A 12 GHz wavelength spacing multi-wavelength laser source for wireless communication systems

NASA Astrophysics Data System (ADS)

Peng, P. C.; Shiu, R. K.; Bitew, M. A.; Chang, T. L.; Lai, C. H.; Junior, J. I.

2017-08-01

This paper presents a multi-wavelength laser source with 12 GHz wavelength spacing based on a single distributed feedback laser. A light wave generated from the distributed feedback laser is fed into a frequency shifter loop consisting of 50:50 coupler, dual-parallel Mach-Zehnder modulator, optical amplifier, optical filter, and polarization controller. The frequency of the input wavelength is shifted and then re-injected into the frequency shifter loop. By re-injecting the shifted wavelengths multiple times, we have generated 84 optical carriers with 12 GHz wavelength spacing and stable output power. For each channel, two wavelengths are modulated by a wireless data using the phase modulator and transmitted through a 25 km single mode fiber. In contrast to previously developed schemes, the proposed laser source does not incur DC bias drift problem. Moreover, it is a good candidate for radio-over-fiber systems to support multiple users using a single distributed feedback laser.

A Surface-Coupled Optical Trap with 1-bp Precision via Active Stabilization

PubMed Central

Okoniewski, Stephen R.; Carter, Ashley R.; Perkins, Thomas T.

2017-01-01

Optical traps can measure bead motions with Å-scale precision. However, using this level of precision to infer 1-bp motion of molecular motors along DNA is difficult, since a variety of noise sources degrade instrumental stability. In this chapter, we detail how to improve instrumental stability by (i) minimizing laser pointing, mode, polarization, and intensity noise using an acousto-optical-modulator mediated feedback loop and (ii) minimizing sample motion relative to the optical trap using a 3-axis piezo-electric-stage mediated feedback loop. These active techniques play a critical role in achieving a surface stability of 1 Å in 3D over tens of seconds and a 1-bp stability and precision in a surface-coupled optical trap over a broad bandwidth (Δf = 0.03–2 Hz) at low force (6 pN). These active stabilization techniques can also aid other biophysical assays that would benefit from improved laser stability and/or Å-scale sample stability, such as atomic force microscopy and super-resolution imaging. PMID:27844426

Optical atomic magnetometer

DOEpatents

Budker, Dmitry; Higbie, James; Corsini, Eric P.

2013-11-19

An optical atomic magnetometers is provided operating on the principles of nonlinear magneto-optical rotation. An atomic vapor is optically pumped using linearly polarized modulated light. The vapor is then probed using a non-modulated linearly polarized light beam. The resulting modulation in polarization angle of the probe light is detected and used in a feedback loop to induce self-oscillation at the resonant frequency.

An integrated optical sensor for GMAW feedback control

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

Taylor, P.L.; Watkins, A.D.; Larsen, E.D.

1992-08-01

The integrated optical sensor (IOS) is a multifunction feedback control sensor for arc welding, that is computer automated and independent of significant operator interaction. It is based on three major ``off-the-shelf`` components: a charged coupled device (CCD) camera, a diode laser, and a processing computer. The sensor head is compact and lightweight to avoid interference with weld head mobility, hardened to survive the harsh operating environment, and free of specialized cooling and power requirements. The sensor is positioned behind the GMAW torch and measures weld pool position and width, standoff distance, and postweld centerline cooling rate. Weld pool position andmore » width are used in a feedback loop, by the weld controller, to track the weld pool relative to the weld joint, thus allowing compensation for such phenomena as arc blow. Sensor stand off distance is used in a feedback loop to control the contact tip to base metal distance during the welding process. Cooling rate information is used to infer the final metallurgical state of the weld bead and heat affected zone, thereby providing a means of controlling post weld mechanical properties.« less

An integrated optical sensor for GMAW feedback control

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

Taylor, P.L.; Watkins, A.D.; Larsen, E.D.

1992-01-01

The integrated optical sensor (IOS) is a multifunction feedback control sensor for arc welding, that is computer automated and independent of significant operator interaction. It is based on three major off-the-shelf'' components: a charged coupled device (CCD) camera, a diode laser, and a processing computer. The sensor head is compact and lightweight to avoid interference with weld head mobility, hardened to survive the harsh operating environment, and free of specialized cooling and power requirements. The sensor is positioned behind the GMAW torch and measures weld pool position and width, standoff distance, and postweld centerline cooling rate. Weld pool position andmore » width are used in a feedback loop, by the weld controller, to track the weld pool relative to the weld joint, thus allowing compensation for such phenomena as arc blow. Sensor stand off distance is used in a feedback loop to control the contact tip to base metal distance during the welding process. Cooling rate information is used to infer the final metallurgical state of the weld bead and heat affected zone, thereby providing a means of controlling post weld mechanical properties.« less

Iterative color-multiplexed, electro-optical processor.

PubMed

Psaltis, D; Casasent, D; Carlotto, M

1979-11-01

A noncoherent optical vector-matrix multiplier using a linear LED source array and a linear P-I-N photodiode detector array has been combined with a 1-D adder in a feedback loop. The resultant iterative optical processor and its use in solving simultaneous linear equations are described. Operation on complex data is provided by a novel color-multiplexing system.

A Surface-Coupled Optical Trap with 1-bp Precision via Active Stabilization.

PubMed

Okoniewski, Stephen R; Carter, Ashley R; Perkins, Thomas T

2017-01-01

Optical traps can measure bead motions with Å-scale precision. However, using this level of precision to infer 1-bp motion of molecular motors along DNA is difficult, since a variety of noise sources degrade instrumental stability. In this chapter, we detail how to improve instrumental stability by (1) minimizing laser pointing, mode, polarization, and intensity noise using an acousto-optical-modulator mediated feedback loop and (2) minimizing sample motion relative to the optical trap using a three-axis piezo-electric-stage mediated feedback loop. These active techniques play a critical role in achieving a surface stability of 1 Å in 3D over tens of seconds and a 1-bp stability and precision in a surface-coupled optical trap over a broad bandwidth (Δf = 0.03-2 Hz) at low force (6 pN). These active stabilization techniques can also aid other biophysical assays that would benefit from improved laser stability and/or Å-scale sample stability, such as atomic force microscopy and super-resolution imaging.

Discovery Channel Telescope active optics system early integration and test

NASA Astrophysics Data System (ADS)

Venetiou, Alexander J.; Bida, Thomas A.

2012-09-01

The Discovery Channel Telescope (DCT) is a 4.3-meter telescope with a thin meniscus primary mirror (M1) and a honeycomb secondary mirror (M2). The optical design is an f/6.1 Ritchey-Chrétien (RC) with an unvignetted 0.5° Field of View (FoV) at the Cassegrain focus. We describe the design, implementation and performance of the DCT active optics system (AOS). The DCT AOS maintains collimation and controls the figure of the mirror to provide seeing-limited images across the focal plane. To minimize observing overhead, rapid settling times are achieved using a combination of feed-forward and low-bandwidth feedback control using a wavefront sensing system. In 2011, we mounted a Shack-Hartmann wavefront sensor at the prime focus of M1, the Prime Focus Test Assembly (PFTA), to test the AOS with the wavefront sensor, and the feedback loop. The incoming wavefront is decomposed using Zernike polynomials, and the mirror figure is corrected with a set of bending modes. Components of the system that we tested and tuned included the Zernike to Bending Mode transformations. We also started open-loop feed-forward coefficients determination. In early 2012, the PFTA was replaced by M2, and the wavefront sensor moved to its normal location on the Cassegrain instrument assembly. We present early open loop wavefront test results with the full optical system and instrument cube, along with refinements to the overall control loop operating at RC Cassegrain focus.

Through-wafer interrogation of microstructure motion for MEMS feedback control

NASA Astrophysics Data System (ADS)

Dawson, Jeremy M.; Chen, Jingdong; Brown, Kolin S.; Famouri, Parviz F.; Hornak, Lawrence A.

1999-09-01

Closed-loop MEMS control enables mechanical microsystems to adapt to the demands of the environment which they are actuating opening a new window of opportunity for future MEMS applications. Planar diffractive optical microsystems have the potential to enable the integrated optical interrogation of MEMS microstructure position fully decoupled from the means of mechanical actuation which is central to realization of feedback control. This paper presents the results of initial research evaluating through-wafer optical microsystems for MEMS integrated optical monitoring. Positional monitoring results obtained from a 1.3 micrometer wavelength through- wafer free-space optical probe of a lateral comb resonator fabricated using the Multi-User MEMS Process Service (MUMPS) are presented. Given the availability of positional information via probe signal feedback, a simulation of the application of nonlinear sliding control is presented illustrating position control of the lateral comb resonator structure.

Phase-Locked Optical Generation of mmW/THz Signals

DTIC Science & Technology

2009-11-01

22 6.2. TIA (Trans-Impedance Amplifier ...24 6.3. Variable gain Amplifier ...loop architectures. Generate models including detector impulse response, feedback amplifier impulse response and laser current tuning response

Secure free-space communication, turbulence mitigation, and other applications using acousto-optic chaos.

PubMed

Chatterjee, Monish R; Mohamed, Ali; Almehmadi, Fares S

2018-04-01

Use of acousto-optic (A-O) chaos via the feedback loop in a Bragg cell for signal encryption began as a conceptual demonstration around 2008. Radio frequency (RF) chaos from a hybrid A-O feedback device may be used for secure communications of analog and digital signals. In this paper, modulation of RF chaos via first-order feedback is discussed with results corroborated by nonlinear dynamics, bifurcation maps, and Lyapunov analyses. Applications based on encryption with profiled optical beams, and extended to medical and embedded steganographic data, and video signals are discussed. It is shown that the resulting encryption is significantly robust with key tolerances potentially less than 0.1%. Results are also presented for the use of chaotic encryption for image restoration during propagation through atmospheric turbulence.

Integrated otpical monitoring of MEMS for closed-loop control

NASA Astrophysics Data System (ADS)

Dawson, Jeremy M.; Wang, Limin; McCormick, W. B.; Rittenhouse, S. A.; Famouri, Parviz F.; Hornak, Lawrence A.

2003-01-01

Robust control and failure assessment of MEMS employed in physically demanding, mission critical applications will allow for higher degrees of quality assurance in MEMS operation. Device fault detection and closed-loop control require detailed knowledge of the operational states of MEMS over the lifetime of the device, obtained by a means decoupled from the system. Preliminary through-wafer optical monitoring research efforts have shown that through-wafer optical probing is suitable for characterizing and monitoring the behavior of MEMS, and can be implemented in an integrated optical monitoring package for continuous in-situ device monitoring. This presentation will discuss research undertaken to establish integrated optical device metrology for closed-loop control of a MUMPS fabricated lateral harmonic oscillator. Successful linear closed-loop control results using a through-wafer optical microprobe position feedback signal will be presented. A theoretical optical output field intensity study of grating structures, fabricated on the shuttle of the resonator, was performed to improve the position resolution of the optical microprobe position signal. Through-wafer microprobe signals providing a positional resolution of 2 μm using grating structures will be shown, along with initial binary Fresnel diffractive optical microelement design layout, process development, and testing results. Progress in the design, fabrication, and test of integrated optical elements for multiple microprobe signal delivery and recovery will be discussed, as well as simulation of device system model parameter changes for failure assessment.

Optical microresonator for application to an opto-electronic oscillator

NASA Astrophysics Data System (ADS)

Wu, Yu-Mei; Vivien, Laurent; Cassan, Eric; Luong, Vu Hai Nam; Nguyen, Lam Duy; Journet, Bernard

2010-02-01

Optoelectronic oscillators are classically based on a feedback fiber loop acting as a delay line for high spectral purity. One of the problems due to long fiber loops is the size and the requirement of temperature control. Going toward integrated solutions requires the introduction of optical resonators with a very high quality factor. A structure based on silicon on insulator material has been designed for application to an oscillator working at 8 GHz. The micro-resonator has a stadium shape with a ridge of 30 nm height, 1 μm width, a millimetric radius and a gap of some microns in agreement with the required free spectral range. A quality factor of 500000 can be achieved leading to an equivalent fiber loop of 2 km.

Recognition of the optical packet header for two channels utilizing the parallel reservoir computing based on a semiconductor ring laser

NASA Astrophysics Data System (ADS)

Bao, Xiurong; Zhao, Qingchun; Yin, Hongxi; Qin, Jie

2018-05-01

In this paper, an all-optical parallel reservoir computing (RC) system with two channels for the optical packet header recognition is proposed and simulated, which is based on a semiconductor ring laser (SRL) with the characteristic of bidirectional light paths. The parallel optical loops are built through the cross-feedback of the bidirectional light paths where every optical loop can independently recognize each injected optical packet header. Two input signals are mapped and recognized simultaneously by training all-optical parallel reservoir, which is attributed to the nonlinear states in the laser. The recognition of optical packet headers for two channels from 4 bits to 32 bits is implemented through the simulation optimizing system parameters and therefore, the optimal recognition error ratio is 0. Since this structure can combine with the wavelength division multiplexing (WDM) optical packet switching network, the wavelength of each channel of optical packet headers for recognition can be different, and a better recognition result can be obtained.

Optical mapping system with real-time control capability.

PubMed

Iravanian, Shahriar; Christini, David J

2007-10-01

Real-time, closed-loop intervention is an emerging experiment-control method that promises to provide invaluable new insight into cardiac electrophysiology. One example is the investigation of closed-loop feedback control of cardiac activity (e.g., alternans) as a possible method of preventing arrhythmia onset. To date, such methods have been investigated only in vitro using microelectrode systems, which are hindered by poor spatial resolution and are not well suited for atrial or ventricular tissue preparations. We have developed a system that uses optical mapping techniques and an electrical stimulator as the sensory and effector arms, respectively, of a closed-loop, real-time control system. The system consists of a 2,048 x 1 pixel line-scan charge-coupled device camera that records optical signals from the tissue. Custom-image processing and control software, which is implemented on top of a hard real-time operation system (RTAI Linux), process the data and make control decisions with a deterministic delay of <1 ms. The system is tested in two ways: 1) it is used to control, in real time, simulated optical signals of electrical alternans; and 2) it uses precisely timed, feedback-controlled initiation of antitachycardia pacing to terminate reentrant arrhythmias in an arterially perfused swine right ventricle stained with voltage-sensitive fluorescent dye 4{beta-[2-(di-n-butylamino)-6-napathy]vinyl}pyridinium (di-4-ANEPPS). Thus real-time control of cardiac activity using optical mapping techniques is feasible. Such a system is attractive because it offers greater measurement resolution than the electrode-based systems with which real-time control has been used previously.

Feedback module for evaluating optical-power stabilization methods

NASA Astrophysics Data System (ADS)

Downing, John

2016-03-01

A feedback module for evaluating the efficacy of optical-power stabilization without thermoelectric coolers (TECs) is described. The module comprises a pickoff optic for sampling a light beam, a photodiode for converting the sample power to electrical current, and a temperature sensor. The components are mounted on an optical bench that makes accurate (0.05°) beam alignment practical as well as providing high thermal-conductivity among the components. The module can be mounted on existing light sources or the components can be incorporated in new designs. Evaluations of optical and electronic stabilization methods are also reported. The optical method combines a novel, weakly reflective, weakly polarizing coating on the pickoff optic with a photodiode and an automatic-power-control (APC) circuit in a closed loop. The shift of emitter wavelength with temperature, coupled with the wavelength-dependent reflectance of the pickoff optic, enable the APC circuit to compensate for temperature errors. In the electronic method, a mixed-signal processor in a quasiclosed loop generates a control signal from temperature and photocurrent inputs and feeds it back to an APC circuit to compensate for temperature errors. These methods result in temperature coefficients less than 20 ppm/°C and relative rms power equal to 05% for the optical method and 0.02% for the electronic method. The later value represents an order of magnitude improvement over rms specifications for cooled, laser-diode modules and a five-fold improvement in wall-plug efficiency is achieved by eliminating TECs.

Maximizing the security of chaotic optical communications.

PubMed

Hou, T T; Yi, L L; Yang, X L; Ke, J X; Hu, Y; Yang, Q; Zhou, P; Hu, W S

2016-10-03

The practical application of chaotic optical communications has been limited by two aspects: the difficulty in concealing the time delay - a critical security parameter in feedback chaotic systems, and the difficulty of significantly enlarging the key space without complicating the implementation. Here we propose an architecture to break the above limits. By introducing a frequency-dependent group delay module with frequency tuning resolution of 1 MHz into the chaotic feedback loop, we demonstrate excellent time delay concealment effect, and an additional huge key space of 10⁴⁸ can be achieved at the same time. The effectiveness is proved by both numerical simulation and experiment. Besides, the proposed scheme is compatible with the existing commercial optical communication systems, thus pave the way for high-speed secure optical communications.

Near-IR laser frequency standard stabilized using FM-spectroscopy

NASA Astrophysics Data System (ADS)

Ružička, Bohdan; Číp, Ondřej; Lazar, Josef

2006-02-01

At the present time fiber-optics and optical communication are in rapid progress. Modern technologies such as DWDM (Dense Wavelength Division Multiplex) need precise stability of laser frequencies. According to this fact, requirements of new etalons of optical frequencies in the telecommunication band is rapidly growing. Lasers working in near infrared telecommunication band (1500-1600 nm) can be stabilized to 12C IIH II or 13C IIH II (acetylene) gas absorption lines. The acetylene gas absorption has been widely studied and accepted by international bodies of standardization as a primary wavelength reference in the near infrared band around 1550nm. Our aim was to design and develop a compact fibre optics laser system generating coherent light in near-JR band with high frequency stability (at least 1.10 -8). This system should become a base for realization of a primary frequency standard for optical communications in the Czech Republic. Such an etalon will be needed for calibration of wavelength-meters and spectral analysers for DWDM communication systems. We are co-operating with CMI (Czech Metrology Institute) on this project. We present stabilized laser system based on a single frequency DFB (Distributed Feedback) laser diode with a narrow spectral profile. The laser is pre-stabilized by means of the FM-spectroscopy on a passive resonator. Thanks to a fast feed-back loop we are able to improve spectral characteristics of the laser. The laser frequency is locked by a relatively slow second feed-back loop on an absorption line of acetylene vapour which is sealed in a cell under the optimised pressure.

Theoretical Design of a Depolarized Interferometric Fiber-Optic Gyroscope (IFOG) on SMF-28 Single-Mode Standard Optical Fiber Based on Closed-Loop Sinusoidal Phase Modulation with Serrodyne Feedback Phase Modulation Using Simulation Tools for Tactical and Industrial Grade Applications

PubMed Central

Pérez, Ramón José; Álvarez, Ignacio; Enguita, José María

2016-01-01

This article presents, by means of computational simulation tools, a full analysis and design of an Interferometric Fiber-Optic Gyroscope (IFOG) prototype based on a closed-loop configuration with sinusoidal bias phase- modulation. The complete design of the different blocks, optical and electronic, is presented, including some novelties as the sinusoidal bias phase-modulation and the use of an integrator to generate the serrodyne phase-modulation signal. The paper includes detailed calculation of most parameter values, and the plots of the resulting signals obtained from simulation tools. The design is focused in the use of a standard single-mode optical fiber, allowing a cost competitive implementation compared to commercial IFOG, at the expense of reduced sensitivity. The design contains an IFOG model that accomplishes tactical and industrial grade applications (sensitivity ≤ 0.055 °/h). This design presents two important properties: (1) an optical subsystem with advanced conception: depolarization of the optical wave by means of Lyot depolarizers, which allows to use a sensing coil made by standard optical fiber, instead by polarization maintaining fiber, which supposes consequent cost savings and (2) a novel and simple electronic design that incorporates a linear analog integrator with reset in feedback chain, this integrator generating a serrodyne voltage-wave to apply to Phase-Modulator (PM), so that it will be obtained the interferometric phase cancellation. This particular feedback design with sawtooth-wave generated signal for a closed-loop configuration with sinusoidal bias phase modulation has not been reported till now in the scientific literature and supposes a considerable simplification with regard to previous designs based on similar configurations. The sensing coil consists of an 8 cm average diameter spool that contains 300 m of standard single-mode optical-fiber (SMF-28 type) realized by quadrupolar winding. The working wavelength will be 1310 nm. The theoretical calculated values of threshold sensitivity and dynamic range for this prototype are 0.052 °/h and 101.38 dB (from ±1.164 × 10−5 °/s up to ±78.19 °/s), respectively. The Scale-Factor (SF) non-linearity for this model is 5.404% relative to full scale, this value being obtained from data simulation results. PMID:27128924

Theoretical Design of a Depolarized Interferometric Fiber-Optic Gyroscope (IFOG) on SMF-28 Single-Mode Standard Optical Fiber Based on Closed-Loop Sinusoidal Phase Modulation with Serrodyne Feedback Phase Modulation Using Simulation Tools for Tactical and Industrial Grade Applications.

PubMed

Pérez, Ramón José; Álvarez, Ignacio; Enguita, José María

2016-04-27

This article presents, by means of computational simulation tools, a full analysis and design of an Interferometric Fiber-Optic Gyroscope (IFOG) prototype based on a closed-loop configuration with sinusoidal bias phase- modulation. The complete design of the different blocks, optical and electronic, is presented, including some novelties as the sinusoidal bias phase-modulation and the use of an integrator to generate the serrodyne phase-modulation signal. The paper includes detailed calculation of most parameter values, and the plots of the resulting signals obtained from simulation tools. The design is focused in the use of a standard single-mode optical fiber, allowing a cost competitive implementation compared to commercial IFOG, at the expense of reduced sensitivity. The design contains an IFOG model that accomplishes tactical and industrial grade applications (sensitivity ≤ 0.055 °/h). This design presents two important properties: (1) an optical subsystem with advanced conception: depolarization of the optical wave by means of Lyot depolarizers, which allows to use a sensing coil made by standard optical fiber, instead by polarization maintaining fiber, which supposes consequent cost savings and (2) a novel and simple electronic design that incorporates a linear analog integrator with reset in feedback chain, this integrator generating a serrodyne voltage-wave to apply to Phase-Modulator (PM), so that it will be obtained the interferometric phase cancellation. This particular feedback design with sawtooth-wave generated signal for a closed-loop configuration with sinusoidal bias phase modulation has not been reported till now in the scientific literature and supposes a considerable simplification with regard to previous designs based on similar configurations. The sensing coil consists of an 8 cm average diameter spool that contains 300 m of standard single-mode optical-fiber (SMF-28 type) realized by quadrupolar winding. The working wavelength will be 1310 nm. The theoretical calculated values of threshold sensitivity and dynamic range for this prototype are 0.052 °/h and 101.38 dB (from ±1.164 × 10(-5) °/s up to ±78.19 °/s), respectively. The Scale-Factor (SF) non-linearity for this model is 5.404% relative to full scale, this value being obtained from data simulation results.

Coherent feedback control of a single qubit in diamond

NASA Astrophysics Data System (ADS)

Hirose, Masashi; Cappellaro, Paola

2016-04-01

Engineering desired operations on qubits subjected to the deleterious effects of their environment is a critical task in quantum information processing, quantum simulation and sensing. The most common approach relies on open-loop quantum control techniques, including optimal-control algorithms based on analytical or numerical solutions, Lyapunov design and Hamiltonian engineering. An alternative strategy, inspired by the success of classical control, is feedback control. Because of the complications introduced by quantum measurement, closed-loop control is less pervasive in the quantum setting and, with exceptions, its experimental implementations have been mainly limited to quantum optics experiments. Here we implement a feedback-control algorithm using a solid-state spin qubit system associated with the nitrogen vacancy centre in diamond, using coherent feedback to overcome the limitations of measurement-based feedback, and show that it can protect the qubit against intrinsic dephasing noise for milliseconds. In coherent feedback, the quantum system is connected to an auxiliary quantum controller (ancilla) that acquires information about the output state of the system (by an entangling operation) and performs an appropriate feedback action (by a conditional gate). In contrast to open-loop dynamical decoupling techniques, feedback control can protect the qubit even against Markovian noise and for an arbitrary period of time (limited only by the coherence time of the ancilla), while allowing gate operations. It is thus more closely related to quantum error-correction schemes, although these require larger and increasing qubit overheads. Increasing the number of fresh ancillas enables protection beyond their coherence time. We further evaluate the robustness of the feedback protocol, which could be applied to quantum computation and sensing, by exploring a trade-off between information gain and decoherence protection, as measurement of the ancilla-qubit correlation after the feedback algorithm voids the protection, even if the rest of the dynamics is unchanged.

Distributed meandering waveguides (DMWs) for novel photonic circuits (Conference Presentation)

NASA Astrophysics Data System (ADS)

Dag, Ceren B.; Anil, Mehmet Ali; Serpengüzel, Ali

2017-05-01

Meandering waveguide distributed feedback structures are novel integrated photonic lightwave and microwave circuit elements. Meandering waveguide distributed feedback structures with a variety of spectral responses can be designed for a variety of lightwave and microwave circuit element functions. Distributed meandering waveguide (DMW) structures [1] show a variety of spectral behaviors with respect to the number of meandering loop mirrors (MLMs) [2] used in their composition as well as their internal coupling constants (Cs). DMW spectral behaviors include Fano resonances, coupled resonator induced transparency (CRIT), notch, add-drop, comb, and hitless filters. What makes the DMW special is the self-coupling property intrinsic to the DMW's nature. The basic example of DMW's nature is motivated through the analogy between the so-called symmetric meandering resonator (SMR), which consists of two coupled MLMs, and the resonator enhanced Mach-Zehnder interferometer (REMZI) [3]. A SMR shows the same spectral characteristics of Fano resonances with its self-coupling property, similar to the single, distributed and binary self coupled optical waveguide (SCOW) resonators [4]. So far DMWs have been studied for their electric field intensity, phase [5] and phasor responses [6]. The spectral analysis is performed using the coupled electric field analysis and the generalization of single meandering loop mirrors to multiple meandering distributed feedback structures is performed with the transfer matrix method. The building block of the meandering waveguide structures, the meandering loop mirror (MLM), is the integrated analogue of the fiber optic loop mirrors. The meandering resonator (MR) is composed of two uncoupled MLM's. The meandering distributed feedback (MDFB) structure is the DFB of the MLM. The symmetric MR (SMR) is composed of two coupled MLM's, and has the characteristics of a Fano resonator in the general case, and tunable power divider or tunable hitless filter in special cases. The antisymmetric MR (AMR) is composed of two coupled MLM's. The AMR has the characteristics of an add-drop filter in the general case, and coupled resonator induced transparency (CRIT) filter in a special case. The symmetric MDFB (SMDFB) is composed of multiple coupled MLM's. The antisymmetric MDFB (AMDFB) is composed of multiple coupled MLM's. The SMDFB and AMDFB can be utilized as band-pass, Fano, or Lorentzian filters, or Rabi splitters. Distributed meandering waveguide elements with extremely rich spectral and phase responses can be designed with creative combinations of distributed meandering waveguides structures for various novel photonic circuits. References [1 ] C. B. Dağ, M. A. Anıl, and A. Serpengüzel, "Meandering Waveguide Distributed Feedback Lightwave Circuits," J. Lightwave Technol, vol. 33, no. 9, pp. 1691-1702, May 2015. [2] N. J. Doran and D. Wood, "Nonlinear-optical loop mirror," Opt. Lett. vol. 13, no. 1, pp. 56-58, Jan. 1988. [3] L. Zhou and A. W. Poon, "Fano resonance-based electrically reconfigurable add-drop filters in silicon microring resonator-coupled Mach-Zehnder interferometers," Opt. Lett. vol. 32, no. 7, pp. 781-783, Apr. 2007. [4] Z. Zou, L. Zhou, X. Sun, J. Xie, H. Zhu, L. Lu, X. Li, and J. Chen, "Tunable two-stage self-coupled optical waveguide resonators," Opt. Lett. vol. 38, no. 8, pp. 1215-1217, Apr. 2013. [5] C. B. Dağ, M. A. Anıl, and A. Serpengüzel, "Novel distributed feedback lightwave circuit elements," in Proc. SPIE, San Francisco, 2015, vol. 9366, p. 93660A. [6] C. B. Dağ, M. A. Anıl, and A. Serpengüzel, "Meandering Waveguide Distributed Feedback Lightwave Elements: Phasor Diagram Analysis," in Proc. PIERS, Prague, 1986-1990 (2015).

Phase-locking and coherent power combining of broadband linearly chirped optical waves.

PubMed

Satyan, Naresh; Vasilyev, Arseny; Rakuljic, George; White, Jeffrey O; Yariv, Amnon

2012-11-05

We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ~ 60 kHz, and a residual phase error variance of < 0.01 rad(2) between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers-where a rapidly chirping seed laser reduces stimulated Brillouin scattering-and electronic beam steering of chirped optical waves.

In-Process Metrology And Control Of Large Optical Grinders

NASA Astrophysics Data System (ADS)

Anderson, D. S.; Ketelsen, D.; Kittrell, W. Cary; Kuhn, Wm; Parks, R. E.; Stahl, P.

1987-01-01

The advent of rapid figure generation at the University of Arizona has prompted the development of rapid metrology techniques. The success and efficiency of the generating process is highly dependent on timely and accurate measurements to update the feedback loop between machine and optician. We will describe the advantages and problems associated with the in-process metrology and control systems used at the Optical Sciences Center.

Design, implementation and investigation of an image guide-based optical flip-flop array

NASA Technical Reports Server (NTRS)

Griffith, P. C.

1987-01-01

Presented is the design for an image guide-based optical flip-flop array created using a Hughes liquid crystal light valve and a flexible image guide in a feedback loop. This design is used to investigate the application of image guides as a communication mechanism in numerical optical computers. It is shown that image guides can be used successfully in this manner but mismatch match between the input and output fiber arrays is extremely limiting.

Real-time Kalman filter: Cooling of an optically levitated nanoparticle

NASA Astrophysics Data System (ADS)

Setter, Ashley; Toroš, Marko; Ralph, Jason F.; Ulbricht, Hendrik

2018-03-01

We demonstrate that a Kalman filter applied to estimate the position of an optically levitated nanoparticle, and operated in real-time within a field programmable gate array, is sufficient to perform closed-loop parametric feedback cooling of the center-of-mass motion to sub-Kelvin temperatures. The translational center-of-mass motion along the optical axis of the trapped nanoparticle has been cooled by 3 orders of magnitude, from a temperature of 300 K to a temperature of 162 ±15 mK.

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.

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

PubMed Central

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

2017-01-01

Climate change-related coral bleaching, i.e., the visible loss of zooxanthellae from the coral host, is increasing in frequency and extent and presents a major threat to coral reefs globally. Coral bleaching has been proposed to involve accelerating light stress of their microalgal endosymbionts via a positive feedback loop of photodamage, symbiont expulsion and excess in vivo light exposure. To test this hypothesis, we used light and O2 microsensors to characterize in vivo light exposure and photosynthesis of Symbiodinium during a thermal stress experiment. We created tissue areas with different densities of Symbiodinium cells in order to understand the optical properties and light microenvironment of corals during bleaching. Our results showed that in bleached Pocillopora damicornis corals, Symbiodinium light exposure was up to fivefold enhanced relative to healthy corals, and the relationship between symbiont loss and light enhancement was well-described by a power-law function. Cell-specific rates of Symbiodinium gross photosynthesis and light respiration were enhanced in bleached P. damicornis compared to healthy corals, while areal rates of net photosynthesis decreased. Symbiodinium light exposure in Favites sp. revealed the presence of low light microniches in bleached coral tissues, suggesting that light scattering in thick coral tissues can enable photoprotection of cryptic symbionts. Our study provides evidence for the acceleration of in vivo light exposure during coral bleaching but this optical feedback mechanism differs between coral hosts. Enhanced photosynthesis in relation to accelerating light exposure shows that coral microscale optics exerts a key role on coral photophysiology and the subsequent degree of radiative stress during coral bleaching. PMID:28174567

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

PubMed

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

2017-01-01

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

A minimal mathematical model combining several regulatory cycles from the budding yeast cell cycle.

PubMed

Sriram, K; Bernot, G; Képès, F

2007-11-01

A novel topology of regulatory networks abstracted from the budding yeast cell cycle is studied by constructing a simple nonlinear model. A ternary positive feedback loop with only positive regulations is constructed with elements that activates the subsequent element in a clockwise fashion. A ternary negative feedback loop with only negative regulations is constructed with the elements that inhibit the subsequent element in an anticlockwise fashion. Positive feedback loop exhibits bistability, whereas the negative feedback loop exhibits limit cycle oscillations. The novelty of the topology is that the corresponding elements in these two homogeneous feedback loops are linked by the binary positive feedback loops with only positive regulations. This results in the emergence of mixed feedback loops in the network that displays complex behaviour like the coexistence of multiple steady states, relaxation oscillations and chaos. Importantly, the arrangement of the feedback loops brings in the notion of checkpoint in the model. The model also exhibits domino-like behaviour, where the limit cycle oscillations take place in a stepwise fashion. As the aforementioned topology is abstracted from the budding yeast cell cycle, the events that govern the cell cycle are considered for the present study. In budding yeast, the sequential activation of the transcription factors, cyclins and their inhibitors form mixed feedback loops. The transcription factors that involve in the positive regulation in a clockwise orientation generates ternary positive feedback loop, while the cyclins and their inhibitors that involve in the negative regulation in an anticlockwise orientation generates ternary negative feedback loop. The mutual regulation between the corresponding elements in the transcription factors and the cyclins and their inhibitors generates binary positive feedback loops. The bifurcation diagram constructed for the whole system can be related to the different events of the cell cycle in terms of dynamical system theory. The checkpoint mechanism that plays an important role in different phases of the cell cycle are accounted for by silencing appropriate feedback loops in the model.

Electro-optic deflectors deliver advantages over acousto-optical deflectors in a high resolution, ultra-fast force-clamp optical trap.

PubMed

Woody, Michael S; Capitanio, Marco; Ostap, E Michael; Goldman, Yale E

2018-04-30

We characterized experimental artifacts arising from the non-linear response of acousto-optical deflectors (AODs) in an ultra-fast force-clamp optical trap and have shown that using electro-optical deflectors (EODs) instead eliminates these artifacts. We give an example of the effects of these artifacts in our ultra-fast force clamp studies of the interaction of myosin with actin filaments. The experimental setup, based on the concept of Capitanio et al. [Nat. Methods 9, 1013-1019 (2012)] utilizes a bead-actin-bead dumbbell held in two force-clamped optical traps which apply a load to the dumbbell to move it at a constant velocity. When myosin binds to actin, the filament motion stops quickly as the total force from the optical traps is transferred to the actomyosin attachment. We found that in our setup, AODs were unsuitable for beam steering due to non-linear variations in beam intensity and deflection angle as a function of driving frequency, likely caused by low-amplitude standing acoustic waves in the deflectors. These aberrations caused instability in the force feedback loops leading to artifactual jumps in the trap position. We demonstrate that beam steering with EODs improves the performance of our instrument. Combining the superior beam-steering capability of the EODs, force acquisition via back-focal-plane interferometry, and dual high-speed FPGA-based feedback loops, we apply precise and constant loads to study the dynamics of interactions between actin and myosin. The same concept applies to studies of other biomolecular interactions.

Adaptive gain, equalization, and wavelength stabilization techniques for silicon photonic microring resonator-based optical receivers

NASA Astrophysics Data System (ADS)

Palermo, Samuel; Chiang, Patrick; Yu, Kunzhi; Bai, Rui; Li, Cheng; Chen, Chin-Hui; Fiorentino, Marco; Beausoleil, Ray; Li, Hao; Shafik, Ayman; Titriku, Alex

2016-03-01

Interconnect architectures based on high-Q silicon photonic microring resonator devices offer a promising solution to address the dramatic increase in datacenter I/O bandwidth demands due to their ability to realize wavelength-division multiplexing (WDM) in a compact and energy efficient manner. However, challenges exist in realizing efficient receivers for these systems due to varying per-channel link budgets, sensitivity requirements, and ring resonance wavelength shifts. This paper reports on adaptive optical receiver design techniques which address these issues and have been demonstrated in two hybrid-integrated prototypes based on microring drop filters and waveguide photodetectors implemented in a 130nm SOI process and high-speed optical front-ends designed in 65nm CMOS. A 10Gb/s powerscalable architecture employs supply voltage scaling of a three inverter-stage transimpedance amplifier (TIA) that is adapted with an eye-monitor control loop to yield the necessary sensitivity for a given channel. As reduction of TIA input-referred noise is more critical at higher data rates, a 25Gb/s design utilizes a large input-stage feedback resistor TIA cascaded with a continuous-time linear equalizer (CTLE) that compensates for the increased input pole. When tested with a waveguide Ge PD with 0.45A/W responsivity, this topology achieves 25Gb/s operation with -8.2dBm sensitivity at a BER=10-12. In order to address microring drop filters sensitivity to fabrication tolerances and thermal variations, efficient wavelength-stabilization control loops are necessary. A peak-power-based monitoring loop which locks the drop filter to the input wavelength, while achieving compatibility with the high-speed TIA offset-correction feedback loop is implemented with a 0.7nm tuning range at 43μW/GHz efficiency.

Optogenetic feedback control of neural activity

PubMed Central

Newman, Jonathan P; Fong, Ming-fai; Millard, Daniel C; Whitmire, Clarissa J; Stanley, Garrett B; Potter, Steve M

2015-01-01

Optogenetic techniques enable precise excitation and inhibition of firing in specified neuronal populations and artifact-free recording of firing activity. Several studies have suggested that optical stimulation provides the precision and dynamic range requisite for closed-loop neuronal control, but no approach yet permits feedback control of neuronal firing. Here we present the ‘optoclamp’, a feedback control technology that provides continuous, real-time adjustments of bidirectional optical stimulation in order to lock spiking activity at specified targets over timescales ranging from seconds to days. We demonstrate how this system can be used to decouple neuronal firing levels from ongoing changes in network excitability due to multi-hour periods of glutamatergic or GABAergic neurotransmission blockade in vitro as well as impinging vibrissal sensory drive in vivo. This technology enables continuous, precise optical control of firing in neuronal populations in order to disentangle causally related variables of circuit activation in a physiologically and ethologically relevant manner. DOI: http://dx.doi.org/10.7554/eLife.07192.001 PMID:26140329

Comparison of two reconfigurable N×N interconnects for a recurrent neural network

NASA Astrophysics Data System (ADS)

Berger, Christoph; Collings, Neil; Pourzand, Ali R.; Volkel, Reinnard

1996-11-01

Two different methods of pattern replication (conventional and interlaced fan-out) have been investigated and experimentally tested in a reconfigurable 5X5 optical interconnect. Similar alignment problems due to imaging errors (field curvature) were observed in both systems. We conclude that of the two methods the interlaced fan-out is better suited to avoid these imaging errors, to reduce system size and to implement an optical feedback loop.

Molecular genetic analysis of circadian timekeeping in Drosophila

PubMed Central

Hardin, Paul E.

2014-01-01

A genetic screen for mutants that alter circadian rhythms in Drosophila identified the first clock gene - the period (per) gene. The per gene is a central player within a transcriptional feedback loop that represents the core mechanism for keeping circadian time in Drosophila and other animals. The per feedback loop, or core loop, is interlocked with the Clock (Clk) feedback loop, but whether the Clk feedback loop contributes to circadian timekeeping is not known. A series of distinct molecular events are thought to control transcriptional feedback in the core loop. The time it takes to complete these events should take much less than 24h, thus delays must be imposed at different steps within the core loop. As new clock genes are identified, the molecular mechanisms responsible for these delays have been revealed in ever-increasing detail, and provide an in depth accounting of how transcriptional feedback loops keep circadian time. The phase of these feedback loops shift to maintain synchrony with environmental cycles, the most reliable of which is light. Although a great deal is known about cell-autonomous mechanisms of light-induced phase shifting by CRYPTOCHROME (CRY), much less is known about non-cell autonomous mechanisms. CRY mediates phase shifts through an uncharacterized mechanism in certain brain oscillator neurons, and carries out a dual role as a photoreceptor and transcription factor in other tissues. Here I will review how transcriptional feedback loops function to keep time in Drosophila, how they impose delays to maintain a 24h cycle, and how they maintain synchrony with environmental light:dark cycles. The transcriptional feedback loops that keep time in Drosophila are well conserved in other animals, thus what we learn about these loops in Drosophila should continue to provide insight into the operation of analogous transcriptional feedback loops in other animals. PMID:21924977

Adaptive optics for the ESO-VLT

NASA Astrophysics Data System (ADS)

Merkle, Fritz

1989-04-01

This paper discusses adaptive optics, its performance, and its requirements for applications in astronomy to overcome limitations due to atmospheric turbulence. Guidelines for the implementation of these devices in telescopes are given, in particular for the Very Large Telescope (VLT) at ESO. It is intended to equip each one of the four 8-m telescopes of the VLT, which are arranged in a linear array with an independent adaptive optical system. These systems will serve the individual and the combined coude foci. A small-scale prototype adaptive system is under development. It is equipped with a 19-piezoelectric-actuator deformable mirror, a Shack-Hartmann-type wavefront sensor, and a dedicated wavefront computer for closing the feedback loop. This system is based on a polychromatic approach; i.e., it senses the wavefront in the visible, but the adaptive correction loop works at 3-5 microns.

Feedback-controlled laser fabrication of micromirror substrates.

PubMed

Petrak, Benjamin; Konthasinghe, Kumarasiri; Perez, Sonia; Muller, Andreas

2011-12-01

Short (40-200 μs) single focused CO(2) laser pulses of energy ≳100 μJ were used to fabricate high quality concave micromirror templates on silica and fluoride glass. The ablated features have diameters of ≈20-100 μm and average root-mean-square (RMS) surface microroughness near their center of less than 0.2 nm. Temporally monitoring the fabrication process revealed that it proceeds on a time scale shorter than the laser pulse duration. We implement a fast feedback control loop (≈20 kHz bandwidth) based on the light emitted by the sample that ensures an RMS size dispersion of less than 5% in arrays on chips or in individually fabricated features on an optical fiber tip, a significant improvement over previous approaches using longer pulses and open loop operation.

Design and Lessons Learned on the Development of a Cryogenic Pupil Select Mechanism (PSM)

NASA Technical Reports Server (NTRS)

Mitchell, Alissa L.; Capon, Thomas L.; Hakun, Claef; Haney, Paul; Koca, Corina; Guzek, Jeffrey

2014-01-01

Calibration and testing of the instruments on the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is being performed by the use of a cryogenic, full-field, optical simulator that was constructed for this purpose. The Pupil Select Mechanism (PSM) assembly is one of several mechanisms and optical elements that compose the Optical Telescope Element SIMulator, or OSIM. The PSM allows for several optical elements to be inserted into the optical plane of OSIM, introducing a variety of aberrations, distortions, obscurations, and other calibration states into the pupil plane. The following discussion focuses on the details of the design evolution, analysis, build, and test of this mechanism along with the challenges associated with creating a sub arc-minute positioning mechanism operating in an extreme cryogenic environment. In addition, difficult challenges in the control system design will be discussed including the incorporation of closed-loop feedback control into a system that was designed to operate in an open-loop fashion.

An open source digital servo for atomic, molecular, and optical physics experiments

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

Leibrandt, D. R., E-mail: david.leibrandt@nist.gov; Heidecker, J.

2015-12-15

We describe a general purpose digital servo optimized for feedback control of lasers in atomic, molecular, and optical physics experiments. The servo is capable of feedback bandwidths up to roughly 1 MHz (limited by the 320 ns total latency); loop filter shapes up to fifth order; multiple-input, multiple-output control; and automatic lock acquisition. The configuration of the servo is controlled via a graphical user interface, which also provides a rudimentary software oscilloscope and tools for measurement of system transfer functions. We illustrate the functionality of the digital servo by describing its use in two example scenarios: frequency control of themore » laser used to probe the narrow clock transition of {sup 27}Al{sup +} in an optical atomic clock, and length control of a cavity used for resonant frequency doubling of a laser.« less

An open source digital servo for atomic, molecular, and optical physics experiments.

PubMed

Leibrandt, D R; Heidecker, J

2015-12-01

We describe a general purpose digital servo optimized for feedback control of lasers in atomic, molecular, and optical physics experiments. The servo is capable of feedback bandwidths up to roughly 1 MHz (limited by the 320 ns total latency); loop filter shapes up to fifth order; multiple-input, multiple-output control; and automatic lock acquisition. The configuration of the servo is controlled via a graphical user interface, which also provides a rudimentary software oscilloscope and tools for measurement of system transfer functions. We illustrate the functionality of the digital servo by describing its use in two example scenarios: frequency control of the laser used to probe the narrow clock transition of (27)Al(+) in an optical atomic clock, and length control of a cavity used for resonant frequency doubling of a laser.

Feedback dew-point sensor utilizing optimally cut plastic optical fibres

NASA Astrophysics Data System (ADS)

Hadjiloucas, S.; Irvine, J.; Keating, D. A.

2000-01-01

A plastic optical fibre reflectance sensor that makes full use of the critical angle of the fibres is implemented to monitor dew formation on a Peltier-cooled reflector surface. The optical configuration permits isolation of optoelectronic components from the sensing head and better light coupling between the reflector and the detecting fibre, giving a better signal of the onset of dew formation on the reflector. Continuous monitoring of the rate of change in reflectance as well as the absolute reflectance signals, the use of a novel polymethyl-methacrylate-coated hydrophobic film reflector on the Peltier element and the application of feedback around the point of dew formation, further reduces the possibility of contamination of the sensor head. Under closed-loop operation, the sensor is capable of cycling around the point of dew formation at a frequency of 2.5 Hz.

An open source digital servo for atomic, molecular, and optical physics experiments

NASA Astrophysics Data System (ADS)

Leibrandt, D. R.; Heidecker, J.

2015-12-01

We describe a general purpose digital servo optimized for feedback control of lasers in atomic, molecular, and optical physics experiments. The servo is capable of feedback bandwidths up to roughly 1 MHz (limited by the 320 ns total latency); loop filter shapes up to fifth order; multiple-input, multiple-output control; and automatic lock acquisition. The configuration of the servo is controlled via a graphical user interface, which also provides a rudimentary software oscilloscope and tools for measurement of system transfer functions. We illustrate the functionality of the digital servo by describing its use in two example scenarios: frequency control of the laser used to probe the narrow clock transition of 27Al+ in an optical atomic clock, and length control of a cavity used for resonant frequency doubling of a laser.

An open source digital servo for atomic, molecular, and optical physics experiments

PubMed Central

Leibrandt, D. R.; Heidecker, J.

2016-01-01

We describe a general purpose digital servo optimized for feedback control of lasers in atomic, molecular, and optical physics experiments. The servo is capable of feedback bandwidths up to roughly 1 MHz (limited by the 320 ns total latency); loop filter shapes up to fifth order; multiple-input, multiple-output control; and automatic lock acquisition. The configuration of the servo is controlled via a graphical user interface, which also provides a rudimentary software oscilloscope and tools for measurement of system transfer functions. We illustrate the functionality of the digital servo by describing its use in two example scenarios: frequency control of the laser used to probe the narrow clock transition of 27Al+ in an optical atomic clock, and length control of a cavity used for resonant frequency doubling of a laser. PMID:26724014

Novel sensor for color control in solid state lighting applications

NASA Astrophysics Data System (ADS)

Gourevitch, Alex; Thurston, Thomas; Singh, Rajiv; Banachowicz, Bartosz; Korobov, Vladimir; Drowley, Cliff

2010-02-01

LED wavelength and luminosity shifts due to temperature, dimming, aging, and binning uncertainty can cause large color errors in open-loop light-mixing illuminators. Multispectral color light sensors combined with feedback circuits can compensate for these LED shifts. Typical color light sensor design variables include the choice of light-sensing material, filter configuration, and read-out circuitry. Cypress Semiconductor has designed and prototyped a color sensor chip that consists of photodiode arrays connected to a I/F (Current to Frequency) converter. This architecture has been chosen to achieve high dynamic range (~100dB) and provide flexibility for tailoring sensor response. Several different optical filter configurations were evaluated in this prototype. The color-sensor chip was incorporated into an RGB light color mixing system with closed-loop optical feedback. Color mixing accuracy was determined by calculating the difference between (u',v') set point values and CIE coordinates measured with a reference colorimeter. A typical color precision ▵u'v' less than 0.0055 has been demonstrated over a wide range of colors, a temperature range of 50C, and light dimming up to 80%.

Feedback traps for virtual potentials

NASA Astrophysics Data System (ADS)

Gavrilov, Momčilo; Bechhoefer, John

2017-03-01

Feedback traps are tools for trapping and manipulating single charged objects, such as molecules in solution. An alternative to optical tweezers and other single-molecule techniques, they use feedback to counteract the Brownian motion of a molecule of interest. The trap first acquires information about a molecule's position and then applies an electric feedback force to move the molecule. Since electric forces are stronger than optical forces at small scales, feedback traps are the best way to trap single molecules without `touching' them (e.g. by putting them in a small box or attaching them to a tether). Feedback traps can do more than trap molecules: they can also subject a target object to forces that are calculated to be the gradient of a desired potential function U(x). If the feedback loop is fast enough, it creates a virtual potential whose dynamics will be very close to those of a particle in an actual potential U(x). But because the dynamics are entirely a result of the feedback loop-absent the feedback, there is only an object diffusing in a fluid-we are free to specify and then manipulate in time an arbitrary potential U(x,t). Here, we review recent applications of feedback traps to studies on the fundamental connections between information and thermodynamics, a topic where feedback plays an even more fundamental role. We discuss how recursive maximum-likelihood techniques allow continuous calibration, to compensate for drifts in experiments that last for days. We consider ways to estimate work and heat, using them to measure fluctuating energies to a precision of ±0.03 kT over these long experiments. Finally, we compare work and heat measurements of the costs of information erasure, the Landauer limit of kT ln 2 per bit of information erased. We argue that, when you want to know the average heat transferred to a bath in a long protocol, you should measure instead the average work and then infer the heat using the first law of thermodynamics. This article is part of the themed issue 'Horizons of cybernetical physics'.

Feedback loop compensates for rectifier nonlinearity

NASA Technical Reports Server (NTRS)

1966-01-01

Signal processing circuit with two negative feedback loops rectifies two sinusoidal signals which are 180 degrees out of phase and produces a single full-wave rectified output signal. Each feedback loop incorporates a feedback rectifier to compensate for the nonlinearity of the circuit.

Relaxation oscillations and hierarchy of feedbacks in MAPK signaling

NASA Astrophysics Data System (ADS)

Kochańczyk, Marek; Kocieniewski, Paweł; Kozłowska, Emilia; Jaruszewicz-Błońska, Joanna; Sparta, Breanne; Pargett, Michael; Albeck, John G.; Hlavacek, William S.; Lipniacki, Tomasz

2017-01-01

We formulated a computational model for a MAPK signaling cascade downstream of the EGF receptor to investigate how interlinked positive and negative feedback loops process EGF signals into ERK pulses of constant amplitude but dose-dependent duration and frequency. A positive feedback loop involving RAS and SOS, which leads to bistability and allows for switch-like responses to inputs, is nested within a negative feedback loop that encompasses RAS and RAF, MEK, and ERK that inhibits SOS via phosphorylation. This negative feedback, operating on a longer time scale, changes switch-like behavior into oscillations having a period of 1 hour or longer. Two auxiliary negative feedback loops, from ERK to MEK and RAF, placed downstream of the positive feedback, shape the temporal ERK activity profile but are dispensable for oscillations. Thus, the positive feedback introduces a hierarchy among negative feedback loops, such that the effect of a negative feedback depends on its position with respect to the positive feedback loop. Furthermore, a combination of the fast positive feedback involving slow-diffusing membrane components with slower negative feedbacks involving faster diffusing cytoplasmic components leads to local excitation/global inhibition dynamics, which allows the MAPK cascade to transmit paracrine EGF signals into spatially non-uniform ERK activity pulses.

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.

A sensor-type application of a self-oscillating dynamic system with a fiber optic feedback line, including chemical sensors and biosensors

NASA Astrophysics Data System (ADS)

Rabinovich, Emmanuel M.

2004-05-01

We present an overview of research, conducted and published by the author and colleagues during the preceding decade, with self-oscillating dynamic systems. Special attention has been addressed to sensor type applications that allow one to design a new type of sensors of different physical parameters as well as using system for chemical and biosensors. Many detection methods exploit self-oscillating systems, such as lasers and RF or microwave oscillators, and use changes introduced into a feedback mechanism (for instance laser inter-cavity spectroscopy) for evaluation of different physical parameters such as refractive indices or absorption coefficients. Typically, that approach is very efficient, is easy to implement, and gives high sensitivity. We have demonstrated that a similar method can be used in the case of an RF optoelectronic self-oscillating system (OSOS) with a fiber-optic feedback line. Using fiber as an element of a positive feedback line allows one to design a new family of fiber-optic sensors each of which can be integrated into a fiber-optic feedback line. Changes introduced into the feedback line of an OSOS typically cause an RF frequency shift that can be measured very precisely with an RF frequency counter or spectrum analyzer. For some types of sensors an OSOS can easily incorporate and utilize advantages of well-developed modern inexpensive light sources (VCSELs, LEDs) and opto-electronic components that have been designed for communication purposes. A single closed loop OSOS can be easily duplicated for sensor array measurement via the use of parallel fiber-optics (for example VCSEL arrays and fiber ribbon cables) that have been well developed for telecommunication systems.

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.

Bio-isolated dc operational amplifier. [for bioelectric measurements

NASA Technical Reports Server (NTRS)

Lee, R. D. (Inventor)

1974-01-01

A bio-isolated dc operational amplifier is described for use in making bioelectrical measurements of a patient while providing isolation of the patient from electrical shocks. The circuit contains a first operational amplifier coupled to the patient with its output coupled in a forward loop through a first optic coupler to a second operational amplifier. The output of the second operational amplifier is coupled to suitable monitoring circuitry via a feedback circuit including a second optic coupler to the input of the first operational amplifier.

Design and Lessons Learned on the Development of a Cryogenic Pupil Select Mechanism used in the Testing and Calibration of the Integrated Science Instrument Module (ISIM) on the James Webb Space Telescope (JWST)

NASA Technical Reports Server (NTRS)

Mitchell, Alissa; Capon, Thomas; Guzek, Jeffrey; Hakun, Claef; Haney, Paul; Koca, Corina

2014-01-01

Calibration and testing of the instruments on the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is being performed by the use of a cryogenic, full-field, optical simulator that was constructed for this purpose. The Pupil Select Mechanism (PSM) assembly is one of several mechanisms and optical elements that compose the Optical Telescope Element SIMulator, or OSIM. The PSM allows for several optical elements to be inserted into the optical plane of OSIM, introducing a variety of aberrations, distortions, obscurations, and other calibration states into the pupil plane. The following discussion focuses on the details of the design evolution, analysis, build, and test of this mechanism along with the challenges associated with creating a sub arc-minute positioning mechanism operating in an extreme cryogenic environment. In addition, difficult challenges in the control system design will be discussed including the incorporation of closed-loop feedback control into a system that was designed to operate in an open-loop fashion.

Design and Lessons Learned on the Development of a Cryogenic Pupil Select Mechanism Used in the Testing and Calibration of the Integrated Science Instrument Module (ISIM) on the James Webb Space Telescope (JWST)

NASA Technical Reports Server (NTRS)

Mitchell, Alissa; Capon, Thomas; Guzek, Jeffrey; Hakun, Claef; Haney, Paul; Koca, Corina

2014-01-01

Calibration and testing of the instruments on the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is being performed by the use of a cryogenic, full-field, optical simulator that was constructed for this purpose. The Pupil Select Mechanism (PSM) assembly is one of several mechanisms and optical elements that compose the Optical Telescope Element SIMulator, or OSIM. The PSM allows for several optical elements to be inserted into the optical plane of OSIM, introducing a variety of aberrations, distortions, obscurations, and other calibration states into the pupil plane. The following discussion focuses on the details of the design evolution, analysis, build, and test of this mechanism along with the challenges associated with creating a sub arc-minute positioning mechanism operating in an extreme cryogenic environment. In addition, difficult challenges in the control system design will be discussed including the incorporation of closed-loop feedback control into a system that was designed to operate in an open-loop fashion.

An inexpensive programmable illumination microscope with active feedback.

PubMed

Tompkins, Nathan; Fraden, Seth

2016-02-01

We have developed a programmable illumination system capable of tracking and illuminating numerous objects simultaneously using only low-cost and reused optical components. The active feedback control software allows for a closed-loop system that tracks and perturbs objects of interest automatically. Our system uses a static stage where the objects of interest are tracked computationally as they move across the field of view allowing for a large number of simultaneous experiments. An algorithmically determined illumination pattern can be applied anywhere in the field of view with simultaneous imaging and perturbation using different colors of light to enable spatially and temporally structured illumination. Our system consists of a consumer projector, camera, 35-mm camera lens, and a small number of other optical and scaffolding components. The entire apparatus can be assembled for under $4,000.

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.

Positive feedback loop for cystitis cystica: the effect of recurrent urinary tract infection on the number of bladder wall mucosa nodules.

PubMed

Vrljicak, Kristina; Turudić, Daniel; Bambir, Ivan; Gradiski, Ivan Pavao; Spajić, Borislav; Batinić, Danica; Topalović-Grković, Marija; Spajić, Marija; Batinić, Danko; Milosević, Danko

2013-12-01

The main purpose of this study was to demonstrate positive feedback loop between bladder wall nodules (nodules being one of the key diagnostic factors), bladder wall thickness, and recurrent urinary tract infections. Cystitis cystica was diagnosed in 115 prepubertal girls (mean age 7.79 +/- 3.05 years) by optic examination of bladder mucosal nodules and by ultrasonographic measurement of bladder wall thickness. Bladder wall thickness increased with the frequency of recurrent urinary tract infections as well as with the number of nodules on bladder wall mucosa (3.52 +/- 0.522 mm < or = 5 nodules vs. 4.42 +/- 0.429 mm 6-10 nodules vs. 5.20 +/- 0.610 mm > 10 nodules, respectively). Study results suggested that early control of urinary tract infections by chemoprophylaxis could prevent higher grades of bladder wall mucosal changes and consequently shorten the length of chemoprophylaxis.

FRET imaging and in silico simulation: analysis of the signaling network of nerve growth factor-induced neuritogenesis.

PubMed

Nakamura, Takeshi; Aoki, Kazuhiro; Matsuda, Michiyuki

2008-08-01

Genetically encoded probes based on Förster resonance energy transfer (FRET) enable us to decipher spatiotemporal information encoded in complex tissues such as the brain. Firstly, this review focuses on FRET probes wherein both the donor and acceptor are fluorescence proteins and are incorporated into a single molecule, i.e. unimolecular probes. Advantages of these probes lie in their easy loading into cells, the simple acquisition of FRET images, and the clear evaluation of data. Next, we introduce our recent study which encompasses FRET imaging and in silico simulation. In nerve growth factor-induced neurite outgrowth in PC12 cells, we found positive and negative signaling feedback loops. We propose that these feedback loops determine neurite-budding sites. We would like to emphasize that it is now time to accelerate crossover research in neuroscience, optics, and computational biology.

Mid-infrared multiheterodyne spectroscopy with phase-locked quantum cascade lasers

NASA Astrophysics Data System (ADS)

Westberg, J.; Sterczewski, L. A.; Wysocki, G.

2017-04-01

Fabry-Pérot (FP) quantum cascade lasers (QCLs) provide purely electronically controlled monolithic sources for broadband mid-infrared (mid-IR) multiheterodyne spectroscopy (MHS), which benefits from the large gain bandwidth of the QCLs without sacrificing the narrowband properties commonly associated with the single mode distributed feedback variant. We demonstrate a FP-QCL based multiheterodyne spectrometer with a short-term noise-equivalent absorption of ˜3 × 10-4/ √{ H z } , a mid-IR spectral coverage of 25 cm-1, and very short acquisition time (10 μs) capability. The broadband potential is demonstrated by measuring the absorption spectra of ammonia and isobutane under atmospheric pressure conditions. The stability of the system is enhanced by a two-stage active frequency inter-locking procedure, where the two QCLs are pre-locked with a slow feedback loop based on an analog frequency discriminator, followed by a high bandwidth optical phase-locked loop. The locking system provides a relative frequency stability in the sub kHz range over seconds of integration time. The strength of the technique lies in the ability to acquire spectral information from all optical modes simultaneously and individually, which bodes for a versatile and cost effective spectrometer for mid-IR chemical gas sensing.

Anomalous electron spin decoherence in an optically pumped quantum dot

NASA Astrophysics Data System (ADS)

Shi, Xiaofeng; Sham, L. J.

2013-03-01

We study the nuclear-spin-fluctuation induced spin decoherence of an electron (SDE) in an optically pumped quantum dot. The SDE is computed in terms of the steady distribution of the nuclear field (SDNF) formed through the hyperfine interaction (HI) with two different nuclear species in the dot. A feedback loop between the optically driven electron spin and the nuclear spin ensemble determines the SDNF [W. Yang and L. J. Sham, Phy. Rev. B 85, 235319(2012)]. Different from that work and others reviewed therein, where a bilinear HI, SαIβ , between the electron (or hole) spin S and the nuclear spin I is used, we use an effective nonlinear interaction of the form SαIβIγ derived from the Fermi-contact HI. Our feedback loop forms a multi-peak SDNF in which the SDE shows remarkable collapses and revivals in nanosecond time scale. Such an anomalous SDE results from a quantum interference effect of the electron Larmor precession in a multi-peak effective magnetic field. In the presence of a bilinear HI that suppresses the nuclear spin fluctuation, the non-Markovian SDE persists whenever there are finite Fermi contact interactions between two or more kinds of nuclei and the electron in the quantum dot. This work is supported by NSF(PHY 1104446) and the US Army Research Office MURI award W911NF0910406.

Primary Radiometry for the mise-en-pratique: The Laser-Based Radiance Method Applied to a Pyrometer

NASA Astrophysics Data System (ADS)

Briaudeau, S.; Sadli, M.; Bourson, F.; Rougi, B.; Rihan, A.; Zondy, J.-J.

2011-12-01

A new setup has been implemented at LCM-LNE-CNAM for the determination "of the spectral responsivity of radiation thermometers for the determination" of the thermodynamic temperature of high-temperature blackbodies at the temperature of a metal-carbon eutectic phase transition. In this new setup, an innovative acoustic-optic modulator feedback loop is used to stabilize the radiance of a wavelength tunable laser. The effect of residual optical interferences on the calibration of a test pyrometer is analyzed. The full uncertainty budget is presented.

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.

Servo control booster system for minimizing following error

DOEpatents

Wise, William L.

1985-01-01

A closed-loop feedback-controlled servo system is disclosed which reduces command-to-response error to the system's position feedback resolution least increment, .DELTA.S.sub.R, on a continuous real-time basis for all operating speeds. The servo system employs a second position feedback control loop on a by exception basis, when the command-to-response error .gtoreq..DELTA.S.sub.R, to produce precise position correction signals. When the command-to-response error is less than .DELTA.S.sub.R, control automatically reverts to conventional control means as the second position feedback control loop is disconnected, becoming transparent to conventional servo control means. By operating the second unique position feedback control loop used herein at the appropriate clocking rate, command-to-response error may be reduced to the position feedback resolution least increment. The present system may be utilized in combination with a tachometer loop for increased stability.

Feedback Regulation and Its Efficiency in Biochemical Networks

NASA Astrophysics Data System (ADS)

Kobayashi, Tetsuya J.; Yokota, Ryo; Aihara, Kazuyuki

2016-03-01

Intracellular biochemical networks fluctuate dynamically due to various internal and external sources of fluctuation. Dissecting the fluctuation into biologically relevant components is important for understanding how a cell controls and harnesses noise and how information is transferred over apparently noisy intracellular networks. While substantial theoretical and experimental advancement on the decomposition of fluctuation was achieved for feedforward networks without any loop, we still lack a theoretical basis that can consistently extend such advancement to feedback networks. The main obstacle that hampers is the circulative propagation of fluctuation by feedback loops. In order to define the relevant quantity for the impact of feedback loops for fluctuation, disentanglement of the causally interlocked influences between the components is required. In addition, we also lack an approach that enables us to infer non-perturbatively the influence of the feedback to fluctuation in the same way as the dual reporter system does in the feedforward networks. In this work, we address these problems by extending the work on the fluctuation decomposition and the dual reporter system. For a single-loop feedback network with two components, we define feedback loop gain as the feedback efficiency that is consistent with the fluctuation decomposition for feedforward networks. Then, we clarify the relation of the feedback efficiency with the fluctuation propagation in an open-looped FF network. Finally, by extending the dual reporter system, we propose a conjugate feedback and feedforward system for estimating the feedback efficiency non-perturbatively only from the statistics of the system.

Polarization chaos and random bit generation in nonlinear fiber optics induced by a time-delayed counter-propagating feedback loop.

PubMed

Morosi, J; Berti, N; Akrout, A; Picozzi, A; Guasoni, M; Fatome, J

2018-01-22

In this manuscript, we experimentally and numerically investigate the chaotic dynamics of the state-of-polarization in a nonlinear optical fiber due to the cross-interaction between an incident signal and its intense backward replica generated at the fiber-end through an amplified reflective delayed loop. Thanks to the cross-polarization interaction between the two-delayed counter-propagating waves, the output polarization exhibits fast temporal chaotic dynamics, which enable a powerful scrambling process with moving speeds up to 600-krad/s. The performance of this all-optical scrambler was then evaluated on a 10-Gbit/s On/Off Keying telecom signal achieving an error-free transmission. We also describe how these temporal and chaotic polarization fluctuations can be exploited as an all-optical random number generator. To this aim, a billion-bit sequence was experimentally generated and successfully confronted to the dieharder benchmarking statistic tools. Our experimental analysis are supported by numerical simulations based on the resolution of counter-propagating coupled nonlinear propagation equations that confirm the observed behaviors.

Through-wafer optical probe characterization for microelectromechanical systems positional state monitoring and feedback control

NASA Astrophysics Data System (ADS)

Dawson, Jeremy M.; Chen, Jingdong; Brown, Kolin S.; Famouri, Parviz F.; Hornak, Lawrence A.

2000-12-01

Implementation of closed-loop microelectromechanical system (MEMS) control enables mechanical microsystems to adapt to the demands of the environment that they are actuating, opening a broad range of new opportunities for future MEMS applications. Integrated optical microsystems have the potential to enable continuous in situ optical interrogation of MEMS microstructure position fully decoupled from the means of mechanical actuation that is necessary for realization of feedback control. We present the results of initial research evaluating through-wafer optical microprobes for surface micromachined MEMS integrated optical position monitoring. Results from the through-wafer free-space optical probe of a lateral comb resonator fabricated using the multiuser MEMS process service (MUMPS) indicate significant positional information content with an achievable return probe signal dynamic range of up to 80% arising from film transmission contrast. Static and dynamic deflection analysis and experimental results indicate a through-wafer probe positional signal sensitivity of 40 mV/micrometers for the present setup or 10% signal change per micrometer. A simulation of the application of nonlinear sliding control is presented illustrating position control of the lateral comb resonator structure given the availability of positional state information.

Shell-Type Micromechanical Oscillator

DTIC Science & Technology

2003-04-01

interferometric setup. A positive feedback loop was implemented by amplifying the red laser signal (related to the oscillator deflection) and using...resonator was actuated by a sharply focused, modulated Ar+ ion (blue) laser beam and detected by a red HeNe laser using an interferometric setup. A positive...top. Fig. 1 shows optical micrograph obtained by DIC (Differential Interference Contrast, known also as Nomarsky contrast). An array of three domes

Positive And Negative Feedback Loops Coupled By Common Transcription Activator And Repressor

NASA Astrophysics Data System (ADS)

Sielewiesiuk, Jan; Łopaciuk, Agata

2015-03-01

Dynamical systems consisting of two interlocked loops with negative and positive feedback have been studied using the linear analysis of stability and numerical solutions. Conditions for saddle-node bifurcation were formulated in a general form. Conditions for Hopf bifurcations were found in a few symmetrical cases. Auto-oscillations, when they exist, are generated by the negative feedback repressive loop. This loop determines the frequency and amplitude of oscillations. The positive feedback loop of activation slightly modifies the oscillations. Oscillations are possible when the difference between Hilll's coefficients of the repression and activation is sufficiently high. The highly cooperative activation loop with a fast turnover slows down or even makes the oscillations impossible. The system under consideration can constitute a component of epigenetic or enzymatic regulation network.

An inexpensive programmable illumination microscope with active feedback

PubMed Central

Tompkins, Nathan; Fraden, Seth

2016-01-01

We have developed a programmable illumination system capable of tracking and illuminating numerous objects simultaneously using only low-cost and reused optical components. The active feedback control software allows for a closed-loop system that tracks and perturbs objects of interest automatically. Our system uses a static stage where the objects of interest are tracked computationally as they move across the field of view allowing for a large number of simultaneous experiments. An algorithmically determined illumination pattern can be applied anywhere in the field of view with simultaneous imaging and perturbation using different colors of light to enable spatially and temporally structured illumination. Our system consists of a consumer projector, camera, 35-mm camera lens, and a small number of other optical and scaffolding components. The entire apparatus can be assembled for under $4,000. PMID:27642182

The magnetosphere as system

NASA Astrophysics Data System (ADS)

Siscoe, G. L.

2012-12-01

What is a system? A group of elements interacting with each other so as to create feedback loops. A system gets complex as the number of feedback loops increases and as the feedback loops exhibit time delays. Positive and negative feedback loops with time delays can give a system intrinsic time dependence and emergent properties. A system generally has input and output flows of something (matter, energy, money), which, if time variable, add an extrinsic component to its behavior. The magnetosphere is a group of elements interacting through feedback loops, some with time delays, driven by energy and mass inflow from a variable solar wind and outflow into the atmosphere and solar wind. The magnetosphere is a complex system. With no solar wind, there is no behavior. With solar wind, there is behavior from intrinsic and extrinsic causes. As a contribution to taking a macroscopic view of magnetospheric dynamics, to treating the magnetosphere as a globally integrated, complex entity, I will discus the magnetosphere as a system, its feedback loops, time delays, emergent behavior, and intrinsic and extrinsic behavior modes.

Indirect Identification of Linear Stochastic Systems with Known Feedback Dynamics

NASA Technical Reports Server (NTRS)

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

1996-01-01

An algorithm is presented for identifying a state-space model of linear stochastic systems operating under known feedback controller. In this algorithm, only the reference input and output of closed-loop data are required. No feedback signal needs to be recorded. The overall closed-loop system dynamics is first identified. Then a recursive formulation is derived to compute the open-loop plant dynamics from the identified closed-loop system dynamics and known feedback controller dynamics. The controller can be a dynamic or constant-gain full-state feedback controller. Numerical simulations and test data of a highly unstable large-gap magnetic suspension system are presented to demonstrate the feasibility of this indirect identification method.

Feedback: A Systems Approach to Evaluation and Course Design. Working Papers No. 21.

ERIC Educational Resources Information Center

Holmes, John

Two types of feedback are examined, and their use in controlling the processes of instructional development and improvement are discussed. Closed-loop feedback, the most direct, uses immediate feedback about a process or product to make immediate adjustments in it. Open-loop feedback, in which input cannot be changed immediately, uses feedback to…

Stability analysis and compensation of a boost regulator with two-loop control

NASA Technical Reports Server (NTRS)

Wester, G. W.

1974-01-01

A useful stability measure has been demonstrated by Wester (1973) for switching regulators with a single feedback loop by applying the Nyquist criterion to the approximate loop gain determined by a time-averaging technique. This approach is extended and applied to the characterization, stability analysis, and compensation design of a switching regulator with two-loop control. The role and relative significance of each control loop is clarified on the basis of a description of circuit operation, and the major and minor loops are identified. In view of the inapplicability of linear feedback theory, describing functions of the feedback loops and power stage are derived, using small-signal analysis. Several phenomena revealed from an analysis of the major loop gain are discussed.

Rigid Body Rate Inference from Attitude Variation

NASA Technical Reports Server (NTRS)

Bar-Itzhack, I. Y.; Harman, Richard R.; Thienel, Julie K.

2006-01-01

In this paper we research the extraction of the angular rate vector from attitude information without differentiation, in particular from quaternion measurements. We show that instead of using a Kalman filter of some kind, it is possible to obtain good rate estimates, suitable for spacecraft attitude control loop damping, using simple feedback loops, thereby eliminating the need for recurrent covariance computation performed when a Kalman filter is used. This considerably simplifies the computations required for rate estimation in gyro-less spacecraft. Some interesting qualities of the Kalman filter gain are explored, proven and utilized. We examine two kinds of feedback loops, one with varying gain that is proportional to the well known Q matrix, which is computed using the measured quaternion, and the other type of feedback loop is one with constant coefficients. The latter type includes two kinds; namely, a proportional feedback loop, and a proportional-integral feedback loop. The various schemes are examined through simulations and their performance is compared. It is shown that all schemes are adequate for extracting the angular velocity at an accuracy suitable for control loop damping.

On the Extraction of Angular Velocity from Attitude Measurements

NASA Technical Reports Server (NTRS)

Bar-Itzhack, I. Y.; Harman, Richard R.; Thienel, Julie K.

2006-01-01

In this paper we research the extraction of the angular rate vector from attitude information without differentiation, in particular from quaternion measurements. We show that instead of using a Kalman filter of some kind, it is possible to obtain good rate estimates, suitable for spacecraft attitude control loop damping, using simple feedback loops, thereby eliminating the need for recurrent covariance computation performed when a Kalman filter is used. This considerably simplifies the computations required for rate estimation in gyro-less spacecraft. Some interesting qualities of the Kalman filter gain are explored, proven and utilized. We examine two kinds of feedback loops, one with varying gain that is proportional to the well known Q matrix, which is computed using the measured quaternion, and the other type of feedback loop is one with constant coefficients. The latter type includes two kinds; namely, a proportional feedback loop, and a proportional-integral feedback loop. The various schemes are examined through simulations and their performance is compared. It is shown that all schemes are adequate for extracting the angular velocity at an accuracy suitable for control loop damping.

Opto-electronic oscillator: moving toward solutions based on polymer materials

NASA Astrophysics Data System (ADS)

Nguyên, Lâm Duy; Journet, Bernard; Zyss, Joseph

2008-02-01

Optoelectronic oscillators have been studied since many years now, their high spectral purity being one of their most interesting quality for photonics signal processing, communication or radio over fiber systems. One part of the structure is a long fiber optic feedback loop acting as a delay line. Different techniques have been introduced such as multiple loops in order to get very narrow spectral lines and large mode spacing. One of the problems due to long fiber loops is the size and the requirement of temperature control. In order to go toward integrated solutions it is also possible to introduce optical resonators instead of a delay line structure (as for classical electronic oscillators). But such resonators should present very high quality factor. In this paper we demonstrate solutions using resonators based on polymer materials such as PMMA-DCM. Structures such as micro-rings, micro-disks or stadium-shaped resonator have been realized at the laboratory. Quality factor of 6000 have already been achieved leading to an equivalent fiber loop of 19 m for an oscillator at 10 GHz. But it has been already theoretically proved that quality factor greater than one thousand hundred could be obtained. These resonators can be directly implemented with Mach-Zehnder optical modulators based on electro-optic polymer such as PMMA-DR1 leading to integrated solutions. And in the future it should be also possible to add a laser made with polymer material, with a structure as stadium-shape polymer micro-laser. The fully integrated photonic chip is not so far. The last important function to be implemented is the tuning of the oscillation frequency.

Servo control booster system for minimizing following error

DOEpatents

Wise, W.L.

1979-07-26

A closed-loop feedback-controlled servo system is disclosed which reduces command-to-response error to the system's position feedback resolution least increment, ..delta..S/sub R/, on a continuous real-time basis, for all operational times of consequence and for all operating speeds. The servo system employs a second position feedback control loop on a by exception basis, when the command-to-response error greater than or equal to ..delta..S/sub R/, to produce precise position correction signals. When the command-to-response error is less than ..delta..S/sub R/, control automatically reverts to conventional control means as the second position feedback control loop is disconnected, becoming transparent to conventional servo control means. By operating the second unique position feedback control loop used herein at the appropriate clocking rate, command-to-response error may be reduced to the position feedback resolution least increment. The present system may be utilized in combination with a tachometer loop for increased stability.

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…

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

ERIC Educational Resources Information Center

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

2016-01-01

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

A 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.

Analysis of TMT primary mirror control-structure interaction

NASA Astrophysics Data System (ADS)

MacMynowski, Douglas G.; Thompson, Peter M.; Sirota, Mark J.

2008-07-01

The primary mirror control system (M1CS) keeps the 492 segments of the Thirty Meter Telescope primary mirror aligned in the presence of disturbances. A global position control loop uses feedback from inter-segment edge sensors to three actuators behind each segment that control segment piston, tip and tilt. If soft force actuators are used (e.g. voice-coil), then in addition to the global position loop there will be a local servo loop to provide stiffness. While the M1 control system at Keck compensates only for slow disturbances such as gravity and thermal variations, the M1CS for TMT will need to provide some compensation for higher frequency wind disturbances in order to meet stringent error budget targets. An analysis of expected high-wavenumber wind forces on M1 suggests that a 1Hz control bandwidth is required for the global feedback of segment edge-sensorbased position information in order to minimize high spatial frequency segment response for both seeing-limited and adaptive optics performance. A much higher bandwidth is required from the local servo loop to provide adequate stiffness to wind or acoustic disturbances. A related paper presents the control designs for the local actuator servo loops. The disturbance rejection requirements would not be difficult to achieve for a single segment, but the structural coupling between segments mounted on a flexible mirror cell results in controlstructure interaction (CSI) that limits the achievable bandwidth. Using a combination of simplified modeling to build intuition and the full telescope finite element model for verification, we present designs and analysis for both the local servo loop and global loop demonstrating sufficient bandwidth and resulting wind-disturbance rejection despite the presence of CSI.

Multivariable control of the Space Shuttle Remote Manipulator System using linearization by state feedback. M.S. Thesis

NASA Technical Reports Server (NTRS)

Gettman, Chang-Ching LO

1993-01-01

This thesis develops and demonstrates an approach to nonlinear control system design using linearization by state feedback. The design provides improved transient response behavior allowing faster maneuvering of payloads by the SRMS. Modeling uncertainty is accounted for by using a second feedback loop designed around the feedback linearized dynamics. A classical feedback loop is developed to provide the easy implementation required for the relatively small on board computers. Feedback linearization also allows the use of higher bandwidth model based compensation in the outer loop, since it helps maintain stability in the presence of the nonlinearities typically neglected in model based designs.

Carrier-envelope phase stabilization and control using a transmission grating compressor and an AOPDF.

PubMed

Canova, Lorenzo; Chen, Xiaowei; Trisorio, Alexandre; Jullien, Aurélie; Assion, Andreas; Tempea, Gabriel; Forget, Nicolas; Oksenhendler, Thomas; Lopez-Martens, Rodrigo

2009-05-01

Carrier-envelope phase (CEP) stabilization of a femtosecond chirped-pulse amplification system featuring a compact transmission grating compressor is demonstrated. The system includes two amplification stages and routinely generates phase-stable (approximately 250 mrad rms) 2 mJ, 25 fs pulses at 1 kHz. Minimizing the optical pathway in the compressor enables phase stabilization without feedback control of the grating separation or beam pointing. We also demonstrate for the first time to the best of our knowledge, out-of-loop control of the CEP using an acousto-optic programmable dispersive filter inside the laser chain.

Closed-Loop Control of Vortex Formation in Separated Flows

NASA Technical Reports Server (NTRS)

Colonius, Tim; Joe, Won Tae; MacMynowski, Doug; Rowley, Clancy; Taira, Sam; Ahuja, Sunil

2010-01-01

In order to phase lock the flow at the desired shedding cycle, particularly at Phi,best, We designed a feedback compensator. (Even though the open-loop forcing at Wf below Wn can lead to phase-locked limit cycles with a high average lift,) This feedback controller resulted in the phase-locked limit cycles that the open-loop control could not achieve for alpha=30 and 40 Particularly for alpha=40, the feedback was able to stabilize the limit cycle that was not stable with any of the open-loop periodic forcing. This results in stable phase-locked limit cycles for a larger range of forcing frequencies than the open-loop control. Also, it was shown that the feedback achieved the high-lift unsteady flow states that open-loop control could not sustain even after the states have been achieved for a long period of time.

Field-programmable gate array-controlled sweep velocity-locked laser pulse generator

NASA Astrophysics Data System (ADS)

Chen, Zhen; Hefferman, Gerald; Wei, Tao

2017-05-01

A field-programmable gate array (FPGA)-controlled sweep velocity-locked laser pulse generator (SV-LLPG) design based on an all-digital phase-locked loop (ADPLL) is proposed. A distributed feedback laser with modulated injection current was used as a swept-frequency laser source. An open-loop predistortion modulation waveform was calibrated using a feedback iteration method to initially improve frequency sweep linearity. An ADPLL control system was then implemented using an FPGA to lock the output of a Mach-Zehnder interferometer that was directly proportional to laser sweep velocity to an on-board system clock. Using this system, linearly chirped laser pulses with a sweep bandwidth of 111.16 GHz were demonstrated. Further testing evaluating the sensing utility of the system was conducted. In this test, the SV-LLPG served as the swept laser source of an optical frequency-domain reflectometry system used to interrogate a subterahertz range fiber structure (sub-THz-FS) array. A static strain test was then conducted and linear sensor results were observed.

The Trade-Off Mechanism in Mammalian Circadian Clock Model with Two Time Delays

NASA Astrophysics Data System (ADS)

Yan, Jie; Kang, Xiaxia; Yang, Ling

Circadian clock is an autonomous oscillator which orchestrates the daily rhythms of physiology and behaviors. This study is devoted to explore how a positive feedback loop affects the dynamics of mammalian circadian clock. We simplify an experimentally validated mathematical model in our previous work, to a nonlinear differential equation with two time delays. This simplified mathematical model incorporates the pacemaker of mammalian circadian clock, a negative primary feedback loop, and a critical positive auxiliary feedback loop, Rev-erbα/Cry1 loop. We perform analytical studies of the system. Delay-dependent conditions for the asymptotic stability of the nontrivial positive steady state of the model are investigated. We also prove the existence of Hopf bifurcation, which leads to self-sustained oscillation of mammalian circadian clock. Our theoretical analyses show that the oscillatory regime is reduced upon the participation of the delayed positive auxiliary loop. However, further simulations reveal that the auxiliary loop can enable the circadian clock gain widely adjustable amplitudes and robust period. Thus, the positive auxiliary feedback loop may provide a trade-off mechanism, to use the small loss in the robustness of oscillation in exchange for adaptable flexibility in mammalian circadian clock. The results obtained from the model may gain new insights into the dynamics of biological oscillators with interlocked feedback loops.

A theory of circular organization and negative feedback: defining life in a cybernetic context.

PubMed

Tsokolov, Sergey

2010-12-01

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

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

NASA Astrophysics Data System (ADS)

Tsokolov, Sergey

2010-12-01

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

Frequency-modulated laser ranging sensor with closed-loop control

NASA Astrophysics Data System (ADS)

Müller, Fabian M.; Böttger, Gunnar; Janeczka, Christian; Arndt-Staufenbiel, Norbert; Schröder, Henning; Schneider-Ramelow, Martin

2018-02-01

Advances in autonomous driving and robotics are creating high demand for inexpensive and mass-producible distance sensors. A laser ranging system (Lidar), based on the frequency-modulated continuous-wave (FMCW) method is built in this work. The benefits of an FMCW Lidar system are the low-cost components and the performance in comparison to conventional time-of-flight Lidar systems. The basic system consists of a DFB laser diode (λ= 1308 nm) and an asymmetric fiber-coupled Mach-Zehnder interferometer with a fixed delay line in one arm. Linear tuning of the laser optical frequency via injection current modulation creates a beat signal at the interferometer output. The frequency of the beat signal is proportional to the optical path difference in the interferometer. Since the laser frequency-to-current response is non-linear, a closed-loop feed-back system is designed to improve the tuning linearity, and consequently the measurement resolution. For fast active control, an embedded system with FPGA is used, resulting in a nearly linear frequency tuning, realizing a narrow peak in the Fourier spectrum of the beat signal. For free-space measurements, a setup with two distinct interferometers is built. The fully fiber-coupled Mach-Zehnder reference interferometer is part of the feed-back loop system, while the other - a Michelson interferometer - has a free-space arm with collimator lens and reflective target. A resolution of 2:0 mm for a 560 mm distance is achieved. The results for varying target distances show high consistency and a linear relation to the measured beat-frequency.

Circuitry, systems and methods for detecting magnetic fields

DOEpatents

Kotter, Dale K [Shelley, ID; Spencer, David F [Idaho Falls, ID; Roybal, Lyle G [Idaho Falls, ID; Rohrbaugh, David T [Idaho Falls, ID

2010-09-14

Circuitry for detecting magnetic fields includes a first magnetoresistive sensor and a second magnetoresistive sensor configured to form a gradiometer. The circuitry includes a digital signal processor and a first feedback loop coupled between the first magnetoresistive sensor and the digital signal processor. A second feedback loop which is discrete from the first feedback loop is coupled between the second magnetoresistive sensor and the digital signal processor.

Digital Phase-Locked Loop With Phase And Frequency Feedback

NASA Technical Reports Server (NTRS)

Thomas, J. Brooks

1991-01-01

Advanced design for digital phase-lock loop (DPLL) allows loop gains higher than those used in other designs. Divided into two major components: counterrotation processor and tracking processor. Notable features include use of both phase and rate-of-change-of-phase feedback instead of frequency feedback alone, normalized sine phase extractor, improved method for extracting measured phase, and improved method for "compressing" output rate.

Plate with decentralised velocity feedback loops: Power absorption and kinetic energy considerations

NASA Astrophysics Data System (ADS)

Gardonio, P.; Miani, S.; Blanchini, F.; Casagrande, D.; Elliott, S. J.

2012-04-01

This paper is focused on the vibration effects produced by an array of decentralised velocity feedback loops that are evenly distributed over a rectangular thin plate to minimise its flexural response. The velocity feedback loops are formed by collocated ideal velocity sensor and point force actuator pairs, which are unconditionally stable and produce 'sky-hook' damping on the plate. The study compares how the overall flexural vibration of the plate and the local absorption of vibration power by the feedback loops vary with the control gains. The analysis is carried out both considering a typical frequency-domain formulation based on kinetic energy and structural power physical quantities, which is normally used to study vibration and noise problems, and a time-domain formulation also based on kinetic energy and structural power, which is usually implemented to investigate control problems. The time-domain formulation shows to be much more computationally efficient and robust with reference to truncation errors. Thus it has been used to perform a parametric study to assess if, and under which conditions, the minimum of the kinetic energy and the maximum of the absorbed power cost functions match with reference to: (a) the number of feedback control loops, (b) the structural damping in the plate, (c) the mutual distance of a pair of control loops and (d) the mutual gains implemented in a pair of feedback loops.

Full parabolic trough qualification from prototype to demonstration loop

NASA Astrophysics Data System (ADS)

Janotte, Nicole; Lüpfert, Eckhard; Pottler, Klaus; Schmitz, Mark

2017-06-01

On the example of the HelioTrough® collector development the full accompanying and supporting qualification program for large-scale parabolic trough collectors for solar thermal power plants is described from prototype to demonstration loop scale. In the evaluation process the actual state and the optimization potential are assessed. This includes the optical and geometrical performance determined by concentrator shape, deformation, assembly quality and local intercept factor values. Furthermore, its mechanical performance in terms of tracking accuracy and torsional stiffness and its thermal system performance on the basis of the overall thermal output and heat loss are evaluated. Demonstration loop tests deliver results of collector modules statistical slope deviation of 1.9 to 2.6 mrad, intercept factor above 98%, peak optical performance of 81.6% and heat loss coefficients from field tests. The benefit of such a closely monitored development lies in prompt feedback on strengths, weaknesses and potential improvements on the new product at any development stage from first module tests until demonstration loop evaluation. The product developer takes advantage of the achieved technical maturity, already before the implementation in a commercial power plant. The well-understood performance characteristics allow the reduction of safety margins making the new HelioTrough collector competitive from the start.

Maximum-likelihood-based extended-source spatial acquisition and tracking for planetary optical communications

NASA Astrophysics Data System (ADS)

Tsou, Haiping; Yan, Tsun-Yee

1999-04-01

This paper describes an extended-source spatial acquisition and tracking scheme for planetary optical communications. This scheme uses the Sun-lit Earth image as the beacon signal, which can be computed according to the current Sun-Earth-Probe angle from a pre-stored Earth image or a received snapshot taken by other Earth-orbiting satellite. Onboard the spacecraft, the reference image is correlated in the transform domain with the received image obtained from a detector array, which is assumed to have each of its pixels corrupted by an independent additive white Gaussian noise. The coordinate of the ground station is acquired and tracked, respectively, by an open-loop acquisition algorithm and a closed-loop tracking algorithm derived from the maximum likelihood criterion. As shown in the paper, the optimal spatial acquisition requires solving two nonlinear equations, or iteratively solving their linearized variants, to estimate the coordinate when translation in the relative positions of onboard and ground transceivers is considered. Similar assumption of linearization leads to the closed-loop spatial tracking algorithm in which the loop feedback signals can be derived from the weighted transform-domain correlation. Numerical results using a sample Sun-lit Earth image demonstrate that sub-pixel resolutions can be achieved by this scheme in a high disturbance environment.

Mean field analysis of a spatial stochastic model of a gene regulatory network.

PubMed

Sturrock, M; Murray, P J; Matzavinos, A; Chaplain, M A J

2015-10-01

A gene regulatory network may be defined as a collection of DNA segments which interact with each other indirectly through their RNA and protein products. Such a network is said to contain a negative feedback loop if its products inhibit gene transcription, and a positive feedback loop if a gene product promotes its own production. Negative feedback loops can create oscillations in mRNA and protein levels while positive feedback loops are primarily responsible for signal amplification. It is often the case in real biological systems that both negative and positive feedback loops operate in parameter regimes that result in low copy numbers of gene products. In this paper we investigate the spatio-temporal dynamics of a single feedback loop in a eukaryotic cell. We first develop a simplified spatial stochastic model of a canonical feedback system (either positive or negative). Using a Gillespie's algorithm, we compute sample trajectories and analyse their corresponding statistics. We then derive a system of equations that describe the spatio-temporal evolution of the stochastic means. Subsequently, we examine the spatially homogeneous case and compare the results of numerical simulations with the spatially explicit case. Finally, using a combination of steady-state analysis and data clustering techniques, we explore model behaviour across a subregion of the parameter space that is difficult to access experimentally and compare the parameter landscape of our spatio-temporal and spatially-homogeneous models.

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

PubMed

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

2014-01-01

Previous research (Whitwell et al. in Exp Brain Res 188:603-611, 2008; Whitwell and Goodale in Exp Brain Res 194:619-629, 2009) has shown that trial history, but not anticipatory knowledge about the presence or absence of visual feedback on an upcoming trial, plays a vital role in determining how that feedback is exploited when grasping with the right hand. Nothing is known about how the non-dominant left hand behaves under the same feedback regimens. In present study, therefore, we compared peak grip aperture (PGA) for left- and right-hand grasps executed with and without visual feedback (i.e., closed- vs. open-loop conditions) in right-handed individuals under three different trial schedules: the feedback conditions were blocked separately, they were randomly interleaved, or they were alternated. When feedback conditions were blocked, the PGA was much larger for open-loop trials as compared to closed-loop trials, although this difference was more pronounced for right-hand grasps than left-hand grasps. Like Whitwell et al., we found that mixing open- and closed-loop trials together, compared to blocking them separately, homogenized the PGA for open- and closed-loop grasping in the right hand (i.e., the PGAs became smaller on open-loop trials and larger on closed-loop trials). In addition, the PGAs for right-hand grasps were entirely determined by trial history and not by knowledge of whether or not visual feedback would be available on an upcoming trial. In contrast to grasps made with the right hand, grasps made by the left hand were affected both by trial history and by anticipatory knowledge of the upcoming visual feedback condition. But these effects were observed only on closed-loop trials, i.e., the PGAs of grasps made with the left hand on closed-loop trials were smaller when participants could anticipate the availability of feedback on an upcoming trial (alternating trials) than when they could not (randomized trials). In contrast, grasps made with the left hand on open-loop trials exhibited the same large PGAs under all feedback schedules: blocked, random, or alternating. In other words, there was no evidence for homogenization. Taken together, these results suggest that in addition to the real-time demands of the task, such as the target's size and position and the availability of visual feedback, the initial (i.e., pre-movement) programming of right-hand grasping relies on what happened on the previous trial, whereas the programming of left-hand grasping is more cognitively supervised and exploits explicit information about trial order to prepare for an upcoming trial.

Performance Evaluation of Photonic Sigma Delta ADCs

DTIC Science & Technology

2010-12-01

resulted in an output at the MZI driver that is too low to drive the MZI itself. It is recommended that a transimpedance amplifier be used instead of...Accumulator The accumulator shown in Figure 1 consists of a single delay, a feedback loop and two amplifiers . The input of the accumulator is the...fiber amplifier (EDFA), an output coupler, an electro–optic modulator, a tunable filter and the fiber that connects these devices together. The piezo

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

PubMed

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

2015-01-01

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

In-cell overlay metrology by using optical metrology tool

NASA Astrophysics Data System (ADS)

Lee, Honggoo; Han, Sangjun; Hong, Minhyung; Kim, Seungyoung; Lee, Jieun; Lee, DongYoung; Oh, Eungryong; Choi, Ahlin; Park, Hyowon; Liang, Waley; Choi, DongSub; Kim, Nakyoon; Lee, Jeongpyo; Pandev, Stilian; Jeon, Sanghuck; Robinson, John C.

2018-03-01

Overlay is one of the most critical process control steps of semiconductor manufacturing technology. A typical advanced scheme includes an overlay feedback loop based on after litho optical imaging overlay metrology on scribeline targets. The after litho control loop typically involves high frequency sampling: every lot or nearly every lot. An after etch overlay metrology step is often included, at a lower sampling frequency, in order to characterize and compensate for bias. The after etch metrology step often involves CD-SEM metrology, in this case in-cell and ondevice. This work explores an alternative approach using spectroscopic ellipsometry (SE) metrology and a machine learning analysis technique. Advanced 1x nm DRAM wafers were prepared, including both nominal (POR) wafers with mean overlay offsets, as well as DOE wafers with intentional across wafer overlay modulation. After litho metrology was measured using optical imaging metrology, as well as after etch metrology using both SE and CD-SEM for comparison. We investigate 2 types of machine learning techniques with SE data: model-less and model-based, showing excellent performance for after etch in-cell on-device overlay metrology.

Optical-Path-Difference Linear Mechanism for the Panchromatic Fourier Transform Spectrometer

NASA Technical Reports Server (NTRS)

Blavier, Jean-Francois L.; Heverly, Matthew C.; Key, Richard W.; Sander, Stanley P.

2011-01-01

A document discusses a mechanism that uses flex-pivots in a parallelogram arrangement to provide frictionless motion with an unlimited lifetime. A voicecoil actuator drives the parallelogram over the required 5-cm travel. An optical position sensor provides feedback for a servo loop that keeps the velocity within 1 percent of expected value. Residual tip/tilt error is compensated for by a piezo actuator that drives the interferometer mirror. This mechanism builds on previous work that targeted ground-based measurements. The main novelty aspects include cryogenic and vacuum operation, high reliability for spaceflight, compactness of the design, optical layout compatible with the needs of an imaging FTS (i.e. wide overall field-of-view), and mirror optical coatings to cover very broad wavelength range (i.e., 0.26 to 15 m).

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.

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.

Compact silicon photonics-based multi laser module for sensing

NASA Astrophysics Data System (ADS)

Ayotte, S.; Costin, F.; Babin, A.; Paré-Olivier, G.; Morin, M.; Filion, B.; Bédard, K.; Chrétien, P.; Bilodeau, G.; Girard-Deschênes, E.; Perron, L.-P.; Davidson, C.-A.; D'Amato, D.; Laplante, M.; Blanchet-Létourneau, J.

2018-02-01

A compact three-laser source for optical sensing is presented. It is based on a low-noise implementation of the Pound Drever-Hall method and comprises high-bandwidth optical phase-locked loops. The outputs from three semiconductor distributed feedback lasers, mounted on thermo-electric coolers (TEC), are coupled with micro-lenses into a silicon photonics (SiP) chip that performs beat note detection and several other functions. The chip comprises phase modulators, variable optical attenuators, multi-mode-interference couplers, variable ratio tap couplers, integrated photodiodes and optical fiber butt-couplers. Electrical connections between a metallized ceramic and the TECs, lasers and SiP chip are achieved by wirebonds. All these components stand within a 35 mm by 35 mm package which is interfaced with 90 electrical pins and two fiber pigtails. One pigtail carries the signals from a master and slave lasers, while another carries that from a second slave laser. The pins are soldered to a printed circuit board featuring a micro-processor that controls and monitors the system to ensure stable operation over fluctuating environmental conditions. This highly adaptable multi-laser source can address various sensing applications requiring the tracking of up to three narrow spectral features with a high bandwidth. It is used to sense a fiber-based ring resonator emulating a resonant fiber optics gyroscope. The master laser is locked to the resonator with a loop bandwidth greater than 1 MHz. The slave lasers are offset frequency locked to the master laser with loop bandwidths greater than 100 MHz. This high performance source is compact, automated, robust, and remains locked for days.

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

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

NASA Technical Reports Server (NTRS)

Broussard, J. R.; Halyo, N.

1984-01-01

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

Optical set-reset latch

DOEpatents

Skogen, Erik J.

2013-01-29

An optical set-reset (SR) latch is formed from a first electroabsorption modulator (EAM), a second EAM and a waveguide photodetector (PD) which are arranged in an optical and electrical feedback loop which controls the transmission of light through the first EAM to latch the first EAM in a light-transmissive state in response to a Set light input. A second waveguide PD controls the transmission of light through the second EAM and is used to switch the first EAM to a light-absorptive state in response to a Reset light input provided to the second waveguide PD. The optical SR latch, which may be formed on a III-V compound semiconductor substrate (e.g. an InP or a GaAs substrate) as a photonic integrated circuit (PIC), stores a bit of optical information and has an optical output for the logic state of that bit of information.

Complexity in built environment, health, and destination walking: a neighborhood-scale analysis.

PubMed

Carlson, Cynthia; Aytur, Semra; Gardner, Kevin; Rogers, Shannon

2012-04-01

This study investigates the relationships between the built environment, the physical attributes of the neighborhood, and the residents' perceptions of those attributes. It focuses on destination walking and self-reported health, and does so at the neighborhood scale. The built environment, in particular sidewalks, road connectivity, and proximity of local destinations, correlates with destination walking, and similarly destination walking correlates with physical health. It was found, however, that the built environment and health metrics may not be simply, directly correlated but rather may be correlated through a series of feedback loops that may regulate risk in different ways in different contexts. In particular, evidence for a feedback loop between physical health and destination walking is observed, as well as separate feedback loops between destination walking and objective metrics of the built environment, and destination walking and perception of the built environment. These feedback loops affect the ability to observe how the built environment correlates with residents' physical health. Previous studies have investigated pieces of these associations, but are potentially missing the more complex relationships present. This study proposes a conceptual model describing complex feedback relationships between destination walking and public health, with the built environment expected to increase or decrease the strength of the feedback loop. Evidence supporting these feedback relationships is presented.

Common mode frequency instability in internally phase-locked terahertz quantum cascade lasers.

PubMed

Wanke, M C; Grine, A D; Fuller, C T; Nordquist, C D; Cich, M J; Reno, J L; Lee, Mark

2011-11-21

Feedback from a diode mixer integrated into a 2.8 THz quantum cascade laser (QCL) was used to phase lock the difference frequencies (DFs) among the Fabry-Perot (F-P) longitudinal modes of a QCL. Approximately 40% of the DF power was phase locked, consistent with feedback loop bandwidth of 10 kHz and phase noise bandwidth ~0.5 MHz. While the locked DF signal has ≤ 1 Hz linewidth and negligible drift over ~30 min, mixing measurements between two QCLs and between a QCL and molecular gas laser show that the common mode frequency stability is no better than a free-running QCL. © 2011 Optical Society of America

Generation of mechanical oscillation applicable to vibratory rate gyroscopes

NASA Technical Reports Server (NTRS)

Lemkin, Mark A. (Inventor); Juneau, Thor N. (Inventor); Clark, William A. (Inventor); Roessig, Allen W. (Inventor)

2001-01-01

To achieve a drive-axis oscillation with improved frequency and amplitude stability, additional feedback loops are used to adjust force-feedback loop parameters. An amplitude-control loop measures oscillation amplitude, compares this value to the desired level, and adjusts damping of the mechanical sense-element to grow or shrink oscillation amplitude as appropriate. A frequency-tuning loop measures the oscillation frequency, compares this value with a highly stable reference, and adjusts the gain in the force-feedback loop to keep the drive-axis oscillation frequency at the reference value. The combined topology simultaneously controls both amplitude and frequency. Advantages of the combined topology include improved stability, fast oscillation start-up, low power consumption, and excellent shock rejection.

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

PubMed

Fei, Juntao; Lu, Cheng

2018-04-01

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

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.

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

PubMed

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

2016-01-01

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

CW injection locking for long-term stability of frequency combs

NASA Astrophysics Data System (ADS)

Williams, Charles; Quinlan, Franklyn; Delfyett, Peter J.

2009-05-01

Harmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Continuous wave (CW) injection locking further reduces linewidth and stabilizes the optical frequencies. The output can be stabilized long-term with the help of a modified Pound-Drever-Hall feedback loop. Optical sidemode suppression of 36 dB has been shown, as well as RF supermode noise suppression of 14 dB for longer than 1 hour. In addition to the injection locking of harmonically mode-locked lasers requiring an external frequency source, recent work shows the viability of the injection locking technique for regeneratively mode-locked lasers, or Coupled Opto-Electronic Oscillators (COEO).

Steering and positioning targets for HWIL IR testing at cryogenic conditions

NASA Astrophysics Data System (ADS)

Perkes, D. W.; Jensen, G. L.; Higham, D. L.; Lowry, H. S.; Simpson, W. R.

2006-05-01

In order to increase the fidelity of hardware-in-the-loop ground-truth testing, it is desirable to create a dynamic scene of multiple, independently controlled IR point sources. ATK-Mission Research has developed and supplied the steering mirror systems for the 7V and 10V Space Simulation Test Chambers at the Arnold Engineering Development Center (AEDC), Air Force Materiel Command (AFMC). A portion of the 10V system incorporates multiple target sources beam-combined at the focal point of a 20K cryogenic collimator. Each IR source consists of a precision blackbody with cryogenic aperture and filter wheels mounted on a cryogenic two-axis translation stage. This point source target scene is steered by a high-speed steering mirror to produce further complex motion. The scene changes dynamically in order to simulate an actual operational scene as viewed by the System Under Test (SUT) as it executes various dynamic look-direction changes during its flight to a target. Synchronization and real-time hardware-in-the-loop control is accomplished using reflective memory for each subsystem control and feedback loop. This paper focuses on the steering mirror system and the required tradeoffs of optical performance, precision, repeatability and high-speed motion as well as the complications of encoder feedback calibration and operation at 20K.

Status of E-ELT M5 scale-one demonstrator

NASA Astrophysics Data System (ADS)

Barriga, Pablo; Sedghi, Babak; Dimmler, Martin; Kornweibel, Nick

2014-07-01

The fifth mirror of the European Extremely Large Telescope optical train is a field stabilization tip/tilt unit responsible for correcting the dynamical tip and tilt caused mainly by wind load on the telescope. A scale-one prototype including the inclined support, the fixed frame and a basic control system was designed and manufactured by NTE-SENER (Spain) and CSEM (Switzerland) as part of the prototyping and design activities. All interfaces to the mirror have been reproduced on a dummy structure reproducing the inertial characteristics of the optical element. The M5 unit is required to have sufficient bandwidth for tip/tilt reference commands coming from the wavefront control system. Such a bandwidth can be achieved using local active damping loop to damp the low frequency mechanical modes before closing a position loop. Prototyping on the M5 unit has been undertaken in order to demonstrate the E-ELT control system architecture, concepts and development standards and to further study active damping strategies. The control system consists of two nested loops: a local damping loop and a position loop. The development of this control system was undertaken following the E-ELT control system development standards in order to determine their applicability and performance and includes hardware selection, communication, synchronization, configuration, and data logging. In this paper we present the current status of the prototype M5 control system and the latest results on the active damping control strategy, in particular the promising results obtained with the method of positive position feedback.

In-line Microwave Warmer for Blood and Intravenous Fluids.

DTIC Science & Technology

1989-12-14

circuit was designed and tested. This circuit uses a digitally controlled optically coupled Triac , a thyristor device, which acts as a switch to allow...three sites of the circuit : Inlet Port of Heating Chamber Interior Path of Heating Chamber Outlet Port of Heating Chamber 4) Feedback Control Mechanism...accomplished through use of a closed loop test circuit depicted in Figure 1-2. This test circuit can be used to heat iv fluids or blood on a continuous

Feedback control methods for drug dosage optimisation. Concepts, classification and clinical application.

PubMed

Vozeh, S; Steimer, J L

1985-01-01

The concept of feedback control methods for drug dosage optimisation is described from the viewpoint of control theory. The control system consists of 5 parts: (a) patient (the controlled process); (b) response (the measured feedback); (c) model (the mathematical description of the process); (d) adaptor (to update the parameters); and (e) controller (to determine optimum dosing strategy). In addition to the conventional distinction between open-loop and closed-loop control systems, a classification is proposed for dosage optimisation techniques which distinguishes between tight-loop and loose-loop methods depending on whether physician's interaction is absent or included as part of the control step. Unlike engineering problems where the process can usually be controlled by fully automated devices, therapeutic situations often require that the physician be included in the decision-making process to determine the 'optimal' dosing strategy. Tight-loop and loose-loop methods can be further divided into adaptive and non-adaptive, depending on the presence of the adaptor. The main application areas of tight-loop feedback control methods are general anaesthesia, control of blood pressure, and insulin delivery devices. Loose-loop feedback methods have been used for oral anticoagulation and in therapeutic drug monitoring. The methodology, advantages and limitations of the different approaches are reviewed. A general feature common to all application areas could be observed: to perform well under routine clinical conditions, which are characterised by large interpatient variability and sometimes also intrapatient changes, control systems should be adaptive. Apart from application in routine drug treatment, feedback control methods represent an important research tool. They can be applied for the investigation of pathophysiological and pharmacodynamic processes. A most promising application is the evaluation of the relationship between an intermediate response (e.g. drug level), which is often used as feedback for dosage adjustment, and the final therapeutic goal.

Focus scanning with feedback control for fiber-optic nonlinear endomicroscopy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Li, Ang; Liang, Wenxuan; Li, Xingde

2017-02-01

Fiber-optic nonlinear endomicroscopy represents a strong promise to enable translation of nonlinear microscopy technologies to in vivo applications, particularly imaging of internal organs. Two-dimensional imaging beam scanning has been accomplished by using fiber-optic scanners or MEMS scanners. Yet nonlinear endomicroscopy still cannot perform rapid and reliable depth or focus scanning while maintaining a small form factor. Shape memory alloy (SMA) wire had shown promise in extending 2D endoscopic imaging to the third dimension. By Joule heating, the SMA wire would contract and move the endomicroscope optics to change beam focus. However, this method suffered from hysteresis, and was susceptible to change in ambient temperature, making it difficult to achieve accurate and reliable depth scanning. Here we present a feedback-controlled SMA actuator which addressed these challenges. The core of the feedback loop was a Hall effect sensor. By measuring the magnetic flux density from a tiny magnet attached to the SMA wire, contraction distance of the SMA wire could be tracked in real time. The distance was then fed to the PID algorithm running in a microprocessor, which computed the error between the command position and the current position of the actuator. The current running through the SMA wire was adjusted accordingly. Our feedback-controlled SMA actuator had a tube-like shape with outer diameter of 5.5 mm and length of 25 mm, and was designed to house the endomicroscope inside. Initial test showed that it allowed more than 300 microns of travel distance, with an average positioning error of less than 2 microns. 3D imaging experiments with the endomicroscope is underway, and its imaging performance will be assessed and discussed.

The Extended-Image Tracking Technique Based on the Maximum Likelihood Estimation

NASA Technical Reports Server (NTRS)

Tsou, Haiping; Yan, Tsun-Yee

2000-01-01

This paper describes an extended-image tracking technique based on the maximum likelihood estimation. The target image is assume to have a known profile covering more than one element of a focal plane detector array. It is assumed that the relative position between the imager and the target is changing with time and the received target image has each of its pixels disturbed by an independent additive white Gaussian noise. When a rotation-invariant movement between imager and target is considered, the maximum likelihood based image tracking technique described in this paper is a closed-loop structure capable of providing iterative update of the movement estimate by calculating the loop feedback signals from a weighted correlation between the currently received target image and the previously estimated reference image in the transform domain. The movement estimate is then used to direct the imager to closely follow the moving target. This image tracking technique has many potential applications, including free-space optical communications and astronomy where accurate and stabilized optical pointing is essential.

Coherent beam combining of collimated fiber array based on target-in-the-loop technique

NASA Astrophysics Data System (ADS)

Li, Xinyang; Geng, Chao; Zhang, Xiaojun; Rao, Changhui

2011-11-01

Coherent beam combining (CBC) of fiber array is a promising way to generate high power and high quality laser beams. Target-in-the-loop (TIL) technique might be an effective way to ensure atmosphere propagation compensation without wavefront sensors. In this paper, we present very recent research work about CBC of collimated fiber array using TIL technique at the Key Lab on Adaptive Optics (KLAO), CAS. A novel Adaptive Fiber Optics Collimator (AFOC) composed of phase-locking module and tip/tilt control module was developed. CBC experimental setup of three-element fiber array was established. Feedback control is realized using stochastic parallel gradient descent (SPGD) algorithm. The CBC based on TIL with piston and tip/tilt correction simultaneously is demonstrated. And the beam pointing to locate or sweep position of combined spot on target was achieved through TIL technique too. The goal of our work is achieve multi-element CBC for long-distance transmission in atmosphere.

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.

An ultra-fast EOD-based force-clamp detects rapid biomechanical transitions

NASA Astrophysics Data System (ADS)

Woody, Michael S.; Capitanio, Marco; Ostap, E. Michael; Goldman, Yale E.

2017-08-01

We assembled an ultra-fast infrared optical trapping system to detect mechanical events that occur less than a millisecond after a ligand binds to its filamentous substrate, such as myosin undergoing its 5 - 10 nm working stroke after actin binding. The instrument is based on the concept of Capitanio et al.1, in which a polymer bead-actin-bead dumbbell is held in two force-clamped optical traps. A force applied by the traps causes the filament to move at a constant velocity as hydrodynamic drag balances the applied load. When the ligand binds, the filament motion stops within 100 μs as the total force from the optical traps is transferred to the attachment. Subsequent translations signal active motions, such as the magnitude and timing of the motor's working stroke. In our instrument, the beads defining the dumbbell are held in independent force clamps utilizing a field-programmable gate array (FPGA) to update the trap beam positions at 250 kHz. We found that in our setup, acousto-optical deflectors (AODs) steering the beams were unsuitable for this purpose due to a slightly non-linear response in the beam intensity and deflection angle vs. the AOD ultra-sound wavelength, likely caused by low-amplitude standing acoustic waves in the deflectors. These aberrations caused instability in the force feedback loops leading to artefactual 20 nm jumps in position. This type of AOD non-linearity has been reported to be absent in electro-optical deflectors (EODs)2. We demonstrate that replacement of the AODs with EODs improves the performance of our instrument. Combining the superior beam-steering capability of the EODs, force acquisition via back-plane interferometry, and the dual high-speed FPGA-based feedback loops, we smoothly and precisely apply constant loads to study the dynamics of interactions between biological molecules such as actin and myosin.

All-Optical Implementation of the Ant Colony Optimization Algorithm

PubMed Central

Hu, Wenchao; Wu, Kan; Shum, Perry Ping; Zheludev, Nikolay I.; Soci, Cesare

2016-01-01

We report all-optical implementation of the optimization algorithm for the famous “ant colony” problem. Ant colonies progressively optimize pathway to food discovered by one of the ants through identifying the discovered route with volatile chemicals (pheromones) secreted on the way back from the food deposit. Mathematically this is an important example of graph optimization problem with dynamically changing parameters. Using an optical network with nonlinear waveguides to represent the graph and a feedback loop, we experimentally show that photons traveling through the network behave like ants that dynamically modify the environment to find the shortest pathway to any chosen point in the graph. This proof-of-principle demonstration illustrates how transient nonlinearity in the optical system can be exploited to tackle complex optimization problems directly, on the hardware level, which may be used for self-routing of optical signals in transparent communication networks and energy flow in photonic systems. PMID:27222098

Decision feedback loop for tracking a polyphase modulated carrier

NASA Technical Reports Server (NTRS)

Simon, M. K. (Inventor)

1974-01-01

A multiple phase modulated carrier tracking loop for use in a frequency shift keying system is described in which carrier tracking efficiency is improved by making use of the decision signals made on the data phase transmitted in each T-second interval. The decision signal is used to produce a pair of decision-feedback quadrature signals for enhancing the loop's performance in developing a loop phase error signal.

Finite Feedback Cycling in Structural Equation Models

ERIC Educational Resources Information Center

Hayduk, Leslie A.

2009-01-01

In models containing reciprocal effects, or longer causal loops, the usual effect estimates assume that any effect touching a loop initiates an infinite cycling of effects around that loop. The real world, in contrast, might permit only finite feedback cycles. I use a simple hypothetical model to demonstrate that if the world permits only a few…

General theory of feedback control of a nuclear spin ensemble in quantum dots

NASA Astrophysics Data System (ADS)

Yang, Wen; Sham, L. J.

2013-12-01

We present a microscopic theory of the nonequilibrium nuclear spin dynamics driven by the electron and/or hole under continuous-wave pumping in a quantum dot. We show the correlated dynamics of the nuclear spin ensemble and the electron and/or hole under optical excitation as a quantum feedback loop and investigate the dynamics of the many nuclear spins as a nonlinear collective motion. This gives rise to three observable effects: (i) hysteresis, (ii) locking (avoidance) of the pump absorption strength to (from) the natural resonance, and (iii) suppression (amplification) of the fluctuation of weakly polarized nuclear spins, leading to prolonged (shortened) electron-spin coherence time. A single nonlinear feedback function is constructed which determines the different outcomes of the three effects listed above depending on the feedback being negative or positive. The general theory also helps to put in perspective the wide range of existing theories on the problem of a single electron spin in a nuclear spin bath.

Balanced bridge feedback control system

NASA Technical Reports Server (NTRS)

Lurie, Boris J. (Inventor)

1990-01-01

In a system having a driver, a motor, and a mechanical plant, a multiloop feedback control apparatus for controlling the movement and/or positioning of a mechanical plant, the control apparatus has a first local bridge feedback loop for feeding back a signal representative of a selected ratio of voltage and current at the output driver, and a second bridge feedback loop for feeding back a signal representative of a selected ratio of force and velocity at the output of the motor. The control apparatus may further include an outer loop for feeding back a signal representing the angular velocity and/or position of the mechanical plant.

Plug-in module acceleration feedback control for fast steering mirror-based beam stabilization systems

NASA Astrophysics Data System (ADS)

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

2017-08-01

A plug-in module acceleration feedback control (Plug-In AFC) strategy based on the disturbance observer (DOB) principle is proposed for charge-coupled device (CCD)-based fast steering mirror (FSM) stabilization systems. In classical FSM tracking systems, dual-loop control (DLC), including velocity feedback and position feedback, is usually utilized to enhance the closed-loop performance. Due to the mechanical resonance of the system and CCD time delay, the closed-loop bandwidth is severely restricted. To solve this problem, cascade acceleration feedback control (AFC), which is a kind of high-precision robust control method, is introduced to strengthen the disturbance rejection property. However, in practical applications, it is difficult to realize an integral algorithm in an acceleration controller to compensate for the quadratic differential contained in the FSM acceleration model, resulting in a challenging controller design and a limited improvement. To optimize the acceleration feedback framework in the FSM system, different from the cascade AFC, the accelerometers are used to construct DOB to compensate for the platform vibrations directly. The acceleration nested loop can be plugged into the velocity loop without changing the system stability, and the controller design is quite simple. A series of comparative experimental results demonstrate that the disturbance rejection property of the CCD-based FSM can be effectively improved by the proposed approach.

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

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

PubMed Central

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

2016-01-01

Son of sevenless (SOS) is a guanine nucleotide exchange factor that regulates cell behavior by activating the small GTPase RAS. Recent in vitro studies have suggested that an interaction between SOS and the GTP-bound active form of RAS generates a positive feedback loop that propagates RAS activation. However, it remains unclear how the multiple domains of SOS contribute to the regulation of the feedback loop in living cells. Here, we observed single molecules of SOS in living cells to analyze the kinetics and dynamics of SOS behavior. The results indicate that the histone fold and Grb2-binding domains of SOS concertedly produce an intermediate state of SOS on the cell surface. The fraction of the intermediated state was reduced in positive feedback mutants, suggesting that the feedback loop functions during the intermediate state. Translocation of RAF, recognizing the active form of RAS, to the cell surface was almost abolished in the positive feedback mutants. Thus, the concerted functions of multiple membrane-associating domains of SOS governed the positive feedback loop, which is crucial for cell fate decision regulated by RAS. PMID:27924253

Closing the Feedback Loop: Ensuring Effective Action from Student Feedback

ERIC Educational Resources Information Center

Watson, Sarah

2003-01-01

Feedback from students can inform improvement in higher education institutions and be part of the students' role in university management. To be effective it is important to"close the loop": from student views, through identifying issues and delegating responsibility for action, to informing students of the action resulting from their expressed…

Feedback Synthesizes Neural Codes for Motion.

PubMed

Clarke, Stephen E; Maler, Leonard

2017-05-08

In senses as diverse as vision, hearing, touch, and the electrosense, sensory neurons receive bottom-up input from the environment, as well as top-down input from feedback loops involving higher brain regions [1-4]. Through connectivity with local inhibitory interneurons, these feedback loops can exert both positive and negative control over fundamental aspects of neural coding, including bursting [5, 6] and synchronous population activity [7, 8]. Here we show that a prominent midbrain feedback loop synthesizes a neural code for motion reversal in the hindbrain electrosensory ON- and OFF-type pyramidal cells. This top-down mechanism generates an accurate bidirectional encoding of object position, despite the inability of the electrosensory afferents to generate a consistent bottom-up representation [9, 10]. The net positive activity of this midbrain feedback is additionally regulated through a hindbrain feedback loop, which reduces stimulus-induced bursting and also dampens the ON and OFF cell responses to interfering sensory input [11]. We demonstrate that synthesis of motion representations and cancellation of distracting signals are mediated simultaneously by feedback, satisfying an accepted definition of spatial attention [12]. The balance of excitatory and inhibitory feedback establishes a "focal" distance for optimized neural coding, whose connection to a classic motion-tracking behavior provides new insight into the computational roles of feedback and active dendrites in spatial localization [13, 14]. Copyright © 2017 Elsevier Ltd. All rights reserved.

Open-loop-feedback control of serum drug concentrations: pharmacokinetic approaches to drug therapy.

PubMed

Jelliffe, R W

1983-01-01

Recent developments to optimize open-loop-feedback control of drug dosage regimens, generally applicable to pharmacokinetically oriented therapy with many drugs, involve computation of patient-individualized strategies for obtaining desired serum drug concentrations. Analyses of past therapy are performed by least squares, extended least squares, and maximum a posteriori probability Bayesian methods of fitting pharmacokinetic models to serum level data. Future possibilities for truly optimal open-loop-feedback therapy with full Bayesian methods, and conceivably for optimal closed-loop therapy in such data-poor clinical situations, are also discussed. Implementation of these various therapeutic strategies, using automated, locally controlled infusion devices, has also been achieved in prototype form.

Log amplifier with pole-zero compensation

DOEpatents

Brookshier, William

1987-01-01

A logarithmic amplifier circuit provides pole-zero compensation for improved stability and response time over 6-8 decades of input signal frequency. The amplifier circuit includes a first operational amplifier with a first feedback loop which includes a second, inverting operational amplifier in a second feedback loop. The compensated output signal is provided by the second operational amplifier with the log elements, i.e., resistors, and the compensating capacitors in each of the feedback loops having equal values so that each break point or pole is offset by a compensating break point or zero.

High alpha feedback control for agile half-loop maneuvers of the F-18 airplane

NASA Technical Reports Server (NTRS)

Stalford, Harold

1988-01-01

A nonlinear feedback control law for the F/A-18 airplane that provides time-optimal or agile maneuvering of the half-loop maneuver at high angles of attack is given. The feedback control law was developed using the mathematical approach of singular perturbations, in which the control devices considered were conventional aerodynamic control surfaces and thrusting. The derived nonlinear control law was used to simulate F/A-18 half-loop maneuvers. The simulated results at Mach 0.6 and 0.9 compared well with pilot simulations conducted at NASA.

Offset quadrature communications with decision-feedback carrier synchronization

NASA Technical Reports Server (NTRS)

Simon, M. K.; Smith, J. G.

1974-01-01

In order to accommodate a quadrature amplitude-shift-keyed (QASK) signal, Simon and Smith (1974) have modified the decision-feedback loop which tracks a quadrature phase-shift-keyed (QPSK). In the investigation reported approaches are considered to modify the loops in such a way that offset QASK signals can be tracked, giving attention to the special case of an offset QPSK. The development of the stochastic integro-differential equation of operation for a decision-feedback offset QASK loop is discussed along with the probability density function of the phase error process.

Generalized fast feedback system in the SLC

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

Hendrickson, L.; Allison, S.; Gromme, T.

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

Development of a laser Doppler displacement encoder system with ultra-low-noise-level for linear displacement measurement with subnanometer resolution - Final CRADA Report

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

Shu, Deming

An U.S. DOE Cooperative Research and Development Agreement (CRADA) between ANL and Optodyne, Inc. has been established to develop a prototype laser Doppler displacement encoder system with ultra-low noise level for linear measurements to sub-nanometer resolution for synchrotron radiation applications. We have improved the heterodyne efficiency and reduced the detector shot noises by proper shielding and adding a low-pass filter. The laser Doppler displacement encoder system prototype demonstrated a ~ 1 nm system output noise floor with single reflection optics. With multiple-pass optical arrangement, 0.1 nm scale closed-loop feedback control is achieved.

A Review of Control Strategies in Closed-Loop Neuroprosthetic Systems

PubMed Central

Wright, James; Macefield, Vaughan G.; van Schaik, André; Tapson, Jonathan C.

2016-01-01

It has been widely recognized that closed-loop neuroprosthetic systems achieve more favorable outcomes for users then equivalent open-loop devices. Improved performance of tasks, better usability, and greater embodiment have all been reported in systems utilizing some form of feedback. However, the interdisciplinary work on neuroprosthetic systems can lead to miscommunication due to similarities in well-established nomenclature in different fields. Here we present a review of control strategies in existing experimental, investigational and clinical neuroprosthetic systems in order to establish a baseline and promote a common understanding of different feedback modes and closed-loop controllers. The first section provides a brief discussion of feedback control and control theory. The second section reviews the control strategies of recent Brain Machine Interfaces, neuromodulatory implants, neuroprosthetic systems, and assistive neurorobotic devices. The final section examines the different approaches to feedback in current neuroprosthetic and neurorobotic systems. PMID:27462202

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

PubMed

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

2016-02-01

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

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

PubMed Central

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

2016-01-01

Background Depression is a complex public health problem with considerable variation in treatment response. The systemic complexity of depression, or the feedback processes among diverse drivers of the disorder, contribute to the persistence of depression. This paper extends prior attempts to understand the complex causal feedback mechanisms that underlie depression by presenting the first broad boundary causal loop diagram of depression dynamics. Method We applied qualitative system dynamics methods to map the broad feedback mechanisms of depression. We used a structured approach to identify candidate causal mechanisms of depression in the literature. We assessed the strength of empirical support for each mechanism and prioritized those with support from validation studies. Through an iterative process, we synthesized the empirical literature and created a conceptual model of major depressive disorder. Results The literature review and synthesis resulted in the development of the first causal loop diagram of reinforcing feedback processes of depression. It proposes candidate drivers of illness, or inertial factors, and their temporal functioning, as well as the interactions among drivers of depression. The final causal loop diagram defines 13 key reinforcing feedback loops that involve nine candidate drivers of depression. Conclusions Future research is needed to expand upon this initial model of depression dynamics. Quantitative extensions may result in a better understanding of the systemic syndrome of depression and contribute to personalized methods of evaluation, prevention and intervention. PMID:26621339

LINC-NIRVANA piston control elements

NASA Astrophysics Data System (ADS)

Brix, Mario; Pott, Jörg-Uwe; Bertram, Thomas; Rost, Steffen; Borelli, Jose Luis; Herbst, Thomas M.; Kuerster, Martin; Rohloff, Ralf-Rainer

2010-07-01

We review the status of hardware developments related to the Linc-Nirvana optical path difference (OPD) control. The status of our telescope vibration measurements is given. We present the design concept of a feed-forward loop to damp the impact of telescope mirror vibrations on the OPD seen by Linc-Nirvana. At the focus of the article is a description of the actuator of the OPD control loop. The weight and vibration optimized construction of this actuator (aka piston mirror) and its mount has a complex dynamical behavior, which prevents classical PI feedback control from delivering fast and precise motion of the mirror surface. Therefore, an H-; optimized control strategy will be applied, custom designed for the piston mirror. The effort of realizing a custom controller on a DSP to drive the piezo is balanced by the outlook of achieving more than 5x faster servo bandwidths. The laboratory set-up to identify the system, and verify the closed loop control performance is presented. Our goal is to achieve 30 Hz closed-loop control bandwidth at a precision of 30 nm.

Good vibrations: Controlling light with sound (Conference Presentation)

NASA Astrophysics Data System (ADS)

Eggleton, Benjamin J.; Choudhary, Amol

2016-10-01

One of the surprises of nonlinear optics, is that light may interact strongly with sound. Intense laser light literally "shakes" the glass in optical fibres, exciting acoustic waves (sound) in the fibre. Under the right conditions, it leads to a positive feedback loop between light and sound termed "Stimulated Brillouin Scattering," or simply SBS. This nonlinear interaction can amplify or filter light waves with extreme precision in frequency which makes it uniquely suited to solve key problems in the fields of defence, biomedicine, wireless communications, spectroscopy and imaging. We have achieved the first demonstration of SBS in compact chip-scale structures, carefully designed so that the optical fields and the acoustic fields are simultaneously confined and guided. This new platform has opened a range of new functionalities that are being applied in communications and defence with breathtaking performance and compactness. My talk will introduce this new field and review our progress and achievements, including silicon based optical phononic processor.

Digital Optical Control System

NASA Astrophysics Data System (ADS)

Jordan, David H.; Tipton, Charles A.; Christmann, Charles E.; Hochhausler, Nils P.

1988-09-01

We describe the digital optical control system (DOGS), a state-of-the-art controller for electrical feedback in an optical system. The need for a versatile optical controller arose from a number of unique experiments being performed by the Air Force Weapons Laboratory. These experiments use similar detectors and actuator-controlled mirrors, but the control requirements vary greatly. The experiments have in common a requirement for parallel control systems. The DOGS satisfies these needs by allowing several control systems to occupy a single chassis with one master controller. The architecture was designed to allow upward compatibility with future configurations. Combinations of off-the-shelf and custom boards are configured to meet the requirements of each experiment. The configuration described here was used to control piston error to X/80 at a wavelength of 0.51 Am. A peak sample rate of 8 kHz, yielding a closed loop bandwidth of 800 Hz, was achieved.

Controlling the 1 μm spontaneous emission in Er/Yb co-doped fiber amplifiers.

PubMed

Sobon, Grzegorz; Kaczmarek, Pawel; Antonczak, Arkadiusz; Sotor, Jaroslaw; Abramski, Krzysztof M

2011-09-26

In this paper we present our experimental studies on controlling the amplified spontaneous emission (ASE) from Yb(3+) ions in Er/Yb co-doped fiber amplifiers. We propose a new method of controlling the Yb-ASE by stimulating a laser emission at 1064 nm in the amplifier, by providing a positive 1 μm signal feedback loop. The results are discussed and compared to a conventional amplifier setup without 1 μm ASE control and to an amplifier with auxiliary 1064 nm seeding. We have shown, that applying a 1064 nm signal loop in an Er/Yb amplifier can increase the output power at 1550 nm and provide stable operation without parasitic lasing at 1 μm. © 2011 Optical Society of America

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.

Digital phase-lock loop

NASA Technical Reports Server (NTRS)

Thomas, Jr., Jess B. (Inventor)

1991-01-01

An improved digital phase lock loop incorporates several distinctive features that attain better performance at high loop gain and better phase accuracy. These features include: phase feedback to a number-controlled oscillator in addition to phase rate; analytical tracking of phase (both integer and fractional cycles); an amplitude-insensitive phase extractor; a more accurate method for extracting measured phase; a method for changing loop gain during a track without loss of lock; and a method for avoiding loss of sampled data during computation delay, while maintaining excellent tracking performance. The advantages of using phase and phase-rate feedback are demonstrated by comparing performance with that of rate-only feedback. Extraction of phase by the method of modeling provides accurate phase measurements even when the number-controlled oscillator phase is discontinuously updated.

Modulation of dynamic modes by interplay between positive and negative feedback loops in gene regulatory networks

NASA Astrophysics Data System (ADS)

Wang, Liu-Suo; Li, Ning-Xi; Chen, Jing-Jia; Zhang, Xiao-Peng; Liu, Feng; Wang, Wei

2018-04-01

A positive and a negative feedback loop can induce bistability and oscillation, respectively, in biological networks. Nevertheless, they are frequently interlinked to perform more elaborate functions in many gene regulatory networks. Coupled positive and negative feedback loops may exhibit either oscillation or bistability depending on the intensity of the stimulus in some particular networks. It is less understood how the transition between the two dynamic modes is modulated by the positive and negative feedback loops. We developed an abstract model of such systems, largely based on the core p53 pathway, to explore the mechanism for the transformation of dynamic behaviors. Our results show that enhancing the positive feedback may promote or suppress oscillations depending on the strength of both feedback loops. We found that the system oscillates with low amplitudes in response to a moderate stimulus and switches to the on state upon a strong stimulus. When the positive feedback is activated much later than the negative one in response to a strong stimulus, the system exhibits long-term oscillations before switching to the on state. We explain this intriguing phenomenon using quasistatic approximation. Moreover, early switching to the on state may occur when the system starts from a steady state in the absence of stimuli. The interplay between the positive and negative feedback plays a key role in the transitions between oscillation and bistability. Of note, our conclusions should be applicable only to some specific gene regulatory networks, especially the p53 network, in which both oscillation and bistability exist in response to a certain type of stimulus. Our work also underscores the significance of transient dynamics in determining cellular outcome.

Information-reduced Carrier Synchronization of Iterative Decoded BPSK and QPSK using Soft Decision (Extrinsic) Feedback

NASA Technical Reports Server (NTRS)

Simon, Marvin; Valles, Esteban; Jones, Christopher

2008-01-01

This paper addresses the carrier-phase estimation problem under low SNR conditions as are typical of turbo- and LDPC-coded applications. In previous publications by the first author, closed-loop carrier synchronization schemes for error-correction coded BPSK and QPSK modulation were proposed that were based on feeding back hard data decisions at the input of the loop, the purpose being to remove the modulation prior to attempting to track the carrier phase as opposed to the more conventional decision-feedback schemes that incorporate such feedback inside the loop. In this paper, we consider an alternative approach wherein the extrinsic soft information from the iterative decoder of turbo or LDPC codes is instead used as the feedback.

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

NASA Technical Reports Server (NTRS)

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

2004-01-01

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

Laser output power stabilization for direct laser writing system by using an acousto-optic modulator.

PubMed

Kim, Dong Ik; Rhee, Hyug-Gyo; Song, Jae-Bong; Lee, Yun-Woo

2007-10-01

We present experimental results on the output power stabilization of an Ar(+) laser for a direct laser writing system (LWS). Instability of the laser output power in the LWS cause resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. In this system, we have achieved the stability of +/-0.20% for 12 min and the relative intensity noise level of 2.1 x 10(-7) Hz(-12) at 100 Hz. In addition, we applied our system to a 2 mW internal mirror He-Ne laser. As a consequence, we achieved the output power stability of +/-0.12% for 25 min.

A Robust Distributed Multipoint Fiber Optic Gas Sensor System Based on AGC Amplifier Structure.

PubMed

Zhu, Cunguang; Wang, Rende; Tao, Xuechen; Wang, Guangwei; Wang, Pengpeng

2016-07-28

A harsh environment-oriented distributed multipoint fiber optic gas sensor system realized by automatic gain control (AGC) technology is proposed. To improve the photoelectric signal reliability, the electronic variable gain can be modified in real time by an AGC closed-loop feedback structure to compensate for optical transmission loss which is caused by the fiber bend loss or other reasons. The deviation of the system based on AGC structure is below 4.02% when photoelectric signal decays due to fiber bending loss for bending radius of 5 mm, which is 20 times lower than the ordinary differential system. In addition, the AGC circuit with the same electric parameters can keep the baseline intensity of signals in different channels of the distributed multipoint sensor system at the same level. This avoids repetitive calibrations and streamlines the installation process.

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

ERIC Educational Resources Information Center

Lee, Eun Jeong

2017-01-01

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

Design of multivariable feedback control systems via spectral assignment using reduced-order models and reduced-order observers

NASA Technical Reports Server (NTRS)

Mielke, R. R.; Tung, L. J.; Carraway, P. I., III

1984-01-01

The feasibility of using reduced order models and reduced order observers with eigenvalue/eigenvector assignment procedures is investigated. A review of spectral assignment synthesis procedures is presented. Then, a reduced order model which retains essential system characteristics is formulated. A constant state feedback matrix which assigns desired closed loop eigenvalues and approximates specified closed loop eigenvectors is calculated for the reduced order model. It is shown that the eigenvalue and eigenvector assignments made in the reduced order system are retained when the feedback matrix is implemented about the full order system. In addition, those modes and associated eigenvectors which are not included in the reduced order model remain unchanged in the closed loop full order system. The full state feedback design is then implemented by using a reduced order observer. It is shown that the eigenvalue and eigenvector assignments of the closed loop full order system rmain unchanged when a reduced order observer is used. The design procedure is illustrated by an actual design problem.

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

PubMed Central

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

2014-01-01

We analyze the microstructure of child-adult interaction during naturalistic, daylong, automatically labeled audio recordings (13,836 hours total) of children (8- to 48-month-olds) with and without autism. We find that adult responses are more likely when child vocalizations are speech-related. In turn, a child vocalization is more likely to be speech-related if the previous speech-related child vocalization received an immediate adult response. Taken together, these results are consistent with the idea that there is a social feedback loop between child and caregiver that promotes speech-language development. Although this feedback loop applies in both typical development and autism, children with autism produce proportionally fewer speech-related vocalizations and the responses they receive are less contingent on whether their vocalizations are speech-related. We argue that such differences will diminish the strength of the social feedback loop with cascading effects on speech development over time. Differences related to socioeconomic status are also reported. PMID:24840717

Linear state feedback, quadratic weights, and closed loop eigenstructures. M.S. Thesis

NASA Technical Reports Server (NTRS)

Thompson, P. M.

1979-01-01

Results are given on the relationships between closed loop eigenstructures, state feedback gain matrices of the linear state feedback problem, and quadratic weights of the linear quadratic regulator. Equations are derived for the angles of general multivariable root loci and linear quadratic optimal root loci, including angles of departure and approach. The generalized eigenvalue problem is used for the first time to compute angles of approach. Equations are also derived to find the sensitivity of closed loop eigenvalues and the directional derivatives of closed loop eigenvectors (with respect to a scalar multiplying the feedback gain matrix or the quadratic control weight). An equivalence class of quadratic weights that produce the same asymptotic eigenstructure is defined, sufficient conditions to be in it are given, a canonical element is defined, and an algorithm to find it is given. The behavior of the optimal root locus in the nonasymptotic region is shown to be different for quadratic weights with the same asymptotic properties.

Design of multivariable feedback control systems via spectral assignment using reduced-order models and reduced-order observers

NASA Technical Reports Server (NTRS)

Mielke, R. R.; Tung, L. J.; Carraway, P. I., III

1985-01-01

The feasibility of using reduced order models and reduced order observers with eigenvalue/eigenvector assignment procedures is investigated. A review of spectral assignment synthesis procedures is presented. Then, a reduced order model which retains essential system characteristics is formulated. A constant state feedback matrix which assigns desired closed loop eigenvalues and approximates specified closed loop eigenvectors is calculated for the reduced order model. It is shown that the eigenvalue and eigenvector assignments made in the reduced order system are retained when the feedback matrix is implemented about the full order system. In addition, those modes and associated eigenvectors which are not included in the reduced order model remain unchanged in the closed loop full order system. The fulll state feedback design is then implemented by using a reduced order observer. It is shown that the eigenvalue and eigenvector assignments of the closed loop full order system remain unchanged when a reduced order observer is used. The design procedure is illustrated by an actual design problem.

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

PubMed

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

2018-04-01

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

Consistency properties of chaotic systems driven by time-delayed feedback

NASA Astrophysics Data System (ADS)

Jüngling, T.; Soriano, M. C.; Oliver, N.; Porte, X.; Fischer, I.

2018-04-01

Consistency refers to the property of an externally driven dynamical system to respond in similar ways to similar inputs. In a delay system, the delayed feedback can be considered as an external drive to the undelayed subsystem. We analyze the degree of consistency in a generic chaotic system with delayed feedback by means of the auxiliary system approach. In this scheme an identical copy of the nonlinear node is driven by exactly the same signal as the original, allowing us to verify complete consistency via complete synchronization. In the past, the phenomenon of synchronization in delay-coupled chaotic systems has been widely studied using correlation functions. Here, we analytically derive relationships between characteristic signatures of the correlation functions in such systems and unequivocally relate them to the degree of consistency. The analytical framework is illustrated and supported by numerical calculations of the logistic map with delayed feedback for different replica configurations. We further apply the formalism to time series from an experiment based on a semiconductor laser with a double fiber-optical feedback loop. The experiment constitutes a high-quality replica scheme for studying consistency of the delay-driven laser and confirms the general theoretical results.

Phase-locked Optical Signal Recovery

DTIC Science & Technology

2009-01-01

detection . However, implementing an optical phase lock loop ( OPLL ) to generate the synchronised carrier for the homodyne technique requires... Loop (OIPLL) in which a narrow bandwidth optical phase lock loop ( OPLL ) is used to control the free -running frequency of an optically injection...receiver uses an Optical Injection Phase Lock Loop (OIPLL) for carrier recovery,

Phase-locked Optical Signal Recovery

DTIC Science & Technology

2009-01-01

detection . However, implementing an optical phase lock loop ( OPLL ) to generate the synchronised carrier for the homodyne technique requires... Loop (OIPLL) in which a narrow bandwidth optical phase lock loop ( OPLL ) is used to control the free -running frequency of an optically injection...The receiver uses an Optical Injection Phase Lock Loop (OIPLL) for carrier

Review of optoelectronic oscillators based on modelocked lasers and resonant tunneling diode optoelectronics

NASA Astrophysics Data System (ADS)

Ironside, C. N.; Haji, Mohsin; Hou, Lianping; Akbar, Jehan; Kelly, Anthony E.; Seunarine, K.; Romeira, Bruno; Figueiredo, José M. L.

2011-05-01

Optoelectronic oscillators can provide low noise oscillators at radio frequencies in the 0.5-40 GHz range and in this paper we review two recently introduced approaches to optoelectronic oscillators. Both approaches use an optical fibre feedback loop. One approach is based on passively modelocked laser diodes and in a 40 GHz oscillator achieves up to 30 dB noise reduction. The other approach is based on resonant tunneling diode optoelectronic devices and in a 1.4 GHz oscillator can achieve up to 30 dB noise reduction.

Passively mode-locked tunable fiber laser in a soliton regime

NASA Astrophysics Data System (ADS)

Endo, Michiyuki; Ghosh, Gorachand

1999-04-01

A stable, passively mode-locked erbium-doped fiber resonator is developed to generate tunable optical pulses with durations of 270 - 325 fs in the soliton regime. The lasing wavelength is tuned continuously over a wavelength range of 60 nm by rotating a bulk band-pass filter inserted in the resonator with a repetition frequency of 45.4 MHz. We reduced the timing jitter by minimizing the intensity fluctuation of the pump source using a feedback loop and by controlling the influence of airflow and temperature fluctuation of the resonator in a sealed box.

Normal-Mode Splitting in a Weakly Coupled Optomechanical System

NASA Astrophysics Data System (ADS)

Rossi, Massimiliano; Kralj, Nenad; Zippilli, Stefano; Natali, Riccardo; Borrielli, Antonio; Pandraud, Gregory; Serra, Enrico; Di Giuseppe, Giovanni; Vitali, David

2018-02-01

Normal-mode splitting is the most evident signature of strong coupling between two interacting subsystems. It occurs when two subsystems exchange energy between themselves faster than they dissipate it to the environment. Here we experimentally show that a weakly coupled optomechanical system at room temperature can manifest normal-mode splitting when the pump field fluctuations are antisquashed by a phase-sensitive feedback loop operating close to its instability threshold. Under these conditions the optical cavity exhibits an effectively reduced decay rate, so that the system is effectively promoted to the strong coupling regime.

Self-seeded injection-locked FEL amplifer

DOEpatents

Sheffield, Richard L.

1999-01-01

A self-seeded free electron laser (FEL) provides a high gain and extraction efficiency for the emitted light. An accelerator outputs a beam of electron pulses to a permanent magnet wiggler having an input end for receiving the electron pulses and an output end for outputting light and the electron pulses. An optical feedback loop collects low power light in a small signal gain regime at the output end of said wiggler and returns the low power light to the input end of the wiggler while outputting high power light in a high signal gain regime.

Generation of dark hollow beam via coherent combination based on adaptive optics.

PubMed

Zheng, Yi; Wang, Xiaohua; Shen, Feng; Li, Xinyang

2010-12-20

A novel method for generating a dark hollow beam (DHB) is proposed and studied both theoretically and experimentally. A coherent combination technique for laser arrays is implemented based on adaptive optics (AO). A beam arraying structure and an active segmented mirror are designed and described. Piston errors are extracted by a zero-order interference detection system with the help of a custom-made photo-detectors array. An algorithm called the extremum approach is adopted to calculate feedback control signals. A dynamic piston error is imported by LiNbO₃ to test the capability of the AO servo. In a closed loop the stable and clear DHB is obtained. The experimental results confirm the feasibility of the concept.

Probe-pin device for optical neurotransmitter sensing in the brain

NASA Astrophysics Data System (ADS)

Kim, Min Hyuck; Song, Kyo D.; Yoon, Hargsoon; Park, Yeonjoon; Choi, Sang H.; Lee, Dae-Sung; Shin, Kyu-Sik; Hwang, Hak-In; Lee, Uhn

2015-04-01

Development of an optical neurotransmitter sensing device using nano-plasmonic probes and a micro-spectrometer for real time monitoring of neural signals in the brain is underway. Clinical application of this device technology is to provide autonomous closed-loop feedback control to a deep brain stimulation (DBS) system and enhance the accuracy and efficacy of DBS treatment. By far, we have developed an implantable probe-pin device based on localized field enhancement of surface plasmonic resonance on a nanostructured sensing domain which can amplify neurochemical signals from evoked neural activity in the brain. In this paper, we will introduce the details of design and sensing performance of a proto-typed microspectrometer and nanostructured probing devices for real time measurement of neurotransmitter concentrations.

Comparison of control and quality of bone cutting by using optical topographical imaging guided mechanical drill and 1070 nm laser with in-line coherent imaging

NASA Astrophysics Data System (ADS)

Razani, Marjan; Soudagar, Yasaman; Yu, Karen; Galbraith, Christopher M.; Webster, Paul J. L.; Van Vlack, Cole; Sun, Cuiru; Mariampillai, Adrian; Leung, Michael K. K.; Standish, Beau; Kiehl, Tim-Rasmus; Fraser, James M.; Yang, Victor X. D.

2013-03-01

Precision depth control of bone resection is necessary for safe surgical procedures in the spine. In this paper, we compare the control and quality of cutting bovine tail bone, as an ex vivo model of laminectomy and bony resection simulating spinal surgery, planned with micro-CT data and executed using two approaches: (a) mechanical milling guided by optical topographical imaging (OTI) and (b) optical milling using closed-loop inline coherent imaging (ICI) to monitor and control the incision depth of a high-power 1070 nm fiber laser in situ. OTI provides the in situ topology of the 2-dimensional surface of the bone orientation in the mechanical mill which is registered with the treatment plan derived from the micro-CT data. The coregistration allows the plan to be programmed into the mill which is then used as a benchmark of current surgical techniques. For laser cutting, 3D optical land marking with coaxial camera vision and the ICI system is used to coregister the treatment plan. The unstable, carbonization-mediated ablation behaviour of 1070 nm light and the unknown initial geometry of bone leads to unpredictable ablation which substantially limits the depth accuracy of open-loop cutting. However, even with such a non-ideal cutting laser, we demonstrate that ICI provides in situ high-speed feedback that automatically and accurately limits the laser's cut depth to effectively create an all-optical analogue to the mechanical mill.

SRC-2 is an essential coactivator for orchastrating metabolism and circadian rhythm

USDA-ARS?s Scientific Manuscript database

Synchrony of the mammalian circadian clock is achieved by complex transcriptional and translational feedback loops centered on the BMAL1:CLOCK heterodimer. Modulation of circadian feedback loops is essential for maintaining rhythmicity, yet the role of transcriptional coactivators in driving BMAL1:C...

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.

Quantitative implementation of the endogenous molecular-cellular network hypothesis in hepatocellular carcinoma.

PubMed

Wang, Gaowei; Zhu, Xiaomei; Gu, Jianren; Ao, Ping

2014-06-06

A quantitative hypothesis for cancer genesis and progression-the endogenous molecular-cellular network hypothesis, intended to include both genetic and epigenetic causes of cancer-has been proposed recently. Using this hypothesis, here we address the molecular basis for maintaining normal liver and hepatocellular carcinoma (HCC), and the potential strategy to cure or relieve HCC. First, we elaborate the basic assumptions of the hypothesis and establish a core working network of HCC according to the hypothesis. Second, we quantify the working network by a nonlinear dynamical system. We show that the working network reproduces the main known features of normal liver and HCC at both the modular and molecular levels. Lastly, the validated working network reveals that (i) specific positive feedback loops are responsible for the maintenance of normal liver and HCC; (ii) inhibiting proliferation and inflammation-related positive feedback loops and simultaneously inducing a liver-specific positive feedback loop is predicated as a potential strategy to cure or relieve HCC; and (iii) the genesis and regression of HCC are asymmetric. In light of the characteristic properties of the nonlinear dynamical system, we demonstrate that positive feedback loops must exist as a simple and general molecular basis for the maintenance of heritable phenotypes, such as normal liver and HCC, and regulating the positive feedback loops directly or indirectly provides potential strategies to cure or relieve HCC.

An improved adaptive interpolation clock recovery loop based on phase splitting algorithm for coherent optical communication system

NASA Astrophysics Data System (ADS)

Liu, Xuan; Liu, Bo; Zhang, Li-jia; Xin, Xiang-jun; Zhang, Qi; Wang, Yong-jun; Tian, Qing-hua; Tian, Feng; Mao, Ya-ya

2018-01-01

Traditional clock recovery scheme achieves timing adjustment by digital interpolation, thus recovering the sampling sequence. Based on this, an improved clock recovery architecture joint channel equalization for coherent optical communication system is presented in this paper. The loop is different from the traditional clock recovery. In order to reduce the interpolation error caused by the distortion in the frequency domain of the interpolator and to suppress the spectral mirroring generated by the sampling rate change, the proposed algorithm joint equalization, improves the original interpolator in the loop, along with adaptive filtering, and makes error compensation for the original signals according to the balanced pre-filtering signals. Then the signals are adaptive interpolated through the feedback loop. Furthermore, the phase splitting timing recovery algorithm is adopted in this paper. The time error is calculated according to the improved algorithm when there is no transition between the adjacent symbols, making calculated timing error more accurate. Meanwhile, Carrier coarse synchronization module is placed before the beginning of timing recovery to eliminate the larger frequency offset interference, which effectively adjust the sampling clock phase. In this paper, the simulation results show that the timing error is greatly reduced after the loop is changed. Based on the phase splitting algorithm, the BER and MSE are better than those in the unvaried architecture. In the fiber channel, using MQAM modulation format, after 100 km-transmission of single-mode fiber, especially when ROF(roll-off factor) values tends to 0, the algorithm shows a better clock performance under different ROFs. When SNR values are less than 8, the BER could achieve 10-2 to 10-1 magnitude. Furthermore, the proposed timing recovery is more suitable for the situation with low SNR values.

A Negative-Feedback Loop between the Detoxification/Antioxidant Response Factor SKN-1 and Its Repressor WDR-23 Matches Organism Needs with Environmental Conditions

PubMed Central

Leung, Chi K.; Wang, Ying; Deonarine, Andrew; Tang, Lanlan; Prasse, Stephanie

2013-01-01

Negative-feedback loops between transcription factors and repressors in responses to xenobiotics, oxidants, heat, hypoxia, DNA damage, and infection have been described. Although common, the function of feedback is largely unstudied. Here, we define a negative-feedback loop between the Caenorhabditis elegans detoxification/antioxidant response factor SKN-1/Nrf and its repressor wdr-23 and investigate its function in vivo. Although SKN-1 promotes stress resistance and longevity, we find that tight regulation by WDR-23 is essential for growth and reproduction. By disabling SKN-1 transactivation of wdr-23, we reveal that feedback is required to set the balance between growth/reproduction and stress resistance/longevity. We also find that feedback is required to set the sensitivity of a core SKN-1 target gene to an electrophile. Interestingly, the effect of feedback on target gene induction is greatly reduced when the stress response is strongly activated, presumably to ensure maximum activation of cytoprotective genes during potentially fatal conditions. Our work provides a framework for understanding the function of negative feedback in inducible stress responses and demonstrates that manipulation of feedback alone can shift the balance of competing animal processes toward cell protection, health, and longevity. PMID:23836880

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

PubMed

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

2017-09-01

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

Dynamics of nonlinear feedback control.

PubMed

Snippe, H P; van Hateren, J H

2007-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2011-06-01

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

An Adapting Auditory-motor Feedback Loop Can Contribute to Generating Vocal Repetition

PubMed Central

Brainard, Michael S.; Jin, Dezhe Z.

2015-01-01

Consecutive repetition of actions is common in behavioral sequences. Although integration of sensory feedback with internal motor programs is important for sequence generation, if and how feedback contributes to repetitive actions is poorly understood. Here we study how auditory feedback contributes to generating repetitive syllable sequences in songbirds. We propose that auditory signals provide positive feedback to ongoing motor commands, but this influence decays as feedback weakens from response adaptation during syllable repetitions. Computational models show that this mechanism explains repeat distributions observed in Bengalese finch song. We experimentally confirmed two predictions of this mechanism in Bengalese finches: removal of auditory feedback by deafening reduces syllable repetitions; and neural responses to auditory playback of repeated syllable sequences gradually adapt in sensory-motor nucleus HVC. Together, our results implicate a positive auditory-feedback loop with adaptation in generating repetitive vocalizations, and suggest sensory adaptation is important for feedback control of motor sequences. PMID:26448054

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

PubMed

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

2018-04-13

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

A Feedback Loop between Dynamin and Actin Recruitment during Clathrin-Mediated Endocytosis

PubMed Central

Taylor, Marcus J.; Lampe, Marko; Merrifield, Christien J.

2012-01-01

Clathrin-mediated endocytosis proceeds by a sequential series of reactions catalyzed by discrete sets of protein machinery. The final reaction in clathrin-mediated endocytosis is membrane scission, which is mediated by the large guanosine triophosphate hydrolase (GTPase) dynamin and which may involve the actin-dependent recruitment of N-terminal containing BIN/Amphiphysin/RVS domain containing (N-BAR) proteins. Optical microscopy has revealed a detailed picture of when and where particular protein types are recruited in the ∼20–30 s preceding scission. Nevertheless, the regulatory mechanisms and functions that underpin protein recruitment are not well understood. Here we used an optical assay to investigate the coordination and interdependencies between the recruitment of dynamin, the actin cytoskeleton, and N-BAR proteins to individual clathrin-mediated endocytic scission events. These measurements revealed that a feedback loop exists between dynamin and actin at sites of membrane scission. The kinetics of dynamin, actin, and N-BAR protein recruitment were modulated by dynamin GTPase activity. Conversely, acute ablation of actin dynamics using latrunculin-B led to a ∼50% decrease in the incidence of scission, an ∼50% decrease in the amplitude of dynamin recruitment, and abolished actin and N-BAR recruitment to scission events. Collectively these data suggest that dynamin, actin, and N-BAR proteins work cooperatively to efficiently catalyze membrane scission. Dynamin controls its own recruitment to scission events by modulating the kinetics of actin and N-BAR recruitment to sites of scission. Conversely actin serves as a dynamic scaffold that concentrates dynamin and N-BAR proteins at sites of scission. PMID:22505844

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

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

Rouse, F.; Allison, S.; Castillo, S.

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

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

PubMed

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

2017-11-01

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

Symposium Proceedings on Quantitative Feedback Theory Held in Fairborn, Ohio on 2-4 August 1992.

DTIC Science & Technology

1992-08-01

modification. This permits a drastic reduction in the cost of feedback, in terms of loop bandwidth and effect of sensor noise . This is the first...High- frequency Bound ( UHB ) but its main use is to ensure that at high frequencies the controlled system cannot go unstable and has sufficient noise ...a 5-cascaded multiple-loop feedback system giving significant reductions in sensor noise amplification (peak reduced by a factor of 4), is

Digital adaptive optics line-scanning confocal imaging system.

PubMed

Liu, Changgeng; Kim, Myung K

2015-01-01

A digital adaptive optics line-scanning confocal imaging (DAOLCI) system is proposed by applying digital holographic adaptive optics to a digital form of line-scanning confocal imaging system. In DAOLCI, each line scan is recorded by a digital hologram, which allows access to the complex optical field from one slice of the sample through digital holography. This complex optical field contains both the information of one slice of the sample and the optical aberration of the system, thus allowing us to compensate for the effect of the optical aberration, which can be sensed by a complex guide star hologram. After numerical aberration compensation, the corrected optical fields of a sequence of line scans are stitched into the final corrected confocal image. In DAOLCI, a numerical slit is applied to realize the confocality at the sensor end. The width of this slit can be adjusted to control the image contrast and speckle noise for scattering samples. DAOLCI dispenses with the hardware pieces, such as Shack–Hartmann wavefront sensor and deformable mirror, and the closed-loop feedbacks adopted in the conventional adaptive optics confocal imaging system, thus reducing the optomechanical complexity and cost. Numerical simulations and proof-of-principle experiments are presented that demonstrate the feasibility of this idea.

A Learning Progression for Feedback Loop Reasoning at Lower Elementary Level

ERIC Educational Resources Information Center

Hokayem, Hayat; Ma, Jingjing; Jin, Hui

2015-01-01

This study examines to what extent elementary students use feedback loop reasoning, a key component of systems thinking, to reason about interactions among organisms in ecosystems. We conducted clinical interviews with 44 elementary students (1st through 4th grades). We asked students to explain how populations change in two contexts: a…

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

PubMed

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

2014-07-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

Analysis and application of a velocity command motor as a reaction mass actuator

NASA Technical Reports Server (NTRS)

Sulla, Jeffrey L.; Juang, Jer-Nan; Horta, Lucas G.

1990-01-01

A commercially available linear stepper motor is applied as a reaction mass (RM) actuator. With the actuator operating in the (RM) relative-velocity command mode, open-loop and closed-loop testing is performed to determine operational limits. With the actuator mounted on a simple beam structure, root strain, RM acceleration, or beam acceleration is used in the feedback loop to augment the structural damping. The RM relative position is also used as feedback to ensure that the RM remains centered.

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.

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.

Unifying Views of Autism Spectrum Disorders: A Consideration of Autoregulatory Feedback Loops

PubMed Central

Mullins, Caitlin; Fishell, Gord

2017-01-01

Understanding the mechanisms underlying autism spectrum disorders (ASD) is a challenging goal. Here we review recent progress on several fronts, including genetics, proteomics, biochemistry and electrophysiology, that raise motivation for forming a viable pathophysiological hypothesis. In place of a traditionally unidirectional progression, we put forward a framework that extends homeostatic hypotheses by explicitly emphasizing autoregulatory feedback loops and known synaptic biology. The regulated biological feature can be neuronal electrical activity, the collective strength of synapses onto a dendritic branch, the local concentration of a signaling molecule, or the relative strengths of synaptic excitation and inhibition. The sensor of the biological variable (which we have termed the homeostat) engages mechanisms that operate as negative feedback elements to keep the biological variable tightly confined. We categorize known ASD-associated gene products according to their roles in such feedback loops, and provide detailed commentary for exemplar genes within each module. PMID:26985722

Screech tones from free and ducted supersonic jets

NASA Technical Reports Server (NTRS)

Tam, C. K. W.; Ahuja, K. K.; Jones, R. R., III

1994-01-01

It is well known that screech tones from supersonic jets are generated by a feedback loop. The loop consists of three main components. They are the downstream propagating instability wave, the shock cell structure in the jet plume, and the feedback acoustic waves immediately outside the jet. Evidence will be presented to show that the screech frequency is largely controlled by the characteristics of the feedback acoustic waves. The feedback loop is driven by the instability wave of the jet. Thus the tone intensity and its occurrence are dictated by the characteristics of the instability wave. In this paper the dependence of the instability wave spectrum on the azimuthal mode number (axisymmetric or helical/flapping mode, etc.), the jet-to-ambient gas temperature ratio, and the jet Mach number are studied. The results of this study provide an explanation for the observed screech tone mode switch phenomenon (changing from axisymmetric to helical mode as Mach number increases) and the often-cited experimental observation that tone intensity reduces with increase in jet temperature. For ducted supersonic jets screech tones can also be generated by feedback loops formed by the coupling of normal duct modes to instability waves of the jet. The screech frequencies are dictated by the frequencies of the duct modes. Super resonance, resonance involving very large pressure oscillations, can occur when the feedback loop is powered by the most amplified instability wave. It is proposed that the observed large amplitude pressure fluctuations and tone in the test cells of Arnold Engineering Development Center were generated by super resonance. Estimated super-resonance frequency for a Mach 1.3 axisymmetric jet tested in the facility agrees well with measurement.

NONLINEAR AND FIBER OPTICS: Propagation of femtosecond solitons in a fiber-optic loop

NASA Astrophysics Data System (ADS)

Zakhidov, É. A.; Mirtadzhiev, F. M.; Khaĭdarov, D. V.; Kuznetsov, A. V.; Okhotnikov, A. G.

1991-03-01

An investigation was made of the propagation of fundamental femtosecond soliton pulses in a fiber-optic loop, which is an element with promising applications in logic operations. It is shown that such a loop can filter off the nonsoliton component effectively. The conditions for high-contrast self-switching of fundamental solitons in a fiber-optic loop are identified.

Application of SPM interferometry in MEMS vibration measurement

NASA Astrophysics Data System (ADS)

Tang, Chaowei; He, Guotian; Xu, Changbiao; Zhao, Lijuan; Hu, Jun

2007-12-01

The resonant frequency measurement of cantilever has an important position in MEMS(Micro Electro Mechanical Systems) research. Meanwhile the SPM interferometry is a high-precision optical measurement technique, which can be used in physical quantity measurement of vibration, displacement, surface profile. Hence, in this paper we propose to apply SPM(SPM) interferometry in measuring the vibration of MEMS cantilever and in the experiment the vibration of MEMS cantilever was driven by light source. Then this kind of vibration was measured in nm precision. Finally the relational characteristics of MEMS cantilever vibration under optical excitation can be gotten and the measurement principle is analyzed. This method eliminates the influence on the measuring precision caused by external interference and light intensity change through feedback control loop. Experiment results prove that this measurement method has a good effect.

Statistical learning methods for aero-optic wavefront prediction and adaptive-optic latency compensation

NASA Astrophysics Data System (ADS)

Burns, W. Robert

Since the early 1970's research in airborne laser systems has been the subject of continued interest. Airborne laser applications depend on being able to propagate a near diffraction-limited laser beam from an airborne platform. Turbulent air flowing over the aircraft produces density fluctuations through which the beam must propagate. Because the index of refraction of the air is directly related to the density, the turbulent flow imposes aberrations on the beam passing through it. This problem is referred to as Aero-Optics. Aero-Optics is recognized as a major technical issue that needs to be solved before airborne optical systems can become routinely fielded. This dissertation research specifically addresses an approach to mitigating the deleterious effects imposed on an airborne optical system by aero-optics. A promising technology is adaptive optics: a feedback control method that measures optical aberrations and imprints the conjugate aberrations onto an outgoing beam. The challenge is that it is a computationally-difficult problem, since aero-optic disturbances are on the order of kilohertz for practical applications. High control loop frequencies and high disturbance frequencies mean that adaptive-optic systems are sensitive to latency in sensors, mirrors, amplifiers, and computation. These latencies build up to result in a dramatic reduction in the system's effective bandwidth. This work presents two variations of an algorithm that uses model reduction and data-driven predictors to estimate the evolution of measured wavefronts over a short temporal horizon and thus compensate for feedback latency. The efficacy of the two methods are compared in this research, and evaluated against similar algorithms that have been previously developed. The best version achieved over 75% disturbance rejection in simulation in the most optically active flow region in the wake of a turret, considerably outperforming conventional approaches. The algorithm is shown to be insensitive to changes in flow condition, and stable in the presence of small latency uncertainty. Consideration is given to practical implementation of the algorithms as well as computational requirement scaling.

Pulsatile desynchronizing delayed feedback for closed-loop deep brain stimulation

PubMed Central

Lysyansky, Borys; Rosenblum, Michael; Pikovsky, Arkady; Tass, Peter A.

2017-01-01

High-frequency (HF) deep brain stimulation (DBS) is the gold standard for the treatment of medically refractory movement disorders like Parkinson’s disease, essential tremor, and dystonia, with a significant potential for application to other neurological diseases. The standard setup of HF DBS utilizes an open-loop stimulation protocol, where a permanent HF electrical pulse train is administered to the brain target areas irrespectively of the ongoing neuronal dynamics. Recent experimental and clinical studies demonstrate that a closed-loop, adaptive DBS might be superior to the open-loop setup. We here combine the notion of the adaptive high-frequency stimulation approach, that aims at delivering stimulation adapted to the extent of appropriately detected biomarkers, with specifically desynchronizing stimulation protocols. To this end, we extend the delayed feedback stimulation methods, which are intrinsically closed-loop techniques and specifically designed to desynchronize abnormal neuronal synchronization, to pulsatile electrical brain stimulation. We show that permanent pulsatile high-frequency stimulation subjected to an amplitude modulation by linear or nonlinear delayed feedback methods can effectively and robustly desynchronize a STN-GPe network of model neurons and suggest this approach for desynchronizing closed-loop DBS. PMID:28273176

A coherent optical feedback system for optical information processing

NASA Technical Reports Server (NTRS)

Jablonowski, D. P.; Lee, S. H.

1975-01-01

A unique optical feedback system for coherent optical data processing is described. With the introduction of feedback, the well-known transfer function for feedback systems is obtained in two dimensions. Operational details of the optical feedback system are given. Experimental results of system applications in image restoration, contrast control and analog computation are presented.

Integration of Haptics in Agricultural Robotics

NASA Astrophysics Data System (ADS)

Kannan Megalingam, Rajesh; Sreekanth, M. M.; Sivanantham, Vinu; Sai Kumar, K.; Ghanta, Sriharsha; Surya Teja, P.; Reddy, Rajesh G.

2017-08-01

Robots can differentiate with open loop system and closed loop system robots. We face many problems when we do not have a feedback from robots. In this research paper, we are discussing all possibilities to achieve complete closed loop system for Multiple-DOF Robotic Arm, which is used in a coconut tree climbing and cutting robot by introducing a Haptic device. We are working on various sensors like tactile, vibration, force and proximity sensors for getting feedback. For monitoring the robotic arm achieved by graphical user interference software which simulates the working of the robotic arm, send the feedback of all the real time analog values which are produced by various sensors and provide real-time graphs for estimate the efficiency of the Robot.

Performance of a modified feedback loop adaptive array with TVRO satellite signals

NASA Technical Reports Server (NTRS)

Steadman, Karl N.; Gupta, Inder J.; Walton, Eric K.

1990-01-01

Performance of an experimental adaptive antenna array system is evaluated using television receive-only (TVRO) satellite signals. The experimental system is a sidelobe canceller with two auxiliary channels. Modified feedback loops are used to enhance the suppression of weak interfering signals. The modified feedback loops used two spatialy separated antennas, each with an individual amplifier for each auxiliary channel. Thus, the experimental system uses five antenna elements. Instead of using five separate antennas, a reflector antenna with multiple feeds is used to receive signals from various TVRO satellites. The details of the earth station are given. It is shown that the experimental system can null up to two signals originating from interfering TVRO satellites while receiving the signals from a desired TVRO satellite.

Research on phase locked loop in optical memory servo system

NASA Astrophysics Data System (ADS)

Qin, Liqin; Ma, Jianshe; Zhang, Jianyong; Pan, Longfa; Deng, Ming

2005-09-01

Phase locked loop (PLL) is a closed loop automatic control system, which can track the phase of input signal. It widely applies in each area of electronic technology. This paper research the phase locked loop in optical memory servo area. This paper introduces the configuration of digital phase locked loop (PLL) and phase locked servo system, the control theory, and analyses system's stability. It constructs the phase locked loop experiment system of optical disk spindle servo, which based on special chip. DC motor is main object, this system adopted phase locked servo technique and digital signal processor (DSP) to achieve constant linear velocity (CLV) in controlling optical spindle motor. This paper analyses the factors that affect the stability of phase locked loop in spindle servo system, and discusses the affection to the optical disk readout signal and jitter due to the stability of phase locked loop.

Peak wavelength shifts and opponent color theory

NASA Astrophysics Data System (ADS)

Ashdown, Ian; Salsbury, Marc

2007-09-01

We adapt the tenets of Hering's opponent color theory to the processing of data obtained from a tristimulus colorimeter to independently determine the intensity and possible peak wavelength shift of a narrowband LED. This information may then be used for example in an optical feedback loop to maintain constant intensity and chromaticity for a light source consisting of two LEDs with different peak wavelengths. This approach is particularly useful for LED backlighting of LCD display panels using red, green, and blue LEDs, wherein a tristimulus colorimeter can be used to maintain primary chromaticities to within broadcast standard limits in real time.

High-efficiency holograms fixed in lithium niobate after recording using a digital fringe stabilization system.

PubMed

Arizmendi, Luis; Ambite, Emilio J

2012-02-20

We used a digital feedback control loop system to produce reproducible fixed volume transmission holograms of high diffraction efficiency. Different strategies were investigated to obtain holograms of good quality and the highest refractive index modulation depth. Using this control system, we were able to record holograms with stationary fringes. Additionally to using the stationary fringe recording, a double recording-fixing schedule resulted in being the most appropriate one to produce reproducible holograms of better characteristics. This strategy is discussed and compared with other already established ones. © 2012 Optical Society of America

Vision-based real-time position control of a semi-automated system for robot-assisted joint fracture surgery.

PubMed

Dagnino, Giulio; Georgilas, Ioannis; Tarassoli, Payam; Atkins, Roger; Dogramadzi, Sanja

2016-03-01

Joint fracture surgery quality can be improved by robotic system with high-accuracy and high-repeatability fracture fragment manipulation. A new real-time vision-based system for fragment manipulation during robot-assisted fracture surgery was developed and tested. The control strategy was accomplished by merging fast open-loop control with vision-based control. This two-phase process is designed to eliminate the open-loop positioning errors by closing the control loop using visual feedback provided by an optical tracking system. Evaluation of the control system accuracy was performed using robot positioning trials, and fracture reduction accuracy was tested in trials on ex vivo porcine model. The system resulted in high fracture reduction reliability with a reduction accuracy of 0.09 mm (translations) and of [Formula: see text] (rotations), maximum observed errors in the order of 0.12 mm (translations) and of [Formula: see text] (rotations), and a reduction repeatability of 0.02 mm and [Formula: see text]. The proposed vision-based system was shown to be effective and suitable for real joint fracture surgical procedures, contributing a potential improvement of their quality.

Interactive Information Seeking and Retrieving: A Third Feedback Framework.

ERIC Educational Resources Information Center

Spink, Amanda

1996-01-01

Presents an overview of feedback within the cybernetics and social frameworks. These feedback concepts are then compared with the interactive feedback concept evolving within the framework of information seeking and retrieving, based on their conceptualization of the feedback loop and notion of information. (Author/AEF)

Prototype high speed optical delay line for stellar interferometry

NASA Astrophysics Data System (ADS)

Colavita, M. M.; Hines, B. E.; Shao, M.; Klose, G. J.; Gibson, B. V.

1991-12-01

The long baselines of the next-generation ground-based optical stellar interferometers require optical delay lines which can maintain nm-level path-length accuracy while moving at high speeds. NASA-JPL is currently designing delay lines to meet these requirements. The design is an enhanced version of the Mark III delay line, with the following key features: hardened, large diameter wheels, rather than recirculating ball bearings, to reduce mechanical noise; a friction-drive cart which bears the cable-dragging forces, and drives the optics cart through a force connection only; a balanced PZT assembly to enable high-bandwidth path-length control; and a precision aligned flexural suspension for the optics assembly to minimize bearing noise feedthrough. The delay line is fully programmable in position and velocity, and the system is controlled with four cascaded software feedback loops. Preliminary performance is a jitter in any 5 ms window of less than 10 nm rms for delay rates of up to 28 mm/s; total jitter is less than 10 nm rms for delay rates up to 20 mm/s.

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

Log amplifier with pole-zero compensation

DOEpatents

Brookshier, W.

1985-02-08

A logarithmic amplifier circuit provides pole-zero compensation for improved stability and response time over 6-8 decades of input signal frequency. The amplifer circuit includes a first operational amplifier with a first feedback loop which includes a second, inverting operational amplifier in a second feedstock loop. The compensated output signal is provided by the second operational amplifier with the log elements, i.e., resistors, and the compensating capacitors in each of the feedback loops having equal values so that each break point is offset by a compensating break point or zero.

A hidden oncogenic positive feedback loop caused by crosstalk between Wnt and ERK pathways.

PubMed

Kim, D; Rath, O; Kolch, W; Cho, K-H

2007-07-05

The Wnt and the extracellular signal regulated-kinase (ERK) pathways are both involved in the pathogenesis of various kinds of cancers. Recently, the existence of crosstalk between Wnt and ERK pathways was reported. Gathering all reported results, we have discovered a positive feedback loop embedded in the crosstalk between the Wnt and ERK pathways. We have developed a plausible model that represents the role of this hidden positive feedback loop in the Wnt/ERK pathway crosstalk based on the integration of experimental reports and employing established basic mathematical models of each pathway. Our analysis shows that the positive feedback loop can generate bistability in both the Wnt and ERK signaling pathways, and this prediction was further validated by experiments. In particular, using the commonly accepted assumption that mutations in signaling proteins contribute to cancerogenesis, we have found two conditions through which mutations could evoke an irreversible response leading to a sustained activation of both pathways. One condition is enhanced production of beta-catenin, the other is a reduction of the velocity of MAP kinase phosphatase(s). This enables that high activities of Wnt and ERK pathways are maintained even without a persistent extracellular signal. Thus, our study adds a novel aspect to the molecular mechanisms of carcinogenesis by showing that mutational changes in individual proteins can cause fundamental functional changes well beyond the pathway they function in by a positive feedback loop embedded in crosstalk. Thus, crosstalk between signaling pathways provides a vehicle through which mutations of individual components can affect properties of the system at a larger scale.

Biocybernetic system evaluates indices of operator engagement in automated task

NASA Technical Reports Server (NTRS)

Pope, A. T.; Bogart, E. H.; Bartolome, D. S.

1995-01-01

A biocybernetic system has been developed as a method to evaluate automated flight deck concepts for compatibility with human capabilities. A biocybernetic loop is formed by adjusting the mode of operation of a task set (e.g., manual/automated mix) based on electroencephalographic (EEG) signals reflecting an operator's engagement in the task set. A critical issue for the loop operation is the selection of features of the EEG to provide an index of engagement upon which to base decisions to adjust task mode. Subjects were run in the closed-loop feedback configuration under four candidate and three experimental control definitions of an engagement index. The temporal patterning of system mode switching was observed for both positive and negative feedback of the index. The indices were judged on the basis of their relative strength in exhibiting expected feedback control system phenomena (stable operation under negative feedback and unstable operation under positive feedback). Of the candidate indices evaluated in this study, an index constructed according to the formula, beta power/(alpha power + theta power), reflected task engagement best.

Optics Recycle Loop Strategy for NIF Operations above UV Laser-Induced Damage Threshold

DOE PAGES

Spaeth, M. L.; Wegner, P. J.; Suratwala, T. I.; ...

2017-03-23

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) houses the world’s largest laser system, composed of 192 individual, 40-cm-aperture beamlines. The NIF laser routinely operates at ultraviolet (UV) fluences above 8 J/cm 2, more than twice the (3ω only) damage threshold of commercially available UV-grade fused silica. NIF is able to maintain such high fluence operation by using an optics recycling loop strategy. Successful operation of the loop relies on a number of technologies specifically developed for NIF. One of the most important is the capability developed by LLNL and their vendors for producing highly damage-resistant optics.more » Other technologies developed for the optics recycle loop raise the operating point of NIF by keeping damage growth in check. LLNL has demonstrated the capability to sustain UV fused silica optic recycling rates of up to 40 optics per week. The optics are ready for reinstallation after a 3-week trip through a recycle loop where the damage state of each optic is assessed and repaired. The impact of the optics recycle loop has been profound, allowing the experimental program to routinely employ energies and fluences that would otherwise have been unachievable. Without the recycle loop, it is likely that the NIF fluence would need to be kept below the UV threshold for damage growth, ~4 J/cm 2, thus keeping the energy delivered to the target significantly below 1 MJ. With the recycle loop implemented during the National Ignition Campaign, NIF can routinely deliver >1.8 MJ on target, an increase in operational capability of more than 100%. Finally, in this paper, the enabling technological advances, optical performance, and operational capability implications of the optics recycle loop are discussed.« less

Optics Recycle Loop Strategy for NIF Operations above UV Laser-Induced Damage Threshold

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

Spaeth, M. L.; Wegner, P. J.; Suratwala, T. I.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) houses the world’s largest laser system, composed of 192 individual, 40-cm-aperture beamlines. The NIF laser routinely operates at ultraviolet (UV) fluences above 8 J/cm 2, more than twice the (3ω only) damage threshold of commercially available UV-grade fused silica. NIF is able to maintain such high fluence operation by using an optics recycling loop strategy. Successful operation of the loop relies on a number of technologies specifically developed for NIF. One of the most important is the capability developed by LLNL and their vendors for producing highly damage-resistant optics.more » Other technologies developed for the optics recycle loop raise the operating point of NIF by keeping damage growth in check. LLNL has demonstrated the capability to sustain UV fused silica optic recycling rates of up to 40 optics per week. The optics are ready for reinstallation after a 3-week trip through a recycle loop where the damage state of each optic is assessed and repaired. The impact of the optics recycle loop has been profound, allowing the experimental program to routinely employ energies and fluences that would otherwise have been unachievable. Without the recycle loop, it is likely that the NIF fluence would need to be kept below the UV threshold for damage growth, ~4 J/cm 2, thus keeping the energy delivered to the target significantly below 1 MJ. With the recycle loop implemented during the National Ignition Campaign, NIF can routinely deliver >1.8 MJ on target, an increase in operational capability of more than 100%. Finally, in this paper, the enabling technological advances, optical performance, and operational capability implications of the optics recycle loop are discussed.« less

Influence of the feedback loops in the trp operon of B. subtilis on the system dynamic response and noise amplitude.

PubMed

Zamora-Chimal, Criseida; Santillán, Moisés; Rodríguez-González, Jesús

2012-10-07

In this paper we introduce a mathematical model for the tryptophan operon regulatory pathway in Bacillus subtilis. This model considers the transcription-attenuation, and the enzyme-inhibition regulatory mechanisms. Special attention is paid to the estimation of all the model parameters from reported experimental data. With the aid of this model we investigate, from a mathematical-modeling point of view, whether the existing multiplicity of regulatory feedback loops is advantageous in some sense, regarding the dynamic response and the biochemical noise in the system. The tryptophan operon dynamic behavior is studied by means of deterministic numeric simulations, while the biochemical noise is analyzed with the aid of stochastic simulations. The model feasibility is tested comparing its stochastic and deterministic results with experimental reports. Our results for the wildtype and for a couple of mutant bacterial strains suggest that the enzyme-inhibition feedback loop, dynamically accelerates the operon response, and plays a major role in the reduction of biochemical noise. Also, the transcription-attenuation feedback loop makes the trp operon sensitive to changes in the endogenous tryptophan level, and increases the amplitude of the biochemical noise. Copyright © 2012 Elsevier Ltd. All rights reserved.

The p53–Mdm2 feedback loop protects against DNA damage by inhibiting p53 activity but is dispensable for p53 stability, development, and longevity

PubMed Central

Pant, Vinod; Xiong, Shunbin; Jackson, James G.; Post, Sean M.; Abbas, Hussein A.; Quintás-Cardama, Alfonso; Hamir, Amirali N.; Lozano, Guillermina

2013-01-01

The p53–Mdm2 feedback loop is perceived to be critical for regulating stress-induced p53 activity and levels. However, this has never been tested in vivo. Using a genetically engineered mouse with mutated p53 response elements in the Mdm2 P2 promoter, we show that feedback loop-deficient Mdm2P2/P2 mice are viable and aphenotypic and age normally. p53 degradation kinetics after DNA damage in radiosensitive tissues remains similar to wild-type controls. Nonetheless, DNA damage response is elevated in Mdm2P2/P2 mice. Enhanced p53-dependent apoptosis sensitizes hematopoietic stem cells (HSCs), causing drastic myeloablation and lethality. These results suggest that while basal Mdm2 levels are sufficient to regulate p53 in most tissues under homeostatic conditions, the p53–Mdm2 feedback loop is critical for regulating p53 activity and sustaining HSC function after DNA damage. Therefore, transient disruption of p53–Mdm2 interaction could be explored as a potential adjuvant/therapeutic strategy for targeting stem cells in hematological malignancies. PMID:23973961

Feedback control in deep drawing based on experimental datasets

NASA Astrophysics Data System (ADS)

Fischer, P.; Heingärtner, J.; Aichholzer, W.; Hortig, D.; Hora, P.

2017-09-01

In large-scale production of deep drawing parts, like in automotive industry, the effects of scattering material properties as well as warming of the tools have a significant impact on the drawing result. In the scope of the work, an approach is presented to minimize the influence of these effects on part quality by optically measuring the draw-in of each part and adjusting the settings of the press to keep the strain distribution, which is represented by the draw-in, inside a certain limit. For the design of the control algorithm, a design of experiments for in-line tests is used to quantify the influence of the blank holder force as well as the force distribution on the draw-in. The results of this experimental dataset are used to model the process behavior. Based on this model, a feedback control loop is designed. Finally, the performance of the control algorithm is validated in the production line.

Stabilization and control of the carrier-envelope phase of high-power femtosecond laser pulses using the direct locking technique.

PubMed

Imran, Tayyab; Lee, Yong S; Nam, Chang H; Hong, Kyung-Han; Yu, Tae J; Sung, Jae H

2007-01-08

We have stabilized and electronically controlled the carrier-envelope phase (CEP) of high-power femtosecond laser pulses, generated in a grating-based chirped-pulse amplification kHz Ti:sapphire laser, using the direct locking technique [Opt. Express 13, 2969 (2005)] combined with a slow feedback loop. An f-2f spectral interferometer has shown the CEP stabilities of 1.2 rad with the direct locking loop applied to the oscillator and of 180 mrad with an additional slow feedback loop, respectively. The electronic CEP modulations that can be easily realized in the direct locking loop are also demonstrated with the amplified pulses.

Hybrid force-velocity sliding mode control of a prosthetic hand.

PubMed

Engeberg, Erik D; Meek, Sanford G; Minor, Mark A

2008-05-01

Four different methods of hand prosthesis control are developed and examined experimentally. Open-loop control is shown to offer the least sensitivity when manipulating objects. Force feedback substantially improves upon open-loop control. However, it is shown that the inclusion of velocity and/or position feedback in a hybrid force-velocity control scheme can further improve the functionality of hand prostheses. Experimental results indicate that the sliding mode controller with force, position, and velocity feedback is less prone to unwanted force overshoot when initially grasping objects than the other controllers.

Performance of a modified feedback loop adaptive array with TVRO satellite signals

NASA Technical Reports Server (NTRS)

Steadman, K.; Gupta, I. J.; Walton, E. K.

1990-01-01

The performance of an experimental adaptive antenna array system is evaluated using television-receive-only (TVRO) satellite signals. The experimental system is a sidelobe canceler with two auxiliary channels. Modified feedback loops are used to enhance the suppression of weak interfering signals. The modified feedback loops use two spatially separate antennas, each with an individual amplifier for each auxiliary channel. Thus, the experimental system uses five antenna elements. Instead of using five separate antennas, a reflector antenna with multiple feeds is used to receive signals from various TVRO satellites. The details of the earth station are given. It is shown that the experimental system can null up to two signals originating from interfering TVRO satellites while receiving the signals from a desired TVRO satellite.

Causal Loop Analysis of coastal geomorphological systems

NASA Astrophysics Data System (ADS)

Payo, Andres; Hall, Jim W.; French, Jon; Sutherland, James; van Maanen, Barend; Nicholls, Robert J.; Reeve, Dominic E.

2016-03-01

As geomorphologists embrace ever more sophisticated theoretical frameworks that shift from simple notions of evolution towards single steady equilibria to recognise the possibility of multiple response pathways and outcomes, morphodynamic modellers are facing the problem of how to keep track of an ever-greater number of system feedbacks. Within coastal geomorphology, capturing these feedbacks is critically important, especially as the focus of activity shifts from reductionist models founded on sediment transport fundamentals to more synthesist ones intended to resolve emergent behaviours at decadal to centennial scales. This paper addresses the challenge of mapping the feedback structure of processes controlling geomorphic system behaviour with reference to illustrative applications of Causal Loop Analysis at two study cases: (1) the erosion-accretion behaviour of graded (mixed) sediment beds, and (2) the local alongshore sediment fluxes of sand-rich shorelines. These case study examples are chosen on account of their central role in the quantitative modelling of geomorphological futures and as they illustrate different types of causation. Causal loop diagrams, a form of directed graph, are used to distil the feedback structure to reveal, in advance of more quantitative modelling, multi-response pathways and multiple outcomes. In the case of graded sediment bed, up to three different outcomes (no response, and two disequilibrium states) can be derived from a simple qualitative stability analysis. For the sand-rich local shoreline behaviour case, two fundamentally different responses of the shoreline (diffusive and anti-diffusive), triggered by small changes of the shoreline cross-shore position, can be inferred purely through analysis of the causal pathways. Explicit depiction of feedback-structure diagrams is beneficial when developing numerical models to explore coastal morphological futures. By explicitly mapping the feedbacks included and neglected within a model, the modeller can readily assess if critical feedback loops are included.

Semiconductor ring lasers subject to both on-chip filtered optical feedback and external conventional optical feedback

NASA Astrophysics Data System (ADS)

Khoder, Mulham; Van der Sande, Guy; Danckaert, Jan; Verschaffelt, Guy

2016-05-01

It is well known that the performance of semiconductor lasers is very sensitive to external optical feedback. This feedback can lead to changes in lasing characteristics and a variety of dynamical effects including chaos and coherence collapse. One way to avoid this external feedback is by using optical isolation, but these isolators and their packaging will increase the cost of the total system. Semiconductor ring lasers nowadays are promising sources in photonic integrated circuits because they do not require cleaved facets or mirrors to form a laser cavity. Recently, some of us proposed to combine semiconductor ring lasers with on chip filtered optical feedback to achieve tunable lasers. The feedback is realized by employing two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifier gates are used to control the feedback strength. In this work, we investigate how such lasers with filtered feedback are influenced by an external conventional optical feedback. The experimental results show intensity fluctuations in the time traces in both the clockwise and counterclockwise directions due to the conventional feedback. We quantify the strength of the conventional feedback induced dynamics be extracting the standard deviation of the intensity fluctuations in the time traces. By using filtered feedback, we can shift the onset of the conventional feedback induced dynamics to larger values of the feedback rate [ Khoder et al, IEEE Photon. Technol. Lett. DOI: 10.1109/LPT.2016.2522184]. The on-chip filtered optical feedback thus makes the semiconductor ring laser less senstive to the effect of (long) conventional optical feedback. We think these conclusions can be extended to other types of lasers.

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.

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

NASA Technical Reports Server (NTRS)

Newman, Brett; Kassem, Ayman

1999-01-01

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

System Dynamics

NASA Astrophysics Data System (ADS)

Morecroft, John

System dynamics is an approach for thinking about and simulating situations and organisations of all kinds and sizes by visualising how the elements fit together, interact and change over time. This chapter, written by John Morecroft, describes modern system dynamics which retains the fundamentals developed in the 1950s by Jay W. Forrester of the MIT Sloan School of Management. It looks at feedback loops and time delays that affect system behaviour in a non-linear way, and illustrates how dynamic behaviour depends upon feedback loop structures. It also recognises improvements as part of the ongoing process of managing a situation in order to achieve goals. Significantly it recognises the importance of context, and practitioner skills. Feedback systems thinking views problems and solutions as being intertwined. The main concepts and tools: feedback structure and behaviour, causal loop diagrams, dynamics, are practically illustrated in a wide variety of contexts from a hot water shower through to a symphony orchestra and the practical application of the approach is described through several real examples of its use for strategic planning and evaluation.

Development of closed-loop neural interface technology in a rat model: combining motor cortex operant conditioning with visual cortex microstimulation.

PubMed

Marzullo, Timothy Charles; Lehmkuhle, Mark J; Gage, Gregory J; Kipke, Daryl R

2010-04-01

Closed-loop neural interface technology that combines neural ensemble decoding with simultaneous electrical microstimulation feedback is hypothesized to improve deep brain stimulation techniques, neuromotor prosthetic applications, and epilepsy treatment. Here we describe our iterative results in a rat model of a sensory and motor neurophysiological feedback control system. Three rats were chronically implanted with microelectrode arrays in both the motor and visual cortices. The rats were subsequently trained over a period of weeks to modulate their motor cortex ensemble unit activity upon delivery of intra-cortical microstimulation (ICMS) of the visual cortex in order to receive a food reward. Rats were given continuous feedback via visual cortex ICMS during the response periods that was representative of the motor cortex ensemble dynamics. Analysis revealed that the feedback provided the animals with indicators of the behavioral trials. At the hardware level, this preparation provides a tractable test model for improving the technology of closed-loop neural devices.

Feedback Control Systems Loop Shaping Design with Practical Considerations

NASA Technical Reports Server (NTRS)

Kopsakis, George

2007-01-01

This paper describes loop shaping control design in feedback control systems, primarily from a practical stand point that considers design specifications. Classical feedback control design theory, for linear systems where the plant transfer function is known, has been around for a long time. But it s still a challenge of how to translate the theory into practical and methodical design techniques that simultaneously satisfy a variety of performance requirements such as transient response, stability, and disturbance attenuation while taking into account the capabilities of the plant and its actuation system. This paper briefly addresses some relevant theory, first in layman s terms, so that it becomes easily understood and then it embarks into a practical and systematic design approach incorporating loop shaping design coupled with lead-lag control compensation design. The emphasis is in generating simple but rather powerful design techniques that will allow even designers with a layman s knowledge in controls to develop effective feedback control designs.

An Iterative Information-Reduced Quadriphase-Shift-Keyed Carrier Synchronization Scheme Using Decision Feedback for Low Signal-to-Noise Ratio Applications

NASA Technical Reports Server (NTRS)

Simon, M.; Tkacenko, A.

2006-01-01

In a previous publication [1], an iterative closed-loop carrier synchronization scheme for binary phase-shift keyed (BPSK) modulation was proposed that was based on feeding back data decisions to the input of the loop, the purpose being to remove the modulation prior to carrier synchronization as opposed to the more conventional decision-feedback schemes that incorporate such feedback inside the loop. The idea there was that, with sufficient independence between the received data and the decisions on it that are fed back (as would occur in an error-correction coding environment with sufficient decoding delay), a pure tone in the presence of noise would ultimately be produced (after sufficient iteration and low enough error probability) and thus could be tracked without any squaring loss. This article demonstrates that, with some modification, the same idea of iterative information reduction through decision feedback can be applied to quadrature phase-shift keyed (QPSK) modulation, something that was mentioned in the previous publication but never pursued.

Sample-Clock Phase-Control Feedback

NASA Technical Reports Server (NTRS)

Quirk, Kevin J.; Gin, Jonathan W.; Nguyen, Danh H.; Nguyen, Huy

2012-01-01

To demodulate a communication signal, a receiver must recover and synchronize to the symbol timing of a received waveform. In a system that utilizes digital sampling, the fidelity of synchronization is limited by the time between the symbol boundary and closest sample time location. To reduce this error, one typically uses a sample clock in excess of the symbol rate in order to provide multiple samples per symbol, thereby lowering the error limit to a fraction of a symbol time. For systems with a large modulation bandwidth, the required sample clock rate is prohibitive due to current technological barriers and processing complexity. With precise control of the phase of the sample clock, one can sample the received signal at times arbitrarily close to the symbol boundary, thus obviating the need, from a synchronization perspective, for multiple samples per symbol. Sample-clock phase-control feedback was developed for use in the demodulation of an optical communication signal, where multi-GHz modulation bandwidths would require prohibitively large sample clock frequencies for rates in excess of the symbol rate. A custom mixedsignal (RF/digital) offset phase-locked loop circuit was developed to control the phase of the 6.4-GHz clock that samples the photon-counting detector output. The offset phase-locked loop is driven by a feedback mechanism that continuously corrects for variation in the symbol time due to motion between the transmitter and receiver as well as oscillator instability. This innovation will allow significant improvements in receiver throughput; for example, the throughput of a pulse-position modulation (PPM) with 16 slots can increase from 188 Mb/s to 1.5 Gb/s.

Constant peak-power single-frequency linearly-polarized all-fiber laser for coherent detection based on closed-loop feedback technology

NASA Astrophysics Data System (ADS)

Ding, Yaqian; Zhang, Xiang; Li, Dong; Wang, Dapeng; Zhang, Renzhong; Song, Chengying; Che, Haozhao; Wang, Rui; Guo, Baoling; Chen, Guanghui

2015-10-01

In this paper, a practical single-frequency high-repetition linearly-polarized eye-safe all-fiber laser with constant peak power is demonstrated. It is based on master-oscillator power amplifier (MOPA) system. A distributed feedback laser diode simulating at 1550nm with narrow linewidth of 2.3 kHz is employed as the seed source. It is modulated to a pulse laser with high repetition of 20 kHz and peak power of 10mW by an acousto-optic modulator (AOM). The pulse width is tunable between 100ns to 400ns. Two-stage cascade amplifier is established, which consists of a pre-amplifier and a power-amplifier. Amplified spontaneous emission (ASE) and stimulated billion scattering are well suppressed by special management. The output peak power of 30W is obtained, which has nearly diffraction-limited beam quality. It operates in linewidth of 1.2MHz, polarization-extinction ratio (PER) of 25dB and signal-to-noise ratio (SNR) of more than 40dB. Gain of the whole amplifier achieves nearly 35dB. Furthermore, an embedded control system (ECS) based on the WinCE operating system (OS) and the chip of S3C2440 is proposed. This control system based on closed-loop feedback technology makes the peak power keeping constant even the pulse width tunable, which is convenient for the end user of the radar. This robust portable laser is remarkable and fulfills the desire of coherent detection excellently.

PREDICT: Privacy and Security Enhancing Dynamic Information Monitoring

DTIC Science & Technology

2015-08-03

consisting of global server-side probabilistic assignment by an untrusted server using cloaked locations, followed by feedback-loop guided local...12], consisting of global server-side probabilistic assignment by an untrusted server using cloaked locations, followed by feedback-loop guided...these methods achieve high sensing coverage with low cost using cloaked locations [3]. In follow-on work, the issue of mobility is addressed. Task

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

Kerns, Q.A.; Jackson, G.; Kerns, C.R.

This paper describes the damper design for 6 proton on 6 pbar bunches in the Tevatron collider. Signal pickup, transient phase detection, derivative networks, and phase correction via the high-level rf are covered. Each rf station is controlled by a slow feedback loop. In addition, global feedback loops control each set of four cavities, one set for protons and one set for antiprotons. Operational experience with these systems is discussed. 7 refs., 9 figs.

Mathematical modeling of planar cell polarity signaling in the Drosophila melanogaster wing

NASA Astrophysics Data System (ADS)

Amonlirdviman, Keith

Planar cell polarity (PCP) signaling refers to the coordinated polarization of cells within the plane of various epithelial tissues to generate sub-cellular asymmetry along an axis orthogonal to their apical-basal axes. For example, in the Drosophila wing, PCP is seen in the parallel orientation of hairs that protrude from each of the approximately 30,000 epithelial cells to robustly point toward the wing tip. Through a poorly understood mechanism, cell clones mutant for some PCP signaling components, including some, but not all alleles of the receptor frizzled, cause polarity disruptions of neighboring, wild-type cells, a phenomenon referred to as domineering nonautonomy. Previous models have proposed diffusible factors to explain nonautonomy, but no such factors have yet been found. This dissertation describes the mathematical modeling of PCP in the Drosophila wing, based on a contact dependent signaling hypothesis derived from experimental results. Intuition alone is insufficient to deduce that this hypothesis, which relies on a local feedback loop acting at the cell membrane, underlies the complex patterns observed in large fields of cells containing mutant clones, and others have argued that it cannot account for observed phenotypes. Through reaction-diffusion, partial differential equation modeling and simulation, the feedback loop is shown to fully reproduce PCP phenotypes, including domineering nonautonomy. The sufficiency of this model and the experimental validation of model predictions argue that previously proposed diffusible factors need not be invoked to explain PCP signaling and reveal how specific protein-protein interactions lead to autonomy or domineering nonautonomy. Based on these results, an ordinary differential equation model is derived to study the relationship of the feedback loop with upstream signaling components. The cadherin Fat transduces a cue to the local feedback loop, biasing the polarity direction of each cell toward the wing tip. The feedback loop then amplifies and propagates PCP across the pupal wing, but polarity information does not always propagate correctly across cells lacking Fat function. Using the simplified model, the presence and severity of polarity defects in fat clones is shown to be an inherent consequence of the feedback loop when confronted with irregular variations in cell geometry.

Dynamic processes in regulation and some implications for biofeedback and biobehavioral interventions.

PubMed

Lehrer, Paul; Eddie, David

2013-06-01

Systems theory has long been used in psychology, biology, and sociology. This paper applies newer methods of control systems modeling for assessing system stability in health and disease. Control systems can be characterized as open or closed systems with feedback loops. Feedback produces oscillatory activity, and the complexity of naturally occurring oscillatory patterns reflects the multiplicity of feedback mechanisms, such that many mechanisms operate simultaneously to control the system. Unstable systems, often associated with poor health, are characterized by absence of oscillation, random noise, or a very simple pattern of oscillation. This modeling approach can be applied to a diverse range of phenomena, including cardiovascular and brain activity, mood and thermal regulation, and social system stability. External system stressors such as disease, psychological stress, injury, or interpersonal conflict may perturb a system, yet simultaneously stimulate oscillatory processes and exercise control mechanisms. Resonance can occur in systems with negative feedback loops, causing high-amplitude oscillations at a single frequency. Resonance effects can be used to strengthen modulatory oscillations, but may obscure other information and control mechanisms, and weaken system stability. Positive as well as negative feedback loops are important for system function and stability. Examples are presented of oscillatory processes in heart rate variability, and regulation of autonomic, thermal, pancreatic and central nervous system processes, as well as in social/organizational systems such as marriages and business organizations. Resonance in negative feedback loops can help stimulate oscillations and exercise control reflexes, but also can deprive the system of important information. Empirical hypotheses derived from this approach are presented, including that moderate stress may enhance health and functioning.

Measuring the photodetector frequency response for ultrasonic applications by a heterodyne system with difference- frequency servo control.

PubMed

Koch, Christian

2010-05-01

A technique for the calibration of photodiodes in ultrasonic measurement systems using standard and cost-effective optical and electronic components is presented. A heterodyne system was realized using two commercially available distributed feedback lasers, and the required frequency stability and resolution were ensured by a difference-frequency servo control scheme. The frequency-sensitive element generating the error signal for the servo loop comprised a delay-line discriminator constructed from electronic elements. Measurements were carried out at up to 450 MHz, and the uncertainties of about 5% (k = 2) can be further reduced by improved radio frequency power measurement without losing the feature of using only simple elements. The technique initially dedicated to the determination of the frequency response of photodetectors applied in ultrasonic applications can be transferred to other application fields of optical measurements.

Single sensor for multiple analytes in different optical channel: Applying for multi-ion response modulation

NASA Astrophysics Data System (ADS)

Liang, Chunshuang; Jiang, Shimei

2017-08-01

A Schiff-base, (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) (L), has been improved to function as a simultaneous multi-ion probe in different optical channel. The probe changes from colorless to orangish upon being deprotonated by F-, while the presence of Al3+ significantly enhances the fluorescence of the probe due to the inhibition of Cdbnd N isomerization, cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT), and chelation enhanced fluorescence (CHEF). Dual-channel "off-on" switching behavior resulted from the sequential input of F- and Al3+, reflecting the balance of independent reactions of Al3+ and F- with L and with one another. This sensing phenomenon realizes transformation between multiple states and beautifully mimics a "Write-Read-Erase-Read" logic circuit with two feedback loops.

Structural control sensors for the CASES GTF

NASA Technical Reports Server (NTRS)

Davis, Hugh W.; Bukley, Angelia P.

1993-01-01

CASES (Controls, Astrophysics and Structures Experiment in Space) is a proposed space experiment to collect x-ray images of the galactic center and solar disk with unprecedented resolution. This requires precision pointing and suppression of vibrations in the long flexible structure that comprises the 32-m x-ray telescope optical bench. Two separate electro-optical sensor systems are provided for the ground test facility (GTF). The Boom Motion Tracker (BMT) measures eigenvector data for post-mission use in system identification. The Tip Displacement Sensor (TDS) measures boom tip position and is used as feedback for the closed-loop control system that stabilizes the boom. Both the BMT and the TDS have met acceptance specifications and were delivered to MSFC in February 1992. This paper describes the sensor concept, the sensor configuration as implemented in the GTF, and the results of characterization and performance testing.

Carrier-envelope phase stabilization with sub-10 as residual timing jitter.

PubMed

Borchers, B; Koke, S; Husakou, A; Herrmann, J; Steinmeyer, G

2011-11-01

We demonstrate carrier-envelope phase (CEP) stabilization of a mode-locked Ti:sapphire oscillator with unprecedented timing jitter of eight attoseconds. The stabilization performance is obtained by a combination of two different stabilization approaches. In a first step the drift of the CEP is stabilized with a conventional feedback loop by means of controlling the oscillator pump power with an acousto-optic modulator (AOM). In a second step we utilize a recently developed feed-forward type stabilization scheme which has a much higher control bandwith. Here an acousto-optic frequency shifter (AOFS) produces the stabilized output in the first diffraction order. Moreover, we present numerical results on the optimization of the length of the photonic crystal fiber, which is used to generate an octave-spanning spectrum, in order to optimize the sensitivity in the f-to-2f interferometers.

Fast flux locked loop

DOEpatents

Ganther, Jr., Kenneth R.; Snapp, Lowell D.

2002-09-10

A flux locked loop for providing an electrical feedback signal, the flux locked loop employing radio-frequency components and technology to extend the flux modulation frequency and tracking loop bandwidth. The flux locked loop of the present invention has particularly useful application in read-out electronics for DC SQUID magnetic measurement systems, in which case the electrical signal output by the flux locked loop represents an unknown magnetic flux applied to the DC SQUID.

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.

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Neuromimetic Event-Based Detection for Closed-Loop Tactile Feedback Control of Upper Limb Prostheses

PubMed Central

Osborn, Luke; Kaliki, Rahul; Soares, Alcimar; Thakor, Nitish

2016-01-01

Upper limb amputees lack the valuable tactile sensing that helps provide context about the surrounding environment. Here we utilize tactile information to provide active touch feedback to a prosthetic hand. First, we developed fingertip tactile sensors for producing biomimetic spiking responses for monitoring contact, release, and slip of an object grasped by a prosthetic hand. We convert the sensor output into pulses, mimicking the rapid and slowly adapting spiking responses of receptor afferents found in the human body. Second, we designed and implemented two neuromimetic event-based algorithms, Compliant Grasping and Slip Prevention, on a prosthesis to create a local closed-loop tactile feedback control system (i.e. tactile information is sent to the prosthesis). Grasping experiments were designed to assess the benefit of this biologically inspired neuromimetic tactile feedback to a prosthesis. Results from able-bodied and amputee subjects show the average number of objects that broke or slipped during grasping decreased by over 50% and the average time to complete a grasping task decreased by at least 10% for most trials when comparing neuromimetic tactile feedback with no feedback on a prosthesis. Our neuromimetic method of closed-loop tactile sensing is a novel approach to improving the function of upper limb prostheses. PMID:27777640

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

PubMed Central

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

2017-01-01

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

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%.

Phase compensation with fiber optic surface profile acquisition and reconstruction system

NASA Astrophysics Data System (ADS)

Bo, En; Duan, Fajie; Feng, Fan; Lv, Changrong; Xiao, Fu; Huang, Tingting

2015-02-01

A fiber-optic sinusoidal phase modulating (SPM) interferometer was proposed for the acquisition and reconstruction of three-dimensional (3-D) surface profile. Sinusoidal phase modulation was induced by controlling the injection current of light source. The surface profile was constructed on the basis of fringe projection. Fringe patterns are vulnerable to external disturbances such as mechanical vibration and temperature fluctuation, which cause phase drift in the interference signal and decrease measuring accuracy. A closed-loop feedback phase compensation system was built. In the subsystem, the initial phase of the interference signal, which was caused by the initial optical path difference between interference arms, could be demodulated using phase generated carrier (PGC) method and counted out using coordinated rotation digital computer (CORDIC) , then a compensation voltage was generated for the PZT driver. The bias value of external disturbances superimposed on fringe patterns could be reduced to about 50 mrad, and the phase stability for interference fringes was less than 6 mrad. The feasibility for real-time profile measurement has been verified.

ASDTIC: A feedback control innovation

NASA Technical Reports Server (NTRS)

Lalli, V. R.; Schoenfeld, A. D.

1972-01-01

The ASDTIC (Analog Signal to Discrete Time Interval Converter) control subsystem provides precise output control of high performance aerospace power supplies. The key to ASDTIC operation is that it stably controls output by sensing output energy change as well as output magnitude. The ASDTIC control subsystem and control module were developed to improve power supply performance during static and dynamic input voltage and output load variations, to reduce output voltage or current regulation due to component variations or aging, to maintain a stable feedback control with variations in the loop gain or loop time constants, and to standardize the feedback control subsystem for power conditioning equipment.

ASDTIC - A feedback control innovation.

NASA Technical Reports Server (NTRS)

Lalli, V. R.; Schoenfeld, A. D.

1972-01-01

The ASDTIC (analog signal to discrete time interval converter) control subsystem provides precise output control of high performance aerospace power supplies. The key to ASDTIC operation is that it stably controls output by sensing output energy change as well as output magnitude. The ASDTIC control subsystem and control module were developed to improve power supply performance during static and dynamic input voltage and output load variations, to reduce output voltage or current regulation due to component variations or aging, to maintain a stable feedback control with variations in the loop gain or loop time constants, and to standardize the feedback control subsystem for power conditioning equipment.

Tower Based Load Measurements for Individual Pitch Control and Tower Damping of Wind Turbines

NASA Astrophysics Data System (ADS)

Kumar, A. A.; Hugues-Salas, O.; Savini, B.; Keogh, W.

2016-09-01

The cost of IPC has hindered adoption outside of Europe despite significant loading advantages for large wind turbines. In this work we presented a method for applying individual pitch control (including for higher-harmonics) using tower-top strain gauge feedback instead of blade-root strain gauge feedback. Tower-top strain gauges offer hardware savings of approximately 50% in addition to the possibility of easier access for maintenance and installation and requiring a less specialised skill-set than that required for applying strain gauges to composite blade roots. A further advantage is the possibility of using the same tower-top sensor array for tower damping control. This method is made possible by including a second order IPC loop in addition to the tower damping loop to reduce the typically dominating 3P content in tower-top load measurements. High-fidelity Bladed simulations show that the resulting turbine spectral characteristics from tower-top feedback IPC and from the combination of tower-top IPC and damping loops largely match those of blade-root feedback IPC and nacelle- velocity feedback damping. Lifetime weighted fatigue analysis shows that the methods allows load reductions within 2.5% of traditional methods.

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

PubMed

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

2016-06-13

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

A flexible continuous-variable QKD system using off-the-shelf components

NASA Astrophysics Data System (ADS)

Comandar, Lucian C.; Brunner, Hans H.; Bettelli, Stefano; Fung, Fred; Karinou, Fotini; Hillerkuss, David; Mikroulis, Spiros; Wang, Dawei; Kuschnerov, Maxim; Xie, Changsong; Poppe, Andreas; Peev, Momtchil

2017-10-01

We present the development of a robust and versatile CV-QKD architecture based on commercially available optical and electronic components. The system uses a pilot tone for phase synchronization with a local oscillator, as well as local feedback loops to mitigate frequency and polarization drifts. Transmit and receive-side digital signal processing is performed fully in software, allowing for rapid protocol reconfiguration. The quantum link is complemented with a software stack for secure-key processing, key storage and encrypted communication. All these features allow for the system to be at the same time a prototype for a future commercial product and a research platform.

Instrument Pointing Control System for the Stellar Interferometry Mission - Planet Quest

NASA Technical Reports Server (NTRS)

Brugarolas, Paul B.; Kang, Bryan

2006-01-01

This paper describes the high precision Instrument Pointing Control System (PCS) for the Stellar Interferometry Mission (SIM) - Planet Quest. The PCS system provides front-end pointing, compensation for spacecraft motion, and feedforward stabilization, which are needed for proper interference. Optical interferometric measurements require very precise pointing (0.03 as, 1-(sigma) radial) for maximizing the interference pattern visibility. This requirement is achieved by fine pointing control of articulating pointing mirrors with feedback from angle tracking cameras. The overall pointing system design concept is presentcd. Functional requirements and an acquisition concept are given. Guide and Science pointing control loops are discussed. Simulation analyses demonstrate the feasibility of the design.

Improved multistage wide band laser frequency stabilization

NASA Astrophysics Data System (ADS)

Kawamura, Seiji; Abramovici, Alex; Zucker, Michael E.

1997-01-01

Suppression of laser frequency fluctuations is an essential technology for planned interferometric detectors for astrophysical gravitational waves. Because of the low degree of residual frequency noise which is ultimately required, control topologies comprising two or more cascaded loops are favored. One such topology, used in the Laser Interferometer Gravitational-Wave Observatory 40 m interferometer, relied on electro-optic Pockels cell phase correction as a fast actuator for the final stage. This actuation method proved susceptible to spurious amplitude modulation effects, which provided an unintended parasitic feedback path. An alternate arrangement, which achieves comparably effective frequency stabilization without using a phase correcting Pockels cell, was introduced and successfully tested.

System and method of designing models in a feedback loop

DOEpatents

Gosink, Luke C.; Pulsipher, Trenton C.; Sego, Landon H.

2017-02-14

A method and system for designing models is disclosed. The method includes selecting a plurality of models for modeling a common event of interest. The method further includes aggregating the results of the models and analyzing each model compared to the aggregate result to obtain comparative information. The method also includes providing the information back to the plurality of models to design more accurate models through a feedback loop.

Modeling Aggressive Medulloblastoma Using Human Induced Pluripotent Stem Cells

DTIC Science & Technology

2017-09-01

and Myc in turn induces expression of AT1R creating a positive feedback loop and development of aggression tumor phenotype. The therapeutic...strengths are the relevant expertise of the applicant and his collaborating team, the novel paracrine positive feedback loop in EC-tumor cell...to as MYC-driven MB. The molecular mechanisms that drive MYC hyper -activation in MB remain incompletely understood. MB cells in actual tumors interact

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

PubMed

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

2015-07-01

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

Designing new classes of high-power, high-brightness VECSELs

NASA Astrophysics Data System (ADS)

Moloney, J. V.; Zakharian, A. R.; Hader, J.; Koch, Stephan W.

2005-10-01

Optically-pumped vertical external cavity semiconductor lasers offer the exciting possibility of designing kW-class solid state lasers that provide significant advantages over their doped YAG, thin-disk YAG and fiber counterparts. The basic VECSEL/OPSL (optically-pumped semiconductor laser) structure consists of a very thin (approximately 6 micron thick) active mirror consisting of a DBR high-reflectivity stack followed by a multiple quantum well resonant periodic (RPG) structure. An external mirror (reflectivity typically between 94%-98%) provides conventional optical feedback to the active semiconductor mirror chip. The "cold" cavity needs to be designed to take into account the semiconductor sub-cavity resonance shift with temperature and, importantly, the more rapid shift of the semiconductor material gain peak with temperature. Thermal management proves critical in optimizing the device for serious power scaling. We will describe a closed-loop procedure that begins with a design of the semiconductor active epi structure. This feeds into the sub-cavity optimization, optical and thermal transport within the active structure and thermal transport though the various heat sinking elements. Novel schemes for power scaling beyond current record performances will be discussed.

Optical modular arithmetic

NASA Astrophysics Data System (ADS)

Pavlichin, Dmitri S.; Mabuchi, Hideo

2014-06-01

Nanoscale integrated photonic devices and circuits offer a path to ultra-low power computation at the few-photon level. Here we propose an optical circuit that performs a ubiquitous operation: the controlled, random-access readout of a collection of stored memory phases or, equivalently, the computation of the inner product of a vector of phases with a binary selector" vector, where the arithmetic is done modulo 2pi and the result is encoded in the phase of a coherent field. This circuit, a collection of cascaded interferometers driven by a coherent input field, demonstrates the use of coherence as a computational resource, and of the use of recently-developed mathematical tools for modeling optical circuits with many coupled parts. The construction extends in a straightforward way to the computation of matrix-vector and matrix-matrix products, and, with the inclusion of an optical feedback loop, to the computation of a weighted" readout of stored memory phases. We note some applications of these circuits for error correction and for computing tasks requiring fast vector inner products, e.g. statistical classification and some machine learning algorithms.

Optics derotator servo control system for SONG Telescope

NASA Astrophysics Data System (ADS)

Xu, Jin; Ren, Changzhi; Ye, Yu

2012-09-01

The Stellar Oscillations Network Group (SONG) is an initiative which aims at designing and building a groundbased network of 1m telescopes dedicated to the study of phenomena occurring in the time domain. Chinese standard node of SONG is an Alt-Az Telescope of F/37 with 1m diameter. Optics derotator control system of SONG telescope adopts the development model of "Industrial Computer + UMAC Motion Controller + Servo Motor".1 Industrial computer is the core processing part of the motion control, motion control card(UMAC) is in charge of the details on the motion control, Servo amplifier accepts the control commands from UMAC, and drives the servo motor. The position feedback information comes from the encoder, to form a closed loop control system. This paper describes in detail hardware design and software design for the optics derotator servo control system. In terms of hardware design, the principle, structure, and control algorithm of servo system based on optics derotator are analyzed and explored. In terms of software design, the paper proposes the architecture of the system software based on Object-Oriented Programming.

Quantum cascade lasers as metrological tools for space optics

NASA Astrophysics Data System (ADS)

Bartalini, S.; Borri, S.; Galli, I.; Mazzotti, D.; Cancio Pastor, P.; Giusfredi, G.; De Natale, P.

2017-11-01

A distributed-feedback quantum-cascade laser working in the 4.3÷4.4 mm range has been frequency stabilized to the Lamb-dip center of a CO2 ro-vibrational transition by means of first-derivative locking to the saturated absorption signal, and its absolute frequency counted with a kHz-level precision and an overall uncertainty of 75 kHz. This has been made possible by an optical link between the QCL and a near-IR Optical Frequency Comb Synthesizer, thanks to a non-linear sum-frequency generation process with a fiber-amplified Nd:YAG laser. The implementation of a new spectroscopic technique, known as polarization spectroscopy, provides an improved signal for the locking loop, and will lead to a narrower laser emission and a drastic improvement in the frequency stability, that in principle is limited only by the stability of the optical frequency comb synthesizer (few parts in 1013). These results confirm quantum cascade lasers as reliable sources not only for high-sensitivity, but also for highprecision measurements, ranking them as optimal laser sources for space applications.

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

PubMed

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

2017-05-15

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

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.

Method for spinning up a three-axis controlled spacecraft

NASA Technical Reports Server (NTRS)

Vorlicek, Preston L. (Inventor)

1988-01-01

A three-axis controlled spacecraft (1), typically a satellite, is spun up about its roll axis (20) prior to firing a motor (2), i.e., a perigee kick motor, to achieve the requisite degree of angular momentum stiffness. Thrusters (21) for imparting rotation about the roll axis (20) are activated in open-loop fashion, typically at less than full duty cycle. Cross-axis torques induced by this rotational motion are compensated for by means of closed control loops for each of the pitch and yaw axes (30, 40, respectively). Each closed control loop combines a prebias torque (72) with torques (75, 74) representative of position and rate feedback information, respectively. A deadband (52) within each closed control loop can be widened during the spinup, to conserve fuel. Position feedback information (75) in each of the control loops is disabled upon saturation of the gyroscope associated with the roll axis (20).

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.

Optical feedback-induced light modulation for fiber-based laser ablation.

PubMed

Kang, Hyun Wook

2014-11-01

Optical fibers have been used as a minimally invasive tool in various medical fields. However, due to excessive heat accumulation, the distal end of a fiber often suffers from severe melting or devitrification, leading to the eventual fiber failure during laser treatment. In order to minimize thermal damage at the fiber tip, an optical feedback sensor was developed and tested ex vivo. Porcine kidney tissue was used to evaluate the feasibility of optical feedback in terms of signal activation, ablation performance, and light transmission. Testing various signal thresholds demonstrated that 3 V was relatively appropriate to trigger the feedback sensor and to prevent the fiber deterioration during kidney tissue ablation. Based upon the development of temporal signal signatures, full contact mode rapidly activated the optical feedback sensor possibly due to heat accumulation. Modulated light delivery induced by optical feedback diminished ablation efficiency by 30% in comparison with no feedback case. However, long-term transmission results validated that laser ablation assisted with optical feedback was able to almost consistently sustain light delivery to the tissue as well as ablation efficiency. Therefore, an optical feedback sensor can be a feasible tool to protect optical fiber tips by minimizing debris contamination and delaying thermal damage process and to ensure more efficient and safer laser-induced tissue ablation.

Cardiac arrhythmias and degradation into chaotic behavior prevention using feedback control

NASA Astrophysics Data System (ADS)

Uzelac, Ilija; Sidorov, Veniamin; Wikswo, John; Gray, Richard

2012-02-01

During normal heart rhythm, cardiac cells behave as a set of oscillators with a distribution of phases but with the same frequency. The heart as a dynamical system in a phase space representation can be modeled as a set of oscillators that have closed overlapping orbits with the same period. These orbits are not stable and in the case of disruption of the cardiac rhythm, such as due to premature beats, the system will have a tendency to leave its periodic unstable orbits. If these orbits become attracted to phase singularities, their disruption may lead to chaotic behavior, which appears as a life-threating ventricular fibrillation. By using closed-loop feedback in the form of an adjustable defibrillation shock, any drift from orbits corresponding to the normal rhythm can be corrected by forcing the system to maintain its orbits. The delay through the feedback network coincides with the period of normal heart beats. To implement this approach we developed a 1 kW arbitrary waveform voltage-to-current converter with a 1 kHz bandwidth driven by a photodiode system that records an optical electrocardiogram and provides a feedback signal in real time. Our goal is to determine whether our novel method to defibrillate the heart will require much lower energies than are currently utilized in single shock defibrillators.

Development of the Mayo Investigational Neuromodulation Control System: toward a closed-loop electrochemical feedback system for deep brain stimulation

PubMed Central

Chang, Su-Youne; Kimble, Christopher J.; Kim, Inyong; Paek, Seungleal B.; Kressin, Kenneth R.; Boesche, Joshua B.; Whitlock, Sidney V.; Eaker, Diane R.; Kasasbeh, Aimen; Horne, April E.; Blaha, Charles D.; Bennet, Kevin E.; Lee, Kendall H.

2014-01-01

Object Conventional deep brain stimulation (DBS) devices continue to rely on an open-loop system in which stimulation is independent of functional neural feedback. The authors previously proposed that as the foundation of a DBS “smart” device, a closed-loop system based on neurochemical feedback, may have the potential to improve therapeutic outcomes. Alterations in neurochemical release are thought to be linked to the clinical benefit of DBS, and fast-scan cyclic voltammetry (FSCV) has been shown to be effective for recording these evoked neurochemical changes. However, the combination of FSCV with conventional DBS devices interferes with the recording and identification of the evoked analytes. To integrate neurochemical recording with neurostimulation, the authors developed the Mayo Investigational Neuromodulation Control System (MINCS), a novel, wirelessly controlled stimulation device designed to interface with FSCV performed by their previously described Wireless Instantaneous Neurochemical Concentration Sensing System (WINCS). Methods To test the functionality of these integrated devices, various frequencies of electrical stimulation were applied by MINCS to the medial forebrain bundle of the anesthetized rat, and striatal dopamine release was recorded by WINCS. The parameters for FSCV in the present study consisted of a pyramidal voltage waveform applied to the carbon-fiber microelectrode every 100 msec, ramping between −0.4 V and +1.5 V with respect to an Ag/AgCl reference electrode at a scan rate of either 400 V/sec or 1000 V/sec. The carbon-fiber microelectrode was held at the baseline potential of −0.4 V between scans. Results By using MINCS in conjunction with WINCS coordinated through an optic fiber, the authors interleaved intervals of electrical stimulation with FSCV scans and thus obtained artifact-free wireless FSCV recordings. Electrical stimulation of the medial forebrain bundle in the anesthetized rat by MINCS elicited striatal dopamine release that was time-locked to stimulation and increased progressively with stimulation frequency. Conclusions Here, the authors report a series of proof-of-principle tests in the rat brain demonstrating MINCS to be a reliable and flexible stimulation device that, when used in conjunction with WINCS, performs wirelessly controlled stimulation concurrent with artifact-free neurochemical recording. These findings suggest that the integration of neurochemical recording with neurostimulation may be a useful first step toward the development of a closed-loop DBS system for human application. PMID:24116724

Dynamic Processes in Regulation and Some Implications for Biofeedback and Biobehavioral Interventions

PubMed Central

Lehrer, Paul; Eddie, David

2013-01-01

Systems theory has long been applied in psychology, biology, and sociology. This paper applies newer methods of control systems modeling to the assessment of system stability in health and disease. Control systems can be characterized as open or closed systems with feedback loops. Feedback produces oscillatory activity, and the complexity of naturally occurring oscillatory patterns reflects the multiplicity of feedback mechanisms, such that many mechanisms operate simultaneously to control the system. Unstable systems, often associated with poor health, are characterized by absence of oscillation, random noise, or a very simple pattern of oscillation. This modeling approach can be applied to a diverse range of phenomena, including cardiovascular and brain activity, mood and thermal regulation, and social system stability. External system stressors such as disease, psychological stress, injury, or interpersonal conflict may perturb a system, yet simultaneously stimulate oscillatory processes and exercise control mechanisms. Resonance can occur in systems with negative feedback loops, causing high-amplitude oscillations at a single frequency. Resonance effects can be used to strengthen modulatory oscillations, but may obscure other information and control mechanisms, and weaken system stability. Positive as well as negative feedback loops are important for system function and stability. Examples are presented of oscillatory processes in heart rate variability, and regulation of autonomic, thermal, pancreatic and central nervous system processes, as well as in social/organizational systems such as marriages and business organizations. Resonance in negative feedback loops can help stimulate oscillations and exercise control reflexes, but also can deprive the system of important information. Empirical hypotheses derived from this approach are presented, including that moderate stress may enhance health and functioning. PMID:23572244

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

Levine, Paul A.; Randerson, James T.; Swenson, Sean C.

The relationship between terrestrial water storage (TWS) and atmospheric processes has important implications for predictability of climatic extremes and projection of future climate change. In places where moisture availability limits evapotranspiration (ET), variability in TWS has the potential to influence surface energy fluxes and atmospheric conditions. Where atmospheric conditions, in turn, influence moisture availability, a full feedback loop exists. Here we developed a novel approach for measuring the strength of both components of this feedback loop, i.e., the forcing of the atmosphere by variability in TWS and the response of TWS to atmospheric variability, using satellite observations of TWS, precipitation,more » solar radiation, and vapor pressure deficit during 2002–2014. Our approach defines metrics to quantify the relationship between TWS anomalies and climate globally on a seasonal to interannual timescale. Metrics derived from the satellite data were used to evaluate the strength of the feedback loop in 38 members of the Community Earth System Model (CESM) Large Ensemble (LENS) and in six models that contributed simulations to phase 5 of the Coupled Model Intercomparison Project (CMIP5). We found that both forcing and response limbs of the feedback loop in LENS were stronger than in the satellite observations in tropical and temperate regions. Feedbacks in the selected CMIP5 models were not as strong as those found in LENS, but were still generally stronger than those estimated from the satellite measurements. Consistent with previous studies conducted across different spatial and temporal scales, our analysis suggests that models may overestimate the strength of the feedbacks between the land surface and the atmosphere. Lastly, we describe several possible mechanisms that may contribute to this bias, and discuss pathways through which models may overestimate ET or overestimate the sensitivity of ET to TWS.« less

Loop Analysis of Causal Feedback in Epidemiology: An Illustration Relating To Urban Neighborhoods and Resident Depressive Experiences

PubMed Central

2008-01-01

The causal feedback implied by urban neighborhood conditions that shape human health experiences, that in turn shape neighborhood conditions through a complex causal web, raises a challenge for traditional epidemiological causal analyses. This article introduces the loop analysis method, and builds off of a core loop model linking neighborhood property vacancy rate, resident depressive symptoms, rate of neighborhood death, and rate of neighborhood exit in a feedback network. I justify and apply loop analysis to the specific example of depressive symptoms and abandoned urban residential property to show how inquiries into the behavior of causal systems can answer different kinds of hypotheses, and thereby compliment those of causal modeling using statistical models. Neighborhood physical conditions that are only indirectly influenced by depressive symptoms may nevertheless manifest in the mental health experiences of their residents; conversely, neighborhood physical conditions may be a significant mental health risk for the population of neighborhood residents. I find that participatory greenspace programs are likely to produce adaptive responses in depressive symptoms and different neighborhood conditions, which are different in character to non-participatory greenspace interventions. PMID:17706851

Digital control of a direct current converter for a hybrid vehicle

NASA Astrophysics Data System (ADS)

Hernandez, Juan Manuel

The nonlinear feedback loops permitting the large signal control of pulse width modulators in direct current converters are discussed. A digital feedback loop on a converter controlling the coupling of a direct current machine is described. It is used in the propulsion of a hybrid vehicle (thermal-electric) with regenerative braking. The protection of the power switches is also studied. An active protection of the MOST bipolar transistor association is proposed.

Power supply with air core transformer and seperated power supplies for high dynamic range

NASA Technical Reports Server (NTRS)

Orient, Otto (Inventor); Chutjian, Ara (Inventor); Aalami, Dean (Inventor); Darrach, Murray (Inventor)

2001-01-01

A power supply for a quadrupole mass spectrometer which operates using an RF signal. The RF signal is controllable via a feedback loop. The feedback loop is from the output, through a comparator, and compared to a digital signal. An air core transformer is used to minimize the weight. The air core transformer is driven via two out of phase sawtooth signals which drive opposite ends of the transformer.

Diurnal suppression of EGFR signalling by glucocorticoids and implications for tumour progression and treatment.

PubMed

Lauriola, Mattia; Enuka, Yehoshua; Zeisel, Amit; D'Uva, Gabriele; Roth, Lee; Sharon-Sevilla, Michal; Lindzen, Moshit; Sharma, Kirti; Nevo, Nava; Feldman, Morris; Carvalho, Silvia; Cohen-Dvashi, Hadas; Kedmi, Merav; Ben-Chetrit, Nir; Chen, Alon; Solmi, Rossella; Wiemann, Stefan; Schmitt, Fernando; Domany, Eytan; Yarden, Yosef

2014-10-03

Signal transduction by receptor tyrosine kinases (RTKs) and nuclear receptors for steroid hormones is essential for body homeostasis, but the cross-talk between these receptor families is poorly understood. We observed that glucocorticoids inhibit signalling downstream of EGFR, an RTK. The underlying mechanism entails suppression of EGFR's positive feedback loops and simultaneous triggering of negative feedback loops that normally restrain EGFR. Our studies in mice reveal that the regulation of EGFR's feedback loops by glucocorticoids translates to circadian control of EGFR signalling: EGFR signals are suppressed by high glucocorticoids during the active phase (night-time in rodents), while EGFR signals are enhanced during the resting phase. Consistent with this pattern, treatment of animals bearing EGFR-driven tumours with a specific kinase inhibitor was more effective if administered during the resting phase of the day, when glucocorticoids are low. These findings support a circadian clock-based paradigm in cancer therapy.

Dual-range linearized transimpedance amplifier system

DOEpatents

Wessendorf, Kurt O.

2010-11-02

A transimpedance amplifier system is disclosed which simultaneously generates a low-gain output signal and a high-gain output signal from an input current signal using a single transimpedance amplifier having two different feedback loops with different amplification factors to generate two different output voltage signals. One of the feedback loops includes a resistor, and the other feedback loop includes another resistor in series with one or more diodes. The transimpedance amplifier system includes a signal linearizer to linearize one or both of the low- and high-gain output signals by scaling and adding the two output voltage signals from the transimpedance amplifier. The signal linearizer can be formed either as an analog device using one or two summing amplifiers, or alternately can be formed as a digital device using two analog-to-digital converters and a digital signal processor (e.g. a microprocessor or a computer).

Study on the characteristic and application of DFB semiconductor lasers under optical injection for microwave photonics

NASA Astrophysics Data System (ADS)

Pu, Tao; Wang, Wei wei

2018-01-01

In order to apply optical injection effect in Microwave Photonics system, The red-shift effect of the cavity mode of the DFB semiconductor laser under single-frequency optical injection is studied experimentally, and the red-shift curve of the cavity mode is measured. The wavelength-selective amplification property of the DFB semiconductor laser under multi-frequency optical injection is also investigated, and the gain curves for the injected signals in different injection ratios are measured in the experiment. A novel and simple structure to implement a single-passband MPF with wideband tunability based on the wavelength-selective amplification of a DFB semiconductor laser under optical injection is proposed and experimentally demonstrated. MPFs with center frequency tuned from 13 to 41 GHz are realized in the experiment. A wideband and frequency-tunable optoelectronic oscillator based on a directly modulated distributed feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. By optical injection, the relaxation oscillation frequency of the DFB laser is enhanced and its high modulation efficiency makes the loop oscillate without the necessary of the electrical filter. An experiment is performed; microwave signals with frequency tuned from 5.98 to 15.22 GHz are generated by adjusting the injection ratio and frequency detuning between the master and slave lasers.

Measuring electrically charged particle fluxes in space using a fiber optic loop sensor

NASA Technical Reports Server (NTRS)

1992-01-01

The purpose of this program was to demonstrate the potential of a fiber optic loop sensor for the measurement of electrically charged particle fluxes in space. The key elements of the sensor are a multiple turn loop of low birefringence, single mode fiber, with a laser diode light source, and a low noise optical receiver. The optical receiver is designed to be shot noise limited, with this being the limiting sensitivity factor for the sensor. The sensing element is the fiber optic loop. Under a magnetic field from an electric current flowing along the axis of the loop, there is a non-vanishing line integral along the fiber optic loop. This causes a net birefringence producing two states of polarization whose phase difference is correlated to magnetic field strength and thus, current in the optical receiver electronic processing. The objectives in this program were to develop a prototype laser diode powered fiber optic sensor. The performance specification of a minimum detectable current density of 1 (mu)amp/sq m-(radical)Hz, should be at the shot noise limit of the detection electronics. OPTRA has successfully built and tested a 3.2 m diameter loop with 137 turns of low birefringence optical fiber and achieved a minimum detectable current density of 5.4 x 10(exp-5) amps/(radical)Hz. If laboratory space considerations were not an issue, with the length of optical fiber available to us, we would have achieved a minimum detectable current density of 4 x 10(exp -7) amps/(radical)Hz.

Fiber Optic Control System Integration program: for optical flight control system development

NASA Astrophysics Data System (ADS)

Weaver, Thomas L.; Seal, Daniel W.

1994-10-01

Hardware and software were developed for optical feedback links in the flight control system of an F/A-18 aircraft. Developments included passive optical sensors and optoelectronics to operate the sensors. Sensors with different methods of operation were obtained from different manufacturers and integrated with common optoelectronics. The sensors were the following: Air Data Temperature; Air Data Pressure; and Leading Edge Flap, Nose Wheel Steering, Trailing Edge Flap, Pitch Stick, Rudder, Rudder Pedal, Stabilator, and Engine Power Lever Control Position. The sensors were built for a variety of aircraft locations and harsh environments. The sensors and optoelectronics were as similar as practical to a production system. The integrated system was installed by NASA for flight testing. Wavelength Division Multiplexing proved successful as a system design philosophy. Some sensors appeared to be better choices for aircraft applications than others, with digital sensors generally being better than analog sensors, and rotary sensors generally being better than linear sensors. The most successful sensor approaches were selected for use in a follow-on program in which the sensors will not just be flown on the aircraft and their performance recorded; but, the optical sensors will be used in closing flight control loops.

Model-Based Angular Scan Error Correction of an Electrothermally-Actuated MEMS Mirror

PubMed Central

Zhang, Hao; Xu, Dacheng; Zhang, Xiaoyang; Chen, Qiao; Xie, Huikai; Li, Suiqiong

2015-01-01

In this paper, the actuation behavior of a two-axis electrothermal MEMS (Microelectromechanical Systems) mirror typically used in miniature optical scanning probes and optical switches is investigated. The MEMS mirror consists of four thermal bimorph actuators symmetrically located at the four sides of a central mirror plate. Experiments show that an actuation characteristics difference of as much as 4.0% exists among the four actuators due to process variations, which leads to an average angular scan error of 0.03°. A mathematical model between the actuator input voltage and the mirror-plate position has been developed to predict the actuation behavior of the mirror. It is a four-input, four-output model that takes into account the thermal-mechanical coupling and the differences among the four actuators; the vertical positions of the ends of the four actuators are also monitored. Based on this model, an open-loop control method is established to achieve accurate angular scanning. This model-based open loop control has been experimentally verified and is useful for the accurate control of the mirror. With this control method, the precise actuation of the mirror solely depends on the model prediction and does not need the real-time mirror position monitoring and feedback, greatly simplifying the MEMS control system. PMID:26690432

Circuit Regulates Speed Of dc Motor

NASA Technical Reports Server (NTRS)

Weaver, Charles; Padden, Robin; Brown, Floyd A., Jr.

1990-01-01

Driving circuit regulates speed of small dc permanent-magnet motor in tape recorder. Two nested feedback loops maintain speed within 1 percent of constant value. Inner loop provides coarse regulation, while outer loop removes most of variation in speed that remains in the presence of regulation by the inner loop. Compares speed of motor with commanded speed and adjusts current supplied to motor accordingly.

Runtime Assurance Framework Development for Highly Adaptive Flight Control Systems

DTIC Science & Technology

2015-12-01

performing a surveillance mission. The demonstration platform consisted of RTA systems for the inner- loop control, outer- loop guidance, ownship flight...For the inner- loop , the concept of employing multiple transition controllers in the reversionary control system was studied. For all feedback levels...5 RTA Protection Applied to Inner- Loop Control Systems .................................................61 5.1 General Description of Morphing Wing

Impact of optical feedback on current-induced polarization behavior of 1550 nm vertical-cavity surface-emitting lasers.

PubMed

Deng, Tao; Wu, Zheng-Mao; Xie, Yi-Yuan; Wu, Jia-Gui; Tang, Xi; Fan, Li; Panajotov, Krassimir; Xia, Guang-Qiong

2013-06-01

Polarization switching (PS) between two orthogonal linearly polarized fundamental modes is experimentally observed in commercial free-running 1550 nm vertical-cavity surface-emitting lasers (VCSELs) (Raycan). The characteristics of this PS are strongly modified after introducing a polarization-preserved (PP) or polarization-orthogonal (PO) optical feedback. Under the case that the external cavity is approximately 30 cm, the PP optical feedback results in the PS point shifting toward a lower injection current, and the region within which the two polarization modes coexist is enlarged with the increase of the PP feedback strength. Under too-strong PP feedback levels, the PS disappears. The impact of PO optical feedback on VCSEL polarization behavior is quite similar to that of PP optical feedback, but larger feedback strength is needed to obtain similar results.

Evaluating the strength of the land$-$atmosphere moisture feedback in Earth system models using satellite observations

DOE PAGES

Levine, Paul A.; Randerson, James T.; Swenson, Sean C.; ...

2016-12-09

The relationship between terrestrial water storage (TWS) and atmospheric processes has important implications for predictability of climatic extremes and projection of future climate change. In places where moisture availability limits evapotranspiration (ET), variability in TWS has the potential to influence surface energy fluxes and atmospheric conditions. Where atmospheric conditions, in turn, influence moisture availability, a full feedback loop exists. Here we developed a novel approach for measuring the strength of both components of this feedback loop, i.e., the forcing of the atmosphere by variability in TWS and the response of TWS to atmospheric variability, using satellite observations of TWS, precipitation,more » solar radiation, and vapor pressure deficit during 2002–2014. Our approach defines metrics to quantify the relationship between TWS anomalies and climate globally on a seasonal to interannual timescale. Metrics derived from the satellite data were used to evaluate the strength of the feedback loop in 38 members of the Community Earth System Model (CESM) Large Ensemble (LENS) and in six models that contributed simulations to phase 5 of the Coupled Model Intercomparison Project (CMIP5). We found that both forcing and response limbs of the feedback loop in LENS were stronger than in the satellite observations in tropical and temperate regions. Feedbacks in the selected CMIP5 models were not as strong as those found in LENS, but were still generally stronger than those estimated from the satellite measurements. Consistent with previous studies conducted across different spatial and temporal scales, our analysis suggests that models may overestimate the strength of the feedbacks between the land surface and the atmosphere. Lastly, we describe several possible mechanisms that may contribute to this bias, and discuss pathways through which models may overestimate ET or overestimate the sensitivity of ET to TWS.« less

Optical feedback structures and methods of making

DOEpatents

None

2014-11-18

An optical resonator can include an optical feedback structure disposed on a substrate, and a composite including a matrix including a chromophore. The composite disposed on the substrate and in optical communication with the optical feedback structure. The chromophore can be a semiconductor nanocrystal. The resonator can provide laser emission when excited.

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

OncomiR Addiction Is Generated by a miR-155 Feedback Loop in Theileria-Transformed Leukocytes

PubMed Central

Medjkane, Souhila; Perichon, Martine; Yin, Qinyan; Flemington, Erik; Weitzman, Matthew D.; Weitzman, Jonathan B.

2013-01-01

The intracellular parasite Theileria is the only eukaryote known to transform its mammalian host cells. We investigated the host mechanisms involved in parasite-induced transformation phenotypes. Tumour progression is a multistep process, yet ‘oncogene addiction’ implies that cancer cell growth and survival can be impaired by inactivating a single gene, offering a rationale for targeted molecular therapies. Furthermore, feedback loops often act as key regulatory hubs in tumorigenesis. We searched for microRNAs involved in addiction to regulatory loops in leukocytes infected with Theileria parasites. We show that Theileria transformation involves induction of the host bovine oncomiR miR-155, via the c-Jun transcription factor and AP-1 activity. We identified a novel miR-155 target, DET1, an evolutionarily-conserved factor involved in c-Jun ubiquitination. We show that miR-155 expression led to repression of DET1 protein, causing stabilization of c-Jun and driving the promoter activity of the BIC transcript containing miR-155. This positive feedback loop is critical to maintain the growth and survival of Theileria-infected leukocytes; transformation is reversed by inhibiting AP-1 activity or miR-155 expression. This is the first demonstration that Theileria parasites induce the expression of host non-coding RNAs and highlights the importance of a novel feedback loop in maintaining the proliferative phenotypes induced upon parasite infection. Hence, parasite infection drives epigenetic rewiring of the regulatory circuitry of host leukocytes, placing miR-155 at the crossroads between infection, regulatory circuits and transformation. PMID:23637592

Direct laser additive fabrication system with image feedback control

DOEpatents

Griffith, Michelle L.; Hofmeister, William H.; Knorovsky, Gerald A.; MacCallum, Danny O.; Schlienger, M. Eric; Smugeresky, John E.

2002-01-01

A closed-loop, feedback-controlled direct laser fabrication system is disclosed. The feedback refers to the actual growth conditions obtained by real-time analysis of thermal radiation images. The resulting system can fabricate components with severalfold improvement in dimensional tolerances and surface finish.

Different designs of kinase-phosphatase interactions and phosphatase sequestration shapes the robustness and signal flow in the MAPK cascade

PubMed Central

2012-01-01

Background The three layer mitogen activated protein kinase (MAPK) signaling cascade exhibits different designs of interactions between its kinases and phosphatases. While the sequential interactions between the three kinases of the cascade are tightly preserved, the phosphatases of the cascade, such as MKP3 and PP2A, exhibit relatively diverse interactions with their substrate kinases. Additionally, the kinases of the MAPK cascade can also sequester their phosphatases. Thus, each topologically distinct interaction design of kinases and phosphatases could exhibit unique signal processing characteristics, and the presence of phosphatase sequestration may lead to further fine tuning of the propagated signal. Results We have built four architecturally distinct types of models of the MAPK cascade, each model with identical kinase-kinase interactions but unique kinases-phosphatases interactions. Our simulations unravelled that MAPK cascade’s robustness to external perturbations is a function of nature of interaction between its kinases and phosphatases. The cascade’s output robustness was enhanced when phosphatases were sequestrated by their target kinases. We uncovered a novel implicit/hidden negative feedback loop from the phosphatase MKP3 to its upstream kinase Raf-1, in a cascade resembling the B cell MAPK cascade. Notably, strength of the feedback loop was reciprocal to the strength of phosphatases’ sequestration and stronger sequestration abolished the feedback loop completely. An experimental method to verify the presence of the feedback loop is also proposed. We further showed, when the models were activated by transient signal, memory (total time taken by the cascade output to reach its unstimulated level after removal of signal) of a cascade was determined by the specific designs of interaction among its kinases and phosphatases. Conclusions Differences in interaction designs among the kinases and phosphatases can differentially shape the robustness and signal response behaviour of the MAPK cascade and phosphatase sequestration dramatically enhances the robustness to perturbations in each of the cascade. An implicit negative feedback loop was uncovered from our analysis and we found that strength of the negative feedback loop is reciprocally related to the strength of phosphatase sequestration. Duration of output phosphorylation in response to a transient signal was also found to be determined by the individual cascade’s kinase-phosphatase interaction design. PMID:22748295

Simple Optoelectronic Feedback in Microwave Oscillators

NASA Technical Reports Server (NTRS)

Maleki, Lute; Iltchenko, Vladimir

2009-01-01

A proposed method of stabilizing microwave and millimeter-wave oscillators calls for the use of feedback in optoelectronic delay lines characterized by high values of the resonance quality factor (Q). The method would extend the applicability of optoelectronic feedback beyond the previously reported class of optoelectronic oscillators that comprise two-port electronic amplifiers in closed loops with high-Q feedback circuits.

Servo control of an optical trap.

PubMed

Wulff, Kurt D; Cole, Daniel G; Clark, Robert L

2007-08-01

A versatile optical trap has been constructed to control the position of trapped objects and ultimately to apply specified forces using feedback control. While the design, development, and use of optical traps has been extensive and feedback control has played a critical role in pushing the state of the art, few comprehensive examinations of feedback control of optical traps have been undertaken. Furthermore, as the requirements are pushed to ever smaller distances and forces, the performance of optical traps reaches limits. It is well understood that feedback control can result in both positive and negative effects in controlled systems. We give an analysis of the trapping limits as well as introducing an optical trap with a feedback control scheme that dramatically improves an optical trap's sensitivity at low frequencies.

Global properties in an experimental realization of time-delayed feedback control with an unstable control loop.

PubMed

Höhne, Klaus; Shirahama, Hiroyuki; Choe, Chol-Ung; Benner, Hartmut; Pyragas, Kestutis; Just, Wolfram

2007-05-25

We demonstrate by electronic circuit experiments the feasibility of an unstable control loop to stabilize torsion-free orbits by time-delayed feedback control. Corresponding analytical normal form calculations and numerical simulations reveal a severe dependence of the basin of attraction on the particular coupling scheme of the control force. Such theoretical predictions are confirmed by the experiments and emphasize the importance of the coupling scheme for the global control performance.

VRILLE Controls PDF Neuropeptide Accumulation and Arborization Rhythms in Small Ventrolateral Neurons to Drive Rhythmic Behavior in Drosophila.

PubMed

Gunawardhana, Kushan L; Hardin, Paul E

2017-11-20

In Drosophila, the circadian clock is comprised of transcriptional feedback loops that control rhythmic gene expression responsible for daily rhythms in physiology, metabolism, and behavior. The core feedback loop, which employs CLOCK-CYCLE (CLK-CYC) activators and PERIOD-TIMELESS (PER-TIM) repressors to drive rhythmic transcription peaking at dusk, is required for circadian timekeeping and overt behavioral rhythms. CLK-CYC also activates an interlocked feedback loop, which uses the PAR DOMAIN PROTEIN 1ε (PDP1ε) activator and the VRILLE (VRI) repressor to drive rhythmic transcription peaking at dawn. Although Pdp1ε mutants disrupt activity rhythms without eliminating clock function, whether vri is required for clock function and/or output is not known. Using a conditionally inactivatable transgene to rescue vri developmental lethality, we show that clock function persists after vri inactivation but that activity rhythms are abolished. The inactivation of vri disrupts multiple output pathways thought to be important for activity rhythms, including PDF accumulation and arborization rhythms in the small ventrolateral neuron (sLN v ) dorsal projection. These results demonstrate that vri acts as a key regulator of clock output and suggest that the primary function of the interlocked feedback loop in Drosophila is to drive rhythmic transcription required for overt rhythms. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

PubMed

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

2013-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

Mathematical Modeling of RNA-Based Architectures for Closed Loop Control of Gene Expression.

PubMed

Agrawal, Deepak K; Tang, Xun; Westbrook, Alexandra; Marshall, Ryan; Maxwell, Colin S; Lucks, Julius; Noireaux, Vincent; Beisel, Chase L; Dunlop, Mary J; Franco, Elisa

2018-05-08

Feedback allows biological systems to control gene expression precisely and reliably, even in the presence of uncertainty, by sensing and processing environmental changes. Taking inspiration from natural architectures, synthetic biologists have engineered feedback loops to tune the dynamics and improve the robustness and predictability of gene expression. However, experimental implementations of biomolecular control systems are still far from satisfying performance specifications typically achieved by electrical or mechanical control systems. To address this gap, we present mathematical models of biomolecular controllers that enable reference tracking, disturbance rejection, and tuning of the temporal response of gene expression. These controllers employ RNA transcriptional regulators to achieve closed loop control where feedback is introduced via molecular sequestration. Sensitivity analysis of the models allows us to identify which parameters influence the transient and steady state response of a target gene expression process, as well as which biologically plausible parameter values enable perfect reference tracking. We quantify performance using typical control theory metrics to characterize response properties and provide clear selection guidelines for practical applications. Our results indicate that RNA regulators are well-suited for building robust and precise feedback controllers for gene expression. Additionally, our approach illustrates several quantitative methods useful for assessing the performance of biomolecular feedback control systems.

Take a Ride Along NIF’s Optics Recycle Loop

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

Bouthillier, Lauren; Folta, Jim; Welday, Brian

The National Ignition Facility uses over 40,000 optics to help guide 192 laser beams onto a target the size of a pencil eraser. Check out how the optics recycle loop repairs optics, saving time and money.

Diversified pulse generation from frequency shifted feedback Tm-doped fibre lasers.

PubMed

Chen, He; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

2016-05-19

Pulsed fibre lasers operating in the eye-safe 2 μm spectral region have numerous potential applications in areas such as remote sensing, medicine, mid-infrared frequency conversion, and free-space communication. Here, for the first time, we demonstrate versatile 2 μm ps-ns pulses generation from Tm-based fibre lasers based on frequency shifted feedback and provide a comprehensive report of their special behaviors. The lasers are featured with elegant construction and the unparalleled capacity of generating versatile pulses. The self-starting mode-locking is initiated by an intra-cavity acousto-optical frequency shifter. Diversified mode-locked pulse dynamics were observed by altering the pump power, intra-cavity polarization state and cavity structure, including as short as 8 ps single pulse sequence, pulse bundle state and up to 12 nJ, 3 ns nanosecond rectangular pulse. A reflective nonlinear optical loop mirror was introduced to successfully shorten the pulses from 24 ps to 8 ps. Beside the mode-locking operation, flexible Q-switching and Q-switched mode-locking operation can also be readily achieved in the same cavity. Up to 78 μJ high energy nanosecond pulse can be generated in this regime. Several intriguing pulse dynamics are characterized and discussed.

Improved performance of analog and digital acousto-optic modulation with feedback under profiled beam propagation for secure communication using chaos

NASA Astrophysics Data System (ADS)

Almehmadi, Fares S.; Chatterjee, Monish R.

2014-12-01

Using intensity feedback, the closed-loop behavior of an acousto-optic hybrid device under profiled beam propagation has been recently shown to exhibit wider chaotic bands potentially leading to an increase in both the dynamic range and sensitivity to key parameters that characterize the encryption. In this work, a detailed examination is carried out vis-à-vis the robustness of the encryption/decryption process relative to parameter mismatch for both analog and pulse code modulation signals, and bit error rate (BER) curves are used to examine the impact of additive white noise. The simulations with profiled input beams are shown to produce a stronger encryption key (i.e., much lower parametric tolerance thresholds) relative to simulations with uniform plane wave input beams. In each case, it is shown that the tolerance for key parameters drops by factors ranging from 10 to 20 times below those for uniform plane wave propagation. Results are shown to be at consistently lower tolerances for secure transmission of analog and digital signals using parameter tolerance measures, as well as BER performance measures for digital signals. These results hold out the promise for considerably greater information transmission security for such a system.

Feedback Augmented Sub-Ranging (FASR) Quantizer

NASA Technical Reports Server (NTRS)

Guilligan, Gerard

2012-01-01

This innovation is intended to reduce the size, power, and complexity of pipeline analog-to-digital converters (ADCs) that require high resolution and speed along with low power. Digitizers are important components in any application where analog signals (such as light, sound, temperature, etc.) need to be digitally processed. The innovation implements amplification of a sampled residual voltage in a switched capacitor amplifier stage that does not depend on charge redistribution. The result is less sensitive to capacitor mismatches that cause gain errors, which are the main limitation of such amplifiers in pipeline ADCs. The residual errors due to mismatch are reduced by at least a factor of 16, which is equivalent to at least 4 bits of improvement. The settling time is also faster because of a higher feedback factor. In traditional switched capacitor residue amplifiers, closed-loop amplification of a sampled and held residue signal is achieved by redistributing sampled charge onto a feedback capacitor around a high-gain transconductance amplifier. The residual charge that was sampled during the acquisition or sampling phase is stored on two or more capacitors, often equal in value or integral multiples of each other. During the hold or amplification phase, all of the charge is redistributed onto one capacitor in the feedback loop of the amplifier to produce an amplified voltage. The key error source is the non-ideal ratios of feedback and input capacitors caused by manufacturing tolerances, called mismatches. The mismatches cause non-ideal closed-loop gain, leading to higher differential non-linearity. Traditional solutions to the mismatch errors are to use larger capacitor values (than dictated by thermal noise requirements) and/or complex calibration schemes, both of which increase the die size and power dissipation. The key features of this innovation are (1) the elimination of the need for charge redistribution to achieve an accurate closed-loop gain of two, (2) a higher feedback factor in the amplifier stage giving a higher closed-loop bandwidth compared to the prior art, and (3) reduced requirement for calibration. The accuracy of the new amplifier is mainly limited by the sampling networks parasitic capacitances, which should be minimized in relation to the sampling capacitors.

Placement of clock gates in time-of-flight optoelectronic circuits

NASA Astrophysics Data System (ADS)

Feehrer, John R.; Jordan, Harry F.

1995-12-01

Time-of-flight synchronized optoelectronic circuits capitalize on the highly controllable delays of optical waveguides. Circuits have no latches; synchronization is achieved by adjustment of the lengths of waveguides that connect circuit elements. Clock gating and pulse stretching are used to restore timing and power. A functional circuit requires that every feedback loop contain at least one clock gate to prevent cumulative timing drift and power loss. A designer specifies an ideal circuit, which contains no or very few clock gates. To make the circuit functional, we must identify locations in which to place clock gates. Because clock gates are expensive, add area, and increase delay, a minimal set of locations is desired. We cast this problem in graph-theoretical form as the minimum feedback edge set problem and solve it by using an adaptation of an algorithm proposed in 1966 [IEEE Trans. Circuit Theory CT-13, 399 (1966)]. We discuss a computer-aided-design implementation of the algorithm that reduces computational complexity and demonstrate it on a set of circuits.

High Accuracy Passive Magnetic Field-Based Localization for Feedback Control Using Principal Component Analysis.

PubMed

Foong, Shaohui; Sun, Zhenglong

2016-08-12

In this paper, a novel magnetic field-based sensing system employing statistically optimized concurrent multiple sensor outputs for precise field-position association and localization is presented. This method capitalizes on the independence between simultaneous spatial field measurements at multiple locations to induce unique correspondences between field and position. This single-source-multi-sensor configuration is able to achieve accurate and precise localization and tracking of translational motion without contact over large travel distances for feedback control. Principal component analysis (PCA) is used as a pseudo-linear filter to optimally reduce the dimensions of the multi-sensor output space for computationally efficient field-position mapping with artificial neural networks (ANNs). Numerical simulations are employed to investigate the effects of geometric parameters and Gaussian noise corruption on PCA assisted ANN mapping performance. Using a 9-sensor network, the sensing accuracy and closed-loop tracking performance of the proposed optimal field-based sensing system is experimentally evaluated on a linear actuator with a significantly more expensive optical encoder as a comparison.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

Quantifying the ice-albedo feedback through decoupling

NASA Astrophysics Data System (ADS)

Kravitz, B.; Rasch, P. J.

2017-12-01

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

Feedback and Sentence Learning.

ERIC Educational Resources Information Center

Guthrie, John T.

The theoretical functions of external feedback in SR and closed loop models of verbal learning are presented. Contradictory predictions from the models are tested with a three by three factorial experiment including three types of feedback and three amounts of rehearsal. There were 90 adult students run individually and they were required to learn…

Multiple feedback control apparatus for power conditioning equipment

NASA Technical Reports Server (NTRS)

Biess, John (Inventor); Yu, Yuan (Inventor)

1977-01-01

An improved feedback control system to govern the cyclic operation of the power switch of a non-dissipative power conditioning equipment. The apparatus includes two or three control loops working in unison. The first causes the output DC level to be compared with a reference, and the error amplified for control purposes. The second utilizes the AC component of the voltage across the output filter inductor or the current through the output filter capacitor, and the third loop senses the output transients.

ONE SHAKE GATE FORMER

DOEpatents

Kalibjian, R.; Perez-Mendez, V.

1957-08-20

An improved circuit for forming square pulses having substantially short and precise durations is described. The gate forming circuit incorporates a secondary emission R. F. pentode adapted to receive input trigger pulses amd having a positive feedback loop comnected from the dynode to the control grid to maintain conduction in response to trigger pulses. A short circuited pulse delay line is employed to precisely control the conducting time of the tube and a circuit for squelching spurious oscillations is provided in the feedback loop.

High precision locating control system based on VCM for Talbot lithography

NASA Astrophysics Data System (ADS)

Yao, Jingwei; Zhao, Lixin; Deng, Qian; Hu, Song

2016-10-01

Aiming at the high precision and efficiency requirements of Z-direction locating in Talbot lithography, a control system based on Voice Coil Motor (VCM) was designed. In this paper, we built a math model of VCM and its moving characteristic was analyzed. A double-closed loop control strategy including position loop and current loop were accomplished. The current loop was implemented by driver, in order to achieve the rapid follow of the system current. The position loop was completed by the digital signal processor (DSP) and the position feedback was achieved by high precision linear scales. Feed forward control and position feedback Proportion Integration Differentiation (PID) control were applied in order to compensate for dynamic lag and improve the response speed of the system. And the high precision and efficiency of the system were verified by simulation and experiments. The results demonstrated that the performance of Z-direction gantry was obviously improved, having high precision, quick responses, strong real-time and easily to expend for higher precision.

Closed-loop and robust control of quantum systems.

PubMed

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

2013-01-01

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

Beyond R0 Maximisation: On Pathogen Evolution and Environmental Dimensions.

PubMed

Lion, Sébastien; Metz, Johan A J

2018-06-01

A widespread tenet is that evolution of pathogens maximises their basic reproduction ratio, R 0 . The breakdown of this principle is typically discussed as exception. Here, we argue that a radically different stance is needed, based on evolutionarily stable strategy (ESS) arguments that take account of the 'dimension of the environmental feedback loop'. The R 0 maximisation paradigm requires this feedback loop to be one-dimensional, which notably excludes pathogen diversification. By contrast, almost all realistic ecological ingredients of host-pathogen interactions (density-dependent mortality, multiple infections, limited cross-immunity, multiple transmission routes, host heterogeneity, and spatial structure) will lead to multidimensional feedbacks. Copyright © 2018 Elsevier Ltd. All rights reserved.

An open-closed-loop iterative learning control approach for nonlinear switched systems with application to freeway traffic control

NASA Astrophysics Data System (ADS)

Sun, Shu-Ting; Li, Xiao-Dong; Zhong, Ren-Xin

2017-10-01

For nonlinear switched discrete-time systems with input constraints, this paper presents an open-closed-loop iterative learning control (ILC) approach, which includes a feedforward ILC part and a feedback control part. Under a given switching rule, the mathematical induction is used to prove the convergence of ILC tracking error in each subsystem. It is demonstrated that the convergence of ILC tracking error is dependent on the feedforward control gain, but the feedback control can speed up the convergence process of ILC by a suitable selection of feedback control gain. A switched freeway traffic system is used to illustrate the effectiveness of the proposed ILC law.

Plasmids as stochastic model systems

NASA Astrophysics Data System (ADS)

Paulsson, Johan

2003-05-01

Plasmids are self-replicating gene clusters present in on average 2-100 copies per bacterial cell. To reduce random fluctuations and thereby avoid extinction, they ubiquitously autoregulate their own synthesis using negative feedback loops. Here I use van Kampen's Ω-expansion for a two-dimensional model of negative feedback including plasmids and ther replication inhibitors. This analytically summarizes the standard perspective on replication control -- including the effects of sensitivity amplification, exponential time-delays and noisy signaling. I further review the two most common molecular sensitivity mechanisms: multistep control and cooperativity. Finally, I discuss more controversial sensitivity schemes, such as noise-enhanced sensitivity, the exploitation of small-number combinatorics and double-layered feedback loops to suppress noise in disordered environments.

Closed-loop stability of linear quadratic optimal systems in the presence of modeling errors

NASA Technical Reports Server (NTRS)

Toda, M.; Patel, R.; Sridhar, B.

1976-01-01

The well-known stabilizing property of linear quadratic state feedback design is utilized to evaluate the robustness of a linear quadratic feedback design in the presence of modeling errors. Two general conditions are obtained for allowable modeling errors such that the resulting closed-loop system remains stable. One of these conditions is applied to obtain two more particular conditions which are readily applicable to practical situations where a designer has information on the bounds of modeling errors. Relations are established between the allowable parameter uncertainty and the weighting matrices of the quadratic performance index, thereby enabling the designer to select appropriate weighting matrices to attain a robust feedback design.

Voltage regulator/amplifier is self-regulated

NASA Technical Reports Server (NTRS)

Day, W. E.; Phillips, D. E.

1967-01-01

Signal modulated, self-regulating voltage regulator/amplifier controls the output b-plus voltage in modulated regulator systems. It uses self-oscillation with feedback to a control circuit with a discontinuous amplitude action feedback loop.

A program to evaluate a control system based on feedback of aerodynamic pressure differentials

NASA Technical Reports Server (NTRS)

Levy, D. W.; Finn, P.; Roskam, J.

1981-01-01

The use of aerodynamic pressure differentials to position a control surface is evaluated. The system is a differential pressure command loop, analogous to a position command loop, where the surface is commanded to move until a desired differential pressure across the surface is achieved. This type of control is more direct and accurate because it is the differential pressure which causes the control forces and moments. A frequency response test was performed in a low speed wind tunnel to measure the performance of the system. Both pressure and position feedback were tested. The pressure feedback performed as well as position feedback implying that the actuator, with a break frequency on the order of 10 Rad/sec, was the limiting component. Theoretical considerations indicate that aerodynamic lags will not appear below frequencies of 50 Rad/sec, or higher.

Drive-amplitude-modulation atomic force microscopy: From vacuum to liquids

PubMed Central

Jaafar, Miriam; Cuenca, Mariano; Melcher, John; Raman, Arvind

2012-01-01

Summary We introduce drive-amplitude-modulation atomic force microscopy as a dynamic mode with outstanding performance in all environments from vacuum to liquids. As with frequency modulation, the new mode follows a feedback scheme with two nested loops: The first keeps the cantilever oscillation amplitude constant by regulating the driving force, and the second uses the driving force as the feedback variable for topography. Additionally, a phase-locked loop can be used as a parallel feedback allowing separation of the conservative and nonconservative interactions. We describe the basis of this mode and present some examples of its performance in three different environments. Drive-amplutide modulation is a very stable, intuitive and easy to use mode that is free of the feedback instability associated with the noncontact-to-contact transition that occurs in the frequency-modulation mode. PMID:22563531

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

PubMed

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

2014-09-01

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

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

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.

Short and long sympathetic-sensory feedback loops in white fat

PubMed Central

Ryu, Vitaly

2014-01-01

We previously demonstrated white adipose tissue (WAT) innervation using the established WAT retrograde sympathetic nervous system (SNS)-specific transneuronal viral tract tracer pseudorabies virus (PRV152) and showed its role in the control of lipolysis. Conversely, we demonstrated WAT sensory innervation using the established anterograde sensory system (SS)-specific transneuronal viral tracer, the H129 strain of herpes simplex virus-1, with sensory nerves showing responsiveness with increases in WAT SNS drive. Several brain areas were part of the SNS outflow to and SS inflow from WAT between these studies suggesting SNS-SS feedback loops. Therefore, we injected both PRV152 and H129 into inguinal WAT (IWAT) of Siberian hamsters. Animals were perfused on days 5 and 6 postinoculation after H129 and PRV152 injections, respectively, and brains, spinal cords, sympathetic, and dorsal root ganglia (DRG) were processed for immunohistochemical detection of each virus across the neuroaxis. The presence of H129+PRV152-colocalized neurons (∼50%) in the spinal segments innervating IWAT suggested short SNS-SS loops with significant coinfections (>60%) in discrete brain regions, signifying long SNS-SS loops. Notably, the most highly populated sites with the double-infected neurons were the medial part of medial preoptic nucleus, medial preoptic area, hypothalamic paraventricular nucleus, lateral hypothalamus, periaqueductal gray, oral part of the pontine reticular nucleus, and the nucleus of the solitary tract. Collectively, these results strongly indicate the neuroanatomical reality of the central SNS-SS feedback loops with short loops in the spinal cord and long loops in the brain, both likely involved in the control of lipolysis or other WAT pad-specific functions. PMID:24717676

Better Bet-Hedging with coupled positive and negative feedback loops

NASA Astrophysics Data System (ADS)

Narula, Jatin; Igoshin, Oleg

2011-03-01

Bacteria use the phenotypic heterogeneity associated with bistable switches to distribute the risk of activating stress response strategies like sporulation and persistence. However bistable switches offer little control over the timing of phenotype switching and first passage times (FPT) for individual cells are found to be exponentially distributed. We show that a genetic circuit consisting of interlinked positive and negative feedback loops allows cells to control the timing of phenotypic switching. Using a mathematical model we find that in this system a stable high expression state and stable low expression limit cycle coexist and the FPT distribution for stochastic transitions between them shows multiple peaks at regular intervals. A multimodal FPT distribution allows cells to detect the persistence of stress and control the rate of phenotype transition of the population. We further show that extracellular signals from cell-cell communication that change the strength of the feedback loops can modulate the FPT distribution and allow cells even greater control in a bet-hedging strategy.

Identification of optimal feedback control rules from micro-quadrotor and insect flight trajectories.

PubMed

Faruque, Imraan A; Muijres, Florian T; Macfarlane, Kenneth M; Kehlenbeck, Andrew; Humbert, J Sean

2018-06-01

This paper presents "optimal identification," a framework for using experimental data to identify the optimality conditions associated with the feedback control law implemented in the measurements. The technique compares closed loop trajectory measurements against a reduced order model of the open loop dynamics, and uses linear matrix inequalities to solve an inverse optimal control problem as a convex optimization that estimates the controller optimality conditions. In this study, the optimal identification technique is applied to two examples, that of a millimeter-scale micro-quadrotor with an engineered controller on board, and the example of a population of freely flying Drosophila hydei maneuvering about forward flight. The micro-quadrotor results show that the performance indices used to design an optimal flight control law for a micro-quadrotor may be recovered from the closed loop simulated flight trajectories, and the Drosophila results indicate that the combined effect of the insect longitudinal flight control sensing and feedback acts principally to regulate pitch rate.

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

PubMed

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

2012-06-01

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

Conceptual model of sedimentation in the Sacramento-San Joaquin River Delta

USGS Publications Warehouse

Schoellhamer, David H.; Wright, Scott A.; Drexler, Judith Z.

2012-01-01

Sedimentation in the Sacramento–San Joaquin River Delta builds the Delta landscape, creates benthic and pelagic habitat, and transports sediment-associated contaminants. Here we present a conceptual model of sedimentation that includes submodels for river supply from the watershed to the Delta, regional transport within the Delta and seaward exchange, and local sedimentation in open water and marsh habitats. The model demonstrates feedback loops that affect the Delta ecosystem. Submerged and emergent marsh vegetation act as ecosystem engineers that can create a positive feedback loop by decreasing suspended sediment, increasing water column light, which in turn enables more vegetation. Sea-level rise in open water is partially countered by a negative feedback loop that increases deposition if there is a net decrease in hydrodynamic energy. Manipulation of regional sediment transport is probably the most feasible method to control suspended sediment and thus turbidity. The conceptual model is used to identify information gaps that need to be filled to develop an accurate sediment transport model.

Ultrahigh-speed clock recovery with optical phase lock loop based on four-wave-mixing in a semiconductor optical amplifier

NASA Astrophysics Data System (ADS)

Kim, Dong Hwan; Kim, Sang Hyuck; Jo, Jae Cheol; Choi, Sang Sam

2000-08-01

A new phase lock loop (PLL) is proposed and demonstrated for clock recovery from 40 Gbps time-division-multiplexed (TDM) optical signal using simple optical phase lock loop circuit. The proposed clock recovery scheme improves the jitter effect in PLL circuit from the clock pulse laser of harmonically-mode locked fiber laser. The cross-correlation component between the optical signal and an optical clock pulse train is detected as a four-wave-mixing (FWM) signal generated in SOA. The lock-in frequency range of the clock recovery is found to be within 10 KHz.

Asymptotic Eigenstructures

NASA Technical Reports Server (NTRS)

Thompson, P. M.; Stein, G.

1980-01-01

The behavior of the closed loop eigenstructure of a linear system with output feedback is analyzed as a single parameter multiplying the feedback gain is varied. An algorithm is presented that computes the asymptotically infinite eigenstructure, and it is shown how a system with high gain, feedback decouples into single input, single output systems. Then a synthesis algorithm is presented which uses full state feedback to achieve a desired asymptotic eigenstructure.

Closed-loop control of gimbal-less MEMS mirrors for increased bandwidth in LiDAR applications

NASA Astrophysics Data System (ADS)

Milanović, Veljko; Kasturi, Abhishek; Yang, James; Hu, Frank

2017-05-01

In 2016, we presented a low SWaP wirelessly controlled MEMS mirror-based LiDAR prototype which utilized an OEM laser rangefinder for distance measurement [1]. The MEMS mirror was run in open loop based on its exceptionally fast design and high repeatability performance. However, to further extend the bandwidth and incorporate necessary eyesafety features, we recently focused on providing mirror position feedback and running the system in closed loop control. Multiple configurations of optical position sensors, mounted on both the front- and the back-side of the MEMS mirror, have been developed and will be presented. In all cases, they include a light source (LED or laser) and a 2D photosensor. The most compact version is mounted on the backside of the MEMS mirror ceramic package and can "view" the mirror's backside through openings in the mirror's PCB and its ceramic carrier. This version increases the overall size of the MEMS mirror submodule from 12mm x 12mm x 4mm to 15mm x 15mm x 7mm. The sensors also include optical and electronic filtering to reduce effects of any interference from the application laser illumination. With relatively simple FPGA-based PID control running at the sample rate of 100 kHz, we could configure the overall response of the system to fully utilize the MEMS mirror's native bandwidth which extends well beyond its first resonance. When compared to the simple open loop method of suppressing overshoot and ringing which significantly limits bandwidth utilization, running the mirrors in closed loop control increased the bandwidth to nearly 3.7 times. A 2.0mm diameter integrated MEMS mirror with a resonant frequency of 1300 Hz was limited to 500Hz bandwidth in open loop driving but was increased to 3kHz bandwidth with the closed loop controller. With that bandwidth it is capable of very sharply defined uniform-velocity scans (sawtooth or triangle waveforms) which are highly desired in scanned mirror LiDAR systems. A 2.4mm diameter mirror with +/-12° of scan angle achieves over 1.3kHz of flat response, allowing sharp triangle waveforms even at 300Hz (600 uniform velocity lines per second). The same methodology is demonstrated with larger, bonded mirrors. Here closed loop control is more challenging due to the additional resonance and a more complex system dynamic. Nevertheless, results are similar - a 5mm diameter mirror bandwidth was increased from 150Hz to 500Hz.

Validation of snow characteristics and snow albedo feedback in the Canadian Regional Climate Model simulations over North America

NASA Astrophysics Data System (ADS)

Fang, B.; Sushama, L.; Diro, G. T.

2015-12-01

Snow characteristics and snow albedo feedback (SAF) over North America, as simulated by the fifth-generation Canadian Regional Climate Model (CRCM5), when driven by ERA-40/ERA-Interim, CanESM2 and MPI-ESM-LR at the lateral boundaries, are analyzed in this study. Validation of snow characteristics is performed by comparing simulations against available observations from MODIS, ISCCP and CMC. Results show that the model is able to represent the main spatial distribution of snow characteristics with some overestimation in snow mass and snow depth over the Canadian high Arctic. Some overestimation in surface albedo is also noted for the boreal region which is believed to be related to the snow unloading parameterization, as well as the overestimation of snow albedo. SAF is assessed both in seasonal and climate change contexts when possible. The strength of SAF is quantified as the amount of additional net shortwave radiation at the top of the atmosphere as surface albedo decreases in association with a 1°C increase in surface temperature. Following Qu and Hall (2007), this is expressed as the product of the variation in planetary albedo with surface albedo and the change in surface albedo for 1°C change in surface air temperature during the season, which in turn is determined by the strength of the snow cover and snowpack metamorphosis feedback loops. Analysis of the latter term in the seasonal cycle suggests that for CRCM5 simulations, the snow cover feedback loop is more dominant compared to the snowpack metamorphosis feedback loop, whereas for MODIS, the two feedback loops have more or less similar strength. Moreover, the SAF strength in the climate change context appears to be weaker than in the seasonal cycle and is sensitive to the driving GCM and the RCP scenario.

MQW Optical Feedback Modulators And Phase Shifters

NASA Technical Reports Server (NTRS)

Jackson, Deborah J.

1995-01-01

Laser diodes equipped with proposed multiple-quantum-well (MQW) optical feedback modulators prove useful in variety of analog and digital optical-communication applications, including fiber-optic signal-distribution networks and high-speed, low-crosstalk interconnections among super computers or very-high-speed integrated circuits. Development exploits accompanying electro-optical aspect of QCSE - variation in index of refraction with applied electric field. Also exploits sensitivity of laser diodes to optical feedback. Approach is reverse of prior approach.

Disturbed P53-MDM2 Feedback Loop Contributes to Thoracic Aortic Dissection Formation and May be a Result of TRIM25 Overexpression.

PubMed

Gong, Bin; Wang, Zhiwei; Zhang, Min; Hu, Zhipeng; Ren, Zongli; Tang, Zheng; Jiang, Wanli; Cheng, Lianghao; Huang, Jun; Ren, Wei; Wang, Qingtao

2017-04-01

The development of thoracic aortic dissection (TAD) is attributed to a broad range of degenerative, genetic, structural, oxidative, apoptotic, and acquired disease states. In this study, we examined the role of the disturbed p53-MDM2 (murine double minute 2) feedback loop in the formation of TAD, and one of a potential feedback loop regulator, TRIM25 (tripartite motif protein-25). Surgical specimens of the aorta from TAD patients (n = 10) and controls (n = 10) were tested for α-smooth muscle actin (α-SMA), p53, MDM2, and TRIM25 by western blot, immunohistochemical staining, and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR), respectively. When compared with controls, western blot shows that the protein levels of p53, MDM2, and TRIM25 were increased significantly in the aortic media of TAD patients. qRT-PCR further verified that the mRNA expression of MDM2 and TRIM25 was also increased 6- and 4-folds, respectively, in the TAD media of the aortic wall. Immunohistochemistry results showed significantly decreased staining of α-SMA, smooth muscle cells, and more collagen deposition in the media of the aortic wall from patients with TAD. This study provided a new insight into the disturbed p53-MDM2 feedback loop in the pathogenesis of TAD, and this may be because of the TRIM25 overexpression. Copyright © 2016 Elsevier Inc. All rights reserved.

A technique for sequential segmental neuromuscular stimulation with closed loop feedback control.

PubMed

Zonnevijlle, Erik D H; Abadia, Gustavo Perez; Somia, Naveen N; Kon, Moshe; Barker, John H; Koenig, Steven; Ewert, D L; Stremel, Richard W

2002-01-01

In dynamic myoplasty, dysfunctional muscle is assisted or replaced with skeletal muscle from a donor site. Electrical stimulation is commonly used to train and animate the skeletal muscle to perform its new task. Due to simultaneous tetanic contractions of the entire myoplasty, muscles are deprived of perfusion and fatigue rapidly, causing long-term problems such as excessive scarring and muscle ischemia. Sequential stimulation contracts part of the muscle while other parts rest, thus significantly improving blood perfusion. However, the muscle still fatigues. In this article, we report a test of the feasibility of using closed-loop control to economize the contractions of the sequentially stimulated myoplasty. A simple stimulation algorithm was developed and tested on a sequentially stimulated neo-sphincter designed from a canine gracilis muscle. Pressure generated in the lumen of the myoplasty neo-sphincter was used as feedback to regulate the stimulation signal via three control parameters, thereby optimizing the performance of the myoplasty. Additionally, we investigated and compared the efficiency of amplitude and frequency modulation techniques. Closed-loop feedback enabled us to maintain target pressures within 10% deviation using amplitude modulation and optimized control parameters (correction frequency = 4 Hz, correction threshold = 4%, and transition time = 0.3 s). The large-scale stimulation/feedback setup was unfit for chronic experimentation, but can be used as a blueprint for a small-scale version to unveil the theoretical benefits of closed-loop control in chronic experimentation.

A novel P53/POMC/Gαs/SASH1 autoregulatory feedback loop activates mutated SASH1 to cause pathologic hyperpigmentation.

PubMed

Zhou, Ding'an; Wei, Zhiyun; Kuang, Zhongshu; Luo, Huangchao; Ma, Jiangshu; Zeng, Xing; Wang, Ke; Liu, Beizhong; Gong, Fang; Wang, Jing; Lei, Shanchuan; Wang, Dongsheng; Zeng, Jiawei; Wang, Teng; He, Yong; Yuan, Yongqiang; Dai, Hongying; He, Lin; Xing, Qinghe

2017-04-01

p53-Transcriptional-regulated proteins interact with a large number of other signal transduction pathways in the cell, and a number of positive and negative autoregulatory feedback loops act upon the p53 response. P53 directly controls the POMC/α-MSH productions induced by ultraviolet (UV) and is associated with UV-independent pathological pigmentation. When identifying the causative gene of dyschromatosis universalis hereditaria (DUH), we found three mutations encoding amino acid substitutions in the gene SAM and SH3 domain containing 1 (SASH1), and SASH1 was associated with guanine nucleotide-binding protein subunit-alpha isoforms short (Gαs). However, the pathological gene and pathological mechanism of DUH remain unknown for about 90 years. We demonstrate that SASH1 is physiologically induced by p53 upon UV stimulation and SASH and p53 is reciprocally induced at physiological and pathophysiological conditions. SASH1 is regulated by a novel p53/POMC/α-MSH/Gαs/SASH1 cascade to mediate melanogenesis. A novel p53/POMC/Gαs/SASH1 autoregulatory positive feedback loop is regulated by SASH1 mutations to induce pathological hyperpigmentation phenotype. Our study demonstrates that a novel p53/POMC/Gαs/SASH1 autoregulatory positive feedback loop is regulated by SASH1 mutations to induce pathological hyperpigmentation phenotype. © 2016 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.

Activation of PI3K/AKT and MAPK Pathway through a PDGFRβ-Dependent Feedback Loop Is Involved in Rapamycin Resistance in Hepatocellular Carcinoma

PubMed Central

Yao, Li-Qing; Tan, Chang-Jun; Huang, Xiao-Yong; Ke, Ai-Wu; Dai, Zhi; Fan, Jia; Zhou, Jian

2012-01-01

Background Rapamycin is an attractive approach for the treatment and prevention of HCC recurrence after liver transplantation. However, the objective response rates of rapamycin achieved with single-agent therapy were modest, supporting that rapamycin resistance is a frequently observed characteristic of many cancers. Some studies have been devoted to understanding the mechanisms of rapamycin resistance, however, the mechanisms are cell-type-dependent and studies on rapamycin resistance in HCC are extremely limited. Methodology/Principal Findings The anti-tumor sensitivity of rapamycin was modest in vitro and in vivo. In both human and rat HCC cells, rapamycin up-regulated the expression and phosphorylation of PDGFRβ in a time and dose-dependent manner as assessed by RT-PCR and western blot analysis. Using siRNA mediated knockdown of PDGFRβ, we confirmed that subsequent activation of AKT and ERK was PDGFRβ-dependent and compromised the anti-tumor activity of rapamycin. Then, blockade of this PDGFRβ-dependent feedback loop by sorafenib enhanced the anti-tumor sensitivity of rapamycin in vitro and in an immunocompetent orthotopic rat model of HCC. Conclusions Activation of PI3K/AKT and MAPK pathway through a PDGFRβ-dependent feedback loop compromises the anti-tumor activity of rapamycin in HCC, and blockade of this feedback loop by sorafenib is an attractive approach to improve the anti-tumor effect of rapamycin, particularly in preventing or treating HCC recurrence after liver transplantation. PMID:22428038

A cognitive neuroprosthetic that uses cortical stimulation for somatosensory feedback.

PubMed

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

2014-10-01

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

Feedback activation of STAT3 mediates trastuzumab resistance via upregulation of MUC1 and MUC4 expression

PubMed Central

Li, Wei; Fan, Kexing; Qian, Weizhu; Hou, Sheng; Wang, Hao; Dai, Jianxin; Wei, Huafeng; Guo, Yajun

2014-01-01

Although HER2-targeting antibody trastuzumab confers a substantial benefit for patients with HER2-overexpressing breast and gastric cancer, overcoming trastuzumab resistance remains a large unmet need. In this study, we revealed a STAT3-centered positive feedback loop that mediates the resistance of trastuzumab. Mechanistically, chronic exposure of trastuzumab causes the upregulation of fibronection (FN), EGF and IL-6 in parental trastuzumab-sensitive breast and gastric cells and convergently leads to STAT3 hyperactivation. Activated STAT3 enhances the expression of FN, EGF and IL-6, thus constituting a positive feedback loop which amplifies and maintains the STAT3 signal; furthermore, hyperactivated STAT3 signal promotes the expression of MUC1 and MUC4, consequently mediating trastuzumab resistance via maintenance of persistent HER2 activation and masking of trastuzumab binding to HER2 respectively. Genetic or pharmacological inhibition of STAT3 disrupted STAT3-dependent positive feedback loop and recovered the trastuzumab sensitivity partially due to increased apoptosis induction. Combined trastuzumab with STAT3 inhibition synergistically suppressed the growth of the trastuzumab-resistant tumor xenografts in vivo. Taken together, our results suggest that feedback activation of STAT3 constitutes a key node mediating trastuzumab resistance. Combinatorial targeting on both HER2 and STAT3 may enhance the efficacy of trastuzumab or other HER2-targeting agents in HER2-positive breast and gastric cancer. PMID:25327561

Feedback activation of STAT3 mediates trastuzumab resistance via upregulation of MUC1 and MUC4 expression.

PubMed

Li, Guangchao; Zhao, Likun; Li, Wei; Fan, Kexing; Qian, Weizhu; Hou, Sheng; Wang, Hao; Dai, Jianxin; Wei, Huafeng; Guo, Yajun

2014-09-30

Although HER2-targeting antibody trastuzumab confers a substantial benefit for patients with HER2-overexpressing breast and gastric cancer, overcoming trastuzumab resistance remains a large unmet need. In this study, we revealed a STAT3-centered positive feedback loop that mediates the resistance of trastuzumab. Mechanistically, chronic exposure of trastuzumab causes the upregulation of fibronection (FN), EGF and IL-6 in parental trastuzumab-sensitive breast and gastric cells and convergently leads to STAT3 hyperactivation. Activated STAT3 enhances the expression of FN, EGF and IL-6, thus constituting a positive feedback loop which amplifies and maintains the STAT3 signal; furthermore, hyperactivated STAT3 signal promotes the expression of MUC1 and MUC4, consequently mediating trastuzumab resistance via maintenance of persistent HER2 activation and masking of trastuzumab binding to HER2 respectively. Genetic or pharmacological inhibition of STAT3 disrupted STAT3-dependent positive feedback loop and recovered the trastuzumab sensitivity partially due to increased apoptosis induction. Combined trastuzumab with STAT3 inhibition synergistically suppressed the growth of the trastuzumab-resistant tumor xenografts in vivo. Taken together, our results suggest that feedback activation of STAT3 constitutes a key node mediating trastuzumab resistance. Combinatorial targeting on both HER2 and STAT3 may enhance the efficacy of trastuzumab or other HER2-targeting agents in HER2-positive breast and gastric cancer.

Stereoscopic distance perception

NASA Technical Reports Server (NTRS)

Foley, John M.

1989-01-01

Limited cue, open-loop tasks in which a human observer indicates distances or relations among distances are discussed. By open-loop tasks, it is meant tasks in which the observer gets no feedback as to the accuracy of the responses. What happens when cues are added and when the loop is closed are considered. The implications of this research for the effectiveness of visual displays is discussed. Errors in visual distance tasks do not necessarily mean that the percept is in error. The error could arise in transformations that intervene between the percept and the response. It is argued that the percept is in error. It is also argued that there exist post-perceptual transformations that may contribute to the error or be modified by feedback to correct for the error.

Modeling gene regulatory network motifs using statecharts

PubMed Central

2012-01-01

Background Gene regulatory networks are widely used by biologists to describe the interactions among genes, proteins and other components at the intra-cellular level. Recently, a great effort has been devoted to give gene regulatory networks a formal semantics based on existing computational frameworks. For this purpose, we consider Statecharts, which are a modular, hierarchical and executable formal model widely used to represent software systems. We use Statecharts for modeling small and recurring patterns of interactions in gene regulatory networks, called motifs. Results We present an improved method for modeling gene regulatory network motifs using Statecharts and we describe the successful modeling of several motifs, including those which could not be modeled or whose models could not be distinguished using the method of a previous proposal. We model motifs in an easy and intuitive way by taking advantage of the visual features of Statecharts. Our modeling approach is able to simulate some interesting temporal properties of gene regulatory network motifs: the delay in the activation and the deactivation of the "output" gene in the coherent type-1 feedforward loop, the pulse in the incoherent type-1 feedforward loop, the bistability nature of double positive and double negative feedback loops, the oscillatory behavior of the negative feedback loop, and the "lock-in" effect of positive autoregulation. Conclusions We present a Statecharts-based approach for the modeling of gene regulatory network motifs in biological systems. The basic motifs used to build more complex networks (that is, simple regulation, reciprocal regulation, feedback loop, feedforward loop, and autoregulation) can be faithfully described and their temporal dynamics can be analyzed. PMID:22536967

Advanced Optical Fiber Communications Systems

DTIC Science & Technology

1994-08-31

phase locking . The PZT port has a tuning coefficient of 3.4 MHz/V. The time constants of the optical phase - locked loop ( OPLL ) filter’s pole and zero are... with the PSK receiver optical phase -I-ocked loop ( OPLL ). As we increased nz in our experiments, the larger signal fluctuations made it increasingly... lasers , since a phase - locked loop is 114 I not required for the DPSK receiver (unlike

A novel feedforward compensation canceling input filter-regulator interaction

NASA Technical Reports Server (NTRS)

Kelkar, S. S.; Lee, F. C.

1983-01-01

The interaction between the input and the control loop of switching regulators often results in deterimental effects, such as loop instability, degradation of transient response, and audiosusceptibility, etc. The concept of pole-zero cancelation is employed to mitigate some of these detrimental effects and is implemented using a novel feedforward loop, in addition to existing feedback loops of a buck regulator. Experimental results are presented which show excellent correlation with theory.

Analytical study of robustness of a negative feedback oscillator by multiparameter sensitivity

PubMed Central

2014-01-01

Background One of the distinctive features of biological oscillators such as circadian clocks and cell cycles is robustness which is the ability to resume reliable operation in the face of different types of perturbations. In the previous study, we proposed multiparameter sensitivity (MPS) as an intelligible measure for robustness to fluctuations in kinetic parameters. Analytical solutions directly connect the mechanisms and kinetic parameters to dynamic properties such as period, amplitude and their associated MPSs. Although negative feedback loops are known as common structures to biological oscillators, the analytical solutions have not been presented for a general model of negative feedback oscillators. Results We present the analytical expressions for the period, amplitude and their associated MPSs for a general model of negative feedback oscillators. The analytical solutions are validated by comparing them with numerical solutions. The analytical solutions explicitly show how the dynamic properties depend on the kinetic parameters. The ratio of a threshold to the amplitude has a strong impact on the period MPS. As the ratio approaches to one, the MPS increases, indicating that the period becomes more sensitive to changes in kinetic parameters. We present the first mathematical proof that the distributed time-delay mechanism contributes to making the oscillation period robust to parameter fluctuations. The MPS decreases with an increase in the feedback loop length (i.e., the number of molecular species constituting the feedback loop). Conclusions Since a general model of negative feedback oscillators was employed, the results shown in this paper are expected to be true for many of biological oscillators. This study strongly supports that the hypothesis that phosphorylations of clock proteins contribute to the robustness of circadian rhythms. The analytical solutions give synthetic biologists some clues to design gene oscillators with robust and desired period. PMID:25605374

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

PubMed

Chen, Yi-Ching; Lin, Linda L; Lin, Yen-Ting; Hu, Chia-Ling; Hwang, Ing-Shiou

2017-01-01

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

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

PubMed Central

Chen, Yi-Ching; Lin, Linda L.; Lin, Yen-Ting; Hu, Chia-Ling; Hwang, Ing-Shiou

2017-01-01

Error amplification (EA) feedback is a promising approach to advance visuomotor skill. As error detection and visuomotor processing at short time scales decline with age, this study examined whether older adults could benefit from EA feedback that included higher-frequency information to guide a force-tracking task. Fourteen young and 14 older adults performed low-level static isometric force-tracking with visual guidance of typical visual feedback and EA feedback containing augmented high-frequency errors. Stabilogram diffusion analysis was used to characterize force fluctuation dynamics. Also, the discharge behaviors of motor units and pooled motor unit coherence were assessed following the decomposition of multi-channel surface electromyography (EMG). EA produced different behavioral and neurophysiological impacts on young and older adults. Older adults exhibited inferior task accuracy with EA feedback than with typical visual feedback, but not young adults. Although stabilogram diffusion analysis revealed that EA led to a significant decrease in critical time points for both groups, EA potentiated the critical point of force fluctuations <ΔFc2>, short-term effective diffusion coefficients (Ds), and short-term exponent scaling only for the older adults. Moreover, in older adults, EA added to the size of discharge variability of motor units and discharge regularity of cumulative discharge rate, but suppressed the pooled motor unit coherence in the 13–35 Hz band. Virtual EA alters the strategic balance between open-loop and closed-loop controls for force-tracking. Contrary to expectations, the prevailing use of closed-loop control with EA that contained high-frequency error information enhanced the motor unit discharge variability and undermined the force steadiness in the older group, concerning declines in physiological complexity in the neurobehavioral system and the common drive to the motoneuronal pool against force destabilization. PMID:29167637

A bio-inspired flying robot sheds light on insect piloting abilities.

PubMed

Franceschini, Nicolas; Ruffier, Franck; Serres, Julien

2007-02-20

When insects are flying forward, the image of the ground sweeps backward across their ventral viewfield and forms an "optic flow," which depends on both the groundspeed and the groundheight. To explain how these animals manage to avoid the ground by using this visual motion cue, we suggest that insect navigation hinges on a visual-feedback loop we have called the optic-flow regulator, which controls the vertical lift. To test this idea, we built a micro-helicopter equipped with an optic-flow regulator and a bio-inspired optic-flow sensor. This fly-by-sight micro-robot can perform exacting tasks such as take-off, level flight, and landing. Our control scheme accounts for many hitherto unexplained findings published during the last 70 years on insects' visually guided performances; for example, it accounts for the fact that honeybees descend in a headwind, land with a constant slope, and drown when travelling over mirror-smooth water. Our control scheme explains how insects manage to fly safely without any of the instruments used onboard aircraft to measure the groundheight, groundspeed, and descent speed. An optic-flow regulator is quite simple in terms of its neural implementation and just as appropriate for insects as it would be for aircraft.

A cognitive neuroprosthetic that uses cortical stimulation for somatosensory feedback

PubMed Central

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

2015-01-01

Present day cortical brain machine interfaces (BMI) have made impressive advances using decoded brain signals to control extracorporeal devices. Although BMIs are used in a closed-loop fashion, sensory feedback typically is visual only. However medical case studies have shown that the loss of somesthesis in a limb greatly reduces the agility of the limb even when visual feedback is available (for review see Robles-De-La-Torre, 2006). To overcome this limitation, this study tested a closed-loop BMI that utilizes intracortical microstimulation (ICMS) to provide ‘tactile’ sensation to a non-human primate (NHP). Using stimulation electrodes in Brodmann area 1 of somatosensory cortex (BA1) and recording electrodes in the anterior intraparietal area (AIP), the parietal reach region (PRR) and dorsal area 5 (area 5d), it was found that this form of feedback can be used in BMI tasks. PMID:25242377

Magnetometer Based on Optoelectronic Microwave Oscillator

NASA Technical Reports Server (NTRS)

Maleki, Lute; Strekalov, Dmitry; Matsko, Andrey

2005-01-01

proposed instrument, intended mainly for use as a magnetometer, would include an optoelectronic oscillator (OEO) stabilized by an atomic cell that could play the role of a magnetically tunable microwave filter. The microwave frequency would vary with the magnetic field in the cell, thereby providing an indication of the magnetic field. The proposed magnetometer would offer a combination of high accuracy and high sensitivity, characterized by flux densities of less than a picotesla. In comparison with prior magnetometers, the proposed magnetometer could, in principle, be constructed as a compact, lightweight instrument: It could fit into a package of about 10 by 10 by 10 cm and would have a mass <0.5 kg. As described in several prior NASA Tech Briefs articles, an OEO is a hybrid of photonic and electronic components that generates highly spectrally pure microwave radiation, and optical radiation modulated by the microwave radiation, through direct conversion between laser light and microwave radiation in an optoelectronic feedback loop. As used here, "atomic cell" signifies a cell containing a vapor, the constituent atoms of which can be made to undergo transitions between quantum states, denoted hyperfine levels, when excited by light in a suitable wavelength range. The laser light must be in this range. The energy difference between the hyperfine levels defines the microwave frequency. In the proposed instrument (see figure), light from a laser would be introduced into an electro-optical modulator (EOM). Amplitude-modulated light from the exit port of the EOM would pass through a fiber-optic splitter having two output branches. The light in one branch would be sent through an atomic cell to a photodiode. The light in the other branch would constitute the microwave-modulated optical output. Part of the light leaving the atomic cell could also be used to stabilize the laser at a frequency in the vicinity of the desired hyperfine or other quantum transition. The microwave signal from the output of the photodiode would be amplified (if necessary, as explained below) and fed back into the EOM. This system would oscillate if the amplification in the closed loop exceeded the linear absorption of the loop. The microwave amplifier may be unnecessary to sustain stable oscillations, depending on the power of the laser radiation at the photodetector and on particular features of the modulator and optical delay line.

Control systems for platform landings cushioned by air bags

NASA Astrophysics Data System (ADS)

Ross, Edward W.

1987-07-01

This report presents an exploratory mathematical study of control systems for airdrop platform landings cushioned by airbags. The basic theory of airbags is reviewed and solutions to special cases are noted. A computer program is presented, which calculates the time-dependence of the principal variables during a landing under the action of various control systems. Two existing control systems of open-loop type are compared with a conceptual feedback (closed-loop) system for a fairly typical set of landing conditions. The feedback controller is shown to have performance much superior to the other systems. The feedback system undergoes an interesting oscillation not present in the other systems, the source of which is investigated. Recommendations for future work are included.

Entry flight control system downmoding evaluation

NASA Technical Reports Server (NTRS)

Barnes, H. A.

1978-01-01

A method to desensitize the entry flight control system to structural vibration feedback which might induce an oscillatory instability is described. Trends in vehicle response and handling characteristics as a function of gain combinations in the FCS forward and rate feedback loops were described as observed in a man-in-the-loop simulation. Among the flight conditions considered are the effects of downmoding with APU failures, off-nominal trajectory conditions, sensed angle of attack errors, the impact on RCS fuel consumption, performance in the presence of aero variations, recovery from large FCS upsets, and default gains.

Adaptive antenna arrays for satellite communication

NASA Technical Reports Server (NTRS)

Gupta, Inder J.

1989-01-01

The feasibility of using adaptive antenna arrays to provide interference protection in satellite communications was studied. The feedback loops as well as the sample matric inversion (SMI) algorithm for weight control were studied. Appropriate modifications in the two were made to achieve the required interference suppression. An experimental system was built to test the modified feedback loops and the modified SMI algorithm. The performance of the experimental system was evaluated using bench generated signals and signals received from TVRO geosynchronous satellites. A summary of results is given. Some suggestions for future work are also presented.

Self-stabilizing optical clock pulse-train generator using SOA and saturable absorber for asynchronous optical packet processing.

PubMed

Nakahara, Tatsushi; Takahashi, Ryo

2013-05-06

We propose a novel, self-stabilizing optical clock pulse-train generator for processing preamble-free, asynchronous optical packets with variable lengths. The generator is based on an optical loop that includes a semiconductor optical amplifier (SOA) and a high-extinction spin-polarized saturable absorber (SA), with the loop being self-stabilized by balancing out the gain and absorption provided by the SOA and SA, respectively. The optical pulse train is generated by tapping out a small portion of a circulating seed pulse. The convergence of the generated pulse energy is enabled by the loop round-trip gain function that has a negative slope due to gain saturation in the SOA. The amplified spontaneous emission (ASE) of the SOA is effectively suppressed by the SA, and a backward optical pulse launched into the SOA enables overcoming the carrier-recovery speed mismatch between the SOA and SA. Without external control for the loop gain, a stable optical pulse train consisting of more than 50 pulses with low jitter is generated from a single 10-ps seed optical pulse even with a variation of 10 dB in the seed pulse intensity.

Photonic-powered cable assembly

DOEpatents

Sanderson, Stephen N.; Appel, Titus James; Wrye, IV, Walter C.

2013-01-22

A photonic-cable assembly includes a power source cable connector ("PSCC") coupled to a power receive cable connector ("PRCC") via a fiber cable. The PSCC electrically connects to a first electronic device and houses a photonic power source and an optical data transmitter. The fiber cable includes an optical transmit data path coupled to the optical data transmitter, an optical power path coupled to the photonic power source, and an optical feedback path coupled to provide feedback control to the photonic power source. The PRCC electrically connects to a second electronic device and houses an optical data receiver coupled to the optical transmit data path, a feedback controller coupled to the optical feedback path to control the photonic power source, and a photonic power converter coupled to the optical power path to convert photonic energy received over the optical power path to electrical energy to power components of the PRCC.

Photonic-powered cable assembly

DOEpatents

Sanderson, Stephen N; Appel, Titus James; Wrye, IV, Walter C

2014-06-24

A photonic-cable assembly includes a power source cable connector ("PSCC") coupled to a power receive cable connector ("PRCC") via a fiber cable. The PSCC electrically connects to a first electronic device and houses a photonic power source and an optical data transmitter. The fiber cable includes an optical transmit data path coupled to the optical data transmitter, an optical power path coupled to the photonic power source, and an optical feedback path coupled to provide feedback control to the photonic power source. The PRCC electrically connects to a second electronic device and houses an optical data receiver coupled to the optical transmit data path, a feedback controller coupled to the optical feedback path to control the photonic power source, and a photonic power converter coupled to the optical power path to convert photonic energy received over the optical power path to electrical energy to power components of the PRCC.

A new design approach to innovative spectrometers. Case study: TROPOLITE

NASA Astrophysics Data System (ADS)

Volatier, Jean-Baptiste; Baümer, Stefan; Kruizinga, Bob; Vink, Rob

2014-05-01

Designing a novel optical system is a nested iterative process. The optimization loop, from a starting point to final system is already mostly automated. However this loop is part of a wider loop which is not. This wider loop starts with an optical specification and ends with a manufacturability assessment. When designing a new spectrometer with emphasis on weight and cost, numerous iterations between the optical- and mechanical designer are inevitable. The optical designer must then be able to reliably produce optical designs based on new input gained from multidisciplinary studies. This paper presents a procedure that can automatically generate new starting points based on any kind of input or new constraint that might arise. These starting points can then be handed over to a generic optimization routine to make the design tasks extremely efficient. The optical designer job is then not to design optical systems, but to meta-design a procedure that produces optical systems paving the way for system level optimization. We present here this procedure and its application to the design of TROPOLITE a lightweight push broom imaging spectrometer.

Regimes of external optical feedback in 5.6 μm distributed feedback mid-infrared quantum cascade lasers

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

Jumpertz, L., E-mail: louise.jumpertz@telecom-paristech.fr; Alcatel Thales III-V Lab, Campus de Polytechnique, 1 avenue Augustin Fresnel, 91767 Palaiseau; Carras, M.

2014-09-29

External optical feedback is studied experimentally in mid-infrared quantum cascade lasers. These structures exhibit a dynamical response close to that observed in interband lasers, with threshold reduction and optical power enhancement when increasing the feedback ratio. The study of the optical spectrum proves that the laser undergoes five distinct regimes depending on the phase and amplitude of the reinjected field. These regimes are mapped in the plane of external cavity length and feedback strength, revealing unstable behavior only for a very narrow range of operation, making quantum cascade lasers much more stable than their interband counterparts.

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

ERIC Educational Resources Information Center

Shah, Mahsood; Cheng, Ming; Fitzgerald, Robert

2017-01-01

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

A Case Study of Representing Signal Transduction in Liver Cells as a Feedback Control Problem

ERIC Educational Resources Information Center

Singh, Abhay; Jayaraman, Arul; Hahn, Juergen

2007-01-01

Cell signaling pathways often contain feedback loops where proteins are produced that regulate signaling. While feedback regulatory mechanisms are commonly found in signaling pathways, there is no example available in the literature that is simple enough to be presented in an undergraduate control class. This paper presents a simulation study of…

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Method and device for measuring single-shot transient signals

DOEpatents

Yin, Yan

2004-05-18

Methods, apparatus, and systems, including computer program products, implementing and using techniques for measuring multi-channel single-shot transient signals. A signal acquisition unit receives one or more single-shot pulses from a multi-channel source. An optical-fiber recirculating loop reproduces the one or more received single-shot optical pulses to form a first multi-channel pulse train for circulation in the recirculating loop, and a second multi-channel pulse train for display on a display device. The optical-fiber recirculating loop also optically amplifies the first circulating pulse train to compensate for signal losses and performs optical multi-channel noise filtration.

Circuit for Driving Piezoelectric Transducers

NASA Technical Reports Server (NTRS)

Randall, David P.; Chapsky, Jacob

2009-01-01

The figure schematically depicts an oscillator circuit for driving a piezoelectric transducer to excite vibrations in a mechanical structure. The circuit was designed and built to satisfy application-specific requirements to drive a selected one of 16 such transducers at a regulated amplitude and frequency chosen to optimize the amount of work performed by the transducer and to compensate for both (1) temporal variations of the resonance frequency and damping time of each transducer and (2) initially unknown differences among the resonance frequencies and damping times of different transducers. In other words, the circuit is designed to adjust itself to optimize the performance of whichever transducer is selected at any given time. The basic design concept may be adaptable to other applications that involve the use of piezoelectric transducers in ultrasonic cleaners and other apparatuses in which high-frequency mechanical drives are utilized. This circuit includes three resistor-capacitor networks that, together with the selected piezoelectric transducer, constitute a band-pass filter having a peak response at a frequency of about 2 kHz, which is approximately the resonance frequency of the piezoelectric transducers. Gain for generating oscillations is provided by a power hybrid operational amplifier (U1). A junction field-effect transistor (Q1) in combination with a resistor (R4) is used as a voltage-variable resistor to control the magnitude of the oscillation. The voltage-variable resistor is part of a feedback control loop: Part of the output of the oscillator is rectified and filtered for use as a slow negative feedback to the gate of Q1 to keep the output amplitude constant. The response of this control loop is much slower than 2 kHz and, therefore, does not introduce significant distortion of the oscillator output, which is a fairly clean sine wave. The positive AC feedback needed to sustain oscillations is derived from sampling the current through the piezoelectric transducer. This positive AC feedback, in combination with the slow feedback to the voltage-variable resistors, causes the overall loop gain to be just large enough to keep the oscillator running. The positive feedback loop includes two 16-channel multiplexers, which are not shown in the figure. One multiplexer is used to select the desired piezoelectric transducer. The other multiplexer, which is provided for use in the event that there are significant differences among the damping times of the 16 piezoelectric transducers, facilitates changing the value of one of the resistors in the positive-feedback loop to accommodate the damping time of the selected transducer.

Computer automation for feedback system design

NASA Technical Reports Server (NTRS)

1975-01-01

Mathematical techniques and explanations of various steps used by an automated computer program to design feedback systems are summarized. Special attention was given to refining the automatic evaluation suboptimal loop transmission and the translation of time to frequency domain specifications.

CUL4B impedes stress-induced cellular senescence by dampening a p53-reactive oxygen species positive feedback loop.

PubMed

Wei, Zhao; Guo, Haiyang; Liu, Zhaojian; Zhang, Xiyu; Liu, Qiao; Qian, Yanyan; Gong, Yaoqin; Shao, Changshun

2015-02-01

Tumor suppressor p53 is known to regulate the level of intracellular reactive oxygen species (ROS). It can either alleviate oxidative stress under physiological and mildly stressed conditions or exacerbate oxidative stress under highly stressed conditions. We here report that a p53-ROS positive feedback loop drives a senescence program in normal human fibroblasts (NHFs) and this senescence-driving loop is negatively regulated by CUL4B. CUL4B, which can assemble various ubiquitin E3 ligases, was found to be downregulated in stress-induced senescent cells, but not in replicative senescent cells. We observed that p53-dependent ROS production was significantly augmented and stress-induced senescence was greatly enhanced when CUL4B was absent or depleted. Ectopic expression of CUL4B, on the other hand, blunted p53 activation, reduced ROS production, and attenuated cellular senescence in cells treated with H2O2. CUL4B was shown to promote p53 ubiquitination and proteosomal degradation in NHFs exposed to oxidative stress, thus dampening the p53-dependent cellular senescence. Together, our results established a critical role of CUL4B in negatively regulating the p53-ROS positive feedback loop that drives cellular senescence. Copyright © 2014 Elsevier Inc. All rights reserved.

Closed-Loop and Robust Control of Quantum Systems

PubMed Central

Wang, Lin-Cheng

2013-01-01

For most practical quantum control systems, it is important and difficult to attain robustness and reliability due to unavoidable uncertainties in the system dynamics or models. Three kinds of typical approaches (e.g., closed-loop learning control, feedback control, and robust control) have been proved to be effective to solve these problems. This work presents a self-contained survey on the closed-loop and robust control of quantum systems, as well as a brief introduction to a selection of basic theories and methods in this research area, to provide interested readers with a general idea for further studies. In the area of closed-loop learning control of quantum systems, we survey and introduce such learning control methods as gradient-based methods, genetic algorithms (GA), and reinforcement learning (RL) methods from a unified point of view of exploring the quantum control landscapes. For the feedback control approach, the paper surveys three control strategies including Lyapunov control, measurement-based control, and coherent-feedback control. Then such topics in the field of quantum robust control as H ∞ control, sliding mode control, quantum risk-sensitive control, and quantum ensemble control are reviewed. The paper concludes with a perspective of future research directions that are likely to attract more attention. PMID:23997680

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

PubMed

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

2018-06-01

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

Electronic Maxwell demon in the coherent strong-coupling regime

NASA Astrophysics Data System (ADS)

Schaller, Gernot; Cerrillo, Javier; Engelhardt, Georg; Strasberg, Philipp

2018-05-01

We consider an external feedback control loop implementing the action of a Maxwell demon. Applying control actions that are conditioned on measurement outcomes, the demon may transport electrons against a bias voltage and thereby effectively converts information into electric power. While the underlying model—a feedback-controlled quantum dot that is coupled to two electronic leads—is well explored in the limit of small tunnel couplings, we can address the strong-coupling regime with a fermionic reaction-coordinate mapping. This exact mapping transforms the setup into a serial triple quantum dot coupled to two leads. We find that a continuous projective measurement of the central dot occupation would lead to a complete suppression of electronic transport due to the quantum Zeno effect. In contrast, by using a microscopic detector model we can implement a weak measurement, which allows for closure of the control loop without transport blockade. Then, in the weak-coupling regime, the energy flows associated with the feedback loop are negligible, and dominantly the information gained in the measurement induces a bound for the generated electric power. In the strong coupling limit, the protocol may require more energy for operating the control loop than electric power produced, such that the whole device is no longer information dominated and can thus not be interpreted as a Maxwell demon.

Differential contributions of the superior and inferior parietal cortex to feedback versus feedforward control of tools.

PubMed

Macuga, Kristen L; Frey, Scott H

2014-05-15

Damage to the superior and/or inferior parietal lobules (SPL, IPL) (Sirigu et al., 1996) or cerebellum (Grealy and Lee, 2011) can selectively disrupt motor imagery, motivating the hypothesis that these regions participate in predictive (i.e., feedforward) control. If so, then the SPL, IPL, and cerebellum should show greater activity as the demands on feedforward control increase from visually-guided execution (closed-loop) to execution without visual feedback (open-loop) to motor imagery. Using fMRI and a Fitts' reciprocal aiming task with tools directed at targets in far space, we found that the SPL and cerebellum exhibited greater activity during closed-loop control. Conversely, open-loop and imagery conditions were associated with increased activity within the IPL and prefrontal areas. These results are consistent with a superior-to-inferior gradient in the representation of feedback-to-feedforward control within the posterior parietal cortex. Additionally, the anterior SPL displayed greater activity when aiming movements were performed with a stick vs. laser pointer. This may suggest that it is involved in the remapping of far into near (reachable) space (Maravita and Iriki, 2004), or in distalization of the end-effector from hand to stick (Arbib et al., 2009). Copyright © 2014 Elsevier Inc. All rights reserved.

Network efficient power control for wireless communication systems.

PubMed

Campos-Delgado, Daniel U; Luna-Rivera, Jose Martin; Martinez-Sánchez, C J; Gutierrez, Carlos A; Tecpanecatl-Xihuitl, J L

2014-01-01

We introduce a two-loop power control that allows an efficient use of the overall power resources for commercial wireless networks based on cross-layer optimization. This approach maximizes the network's utility in the outer-loop as a function of the averaged signal to interference-plus-noise ratio (SINR) by considering adaptively the changes in the network characteristics. For this purpose, the concavity property of the utility function was verified with respect to the SINR, and an iterative search was proposed with guaranteed convergence. In addition, the outer-loop is in charge of selecting the detector that minimizes the overall power consumption (transmission and detection). Next the inner-loop implements a feedback power control in order to achieve the optimal SINR in the transmissions despite channel variations and roundtrip delays. In our proposal, the utility maximization process and detector selection and feedback power control are decoupled problems, and as a result, these strategies are implemented at two different time scales in the two-loop framework. Simulation results show that substantial utility gains may be achieved by improving the power management in the wireless network.

Network Efficient Power Control for Wireless Communication Systems

PubMed Central

Campos-Delgado, Daniel U.; Luna-Rivera, Jose Martin; Martinez-Sánchez, C. J.; Gutierrez, Carlos A.; Tecpanecatl-Xihuitl, J. L.

2014-01-01

We introduce a two-loop power control that allows an efficient use of the overall power resources for commercial wireless networks based on cross-layer optimization. This approach maximizes the network's utility in the outer-loop as a function of the averaged signal to interference-plus-noise ratio (SINR) by considering adaptively the changes in the network characteristics. For this purpose, the concavity property of the utility function was verified with respect to the SINR, and an iterative search was proposed with guaranteed convergence. In addition, the outer-loop is in charge of selecting the detector that minimizes the overall power consumption (transmission and detection). Next the inner-loop implements a feedback power control in order to achieve the optimal SINR in the transmissions despite channel variations and roundtrip delays. In our proposal, the utility maximization process and detector selection and feedback power control are decoupled problems, and as a result, these strategies are implemented at two different time scales in the two-loop framework. Simulation results show that substantial utility gains may be achieved by improving the power management in the wireless network. PMID:24683350

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

NASA Astrophysics Data System (ADS)

Abram, Joseph; Dyke, James

2016-04-01

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

Modeling and control of non-square MIMO system using relay feedback.

PubMed

Kalpana, D; Thyagarajan, T; Gokulraj, N

2015-11-01

This paper proposes a systematic approach for the modeling and control of non-square MIMO systems in time domain using relay feedback. Conventionally, modeling, selection of the control configuration and controller design of non-square MIMO systems are performed using input/output information of direct loop, while the output of undesired responses that bears valuable information on interaction among the loops are not considered. However, in this paper, the undesired response obtained from relay feedback test is also taken into consideration to extract the information about the interaction between the loops. The studies are performed on an Air Path Scheme of Turbocharged Diesel Engine (APSTDE) model, which is a typical non-square MIMO system, with input and output variables being 3 and 2 respectively. From the relay test response, the generalized analytical expressions are derived and these analytical expressions are used to estimate unknown system parameters and also to evaluate interaction measures. The interaction is analyzed by using Block Relative Gain (BRG) method. The model thus identified is later used to design appropriate controller to carry out closed loop studies. Closed loop simulation studies were performed for both servo and regulatory operations. Integral of Squared Error (ISE) performance criterion is employed to quantitatively evaluate performance of the proposed scheme. The usefulness of the proposed method is demonstrated on a lab-scale Two-Tank Cylindrical Interacting System (TTCIS), which is configured as a non-square system. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Dim star fringe stabilization demonstration using pathlength feed-forward on the SIM testbed 3 (STB3)

NASA Astrophysics Data System (ADS)

Goullioud, Renaud; Alvarez-Salazar, Oscar S.; Nemati, Bijan

2003-02-01

Future space-based optical interferometers such as the Space Interferometer Mission require fringe stabilization to the level of nanometers in order to produce astrometric data at the micro-arc-second level. Even the best attitude control system available to date will not be able to stabilize the attitude of a several thousand pound spacecraft to a few milli-arc-seconds. Active pathlength control is usually implemented to compensate for attitude drift of the spacecraft. This issue has been addressed in previous experiments while tracking bright stars. In the case of dim stars, as the sensor bandwidth falls below one hertz, feedback control will not provide sufficient rejection. However, stabilization of the fringes from a dim-star down to the nanometer level can be done open loop using information from additional interferometers looking at bright guide stars. The STB3 testbed developed at the Jet Propulsion Laboratory features three optical interferometers sharing a common baseline, dynamically representative to the SIM interferometer. An artificial star feeding the interferometers is installed on a separate optics bench. Voice coils are used to simulate the attitude motion of the spacecraft by moving the entire bench. Data measured on STB3 show that fringe motion of a dim star due to spacecraft attitude changes can be attenuated by 80 dB at 0.1Hz without feedback control, using only information from two guide stars. This paper describes the STB3 setup, the pathlength feed-forward architecture, implementation issues and data collected with the system.

Optical fiber loops and helices: tools for integrated photonic device characterization and microfluidic trapping

NASA Astrophysics Data System (ADS)

Ren, Yundong; Zhang, Rui; Ti, Chaoyang; Liu, Yuxiang

2016-09-01

Tapered optical fibers can deliver guided light into and carry light out of micro/nanoscale systems with low loss and high spatial resolution, which makes them ideal tools in integrated photonics and microfluidics. Special geometries of tapered fibers are desired for probing monolithic devices in plane as well as optical manipulation of micro particles in fluids. However, for many specially shaped tapered fibers, it remains a challenge to fabricate them in a straightforward, controllable, and repeatable way. In this work, we fabricated and characterized two special geometries of tapered optical fibers, namely fiber loops and helices, that could be switched between one and the other. The fiber loops in this work are distinct from previous ones in terms of their superior mechanical stability and high optical quality factors in air, thanks to a post-annealing process. We experimentally measured an intrinsic optical quality factor of 32,500 and a finesse of 137 from a fiber loop. A fiber helix was used to characterize a monolithic cavity optomechanical device. Moreover, a microfluidic "roller coaster" was demonstrated, where microscale particles in water were optically trapped and transported by a fiber helix. Tapered fiber loops and helices can find various applications ranging from on-the-fly characterization of integrated photonic devices to particle manipulation and sorting in microfluidics.

Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν-gap metric

PubMed Central

Morgans, Aimee S.

2016-01-01

Combustion instabilities arise owing to a two-way coupling between acoustic waves and unsteady heat release. Oscillation amplitudes successively grow, until nonlinear effects cause saturation into limit cycle oscillations. Feedback control, in which an actuator modifies some combustor input in response to a sensor measurement, can suppress combustion instabilities. Linear feedback controllers are typically designed, using linear combustor models. However, when activated from within limit cycle, the linear model is invalid, and such controllers are not guaranteed to stabilize. This work develops a feedback control strategy guaranteed to stabilize from within limit cycle oscillations. A low-order model of a simple combustor, exhibiting the essential features of more complex systems, is presented. Linear plane acoustic wave modelling is combined with a weakly nonlinear describing function for the flame. The latter is determined numerically using a level set approach. Its implication is that the open-loop transfer function (OLTF) needed for controller design varies with oscillation level. The difference between the mean and the rest of the OLTFs is characterized using the ν-gap metric, providing the minimum required ‘robustness margin’ for an H∞ loop-shaping controller. Such controllers are designed and achieve stability both for linear fluctuations and from within limit cycle oscillations. PMID:27493558

Steady state statistical correlations predict bistability in reaction motifs.

PubMed

Chakravarty, Suchana; Barik, Debashis

2017-03-28

Various cellular decision making processes are regulated by bistable switches that take graded input signals and convert them to binary all-or-none responses. Traditionally, a bistable switch generated by a positive feedback loop is characterized either by a hysteretic signal response curve with two distinct signaling thresholds or by characterizing the bimodality of the response distribution in the bistable region. To identify the intrinsic bistability of a feedback regulated network, here we propose that bistability can be determined by correlating higher order moments and cumulants (≥2) of the joint steady state distributions of two components connected in a positive feedback loop. We performed stochastic simulations of four feedback regulated models with intrinsic bistability and we show that for a bistable switch with variation of the signal dose, the steady state variance vs. covariance adopts a signatory cusp-shaped curve. Further, we find that the (n + 1)th order cross-cumulant vs. nth order cross-cumulant adopts a closed loop structure for at least n = 3. We also propose that our method is capable of identifying systems without intrinsic bistability even though the system may show bimodality in the marginal response distribution. The proposed method can be used to analyze single cell protein data measured at steady state from experiments such as flow cytometry.

Impact of time delays on oscillatory dynamics of interlinked positive and negative feedback loops

NASA Astrophysics Data System (ADS)

Huang, Bo; Tian, Xinyu; Liu, Feng; Wang, Wei

2016-11-01

Interlinking a positive feedback loop (PFL) with a negative feedback loop (NFL) constitutes a typical motif in genetic networks, performing various functions in cell signaling. How time delay in feedback regulation affects the dynamics of such systems still remains unclear. Here, we investigate three systems of interlinked PFL and NFL with time delays: a synthetic genetic oscillator, a three-node circuit, and a simplified single-node model. The stability of steady states and the routes to oscillation in the single-node model are analyzed in detail. The amplitude and period of oscillations vary with a pointwise periodicity over a range of time delay. Larger-amplitude oscillations can be induced when the PFL has an appropriately long delay, in comparison with the PFL with no delay or short delay; this conclusion holds true for all the three systems. We unravel the underlying mechanism for the above effects via analytical derivation under a limiting condition. We also develop a stochastic algorithm for simulating a single reaction with two delays and show that robust oscillations can be maintained by the PFL with a properly long delay in the single-node system. This work presents an effective method for constructing robust large-amplitude oscillators and interprets why similar circuit architectures are engaged in timekeeping systems such as circadian clocks.

The Paracrine Feedback Loop Between Vitamin D3 (1,25(OH)2D3) and PTHrP in Prehypertrophic Chondrocytes

PubMed Central

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

2014-01-01

The endocrine feedback loop between vitamin D3 (1,25(OH)2D3) and parathyroid hormone (PTH) plays a central role in skeletal development. PTH-related protein (PTHrP) shares homology and its receptor (PTHR1) with PTH. The aim of this study was to investigate whether there is a functional paracrine feedback loop between 1,25(OH)2D3 and PTHrP in the growth plate, in parallel with the endocrine feedback loop between 1,25(OH)2D3 and PTH. This was investigated in ATDC5 cells treated with 10−8 M 1,25(OH)2D3 or PTHrP, Col2-pd2EGFP transgenic mice, and primary Col2-pd2EGFP growth plate chondrocytes isolated by FACS, using RT-qPCR, Western blot, PTHrP ELISA, chromatin immunoprecipitation (ChIP) assay, silencing of the 1,25(OH)2D3 receptor (VDR), immunofluorescent staining, immunohistochemistry, and histomorphometric analysis of the growth plate. The ChIP assay confirmed functional binding of the VDR to the PTHrP promoter, but not to the PTHR1 promoter. Treatment with 1,25(OH)2D3 decreased PTHrP protein production, an effect which was prevented by silencing of the VDR. Treatment with PTHrP significantly induced VDR production, but did not affect 1α- and 24-hydroxylase expression. Hypertrophic differentiation was inhibited by PTHrP and 1,25(OH)2D3 treatment. Taken together, these findings indicate that there is a functional paracrine feedback loop between 1,25(OH)2D3 and PTHrP in the growth plate. 1,25(OH)2D3 decreases PTHrP production, while PTHrP increases chondrocyte sensitivity to 1,25(OH)2D3 by increasing VDR production. In light of the role of 1,25(OH)2D3 and PTHrP in modulating chondrocyte differentiation, 1,25(OH)2D3 in addition to PTHrP could potentially be used to prevent undesirable hypertrophic chondrocyte differentiation during cartilage repair or regeneration. PMID:24777663

Automatic Gain Control in Compact Spectrometers.

PubMed

Protopopov, Vladimir

2016-03-01

An image intensifier installed in the optical path of a compact spectrometer may act not only as a fast gating unit, which is widely used for time-resolved measurements, but also as a variable attenuator-amplifier in a continuous wave mode. This opens the possibility of an automatic gain control, a new feature in spectroscopy. With it, the user is relieved from the necessity to manually adjust signal level at a certain value that it is done automatically by means of an electronic feedback loop. It is even more important that automatic gain control is done without changing exposure time, which is an additional benefit in time-resolved experiments. The concept, algorithm, design considerations, and experimental results are presented. © The Author(s) 2016.

Localization control of few-photon states in parity-symmetric ‘photonic molecules’ under balanced pumping

NASA Astrophysics Data System (ADS)

Bentley, C. D. B.; Celestino, A.; Yacomotti, A. M.; El-Ganainy, R.; Eisfeld, A.

2018-06-01

We theoretically investigate the problem of localization control of few-photon states in driven-dissipative parity-symmetric photonic molecules. Photonic molecules are multi-cavity photonic systems. We show that a quantum feedback loop can utilize the information of the spontaneously-emitted photons from each cavity to induce asymmetric photon population in the cavities, while maintaining a balanced pump that respects parity symmetry. To better understand the system’s behavior, we characterize the degree of asymmetry as a function of the coupling between the two optical cavities. Contrary to intuitive expectations, we find that in some regimes the coupling can enhance the population asymmetry. We also show that these results are robust against experimental imperfections and limitations such as detection efficiency.

Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field.

PubMed

Palma, A J; Ortigosa, J M; Lapresta-Fernández, A; Fernández-Ramos, M D; Carvajal, M A; Capitán-Vallvey, L F

2008-10-01

This report describes the electronics of a portable, low-cost, light-emitting diode (LED)-based photometer dedicated to one-shot optochemical sensors. Optical detection is made through a monolithic photodiode with an on-chip single-supply transimpedance amplifier that reduces some drawbacks such as leakage currents, interferences, and parasitic capacitances. The main instrument characteristics are its high light source stability and thermal correction. The former is obtained by means of the optical feedback from the LED polarization circuit, implementing a pseudo-two light beam scheme from a unique light source with a built-in beam splitter. The feedback loop has also been used to adjust the LED power in several ranges. Moreover, the low-thermal coefficient achieved (-90 ppm/degrees C) is compensated by thermal monitoring and calibration function compensation in the digital processing. The hand-held instrument directly gives the absorbance ratio used as the analytical parameter and the analyte concentration after programming the calibration function in the microcontroller. The application of this photometer for the determination of potassium and nitrate, using one-shot sensors with ionophore-based chemistries is also demonstrated, with a simple analytical methodology that shortens the analysis time, eliminating some calibrating solutions (HCl, NaOH, and buffer). Therefore, this compact instrument is suitable for real-time analyte determination and operation in the field.

Phase-locked loop based on nanoelectromechanical resonant-body field effect transistor

NASA Astrophysics Data System (ADS)

Bartsch, S. T.; Rusu, A.; Ionescu, A. M.

2012-10-01

We demonstrate the room-temperature operation of a silicon nanoelectromechanical resonant-body field effect transistor (RB-FET) embedded into phase-locked loop (PLL). The very-high frequency resonator uses on-chip electrostatic actuation and transistor-based displacement detection. The heterodyne frequency down-conversion based on resistive FET mixing provides a loop feedback signal with high signal-to-noise ratio. We identify key parameters for PLL operation, and analyze the performance of the RB-FET at the system level. Used as resonant mass detector, the experimental frequency stability in the ppm-range translates into sub atto-gram (10-18 g) sensitivity in high vacuum. The feedback and control system are generic and may be extended to other mechanical resonators with transistor properties, such as graphene membranes and carbon nanotubes.

The effect of jitter on the performance of space coherent optical communication system with Costas loop

NASA Astrophysics Data System (ADS)

Li, Xin; Hong, Yifeng; Wang, Jinfang; Liu, Yang; Sun, Xun; Li, Mi

2018-01-01

Numerous communication techniques and optical devices successfully applied in space optical communication system indicates a good portability of it. With this good portability, typical coherent demodulation technique of Costas loop can be easily adopted in space optical communication system. As one of the components of pointing error, the effect of jitter plays an important role in the communication quality of such system. Here, we obtain the probability density functions (PDF) of different jitter degrees and explain their essential effect on the bit error rate (BER) space optical communication system. Also, under the effect of jitter, we research the bit error rate of space coherent optical communication system using Costas loop with different system parameters of transmission power, divergence angle, receiving diameter, avalanche photodiode (APD) gain, and phase deviation caused by Costas loop. Through a numerical simulation of this kind of communication system, we demonstrate the relationship between the BER and these system parameters, and some corresponding methods of system optimization are presented to enhance the communication quality.

Feedback linearization for control of air breathing engines

NASA Technical Reports Server (NTRS)

Phillips, Stephen; Mattern, Duane

1991-01-01

The method of feedback linearization for control of the nonlinear nozzle and compressor components of an air breathing engine is presented. This method overcomes the need for a large number of scheduling variables and operating points to accurately model highly nonlinear plants. Feedback linearization also results in linear closed loop system performance simplifying subsequent control design. Feedback linearization is used for the nonlinear partial engine model and performance is verified through simulation.

Functional characteristics of a double positive feedback loop coupled with autorepression

NASA Astrophysics Data System (ADS)

Banerjee, Subhasis; Bose, Indrani

2008-12-01

We study the functional characteristics of a two-gene motif consisting of a double positive feedback loop and an autoregulatory negative feedback loop. The motif appears in the gene regulatory network controlling the functional activity of pancreatic β-cells. The model exhibits bistability and hysteresis in appropriate parameter regions. The two stable steady states correspond to low (OFF state) and high (ON state) protein levels, respectively. Using a deterministic approach, we show that the region of bistability increases in extent when the copy number of one of the genes is reduced from 2 to 1. The negative feedback loop has the effect of reducing the size of the bistable region. Loss of a gene copy, brought about by mutations, hampers the normal functioning of the β-cells giving rise to the genetic disorder, maturity-onset diabetes of the young (MODY). The diabetic phenotype makes its appearance when a sizable fraction of the β-cells is in the OFF state. Using stochastic simulation techniques we show that, on reduction of the gene copy number, there is a transition from the monostable ON to the ON state in the bistable region of the parameter space. Fluctuations in the protein levels, arising due to the stochastic nature of gene expression, can give rise to transitions between the ON and OFF states. We show that as the strength of autorepression increases, the ON → OFF state transitions become less probable whereas the reverse transitions are more probable. The implications of the results in the context of the occurrence of MODY are pointed out.

Real-time optical signal processors employing optical feedback: amplitude and phase control.

PubMed

Gallagher, N C

1976-04-01

The development of real-time coherent optical signal processors has increased the appeal of optical computing techniques in signal processing applications. A major limitation of these real-time systems is the. fact that the optical processing material is generally of a phase-only type. The result is that the spatial filters synthesized with these systems must be either phase-only filters or amplitude-only filters. The main concern of this paper is the application of optical feedback techniques to obtain simultaneous and independent amplitude and phase control of the light passing through the system. It is shown that optical feedback techniques may be employed with phase-only spatial filters to obtain this amplitude and phase control. The feedback system with phase-only filters is compared with other feedback systems that employ combinations of phase-only and amplitude-only filters; it is found that the phase-only system is substantially more flexible than the other two systems investigated.

Feedback control for stabilizing chaotic spiral waves during cardiac ventricular fibrillation

NASA Astrophysics Data System (ADS)

Uzelac, Ilija; Wikswo, John; Gray, Richard

2011-03-01

The cardiac arrhythmias that lead to ventricular fibrillation (VF) arise from electrical spiral waves (SW) rotating within the heart with a characteristic period τ . A single drifting SW can degenerate into a chaotic system of multiple SWs and VF. Hence early SW detection and termination is crucial to prevent VF. Time-delayed feedback control (TDFC) is well known approach for stabilizing unstable periodic orbits embedded in chaotic attractors. We hypothesize that cardiac SWs can be stabilized by TDFC with a time-delay of τ . Implementing this approach will require precise, closed-loop control of the charge delivered to the heart during the defibrillation process. To do this, we have developed a 2 kW arbitrary-waveform voltage-to-current converter (V2CC) with a 1 kHz bandwidth that can deliver up to 5 A at 400 V for 500 ms, and a photodiode system for recording in real time an optical electrocardiogram, OECG(t). The feedback signal driving the V2CC will be the time-difference (OECG(t) - OECG(t-T), where we hypothesize that T is τ , the period of the SW. This may dramatically decrease defibrillation voltages by using a defibrillation waveform customized to the VF event, unlike commercial capacitor defibrillators. Supported in part by NIH R01 HL58241-11 through ARRA 2009.

Method for removing tilt control in adaptive optics systems

DOEpatents

Salmon, Joseph Thaddeus

1998-01-01

A new adaptive optics system and method of operation, whereby the method removes tilt control, and includes the steps of using a steering mirror to steer a wavefront in the desired direction, for aiming an impinging aberrated light beam in the direction of a deformable mirror. The deformable mirror has its surface deformed selectively by means of a plurality of actuators, and compensates, at least partially, for existing aberrations in the light beam. The light beam is split into an output beam and a sample beam, and the sample beam is sampled using a wavefront sensor. The sampled signals are converted into corresponding electrical signals for driving a controller, which, in turn, drives the deformable mirror in a feedback loop in response to the sampled signals, for compensating for aberrations in the wavefront. To this purpose, a displacement error (gradient) of the wavefront is measured, and adjusted by a modified gain matrix, which satisfies the following equation: G'=(I-X(X.sup.T X).sup.-1 X.sup.T)G(I-A)

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

Ren, Jinqi; Cook, Aaron A.; Bergmeier, Wolfgang

The dynamic regulation of ERK1 and -2 (ERK1/2) is required for precise signal transduction controlling cell proliferation, differentiation, and survival. However, the underlying mechanisms regulating the activation of ERK1/2 are not completely understood. In this study, we show that phosphorylation of RasGRP2, a guanine nucleotide exchange factor (GEF), inhibits its ability to activate the small GTPase Rap1 that ultimately leads to decreased activation of ERK1/2 in cells. ERK2 phosphorylates RasGRP2 at Ser394 located in the linker region implicated in its autoinhibition. These studies identify RasGRP2 as a novel substrate of ERK1/2 and define a negative-feedback loop that regulates the BRaf–MEK–ERKmore » signaling cascade. This negative-feedback loop determines the amplitude and duration of active ERK1/2. -- Highlights: •ERK2 phosphorylates the guanine nucleotide exchange factor RasGRP2 at Ser394. •Phosphorylated RasGRP2 has decreased capacity to active Rap1b in vitro and in cells. •Phosphorylation of RasGRP2 by ERK1/2 introduces a negative-feedback loop into the BRaf-MEK-ERK pathway.« less

The LSD1 Family of Histone Demethylases and the Pumilio Posttranscriptional Repressor Function in a Complex Regulatory Feedback Loop

PubMed Central

Miles, Wayne O.; Lepesant, Julie M. J.; Bourdeaux, Jessie; Texier, Manuela; Kerenyi, Marc A.; Nakakido, Makoto; Hamamoto, Ryuji; Orkin, Stuart H.; Dyson, Nicholas J.

2015-01-01

The lysine (K)-specific demethylase (LSD1) family of histone demethylases regulates chromatin structure and the transcriptional potential of genes. LSD1 is frequently deregulated in tumors, and depletion of LSD1 family members causes developmental defects. Here, we report that reductions in the expression of the Pumilio (PUM) translational repressor complex enhanced phenotypes due to dLsd1 depletion in Drosophila. We show that the PUM complex is a target of LSD1 regulation in fly and mammalian cells and that its expression is inversely correlated with LSD1 levels in human bladder carcinoma. Unexpectedly, we find that PUM posttranscriptionally regulates LSD1 family protein levels in flies and human cells, indicating the existence of feedback loops between the LSD1 family and the PUM complex. Our results highlight a new posttranscriptional mechanism regulating LSD1 activity and suggest that the feedback loop between the LSD1 family and the PUM complex may be functionally important during development and in human malignancies. PMID:26438601

Closed-loop Separation Control Using Oscillatory Flow Excitation

NASA Technical Reports Server (NTRS)

Allan, Brian G.; Juang, Jer-Nan; Raney, David L.; Seifert, Avi; Pack, latunia G.; Brown, Donald E.

2000-01-01

Design and implementation of a digital feedback controller for a flow control experiment was performed. The experiment was conducted in a cryogenic pressurized wind tunnel on a generic separated configuration at a chord Reynolds number of 16 million and a Mach number of 0.25. The model simulates the upper surface of a 20% thick airfoil at zero angle-of-attack. A moderate favorable pressure gradient, up to 55% of the chord, is followed by a severe adverse pressure gradient which is relaxed towards the trailing edge. The turbulent separation bubble, behind the adverse pressure gradient, is then reduced by introducing oscillatory flow excitation just upstream of the point of flow separation. The degree of reduction in the separation region can be controlled by the amplitude of the oscillatory excitation. A feedback controller was designed to track a given trajectory for the desired degree of flow reattachment and to improve the transient behavior of the flow system. Closed-loop experiments demonstrated that the feedback controller was able to track step input commands and improve the transient behavior of the open-loop response.

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.

Linear state feedback, quadratic weights, and closed loop eigenstructures. M.S. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Thompson, P. M.

1980-01-01

Equations are derived for the angles of general multivariable root loci and linear quadratic optimal root loci, including angles of departure and approach. The generalized eigenvalue problem is used to compute angles of approach. Equations are also derived to find the sensitivity of closed loop eigenvalue and the directional derivatives of closed loop eigenvectors. An equivalence class of quadratic weights that produce the same asymptotic eigenstructure is defined, a canonical element is defined, and an algorithm to find it is given. The behavior of the optimal root locus in the nonasymptotic region is shown to be different for quadratic weights with the same asymptotic properties. An algorithm is presented that can be used to select a feedback gain matrix for the linear state feedback problem which produces a specified asymptotic eigenstructure. Another algorithm is given to compute the asymptotic eigenstructure properties inherent in a given set of quadratic weights. Finally, it is shown that optimal root loci for nongeneric problems can be approximated by generic ones in the nonasymptotic region.

A low noise and ultra-narrow bandwidth frequency-locked loop based on the beat method.

PubMed

Gao, Wei; Sui, Jianping; Chen, Zhiyong; Yu, Fang; Sheng, Rongwu

2011-06-01

A novel frequency-locked loop (FLL) based on the beat method is proposed in this paper. Compared with other frequency feedback loops, this FLL is a digital loop with simple structure and very low noise. As shown in the experimental results, this FLL can be used to reduce close-in phase noise on atomic frequency standards, through which a composite frequency standard with ultra-low phase noise and low cost can be easily realized.

Polarization Dependence Suppression of Optical Fiber Grating Sensor in a π-Shifted Sagnac Loop Interferometer

PubMed Central

Son, Jaebum; Lee, Min-Kyoung; Jeong, Myung Yung; Kim, Chang-Seok

2010-01-01

In the sensing applications of optical fiber grating, it is necessary to reduce the transmission-type polarization dependence to isolate the sensing parameter. It is experimentally shown that the polarization-dependent spectrum of acousto-optic long-period fiber grating sensors can be suppressed in the transmission port of a π-shifted Sagnac loop interferometer. General expressions for the transmittance and reflectance are derived for transmission-type, reflection-type, and partially reflecting/transmitting-type polarization-dependent optical devices. The compensation of polarization dependence through the counter propagation in the Sagnac loop interferometer is quantitatively measured for a commercial in-line polarizer and an acousto-optic long-period fiber grating sensor. PMID:22399884

Theoretical modeling of the dynamics of a semiconductor laser subject to double-reflector optical feedback

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

Bakry, A.; Abdulrhmann, S.; Ahmed, M., E-mail: mostafa.farghal@mu.edu.eg

2016-06-15

We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding themore » second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.« less

Phase-lock-loop application for fiber optic receiver

NASA Astrophysics Data System (ADS)

Ruggles, Stephen L.; Wills, Robert W.

1991-02-01

Phase-locked loop circuits are frequently employed in communication systems. In recent years, digital phase-locked loop circuits were utilized in optical communications systems. In an optical transceiver system, the digital phase-locked loop circuit is connected to the output of the receiver to extract a clock signal from the received coded data (NRZ, Bi-Phase, or Manchester). The clock signal is then used to reconstruct or recover the original data from the coded data. A theoretical approach to the design of a digital phase-locked loop circuit operation at 1 and 50 MHz is described. Hardware implementation of a breadboard design to function at 1 MHz and a printed-circuit board designed to function at 50 MHz were assembled using emitter coupled logic (ECL) to verify experimentally the theoretical design.

Phase-lock-loop application for fiber optic receiver

NASA Technical Reports Server (NTRS)

Ruggles, Stephen L.; Wills, Robert W.

1991-01-01

Phase-locked loop circuits are frequently employed in communication systems. In recent years, digital phase-locked loop circuits were utilized in optical communications systems. In an optical transceiver system, the digital phase-locked loop circuit is connected to the output of the receiver to extract a clock signal from the received coded data (NRZ, Bi-Phase, or Manchester). The clock signal is then used to reconstruct or recover the original data from the coded data. A theoretical approach to the design of a digital phase-locked loop circuit operation at 1 and 50 MHz is described. Hardware implementation of a breadboard design to function at 1 MHz and a printed-circuit board designed to function at 50 MHz were assembled using emitter coupled logic (ECL) to verify experimentally the theoretical design.

A tutorial on the LQG/LTR method. [Linear Quadratic Gaussian/Loop Transfer Recovery

NASA Technical Reports Server (NTRS)

Athans, M.

1986-01-01

In this paper the so-called Linear-Quadratic-Gaussian method with Loop-Transfer-Recovery is surveyed. The objective is to provide a pragmatic exposition, with special emphasis on the step-by-step characteristics for designing multivariable feedback control systems.

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.

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

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

Portmann, G.; Bengtsson, J.

1993-05-01

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

Development of a low noise induction magnetic sensor using magnetic flux negative feedback in the time domain.

PubMed

Wang, X G; Shang, X L; Lin, J

2016-05-01

Time-domain electromagnetic system can implement great depth detection. As for the electromagnetic system, the receiver utilized an air coil sensor, and the matching mode of the sensor employed the resistance matching method. By using the resistance matching method, the vibration of the coil in the time domain can be effectively controlled. However, the noise of the sensor, especially the noise at the resonance frequency, will be increased as well. In this paper, a novel design of a low noise induction coil sensor is proposed, and the experimental data and noise characteristics are provided. The sensor is designed based on the principle that the amplified voltage will be converted to current under the influence of the feedback resistance of the coil. The feedback loop around the induction coil exerts a magnetic field and sends the negative feedback signal to the sensor. The paper analyses the influence of the closed magnetic feedback loop on both the bandwidth and the noise of the sensor. The signal-to-noise ratio is improved dramatically.

Antagonistic autoregulation speeds up a homogeneous response in Escherichia coli.

PubMed

Rodrigo, Guillermo; Bajic, Djordje; Elola, Ignacio; Poyatos, Juan F

2016-10-31

By integrating positive and negative feedback loops, biological systems establish intricate gene expression patterns linked to multistability, pulsing, and oscillations. This depends on the specific characteristics of each interlinked feedback, and thus one would expect additional expression programs to be found. Here, we investigate one such program associated with an antagonistic positive and negative transcriptional autoregulatory motif derived from the multiple antibiotic resistance (mar) system of Escherichia coli. We studied the dynamics of the system by combining a predictive mathematical model with high-resolution experimental measures of the response both at the population and single-cell level. We show that in this motif the weak positive autoregulation does not slow down but rather enhances response speedup in combination with a strong negative feedback loop. This balance of feedback strengths anticipates a homogeneous population phenotype, which we corroborate experimentally. Theoretical analysis also emphasized the specific molecular properties that determine the dynamics of the mar phenotype. More broadly, response acceleration could provide a rationale for the presence of weak positive feedbacks in other biological scenarios exhibiting these interlinked regulatory architectures.

A dual-loop model of the human controller

NASA Technical Reports Server (NTRS)

Hess, R. A.

1977-01-01

A representative model of the human controller in single-axis compensatory tracking tasks that exhibits an internal feedback loop which is not evident in single-loop models now in common use is presented. This hypothetical inner-loop involves a neuromuscular command signal derived from the time rate of change of controlled element output which is due to control activity. It is not contended that the single-loop human controller models now in use are incorrect, but that they contain an implicit but important internal loop closure, which, if explicitly considered, can account for a good deal of the adaptive nature of the human controller in a systematic manner.

Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop

PubMed Central

Kim, Hyunjin; Sampath, Umesh; Song, Minho

2015-01-01

Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems. PMID:26230700

Prediction performance of reservoir computing systems based on a diode-pumped erbium-doped microchip laser subject to optical feedback.

PubMed

Nguimdo, Romain Modeste; Lacot, Eric; Jacquin, Olivier; Hugon, Olivier; Van der Sande, Guy; Guillet de Chatellus, Hugues

2017-02-01

Reservoir computing (RC) systems are computational tools for information processing that can be fully implemented in optics. Here, we experimentally and numerically show that an optically pumped laser subject to optical delayed feedback can yield similar results to those obtained for electrically pumped lasers. Unlike with previous implementations, the input data are injected at a time interval that is much larger than the time-delay feedback. These data are directly coupled to the feedback light beam. Our results illustrate possible new avenues for RC implementations for prediction tasks.

Feedback-controlled radiation pressure cooling

NASA Astrophysics Data System (ADS)

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

2008-03-01

We propose a new approach to laser cooling of micromechanical devices, which is based on the phenomenon of optical bistability. These devices are modeled as a Fabry-Perot resonator with one fixed and one oscillating mirror. The bistability may be induced by an external feedback loop. When excited by an external laser, the cavity field has two co-existing stable steady-states depending on the position of the moving mirror. If the latter moves slow enough, the field in the cavity adjusts itself adiabatically to the mirror's instantaneous position. The mirror experiences radiation pressure corresponding to the intensity value. A sharp transition between two values of the radiation pressure force happens twice per every period of the mirror oscillation at non-equivalent positions (hysteresis effect), which leads to a non-zero net energy loss. The cooling mechanism resembles Sisyphus cooling in which the cavity mode performs sudden transitions between two stable states. We provide a dynamical stability analysis of the coupled moving mirror -- cavity field system, and find the parameters for efficient cooling. Direct numerical simulations show that a bistable cavity provides much more efficient cooling compared to the regular one.

Flexible body stability analysis of Space Shuttle ascent flight control system by using lambda matrix solution techniques

NASA Technical Reports Server (NTRS)

Bown, R. L.; Christofferson, A.; Lardas, M.; Flanders, H.

1980-01-01

A lambda matrix solution technique is being developed to perform an open loop frequency analysis of a high order dynamic system. The procedure evaluates the right and left latent vectors corresponding to the respective latent roots. The latent vectors are used to evaluate the partial fraction expansion formulation required to compute the flexible body open loop feedback gains for the Space Shuttle Digital Ascent Flight Control System. The algorithm is in the final stages of development and will be used to insure that the feedback gains meet the design specification.

The Search for Perpetual Motion: Fatigue, Friction, and Drag in Quality Improvement.

PubMed

Cumbler, Ethan; Pierce, Read

Most people who have worked on continuous quality improvement (QI) with teams in the clinical microsystem have experienced "change fatigue." Application of the "Limit-to-Growth" system archetype to QI teams within health care can be used to understand negative feedback loops generated by successful QI that can limit future progress. Awareness of these factors can result in actions designed to reduce drag on forward momentum. Leaders in health care QI can anticipate and minimize negative feedback loops that accumulate to slow subsequent progress of highly functioning improvement teams within clinical microsystems.

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.

Air Force research in human sensory feedback for telepresence

NASA Technical Reports Server (NTRS)

Julian, Ronald G.

1993-01-01

Telepresence operations require high quality information transfer between the human master and the remotely located slave. Present Air Force research focuses on the human aspects of the information needed to complete the control/feedback loop. Work in three key areas of human sensory feedback for manipulation of objects are described. Specific projects in each key area are outlined, including research tools (hardware), planned research, and test results. Nonmanipulative feedback technologies are mentioned to complete the advanced teleoperation discussions.

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.

Programmable Iterative Optical Image And Data Processing

NASA Technical Reports Server (NTRS)

Jackson, Deborah J.

1995-01-01

Proposed method of iterative optical image and data processing overcomes limitations imposed by loss of optical power after repeated passes through many optical elements - especially, beam splitters. Involves selective, timed combination of optical wavefront phase conjugation and amplification to regenerate images in real time to compensate for losses in optical iteration loops; timing such that amplification turned on to regenerate desired image, then turned off so as not to regenerate other, undesired images or spurious light propagating through loops from unwanted reflections.

Linear motor drive system for continuous-path closed-loop position control of an object

DOEpatents

Barkman, William E.

1980-01-01

A precision numerical controlled servo-positioning system is provided for continuous closed-loop position control of a machine slide or platform driven by a linear-induction motor. The system utilizes filtered velocity feedback to provide system stability required to operate with a system gain of 100 inches/minute/0.001 inch of following error. The filtered velocity feedback signal is derived from the position output signals of a laser interferometer utilized to monitor the movement of the slide. Air-bearing slides mounted to a stable support are utilized to minimize friction and small irregularities in the slideway which would tend to introduce positioning errors. A microprocessor is programmed to read command and feedback information and converts this information into the system following error signal. This error signal is summed with the negative filtered velocity feedback signal at the input of a servo amplifier whose output serves as the drive power signal to the linear motor position control coil.

Velocity feedback control with a flywheel proof mass actuator

NASA Astrophysics Data System (ADS)

Kras, Aleksander; Gardonio, Paolo

2017-08-01

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

A multiloop generalization of the circle criterion for stability margin analysis

NASA Technical Reports Server (NTRS)

Safonov, M. G.; Athans, M.

1979-01-01

In order to provide a theoretical tool suited for characterizing the stability margins of multiloop feedback systems, multiloop input-output stability results generalizing the circle stability criterion are considered. Generalized conic sectors with 'centers' and 'radii' determined by linear dynamical operators are employed to specify the stability margins as a frequency dependent convex set of modeling errors (including nonlinearities, gain variations and phase variations) which the system must be able to tolerate in each feedback loop without instability. The resulting stability criterion gives sufficient conditions for closed loop stability in the presence of frequency dependent modeling errors, even when the modeling errors occur simultaneously in all loops. The stability conditions yield an easily interpreted scalar measure of the amount by which a multiloop system exceeds, or falls short of, its stability margin specifications.

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.

Adaptive Inner-Loop Rover Control

NASA Technical Reports Server (NTRS)

Kulkarni, Nilesh; Ippolito, Corey; Krishnakumar, Kalmanje; Al-Ali, Khalid M.

2006-01-01

Adaptive control technology is developed for the inner-loop speed and steering control of the MAX Rover. MAX, a CMU developed rover, is a compact low-cost 4-wheel drive, 4-wheel steer (double Ackerman), high-clearance agile durable chassis, outfitted with sensors and electronics that make it ideally suited for supporting research relevant to intelligent teleoperation and as a low-cost autonomous robotic test bed and appliance. The design consists of a feedback linearization based controller with a proportional - integral (PI) feedback that is augmented by an online adaptive neural network. The adaptation law has guaranteed stability properties for safe operation. The control design is retrofit in nature so that it fits inside the outer-loop path planning algorithms. Successful hardware implementation of the controller is illustrated for several scenarios consisting of actuator failures and modeling errors in the nominal design.

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

PubMed Central

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

2018-01-01

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

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

PubMed

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

2018-01-01

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

Application of system dynamics for developing financially self-sustaining management policies for water and wastewater systems.

PubMed

Rehan, R; Knight, M A; Haas, C T; Unger, A J A

2011-10-15

Recently enacted regulations in Canada and elsewhere require water utilities to be financially self-sustaining over the long-term. This implies full cost recovery for providing water and wastewater services to users. This study proposes a new approach to help water utilities plan to meet the requirements of the new regulations. A causal loop diagram is developed for a financially self-sustaining water utility which frames water and wastewater network management as a complex system with multiple interconnections and feedback loops. The novel System Dynamics approach is used to develop a demonstration model for water and wastewater network management. This is the first known application of System Dynamics to water and wastewater network management. The network simulated is that of a typical Canadian water utility that has under invested in maintenance. Model results show that with no proactive rehabilitation strategy the utility will need to substantially increase its user fees to achieve financial sustainability. This increase is further exacerbated when price elasticity of water demand is considered. When the utility pursues proactive rehabilitation, financial sustainability is achieved with lower user fees. Having demonstrated the significance of feedback loops for financial management of water and wastewater networks, the paper makes the case for a more complete utility model that considers the complexity of the system by incorporating all feedback loops. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

Positive and negative feedback regulatory loops of thiol-oxidative stress response mediated by an unstable isoform of sigmaR in actinomycetes.

PubMed

Kim, Min-Sik; Hahn, Mi-Young; Cho, Yoobok; Cho, Sang-Nae; Roe, Jung-Hye

2009-09-01

Alternate sigma factors provide an effective way of diversifying bacterial gene expression in response to environmental changes. In Streptomyces coelicolor where more than 65 sigma factors are predicted, sigma(R) is the major regulator for response to thiol-oxidative stresses. sigma(R) becomes available when its bound anti-sigma factor RsrA is oxidized at sensitive cysteine thiols to form disulphide bonds. sigma(R) regulon includes genes for itself and multiple thiol-reducing systems, which constitute positive and negative feedback loops respectively. We found that the positive amplification loop involves an isoform of sigma(R) (sigma(R')) with an N-terminal extension of 55 amino acids, produced from an upstream start codon. A major difference between constitutive sigma(R) and inducible sigma(R') is that the latter is markedly unstable (t(1/2) approximately 10 min) compared with the former (> 70 min). The rapid turnover of sigma(R') is partly due to induced ClpP1/P2 proteases from the sigma(R) regulon. This represents a novel way of elaborating positive and negative feedback loops in a control circuit. Similar phenomenon may occur in other actinomycetes that harbour multiple start codons in the sigR homologous gene. We observed that sigH gene, the sigR orthologue in Mycobacterium smegmatis, produces an unstable larger isoform of sigma(H) upon induction by thiol-oxidative stress.

Functional anatomy of nonvisual feedback loops during reaching: a positron emission tomography study.

PubMed

Desmurget, M; Gréa, H; Grethe, J S; Prablanc, C; Alexander, G E; Grafton, S T

2001-04-15

Reaching movements performed without vision of the moving limb are continuously monitored, during their execution, by feedback loops (designated nonvisual). In this study, we investigated the functional anatomy of these nonvisual loops using positron emission tomography (PET). Seven subjects had to "look at" (eye) or "look and point to" (eye-arm) visual targets whose location either remained stationary or changed undetectably during the ocular saccade (when vision is suppressed). Slightly changing the target location during gaze shift causes an increase in the amount of correction to be generated. Functional anatomy of nonvisual feedback loops was identified by comparing the reaching condition involving large corrections (jump) with the reaching condition involving small corrections (stationary), after subtracting the activations associated with saccadic movements and hand movement planning [(eye-arm-jumping minus eye-jumping) minus (eye-arm-stationary minus eye-stationary)]. Behavioral data confirmed that the subjects were both accurate at reaching to the stationary targets and able to update their movement smoothly and early in response to the target jump. PET difference images showed that these corrections were mediated by a restricted network involving the left posterior parietal cortex, the right anterior intermediate cerebellum, and the left primary motor cortex. These results are consistent with our knowledge of the functional properties of these areas and more generally with models emphasizing parietal-cerebellar circuits for processing a dynamic motor error signal.

Flexible and evolutionary optical access networks

NASA Astrophysics Data System (ADS)

Hsueh, Yu-Li

Passive optical networks (PONs) are promising solutions that will open the first-mile bottleneck. Current PONs employ time division multiplexing (TDM) to share bandwidth among users, leading to low cost but limited capacity. In the future, wavelength division multiplexing (WDM) technologies will be deployed to achieve high performance. This dissertation describes several advanced technologies to enhance PON systems. A spectral shaping line coding scheme is developed to allow a simple and cost-effective overlay of high data-rate services in existing PONs, leaving field-deployed fibers and existing services untouched. Spectral shapes of coded signals can be manipulated to adapt to different systems. For a specific tolerable interference level, the optimal line code can be found which maximizes the data throughput. Experiments are conducted to demonstrate and compare several optimized line codes. A novel PON employing dynamic wavelength allocation to provide bandwidth sharing across multiple physical PONs is designed and experimentally demonstrated. Tunable lasers, arrayed waveguide gratings, and coarse/fine filtering combine to create a flexible optical access solution. The network's excellent scalability can bridge the gap between conventional TDM PONs and WDM PONs. Scheduling algorithms with quality of service support are also investigated. Simulation results show that the proposed architecture exhibits significant performance gain over conventional PON systems. Streaming video transmission is demonstrated on the prototype experimental testbed. The powerful architecture is a promising candidate for next-generation optical access networks. A new CDR circuit for receiving the bursty traffic in PONs is designed and analyzed. It detects data transition edges upon arrival of the data burst and quickly selects the best clock phase by a control logic circuit. Then, an analog delay-locked loop (DLL) keeps track of data transitions and removes phase errors throughout the burst. The combination of the fast phase detection mechanism and a feedback loop based on DLL allows both fast response and manageable jitter performance in the burst-mode application. A new efficient numerical algorithm is developed to analyze holey optical fibers. The algorithm has been verified against experimental data, and is exploited to design holey optical fibers optimized for the discrete Raman amplification.

Differential ability of formononetin to stimulate proliferation of endothelial cells and breast cancer cells via a feedback loop involving MicroRNA-375, RASD1, and ERα.

PubMed

Chen, Jian; Zhang, Xing; Wang, Yong; Ye, Yu; Huang, Zhaoquan

2018-05-02

For postmenopausal cardiovascular disease, long-term estrogen therapy may increase the risk of breast cancer. To reduce this risk, estrogen may be replaced with the phytoestrogen formononetin, but how formononetin acts on vascular endothelial cells (ECs) and breast cancer cells is unclear. Here, we show that low concentrations of formononetin induced proliferation and inhibited apoptosis more strongly in cultured human umbilical vein endothelial cells (HUVECs) than in breast cancer cells expressing estrogen receptor α (ERα) (MCF-7, BT474) or not (MDA-MB-231), and that this differential stimulation was associated with miR-375 up-regulation in HUVECs. For the first time, we demonstrate the presence of a feedback loop involving miR-375, ras dexamethasone-induced 1 (RASD1), and ERα in normal HUVECs, and we show that formononetin stimulated this feedback loop in HUVECs but not in MCF-7 or BT474 cells. In all three cell lines, formononetin increased Akt phosphorylation and Bcl-2 expression. Inhibiting miR-375 blocked these changes and increased proliferation in HUVECs, but not in MCF-7 or BT474 cells. In ovariectomized rats, formononetin increased uterine weight and caused similar changes in levels of miR-375, RASD1, ERα, and Bcl-2 in aortic ECs as in cultured HUVECs. In mice bearing MCF-7 xenografts, tumor growth was stimulated by 17β-estradiol but not by formononetin. These results suggest selective action of formononetin in ECs (proliferation stimulation and apoptosis inhibition) relative to breast cancer cells, possibly via a feedback loop involving miR-375, RASD1, and ERα. This differential effect may explain why formononetin may not increase the risk of postmenopausal breast cancer. © 2018 Wiley Periodicals, Inc.

Use of an open-loop system to increase physical activity

USDA-ARS?s Scientific Manuscript database

This study evaluated the effectiveness of an open-loop system that reinforces physical activity with TV watching to increase children’s physical activity. Non-overweight, sedentary boys and girls (8-12 y) were randomized to a group that received feedback of activity counts + reinforcement for physic...

Clinical and optical intraocular performance of rotationally asymmetric multifocal IOL plate-haptic design versus C-loop haptic design.

PubMed

Alió, Jorge L; Plaza-Puche, Ana B; Javaloy, Jaime; Ayala, María José; Vega-Estrada, Alfredo

2013-04-01

To compare the visual and intraocular optical quality outcomes with different designs of the refractive rotationally asymmetric multifocal intraocular lens (MFIOL) (Lentis Mplus; Oculentis GmbH, Berlin, Germany) with or without capsular tension ring (CTR) implantation. One hundred thirty-five consecutive eyes of 78 patients with cataract (ages 36 to 82 years) were divided into three groups: 43 eyes implanted with the C-Loop haptic design without CTR (C-Loop haptic only group); 47 eyes implanted with the C-Loop haptic design with CTR (C-Loop haptic with CTR group); and 45 eyes implanted with the plate-haptic design (plate-haptic group). Visual acuity, contrast sensitivity, defocus curve, and ocular and intraocular optical quality were evaluated at 3 months postoperatively. Significant differences in the postoperative sphere were found (P = .01), with a more myopic postoperative refraction for the C-Loop haptic only group. No significant differences were detected in photopic and scotopic contrast sensitivity among groups (P ⩾ .05). Significantly better visual acuities were present in the C-Loop haptic with CTR group for the defocus levels of -2.0, -1.5, -1.0, and -0.50 D (P ⩽.03). Statistically significant differences among groups were found in total intraocular root mean square (RMS), high-order intraocular RMS, and intraocular coma-like RMS aberrations (P ⩽.04), with lower values from the plate-haptic group. The plate-haptic design and the C-Loop haptic design with CTR implantation both allow good visual rehabilitation. However, better refractive predictability and intraocular optical quality was obtained with the plate-haptic design without CTR implantation. The plate-haptic design seems to be a better design to support rotational asymmetric MFIOL optics. Copyright 2013, SLACK Incorporated.

Identifying Functional Mechanisms of Gene and Protein Regulatory Networks in Response to a Broader Range of Environmental Stresses

PubMed Central

Li, Cheng-Wei; Chen, Bor-Sen

2010-01-01

Cellular responses to sudden environmental stresses or physiological changes provide living organisms with the opportunity for final survival and further development. Therefore, it is an important topic to understand protective mechanisms against environmental stresses from the viewpoint of gene and protein networks. We propose two coupled nonlinear stochastic dynamic models to reconstruct stress-activated gene and protein regulatory networks via microarray data in response to environmental stresses. According to the reconstructed gene/protein networks, some possible mutual interactions, feedforward and feedback loops are found for accelerating response and filtering noises in these signaling pathways. A bow-tie core network is also identified to coordinate mutual interactions and feedforward loops, feedback inhibitions, feedback activations, and cross talks to cope efficiently with a broader range of environmental stresses with limited proteins and pathways. PMID:20454442

Towards random matrix model of breaking the time-reversal invariance of elastic waves in chaotic cavities by feedback

NASA Astrophysics Data System (ADS)

Antoniuk, Oleg; Sprik, Rudolf

2010-03-01

We developed a random matrix model to describe the statistics of resonances in an acoustic cavity with broken time-reversal invariance. Time-reversal invariance braking is achieved by connecting an amplified feedback loop between two transducers on the surface of the cavity. The model is based on approach [1] that describes time- reversal properties of the cavity without a feedback loop. Statistics of eigenvalues (nearest neighbor resonance spacing distributions and spectral rigidity) has been calculated and compared to the statistics obtained from our experimental data. Experiments have been performed on aluminum block of chaotic shape confining ultrasound waves. [1] Carsten Draeger and Mathias Fink, One-channel time- reversal in chaotic cavities: Theoretical limits, Journal of Acoustical Society of America, vol. 105, Nr. 2, pp. 611-617 (1999)

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.

Multiplexing Readout of TES Microcalorimeters Based on Analog Baseband Feedback

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

Takei, Y.; Yamasaki, N.Y; Mitsuda, K.

2009-12-16

A TES microcalorimeter array is a promising spectrometer with excellent energy resolution and a moderate imaging capability. To realize a large format array in space, multiplexing the TES signals at the low tempersture stage is mandatory. We are developing frequency division multiplexing (FDM) based on baseband feedback technique. In FDM, each TES is AC-biased with a different carrier frequency. Signals from several pixels are summed and then read out by one SQUID. The maximum number of multiplexed pixels are limited by the frequency band in which the SQUID can be operated in a flux-locked loop, which is {approx}1 MHz withmore » standard flux-locked loop circuit. In the baseband feedback, the signal ({approx}10 kHz band) from the TES is once demodulated. Then a reconstructed copy of the modulated signal with an appropriate phase is fed back to the SQUID input coil to maintain an approximately constant magnetic flux. This can be implemented even for large cable delays and automatically suppresses the carrier. We developed a prototype electronics for the baseband feedback based on an analog phase sensitive detector (PSD) and a multiplier. Combined with Seiko 80-SSA SQUID amp, open-loop gain of 8 has been obtained for 10 kHz baseband signal at 5 MHz carrier frequency, with a moderate noise contribution of 27pA/{radical}(Hz) at input.« less

Solid-state lasers for coherent communication and remote sensing

NASA Technical Reports Server (NTRS)

Byer, Robert L.

1992-01-01

Semiconductor-diode laser-pumped solid-state lasers have properties that are superior to other lasers for the applications of coherent communication and remote sensing. These properties include efficiency, reliability, stability, and capability to be scaled to higher powers. We have demonstrated that an optical phase-locked loop can be used to lock the frequency of two diode-pumped 1.06 micron Nd:YAG lasers to levels required for coherent communication. Monolithic nonplanar ring oscillators constructed from solid pieces of the laser material provide better than 10 kHz frequency stability over 0.1 sec intervals. We have used active feedback stabilization of the cavity length of these lasers to demonstrate 0.3 Hz frequency stabilization relative to a reference cavity. We have performed experiments and analysis to show that optical parametric oscillators (OPO's) reproduce the frequency stability of the pump laser in outputs that can be tuned to arbitrary wavelengths. Another measurement performed in this program has demonstrated the sub-shot-noise character of correlations of the fluctuations in the twin output of OPO's. Measurements of nonlinear optical coefficients by phase-matched second harmonic generation are helping to resolve inconsistency in these important parameters.

Passive method of eliminating accommodation/convergence disparity in stereoscopic head-mounted displays

NASA Astrophysics Data System (ADS)

Eichenlaub, Jesse B.

2005-03-01

The difference in accommodation and convergence distance experienced when viewing stereoscopic displays has long been recognized as a source of visual discomfort. It is especially problematic in head mounted virtual reality and enhanced reality displays, where images must often be displayed across a large depth range or superimposed on real objects. DTI has demonstrated a novel method of creating stereoscopic images in which the focus and fixation distances are closely matched for all parts of the scene from close distances to infinity. The method is passive in the sense that it does not rely on eye tracking, moving parts, variable focus optics, vibrating optics, or feedback loops. The method uses a rapidly changing illumination pattern in combination with a high speed microdisplay to create cones of light that converge at different distances to form the voxels of a high resolution space filling image. A bench model display was built and a series of visual tests were performed in order to demonstrate the concept and investigate both its capabilities and limitations. Results proved conclusively that real optical images were being formed and that observers had to change their focus to read text or see objects at different distances

Stabilizing Microwave Frequency of a Photonic Oscillator

NASA Technical Reports Server (NTRS)

Maleki, Lute; Yu, Nan; Tu, Meirong

2006-01-01

A scheme for stabilizing the frequency of a microwave signal is proposed that exploits the operational characteristics of a coupled optoelectronic oscillator (COEO) and related optoelectronic equipment. An essential element in the scheme is a fiber mode-locked laser (MLL), the optical frequency of which is locked to an atomic transition. In this scheme, the optical frequency stability of the mode-locked laser is transferred to that of the microwave in the same device. Relative to prior schemes for using wideband optical frequency comb to stabilize microwave signals, this scheme is simpler and lends itself more readily to implementation in relatively compact, rugged equipment. The anticipated development of small, low-power, lightweight, highly stable microwave oscillators based on this scheme would afford great benefits in communication, navigation, metrology, and fundamental sciences. COEOs of various designs, at various stages of development, in some cases called by different names, have been described in a number of prior NASA Tech Briefs articles. A COEO is an optoelectronic apparatus that generates both short (picosecond) optical pulses and a steady microwave signal having an ultrahigh degree of spectral purity. The term "coupled optoelectronic" in the full name of such an apparatus signifies that its optical and electronic oscillations are coupled to each other in a single device. The present frequency-stabilization scheme is best described indirectly by describing the laboratory apparatus used to demonstrate it. The apparatus (see figure) includes a COEO that generates a comb-like optical spectrum, the various frequency components of which interfere, producing short optical pulses. This spectrum is centered at a nominal wavelength of 1,560 nm. The spectrum separation of this comb is about 10 GHz, as determined primarily by the length of an optical loop and the bandpass filter in the microwave feedback loop. The optical loop serves as microwave resonator having a very high value of the resonance quality factor (Q). The optical frequency of MLL is then stabilized by locking it to an atomic transition as described below. The COEO contains a tunable 1-nm band-pass optical filter and a piezoelectric-transducer (PZT) drum over which a stretch of fiber is wound. The 1-nm-wide pass band of the filter provides coarse tuning to overlap the frequency comb with the atomic transition frequency. Controlled stretching of the fiber by means of the PZT drum can be used in conjunction with temperature control for locking the laser frequency. To reference to an atomic resonance at 780 nm in this demonstration setup, the optical output of the COEO at 1,560 nm is fed through an erbium-doped-fiber amplifier (EDFA) to a frequency doubler in the form of a periodically poled lithium niobate (PPLN) crystal. The frequency-doubled output is combined with the output of a separate frequency-stabilized diode laser at a photodetector. As described thus far, the two 780-nm laser subsystems are nominally independent of each other and can, therefore, operate at different frequencies. Hence, at the photodetector, the two laser beams interfere, so that the output of the photodetector includes a beat note (a component at the difference between the two laser frequencies).

All-digital signal-processing open-loop fiber-optic gyroscope with enlarged dynamic range.

PubMed

Wang, Qin; Yang, Chuanchuan; Wang, Xinyue; Wang, Ziyu

2013-12-15

We propose and realize a new open-loop fiber-optic gyroscope (FOG) with an all-digital signal-processing (DSP) system where an all-digital phase-locked loop is employed for digital demodulation to eliminate the variation of the source intensity and suppress the bias drift. A Sagnac phase-shift tracking method is proposed to enlarge the dynamic range, and, with its aid, a new open-loop FOG, which can achieve a large dynamic range and high sensitivity at the same time, is realized. The experimental results show that compared with the conventional open-loop FOG with the same fiber coil and optical devices, the proposed FOG reduces the bias instability from 0.259 to 0.018 deg/h, and the angle random walk from 0.031 to 0.006 deg/h(1/2), moreover, enlarges the dynamic range to ±360 deg/s, exceeding the maximum dynamic range ±63 deg/s of the conventional open-loop FOG.

System properties, feedback control and effector coordination of human temperature regulation.

PubMed

Werner, Jürgen

2010-05-01

The aim of human temperature regulation is to protect body processes by establishing a relative constancy of deep body temperature (regulated variable), in spite of external and internal influences on it. This is basically achieved by a distributed multi-sensor, multi-processor, multi-effector proportional feedback control system. The paper explains why proportional control implies inherent deviations of the regulated variable from the value in the thermoneutral zone. The concept of feedback of the thermal state of the body, conveniently represented by a high-weighted core temperature (T (c)) and low-weighted peripheral temperatures (T (s)) is equivalent to the control concept of "auxiliary feedback control", using a main (regulated) variable (T (c)), supported by an auxiliary variable (T (s)). This concept implies neither regulation of T (s) nor feedforward control. Steady-states result in the closed control-loop, when the open-loop properties of the (heat transfer) process are compatible with those of the thermoregulatory processors. They are called operating points or balance points and are achieved due to the inherent property of dynamical stability of the thermoregulatory feedback loop. No set-point and no comparison of signals (e.g. actual-set value) are necessary. Metabolic heat production and sweat production, though receiving the same information about the thermal state of the body, are independent effectors with different thresholds and gains. Coordination between one of these effectors and the vasomotor effector is achieved by the fact that changes in the (heat transfer) process evoked by vasomotor control are taken into account by the metabolic/sweat processor.

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

CALL FOR PAPERS: Quantum control

NASA Astrophysics Data System (ADS)

Mancini, Stefano; Wiseman, Howard M.; Man'ko, Vladimir I.

2004-10-01

Over the last few decades, the achievements of highly precise technologies for manipulating systems at quantum scales have paved the way for the development of quantum control. Moreover, the proliferation of results in quantum information suggest that control theory might profitably be re-examined from this perspective. Journal of Optics B: Quantum and Semiclassical Optics will publish a topical issue devoted to quantum control. The Guest Editors invite contributions from researchers working in any area related to quantum control. Topics to be covered include: • Quantum Hamiltonian dynamics and programming control • Quantum decoherence control • Open loop control • Closed loop (feedback) control • Quantum measurement theory • Quantum noise and filtering • Estimation and decision theory • Quantum error correction • Group representation in quantum control • Coherent control in quantum optics and lasers • Coherent control in cavity QED and atom optics • Coherent control in molecular dynamics The topical issue is scheduled for publication in November 2005 and the DEADLINE for submission of contributions is 28 February 2005. All contributions will be peer-reviewed in accordance with the normal refereeing procedures and standards of Journal of Optics B: Quantum and Semiclassical Optics. Submissions should preferably be in either standard LaTeX form or Microsoft Word. Advice on publishing your work in the journal may be found at www.iop.org/journals/authors/jopb. Enquiries regarding this topical issue may be addressed to the Publisher, Dr Claire Bedrock (claire.bedrock@iop.org). There are no page charges for publication. The corresponding author of each paper published will receive a complimentary copy of the topical issue. Contributions to the topical issue should preferably be submitted electronically at www.iop.org/journals/authors/jopb or by e-mail to jopb@iop.org. Authors unable to submit online or by e-mail may send hard copy contributions (enclosing the electronic code) to: Journal of Optics B: Quantum and Semiclassical Optics, Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK. All contributions should be accompanied by a readme file or covering letter, quoting `JOPB Topical Issue - Quantum control', giving the postal and e-mail addresses for correspondence. Any subsequent change of address should be notified to the publishing office. We look forward to receiving your contribution to this topical issue.

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber and feedback fiber loop

NASA Astrophysics Data System (ADS)

Feng, Suchun; Xu, Ou; Lu, Shaohua; Ning, Tigang; Jian, Shuisheng

2009-06-01

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating (PMFBG) is demonstrated. Due to the enhancement of the polarization hole burning (PHB) by the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a compound-ring cavity and a saturable absorber (SA). The optical signal-to-noise ratio (OSNR) is over 45 dB. The amplitude variation in nearly one and half an hour is less than 0.2 dB.

Extended-bandwidth frequency sweeps of a distributed feedback laser using combined injection current and temperature modulation

NASA Astrophysics Data System (ADS)

Hefferman, Gerald; Chen, Zhen; Wei, Tao

2017-07-01

This article details the generation of an extended-bandwidth frequency sweep using a single, communication grade distributed feedback (DFB) laser. The frequency sweep is generated using a two-step technique. In the first step, injection current modulation is employed as a means of varying the output frequency of a DFB laser over a bandwidth of 99.26 GHz. A digital optical phase lock loop is used to lock the frequency sweep speed during current modulation, resulting in a linear frequency chirp. In the second step, the temperature of the DFB laser is modulated, resulting in a shifted starting laser output frequency. A laser frequency chirp is again generated beginning at this shifted starting frequency, resulting in a frequency-shifted spectrum relative to the first recorded data. This process is then repeated across a range of starting temperatures, resulting in a series of partially overlapping, frequency-shifted spectra. These spectra are then aligned using cross-correlation and combined using averaging to form a single, broadband spectrum with a total bandwidth of 510.9 GHz. In order to investigate the utility of this technique, experimental testing was performed in which the approach was used as the swept-frequency source of a coherent optical frequency domain reflectometry system. This system was used to interrogate an optical fiber containing a 20 point, 1-mm pitch length fiber Bragg grating, corresponding to a period of 100 GHz. Using this technique, both the periodicity of the grating in the frequency domain and the individual reflector elements of the structure in the time domain were resolved, demonstrating the technique's potential as a method of extending the sweeping bandwidth of semiconductor lasers for frequency-based sensing applications.

A robust optical parametric oscillator and receiver telescope for differential absorption lidar of greenhouse gases

NASA Astrophysics Data System (ADS)

Robinson, Iain; Jack, James W.; Rae, Cameron F.; Moncrieff, John B.

2015-10-01

We report the development of a differential absorption lidar instrument (DIAL) designed and built specifically for the measurement of anthropogenic greenhouse gases in the atmosphere. The DIAL is integrated into a commercial astronomical telescope to provide high-quality receiver optics and enable automated scanning for three-dimensional lidar acquisition. The instrument is portable and can be set up within a few hours in the field. The laser source is a pulsed optical parametric oscillator (OPO) which outputs light at a wavelength tunable near 1.6 μm. This wavelength region, which is also used in telecommunications devices, provides access to absorption lines in both carbon dioxide at 1573 nm and methane at 1646 nm. To achieve the critical temperature stability required for a laserbased field instrument the four-mirror OPO cavity is machined from a single aluminium block. A piezoactuator adjusts the cavity length to achieve resonance and this is maintained over temperature changes through the use of a feedback loop. The laser output is continuously monitored with pyroelectric detectors and a custom-built wavemeter. The OPO is injection seeded by a temperature-stabilized distributed feedback laser diode (DFB-LD) with a wavelength locked to the absorption line centre (on-line) using a gas cell containing pure carbon dioxide. A second DFB-LD is tuned to a nearby wavelength (off-line) to provide the reference required for differential absorption measurements. A similar system has been designed and built to provide the injection seeding wavelengths for methane. The system integrates the DFB-LDs, drivers, locking electronics, gas cell and balanced photodetectors. The results of test measurements of carbon dioxide are presented and the development of the system is discussed, including the adaptation required for the measurement of methane.

Extended-bandwidth frequency sweeps of a distributed feedback laser using combined injection current and temperature modulation.

PubMed

Hefferman, Gerald; Chen, Zhen; Wei, Tao

2017-07-01

This article details the generation of an extended-bandwidth frequency sweep using a single, communication grade distributed feedback (DFB) laser. The frequency sweep is generated using a two-step technique. In the first step, injection current modulation is employed as a means of varying the output frequency of a DFB laser over a bandwidth of 99.26 GHz. A digital optical phase lock loop is used to lock the frequency sweep speed during current modulation, resulting in a linear frequency chirp. In the second step, the temperature of the DFB laser is modulated, resulting in a shifted starting laser output frequency. A laser frequency chirp is again generated beginning at this shifted starting frequency, resulting in a frequency-shifted spectrum relative to the first recorded data. This process is then repeated across a range of starting temperatures, resulting in a series of partially overlapping, frequency-shifted spectra. These spectra are then aligned using cross-correlation and combined using averaging to form a single, broadband spectrum with a total bandwidth of 510.9 GHz. In order to investigate the utility of this technique, experimental testing was performed in which the approach was used as the swept-frequency source of a coherent optical frequency domain reflectometry system. This system was used to interrogate an optical fiber containing a 20 point, 1-mm pitch length fiber Bragg grating, corresponding to a period of 100 GHz. Using this technique, both the periodicity of the grating in the frequency domain and the individual reflector elements of the structure in the time domain were resolved, demonstrating the technique's potential as a method of extending the sweeping bandwidth of semiconductor lasers for frequency-based sensing applications.

Optimization of Closed Loop Eigenvalues: Maneuvering, Vibration Control, and Structure/Control Design Iteration for Flexible Spacecraft.

DTIC Science & Technology

1986-05-31

Nonlinear Feedback Control 8-16 for Spacecraft Attitude Maneuvers" 2. " Spacecraft Attitude Control Using 17-35... nonlinear state feedback control laws are developed for space- craft attitude control using the Euler parameters and conjugate angular momenta. Time... Nonlinear Feedback Control for Spacecraft Attitude Maneuvers," to appear in AIAA J. of Guidance, Control, and Dynamics, (AIAA Paper No. 83-2230-CP,

Closed-form recursive formula for an optimal tracker with terminal constraints

NASA Technical Reports Server (NTRS)

Juang, J. N.; Turner, J. D.; Chun, H. M.

1986-01-01

Feedback control laws are derived for a class of optimal finite time tracking problems with terminal constraints. Analytical solutions are obtained for the feedback gain and the closed-loop response trajectory. Such formulations are expressed in recursive forms so that a real-time computer implementation becomes feasible. An example involving the feedback slewing of a flexible spacecraft is given to illustrate the validity and usefulness of the formulations.

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

PubMed

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

2017-11-01

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

Highly integrated optical heterodyne phase-locked loop with phase/frequency detection.

PubMed

Lu, Mingzhi; Park, Hyunchul; Bloch, Eli; Sivananthan, Abirami; Bhardwaj, Ashish; Griffith, Zach; Johansson, Leif A; Rodwell, Mark J; Coldren, Larry A

2012-04-23

A highly-integrated optical phase-locked loop with a phase/frequency detector and a single-sideband mixer (SSBM) has been proposed and demonstrated for the first time. A photonic integrated circuit (PIC) has been designed, fabricated and tested, together with an electronic IC (EIC). The PIC integrates a widely-tunable sampled-grating distributed-Bragg-reflector laser, an optical 90 degree hybrid and four high-speed photodetectors on the InGaAsP/InP platform. The EIC adds a single-sideband mixer, and a digital phase/frequency detector, to provide single-sideband heterodyne locking from -9 GHz to 7.5 GHz. The loop bandwith is 400 MHz. © 2012 Optical Society of America

Laboratory demonstrations on a pyramid wavefront sensor without modulation for closed-loop adaptive optics system.

PubMed

Wang, Shengqian; Rao, Changhui; Xian, Hao; Zhang, Jianlin; Wang, Jianxin; Liu, Zheng

2011-04-25

The feasibility and performance of the pyramid wavefront sensor without modulation used in closed-loop adaptive optics system is investigated in this paper. The theory concepts and some simulation results are given to describe the detection trend and the linearity range of such a sensor with the aim to better understand its properties, and then a laboratory setup of the adaptive optics system based on this sensor and the liquid-crystal spatial light modulator is built. The correction results for the individual Zernike aberrations and the Kolmogorov phase screens are presented to demonstrate that the pyramid wavefront sensor without modulation can work as expected for closed-loop adaptive optics system.

The early history of the closed loop fiber optic gyro and derivative sensors at McDonnell Douglas, Blue Road Research and Columbia Gorge Research

NASA Astrophysics Data System (ADS)

Udd, Eric

2016-05-01

On September 29, 1977 the first written disclosure of a closed loop fiber optic gyro was witnessed and signed off by four people at McDonnell Douglas Astronautics Company in Huntington Beach, California. Over the next ten years a breadboard demonstration unit, and several prototypes were built. In 1987 the fundamental patent for closed loop operation began a McDonnell Douglas worldwide licensing process. Internal fiber optic efforts were redirected to derivative sensors and inventions. This included development of acoustic, strain and distributed sensors as well as a Sagnac interferometer based secure fiber optic communication system and the new field of fiber optic smart structures. This paper provides an overview of these activities and transitions.

Identification of pilot-vehicle dynamics from simulation and flight test

NASA Technical Reports Server (NTRS)

Hess, Ronald A.

1990-01-01

The paper discusses an identification problem in which a basic feedback control structure, or pilot control strategy, is hypothesized. Identification algorithms are employed to determine the particular form of pilot equalization in each feedback loop. It was found that both frequency- and time-domain identification techniques provide useful information.

Using Control Theory to Teach Control Theory (or Any Other Course).

ERIC Educational Resources Information Center

Mansfield, George

1979-01-01

Describes an undergraduate automatic controls course in which the teaching-learning process is regarded as a closed loop feedback system. The three basic components of the system: the controller, the plant, and the learning sensors are identified as the teacher, the student, and student feedback respectively. (SMB)

Smith predictor-based multiple periodic disturbance compensation for long dead-time processes

NASA Astrophysics Data System (ADS)

Tan, Fang; Li, Han-Xiong; Shen, Ping

2018-05-01

Many disturbance rejection methods have been proposed for processes with dead-time, while these existing methods may not work well under multiple periodic disturbances. In this paper, a multiple periodic disturbance rejection is proposed under the Smith predictor configuration for processes with long dead-time. One feedback loop is added to compensate periodic disturbance while retaining the advantage of the Smith predictor. With information of the disturbance spectrum, the added feedback loop can remove multiple periodic disturbances effectively. The robust stability can be easily maintained through the rigorous analysis. Finally, simulation examples demonstrate the effectiveness and robustness of the proposed method for processes with long dead-time.

Nonlinear cellular dynamics of keratinocytes in normal and psoriatic epidermis under action of UV radiation

NASA Astrophysics Data System (ADS)

Stolnitz, Mikhail M.; Medvedev, Boris A.; Gribko, Tatyana V.

2004-05-01

The semi-phenomenological model of epidermal cell dynamics is submitted. The model takes into account three types of basal layer keratinocytes (stem, transient amplifying, terminally differentiated), distribution of first two types cells on mitotic cycle stages and resting states, keratinocytes-lymphocytes interactions that provide a positive feedback loop, influence of more differentiated cells on their progenitors that provide a negative feedback loop. Simplified model are developed and its stationary solutions are received. The opportunity of interpretation of some received modes as corresponding to various stages of psoriasis is discussed. Influence of UV-radiation on transitions between various modes of epidermis functioning is qualitatively analyzed.

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

PubMed

Ho, Hung-Jung; Chen, Tien-Chi

2009-11-01

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

? PID output-feedback control under event-triggered protocol

NASA Astrophysics Data System (ADS)

Zhao, Di; Wang, Zidong; Ding, Derui; Wei, Guoliang; Alsaadi, Fuad E.

2018-07-01

This paper is concerned with the ? proportional-integral-derivative (PID) output-feedback control problem for a class of linear discrete-time systems under event-triggered protocols. The controller and the actuators are connected through a communication network of limited bandwidth, and an event-triggered communication mechanism is adopted to decide when a certain control signal should be transmitted to the respective actuator. Furthermore, a novel PID output-feedback controller is designed where the accumulative sum-loop (the counterpart to the integral-loop in the continues-time setting) operates on a limited time-window with hope to mitigate the effect from the past measurement data. The main objective of the problem under consideration is to design a desired PID controller such that the closed-loop system is exponentially stable and the prescribed ? disturbance rejection attenuation level is guaranteed under event-triggered protocols. By means of the Lyapunov stability theory combined with the orthogonal decomposition, sufficient conditions are established under which the addressed PID controller design problem is recast into a linear convex optimization one that can be easily solved via available software packages. Finally, a simulation example is exploited to illustrate the usefulness and effectiveness of the established control scheme.

Evolutionary divergence of core and post-translational circadian clock genes in the pitcher-plant mosquito, Wyeomyia smithii.

PubMed

Tormey, Duncan; Colbourne, John K; Mockaitis, Keithanne; Choi, Jeong-Hyeon; Lopez, Jacqueline; Burkhart, Joshua; Bradshaw, William; Holzapfel, Christina

2015-10-06

Internal circadian (circa, about; dies, day) clocks enable organisms to maintain adaptive timing of their daily behavioral activities and physiological functions. Eukaryotic clocks consist of core transcription-translation feedback loops that generate a cycle and post-translational modifiers that maintain that cycle at about 24 h. We use the pitcher-plant mosquito, Wyeomyia smithii (subfamily Culicini, tribe Sabethini), to test whether evolutionary divergence of the circadian clock genes in this species, relative to other insects, has involved primarily genes in the core feedback loops or the post-translational modifiers. Heretofore, there is no reference transcriptome or genome sequence for any mosquito in the tribe Sabethini, which includes over 375 mainly circumtropical species. We sequenced, assembled and annotated the transcriptome of W. smithii containing nearly 95 % of conserved single-copy orthologs in animal genomes. We used the translated contigs and singletons to determine the average rates of circadian clock-gene divergence in W. smithii relative to three other mosquito genera, to Drosophila, to the butterfly, Danaus, and to the wasp, Nasonia. Over 1.08 million cDNA sequence reads were obtained consisting of 432.5 million nucleotides. Their assembly produced 25,904 contigs and 54,418 singletons of which 62 % and 28 % are annotated as protein-coding genes, respectively, sharing homology with other animal proteomes. The W. smithii transcriptome includes all nine circadian transcription-translation feedback-loop genes and all eight post-translational modifier genes we sought to identify (Fig. 1). After aligning translated W. smithii contigs and singletons from this transcriptome with other insects, we determined that there was no significant difference in the average divergence of W. smithii from the six other taxa between the core feedback-loop genes and post-translational modifiers. The characterized transcriptome is sufficiently complete and of sufficient quality to have uncovered all of the insect circadian clock genes we sought to identify (Fig. 1). Relative divergence does not differ between core feedback-loop genes and post-translational modifiers of those genes in a Sabethine species (W. smithii) that has experienced a continual northward dispersal into temperate regions of progressively longer summer day lengths as compared with six other insect taxa. An associated microarray platform derived from this work will enable the investigation of functional genomics of circadian rhythmicity, photoperiodic time measurement, and diapause along a photic and seasonal geographic gradient.

Reliable numerical computation in an optimal output-feedback design

NASA Technical Reports Server (NTRS)

Vansteenwyk, Brett; Ly, Uy-Loi

1991-01-01

A reliable algorithm is presented for the evaluation of a quadratic performance index and its gradients with respect to the controller design parameters. The algorithm is a part of a design algorithm for optimal linear dynamic output-feedback controller that minimizes a finite-time quadratic performance index. The numerical scheme is particularly robust when it is applied to the control-law synthesis for systems with densely packed modes and where there is a high likelihood of encountering degeneracies in the closed-loop eigensystem. This approach through the use of an accurate Pade series approximation does not require the closed-loop system matrix to be diagonalizable. The algorithm was included in a control design package for optimal robust low-order controllers. Usefulness of the proposed numerical algorithm was demonstrated using numerous practical design cases where degeneracies occur frequently in the closed-loop system under an arbitrary controller design initialization and during the numerical search.

Structural Damage Detection Using Virtual Passive Controllers

NASA Technical Reports Server (NTRS)

Lew, Jiann-Shiun; Juang, Jer-Nan

2001-01-01

This paper presents novel approaches for structural damage detection which uses the virtual passive controllers attached to structures, where passive controllers are energy dissipative devices and thus guarantee the closed-loop stability. The use of the identified parameters of various closed-loop systems can solve the problem that reliable identified parameters, such as natural frequencies of the open-loop system may not provide enough information for damage detection. Only a small number of sensors are required for the proposed approaches. The identified natural frequencies, which are generally much less sensitive to noise and more reliable than the identified natural frequencies, are used for damage detection. Two damage detection techniques are presented. One technique is based on the structures with direct output feedback controllers while the other technique uses the second-order dynamic feedback controllers. A least-squares technique, which is based on the sensitivity of natural frequencies to damage variables, is used for accurately identifying the damage variables.

A functional genomics approach reveals CHE as a component of the Arabidopsis circadian clock.

PubMed

Pruneda-Paz, Jose L; Breton, Ghislain; Para, Alessia; Kay, Steve A

2009-03-13

Transcriptional feedback loops constitute the molecular circuitry of the plant circadian clock. In Arabidopsis, a core loop is established between CCA1 and TOC1. Although CCA1 directly represses TOC1, the TOC1 protein has no DNA binding domains, which suggests that it cannot directly regulate CCA1. We established a functional genomic strategy that led to the identification of CHE, a TCP transcription factor that binds specifically to the CCA1 promoter. CHE is a clock component partially redundant with LHY in the repression of CCA1. The expression of CHE is regulated by CCA1, thus adding a CCA1/CHE feedback loop to the Arabidopsis circadian network. Because CHE and TOC1 interact, and CHE binds to the CCA1 promoter, a molecular linkage between TOC1 and CCA1 gene regulation is established.

Self-referenced locking of optical coherence by single-detector electronic-frequency tagging

NASA Astrophysics Data System (ADS)

Shay, T. M.; Benham, Vincent; Spring, Justin; Ward, Benjamin; Ghebremichael, F.; Culpepper, Mark A.; Sanchez, Anthony D.; Baker, J. T.; Pilkington, D.; Berdine, Richard

2006-02-01

We report a novel coherent beam combining technique. This is the first actively phase locked optical fiber array that eliminates the need for a separate reference beam. In addition, only a single photodetector is required. The far-field central spot of the array is imaged onto the photodetector to produce the phase control loop signals. Each leg of the fiber array is phase modulated with a separate RF frequency, thus tagging the optical phase shift for each leg by a separate RF frequency. The optical phase errors for the individual array legs are separated in the electronic domain. In contrast with the previous active phase locking techniques, in our system the reference beam is spatially overlapped with all the RF modulated fiber leg beams onto a single detector. The phase shift between the optical wave in the reference leg and in the RF modulated legs is measured separately in the electronic domain and the phase error signal is feedback to the LiNbO 3 phase modulator for that leg to minimize the phase error for that leg relative to the reference leg. The advantages of this technique are 1) the elimination of the reference beam and beam combination optics and 2) the electronic separation of the phase error signals without any degradation of the phase locking accuracy. We will present the first theoretical model for self-referenced LOCSET and describe experimental results for a 3 x 3 array.

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

PubMed

Sastrawan, J; Jones, C; Akhalwaya, I; Uys, H; Biercuk, M J

2016-08-01

We introduce concepts from optimal estimation to the stabilization of precision frequency standards limited by noisy local oscillators. We develop a theoretical framework casting various measures for frequency standard variance in terms of frequency-domain transfer functions, capturing the effects of feedback stabilization via a time series of Ramsey measurements. Using this framework, we introduce an optimized hybrid predictive feedforward measurement protocol that employs results from multiple past measurements and transfer-function-based calculations of measurement covariance to improve the accuracy of corrections within the feedback loop. In the presence of common non-Markovian noise processes these measurements will be correlated in a calculable manner, providing a means to capture the stochastic evolution of the local oscillator frequency during the measurement cycle. We present analytic calculations and numerical simulations of oscillator performance under competing feedback schemes and demonstrate benefits in both correction accuracy and long-term oscillator stability using hybrid feedforward. Simulations verify that in the presence of uncompensated dead time and noise with significant spectral weight near the inverse cycle time predictive feedforward outperforms traditional feedback, providing a path towards developing a class of stabilization software routines for frequency standards limited by noisy local oscillators.

Squeezed light in an optical parametric oscillator network with coherent feedback quantum control.

PubMed

Crisafulli, Orion; Tezak, Nikolas; Soh, Daniel B S; Armen, Michael A; Mabuchi, Hideo

2013-07-29

We present squeezing and anti-squeezing spectra of the output from a degenerate optical parametric oscillator (OPO) network arranged in different coherent quantum feedback configurations. One OPO serves as a quantum plant, the other as a quantum controller. The addition of coherent feedback enables shaping of the output squeezing spectrum of the plant, and is found to be capable of pushing the frequency of maximum squeezing away from the optical driving frequency and broadening the spectrum over a wider frequency band. The experimental results are in excellent agreement with the developed theory, and illustrate the use of coherent quantum feedback to engineer the quantum-optical properties of the plant OPO output.

Model for a pulsed terahertz quantum cascade laser under optical feedback.

PubMed

Agnew, Gary; Grier, Andrew; Taimre, Thomas; Lim, Yah Leng; Bertling, Karl; Ikonić, Zoran; Valavanis, Alexander; Dean, Paul; Cooper, Jonathan; Khanna, Suraj P; Lachab, Mohammad; Linfield, Edmund H; Davies, A Giles; Harrison, Paul; Indjin, Dragan; Rakić, Aleksandar D

2016-09-05

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

Design of a haptic device with grasp and push-pull force feedback for a master-slave surgical robot.

PubMed

Hu, Zhenkai; Yoon, Chae-Hyun; Park, Samuel Byeongjun; Jo, Yung-Ho

2016-07-01

We propose a portable haptic device providing grasp (kinesthetic) and push-pull (cutaneous) sensations for optical-motion-capture master interfaces. Although optical-motion-capture master interfaces for surgical robot systems can overcome the stiffness, friction, and coupling problems of mechanical master interfaces, it is difficult to add haptic feedback to an optical-motion-capture master interface without constraining the free motion of the operator's hands. Therefore, we utilized a Bowden cable-driven mechanism to provide the grasp and push-pull sensation while retaining the free hand motion of the optical-motion capture master interface. To evaluate the haptic device, we construct a 2-DOF force sensing/force feedback system. We compare the sensed force and the reproduced force of the haptic device. Finally, a needle insertion test was done to evaluate the performance of the haptic interface in the master-slave system. The results demonstrate that both the grasp force feedback and the push-pull force feedback provided by the haptic interface closely matched with the sensed forces of the slave robot. We successfully apply our haptic interface in the optical-motion-capture master-slave system. The results of the needle insertion test showed that our haptic feedback can provide more safety than merely visual observation. We develop a suitable haptic device to produce both kinesthetic grasp force feedback and cutaneous push-pull force feedback. Our future research will include further objective performance evaluations of the optical-motion-capture master-slave robot system with our haptic interface in surgical scenarios.

Loop Heat Pipe Operation Using Heat Source Temperature for Set Point Control

NASA Technical Reports Server (NTRS)

Ku, Jentung; Paiva, Kleber; Mantelli, Marcia

2011-01-01

Loop heat pipes (LHPs) have been used for thermal control of several NASA and commercial orbiting spacecraft. The LHP operating temperature is governed by the saturation temperature of its compensation chamber (CC). Most LHPs use the CC temperature for feedback control of its operating temperature. There exists a thermal resistance between the heat source to be cooled by the LHP and the LHP's CC. Even if the CC set point temperature is controlled precisely, the heat source temperature will still vary with its heat output. For most applications, controlling the heat source temperature is of most interest. A logical question to ask is: "Can the heat source temperature be used for feedback control of the LHP operation?" A test program has been implemented to answer the above question. Objective is to investigate the LHP performance using the CC temperature and the heat source temperature for feedback control

Single link flexible beam testbed project. Thesis

NASA Technical Reports Server (NTRS)

Hughes, Declan

1992-01-01

This thesis describes the single link flexible beam testbed at the CLaMS laboratory in terms of its hardware, software, and linear model, and presents two controllers, each including a hub angle proportional-derivative (PD) feedback compensator and one augmented by a second static gain full state feedback loop, based upon a synthesized strictly positive real (SPR) output, that increases specific flexible mode pole damping ratios w.r.t the PD only case and hence reduces unwanted residual oscillation effects. Restricting full state feedback gains so as to produce a SPR open loop transfer function ensures that the associated compensator has an infinite gain margin and a phase margin of at least (-90, 90) degrees. Both experimental and simulation data are evaluated in order to compare some different observer performance when applied to the real testbed and to the linear model when uncompensated flexible modes are included.

Performance assessment of static lead-lag feedforward controllers for disturbance rejection in PID control loops.

PubMed

Yu, Zhenpeng; Wang, Jiandong

2016-09-01

This paper assesses the performance of feedforward controllers for disturbance rejection in univariate feedback plus feedforward control loops. The structures of feedback and feedforward controllers are confined to proportional-integral-derivative and static-lead-lag forms, respectively, and the effects of feedback controllers are not considered. The integral squared error (ISE) and total squared variation (TSV) are used as performance metrics. A performance index is formulated by comparing the current ISE and TSV metrics to their own lower bounds as performance benchmarks. A controller performance assessment (CPA) method is proposed to calculate the performance index from measurements. The proposed CPA method resolves two critical limitations in the existing CPA methods, in order to be consistent with industrial scenarios. Numerical and experimental examples illustrate the effectiveness of the obtained results. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

Experimental realization of a feedback optical parametric amplifier with four-wave mixing

NASA Astrophysics Data System (ADS)

Pan, Xiaozhou; Chen, Hui; Wei, Tianxiang; Zhang, Jun; Marino, Alberto M.; Treps, Nicolas; Glasser, Ryan T.; Jing, Jietai

2018-04-01

Optical parametric amplifiers (OPAs) play a fundamental role in the generation of quantum correlation for quantum information processing and quantum metrology. In order to increase the communication fidelity of the quantum information protocol and the measurement precision of quantum metrology, it requires a high degree of quantum correlation. In this Rapid Communication we report a feedback optical parametric amplifier that employs a four-wave mixing (FWM) process as the underlying OPA and a beam splitter as the feedback controller. We first construct a theoretical model for this feedback-based FWM process and experimentally study the effect of the feedback control on the quantum properties of the system. Specifically, we find that the quantum correlation between the output fields can be enhanced by tuning the strength of the feedback.

Cloud-radiation interactions - Effects of cirrus optical thickness feedbacks

NASA Technical Reports Server (NTRS)

Somerville, Richard C. J.; Iacobellis, Sam

1987-01-01

The paper is concerned with a cloud-radiation feedback mechanism which may be an important component of the climate changes expected from increased atmospheric concentrations of carbon dioxide and other trace greenhouse gases. A major result of the study is that cirrus cloud optical thickness feedbacks may indeed tend to increase the surface warming due to trace gas increases. However, the positive feedback from cirrus appears to be generally weaker than the negative effects due to lower clouds. The results just confirm those of earlier research indicating that the net effect of cloud optical thickness feedbacks may be a negative feedback which may substantially (by a factor of about 2) reduce the surface warming due to the doubling of CO2, even in the presence of cirrus clouds.

Convection and the Soil-Moisture Precipitation Feedback

NASA Astrophysics Data System (ADS)

Schar, C.; Froidevaux, P.; Keller, M.; Schlemmer, L.; Langhans, W.; Schmidli, J.

2014-12-01

The soil moisture - precipitation (SMP) feedback is of key importance for climate and climate change. A positive SMP feedback tends to amplify the hydrological response to external forcings (and thereby fosters precipitation and drought extremes), while a negative SMP feedback tends to moderate the influence of external forcings (and thereby stabilizes the hydrological cycle). The sign of the SMP feedback is poorly constrained by the current literature. Theoretical, modeling and observational studies partly disagree, and have suggested both negative and positive feedback loops. Can wet soil anomalies indeed result in either an increase or a decrease of precipitation (positive or negative SMP feedback, respectively)? Here we investigate the local SMP feedback using real-case and idealized convection-resolving simulations. An idealized simulation strategy is developed, which is able to replicate both signs of the feedback loop, depending on the environmental parameters. The mechanism relies on horizontal soil moisture variations, which may develop and intensify spontaneously. The positive expression of the feedback is associated with the initiation of convection over dry soil patches, but the convective cells then propagate over wet patches, where they strengthen and preferentially precipitate. The negative feedback may occur when the wind profile is too weak to support the propagation of convective features from dry to wet areas. Precipitation is then generally weaker and falls preferentially over dry patches. The results highlight the role of the mid-tropospheric flow in determining the sign of the feedback. A key element of the positive feedback is the exploitation of both low convective inhibition (CIN) over dry patches (for the initiation of convection), and high CAPE over wet patches (for the generation of precipitation). The results of this study will also be discussed in relation to climate change scenarios that exhibit large biases in surface temperature and interannual variability over mid-latitude summer climates, both over Europe and North America. It is argued that parameterized convection may contribute towards such biases by overemphasizing a positive SMP feedback.

Characteristics of tuneable optical filters using optical ring resonator with PCF resonance loop

NASA Astrophysics Data System (ADS)

Shalmashi, K.; Seraji, F. E.; Mersagh, M. R.

2012-05-01

A theoretical analysis of a tuneable optical filter is presented by proposing an optical ring resonator (ORR) using photonic crystal fiber (PCF) as the resonance loop. The influences of the characteristic parameters of the PCF on the filter response have been analyzed under steady-state condition of the ORR. It is shown that the tuneability of the filter is mainly achieved by changing the modulation frequency of the light signal applied to the resonator. The analyses have shown that the sharpness and the depth of the filter response are controlled by parameters such as amplitude modulation index of applied field, the coupling coefficient of the ORR, and hole-spacing and air-filling ratio of the PCF, respectively. When transmission coefficient of the loop approaches the coupling coefficient, the filter response enhances sharply with PCF parameters. The depth and the full-width at half-maximum (FWHM) of the response strongly depend on the number of field circulations in the resonator loop. With the proposed tuneability scheme for optical filter, we achieved an FWHM of ~1.55 nm. The obtained results may be utilized in designing optical add/drop filters used in WDM communication systems.

Fiber distributed feedback laser

NASA Technical Reports Server (NTRS)

Elachi, C.; Evans, G. A.; Yeh, C. (Inventor)

1976-01-01

Utilizing round optical fibers as communication channels in optical communication networks presents the problem of obtaining a high efficiency coupling between the optical fiber and the laser. A laser is made an integral part of the optical fiber channel by either diffusing active material into the optical fiber or surrounding the optical fiber with the active material. Oscillation within the active medium to produce lasing action is established by grating the optical fiber so that distributed feedback occurs.

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.

Temperature feedback control for long-term carrier-envelope phase locking

DOEpatents

Chang, Zenghu [Manhattan, KS; Yun, Chenxia [Manhattan, KS; Chen, Shouyuan [Manhattan, KS; Wang, He [Manhattan, KS; Chini, Michael [Manhattan, KS

2012-07-24

A feedback control module for stabilizing a carrier-envelope phase of an output of a laser oscillator system comprises a first photodetector, a second photodetector, a phase stabilizer, an optical modulator, and a thermal control element. The first photodetector may generate a first feedback signal corresponding to a first portion of a laser beam from an oscillator. The second photodetector may generate a second feedback signal corresponding to a second portion of the laser beam filtered by a low-pass filter. The phase stabilizer may divide the frequency of the first feedback signal by a factor and generate an error signal corresponding to the difference between the frequency-divided first feedback signal and the second feedback signal. The optical modulator may modulate the laser beam within the oscillator corresponding to the error signal. The thermal control unit may change the temperature of the oscillator corresponding to a signal operable to control the optical modulator.

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.

Finite-time state feedback stabilisation of stochastic high-order nonlinear feedforward systems

NASA Astrophysics Data System (ADS)

Xie, Xue-Jun; Zhang, Xing-Hui; Zhang, Kemei

2016-07-01

This paper studies the finite-time state feedback stabilisation of stochastic high-order nonlinear feedforward systems. Based on the stochastic Lyapunov theorem on finite-time stability, by using the homogeneous domination method, the adding one power integrator and sign function method, constructing a ? Lyapunov function and verifying the existence and uniqueness of solution, a continuous state feedback controller is designed to guarantee the closed-loop system finite-time stable in probability.

Changes in regional and temporal patterns of activity associated with aging during the performance of a lexical set-shifting task.

PubMed

Martins, Ruben; Simard, France; Provost, Jean-Sebastien; Monchi, Oury

2012-06-01

Some older individuals seem to use compensatory mechanisms to maintain high-level performance when submitted to cognitive tasks. However, whether and how these mechanisms affect fronto-striatal activity has never been explored. The purpose of this study was to investigate how aging affects brain patterns during the performance of a lexical analog of the Wisconsin Card Sorting Task, which has been shown to strongly depend on fronto-striatal activity. In the present study, both younger and older individuals revealed significant fronto-striatal loop activity associated with planning and execution of set-shifts, though age-related striatal activity reduction was observed. Most importantly, while the younger group showed the involvement of a "cognitive loop" during the receiving negative feedback period (which indicates that a set-shift will be required to perform the following trial) and the involvement of a "motor loop" during the matching after negative feedback period (when the set-shift must be performed), older participants showed significant activation of both loops during the matching after negative feedback period only. These findings are in agreement with the "load-shift" model postulated by Velanova et al. (Velanova K, Lustig C, Jacoby LL, Buckner RL. 2007. Evidence for frontally mediated controlled processing differences in older adults. Cereb Cortex. 17:1033-1046.) and indicate that the model is not limited to memory retrieval but also applies to executive processes relying on fronto-striatal regions.

Tunable optical filter based on Sagnac phase-shift using single optical ring resonator

NASA Astrophysics Data System (ADS)

Seraji, Faramarz E.; Asghari, Fatemeh

2010-02-01

In this paper, a single optical ring resonator connected to a Sagnac loop is used to demonstrate theoretically a novel narrow band optical filter response that is based on Sagnac phase-shift Δ φ. The given filter structure permits the Sagnac rotation to control the filter response. It is shown that by changing the Sagnac rotation rate, we can tune the filter response for desired bandwidths. To increase the wavelength selectivity of the filter, the Sagnac phase-shift should be as small as possible that is limited by the loop length. For Δ φ=0.1 rad, the obtained FWHM is 2.63 MHz for tuning loop length of 2 m. The simulation response agrees fairly with the recently reported experimental result.

BioMEMS for biosensors and closed-loop drug delivery.

PubMed

Coffel, Joel; Nuxoll, Eric

2018-06-15

The efficacy of pharmaceutical treatments can be greatly enhanced by physiological feedback from the patient using biosensors, though this is often invasive or infeasible. By adapting microelectromechanical systems (MEMS) technology to miniaturize such biosensors, previously inaccessible signals can be obtained, often from inside the patient. This is enabled by the device's extremely small footprint which minimizes both power consumption and implantation trauma, as well as the transport time for chemical analytes, in turn decreasing the sensor's response time. MEMS fabrication also allows mass production which can be easily scaled without sacrificing its high reproducibility and reliability, and allows seamless integration with control circuitry and telemetry which is already produced using the same materials and fabrication steps. By integrating these systems with drug delivery devices, many of which are also MEMS-based, closed loop drug delivery can be achieved. This paper surveys the types of signal transduction devices available for biosensing-primarily electrochemical, optical, and mechanical-looking at their implementation via MEMS technology. The impact of MEMS technology on the challenges of biosensor development, particularly safety, power consumption, degradation, fouling, and foreign body response, are also discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

Optically phase-locked electronic speckle pattern interferometer

NASA Astrophysics Data System (ADS)

Moran, Steven E.; Law, Robert; Craig, Peter N.; Goldberg, Warren M.

1987-02-01

The design, theory, operation, and characteristics of an optically phase-locked electronic speckle pattern interferometer (OPL-ESPI) are described. The OPL-ESPI system couples an optical phase-locked loop with an ESPI system to generate real-time equal Doppler speckle contours of moving objects from unstable sensor platforms. In addition, the optical phase-locked loop provides the basis for a new ESPI video signal processing technique which incorporates local oscillator phase shifting coupled with video sequential frame subtraction.

Beam shaping in high-power broad-area quantum cascade lasers using optical feedback

PubMed Central

Ferré, Simon; Jumpertz, Louise; Carras, Mathieu; Ferreira, Robson; Grillot, Frédéric

2017-01-01

Broad-area quantum cascade lasers with high output powers are highly desirable sources for various applications including infrared countermeasures. However, such structures suffer from strongly deteriorated beam quality due to multimode behavior, diffraction of light and self-focusing. Quantum cascade lasers presenting high performances in terms of power and heat-load dissipation are reported and their response to a nonlinear control based on optical feedback is studied. Applying optical feedback enables to efficiently tailor its near-field beam profile. The different cavity modes are sequentially excited by shifting the feedback mirror angle. Further control of the near-field profile is demonstrated using spatial filtering. The impact of an inhomogeneous gain as well as the influence of the cavity width are investigated. Compared to existing technologies, that are complex and costly, beam shaping with optical feedback is a more flexible solution to obtain high-quality mid-infrared sources. PMID:28287175

Beam shaping in high-power broad-area quantum cascade lasers using optical feedback.

PubMed

Ferré, Simon; Jumpertz, Louise; Carras, Mathieu; Ferreira, Robson; Grillot, Frédéric

2017-03-13

Broad-area quantum cascade lasers with high output powers are highly desirable sources for various applications including infrared countermeasures. However, such structures suffer from strongly deteriorated beam quality due to multimode behavior, diffraction of light and self-focusing. Quantum cascade lasers presenting high performances in terms of power and heat-load dissipation are reported and their response to a nonlinear control based on optical feedback is studied. Applying optical feedback enables to efficiently tailor its near-field beam profile. The different cavity modes are sequentially excited by shifting the feedback mirror angle. Further control of the near-field profile is demonstrated using spatial filtering. The impact of an inhomogeneous gain as well as the influence of the cavity width are investigated. Compared to existing technologies, that are complex and costly, beam shaping with optical feedback is a more flexible solution to obtain high-quality mid-infrared sources.

Optimization of Sensing and Feedback Control for Vibration/Flutter of Rotating Disk by PZT Actuators via Air Coupled Pressure

PubMed Central

Yan, Tianhong; Xu, Xinsheng; Han, Jianqiang; Lin, Rongming; Ju, Bingfeng; Li, Qing

2011-01-01

In this paper, a feedback control mechanism and its optimization for rotating disk vibration/flutter via changes of air-coupled pressure generated using piezoelectric patch actuators are studied. A thin disk rotates in an enclosure, which is equipped with a feedback control loop consisting of a micro-sensor, a signal processor, a power amplifier, and several piezoelectric (PZT) actuator patches distributed on the cover of the enclosure. The actuator patches are mounted on the inner or the outer surfaces of the enclosure to produce necessary control force required through the airflow around the disk. The control mechanism for rotating disk flutter using enclosure surfaces bonded with sensors and piezoelectric actuators is thoroughly studied through analytical simulations. The sensor output is used to determine the amount of input to the actuator for controlling the response of the disk in a closed loop configuration. The dynamic stability of the disk-enclosure system, together with the feedback control loop, is analyzed as a complex eigenvalue problem, which is solved using Galerkin’s discretization procedure. The results show that the disk flutter can be reduced effectively with proper configurations of the control gain and the phase shift through the actuations of PZT patches. The effectiveness of different feedback control methods in altering system characteristics and system response has been investigated. The control capability, in terms of control gain, phase shift, and especially the physical configuration of actuator patches, are also evaluated by calculating the complex eigenvalues and the maximum displacement produced by the actuators. To achieve a optimal control performance, sizes, positions and shapes of PZT patches used need to be optimized and such optimization has been achieved through numerical simulations. PMID:22163788

Optimization of sensing and feedback control for vibration/flutter of rotating disk by PZT actuators via air coupled pressure.

PubMed

Yan, Tianhong; Xu, Xinsheng; Han, Jianqiang; Lin, Rongming; Ju, Bingfeng; Li, Qing

2011-01-01

In this paper, a feedback control mechanism and its optimization for rotating disk vibration/flutter via changes of air-coupled pressure generated using piezoelectric patch actuators are studied. A thin disk rotates in an enclosure, which is equipped with a feedback control loop consisting of a micro-sensor, a signal processor, a power amplifier, and several piezoelectric (PZT) actuator patches distributed on the cover of the enclosure. The actuator patches are mounted on the inner or the outer surfaces of the enclosure to produce necessary control force required through the airflow around the disk. The control mechanism for rotating disk flutter using enclosure surfaces bonded with sensors and piezoelectric actuators is thoroughly studied through analytical simulations. The sensor output is used to determine the amount of input to the actuator for controlling the response of the disk in a closed loop configuration. The dynamic stability of the disk-enclosure system, together with the feedback control loop, is analyzed as a complex eigenvalue problem, which is solved using Galerkin's discretization procedure. The results show that the disk flutter can be reduced effectively with proper configurations of the control gain and the phase shift through the actuations of PZT patches. The effectiveness of different feedback control methods in altering system characteristics and system response has been investigated. The control capability, in terms of control gain, phase shift, and especially the physical configuration of actuator patches, are also evaluated by calculating the complex eigenvalues and the maximum displacement produced by the actuators. To achieve a optimal control performance, sizes, positions and shapes of PZT patches used need to be optimized and such optimization has been achieved through numerical simulations.

Feasibility of a feedback control of atomic self-organization in an optical cavity

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

Ivanov, D. A., E-mail: ivanov-den@yandex.ru; Ivanova, T. Yu.

Many interesting nonlinear effects are based on the strong interaction of motional degrees of freedom of atoms with an optical cavity field. Among them is the spatial self-organization of atoms in a pattern where the atoms group in either odd or even sites of the cavity-induced optical potential. An experimental observation of this effect can be simplified by using, along with the original cavity-induced feedback, an additional electronic feedback based on the detection of light leaking the cavity and the control of the optical potential for the atoms. Following our previous study, we show that this approach is more efficientmore » from the laser power perspective than the original scheme without the electronic feedback.« less

Parallel multiplex laser feedback interferometry

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

Zhang, Song; Tan, Yidong; Zhang, Shulian, E-mail: zsl-dpi@mail.tsinghua.edu.cn

2013-12-15

We present a parallel multiplex laser feedback interferometer based on spatial multiplexing which avoids the signal crosstalk in the former feedback interferometer. The interferometer outputs two close parallel laser beams, whose frequencies are shifted by two acousto-optic modulators by 2Ω simultaneously. A static reference mirror is inserted into one of the optical paths as the reference optical path. The other beam impinges on the target as the measurement optical path. Phase variations of the two feedback laser beams are simultaneously measured through heterodyne demodulation with two different detectors. Their subtraction accurately reflects the target displacement. Under typical room conditions, experimentalmore » results show a resolution of 1.6 nm and accuracy of 7.8 nm within the range of 100 μm.« less

The MYB23 Gene Provides a Positive Feedback Loop for Cell Fate Specification in the Arabidopsis Root Epidermis[C][W

PubMed Central

Kang, Yeon Hee; Kirik, Victor; Hulskamp, Martin; Nam, Kyoung Hee; Hagely, Katherine; Lee, Myeong Min; Schiefelbein, John

2009-01-01

The specification of cell fates during development requires precise regulatory mechanisms to ensure robust cell type patterns. Theoretical models of pattern formation suggest that a combination of negative and positive feedback mechanisms are necessary for efficient specification of distinct fates in a field of differentiating cells. Here, we examine the role of the R2R3-MYB transcription factor gene, AtMYB23 (MYB23), in the establishment of the root epidermal cell type pattern in Arabidopsis thaliana. MYB23 is closely related to, and is positively regulated by, the WEREWOLF (WER) MYB gene during root epidermis development. Furthermore, MYB23 is able to substitute for the function of WER and to induce its own expression when controlled by WER regulatory sequences. We also show that the MYB23 protein binds to its own promoter, suggesting a MYB23 positive feedback loop. The localization of MYB23 transcripts and MYB23-green fluorescent protein (GFP) fusion protein, as well as the effect of a chimeric MYB23-SRDX repressor construct, links MYB23 function to the developing non-hair cell type. Using mutational analyses, we find that MYB23 is necessary for precise establishment of the root epidermal pattern, particularly under conditions that compromise the cell specification process. These results suggest that MYB23 participates in a positive feedback loop to reinforce cell fate decisions and ensure robust establishment of the cell type pattern in the Arabidopsis root epidermis. PMID:19395683

The MYB23 gene provides a positive feedback loop for cell fate specification in the Arabidopsis root epidermis.

PubMed

Kang, Yeon Hee; Kirik, Victor; Hulskamp, Martin; Nam, Kyoung Hee; Hagely, Katherine; Lee, Myeong Min; Schiefelbein, John

2009-04-01

The specification of cell fates during development requires precise regulatory mechanisms to ensure robust cell type patterns. Theoretical models of pattern formation suggest that a combination of negative and positive feedback mechanisms are necessary for efficient specification of distinct fates in a field of differentiating cells. Here, we examine the role of the R2R3-MYB transcription factor gene, AtMYB23 (MYB23), in the establishment of the root epidermal cell type pattern in Arabidopsis thaliana. MYB23 is closely related to, and is positively regulated by, the WEREWOLF (WER) MYB gene during root epidermis development. Furthermore, MYB23 is able to substitute for the function of WER and to induce its own expression when controlled by WER regulatory sequences. We also show that the MYB23 protein binds to its own promoter, suggesting a MYB23 positive feedback loop. The localization of MYB23 transcripts and MYB23-green fluorescent protein (GFP) fusion protein, as well as the effect of a chimeric MYB23-SRDX repressor construct, links MYB23 function to the developing non-hair cell type. Using mutational analyses, we find that MYB23 is necessary for precise establishment of the root epidermal pattern, particularly under conditions that compromise the cell specification process. These results suggest that MYB23 participates in a positive feedback loop to reinforce cell fate decisions and ensure robust establishment of the cell type pattern in the Arabidopsis root epidermis.