Frequency‐dependent responses of plasmaspheric hiss to the impact of an interplanetary shock

Abstract. Solar wind forcing, e.g. interplanetary shock and/or solar wind dynamic pressure pulses impact on the Earth’s magnetosphere manifests many fundamental important space physics phenomena including producing electromagnetic waves, plasma heating and energetic particle acceleration. This paper summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma physics based on in situ spacecraft measurements, ground-based magnetometer data, MHD and kinetic simulations. Magnetosphere response to solar wind forcing, is not just a “one-kick” scenario. It is found that after the impact of solar wind forcing on the Earth’s magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change of interplanetary shock or solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to generate series kind of waves including poloidal mode ultra-low frequency (ULF) waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region response to the impact usually contains two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression; (2) followed by the wave-particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. Generalized theory of drift and drift-bounce resonance with growth or decay localized ULF waves has been developed to explain in situ spacecraft observations. The wave related observational features like distorted energy spectrum, boomerang and fishbone pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the frame work of this generalized theory. It is worthy to point out here that poloidal ULF waves are much more efficient to accelerate and modulate electrons (fundamental mode) in the radiation belt and charged ions (second harmonic) in the ring current region. The results presented in this paper can be widely used in solar wind interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune, and other astrophysical objects with magnetic fields.

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Elucidating the Impact of Charge Selective Contact in Halide Perovskite Through Impedance Spectroscopy

10.26434/chemrxiv.9741335.v1 ◽

2019 ◽

Author(s):

Mohd Taukeer Khan ◽

Manuel Salado ◽

Abdullah R. D. Almohammedi ◽

Samrana Kazim ◽

Shahzada Ahmad

Keyword(s):

Solar Cells ◽

Impedance Spectroscopy ◽

Charge Carrier ◽

Carrier Mobility ◽

Short Circuit ◽

Perovskite Solar Cells ◽

Charge Carrier Mobility ◽

Charge Accumulation ◽

Frequency Dependent ◽

The Impact

The electron and hole selective contact (SC) play a pivotal role in the performance of perovskite solar cells. In order to separate the interfacial phenomenon from bulk, the influence of charge SC was elucidated, by means of impedance spectroscopy. The specific role played by TiO2 and Spiro-OMeTAD as electron and hole SC in perovskite solar cells was investigated at short circuit condition at different temperatures. We have probed MAPbI3 and (FAPbI3)0.85(MAPbBr3)0.15 and elucidated parameters such as charge carrier mobility, recombination resistance, time constant and charge carrier kinetics in perovskite layer and at the interface of perovskite/SC. Charge carrier mobility in mixed perovskite was found to be nearly two order of magnitude higher as compared to MAPbI3. Moreover, the carrier mobility in devices with only electron SC was found to be higher as compared only hole SC. The charge accumulation at TiO2/perovskite/Spiro-OMeTAD interfaces were studied via frequency dependent capacitance, revealing higher charge accumulation at perovskite/Spiro-OMeTAD than at TiO2/perovskite interface. By performing varying temperature frequency dependent capacitance measurements the distribution of density of state within the bandgap of the perovskites, the emission rate of electrons from the trap states and traps activation energy was determined.

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Rheometer enabled study of cartilage frequency-dependent properties

Scientific Reports ◽

10.1038/s41598-020-77758-9 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Stefano Perni ◽

Polina Prokopovich

Keyword(s):

Applied Load ◽

Cost Effective ◽

Constant Load ◽

Hydraulic Permeability ◽

Frequency Dependent ◽

Shear Moduli ◽

Tissue Replacement ◽

Cost Effective Approach ◽

The Impact

AbstractDespite the well-established dependence of cartilage mechanical properties on the frequency of the applied load, most research in the field is carried out in either load-free or constant load conditions because of the complexity of the equipment required for the determination of time-dependent properties. These simpler analyses provide a limited representation of cartilage properties thus greatly reducing the impact of the information gathered hindering the understanding of the mechanisms involved in this tissue replacement, development and pathology. More complex techniques could represent better investigative methods, but their uptake in cartilage research is limited by the highly specialised training required and cost of the equipment. There is, therefore, a clear need for alternative experimental approaches to cartilage testing to be deployed in research and clinical settings using more user-friendly and financial accessible devices. Frequency dependent material properties can be determined through rheometry that is an easy to use requiring a relatively inexpensive device; we present how a commercial rheometer can be adapted to determine the viscoelastic properties of articular cartilage. Frequency-sweep tests were run at various applied normal loads on immature, mature and trypsinased (as model of osteoarthritis) cartilage samples to determine the dynamic shear moduli (G*, G′ G″) of the tissues. Moduli increased with increasing frequency and applied load; mature cartilage had generally the highest moduli and GAG depleted samples the lowest. Hydraulic permeability (KH) was estimated from the rheological data and decreased with applied load; GAG depleted cartilage exhibited higher hydraulic permeability than either immature or mature tissues. The rheometer-based methodology developed was validated by the close comparison of the rheometer-obtained cartilage characteristics (G*, G′, G″, KH) with results obtained with more complex testing techniques available in literature. Rheometry is relatively simpler and does not require highly capital intensive machinery and staff training is more accessible; thus the use of a rheometer would represent a cost-effective approach for the determination of frequency-dependent properties of cartilage for more comprehensive and impactful results for both healthcare professional and R&D.

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A Study on the Leakage and Rotordynamic Performance of a Long Labyrinth Seal Under Mainly Air Conditions

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4045257 ◽

2019 ◽

Vol 141 (12) ◽

Cited By ~ 2

Author(s):

Min Zhang ◽

Dara W. Childs

Keyword(s):

Silicone Oil ◽

Dynamic Stiffness ◽

Excitation Frequency ◽

Labyrinth Seal ◽

System Stability ◽

Test Fluid ◽

Liquid Volume ◽

Frequency Dependent ◽

Frequency Independent ◽

The Impact

Abstract This paper investigates the impact of liquid presence in air on the leakage and rotordynamic coefficients of a long (length-to-diameter ratio L/D = 0.747) teeth-on-stator labyrinth seal. The test fluid is a mixture of air and silicone oil (PSF-5cSt). Tests are carried out at inlet pressure Pi = 62.1 bars, three pressure ratios from 0.21 to 0.46, three speeds from 10 to 20 krpm, and six inlet liquid volume fractions (LVFs) from 0% to 15%. Complex dynamic-stiffness coefficients Hij are measured. The real parts of Hij are too frequency dependent to be fitted by frequency-independent stiffness and virtual-mass coefficients. Therefore, this paper presents frequency-dependent direct stiffness KΩ and cross-coupled stiffness kΩ. The imaginary parts of Hij produce frequency-independent direct damping C. Test results show that, under both pure- and mainly air conditions, the leakage mass flowrate m˙ of the test seal steadily increases as inlet LVF increases. KΩ is negative under all test conditions, and the magnitude of KΩ increases as inlet LVF increases, leading to a larger negative centering force on the associated compressor rotor. Under pure-air conditions, kΩ is a small negative value. Injecting oil into the air increases kΩ slightly and make the magnitude of kΩ closer to zero. Under mainly air conditions, increasing inlet LVF from 2% to 15% has little impact on kΩ. C normally increases as inlet LVF increases. The value of the effective damping Ceff = C − kΩ/Ω near 0.5ω is of significant interest to the system stability since an unstable centrifugal compressor may precess at approximately 0.5ω. Ω denotes the excitation frequency. The oil presence in the air has little impact on the value of Ceff near 0.5ω. Also, the liquid presence does not change the insensitiveness of m˙, KΩ, kΩ, C, and Ceff to change in ω; i.e., under both pure- and mainly air conditions, changes in ω has little impact on m˙, KΩ, kΩ, C, and Ceff.

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Variability Analysis of Modal Characteristics of Frequency-Dependent Visco-Elastic Three-Layered Sandwich Beams With Spatial Random Geometrical and Material Properties

Journal of Vibration and Acoustics ◽

10.1115/1.4036930 ◽

2017 ◽

Vol 139 (6) ◽

Cited By ~ 6

Author(s):

Frédéric Druesne ◽

Mohamed Hamdaoui ◽

Qi Yin ◽

El Mostafa Daya

Keyword(s):

Random Fields ◽

Loss Factor ◽

Natural Frequencies ◽

Sandwich Beam ◽

Frequency Dependent ◽

Geometrical Properties ◽

Variability Analysis ◽

Output Variability ◽

The Face ◽

The Impact

Material and physical properties of a frequency-dependent visco-elastic sandwich beam are modeled as a set of spatial random fields and represented by means of the Karhunen–Loève expansion. Variability analysis of frequency and loss factor are performed. An efficient approach based on modal stability procedure (MSP) is used, the so-called Monte Carlo simulation (MCS)–MSP method. The latter provides very reliable results and allows to analyze the impact of the input variability of a high number of random spatial quantities on the output response. The effect of independent and correlated couples of spatial random fields is investigated. It is shown that the output variability is generally more important for damping than for natural frequencies. Moreover, it is demonstrated that the input variability in geometrical properties are the most impacting for damping and frequency. The influence of input coefficient of variation on output variability is also studied. It is shown that a negative correlation between the face and core thicknesses result in high levels of output variability, when one parameter increases as the other decreases.

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Application of MADYN 2000 to Rotordynamic Problems of Industrial Machinery

Volume 5: Turbo Expo 2007 ◽

10.1115/gt2007-27302 ◽

2007 ◽

Author(s):

Joachim Schmied ◽

Marco Perucchi ◽

Jean-Claude Pradetto

Keyword(s):

Magnetic Bearings ◽

Fluid Film ◽

Torsional Vibrations ◽

Turbine Generator ◽

Frequency Dependent ◽

Fluid Film Bearings ◽

Engineering Work ◽

Honeycomb Seals ◽

The Impact

The special requirements of rotordynamics engineering are illustrated by means of different examples of turbomachines. The differences between the properties of magnetic bearings and the more common fluid film bearings are pointed out in the examples of two turbocompressors. The importance of the bearing support properties are shown for a turbine generator train. The impact of seal forces are demonstrated for the turbocompressor supported on fluid film bearings. Two of the considered seals are honeycomb seals with frequency dependent characteristics. The consequences of the coupling of lateral and torsional vibrations in gears are illustrated for a gear compressor with three pinions. All examples have a practical background from troubleshooting and engineering work although they do not exactly correspond to real cases.

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Consideration of Hysteresis, Saturation, Fringing and Leakage Fluxes in the Frequency-Dependent Analytical Model of Nonlaminated Cylindrical Actuators

10.36227/techrxiv.14473641.v1 ◽

2021 ◽

Author(s):

Robert Seifert ◽

Johannes Porstmann ◽

Wilfried Hofmann

Keyword(s):

Real Time ◽

Analytical Models ◽

Solid Core ◽

Real Time Control ◽

Frequency Dependent ◽

Pass Filter ◽

Digital Implementation ◽

Time Control ◽

Reluctance Network ◽

The Impact

Previous works have demonstrated that analytical high-fidelity models of nonlaminated actuators and magnetic thrust bearings cannot just describe the magnetic skin effect inside the solid core, but also be applied directly within the control circuit. By an appropriate rational approximation a digital implementation on a microcontroller becomes possible. However, these approximated models neither considered hysteresis and saturation nor frequency-dependent fringing and leakage fluxes. This article elaborates whether or not these nonlinearities can and should be included in real-time control systems. We present an improved process to map an analytical hysteresis model to a limited measured dataset and discuss the impact of the nonlinear magnetization curve. It leads to a novel fractional-order all-pass filter, modeling the frequency-dependent hysteresis angle for a single load point. Its rational filter form is suitable for implementation in Matlab/Simulink as well as real-time applications. Leakage and fringing fluxes, on the other hand, can be considered with relatively low effort within the original analytical models. The underlying reluctance network is determined by a FE-analysis as well as analytically and reduced to a highly simplified form. Depending on whether the total flux or the force-dependent flux is of interest, the model order may increase significantly and constant correction factors are preferable.

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Sources of uncertainties and artifacts in back-projection results

Geophysical Journal International ◽

10.1093/gji/ggz482 ◽

2019 ◽

Author(s):

Zeng Hongyu ◽

Wei Shengji ◽

Wu Wenbo

Keyword(s):

High Frequency ◽

Synthetic Data ◽

Water Layer ◽

Focal Mechanisms ◽

Coda Waves ◽

Back Projection ◽

Common Procedure ◽

Frequency Dependent ◽

Synthetic Test ◽

The Impact

Summary Back-projecting high-frequency (HF) waves is a common procedure for imaging rupture processes of large earthquakes (i.e. Mw > 7.0). However, obtained back-projection (BP) results could suffer from large uncertainties since high-frequency seismic waveforms are strongly affected by factors like source depth, focal mechanisms, and the Earth's 3D velocity structures. So far, these uncertainties have not been thoroughly investigated. Here, we use synthetic tests to investigate the influencing factors for which scenarios with various source and/or velocity set-ups are designed, using either Tohoku-Oki (Japan), Kaikoura (New Zealand), Java/Wharton Basin (Indonesia) as test areas. For the scenarios, we generate either 1D or 3D teleseismic synthetic data, which are then back-projected using a representative BP method, MUltiple SIgnal Classification (MUSIC). We also analyze corresponding real cases to verify the synthetic test results. The Tohoku-Oki scenario shows that depth phases of a point source can be back-projected as artifacts at their bounce points on the earth's surface, with these artifacts located far away from the epicenter if earthquakes occur at large depths, which could significantly contaminate BP images of large intermediate-depth earthquakes. The Kaikoura scenario shows that for complicated earthquakes, composed of multiple sub-events with varying focal mechanisms, BP tends to image sub-events emanating large amplitude coherent waveforms, while missing sub-events whose P nodal directions point to the arrays, leading to discrepancies either between BP images from different arrays, or between BP images and other source models. Using the Java event, we investigate the impact of 3D source-side velocity structures. The 3D bathymetry together with a water layer can generate strong and long-lasting coda waves, which are mirrored as artifacts far from the true source location. Finally, we use a Wharton Basin outer-rise event to show that the wavefields generated by 3D near trench structures contain frequency-dependent coda waves, leading to frequency-dependent BP results. In summary, our analyses indicate that depth phases, focal mechanism variations, and 3D source-side structures can affect various aspects of BP results. Thus, we suggest that target-oriented synthetic tests, for example, synthetic tests for subduction earthquakes using more realistic 3D source-side velocity structures, should be conducted to understand the uncertainties and artifacts before we interpret detailed BP images to infer earthquake rupture kinematics and dynamics.

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Frequency-dependent fitness induces multistability in coevolutionary dynamics

Journal of The Royal Society Interface ◽

10.1098/rsif.2012.0464 ◽

2012 ◽

Vol 9 (77) ◽

pp. 3387-3396 ◽

Cited By ~ 11

Author(s):

Hinrich Arnoldt ◽

Marc Timme ◽

Stefan Grosskinsky

Keyword(s):

Frequency Dependence ◽

Evolutionary Dynamics ◽

Metastable States ◽

Theoretical Research ◽

Nonlinear Frequency ◽

Frequency Dependent ◽

Switching Dynamics ◽

Game Theoretic ◽

System Properties ◽

The Impact

Evolution is simultaneously driven by a number of processes such as mutation, competition and random sampling. Understanding which of these processes is dominating the collective evolutionary dynamics in dependence on system properties is a fundamental aim of theoretical research. Recent works quantitatively studied coevolutionary dynamics of competing species with a focus on linearly frequency-dependent interactions, derived from a game-theoretic viewpoint. However, several aspects of evolutionary dynamics, e.g. limited resources, may induce effectively nonlinear frequency dependencies. Here we study the impact of nonlinear frequency dependence on evolutionary dynamics in a model class that covers linear frequency dependence as a special case. We focus on the simplest non-trivial setting of two genotypes and analyse the co-action of nonlinear frequency dependence with asymmetric mutation rates. We find that their co-action may induce novel metastable states as well as stochastic switching dynamics between them. Our results reveal how the different mechanisms of mutation, selection and genetic drift contribute to the dynamics and the emergence of metastable states, suggesting that multistability is a generic feature in systems with frequency-dependent fitness.

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