the closed-loop and robust control of quantum systems, as well as a brief introduction to a selection of basic theories and methods in this research area, to provide interested readers with a general idea for further studies. In the area of closed-loop learning control of quantum systems, we survey and introduce such learning control methods as gradient-based methods, genetic algorithms (GA, and reinforcement learning (RL methods from a unified point of view of exploring the quantum control landscapes. For the feedback control approach, the paper surveys three control strategies including Lyapunov control, measurement-based control, and coherent-feedback control. Then such topics in the field of quantum robust control as H∞ control, sliding mode control, quantum risk-sensitive control, and quantum ensemble control are reviewed. The paper concludes with a perspective of future research directions that are likely to attract more attention.

Closed-loop and robust control of quantum systems.

Science.gov (United States)

Chen, Chunlin; Wang, Lin-Cheng; Wang, Yuanlong

2013-01-01

For most practical quantum control systems, it is important and difficult to attain robustness and reliability due to unavoidable uncertainties in the system dynamics or models. Three kinds of typical approaches (e.g., closed-loop learning control, feedback control, and robust control) have been proved to be effective to solve these problems. This work presents a self-contained survey on the closed-loop and robust control of quantum systems, as well as a brief introduction to a selection of basic theories and methods in this research area, to provide interested readers with a general idea for further studies. In the area of closed-loop learning control of quantum systems, we survey and introduce such learning control methods as gradient-based methods, genetic algorithms (GA), and reinforcement learning (RL) methods from a unified point of view of exploring the quantum control landscapes. For the feedback control approach, the paper surveys three control strategies including Lyapunov control, measurement-based control, and coherent-feedback control. Then such topics in the field of quantum robust control as H(∞) control, sliding mode control, quantum risk-sensitive control, and quantum ensemble control are reviewed. The paper concludes with a perspective of future research directions that are likely to attract more attention.

Cholesterol-induced conformational changes in the sterol-sensing domain of the Scap protein suggest feedback mechanism to control cholesterol synthesis.

Science.gov (United States)

Gao, Yansong; Zhou, Yulian; Goldstein, Joseph L; Brown, Michael S; Radhakrishnan, Arun

2017-05-26

Scap is a polytopic protein of endoplasmic reticulum (ER) membranes that transports sterol regulatory element-binding proteins to the Golgi complex for proteolytic activation. Cholesterol accumulation in ER membranes prevents Scap transport and decreases cholesterol synthesis. Previously, we provided evidence that cholesterol inhibition is initiated when cholesterol binds to loop 1 of Scap, which projects into the ER lumen. Within cells, this binding causes loop 1 to dissociate from loop 7, another luminal Scap loop. However, we have been unable to demonstrate this dissociation when we added cholesterol to isolated complexes of loops 1 and 7. We therefore speculated that the dissociation requires a conformational change in the intervening polytopic sequence separating loops 1 and 7. Here we demonstrate such a change using a protease protection assay in sealed membrane vesicles. In the absence of cholesterol, trypsin or proteinase K cleaved cytosolic loop 4, generating a protected fragment that we visualized with a monoclonal antibody against loop 1. When cholesterol was added to these membranes, cleavage in loop 4 was abolished. Because loop 4 is part of the so-called sterol-sensing domain separating loops 1 and 7, these results support the hypothesis that cholesterol binding to loop 1 alters the conformation of the sterol-sensing domain. They also suggest that this conformational change helps transmit the cholesterol signal from loop 1 to loop 7, thereby allowing separation of the loops and facilitating the feedback inhibition of cholesterol synthesis. These insights suggest a new structural model for cholesterol-mediated regulation of Scap activity. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Correction: The role of coupled positive feedback in the expression of the SPI1 type three secretion system in Salmonella.

Directory of Open Access Journals (Sweden)

Supreet Saini

2010-08-01

Full Text Available Salmonella enterica serovar Typhimurium is a common food-borne pathogen that induces inflammatory diarrhea and invades intestinal epithelial cells using a type three secretion system (T3SS encoded within Salmonella pathogenicity island 1 (SPI1. The genes encoding the SPI1 T3SS are tightly regulated by a network of interacting transcriptional regulators involving three coupled positive feedback loops. While the core architecture of the SPI1 gene circuit has been determined, the relative roles of these interacting regulators and associated feedback loops are still unknown. To determine the function of this circuit, we measured gene expression dynamics at both population and single-cell resolution in a number of SPI1 regulatory mutants. Using these data, we constructed a mathematical model of the SPI1 gene circuit. Analysis of the model predicted that the circuit serves two functions. The first is to place a threshold on SPI1 activation, ensuring that the genes encoding the T3SS are expressed only in response to the appropriate combination of environmental and cellular cues. The second is to amplify SPI1 gene expression. To experimentally test these predictions, we rewired the SPI1 genetic circuit by changing its regulatory architecture. This enabled us to directly test our predictions regarding the function of the circuit by varying the strength and dynamics of the activating signal. Collectively, our experimental and computational results enable us to deconstruct this complex circuit and determine the role of its individual components in regulating SPI1 gene expression dynamics.

The interplay of multiple feedback loops with post-translational kinetics results in bistability of mycobacterial stress response

International Nuclear Information System (INIS)

Tiwari, Abhinav; Igoshin, Oleg A; Balázsi, Gábor; Gennaro, Maria Laura

2010-01-01

Bacterial persistence is the phenomenon in which a genetically identical fraction of a bacterial population can survive exposure to stress by reduction or cessation of growth. Persistence in mycobacteria has been recently linked to a stress-response network, consisting of the MprA/MprB two-component system and alternative sigma factor σ E . This network contains multiple positive transcriptional feedback loops which may give rise to bistability, making it a good candidate for controlling the mycobacterial persistence switch. To analyze the possibility of bistability, we develop a method that involves decoupling of the network into transcriptional and post-translational interaction modules. As a result we reduce the dimensionality of the dynamical system and independently analyze input–output relations in the two modules to formulate a necessary condition for bistability in terms of their logarithmic gains. We show that neither the positive autoregulation in the MprA/MprB network nor the σ E -mediated transcriptional feedback is sufficient to induce bistability in a biochemically realistic parameter range. Nonetheless, inclusion of the post-translational regulation of σ E by RseA increases the effective cooperativity of the system, resulting in bistability that is robust to parameter variation. We predict that overexpression or deletion of RseA, the key element controlling the ultrasensitive response, can eliminate bistability

An investigation into closed-loop treatment of neurological disorders based on sensing mitochondrial dysfunction.

Science.gov (United States)

Adams, Scott D; Kouzani, Abbas Z; Tye, Susannah J; Bennet, Kevin E; Berk, Michael

2018-02-13

Dynamic feedback based closed-loop medical devices offer a number of advantages for treatment of heterogeneous neurological conditions. Closed-loop devices integrate a level of neurobiological feedback, which allows for real-time adjustments to be made with the overarching aim of improving treatment efficacy and minimizing risks for adverse events. One target which has not been extensively explored as a potential feedback component in closed-loop therapies is mitochondrial function. Several neurodegenerative and psychiatric disorders including Parkinson's disease, Major Depressive disorder and Bipolar disorder have been linked to perturbations in the mitochondrial respiratory chain. This paper investigates the potential to monitor this mitochondrial function as a method of feedback for closed-loop neuromodulation treatments. A generic model of the closed-loop treatment is developed to describe the high-level functions of any system designed to control neural function based on mitochondrial response to stimulation, simplifying comparison and future meta-analysis. This model has four key functional components including: a sensor, signal manipulator, controller and effector. Each of these components are described and several potential technologies for each are investigated. While some of these candidate technologies are quite mature, there are still technological gaps remaining. The field of closed-loop medical devices is rapidly evolving, and whilst there is a lot of interest in this area, widespread adoption has not yet been achieved due to several remaining technological hurdles. However, the significant therapeutic benefits offered by this technology mean that this will be an active area for research for years to come.

Parallel arrangements of positive feedback loops limit cell-to-cell variability in differentiation.

Science.gov (United States)

Dey, Anupam; Barik, Debashis

2017-01-01

Cellular differentiations are often regulated by bistable switches resulting from specific arrangements of multiple positive feedback loops (PFL) fused to one another. Although bistability generates digital responses at the cellular level, stochasticity in chemical reactions causes population heterogeneity in terms of its differentiated states. We hypothesized that the specific arrangements of PFLs may have evolved to minimize the cellular heterogeneity in differentiation. In order to test this we investigated variability in cellular differentiation controlled either by parallel or serial arrangements of multiple PFLs having similar average properties under extrinsic and intrinsic noises. We find that motifs with PFLs fused in parallel to one another around a central regulator are less susceptible to noise as compared to the motifs with PFLs arranged serially. Our calculations suggest that the increased resistance to noise in parallel motifs originate from the less sensitivity of bifurcation points to the extrinsic noise. Whereas estimation of mean residence times indicate that stable branches of bifurcations are robust to intrinsic noise in parallel motifs as compared to serial motifs. Model conclusions are consistent both in AND- and OR-gate input signal configurations and also with two different modeling strategies. Our investigations provide some insight into recent findings that differentiation of preadipocyte to mature adipocyte is controlled by network of parallel PFLs.

Engineering the on-axis intensity of Bessel beam by a feedback tuning loop

Science.gov (United States)

Li, Runze; Yu, Xianghua; Yang, Yanlong; Peng, Tong; Yao, Baoli; Zhang, Chunmin; Ye, Tong

2018-02-01

The Bessel beam belongs to a typical class of non-diffractive optical fields that are characterized by their invariant focal profiles along the propagation direction. However, ideal Bessel beams only rigorously exist in theory; Bessel beams generated in the lab are quasi-Bessel beams with finite focal extensions and varying intensity profiles along the propagation axis. The ability to engineer the on-axis intensity profile to the desired shape is essential for many applications. Here we demonstrate an iterative optimization-based approach to engineering the on-axis intensity of Bessel beams. The genetic algorithm is used to demonstrate this approach. Starting with a traditional axicon phase mask, in the design process, the computed on-axis beam profile is fed into a feedback tuning loop of an iterative optimization process, which searches for an optimal radial phase distribution that can generate a generalized Bessel beam with the desired onaxis intensity profile. The experimental implementation involves a fine-tuning process that adjusts the originally targeted profile so that the optimization process can optimize the phase mask to yield an improved on-axis profile. Our proposed method has been demonstrated in engineering several zeroth-order Bessel beams with customized on-axis profiles. High accuracy and high energy throughput merit its use in many applications.

Possible hysteresis loops of resonatorless optical bistability

International Nuclear Information System (INIS)

Nguyen Ba An; Le Thi Cat Tuong.

1990-05-01

We qualitatively show that hysteresis loops of intrinsic optical bistability phenomena without any additional feedback may be of various shapes including those of a butterfly and a three-winged bow. (author). 15 refs, 4 figs

The Drosophila Duox maturation factor is a key component of a positive feedback loop that sustains regeneration signaling.

Science.gov (United States)

Khan, Sumbul Jawed; Abidi, Syeda Nayab Fatima; Skinner, Andrea; Tian, Yuan; Smith-Bolton, Rachel K

2017-07-01

Regenerating tissue must initiate the signaling that drives regenerative growth, and sustain that signaling long enough for regeneration to complete. How these key signals are sustained is unclear. To gain a comprehensive view of the changes in gene expression that occur during regeneration, we performed whole-genome mRNAseq of actively regenerating tissue from damaged Drosophila wing imaginal discs. We used genetic tools to ablate the wing primordium to induce regeneration, and carried out transcriptional profiling of the regeneration blastema by fluorescently labeling and sorting the blastema cells, thus identifying differentially expressed genes. Importantly, by using genetic mutants of several of these differentially expressed genes we have confirmed that they have roles in regeneration. Using this approach, we show that high expression of the gene moladietz (mol), which encodes the Duox-maturation factor NIP, is required during regeneration to produce reactive oxygen species (ROS), which in turn sustain JNK signaling during regeneration. We also show that JNK signaling upregulates mol expression, thereby activating a positive feedback signal that ensures the prolonged JNK activation required for regenerative growth. Thus, by whole-genome transcriptional profiling of regenerating tissue we have identified a positive feedback loop that regulates the extent of regenerative growth.

Commissioning of FPGA-based Transverse and Longitudinal Bunch-by-Bunch Feedback System for the TLS

International Nuclear Information System (INIS)

Hu, K. H.; Kuo, C. H.; Lau, W. K.; Yeh, M. S.; Hsu, S. Y.; Chou, P. J.; Wang, M. H.; Lee, Demi; Chen, Jenny; Wang, C. J.; Hsu, K. T.; Kobayashi, K.; Nakamura, T.; Dehler, M.

2006-01-01

Multi-bunch instabilities deteriorate beam quality, increasing beam emittance, or even causing beam loss in the synchrotron light source. The feedback system is essential to suppress multi-bunch instabilities caused by the impedances of beam ducts, and trapped ions. A new FPGA based transverse and longitudinal bunch-by-bunch feedback system have been commissioned at the Taiwan Light Source recently, A single feedback loop is used to simultaneously suppress the horizontal and the vertical multi-bunch instabilities. Longitudinal instabilities caused by cavity-like structures are suppressed by the longitudinal feedback loop. The same FPGA processor is employed in the transverse feedback and the longitudinal feedback system respectively. Diagnostic memory is included in the system to capture the bunch oscillation signal, which supports various studies

A Positive Regulatory Loop between a Wnt-Regulated Non-coding RNA and ASCL2 Controls Intestinal Stem Cell Fate.

Science.gov (United States)

Giakountis, Antonis; Moulos, Panagiotis; Zarkou, Vasiliki; Oikonomou, Christina; Harokopos, Vaggelis; Hatzigeorgiou, Artemis G; Reczko, Martin; Hatzis, Pantelis

2016-06-21

The canonical Wnt pathway plays a central role in stem cell maintenance, differentiation, and proliferation in the intestinal epithelium. Constitutive, aberrant activity of the TCF4/β-catenin transcriptional complex is the primary transforming factor in colorectal cancer. We identify a nuclear long non-coding RNA, termed WiNTRLINC1, as a direct target of TCF4/β-catenin in colorectal cancer cells. WiNTRLINC1 positively regulates the expression of its genomic neighbor ASCL2, a transcription factor that controls intestinal stem cell fate. WiNTRLINC1 interacts with TCF4/β-catenin to mediate the juxtaposition of its promoter with the regulatory regions of ASCL2. ASCL2, in turn, regulates WiNTRLINC1 transcriptionally, closing a feedforward regulatory loop that controls stem cell-related gene expression. This regulatory circuitry is highly amplified in colorectal cancer and correlates with increased metastatic potential and decreased patient survival. Our results uncover the interplay between non-coding RNA-mediated regulation and Wnt signaling and point to the diagnostic and therapeutic potential of WiNTRLINC1. Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.

Study on real-time force feedback for a master-slave interventional surgical robotic system.

Science.gov (United States)

Guo, Shuxiang; Wang, Yuan; Xiao, Nan; Li, Youxiang; Jiang, Yuhua

2018-04-13

In robot-assisted catheterization, haptic feedback is important, but is currently lacking. In addition, conventional interventional surgical robotic systems typically employ a master-slave architecture with an open-loop force feedback, which results in inaccurate control. We develop herein a novel real-time master-slave (RTMS) interventional surgical robotic system with a closed-loop force feedback that allows a surgeon to sense the true force during remote operation, provide adequate haptic feedback, and improve control accuracy in robot-assisted catheterization. As part of this system, we also design a unique master control handle that measures the true force felt by a surgeon, providing the basis for the closed-loop control of the entire system. We use theoretical and empirical methods to demonstrate that the proposed RTMS system provides a surgeon (using the master control handle) with a more accurate and realistic force sensation, which subsequently improves the precision of the master-slave manipulation. The experimental results show a substantial increase in the control accuracy of the force feedback and an increase in operational efficiency during surgery.

Modeling and simulation of Indus-2 RF feedback control system

International Nuclear Information System (INIS)

Sharma, D.; Bagduwal, P.S.; Tiwari, N.; Lad, M.; Hannurkar, P.R.

2012-01-01

Indus-2 synchrotron radiation source has four RF stations along with their feedback control systems. For higher beam energy and current operation amplitude and phase feedback control systems of Indus-2 are being upgraded. To understand the behaviour of amplitude and phase control loop under different operating conditions, modelling and simulation of RF feedback control system is done. RF cavity baseband I/Q model has been created due to its close correspondence with actual implementation and better computational efficiency which makes the simulation faster. Correspondence between cavity baseband and RF model is confirmed by comparing their simulation results. Low Level RF (LLRF) feedback control system simulation is done using the same cavity baseband I/Q model. Error signals are intentionally generated and response of the closed loop system is observed. Simulation will help us in optimizing parameters of upgraded LLRF system for higher beam energy and current operation. (author)

Multi-bunch Feedback Systems

International Nuclear Information System (INIS)

Lonza, M; Schmickler, H

2014-01-01

Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. Advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. We first introduce coupled-bunch instabilities, analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedback systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback systems. The main components of a feedback system and the related issues will also be analysed. Finally, we shall focus on digital feedback systems, their characteristics, and features, as well as on how they can be concretely exploited for both the optimization of feedback performance and for beam dynamics studies

Comparison of squashing and self-consistent input-output models of quantum feedback

Science.gov (United States)

Peřinová, V.; Lukš, A.; Křepelka, J.

2018-03-01

The paper (Yanagisawa and Hope, 2010) opens with two ways of analysis of a measurement-based quantum feedback. The scheme of the feedback includes, along with the homodyne detector, a modulator and a beamsplitter, which does not enable one to extract the nonclassical field. In the present scheme, the beamsplitter is replaced by the quantum noise evader, which makes it possible to extract the nonclassical field. We re-approach the comparison of two models related to the same scheme. The first one admits that in the feedback loop between the photon annihilation and creation operators, unusual commutation relations hold. As a consequence, in the feedback loop, squashing of the light occurs. In the second one, the description arrives at the feedback loop via unitary transformations. But it is obvious that the unitary transformation which describes the modulator changes even the annihilation operator of the mode which passes by the modulator which is not natural. The first model could be called "squashing model" and the second one could be named "self-consistent model". Although the predictions of the two models differ only a little and both the ways of analysis have their advantages, they have also their drawbacks and further investigation is possible.

LHX2 Mediates the FGF-to-SHH Regulatory Loop during Limb Development

Directory of Open Access Journals (Sweden)

Billy A. Watson

2018-06-01

Full Text Available During limb development, fibroblast growth factors (Fgfs govern proximal–distal outgrowth and patterning. FGFs also synchronize developmental patterning between the proximal–distal and anterior–posterior axes by maintaining Sonic hedgehog (Shh expression in cells of the zone of polarizing activity (ZPA in the distal posterior mesoderm. Shh, in turn, maintains Fgfs in the apical ectodermal ridge (AER that caps the distal tip of the limb bud. Crosstalk between Fgf and Shh signaling is critical for patterned limb development, but the mechanisms underlying this feedback loop are not well-characterized. Implantation of Fgf beads in the proximal posterior limb bud can maintain SHH expression in the former ZPA domain (evident 3 h after application, while prolonged exposure (24 h can induce SHH outside of this domain. Although temporally and spatially disparate, comparative analysis of transcriptome data from these different populations accentuated genes involved in SHH regulation. Comparative analysis identified 25 candidates common to both treatments, with eight linked to SHH expression or function. Furthermore, we demonstrated that LHX2, a LIM Homeodomain transcription factor, is an intermediate in the FGF-mediated regulation of SHH. Our data suggest that LHX2 acts as a competency factor maintaining distal posterior SHH expression subjacent to the AER.

A novel approach to negative feedback in RX front-ends

DEFF Research Database (Denmark)

Vandi, Luca; Andreani, Pietro; Tired, Tobias

2006-01-01

A new approach to negative feedback is proposed and applied to active mixer cells based on Gilbert multiplier. The feedback can be exploited in several ways, and different configurations are derived. A dual-loop topology provides a solution for inductor-less broad-band receiver stages. The nature...

Hepatitis B virus nuclear export elements: RNA stem-loop α and β, key parts of the HBV post-transcriptional regulatory element.

Science.gov (United States)

Lim, Chun Shen; Brown, Chris M

2016-09-01

Many viruses contain RNA elements that modulate splicing and/or promote nuclear export of their RNAs. The RNAs of the major human pathogen, hepatitis B virus (HBV) contain a large (~600 bases) composite cis-acting 'post-transcriptional regulatory element' (PRE). This element promotes expression from these naturally intronless transcripts. Indeed, the related woodchuck hepadnavirus PRE (WPRE) is used to enhance expression in gene therapy and other expression vectors. These PRE are likely to act through a combination of mechanisms, including promotion of RNA nuclear export. Functional components of both the HBV PRE and WPRE are 2 conserved RNA cis-acting stem-loop (SL) structures, SLα and SLβ. They are within the coding regions of polymerase (P) gene, and both P and X genes, respectively. Based on previous studies using mutagenesis and/or nuclear magnetic resonance (NMR), here we propose 2 covariance models for SLα and SLβ. The model for the 30-nucleotide SLα contains a G-bulge and a CNGG(U) apical loop of which the first and the fourth loop residues form a CG pair and the fifth loop residue is bulged out, as observed in the NMR structure. The model for the 23-nucleotide SLβ contains a 7-base-pair stem and a 9-nucleotide loop. Comparison of the models with other RNA structural elements, as well as similarity searches of human transcriptome and viral genomes demonstrate that SLα and SLβ are specific to HBV transcripts. However, they are well conserved among the hepadnaviruses of non-human primates, the woodchuck and ground squirrel.

The application of system identification techniques to an R.F. Cavity tuning loop

International Nuclear Information System (INIS)

Mestha, L.K.

1989-09-01

System identification is the terminology used for the process of characterising a given control system. A mathematical representation of the frequency response characteristic is obtained to utilise all the known design techniques to arrange the feed-back loop to meet required control performance criterion. This is known as parametric system identification. The intention of this paper is to speed up the process of identifying the R.F. Cavity tuning system of the 800 MeV accelerator, ISIS. While achieving this goal the computer must not disturb noticeably the normal function set out by the system. This task of automatic characterisation is necessary so that a self-adapting feed-back loop can be arranged to adjust itself without human interference and meet severe R.F. tuning requirements on ISIS. In any case the results of parametric identifications are useful in designing a robust feed-back loop with appropriate gain and phase margins. The approach using a Pseudo Random Signal is currently practised in Process Industries. (author)

A Quasi-Type-1 Phase-Locked Loop Structure

DEFF Research Database (Denmark)

Golestan, Saeed; Fernandez, Francisco Daniel Freijedo; Vidal, Ana

2014-01-01

The grid voltage phase and frequency are crucial information in control of most grid connected power electronic based equipment. Most often, a phase-locked loop (PLL) is employed for this purpose. A PLL is a closed-loop feedback control system that the phase of its output signal is related...... to the phase of its input signal. Arguably, the simplest PLL is a type-1 PLL. The type-1 PLLs are characterized by having only one integrator in their control loop and therefore having a high stability margin. However, they suffer from a serious drawback: they cannot achieve zero average steady-state phase...

Functional architecture and global properties of the Corynebacterium glutamicum regulatory network: Novel insights from a dataset with a high genomic coverage.

Science.gov (United States)

Freyre-González, Julio A; Tauch, Andreas

2017-09-10

Corynebacterium glutamicum is a Gram-positive, anaerobic, rod-shaped soil bacterium able to grow on a diversity of carbon sources like sugars and organic acids. It is a biotechnological relevant organism because of its highly efficient ability to biosynthesize amino acids, such as l-glutamic acid and l-lysine. Here, we reconstructed the most complete C. glutamicum regulatory network to date and comprehensively analyzed its global organizational properties, systems-level features and functional architecture. Our analyses show the tremendous power of Abasy Atlas to study the functional organization of regulatory networks. We created two models of the C. glutamicum regulatory network: all-evidences (containing both weak and strong supported interactions, genomic coverage=73%) and strongly-supported (only accounting for strongly supported evidences, genomic coverage=71%). Using state-of-the-art methodologies, we prove that power-law behaviors truly govern the connectivity and clustering coefficient distributions. We found a non-previously reported circuit motif that we named complex feed-forward motif. We highlighted the importance of feedback loops for the functional architecture, beyond whether they are statistically over-represented or not in the network. We show that the previously reported top-down approach is inadequate to infer the hierarchy governing a regulatory network because feedback bridges different hierarchical layers, and the top-down approach disregards the presence of intermodular genes shaping the integration layer. Our findings all together further support a diamond-shaped, three-layered hierarchy exhibiting some feedback between processing and coordination layers, which is shaped by four classes of systems-level elements: global regulators, locally autonomous modules, basal machinery and intermodular genes. Copyright © 2016 Elsevier B.V. All rights reserved.

Shaping meiotic chromosomes with SUMO: a feedback loop controls the assembly of the synaptonemal complex in budding yeast

Directory of Open Access Journals (Sweden)

Hideo Tsubouchi

2016-02-01

Full Text Available The synaptonemal complex (SC is a meiosis-specific chromosomal structure in which homologous chromosomes are intimately linked through arrays of specialized proteins called transverse filaments (TF. Widely conserved in eukaryote meiosis, the SC forms during prophase I and is essential for accurate segregation of homologous chromosomes at meiosis I. However, the basic mechanism overlooking formation and regulation of the SC has been poorly understood. By using the budding yeast Saccharomyces cerevisiae, we recently showed that SC formation is controlled through the attachment of multiple molecules of small ubiquitin-like modifier (SUMO to a regulator of TF assembly. Intriguingly, this SUMOylation is activated by TF, implicating the involvement of a positive feedback loop in the control of SC assembly. We discuss the implication of this finding and possible involvement of a similar mechanism in regulating other processes.

Computational advantages of reverberating loops for sensorimotor learning.

Science.gov (United States)

Fortney, Kristen; Tweed, Douglas B

2012-03-01

When we learn something new, our brain may store the information in synapses or in reverberating loops of electrical activity, but current theories of motor learning focus almost entirely on the synapses. Here we show that loops could also play a role and would bring advantages: loop-based algorithms can learn complex control tasks faster, with exponentially fewer neurons, and avoid the problem of weight transport. They do all this at a cost: in the presence of long feedback delays, loop algorithms cannot control very fast movements, but in this case, loop and synaptic mechanisms can complement each other-mixed systems quickly learn to make accurate but not very fast motions and then gradually speed up. Loop algorithms explain aspects of consolidation, the role of attention, and the relapses that are sometimes seen after a task has apparently been learned, and they make further predictions.

Online Reconstruction and Calibration with Feedback Loop in the ALICE High Level Trigger

Directory of Open Access Journals (Sweden)

Rohr David

2016-01-01

at the Large Hadron Collider (LHC at CERN. The High Level Trigger (HLT is an online computing farm, which reconstructs events recorded by the ALICE detector in real-time. The most computing-intensive task is the reconstruction of the particle trajectories. The main tracking devices in ALICE are the Time Projection Chamber (TPC and the Inner Tracking System (ITS. The HLT uses a fast GPU-accelerated algorithm for the TPC tracking based on the Cellular Automaton principle and the Kalman filter. ALICE employs gaseous subdetectors which are sensitive to environmental conditions such as ambient pressure and temperature and the TPC is one of these. A precise reconstruction of particle trajectories requires the calibration of these detectors. As our first topic, we present some recent optimizations to our GPU-based TPC tracking using the new GPU models we employ for the ongoing and upcoming data taking period at LHC. We also show our new approach to fast ITS standalone tracking. As our second topic, we present improvements to the HLT for facilitating online reconstruction including a new flat data model and a new data flow chain. The calibration output is fed back to the reconstruction components of the HLT via a feedback loop. We conclude with an analysis of a first online calibration test under real conditions during the Pb-Pb run in November 2015, which was based on these new features.

Parallel arrangements of positive feedback loops limit cell-to-cell variability in differentiation.

Directory of Open Access Journals (Sweden)

Anupam Dey

Full Text Available Cellular differentiations are often regulated by bistable switches resulting from specific arrangements of multiple positive feedback loops (PFL fused to one another. Although bistability generates digital responses at the cellular level, stochasticity in chemical reactions causes population heterogeneity in terms of its differentiated states. We hypothesized that the specific arrangements of PFLs may have evolved to minimize the cellular heterogeneity in differentiation. In order to test this we investigated variability in cellular differentiation controlled either by parallel or serial arrangements of multiple PFLs having similar average properties under extrinsic and intrinsic noises. We find that motifs with PFLs fused in parallel to one another around a central regulator are less susceptible to noise as compared to the motifs with PFLs arranged serially. Our calculations suggest that the increased resistance to noise in parallel motifs originate from the less sensitivity of bifurcation points to the extrinsic noise. Whereas estimation of mean residence times indicate that stable branches of bifurcations are robust to intrinsic noise in parallel motifs as compared to serial motifs. Model conclusions are consistent both in AND- and OR-gate input signal configurations and also with two different modeling strategies. Our investigations provide some insight into recent findings that differentiation of preadipocyte to mature adipocyte is controlled by network of parallel PFLs.

Adaptive cascaded beam-based feedback at the SLC

International Nuclear Information System (INIS)

Himel, T.; Allison, S.; Grossberg, P.; Hendrickson, L.; Sass, R.; Shoaee, H.

1993-05-01

The SLAC Linear Collider now has a total of twenty-four beam-steering feedback loops used to keep the electron and positron beams on their desired trajectories. Seven of these loops measure and control the same beam as it proceeds down the linac through the arcs to the final focus. Ideally each loop should correct only for disturbances that occur between it and the immediate upstream loop. In fact, in the original system each loop corrected for all upstream disturbances. This resulted in undesirable over-correction and ringing. We added MIMO (Multiple Input Multiple Output) adaptive noise cancellers to separate the signal we wish to correct from disturbances further up-stream. This adaptive control improved performance in the 1992 run

Feedback control of superconducting quantum circuits

NARCIS (Netherlands)

Ristè, D.

2014-01-01

Superconducting circuits have recently risen to the forefront of the solid-state prototypes for quantum computing. Reaching the stage of robust quantum computing requires closing the loop between measurement and control of quantum bits (qubits). This thesis presents the realization of feedback

Parallelizing More Loops with Compiler Guided Refactoring

DEFF Research Database (Denmark)

Larsen, Per; Ladelsky, Razya; Lidman, Jacob

2012-01-01

an interactive compilation feedback system that guides programmers in iteratively modifying their application source code. This helps leverage the compiler’s ability to generate loop-parallel code. We employ our system to modify two sequential benchmarks dealing with image processing and edge detection...

Control-structure interaction in precision pointing servo loops

Science.gov (United States)

Spanos, John T.

1989-01-01

The control-structure interaction problem is addressed via stability analysis of a generic linear servo loop model. With the plant described by the rigid body mode and a single elastic mode, structural flexibility is categorized into one of three types: (1) appendage, (2) in-the-loop minimum phase, and (3) in-the-loop nonminimum phase. Closing the loop with proportional-derivative (PD) control action and introducing sensor roll-off dynamics in the feedback path, stability conditions are obtained. Trade studies are conducted with modal frequency, modal participation, modal damping, loop bandwidth, and sensor bandwidth treated as free parameters. Results indicate that appendage modes are most likely to produce instability if they are near the sensor rolloff, whereas in-the-loop modes are most dangerous near the loop bandwidth. The main goal of this paper is to provide a fundamental understanding of the control-structure interaction problem so that it may benefit the design of complex spacecraft and pointing system servo loops. In this framework, the JPL Pathfinder gimbal pointer is considered as an example.

Feedback control of chlorine inductively coupled plasma etch processing

International Nuclear Information System (INIS)

Lin Chaung; Leou, K.-C.; Shiao, K.-M.

2005-01-01

Feedback control has been applied to poly-Si etch processing using a chlorine inductively coupled plasma. Since the positive ion flux and ion energy incident upon the wafer surface are the key factors that influence the etch rate, the ion current and the root mean square (rms) rf voltage on the wafer stage, which are measured using an impedance meter connected to the wafer stage, are adopted as the controlled variables to enhance etch rate. The actuators are two 13.56 MHz rf power generators, which adjust ion density and ion energy, respectively. The results of closed-loop control show that the advantages of feedback control can be achieved. For example, with feedback control, etch rate variation under the transient chamber wall condition is reduced roughly by a factor of 2 as compared to the open-loop case. In addition, the capability of the disturbance rejection was also investigated. For a gas pressure variation of 20%, the largest etch rate variation is about 2.4% with closed-loop control as compared with as large as about 6% variation using open-loop control. Also the effect of ion current and rms rf voltage on etch rate was studied using 2 2 factorial design whose results were used to derive a model equation. The obtained formula was used to adjust the set point of ion current and rf voltage so that the desired etch rate was obtained

Electrotactile feedback improves performance and facilitates learning in the routine grasping task

Directory of Open Access Journals (Sweden)

Milica Isaković

2016-06-01

Full Text Available Aim of this study was to investigate the feasibility of electrotactile feedback in closed loop training of force control during the routine grasping task. The feedback was provided using an array electrode and a simple six-level spatial coding, and the experiment was conducted in three amputee subjects. The psychometric tests confirmed that the subjects could perceive and interpret the electrotactile feedback with a high success rate. The subjects performed the routine grasping task comprising 4 blocks of 60 grasping trials. In each trial, the subjects employed feedforward control to close the hand and produce the desired grasping force (four levels. First (baseline and the last (validation session were performed in open loop, while the second and the third session (training included electrotactile feedback. The obtained results confirmed that using the feedback improved the accuracy and precision of the force control. In addition, the subjects performed significantly better in the validation vs. baseline session, therefore suggesting that electrotactile feedback can be used for learning and training of myoelectric control.

Electrotactile Feedback Improves Performance and Facilitates Learning in the Routine Grasping Task.

Science.gov (United States)

Isaković, Milica; Belić, Minja; Štrbac, Matija; Popović, Igor; Došen, Strahinja; Farina, Dario; Keller, Thierry

2016-06-13

Aim of this study was to investigate the feasibility of electrotactile feedback in closed loop training of force control during the routine grasping task. The feedback was provided using an array electrode and a simple six-level spatial coding, and the experiment was conducted in three amputee subjects. The psychometric tests confirmed that the subjects could perceive and interpret the electrotactile feedback with a high success rate. The subjects performed the routine grasping task comprising 4 blocks of 60 grasping trials. In each trial, the subjects employed feedforward control to close the hand and produce the desired grasping force (four levels). First (baseline) and the last (validation) session were performed in open loop, while the second and the third session (training) included electrotactile feedback. The obtained results confirmed that using the feedback improved the accuracy and precision of the force control. In addition, the subjects performed significantly better in the validation vs. baseline session, therefore suggesting that electrotactile feedback can be used for learning and training of myoelectric control.

The role of feedback resistors and tid effects in the ASET response of a high speed current feedback amplifier

International Nuclear Information System (INIS)

Roig, F.; Dusseau, L.; Privat, A.; Vaille, J.R.; Boch, J.; Saigne, F.; Ribeiro, P.; Auriel, G.; Roche, N.J.H.; Marec, R.; Calvel, P.; Bezerra, F.; Ecoffet, R.; Azais, B.

2014-01-01

The influence of external circuit designs on ASET shapes in a high speed current feedback amplifier (CFA) (AD844) is investigated by means of the pulsed laser single event effect (PLSEE) simulation technique. Changes of the feedback resistors modify circuit's electrical parameters such as closed-loop gain and bandwidth, affecting amplifier stability and so ASET shapes. Qualitative explanations based on general electronic rules and feedback theories enable the understanding of a CFA operation establishing a correlation between the evolution of external feedback resistor values and ASET parameters. TID effects on the ASET sensitivity in AD844 CFA are also investigated in this work highlighting different behaviors according to the impacted bipolar transistor in the integrated circuit. (authors)

A comparative approach to closed-loop computation.

Science.gov (United States)

Roth, E; Sponberg, S; Cowan, N J

2014-04-01

Neural computation is inescapably closed-loop: the nervous system processes sensory signals to shape motor output, and motor output consequently shapes sensory input. Technological advances have enabled neuroscientists to close, open, and alter feedback loops in a wide range of experimental preparations. The experimental capability of manipulating the topology-that is, how information can flow between subsystems-provides new opportunities to understand the mechanisms and computations underlying behavior. These experiments encompass a spectrum of approaches from fully open-loop, restrained preparations to the fully closed-loop character of free behavior. Control theory and system identification provide a clear computational framework for relating these experimental approaches. We describe recent progress and new directions for translating experiments at one level in this spectrum to predictions at another level. Operating across this spectrum can reveal new understanding of how low-level neural mechanisms relate to high-level function during closed-loop behavior. Copyright © 2013 Elsevier Ltd. All rights reserved.

Dynamics of a broad-area diode laser with lateral-mode-selected long-cavity feedback

DEFF Research Database (Denmark)

Chi, Mingjun; Petersen, Paul Michael

2014-01-01

The temporal dynamics of a broad-area diode laser with lateral-mode-selected long-cavity feedback is studied experimentally. Different dynamics are observed when different lateral modes are selected. When the feedback mirror is aligned perfectly and high-order modes are selected, in most....... When the feedback mirror is aligned non-perfectly, pulse-package oscillation is observed, for the first time to our knowledge, in a diode laser with long-cavity feedback....... of the cases, the output of the laser shows a periodic oscillation corresponding to a single roundtrip external-cavity loop, but the dynamic behavior disappears in some case; when the zero-order lateral-mode is selected, periodic oscillation corresponding to a double roundtrip external-cavity loop is observed...

Feedback stabilization of electrostatic reactive instabilities

International Nuclear Information System (INIS)

Richards, R.K.

1976-01-01

A general theory for the feedback stabilization of electrostatic reactive instabilities is developed which includes the effects of dissipation in the plasma and frequency dependence in the sensor-suppressor elements and in the external feedback circuit. This theory is compared to experiments involving particular reactive instability, an interchange mode, found in a magnetic mirror device; these results are found to be in good agreement with theory. One noteworthy result is that a frequency dependence in the overall gain and phase shift of the feedback loop can cause destabilization at large gain. Multimode feedback stabilization is studied using the spatial variation of two interchange modes to separate them such that each can be acted upon individually by the feedback system. The transfer function of the plasma is also examined. This analysis is used for mode identification and location of the pole positions. As an example of using feedback as a diagnostic tool, instability induced transport is studied. Here feedback is used to control the amplitude of fluctuations at saturation

Healthy Change Processes-A Diary Study of Five Organizational Units. Establishing a Healthy Change Feedback Loop.

Science.gov (United States)

Lien, Mathilde; Saksvik, Per Øystein

2016-10-01

This paper explores a change process in the Central Norway Regional Health Authority that was brought about by the implementation of a new economics and logistics system. The purpose of this paper is to contribute to understanding of how employees' attitudes towards change develop over time and how attitudes differ between the five health trusts under this authority. In this paper, we argue that a process-oriented focus through a longitudinal diary method, in addition to action research and feedback loops, will provide greater understanding of the evaluation of organizational change and interventions. This is explored through the assumption that different units will have different perspectives and attitudes towards the same intervention over time because of different contextual and time-related factors. The diary method aims to capture the context, events, reflections and interactions when they occur and allows for a nuanced frame of reference for the different phases of the implementation process and how these phases are perceived by employees. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Active Control of Thermal Convection in a Rectangular Loop by Changing its Spatial Orientation

Science.gov (United States)

Bratsun, Dmitry A.; Krasnyakov, Ivan V.; Zyuzgin, Alexey V.

2018-02-01

The problem of the automatic control of the fluid flow in a rectangular convective loop heated from below is studied theoretically and experimentally. The control is performed by using a feedback subsystem which changes the convection regimes by introducing small discrete changes in the spatial orientation of the loop with respect to gravity. We focus on effects that arise when the feedback controller operates with an unavoidable time delay, which is cause by the thermal inertia of the medium. The mathematical model of the phenomenon is developed. The dynamic regimes of the convection in the thermosyphon loop under control are studied. It is shown that the proposed control method can successfully stabilize not only a no-motion state of the fluid, but also time-dependent modes of convection including the irregular fluid flow at high values of the Rayleigh number. It is shown that the excessive gain of the proportional feedback can result in oscillations in the loop orientation exciting the unsteady convection modes. The comparison of the experimental data obtained for dielectric oil and dodecane with theory is given, and their good agreement is demonstrated.

Bandwidth limitations in current mode and voltage mode integrated feedback amplifiers

DEFF Research Database (Denmark)

Bruun, Erik

1995-01-01

loop bandwidth remains constant for a feedback amplifier. The constant-bandwidth relations of such amplifier designs are reviewed in this paper and they are combined with the constraints imposed by technology when the feedback amplifier is to be designed in an integrated technology. From this analysis...

Combining experimental observations and modelling in investigating feedback and emotions in repeated selection tasks

NARCIS (Netherlands)

Fischer, A.R.H.; Blommaert, F.J.J.; Midden, C.J.H.

2005-01-01

People seem to learn tasks even without formal training. This can be modelled as the outcome of a feedback system that accumulates experience. In this paper we investigate such a feedback system, following an iterative research approach. A feedback loop is specified that is detailed using

Combining experimental observation and modelling in investigating feedback and emotions in repeated selection tasks

NARCIS (Netherlands)

Fischer, A.R.H.; Blommaert, F.J.J.; Midden, C.J.H.

2005-01-01

People seem to learn tasks even without formal training. This can be modelled as the outcome of a feedback system that accumulates experience. In this paper we investigate such a feedback system, following an iterative research approach. A feedback loop is specified that is detailed using

The hardware implementation of the CERN SPS ultrafast feedback processor demonstrator

CERN Document Server

Dusakto, J E; Fox, J D; Olsen, J; Rivetta, C H; Höfle, W

2013-01-01

An ultrafast 4GSa/s transverse feedback processor has been developed for proof-of-concept studies of feedback control of e-cloud driven and transverse mode coupled intra-bunch instabilities in the CERN SPS. This system consists of a high-speed ADC on the front end and equally fast DAC on the back end. All control and signal processing is implemented in FPGA logic. This system is capable of taking up to 16 sample slices across a single SPS bunch and processing each slice individually within a reconfigurable signal processor. This demonstrator system is a rapidly developed prototype, consisting of both commercial and custom-design components. It can stabilize the motion of a single particle bunch using closed loop feedback. The system can also run open loop as a high-speed arbitrary waveform generator and contains diagnostic features including a special ADC snapshot capture memory. This paper describes the overall system, the feedback processor and focuses on the hardware architecture, design ...

Inner Current Loop Analysis and Design Based on Resonant Regulators for Isolated Microgrids

DEFF Research Database (Denmark)

Federico, de Bosio; de Sousa Ribeiro, Luiz Antonio; Soares Lima, Marcel

2015-01-01

Inner current and voltage loops are fundamental in achieving good performance of microgrids based on power electronics voltage source inverters. The analysis and design of these loops are essential for the adequate operation of these systems. This paper investigates the effect of state feedback...

Frequency domain indirect identification of AMB rotor systems based on fictitious proportional feedback gain

Energy Technology Data Exchange (ETDEWEB)

Ahn, Hyeong Joon [Dept. of Mechanical Engineering, Soongsil University, Seoul (Korea, Republic of); Kim, Chan Jung [Dept. of Mechanical Design Engineering, Pukyong National University, Busan(Korea, Republic of)

2016-12-15

It is very difficult to directly identify an unstable system with uncertain dynamics from frequency domain input-output data. Hence, in these cases, closed-loop frequency responses calculated using a fictitious feedback could be more identifiable than open-loop data. This paper presents a frequency domain indirect identification of AMB rotor systems based on a Fictitious proportional feedback gain (FPFG). The closed-loop effect due to the FPFG can enhance the detectability of the system by moving the system poles, and significantly weigh the target mode in the frequency domain. The effectiveness of the proposed identification method was verified through the frequency domain identification of active magnetic bearing rotor systems.

Conserved cis-regulatory regions in a large genomic landscape control SHH and BMP-regulated Gremlin1 expression in mouse limb buds

Directory of Open Access Journals (Sweden)

Zuniga Aimée

2012-08-01

Full Text Available Abstract Background Mouse limb bud is a prime model to study the regulatory interactions that control vertebrate organogenesis. Major aspects of limb bud development are controlled by feedback loops that define a self-regulatory signalling system. The SHH/GREM1/AER-FGF feedback loop forms the core of this signalling system that operates between the posterior mesenchymal organiser and the ectodermal signalling centre. The BMP antagonist Gremlin1 (GREM1 is a critical node in this system, whose dynamic expression is controlled by BMP, SHH, and FGF signalling and key to normal progression of limb bud development. Previous analysis identified a distant cis-regulatory landscape within the neighbouring Formin1 (Fmn1 locus that is required for Grem1 expression, reminiscent of the genomic landscapes controlling HoxD and Shh expression in limb buds. Results Three highly conserved regions (HMCO1-3 were identified within the previously defined critical genomic region and tested for their ability to regulate Grem1 expression in mouse limb buds. Using a combination of BAC and conventional transgenic approaches, a 9 kb region located ~70 kb downstream of the Grem1 transcription unit was identified. This region, termed Grem1 Regulatory Sequence 1 (GRS1, is able to recapitulate major aspects of Grem1 expression, as it drives expression of a LacZ reporter into the posterior and, to a lesser extent, in the distal-anterior mesenchyme. Crossing the GRS1 transgene into embryos with alterations in the SHH and BMP pathways established that GRS1 depends on SHH and is modulated by BMP signalling, i.e. integrates inputs from these pathways. Chromatin immunoprecipitation revealed interaction of endogenous GLI3 proteins with the core cis-regulatory elements in the GRS1 region. As GLI3 is a mediator of SHH signal transduction, these results indicated that SHH directly controls Grem1 expression through the GRS1 region. Finally, all cis-regulatory regions within the Grem1

Design strategies for dynamic closed-loop optogenetic neurocontrol in vivo

Science.gov (United States)

Bolus, M. F.; Willats, A. A.; Whitmire, C. J.; Rozell, C. J.; Stanley, G. B.

2018-04-01

Objective. Controlling neural activity enables the possibility of manipulating sensory perception, cognitive processes, and body movement, in addition to providing a powerful framework for functionally disentangling the neural circuits that underlie these complex phenomena. Over the last decade, optogenetic stimulation has become an increasingly important and powerful tool for understanding neural circuit function, owing to the ability to target specific cell types and bidirectionally modulate neural activity. To date, most stimulation has been provided in open-loop or in an on/off closed-loop fashion, where previously-determined stimulation is triggered by an event. Here, we describe and demonstrate a design approach for precise optogenetic control of neuronal firing rate modulation using feedback to guide stimulation continuously. Approach. Using the rodent somatosensory thalamus as an experimental testbed for realizing desired time-varying patterns of firing rate modulation, we utilized a moving average exponential filter to estimate firing rate online from single-unit spiking measured extracellularly. This estimate of instantaneous rate served as feedback for a proportional integral (PI) controller, which was designed during the experiment based on a linear-nonlinear Poisson (LNP) model of the neuronal response to light. Main results. The LNP model fit during the experiment enabled robust closed-loop control, resulting in good tracking of sinusoidal and non-sinusoidal targets, and rejection of unmeasured disturbances. Closed-loop control also enabled manipulation of trial-to-trial variability. Significance. Because neuroscientists are faced with the challenge of dissecting the functions of circuit components, the ability to maintain control of a region of interest in spite of changes in ongoing neural activity will be important for disambiguating function within networks. Closed-loop stimulation strategies are ideal for control that is robust to such changes

A cognitive neuroprosthetic that uses cortical stimulation for somatosensory feedback

Science.gov (United States)

Klaes, Christian; Shi, Ying; Kellis, Spencer; Minxha, Juri; Revechkis, Boris; Andersen, Richard A.

2014-10-01

Objective. Present day cortical brain-machine interfaces (BMIs) have made impressive advances using decoded brain signals to control extracorporeal devices. Although BMIs are used in a closed-loop fashion, sensory feedback typically is visual only. However medical case studies have shown that the loss of somesthesis in a limb greatly reduces the agility of the limb even when visual feedback is available. Approach. To overcome this limitation, this study tested a closed-loop BMI that utilizes intracortical microstimulation to provide ‘tactile’ sensation to a non-human primate. Main result. Using stimulation electrodes in Brodmann area 1 of somatosensory cortex (BA1) and recording electrodes in the anterior intraparietal area, the parietal reach region and dorsal area 5 (area 5d), it was found that this form of feedback can be used in BMI tasks. Significance. Providing somatosensory feedback has the poyential to greatly improve the performance of cognitive neuroprostheses especially for fine control and object manipulation. Adding stimulation to a BMI system could therefore improve the quality of life for severely paralyzed patients.

PROGRESS IN TUNE, COUPLING, AND CHROMATICITY MEASUREMENT AND FEEDBACK DURING RHIC RUN 7

Energy Technology Data Exchange (ETDEWEB)

CAMERON,P.; DELLAPENNA, A.; HOFF, L.; LUO, Y.; MARUSIC, A.; SCHULTHEISS, C.; TEPIKIAN, S.; ET AL.

2007-06-25

Tune feedback was first implemented in RHIC in 2002, as a specialist activity. The transition of the tune feedback system to full operational status was impeded by dynamic range problems, as well as by overall loop instabilities driven by large coupling. The dynamic range problem was solved by the CERN development of the Direct Diode Detection Analog Front End. Continuous measurement of all projections of the betatron eigenmodes made possible the world's first implementation of coupling feedback during beam acceleration, resolving the problem of overall loop instabilities. Simultaneous tune and coupling feedbacks were utilized as specialist activities for ramp development during the 2006 RHIC run. At the beginning of the 2007 RHIC run there remained two obstacles to making these feedbacks fully operational in RHIC - chromaticity measurement and control, and the presence of strong harmonics of the power line frequency in the betatron spectrum. We report on progress in tune, coupling, and chromaticity measurement and feedback, and discuss the relevance of our results to LHC commissioning.

Causal structure of oscillations in gene regulatory networks: Boolean analysis of ordinary differential equation attractors.

Science.gov (United States)

Sun, Mengyang; Cheng, Xianrui; Socolar, Joshua E S

2013-06-01

A common approach to the modeling of gene regulatory networks is to represent activating or repressing interactions using ordinary differential equations for target gene concentrations that include Hill function dependences on regulator gene concentrations. An alternative formulation represents the same interactions using Boolean logic with time delays associated with each network link. We consider the attractors that emerge from the two types of models in the case of a simple but nontrivial network: a figure-8 network with one positive and one negative feedback loop. We show that the different modeling approaches give rise to the same qualitative set of attractors with the exception of a possible fixed point in the ordinary differential equation model in which concentrations sit at intermediate values. The properties of the attractors are most easily understood from the Boolean perspective, suggesting that time-delay Boolean modeling is a useful tool for understanding the logic of regulatory networks.

Short- and Long-Term Learning of Feedforward Control of a Myoelectric Prosthesis with Sensory Feedback by Amputees.

Science.gov (United States)

Strbac, Matija; Isakovic, Milica; Belic, Minja; Popovic, Igor; Simanic, Igor; Farina, Dario; Keller, Thierry; Dosen, Strahinja

2017-11-01

Human motor control relies on a combination of feedback and feedforward strategies. The aim of this study was to longitudinally investigate artificial somatosensory feedback and feedforward control in the context of grasping with myoelectric prosthesis. Nine amputee subjects performed routine grasping trials, with the aim to produce four levels of force during four blocks of 60 trials across five days. The electrotactile force feedback was provided in the second and third block using multipad electrode and spatial coding. The first baseline and last validation block (open-loop control) evaluated the effects of long- (across sessions) and short-term (within session) learning, respectively. The outcome measures were the absolute error between the generated and target force, and the number of force saturations. The results demonstrated that the electrotactile feedback improved the performance both within and across sessions. In the validation block, the performance did not significantly decrease and the quality of open-loop control (baseline) improved across days, converging to the performance characterizing closed-loop control. This paper provides important insights into the feedback and feedforward processes in prosthesis control, contributing to the better understanding of the role and design of feedback in prosthetic systems.

In vivo Microscale Measurements of Light and Photosynthesis during Coral Bleaching: Evidence for the Optical Feedback Loop?

Science.gov (United States)

Wangpraseurt, Daniel; Holm, Jacob B; Larkum, Anthony W D; Pernice, Mathieu; Ralph, Peter J; Suggett, David J; Kühl, Michael

2017-01-01

Climate change-related coral bleaching, i.e., the visible loss of zooxanthellae from the coral host, is increasing in frequency and extent and presents a major threat to coral reefs globally. Coral bleaching has been proposed to involve accelerating light stress of their microalgal endosymbionts via a positive feedback loop of photodamage, symbiont expulsion and excess in vivo light exposure. To test this hypothesis, we used light and O 2 microsensors to characterize in vivo light exposure and photosynthesis of Symbiodinium during a thermal stress experiment. We created tissue areas with different densities of Symbiodinium cells in order to understand the optical properties and light microenvironment of corals during bleaching. Our results showed that in bleached Pocillopora damicornis corals, Symbiodinium light exposure was up to fivefold enhanced relative to healthy corals, and the relationship between symbiont loss and light enhancement was well-described by a power-law function. Cell-specific rates of Symbiodinium gross photosynthesis and light respiration were enhanced in bleached P. damicornis compared to healthy corals, while areal rates of net photosynthesis decreased. Symbiodinium light exposure in Favites sp. revealed the presence of low light microniches in bleached coral tissues, suggesting that light scattering in thick coral tissues can enable photoprotection of cryptic symbionts. Our study provides evidence for the acceleration of in vivo light exposure during coral bleaching but this optical feedback mechanism differs between coral hosts. Enhanced photosynthesis in relation to accelerating light exposure shows that coral microscale optics exerts a key role on coral photophysiology and the subsequent degree of radiative stress during coral bleaching.

Reconstruction and analysis of transcription factor-miRNA co-regulatory feed-forward loops in human cancers using filter-wrapper feature selection.

Directory of Open Access Journals (Sweden)

Chen Peng

Full Text Available BACKGROUND: As one of the most common types of co-regulatory motifs, feed-forward loops (FFLs control many cell functions and play an important role in human cancers. Therefore, it is crucial to reconstruct and analyze cancer-related FFLs that are controlled by transcription factor (TF and microRNA (miRNA simultaneously, in order to find out how miRNAs and TFs cooperate with each other in cancer cells and how they contribute to carcinogenesis. Current FFL studies rely on predicted regulation information and therefore suffer the false positive issue in prediction results. More critically, FFLs generated by existing approaches cannot represent the dynamic and conditional regulation relationship under different experimental conditions. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we proposed a novel filter-wrapper feature selection method to accurately identify co-regulatory mechanism by incorporating prior information from predicted regulatory interactions with parallel miRNA/mRNA expression datasets. By applying this method, we reconstructed 208 and 110 TF-miRNA co-regulatory FFLs from human pan-cancer and prostate datasets, respectively. Further analysis of these cancer-related FFLs showed that the top-ranking TF STAT3 and miRNA hsa-let-7e are key regulators implicated in human cancers, which have regulated targets significantly enriched in cellular process regulations and signaling pathways that are involved in carcinogenesis. CONCLUSIONS/SIGNIFICANCE: In this study, we introduced an efficient computational approach to reconstruct co-regulatory FFLs by accurately identifying gene co-regulatory interactions. The strength of the proposed feature selection method lies in the fact it can precisely filter out false positives in predicted regulatory interactions by quantitatively modeling the complex co-regulation of target genes mediated by TFs and miRNAs simultaneously. Moreover, the proposed feature selection method can be generally applied to

Design of Cognitive Interfaces for Personal Informatics Feedback

DEFF Research Database (Denmark)

Jensen, Camilla Birgitte Falk

to personal informatics systems, and propose an approach to design cognitive interfaces, which considers both users’ motivations, needs, and goals. In this thesis I propose a new personal informatics framework, the feedback loop, which incorporates lean agile design principles. Including hierarchical modeling...... of goals, activities, and tasks to create minimal viable products. While considering how micro-interactions based on an understanding of data, couples with user needs and the context they appear in, can contribute to creating cognitive interfaces. Designing cognitive interfaces requires a focus....... For instance, examining emotional responses to pleasant and unpleasant media content from brain activity, reveals the large amount of data and extensive analysis required to apply this to future personal informatics systems. In addition we analyse challenges related to temporal aspects of the feedback loop...

Augmenting Environmental Interaction in Audio Feedback Systems

Directory of Open Access Journals (Sweden)

Seunghun Kim

2016-04-01

Full Text Available Audio feedback is defined as a positive feedback of acoustic signals where an audio input and output form a loop, and may be utilized artistically. This article presents new context-based controls over audio feedback, leading to the generation of desired sonic behaviors by enriching the influence of existing acoustic information such as room response and ambient noise. This ecological approach to audio feedback emphasizes mutual sonic interaction between signal processing and the acoustic environment. Mappings from analyses of the received signal to signal-processing parameters are designed to emphasize this specificity as an aesthetic goal. Our feedback system presents four types of mappings: approximate analyses of room reverberation to tempo-scale characteristics, ambient noise to amplitude and two different approximations of resonances to timbre. These mappings are validated computationally and evaluated experimentally in different acoustic conditions.

Evaluating Land-Atmosphere Moisture Feedbacks in Earth System Models With Spaceborne Observations

Science.gov (United States)

Levine, P. A.; Randerson, J. T.; Lawrence, D. M.; Swenson, S. C.

2016-12-01

We have developed a set of metrics for measuring the feedback loop between the land surface moisture state and the atmosphere globally on an interannual time scale. These metrics consider both the forcing of terrestrial water storage (TWS) on subsequent atmospheric conditions as well as the response of TWS to antecedent atmospheric conditions. We designed our metrics to take advantage of more than one decade's worth of satellite observations of TWS from the Gravity Recovery and Climate Experiment (GRACE) along with atmospheric variables from the Atmospheric Infrared Sounder (AIRS), the Global Precipitation Climatology Project (GPCP), and Clouds and the Earths Radiant Energy System (CERES). Metrics derived from spaceborne observations were used to evaluate the strength of the feedback loop in the Community Earth System Model (CESM) Large Ensemble (LENS) and in several models that contributed simulations to Phase 5 of the Coupled Model Intercomparison Project (CMIP5). We found that both forcing and response limbs of the feedback loop were generally stronger in tropical and temperate regions in CMIP5 models and even more so in LENS compared to satellite observations. Our analysis suggests that models may overestimate the strength of the feedbacks between the land surface and the atmosphere, which is consistent with previous studies conducted across different spatial and temporal scales.

Decorrelation of Neural-Network Activity by Inhibitory Feedback

Science.gov (United States)

Einevoll, Gaute T.; Diesmann, Markus

2012-01-01

Correlations in spike-train ensembles can seriously impair the encoding of information by their spatio-temporal structure. An inevitable source of correlation in finite neural networks is common presynaptic input to pairs of neurons. Recent studies demonstrate that spike correlations in recurrent neural networks are considerably smaller than expected based on the amount of shared presynaptic input. Here, we explain this observation by means of a linear network model and simulations of networks of leaky integrate-and-fire neurons. We show that inhibitory feedback efficiently suppresses pairwise correlations and, hence, population-rate fluctuations, thereby assigning inhibitory neurons the new role of active decorrelation. We quantify this decorrelation by comparing the responses of the intact recurrent network (feedback system) and systems where the statistics of the feedback channel is perturbed (feedforward system). Manipulations of the feedback statistics can lead to a significant increase in the power and coherence of the population response. In particular, neglecting correlations within the ensemble of feedback channels or between the external stimulus and the feedback amplifies population-rate fluctuations by orders of magnitude. The fluctuation suppression in homogeneous inhibitory networks is explained by a negative feedback loop in the one-dimensional dynamics of the compound activity. Similarly, a change of coordinates exposes an effective negative feedback loop in the compound dynamics of stable excitatory-inhibitory networks. The suppression of input correlations in finite networks is explained by the population averaged correlations in the linear network model: In purely inhibitory networks, shared-input correlations are canceled by negative spike-train correlations. In excitatory-inhibitory networks, spike-train correlations are typically positive. Here, the suppression of input correlations is not a result of the mere existence of correlations between

Dose response relationship in anti-stress gene regulatory networks.

Science.gov (United States)

Zhang, Qiang; Andersen, Melvin E

2007-03-02

To maintain a stable intracellular environment, cells utilize complex and specialized defense systems against a variety of external perturbations, such as electrophilic stress, heat shock, and hypoxia, etc. Irrespective of the type of stress, many adaptive mechanisms contributing to cellular homeostasis appear to operate through gene regulatory networks that are organized into negative feedback loops. In general, the degree of deviation of the controlled variables, such as electrophiles, misfolded proteins, and O2, is first detected by specialized sensor molecules, then the signal is transduced to specific transcription factors. Transcription factors can regulate the expression of a suite of anti-stress genes, many of which encode enzymes functioning to counteract the perturbed variables. The objective of this study was to explore, using control theory and computational approaches, the theoretical basis that underlies the steady-state dose response relationship between cellular stressors and intracellular biochemical species (controlled variables, transcription factors, and gene products) in these gene regulatory networks. Our work indicated that the shape of dose response curves (linear, superlinear, or sublinear) depends on changes in the specific values of local response coefficients (gains) distributed in the feedback loop. Multimerization of anti-stress enzymes and transcription factors into homodimers, homotrimers, or even higher-order multimers, play a significant role in maintaining robust homeostasis. Moreover, our simulation noted that dose response curves for the controlled variables can transition sequentially through four distinct phases as stressor level increases: initial superlinear with lesser control, superlinear more highly controlled, linear uncontrolled, and sublinear catastrophic. Each phase relies on specific gain-changing events that come into play as stressor level increases. The low-dose region is intrinsically nonlinear, and depending on

Dose response relationship in anti-stress gene regulatory networks.

Directory of Open Access Journals (Sweden)

Qiang Zhang

2007-03-01

Full Text Available To maintain a stable intracellular environment, cells utilize complex and specialized defense systems against a variety of external perturbations, such as electrophilic stress, heat shock, and hypoxia, etc. Irrespective of the type of stress, many adaptive mechanisms contributing to cellular homeostasis appear to operate through gene regulatory networks that are organized into negative feedback loops. In general, the degree of deviation of the controlled variables, such as electrophiles, misfolded proteins, and O2, is first detected by specialized sensor molecules, then the signal is transduced to specific transcription factors. Transcription factors can regulate the expression of a suite of anti-stress genes, many of which encode enzymes functioning to counteract the perturbed variables. The objective of this study was to explore, using control theory and computational approaches, the theoretical basis that underlies the steady-state dose response relationship between cellular stressors and intracellular biochemical species (controlled variables, transcription factors, and gene products in these gene regulatory networks. Our work indicated that the shape of dose response curves (linear, superlinear, or sublinear depends on changes in the specific values of local response coefficients (gains distributed in the feedback loop. Multimerization of anti-stress enzymes and transcription factors into homodimers, homotrimers, or even higher-order multimers, play a significant role in maintaining robust homeostasis. Moreover, our simulation noted that dose response curves for the controlled variables can transition sequentially through four distinct phases as stressor level increases: initial superlinear with lesser control, superlinear more highly controlled, linear uncontrolled, and sublinear catastrophic. Each phase relies on specific gain-changing events that come into play as stressor level increases. The low-dose region is intrinsically nonlinear

The effects of plasma deformability on the feedback stabilization of axisymmetric modes in tokamak plasmas

International Nuclear Information System (INIS)

Ward, D.J.; Jardin, S.C.

1991-09-01

The effects of plasma deformability on the feedback stabilization of axisymmetric modes of tokamak plasmas are studied. It is seen that plasmas with strongly shaped cross sections have unstable motion different from a rigid shift. Furthermore, the placement of passive conductors is shown to modify the non-rigid components of the eigenfunction in a way that reduces the stabilizing eddy currents in these conductors. Passive feedback results using several equilibria of varying shape are presented. The eigenfunction is also modified under the effects of active feedback. This deformation is seen to depend strongly on the position of the flux loops which are used to determine plasma vertical position for the active feedback system. The variations of these non-rigid components of the eigenfunction always serve to reduce the stabilizing effect of the active feedback system by reducing the measurable poloidal flux at the flux-loop locations. Active feedback results are presented for the PBX-M tokamak configuration. (author) 19 figs., 2 tabs., 30 refs

Self-starting and overclocking a harmonically mode-locking WRC-FPLD with a dual-loop feedback controller for 10 Gb s−1 pulse-data transmission

International Nuclear Information System (INIS)

Lin, Chun-Ju; Chi, Yu-Chieh; Lin, Gong-Ru

2013-01-01

The self-starting and overclocking of a harmonically mode-locked weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD) with a dual-loop coupled optoelectronic oscillator (COEO) based feedback controller is demonstrated to perform a clock-free pulsed data transmission at 10 Gb s −1 . The WRC-FPLD is considered as the preferred candidate for harmonic mode-locking due to its highly asymmetric cavity architecture, whereby the spontaneous noise can be significantly suppressed without inducing large intra-cavity loss. With the dual-loop COEO configuration, the WRC-FPLD can be boosted to four times of its original modulation bandwidth such that the pulsed carrier quality can be refined. The structure-optimizing principle with the closed-loop model is corroborated by the effective spurious-noise-suppression. The lowest phase noises as low as −100 dBc Hz −1 at 10 kHz with corresponding RMS timing jitter of 0.67 ps are measured. This is achieved by individually inserting 100 and 120 m long single mode fiber segments into two decoupled arms, the dual-loop COEO before the optical receiver pair. The BER performance reaches a minimum with the optimized SMF segment lengths. However, the spurious peaks arise to degrade the BER performance as the phase noise and jitter are inevitably enlarged when inserting longer SMF segments. After modulating the optimized output pulse train with the pseudo-random-bit-sequence data triggered by the same COEO clock, the SNR can achieve 10.9 dB and the receiving sensitivity is −19.2 dBm. (letter)

Stability, gain, and robustness in quantum feedback networks

International Nuclear Information System (INIS)

D'Helon, C.; James, M. R.

2006-01-01

In this paper we are concerned with the problem of stability for quantum feedback networks. We demonstrate in the context of quantum optics how stability of quantum feedback networks can be guaranteed using only simple gain inequalities for network components and algebraic relationships determined by the network. Quantum feedback networks are shown to be stable if the loop gain is less than one--this is an extension of the famous small gain theorem of classical control theory. We illustrate the simplicity and power of the small gain approach with applications to important problems of robust stability and robust stabilization

Derivation of three closed loop kinematic velocity models using normalized quaternion feedback for an autonomous redundant manipulator with application to inverse kinematics

Energy Technology Data Exchange (ETDEWEB)

Unseren, M.A.

1993-04-01

The report discusses the orientation tracking control problem for a kinematically redundant, autonomous manipulator moving in a three dimensional workspace. The orientation error is derived using the normalized quaternion error method of Ickes, the Luh, Walker, and Paul error method, and a method suggested here utilizing the Rodrigues parameters, all of which are expressed in terms of normalized quaternions. The analytical time derivatives of the orientation errors are determined. The latter, along with the translational velocity error, form a dosed loop kinematic velocity model of the manipulator using normalized quaternion and translational position feedback. An analysis of the singularities associated with expressing the models in a form suitable for solving the inverse kinematics problem is given. Two redundancy resolution algorithms originally developed using an open loop kinematic velocity model of the manipulator are extended to properly take into account the orientation tracking control problem. This report furnishes the necessary mathematical framework required prior to experimental implementation of the orientation tracking control schemes on the seven axis CESARm research manipulator or on the seven-axis Robotics Research K1207i dexterous manipulator, the latter of which is to be delivered to the Oak Ridge National Laboratory in 1993.

Derivation of three closed loop kinematic velocity models using normalized quaternion feedback for an autonomous redundant manipulator with application to inverse kinematics

International Nuclear Information System (INIS)

Unseren, M.A.

1993-04-01

The report discusses the orientation tracking control problem for a kinematically redundant, autonomous manipulator moving in a three dimensional workspace. The orientation error is derived using the normalized quaternion error method of Ickes, the Luh, Walker, and Paul error method, and a method suggested here utilizing the Rodrigues parameters, all of which are expressed in terms of normalized quaternions. The analytical time derivatives of the orientation errors are determined. The latter, along with the translational velocity error, form a dosed loop kinematic velocity model of the manipulator using normalized quaternion and translational position feedback. An analysis of the singularities associated with expressing the models in a form suitable for solving the inverse kinematics problem is given. Two redundancy resolution algorithms originally developed using an open loop kinematic velocity model of the manipulator are extended to properly take into account the orientation tracking control problem. This report furnishes the necessary mathematical framework required prior to experimental implementation of the orientation tracking control schemes on the seven axis CESARm research manipulator or on the seven-axis Robotics Research K1207i dexterous manipulator, the latter of which is to be delivered to the Oak Ridge National Laboratory in 1993

Regulatory role for the memory B cell as suppressor-inducer of feedback control

International Nuclear Information System (INIS)

Kennedy, M.W.; Thomas, D.B.

1983-01-01

A regulatory role is proposed for the antigen-responsive B cell, as suppressor-inducer of feedback control during the secondary response in vivo. In a double adoptive transfer of memory cells primed to a thymus-dependent antigen from one irradiated host to another, antigen-specific suppressors are generated after a critical time in the primary recipient, able to entirely ablate a secondary anti-hapten response. Positive cell selection in the fluorescence-activated cell sorter confirmed that suppression was mediated by an Lyt-2+ T cell; however, positively selected B cells were also inhibitory and able to induce suppressors in a carrier-specific manner: B hapten induced suppressors in a carrier-primed population, and B carrier induced suppressors in a hapten-carrier population. At the peak of the antibody response in the primary host, memory B cells and their progeny were unable to differentiate further to plasma cells due to their intrinsic suppressor-inducer activity, but this autoregulatory circuit could be severed by adoptive transfer to carrier-primed, X-irradiated recipients

Review article: closed-loop systems in anesthesia: is there a potential for closed-loop fluid management and hemodynamic optimization?

Science.gov (United States)

Rinehart, Joseph; Liu, Ngai; Alexander, Brenton; Cannesson, Maxime

2012-01-01

Closed-loop (automated) controllers are encountered in all aspects of modern life in applications ranging from air-conditioning to spaceflight. Although these systems are virtually ubiquitous, they are infrequently used in anesthesiology because of the complexity of physiologic systems and the difficulty in obtaining reliable and valid feedback data from the patient. Despite these challenges, closed-loop systems are being increasingly studied and improved for medical use. Two recent developments have made fluid administration a candidate for closed-loop control. First, the further description and development of dynamic predictors of fluid responsiveness provides a strong parameter for use as a control variable to guide fluid administration. Second, rapid advances in noninvasive monitoring of cardiac output and other hemodynamic variables make goal-directed therapy applicable for a wide range of patients in a variety of clinical care settings. In this article, we review the history of closed-loop controllers in clinical care, discuss the current understanding and limitations of the dynamic predictors of fluid responsiveness, and examine how these variables might be incorporated into a closed-loop fluid administration system.

Automatic Loop Parallelization via Compiler Guided Refactoring

DEFF Research Database (Denmark)

Larsen, Per; Ladelsky, Razya; Lidman, Jacob

For many parallel applications, performance relies not on instruction-level parallelism, but on loop-level parallelism. Unfortunately, many modern applications are written in ways that obstruct automatic loop parallelization. Since we cannot identify sufficient parallelization opportunities...... for these codes in a static, off-line compiler, we developed an interactive compilation feedback system that guides the programmer in iteratively modifying application source, thereby improving the compiler’s ability to generate loop-parallel code. We use this compilation system to modify two sequential...... benchmarks, finding that the code parallelized in this way runs up to 8.3 times faster on an octo-core Intel Xeon 5570 system and up to 12.5 times faster on a quad-core IBM POWER6 system. Benchmark performance varies significantly between the systems. This suggests that semi-automatic parallelization should...

Design and Implementation of Output Feedback Control for Piezo Actuated Structure Using Embedded System

Directory of Open Access Journals (Sweden)

R.Maheswari

2008-06-01

Full Text Available This paper presents the design of periodic output feedback control using state feedback gain to control the vibration of piezo actuated cantilever beam. The effectiveness of the controller is evaluated through simulation and experimentally by exciting the structure at resonance. Real time implementation of the controller is done using microcontroller. The closed loop eigen values of the system with periodic output feedback and state feedback are identical.

State Feedback Decoupling with In-Loop Lead Compensator in Stand-Alone VSIs

DEFF Research Database (Denmark)

Federico, de Bosio; Pastorelli, Michele; de Sousa Ribeiro, Luiz Antonio

2016-01-01

The performance of current and voltage regulators during transients and steady-state is of primary concern for power converters intended for stand-alone applications. Dynamics performance and command tracking capability are enhanced by actively decoupling the controlled states variables. To further...... widen the current loop bandwidth while still preserving a well-damped system a lead compensator structure on the forward loop is proposed. A 3 kHz bandwidth with 0.707 damping factor is achieved for the inner current controller. Accordingly, also the voltage regulator bandwidth can be widen, thus...

Improving Convergence of Iterative Feedback Tuning using Optimal External Perturbations

DEFF Research Database (Denmark)

Huusom, Jakob Kjøbsted; Hjalmarsson, Håkon; Poulsen, Niels Kjølstad

2008-01-01

Iterative feedback tuning constitutes an attractive control loop tuning method for processes in the absence of sufficient process insight. It is a purely data driven approach to optimization of the loop performance. The standard formulation ensures an unbiased estimate of the loop performance cost...... function gradient, which is used in a search algorithm. A slow rate of convergence of the tuning method is often experienced when tuning for disturbance rejection. This is due to a poor signal to noise ratio in the process data. A method is proposed for increasing the information content in data...

Virtual velocity loop based on MEMS accelerometers for optical stabilization control system

Science.gov (United States)

Ren, Wei; Deng, Chao; Mao, Yao; Ren, Ge

2017-08-01

In the optical stabilization control system (OSCS) control system based on a charge-coupled device (CCD), stabilization performance of the line-of-sight is severely limited by the mechanical resonance and the low sampling rate of the CCD. An approach to improve the stabilization performance of the OSCS control system with load restriction based on three loops, including an acceleration loop, a virtual velocity loop, and a position loop, by using MEMS accelerometers and a CCD is proposed. The velocity signal is obtained by accelerators instead of gyro sensors. Its advantages are low power, low cost, small size, and wide measuring range. A detailed analysis is provided to show how to design the virtual velocity loop and correct virtual velocity loop drift. Experimental results show that the proposed multiloop feedback control method with virtual velocity loop in which the disturbance suppression performance is better than that of the dual loop control with only an acceleration loop and a position loop at low frequency.

Multi-model MPC with output feedback

Directory of Open Access Journals (Sweden)

J. M. Perez

2014-03-01

Full Text Available In this work, a new formulation is presented for the model predictive control (MPC of a process system that is represented by a finite set of models, each one corresponding to a different operating point. The general case is considered of systems with stable and integrating outputs in closed-loop with output feedback. For this purpose, the controller is based on a non-minimal order model where the state is built with the measured outputs and the manipulated inputs of the control system. Therefore, the state can be considered as perfectly known and, consequently, there is no need to include a state observer in the control loop. This property of the proposed modeling approach is convenient to extend previous stability results of the closed loop system with robust MPC controllers based on state feedback. The controller proposed here is based on the solution of two optimization problems that are solved sequentially at the same time step. The method is illustrated with a simulated example of the process industry. The rigorous simulation of the control of an adiabatic flash of a multi-component hydrocarbon mixture illustrates the application of the robust controller. The dynamic simulation of this process is performed using EMSO - Environment Model Simulation and Optimization. Finally, a comparison with a linear MPC using a single model is presented.

Velocity feedback control with a flywheel proof mass actuator

Science.gov (United States)

Kras, Aleksander; Gardonio, Paolo

2017-08-01

This paper presents four new proof mass actuators to be used in velocity feedback control systems for the control of vibrations of machines and flexible structures. A classical proof mass actuator is formed by a coil-magnet linear motor, with either the magnet or the armature-coil proof mass suspended on soft springs. This arrangement produces a net force effect at frequencies above the fundamental resonance frequency of the springs-proof mass system. Thus, it can be used to implement point velocity feedback loops, although the dynamic response and static deflection of the springs-proof mass system poses some stability and control performance limitations. The four proof mass actuators presented in this study include a flywheel element, which is used to augment the inertia effect of the suspended proof mass. The paper shows that the flywheel element modifies both the dynamic response and static deflection of the springs-proof mass system in such a way as the stability and control performance of velocity feedback loops using these actuators are significantly improved.

A mixed incoherent feed-forward loop contributes to the regulation of bacterial photosynthesis genes.

Science.gov (United States)

Mank, Nils N; Berghoff, Bork A; Klug, Gabriele

2013-03-01

Living cells use a variety of regulatory network motifs for accurate gene expression in response to changes in their environment or during differentiation processes. In Rhodobacter sphaeroides, a complex regulatory network controls expression of photosynthesis genes to guarantee optimal energy supply on one hand and to avoid photooxidative stress on the other hand. Recently, we identified a mixed incoherent feed-forward loop comprising the transcription factor PrrA, the sRNA PcrZ and photosynthesis target genes as part of this regulatory network. This point-of-view provides a comparison to other described feed-forward loops and discusses the physiological relevance of PcrZ in more detail.

Dynamic Intelligent Feedback Scheduling in Networked Control Systems

Directory of Open Access Journals (Sweden)

Hui-ying Chen

2013-01-01

Full Text Available For the networked control system with limited bandwidth and flexible workload, a dynamic intelligent feedback scheduling strategy is proposed. Firstly, a monitor is used to acquire the current available network bandwidth. Then, the new available bandwidth in the next interval is predicted by using LS_SVM approach. At the same time, the dynamic performance indices of all control loops are obtained with a two-dimensional fuzzy logic modulator. Finally, the predicted network bandwidth is dynamically allocated by the bandwidth manager and the priority allocator in terms of the loops' dynamic performance indices. Simulation results show that the sampling periods and priorities of control loops are adjusted timely according to the network workload condition and the dynamic performance of control loops, which make the system running in the optimal state all the time.

Downregulation of IL6 Targeted MiR-376b May Contribute to a Positive IL6 Feedback Loop During Early Liver Regeneration in Mice

Directory of Open Access Journals (Sweden)

Shan Lu

2015-08-01

Full Text Available Background/Aims: MicroRNAs (miRNAs are a group of endogenous, small, noncoding RNAs implicated in a variety of biological processes, including cell proliferation, apoptosis, differentiation and metabolism. The present study aims to explore the potential role and molecular mechanism of miR-376b during the early phase of liver regeneration. Methods: MiRNA profiling microarrays were used to assess the changes in miRNA expression. For functional analysis, cell proliferation, apoptosis assays, real time quantitative PCR and westernblot analysis were performed. Results: The comprehensive miRNA expression profiling assays on regenerating liver tissues 4 h after partial hepatectomy (PH showed that three miRNAs (miR-127, miR-376b and miR-494 located in the Dlk1-Gtl2 miRNA cluster were significantly downregulated. In vitro functional studies demonstrated that high-level interleukin 6 (IL6 inhibited the expression of miR-376b, and miR-376b mimics treatment decreased cell proliferation and increased apoptosis. Further target analysis showed that miR-376b reduced the mRNA and protein expression levels of NF-kappa-B inhibitor zeta (NFKBIZ and signal transducers and transcription activators 3 (STAT3. Additionally, IL6-induced miR-376b downregulation would, in turn, increase the expression of IL-6 possibly via a feedback loop involving NFKBIZ or/and STAT3. Conclusion: During the early phase of liver regeneration, miR-376b expression was significantly decreased. Our findings reveal that a regulatory circuitry between miR-376b and IL-6 may exist, which trigger the initiation of liver regeneration.

Temperature control feedback loops for the linac upgrade side coupled cavities at Fermilab

International Nuclear Information System (INIS)

Crisp, J.

1990-01-01

The linac upgrade project at Fermilab will replace the last 4 drift-tube linac tanks with seven side coupled cavity strings. This will increase the beam energy from 200 to 400 MeV at injection into the Booster accelerator. The main objective of the temperature loop is to control the resonant frequency of the cavity strings. A cavity string will constant of 4 sections connected with bridge couplers driven with a 12 MW klystron at 805 MHz. Each section is a side coupled cavity chain consisting of 16 accelerating cells and 15 side coupling cells. For the linac upgrade, 7 full cavity strings will be used. A separate temperature control system is planned for each of the 28 accelerating sections, the two transition sections, and the debuncher section. The cavity strings will be tuned to resonance for full power beam loaded conditions. A separate frequency loop is planned that will sample the phase difference between a monitor placed in the end cell of each section and the rf drive. The frequency loop will control the set point for the temperature loop which will be able to maintain the resonant frequency through periods within beam or rf power. The frequency loop will need the intelligence required to determine under what conditions the phase error information is valid and the temperature set point should be adjusted. This paper will discuss some of the reason for temperature control, the implementation, and some of the problems encountered. An appendix contains some useful constants and descriptions of some of the sensor and control elements used. 13 figs

Efficient Closed-Loop Schemes for MIMO-OFDM-Based WLANs

Directory of Open Access Journals (Sweden)

Jiang Yi

2006-01-01

Full Text Available The single-input single-output (SISO orthogonal frequency-division multiplexing (OFDM systems for wireless local area networks (WLAN defined by the IEEE 802.11a standard can support data rates up to 54 Mbps. In this paper, we consider deploying two transmit and two receive antennas to increase the data rate up to 108 Mbps. Applying our recent multiple-input multiple-output (MIMO transceiver designs, that is, the geometric mean decomposition (GMD and the uniform channel decomposition (UCD schemes, we propose simple and efficient closed-loop MIMO-OFDM designs for much improved performance, compared to the standard singular value decomposition (SVD based schemes as well as the open-loop V-BLAST (vertical Bell Labs layered space-time based counterparts. In the explicit feedback mode, precoder feedback is needed for the proposed schemes. We show that the overhead of feedback can be made very moderate by using a vector quantization method. In the time-division duplex (TDD mode where the channel reciprocity is exploited, our schemes turn out to be robust against the mismatch between the uplink and downlink channels. The advantages of our schemes are demonstrated via extensive numerical examples.

Laser cooling in a feedback-controlled optical shaker

International Nuclear Information System (INIS)

Vilensky, Mark Y.; Averbukh, Ilya Sh.; Prior, Yehiam

2006-01-01

We explore the prospects of optical shaking, a recently suggested generic approach to laser cooling of neutral atoms and molecules. Optical shaking combines elements of Sisyphus cooling and of stochastic cooling techniques and is based on feedback-controlled interaction of particles with strong nonresonant laser fields. The feedback loop guarantees a monotonous energy decrease without a loss of particles. We discuss two types of feedback algorithms and provide an analytical estimation of their cooling rate. We study the robustness of optical shaking against noise and establish minimal stability requirements for the lasers. The analytical predictions are in a good agreement with the results of detailed numerical simulations

JMJD3 Is Crucial for the Female AVPV RIP-Cre Neuron-Controlled Kisspeptin-Estrogen Feedback Loop and Reproductive Function.

Science.gov (United States)

Song, Anying; Jiang, Shujun; Wang, Qinghua; Zou, Jianghuan; Lin, Zhaoyu; Gao, Xiang

2017-06-01

The hypothalamic-pituitary-gonadal axis controls development, reproduction, and metabolism. Although most studies have focused on the hierarchy from the brain to the gonad, many questions remain unresolved concerning the feedback from the gonad to the central nervous system, especially regarding the potential epigenetic modifications in hypothalamic neurons. In the present report, we generated genetically modified mice lacking histone H3 lysine 27 (H3K27) demethylase Jumonji domain-containing 3 (JMJD3) in hypothalamic rat-insulin-promoter-expressing neurons (RIP-Cre neurons). The female mutant mice displayed late-onset obesity owing to reduced locomotor activity and decreased energy expenditure. JMJD3 deficiency in RIP-Cre neurons also results in delayed pubertal onset, an irregular estrous cycle, impaired fertility, and accelerated ovarian failure in female mice owing to the dysregulation of the hypothalamic-ovarian axis. We found that JMJD3 directly regulates Kiss1 gene expression by binding to the Kiss1 promoter and triggering H3K27me3 demethylation in the anteroventral periventricular (AVPV) nucleus. Further study confirmed that the aberrations arose from impaired kisspeptin signaling in the hypothalamic AVPV nucleus and subsequent estrogen deficiency. Estrogen replacement therapy can reverse obesity in mutant mice. Moreover, we demonstrated that Jmjd3 is an estrogen target gene in the hypothalamus. These results provide direct genetic and molecular evidence that JMJD3 is a key mediator for the kisspeptin-estrogen feedback loop. Copyright © 2017 Endocrine Society.

Estimation of Parametric Fault in Closed-loop Systems

DEFF Research Database (Denmark)

Niemann, Hans Henrik; Poulsen, Niels Kjølstad

2015-01-01

The aim of this paper is to present a method for estimation of parametric faults in closed-loop systems. The key technology applied in this paper is coprime factorization of both the dynamic system as well as the feedback controller. Using the Youla-Jabr-Bongiorno-Kucera (YJBK) parameterization...

A closed-loop photon beam control study for the Advanced Light Source

International Nuclear Information System (INIS)

Portmann, G.; Bengtsson, J.

1993-05-01

The third generation Advanced Light Source (ALS) will produce extremely bright photon beams using undulators and wigglers. In order to position the photon beams accurate to the micron level, a closed-loop feedback system is being developed. Using photon position monitors and dipole corrector magnets, a closed-loop system can automatically compensate for modeling uncertainties and exogenous disturbances. The following paper will present a dynamics model for the perturbations of the closed orbit of the electron beam in the ALS storage ring including the vacuum chamber magnetic field penetration effects. Using this reference model, two closed-loop feedback algorithms will be compared -- a classical PI controller and a two degree-of-freedom approach. The two degree-of-freedom method provides superior disturbance rejection while maintaining the desired performance goals. Both methods will address the need to gain schedule the controller due to the time varying dynamics introduced by changing field strengths when scanning the insertion devices

Oncogenic MYC Activates a Feedforward Regulatory Loop Promoting Essential Amino Acid Metabolism and Tumorigenesis.

Science.gov (United States)

Yue, Ming; Jiang, Jue; Gao, Peng; Liu, Hudan; Qing, Guoliang

2017-12-26

Most tumor cells exhibit obligatory demands for essential amino acids (EAAs), but the regulatory mechanisms whereby tumor cells take up EAAs and EAAs promote malignant transformation remain to be determined. Here, we show that oncogenic MYC, solute carrier family (SLC) 7 member 5 (SLC7A5), and SLC43A1 constitute a feedforward activation loop to promote EAA transport and tumorigenesis. MYC selectively activates Slc7a5 and Slc43a1 transcription through direct binding to specific E box elements within both genes, enabling effective EAA import. Elevated EAAs, in turn, stimulate Myc mRNA translation, in part through attenuation of the GCN2-eIF2α-ATF4 amino acid stress response pathway, leading to MYC-dependent transcriptional amplification. SLC7A5/SLC43A1 depletion inhibits MYC expression, metabolic reprogramming, and tumor cell growth in vitro and in vivo. These findings thus reveal a MYC-SLC7A5/SLC43A1 signaling circuit that underlies EAA metabolism, MYC deregulation, and tumorigenesis. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

Kalman Orbit Optimized Loop Tracking

Science.gov (United States)

Young, Lawrence E.; Meehan, Thomas K.

2011-01-01

Under certain conditions of low signal power and/or high noise, there is insufficient signal to noise ratio (SNR) to close tracking loops with individual signals on orbiting Global Navigation Satellite System (GNSS) receivers. In addition, the processing power available from flight computers is not great enough to implement a conventional ultra-tight coupling tracking loop. This work provides a method to track GNSS signals at very low SNR without the penalty of requiring very high processor throughput to calculate the loop parameters. The Kalman Orbit-Optimized Loop (KOOL) tracking approach constitutes a filter with a dynamic model and using the aggregate of information from all tracked GNSS signals to close the tracking loop for each signal. For applications where there is not a good dynamic model, such as very low orbits where atmospheric drag models may not be adequate to achieve the required accuracy, aiding from an IMU (inertial measurement unit) or other sensor will be added. The KOOL approach is based on research JPL has done to allow signal recovery from weak and scintillating signals observed during the use of GPS signals for limb sounding of the Earth s atmosphere. That approach uses the onboard PVT (position, velocity, time) solution to generate predictions for the range, range rate, and acceleration of the low-SNR signal. The low- SNR signal data are captured by a directed open loop. KOOL builds on the previous open loop tracking by including feedback and observable generation from the weak-signal channels so that the MSR receiver will continue to track and provide PVT, range, and Doppler data, even when all channels have low SNR.

Learning from experience. Feedback to design

International Nuclear Information System (INIS)

Hopwood, J.M.; Shalaby, B.A.; Keil, H.

1997-01-01

AECL has been the designer of 25 commercial scale CANDU reactors now in operation, with more under construction. AECL has taken the evolutionary approach in developing its current designs, the CANDU 6 and CANDU 9 Nuclear Power Plants. An integral part of this approach is to emphasize feedback of experience to the designers, in a continuous improvement process. AECL has implemented a formal process of gathering and responding to feedback from: NPP operation, construction and commissioning; regulatory input; R and D results: as well as paying close attention to market input. A number of recent examples of design improvement via this feedback process are described

Assisted closed-loop optimization of SSVEP-BCI efficiency

Directory of Open Access Journals (Sweden)

Jacobo eFernandez-Vargas

2013-02-01

Full Text Available We designed a novel assisted closed-loop optimization protocol to improve the efficiency of brain computer interfaces (BCI based on steady state visually evoked potentials (SSVEP. In traditional paradigms, the control over the BCI-performance completely depends on the subjects’ ability to learn from the given feedback cues. By contrast, in the proposed protocol both the subject and the machine share information and control over the BCI goal. Generally, the innovative assistance consists in the delivery of online information together with the online adaptation of BCI stimuli properties. In our case, this adaptive optimization process is realized by (i a closed-loop search for the best set of SSVEP flicker frequencies and (ii feedback of actual SSVEP magnitudes to both the subject and the machine. These closed-loop interactions between subject and machine are evaluated in real-time by continuous measurement of their efficiencies, which are used as online criteria to adapt the BCI control parameters. The proposed protocol aims to compensate for variability in possibly unknown subjects’ state and trait dimensions. In a study with N = 18 subjects, we found significant evidence that our protocol outperformed classic SSVEP-BCI control paradigms. Evidence is presented that it takes indeed into account interindividual variabilities: e.g. under the new protocol, baseline resting state EEG measures predict subjects’ BCI performances. This paper illustrates the promising potential of assisted closed-loop protocols in BCI systems. Probably their applicability might be expanded to innovative uses, e.g. as possible new diagnostic/therapeutic tools for clinical contexts and as new paradigms for basic research.

Performance Measure as Feedback Variable in Image Processing

Directory of Open Access Journals (Sweden)

Ristić Danijela

2006-01-01

Full Text Available This paper extends the view of image processing performance measure presenting the use of this measure as an actual value in a feedback structure. The idea behind is that the control loop, which is built in that way, drives the actual feedback value to a given set point. Since the performance measure depends explicitly on the application, the inclusion of feedback structures and choice of appropriate feedback variables are presented on example of optical character recognition in industrial application. Metrics for quantification of performance at different image processing levels are discussed. The issues that those metrics should address from both image processing and control point of view are considered. The performance measures of individual processing algorithms that form a character recognition system are determined with respect to the overall system performance.

Sensing loop performance monitoring in the safety systems of nuclear power stations

International Nuclear Information System (INIS)

Colley, R.C.; Widmeyer, M.; Weiss, J.H.; Wiegle, H.R.

1991-01-01

This paper reports on plant technical specifications and NRC regulatory guides which require testing of sensing loops to detect degradation and failure. Industry efforts have focused on specific manual testing to detect individual failure modes such as increased response time and calibration drift. Recent work performed by EPRI and by others using instrument loop data, failure modes, and effects analyses (FMEAs), and experience with utility on-line sensor health monitoring programs has established qualitative physical models of the sensing loop. This methodology has demonstrated that sensing loop cross comparison techniques can provide equivalent indication of sensing loop performance. It also provides more frequent sensing loop health indication than manual testing and reduces the requirement for manual testing

Dual Nature of Translational Control by Regulatory BC RNAs ▿

Science.gov (United States)

Eom, Taesun; Berardi, Valerio; Zhong, Jun; Risuleo, Gianfranco; Tiedge, Henri

2011-01-01

In higher eukaryotes, increasing evidence suggests, gene expression is to a large degree controlled by RNA. Regulatory RNAs have been implicated in the management of neuronal function and plasticity in mammalian brains. However, much of the molecular-mechanistic framework that enables neuronal regulatory RNAs to control gene expression remains poorly understood. Here, we establish molecular mechanisms that underlie the regulatory capacity of neuronal BC RNAs in the translational control of gene expression. We report that regulatory BC RNAs employ a two-pronged approach in translational control. One of two distinct repression mechanisms is mediated by C-loop motifs in BC RNA 3′ stem-loop domains. These C-loops bind to eIF4B and prevent the factor's interaction with 18S rRNA of the small ribosomal subunit. In the second mechanism, the central A-rich domains of BC RNAs target eIF4A, specifically inhibiting its RNA helicase activity. Thus, BC RNAs repress translation initiation in a bimodal mechanistic approach. As BC RNA functionality has evolved independently in rodent and primate lineages, our data suggest that BC RNA translational control was necessitated and implemented during mammalian phylogenetic development of complex neural systems. PMID:21930783

Focal Dystonia and the Sensory-Motor Integrative Loop for Enacting (SMILE)

OpenAIRE

David ePerruchoud; Micah M Murray; Micah M Murray; Jeremie eLefebvre; Silvio eIonta

2014-01-01

Performing accurate movements requires preparation, execution, and monitoring mechanisms. The first two are coded by the motor system, and the latter by the sensory system. To provide an adaptive neural basis to overt behaviors, motor and sensory information has to be properly integrated in a reciprocal feedback loop. Abnormalities in this sensory-motor loop are involved in movement disorders such as focal dystonia, a hyperkinetic alteration affecting only a specific body part and characteriz...

Focal dystonia and the Sensory-Motor Integrative Loop for Enacting (SMILE)

OpenAIRE

Perruchoud David; Murray Micah; Lefebvre Jeremie; Ionta Silvio

2014-01-01

Performing accurate movements requires preparation, execution, and monitoring mechanisms. The first two are coded by the motor system, the latter by the sensory system. To provide an adaptive neural basis to overt behaviors, motor and sensory information has to be properly integrated in a reciprocal feedback loop. Abnormalities in this sensory-motor loop are involved in movement disorders such as focal dystonia, a hyperkinetic alteration affecting only a specific body part and characterized b...

Brain-actuated gait trainer with visual and proprioceptive feedback

Science.gov (United States)

Liu, Dong; Chen, Weihai; Lee, Kyuhwa; Chavarriaga, Ricardo; Bouri, Mohamed; Pei, Zhongcai; Millán, José del R.

2017-10-01

Objective. Brain-machine interfaces (BMIs) have been proposed in closed-loop applications for neuromodulation and neurorehabilitation. This study describes the impact of different feedback modalities on the performance of an EEG-based BMI that decodes motor imagery (MI) of leg flexion and extension. Approach. We executed experiments in a lower-limb gait trainer (the legoPress) where nine able-bodied subjects participated in three consecutive sessions based on a crossover design. A random forest classifier was trained from the offline session and tested online with visual and proprioceptive feedback, respectively. Post-hoc classification was conducted to assess the impact of feedback modalities and learning effect (an improvement over time) on the simulated trial-based performance. Finally, we performed feature analysis to investigate the discriminant power and brain pattern modulations across the subjects. Main results. (i) For real-time classification, the average accuracy was 62.33 +/- 4.95 % and 63.89 +/- 6.41 % for the two online sessions. The results were significantly higher than chance level, demonstrating the feasibility to distinguish between MI of leg extension and flexion. (ii) For post-hoc classification, the performance with proprioceptive feedback (69.45 +/- 9.95 %) was significantly better than with visual feedback (62.89 +/- 9.20 %), while there was no significant learning effect. (iii) We reported individual discriminate features and brain patterns associated to each feedback modality, which exhibited differences between the two modalities although no general conclusion can be drawn. Significance. The study reported a closed-loop brain-controlled gait trainer, as a proof of concept for neurorehabilitation devices. We reported the feasibility of decoding lower-limb movement in an intuitive and natural way. As far as we know, this is the first online study discussing the role of feedback modalities in lower-limb MI decoding. Our results suggest that

RF feedback simulation for the PEP-II B Factory

International Nuclear Information System (INIS)

Tighe, R.

1994-06-01

A model, of the beam and RF system for PEP-11 has been developed to allow both time-domain simulation and frequency-domain analysis of the complete system. The model includes the full set of feedback loops and nonlinear elements such as the beam and klystron. The model may be used to predict beam and feedback stability in the presence of nonlinearities through time-domain simulation as well as system frequency response about a given operating point

Closing the Loop on Student Feedback: The Case of Australian and Scottish Universities

Science.gov (United States)

Shah, Mahsood; Cheng, Ming; Fitzgerald, Robert

2017-01-01

Universities have a long history of collecting student feedback using surveys and other mechanisms. The last decade has witnessed a significant shift in how student feedback is systematically collected, analysed, reported, and used by governments and institutions. This shift is due to a number of factors, including changes in government policy…

Mathematical Modeling of the Pituitary-Thyroid Feedback Loop: Role of a TSH-T3-Shunt and Sensitivity Analysis.

Science.gov (United States)

Berberich, Julian; Dietrich, Johannes W; Hoermann, Rudolf; Müller, Matthias A

2018-01-01

Despite significant progress in assay technology, diagnosis of functional thyroid disorders may still be a challenge, as illustrated by the vague upper limit of the reference range for serum thyrotropin ( TSH ). Diagnostical problems also apply to subjects affected by syndrome T, i.e., those 10% of hypothyroid patients who continue to suffer from poor quality of life despite normal TSH concentrations under substitution therapy with levothyroxine ( L - T 4 ). In this paper, we extend a mathematical model of the pituitary-thyroid feedback loop in order to improve the understanding of thyroid hormone homeostasis. In particular, we incorporate a TSH - T 3 -shunt inside the thyroid, whose existence has recently been demonstrated in several clinical studies. The resulting extended model shows good accordance with various clinical observations, such as a circadian rhythm in free peripheral triiodothyronine ( FT 3 ). Furthermore, we perform a sensitivity analysis of the derived model, revealing the dependence of TSH and hormone concentrations on different system parameters. The results have implications for clinical interpretation of thyroid tests, e.g., in the differential diagnosis of subclinical hypothyroidism.

Mathematical Modeling of the Pituitary–Thyroid Feedback Loop: Role of a TSH-T3-Shunt and Sensitivity Analysis

Directory of Open Access Journals (Sweden)

Julian Berberich

2018-03-01

Full Text Available Despite significant progress in assay technology, diagnosis of functional thyroid disorders may still be a challenge, as illustrated by the vague upper limit of the reference range for serum thyrotropin (TSH. Diagnostical problems also apply to subjects affected by syndrome T, i.e., those 10% of hypothyroid patients who continue to suffer from poor quality of life despite normal TSH concentrations under substitution therapy with levothyroxine (L-T4. In this paper, we extend a mathematical model of the pituitary–thyroid feedback loop in order to improve the understanding of thyroid hormone homeostasis. In particular, we incorporate a TSH-T3-shunt inside the thyroid, whose existence has recently been demonstrated in several clinical studies. The resulting extended model shows good accordance with various clinical observations, such as a circadian rhythm in free peripheral triiodothyronine (FT3. Furthermore, we perform a sensitivity analysis of the derived model, revealing the dependence of TSH and hormone concentrations on different system parameters. The results have implications for clinical interpretation of thyroid tests, e.g., in the differential diagnosis of subclinical hypothyroidism.

Mathematical Modeling of the Pituitary–Thyroid Feedback Loop: Role of a TSH-T3-Shunt and Sensitivity Analysis

Science.gov (United States)

Berberich, Julian; Dietrich, Johannes W.; Hoermann, Rudolf; Müller, Matthias A.

2018-01-01

Despite significant progress in assay technology, diagnosis of functional thyroid disorders may still be a challenge, as illustrated by the vague upper limit of the reference range for serum thyrotropin (TSH). Diagnostical problems also apply to subjects affected by syndrome T, i.e., those 10% of hypothyroid patients who continue to suffer from poor quality of life despite normal TSH concentrations under substitution therapy with levothyroxine (L-T4). In this paper, we extend a mathematical model of the pituitary–thyroid feedback loop in order to improve the understanding of thyroid hormone homeostasis. In particular, we incorporate a TSH-T3-shunt inside the thyroid, whose existence has recently been demonstrated in several clinical studies. The resulting extended model shows good accordance with various clinical observations, such as a circadian rhythm in free peripheral triiodothyronine (FT3). Furthermore, we perform a sensitivity analysis of the derived model, revealing the dependence of TSH and hormone concentrations on different system parameters. The results have implications for clinical interpretation of thyroid tests, e.g., in the differential diagnosis of subclinical hypothyroidism. PMID:29619006

A Complete Parametric Solutions of Eigenstructure Assignment by State-Derivative Feedback for Linear Control Systems

Directory of Open Access Journals (Sweden)

T. H. S. Abdelaziz

2005-01-01

Full Text Available In this paper we introduce a complete parametric approach for solving the problem of eigenstructure assignment via state-derivative feedback for linear systems. This problem is always solvable for any controllable systems iff the open-loop system matrix is nonsingular. In this work, two parametric solutions to the feedback gain matrix are introduced that describe the available degrees of freedom offered by the state-derivative feedback in selecting the associated eigenvectors from an admissible class. These freedoms can be utilized to improve robustness of the closed-loop system. Accordingly, the sensitivity of the assigned eigenvalues to perturbations in the system and gain matrix is minimized. Numerical examples are included to show the effectiveness of the proposed approach. 

Auto-Regulatory RNA Editing Fine-Tunes mRNA Re-Coding and Complex Behaviour in Drosophila

Science.gov (United States)

Savva, Yiannis A.; Jepson, James E.C; Sahin, Asli; Sugden, Arthur U.; Dorsky, Jacquelyn S.; Alpert, Lauren; Lawrence, Charles; Reenan, Robert A.

2014-01-01

Auto-regulatory feedback loops are a common molecular strategy used to optimize protein function. In Drosophila many mRNAs involved in neuro-transmission are re-coded at the RNA level by the RNA editing enzyme dADAR, leading to the incorporation of amino acids that are not directly encoded by the genome. dADAR also re-codes its own transcript, but the consequences of this auto-regulation in vivo are unclear. Here we show that hard-wiring or abolishing endogenous dADAR auto-regulation dramatically remodels the landscape of re-coding events in a site-specific manner. These molecular phenotypes correlate with altered localization of dADAR within the nuclear compartment. Furthermore, auto-editing exhibits sexually dimorphic patterns of spatial regulation and can be modified by abiotic environmental factors. Finally, we demonstrate that modifying dAdar auto-editing affects adaptive complex behaviors. Our results reveal the in vivo relevance of auto-regulatory control over post-transcriptional mRNA re-coding events in fine-tuning brain function and organismal behavior. PMID:22531175

COMMISSIONING OF THE DIGITAL TRANSVERSE BUNCH-BY-BUNCH FEEDBACK SYSTEM FOR THE TLS

International Nuclear Information System (INIS)

HU, K.H.; KUO, C.H.; CHOU, P.J.; LEE, D.; HSU, S.Y.; CHEN, J.; WANG, C.J.; HSU, K.T.; KOBAYASHI, K.; NAKAMURA, T.; CHAO, A.W.; WENG, W.T.

2006-01-01

Multi-bunch instabilities degrade beam quality through increased beam emittance, energy spread and even beam loss. Feedback systems are used to suppress multi-bunch instabilities associated with the resistive wall of the beam ducts, cavity-like structures, and trapped ions. A new digital transverse bunch-by-bunch feedback system has recently been commissioned at the Taiwan Light Source, and has replaced the previous analog system. The new system has the advantages that it enlarges the tune acceptance and improves damping for transverse instability at high currents, such that top-up operation is achieved. After a coupled-bunch transverse instability was suppressed, more than 350 mA was successfully stored during preliminary commissioning. In this new system, a single feedback loop simultaneously suppresses both horizontal and vertical multi-bunch instabilities. Investigating the characteristics of the feedback loop and further improving the system performances are the next short-term goals. The feedback system employs the latest generation of field-programmable gate array (FPGA) processor to process bunch signals. Memory has been installed to capture up to 250 msec of bunch oscillation signal, considering system diagnostics suitable to support various beam physics studies

RF Feedback Analysis for 4 cavities per klystron in PEP-II

International Nuclear Information System (INIS)

Corredoura, P.; Tighe, R.

1994-06-01

Lattice changes in the PEP-II high energy ring have made the concept of driving four cavities with a single klystron an attractive option. This paper examines the topology from a RF feedback point of view. Sources of error are identified and their magnitudes are estimated. The effect on the performance of the longitudinal impedance reducing feedback loops is calculated using control theory and Mathematica

A Looping-Based Model for Quenching Repression.

Directory of Open Access Journals (Sweden)

Yaroslav Pollak

2017-01-01

Full Text Available We model the regulatory role of proteins bound to looped DNA using a simulation in which dsDNA is represented as a self-avoiding chain, and proteins as spherical protrusions. We simulate long self-avoiding chains using a sequential importance sampling Monte-Carlo algorithm, and compute the probabilities for chain looping with and without a protrusion. We find that a protrusion near one of the chain's termini reduces the probability of looping, even for chains much longer than the protrusion-chain-terminus distance. This effect increases with protrusion size, and decreases with protrusion-terminus distance. The reduced probability of looping can be explained via an eclipse-like model, which provides a novel inhibitory mechanism. We test the eclipse model on two possible transcription-factor occupancy states of the D. melanogaster eve 3/7 enhancer, and show that it provides a possible explanation for the experimentally-observed eve stripe 3 and 7 expression patterns.

Block compressed sensing for feedback reduction in relay-aided multiuser full duplex networks

KAUST Repository

Elkhalil, Khalil

2016-08-11

Opportunistic user selection is a simple technique that exploits the spatial diversity in multiuser relay-aided networks. Nonetheless, channel state information (CSI) from all users (and cooperating relays) is generally required at a central node in order to make selection decisions. Practically, CSI acquisition generates a great deal of feedback overhead that could result in significant transmission delays. In addition to this, the presence of a full-duplex cooperating relay corrupts the fed back CSI by additive noise and the relay\\'s loop (or self) interference. This could lead to transmission outages if user selection is based on inaccurate feedback information. In this paper, we propose an opportunistic full-duplex feedback algorithm that tackles the above challenges. We cast the problem of joint user signal-to-noise ratio (SNR) and the relay loop interference estimation at the base-station as a block sparse signal recovery problem in compressive sensing (CS). Using existing CS block recovery algorithms, the identity of the strong users is obtained and their corresponding SNRs are estimated. Numerical results show that the proposed technique drastically reduces the feedback overhead and achieves a rate close to that obtained by techniques that require dedicated error-free feedback from all users. Numerical results also show that there is a trade-off between the feedback interference and load, and for short coherence intervals, full-duplex feedback achieves higher throughput when compared to interference-free (half-duplex) feedback. © 2016 IEEE.

Block compressed sensing for feedback reduction in relay-aided multiuser full duplex networks

KAUST Repository

Elkhalil, Khalil; Eltayeb, Mohammed; Kammoun, Abla; Al-Naffouri, Tareq Y.; Bahrami, Hamid Reza

2016-01-01

Opportunistic user selection is a simple technique that exploits the spatial diversity in multiuser relay-aided networks. Nonetheless, channel state information (CSI) from all users (and cooperating relays) is generally required at a central node in order to make selection decisions. Practically, CSI acquisition generates a great deal of feedback overhead that could result in significant transmission delays. In addition to this, the presence of a full-duplex cooperating relay corrupts the fed back CSI by additive noise and the relay's loop (or self) interference. This could lead to transmission outages if user selection is based on inaccurate feedback information. In this paper, we propose an opportunistic full-duplex feedback algorithm that tackles the above challenges. We cast the problem of joint user signal-to-noise ratio (SNR) and the relay loop interference estimation at the base-station as a block sparse signal recovery problem in compressive sensing (CS). Using existing CS block recovery algorithms, the identity of the strong users is obtained and their corresponding SNRs are estimated. Numerical results show that the proposed technique drastically reduces the feedback overhead and achieves a rate close to that obtained by techniques that require dedicated error-free feedback from all users. Numerical results also show that there is a trade-off between the feedback interference and load, and for short coherence intervals, full-duplex feedback achieves higher throughput when compared to interference-free (half-duplex) feedback. © 2016 IEEE.

Effect of State Feedback Coupling and System Delays on the Transient Performance of Stand-Alone VSI with LC Output Filter

DEFF Research Database (Denmark)

Federico, de Bosio; de Sousa Ribeiro, Luiz Antonio; Freijedo Fernandez, Francisco Daniel

2016-01-01

The influence of state feedback coupling in the dynamics performance of power converters for stand-alone microgrids is investigated. Computation and PWM delays are the main factors that limit the achievable bandwidth of current regulators in digital implementations. In particular, the performance...... of state feedback decoupling is degraded because of these delays. Two decoupling techniques to improve the transient response of the system are investigated, named non-ideal and ideal capacitor voltage decoupling respectively. In particular, the latter solution consists in leading the capacitor voltage...... on the state feedback decoupling path in order to compensate for system delays. Practical implementation issues are discussed with reference to both the decoupling techniques. A design methodology for the voltage loop, that considers the closed loop transfer functions developed for the inner loop, is also...

Constructive feedback as a learning tool to enhance students' self ...

African Journals Online (AJOL)

If feedback is provided in a way that can develop students' self-regulatory skills, it could enhance learning and, consequently, lead to improved performance. To improve teaching and learning in higher education (HE), this study sought to determine whether the feedback to first-year students affords them an opportunity to ...

Numerical static state feedback laws for closed-loop singular optimal control

NARCIS (Netherlands)

Graaf, de S.C.; Stigter, J.D.; Straten, van G.

2005-01-01

Singular and non-singular control trajectories of agricultural and (bio) chemical processes may need to be recalculated from time to time for use in closed-loop optimal control, because of unforeseen changes in state values and noise. This is time consuming. As an alternative, in this paper,

SPIRONOLACTONE IN BIOFEEDBACK SESSIONS IN THE LOOP OF PACED BREATHING AND HEART RATE VARIABILITY IN HEALTHY VOLUNTEERS

Directory of Open Access Journals (Sweden)

E. Nazarenko

2015-12-01

Full Text Available In 7 conditionally healthy volunteers, aged from 19 to 21 years (average age is 19,53 ± 1,55 years, influence of spironolactone on alterations of regulatory systems state of the organism combined with biofeedback (BFB sessions in the loop of paced breathing (PB and heart rate variability (HRV parameters was evaluated. All volunteers were conducted 2 series of everyday BFB sessions in analyzed loop for 5 days with a 3 months interval between them, 2nd series of sessions were conducted 6 hours after oral application of 25 mg spironolactone. The data was analyzed using non-parametric statistical methods. Optimization of regulatory systems state under influence of BFB sessions in the loop of PB and HRV parameters was found. Spironolactone in studied dose had no significant effect on optimization of regulatory systems state.

Reduction of the elevator illusion from continued hypergravity exposure and visual error-corrective feedback

Science.gov (United States)

Welch, R. B.; Cohen, M. M.; DeRoshia, C. W.

1996-01-01

Ten subjects served as their own controls in two conditions of continuous, centrifugally produced hypergravity (+2 Gz) and a 1-G control condition. Before and after exposure, open-loop measures were obtained of (1) motor control, (2) visual localization, and (3) hand-eye coordination. During exposure in the visual feedback/hypergravity condition, subjects received terminal visual error-corrective feedback from their target pointing, and in the no-visual feedback/hypergravity condition they pointed open loop. As expected, the motor control measures for both experimental conditions revealed very short lived underreaching (the muscle-loading effect) at the outset of hypergravity and an equally transient negative aftereffect on returning to 1 G. The substantial (approximately 17 degrees) initial elevator illusion experienced in both hypergravity conditions declined over the course of the exposure period, whether or not visual feedback was provided. This effect was tentatively attributed to habituation of the otoliths. Visual feedback produced a smaller additional decrement and a postexposure negative after-effect, possible evidence for visual recalibration. Surprisingly, the target-pointing error made during hypergravity in the no-visual-feedback condition was substantially less than that predicted by subjects' elevator illusion. This finding calls into question the neural outflow model as a complete explanation of this illusion.

Closed-Loop Tension Control System for Injection Moulding Machine

African Journals Online (AJOL)

When the mould unit is full, this drive keeps transporting filament materials without proper control. This project developed a closed loop feedback tension control system and it is to replace servo motor drive system for the transportation of filament and it demonstrated a new technological advancement and the theory of ...

Closed-loop control of renal perfusion pressure in physiological experiments.

Science.gov (United States)

Campos-Delgado, D U; Bonilla, I; Rodríguez-Martínez, M; Sánchez-Briones, M E; Ruiz-Hernández, E

2013-07-01

This paper presents the design, experimental modeling, and control of a pump-driven renal perfusion pressure (RPP)-regulatory system to implement precise and relatively fast RPP regulation in rats. The mechatronic system is a simple, low-cost, and reliable device to automate the RPP regulation process based on flow-mediated occlusion. Hence, the regulated signal is the RPP measured in the left femoral artery of the rat, and the manipulated variable is the voltage applied to a dc motor that controls the occlusion of the aorta. The control system is implemented in a PC through the LabView software, and a data acquisition board NI USB-6210. A simple first-order linear system is proposed to approximate the dynamics in the experiment. The parameters of the model are chosen to minimize the error between the predicted and experimental output averaged from eight input/output datasets at different RPP operating conditions. A closed-loop servocontrol system based on a pole-placement PD controller plus dead-zone compensation was proposed for this purpose. First, the feedback structure was validated in simulation by considering parameter uncertainty, and constant and time-varying references. Several experimental tests were also conducted to validate in real time the closed-loop performance for stepwise and fast switching references, and the results show the effectiveness of the proposed automatic system to regulate the RPP in the rat, in a precise, accurate (mean error less than 2 mmHg) and relatively fast mode (10-15 s of response time).

Controllability analysis of transcriptional regulatory networks reveals circular control patterns among transcription factors

DEFF Research Database (Denmark)

Österlund, Tobias; Bordel, Sergio; Nielsen, Jens

2015-01-01

% for the human network. The high controllability (low number of drivers needed to control the system) in yeast, mouse and human is due to the presence of internal loops in their regulatory networks where the TFs regulate each other in a circular fashion. We refer to these internal loops as circular control...... motifs (CCM). The E. coli transcriptional regulatory network, which does not have any CCMs, shows a hierarchical structure of the transcriptional regulatory network in contrast to the eukaryal networks. The presence of CCMs also has influence on the stability of these networks, as the presence of cycles...

Joint angle sensors for closed-loop control

Science.gov (United States)

Ko, Wen H.; Miao, Chih-Lei

In order to substitute braces that have built-in goniometers and to provide feedback signals for closed loop control of lower extremity Functional Neuromuscular System in paraplegics, a stretchable capacitive sensor was developed to accurately detect angular movement in joints. Promising clinical evaluations on the knee joints of a paraplegic and a volunteer were done. The evaluations show great promise for the possibility of implantation applications.

Global output feedback stabilisation of stochastic high-order feedforward nonlinear systems with time-delay

Science.gov (United States)

Zhang, Kemei; Zhao, Cong-Ran; Xie, Xue-Jun

2015-12-01

This paper considers the problem of output feedback stabilisation for stochastic high-order feedforward nonlinear systems with time-varying delay. By using the homogeneous domination theory and solving several troublesome obstacles in the design and analysis, an output feedback controller is constructed to drive the closed-loop system globally asymptotically stable in probability.

Linking Multimodal Communication and Feedback Loops to Reinforce Plagiarism Awareness

Science.gov (United States)

O'Donnell, Kerri

2011-01-01

In this article, the author describes the use of an electronic quiz on a trial basis as a means of improving students' awareness of academic misconduct issues and their understanding of how to avoid those issues. The quiz integrated several new factors into information-sharing processes, increasing feedback to both students and staff. It was by no…

Self-sustained oscillations of complex genomic regulatory networks

International Nuclear Information System (INIS)

Ye Weiming; Huang Xiaodong; Huang Xuhui; Li Pengfei; Xia Qinzhi; Hu Gang

2010-01-01

Recently, self-sustained oscillations in complex networks consisting of non-oscillatory nodes have attracted great interest in diverse natural and social fields. Oscillatory genomic regulatory networks are one of the most typical examples of this kind. Given an oscillatory genomic network, it is important to reveal the central structure generating the oscillation. However, if the network consists of large numbers of genes and interactions, the oscillation generator is deeply hidden in the complicated interactions. We apply the dominant phase-advanced driving path method proposed in Qian et al. (2010) to reduce complex genomic regulatory networks to one-dimensional and unidirectionally linked network graphs where negative regulatory loops are explored to play as the central generators of the oscillations, and oscillation propagation pathways in the complex networks are clearly shown by tree branches radiating from the loops. Based on the above understanding we can control oscillations of genomic networks with high efficiency.

Feedback stabilization of the axisymmetric instability of a deformable tokamak plasma

International Nuclear Information System (INIS)

Pomphrey, N.; Jardin, S.C.; Ward, D.J.

1989-01-01

The paper presents an analysis of the magnetohydrodynamic stability of the axisymmetric system consisting of a free boundary tokamak plasma with non-circular cross-section, finite resistivity passive conductors, and an active feedback system with magnetic flux pickup loops, a proportional amplifier with gain G and current carrying poloidal field coils. A numerical simulation of the system when G is set to zero identifies flux loop locations which correctly sense the plasma motion. However, when certain of these locations are incorporated into an active feedback scheme, the plasma fails to be stabilized, no matter what value of the gain is chosen. Analysis on the basis of an extended energy principle indicates that this failure is due to the deformability of the plasma cross-section. (author). 14 refs, 7 figs

The regulatory function of self-esteem: testing the epistemic and acceptance signaling systems.

Science.gov (United States)

Stinson, Danu Anthony; Logel, Christine; Holmes, John G; Wood, Joanne V; Forest, Amanda L; Gaucher, Danielle; Fitzsimons, Grainné M; Kath, Jennifer

2010-12-01

The authors draw on sociometer theory (e.g., Leary, 2004) and self-verification theory (e.g., Swann, 1997) to propose an expanded model of the regulatory function of self-esteem. The model suggests that people not only possess an acceptance signaling system that indicates whether relational value is high or low but also possess an epistemic signaling system that indicates whether social feedback is consistent or inconsistent with chronic perceived relational value (i.e., global self-esteem). One correlational study and 5 experiments, with diverse operationalizations of social feedback, demonstrated that the epistemic signaling system responds to self-esteem consistent or inconsistent relational-value feedback with increases or deceases in epistemic certainty. Moreover, Studies 3-6 demonstrated that the acceptance and epistemic signaling systems respond uniquely to social feedback. Finally, Studies 5 and 6 provide evidence that the epistemic signaling system is part of a broader self-regulatory system: Self-esteem inconsistent feedback caused cognitive efforts to decrease the discrepancy between self-views and feedback and caused depleted self-regulatory capacity on a subsequent self-control task. PsycINFO Database Record (c) 2010 APA, all rights reserved.

Including model uncertainty in the model predictive control with output feedback

Directory of Open Access Journals (Sweden)

Rodrigues M.A.

2002-01-01

Full Text Available This paper addresses the development of an efficient numerical output feedback robust model predictive controller for open-loop stable systems. Stability of the closed loop is guaranteed by using an infinite horizon predictive controller and a stable state observer. The performance and the computational burden of this approach are compared to a robust predictive controller from the literature. The case used for this study is based on an industrial gasoline debutanizer column.

Physical limits of feedback noise-suppression in biological networks

International Nuclear Information System (INIS)

Zhang, Jiajun; Yuan, Zhanjiang; Zhou, Tianshou

2009-01-01

Feedback is a ubiquitous control mechanism of biological networks, and has also been identified in a variety of regulatory systems and organisms. It has been shown that, for a given gain and with negligible intrinsic noise, negative feedback impairs noise buffering whereas positive feedback enhances noise buffering. We further investigate the influence of negative and positive feedback on noise in output signals by considering both intrinsic and extrinsic noise as well as operator noise. We find that, while maintaining the system sensitivity, either there exists a minimum of the output noise intensity corresponding to a biologically feasible feedback strength, or the output noise intensity is a monotonic function of feedback strength bounded by both biological and dynamical constraints. In both cases, feedback noise-suppression is physically limited. In other words, noise suppressed by negative or positive feedback cannot be reduced without limitation even in the case of slow transcription

Normal mode approach to modelling of feedback stabilization of the resistive wall mode

International Nuclear Information System (INIS)

Chu, M.S.; Chance, M.S.; Okabayashi, M.; Glasser, A.H.

2003-01-01

Feedback stabilization of the resistive wall mode (RWM) of a plasma in a general feedback configuration is formulated in terms of the normal modes of the plasma-resistive wall system. The growth/damping rates and the eigenfunctions of the normal modes are determined by an extended energy principle for the plasma during its open (feedback) loop operation. A set of equations are derived for the time evolution of these normal modes with currents in the feedback coils. The dynamics of the feedback system is completed by the prescription of the feedback logic. The feasibility of the feedback is evaluated by using the Nyquist diagram method or by solving the characteristic equations. The elements of the characteristic equations are formed from the growth and damping rates of the normal modes, the sensor matrix of the perturbation fluxes detected by the sensor loops, the excitation matrix of the energy input to the normal modes by the external feedback coils, and the feedback logic. (The RWM is also predicted to be excited by an external error field to a large amplitude when it is close to marginal stability.) This formulation has been implemented numerically and applied to the DIII-D tokamak. It is found that feedback with poloidal sensors is much more effective than feedback with radial sensors. Using radial sensors, increasing the number of feedback coils from a central band on the outboard side to include an upper and a lower band can substantially increase the effectiveness of the feedback system. The strength of the RWM that can be stabilized is increased from γτ w = 1 to 30 (γ is the growth rate of the RWM in the absence of feedback and τ w is the resistive wall time constant) Using poloidal sensors, just one central band of feedback coils is sufficient for the stabilization of the RWM with γτ w = 30. (author)

Impact of biogenic emissions on feedbacks in the climate system

Science.gov (United States)

Krüger, Olaf

2017-04-01

Impact of biogenic emissions on feedbacks in the climate system Bio-geophysical feedback between marine or continental ecosystems and the atmosphere potentially can alter climate change. A prominent feedback loop which is under discussion since 1983 bases on the emission of biologically produced gases - molecular oxygen, sulphur containing compounds and possibly isoprene, supersaturated in oceanic waters - into the marine troposphere. These by-products of phytoplankton metabolism lead to aerosol production and procure sustained influence on climate via modulation of cloud optical properties. In this contribution some findings related to the above mentioned climate processes are presented with special emphasis on marine ecosystems. A comparison of marine and continental ecosystems is made and different processes with major impact on feedbacks in the climate system are discussed.

Feedbacks in human-landscape systems

Science.gov (United States)

Chin, Anne

2015-04-01

As human interactions with Earth systems intensify in the "Anthropocene", understanding the complex relationships among human activity, landscape change, and societal responses to those changes is increasingly important. Interdisciplinary research centered on the theme of "feedbacks" in human-landscape systems serves as a promising focus for unraveling these interactions. Deciphering interacting human-landscape feedbacks extends our traditional approach of considering humans as unidirectional drivers of change. Enormous challenges exist, however, in quantifying impact-feedback loops in landscapes with significant human alterations. This paper illustrates an example of human-landscape interactions following a wildfire in Colorado (USA) that elicited feedback responses. After the 2012 Waldo Canyon Fire, concerns for heightened flood potential and debris flows associated with post-fire hydrologic changes prompted local landowners to construct tall fences at the base of a burned watershed. These actions changed the sediment transport regime and promoted further landscape change and human responses in a positive feedback cycle. The interactions ultimately increase flood and sediment hazards, rather than dampening the effects of fire. A simple agent-based model, capable of integrating social and hydro-geomorphological data, demonstrates how such interacting impacts and feedbacks could be simulated. Challenges for fully capturing human-landscape feedback interactions include the identification of diffuse and subtle feedbacks at a range of scales, the availability of data linking impact with response, the identification of multiple thresholds that trigger feedback mechanisms, and the varied metrics and data needed to represent both the physical and human systems. By collaborating with social scientists with expertise in the human causes of landscape change, as well as the human responses to those changes, geoscientists could more fully recognize and anticipate the coupled

PKC-theta in regulatory and effector T-cell functions

Directory of Open Access Journals (Sweden)

Vedran eBrezar

2015-10-01

Full Text Available One of the major goals in immunology research is to understand the regulatory mechanisms that underpin the rapid switch on/off of robust and efficient effector (Teff or regulatory (Tregs T-cell responses. Understanding the molecular mechanisms underlying the regulation of such responses is critical for the development of effective therapies. T-cell activation involves the engagement of T-cell receptor and co-stimulatory signals, but the subsequent recruitment of serine/threonine-specific protein Kinase C-theta (PKC-θ to the immunological synapse is instrumental for the formation of signalling complexes, that ultimately lead to a transcriptional network in T cells. Recent studies demonstrated that major differences between Teffs and Tregs occurred at the immunological synapse where its formation induces altered signalling pathways in Tregs. These pathways are characterized by reduced recruitment of PKC-θ, suggesting that PKC-θ inhibits Tregs suppressive function in a negative feedback loop. As the balance of Teffs and Tregs has been shown to be central in several diseases, it was not surprising that some studies revealed that PKC-θ plays a major role in the regulation of this balance.This review will examine recent knowledge on the role of PKC-θ in T-cell transcriptional responses and how this protein can impact on the function of both Tregs and Teffs.

HER2 in Breast Cancer Stemness: A Negative Feedback Loop towards Trastuzumab Resistance

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Babak Nami

2017-04-01

Full Text Available HER2 receptor tyrosine kinase that is overexpressed in approximately 20% of all breast cancers (BCs is a poor prognosis factor and a precious target for BC therapy. Trastuzumab is approved by FDA to specifically target HER2 for treating HER2+ BC. However, about 60% of patients with HER2+ breast tumor develop de novo resistance to trastuzumab, partially due to the loss of expression of HER2 extracellular domain on their tumor cells. This is due to shedding/cleavage of HER2 by metalloproteinases (ADAMs and MMPs. HER2 shedding results in the accumulation of intracellular carboxyl-terminal HER2 (p95HER2, which is a common phenomenon in trastuzumab-resistant tumors and is suggested as a predictive marker for trastuzumab resistance. Up-regulation of the metalloproteinases is a poor prognosis factor and is commonly seen in mesenchymal-like cancer stem cells that are risen during epithelial to mesenchymal transition (EMT of tumor cells. HER2 cleavage during EMT can explain why secondary metastatic tumors with high percentage of mesenchymal-like cancer stem cells are mostly resistant to trastuzumab but still sensitive to lapatinib. Importantly, many studies report HER2 interaction with oncogenic/stemness signaling pathways including TGF-β/Smad, Wnt/β-catenin, Notch, JAK/STAT and Hedgehog. HER2 overexpression promotes EMT and the emergence of cancer stem cell properties in BC. Increased expression and activation of metalloproteinases during EMT leads to proteolytic cleavage and shedding of HER2 receptor, which downregulates HER2 extracellular domain and eventually increases trastuzumab resistance. Here, we review the hypothesis that a negative feedback loop between HER2 and stemness signaling drives resistance of BC to trastuzumab.

Brain-Computer Interfaces With Multi-Sensory Feedback for Stroke Rehabilitation: A Case Study.

Science.gov (United States)

Irimia, Danut C; Cho, Woosang; Ortner, Rupert; Allison, Brendan Z; Ignat, Bogdan E; Edlinger, Guenter; Guger, Christoph

2017-11-01

Conventional therapies do not provide paralyzed patients with closed-loop sensorimotor integration for motor rehabilitation. This work presents the recoveriX system, a hardware and software platform that combines a motor imagery (MI)-based brain-computer interface (BCI), functional electrical stimulation (FES), and visual feedback technologies for a complete sensorimotor closed-loop therapy system for poststroke rehabilitation. The proposed system was tested on two chronic stroke patients in a clinical environment. The patients were instructed to imagine the movement of either the left or right hand in random order. During these two MI tasks, two types of feedback were provided: a bar extending to the left or right side of a monitor as visual feedback and passive hand opening stimulated from FES as proprioceptive feedback. Both types of feedback relied on the BCI classification result achieved using common spatial patterns and a linear discriminant analysis classifier. After 10 sessions of recoveriX training, one patient partially regained control of wrist extension in her paretic wrist and the other patient increased the range of middle finger movement by 1 cm. A controlled group study is planned with a new version of the recoveriX system, which will have several improvements. © 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Feedback Linearization Based Arc Length Control for Gas Metal Arc Welding

DEFF Research Database (Denmark)

Thomsen, Jesper Sandberg

2005-01-01

a linear system to be controlled by linear state feedback control. The advantage of using a nonlinear approach as feedback linearization is the ability of this method to cope with nonlinearities and different operating points. However, the model describing the GMAW process is not exact, and therefore......In this paper a feedback linearization based arc length controller for gas metal arc welding (GMAW) is described. A nonlinear model describing the dynamic arc length is transformed into a system where nonlinearities can be cancelled by a nonlinear state feedback control part, and thus, leaving only......, the cancellation of nonlinear terms might give rise to problems with respect to robustness. Robustness of the closed loop system is therefore nvestigated by simulation....

Towards the use of Structural Loop Analysis to Study System Behaviour of Socio-Ecological Systems.

Science.gov (United States)

Abram, Joseph; Dyke, James

2016-04-01

Maintaining socio-ecological systems in desirable states is key to developing a growing economy, alleviating poverty and achieving a sustainable future. While the driving forces of an environmental system are often well known, the dynamics impacting these drivers can be hidden within a tangled structure of causal chains and feedback loops. A lack of understanding of a system's dynamic structure and its influence on a system's behaviour can cause unforeseen side-effects during model scenario testing and policy implementation. Structural Loop analysis of socio-ecological system models identifies dominant feedback structures during times of behavioural shift, allowing the user to monitor key influential drivers during model simulation. This work carries out Loop Eigenvalue Elasticity Analysis (LEEA) on three system dynamic models, exploring tipping points in lake systems undergoing eutrophication. The purpose is to explore the potential benefits and limitations of the technique in the field of socio-ecology. The LEEA technique shows promise for socio-ecological systems which undergo regime shifts or express oscillatory trends, but shows limited usefulness with large models. The results of this work highlight changes in feedback loop dominance, years prior to eutrophic tipping events in lake systems. LEEA could be used as an early warning signal to impending system changes, complementary to other known early warning signals. This approach could improve our understanding during critical times of a system's behaviour, changing how we approach model analysis and the way scenario testing and policy implementation are addressed in socio-ecological system models.

Pharmacodynamic/Pharmacogenomic Modeling of Insulin Resistance Genes in Rat Muscle After Methylprednisolone Treatment: Exploring Regulatory Signaling Cascades

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Zhenling Yao

2008-01-01

Full Text Available Corticosteroids (CS effects on insulin resistance related genes in rat skeletal muscle were studied. In our acute study, adrenalectomized (ADX rats were given single doses of 50 mg/kg methylprednisolone (MPL intravenously. In our chronic study, ADX rats were implanted with Alzet mini-pumps giving zero-order release rates of 0.3 mg/kg/h MPL and sacrificed at various times up to 7 days. Total RNA was extracted from gastrocnemius muscles and hybridized to Affymetrix GeneChips. Data mining and literature searches identified 6 insulin resistance related genes which exhibited complex regulatory pathways. Insulin receptor substrate-1 (IRS-1, uncoupling protein 3 (UCP3, pyruvate dehydrogenase kinase isoenzyme 4 (PDK4, fatty acid translocase (FAT and glycerol-3-phosphate acyltransferase (GPAT dynamic profiles were modeled with mutual effects by calculated nuclear drug-receptor complex (DR(N and transcription factors. The oscillatory feature of endothelin-1 (ET-1 expression was depicted by a negative feedback loop. These integrated models provide test- able quantitative hypotheses for these regulatory cascades.

An optimal open/closed-loop control method with application to a pre-stressed thin duralumin plate

Science.gov (United States)

Nadimpalli, Sruthi Raju

The excessive vibrations of a pre-stressed duralumin plate, suppressed by a combination of open-loop and closed-loop controls, also known as open/closed-loop control, is studied in this thesis. The two primary steps involved in this process are: Step (I) with an assumption that the closed-loop control law is proportional, obtain the optimal open-loop control by direct minimization of the performance measure consisting of energy at terminal time and a penalty on open-loop control force via calculus of variations. If the performance measure also involves a penalty on closed-loop control effort then a Fourier based method is utilized. Step (II) the energy at terminal time is minimized numerically to obtain optimal values of feedback gains. The optimal closed-loop control gains obtained are used to describe the displacement and the velocity of open-loop, closed-loop and open/closed-loop controlled duralumin plate.

Feedback-Controlled LED Photobioreactor for Photophysiological Studies of Cyanobacteria

Energy Technology Data Exchange (ETDEWEB)

Melnicki, Matthew R.; Pinchuk, Grigoriy E.; Hill, Eric A.; Kucek, Leo A.; Stolyar, Sergey; Fredrickson, Jim K.; Konopka, Allan; Beliaev, Alex S.

2013-04-09

A custom photobioreactor (PBR) was designed to enable automatic light adjustments using computerized feedback control. A black anodized aluminum enclosure, constructed to surround the borosilicate reactor vessel, prevents the transmission of ambient light and serves as a mount for arrays of light-emitting diodes (LEDs). The high-output LEDs provide narrow-band light of either 630 or 680 nm for preferential excitation of the cyanobacterial light-harvesting pigments, phycobilin or chlorophyll a, respectively. Custom developed software BioLume provides automatic control of optical properties and a computer feedback loop can automatically adjust the incident irradiance as necessary to maintain a fixed transmitted light through the culture, based on user-determined set points. This feedback control serves to compensate for culture dynamics which have optical effects, (e.g., changing cell density, pigment adaptations) and thus can determine the appropriate light conditions for physiological comparisons or to cultivate light-sensitive strains, without prior analyses. The LED PBR may also be controlled as a turbidostat, using a feedback loop to continuously adjust the rate of media-dilution based on the transmitted light measurements, with a fast and precise response. This cultivation system gains further merit as a high-performance analytical device, using non-invasive tools (e.g., dissolved gas sensors, online mass spectrometry) to automate real-time measurements, thus permitting unsupervised experiments to search for optimal growth conditions, to monitor physiological responses to perturbations, as well as to quantitate photophysiological parameters using an in situ light-saturation response routine.

Accountability feedback assessments for improving efficiency of nuclear regulatory institutions

International Nuclear Information System (INIS)

Lavarenne, Jean; Shwageraus, Eugene; Weightman, Michael

2016-01-01

The Fukushima-Daiichi Accident demonstrated the need of assessing and strengthening institutions involved in nuclear safety, including the accountability of regulators. There are a few problems hindering the path towards a greater understanding of accountability systems, the ensemble of mechanisms holding to account the nuclear regulator on behalf of the public. There is no consensus on what it should deliver and no systematic assessment method exists. This article proposes a method of assessing institutions based on defence in depth concepts and inspired from risk-assessment techniques used for nuclear safety. As a first step in testing the proposal, it presents a simple Monte-Carlo simulation, illustrating some of the workings of the method of assessment and demonstrating the kind of results it will be able to supply. This on-going work will assist policy-makers take better informed decisions about the size, structure and organisation of a nuclear regulator and the cost-effective funding of its accountability system. It will assist in striking a balance between efficiency and resilience of regulatory decision-making processes. It will also promote the involvement of stakeholders and allow them to have a more meaningful impact on regulatory decisions, thereby enhancing the robustness of the regulatory system and potentially trust and confidence. - Highlights: •A general introduction to regulatory accountability is given. •A definition of an effective accountability system is proposed. •A method to assess accountability systems is proposed. •A simplified simulation of a regulatory system demonstrates the method’s capabilities.

Generation of “gigantic” ultra-short microwave pulses based on passive mode-locking effect in electron oscillators with saturable absorber in the feedback loop

International Nuclear Information System (INIS)

Ginzburg, N. S.; Denisov, G. G.; Vilkov, M. N.; Zotova, I. V.; Sergeev, A. S.

2016-01-01

A periodic train of powerful ultrashort microwave pulses can be generated in electron oscillators with a non-linear saturable absorber installed in the feedback loop. This method of pulse formation resembles the passive mode-locking widely used in laser physics. Nevertheless, there is a specific feature in the mechanism of pulse amplification when consecutive energy extraction from different fractions of a stationary electron beam takes place due to pulse slippage over the beam caused by the difference between the wave group velocity and the electron axial velocity. As a result, the peak power of generated “gigantic” pulses can exceed not only the level of steady-state generation but also, in the optimal case, the power of the driving electron beam.

Individualising Media Practice Education Using a Feedback Loop and Instructional Videos Within an eLearning Environment.

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Trevor Harris

2012-06-01

Full Text Available This paper explores the development and impact of the author’s TELE (Technology Enhanced Learning Environment action research project for individualising media practice education. The latest iteration of different classroom methodologies being employed to develop high-level skills in media production, the author has combined an interactive eLearning approach with instructional videos and, crucially, an individual feedback loop in order to widen access to the curriculum and create a more efficient teaching and learning environment. The focus therefore is on student engagement and organisational efficiencies as a result of the research. It should be noted that there has been no funding attached to this work, nor are there any institutional imperatives or other stakeholder involvement in this research. This project has been undertaken by the author as an evolutionary development of the various methodologies developed, cognisant of the increased technology literacy of the student cohort. The educational benefit of bringing video instruction into the curriculum as part of the project is examined as a creative pedagogy of direct benefit to students rather than as a subliminal marketing tool that other systems are often used for. Over 16K words of written data was collected during the project, and this is analysed both quantitatively and qualitatively with reference to the initial objectives of the research

Fuzzy combination of fuzzy and switching state-feedback controllers for nonlinear systems subject to parameter uncertainties.

Science.gov (United States)

Lam, H K; Leung, Frank H F

2005-04-01

This paper presents a fuzzy controller, which involves a fuzzy combination of local fuzzy and global switching state-feedback controllers, for nonlinear systems subject to parameter uncertainties with known bounds. The nonlinear system is represented by a fuzzy combined Takagi-Sugeno-Kang model, which is a fuzzy combination of the global and local fuzzy plant models. By combining the local fuzzy and global switching state-feedback controllers using fuzzy logic techniques, the advantages of both controllers can be retained and the undesirable chattering effect introduced by the global switching state-feedback controller can be eliminated. The steady-state error introduced by the global switching state-feedback controller when a saturation function is used can also be removed. Stability conditions, which are related to the system matrices of the local and global closed-loop systems, are derived to guarantee the closed-loop system stability. An application example will be given to demonstrate the merits of the proposed approach.

Rail-to-rail low-power fully differential OTA utilizing adaptive biasing and partial feedback

DEFF Research Database (Denmark)

Tuan Vu, Cao; Wisland, Dag T.; Lande, Tor Sverre

consumption. The DC-gain of the proposed OTA is improved by adding a partial feedback loop. A Common-Mode Feedback (CMFB) circuit is required for fully differential rail-to-rail operation. Simulations show that the OTA topology has a low stand-by power consumption of 96μW and a high FoM of 3.84 [(V...

Leukemia Mediated Endothelial Cell Activation Modulates Leukemia Cell Susceptibility to Chemotherapy through a Positive Feedback Loop Mechanism.

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Bahareh Pezeshkian

Full Text Available In acute myeloid leukemia (AML, the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML.

A Design Algorithm using External Perturbation to Improve Iterative Feedback Tuning Convergence

DEFF Research Database (Denmark)

Huusom, Jakob Kjøbsted; Hjalmarsson, Håkan; Poulsen, Niels Kjølstad

2011-01-01

Iterative Feedback Tuning constitutes an attractive control loop tuning method for processes in the absence of process insight. It is a purely data driven approach for optimization of the loop performance. The standard formulation ensures an unbiased estimate of the loop performance cost function...... gradient, which is used in a search algorithm for minimizing the performance cost. A slow rate of convergence of the tuning method is often experienced when tuning for disturbance rejection. This is due to a poor signal to noise ratio in the process data. A method is proposed for increasing the data...

Gene dosage compensation calibrates four regulatory RNAs to control Vibrio cholerae quorum sensing

DEFF Research Database (Denmark)

Svenningsen, Sine L; Tu, Kimberly C; Bassler, Bonnie L

2009-01-01

the quorum regulatory RNAs 1-4 (Qrr1-4). The four Qrr sRNAs are functionally redundant. That is, expression of any one of them is sufficient for wild-type quorum-sensing behaviour. Here, we show that the combined action of two feedback loops, one involving the sRNA-activator LuxO and one involving the sRNA......Quorum sensing is a mechanism of cell-to-cell communication that allows bacteria to coordinately regulate gene expression in response to changes in cell-population density. At the core of the Vibrio cholerae quorum-sensing signal transduction pathway reside four homologous small RNAs (sRNAs), named......-target HapR, promotes gene dosage compensation between the four qrr genes. Gene dosage compensation adjusts the total Qrr1-4 sRNA pool and provides the molecular mechanism underlying sRNA redundancy. The dosage compensation mechanism is exquisitely sensitive to small perturbations in Qrr levels. Precisely...

Stability of longitudinal bunch length feedback for heavy-ion synchrotrons

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D. Lens

2013-03-01

Full Text Available In heavy-ion synchrotrons such as the SIS18 at Helmholtzzentrum für Schwerionenforschung, Helmholtz Centre for Heavy Ion Research (GSI, coherent oscillations of the particle bunches are damped by rf feedback systems to increase the stability and to improve the beam quality. In the longitudinal direction, important modes are the coherent longitudinal dipole and quadrupole oscillation. In this paper we present a new and rigorous approach to analyze the longitudinal feedback to damp these modes. The results are applied to the rf feedback loop at GSI that damps the quadrupole mode. The stability analysis is compared with simulations and is in good agreement with results of a beam experiment. Finally, we summarize practical implications for the operation of the feedback system regarding performance and stability.

Optimizing the feedback control of Galvo scanners for laser manufacturing systems

Science.gov (United States)

Mirtchev, Theodore; Weeks, Robert; Minko, Sergey

2010-06-01

This paper summarizes the factors that limit the performance of moving-magnet galvo scanners driven by closed-loop digital servo amplifiers: torsional resonances, drifts, nonlinearities, feedback noise and friction. Then it describes a detailed Simulink® simulator that takes into account these factors and can be used to automatically tune the controller for best results with given galvo type and trajectory patterns. It allows for rapid testing of different control schemes, for instance combined position/velocity PID loops and displays the corresponding output in terms of torque, angular position and feedback sensor signal. The tool is configurable and can either use a dynamical state-space model of galvo's open-loop response, or can import the experimentally measured frequency domain transfer function. Next a drive signal digital pre-filtering technique is discussed. By performing a real-time Fourier analysis of the raw command signal it can be pre-warped to minimize all harmonics around the torsional resonances while boosting other non-resonant high frequencies. The optimized waveform results in much smaller overshoot and better settling time. Similar performance gain cannot be extracted from the servo controller alone.

Skin barrier homeostasis in atopic dermatitis: feedback regulation of kallikrein activity.

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Reiko J Tanaka

Full Text Available Atopic dermatitis (AD is a widely spread cutaneous chronic disease characterised by sensitive reactions (eg. eczema to normally innocuous elements. Although relatively little is understood about its underlying mechanisms due to its complexity, skin barrier dysfunction has been recognised as a key factor in the development of AD. Skin barrier homeostasis requires tight control of the activity of proteases, called kallikreins (KLKs, whose activity is regulated by a complex network of protein interactions that remains poorly understood despite its pathological importance. Characteristic symptoms of AD include the outbreak of inflammation triggered by external (eg. mechanical and chemical stimulus and the persistence and aggravation of inflammation even if the initial stimulus disappears. These characteristic symptoms, together with some experimental data, suggest the presence of positive feedback regulation for KLK activity by inflammatory signals. We developed simple mathematical models for the KLK activation system to study the effects of feedback loops and carried out bifurcation analysis to investigate the model behaviours corresponding to inflammation caused by external stimulus. The model analysis confirmed that the hypothesised core model mechanisms capture the essence of inflammation outbreak by a defective skin barrier. Our models predicted the outbreaks of inflammation at weaker stimulus and its longer persistence in AD patients compared to healthy control. We also proposed a novel quantitative indicator for inflammation level by applying principal component analysis to microarray data. The model analysis reproduced qualitative AD characteristics revealed by this indicator. Our results strongly implicate the presence and importance of feedback mechanisms in KLK activity regulation. We further proposed future experiments that may provide informative data to enhance the system-level understanding on the regulatory mechanisms of skin barrier

Studies of feedback stabilization of axisymmetric modes in deformable tokamak plasmas

International Nuclear Information System (INIS)

Ward, D.J.

1991-01-01

A new linear MHD stability code, NOVA-W, is described and applied to the study of the feedback stabilization of the axisymmetric mode in deformable tokamak plasma. The NOVA-W code is a modification of the non-variational MHD stability code NOVA that includes the effects of resistive passive conductors and active feedback circuits. The vacuum calculation has been reformulated in terms of the perturbed poloidal flux to allow the inclusion of perturbed toroidal currents outside the plasma. The boundary condition at the plasma-vacuum interface relates the instability displacement to the perturbed poloidal flux. This allows a solution of the linear MHD stability equations with the feedback effects included. The code has been tested for the case of passive stabilization against a simplified analytic model and against a different numerical calculation for a realistic tokamak configuration. The comparisons demonstrate the accuracy of the NOVA-W results. The NOVA-W code is used to examine the effects of plasma deformability on feedback stabilization. It is seen that plasmas with shaped cross sections have unstable motion different from a rigid shift. Plasma equilibria with large triangularity show particularly significant deviations from a uniform rigid shift. Furthermore, the placement of passive conductors is shown to modify the non-rigid components of the motion in a way that reduces the stabilizing effects of these conductors. The eigenfunction is also modified under the effects of active feedback. This deformation is seen to depend strongly on the position of the flux loops. These non-rigid components of the eigenfunction always serve to reduce the stabilizing effect of the active feedback system by reducing the measurable poloidal flux at the flux-loop locations

Operation of the PEP transverse beam feedback

International Nuclear Information System (INIS)

Olson, C.W.; Paterson, J.M.; Pellegrin, J.L.; Rees, J.R.

1981-02-01

The PEP Storage Ring has been equipped with a wide band beam feedback system capable of damping the vertical and horizontal motion of six bunches. The oscillation detection is done at a symmetry point on the Storage Ring and feedback is applied at the same location one orbital period later. The signal is synchronously gated and the system appears as twelve independent feedback loops, operating on the two coordinates of each of the six bunches. Two beam deflection electrodes are driven each by a low-Q push-pull amplifier which is tuned at the 72nd harmonic of the revolution frequency and suppressed-carrier modulation is generated by a sequence of the detected bunch oscillations. The design parameters are reviewed as well as the salient features of the hardware, and the impact of this system on the machine operation is evaluated in the light of experimental results

MHD computation of feedback of resistive-shell instabilities in the reversed field pinch

International Nuclear Information System (INIS)

Zita, E.J.; Prager, S.C.

1992-05-01

MHD computation demonstrates that feedback can sustain reversal and reduce loop voltage in resistive-shell reversed field pinch (RFP) plasmas. Edge feedback on ∼2R/a tearing modes resonant near axis is found to restore plasma parameters to nearly their levels with a close-fitting conducting shell. When original dynamo modes are stabilized, neighboring tearing modes grow to maintain the RFP dynamo more efficiently. This suggests that experimentally observed limits on RFP pulselengths to the order of the shell time can be overcome by applying feedback to a few helical modes

Coherent feedback control of multipartite quantum entanglement for optical fields

Energy Technology Data Exchange (ETDEWEB)

Yan, Zhihui; Jia, Xiaojun; Xie, Changde; Peng, Kunchi [State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, 030006 (China)

2011-12-15

Coherent feedback control (CFC) of multipartite optical entangled states produced by a nondegenerate optical parametric amplifier is theoretically studied. The features of the quantum correlations of amplitude and phase quadratures among more than two entangled optical modes can be controlled by tuning the transmissivity of the optical beam splitter in the CFC loop. The physical conditions to enhance continuous variable multipartite entanglement of optical fields utilizing the CFC loop are obtained. The numeric calculations based on feasible physical parameters of realistic systems provide direct references for the design of experimental devices.

Operation and performance of a longitudinal feedback system using digital signal processing

International Nuclear Information System (INIS)

Teytelman, D.; Fox, J.; Hindi, H.

1994-01-01

A programmable longitudinal feedback system using a parallel array of AT ampersand T 1610 digital signal processors has been developed as a component of the PEP-II R ampersand D program. This system has been installed at the Advanced Light Source (LBL) and implements full speed bunch by bunch signal processing for storage rings with bunch spacing of 4ns. Open and closed loop results showing the action of the feedback system are presented, and the system is shown to damp coupled-bunch instabilities in the ALS. A unified PC-based software environment for the feedback system operation is also described

A switched state feedback law for the stabilization of LTI systems.

Energy Technology Data Exchange (ETDEWEB)

Santarelli, Keith R.

2009-09-01

Inspired by prior work in the design of switched feedback controllers for second order systems, we develop a switched state feedback control law for the stabilization of LTI systems of arbitrary dimension. The control law operates by switching between two static gain vectors in such a way that the state trajectory is driven onto a stable n - 1 dimensional hyperplane (where n represents the system dimension). We begin by briefly examining relevant geometric properties of the phase portraits in the case of two-dimensional systems to develop intuition, and we then show how these geometric properties can be expressed as algebraic constraints on the switched vector fields that are applicable to LTI systems of arbitrary dimension. We then derive necessary and sufficient conditions to ensure stabilizability of the resulting switched system (characterized primarily by simple conditions on eigenvalues), and describe an explicit procedure for designing stabilizing controllers. We then show how the newly developed control law can be applied to the problem of minimizing the maximal Lyapunov exponent of the corresponding closed-loop state trajectories, and we illustrate the closed-loop transient performance of these switched state feedback controllers via multiple examples.

Theoretical Approaches in Evolutionary Ecology: Environmental Feedback as a Unifying Perspective.

Science.gov (United States)

Lion, Sébastien

2018-01-01

Evolutionary biology and ecology have a strong theoretical underpinning, and this has fostered a variety of modeling approaches. A major challenge of this theoretical work has been to unravel the tangled feedback loop between ecology and evolution. This has prompted the development of two main classes of models. While quantitative genetics models jointly consider the ecological and evolutionary dynamics of a focal population, a separation of timescales between ecology and evolution is assumed by evolutionary game theory, adaptive dynamics, and inclusive fitness theory. As a result, theoretical evolutionary ecology tends to be divided among different schools of thought, with different toolboxes and motivations. My aim in this synthesis is to highlight the connections between these different approaches and clarify the current state of theory in evolutionary ecology. Central to this approach is to make explicit the dependence on environmental dynamics of the population and evolutionary dynamics, thereby materializing the eco-evolutionary feedback loop. This perspective sheds light on the interplay between environmental feedback and the timescales of ecological and evolutionary processes. I conclude by discussing some potential extensions and challenges to our current theoretical understanding of eco-evolutionary dynamics.

Phase loop bandwidth measurements on the advanced photon source 352 MHz rf systems

International Nuclear Information System (INIS)

Horan, D.; Nassiri, A.; Schwartz, C.

1997-01-01

Phase loop bandwidth tests were performed on the Advanced Photon Source storage ring 352-MHz rf systems. These measurements were made using the HP3563A Control Systems Analyzer, with the rf systems running at 30 kilowatts into each of the storage ring cavities, without stored beam. An electronic phase shifter was used to inject approximately 14 degrees of stimulated phase shift into the low-level rf system, which produced measureable response voltage in the feedback loops without upsetting normal rf system operation. With the PID (proportional-integral-differential) amplifier settings at the values used during accelerator operation, the measurement data revealed that the 3-dB response for the cavity sum and klystron power-phase loops is approximately 7 kHz and 45 kHz, respectively, with the cavities the primary bandwidth-limiting factor in the cavity-sum loop. Data were taken at various PID settings until the loops became unstable. Crosstalk between the two phase loops was measured

Regulatory Oversight for New Projects - Challenges and Improvement in Regulation

International Nuclear Information System (INIS)

Lall, F.

2016-01-01

From inception, there has been rise in number of Nuclear Power Plants (NPP) even though very few accidents / events led to intermittent setbacks. However these accidents / events have posed challenges towards enhancement of safety and scope of regulation in all phases of NPP such as siting, design, construction, commissioning and decommissioning. It is essential to ensure compliance to these enhanced safety requirements during all phases of NPP. New and evolutionary reactors are under threshold for regulatory consideration world over. The variety of technologies and genres by themselves pose challenges to regulatory bodies. These challenges are to be addressed through systematic enhancement of the regulation including updating of regulatory documents. The paper touches upon some key elements to be considered towards such enhancement of regulation during all stages of NPP. These being; ensuring quality assurance, regulatory oversight especially over supply chain and contractors, counterfeit material specifically in case of international dealings, emergency handling in case of multi-unit site, feedback and associated enhancements from international events, construction experience database and feedback for safety enhancement, qualification and acceptance of first of a kind systems, regulatory enforcement specifically in case of imported reactors and maintaining interface between safety and security. Regulation in present context has become dynamic and Regulatory bodies need to continue enhancement of its current regulation taking into account the technological developments, feedback from construction, operation and accidents in the current fleet of plants. The paper touches upon some of these elements and highlights the challenges and improvements in regulation. (author)

Variations in Static Force Control and Motor Unit Behavior with Error Amplification Feedback in the Elderly

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Yi-Ching Chen

2017-11-01

Full Text Available Error amplification (EA feedback is a promising approach to advance visuomotor skill. As error detection and visuomotor processing at short time scales decline with age, this study examined whether older adults could benefit from EA feedback that included higher-frequency information to guide a force-tracking task. Fourteen young and 14 older adults performed low-level static isometric force-tracking with visual guidance of typical visual feedback and EA feedback containing augmented high-frequency errors. Stabilogram diffusion analysis was used to characterize force fluctuation dynamics. Also, the discharge behaviors of motor units and pooled motor unit coherence were assessed following the decomposition of multi-channel surface electromyography (EMG. EA produced different behavioral and neurophysiological impacts on young and older adults. Older adults exhibited inferior task accuracy with EA feedback than with typical visual feedback, but not young adults. Although stabilogram diffusion analysis revealed that EA led to a significant decrease in critical time points for both groups, EA potentiated the critical point of force fluctuations <ΔFc2>, short-term effective diffusion coefficients (Ds, and short-term exponent scaling only for the older adults. Moreover, in older adults, EA added to the size of discharge variability of motor units and discharge regularity of cumulative discharge rate, but suppressed the pooled motor unit coherence in the 13–35 Hz band. Virtual EA alters the strategic balance between open-loop and closed-loop controls for force-tracking. Contrary to expectations, the prevailing use of closed-loop control with EA that contained high-frequency error information enhanced the motor unit discharge variability and undermined the force steadiness in the older group, concerning declines in physiological complexity in the neurobehavioral system and the common drive to the motoneuronal pool against force destabilization.

Epidermal growth factor receptor mediated proliferation depends on increased lipid droplet density regulated via a negative regulatory loop with FOXO3/Sirtuin6

Energy Technology Data Exchange (ETDEWEB)

Penrose, Harrison; Heller, Sandra; Cable, Chloe [Department of Pathology and Laboratory Medicine, Tulane University School of Medicine, 1430 Tulane Ave SL-79, New Orleans, LA 70112 (United States); Makboul, Rania [Department of Pathology and Laboratory Medicine, Tulane University School of Medicine, 1430 Tulane Ave SL-79, New Orleans, LA 70112 (United States); Pathology Department, Assiut University, Assiut (Egypt); Chadalawada, Gita; Chen, Ying [Department of Pathology and Laboratory Medicine, Tulane University School of Medicine, 1430 Tulane Ave SL-79, New Orleans, LA 70112 (United States); Crawford, Susan E. [Department of Pathology, Saint Louis University School of Medicine, 1402 South Grand Blvd, Saint Louis, MO 63104 (United States); Savkovic, Suzana D., E-mail: ssavkovi@tulane.edu [Department of Pathology and Laboratory Medicine, Tulane University School of Medicine, 1430 Tulane Ave SL-79, New Orleans, LA 70112 (United States)

2016-01-15

The proliferation of colon cancer cells is mediated in part by epidermal growth factor receptor (EGFR) signaling and requires sustained levels of cellular energy to meet its high metabolic needs. Intracellular lipid droplets (LDs) are a source of energy used for various cellular functions and they are elevated in density in human cancer, yet their regulation and function are not well understood. Here, in human colon cancer cells, EGF stimulates increases in LD density, which depends on EGFR expression and activation as well as the individual cellular capacity for lipid synthesis. Increases in LDs are blockaded by inhibition of PI3K/mTOR and PGE2 synthesis, supporting their dependency on select upstream pathways. In colon cancer cells, silencing of the FOXO3 transcription factor leads to down regulation of SIRT6, a negative regulator of lipid synthesis, and consequent increases in the LD coat protein PLIN2, revealing that increases in LDs depend on loss of FOXO3/SIRT6. Moreover, EGF stimulates loss of FOXO3/SIRT6, which is blockaded by the inhibition of upstream pathways as well as lipid synthesis, revealing existence of a negative regulatory loop between LDs and FOXO3/SIRT6. Elevated LDs are utilized by EGF treatment and their depletion through the inhibition of lipid synthesis or silencing of PLIN2 significantly attenuates proliferation. This novel mechanism of proliferative EGFR signaling leading to elevated LD density in colon cancer cells could potentially be therapeutically targeted for the treatment of tumor progression. - Highlights: • In colon cancer cells, EGFR activation leads to increases in LD density. • EGFR signaling includes PI3K/mTOR and PGE2 leading to lipid synthesis. • Increases in LDs are controlled by a negative regulatory loop with FOXO3/SIRT6. • EGFR mediated colon cancer cell proliferation depends on increased LD density.

Epidermal growth factor receptor mediated proliferation depends on increased lipid droplet density regulated via a negative regulatory loop with FOXO3/Sirtuin6

International Nuclear Information System (INIS)

Penrose, Harrison; Heller, Sandra; Cable, Chloe; Makboul, Rania; Chadalawada, Gita; Chen, Ying; Crawford, Susan E.; Savkovic, Suzana D.

2016-01-01

The proliferation of colon cancer cells is mediated in part by epidermal growth factor receptor (EGFR) signaling and requires sustained levels of cellular energy to meet its high metabolic needs. Intracellular lipid droplets (LDs) are a source of energy used for various cellular functions and they are elevated in density in human cancer, yet their regulation and function are not well understood. Here, in human colon cancer cells, EGF stimulates increases in LD density, which depends on EGFR expression and activation as well as the individual cellular capacity for lipid synthesis. Increases in LDs are blockaded by inhibition of PI3K/mTOR and PGE2 synthesis, supporting their dependency on select upstream pathways. In colon cancer cells, silencing of the FOXO3 transcription factor leads to down regulation of SIRT6, a negative regulator of lipid synthesis, and consequent increases in the LD coat protein PLIN2, revealing that increases in LDs depend on loss of FOXO3/SIRT6. Moreover, EGF stimulates loss of FOXO3/SIRT6, which is blockaded by the inhibition of upstream pathways as well as lipid synthesis, revealing existence of a negative regulatory loop between LDs and FOXO3/SIRT6. Elevated LDs are utilized by EGF treatment and their depletion through the inhibition of lipid synthesis or silencing of PLIN2 significantly attenuates proliferation. This novel mechanism of proliferative EGFR signaling leading to elevated LD density in colon cancer cells could potentially be therapeutically targeted for the treatment of tumor progression. - Highlights: • In colon cancer cells, EGFR activation leads to increases in LD density. • EGFR signaling includes PI3K/mTOR and PGE2 leading to lipid synthesis. • Increases in LDs are controlled by a negative regulatory loop with FOXO3/SIRT6. • EGFR mediated colon cancer cell proliferation depends on increased LD density.

Why do quality and reliability feedback loops not always work in practice: a case study

Energy Technology Data Exchange (ETDEWEB)

Molenaar, P.A.; Huijben, A.J.M.; Bouwhuis, D.; Brombacher, A.C

2002-03-01

The increasing competition in the market of consumer electronics forces industry to simultaneously improve the functionability, reliability and costs of their products. Due to the strong dynamics of this field an important measure in improving product quality is the feedback of information on actual field behaviour of a product which is extremely relevant for product development. This information, usually gathered by the service department, can help development to learn from the failures of earlier products and to improve the next product generations. This feedback process, however, does not always bring the expected benefits. This paper presents a model, based on an actual case study, of the structure of the feedback process in terms of information flows. The information flow model describes the chain or network of activities in the feedback process as a function of (different) drivers such as cost, time or quality. Using this information flow model it is possible to explain how quality and reliability related information propagates through a business process and where and why communication problems lead to disruptions in the feedback of this information. With this model, it is easier to understand the function of different parties in the service or after sales process, so that management of the information in this process becomes more transparent and can be improved.

Why do quality and reliability feedback loops not always work in practice: a case study

International Nuclear Information System (INIS)

Molenaar, P.A.; Huijben, A.J.M.; Bouwhuis, D.; Brombacher, A.C.

2002-01-01

The increasing competition in the market of consumer electronics forces industry to simultaneously improve the functionability, reliability and costs of their products. Due to the strong dynamics of this field an important measure in improving product quality is the feedback of information on actual field behaviour of a product which is extremely relevant for product development. This information, usually gathered by the service department, can help development to learn from the failures of earlier products and to improve the next product generations. This feedback process, however, does not always bring the expected benefits. This paper presents a model, based on an actual case study, of the structure of the feedback process in terms of information flows. The information flow model describes the chain or network of activities in the feedback process as a function of (different) drivers such as cost, time or quality. Using this information flow model it is possible to explain how quality and reliability related information propagates through a business process and where and why communication problems lead to disruptions in the feedback of this information. With this model, it is easier to understand the function of different parties in the service or after sales process, so that management of the information in this process becomes more transparent and can be improved

Control characteristics of cryogenic distillation column with a feedback stream for fusion reactor

International Nuclear Information System (INIS)

Yamanishi, Toshihiko; Okuno, Kenji

1997-01-01

The control characteristics of the cryogenic distillation column with a feedback stream have been discussed based on computer simulation results. This column plays an important role in fusion reactor. A new control system was proposed from the simulation results. The flow rate of top product is determined from the composition and flow rate of a main feed stream by a feedforward control loop. The flow rates of the feedback stream and vapor stream within the column are proportionally changed with a corresponding change of feed flow rate. The flow rate of vapor stream within the column is further adjusted to maintain product purity by a feedback control loop. The proposed system can control the product purity for a large fluctuation of feed composition, a change of feed flow rate, and an increase or decrease of the number of total theoretical stages of the column. The control system should be designed for each column by considering its operating conditions and function. The present study gives us a basic procedure for the design method of the control system of the cryogenic distillation column. (author)

Ombud’s Corner: the gift of feedback (part 2)

CERN Multimedia

Sudeshna Datta-Cockerill

2016-01-01

“When feedback is specific and timely, and also accompanied by a genuinely positive intention, it may be considered to be a gift”. This was the concluding message of the article in the last Bulletin. But how can negative feedback be perceived as an appreciated and useful gift?   As discussed in the previous article, delivering meaningful and effective feedback is an art, and as such, it may also be considered a duty for supervisors, in particular, to invest in honing their skills in order to achieve this aim without triggering demotivation or frustration in their supervisees. But the feedback loop is a two-way process, and requires an open mind on the receiving end in order to be truly useful. If delivered in a constructive and respectful way, feedback can provide us with important clues as to our own possible weaknesses and point us towards ways in which to develop and grow professionally. However, for it to be truly effective, it is up to each of us to hold back our initial ...

General Output Feedback Stabilization for Fractional Order Systems: An LMI Approach

Directory of Open Access Journals (Sweden)

Yiheng Wei

2014-01-01

Full Text Available This paper is concerned with the problem of general output feedback stabilization for fractional order linear time-invariant (FO-LTI systems with the fractional commensurate order 0<α<2. The objective is to design suitable output feedback controllers that guarantee the stability of the resulting closed-loop systems. Based on the slack variable method and our previous stability criteria, some new results in the form of linear matrix inequality (LMI are developed to the static and dynamic output feedback controllers synthesis for the FO-LTI system with 0<α<1. Furthermore, the results are extended to stabilize the FO-LTI systems with 1≤α<2. Finally, robust output feedback control is discussed. Numerical examples are given to illustrate the effectiveness of the proposed design methods.

78 FR 55251 - Hydropower Regulatory Efficiency Act of 2013; Notice of Workshop

Science.gov (United States)

2013-09-10

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. AD13-9-000] Hydropower... hydropower development at non-powered dams and closed-loop pumped storage projects in compliance with section 6 of the Hydropower Regulatory Efficiency Act of 2013. Participants should be prepared to discuss...

RTVP-1 promotes mesenchymal transformation of glioma via a STAT-3/IL-6-dependent positive feedback loop

Science.gov (United States)

Giladi, Nis David; Ziv-Av, Amotz; Lee, Hae Kyung; Finniss, Susan; Cazacu, Simona; Xiang, Cunli; Ben-Asher, Hiba Waldman; deCarvalho, Ana; Mikkelsen, Tom; Poisson, Laila; Brodie, Chaya

2015-01-01

Glioblastomas (GBMs), the most aggressive primary brain tumors, exhibit increased invasiveness and resistance to anti-tumor treatments. We explored the role of RTVP-1, a glioma-associated protein that promotes glioma cell migration, in the mesenchymal transformation of GBM. Analysis of The Cancer Genome Atlas (TCGA) demonstrated that RTVP-1 expression was higher in mesenchymal GBM and predicted tumor recurrence and poor clinical outcome. ChiP analysis revealed that the RTVP-1 promoter binds STAT3 and C/EBPβ, two master transcription factors that regulate mesenchymal transformation of GBM. In addition, IL-6 induced RTVP-1 expression in a STAT3-dependent manner. RTVP-1 increased the migration and mesenchymal transformation of glioma cells. Similarly, overexpression of RTVP-1 in human neural stem cells induced mesenchymal differentiation, whereas silencing of RTVP-1 in glioma stem cells (GSCs) decreased the mesenchymal transformation and stemness of these cells. Silencing of RTVP-1 also increased the survival of mice bearing GSC-derived xenografts. Using gene array analysis of RTVP-1 silenced glioma cells we identified IL-6 as a mediator of RTVP-1 effects on the mesenchymal transformation and migration of GSCs, therefore acting in a positive feedback loop by upregulating RTVP-1 expression via the STAT3 pathway. Collectively, these results implicate RTVP-1 as a novel prognostic marker and therapeutic target in GBM. PMID:26267319

Invariant TAD Boundaries Constrain Cell-Type-Specific Looping Interactions between Promoters and Distal Elements around the CFTR Locus.

Science.gov (United States)

Smith, Emily M; Lajoie, Bryan R; Jain, Gaurav; Dekker, Job

2016-01-07

Three-dimensional genome structure plays an important role in gene regulation. Globally, chromosomes are organized into active and inactive compartments while, at the gene level, looping interactions connect promoters to regulatory elements. Topologically associating domains (TADs), typically several hundred kilobases in size, form an intermediate level of organization. Major questions include how TADs are formed and how they are related to looping interactions between genes and regulatory elements. Here we performed a focused 5C analysis of a 2.8 Mb chromosome 7 region surrounding CFTR in a panel of cell types. We find that the same TAD boundaries are present in all cell types, indicating that TADs represent a universal chromosome architecture. Furthermore, we find that these TAD boundaries are present irrespective of the expression and looping of genes located between them. In contrast, looping interactions between promoters and regulatory elements are cell-type specific and occur mostly within TADs. This is exemplified by the CFTR promoter that in different cell types interacts with distinct sets of distal cell-type-specific regulatory elements that are all located within the same TAD. Finally, we find that long-range associations between loci located in different TADs are also detected, but these display much lower interaction frequencies than looping interactions within TADs. Interestingly, interactions between TADs are also highly cell-type-specific and often involve loci clustered around TAD boundaries. These data point to key roles of invariant TAD boundaries in constraining as well as mediating cell-type-specific long-range interactions and gene regulation. Copyright © 2016 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

A novel charge sensitive preamplifier without the feedback resistor

International Nuclear Information System (INIS)

Bertuccio, G.

1992-01-01

A novel charge sensitive preamplifier which has no resistor in parallel with the feedback capacitor is presented. No external device or circuit is required to discharge the feedback capacitor. The detector leakage and signal current flows away through the gate of the first JFET which works with its gate to source junction slightly forward biased. The DC stabilization of the preamplifier is accomplished by an additional feedback loop, which permits to equalize the current flowing through the forward baised gate to source junction and the current coming from the detector. An equivalent noise charge of less than 20 electrons r.m.s. has been measured at room temperature by using an input JFET with a transconductance to gate capacitance ratio of 4 mS/5.4 pF

Highly stable microwave carrier generation using a dual-frequency distributed feedback laser

NARCIS (Netherlands)

Khan, M.R.H.; Bernhardi, Edward; Marpaung, D.A.I.; Burla, M.; de Ridder, R.M.; Worhoff, Kerstin; Pollnau, Markus; Roeloffzen, C.G.H.

2012-01-01

Photonic generation of microwave carriers by using a dual-frequency distributed feedback waveguide laser in ytterbium-doped aluminum oxide is demonstrated. A highperformance optical frequency locked loop is implemented to stabilize the microwave carrier. This approach results in a microwave

The influence of visual feedback from the recent past on the programming of grip aperture is grasp-specific, shared between hands, and mediated by sensorimotor memory not task set.

Science.gov (United States)

Tang, Rixin; Whitwell, Robert L; Goodale, Melvyn A

2015-05-01

Goal-directed movements, such as reaching out to grasp an object, are necessarily constrained by the spatial properties of the target such as its size, shape, and position. For example, during a reach-to-grasp movement, the peak width of the aperture formed by the thumb and fingers in flight (peak grip aperture, PGA) is linearly related to the target's size. Suppressing vision throughout the movement (visual open loop) has a small though significant effect on this relationship. Visual open loop conditions also produce a large increase in the PGA compared to when vision is available throughout the movement (visual closed loop). Curiously, this differential effect of the availability of visual feedback is influenced by the presentation order: the difference in PGA between closed- and open-loop trials is smaller when these trials are intermixed (an effect we have called 'homogenization'). Thus, grasping movements are affected not only by the availability of visual feedback (closed loop or open loop) but also by what happened on the previous trial. It is not clear, however, whether this carry-over effect is mediated through motor (or sensorimotor) memory or through the interference of different task sets for closed-loop and open-loop feedback that determine when the movements are fully specified. We reasoned that sensorimotor memory, but not a task set for closed and open loop feedback, would be specific to the type of response. We tested this prediction in a condition in which pointing to targets was alternated with grasping those same targets. Critically, in this condition, when pointing was performed in open loop, grasping was always performed in closed loop (and vice versa). Despite the fact that closed- and open-loop trials were alternating in this condition, we found no evidence for homogenization of the PGA. Homogenization did occur, however, in a follow-up experiment in which grasping movements and visual feedback were alternated between the left and the right

A double-gate double-feedback JFET charge-sensitive preamplifier

International Nuclear Information System (INIS)

Fazzi, A.

1996-01-01

A new charge-sensitive preamplifier (CSP) without a physical resistance in the feedback is presented. The input device has to be a double-gate JFET. In this new preamplifier configuration the feedback capacitor is continuously discharged by means of a second DC current feedback loop closed through the bottom gate of the input JFET. The top gate-channel junction works as usual in reverse bias, the bottom gate-channel is forward biased. A fraction of the current injected by the bottom gate reaches the top gate discharging the feedback capacitor. The n-channel double-gate JFET is considered from the viewpoint of the restoring action as a parasitic p-n-p ''transversal'' bipolar junction transistor. The new preamplifier is also suited for detectors operating at room temperature with leakage current which may vary with time. The DC behaviour and the dynamic behaviour of the circuit is analyzed and new measurements presented. (orig.)

Regionally strong feedbacks between the atmosphere and terrestrial biosphere

Science.gov (United States)

Green, Julia K.; Konings, Alexandra G.; Alemohammad, Seyed Hamed; Berry, Joseph; Entekhabi, Dara; Kolassa, Jana; Lee, Jung-Eun; Gentine, Pierre

2017-06-01

The terrestrial biosphere and atmosphere interact through a series of feedback loops. Variability in terrestrial vegetation growth and phenology can modulate fluxes of water and energy to the atmosphere, and thus affect the climatic conditions that in turn regulate vegetation dynamics. Here we analyse satellite observations of solar-induced fluorescence, precipitation, and radiation using a multivariate statistical technique. We find that biosphere-atmosphere feedbacks are globally widespread and regionally strong: they explain up to 30% of precipitation and surface radiation variance in regions where feedbacks occur. Substantial biosphere-precipitation feedbacks are often found in regions that are transitional between energy and water limitation, such as semi-arid or monsoonal regions. Substantial biosphere-radiation feedbacks are often present in several moderately wet regions and in the Mediterranean, where precipitation and radiation increase vegetation growth. Enhancement of latent and sensible heat transfer from vegetation accompanies this growth, which increases boundary layer height and convection, affecting cloudiness, and consequently incident surface radiation. Enhanced evapotranspiration can increase moist convection, leading to increased precipitation. Earth system models underestimate these precipitation and radiation feedbacks mainly because they underestimate the biosphere response to radiation and water availability. We conclude that biosphere-atmosphere feedbacks cluster in specific climatic regions that help determine the net CO2 balance of the biosphere.

Motorized CPM/CAM physiotherapy device with sliding-mode Fuzzy Neural Network control loop.

Science.gov (United States)

Ho, Hung-Jung; Chen, Tien-Chi

2009-11-01

Continuous passive motion (CPM) and controllable active motion (CAM) physiotherapy devices promote rehabilitation of damaged joints. This paper presents a computerized CPM/CAM system that obviates the need for mechanical resistance devices such as springs. The system is controlled by a computer which performs sliding-mode Fuzzy Neural Network (FNN) calculations online. CAM-type resistance force is generated by the active performance of an electric motor which is controlled so as to oppose the motion of the patient's leg. A force sensor under the patient's foot on the device pedal provides data for feedback in a sliding-mode FNN control loop built around the motor. Via an active impedance control feedback system, the controller drives the motor to behave similarly to a damped spring by generating and controlling the amplitude and direction of the pedal force in relation to the patient's leg. Experiments demonstrate the high sensitivity and speed of the device. The PC-based feedback nature of the control loop means that sophisticated auto-adaptable CPM/CAM custom-designed physiotherapy becomes possible. The computer base also allows extensive data recording, data analysis and network-connected remote patient monitoring.

Persistent disturbance rejection via state feedback for networked control systems

Energy Technology Data Exchange (ETDEWEB)

Yue Dong [Institute of Information and Control Engineering Technology, Nanjing Normal University, 78 Bancang Street, Nanjing, Jiangsu 210042 (China)], E-mail: medongy@njnu.edu.cn; Lam, James [Department of Mechanical Engineering, University of Hong Kong, Pokfulam Road (Hong Kong); Wang Zidong [Department of Information Systems and Computing, Brunel University, Uxbridge, Middlesex UB8 3PH (United Kingdom)], E-mail: Zidong.Wang@brunel.ac.uk

2009-04-15

The problem of persistent disturbance rejection via state feedback for networked control systems is concerned based on the Lyapunov function method. The effect of the network conditions, such as network-induced delay and data dropout, is considered in the modeling of the system. It is assumed that the state and the control signals are individually quantized by quantizers on the sensor side and the controller side. The feedback gain and the quantizer parameters that guarantee the internal stability and the disturbance rejection performance of the closed-loop system are obtained by solving some linear matrix inequalities. To illustrate the effectiveness of the proposed method, a numerical example is provided for the design of the feedback gain and the quantizer parameters.

Persistent disturbance rejection via state feedback for networked control systems

International Nuclear Information System (INIS)

Yue Dong; Lam, James; Wang Zidong

2009-01-01

The problem of persistent disturbance rejection via state feedback for networked control systems is concerned based on the Lyapunov function method. The effect of the network conditions, such as network-induced delay and data dropout, is considered in the modeling of the system. It is assumed that the state and the control signals are individually quantized by quantizers on the sensor side and the controller side. The feedback gain and the quantizer parameters that guarantee the internal stability and the disturbance rejection performance of the closed-loop system are obtained by solving some linear matrix inequalities. To illustrate the effectiveness of the proposed method, a numerical example is provided for the design of the feedback gain and the quantizer parameters.

Software feedback for monochromator tuning at UNICAT (abstract)

Science.gov (United States)

Jemian, Pete R.

2002-03-01

Automatic tuning of double-crystal monochromators presents an interesting challenge in software. The goal is to either maximize, or hold constant, the throughput of the monochromator. An additional goal of the software feedback is to disable itself when there is no beam and then, at the user's discretion, re-enable itself when the beam returns. These and other routine goals, such as adherence to limits of travel for positioners, are maintained by software controls. Many solutions exist to lock in and maintain a fixed throughput. Among these include a hardware solution involving a wave form generator, and a lock-in amplifier to autocorrelate the movement of a piezoelectric transducer (PZT) providing fine adjustment of the second crystal Bragg angle. This solution does not work when the positioner is a slow acting device such as a stepping motor. Proportional integral differential (PID) loops have been used to provide feedback through software but additional controls must be provided to maximize the monochromator throughput. Presented here is a software variation of the PID loop which meets the above goals. By using two floating point variables as inputs, representing the intensity of x rays measured before and after the monochromator, it attempts to maximize (or hold constant) the ratio of these two inputs by adjusting an output floating point variable. These floating point variables are connected to hardware channels corresponding to detectors and positioners. When the inputs go out of range, the software will stop making adjustments to the control output. Not limited to monochromator feedback, the software could be used, with beam steering positioners, to maintain a measure of beam position. Advantages of this software feedback are the flexibility of its various components. It has been used with stepping motors and PZTs as positioners. Various devices such as ion chambers, scintillation counters, photodiodes, and photoelectron collectors have been used as

The radiation safety assessment of the heating loop of district heating reactors

International Nuclear Information System (INIS)

Liu Yuanzhong

1993-01-01

The district heating reactors are used to supply heating to the houses in cities. The concerned problems are whether the radioactive materials reach the heated houses through heating loop, and whether the safety of the dwellers can be ensured. In order to prevent radioactive materials getting into the heated houses, the district heating reactors have three loops, namely, primary loop, intermediate loop, and heating loop. In the paper, the measures of preventing radioactive materials getting into the heating loop are presented, and the possible sources of the radioactivity in the water of the intermediate loop and the heating loop are given. The regulatory aim limit of radioactive concentration in the water of the intermediate loop is put forward, which is 18.5 Bq/l. Assuming that specific radioactivity of the water of contaminated intermediate loop is up to 18.5 Bq/l, the maximum concentration of radionuclides in water of the heating loop is calculated for the normal operation and the accident of district heating reactor. The results show that the maximum possible concentration is 5.7 x 10 -3 Bq/l. The radiation safety assessment of the heating loop is made out. The conclusions are that the district heating reactors do not bring any harmful impact to the dwellers, and the safety of the dwellers can be safeguarded completely

SQUID multiplexing using baseband feedback for space application of transition-edge sensor microcalorimeters

Energy Technology Data Exchange (ETDEWEB)

Takei, Y; Yamasaki, N Y; Hirakoso, W; Kimura, S; Mitsuda, K, E-mail: takei@astro.isas.jaxa.j [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, 229-8510 (Japan)

2009-11-15

A microcalorimeter array based on a transition-edge sensor (TES) thermometer is a promising imaging spectrometer for use in future x-ray astronomy missions. A TES microcalorimeter achieves {approx}<5 eV energy resolution and an array of >100 pixels also provides a moderate imaging capability. For a large format array, signal multiplexing at the low temperature stage is mandatory in order to reduce heat loads from cold stage preamplifiers and through wirings. We are developing frequency division multiplexing (FDM). In FDM, each TES is ac-biased with a different carrier frequency. Signals from several pixels are summed and then read out by one dc SQUID (superconducting quantum interference device). The maximum number of multiplexed pixels is limited by the bandwidth of a SQUID in a flux-locked loop. Assuming 1 m cable length between the room temperature and the cold stage, the bandwidth is only <1 MHz with a standard flux-locked loop, due to the delay and phase shift of wirings. We report our development of baseband feedback, a new feedback scheme that overcomes the bandwidth limitation. In baseband feedback, the signal ({approx}<10 kHz) from the TES is sent back to the SQUID after the phase of carrier frequency ({approx}1 MHz) has been adjusted. We demonstrated open-loop gain of 8 for 10 kHz signal at 5 MHz carrier frequency, which indicates the possibility of {approx}40-pixel multiplexing of the TES signal.

Feedback stabilization of the axisymmetric instability of a deformable tokamak plasma

International Nuclear Information System (INIS)

Pomphrey, N.; Jardin, S.C.

1987-09-01

We analyze the magnetohydrodynamic (MHD) stability of the axisymmetric system consisting of a free boundary, non-circular cross-section tokamak plasma, finite resistivity passive conductors, and an active feedback system with magnetic flux pickup loops, a proportional amplifier with gain G, and current carrying poloidal field coils. Numerical simulation of a system that is unstable with G = 0 shows that for some placements of the pickup loops, the system will remain unstable for all values of G, while for other placements of the loops, the system will be stable for G > G/sub crit/. This behavior is explained by analysis using an extended energy principle, and it is shown to result from the deformability of the plasma cross section. 9 refs., 5 figs

Finite-time output feedback stabilization of high-order uncertain nonlinear systems

Science.gov (United States)

Jiang, Meng-Meng; Xie, Xue-Jun; Zhang, Kemei

2018-06-01

This paper studies the problem of finite-time output feedback stabilization for a class of high-order nonlinear systems with the unknown output function and control coefficients. Under the weaker assumption that output function is only continuous, by using homogeneous domination method together with adding a power integrator method, introducing a new analysis method, the maximal open sector Ω of output function is given. As long as output function belongs to any closed sector included in Ω, an output feedback controller can be developed to guarantee global finite-time stability of the closed-loop system.

Closed-loop, open-source electrophysiology

Directory of Open Access Journals (Sweden)

John D Rolston

2010-09-01

Full Text Available Multiple extracellular microelectrodes (multi-electrode arrays, or MEAs effectively record rapidly varying neural signals, and can also be used for electrical stimulation. Multi-electrode recording can serve as artificial output (efferents from a neural system, while complex spatially and temporally targeted stimulation can serve as artificial input (afferents to the neuronal network. Multi-unit or local field potential recordings can not only be used to control real world artifacts, such as prostheses, computers or robots, but can also trigger or alter subsequent stimulation. Real-time feedback stimulation may serve to modulate or normalize aberrant neural activity, to induce plasticity, or to serve as artificial sensory input. Despite promising closed-loop applications, commercial electrophysiology systems do not yet take advantage of the bidirectional capabilities of multi-electrodes, especially for use in freely moving animals. We addressed this lack of tools for closing the loop with NeuroRighter, an open-source system including recording hardware, stimulation hardware, and control software with a graphical user interface. The integrated system is capable of multi-electrode recording and simultaneous patterned microstimulation triggered by recordings with minimal stimulation artifact. The potential applications of closed-loop systems as research tools and clinical treatments are broad; we provide one example where epileptic activity recorded by a multi-electrode probe is used to trigger targeted stimulation, via that probe, to freely moving rodents.

Pilot-in-the-Loop Analysis of Propulsive-Only Flight Control Systems

Science.gov (United States)

Chou, Hwei-Lan; Biezad, Daniel J.

1996-01-01

Longitudinal control system architectures are presented which directly couple flight stick motions to throttle commands for a multi-engine aircraft. This coupling enables positive attitude control with complete failure of the flight control system. The architectures chosen vary from simple feedback gains to classical lead-lag compensators with and without prefilters. Each architecture is reviewed for its appropriateness for piloted flight. The control systems are then analyzed with pilot-in-the-loop metrics related to bandwidth required for landing. Results indicate that current and proposed bandwidth requirements should be modified for throttles only flight control. Pilot ratings consistently showed better ratings than predicted by analysis. Recommendations are made for more robust design and implementation. The use of Quantitative Feedback Theory for compensator design is discussed. Although simple and effective augmented control can be achieved in a wide variety of failed configurations, a few configuration characteristics are dominant for pilot-in-the-loop control. These characteristics will be tested in a simulator study involving failed flight controls for a multi-engine aircraft.

Dynamic Mesoscale Land-Atmosphere Feedbacks in Fragmented Forests in Amazonia

Science.gov (United States)

Rastogi, D.; Baidya Roy, S.

2011-12-01

This paper investigates land-atmosphere feedbacks in disturbed rainforests of Amazonia. Deforestation along the rapidly expanding highways and road network has created the unique fishbone land cover pattern in Rondonia, a state in southwestern Amazonia. Numerical experiments and observations show that sharp gradients in land cover due to the fishbone heterogeneity triggers mesoscale circulations. These circulations significantly change the spatial pattern of local hydrometeorology, especially convection, clouds and precipitation. The primary research question now is can these changes in local hydrometeorology affect vegetation growth in the clearings. If so, that would be a clear indication that land-atmosphere feedbacks can affect vegetation recovery in fragmented forests. A computationally-efficient modeling tool consisting of a mesoscale atmospheric model dynamically coupled with a plant growth model has been specifically developed to identify the atmospheric feedback pathways. Preliminary experiments focus on the seasonal-scale feedbacks during the dry season. Results show that temperature, incoming shortwave and precipitation are the three primary drivers through which the feedbacks operate. Increasing temperature increases respiratory losses generating a positive feedback. Increased cloud cover reduces incoming PAR and photosynthesis, resulting in a positive feedback. Increased precipitation reduces water stress and promotes growth resulting in a negative feedback. The net effect is a combination of these 3 feedback loops. These findings can significantly improve our understanding of ecosystem resiliency in disturbed tropical forests.

Cardinal features of involuntary force variability can arise from the closed-loop control of viscoelastic afferented muscles

Science.gov (United States)

Laine, Christopher M.; Valero-Cuevas, Francisco J.

2018-01-01

Involuntary force variability below 15 Hz arises from, and is influenced by, many factors including descending neural drive, proprioceptive feedback, and mechanical properties of muscles and tendons. However, their potential interactions that give rise to the well-structured spectrum of involuntary force variability are not well understood due to a lack of experimental techniques. Here, we investigated the generation, modulation, and interactions among different sources of force variability using a physiologically-grounded closed-loop simulation of an afferented muscle model. The closed-loop simulation included a musculotendon model, muscle spindle, Golgi tendon organ (GTO), and a tracking controller which enabled target-guided force tracking. We demonstrate that closed-loop control of an afferented musculotendon suffices to replicate and explain surprisingly many cardinal features of involuntary force variability. Specifically, we present 1) a potential origin of low-frequency force variability associated with co-modulation of motor unit firing rates (i.e.,‘common drive’), 2) an in-depth characterization of how proprioceptive feedback pathways suffice to generate 5-12 Hz physiological tremor, and 3) evidence that modulation of those feedback pathways (i.e., presynaptic inhibition of Ia and Ib afferents, and spindle sensitivity via fusimotor drive) influence the full spectrum of force variability. These results highlight the previously underestimated importance of closed-loop neuromechanical interactions in explaining involuntary force variability during voluntary ‘isometric’ force control. Furthermore, these results provide the basis for a unifying theory that relates spinal circuitry to various manifestations of altered involuntary force variability in fatigue, aging and neurological disease. PMID:29309405

Cardinal features of involuntary force variability can arise from the closed-loop control of viscoelastic afferented muscles.

Science.gov (United States)

Nagamori, Akira; Laine, Christopher M; Valero-Cuevas, Francisco J

2018-01-01

Involuntary force variability below 15 Hz arises from, and is influenced by, many factors including descending neural drive, proprioceptive feedback, and mechanical properties of muscles and tendons. However, their potential interactions that give rise to the well-structured spectrum of involuntary force variability are not well understood due to a lack of experimental techniques. Here, we investigated the generation, modulation, and interactions among different sources of force variability using a physiologically-grounded closed-loop simulation of an afferented muscle model. The closed-loop simulation included a musculotendon model, muscle spindle, Golgi tendon organ (GTO), and a tracking controller which enabled target-guided force tracking. We demonstrate that closed-loop control of an afferented musculotendon suffices to replicate and explain surprisingly many cardinal features of involuntary force variability. Specifically, we present 1) a potential origin of low-frequency force variability associated with co-modulation of motor unit firing rates (i.e.,'common drive'), 2) an in-depth characterization of how proprioceptive feedback pathways suffice to generate 5-12 Hz physiological tremor, and 3) evidence that modulation of those feedback pathways (i.e., presynaptic inhibition of Ia and Ib afferents, and spindle sensitivity via fusimotor drive) influence the full spectrum of force variability. These results highlight the previously underestimated importance of closed-loop neuromechanical interactions in explaining involuntary force variability during voluntary 'isometric' force control. Furthermore, these results provide the basis for a unifying theory that relates spinal circuitry to various manifestations of altered involuntary force variability in fatigue, aging and neurological disease.

Positive feedback loop between introductions of non-native marine species and cultivation of oysters in Europe.

Science.gov (United States)

Mineur, Frederic; Le Roux, Auguste; Maggs, Christine A; Verlaque, Marc

2014-12-01

With globalization, agriculture and aquaculture activities are increasingly affected by diseases that are spread through movement of crops and stock. Such movements are also associated with the introduction of non-native species via hitchhiking individual organisms. The oyster industry, one of the most important forms of marine aquaculture, embodies these issues. In Europe disease outbreaks affecting cultivated populations of the naturalized oyster Crassostrea gigas caused a major disruption of production in the late 1960s and early 1970s. Mitigation procedures involved massive imports of stock from the species' native range in the northwestern Pacific from 1971 to 1977. We assessed the role stock imports played in the introduction of non-native marine species (including pathogens) from the northwestern Pacific to Europe through a methodological and critical appraisal of record data. The discovery rate of non-native species (a proxy for the introduction rate) from 1966 to 2012 suggests a continuous vector activity over the entire period. Disease outbreaks that have been affecting oyster production since 2008 may be a result of imports from the northwestern Pacific, and such imports are again being considered as an answer to the crisis. Although successful as a remedy in the short and medium terms, such translocations may bring new diseases that may trigger yet more imports (self-reinforcing or positive feedback loop) and lead to the introduction of more hitchhikers. Although there is a legal framework to prevent or reduce these introductions, existing procedures should be improved. © 2014 Society for Conservation Biology.

Double closed-loop cascade control for lower limb exoskeleton with elastic actuation.

Science.gov (United States)

Zhu, Yanhe; Zheng, Tianjiao; Jin, Hongzhe; Yang, Jixing; Zhao, Jie

2015-01-01

Unlike traditional rigid actuators, the significant features of Series Elastic Actuator (SEA) are stable torque control, lower output impedance, impact resistance and energy storage. Recently, SEA has been applied in many exoskeletons. In such applications, a key issue is how to realize the human-exoskeleton movement coordination. In this paper, double closed-loop cascade control for lower limb exoskeleton with SEA is proposed. This control method consists of inner SEA torque loop and outer contact force loop. Utilizing the SEA torque control with a motor velocity loop, actuation performances of SEA are analyzed. An integrated exoskeleton control system is designed, in which joint angles are calculated by internal encoders and resolvers and contact forces are gathered by external pressure sensors. The double closed-loop cascade control model is established based on the feedback signals of internal and external sensor. Movement experiments are accomplished in our prototype of lower limb exoskeleton. Preliminary results indicate the exoskeleton movements with pilot can be realized stably by utilizing this double closed-loop cascade control method. Feasibility of the SEA in our exoskeleton robot and effectiveness of the control method are verified.

78 FR 58535 - Hydropower Regulatory Efficiency Act of 2013; Supplemental Notice of Workshop

Science.gov (United States)

2013-09-24

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. AD13-9-000] Hydropower... license for hydropower development at non-powered dams and closed-loop pumped storage projects in compliance with section 6 of the Hydropower Regulatory Efficiency Act of 2013. The workshop will be held in...

New numerical methods for open-loop and feedback solutions to dynamic optimization problems

Science.gov (United States)

Ghosh, Pradipto

The topic of the first part of this research is trajectory optimization of dynamical systems via computational swarm intelligence. Particle swarm optimization is a nature-inspired heuristic search method that relies on a group of potential solutions to explore the fitness landscape. Conceptually, each particle in the swarm uses its own memory as well as the knowledge accumulated by the entire swarm to iteratively converge on an optimal or near-optimal solution. It is relatively straightforward to implement and unlike gradient-based solvers, does not require an initial guess or continuity in the problem definition. Although particle swarm optimization has been successfully employed in solving static optimization problems, its application in dynamic optimization, as posed in optimal control theory, is still relatively new. In the first half of this thesis particle swarm optimization is used to generate near-optimal solutions to several nontrivial trajectory optimization problems including thrust programming for minimum fuel, multi-burn spacecraft orbit transfer, and computing minimum-time rest-to-rest trajectories for a robotic manipulator. A distinct feature of the particle swarm optimization implementation in this work is the runtime selection of the optimal solution structure. Optimal trajectories are generated by solving instances of constrained nonlinear mixed-integer programming problems with the swarming technique. For each solved optimal programming problem, the particle swarm optimization result is compared with a nearly exact solution found via a direct method using nonlinear programming. Numerical experiments indicate that swarm search can locate solutions to very great accuracy. The second half of this research develops a new extremal-field approach for synthesizing nearly optimal feedback controllers for optimal control and two-player pursuit-evasion games described by general nonlinear differential equations. A notable revelation from this development

Information transfer through a signaling module with feedback: A perturbative approach

Czech Academy of Sciences Publication Activity Database

Aquino, G.; Zápotocký, Martin

2015-01-01

Roč. 136, Oct (2015), s. 66-72 ISSN 0303-2647 R&D Projects: GA ČR(CZ) GBP304/12/G069 Institutional support: RVO:67985823 Keywords : signal transduction * communication channel * poisson process * information theory * feedback loop * Non-Markovian process Subject RIV: ED - Physiology Impact factor: 1.495, year: 2015

Design and Validation of Optimized Feedforward with Robust Feedback Control of a Nuclear Reactor

International Nuclear Information System (INIS)

Shaffer, Roman; He Weidong; Edwards, Robert M.

2004-01-01

Design applications for robust feedback and optimized feedforward control, with confirming results from experiments conducted on the Pennsylvania State University TRIGA reactor, are presented. The combination of feedforward and feedback control techniques complement each other in that robust control offers guaranteed closed-loop stability in the presence of uncertainties, and optimized feedforward offers an approach to achieving performance that is sometimes limited by overly conservative robust feedback control. The design approach taken in this work combines these techniques by first designing robust feedback control. Alternative methods for specifying a low-order linear model and uncertainty specifications, while seeking as much performance as possible, are discussed and evaluated. To achieve desired performance characteristics, the optimized feedforward control is then computed by using the nominal nonlinear plant model that incorporates the robust feedback control

Aeroassisted orbital maneuvering using Lyapunov optimal feedback control

Science.gov (United States)

Grantham, Walter J.; Lee, Byoung-Soo

1987-01-01

A Liapunov optimal feedback controller incorporating a preferred direction of motion at each state of the system which is opposite to the gradient of a specified descent function is developed for aeroassisted orbital transfer from high-earth orbit to LEO. The performances of the Liapunov controller and a calculus-of-variations open-loop minimum-fuel controller, both of which are based on the 1962 U.S. Standard Atmosphere, are simulated using both the 1962 U.S. Standard Atmosphere and an atmosphere corresponding to the STS-6 Space Shuttle flight. In the STS-6 atmosphere, the calculus-of-variations open-loop controller fails to exit the atmosphere, while the Liapunov controller achieves the optimal minimum-fuel conditions, despite the + or - 40 percent fluctuations in the STS-6 atmosphere.

Modeling the interaction of a heavily beam loaded SRF cavity with its low-level RF feedback loops

Science.gov (United States)

Liu, Zong-Kai; Wang, Chaoen; Chang, Lung-Hai; Yeh, Meng-Shu; Chang, Fu-Yu; Chang, Mei-Hsia; Chang, Shian-Wen; Chen, Ling-Jhen; Chung, Fu-Tsai; Lin, Ming-Chyuan; Lo, Chih-Hung; Yu, Tsung-Chi

2018-06-01

A superconducting radio frequency (SRF) cavity provides superior stability to power high intensity light sources and can suppress coupled-bunch instabilities due to its smaller impedance for higher order modes. Because of these features, SRF cavities are commonly used for modern light sources, such as the TLS, CLS, DLS, SSRF, PLS-II, TPS, and NSLS-II, with an aggressive approach to operate the light sources at high beam currents. However, operating a SRF cavity at high beam currents may result with unacceptable stability problems of the low level RF (LLRF) system, due to drifts of the cavity resonant frequency caused by unexpected perturbations from the environment. As the feedback loop gets out of control, the cavity voltage may start to oscillate with a current-dependent characteristic frequency. Such situations can cause beam abort due to the activation of the interlock protection system, i.e. false alarm of quench detection. This malfunction of the light source reduces the reliability of SRF operation. Understanding this unstable mechanism to prevent its appearance becomes a primary task in the pursuit of highly reliable SRF operation. In this paper, a Pedersen model, including the response of the LLRF system, was used to simulate the beam-cavity interaction of a SRF cavity under heavy beam loading. Causes for the onset of instability at high beam current will be discussed as well as remedies to assure the design of a stable LLRF system.

Functional Conservation of the Glide/Gcm Regulatory Network Controlling Glia, Hemocyte, and Tendon Cell Differentiation in Drosophila

Science.gov (United States)

Cattenoz, Pierre B.; Popkova, Anna; Southall, Tony D.; Aiello, Giuseppe; Brand, Andrea H.; Giangrande, Angela

2016-01-01

High-throughput screens allow us to understand how transcription factors trigger developmental processes, including cell specification. A major challenge is identification of their binding sites because feedback loops and homeostatic interactions may mask the direct impact of those factors in transcriptome analyses. Moreover, this approach dissects the downstream signaling cascades and facilitates identification of conserved transcriptional programs. Here we show the results and the validation of a DNA adenine methyltransferase identification (DamID) genome-wide screen that identifies the direct targets of Glide/Gcm, a potent transcription factor that controls glia, hemocyte, and tendon cell differentiation in Drosophila. The screen identifies many genes that had not been previously associated with Glide/Gcm and highlights three major signaling pathways interacting with Glide/Gcm: Notch, Hedgehog, and JAK/STAT, which all involve feedback loops. Furthermore, the screen identifies effector molecules that are necessary for cell-cell interactions during late developmental processes and/or in ontogeny. Typically, immunoglobulin (Ig) domain–containing proteins control cell adhesion and axonal navigation. This shows that early and transiently expressed fate determinants not only control other transcription factors that, in turn, implement a specific developmental program but also directly affect late developmental events and cell function. Finally, while the mammalian genome contains two orthologous Gcm genes, their function has been demonstrated in vertebrate-specific tissues, placenta, and parathyroid glands, begging questions on the evolutionary conservation of the Gcm cascade in higher organisms. Here we provide the first evidence for the conservation of Gcm direct targets in humans. In sum, this work uncovers novel aspects of cell specification and sets the basis for further understanding of the role of conserved Gcm gene regulatory cascades. PMID:26567182

Fundamentals of force feedback and application to a surgery simulator.

Science.gov (United States)

Maass, Heiko; Chantier, Benjamin B A; Cakmak, Hueseyin K; Trantakis, Christos; Kuehnapfel, Uwe G

2003-01-01

Force feedback increases the effectiveness of virtual-reality surgery training systems. An overview of the fundamentals of applying force feedback is presented. An impedance control technique and data processing methods for stability preservation are illustrated. A flexible interface for general force-feedback applications has been developed. This interface is capable of controlling several different force-feedback hardware systems, including the SensAble PHANTOM, the Laparoscopic Impulse Engines from Immersion, and the VS-One virtual endoscopic surgery trainer. The findings are evaluated using the main simulation system, KISMET, and the modeling tools KISMO and VESUV. Within the scope of a cooperative project called HapticIO (funded by the German Ministry of Education and Research [BMBF]), new haptic devices have been designed for virtual neuroendoscopy and laparoscopy. The concept and implementations presented in this paper have been found to be flexible, stable and suitable for universal use. The impedance method, combined with the open-loop feed-forward control technique, is well suited and appropriate for the task.

Learning from experience: feedback to CANDU design

International Nuclear Information System (INIS)

Allen, P.J.; Hopwood, J.M.; Rousseau, G.P.

1998-01-01

AECL's main product line is based on two single unit CANDU nuclear power plant designs; CANDU 6 and CANDU 9, each of which is based on successfully operating CANDU plants. AECL's CANDU development program is based upon evolutionary improvement. The evolutionary design approach ensures the maximum degree of operational provenness. It also allows successful features of today's plants to be retained while incorporating improvements as they develop to the appropriate level of design maturity. A key component of this evolutionary development is a formal process of gathering and responding to feedback from: NPP operation, construction and commissioning; regulatory input; equipment supplier input; R and D results; market input. The progresses for gathering and implementing the experience feedback and a number of recent examples of design improvements from this feedback process are described in the paper. (author)

Getting in (and out of) the loop: regulating higher order telomere structures.

Science.gov (United States)

Luke-Glaser, Sarah; Poschke, Heiko; Luke, Brian

2012-01-01

The DNA at the ends of linear chromosomes (the telomere) folds back onto itself and forms an intramolecular lariat-like structure. Although the telomere loop has been implicated in the protection of chromosome ends from nuclease-mediated resection and unscheduled DNA repair activities, it potentially poses an obstacle to the DNA replication machinery during S-phase. Therefore, the coordinated regulation of telomere loop formation, maintenance, and resolution is required in order to establish a balance between protecting the chromosome ends and promoting their duplication prior to cell division. Until recently, the only factor known to influence telomere looping in human cells was TRF2, a component of the shelterin complex. Recent work in yeast and mouse cells has uncovered additional regulatory factors that affect the loop structure at telomeres. In the following "perspective" we outline what is known about telomere looping and highlight the latest results regarding the regulation of this chromosome end structure. We speculate about how the manipulation of the telomere loop may have therapeutic implications in terms of diseases associated with telomere dysfunction and uncontrolled proliferation.

Real-time calibration of a feedback trap

OpenAIRE

Gavrilov, Momčilo; Jun, Yonggun; Bechhoefer, John

2014-01-01

Feedback traps use closed-loop control to trap or manipulate small particles and molecules in solution. They have been applied to the measurement of physical and chemical properties of particles and to explore fundamental questions in the non-equilibrium statistical mechanics of small systems. These applications have been hampered by drifts in the electric forces used to manipulate the particles. Although the drifts are small for measurements on the order of seconds, they dominate on time sca...

Robust Admissibilization of Descriptor Systems by Static Output-Feedback: An LMI Approach

Directory of Open Access Journals (Sweden)

M. Chaabane

2011-01-01

static output-feedback is studied in this paper and an approach to solve it is proposed. For this, sufficient conditions are derived for the closed-loop system to be admissible (i.e., stable, regular, and impulse-free. These conditions are expressed in terms of a strict Linear Matrix Inequality (LMI; so they are tractable using numerical computations. The proposed controller design methodology is based on two steps: the first is dedicated to synthesizing a classical state-feedback controller, which is used as the initial value for the second step, which uses an LMI problem to obtain static output-feedback controllers that give admissibility. Finally, a numerical example is given to illustrate the results.

Closed-loop waveform control of boost inverter

DEFF Research Database (Denmark)

Zhu, Guo Rong; Xiao, Cheng Yuan; Wang, Haoran

2016-01-01

The input current of single-phase inverter typically has an AC ripple component at twice the output frequency, which causes a reduction in both the operating lifetime of its DC source and the efficiency of the system. In this paper, the closed-loop performance of a proposed waveform control method...... to eliminate such a ripple current in boost inverter is investigated. The small-signal stability and the dynamic characteristic of the inverter system for input voltage or wide range load variations under the closed-loop waveform control method are studied. It is validated that with the closedloop waveform...... control, not only was stability achieved, the reference voltage of the boost inverter capacitors can be instantaneously adjusted to match the new load, thereby achieving improved ripple mitigation for a wide load range. Furthermore, with the control and feedback mechanism, there is minimal level of ripple...

Feedback Linearization approach for Standard and Fault Tolerant control: Application to a Quadrotor UAV Testbed

International Nuclear Information System (INIS)

Ghandour, J; Aberkane, S; Ponsart, J-C

2014-01-01

In this paper the control problem of a quadrotor vehicle experiencing a rotor failure is investigated. We develop a Feedback linearization approach to design a controller whose task is to make the vehicle performs trajectory following. Then we use the same approach to design a controller whose task is to make the vehicle enter a stable spin around its vertical axis, while retaining zero angular velocities around the other axis when a rotor failure is present. These conditions can be exploited to design a second control loop, which is used to perform trajectory following. The proposed double control loop architecture allows the vehicle to perform both trajectory and roll/pitch control. At last, to test the robustness of the feedback linearization technique, we applied wind to the quadrotor in mid flight

A high precision dual feedback discrete control system designed for satellite trajectory simulator

Science.gov (United States)

Liu, Ximin; Liu, Liren; Sun, Jianfeng; Xu, Nan

2005-08-01

Cooperating with the free-space laser communication terminals, the satellite trajectory simulator is used to test the acquisition, pointing, tracking and communicating performances of the terminals. So the satellite trajectory simulator plays an important role in terminal ground test and verification. Using the double-prism, Sun etc in our group designed a satellite trajectory simulator. In this paper, a high precision dual feedback discrete control system designed for the simulator is given and a digital fabrication of the simulator is made correspondingly. In the dual feedback discrete control system, Proportional- Integral controller is used in velocity feedback loop and Proportional- Integral- Derivative controller is used in position feedback loop. In the controller design, simplex method is introduced and an improvement to the method is made. According to the transfer function of the control system in Z domain, the digital fabrication of the simulator is given when it is exposed to mechanism error and moment disturbance. Typically, when the mechanism error is 100urad, the residual standard error of pitching angle, azimuth angle, x-coordinate position and y-coordinate position are 0.49urad, 6.12urad, 4.56urad, 4.09urad respectively. When the moment disturbance is 0.1rad, the residual standard error of pitching angle, azimuth angle, x-coordinate position and y-coordinate position are 0.26urad, 0.22urad, 0.16urad, 0.15urad respectively. The digital fabrication results demonstrate that the dual feedback discrete control system designed for the simulator can achieve the anticipated high precision performance.

The clinical relevance of advanced artificial feedback in the control of a multi-functional myoelectric prosthesis.

Science.gov (United States)

Markovic, Marko; Schweisfurth, Meike A; Engels, Leonard F; Bentz, Tashina; Wüstefeld, Daniela; Farina, Dario; Dosen, Strahinja

2018-03-27

To effectively replace the human hand, a prosthesis should seamlessly respond to user intentions but also convey sensory information back to the user. Restoration of sensory feedback is rated highly by the prosthesis users, and feedback is critical for grasping in able-bodied subjects. Nonetheless, the benefits of feedback in prosthetics are still debated. The lack of consensus is likely due to the complex nature of sensory feedback during prosthesis control, so that its effectiveness depends on multiple factors (e.g., task complexity, user learning). We evaluated the impact of these factors with a longitudinal assessment in six amputee subjects, using a clinical setup (socket, embedded control) and a range of tasks (box and blocks, block turn, clothespin and cups relocation). To provide feedback, we have proposed a novel vibrotactile stimulation scheme capable of transmitting multiple variables from a multifunction prosthesis. The subjects wore a bracelet with four by two uniformly placed vibro-tactors providing information on contact, prosthesis state (active function), and grasping force. The subjects also completed a questionnaire for the subjective evaluation of the feedback. The tests demonstrated that feedback was beneficial only in the complex tasks (block turn, clothespin and cups relocation), and that the training had an important, task-dependent impact. In the clothespin relocation and block turn tasks, training allowed the subjects to establish successful feedforward control, and therefore, the feedback became redundant. In the cups relocation task, however, the subjects needed some training to learn how to properly exploit the feedback. The subjective evaluation of the feedback was consistently positive, regardless of the objective benefits. These results underline the multifaceted nature of closed-loop prosthesis control as, depending on the context, the same feedback interface can have different impact on performance. Finally, even if the closed-loop

Closed-loop, multichannel experimentation using the open-source NeuroRighter electrophysiology platform

Directory of Open Access Journals (Sweden)

Jonathan Paul Newman

2013-01-01

Full Text Available Single neuron feedback control techniques, such as voltage clamp and dynamic clamp, have enabled numerous advances in our understanding of ion channels, electrochemical signaling, and neural dynamics. Although commercially available multichannel recording and stimulation systems are commonly used for studying neural processing at the network level, they provide little native support for real-time feedback. We developed the open-source NeuroRighter multichannel electrophysiology hardware and software platform for closed-loop multichannel control with a focus on accessibility and low cost. NeuroRighter allows 64 channels of stimulation and recording for around US $10,000, along with the ability to integrate with other software and hardware. Here, we present substantial enhancements to the NeuroRighter platform, including a redesigned desktop application, a new stimulation subsystem allowing arbitrary stimulation patterns, low-latency data servers for accessing data streams, and a new application programming interface (API for creating closed-loop protocols that can be inserted into NeuroRighter as plugin programs. This greatly simplifies the design of sophisticated real-time experiments without sacrificing the power and speed of a compiled programming language. Here we present a detailed description of NeuroRighter as a stand alone application, its plugin API, and an extensive set of case studies that highlight the system's abilities for conducting closed-loop, multichannel interfacing experiments.

A fast intracortical brain-machine interface with patterned optogenetic feedback.

Science.gov (United States)

Abbasi, Aamir; Goueytes, Dorian; Shulz, Daniel E; Ego-Stengel, Valerie; Estebanez, Luc

2018-04-04

The development of brain-machine interfaces (BMIs) brings a new perspective to patients with a loss of autonomy. By combining online recordings of brain activity with a decoding algorithm, patients can learn to control a robotic arm in order to perform simple actions. However, in contrast to the vast amounts of somatosensory information channeled by limbs to the brain, current BMIs are devoid of touch and force sensors. Patients must therefore rely solely on vision and audition, which are maladapted to the control of a prosthesis. In contrast, in a healthy limb, somatosensory inputs alone can efficiently guide the handling of a fragile object, or ensure a smooth trajectory. We have developed a BMI in the mouse that includes a rich artificial somatosensory-like cortical feedback. Our setup includes online recordings of the activity of multiple neurons in the whisker primary motor cortex (vM1), and delivers feedback simultaneously via a low-latency, high-refresh rate and spatially structured photo-stimulation of the whisker primary somatosensory cortex (vS1), based on a mapping obtained by intrinsic imaging. We demonstrate the operation of the loop and show that mice can detect the neuronal spiking in vS1 triggered by the photo-stimulations. Finally, we show that the mice can learn a behavioral task relying only on the artificial inputs and outputs of the closed-loop BMI. This is the first motor BMI that includes a short-latency, intracortical, somatosensory-like feedback. It will be a useful platform to discover efficient cortical feedback schemes towards future human BMI applications. Creative Commons Attribution license.

LoopIng: a template-based tool for predicting the structure of protein loops.

KAUST Repository

Messih, Mario Abdel

2015-08-06

Predicting the structure of protein loops is very challenging, mainly because they are not necessarily subject to strong evolutionary pressure. This implies that, unlike the rest of the protein, standard homology modeling techniques are not very effective in modeling their structure. However, loops are often involved in protein function, hence inferring their structure is important for predicting protein structure as well as function.We describe a method, LoopIng, based on the Random Forest automated learning technique, which, given a target loop, selects a structural template for it from a database of loop candidates. Compared to the most recently available methods, LoopIng is able to achieve similar accuracy for short loops (4-10 residues) and significant enhancements for long loops (11-20 residues). The quality of the predictions is robust to errors that unavoidably affect the stem regions when these are modeled. The method returns a confidence score for the predicted template loops and has the advantage of being very fast (on average: 1 min/loop).www.biocomputing.it/loopinganna.tramontano@uniroma1.itSupplementary data are available at Bioinformatics online.

Static inverter with synchronous output waveform synthesized by time-optimal-response feedback

Science.gov (United States)

Kernick, A.; Stechschulte, D. L.; Shireman, D. W.

1976-01-01

Time-optimal-response 'bang-bang' or 'bang-hang' technique, using four feedback control loops, synthesizes static-inverter sinusoidal output waveform by self-oscillatory but yet synchronous pulse-frequency-modulation (SPFM). A single modular power stage per phase of ac output entails the minimum of circuit complexity while providing by feedback synthesis individual phase voltage regulation, phase position control and inherent compensation simultaneously for line and load disturbances. Clipped sinewave performance is described under off-limit load or input voltage conditions. Also, approaches to high power levels, 3-phase arraying and parallel modular connection are given.

False feedback and beliefs influence name recall in younger and older adults.

Science.gov (United States)

Strickland-Hughes, Carla M; West, Robin Lea; Smith, Kimberly A; Ebner, Natalie C

2017-09-01

Feedback is an important self-regulatory process that affects task effort and subsequent performance. Benefits of positive feedback for list recall have been explored in research on goals and feedback, but the effect of negative feedback on memory has rarely been studied. The current research extends knowledge of memory and feedback effects by investigating face-name association memory and by examining the potential mediation of feedback effects, in younger and older adults, through self-evaluative beliefs. Beliefs were assessed before and after name recognition and name recall testing. Repeated presentation of false positive feedback was compared to false negative feedback and a no feedback condition. Results showed that memory self-efficacy declined over time for participants in the negative and no feedback conditions but was sustained for those receiving positive feedback. Furthermore, participants who received negative feedback felt older after testing than before testing. For name recall, the positive feedback group outperformed the negative feedback and no feedback groups combined, with no age interactions. The observed feedback-related effects on memory were fully mediated by changes in memory self-efficacy. These findings advance our understanding of how beliefs are related to feedback in memory and inform future studies examining the importance of self-regulation in memory.

Quantized Passive Dynamic Output Feedback Control with Actuator Failure

Directory of Open Access Journals (Sweden)

Zu-Xin Li

2016-01-01

Full Text Available This paper investigates the problem of passive dynamic output feedback control for fuzzy discrete nonlinear systems with quantization and actuator failures, where the measurement output of the system is quantized by a logarithmic quantizer before being transferred to the fuzzy controller. By employing the fuzzy-basis-dependent Lyapunov function, sufficient condition is established to guarantee the closed-loop system to be mean-square stable and the prescribed passive performance. Based on the sufficient condition, the fuzzy dynamic output feedback controller is proposed for maintaining acceptable performance levels in the case of actuator failures and quantization effects. Finally, a numerical example is given to show the usefulness of the proposed method.

Digitally tunable dual wavelength emission from semiconductor ring lasers with filtered optical feedback

International Nuclear Information System (INIS)

Khoder, Mulham; Verschaffelt, Guy; Nguimdo, Romain Modeste; Danckaert, Jan; Leijtens, Xaveer; Bolk, Jeroen

2013-01-01

We report on a novel integrated approach to obtain dual wavelength emission from a semiconductor laser based on on-chip filtered optical feedback. Using this approach, we show experiments and numerical simulations of dual wavelength emission of a semiconductor ring laser. The filtered optical feedback is realized on-chip by employing two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback strength of each wavelength channel independently. By tuning the current injected into each of the amplifiers, we can effectively cancel the gain difference between the wavelength channels due to fabrication and material dichroism, thus resulting in stable dual wavelength emission. We also explore the accuracy needed in the operational parameters to maintain this dual wavelength emission. (letter)

Diabetes-Induced Oxidative Stress in Endothelial Progenitor Cells May Be Sustained by a Positive Feedback Loop Involving High Mobility Group Box-1

Directory of Open Access Journals (Sweden)

Han Wu

2016-01-01

Full Text Available Oxidative stress is considered to be a critical factor in diabetes-induced endothelial progenitor cell (EPC dysfunction, although the underlying mechanisms are not fully understood. In this study, we investigated the role of high mobility group box-1 (HMGB-1 in diabetes-induced oxidative stress. HMGB-1 was upregulated in both serum and bone marrow-derived monocytes from diabetic mice compared with control mice. In vitro, advanced glycation end productions (AGEs induced, expression of HMGB-1 in EPCs and in cell culture supernatants in a dose-dependent manner. However, inhibition of oxidative stress with N-acetylcysteine (NAC partially inhibited the induction of HMGB-1 induced by AGEs. Furthermore, p66shc expression in EPCs induced by AGEs was abrogated by incubation with glycyrrhizin (Gly, while increased superoxide dismutase (SOD activity in cell culture supernatants was observed in the Gly treated group. Thus, HMGB-1 may play an important role in diabetes-induced oxidative stress in EPCs via a positive feedback loop involving the AGE/reactive oxygen species/HMGB-1 pathway.

A time-dependent stop operator for modeling a class of singular hysteresis loops in a piezoceramic actuator

International Nuclear Information System (INIS)

Al Janaideh, Mohammad

2013-01-01

We present a time-dependent stop operator-based Prandtl–Ishlinskii model to characterize singular hysteresis loops in a piezoceramic actuator. The model is constructed based on the time-dependent threshold. The inverse time-dependent stop operator-based Prandtl–Ishlinskii model is obtained analytically and it can be applied as a feedforward compensator to compensate for singular hysteresis loops in a class of smart-material-based actuators. The objective of this study is to present an invertible Prandtl–Ishlinskii model that can be applied as a feedforward compensator to compensate for singular hysteresis loops without inserting a feedback control system

A time-dependent stop operator for modeling a class of singular hysteresis loops in a piezoceramic actuator

Energy Technology Data Exchange (ETDEWEB)

Al Janaideh, Mohammad, E-mail: aljanaideh@gmail.com [Department of Mechatronics Engineering, The University of Jordan, 11942 Amman (Jordan)

2013-03-15

We present a time-dependent stop operator-based Prandtl–Ishlinskii model to characterize singular hysteresis loops in a piezoceramic actuator. The model is constructed based on the time-dependent threshold. The inverse time-dependent stop operator-based Prandtl–Ishlinskii model is obtained analytically and it can be applied as a feedforward compensator to compensate for singular hysteresis loops in a class of smart-material-based actuators. The objective of this study is to present an invertible Prandtl–Ishlinskii model that can be applied as a feedforward compensator to compensate for singular hysteresis loops without inserting a feedback control system.

An Augmented Lecture Feedback System to Support Learner and Teacher Communication

Science.gov (United States)

Zarraonandia, Telmo; Aedo, Ignacio; Diaz, Paloma; Montero, Alvaro

2013-01-01

In this paper, it is advocated that the feedback loop between learners and teachers could be improved by making use of augmented reality (AR) techniques. The bidirectional communication between teacher and learners is sometimes hampered by students' fear of showing themselves up in front of their classmates. In order to overcome this problem, a…

Application of a Virtual Reactivity Feedback Control Loop in Non-Nuclear Testing of a Fast Spectrum Reactor

International Nuclear Information System (INIS)

Bragg-Sitton, Shannon M.; Forsbacka, Matthew

2004-01-01

For a compact, fast-spectrum reactor, reactivity feedback is dominated by core deformation at elevated temperature. Given the use of accurate deformation measurement techniques, it is possible to simulate nuclear feedback in non-nuclear electrically heated reactor tests. Implementation of simulated reactivity feedback in response to measured deflection is being tested at the Nasa Marshall Space Flight Center Early Flight Fission Test Facility (EFF-TF). During tests of the SAFE-100 reactor prototype, core deflection was monitored using a high resolution camera. 'Virtual' reactivity feedback was accomplished by applying the results of Monte Carlo calculations (MCNPX) to core deflection measurements; the computational analysis was used to establish the reactivity worth of various core deformations. The power delivered to the SAFE-100 prototype was then adjusted accordingly via kinetics calculations. The work presented in this paper will demonstrate virtual reactivity feedback as core power was increased from 1 kWt to 10 kWt, held approximately constant at 10 kWt, and then allowed to decrease based on the negative thermal reactivity coefficient. (authors)

An active feedback system to control synchrotron oscillations in the SLC Damping Rings

International Nuclear Information System (INIS)

Corredoura, P.L.; Pellegrin, J.L.; Schwarz, H.D.; Sheppard, J.C.

1989-03-01

Initially the SLC Damping Rings accomplished Robinson instability damping by operating the RF accelerating cavities slightly detuned. In order to be able to run the cavities tuned and achieve damping for Robinson instability and synchrotron oscillations at injection an active feedback system has been developed. This paper describes the theoretical basis for the feedback system and the development of the hardware. Extensive measurements of the loop response including stored beam were performed. Overall performance of the system is also reported. 3 refs., 6 figs

Using deflation in the pole assignment problem with output feedback

Science.gov (United States)

Miminis, George

1989-01-01

A direct algorithm is suggested for the computation of a linear output feedback for a multi input, multi output system such that the resultant closed-loop matrix has eigenvalues that include a specified set of eigenvalues. The algorithm uses deflation based on unitary similarity transformations. Thus researchers hope the algorithm is numerically stable; however, this has not been proven as yet.

Differential contributions of the superior and inferior parietal cortex to feedback versus feedforward control of tools.

Science.gov (United States)

Macuga, Kristen L; Frey, Scott H

2014-05-15

Damage to the superior and/or inferior parietal lobules (SPL, IPL) (Sirigu et al., 1996) or cerebellum (Grealy and Lee, 2011) can selectively disrupt motor imagery, motivating the hypothesis that these regions participate in predictive (i.e., feedforward) control. If so, then the SPL, IPL, and cerebellum should show greater activity as the demands on feedforward control increase from visually-guided execution (closed-loop) to execution without visual feedback (open-loop) to motor imagery. Using fMRI and a Fitts' reciprocal aiming task with tools directed at targets in far space, we found that the SPL and cerebellum exhibited greater activity during closed-loop control. Conversely, open-loop and imagery conditions were associated with increased activity within the IPL and prefrontal areas. These results are consistent with a superior-to-inferior gradient in the representation of feedback-to-feedforward control within the posterior parietal cortex. Additionally, the anterior SPL displayed greater activity when aiming movements were performed with a stick vs. laser pointer. This may suggest that it is involved in the remapping of far into near (reachable) space (Maravita and Iriki, 2004), or in distalization of the end-effector from hand to stick (Arbib et al., 2009). Copyright © 2014 Elsevier Inc. All rights reserved.

Diagnosis of Fault Modes Masked by Control Loops with an Application to Autonomous Hovercraft Systems

Directory of Open Access Journals (Sweden)

Ioannis A. Raptis

2013-01-01

Full Text Available This paper introduces a methodology for the design, testing and assessment of incipient failure detection techniques for failing components/systems of an autonomous vehicle masked or hidden by feedback control loops. It is recognized that the optimum operation of critical assets (aircraft, autonomous systems, etc. may be compromised by feedback control loops by masking severe fault modes while compensating for typical disturbances. Detrimental consequences of such occurrences include the inability to detect expeditiously and accurately incipient failures, loss of control and inefficient operation of assets in the form of fuel overconsumption and adverse environmental impact. We pursue a systems engineering process to design, construct and test an autonomous hovercraft instrumented appropriately for improved autonomy. Hidden fault modes are detected with performance guarantees by invoking a Bayesian estimation approach called particle filtering. Simulation and experimental studies are employed to demonstrate the efficacy of the proposed methods.

Edge turbulence control on the KT-5C tokamak by feedback using electrostatic probes

International Nuclear Information System (INIS)

Zhai Kan; Wang Cheng; Wen Yizi; Yu Changxuan; Wan Shude; Liu Wandong; Xu Zhizhan

1998-01-01

Experiments on edge turbulence control have been performed on the KT-5C tokamak by feedback using two sets of electrostatic probes as the driving probe and detective probe. The results indicate that the feedback can enhance or reduce the turbulence amplitude depending upon the phase shift and gain of the feedback network. When the feedback with 90 degree phase shift and with certain loop gain is applied, the spectrum component of turbulence is reduced obviously and the fluctuation amplitude of the electron density and electron temperature become lower by about 25%. consistently the particle flux across the magnetic field induced by the electrostatic fluctuation also decreases by about 25%. On the other hand, the feedback with 0 degree or 180 degree or -90 degree phase shift can enhance the amplitude of the edge turbulence. These results indicate a nonlinear mechanism of the influence of feedback on the edge turbulence, which to some extent also reflect a specific nonlinear characteristic of the edge turbulence

Chromosome segregation regulation in human zygotes : Altered mitotic histone phosphorylation dynamics underlying centromeric targeting of the chromosomal passenger complex

NARCIS (Netherlands)

Van De Werken, C.; Avo Santos, M.; Laven, J. S E; Eleveld, C.; Fauser, B. C J M; Lens, S. M A; Baart, E. B.

2015-01-01

STUDY QUESTION Are the kinase feedback loops that regulate activation and centromeric targeting of the chromosomal passenger complex (CPC), functional during mitosis in human embryos? SUMMARY ANSWER Investigation of the regulatory kinase pathways involved in centromeric CPC targeting revealed normal

Investigations of the influence of feedback and coupling effects on neutron noise in a nuclear reactor

International Nuclear Information System (INIS)

Vath, W.

1975-01-01

Investigations are described of the influence of a known feedback, i.e., a control loop with known transfer function, on the spectra of neutron chamber signals. Theoretical formulas for the spectra are derived using the point reactor model. These formulas were verified by noise measurements in a zero power reactor. Special attention is given to the noise generated by the control loop, the influence of this feedback noise on the spectra being verified experimentally. In large reactors space dependent transfer functions must be taken into account. As a first approximation to handle the spatial dependence, the afore-mentioned investigations were extended to the two-point reactor model. Corresponding experimental work was done for the Argonaut Reactor Karlsruhe (ARK) with a symmetrical two-slab core loading. Coolant boiling in a BWR was investigated. The boiling must be considered as a feedback mechanism as well as an extrnal reactivity perturbation. In order to simulate the steam bubble content, nitrogen gas was injected into the water moderator of the ARK. By modulating the total gas flow according to the instantaneous reactor power the feedback effect was simulated. The gas flow produced a band-limited, white reactivity noise. The upper break frequency could be used to determine the travelling time of the bubbles through the core. (author)

Getting in (and out of the loop: regulating higher order telomere structures

Directory of Open Access Journals (Sweden)

Sarah eLuke-Glaser

2012-11-01

Full Text Available The DNA at the ends of linear chromosomes (the telomere folds back onto itself and forms an intramolecular lariat-like structure. Although the telomere loop has been implicated in the protection of chromosome ends from nuclease-mediated resection and unscheduled DNA repair activities, it potentially poses an obstacle to the DNA replication machinery during S phase. Therefore, the coordinated regulation of telomere loop formation, maintenance and resolution is required in order to establish a balance between protecting the chromosome ends and promoting their duplication prior to cell division. Until recently, the only factor know to influence telomere looping in human cells was TRF2, a component of the shelterin complex. Recent work in yeast and mouse cells has uncovered additional regulatory factors that affect the loop structure at telomeres. In the following perspective we will outline what is known about telomere looping and highlight the latest results regarding the regulation of this chromosome end structure. We will speculate about how the manipulation of the telomere loop may have therapeutic implications in terms of diseases associated with telomere dysfunction and uncontrolled proliferation.

Myoelectric hand prosthesis force control through servo motor current feedback.

Science.gov (United States)

Sono, Tálita Saemi Payossim; Menegaldo, Luciano Luporini

2009-10-01

This paper presents the prehension force closed-loop control design of a mechanical finger commanded by electromyographic signal (EMG) from a patient's arm. The control scheme was implemented and tested in a mechanical finger prototype with three degrees of freedom and one actuator, driven by arm muscles EMG of normal volunteers. Real-time indirect estimation of prehension force was assessed by measuring the DC servo motor actuator current. A model of the plant comprising finger, motor, and grasped object was proposed. Model parameters were identified experimentally and a classical feedback phase-lead compensator was designed. The controlled mechanical finger was able to provide a more accurate prehension force modulation of a compliant object when compared to open-loop control.

The impact of local loop and retail unbundling

OpenAIRE

Klein, Gordon J.; Wendel, Julia

2014-01-01

For more than a decade the unbundling of telecommunications networks has been used as a regulatory means to stifle competition. However, despite its assumed positive effects on market entry and competition intensity, the negative effects on network investment incentives are widely shown in the theoretical literature. Therefore broadband penetration might also be affected negatively. In our paper we concentrate on the impact of local loop unbundling and Bitstream access on broadband penetratio...

Combining Charge Couple Devices and Rate Sensors for the Feedforward Control System of a Charge Coupled Device Tracking Loop.

Science.gov (United States)

Tang, Tao; Tian, Jing; Zhong, Daijun; Fu, Chengyu

2016-06-25

A rate feed forward control-based sensor fusion is proposed to improve the closed-loop performance for a charge couple device (CCD) tracking loop. The target trajectory is recovered by combining line of sight (LOS) errors from the CCD and the angular rate from a fiber-optic gyroscope (FOG). A Kalman filter based on the Singer acceleration model utilizes the reconstructive target trajectory to estimate the target velocity. Different from classical feed forward control, additive feedback loops are inevitably added to the original control loops due to the fact some closed-loop information is used. The transfer function of the Kalman filter in the frequency domain is built for analyzing the closed loop stability. The bandwidth of the Kalman filter is the major factor affecting the control stability and close-loop performance. Both simulations and experiments are provided to demonstrate the benefits of the proposed algorithm.

Concentration and length dependence of DNA looping in transcriptional regulation.

Directory of Open Access Journals (Sweden)

Lin Han

2009-05-01

Full Text Available In many cases, transcriptional regulation involves the binding of transcription factors at sites on the DNA that are not immediately adjacent to the promoter of interest. This action at a distance is often mediated by the formation of DNA loops: Binding at two or more sites on the DNA results in the formation of a loop, which can bring the transcription factor into the immediate neighborhood of the relevant promoter. These processes are important in settings ranging from the historic bacterial examples (bacterial metabolism and the lytic-lysogeny decision in bacteriophage, to the modern concept of gene regulation to regulatory processes central to pattern formation during development of multicellular organisms. Though there have been a variety of insights into the combinatorial aspects of transcriptional control, the mechanism of DNA looping as an agent of combinatorial control in both prokaryotes and eukaryotes remains unclear. We use single-molecule techniques to dissect DNA looping in the lac operon. In particular, we measure the propensity for DNA looping by the Lac repressor as a function of the concentration of repressor protein and as a function of the distance between repressor binding sites. As with earlier single-molecule studies, we find (at least two distinct looped states and demonstrate that the presence of these two states depends both upon the concentration of repressor protein and the distance between the two repressor binding sites. We find that loops form even at interoperator spacings considerably shorter than the DNA persistence length, without the intervention of any other proteins to prebend the DNA. The concentration measurements also permit us to use a simple statistical mechanical model of DNA loop formation to determine the free energy of DNA looping, or equivalently, the for looping.

Enhanced Stability of Capacitor-Current Feedback Active Damping for LCL-Filtered Grid Converters

DEFF Research Database (Denmark)

Xin, Zhen; Wang, Xiongfei; Loh, Poh Chiang

2015-01-01

The proportional capacitor-current feedback active damping method has been widely used to suppress the LCL-filter resonance. However, the time delay in the damping control loop may lead to non-minimum phase or even unstable responses when the resonance frequency varies in a wide range. To improve...

Technology transfer of operator-in-the-loop simulation

Science.gov (United States)

Yae, K. H.; Lin, H. C.; Lin, T. C.; Frisch, H. P.

1994-01-01

The technology developed for operator-in-the-loop simulation in space teleoperation has been applied to Caterpillar's backhoe, wheel loader, and off-highway truck. On an SGI workstation, the simulation integrates computer modeling of kinematics and dynamics, real-time computational and visualization, and an interface with the operator through the operator's console. The console is interfaced with the workstation through an IBM-PC in which the operator's commands were digitized and sent through an RS-232 serial port. The simulation gave visual feedback adequate for the operator in the loop, with the camera's field of vision projected on a large screen in multiple view windows. The view control can emulate either stationary or moving cameras. This simulator created an innovative engineering design environment by integrating computer software and hardware with the human operator's interactions. The backhoe simulation has been adopted by Caterpillar in building a virtual reality tool for backhoe design.

Loop Mirror Laser Neural Network with a Fast Liquid-Crystal Display

Science.gov (United States)

Mos, Evert C.; Schleipen, Jean J. H. B.; de Waardt, Huug; Khoe, Djan G. D.

1999-07-01

In our laser neural network (LNN) all-optical threshold action is obtained by application of controlled optical feedback to a laser diode. Here an extended experimental LNN is presented with as many as 32 neurons and 12 inputs. In the setup we use a fast liquid-crystal display to implement an optical matrix vector multiplier. This display, based on ferroelectric liquid-crystal material, enables us to present 125 training examples s to the LNN. To maximize the optical feedback efficiency of the setup, a loop mirror is introduced. We use a -rule learning algorithm to train the network to perform a number of functions toward the application area of telecommunication data switching.

Light storage in a doped solid enhanced by feedback-controlled pulse shaping

International Nuclear Information System (INIS)

Beil, F.; Buschbeck, M.; Heinze, G.; Halfmann, T.

2010-01-01

We report on experiments dealing with feedback-controlled pulse shaping to optimize the efficiency of light storage by electromagnetically induced transparency (EIT) in a Pr 3+ :Y 2 SiO 5 crystal. A learning loop in combination with an evolutionary algorithm permits the automatic determination of optimal temporal profiles of intensities and frequencies in the driving laser pulses (i.e., the probe and coupling pulses). As a main advantage, the technique finds optimal solutions even in the complicated multilevel excitation scheme of a doped solid, involving large inhomogeneous broadening. The learning loop experimentally determines optimal temporal intensity profiles of the coupling pulses for a given probe pulse. The optimized intensity pulse shapes enhance the light-storage efficiency in the doped solid by a factor of 2. The learning loop also determines a fast and efficient preparation pulse sequence, which serves to optically prepare the crystal prior to light-storage experiments. The optimized preparation sequence is 5 times faster than standard preparation sequences. Moreover, the optimized preparation sequence enhances the optical depth in the medium by a factor of 5. As a consequence, the efficiency of light storage also increases by another factor of 3. Our experimental data clearly demonstrate the considerable potential of feedback-controlled pulse shaping, applied to EIT-driven light storage in solid media.

Managing Regulatory Body Competence

International Nuclear Information System (INIS)

2013-01-01

In 2001, the IAEA published TECDOC 1254, which examined the way in which the recognized functions of a regulatory body for nuclear facilities results in competence needs. Using the systematic approach to training (SAT), TECDOC 1254 provided a framework for regulatory bodies for managing training and developing and their maintaining their competence. It has been successfully used by many regulators. The IAEA has also introduced a methodology and an assessment tool - Guidelines for Systematic Assessment of Regulatory Competence Needs (SARCoN) - which provides practical guidance on analysing the training and development needs of a regulatory body and, through a gap analysis, guidance on establishing competence needs and how to meet them. In 2009, the IAEA established a steering committee (supported by a bureau) with the mission to advise the IAEA on how it could best assist Member States to develop suitable competence management systems for their regulatory bodies. The committee recommended the development of a safety report on managing staff competence as an integral part of a regulatory body's management system. This Safety Report was developed in response to this request. It supersedes TECDOC 1254, broadens its application to regulatory bodies for all facilities and activities, and builds upon the experience gained through the application of TECDOC 1254 and SARCoN and the feedback received from Member States. This Safety Report applies to the management of adequate competence as needs change, and as such is equally applicable to the needs of States 'embarking' on a nuclear power programme. It also deals with the special case of building up the competence of regulatory bodies as part of the overall process of establishing an 'embarking' State's regulatory system

Dynamic behaviors of a broad-area diode laser with lateral-mode-selected external feedback

DEFF Research Database (Denmark)

Chi, Mingjun; Petersen, Paul Michael

2014-01-01

In this paper, we investigate the dynamics of a BAL with lateral-mode selected external feedback experimentally by measuring the far-field profile, intensity noise spectrum and time series of the output beam. The mode-selection is achieved by adjusting a stripe mirror at the pseudo far-field plan...... with a frequency of the single roundtrip external-cavity loop modulated by periodic low-frequency fluctuation. This is the first observation of pulse-package oscillation in a diode laser with long-cavity feedback, to our knowledge....

Glucocorticoid and cytokine crosstalk: Feedback, feedforward, and co-regulatory interactions determine repression or resistance.

Science.gov (United States)

Newton, Robert; Shah, Suharsh; Altonsy, Mohammed O; Gerber, Antony N

2017-04-28

Inflammatory signals induce feedback and feedforward systems that provide temporal control. Although glucocorticoids can repress inflammatory gene expression, glucocorticoid receptor recruitment increases expression of negative feedback and feedforward regulators, including the phosphatase, DUSP1, the ubiquitin-modifying enzyme, TNFAIP3, or the mRNA-destabilizing protein, ZFP36. Moreover, glucocorticoid receptor cooperativity with factors, including nuclear factor-κB (NF-κB), may enhance regulator expression to promote repression. Conversely, MAPKs, which are inhibited by glucocorticoids, provide feedforward control to limit expression of the transcription factor IRF1, and the chemokine, CXCL10. We propose that modulation of feedback and feedforward control can determine repression or resistance of inflammatory gene expression toglucocorticoid. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

High-speed clock recovery and demodulation using short pulse sources and phase-locked loop techniques

DEFF Research Database (Denmark)

Zibar, Darko

2007-01-01

clocktiming jitter, i.e. 3.5 ps at 40 Gb/s and 0.5 ps at 160 Gb/s. In the last part of the thesis, a novel phase-locked coherent optical phase demodulator with feedback and sampling, to be used in phase-modulated radio-over-fibre optical links, is also presented, theoretically investigated and experimentally...... demonstrated. It is experimentally shown that the proposed approach results in 18 dB of spur-free-dynamic range improve- ment compared to a traditional demodulator without feedback. A new time-domain, large signal, numerical model of the phase locked coherent demodulator is developed and shown...... loop with noise at a bit-rate of 160 Gb/s. It has been shown that it is important to reduce the time delay in the loop since it results in the increased timing jitter of the recovered clock signal. We also investigate the requirement for the free-running timing jitter of the local electrical...

A Feedback Passivation Design for DC Microgrid and Its DC/DC Converters

Directory of Open Access Journals (Sweden)

Feifan Ji

2016-12-01

Full Text Available There are difficulties in analyzing the stability of microgrids since they are located on various network structures. However, considering that the network often consists of passive elements, the passivity theory is applied in this paper to solve the above-mentioned problem. It has been formerly shown that when the network is weakly strictly positive real (WSPR, the DC microgrid is stable if all interfaces between the microgrid and converters are made to be passive, which is called interface passivity. Then, the feedback passivation method is proposed for the controller design of various DC–DC converters to achieve the interface passivity. The interface passivity is different from the passivity of closed-loop systems on which the passivity based control (PBC concentrates. The feedback passivation design is detailed for typical buck converters and boost converters in terms of conditions that the controller parameters should satisfy. The theoretical results are verified by a hardware-in-loop real-time labotray (RTLab simulation of a DC microgrid with four generators.

Senataxin Mutation Reveals How R-Loops Promote Transcription by Blocking DNA Methylation at Gene Promoters.

Science.gov (United States)

Grunseich, Christopher; Wang, Isabel X; Watts, Jason A; Burdick, Joshua T; Guber, Robert D; Zhu, Zhengwei; Bruzel, Alan; Lanman, Tyler; Chen, Kelian; Schindler, Alice B; Edwards, Nancy; Ray-Chaudhury, Abhik; Yao, Jianhua; Lehky, Tanya; Piszczek, Grzegorz; Crain, Barbara; Fischbeck, Kenneth H; Cheung, Vivian G

2018-02-01

R-loops are three-stranded nucleic acid structures found abundantly and yet often viewed as by-products of transcription. Studying cells from patients with a motor neuron disease (amyotrophic lateral sclerosis 4 [ALS4]) caused by a mutation in senataxin, we uncovered how R-loops promote transcription. In ALS4 patients, the senataxin mutation depletes R-loops with a consequent effect on gene expression. With fewer R-loops in ALS4 cells, the expression of BAMBI, a negative regulator of transforming growth factor β (TGF-β), is reduced; that then leads to the activation of the TGF-β pathway. We uncovered that genome-wide R-loops influence promoter methylation of over 1,200 human genes. DNA methyl-transferase 1 favors binding to double-stranded DNA over R-loops. Thus, in forming R-loops, nascent RNA blocks DNA methylation and promotes further transcription. Hence, our results show that nucleic acid structures, in addition to sequences, influence the binding and activity of regulatory proteins. Copyright © 2017 Elsevier Inc. All rights reserved.

Push-Pull and Feedback Mechanisms Can Align Signaling System Outputs with Inputs.

Science.gov (United States)

Andrews, Steven S; Peria, William J; Yu, Richard C; Colman-Lerner, Alejandro; Brent, Roger

2016-11-23

Many cell signaling systems, including the yeast pheromone response system, exhibit "dose-response alignment" (DoRA), in which output of one or more downstream steps closely matches the fraction of occupied receptors. DoRA can improve the fidelity of transmitted dose information. Here, we searched systematically for biochemical network topologies that produced DoRA. Most networks, including many containing feedback and feedforward loops, could not produce DoRA. However, networks including "push-pull" mechanisms, in which the active form of a signaling species stimulates downstream activity and the nominally inactive form reduces downstream activity, enabled perfect DoRA. Networks containing feedbacks enabled DoRA, but only if they also compared feedback to input and adjusted output to match. Our results establish push-pull as a non-feedback mechanism to align output with variable input and maximize information transfer in signaling systems. They also suggest genetic approaches to determine whether particular signaling systems use feedback or push-pull control. Copyright © 2016 Elsevier Inc. All rights reserved.

Finite-time stabilization of uncertain nonholonomic systems in feedforward-like form by output feedback.

Science.gov (United States)

Gao, Fangzheng; Wu, Yuqiang; Zhang, Zhongcai

2015-11-01

This paper investigates the problem of finite-time stabilization by output feedback for a class of nonholonomic systems in chained form with uncertainties. Comparing with the existing relevant literature, a distinguishing feature of the systems under investigation is that the x-subsystem is a feedforward-like rather than feedback-like system. This renders the existing control methods inapplicable to the control problems of the systems. A constructive design procedure for output feedback control is given. The designed controller renders that the states of closed-loop system are regulated to zero in a finite time. Two simulation examples are provided to illustrate the effectiveness of the proposed approach. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Exploring a minimal two-component p53 model

International Nuclear Information System (INIS)

Sun, Tingzhe; Zhu, Feng; Shen, Pingping; Yuan, Ruoshi; Xu, Wei

2010-01-01

The tumor suppressor p53 coordinates many attributes of cellular processes via interlocked feedback loops. To understand the biological implications of feedback loops in a p53 system, a two-component model which encompasses essential feedback loops was constructed and further explored. Diverse bifurcation properties, such as bistability and oscillation, emerge by manipulating the feedback strength. The p53-mediated MDM2 induction dictates the bifurcation patterns. We first identified irradiation dichotomy in p53 models and further proposed that bistability and oscillation can behave in a coordinated manner. Further sensitivity analysis revealed that p53 basal production and MDM2-mediated p53 degradation, which are central to cellular control, are most sensitive processes. Also, we identified that the much more significant variations in amplitude of p53 pulses observed in experiments can be derived from overall amplitude parameter sensitivity. The combined approach with bifurcation analysis, stochastic simulation and sampling-based sensitivity analysis not only gives crucial insights into the dynamics of the p53 system, but also creates a fertile ground for understanding the regulatory patterns of other biological networks

Renal phosphate handling: Physiology

Directory of Open Access Journals (Sweden)

Narayan Prasad

2013-01-01

Full Text Available Phosphorus is a common anion. It plays an important role in energy generation. Renal phosphate handling is regulated by three organs parathyroid, kidney and bone through feedback loops. These counter regulatory loops also regulate intestinal absorption and thus maintain serum phosphorus concentration in physiologic range. The parathyroid hormone, vitamin D, Fibrogenic growth factor 23 (FGF23 and klotho coreceptor are the key regulators of phosphorus balance in body.

Cross-cohort analysis identifies a TEAD4 ↔ MYCN positive-feedback loop as the core regulatory element of high-risk neuroblastoma. | Office of Cancer Genomics

Science.gov (United States)

High-risk neuroblastomas show a paucity of recurrent somatic mutations at diagnosis. As a result, the molecular basis for this aggressive phenotype remains elusive. Recent progress in regulatory network analysis helped us elucidate disease-driving mechanisms downstream of genomic alterations, including recurrent chromosomal alterations. Our analysis identified three molecular subtypes of high-risk neuroblastomas, consistent with chromosomal alterations, and identified subtype-specific master regulator (MR) proteins that were conserved across independent cohorts.

Modeling and Analysis of a Closed-Loop System for High-Q MEMS Accelerometer Sensor

Directory of Open Access Journals (Sweden)

Wang Yalin

2018-01-01

Full Text Available High-Q sensing element is desirable for high performance while makes the loop control a great challenge. This paper presents a closed-loop system for high-Q capacitive MEMS accelerometer which has achieved loop control effectively. The proportional-derivative(PDcontrol is developed in the system to improve the system stability. In addition, pulse width modulation (PWM electrostatic force feedback is designed in the loop to overcome the nonlinearity. Furthermore, a sigma-delta (ΣΔ modulator with noise shaping is built to realize digital output. System model is built in Matlab/Simulink. The simulation results indicate that equivalent Q value is reduced to 1.5 to ensure stability and responsiveness of the system. The effective number of bits of system output is 14.7 bits. The system nonlinearity is less than 5‰. The equivalent linear model including main noise factors is built, and then a complete theory of noise and linearity analysis is established to contribute to common MEMS accelerometer research.

Status of Digital Orbit Feedback for SPEAR

International Nuclear Information System (INIS)

Hettel, Robert

2003-01-01

The present global orbit feedback system for SPEAR can adjust the electron beam position with a cycle time of 5 s. In addition, 50 Hz analog local servos stabilize the vertical photon beam position at monitors situated in the ten SSRL beamlines. The global and local systems will soon be merged into a single unified system operating from a dedicated DSP board. The goal is to acquire orbits, process the data, and correct beam position in a 1-2 ms interval to achieve a 30-50 Hz closed-loop bandwidth

Report of the peer review mission of national operational safety experience feedback process to the Ukraine 11-15 November 1996 Kiev

International Nuclear Information System (INIS)

1996-01-01

At the invitation of the Nuclear Regulatory Administration of Ukraine (NRA), the IAEA carried out a Peer review mission of national operational safety experience feedback process at Kiev from 11 to 15 November 1996. The objective of this mission was to provide the host country, represented by the regulatory body, with independent and comprehensive review of current status of operational safety experience feedback (OSEF) process with respect to the IAEA's recommendations and international practices. The mission concluded that principal arrangements of operational feedback process in Ukraine are, at present, in force and brought positive results since their introduction. The mission also noted several good practices in these activities. 1 tab

Low-Latency Digital Signal Processing for Feedback and Feedforward in Quantum Computing and Communication

Science.gov (United States)

Salathé, Yves; Kurpiers, Philipp; Karg, Thomas; Lang, Christian; Andersen, Christian Kraglund; Akin, Abdulkadir; Krinner, Sebastian; Eichler, Christopher; Wallraff, Andreas

2018-03-01

Quantum computing architectures rely on classical electronics for control and readout. Employing classical electronics in a feedback loop with the quantum system allows us to stabilize states, correct errors, and realize specific feedforward-based quantum computing and communication schemes such as deterministic quantum teleportation. These feedback and feedforward operations are required to be fast compared to the coherence time of the quantum system to minimize the probability of errors. We present a field-programmable-gate-array-based digital signal processing system capable of real-time quadrature demodulation, a determination of the qubit state, and a generation of state-dependent feedback trigger signals. The feedback trigger is generated with a latency of 110 ns with respect to the timing of the analog input signal. We characterize the performance of the system for an active qubit initialization protocol based on the dispersive readout of a superconducting qubit and discuss potential applications in feedback and feedforward algorithms.

Identification of a feedback loop involving β-glucosidase 2 and its product sphingosine sheds light on the molecular mechanisms in Gaucher disease.

Science.gov (United States)

Schonauer, Sophie; Körschen, Heinz G; Penno, Anke; Rennhack, Andreas; Breiden, Bernadette; Sandhoff, Konrad; Gutbrod, Katharina; Dörmann, Peter; Raju, Diana N; Haberkant, Per; Gerl, Mathias J; Brügger, Britta; Zigdon, Hila; Vardi, Ayelet; Futerman, Anthony H; Thiele, Christoph; Wachten, Dagmar

2017-04-14

The lysosomal acid β-glucosidase GBA1 and the non-lysosomal β-glucosidase GBA2 degrade glucosylceramide (GlcCer) to glucose and ceramide in different cellular compartments. Loss of GBA2 activity and the resulting accumulation of GlcCer results in male infertility, whereas mutations in the GBA1 gene and loss of GBA1 activity cause the lipid-storage disorder Gaucher disease. However, the role of GBA2 in Gaucher disease pathology and its relationship to GBA1 is not well understood. Here, we report a GBA1-dependent down-regulation of GBA2 activity in patients with Gaucher disease. Using an experimental approach combining cell biology, biochemistry, and mass spectrometry, we show that sphingosine, the cytotoxic metabolite accumulating in Gaucher cells through the action of GBA2, directly binds to GBA2 and inhibits its activity. We propose a negative feedback loop, in which sphingosine inhibits GBA2 activity in Gaucher cells, preventing further sphingosine accumulation and, thereby, cytotoxicity. Our findings add a new chapter to the understanding of the complex molecular mechanism underlying Gaucher disease and the regulation of β-glucosidase activity in general. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Grid-Current-Feedback Active Damping for LCL Resonance in Grid-Connected Voltage-Source Converters

DEFF Research Database (Denmark)

Wang, Xiongfei; Blaabjerg, Frede; Loh, Poh Chiang

2016-01-01

This paper investigates active damping of LCL-filter resonance in a grid-connected voltage-source converter with only grid-current feedback control. Basic analysis in the s-domain shows that the proposed damping technique with a negative high-pass filter along its damping path is equivalent...... of phase-lag, in turn, helps to shrink the region of nonminimum-phase behavior caused by negative virtual resistance inserted unintentionally by most digitally implemented active damping techniques. The presented high-pass-filtered active damping technique with a single grid-current feedback loop is thus...

Loop Transfer Matrix and Loop Quantum Mechanics

International Nuclear Information System (INIS)

Savvidy, George K.

2000-01-01

The gonihedric model of random surfaces on a 3d Euclidean lattice has equivalent representation in terms of transfer matrix K(Q i ,Q f ), which describes the propagation of loops Q. We extend the previous construction of the loop transfer matrix to the case of nonzero self-intersection coupling constant κ. We introduce the loop generalization of Fourier transformation which allows to diagonalize transfer matrices, that depend on symmetric difference of loops only and express all eigenvalues of 3d loop transfer matrix through the correlation functions of the corresponding 2d statistical system. The loop Fourier transformation allows to carry out the analogy with quantum mechanics of point particles, to introduce conjugate loop momentum P and to define loop quantum mechanics. We also consider transfer matrix on 4d lattice which describes propagation of memebranes. This transfer matrix can also be diagonalized by using the generalized Fourier transformation, and all its eigenvalues are equal to the correlation functions of the corresponding 3d statistical system. In particular the free energy of the 4d membrane system is equal to the free energy of 3d gonihedric system of loops and is equal to the free energy of 2d Ising model. (author)

Closed loop deep brain stimulation: an evolving technology.

Science.gov (United States)

Hosain, Md Kamal; Kouzani, Abbas; Tye, Susannah

2014-12-01

Deep brain stimulation is an effective and safe medical treatment for a variety of neurological and psychiatric disorders including Parkinson's disease, essential tremor, dystonia, and treatment resistant obsessive compulsive disorder. A closed loop deep brain stimulation (CLDBS) system automatically adjusts stimulation parameters by the brain response in real time. The CLDBS continues to evolve due to the advancement in the brain stimulation technologies. This paper provides a study on the existing systems developed for CLDBS. It highlights the issues associated with CLDBS systems including feedback signal recording and processing, stimulation parameters setting, control algorithm, wireless telemetry, size, and power consumption. The benefits and limitations of the existing CLDBS systems are also presented. Whilst robust clinical proof of the benefits of the technology remains to be achieved, it has the potential to offer several advantages over open loop DBS. The CLDBS can improve efficiency and efficacy of therapy, eliminate lengthy start-up period for programming and adjustment, provide a personalized treatment, and make parameters setting automatic and adaptive.

A Simple Negative Interaction in the Positive Transcriptional Feedback of a Single Gene Is Sufficient to Produce Reliable Oscillations

Science.gov (United States)

Miró-Bueno, Jesús M.; Rodríguez-Patón, Alfonso

2011-01-01

Negative and positive transcriptional feedback loops are present in natural and synthetic genetic oscillators. A single gene with negative transcriptional feedback needs a time delay and sufficiently strong nonlinearity in the transmission of the feedback signal in order to produce biochemical rhythms. A single gene with only positive transcriptional feedback does not produce oscillations. Here, we demonstrate that this single-gene network in conjunction with a simple negative interaction can also easily produce rhythms. We examine a model comprised of two well-differentiated parts. The first is a positive feedback created by a protein that binds to the promoter of its own gene and activates the transcription. The second is a negative interaction in which a repressor molecule prevents this protein from binding to its promoter. A stochastic study shows that the system is robust to noise. A deterministic study identifies that the dynamics of the oscillator are mainly driven by two types of biomolecules: the protein, and the complex formed by the repressor and this protein. The main conclusion of this paper is that a simple and usual negative interaction, such as degradation, sequestration or inhibition, acting on the positive transcriptional feedback of a single gene is a sufficient condition to produce reliable oscillations. One gene is enough and the positive transcriptional feedback signal does not need to activate a second repressor gene. This means that at the genetic level an explicit negative feedback loop is not necessary. The model needs neither cooperative binding reactions nor the formation of protein multimers. Therefore, our findings could help to clarify the design principles of cellular clocks and constitute a new efficient tool for engineering synthetic genetic oscillators. PMID:22205920

Feedback characteristics between implantable microphone and transducer in middle ear cavity.

Science.gov (United States)

Arman Woo, S H; Woo, Seong Tak; Song, Byung Seop; Cho, Jin-Ho

2013-10-01

With the advent of implantable hearing aids, implementation and acoustic sensing strategy of the implantable microphone becomes an important issue; among the many types of implantable microphone, placing the microphone in middle ear cavity (MEC) has advantages including simple operation and insensitive to skin touching or chewing motion. In this paper, an implantable microphone was implemented and researched feedback characteristic when both the implantable microphone and the transducer were placed in the MEC. Analytical and finite element analysis were conducted to design the microphone to have a natural frequency of 7 kHz and showed good characteristics of SNR and sensitivity. For the feedback test, simple analytical and finite element analysis were calculated and compared with in vitro experiments (n = 4). From the experiments, the open-loop gain and feedback factor were measured and the minimum gain margin measured as 14.3 dB.

MicroRNA-200b Suppresses Arsenic-transformed Cell Migration by Targeting Protein Kinase Cα and Wnt5b-Protein Kinase Cα Positive Feedback Loop and Inhibiting Rac1 Activation*

Science.gov (United States)

Wang, Zhishan; Humphries, Brock; Xiao, Hua; Jiang, Yiguo; Yang, Chengfeng

2014-01-01

MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase Cα (PKCα) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKCα 3′-untranslated region vector luciferase reporter assays, we showed that PKCα is a direct target of miR-200b. Inhibiting PKCα activity or knocking down PKCα expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKCα in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKCα in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKCα expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKCα increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKCα or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKCα and Wnt5b-PKCα positive feedback loop and subsequently inhibiting Rac1 activation. PMID:24841200

MicroRNA-200b suppresses arsenic-transformed cell migration by targeting protein kinase Cα and Wnt5b-protein kinase Cα positive feedback loop and inhibiting Rac1 activation.