Continuous-time Measurements Research Articles

Non-Invasive Continuous-Time Blood Pressure Estimation from a Single Channel PPG Signal using Regularized ARX Models.

Continuous blood pressure (BP) monitoring can help in preventing hypertension and other cardiovascular diseases. In principle, an indirect non-invasive continuous-time measurement of BP is possible by exploiting the photoplethysmography (PPG) signal, which can be obtained through wearable optical sensor devices. However, a model of the PPG-to-BP dynamical system is needed. In this study, we investigate if autoregressive with exogenous input (ARX) models with kernel-based regularization are suited for the scope. We analyzed 10 PPG time-series acquired on different individuals by a wearable optical sensor and correspondent BP reference values to evaluate feasibility of continuous BP estimation from a single PPG source. This first proof-of-concept study shows promising results in continuous BP estimation during resting states.

Asymmetric injection and distribution of space charges in propylene carbonate under impulse voltage

Space charge can distort the electric field in high voltage stressed liquid dielectrics and lead to breakdown. Observing the evolution of space charge in real time and determining the influencing factors are of considerable significance. The spatio-temporal evolution of space charge in propylene carbonate, which is very complex under impulse voltage, was measured in this study through the time-continuous Kerr electro-optic field mapping measurement. We found that the injection charge from a brass electrode displayed an asymmetric effect; that is, the negative charge injection near the cathode lags behind the positive charge injection near the anode. Physical mechanisms, including charge generation and drift, are analyzed, and a voltage-dependent saturated drift rectification model was established to explain the interesting phenomena. Mutual validation of models and our measurement data indicated that a barrier layer, which is similar to metal-semiconductor contact, was formed in the contact interface between the electrode and propylene carbonate and played an important role in the space charge injection.

Exponential Synchronization of Chaotic Lur’e Systems Using an Adaptive Event-Triggered Mechanism

This paper investigates event-triggered exponential synchronization of master-slave chaotic Lur'e systems (CLSs). First, in order to save communication resources, a novel event-based transmission strategy is developed using continuous-time measurements while a positive minimum inter-event time can be ensured. Second, an adaptive law is adopted to adjust dynamically the event-triggered threshold parameter. Compared with some existing static event-triggered mechanisms, the proposed event-triggered mechanism can provide a better tradeoff between communication resource saving and desired synchronization performance. Third, a switched Lyapunov-Krasovskii functional (LKF) is introduced, which is continuous at the switching instants but not necessarily positive definite at sampling intervals. This LKF is employed to derive a less conservative synchronization criterion for CLSs, based on which, the synchronization controller gain and the event-triggered parameters can be co-designed in terms of linear matrix inequalities. Finally, numerical simulations of Chua's circuit and neural network are provided to illustrate the efficiency of the proposed method.

DEVELOPING A LOGGING UNIT FOR MEASURING AND RECORDING POWER DATA USING ARDUINO BOARD

A logging unit for measuring and recording power data for tillage implements was investigated. The system of sensor for a continuous and real time measurement of draft data is a set of electronic circuit made around the Arduino UNO board. It consisted of a conditioning circuit for strain gauges pull meter. The developed system was an alternative of the commercial data logger namely Daytronic system 10K4 in draft measurement system(Khadr, 2008). As with the hardware, the Arduino integrated development environment is open source and can be down-loaded freely from the project’s internet website for programming, serves for compiling and up-loading programs to the microcontroller. Laboratory evaluation demonstrated that the developed system has been successfully gathered data from strain gauge pull meter. The entire system was fixed on a tractor and a field experiment with chisel plow was conducted to evaluate the performance of the developed instrumentation system by determining the required chisel plow draft. The plowing speed measurement was done manually. The drawbar pull was measured at three tractor plowing speeds. The draft results were compared with those obtained through ASAE (2000) equation for chisel plow and the relative error was about 27%. The very limited cost of the system presented in this paper could represent a step towards a more widespread application of accurate monitoring of tillage and tractor performance data potential, leading to an improvement of farm machinery management.

Generation of coherence via Gaussian measurements

We address measurement-based generation of quantum coherence in continuous variable systems. We consider Gaussian measurements performed on Gaussian states and focus on two scenarios. In the first one, we assume an initially correlated bipartite state shared by two parties and study how correlations may be exploited to remotely create quantum coherence via measurement back-action. In particular, we focus on conditional states with zero first moments, so as to address coherence due to properties of the covariance matrix. We consider different classes of bipartite states with incoherent marginals and show that the larger the measurement squeezing, the larger the conditional coherence. Homodyne detection is thus the optimal Gaussian measurement to remotely generate coherence. We also show that for squeezed thermal states there exists a threshold value for the generated coherence which separates entangled and separable states at a fixed energy. Finally, we briefly discuss the tripartite case and the relationship between tripartite correlations and the conditional two-mode coherence. In the second scenario, we address the steady state coherence of a system interacting with an environment which is continuously monitored. In particular, we discuss the dynamics of an optical parametric oscillator in order to investigate how the coherence of a Gaussian state may be increased by means of time-continuous Gaussian measurement on the interacting environment.

Design and Experimental Validation of Nonlinear Infinite-Dimensional Adaptive Observer in Automated Managed Pressure Drilling

Utilizing flow rate and pressure data in and out of the fluid circulation loop provides a driller with real-time trends for early detection of well-control problems that impact the drilling efficiency. Due to limited number of sensors and time delay in processing and measurements, the flow rate and pressure along the annulus and drill string need to be estimated. This paper presents state and parameter estimations for infinite-dimensional models used in automated managed pressure drilling (MPD). The objective is to monitor the key process variables associated with process safety by designing a nonlinear adaptive observer that use the available information coming from the continuous-time online process measurements at the outlet of the well. The adaptive observer consists of a copy of the infinite-dimensional model plus output injection terms where the gain is computed analytically in terms of the Bessel function of the first kind. The design is tested using field data from a drilling commissioning test by Statoil ASA, Stavanger, Norway. The results show that the nonlinear adaptive observer estimates the flow rate and pressure of the drilling fluid accurately.

Interval Estimation for Linear Switched System

In this paper, the problem of state estimation is investigated for linear switched system, a subclass of hybrid systems. It will be shown that the interval observer is very often exists under moderate conditions at least in discrete time instants from continuous-time measurements. The novelty consists in proposing new conditions of cooperativity for switched systems in discrete time instants, which guarantee errors nonnegativity of interval observation. The efficiency of the interval observers is shown through simulation examples.

Learning Curve Analysis Using Intensive Longitudinal and Cluster-Correlated Data

Intensive longitudinal and cluster-correlated data (ILCCD) can be generated in any situation where numerical or categorical characteristics of multiple individuals or study units are observed and measured at tens, hundreds, or thousands of occasions. The spacing of measurements in time for each individual can be regular or irregular, fixed or random, and the number of characteristics measured at each occasion may be few or many. Such data can also arise in situations involving continuous-time measurements of recurrent events. Generalized linear models (GLMs) are usually considered for the analysis of correlated non-normal data, while multivariate analysis of variance (MANOVA) is another option. In the paper, both GLMs and MANOVA are applied to ASSISTments online teaching system via the Wald test in order to estimate and predict the learning effects of the students after taking an Algebra course for three months in the system. Three case studies based on these two methodologies are presented in a mathematical and statistical manner.

Analysis and synthesis of networked control systems: A survey of recent advances and challenges

A networked control system (NCS) is a control system which involves a communication network. In NCSs, the continuous-time measurement is usually sampled and quantized before transmission. Then, the measurement is transmitted to the remote controller via the communication channel, during which the signal may be delayed, lost or even sometimes not allowed for transmission due to the communication or energy constraints. In recent years, the modeling, analysis and synthesis of networked control systems (NCSs) have received great attention, which leads to a large number of publications. This paper attempts to present an overview of recent advances and unify them in a framework of network-induced issues such as signal sampling, data quantization, communication delay, packet dropouts, medium access constraints, channel fading and power constraint, and present respective solution approaches to each of these issues. We draw some conclusions and highlight future research directions in end.

Event-Triggered <inline-formula> <tex-math notation="LaTeX">$H_{\infty}$</tex-math> </inline-formula> Control: A Switching Approach

Event-triggered approach to networked control systems is used to reduce the workload of the communication network. For the static output-feedback continuous event-trigger may generate an infinite number of sampling instants in finite time (Zeno phenomenon) what makes it inapplicable to the real-world systems. Periodic event-trigger avoids this behavior but does not use all the available information. In the present paper we aim to exploit the advantage of the continuous-time measurements and guarantee a positive lower bound on the inter-event times by introducing a switching approach for finding a waiting time in the event-triggered mechanism. Namely, our idea is to present the closed-loop system as a switching between the system under periodic sampling and the one under continuous event-trigger and take the maximum sampling preserving the stability as the waiting time. We extend this idea to the $L_2$-gain and ISS analysis of perturbed networked control systems with network-induced delays. By examples we demonstrate that the switching approach to event-triggered control can essentially reduce the amount of measurements to be sent through a communication network compared to the existing methods.

Quantum Stochastic Equations for an Opto-Mechanical Oscillator with Radiation Pressure Interaction and Non-Markovian Effects

The quantum stochastic Schroedinger equation or Hudson-Parthasareathy (HP) equation is a powerful tool to construct unitary dilations of quantum dynamical semigroups and to develop the theory of measurements in continuous time via the construction of output fields. An important feature of such an equation is that it allows to treat not only absorption and emission of quanta, but also scattering processes, which however had very few applications in physical modelling. Moreover, recent developments have shown that also some non-Markovian dynamics can be generated by suitable choices of the state of the quantum noises involved in the HP-equation. This paper is devoted to an application involving these two features, non-Markovianity and scattering process. We consider a micro-mirror mounted on a vibrating structure and reflecting a laser beam, a process giving rise to a radiation-pressure force on the mirror. We show that this process needs the scattering part of the HP-equation to be described. On the other side, non-Markovianity is introduced by the dissipation due to the interaction with some thermal environment which we represent by a phonon field, with a nearly arbitrary excitation spectrum, and by the introduction of phase noise in the laser beam. Finally, we study the full power spectrum of the reflected light and we show how the laser beam can be used as a temperature probe.

Experiment research on dynamic response of copper film at high strain rate by chirped pulse spectral interferometry

That the femtosecond laser pulses irradiate metallic materials thereby inducing ultrahigh strain rates, is an important experimental approach to studying the material behavior under extreme conditions. Femtosecond laser-generated shock waves in metal films have rise times of several picoseconds, the corresponding diagnostic technique is required to work with a higher time resolution, which makes the experimental measurements difficult. Chirped pulse spectral interferometry (CPSI) possesses capabilities of ultrafast time resolution and continuous measurement, thus it provides a diagnostic technique for studying the ultrashort shock wave. In this article, we carry out an experiment on femtosecond laser driven shock wave in copper film and the measurement by CPSI. Laser pulse of 25 fs duration at the central wavelength 800 nm is used, the tested samples are copper films of (5025) nm in thickness fabricated by electron beam sputtering deposition onto cover slip substrate of 180 m in thickness, pump beam focuses onto front surface of the copper film through the transparent substrate and this laser intensity is 2.31013 W/cm2. Chirped pulse spectral interferometry is used to detect the movements of the free rear surfaces of the copper films with temporal and spatial resolution. In the spectral interferometry, linearly chirped pulse is required and obtained by stretching the femtosecond laser pulse with a pair of gratings. The relation between frequency and time of the chirped pulse is accurately measured using asymmetric spectral interference method, which is required for explaining the experimental data. Since CPSI is a single shot diagnostic technique, we obtain the displacement and velocity history of the free rear surface with picosecond time resolution in a single measurement. From the results, the average shock velocity is calculated to be (5.60.2) km/s and the shock wave rise time is determined to be 6.9 ps. According to the shock wave relations, impact pressure and strain rate in the copper film are (57.18.8) GPa and 8109 s-1 respectively, the strain rate is so high that it is hard to achieve by long-pulse laser driven or other loading approaches. Additionally, experimental results also show that the free rear surface alternately experiences acceleration and deceleration, which indicates the spallation in the copper target. It is obvious that chirped pulse spectral interferometry is a reliable approach to studying ultrashort shock waves in metal films.

Effect of Fe3O4 nanoparticles on space charge distribution in propylene carbonate under impulse voltage

Addition of nanoparticles of the ferromagnetic material Fe3O4 can increase the positive impulse breakdown voltage of propylene carbonate by 11.65%. To further investigate the effect of ferromagnetic nanoparticles on the space charge distribution in the discharge process, the present work set up a Kerr electro-optic field mapping measurement system using an array photodetector to carry out time-continuous measurement of the electric field and space charge distribution in propylene carbonate before and after modification. Test results show that fast electrons can be captured by Fe3O4 nanoparticles and converted into relatively slow, negatively charged particles, inhibiting the generation and transportation of the space charge, especially the negative space charge.

Fast fitting of non-Gaussian state-space models to animal movement data via Template Model Builder.

State-space models (SSM) are often used for analyzing complex ecological processes that are not observed directly, such as marine animal movement. When outliers are present in the measurements, special care is needed in the analysis to obtain reliable location and process estimates. Here we recommend using the Laplace approximation combined with automatic differentiation (as implemented in the novel R package Template Model Builder; TMB) for the fast fitting of continuous-time multivariate non-Gaussian SSMs. Through Argos satellite tracking data, we demonstrate that the use of continuous-time t-distributed measurement errors for error-prone data is more robust to outliers and improves the location estimation compared to using discretized-time t-distributed errors (implemented with a Gibbs sampler) or using continuous-time Gaussian errors (as with the Kalman filter). Using TMB, we are able to estimate additional parameters compared to previous methods, all without requiring a substantial increase in computational time. The model implementation is made available through the R package argosTrack.

Time-continuous Kerr electro-optic field mapping measurement under impulse voltage using array photodetector

Space charge affects the electric field distribution in high voltage-stressed liquid dielectrics and can cause insulation degradation. This letter reports on research using a Kerr electro-optic measurement system with an array photodetector for Kerr electro-optic field mapping measurements in propylene carbonate under application of switching impulse voltages to investigate the electric field and space charge effects in high voltage-stressed liquid dielectrics. The electric field distribution between parallel aluminum electrodes is measured, and the results are compared with those measured using a charge-coupled device measurement system. The array photodetector measurement system has the advantages of higher sensitivity and higher time resolution because simultaneous optical Kerr measurements can be taken at multiple positions using a multi-element array photodetector. The results show that bipolar homo-charge injection occurs between the parallel aluminum electrodes. In the near future, this measurement system will be used in continuing research into the measurement of space charge effects using low Kerr constant liquids such as transformer oil.

A Nonlinear Stochastic Filter for Continuous-Time State Estimation.

Nonlinear filters produce a nonparametric estimate of the probability density of state at each point in time. Currently-known nonlinear filters include Particle Filters and the Kushner equation (and its un-normalized version: the Zakai equation). However, these filters have limited measurement models: Particle Filters require measurement at discrete times, and the Kushner and Zakai equations only apply when the measurement can be represented as a function of the state. We present a new nonlinear filter for continuous-time measurements with a much more general stochastic measurement model. It integrates to Bayes' rule over short time intervals and provides Bayes-optimal estimates from quantized, intermittent, or ambiguous sensor measurements. The filter has a close link to Information Theory, and we show that the rate of change of entropy of the density estimate is equal to the mutual information between the measurement and the state and thus the maximum achievable. This is a fundamentally new class of filter that is widely applicable to nonlinear estimation for continuous-time control.

Quantum cooling and squeezing of a levitating nanosphere via time-continuous measurements

With the purpose of controlling the steady state of a dielectric nanosphere levitated within an optical cavity, we study its conditional dynamics under simultaneous sideband cooling and additional time-continuous measurement of either the output cavity mode or the nanosphere’s position. We find that the average phonon number, purity and quantum squeezing of the steady-states can all be made more non-classical through the addition of time-continuous measurement. We predict that the continuous monitoring of the system, together with Markovian feedback, allows one to stabilize the dynamics for any value of the laser frequency driving the cavity. By considering state of the art values of the experimental parameters, we prove that one can in principle obtain a non-classical (squeezed) steady-state with an average phonon number .

Experimental Studies of Alternating and Direct Current Impedance Properties of Ag/AgCl Electrodes

Ag/AgCl electrodes as an important sensor are used in modern clinical detection and biomedical measurement, which have been widely applied in electrocardiograph (ECG), electroencephalogram (EEG), electromyography (EMG), electricity impedance technology (EIT) and so on. In this study, the electrode pairs were gel-to-gel connected. After a stimulating current, the alternating current (AC) or the direct current (DC), was injected through the electrode pair, the electrical potential was recorded, then impedance data of Ag/AgCl electrode was obtained. The results showed that the AC impedance of electrode increased, and then gradually decreased with the increase of current size. It was found that the DC impedance data of Ag/AgCl electrode was changed greatly after the electrode pair was injected into the alternating current. With the long time continuous measurement, the AC impedance of electrode pair gradually increased within the 12 hours. However, the significant fluctuations of AC impedance were observed after 12 hours. Comparing with the AC impedance, the DC impedance of electrode pair exhibited a great increase with the increase of measurement time.

Is spontaneous wave function collapse testable at all?

Mainstream literature on spontaneous wave function collapse never reflects on or profits from the formal coincidence and conceptual relationship with standard collapse under time-continuous quantum measurement (monitoring). I propose some easy lessons of standard monitoring theory which would make spontaneous collapse models revise some of their claims. In particular, the objective detection of spontaneous collapse remains impossible as long as the correct identification of what corresponds to the signal in standard monitoring is missing from spontaneous collapse models, the physical detectability of the “signal” is not stated explicitly and, finally, the principles of physical detection are not revealed.

Sampled-Data Nonlinear Observer Design for Sensorless Synchronous PMSM

The problem of designing sensorless nonlinear observers for permanent magnet synchronous motors (PMSMs) has been given a great deal of interest, especially over the few last years. In this respect, various classes of nonlinear observers have been proposed, but all of them require continuous-time measurements of the machine outputs and most of them are either designed on the basis of simplifed approximate model (not accounting for all machine nonlinear dynamics) or are not backed by a technically sound convergence analysis. Designing sampled-data sensorless observers, based on the machine nonlinear model and backed by a formal convergence analysis, has yet to be solved. In this paper, a solution to this problem is developed by combining ideas from the high gain design approach and and an inter-sample time predictor. Compared with classical high-gain observers, the new sampled-data sensorless observer includes an inter-sampled time predictor to allow large sampling period and play a crucial role in improving and enhancing the observer performances.