scholarly journals Structure–Function Relationships of Healthy and Osteoarthritic Human Tibial Cartilage: Experimental and Numerical Investigation

2020 ◽  
Vol 48 (12) ◽  
pp. 2887-2900
Author(s):  
Mohammadhossein Ebrahimi ◽  
Mikael J. Turunen ◽  
Mikko A. Finnilä ◽  
Antti Joukainen ◽  
Heikki Kröger ◽  
...  
Keyword(s):  
Phase Difference ◽  
Low Frequency ◽  
Orientation Angle ◽  
Human Articular Cartilage ◽  
Tibial Cartilage ◽  
Collagen Orientation ◽  
Healthy Group ◽  
Frequency Regime ◽  
Proteoglycan Content ◽  
Composition Structure

AbstractRelationships between composition, structure and constituent-specific functional properties of human articular cartilage at different stages of osteoarthritis (OA) are poorly known. We established these relationships by comparison of elastic, viscoelastic and fibril-reinforced poroelastic mechanical properties with microscopic and spectroscopic analysis of structure and composition of healthy and osteoarthritic human tibial cartilage (n = 27). At a low frequency (0.005 Hz), proteoglycan content correlated negatively and collagen content correlated positively with the phase difference (i.e. tissue viscosity). At a high-frequency regime (> 0.05 Hz), proteoglycan content correlated negatively and collagen orientation angle correlated positively with the phase difference. Proteoglycans were lost in the early and advanced OA groups compared to the healthy group, while the superficial collagen orientation angle was greater only in the advanced OA group compared to the healthy group. Simultaneously, the initial fibril network modulus (fibril pretension) was smaller in the early and advanced OA groups compared to the healthy group. These findings suggest different mechanisms contribute to cartilage viscosity in low and high frequencies, and that the loss of superficial collagen pretension during early OA is due to lower tissue swelling (PG loss), while in advanced OA, both collagen disorganization and lower swelling modulate the collagen fibril pretension.

scholarly journals Influence of Li2CO3 addition on electrical and magnetic properties of Ni0.6Mg0.4Fe2O4

2020 ◽  
Vol 10 (03) ◽  
pp. 2050003
Author(s):  
M. R. Hassan ◽  
M. T. Islam ◽  
M. N. I. Khan
Keyword(s):  
Magnetic Properties ◽  
Single Phase ◽  
Low Frequency ◽  
Solid State Reaction Method ◽  
Charge Carriers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electrical And Magnetic Properties ◽  
Frequency Regime ◽  
Xrd Patterns

In this research, influence of adding Li2CO3 (at 0%, 2%, 4%, 6%) on electrical and magnetic properties of [Formula: see text][Formula: see text]Fe2O4 (with 60% Ni and 40% Mg) ferrite has been studied. The samples are prepared by solid state reaction method and sintered at 1300∘C for 6[Formula: see text]h. X-ray diffraction (XRD) patterns show the samples belong to single-phase cubic structure without any impurity phase. The magnetic properties (saturation magnetization and coercivity) of the samples have been investigated by VSM and found that the higher concentration of Li2CO3 reduces the hysteresis loss. DC resistivity increases with Li2CO3 contents whereas it decreases initially and then becomes constant at lower value with temperature which indicates that the studied samples are semiconductor. The dielectric dispersion occurs at a low-frequency regime and the loss peaks are formed in a higher frequency regime, which are due to the presence of resonance between applied frequency and hopping frequency of charge carriers. Notably, the loss peaks are shifted to the lower frequency with Li2CO3 additions.

Design and optimization of acoustic liners with a shear grazing flow: OPAL software platform applications

2021 ◽  
Vol 263 (6) ◽  
pp. 152-163
Author(s):  
Remi Roncen ◽  
Pierre Vuillemin ◽  
Patricia Klotz ◽  
Frank Simon ◽  
Fabien Méry ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Low Frequency ◽  
Small Scale ◽  
Software Platform ◽  
Total Size ◽  
Linearized Euler Equations ◽  
Design And Optimization ◽  
Acoustic Liners ◽  
Frequency Regime ◽  
Grazing Flow

In the context of noise reduction in diverse applications where a shear grazing flow is present (i.e., engine nacelle, jet pump, landing gear), improved acoustic liner solutions are being sought. This is particularly true in the low-frequency regime, where space constraints currently limit the efficiency of classic liner technology. To perform the required multi-objective optimization of complex meta-surface liner candidates, a software platform called OPAL was developed. Its first goal is to allow the user to assemble a large panel of parallel/serial assembly of unit acoustic elements, including the recent concept of LEONAR materials. Then, the physical properties of this liner can be optimized, relatively to given weighted objectives (noise reduction, total size of the sample, weight), for a given configuration. Alternatively, properties such as the different impedances of liner unit surfaces can be optimized. To accelerate the process, different nested levels of optimization are considered, from 0D analytical coarse designs in order to reduce the parameter space, up to 2D plan or axisymmetric high-order Discontinuous Galerkin resolution of the Linearized Euler Equations. The presentation will focus on the different aspects of liner design considered in OPAL, and present an application on different samples made for a small scale aeroacoustic bench.

scholarly journals Spacecraft and interplanetary contributions to the magnetic environment on-board LISA Pathfinder

2020 ◽  
Vol 494 (2) ◽  
pp. 3014-3027
Author(s):  
M Armano ◽  
H Audley ◽  
J Baird ◽  
P Binetruy ◽  
M Born ◽  
...  
Keyword(s):  
Magnetic Field ◽  
New Technologies ◽  
Magnetic Measurements ◽  
Magnetic Measurement ◽  
Low Frequency ◽  
Lisa Pathfinder ◽  
Frequency Regime ◽  
The Magnetic Field ◽  
Instrument Sensitivity ◽  
Stationary Component

ABSTRACT LISA Pathfinder (LPF) has been a space-based mission designed to test new technologies that will be required for a gravitational wave observatory in space. Magnetically driven forces play a key role in the instrument sensitivity in the low-frequency regime (mHz and below), the measurement band of interest for a space-based observatory. The magnetic field can couple to the magnetic susceptibility and remanent magnetic moment from the test masses and disturb them from their geodesic movement. LPF carried on-board a dedicated magnetic measurement subsystem with noise levels of 10 $\rm nT \ Hz^{-1/2}$ from 1 Hz down to 1 mHz. In this paper we report on the magnetic measurements throughout LPF operations. We characterize the magnetic environment within the spacecraft, study the time evolution of the magnetic field and its stability down to 20 μHz, where we measure values around 200 $\rm nT \ Hz^{-1/2}$, and identify two different frequency regimes, one related to the interplanetary magnetic field and the other to the magnetic field originating inside the spacecraft. Finally, we characterize the non-stationary component of the fluctuations of the magnetic field below the mHz and relate them to the dynamics of the solar wind.

scholarly journals Geomagnetic activity and local time dependence of the distribution of ultra low-frequency wave power in azimuthal wavenumbers, <i>m</i>

2017 ◽  
Vol 35 (3) ◽  
pp. 629-638 ◽  
Author(s):  
Theodore E. Sarris ◽  
Xinlin Li
Keyword(s):  
Phase Difference ◽  
Low Frequency ◽  
Field Measurements ◽  
Resonant Interaction ◽  
Total Power ◽  
Ulf Waves ◽  
Quiet Time ◽  
Frequency Wave ◽  
Drift Frequency ◽  
Diffusion Rates

Abstract. The azimuthal wavenumber m of ultra low-frequency (ULF) waves in the magnetosphere is a required parameter in the calculations of the diffusion rates of energetic electrons and protons in the magnetosphere, as electrons and protons of drift frequency ωd have been shown to radially diffuse due to resonant interaction with ULF waves of frequency ω = mωd. However, there are difficulties in estimating m, due to lack of multipoint measurements. In this paper we use magnetic field measurements at geosynchronous orbit to calculate the cross-spectrogram power and phase differences between time series from magnetometer pairs. Subsequently, assuming that ULF waves of a certain frequency and m would be observed with a certain phase difference between two azimuthally aligned magnetometers, the fraction of the total power in each phase difference range is calculated. As part of the analysis, both quiet-time and storm-time distributions of power per m number are calculated, and it is shown that during active times, a smaller fraction of total power is confined to lower m than during quiet times. It is also shown that in the dayside region, power is distributed mostly to the lowest azimuthal wavenumbers m = 1 and 2, whereas on the nightside it is more equally distributed to all m that can be resolved by the azimuthal separation between two spacecraft.

scholarly journals Sub-wavelength focusing of acoustic waves in bubbly media

2017 ◽  
Vol 473 (2208) ◽  
pp. 20170469 ◽  
Author(s):  
Habib Ammari ◽  
Brian Fitzpatrick ◽  
David Gontier ◽  
Hyundae Lee ◽  
Hai Zhang
Keyword(s):  
Acoustic Waves ◽  
Wave Scattering ◽  
Low Frequency ◽  
Scattering Function ◽  
Point Scatterer ◽  
Layer Potential ◽  
Spherical Bubble ◽  
Acoustic Wave Scattering ◽  
Frequency Regime ◽  
Sub Wavelength

The purpose of this paper is to investigate acoustic wave scattering by a large number of bubbles in a liquid at frequencies near the Minnaert resonance frequency. This bubbly media has been exploited in practice to obtain super-focusing of acoustic waves. Using layer potential techniques, we derive the scattering function for a single spherical bubble excited by an incident wave in the low frequency regime. We then propose a point scatterer approximation for N bubbles, and describe several numerical simulations based on this approximation, that demonstrate the possibility of achieving super-focusing using bubbly media.

Oscillatory Flow of a Magnetic Fluid in a Pipe at Low Frequency Range Under a Magnetic Field: Phase Difference of Pressure

2003 ◽  
Author(s):  
Kunio Shimada ◽  
Shigemitsu Shuchi ◽  
Shinichi Kamiyama
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Phase Difference ◽  
Mass Concentration ◽  
Oscillatory Flow ◽  
Low Frequency ◽  
Nonuniform Distribution ◽  
Straight Pipe ◽  
Number Range ◽  
Steady Magnetic Field

We made on numerical analysis of phase difference between pressure along the pipe axis and given oscillatory flow velocity in an straight pipe under a nonuniform steady magnetic field. In the analysis, a few cases under the assumption of numerical condition were conducted on: the first is taking into account the least compressibility of the fluid with using the obtained experimental data of the bulk modulus, the second taking into account the nonuniform distribution of mass concentration of particles, and the thrid taking into account the aggregation with the number of aggregated particles proposing as a prorate spheroid. By considering the three effects of the least compressibility and the nonuniform distribution of mass concentration, the aggregation as a prorate spheroid, the phase difference varies quantitatively at the lowest Womersley number range. And then, the numerical results were compared with the experimental data.

Magnetoimpedance of Epitaxial Y3Fe5O12 (001) Thin Film in Low-Frequency Regime

2020 ◽  
Vol 12 (37) ◽  
pp. 41802-41809
Author(s):  
Rohit Medwal ◽  
Ushnish Chaudhuri ◽  
Joseph Vimal Vas ◽  
Angshuman Deka ◽  
Surbhi Gupta ◽  
...  
Keyword(s):  
Thin Film ◽  
Low Frequency ◽  
Frequency Regime

scholarly journals Greybody Factors for Schwarzschild Black Holes: Path-Ordered Exponentials and Product Integrals

Universe ◽  
2018 ◽  
Vol 4 (9) ◽  
pp. 93 ◽  
Author(s):  
Finnian Gray ◽  
Matt Visser
Keyword(s):  
Black Holes ◽  
High Frequency ◽  
Low Frequency ◽  
Intermediate Frequency ◽  
General Context ◽  
Matrix Formalism ◽  
Barrier Penetration ◽  
Frequency Regime ◽  
Transfer Matrix Formalism ◽  
Numerical Approaches

In earlier work concerning the sparsity of the Hawking flux, we found it necessary to re-examine what is known regarding the greybody factors of black holes, with a view to extending and expanding on some old results from the 1970s. Focusing specifically on Schwarzschild black holes, we have re-calculated and re-assessed the greybody factors using a path-ordered-exponential approach, a technique which has the virtue of providing a pedagogically useful semi-explicit formula for the relevant Bogoliubov coefficients. These path-ordered-exponentials, being based on a variant of the “transfer matrix” formalism, are closely related to so-called “product integrals”, leading to quite straightforward and direct numerical evaluation, while side-stepping any need for numerically solving the relevant ordinary differential equations. Furthermore, while considerable analytic information is already available regarding both the high-frequency and low-frequency asymptotics of these greybody factors, numerical approaches seem better adapted to finding suitable “global models” for these greybody factors in the intermediate frequency regime, where most of the Hawking flux is actually concentrated. Working in a more general context, these path-ordered-exponential techniques are also likely to be of interest for generic barrier-penetration problems.

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