The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform
Markus Zahn - One of the best experts on this subject based on the ideXlab platform.
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negative electrorheological responses of micro polar fluids in the finite Spin viscosity small Spin Velocity limit ii poiseuille flow geometries
Journal of Electrostatics, 2011Co-Authors: Hsinfu Huang, Markus Zahn, Francois Peters, Elisabeth LemaireAbstract:Analytical solutions to the continuum Spin and linear velocities as well as the two-dimensional volume flow rate are solved and presented for negative electrorheological Poiseuille flows induced by internal micro-particle Quincke electrorotation using continuum anti-symmetric/couple stress theories with finite Spin viscosities and small Spin velocities. Theoretical predictions on the volume flow rate and linear Velocity profile obtained from the continuum finite Spin viscosity small Spin Velocity theory presented herein agree very well with the experimental measurements in the parametric regime of low or small driving pressure gradients as reported in current literature.
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ultrasound velocimetry of ferrofluid Spin up flow measurements using a spherical coil assembly to impose a uniform rotating magnetic field
Journal of Magnetism and Magnetic Materials, 2011Co-Authors: Shahriar Rohinton Khushrushahi, Markus ZahnAbstract:Abstract Ferrofluid Spin-up flow is studied within a sphere subjected to a uniform rotating magnetic field from two surrounding spherical coils carrying sinusoidally varying currents at right angles and 90° phase difference. Ultrasound velocimetry measurements in a full sphere of ferrofluid shows no measureable flow. There is significant bulk flow in a partially filled sphere (1–14 mm/s) of ferrofluid or a finite height cylinder of ferrofluid with no cover (1–4 mm/s) placed in the spherical coil apparatus. The flow is due to free surface effects and the non-uniform magnetic field associated with the shape demagnetizing effects. Flow is also observed in the fully filled ferrofluid sphere (1–20 mm/s) when the field is made non-uniform by adding a permanent magnet or a DC or AC excited small solenoidal coil. This confirms that a non-uniform magnetic field or a non-uniform distribution of magnetization due to a non-uniform magnetic field are causes of Spin-up flow in ferrofluids with no free surface, while tangential magnetic surface stress contributes to flow in the presence of a free surface. Recent work has fitted Velocity flow measurements of ferrofluid filled finite height cylinders with no free surface, subjected to uniform rotating magnetic fields, neglecting the container shape effects which cause non-uniform demagnetizing fields, and resulting in much larger non-physical effective values of Spin viscosity η ′∼10 −8 −10 −12 N s than those obtained from theoretical Spin diffusion analysis where η ′≤10 −18 N s. COMSOL Multiphysics finite element computer simulations of spherical geometry in a uniform rotating magnetic field using non-physically large experimental fit values of Spin viscosity η ′∼10 −8 −10 −12 N s with a zero Spin-Velocity boundary condition at the outer wall predicts measureable flow, while simulations setting Spin viscosity to zero ( η ′ = 0) results in negligible flow, in agreement with the ultrasound velocimetry measurements. COMSOL simulations also confirm that a non-uniform rotating magnetic field or a uniform rotating magnetic field with a non-uniform distribution of magnetization due to an external magnet or a current carrying coil can drive a measureable flow in an infinitely long ferrofluid cylinder with zero Spin viscosity ( η ′ = 0).
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simulating magnetic nanoparticle behavior in low field mri under transverse rotating fields and imposed fluid flow
Journal of Magnetism and Magnetic Materials, 2010Co-Authors: Lawrence L Wald, Padraig Cantillonmurphy, Elfar Adalsteinsson, Markus ZahnAbstract:Abstract In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ . As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω , in rad s −1 . Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4 and 7 °C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B 0 . Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B 0 . Results are presented for the expected temperature increase in small tumors ( ∼ 1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002–0.01 solid volume fraction) and nanoparticle radii (1–10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful the goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B 0 field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations of the transverse rotating magnetic field in the presence of B 0 are investigated to demonstrate the effect of Ω , the rotating field frequency, and the magnetic field amplitude on the fluid suspension magnetization. The transverse magnetization due to the rotating transverse field shows strong dependence on the characteristic time constant of the fluid suspension, τ . The analysis shows that as the rotating field frequency increases so that Ω τ approaches unity, the transverse fluid magnetization vector is significantly non-aligned with the applied rotating field and the magnetization's magnitude is a strong function of the field frequency. In this frequency range, the fluid's transverse magnetization is controlled by the applied field which is determined by the operator. The phenomenon, which is due to the physical rotation of the magnetic nanoparticles in the suspension, is demonstrated analytically when the nanoparticles are present in high concentrations (1–3% solid volume fractions) more typical of hyperthermia rather than in clinical imaging applications, and in low MRI field strengths (such as open MRI systems), where the magnetic nanoparticles are not magnetically saturated. The effect of imposed Poiseuille flow in a planar channel geometry and changing nanoparticle concentration is examined. The work represents the first known attempt to analyze the dynamic behavior of magnetic nanoparticles in the MRI environment including the effects of the magnetic nanoparticle Spin-Velocity. It is shown that the magnitude of the transverse magnetization is a strong function of the rotating transverse field frequency. Interactive fluid magnetization effects are predicted due to non-uniform fluid magnetization in planar Poiseuille flow with high nanoparticle concentrations.
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magnetic fluid rheology and flows
Current Opinion in Colloid and Interface Science, 2005Co-Authors: Carlos Rinaldi, Arlex Chaves, Shihab Elborai, Markus ZahnAbstract:Abstract Major recent advances Magnetic fluid rheology and flow advances in the past year include: (1) generalization of the magnetization relaxation equation by Shliomis and Felderhof and generalization of the governing ferrohydrodynamic equations by Rosensweig and Felderhof; (2) advances in such biomedical applications as drug delivery, hyperthermia, and magnetic resonance imaging; (3) use of the antisymmetric part of the viscous stress tensor due to Spin Velocity to lower the effective magnetoviscosity to zero and negative values; (4) and ultrasound Velocity profile measurements of Spin-up flow showing counter-rotating surface and co-rotating volume flows in a uniform rotating magnetic field. Recent advances in magnetic fluid rheology and flows are reviewed including extensions of the governing magnetization relaxation and ferrohydrodynamic equations with a viscous stress tensor that has an antisymmetric part due to Spin Velocity; derivation of the magnetic susceptibility tensor in a ferrofluid with Spin Velocity and its relationship to magnetically controlled heating; magnetic force and torque analysis, measurements, resulting flow phenomena, with device and biomedical applications; effective magnetoviscosity analysis and measurements including zero and negative values, not just reduced viscosity; ultrasound Velocity profile measurements of Spin-up flow showing counter-rotating surface and co-rotating volume flows in a uniform rotating magnetic field; theory and optical measurements of ferrofluid meniscus shape for tangential and perpendicular magnetic fields; new theory and measurements of ferrohydrodynamic flows and instabilities and of thermodiffusion (Soret effect) phenomena.
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effects of Spin viscosity on ferrofluid flow profiles in alternating and rotating magnetic fields
Physics of Fluids, 2002Co-Authors: Carlos Rinaldi, Markus ZahnAbstract:Previous models of plane-Poiseuille flow of ferrofluids in alternating and rotating magnetic fields are extended by including the effects of Spin diffusion and planar Couette flow. Accurate modeling of this problem is required for the design of experiments to determine key parameters for previously reported anomalous forward and backward ferrofluid pumping behavior in alternating and rotating magnetic fields. The previously derived zero-Spin-viscosity analysis predicted multi-valued and singular flow solutions with possible zero and negative effective magnetoviscosity. This analysis calculates analytical expressions for the translational and Spin Velocity profiles, vorticity profiles, volumetric flow rate, and the shear force on a moving duct surface, comparing the effects of boundary conditions of zero Spin Velocity and Spin Velocity equal to half the vorticity at the duct walls. The analysis shows that the single singularity in flow behavior corresponding to zero magnetoviscosity in the zero-Spin-viscosity analysis expands to multiple possible flow singularities for the nonzero Spin viscosity case. Simple representative shearing experiments are proposed to differentiate between the zero and nonzero Spin viscosity solutions, to calculate the values of key viscous parameters, and to show how wall boundary conditions can be determined from shear stress measurements.
K A Postnov - One of the best experts on this subject based on the ideXlab platform.
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pulsar Spin Velocity alignment from single and binary neutron star progenitors
Monthly Notices of the Royal Astronomical Society, 2009Co-Authors: A G Kuranov, S B Popov, K A PostnovAbstract:The role of binary progenitors of neutron stars (NSs) in the apparent distribution of space velocities and Spin-Velocity alignment observed in young pulsars is studied. We performed a Monte Carlo synthesis of pulsar populations originated from single and binary stars with different assumptions about the NS natal kick (kick―Spin alignment, kick amplitude and kick reduction in electron-capture supernovae in binary progenitors with initial main-sequence masses from the range 8-11 M ⊙ which experienced mass exchange due to Roche lobe overflow). The calculated Spin-Velocity alignment in pulsars is compared with data inferred from radio polarization measurements. The observed space Velocity of pulsars is found to be mostly affected by the natal kick Velocity form and its amplitude; the fraction of binaries is not important here for reasonably large kicks. The natal kick―Spin alignment is found to strongly affect the Spin-Velocity correlation of pulsars. Comparison with the observed pulsar Spin―Velocity angles favours a sizeable fraction of binary progenitors and kick-Spin angles ∼5°―20°.
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pulsar Spin Velocity alignment from single and binary neutron star progenitors
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: A G Kuranov, S B Popov, K A PostnovAbstract:The role of binary progenitors of neutron stars in the apparent distribution of space velocities and Spin-Velocity alignment observed in young pulsars is studied. A Monte-Carlo synthesis of pulsar population from single and binary stars with different assumptions about the NS natal kick model (direction distribution, amplitude, and kick reduction in binary progenitors which experienced mass exchange due to Roche lobe overflow with initial masses on the main sequence from the range 8-11 $M_\odot$) is performed. The calculated Spin-Velocity alignment distributions are compared with observational data obtained from radio polarization measurements. The observed space Velocity of pulsars is found to be mostly shaped by the natal kick Velocity form and its amplitude; the fraction of binaries is not important here for reasonably large kicks. The distribution of kick direction relative to the Spin axis during the formation of a NS is found to affect strongly the Spin-Velocity correlation of pulsars. Comparison with observed pulsar Spin-Velocity angles favours a sizeable fraction of binary progenitors and the kick-Spin angle $\sim 5-20^\circ$. The form of the initial binary mass ratio distribution does not affect our results.
Shihang Shen - One of the best experts on this subject based on the ideXlab platform.
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harmonic potential theorem extension to Spin Velocity and density dependent interactions
Physical Review Letters, 2019Co-Authors: Samantha Zanoli, Gianluca Colò, X Rocamaza, Shihang ShenAbstract:: One of the few exact results for the description of the time evolution of an inhomogeneous, interacting many-particle system is given by the harmonic potential theorem (HPT). The relevance of this theorem is that it sets a tight constraint on time-dependent many-body approximations. In this contribution, we show that the original formulation of the HPT is valid also for the case of Spin-, Velocity-, and density-dependent interactions. This result is completely general and relevant, among the rest, for nuclear structure theory both in the case of ab initio and of more phenomenological approaches. As an example, we report on a numerical implementation by testing the small-amplitude limit of the time-dependent Hartree-Fock-also known as the random phase approximation-for the translational frequencies of a neutron system trapped in a harmonic potential.
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harmonic potential theorem extension to Spin Velocity and density dependent interactions
arXiv: Nuclear Theory, 2019Co-Authors: Samantha Zanoli, Gianluca Colò, X Rocamaza, Shihang ShenAbstract:One of the few exact results for the description of the time-evolution of an inhomogeneous, interacting many-particle system is given by the Harmonic Potential Theorem (HPT). The relevance of this theorem is that it sets a tight constraint on time-dependent many-body approximations. In this contribution, we show that the original formulation of the HPT is valid also for the case of Spin-, Velocity- and density-dependent interactions. This result is completely general and relevant, among the rest, for nuclear structure theory both in the case of ab initio and of more phenomenological approaches. As an example, we report on a numerical implementation by testing the small-amplitude limit of the time-dependent Hartree-Fock -- also known as Random Phase Approximation (RPA) -- for the translational frequencies of a neutron system trapped in a harmonic potential.
Yasushi Suto - One of the best experts on this subject based on the ideXlab platform.
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the rossiter mclaughlin effect and analytic radial Velocity curves for transiting extrasolar planetary systems
The Astrophysical Journal, 2005Co-Authors: Yasuhiro Ohta, Atsushi Taruya, Yasushi SutoAbstract:A transiting extrasolar planet sequentially blocks off the light coming from the different parts of the disk of the host star in a time-dependent manner. Because of the Spin of the star, this produces an asymmetric distortion in the line profiles of the stellar spectrum, leading to an apparent anomaly in the the radial Velocity curves, known as the Rossiter-McLaughlin effect. Here, we derive approximate but accurate analytic formulae for the anomaly in the radial Velocity curves, taking into account the stellar limb darkening. The formulae are particularly useful in extracting information on the projected angle between the planetary orbit axis and the stellar Spin axis, λ, and the projected stellar Spin Velocity, V sin Is. We create mock samples for the radial curves for the transiting extrasolar system HD 209458 and demonstrate that constraints on the Spin parameters (V sin Is, λ) can be significantly improved by combining our analytic template formulae and the precision Velocity curves from high-resolution spectroscopic observations with 8-10 m class telescopes. Thus, future observational exploration of transiting systems using the Rossiter-McLaughlin effect will be one of the most important probes for a better understanding of the origin of extrasolar planetary systems, especially the origin of their angular momentum.
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the rossiter mclaughlin effect and analytic radial Velocity curves for transiting extrasolar planetary systems
arXiv: Astrophysics, 2004Co-Authors: Yasuhiro Ohta, Atsushi Taruya, Yasushi SutoAbstract:A transiting extrasolar planet sequentially blocks off the light coming from the different parts of the disk of the host star in a time dependent manner. Due to the Spin of the star, this produces an asymmetric distortion in the line profiles of the stellar spectrum, leading to an apparent anomaly of the radial Velocity curves, known as the Rossiter - McLaughlin effect. Here, we derive approximate but accurate analytic formulae for the anomaly of radial Velocity curves taking account of the stellar limb darkening. The formulae are particularly useful in extracting information of the projected angle between the planetary orbit axis and the stellar Spin axis, \lambda, and the projected stellar Spin Velocity, V sin I_s. We create mock samples for the radial curves for the transiting extrasolar system HD209458, and demonstrate that constraints on the Spin parameters (V sin I_s, \lambda) may be significantly improved by combining our analytic template formulae and the precision Velocity curves from high-resolution spectroscopic observations with 8-10 m class telescopes. Thus future observational exploration of transiting systems using the Rossiter - McLaughlin effect is one of the most important probes to better understanding of the origin of extrasolar planetary systems, especially the origin of their angular momentum.
Haiyang Yan - One of the best experts on this subject based on the ideXlab platform.
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new experimental limits on exotic Spin Spin Velocity dependent interactions by using smco 5 Spin sources
Physical Review Letters, 2018Co-Authors: Yao Chen, Ming Ding, Jiancheng Fang, Z G Xiao, Kai Wei, Haiyang YanAbstract:Despite the great success of the standard model (SM), there still exist mysteries like the nature of dark matter, the strong $CP$ problems, etc. To solve them, many theories proposed new bosons beyond the SM that can mediate new forces. Here, we report the latest results of searching for possible new long-range Spin-Spin-Velocity-dependent forces (SSVDFs), based on specially designed iron-shielded ${\mathrm{SmCo}}_{5}$ Spin sources and a Spin exchange relaxation free comagnetometer. With help from the similarity analysis method, new constraints on some forms of SSVDFs between electrons have been obtained, which represent up to more than 11 orders of magnitude tighter limits than previous experiments for the force range of 5 cm--1 km.
