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O’Steen, Lance, i David Werth. "The Application of an Evolutionary Algorithm to the Optimization of a Mesoscale Meteorological Model". Journal of Applied Meteorology and Climatology 48, nr 2 (1.02.2009): 317–29. http://dx.doi.org/10.1175/2008jamc1967.1.
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Abstract It is shown that a simple evolutionary algorithm can optimize a set of mesoscale atmospheric model parameters with respect to agreement between the mesoscale simulation and a limited set of synthetic observations. This is illustrated using the Regional Atmospheric Modeling System (RAMS). A set of 23 RAMS parameters is optimized by minimizing a cost function based on the root-mean-square (rms) error between the RAMS simulation and synthetic data (observations derived from a separate RAMS simulation). It is found that the optimization can be done with relatively modest computer resources; therefore, operational implementation is possible. The overall number of simulations needed to obtain a specific reduction of the cost function is found to depend strongly on the procedure used to perturb the “child” parameters relative to their “parents” within the evolutionary algorithm. In addition, the choice of meteorological variables that are included in the rms error and their relative weighting are also found to be important factors in the optimization.
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Mello, Brian, i Mark Stein. "Integrative Learning and Simulating Revolution and Protest in the Middle East". Review of Middle East Studies 55, nr 1 (czerwiec 2021): 110–23. http://dx.doi.org/10.1017/rms.2021.41.
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AbstractThis essay explores insights from our experiences teaching undergraduates a set of paired history and political science courses on protest and revolution in the Middle East. Working in groups, students developed simulations of key moments of revolution or protest explored during the courses. The simulation assignment was designed to engage students in an active learning setting and as a shared assignment across both courses. The most interesting result of this project, from the teaching perspective, was its unanticipated ability to expose students to the contingency and emotion that scholarship has recently emphasized as critical to understanding social movements, but which so often falls out of the study of history and political science analyses of protest and revolution. In this paper we explore the simulation assignment, how student groups designed the simulations with limited guidance from instructors, how students took on the assigned roles by engaging deeply with the histories of the events, and how the engagement in the simulations complicated the analyses that formed the bedrock of our course readings. In our analysis we draw on two iterations of the paired courses and use both student qualitative assessments of the course and student reflections on the simulations that were included in group papers.
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Arabnejad, Mohammad Hossein, Håkan Nilsson i Rickard E. Bensow. "Scale-resolving simulations of the flow in the Francis-99 turbine at part-load condition". IOP Conference Series: Earth and Environmental Science 1079, nr 1 (1.09.2022): 012085. http://dx.doi.org/10.1088/1755-1315/1079/1/012085.
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Abstract In this paper, we investigate the formation of the Rotating Vortex Rope (RVR) using scale-resolving methods, SAS and Wall-Modeled LES (WMLES). We compare the results from these simulation methods with the experimental data of the Francis-99 workshop. This comparison shows that the general features of the RVR can be captured with both methods. However, using WMLES methods would lead to a better quantitative agreement between the velocity profiles in the draft tube in the simulation and the experiment. The reasons for this better agreement are discussed in detail. A comparison of the pressure fluctuations in the draft tube captured in the simulations and the experiment is also presented. This comparison shows that all simulations under-predict the Root Mean Square (RMS) of these pressure fluctuations, although the RMS values predicted by the WMLES simulation are closer to the experimental values.
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Yuile, Adam, Alexander Schulz, Erik Wiss, Jens Müller i Steffen Wiese. "The Simulated Effect of Adding Solder Layers on Reactive Multilayer Films Used for Joining Processes". Applied Sciences 12, nr 5 (25.02.2022): 2397. http://dx.doi.org/10.3390/app12052397.
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In order to introduce new bonding methods in the area of electronic packaging a theoretical analysis was conducted, which should give substantial information about the potential of reactive multilayer systems (rms) to create sufficient local heat for joining processes between silicon chips and ceramic substrates. For this purpose, thermal CFD (computational fluid dynamics) simulations have been carried out to simulate the temperature profile of the bonding zone during and after the reaction of the rms. This thermal analysis considers two different configurations. The first configuration consists of a silicon chip that is bonded to an LTCC-substrate (Low Temperature Co-fired Ceramics) using a bonding layer that contains an rms and a solder preform. The reaction propagation speed of the reactive multilayer was set to a value of 1 m/s, in order to partially melt a solder preform underneath a silicon chip. The second configuration, which consists only of the LTCC-substrate and the rms, was chosen to study the differences between the thermal outputs of the two arrangements. The analysis of the CFD simulations was particularly focused on interpretations of the temperature and liquid fraction contours. The CFD thermal simulation analysis conducted contains a melting/solidification model which can track the molten/solid state of the solder in addition to modelling the influence of latent heat. To provide information for the design of a test-substrate for experimental investigations, the real behaviour of Pt-100 temperature probes on the LTCC-substrate was simulated, in order to monitor an actual bonding in the experiment. All simulations were carried out using the ANSYS Fluent software.
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Philpott, Thomas, Ashish P. Agalgaonkar, Thomas Brinsmead i Kashem M. Muttaqi. "An Open-Source Julia Package for RMS Time-Domain Simulations of Power Systems". Energies 17, nr 22 (13.11.2024): 5677. http://dx.doi.org/10.3390/en17225677.
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This paper presents RMSPowerSims.jl, an open-source Julia package for the time-domain simulation of power systems. The package is designed to be used in conjunction with PowerModels.jl, a widely used Julia package for power system optimization. RMSPowerSims.jl provides a framework for the simulation of power systems in the time domain, allowing for the study of transient stability, frequency stability, and other dynamic phenomena. The package is designed to be intuitive and flexible, allowing users to easily define custom models for network components and disturbances, while also providing a range of pre-constructed models for common power system components. RMSPowerSims.jl simplifies the process of performing RMS simulations on power system models developed using the PowerModels.jl ecosystem, and provides an easy-to-use modeling that reduces the barrier to entry for new users wishing to perform RMS simulations. The accuracy of the package is verified against DIgSILENT PowerFactory for short-circuit and load-increase disturbances, using the New England 39-bus system. The active power generation delivered by several generators in the network, and the voltage magnitudes of selected busbars are analyzed and noted to be in close agreement with those obtained using PowerFactory. The computational performance of the package is compared to that of PowerFactory and is found to be comparable for load-step simulations; however, PowerFactory is found to be considerably faster for short-circuit simulations. As computational performance is not a priority at this stage of development, this is expected, and speed optimization is planned for future work. RMSPowerSims.jl is available under an open-source license and can be downloaded from GitHub.
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Petrović, Predrag B. "Tuneable Current Mode RMS Detector". Journal of Electrical Engineering 66, nr 1 (1.01.2015): 11–18. http://dx.doi.org/10.1515/jee-2015-0002.
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Abstract A new realization of RMS detector, employing two CCCIIs (controlled current conveyors), metal-oxide-semiconductor transistors and single grounded capacitor is present in this paper, without any external resistors and components matching requirements. The proposed circuit can be applied in measuring the RMS value of periodic, band-limited signals. The proposed circuit is very appropriate to further develop into integrated circuits. The errors related to the signal processing and errors bound were investigated and provided. To verify the theoretical analysis, the circuit PSpice simulations have also been included, showing good agreement with the theory.
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Xiao, Jianguang, Yanxin Wang, Dongmo Zhou, Chenglong He i Xiangrong Li. "Research on the Impact-Induced Deflagration Behavior by Aluminum/Teflon Projectile". Crystals 12, nr 4 (28.03.2022): 471. http://dx.doi.org/10.3390/cryst12040471.
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Although the ignition-and-growth model can simulate the ignition and detonation behavior of traditional energy materials well, it seems insufficient to simulate the impact-induced deflagration behavior of reactive materials (RMs) using current finite element codes due to their more complicated ignition threshold and lower reaction rates. Therefore, a simulation method for the impact-induced deflagration behavior of a reactive materials projectile (RMP) is developed by introducing tunable ignition threshold conditions for RMs, and a user-defined subroutine is formed by the secondary development on the equation of state (EOS). High-velocity impact experiments were performed to prove the validity of simulations. The results show that the user-defined subroutine for RMs is competent in simulating the ignition and deflagration behavior under impact conditions, because the reaction ratio, morphology and temperature distribution of RMP fragments are all well consistent with experiments, theory, and current reports from other researchers. In this way, the quantitative study on the deflagration reaction of RMs can be implemented and relevant mechanisms are revealed more clearly.
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Li, Xiaoning, Chuanhai Wang, Gang Chen, Xing Fang, Pingnan Zhang i Wenjuan Hua. "Distributed-Framework Basin Modeling System: Ⅲ. Hydraulic Modeling System". Water 13, nr 5 (28.02.2021): 649. http://dx.doi.org/10.3390/w13050649.
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A distributed-framework basin modeling system (DFBMS) was developed to simulate the runoff generation and movement on a basin scale. This study is part of a series of papers on DFBMS that focuses on the hydraulic calculation methods in runoff concentration on underlying surfaces and flow movement in river networks and lakes. This paper introduces the distributed-framework river modeling system (DF-RMS) that is a professional modeling system for hydraulic modeling. The DF-RMS contains different hydrological feature units (HFUs) to simulate the runoff movement through a system of rivers, storage units, lakes, and hydraulic structures. The river network simulations were categorized into different types, including one-dimensional river branch, dendritic river network, loop river network, and intersecting river network. The DF-RMS was applied to the middle and downstream portions of the Huai River Plain in China using different HFUs for river networks and lakes. The simulation results showed great consistency with the observed data, which proves that DF-RMS is a reliable system to simulate the flow movement in river networks and lakes.
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Bollimpalli, D. A., R. Mahmoud, C. Done, P. C. Fragile, W. Kluźniak, R. Narayan i C. J. White. "Looking for the underlying cause of black hole X-ray variability in GRMHD simulations". Monthly Notices of the Royal Astronomical Society 496, nr 3 (23.06.2020): 3808–28. http://dx.doi.org/10.1093/mnras/staa1808.
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ABSTRACT Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time-scales of a few milliseconds to seconds. The observed light curves display various characteristic features like a lognormal distribution of flux and a linear rms–flux relation, which indicate that the underlying variability process is stochastic in nature. It is also thought to be intrinsic to accretion. This variability has been modelled as inward propagating fluctuations of mass accretion rate, although the physical process driving the fluctuations remains puzzling. In this work, we analyse five exceptionally long-duration general relativistic magnetohydrodynamic (GRMHD) simulations of optically thin, geometrically thick, black hole accretion flows to look for hints of propagating fluctuations in the simulation data. We find that the accretion profiles from these simulations do show evidence for inward propagating fluctuations below the viscous frequency by featuring strong radial coherence and positive time lags when comparing smaller to larger radii, although these time lags are generally shorter than the viscous time-scale and are frequency-independent. Our simulations also support the notion that the fluctuations in $\dot{M}$ build up in a multiplicative manner, as the simulations exhibit linear rms–mass flux relations, as well as lognormal distributions of their mass fluxes. When combining the mass fluxes from the simulations with an assumed emissivity profile, we additionally find broad agreement with observed power spectra and time lags, including a recovery of the frequency dependency of the time lags.
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Zima, Beata, i Rafal Kedra. "RMS-based damage detection in reinforced concrete beams: numerical simulations". Diagnostyka 20, nr 4 (17.09.2019): 3–10. http://dx.doi.org/10.29354/diag/112395.
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Sur, Sharanya. "Decaying turbulence and magnetic fields in galaxy clusters". Monthly Notices of the Royal Astronomical Society 488, nr 3 (11.07.2019): 3439–45. http://dx.doi.org/10.1093/mnras/stz1918.
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Abstract We explore the decay of turbulence and magnetic fields generated by fluctuation dynamo action in the context of galaxy clusters where such a decaying phase can occur in the aftermath of a major merger event. Using idealized numerical simulations that start from a kinetically dominated regime we focus on the decay of the steady state rms velocity and the magnetic field for a wide range of conditions that include varying the compressibility of the flow, the forcing wavenumber, and the magnetic Prandtl number. Irrespective of the compressibility of the flow, both the rms velocity and the rms magnetic field decay as a power law in time. In the subsonic case we find that the exponent of the power law is consistent with the −3/5 scaling reported in previous studies. However, in the transonic regime both the rms velocity and the magnetic field initially undergo rapid decay with an ≈t−1.1 scaling with time. This is followed by a phase of slow decay where the decay of the rms velocity exhibits an ≈−3/5 scaling in time, while the rms magnetic field scales as ≈−5/7. Furthermore, analysis of the Faraday rotation measure (RM) reveals that the Faraday RM also decays as a power law in time ≈t−5/7; steeper than the ∼t−2/5 scaling obtained in previous simulations of magnetic field decay in subsonic turbulence. Apart from galaxy clusters, our work can have potential implications in the study of magnetic fields in elliptical galaxies.
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Hernández Velázquez, J. D., i A. Gama Goicochea. "Synergy between surfactants’ stiffness and concentration on their self-assembly into reverse micelles as water droplet carriers in nonpolar solvents". PLOS ONE 19, nr 2 (2.02.2024): e0294913. http://dx.doi.org/10.1371/journal.pone.0294913.
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A study of the self-assembly process into reverse micelles (RMs) of linear surfactants and monomeric aqueous solutes dissolved in nonpolar solvents, varying the concentration (cs) and the persistence length (Lp) of the surfactants is presented here. The influence of cs and Lp on the structural and dynamic properties of the aggregates is investigated through mesoscopic simulations carried out with the dissipative particle dynamics method. All simulations are performed at a fixed water/surfactant molecular ratio of 2:1, varying the surfactant concentration from c = 6 wt% up to c = 12 wt%, for increasing surfactants’ rigidity from Lp = 0.73 nm up to Lp = 44.99 nm. It is found that there exists a collaborative interplay between cs and Lp that enhances the number of RMs assembled and their diffusion as carriers of water droplets. These results should be useful as guidelines to understand and improve processes where the RMs are implemented to carry aqueous solutes in nonpolar solvents.
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Gola, Arkadiusz, Zbigniew Pastuszak, Marcin Relich, Łukasz Sobaszek i Eryk Szwarc. "Scalability analysis of selected structures of a reconfigurable manufacturing system taking into account a reduction in machine tools reliability". Eksploatacja i Niezawodnosc - Maintenance and Reliability 23, nr 2 (8.02.2021): 242–52. http://dx.doi.org/10.17531/ein.2021.2.4.
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Scalability is a key feature of reconfigurable manufacturing systems (RMS). It enables fast and cost-effective adaptation of their structure to sudden changes in product demand. In principle, it allows to adjust a system's production capacity to match the existing orders. However, scalability can also act as a "safety buffer" to ensure a required minimum level of productivity, even when there is a decline in the reliability of the machines that are part of the machine tool subsystem of a manufacturing system. In this article, we analysed selected functional structures of an RMS under design to see whether they could be expanded should the reliability of machine tools decrease making it impossible to achieve a defined level of productivity. We also investigated the impact of the expansion of the system on its reliability. To identify bottlenecks in the manufacturing process, we ran computer simulations in which the course of the manufacturing process was modelled and simulated for 2-, 3-, 4- and 5-stage RMS structures using Tecnomatix Plant Simulation software.
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Jensen, Konrad Johan, Morten Kjeld Ebbesen i Michael Rygaard Hansen. "Adaptive Feedforward Control of a Pressure Compensated Differential Cylinder". Applied Sciences 10, nr 21 (5.11.2020): 7847. http://dx.doi.org/10.3390/app10217847.
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This paper presents the design, simulation and experimental verification of adaptive feedforward motion control for a hydraulic differential cylinder. The proposed solution is implemented on a hydraulic loader crane. Based on common adaptation methods, a typical electro-hydraulic motion control system has been extended with a novel adaptive feedforward controller that has two separate feedforward states, i.e, one for each direction of motion. Simulations show convergence of the feedforward states, as well as 23% reduction in root mean square (RMS) cylinder position error compared to a fixed gain feedforward controller. The experiments show an even more pronounced advantage of the proposed controller, with an 80% reduction in RMS cylinder position error, and that the separate feedforward states are able to adapt to model uncertainties in both directions of motion.
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Bartello, Peter, Olivier Métais i Marcel Lesieur. "Coherent structures in rotating three-dimensional turbulence". Journal of Fluid Mechanics 273 (25.08.1994): 1–29. http://dx.doi.org/10.1017/s0022112094001837.
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Numerical simulations investigating the formation and stability of quasi-two-dimensional coherent vortices in rotating homogeneous three-dimensional flow are described. In a numerical study of shear flows Lesieur, Yanase & Métais (1991) found that cyclones (respectively anticyclones) with |ω2D| ∼ O(2Ω), where ω2D is the vorticity and Ω is the rotation rate, are stabilized (respectively destabilized) by the rotation. A study of triply periodic pseudo-spectral simulations (643) was undertaken in order to investigate the vorticity asymmetry in homogeneous turbulence. Specifically, we examine (i) the possible three-dimensionalization of initially two-dimensional vortices and (ii) the emergence of quasi-two-dimensional structures in initially-isotropic three-dimensional turbulence. Direct numerical simulations of the Navier—Stokes equations are compared with large-eddy simulations employing a subgridscale model based on the second-order velocity structure function evaluated at the grid separation and with simulations employing hyperviscosity.Isolated coherent two-dimensional vortices, obtained from a two-dimensional decay simulation, were superposed with a low-amplitude three-dimensional perturbation, and used to initialize the first set of simulations. With Ω = 0, a three-dimensionalization of all vortices was observed. This occurred first in the small scales in conjunction with the formation of longitudinal hairpin vortices with vorticity perpendicular to that of the initial quasi-two-dimensional flow. In agreement with centrifugal stability arguments, when 2Ω = [ω2D]rms a rapid destabilization of anticyclones was observed to occur, whereas the initial two-dimensional cyclonic vortices persisted throughout the simulation. At larger Ω, both cyclones and anticyclones remained two-dimensional, consistent with the Taylor—Proudman theorem. A second set of simulations starting from isotropic three-dimensional fields was initialized by allowing a random velocity field to evolve (Ω = 0) until maximum energy dissipation. When the simulations were continued with 2Ω = [ω · Ω]rms/Ω, the three-dimensional flow was observed to organize into two-dimensional cyclonic vortices. At larger Ω, two-dimensional anticyclones also emerged from the initially-isotropic flow. The consequences for a variety of industrial and geophysical applications are clear. For quasi-two-dimensional eddies whose characteristic circulation times are of the order ofder of Ω−1, rotation induces a complete disruption of anticyclonic vortices, while stabilizing cyclonic ones.
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Jeong, Jaeyoon, Sangshin Kwak i Seungdeog Choi. "Degradation-Sensitive Control Algorithm Based on Phase Optimization for Interleaved DC–DC Converters". Machines 11, nr 6 (5.06.2023): 624. http://dx.doi.org/10.3390/machines11060624.
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As the use of interleaved DC–DC converters in electric vehicles (EVs) increases, research on reliability improvement is required. In the case of interleaved DC–DC converters, degradation occurs between transistors and capacitors. In particular, transistor degradation imbalances cause an increase in output capacitor RMS current, which increases power loss and accelerates capacitor degradation. This degradation affects system reliability by increasing thermal stress. In this paper, based on a degraded 2-leg interleaved DC–DC boost converter, research to reduce the converter’s output capacitor RMS current was conducted. The output capacitor RMS current according to the transistor degradation imbalance was analyzed. As a result, it was confirmed that the transistor degradation imbalance causes an increase in the capacitor RMS current. To address this issue, a phase optimization algorithm for reducing increased capacitor RMS current is presented in this paper. Next, the phase optimization algorithm is mathematically analyzed. Finally, its efficacy is proved through simulations and experiments.
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Girard, J. W., J. Y. Chen, R. W. Dibble, J. Janicka i R. Homma. "Fuel-Air Mixing In A Turbulent Coannular Pipe Flow Measured Using Laser Absorption With Genetic Algorithm-Based Tomographic Reconstruction And Modeled With LES". Eurasian Chemico-Technological Journal 16, nr 2-3 (8.04.2014): 117. http://dx.doi.org/10.18321/ectj176.
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This research aims at improving the knowledge base of fuel-air mixing through measurements and modeling. The measurements are from an improved tomographic reconstruction method that is relatively easy to accomplish. A novel aspect of this research is the use of tomography for generating the RMS of fuel concentration. Measurements of fuel concentration for a mixing field were tomographically reconstructed from time resolved line of sight laser absorption measurements. The modeling is done using large eddy simulations (LES). LES predictions were compared to measurements of the mean and RMS of fuel concentration. The LES model predicted time-averaged radial fuel concentration profiles to within 5%, and overpredicted the RMS of fuel concentration slightly, predicting the trends correctly.
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Ito, Hirotaka, Amir Levinson i Shigehiro Nagataki. "Monte Carlo simulations of relativistic radiation-mediated shocks: II. photon-starved regime". Monthly Notices of the Royal Astronomical Society 492, nr 2 (23.12.2019): 1902–13. http://dx.doi.org/10.1093/mnras/stz3591.
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ABSTRACT Radiation-mediated shocks (RMS) play a key role in shaping the early emission observed in many transients. In most cases, e.g. shock breakout in supernovae, llGRBs, and neutron star mergers, the upstream plasma is devoid of radiation, and the photons that ultimately reach the observer are generated predominantly inside and downstream of the shock. Predicting the observed spectrum requires detailed calculations of the shock structure and thermodynamic state that account properly for the shock microphysics. We present results of self-consistent Monte Carlo simulations of photon-starved RMS, which yield the shock structure and emission for a broad range of shock velocities, from subrelativistic (βsh = 0.1) to highly relativistic (Γsh = 20). Our simulations confirm that in relativistic RMS the immediate downstream temperature is regulated by exponential pair creation, ranging from 50 keV at βsh = 0.5–200 keV at Γsh = 20. At lower velocities, the temperature becomes sensitive to the shock velocity, with kT ∼ 0.5 keV at βsh = 0.1. We also confirm that in relativistic shocks the opacity is completely dominated by newly created pairs, which has important implications for the breakout physics. We find the transition to pair dominance to occur at βsh = 0.5 roughly. In all cases examined, the spectrum below the νFν peak has been found to be substantially softer than the Planck distribution. This has important implications for the optical emission in fast and relativistic breakouts, and their detection. The applications to GRB 060218 and GRB 170817A are discussed.
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Ishimoto, Hiroshi, Masahiro Hayashi i Yuzo Mano. "Ash particle refractive index model for simulating the brightness temperature spectrum of volcanic ash clouds from satellite infrared sounder measurements". Atmospheric Measurement Techniques 15, nr 2 (27.01.2022): 435–58. http://dx.doi.org/10.5194/amt-15-435-2022.
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Abstract. Using data from the Infrared Atmospheric Sounding Interferometer (IASI) measurements of volcanic ash clouds (VACs) and radiative transfer calculations, we attempt to simulate the measured brightness temperature spectra (BTS) of volcanic ash aerosols in the infrared region. In particular, the dependence on the ash refractive index (RI) model is investigated. We apply 21 RI models for the optical properties of ash particles, including recently published models. The results of BTS simulations are evaluated using the root mean square (rms) of the brightness temperature difference between measurements and simulations for channels in the wavenumber range of 750–1400 cm−1. The results of numerical simulations for 156 pixels of IASI measurements for ash plumes from seven volcanoes indicated that some newly established RI models have smaller rms than those obtained with the conventional ash RI model. For some eruption events, the RI models deduced from the chemical composition of ash samples for the same volcanic eruption events simulate the measured BTS well. The results suggest that infrared sounder measurements and precise BTS simulations of the VACs contribute to estimating the appropriate RI model in satellite VAC analysis.
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Xu, Songhua, Chunwei Zhang i Ardashir Mohammadzadeh. "Type-3 Fuzzy Control of Robotic Manipulators". Symmetry 15, nr 2 (11.02.2023): 483. http://dx.doi.org/10.3390/sym15020483.
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In this paper, the control of robotic manipulators (RMs) is studied. The RMs are widely used in industry. The RMs are multi-input-multi-output systems, and their dynamics are highly nonlinear. To improve the accuracy in practice, it is impossible to ignore the influence of nonlinear dynamics and the interaction of inputs–outputs. Non-structural uncertainties such as friction, disturbance, and unmodeled dynamics are other challenges of these systems. Recently, type-3 (T3) fuzzy logic systems (FLSs) have been suggested that result in better accuracy in a noisy environment. In this paper, a new control idea on the basis of T3-FLSs is suggested. T3-FLSs are used to estimate the dynamics of RMs and the symmetrical perturbations. The T3-FLSs are learned using online laws to enhance the stability. To eliminate the effect of the interconnection of inputs and estimation errors , a compensator is developed. By several simulations, the superiority of the suggested controller is demonstrated.
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Samuelsson, Filip, Christoffer Lundman i Felix Ryde. "An Efficient Method for Fitting Radiation-mediated Shocks to Gamma-Ray Burst Data: The Kompaneets RMS Approximation". Astrophysical Journal 925, nr 1 (1.01.2022): 65. http://dx.doi.org/10.3847/1538-4357/ac332a.
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Abstract Shocks that occur below a gamma-ray burst (GRB) jet photosphere are mediated by radiation. Such radiation-mediated shocks (RMSs) could be responsible for shaping the prompt GRB emission. Although well studied theoretically, RMS models have not yet been fitted to data owing to the computational cost of simulating RMSs from first principles. Here we bridge the gap between theory and observations by developing an approximate method capable of accurately reproducing radiation spectra from mildly relativistic (in the shock frame) or slower RMSs, called the Kompaneets RMS approximation (KRA). The approximation is based on the similarities between thermal Comptonization of radiation and the bulk Comptonization that occurs inside an RMS. We validate the method by comparing simulated KRA radiation spectra to first-principle radiation hydrodynamics simulations, finding excellent agreement both inside the RMS and in the RMS downstream. The KRA is then applied to a shock scenario inside a GRB jet, allowing for fast and efficient fitting to GRB data. We illustrate the capabilities of the developed method by performing a fit to a nonthermal spectrum in GRB 150314A. The fit allows us to uncover the physical properties of the RMS responsible for the prompt emission, such as the shock speed and the upstream plasma temperature.
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Xiong, Lei, Zhiyi Yao, Haiyang Miao i Bo Ai. "Vehicle-to-Vehicle Channel Characterization Based on Ray-Tracing for Urban Road Scenarios". Wireless Communications and Mobile Computing 2021 (30.03.2021): 1–15. http://dx.doi.org/10.1155/2021/8854247.
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In this paper, the vehicle-to-vehicle (V2V) channel characteristics in peak hours at the 5.9 GHz band in two typical urban road scenarios, the urban straight road and the intersection, are investigated. The channel characteristics, such as path loss, root mean square (RMS) delay spread, and angular spread, are derived from the ray-tracing (RT) simulations. Due to the low height of antennas at both the transmitter (Tx) and the receiver (Rx), the line of sight (LOS) between the Tx and the Rx will often be obstructed by other vehicles. Based on the RT simulation results, the shadowing loss is modelled by the multimodal Gaussian distribution, and path loss models in both LOS and non-LOS (NLOS) conditions are obtained. And the RMS delay spread in two scenarios can be modelled by the Weibull distribution. In addition, the deployment of an antenna array is discussed based on the statistics distribution of the angular spread.
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Zhang, Yu, Sanbao Hu, Yunqing Zhang i Liping Chen. "Optimization and Analysis of Centrifugal Pump considering Fluid-Structure Interaction". Scientific World Journal 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/131802.
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This paper presents the optimization of vibrations of centrifugal pump considering fluid-structure interaction (FSI). A set of centrifugal pumps with various blade shapes were studied using FSI method, in order to investigate the transient vibration performance. The Kriging model, based on the results of the FSI simulations, was established to approximate the relationship between the geometrical parameters of pump impeller and the root mean square (RMS) values of the displacement response at the pump bearing block. Hence, multi-island genetic algorithm (MIGA) has been implemented to minimize the RMS value of the impeller displacement. A prototype of centrifugal pump has been manufactured and an experimental validation of the optimization results has been carried out. The comparison among results of Kriging surrogate model, FSI simulation, and experimental test showed a good consistency of the three approaches. Finally, the transient mechanical behavior of pump impeller has been investigated using FSI method based on the optimized geometry parameters of pump impeller.
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Zhang, Jie, Liang Zhang, Ahn Kiet Tieu, Guillaume Michal, Hong Tao Zhu i Guan Yu Deng. "Finite-Temperature Multiscale Simulations for 3D Nanoscale Contacts". Applied Mechanics and Materials 846 (lipiec 2016): 288–93. http://dx.doi.org/10.4028/www.scientific.net/amm.846.288.
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A finite-temperature analysis of a multiscale model, which couples finite element and molecular dynamics, is presented in this paper. The model is evaluated by the patch test and demonstrates its capacity. Then, the multiscale scheme is used to study 3D nanoscale contacts. The linear relationship between the contact area ratio and load is observed at small loads, but the temperature effect is small. However, the change in the root mean square (RMS) of heights depends on the temperature at high loads.
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Lan 藍鼎文, Ting-Wen, i J. Xavier Prochaska. "Constraining magnetic fields in the circumgalactic medium". Monthly Notices of the Royal Astronomical Society 496, nr 3 (19.06.2020): 3142–51. http://dx.doi.org/10.1093/mnras/staa1750.
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ABSTRACT We study the properties of magnetic fields in the circumgalactic medium (CGM) of z < 1 galaxies by correlating Faraday rotation measures (RMs) of ∼1000 high-redshift radio sources with the foreground galaxy number density estimated from the DESI Legacy Imaging Surveys. This method enables us to extract signals of RMs contributed by intervening gas around multiple galaxies. Our results show that there is no detectable correlation between the distribution of RMs and the number of foreground galaxies, contrary to several previous results. Utilizing the non-detection signals, we estimate 3σ upper limits to the RMs from the CGM of $\sim \!20 \rm \ rad\, m^{-2}$ within 50 kpc and $\sim \!10 \rm \ rad \, m^{-2}$ at separations of 100 kpc. By adopting a column density distribution of ionized gas obtained from absorption-line measurements, we further estimate the strengths of coherent magnetic fields parallel to the line of sight of $\lt \rm 2 \ \mu G$ in the CGM. We show that the estimated upper limits of RMs and magnetic field strengths are sufficient to constrain outputs of recent galaxy magnetohydrodynamic simulations. Finally, we discuss possible causes for the inconsistency between our results and previous works.
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Dumitriu, Mădălina, i Ionuţ Radu Răcănel. "Experimental Verification of Method to Synthesize the Track Vertical Irregularities". Romanian Journal of Transport Infrastructure 7, nr 2 (1.12.2018): 40–60. http://dx.doi.org/10.2478/rjti-2018-0011.
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Abstract The paper focuses on the experimental verification of the results derived from numerical simulations, based on a model of the bogie-track system, where the vertical track irregularities are introduced in the form of a pseudorandom function. This function comes from an original method of synthesizing the vertical track irregularities, depending on the geometric quality of the track and on the velocity. To verify the method, the root mean square (RMS) of the simulated accelerations in the axles and the bogie frame against each axle is compared to the experimental accelerations within the frequency range of wavelengths of the track vertical irregularities from 3 to 120 m. The results have shown a good correlation between the simulated RMS accelerations for a low quality track and the measured RMS accelerations.
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Mähönen, Petri, Tetsuya Hara, Toivo Voll i Shigeru Miyoshi. "Statistics of Cosmic Microwave Background Radiation with the Cosmic String Model". International Journal of Modern Physics D 06, nr 05 (październik 1997): 535–44. http://dx.doi.org/10.1142/s0218271897000327.
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We have studied the cosmic microwave background radiation by simulating the cosmic string network induced anisotropies on the sky. The large-angular size simulations are based on the Kaiser–Stebbins effect calculated from full cosmic-string network simulation. The small-angular size simulations are done by Monte-Carlo simulation of perturbations from a time-discretized toy model. We use these results to find the normalization of μ, the string mass per unit length, and compare this result with one needed for large-scale structure formation. We show that the cosmic string scenario is in good agreement with COBE, SK94, and MSAM94 microwave background radiation experiments with reasonable string network parameters. The predicted rms-temperature fluctuations for SK94 and MSAM94 experiments are Δ T/T=1.57×10-5 and Δ T/T=1.62×10-5, respectively, when the string mass density parameter is chosen to be Gμ=1.4×10-6. The possibility of detecting non-Gaussian signals using the present day experiments is also discussed.
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DUAN, L., I. BEEKMAN i M. P. MARTÍN. "Direct numerical simulation of hypersonic turbulent boundary layers. Part 3. Effect of Mach number". Journal of Fluid Mechanics 672 (2.03.2011): 245–67. http://dx.doi.org/10.1017/s0022112010005902.
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In this paper, we perform direct numerical simulations (DNS) of turbulent boundary layers with nominal free-stream Mach number ranging from 0.3 to 12. The main objective is to assess the scalings with respect to the mean and turbulence behaviours as well as the possible breakdown of the weak compressibility hypothesis for turbulent boundary layers at high Mach numbers (M > 5). We find that many of the scaling relations, such as the van Driest transformation for mean velocity, Walz's relation, Morkovin's scaling and the strong Reynolds analogy, which are derived based on the weak compressibility hypothesis, remain valid for the range of free-stream Mach numbers considered. The explicit dilatation terms such as pressure dilatation and dilatational dissipation remain small for the present Mach number range, and the pressure–strain correlation and the anisotropy of the Reynolds stress tensor are insensitive to the free-stream Mach number. The possible effects of intrinsic compressibility are reflected by the increase in the fluctuations of thermodynamic quantities (p′rms/pw, ρ′rms/ρ, T′rms/T) and turbulence Mach numbers (Mt, M′rms), the existence of shocklets, the modification of turbulence structures (near-wall streaks and large-scale motions) and the variation in the onset of intermittency.
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Wayne Woo, Yao Wen, Lit Ken Tan, Yutaka Asako, Kok Yee Lai, Yu Feng Tan, Zun Liang Chuan, Yee Siang Gan i in. "Adaptive Structural Design of River Monitoring Systems: Enhancing Environmental Monitoring Capabilities and Sustainability". Semarak International Journal of Civil and Structural Engineering 2, nr 1 (1.09.2024): 1–18. https://doi.org/10.37934/sijcse.2.1.118.
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The accelerating degradation of river ecosystems due to pollution necessitates the innovation of River Monitoring Systems (RMS) to protect these critical waterways. This research presents a novel design for adaptive RMS camera structures, aimed at enhancing monitoring capabilities and addressing the limitations of current systems. Highlighting the essential role rivers play in sustaining biodiversity, our study underscores the severe consequences of pollution, as exemplified by the deteriorating condition of Malaysia’s Klang River. We identify the need for a flexible RMS structure to overcome challenges such as excessive weight, corrosion susceptibility, and maintenance difficulties. Our methodology integrates advanced 3D Drawing Software for structural design, Fusion 360 for weight analysis, and a combination of manual calculations and simulations for vibration analysis. The findings reveal that Carbon Fiber Reinforced Polymers (CFRP) are the optimal material choice, offering an excellent balance of performance and cost-efficiency. This research successfully develops a structurally sound, user-friendly, and dynamically stable RMS camera structure, significantly advancing environmental monitoring practices. The study's contributions provide a foundation for future innovations in adaptive structural design, with broad implications for safeguarding river ecosystems worldwide.
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Thomas, Karin, Mårten Grabbe, Katarina Yuen i Mats Leijon. "A Permanent Magnet Generator for Energy Conversion from Marine Currents: No Load and Load Experiments". ISRN Renewable Energy 2012 (28.06.2012): 1–7. http://dx.doi.org/10.5402/2012/489379.
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This paper presents experiments and measurements on a low speed permanent magnet cable wound generator for marine current energy conversion. Measurements were made for no load and nominal load (4.44 Ω/phase) conditions at nominal speed (10 rpm). For either load condition, the magnetic fields in the air gap were also measured. The measurements on the generator were compared with the corresponding finite element method simulations used to design the machine. It is shown in the paper that measurements and corresponding case simulations show good agreement. At nominal speed, the measured and simulated load voltages (nominal load) differ less than 1% for the rms values and less than 5% for peak values. At no load, measured and simulated voltages had larger differences, that is, <9% for rms values and <5% for peak values. Harmonic analyses of measured and simulated phase voltages and currents show only the presence of third harmonics. The percentage of harmonics in the measured data was comparable with the corresponding predictions of the simulations. The discussions and results presented in the paper could be beneficial for future design of efficient and reliable marine current energy converter systems.
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Dobry, Marian Witalis. "Semi-Active Method of Motion Stabilization Applied to Mechanical System with the Constant Reaction Force Vibroisolation (CRF) – Model Study". Solid State Phenomena 248 (marzec 2016): 103–10. http://dx.doi.org/10.4028/www.scientific.net/ssp.248.103.
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The use of the CRF vibration isolation system with zero natural frequency for machinery and equipment in the Earth's gravity field requires stabilization of motion because of its high susceptibility. For this purpose, an additional spring element with a low elastic coefficient “k1” and a semi-active damper “c (t, x, v, ff)”, was included in the vibration isolation system and parallel-attached to the CRF vibroisolator. Investigation of the effect of the additional element to stabilize the motion of the mechanical system was carried out by a numerical simulation of its motion. The simulation was based on a physical and mathematical model of the system including the spring and the magnetorheological damper (MR). The mathematical model was then used to develop a dynamics simulation program of the system and conduct simulations using sample data in order to study transitional processes and their stability. Simulation results indicate a substantially improved stability of motion in the system. Stability studies of motion were also combined with an analysis of power distribution in the system. The aim of this study was to determine energy efficiency of the system developed, defined as the ratio of the RMS power of the exciting force to RMS power of the elastic force. The resulting energy efficiency of CRF vibroisolation was equal to 5168 for a simulation period of 6 seconds.
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Youn, Iljoong, i Ejaz Ahmad. "Anti-Jerk Optimal Preview Control Strategy to Enhance Performance of Active and Semi-Active Suspension Systems". Electronics 11, nr 10 (23.05.2022): 1657. http://dx.doi.org/10.3390/electronics11101657.
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This study aims to demonstrate how to compute the damping coefficient of a continuously variable damper for semi-active preview control suspensions while considering the sprung-mass jerk and the controller’s performance advantage. Optimal control theory is used to derive and validate the proposed preview approach to future road disturbances. Despite reduced body acceleration, semi-active suspensions with preview control display an increase in body jerk, implying that ride comfort may not be improved in practice. The optimal preview jerk controller for a semi-active system, on the other hand, can improve ride comfort without degrading road holding by minimizing the performance index that comprises the RMS value of jerk in addition to the RMS values of other outputs. The anti-jerk preview control suspension simulations considering frequency characteristics reveal a difference between suspension systems that consider jerk and those that ignore jerk. The time-domain simulations suggest that the proposed preview control strategy effectively to reduce body jerk, which other controllers cannot.
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Șandric, Ionuț, Radu Irimia, Viorel Ilinca, Zenaida Chițu i Ion Gheuca. "Using UAV Time Series to Estimate Landslides’ Kinematics Uncertainties, Case Study: Chirlești Earthflow, Romania". Remote Sensing 15, nr 8 (19.04.2023): 2161. http://dx.doi.org/10.3390/rs15082161.
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This paper presents a methodology for evaluating the uncertainties caused by the misalignment between two digital elevation models in estimating landslide kinematics. The study focuses on the earthflow near the town of Chirlești, located in the Bend Subcarpathians, Buzău County, Romania, which poses a high risk of blocking the DN10 national road. Four flights were conducted between 2018 and 2022 using a DJI Phantom 4 UAV using the same flight plan. Monte Carlo simulations were used to model uncertainty propagation of the DEM misalignments in the landslide kinematics analysis. The simulations were applied to the accuracy values of the structure from a motion process used to generate the digital elevation models. The degree of uncertainty was assessed using the displaced material’s total amount in conjunction with the spatial correlation of the displaced material between two consecutive flights. The results revealed that the increase in the RMS values did not determine an increase in the displaced earth between two UAV flights. Instead, combining the RMS values and the correlation coefficient clearly indicated the correspondence between the spatial distribution of the displaced earth material and the overall changes reported between the two UAV flights. An RMS value of up to 1 unit associated with a correlation coefficient of 0.95 could be considered the maximum allowable error for estimating landslide kinematics across space and time. The current methodology is reliable when studying slow-movement landslides and when using short intervals between UAV flights. For rapid movements or significant terrain changes, such as translational and rotational landslides, careful analysis of the correlation coefficient in conjunction with the RMS values is recommended.
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Bos, S. P., D. S. Doelman, J. Lozi, O. Guyon, C. U. Keller, K. L. Miller, N. Jovanovic, F. Martinache i F. Snik. "Focal-plane wavefront sensing with the vector-Apodizing Phase Plate". Astronomy & Astrophysics 632 (26.11.2019): A48. http://dx.doi.org/10.1051/0004-6361/201936062.
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Context. One of the key limitations of the direct imaging of exoplanets at small angular separations are quasi-static speckles that originate from evolving non-common path aberrations (NCPA) in the optical train downstream of the instrument’s main wavefront sensor split-off. Aims. In this article we show that the vector-Apodizing Phase Plate (vAPP) coronagraph can be designed such that the coronagraphic point spread functions (PSFs) can act as wavefront sensors to measure and correct the (quasi-)static aberrations without dedicated wavefront sensing holograms or modulation by the deformable mirror. The absolute wavefront retrieval is performed with a non-linear algorithm. Methods. The focal-plane wavefront sensing (FPWFS) performance of the vAPP and the algorithm are evaluated via numerical simulations to test various photon and read noise levels, the sensitivity to the 100 lowest Zernike modes, and the maximum wavefront error (WFE) that can be accurately estimated in one iteration. We apply these methods to the vAPP within SCExAO, first with the internal source and subsequently on-sky. Results. In idealized simulations we show that for 107 photons the root mean square (rms) WFE can be reduced to ∼λ/1000, which is 1 nm rms in the context of the SCExAO system. We find that the maximum WFE that can be corrected in one iteration is ∼λ/8 rms or ∼200 nm rms (SCExAO). Furthermore, we demonstrate the SCExAO vAPP capabilities by measuring and controlling the 30 lowest Zernike modes with the internal source and on-sky. On-sky, we report a raw contrast improvement of a factor ∼2 between 2 and 4 λ/D after five iterations of closed-loop correction. When artificially introducing 150 nm rms WFE, the algorithm corrects it within five iterations of closed-loop operation. Conclusions. FPWFS with the vAPP coronagraphic PSFs is a powerful technique since it integrates coronagraphy and wavefront sensing, eliminating the need for additional probes and thus resulting in a 100% science duty cycle and maximum throughput for the target.
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Schutgens, N. A. J. "Simulated Doppler Radar Observations of Inhomogeneous Clouds: Application to the EarthCARE Space Mission". Journal of Atmospheric and Oceanic Technology 25, nr 1 (1.01.2008): 26–42. http://dx.doi.org/10.1175/2007jtecha956.1.
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Abstract A new simulation technique for spaceborne Doppler radar observations that was developed specifically for inhomogeneous targets is presented. Cloud inhomogeneity affects Doppler observations in two ways. First, line-of-sight velocities within the instantaneous field of view are unequally weighted. As the large forward motion of a spaceborne radar contributes to these line-of-sight velocities this causes biases in observed Doppler speeds. Second, receiver voltages now have time-varying stochastical properties, increasing the inaccuracy of Doppler observations. The new technique predicts larger inaccuracies of observed Doppler speeds than the traditional random signal simulations based on the inverse Fourier transform. The accuracy of Doppler speed observations by a spaceborne 95-GHz radar [as part of the proposed European Space Agency (ESA)/Japan Aerospace Exploration Agency (JAXA)/National Institute for Information and Communications Technology (NICT) EarthCARE mission] is assessed through simulations for realistic cloud scenes based on observations made by ground-based cloud-profiling radars. Close to lateral cloud boundary biases as large as several meters per second occur. For half of the cloud scenes investigated, the distribution of the in-cloud bias has an rms of 0.5 m s−1, implying that a bias in excess of 0.5 m s−1 will not be uncommon. An algorithm to correct the bias in observed Doppler observations, based on the observed gradient of reflectivity along track, is suggested and shown to be effective; that is, the aforementioned rms bias reduces to 0.14 m s−1.
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Imani Nejad, Zohreh, Khalil Khalili, Seyyed Hamed Hosseini Nasab, Pascal Schütz, Philipp Damm, Adam Trepczynski, William R. Taylor i Colin R. Smith. "The Capacity of Generic Musculoskeletal Simulations to Predict Knee Joint Loading Using the CAMS-Knee Datasets". Annals of Biomedical Engineering 48, nr 4 (30.01.2020): 1430–40. http://dx.doi.org/10.1007/s10439-020-02465-5.
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Abstract Musculoskeletal models enable non-invasive estimation of knee contact forces (KCFs) during functional movements. However, the redundant nature of the musculoskeletal system and uncertainty in model parameters necessitates that model predictions are critically evaluated. This study compared KCF and muscle activation patterns predicted using a scaled generic model and OpenSim static optimization tool against in vivo measurements from six patients in the CAMS-knee datasets during level walking and squatting. Generally, the total KCFs were under-predicted (RMS: 47.55%BW, R 2: 0.92) throughout the gait cycle, but substiantially over-predicted (RMS: 105.7%BW, R 2: 0.81) during squatting. To understand the underlying etiology of the errors, muscle activations were compared to electromyography (EMG) signals, and showed good agreement during level walking. For squatting, however, the muscle activations showed large descrepancies especially for the biceps femoris long head. Errors in the predicted KCF and muscle activation patterns were greatest during deep squat. Hence suggesting that the errors mainly originate from muscle represented at the hip and an associated muscle co-contraction at the knee. Furthermore, there were substaintial differences in the ranking of subjects and activities based on peak KCFs in the simulations versus measurements. Thus, future simulation study designs must account for subject-specific uncertainties in musculoskeletal predictions.
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Lee, Jooyong, Jonggu Jeon, Min-Seok Kim, Hochan Lee i Minhaeng Cho. "Amide I IR probing of core and shell hydrogen-bond structures in reverse micelles". Pure and Applied Chemistry 86, nr 2 (1.02.2014): 135–49. http://dx.doi.org/10.1515/pac-2014-5016.
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Abstract The properties of N-methylacetamide (NMA) molecules encapsulated in the reverse micelles (RMs) formed by anionic surfactant aerosol OT (AOT), are studied with vibrational spectroscopy and computation. Vibrational spectra of the amide I′ mode of the fully deuterated NMA-d7 show gradual increase of peak frequencies and line broadening as the size of RMs decreases. Analyses of the spectral features reveal the presence of three states of NMA-d7 that correspond to NMA located in the core of water phase (absorption frequency of 1606 cm–1) and two types of interfacial NMA near the surfactant layer (1620 and 1644 cm–1). In larger RMs with water content w0 = [D2O]/[AOT] ≥ 10, only the first two states are observed, whereas in smaller RMs, the population of the third state grows up to 25 % at w0 = 2. These results indicate the general validity of the two-state core/shell model for the confined aqueous solution of NMA, with small modifications due to the system-dependent solute-interface interaction. However, simulations of small RM systems with w0 ≤ 15 show continuous variations of the population, frequency shifts, and the solute-solvent interaction strengths at solute-interface distance less than 4 Å. Thus, the distinction of solute core/shell states tends to be blurred in small RMs but is still effective in interpreting the average spectroscopic observables.
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Kara, A. Birol, Harley E. Hurlburt, Alan J. Wallcraft i Mark A. Bourassa. "Black Sea Mixed Layer Sensitivity to Various Wind and Thermal Forcing Products on Climatological Time Scales*". Journal of Climate 18, nr 24 (15.12.2005): 5266–93. http://dx.doi.org/10.1175/jcli3573r2.1.
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Abstract This study describes atmospheric forcing parameters constructed from different global climatologies, applied to the Black Sea, and investigates the sensitivity of Hybrid Coordinate Ocean Model (HYCOM) simulations to these products. Significant discussion is devoted to construction of these parameters before using them in the eddy-resolving (≈3.2-km resolution) HYCOM simulations. The main goal is to answer how the model dynamics can be substantially affected by different atmospheric forcing products in the Black Sea. Eight wind forcing products are used: four obtained from observation-based climatologies, including one based on measurements from the SeaWinds scatterometer on the Quick Scatterometer (QuikSCAT) satellite, and the rest formed from operational model products. Thermal forcing parameters, including solar radiation, are formed from two operational models: the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Fleet Numerical Meteorology and Oceanography Center (FNMOC) Navy Operational Global Atmospheric Prediction System (NOGAPS). Climatologically forced Black Sea HYCOM simulations (without ocean data assimilation) are then performed to assess the accuracy and sensitivity of the model sea surface temperature (SST) and sea surface circulation to these wind and thermal forcing products. Results demonstrate that the model-simulated SST structure is quite sensitive to the wind and thermal forcing products, especially near coastal regions. Despite this sensitivity, several robust features are found in the model SST in comparison to a monthly 9.3-km-resolution satellite-based Pathfinder SST climatology. Annual mean HYCOM SST usually agreed to within ≈±0.2° of the climatology in the interior of the Black Sea for any of the wind and thermal forcing products used. The fine-resolution (0.25° × 0.25°) wind forcing from the scatterometer data along with thermal forcing from NOGAPS gave the best SST simulation with a basin-averaged rms difference value of 1.21°C, especially improving model results near coastal regions. Specifically, atmospherically forced model simulations with no assimilation of any ocean data suggest that the basin-averaged rms SST differences with respect to the Pathfinder SST climatology can vary from 1.21° to 2.15°C depending on the wind and thermal forcing product. The latter rms SST difference value is obtained when using wind forcing from the National Centers for Environmental Prediction (NCEP), a product that has a too-coarse grid resolution of 1.875° × 1.875° for a small ocean basin such as the Black Sea. This paper also highlights the importance of using high-frequency (hybrid) wind forcing as opposed to monthly mean wind forcing in the model simulations. Finally, there are large variations in the annual mean surface circulation simulated using the different wind sets, with general agreement between those forced by the model-based products (vector correlation is usually >0.7). Three of the observation-based climatologies generally yield unrealistic circulation features and currents that are too weak.
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Hunaini, Fachrudin, Fressy Nugroho, Purbo Suwandono i Gatot Subiyakto. "The cascade optimal control of steer by wire system using hardware in the loop simulations". International Journal of Power Electronics and Drive Systems (IJPEDS) 13, nr 2 (1.06.2022): 764. http://dx.doi.org/10.11591/ijpeds.v13.i2.pp764-772.
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This paper aims to further improve the performance of the control system on the steer by wire (SbW) of vehicle steering system, by presenting the development of optimal control system strategy for lateral motion and yaw motion which is arranged in a cascade so that the vehicle can always be maintained on the desired trajectory. The control system strategy to be developed is fuzzy logic control (FLC) as a lateral motion control and proportional integral derivative (PID) control as a yaw motion control, and to obtain an optimal control system, the modified-quantum particle swarm optimization (MQPSO) optimization method is used. The simulations are carried out using hardware in the loop simulations (HILS) which involve hardware, namely; motor stepper actuator and rotary encoder to determine and monitor the direction of the front wheels which are applied to the vehicle dynamics model in a real time. HILS test results show that vehicle movement can be maintained according to the desired trajectory (double lane change) with an average continues-root mean square (C-RMS) error of 0.015366 for lateral motion and 0.014967 for yaw motion, the average C-RMS error is greater 23.75% for lateral motion and 28.18% for yaw motion against the results of the software in the loop simulations (SILS) test.
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Kwun, Min Jung, Marco R. Oggioni, Stephen D. Bentley, Christophe Fraser i Nicholas J. Croucher. "Synergistic Activity of Mobile Genetic Element Defences in Streptococcus pneumoniae". Genes 10, nr 9 (13.09.2019): 707. http://dx.doi.org/10.3390/genes10090707.
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A diverse set of mobile genetic elements (MGEs) transmit between Streptococcus pneumoniae cells, but many isolates remain uninfected. The best-characterised defences against horizontal transmission of MGEs are restriction-modification systems (RMSs), of which there are two phase-variable examples in S. pneumoniae. Additionally, the transformation machinery has been proposed to limit vertical transmission of chromosomally integrated MGEs. This work describes how these mechanisms can act in concert. Experimental data demonstrate RMS phase variation occurs at a sub-maximal rate. Simulations suggest this may be optimal if MGEs are sometimes vertically inherited, as it reduces the probability that an infected cell will switch between RMS variants while the MGE is invading the population, and thereby undermine the restriction barrier. Such vertically inherited MGEs can be deleted by transformation. The lack of between-strain transformation hotspots at known prophage att sites suggests transformation cannot remove an MGE from a strain in which it is fixed. However, simulations confirmed that transformation was nevertheless effective at preventing the spread of MGEs into a previously uninfected cell population, if a recombination barrier existed between co-colonising strains. Further simulations combining these effects of phase variable RMSs and transformation found they synergistically inhibited MGEs spreading, through limiting both vertical and horizontal transmission.
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Rafiq, Tariq, Zibo Wang, Shira Morosohk, Eugenio Schuster, Jan Weiland, Wilkie Choi i Hyun-Tae Kim. "Validating the Multi-Mode Model’s Ability to Reproduce Diverse Tokamak Scenarios". Plasma 6, nr 3 (24.07.2023): 435–58. http://dx.doi.org/10.3390/plasma6030030.
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A large-scale validation exercise was conducted to assess the multi-mode model (MMM) anomalous transport model in the integrated modeling code TRANSP. The validation included 6 EAST discharges, 17 KSTAR discharges, 72 JET ITER-like wall D-D discharges, and 4 DIII-D fusion plasma discharges. Using the MMM, the study computed anomalous thermal, particle, impurity, and momentum transport within TRANSP. Simulations for EAST, KSTAR, and JET focused on electron and ion temperatures and safety factor profiles, while DIII-D simulations also considered electron density, toroidal rotation frequency, and flow shear. The predicted profiles were compared to experimental data at the diagnostic time, quantifying the comparison using root-mean-square (RMS) deviation and relative offsets. The study found an average RMS deviation of 9.3% for predicted electron temperature and 10.5% for ion temperature, falling within the experimental measurement error range 20%. The MMM model demonstrated computational efficiency and the ability to accurately reproduce a wide range of discharges, including various scenarios and plasma parameters, such as plasma density, gyroradius, collisionality, beta, safety factor and heating method variations.
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Sheikh, Nadeem Ahmed, Shehryar Manzoor i Muzaffar Ali. "Variation of Heat Flux at Lower Frequencies of Vibration in a Vibrated Granular Bed". Advances in Condensed Matter Physics 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/598354.
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Granular flows in vibrated bed exhibit various physical phenomena primarily driven by vibrating base. As the vibrating surface is the only source of energy in an otherwise dissipative flow, most of the theoretical models relate the steady state energy input to the RMS velocity of vibration. Here variation of heat flux is studied at varying frequency of vibration while keeping the RMS vibration velocity and the cell loading constant. Using single particle analysis and MD simulations, an extended version of grain-base collision is observed resulting in the reduction of heat flux at lower frequencies (<50 Hz) of vibration. The presented findings are important as most experimental studies are reported at these frequencies of excitation.
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Khani, Sina, i Michael L. Waite. "Buoyancy scale effects in large-eddy simulations of stratified turbulence". Journal of Fluid Mechanics 754 (30.07.2014): 75–97. http://dx.doi.org/10.1017/jfm.2014.381.
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AbstractIn this paper large-eddy simulations (LES) of forced stratified turbulence using two common subgrid scale (SGS) models, the Kraichnan and Smagorinsky models, are studied. As found in previous studies using regular and hyper-viscosity, vorticity contours show elongated horizontal motions, which are layered in the vertical direction, along with intermittent Kelvin–Helmholtz (KH) instabilities. Increased stratification causes the layer thickness to collapse towards the dissipation scale, ultimately suppressing these instabilities. The vertical energy spectra are relatively flat out to a local maximum, which varies with the buoyancy frequency $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}N$. The horizontal energy spectra depend on the grid spacing $\varDelta $; if the resolution is fine enough, the horizontal spectrum shows an approximately $-5/3$ slope along with a bump at the buoyancy wavenumber $k_b = N/u_{rms}$, where $u_{rms}$ is the root-mean-square (r.m.s.) velocity. Our results show that there is a critical value of the grid spacing $\varDelta $, below which dynamics of stratified turbulence are well-captured in LES. This critical $\varDelta $ depends on the buoyancy scale $L_b$ and varies with different SGS models: the Kraichnan model requires $\varDelta < 0.47 L_b$, while the Smagorinsky model requires $\varDelta < 0.17 L_b$. In other words, the Smagorinsky model is significantly more costly than the Kraichnan approach, as it requires three times the resolution to adequately capture stratified turbulence.
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Almirante, Italo, i Emilio Lorenzani. "Simple Strategy for Torque Ripple Minimization in Switched Reluctance Motor Drives". Energies 16, nr 19 (29.09.2023): 6885. http://dx.doi.org/10.3390/en16196885.
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This article proposes a new simulation strategy to support the calculation of the angular interval of the current supply to minimize the torque ripple in switched reluctance machines, focusing on the motor working condition. Supposing the best angular interval is strongly linked to the working condition of the machine, a formula is needed to calculate the boundary angles of the intervals of the current supply for each phase, starting from real-time speed and electromagnetic torque. Starting from the dataset of simulations made with this new strategy, linear regression was used to train a model that computes useful formulas. The aim of this research is to show how the application of simple calculations allows torque ripple and power losses to be reduced, i.e., RMS phase currents, without altering the geometry of the machine. Simulations on a virtual four-phase 8/6 SRM are carried out to verify the model’s feasibility and effectiveness, even though this strategy can be easily applied to all other configurations of SRMs.
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Wandowski, T., P. Kudela i M. Radzienski. "Low-frequency air-coupled transducer based damage detection in composite materials". Journal of Physics: Conference Series 2692, nr 1 (1.02.2024): 012026. http://dx.doi.org/10.1088/1742-6596/2692/1/012026.
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Abstract In this paper results of simulations of non-contact elastic wave generation in the composite panel based on acoustic to elastic wave transformation are presented. For this purpose simulations of acoustic wave generation and processing are based on the FEM method in COMSOL. Elastic wave generation and propagation are based on the spectral element method (SEM) in the time domain. The SEM model utilises time-varying acoustic pressure distributions calculated in the FEM. The SEM allows to simulate the interactions of elastic waves with the delamination. Damage localization is based on RMS elastic wave energy maps. In this research a panel made of carbon fibre-reinforced polymer composite is investigated. Research related to low-frequency air-coupled transducer (ACT) is presented. The utilisation of low-frequency waves allows for the reduction of the effects of the wave attenuation in composite material. The proposed combination of FEM and SEM gives an efficient tool for the simulation of non-contact wave generation for non-destructive testing analysis.
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Shapovalov, P. G., A. N. Oleinik i P. V. Karataev. "Computer simulations of the phase-space characteristics of electrons in a pyroelectric accelerator". Journal of Instrumentation 19, nr 09 (1.09.2024): C09001. http://dx.doi.org/10.1088/1748-0221/19/09/c09001.
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Abstract In this paper, we focus on simulating a pyroelectric accelerator using COMSOL Multiphysics. We utilize the static surface charge distribution obtained from an experiment conducted on a LiTaO3 single crystal surface. We analyze the characteristics of the electron flow generated by the accelerator and determine the emittance and Twiss parameters. Our findings reveal that the normalized RMS emittance remains relatively constant in the space behind the target.
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Gao, Wenwei, Hairong Yang, Le Wang i Ruilin Hu. "Numerical Simulations of the Soil–Rock Mixture Mechanical Properties Considering the Influence of Rock Block Proportions by PFC2D". Materials 14, nr 18 (20.09.2021): 5442. http://dx.doi.org/10.3390/ma14185442.
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Soil-rock mixtures (S-RMs), as a kind of special engineering geological material, need to be studied because of the special structure and complex movement mechanism of their rock blocks, their physical and mechanical properties, and the factors underlying rock block movement in the process of their deformation and failure. In this paper, a series of discrete-element numerical models are constructed in particle flow code software (PFC2D). First, the random structure numerical models of S-RMs with different rock block proportions are established. Then, the parameters of the soil meso-structure are inversed by the biaxial simulation test, and a series of biaxial compressive tests are performed. The characteristics of stress and strain, deformation and failure, and rock block rotation and energy evolution are systematically investigated. The results show the following. (1) As the rock block proportion (confining pressure 0.5 MPa) increases, the peak strength of increases, the fluctuations of the post-peak become more obvious, and the dilatancy of the sample increases. (2) As the rock block proportion increases, the width of the shear band increases, the distribution of cracks becomes more complex and dispersed, and the range of the shear zone increases. (3) The number of rock blocks with rotation also increases significantly as rock block proportion increases, and the rotation angles are mostly between −5° and 5°. (4) The strain energy of S-RMs with different rock block proportions follows the same change rule as axial strain, showing a trend of first increasing and then decreasing, like the stress–strain curve.
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Hadj Benali, Farouk, i Fouad Azzouz. "Comparison of Flying Capacitor Fifteen Level Inverter and Thirty Three Level Inverter PWM Control Strategies". Indonesian Journal of Electrical Engineering and Computer Science 6, nr 2 (1.05.2017): 368. http://dx.doi.org/10.11591/ijeecs.v6.i2.pp368-378.
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<p>In the paper two PWM control strategies of multilevel flying capacitor inverter is proposed. The study starts with a presentation of the Flying capacitor inverter and the two PWM control strategies (SPWM and Suboptimal PWM). Than a section which presents a brief recall of the triangular multicarrier PWM and the sinusoidal multicarrier PWM. A comparison between the two PWM control strategies based on the simulation results is made. The subjects of comparison are the root mean square rms of the output voltage and the total harmonic distortion THD. The obtained results have proved that the Suboptimal PWM is better than the SPWM. Simulations are carried out by PSIM program.</p>
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Laws, Kenneth, Jeffrey D. Paduan i John Vesecky. "Estimation and Assessment of Errors Related to Antenna Pattern Distortion in CODAR SeaSonde High-Frequency Radar Ocean Current Measurements". Journal of Atmospheric and Oceanic Technology 27, nr 6 (1.06.2010): 1029–43. http://dx.doi.org/10.1175/2009jtecho658.1.
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Abstract A simulation-based investigation of errors in HF radar–derived, near-surface ocean current measurements is presented. The simulation model is specific to Coastal Ocean Dynamics Application Radar (CODAR) SeaSonde radar systems that employ a compact, collocated antenna geometry. In this study, radial current retrievals are obtained by processing simulated data using unmodified CODAR data processing software. To avoid limiting the results to specific ocean current and wind wave scenarios, the analyses employ large ensembles of randomly varying simulated environmental conditions. The effect of antenna pattern distortion on the accuracy of retrievals is investigated using 40 different antenna sensitivity patterns of varying levels of distortion. A single parameter is derived to describe the level of the antenna pattern distortion. This parameter is found to be highly correlated with the rms error of the simulated radial currents (r = 0.94) and therefore can be used as a basis for evaluating the severity of site-specific antenna pattern distortions. Ensemble averages of the subperiod simulated current retrieval standard deviations are found to be highly correlated with the antenna pattern distortion parameter (r = 0.92). Simulations without distortions of the antenna pattern indicate that an rms radial current error of 2.9 cm s−1 is a minimum bound on the error of a SeaSonde ocean radar system, given a typical set of operating parameters and a generalized ensemble of ocean conditions.
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Tatosian, D., J. Shen, L. Chen, J. Lavigne, N. Teuscher, S. Harris, D. Chitkara, G. S. Tirucherai i C. Marta. "P315 Population pharmacokinetics and pharmacodynamics of ozanimod in ulcerative colitis". Journal of Crohn's and Colitis 15, Supplement_1 (1.05.2021): S341—S342. http://dx.doi.org/10.1093/ecco-jcc/jjab076.439.
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Abstract Background Ozanimod is an oral small molecule sphingosine 1-phosphate receptor modulator approved for relapsing forms of multiple sclerosis (RMS) and under development for ulcerative colitis (UC) and Crohn’s disease. Ozanimod and its major active metabolites CC112273 and CC1084037 block lymphocyte egress from lymphoid tissues, reducing the absolute lymphocyte count (ALC) in blood. To characterise the influence of patient characteristics on ALC response, a population PK/PD analysis was conducted. Methods A nonlinear mixed-effects Emax model described the ALC time course and relationship to CC112273 concentrations in healthy subjects and patients with UC or RMS. The analysed data included 34,449 ALC values obtained from 4122 subjects enrolled in 11 Phase 1, 2, and 3 clinical studies. The effect of age, sex, smoking status, disease type, body weight, total bilirubin, and baseline ALC on the maximum ALC reduction (Emax) and half-maximal concentration (EC50) were investigated. Simulations of typical ALC reductions for healthy subjects and patients with UC or RMS receiving 0.5 or 1 mg ozanimod were conducted to explore the influence of smoking and assess the time for ALC recovery. Results Increasing CC112273 concentrations were associated with reductions in ALC to a maximum of 74% from baseline, with an estimated EC50 of 2.8 nM CC112273. Healthy subjects, females, and higher body weights were associated with larger ALC Emax (Figure 1), while healthy subjects, increased age, nonsmokers and higher baseline ALC were associated with an increased EC50 (Figure 2). UC patients receiving 0.5 mg and 1 mg ozanimod HCl are predicted to have mean ALC reductions of 46.1% and 57.2%, respectively, with similar reductions for RMS patients of 48.0% and 57.4%. Smoking was associated with a 27.2% reduction in the ALC EC50, which partially offsets the reduced plasma CC112273 concentrations in smokers. Simulations show that 1 mg ozanimod has comparable ALC reductions of 57.4% in nonsmokers and 52.7% in smokers. Upon discontinuing ozanimod 1 mg in UC patients, a mean recovery time to normal (1 x 109/L ALC count) of 32.8 days was predicted, with 90% of the population recovering in 3 months. Overall results were consistent with findings from clinical trials. Conclusion Population analysis demonstrated a similar PK/PD relationship for ALC reductions in patients with RMS and UC. Smoking was not associated with substantial difference in ALC, consistent with no loss of efficacy in smokers. Upon discontinuation of ozanimod treatment, the majority of UC and RMS patients will recover lymphocyte counts to normal within 3 months.