Loop Model Research Articles

Patient-specific, echocardiography compatible flow loop model of aortic valve regurgitation in the setting of a mechanical assist device.

Aortic regurgitation (AR) occurs commonly in patients with continuous-flow left ventricular assist devices (LVAD). No gold standard is available to assess AR severity in this setting. Aim of this study was to create a patient-specific model of AR-LVAD with tailored AR flow assessed by Doppler echocardiography. An echo-compatible flow loop incorporating a 3D printed left heart of a Heart Mate II (HMII) recipient with known significant AR was created. Forward flow and LVAD flow at different LVAD speed were directly measured and AR regurgitant volume (RegVol) obtained by subtraction. Doppler parameters of AR were simultaneously measured at each LVAD speed. We reproduced hemodynamics in a LVAD recipient with AR. AR in the model replicated accurately the AR in the index patient by comparable Color Doppler assessment. Forward flow increased from 4.09 to 5.61 L/min with LVAD speed increasing from 8,800 to 11,000 RPM while RegVol increased by 0.5 L/min (2.01 to 2.5 L/min). Our circulatory flow loop was able to accurately replicate AR severity and flow hemodynamics in an LVAD recipient. This model can be reliably used to study echo parameters and aid clinical management of patients with LVAD.

Role of DAMPs and cell death in autoimmune diseases: the example of multiple sclerosis.

Multiple sclerosis is a chronic neuroinflammatory demyelinating disease of the central nervous system (CNS) of unknown etiology and still incompletely clarified pathogenesis. The disease is generally considered a disorder resulting from a complex interplay between environmental risk factors and predisposing causal genetic variants. To examine the etiopathogenesis of the disease, two complementary pre-clinical models are currently discussed: the "outside-in" model proposing a peripherally elicited inflammatory/autoimmune attack against degraded myelin as the cause of the disease, and the "inside-out" paradigm implying a primary cytodegenerative process of cells in the CNS that triggers secondary reactive inflammatory/autoimmune responses against myelin debris. In this review, the integrating pathogenetic role of damage-associated molecular patterns (DAMPs) in these two scenario models is examined by focusing on the origin and sources of these molecules, which are known to promote neuroinflammation and, via activation of pattern recognition receptor-bearing antigen-presenting cells, drive and shape autoimmune responses. In particular, environmental factors are discussed that are conceptually defined as agents which produce endogenous DAMPs via induction of regulated cell death (RCD) or act themselves as exogenous DAMPs. Indeed, in the field of autoimmune diseases, including multiple sclerosis, recent research has focused on environmental triggers that cause secondary events in terms of subroutines of RCD, which have been identified as prolific sources of DAMPs. Finally, a model of a DAMP-driven positive feed-forward loop of chronic inflammatory demyelinating processes is proposed, aimed at reconciling the competing "inside-out" and "outside-in" paradigms.

COMPARISON OF MODELS OF MAGNETIZATION CURVES AND HYSTERESIS LOOPS ACCORDING TO THE GILES-ATHERTON MODEL FOR SOFT MAGNETIC AMORPHOUS ALLOYS

The subject of research in the article is ferromagnetic soft magnetic amorphous materials and alloys, which are used in power sources of automated control systems, and in vehicle electrical installations. The aim of the work is an objective comparison of two magnetization models for soft magnetic amorphous alloys - the main magnetization curve using approximation functions and the Giles-Atherton hysteresis loop model. In the study, the least squares method was used to optimize the main magnetization curve and the Giles-Atherton hysteresis loop optimization method with the aim of its maximum coincidence with the experimentally obtained loop. Experimental and reference data for common types of magnetically soft amorphous alloys were used for modeling. As a criterion of model accuracy for both modeling methods, the relative error in determining the magnetic induction value was chosen, and the experimental value obtained from the real hysteresis loop of a magnetically soft amorphous alloy was taken as its exact value, and the approximate value was taken from calculations of the magnetic induction value using the methods of approximating the magnetization curve and simulation of the hysteresis loop using the Giles-Atherton method. As a result of the research, it was revealed that both models of magnetization of magnetically soft amorphous materials give simulation results similar in accuracy. The obtained results of the study can be used to select an appropriate magnetization model for the mathematical description of ferromagnetic devices using magnetically soft amorphous metals and alloys. The final conclusion about the advantages of a particular model can only be made on the basis of the ultimate goals of the analysis.

A Model for Gradual-phase Heating Driven by MHD Turbulence in Solar Flares

Coronal flare emission is commonly observed to decay on timescales longer than those predicted by impulsively driven, one-dimensional flare loop models. This discrepancy is most apparent during the gradual phase, where emission from these models decays over minutes, in contrast to the hour or more often observed. Magnetic reconnection is invoked as the energy source of a flare, but should deposit energy into a given loop within a matter of seconds. Models which supplement this impulsive energization with a long, persistent ad hoc heating have successfully reproduced long-duration emission, but without providing a clear physical justification. Here we propose a model for extended flare heating by the slow dissipation of turbulent Alfvén waves initiated during the retraction of newly reconnected flux tubes through a current sheet. Using one-dimensional simulations, we track the production and evolution of MHD wave turbulence trapped by reflection from high-density gradients in the transition region. Turbulent energy dissipates through nonlinear interaction between counter-propagating waves, modeled here using a phenomenological one-point closure model. Atmospheric Imaging Assembly EUV light curves synthesized from the simulation were able to reproduce emission decay on the order of tens of minutes. We find this simple model offers a possible mechanism for generating the extended heating demanded by observed coronal flare emissions self-consistently from reconnection-powered flare energy release.

Quantifying and interpreting the hysteresis patterns of monthly sediment concentration and water discharge in karst watersheds

Hysteresis loop models are one of the most common and effective tools for quantifying time-scale dynamics of sediment-discharge relationships. These models can successfully characterize sediment dynamics in watersheds and facilitate developing effective measures to manage sediment-discharge resources. Considering the characteristics of a proportional hysteresis index, an improved differential hysteresis index was developed. The improved model was used to quantify typical patterns of monthly sediment-discharge relationships in six karst watersheds in southwest China during 2003–2019. Partial least squares structural equation modeling was conducted to decouple the effects of climatic factors and vegetation extent on the hysteresis index. The results indicate that clockwise hysteresis accounted for 74 % of the total hysteresis occurring in the watersheds, whereas counterclockwise and 8-shaped hysteresis accounted for only 22 % and 3.9 %, respectively. The improved hysteresis index varied from −10 to 10, effectively reflecting the degree of hysteresis occurring in the watersheds. Partial least squares structural equation modeling shows that climatic factors (e.g., temperature and precipitation) and vegetation extent in the Hongshui, Yujiang, Liujiang and Wujiang watersheds explained 50 %∼75 % of the hysteresis between sediment concentration and water discharge. The combined effect of temperature and precipitation on the hysteresis index was larger than that of vegetation extent. The improved differential hysteresis index proposed in this study effectively extended the applicability of differential hysteresis indices and facilitated comparing the degree of hysteresis among watersheds with different sediment concentrations. This study can improve the understanding of sediment sources and transport pathways and provide valuable information for decision making on soil erosion control in karst watersheds.

Poisson-Dirichlet distributions and weakly first-order spin-nematic phase transitions

We provide a quantitative characterization of generic weakly first-order thermal phase transitions out of planar spin-nematic states in three-dimensional spin-one quantum magnets, based on calculations using Poisson-Dirichlet distributions (PD) within a universal loop model formulation, combined with large-scale quantum Monte Carlo calculations. In contrast to earlier claims, the thermal melting of the nematic state is not continuous, instead a weakly first-order transition is identified from both thermal properties and the distribution of the nematic order parameter. Furthermore, based on PD calculations, we obtain exact results for the order parameter distribution and Binder cumulants at the discontinuous melting transition. Our findings establish the thermal melting of planar spin-nematic states as a generic platform for quantitative approaches to weakly first-order phase transitions in quantum systems with a continuous SU(2) internal symmetry.

A Novel Window into Angiogenesis-Intravital Microscopy in the AV-Loop-Model.

Due to the limitations of current in vivo experimental designs, our comprehensive knowledge of vascular development and its implications for the development of large-scale engineered tissue constructs is very limited. Therefore, the purpose of this study was to develop unique in vivo imaging chambers that allow the live visualization of cellular processes in the arteriovenous (AV) loop model in rats. We have developed two different types of chambers. Chamber A is installed in the skin using the purse sting fixing method, while chamber B is installed subcutaneously under the skin. Both chambers are filled with modified gelatin hydrogel as a matrix. Intravital microscopy (IVM) was performed after the injection of fluorescein isothiocyanate (FITC)-labeled dextran and rhodamine 6G dye. The AV loop was functional for two weeks in chamber A and allowed visualization of the leukocyte trafficking. In chamber B, microvascular development in the AV loop could be examined for 21 days. Quantification of the microvascular outgrowth was performed using Fiji-ImageJ. Overall, by combining these two IVM chambers, we can comprehensively understand vascular development in the AV loop tissue engineering model¯.

Interrogating solar flare loop models with IRIS observations 2: Plasma properties, energy transport, and future directions

During solar flares a tremendous amount of magnetic energy is released and transported through the Sun’s atmosphere and out into the heliosphere. Despite over a century of study, many unresolved questions surrounding solar flares are still present. Among those are how does the solar plasma respond to flare energy deposition, and what are the important physical processes that transport that energy from the release site in the corona through the transition region and chromosphere? Attacking these questions requires the concert of advanced numerical simulations and high spatial-, temporal-, and spectral-resolution observations. While flares are 3D phenomenon, simulating the NLTE flaring chromosphere in 3D and performing parameter studies of 3D models is largely outwith our current computational capabilities. We instead rely on state-of-the-art 1D field-aligned simulations to study the physical processes that govern flares. Over the last decade, data from the Interface Region Imaging Spectrograph (IRIS) have provided the crucial observations with which we can critically interrogate the predictions of those flare loop models. Here in Paper 2 of a two-part review of IRIS and flare loop models, I discuss how forward modelling flares can help us understand the observations from IRIS, and how IRIS can reveal where our models do well and where we are likely missing important processes, focussing in particular on the plasma properties, energy transport mechanisms, and future directions of flare modelling.

Adoption of Internet of Medical Things: A Systems Thinking Approach

ABSTRACT As an emerging information technology, the Internet of Medical Things (IoMT) has the capability to contribute toward sustainable healthcare, but its adoption in emerging economies is challenging. This research was undertaken to conduct a holistic analysis of the complexities associated with the adoption of IoMT in emerging economies like India using a systems thinking approach. Three qualitative phases of the systems thinking and modeling methodology, namely, problem structuring, causal loop modeling, and developing strategic interventions, were used in this study by collecting data from 24 interviews and secondary research. The reference mode developed in the study captured the system behavior, showing IoMT adoption increasing in tier I Indian cities but struggling in tier II/III cities and rural Indian communities. The qualitative systems model developed explained this behavior by capturing the underlying system structure using six interconnected feedback loops. Three strategic interventions were then formulated to change the system structure that can improve the adoption of IoMT in an emerging economy like India, thereby contributing to the journey toward sustainable healthcare. Implications for similar emerging economies in Latin America are also discussed in this article. Overall, this study provides a holistic analysis of the complexities involved in the adoption of IoMT using a systems thinking approach.

In vivo vascularized scaffold with different shear-exposed models for lymphatic tissue regeneration

Current clinical treatments on lymphedema provide promising results, but also result in donor site morbidities. The establishment of a microenvironment optimized for lymphangiogenesis can be an alternative way to enhance lymphatic tissue formation. Hemodynamic flow stimuli have been confirmed to have an influential effect on angiogenesis in tissue engineering, but not on lymphatic vessel formation. Here, the three in vivo scaffolds generated from different blood stimuli in the subcutaneous layer, in the flow through pedicle, and in an arterio-venous (AV) loop model, were created to investigate potential of lymphangiogenesis of scaffolds containing lymphatic endothelial cells (LECs). Our results indicated that AV loop model displayed better lymphangiogenesis in comparison to the other two models with slower flow or no stimuli. Other than hemodynamic force, the supplement of LECs is required for lymphatic vessel regeneration. The in vivo scaffold generated from AV loop model provides an effective approach for engineering lymphatic tissue in the clinical treatment of lymphedema.

Modeling, Stability, and Design of the Single-Phase SOGI-Based Phase-Locked Loop Considering the Frequency Feedback Loop Effect

For single-phase grid-connected inverters, the second-order generalized integrator-based phase-locked loop (SOGI-PLL) is widely used for good harmonics attenuation and frequency adaptability. However, existing studies usually neglect the frequency feedback loop in the modeling and design process, and thus, the potential instability caused by the frequency feedback loop is not well explained. Besides, the improper design of SOGI-PLL can lead to the inverter instability both under ideal and weak grid conditions. Therefore, by fully considering the coupling of the frequency feedback loop, this article establishes an accurate model for SOGI-PLL. Furthermore, effects of different PLL parameters on behaviors of both the SOGI-PLL itself and the inverter are studied, based on which a graphical method for PLL parameters design is proposed. As proved, the frequency feedback loop can deteriorate the stability and performance of both SOGI-PLL itself and inverter system, especially if rapid transient is expected. The modeling method is also extended to the low-pass filter-SOGI-PLL and the improved parameters design is discussed. Experimental results verify the correctness of the proposed PLL model and the abovementioned analysis results. The proposed model is helpful to deeply reveal the instability mechanism and provides a reference for the PLL design under nonideal grid conditions.

Research on Automatic Driving Control of Tracked Transport Vehicle Based on Labview

HighlightsAn indirect Kalman filter algorithm is proposed to fuse GNSS/INS positioning information.Detailed kinematics and dynamics model of track vehicles was established.An MPC-based double-layer closed-loop controller combined with tracked vehicle model is designed.Tracked transport vehicle performs well in path tracking on soft soil road.Abstract. Orchards in hills and mountainous regions are more occluded and single satellite navigation is unstable. Therefore, the indirect Kalman filter information fusion algorithm was proposed to achieve high-precision positioning by establishing a state error equation based on GNSS/INS. A complete kinematics and dynamics model of tracked chassis was established. A double-layer closed-loop controller based on model predictive control (MPC) was designed. An MPC controller based on the kinematics model in the outer loop was designed to output the expected control value of the tracked transporter. The inner loop design was based on the extended state observer of the dynamic model to estimate and compensate for the internal and external disturbances of the system. The performance test was based on a tracked chassis platform. The test results presented that when driving at a speed of 0.50 m/s under soft soil road conditions, the maximum lateral deviation was 0.15 m, and the average absolute deviation was 0.05 m. This high level of control accuracy means that this control design enables the transfer vehicle to follow the navigation path precisely and complete its task. Keywords: Hills and mountainous regions, Integrated navigation, Model predictive control, Vehicle dynamics model.

Comparative Analysis of Open Loop and Closed Loop Models of Boost Converter

This work aims to construct a DC-DC boost converter that can provide stabilized output in response to input variations in open-loop and closed-loop modes. Several optimization strategies that have easier implementation, higher convergence quality, and more computing power are used to create a suitable controller that can be effectively implemented for DC-DC boost converters. In the presence of R-load, the PID controller parameters are optimized through the use of different optimization techniques to improve the dynamic response of the converter, and to improve the R-load's efficiency by fine-tuning the PID controller's parameters using a variety of optimization techniques. In terms of time domain specifications, including settling time, rise time, peak time, and overshoot, the efficiency of the open loop and closed loop techniques is examined. The research modeling of this technique is done in MATLAB/SIMULINK 2014 platform in terms of various performance metrics.

Pulmonary Response Prediction Comparison through Three Personalized Basis Functions in a Virtual Patient Model

Recruitment manoeuvres with subsequent positive-end-expiratory-pressure (PEEP) have proved effective in recruiting lung volume and preventing alveoli collapse. However, determining a safe, effective, and patient-specific positive end-expiratory pressure (PEEP) is not standardized. This study examines three physiologically relevant basis function sets in conjunction with Hysteresis Loop Modelling (HLM) to enable better elastance evolution predictions for a virtual patient model, adding novel elements to model and predict distension. Prediction accuracy and robustness are validated against 18 volume controlled ventilated (VCV) patients at 7 different baseline PEEP levels (0 to 12cmH2O) yielding 623 cases. Predictions were made, up to 12cmH2O covering 6 × 2cmH2O PEEP steps. The 3 basis function sets yield an absolute median peak inspiratory pressure prediction error of 1.63cmH2O for VCV patients. Overall results demonstrate recruitment mechanics are best captured by an exponential basis function, matching physiological expectations, and accurately capture, for the first time, distension mechanics enabling the risk of lung injury to be predicted before changing ventilator settings. The overall outcomes significantly extend and more fully validate this virtual mechanical ventilation patient model.

The Vicious Circles of Skill Erosion: A Case Study of Cognitive Automation

Cognitive automation powered by advanced intelligent technologies is increasingly enabling organizations to automate more of their knowledge work tasks. Although this often offers higher efficiency and lower costs, cognitive automation exacerbates the erosion of human skill and expertise in automated tasks. Accepting the erosion of obsolete skills is necessary to reap the benefits of technology—however, the erosion of essential human expertise is problematic if workers remain accountable for tasks for which they lack sufficient understanding, rendering them incapable of responding if the automation fails. Though the phenomenon is widely acknowledged, the dynamics behind such undesired skill erosion are poorly understood. Thus, taking the perspective of sociotechnical systems, we conducted a case study of an accounting firm that had experienced skill erosion over a number of years due to reliance on their software’s automated functions. We synthesized our findings using causal loop modeling based on system dynamics. The resulting dynamic model explains skill erosion via an interplay between humans’ automation reliance, complacency, and mindful conduction. It shows how increasing reliance on automation fosters complacency at both individual and organizational levels, weakening workers’ mindfulness across three work task facets (activity awareness, competence maintenance, and output assessment), resulting in skill erosion. Such skill erosion may remain obscure, acknowledged by neither workers nor managers. We conclude by discussing the implications for theory and practice and identifying directions for future research.

Weak-light phase locking aided by frequency division phase meter for intersatellite laser interferometry

Weak light phase locking is an important part of intersatellite laser interference ranging. Phase-locked loop (PLL) is used to track the phase of heterodyne interference optical signal. Owing to shot noise, laser frequency and other kinds of noise, there is a phase difference between the internal PLL local oscillator and the heterodyne signal, while the phase detection range of the PLL is only one period. If the phase difference exceeds the phase detection range at a certain time, the local oscillator may enter the wrong operating point under feedback regulation, resulting in cycle clip, which leads to subsequent phase reconstruction errors. In this paper, a cycle clip diagnosis method based on the detection background of gravitational waves is proposed. Based on the original PLL, an auxiliary frequency phase divider with larger phase detection range is introduced, which can provide a basis for judging whether the cycle clip occurs in the PLL. In this paper, a digital weak-light PLL model is established to evaluate the influence of various noise. The theoretical spectral density of the error phase is given according to the two main kinds of noise (laser phase noise and particle noise). Considering the limited detection range of PLL, large error phase may lead to cycle clip, making the PLL work at the wrong locking point. A phase meter with smaller frequency division phase range can be used to solve this problem. First, the input heterodyne sine signal is converted into in-phase square wave N frequency division. Then the phase difference is determined by comparing the output signal with output signal reduced by 1/<i>N</i> through the time-to-degital converter (TDC) Based on the theory of PLL and noise, the theoretical model of frequency division phase meter is established. The simulation results show that the frequency division phase meter can realize a wide range of phase detection under the current theoretical framework and has the ability to judge the cycle clip of weak light phase locking. It can be used in the weak- light phase locking task represented by LISA.

Low-Frequency Oscillation Analysis of Grid-Connected VSG System Considering Multi-Parameter Coupling

With the increasing integration of new energy generation into the power system and the massive withdrawal of traditional fossil fuel generation, the power system is faced with a large number of stability problems. The phenomenon of low-frequency oscillation caused by lack of damping and moment of inertia is worth studying. In recent years, virtual synchronous generator (VSG) technique has been developed rapidly because it can provide considerable damping and moment of inertia. While improving the stability of the system, it also inevitably causes the problem of active power oscillation, especially the low mutual damping between the VSG and the power grid will make the oscillation more severe. The traditional time-domain state-space method cannot reflect the interaction among state variables and study the interaction between different nodes and branches of the power grid. In this paper, a frequency-domain method for analyzing low-frequency oscillations considering VSG parameter coupling is proposed. First, based on the rotor motion equation of the synchronous generator (SG), a second-order VSG model and linearized power-frequency control loop model are established. Then, the differences and connections between the coupling of key VSG parameters and low-frequency oscillation characteristics are studied through frequency domain analysis. The path and influence mechanism of a VSG during low-frequency power grid oscillations are illustrated. Finally, the correctness of the theoretical analysis model is verified by simulation.

Hardware in the loop modeling of T-type voltage source inverter for vehicle to grid applications

The grid-tied three-phase T-type voltage source inverter (T-type VSI) modeling process for residential battery charging stations is described in this paper. The primary goal is to create a HIL simulation model and control algorithm for the PLECS circuit simulator. This paper focused on the importance of the HIL simulation system in testing the control algorithm and power electronics. The hardware architecture of the system, the software tool, and the required modifications are described. Additionally, the proposed converter's simulation results are evaluated.

Multi-Channel Networked MIMO-MPC-based SiL/HiL/MiL for CC/CV Sections’ Optimization in 6th Gen Hybrid/Islanded Inverters for Mobile Green Nano-Grids in FEW Nexus

The Food, Energy, and Water (FEW) Nexus is an ever-existing paradigm since the big bang. Resilient and mobile green energy nano-grid fabric is the horizon at the pinnacle of 6th generation inverters where FEW and major UNDP SDGs seem to meet. Three major challenges exist in the existing inverters: a) are based on uni-variable PID controllers and do not provide abstract grid parameters that make the decision-making for the consumers and OEMs, especially in islanded nano-grids; b) there is not a single MIMO-MPC-based solution that can employ a mesh network of spatially deployed Nanogrids nodes to derive the abstract key performance indicators (KPIs) in nano-grids, and c) the hardcoded smart inverters’ firmware is impossible to optimize like SoC-based SiL/MiL/MiL looped embedded systems that hamper the adaptation of SISO-MPC and MIMO-MPCs. In this work design, development, and optimization of multi-channel CC/CV section modules based on MIMO-MPC using Hardware in Loop (HiL), Software in Loop (SiL), and Model in Loop (MiL) integrated 6th generation inverters architecture was proposed to achieve the autonomous green mobility nano-girds. The system achieved an efficiency of 7.8kWh/day at 20.8ᵒ tilt with charging states of [23% to 65%].

Interrogating solar flare loop models with IRIS observations 1: Overview of the models, and mass flows

Solar flares are transient yet dramatic events in the atmosphere of the Sun, during which a vast amount of magnetic energy is liberated. This energy is subsequently transported through the solar atmosphere or into the heliosphere, and together with coronal mass ejections flares comprise a fundamental component of space weather. Thus, understanding the physical processes at play in flares is vital. That understanding often requires the use of forward modelling in order to predict the hydrodynamic and radiative response of the solar atmosphere. Those predictions must then be critiqued by observations to show us where our models are missing ingredients. While flares are of course 3D phenomenon, simulating the flaring atmosphere including an accurate chromosphere with the required spatial scales in 3D is largely beyond current computational capabilities, and certainly performing parameter studies of energy transport mechanisms is not yet tractable in 3D. Therefore, field-aligned 1D loop models that can resolve the relevant scales have a crucial role to play in advancing our knowledge of flares. In recent years, driven in part by the spectacular observations from the Interface Region Imaging Spectrograph (IRIS), flare loop models have revealed many interesting features of flares. For this review I highlight some important results that illustrate the utility of attacking the problem of solar flares with a combination of high quality observations, and state-of-the-art flare loop models, demonstrating: 1) how models help to interpret flare observations from IRIS, 2) how those observations show us where we are missing physics from our models, and 3) how the ever increasing quality of solar observations drives model improvements. Here in Paper one of this two part review I provide an overview of modern flare loop models, and of electron-beam driven mass flows during solar flares.