closed-loop transfer function: Topics by Science.gov

Sample records for closed-loop transfer function

Closed-loop spontaneous baroreflex transfer function is inappropriate for system identification of neural arc but partly accurate for peripheral arc: predictability analysis

PubMed Central

Kamiya, Atsunori; Kawada, Toru; Shimizu, Shuji; Sugimachi, Masaru

2011-01-01

Abstract Although the dynamic characteristics of the baroreflex system have been described by baroreflex transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex transfer function have not been evaluated compared with the open-loop transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n = 10), we identified open-loop baroreflex transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex transfer functions for the neural and peripheral arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex transfer function for the neural arc was markedly different from the open-loop transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex transfer function of the peripheral arc partially matched the open-loop transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural arc transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex transfer function obtained by closed-loop analysis has been believed to represent the neural arc function, it is inappropriate for system identification of the neural arc but is essentially appropriate for the peripheral arc under resting conditions, when compared with open-loop analysis. PMID:21486839
Causal transfer function analysis to describe closed loop interactions between cardiovascular and cardiorespiratory variability signals.

PubMed

Faes, L; Porta, A; Cucino, R; Cerutti, S; Antolini, R; Nollo, G

2004-06-01

Although the concept of transfer function is intrinsically related to an input-output relationship, the traditional and widely used estimation method merges both feedback and feedforward interactions between the two analyzed signals. This limitation may endanger the reliability of transfer function analysis in biological systems characterized by closed loop interactions. In this study, a method for estimating the transfer function between closed loop interacting signals was proposed and validated in the field of cardiovascular and cardiorespiratory variability. The two analyzed signals x and y were described by a bivariate autoregressive model, and the causal transfer function from x to y was estimated after imposing causality by setting to zero the model coefficients representative of the reverse effects from y to x. The method was tested in simulations reproducing linear open and closed loop interactions, showing a better adherence of the causal transfer function to the theoretical curves with respect to the traditional approach in presence of non-negligible reverse effects. It was then applied in ten healthy young subjects to characterize the transfer functions from respiration to heart period (RR interval) and to systolic arterial pressure (SAP), and from SAP to RR interval. In the first two cases, the causal and non-causal transfer function estimates were comparable, indicating that respiration, acting as exogenous signal, sets an open loop relationship upon SAP and RR interval. On the contrary, causal and traditional transfer functions from SAP to RR were significantly different, suggesting the presence of a considerable influence on the opposite causal direction. Thus, the proposed causal approach seems to be appropriate for the estimation of parameters, like the gain and the phase lag from SAP to RR interval, which have a large clinical and physiological relevance.
Diagonalizing controller for a superconducting six-axis accelerometer

NASA Astrophysics Data System (ADS)

Bachrach, B.; Canavan, E. R.; Levine, W. S.

A relatively simple MIMO (multiple input, multiple output) controller which converts an instrument with a nondiagonally dominant transfer function matrix into a strongly diagonally dominant device is developed. The instrument, which uses inductance bridges to sense the position of a magnetically levitated superconducting mass, has very lightly damped resonances and fairly strong cross coupling. By taking advantage of the particular structure of the instrument's transfer function matrix, it is possible to develop a relatively simple controller which achieves the desired decoupling. This controller consists of two parts. The first part cancels the nondiagonal terms of the open-loop transfer function matrix, while the second part is simply a set of SISO (single input, single output) controllers. The stability of the closed-loop system is studied using Rosenbrock's INA (inverse Nyguist array) technique, which produces a simple set of conditions guaranteeing stability. Simulation of the closed-loop system indicates that it should easily achieve its performance goals.
Digital control algorithms for microgravity isolation systems

NASA Technical Reports Server (NTRS)

Sinha, Alok; Wang, Yung-Peng

1992-01-01

New digital control algorithms were developed to achieve the desired acceleration transmissibility function. The attractive electromagnets have been taken as actuators. The relative displacement and the acceleration of the mass were used as feedback signals. Two approaches were developed to find that controller transfer function in Z-domain, which yields the desired transmissibility at each frequency. In the first approach, the controller transfer function is obtained by assuming that the desired transmissibility is known in Z-domain. Since the desired transmissibility H sub d(S) = 1/(tauS+1)(exp 2) is given in S-domain, the first task is to obtain the desired transmissibility in Z-domain. There are three methods to perform this task: bilinear transformation, and backward and forward rectangular rules. The bilinear transformation and backward rectangular rule lead to improper controller transfer functions, which are physically not realizable. The forward rectangular rule does lead to a physically realizable controller. However, this controller is found to be marginally stable because of a pole at Z=1. In order to eliminate this pole, a hybrid control structure is proposed. Here the control input is composed of two parts: analog and digital. The analog input simply represents the velocity (or the integral of acceleration) feedback; and the digital controller which uses only relative displacement signal, is then obtained to achieve the desired closed-loop transfer function. The stability analysis indicates that the controller transfer function is stable for typical values of sampling period. In the second approach, the aforementioned hybrid control structure is again used. First, an analog controller transfer function corresponding to relative displacement feedback is obtained to achieve the transmissibility as 1/(tauS+1)(exp 2). Then the transfer function for the digital control input is obtained by discretizing this analog controller transfer function via bilinear transformation. The stability of the resulting Z-domain closed loop system is analyzed. Also, the frequency response of the Z-domain closed-loop transfer function is determined to evaluate the performance of the control system.
Direct-contact closed-loop heat exchanger

DOEpatents

Berry, Gregory F.; Minkov, Vladimir; Petrick, Michael

1984-01-01

A high temperature heat exchanger with a closed loop and a heat transfer liquid within the loop, the closed loop having a first horizontal channel with inlet and outlet means for providing direct contact of a first fluid at a first temperature with the heat transfer liquid, a second horizontal channel with inlet and outlet means for providing direct contact of a second fluid at a second temperature with the heat transfer liquid, and means for circulating the heat transfer liquid.
Analysis and design of a 3rd order velocity-controlled closed-loop for MEMS vibratory gyroscopes.

PubMed

Wu, Huan-ming; Yang, Hai-gang; Yin, Tao; Jiao, Ji-wei

2013-09-18

The time-average method currently available is limited to analyzing the specific performance of the automatic gain control-proportional and integral (AGC-PI) based velocity-controlled closed-loop in a micro-electro-mechanical systems (MEMS) vibratory gyroscope, since it is hard to solve nonlinear functions in the time domain when the control loop reaches to 3rd order. In this paper, we propose a linearization design approach to overcome this limitation by establishing a 3rd order linear model of the control loop and transferring the analysis to the frequency domain. Order reduction is applied on the built linear model's transfer function by constructing a zero-pole doublet, and therefore mathematical expression of each control loop's performance specification is obtained. Then an optimization methodology is summarized, which reveals that a robust, stable and swift control loop can be achieved by carefully selecting the system parameters following a priority order. Closed-loop drive circuits are designed and implemented using 0.35 μm complementary metal oxide semiconductor (CMOS) process, and experiments carried out on a gyroscope prototype verify the optimization methodology that an optimized stability of the control loop can be achieved by constructing the zero-pole doublet, and disturbance rejection capability (D.R.C) of the control loop can be improved by increasing the integral term.
An estimator-predictor approach to PLL loop filter design

NASA Technical Reports Server (NTRS)

Statman, Joseph I.; Hurd, William J.

1990-01-01

The design of digital phase locked loops (DPLL) using estimation theory concepts in the selection of a loop filter is presented. The key concept, that the DPLL closed-loop transfer function is decomposed into an estimator and a predictor, is discussed. The estimator provides recursive estimates of phase, frequency, and higher-order derivatives, and the predictor compensates for the transport lag inherent in the loop.
Direct-contact closed-loop heat exchanger

DOEpatents

Berry, G.F.; Minkov, V.; Petrick, M.

1981-11-02

A high temperature heat exchanger is disclosed which has a closed loop and a heat transfer liquid within the loop, the closed loop having a first horizontal channel with inlet and outlet means for providing direct contact of a first fluid at a first temperature with the heat transfer liquid, a second horizontal channel with inlet and outlet means for providing direct contact of a second fluid at a second temperature with the heat transfer liquid, and means for circulating the heat transfer liquid.
Combining Charge Couple Devices and Rate Sensors for the Feedforward Control System of a Charge Coupled Device Tracking Loop.

PubMed

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.
Retrospective Cost Adaptive Control with Concurrent Closed-Loop Identification

NASA Astrophysics Data System (ADS)

Sobolic, Frantisek M.

Retrospective cost adaptive control (RCAC) is a discrete-time direct adaptive control algorithm for stabilization, command following, and disturbance rejection. RCAC is known to work on systems given minimal modeling information which is the leading numerator coefficient and any nonminimum-phase (NMP) zeros of the plant transfer function. This information is normally needed a priori and is key in the development of the filter, also known as the target model, within the retrospective performance variable. A novel approach to alleviate the need for prior modeling of both the leading coefficient of the plant transfer function as well as any NMP zeros is developed. The extension to the RCAC algorithm is the use of concurrent optimization of both the target model and the controller coefficients. Concurrent optimization of the target model and controller coefficients is a quadratic optimization problem in the target model and controller coefficients separately. However, this optimization problem is not convex as a joint function of both variables, and therefore nonconvex optimization methods are needed. Finally, insights within RCAC that include intercalated injection between the controller numerator and the denominator, unveil the workings of RCAC fitting a specific closed-loop transfer function to the target model. We exploit this interpretation by investigating several closed-loop identification architectures in order to extract this information for use in the target model.
Operation of a cascade air conditioning system with two-phase loop

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Yinshan; Wang, Jinliang; Zhao, Futao

A method of operating a heat transfer system includes starting operation of a first heat transfer fluid vapor/compression circulation loop including a fluid pumping mechanism, a heat exchanger for rejecting thermal energy from a first heat transfer fluid, and a heat absorption side of an internal heat exchanger. A first conduit in a closed fluid circulation loop circulates the first heat transfer fluid therethrough. Operation of a second two-phase heat transfer fluid circulation loop is started after starting operation of the first heat transfer fluid circulation loop. The second heat transfer fluid circulation loop transfers heat to the first heatmore » transfer fluid circulation loop through the internal heat exchanger and includes a heat rejection side of the internal heat exchanger, a liquid pump, and a heat exchanger evaporator. A second conduit in a closed fluid circulation loop circulates a second heat transfer fluid therethrough.« less
Centralized PI control for high dimensional multivariable systems based on equivalent transfer function.

PubMed

Luan, Xiaoli; Chen, Qiang; Liu, Fei

2014-09-01

This article presents a new scheme to design full matrix controller for high dimensional multivariable processes based on equivalent transfer function (ETF). Differing from existing ETF method, the proposed ETF is derived directly by exploiting the relationship between the equivalent closed-loop transfer function and the inverse of open-loop transfer function. Based on the obtained ETF, the full matrix controller is designed utilizing the existing PI tuning rules. The new proposed ETF model can more accurately represent the original processes. Furthermore, the full matrix centralized controller design method proposed in this paper is applicable to high dimensional multivariable systems with satisfactory performance. Comparison with other multivariable controllers shows that the designed ETF based controller is superior with respect to design-complexity and obtained performance. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.
Designing Estimator/Predictor Digital Phase-Locked Loops

NASA Technical Reports Server (NTRS)

Statman, J. I.; Hurd, W. J.

1988-01-01

Signal delays in equipment compensated automatically. New approach to design of digital phase-locked loop (DPLL) incorporates concepts from estimation theory and involves decomposition of closed-loop transfer function into estimator and predictor. Estimator provides recursive estimates of phase, frequency, and higher order derivatives of phase with respect to time, while predictor compensates for delay, called "transport lag," caused by PLL equipment and by DPLL computations.
Detection of no-model input-output pairs in closed-loop systems.

PubMed

Potts, Alain Segundo; Alvarado, Christiam Segundo Morales; Garcia, Claudio

2017-11-01

The detection of no-model input-output (IO) pairs is important because it can speed up the multivariable system identification process, since all the pairs with null transfer functions are previously discarded and it can also improve the identified model quality, thus improving the performance of model based controllers. In the available literature, the methods focus just on the open-loop case, since in this case there is not the effect of the controller forcing the main diagonal in the transfer matrix to one and all the other terms to zero. In this paper, a modification of a previous method able to detect no-model IO pairs in open-loop systems is presented, but adapted to perform this duty in closed-loop systems. Tests are performed by using the traditional methods and the proposed one to show its effectiveness. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Measurement techniques for the characterization in the frequency domain of regulated energy-storage DC-to-DC converters. M.S. Thesis

NASA Technical Reports Server (NTRS)

Bahler, D. D.

1978-01-01

Procedures are presented for obtaining valid frequency-domain transfer functions of regulated reactor energy-storage dc-to-dc converters. These procedures are for measuring loop gain, closed loop gain, output impedance, and audio susceptibility. The applications of these measurements are discussed.
Transfer function tests of the Joy longwall shearer

NASA Technical Reports Server (NTRS)

Fisher, P. H., Jr.

1978-01-01

A series of operational tests was performed on the Joy longwall shearer located at the Bureau of Mines in Bructon, Pennsylvania. The purpose of these tests was to determine the transfer function and operational characteristics of the system. These characteristics will be used to generate a simulation model of the longwall shearer used in the development of the closed-loop vertical control system.
Theoretical constraints in the design of multivariable control systems

NASA Technical Reports Server (NTRS)

Rynaski, E. G.; Mook, D. J.

1993-01-01

The theoretical constraints inherent in the design of multivariable control systems were defined and investigated. These constraints are manifested by the system transmission zeros that limit or bound the areas in which closed loop poles and individual transfer function zeros may be placed. These constraints were investigated primarily in the context of system decoupling or non-interaction. It was proven that decoupling requires the placement of closed loop poles at the system transmission zeros. Therefore, the system transmission zeros must be minimum phase to guarantee a stable decoupled system. Once decoupling has been accomplished, the remaining part of the system exhibits transmission zeros at infinity, so nearly complete design freedom is possible in terms of placing both poles and zeros of individual closed loop transfer functions. A general, dynamic inversion model following system architecture was developed that encompasses both the implicit and explicit configuration. Robustness properties are developed along with other attributes of this type of system. Finally, a direct design is developed for the longitudinal-vertical degrees of freedom of aircraft motion to show how a direct lift flap can be used to improve the pitch-heave maneuvering coordination for enhanced flying qualities.
Experimental Verification of AUV (Autonomous Underwater Vehicle) Performance.

DTIC Science & Technology

1988-03-01

7 3 First Order Plant Model 10 4 Closed Loop System Block Diagram 11 5 RLP[Kpz=l,U=0.5] 13 6 RLP[Kpz=I,U=I] 147 RLP[Kpz=0.5,U-0.5] 15 8 RLP[Kpz=0.5,U...circuit. The control circuit would then generate a radio control signal to maneuver the vehicle. 6 *’%4 MUMNT -. %Am -W’ This takes the man out of the loop ...angle, the constant Ky is 0.14i_" IN’ ft-lbf/rad. Estimated values of J and B were determined. The closed loop transfer function Go could then be
Cloverleaf microgyroscope with electrostatic alignment and tuning

NASA Technical Reports Server (NTRS)

Challoner, A. Dorian (Inventor); Gutierrez, Roman C. (Inventor); Tang, Tony K. (Inventor)

2007-01-01

A micro-gyroscope (10) having closed loop output operation by a control voltage (V.sub.ty), that is demodulated by a drive axis (x-axis) signal V.sub.thx of the sense electrodes (S1, S2), providing Coriolis torque rebalance to prevent displacement of the micro-gyroscope (10) on the output axis (y-axis) V.sub.thy.about.0. Closed loop drive axis torque, V.sub.tx maintains a constant drive axis amplitude signal, V.sub.thx. The present invention provides independent alignment and tuning of the micro-gyroscope by using separate electrodes and electrostatic bias voltages to adjust alignment and tuning. A quadrature amplitude signal, or cross-axis transfer function peak amplitude is used to detect misalignment that is corrected to zero by an electrostatic bias voltage adjustment. The cross-axis transfer function is either V.sub.thy/V.sub.ty or V.sub.tnx/V.sub.tx. A quadrature signal noise level, or difference in natural frequencies estimated from measurements of the transfer functions is used to detect residual mistuning, that is corrected to zero by a second electrostatic bias voltage adjustment.
Theoretical constraints in the design of multivariable control systems

NASA Technical Reports Server (NTRS)

Rynaski, E. G.; Mook, D. Joseph; Depena, Juan

1991-01-01

The research being performed under NASA Grant NAG1-1361 involves a more clear understanding and definition of the constraints involved in the pole-zero placement or assignment process for multiple input, multiple output systems. Complete state feedback to more than a single controller under conditions of complete controllability and observability is redundant if pole placement alone is the design objective. The additional feedback gains, above and beyond those required for pole placement can be used for eignevalue assignment or zero placement of individual closed loop transfer functions. Because both poles and zeros of individual closed loop transfer functions strongly affect the dynamic response to a pilot command input, the pole-zero placement problem is important. When fewer controllers than degrees of freedom of motion are available, complete design freedom is not possible, the transmission zeros constrain the regions of possible pole-zero placement. The effect of transmission zero constraints on the design possibilities, selection of transmission zeros and the avoidance of producing non-minimum phase transfer functions is the subject of the research being performed under this grant.

Thermal Interface Evaluation of Heat Transfer from a Pumped Loop to Titanium-Water Thermosyphons

NASA Technical Reports Server (NTRS)

Jaworske, Donald A.; Sanzi, James L.; Gibson, Marc A.; Sechkar, Edward A.

2009-01-01

Titanium-water thermosyphons are being considered for use in the heat rejection system for lunar outpost fission surface power. Key to their use is heat transfer between a closed loop heat source and the heat pipe evaporators. This work describes laboratory testing of several interfaces that were evaluated for their thermal performance characteristics, in the temperature range of 350 to 400 K, utilizing a water closed loop heat source and multiple thermosyphon evaporator geometries. A gas gap calorimeter was used to measure heat flow at steady state. Thermocouples in the closed loop heat source and on the evaporator were used to measure thermal conductance. The interfaces were in two generic categories, those immersed in the water closed loop heat source and those clamped to the water closed loop heat source with differing thermal conductive agents. In general, immersed evaporators showed better overall performance than their clamped counterparts. Selected clamped evaporator geometries offered promise.
Transfer function verification and block diagram simplification of a very high-order distributed pole closed-loop servo by means of non-linear time-response simulation

NASA Technical Reports Server (NTRS)

Mukhopadhyay, A. K.

1975-01-01

Linear frequency domain methods are inadequate in analyzing the 1975 Viking Orbiter (VO75) digital tape recorder servo due to dominant nonlinear effects such as servo signal limiting, unidirectional servo control, and static/dynamic Coulomb friction. The frequency loop (speed control) servo of the VO75 tape recorder is used to illustrate the analytical tools and methodology of system redundancy elimination and high order transfer function verification. The paper compares time-domain performance parameters derived from a series of nonlinear time responses with the available experimental data in order to select the best possible analytical transfer function representation of the tape transport (mechanical segment of the tape recorder) from several possible candidates. The study also shows how an analytical time-response simulation taking into account most system nonlinearities can pinpoint system redundancy and overdesign stemming from a strictly empirical design approach. System order reduction is achieved through truncation of individual transfer functions and elimination of redundant blocks.
Theoretical linear approach to the combined man-manipulator system in manual control of an aircraft

NASA Technical Reports Server (NTRS)

Brauser, K.

1981-01-01

An approach to the calculation of the dynamic characteristics of the combined man manipulator system in manual aircraft control was derived from a model of the neuromuscular system. This model combines the neuromuscular properties of man with the physical properties of the manipulator system which is introduced as pilot manipulator model into the manual aircraft control. The assumption of man as a quasilinear and time invariant control operator adapted to operating states, depending on the flight phases, of the control system gives rise to interesting solutions of the frequency domain transfer functions of both the man manipulator system and the closed loop pilot aircraft control system. It is shown that it is necessary to introduce the complete precision pilot manipulator model into the closed loop pilot aircraft transfer function in order to understand the well known handling quality criteria, and to derive these criteria directly from human operator properties.
Robust Control Design via Linear Programming

NASA Technical Reports Server (NTRS)

Keel, L. H.; Bhattacharyya, S. P.

1998-01-01

This paper deals with the problem of synthesizing or designing a feedback controller of fixed dynamic order. The closed loop specifications considered here are given in terms of a target performance vector representing a desired set of closed loop transfer functions connecting various signals. In general these point targets are unattainable with a fixed order controller. By enlarging the target from a fixed point set to an interval set the solvability conditions with a fixed order controller are relaxed and a solution is more easily enabled. Results from the parametric robust control literature can be used to design the interval target family so that the performance deterioration is acceptable, even when plant uncertainty is present. It is shown that it is possible to devise a computationally simple linear programming approach that attempts to meet the desired closed loop specifications.
Disturbance rejection performance analyses of closed loop control systems by reference to disturbance ratio.

PubMed

Alagoz, Baris Baykant; Deniz, Furkan Nur; Keles, Cemal; Tan, Nusret

2015-03-01

This study investigates disturbance rejection capacity of closed loop control systems by means of reference to disturbance ratio (RDR). The RDR analysis calculates the ratio of reference signal energy to disturbance signal energy at the system output and provides a quantitative evaluation of disturbance rejection performance of control systems on the bases of communication channel limitations. Essentially, RDR provides a straightforward analytical method for the comparison and improvement of implicit disturbance rejection capacity of closed loop control systems. Theoretical analyses demonstrate us that RDR of the negative feedback closed loop control systems are determined by energy spectral density of controller transfer function. In this manner, authors derived design criteria for specifications of disturbance rejection performances of PID and fractional order PID (FOPID) controller structures. RDR spectra are calculated for investigation of frequency dependence of disturbance rejection capacity and spectral RDR analyses are carried out for PID and FOPID controllers. For the validation of theoretical results, simulation examples are presented. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.
A translational platform for prototyping closed-loop neuromodulation systems

PubMed Central

Afshar, Pedram; Khambhati, Ankit; Stanslaski, Scott; Carlson, David; Jensen, Randy; Linde, Dave; Dani, Siddharth; Lazarewicz, Maciej; Cong, Peng; Giftakis, Jon; Stypulkowski, Paul; Denison, Tim

2013-01-01

While modulating neural activity through stimulation is an effective treatment for neurological diseases such as Parkinson's disease and essential tremor, an opportunity for improving neuromodulation therapy remains in automatically adjusting therapy to continuously optimize patient outcomes. Practical issues associated with achieving this include the paucity of human data related to disease states, poorly validated estimators of patient state, and unknown dynamic mappings of optimal stimulation parameters based on estimated states. To overcome these challenges, we present an investigational platform including: an implanted sensing and stimulation device to collect data and run automated closed-loop algorithms; an external tool to prototype classifier and control-policy algorithms; and real-time telemetry to update the implanted device firmware and monitor its state. The prototyping system was demonstrated in a chronic large animal model studying hippocampal dynamics. We used the platform to find biomarkers of the observed states and transfer functions of different stimulation amplitudes. Data showed that moderate levels of stimulation suppress hippocampal beta activity, while high levels of stimulation produce seizure-like after-discharge activity. The biomarker and transfer function observations were mapped into classifier and control-policy algorithms, which were downloaded to the implanted device to continuously titrate stimulation amplitude for the desired network effect. The platform is designed to be a flexible prototyping tool and could be used to develop improved mechanistic models and automated closed-loop systems for a variety of neurological disorders. PMID:23346048
A translational platform for prototyping closed-loop neuromodulation systems.

PubMed

Afshar, Pedram; Khambhati, Ankit; Stanslaski, Scott; Carlson, David; Jensen, Randy; Linde, Dave; Dani, Siddharth; Lazarewicz, Maciej; Cong, Peng; Giftakis, Jon; Stypulkowski, Paul; Denison, Tim

2012-01-01

While modulating neural activity through stimulation is an effective treatment for neurological diseases such as Parkinson's disease and essential tremor, an opportunity for improving neuromodulation therapy remains in automatically adjusting therapy to continuously optimize patient outcomes. Practical issues associated with achieving this include the paucity of human data related to disease states, poorly validated estimators of patient state, and unknown dynamic mappings of optimal stimulation parameters based on estimated states. To overcome these challenges, we present an investigational platform including: an implanted sensing and stimulation device to collect data and run automated closed-loop algorithms; an external tool to prototype classifier and control-policy algorithms; and real-time telemetry to update the implanted device firmware and monitor its state. The prototyping system was demonstrated in a chronic large animal model studying hippocampal dynamics. We used the platform to find biomarkers of the observed states and transfer functions of different stimulation amplitudes. Data showed that moderate levels of stimulation suppress hippocampal beta activity, while high levels of stimulation produce seizure-like after-discharge activity. The biomarker and transfer function observations were mapped into classifier and control-policy algorithms, which were downloaded to the implanted device to continuously titrate stimulation amplitude for the desired network effect. The platform is designed to be a flexible prototyping tool and could be used to develop improved mechanistic models and automated closed-loop systems for a variety of neurological disorders.
Noncolocated Structural Vibration Suppression Using Zero Annihilation Periodic Control

NASA Technical Reports Server (NTRS)

Bayard, David S.; Boussalis, Dhemetrios

1993-01-01

The Zero Annihilation Periodic (ZAP) controller is applied to the problem of vibration control of a noncolocated flexible structure. It is shown that even though the transfer function is nonminimum-phase, a plant inverse controller can be designed which elicits a deadbeat closed-loop response.
Design and test hardware for a solar array switching unit

NASA Technical Reports Server (NTRS)

Patil, A. R.; Cho, B. H.; Sable, D.; Lee, F. C.

1992-01-01

This paper describes the control of a pulse width modulated (PWM) type sequential shunt switching unit (SSU) for spacecraft applications. It is found that the solar cell output capacitance has a significant impact on SSU design. Shorting of this cell capacitance by the PWM switch causes input current surges. These surges are minimized by the use of a series filter inductor. The system with a filter is analyzed for ripple and the control to output-voltage transfer function. Stable closed loop design considerations are discussed. The results are supported by modeling and measurements of loop gain and of closed-loop bus impedance on test hardware for NASA's 120 V Earth Observation System (EOS). The analysis and modeling are also applicable to NASA's 160 V Space Station power system.
Combined line-of-sight error and angular position to generate feedforward control for a charge-coupled device-based tracking loop

NASA Astrophysics Data System (ADS)

Tang, Tao; Cai, Huaxiang; Huang, Yongmei; Ren, Ge

2015-10-01

A feedforward control based on data fusion is proposed to enhance closed-loop performance. The target trajectory as the observed value of a Kalman filter is recovered by synthesizing line-of-sight error and angular position from the encoder. A Kalman filter based on a Singer acceleration model is employed to estimate the target velocity. In this control scheme, the control stability is influenced by the bandwidth of the Kalman filter and time misalignment. The transfer function of the Kalman filter in the frequency domain is built for analyzing the closed loop stability, which shows that the Kalman filter is the major factor that affects the control stability. The feedforward control proposed here is verified through simulations and experiments.
An estimator-predictor approach to PLL loop filter design

NASA Technical Reports Server (NTRS)

Statman, J. I.; Hurd, W. J.

1986-01-01

An approach to the design of digital phase locked loops (DPLLs), using estimation theory concepts in the selection of a loop filter, is presented. The key concept is that the DPLL closed-loop transfer function is decomposed into an estimator and a predictor. The estimator provides recursive estimates of phase, frequency, and higher order derivatives, while the predictor compensates for the transport lag inherent in the loop. This decomposition results in a straightforward loop filter design procedure, enabling use of techniques from optimal and sub-optimal estimation theory. A design example for a particular choice of estimator is presented, followed by analysis of the associated bandwidth, gain margin, and steady state errors caused by unmodeled dynamics. This approach is under consideration for the design of the Deep Space Network (DSN) Advanced Receiver Carrier DPLL.
Rational positive real approximations for LQG optimal compensators arising in active stabilization of flexible structures

NASA Technical Reports Server (NTRS)

Desantis, A.

1994-01-01

In this paper the approximation problem for a class of optimal compensators for flexible structures is considered. The particular case of a simply supported truss with an offset antenna is dealt with. The nonrational positive real optimal compensator transfer function is determined, and it is proposed that an approximation scheme based on a continued fraction expansion method be used. Comparison with the more popular modal expansion technique is performed in terms of stability margin and parameters sensitivity of the relative approximated closed loop transfer functions.
A novel pulsed gas metal arc welding system with direct droplet transfer close-loop control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Q.; Li, P.; Zhang, L.

1994-12-31

In pulsed gas metal arc welding (GMAW), a predominant parameter that has to be monitored and controlled in real time for maintaining process stability and ensuring weld quality, is droplet transfer. Based on the close correlation between droplet transfer and arc light radiant flux in GMAW of steel and aluminum, a direct closed-loop droplet transfer control system for pulsed GMAW with arc light sensor has been developed. By sensing the droplet transfer directly via the arc light signal, a pulsed GMAW process with real and exact one-pulse, one-droplet transfer has been achieved. The novel pulsed GMAW machine consists of threemore » parts: a sensing system, a controlling system, and a welding power system. The software used in this control system is capable of data sampling and processing, parameter matching, optimum parameter restoring, and resetting. A novel arc light sensing system has been developed. The sensor is small enough to be clamped to a semiautomatic welding torch. Based on thissensingn system, a closed-loop droplet transfer control system of GMAW of steel and aluminum has been built and a commercial prototype has been made. The system is capable of keeping one-pulse, one-droplet transfer against external interferences. The welding process with this control system has been proved to be stable, quiet, with no spatter, and provide good weld formation.« less
Comparison of control structures for a bidirectional high-frequency dc-dc converter

NASA Astrophysics Data System (ADS)

Himmelstoss, Felix A.; Kolar, Johann W.; Zach, Franz C.

1989-08-01

A system for dc-dc power conversion based on a buck-boost converter topology is presented. It makes power flow in both directions possible. The possibility of bidirectional power flow is useful for certain applications, such as uninterruptable power supplies. Starting from a structural diagram the transfer function of the system is derived. The controller for the converter is then designed. It is made up of a simple voltage controller, a voltage controller with an inner loop current controller (cascade control) and with two kinds of state space control. The transfer functions of the different system parts are derived and dimensioning guidelines for the controller sections are presented. The closed loop behavior of the bidirectional converter for the different control structures is analyzed based on simulation using duty cycle averaging. Bodediagrams and step responses are shown.
A recursive solution for a fading memory filter derived from Kalman filter theory

NASA Technical Reports Server (NTRS)

Statman, J. I.

1986-01-01

A simple recursive solution for a class of fading memory tracking filters is presented. A fading memory filter provides estimates of filter states based on past measurements, similar to a traditional Kalman filter. Unlike a Kalman filter, an exponentially decaying weight is applied to older measurements, discounting their effect on present state estimates. It is shown that Kalman filters and fading memory filters are closely related solutions to a general least squares estimator problem. Closed form filter transfer functions are derived for a time invariant, steady state, fading memory filter. These can be applied in loop filter implementation of the Deep Space Network (DSN) Advanced Receiver carrier phase locked loop (PLL).
On the formulation of a minimal uncertainty model for robust control with structured uncertainty

NASA Technical Reports Server (NTRS)

Belcastro, Christine M.; Chang, B.-C.; Fischl, Robert

1991-01-01

In the design and analysis of robust control systems for uncertain plants, representing the system transfer matrix in the form of what has come to be termed an M-delta model has become widely accepted and applied in the robust control literature. The M represents a transfer function matrix M(s) of the nominal closed loop system, and the delta represents an uncertainty matrix acting on M(s). The nominal closed loop system M(s) results from closing the feedback control system, K(s), around a nominal plant interconnection structure P(s). The uncertainty can arise from various sources, such as structured uncertainty from parameter variations or multiple unsaturated uncertainties from unmodeled dynamics and other neglected phenomena. In general, delta is a block diagonal matrix, but for real parameter variations delta is a diagonal matrix of real elements. Conceptually, the M-delta structure can always be formed for any linear interconnection of inputs, outputs, transfer functions, parameter variations, and perturbations. However, very little of the currently available literature addresses computational methods for obtaining this structure, and none of this literature addresses a general methodology for obtaining a minimal M-delta model for a wide class of uncertainty, where the term minimal refers to the dimension of the delta matrix. Since having a minimally dimensioned delta matrix would improve the efficiency of structured singular value (or multivariable stability margin) computations, a method of obtaining a minimal M-delta would be useful. Hence, a method of obtaining the interconnection system P(s) is required. A generalized procedure for obtaining a minimal P-delta structure for systems with real parameter variations is presented. Using this model, the minimal M-delta model can then be easily obtained by closing the feedback loop. The procedure involves representing the system in a cascade-form state-space realization, determining the minimal uncertainty matrix, delta, and constructing the state-space representation of P(s). Three examples are presented to illustrate the procedure.
Distributed model predictive control for constrained nonlinear systems with decoupled local dynamics.

PubMed

Zhao, Meng; Ding, Baocang

2015-03-01

This paper considers the distributed model predictive control (MPC) of nonlinear large-scale systems with dynamically decoupled subsystems. According to the coupled state in the overall cost function of centralized MPC, the neighbors are confirmed and fixed for each subsystem, and the overall objective function is disassembled into each local optimization. In order to guarantee the closed-loop stability of distributed MPC algorithm, the overall compatibility constraint for centralized MPC algorithm is decomposed into each local controller. The communication between each subsystem and its neighbors is relatively low, only the current states before optimization and the optimized input variables after optimization are being transferred. For each local controller, the quasi-infinite horizon MPC algorithm is adopted, and the global closed-loop system is proven to be exponentially stable. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.
Method and apparatus for transfer function simulator for testing complex systems

NASA Technical Reports Server (NTRS)

Kavaya, M. J. (Inventor)

1985-01-01

A method and apparatus for testing the operation of a complex stabilization circuit in a closed loop system is presented. The method is comprised of a programmed analog or digital computing system for implementing the transfer function of a load thereby providing a predictable load. The digital computing system employs a table stored in a microprocessor in which precomputed values of the load transfer function are stored for values of input signal from the stabilization circuit over the range of interest. This technique may be used not only for isolating faults in the stabilization circuit, but also for analyzing a fault in a faulty load by so varying parameters of the computing system as to simulate operation of the actual load with the fault.
Diagonal dominance for the multivariable Nyquist array using function minimization

NASA Technical Reports Server (NTRS)

Leininger, G. G.

1977-01-01

A new technique for the design of multivariable control systems using the multivariable Nyquist array method was developed. A conjugate direction function minimization algorithm is utilized to achieve a diagonal dominant condition over the extended frequency range of the control system. The minimization is performed on the ratio of the moduli of the off-diagonal terms to the moduli of the diagonal terms of either the inverse or direct open loop transfer function matrix. Several new feedback design concepts were also developed, including: (1) dominance control parameters for each control loop; (2) compensator normalization to evaluate open loop conditions for alternative design configurations; and (3) an interaction index to determine the degree and type of system interaction when all feedback loops are closed simultaneously. This new design capability was implemented on an IBM 360/75 in a batch mode but can be easily adapted to an interactive computer facility. The method was applied to the Pratt and Whitney F100 turbofan engine.
Application of the MNA design method to a nonlinear turbofan engine. [multivariable Nyquist array method

NASA Technical Reports Server (NTRS)

Leininger, G. G.

1981-01-01

Using nonlinear digital simulation as a representative model of the dynamic operation of the QCSEE turbofan engine, a feedback control system is designed by variable frequency design techniques. Transfer functions are generated for each of five power level settings covering the range of operation from approach power to full throttle (62.5% to 100% full power). These transfer functions are then used by an interactive control system design synthesis program to provide a closed loop feedback control using the multivariable Nyquist array and extensions to multivariable Bode diagrams and Nichols charts.

Effect of pole zero location on system dynamics of boost converter for micro grid

NASA Astrophysics Data System (ADS)

Lavanya, A.; Vijayakumar, K.; Navamani, J. D.; Jayaseelan, N.

2018-04-01

Green clean energy like photo voltaic, wind energy, fuel cell can be brought together by microgrid.For low voltage sources like photovoltaic cell boost converter is very much essential. This paper explores the dynamic analysis of boost converter in a continuous conduction mode (CCM). The transient performance and stability analysis is carried out in this paper using time domain analysis and frequency domain analysis techniques. Boost converter is simulated using both PSIM and MATLAB software. Furthermore, state space model obtained and the transfer function is derived. The converter behaviour when a step input is applied is analyzed and stability of the converter is analyzed from bode plot frequency for open loop. Effect of the locations of poles and zeros in the transfer function of boost converter and how the performance parameters are affected is discussed in this paper. Closed loop performance with PI controller is also analyzed for boost converter.
Passivity-based control of linear time-invariant systems modelled by bond graph

NASA Astrophysics Data System (ADS)

Galindo, R.; Ngwompo, R. F.

2018-02-01

Closed-loop control systems are designed for linear time-invariant (LTI) controllable and observable systems modelled by bond graph (BG). Cascade and feedback interconnections of BG models are realised through active bonds with no loading effect. The use of active bonds may lead to non-conservation of energy and the overall system is modelled by proposed pseudo-junction structures. These structures are build by adding parasitic elements to the BG models and the overall system may become singularly perturbed. The structures for these interconnections can be seen as consisting of inner structures that satisfy energy conservation properties and outer structures including multiport-coupled dissipative fields. These fields highlight energy properties like passivity that are useful for control design. In both interconnections, junction structures and dissipative fields for the controllers are proposed, and passivity is guaranteed for the closed-loop systems assuring robust stability. The cascade interconnection is applied to the structural representation of closed-loop transfer functions, when a stabilising controller is applied to a given nominal plant. Applications are given when the plant and the controller are described by state-space realisations. The feedback interconnection is used getting necessary and sufficient stability conditions based on the closed-loop characteristic polynomial, solving a pole-placement problem and achieving zero-stationary state error.
Closed-loop carrier phase synchronization techniques motivated by likelihood functions

NASA Technical Reports Server (NTRS)

Tsou, H.; Hinedi, S.; Simon, M.

1994-01-01

This article reexamines the notion of closed-loop carrier phase synchronization motivated by the theory of maximum a posteriori phase estimation with emphasis on the development of new structures based on both maximum-likelihood and average-likelihood functions. The criterion of performance used for comparison of all the closed-loop structures discussed is the mean-squared phase error for a fixed-loop bandwidth.
A technique for pole-zero placement for dual-input control systems. [computer simulation of CH-47 helicopter longitudinal dynamics

NASA Technical Reports Server (NTRS)

Reid, G. F.

1976-01-01

A technique is presented for determining state variable feedback gains that will place both the poles and zeros of a selected transfer function of a dual-input control system at pre-determined locations in the s-plane. Leverrier's algorithm is used to determine the numerator and denominator coefficients of the closed-loop transfer function as functions of the feedback gains. The values of gain that match these coefficients to those of a pre-selected model are found by solving two systems of linear simultaneous equations. The algorithm has been used in a computer simulation of the CH-47 helicopter to control longitudinal dynamics.
Reliable Control Using Disturbance Observer and Equivalent Transfer Function for Position Servo System in Current Feedback Loop Failure

NASA Astrophysics Data System (ADS)

Ishikawa, Kaoru; Nakamura, Taro; Osumi, Hisashi

A reliable control method is proposed for multiple loop control system. After a feedback loop failure, such as case of the sensor break down, the control system becomes unstable and has a big fluctuation even if it has a disturbance observer. To cope with this problem, the proposed method uses an equivalent transfer function (ETF) as active redundancy compensation after the loop failure. The ETF is designed so that it does not change the transfer function of the whole system before and after the loop failure. In this paper, the characteristic of reliable control system that uses an ETF and a disturbance observer is examined by the experiment that uses the DC servo motor for the current feedback loop failure in the position servo system.
Wide-beam sensors for controlling dual-delay systems

NASA Astrophysics Data System (ADS)

Edwards, J. B.; Twemlow, J. K.

1982-09-01

A class of dual delay feedback systems of open loop transfer function G(s) = k exp(-Xs)/l - exp(-Ws) is shown to be unstable if ratio X/W is noninteger. By means of z-transform techniques it is shown that, by using a feedback transducer that senses over a substantial distance either side of its central axis, closed-loop stability may be restored. Such transducers, termed widebeam sensors, include transmission, backscatter and natural radiation types as well as electromechanical conveyor belt weighers. Designing transducers for very narrow beams may not be desirable from the overall system viewpoint.
A novel double loop control model design for chemical unstable processes.

PubMed

Cong, Er-Ding; Hu, Ming-Hui; Tu, Shan-Tung; Xuan, Fu-Zhen; Shao, Hui-He

2014-03-01

In this manuscript, based on Smith predictor control scheme for unstable process in industry, an improved double loop control model is proposed for chemical unstable processes. Inner loop is to stabilize integrating the unstable process and transform the original process to first-order plus pure dead-time dynamic stable process. Outer loop is to enhance the performance of set point response. Disturbance controller is designed to enhance the performance of disturbance response. The improved control system is simple with exact physical meaning. The characteristic equation is easy to realize stabilization. Three controllers are separately design in the improved scheme. It is easy to design each controller and good control performance for the respective closed-loop transfer function separately. The robust stability of the proposed control scheme is analyzed. Finally, case studies illustrate that the improved method can give better system performance than existing design methods. © 2013 ISA Published by ISA All rights reserved.
The power of sound: miniaturized medical implants with ultrasonic links

NASA Astrophysics Data System (ADS)

Wang, Max L.; Chang, Ting Chia; Charthad, Jayant; Weber, Marcus J.; Arbabian, Amin

2017-05-01

Miniaturized wirelessly powered implants capable of operating and communicating deep in the body are necessary for the next-generation of diagnostics and therapeutics. A major challenge in developing these minimally invasive implants is the tradeoff between device size, functionality, and operating depth. Here, we review two different wireless powering methods, inductive and ultrasonic power transfer, examine how to analyze their power transfer efficiency, and evaluate their potential for powering implantable medical devices. In particular, we show how ultrasonic wireless power transfer can address these challenges due to its safety, low attenuation, and millimeter wavelengths in the body. Finally, we demonstrate two ultrasonically powered implants capable of active power harvesting and bidirectional communication for closed-loop operation while functioning through multiple centimeters of tissue.
A FORTRAN program for the analysis of linear continuous and sample-data systems

NASA Technical Reports Server (NTRS)

Edwards, J. W.

1976-01-01

A FORTRAN digital computer program which performs the general analysis of linearized control systems is described. State variable techniques are used to analyze continuous, discrete, and sampled data systems. Analysis options include the calculation of system eigenvalues, transfer functions, root loci, root contours, frequency responses, power spectra, and transient responses for open- and closed-loop systems. A flexible data input format allows the user to define systems in a variety of representations. Data may be entered by inputing explicit data matrices or matrices constructed in user written subroutines, by specifying transfer function block diagrams, or by using a combination of these methods.
Closed-loop transfer recovery with observer-based controllers. I - Analysis. II - Design

NASA Technical Reports Server (NTRS)

Chen, Ben M.; Saberi, Ali; Ly, Uy-Loi

1992-01-01

A detailed study is presented of three fundamental issues related to the problem of closed-loop transfer (CLT) recovery. The first issues concerns what can and cannot be achieved for a given system and for an arbitrary target CLT function (TCLTF). The second issue involves developing necessary and/or sufficient conditions for a TCLTF to be recoverable either exactly or approximately. The third issue involves the necessary and/or sufficient conditions on a given system such that it has at least one recoverable TCLTF. The results of the analysis identify some fundamental limitations of the given system as a consequence of its structural properties which enables designers to appreciate at the outset different design limitations incurred in the synthesis of output-feedback controllers. Then, the actual design of full-order or reduced-order observer-based controllers is addressed which will achieve as close as possibly the desired TCLTF. Three design methods are considered: (1) the ATEA method, (2) a method that minimizes the H2-norm of a recovery matrix, and (3) a method that minimizes the respective H(infinity) norm. The relative merits of the methods are discussed.
Comparison of Five System Identification Algorithms for Rotorcraft Higher Harmonic Control

NASA Technical Reports Server (NTRS)

Jacklin, Stephen A.

1998-01-01

This report presents an analysis and performance comparison of five system identification algorithms. The methods are presented in the context of identifying a frequency-domain transfer matrix for the higher harmonic control (HHC) of helicopter vibration. The five system identification algorithms include three previously proposed methods: (1) the weighted-least- squares-error approach (in moving-block format), (2) the Kalman filter method, and (3) the least-mean-squares (LMS) filter method. In addition there are two new ones: (4) a generalized Kalman filter method and (5) a generalized LMS filter method. The generalized Kalman filter method and the generalized LMS filter method were derived as extensions of the classic methods to permit identification by using more than one measurement per identification cycle. Simulation results are presented for conditions ranging from the ideal case of a stationary transfer matrix and no measurement noise to the more complex cases involving both measurement noise and transfer-matrix variation. Both open-loop identification and closed- loop identification were simulated. Closed-loop mode identification was more challenging than open-loop identification because of the decreasing signal-to-noise ratio as the vibration became reduced. The closed-loop simulation considered both local-model identification, with measured vibration feedback and global-model identification with feedback of the identified uncontrolled vibration. The algorithms were evaluated in terms of their accuracy, stability, convergence properties, computation speeds, and relative ease of implementation.
Study of the Open Loop and Closed Loop Oscillator Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imel, George R.; Baker, Benjamin; Riley, Tony

This report presents the progress and completion of a five-year study undertaken at Idaho State University of the measurement of very small worth reactivity samples comparing open and closed loop oscillator techniques.The study conclusively demonstrated the equivalency of the two techniques with regard to uncertainties in reactivity values, i.e., limited by reactor noise. As those results are thoroughly documented in recent publications, in this report we will concentrate on the support work that was necessary. For example, we describe in some detail the construction and calibration of a pilot rod for the closed loop system. We discuss the campaign tomore » measure the required reactor parameters necessary for inverse-kinetics. Finally, we briefly discuss the transfer of the open loop technique to other reactor systems.« less
Study of the open loop and closed loop oscillator techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Benjamin; Riley, Tony; Langbehn, Adam

This paper presents some aspects of a five year study undertaken at Idaho State University of the measurement of very small worth reactivity samples comparing open and closed loop oscillator techniques. The study conclusively demonstrated the equivalency of the two techniques with regard to uncertainties in reactivity values, i.e., limited by reactor noise. As those results are thoroughly documented in recent publications, in this paper we will concentrate on the support work that was necessary. For example, we describe in some detail the construction and calibration of a pilot rod for the closed loop system. We discuss the campaign tomore » measure the required reactor parameters necessary for inverse-kinetics. Finally, we briefly discuss the transfer of the open loop technique to other reactor systems. (authors)« less
High-Performance Computing Data Center Cooling System Energy Efficiency |

Science.gov Websites

approaches involve a cooling distribution unit (CDU) (2), which interfaces with the facility cooling loop and to the energy recovery water (ERW) loop (5), which is a closed-loop system. There are three heat rejection options for this IT load: When possible, heat energy from the energy recovery loop is transferred
Experimental investigation on thermal performance of a closed loop pulsating heat pipe (CLPHP) using methanol and distilled water at different filling ratios

NASA Astrophysics Data System (ADS)

Rahman, Md. Lutfor; Swarna, Anindita Dhar; Ahmed, Syed Nasif Uddin; Perven, Sanjida; Ali, Mohammad

2016-07-01

Pulsating Heat Pipes, the new two-phase heat transfer devices, with no counter current flow between liquid and vapor have become a modern topic for research in the field of thermal management. This paper focuses on the performance of methanol and distilled water as working fluid in a closed loop pulsating heat pipe (CLPHP). This performances are compared in terms of thermal resistance, heat transfer co-efficient, and evaporator and condenser wall temperature with variable heat inputs. Methanol and Distilled water are selected for their lower surface tension, dynamic viscosity and sensible heat. A closed loop PHP made of copper with 2mm ID and 2.5mm OD having total 8 loops are supplied with power input varied from 10W to 60W. During the experiment the PHP is kept vertical, while the filling ratio (FR) is increased gradually from 40% to 70% with 10% increment. The optimum filling ratio for a minimum thermal resistance is found to be 60% and 40% for distilled water and methanol respectively and methanol is found to be the better working fluid compared to distilled water in terms of its lower thermal resistance and higher heat transfer coefficient.
The insertion of human dynamics models in the flight control loops of V/STOL research aircraft. Appendix 2: The optimal control model of a pilot in V/STOL aircraft control loops

NASA Technical Reports Server (NTRS)

Zipf, Mark E.

1989-01-01

An overview is presented of research work focussed on the design and insertion of classical models of human pilot dynamics within the flight control loops of V/STOL aircraft. The pilots were designed and configured for use in integrated control system research and design. The models of human behavior that were considered are: McRuer-Krendel (a single variable transfer function model); and Optimal Control Model (a multi-variable approach based on optimal control and stochastic estimation theory). These models attempt to predict human control response characteristics when confronted with compensatory tracking and state regulation tasks. An overview, mathematical description, and discussion of predictive limitations of the pilot models is presented. Design strategies and closed loop insertion configurations are introduced and considered for various flight control scenarios. Models of aircraft dynamics (both transfer function and state space based) are developed and discussed for their use in pilot design and application. Pilot design and insertion are illustrated for various flight control objectives. Results of pilot insertion within the control loops of two V/STOL research aricraft (Sikorski Black Hawk UH-60A, McDonnell Douglas Harrier II AV-8B) are presented and compared against actual pilot flight data. Conclusions are reached on the ability of the pilot models to adequately predict human behavior when confronted with similar control objectives.
Robustness analysis of an air heating plant and control law by using polynomial chaos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colón, Diego; Ferreira, Murillo A. S.; Bueno, Átila M.

2014-12-10

This paper presents a robustness analysis of an air heating plant with a multivariable closed-loop control law by using the polynomial chaos methodology (MPC). The plant consists of a PVC tube with a fan in the air input (that forces the air through the tube) and a mass flux sensor in the output. A heating resistance warms the air as it flows inside the tube, and a thermo-couple sensor measures the air temperature. The plant has thus two inputs (the fan's rotation intensity and heat generated by the resistance, both measured in percent of the maximum value) and two outputsmore » (air temperature and air mass flux, also in percent of the maximal value). The mathematical model is obtained by System Identification techniques. The mass flux sensor, which is nonlinear, is linearized and the delays in the transfer functions are properly approximated by non-minimum phase transfer functions. The resulting model is transformed to a state-space model, which is used for control design purposes. The multivariable robust control design techniques used is the LQG/LTR, and the controllers are validated in simulation software and in the real plant. Finally, the MPC is applied by considering some of the system's parameters as random variables (one at a time, and the system's stochastic differential equations are solved by expanding the solution (a stochastic process) in an orthogonal basis of polynomial functions of the basic random variables. This method transforms the stochastic equations in a set of deterministic differential equations, which can be solved by traditional numerical methods (That is the MPC). Statistical data for the system (like expected values and variances) are then calculated. The effects of randomness in the parameters are evaluated in the open-loop and closed-loop pole's positions.« less
An investigation into closed-loop treatment of neurological disorders based on sensing mitochondrial dysfunction.

PubMed

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.
Ground-based adaptive optics coronagraphic performance under closed-loop predictive control

NASA Astrophysics Data System (ADS)

Males, Jared R.; Guyon, Olivier

2018-01-01

The discovery of the exoplanet Proxima b highlights the potential for the coming generation of giant segmented mirror telescopes (GSMTs) to characterize terrestrial-potentially habitable-planets orbiting nearby stars with direct imaging. This will require continued development and implementation of optimized adaptive optics systems feeding coronagraphs on the GSMTs. Such development should proceed with an understanding of the fundamental limits imposed by atmospheric turbulence. Here, we seek to address this question with a semianalytic framework for calculating the postcoronagraph contrast in a closed-loop adaptive optics system. We do this starting with the temporal power spectra of the Fourier basis calculated assuming frozen flow turbulence, and then apply closed-loop transfer functions. We include the benefits of a simple predictive controller, which we show could provide over a factor of 1400 gain in raw point spread function contrast at 1 λ/D on bright stars, and more than a factor of 30 gain on an I=7.5 mag star such as Proxima. More sophisticated predictive control can be expected to improve this even further. Assuming a photon-noise limited observing technique such as high-dispersion coronagraphy, these gains in raw contrast will decrease integration times by the same large factors. Predictive control of atmospheric turbulence should therefore be seen as one of the key technologies that will enable ground-based telescopes to characterize terrestrial planets.
INCA- INTERACTIVE CONTROLS ANALYSIS

NASA Technical Reports Server (NTRS)

Bauer, F. H.

1994-01-01

The Interactive Controls Analysis (INCA) program was developed to provide a user friendly environment for the design and analysis of linear control systems, primarily feedback control systems. INCA is designed for use with both small and large order systems. Using the interactive graphics capability, the INCA user can quickly plot a root locus, frequency response, or time response of either a continuous time system or a sampled data system. The system configuration and parameters can be easily changed, allowing the INCA user to design compensation networks and perform sensitivity analysis in a very convenient manner. A journal file capability is included. This stores an entire sequence of commands, generated during an INCA session into a file which can be accessed later. Also included in INCA are a context-sensitive help library, a screen editor, and plot windows. INCA is robust to VAX-specific overflow problems. The transfer function is the basic unit of INCA. Transfer functions are automatically saved and are available to the INCA user at any time. A powerful, user friendly transfer function manipulation and editing capability is built into the INCA program. The user can do all transfer function manipulations and plotting without leaving INCA, although provisions are made to input transfer functions from data files. By using a small set of commands, the user may compute and edit transfer functions, and then examine these functions by using the ROOT_LOCUS, FREQUENCY_RESPONSE, and TIME_RESPONSE capabilities. Basic input data, including gains, are handled as single-input single-output transfer functions. These functions can be developed using the function editor or by using FORTRAN- like arithmetic expressions. In addition to the arithmetic functions, special functions are available to 1) compute step, ramp, and sinusoid functions, 2) compute closed loop transfer functions, 3) convert from S plane to Z plane with optional advanced Z transform, and 4) convert from Z plane to W plane and back. These capabilities allow the INCA user to perform block diagram algebraic manipulations quickly for functions in the S, Z, and W domains. Additionally, a versatile digital control capability has been included in INCA. Special plane transformations allow the user to easily convert functions from one domain to another. Other digital control capabilities include: 1) totally independent open loop frequency response analyses on a continuous plant, discrete control system with a delay, 2) advanced Z-transform capability for systems with delays, and 3) multirate sampling analyses. The current version of INCA includes Dynamic Functions (which change when a parameter changes), standard filter generation, PD and PID controller generation, incorporation of the QZ-algorithm (function addition, inverse Laplace), and describing functions that allow the user to calculate the gain and phase characteristics of a nonlinear device. The INCA graphic modes provide the user with a convenient means to document and study frequency response, time response, and root locus analyses. General graphics features include: 1) zooming and dezooming, 2) plot documentation, 3) a table of analytic computation results, 4) multiple curves on the same plot, and 5) displaying frequency and gain information for a specific point on a curve. Additional capabilities in the frequency response mode include: 1) a full complement of graphical methods Bode magnitude, Bode phase, Bode combined magnitude and phase, Bode strip plots, root contour plots, Nyquist, Nichols, and Popov plots; 2) user selected plot scaling; and 3) gain and phase margin calculation and display. In the time response mode, additional capabilities include: 1) support for inverse Laplace and inverse Z transforms, 2) support for various input functions, 3) closed loop response evaluation, 4) loop gain sensitivity analyses, 5) intersample time response for discrete systems using the advanced Z transform, and 6) closed loop time response using mixed plane (S, Z, W) operations with delay. A Graphics mode command was added to the current version of INCA, version 3.13, to produce Metafiles (graphic files) of the currently displayed plot. The metafile can be displayed and edited using the QPLOT Graphics Editor and Replotter for Metafiles (GERM) program included with the INCA package. The INCA program is written in Pascal and FORTRAN for interactive or batch execution and has been implemented on a DEC VAX series computer under VMS. Both source code and executable code are supplied for INCA. Full INCA graphics capabilities are supported for various Tektronix 40xx and 41xx terminals; DEC VT graphics terminals; many PC and Macintosh terminal emulators; TEK014 hardcopy devices such as the LN03 Laserprinter; and bit map graphics external hardcopy devices. Also included for the TEK4510 rasterizer users are a multiple copy feature, a wide line feature, and additional graphics fonts. The INCA program was developed in 1985, Version 2.04 was released in 1986, Version 3.00 was released in 1988, and Version 3.13 was released in 1989. An INCA version 2.0X conversion program is included.

Autopilot for frequency-modulation atomic force microscopy.

PubMed

Kuchuk, Kfir; Schlesinger, Itai; Sivan, Uri

2015-10-01

One of the most challenging aspects of operating an atomic force microscope (AFM) is finding optimal feedback parameters. This statement applies particularly to frequency-modulation AFM (FM-AFM), which utilizes three feedback loops to control the cantilever excitation amplitude, cantilever excitation frequency, and z-piezo extension. These loops are regulated by a set of feedback parameters, tuned by the user to optimize stability, sensitivity, and noise in the imaging process. Optimization of these parameters is difficult due to the coupling between the frequency and z-piezo feedback loops by the non-linear tip-sample interaction. Four proportional-integral (PI) parameters and two lock-in parameters regulating these loops require simultaneous optimization in the presence of a varying unknown tip-sample coupling. Presently, this optimization is done manually in a tedious process of trial and error. Here, we report on the development and implementation of an algorithm that computes the control parameters automatically. The algorithm reads the unperturbed cantilever resonance frequency, its quality factor, and the z-piezo driving signal power spectral density. It analyzes the poles and zeros of the total closed loop transfer function, extracts the unknown tip-sample transfer function, and finds four PI parameters and two lock-in parameters for the frequency and z-piezo control loops that optimize the bandwidth and step response of the total system. Implementation of the algorithm in a home-built AFM shows that the calculated parameters are consistently excellent and rarely require further tweaking by the user. The new algorithm saves the precious time of experienced users, facilitates utilization of FM-AFM by casual users, and removes the main hurdle on the way to fully automated FM-AFM.
Autopilot for frequency-modulation atomic force microscopy

NASA Astrophysics Data System (ADS)

Kuchuk, Kfir; Schlesinger, Itai; Sivan, Uri

2015-10-01

One of the most challenging aspects of operating an atomic force microscope (AFM) is finding optimal feedback parameters. This statement applies particularly to frequency-modulation AFM (FM-AFM), which utilizes three feedback loops to control the cantilever excitation amplitude, cantilever excitation frequency, and z-piezo extension. These loops are regulated by a set of feedback parameters, tuned by the user to optimize stability, sensitivity, and noise in the imaging process. Optimization of these parameters is difficult due to the coupling between the frequency and z-piezo feedback loops by the non-linear tip-sample interaction. Four proportional-integral (PI) parameters and two lock-in parameters regulating these loops require simultaneous optimization in the presence of a varying unknown tip-sample coupling. Presently, this optimization is done manually in a tedious process of trial and error. Here, we report on the development and implementation of an algorithm that computes the control parameters automatically. The algorithm reads the unperturbed cantilever resonance frequency, its quality factor, and the z-piezo driving signal power spectral density. It analyzes the poles and zeros of the total closed loop transfer function, extracts the unknown tip-sample transfer function, and finds four PI parameters and two lock-in parameters for the frequency and z-piezo control loops that optimize the bandwidth and step response of the total system. Implementation of the algorithm in a home-built AFM shows that the calculated parameters are consistently excellent and rarely require further tweaking by the user. The new algorithm saves the precious time of experienced users, facilitates utilization of FM-AFM by casual users, and removes the main hurdle on the way to fully automated FM-AFM.
Effect of using ethanol and methanol on thermal performance of a closed loop pulsating heat pipe (CLPHP) with different filling ratios

NASA Astrophysics Data System (ADS)

Rahman, Md. Lutfor; Salsabil, Zaimaa; Yasmin, Nusrat; Nourin, Farah Nazifa; Ali, Mohammad

2016-07-01

This paper presents an experimental study of a closed loop Pulsating Heat Pipe (CLPHP) as the demand of smaller and effective heat transfer devices is increasing day by day. PHP is a two phase heat transfer device suited for heat transfer applications, especially suited for handling moderate to high heat fluxes in different applications. A copper made Pulsating Heat Pipe (PHP) of 250 mm length is used in this experimental work with 2 mm ID and 3 mm OD, closed end-to-end in 8 looped, evacuated and then partially filled with working fluids. The evaporation section is 50 mm, adiabatic section is 120 mm and condensation section is 80 mm. The performance characterization is done for two working fluids at Vertical (0°) orientations. The working fluids are Methanol and Ethanol and the filling ratios are 40%, 50%, 60% & 70% based on total volume, respectively. The results show that the influence of various parameters, the heat input flux, and different filling ratios on a heat transfer performance of CLPHP. Methanol shows better performance as working fluid in PHP than ethanol at present orientation for a wide range of heat inputs and can be used at high heat input conditions. Ethanol is better choice to be used in low heat input conditions.
Output Feedback Pole-Placement in the Design of Compensators for Suboptimal Linear Quadratic Regulators.

DTIC Science & Technology

1979-06-01

also extended to the class of stabilizable systems and the required compensator shown to possess a separation property. Finally the design methodology...Page 1.1. Block diagram of transfer function given in (1.28) ........... 15 3.3.1. Compensator structure for controllable and stabilizable systems ...response will be stable. The implemented output feedback control law will stabilize the total closed loop system . n nn Let [uin and iJi= 1 be the
DOE Office of Scientific and Technical Information (OSTI.GOV)

Hessell, Steven M.; Morris, Robert L.; McGrogan, Sean W.

A powertrain including an engine and torque machines is configured to transfer torque through a multi-mode transmission to an output member. A method for controlling the powertrain includes employing a closed-loop speed control system to control torque commands for the torque machines in response to a desired input speed. Upon approaching a power limit of a power storage device transferring power to the torque machines, power limited torque commands are determined for the torque machines in response to the power limit and the closed-loop speed control system is employed to determine an engine torque command in response to the desiredmore » input speed and the power limited torque commands for the torque machines.« less
Loop transfer recovery for general nonminimum phase discrete time systems. I - Analysis

NASA Technical Reports Server (NTRS)

Chen, Ben M.; Saberi, Ali; Sannuti, Peddapullaiah; Shamash, Yacov

1992-01-01

A complete analysis of loop transfer recovery (LTR) for general nonstrictly proper, not necessarily minimum phase discrete time systems is presented. Three different observer-based controllers, namely, `prediction estimator' and full or reduced-order type `current estimator' based controllers, are used. The analysis corresponding to all these three controllers is unified into a single mathematical framework. The LTR analysis given here focuses on three fundamental issues: (1) the recoverability of a target loop when it is arbitrarily given, (2) the recoverability of a target loop while taking into account its specific characteristics, and (3) the establishment of necessary and sufficient conditions on the given system so that it has at least one recoverable target loop transfer function or sensitivity function. Various differences that arise in LTR analysis of continuous and discrete systems are pointed out.
Modified superposition: A simple time series approach to closed-loop manual controller identification

NASA Technical Reports Server (NTRS)

Biezad, D. J.; Schmidt, D. K.; Leban, F.; Mashiko, S.

1986-01-01

Single-channel pilot manual control output in closed-tracking tasks is modeled in terms of linear discrete transfer functions which are parsimonious and guaranteed stable. The transfer functions are found by applying a modified super-position time series generation technique. A Levinson-Durbin algorithm is used to determine the filter which prewhitens the input and a projective (least squares) fit of pulse response estimates is used to guarantee identified model stability. Results from two case studies are compared to previous findings, where the source of data are relatively short data records, approximately 25 seconds long. Time delay effects and pilot seasonalities are discussed and analyzed. It is concluded that single-channel time series controller modeling is feasible on short records, and that it is important for the analyst to determine a criterion for best time domain fit which allows association of model parameter values, such as pure time delay, with actual physical and physiological constraints. The purpose of the modeling is thus paramount.
Identification of flame transfer functions in the presence of intrinsic thermoacoustic feedback and noise

NASA Astrophysics Data System (ADS)

Jaensch, Stefan; Merk, Malte; Emmert, Thomas; Polifke, Wolfgang

2018-05-01

The Large Eddy Simulation/System Identification (LES/SI) approach is a general and efficient numerical method for deducing a Flame Transfer Function (FTF) from the LES of turbulent reacting flow. The method may be summarised as follows: a simulated flame is forced with a broadband excitation signal. The resulting fluctuations of the reference velocity and of the global heat release rate are post-processed via SI techniques in order to estimate a low-order model of the flame dynamics. The FTF is readily deduced from the low-order model. The SI method most frequently applied in aero- and thermo-acoustics has been Wiener-Hopf Inversion (WHI). This method is known to yield biased estimates in situations with feedback, thus it was assumed that non-reflective boundary conditions are required to generate accurate results with the LES/SI approach. Recent research has shown that the FTF is part of the so-called Intrinsic ThermoAcoustic (ITA) feedback loop. Hence, identifying an FTF from a compressible LES is always a closed-loop problem, and consequently one should expect that the WHI would yield biased results. However, several studies proved that WHI results compare favourably with validation data. To resolve this apparent contradiction, a variety of identification methods are compared against each other, including models designed for closed-loop identification. In agreement with theory, we show that the estimate given by WHI does not converge to the actual FTF. Fortunately, the error made is small if excitation amplitudes can be set such that the signal-to-noise ratio is large, but not large enough to trigger nonlinear flame dynamics. Furthermore, we conclude that non-reflective boundary conditions are not essentially necessary to apply the LES/SI approach.
Human life support during interplanetary travel and domicile. III - Mars expedition system trade study

NASA Technical Reports Server (NTRS)

Seshan, P. K.; Ferrall, Joseph F.; Rohatgi, Naresh K.

1991-01-01

Several alternative configurations of life-support systems (LSSs) for a Mars missions are compared analytically on a quantitative basis in terms of weight, volume, and power. A baseline technology set is utilized for the illustrations of systems including totally open loop, carbon dioxide removal only, partially closed loop, and totally closed loop. The analytical model takes advantage of a modular, top-down hierarchical breakdown of LSS subsystems into functional elements that represent individual processing technologies. The open-loop systems are not competitive in terms of weight for both long-duration orbiters and short-duration lander vehicles, and power demands are lowest with the open loop and highest with the closed loop. The closed-loop system can reduce vehicle weight by over 70,000 lbs and thereby overcome the power penalty of 1600 W; the closed-loop variety is championed as the preferred system for a Mars expedition.
Full-Authority Fault-Tolerant Electronic Engine Control Systems for Variable Cycle Engines.

DTIC Science & Technology

1981-12-01

Geometry or Fuel Flow Scheduled as a Function of Engine State, i.e. FIGV = f( N1 C2 ) Closed Loop - Geometry or Fuel Flow Modulated To Maintain an Engine...Low Pressure Turbine Inlet Area (A41) Closed Loop (Integral) N2, T22 Core Stream Exhaust Nozzle Area (AJE) Closed Loop (Integral) N1 , T2 Duct Stream...to remain at the breakpoint value while low rotor speed reference ( N1 reference) is scheduled to decrease as a function of power lever angle (PLA), to
Closed-Loop Control and Advisory Mode Evaluation of an Artificial Pancreatic β Cell: Use of Proportional–Integral–Derivative Equivalent Model-Based Controllers

PubMed Central

Percival, Matthew W.; Zisser, Howard; Jovanovič, Lois; Doyle, Francis J.

2008-01-01

Background Using currently available technology, it is possible to apply modern control theory to produce a closed-loop artificial β cell. Novel use of established control techniques would improve glycemic control, thereby reducing the complications of diabetes. Two popular controller structures, proportional–integral–derivative (PID) and model predictive control (MPC), are compared first in a theoretical sense and then in two applications. Methods The Bergman model is transformed for use in a PID equivalent model-based controller. The internal model control (IMC) structure, which makes explicit use of the model, is compared with the PID controller structure in the transfer function domain. An MPC controller is then developed as an optimization problem with restrictions on its tuning parameters and is shown to be equivalent to an IMC controller. The controllers are tuned for equivalent performance and evaluated in a simulation study as a closed-loop controller and in an advisory mode scenario on retrospective clinical data. Results Theoretical development shows conditions under which PID and MPC controllers produce equivalent output via IMC. The simulation study showed that the single tuning parameter for the equivalent controllers relates directly to the closed-loop speed of response and robustness, an important result considering system uncertainty. The risk metric allowed easy identification of instances of inadequate control. Results of the advisory mode simulation showed that suitable tuning produces consistently appropriate delivery recommendations. Conclusion The conditions under which PID and MPC are equivalent have been derived. The MPC framework is more suitable given the extensions necessary for a fully closed-loop artificial β cell, such as consideration of controller constraints. Formulation of the control problem in risk space is attractive, as it explicitly addresses the asymmetry of the problem; this is done easily with MPC. PMID:19885240
Deflection amplifier for image dissectors

NASA Technical Reports Server (NTRS)

Salomon, P. M.

1977-01-01

Balanced symmetrical y-axis amplifier uses zener-diode level shifting to interface operational amplifiers to high voltage bipolar output stages. Nominal voltage transfer characteristic is 40 differential output volts per input volt; bandwidth, between -3-dB points, is approximately 8 kHz; loop gain is nominally 89 dB with closed loop gain of 26 dB.
Design and Simulation of a PID Controller for Motion Control Systems

NASA Astrophysics Data System (ADS)

Hassan Abdullahi, Zakariyya; Danzomo, Bashir Ahmed; Suleiman Abdullahi, Zainab

2018-04-01

Motion control system plays important role in many industrial applications among which are in robot system, missile launching, positioning systems etc. However, the performance requirement for these applications in terms of high accuracy, high speed, insignificant or no overshoot and robustness have generated continuous challenges in the field of motion control system design and implementation. To compensate this challenge, a PID controller was design using mathematical model of a DC motor based on classical root-locus approach. The reason for adopting root locus design is to remodel the closed-loop response by putting the closed-loop poles of the system at desired points. Adding poles and zeros to the initial open-loop transfer function through the controller provide a way to transform the root locus in order to place the closed-loop poles at the required points. This process can also be used for discrete-time models. The Advantages of root locus over other methods is that, it gives the better way of pinpointing the parameters and can easily predict the fulfilment of the whole system. The controller performance was simulated using MATLAB code and a reasonable degree of accuracy was obtained. Implementation of the proposed model was conducted using-Simulink and the result obtained shows that the PID controller met the transient performance specifications with both settling time and overshoot less than 0.1s and 5% respectively. In terms of steady state error, the PID controller gave good response for both step input and ramp.
Autopilot for frequency-modulation atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuchuk, Kfir; Schlesinger, Itai; Sivan, Uri, E-mail: phsivan@tx.technion.ac.il

2015-10-15

One of the most challenging aspects of operating an atomic force microscope (AFM) is finding optimal feedback parameters. This statement applies particularly to frequency-modulation AFM (FM-AFM), which utilizes three feedback loops to control the cantilever excitation amplitude, cantilever excitation frequency, and z-piezo extension. These loops are regulated by a set of feedback parameters, tuned by the user to optimize stability, sensitivity, and noise in the imaging process. Optimization of these parameters is difficult due to the coupling between the frequency and z-piezo feedback loops by the non-linear tip-sample interaction. Four proportional-integral (PI) parameters and two lock-in parameters regulating these loopsmore » require simultaneous optimization in the presence of a varying unknown tip-sample coupling. Presently, this optimization is done manually in a tedious process of trial and error. Here, we report on the development and implementation of an algorithm that computes the control parameters automatically. The algorithm reads the unperturbed cantilever resonance frequency, its quality factor, and the z-piezo driving signal power spectral density. It analyzes the poles and zeros of the total closed loop transfer function, extracts the unknown tip-sample transfer function, and finds four PI parameters and two lock-in parameters for the frequency and z-piezo control loops that optimize the bandwidth and step response of the total system. Implementation of the algorithm in a home-built AFM shows that the calculated parameters are consistently excellent and rarely require further tweaking by the user. The new algorithm saves the precious time of experienced users, facilitates utilization of FM-AFM by casual users, and removes the main hurdle on the way to fully automated FM-AFM.« less
Upward and downward heat and mass transfer with miniature periodically operating loop thermosyphons

NASA Astrophysics Data System (ADS)

Fantozzi, Fabio; Filippeschi, Sauro; Latrofa, Enrico Maria

2004-03-01

Upward and downward two-phase heat and mass transfer has been considered in the present paper. The heat and mass transfer with the condenser located below the evaporator has been obtained by inserting an accumulator tank in the liquid line of a loop thermosyphon and enforcing a pressure pulsation. In previous papers these heat transfer devices have been called pulsated two phase thermosyphons (PTPT). A mini PTPT has been experimentally investigated. It has shown a stable periodic heat transfer regime weakly influenced by the position of the condenser with respect to the evaporator. In contrast a classical loop mini thermosyphon (diameter of connecting pipes 4 mm) did not achieve a stable functioning for the investigated level differences between evaporator and condenser lower than 0.37 m. The present study shows that the functioning of a PTPT device does not directly depend on the level difference or the presence of noncondensable gas. In order to obtain a natural circulation in mini or micro loops, a periodically operating heat transfer regime should therefore be considered.
An Adaptive Impedance Matching Network with Closed Loop Control Algorithm for Inductive Wireless Power Transfer

PubMed Central

Miao, Zhidong; Liu, Dake

2017-01-01

For an inductive wireless power transfer (IWPT) system, maintaining a reasonable power transfer efficiency and a stable output power are two most challenging design issues, especially when coil distance varies. To solve these issues, this paper presents a novel adaptive impedance matching network (IMN) for IWPT system. In our adaptive IMN IWPT system, the IMN is automatically reconfigured to keep matching with the coils and to adjust the output power adapting to coil distance variation. A closed loop control algorithm is used to change the capacitors continually, which can compensate mismatches and adjust output power simultaneously. The proposed adaptive IMN IWPT system is working at 125 kHz for 2 W power delivered to load. Comparing with the series resonant IWPT system and fixed IMN IWPT system, the power transfer efficiency of our system increases up to 31.79% and 60% when the coupling coefficient varies in a large range from 0.05 to 0.8 for 2 W output power. PMID:28763011
An Adaptive Impedance Matching Network with Closed Loop Control Algorithm for Inductive Wireless Power Transfer.

PubMed

Miao, Zhidong; Liu, Dake; Gong, Chen

2017-08-01

For an inductive wireless power transfer (IWPT) system, maintaining a reasonable power transfer efficiency and a stable output power are two most challenging design issues, especially when coil distance varies. To solve these issues, this paper presents a novel adaptive impedance matching network (IMN) for IWPT system. In our adaptive IMN IWPT system, the IMN is automatically reconfigured to keep matching with the coils and to adjust the output power adapting to coil distance variation. A closed loop control algorithm is used to change the capacitors continually, which can compensate mismatches and adjust output power simultaneously. The proposed adaptive IMN IWPT system is working at 125 kHz for 2 W power delivered to load. Comparing with the series resonant IWPT system and fixed IMN IWPT system, the power transfer efficiency of our system increases up to 31.79% and 60% when the coupling coefficient varies in a large range from 0.05 to 0.8 for 2 W output power.
Extension of the root-locus method to a certain class of fractional-order systems.

PubMed

Merrikh-Bayat, Farshad; Afshar, Mahdi; Karimi-Ghartemani, Masoud

2009-01-01

In this paper, the well-known root-locus method is developed for the special subset of linear time-invariant systems commonly known as fractional-order systems. Transfer functions of these systems are rational functions with polynomials of rational powers of the Laplace variable s. Such systems are defined on a Riemann surface because of their multi-valued nature. A set of rules for plotting the root loci on the first Riemann sheet is presented. The important features of the classical root-locus method such as asymptotes, roots condition on the real axis and breakaway points are extended to the fractional case. It is also shown that the proposed method can assess the closed-loop stability of fractional-order systems in the presence of a varying gain in the loop. Moreover, the effect of perturbation on the root loci is discussed. Three illustrative examples are presented to confirm the effectiveness of the proposed algorithm.
Human life support during interplanetary travel and domicile. II - Generic Modular Flow Schematic modeling

NASA Technical Reports Server (NTRS)

Farral, Joseph F.; Seshan, P. K.; Rohatgi, Naresh K.

1991-01-01

This paper describes the Generic Modular Flow Schematic (GMFS) architecture capable of encompassing all functional elements of a physical/chemical life support system (LSS). The GMFS can be implemented to synthesize, model, analyze, and quantitatively compare many configurations of LSSs, from a simple, completely open-loop to a very complex closed-loop. The GMFS model is coded in ASPEN, a state-of-the-art chemical process simulation program, to accurately compute the material, heat, and power flow quantities for every stream in each of the subsystem functional elements (SFEs) in the chosen configuration of a life support system. The GMFS approach integrates the various SFEs and subsystems in a hierarchical and modular fashion facilitating rapid substitutions and reconfiguration of a life support system. The comprehensive ASPEN material and energy balance output is transferred to a systems and technology assessment spreadsheet for rigorous system analysis and trade studies.
Closed-loop, pilot/vehicle analysis of the approach and landing task

NASA Technical Reports Server (NTRS)

Anderson, M. R.; Schmidt, D. K.

1986-01-01

In the case of approach and landing, it is universally accepted that the pilot uses more than one vehicle response, or output, to close his control loops. Therefore, to model this task, a multi-loop analysis technique is required. The analysis problem has been in obtaining reasonable analytic estimates of the describing functions representing the pilot's loop compensation. Once these pilot describing functions are obtained, appropriate performance and workload metrics must then be developed for the landing task. The optimal control approach provides a powerful technique for obtaining the necessary describing functions, once the appropriate task objective is defined in terms of a quadratic objective function. An approach is presented through the use of a simple, reasonable objective function and model-based metrics to evaluate loop performance and pilot workload. The results of an analysis of the LAHOS (Landing and Approach of Higher Order Systems) study performed by R.E. Smith is also presented.

Modeling and control for vibration suppression of a flexible smart structure

NASA Technical Reports Server (NTRS)

Dosch, J.; Leo, D.; Inman, D.

1993-01-01

Theoretical and experimental results of the modeling and control of a flexible ribbed antenna are presented. The antenna consists of eight flexible ribs which constitutes a smart antenna in the sense that the actuator and sensors are an integral part of the structure. The antenna exhibits closely space and repeated modes, thus multi-input multi-output (MIMO) control is necessary for controllability and observability of the structure. The structure also exhibits mode localization phenomenon and contains post buckled members making an accurate finite element model of the structure difficult to obtain. An identified MIMO minimum order model of the antenna is synthesized from identified single-input single-output (SISO) transfer functions curve fit in the frequency domain. The identified model is used to design a positive position feedback (PPF) controller that increases damping in all of the modes in the targeted frequency range. Due to the accuracy of the open loop model of the antenna, the closed loop response predicted by the identified model correlates well wtih experimental results.
Function projective synchronization in chaotic and hyperchaotic systems through open-plus-closed-loop coupling.

PubMed

Sudheer, K Sebastian; Sabir, M

2010-03-01

Recently introduced function projective synchronization in which chaotic systems synchronize up to a scaling function has important applications in secure communications. We design coupling function for unidirectional coupling in identical and mismatched oscillators to realize function projective synchronization through open-plus-closed-loop coupling method. Numerical simulations on Lorenz system, Rossler system, hyperchaotic Lorenz, and hyperchaotic Chen system are presented to verify the effectiveness of the proposed scheme.
Filter for third order phase locked loops

NASA Technical Reports Server (NTRS)

Crow, R. B.; Tausworthe, R. C. (Inventor)

1973-01-01

Filters for third-order phase-locked loops are used in receivers to acquire and track carrier signals, particularly signals subject to high doppler-rate changes in frequency. A loop filter with an open-loop transfer function and set of loop constants, setting the damping factor equal to unity are provided.
Thermal boundary layer due to sudden heating of fluid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurkal, K.R.; Munukutla, S.

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers. 6 refs.
Thermal boundary layer due to sudden heating of fluid

NASA Astrophysics Data System (ADS)

Kurkal, K. R.; Munukutla, S.

1989-10-01

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers.
A comparative approach to closed-loop computation.

PubMed

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.
Classical and adaptive control of ex vivo skeletal muscle contractions using Functional Electrical Stimulation (FES)

PubMed Central

Shoemaker, Adam; Grange, Robert W.; Abaid, Nicole; Leonessa, Alexander

2017-01-01

Functional Electrical Stimulation is a promising approach to treat patients by stimulating the peripheral nerves and their corresponding motor neurons using electrical current. This technique helps maintain muscle mass and promote blood flow in the absence of a functioning nervous system. The goal of this work is to control muscle contractions from FES via three different algorithms and assess the most appropriate controller providing effective stimulation of the muscle. An open-loop system and a closed-loop system with three types of model-free feedback controllers were assessed for tracking control of skeletal muscle contractions: a Proportional-Integral (PI) controller, a Model Reference Adaptive Control algorithm, and an Adaptive Augmented PI system. Furthermore, a mathematical model of a muscle-mass-spring system was implemented in simulation to test the open-loop case and closed-loop controllers. These simulations were carried out and then validated through experiments ex vivo. The experiments included muscle contractions following four distinct trajectories: a step, sine, ramp, and square wave. Overall, the closed-loop controllers followed the stimulation trajectories set for all the simulated and tested muscles. When comparing the experimental outcomes of each controller, we concluded that the Adaptive Augmented PI algorithm provided the best closed-loop performance for speed of convergence and disturbance rejection. PMID:28273101
Gas turbine cooling system

DOEpatents

Bancalari, Eduardo E.

2001-01-01

A gas turbine engine (10) having a closed-loop cooling circuit (39) for transferring heat from the hot turbine section (16) to the compressed air (24) produced by the compressor section (12). The closed-loop cooling system (39) includes a heat exchanger (40) disposed in the flow path of the compressed air (24) between the outlet of the compressor section (12) and the inlet of the combustor (14). A cooling fluid (50) may be driven by a pump (52) located outside of the engine casing (53) or a pump (54) mounted on the rotor shaft (17). The cooling circuit (39) may include an orifice (60) for causing the cooling fluid (50) to change from a liquid state to a gaseous state, thereby increasing the heat transfer capacity of the cooling circuit (39).
Design of biomass management systems and components for closed loop life support systems

NASA Technical Reports Server (NTRS)

1991-01-01

The goal of the EGM 4000/1 Design class was to investigate a Biomass Management System (BMS) and design, fabricate, and test components for biomass management in a closed-loop life support system (CLLSS). The designs explored were to contribute to the development of NASA's Controlled Ecological Life Support System (CELSS) at Kennedy Space Center. Designs included a sectored plant growth unit, a container and transfer mechanism, and an air curtain system for fugitive particle control. The work performed by the class members is summarized.
Development of atomic force microscope with wide-band magnetic excitation for study of soft matter dynamics

NASA Astrophysics Data System (ADS)

Kageshima, Masami; Chikamoto, Takuma; Ogawa, Tatsuya; Hirata, Yoshiki; Inoue, Takahito; Naitoh, Yoshitaka; Li, Yan Jun; Sugawara, Yasuhiro

2009-02-01

In order to probe dynamical properties of mesoscopic soft matter systems such as polymers, structured liquid, etc., a new atomic force microscopy apparatus with a wide-band magnetic cantilever excitation system was developed. Constant-current driving of an electromagnet up to 1 MHz was implemented with a closed-loop driver circuit. Transfer function of a commercial cantilever attached with a magnetic particle was measured in a frequency range of 1-1000 kHz in distilled water. Effects of the laser spot position, distribution of the force exerted on the cantilever, and difference in the detection scheme on the obtained transfer function are discussed in comparison with theoretical predictions by other research groups. A preliminary result of viscoelasticity spectrum measurement of a single dextran chain is shown and is compared with a recent theoretical calculation.
DC servomechanism parameter identification: a Closed Loop Input Error approach.

PubMed

Garrido, Ruben; Miranda, Roger

2012-01-01

This paper presents a Closed Loop Input Error (CLIE) approach for on-line parametric estimation of a continuous-time model of a DC servomechanism functioning in closed loop. A standard Proportional Derivative (PD) position controller stabilizes the loop without requiring knowledge on the servomechanism parameters. The analysis of the identification algorithm takes into account the control law employed for closing the loop. The model contains four parameters that depend on the servo inertia, viscous, and Coulomb friction as well as on a constant disturbance. Lyapunov stability theory permits assessing boundedness of the signals associated to the identification algorithm. Experiments on a laboratory prototype allows evaluating the performance of the approach. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.
Control of a flexible link by shaping the closed loop frequency response function through optimised feedback filters

NASA Astrophysics Data System (ADS)

Del Vescovo, D.; D'Ambrogio, W.

1995-01-01

A frequency domain method is presented to design a closed-loop control for vibration reduction flexible mechanisms. The procedure is developed on a single-link flexible arm, driven by one rotary degree of freedom servomotor, although the same technique may be applied to similar systems such as supports for aerospace antennae or solar panels. The method uses the structural frequency response functions (FRFs), thus avoiding system identification, that produces modeling uncertainties. Two closed-loops are implemented: the inner loop uses acceleration feedback with the aim of making the FRF similar to that of an equivalent rigid link; the outer loop feeds back displacements to achieve a fast positioning response and null steady state error. In both cases, the controller type is established a priori, while actual characteristics are defined by an optimisation procedure in which the relevant FRF is constrained into prescribed bounds and stability is taken into account.
Turbofan engine control system design using the LQG/LTR methodology

NASA Technical Reports Server (NTRS)

Garg, Sanjay

1989-01-01

Application of the linear-quadratic-Gaussian with loop-transfer-recovery methodology to design of a control system for a simplified turbofan engine model is considered. The importance of properly scaling the plant to achieve the desired target feedback loop is emphasized. The steps involved in the application of the methodology are discussed via an example, and evaluation results are presented for a reduced-order compensator. The effect of scaling the plant on the stability robustness evaluation of the closed-loop system is studied in detail.
Turbofan engine control system design using the LQG/LTR methodology

NASA Technical Reports Server (NTRS)

Garg, Sanjay

1989-01-01

Application of the Linear-Quadratic-Gaussian with Loop-Transfer-Recovery methodology to design of a control system for a simplified turbofan engine model is considered. The importance of properly scaling the plant to achieve the desired Target-Feedback-Loop is emphasized. The steps involved in the application of the methodology are discussed via an example, and evaluation results are presented for a reduced-order compensator. The effect of scaling the plant on the stability robustness evaluation of the closed-loop system is studied in detail.
The influence of a prediction display on the quasi-linear describing function and remnant measured with an adaptive analog-pilot in a closed loop

NASA Technical Reports Server (NTRS)

Dey, D.

1972-01-01

The effect of a prediction display on the human transfer characteristics is explained with the aid of a quasi-linear model. The prediction display causes an increase of the gain factor and the lead factor, a diminishing of the lag factor and a decrease of the remnant. Altogether, these factors yield a smaller mean square value of the control deviation and a simultaneous decrease of the mean square value of the stick signal.
A closed expression for the UV-divergent parts of one-loop tensor integrals in dimensional regularization

NASA Astrophysics Data System (ADS)

Sulyok, G.

2017-07-01

Starting from the general definition of a one-loop tensor N-point function, we use its Feynman parametrization to calculate the ultraviolet (UV-)divergent part of an arbitrary tensor coefficient in the framework of dimensional regularization. In contrast to existing recursion schemes, we are able to present a general analytic result in closed form that enables direct determination of the UV-divergent part of any one-loop tensor N-point coefficient independent from UV-divergent parts of other one-loop tensor N-point coefficients. Simplified formulas and explicit expressions are presented for A-, B-, C-, D-, E-, and F-functions.
A uniform LMI formulation for tuning PID, multi-term fractional-order PID, and Tilt-Integral-Derivative (TID) for integer and fractional-order processes.

PubMed

Merrikh-Bayat, Farshad

2017-05-01

In this paper first the Multi-term Fractional-Order PID (MFOPID) whose transfer function is equal to [Formula: see text] , where k j and α j are unknown and known real parameters respectively, is introduced. Without any loss of generality, a special form of MFOPID with transfer function k p +k i /s+k d1 s+k d2 s μ where k p , k i , k d1 , and k d2 are unknown real and μ is a known positive real parameter, is considered. Similar to PID and TID, MFOPID is also linear in its parameters which makes it possible to study all of them in a same framework. Tuning the parameters of PID, TID, and MFOPID based on loop shaping using Linear Matrix Inequalities (LMIs) is discussed. For this purpose separate LMIs for closed-loop stability (of sufficient type) and adjusting different aspects of the open-loop frequency response are developed. The proposed LMIs for stability are obtained based on the Nyquist stability theorem and can be applied to both integer and fractional-order (not necessarily commensurate) processes which are either stable or have one unstable pole. Numerical simulations show that the performance of the four-variable MFOPID can compete the trivial five-variable FOPID and often excels PID and TID. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Open-Loop HIRF Experiments Performed on a Fault Tolerant Flight Control Computer

NASA Technical Reports Server (NTRS)

Koppen, Daniel M.

1997-01-01

During the third quarter of 1996, the Closed-Loop Systems Laboratory was established at the NASA Langley Research Center (LaRC) to study the effects of High Intensity Radiated Fields on complex avionic systems and control system components. This new facility provided a link and expanded upon the existing capabilities of the High Intensity Radiated Fields Laboratory at LaRC that were constructed and certified during 1995-96. The scope of the Closed-Loop Systems Laboratory is to place highly integrated avionics instrumentation into a high intensity radiated field environment, interface the avionics to a real-time flight simulation that incorporates aircraft dynamics, engines, sensors, actuators and atmospheric turbulence, and collect, analyze, and model aircraft performance. This paper describes the layout and functionality of the Closed-Loop Systems Laboratory, and the open-loop calibration experiments that led up to the commencement of closed-loop real-time flight experiments.
Centrifuge Testing of a Partially-Confined FC-72 Spray

DTIC Science & Technology

2006-11-01

induced body forces. Heat transfer associated with closed - loop spray cooling will be affected by acceleration body forces, the extent of which is not...impingement cooling, spray cooling, heat pipes , loop heat pipes , carbon foam impregnated with phase-change materials, and combinations of the above...reduced gravity and elevated gravity experiments to help prove viability of pulsating heat pipes (PHPs) for space applications. The PHPs, filled
An Investigation Relating Longitudinal Pilot-Induced Oscillation Tendency Rating to Describing Function Predictions for Rate-Limited Actuators

DTIC Science & Technology

2004-03-01

2-15 2-10. Pitch Tracking Closed Loop System for Gap Criterion...................................... 2-16 2-11. Four Resulting Gap ...Level 1 Minimize Resonance Closed Loop Bode Diagram ( ) ( ) s sCommand θ θ ( ) ( ) s sCommand θ θ         BWω 2-16 Gap Criterion...System for Gap Criterion In modern fly-by-wire aircraft, feedback is an integral part of obtaining more desirable closed loop flying qualities

Parameter estimation in linear models of the human operator in a closed loop with application of deterministic test signals

NASA Technical Reports Server (NTRS)

Vanlunteren, A.; Stassen, H. G.

1973-01-01

Parameter estimation techniques are discussed with emphasis on unbiased estimates in the presence of noise. A distinction between open and closed loop systems is made. A method is given based on the application of external forcing functions consisting of a sun of sinusoids; this method is thus based on the estimation of Fourier coefficients and is applicable for models with poles and zeros in open and closed loop systems.
A training rule which guarantees finite-region stability for a class of closed-loop neural-network control systems.

PubMed

Kuntanapreeda, S; Fullmer, R R

1996-01-01

A training method for a class of neural network controllers is presented which guarantees closed-loop system stability. The controllers are assumed to be nonlinear, feedforward, sampled-data, full-state regulators implemented as single hidden-layer neural networks. The controlled systems must be locally hermitian and observable. Stability of the closed-loop system is demonstrated by determining a Lyapunov function, which can be used to identify a finite stability region about the regulator point.
Fully probabilistic control design in an adaptive critic framework.

PubMed

Herzallah, Randa; Kárný, Miroslav

2011-12-01

Optimal stochastic controller pushes the closed-loop behavior as close as possible to the desired one. The fully probabilistic design (FPD) uses probabilistic description of the desired closed loop and minimizes Kullback-Leibler divergence of the closed-loop description to the desired one. Practical exploitation of the fully probabilistic design control theory continues to be hindered by the computational complexities involved in numerically solving the associated stochastic dynamic programming problem; in particular, very hard multivariate integration and an approximate interpolation of the involved multivariate functions. This paper proposes a new fully probabilistic control algorithm that uses the adaptive critic methods to circumvent the need for explicitly evaluating the optimal value function, thereby dramatically reducing computational requirements. This is a main contribution of this paper. Copyright © 2011 Elsevier Ltd. All rights reserved.
Robustness properties of LQG optimized compensators for collocated rate sensors

NASA Technical Reports Server (NTRS)

Balakrishnan, A. V.

1994-01-01

In this paper we study the robustness with respect to stability of the closed-loop system with collocated rate sensor using LQG (mean square rate) optimized compensators. Our main result is that the transmission zeros of the compensator are precisely the structure modes when the actuator/sensor locations are 'pinned' and/or 'clamped': i.e., motion in the direction sensed is not allowed. We have stability even under parameter mismatch, except in the unlikely situation where such a mode frequency of the assumed system coincides with an undamped mode frequency of the real system and the corresponding mode shape is an eigenvector of the compensator transfer function matrix at that frequency. For a truncated modal model - such as that of the NASA LaRC Phase Zero Evolutionary model - the transmission zeros of the corresponding compensator transfer function can be interpreted as the structure modes when motion in the directions sensed is prohibited.
Staged regenerative sorption heat pump

NASA Technical Reports Server (NTRS)

Jones, Jack A. (Inventor)

1995-01-01

A regenerative adsorbent heat pump process and system for cooling and heating a space. A sorbent is confined in a plurality of compressors of which at least four are first stage and at least four are second stage. The first stage operates over a first pressure region and the second stage over a second pressure region which is higher than the first. Sorbate from the first stage enters the second stage. The sorbate loop includes a condenser, expansion valve, evaporator and the compressors. A single sorbate loop can be employed for single-temperature-control such as air conditioning and heating. Two sorbate loops can be used for two-temperature-control as in a refrigerator and freezer. The evaporator temperatures control the freezer and refrigerator temperatures. Alternatively the refrigerator temperature can be cooled by the freezer with one sorbate loop. A heat transfer fluid is circulated in a closed loop which includes a radiator and the compressors. Low temperature heat is exhausted by the radiator. High temperature heat is added to the heat transfer fluid entering the compressors which are desorbing vapor. Heat is transferred from compressors which are sorbing vapor to the heat transfer fluid, and from the heat transfer fluid to the compressors which are desorbing vapor. Each compressor is subjected to the following phases, heating to its highest temperature, cooling down from its highest temperature, cooling to its lowest temperature, and warming up from its lowest temperature. The phases are repeated to complete a cycle and regenerate heat.
Closed-loop model identification of cooperative manipulators holding deformable objects

NASA Astrophysics Data System (ADS)

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%.
Digital PI-PD controller design for arbitrary order systems: Dominant pole placement approach.

PubMed

Dincel, Emre; Söylemez, Mehmet Turan

2018-05-02

In this paper, a digital PI-PD controller design method is proposed for arbitrary order systems with or without time-delay to achieve desired transient response in the closed-loop via dominant pole placement approach. The digital PI-PD controller design problem is solved by converting the original problem to the digital PID controller design problem. Firstly, parametrization of the digital PID controllers which assign dominant poles to desired location is done. After that the subset of digital PID controller parameters in which the remaining poles are located away from the dominant pole pair is found via Chebyshev polynomials. The obtained PID controller parameters are then transformed into the PI-PD controller parameters by considering the closed-loop controller zero and the design is completed. Success of the proposed design method is firstly demonstrated on an example transfer function and compared with the well-known PID controller methods from the literature through simulations. After that the design method is implemented on the fan and plate laboratory system in a real environment. Copyright © 2018 ISA. Published by Elsevier Ltd. All rights reserved.
Method and apparatus for operating a powertrain system upon detecting a stuck-closed clutch

DOEpatents

Hansen, R. Anthony

2014-02-18

A powertrain system includes a multi-mode transmission having a plurality of torque machines. A method for controlling the powertrain system includes identifying all presently applied clutches including commanded applied clutches and the stuck-closed clutch upon detecting one of the torque-transfer clutches is in a stuck-closed condition. A closed-loop control system is employed to control operation of the multi-mode transmission accounting for all the presently applied clutches.
Simulating closed- and open-loop voluntary movement: a nonlinear control-systems approach.

PubMed

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.
Non-polynomial closed string field theory: loops and conformal maps

NASA Astrophysics Data System (ADS)

Hua, Long; Kaku, Michio

1990-11-01

Recently, we proposed the complete classical action for the non-polynomial closed string field theory, which succesfully reproduced all closed string tree amplitudes. (The action was simultaneously proposed by the Kyoto group). In this paper, we analyze the structure of the theory. We (a) compute the explicit conformal map for all g-loop, p-puncture diagrams, (b) compute all one-loop, two-puncture maps in terms of hyper-elliptic functions, and (c) analyze their modular structure. We analyze, but do not resolve, the question of modular invariance.
Automated Droplet Manipulation Using Closed-Loop Axisymmetric Drop Shape Analysis.

PubMed

Yu, Kyle; Yang, Jinlong; Zuo, Yi Y

2016-05-17

Droplet manipulation plays an important role in a wide range of scientific and industrial applications, such as synthesis of thin-film materials, control of interfacial reactions, and operation of digital microfluidics. Compared to micron-sized droplets, which are commonly considered as spherical beads, millimeter-sized droplets are generally deformable by gravity, thus introducing nonlinearity into control of droplet properties. Such a nonlinear drop shape effect is especially crucial for droplet manipulation, even for small droplets, at the presence of surfactants. In this paper, we have developed a novel closed-loop axisymmetric drop shape analysis (ADSA), integrated into a constrained drop surfactometer (CDS), for manipulating millimeter-sized droplets. The closed-loop ADSA generalizes applications of the traditional drop shape analysis from a surface tension measurement methodology to a sophisticated tool for manipulating droplets in real time. We have demonstrated the feasibility and advantages of the closed-loop ADSA in three applications, including control of drop volume by automatically compensating natural evaporation, precise control of surface area variations for high-fidelity biophysical simulations of natural pulmonary surfactant, and steady control of surface pressure for in situ Langmuir-Blodgett transfer from droplets. All these applications have demonstrated the accuracy, versatility, applicability, and automation of this new ADSA-based droplet manipulation technique. Combining with CDS, the closed-loop ADSA holds great promise for advancing droplet manipulation in a variety of material and surface science applications, such as thin-film fabrication, self-assembly, and biophysical study of pulmonary surfactant.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Imani, Mohammadreza F., E-mail: mohamad.imani@gmail.com; Grbic, Anthony

One of the obstacles preventing wireless power transfer from becoming ubiquitous is their leakage of power: high-amplitude electromagnetic fields that can interfere with other electronic devices, increase health concerns, or hinder power metering. In this paper, we present near-field plates (NFPs) as a novel method to tailor the electromagnetic fields generated by a wireless power transfer system while maintaining high efficiency. NFPs are modulated arrays or surfaces designed to form prescribed near-field patterns. The NFP proposed in this paper consists of an array of loaded loops that are designed to confine the electromagnetic fields of a resonant transmitting loop tomore » the desired direction (receiving loop) while suppressing fields in other directions. The step-by-step design procedure for this device is outlined. Two NFPs are designed and examined in full-wave simulation. Their performance is shown to be in close agreement with the design predictions, thereby verifying the proposed design and operation. A NFP is also fabricated and experimentally shown to form a unidirectional wireless power transfer link with high efficiency.« less
Feasibility of outpatient fully integrated closed-loop control: first studies of wearable artificial pancreas.

PubMed

Kovatchev, Boris P; Renard, Eric; Cobelli, Claudio; Zisser, Howard C; Keith-Hynes, Patrick; Anderson, Stacey M; Brown, Sue A; Chernavvsky, Daniel R; Breton, Marc D; Farret, Anne; Pelletier, Marie-Josée; Place, Jérôme; Bruttomesso, Daniela; Del Favero, Simone; Visentin, Roberto; Filippi, Alessio; Scotton, Rachele; Avogaro, Angelo; Doyle, Francis J

2013-07-01

To evaluate the feasibility of a wearable artificial pancreas system, the Diabetes Assistant (DiAs), which uses a smart phone as a closed-loop control platform. Twenty patients with type 1 diabetes were enrolled at the Universities of Padova, Montpellier, and Virginia and at Sansum Diabetes Research Institute. Each trial continued for 42 h. The United States studies were conducted entirely in outpatient setting (e.g., hotel or guest house); studies in Italy and France were hybrid hospital-hotel admissions. A continuous glucose monitoring/pump system (Dexcom Seven Plus/Omnipod) was placed on the subject and was connected to DiAs. The patient operated the system via the DiAs user interface in open-loop mode (first 14 h of study), switching to closed-loop for the remaining 28 h. Study personnel monitored remotely via 3G or WiFi connection to DiAs and were available on site for assistance. The total duration of proper system communication functioning was 807.5 h (274 h in open-loop and 533.5 h in closed-loop), which represented 97.7% of the total possible time from admission to discharge. This exceeded the predetermined primary end point of 80% system functionality. This study demonstrated that a contemporary smart phone is capable of running outpatient closed-loop control and introduced a prototype system (DiAs) for further investigation. Following this proof of concept, future steps should include equipping insulin pumps and sensors with wireless capabilities, as well as studies focusing on control efficacy and patient-oriented clinical outcomes.
Experimental study on heat transfer to supercritical water flowing through tubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, M.; Gu, H.; Cheng, X.

2012-07-01

A test facility named SWAMUP (Supercritical Water Multi-Purpose Loop) has been constructed in Shanghai Jiao Tong Univ. to investigate heat transfer and pressure drop through tubes and rod bundles. SWAMUP is a closed loop with operating pressure up to 30 MPa, outlet-water temperature up to 550 deg. C, and mass flow rate up to 5 t/h. In this paper, experimental study has been carried out on heat transfer of supercritical water flowing vertically through tubes (ID=7.6 and 10 mm). A large number of test points in tubes has been obtained with a wide range of heat flux (200-1500 kw/m{sup 2})more » and mass flux (450-2000 kg/m{sup 2}s). Test results showed that heat transfer deterioration (HTD) caused by buoyancy effect only appears in upward flow and HTD caused by acceleration effect appears both in upward flow and downward flow. The heat transfer coefficients (HTC) produced in tube tests were compared with existing heat transfer correlations. (authors)« less
Closing the Loop on Space Waste

NASA Astrophysics Data System (ADS)

Meier, A. J.; Hintze, P. E.

2018-02-01

A heat transfer study of mission mixed waste streams in a reactor hot zone, along with solid, tar, and water recovery. This research enables reliability and benefit on waste conversion systems to manage our environmental impact, on- and off-Earth.
Closed loop air cooling system for combustion turbines

DOEpatents

Huber, David John; Briesch, Michael Scot

1998-01-01

Convective cooling of turbine hot parts using a closed loop system is disclosed. Preferably, the present invention is applied to cooling the hot parts of combustion turbine power plants, and the cooling provided permits an increase in the inlet temperature and the concomitant benefits of increased efficiency and output. In preferred embodiments, methods and apparatus are disclosed wherein air is removed from the combustion turbine compressor and delivered to passages internal to one or more of a combustor and turbine hot parts. The air cools the combustor and turbine hot parts via convection and heat is transferred through the surfaces of the combustor and turbine hot parts.
Closed loop air cooling system for combustion turbines

DOEpatents

Huber, D.J.; Briesch, M.S.

1998-07-21

Convective cooling of turbine hot parts using a closed loop system is disclosed. Preferably, the present invention is applied to cooling the hot parts of combustion turbine power plants, and the cooling provided permits an increase in the inlet temperature and the concomitant benefits of increased efficiency and output. In preferred embodiments, methods and apparatus are disclosed wherein air is removed from the combustion turbine compressor and delivered to passages internal to one or more of a combustor and turbine hot parts. The air cools the combustor and turbine hot parts via convection and heat is transferred through the surfaces of the combustor and turbine hot parts. 1 fig.
The multiple-function multi-input/multi-output digital controller system for the AFW wind-tunnel model

NASA Technical Reports Server (NTRS)

Hoadley, Sherwood T.; Mcgraw, Sandra M.

1992-01-01

A real time multiple-function digital controller system was developed for the Active Flexible Wing (AFW) Program. The digital controller system (DCS) allowed simultaneous execution of two control laws: flutter suppression and either roll trim or a rolling maneuver load control. The DCS operated within, but independently of, a slower host operating system environment, at regulated speeds up to 200 Hz. It also coordinated the acquisition, storage, and transfer of data for near real time controller performance evaluation and both open- and closed-loop plant estimation. It synchronized the operation of four different processing units, allowing flexibility in the number, form, functionality, and order of control laws, and variability in the selection of the sensors and actuators employed. Most importantly, the DCS allowed for the successful demonstration of active flutter suppression to conditions approximately 26 percent (in dynamic pressure) above the open-loop boundary in cases when the model was fixed in roll and up to 23 percent when it was free to roll. Aggressive roll maneuvers with load control were achieved above the flutter boundary. The purpose here is to present the development, validation, and wind tunnel testing of this multiple-function digital controller system.
Drell-Yan production at small q T , transverse parton distributions and the collinear anomaly

NASA Astrophysics Data System (ADS)

Becher, Thomas; Neubert, Matthias

2011-06-01

Using methods from effective field theory, an exact all-order expression for the Drell-Yan cross section at small transverse momentum is derived directly in q T space, in which all large logarithms are resummed. The anomalous dimensions and matching coefficients necessary for resummation at NNLL order are given explicitly. The precise relation between our result and the Collins-Soper-Sterman formula is discussed, and as a by-product the previously unknown three-loop coefficient A (3) is obtained. The naive factorization of the cross section at small transverse momentum is broken by a collinear anomaly, which prevents a process-independent definition of x T -dependent parton distribution functions. A factorization theorem is derived for the product of two such functions, in which the dependence on the hard momentum transfer is separated out. The remainder factors into a product of two functions of longitudinal momentum variables and xT2, whose renormalization-group evolution is derived and solved in closed form. The matching of these functions at small x T onto standard parton distributions is calculated at O(αs), while their anomalous dimensions are known to three loops.
Design strategies for dynamic closed-loop optogenetic neurocontrol in vivo

NASA Astrophysics Data System (ADS)

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, and the employment of continuous feedback to adjust stimulation in real-time can improve the quality of data collected using optogenetic manipulation.

Integrated tools for control-system analysis

NASA Technical Reports Server (NTRS)

Ostroff, Aaron J.; Proffitt, Melissa S.; Clark, David R.

1989-01-01

The basic functions embedded within a user friendly software package (MATRIXx) are used to provide a high level systems approach to the analysis of linear control systems. Various control system analysis configurations are assembled automatically to minimize the amount of work by the user. Interactive decision making is incorporated via menu options and at selected points, such as in the plotting section, by inputting data. There are five evaluations such as the singular value robustness test, singular value loop transfer frequency response, Bode frequency response, steady-state covariance analysis, and closed-loop eigenvalues. Another section describes time response simulations. A time response for random white noise disturbance is available. The configurations and key equations used for each type of analysis, the restrictions that apply, the type of data required, and an example problem are described. One approach for integrating the design and analysis tools is also presented.
Stability of two-mode internal resonance in a nonlinear oscillator

NASA Astrophysics Data System (ADS)

Zanette, Damián H.

2018-05-01

We analyze the stability of synchronized periodic motion for two coupled oscillators, representing two interacting oscillation modes in a nonlinear vibrating beam. The main oscillation mode is governed by the forced Duffing equation, while the other mode is linear. By means of the multiple-scale approach, the system is studied in two situations: an open-loop configuration, where the excitation is an external force, and a closed-loop configuration, where the system is fed back with an excitation obtained from the oscillation itself. The latter is relevant to the functioning of time-keeping micromechanical devices. While the accessible amplitudes and frequencies of stationary oscillations are identical in the two situations, their stability properties are substantially different. Emphasis is put on resonant oscillations, where energy transfer between the two coupled modes is maximized and, consequently, the strong interdependence between frequency and amplitude caused by nonlinearity is largely suppressed.
Open-cycle magnetohydrodynamic power plant based upon direct-contact closed-loop high-temperature heat exchanger

DOEpatents

Berry, G.F.; Minkov, V.; Petrick, M.

1981-11-02

A magnetohydrodynamic (MHD) power generating system is described in which ionized combustion gases with slag and seed are discharged from an MHD combustor and pressurized high temperature inlet air is introduced into the combustor for supporting fuel combustion at high temperatures necessary to ionize the combustion gases, and including a heat exchanger in the form of a continuous loop with a circulating heat transfer liquid such as copper oxide. The heat exchanger has an upper horizontal channel for providing direct contact between the heat transfer liquid and the combustion gases to cool the gases and condense the slag which thereupon floats on the heat transfer liquid and can be removed from the channel, and a lower horizontal channel for providing direct contact between the heat transfer liquid and pressurized air for preheating the inlet air. The system further includes a seed separator downstream of the heat exchanger.
Open-cycle magnetohydrodynamic power plant based upon direct-contact closed-loop high-temperature heat exchanger

DOEpatents

Berry, Gregory F.; Minkov, Vladimir; Petrick, Michael

1988-01-05

A magnetohydrodynamic (MHD) power generating system in which ionized combustion gases with slag and seed are discharged from an MHD combustor and pressurized high temperature inlet air is introduced into the combustor for supporting fuel combustion at high temperatures necessary to ionize the combustion gases, and including a heat exchanger in the form of a continuous loop with a circulating heat transfer liquid such as copper oxide. The heat exchanger has an upper horizontal channel for providing direct contact between the heat transfer liquid and the combustion gases to cool the gases and condense the slag which thereupon floats on the heat transfer liquid and can be removed from the channel, and a lower horizontal channel for providing direct contact between the heat transfer liquid and pressurized air for preheating the inlet air. The system further includes a seed separator downstream of the heat exchanger.
Open-cycle magnetohydrodynamic power plant based upon direct-contact closed-loop high-temperature heat exchanger

DOEpatents

Berry, Gregory F.; Minkov, Vladimir; Petrick, Michael

1988-01-01

A magnetohydrodynamic (MHD) power generating system in which ionized combustion gases with slag and seed are discharged from an MHD combustor and pressurized high temperature inlet air is introduced into the combustor for supporting fuel combustion at high temperatures necessary to ionize the combustion gases, and including a heat exchanger in the form of a continuous loop with a circulating heat transfer liquid such as copper oxide. The heat exchanger has an upper horizontal channel for providing direct contact between the heat transfer liquid and the combustion gases to cool the gases and condense the slag which thereupon floats on the heat transfer liquid and can be removed from the channel, and a lower horizontal channel for providing direct contact between the heat transfer liquid and pressurized air for preheating the inlet air. The system further includes a seed separator downstream of the heat exchanger.
A wirelessly-powered homecage with animal behavior analysis and closed-loop power control.

PubMed

Yaoyao Jia; Zheyuan Wang; Canales, Daniel; Tinkler, Morgan; Chia-Chun Hsu; Madsen, Teresa E; Mirbozorgi, S Abdollah; Rainnie, Donald; Ghovanloo, Maysam

2016-08-01

This paper presents a new EnerCage-homecage system, EnerCage-HC2, for longitudinal electrophysiology data acquisition experiments on small freely moving animal subjects, such as rodents. EnerCage-HC2 is equipped with multi-coil wireless power transmission (WPT), closed-loop power control, bidirectional data communication via Bluetooth Low Energy (BLE), and Microsoft Kinect® based animal behavior tracking and analysis. The EnerCage-HC2 achieves a homogeneous power transfer efficiency (PTE) of 14% on average, with ~42 mW power delivered to the load (PDL) at a nominal height of 7 cm by the closed-loop power control mechanism. The Microsoft Kinect® behavioral analysis algorithm can not only track the animal position in real-time but also classify 5 different types of rodent behaviors: standstill, walking, grooming, rearing, and rotating. A proof-of-concept in vivo experiment was conducted on two awake freely behaving rats while successfully operating a one-channel stimulator and generating an ethogram.
Eigenspace techniques for active flutter suppression

NASA Technical Reports Server (NTRS)

Garrard, William L.; Liebst, Bradley S.; Farm, Jerome A.

1987-01-01

The use of eigenspace techniques for the design of an active flutter suppression system for a hypothetical research drone is discussed. One leading edge and two trailing edge aerodynamic control surfaces and four sensors (accelerometers) are available for each wing. Full state control laws are designed by selecting feedback gains which place closed loop eigenvalues and shape closed loop eigenvectors so as to stabilize wing flutter and reduce gust loads at the wing root while yielding accepatable robustness and satisfying constrains on rms control surface activity. These controllers are realized by state estimators designed using an eigenvalue placement/eigenvector shaping technique which results in recovery of the full state loop transfer characteristics. The resulting feedback compensators are shown to perform almost as well as the full state designs. They also exhibit acceptable performance in situations in which the failure of an actuator is simulated.
Modeling of Atmospheric Turbulence as Disturbances for Control Design and Evaluation of High Speed Propulsion Systems

NASA Technical Reports Server (NTRS)

Kopasakis, George

2010-01-01

Atmospheric turbulence models are necessary for the design of both inlet/engine and flight controls, as well as for studying integrated couplings between the propulsion and the vehicle structural dynamics for supersonic vehicles. Models based on the Kolmogorov spectrum have been previously utilized to model atmospheric turbulence. In this paper, a more accurate model is developed in its representative fractional order form, typical of atmospheric disturbances. This is accomplished by first scaling the Kolmogorov spectral to convert them into finite energy von Karman forms. Then a generalized formulation is developed in frequency domain for these scale models that approximates the fractional order with the products of first order transfer functions. Given the parameters describing the conditions of atmospheric disturbances and utilizing the derived formulations, the objective is to directly compute the transfer functions that describe these disturbances for acoustic velocity, temperature, pressure and density. Utilizing these computed transfer functions and choosing the disturbance frequencies of interest, time domain simulations of these representative atmospheric turbulences can be developed. These disturbance representations are then used to first develop considerations for disturbance rejection specifications for the design of the propulsion control system, and then to evaluate the closed-loop performance.
A Method for Precision Closed-Loop Irrigation Using a Modified PID Control Algorithm

NASA Astrophysics Data System (ADS)

Goodchild, Martin; Kühn, Karl; Jenkins, Malcolm; Burek, Kazimierz; Dutton, Andrew

2016-04-01

The benefits of closed-loop irrigation control have been demonstrated in grower trials which show the potential for improved crop yields and resource usage. Managing water use by controlling irrigation in response to soil moisture changes to meet crop water demands is a popular approach but requires knowledge of closed-loop control practice. In theory, to obtain precise closed-loop control of a system it is necessary to characterise every component in the control loop to derive the appropriate controller parameters, i.e. proportional, integral & derivative (PID) parameters in a classic PID controller. In practice this is often difficult to achieve. Empirical methods are employed to estimate the PID parameters by observing how the system performs under open-loop conditions. In this paper we present a modified PID controller, with a constrained integral function, that delivers excellent regulation of soil moisture by supplying the appropriate amount of water to meet the needs of the plant during the diurnal cycle. Furthermore, the modified PID controller responds quickly to changes in environmental conditions, including rainfall events which can result in: controller windup, under-watering and plant stress conditions. The experimental work successfully demonstrates the functionality of a constrained integral PID controller that delivers robust and precise irrigation control. Coir substrate strawberry growing trial data is also presented illustrating soil moisture control and the ability to match water deliver to solar radiation.
In situ heat treatment process utilizing a closed loop heating system

DOEpatents

Vinegar, Harold J.; Nguyen, Scott Vinh

2010-12-07

Systems and methods for an in situ heat treatment process that utilizes a circulation system to heat one or more treatment areas are described herein. The circulation system may use a heated liquid heat transfer fluid that passes through piping in the formation to transfer heat to the formation. In some embodiments, the piping may be positioned in at least two of the wellbores.
Inverted Pendulum Standing Apparatus for Investigating Closed-Loop Control of Ankle Joint Muscle Contractions during Functional Electrical Stimulation.

PubMed

Tan, John F; Masani, Kei; Vette, Albert H; Zariffa, José; Robinson, Mark; Lynch, Cheryl; Popovic, Milos R

2014-01-01

The restoration of arm-free standing in individuals with paraplegia can be facilitated via functional electrical stimulation (FES). In developing adequate control strategies for FES systems, it remains challenging to test the performance of a particular control scheme on human subjects. In this study, we propose a testing platform for developing effective control strategies for a closed-loop FES system for standing. The Inverted Pendulum Standing Apparatus (IPSA) is a mechanical inverted pendulum, whose angular position is determined by the subject's ankle joint angle as controlled by the FES system while having the subject's body fixed in a standing frame. This approach provides a setup that is safe, prevents falling, and enables a research and design team to rigorously test various closed-loop controlled FES systems applied to the ankle joints. To demonstrate the feasibility of using the IPSA, we conducted a case series that employed the device for studying FES closed-loop controllers for regulating ankle joint kinematics during standing. The utilized FES system stimulated, in able-bodied volunteers, the plantarflexors as they prevent toppling during standing. Four different conditions were compared, and we were able to show unique performance of each condition using the IPSA. We concluded that the IPSA is a useful tool for developing and testing closed-loop controlled FES systems for regulating ankle joint position during standing.
Inverted Pendulum Standing Apparatus for Investigating Closed-Loop Control of Ankle Joint Muscle Contractions during Functional Electrical Stimulation

PubMed Central

Tan, John F.; Masani, Kei; Vette, Albert H.; Zariffa, José; Robinson, Mark; Lynch, Cheryl; Popovic, Milos R.

2014-01-01

The restoration of arm-free standing in individuals with paraplegia can be facilitated via functional electrical stimulation (FES). In developing adequate control strategies for FES systems, it remains challenging to test the performance of a particular control scheme on human subjects. In this study, we propose a testing platform for developing effective control strategies for a closed-loop FES system for standing. The Inverted Pendulum Standing Apparatus (IPSA) is a mechanical inverted pendulum, whose angular position is determined by the subject's ankle joint angle as controlled by the FES system while having the subject's body fixed in a standing frame. This approach provides a setup that is safe, prevents falling, and enables a research and design team to rigorously test various closed-loop controlled FES systems applied to the ankle joints. To demonstrate the feasibility of using the IPSA, we conducted a case series that employed the device for studying FES closed-loop controllers for regulating ankle joint kinematics during standing. The utilized FES system stimulated, in able-bodied volunteers, the plantarflexors as they prevent toppling during standing. Four different conditions were compared, and we were able to show unique performance of each condition using the IPSA. We concluded that the IPSA is a useful tool for developing and testing closed-loop controlled FES systems for regulating ankle joint position during standing. PMID:27350992
Optimizing the feedback control of Galvo scanners for laser manufacturing systems

NASA Astrophysics Data System (ADS)

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.
A methodology for the synthesis of robust feedback systems. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Milich, David Albert

1988-01-01

A new methodology is developed for the synthesis of linear, time-variant (LTI) controllers for multivariable LTI systems. The resulting closed-loop system is nominally stable and exhibits a known level of performance. In addition, robustness of the feedback system is guaranteed, i.e., stability and performance are retained in the presence of multiple unstructured uncertainty blocks located at various points in the feedback loop. The design technique is referred to as the Causality Recovery Methodology (CRM). The CRM relies on the Youla parameterization of all stabilizing compensators to ensure nominal stability of the feedback system. A frequency-domain inequality in terms of the structured singular value mu defines the robustness specification. The optimal compensator, with respect to the mu condition, is shown to be noncausal in general. The aim of the CRM is to find a stable, causal transfer function matrix that approximates the robustness characteristics of the optimal solution. The CRM, via a series of infinite-dimensional convex programs, produces a closed-loop system whose performance robustness is at least as good as that of any initial design. The algorithm is approximated by a finite dimensional process for the purposes of implementation. Two numerical examples confirm the potential viability of the CRM concept; however, the robustness improvement comes at the expense of increased computational burden and compensator complexity.
Real-time control of hind limb functional electrical stimulation using feedback from dorsal root ganglia recordings

NASA Astrophysics Data System (ADS)

Bruns, Tim M.; Wagenaar, Joost B.; Bauman, Matthew J.; Gaunt, Robert A.; Weber, Douglas J.

2013-04-01

Objective. Functional electrical stimulation (FES) approaches often utilize an open-loop controller to drive state transitions. The addition of sensory feedback may allow for closed-loop control that can respond effectively to perturbations and muscle fatigue. Approach. We evaluated the use of natural sensory nerve signals obtained with penetrating microelectrode arrays in lumbar dorsal root ganglia (DRG) as real-time feedback for closed-loop control of FES-generated hind limb stepping in anesthetized cats. Main results. Leg position feedback was obtained in near real-time at 50 ms intervals by decoding the firing rates of more than 120 DRG neurons recorded simultaneously. Over 5 m of effective linear distance was traversed during closed-loop stepping trials in each of two cats. The controller compensated effectively for perturbations in the stepping path when DRG sensory feedback was provided. The presence of stimulation artifacts and the quality of DRG unit sorting did not significantly affect the accuracy of leg position feedback obtained from the linear decoding model as long as at least 20 DRG units were included in the model. Significance. This work demonstrates the feasibility and utility of closed-loop FES control based on natural neural sensors. Further work is needed to improve the controller and electrode technologies and to evaluate long-term viability.
Real-time control of hind limb functional electrical stimulation using feedback from dorsal root ganglia recordings

PubMed Central

Bruns, Tim M; Wagenaar, Joost B; Bauman, Matthew J; Gaunt, Robert A; Weber, Douglas J

2013-01-01

Objective Functional electrical stimulation (FES) approaches often utilize an open-loop controller to drive state transitions. The addition of sensory feedback may allow for closed-loop control that can respond effectively to perturbations and muscle fatigue. Approach We evaluated the use of natural sensory nerve signals obtained with penetrating microelectrode arrays in lumbar dorsal root ganglia (DRG) as real-time feedback for closed-loop control of FES-generated hind limb stepping in anesthetized cats. Main results Leg position feedback was obtained in near real-time at 50 ms intervals by decoding the firing rates of more than 120 DRG neurons recorded simultaneously. Over 5 m of effective linear distance was traversed during closed-loop stepping trials in each of two cats. The controller compensated effectively for perturbations in the stepping path when DRG sensory feedback was provided. The presence of stimulation artifacts and the quality of DRG unit sorting did not significantly affect the accuracy of leg position feedback obtained from the linear decoding model as long as at least 20 DRG units were included in the model. Significance This work demonstrates the feasibility and utility of closed-loop FES control based on natural neural sensors. Further work is needed to improve the controller and electrode technologies and to evaluate long-term viability. PMID:23503062
Closed-loop conductance scanning tunneling spectroscopy: demonstrating the equivalence to the open-loop alternative.

PubMed

Hellenthal, Chris; Sotthewes, Kai; Siekman, Martin H; Kooij, E Stefan; Zandvliet, Harold J W

2015-01-01

We demonstrate the validity of using closed-loop z(V) conductance scanning tunneling spectroscopy (STS) measurements for the determination of the effective tunneling barrier by comparing them to more conventional open-loop I(z) measurements. Through the development of a numerical model, the individual contributions to the effective tunneling barrier present in these experiments, such as the work function and the presence of an image charge, are determined quantitatively. This opens up the possibility of determining tunneling barriers of both vacuum and molecular systems in an alternative and more detailed manner.
A theory of how active behavior stabilises neural activity: Neural gain modulation by closed-loop environmental feedback

PubMed Central

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 of neural fluctuations, across the brain, on closed-loop brain/body/environment interactions strongly supporting the idea that brain function cannot be fully understood through open-loop approaches alone. PMID:29342146
A theory of how active behavior stabilises neural activity: Neural gain modulation by closed-loop environmental feedback.

PubMed

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 of neural fluctuations, across the brain, on closed-loop brain/body/environment interactions strongly supporting the idea that brain function cannot be fully understood through open-loop approaches alone.
Simple piezoelectric-actuated mirror with 180 kHz servo bandwidth.

PubMed

Briles, Travis C; Yost, Dylan C; Cingöz, Arman; Ye, Jun; Schibli, Thomas R

2010-05-10

We present a high bandwidth piezoelectric-actuated mirror for length stabilization of an optical cavity. The actuator displays a transfer function with a flat amplitude response and greater than 135 masculine phase margin up to 200 kHz, allowing a 180 kHz unity gain frequency to be achieved in a closed servo loop. To the best of our knowledge, this actuator has achieved the largest servo bandwidth for a piezoelectric transducer (PZT). The actuator should be very useful in a wide variety of applications requiring precision control of optical lengths, including laser frequency stabilization, optical interferometers, and optical communications. (c) 2010 Optical Society of America.

Kalman filter estimation of human pilot-model parameters

NASA Technical Reports Server (NTRS)

Schiess, J. R.; Roland, V. R.

1975-01-01

The parameters of a human pilot-model transfer function are estimated by applying the extended Kalman filter to the corresponding retarded differential-difference equations in the time domain. Use of computer-generated data indicates that most of the parameters, including the implicit time delay, may be reasonably estimated in this way. When applied to two sets of experimental data obtained from a closed-loop tracking task performed by a human, the Kalman filter generated diverging residuals for one of the measurement types, apparently because of model assumption errors. Application of a modified adaptive technique was found to overcome the divergence and to produce reasonable estimates of most of the parameters.
Real-time tracking control of electro-hydraulic force servo systems using offline feedback control and adaptive control.

PubMed

Shen, Gang; Zhu, Zhencai; Zhao, Jinsong; Zhu, Weidong; Tang, Yu; Li, Xiang

2017-03-01

This paper focuses on an application of an electro-hydraulic force tracking controller combined with an offline designed feedback controller (ODFC) and an online adaptive compensator in order to improve force tracking performance of an electro-hydraulic force servo system (EHFS). A proportional-integral controller has been employed and a parameter-based force closed-loop transfer function of the EHFS is identified by a continuous system identification algorithm. By taking the identified system model as a nominal plant model, an H ∞ offline design method is employed to establish an optimized feedback controller with consideration of the performance, control efforts, and robustness of the EHFS. In order to overcome the disadvantage of the offline designed controller and cope with the varying dynamics of the EHFS, an online adaptive compensator with a normalized least-mean-square algorithm is cascaded to the force closed-loop system of the EHFS compensated by the ODFC. Some comparative experiments are carried out on a real-time EHFS using an xPC rapid prototype technology, and the proposed controller yields a better force tracking performance improvement. Copyright © 2016. Published by Elsevier Ltd.
Tuning algorithms for fractional order internal model controllers for time delay processes

NASA Astrophysics Data System (ADS)

Muresan, Cristina I.; Dutta, Abhishek; Dulf, Eva H.; Pinar, Zehra; Maxim, Anca; Ionescu, Clara M.

2016-03-01

This paper presents two tuning algorithms for fractional-order internal model control (IMC) controllers for time delay processes. The two tuning algorithms are based on two specific closed-loop control configurations: the IMC control structure and the Smith predictor structure. In the latter, the equivalency between IMC and Smith predictor control structures is used to tune a fractional-order IMC controller as the primary controller of the Smith predictor structure. Fractional-order IMC controllers are designed in both cases in order to enhance the closed-loop performance and robustness of classical integer order IMC controllers. The tuning procedures are exemplified for both single-input-single-output as well as multivariable processes, described by first-order and second-order transfer functions with time delays. Different numerical examples are provided, including a general multivariable time delay process. Integer order IMC controllers are designed in each case, as well as fractional-order IMC controllers. The simulation results show that the proposed fractional-order IMC controller ensures an increased robustness to modelling uncertainties. Experimental results are also provided, for the design of a multivariable fractional-order IMC controller in a Smith predictor structure for a quadruple-tank system.
Enhanced IMC design of load disturbance rejection for integrating and unstable processes with slow dynamics.

PubMed

Liu, Tao; Gao, Furong

2011-04-01

In view of the deficiencies in existing internal model control (IMC)-based methods for load disturbance rejection for integrating and unstable processes with slow dynamics, a modified IMC-based controller design is proposed to deal with step- or ramp-type load disturbance that is often encountered in engineering practices. By classifying the ways through which such load disturbance enters into the process, analytical controller formulae are correspondingly developed, based on a two-degree-of-freedom (2DOF) control structure that allows for separate optimization of load disturbance rejection from setpoint tracking. An obvious merit is that there is only a single adjustable parameter in the proposed controller, which in essence corresponds to the time constant of the closed-loop transfer function for load disturbance rejection, and can be monotonically tuned to meet a good trade-off between disturbance rejection performance and closed-loop robust stability. At the same time, robust tuning constraints are given to accommodate process uncertainties in practice. Illustrative examples from the recent literature are used to show effectiveness and merits of the proposed method for different cases of load disturbance. Copyright © 2010. Published by Elsevier Ltd.
Design of PI Controlled Non Isolated Bidirectional DC to DC Converter for Electric Vehicle Application

NASA Astrophysics Data System (ADS)

Geetha, A.; Subramani, C.; Thamizh Thentral, T. M.; Krithika, V.; Usha, S.

2018-04-01

Non isolated Bidirectional DC-DC Converter (NIBDDC) is a good interface between DC source and inverter Fed induction motor drive. This paper deals with comparison between open loop and PI controlled Bidirectional DC to DC Converter Inverter System (BDDCIS). The modelling and control of BDDC is becomes an important issue. Open loop BDDCIS and closed loop PI controlled BDDCIS are designed, modelled and simulated using Matlab- simulink and their results are presented. The investigations indicate superior performance of PI controlled BDDCIS. The proposed BDDCIS has advantages like bidirectional power transfer ability, reduced hardware count and improved dynamic response.
Statistical Time Series Models of Pilot Control with Applications to Instrument Discrimination

NASA Technical Reports Server (NTRS)

Altschul, R. E.; Nagel, P. M.; Oliver, F.

1984-01-01

A general description of the methodology used in obtaining the transfer function models and verification of model fidelity, frequency domain plots of the modeled transfer functions, numerical results obtained from an analysis of poles and zeroes obtained from z plane to s-plane conversions of the transfer functions, and the results of a study on the sequential introduction of other variables, both exogenous and endogenous into the loop are contained.
Some computational techniques for estimating human operator describing functions

NASA Technical Reports Server (NTRS)

Levison, W. H.

1986-01-01

Computational procedures for improving the reliability of human operator describing functions are described. Special attention is given to the estimation of standard errors associated with mean operator gain and phase shift as computed from an ensemble of experimental trials. This analysis pertains to experiments using sum-of-sines forcing functions. Both open-loop and closed-loop measurement environments are considered.
Closed-loop control of zebrafish response using a bioinspired robotic-fish in a preference test

PubMed Central

Kopman, Vladislav; Laut, Jeffrey; Polverino, Giovanni; Porfiri, Maurizio

2013-01-01

In this paper, we study the response of zebrafish to a robotic-fish whose morphology and colour pattern are inspired by zebrafish. Experiments are conducted in a three-chambered instrumented water tank where a robotic-fish is juxtaposed with an empty compartment, and the preference of live subjects is scored as the mean time spent in the vicinity of the tank's two lateral sides. The tail-beating of the robotic-fish is controlled in real-time based on feedback from fish motion to explore a spectrum of closed-loop systems, including proportional and integral controllers. Closed-loop control systems are complemented by open-loop strategies, wherein the tail-beat of the robotic-fish is independent of the fish motion. The preference space and the locomotory patterns of fish for each experimental condition are analysed and compared to understand the influence of real-time closed-loop control on zebrafish response. The results of this study show that zebrafish respond differently to the pattern of tail-beating motion executed by the robotic-fish. Specifically, the preference and behaviour of zebrafish depend on whether the robotic-fish tail-beating frequency is controlled as a function of fish motion and how such closed-loop control is implemented. PMID:23152102
Prediction-based sampled-data H∞ controller design for attitude stabilisation of a rigid spacecraft with disturbances

NASA Astrophysics Data System (ADS)

Zhu, Baolong; Zhang, Zhiping; Zhou, Ding; Ma, Jie; Li, Shunli

2017-08-01

This paper investigates the H∞ control problem of the attitude stabilisation of a rigid spacecraft with external disturbances using prediction-based sampled-data control strategy. Aiming to achieve a 'virtual' closed-loop system, a type of parameterised sampled-data controller is designed by introducing a prediction mechanism. The resultant closed-loop system is equivalent to a hybrid system featured by a continuous-time and an impulsive differential system. By using a time-varying Lyapunov functional, a generalised bounded real lemma (GBRL) is first established for a kind of impulsive differential system. Based on this GBRL and Lyapunov functional approach, a sufficient condition is derived to guarantee the closed-loop system to be asymptotically stable and to achieve a prescribed H∞ performance. In addition, the controller parameter tuning is cast into a convex optimisation problem. Simulation and comparative results are provided to illustrate the effectiveness of the developed control scheme.
Closed-loop for type 1 diabetes - an introduction and appraisal for the generalist.

PubMed

Bally, Lia; Thabit, Hood; Hovorka, Roman

2017-01-23

Rapid progress over the past decade has been made with the development of the 'Artificial Pancreas', also known as the closed-loop system, which emulates the feedback glucose-responsive functionality of the pancreatic beta cell. The recent FDA approval of the first hybrid closed-loop system makes the Artificial Pancreas a realistic therapeutic option for people with type 1 diabetes. In anticipation of its advent into clinical care, we provide a primer and appraisal of this novel therapeutic approach in type 1 diabetes for healthcare professionals and non-specialists in the field. Randomised clinical studies in outpatient and home settings have shown improved glycaemic outcomes, reduced risk of hypoglycaemia and positive user attitudes. User input and interaction with existing closed-loop systems, however, are still required. Therefore, management of user expectations, as well as training and support by healthcare providers are key to ensure optimal uptake, satisfaction and acceptance of the technology. An overview of closed-loop technology and its clinical implications are discussed, complemented by our extensive hands-on experience with closed-loop system use during free daily living. The introduction of the artificial pancreas into clinical practice represents a milestone towards the goal of improving the care of people with type 1 diabetes. There remains a need to understand the impact of user interaction with the technology, and its implication on current diabetes management and care.
Functional Loop Dynamics of the Streptavidin-Biotin Complex

PubMed Central

Song, Jianing; Li, Yongle; Ji, Changge; Zhang, John Z. H.

2015-01-01

Accelerated molecular dynamics (aMD) simulation is employed to study the functional dynamics of the flexible loop3-4 in the strong-binding streptavidin-biotin complex system. Conventional molecular (cMD) simulation is also performed for comparison. The present study reveals the following important properties of the loop dynamics: (1) The transition of loop3-4 from open to closed state is observed in 200 ns aMD simulation. (2) In the absence of biotin binding, the open-state streptavidin is more stable, which is consistent with experimental evidences. The free energy (ΔG) difference is about 5 kcal/mol between two states. But with biotin binding, the closed state is more stable due to electrostatic and hydrophobic interactions between the loop3-4 and biotin. (3) The closure of loop3-4 is concerted to the stable binding of biotin to streptavidin. When the loop3-4 is in its open-state, biotin moves out of the binding pocket, indicating that the interactions between the loop3-4 and biotin are essential in trapping biotin in the binding pocket. (4) In the tetrameric streptavidin system, the conformational change of the loop3-4 in each monomer is independent of each other. That is, there is no cooperative binding for biotin bound to the four subunits of the tetramer. PMID:25601277
Does Mckuer's Law Hold for Heart Rate Control via Biofeedback Display?

NASA Technical Reports Server (NTRS)

Courter, B. J.; Jex, H. R.

1984-01-01

Some persons can control their pulse rate with the aid of a biofeedback display. If the biofeedback display is modified to show the error between a command pulse-rate and the measured rate, a compensatory (error correcting) heart rate tracking control loop can be created. The dynamic response characteristics of this control loop when subjected to step and quasi-random disturbances were measured. The control loop includes a beat-to-beat cardiotachmeter differenced with a forcing function from a quasi-random input generator; the resulting error pulse-rate is displayed as feedback. The subject acts to null the displayed pulse-rate error, thereby closing a compensatory control loop. McRuer's Law should hold for this case. A few subjects already skilled in voluntary pulse-rate control were tested for heart-rate control response. Control-law properties are derived, such as: crossover frequency, stability margins, and closed-loop bandwidth. These are evaluated for a range of forcing functions and for step as well as random disturbances.
Method-Unifying View of Loop-Formation Kinetics in Peptide and Protein Folding.

PubMed

Jacob, Maik H; D'Souza, Roy N; Schwarzlose, Thomas; Wang, Xiaojuan; Huang, Fang; Haas, Elisha; Nau, Werner M

2018-04-26

Protein folding can be described as a probabilistic succession of events in which the peptide chain forms loops closed by specific amino acid residue contacts, herein referred to as loop nodes. To measure loop rates, several photophysical methods have been introduced where a pair of optically active probes is incorporated at selected chain positions and the excited probe undergoes contact quenching (CQ) upon collision with the second probe. The quenching mechanisms involved triplet-triplet energy transfer, photoinduced electron transfer, and collision-induced fluorescence quenching, where the fluorescence of Dbo, an asparagine residue conjugated to 2,3-diazabicyclo[2.2.2]octane, is quenched by tryptophan. The discrepancy between the loop rates afforded from these three CQ techniques has, however, remained unresolved. In analyzing this discrepancy, we now report two short-distance FRET methods where Dbo acts as an energy acceptor in combination with tryptophan and naphtylalanine, two donors with largely different fluorescence lifetimes of 1.3 and 33 ns, respectively. Despite the different quenching mechanisms, the rates from FRET and CQ methods were, surprisingly, of comparable magnitude. This combination of FRET and CQ data led to a unifying physical model and to the conclusion that the rate of loop formation in folding reactions varies not only with the kind and number of residues that constitute the chain but also in particular with the size and properties of the residues that constitute the loop node.
Coupled Riccati equations for complex plane constraint

NASA Technical Reports Server (NTRS)

Strong, Kristin M.; Sesak, John R.

1991-01-01

A new Linear Quadratic Gaussian design method is presented which provides prescribed imaginary axis pole placement for optimal control and estimation systems. This procedure contributes another degree of design freedom to flexible spacecraft control. Current design methods which interject modal damping into the system tend to have little affect on modal frequencies, i.e., they predictably shift open plant poles horizontally in the complex plane to form the closed loop controller or estimator pole constellation, but make little provision for vertical (imaginary axis) pole shifts. Imaginary axis shifts which reduce the closed loop model frequencies (the bandwidths) are desirable since they reduce the sensitivity of the system to noise disturbances. The new method drives the closed loop modal frequencies to predictable (specified) levels, frequencies as low as zero rad/sec (real axis pole placement) can be achieved. The design procedure works through rotational and translational destabilizations of the plant, and a coupling of two independently solved algebraic Riccati equations through a structured state weighting matrix. Two new concepts, gain transference and Q equivalency, are introduced and their use shown.
Joint angle sensors for closed-loop control

NASA Astrophysics Data System (ADS)

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.
[Research on the Clinical Alarm Management Mechanism Based on Closed-loop Control Theory].

PubMed

Lin, Zhongkuan; Zheng, Kun; Shen, Yunming; Wu, Yunyun

2018-05-30

This paper proposes a clinical alarm management system based on the theory of the closed loop control. The alarm management mechanism can be divided into the expected standard, improving execution rule, rule execution, medical devices with alarm functions, results analysis strategy and the output link. And, we make relevant application and discussion. Results showed that the mechanism can be operable and effective.
Galileo attitude and articulation control subsystem closed loop testing

NASA Technical Reports Server (NTRS)

Lembeck, M. F.; Pignatano, N. D.

1983-01-01

In order to ensure the reliable operation of the Attitude and Articulation Control Subsystem (AACS) which will guide the Galileo spacecraft on its two and one-half year journey to Jupiter, the AACS is being rigorously tested. The primary objectives of the test program are the verification of the AACS's form, fit, and function, especially with regard to subsystem external interfaces and the functional operation of the flight software. Attention is presently given to the Galileo Closed Loop Test System, which simulates the dynamic and 'visual' flight environment for AACS components in the laboratory.
An Exploratory Investigation on the Use of Closed-Loop Electrical Stimulation to Assist Individuals with Stroke to Perform Fine Movements with Their Hemiparetic Arm.

PubMed

Lew, Brian; Alavi, Nezam; Randhawa, Bubblepreet K; Menon, Carlo

2016-01-01

Stroke is the leading cause of upper limb impairments resulting in disability. Modern rehabilitation includes training with robotic exoskeletons and functional electrical stimulation (FES). However, there is a gap in knowledge to define the detailed use of FES in stroke rehabilitation. In this paper, we explore applying closed-loop FES to the upper extremities of healthy volunteers and individuals with a hemiparetic arm resulting from stroke. We used a set of gyroscopes to monitor arm movements and used a non-linear controller, namely, the robust integral of the sign of the error (RISE), to assess the viability of controlling FES in closed loop. Further, we explored the application of closed-loop FES in improving functional tasks performed by individuals with stroke. Four healthy individuals of ages 27-32 years old and five individuals with stroke of ages 61-83 years old participated in this study. We used the Rehastim FES unit (Hasomed Ltd.) with real-time modulation of pulse width and amplitude. Both healthy and stroke individuals were tested in RISE-controlled single and multi-joint upper limb motions following first a sinusoidal trajectory. Individuals with stroke were also asked to perform the following functional tasks: picking up a basket, picking and placing an object on a table, cutting a pizza, pulling back a chair, eating with a spoon, as well as using a stapler and grasping a pen. Healthy individuals were instructed to keep their arm relaxed during the experiment. Most individuals with stroke were able to follow the sinusoid trajectories with their arm joints under the sole excitation of the closed-loop-controlled FES. One individual with stroke, who was unable to perform any of the functional tasks independently, succeeded in completing all the tasks when FES was used. Three other individuals with stroke, who were unable to complete a few tasks independently, completed some of them when FES was used. The remaining stroke participant was able to complete all tasks with and without FES. Our results suggest that individuals with a low Fugl-Meyer score or a higher level of disability may benefit the most with the use of closed-loop-controlled FES.
An Exploratory Investigation on the Use of Closed-Loop Electrical Stimulation to Assist Individuals with Stroke to Perform Fine Movements with Their Hemiparetic Arm

PubMed Central

Lew, Brian; Alavi, Nezam; Randhawa, Bubblepreet K.; Menon, Carlo

2016-01-01

Stroke is the leading cause of upper limb impairments resulting in disability. Modern rehabilitation includes training with robotic exoskeletons and functional electrical stimulation (FES). However, there is a gap in knowledge to define the detailed use of FES in stroke rehabilitation. In this paper, we explore applying closed-loop FES to the upper extremities of healthy volunteers and individuals with a hemiparetic arm resulting from stroke. We used a set of gyroscopes to monitor arm movements and used a non-linear controller, namely, the robust integral of the sign of the error (RISE), to assess the viability of controlling FES in closed loop. Further, we explored the application of closed-loop FES in improving functional tasks performed by individuals with stroke. Four healthy individuals of ages 27–32 years old and five individuals with stroke of ages 61–83 years old participated in this study. We used the Rehastim FES unit (Hasomed Ltd.) with real-time modulation of pulse width and amplitude. Both healthy and stroke individuals were tested in RISE-controlled single and multi-joint upper limb motions following first a sinusoidal trajectory. Individuals with stroke were also asked to perform the following functional tasks: picking up a basket, picking and placing an object on a table, cutting a pizza, pulling back a chair, eating with a spoon, as well as using a stapler and grasping a pen. Healthy individuals were instructed to keep their arm relaxed during the experiment. Most individuals with stroke were able to follow the sinusoid trajectories with their arm joints under the sole excitation of the closed-loop-controlled FES. One individual with stroke, who was unable to perform any of the functional tasks independently, succeeded in completing all the tasks when FES was used. Three other individuals with stroke, who were unable to complete a few tasks independently, completed some of them when FES was used. The remaining stroke participant was able to complete all tasks with and without FES. Our results suggest that individuals with a low Fugl–Meyer score or a higher level of disability may benefit the most with the use of closed-loop-controlled FES. PMID:27014683
Multi-Nozzle Spray Cooling in a Closed Loop (POSTPRINT)

DTIC Science & Technology

2011-03-01

characteristics and critical heat flux (CHF) at cooling surfaces (Sehmbey et al., 1992, Mudawar and Estes, 1996, Rini et al., 2002, Lin and Ponnappan, 2003...surface characteristics in evaporative spray cooling, Journal of Thermophysics and heat Transfer, 1992, Vol. 6, pp. 505-512. 3. Mudawar , I., and

System identification from closed-loop data with known output feedback dynamics

NASA Technical Reports Server (NTRS)

Phan, Minh; Juang, Jer-Nan; Horta, Lucas G.; Longman, Richard W.

1992-01-01

This paper presents a procedure to identify the open loop systems when it is operating under closed loop conditions. First, closed loop excitation data are used to compute the system open loop and closed loop Markov parameters. The Markov parameters, which are the pulse response samples, are then used to compute a state space representation of the open loop system. Two closed loop configurations are considered in this paper. The closed loop system can have either a linear output feedback controller or a dynamic output feedback controller. Numerical examples are provided to illustrate the proposed closed loop identification method.
Closed-Loop- and Decision-Assist-Guided Fluid Therapy of Human Hemorrhage.

PubMed

Hundeshagen, Gabriel; Kramer, George C; Ribeiro Marques, Nicole; Salter, Michael G; Koutrouvelis, Aristides K; Li, Husong; Solanki, Daneshvari R; Indrikovs, Alexander; Seeton, Roger; Henkel, Sheryl N; Kinsky, Michael P

2017-10-01

We sought to evaluate the efficacy, efficiency, and physiologic consequences of automated, endpoint-directed resuscitation systems and compare them to formula-based bolus resuscitation. Experimental human hemorrhage and resuscitation. Clinical research laboratory. Healthy volunteers. Subjects (n = 7) were subjected to hemorrhage and underwent a randomized fluid resuscitation scheme on separate visits 1) formula-based bolus resuscitation; 2) semiautonomous (decision assist) fluid administration; and 3) fully autonomous (closed loop) resuscitation. Hemodynamic variables, volume shifts, fluid balance, and cardiac function were monitored during hemorrhage and resuscitation. Treatment modalities were compared based on resuscitation efficacy and efficiency. All approaches achieved target blood pressure by 60 minutes. Following hemorrhage, the total amount of infused fluid (bolus resuscitation: 30 mL/kg, decision assist: 5.6 ± 3 mL/kg, closed loop: 4.2 ± 2 mL/kg; p < 0.001), plasma volume, extravascular volume (bolus resuscitation: 17 ± 4 mL/kg, decision assist: 3 ± 1 mL/kg, closed loop: -0.3 ± 0.3 mL/kg; p < 0.001), body weight, and urinary output remained stable under decision assist and closed loop and were significantly increased under bolus resuscitation. Mean arterial pressure initially decreased further under bolus resuscitation (-10 mm Hg; p < 0.001) and was lower under bolus resuscitation than closed loop at 20 minutes (bolus resuscitation: 57 ± 2 mm Hg, closed loop: 69 ± 4 mm Hg; p = 0.036). Colloid osmotic pressure (bolus resuscitation: 19.3 ± 2 mm Hg, decision assist, closed loop: 24 ± 0.4 mm Hg; p < 0.05) and hemoglobin concentration were significantly decreased after bolus fluid administration. We define efficacy of decision-assist and closed-loop resuscitation in human hemorrhage. In comparison with formula-based bolus resuscitation, both semiautonomous and autonomous approaches were more efficient in goal-directed resuscitation of hemorrhage. They provide favorable conditions for the avoidance of over-resuscitation and its adverse clinical sequelae. Decision-assist and closed-loop resuscitation algorithms are promising technological solutions for constrained environments and areas of limited resources.
Accessibility, stabilizability, and feedback control of continuous orbital transfer.

PubMed

Gurfil, Pini

2004-05-01

This paper investigates the problem of low-thrust orbital transfer using orbital element feedback from a control-theoretic standpoint, concepts of controllability, feedback stabilizability, and their interaction. The Gauss variational equations (GVEs) are used to model the state-space dynamics. First, the notion of accessibility, a weaker form of controllability, is presented. It is then shown that the GVEs are globally accessible. Based on the accessibility result, a nonlinear feedback controller is derived that asymptotically steers a vehicle from an initial elliptic Keplerian orbit to any given elliptic Keplerian orbit. The performance of the new controller is illustrated by simulating an orbital transfer between two geosynchronous Earth orbits. It is shown that the low-thrust controller requires less fuel than an impulsive maneuver for the same transfer time. Closed-form, analytic expressions for the new orbital transfer controller are given. Finally, it is proved, based on a topological nonlinear stabilizability test, that there does not exist a continuous closed-loop controller that can transfer a spacecraft to a parabolic escape trajectory.
Conformational motions regulate phosphoryl transfer in related protein tyrosine phosphatases

PubMed Central

Whittier, Sean K.; Hengge, Alvan C.; Loria, J. Patrick

2014-01-01

Many studies have implicated a role for conformational motions during the catalytic cycle, acting to optimize the binding pocket or facilitate product release, but a more intimate role in the chemical reaction has not been described. We address this by monitoring active-site loop motion in two protein tyrosine phosphatases (PTPs) using NMR spectroscopy. The PTPs, YopH and PTP1B, have very different catalytic rates, however we find in both that the active-site loop closes to its catalytically competent position at rates that mirror the phosphotyrosine cleavage kinetics. This loop contains the catalytic acid, suggesting that loop closure occurs concomitantly with the protonation of the leaving group tyrosine and explains the different kinetics of two otherwise chemically and mechanistically indistinguishable enzymes. PMID:23970698
Closed Loop Experiment Manager (CLEM)-An Open and Inexpensive Solution for Multichannel Electrophysiological Recordings and Closed Loop Experiments.

PubMed

Hazan, Hananel; Ziv, Noam E

2017-01-01

There is growing need for multichannel electrophysiological systems that record from and interact with neuronal systems in near real-time. Such systems are needed, for example, for closed loop, multichannel electrophysiological/optogenetic experimentation in vivo and in a variety of other neuronal preparations, or for developing and testing neuro-prosthetic devices, to name a few. Furthermore, there is a need for such systems to be inexpensive, reliable, user friendly, easy to set-up, open and expandable, and possess long life cycles in face of rapidly changing computing environments. Finally, they should provide powerful, yet reasonably easy to implement facilities for developing closed-loop protocols for interacting with neuronal systems. Here, we survey commercial and open source systems that address these needs to varying degrees. We then present our own solution, which we refer to as Closed Loop Experiments Manager (CLEM). CLEM is an open source, soft real-time, Microsoft Windows desktop application that is based on a single generic personal computer (PC) and an inexpensive, general-purpose data acquisition board. CLEM provides a fully functional, user-friendly graphical interface, possesses facilities for recording, presenting and logging electrophysiological data from up to 64 analog channels, and facilities for controlling external devices, such as stimulators, through digital and analog interfaces. Importantly, it includes facilities for running closed-loop protocols written in any programming language that can generate dynamic link libraries (DLLs). We describe the application, its architecture and facilities. We then demonstrate, using networks of cortical neurons growing on multielectrode arrays (MEA) that despite its reliance on generic hardware, its performance is appropriate for flexible, closed-loop experimentation at the neuronal network level.
Closed Loop Experiment Manager (CLEM)—An Open and Inexpensive Solution for Multichannel Electrophysiological Recordings and Closed Loop Experiments

PubMed Central

Hazan, Hananel; Ziv, Noam E.

2017-01-01

There is growing need for multichannel electrophysiological systems that record from and interact with neuronal systems in near real-time. Such systems are needed, for example, for closed loop, multichannel electrophysiological/optogenetic experimentation in vivo and in a variety of other neuronal preparations, or for developing and testing neuro-prosthetic devices, to name a few. Furthermore, there is a need for such systems to be inexpensive, reliable, user friendly, easy to set-up, open and expandable, and possess long life cycles in face of rapidly changing computing environments. Finally, they should provide powerful, yet reasonably easy to implement facilities for developing closed-loop protocols for interacting with neuronal systems. Here, we survey commercial and open source systems that address these needs to varying degrees. We then present our own solution, which we refer to as Closed Loop Experiments Manager (CLEM). CLEM is an open source, soft real-time, Microsoft Windows desktop application that is based on a single generic personal computer (PC) and an inexpensive, general-purpose data acquisition board. CLEM provides a fully functional, user-friendly graphical interface, possesses facilities for recording, presenting and logging electrophysiological data from up to 64 analog channels, and facilities for controlling external devices, such as stimulators, through digital and analog interfaces. Importantly, it includes facilities for running closed-loop protocols written in any programming language that can generate dynamic link libraries (DLLs). We describe the application, its architecture and facilities. We then demonstrate, using networks of cortical neurons growing on multielectrode arrays (MEA) that despite its reliance on generic hardware, its performance is appropriate for flexible, closed-loop experimentation at the neuronal network level. PMID:29093659
Kuiper Airborne Observatory's Telescope Stabilization System: Disturbance Sensitivity Reduction Via Velocity Loop Feedback

NASA Technical Reports Server (NTRS)

Lawrence, David P.; Tsui, K. C.; Tucker, John; Mancini, Ronald E. (Technical Monitor)

1995-01-01

In July of 1994 the Kuiper Airborne Observatory's (KAO) Telescope Stabilization System (TSS) was upgraded to meet performance goals necessary to view the Shoemaker-Levy 9 comet collision with Jupiter. The KAO is a modified C-141 Aircraft supporting a 36 inch Infrared telescope used to gather and analyze astronomical data. Before the upgrade, the TSS exhibited approximately a 10 arc-second resolution pointing accuracy. The majority of the inaccuracy was attributable to aircraft vibration and wind buffeting entering through the aircraft's telescope door opening; in other words, the TSS was overly sensitive to external disturbances. Because of power limitations and noise requirements, improving the pointing accuracy of the telescope required more sophistication than simply raising the bandwidth as some classical control strategies might suggest. Instead, relationships were developed between the disturbance sensitivity and closed loop transfer functions. These relationships suggested that employing velocity feedback along with an increase in current loop gain would dramatically improve the pointing resolution of the TSS by decreasing the control system's sensitivity to external disturbances. With the implementation of some classical control techniques and the above philosophy, the KAO's TSS's resolution was improved to approximately 2-3 arc-seconds.
Movement Forms: A Graph-Dynamic Perspective

PubMed Central

Saltzman, Elliot; Holt, Ken

2014-01-01

The focus of this paper is on characterizing the physical movement forms (e.g., walk, crawl, roll, etc.) that can be used to actualize abstract, functionally-specified behavioral goals (e.g., locomotion). Emphasis is placed on how such forms are distinguished from one another, in part, by the set of topological patterns of physical contact between agent and environment (i.e., the set of physical graphs associated with each form) and the transitions among these patterns displayed over the course of performance (i.e., the form’s physical graph dynamics). Crucial in this regard is the creation and dissolution of loops in these graphs, which can be related to the distinction between open and closed kinematic chains. Formal similarities are described within the theoretical framework of task-dynamics between physically-closed kinematic chains (physical loops) that are created during various movement forms and functionally-closed kinematic chains (functional loops) that are associated with task-space control of end-effectors; it is argued that both types of loop must be flexibly incorporated into the coordinative structures that govern skilled action. Final speculation is focused on the role of graphs and their dynamics, not only in processes of coordination and control for individual agents, but also in processes of inter-agent coordination and the coupling of agents with (non-sentient) environmental objects. PMID:24910507
Movement Forms: A Graph-Dynamic Perspective.

PubMed

Saltzman, Elliot; Holt, Ken

2014-01-01

The focus of this paper is on characterizing the physical movement forms (e.g., walk, crawl, roll, etc.) that can be used to actualize abstract, functionally-specified behavioral goals (e.g., locomotion). Emphasis is placed on how such forms are distinguished from one another, in part, by the set of topological patterns of physical contact between agent and environment (i.e., the set of physical graphs associated with each form) and the transitions among these patterns displayed over the course of performance (i.e., the form's physical graph dynamics ). Crucial in this regard is the creation and dissolution of loops in these graphs, which can be related to the distinction between open and closed kinematic chains. Formal similarities are described within the theoretical framework of task-dynamics between physically-closed kinematic chains (physical loops) that are created during various movement forms and functionally-closed kinematic chains (functional loops) that are associated with task-space control of end-effectors; it is argued that both types of loop must be flexibly incorporated into the coordinative structures that govern skilled action. Final speculation is focused on the role of graphs and their dynamics, not only in processes of coordination and control for individual agents, but also in processes of inter-agent coordination and the coupling of agents with (non-sentient) environmental objects.
Experimental Study of a Nitrogen Natural Circulation Loop at Low Heat Flux

NASA Astrophysics Data System (ADS)

Baudouy, B.

2010-04-01

A natural convection circulation loop in liquid nitrogen, i.e. an open thermosiphon flow configuration, has been investigated experimentally near atmospheric pressure. The experiments were conducted on a 2 m high loop with a copper tube of 10 mm inner diameter uniformly heated over a length of 0.95 m. Evolution of the total mass flow rate of the loop and the pressure difference along the tube are described. We also report the boiling curves where single phase and two-phase flows are identified with increasing heat flux. We focus our heat transfer analysis on the single phase regime where mixed convection is encountered. A heat transfer coefficient correlation is proposed. We also examine the boiling incipience as a function of the tube height.
Heat exchanger with oscillating flow

NASA Technical Reports Server (NTRS)

Scotti, Stephen J. (Inventor); Blosser, Max L. (Inventor); Camarda, Charles J. (Inventor)

1992-01-01

Various heat exchange apparatuses are described in which an oscillating flow of primary coolant is used to dissipate an incident heat flux. The oscillating flow may be imparted by a reciprocating piston, a double action twin reciprocating piston, fluidic oscillators, or electromagnetic pumps. The oscillating fluid flows through at least one conduit in either an open loop or a closed loop. A secondary flow of coolant may be used to flow over the outer walls of at least one conduit to remove heat transferred from the primary coolant to the walls of the conduit.
Heat exchanger with oscillating flow

NASA Technical Reports Server (NTRS)

Scotti, Stephen J. (Inventor); Blosser, Max L. (Inventor); Camarda, Charles J. (Inventor)

1993-01-01

Various heat exchange apparatuses are described in which an oscillating flow of primary coolant is used to dissipate an incident heat flux. The oscillating flow may be imparted by a reciprocating piston, a double action twin reciprocating piston, fluidic oscillators or electromagnetic pumps. The oscillating fluid flows through at least one conduit in either an open loop or a closed loop. A secondary flow of coolant may be used to flow over the outer walls of at least one conduit to remove heat transferred from the primary coolant to the walls of the conduit.
A new class of energy based control laws for revolute robot arms - Tracking control, robustness enhancement and adaptive control

NASA Technical Reports Server (NTRS)

Wen, John T.; Kreutz, Kenneth; Bayard, David S.

1988-01-01

A class of joint-level control laws for all-revolute robot arms is introduced. The analysis is similar to the recently proposed energy Liapunov function approach except that the closed-loop potential function is shaped in accordance with the underlying joint space topology. By using energy Liapunov functions with the modified potential energy, a much simpler analysis can be used to show closed-loop global asymptotic stability and local exponential stability. When Coulomb and viscous friction and model parameter errors are present, a sliding-mode-like modification of the control law is proposed to add a robustness-enhancing outer loop. Adaptive control is also addressed within the same framework. A linear-in-the-parameters formulation is adopted, and globally asymptotically stable adaptive control laws are derived by replacing the model parameters in the nonadaptive control laws by their estimates.
Approximate analytical relationships for linear optimal aeroelastic flight control laws

NASA Astrophysics Data System (ADS)

Kassem, Ayman Hamdy

1998-09-01

This dissertation introduces new methods to uncover functional relationships between design parameters of a contemporary control design technique and the resulting closed-loop properties. Three new methods are developed for generating such relationships through analytical expressions: the Direct Eigen-Based Technique, the Order of Magnitude Technique, and the Cost Function Imbedding Technique. Efforts concentrated on the linear-quadratic state-feedback control-design technique applied to an aeroelastic flight control task. For this specific application, simple and accurate analytical expressions for the closed-loop eigenvalues and zeros in terms of basic parameters such as stability and control derivatives, structural vibration damping and natural frequency, and cost function weights are generated. These expressions explicitly indicate how the weights augment the short period and aeroelastic modes, as well as the closed-loop zeros, and by what physical mechanism. The analytical expressions are used to address topics such as damping, nonminimum phase behavior, stability, and performance with robustness considerations, and design modifications. This type of knowledge is invaluable to the flight control designer and would be more difficult to formulate when obtained from numerical-based sensitivity analysis.
Application handbook for a Standardized Control Module (SCM) for DC-DC converters, volume 1

NASA Astrophysics Data System (ADS)

Lee, F. C.; Mahmoud, M. F.; Yu, Y.

1980-04-01

The standardized control module (SCM) was developed for application in the buck, boost and buck/boost DC-DC converters. The SCM used multiple feedback loops to provide improved input line and output load regulation, stable feedback control system, good dynamic transient response and adaptive compensation of the control loop for changes in open loop gain and output filter time constraints. The necessary modeling and analysis tools to aid the design engineer in the application of the SCM to DC-DC Converters were developed. The SCM functional block diagram and the different analysis techniques were examined. The average time domain analysis technique was chosen as the basic analytical tool. The power stage transfer functions were developed for the buck, boost and buck/boost converters. The analog signal and digital signal processor transfer functions were developed for the three DC-DC Converter types using the constant on time, constant off time and constant frequency control laws.
Application handbook for a Standardized Control Module (SCM) for DC-DC converters, volume 1

NASA Technical Reports Server (NTRS)

Lee, F. C.; Mahmoud, M. F.; Yu, Y.

1980-01-01

The standardized control module (SCM) was developed for application in the buck, boost and buck/boost DC-DC converters. The SCM used multiple feedback loops to provide improved input line and output load regulation, stable feedback control system, good dynamic transient response and adaptive compensation of the control loop for changes in open loop gain and output filter time constraints. The necessary modeling and analysis tools to aid the design engineer in the application of the SCM to DC-DC Converters were developed. The SCM functional block diagram and the different analysis techniques were examined. The average time domain analysis technique was chosen as the basic analytical tool. The power stage transfer functions were developed for the buck, boost and buck/boost converters. The analog signal and digital signal processor transfer functions were developed for the three DC-DC Converter types using the constant on time, constant off time and constant frequency control laws.
Optimal spacecraft formation establishment and reconfiguration propelled by the geomagnetic Lorentz force

NASA Astrophysics Data System (ADS)

Huang, Xu; Yan, Ye; Zhou, Yang

2014-12-01

The Lorentz force acting on an electrostatically charged spacecraft as it moves through the planetary magnetic field could be utilized as propellantless electromagnetic propulsion for orbital maneuvering, such as spacecraft formation establishment and formation reconfiguration. By assuming that the Earth's magnetic field could be modeled as a tilted dipole located at the center of Earth that corotates with Earth, a dynamical model that describes the relative orbital motion of Lorentz spacecraft is developed. Based on the proposed dynamical model, the energy-optimal open-loop trajectories of control inputs, namely, the required specific charges of Lorentz spacecraft, for Lorentz-propelled spacecraft formation establishment or reconfiguration problems with both fixed and free final conditions constraints are derived via Gauss pseudospectral method. The effect of the magnetic dipole tilt angle on the optimal control inputs and the relative transfer trajectories for formation establishment or reconfiguration is also investigated by comparisons with the results derived from a nontilted dipole model. Furthermore, a closed-loop integral sliding mode controller is designed to guarantee the trajectory tracking in the presence of external disturbances and modeling errors. The stability of the closed-loop system is proved by a Lyapunov-based approach. Numerical simulations are presented to verify the validity of the proposed open-loop control methods and demonstrate the performance of the closed-loop controller. Also, the results indicate the dipole tilt angle should be considered when designing control strategies for Lorentz-propelled spacecraft formation establishment or reconfiguration.
An optimal open/closed-loop control method with application to a pre-stressed thin duralumin plate

NASA Astrophysics Data System (ADS)

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.
Application of computational fluid dynamics to closed-loop bioreactors: I. Characterization and simulation of fluid-flow pattern and oxygen transfer.

PubMed

Littleton, Helen X; Daigger, Glen T; Strom, Peter F

2007-06-01

A full-scale, closed-loop bioreactor (Orbal oxidation ditch, Envirex brand technologies, Siemens, Waukesha, Wisconsin), previously examined for simultaneous biological nutrient removal (SBNR), was further evaluated using computational fluid dynamics (CFD). A CFD model was developed first by imparting the known momentum (calculated by tank fluid velocity and mass flowrate) to the fluid at the aeration disc region. Oxygen source (aeration) and sink (consumption) terms were introduced, and statistical analysis was applied to the CFD simulation results. The CFD model was validated with field data obtained from a test tank and a full-scale tank. The results indicated that CFD could predict the mixing pattern in closed-loop bioreactors. This enables visualization of the flow pattern, both with regard to flow velocity and dissolved-oxygen-distribution profiles. The velocity and oxygen-distribution gradients suggested that the flow patterns produced by directional aeration in closed-loop bioreactors created a heterogeneous environment that can result in dissolved oxygen variations throughout the bioreactor. Distinct anaerobic zones on a macroenvironment scale were not observed, but it is clear that, when flow passed around curves, a secondary spiral flow was generated. This second current, along with the main recirculation flow, could create alternating anaerobic and aerobic conditions vertically and horizontally, which would allow SBNR to occur. Reliable SBNR performance in Orbal oxidation ditches may be a result, at least in part, of such a spatially varying environment.
An error criterion for determining sampling rates in closed-loop control systems

NASA Technical Reports Server (NTRS)

Brecher, S. M.

1972-01-01

The determination of an error criterion which will give a sampling rate for adequate performance of linear, time-invariant closed-loop, discrete-data control systems was studied. The proper modelling of the closed-loop control system for characterization of the error behavior, and the determination of an absolute error definition for performance of the two commonly used holding devices are discussed. The definition of an adequate relative error criterion as a function of the sampling rate and the parameters characterizing the system is established along with the determination of sampling rates. The validity of the expressions for the sampling interval was confirmed by computer simulations. Their application solves the problem of making a first choice in the selection of sampling rates.

The effects of spaceflight on open-loop and closed-loop postural control mechanisms: human neurovestibular studies on SLS-2

NASA Technical Reports Server (NTRS)

Collins, J. J.; De Luca, C. J.; Pavlik, A. E.; Roy, S. H.; Emley, M. S.; Young, L. R. (Principal Investigator)

1995-01-01

Stabilogram-diffusion analysis was used to examine how prolonged periods in microgravity affect the open-loop and closed-loop postural control mechanisms. It was hypothesized that following spaceflight: (1) the effective stochastic activity of the open-loop postural control schemes in astronauts is increased; (2) the effective stochastic activity and uncorrelated behavior, respectively, of the closed-loop postural control mechanisms in astronauts are increased; and (3) astronauts utilized open-loop postural controls schemes for shorter time intervals and smaller displacements. Four crew members and two alternates from the 14-day Spacelab Life Sciences 2 Mission were included in the study. Each subject was tested under eyes-open, quiet-standing conditions on multiple preflight and postflight days. The subjects' center-of-pressure trajectories were measured with a force platform and analyzed according to stabilogram-diffusion analysis. It was found that the effective stochastic activity of the open-loop postural control schemes in three of the four crew members was increased following spaceflight. This result is interpreted as an indication that there may be in-flight adaptations to higher-level descending postural control pathways, e.g., a postflight increase in the tonic activation of postural muscles. This change may also be the consequence of a compensatory (e.g., "stiffening") postural control strategy that is adopted by astronauts to account for general feeling of postflight unsteadiness. The crew members, as a group, did not exhibit any consistent preflight/postflight differences in the steady-state behavior of their closed-loop postural control mechanisms or in the functional interaction of their open-loop and closed-loop postural control mechanisms. These results are interpreted as indications that although there may be in-flight adaptations to the vestibular system and/or proprioceptive system, input from the visual system can compensate for such changes during undisturbed stance.
Capillary-Condenser-Pumped Heat-Transfer Loop

NASA Technical Reports Server (NTRS)

Silverstein, Calvin C.

1989-01-01

Heat being transferred supplies operating power. Capillary-condenser-pumped heat-transfer loop similar to heat pipe and to capillary-evaporator-pumped heat-transfer loop in that heat-transfer fluid pumped by evaporation and condensation of fluid at heat source and sink, respectively. Capillary condenser pump combined with capillary evaporator pump to form heat exchanger circulating heat-transfer fluids in both loops. Transport of heat more nearly isothermal. Thermal stress in loop reduced, and less external surface area needed in condenser section for rejection of heat to heat sink.
Open-closed-loop iterative learning control for a class of nonlinear systems with random data dropouts

NASA Astrophysics Data System (ADS)

Cheng, X. Y.; Wang, H. B.; Jia, Y. L.; Dong, YH

2018-05-01

In this paper, an open-closed-loop iterative learning control (ILC) algorithm is constructed for a class of nonlinear systems subjecting to random data dropouts. The ILC algorithm is implemented by a networked control system (NCS), where only the off-line data is transmitted by network while the real-time data is delivered in the point-to-point way. Thus, there are two controllers rather than one in the control system, which makes better use of the saved and current information and thereby improves the performance achieved by open-loop control alone. During the transfer of off-line data between the nonlinear plant and the remote controller data dropout occurs randomly and the data dropout rate is modeled as a binary Bernoulli random variable. Both measurement and control data dropouts are taken into consideration simultaneously. The convergence criterion is derived based on rigorous analysis. Finally, the simulation results verify the effectiveness of the proposed method.
Closed Loop Two-Phase Thermosyphon of Small Dimensions: a Review of the Experimental Results

NASA Astrophysics Data System (ADS)

Franco, Alessandro; Filippeschi, Sauro

2012-06-01

A bibliographical review on the heat and mass transfer in gravity assisted Closed Loop Two Phase Thermosyphons (CLTPT) with channels having a hydraulic diameter of the order of some millimetres and input power below 1 kW is proposed. The available experimental works in the literature are critically analysed in order to highlight the main results and the correlation between mass flow rate and heat input in natural circulation loops. A comparison of different experimental apparatuses and results is made. It is observed that the results are very different among them and in many cases the experimental data disagree with the conventional theory developed for an imposed flow rate. The paper analyses the main differences among the experimental devices and try to understand these disagreements. From the present analysis it is evident that further systematic studies are required to generate a meaningful body of knowledge of the heat and mass transport mechanism in these devices for practical applications in cooling devices or energy systems.
CLOSED-FIELD CORONAL HEATING DRIVEN BY WAVE TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Downs, Cooper; Lionello, Roberto; Mikić, Zoran

To simulate the energy balance of coronal plasmas on macroscopic scales, we often require the specification of the coronal heating mechanism in some functional form. To go beyond empirical formulations and to build a more physically motivated heating function, we investigate the wave-turbulence-driven (WTD) phenomenology for the heating of closed coronal loops. Our implementation is designed to capture the large-scale propagation, reflection, and dissipation of wave turbulence along a loop. The parameter space of this model is explored by solving the coupled WTD and hydrodynamic evolution in 1D for an idealized loop. The relevance to a range of solar conditionsmore » is also established by computing solutions for over one hundred loops extracted from a realistic 3D coronal field. Due to the implicit dependence of the WTD heating model on loop geometry and plasma properties along the loop and at the footpoints, we find that this model can significantly reduce the number of free parameters when compared to traditional empirical heating models, and still robustly describe a broad range of quiet-Sun and active region conditions. The importance of the self-reflection term in producing relatively short heating scale heights and thermal nonequilibrium cycles is also discussed.« less
Closed-field Coronal Heating Driven by Wave Turbulence

NASA Astrophysics Data System (ADS)

Downs, Cooper; Lionello, Roberto; Mikić, Zoran; Linker, Jon A.; Velli, Marco

2016-12-01

To simulate the energy balance of coronal plasmas on macroscopic scales, we often require the specification of the coronal heating mechanism in some functional form. To go beyond empirical formulations and to build a more physically motivated heating function, we investigate the wave-turbulence-driven (WTD) phenomenology for the heating of closed coronal loops. Our implementation is designed to capture the large-scale propagation, reflection, and dissipation of wave turbulence along a loop. The parameter space of this model is explored by solving the coupled WTD and hydrodynamic evolution in 1D for an idealized loop. The relevance to a range of solar conditions is also established by computing solutions for over one hundred loops extracted from a realistic 3D coronal field. Due to the implicit dependence of the WTD heating model on loop geometry and plasma properties along the loop and at the footpoints, we find that this model can significantly reduce the number of free parameters when compared to traditional empirical heating models, and still robustly describe a broad range of quiet-Sun and active region conditions. The importance of the self-reflection term in producing relatively short heating scale heights and thermal nonequilibrium cycles is also discussed.
Closed loop engine control for regulating NOx emissions, using a two-dimensional fuel-air curve

DOEpatents

Bourn, Gary D.; Smith, Jack A.; Gingrich, Jess W.

2007-01-30

An engine control strategy that ensures that NOx emissions from the engine will be maintained at an acceptable level. The control strategy is based on a two-dimensional fuel-air curve, in which air manifold pressure (AMP) is a function of fuel header pressure and engine speed. The control strategy provides for closed loop NOx adjustment to a base AMP value derived from the fuel-air curve.
PID tuning rules for SOPDT systems: review and some new results.

PubMed

Panda, Rames C; Yu, Cheng-Ching; Huang, Hsiao-Ping

2004-04-01

PID controllers are widely used in industries and so many tuning rules have been proposed over the past 50 years that users are often lost in the jungle of tuning formulas. Moreover, unlike PI control, different control laws and structures of implementation further complicate the use of the PID controller. In this work, five different tuning rules are taken for study to control second-order plus dead time systems with wide ranges of damping coefficients and dead time to time constant ratios (D/tau). Four of them are based on IMC design with different types of approximations on dead time and the other on desired closed-loop specifications (i.e., specified forward transfer function). The method of handling dead time in the IMC type of design is important especially for systems with large D/tau ratios. A systematic approach was followed to evaluate the performance of controllers. The regions of applicability of suitable tuning rules are highlighted and recommendations are also given. It turns out that IMC designed with the Maclaurin series expansion type PID is a better choice for both set point and load changes for systems with D/tau greater than 1. For systems with D/tau less than 1, the desired closed-loop specification approach is favored.
A reconfigurable visual-programming library for real-time closed-loop cellular electrophysiology

PubMed Central

Biró, István; Giugliano, Michele

2015-01-01

Most of the software platforms for cellular electrophysiology are limited in terms of flexibility, hardware support, ease of use, or re-configuration and adaptation for non-expert users. Moreover, advanced experimental protocols requiring real-time closed-loop operation to investigate excitability, plasticity, dynamics, are largely inaccessible to users without moderate to substantial computer proficiency. Here we present an approach based on MATLAB/Simulink, exploiting the benefits of LEGO-like visual programming and configuration, combined to a small, but easily extendible library of functional software components. We provide and validate several examples, implementing conventional and more sophisticated experimental protocols such as dynamic-clamp or the combined use of intracellular and extracellular methods, involving closed-loop real-time control. The functionality of each of these examples is demonstrated with relevant experiments. These can be used as a starting point to create and support a larger variety of electrophysiological tools and methods, hopefully extending the range of default techniques and protocols currently employed in experimental labs across the world. PMID:26157385
Minimizing Uncertainties Impact in Decision Making with an Applicability Study for Economic Power Dispatch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hong; Wang, Shaobu; Fan, Rui

This report summaries the work performed under the LDRD project on the preliminary study on knowledge automation, where specific focus has been made on the investigation of the impact of uncertainties of human decision making onto the optimization of the process operation. At first the statistics on signals from the Brain-Computing Interface (BCI) is analyzed so as to obtain the uncertainties characterization of human operators during the decision making phase using the electroencephalogram (EEG) signals. This is then followed by the discussions of an architecture that reveals the equivalence between optimization and closed loop feedback control design, where it hasmore » been shown that all the optimization problems can be transferred into the control design problem for closed loop systems. This has led to a “closed loop” framework, where the structure of the decision making is shown to be subjected to both process disturbances and controller’s uncertainties. The latter can well represent the uncertainties or randomness occurred during human decision making phase. As a result, a stochastic optimization problem has been formulated and a novel solution has been proposed using probability density function (PDF) shaping for both the cost function and the constraints using stochastic distribution control concept. A sufficient condition has been derived that guarantees the convergence of the optimal solution and discussions have been made for both the total probabilistic solution and chanced constrained optimization which have been well-studied in optimal power flows (OPF) area. A simple case study has been carried out for the economic dispatch of powers for a grid system when there are distributed energy resources (DERs) in the system, and encouraging results have been obtained showing that a significant savings on the generation cost can be expected.« less
Numerical investigation on pulsating heat pipes with nitrogen or hydrogen

NASA Astrophysics Data System (ADS)

Y Han, D.; Sun, X.; Gan, Z. H.; Y Luo, R.; Pfotenhauer, J. M.; Jiao, B.

2017-12-01

With flexible structure and excellent performance, pulsating heat pipes (PHP) are regarded as a great solution to distribute cooling power for cryocoolers. The experiments on PHPs with cryogenic fluids have been carried out, indicating their efficient performances in cryogenics. There are large differences in physical properties between the fluids at room and cryogenic temperature, resulting in their different heat transfer and oscillation characteristics. Up to now, the numerical investigations on cryogenic fluids have rarely been carried out. In this paper, the model of the closed-loop PHP with multiple liquid slugs and vapor plugs is performed with nitrogen and hydrogen as working fluids, respectively. The effects of heating wall temperature on the performance of close-looped PHPs are investigated and compared with that of water PHP.
Dynamics and control of instrumented harmonic drives

NASA Technical Reports Server (NTRS)

Kazerooni, H.; Ellis, S. R. (Principal Investigator)

1995-01-01

Since torque in harmonic drives is transmitted by a pure couple, harmonic drives do not generate radial forces and therefore can be instrumented with torque sensors without interference from radial forces. The installation of torque sensors on the stationary component of harmonic drives (the Flexipline cup in this research work) produce backdrivability needed for robotic and telerobotic compliant maneuvers. Backdrivability of a harmonic drive, when used as torque increaser, means that the output shaft can be rotated via finite amount of torque. A high ratio harmonic drive is non-backdrivable because its output shaft cannot be turned by applying a torque on it. This article first develops the dynamic behavior of a harmonic drive, in particular the non-backdrivability, in terms of a sensitivity transfer function. The instrumentation of the harmonic drive with torque sensor is then described. This leads to a description of the control architecture which allows modulation of the sensitivity transfer function within the limits established by the closed-loop stability. A set of experiments on an active hand controller, powered by a DC motor coupled to an instrumented harmonic drive, is given to exhibit this method's limitations.
A Triple-Loop Inductive Power Transmission System for Biomedical Applications.

PubMed

Lee, Byunghun; Kiani, Mehdi; Ghovanloo, Maysam

2016-02-01

A triple-loop wireless power transmission (WPT) system equipped with closed-loop global power control, adaptive transmitter (Tx) resonance compensation (TRC), and automatic receiver (Rx) resonance tuning (ART) is presented. This system not only opposes coupling and load variations but also compensates for changes in the environment surrounding the inductive link to enhance power transfer efficiency (PTE) in applications such as implantable medical devices (IMDs). The Tx was built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader, operating at 13.56 MHz. A local Tx loop finds the optimal capacitance in parallel with the Tx coil by adjusting a varactor. A global power control loop maintains the received power at a desired level in the presence of changes in coupling distance, coil misalignments, and loading. Moreover, a local Rx loop is implemented inside a power management integrated circuit (PMIC) to avoid PTE degradation due to the Rx coil surrounding environment and process variations. The PMIC was fabricated in a 0.35- μm 4M2P standard CMOS process with 2.54 mm(2) active area. Measurement results show that the proposed triple-loop system improves the overall PTE by up to 10.5% and 4.7% compared to a similar open- and single closed-loop system, respectively, at nominal coil distance of 2 cm. The added TRC and ART loops contribute 2.3% and 1.4% to the overall PTE of 13.5%, respectively. This is the first WPT system to include three loops to dynamically compensate for environment and circuit variations and improve the overall power efficiency all the way from the driver output in Tx to the load in Rx.
Computer program for single input-output, single-loop feedback systems

NASA Technical Reports Server (NTRS)

1976-01-01

Additional work is reported on a completely automatic computer program for the design of single input/output, single loop feedback systems with parameter uncertainly, to satisfy time domain bounds on the system response to step commands and disturbances. The inputs to the program are basically the specified time-domain response bounds, the form of the constrained plant transfer function and the ranges of the uncertain parameters of the plant. The program output consists of the transfer functions of the two free compensation networks, in the form of the coefficients of the numerator and denominator polynomials, and the data on the prescribed bounds and the extremes actually obtained for the system response to commands and disturbances.
Closed-Loop Control Better than Open-Loop Control of Profofol TCI Guided by BIS: A Randomized, Controlled, Multicenter Clinical Trial to Evaluate the CONCERT-CL Closed-Loop System

PubMed Central

Zhang, Xuena; Wu, Anshi; Yao, Shanglong; Xue, Zhanggang; Yue, Yun

2015-01-01

Background The CONCERT-CL closed-loop infusion system designed by VERYARK Technology Co., Ltd. (Guangxi, China) is an innovation using TCI combined with closed-loop controlled intravenous anesthesia under the guide of BIS. In this study we performed a randomized, controlled, multicenter study to compare closed-loop control and open-loop control of propofol by using the CONCERT-CL closed-loop infusion system. Methods 180 surgical patients from three medical centers undergone TCI intravenous anesthesia with propofol and remifentanil were randomly assigned to propofol closed-loop group and propofol opened-loop groups. Primary outcome was global score (GS, GS = (MDAPE+Wobble)/% of time of bispectral index (BIS) 40-60). Secondary outcomes were doses of the anesthetics and emergence time from anesthesia, such as, time to tracheal extubation. Results There were 89 and 86 patients in the closed-loop and opened-loop groups, respectively. GS in the closed-loop groups (22.21±8.50) were lower than that in the opened-loop group (27.19±15.26) (p=0.009). The higher proportion of time of BIS between 40 and 60 was also observed in the closed-loop group (84.11±9.50%), while that was 79.92±13.17% in the opened-loop group, (p=0.016). No significant differences in propofol dose and time of tracheal extubation were observed. The frequency of propofol regulation in the closed-loop group (31.55±9.46 times/hr) was obverse higher than that in the opened-loop group (6.84±6.21 times/hr) (p=0.000). Conclusion The CONCERT-CL closed-loop infusion system can automatically regulate the TCI of propofol, maintain the BIS value in an adequate range and reduce the workload of anesthesiologists better than open-loop system. Trial Registration ChiCTR ChiCTR-OOR-14005551 PMID:25886041
Stability of multiloop LQ regulators with nonlinearities. I - Regions of attraction. II - Regions of ultimate boundedness

NASA Technical Reports Server (NTRS)

Joshi, S. M.

1986-01-01

An investigation is conducted for the closed loop stability of linear time-invariant systems controlled by linear quadratic (LQ) regulators, in cases where nonlinearities exist in the control channels lying outside the stability sector in regions away from the origin. The estimate of the region of attraction thus obtained furnishes methods for the selection of performance function weights for more robust LQ designs. Attention is then given to the closed loop stability of linear time-invariant systems controlled by the LQ regulators when the nonlinearities in the loops escape the stability sector in a bounded region containing the origin.
Dynamics of the active site loops in catalyzing aminoacylation reaction in seryl and histidyl tRNA synthetases.

PubMed

Dutta, Saheb; Kundu, Soumya; Saha, Amrita; Nandi, Nilashis

2018-03-01

Aminoacylation reaction is the first step of protein biosynthesis. The catalytic reorganization at the active site of aminoacyl tRNA synthetases (aaRSs) is driven by the loop motions. There remain lacunae of understanding concerning the catalytic loop dynamics in aaRSs. We analyzed the functional loop dynamics in seryl tRNA synthetase from Methanopyrus kandleri ( mk SerRS) and histidyl tRNA synthetases from Thermus thermophilus ( tt HisRS), respectively, using molecular dynamics. Results confirm that the motif 2 loop and other active site loops are flexible spots within the catalytic domain. Catalytic residues of the loops form a network of interaction with the substrates to form a reactive state. The loops undergo transitions between closed state and open state and the relaxation of the constituent residues occurs in femtosecond to nanosecond time scale. Order parameters are higher for constituent catalytic residues which form a specific network of interaction with the substrates to form a reactive state compared to the Gly residues within the loop. The development of interaction is supported from mutation studies where the catalytic domain with mutated loop exhibits unfavorable binding energy with the substrates. During the open-close motion of the loops, the catalytic residues make relaxation by ultrafast librational motion as well as fast diffusive motion and subsequently relax rather slowly via slower diffusive motion. The Gly residues act as a hinge to facilitate the loop closing and opening by their faster relaxation behavior. The role of bound water is analyzed by comparing implicit solvent-based and explicit solvent-based simulations. Loops fail to form catalytically competent geometry in absence of water. The present result, for the first time reveals the nature of the active site loop dynamics in aaRS and their influence on catalysis.
Postural control model interpretation of stabilogram diffusion analysis

NASA Technical Reports Server (NTRS)

Peterka, R. J.

2000-01-01

Collins and De Luca [Collins JJ. De Luca CJ (1993) Exp Brain Res 95: 308-318] introduced a new method known as stabilogram diffusion analysis that provides a quantitative statistical measure of the apparently random variations of center-of-pressure (COP) trajectories recorded during quiet upright stance in humans. This analysis generates a stabilogram diffusion function (SDF) that summarizes the mean square COP displacement as a function of the time interval between COP comparisons. SDFs have a characteristic two-part form that suggests the presence of two different control regimes: a short-term open-loop control behavior and a longer-term closed-loop behavior. This paper demonstrates that a very simple closed-loop control model of upright stance can generate realistic SDFs. The model consists of an inverted pendulum body with torque applied at the ankle joint. This torque includes a random disturbance torque and a control torque. The control torque is a function of the deviation (error signal) between the desired upright body position and the actual body position, and is generated in proportion to the error signal, the derivative of the error signal, and the integral of the error signal [i.e. a proportional, integral and derivative (PID) neural controller]. The control torque is applied with a time delay representing conduction, processing, and muscle activation delays. Variations in the PID parameters and the time delay generate variations in SDFs that mimic real experimental SDFs. This model analysis allows one to interpret experimentally observed changes in SDFs in terms of variations in neural controller and time delay parameters rather than in terms of open-loop versus closed-loop behavior.
Hardware-in-the-Loop Rendezvous Tests of a Novel Actuators Command Concept

NASA Astrophysics Data System (ADS)

Gomes dos Santos, Willer; Marconi Rocco, Evandro; Boge, Toralf; Benninghoff, Heike; Rems, Florian

2016-12-01

Integration, test and validation results, in a real-time environment, of a novel concept for spacecraft control are presented in this paper. The proposed method commands simultaneously a group of actuators optimizing a given set of objective functions based on a multiobjective optimization technique. Since close proximity maneuvers play an important role in orbital servicing missions, the entire GNC system has been integrated and tested at a hardware-in-the-loop (HIL) rendezvous and docking simulator known as European Proximity Operations Simulator (EPOS). During the test campaign at EPOS facility, a visual camera has been used to provide the necessary measurements for calculating the relative position with respect to the target satellite during closed-loop simulations. In addition, two different configurations of spacecraft control have been considered in this paper: a thruster reaction control system and a mixed actuators mode which includes thrusters, reaction wheels, and magnetic torqrods. At EPOS, results of HIL closed-loop tests have demonstrated that a safe and stable rendezvous approach can be achieved with the proposed GNC loop.
A functional electrical stimulation system for human walking inspired by reflexive control principles.

PubMed

Meng, Lin; Porr, Bernd; Macleod, Catherine A; Gollee, Henrik

2017-04-01

This study presents an innovative multichannel functional electrical stimulation gait-assist system which employs a well-established purely reflexive control algorithm, previously tested in a series of bipedal walking robots. In these robots, ground contact information was used to activate motors in the legs, generating a gait cycle similar to that of humans. Rather than developing a sophisticated closed-loop functional electrical stimulation control strategy for stepping, we have instead utilised our simple reflexive model where muscle activation is induced through transfer functions which translate sensory signals, predominantly ground contact information, into motor actions. The functionality of the functional electrical stimulation system was tested by analysis of the gait function of seven healthy volunteers during functional electrical stimulation-assisted treadmill walking compared to unassisted walking. The results demonstrated that the system was successful in synchronising muscle activation throughout the gait cycle and was able to promote functional hip and ankle movements. Overall, the study demonstrates the potential of human-inspired robotic systems in the design of assistive devices for bipedal walking.

Impact of lipopolysaccharide-induced acute inflammation on baroreflex-controlled sympathetic arterial pressure regulation

PubMed Central

Tohyama, Takeshi; Kawada, Toru; Kishi, Takuya; Yoshida, Keimei; Nishikawa, Takuya; Mannoji, Hiroshi; Kamada, Kazuhiro; Sunagawa, Kenji; Tsutsui, Hiroyuki

2018-01-01

Background Lipopolysaccharide (LPS) induces acute inflammation, activates sympathetic nerve activity (SNA) and alters hemodynamics. Since the arterial baroreflex is a negative feedback system to stabilize arterial pressure (AP), examining the arterial baroreflex function is a prerequisite to understanding complex hemodynamics under LPS challenge. We investigated the impact of LPS-induced acute inflammation on SNA and AP regulation by performing baroreflex open-loop analysis. Methods Ten anesthetized Sprague-Dawley rats were used. Acute inflammation was induced by an intravenous injection of LPS (60 μg/kg). We isolated the carotid sinuses from the systemic circulation and controlled carotid sinus pressure (CSP) by a servo-controlled piston pump. We matched CSP to AP to establish the baroreflex closed-loop condition, whereas we decoupled CSP from AP to establish the baroreflex open-loop condition and changed CSP stepwise to evaluate the baroreflex open-loop function. We recorded splanchnic SNA and hemodynamic parameters under baroreflex open- and closed-loop conditions at baseline and at 60 and 120 min after LPS injection. Results In the baroreflex closed-loop condition, SNA continued to increase after LPS injection, reaching three-fold the baseline value at 120 min (baseline: 94.7 ± 3.6 vs. 120 min: 283.9 ± 31.9 a.u.). In contrast, AP increased initially (until 75 min), then declined to the baseline level. In the baroreflex open-loop condition, LPS reset the neural arc (CSP-SNA relationship) upward to higher SNA, while shifted the peripheral arc (SNA-AP relationship) downward at 120 min after the injection. As a result, the operating point determined by the intersection between function curves of neural arc and peripheral arc showed marked sympatho-excitation without substantial changes in AP. Conclusions LPS-induced acute inflammation markedly increased SNA via resetting of the baroreflex neural arc, and suppressed the peripheral arc. The balance between the augmented neural arc and suppressed peripheral arc determines SNA and hemodynamics in LPS-induced acute inflammation. PMID:29329321
Impact of lipopolysaccharide-induced acute inflammation on baroreflex-controlled sympathetic arterial pressure regulation.

PubMed

Tohyama, Takeshi; Saku, Keita; Kawada, Toru; Kishi, Takuya; Yoshida, Keimei; Nishikawa, Takuya; Mannoji, Hiroshi; Kamada, Kazuhiro; Sunagawa, Kenji; Tsutsui, Hiroyuki

2018-01-01

Lipopolysaccharide (LPS) induces acute inflammation, activates sympathetic nerve activity (SNA) and alters hemodynamics. Since the arterial baroreflex is a negative feedback system to stabilize arterial pressure (AP), examining the arterial baroreflex function is a prerequisite to understanding complex hemodynamics under LPS challenge. We investigated the impact of LPS-induced acute inflammation on SNA and AP regulation by performing baroreflex open-loop analysis. Ten anesthetized Sprague-Dawley rats were used. Acute inflammation was induced by an intravenous injection of LPS (60 μg/kg). We isolated the carotid sinuses from the systemic circulation and controlled carotid sinus pressure (CSP) by a servo-controlled piston pump. We matched CSP to AP to establish the baroreflex closed-loop condition, whereas we decoupled CSP from AP to establish the baroreflex open-loop condition and changed CSP stepwise to evaluate the baroreflex open-loop function. We recorded splanchnic SNA and hemodynamic parameters under baroreflex open- and closed-loop conditions at baseline and at 60 and 120 min after LPS injection. In the baroreflex closed-loop condition, SNA continued to increase after LPS injection, reaching three-fold the baseline value at 120 min (baseline: 94.7 ± 3.6 vs. 120 min: 283.9 ± 31.9 a.u.). In contrast, AP increased initially (until 75 min), then declined to the baseline level. In the baroreflex open-loop condition, LPS reset the neural arc (CSP-SNA relationship) upward to higher SNA, while shifted the peripheral arc (SNA-AP relationship) downward at 120 min after the injection. As a result, the operating point determined by the intersection between function curves of neural arc and peripheral arc showed marked sympatho-excitation without substantial changes in AP. LPS-induced acute inflammation markedly increased SNA via resetting of the baroreflex neural arc, and suppressed the peripheral arc. The balance between the augmented neural arc and suppressed peripheral arc determines SNA and hemodynamics in LPS-induced acute inflammation.
Performance verification and system parameter identification of spacecraft tape recorder control servo

NASA Technical Reports Server (NTRS)

Mukhopadhyay, A. K.

1979-01-01

Design adequacy of the lead-lag compensator of the frequency loop, accuracy checking of the analytical expression for the electrical motor transfer function, and performance evaluation of the speed control servo of the digital tape recorder used on-board the 1976 Viking Mars Orbiters and Voyager 1977 Jupiter-Saturn flyby spacecraft are analyzed. The transfer functions of the most important parts of a simplified frequency loop used for test simulation are described and ten simulation cases are reported. The first four of these cases illustrate the method of selecting the most suitable transfer function for the hysteresis synchronous motor, while the rest verify and determine the servo performance parameters and alternative servo compensation schemes. It is concluded that the linear methods provide a starting point for the final verification/refinement of servo design by nonlinear time response simulation and that the variation of the parameters of the static/dynamic Coulomb friction is as expected in a long-life space mission environment.
Visual and Kinesthetic Components of Pursuit-Tracking Performance.

ERIC Educational Resources Information Center

Thorsheim, Howard I.; And Others

Seventy-five subjects were trained on a pursuit rotor for 10 trials, with ambient illumination from a strobe light flashing at frequencies of either 2,5,10,15, or 20 per second. A transfer trial followed, with a strobe flashing frequency of 10 per second for all subjects. Results supported hypotheses derived from Adams' closed-loop theory of motor…
Site-Directed Spin Labeling Reveals Pentameric Ligand-Gated Ion Channel Gating Motions

PubMed Central

Dellisanti, Cosma D.; Ghosh, Borna; Hanson, Susan M.; Raspanti, James M.; Grant, Valerie A.; Diarra, Gaoussou M.; Schuh, Abby M.; Satyshur, Kenneth; Klug, Candice S.; Czajkowski, Cynthia

2013-01-01

Pentameric ligand-gated ion channels (pLGICs) are neurotransmitter-activated receptors that mediate fast synaptic transmission. In pLGICs, binding of agonist to the extracellular domain triggers a structural rearrangement that leads to the opening of an ion-conducting pore in the transmembrane domain and, in the continued presence of neurotransmitter, the channels desensitize (close). The flexible loops in each subunit that connect the extracellular binding domain (loops 2, 7, and 9) to the transmembrane channel domain (M2–M3 loop) are essential for coupling ligand binding to channel gating. Comparing the crystal structures of two bacterial pLGIC homologues, ELIC and the proton-activated GLIC, suggests channel gating is associated with rearrangements in these loops, but whether these motions accurately predict the motions in functional lipid-embedded pLGICs is unknown. Here, using site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy and functional GLIC channels reconstituted into liposomes, we examined if, and how far, the loops at the ECD/TMD gating interface move during proton-dependent gating transitions from the resting to desensitized state. Loop 9 moves ∼9 Å inward toward the channel lumen in response to proton-induced desensitization. Loop 9 motions were not observed when GLIC was in detergent micelles, suggesting detergent solubilization traps the protein in a nonactivatable state and lipids are required for functional gating transitions. Proton-induced desensitization immobilizes loop 2 with little change in position. Proton-induced motion of the M2–M3 loop was not observed, suggesting its conformation is nearly identical in closed and desensitized states. Our experimentally derived distance measurements of spin-labeled GLIC suggest ELIC is not a good model for the functional resting state of GLIC, and that the crystal structure of GLIC does not correspond to a desensitized state. These findings advance our understanding of the molecular mechanisms underlying pLGIC gating. PMID:24260024
Design and Test of a Closed-Loop FES System for Supporting Function of the Hemiparetic Hand Based on Automatic Detection using the Microsoft Kinect sensor.

PubMed

Simonsen, Daniel; Spaich, Erika G; Hansen, John; Andersen, Ole K

2016-10-26

This paper describes the design of a FES system automatically controlled in a closed loop using a Microsoft Kinect sensor, for assisting both cylindrical grasping and hand opening. The feasibility of the system was evaluated in real-time in stroke patients with hand function deficits. A hand function exercise was designed in which the subjects performed an arm and hand exercise in sitting position. The subject had to grasp one of two differently sized cylindrical objects and move it forward or backwards in the sagittal plane. This exercise was performed with each cylinder with and without FES support. Results showed that the stroke patients were able to perform up to 29% more successful grasps when they were assisted by FES. Moreover, the hand grasp-and-hold and hold-and-release durations were shorter for the smaller of the two cylinders. FES was appropriately timed in more than 95% of all trials indicating successful closed loop FES control. Future studies should incorporate options for assisting forward reaching in order to target a larger group of stroke patients.
Comparison between solar utilization of a closed microalgae-based bio-loop and that of a stand-alone photovoltaic system.

PubMed

Jin, Qiang; Chen, Lei; Li, Aimin; Liu, Fuqiang; Long, Chao; Shan, Aidang; Borthwick, Alistair G L

2015-05-01

This study compared the solar energy utilization of a closed microalgae-based bio-loop for energy efficient production of biogas with fertilizer recovery against that of a stand-alone photovoltaic (PV) system. The comparison was made from the perspective of broad life cycle assessment, simultaneously taking exergy to be the functional unit. The results indicated that the bio-loop was more environmentally competitive than an equivalent stand-alone PV system, but had higher economic cost due to high energy consumption during the operational phase. To fix the problem, a patented, interior pressurization scheduling method was used to operate the bio-loop, with microalgae and aerobic bacterial placed together in the same reactor. As a result, the overall environmental impact and total investment were respectively reduced by more than 75% and 84%, a vast improvement on the bio-loop. Copyright © 2014 Elsevier Ltd. All rights reserved.
Learning from ISS-modular adaptive NN control of nonlinear strict-feedback systems.

PubMed

Wang, Cong; Wang, Min; Liu, Tengfei; Hill, David J

2012-10-01

This paper studies learning from adaptive neural control (ANC) for a class of nonlinear strict-feedback systems with unknown affine terms. To achieve the purpose of learning, a simple input-to-state stability (ISS) modular ANC method is first presented to ensure the boundedness of all the signals in the closed-loop system and the convergence of tracking errors in finite time. Subsequently, it is proven that learning with the proposed stable ISS-modular ANC can be achieved. The cascade structure and unknown affine terms of the considered systems make it very difficult to achieve learning using existing methods. To overcome these difficulties, the stable closed-loop system in the control process is decomposed into a series of linear time-varying (LTV) perturbed subsystems with the appropriate state transformation. Using a recursive design, the partial persistent excitation condition for the radial basis function neural network (NN) is established, which guarantees exponential stability of LTV perturbed subsystems. Consequently, accurate approximation of the closed-loop system dynamics is achieved in a local region along recurrent orbits of closed-loop signals, and learning is implemented during a closed-loop feedback control process. The learned knowledge is reused to achieve stability and an improved performance, thereby avoiding the tremendous repeated training process of NNs. Simulation studies are given to demonstrate the effectiveness of the proposed method.
A class of optimum digital phase locked loops

NASA Technical Reports Server (NTRS)

Kumar, R.; Hurd, W. J.

1986-01-01

This paper presents a class of optimum digital filters for digital phase locked loops, for the important case in which the maximum update rate of the loop filter and numerically controlled oscillator (NCO) is limited. This case is typical when the loop filter is implemented in a microprocessor. In these situations, pure delay is encountered in the loop transfer function and thus the stability and gain margin of the loop are of crucial interest. The optimum filters designed for such situations are evaluated in terms of their gain margin for stability, dynamic error, and steady-state error performance. For situations involving considerably high phase dynamics an adaptive and programmable implementation is also proposed to obtain an overall optimum strategy.
Digital adaptive control of a VTOL aircraft

NASA Technical Reports Server (NTRS)

Reid, G. F.

1976-01-01

A technique has been developed for calculating feedback and feedforward gain matrices that stabilize a VTOL aircraft while enabling it to track input commands of forward and vertical velocity. Leverrier's algorithm is used in a procedure for determining a set of state variable, feedback gains that force the closed loop poles and zeroes of one pilot input transfer function to be at preselected positions in the s plane. This set of feedback gains is then used to calculate the feedback and feedforward gains for the velocity command controller. The method is computationally attractive since the gains are determined by solving systems of linear, simultaneous equations. Responses obtained using a digital simulation of the longitudinal dynamics of the CH-47 helicopter are presented.
Relative position control design of receiver UAV in flying-boom aerial refueling phase.

PubMed

An, Shuai; Yuan, Suozhong

2018-02-01

This paper proposes the design of the relative position-keeping control of the receiver unmanned aerial vehicle (UAV) with the time-varying mass in the refueling phase utilizing an inner-outer loop structure. Firstly, the model of the receiver in the refueling phase is established. And then tank model is set up to analyze the influence of fuel transfer on the receiver. Subsequently, double power reaching law based sliding mode controller is designed to control receiver translational motion relative to tanker aircraft in the outer loop while active disturbance rejection control technique is applied to the inner loop to stabilize the receiver. In addition, the closed-loop stabilities of the subsystems are established, respectively. Finally, an aerial refueling model under various refueling strategies is utilized. Simulations and comparative analysis demonstrate the effectiveness and robustness of the proposed controllers. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Combining short- and long-range fluorescence reporters with simulations to explore the intramolecular dynamics of an intrinsically disordered protein.

PubMed

Zosel, Franziska; Haenni, Dominik; Soranno, Andrea; Nettels, Daniel; Schuler, Benjamin

2017-10-21

Intrinsically disordered proteins (IDPs) are increasingly recognized as a class of molecules that can exert essential biological functions even in the absence of a well-defined three-dimensional structure. Understanding the conformational distributions and dynamics of these highly flexible proteins is thus essential for explaining the molecular mechanisms underlying their function. Single-molecule fluorescence spectroscopy in combination with Förster resonance energy transfer (FRET) is a powerful tool for probing intramolecular distances and the rapid long-range distance dynamics in IDPs. To complement the information from FRET, we combine it with photoinduced electron transfer (PET) quenching to monitor local loop-closure kinetics at the same time and in the same molecule. Here we employed this combination to investigate the intrinsically disordered N-terminal domain of HIV-1 integrase. The results show that both long-range dynamics and loop closure kinetics on the sub-microsecond time scale can be obtained reliably from a single set of measurements by the analysis with a comprehensive model of the underlying photon statistics including both FRET and PET. A more detailed molecular interpretation of the results is enabled by direct comparison with a recent extensive atomistic molecular dynamics simulation of integrase. The simulations are in good agreement with experiment and can explain the deviation from simple models of chain dynamics by the formation of persistent local secondary structure. The results illustrate the power of a close combination of single-molecule spectroscopy and simulations for advancing our understanding of the dynamics and detailed mechanisms in unfolded and intrinsically disordered proteins.
Combining short- and long-range fluorescence reporters with simulations to explore the intramolecular dynamics of an intrinsically disordered protein

NASA Astrophysics Data System (ADS)

Zosel, Franziska; Haenni, Dominik; Soranno, Andrea; Nettels, Daniel; Schuler, Benjamin

2017-10-01

Intrinsically disordered proteins (IDPs) are increasingly recognized as a class of molecules that can exert essential biological functions even in the absence of a well-defined three-dimensional structure. Understanding the conformational distributions and dynamics of these highly flexible proteins is thus essential for explaining the molecular mechanisms underlying their function. Single-molecule fluorescence spectroscopy in combination with Förster resonance energy transfer (FRET) is a powerful tool for probing intramolecular distances and the rapid long-range distance dynamics in IDPs. To complement the information from FRET, we combine it with photoinduced electron transfer (PET) quenching to monitor local loop-closure kinetics at the same time and in the same molecule. Here we employed this combination to investigate the intrinsically disordered N-terminal domain of HIV-1 integrase. The results show that both long-range dynamics and loop closure kinetics on the sub-microsecond time scale can be obtained reliably from a single set of measurements by the analysis with a comprehensive model of the underlying photon statistics including both FRET and PET. A more detailed molecular interpretation of the results is enabled by direct comparison with a recent extensive atomistic molecular dynamics simulation of integrase. The simulations are in good agreement with experiment and can explain the deviation from simple models of chain dynamics by the formation of persistent local secondary structure. The results illustrate the power of a close combination of single-molecule spectroscopy and simulations for advancing our understanding of the dynamics and detailed mechanisms in unfolded and intrinsically disordered proteins.
Hippocampal closed-loop modeling and implications for seizure stimulation design

NASA Astrophysics Data System (ADS)

Sandler, Roman A.; Song, Dong; Hampson, Robert E.; Deadwyler, Sam A.; Berger, Theodore W.; Marmarelis, Vasilis Z.

2015-10-01

Objective. Traditional hippocampal modeling has focused on the series of feedforward synapses known as the trisynaptic pathway. However, feedback connections from CA1 back to the hippocampus through the entorhinal cortex (EC) actually make the hippocampus a closed-loop system. By constructing a functional closed-loop model of the hippocampus, one may learn how both physiological and epileptic oscillations emerge and design efficient neurostimulation patterns to abate such oscillations. Approach. Point process input-output models where estimated from recorded rodent hippocampal data to describe the nonlinear dynamical transformation from CA3 → CA1, via the schaffer-collateral synapse, and CA1 → CA3 via the EC. Each Volterra-like subsystem was composed of linear dynamics (principal dynamic modes) followed by static nonlinearities. The two subsystems were then wired together to produce the full closed-loop model of the hippocampus. Main results. Closed-loop connectivity was found to be necessary for the emergence of theta resonances as seen in recorded data, thus validating the model. The model was then used to identify frequency parameters for the design of neurostimulation patterns to abate seizures. Significance. Deep-brain stimulation (DBS) is a new and promising therapy for intractable seizures. Currently, there is no efficient way to determine optimal frequency parameters for DBS, or even whether periodic or broadband stimuli are optimal. Data-based computational models have the potential to be used as a testbed for designing optimal DBS patterns for individual patients. However, in order for these models to be successful they must incorporate the complex closed-loop structure of the seizure focus. This study serves as a proof-of-concept of using such models to design efficient personalized DBS patterns for epilepsy.
Hippocampal closed-loop modeling and implications for seizure stimulation design.

PubMed

Sandler, Roman A; Song, Dong; Hampson, Robert E; Deadwyler, Sam A; Berger, Theodore W; Marmarelis, Vasilis Z

2015-10-01

Traditional hippocampal modeling has focused on the series of feedforward synapses known as the trisynaptic pathway. However, feedback connections from CA1 back to the hippocampus through the entorhinal cortex (EC) actually make the hippocampus a closed-loop system. By constructing a functional closed-loop model of the hippocampus, one may learn how both physiological and epileptic oscillations emerge and design efficient neurostimulation patterns to abate such oscillations. Point process input-output models where estimated from recorded rodent hippocampal data to describe the nonlinear dynamical transformation from CA3 → CA1, via the schaffer-collateral synapse, and CA1 → CA3 via the EC. Each Volterra-like subsystem was composed of linear dynamics (principal dynamic modes) followed by static nonlinearities. The two subsystems were then wired together to produce the full closed-loop model of the hippocampus. Closed-loop connectivity was found to be necessary for the emergence of theta resonances as seen in recorded data, thus validating the model. The model was then used to identify frequency parameters for the design of neurostimulation patterns to abate seizures. Deep-brain stimulation (DBS) is a new and promising therapy for intractable seizures. Currently, there is no efficient way to determine optimal frequency parameters for DBS, or even whether periodic or broadband stimuli are optimal. Data-based computational models have the potential to be used as a testbed for designing optimal DBS patterns for individual patients. However, in order for these models to be successful they must incorporate the complex closed-loop structure of the seizure focus. This study serves as a proof-of-concept of using such models to design efficient personalized DBS patterns for epilepsy.
Hippocampal Closed-Loop Modeling and Implications for Seizure Stimulation Design

PubMed Central

Sandler, Roman A.; Song, Dong; Hampson, Robert E.; Deadwyler, Sam A.; Berger, Theodore W.; Marmarelis, Vasilis Z.

2016-01-01

Objective Traditional hippocampal modeling has focused on the series of feedforward synapses known as the trisynaptic pathway. However, feedback connections from CA1 back to the hippocampus through the Entorhinal Cortex (EC) actually make the hippocampus a closed-loop system. By constructing a functional closed-loop model of the hippocampus, one may learn how both physiological and epileptic oscillations emerge and design efficient neurostimulation patterns to abate such oscillations. Approach Point process input-output models where estimated from recorded rodent hippocampal data to describe the nonlinear dynamical transformation from CA3→CA1, via the Schaffer-Collateral synapse, and CA1→CA3 via the EC. Each Volterra-like subsystem was composed of linear dynamics (Principal Dynamic Modes) followed by static nonlinearities. The two subsystems were then wired together to produce the full closed-loop model of the hippocampus. Main Results Closed-loop connectivity was found to be necessary for the emergence of theta resonances as seen in recorded data, thus validating the model. The model was then used to identify frequency parameters for the design of neurostimulation patterns to abate seizures. Significance DBS is a new and promising therapy for intractable seizures. Currently, there is no efficient way to determine optimal frequency parameters for DBS, or even whether periodic or broadband stimuli are optimal. Data-based computational models have the potential to be used as a testbed for designing optimal DBS patterns for individual patients. However, in order for these models to be successful they must incorporate the complex closed-loop structure of the seizure focus. This study serves as a proof-of-concept of using such models to design efficient personalized DBS patterns for epilepsy. PMID:26355815
Estimation of joint stiffness with a compliant load.

PubMed

Ludvig, Daniel; Kearney, Robert E

2009-01-01

Joint stiffness defines the dynamic relationship between the position of the joint and the torque acting about it. It consists of two components: intrinsic and reflex stiffness. Many previous studies have investigated joint stiffness in an open-loop environment, because the current algorithm in use is an open-loop algorithm. This paper explores issues related to the estimation of joint stiffness when subjects interact with compliant loads. First, we show analytically how the bias in closed-loop estimates of joint stiffness depends on the properties of the load, the noise power, and length of the estimated impulse response functions (IRF). We then demonstrate with simulations that the open-loop analysis will fail completely for an elastic load but may succeed for an inertial load. We further show that the open-loop analysis can yield unbiased results with an inertial load and document IRF length, signal-to-noise ratio needed, and minimum inertia needed for the analysis to succeed. Thus, by using a load with a properly selected inertia, open-loop analysis can be used under closed-loop conditions.
Closed-loop control of cellular functions using combinatory drugs guided by a stochastic search algorithm

PubMed Central

Wong, Pak Kin; Yu, Fuqu; Shahangian, Arash; Cheng, Genhong; Sun, Ren; Ho, Chih-Ming

2008-01-01

A mixture of drugs is often more effective than using a single effector. However, it is extremely challenging to identify potent drug combinations by trial and error because of the large number of possible combinations and the inherent complexity of the underlying biological network. With a closed-loop optimization modality, we experimentally demonstrate effective searching for potent drug combinations for controlling cellular functions through a large parametric space. Only tens of iterations out of one hundred thousand possible trials were needed to determine a potent combination of drugs for inhibiting vesicular stomatitis virus infection of NIH 3T3 fibroblasts. In addition, the drug combination reduced the required dosage by ≈10-fold compared with individual drugs. In another example, a potent mixture was identified in thirty iterations out of a possible million combinations of six cytokines that regulate the activity of nuclear factor kappa B in 293T cells. The closed-loop optimization approach possesses the potential of being an effective approach for manipulating a wide class of biological systems. PMID:18356295
Optical Closed-Loop Propulsion Control System Development

NASA Technical Reports Server (NTRS)

Poppel, Gary L.

1998-01-01

The overall objective of this program was to design and fabricate the components required for optical closed-loop control of a F404-400 turbofan engine, by building on the experience of the NASA Fiber Optic Control System Integration (FOCSI) program. Evaluating the performance of fiber optic technology at the component and system levels will result in helping to validate its use on aircraft engines. This report includes descriptions of three test plans. The EOI Acceptance Test is designed to demonstrate satisfactory functionality of the EOI, primarily fail-safe throughput of the F404 sensor signals in the normal mode, and validation, switching, and output of the five analog sensor signals as generated from validated optical sensor inputs, in the optical mode. The EOI System Test is designed to demonstrate acceptable F404 ECU functionality as interfaced with the EOI, making use of a production ECU test stand. The Optical Control Engine Test Request describes planned hardware installation, optical signal calibrations, data system coordination, test procedures, and data signal comparisons for an engine test demonstration of the optical closed-loop control.
A lumped parameter mathematical model for simulation of subsonic wind tunnels

NASA Technical Reports Server (NTRS)

Krosel, S. M.; Cole, G. L.; Bruton, W. M.; Szuch, J. R.

1986-01-01

Equations for a lumped parameter mathematical model of a subsonic wind tunnel circuit are presented. The equation state variables are internal energy, density, and mass flow rate. The circuit model is structured to allow for integration and analysis of tunnel subsystem models which provide functions such as control of altitude pressure and temperature. Thus the model provides a useful tool for investigating the transient behavior of the tunnel and control requirements. The model was applied to the proposed NASA Lewis Altitude Wind Tunnel (AWT) circuit and included transfer function representations of the tunnel supply/exhaust air and refrigeration subsystems. Both steady state and frequency response data are presented for the circuit model indicating the type of results and accuracy that can be expected from the model. Transient data for closed loop control of the tunnel and its subsystems are also presented, demonstrating the model's use as a control analysis tool.

An approach to the determination of aircraft handling qualities using pilot transfer functions

NASA Technical Reports Server (NTRS)

Adams, J. J.; Hatch, H. G., Jr.

1978-01-01

It was shown that a correlation exists between pilot-aircraft system closed-loop characteristics, determined by using analytical expressions for pilot response along with the analytical expression for the aircraft response, and pilot ratings obtained in many previous flight and simulation studies. Two different levels of preferred pilot response were used. These levels were: (1) a static gain and a second-order lag function with a lag time constant of 0.2 second; and (2) a static gain, a lead time constant of 1 second, and a 0.2-second lag time constant. If a system response with a pitch-angle time constant of 2.6 seconds and a stable oscillatory mode of motion with a period of 2.5 seconds could be achieved with the first-level pilot model, it was shown that the pilot rating will be satisfactory for that vehicle.
Apparatus and method of direct water cooling several parallel circuit cards each containing several chip packages

DOEpatents

Cipolla, Thomas M [Katonah, NY; Colgan, Evan George [Chestnut Ridge, NY; Coteus, Paul W [Yorktown Heights, NY; Hall, Shawn Anthony [Pleasantville, NY; Tian, Shurong [Mount Kisco, NY

2011-12-20

A cooling apparatus, system and like method for an electronic device includes a plurality of heat producing electronic devices affixed to a wiring substrate. A plurality of heat transfer assemblies each include heat spreaders and thermally communicate with the heat producing electronic devices for transferring heat from the heat producing electronic devices to the heat transfer assemblies. The plurality of heat producing electronic devices and respective heat transfer assemblies are positioned on the wiring substrate having the regions overlapping. A heat conduit thermally communicates with the heat transfer assemblies. The heat conduit circulates thermally conductive fluid therethrough in a closed loop for transferring heat to the fluid from the heat transfer assemblies via the heat spreader. A thermally conductive support structure supports the heat conduit and thermally communicates with the heat transfer assemblies via the heat spreader transferring heat to the fluid of the heat conduit from the support structure.
A platform for dynamic simulation and control of movement based on OpenSim and MATLAB.

PubMed

Mansouri, Misagh; Reinbolt, Jeffrey A

2012-05-11

Numerical simulations play an important role in solving complex engineering problems and have the potential to revolutionize medical decision making and treatment strategies. In this paper, we combine the rapid model-based design, control systems and powerful numerical method strengths of MATLAB/Simulink with the simulation and human movement dynamics strengths of OpenSim by developing a new interface between the two software tools. OpenSim is integrated with Simulink using the MATLAB S-function mechanism, and the interface is demonstrated using both open-loop and closed-loop control systems. While the open-loop system uses MATLAB/Simulink to separately reproduce the OpenSim Forward Dynamics Tool, the closed-loop system adds the unique feature of feedback control to OpenSim, which is necessary for most human movement simulations. An arm model example was successfully used in both open-loop and closed-loop cases. For the open-loop case, the simulation reproduced results from the OpenSim Forward Dynamics Tool with root mean square (RMS) differences of 0.03° for the shoulder elevation angle and 0.06° for the elbow flexion angle. MATLAB's variable step-size integrator reduced the time required to generate the forward dynamic simulation from 7.1s (OpenSim) to 2.9s (MATLAB). For the closed-loop case, a proportional-integral-derivative controller was used to successfully balance a pole on model's hand despite random force disturbances on the pole. The new interface presented here not only integrates the OpenSim and MATLAB/Simulink software tools, but also will allow neuroscientists, physiologists, biomechanists, and physical therapists to adapt and generate new solutions as treatments for musculoskeletal conditions. Copyright © 2012 Elsevier Ltd. All rights reserved.
A platform for dynamic simulation and control of movement based on OpenSim and MATLAB

PubMed Central

Mansouri, Misagh; Reinbolt, Jeffrey A.

2013-01-01

Numerical simulations play an important role in solving complex engineering problems and have the potential to revolutionize medical decision making and treatment strategies. In this paper, we combine the rapid model-based design, control systems and powerful numerical method strengths of MATLAB/Simulink with the simulation and human movement dynamics strengths of OpenSim by developing a new interface between the two software tools. OpenSim is integrated with Simulink using the MATLAB S-function mechanism, and the interface is demonstrated using both open-loop and closed-loop control systems. While the open-loop system uses MATLAB/Simulink to separately reproduce the OpenSim Forward Dynamics Tool, the closed-loop system adds the unique feature of feedback control to OpenSim, which is necessary for most human movement simulations. An arm model example was successfully used in both open-loop and closed-loop cases. For the open-loop case, the simulation reproduced results from the OpenSim Forward Dynamics Tool with root mean square (RMS) differences of 0.03° for the shoulder elevation angle and 0.06° for the elbow flexion angle. MATLAB’s variable step-size integrator reduced the time required to generate the forward dynamic simulation from 7.1 s (OpenSim) to 2.9 s (MATLAB). For the closed-loop case, a proportional–integral–derivative controller was used to successfully balance a pole on model’s hand despite random force disturbances on the pole. The new interface presented here not only integrates the OpenSim and MATLAB/Simulink software tools, but also will allow neuroscientists, physiologists, biomechanists, and physical therapists to adapt and generate new solutions as treatments for musculoskeletal conditions. PMID:22464351
eIF4B stimulates translation of long mRNAs with structured 5′ UTRs and low closed-loop potential but weak dependence on eIF4G

PubMed Central

Sen, Neelam Dabas; Zhou, Fujun; Harris, Michael S.; Ingolia, Nicholas T.

2016-01-01

DEAD-box RNA helicases eukaryotic translation initiation factor 4A (eIF4A) and Ded1 promote translation by resolving mRNA secondary structures that impede preinitiation complex (PIC) attachment to mRNA or scanning. Eukaryotic translation initiation factor 4B (eIF4B) is a cofactor for eIF4A but also might function independently of eIF4A. Ribosome profiling of mutants lacking eIF4B or with impaired eIF4A or Ded1 activity revealed that eliminating eIF4B reduces the relative translational efficiencies of many more genes than does inactivation of eIF4A, despite comparable reductions in bulk translation, and few genes display unusually strong requirements for both factors. However, either eliminating eIF4B or inactivating eIF4A preferentially impacts mRNAs with longer, more structured 5′ untranslated regions (UTRs). These findings reveal an eIF4A-independent role for eIF4B in addition to its function as eIF4A cofactor in promoting PIC attachment or scanning on structured mRNAs. eIF4B, eIF4A, and Ded1 mutations also preferentially impair translation of longer mRNAs in a fashion mitigated by the ability to form closed-loop messenger ribonucleoprotein particles (mRNPs) via eIF4F–poly(A)-binding protein 1 (Pab1) association, suggesting cooperation between closed-loop assembly and eIF4B/helicase functions. Remarkably, depleting eukaryotic translation initiation factor 4G (eIF4G), the scaffold subunit of eukaryotic translation initiation factor 4F (eIF4F), preferentially impacts short mRNAs with strong closed-loop potential and unstructured 5′ UTRs, exactly the opposite features associated with hyperdependence on the eIF4B/helicases. We propose that short, highly efficient mRNAs preferentially depend on the stimulatory effects of eIF4G-dependent closed-loop assembly. PMID:27601676
Effect of filling ratio and orientation on the thermal performance of closed loop pulsating heat pipe using ethanol

NASA Astrophysics Data System (ADS)

Rahman, Md. Lutfor; Chowdhury, Mehrin; Islam, Nawshad Arslan; Mufti, Sayed Muhammad; Ali, Mohammad

2016-07-01

Pulsating heat pipe (PHP) is a new, promising yet ambiguous technology for effective heat transfer of microelectronic devices where heat is carried by the vapor plugs and liquid slugs of the working fluid. The aim of this research paper is to better understand the operation of PHP through experimental investigations and obtain comparative results for different parameters. A series of experiments are conducted on a closed loop PHP (CLPHP) with 8 loops made of copper capillary tube of 2 mm inner diameter. Ethanol is taken as the working fluid. The operating characteristics are studied for the variation of heat input, filling ratio (FR) and orientation. The filling ratios are 40%, 50%, 60% and 70% based on its total volume. The orientations are 0° (vertical), 30°, 45° and 60°. The results clearly demonstrate the effect of filling ratio and inclination angle on the performance, operational stability and heat transfer capability of ethanol as working fluid of CLPHP. Important insight of the operational characteristics of CLPHP is obtained and optimum performance of CLPHP using ethanol is thus identified. Ethanol works best at 50-60%FR at wide range of heat inputs. At very low heat inputs, 40%FR can be used for attaining a good performance. Filling ratio below 40%FR is not suitable for using in CLPHP as it gives a low performance. The optimum performance of the device can be obtained at vertical position.
A low-dimensional approach to closed-loop control of a Mach 0.6 jet

NASA Astrophysics Data System (ADS)

Low, Kerwin R.; Berger, Zachary P.; Kostka, Stanislav; ElHadidi, Basman; Gogineni, Sivaram; Glauser, Mark N.

2013-04-01

Simultaneous time-resolved measurements of the near-field hydrodynamic pressure field, 2-component streamwise velocity field, and far-field acoustics are taken for an un-heated, axisymmetric Mach 0.6 jet in co-flow. Synthetic jet actuators placed around the periphery of the nozzle lip provide localized perturbations to the shear layer. The goal of this study was to develop an understanding of how the acoustic nature of the jet responds to unsteady shear layer excitation, and subsequently how this can be used to reduce the far-field noise. Review of the cross-correlations between the most energetic low-order spatial Fourier modes of the pressure and the far-field region reveals that mode 0 has a strong correlation and mode 1 has a weak correlation with the far-field. These modes are emulated with the synthetic jet array and used as drivers of the developing shear layer. In open loop forcing configurations, there is energy transfer among spatial scales, enhanced mixing, a reconfiguration of the low-dimensional spatial structure, and an increase in the overall sound pressure level (OASPL). In the closed loop configuration, changes to these quantities are more subtle but there is a reduction in the overall fluctuating sound pressure level OASPLf by 1.35 dB. It is argued that this reduction is correlated with the closed loop control feeding back the dynamical low-order information measured in the largest noise producing region.
Modeling Transients and Designing a Passive Safety System for a Nuclear Thermal Rocket Using Relap5

NASA Astrophysics Data System (ADS)

Khatry, Jivan

Long-term high payload missions necessitate the need for nuclear space propulsion. Several nuclear reactor types were investigated by the Nuclear Engine for Rocket Vehicle Application (NERVA) program of National Aeronautics and Space Administration (NASA). Study of planned/unplanned transients on nuclear thermal rockets is important due to the need for long-term missions. A NERVA design known as the Pewee I was selected for this purpose. The following transients were run: (i) modeling of corrosion-induced blockages on the peripheral fuel element coolant channels and their impact on radiation heat transfer in the core, and (ii) modeling of loss-of-flow-accidents (LOFAs) and their impact on radiation heat transfer in the core. For part (i), the radiation heat transfer rate of blocked channels increases while their neighbors' decreases. For part (ii), the core radiation heat transfer rate increases while the flow rate through the rocket system is decreased. However, the radiation heat transfer decreased while there was a complete LOFA. In this situation, the peripheral fuel element coolant channels handle the majority of the radiation heat transfer. Recognizing the LOFA as the most severe design basis accident, a passive safety system was designed in order to respond to such a transient. This design utilizes the already existing tie rod tubes and connects them to a radiator in a closed loop. Hence, this is basically a secondary loop. The size of the core is unchanged. During normal steady-state operation, this secondary loop keeps the moderator cool. Results show that the safety system is able to remove the decay heat and prevent the fuel elements from melting, in response to a LOFA and subsequent SCRAM.
Experimental determination of frequency response function estimates for flexible joint industrial manipulators with serial kinematics

NASA Astrophysics Data System (ADS)

Saupe, Florian; Knoblach, Andreas

2015-02-01

Two different approaches for the determination of frequency response functions (FRFs) are used for the non-parametric closed loop identification of a flexible joint industrial manipulator with serial kinematics. The two applied experiment designs are based on low power multisine and high power chirp excitations. The main challenge is to eliminate disturbances of the FRF estimates caused by the numerous nonlinearities of the robot. For the experiment design based on chirp excitations, a simple iterative procedure is proposed which allows exploiting the good crest factor of chirp signals in a closed loop setup. An interesting synergy of the two approaches, beyond validation purposes, is pointed out.
Recycling Pricing and Coordination of WEEE Dual-Channel Closed-Loop Supply Chain Considering Consumers' Bargaining.

PubMed

Zhu, Xiaodong; Wang, Jing; Tang, Juan

2017-12-15

Environmentally friendly handling and efficient recycling of waste electrical on Waste Electrical and Electronic Equipment (WEEE) have grown to be a global social problem. As holders of WEEE, consumers have a significant effect on the recycling process. A consideration of and attention to the influence of consumer behavior in the recycling process can help achieve more effective recycling of WEEE. In this paper, we built a dual-channel closed-loop supply chain model composed of manufacturers, retailers, and network recycling platforms. Based on the influence of customer bargaining behavior, we studied several different scenarios of centralized decision-making, decentralized decision-making, and contract coordination, using the Stackelberg game theory. The results show that retailers and network recycling platforms will reduce the direct recovery prices to maintain their own profit when considering the impact of consumer bargaining behavior, while remanufacturers will improve the transfer payment price for surrendering part of the profit under revenue and the expense sharing contract. Using this contract, we can achieve supply chain coordination and eliminate the effect of consumer bargaining behavior on supply chain performance. It can be viewed from the parameter sensitivity analysis that when we select the appropriate sharing coefficient, the closed-loop supply chain can achieve the same system performance under a centralized decision.
Recycling Pricing and Coordination of WEEE Dual-Channel Closed-Loop Supply Chain Considering Consumers’ Bargaining

PubMed Central

Zhu, Xiaodong; Wang, Jing; Tang, Juan

2017-01-01

Environmentally friendly handling and efficient recycling of waste electrical on Waste Electrical and Electronic Equipment (WEEE) have grown to be a global social problem. As holders of WEEE, consumers have a significant effect on the recycling process. A consideration of and attention to the influence of consumer behavior in the recycling process can help achieve more effective recycling of WEEE. In this paper, we built a dual-channel closed-loop supply chain model composed of manufacturers, retailers, and network recycling platforms. Based on the influence of customer bargaining behavior, we studied several different scenarios of centralized decision-making, decentralized decision-making, and contract coordination, using the Stackelberg game theory. The results show that retailers and network recycling platforms will reduce the direct recovery prices to maintain their own profit when considering the impact of consumer bargaining behavior, while remanufacturers will improve the transfer payment price for surrendering part of the profit under revenue and the expense sharing contract. Using this contract, we can achieve supply chain coordination and eliminate the effect of consumer bargaining behavior on supply chain performance. It can be viewed from the parameter sensitivity analysis that when we select the appropriate sharing coefficient, the closed-loop supply chain can achieve the same system performance under a centralized decision. PMID:29244778
Study of Compatibility of Stainless Steel Weld Joints with Liquid Sodium-Potassium Coolants for Fission Surface Power Reactors for Lunar and Space Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grossbeck, Martin; Qualls, Louis

To make a manned mission to the surface of the moon or to Mars with any significant residence time, the power requirements will make a nuclear reactor the most feasible source of energy. To prepare for such a mission, NASA has teamed with the DOE to develop Fission Surface Power technology with the goal of developing viable options. The Fission Surface Power System (FSPS) recommended as the initial baseline design includes a liquid metal reactor and primary coolant system that transfers heat to two intermediate liquid metal heat transfer loops. Each intermediate loop transfers heat to two Stirling heat exchangersmore » that each power two Stirling converters. Both the primary and the intermediate loops will use sodium-potassium (NaK) as the liquid metal coolant, and the primary loop will operate at temperatures exceeding 600°C. The alloy selected for the heat exchangers and piping is AISI Type 316L stainless steel. The extensive experience with NaK in breeder reactor programs and with earlier space reactors for unmanned missions lends considerable confidence in using NaK as a coolant in contact with stainless steel alloys. However, the microstructure, chemical segregation, and stress state of a weld leads to the potential for corrosion and cracking. Such failures have been experienced in NaK systems that have operated for times less than the eight year goal for the FSPS. For this reason, it was necessary to evaluate candidate weld techniques and expose welds to high-temperature, flowing NaK in a closed, closely controlled system. The goal of this project was to determine the optimum weld configuration for a NaK system that will withstand service for eight years under FSPS conditions. Since the most difficult weld to make and to evaluate is the tube to tube sheet weld in the intermediate heat exchangers, it was the focus of this research. A pumped loop of flowing NaK was fabricated for exposure of candidate weld specimens at temperatures of 600°C, the expected temperature within the intermediate heat exchangers. Since metal transfer from a high-temperature region to a cooler region is a predominant mode of corrosion in liquid metal systems, specimens were placed at zones in the loop at the above temperature to evaluate the effects of both alloy component leaching and metal deposition. Microstructural analysis was performed to evaluate weld performance on control weld specimens. The research was coordinated with Oak Ridge National Laboratory (ORNL) where most of the weld samples were prepared. In addition, ORNL participated in the loop operation to assist in keeping the testing relevant to the project and to take advantage of the extensive experience in liquid metal research at ORNL.« less
Molecular Dynamics Analysis Reveals Structural Insights into Mechanism of Nicotine N-Demethylation Catalyzed by Tobacco Cytochrome P450 Mono-Oxygenase

PubMed Central

Wang, Shan; Yang, Shuo; An, Baiyi; Wang, Shichen; Yin, Yuejia; Lu, Yang; Xu, Ying; Hao, Dongyun

2011-01-01

CYP82E4, a cytochrome P450 monooxygenase, has nicotine N-demethylase (NND) activity, which mediates the bioconversion of nicotine into nornicotine in senescing tobacco leaves. Nornicotine is a precursor of the carcinogen, tobacco-specific nitrosamine. CYP82E3 is an ortholog of CYP82E4 with 95% sequence identity, but it lacks NND activity. A recent site-directed mutagenesis study revealed that a single amino acid substitution, i.e., cysteine to tryptophan at the 330 position in the middle of protein, restores the NND activity of CYP82E3 entirely. However, the same amino acid change caused the loss of the NND activity of CYP82E4. To determine the mechanism of the functional turnover of the two molecules, four 3D structures, i.e., the two molecules and their corresponding cys–trp mutants were modeled. The resulting structures exhibited that the mutation site is far from the active site, which suggests that no direct interaction occurs between the two sites. Simulation studies in different biological scenarios revealed that the mutation introduces a conformation drift with the largest change at the F-G loop. The dynamics trajectories analysis using principal component analysis and covariance analysis suggests that the single amino acid change causes the opening and closing of the transfer channels of the substrates, products, and water by altering the motion of the F-G and B-C loops. The motion of helix I is also correlated with the motion of both the F-G loop and the B-C loop and; the single amino acid mutation resulted in the curvature of helix I. These results suggest that the single amino acid mutation outside the active site region may have indirectly mediated the flexibility of the F-G and B-C loops through helix I, causing a functional turnover of the P450 monooxygenase. PMID:21858078
PID Tuning Using Extremum Seeking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Killingsworth, N; Krstic, M

2005-11-15

Although proportional-integral-derivative (PID) controllers are widely used in the process industry, their effectiveness is often limited due to poor tuning. Manual tuning of PID controllers, which requires optimization of three parameters, is a time-consuming task. To remedy this difficulty, much effort has been invested in developing systematic tuning methods. Many of these methods rely on knowledge of the plant model or require special experiments to identify a suitable plant model. Reviews of these methods are given in [1] and the survey paper [2]. However, in many situations a plant model is not known, and it is not desirable to openmore » the process loop for system identification. Thus a method for tuning PID parameters within a closed-loop setting is advantageous. In relay feedback tuning [3]-[5], the feedback controller is temporarily replaced by a relay. Relay feedback causes most systems to oscillate, thus determining one point on the Nyquist diagram. Based on the location of this point, PID parameters can be chosen to give the closed-loop system a desired phase and gain margin. An alternative tuning method, which does not require either a modification of the system or a system model, is unfalsified control [6], [7]. This method uses input-output data to determine whether a set of PID parameters meets performance specifications. An adaptive algorithm is used to update the PID controller based on whether or not the controller falsifies a given criterion. The method requires a finite set of candidate PID controllers that must be initially specified [6]. Unfalsified control for an infinite set of PID controllers has been developed in [7]; this approach requires a carefully chosen input signal [8]. Yet another model-free PID tuning method that does not require opening of the loop is iterative feedback tuning (IFT). IFT iteratively optimizes the controller parameters with respect to a cost function derived from the output signal of the closed-loop system, see [9]. This method is based on the performance of the closed-loop system during a step response experiment [10], [11]. In this article we present a method for optimizing the step response of a closed-loop system consisting of a PID controller and an unknown plant with a discrete version of extremum seeking (ES). Specifically, ES is used to minimize a cost function similar to that used in [10], [11], which quantifies the performance of the PID controller. ES, a non-model-based method, iteratively modifies the arguments (in this application the PID parameters) of a cost function so that the output of the cost function reaches a local minimum or local maximum. In the next section we apply ES to PID controller tuning. We illustrate this technique through simulations comparing the effectiveness of ES to other PID tuning methods. Next, we address the importance of the choice of cost function and consider the effect of controller saturation. Furthermore, we discuss the choice of ES tuning parameters. Finally, we offer some conclusions.« less
PI controller design of a wind turbine: evaluation of the pole-placement method and tuning using constrained optimization

NASA Astrophysics Data System (ADS)

Mirzaei, Mahmood; Tibaldi, Carlo; Hansen, Morten H.

2016-09-01

PI/PID controllers are the most common wind turbine controllers. Normally a first tuning is obtained using methods such as pole-placement or Ziegler-Nichols and then extensive aeroelastic simulations are used to obtain the best tuning in terms of regulation of the outputs and reduction of the loads. In the traditional tuning approaches, the properties of different open loop and closed loop transfer functions of the system are not normally considered. In this paper, an assessment of the pole-placement tuning method is presented based on robustness measures. Then a constrained optimization setup is suggested to automatically tune the wind turbine controller subject to robustness constraints. The properties of the system such as the maximum sensitivity and complementary sensitivity functions (Ms and Mt ), along with some of the responses of the system, are used to investigate the controller performance and formulate the optimization problem. The cost function is the integral absolute error (IAE) of the rotational speed from a disturbance modeled as a step in wind speed. Linearized model of the DTU 10-MW reference wind turbine is obtained using HAWCStab2. Thereafter, the model is reduced with model order reduction. The trade-off curves are given to assess the tunings of the poles- placement method and a constrained optimization problem is solved to find the best tuning.
Modulation of critical brain dynamics using closed-loop neurofeedback stimulation.

PubMed

Zhigalov, Alexander; Kaplan, Alexander; Palva, J Matias

2016-08-01

EEG long-range temporal correlations (LRTCs) are a significant for both human cognition and brain disorders, but beyond suppression by sensory disruption, there are little means for influencing them non-invasively. We hypothesized that LRTCs could be controlled by engaging intrinsic neuroregulation through closed-loop neurofeedback stimulation. We used a closed-loop-stimulation paradigm where supra-threshold α-waves trigger visual flash stimuli while the subject performs the standard eyes-closed resting-state task. As a "sham" control condition, we applied similar stimulus sequences without the neurofeedback. Over three sessions, a significant difference in the LRTCs of α-band oscillations (U=89, p<0.028, Wilcoxon rank sum test) and their scalp topography (T=-2.92, p<0.010, T-test) emerged between the neurofeedback and sham conditions so that the LRTCs were stronger during neurofeedback than sham. No changes (F=0.16, p>0.69, ANOVA test) in the scalp topography of α-band power were observed in either condition. This study provides proof-of-concept for that EEG LRTCs, and hence critical brain dynamics, can be modulated with closed-loop stimulation in an automatic, involuntary fashion. We suggest that this modulation is mediated by an excitation-inhibition balance change achieved by the closed-loop neuroregulation. Automatic LRTC modulation opens novel avenues for both examining the functional roles of brain criticality in healthy subjects and for developing novel therapeutic approaches for brain disorders associated with abnormal LRTCs. Copyright © 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Numerical Analysis of Combined Well and Open-Closed Loops Geothermal (CWG) Systems

NASA Astrophysics Data System (ADS)

Park, Yu-Chul

2016-04-01

Open-loop geothermal heat pump (GHP) system and closed-loop heat pump systems have been used in Korea to reduce emission of greenhouse gases such as carbon dioxide (CO2). The GHP systems have the pros and cons, for example, the open-loop GHP system is good energy-efficient and the closed-loop GHP system requires minimum maintenance costs. The open-loop GHP system can be used practically only with large amount of groundwater supply. The closed-loop GHP system can be used with high costs of initial installation. The performance and efficiency of the GHP system depend on the characteristics of the GHP system itself in addition to the geologic conditions. To overcome the cons of open-loop or closed-loop GHP system, the combined well and open-closed loops geothermal (CWG) system was designed. The open-loop GHP system is surrounded with closed-loop GHP systems in the CWG system. The geothermal energy in closed-loop GHP systems is supplied by the groundwater pumped by the open-loop GHP system. In this study, 2 different types of the CWG systems (small aperture hybrid CWG system and large aperture CWG system) are estimated using numerical simulation models in the aspect of energy efficiency. This work was supported by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea. (No.20153030111120).
The serpentine optical waveguide: engineering the dispersion relations and the stopped light points.

PubMed

Scheuer, Jacob; Weiss, Ori

2011-06-06

We present a study a new type of optical slow-light structure comprising a serpentine shaped waveguide were the loops are coupled. The dispersion relation, group velocity and GVD are studied analytically using a transfer matrix method and numerically using finite difference time domain simulations. The structure exhibits zero group velocity points at the ends of the Brillouin zone, but also within the zone. The position of mid-zone zero group velocity point can be tuned by modifying the coupling coefficient between adjacent loops. Closed-form analytic expressions for the dispersion relations, group velocity and the mid-zone zero v(g) points are found and presented.
A distal mutation perturbs dynamic amino acid networks in dihydrofolate reductase

PubMed Central

Bae, Sung-Hun; Duggan, Brendan M.; Benkovic, Stephen J.; Dyson, H. Jane; Wright, Peter E

2013-01-01

Correlated networks of amino acids have been proposed to play a fundamental role in allostery and enzyme catalysis. These networks of amino acids can be traced from surface-exposed residues all the way into the active site, and disruption of these networks can decrease enzyme activity. Substitution of the distal Gly121 residue in E.coli dihydrofolate reductase results in up to a 200-fold decrease in the hydride transfer rate despite the fact that the residue is located 15 Å from the active-site center. In the present study, NMR relaxation experiments are used to demonstrate that dynamics on the ps-ns and μs-ms timescales are changed significantly in the G121V mutant of dihydrofolate reductase. In particular, ps-ns timescale dynamics are decreased in the FG loop (containing the mutated residue 121) and the neighboring active-site loop (the Met20 loop) in the mutant compared to wild-type enzyme, suggesting that these loops are dynamically coupled. Changes in methyl order parameters reveal a pathway by which dynamic perturbations can be propagated more than 25 Å across the protein from the site of mutation. All of the enzyme complexes, including the model Michaelis complex with folate and NADP+ bound, assume an occluded ground state conformation, and we do not observe sampling of a higher energy closed conformation by 15N R2 relaxation dispersion. This is highly significant, since it is only in the closed conformation that the cofactor and substrate reactive centers are positioned for reaction. The mutation also impairs μs - ms timescale fluctuations that have been implicated in product release from the wild type enzyme. Our results are consistent with an important role for Gly121 in controlling protein dynamics critical for enzyme function and further validate the dynamic energy landscape hypothesis of enzyme catalysis. PMID:23758161
Mechanical-thermal noise in drive-mode of a silicon micro-gyroscope.

PubMed

Yang, Bo; Wang, Shourong; Li, Hongsheng; Zhou, Bailing

2009-01-01

A new closed-loop drive scheme which decouples the phase and the gain of the closed-loop driving system was designed in a Silicon Micro-Gyroscope (SMG). We deduce the system model of closed-loop driving and use stochastic averaging to obtain an approximate "slow" system that clarifies the effect of thermal noise. The effects of mechanical-thermal noise on the driving performance of the SMG, including the noise spectral density of the driving amplitude and frequency, are derived. By calculating and comparing the noise amplitude due to thermal noise both in the opened-loop driving and in the closed-loop driving, we find that the closed-loop driving does not reduce the RMS noise amplitude. We observe that the RMS noise frequency can be reduced by increasing the quality factor and the drive amplitude in the closed-loop driving system. The experiment and simulation validate the feasibility of closed-loop driving and confirm the validity of the averaged equation and its stablility criterion. The experiment and simulation results indicate the electrical noise of closed-loop driving circuitry is bigger than the mechanical-thermal noise and as the driving mass decreases, the mechanical-thermal noise may get bigger than the electrical noise of the closed-loop driving circuitry.

Closing the Loop for Memory Prostheses: Detecting the Role of Hippocampal Neural Ensembles Using Nonlinear Models

PubMed Central

Hampson, Robert E.; Song, Dong; Chan, Rosa H.M.; Sweatt, Andrew J.; Riley, Mitchell R.; Goonawardena, Anushka V.; Marmarelis, Vasilis Z.; Gerhardt, Greg A.; Berger, Theodore W.; Deadwyler, Sam A.

2012-01-01

A major factor involved in providing closed loop feedback for control of neural function is to understand how neural ensembles encode online information critical to the final behavioral endpoint. This issue was directly assessed in rats performing a short-term delay memory task in which successful encoding of task information is dependent upon specific spatiotemporal firing patterns recorded from ensembles of CA3 and CA1 hippocampal neurons. Such patterns, extracted by a specially designed nonlinear multi-input multi-output (MIMO) nonlinear mathematical model, were used to predict successful performance online via a closed loop paradigm which regulated trial difficulty (time of retention) as a function of the “strength” of stimulus encoding. The significance of the MIMO model as a neural prosthesis has been demonstrated by substituting trains of electrical stimulation pulses to mimic these same ensemble firing patterns. This feature was used repeatedly to vary “normal” encoding as a means of understanding how neural ensembles can be “tuned” to mimic the inherent process of selecting codes of different strength and functional specificity. The capacity to enhance and tune hippocampal encoding via MIMO model detection and insertion of critical ensemble firing patterns shown here provides the basis for possible extension to other disrupted brain circuitry. PMID:22498704
Advances in bioresponsive closed-loop drug delivery systems.

PubMed

Yu, Jicheng; Zhang, Yuqi; Yan, Junjie; Kahkoska, Anna R; Gu, Zhen

2017-11-27

Controlled drug delivery systems are able to improve efficacy and safety of therapeutics by optimizing the duration and kinetics of release. Among them, closed-loop delivery strategies, also known as self-regulated administration, have proven to be a practical tool for homeostatic regulation, by tuning drug release as a function of biosignals relevant to physiological and pathological processes. A typical example is glucose-responsive insulin delivery system, which can mimic the pancreatic beta cells to release insulin with a proper dose at a proper time point by responding to plasma glucose levels. Similar self-regulated systems are also important in the treatment of other diseases including thrombosis and bacterial infection. In this review, we survey the recent advances in bioresponsive closed-loop drug delivery systems, including glucose-responsive, enzyme-activated, and other biosignal-mediated delivery systems. We also discuss the future opportunities and challenges in this field. Copyright © 2017 Elsevier B.V. All rights reserved.
Closed-Loop Optogenetic Intervention in Mice

PubMed Central

Oijala, Mikko; Soltesz, Ivan

2014-01-01

Optogenetic interventions offer novel ways of probing, in a temporally specific manner, the roles of specific cell types in neuronal network functions of awake, behaving animals. Despite the unique potential for temporally specific optogenetic interventions in disease states, a major hurdle in its broad application to unpredictable brain states in a laboratory setting is constructing a real-time responsive system. We recently created a closed-loop system for stopping spontaneous seizures in chronically epileptic mice using optogenetic intervention. This system performs with very high sensitivity and specificity, and the strategy is relevant not only to epilepsy, but can also be used to react in real time, with optogenetic or other interventions, to diverse brain states. The protocol presented here is highly modular and requires variable time to perform. We describe the basic construction of a complete system, and include our downloadable custom closed-loop detection software which can be employed for this purpose. PMID:23845961
Origin and control of instability in SCR/triac three-phase motor controllers

NASA Technical Reports Server (NTRS)

Dearth, J. J.

1982-01-01

The energy savings and reactive power reduction functions initiated by the power factor controller (PFC) are discussed. A three-phase PFC with soft start is examined analytically and experimentally to determine how well it controls the open loop instability and other possible modes of instability. The detailed mechanism of the open loop instability is determined and shown to impose design constraints on the closed loop system. The design is shown to meet those constraints.
Closed Field Coronal Heating Models Inspired by Wave Turbulence

NASA Astrophysics Data System (ADS)

Downs, C.; Lionello, R.; Mikic, Z.; Linker, J.; Velli, M. M.

2013-12-01

To simulate the energy balance of coronal plasmas on macroscopic scales, we often require the specification of the coronal heating mechanism in some functional form. To go beyond empirical formulations and to build a more physically motivated heating function, we investigate the wave-turbulence dissipation (WTD) phenomenology for the heating of closed coronal loops. To do so, we employ an implementation of non-WKB equations designed to capture the large-scale propagation, reflection, and dissipation of wave turbulence along a loop. The parameter space of this model is explored by solving the coupled WTD and hydrodynamic equations in 1D for an idealized loop, and the relevance to a range of solar conditions is established by computing solutions for several hundred loops extracted from a realistic 3D coronal field. Due to the implicit dependence of the WTD heating model on loop geometry and plasma properties along the loop and at the footpoints, we find that this model can significantly reduce the number of free parameters when compared to traditional empirical heating models, and still robustly describe a broad range of quiet-sun and active region conditions. The importance of the self-reflection term in producing realistic heating scale heights and thermal non-equilibrium cycles is discussed, and preliminary 3D thermodynamic MHD simulations using this formulation are presented. Research supported by NASA and NSF.
The structural coupling between ATPase activation and recovery stroke in the myosin II motor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koppole, Sampath; Smith, Jeremy C; Fischer, S.

2007-07-01

Before the myosin motor head can perform the next power stroke, it undergoes a large conformational transition in which the converter domain, bearing the lever arm, rotates {approx} 65{sup o}. Simultaneous with this 'recovery stroke', myosin activates its ATPase function by closing the Switch-2 loop over the bound ATP. This coupling between the motions of the converter domain and of the 40 {angstrom}-distant Switch-2 loop is essential to avoid unproductive ATP hydrolysis. The coupling mechanism is determined here by finding a series of optimized intermediates between crystallographic end structures of the recovery stroke (Dictyostelium discoideum), yielding movies of the transitionmore » at atomic detail. The successive formation of two hydrogen bonds by the Switch-2 loop is correlated with the successive see-saw motions of the relay and SH1 helices that hold the converter domain. SH1 helix and Switch-2 loop communicate via a highly conserved loop that wedges against the SH1-helix upon Switch-2 closing.« less
The structural coupling between ATPase activation and recovery stroke in the myosin II motor.

PubMed

Koppole, Sampath; Smith, Jeremy C; Fischer, Stefan

2007-07-01

Before the myosin motor head can perform the next power stroke, it undergoes a large conformational transition in which the converter domain, bearing the lever arm, rotates approximately 65 degrees . Simultaneous with this "recovery stroke," myosin activates its ATPase function by closing the Switch-2 loop over the bound ATP. This coupling between the motions of the converter domain and of the 40 A-distant Switch-2 loop is essential to avoid unproductive ATP hydrolysis. The coupling mechanism is determined here by finding a series of optimized intermediates between crystallographic end structures of the recovery stroke (Dictyostelium discoideum), yielding movies of the transition at atomic detail. The successive formation of two hydrogen bonds by the Switch-2 loop is correlated with the successive see-saw motions of the relay and SH1 helices that hold the converter domain. SH1 helix and Switch-2 loop communicate via a highly conserved loop that wedges against the SH1-helix upon Switch-2 closing.
Falcon: a highly flexible open-source software for closed-loop neuroscience.

PubMed

Ciliberti, Davide; Kloosterman, Fabian

2017-08-01

Closed-loop experiments provide unique insights into brain dynamics and function. To facilitate a wide range of closed-loop experiments, we created an open-source software platform that enables high-performance real-time processing of streaming experimental data. We wrote Falcon, a C++ multi-threaded software in which the user can load and execute an arbitrary processing graph. Each node of a Falcon graph is mapped to a single thread and nodes communicate with each other through thread-safe buffers. The framework allows for easy implementation of new processing nodes and data types. Falcon was tested both on a 32-core and a 4-core workstation. Streaming data was read from either a commercial acquisition system (Neuralynx) or the open-source Open Ephys hardware, while closed-loop TTL pulses were generated with a USB module for digital output. We characterized the round-trip latency of our Falcon-based closed-loop system, as well as the specific latency contribution of the software architecture, by testing processing graphs with up to 32 parallel pipelines and eight serial stages. We finally deployed Falcon in a task of real-time detection of population bursts recorded live from the hippocampus of a freely moving rat. On Neuralynx hardware, round-trip latency was well below 1 ms and stable for at least 1 h, while on Open Ephys hardware latencies were below 15 ms. The latency contribution of the software was below 0.5 ms. Round-trip and software latencies were similar on both 32- and 4-core workstations. Falcon was used successfully to detect population bursts online with ~40 ms average latency. Falcon is a novel open-source software for closed-loop neuroscience. It has sub-millisecond intrinsic latency and gives the experimenter direct control of CPU resources. We envisage Falcon to be a useful tool to the neuroscientific community for implementing a wide variety of closed-loop experiments, including those requiring use of complex data structures and real-time execution of computationally intensive algorithms, such as population neural decoding/encoding from large cell assemblies.
Falcon: a highly flexible open-source software for closed-loop neuroscience

NASA Astrophysics Data System (ADS)

Ciliberti, Davide; Kloosterman, Fabian

2017-08-01

Objective. Closed-loop experiments provide unique insights into brain dynamics and function. To facilitate a wide range of closed-loop experiments, we created an open-source software platform that enables high-performance real-time processing of streaming experimental data. Approach. We wrote Falcon, a C++ multi-threaded software in which the user can load and execute an arbitrary processing graph. Each node of a Falcon graph is mapped to a single thread and nodes communicate with each other through thread-safe buffers. The framework allows for easy implementation of new processing nodes and data types. Falcon was tested both on a 32-core and a 4-core workstation. Streaming data was read from either a commercial acquisition system (Neuralynx) or the open-source Open Ephys hardware, while closed-loop TTL pulses were generated with a USB module for digital output. We characterized the round-trip latency of our Falcon-based closed-loop system, as well as the specific latency contribution of the software architecture, by testing processing graphs with up to 32 parallel pipelines and eight serial stages. We finally deployed Falcon in a task of real-time detection of population bursts recorded live from the hippocampus of a freely moving rat. Main results. On Neuralynx hardware, round-trip latency was well below 1 ms and stable for at least 1 h, while on Open Ephys hardware latencies were below 15 ms. The latency contribution of the software was below 0.5 ms. Round-trip and software latencies were similar on both 32- and 4-core workstations. Falcon was used successfully to detect population bursts online with ~40 ms average latency. Significance. Falcon is a novel open-source software for closed-loop neuroscience. It has sub-millisecond intrinsic latency and gives the experimenter direct control of CPU resources. We envisage Falcon to be a useful tool to the neuroscientific community for implementing a wide variety of closed-loop experiments, including those requiring use of complex data structures and real-time execution of computationally intensive algorithms, such as population neural decoding/encoding from large cell assemblies.
Advanced physical-chemical life support systems research

NASA Technical Reports Server (NTRS)

Evanich, Peggy L.

1988-01-01

A proposed NASA space research and technology development program will provide adequate data for designing closed loop life support systems for long-duration manned space missions. This program, referred to as the Pathfinder Physical-Chemical Closed Loop Life Support Program, is to identify and develop critical chemical engineering technologies for the closure of air and water loops within the spacecraft, surface habitats or mobility devices. Computerized simulation can be used both as a research and management tool. Validated models will guide the selection of the best known applicable processes and in the development of new processes. For the integration of the habitat system, a biological subsystem would be introduced to provide food production and to enhance the physical-chemical life support functions on an ever-increasing basis.
Long range dynamic effects of point-mutations trap a response regulator in an active conformation

PubMed Central

Bobay, Benjamin G.; Thompson, Richele J.; Hoch, James A.; Cavanagh, John

2010-01-01

When a point-mutation in a protein elicits a functional change, it is most common to assign this change to local structural perturbations. Here we show that point-mutations, distant from an essential highly dynamic kinase recognition loop in the response regulator Spo0F, lock this loop in an active conformation. This ‘conformational trapping’ results in functionally hyperactive Spo0F. Consequently, point-mutations are seen to affect functionally critical motions both close to and far from the mutational site. PMID:20828564
Efficient Computation of Closed-loop Frequency Response for Large Order Flexible Systems

NASA Technical Reports Server (NTRS)

Maghami, Peiman G.; Giesy, Daniel P.

1997-01-01

An efficient and robust computational scheme is given for the calculation of the frequency response function of a large order, flexible system implemented with a linear, time invariant control system. Advantage is taken of the highly structured sparsity of the system matrix of the plant based on a model of the structure using normal mode coordinates. The computational time per frequency point of the new computational scheme is a linear function of system size, a significant improvement over traditional, full-matrix techniques whose computational times per frequency point range from quadratic to cubic functions of system size. This permits the practical frequency domain analysis of systems of much larger order than by traditional, full-matrix techniques. Formulations are given for both open and closed loop loop systems. Numerical examples are presented showing the advantages of the present formulation over traditional approaches, both in speed and in accuracy. Using a model with 703 structural modes, a speed-up of almost two orders of magnitude was observed while accuracy improved by up to 5 decimal places.
Shrunk loop theorem for the topology probabilities of closed Brownian (or Feynman) paths on the twice punctured plane

NASA Astrophysics Data System (ADS)

Giraud, O.; Thain, A.; Hannay, J. H.

2004-02-01

The shrunk loop theorem proved here is an integral identity which facilitates the calculation of the relative probability (or probability amplitude) of any given topology that a free, closed Brownian (or Feynman) path of a given 'duration' might have on the twice punctured plane (plane with two marked points). The result is expressed as a 'scattering' series of integrals of increasing dimensionality based on the maximally shrunk version of the path. Physically, this applies in different contexts: (i) the topology probability of a closed ideal polymer chain on a plane with two impassable points, (ii) the trace of the Schrödinger Green function, and thence spectral information, in the presence of two Aharonov-Bohm fluxes and (iii) the same with two branch points of a Riemann surface instead of fluxes. Our theorem starts from the Stovicek scattering expansion for the Green function in the presence of two Aharonov-Bohm flux lines, which itself is based on the famous Sommerfeld one puncture point solution of 1896 (the one puncture case has much easier topology, just one winding number). Stovicek's expansion itself can supply the results at the expense of choosing a base point on the loop and then integrating it away. The shrunk loop theorem eliminates this extra two-dimensional integration, distilling the topology from the geometry.
Open Ephys: an open-source, plugin-based platform for multichannel electrophysiology.

PubMed

Siegle, Joshua H; López, Aarón Cuevas; Patel, Yogi A; Abramov, Kirill; Ohayon, Shay; Voigts, Jakob

2017-08-01

Closed-loop experiments, in which causal interventions are conditioned on the state of the system under investigation, have become increasingly common in neuroscience. Such experiments can have a high degree of explanatory power, but they require a precise implementation that can be difficult to replicate across laboratories. We sought to overcome this limitation by building open-source software that makes it easier to develop and share algorithms for closed-loop control. We created the Open Ephys GUI, an open-source platform for multichannel electrophysiology experiments. In addition to the standard 'open-loop' visualization and recording functionality, the GUI also includes modules for delivering feedback in response to events detected in the incoming data stream. Importantly, these modules can be built and shared as plugins, which makes it possible for users to extend the functionality of the GUI through a simple API, without having to understand the inner workings of the entire application. In combination with low-cost, open-source hardware for amplifying and digitizing neural signals, the GUI has been used for closed-loop experiments that perturb the hippocampal theta rhythm in a phase-specific manner. The Open Ephys GUI is the first widely used application for multichannel electrophysiology that leverages a plugin-based workflow. We hope that it will lower the barrier to entry for electrophysiologists who wish to incorporate real-time feedback into their research.
Implementing Audio Digital Feedback Loop Using the National Instruments RIO System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, G.; Byrd, J. M.

2006-11-20

Development of system for high precision RF distribution and laser synchronization at Berkeley Lab has been ongoing for several years. Successful operation of these systems requires multiple audio bandwidth feedback loops running at relatively high gains. Stable operation of the feedback loops requires careful design of the feedback transfer function. To allow for flexible and compact implementation, we have developed digital feedback loops on the National Instruments Reconfigurable Input/Output (RIO) platform. This platform uses an FPGA and multiple I/Os that can provide eight parallel channels running different filters. We present the design and preliminary experimental results of this system.
Analysis of spacecraft battery charger systems

NASA Astrophysics Data System (ADS)

Kim, Seong J.; Cho, Bo H.

In spacecraft battery charger systems, switching regulators are widely used for bus voltage regulation, charge current regulation, and peak power tracking. Small-signal dynamic characteristics of the battery charging subsystem of direct energy transfer (DET) and peak power tracking (PPT) systems are analyzed to facilitate design of the control loop for optimum performance and stability. Control loop designs of the charger in various modes of operation are discussed. Analyses are verified through simulations. It is shown that when the charger operates in the bus voltage regulation mode, the control-to-voltage transfer function has a negative DC gain and two LHP zeros in both the DET and PPT systems. The control-to-inductor current transfer function also has a negative DC gain and a RHP zero. Thus, in the current-mode control, the current loop can no longer be used to stabilize the system. When the system operates in the charge current regulation mode, the charger operates with a fixed duty cycle which is determined by the regulated bus voltage and the battery voltage. Without an input filter, the converter becomes a first-order system. When the peak power tracker is inactive, the operating point of the solar array output moves to the voltage source region. Thus, the solar array behaves as a stiff voltage source to a constant power load.
Coupling between Catalytic Loop Motions and Enzyme Global Dynamics

PubMed Central

Kurkcuoglu, Zeynep; Bakan, Ahmet; Kocaman, Duygu; Bahar, Ivet; Doruker, Pemra

2012-01-01

Catalytic loop motions facilitate substrate recognition and binding in many enzymes. While these motions appear to be highly flexible, their functional significance suggests that structure-encoded preferences may play a role in selecting particular mechanisms of motions. We performed an extensive study on a set of enzymes to assess whether the collective/global dynamics, as predicted by elastic network models (ENMs), facilitates or even defines the local motions undergone by functional loops. Our dataset includes a total of 117 crystal structures for ten enzymes of different sizes and oligomerization states. Each enzyme contains a specific functional/catalytic loop (10–21 residues long) that closes over the active site during catalysis. Principal component analysis (PCA) of the available crystal structures (including apo and ligand-bound forms) for each enzyme revealed the dominant conformational changes taking place in these loops upon substrate binding. These experimentally observed loop reconfigurations are shown to be predominantly driven by energetically favored modes of motion intrinsically accessible to the enzyme in the absence of its substrate. The analysis suggests that robust global modes cooperatively defined by the overall enzyme architecture also entail local components that assist in suitable opening/closure of the catalytic loop over the active site. PMID:23028297
A Fabry-Pérot electro-optic sensing system using a drive-current-tuned wavelength laser diode.

PubMed

Kuo, Wen-Kai; Wu, Pei-Yu; Lee, Chang-Ching

2010-05-01

A Fabry-Pérot enhanced electro-optic sensing system that utilizes a drive-current-tuned wavelength laser diode is presented. An electro-optic prober made of LiNbO(3) crystal with an asymmetric Fabry-Pérot cavity is used in this system. To lock the wavelength of the laser diode at resonant condition, a closed-loop power control scheme is proposed. Experiment results show that the system can keep the electro-optic prober at high sensitivity for a long working time when the closed-loop control function is on. If this function is off, the sensitivity may be fluctuated and only one-third of the best level in the worst case.
Testing of a Helium Loop Heat Pipe for Large Area Cryocooling

NASA Technical Reports Server (NTRS)

Ku, Jentung; Robinson, Franklin

2016-01-01

Future NASA space telescopes and exploration missions require cryocooling of large areas such as optics, detector arrays, and cryogenic propellant tanks. One device that can potentially be used to provide closed-loop cryocooling is the cryogenic loop heat pipe (CLHP). A CLHP has many advantages over other devices in terms of reduced mass, reduced vibration, high reliability, and long life. A helium CLHP has been tested extensively in a thermal vacuum chamber using a cryocooler as the heat sink to characterize its transient and steady performance and verify its ability to cool large areas or components in the 3K temperature range. A copper plate with attached electrical heaters was used to simulate the heat source, and heat was collected by the CLHP evaporator and transferred to the cryocooler for ultimate heat rejection. The helium CLHP thermal performance test included cool-down from the ambient temperature, startup, capillary limit, heat removal capability, rapid power changes, and long duration steady state operation. The helium CLHP demonstrated robust operation under steady state and transient conditions. The loop could be cooled from the ambient temperature to subcritical temperatures very effectively, and could start successfully without pre-conditioning by simply applying power to both the capillary pump and the evaporator plate. It could adapt to rapid changes in the heat load, and reach a new steady state very quickly. Heat removal between 10mW and 140mW was demonstrated, yielding a power turn down ratio of 14. When the CLHP capillary limit was exceeded, the loop could resume its normal function by reducing the power to the capillary pump. Steady state operations up to 17 hours at several heat loads were demonstrated. The ability of the helium CLHP to cool large areas was therefore successfully verified.
Testing of a Helium Loop Heat Pipe for Large Area Cryocooling

NASA Technical Reports Server (NTRS)

Ku, Jentung; Robinson, Franklin Lee

2015-01-01

Future NASA space telescopes and exploration missions require cryocooling of large areas such as optics, detector arrays, and cryogenic propellant tanks. One device that can potentially be used to provide closed-loop cryocooling is the cryogenic loop heat pipe (CLHP). A CLHP has many advantages over other devices in terms of reduced mass, reduced vibration, high reliability, and long life. A helium CLHP has been tested extensively in a thermal vacuum chamber using a cryocooler as the heat sink to characterize its transient and steady performance and verify its ability to cool large areas or components in the 3K temperature range. A copper plate with attached electrical heters was used to simulate the heat source, and heat was collected by the CLHP evaporator and transferred to the cryocooler for ultimate heat rejection. The helium CLHP thermal performance test included cool-down from the ambient temperature, startup, capillary limit, heat removal capability, rapid power changes, and long duration steady state operation. The helium CLHP demonstrated robust operation under steady state and transient conditions. The loop could be cooled from the ambient temperature to subcritical temperatures very effectively, and could start successfully without pre-conditioning by simply applying power to both the capillary pump and the evaporator plate. It could adapt to rapid changes in the heat load, and reach a new steady state very quickly. Heat removal between 10mW and 140mW was demonstrated, yielding a power turn down ratio of 14. When the CLHP capillary limit was exceeded, the loop could resume its normal function by reducing the power to the capillary pump. Steady state operations up to 17 hours at several heat loads were demonstrated. The ability of the helium CLHP to cool large areas was therefore successfully verified.

Plasticity of 150-loop in influenza neuraminidase explored by Hamiltonian replica exchange molecular dynamics simulations.

PubMed

Han, Nanyu; Mu, Yuguang

2013-01-01

Neuraminidase (NA) of influenza is a key target for antiviral inhibitors, and the 150-cavity in group-1 NA provides new insight in treating this disease. However, NA of 2009 pandemic influenza (09N1) was found lacking this cavity in a crystal structure. To address the issue of flexibility of the 150-loop, Hamiltonian replica exchange molecular dynamics simulations were performed on different groups of NAs. Free energy landscape calculated based on the volume of 150-cavity indicates that 09N1 prefers open forms of 150-loop. The turn A (residues 147-150) of the 150-loop is discovered as the most dynamical motif which induces the inter-conversion of this loop among different conformations. In the turn A, the backbone dynamic of residue 149 is highly related with the shape of 150-loop, thus can function as a marker for the conformation of 150-loop. As a contrast, the closed conformation of 150-loop is more energetically favorable in N2, one of group-2 NAs. The D147-H150 salt bridge is found having no correlation with the conformation of 150-loop. Instead the intimate salt bridge interaction between the 150 and 430 loops in N2 variant contributes the stabilizing factor for the closed form of 150-loop. The clustering analysis elaborates the structural plasticity of the loop. This enhanced sampling simulation provides more information in further structural-based drug discovery on influenza virus.
Plasticity of 150-Loop in Influenza Neuraminidase Explored by Hamiltonian Replica Exchange Molecular Dynamics Simulations

PubMed Central

Han, Nanyu; Mu, Yuguang

2013-01-01

Neuraminidase (NA) of influenza is a key target for antiviral inhibitors, and the 150-cavity in group-1 NA provides new insight in treating this disease. However, NA of 2009 pandemic influenza (09N1) was found lacking this cavity in a crystal structure. To address the issue of flexibility of the 150-loop, Hamiltonian replica exchange molecular dynamics simulations were performed on different groups of NAs. Free energy landscape calculated based on the volume of 150-cavity indicates that 09N1 prefers open forms of 150-loop. The turn A (residues 147–150) of the 150-loop is discovered as the most dynamical motif which induces the inter-conversion of this loop among different conformations. In the turn A, the backbone dynamic of residue 149 is highly related with the shape of 150-loop, thus can function as a marker for the conformation of 150-loop. As a contrast, the closed conformation of 150-loop is more energetically favorable in N2, one of group-2 NAs. The D147-H150 salt bridge is found having no correlation with the conformation of 150-loop. Instead the intimate salt bridge interaction between the 150 and 430 loops in N2 variant contributes the stabilizing factor for the closed form of 150-loop. The clustering analysis elaborates the structural plasticity of the loop. This enhanced sampling simulation provides more information in further structural-based drug discovery on influenza virus. PMID:23593372
A Markov chain technique for determining the acquisition behavior of a digital tracking loop

NASA Technical Reports Server (NTRS)

Chadwick, H. D.

1972-01-01

An iterative procedure is presented for determining the acquisition behavior of discrete or digital implementations of a tracking loop. The technique is based on the theory of Markov chains and provides the cumulative probability of acquisition in the loop as a function of time in the presence of noise and a given set of initial condition probabilities. A digital second-order tracking loop to be used in the Viking command receiver for continuous tracking of the command subcarrier phase was analyzed using this technique, and the results agree closely with experimental data.
Optical phase-locked loop (OPLL) for free-space laser communications with heterodyne detection

NASA Technical Reports Server (NTRS)

Win, Moe Z.; Chen, Chien-Chung; Scholtz, Robert A.

1991-01-01

Several advantages of coherent free-space optical communications are outlined. Theoretical analysis is formulated for an OPLL disturbed by shot noise, modulation noise, and frequency noise consisting of a white component, a 1/f component, and a 1/f-squared component. Each of the noise components is characterized by its associated power spectral density. It is shown that the effect of modulation depends only on the ratio of loop bandwidth and data rate, and is negligible for an OPLL with loop bandwidth smaller than one fourth the data rate. Total phase error variance as a function of loop bandwidth is displayed for several values of carrier signal to noise ratio. Optimal loop bandwidth is also calculated as a function of carrier signal to noise ratio. An OPLL experiment is performed, where it is shown that the measured phase error variance closely matches the theoretical predictions.
Bio-Inspired Controller on an FPGA Applied to Closed-Loop Diaphragmatic Stimulation

PubMed Central

Zbrzeski, Adeline; Bornat, Yannick; Hillen, Brian; Siu, Ricardo; Abbas, James; Jung, Ranu; Renaud, Sylvie

2016-01-01

Cervical spinal cord injury can disrupt connections between the brain respiratory network and the respiratory muscles which can lead to partial or complete loss of ventilatory control and require ventilatory assistance. Unlike current open-loop technology, a closed-loop diaphragmatic pacing system could overcome the drawbacks of manual titration as well as respond to changing ventilation requirements. We present an original bio-inspired assistive technology for real-time ventilation assistance, implemented in a digital configurable Field Programmable Gate Array (FPGA). The bio-inspired controller, which is a spiking neural network (SNN) inspired by the medullary respiratory network, is as robust as a classic controller while having a flexible, low-power and low-cost hardware design. The system was simulated in MATLAB with FPGA-specific constraints and tested with a computational model of rat breathing; the model reproduced experimentally collected respiratory data in eupneic animals. The open-loop version of the bio-inspired controller was implemented on the FPGA. Electrical test bench characterizations confirmed the system functionality. Open and closed-loop paradigm simulations were simulated to test the FPGA system real-time behavior using the rat computational model. The closed-loop system monitors breathing and changes in respiratory demands to drive diaphragmatic stimulation. The simulated results inform future acute animal experiments and constitute the first step toward the development of a neuromorphic, adaptive, compact, low-power, implantable device. The bio-inspired hardware design optimizes the FPGA resource and time costs while harnessing the computational power of spike-based neuromorphic hardware. Its real-time feature makes it suitable for in vivo applications. PMID:27378844
Introducing uncertainty analysis of nucleation and crystal growth models in Process Analytical Technology (PAT) system design of crystallization processes.

PubMed

Samad, Noor Asma Fazli Abdul; Sin, Gürkan; Gernaey, Krist V; Gani, Rafiqul

2013-11-01

This paper presents the application of uncertainty and sensitivity analysis as part of a systematic model-based process monitoring and control (PAT) system design framework for crystallization processes. For the uncertainty analysis, the Monte Carlo procedure is used to propagate input uncertainty, while for sensitivity analysis, global methods including the standardized regression coefficients (SRC) and Morris screening are used to identify the most significant parameters. The potassium dihydrogen phosphate (KDP) crystallization process is used as a case study, both in open-loop and closed-loop operation. In the uncertainty analysis, the impact on the predicted output of uncertain parameters related to the nucleation and the crystal growth model has been investigated for both a one- and two-dimensional crystal size distribution (CSD). The open-loop results show that the input uncertainties lead to significant uncertainties on the CSD, with appearance of a secondary peak due to secondary nucleation for both cases. The sensitivity analysis indicated that the most important parameters affecting the CSDs are nucleation order and growth order constants. In the proposed PAT system design (closed-loop), the target CSD variability was successfully reduced compared to the open-loop case, also when considering uncertainty in nucleation and crystal growth model parameters. The latter forms a strong indication of the robustness of the proposed PAT system design in achieving the target CSD and encourages its transfer to full-scale implementation. Copyright © 2013 Elsevier B.V. All rights reserved.
Human operator identification model and related computer programs

NASA Technical Reports Server (NTRS)

Kessler, K. M.; Mohr, J. N.

1978-01-01

Four computer programs which provide computational assistance in the analysis of man/machine systems are reported. The programs are: (1) Modified Transfer Function Program (TF); (2) Time Varying Response Program (TVSR); (3) Optimal Simulation Program (TVOPT); and (4) Linear Identification Program (SCIDNT). The TV program converts the time domain state variable system representative to frequency domain transfer function system representation. The TVSR program computes time histories of the input/output responses of the human operator model. The TVOPT program is an optimal simulation program and is similar to TVSR in that it produces time histories of system states associated with an operator in the loop system. The differences between the two programs are presented. The SCIDNT program is an open loop identification code which operates on the simulated data from TVOPT (or TVSR) or real operator data from motion simulators.
Closing loop base pairs in RNA loop-loop complexes: structural behavior, interaction energy and solvation analysis through molecular dynamics simulations.

PubMed

Golebiowski, Jérôme; Antonczak, Serge; Fernandez-Carmona, Juan; Condom, Roger; Cabrol-Bass, Daniel

2004-12-01

Nanosecond molecular dynamics using the Ewald summation method have been performed to elucidate the structural and energetic role of the closing base pair in loop-loop RNA duplexes neutralized by Mg2+ counterions in aqueous phases. Mismatches GA, CU and Watson-Crick GC base pairs have been considered for closing the loop of an RNA in complementary interaction with HIV-1 TAR. The simulations reveal that the mismatch GA base, mediated by a water molecule, leads to a complex that presents the best compromise between flexibility and energetic contributions. The mismatch CU base pair, in spite of the presence of an inserted water molecule, is too short to achieve a tight interaction at the closing-loop junction and seems to force TAR to reorganize upon binding. An energetic analysis has allowed us to quantify the strength of the interactions of the closing and the loop-loop pairs throughout the simulations. Although the water-mediated GA closing base pair presents an interaction energy similar to that found on fully geometry-optimized structure, the water-mediated CU closing base pair energy interaction reaches less than half the optimal value.
PLATSIM: A Simulation and Analysis Package for Large-Order Flexible Systems. Version 2.0

NASA Technical Reports Server (NTRS)

Maghami, Peiman G.; Kenny, Sean P.; Giesy, Daniel P.

1997-01-01

The software package PLATSIM provides efficient time and frequency domain analysis of large-order generic space platforms. PLATSIM can perform open-loop analysis or closed-loop analysis with linear or nonlinear control system models. PLATSIM exploits the particular form of sparsity of the plant matrices for very efficient linear and nonlinear time domain analysis, as well as frequency domain analysis. A new, original algorithm for the efficient computation of open-loop and closed-loop frequency response functions for large-order systems has been developed and is implemented within the package. Furthermore, a novel and efficient jitter analysis routine which determines jitter and stability values from time simulations in a very efficient manner has been developed and is incorporated in the PLATSIM package. In the time domain analysis, PLATSIM simulates the response of the space platform to disturbances and calculates the jitter and stability values from the response time histories. In the frequency domain analysis, PLATSIM calculates frequency response function matrices and provides the corresponding Bode plots. The PLATSIM software package is written in MATLAB script language. A graphical user interface is developed in the package to provide convenient access to its various features.
Optimal thrust level for orbit insertion

NASA Astrophysics Data System (ADS)

Cerf, Max

2017-07-01

The minimum-fuel orbital transfer is analyzed in the case of a launcher upper stage using a constantly thrusting engine. The thrust level is assumed to be constant and its value is optimized together with the thrust direction. A closed-loop solution for the thrust direction is derived from the extremal analysis for a planar orbital transfer. The optimal control problem reduces to two unknowns, namely the thrust level and the final time. Guessing and propagating the costates is no longer necessary and the optimal trajectory is easily found from a rough initialization. On the other hand the initial costates are assessed analytically from the initial conditions and they can be used as initial guess for transfers at different thrust levels. The method is exemplified on a launcher upper stage targeting a geostationary transfer orbit.
A Functional-Genetic Scheme for Seizure Forecasting in Canine Epilepsy.

PubMed

Bou Assi, Elie; Nguyen, Dang K; Rihana, Sandy; Sawan, Mohamad

2018-06-01

The objective of this work is the development of an accurate seizure forecasting algorithm that considers brain's functional connectivity for electrode selection. We start by proposing Kmeans-directed transfer function, an adaptive functional connectivity method intended for seizure onset zone localization in bilateral intracranial EEG recordings. Electrodes identified as seizure activity sources and sinks are then used to implement a seizure-forecasting algorithm on long-term continuous recordings in dogs with naturally-occurring epilepsy. A precision-recall genetic algorithm is proposed for feature selection in line with a probabilistic support vector machine classifier. Epileptic activity generators were focal in all dogs confirming the diagnosis of focal epilepsy in these animals while sinks spanned both hemispheres in 2 of 3 dogs. Seizure forecasting results show performance improvement compared to previous studies, achieving average sensitivity of 84.82% and time in warning of 0.1. Achieved performances highlight the feasibility of seizure forecasting in canine epilepsy. The ability to improve seizure forecasting provides promise for the development of EEG-triggered closed-loop seizure intervention systems for ambulatory implantation in patients with refractory epilepsy.
Blood transfer devices for malaria rapid diagnostic tests: evaluation of accuracy, safety and ease of use.

PubMed

Hopkins, Heidi; Oyibo, Wellington; Luchavez, Jennifer; Mationg, Mary Lorraine; Asiimwe, Caroline; Albertini, Audrey; González, Iveth J; Gatton, Michelle L; Bell, David

2011-02-08

Malaria rapid diagnostic tests (RDTs) are increasingly used by remote health personnel with minimal training in laboratory techniques. RDTs must, therefore, be as simple, safe and reliable as possible. Transfer of blood from the patient to the RDT is critical to safety and accuracy, and poses a significant challenge to many users. Blood transfer devices were evaluated for accuracy and precision of volume transferred, safety and ease of use, to identify the most appropriate devices for use with RDTs in routine clinical care. Five devices, a loop, straw-pipette, calibrated pipette, glass capillary tube, and a new inverted cup device, were evaluated in Nigeria, the Philippines and Uganda. The 227 participating health workers used each device to transfer blood from a simulated finger-prick site to filter paper. For each transfer, the number of attempts required to collect and deposit blood and any spilling of blood during transfer were recorded. Perceptions of ease of use and safety of each device were recorded for each participant. Blood volume transferred was calculated from the area of blood spots deposited on filter paper. The overall mean volumes transferred by devices differed significantly from the target volume of 5 microliters (p < 0.001). The inverted cup (4.6 microliters) most closely approximated the target volume. The glass capillary was excluded from volume analysis as the estimation method used is not compatible with this device. The calibrated pipette accounted for the largest proportion of blood exposures (23/225, 10%); exposures ranged from 2% to 6% for the other four devices. The inverted cup was considered easiest to use in blood collection (206/226, 91%); the straw-pipette and calibrated pipette were rated lowest (143/225 [64%] and 135/225 [60%] respectively). Overall, the inverted cup was the most preferred device (72%, 163/227), followed by the loop (61%, 138/227). The performance of blood transfer devices varied in this evaluation of accuracy, blood safety, ease of use, and user preference. The inverted cup design achieved the highest overall performance, while the loop also performed well. These findings have relevance for any point-of-care diagnostics that require blood sampling.
A methodology for designing robust multivariable nonlinear control systems. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Grunberg, D. B.

1986-01-01

A new methodology is described for the design of nonlinear dynamic controllers for nonlinear multivariable systems providing guarantees of closed-loop stability, performance, and robustness. The methodology is an extension of the Linear-Quadratic-Gaussian with Loop-Transfer-Recovery (LQG/LTR) methodology for linear systems, thus hinging upon the idea of constructing an approximate inverse operator for the plant. A major feature of the methodology is a unification of both the state-space and input-output formulations. In addition, new results on stability theory, nonlinear state estimation, and optimal nonlinear regulator theory are presented, including the guaranteed global properties of the extended Kalman filter and optimal nonlinear regulators.
Topology-driven phase transitions in the classical monomer-dimer-loop model.

PubMed

Li, Sazi; Li, Wei; Chen, Ziyu

2015-06-01

In this work, we investigate the classical loop models doped with monomers and dimers on a square lattice, whose partition function can be expressed as a tensor network (TN). In the thermodynamic limit, we use the boundary matrix product state technique to contract the partition function TN, and determine the thermodynamic properties with high accuracy. In this monomer-dimer-loop model, we find a second-order phase transition between a trivial monomer-condensation and a loop-condensation (LC) phase, which cannot be distinguished by any local order parameter, while nevertheless the two phases have distinct topological properties. In the LC phase, we find two degenerate dominating eigenvalues in the transfer-matrix spectrum, as well as a nonvanishing (nonlocal) string order parameter, both of which identify the topological ergodicity breaking in the LC phase and can serve as the order parameter for detecting the phase transitions.
Probing the elastic limit of DNA bending

PubMed Central

Le, Tung T.; Kim, Harold D.

2014-01-01

Sharp bending of double-stranded DNA (dsDNA) plays an essential role in genome structure and function. However, the elastic limit of dsDNA bending remains controversial. Here, we measured the opening rates of small dsDNA loops with contour lengths ranging between 40 and 200 bp using single-molecule Fluorescence Resonance Energy Transfer. The relationship of loop lifetime to loop size revealed a critical transition in bending stress. Above the critical loop size, the loop lifetime changed with loop size in a manner consistent with elastic bending stress, but below it, became less sensitive to loop size, indicative of softened dsDNA. The critical loop size increased from ∼60 bp to ∼100 bp with the addition of 5 mM magnesium. We show that our result is in quantitative agreement with the kinkable worm-like chain model, and furthermore, can reproduce previously reported looping probabilities of dsDNA over the range between 50 and 200 bp. Our findings shed new light on the energetics of sharply bent dsDNA. PMID:25122748
Electronic Warfare Closed Loop Laboratory (EWCLL) Antenna Motor Software and Hardware Development

DTIC Science & Technology

2016-09-01

ARL-TN-0779 ● SEP 2016 US Army Research Laboratory Electronic Warfare Closed Loop Laboratory (EWCLL) Antenna Motor Software and...Electronic Warfare Closed Loop Laboratory (EWCLL) Antenna Motor Software and Hardware Development by Neal Tesny Sensors and Electron Devices Directorate...TITLE AND SUBTITLE Electronic Warfare Closed Loop Laboratory (EWCLL) Antenna Motor Software and Hardware Development 5a. CONTRACT NUMBER 5b
Pump, and earth-testable spacecraft capillary heat transport loop using augmentation pump and check valves

NASA Technical Reports Server (NTRS)

Baker, David (Inventor)

1998-01-01

A spacecraft includes heat-generating payload equipment, and a heat transport system with a cold plate thermally coupled to the equipment and a capillary-wick evaporator, for evaporating coolant liquid to cool the equipment. The coolant vapor is coupled to a condenser and in a loop back to the evaporator. A heated coolant reservoir is coupled to the loop for pressure control. If the wick is not wetted, heat transfer will not begin or continue. A pair of check valves are coupled in the loop, and the heater is cycled for augmentation pumping of coolant to and from the reservoir. This augmentation pumping, in conjunction with the check valves, wets the wick. The wick liquid storage capacity allows the augmentation pump to provide continuous pulsed liquid flow to assure continuous vapor transport and a continuously operating heat transport system. The check valves are of the ball type to assure maximum reliability. However, any type of check valve can be used, including designs which are preloaded in the closed position. The check valve may use any ball or poppet material which resists corrosion. For optimum performance during testing on Earth, the ball or poppet would have neutral buoyancy or be configured in a closed position when the heat transport system is not operating. The ball may be porous to allow passage of coolant vapor.
Loop series for discrete statistical models on graphs

NASA Astrophysics Data System (ADS)

Chertkov, Michael; Chernyak, Vladimir Y.

2006-06-01

In this paper we present the derivation details, logic, and motivation for the three loop calculus introduced in Chertkov and Chernyak (2006 Phys. Rev. E 73 065102(R)). Generating functions for each of the three interrelated discrete statistical models are expressed in terms of a finite series. The first term in the series corresponds to the Bethe-Peierls belief-propagation (BP) contribution; the other terms are labelled by loops on the factor graph. All loop contributions are simple rational functions of spin correlation functions calculated within the BP approach. We discuss two alternative derivations of the loop series. One approach implements a set of local auxiliary integrations over continuous fields with the BP contribution corresponding to an integrand saddle-point value. The integrals are replaced by sums in the complementary approach, briefly explained in Chertkov and Chernyak (2006 Phys. Rev. E 73 065102(R)). Local gauge symmetry transformations that clarify an important invariant feature of the BP solution are revealed in both approaches. The individual terms change under the gauge transformation while the partition function remains invariant. The requirement for all individual terms to be nonzero only for closed loops in the factor graph (as opposed to paths with loose ends) is equivalent to fixing the first term in the series to be exactly equal to the BP contribution. Further applications of the loop calculus to problems in statistical physics, computer and information sciences are discussed.
Conditions for Stabilizability of Linear Switched Systems

NASA Astrophysics Data System (ADS)

Minh, Vu Trieu

2011-06-01

This paper investigates some conditions that can provide stabilizability for linear switched systems with polytopic uncertainties via their closed loop linear quadratic state feedback regulator. The closed loop switched systems can stabilize unstable open loop systems or stable open loop systems but in which there is no solution for a common Lyapunov matrix. For continuous time switched linear systems, we show that if there exists solution in an associated Riccati equation for the closed loop systems sharing one common Lyapunov matrix, the switched linear systems are stable. For the discrete time switched systems, we derive a Linear Matrix Inequality (LMI) to calculate a common Lyapunov matrix and solution for the stable closed loop feedback systems. These closed loop linear quadratic state feedback regulators guarantee the global asymptotical stability for any switched linear systems with any switching signal sequence.
A fuzzy cost-benefit function to select economical products for processing in a closed-loop supply chain

NASA Astrophysics Data System (ADS)

Pochampally, Kishore K.; Gupta, Surendra M.; Cullinane, Thomas P.

2004-02-01

The cost-benefit analysis of data associated with re-processing of used products often involves the uncertainty feature of cash-flow modeling. The data is not objective because of uncertainties in supply, quality and disassembly times of used products. Hence, decision-makers must rely on "fuzzy" data for analysis. The same parties that are involved in the forward supply chain often carry out the collection and re-processing of used products. It is therefore important that the cost-benefit analysis takes the data of both new products and used products into account. In this paper, a fuzzy cost-benefit function is proposed that is used to perform a multi-criteria economic analysis to select the most economical products to process in a closed-loop supply chain. Application of the function is detailed through an illustrative example.

RELAP5-3D Modeling of Heat Transfer Components (Intermediate Heat Exchanger and Helical-Coil Steam Generator) for NGNP Application

DOE Office of Scientific and Technical Information (OSTI.GOV)

N. A. Anderson; P. Sabharwall

2014-01-01

The Next Generation Nuclear Plant project is aimed at the research and development of a helium-cooled high-temperature gas reactor that could generate both electricity and process heat for the production of hydrogen. The heat from the high-temperature primary loop must be transferred via an intermediate heat exchanger to a secondary loop. Using RELAP5-3D, a model was developed for two of the heat exchanger options a printed-circuit heat exchanger and a helical-coil steam generator. The RELAP5-3D models were used to simulate an exponential decrease in pressure over a 20 second period. The results of this loss of coolant analysis indicate thatmore » heat is initially transferred from the primary loop to the secondary loop, but after the decrease in pressure in the primary loop the heat is transferred from the secondary loop to the primary loop. A high-temperature gas reactor model should be developed and connected to the heat transfer component to simulate other transients.« less
Extended cooperative control synthesis

NASA Technical Reports Server (NTRS)

Davidson, John B.; Schmidt, David K.

1994-01-01

This paper reports on research for extending the Cooperative Control Synthesis methodology to include a more accurate modeling of the pilot's controller dynamics. Cooperative Control Synthesis (CCS) is a methodology that addresses the problem of how to design control laws for piloted, high-order, multivariate systems and/or non-conventional dynamic configurations in the absence of flying qualities specifications. This is accomplished by emphasizing the parallel structure inherent in any pilot-controlled, augmented vehicle. The original CCS methodology is extended to include the Modified Optimal Control Model (MOCM), which is based upon the optimal control model of the human operator developed by Kleinman, Baron, and Levison in 1970. This model provides a modeling of the pilot's compensation dynamics that is more accurate than the simplified pilot dynamic representation currently in the CCS methodology. Inclusion of the MOCM into the CCS also enables the modeling of pilot-observation perception thresholds and pilot-observation attention allocation affects. This Extended Cooperative Control Synthesis (ECCS) allows for the direct calculation of pilot and system open- and closed-loop transfer functions in pole/zero form and is readily implemented in current software capable of analysis and design for dynamic systems. Example results based upon synthesizing an augmentation control law for an acceleration command system in a compensatory tracking task using the ECCS are compared with a similar synthesis performed by using the original CCS methodology. The ECCS is shown to provide augmentation control laws that yield more favorable, predicted closed-loop flying qualities and tracking performance than those synthesized using the original CCS methodology.
Energy transport in cooling device by magnetic fluid

NASA Astrophysics Data System (ADS)

Yamaguchi, Hiroshi; Iwamoto, Yuhiro

2017-06-01

Temperature sensitive magnetic fluid has a great potential with high performance heat transport ability as well as long distance energy (heat) transporting. In the present study experimental set-up was newly designed and constructed in order to measure basic heat transport characteristics under various magnetic field conditions. Angular dependence for the device (heat transfer section) was also taken into consideration for a sake of practical applications. The energy transfer characteristic (heat transport capability) in the magnetically-driven heat transport (cooling) device using the binary TSMF was fully investigated with the set-up. The obtained results indicate that boiling of the organic mixture (before the magnetic fluid itself reaching boiling point) effectively enhances the heat transfer as well as boosting the flow to circulate in the closed loop by itself. A long-distance heat transport of 5 m is experimentally confirmed, transferring the thermal energy of 35.8 W, even when the device (circulation loop) is horizontally placed. The highlighted results reveal that the proposed cooling device is innovative in a sense of transporting substantial amount of thermal energy (heat) as well as a long distance heat transport. The development of the magnetically-driven heat transport device has a great potential to be replaced for the conventional heat pipe in application of thermal engineering.
Chemically controlled closed-loop insulin delivery.

PubMed

Ravaine, Valérie; Ancla, Christophe; Catargi, Bogdan

2008-11-24

Alternative treatments for diabetes are currently being investigated to improve both patient comfort and avoid complications due to hyperglycaemia episodes. In the absence of a cure like pancreas or beta-islets transplants, the ideal method would be an artificial "closed-loop" system able to mimic pancreas activity. This would operate continuously and automatically, causing appropriate response to losses and gains in glucose levels. Chemically controlled closed-loop insulin delivery has been explored by two main strategies. The first one consists in delivering insulin with a glucose-responsive matrix. Polymeric hydrogels that swell or shrink according to the glucose concentration allow delivering insulin doses adapted to the glucose concentration. The second strategy consists in modifying insulin itself with glucose-sensitive functional groups that trigger its activity. Recent developments made in these areas represent significant progress in terms of biocompatibility, selectivity, pharmacokinetics, and easiness of administration, as required for in vivo applications. Although some issues still have to be overcome, this field of research is promising as a possible alternative to other approaches for diabetes treatment.
Closed Loop Interactions between Spiking Neural Network and Robotic Simulators Based on MUSIC and ROS.

PubMed

Weidel, Philipp; Djurfeldt, Mikael; Duarte, Renato C; Morrison, Abigail

2016-01-01

In order to properly assess the function and computational properties of simulated neural systems, it is necessary to account for the nature of the stimuli that drive the system. However, providing stimuli that are rich and yet both reproducible and amenable to experimental manipulations is technically challenging, and even more so if a closed-loop scenario is required. In this work, we present a novel approach to solve this problem, connecting robotics and neural network simulators. We implement a middleware solution that bridges the Robotic Operating System (ROS) to the Multi-Simulator Coordinator (MUSIC). This enables any robotic and neural simulators that implement the corresponding interfaces to be efficiently coupled, allowing real-time performance for a wide range of configurations. This work extends the toolset available for researchers in both neurorobotics and computational neuroscience, and creates the opportunity to perform closed-loop experiments of arbitrary complexity to address questions in multiple areas, including embodiment, agency, and reinforcement learning.
Closed Loop Interactions between Spiking Neural Network and Robotic Simulators Based on MUSIC and ROS

PubMed Central

Weidel, Philipp; Djurfeldt, Mikael; Duarte, Renato C.; Morrison, Abigail

2016-01-01

In order to properly assess the function and computational properties of simulated neural systems, it is necessary to account for the nature of the stimuli that drive the system. However, providing stimuli that are rich and yet both reproducible and amenable to experimental manipulations is technically challenging, and even more so if a closed-loop scenario is required. In this work, we present a novel approach to solve this problem, connecting robotics and neural network simulators. We implement a middleware solution that bridges the Robotic Operating System (ROS) to the Multi-Simulator Coordinator (MUSIC). This enables any robotic and neural simulators that implement the corresponding interfaces to be efficiently coupled, allowing real-time performance for a wide range of configurations. This work extends the toolset available for researchers in both neurorobotics and computational neuroscience, and creates the opportunity to perform closed-loop experiments of arbitrary complexity to address questions in multiple areas, including embodiment, agency, and reinforcement learning. PMID:27536234
Passive decay heat removal system for water-cooled nuclear reactors

DOEpatents

Forsberg, Charles W.

1991-01-01

A passive decay-heat removal system for a water-cooled nuclear reactor employs a closed heat transfer loop having heat-exchanging coils inside an open-topped, insulated box located inside the reactor vessel, below its normal water level, in communication with a condenser located outside of containment and exposed to the atmosphere. The heat transfer loop is located such that the evaporator is in a position where, when the water level drops in the reactor, it will become exposed to steam. Vapor produced in the evaporator passes upward to the condenser above the normal water level. In operation, condensation in the condenser removes heat from the system, and the condensed liquid is returned to the evaporator. The system is disposed such that during normal reactor operations where the water level is at its usual position, very little heat will be removed from the system, but during emergency, low water level conditions, substantial amounts of decay heat will be removed.
Tutorial on Quantification of Differences between Single- and Two-Component Two-Phase Flow and Heat Transfer

NASA Astrophysics Data System (ADS)

Delil, A. A. M.

2003-01-01

Single-component two-phase systems are envisaged for aerospace thermal control applications: Mechanically Pumped Loops, Vapour Pressure Driven Loops, Capillary Pumped Loops and Loop Heat Pipes. Thermal control applications are foreseen in different gravity environments: Micro-g, reduced-g for Mars or Moon bases, 1-g during terrestrial testing, and hyper-g in rotating spacecraft, during combat aircraft manoeuvres and in systems for outer planets. In the evaporator, adiabatic line and condenser sections of such single-component two-phase systems, the fluid is a mixture of the working liquid (for example ammonia, carbon dioxide, ethanol, or other refrigerants, etc.) and its saturated vapour. Results of two-phase two-component flow and heat transfer research (pertaining to liquid-gas mixtures, e.g. water/air, or argon or helium) are often applied to support research on flow and heat transfer in two-phase single-component systems. The first part of the tutorial updates the contents of two earlier tutorials, discussing various aerospace-related two-phase flow and heat transfer research. It deals with the different pressure gradient constituents of the total pressure gradient, with flow regime mapping (including evaporating and condensing flow trajectories in the flow pattern maps), with adiabatic flow and flashing, and with thermal-gravitational scaling issues. The remaining part of the tutorial qualitatively and quantitatively determines the differences between single- and two-component systems: Two systems that physically look similar and close, but in essence are fully different. It was already elucidated earlier that, though there is a certain degree of commonality, the differences will be anything but negligible, in many cases. These differences (quantified by some examples) illustrates how careful one shall be in interpreting data resulting from two-phase two-component simulations or experiments, for the development of single-component two-phase thermal control systems for various gravity environments.
A New Approach to Attitude Stability and Control for Low Airspeed Vehicles

NASA Technical Reports Server (NTRS)

Lim, K. B.; Shin, Y-Y.; Moerder, D. D.; Cooper, E. G.

2004-01-01

This paper describes an approach for controlling the attitude of statically unstable thrust-levitated vehicles in hover or slow translation. The large thrust vector that characterizes such vehicles can be modulated to provide control forces and moments to the airframe, but such modulation is accompanied by significant unsteady flow effects. These effects are difficult to model, and can compromise the practical value of thrust vectoring in closed-loop attitude stability, even if the thrust vectoring machinery has sufficient bandwidth for stabilization. The stabilization approach described in this paper is based on using internal angular momentum transfer devices for stability, augmented by thrust vectoring for trim and other "outer loop" control functions. The three main components of this approach are: (1) a z-body axis angular momentum bias enhances static attitude stability, reducing the amount of control activity needed for stabilization, (2) optionally, gimbaled reaction wheels provide high-bandwidth control torques for additional stabilization, or agility, and (3) the resulting strongly coupled system dynamics are controlled by a multivariable controller. A flight test vehicle is described, and nonlinear simulation results are provided that demonstrate the efficiency of the approach.
Synthesis and operation of an FFT-decoupled fixed-order reversed-field pinch plasma control system based on identification data

NASA Astrophysics Data System (ADS)

Olofsson, K. Erik J.; Brunsell, Per R.; Witrant, Emmanuel; Drake, James R.

2010-10-01

Recent developments and applications of system identification methods for the reversed-field pinch (RFP) machine EXTRAP T2R have yielded plasma response parameters for decoupled dynamics. These data sets are fundamental for a real-time implementable fast Fourier transform (FFT) decoupled discrete-time fixed-order strongly stabilizing synthesis as described in this work. Robustness is assessed over the data set by bootstrap calculation of the sensitivity transfer function worst-case H_{\\infty} -gain distribution. Output tracking and magnetohydrodynamic mode m = 1 tracking are considered in the same framework simply as two distinct weighted traces of a performance channel output-covariance matrix as derived from the closed-loop discrete-time Lyapunov equation. The behaviour of the resulting multivariable controller is investigated with dedicated T2R experiments.
Closed loop statistical performance analysis of N-K knock controllers

NASA Astrophysics Data System (ADS)

Peyton Jones, James C.; Shayestehmanesh, Saeed; Frey, Jesse

2017-09-01

The closed loop performance of engine knock controllers cannot be rigorously assessed from single experiments or simulations because knock behaves as a random process and therefore the response belongs to a random distribution also. In this work a new method is proposed for computing the distributions and expected values of the closed loop response, both in steady state and in response to disturbances. The method takes as its input the control law, and the knock propensity characteristic of the engine which is mapped from open loop steady state tests. The method is applicable to the 'n-k' class of knock controllers in which the control action is a function only of the number of cycles n since the last control move, and the number k of knock events that have occurred in this time. A Cumulative Summation (CumSum) based controller falls within this category, and the method is used to investigate the performance of the controller in a deeper and more rigorous way than has previously been possible. The results are validated using onerous Monte Carlo simulations, which confirm both the validity of the method and its high computational efficiency.
Measurement and numerical simulation of the changes in the open-loop transfer function in hearing aid as a function telephone handset proximity

NASA Astrophysics Data System (ADS)

Daigle, Gilles A.; Stinson, Michael R.

2002-11-01

The presence of a nearby object (telephone handset, cupped hand, etc.) can cause acoustical feedback to occur in a hearing aid. The object reflects or scatters additional sound energy to the microphone position causing the open-loop transfer function (OLTF) to increase. Feedback can occur when the OLTF>0 dB. To investigate this problem, measurements of the OLTF were made for three hearing aids (BTE, ITC, ITE) mounted on a KEMAR manikin. A telephone handset, positioned initially in a typical user position, was translated to positions between 0 and 100 mm away from the pinna, repeatibly, using a linear translation system. Changes of up to 15 dB or more were observed as the handset moved, particularly for positions within 20 mm of the pinna. In parallel, numerical simulations were made using a boundary element method. Computed changes in OLTF were consistent with the measured changes.
Conformational Changes of NADPH-Cytochrome P450 Oxidoreductase Are Essential for Catalysis and Cofactor Binding*

PubMed Central

Xia, Chuanwu; Hamdane, Djemel; Shen, Anna L.; Choi, Vivian; Kasper, Charles B.; Pearl, Naw May; Zhang, Haoming; Im, Sang-Choul; Waskell, Lucy; Kim, Jung-Ja P.

2011-01-01

The crystal structure of NADPH-cytochrome P450 reductase (CYPOR) implies that a large domain movement is essential for electron transfer from NADPH via FAD and FMN to its redox partners. To test this hypothesis, a disulfide bond was engineered between residues Asp147 and Arg514 in the FMN and FAD domains, respectively. The cross-linked form of this mutant protein, designated 147CC514, exhibited a significant decrease in the rate of interflavin electron transfer and large (≥90%) decreases in rates of electron transfer to its redox partners, cytochrome c and cytochrome P450 2B4. Reduction of the disulfide bond restored the ability of the mutant to reduce its redox partners, demonstrating that a conformational change is essential for CYPOR function. The crystal structures of the mutant without and with NADP+ revealed that the two flavin domains are joined by a disulfide linkage and that the relative orientations of the two flavin rings are twisted ∼20° compared with the wild type, decreasing the surface contact area between the two flavin rings. Comparison of the structures without and with NADP+ shows movement of the Gly631–Asn635 loop. In the NADP+-free structure, the loop adopts a conformation that sterically hinders NADP(H) binding. The structure with NADP+ shows movement of the Gly631–Asn635 loop to a position that permits NADP(H) binding. Furthermore, comparison of these mutant and wild type structures strongly suggests that the Gly631–Asn635 loop movement controls NADPH binding and NADP+ release; this loop movement in turn facilitates the flavin domain movement, allowing electron transfer from FMN to the CYPOR redox partners. PMID:21345800
A 16-Channel CMOS Chopper-Stabilized Analog Front-End ECoG Acquisition Circuit for a Closed-Loop Epileptic Seizure Control System.

PubMed

Wu, Chung-Yu; Cheng, Cheng-Hsiang; Chen, Zhi-Xin

2018-06-01

In this paper, a 16-channel analog front-end (AFE) electrocorticography signal acquisition circuit for a closed-loop seizure control system is presented. It is composed of 16 input protection circuits, 16 auto-reset chopper-stabilized capacitive-coupled instrumentation amplifiers (AR-CSCCIA) with bandpass filters, 16 programmable transconductance gain amplifiers, a multiplexer, a transimpedance amplifier, and a 128-kS/s 10-bit delta-modulated successive-approximation-register analog-to-digital converter (SAR ADC). In closed-loop seizure control system applications, the stimulator shares the same electrode with the AFE amplifier for effective suppression of epileptic seizures. To prevent from overstress in MOS devices caused by high stimulation voltage, an input protection circuit with a high-voltage-tolerant switch is proposed for the AFE amplifier. Moreover, low input-referred noise is achieved by using the chopper modulation technique in the AR-CSCCIA. To reduce the undesired effects of chopper modulation, an improved offset reduction loop is proposed to reduce the output offset generated by input chopper mismatches. The digital ripple reduction loop is also used to reduce the chopper ripple. The fabricated AFE amplifier has 49.1-/59.4-/67.9-dB programmable gain and 2.02-μVrms input referred noise in a bandwidth of 0.59-117 Hz. The measured power consumption of the AFE amplifier is 3.26 μW per channel, and the noise efficiency factor is 3.36. The in vivo animal test has been successfully performed to verify the functions. It is shown that the proposed AFE acquisition circuit is suitable for implantable closed-loop seizure control systems.
A parameter optimization approach to controller partitioning for integrated flight/propulsion control application

NASA Technical Reports Server (NTRS)

Schmidt, Phillip; Garg, Sanjay; Holowecky, Brian

1992-01-01

A parameter optimization framework is presented to solve the problem of partitioning a centralized controller into a decentralized hierarchical structure suitable for integrated flight/propulsion control implementation. The controller partitioning problem is briefly discussed and a cost function to be minimized is formulated, such that the resulting 'optimal' partitioned subsystem controllers will closely match the performance (including robustness) properties of the closed-loop system with the centralized controller while maintaining the desired controller partitioning structure. The cost function is written in terms of parameters in a state-space representation of the partitioned sub-controllers. Analytical expressions are obtained for the gradient of this cost function with respect to parameters, and an optimization algorithm is developed using modern computer-aided control design and analysis software. The capabilities of the algorithm are demonstrated by application to partitioned integrated flight/propulsion control design for a modern fighter aircraft in the short approach to landing task. The partitioning optimization is shown to lead to reduced-order subcontrollers that match the closed-loop command tracking and decoupling performance achieved by a high-order centralized controller.
A parameter optimization approach to controller partitioning for integrated flight/propulsion control application

NASA Technical Reports Server (NTRS)

Schmidt, Phillip H.; Garg, Sanjay; Holowecky, Brian R.

1993-01-01

A parameter optimization framework is presented to solve the problem of partitioning a centralized controller into a decentralized hierarchical structure suitable for integrated flight/propulsion control implementation. The controller partitioning problem is briefly discussed and a cost function to be minimized is formulated, such that the resulting 'optimal' partitioned subsystem controllers will closely match the performance (including robustness) properties of the closed-loop system with the centralized controller while maintaining the desired controller partitioning structure. The cost function is written in terms of parameters in a state-space representation of the partitioned sub-controllers. Analytical expressions are obtained for the gradient of this cost function with respect to parameters, and an optimization algorithm is developed using modern computer-aided control design and analysis software. The capabilities of the algorithm are demonstrated by application to partitioned integrated flight/propulsion control design for a modern fighter aircraft in the short approach to landing task. The partitioning optimization is shown to lead to reduced-order subcontrollers that match the closed-loop command tracking and decoupling performance achieved by a high-order centralized controller.
Constant-current control method of multi-function electromagnetic transmitter.

PubMed

Xue, Kaichang; Zhou, Fengdao; Wang, Shuang; Lin, Jun

2015-02-01

Based on the requirements of controlled source audio-frequency magnetotelluric, DC resistivity, and induced polarization, a constant-current control method is proposed. Using the required current waveforms in prospecting as a standard, the causes of current waveform distortion and current waveform distortion's effects on prospecting are analyzed. A cascaded topology is adopted to achieve 40 kW constant-current transmitter. The responsive speed and precision are analyzed. According to the power circuit of the transmitting system, the circuit structure of the pulse width modulation (PWM) constant-current controller is designed. After establishing the power circuit model of the transmitting system and the PWM constant-current controller model, analyzing the influence of ripple current, and designing an open-loop transfer function according to the amplitude-frequency characteristic curves, the parameters of the PWM constant-current controller are determined. The open-loop transfer function indicates that the loop gain is no less than 28 dB below 160 Hz, which assures the responsive speed of the transmitting system; the phase margin is 45°, which assures the stabilization of the transmitting system. Experimental results verify that the proposed constant-current control method can keep the control error below 4% and can effectively suppress load change caused by the capacitance of earth load.
Constant-current control method of multi-function electromagnetic transmitter

NASA Astrophysics Data System (ADS)

Xue, Kaichang; Zhou, Fengdao; Wang, Shuang; Lin, Jun

2015-02-01

Based on the requirements of controlled source audio-frequency magnetotelluric, DC resistivity, and induced polarization, a constant-current control method is proposed. Using the required current waveforms in prospecting as a standard, the causes of current waveform distortion and current waveform distortion's effects on prospecting are analyzed. A cascaded topology is adopted to achieve 40 kW constant-current transmitter. The responsive speed and precision are analyzed. According to the power circuit of the transmitting system, the circuit structure of the pulse width modulation (PWM) constant-current controller is designed. After establishing the power circuit model of the transmitting system and the PWM constant-current controller model, analyzing the influence of ripple current, and designing an open-loop transfer function according to the amplitude-frequency characteristic curves, the parameters of the PWM constant-current controller are determined. The open-loop transfer function indicates that the loop gain is no less than 28 dB below 160 Hz, which assures the responsive speed of the transmitting system; the phase margin is 45°, which assures the stabilization of the transmitting system. Experimental results verify that the proposed constant-current control method can keep the control error below 4% and can effectively suppress load change caused by the capacitance of earth load.
Review article: closed-loop systems in anesthesia: is there a potential for closed-loop fluid management and hemodynamic optimization?

PubMed

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.
pH-regulated metal-ligand switching in the HM loop of ATP7A: a new paradigm for metal transfer chemistry.

PubMed

Kline, Chelsey D; Gambill, Benjamin F; Mayfield, Mary; Lutsenko, Svetlana; Blackburn, Ninian J

2016-08-01

Cuproproteins such as PHM and DBM mature in late endosomal vesicles of the mammalian secretory pathway where changes in vesicle pH are employed for sorting and post-translational processing. Colocation with the P1B-type ATPase ATP7A suggests that the latter is the source of copper and supports a mechanism where selectivity in metal transfer is achieved by spatial colocation of partner proteins in their specific organelles or vesicles. In previous work we have suggested that a lumenal loop sequence located between trans-membrane helices TM1 and TM2 of the ATPase, and containing five histidines and four methionines, acts as an organelle-specific chaperone for metallation of the cuproproteins. The hypothesis posits that the pH of the vesicle regulates copper ligation and loop conformation via a mechanism which involves His to Met ligand switching induced by histidine protonation. Here we report the effect of pH on the HM loop copper coordination using X-ray absorption spectroscopy (XAS), and show via selenium substitution of the Met residues that the HM loop undergoes similar conformational switching to that found earlier for its partner PHM. We hypothesize that in the absence of specific chaperones, HM motifs provide a template for building a flexible, pH-sensitive transfer site whose structure and function can be regulated to accommodate the different active site structural elements and pH environments of its partner proteins.

Development status of regenerable solid amine CO2 control systems

NASA Technical Reports Server (NTRS)

Colling, A. K., Jr.; Nalette, T. A.; Cusick, R. J.; Reysa, R. P.

1985-01-01

The development history of solid amine/water desorbed (SAWD) CO2 control systems is reviewed. The design of the preprototype SAWD I CO2 system on the basis of a three-man metabolic load at the 3.8 mm Hg ambient CO2 level, and the functions of the CO2 removal, CO2 storage/delivery, controller, and life test laboratory support packages are described. The development of a full-scale multiple canister SAWD II preprototype system, which is capable of conducting the CO2 removal/concentration function in a closed-loop atmosphere revitalization system during zero-gravity operation, is examined. The operation of the SAWD II system, including the absorption and desorption cycles, is analyzed. A reduction in the thermal mass of the canister and the system's energy transfer technique result in efficient energy use. The polyether foam, nylon felt, nickel foam, spring retained, and metal bellows bed tests performed to determine the design of the zero-gravity canister are studied; metal bellows are selected for the canister's configuration.
Comparative assessment of the efficacy of closed helical loop and T-loop for space closure in lingual orthodontics-a finite element study.

PubMed

Chacko, Ajay; Tikku, Tripti; Khanna, Rohit; Maurya, Rana Pratap; Srivastava, Kamna

2018-05-28

Retraction in lingual orthodontics has biomechanical differences when compared to labial orthodontics, which is not yet established. Thus, we have intended to compare the biomechanical characteristics of closed helical loop and T-loop on 1 mm activation with 30° of compensatory curvatures during retraction in lingual orthodontics. STb lingual brackets were indirectly bonded to maxillary typhodont model that was scanned to obtain FEM model. Closed helical loop (2 × 7 mm) and T-loop (6 × 2 × 7 mm) of 0.016″ × 0.016″ TMA wire were modeled without preactivation bends. Preactivation bends at 30° were given in the software. Boundary conditions were set. The force (F) and moment (M) of both the loops were determined on 1 mm activation, using ANSYS software. M/F ratio was also calculated for both the loops. T-loop exerted less force, thus increased M/F ratio as compared to closed helical loop on 1 mm activation. When torque has to be preserved in the anterior segment during retraction in lingual orthodontics, T-loop can be preferred over closed helical loop.
A double closed loop to enhance the quality of life of Parkinson's Disease patients: REMPARK system.

PubMed

Samà, Albert; Pérez-López, Carlos; Rodríguez-Martín, Daniel; Moreno-Aróstegui, J Manuel; Rovira, Jordi; Ahlrichs, Claas; Castro, Rui; Cevada, João; Graça, Ricardo; Guimarães, Vânia; Pina, Bernardo; Counihan, Timothy; Lewy, Hadas; Annicchiarico, Roberta; Bayés, Angels; Rodríguez-Molinero, Alejandro; Cabestany, Joan

2014-01-01

This paper presents REMPARK system, a novel approach to deal with Parkinson's Disease (PD). REMPARK system comprises two closed loops of actuation onto PD. The first loop consists in a wearable system that, based on a belt-worn movement sensor, detects movement alterations that activate an auditory cueing system controlled by a smartphone in order to improve patient's gait. The belt-worn sensor analyzes patient's movement through real-time learning algorithms that were developed on the basis of a database previously collected from 93 PD patients. The second loop consists in disease management based on the data collected during long periods and that enables neurologists to tailor medication of their PD patients and follow the disease evolution. REMPARK system is going to be tested in 40 PD patients in Spain, Ireland, Italy and Israel. This paper describes the approach followed to obtain this system, its components, functionalities and trials in which the system will be validated.
Mature data transport and command management services for the Space Station

NASA Technical Reports Server (NTRS)

Carper, R. D.

1986-01-01

The duplex space/ground/space data services for the Space Station are described. The need to separate the uplink data service functions from the command functions is discussed. Command management is a process shared by an operation control center and a command management system and consists of four functions: (1) uplink data communications, (2) management of the on-board computer, (3) flight resource allocation and management, and (4) real command management. The new data service capabilities provided by microprocessors, ground and flight nodes, and closed loop and open loop capabilities are studied. The need for and functions of a flight resource allocation management service are examined. The system is designed so only users can access the system; the problems encountered with open loop uplink access are analyzed. The procedures for delivery of operational, verification, computer, and surveillance and monitoring data directly to users are reviewed.
Potential and benefits of closed loop ECLS systems on the ISS.

PubMed

Raatschen, W; Preiss, H

2001-01-01

To close open loops for long manned missions in space is a big challenge for aeronautic engineers throughout the world. The paper's focus is on the oxygen reclamation from carbon dioxide within a space habitat. A brief description of the function principle of a fixed alkaline electrolyzer, a solid amine carbon dioxide concentrator and a Sabatier reactor is given. By combining these devices to an air revitalization system the technical and economical benefits are explained. Astrium's Air Revitalization System (ARES) as a potential future part of the International Space Station's Environmental Control and Life Support System would close the oxygen loop. The amount of oxygen, needed for an ISS crew of seven astronauts could be provided by ARES. The upload of almost 1500 kg of water annually for oxygen generation through the onboard electrolyzer would be reduced by more than 1000 kg, resulting in savings of more than 30M$ per year. Additionally, the payload capacity of supply flights would be increased by this amount of mass. Further possibilities are addressed to combine ECLS mass flows with those of the power, propulsion and attitude control systems. Such closed loop approaches will contribute to ease long time missions (e. g. Mars, Moon) from a cost and logistic point of view. The hardware realization of Astrium's space-sized operating ARES is shown and test results of continuous and intermittent closed chamber tests are presented. c2001 Astrium GmbH. Published by Elsevier Science Ltd.
Ground Source Heat Pumps vs. Conventional HVAC: A Comparison of Economic and Environmental Costs

DTIC Science & Technology

2009-03-26

of systems are surface water heat pumps (SWHPs), ground water heat pumps (GWHPs), and ground coupled heat pumps ( GCHPs ) (Kavanaugh & Rafferty, 1997...Kavanaugh & Rafferty, 1997). Ground Coupled Heat Pumps (Closed-Loop Ground Source Heat Pumps) GCHPs , otherwise known as closed-loop GSHPs, are the...Significant confusion has arisen through the use of GCHP and closed-loop GSHP terminology. Closed-loop GSHP is the preferred nomenclature for this
Design of an ammonia closed-loop storage system in a CSP power plant with a power tower cavity receiver

NASA Astrophysics Data System (ADS)

Abdiwe, Ramadan; Haider, Markus

2017-06-01

In this study the thermochemical system using ammonia as energy storage carrier is investigated and a transient mathematical model using MATLAB software was developed to predict the behavior of the ammonia closed-loop storage system including but not limited to the ammonia solar reactor and the ammonia synthesis reactor. The MATLAB model contains transient mass and energy balances as well as chemical equilibrium model for each relevant system component. For the importance of the dissociation and formation processes in the system, a Computational Fluid Dynamics (CFD) simulation on the ammonia solar and synthesis reactors has been performed. The CFD commercial package FLUENT is used for the simulation study and all the important mechanisms for packed bed reactors are taken into account, such as momentum, heat and mass transfer, and chemical reactions. The FLUENT simulation reveals the profiles inside both reactors and compared them with the profiles from the MATLAB code.
Performance of the dark energy camera liquid nitrogen cooling system

NASA Astrophysics Data System (ADS)

Cease, H.; Alvarez, M.; Alvarez, R.; Bonati, M.; Derylo, G.; Estrada, J.; Flaugher, B.; Flores, R.; Lathrop, A.; Munoz, F.; Schmidt, R.; Schmitt, R. L.; Schultz, K.; Kuhlmann, S.; Zhao, A.

2014-01-01

The Dark Energy Camera, the Imager and its cooling system was installed onto the Blanco 4m telescope at the Cerro Tololo Inter-American Observatory in Chile in September 2012. The imager cooling system is a LN2 two-phase closed loop cryogenic cooling system. The cryogenic circulation processing is located off the telescope. Liquid nitrogen vacuum jacketed transfer lines are run up the outside of the telescope truss tubes to the imager inside the prime focus cage. The design of the cooling system along with commissioning experiences and initial cooling system performance is described. The LN2 cooling system with the DES imager was initially operated at Fermilab for testing, then shipped and tested in the Blanco Coudé room. Now the imager is operating inside the prime focus cage. It is shown that the cooling performance sufficiently cools the imager in a closed loop mode, which can operate for extended time periods without maintenance or LN2 fills.
Closed-loop fiber optic gyroscope with homodyne detection

NASA Astrophysics Data System (ADS)

Zhu, Yong; Qin, BingKun; Chen, Shufen

1996-09-01

Interferometric fiber optic gyroscope (IFOG) has been analyzed with autocontrol theory in this paper. An open-loop IFOG system is not able to restrain the bias drift, but a closed-loop IFOG system can do it very well using negative feedback in order to suppress zero drift. The result of our theoretic analysis and computer simulation indicate that the bias drift of a closed-loop system is smaller than an open- loop one.
Design study of steady-state 30-tesla liquid-neon-cooled magnet

NASA Technical Reports Server (NTRS)

Prok, G. M.; Brown, G. V.

1976-01-01

A design for a 30-tesla, liquid-neon-cooled magnet was reported which is capable of continuous operation. Cooled by nonboiling, forced-convection heat transfer to liquid neon flowing at 2.8 cu m/min in a closed, pressurized heat-transfer loop and structurally supported by a tapered structural ribbon, the tape-wound coils with a high-purity-aluminum conductor will produce over 30 teslas for 1 minute at 850 kilowatts. The magnet will have an inside diameter of 7.5 centimeters and an outside diameter of 54 centimeters. The minimum current density at design field will be 15.7 kA/sq cm.
Integrated Testing of a 4-Bed Molecular Sieve and a Temperature-Swing Adsorption Compressor for Closed-Loop Air Revitalization

NASA Technical Reports Server (NTRS)

Knox, James C.; Mulloth, Lila M.; Affleck, David L.

2004-01-01

Accumulation and subsequent compression of carbon dioxide that is removed from space cabin are two important processes involved in a closed-loop air revitalization scheme of the International Space Station (ISS). The 4-Bed Molecular Sieve (4BMS) of ISS currently operates in an open loop mode without a compressor. This paper reports the integrated 4BMS and liquid-cooled TSAC testing conducted during the period of March 3 to April 18, 2003. The TSAC prototype was developed at NASA Ames Research Center (ARC). The 4BMS was modified to a functionally flight-like condition at NASA Marshall Space Flight Center (MSFC). Testing was conducted at MSFC. The paper provides details of the TSAC operation at various CO2 loadings and corresponding performance of CDRA.
Efficient dynamic coherence transfer relying on offset locking using optical phase-locked loop

NASA Astrophysics Data System (ADS)

Xie, Weilin; Dong, Yi; Bretenaker, Fabien; Shi, Hongxiao; Zhou, Qian; Xia, Zongyang; Qin, Jie; Zhang, Lin; Lin, Xi; Hu, Weisheng

2018-01-01

We design and experimentally demonstrate a highly efficient coherence transfer based on composite optical phaselocked loop comprising multiple feedback servo loops. The heterodyne offset-locking is achieved by conducting an acousto-optic frequency shifter in combination with the current tuning and the temperature controlling of the semiconductor laser. The adaptation of the composite optical phase-locked loop enables the tight coherence transfer from a frequency comb to a semiconductor laser in a fully dynamic manner.
Low Speed and High Speed Correlation of SMART Active Flap Rotor Loads

NASA Technical Reports Server (NTRS)

Kottapalli, Sesi B. R.

2010-01-01

Measured, open loop and closed loop data from the SMART rotor test in the NASA Ames 40- by 80- Foot Wind Tunnel are compared with CAMRAD II calculations. One open loop high-speed case and four closed loop cases are considered. The closed loop cases include three high-speed cases and one low-speed case. Two of these high-speed cases include a 2 deg flap deflection at 5P case and a test maximum-airspeed case. This study follows a recent, open loop correlation effort that used a simple correction factor for the airfoil pitching moment Mach number. Compared to the earlier effort, the current open loop study considers more fundamental corrections based on advancing blade aerodynamic conditions. The airfoil tables themselves have been studied. Selected modifications to the HH-06 section flap airfoil pitching moment table are implemented. For the closed loop condition, the effect of the flap actuator is modeled by increased flap hinge stiffness. Overall, the open loop correlation is reasonable, thus confirming the basic correctness of the current semi-empirical modifications; the closed loop correlation is also reasonable considering that the current flap model is a first generation model. Detailed correlation results are given in the paper.
Visualizing Active-Site Dynamics in Single Crystals of HePTP: Opening of the WPD Loop Involves Coordinated Movement of the E Loop

DOE Office of Scientific and Technical Information (OSTI.GOV)

D Critton; L Tautz; R Page

2011-12-31

Phosphotyrosine hydrolysis by protein tyrosine phosphatases (PTPs) involves substrate binding by the PTP loop and closure over the active site by the WPD loop. The E loop, located immediately adjacent to the PTP and WPD loops, is conserved among human PTPs in both sequence and structure, yet the role of this loop in substrate binding and catalysis is comparatively unexplored. Hematopoietic PTP (HePTP) is a member of the kinase interaction motif (KIM) PTP family. Compared to other PTPs, KIM-PTPs have E loops that are unique in both sequence and structure. In order to understand the role of the E loopmore » in the transition between the closed state and the open state of HePTP, we identified a novel crystal form of HePTP that allowed the closed-state-to-open-state transition to be observed within a single crystal form. These structures, which include the first structure of the HePTP open state, show that the WPD loop adopts an 'atypically open' conformation and, importantly, that ligands can be exchanged at the active site, which is critical for HePTP inhibitor development. These structures also show that tetrahedral oxyanions bind at a novel secondary site and function to coordinate the PTP, WPD, and E loops. Finally, using both structural and kinetic data, we reveal a novel role for E-loop residue Lys182 in enhancing HePTP catalytic activity through its interaction with Asp236 of the WPD loop, providing the first evidence for the coordinated dynamics of the WPD and E loops in the catalytic cycle, which, as we show, is relevant to multiple PTP families.« less
Functional role of a mobile loop of Escherichia coli dihydrofolate reductase in transition-state stabilization.

PubMed

Li, L; Falzone, C J; Wright, P E; Benkovic, S J

1992-09-01

The function of a highly mobile loop in Escherichia coli dihydrofolate reductase was studied by constructing a mutant (DL1) using cassette mutagenesis that had four residues deleted in the middle section of the loop (Met16-Ala19) and a glycine inserted to seal the gap. This part of the loop involves residues 16-20 and is disordered in the X-ray crystal structures of the apoprotein and the NADP+ binary complex but forms a hairpin turn that folds over the nicotinamide moiety of NADP+ and the pteridine moiety of folate in the ternary complex [Bystroff, C., & Kraut, J. (1991) Biochemistry 30, 2227-2239]. The steady-state and pre-steady-state kinetics and two-dimensional 1H NMR spectra were analyzed and compared to the wild-type protein. The kinetics on the DL1 mutant enzyme show that the KM value for NADPH (5.3 microM), the KM for dihydrofolate (2 microM), the rate constant for the release of the product tetrahydrofolate (10.3 s-1), and the intrinsic pKa value (6.2) are similar to those exhibited by the wild-type enzyme. However, the hydride-transfer rate declines markedly from the wild-type value of 950 s-1 to 1.7 s-1 for the DL1 mutant and when taken with data for substrate binding indicates that the loop contributes to substrate flux by a factor of 3.5 x 10(4). Thus, the mobility of loop I may provide a mechanism of recruiting hydrophobic residues which can properly align the nicotinamide and pteridine rings for the hydride-transfer process (a form of transition-state stabilization).(ABSTRACT TRUNCATED AT 250 WORDS)
A Model for Developing Clinical Analytics Capacity: Closing the Loops on Outcomes to Optimize Quality.

PubMed

Eggert, Corinne; Moselle, Kenneth; Protti, Denis; Sanders, Dale

2017-01-01

Closed Loop Analytics© is receiving growing interest in healthcare as a term referring to information technology, local data and clinical analytics working together to generate evidence for improvement. The Closed Loop Analytics model consists of three loops corresponding to the decision-making levels of an organization and the associated data within each loop - Patients, Protocols, and Populations. The authors propose that each of these levels should utilize the same ecosystem of electronic health record (EHR) and enterprise data warehouse (EDW) enabled data, in a closed-loop fashion, with that data being repackaged and delivered to suit the analytic and decision support needs of each level, in support of better outcomes.
A Conserved Surface Loop in Type I Dehydroquinate Dehydratases Positions an Active Site Arginine and Functions in Substrate Binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Light, Samuel H.; Minasov, George; Shuvalova, Ludmilla

2012-04-18

Dehydroquinate dehydratase (DHQD) catalyzes the third step in the biosynthetic shikimate pathway. We present three crystal structures of the Salmonella enterica type I DHQD that address the functionality of a surface loop that is observed to close over the active site following substrate binding. Two wild-type structures with differing loop conformations and kinetic and structural studies of a mutant provide evidence of both direct and indirect mechanisms of involvement of the loop in substrate binding. In addition to allowing amino acid side chains to establish a direct interaction with the substrate, closure of the loop necessitates a conformational change ofmore » a key active site arginine, which in turn positions the substrate productively. The absence of DHQD in humans and its essentiality in many pathogenic bacteria make the enzyme a target for the development of nontoxic antimicrobials. The structures and ligand binding insights presented here may inform the design of novel type I DHQD inhibiting molecules.« less
An adaptive human response mechanism controlling the V/STOL aircraft. Appendix 3: The adaptive control model of a pilot in V/STOL aircraft control loops. M.S. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Kucuk, Senol

1988-01-01

Importance of the role of human operator in control systems has led to the particular area of manual control theory. Human describing functions were developed to model human behavior for manual control studies to take advantage of the successful and safe human operations. A single variable approach is presented that can be extended for multi-variable tasks where a low order human response model is used together with its rules, to adapt the model on-line, being capable of responding to the changes in the controlled element dynamics. Basic control theory concepts are used to combine the model, constrained with the physical observations, particularly, for the case of aircraft control. Pilot experience is represented as the initial model parameters. An adaptive root-locus method is presented as the adaptation law of the model where the closed loop bandwidth of the system is to be preserved in a stable manner with the adjustments of the pilot handling qualities which relate the latter to the closed loop bandwidth and damping of the closed loop pilot aircraft combination. A Kalman filter parameter estimator is presented as the controlled element identifier of the adaptive model where any discrepancies of the open loop dynamics from the presented one, are sensed to be compensated.
Strain actuated aeroelastic control

NASA Technical Reports Server (NTRS)

Lazarus, Kenneth B.

1992-01-01

Viewgraphs on strain actuated aeroelastic control are presented. Topics covered include: structural and aerodynamic modeling; control law design methodology; system block diagram; adaptive wing test article; bench-top experiments; bench-top disturbance rejection: open and closed loop response; bench-top disturbance rejection: state cost versus control cost; wind tunnel experiments; wind tunnel gust alleviation: open and closed loop response at 60 mph; wind tunnel gust alleviation: state cost versus control cost at 60 mph; wind tunnel command following: open and closed loop error at 60 mph; wind tunnel flutter suppression: open loop flutter speed; and wind tunnel flutter suppression: closed loop state cost curves.
Auditory closed-loop stimulation of the sleep slow oscillation enhances memory.

PubMed

Ngo, Hong-Viet V; Martinetz, Thomas; Born, Jan; Mölle, Matthias

2013-05-08

Brain rhythms regulate information processing in different states to enable learning and memory formation. The <1 Hz sleep slow oscillation hallmarks slow-wave sleep and is critical to memory consolidation. Here we show in sleeping humans that auditory stimulation in phase with the ongoing rhythmic occurrence of slow oscillation up states profoundly enhances the slow oscillation rhythm, phase-coupled spindle activity, and, consequently, the consolidation of declarative memory. Stimulation out of phase with the ongoing slow oscillation rhythm remained ineffective. Closed-loop in-phase stimulation provides a straight-forward tool to enhance sleep rhythms and their functional efficacy. Copyright © 2013 Elsevier Inc. All rights reserved.

Control of a 30 cm diameter mercury bombardment thruster

NASA Technical Reports Server (NTRS)

Terdan, F. F.; Bechtel, R. T.

1973-01-01

Increased thruster performance has made closed-loop automatic control more difficult than previously. Specifically, high perveance optics tend to make reliable recycling more difficult. Control logic functions were established for three automatic modes of operation of a 30-cm thruster using a power conditioner console with flight-like characteristics. The three modes provide (1) automatic startup to reach thermal stability, (2) steady-state closed-loop control, and (3) the reliable recycling of the high voltages following an arc breakdown to reestablish normal operation. Power supply impedance characteristics necessary for stable operation and the effect of the magnetic baffle on the reliable recycling was studied.
Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop Laboratory Radio Frequency (RF) Propagation Section

DTIC Science & Technology

2016-10-01

ARL-TR-7860 ● OCT 2016 US Army Research Laboratory Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop ...ARL-TR-7860 ● OCT 2016 US Army Research Laboratory Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop Laboratory...Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop Laboratory Radio Frequency (RF) Propagation Section 5a. CONTRACT NUMBER
Hypoglycaemia incidence and recovery during home use of hybrid closed-loop insulin delivery in adults with type 1 diabetes.

PubMed

Ruan, Yue; Bally, Lia; Thabit, Hood; Leelarathna, Lalantha; Hartnell, Sara; Tauschmann, Martin; Wilinska, Malgorzata E; Evans, Mark L; Mader, Julia K; Kojzar, Harald; Dellweg, Sibylle; Benesch, Carsten; Arnolds, Sabine; Pieber, Thomas R; Hovorka, Roman

2018-03-25

Glucose excursion was assessed prior to and post hypoglycaemia to increase understanding of hypoglycaemia incidence and recovery during hybrid closed-loop insulin delivery. We retrospectively analysed data from 60 adults with type 1 diabetes who received, in a crossover randomized design, day-and-night hybrid closed-loop insulin delivery and insulin pump therapy, the latter with or without real-time continuous glucose monitoring. Over 4-week study periods, we identified hypoglycaemic episodes, defined as sensor glucose <3.0 mmol/L, and analysed sensor glucose relative to the onset of hypoglycaemia. We identified 377 hypoglycaemic episodes during hybrid closed-loop intervention vs 662 during control intervention (P < .001), with a predominant reduction of nocturnal hypoglycaemia. The slope of sensor glucose prior to hypoglycaemia was steeper during closed-loop intervention than during control intervention (P < .01), while insulin delivery was reduced (P < .01). During both day and night, participants recovered from hypoglycaemia faster when treated by closed-loop intervention. At 120 minutes post hypoglycaemia, sensor glucose levels were higher during closed-loop intervention compared to the control period (P < .05). In conclusion, closed-loop intervention reduces the risk of hypoglycaemia, particularly overnight, with swift recovery from hypoglycaemia leading to higher 2-hour post-hypoglycaemia glucose levels. © 2018 John Wiley & Sons Ltd.
A Closed-loop Brain Computer Interface to a Virtual Reality Avatar: Gait Adaptation to Visual Kinematic Perturbations

PubMed Central

Luu, Trieu Phat; He, Yongtian; Brown, Samuel; Nakagome, Sho; Contreras-Vidal, Jose L.

2016-01-01

The control of human bipedal locomotion is of great interest to the field of lower-body brain computer interfaces (BCIs) for rehabilitation of gait. While the feasibility of a closed-loop BCI system for the control of a lower body exoskeleton has been recently shown, multi-day closed-loop neural decoding of human gait in a virtual reality (BCI-VR) environment has yet to be demonstrated. In this study, we propose a real-time closed-loop BCI that decodes lower limb joint angles from scalp electroencephalography (EEG) during treadmill walking to control the walking movements of a virtual avatar. Moreover, virtual kinematic perturbations resulting in asymmetric walking gait patterns of the avatar were also introduced to investigate gait adaptation using the closed-loop BCI-VR system over a period of eight days. Our results demonstrate the feasibility of using a closed-loop BCI to learn to control a walking avatar under normal and altered visuomotor perturbations, which involved cortical adaptations. These findings have implications for the development of BCI-VR systems for gait rehabilitation after stroke and for understanding cortical plasticity induced by a closed-loop BCI system. PMID:27713915
Virtual grasping: closed-loop force control using electrotactile feedback.

PubMed

Jorgovanovic, Nikola; Dosen, Strahinja; Djozic, Damir J; Krajoski, Goran; Farina, Dario

2014-01-01

Closing the control loop by providing somatosensory feedback to the user of a prosthesis is a well-known, long standing challenge in the field of prosthetics. Various approaches have been investigated for feedback restoration, ranging from direct neural stimulation to noninvasive sensory substitution methods. Although there are many studies presenting closed-loop systems, only a few of them objectively evaluated the closed-loop performance, mostly using vibrotactile stimulation. Importantly, the conclusions about the utility of the feedback were partly contradictory. The goal of the current study was to systematically investigate the capability of human subjects to control grasping force in closed loop using electrotactile feedback. We have developed a realistic experimental setup for virtual grasping, which operated in real time, included a set of real life objects, as well as a graphical and dynamical model of the prosthesis. We have used the setup to test 10 healthy, able bodied subjects to investigate the role of training, feedback and feedforward control, robustness of the closed loop, and the ability of the human subjects to generalize the control to previously "unseen" objects. Overall, the outcomes of this study are very optimistic with regard to the benefits of feedback and reveal various, practically relevant, aspects of closed-loop control.
Restoration of motor function following spinal cord injury via optimal control of intraspinal microstimulation: toward a next generation closed-loop neural prosthesis

PubMed Central

Grahn, Peter J.; Mallory, Grant W.; Berry, B. Michael; Hachmann, Jan T.; Lobel, Darlene A.; Lujan, J. Luis

2014-01-01

Movement is planned and coordinated by the brain and carried out by contracting muscles acting on specific joints. Motor commands initiated in the brain travel through descending pathways in the spinal cord to effector motor neurons before reaching target muscles. Damage to these pathways by spinal cord injury (SCI) can result in paralysis below the injury level. However, the planning and coordination centers of the brain, as well as peripheral nerves and the muscles that they act upon, remain functional. Neuroprosthetic devices can restore motor function following SCI by direct electrical stimulation of the neuromuscular system. Unfortunately, conventional neuroprosthetic techniques are limited by a myriad of factors that include, but are not limited to, a lack of characterization of non-linear input/output system dynamics, mechanical coupling, limited number of degrees of freedom, high power consumption, large device size, and rapid onset of muscle fatigue. Wireless multi-channel closed-loop neuroprostheses that integrate command signals from the brain with sensor-based feedback from the environment and the system's state offer the possibility of increasing device performance, ultimately improving quality of life for people with SCI. In this manuscript, we review neuroprosthetic technology for improving functional restoration following SCI and describe brain-machine interfaces suitable for control of neuroprosthetic systems with multiple degrees of freedom. Additionally, we discuss novel stimulation paradigms that can improve synergy with higher planning centers and improve fatigue-resistant activation of paralyzed muscles. In the near future, integration of these technologies will provide SCI survivors with versatile closed-loop neuroprosthetic systems for restoring function to paralyzed muscles. PMID:25278830
Magellan attitude and articulation control subsystem closed loop testing

NASA Technical Reports Server (NTRS)

Olschansky, David G.

1987-01-01

In the spring of 1989, the Magellan spacecraft will embark on a two-year mission to map the surface of the planet Venus. Guiding it there will be the Attitude and Articulation Control Subsystem (AACS). To ensure reliable operations the AACS is being put through a rigorous test program at Martin Marietta Denver Aerospace. Before Magellan ever leaves the Space Shuttle bay from which it is to be launched, its components will have flown a simulated spaceflight in a ground-based lab. The primary objectives of the test program are to verify form, fit, and function of the AACS, particularly subsystem external interfaces and functional operation of the flight software. This paper discusses the Magellan Closed Loop Test Systems which makes realistic tests possible by simulating the dynamic and 'visual' flight environment for AACS components in the lab.
Bandwidth controller for phase-locked-loop

NASA Technical Reports Server (NTRS)

Brockman, Milton H. (Inventor)

1992-01-01

A phase locked loop utilizing digital techniques to control the closed loop bandwidth of the RF carrier phase locked loop in a receiver provides high sensitivity and a wide dynamic range for signal reception. After analog to digital conversion, a digital phase locked loop bandwidth controller provides phase error detection with automatic RF carrier closed loop tracking bandwidth control to accommodate several modes of transmission.
Probing the dynamics of restriction endonuclease NgoMIV-DNA interaction by single-molecule FRET.

PubMed

Tutkus, Marijonas; Sasnauskas, Giedrius; Rutkauskas, Danielis

2017-12-01

Many type II restriction endonucleases require two copies of their recognition sequence for optimal activity. Concomitant binding of two DNA sites by such an enzyme produces a DNA loop. Here we exploit single-molecule Förster resonance energy transfer (smFRET) of surface-immobilized DNA fragments to study the dynamics of DNA looping induced by tetrameric endonuclease NgoMIV. We have employed a DNA fragment with two NgoMIV recognition sites and a FRET dye pair such that upon protein-induced DNA looping the dyes are brought to close proximity resulting in a FRET signal. The dynamics of DNA-NgoMIV interactions proved to be heterogeneous, with individual smFRET trajectories exhibiting broadly different average looped state durations. Distinct types of the dynamics were attributed to different types of DNA-protein complexes, mediated either by one NgoMIV tetramer simultaneously bound to two specific sites ("slow" trajectories) or by semi-specific interactions of two DNA-bound NgoMIV tetramers ("fast" trajectories), as well as to conformational heterogeneity of individual NgoMIV molecules. © 2017 Wiley Periodicals, Inc.
3D-Stereoscopic Analysis of Solar Active Region Loops: I: SoHo/EIT Observations at Temperatures of 1.0-1.5 MK

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Newmark, Jeff; Delaboudiniere, Jean-Pierre; Neupert, Werner M.; Portier-Fozzani, Fabrice; Gary, G. Allen; Zucker, Arik

1998-01-01

The three-dimensional (3D) structure of solar active region NOAA 7986 observed on 1996 August 30 with the Extrem-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SoHO) is analyzed. We develop a new method of Dynamic Stereoscopy to reconstruct the 3D geometry of dynamically changing loops, which allows us to determine the orientation of the loop plane with respect to the line-of-sight, a prerequisite to correct properly for projection effects in 3D loop models. With this method and the filter-ratio technique applied to EIT 171 A and 195 A images we determine the 3D coordinates (x(s), y(s), z(s)), the loop width) w(s), the electron density n(sub e)(s), and the electron temperature T(sub e)(s) as function of the loop length s for 30 loop segments. Fitting the loop densities with an exponential density model n(sub e)(h) we find that the so inferred scale height temperatures, T(sub e)(sup lambda) = 1.22 +/- 0.23 MK, match closely the EIT filter-ratio temperatures, T(sub e)(sup FIT) = 1.21 +/- 0.06 MK. We conclude that these rather large-scale loops (with heights of h approx. equals 50 - 200 Mm) that dominate EIT 171 A images are close to thermal equilibrium. Most of the loops show no significant thickness variation w(s), but many exhibit a trend of increasing temperature (dT/ds greater than 0) above the footpoint.
Iterative LQG Controller Design Through Closed-Loop Identification

NASA Technical Reports Server (NTRS)

Hsiao, Min-Hung; Huang, Jen-Kuang; Cox, David E.

1996-01-01

This paper presents an iterative Linear Quadratic Gaussian (LQG) controller design approach for a linear stochastic system with an uncertain open-loop model and unknown noise statistics. This approach consists of closed-loop identification and controller redesign cycles. In each cycle, the closed-loop identification method is used to identify an open-loop model and a steady-state Kalman filter gain from closed-loop input/output test data obtained by using a feedback LQG controller designed from the previous cycle. Then the identified open-loop model is used to redesign the state feedback. The state feedback and the identified Kalman filter gain are used to form an updated LQC controller for the next cycle. This iterative process continues until the updated controller converges. The proposed controller design is demonstrated by numerical simulations and experiments on a highly unstable large-gap magnetic suspension system.
A helium based pulsating heat pipe for superconducting magnets

NASA Astrophysics Data System (ADS)

Fonseca, Luis Diego; Miller, Franklin; Pfotenhauer, John

2014-01-01

This study was inspired to investigate an alternative cooling system using a helium-based pulsating heat pipes (PHP), for low temperature superconducting magnets. In addition, the same approach can be used for exploring other low temperature applications. The advantages of PHP for transferring heat and smoothing temperature profiles in various room temperature applications have been explored for the past 20 years. An experimental apparatus has been designed, fabricated and operated and is primarily composed of an evaporator and a condenser; in which both are thermally connected by a closed loop capillary tubing. The main goal is to measure the heat transfer properties of this device using helium as the working fluid. The evaporator end of the PHP is comprised of a copper winding in which heat loads up to 10 watts are generated, while the condenser is isothermal and can reach 4.2 K via a two stage Sumitomo RDK408A2 GM cryocooler. Various experimental design features are highlighted. Additionally, performance results in the form of heat transfer and temperature characteristics are provided as a function of average condenser temperature, PHP fill ratio, and evaporator heat load. Results are summarized in the form of a dimensionless correlation and compared to room temperature systems. Implications for superconducting magnet stability are highlighted.
Temperature Oscillations in Loop Heat Pipe Operation

NASA Technical Reports Server (NTRS)

Ku, Jentung; Ottenstein, Laura; Kobel, Mark; Rogers, Paul; Kaya, Tarik; Paquin, Krista C. (Technical Monitor)

2000-01-01

Loop heat pipes (LHPs) are versatile two-phase heat transfer devices that have gained increasing acceptance for space and terrestrial applications. The operating temperature of an LHP is a function of its operating conditions. The LHP usually reaches a steady operating temperature for a given heat load and sink temperature. The operating temperature will change when the heat load and/or the sink temperature changes, but eventually reaches another steady state in most cases. Under certain conditions, however, the loop operating temperature never really reaches a true steady state, but instead becomes oscillatory. This paper discusses the temperature oscillation phenomenon using test data from a miniature LHP.
A proof-of-principle simulation for closed-loop control based on preexisting experimental thalamic DBS-enhanced instrumental learning.

PubMed

Wang, Ching-Fu; Yang, Shih-Hung; Lin, Sheng-Huang; Chen, Po-Chuan; Lo, Yu-Chun; Pan, Han-Chi; Lai, Hsin-Yi; Liao, Lun-De; Lin, Hui-Ching; Chen, Hsu-Yan; Huang, Wei-Chen; Huang, Wun-Jhu; Chen, You-Yin

Deep brain stimulation (DBS) has been applied as an effective therapy for treating Parkinson's disease or essential tremor. Several open-loop DBS control strategies have been developed for clinical experiments, but they are limited by short battery life and inefficient therapy. Therefore, many closed-loop DBS control systems have been designed to tackle these problems by automatically adjusting the stimulation parameters via feedback from neural signals, which has been reported to reduce the power consumption. However, when the association between the biomarkers of the model and stimulation is unclear, it is difficult to develop an optimal control scheme for other DBS applications, i.e., DBS-enhanced instrumental learning. Furthermore, few studies have investigated the effect of closed-loop DBS control for cognition function, such as instrumental skill learning, and have been implemented in simulation environments. In this paper, we proposed a proof-of-principle design for a closed-loop DBS system, cognitive-enhancing DBS (ceDBS), which enhanced skill learning based on in vivo experimental data. The ceDBS acquired local field potential (LFP) signal from the thalamic central lateral (CL) nuclei of animals through a neural signal processing system. A strong coupling of the theta oscillation (4-7 Hz) and the learning period was found in the water reward-related lever-pressing learning task. Therefore, the theta-band power ratio, which was the averaged theta band to averaged total band (1-55 Hz) power ratio, could be used as a physiological marker for enhancement of instrumental skill learning. The on-line extraction of the theta-band power ratio was implemented on a field-programmable gate array (FPGA). An autoregressive with exogenous inputs (ARX)-based predictor was designed to construct a CL-thalamic DBS model and forecast the future physiological marker according to the past physiological marker and applied DBS. The prediction could further assist the design of a closed-loop DBS controller. A DBS controller based on a fuzzy expert system was devised to automatically control DBS according to the predicted physiological marker via a set of rules. The simulated experimental results demonstrate that the ceDBS based on the closed-loop control architecture not only reduced power consumption using the predictive physiological marker, but also achieved a desired level of physiological marker through the DBS controller. Copyright © 2017 Elsevier Inc. All rights reserved.
An experimental study on the performance of closed loop pulsating heat pipe (CLPHP) with methanol as a working fluid

NASA Astrophysics Data System (ADS)

Rahman, Md. Lutfor; Nourin, Farah Nazifa; Salsabil, Zaimaa; Yasmin, Nusrat; Ali, Mohammad

2016-07-01

Thermal control is an important topic for thermal management of small electrical and electronic devices. Closed loop pulsating heat pipe (CLPHP) arises as the best solution for thermal control. The aim of this experimental study is to search a CLPHP of better thermal performance for cooling different electrical and electronic devices. In this experiment, methanol is used as working fluid. The effect of using methanol as a working fluid is studied on thermal performance in different filling ratios and angles of inclination. A copper capillary tube is used where the inner diameter is 2mm,outer diameter is 2.5mm and 250mm long. The CLPHP has 8 loops where the evaporation section is 50mm, adiabatic section is 120mm and condensation section is 80mm. The experiment is done using FR of 40%-70% with 10% of interval and angles of inclination 0° (vertical), 30°, 45°, 60° varying heat input. The results are compared on the basis of evaporator temperature, condenser temperature and their differences, thermal resistance, heat transfer co-efficient, power input and pulsating time. The results demonstrate the effect of methanol in different filling ratios and angles of inclination. M ethanol shows better performance at 30° inclination with 40% FR.
Finite-time output feedback stabilization of high-order uncertain nonlinear systems

NASA Astrophysics Data System (ADS)

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.
Incorporation of SemiSpan SuperSonic Transport (S4T) Aeroservoelastic Models into SAREC-ASV Simulation

NASA Technical Reports Server (NTRS)

Christhilf, David M.; Pototzky, Anthony S.; Stevens, William L.

2010-01-01

The Simulink-based Simulation Architecture for Evaluating Controls for Aerospace Vehicles (SAREC-ASV) was modified to incorporate linear models representing aeroservoelastic characteristics of the SemiSpan SuperSonic Transport (S4T) wind-tunnel model. The S4T planform is for a Technology Concept Aircraft (TCA) design from the 1990s. The model has three control surfaces and is instrumented with accelerometers and strain gauges. Control laws developed for wind-tunnel testing for Ride Quality Enhancement, Gust Load Alleviation, and Flutter Suppression System functions were implemented in the simulation. The simulation models open- and closed-loop response to turbulence and to control excitation. It provides time histories for closed-loop stable conditions above the open-loop flutter boundary. The simulation is useful for assessing the potential impact of closed-loop control rate and position saturation. It also provides a means to assess fidelity of system identification procedures by providing time histories for a known plant model, with and without unmeasured turbulence as a disturbance. Sets of linear models representing different Mach number and dynamic pressure conditions were implemented as MATLAB Linear Time Invariant (LTI) objects. Configuration changes were implemented by selecting which LTI object to use in a Simulink template block. A limited comparison of simulation versus wind-tunnel results is shown.
Harwell high pressure heat transfer loop

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bennett, A.W.; Keeys, R.K.F.

1967-12-15

A detailed description is presented of the Harwell (Chemical Engineering and Process Technology Division) high pressure, steam-water heat transfer loop; this description is aimed at supplementing the information given in reports on individual experiments. The operating instructions for the loop are given in an appendix. (auth)
Heat transfer analysis of catheters used for localized tissue cooling to attenuate reperfusion injury.

PubMed

Merrill, Thomas L; Mitchell, Jennifer E; Merrill, Denise R

2016-08-01

Recent revascularization success for ischemic stroke patients using stentrievers has created a new opportunity for therapeutic hypothermia. By using short term localized tissue cooling interventional catheters can be used to reduce reperfusion injury and improve neurological outcomes. Using experimental testing and a well-established heat exchanger design approach, the ɛ-NTU method, this paper examines the cooling performance of commercially available catheters as function of four practical parameters: (1) infusion flow rate, (2) catheter location in the body, (3) catheter configuration and design, and (4) cooling approach. While saline batch cooling outperformed closed-loop autologous blood cooling at all equivalent flow rates in terms of lower delivered temperatures and cooling capacity, hemodilution, systemic and local, remains a concern. For clinicians and engineers this paper provides insights for the selection, design, and operation of commercially available catheters used for localized tissue cooling. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.
Power Approaches for Implantable Medical Devices.

PubMed

Ben Amar, Achraf; Kouki, Ammar B; Cao, Hung

2015-11-13

Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources.

Demonstration of frequency-sweep testing technique using a Bell 214-ST helicopter

NASA Technical Reports Server (NTRS)

Tischler, Mark B.; Fletcher, Jay W.; Diekmann, Vernon L.; Williams, Robert A.; Cason, Randall W.

1987-01-01

A demonstration of frequency-sweep testing using a Bell-214ST single-rotor helicopter was completed in support of the Army's development of an updated MIL-H-8501A, and an LHX (ADS-33) handling-qualities specification. Hover and level-flight (V sub a = 0 knots and V sub a = 90 knots) tests were conducted in 3 flight hours by Army test pilots at the Army Aviation Engineering Flight Activity (AEFA) at Edwards AFB, Calif. Bandwidth and phase-delay parameters were determined from the flight-extracted frequency responses as required by the proposed specifications. Transfer function modeling and verification demonstrates the validity of the frequency-response concept for characterizing closed-loop flight dynamics of single-rotor helicopters -- even in hover. This report documents the frequency-sweep flight-testing technique and data-analysis procedures. Special emphasis is given to piloting and analysis considerations which are important for demonstrating frequency-domain specification compliance.
Closed-loop Habitation Air Revitalization Model for Regenerative Life Support Systems

NASA Technical Reports Server (NTRS)

Hart, Maxwell M.

1991-01-01

The primary function of any life support system is to keep the crew alive by providing breathable air, potable water, edible food, and for disposal of waste. In a well-balanced or regenerative life support system, the various components are each using what is available and producing what is needed by other components so that there will always be enough chemicals in the form in which they are needed. Humans are not just users, but also one of the participating parts of the system. If a system could continuously recycle the original chemicals, this would make it virtually a Closed-loop Habitation (CH). Some difficulties in trying to create a miniature version of a CH are briefly discussed. In a miniature CH, a minimal structure must be provided and the difference must be made up by artificial parts such as physicochemical systems that perform the conversions that the Earth can achieve naturally. To study the interactions of these parts, a computer model was designed that simulates a miniature CH with emphasis on the air revitalization part. It is called the Closed-loop Habitation Air Revitalization Model (CHARM).
Robustness Analysis and Optimally Robust Control Design via Sum-of-Squares

NASA Technical Reports Server (NTRS)

Dorobantu, Andrei; Crespo, Luis G.; Seiler, Peter J.

2012-01-01

A control analysis and design framework is proposed for systems subject to parametric uncertainty. The underlying strategies are based on sum-of-squares (SOS) polynomial analysis and nonlinear optimization to design an optimally robust controller. The approach determines a maximum uncertainty range for which the closed-loop system satisfies a set of stability and performance requirements. These requirements, de ned as inequality constraints on several metrics, are restricted to polynomial functions of the uncertainty. To quantify robustness, SOS analysis is used to prove that the closed-loop system complies with the requirements for a given uncertainty range. The maximum uncertainty range, calculated by assessing a sequence of increasingly larger ranges, serves as a robustness metric for the closed-loop system. To optimize the control design, nonlinear optimization is used to enlarge the maximum uncertainty range by tuning the controller gains. Hence, the resulting controller is optimally robust to parametric uncertainty. This approach balances the robustness margins corresponding to each requirement in order to maximize the aggregate system robustness. The proposed framework is applied to a simple linear short-period aircraft model with uncertain aerodynamic coefficients.
Accurate predictor-corrector skip entry guidance for low lift-to-drag ratio spacecraft

NASA Astrophysics Data System (ADS)

Enmi, Y.; Qian, W.; He, K.; Di, D.

2018-06-01

This paper develops numerical predictor-corrector skip en try guidance for vehicles with low lift-to-drag L/D ratio during the skip entry phase of a Moon return mission. The guidance method is composed of two parts: trajectory planning before entry and closed-loop gu idance during skip entry. The result of trajectory planning before entry is able to present an initial value for predictor-corrector algorithm in closed-loop guidance for fast convergence. The magnitude of bank angle, which is parameterized as a linear function of the range-to-go, is modulated to satisfy the downrange requirements. The sign of the bank ang le is determined by the bank-reversal logic. The predictor-corrector algorithm repeatedly applied onboard in each guidance cycle to realize closed-loop guidance in the skip entry phase. The effectivity of the proposed guidance is validated by simulations in nominal conditions, including skip entry, loft entry, and direct entry, as well as simulations in dispersion conditions considering the combination disturbance of the entry interface, the aerodynamic coefficients, the air density, and the mass of the vehicle.
The Structure, Design, and Closed-Loop Motion Control of a Differential Drive Soft Robot.

PubMed

Wu, Pang; Jiangbei, Wang; Yanqiong, Fei

2018-02-01

This article presents the structure, design, and motion control of an inchworm inspired pneumatic soft robot, which can perform differential movement. This robot mainly consists of two columns of pneumatic multi-airbags (actuators), one sensor, one baseboard, front feet, and rear feet. According to the different inflation time of left and right actuators, the robot can perform both linear and turning movements. The actuators of this robot are composed of multiple airbags, and the design of the airbags is analyzed. To deal with the nonlinear performance of the soft robot, we use radial basis function neural networks to train the turning ability of this robot on three different surfaces and create a mathematical model among coefficient of friction, deflection angle, and inflation time. Then, we establish the closed-loop automatic control model using three-axis electronic compass sensor. Finally, the automatic control model is verified by linear and turning movement experiments. According to the experiment, the robot can finish the linear and turning movements under the closed-loop control system.
Advanced ECCD based NTM control in closed-loop operation at ASDEX Upgrade (AUG)

NASA Astrophysics Data System (ADS)

Reich, Matthias; Barrera-Orte, Laura; Behler, Karl; Bock, Alexander; Giannone, Louis; Maraschek, Marc; Poli, Emanuele; Rapson, Chris; Stober, Jörg; Treutterer, Wolfgang

2012-10-01

In high performance plasmas, Neoclassical Tearing Modes (NTMs) are regularly observed at reactor-grade beta-values. They limit the achievable normalized beta, which is undesirable because fusion performance scales as beta squared. The method of choice for controlling and avoiding NTMs at AUG is the deposition of ECCD inside the magnetic island for stabilization in real-time (rt). Our approach to tackling such complex control problems using real-time diagnostics allows rigorous optimization of all subsystems. Recent progress in rt-equilibrium reconstruction (< 3.5 ms), rt-localization of NTMs (< 8 ms) and rt beam tracing (< 25 ms) allows closed-loop feedback operation using multiple movable mirrors as the ECCD deposition actuator. The rt-equilibrium uses function parametrization or a fast Grad-Shafranov solver with an option to include rt-MSE measurements. The island localization is based on a correlation of ECE and filtered Mirnov signals. The rt beam-tracing module provides deposition locations and their derivative versus actuator position of multiple gyrotrons. The ``MHD controller'' finally drives the actuators. Results utilizing closed-loop operation with multiple gyrotrons and their effect on NTMs are shown.
Phase transitions in single macromolecules: Loop-stretch transition versus loop adsorption transition in end-grafted polymer chains

NASA Astrophysics Data System (ADS)

Zhang, Shuangshuang; Qi, Shuanhu; Klushin, Leonid I.; Skvortsov, Alexander M.; Yan, Dadong; Schmid, Friederike

2018-01-01

We use Brownian dynamics simulations and analytical theory to compare two prominent types of single molecule transitions. One is the adsorption transition of a loop (a chain with two ends bound to an attractive substrate) driven by an attraction parameter ɛ and the other is the loop-stretch transition in a chain with one end attached to a repulsive substrate, driven by an external end-force F applied to the free end. Specifically, we compare the behavior of the respective order parameters of the transitions, i.e., the mean number of surface contacts in the case of the adsorption transition and the mean position of the chain end in the case of the loop-stretch transition. Close to the transition points, both the static behavior and the dynamic behavior of chains with different length N are very well described by a scaling ansatz with the scaling parameters (ɛ - ɛ*)Nϕ (adsorption transition) and (F - F*)Nν (loop-stretch transition), respectively, where ϕ is the crossover exponent of the adsorption transition and ν is the Flory exponent. We show that both the loop-stretch and the loop adsorption transitions provide an exceptional opportunity to construct explicit analytical expressions for the crossover functions which perfectly describe all simulation results on static properties in the finite-size scaling regime. Explicit crossover functions are based on the ansatz for the analytical form of the order parameter distributions at the respective transition points. In contrast to the close similarity in equilibrium static behavior, the dynamic relaxation at the two transitions shows qualitative differences, especially in the strongly ordered regimes. This is attributed to the fact that the surface contact dynamics in a strongly adsorbed chain is governed by local processes, whereas the end height relaxation of a strongly stretched chain involves the full spectrum of Rouse modes.
Multiday Fully Closed Loop Insulin Delivery in Monitored Outpatient Conditions

ClinicalTrials.gov

2014-04-29

To Demonstrate That the Closed Loop System Can be Used Safely Over a Few Consecutive Days.; To Assess Effectiveness in Maintaining Patients' Glucose Levels in the Target Range of 70 to 180 mg/dl, Measured by Blood Glucose Sensor.; To Evaluate the User Experience With a Closed Loop System
Closed Loop Vibrational Control: Theory and Applications

DTIC Science & Technology

1993-10-01

the open loop system dynamics will be close to that of Bit. However, in general, in a closed loop system with a specified feedback co-’ - oller , for...Juang, and G. Rodriguez , "Formulations and Applications of Large Structure Actuator and Sensor Placements," Second VPI & SU/AIAA Symposium on Dynamics
New method of computing the contributions of graphs without lepton loops to the electron anomalous magnetic moment in QED

NASA Astrophysics Data System (ADS)

Volkov, Sergey

2017-11-01

This paper presents a new method of numerical computation of the mass-independent QED contributions to the electron anomalous magnetic moment which arise from Feynman graphs without closed electron loops. The method is based on a forestlike subtraction formula that removes all ultraviolet and infrared divergences in each Feynman graph before integration in Feynman-parametric space. The integration is performed by an importance sampling Monte-Carlo algorithm with the probability density function that is constructed for each Feynman graph individually. The method is fully automated at any order of the perturbation series. The results of applying the method to 2-loop, 3-loop, 4-loop Feynman graphs, and to some individual 5-loop graphs are presented, as well as the comparison of this method with other ones with respect to Monte Carlo convergence speed.
Neural Network Based Modeling and Analysis of LP Control Surface Allocation

NASA Technical Reports Server (NTRS)

Langari, Reza; Krishnakumar, Kalmanje; Gundy-Burlet, Karen

2003-01-01

This paper presents an approach to interpretive modeling of LP based control allocation in intelligent flight control. The emphasis is placed on a nonlinear interpretation of the LP allocation process as a static map to support analytical study of the resulting closed loop system, albeit in approximate form. The approach makes use of a bi-layer neural network to capture the essential functioning of the LP allocation process. It is further shown via Lyapunov based analysis that under certain relatively mild conditions the resulting closed loop system is stable. Some preliminary conclusions from a study at Ames are stated and directions for further research are given at the conclusion of the paper.
Investigation of creep by use of closed loop servo-hydraulic test system

NASA Technical Reports Server (NTRS)

Wu, H. C.; Yao, J. C.

1981-01-01

Creep tests were conducted by means of a closed loop servo-controlled materials test system. These tests are different from the conventional creep tests in that the strain history prior to creep may be carefully monitored. Tests were performed for aluminum alloy 6061-0 at 150 C and monitored by a PDP 11/04 minicomputer at a preset constant plastic-strain rate prehistory. The results show that the plastic-strain rate prior to creep plays a significant role in creep behavior. The endochronic theory of viscoplasticity was applied to describe the observed creep curves. The concepts of intrinsic time and strain rate sensitivity function are employed and modified according to the present observation.
Folding of the natural hammerhead ribozyme is enhanced by interaction of auxiliary elements

PubMed Central

PENEDO, J. CARLOS; WILSON, TIMOTHY J.; JAYASENA, SUMEDHA D.; KHVOROVA, ANASTASIA; LILLEY, DAVID M.J.

2004-01-01

It has been shown that the activity of the hammerhead ribozyme at μM magnesium ion concentrations is markedly increased by the inclusion of loops in helices I and II. We have studied the effect of such loops on the magnesium ion-induced folding of the ribozyme, using fluorescence resonance energy transfer. We find that with the loops in place, folding into the active conformation occurs in a single step, in the μM range of magnesium ion concentration. Disruption of the loop–loop interaction leads to a reversion to two-step folding, with the second stage requiring mM concentrations of magnesium ion. Sodium ions also promote the folding of the natural form of the ribozyme at high concentrations, but the folding occurs as a two-stage process. The loops clearly act as important auxiliary elements in the function of the ribozyme, permitting folding to occur efficiently under physiological conditions. PMID:15100442
Research study on stabilization and control: Modern sampled-data control theory. Continuous and discrete describing function analysis of the LST system. [with emphasis on the control moment gyroscope control loop

NASA Technical Reports Server (NTRS)

Kuo, B. C.; Singh, G.

1974-01-01

The dynamics of the Large Space Telescope (LST) control system were studied in order to arrive at a simplified model for computer simulation without loss of accuracy. The frictional nonlinearity of the Control Moment Gyroscope (CMG) Control Loop was analyzed in a model to obtain data for the following: (1) a continuous describing function for the gimbal friction nonlinearity; (2) a describing function of the CMG nonlinearity using an analytical torque equation; and (3) the discrete describing function and function plots for CMG functional linearity. Preliminary computer simulations are shown for the simplified LST system, first without, and then with analytical torque expressions. Transfer functions of the sampled-data LST system are also described. A final computer simulation is presented which uses elements of the simplified sampled-data LST system with analytical CMG frictional torque expressions.
Optimal Lorentz-augmented spacecraft formation flying in elliptic orbits

NASA Astrophysics Data System (ADS)

Huang, Xu; Yan, Ye; Zhou, Yang

2015-06-01

An electrostatically charged spacecraft accelerates as it moves through the Earth's magnetic field due to the induced Lorentz force, providing a new means of propellantless electromagnetic propulsion for orbital maneuvers. The feasibility of Lorentz-augmented spacecraft formation flying in elliptic orbits is investigated in this paper. Assuming the Earth's magnetic field as a tilted dipole corotating with Earth, a nonlinear dynamical model that characterizes the orbital motion of Lorentz spacecraft in the vicinity of arbitrary elliptic orbits is developed. To establish a predetermined formation configuration at given terminal time, pseudospectral method is used to solve the optimal open-loop trajectories of hybrid control inputs consisted of Lorentz acceleration and thruster-generated control acceleration. A nontilted dipole model is also introduced to analyze the effect of dipole tilt angle via comparisons with the tilted one. Meanwhile, to guarantee finite-time convergence and system robustness against external perturbations, a continuous fast nonsingular terminal sliding mode controller is designed and the closed-loop system stability is proved by Lyapunov theory. Numerical simulations substantiate the validity of proposed open-loop and closed-loop control schemes, and the results indicate that an almost propellantless formation establishment can be achieved by choosing appropriate objective function in the pseudospectral method. Furthermore, compared to the nonsingular terminal sliding mode controller, the closed-loop controller presents superior convergence rate with only a bit more control effort. And the proposed controller can be applied in other Lorentz-augmented relative orbital control problems.
Closed-loop thrust and pressure profile throttling of a nitrous oxide/hydroxyl-terminated polybutadiene hybrid rocket motor

NASA Astrophysics Data System (ADS)

Peterson, Zachary W.

Hybrid motors that employ non-toxic, non-explosive components with a liquid oxidizer and a solid hydrocarbon fuel grain have inherently safe operating characteristics. The inherent safety of hybrid rocket motors offers the potential to greatly reduce overall operating costs. Another key advantage of hybrid rocket motors is the potential for in-flight shutdown, restart, and throttle by controlling the pressure drop between the oxidizer tank and the injector. This research designed, developed, and ground tested a closed-loop throttle controller for a hybrid rocket motor using nitrous oxide and hydroxyl-terminated polybutadiene as propellants. The research simultaneously developed closed-loop throttle algorithms and lab scale motor hardware to evaluate the fidelity of the throttle simulations and algorithms. Initial open-loop motor tests were performed to better classify system parameters and to validate motor performance values. Deep-throttle open-loop tests evaluated limits of stable thrust that can be achieved on the test hardware. Open-loop tests demonstrated the ability to throttle the motor to less than 10% of maximum thrust with little reduction in effective specific impulse and acoustical stability. Following the open-loop development, closed-loop, hardware-in-the-loop tests were performed. The closed-loop controller successfully tracked prescribed step and ramp command profiles with a high degree of fidelity. Steady-state accuracy was greatly improved over uncontrolled thrust.
System and method for correcting attitude estimation

NASA Technical Reports Server (NTRS)

Josselson, Robert H. (Inventor)

2010-01-01

A system includes an angular rate sensor disposed in a vehicle for providing angular rates of the vehicle, and an instrument disposed in the vehicle for providing line-of-sight control with respect to a line-of-sight reference. The instrument includes an integrator which is configured to integrate the angular rates of the vehicle to form non-compensated attitudes. Also included is a compensator coupled across the integrator, in a feed-forward loop, for receiving the angular rates of the vehicle and outputting compensated angular rates of the vehicle. A summer combines the non-compensated attitudes and the compensated angular rates of the to vehicle to form estimated vehicle attitudes for controlling the instrument with respect to the line-of-sight reference. The compensator is configured to provide error compensation to the instrument free-of any feedback loop that uses an error signal. The compensator may include a transfer function providing a fixed gain to the received angular rates of the vehicle. The compensator may, alternatively, include a is transfer function providing a variable gain as a function of frequency to operate on the received angular rates of the vehicle.
Sustainable pyrolytic sludge-char preparation on improvement of closed-loop sewage sludge treatment: Characterization and combined in-situ application.

PubMed

Jin, Zhengyu; Chang, Fengmin; Meng, Fanlin; Wang, Cuiping; Meng, Yao; Liu, Xiaoji; Wu, Jing; Zuo, Jiane; Wang, Kaijun

2017-10-01

Aiming at closed-loop sustainable sewage sludge treatment, an optimal and economical pyrolytic temperature was found at 400-450 °C considering its pyrolysis efficiency of 65%, fast cracking of hydrocarbons, proteins and lipids and development of aromatized porous structure. Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) tests demonstrated the development of adsorptive functional groups and crystallographic phases of adsorptive minerals. The optimal sludge-char, with a medium specific surface area of 39.6 m 2 g -1 and an iodine number of 327 mgI 2 g -1 , performed low heavy metals lixiviation. The application of sludge-char in raw sewage could remove 30% of soluble chemical oxygen demand (SCOD), along with an acetic acid adsorption capacity of 18.0 mg g -1 . The developed mesopore and/or macropore structures, containing rich acidic and basic functional groups, led to good biofilm matrices for enhanced microbial activities and improved autotrophic nitrification in anoxic stage of an A/O reactor through adsorbed extra carbon source, and hence achieved the total nitrogen (TN) removal up to 50.3%. It is demonstrated that the closed-loop sewage sludge treatment that incorporates pyrolytic sludge-char into in-situ biological sewage treatment can be a promising sustainable strategy by further optimization. Copyright © 2017 Elsevier Ltd. All rights reserved.
Open Ephys: an open-source, plugin-based platform for multichannel electrophysiology

NASA Astrophysics Data System (ADS)

Siegle, Joshua H.; Cuevas López, Aarón; Patel, Yogi A.; Abramov, Kirill; Ohayon, Shay; Voigts, Jakob

2017-08-01

Objective. Closed-loop experiments, in which causal interventions are conditioned on the state of the system under investigation, have become increasingly common in neuroscience. Such experiments can have a high degree of explanatory power, but they require a precise implementation that can be difficult to replicate across laboratories. We sought to overcome this limitation by building open-source software that makes it easier to develop and share algorithms for closed-loop control. Approach. We created the Open Ephys GUI, an open-source platform for multichannel electrophysiology experiments. In addition to the standard ‘open-loop’ visualization and recording functionality, the GUI also includes modules for delivering feedback in response to events detected in the incoming data stream. Importantly, these modules can be built and shared as plugins, which makes it possible for users to extend the functionality of the GUI through a simple API, without having to understand the inner workings of the entire application. Main results. In combination with low-cost, open-source hardware for amplifying and digitizing neural signals, the GUI has been used for closed-loop experiments that perturb the hippocampal theta rhythm in a phase-specific manner. Significance. The Open Ephys GUI is the first widely used application for multichannel electrophysiology that leverages a plugin-based workflow. We hope that it will lower the barrier to entry for electrophysiologists who wish to incorporate real-time feedback into their research.
A closed-loop system for frequency tracking of piezoresistive cantilever sensors

NASA Astrophysics Data System (ADS)

Wasisto, Hutomo Suryo; Zhang, Qing; Merzsch, Stephan; Waag, Andreas; Peiner, Erwin

2013-05-01

A closed loop circuit capable of tracking resonant frequencies for MEMS-based piezoresistive cantilever resonators is developed in this work. The proposed closed-loop system is mainly based on a phase locked loop (PLL) circuit. In order to lock onto the resonant frequency of the resonator, an actuation signal generated from a voltage-controlled oscillator (VCO) is locked to the phase of the input reference signal of the cantilever sensor. In addition to the PLL component, an instrumentation amplifier and an active low pass filter (LPF) are connected to the system for gaining the amplitude and reducing the noise of the cantilever output signals. The LPF can transform a rectangular signal into a sinusoidal signal with voltage amplitudes ranging from 5 to 10 V which are sufficient for a piezoactuator input (i.e., maintaining a large output signal of the cantilever sensor). To demonstrate the functionality of the system, a self-sensing silicon cantilever resonator with a built-in piezoresistive Wheatstone bridge is fabricated and integrated with the circuit. A piezoactuator is utilized for actuating the cantilever into resonance. Implementation of this closed loop system is used to track the resonant frequency of a silicon cantilever-based sensor resonating at 9.4 kHz under a cross-sensitivity test of ambient temperature. The changes of the resonant frequency are interpreted using a frequency counter connected to the system. From the experimental results, the temperature sensitivity and coefficient of the employed sensor are 0.3 Hz/°C and 32.8 ppm/°C, respectively. The frequency stability of the system can reach up to 0.08 Hz. The development of this system will enable real-time nanoparticle monitoring systems and provide a miniaturization of the instrumentation modules for cantilever-based nanoparticle detectors.

A neuro-inspired model-based closed-loop neuroprosthesis for the substitution of a cerebellar learning function in anesthetized rats

NASA Astrophysics Data System (ADS)

Hogri, Roni; Bamford, Simeon A.; Taub, Aryeh H.; Magal, Ari; Giudice, Paolo Del; Mintz, Matti

2015-02-01

Neuroprostheses could potentially recover functions lost due to neural damage. Typical neuroprostheses connect an intact brain with the external environment, thus replacing damaged sensory or motor pathways. Recently, closed-loop neuroprostheses, bidirectionally interfaced with the brain, have begun to emerge, offering an opportunity to substitute malfunctioning brain structures. In this proof-of-concept study, we demonstrate a neuro-inspired model-based approach to neuroprostheses. A VLSI chip was designed to implement essential cerebellar synaptic plasticity rules, and was interfaced with cerebellar input and output nuclei in real time, thus reproducing cerebellum-dependent learning in anesthetized rats. Such a model-based approach does not require prior system identification, allowing for de novo experience-based learning in the brain-chip hybrid, with potential clinical advantages and limitations when compared to existing parametric ``black box'' models.
Adaptive Neural Control of Uncertain MIMO Nonlinear Systems With State and Input Constraints.

PubMed

Chen, Ziting; Li, Zhijun; Chen, C L Philip

2017-06-01

An adaptive neural control strategy for multiple input multiple output nonlinear systems with various constraints is presented in this paper. To deal with the nonsymmetric input nonlinearity and the constrained states, the proposed adaptive neural control is combined with the backstepping method, radial basis function neural network, barrier Lyapunov function (BLF), and disturbance observer. By ensuring the boundedness of the BLF of the closed-loop system, it is demonstrated that the output tracking is achieved with all states remaining in the constraint sets and the general assumption on nonsingularity of unknown control coefficient matrices has been eliminated. The constructed adaptive neural control has been rigorously proved that it can guarantee the semiglobally uniformly ultimate boundedness of all signals in the closed-loop system. Finally, the simulation studies on a 2-DOF robotic manipulator system indicate that the designed adaptive control is effective.
INTESTINAL OBSTRUCTION

PubMed Central

Whipple, G. H.; Stone, H. B.; Bernheim, B. M.

1913-01-01

Closed duodenal loops may be made in dogs by ligatures placed just below the pancreatic duct and just beyond the duodenojejunal junction, together with a posterior gastro-enterostomy. These closed duodenal loop dogs die with symptoms like those of patients suffering from volvulus or high intestinal obstruction. This duodenal loop may simulate closely a volvulus in which there has been no vascular disturbance. Dogs with closed duodenal loops which have been washed out carefully survive a little longer on the average than animals with unwashed loops. The duration of life in the first instance is one to three days, with an average of about forty-eight hours. The dogs usually lose considerable fluid by vomiting and diarrhea. A weak pulse, low blood pressure and temperature are usually conspicuous in the last stages. Autopsy shows more or less splanchnic congestion which may be most marked in the mucosa of the upper small intestine. The peritoneum is usually clear and the closed loop may be distended with thin fluid, or collapsed, and contain only a small amount of pasty brown material. The mucosa of the loop may show ulceration and even perforation, but in the majority of cases it is intact and exhibits only a moderate congestion. Simple intestinal obstruction added to a closed duodenal loop does not modify the result in any manner, but it may hasten the fatal outcome. The liver plays no essential role as a protective agent against this poison, for a dog with an Eck fistula may live three days with a closed loop. A normal dog reacts to intraportal injection and to intravenous injection of the toxic substance in an identical manner. Drainage of this loop under certain conditions may not interfere with the general health over a period of weeks or months. Excision of the part of the duodenum included in this loop causes no disturbance. The material from the closed duodenal loops contains no bile, pancreatic juice, gastric juice, or split products from the food. It can be formed in no other way than by the activity of the intestinal mucosa and the growth of the intestinal bacteria. This material after dilution, autolysis, sterilization, and filtration produces a characteristic effect when introduced intravenously. When in toxic doses it causes a profound drop in blood pressure, general collapse, drop in temperature, salivation, vomiting, and profuse diarrhea, which is often blood-stained. Splanchnic congestion is the conspicuous feature at autopsy and shows especially in the villi of the duodenal and jejunal mucosæ. Adrenalin, during this period of low blood pressure and splanchnic congestion, will cause the usual reaction when given intravenously, but applied locally or given intravenously it causes no bleaching of the engorged intestinal mucosa. Secretin is not found in the duodenal loop fluid, and the loop material does not influence the pancreatic secretion. Intraportal injection of the toxic material gives a reaction similar to intravenous injection. Intraperitoneal and subcutaneous injections produce a relatively slow reaction which closely resembles the picture seen in the closed duodenal loop dog. In both cases there is a relatively slow absorption, but the splanchnic congestion and other findings, though less intense, are present in both groups. There seems, therefore, to be no escape from the conclusion that a poisonous substance is formed in this closed duodenal loop which is absorbed from it and causes intoxication and death. Injection of this toxic substance into a normal dog gives intoxication and a reaction more intense but similar to that developing in a closed-loop dog. PMID:19867644
A linear quadratic Gaussian with loop transfer recovery proximity operations autopilot for spacecraft. M.S. Thesis - MIT

NASA Technical Reports Server (NTRS)

Chen, George T.

1987-01-01

An automatic control scheme for spacecraft proximity operations is presented. The controller is capable of holding the vehicle at a prescribed location relative to a target, or maneuvering it to a different relative position using straight line-of-sight translations. The autopilot uses a feedforward loop to initiate and terminate maneuvers, and for operations at nonequilibrium set-points. A multivariate feedback loop facilitates precise position and velocity control in the presence of sensor noise. The feedback loop is formulated using the Linear Quadratic Gaussian (LQG) with Loop Transfer Recovery (LTR) design procedure. Linear models of spacecraft dynamics, adapted from Clohessey-Wiltshire Equations, are augmented and loop shaping techniques are applied to design a target feedback loop. The loop transfer recovery procedure is used to recover the frequency domain properties of the target feedback loop. The resulting compensator is integrated into an autopilot which is tested in a high fidelity Space Shuttle Simulator. The autopilot performance is evaluated for a variety of proximity operations tasks envisioned for future Shuttle flights.
78 FR 58535 - Hydropower Regulatory Efficiency Act of 2013; Supplemental Notice of Workshop

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-24

... license for hydropower development at non-powered dams and closed-loop pumped storage projects in... for licensing hydropower development at non-powered dams and closed-loop pumped storage projects... closed- loop pumped storage) affect the steps included in a two-year process? 3.9 Should there be a...
Integrated flight/propulsion control system design based on a centralized approach

NASA Technical Reports Server (NTRS)

Garg, Sanjay; Mattern, Duane L.; Bullard, Randy E.

1989-01-01

An integrated flight/propulsion control system design is presented for the piloted longitudinal landing task with a modern, statically unstable, fighter aircraft. A centralized compensator based on the Linear Quadratic Gaussian/Loop Transfer Recovery methodology is first obtained to satisfy the feedback loop performance and robustness specificiations. This high-order centralized compensator is then partitioned into airframe and engine sub-controllers based on modal controllability/observability for the compensator modes. The order of the sub-controllers is then reduced using internally-balanced realization techniques and the sub-controllers are simplified by neglecting the insignificant feedbacks. These sub-controllers have the advantage that they can be implemented as separate controllers on the airframe and the engine while still retaining the important performance and stability characteristics of the full-order centralized compensator. Command prefilters are then designed for the closed-loop system with the simplified sub-controllers to obtain the desired system response to airframe and engine command inputs, and the overall system performance evaluation results are presented.
The Effects of Closed-Loop Medical Devices on the Autonomy and Accountability of Persons and Systems.

PubMed

Kellmeyer, Philipp; Cochrane, Thomas; Müller, Oliver; Mitchell, Christine; Ball, Tonio; Fins, Joseph J; Biller-Andorno, Nikola

2016-10-01

Closed-loop medical devices such as brain-computer interfaces are an emerging and rapidly advancing neurotechnology. The target patients for brain-computer interfaces (BCIs) are often severely paralyzed, and thus particularly vulnerable in terms of personal autonomy, decisionmaking capacity, and agency. Here we analyze the effects of closed-loop medical devices on the autonomy and accountability of both persons (as patients or research participants) and neurotechnological closed-loop medical systems. We show that although BCIs can strengthen patient autonomy by preserving or restoring communicative abilities and/or motor control, closed-loop devices may also create challenges for moral and legal accountability. We advocate the development of a comprehensive ethical and legal framework to address the challenges of emerging closed-loop neurotechnologies like BCIs and stress the centrality of informed consent and refusal as a means to foster accountability. We propose the creation of an international neuroethics task force with members from medical neuroscience, neuroengineering, computer science, medical law, and medical ethics, as well as representatives of patient advocacy groups and the public.
75 FR 16576 - Credit for Renewable Electricity Production, Refined Coal Production, and Indian Coal Production...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-01

..., open-loop biomass, geothermal energy, solar energy, small irrigation power, municipal solid waste... electricity produced from closed-loop biomass, open-loop biomass, geothermal energy, solar energy, small... electricity produced from the qualified energy resources of wind, closed-loop biomass, geothermal energy, and...
77 FR 21835 - Credit for Renewable Electricity Production, Refined Coal Production, and Indian Coal Production...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-11

..., open-loop biomass, geothermal energy, solar energy, small irrigation power, municipal solid waste... electricity produced from closed-loop biomass, open-loop biomass, geothermal energy, solar energy, small... electricity produced from the qualified energy resources of wind, closed-loop biomass, geothermal energy, and...
76 FR 21947 - Credit for Renewable Electricity Production, Refined Coal Production, and Indian Coal Production...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-19

..., open-loop biomass, geothermal energy, solar energy, small irrigation power, municipal solid waste... electricity produced from closed-loop biomass, open-loop biomass, geothermal energy, solar energy, small... electricity produced from the qualified energy resources of wind, closed-loop biomass, geothermal energy, and...
Dynamic optimization of ISR sensors using a risk-based reward function applied to ground and space surveillance scenarios

NASA Astrophysics Data System (ADS)

DeSena, J. T.; Martin, S. R.; Clarke, J. C.; Dutrow, D. A.; Newman, A. J.

2012-06-01

As the number and diversity of sensing assets available for intelligence, surveillance and reconnaissance (ISR) operations continues to expand, the limited ability of human operators to effectively manage, control and exploit the ISR ensemble is exceeded, leading to reduced operational effectiveness. Automated support both in the processing of voluminous sensor data and sensor asset control can relieve the burden of human operators to support operation of larger ISR ensembles. In dynamic environments it is essential to react quickly to current information to avoid stale, sub-optimal plans. Our approach is to apply the principles of feedback control to ISR operations, "closing the loop" from the sensor collections through automated processing to ISR asset control. Previous work by the authors demonstrated non-myopic multiple platform trajectory control using a receding horizon controller in a closed feedback loop with a multiple hypothesis tracker applied to multi-target search and track simulation scenarios in the ground and space domains. This paper presents extensions in both size and scope of the previous work, demonstrating closed-loop control, involving both platform routing and sensor pointing, of a multisensor, multi-platform ISR ensemble tasked with providing situational awareness and performing search, track and classification of multiple moving ground targets in irregular warfare scenarios. The closed-loop ISR system is fullyrealized using distributed, asynchronous components that communicate over a network. The closed-loop ISR system has been exercised via a networked simulation test bed against a scenario in the Afghanistan theater implemented using high-fidelity terrain and imagery data. In addition, the system has been applied to space surveillance scenarios requiring tracking of space objects where current deliberative, manually intensive processes for managing sensor assets are insufficiently responsive. Simulation experiment results are presented. The algorithm to jointly optimize sensor schedules against search, track, and classify is based on recent work by Papageorgiou and Raykin on risk-based sensor management. It uses a risk-based objective function and attempts to minimize and balance the risks of misclassifying and losing track on an object. It supports the requirement to generate tasking for metric and feature data concurrently and synergistically, and account for both tracking accuracy and object characterization, jointly, in computing reward and cost for optimizing tasking decisions.
Adaptive control of large space structures using recursive lattice filters

NASA Technical Reports Server (NTRS)

Sundararajan, N.; Goglia, G. L.

1985-01-01

The use of recursive lattice filters for identification and adaptive control of large space structures is studied. Lattice filters were used to identify the structural dynamics model of the flexible structures. This identification model is then used for adaptive control. Before the identified model and control laws are integrated, the identified model is passed through a series of validation procedures and only when the model passes these validation procedures is control engaged. This type of validation scheme prevents instability when the overall loop is closed. Another important area of research, namely that of robust controller synthesis, was investigated using frequency domain multivariable controller synthesis methods. The method uses the Linear Quadratic Guassian/Loop Transfer Recovery (LQG/LTR) approach to ensure stability against unmodeled higher frequency modes and achieves the desired performance.
Method for Determination of Less Than 5 ppm Oxygen in Sodium Samples

NASA Technical Reports Server (NTRS)

Reid, R. S.; Martin, J. J.; Schmidt, G. L.

2005-01-01

Alkali metals used in pumped loops or heat pipes must be sufficiently free of nonmetallic impurities to ensure long heat rejection system life. Life issues are well established for alkali metal systems. Impurities can form ternary compounds between the container and working fluid, leading to corrosion. This Technical Memorandum discusses the consequences of impurities and candidate measurement techniques to determine whether impurities have been reduced to suf.ciently low levels within a single-phase liquid metal loop or a closed two-phase heat transfer system, such as a heat pipe. These techniques include the vanadium wire equilibration, neutron activation analysis, plug traps, distillation, and chemical analysis. Conceptual procedures for performing vanadium wire equilibration purity measurements on sodium contained in a heat pipe are discussed in detail.
Loop-bed combustion apparatus

DOEpatents

Shang, Jer-Yu; Mei, Joseph S.; Slagle, Frank D.; Notestein, John E.

1984-01-01

The present invention is directed to a combustion apparatus in the configuration of a oblong annulus defining a closed loop. Particulate coal together with a sulfur sorbent such as sulfur or dolomite is introduced into the closed loop, ignited, and propelled at a high rate of speed around the loop. Flue gas is withdrawn from a location in the closed loop in close proximity to an area in the loop where centrifugal force imposed upon the larger particulate material maintains these particulates at a location spaced from the flue gas outlet. Only flue gas and smaller particulates resulting from the combustion and innerparticle grinding are discharged from the combustor. This structural arrangement provides increased combustion efficiency due to the essentially complete combustion of the coal particulates as well as increased sulfur absorption due to the innerparticle grinding of the sorbent which provides greater particle surface area.
Reduced modeling of flexible structures for decentralized control

NASA Technical Reports Server (NTRS)

Yousuff, A.; Tan, T. M.; Bahar, L. Y.; Konstantinidis, M. F.

1986-01-01

Based upon the modified finite element-transfer matrix method, this paper presents a technique for reduced modeling of flexible structures for decentralized control. The modeling decisions are carried out at (finite-) element level, and are dictated by control objectives. A simply supported beam with two sets of actuators and sensors (linear force actuator and linear position and velocity sensors) is considered for illustration. In this case, it is conjectured that the decentrally controlled closed loop system is guaranteed to be at least marginally stable.
Preliminary demonstration of a robust controller design method

NASA Technical Reports Server (NTRS)

Anderson, L. R.

1980-01-01

Alternative computational procedures for obtaining a feedback control law which yields a control signal based on measurable quantitites are evaluated. The three methods evaluated are: (1) the standard linear quadratic regulator design model; (2) minimization of the norm of the feedback matrix, k via nonlinear programming subject to the constraint that the closed loop eigenvalues be in a specified domain in the complex plane; and (3) maximize the angles between the closed loop eigenvectors in combination with minimizing the norm of K also via the constrained nonlinear programming. The third or robust design method was chosen to yield a closed loop system whose eigenvalues are insensitive to small changes in the A and B matrices. The relationship between orthogonality of closed loop eigenvectors and the sensitivity of closed loop eigenvalues is described. Computer programs are described.
Adaptive robust control of a class of non-affine variable-speed variable-pitch wind turbines with unmodeled dynamics.

PubMed

Bagheri, Pedram; Sun, Qiao

2016-07-01

In this paper, a novel synthesis of Nussbaum-type functions, and an adaptive radial-basis function neural network is proposed to design controllers for variable-speed, variable-pitch wind turbines. Dynamic equations of the wind turbine are highly nonlinear, uncertain, and affected by unknown disturbance sources. Furthermore, the dynamic equations are non-affine with respect to the pitch angle, which is a control input. To address these problems, a Nussbaum-type function, along with a dynamic control law are adopted to resolve the non-affine nature of the equations. Moreover, an adaptive radial-basis function neural network is designed to approximate non-parametric uncertainties. Further, the closed-loop system is made robust to unknown disturbance sources, where no prior knowledge of disturbance bound is assumed in advance. Finally, the Lyapunov stability analysis is conducted to show the stability of the entire closed-loop system. In order to verify analytical results, a simulation is presented and the results are compared to both a PI and an existing adaptive controllers. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.
Miniature Loop Heat Pipe with Multiple Evaporators for Thermal Control of Small Spacecraft

NASA Technical Reports Server (NTRS)

Ku, Jentung; Ottenstein, Laura; Douglas, Denya; Pauken, Michael; Birur, Gajanana

2005-01-01

This paper presents an advanced miniature heat transport system for thermal control of small spacecraft. The thermal system consists of a loop heat pipe (LHP) with multiple evaporators and multiple deployable radiators for heat transfer, and variable emittance coatings on the radiators for performance enhancement. Thermoelectric coolers are used to control the loop operating temperature. The thermal system combines the functions of variable conductance heat pipes, thermal switches, thermal diodes, and the state-of-the-art LHPs into a single integrated thermal system. It retains all the performance characteristics of state-of-the-art LHPs and offers additional advantages to enhance the functionality, performance, versatility, and reliability of the system. Steady state and transient analytical models have been developed, and scaling criteria have also been established. A breadboard unit has been built for functional testing in laboratory and thermal vacuum environments. Experimental results show excellent performance of the thermal system and correlate very well with theoretical predictions.
Functional structure and dynamics of the human nervous system

NASA Technical Reports Server (NTRS)

Lawrence, J. A.

1981-01-01

The status of an effort to define the directions needed to take in extending pilot models is reported. These models are needed to perform closed-loop (man-in-the-loop) feedback flight control system designs and to develop cockpit display requirements. The approach taken is to develop a hypothetical working model of the human nervous system by reviewing the current literature in neurology and psychology and to develop a computer model of this hypothetical working model.
Heat transfer in an evaporation-condensation system in simulated weightlessness conditions

NASA Astrophysics Data System (ADS)

Bologa, M. K.; Grosu, F. P.; Kozhevnikov, I. V.; Motorin, O. V.; Polikarpov, A. A.

2017-10-01

The process of heat transfer in an evaporation-condensation system (ECS) at circulation of dielectric liquid in a closed thermoelectrohydrodynamic (TEHD) loop consisting of an evaporator, a condenser and electrohydrodynamic (EHD) pump for pumping of heat carrier, is considered. Previously, the authors studied the dependence of heat transfer on the angle of rotation of TEHD loop in a vertical plane. The report contains the results of studies of heat transfer at electrohydrodynamic pumping of the heat carrier (8% solution of acetone in Freon 113) in the condenser area by means of EHD pump of “cone-cone” type. All elements of the ECS are arranged in a horizontal plane and the heat transfer from the heater to the condenser without EHD pumping is impossible. A pulsating heat carrier flow mode, depending on the heat input and the voltage applied to the pump, takes place at EHD pumping. As the input power is decreasing the frequency of the coolant pulsations as well as the departure diameter and number of vapour bubbles are also decreasing. At some critical heat input the pulsations disappear and the transition from turbulent mode to the laminar one takes place causing the decrease of the heat transfer coefficient. The increase of the pumping flow rate by raising the voltage applied to the EHD pump, results in a partial suppression of boiling. The maximum intensification of heat transfer is reached at pulsation frequency of 1.25 Hz. The maximum heat flow from the heater was 4.2·104 W/m2. Graphical representation and the physical interpretation of the results, which reflect the essence of the process, are given.

Automated hybrid closed-loop control with a proportional-integral-derivative based system in adolescents and adults with type 1 diabetes: individualizing settings for optimal performance.

PubMed

Ly, Trang T; Weinzimer, Stuart A; Maahs, David M; Sherr, Jennifer L; Roy, Anirban; Grosman, Benyamin; Cantwell, Martin; Kurtz, Natalie; Carria, Lori; Messer, Laurel; von Eyben, Rie; Buckingham, Bruce A

2017-08-01

Automated insulin delivery systems, utilizing a control algorithm to dose insulin based upon subcutaneous continuous glucose sensor values and insulin pump therapy, will soon be available for commercial use. The objective of this study was to determine the preliminary safety and efficacy of initialization parameters with the Medtronic hybrid closed-loop controller by comparing percentage of time in range, 70-180 mg/dL (3.9-10 mmol/L), mean glucose values, as well as percentage of time above and below target range between sensor-augmented pump therapy and hybrid closed-loop, in adults and adolescents with type 1 diabetes. We studied an initial cohort of 9 adults followed by a second cohort of 15 adolescents, using the Medtronic hybrid closed-loop system with the proportional-integral-derivative with insulin feed-back (PID-IFB) algorithm. Hybrid closed-loop was tested in supervised hotel-based studies over 4-5 days. The overall mean percentage of time in range (70-180 mg/dL, 3.9-10 mmol/L) during hybrid closed-loop was 71.8% in the adult cohort and 69.8% in the adolescent cohort. The overall percentage of time spent under 70 mg/dL (3.9 mmol/L) was 2.0% in the adult cohort and 2.5% in the adolescent cohort. Mean glucose values were 152 mg/dL (8.4 mmol/L) in the adult cohort and 153 mg/dL (8.5 mmol/L) in the adolescent cohort. Closed-loop control using the Medtronic hybrid closed-loop system enables adaptive, real-time basal rate modulation. Initializing hybrid closed-loop in clinical practice will involve individualizing initiation parameters to optimize overall glucose control. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
Beyond Poisson-Boltzmann: Fluctuation effects and correlation functions

NASA Astrophysics Data System (ADS)

Netz, R. R.; Orland, H.

2000-02-01

We formulate the exact non-linear field theory for a fluctuating counter-ion distribution in the presence of a fixed, arbitrary charge distribution. The Poisson-Boltzmann equation is obtained as the saddle-point of the field-theoretic action, and the effects of counter-ion fluctuations are included by a loop-wise expansion around this saddle point. The Poisson equation is obeyed at each order in this loop expansion. We explicitly give the expansion of the Gibbs potential up to two loops. We then apply our field-theoretic formalism to the case of a single impenetrable wall with counter ions only (in the absence of salt ions). We obtain the fluctuation corrections to the electrostatic potential and the counter-ion density to one-loop order without further approximations. The relative importance of fluctuation corrections is controlled by a single parameter, which is proportional to the cube of the counter-ion valency and to the surface charge density. The effective interactions and correlation functions between charged particles close to the charged wall are obtained on the one-loop level.
Closed-Loop Lifecycle Management of Service and Product in the Internet of Things: Semantic Framework for Knowledge Integration.

PubMed

Yoo, Min-Jung; Grozel, Clément; Kiritsis, Dimitris

2016-07-08

This paper describes our conceptual framework of closed-loop lifecycle information sharing for product-service in the Internet of Things (IoT). The framework is based on the ontology model of product-service and a type of IoT message standard, Open Messaging Interface (O-MI) and Open Data Format (O-DF), which ensures data communication. (1) BACKGROUND: Based on an existing product lifecycle management (PLM) methodology, we enhanced the ontology model for the purpose of integrating efficiently the product-service ontology model that was newly developed; (2) METHODS: The IoT message transfer layer is vertically integrated into a semantic knowledge framework inside which a Semantic Info-Node Agent (SINA) uses the message format as a common protocol of product-service lifecycle data transfer; (3) RESULTS: The product-service ontology model facilitates information retrieval and knowledge extraction during the product lifecycle, while making more information available for the sake of service business creation. The vertical integration of IoT message transfer, encompassing all semantic layers, helps achieve a more flexible and modular approach to knowledge sharing in an IoT environment; (4) Contribution: A semantic data annotation applied to IoT can contribute to enhancing collected data types, which entails a richer knowledge extraction. The ontology-based PLM model enables as well the horizontal integration of heterogeneous PLM data while breaking traditional vertical information silos; (5) CONCLUSION: The framework was applied to a fictive case study with an electric car service for the purpose of demonstration. For the purpose of demonstrating the feasibility of the approach, the semantic model is implemented in Sesame APIs, which play the role of an Internet-connected Resource Description Framework (RDF) database.
Closed-Loop Lifecycle Management of Service and Product in the Internet of Things: Semantic Framework for Knowledge Integration

PubMed Central

Yoo, Min-Jung; Grozel, Clément; Kiritsis, Dimitris

2016-01-01

This paper describes our conceptual framework of closed-loop lifecycle information sharing for product-service in the Internet of Things (IoT). The framework is based on the ontology model of product-service and a type of IoT message standard, Open Messaging Interface (O-MI) and Open Data Format (O-DF), which ensures data communication. (1) Background: Based on an existing product lifecycle management (PLM) methodology, we enhanced the ontology model for the purpose of integrating efficiently the product-service ontology model that was newly developed; (2) Methods: The IoT message transfer layer is vertically integrated into a semantic knowledge framework inside which a Semantic Info-Node Agent (SINA) uses the message format as a common protocol of product-service lifecycle data transfer; (3) Results: The product-service ontology model facilitates information retrieval and knowledge extraction during the product lifecycle, while making more information available for the sake of service business creation. The vertical integration of IoT message transfer, encompassing all semantic layers, helps achieve a more flexible and modular approach to knowledge sharing in an IoT environment; (4) Contribution: A semantic data annotation applied to IoT can contribute to enhancing collected data types, which entails a richer knowledge extraction. The ontology-based PLM model enables as well the horizontal integration of heterogeneous PLM data while breaking traditional vertical information silos; (5) Conclusion: The framework was applied to a fictive case study with an electric car service for the purpose of demonstration. For the purpose of demonstrating the feasibility of the approach, the semantic model is implemented in Sesame APIs, which play the role of an Internet-connected Resource Description Framework (RDF) database. PMID:27399717
Large signal-to-noise ratio quantification in MLE for ARARMAX models

NASA Astrophysics Data System (ADS)

Zou, Yiqun; Tang, Xiafei

2014-06-01

It has been shown that closed-loop linear system identification by indirect method can be generally transferred to open-loop ARARMAX (AutoRegressive AutoRegressive Moving Average with eXogenous input) estimation. For such models, the gradient-related optimisation with large enough signal-to-noise ratio (SNR) can avoid the potential local convergence in maximum likelihood estimation. To ease the application of this condition, the threshold SNR needs to be quantified. In this paper, we build the amplitude coefficient which is an equivalence to the SNR and prove the finiteness of the threshold amplitude coefficient within the stability region. The quantification of threshold is achieved by the minimisation of an elaborately designed multi-variable cost function which unifies all the restrictions on the amplitude coefficient. The corresponding algorithm based on two sets of physically realisable system input-output data details the minimisation and also points out how to use the gradient-related method to estimate ARARMAX parameters when local minimum is present as the SNR is small. Then, the algorithm is tested on a theoretical AutoRegressive Moving Average with eXogenous input model for the derivation of the threshold and a gas turbine engine real system for model identification, respectively. Finally, the graphical validation of threshold on a two-dimensional plot is discussed.
Closed-Loop Control of Complex Networks: A Trade-Off between Time and Energy

NASA Astrophysics Data System (ADS)

Sun, Yong-Zheng; Leng, Si-Yang; Lai, Ying-Cheng; Grebogi, Celso; Lin, Wei

2017-11-01

Controlling complex nonlinear networks is largely an unsolved problem at the present. Existing works focus either on open-loop control strategies and their energy consumptions or on closed-loop control schemes with an infinite-time duration. We articulate a finite-time, closed-loop controller with an eye toward the physical and mathematical underpinnings of the trade-off between the control time and energy as well as their dependence on the network parameters and structure. The closed-loop controller is tested on a large number of real systems including stem cell differentiation, food webs, random ecosystems, and spiking neuronal networks. Our results represent a step forward in developing a rigorous and general framework to control nonlinear dynamical networks with a complex topology.
GalaxyGPCRloop: Template-Based and Ab Initio Structure Sampling of the Extracellular Loops of G-Protein-Coupled Receptors.

PubMed

Won, Jonghun; Lee, Gyu Rie; Park, Hahnbeom; Seok, Chaok

2018-06-07

The second extracellular loops (ECL2s) of G-protein-coupled receptors (GPCRs) are often involved in GPCR functions, and their structures have important implications in drug discovery. However, structure prediction of ECL2 is difficult because of its long length and the structural diversity among different GPCRs. In this study, a new ECL2 conformational sampling method involving both template-based and ab initio sampling was developed. Inspired by the observation of similar ECL2 structures of closely related GPCRs, a template-based sampling method employing loop structure templates selected from the structure database was developed. A new metric for evaluating similarity of the target loop to templates was introduced for template selection. An ab initio loop sampling method was also developed to treat cases without highly similar templates. The ab initio method is based on the previously developed fragment assembly and loop closure method. A new sampling component that takes advantage of secondary structure prediction was added. In addition, a conserved disulfide bridge restraining ECL2 conformation was predicted and analytically incorporated into sampling, reducing the effective dimension of the conformational search space. The sampling method was combined with an existing energy function for comparison with previously reported loop structure prediction methods, and the benchmark test demonstrated outstanding performance.
Molecular principles underlying dual RNA specificity in the Drosophila SNF protein.

PubMed

Weber, Gert; DeKoster, Gregory T; Holton, Nicole; Hall, Kathleen B; Wahl, Markus C

2018-06-07

The first RNA recognition motif of the Drosophila SNF protein is an example of an RNA binding protein with multi-specificity. It binds different RNA hairpin loops in spliceosomal U1 or U2 small nuclear RNAs, and only in the latter case requires the auxiliary U2A' protein. Here we investigate its functions by crystal structures of SNF alone and bound to U1 stem-loop II, U2A' or U2 stem-loop IV and U2A', SNF dynamics from NMR spectroscopy, and structure-guided mutagenesis in binding studies. We find that different loop-closing base pairs and a nucleotide exchange at the tips of the loops contribute to differential SNF affinity for the RNAs. U2A' immobilizes SNF and RNA residues to restore U2 stem-loop IV binding affinity, while U1 stem-loop II binding does not require such adjustments. Our findings show how U2A' can modulate RNA specificity of SNF without changing SNF conformation or relying on direct RNA contacts.
Closing the Feedback Loop Is Not Enough: The Assessment Spiral

ERIC Educational Resources Information Center

Wehlburg, Catherine M.

2007-01-01

For quite some time, the call to close the feedback loop has been heard throughout higher education. Faculty and administrators have paid attention, and now they can more easily than ever point to the fact that at their institution, the feedback loop is almost always closed. As reviewers from accreditation teams visit campuses, they often hear…
78 FR 62322 - Hydropower Regulatory Efficiency Act of 2013; Notice of Rescheduled Two-Year Licensing Process...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-16

... at non-powered dams and closed-loop pumped storage projects in compliance with section 6 of the... process for licensing hydropower development at non-powered dams and closed-loop pumped storage projects...-powered dam versus closed- loop pumped storage) affect the steps included in a two-year process? 3.9...
Conceptualization and validation of an open-source closed-loop deep brain stimulation system in rat.

PubMed

Wu, Hemmings; Ghekiere, Hartwin; Beeckmans, Dorien; Tambuyzer, Tim; van Kuyck, Kris; Aerts, Jean-Marie; Nuttin, Bart

2015-04-21

Conventional deep brain stimulation (DBS) applies constant electrical stimulation to specific brain regions to treat neurological disorders. Closed-loop DBS with real-time feedback is gaining attention in recent years, after proved more effective than conventional DBS in terms of pathological symptom control clinically. Here we demonstrate the conceptualization and validation of a closed-loop DBS system using open-source hardware. We used hippocampal theta oscillations as system input, and electrical stimulation in the mesencephalic reticular formation (mRt) as controller output. It is well documented that hippocampal theta oscillations are highly related to locomotion, while electrical stimulation in the mRt induces freezing. We used an Arduino open-source microcontroller between input and output sources. This allowed us to use hippocampal local field potentials (LFPs) to steer electrical stimulation in the mRt. Our results showed that closed-loop DBS significantly suppressed locomotion compared to no stimulation, and required on average only 56% of the stimulation used in open-loop DBS to reach similar effects. The main advantages of open-source hardware include wide selection and availability, high customizability, and affordability. Our open-source closed-loop DBS system is effective, and warrants further research using open-source hardware for closed-loop neuromodulation.
Conceptualization and validation of an open-source closed-loop deep brain stimulation system in rat

PubMed Central

Wu, Hemmings; Ghekiere, Hartwin; Beeckmans, Dorien; Tambuyzer, Tim; van Kuyck, Kris; Aerts, Jean-Marie; Nuttin, Bart

2015-01-01

Conventional deep brain stimulation (DBS) applies constant electrical stimulation to specific brain regions to treat neurological disorders. Closed-loop DBS with real-time feedback is gaining attention in recent years, after proved more effective than conventional DBS in terms of pathological symptom control clinically. Here we demonstrate the conceptualization and validation of a closed-loop DBS system using open-source hardware. We used hippocampal theta oscillations as system input, and electrical stimulation in the mesencephalic reticular formation (mRt) as controller output. It is well documented that hippocampal theta oscillations are highly related to locomotion, while electrical stimulation in the mRt induces freezing. We used an Arduino open-source microcontroller between input and output sources. This allowed us to use hippocampal local field potentials (LFPs) to steer electrical stimulation in the mRt. Our results showed that closed-loop DBS significantly suppressed locomotion compared to no stimulation, and required on average only 56% of the stimulation used in open-loop DBS to reach similar effects. The main advantages of open-source hardware include wide selection and availability, high customizability, and affordability. Our open-source closed-loop DBS system is effective, and warrants further research using open-source hardware for closed-loop neuromodulation. PMID:25897892
Performance constraints and compensation for teleoperation with delay

NASA Technical Reports Server (NTRS)

Mclaughlin, J. S.; Staunton, B. D.

1989-01-01

A classical control perspective is used to characterize performance constraints and evaluate compensation techniques for teleoperation with delay. Use of control concepts such as open and closed loop performance, stability, and bandwidth yield insight to the delay problem. Teleoperator performance constraints are viewed as an open loop time delay lag and as a delay-induced closed loop bandwidth constraint. These constraints are illustrated with a simple analytical tracking example which is corroborated by a real time, 'man-in-the-loop' tracking experiment. The experiment also provides insight to those controller characteristics which are unique to a human operator. Predictive displays and feedforward commands are shown to provide open loop compensation for delay lag. Low pass filtering of telemetry or feedback signals is interpreted as closed loop compensation used to maintain a sufficiently low bandwidth for stability. A new closed loop compensation approach is proposed that uses a reactive (or force feedback) hand controller to restrict system bandwidth by impeding operator inputs.
Closing the loop of deep brain stimulation

PubMed Central

Carron, Romain; Chaillet, Antoine; Filipchuk, Anton; Pasillas-Lépine, William; Hammond, Constance

2013-01-01

High-frequency deep brain stimulation is used to treat a wide range of brain disorders, like Parkinson's disease. The stimulated networks usually share common electrophysiological signatures, including hyperactivity and/or dysrhythmia. From a clinical perspective, HFS is expected to alleviate clinical signs without generating adverse effects. Here, we consider whether the classical open-loop HFS fulfills these criteria and outline current experimental or theoretical research on the different types of closed-loop DBS that could provide better clinical outcomes. In the first part of the review, the two routes followed by HFS-evoked axonal spikes are explored. In one direction, orthodromic spikes functionally de-afferent the stimulated nucleus from its downstream target networks. In the opposite direction, antidromic spikes prevent this nucleus from being influenced by its afferent networks. As a result, the pathological synchronized activity no longer propagates from the cortical networks to the stimulated nucleus. The overall result can be described as a reversible functional de-afferentation of the stimulated nucleus from its upstream and downstream nuclei. In the second part of the review, the latest advances in closed-loop DBS are considered. Some of the proposed approaches are based on mathematical models, which emphasize different aspects of the parkinsonian basal ganglia: excessive synchronization, abnormal firing-rate rhythms, and a deficient thalamo-cortical relay. The stimulation strategies are classified depending on the control-theory techniques on which they are based: adaptive and on-demand stimulation schemes, delayed and multi-site approaches, stimulations based on proportional and/or derivative control actions, optimal control strategies. Some of these strategies have been validated experimentally, but there is still a large reservoir of theoretical work that may point to ways of improving practical treatment. PMID:24391555
Closing the loop of deep brain stimulation.

PubMed

Carron, Romain; Chaillet, Antoine; Filipchuk, Anton; Pasillas-Lépine, William; Hammond, Constance

2013-12-20

High-frequency deep brain stimulation is used to treat a wide range of brain disorders, like Parkinson's disease. The stimulated networks usually share common electrophysiological signatures, including hyperactivity and/or dysrhythmia. From a clinical perspective, HFS is expected to alleviate clinical signs without generating adverse effects. Here, we consider whether the classical open-loop HFS fulfills these criteria and outline current experimental or theoretical research on the different types of closed-loop DBS that could provide better clinical outcomes. In the first part of the review, the two routes followed by HFS-evoked axonal spikes are explored. In one direction, orthodromic spikes functionally de-afferent the stimulated nucleus from its downstream target networks. In the opposite direction, antidromic spikes prevent this nucleus from being influenced by its afferent networks. As a result, the pathological synchronized activity no longer propagates from the cortical networks to the stimulated nucleus. The overall result can be described as a reversible functional de-afferentation of the stimulated nucleus from its upstream and downstream nuclei. In the second part of the review, the latest advances in closed-loop DBS are considered. Some of the proposed approaches are based on mathematical models, which emphasize different aspects of the parkinsonian basal ganglia: excessive synchronization, abnormal firing-rate rhythms, and a deficient thalamo-cortical relay. The stimulation strategies are classified depending on the control-theory techniques on which they are based: adaptive and on-demand stimulation schemes, delayed and multi-site approaches, stimulations based on proportional and/or derivative control actions, optimal control strategies. Some of these strategies have been validated experimentally, but there is still a large reservoir of theoretical work that may point to ways of improving practical treatment.
Overnight closed-loop insulin delivery with model predictive control: assessment of hypoglycemia and hyperglycemia risk using simulation studies.

PubMed

Wilinska, Malgorzata E; Budiman, Erwin S; Taub, Marc B; Elleri, Daniela; Allen, Janet M; Acerini, Carlo L; Dunger, David B; Hovorka, Roman

2009-09-01

Hypoglycemia and hyperglycemia during closed-loop insulin delivery based on subcutaneous (SC) glucose sensing may arise due to (1) overdosing and underdosing of insulin by control algorithm and (2) difference between plasma glucose (PG) and sensor glucose, which may be transient (kinetics origin and sensor artifacts) or persistent (calibration error [CE]). Using in silico testing, we assessed hypoglycemia and hyperglycemia incidence during over-night closed loop. Additionally, a comparison was made against incidence observed experimentally during open-loop single-night in-clinic studies in young people with type 1 diabetes mellitus (T1DM) treated by continuous SC insulin infusion. Simulation environment comprising 18 virtual subjects with T1DM was used to simulate overnight closed-loop study with a model predictive control (MPC) algorithm. A 15 h experiment started at 17:00 and ended at 08:00 the next day. Closed loop commenced at 21:00 and continued for 11 h. At 18:00, protocol included meal (50 g carbohydrates) accompanied by prandial insulin. The MPC algorithm advised on insulin infusion every 15 min. Sensor glucose was obtained by combining model-calculated noise-free interstitial glucose with experimentally derived transient and persistent sensor artifacts associated with FreeStyle Navigator (FSN). Transient artifacts were obtained from FSN sensor pairs worn by 58 subjects with T1DM over 194 nighttime periods. Persistent difference due to FSN CE was quantified from 585 FSN sensor insertions, yielding 1421 calibration sessions from 248 subjects with diabetes. Episodes of severe (PG < or = 36 mg/dl) and significant (PG < or = 45 mg/dl) hypoglycemia and significant hyperglycemia (PG > or = 300 mg/dl) were extracted from 18,000 simulated closed-loop nights. Severe hypoglycemia was not observed when FSN CE was less than 45%. Hypoglycemia and hyperglycemia incidence during open loop was assessed from 21 overnight studies in 17 young subjects with T1DM (8 males; 13.5 +/- 3.6 years of age; body mass index 21.0 +/- 4.0 kg/m2; duration diabetes 6.4 +/- 4.1 years; hemoglobin A1c 8.5% +/- 1.8%; mean +/- standard deviation) participating in the Artificial Pancreas Project at Cambridge. Severe and significant hypoglycemia during simulated closed loop occurred 0.75 and 17.11 times per 100 person years compared to 1739 and 3479 times per 100 person years during experimental open loop, respectively. Significant hyperglycemia during closed loop and open loop occurred 75 and 15,654 times per 100 person years, respectively. The incidence of severe and significant hypoglycemia reduced 2300- and 200-fold, respectively, during stimulated overnight closed loop with MPC compared to that observed during open-loop overnight clinical studies in young subjects with T1DM. Hyperglycemia was 200 times less likely. Overnight closed loop with the FSN and the MPC algorithm is expected to reduce substantially the risk of hypoglycemia and hyperglycemia. 2009 Diabetes Technology Society.
Effects of backlash and dead band on temperature control of the primary loop of a conceptual nuclear Brayton space powerplant

NASA Technical Reports Server (NTRS)

Petrick, E. J.

1973-01-01

An analytical study was made of the stability of a closed-loop liquid-lithium temperature control of the primary loop of a conceptual nuclear Brayton space powerplant. The operating point was varied from 20 to 120 percent of design. A describing-function technique was used to evaluate the effects of temperature dead band and control coupling backlash. From the system investigation, it was predicted that a limit cycle will not exist with a temperature dead band, but a limit cycle will not exist when backlash is present. The results compare favorably with a digital computer simulation.
Closed loop oscillating heat pipe as heating device for copper plate

NASA Astrophysics Data System (ADS)

Kamonpet, Patrapon; Sangpen, Waranphop

2017-04-01

In manufacturing parts by molding method, temperature uniformity of the mold holds a very crucial aspect for the quality of the parts. Studies have been carried out in searching for effective method in controlling the mold temperature. Using of heat pipe is one of the many effective ways to control the temperature of the molding area to the right uniform level. Recently, there has been the development of oscillating heat pipe and its application is very promising. The semi-empirical correlation for closed-loop oscillating heat pipe (CLOHP) with the STD of ±30% was used in design of CLOHP in this study. By placing CLOHP in the copper plate at some distance from the plate surface and allow CLOHP to heat the plate up to the set surface temperature, the temperature of the plate was recorded. It is found that CLOHP can be effectively used as a heat source to transfer heat to copper plate with excellent temperature distribution. The STDs of heat rate of all experiments are well in the range of ±30% of the correlation used.
Orbital Disturbance Analysis due to the Lunar Gravitational Potential and Deviation Minimization through the Trajectory Control in Closed Loop

NASA Astrophysics Data System (ADS)

Gonçalves, L. D.; Rocco, E. M.; de Moraes, R. V.

2013-10-01

A study evaluating the influence due to the lunar gravitational potential, modeled by spherical harmonics, on the gravity acceleration is accomplished according to the model presented in Konopliv (2001). This model provides the components x, y and z for the gravity acceleration at each moment of time along the artificial satellite orbit and it enables to consider the spherical harmonic degree and order up to100. Through a comparison between the gravity acceleration from a central field and the gravity acceleration provided by Konopliv's model, it is obtained the disturbing velocity increment applied to the vehicle. Then, through the inverse problem, the Keplerian elements of perturbed orbit of the satellite are calculated allowing the orbital motion analysis. Transfer maneuvers and orbital correction of lunar satellites are simulated considering the disturbance due to non-uniform gravitational potential of the Moon, utilizing continuous thrust and trajectory control in closed loop. The simulations are performed using the Spacecraft Trajectory Simulator-STRS, Rocco (2008), which evaluate the behavior of the orbital elements, fuel consumption and thrust applied to the satellite over the time.
Fundamental Physics and Practical Applications of Electromagnetic Local Flow Control in High Speed Flows (Rutgers)

DTIC Science & Technology

2010-02-16

field. Techniques utilizing this design use an open- loop control and no flow monitoring sensors are required. Conversely, reactive (or closed - loop ...and closed (dashed line) configuration. 38 closed configuration described above, the ambiguity in the critical limits of the transition...flow; a new vortex is then shed from the cavity leading edge, closing the feedback loop .[31] Open cavities with an L/D approximately greater than

Intraoperative stroke volume optimization using stroke volume, arterial pressure, and heart rate: closed-loop (learning intravenous resuscitator) versus anesthesiologists.

PubMed

Rinehart, Joseph; Chung, Elena; Canales, Cecilia; Cannesson, Maxime

2012-10-01

The authors compared the performance of a group of anesthesia providers to closed-loop (Learning Intravenous Resuscitator [LIR]) management in a simulated hemorrhage scenario using cardiac output monitoring. A prospective cohort study. In silico simulation. University hospital anesthesiologists and the LIR closed-loop fluid administration system. Using a patient simulator, a 90-minute simulated hemorrhage protocol was run, which included a 1,200-mL blood loss over 30 minutes. Twenty practicing anesthesiology providers were asked to manage this scenario by providing fluids and vasopressor medication at their discretion. The simulation program was also run 20 times with the LIR closed-loop algorithm managing fluids and an additional 20 times with no intervention. Simulated patient weight, height, heart rate, mean arterial pressure, and cardiac output (CO) were similar at baseline. The mean stroke volume, the mean arterial pressure, CO, and the final CO were higher in the closed-loop group than in the practitioners group, and the coefficient of variance was lower. The closed-loop group received slightly more fluid (2.1 v 1.9 L, p < 0.05) than the anesthesiologist group. Despite the roughly similar volumes of fluid given, the closed-loop maintained more stable hemodynamics than the practitioners primarily because the fluid was given earlier in the protocol and CO optimized before the hemorrhage began, whereas practitioners tended to resuscitate well but only after significant hemodynamic change indicated the need. Overall, these data support the potential usefulness of this closed-loop algorithm in clinical settings in which dynamic predictors are not available or applicable. Published by Elsevier Inc.
Assessing performance of closed-loop insulin delivery systems by continuous glucose monitoring: drawbacks and way forward.

PubMed

Hovorka, Roman; Nodale, Marianna; Haidar, Ahmad; Wilinska, Malgorzata E

2013-01-01

We investigated whether continuous glucose monitoring (CGM) levels can accurately assess glycemic control while directing closed-loop insulin delivery. Data were analyzed retrospectively from 33 subjects with type 1 diabetes who underwent closed-loop and conventional pump therapy on two separate nights. Glycemic control was evaluated by reference plasma glucose and contrasted against three methods based on Navigator (Abbott Diabetes Care, Alameda, CA) CGM levels. Glucose mean and variability were estimated by unmodified CGM levels with acceptable clinical accuracy. Time when glucose was in target range was overestimated by CGM during closed-loop nights (CGM vs. plasma glucose median [interquartile range], 86% [65-97%] vs. 75% [59-91%]; P=0.04) but not during conventional pump therapy (57% [32-72%] vs. 51% [29-68%]; P=0.82) providing comparable treatment effect (mean [SD], 28% [29%] vs. 23% [21%]; P=0.11). Using the CGM measurement error of 15% derived from plasma glucose-CGM pairs (n=4,254), stochastic interpretation of CGM gave unbiased estimate of time in target during both closed-loop (79% [62-86%] vs. 75% [59-91%]; P=0.24) and conventional pump therapy (54% [33-66%] vs. 51% [29-68%]; P=0.44). Treatment effect (23% [24%] vs. 23% [21%]; P=0.96) and time below target were accurately estimated by stochastic CGM. Recalibrating CGM using reference plasma glucose values taken at the start and end of overnight closed-loop was not superior to stochastic CGM. CGM is acceptable to estimate glucose mean and variability, but without adjustment it may overestimate benefit of closed-loop. Stochastic CGM provided unbiased estimate of time when glucose is in target and below target and may be acceptable for assessment of closed-loop in the outpatient setting.
Comparison of cardiac output optimization with an automated closed-loop goal-directed fluid therapy versus non standardized manual fluid administration during elective abdominal surgery: first prospective randomized controlled trial.

PubMed

Lilot, Marc; Bellon, Amandine; Gueugnon, Marine; Laplace, Marie-Christine; Baffeleuf, Bruno; Hacquard, Pauline; Barthomeuf, Felicie; Parent, Camille; Tran, Thomas; Soubirou, Jean-Luc; Robinson, Philip; Bouvet, Lionel; Vassal, Olivia; Lehot, Jean-Jacques; Piriou, Vincent

2018-01-27

An intraoperative automated closed-loop system for goal-directed fluid therapy has been successfully tested in silico, in vivo and in a clinical case-control matching. This trial compared intraoperative cardiac output (CO) in patients managed with this closed-loop system versus usual practice in an academic medical center. The closed-loop system was connected to a CO monitoring system and delivered automated colloid fluid boluses. Moderate to high-risk abdominal surgical patients were randomized either to the closed-loop or the manual group. Intraoperative final CO was the primary endpoint. Secondary endpoints were intraoperative overall mean cardiac index (CI), increase from initial to final CI, intraoperative fluid volume and postoperative outcomes. From January 2014 to November 2015, 46 patients were randomized. There was a lower initial CI (2.06 vs. 2.51 l min -1 m -2 , p = 0.042) in the closed-loop compared to the control group. No difference in final CO and in overall mean intraoperative CI was observed between groups. A significant relative increase from initial to final CI values was observed in the closed-loop but not the control group (+ 28.6%, p = 0.006 vs. + 1.2%, p = 0.843). No difference was found for intraoperative fluid management and postoperative outcomes between groups. There was no significant impact on the primary study endpoint, but this was found in a context of unexpected lower initial CI in the closed-loop group.Trial registry number ID-RCB/EudraCT: 2013-A00770-45. ClinicalTrials.gov Identifier NCT01950845, date of registration: 17 September 2013.
Dynamic simulation of perturbation responses in a closed-loop virtual arm model.

PubMed

Du, Yu-Fan; He, Xin; Lan, Ning

2010-01-01

A closed-loop virtual arm (VA) model has been developed in SIMULINK environment by adding spinal reflex circuits and propriospinal neural networks to the open-loop VA model developed in early study [1]. An improved virtual muscle model (VM4.0) is used to speed up simulation and to generate more precise recruitment of muscle force at low levels of muscle activation. Time delays in the reflex loops are determined by their synaptic connections and afferent transmission back to the spinal cord. Reflex gains are properly selected so that closed-loop responses are stable. With the closed-loop VA model, we are developing an approach to evaluate system behaviors by dynamic simulation of perturbation responses. Joint stiffness is calculated based on simulated perturbation responses by a least-squares algorithm in MATLAB. This method of dynamic simulation will be essential for further evaluation of feedforward and reflex control of arm movement and position.
Perception as a closed-loop convergence process.

PubMed

Ahissar, Ehud; Assa, Eldad

2016-05-09

Perception of external objects involves sensory acquisition via the relevant sensory organs. A widely-accepted assumption is that the sensory organ is the first station in a serial chain of processing circuits leading to an internal circuit in which a percept emerges. This open-loop scheme, in which the interaction between the sensory organ and the environment is not affected by its concurrent downstream neuronal processing, is strongly challenged by behavioral and anatomical data. We present here a hypothesis in which the perception of external objects is a closed-loop dynamical process encompassing loops that integrate the organism and its environment and converging towards organism-environment steady-states. We discuss the consistency of closed-loop perception (CLP) with empirical data and show that it can be synthesized in a robotic setup. Testable predictions are proposed for empirical distinction between open and closed loop schemes of perception.
Perception as a closed-loop convergence process

PubMed Central

Ahissar, Ehud; Assa, Eldad

2016-01-01

Perception of external objects involves sensory acquisition via the relevant sensory organs. A widely-accepted assumption is that the sensory organ is the first station in a serial chain of processing circuits leading to an internal circuit in which a percept emerges. This open-loop scheme, in which the interaction between the sensory organ and the environment is not affected by its concurrent downstream neuronal processing, is strongly challenged by behavioral and anatomical data. We present here a hypothesis in which the perception of external objects is a closed-loop dynamical process encompassing loops that integrate the organism and its environment and converging towards organism-environment steady-states. We discuss the consistency of closed-loop perception (CLP) with empirical data and show that it can be synthesized in a robotic setup. Testable predictions are proposed for empirical distinction between open and closed loop schemes of perception. DOI: http://dx.doi.org/10.7554/eLife.12830.001 PMID:27159238
Competition and quality in health care markets: a differential-game approach.

PubMed

Brekke, Kurt R; Cellini, Roberto; Siciliani, Luigi; Straume, Odd Rune

2010-07-01

We investigate the effect of competition on quality in health care markets with regulated prices taking a differential game approach, in which quality is a stock variable. Using a Hotelling framework, we derive the open-loop solution (health care providers set the optimal investment plan at the initial period) and the feedback closed-loop solution (providers move investments in response to the dynamics of the states). Under the closed-loop solution competition is more intense in the sense that providers observe quality in each period and base their investment on this information. If the marginal provision cost is constant, the open-loop and closed-loop solutions coincide, and the results are similar to the ones obtained by static models. If the marginal provision cost is increasing, investment and quality are lower in the closed-loop solution (when competition is more intense). In this case, static models tend to exaggerate the positive effect of competition on quality.
Monitoring and control of atmosphere in a closed environment

NASA Technical Reports Server (NTRS)

Humphries, R.; Perry, J.

1991-01-01

Applications requiring new technologies for atmosphere monitoring and control in the closed environment and their principal functions aboard the Space Station Freedom are described. Oxygen loop closure, involving the conversion of carbon dioxide to oxygen; carbon dioxide reduction and removal; and monitoring of atmospheric contamination are discussed. The Trace Contaminant Monitor, the Major Constituent Analyzer, the Carbon Dioxide Monitor, and the Particulate Counter Monitor are discussed.
Probing the closed-loop model of mRNA translation in living cells

PubMed Central

Archer, Stuart K; Shirokikh, Nikolay E; Hallwirth, Claus V; Beilharz, Traude H; Preiss, Thomas

2015-01-01

The mRNA closed-loop, formed through interactions between the cap structure, poly(A) tail, eIF4E, eIF4G and PAB, features centrally in models of eukaryotic translation initiation, although direct support for its existence in vivo is not well established. Here, we investigated the closed-loop using a combination of mRNP isolation from rapidly cross-linked cells and high-throughput qPCR. Using the interaction between these factors and the opposing ends of mRNAs as a proxy for the closed-loop, we provide evidence that it is prevalent for eIF4E/4G-bound but unexpectedly sparse for PAB1-bound mRNAs, suggesting it primarily occurs during a distinct phase of polysome assembly. We observed mRNA-specific variation in the extent of closed-loop formation, consistent with a role for polysome topology in the control of gene expression. PMID:25826658
Aerodynamic Indicial Functions and Their Use in Aeroelastic Formulation of Lifting Surfaces

NASA Technical Reports Server (NTRS)

Marzocca, Piergiovanni; Librescu, Liviu; Silva, Walter A.

2000-01-01

An investigation related to the use of linear indicial functions in the time and frequency domains, enabling one to derive the proper aerodynamic loads as to study the subcritical response and flutter of swept lifting surfaces, respectively, of the open/closed loop aeroelastic system is presented. The expressions of the lift and aerodynamic moment in the frequency domain are given in terms of the Theodorsen's function, while, in the time domain, these are obtained directly with the help of the Wagner's function. Closed form solutions of aerodynamic derivatives are obtained, graphical representations are supplied and conclusions and prospects for further developments are outlined.
A dihydropyridine receptor alpha1s loop region critical for skeletal muscle contraction is intrinsically unstructured and binds to a SPRY domain of the type 1 ryanodine receptor.

PubMed

Cui, Yanfang; Tae, Han-Shen; Norris, Nicole C; Karunasekara, Yamuna; Pouliquin, Pierre; Board, Philip G; Dulhunty, Angela F; Casarotto, Marco G

2009-03-01

The II-III loop of the dihydropyridine receptor (DHPR) alpha(1s) subunit is a modulator of the ryanodine receptor (RyR1) Ca(2+) release channel in vitro and is essential for skeletal muscle contraction in vivo. Despite its importance, the structure of this loop has not been reported. We have investigated its structure using a suite of NMR techniques which revealed that the DHPR II-III loop is an intrinsically unstructured protein (IUP) and as such belongs to a burgeoning structural class of functionally important proteins. The loop does not possess a stable tertiary fold: it is highly flexible, with a strong N-terminal helix followed by nascent helical/turn elements and unstructured segments. Its residual structure is loosely globular with the N and C termini in close proximity. The unstructured nature of the II-III loop may allow it to easily modify its interaction with RyR1 following a surface action potential and thus initiate rapid Ca(2+) release and contraction. The in vitro binding partner for the II-III was investigated. The II-III loop interacts with the second of three structurally distinct SPRY domains in RyR1, whose function is unknown. This interaction occurs through two preformed N-terminal alpha-helical regions and a C-terminal hydrophobic element. The A peptide corresponding to the helical N-terminal region is a common probe of RyR function and binds to the same SPRY domain as the full II-III loop. Thus the second SPRY domain is an in vitro binding site for the II-III loop. The possible in vivo role of this region is discussed.
Behavioural system identification of visual flight speed control in Drosophila melanogaster

PubMed Central

Rohrseitz, Nicola; Fry, Steven N.

2011-01-01

Behavioural control in many animals involves complex mechanisms with intricate sensory-motor feedback loops. Modelling allows functional aspects to be captured without relying on a description of the underlying complex, and often unknown, mechanisms. A wide range of engineering techniques are available for modelling, but their ability to describe time-continuous processes is rarely exploited to describe sensory-motor control mechanisms in biological systems. We performed a system identification of visual flight speed control in the fruitfly Drosophila, based on an extensive dataset of open-loop responses previously measured under free flight conditions. We identified a second-order under-damped control model with just six free parameters that well describes both the transient and steady-state characteristics of the open-loop data. We then used the identified control model to predict flight speed responses after a visual perturbation under closed-loop conditions and validated the model with behavioural measurements performed in free-flying flies under the same closed-loop conditions. Our system identification of the fruitfly's flight speed response uncovers the high-level control strategy of a fundamental flight control reflex without depending on assumptions about the underlying physiological mechanisms. The results are relevant for future investigations of the underlying neuromotor processing mechanisms, as well as for the design of biomimetic robots, such as micro-air vehicles. PMID:20525744
Behavioural system identification of visual flight speed control in Drosophila melanogaster.

PubMed

Rohrseitz, Nicola; Fry, Steven N

2011-02-06

Behavioural control in many animals involves complex mechanisms with intricate sensory-motor feedback loops. Modelling allows functional aspects to be captured without relying on a description of the underlying complex, and often unknown, mechanisms. A wide range of engineering techniques are available for modelling, but their ability to describe time-continuous processes is rarely exploited to describe sensory-motor control mechanisms in biological systems. We performed a system identification of visual flight speed control in the fruitfly Drosophila, based on an extensive dataset of open-loop responses previously measured under free flight conditions. We identified a second-order under-damped control model with just six free parameters that well describes both the transient and steady-state characteristics of the open-loop data. We then used the identified control model to predict flight speed responses after a visual perturbation under closed-loop conditions and validated the model with behavioural measurements performed in free-flying flies under the same closed-loop conditions. Our system identification of the fruitfly's flight speed response uncovers the high-level control strategy of a fundamental flight control reflex without depending on assumptions about the underlying physiological mechanisms. The results are relevant for future investigations of the underlying neuromotor processing mechanisms, as well as for the design of biomimetic robots, such as micro-air vehicles.
Closed-Loop HIRF Experiments Performed on a Fault Tolerant Flight Control Computer

NASA Technical Reports Server (NTRS)

Belcastro, Celeste M.

1997-01-01

ABSTRACT Closed-loop HIRF experiments were performed on a fault tolerant flight control computer (FCC) at the NASA Langley Research Center. The FCC used in the experiments was a quad-redundant flight control computer executing B737 Autoland control laws. The FCC was placed in one of the mode-stirred reverberation chambers in the HIRF Laboratory and interfaced to a computer simulation of the B737 flight dynamics, engines, sensors, actuators, and atmosphere in the Closed-Loop Systems Laboratory. Disturbances to the aircraft associated with wind gusts and turbulence were simulated during tests. Electrical isolation between the FCC under test and the simulation computer was achieved via a fiber optic interface for the analog and discrete signals. Closed-loop operation of the FCC enabled flight dynamics and atmospheric disturbances affecting the aircraft to be represented during tests. Upset was induced in the FCC as a result of exposure to HIRF, and the effect of upset on the simulated flight of the aircraft was observed and recorded. This paper presents a description of these closed- loop HIRF experiments, upset data obtained from the FCC during these experiments, and closed-loop effects on the simulated flight of the aircraft.
Method for determining how to operate and control wind turbine arrays in utility systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Javid, S.H.; Hauth, R.L.; Younkins, T.D.

1984-01-01

A method for determining how utility wind turbine arrays should be controlled and operated on the load frequency control time-scale is presented. Initial considerations for setting wind turbine control requirements are followed by a description of open loop operation and of closed loop and feed forward wind turbine array control concepts. The impact of variations in array output on meeting minimum criteria are developed. The method for determining the required control functions is then presented and results are tabulated. (LEW)
An Energy-Based Thermodynamic Stabilization Framework for Hybrid Control Design of Large-Scale Aerospace Systems

DTIC Science & Technology

2009-02-27

exchanged by means of line-of-sight sensors that experience periodic communication dropouts due to agent motion. Variation in network topology in...respiratory, and cardiovascular function by man- ual control based on the clinician’s experience and intuition. Open-loop control by clinical personnel can be...to ap- pear. [29] W. M. Haddad and J. M. Bailey, "Closed-Loop Control for Intensive Care Unit Seda- tion," Best Prac. Res. Clinical Anaesthesiology
A general transfer-function approach to noise filtering in open-loop quantum control

NASA Astrophysics Data System (ADS)

Viola, Lorenza

2015-03-01

Hamiltonian engineering via unitary open-loop quantum control provides a versatile and experimentally validated framework for manipulating a broad class of non-Markovian open quantum systems of interest, with applications ranging from dynamical decoupling and dynamically corrected quantum gates, to noise spectroscopy and quantum simulation. In this context, transfer-function techniques directly motivated by control engineering have proved invaluable for obtaining a transparent picture of the controlled dynamics in the frequency domain and for quantitatively analyzing performance. In this talk, I will show how to identify a computationally tractable set of ``fundamental filter functions,'' out of which arbitrary filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental set suffices to characterize the error suppression capabilities of the control protocol in both the time and frequency domain. I will show, in particular, how the resulting notion of ``filtering order'' reveals conceptually distinct, albeit complementary, features of the controlled dynamics as compared to the ``cancellation order,'' traditionally defined in the Magnus sense. Implications for current quantum control experiments will be discussed. Work supported by the U.S. Army Research Office under Contract No. W911NF-14-1-0682.
Structural and mechanistic insights into phospholipid transfer by Ups1-Mdm35 in mitochondria

NASA Astrophysics Data System (ADS)

Watanabe, Yasunori; Tamura, Yasushi; Kawano, Shin; Endo, Toshiya

2015-08-01

Eukaryotic cells are compartmentalized into membrane-bounded organelles whose functions rely on lipid trafficking to achieve membrane-specific compositions of lipids. Here we focused on the Ups1-Mdm35 system, which mediates phosphatidic acid (PA) transfer between the outer and inner mitochondrial membranes, and determined the X-ray structures of Mdm35 and Ups1-Mdm35 with and without PA. The Ups1-Mdm35 complex constitutes a single domain that has a deep pocket and flexible Ω-loop lid. Structure-based mutational analyses revealed that a basic residue at the pocket bottom and the Ω-loop lid are important for PA extraction from the membrane following Ups1 binding. Ups1 binding to the membrane is enhanced by the dissociation of Mdm35. We also show that basic residues around the pocket entrance are important for Ups1 binding to the membrane and PA extraction. These results provide a structural basis for understanding the mechanism of PA transfer between mitochondrial membranes.
A Comparison of Multivariable Control Design Techniques for a Turbofan Engine Control

NASA Technical Reports Server (NTRS)

Garg, Sanjay; Watts, Stephen R.

1995-01-01

This paper compares two previously published design procedures for two different multivariable control design techniques for application to a linear engine model of a jet engine. The two multivariable control design techniques compared were the Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) and the H-Infinity synthesis. The two control design techniques were used with specific previously published design procedures to synthesize controls which would provide equivalent closed loop frequency response for the primary control loops while assuring adequate loop decoupling. The resulting controllers were then reduced in order to minimize the programming and data storage requirements for a typical implementation. The reduced order linear controllers designed by each method were combined with the linear model of an advanced turbofan engine and the system performance was evaluated for the continuous linear system. Included in the performance analysis are the resulting frequency and transient responses as well as actuator usage and rate capability for each design method. The controls were also analyzed for robustness with respect to structured uncertainties in the unmodeled system dynamics. The two controls were then compared for performance capability and hardware implementation issues.
HALOS: fast, autonomous, holographic adaptive optics

NASA Astrophysics Data System (ADS)

Andersen, Geoff P.; Gelsinger-Austin, Paul; Gaddipati, Ravi; Gaddipati, Phani; Ghebremichael, Fassil

2014-08-01

We present progress on our holographic adaptive laser optics system (HALOS): a compact, closed-loop aberration correction system that uses a multiplexed hologram to deconvolve the phase aberrations in an input beam. The wavefront characterization is based on simple, parallel measurements of the intensity of fixed focal spots and does not require any complex calculations. As such, the system does not require a computer and is thus much cheaper, less complex than conventional approaches. We present details of a fully functional, closed-loop prototype incorporating a 32-element MEMS mirror, operating at a bandwidth of over 10kHz. Additionally, since the all-optical sensing is made in parallel, the speed is independent of actuator number - running at the same bandwidth for one actuator as for a million.

Paired Associative Stimulation Using Brain-Computer Interfaces for Stroke Rehabilitation: A Pilot Study.

PubMed

Cho, Woosang; Sabathiel, Nikolaus; Ortner, Rupert; Lechner, Alexander; Irimia, Danut C; Allison, Brendan Z; Edlinger, Guenter; Guger, Christoph

2016-06-13

Conventional therapies do not provide paralyzed patients with closed-loop sensorimotor integration for motor rehabilitation. Paired associative stimulation (PAS) uses brain-computer interface (BCI) technology to monitor patients' movement imagery in real-time, and utilizes the information to control functional electrical stimulation (FES) and bar feedback for complete sensorimotor closed loop. To realize this approach, we introduce the recoveriX system, a hardware and software platform for PAS. After 10 sessions of recoveriX training, one stroke patient partially regained control of dorsiflexion in her paretic wrist. A controlled group study is planned with a new version of the recoveriX system, which will use a new FES system and an avatar instead of bar feedback.
A statistical learning strategy for closed-loop control of fluid flows

NASA Astrophysics Data System (ADS)

Guéniat, Florimond; Mathelin, Lionel; Hussaini, M. Yousuff

2016-12-01

This work discusses a closed-loop control strategy for complex systems utilizing scarce and streaming data. A discrete embedding space is first built using hash functions applied to the sensor measurements from which a Markov process model is derived, approximating the complex system's dynamics. A control strategy is then learned using reinforcement learning once rewards relevant with respect to the control objective are identified. This method is designed for experimental configurations, requiring no computations nor prior knowledge of the system, and enjoys intrinsic robustness. It is illustrated on two systems: the control of the transitions of a Lorenz'63 dynamical system, and the control of the drag of a cylinder flow. The method is shown to perform well.
Analysis of the bacterial luciferase mobile loop by replica-exchange molecular dynamics.

PubMed

Campbell, Zachary T; Baldwin, Thomas O; Miyashita, Osamu

2010-12-15

Bacterial luciferase contains an extended 29-residue mobile loop. Movements of this loop are governed by binding of either flavin mononucleotide (FMNH2) or polyvalent anions. To understand this process, loop dynamics were investigated using replica-exchange molecular dynamics that yielded conformational ensembles in either the presence or absence of FMNH2. The resulting data were analyzed using clustering and network analysis. We observed the closed conformations that are visited only in the simulations with the ligand. Yet the mobile loop is intrinsically flexible, and FMNH2 binding modifies the relative populations of conformations. This model provides unique information regarding the function of a crystallographically disordered segment of the loop near the binding site. Structures at or near the fringe of this network were compatible with flavin binding or release. Finally, we demonstrate that the crystallographically observed conformation of the mobile loop bound to oxidized flavin was influenced by crystal packing. Thus, our study has revealed what we believe are novel conformations of the mobile loop and additional context for experimentally determined structures. Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.
A control problem for Burgers' equation with bounded input/output

NASA Technical Reports Server (NTRS)

Burns, John A.; Kang, Sungkwon

1990-01-01

A stabilization problem for Burgers' equation is considered. Using linearization, various controllers are constructed which minimize certain weighted energy functionals. These controllers produce the desired degree of stability for the closed-loop nonlinear system. A numerical scheme for computing the feedback gain functional is developed and several numerical experiments are performed to show the theoretical results.
Studying NASA's Transition to Ka-Band Communications for Low Earth Orbit

NASA Technical Reports Server (NTRS)

Chelmins, David; Reinhart, Richard; Mortensen, Dale; Welch, Bryan; Downey, Joseph; Evans, Mike

2014-01-01

As the S-band spectrum becomes crowded, future space missions will need to consider moving command and telemetry services to Ka-band. NASAs Space Communications and Navigation (SCaN) Testbed provides a software-defined radio (SDR) platform that is capable of supporting investigation of this service transition. The testbed contains two S-band SDRs and one Ka-band SDR. Over the past year, SCaN Testbed has demonstrated Ka-band communications capabilities with NASAs Tracking and Data Relay Satellite System (TDRSS) using both open- and closed-loop antenna tracking profiles. A number of technical areas need to be addressed for successful transition to Ka-band. The smaller antenna beamwidth at Ka-band increases the criticality of antenna pointing, necessitating closed loop tracking algorithms and new techniques for received power estimation. Additionally, the antenna pointing routines require enhanced knowledge of spacecraft position and attitude for initial acquisition, versus an S-band antenna. Ka-band provides a number of technical advantages for bulk data transfer. Unlike at S-band, a larger bandwidth may be available for space missions, allowing increased data rates. The potential for high rate data transfer can also be extended for direct-to-ground links through use of variable or adaptive coding and modulation. Specific examples of Ka-band research from SCaN Testbeds first year of operation will be cited, such as communications link performance with TDRSS, and the effects of truss flexure on antenna pointing.
Studying NASA's Transition to Ka-Band Communications for Low Earth Orbit

NASA Technical Reports Server (NTRS)

Chelmins, David T.; Reinhart, Richard C.; Mortensen, Dale; Welch, Bryan; Downey, Joseph; Evans, Michael

2014-01-01

As the S-band spectrum becomes crowded, future space missions will need to consider moving command and telemetry services to Ka-band. NASA's Space Communications and Navigation (SCaN) Testbed provides a software-defined radio (SDR) platform that is capable of supporting investigation of this service transition. The testbed contains two S-band SDRs and one Ka-band SDR. Over the past year, SCaN Testbed has demonstrated Ka-band communications capabilities with NASAs Tracking and Data Relay Satellite System (TDRSS) using both open- and closed-loop antenna tracking profiles. A number of technical areas need to be addressed for successful transition to Ka-band. The smaller antenna beamwidth at Ka-band increases the criticality of antenna pointing, necessitating closed loop tracking algorithms and new techniques for received power estimation. Additionally, the antenna pointing routines require enhanced knowledge of spacecraft position and attitude for initial acquisition, versus an S-band antenna. Ka-band provides a number of technical advantages for bulk data transfer. Unlike at S-band, a larger bandwidth may be available for space missions, allowing increased data rates. The potential for high rate data transfer can also be extended for direct-to-ground links through use of variable or adaptive coding and modulation. Specific examples of Ka-band research from SCaN Testbeds first year of operation will be cited, such as communications link performance with TDRSS, and the effects of truss flexure on antenna pointing.
Predictive lethal proarrhythmic risk evaluation using a closed-loop-circuit cell network with human induced pluripotent stem cells derived cardiomyocytes

NASA Astrophysics Data System (ADS)

Nomura, Fumimasa; Hattori, Akihiro; Terazono, Hideyuki; Kim, Hyonchol; Odaka, Masao; Sugio, Yoshihiro; Yasuda, Kenji

2016-06-01

For the prediction of lethal arrhythmia occurrence caused by abnormality of cell-to-cell conduction, we have developed a next-generation in vitro cell-to-cell conduction assay, i.e., a quasi in vivo assay, in which the change in spatial cell-to-cell conduction is quantitatively evaluated from the change in waveforms of the convoluted electrophysiological signals from lined-up cardiomyocytes on a single closed loop of a microelectrode of 1 mm diameter and 20 µm width in a cultivation chip. To evaluate the importance of the closed-loop arrangement of cardiomyocytes for prediction, we compared the change in waveforms of convoluted signals of the responses in the closed-loop circuit arrangement with that of the response of cardiomyocyte clusters using a typical human ether a go-go related gene (hERG) ion channel blocker, E-4031. The results showed that (1) waveform prolongation and fluctuation both in the closed loops and clusters increased depending on the E-4031 concentration increase. However, (2) only the waveform signals in closed loops showed an apparent temporal change in waveforms from ventricular tachycardia (VT) to ventricular fibrillation (VF), which is similar to the most typical cell-to-cell conductance abnormality. The results indicated the usefulness of convoluted waveform signals of a closed-loop cell network for acquiring reproducible results acquisition and more detailed temporal information on cell-to-cell conduction.
An experimental study on the performance of closed loop pulsating heat pipe (CLPHP) with methanol as a working fluid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahman, Md. Lutfor; Nourin, Farah Nazifa, E-mail: farahnazifanourin@gmail.com; Salsabil, Zaimaa

Thermal control is an important topic for thermal management of small electrical and electronic devices. Closed loop pulsating heat pipe (CLPHP) arises as the best solution for thermal control. The aim of this experimental study is to search a CLPHP of better thermal performance for cooling different electrical and electronic devices. In this experiment, methanol is used as working fluid. The effect of using methanol as a working fluid is studied on thermal performance in different filling ratios and angles of inclination. A copper capillary tube is used where the inner diameter is 2 mm,outer diameter is 2.5 mm andmore » 250 mm long. The CLPHP has 8 loops where the evaporation section is 50 mm, adiabatic section is 120 mm and condensation section is 80 mm. The experiment is done using FR of 40%-70% with 10% of interval and angles of inclination 0° (vertical), 30°, 45°, 60° varying heat input. The results are compared on the basis of evaporator temperature, condenser temperature and their differences, thermal resistance, heat transfer co-efficient, power input and pulsating time. The results demonstrate the effect of methanol in different filling ratios and angles of inclination. M ethanol shows better performance at 30° inclination with 40% FR.« less
Renormalization of loop functions for all loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brandt, R.A.; Neri, F.; Sato, M.

1981-08-15

It is shown that the vacuum expectation values W(C/sub 1/,xxx, C/sub n/) of products of the traces of the path-ordered phase factors P exp(igcontour-integral/sub C/iA/sub ..mu../(x)dx/sup ..mu../) are multiplicatively renormalizable in all orders of perturbation theory. Here A/sub ..mu../(x) are the vector gauge field matrices in the non-Abelian gauge theory with gauge group U(N) or SU(N), and C/sub i/ are loops (closed paths). When the loops are smooth (i.e., differentiable) and simple (i.e., non-self-intersecting), it has been shown that the generally divergent loop functions W become finite functions W when expressed in terms of the renormalized coupling constant and multipliedmore » by the factors e/sup -K/L(C/sub i/), where K is linearly divergent and L(C/sub i/) is the length of C/sub i/. It is proved here that the loop functions remain multiplicatively renormalizable even if the curves have any finite number of cusps (points of nondifferentiability) or cross points (points of self-intersection). If C/sub ..gamma../ is a loop which is smooth and simple except for a single cusp of angle ..gamma.., then W/sub R/(C/sub ..gamma../) = Z(..gamma..)W(C/sub ..gamma../) is finite for a suitable renormalization factor Z(..gamma..) which depends on ..gamma.. but on no other characteristic of C/sub ..gamma../. This statement is made precise by introducing a regularization, or via a loop-integrand subtraction scheme specified by a normalization condition W/sub R/(C-bar/sub ..gamma../) = 1 for an arbitrary but fixed loop C-bar/sub ..gamma../. Next, if C/sub ..beta../ is a loop which is smooth and simple except for a cross point of angles ..beta.., then W(C/sub ..beta../) must be renormalized together with the loop functions of associated sets S/sup i//sub ..beta../ = )C/sup i//sub 1/,xxx, C/sup i//sub p/i) (i = 2,xxx,I) of loops C/sup i//sub q/ which coincide with certain parts of C/sub ..beta../equivalentC/sup 1//sub 1/. Then W/sub R/(S/sup i//sub ..beta../) = Z/sup i/j(..beta..)W(S/sup j//sub ..beta../) is finite for a suitable matrix Z/sup i/j(..beta..).« less
Accounting for respiration is necessary to reliably infer Granger causality from cardiovascular variability series.

PubMed

Porta, Alberto; Bassani, Tito; Bari, Vlasta; Pinna, Gian D; Maestri, Roberto; Guzzetti, Stefano

2012-03-01

This study was designed to demonstrate the need of accounting for respiration (R) when causality between heart period (HP) and systolic arterial pressure (SAP) is under scrutiny. Simulations generated according to a bivariate autoregressive closed-loop model were utilized to assess how causality changes as a function of the model parameters. An exogenous (X) signal was added to the bivariate autoregressive closed-loop model to evaluate the bias on causality induced when the X source was disregarded. Causality was assessed in the time domain according to a predictability improvement approach (i.e., Granger causality). HP and SAP variability series were recorded with R in 19 healthy subjects during spontaneous and controlled breathing at 10, 15, and 20 breaths/min. Simulations proved the importance of accounting for X signals. During spontaneous breathing, assessing causality without taking into consideration R leads to a significantly larger percentage of closed-loop interactions and a smaller fraction of unidirectional causality from HP to SAP. This finding was confirmed during paced breathing and it was independent of the breathing rate. These results suggest that the role of baroreflex cannot be correctly assessed without accounting for R.
Algorithms for a Closed-Loop Artificial Pancreas: The Case for Model Predictive Control

PubMed Central

Bequette, B. Wayne

2013-01-01

The relative merits of model predictive control (MPC) and proportional-integral-derivative (PID) control are discussed, with the end goal of a closed-loop artificial pancreas (AP). It is stressed that neither MPC nor PID are single algorithms, but rather are approaches or strategies that may be implemented very differently by different engineers. The primary advantages to MPC are that (i) constraints on the insulin delivery rate (and/or insulin on board) can be explicitly included in the control calculation; (ii) it is a general framework that makes it relatively easy to include the effect of meals, exercise, and other events that are a function of the time of day; and (iii) it is flexible enough to include many different objectives, from set-point tracking (target) to zone (control to range). In the end, however, it is recognized that the control algorithm, while important, represents only a portion of the effort required to develop a closed-loop AP. Thus, any number of algorithms/approaches can be successful—the engineers involved in the design must have experience with the particular technique, including the important experience of implementing the algorithm in human studies and not simply through simulation studies. PMID:24351190
Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2).

PubMed

Harel, Elad; Engel, Gregory S

2012-01-17

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2.
Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2)

PubMed Central

Harel, Elad; Engel, Gregory S.

2012-01-01

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2. PMID:22215585
Open and closed loop manipulation of charged microchiplets in an electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, J. P., E-mail: jplu@parc.com; Thompson, J. D.; Whiting, G. L.

We demonstrate the ability to orient, position, and transport microchips (“chiplets”) with electric fields. In an open-loop approach, modified four phase traveling wave potential patterns manipulate chiplets in a dielectric solution using dynamic template agitation techniques. Repeatable parallel assembly of chiplets is demonstrated to a positional accuracy of 6.5 μm using electrodes of 200 μm pitch. Chiplets with dipole surface charge patterns are used to show that orientation can be controlled by adding unique charge patterns on the chiplets. Chip path routing is also demonstrated. With a closed-loop control system approach using video feedback, dielectric, and electrophoretic forces are used to achievemore » positioning accuracy of better than 1 μm with 1 mm pitch driving electrodes. These chip assembly techniques have the potential to enable future printer systems where inputs are electronic chiplets and the output is a functional electronic system.« less
OPTICON: Pro-Matlab software for large order controlled structure design

NASA Technical Reports Server (NTRS)

Peterson, Lee D.

1989-01-01

A software package for large order controlled structure design is described and demonstrated. The primary program, called OPTICAN, uses both Pro-Matlab M-file routines and selected compiled FORTRAN routines linked into the Pro-Matlab structure. The program accepts structural model information in the form of state-space matrices and performs three basic design functions on the model: (1) open loop analyses; (2) closed loop reduced order controller synthesis; and (3) closed loop stability and performance assessment. The current controller synthesis methods which were implemented in this software are based on the Generalized Linear Quadratic Gaussian theory of Bernstein. In particular, a reduced order Optimal Projection synthesis algorithm based on a homotopy solution method was successfully applied to an experimental truss structure using a 58-state dynamic model. These results are presented and discussed. Current plans to expand the practical size of the design model to several hundred states and the intention to interface Pro-Matlab to a supercomputing environment are discussed.
Coherent transfer of orbital angular momentum to excitons by optical four-wave mixing.

PubMed

Ueno, Y; Toda, Y; Adachi, S; Morita, R; Tawara, T

2009-10-26

We demonstrate the coherent transfer of optical orbital angular momentum (OAM) to the center of mass momentum of excitons in semiconductor GaN using a four-wave mixing (FWM) process. When we apply the optical vortex (OV) as an excitation pulse, the diffracted FWM signal exhibits phase singularities that satisfy the OAM conservation law, which remain clear within the exciton dephasing time (approximately 1ps). We also demonstrate the arbitrary control of the topological charge in the output signal by changing the OAM of the input pulse. The results provide a way of controlling the optical OAM through carriers in solids. Moreover, the time evolution of the FWM with OAM leads to the study of the closed-loop carrier coherence in materials.
In situ conversion process utilizing a closed loop heating system

DOEpatents

Sandberg, Chester Ledlie [Palo Alto, CA; Fowler, Thomas David [Houston, TX; Vinegar, Harold J [Bellaire, TX; Schoeber, Willen Jan Antoon Henri

2009-08-18

An in situ conversion system for producing hydrocarbons from a subsurface formation is described. The system includes a plurality of u-shaped wellbores in the formation. Piping is positioned in at least two of the u-shaped wellbores. A fluid circulation system is coupled to the piping. The fluid circulation system is configured to circulate hot heat transfer fluid through at least a portion of the piping to form at least one heated portion of the formation. An electrical power supply is configured to provide electrical current to at least a portion of the piping located below an overburden in the formation to resistively heat at least a portion of the piping. Heat transfers from the piping to the formation.
Closing the Loop: A Study of How the National Survey of Student Engagement (NSSE) Is Used for Decision-Making and Planning in Student Affairs

ERIC Educational Resources Information Center

McCaul, Jennifer Lee

2015-01-01

"Closing the loop" is a commonly used phrase in discussing cyclical processes, such as the area of outcomes assessment in higher education. Increased interest in accountability and a shift in accreditation focus have necessitated that higher education institutions are closing the assessment loop and creating a culture of evidence to…
Trade Study for 9 kW Water Membrane Evaporator

NASA Technical Reports Server (NTRS)

Bue, Grant C.; Ungar, Gene; Stephan, Ryan

2010-01-01

Sublimators have been proposed and used in spacecraft for heat rejection. Sublimators are desirable heat rejection devices for short duration use because they can transfer large amounts of heat using little mass and are self-regulating devices. Sublimators reject heat into space by freezing water inside a porous substrate, allowing it to sublimate into vapor, and finally venting it into space. The state of the art thermal control system in orbiting spacecraft is a two loop, two fluid system. The external coolant loop typically uses a toxic single phase fluid that acquires heat from the spacecraft and rejects most of it via a radiator. The sublimator functions as a transient topper for orbiting spacecraft during day pass periods when radiator efficiency decreases. The sublimator interfaces with the internal loop through a built in heat exchanger. The internal loop fluid is non-toxic and is typically a propylene glycol and water solution with inhibitors to prevent corrosion with aluminum fins of the heat exchangers. Feedwater is supplied from a separate line to the sublimator to maintain temperature control of the cabin and vehicle hardware. Water membrane evaporators have been developed for spacecraft and spacesuits. They function similar to a sublimator but require a backpressure valve which could be actuated for this application with a simple fully open or fully closed modes. This technology would be applied to orbital thermal control (lunar or planetary). This paper details a trade study showing that evaporators would greatly reduce the consumable that is used, effectively wasted, by sublimators during start up and shut down during the topping phases of each orbit. State of the art for 9 kW sublimators reject about 870 W per kilogram of mass and 1150 W per liter of volume. If water with corrosion inhibitors is used the evaporators would be about 80% of the mass and volume of the equivalent system. The size and mass increases to about 110% if the internal fluid is 50% propylene glycol/50% water. The true benefit comes from the backpressure valve, that prevents the cyclical shutdown/startup loss of the sublimator and amounts to as much as 0.85 kg per orbit.
Tonic accommodation predicts closed-loop accommodation responses.

PubMed

Liu, Chunming; Drew, Stefanie A; Borsting, Eric; Escobar, Amy; Stark, Lawrence; Chase, Christopher

2016-12-01

The purpose of this study is to examine the potential relationship between tonic accommodation (TA), near work induced TA-adaptation and the steady state closed-loop accommodation response (AR). Forty-two graduate students participated in the study. Various aspects of their accommodation system were objectively measured using an open-field infrared auto-refractor (Grand Seiko WAM-5500). Tonic accommodation was assessed in a completely dark environment. The association between TA and closed-loop AR was assessed using linear regression correlations and t-test comparisons. Initial mean baseline TA was 1.84diopter (D) (SD±1.29D) with a wide distribution range (-0.43D to 5.14D). For monocular visual tasks, baseline TA was significantly correlated with the closed-loop AR. The slope of the best fit line indicated that closed-loop AR varied by approximately 0.3D for every 1D change in TA. This ratio was consistent across a variety of viewing distances and different near work tasks, including both static targets and continuous reading. Binocular reading conditions weakened the correlation between baseline TA and AR, although results remained statistically significant. The 10min near reading task with a 3D demand did not reveal significant near work induced TA-adaptation for either monocular or binocular conditions. Consistently, the TA-adaptation did not show any correlation with AR during reading. This study found a strong association between open-loop TA and closed-loop AR across a variety of viewing distances and different near work tasks. Difference between the correlations under monocular and binocular reading condition suggests a potential role for vergence compensation during binocular closed-loop AR. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

PubMed

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.
A bi-directional two-phase/two-phase heat exchanger

NASA Technical Reports Server (NTRS)

Ku, Jentung; Ottenstein, Laura

1993-01-01

This paper describes the design and test of a heat exchanger that transfers heat from one two-phase thermal loop to another with very small drops in temperature and pressure. The heat exchanger condenses the vapor in one loop while evaporating the liquid in the other without mixing of the condensing and evaporating fluids. The heat exchanger is bidirectional in that it can transfer heat in reverse, condensing on the normally evaporating side and vice versa. It is fully compatible with capillary pumped loops and mechanically pumped loops. Test results verified that performance of the heat exchanger met the design requirements. It demonstrated a heat transfer rate of 6800 watts in the normal mode of operation and 1000 watts in the reverse mode with temperature drops of less than 5 C between two thermal loops.
Wilson loops in supersymmetric gauge theories

NASA Astrophysics Data System (ADS)

Pestun, Vasily

This thesis is devoted to several exact computations in four-dimensional supersymmetric gauge field theories. In the first part of the thesis we prove conjecture due to Erickson-Semenoff-Zarembo and Drukker-Gross which relates supersymmetric circular Wilson loop operators in the N = 4 supersymmetric Yang-Mills theory with a Gaussian matrix model. We also compute the partition function and give a new matrix model formula for the expectation value of a supersymmetric circular Wilson loop operator for the pure N = 2 and the N* = 2 supersymmetric Yang-Mills theory on a four-sphere. Circular supersymmetric Wilson loops in four-dimensional N = 2 superconformal gauge theory are treated similarly. In the second part we consider supersymmetric Wilson loops of arbitrary shape restricted to a two-dimensional sphere in the four-dimensional N = 4 supersymmetric Yang-Mills theory. We show that expectation value for these Wilson loops can be exactly computed using a two-dimensional theory closely related to the topological two-dimensional Higgs-Yang-Mills theory, or two-dimensional Yang-Mills theory for the complexified gauge group.
Experimental validation of a predicted feedback loop in the multi-oscillator clock of Arabidopsis thaliana

PubMed Central

Locke, James C W; Kozma-Bognár, László; Gould, Peter D; Fehér, Balázs; Kevei, Éva; Nagy, Ferenc; Turner, Matthew S; Hall, Anthony; Millar, Andrew J

2006-01-01

Our computational model of the circadian clock comprised the feedback loop between LATE ELONGATED HYPOCOTYL (LHY), CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and TIMING OF CAB EXPRESSION 1 (TOC1), and a predicted, interlocking feedback loop involving TOC1 and a hypothetical component Y. Experiments based on model predictions suggested GIGANTEA (GI) as a candidate for Y. We now extend the model to include a recently demonstrated feedback loop between the TOC1 homologues PSEUDO-RESPONSE REGULATOR 7 (PRR7), PRR9 and LHY and CCA1. This three-loop network explains the rhythmic phenotype of toc1 mutant alleles. Model predictions fit closely to new data on the gi;lhy;cca1 mutant, which confirm that GI is a major contributor to Y function. Analysis of the three-loop network suggests that the plant clock consists of morning and evening oscillators, coupled intracellularly, which may be analogous to coupled, morning and evening clock cells in Drosophila and the mouse. PMID:17102804
Asymmetric dual-loop feedback to suppress spurious tones and reduce timing jitter in self-mode-locked quantum-dash lasers emitting at 155 μm

NASA Astrophysics Data System (ADS)

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.
Closed-loop analysis and control of a non-inverting buck-boost converter

NASA Astrophysics Data System (ADS)

Chen, Zengshi; Hu, Jiangang; Gao, Wenzhong

2010-11-01

In this article, a cascade controller is designed and analysed for a non-inverting buck-boost converter. The fast inner current loop uses sliding mode control. The slow outer voltage loop uses the proportional-integral (PI) control. Stability analysis and selection of PI gains are based on the nonlinear closed-loop error dynamics incorporating both the inner and outer loop controllers. The closed-loop system is proven to have a nonminimum phase structure. The voltage transient due to step changes of input voltage or resistance is predictable. The operating range of the reference voltage is discussed. The controller is validated by a simulation circuit. The simulation results show that the reference output voltage is well-tracked under system uncertainties or disturbances, confirming the validity of the proposed controller.
Window-closing safety system

DOEpatents

McEwan, Thomas E.

1997-01-01

A safety device includes a wire loop embedded in the glass of a passenger car window and routed near the closing leading-edge of the window. The wire loop carries microwave pulses around the loop to and from a transceiver with separate output and input ports. An evanescent field only and inch or two in radius is created along the wire loop by the pulses. Just about any object coming within the evanescent field will dramatically reduce the energy of the microwave pulses received back by the transceiver. Such a loss in energy is interpreted as a closing area blockage, and electrical interlocks are provided to halt or reverse a power window motor that is actively trying to close the window.
Window-closing safety system

DOEpatents

McEwan, T.E.

1997-08-26

A safety device includes a wire loop embedded in the glass of a passenger car window and routed near the closing leading-edge of the window. The wire loop carries microwave pulses around the loop to and from a transceiver with separate output and input ports. An evanescent field only an inch or two in radius is created along the wire loop by the pulses. Just about any object coming within the evanescent field will dramatically reduce the energy of the microwave pulses received back by the transceiver. Such a loss in energy is interpreted as a closing area blockage, and electrical interlocks are provided to halt or reverse a power window motor that is actively trying to close the window. 5 figs.
Output Feedback-Based Boundary Control of Uncertain Coupled Semilinear Parabolic PDE Using Neurodynamic Programming.

PubMed

Talaei, Behzad; Jagannathan, Sarangapani; Singler, John

2018-04-01

In this paper, neurodynamic programming-based output feedback boundary control of distributed parameter systems governed by uncertain coupled semilinear parabolic partial differential equations (PDEs) under Neumann or Dirichlet boundary control conditions is introduced. First, Hamilton-Jacobi-Bellman (HJB) equation is formulated in the original PDE domain and the optimal control policy is derived using the value functional as the solution of the HJB equation. Subsequently, a novel observer is developed to estimate the system states given the uncertain nonlinearity in PDE dynamics and measured outputs. Consequently, the suboptimal boundary control policy is obtained by forward-in-time estimation of the value functional using a neural network (NN)-based online approximator and estimated state vector obtained from the NN observer. Novel adaptive tuning laws in continuous time are proposed for learning the value functional online to satisfy the HJB equation along system trajectories while ensuring the closed-loop stability. Local uniformly ultimate boundedness of the closed-loop system is verified by using Lyapunov theory. The performance of the proposed controller is verified via simulation on an unstable coupled diffusion reaction process.
Leader-follower formation control of underactuated surface vehicles based on sliding mode control and parameter estimation.

PubMed

Sun, Zhijian; Zhang, Guoqing; Lu, Yu; Zhang, Weidong

2018-01-01

This paper studies the leader-follower formation control of underactuated surface vehicles with model uncertainties and environmental disturbances. A parameter estimation and upper bound estimation based sliding mode control scheme is proposed to solve the problem of the unknown plant parameters and environmental disturbances. For each of these leader-follower formation systems, the dynamic equations of position and attitude are analyzed using coordinate transformation with the aid of the backstepping technique. All the variables are guaranteed to be uniformly ultimately bounded stable in the closed-loop system, which is proven by the distribution design Lyapunov function synthesis. The main advantages of this approach are that: first, parameter estimation based sliding mode control can enhance the robustness of the closed-loop system in presence of model uncertainties and environmental disturbances; second, a continuous function is developed to replace the signum function in the design of sliding mode scheme, which devotes to reduce the chattering of the control system. Finally, numerical simulations are given to demonstrate the effectiveness of the proposed method. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Structural robustness with suboptimal responses for linear state space model

NASA Technical Reports Server (NTRS)

Keel, L. H.; Lim, Kyong B.; Juang, Jer-Nan

1989-01-01

A relationship between the closed-loop eigenvalues and the amount of perturbations in the open-loop matrix is addressed in the context of performance robustness. If the allowable perturbation ranges of elements of the open-loop matrix A and the desired tolerance of the closed-loop eigenvalues are given such that max(j) of the absolute value of Delta-lambda(j) (A+BF) should be less than some prescribed value, what is a state feedback controller F which satisfies the closed-loop eigenvalue perturbation-tolerance requirement for a class of given perturbation in A? The paper gives an algorithm to design such a controller. Numerical examples are included for illustration.
Development of Flow Boiling and Condensation Experiment on the International Space Station- Normal and Low Gravity Flow Boiling Experiment Development and Test Results

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Hall, Nancy R.; Hasan, Mohammad M.; Wagner, James D.; May, Rochelle L.; Mackey, Jeffrey R.; Kolacz, John S.; Butcher, Robert L.; Frankenfield, Bruce J.; Mudawar, Issam;

2013-01-01

Flow boiling and condensation have been identified as two key mechanisms for heat transport that are vital for achieving weight and volume reduction as well as performance enhancement in future space systems. Since inertia driven flows are demanding on power usage, lower flows are desirable. However, in microgravity, lower flows are dominated by forces other than inertia (like the capillary force). It is of paramount interest to investigate limits of low flows beyond which the flow is inertial enough to be gravity independent. One of the objectives of the Flow Boiling and Condensation Flight Experiment sets to investigate these limits for flow boiling and condensation. A two-phase flow loop consisting of a Flow Boiling Module and two Condensation Modules has been developed to experimentally study flow boiling condensation heat transfer in the reduced gravity environment provided by the reduced gravity platform. This effort supports the development of a flow boiling and condensation facility for the International Space Station (ISS). The closed loop test facility is designed to deliver the test fluid, FC-72 to the inlet of any one of the test modules at specified thermodynamic and flow conditions. The zero-g-aircraft tests will provide subcooled and saturated flow boiling critical heat flux and flow condensation heat transfer data over wide range of flow velocities. Additionally, these tests will verify the performance of all gravity sensitive components, such as evaporator, condenser and accumulator associated with the two-phase flow loop. We will present in this paper the breadboard development and testing results which consist of detailed performance evaluation of the heater and condenser combination in reduced and normal gravity. We will also present the design of the reduced gravity aircraft rack and the results of the ground flow boiling heat transfer testing performed with the Flow Boiling Module that is designed to investigate flow boiling heat transfer and Critical Heat Flux (CHF) phenomena.

Closed-loop endo-atmospheric ascent guidance for reusable launch vehicle

NASA Astrophysics Data System (ADS)

Sun, Hongsheng

This dissertation focuses on the development of a closed-loop endo-atmospheric ascent guidance algorithm for the 2nd generation reusable launch vehicle. Special attention has been given to the issues that impact on viability, complexity and reliability in on-board implementation. The algorithm is called once every guidance update cycle to recalculate the optimal solution based on the current flight condition, taking into account atmospheric effects and path constraints. This is different from traditional ascent guidance algorithms which operate in a simple open-loop mode inside atmosphere, and later switch to a closed-loop vacuum ascent guidance scheme. The classical finite difference method is shown to be well suited for fast solution of the constrained optimal three-dimensional ascent problem. The initial guesses for the solutions are generated using an analytical vacuum optimal ascent guidance algorithm. Homotopy method is employed to gradually introduce the aerodynamic forces to generate the optimal solution from the optimal vacuum solution. The vehicle chosen for this study is the Lockheed Martin X-33 lifting-body reusable launch vehicle. To verify the algorithm presented in this dissertation, a series of open-loop and closed-loop tests are performed for three different missions. Wind effects are also studied in the closed-loop simulations. For comparison, the solutions for the same missions are also obtained by two independent optimization softwares. The results clearly establish the feasibility of closed-loop endo-atmospheric ascent guidance of rocket-powered launch vehicles. ATO cases are also tested to assess the adaptability of the algorithm to autonomously incorporate the abort modes.
Bidirectional neural interface: Closed-loop feedback control for hybrid neural systems.

PubMed

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.
Domain Hierarchy and closed Loops (DHcL): a server for exploring hierarchy of protein domain structure

PubMed Central

Koczyk, Grzegorz; Berezovsky, Igor N.

2008-01-01

Domain hierarchy and closed loops (DHcL) (http://sitron.bccs.uib.no/dhcl/) is a web server that delineates energy hierarchy of protein domain structure and detects domains at different levels of this hierarchy. The server also identifies closed loops and van der Waals locks, which constitute a structural basis for the protein domain hierarchy. The DHcL can be a useful tool for an express analysis of protein structures and their alternative domain decompositions. The user submits a PDB identifier(s) or uploads a 3D protein structure in a PDB format. The results of the analysis are the location of domains at different levels of hierarchy, closed loops, van der Waals locks and their interactive visualization. The server maintains a regularly updated database of domains, closed loop and van der Waals locks for all X-ray structures in PDB. DHcL server is available at: http://sitron.bccs.uib.no/dhcl. PMID:18502776
Novel imaging closed loop control strategy for heliostats

NASA Astrophysics Data System (ADS)

Bern, Gregor; Schöttl, Peter; Heimsath, Anna; Nitz, Peter

2017-06-01

Central Receiver Systems use up to thousands of heliostats to concentrate solar radiation. The precise control of heliostat aiming points is crucial not only for efficiency but also for reliable plant operation. Besides the calibration of open loop control systems, closed loop tracking strategies are developed to address a precise and efficient aiming strategy. The need for cost reductions in the heliostat field intensifies the motivation for economic closed loop control systems. This work introduces an approach for a closed loop heliostat tracking strategy using image analysis and signal modulation. The approach aims at the extraction of heliostat focal spot position within the receiver domain by means of a centralized remote vision system decoupled from the rough conditions close to the focal area. Taking an image sequence of the receiver while modulating a signal on different heliostats, their aiming points are retrieved. The work describes the methodology and shows first results from simulations and practical tests performed in small scale, motivating further investigation and deployment.
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.

PubMed

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 hand, indicating that sensorimotor (or motor) memory can operate both within and between hands when the response type is kept the same. In a final experiment, we ruled out the possibility that simply alternating the hand used to perform the grasp interferes with motor or sensorimotor memory. We did this by showing that when the hand was alternated within a block of exclusively closed- or open-loop trials, homogenization of the PGA did not occur. Taken together, the results suggest that (1) interference from simply switching between task sets for closed or open-loop feedback or from switching between the hands cannot account homogenization in the PGA and that (2) the programming and execution of grasps can borrow not only from grasping movements executed in the past by the same hand, but also from grasping movements executed with the other hand. Copyright © 2015 Elsevier B.V. All rights reserved.
Solution NMR analyses of the anticodon arms of proteinogenic and non-proteinogenic tRNAGly

PubMed Central

Chang, Andrew T.; Nikonowicz, Edward P.

2012-01-01

Although the fate of most tRNA molecules in the cell is aminoacylation and delivery to the ribosome, some tRNAs are destined to fulfill other functional roles. In addition to their central role in translation, tRNA molecules participate in processes such as regulation of gene expression, bacterial cell wall biosynthesis, viral replication, antibiotic biosynthesis, and suppression of alternative splicing. In bacteria, glycyl-tRNA molecules with anticodon sequences GCC and UCC exhibit multiple extra-translational functions including transcriptional regulation and cell wall biosynthesis. We have determined the high-resolution structures of three glycyl-tRNA anticodon arms with anticodon sequences GCC and UCC. Two of the tRNA molecules are proteinogenic (tRNAGly,GCC and tRNAGly,UCC) and the third is non-proteinogenic (np-tRNAGly,UCC) and participates in cell wall biosynthesis. The UV-monitored thermal melting curves show that the anticodon arm of tRNAGly,UCC with a loop-closing C-A+ base pair melts at a 10 °C lower temperature than those of tRNAGly,GCC or np-tRNAGly,UCC. U-A and C-G pairs close the loops of the later two molecules and enhance stem stability. Mg2+ stabilizes the tRNAGly,UCC anticodon arm and lessens the Tm differential. The structures of the three tRNAGly anticodon arms exhibit small differences between one another, but none of them form the classical U-turn motif. The anticodon loop of tRNAGly,GCC becomes more dynamic and disordered in the presence of multivalent cations, whereas metal ion coordination in the anticodon loops of tRNAGly,UCC and np-tRNAGly,UCC establishes conformational homogeneity. The conformational similarity of the molecules is greater than their functional differences might suggest. Because aminoacylation of the full-length tRNA molecules is accomplished by one tRNA synthetase, the similar structural context of the loop may facilitate efficient recognition of each of the anticodon sequences. PMID:22468768
Time delay compensation for closed-loop insulin delivery systems: a simulation study.

PubMed

Reboldi, G P; Home, P D; Calabrese, G; Fabietti, P G; Brunetti, P; Massi Benedetti, M

1991-06-01

Closed loop insulin therapy certainly represents the best possible approach to insulin replacement. However, present limitations preclude wider application of the so-called artificial pancreas. Therefore, a thorough understanding of these limitations is needed to design better systems for future long-term use. The present simulation study was design: to obtain better information on the impact of the measurement delay of currently available closed-loop devices both during closed-loop insulin delivery and blood glucose clamp studies, and to design and test a time delay compensator based on the method originally described by O.J. Smith. Simulations were performed on a Compaq Deskpro 486/25 personal computer under MS-DOS operating system using Simnon rel. 3.00 software. There was a direct relationship between measurement delay and amount of insulin delivered, i.e., the longer the delay the higher the insulin dose needed to control a rise in blood glucose; the closed-loop response in presence of a time delay was qualitatively impaired both during insulin delivery and blood glucose clamp studies; time delay compensation was effective in reducing the insulin dose and improving controller stability during the early phase of clamp studies. However, the robustness of a Smith's predictor-based controller should be carefully evaluated before implementation in closed-loop systems can be considered.
A review of implantable biosensors for closed-loop glucose control and other drug delivery applications.

PubMed

Scholten, Kee; Meng, Ellis

2018-06-15

Closed-loop drug delivery promises autonomous control of pharmacotherapy through the continuous monitoring of biomarker levels. For decades, researchers have strived for portable closed-loop systems capable of treating ambulatory patients with chronic conditions such as diabetes mellitus. After years of development, the first of these systems have left the laboratory and entered commercial use. This long-awaited advance reflects recent development of chronically stable implantable biosensors able to accurately measure biomarker levels in vivo. This review discusses the role of implantable biosensors in closed-loop drug delivery applications, with the intent to provide a resource for engineers and researchers studying such systems. We provide an overview of common biosensor designs and review the principle challenges in implementing long indwelling sensors: namely device sensitivity, selectivity, and lifetime. This review examines novel advances in transducer design, biological interface, and material biocompatibility, with a focus on recent academic and commercial work which provide successful strategies to overcome perennial challenges. This review focuses primarily on the topics of closed-loop glucose control and continuous glucose monitoring biosensors, which make up the overwhelming majority of published research in this area. We conclude with an overview of recent advances in closed-loop systems targeting applications outside blood glucose management. Copyright © 2018 Elsevier B.V. All rights reserved.

Irradiation Testing Vehicles for Fast Reactors from Open Test Assemblies to Closed Loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sienicki, James J.; Grandy, Christopher

A review of irradiation testing vehicle approaches and designs that have been incorporated into past Sodium-Cooled Fast Reactors (SFRs) or envisioned for incorporation has been carried out. The objective is to understand the essential features of the approaches and designs so that they can inform test vehicle designs for a future U.S. Fast Test Reactor. Fast test reactor designs examined include EBR-II, FFTF, JOYO, BOR-60, PHÉNIX, JHR, and MBIR. Previous designers exhibited great ingenuity in overcoming design and operational challenges especially when the original reactor plant’s mission changed to an irradiation testing mission as in the EBRII reactor plant. Themore » various irradiation testing vehicles can be categorized as: Uninstrumented open assemblies that fit into core locations; Instrumented open test assemblies that fit into special core locations; Self-contained closed loops; and External closed loops. A special emphasis is devoted to closed loops as they are regarded as a very desirable feature of a future U.S. Fast Test Reactor. Closed loops are an important technology for irradiation of fuels and materials in separate controlled environments. The impact of closed loops on the design of fast reactors is also discussed in this report.« less
Pre-frontal control of closed-loop limbic neurostimulation by rodents using a brain-computer interface

NASA Astrophysics Data System (ADS)

Widge, Alik S.; Moritz, Chet T.

2014-04-01

Objective. There is great interest in closed-loop neurostimulators that sense and respond to a patient's brain state. Such systems may have value for neurological and psychiatric illnesses where symptoms have high intraday variability. Animal models of closed-loop stimulators would aid preclinical testing. We therefore sought to demonstrate that rodents can directly control a closed-loop limbic neurostimulator via a brain-computer interface (BCI). Approach. We trained rats to use an auditory BCI controlled by single units in prefrontal cortex (PFC). The BCI controlled electrical stimulation in the medial forebrain bundle, a limbic structure involved in reward-seeking. Rigorous offline analyses were performed to confirm volitional control of the neurostimulator. Main results. All animals successfully learned to use the BCI and neurostimulator, with closed-loop control of this challenging task demonstrated at 80% of PFC recording locations. Analysis across sessions and animals confirmed statistically robust BCI control and specific, rapid modulation of PFC activity. Significance. Our results provide a preliminary demonstration of a method for emotion-regulating closed-loop neurostimulation. They further suggest that activity in PFC can be used to control a BCI without pre-training on a predicate task. This offers the potential for BCI-based treatments in refractory neurological and mental illness.
LPV gain-scheduled control of SCR aftertreatment systems

NASA Astrophysics Data System (ADS)

Meisami-Azad, Mona; Mohammadpour, Javad; Grigoriadis, Karolos M.; Harold, Michael P.; Franchek, Matthew A.

2012-01-01

Hydrocarbons, carbon monoxide and some of other polluting emissions produced by diesel engines are usually lower than those produced by gasoline engines. While great strides have been made in the exhaust aftertreatment of vehicular pollutants, the elimination of nitrogen oxide (NO x ) from diesel vehicles is still a challenge. The primary reason is that diesel combustion is a fuel-lean process, and hence there is significant unreacted oxygen in the exhaust. Selective catalytic reduction (SCR) is a well-developed technology for power plants and has been recently employed for reducing NO x emissions from automotive sources and in particular, heavy-duty diesel engines. In this article, we develop a linear parameter-varying (LPV) feedforward/feedback control design method for the SCR aftertreatment system to decrease NO x emissions while keeping ammonia slippage to a desired low level downstream the catalyst. The performance of the closed-loop system obtained from the interconnection of the SCR system and the output feedback LPV control strategy is then compared with other control design methods including sliding mode, and observer-based static state-feedback parameter-varying control. To reduce the computational complexity involved in the control design process, the number of LPV parameters in the developed quasi-LPV (qLPV) model is reduced by applying the principal component analysis technique. An LPV feedback/feedforward controller is then designed for the qLPV model with reduced number of scheduling parameters. The designed full-order controller is further simplified to a first-order transfer function with a parameter-varying gain and pole. Finally, simulation results using both a low-order model and a high-fidelity and high-order model of SCR reactions in GT-POWER interfaced with MATLAB/SIMULINK illustrate the high NO x conversion efficiency of the closed-loop SCR system using the proposed parameter-varying control law.
A Multiple-Plasticity Spiking Neural Network Embedded in a Closed-Loop Control System to Model Cerebellar Pathologies.

PubMed

Geminiani, Alice; Casellato, Claudia; Antonietti, Alberto; D'Angelo, Egidio; Pedrocchi, Alessandra

2018-06-01

The cerebellum plays a crucial role in sensorimotor control and cerebellar disorders compromise adaptation and learning of motor responses. However, the link between alterations at network level and cerebellar dysfunction is still unclear. In principle, this understanding would benefit of the development of an artificial system embedding the salient neuronal and plastic properties of the cerebellum and operating in closed-loop. To this aim, we have exploited a realistic spiking computational model of the cerebellum to analyze the network correlates of cerebellar impairment. The model was modified to reproduce three different damages of the cerebellar cortex: (i) a loss of the main output neurons (Purkinje Cells), (ii) a lesion to the main cerebellar afferents (Mossy Fibers), and (iii) a damage to a major mechanism of synaptic plasticity (Long Term Depression). The modified network models were challenged with an Eye-Blink Classical Conditioning test, a standard learning paradigm used to evaluate cerebellar impairment, in which the outcome was compared to reference results obtained in human or animal experiments. In all cases, the model reproduced the partial and delayed conditioning typical of the pathologies, indicating that an intact cerebellar cortex functionality is required to accelerate learning by transferring acquired information to the cerebellar nuclei. Interestingly, depending on the type of lesion, the redistribution of synaptic plasticity and response timing varied greatly generating specific adaptation patterns. Thus, not only the present work extends the generalization capabilities of the cerebellar spiking model to pathological cases, but also predicts how changes at the neuronal level are distributed across the network, making it usable to infer cerebellar circuit alterations occurring in cerebellar pathologies.
Effect of closed-loop order processing on the time to initial antimicrobial therapy.

PubMed

Panosh, Nicole; Rew, Richardd; Sharpe, Michelle

2012-08-15

The results of a study comparing the average time to initiation of i.v. antimicrobial therapy with closed-versus open-loop order entry and processing are reported. A retrospective cohort study was performed to compare order-to-administration times for initial doses of i.v. antimicrobials before and after a closed-loop order-processing system including computerized prescriber order entry (CPOE) was implemented at a large medical center. A total of 741 i.v. antimicrobial administrations to adult patients during designated five-month preimplementation and postimplementation study periods were assessed. Drug-use reports generated by the pharmacy database were used to identify order-entry times, and medication administration records were reviewed to determine times of i.v. antimicrobial administration. The mean ± S.D. order-to-administration times before and after the implementation of the CPOE system and closed-loop order processing were 3.18 ± 2.60 and 2.00 ± 1.89 hours, respectively, a reduction of 1.18 hours (p < 0.0001). Closed-loop order processing was associated with significant reductions in the average time to initiation of i.v. therapy in all patient care areas evaluated (cardiology, general medicine, and oncology). The study results suggest that CPOE-based closed-loop order processing can play an important role in achieving compliance with current practice guidelines calling for increased efforts to ensure the prompt initiation of i.v. antimicrobials for severe infections (e.g., sepsis, meningitis). Implementation of a closed-loop order-processing system resulted in a significant decrease in order-to-administration times for i.v. antimicrobial therapy.
Sensory feedback in prosthetics: a standardized test bench for closed-loop control.

PubMed

Dosen, Strahinja; Markovic, Marko; Hartmann, Cornelia; Farina, Dario

2015-03-01

Closing the control loop by providing sensory feedback to the user of a prosthesis is an important challenge, with major impact on the future of prosthetics. Developing and comparing closed-loop systems is a difficult task, since there are many different methods and technologies that can be used to implement each component of the system. Here, we present a test bench developed in Matlab Simulink for configuring and testing the closed-loop human control system in standardized settings. The framework comprises a set of connected generic blocks with normalized inputs and outputs, which can be customized by selecting specific implementations from a library of predefined components. The framework is modular and extensible and it can be used to configure, compare and test different closed-loop system prototypes, thereby guiding the development towards an optimal system configuration. The use of the test bench was demonstrated by investigating two important aspects of closed-loop control: performance of different electrotactile feedback interfaces (spatial versus intensity coding) during a pendulum stabilization task and feedforward methods (joystick versus myocontrol) for force control. The first experiment demonstrated that in the case of trained subjects the intensity coding might be superior to spatial coding. In the second experiment, the control of force was rather poor even with a stable and precise control interface (joystick), demonstrating that inherent characteristics of the prosthesis can be an important limiting factor when considering the overall effectiveness of the closed-loop control. The presented test bench is an important instrument for investigating different aspects of human manual control with sensory feedback.
Critical points of the O(n) loop model on the martini and the 3-12 lattices

NASA Astrophysics Data System (ADS)

Ding, Chengxiang; Fu, Zhe; Guo, Wenan

2012-06-01

We derive the critical line of the O(n) loop model on the martini lattice as a function of the loop weight n basing on the critical points on the honeycomb lattice conjectured by Nienhuis [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.49.1062 49, 1062 (1982)]. In the limit n→0 we prove the connective constant μ=1.7505645579⋯ of self-avoiding walks on the martini lattice. A finite-size scaling analysis based on transfer matrix calculations is also performed. The numerical results coincide with the theoretical predictions with a very high accuracy. Using similar numerical methods, we also study the O(n) loop model on the 3-12 lattice. We obtain similarly precise agreement with the critical points given by Batchelor [J. Stat. Phys.JSTPBS0022-471510.1023/A:1023065215233 92, 1203 (1998)].
Gait adaptation to visual kinematic perturbations using a real-time closed-loop brain-computer interface to a virtual reality avatar

NASA Astrophysics Data System (ADS)

Phat Luu, Trieu; He, Yongtian; Brown, Samuel; Nakagome, Sho; Contreras-Vidal, Jose L.

2016-06-01

Objective. The control of human bipedal locomotion is of great interest to the field of lower-body brain-computer interfaces (BCIs) for gait rehabilitation. While the feasibility of closed-loop BCI systems for the control of a lower body exoskeleton has been recently shown, multi-day closed-loop neural decoding of human gait in a BCI virtual reality (BCI-VR) environment has yet to be demonstrated. BCI-VR systems provide valuable alternatives for movement rehabilitation when wearable robots are not desirable due to medical conditions, cost, accessibility, usability, or patient preferences. Approach. In this study, we propose a real-time closed-loop BCI that decodes lower limb joint angles from scalp electroencephalography (EEG) during treadmill walking to control a walking avatar in a virtual environment. Fluctuations in the amplitude of slow cortical potentials of EEG in the delta band (0.1-3 Hz) were used for prediction; thus, the EEG features correspond to time-domain amplitude modulated potentials in the delta band. Virtual kinematic perturbations resulting in asymmetric walking gait patterns of the avatar were also introduced to investigate gait adaptation using the closed-loop BCI-VR system over a period of eight days. Main results. Our results demonstrate the feasibility of using a closed-loop BCI to learn to control a walking avatar under normal and altered visuomotor perturbations, which involved cortical adaptations. The average decoding accuracies (Pearson’s r values) in real-time BCI across all subjects increased from (Hip: 0.18 ± 0.31 Knee: 0.23 ± 0.33 Ankle: 0.14 ± 0.22) on Day 1 to (Hip: 0.40 ± 0.24 Knee: 0.55 ± 0.20 Ankle: 0.29 ± 0.22) on Day 8. Significance. These findings have implications for the development of a real-time closed-loop EEG-based BCI-VR system for gait rehabilitation after stroke and for understanding cortical plasticity induced by a closed-loop BCI-VR system.
Temporary Urine and Brine Stowage System (TUBSS) Materials Selection and Testing

NASA Technical Reports Server (NTRS)

Carrigan, Caitlin; Dries, Kevin; Pensinger, Stuart

2011-01-01

Storing wastewater in the event of a system anomaly is a necessity for closed loop water recovery systems. The temporary urine and brine stowage system (TUBSS) is an assembly used to store and transfer pre-treated urine (PTU) and brine for processing or disposal at a later date. This paper describes the selection and testing of several candidate materials from both a chemical and material strength standpoint. In addition, this paper will provide results of testing as well as lessons learned from the project, culminating in the successful launch of the hardware.
Closed Loop Real-Time Evaluation of Missile Guidance and Control Components: Simulator Hardware/Software Characteristics and Use

DTIC Science & Technology

1974-08-01

Node Control Logic 2-27 2.16 Pitch Channel Frequence Response 2-36 2.17 Yaw Channel Frequency Response 2-37 K 4 2.18 Analog Computer Mechanlzation of...8217S 0 121 £l1:c IL-I. TABLE I Elements of the Slgma 5 Digital Computer System Xerox Model- Performance MIOP Channel Description Number Characteristics...transfer control signals to or from the CPU. The MIOP can handle up to 32 I/0 channels each operating simultaneously, provided the overall data
A Rodent Model of Dynamic Facial Reanimation Using Functional Electrical Stimulation

PubMed Central

Attiah, Mark A.; de Vries, Julius; Richardson, Andrew G.; Lucas, Timothy H.

2017-01-01

Facial paralysis can be a devastating condition, causing disfiguring facial droop, slurred speech, eye dryness, scarring and blindness. This study investigated the utility of closed-loop functional electric stimulation (FES) for reanimating paralyzed facial muscles in a quantitative rodent model. The right buccal and marginal mandibular branches of the rat facial nerve were transected for selective, unilateral paralysis of whisker muscles. Microwire electrodes were implanted bilaterally into the facial musculature for FES and electromyographic (EMG) recording. With the rats awake and head-fixed, whisker trajectories were tracked bilaterally with optical micrometers. First, the relationship between EMG and volitional whisker movement was quantified on the intact side of the face. Second, the effect of FES on whisker trajectories was quantified on the paralyzed side. Third, closed-loop experiments were performed in which the EMG signal on the intact side triggered FES on the paralyzed side to restore symmetric whisking. The results demonstrate a novel in vivo platform for developing control strategies for neuromuscular facial prostheses. PMID:28424583
Algorithms for Efficient Computation of Transfer Functions for Large Order Flexible Systems

NASA Technical Reports Server (NTRS)

Maghami, Peiman G.; Giesy, Daniel P.

1998-01-01

An efficient and robust computational scheme is given for the calculation of the frequency response function of a large order, flexible system implemented with a linear, time invariant control system. Advantage is taken of the highly structured sparsity of the system matrix of the plant based on a model of the structure using normal mode coordinates. The computational time per frequency point of the new computational scheme is a linear function of system size, a significant improvement over traditional, still-matrix techniques whose computational times per frequency point range from quadratic to cubic functions of system size. This permits the practical frequency domain analysis of systems of much larger order than by traditional, full-matrix techniques. Formulations are given for both open- and closed-loop systems. Numerical examples are presented showing the advantages of the present formulation over traditional approaches, both in speed and in accuracy. Using a model with 703 structural modes, the present method was up to two orders of magnitude faster than a traditional method. The present method generally showed good to excellent accuracy throughout the range of test frequencies, while traditional methods gave adequate accuracy for lower frequencies, but generally deteriorated in performance at higher frequencies with worst case errors being many orders of magnitude times the correct values.
Antenna Linear-Quadratic-Gaussian (LQG) Ccontrollers: Properties, Limits of Performance, and Tuning

NASA Technical Reports Server (NTRS)

Gawronski, Wodek K.

2004-01-01

The LQG controllers significantly improve antenna tracking precision, but their tuning is a trial-and-error process. A control engineer has two tools to tune an LQG controller: the choice of coordinate system of the controller, and the selection of weights of the LQG performance index. The paper selects the coordinates of the open-loop model that simplify the shaping of the closed-loop performance. and analyzes the impact of thc weights on the antenna closed-loop bandwidth, disturbance rejection properties, and antenna acceleration. Finally, it presents the LQG controller tuning procedure that rationally shapes the closed-loop performance.
Temperature initiated passive cooling system

DOEpatents

Forsberg, Charles W.

1994-01-01

A passive cooling system for cooling an enclosure only when the enclosure temperature exceeds a maximum standby temperature comprises a passive heat transfer loop containing heat transfer fluid having a particular thermodynamic critical point temperature just above the maximum standby temperature. An upper portion of the heat transfer loop is insulated to prevent two phase operation below the maximum standby temperature.
A control system design approach for flexible spacecraft

NASA Technical Reports Server (NTRS)

Silverberg, L. M.

1985-01-01

A control system design approach for flexible spacecraft is presented. The control system design is carried out in two steps. The first step consists of determining the ideal control system in terms of a desirable dynamic performance. The second step consists of designing a control system using a limited number of actuators that possess a dynamic performance that is close to the ideal dynamic performance. The effects of using a limited number of actuators is that the actual closed-loop eigenvalues differ from the ideal closed-loop eigenvalues. A method is presented to approximate the actual closed-loop eigenvalues so that the calculation of the actual closed-loop eigenvalues can be avoided. Depending on the application, it also may be desirable to apply the control forces as impulses. The effect of digitizing the control to produce the appropriate impulses is also examined.
Software Tools for Developing and Simulating the NASA LaRC CMF Motion Base

NASA Technical Reports Server (NTRS)

Bryant, Richard B., Jr.; Carrelli, David J.

2006-01-01

The NASA Langley Research Center (LaRC) Cockpit Motion Facility (CMF) motion base has provided many design and analysis challenges. In the process of addressing these challenges, a comprehensive suite of software tools was developed. The software tools development began with a detailed MATLAB/Simulink model of the motion base which was used primarily for safety loads prediction, design of the closed loop compensator and development of the motion base safety systems1. A Simulink model of the digital control law, from which a portion of the embedded code is directly generated, was later added to this model to form a closed loop system model. Concurrently, software that runs on a PC was created to display and record motion base parameters. It includes a user interface for controlling time history displays, strip chart displays, data storage, and initializing of function generators used during motion base testing. Finally, a software tool was developed for kinematic analysis and prediction of mechanical clearances for the motion system. These tools work together in an integrated package to support normal operations of the motion base, simulate the end to end operation of the motion base system providing facilities for software-in-the-loop testing, mechanical geometry and sensor data visualizations, and function generator setup and evaluation.
Synthesis of feedback systems with large plant ignorance for prescribed time domain tolerances

NASA Technical Reports Server (NTRS)

Horowitz, I. M.; Sidi, M.

1971-01-01

There is given a minimum-phase plant transfer function, with prescribed bounds on its parameter values. The plant is imbedded in a two-degree-of freedom feedback system, which is to be designed such that the system time response to a deterministic input lies within specified boundaries. Subject to the above, the design should be such as to minimize the effect of sensor noise at the input to the plant. This report presents a design procedure for this purpose, based on frequency response concepts. The time-domain tolerances are translated into equivalent frequency response tolerances. The latter lead to bounds on the loop transmission function in the form of continuous curves on the Nichols chart. The properties of the loop transmission function which satisfy these bounds with minimum effect of sensor noise, are derived.
Modeling of Autovariator Operation as Power Components Adjuster in Adaptive Machine Drives

NASA Astrophysics Data System (ADS)

Balakin, P. D.; Belkov, V. N.; Shtripling, L. O.

2018-01-01

Full application of the available power and stationary mode preservation for the power station (engine) operation of the transport machine under the conditions of variable external loading, are topical issues. The issues solution is possible by means of mechanical drives with the autovaried rate transfer function and nonholonomic constraint of the main driving mediums. Additional to the main motion, controlled motion of the driving mediums is formed by a variable part of the transformed power flow and is implemented by the integrated control loop, functioning only on the basis of the laws of motion. The mathematical model of the mechanical autovariator operation is developed using Gibbs function, acceleration energy; the study results are presented; on their basis, the design calculations of the autovariator driving mediums and constraints, including its automatic control loop, are possible.
Geometrical criteria for characterizing open and closed states of WPD-loop in PTP1B

NASA Astrophysics Data System (ADS)

Shinde, Ranajit Nivrutti; Elizabeth Sobhia, M.

2012-06-01

Distinctive movement of WPD-loop occurs during the catalysis of phosphotyrosine by protein tyrosine phosphatase 1B (PTP1B). This loop is in the "open" state in apo-form whereas it is catalytically competent in the "closed" state. During the closure of this loop, unique hydrogen bond interactions are formed between different residues of the PTP1B. Present study examines such interactions from the available 118 crystal structures of PTP1B. It gives insights into the five novel hydrogen bonds essentially formed in the "closed" loop structures. Additionally, the study provides distance ranges between the atoms involved in the hydrogen bonds. This information can be used as a geometrical criterion in the characterization of conformational state of the WPD-loop especially in the molecular dynamics simulations.
78 FR 20176 - Credit for Renewable Electricity Production, Refined Coal Production, and Indian Coal Production...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-03

... electricity from closed-loop biomass, open-loop biomass, geothermal energy, solar energy, small irrigation..., geothermal energy, solar energy, small irrigation power, municipal solid waste, qualified hydropower... from the qualified energy resources of wind, closed-loop biomass, geothermal energy, and solar energy...

Optimization of the structural and control system for LSS with reduced-order model

NASA Technical Reports Server (NTRS)

Khot, N. S.

1989-01-01

The objective is the simultaneous design of the structural and control system for space structures. The minimum weight of the structure is the objective function, and the constraints are placed on the closed loop distribution of the frequencies and the damping parameters. The controls approach used is linear quadratic regulator with constant feedback. A reduced-order control system is used. The effect of uncontrolled modes is taken into consideration by the model error sensitivity suppression (MESS) technique which modified the weighting parameters for the control forces. For illustration, an ACOSS-FOUR structure is designed for a different number of controlled modes with specified values for the closed loop damping parameters and frequencies. The dynamic response of the optimum designs for an initial disturbance is compared.
Enabling Medical Device Interoperability for the Integrated Clinical Environment

DTIC Science & Technology

2016-02-01

Pajic M, Mangharam R, Sokolsky O, Arney D, Goldman JM, Lee I. Model-Driven Safety Analysis of Closed - Loop Medical Systems. IEEE Transactions on...Manigel J, Osborn D, Roellike T, Weininger S, Westenskow D, “Development of a Standard for Physiologic Closed Loop Controllers in Medical Devices...3 2010. 27. Arney D, Pajic M, Goldman JM, Lee I, Mangharam R, Sokolsky O, “Toward Patient Safety in Closed - Loop Medical Device Systems,” In
Closed Loop Control of Oxygen Delivery and Oxygen Generation

DTIC Science & Technology

2017-08-01

AFRL-SA-WP-SR-2017-0024 Closed Loop Control of Oxygen Delivery and Oxygen Generation Dr. Jay Johannigman1, Richard Branson1...for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO...TITLE AND SUBTITLE Closed Loop Control of Oxygen Delivery and Oxygen Generation 5a. CONTRACT NUMBER FA8650-10-2-6140 5b. GRANT NUMBER
Thermal management systems and methods

DOEpatents

Gering, Kevin L.; Haefner, Daryl R.

2006-12-12

A thermal management system for a vehicle includes a heat exchanger having a thermal energy storage material provided therein, a first coolant loop thermally coupled to an electrochemical storage device located within the first coolant loop and to the heat exchanger, and a second coolant loop thermally coupled to the heat exchanger. The first and second coolant loops are configured to carry distinct thermal energy transfer media. The thermal management system also includes an interface configured to facilitate transfer of heat generated by an internal combustion engine to the heat exchanger via the second coolant loop in order to selectively deliver the heat to the electrochemical storage device. Thermal management methods are also provided.
Sub-Poissonian light and photocurrent shot-noise suppression in closed opto-electronic loop

NASA Technical Reports Server (NTRS)

Masalov, A. V.; Putilin, A. A.; Vasilyev, Michael V.

1994-01-01

We examine experimentally photocurrent noise reduction in the opto-electronic closed loop. Photocurrent noise density 12.5 dB below the shot-noise was observed. So large suppression was not reached in previous experiments and cannot be explained in terms of an ordinary sub-Poissonian light in the loop. We propose the concept of anticorrelation state for the description of light in the loop.
Load compensation in a lean burn natural gas vehicle

NASA Astrophysics Data System (ADS)

Gangopadhyay, Anupam

A new multivariable PI tuning technique is developed in this research that is primarily developed for regulation purposes. Design guidelines are developed based on closed-loop stability. The new multivariable design is applied in a natural gas vehicle to combine idle and A/F ratio control loops. This results in better recovery during low idle operation of a vehicle under external step torques. A powertrain model of a natural gas engine is developed and validated for steady-state and transient operation. The nonlinear model has three states: engine speed, intake manifold pressure and fuel fraction in the intake manifold. The model includes the effect of fuel partial pressure in the intake manifold filling and emptying dynamics. Due to the inclusion of fuel fraction as a state, fuel flow rate into the cylinders is also accurately modeled. A linear system identification is performed on the nonlinear model. The linear model structure is predicted analytically from the nonlinear model and the coefficients of the predicted transfer function are shown to be functions of key physical parameters in the plant. Simulations of linear system and model parameter identification is shown to converge to the predicted values of the model coefficients. The multivariable controller developed in this research could be designed in an algebraic fashion once the plant model is known. It is thus possible to implement the multivariable PI design in an adaptive fashion combining the controller with identified plant model on-line. This will result in a self-tuning regulator (STR) type controller where the underlying design criteria is the multivariable tuning technique designed in this research.
40 CFR 63.166 - Standards: Sampling connection systems.

Code of Federal Regulations, 2013 CFR

2013-07-01

... defined in 40 CFR part 261. (c) In-situ sampling systems and sampling systems without purges are exempt..., closed-loop, or closed-vent system, except as provided in § 63.162(b) of this subpart. Gases displaced...-purge, closed-loop, or closed-vent system as required in paragraph (a) of this section shall: (1) Return...
Metrics of Balance Control for Use in Screening Tests of Vestibular Function

NASA Technical Reports Server (NTRS)

Fiedler, Matthew; Cohen, Helen; Mulavara, Ajitkumar; Peters, Brian; Miller, Chris; Bloomberg, Jacob

2011-01-01

Decrements in balance control have been documented in astronauts after space flight. Reliable measures of balance control are needed for use in postflight field tests at remote landing sites. Diffusion analysis (DA) is a statistical mechanical tool that shows the average difference of the dependent variable on varying time scales. These techniques have been shown to measure differences in open-loop and closed-loop postural control in astronauts and elderly subjects. The goal of this study was to investigate the reliability of these measures of balance control. Eleven subjects were tested using the Clinical Test of Sensory Interaction on Balance: the subject stood with feet together and arms crossed on a stable or compliant surface, with eyes open or closed and with or without head movements in the pitch or yaw plane. Subjects were instrumented with inertial motion sensors attached to their trunk segment. The DA curves for linear acceleration measures were characterized by linear fits measuring open- (Ds) and closed-loop (Dl) control, and their intersection point (X-int, Y-int). Ds and Y-int showed significant differences between the test conditions. Additionally, Ds was correlated with the root mean square (RMS) of the signal, indicating that RMS was dominated by open-loop events (< 0.5 seconds). The Y-int was found to be correlated with the average linear velocity of trunk movements. Thus DA measures could be applied to derive reliable metrics of balance stability during field tests.
Singular Differential Game Numerical Technique and Closed Loop Guidance and Control Strategies,

DTIC Science & Technology

1982-03-01

zero sum games one player tries to minimize and the other player tries to maxwm e payoff functions. In such games a saddle point solu- tion is sought...period- ically in a a-all time interval At tK - ti, i - O,,. e . Whe the game starts running, the pursuer takes a measurement at t 1 t 0 + At and...Loop Solutions to Non-Linear-Zero-Sum Differential Games ," Int. J. Syst., Vol. 7 (5), 1976. 41 . Johnson, D. E ., Convergence Properties of the Method
Fast reactor power plant design having heat pipe heat exchanger

DOEpatents

Huebotter, P.R.; McLennan, G.A.

1984-08-30

The invention relates to a pool-type fission reactor power plant design having a reactor vessel containing a primary coolant (such as liquid sodium), and a steam expansion device powered by a pressurized water/steam coolant system. Heat pipe means are disposed between the primary and water coolants to complete the heat transfer therebetween. The heat pipes are vertically oriented, penetrating the reactor deck and being directly submerged in the primary coolant. A U-tube or line passes through each heat pipe, extended over most of the length of the heat pipe and having its walls spaced from but closely proximate to and generally facing the surrounding walls of the heat pipe. The water/steam coolant loop includes each U-tube and the steam expansion device. A heat transfer medium (such as mercury) fills each of the heat pipes. The thermal energy from the primary coolant is transferred to the water coolant by isothermal evaporation-condensation of the heat transfer medium between the heat pipe and U-tube walls, the heat transfer medium moving within the heat pipe primarily transversely between these walls.
Fast reactor power plant design having heat pipe heat exchanger

DOEpatents

Huebotter, Paul R.; McLennan, George A.

1985-01-01

The invention relates to a pool-type fission reactor power plant design having a reactor vessel containing a primary coolant (such as liquid sodium), and a steam expansion device powered by a pressurized water/steam coolant system. Heat pipe means are disposed between the primary and water coolants to complete the heat transfer therebetween. The heat pipes are vertically oriented, penetrating the reactor deck and being directly submerged in the primary coolant. A U-tube or line passes through each heat pipe, extended over most of the length of the heat pipe and having its walls spaced from but closely proximate to and generally facing the surrounding walls of the heat pipe. The water/steam coolant loop includes each U-tube and the steam expansion device. A heat transfer medium (such as mercury) fills each of the heat pipes. The thermal energy from the primary coolant is transferred to the water coolant by isothermal evaporation-condensation of the heat transfer medium between the heat pipe and U-tube walls, the heat transfer medium moving within the heat pipe primarily transversely between these walls.
Dynamics driving function: new insights from electron transferring flavoproteins and partner complexes.

PubMed

Toogood, Helen S; Leys, David; Scrutton, Nigel S

2007-11-01

Electron transferring flavoproteins (ETFs) are soluble heterodimeric FAD-containing proteins that function primarily as soluble electron carriers between various flavoprotein dehydrogenases. ETF is positioned at a key metabolic branch point, responsible for transferring electrons from up to 10 primary dehydrogenases to the membrane-bound respiratory chain. Clinical mutations of ETF result in the often fatal disease glutaric aciduria type II. Structural and biophysical studies of ETF in complex with partner proteins have shown that ETF partitions the functions of partner binding and electron transfer between (a) a 'recognition loop', which acts as a static anchor at the ETF-partner interface, and (b) a highly mobile redox-active FAD domain. Together, this enables the FAD domain of ETF to sample a range of conformations, some compatible with fast interprotein electron transfer. This 'conformational sampling' enables ETF to recognize structurally distinct partners, whilst also maintaining a degree of specificity. Complex formation triggers mobility of the FAD domain, an 'induced disorder' mechanism contrasting with the more generally accepted models of protein-protein interaction by induced fit mechanisms. We discuss the implications of the highly dynamic nature of ETFs in biological interprotein electron transfer. ETF complexes point to mechanisms of electron transfer in which 'dynamics drive function', a feature that is probably widespread in biology given the modular assembly and flexible nature of biological electron transfer systems.
Learning from adaptive neural dynamic surface control of strict-feedback systems.

PubMed

Wang, Min; Wang, Cong

2015-06-01

Learning plays an essential role in autonomous control systems. However, how to achieve learning in the nonstationary environment for nonlinear systems is a challenging problem. In this paper, we present learning method for a class of n th-order strict-feedback systems by adaptive dynamic surface control (DSC) technology, which achieves the human-like ability of learning by doing and doing with learned knowledge. To achieve the learning, this paper first proposes stable adaptive DSC with auxiliary first-order filters, which ensures the boundedness of all the signals in the closed-loop system and the convergence of tracking errors in a finite time. With the help of DSC, the derivative of the filter output variable is used as the neural network (NN) input instead of traditional intermediate variables. As a result, the proposed adaptive DSC method reduces greatly the dimension of NN inputs, especially for high-order systems. After the stable DSC design, we decompose the stable closed-loop system into a series of linear time-varying perturbed subsystems. Using a recursive design, the recurrent property of NN input variables is easily verified since the complexity is overcome using DSC. Subsequently, the partial persistent excitation condition of the radial basis function NN is satisfied. By combining a state transformation, accurate approximations of the closed-loop system dynamics are recursively achieved in a local region along recurrent orbits. Then, the learning control method using the learned knowledge is proposed to achieve the closed-loop stability and the improved control performance. Simulation studies are performed to demonstrate the proposed scheme can not only reuse the learned knowledge to achieve the better control performance with the faster tracking convergence rate and the smaller tracking error but also greatly alleviate the computational burden because of reducing the number and complexity of NN input variables.
Dynamic graciloplasty for urinary incontinence: the potential for sequential closed-loop stimulation.

PubMed

Zonnevijlle, Erik D H; Perez-Abadia, Gustavo; Stremel, Richard W; Maldonado, Claudio J; Kon, Moshe; Barker, John H

2003-11-01

Muscle tissue transplantation applied to regain or dynamically assist contractile functions is known as 'dynamic myoplasty'. Success rates of clinical applications are unpredictable, because of lack of endurance, ischemic lesions, abundant scar formation and inadequate performance of tasks due to lack of refined control. Electrical stimulation is used to control dynamic myoplasties and should be improved to reduce some of these drawbacks. Sequential segmental neuromuscular stimulation improves the endurance and closed-loop control offers refinement in rate of contraction of the muscle, while function-controlling stimulator algorithms present the possibility of performing more complex tasks. An acute feasibility study was performed in anaesthetised dogs combining these techniques. Electrically stimulated gracilis-based neo-sphincters were compared to native sphincters with regard to their ability to maintain continence. Measurements were made during fast bladder pressure changes, static high bladder pressure and slow filling of the bladder, mimicking among others posture changes, lifting heavy objects and diuresis. In general, neo-sphincter and native sphincter performance showed no significant difference during these measurements. However, during high bladder pressures reaching 40 cm H(2)O the neo-sphincters maintained positive pressure gradients, whereas most native sphincters relaxed. During slow filling of the bladder the neo-sphincters maintained a controlled positive pressure gradient for a prolonged time without any form of training. Furthermore, the accuracy of these maintained pressure gradients proved to be within the limits set up by the native sphincters. Refinements using more complicated self-learning function-controlling algorithms proved to be effective also and are briefly discussed. In conclusion, a combination of sequential stimulation, closed-loop control and function-controlling algorithms proved feasible in this dynamic graciloplasty-model. Neo-sphincters were created, which would probably provide an acceptable performance, when the stimulation system could be implanted and further tested. Sizing this technique down to implantable proportions seems to be justified and will enable exploration of the possible benefits.
"It Is Definitely a Game Changer": A Qualitative Study of Experiences with In-home Overnight Closed-Loop Technology Among Adults with Type 1 Diabetes.

PubMed

Hendrieckx, Christel; Poole, Lucinda A; Sharifi, Amin; Jayawardene, Dilshani; Loh, Margaret M; Horsburgh, Jodie C; Bach, Leon A; Colman, Peter G; Kumareswaran, Kavita; Jenkins, Alicia J; MacIsaac, Richard J; Ward, Glenn M; Grosman, Benyamin; Roy, Anirban; O'Neal, David N; Speight, Jane

2017-07-01

This qualitative study explored trial participants' experiences of four nights of in-home closed loop. Sixteen adults with type 1 diabetes, who completed a randomized crossover trial, were interviewed after four consecutive nights of closed-loop. Interviews were audio recorded, transcribed, and analyzed with a coding framework developed to identify the main themes. Participants had a mean age of 42 ± 10 years, nine were women; mean diabetes duration was 27 ± 7 years, and all were using insulin pumps. Overall, first impressions were positive. Participants found closed-loop easy to use and understand. Most experienced more stable overnight glucose levels, although for some these were similar to usual care or higher than they expected. Compared with their usual treatment, they noticed the proactive nature of the closed-loop, being able to predict trends and deliver micro amounts of insulin. Most reported technical glitches or inconveniences during one or more nights, such as transmission problems, problematic connectivity between devices, ongoing alarms despite addressing low glucose levels, and sensor inaccuracy. Remote monitoring by the trial team and their own hypoglycemic awareness contributed to feelings of trust and safety. Although rare, safety concerns were raised, related to feeling unsure whether the system would respond in time to falling glucose levels. This study provides relevant insights for implementation of closed-loop in the real world. For people with diabetes who are less familiar with technology, remote monitoring for the first few days may provide reassurance, strengthen their trust/skills, and make closed-loop an acceptable option for more people with type 1 diabetes.
Lateral-Directional Eigenvector Flying Qualities Guidelines for High Performance Aircraft

NASA Technical Reports Server (NTRS)

Davidson, John B.; Andrisani, Dominick, II

1996-01-01

This report presents the development of lateral-directional flying qualities guidelines with application to eigenspace (eigenstructure) assignment methods. These guidelines will assist designers in choosing eigenvectors to achieve desired closed-loop flying qualities or performing trade-offs between flying qualities and other important design requirements, such as achieving realizable gain magnitudes or desired system robustness. This has been accomplished by developing relationships between the system's eigenvectors and the roll rate and sideslip transfer functions. Using these relationships, along with constraints imposed by system dynamics, key eigenvector elements are identified and guidelines for choosing values of these elements to yield desirable flying qualities have been developed. Two guidelines are developed - one for low roll-to-sideslip ratio and one for moderate-to-high roll-to-sideslip ratio. These flying qualities guidelines are based upon the Military Standard lateral-directional coupling criteria for high performance aircraft - the roll rate oscillation criteria and the sideslip excursion criteria. Example guidelines are generated for a moderate-to-large, an intermediate, and low value of roll-to-sideslip ratio.
A long time low drift integrator with temperature control

NASA Astrophysics Data System (ADS)

Zhang, Donglai; Yan, Xiaolan; Zhang, Enchao; Pan, Shimin

2016-10-01

The output of an operational amplifier always contains signals that could not have been predicted, even with knowledge of the input and an accurately determined closed-loop transfer function. These signals lead to integrator zero-drift over time. A new type of integrator system with a long-term low-drift characteristic has therefore been designed. The integrator system is composed of a temperature control module and an integrator module. The aluminum printed circuit board of the integrator is glued to a thermoelectric cooler to maintain the electronic components at a stable temperature. The integration drift is automatically compensated using an analog-to-digital converter/proportional integration/digital-to-analog converter control circuit. Performance testing in a standard magnet shows that the proposed integrator, which has an integration time constant of 10 ms, has a low integration drift (<5 mV) over 1000 s after repeated measurements. The integrator can be used for magnetic flux measurements in most tokamaks and in the wire rope nondestructive test.
Power Approaches for Implantable Medical Devices

PubMed Central

Ben Amar, Achraf; Kouki, Ammar B.; Cao, Hung

2015-01-01

Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources. PMID:26580626
A long time low drift integrator with temperature control.

PubMed

Zhang, Donglai; Yan, Xiaolan; Zhang, Enchao; Pan, Shimin

2016-10-01

The output of an operational amplifier always contains signals that could not have been predicted, even with knowledge of the input and an accurately determined closed-loop transfer function. These signals lead to integrator zero-drift over time. A new type of integrator system with a long-term low-drift characteristic has therefore been designed. The integrator system is composed of a temperature control module and an integrator module. The aluminum printed circuit board of the integrator is glued to a thermoelectric cooler to maintain the electronic components at a stable temperature. The integration drift is automatically compensated using an analog-to-digital converter/proportional integration/digital-to-analog converter control circuit. Performance testing in a standard magnet shows that the proposed integrator, which has an integration time constant of 10 ms, has a low integration drift (<5 mV) over 1000 s after repeated measurements. The integrator can be used for magnetic flux measurements in most tokamaks and in the wire rope nondestructive test.
Functional Association between Regulatory RNAs and the Annexins

PubMed Central

Monastyrskaya, Katia

2018-01-01

Cells respond to pathophysiological states by activation of stress-induced signalling. Regulatory non-coding microRNAs (miRNAs) often form stable feed-forward loops which ensure prolongation of the signal, contributing to sustained activation. Members of the annexin protein family act as sensors for Ca2+, pH, and lipid second messengers, and regulate various signalling pathways. Recently, annexins were reported to participate in feedback loops, suppressing miRNA synthesis and attenuating stress-induced dysregulation of gene expression. They can directly or indirectly associate with RNAs, and are transferred between the cells in exosomes and shed microvesicles. The ability of annexins to recruit other proteins and miRNAs into exosomes implicates them in control of cell–cell interactions, affecting the adaptive responses and remodelling processes during disease. The studies summarized in this Review point to an emerging role of annexins in influencing the synthesis, localisation, and transfer of regulatory RNAs. PMID:29462943

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