Effects Of Parameter Variations Research Articles

Dynamic regulation of resource transport induces criticality in interdependent networks of excitable units.

Various functions of a network of excitable units can be enhanced if the network is in the "critical regime," where excitations are, on average, neither damped nor amplified. An important question is how can such networks self-organize to operate in the critical regime. Previously, it was shown that regulation via resource transport on a secondary network can robustly maintain the primary network dynamics in a balanced state where activity doesn't grow or decay. Here we show that this internetwork regulation process robustly produces a power-law distribution of activity avalanches, as observed in experiments, over ranges of model parameters spanning orders of magnitude. We also show that the resource transport over the secondary network protects the system against the destabilizing effect of local variations in parameters and heterogeneity in network structure. For homogeneous networks, we derive a reduced three-dimensional map which reproduces the behavior of the full system.

CoHOG: A Light-Weight, Compute-Efficient, and Training-Free Visual Place Recognition Technique for Changing Environments

This letter presents a novel, compute-efficient and training-free approach based on Histogram-of-Oriented-Gradients (HOG) descriptor for achieving state-of-the-art performance-per-compute-unit in Visual Place Recognition (VPR). The inspiration for this approach (namely CoHOG) is based on the convolutional scanning and regions-based feature extraction employed by Convolutional Neural Networks (CNNs). By using image entropy to extract regions-of-interest (ROI) and regional-convolutional descriptor matching, our technique performs successful place recognition in changing environments. We use viewpoint- and appearance-variant public VPR datasets to report this matching performance, at lower RAM commitment, zero training requirements and 20 times lesser feature encoding time compared to state-of-the-art neural networks. We also discuss the image retrieval time of CoHOG and the effect of CoHOG's parametric variation on its place matching performance and encoding time.

Spectral finite element method for wave propagation analysis in smart composite beams containing delamination

PurposeThe purpose of the study is to present a frequency domain spectral finite element model (SFEM) based on fast Fourier transform (FFT) for wave propagation analysis of smart laminated composite beams with embedded delamination. For generating and sensing high-frequency elastic waves in composite beams, piezoelectric materials such as lead zirconate titanate (PZT) are used because they can act as both actuators and sensors. The present model is used to investigate the effects of parametric variation of delamination configuration on the propagation of fundamental anti-symmetric wave mode in piezoelectric composite beams.Design/methodology/approachThe spectral element is derived from the exact solution of the governing equation of motion in frequency domain, obtained through fast Fourier transformation of the time domain equation. The beam is divided into two sublaminates (delamination region) and two base laminates (integral regions). The delamination region is modeled by assuming constant and continuous cross-sectional rotation at the interfaces between the base laminate and sublaminates. The governing differential equation of motion for delaminated composite beam with piezoelectric lamina is obtained using Hamilton’s principle by introducing an electrical potential function.FindingsA detailed study of the wave response at the sensor shows that the A0 mode can be used for delamination detection in a wide region and is more suitable for detecting small delamination. It is observed that the amplitude and time of arrival of the reflected A0 wave from a delamination are strongly dependent on the size, position of the delamination and the stacking sequence. The degraded material properties because of the loss of stiffness and density in damaged area differently alter the S0 and A0 wave response and the group speed. The present method provides a potential technique for researchers to accurately model delaminations in piezoelectric composite beam structures. The delamination position can be identified if the time of flight of a reflected wave from delamination and the wave propagation speed of A0 (or S0) mode is known.Originality/valueSpectral finite element modeling of delaminated composite beams with piezoelectric layers has not been reported in the literature yet. The spectral element developed is validated by comparing the present results with those available in the literature. The spectral element developed is then used to investigate the wave propagation characteristics and interaction with delamination in the piezoelectric composite beam.

An analytical process-based approach to predicting breach width in levees constructed from dilatant soils

An accurate prediction of the breach widening rate after the onset of a levee failure is essential for flood risk assessments. Current state-of-the-art analytical breach growth relations are empirical in nature. The large variety in loading conditions, levee design, and levee construction material, combined with the limited amount of accurate measurements of breach growth, make the development of accurate empirical breach growth relations challenging. In this paper, a process-based breach widening relation is presented for levees constructed of dilatant soils. The process-based relation is derived from the weir flow equation and a process-based erosion equation. The breach widening relation can account for the effects of variations in soil parameters. For those cases for which soil parameters are unknown, a calibrated catch-all-coefficient is provided. The relation is benchmarked against the state-of-the-art empirical breach growth relation used in the Netherlands and validated against data on historical levee failures and experimental data.

Thermodynamic analysis of phase diagram of H2O-DMF-PCL system: investigation on the influence of inorganic additives TiO2/MMT

Phase diagrams for H2O-DMF-PCL ternary system and with the presence of inorganic additives, H2O-DMF-PCL–(TiO2/MMT) quaternary system are studied using Flory–Huggins theory, which explains the thermodynamic behavior of polymeric membranes formed out of phase inversion process. The experimental binodal curves were plotted using cloud points obtained from the titration method. Also, the experimental spinodal curve was drawn using the compositions at the onset of phase separation in the titration method and found matching with the theoretical spinodal curve. The effect of variations in the interaction parameters on the location of the binodal curve is studied. The ternary interaction parameter was determined by fitting the binodal curve with the cloud point data for the ternary and quaternary system. The interaction of PCL-DMF-H2O is found to be consistent even in the presence of TiO2 or MMT. Also, the ternary and quaternary interaction parameters involving these additives were found to be negligible within the system. On the other hand, the presence of additives shifted the binodal curve toward the solvent-polymer axis manifesting the less requirement of non-solvent for phase separation. The critical point for the ternary system obtained in both experiment and theoretical calculation was at the polymer concentration of around 6 wt%. Membranes having composition above the critical point were synthesized using phase inversion technique, and their morphology was examined using SEM images.

A procedure for ranking parameter importance for estimation in predictive mechanistic models

We begin with a mechanistic model that is considered to be a reasonably good predictor of the real-life system with a set of parameters determined from prior biophysical studies and expert knowledge. For complex mechanistic growth models, it is usually advantageous to numerically estimate a subset of the ‘most important’ parameters (i.e., those that most influence dynamic model behavior) based on data and fix the others at their estimated a priori values. Determining a reduced-order parameter subset for end-user estimation can be challenging, often relying heavily on expert knowledge and trial-and-error. A straightforward but oversimplified method relies on one-at-a-time (OAT) sensitivity of model outputs to changes in individual parameters. However, this commonly used method fails to account for how simultaneous changes in multiple parameters can significantly impact model outputs in unpredictable ways due to model nonlinearities. Additionally, hidden relationships between parameters can prevent consistent identifiability of parameters from different initial estimates. Rather than analyzing the effect of individual parameter variation on the model outputs, we evaluate the importance of parameters to the curvature of the quadratic cost function (sum squared difference between reference and model output sequences). This analysis is carried out by calculating the matrix of second-order partial derivatives of the cost function (aka Hessian matrix) with respect to the model parameters. Calculating the cost function Hessian allows analysis of changes in multiple parameters simultaneously. The method is presented as an analytic, reproducible procedure for determining a ranking for parameter importance. The procedure is demonstrated on a limited version of the Yield-SAFE predictive agroforestry growth model. For the analysis, 12 model parameters are considered with their nominal values set to those given in a published implementation of Yield-SAFE. The Hessian was calculated at 212 ( = 4096) locations systematically selected in the neighborhood of the nominal parameter setting, each generating a parameter ranking determined by the relative contribution of each parameter to the cost function curvature. The top ranked 6 parameters were the same for 4091 of 4096 locations, suggesting that this procedure has potential to guide modelers in recommending the most important parameters for estimation given reasonably good initial parameter estimates and real data.

Noninvasive and Improved Torque and Efficiency Calculation Toward Current Advance Angle Determination for Maximum Efficiency Control of PMSM

This article proposes improved mathematical models for torque and system efficiency used toward obtaining accurate current advance angle for maximizing the efficiency of an interior permanent magnet (IPM) synchronous motor. First, improved torque and efficiency calculation procedure that consider the effects of parameter variations, such as inductance, stator resistance and PM flux linkage simultaneously, and motor and inverter losses, have been developed from a combination of analytical models and practical experiments. Subsequently, an offline search procedure has been utilized to determine the optimal current angle using the improved dq -axis-based models. The novelty of the efficiency model is that the method uses preliminary noninvasive experimental tests to consider the saturation and temperature effects simultaneously and successfully determine the relationship between stator and rotor temperatures by using only controller command voltages and currents. Experimental investigations are performed on a laboratory IPM for validating the developed control method through interpolation of improved look-up tables with the derived current angle values for varying speed, torque, and temperature conditions. The effectiveness of the proposed method in improving efficiency is also verified and compared with maximum efficiency and maximum torque per ampere methods using experimental sweep tests.

Integrated Fixed Film Activated Sludge (IFAS) membrane BioReactor: The influence of the operational parameters

The present paper investigated an Integrated Fixed Film Activated Sludge (IFAS) Membrane BioReactor (MBR) system monitored for 340 days. In particular, the short-term effects of some operational parameters variation was evaluated. Results showed a decrease of the removal rates under low C/N values. Respirometry results highlighted that activated sludge was more active in the organic carbon removal. Conversely, biofilm has a key role during nitrification. The major fouling mechanism was represented by the cake deposition (irreversible).

Coupled dynamic analysis of a heavily-loaded propulsion shafting system with continuous bearing-shaft friction

This paper studies the friction-induced instability and nonlinear dynamics of a heavily-loaded slow speed propulsion shafting subjected to the uninterrupted contact between the shaft and the water-lubricated rubber bearing. A high-dimensional analytical model is developed to take into consideration the intrinsic interactions among the torsional and lateral vibrations of the continuous shaft, bearing vibrations and the friction nonlinearity. The exponential friction model derived from experimental data is adopted to qualitatively represent the velocity-dependent behaviours of friction for water-lubricated rubber bearings. A stability analysis based on the complex eigenvalue calculations of the linearised system is performed to estimate the effects of parameter variations on instabilities. Two potential instabilities concerning the self-excited whirl motions and stick-slip torsional motions are identified. Corresponding transient dynamics are then numerically studied to explore the roles of different types of vibrations on nonlinear behaviours. The results reveal that the velocity-weakening and discontinuity effects of nonlinear friction may induce the occurrence of limit-cycle type self-excited vibrations for both instabilities. Additionally, the effects of cross-coupling and the kinematic coupling at the bearing-shaft interface on the dynamic interaction among different vibration modes are also highlighted.

Improved MR fingerprinting for relaxation measurement in the presence of semisolid magnetization transfer.

To characterize and minimize the magnetization transfer (MT) effect in MR fingerprinting (MRF) relaxation measurements with a 2-pool (2P) MT model of multiple tissue types. Semisolid MT effect in MRF was modeled using 2P Bloch-McConnell equations. The combinations of MT parameters of multiple tissues (white [WM] and gray matter [GM]) were used to build the MRF dictionary. Both 1-pool (1P) and 2P models were simulated to characterize the dependence on MT. Relaxations measured using MRF with spin-echo saturation-recovery (SR) or inversion-recovery preparations were compared with conventional SR-prepared T1 and multiple spin-echo T2 measurements. The simulations results were validated with phantoms and brain tissue samples. The MRF signal was different from the 1P and 2P models. 1P MRF produced significantly (P < .05) underestimated T1 in WM (20-30%) and GM (7-10%), while 2P MRF measured consistent T1 and T2 in both WM and GM with conventional measurements (pairwise test P > .1; correlated P < .05). Simulations showed that SR-prepared MRF measuring T1 had much less errors against the variation of the macromolecular fraction. Compared with inversion-recovery preparation, SR-prepared MRF produced higher relaxation correlations (R > 0.9) with conventional measurements in both WM and GM across samples, suggesting that SR-prepared MRF was less sensitive to the compositive effect of multiple MT parameters variations. 2P MRF using a combination of MT parameters for multiple tissue types can measure consistent relaxations with conventional methods. With the 2P models, SR-prepared MRF would provide an option for robust relaxation measurement under heterogeneous MT.

Investigation of LPBF A800H steel parts using Computed Tomography and Mössbauer spectroscopy

Laser powder bed fusion (LPBF) was applied in this study to produce a prototype of a miniaturized catalytic burner (CAB), which is a key component of high-temperature polymer electrolyte fuel cells. This prototype was characterized by its complex design with numerous channels, chambers, and thin walls. The test samples and CAB prototype were made of a heat-resistant, anti-corrodible steel called "Alloy 800H" (1.4876), a material that poses problems for welding operations and especially for the LPBF process due to its strong susceptibility to hot cracking and spatters. The effects of LPBF parameter variation on preliminary test samples were investigated by nano-focus Computed Tomography (CT) and Optical microscopy to clarify the internal structure and defects for further LPBF process optimization. Mössbauer spectroscopy points out that LPBF process does not lead to either local phase separation nor oxidation of steel, which is critical factor for use of CAB at high temperatures. The sufficient LPBF parameter sets were used to manufacture the CAB prototype, which was examined by micro-CT and optics as well. The main result of the investigation is a demonstration of the technological feasibility to decrease the number and size of defects in complex LPBF-manufactured Alloy 800H constructions without changes in phase composition at high temperatures.

Synchronverter: A Comprehensive Review of Modifications, Stability Assessment, Applications and Future Perspectives

The increase in the penetration of renewable energy sources (RES) has reduced the effective inertia of the power system dominated by synchronous machines. The reduction in inertia has paved the way to the development of inertia emulation techniques, which complements the increased penetration of RES. The synchronverter technology is one among the virtual inertia emulation techniques which resembles close to the synchronous machine. The advancements in control and adaptations of synchronverter for various applications demand a comprehensive yet critical review. Thus, the main objective of this paper is to present a critical review of synchronverter technology which could increase the inertial response of RES. A critical analysis of modifications made to original synchronverter and the stability assessment techniques is presented. The effect of parameter variation on stability and dynamic performance is brought out as a decision matrix by analysing the movement of eigenvalues presented in various works. Towards the end, a synoptic overview is presented to depict the research trend and emphasize the domain which requires further attention. Furthermore, a brief discussion of the research gaps perceived during the phase of review is presented to leverage future research in the field.

Effects of process parameters in joining of Inconel-625 alloy through microwave hybrid heating

Microwave joining is a new field of research that needs to be explored and standardized to make it commercially viable. In this work, effects of process parameters are analyzed during joining of Inconel-625 through microwave hybrid heating. Experiments are conducted inside a microwave applicator under varied experimental conditions. Effects of variation in process parameters are analyzed to see their effect on melting of the joint interface. Effect of four input parameters (size of drilled hole of vertical charcoal feeder, thickness of graphite sheet, thickness of insulation brick, surface contact between refractory and insulation brick) on the melting region have been investigated during this work. Results of this work show the correct melting of the joint zone, absence of defects such as crater formation and no spreading of the charcoal powder on specimen.

Design and development of modified RTD-A controller for unstable bioreactor

Control of open loop unstable process is a challenging one owing to the presence of right hand plane pole(s). The spotlight of this paper is to develop modified Robustness set point Tracking Disturbance rejection and Aggressiveness controller(RTD-A) for an unstable process. The RTD-A controller formulation is modified accordingly to suit the unstable process. The proposed control scheme has two control loops. The unstable process is initially stabilized by an inner feedback loop consisting of a proportional controller. The RTD-A control strategy is then implemented on the stabilized plant. The developed control scheme is validated on an nonlinear unstable bioreactor plant model in a simulation environment. It is found that the proposed controller has better servo and regulatory performance when compared to the conventional IMC-PID controller. Effect of variation in the tuning parameters of the controllers on the process output is analysed in detail.

The Effect of Source and Drain Pocketing on the Performance of Double-Gate Tunnelling Field-Effect Transistor

In this paper the digital and analogue performance of double-gate tunnelling FET, DGTFET, is reported, when a pocket of different dielectric is inserted near the source, drain or both. The variation of these pocket lengths and their relative shift to the edge of source or drain region affects device performance. The investigated performance parameters include the ON/OFF ratio, the maximum cut-off frequency, fT, the subthreshold swing, SS, and the ambipolar current, Iambi. With the aid of TCAD simulator, the effect of pocket parameter variation is studied. Our study shows that when the main gate dielectric is hafnium dioxide, the source pocket is favored to be of low dielectric constant and high width. However, for the drain case, it is better to have shorter pockets with a low dielectric constant. The investigation shown here proves that pocketing the DGTFET can enhance its whole performance in terms of investigated parameters.

Tool wear and chip formation analysis of aluminium hybrid metal matrix composite

Since last two decades technology has changed rapidly in each industry from consumer goods to aerospace. To quench the thrust of technology advancement of industries, the research community has to develop novel materials. As a part of the ongoing process of material development and machinability study, present work carried out to find out the effect of reinforcement and machining parameter variation on the cutting tool. Furthermore, chip analysis was carried out to find out the effect of reinforcement and cutting parameter variation on types of chip formed. The desirability of the chips was decided based on the surface finish value. Pure aluminium was used as a matrix material while; B4C, Mg, Ti and Graphite were used as reinforcement. It was observed that the unfavourable machining parameter reduces tool life considerably and this phenomenon was more evident in the carbide coated insert compared to PCD insert. High tool wear was observed during machining of composite material compared to the aluminium matrix. An undesired chip produced when feed increases and speed reduces. Moreover, change in reinforcement amount also has an effect on the types of chip produces. The surface roughness value up to 0.50 μm was reduced by a combination of optimized cutting parameters and change in reinforcement amount.

Early Stage Calibration of a Formula SAE Engine 1-D Fluid Dynamic Model with Limited Experimental Data

This work addresses the early stage calibration of a Formula SAE engine 1-D fluid dynamic model starting from limited experimental data. The availability of an engine model since the early stages of the development of a new Formula SAE vehicle allows to carry out preliminary analyses or ECU calibration. A few experimental tests have been executed at wide open throttle and variable engine speed. Then, a 1D thermo-fluid dynamic engine model has been developed starting from the geometry data of the engine. A vector optimization problem has been then solved to calibrate the engine model. In particular, the error minimization between numerical and experimental values of the torque in different engine operating conditions has been set as objective of the optimization process. Finally, starting from the results of the proposed calibration methodology, a decision-making criterion allowed the identification of a single optimal solution within the Pareto optimal front together with the related values for the set of calibration parameters. The results highlight how the proposed calibration procedure could be usefully adopted to set an early stage engine model which could be properly adopted to preliminarily detect the effects of geometric changes or control parameters variations on the main engine performance.

Automated calculation of spectral-reflectance marker-points to enable analysis of plant colour-signalling to pollinators

A spectral reflectance curve for a coloured surface can be constructed from a set of radiation reflectance value measurements made across the spectrum at discrete wavelengths. The curve gives an indication of the pattern of light entering the eye of an organism viewing an illuminated object. Marker points represent the positions along a reflectance curve at which sharp transitions in reflectance occur, these being potentially important to visual perception, for instance by insects discriminating between two flowers, each of a different colour. Consequently, methods of marker point analysis have been applied in several studies evaluating flower colours. These studies have sometimes required researchers to place marker points on reflectance curves by eye, or they have used algorithms written as unreleased software. To automate the process systematically and provide open access, we implemented special-purpose software in C++. Below we provide a summary of the approach adopted in our implementation and made available online in a port to TypeScript. The main benefits of our method are summarized as being:•Automation and repeatability.•Standardisation, cross-platform compatibility and Open Access.•Interactive exploration of the effects of parameter variation.

Pseudo-Static Limit Equilibrium Method for Bearing Capacity of Footing on Slope and Seismic Uplift Capacity of Horizontal Strip Anchor

Seismic bearing capacity for a shallow strip footing embedded in a sloping ground is derived along with seismic uplift capacity of horizontal strip anchors. c-ϕ soil medium is used with limit equilibrium method of analysis. A planar failure mechanism has been adopted. The seismic bearing capacity is determined in the form of a single pseudo-static bearing capacity coefficient (N γe ) in association with unit weight, surcharge and cohesion, which becomes more practical to simulate the actual field problem. The seismic forces are considered to act both on the footing and on the soil below the footing. The effects of soil friction angle, soil cohesion, wall friction angle, horizontal and vertical seismic accelerations are taken into account to evaluate the seismic bearing capacity of the foundation. Also seismic uplift capacity factors for horizontal strip anchors is found. The factor is determined as a function of embedment ratio, angle of internal friction of soil, angle of wall friction, cohesion of soil and seismic acceleration coefficients. The uplift capacity factors have been determined for the simultaneous resistance of cohesion and unit weight of soil. Effect of the vertical seismic acceleration coefficient has been found to always reduce the uplift capacity factor whereas the effect of horizontal seismic acceleration coefficient has also been found to reduce the uplift capacity factor in maximum cases. The results obtained from both the cases has been compared with existing literature and the effect of parametric variations discussed.

Wind Turbine’s Gearbox Aided Design Approach Using Bond Graph Methodology and Monte Carlo Simulation

Uncertainties in geared products vary according to different levels; there are design uncertainties (physical assumptions, parameters estimations, etc.), manufacturing errors (cutting defects, assembly errors, defects due to heat treatments, etc.) and operating errors such as lubrication. In this paper, uncertainties effect on the transmitted power within a 750 kW Horizontal Axis Wind Turbine gearbox is investigated. A methodology for transmission chain modelling and parametric synthesis in the design phase is detailed. It is based on Bond Graph theory to establish uncertain physical model and Monte Carlo Simulation to conduct a parametric synthesis allowing the definition of each parameter’s interval of variation. After model verification by means of 20-Sim (Controllab product), power gap reveals a variation of 34.87 kW around the nominal value. In addition, Monte Carlo Simulation allows the prediction of each parameter variation effect on the torque transmitted to the induction machine. Study’s results will provide designers with information to conduct a robust design and then achieve high machine’s efficiency.