External Reference Signal Research Articles

Accelerated motion correction with deep generative diffusion models.

The aim of this work is to develop a method to solve the ill-posed inverse problem of accelerated image reconstruction while correcting forward model imperfections in the context of subject motion during MRI examinations. The proposed solution uses a Bayesian framework based on deep generative diffusion models to jointly estimate a motion-free image and rigid motion estimates from subsampled and motion-corrupt two-dimensional (2D) k-space data. We demonstrate the ability to reconstruct motion-free images from accelerated two-dimensional (2D) Cartesian and non-Cartesian scans without any external reference signal. We show that our method improves over existing correction techniques on both simulated and prospectively accelerated data. We propose a flexible framework for retrospective motion correction of accelerated MRI based on deep generative diffusion models, with potential application to other forward model corruptions.

Role of ultrasensitivity in biomolecular circuitry for achieving homeostasis

Living systems have developed control mechanisms for achieving homeostasis. Here, we propose a plausible biological feedback architecture that exploits ultrasensitivity and shows adaptive responses without requiring error detection mechanism (i.e., by measuring an external reference signal and deviation from this). While standard engineering control systems are usually based on error measurements, this is not the case for biological systems. We find that a two-state negative feedback control system, without explicit error measurements, is able to track a reference signal that is implicitly determined by the tunable threshold and slope characterizing the sigmoidal ultrasensitive relationship implemented by the control system. We design different ultrasensitive control functions (ultrasensitive up- or down-regulation, or both) and, by performing sensitivity analysis, show that increasing the sensitivity level of the control allows achieving robust adaptive responses to the effects of parameter variations and step disturbances. Finally, we show that the devised control system architecture without error detection is implemented within the yeast osmoregulatory response network and allows achieving adaptive responses to osmotic stress, by exploiting the ubiquitous ultrasensitive features of the involved biomolecular circuitry.

Asymptotic Output Tracking Control of a Class of Linear Systems by Finite-and-Quantized Output Feedback

This paper presents a novel finite-and-quantized output feedback asymptotic tracking control method for a general class of continuous-time linear time-invariant systems. First, we construct a finite quantizer with time-varying thresholds and design a pole placement control law that exclusively utilizes the finite-and-quantized output signal and an external reference signal. Then, we establish the boundedness of all closed-loop signals and prove the asymptotic convergence of the output tracking error to zero. The proposed method combines the advantages of classical pole placement control technique and finite quantization feedback technique. It not only reduces the requirement for feedback information compared with existing tracking control methods but also effectively handles unstable poles and zeros in controlled systems, thereby achieving asymptotic output tracking. Finally, we provide a representative example to validate the effectiveness and new features of our proposed method.

Method for comparison of data driven gating algorithms in emission tomography.

Multiple algorithms have been proposed for Data Driven Gating (DDG) in Single Photon Emission Computed Tomography (SPECT) and have successfully been applied to Myocardial Perfusion Imaging (MPI). Application of DDG to acquisition types other than SPECT MPI has not been demonstrated so far, as limitations and pitfalls of current methods are unknown. 

Approach: We create a comprehensive set of phantoms simulating the influence of different motion artifacts, view angles, moving objects, contrast, and count levels in SPECT. We perform Monte Carlo Simulation (MCS) of the phantoms, allowing the characterization of DDG algorithms using quantitative metrics derived from the data and evaluate the Center of Light (COL) and Laplacian Eigenmaps (LE) methods as sample DDG algorithms. 

Main results: View angle, object size, count rate density, and contrast influence the accuracy of both DDG methods. Moreover, the ability to extract the respiratory motion in the phantom was shown to correlate with the contrast of the moving feature to the background, the Signal to Noise ratio, and the noise in the data. 

Significance: We showed that reporting the average correlation to an external physical reference signal per acquisition is not sufficient to characterize DDG methods. Assessing DDG methods on a view-by-view basis using the simulations and metrics from this work could enable the identification of pitfalls of current methods, and extend their application to acquisitions beyond SPECT MPI.

A Fiber-Optic Array Spectrometer With Parallel Multichannel Optical Lock-in Detection and its Application to in Situ Lighting Measurements

This paper describes a new optical spectroscopy instrument achieving lock-in detection in all its spectral output channels in a parallel and simultaneous fashion. It is based on two identical compact array spectrometers working in phase quadrature thanks to optical modulators synchronized with an external reference signal. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In the application example, the optical lock-in spectrometer was used to perform spectral irradiance measurements with commercial LED lamps exhibiting temporal light modulation at different frequencies. A remote sensing optical device was designed to measure from a distance the temporal luminous waveform of a specific LED lamp and send it to the reference input of the optical lock-in spectrometer. When the lamps were operating together on top of a large continuous luminous background, the optical lock-in spectrometer successfully retrieved the respective spectral irradiance distributions and color parameters of each lamp, allowing their characterization to be performed independently of the other light sources illuminating the sensor during the measurements.

Flexible, low-cost phase-sensitive detection for the undergraduate laboratory with a Teensy microcontroller

We perform phase-sensitive detection with an inexpensive microcontroller, the Teensy 3.5. The programming and pricing of this microcontroller is similar to that of commonly used Arduino microcontrollers, but the Teensy 3.5 offers superior hardware performance. Our Teensy-based phase-sensitive detector can operate either with an external reference signal or by internally generating a reference signal. Additionally, we have developed an open-source graphical user interface for controlling the instrument. We demonstrate that our phase-sensitive detector exhibits good linearity in amplitude and phase, even with 25 mV signals dominated by larger-amplitude noise. We also use our phase-sensitive detector in a simple laboratory measurement: determining the distance dependence of the intensity of a light-emitting diode (LED) with the room lights on. Our instrument is a useful tool for teaching students about phase-sensitive detection and can be a viable low-cost alternative to commercial lock-in amplifiers.

Targeted metabolomics analyses for brain tumor margin assessment during surgery.

Identification and removal of micro-scale residual tumor tissue during brain tumor surgery are key for survival in glioma patients. For this goal, High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HRMAS NMR) spectroscopy-based assessment of tumor margins during surgery has been an effective method. However, the time required for metabolite quantification and the need for human experts such as a pathologist to be present during surgery are major bottlenecks of this technique. While machine learning techniques that analyze the NMR spectrum in an untargeted manner (i.e. using the full raw signal) have been shown to effectively automate this feedback mechanism, high dimensional and noisy structure of the NMR signal limits the attained performance. In this study, we show that identifying informative regions in the HRMAS NMR spectrum and using them for tumor margin assessment improves the prediction power. We use the spectra normalized with the ERETIC (electronic reference to access in vivo concentrations) method which uses an external reference signal to calibrate the HRMAS NMR spectrum. We train models to predict quantities of metabolites from annotated regions of this spectrum. Using these predictions for tumor margin assessment provides performance improvements up to 4.6% the Area Under the ROC Curve (AUC-ROC) and 2.8% the Area Under the Precision-Recall Curve (AUC-PR). We validate the importance of various tumor biomarkers and identify a novel region between 7.97 ppm and 8.09 ppm as a new candidate for a glioma biomarker. The code is released at https://github.com/ciceklab/targeted_brain_tumor_margin_assessment. The data underlying this article are available in Zenodo, at https://doi.org/10.5281/zenodo.5781769. Supplementary data are available at Bioinformatics online.

Implementation of Hardware Architecture for SVPWM With Arbitrary Parameters

A novel hardware digital architecture for the Space Vector Pulse Width Modulation technique is proposed. Its features are the reduced hardware resources and the real-time variation of the values of the carrier and switching frequencies, of the phase and of the amplitude of the three-phase output voltages in addition to not require external reference signals or further processors, like Digital Signal Processor. The basic idea is to pre-calculate a set of normalized dwell-time for only one sixth of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\beta $ </tex-math></inline-formula> -plane and, then, to reconstruct through our architecture the effective dwell-times and the right inverter configurations by an optimized management of the memory. The architecture is implemented in a Field Programmable Gate Array Cyclone V using the 6% and the 1.01%, respectively, of the Look-Up Tables and of the Flip Flops and the experimental measurements show the goodness of the generated waveforms and the high numbers of degrees of freedom without the demand of Digital Signal Processor or Personal Computer.

Imposing Constraints in a Full State Feedback System Using Multithreaded Controller

The article proposes a ground-breaking solution to address the challenge of imposing constraints in a full state feedback (FSF) control system. Its simplicity is comparable to the introduction of saturation blocks in the cascaded control system. In the developed control system, a given state variable is stabilized at the threshold value using a separate FSF controller. The overall controller consists then of a set of controllers, the main one with an external reference signal and auxiliary controllers with the internal references set to the desired limits to be imposed on each of the physical states of the investigated plant, operating in parallel fashion (hence the proposed name-multithreaded). This means that in each time instance, the processor executes all FSF controllers. Additionally, if the auxiliary integral states are implemented, a back-calculation algorithm is employed to keep the auxiliary states at the desired level for the controllers that are idling at a given time instance. The median of the calculated control signals is put through to the plant as a control signal. Such an elegant and straightforward way of handling constraints in the state feedback system has never been reported before and is currently patent pending. The proposed method is validated for a servo drive using hardware-in-the-loop setup. All the obtained results confirm technical feasibility of the controller structure and its ability to keep all the state variables within the required intervals.

Performance Residual Based Fault Detection for Feedback Control Systems

This brief is devoted to the issues of performance supervised fault detection (FD) for two types of feedback control systems by adopting the novel performance residual as the process evaluator. Specifically, for a class of uncertain state feedback control systems, the boundaries of the performance residual caused by the model uncertainties are analyzed theoretically, then the randomized algorithm is exploited to construct the threshold, aiming at avoiding the worst-case handling and improving the FD performance. The second part considers the general dynamic output feedback control systems with external reference signals. For the FD purpose, the performance residual is derived based on the backward computation, and the state variables of the closed-loop system are constructed by the accessible input, output, and reference signals to release the strict requirements for full state measurements. Finally, the effectiveness of the developed FD approaches is demonstrated on the model of a DC motor system.

Self-excited periodic motion in underactuated mechanical systems using two-fuzzy inference system

Dynamic systems with self-excited periodic motion have a wide range of applications in mechanical systems. For instance, a class of non-minimum phase underactuated and nonprehensile systems require self-oscillations instead of tracking an external reference signal. To solve this problem, we proposed a two fuzzy inference system, which is based on fuzzy logic theory, in order to generate a periodic output. The idea is to enforce the conditions that ensure the orbital asymptotic stability of the periodic solution of the closed-loop system. In this study, we considered Euler-Lagrange systems, with emphasis in underactuated systems. The describing function method was used to design the fuzzy controller and set the desired frequency and amplitude of the periodic output. Moreover, in accordance with Loeb's criteria, we established sufficient conditions for orbital stability. Finally, we tested and validated our proposal, via simulation and experiments on two laboratory platforms: a single-link pendulum and an underactuated non-minimum-phase rotational inverted pendulum.

The Virtual Lock-in Amplifiers - Accuracy of Measurement Results in Light Transmission Experiments

This research focuses on the analysis of the measurement result of the virtual lock-in amplifier (virtual-LIA) in the light transmission experiment as the trial step of developing the virtual-LIA. The virtual-LIA used in this research is designed by using the Vernier sensor DAQ as the data acquisition and the LabVIEW as the programming media. The design of virtual-LIA is based on the mathematical operations of LIA. The type of virtual-LIA is a single phase with the capabilities to process the external reference signal. Light transmission experiments are carried out using formazin polymer suspension with turbidity level of 3000 NTU, 3500 NTU, and 4000 NTU as the medium in which light is passed. The accuracy of the measurement results is known by comparing the results of virtual-LIA with real-LIA SR510. The experiments are also carried out in bright and darkroom conditions to determine the ability of virtual-LIA in reducing noise signals. Based on the experiment, the results obtained that the measurement accuracy of the virtual-LIA developed is above 94% compared to the LIA SR510. Virtual-LIA could measure small signals with and without noise with the average percentage of differences measured between dark and bright conditions is 0.54%.

Output regulation of switched singular systems based on extended state observer approach

The observer-based output regulation for the linear switched singular systems is studied in this paper, both the full-order and reduced-order observer approaches are considered. Firstly, by introducing the full-order extended state observer to estimate the states of system and the external reference signals simultaneously, under some standard assumptions, feasible criteria for switched singular systems to achieve the output regulation goals are developed and the observer design methods are presented. Furthermore, based on the restricted system equivalent (r.s.e) transformation, a reduced-order observer is employed, under average dwell time (ADT) switching, feasible criteria for the transformed systems to satisfy the output regulation aims are presented and the procedure for designing the reduced-order observer is given. At last, an illustrative example is proposed to confirm the effectiveness of the developed results.

Single-sided NMR to estimate morphological parameters of the trabecular bone structure.

Single-sided 1 H-NMR is proposed for the estimation of morphological parameters of trabecular bone, and potentially the detection of pathophysiological alterations of bone structure. In this study, a new methodology was used to estimate such parameters without using an external reference signal, and to study intratrabecular and intertrabecular porosities, with a view to eventually scanning patients. Animal trabecular bone samples were analyzed by a single-sided device. The Carr-Purcell-Meiboom-Gill sequence of 1 H nuclei of fluids, including marrow, confined inside the bone, was analyzed by quasi-continuous T2 distributions and separated into two 1 H pools: short and long T2 components. The NMR parameters were estimated using models of trabecular bone structure, and compared with the corresponding micro-CT. Without any further assumptions, the internal reference parameter (short T2 signal intensity fraction) enabled prediction of the micro-CT parameters BV/TV (volume of the trabeculae/total sample volume) and BS/TV (external surface of the trabeculae/total sample volume) with linear correlation coefficient >0.80. The assignment of the two pools to intratrabecular and intertrabecular components yielded an estimate of average intratrabecular porosity (33±5)%. Using the proposed models, the NMR-estimated BV/TV and BS/TV were found to be linearly related to the corresponding micro-CT values with high correlation (>0.90 for BV/TV; >0.80 for BS/TV) and agreement coefficients. Low-field, low-cost portable devices that rely on intrinsic magnetic field gradients and do not use ionizing radiation are viable tools for in vitro preclinical studies of pathophysiological structural alterations of trabecular bone.

Synchronization of surface acoustic wave (SAW)-based delay-coupled self-oscillating MEMS

Coupled limit cycle oscillators have potential usage in neurocomputing, pattern recognition, signal processing units such as multilayer perceptrons and stable timekeeping devices. Here, we study the synchronization dynamics of parametrically excited coupled dome-shaped MEMS (microelectromechanical system), exhibiting limit cycle oscillations and hysteresis, which have previously been shown to synchronize with an external reference signal [1, 2]. The coupling considered here is through surface acoustic wave (SAW), emanating in the substrate near each oscillator, due to periodic forcing of the same, which acts as a base vibration term for the forced oscillator. Dynamics of the individual MEMS can be adequately modeled as Mathieu–van der Pol–Duffing (MVDPD) oscillator [3], while the effect of SAW can be added as a delay coupling term, because of finite time involved in travel of this signal, resulting in a set of delay differential equations (DDEs). Various solutions for different parameter values are identified and the synchronization regions mapped under the case of a general dissipative type coupling. Numerical integration of the DDE for the system as well as the ODE obtained by applying the Krylov–Bogoliubov averaging method to the same is used for detailed analysis. The averaged equations are further reduced to get a phase equation which can be used to map the regions of synchronization at a much smaller computational budget. It is found that in general the delay terms lead to an increase in the synchronization region, while a cubic coupling term would be more effective. Effect of different parameters of individual oscillator on synchronization is also studied, which provide guidance for fabrication and testing of the optimized system.

The Decoupling Cooperative Control With Dominant Poles Assignment

This article studies a decoupling cooperative control (DCC) with state feedback. It solves the output consensus problem on heterogeneous multiagent systems (MASs) over the input graph whose all nodes are reachable from the external reference signal. In light of the communication topology, the DCC forces each agent to reach a consensus on the given trajectory, which is from the reference signal of the common exosystem. Here, the output consensus problem is first equivalently converted into a stabilization one. Second the DCC involves a mapping <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{ L}}_{d}$ </tex-math></inline-formula> of Laplacian matrix <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{ L}}$ </tex-math></inline-formula> , i.e., every diagonal element of the Laplacian matrix is multiplied by a parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d_{i}$ </tex-math></inline-formula> . <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{ L}}_{d}$ </tex-math></inline-formula> moves Ger <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">š</i> gorin circles of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{ L}}$ </tex-math></inline-formula> . By the merit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{ L}}_{d}$ </tex-math></inline-formula> , the equivalent stabilization problem is solved by the strictly positive real (SPR). In fact, the DCC is an approximate distributed decoupling control, when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d_{i}$ </tex-math></inline-formula> is sufficiently large. In addition, under the framework of the DCC, the assignment problem of the dominant poles for each agent is also solved by inverse optimal regulator technology in this article. Finally, several simulation examples verify the effectiveness of our method.

A digital phase-locked loop based LLRF system

TRIUMF’s ARIEL pre-buncher is powered by a sawtooth waveform which is the combination of 11.79 MHz, 23.57 MHz and 35.36 MHz harmonics. To upgrade the existing analog and digital hybrid LLRF control system, reduce the hardware cost, and achieve more flexible control of the system, an FPGA based digital daughter board is designed. The generation, control, and regulation of these three harmonics are all incorporated digitally inside a single FPGA. To reduce the number of RF interfaces on the motherboard, the new daughter board is designed to control the amplitude and phase of the sawtooth waveform with one channel ADC and DAC. To lock the output phase of the sawtooth waveform to the reference signal, a digital phase-locked loop is designed to lock all three harmonics to the external reference signal. The related work, including the system design of the LLRF control system and the development of the digital phase-locked loop, are presented in this paper.

Assessment Criteria for the Mechanical Loads of Wind Turbines applied to the example of Active Power Control

Assessment criteria for design of wind turbines controller are discussed since conventional control performance criteria are not sufficient to evaluate the mechanical loads as dependency of the controller type and settings. This will be presented and discussed using the example of the active power control of wind turbines. In contrast to the nominal operation of wind turbines divided into power optimization in the partial and power limitation in the full load region, the power output is guided by an external power reference signal. The reference signal may be delivered either directly by higher-level load frequency controller of the power system or by the wind farm controller. In both cases the external variation of the power to be delivered has an enormous influence on the dynamics and mechanical loads of the wind turbine. To quantify these loads that occur during power tracking operation the Damage Equivalent Load amplitude as appropriated load assessment criteria is described and prepared for control design.

Real-time visualization of instantaneous frequency from bubble cavitation using color Doppler ultrasound imaging

Time-resolved observations of acoustic cavitation emission signals are important in understanding bubble cavitation dynamics and monitoring sonoporation efficiencies of ultrasound-assisted drug delivery systems. Previous methods using back propagation of such signals measure frequencies with high time resolutions but require post-processing. We propose a method using color Doppler ultrasound to obtain instantaneous frequencies of these signals from the phase differences with an external reference signal. Standard color Doppler processing is applied to both emissions and reference signals to enable real-time observations of bubble cavitation generated by high-intensity ultrasound wave irradiation. A sinusoidal wave signal was used to confirm the accuracy of our method with an estimation error of 8.59%. Experiments were performed using Sonazoid suspensions of two different concentrations. With a sound pressure of 1.0 MPa for the ultrasound wave, the type of bubble cavitation that is dominant is different before and after irradiation of about ten pulses.

Attitude Synchronization For Multiple 3-DOF Helicopters With Actuator Faults

The attitude synchronization for multiple three-degree-of-freedom helicopters in the presence of system uncertainties and time-varying actuator faults is investigated. A fault-tolerant cooperative control algorithm based on robust adaptive control is proposed to synchronize attitudes of multiple helicopter systems in the case where some of the helicopters are subjected to both partial losses of control effectiveness and additive actuator faults. The proposed design is a distributed control method that allows each vehicle to track external reference signals merely in light of its neighborhood information. With the proposed design, time-varying actuator faults are tolerated without sacrificing the attitude synchronization performance. The effectiveness of the proposed control method is verified via a comparative experimental study.